Co-reporter:Jie Wang, Yingke Zhou, Zongping Shao
Electrochimica Acta 2015 Volume 155() pp:483
Publication Date(Web):10 February 2015
DOI:10.1016/j.electacta.2015.01.124
Co-reporter:Guan Wu, Yingke Zhou, Zongping Shao
Applied Surface Science 2015 Volume 328() pp:658
Publication Date(Web):15 February 2015
DOI:10.1016/j.apsusc.2014.12.176
Co-reporter:Bin Xiong, Yingke Zhou, Ryan O’Hayre, Zongping Shao
Applied Surface Science 2015 Volume 328() pp:659
Publication Date(Web):15 February 2015
DOI:10.1016/j.apsusc.2014.12.178
Co-reporter:Yuanyuan Zhao, Yingke Zhou, Ryan O’Hayre, Zongping Shao
Journal of Physics and Chemistry of Solids 2015 80() pp: 118
Publication Date(Web):
DOI:10.1016/j.jpcs.2015.02.001
Co-reporter:Zhenbao Zhang, Yubo Chen, Moses O. Tade, Yong Hao, Shaomin Liu and Zongping Shao
Journal of Materials Chemistry A 2014 vol. 2(Issue 25) pp:9666-9674
Publication Date(Web):24 Apr 2014
DOI:10.1039/C4TA00926F
In this study, we propose a new tin-doped perovskite oxide, BaCo0.7Fe0.2Sn0.1O3−δ (BCFSn0.1), as a promising alternative material for a ceramic oxygen-permeating membrane. A high energy ball milling-assisted solid-state reaction method is used for the material synthesis. The effect of tin doping on the structure, electrical conductivity, oxygen activity, oxygen bulk diffusivity and surface exchange properties of the materials, sintering behaviour, and oxygen permeability of the related membranes is systematically investigated via transmission electron microscopy (TEM), environmental scanning electron microscopy (E-SEM), thermo-gravimetric analysis (TGA), oxygen temperature-programmed desorption (O2-TPD) and electrical conductivity relaxation (ECR), and oxygen permeation test. The minor substitution of B-site cations in BaCo0.7Fe0.3O3−δ (BCF) with tin is found to be highly effective in improving oxygen flux of the resultant membrane. Under an oxygen gradient created by air/helium, BCFSn0.1 membrane reaches fluxes of 9.62 × 10−7 and 3.55 × 10−7 mol m−2 s−1 Pa−1 [STP], respectively, at 900 and 700 °C, in sharp contrast with the flux values of 4.42 × 10−7 and 2.84 × 10−8 mol m−2 s−1 Pa−1 for BCF membrane with the same thickness of 1 mm. Favorable permeation stability is also demonstrated for the tin-doped membrane, and oxygen bulk diffusion is the main rate-limiting step for oxygen permeation, indicating a further increase in fluxes by reducing the membrane thickness.
Co-reporter:Yu Liu, Ran Ran, Sidian Li, Yong Jiao, Moses O. Tade, Zongping Shao
Journal of Power Sources 2014 Volume 257() pp:308-318
Publication Date(Web):1 July 2014
DOI:10.1016/j.jpowsour.2014.02.013
•Enhancing the performance of BCY through a Pd ingress–egress approach.•The introduction of Pd significantly improve sinterability.•Pd egress from the BCYP10 perovskite lattice after reduction or calcination.•A single cell with a BCYP10 electrolyte reaches a peak power density of 645 mA cm−2 at 700 °C.Proton-conducting perovskite oxides are excellent electrolyte materials for SOFCs that may improve power density at reduced temperatures and increase fuel efficiency, thus encouraging the widespread implementation of this attractive technology. The main challenges in the application of these oxides in SOFCs are difficult sintering and insufficient conductivity in real cells. In this study, we propose a novel method to significantly enhance the performance of a yttrium-doped barium cerate proton conductor as an electrolyte for SOFCs through a Pd ingress–egress approach to the development of BaCe0.8Y0.1Pd0.1O3−δ (BCYP10). The capability of the Pd egress from the BCYP10 perovskite lattice is demonstrated by H2-TPR, XRD, EDX mapping of STEM and XPS. Significant improvement in the sinterability is observed after the introduction of Pd due to the increased ionic conductivity and the sintering aid effect of egressed Pd. The formation of a B-site cation defect structure after Pd egress and the consequent modification of perovskite grain boundaries with Pd nanoparticles leads to a proton conductivity of BCYP10 that is approximately 3 times higher than that of BCY under a reducing atmosphere. A single cell with a thin film BCYP10 electrolyte reaches a peak power density as high as 645 mA cm−2 at 700 °C.
Co-reporter:Jie Wang, Ran Ran, Moses O. Tade, Zongping Shao
Journal of Power Sources 2014 Volume 254() pp:18-28
Publication Date(Web):15 May 2014
DOI:10.1016/j.jpowsour.2013.12.090
•TiO2/CNT hybrids were prepared by a facile PEO-aided self-assembled process.•CNTs in the TiO2/CNT hybrids construct a 3D conductive network.•PEO plays an important role on the TiO2 well dispersion in the TiO2/CNT hybrids.•TiO2/CNTs-110 C hybrids showed a high electronic conductivity (5.13 S cm−1).•TiO2/CNTs-110 C anodes revealed excellent rate and good cycling performance.Mesoporous three-dimensional (3D) TiO2/carbon nanotube conductive hybrid nanostructures can be successfully developed using polyethylene oxide (PEO) to modify the surfaces of carbon nanotubes (CNTs). During the synthesis process, PEO acts as not only “bridges” to connect the TiO2 nanoparticles to the CNT surfaces but also as “hosts” to accommodate and stabilize the in situ generated TiO2 particles. As the electrodes for lithium-ion batteries, such mesoporous 3D TiO2/CNT hybrids, demonstrate high Li storage capacity, superior rate performance and excellent long-term cycling stability. They exhibit a reversible specific capacity of 203 mA h g−1 at 100 mA g−1 and a stable capacity retention of 91 mA h g−1 at 8000 mA g−1 (47.6 C) over 100 cycles; they also retain approximately 90% (71 mA h g−1) of their initial discharge capacity after 900 cycles at an extremely high rate of 15,000 mA g−1 (89 C). This facile synthetic strategy to construct mesoporous 3D TiO2/CNT conductive hybrids provides a convenient route that efficiently assembles various inorganic oxide components on the CNTs' surfaces and enables the formation of heterogeneous nanostructures with novel functionalities. In particular, utilizing a conductive 3D CNT network can serve as a promising strategy for developing high-performance electrodes for Li secondary batteries and supercapacitors.3D conductive network TiO2/CNTs hybrids synthesized via a facile PEO-aided self-assembled process and thermal treatment approach exhibit superior electrochemical performance for LIBs.
Co-reporter:Wei Wang, Huaiyu Zhu, Guangming Yang, Hee Jung Park, Doh Won Jung, Chan Kwak, Zongping Shao
Journal of Power Sources 2014 Volume 258() pp:134-141
Publication Date(Web):15 July 2014
DOI:10.1016/j.jpowsour.2014.02.008
•NiFeCu alloy catalysts were prepared by three different methods.•NiFe–ZrO2/Cu (IMP) catalyst showed highest coking resistance toward methane.•High power output of 1165 mW cm−2 was obtained with CH4–O2 as fuel at 850 °C.•The fuel cell with this NiFe–ZrO2/Cu (IMP) catalyst layer delivered good stability.In this study, a new anode catalyst based on a NiFeCu alloy is investigated for use in direct-methane solid oxide fuel cells (SOFCs). The influence of the conductive copper introduced into the anode catalyst layer on the performance of the SOFCs is systematically studied. The catalytic activity for partial oxidation of methane and coking resistance tests are proposed with various anode catalyst layer materials prepared using different methods, including glycine nitrate process (GNP), physical mixing (PM) and impregnation (IMP). The surface conductivity tests indicate that the conductivities of the NiFe–ZrO2/Cu (PM) and NiFe–ZrO2/Cu (IMP) catalysts are considerably greater than that of NiFe–ZrO2/Cu (GNP), which is consistent with the SEM results. Among the three preparation methods, the cell containing the NiFe–ZrO2/Cu (IMP) catalyst layer performs best on CH4–O2 fuel, especially under reduced temperatures, because the coking resistance should be considered in real fuel cell conditions. The cell containing the NiFe–ZrO2/Cu (IMP) catalyst layer also delivers an excellent operational stability using CH4–O2 fuel for 100 h without any signs of decay. In summary, this work provides new alternative anode catalytic materials to accelerate the commercialization of SOFC technology.
Co-reporter:Yingjie Niu, Jaka Sunarso, Wei Zhou, Fengli Liang, Lei Ge, Zhonghua Zhu, Zongping Shao
International Journal of Hydrogen Energy 2014 Volume 39(Issue 27) pp:15156
Publication Date(Web):12 September 2014
DOI:10.1016/j.ijhydene.2014.05.024
Co-reporter:Fei Ye;Bote Zhao; Ran Ran; Zongping Shao
Chemistry - A European Journal 2014 Volume 20( Issue 14) pp:4055-4063
Publication Date(Web):
DOI:10.1002/chem.201304720
Abstract
A facile method for the large-scale synthesis of SnO2 nanocrystal/graphene composites by using coarse metallic Sn particles and cheap graphite oxide (GO) as raw materials is demonstrated. This method uses simple ball milling to realize a mechanochemical reaction between Sn particles and GO. After the reaction, the initial coarse Sn particles with sizes of 3–30 μm are converted to SnO2 nanocrystals (approximately 4 nm) while GO is reduced to graphene. Composite with different grinding times (1 h 20 min, 2 h 20 min or 8 h 20 min, abbreviated to 1, 2 or 8 h below) and raw material ratios (Sn:GO, 1:2, 1:1, 2:1, w/w) are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy and transmission electron microscopy. The as-prepared SnO2/graphene composite with a grinding time of 8 h and raw material ratio of 1:1 forms micrometer-sized architected chips composed of composite sheets, and demonstrates a high tap density of 1.53 g cm−3. By using such composites as anode material for LIBs, a high specific capacity of 891 mA h g−1 is achieved even after 50 cycles at 100 mA g−1.
Co-reporter:Dong Xu, Feifei Dong, Yubo Chen, Bote Zhao, Shaomin Liu, Moses O. Tade, Zongping Shao
Journal of Membrane Science 2014 455() pp: 75-82
Publication Date(Web):
DOI:10.1016/j.memsci.2013.12.030
Co-reporter:Yubo Chen, Baoming Qian, Yong Hao, Shaomin Liu, Moses O. Tade, Zongping Shao
Journal of Membrane Science 2014 470() pp: 102-111
Publication Date(Web):
DOI:10.1016/j.memsci.2014.07.027
Co-reporter:Yubo Chen, Baoming Qian, Sidian Li, Yong Jiao, Moses O. Tade, Zongping Shao
Journal of Membrane Science 2014 449() pp: 86-96
Publication Date(Web):
DOI:10.1016/j.memsci.2013.08.021
Co-reporter:Bote Zhao, Liangliang Sun, Ran Ran, Zongping Shao
Solid State Ionics 2014 Volume 262() pp:313-318
Publication Date(Web):1 September 2014
DOI:10.1016/j.ssi.2013.08.025
•CCMs with dual-layer structured electrodes were successfully fabricated.•Dual-layer structured anode and cathode were investigated systematically.•800 mW cm− 2 was achieved with the dual catalyst layers cathode.With an aim to develop a proton-exchange-membrane fuel cell (PEMFC) with improved water management, catalyst-coated membranes based upon Nafion 212 membrane with electrodes of dual-layer structure which consist of one hydrophilic layer of Pt/C + Nafion and one hydrophobic layer of Pt/C + PTFE arranged in a proper order, is specifically designed and successfully fabricated by a facile high-temperature spray deposition technique. Dual-layer structured anode and cathode are separately evaluated by electrochemical performance in single cells. Effect of relative thickness of the dual layers in the electrode on the cell performance is investigated. No improvement in cell performance is observed by adopting the dual-layer structure for the anode as compared to conventional anode with single hydrophilic catalyst layer. However, better cell performance is observed for the cell with dual-layer structured cathode, and the optimal cell reaches a peak power density of about 800 mW cm− 2 at 50 °C with humidified hydrogen and oxygen as fuel and oxidant respectively.
Co-reporter:Wei Wang, Chao Su, Yuzhou Wu, Ran Ran, and Zongping Shao
Chemical Reviews 2013 Volume 113(Issue 10) pp:8104
Publication Date(Web):July 31, 2013
DOI:10.1021/cr300491e
Co-reporter:Xia Chen, Bote Zhao, Yong Cai, Moses O. Tadé and Zongping Shao
Nanoscale 2013 vol. 5(Issue 24) pp:12589-12597
Publication Date(Web):14 Oct 2013
DOI:10.1039/C3NR04484J
Flexible V–O–C composite nanofibers were fabricated from solution precursors via electrospinning and were investigated as free-standing and additive-free film electrodes for supercapacitors. Specifically, composite nanofibers (V0, V5, V10 and V20) with different vanadyl acetylacetonate (VO(acac)2) contents of 0, 5, 10 and 20 wt% with respect to polyacrylonitrile (PAN) were prepared. The composite nanofibers were comparatively studied using XRD, Raman spectroscopy, XPS, N2 adsorption–desorption, FE-SEM, TEM and S-TEM. The vanadium element was found to be well-dispersed in the carbon nanofibers, free from the formation of an aggregated crystalline phase, even in the case of V20. A specific surface area of 587.9 m2 g−1 was reached for V10 after calcination, which is approximately twice that of the vanadium-free carbon nanofibers (V0, 300.9 m2 g−1). To perform as an electrode for supercapacitors in an aqueous electrolyte, the V10 film delivered a specific capacitance of 463 F g−1 at 1 A g−1. V10 was also able to retain a specific capacitance of 380 F g−1, even at a current density of 10 A g−1. Additionally, very stable cycling stability was achieved, maintaining an outstanding specific capacitance of 400 F g−1 at 5 A g−1 after charge–discharge cycling 5000 times. Thus, V–O–C composite nanofibers are highly attractive electrode materials for flexible, high-power, thin film energy storage devices and applications.
Co-reporter:Yujing Sha, Bote Zhao, Ran Ran, Rui Cai and Zongping Shao
Journal of Materials Chemistry A 2013 vol. 1(Issue 42) pp:13233-13243
Publication Date(Web):09 Sep 2013
DOI:10.1039/C3TA12620J
As a lithium-intercalation material, high crystallinity is important for Li4Ti5O12 to achieve good capacity and cycling stability, while a large surface area and a short lithium diffusion distance are critical to increase rate capacity. In this study, well-crystallized Li4Ti5O12 nanoplates with outstanding electrochemical performance were facially prepared through a two-step hydrothermal preparation with benzyl alcohol–NH3·H2O (BN) as the solvent and a subsequent intermediate-temperature calcination at 500 °C for 2 h in air. To support the superiority of benzyl alcohol–NH3·H2O (BN) for hydrothermal synthesis, ethanol–NH3·H2O (EN) was also comparatively studied as solvent. In addition, different hydrothermal reaction times were tried to locate the optimal reaction time. The nature of as-prepared Li4Ti5O12–BN (LTO–BN) and Li4Ti5O12–EN (LTO–EN) was characterized by XRD, N2 adsorption/desorption tests, SEM, TEM and TGA-DSC. Compared with EN, the BN hydrothermal solvent facilitated the formation of nanosheet-Li4Ti5O12 with wall thicknesses of 8–15 nm and better crystallization. After a 6 h hydrothermal reaction at 180 °C and subsequent calcination, well-crystallized Li4Ti5O12–BN nanoplates were produced, which demonstrate a superior discharge capacity of 160 mA h g−1, even at 40 C, maintaining a capacity of 88.8% compared with that at 1 C. The nanoplates also exhibited excellent cycling stability, retaining a discharge capacity of 153 mA h g−1 after 1000 charge–discharge cycles at 10 C.
Co-reporter:Bote Zhao, Simin Jiang, Chao Su, Rui Cai, Ran Ran, Moses O. Tadé and Zongping Shao
Journal of Materials Chemistry A 2013 vol. 1(Issue 39) pp:12310-12320
Publication Date(Web):08 Aug 2013
DOI:10.1039/C3TA12770B
To develop high-power and fast energy storage devices, electrode materials with superior ionic and electronic transport properties should be developed. Herein, a novel composite electrode with TiO2 nanotubes connected onto a conductive carbon nanofiber network is designed and realized through a general route. The carbon matrix is first synthesized using an electrospinning technique and heat-treatment, and the embedded rutile TiO2 nanoparticles are formed in situ as the starting materials for the hydrothermal reaction. After hydrothermal treatment, a three-dimensional (3D) porous architecture is developed. The mechanistic analysis demonstrates that the raw embedded rutile TiO2 nanoparticles react with NaOH solution and go out around the carbon nanofiber matrix to form a well-connected 3D porous nanotube/nanofiber architecture. By using the as-prepared films as electrodes for lithium-ion batteries (LIBs) without the application of any additional conductive agent or binder, high initial capacity and excellent rate performance (214 mA h g−1 at 5 C rate, 180 mA h g−1 at 10 C rate, 138 mA h g−1 at 20 C rate and 112 mA h g−1 at 30 C rate) are achieved. Moreover, the electrode shows stable cycling performance, especially at a high rate of 30 C, without undergoing decay after 1000 cycles.
Co-reporter:Shanshan Jiang, Jaka Sunarso, Wei Zhou and Zongping Shao
Journal of Materials Chemistry A 2013 vol. 1(Issue 36) pp:11026-11032
Publication Date(Web):16 Jul 2013
DOI:10.1039/C3TA12376F
Layered oxides of Sr4Fe4Co2O13 (SFC2) which contains alternating perovskite oxide octahedral and polyhedral oxide double layers are attractive for their mixed ionic and electronic conducting and oxygen reduction reaction properties. In this work, we used the EDTA–citrate synthesis technique to prepare SFC2 and vary the calcination temperature between 900 and 1100 °C to obtain SFC2, containing different phase content of perovskite (denoted as SFC-P) and (Fe,Co) layered oxide phases (SFC-L). Rietveld refinements show that the SFC-P phase content increased from ∼39 wt% to ∼50 wt% and ∼61 wt% as the calcination temperature increased from 900 °C (SFC2-900) to 1000 °C (SFC2-1000) and 1050 °C (SFC2-1050). At 1100 °C (SFC2-1100), SFC-P became the dominant phase. The oxygen transport properties (e.g. oxygen chemical diffusion coefficient and oxygen permeability), electrical conductivity and oxygen reduction reaction activity is enhanced in the order of SFC2-1000, SFC2-1100 and SFC2-1050. The trend established here therefore negates the hypothesis that the perovskite phase content correlates with the oxygen transport property enhancement. The results suggest instead that there is an optimum composition value (e.g. 61 wt% of SFC-L for SFC2-1050 in this work) on which synergistic effects take place between the SFC-P and SFC-L phase.
Co-reporter:Feifei Dong, Yubo Chen, Ran Ran, Dengjie Chen, Moses O. Tadé, Shaomin Liu and Zongping Shao
Journal of Materials Chemistry A 2013 vol. 1(Issue 34) pp:9781-9791
Publication Date(Web):04 Jun 2013
DOI:10.1039/C3TA11447C
Cobalt-free perovskite BaNb0.05Fe0.95O3−δ (BNF) is synthesized and characterized towards application as a cathode material for intermediate temperature solid oxide fuel cells. In situ X-ray diffraction and transmission electron microscopy are applied to study the crystal structure and thermally induced phase transformation. BNF exists as a multiphase structure composed of a monoclinic phase and a cubic phase at room temperature, and then undergoes a phase transformation to a cubic structure starting at ∼400 °C, which is maintained at temperatures up to 900 °C during a thermal cycle between room temperature and 900 °C; while it retains the cubic perovskite lattice structure on cooling from 900 °C to room temperature. Oxygen temperature-programmed desorption, combined thermal expansion and thermo-gravimetric analysis are used to clarify the thermal reducibility of BNF. A relatively good stability of BNF is demonstrated by electrical conductivity and electrochemical impedance spectroscopy measurements. The activity of BNF for oxygen reduction reaction is probed by symmetrical cell and single fuel cell tests. Favorable electrochemical activities at intermediate temperature, e.g. very low interfacial resistance of only ∼0.016 Ω cm2 and maximum power density of 1162 mW cm−2 at 750 °C, are demonstrated, which could be attributed to the cubic lattice structure of BNF within the temperature range of cell operation.
Co-reporter:Chao Su, Wei Wang, Ran Ran, Zongping Shao, Moses O. Tade and Shaomin Liu
Journal of Materials Chemistry A 2013 vol. 1(Issue 18) pp:5620-5627
Publication Date(Web):05 Mar 2013
DOI:10.1039/C3TA10538E
The feasibility of renewable acetic acid as a direct fuel of SOFCs for sustainable electric power generation was investigated. To solve the problem of carbon deposition over conventional nickel cermet anodes, an advanced catalyst for acetic acid catalytic decomposition/internal reforming reaction was exploited. A comparative study of coke formation over Ni/Al2O3, Ni/MgO–Al2O3 and Ni–YSZ catalysts was conducted by oxygen-temperature programmed oxidation analysis. We found that the Ni/MgO–Al2O3 catalyst is much superior to the other two catalysts in suppressing carbon deposition, especially under the condition of the presence of steam in the acetic acid fuel. Various cells were fabricated and tested under different conditions. The differences in OCVs and power outputs of the cells caused by the usage of hydrogen and acetic acid as fuels were studied and explained based on the thermodynamic calculation and EIS measurement. After optimization, a peak power density of 1325 mW cm−2 at a furnace temperature of 800 °C was achieved for the cell with a catalyst layer operating on acetic acid fuel. The cell was successfully operated continuously on acetic acid–steam fuel for a period of at least 200 h without any noticeable performance degradation, delamination of the catalyst layer and carbon deposition. The promising results of this work show the possibility of better utilization of the abundant bio-mass or bio-oil for future energy generation.
Co-reporter:Yixin Sun, Jie Wang, Bote Zhao, Rui Cai, Ran Ran and Zongping Shao
Journal of Materials Chemistry A 2013 vol. 1(Issue 15) pp:4736-4746
Publication Date(Web):07 Feb 2013
DOI:10.1039/C3TA01285A
We demonstrate a facile and effective way for the fabrication of a flexible, homogeneous and neat α-MoO3 thin-film electrode for lithium-ion batteries with high performance without using any binder and conductive additives. Single-crystalline α-MoO3 nanobelts with uniform width of around 200 nm and length at the micrometer level are first synthesized by a simple water-based hydrothermal route. The as-obtained α-MoO3 slurry is then directly deposited onto a copper foil current collector by the doctor blade method. The formation of the α-MoO3 film and its good adhesion to the current collector is realized via van der Waals attraction forces through a drying process. The structure and morphology of the α-MoO3 nanobelt particles and thin-film electrode are systematically characterized by XRD, Raman spectra, TEM, SEM and XPS techniques, and the electrochemical properties are investigated by CV and constant current discharge–charge test techniques. The α-MoO3 film electrode exhibits a reversible specific capacity of ∼1000 mA h g−1 at 50 mA g−1 and a stable capacity retention of 387–443 mA h g−1 at 2000 mA g−1, indicating its high Li storage capacity, superior rate performance and good cycling stability. The electrode material, as well as the fabrication technique, is highly promising for practical use in high energy and power density lithium-ion batteries.
Co-reporter:Yu Liu, Youmin Guo, Ran Ran, Zongping Shao
Journal of Membrane Science 2013 Volume 437() pp:189-195
Publication Date(Web):15 June 2013
DOI:10.1016/j.memsci.2013.03.002
•The sintering aid was added into the green pellets by impregnation method.•BZCY4 showed an excellent sintering ability after introduction of zinc nitrate.•An integrated SOFC with BZCY4+4 wt% Zn electrolyte was fabricated without cracks.•Zinc nitrate as sintering aid did not obstructed the peak power density of SOFC.BaZr0.4Ce0.4Y0.2O3−δ (BZCY4) has been widely considered to be a promising electrolyte material for H+-SOFC, but it is restricted to commercial applications due to its poor densification behavior. A dense BZCY4 pellet was obtained by sintering at 1250 °C after impregnating the material with a zinc nitrate solution. The dilatometer curves and scanning electron microscopy (SEM) images indicated that the sinterability of the BZCY4 material is effectively improved by impregnating the green membrane with 4 wt% Zn. Moreover, EDX mapping indicated that the Ba, Zr and Ce elements were homogeneously distributed in the BZCY4+4 wt% Zn sample sintered at 1250 °C. In addition, an integrated SOFC employing a BZCY4+4 wt% Zn electrolyte was successfully fabricated without any cracks and delamination by impregnating the BZCY4 electrolyte membrane with zinc nitrate as a sintering aid. This single cell with a 25 mm thick BZCY4+4 wt% Zn electrolyte membrane exhibited power densities as high as 360 and 276 mW cm−2 at 700 and 600 °C, respectively. Electrical conductivity measurements demonstrated that the total conductivities of BZCY4+4 wt% Zn were 0.46×10−2 S cm−1, 0.56×10−2 S cm−1, 0.20×10−2 S cm−1 and 0.40×10−2 S cm−1 at 600 °C in air, wet air, 10% H2–Ar and wet 10% H2–Ar, respectively.
Co-reporter:Simin Jiang, Bote Zhao, Yubo Chen, Rui Cai, Zongping Shao
Journal of Power Sources 2013 Volume 238() pp:356-365
Publication Date(Web):15 September 2013
DOI:10.1016/j.jpowsour.2013.03.017
Lithium titanate (Li4Ti5O12) and SiO2-incorporated Li4Ti5O12 are synthesized, using a facile cellulose-assisted combustion technique, as anodes for lithium-ion batteries tested under different conditions, i.e., discharge to an end potential of 1.0 V/0.01 V at room/elevated temperature (55 °C). The particles are characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), nitrogen adsorption–desorption isotherms, X-ray spectrometry (EDX) and transmission electron microscopy (TEM). The results show that silicon element is successfully incorporated with Li4Ti5O12 homogeneously in the forms of Si-doping and SiO2 separate phase. When discharged in the potential range of 0.01–3.0 V, initial discharge capacities of 260 mA h g−1 and 298 mA h g−1 are obtained for the Li4Ti5O12 and SiO2-incorporated Li4Ti5O12 electrodes, respectively. Both electrodes show stable cycling performance for 400 cycles (approximately 1.5 months) at room temperature between 0.01 and 3.0 V at a current density of 175 mA g−1. In addition, the stability of the electrodes under hurdle conditions (0.01–3.0 V at 55 °C) are explored and discussed, and a proposed mechanism for the “decrease–increase–decrease” cycling behavior is confirmed using electrochemical impedance spectroscopy (EIS) and TEM observations. The incorporation of SiO2 was found to improve the cycling stability under hurdle conditions.Highlights► Si is incorporated with Li4Ti5O12 in the forms of Si-doping and SiO2-coating. ► Li4Ti5O12 and SiO2-incorporated Li4Ti5O12 are tested under different conditions. ► Mechanism for “decrease–increase–decrease” cycling behavior is explained. ► SiO2 incorporation does improve the cycling stability under hurdle conditions.
Co-reporter:Yujing Sha, Tao Yuan, Bote Zhao, Rui Cai, Huanting Wang, Zongping Shao
Journal of Power Sources 2013 Volume 231() pp:177-185
Publication Date(Web):1 June 2013
DOI:10.1016/j.jpowsour.2012.12.081
Co-reporter:Jie Wang, Yingke Zhou, Zongping Shao
Electrochimica Acta 2013 Volume 97() pp:386-392
Publication Date(Web):1 May 2013
DOI:10.1016/j.electacta.2013.03.015
•Hierarchical porous TiO2(B)/anatase microspheres have been prepared by a facile solvothermal approach.•The porous microspheres are assembled by porous TiO2 nanosheets constructed by aggregations of primary nanocrystallites.•The porous microspheres present excellent lithium storage capacity and superior long-time cycling performance.•The formation of TiO2(B)/anatase heterojunction and the pseudocapacitance of TiO2(B) contribute to the remarkable electrode performance.•Such hierarchical porous materials might be promising for applications in advanced power type lithium-ion batteries.Novel hierarchical porous TiO2(B)/anatase microspheres have been prepared by a facile solvothermal approach and evaluated as anode materials for advanced lithium-ion battery applications. The obtained porous microspheres, with diameters ranging from 2.5 to 5.5 μm, are assembled by porous TiO2 nanosheets with the lateral size of a few micrometers and thickness of ~13 nm; whilst, the nanosheets are formed by aggregations of nanosized primary TiO2 crystallites (~5–7 nm). The hierarchical porous structures are verified by BET test results with a typical type-IV isotherm curve, a high surface area (~186.2 m2 g−1) and two kinds of pores (~4 and 8.3 nm). The hierarchical porous TiO2 microspheres present excellent electrochemical performance with high Li storage capacity and excellent high-rate cycling capability (a specific capacity of 117 mAh g−1 at the rate of 4000 mA g−1 after 4500 cycles), which might be attributed to the enhanced Li+ diffusion and electronic conductivity induced by the hierarchical microstructures, the TiO2(B)/anatase heterojunction, and the pseudocapacitance of TiO2(B). Such hierarchical porous materials might be promising for applications in advanced power type lithium-ion batteries.
Co-reporter:Fucun Wang, Dengjie Chen, Zongping Shao
Electrochimica Acta 2013 Volume 103() pp:23-31
Publication Date(Web):30 July 2013
DOI:10.1016/j.electacta.2013.04.054
Ba1−xCo0.7Fe0.2Nb0.1O3−δ oxides (x = 0, 0.05 and 0.10) were optimized as potential cathodes on oxygen ionic conductor electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). The creation of additional oxygen vacancies in Ba0.9Co0.7Fe0.2Nb0.1O3−δ was confirmed. Low polarization resistances of 0.015, 0.029 and 0.089 Ω cm2 were achieved at 700, 650 and 600 °C, respectively. By further optimizing the microstructure of the Ba0.9Co0.7Fe0.2Nb0.1O3−δ electrode by using polyvinyl butyral as a pore former and adjusting the sintering temperature, the maximum power density was improved from 682 to 955 mW cm−2 at 650 °C. The operational stability of the Ba0.9Co0.7Fe0.2Nb0.1O3−δ electrode was also investigated. The CO2 in the surrounding air was detrimental to the oxygen reduction reaction; however, the performance of the cell was recovered after removing the CO2 in the air at 650 or 700 °C. In addition, the Ba0.9Co0.7Fe0.2Nb0.1O3−δ electrode in symmetrical cells exhibited a stable performance at 650 °C for 400 h and maintained a reliable performance after repeated thermal cycles from room temperature to 700 °C. The results showed that Ba0.9Co0.7Fe0.2Nb0.1O3−δ was a promising cathode material for practical application in IT-SOFCs.
Co-reporter:Bin Xiong, Yingke Zhou, Ryan O’Hayre, Zongping Shao
Applied Surface Science 2013 Volume 266() pp:433-439
Publication Date(Web):1 February 2013
DOI:10.1016/j.apsusc.2012.12.053
Abstract
In this work, we present a facile route to prepare electrocatalysts for methanol oxidation. The catalyst synthesis route involves the simultaneous reduction and nitrogen doping of graphene oxide (GO) along with the reduction of H2PtCl6 to Pt by a facile ammonia gas heat-treatment and quenching process. The resulting catalysts are characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy while their electrocatalytic activity toward the oxidation of methanol is evaluated by cyclic voltammetry. The obtained Pt/graphene composites consist of crystalline Pt nanoparticles in the range of 1–4 nm which are well-dispersed on the N-doped graphene sheets. The best Pt/N-graphene catalyst composite is obtained after a 5 min ammonia treatment at 800 °C followed by rapid ammonia gas quenching at room temperature. This catalyst demonstrates superior catalytic activity for methanol electro-oxidation, with a peak current density of 0.218 A mgPt−1, which is about five times higher than an undoped (hydrogen treated and quenched) Pt/graphene control catalyst. The excellent electrocatalytic performance of the ammonia quenched catalyst is attributed to the nitrogenous functional groups and dopants in the graphene sheets that are formed during the facile quenching process in ammonia.
Co-reporter:Chao Li, Huangang Shi, Ran Ran, Chao Su, Zongping Shao
International Journal of Hydrogen Energy 2013 Volume 38(Issue 22) pp:9310-9319
Publication Date(Web):26 July 2013
DOI:10.1016/j.ijhydene.2013.05.025
•Provide a thermal inkjet printing technique for the fabrication of electrolytes.•Stable YSZ and SDC inks with high solids contents are prepared.•The YSZ layers are prepared with precise thickness control.•The Z values of the prepared inks fit well within the printable range.In this study, we report the facile fabrication of thin-film yttria-stabilized zirconia (YSZ) electrolytes and Sm0.2Ce0.8O1.9 (SDC) buffering layers for solid oxide fuel cells (SOFCs) using a thermal inkjet printing technique. Stable YSZ and SDC inks with solids contents as high as 20 and 10 wt.%, respectively, were first prepared. One single printing typically resulted in an YSZ membrane with thickness of approximately 1.5 μm, and membranes with thicknesses varied from 1.5 to 7.5 μm were fabricated with multiple sequential printing. An as-fabricated cell with a La0.8Sr0.2MnO3 (LSM) cathode delivered a peak power density (PPD) of 860 mW cm−2 at 800 °C. The SDC layer prepared using the inkjet printing method exhibited enclosed pores and a rough surface, which was, however, ideal for its application as a buffering layer. A cell with a dense 7.5-μm-thick YSZ layer, a 2-μm-thick SDC buffering layer and a Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) cathode was fabricated; this cell delivered a PPD of 1040 mW cm−2 at 750 °C and a high open circuit voltage (OCV) of approximately 1.10 V. The described technique provides a facile method for the fabrication of electrolytes for SOFCs with precise thickness control.
Co-reporter:Huaiyu Zhu, Wei Wang, Ran Ran, Zongping Shao
International Journal of Hydrogen Energy 2013 Volume 38(Issue 9) pp:3741-3749
Publication Date(Web):27 March 2013
DOI:10.1016/j.ijhydene.2013.01.032
Various Ni–LaxCe1−xOy composites were synthesized and their catalytic activity, catalytic stability and carbon deposition properties for steam reforming of methane were investigated. Among the catalysts, Ni–La0.1Ce0.9Oy showed the highest catalytic performance and also the best coking resistance. The Ni–LaxCe1−xOy catalysts with a higher Ni content were further sintered at 1400 °C and investigated as anodes of solid oxide fuel cells for operating on methane fuel. The Ni–La0.1Ce0.9Oy anode presented the best catalytic activity and coking resistance in the various Ni–LaxCe1−xOy catalysts with different ceria contents. In addition, the Ni–La0.1Ce0.9Oy also showed improved coking resistance over a Ni–SDC cermet anode due to its improved surface acidity. A fuel cell with a Ni–La0.1Ce0.9Oy anode and a catalyst yielded a peak power density of 850 mW cm−2 at 650 °C while operating on a CH4–H2O gas mixture, which was only slightly lower than that obtained while operating on hydrogen fuel. No obvious carbon deposition or nickel aggregation was observed on the Ni–La0.1Ce0.9Oy anode after the operation on methane. Such remarkable performances suggest that nickel and La-doped CeO2 composites are attractive anodes for direct hydrocarbon SOFCs and might also be used as catalysts for the steam reforming of hydrocarbons.Highlights► Ni–LaxCe1−xOy (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) cermets were synthesized. ► Ni–La0.1Ce0.9Oy showed the best catalytic activity and highest coking resistance. ► Ni–La0.1Ce0.9Oy anode also showed excellent operational stability. ► High power output of 850 mW cm−2 was obtained with methane–steam as fuel at 650 °C.
Co-reporter:Yuanyuan Zhao, Yingke Zhou, Ryan O’Hayre, Zongping Shao
Journal of Physics and Chemistry of Solids 2013 Volume 74(Issue 11) pp:1608-1614
Publication Date(Web):November 2013
DOI:10.1016/j.jpcs.2013.06.004
•Hydrazine reduction introduces nitrogen doping on the reduced graphene oxide.•The nitrogen-doped graphene substrate leads to improved Pt nanoparticles with altered electronic sructure.•The composite catalysts present excellent electrocatalytic activity towards methanol oxidation reaction.Hydrazine is often used to reduce graphene oxide (GO) to produce graphene. Recent observations suggested that when hydrazine is used to reduce GO, the resulting reduced graphene actually contains certain amounts of nitrogen dopants, which may influence the properties of the obtained material, and in some cases may be deployed for beneficial advantage. In this work, we prepared graphene oxide by the chemical oxidation method, then used either hydrazine or sodium borohydride (as a control) to reduce the graphene oxide to graphene and to explore the nature of the nitrogen functionalities introduced by hydrazine reduction. Pt nanoparticles were then deposited on the nitrogen doped (hydrazine-reduced) and undoped (control) graphene substrates, and the morphology, structure, and electrocatalytic methanol oxidation activity were characterized and evaluated. The results show that the nitrogen functional groups introduced into the graphene by hydrazine reduction greatly improve the electrocatalytic activity of the underlying Pt nanoparticles towards the methanol oxidation reaction.
Co-reporter:Guan Wu, Yingke Zhou, Xuefeng Gao, Zongping Shao
Solid State Sciences 2013 Volume 24() pp:15-20
Publication Date(Web):October 2013
DOI:10.1016/j.solidstatesciences.2013.06.015
•Novel LiFePO4 nanoplate and carbon nanotube composites were synthesized.•Crystalline LiFePO4 nanoplates were obtained by the low temperature polyol process.•Carbon nanotubes were evenly distributed and embedded into the plate like LiFePO4 particles.•The composite network structures offer favorable transport speed for both Li ions and electrons.•The facile process is potential to be extended for other composite materials.Crystalline LiFePO4 nanoplates were incorporated with 5 wt.% multi-walled carbon nanotubes (CNTs) via a facile low temperature polyol process, in one single step without any post heat treatment. The CNTs were embedded into the LiFePO4 particles to form a network to enhance the electrochemical performance of LiFePO4 electrode for lithium-ion battery applications. The structural and morphological characters of the LiFePO4–CNT composites were investigated by X-ray diffraction, Fourier Transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The electrochemical properties were analyzed by cyclic voltammetry, electrochemical impedance spectroscopy and charge/discharge tests. Primary results showed that well crystallized olivine-type structure without any impurity phases was developed, and the LiFePO4–CNT composites exhibited good electrochemical performance, with a reversible specific capacity of 155 mAh g−1 at the current rate of 10 mA g−1, and a capacity retention ratio close to 100% after 100 cycles.
Co-reporter:Yinlong Zhu;Dr. Zhi-Gang Chen;Dr. Wei Zhou;Shanshan Jiang; Jin Zou; Zongping Shao
ChemSusChem 2013 Volume 6( Issue 12) pp:2249-2254
Publication Date(Web):
DOI:10.1002/cssc.201300694
Abstract
Solid oxide fuel cells (SOFCs) directly convert fossil and/or renewable fuels into electricity and/or high-quality heat in an environmentally friendly way. However, high operating temperatures result in high cost and material issues, which have limited the commercialization of SOFCs. To lower their operating temperatures, highly active and stable cathodes are required to maintain a reasonable power output. Here, we report a layer-structured A-site deficient perovskite Sr0.95Nb0.1Co0.9O3−δ (SNC0.95) prepared by solid-state reactions that shows not only high activity towards the oxygen reduction reaction (ORR) at operating temperatures below 600 °C, but also offers excellent structural stability and compatibility, and improved CO2 resistivity. An anode-supported fuel cell with SNC0.95 cathode delivers a peak power density as high as 1016 mW cm−2 with an electrode-area-specific resistance of 0.052 Ω cm2 at 500 °C.
Co-reporter:Yuanyuan Zhao;Yingke Zhou;Bin Xiong;Jie Wang
Journal of Solid State Electrochemistry 2013 Volume 17( Issue 4) pp:1089-1098
Publication Date(Web):2013 April
DOI:10.1007/s10008-012-1968-0
In this work, we describe a facile single-step approach for the simultaneous reduction of graphene oxide to graphene, functional doping of graphene with nitrogen, and loading of the doped graphene with well-dispersed platinum (Pt) nanoparticles using a solvent mixture of ethylene glycol and N-methyl-2-pyrrolidone. The as-prepared Pt/nitrogen-doped graphene (N-graphene) catalysts are characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy while the electrocatalytic methanol oxidation properties of the catalysts are evaluated by cyclic voltammetry and chronoamperometry. Compared with an updoped Pt/graphene control catalyst, the Pt/N-graphene catalyst shows a narrower particle size distribution and improved catalytic performance. Considering the facile, green and effective single-step synthetic process for the Pt/N-graphene catalyst, the results are promising for the potential application of these materials in emerging fuel cell technologies.
Co-reporter:Zongping Shao, Wei Zhou, Zhonghua Zhu
Progress in Materials Science 2012 Volume 57(Issue 4) pp:804-874
Publication Date(Web):May 2012
DOI:10.1016/j.pmatsci.2011.08.002
Solid-oxide fuel cells (SOFCs) technology has a substantial potential in the application of clean and efficient electric power generation. However, the widespread utilization of SOFCs has not been realized because the cost associated with cell fabrication, materials and maintenance is still too high. To increase its competitiveness, lowering the operation temperature to the intermediate range of around 500–800 °C is one of the main goals in current SOFCs research. A major challenge is the development of cell materials with acceptably low ohmic and polarization losses to maintain sufficiently high electrochemical activity at reduced temperatures. During the past few decades, tremendous progress has been made in the development of cell materials and stack design, which have been recently reviewed. SOFCs are fabricated from ceramic or cermet powders. The performances of SOFCs are also closely related to the ways in which the cell materials are processed. Therefore, the optimization of synthetic processes for such materials is of great importance. The conventional solid-phase reaction method of synthesizing SOFCs materials requires high calcination and sintering temperatures, which worsen their microstructure, consequently, their electrochemical properties. Various wet chemical routes have recently been developed to synthesize submicro- to nano-sized oxide powders. This paper provides a comprehensive review on the advanced synthesis of materials for intermediate-temperature SOFCs and their impact on fuel cell performance. Combustion, co-precipitation, hydrothermal, sol–gel and polymeric-complexing processes are thoroughly reviewed. In addition, the parameters relevant to each synthesis process are compared and discussed. The effect of different processes on the electrochemical performance of the materials is evaluated and optimization of the synthesis processes is discussed and some emerging synthetic techniques are also briefly presented.
Co-reporter:Bote Zhao, Xing Yu, Rui Cai, Ran Ran, Huanting Wang and Zongping Shao
Journal of Materials Chemistry A 2012 vol. 22(Issue 7) pp:2900-2907
Publication Date(Web):22 Dec 2011
DOI:10.1039/C1JM14362J
A facile way for the synthesis of LiFePO4 composite using a solution combustion technique based on the glycine–nitrate process with inexpensive iron (III) as the raw material is introduced. Pure phase LiFePO4 was obtained at an optimal glycine to LiFePO4 ratio of 4:1. To further increase the electrode performance, sucrose is applied as an organic carbon source. The introduction of sucrose after the auto-combustion is found to be the most effective way in improving electrode performance. The as-synthesized LiFePO4/C sample contained about 2.86 wt.% carbon shows an attractive discharge capacity of about 160 mA h g−1 at a 0.1 C rate and retains a capacity of 110 mA h g−1 at a 5 C rate. In addition, the electrodes show excellent cycling performance during the 90 cycles at various rates. The rate limiting step for the electrode reaction is explored with the chronoamperometry technique and it demonstrates the surface kinetics is effectively improved for the LiFePO4 electrode modified with a proper amount of carbon.
Co-reporter:Zinan Wan, Rui Cai, Simin Jiang and Zongping Shao
Journal of Materials Chemistry A 2012 vol. 22(Issue 34) pp:17773-17781
Publication Date(Web):06 Jul 2012
DOI:10.1039/C2JM33346E
It is believed that a TiN coating can increase the electrical conductivity, and consequently the performance, of an electrode. In this work, a simple one-step synthesis of nitrogen- and TiN-modified Li4Ti5O12, i.e. solid-state reaction of Li2CO3 and TiO2 anatase in an ammonia-containing atmosphere, is introduced. The reducing ammonia atmosphere could cause the partial reduction of Ti4+ to Ti3+ and the doping of nitrogen into the Li4Ti5O12 lattice, in addition to the formation of the TiN phase. By controlling the ammonia concentration of the atmosphere and using a slight Ti excess in the reactants, Li4Ti5O12, nitrogen-doped Li4Ti5O12, or TiN-coated nitrogen-doped Li4Ti5O12 were obtained. Both the electrical conductivity and the TiN thickness were closely related to the ammonia concentration in the atmosphere. Synthesis under reducing atmosphere also resulted in powders with a different plate shape particulate morphology from that synthesized in air, and such plate-shape powders had an ultrahigh tap density of ∼1.9 g cm−3. Interestingly, the formation of TiN was not beneficial for capacity improvement due to its insulation towards lithium ions, unlike the nitrogen doping. The sample prepared under 3% NH3–N2, which was free of TiN coating, showed the best electrode performance with a capacity of 103 mA h g−1 even at 20 C with only 3% capacity decay after cycling 100 times.
Co-reporter:Shanshan Jiang, Fengli Liang, Wei Zhou and Zongping Shao
Journal of Materials Chemistry A 2012 vol. 22(Issue 32) pp:16214-16218
Publication Date(Web):27 Jun 2012
DOI:10.1039/C2JM33311B
A 3D hierarchical porous ceramic electrode is fabricated directly from a carbon-oxides precursor by a general, cost-effective, and facile method. The oxygen reduction reaction activity of the electrode is significantly enhanced due to enlarged active areas and optimized gas transport channels. For the first time, this study demonstrates that a cobalt-free cathode is able to reach the target area specific resistance value of 0.15 Ω cm2 at 600 °C. The new material has been successfully used as the cathode for a SOFC and shows high power generation ability below 600 °C.
Co-reporter:Feifei Dong, Dengjie Chen, Yubo Chen, Qing Zhao and Zongping Shao
Journal of Materials Chemistry A 2012 vol. 22(Issue 30) pp:15071-15079
Publication Date(Web):28 May 2012
DOI:10.1039/C2JM31711G
Cobalt-free small La3+-doped BaFeO3−δ is synthesized and systematically characterized towards application as an oxygen reduction electrode material for intermediate temperature solid oxide fuel cells (IT-SOFCs) with oxygen-ion conducting electrolyte. The formation of an oxygen vacancy-disordered perovskite oxide with cubic lattice symmetry is demonstrated by XRD, after the doping of only 5 mol% La3+ into BaFeO3−δ parent oxide with the formation of Ba0.95La0.05FeO3−δ (BLF). The structural, thermal, electrical and electrochemical properties of BLF have been evaluated. High structural stability, high thermal expansion coefficient, high oxygen vacancy concentration, and relatively low electrical conductivity, are demonstrated. BLF shows a superior electrocatalytic activity, which is comparable to those state-of-the-art cobalt-based mixed conducting cathodes, in addition, it demonstrates a favorable long-term operational stability. It thus promises as a new cathode candidate for IT-SOFCs with oxygen-ion conducting electrolyte.
Co-reporter:Rui Cai, Simin Jiang, Xing Yu, Bote Zhao, Huanting Wang and Zongping Shao
Journal of Materials Chemistry A 2012 vol. 22(Issue 16) pp:8013-8021
Publication Date(Web):14 Mar 2012
DOI:10.1039/C2JM15731D
An amenable method for improving rate performance of Li4Ti4.85Al0.15O12 electrode by post-synthesis treatment in formaldehyde aqueous solution at room temperature is introduced. The as-prepared samples are characterized by XRD, BET, SEM, HR-TEM, XPS and electronic conductivity measurement. The treatment causes no noticeable change on the phase structure and has only little effect on the specific surface area and particulate morphologies. It also only slightly decreases the lithium ion diffusion coefficient. However, it substantially increases the electronic conductivity due to the creation of Ti3+ in the oxide lattice. The post-synthesis treatment for a period of 4 h effectively increases the capacity at 10 C rate for Li4Ti4.85Al0.15O12 from 125 mA h g−1 for the untreated sample to 160 mA h g−1, and the electrode performance is also fairly stable. This method is highly attractive for synthesis of high-performance Li4Ti5O12 electrodes owing to its simplicity, energy saving and efficiency. As a general method, post-synthesis treatment using formaldehyde may be applicable to other electrodes.
Co-reporter:Yu Liu, Youmin Guo, Ran Ran, Zongping Shao
Journal of Membrane Science 2012 Volumes 415–416() pp:391-398
Publication Date(Web):1 October 2012
DOI:10.1016/j.memsci.2012.05.062
Chemically stable BaZr0.8Y0.2O3−δ (BZY) oxide is limited to applications as an electrolyte for solid oxide fuel cells (SOFCs) because of its poor sintering behavior. This study attempts to improve the sinterability and conductivity of BZY using the partial substitution of Zr4+ in BZY with Nd3+. An oxide with the nominal composition of BaZr0.7Nd0.1Y0.2O3−δ (BZNY) is specifically investigated. Results from X-ray diffraction (XRD) demonstrate Nd3+ is successfully doped into the lattice as anticipated and transmission electron microscopy (TEM) characterizations verify the morphology and crystal structure of the BZNY powder. Dilatometric measurement and scanning electron microscopy (SEM) observations provide verification that the sinterability of the oxide is effectively improved by introducing Nd3+. XRD and CO2-TPD results demonstrate that BZNY is relatively stable with respect to the CO2 atmosphere. The total conductivity of BZNY in wet H2 is 2.76×10−3 S cm−1 at 600 °C. An anode-supported thin-film BZNY electrolyte (∼30 μm) cell is fabricated, and the electrolyte layer is found to be well densified after co-sintering with the anode substrate at 1450 °C for 5 h. The cell delivers a peak power density of 142 mW cm−2 at 700 °C, higher than the reported values for a similar cell with BZY electrolyte.Highlights▸ Synthesized BZNY has a cubic perovskite structure demonstrated by XRD and TEM. ▸ BZNY shows a low sintering temperature and maintains excellent chemical stability. ▸ Conductivity of BZNY electrolyte shows a higher value than BZY. ▸ A dense BZNY electrolyte in the anode-supported SOFC was obtained at 1450 °C.
Co-reporter:Fucun Wang, Dengjie Chen, Zongping Shao
Journal of Power Sources 2012 Volume 216() pp:208-215
Publication Date(Web):15 October 2012
DOI:10.1016/j.jpowsour.2012.05.068
Sm0.5Sr0.5CoO3−δ (SSC)-impregnated cathodes are fabricated by the solution infiltration of metal nitrates. The effects of complexing agents on the phase structure and the effects of pore formers on the porosity of the scaffold are examined and optimized. The thermal expansion behavior, electrical conductivities and electrochemical performance of the cathodes are characterized and optimized. A pure perovskite phase is formed after heating at 800 °C by adding a relatively small quantity of glycine as the complexing agent. Polyvinyl butyral is selected as the pore former for the preparation of porous Sm0.2Ce0.8O1.9 (SDC) scaffolds. The thermal expansion coefficient increases slightly from 12.74 × 10−6 K−1 to 13.28 × 10−6 K−1 after infiltrating 20 wt% SSC into the SDC scaffold. The infiltrated cathode with 20 wt% SSC + 80 wt% SDC shows the electrical conductivity of 15 S cm−1 at 700 °C. A well-connected SSC network is formed in the cathode after infiltrating 20 wt% SSC into the SDC scaffold. Cathode polarization resistance values as low as 0.05 Ω cm2, peak power density values as high as 936 mW cm−2 and stable performance throughout 325 h of operation at 700 °C suggest that the cathodes with the 20 wt% SSC-infiltrated SDC are suitable for practical application. However, for the SSC infiltrated into the 8 mol% yttria-stabilized zirconia scaffold, the interfacial reaction continues to occur during the stability test at 700 °C. SDC is preferred as a scaffold for the infiltration of SSC to ensure long-term operational stability.Highlights► Sm0.2Ce0.8O1.9 (SDC) was preferred as a porous scaffold for the infiltration. ► A pure Sm0.5Sr0.5CoO3−δ (SSC) phase was formed with glycine as a complexing agent. ► Electrical conductivities of ∼15 S cm−1 were achieved with 20 wt% SSC + 80 wt% SDC. ► A stable performance was obtained with a 20 wt% SSC + 80 wt% SDC electrode. ► A 20 wt% SSC + 80 wt% SDC electrode showed a resistance of 0.05 Ω cm2 at 700 °C.
Co-reporter:Ye Lin, Chao Su, Cheng Huang, Ju Sik Kim, Chan Kwak, Zongping Shao
Journal of Power Sources 2012 Volume 197() pp:57-64
Publication Date(Web):1 January 2012
DOI:10.1016/j.jpowsour.2011.09.040
A new symmetric SOFC with an SDC framework and a silver-infiltrated electrocatalyst is presented for the first time in this paper. A three-electrode polarization test shows that the Ag–SDC has a low area specific resistance of 1.07 Ω cm2 at 600 °C, a low activation energy of 85 kJ mol−1 and high exchange current densities of 428.2 and 129.0 mA cm−2 at 750 and 650 °C, respectively, when it is used as an oxygen reduction electrode. It also exhibits low polarization resistance in a humidified hydrogen atmosphere. A symmetric single cell is used in real fuel cell conditions to deliver peak power densities of 200 and 84 mW cm−2 at 750 and 650 °C, respectively, when humidified hydrogen is used as a fuel and ambient air is used as the cathode atmosphere. The cell still reaches a peak power density of 81 mW cm−2 at 750 °C when operating on CO. O2-TPO analysis demonstrates that the Ag–SDC electrode has even better coking resistance than the pure SDC scaffold. The results indicate that Ag–SDC|SDC|Ag–SDC symmetric cells with an infiltrated silver electrocatalyst are a promising new type of fuel cell for use with both hydrogen fuel and carbon-containing fuels.Graphical abstractA novel symmetric SOFC with the whole cell of samaria-doped ceria (SDC) framework is successfully fabricated. Coupled with two symmetric silver infiltrated SDC electrodes which show perfect match of thermal expansion to the SDC electrolyte, good electrochemical performance in oxidizing or reducing atmosphere, and high coke tolerant property in CO atmosphere, the cost effective symmetric SOFC delivers a promising power output of 200 mW cm−2, 81 mW cm−2 at 750 °C operating on hydrogen and carbon monoxide respectively with a 0.4 mm thick SDC electrolyte.Highlights► A symmetric SOFC with whole cell of SDC framework was fabricated. ► The Ag/SDC electrode showed very promising electrochemical performance. ► The use of silver as the electrocatalyst prevented coke formation over the anode.
Co-reporter:Bote Zhao, Rui Cai, Simin Jiang, Yujing Sha, Zongping Shao
Electrochimica Acta 2012 Volume 85() pp:636-643
Publication Date(Web):15 December 2012
DOI:10.1016/j.electacta.2012.08.126
There is increasing interest in flexible, safe, high-power thin-film lithium-ion batteries which can be applied to various modern devices. Although TiO2 in rutile phase is highly attractive as an anode material of lithium-ion batteries for its high thermal stability and theoretical capacity of 336 mA h g−1 and low price, its inflexibility and sluggish lithium intercalation kinetics of bulk phase strongly limit its practical application for particular in thin-film electrode. Here we show a simple way to prepare highly flexible self-standing thin-film electrodes composed of mesoporous rutile TiO2/C nanofibers with low carbon content (<15 wt.%) by electrospinning technique with outstanding electrochemical performance, which can be applied directly as electrodes of lithium-ion batteries without the further use of any additive and binder. The atmosphere during calcination plays a critical role in determining the flexible nature of thin film and particle size of TiO2 in as-fabricated nanofibers. Big size (10 cm × 4 cm), flexible thin film is obtained after heat treatment under 10%H2–Ar at 900 °C for 3 h. After optimization, the diameter of fibers can reach as small as ∼110 nm, and the as-prepared rutile TiO2 films show high initial electrochemical activity with the first discharge capacity as high as 388 mA h g−1. What is more, very stable reversible capacities of ∼122, 92, and 70 mA h g−1 are achieved respectively at 1, 5 and 10 C rates with negligible decay rate within 100 cycling times.
Co-reporter:Dengjie Chen, Fucun Wang, Huangang Shi, Ran Ran, Zongping Shao
Electrochimica Acta 2012 Volume 78() pp:466-474
Publication Date(Web):1 September 2012
DOI:10.1016/j.electacta.2012.06.073
Co-free oxides with a nominal composition of LnBaFe2O5+δ, where Ln = La, Pr, Nd, Sm, Gd, and Y, were synthesized and phase structure, oxygen content, electronic conductivity, oxygen desorption, thermal expansion, microstructure and electrochemical performance were systematically investigated. Among the series of materials tested, LaBaFe2O5+δ oxide showed the largest electronic conductivity and YBaFe2O5+δ oxide had the smallest thermal expansion coefficient (TEC) of 14.6 × 10−6 K−1 within a temperature range of 200–900 °C. All LnBaFe2O5+δ oxides typically possess the TEC values smaller than 20 × 10−6 K−1. The oxygen content, electronic conductivity and TEC values are highly dependent on the cation size of the Ln3+ dopant. The lowest electrode polarization resistance in air under open circuit voltage condition was obtained for SmBaFe2O5+δ electrode and was approximately 0.043, 0.084, 0.196, 0.506 and 1.348 Ω cm2 at 800, 750, 700, 650 and 600 °C, respectively. The SmBaFe2O5+δ oxide also demonstrated the best performance after a cathodic polarization. A cell with a SmBaFe2O5+δ cathode delivered peak power densities of 1026, 748, 462, 276 and 148 mW cm−2 at 800, 750, 700, 650 and 600 °C, respectively. The results suggest that certain LnBaFe2O5+δ oxides have sufficient electrochemical performance to be promising candidates for cathodes in intermediate-temperature solid oxide fuel cells.
Co-reporter:Yubo Chen, Dengjie Chen, Ran Ran, Hee Jung Park, Chan Kwak, Sung Jin Ahn, Kyeong Suk Moon, Zongping Shao
Electrochemistry Communications 2012 Volume 14(Issue 1) pp:36-38
Publication Date(Web):January 2012
DOI:10.1016/j.elecom.2011.10.024
Nickel oxide was introduced as a grain growth inhibitor into Ba0.5Sr0.5Co0.8Fe0.2O3 − δ (BSCF) electrode to increase its activity for oxygen reduction reaction. Small amount of NiO can effectively suppress the grain growth of BSCF by spinning the grain boundary and thus increase the electrode surface area, while the particle connection is not obviously affected. Electrochemical impedance spectra of symmetric cells indicate that the electrode activity for oxygen reduction is indeed effectively improved by introducing NiO additive. At 600 °C, area specific resistance of BSCF+5wt.% NiO is about 36.5% lower than that of pure BSCF electrode. Single cell tests also demonstrate an improved cell power output by introducing NiO additive. It implies that the adoption of a sintering inhibitor may be a facile and practical way to increase electrode activity for oxygen reduction.Highlights► NiO is introduced into Ba0.5Sr0.5Co0.8Fe0.2O3 − δ (BSCF) as a grain growth inhibitor. ► Connection of BSCF grains and adhesion between electrode and electrolyte are good. ► Polarization resistance of BSCF+NiO is 36.5% lower than that of BSCF at 600 °C. ► Peak power density is 1773 mW cm− 2 with the BSCF+NiO cathode at 750 °C.
Co-reporter:Chao Su, Zongping Shao, Ye Lin, Yuzhou Wu and Huanting Wang
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 35) pp:12173-12181
Publication Date(Web):26 Jul 2012
DOI:10.1039/C2CP41166K
An intriguing cell concept by applying proton-conducting oxide as the ionic conducting phase in the anode and taking advantage of beneficial interfacial reaction between anode and electrolyte is proposed to successfully achieve both high open circuit voltage (OCV) and power output for SOFCs with thin-film samarium doped ceria (SDC) electrolyte at temperatures higher than 600 °C. The fuel cells were fabricated by conventional route without introducing an additional processing step. A very thin and dense interfacial layer (2–3 μm) with compositional gradient was created by in situ reaction between anode and electrolyte although the anode substrate had high surface roughness (>5 μm), which is, however, beneficial for increasing triple phase boundaries where electrode reactions happen. A fuel cell with Ni–BaZr0.4Ce0.4Y0.2O3 anode, thin-film SDC electrolyte and Ba0.5Sr0.5Co0.8Fe0.2O3–δ (BSCF) cathode has an OCV as high as 1.022 V and delivered a power density of 462 mW cm−2 at 0.7 V at 600 °C. It greatly promises an intriguing fuel cell concept for efficient power generation.
Co-reporter:Youmin Guo, Yu Liu, Rui Cai, Dengjie Chen, Ran Ran, Zongping Shao
International Journal of Hydrogen Energy 2012 Volume 37(Issue 19) pp:14492-14500
Publication Date(Web):October 2012
DOI:10.1016/j.ijhydene.2012.07.031
Nowadays, there is a doubt about the electrochemical contribution of silver current collector on the oxygen reduction reaction (ORR) over oxide electrodes in SOFCs since many reports have demonstrated that the modification of porous oxide electrodes with nano-size silver can obviously improve the electrocatalytic activity for ORR. In this study, the electrochemical contribution of silver current collector to the performance of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) electrode on Sm0.2Ce0.8O1.9 (SDC) electrolyte for ORR was specifically investigated. The active layer of BSCF electrode was found to be around 25 μm by using both silver and gold current collectors. Much better performance was demonstrated by using silver current collector, both from symmetric cell and single cell tests. However, EIS of silver on SDC electrolyte demonstrated the silver alone as electrode actually had poor performance for ORR. In addition, SEM-EDX confirmed that there was no silver diffused from the current collector layer to modify the porous BSCF electrode. Interestingly, the activation energy for oxygen reduction over BSCF electrode was reduced by applying silver current collector. We then proposed a mechanism to explain the improved electrochemical performance of BSCF electrode by considering the high activity of silver for oxygen surface diffusion.Highlights► The active layer of BSCF electrode was found to be around 25 μm. ► Ag current collector showed a beneficial effect on ORR of BSCF on SDC. ► Ag current collector can improve oxygen surface exchange kinetic of BSCF.
Co-reporter:Yuzhou Wu, Wei Wang, Kun Wang, Yao Zeng, Dehua Dong, Zongping Shao, and Huanting Wang
Industrial & Engineering Chemistry Research 2012 Volume 51(Issue 18) pp:6387-6394
Publication Date(Web):April 17, 2012
DOI:10.1021/ie300123x
The flake-shaped NiO-yttria-stabilized zirconia (YSZ) particles with nanocrystalline YSZ grains were synthesized using the sucrose-concentrated H2SO4 dehydration reaction, and their microstructure was characterized by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). To evaluate the properties of the flake-shaped NiO-YSZ particles as the anode materials for solid oxide fuel cells, the reduction temperature of the flake-shaped NiO-YSZ particles and catalytic activity on the methane steam/CO2 reforming reactions of the H2-reduced particles as well as the electrochemical impedance spectra of the YSZ supported symmetrical cells with the electrodes made from these particles were examined in comparison with the mixed commercial NiO-YSZ. HRTEM revealed that the nanocrystalline YSZ was dispersed in the NiO matrix and distributed on the surface of the flake-shaped NiO-YSZ particles. The catalytic performance of the flake-shaped NiO-YSZ particles was better than that of the mixed commercial NiO-YSZ in both steam reforming and CO2 reforming of methane. The symmetrical cell made from the flake-shaped NiO-YSZ exhibited a much lower polarization resistance at the operating temperatures below 800 °C than that made from the mixed commercial NiO-YSZ.
Co-reporter:Chao Su, Wei Wang, Ran Ran, Tao Zheng, Zongping Shao
International Journal of Hydrogen Energy 2012 Volume 37(Issue 8) pp:6844-6852
Publication Date(Web):April 2012
DOI:10.1016/j.ijhydene.2012.01.057
In order to increase the coking resistance of SOFCs operating on DME fuel, a Pt/Al2O3–Ni/MgO mixture catalyst was investigated for internal partial oxidation of DME. Catalytic test demonstrated the mixture catalyst has higher activity for DME partial oxidation and lower CH4 selectivity than the individual Pt/Al2O3 and Ni/MgO catalysts. O2-TPO analysis demonstrated that the mixture catalyst also had much higher coke resistance than sintered Ni-YSZ anode, especially at high O2 to DME ratio. Raman spectroscopy of the carbon-deposited catalysts demonstrates that the graphitization degree of carbon is reduced with introducing O2 into DME, and the carbon deposited on the mixture catalyst is almost in amorphous structure. Two operation modes of the mixture catalyst for indirect internal partial oxidation of DME, i.e, directly depositing on the anode surface and locating in the anode chamber were tried. The performance of the cells operating on DME fuel through both operation modes was studied by I–V polarization test and EIS characterization. The cells delivered attractive peak power density of around 750 mW cm−2 by operating on DME-O2 mixture gas, modestly lower than 1012–1065 mW cm−2 operating on pure hydrogen fuel at 700 °C. The direct deposition of Pt/Al2O3–Ni/MgO onto anode surface to perform as a functional layer and a DME to O2 ratio of 2:1 in the mixture gas is preferred to minimize coke formation and maximize power output for the cell to operate on DME fuel.Highlights► Pt/Al2O3–Ni/MgO catalyst has high activity for DME partial oxidation. ► This catalyst has much higher coking resistance than sintered Ni-YSZ anode. ► The cells with the mixed catalyst deliver high power output operating on DME-O2.
Co-reporter:Feifei Dong, Dengjie Chen, Ran Ran, Heejung Park, Chan Kwak, Zongping Shao
International Journal of Hydrogen Energy 2012 Volume 37(Issue 5) pp:4377-4387
Publication Date(Web):March 2012
DOI:10.1016/j.ijhydene.2011.11.150
Sm0.5Sr0.5MO3−δ (M = Co and Mn) materials are synthesized, and their properties and performance as cathodes for solid oxide fuel cells (SOFCs) on Sm0.2Ce0.8O1.9 (SDC) and Y0.16Zr0.92O2.08 (YSZ) electrolytes are comparatively studied. The phase structure, thermal expansion behavior, oxygen mobility, oxygen vacancy concentration and electrical conductivity of the oxides are systematically investigated. Sm0.5Sr0.5CoO3−δ (SSC) has a much larger oxygen vacancy concentration, electrical conductivity and TEC than Sm0.5Sr0.5MnO3−δ (SSM). A powder reaction demonstrates that SSM is more chemically compatible with the YSZ electrolyte than SSC, while both are compatible with the SDC electrolyte. EIS results indicate that the performances of SSC and SSM electrodes depend on the electrolyte that they are deposited on. SSC is suitable for the SDC electrolyte, while SSM is preferred for the YSZ electrolyte. A peak power density as high as 690 mW cm−2 at 600 °C is observed for a thin-film SDC electrolyte with SSC cathode, while a similar cell with YSZ electrolyte performs poorly. However, SSM performs well on YSZ electrolyte at an operation temperature of higher than 700 °C, and a fuel cell with SSM cathode and a thin-film YSZ electrolyte delivers a peak power density of ∼590 mW cm−2 at 800 °C. The poor performances of SSM cathode on both YSZ and SDC electrolytes are obtained at a temperature of lower than 650 °C.Highlights► Co and Mn ions showed varied effects on intrinsic properties of explored materials. ► The performances of SSM and SSC electrodes depended on the deposited electrolytes. ► Cathodic polarization led to distinct improvements for SSM and SSC electrode.
Co-reporter:Ye Lin, Wei Zhou, Jaka Sunarso, Ran Ran, Zongping Shao
International Journal of Hydrogen Energy 2012 Volume 37(Issue 1) pp:484-497
Publication Date(Web):January 2012
DOI:10.1016/j.ijhydene.2011.09.010
This study characterizes BaCo0.7Fe0.2Nb0.1O3−δ (BCFN) perovskite oxide and evaluates it as a potential cathode material for proton-conducting SOFCs with a BaZr0.1Ce0.7Y0.2O3-δ (BZCY) electrolyte. A four-probe DC conductivity measurement demonstrated that BCFN has a modest electrical conductivity of 2–15 S cm−1 in air with p-type semiconducting behavior. An electrical conductivity relaxation test showed that BCFN has higher Dchem and Kchem than the well-known Ba0.5Sr0.5Co0.8Fe0.2O3−δ oxide. In addition, it has relatively low thermal expansion coefficients (TECs) with values of 18.2 × 10−6 K−1 and 14.4 × 10−6 K−1 at temperature ranges of 30–900 °C and 30–500 °C, respectively. The phase reaction between BCFN and BZCY was investigated using powder and pellet reactions. EDX and XRD characterizations demonstrated that BCFN had lower reactivity with the BZCY electrolyte than strontium-containing perovskite oxides such as SrCo0.9Nb0.1O3-δ and Ba0.6Sr0.4Co0.9Nb0.1O3−δ. The impedance of BCFN was oxygen partial pressure dependent. Introducing water into the cathode atmosphere reduced the size of both the high-frequency and low-frequency arcs of the impedance spectra due to facilitated proton hopping. The cathode polarization resistance and overpotential at a current density of 100 mA cm−2 were 0.85 Ω cm−2 and 110 mV in dry air, which decreased to 0.43 Ω cm−2 and 52 mV, respectively, in wet air (∼3% H2O) at 650 °C. A decrease in impedance was also observed with polarization time; this was possibly caused by polarization-induced microstructure optimization. A promising peak power density of ∼585 mW cm−2 was demonstrated by an anode-supported cell with a BCFN cathode at 700 °C.Highlights► Electrical conductivity relaxation tests show BCFN has even higher Dchem and kchem than the well-known BSCF oxide. ► BCFN has better chemical stability with BZCY than SCN and BSCN. ► BCFN shows lower ASR in wet air than in dry air. ► BCFN shows low overpotential and good stability during the polarization tests. ► We achieve high fuel cell performance while using BCFN as the cathode and BZCY as the electrolyte.
Co-reporter:Yao Zheng, Ran Ran, Shi Zhang Qiao, Zongping Shao
International Journal of Hydrogen Energy 2012 Volume 37(Issue 5) pp:4328-4338
Publication Date(Web):March 2012
DOI:10.1016/j.ijhydene.2011.11.122
Single-chamber solid oxide fuel cells (SC-SOFCs), which apply fuel-oxidant (air) gas mixture as the atmosphere for both anode and cathode, are receiving many interests recently. This study aims to clarify the mechanism of oxygen reduction and methane oxidization over La0.8Sr0.2MnO3 (LSM) cathode in SC-SOFCs by an electrochemical method in combination with mass spectrometry (MS). Before cathodic polarization, a large polarization resistance (Rp) for oxygen reduction reaction (ORR) was observed and methane did not cause obvious effect on ORR because of the weak adsorption of methane over LSM surface. Cathodic polarization could decrease the Rp obviously due to the in-situ creation of oxygen vacancies; methane likely adsorbed on those oxygen vacancy sites to enhance its effect on ORR. Both the anodic and cathodic polarizations significantly increased the rate of methane oxidation over LSM electrode; in particular, the pumped oxygen anion was highly active for methane oxidation.Highlights► Adsorption activity of methane and oxygen on of La0.8Sr0.2MnO3 surface. ► The influence of cathodic polarization on oxygen reduction and methane oxidation. ► A fundamental mechanism of methane oxidation reaction on La0.8Sr0.2MnO3.
Co-reporter:Dengjie Chen, Fucun Wang, Zongping Shao
International Journal of Hydrogen Energy 2012 Volume 37(Issue 16) pp:11946-11954
Publication Date(Web):August 2012
DOI:10.1016/j.ijhydene.2012.05.053
The influence of Co3O4 as a sintering aid for a series of cobalt-containing perovskite oxides on the microstructure and electrical properties have been investigated. X-ray diffraction and scanning electron microscopic results showed that well connected electrode particles with firm adhesion to the 8 mol% yttria-stabilized zirconia (YSZ) electrolyte surface were realized at a temperature free from interfacial phase reaction. Both ohmic and polarization resistances of symmetric cells by adopting YSZ electrolyte, measured by electrochemical impedance spectroscopy, were much lower than that without adding Co3O4. The peak power density of 1176 mW cm−2 at 750 °C was achieved when La0.6Sr0.4Co0.2Fe0.8O3−δ + Co3O4 was selected as a representative cobaltite cathode, which is much higher than a similar fuel cell with the cathode fabricated by a conventional way. Fabrication of interlayer-free electrodes by applying Co3O4 as a sintering aid is very simple and general, applicable for a wide range of cobalt-containing electrode materials.Highlights► Interlayer-free electrodes by applying Co3O4 as a sintering aid are developed. ► Well-connected electrode particles are formed at the firing of 800 °C. ► Firm adhesion is realized at a temperature free from interfacial phase reaction. ► The method is applicable for a wide range of cobalt-containing electrode materials.
Co-reporter:Huaiyu Zhu, Wei Wang, Ran Ran, Chao Su, Huangang Shi, Zongping Shao
International Journal of Hydrogen Energy 2012 Volume 37(Issue 12) pp:9801-9808
Publication Date(Web):June 2012
DOI:10.1016/j.ijhydene.2012.03.060
On the purpose to perform as functional layer of SOFCs operating on methane fuel, NiFe–ZrO2 alloy catalysts have been synthesized and investigated for methane partial oxidation reactions. Ni4Fe1–ZrO2 shows catalytic activity comparable to that of Ni–ZrO2 and superior to other Fe-containing catalysts. In addition, O2-TPO analysis indicates iron is also prone to coke formation; as a result, most of NiFe–ZrO2 catalysts do not show improved coking resistance than Ni–ZrO2. Anyway, Ni4Fe1–ZrO2 (Ni:Fe = 4:1 by weight) prepared by glycine-nitrate process shows somewhat less carbon deposition than the others. However, Raman spectroscopy demonstrates that the addition of Fe does reduce the graphitization degree of the deposited carbon, suggesting the easier elimination of carbon once it is deposited over the catalyst. Ni4Fe1–ZrO2 has an excellent long-term stability for partial oxidation of methane reaction at 850 °C. A solid oxide fuel cell with conventional nickel cermet anode and Ni4Fe1–ZrO2 functional layer is operated on CH4–O2 gas mixture to yield a peak power density of 1038 mW cm−2 at 850 °C, which is comparable to that of hydrogen fuel. In summary, the Ni4Fe1–ZrO2 catalyst is potential catalyst as functional layer for solid-oxide fuel cells operating on methane fuel.Highlights► A small amount of iron addition improves coke resistance of the nickel catalyst. ► Ni4Fe1–ZrO2 shows good catalytic activity for partial oxidation of methane. ► The fuel cell with the Ni4Fe1–ZrO2 catalyst layer delivers high power output.
Co-reporter:Yuzhou Wu, Chao Su, Wei Wang, Huanting Wang, Zongping Shao
International Journal of Hydrogen Energy 2012 Volume 37(Issue 11) pp:9287-9297
Publication Date(Web):June 2012
DOI:10.1016/j.ijhydene.2012.03.034
Ni/Fe alloy-based anodes have attracted much attention recently due to their potential for improving anodic activity and suppressing carbon deposition when operating on carbon-containing fuels. However, some inconsistent results about the iron alloying effect were reported in literature. In the present work, we systematically studied the influence of synthesis method on properties and cell performances of a Ni0.75Fe0.25 + SDC (60:40 v/o) alloy-ceramic anode for solid oxide fuel cells. Three different methods, i.e. physical mixing route (PMR), simultaneous glycine nitrate process/sol–gel route (S-GNP) and combined GNP sol–gel route (C-GNP), were used. Samples were analysed by X-ray diffraction, temperature-programmed reduction/oxidation, scanning electron microscopy and electrochemical impedance spectroscopy. It was revealed that the phase structure of anode components, chemical interaction between nickel and iron, and the electrode microstructure were strongly dependent on the synthesis method. The coking resistance was found to be more sensitive to anode phase structure and chemical binding between Ni and Fe phases, whereas the cell power output was mainly determined by the electrode microstructure. As a result, the iron content of the NiFe-based anode should be carefully controlled in different preparation methods to achieve high cell performances.Highlights► Synthesis methods affect a lot on Ni/Fe alloy anode and cell performances. ► Coking resistance is sensitive to phase structure and chemical binding of Ni–Fe. ► The cell power output is mainly determined by the electrode microstructure.
Co-reporter:Wei Wang, Chao Su, Tao Zheng, Mingming Liao, Zongping Shao
International Journal of Hydrogen Energy 2012 Volume 37(Issue 10) pp:8603-8612
Publication Date(Web):May 2012
DOI:10.1016/j.ijhydene.2012.02.138
Ni + CexZr1−xO2 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) cermets were synthesized and their catalytic performance for partial oxidation of ethanol (POE) reaction was studied. The structure, reducibility properties and carbon deposition behavior of the various catalysts were investigated. Among the various catalysts, Ni + Ce0.8Zr0.2O2 displayed the best catalytic activity in terms of H2 selectivity and also the highest coking resistance. The fuel cell with Ni + Ce0.8Zr0.2O2 catalyst layer delivered a peak power density of 692 mW cm−2 at 700 °C when operating on ethanol–O2 gas mixtures, comparable to that applying hydrogen fuel. The fuel cell also showed an improved operation stability on ethanol–O2 fuel for 150 h at 700 °C. Ni + Ce0.8Zr0.2O2 is promising as an active and coke-tolerant catalyst layer for solid oxide fuel cells operating on ethanol-O2 fuel, which makes it highly attractive by applying biofuel in an SOFC system for efficiency electric power generation.Highlights► Ni + CexZr1−xO2 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) cermets were synthesized. ► Ni + Ce0.8Zr0.2O2 showed the best catalytic activity and highest coking resistance. ► High power output of 692 mW cm−2 was obtained with ethanol–O2 as fuel at 700 °C.
Co-reporter:Shanshan Jiang;Dr. Wei Zhou;Yingjie Niu; Zhonghua Zhu; Zongping Shao
ChemSusChem 2012 Volume 5( Issue 10) pp:2023-2031
Publication Date(Web):
DOI:10.1002/cssc.201200264
Abstract
It is generally recognized that the phase transition of a perovskite may be detrimental to the connection between cathode and electrolyte. Moreover, certain phase transitions may induce the formation of poor electronic and ionic conducting phase(s), thereby lowering the electrochemical performance of the cathode. Here, we present a study on the phase transition of a cobalt-free perovskite (SrNb0.1Fe0.9O3−δ, SNF) and evaluate its effect on the electrochemical performance of the fuel cell. SNF exists as a primitive perovskite structure with space group P4mm (99) at room temperature. As evidenced by in situ high-temperature X-ray diffraction measurements over the temperature range of 600 to 1000 °C, SNF undergoes a transformation to a tetragonal structure with a space group I4/m (87). This phase transition is accompanied by a moderate change in the volume, allowing a good cathode/electrolyte interface on thermal cycling. According to the electrochemical impedance spectroscopy evaluation, the I4/m phase exhibits positive effects on the cathode’s performance, showing the highest oxygen reduction reaction activity of cobalt-free cathodes reported so far. This activity improvement is attributed to enhanced oxygen surface processes.
Co-reporter:Bote Zhao
The Journal of Physical Chemistry C 2012 Volume 116(Issue 33) pp:17440-17447
Publication Date(Web):August 1, 2012
DOI:10.1021/jp305744c
A paper-like self-standing film electrode composed of hierarchical mesoporous anatase TiO2 was designed and prepared through a facile route of filter paper templating in combination with an additional deep hydrolysis treatment process. The specific surface area of hierarchical mesoporous TiO2 increased to 155.6 m2 g–1 compared to the sample without the additional deep hydrolysis, which is only 16.0 m2 g–1. The results are consistent with a simple model of sphere stacking which suggests that the rich mesopores were from the void space created by the TiO2 stacking. By applying such film as binder-free electrode in lithium-ion batteries (LIBs), good rate performance was demonstrated, and the capacity was still 100 mA h g–1 even at the high rate of 20 C. The contributions of Li+ insertion/extraction reaction and capacitive effect on the capacities were investigated by cyclic voltammetry and calculation. With the sweep rate increased from 0.1 to 10 mV s–1, the contributions of capacitive effects increased from 46% to 88% of the total capacities. The uniquely architectural TiO2 film electrode showed excellent cycling performance at high rate of 10 C through 400 cycles. It highly promises as a new anode for thin-film batteries with versatile application fields.
Co-reporter:Wei Zhou, Zongping Shao, Fengli Liang, Zhi-Gang Chen, Zhonghua Zhu, Wanqin Jin and Nanping Xu
Journal of Materials Chemistry A 2011 vol. 21(Issue 39) pp:15343-15351
Publication Date(Web):30 Aug 2011
DOI:10.1039/C1JM12660A
As highly efficient energy conversion devices with the capability for power/heat co-generation and fuel flexibility, solid-oxide fuel cells (SOFCs) have received considerable attention recently as a keystone of the future energy economy. Nowadays, lack of a proper cathode with high performance at intermediate temperature (IT) has become the main obstacle in realizing this fascinating technology. Here we present (La0.8Sr0.2)0.95Ag0.05MnO3−δ as a novel CO2 tolerant cathode of IT-SOFCs, which shows silver intercalation/de-intercalation capability. Under cathodic polarization, silver can be extracted from perovskite lattice to form a 5–15 nm silver modified A-site cation deficient (La0.8Sr0.2)0.95MnO3−δelectrode with superior electrocatalytic activity and improved stability. Any performance degradation due to silver sintering can be easily in situ restored by re-intercalating silver into the perovskite lattice under anodic polarization. Through electrochemically adjusting the oxidation state and location of silver, we introduce a way for the development of high-performance silver-modified cathode for IT-SOFCs, which may contribute significantly to a sustainable future.
Co-reporter:Wei Wang, Ran Ran, Zongping Shao
Journal of Power Sources 2011 Volume 196(Issue 1) pp:90-97
Publication Date(Web):1 January 2011
DOI:10.1016/j.jpowsour.2010.07.033
Ni-Al2O3 catalyst is modified with Li2O3, La2O3 and CaO promoters to improve its resistance to coking. These catalysts are used as the materials of the anode catalyst layer in solid-oxide fuel cells operating on methane. Their catalytic activity for the partial oxidation, steam reforming and CO2 reforming of methane at 600–850 °C is investigated. Their catalytic stability and carbon deposition properties are also studied. The LiLaNi-Al2O3 catalyst shows a catalytic activity that is comparable to those of LaNi-Al2O3 and LiNi-Al2O3 catalysts for all three reactions. However, it displays a higher catalytic activity than those of CaLaNi-Al2O3 and CaNi-Al2O3 catalysts. Among the various catalysts, the LiLaNi-Al2O3 catalyst presents the highest catalytic stability. O2-TPO profiles indicate that the modification of the Ni-Al2O3 catalyst with Li and La greatly reduces carbon deposition under pure methane atmosphere. The LiLaNi-Al2O3 catalyst is applied as the anode functional layer of a Ni + ScSZ anode-supported fuel cell. The cell is operated on methane-O2, methane-H2O or methane-CO2 gas mixtures and yields peak power densities of 538, 532 and 529 mW cm−2 at 850 °C, respectively, comparable to that of hydrogen fuel. In sum, the LiLaNi-Al2O3 is highly promising as a highly coking resistant catalyst layer for solid-oxide fuel cells.
Co-reporter:Wei Wang, Chao Su, Ran Ran, Zongping Shao
Journal of Power Sources 2011 Volume 196(Issue 8) pp:3855-3862
Publication Date(Web):15 April 2011
DOI:10.1016/j.jpowsour.2010.12.072
The effect of lanthanide promoters on a Ni–Al2O3 catalyst for methane partial oxidation, steam reforming and CO2 reforming at 600–850 °C is systematically investigated. The promoters include La2O3, CeO2, Pr2O3, Sm2O3 and Gd2O3. GdNi–Al2O3 shows comparable catalytic activity to LaNi–Al2O3 and PrNi–Al2O3 but higher activity than CeNi–Al2O3 and SmNi–Al2O3 for all three reactions. The O2-TPO results show that GdNi–Al2O3 possesses the best coke resistance among those tested. It also displays good stability at 850 °C for 300 h. Raman spectroscopy indicates that the addition of lanthanide promoters can reduce the degree of graphitization of the carbon deposited on Ni–Al2O3. The GdNi–Al2O3 is further applied as an anode functional layer in solid-oxide fuel cells operating on methane. The cell yields peak power densities of 1068, 996 and 986 mW cm−2 at 850 °C, respectively, for operating on methane–O2, methane–H2O and methane–CO2 gas mixtures, which is comparable to operating on hydrogen fuel. GdNi–Al2O3 is promising as a highly coking-resistant catalyst layer for solid-oxide fuel cells.Research highlights▶ Gd-promoted Ni–Al2O3 catalyst presents good coking resistance toward methane. ▶ This catalyst also shows good catalytic activity for methane conversion. ▶ The GdNi–Al2O3 catalyst yields high-quality syngas for chemical synthesis. ▶ The fuel cell with the GdNi–Al2O3 catalyst layer delivers high power output.
Co-reporter:Chao Su, Ran Ran, Wei Wang, Zongping Shao
Journal of Power Sources 2011 Volume 196(Issue 4) pp:1967-1974
Publication Date(Web):15 February 2011
DOI:10.1016/j.jpowsour.2010.10.011
Dimethyl ether (DME) as a fuel of SOFCs is investigated with great attention paid to coke formation over the Ni-YSZ anode. DME is easily decomposed to CH4, CO and H2 at temperatures above 700 °C, with total conversion occurring at 850 °C over the Ni-YSZ catalyst. These data suggest that the DME electro-oxidation likely proceeds via an indirect pathway. O2-TPO analysis, laser Raman spectroscopy and SEM–EDX characterizations demonstrate coke formation over Ni-YSZ, which is obvious and become more prevalent at higher temperatures. The introduction of CO2 in the fuel gas decreases the CH4 selectivity and effectively suppresses coke formation above 700 °C. The suppression effect is increasingly apparent at higher temperatures. At 850 °C, the anode still maintains geometric integrity after exposure to DME–CO2 (1:1, volume ratio) under OCV condition. With DME or DME–CO2, the fuel cell power output is comparable to results obtained by operating with 3% water humidified hydrogen. No obvious cell degradation from the anode is observed when operating with DME–CO2, while it is obvious with DME. The introduction of CO2 may be a good choice to suppress the coke formation when operating on DME; however, the proper selection of operation temperature is of significant importance.
Co-reporter:Dongmei Gao, Jing Zhao, Wei Zhou, Ran Ran, Zongping Shao
Journal of Membrane Science 2011 Volume 366(1–2) pp:203-211
Publication Date(Web):1 January 2011
DOI:10.1016/j.memsci.2010.10.001
The effect of high-energy ball milling (HEBM) of the starting material of crystalline Ba0.5Sr0.5Co0.5Fe0.5O3−δ (BSCF) powders on the sintering and oxygen permeability of the corresponding ceramic membrane was systematically investigated. Two different methods of dry milling and wet milling in a liquid alcohol medium were investigated along with three ball milling times (1, 2 and 3 h), two different types of starting powders, and three different sintering temperatures (1000, 1050 and 1100 °C). XRD, SEM and oxygen permeation measurements were performed on as-prepared membranes. The experimental results showed that HEBM is an effective way to improve the sintering, microstructure and oxygen permeability of BSCF membranes. By optimizing the HEBM process, the relative density of BSCF membranes improved significantly; as a result, the oxygen permeation flux of BSCF membranes improved by about 20% in comparison to BSCF membranes whose starting powders were not ball milled. Thus, HEBM is a promising way to increase the performance of BSCF membranes for oxygen separation.Research highlights▶ BSCF powders show smaller particle sizes after the HEBM process. ▶ BSCF powders show a more homogenous particle distribution after the HEBM process. ▶ The oxygen permeation flux improve by about 20% with the optimized HEBM process. ▶ HEBM is a promising method to fabricate oxygen semi-permeable membranes.
Co-reporter:Yu Liu, Youmin Guo, Wei Wang, Chao Su, Ran Ran, Huanting Wang, Zongping Shao
Journal of Power Sources 2011 Volume 196(Issue 22) pp:9246-9253
Publication Date(Web):15 November 2011
DOI:10.1016/j.jpowsour.2011.07.051
This study investigates dimethyl ether (DME) as a potential fuel for proton-conducting SOFCs with a conventional nickel cermet anode and a BaZr0.4Ce0.4Y0.2O3−δ (BZCY4) electrolyte. A catalytic test demonstrates that the sintered Ni + BZCY4 anode has an acceptable catalytic activity for the decomposition and steam reforming of DME with CO, CH4 and CO2 as the only gaseous carbon-containing products. An O2-TPO analysis demonstrates the presence of a large amount of coke formation over the anode catalyst when operating on pure DME, which is effectively suppressed by introducing steam into the fuel gas. The selectivity towards CH4 is also obviously reduced. Peak power densities of 252, 280 and 374 mW cm−2 are achieved for the cells operating on pure DME, a DME + H2O gas mixture (1:3) and hydrogen at 700 °C, respectively. After the test, the cell operating on pure DME is seriously cracked whereas the cell operating on DME + H2O maintains its original integrity. A lower power output is obtained for the cell operating on DME + H2O than on H2 at low temperature, which is mainly due to the increased electrode polarization resistance. The selection of a better proton-conducting phase in the anode is critical to further increase the cell power output.Highlights► The sintered Ni + BZCY4 anode has acceptable activity for the decomposition and steam reforming of DME. ► Introducing steam to the DME fuel can suppress the coke formation over the Ni + BZCY4 anode. ► The DME conversion increased sharply by introducing steam into the DME fuel. ► Selecting of a better proton-conducting phase of anode is critical.
Co-reporter:Chao Su, Wei Wang, Huangang Shi, Ran Ran, Hee Jung Park, Chan Kwak, Zongping Shao
Journal of Power Sources 2011 Volume 196(Issue 18) pp:7601-7608
Publication Date(Web):15 September 2011
DOI:10.1016/j.jpowsour.2011.04.056
Dimethyl ether (DME)-oxygen mixture as the fuel of an anode-supported SOFC with a conventional nickel-cermet anode for operating at reduced temperatures is systematically investigated. The results of the catalytic tests indicate that sintered Ni-YSZ has high activity for DME partial oxidation, and DME conversion exceeds 90% at temperatures higher than 700 °C. Maximum methane selectivity is reached at 700 °C. Cell performance is observed between 600 and 800 °C. Peak power densities of approximately 400 and 1400 mW cm−2 at 600 and 800 °C, respectively, are reached for the cell operating on DME-O2 mixture. These values are comparable to those obtained using hydrogen as a fuel, and cell performance is reasonably stable at 700 °C for a test period of 340 min. SEM results demonstrate that the cell maintains good geometric integrity without any delimitation of respective layer after the stability test, and EDX results show that carbon deposition occurrs only at the outer surface of the anode. O2-TPO analysis shows that carbon deposition over the Ni-YSZ operating on DME is greatly suppressed in the presence of oxygen. Internal partial oxidation may be a practical way to achieve high cell performance at intermediate-temperatures for SOFCs operating on DME fuel.Highlights► The sintered Ni-YSZ anode has high activity for DME partial oxidation. ► The fuel cell operating on DME-O2 delivers high power output. ► Cell performance is reasonably stable at 700 °C for a test period of 340 min. ► Carbon deposition over Ni-YSZ is greatly suppressed by introducing O2 to DME.
Co-reporter:Mingming Liao, Wei Wang, Ran Ran, Zongping Shao
Journal of Power Sources 2011 Volume 196(Issue 15) pp:6177-6185
Publication Date(Web):1 August 2011
DOI:10.1016/j.jpowsour.2011.03.018
Inexpensive 20 wt.% Ni–Ce0.8Zr0.2O2 catalysts are synthesized by a glycine nitrate process (GNP) and an impregnation process (IMP). The catalytic activity for ethanol steam reforming (ESR) at 400–650 °C, catalytic stability and carbon deposition properties are investigated. Ni–Ce0.8Zr0.2O2 (GNP) shows a higher catalytic performance than Ni–Ce0.8Zr0.2O2 (IMP), especially at lower temperatures. It also presents a better coking resistance and a lower graphitization degree of the deposited carbon. The superior catalytic activity and coke resistance of Ni–Ce0.8Zr0.2O2 (GNP) is attributed to the small particle size of the active metallic nickel phase and the strong interaction between the nickel and the Ce0.8Zr0.2O2 support, as evidenced by the XRD and H2-TPR. The Ni–Ce0.8Zr0.2O2 (GNP) is further applied as an anode functional layer in solid oxide fuel cells operating on ethanol steam. The cell yields a peak power density of 536 mW cm−2 at 700 °C when operating on EtOH–H2O gas mixtures, which is only slightly lower than that of hydrogen fuel, whereas the cell without the functional layer failed for short-term operations. Ni–Ce0.8Zr0.2O2 (GNP) is promising as an active and highly coking-resistant catalyst layer for solid-oxide fuel cells operating on ethanol steam fuel.Highlights► Ni–Ce0.8Zr0.2O2 (GNP) shows good catalytic activity for ethanol steam reforming. ► This catalyst also presents good coking resistance towards ethanol. ► The Ni–Ce0.8Zr0.2O2 (GNP) catalyst can yield high-quality hydrogen from ethanol. ► The fuel cell with this Ni–Ce0.8Zr0.2O2 catalyst layer delivers high power output.
Co-reporter:Youmin Guo, Yunbo Zhou, Dengjie Chen, Huangang Shi, Ran Ran, Zongping Shao
Journal of Power Sources 2011 Volume 196(Issue 13) pp:5511-5519
Publication Date(Web):1 July 2011
DOI:10.1016/j.jpowsour.2011.02.056
The effects of the current collection material and method on the performance of SOFCs with Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) cathodes are investigated. Ag paste and LaCoO3 (LC) oxide are studied as current collection materials, and five different current collecting techniques are attempted. Cell performances are evaluated using a current-voltage test and electrochemical impedance spectra (EIS) based on two types of anode-supported fuel cells, i.e., NiO + SDC|SDC|BSCF and NiO + YSZ|YSZ|SDC|BSCF. The cell with diluted Ag paste as the current collector exhibits the highest peak power density, nearly 16 times that of a similar cell without current collector. The electrochemical characteristics of the BSCF cathode with different current collectors are further determined by EIS at 600 °C using symmetrical cells. The cell with diluted Ag paste as the current collector displays the lowest ohmic resistance (1.4 Ω cm2) and polarization resistance (0.1 Ω cm2). Meanwhile, the surface conductivities of various current collectors are measured by a four-probe DC conductivity technique. The surface conductivity of diluted Ag paste is 2–3 orders of magnitude higher than that of LC or BSCF. The outstanding surface conductivity of silver may reduce the contact resistance at the current collector/electrode interface and, thus, contributes to better electrode performance.Highlights▶ Current collection material and method influence cell performance of BSCF cathode. ▶ Cell with diluted silver paste has the lowest ohmic and polarization resistance. ▶ Surface conductivity of silver paste is larger than 2000 times that of LC or BSCF. ▶ High surface conductivity decreases polarization and ohmic resistance of cell.
Co-reporter:Yingjie Niu, Wei Zhou, Jaka Sunarso, Fengli Liang, Zhonghua Zhu, Zongping Shao
Electrochemistry Communications 2011 Volume 13(Issue 12) pp:1340-1343
Publication Date(Web):December 2011
DOI:10.1016/j.elecom.2011.08.007
Cobalt-free perovskite cathode with excellent oxygen reduction reaction (ORR) properties below 800 °C is a key material toward wide implementation of intermediate-temperature solid oxide fuel cells. This work reports the phase structure, microstructure and performance of such cathode based on the composite phases of triclinic Ba0.9Bi0.1FeO3-δ, cubic BaFeO3 and orthorhombic BaFe2O4 prepared by sol–gel route. The resultant barium ferrites composite cathode exhibits uniform particles, pores and elements distribution. In particular, favorable ORR properties of this cathode is demonstrated by very low interfacial resistance of only 0.036 and 0.072 Ω cm2 at 750 and 700 °C and maximum power density of 1295 and 840 mW cm−2 at 750 and 700 °C.Highlights► Cobalt-free barium ferrites composite cathode prepared by sol-gel route in single step. ► The composite cathode shows homogeneous distribution of elements and uniform microstructure. ► The composite cathode demonstrates an interfacial resistance of only 0.036 Ω cm2 at 750°C. ► A single fuel cell with the composite cathode shows a peak power density of 1295 mW cm-2 at 750°C.
Co-reporter:Youmin Guo, Dengjie Chen, Huangang Shi, Ran Ran, Zongping Shao
Electrochimica Acta 2011 Volume 56(Issue 7) pp:2870-2876
Publication Date(Web):28 February 2011
DOI:10.1016/j.electacta.2010.12.075
SmxSr1 − xCoO3 − δ (SSCx) materials are promising cathodes for IT-SOFCs. The influence of Sm content in SSCx (0.2 ≤ x ≤ 0.8) oxides on their oxygen nonstoichiometry, oxygen desorption, thermal expansion behavior, electrical conductivity and electrochemical activity for oxygen reduction is systematically studied by iodometric titration, oxygen-temperature programmed desorption (O2-TPD), dilatometer, four-probe DC conductivity, electrochemical impedance spectroscopy (EIS) and three-electrode polarization test, respectively. Iodometric titration experiments demonstrate that the electrical charge neutrality compensation in SSCx proceeds preferably through the oxidation of cobalt ion for high Sm3+ contents (x ≥ 0.6). However, it proceeds mainly through the creation of oxygen vacancies at x ≤ 0.5. O2-TPD shows SSC5 possesses the highest oxygen desorption ability among the range of SSCx materials tested. The thermal expansion coefficients (TECs) are high between the transition temperature and 900 °C, showing values typically larger than 20 × 10−6 K−1. All dense materials show high electrical conductivity with a maximum value of ∼1885 S cm−1 for SSC6 in air, while SSC5 has the highest electrical conductivity in nitrogen. EIS analysis of porous electrodes demonstrates that SSC5 has the lowest area specific resistance (ASR) value (0.42 Ω cm2) at 600 °C. Cathodic overpotential testing demonstrates that SSC5 also has the largest exchange current density of 60 mA cm−2 at 600 °C in air.
Co-reporter:Dengjie Chen, Cheng Huang, Ran Ran, Hee Jung Park, Chan Kwak, Zongping Shao
Electrochemistry Communications 2011 Volume 13(Issue 2) pp:197-199
Publication Date(Web):February 2011
DOI:10.1016/j.elecom.2010.12.012
Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) + Co3O4 composites with different Co3O4 contents were synthesized, and their properties and performance as cathodes in IT-SOFCs were investigated. The diffraction patterns of the composites were well indexed based on the physical mixture of the BSCF phase and the Co3O4 phase. A surprising increase in the total conductivity of the composites was observed even though Co3O4 is a p-type semiconductor with a low conductivity. Electrochemical impedance spectra of symmetric cells indicated that both the area specific resistance and the activation energy were reduced in samples with Co3O4 contents of 5–20 wt.% with minimum values reaching 10 wt.%. A synergistic effect likely occurred between BSCF and Co3O4 that led to the better performance. An anode-supported single cell with 90 wt.% BSCF + 10 wt.% Co3O4 delivered a promising peak power density of 1150 mW cm− 2 at 600 °C.
Co-reporter:Wei Wang, Chao Su, Ran Ran, Hee Jung Park, Chan Kwak, Zongping Shao
International Journal of Hydrogen Energy 2011 Volume 36(Issue 9) pp:5632-5643
Publication Date(Web):May 2011
DOI:10.1016/j.ijhydene.2011.01.163
Different concentrations of copper are added to LiLaNi–Al2O3 to improve the electronic conductivity property for application as the materials of the anode catalyst layer for solid oxide fuel cells operating on methane. Their catalytic activity for the methane partial oxidation, steam and CO2 reforming reactions at 600–850 °C is systematically investigated. Among the three catalysts, the LiLaNi–Al2O3/Cu (50:50, by weight) catalyst presents the best catalytic activity. Thus, the catalytic stability, carbon deposition and surface conductivity of the LiLaNi–Al2O3/Cu catalyst are further studied in detail. O2-TPO results indicate that the coking resistance of LiLaNi–Al2O3/Cu is satisfactory and comparable to that of LiLaNi–Al2O3. The surface conductivity tests demonstrate it is extremely improved for LiLaNi–Al2O3 catalyst due to the addition of 50 wt.% copper. A cell with LiLaNi–Al2O3/Cu (50:50) catalyst layer is operated on mixtures of methane–O2, methane–H2O and methane–CO2, and peak power densities of 1081, 1036 and 988 mW cm−2 are obtained at 850 °C, respectively, comparable to the cell with LiLaNi–Al2O3 catalyst layer. In summary, the results of the present study indicate that LiLaNi–Al2O3/Cu (50:50) catalysts are highly coking resistant and conductive catalyst layers for solid oxide fuel cells.Highlights► LiLaNi–Al2O3/Cu (50:50) catalyst presents good coking resistance towards methane. ► This catalyst also shows good catalytic activity for methane conversion. ► The addition of copper extremely improves the conductivity of LiLaNi–Al2O3. ► The fuel cell with the LiLaNi–Al2O3/Cu catalyst layer delivers high power output.
Co-reporter:Dengjie Chen, Zongping Shao
International Journal of Hydrogen Energy 2011 Volume 36(Issue 11) pp:6948-6956
Publication Date(Web):June 2011
DOI:10.1016/j.ijhydene.2011.02.087
Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) is a mixed conducting oxide that shows high oxygen permeability to perform as a ceramic membrane and high electrochemical activity for oxygen reduction to perform as a cathode of solid oxide fuel cells. Both performances are closely related to the bulk and surface properties of the BSCF oxide. In this study, the chemical bulk diffusion coefficient (Dchem) and chemical surface exchange coefficient (kchem) of BSCF at various temperatures and oxygen partial pressures are determined by an electrical conductivity relaxation (ECR) method. Both Dchem and kchem are found to be dependent on pO2pO2 with positive effect. Ea of Dchem and kchem are respectively 111 ± 5 and 110 ± 6 kJ mol−1 between 600 and 800 °C. Oxygen-ion diffusion and tracer diffusion coefficients are estimated from Dchem and compared with the literature results. Ionic conductivities are further derived according to the Nernst–Einstein relation. The poisoning effect of CO2 on the performances of BSCF is further investigated by the ECR method in combination with oxygen temperature-programmed desorption technique. The presence of CO2 causes a substantial decrease in kchem, however, the surface kinetics can be recovered by performing re-calcination in an oxidative atmosphere at 900 °C, agreeing well with literature reports.
Co-reporter:Yingjie Niu, Jaka Sunarso, Wei Zhou, Fengli Liang, Lei Ge, Zhonghua Zhu, Zongping Shao
International Journal of Hydrogen Energy 2011 Volume 36(Issue 4) pp:3179-3186
Publication Date(Web):February 2011
DOI:10.1016/j.ijhydene.2010.11.109
Co-reporter:Wei Wang, Ran Ran, Zongping Shao
International Journal of Hydrogen Energy 2011 Volume 36(Issue 1) pp:755-764
Publication Date(Web):January 2011
DOI:10.1016/j.ijhydene.2010.09.048
Ru–Al2O3 composites with varied Ru contents were synthesized by a glycine–nitrate combustion technique. Their potential application as anode catalyst functional layer of a solid–oxide fuel cell operating on methane fuel was investigated. Catalytic tests demonstrated the 3–7 wt.% Ru–Al2O3 composites had high catalytic activity for methane partial oxidation and CO2/H2O reforming reactions, while 1 wt.% Ru–Al2O3 had insufficient activity. The 3 wt.% Ru–Al2O3 catalyst also showed excellent operation stability and good thermal–mechanical compatibility with Ni–YSZ anode. H2-TPR and TEM results indicated there was strong interaction between RuOx and Al2O3 in the as-synthesized catalysts, which may account for the good catalytic stability of 3 wt.% Ru–Al2O3 catalyst. O2-TPO results demonstrated Ru–Al2O3 also had excellent coking resistance. Furthermore, the carbon deposited over Ru–Al2O3 had lower graphitization degree than that deposited over Ni–Al2O3, suggesting the easier elimination of potential carbon deposited over the Ru–Al2O3 catalysts. A cell with 3 wt.% Ru–Al2O3 catalyst functional layer was prepared, wh-ich delivered peak power densities of 1006, 952 and 929 mW cm−2 at 850 °C, operating on methane–O2, methane–H2O and methane–CO2 gas mixtures, respectively, comparable to that operating on hydrogen fuel. It highly promised 3 wt.% Ru–Al2O3 as a coking resistant catalyst layer for solid–oxide fuel cells.
Co-reporter:Youmin Guo, Ran Ran, Zongping Shao, Shaomin Liu
International Journal of Hydrogen Energy 2011 Volume 36(Issue 14) pp:8450-8460
Publication Date(Web):July 2011
DOI:10.1016/j.ijhydene.2011.04.037
The influence of Ba nonstoichiometry on the phase structure, sintering, electrical conductivity and chemical stability under CO2 atmosphere of proton conductors with a nominal composition of Ba1±xCe0.4Zr0.4Y0.2O3−δ (B1±xZCY4, 0 ≤ x ≤ 0.20) was systematically investigated. A complexing sol-gel process was applied to synthesize the B1±xZCY4 powders. The X-ray diffraction patterns of the well-calcined powders indicate that the specimens with 0 ≤ x ≤ 0.10 possessed a single-phase of orthorhombic perovskite-type oxides. Additionally, impurity phases of (Y,Ce)O2−δ existed in B1−xZCY4, and BaCO3 was found in B1+xZCY4 with x = 0.15 and 0.20. After sintering at 1500 °C for 5 h, all B1+xZCY4 samples became pure phased, whereas impurities still existed in samples with large Ba deficiencies. A study of the sintering behavior showed that the proper amount of Ba excess or deficiency facilitated electrolyte densification and that a large Ba nonstoichiometry hindered sintering. The electrical conductivities of B1±xZCY4 specimens with 0 ≤ x ≤ 0.05 were studied in the temperature range of 100–700 °C, and the results showed that the Ba nonstoichiometry influenced the electrical conductivity, especially with respect to grain boundary resistance. The chemical stability was also studied using temperature-programmed CO2 desorption, and it was determined that the chemical stability was affected by the Ba content.Highlights► Ba nonstoichiometry influenced the properties of BaZr0.4Ce0.4Y0.2O3−δ oxide. ► Ba-deficient specimens exhibited improved chemical stability and sinterability. ► Ba0.95Zr0.4Ce0.4Y0.2O3−δ might be a good candidate as the electrolyte of H+-SOFC’s.
Co-reporter:Yuan Zou, Wei Zhou, Jaka Sunarso, Fengli Liang, Zongping Shao
International Journal of Hydrogen Energy 2011 Volume 36(Issue 15) pp:9195-9204
Publication Date(Web):July 2011
DOI:10.1016/j.ijhydene.2011.04.187
This manuscript describes a facile alternative route to make thin-film yttria-stabilized zirconia (YSZ) electrolyte by liquid-phase assisted electrophoretic deposition utilizing electrostatic-steric stabilized YSZ suspension followed by sintering. Very fine YSZ particles in ball-milled suspension facilitate their sustained dispersion through electrostatic mechanism as evidenced by their higher zeta potentials. Binder addition into the ball-milled suspension is also demonstrated to contribute complementary steric hindrance effects on suspension stability. As the consequence, the film quality and sinterability improve in the sequence of film made from non ball-milled suspension, film made from ball-milled suspension and film made from ball-milled suspension with binder addition. The specific deposition mechanisms pertaining to each suspension are also postulated and discussed below. A very thin dense electrolyte layer of ∼10 μm can be achieved via electrophoretic deposition route utilizing ball-milled suspension and binder addition. This in turn, makes the electrolyte resistance a more negligible part of the overall cell resistance. Further on, we also tested the performance of SOFC utilizing as-formed 10 μm YSZ electrolyte i.e. YSZ-NiO|YSZ|LSM (La0.8Sr0.2MnO3-δ), whereby a maximum power density of ∼850 mW cm−2 at 850 °C was demonstrated.Highlights► Thin YSZ film is deposited utilizing electrostatic-steric stabilized suspension. ► Ball-milling facilitates suspension stability via electrostatic mechanism. ► Binder contributes complementary steric hindrance effects on suspension stability. ► A dense YSZ electrolyte with optimized internal ohmic resistance wasdemonstrated.
Co-reporter:Youmin Guo, Ran Ran, Zongping Shao
International Journal of Hydrogen Energy 2011 Volume 36(Issue 2) pp:1683-1691
Publication Date(Web):January 2011
DOI:10.1016/j.ijhydene.2010.10.081
We proposed a novel way to improve the cell performance of proton-conducting solid-oxide fuel cells by increasing the chemical interaction between the anode components using BaZr0.4Ce0.4Y0.2O3−δ (BZCY4) as the ionic conducting phase of anode for a fuel cell with a BaCe0.8Y0.2O3−δ (BCY) electrolyte. The strength of the chemical interaction between NiO and the ionic conducting phase (BZCY4 or BCY) was analyzed by the hydrogen temperature-programmed reduction (H2-TPR) technique. The effect of chemical interaction between NiO and the ionic conducting phase on the NiO diffusivity was investigated by SEM-EDX. The results demonstrated NiO had a much stronger interaction with BZCY4 than with BCY, thereby resulting in suppressed diffusivity of NiO into the BCY electrolyte. Using BZCY4 as the ionic conducting phase of the anode, a cell with an ohmic resistance of 0.65 Ω cm2 at 700 °C was obtained. In contrast, a cell with BCY as the ionic conducting phase of the anode had an ohmic resistance of 0.82 Ω cm2 at 700 °C. Therefore, the single cell with NiO + BZCY4 anode showed a peak power density higher than that of the cell with the NiO + BCY anode.
Co-reporter:Wei Wang, Ran Ran, Chao Su, Zongping Shao, Doh Won Jung, Sooyeon Seo, Sang Mock Lee
International Journal of Hydrogen Energy 2011 Volume 36(Issue 17) pp:10958-10967
Publication Date(Web):August 2011
DOI:10.1016/j.ijhydene.2011.05.109
Ni-Al2O3 composites with varying contents of nickel are synthesized via a glycine nitrate process (GNP) and an impregnation process (IMP). Their potential application as an anode functional layer for internal methane CO2 reforming in a solid oxide fuel cell is investigated. H2-TPR results show that the chemical interaction between NiO and Al2O3 decreases as the nickel content increases. Catalytic tests demonstrate that 15 wt.% Ni-Al2O3 catalysts exhibit the best catalytic activity for methane CO2 reforming. However, the carbon formation rates over Ni-Al2O3 prepared via GNP are lower than those over Ni-Al2O3 prepared via IMP using the same amounts of nickel, with the exception of the 1 wt.% Ni-Al2O3 catalyst. Raman spectroscopy and O2-TPO results indicate that the degree of graphitization and the amount of carbon deposited on the 15 wt.% Ni-Al2O3 catalyst synthesized via GNP are lower than those of the catalyst prepared via IMP following a 60 h stability test. A cell with a 15 wt.% Ni-Al2O3 catalyst layer prepared via GNP is fabricated that delivers a peak power density of 1006 mW cm−2 at 850 °C when operating on methane-CO2 gas mixtures, which is comparable to that observed when operating on hydrogen fuel.Highlights► Ni-Al2O3 prepared by GNP showed better catalytic activity and stability than IMP. ► Ni-Al2O3 prepared by GNP also presented better coking resistance than IMP. ► The 15 wt.% Ni-Al2O3 showed best catalytic activity for both GNP and IMP methods. ► The cell with this catalyst layer delivers high power output operating on CH4–CO2.
Co-reporter:Ran Ran, Youmin Guo, Dongmei Gao, Shaomin Liu, Zongping Shao
Separation and Purification Technology 2011 Volume 81(Issue 3) pp:384-391
Publication Date(Web):10 October 2011
DOI:10.1016/j.seppur.2011.08.005
A series of foreign oxides including CuO, ZnO, NiO, Co2O3 and Al2O3 were investigated as sintering aids to facilitate the densification of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) membranes for oxygen separation. The effects of these oxides on the phase structure, sintering behavior, electrical conductivity and oxygen permeability of BSCF oxide were systematically studied by X-ray diffraction (XRD), oxygen temperature-programmed desorption (O2-TPD), environmental scanning electron microscopy (ESEM), four-probe direct current (DC) conductivity and gas permeation measurements. The results showed that reactions between the membrane material and the foreign oxides took place at elevated temperatures. These oxides displayed different sintering behaviors during the sintering process of BSCF perovskite, with obvious improvement demonstrated in the case of CuO, minimal effects observed from ZnO, Co2O3 and NiO samples, and suppressing effects from Al2O3. The electrical conductivity was clearly increased by introducing Co2O3 as a sintering aid, yielding a maximum value of 70 S cm−1 at 900 °C. The oxygen permeation fluxes of the membrane samples from BSCF + NiO (5 wt.%) and BSCF + ZnO (5 wt.%) are comparable to those of pristine BSCF membranes, whereas the fluxes decreased noticeably when the other foreign oxides were introduced.Highlights► Foreign oxides have different effects on the properties of BSCF perovskite. ► Foreign oxides influence oxygen vacancy concentration and oxygen mobility in BSCF. ► Adding ZnO does not affect oxygen permeability and oxygen ionic conductivity of BSCF. ► BSCF + 5 wt.% ZnO might be good candidate as a cathode material for SOFC.
Co-reporter:Yuan Zou, Wei Zhou, Shaomin Liu, Zongping Shao
Journal of the European Ceramic Society 2011 Volume 31(Issue 15) pp:2931-2938
Publication Date(Web):December 2011
DOI:10.1016/j.jeurceramsoc.2011.07.028
High purity raw materials are used for synthesizing La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF6428) powders to reduce the effect of impurity phases on oxygen permeability of the corresponding membranes. The as-synthesized LSCF6428 powders require a sintering temperature above 1180 °C to achieve membrane density over 90%. Ball milling of the powders increases the membrane sintering. It also increases oxygen permeation flux from 0.37 to 0.43 ml cm−2 min−1 at 950 °C for the membranes sintered at 1100 °C. A decrease in oxygen permeation fluxes with the further increase in sintering temperature is observed for the membranes with ball-milled starting powders, accompanied by an obvious increase in grain size. It suggests, at low level of impurity phases, the grain boundaries facilitate the oxygen diffusion. The combination of ball milling of the starting powders and a sintering temperature of 1100 °C is optimal to achieve high oxygen permeability of LSCF6428 membranes with improved purity.
Co-reporter:Yuanyuan Hu, Yingke Zhou, Jie Wang, Zongping Shao
Materials Chemistry and Physics 2011 Volume 129(1–2) pp:296-300
Publication Date(Web):15 September 2011
DOI:10.1016/j.matchemphys.2011.04.007
Macroporous LiNi1/3Co1/3Mn1/3O2 cathode materials were synthesized by sol–gel method with carbon spheres as the pore tuning template. The phase structure, morphology and pore nature were analyzed by X-ray diffraction, field-emission scanning electron microscopy and BET measurements. The electrochemical properties were investigated by employing cyclic voltammetry, constant current charge–discharge test, and electrochemical impedance techniques. Well developed layered structures were obtained, and removal of the carbon sphere during the calcination process led to plenty of macropores in the product, compared to the pristine dense sample without using any template. The XRD pattern showed that the structure of porous LiNi1/3Co1/3Mn1/3O2 was not affected by using the template, as which could be fully indexed to the layered structure of the a-NaFeO2 phase with crystalline size smaller than that of the pristine one. In contrast to the pristine dense sample, the templated macroporous LiNi1/3Co1/3Mn1/3O2 showed improved discharge capacity and rate capability. The specific discharge capacity of the macroporous and pristine LiNi1/3Co1/3Mn1/3O2 materials are around 189 and 155 mAh g−1 respectively at 20 mA g−1, and better cycling capacity retention was observed for the porous sample. The electrochemical impedance studies indicated the possible underlying mechanisms of the performance differences between the porous and pristine dense materials. These investigations indicate that the templated macroporous LiNi1/3Co1/3Mn1/3O2 might be a promising cathode material for lithium-ion battery applications.Highlights► Macroporous LiNi1/3Co1/3Mn1/3O2 as cathode material for lithium-ion batteries. ► Carbon spheres as the pore tuning templates. ► Well-developed layered structure macroporous materials were obtained. ► The macroporous materials presented improved electrochemical performances than the pristine dense materials.
Co-reporter: Zongping Shao;Chunming Zhang;Wei Wang;Chao Su;Dr. Wei Zhou; Zhonghua Zhu;Dr. Hee Jung Park;Dr. Chan Kwak
Angewandte Chemie International Edition 2011 Volume 50( Issue 8) pp:1792-1797
Publication Date(Web):
DOI:10.1002/anie.201006855
Co-reporter: Zongping Shao;Chunming Zhang;Wei Wang;Chao Su;Dr. Wei Zhou; Zhonghua Zhu;Dr. Hee Jung Park;Dr. Chan Kwak
Angewandte Chemie 2011 Volume 123( Issue 8) pp:1832-1837
Publication Date(Web):
DOI:10.1002/ange.201006855
Co-reporter:Jie Wang ; Yingke Zhou ; Yuanyuan Hu ; Ryan O’Hayre
The Journal of Physical Chemistry C 2011 Volume 115(Issue 5) pp:2529-2536
Publication Date(Web):January 5, 2011
DOI:10.1021/jp1087509
TiO2 mesoporous nanocrystalline microspheres assembled from uniform nanoparticles were synthesized by a facile and template-free hydrolytic precipitation route in normal solvent media. The phase structure, morphology, and pore nature were analyzed by X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy, and BET measurements. The electrochemical properties were investigated by cyclic voltammetry, constant current discharge−charge tests, and electrochemical impedance techniques. Microspheres with diameters ranging from 0.2 to 1.0 μm were assembled by aggregation of nanosized TiO2 crystallites (∼8−15 nm) and yielded a typical type-IV BET isotherm curve with a surface area of ∼116.9 m2 g−1 and a pore size of ∼5.4 nm. A simplified model was proposed to demonstrate the nanoparticle packing modes to form the mesoporous structure. The initial discharge capacity reached 265 mAh g−1 at a rate of 0.06 C and 234 mAh g−1 at a rate of 0.12 C. The samples demonstrated high rate capacity of 175 mAh g−1 at 0.6 C and 151 mAh g−1 at 1.2 C even after 50 cycles, and the Coulombic efficiency was approximately 99%, indicating excellent cycling stability and reversibility. Details of the kinetic process of the nanocrystalline mesoporous microspheres electrode reaction from electrochemical impedance spectra provided further insights into the possible mechanisms responsible for the good reversibility and stability. These investigations indicate that TiO2 nanocrystalline mesoporous microspheres might be a promising anode material for high-energy density lithium-ion batteries.
Co-reporter:Tao Yuan ; Rui Cai
The Journal of Physical Chemistry C 2011 Volume 115(Issue 11) pp:4943-4952
Publication Date(Web):March 2, 2011
DOI:10.1021/jp111353e
Pristine Li4Ti5O12 and Li4Ti5O12/C composite are prepared by high-energy ball-milling (HEBM)-assisted solid-state reaction with TiO2 anatase and Li2CO3 or carbon-precoated TiO2 anatase and Li2CO3 as reactants. The influence of calcination atmosphere on the phase formation and particulate morphology of those two products are systematically investigated by XRD, SEM, TEM, O2-TPO, and TPR techniques. The optimal calcination atmospheres for the synthesis of Li4Ti5O12 and Li4Ti5O12/C are diluted hydrogen and nitrogen atmospheres, respectively. TPR in various atmospheres demonstrates the difference in optimal atmospheres is due to the suppressing effect of hydrogen for Li2CO3 decomposition, the reducing properties of carbon and hydrogen, and the blocking effect of carbon for the reaction between TiO2 and Li2O. Both the pristine and carbon-coated Li4Ti5O12 show good rate and cycling performance. A near theoretical capacity of 175 mA h g−1 is achieved for both samples at 0.5 C rate. After a total cycling number of 40 at various rates between 0.5 and 40 C, the capacity retention for Li4Ti5O12 and Li4Ti5O12/C is 97.8 and 98.5%, respectively. The HEBM-assisted solid-state reaction in controlled atmosphere may be a practical way for the economic synthesis of both pristine and carbon-coated Li4Ti5O12 as high-performance electrodes of lithium-ion batteries.
Co-reporter:Yingjie Niu;Dr. Fengli Liang;Dr. Wei Zhou;Dr. Jaka Sunarso; Zhonghua Zhu; Zongping Shao
ChemSusChem 2011 Volume 4( Issue 11) pp:1582-1586
Publication Date(Web):
DOI:10.1002/cssc.201100254
Co-reporter:Yingjie Niu, Wei Zhou, Jaka Sunarso, Lei Ge, Zhonghua Zhu and Zongping Shao
Journal of Materials Chemistry A 2010 vol. 20(Issue 43) pp:9619-9622
Publication Date(Web):27 Sep 2010
DOI:10.1039/C0JM02816A
Bi doping of SrFeO3−δ results in the formation of a structure with high symmetry and extraordinary electrochemical performance for Bi0.5Sr0.5FeO3-δ, which is capable of competing effectively with the current Co-based cathode benchmark with additional advantages of lower thermal expansion and cost.
Co-reporter:Yingke Zhou, Jie Wang, Yuanyuan Hu, Ryan O’Hayre and Zongping Shao
Chemical Communications 2010 vol. 46(Issue 38) pp:7151-7153
Publication Date(Web):02 Aug 2010
DOI:10.1039/C0CC01721C
A novel composite electrode structure with highly-conductive 3D nanotube networks superimposed into interlaced porous LiFePO4 media was designed and realized via an in situ sol–gel process, yielding a high-performance multidimensional composite cathode for high-energy and high-power lithium-ion batteries.
Co-reporter:Tao Yuan, Xing Yu, Rui Cai, Yingke Zhou, Zongping Shao
Journal of Power Sources 2010 Volume 195(Issue 15) pp:4997-5004
Publication Date(Web):1 August 2010
DOI:10.1016/j.jpowsour.2010.02.020
Pristine and carbon-coated Li4Ti5O12 oxide electrodes are synthesized by a cellulose-assisted combustion technique with sucrose as organic carbon source and their low-temperature electrochemical performance as anodes for lithium-ion batteries are investigated. X-ray diffraction (XRD), infrared spectroscopy (IR), Raman spectroscopy, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) are applied to characterize the phase structure, composition, and morphology of the composites. It is found that the sequence of sucrose addition has significant effect on the phase formation of Li4Ti5O12. Carbon-coated Li4Ti5O12 is successfully prepared by coating the pre-crystallized Li4Ti5O12 phase with sucrose followed by thermal treatment. Electrochemical lithium insertion/extraction performance is evaluated by the galvanostatic charge/discharge tests, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), from room temperature (25 °C) to −20 °C. The carbon-coated composite anode materials show improved lithium insertion/extraction capacity and electrode kinetics, especially at high rates and low temperature. Both of the two samples show fairly stable cycling performance at various temperatures, which is highly promising for practical applications in power sources of electric or electric-hybrid vehicles.
Co-reporter:Tao Yuan, Rui Cai, Peng Gu, Zongping Shao
Journal of Power Sources 2010 Volume 195(Issue 9) pp:2883-2887
Publication Date(Web):1 May 2010
DOI:10.1016/j.jpowsour.2009.11.073
The synthesis of spinel-type lithium titanate, Li4Ti5O12, a promising anode material of secondary lithium-ion battery, from “inert” rutile TiO2, is investigated. On the purpose of increasing the reactivity of rutile TiO2, it is treated by concentrated HNO3. By applying such activated rutile TiO2 as the titanium source in combination with the cellulose-assisted combustion synthesis, phase-pure Li4Ti5O12 is successfully synthesized at 800 °C, at least 150 °C lower than that based on solid-state reaction. The resulted oxide shows a reversible discharge capacity of ∼175 mAh g−1 at 1 C rate, near the theoretical value. The resulted oxide also shows promising high rate performance with a discharge capacity of ∼100 mAh g−1 at 10 C rate and high cycling stability.
Co-reporter:Huangang Shi, Wei Zhou, Ran Ran, Zongping Shao
Journal of Power Sources 2010 Volume 195(Issue 2) pp:393-401
Publication Date(Web):15 January 2010
DOI:10.1016/j.jpowsour.2009.07.056
Fabrication of dense Sm0.2Ce0.8O1.9 (SDC) thin-film electrolytes by wet powder spraying in combination with high-temperature sintering is investigated. Two powder synthesis techniques, i.e., a hydrothermal synthesis and an EDTA–citrate complexing sol–gel process, were investigated. X-ray diffraction, BET surface area and laser particle size analysis demonstrate there is certain level of aggregation in both powders. However, it is more pronounced in powders obtained by the complexing process, and only the colloidal suspensions of powders prepared by hydrothermal synthesis are stable. SEM analysis of the green and sintered thin-film electrolytes demonstrate that the SDC electrolyte with powders prepared via the hydrothermal synthesis is denser. By optimizing the fabrication conditions, dense SDC electrolytes with a thickness of ∼12 μm are successfully fabricated. The cells with SDC prepared from hydrothermal synthesis demonstrate open circuit voltages and power outputs similar to those of similar cells fabricated from other advanced techniques. Because of its simplicity and flexibility for anode substrate geometric shape, it turns out to be a promising technology to fabricate thin-film SDC electrolyte for solid-oxide fuel cell application.
Co-reporter:Wei Wang, Chao Su, Yuzhou Wu, Ran Ran, Zongping Shao
Journal of Power Sources 2010 Volume 195(Issue 2) pp:402-411
Publication Date(Web):15 January 2010
DOI:10.1016/j.jpowsour.2009.07.053
An inexpensive 7 wt.% Ni–Al2O3 composite is synthesized by a glycine–nitrate process and systematically investigated as anode catalyst layer of solid-oxide fuel cells operating on methane fuel by examining its catalytic activity towards methane partial oxidation, steam and CO2 reforming at 600–850 °C, cell performance, mechanical performance, and carbon deposition properties. Ni–Al2O3 shows comparable catalytic activities to Ru–CeO2 for the above three reactions. The cell with a Ni–Al2O3 catalyst layer delivers maximum peak power densities of 494 and 532 mW cm−2 at 850 °C, operating on methane–H2O and methane–CO2 mixture gases, respectively, which are comparable to those operating on hydrogen. Ni–Al2O3 is found to have better mechanical performance than Ru–CeO2. O2-TPO demonstrates that Ni–Al2O3 does not inhibit the carbon formation under pure methane atmosphere, while the introduction of steam or CO2 can effectively suppress coke formation. However, due to the low nickel content in the catalyst layer, the coke formation over the catalyst layer is actually not serious under real cell operation conditions. More importantly, Ni–Al2O3 effectively protects the anode layer by greatly suppressing carbon formation over the anode layer, especially near the anode–electrolyte interface. Ni–Al2O3 is highly promising as an anode functional layer for solid-oxide fuel cells.
Co-reporter:Cheng Huang, Dengjie Chen, Ye Lin, Ran Ran, Zongping Shao
Journal of Power Sources 2010 Volume 195(Issue 16) pp:5176-5184
Publication Date(Web):15 August 2010
DOI:10.1016/j.jpowsour.2010.02.080
A perovskite-type Ba0.6Sr0.4Co0.9Nb0.1O3−δ (BSCN) oxide is investigated as the cathode material of oxygen-ionic solid-oxide fuel cells (SOFCs) with Sm0.2Ce0.8O3−δ (SDC) electrolyte. Powder X-ray diffraction and SEM characterization demonstrate that solid phase reactions between BSCN and SDC are negligible at temperatures up to 1100 °C. The results of thermal-expansion and electrical conductivity measurements indicate the introduction of Ba2+ into the A-site of SrCo0.9N0.1O3−δ (SCN) led to a decrease in the thermal-expansion coefficient (TEC) and electrical conductivity of the compound. A TEC of 14.4 × 10−6 K−1 is observed for BSCN within a temperature range of 200–500 °C. The chemical diffusion coefficient (Dchem) and surface exchange constant (kex) of BSCN and SCN are obtained using an electrical conductivity relaxation technique and BSCN prove to have higher Dchem and kex than SCN. An area-specific resistance of 0.1 Ω cm−2 is achieved for BSCN cathodes at 600 °C based on symmetric cells test. Peak power density of ∼1150 mW cm−2 is reached for a thin-film electrolyte cell with BSCN cathode at 600 °C, which is higher than a similar cell with SCN cathode (∼1008 mW cm−2). BSCN is a promising cathode material for oxygen-ionic IT-SOFCs.
Co-reporter:Rui Cai, Xing Yu, Xiaoqin Liu, Zongping Shao
Journal of Power Sources 2010 Volume 195(Issue 24) pp:8244-8250
Publication Date(Web):15 December 2010
DOI:10.1016/j.jpowsour.2010.07.059
Li4Ti5O12/tin phase composites are successfully prepared by cellulose-assisted combustion synthesis of Li4Ti5O12 matrix and precipitation of the tin phase. The effect of firing temperature on the particulate morphologies, particle size, specific surface area and electrochemical performance of Li4Ti5O12/tin oxide composites is systematically investigated by SEM, XRD, TG, BET and charge–discharge characterizations. The grain growth of tin phase is suppressed by forming composite with Li4Ti5O12 at a calcination of 500 °C, due to the steric effect of Li4Ti5O12 and chemical interaction between Li4Ti5O12 and tin oxide. The experimental results indicate that Li4Ti5O12/tin phase composite fired at 500 °C has the best electrochemical performance. A capacity of 224 mAh g−1 is maintained after 50 cycles at 100 mA g−1 current density, which is still higher than 195 mAh g−1 for the pure Li4Ti5O12 after the same charge/discharge cycles. It suggests Li4Ti5O12/tin phase composite may be a potential anode of lithium-ion batteries through optimizing the synthesis process.
Co-reporter:Ye Lin, Ran Ran, Dengjie Chen, Zongping Shao
Journal of Power Sources 2010 Volume 195(Issue 15) pp:4700-4703
Publication Date(Web):1 August 2010
DOI:10.1016/j.jpowsour.2010.02.062
Ba0.6Sr0.4Co0.9Nb0.1O3−δ (BSCN), originated from SrCo0.9Nb0.1O3−δ (SCN), is investigated as a cathode material in a protonic solid-oxide fuel cell (SOFC-H+) with a BaZr0.1Ce0.7Y0.2O3 (BZCY) electrolyte. The surface-exchange and bulk-diffusion properties, phase reaction with the electrolyte, electrochemical activity for oxygen reduction, and performance in the real fuel cell condition of SCN and BSCN electrodes are comparatively studied by conductivity relaxation, XRD, EIS and I–V polarization characterizations. Much better performance is found for BSCN than SCN. Furthermore, water has a positive effect on oxygen reduction over BSCN while it has the opposite effect with SCN. A peak power density of 630 mW cm−2 at 700 °C is achieved for a thin-film BZCY electrolyte cell with a BSCN cathode compared to only 287 mW cm−2 for a similar cell with an SCN cathode. The results highly recommend BSCN as a potential cathode material for protonic SOFCs.
Co-reporter:Dengjie Chen, Ran Ran, Zongping Shao
Journal of Power Sources 2010 Volume 195(Issue 15) pp:4667-4675
Publication Date(Web):1 August 2010
DOI:10.1016/j.jpowsour.2010.01.082
The effect of firing temperature on the microstructure and performance of PrBaCo2O5+δ cathodes on Sm0.2Ce0.8O1.9 electrolytes fabricated by spray deposition-firing processes is systematically studied by various characterization techniques. The grain size, porosity and particle connection of the electrode as well as the physical contact between the PrBaCo2O5+δ and Sm0.2Ce0.8O1.9 layers are influenced differently by the firing temperature. The area specific resistances (ASRs) of the various PrBaCo2O5+δ cathodes are measured by electrochemical impedance spectroscopy in both symmetrical two-electrode and three-electrode configurations. The lowest ASR and cathode overpotential are achieved at a firing temperature of 1000 °C. Two main oxygen reduction reaction processes are proposed according to the oxygen partial pressure dependence of the electrode ASR. The rate-determining step is transmitted from a charge-transfer process at low firing temperatures to a non-charge-transfer process at high firing temperatures. A fuel cell with the PrBaCo2O5+δ cathode fired at an optimal temperature of 1000 °C delivers the attractive peak power density of 835 mW cm−2 at 650 °C, while this density is much lower for other firing temperatures. This result suggests the firing temperature of PrBaCo2O5+δ electrodes should be carefully optimized for practical applications.
Co-reporter:Chao Su, Yuzhou Wu, Wei Wang, Yao Zheng, Ran Ran, Zongping Shao
Journal of Power Sources 2010 Volume 195(Issue 5) pp:1333-1343
Publication Date(Web):1 March 2010
DOI:10.1016/j.jpowsour.2009.09.015
Ni-SDC, Ni-ScSZ, and La0.8Sr0.2Sc0.2Mn0.8O3 (LSSM) anodes are investigated for SOFCs operating on CO. O2-TPO and SEM results demonstrate LSSM is greatly superior to nickel cermet anodes in suppressing carbon deposition. H2-TPR suggests there is strong chemical interaction between NiO and ScSZ, which helps to suppress the carbon deposition. Raman spectroscopy of the carbon-deposited nickel cermet anodes demonstrates the graphitization degree of carbon is enhanced with increasing temperature. The cell performance is much lower operating on CO as compared to H2, and the reduction is the largest for the cell with Ni-SDC anode. Furthermore, steady performance degradation is observed for all three cells operating on pure CO which is irreversible for the cell with Ni-SDC anode while largely reversible for the cell with Ni-ScSZ anode. The degradation for the cell with an LSSM anode is found to be due to the phase instability of LSSM in pure CO atmosphere. By applying a mixture of CO and CO2 as the fuel or under polarization, the phase of LSSM is stabilized; as a result, the cell is stably operated on CO under current polarization. This suggests that LSSM and Ni-ScSZ anodes are greatly superior to the Ni-SDC anode for operation on CO.
Co-reporter:Peng Gu, Rui Cai, Yingke Zhou, Zongping Shao
Electrochimica Acta 2010 Volume 55(Issue 12) pp:3876-3883
Publication Date(Web):30 April 2010
DOI:10.1016/j.electacta.2010.02.006
Silicon and related materials have recently received considerable attention as potential anodes in Li-ion batteries for their high theoretical specific capacities. To overcome the problem of volume variations during the Li insertion/extraction process, in this work, Si/C composites with low carbon content were synthesized from cheap coarse silicon and citric acid by simple ball milling and subsequent thermal treatment. The effects of ball milling time and calcination temperature on the structure, composition and morphology of the composites were systematically investigated by the determination of specific surface area (BET) and particle-size distribution, X-ray diffraction (XRD), O2-TPO, and scanning electron microscopy (SEM). The capacity and cycling stability of the composites were systematically evaluated by electrochemical charge/discharge tests. It was found that both the initial capacity and the cycling stability of the composites were dependent on the milling and calcination conditions, and attractive overall electrochemical performance could be obtained by optimizing the synthesis process.
Co-reporter:Di Zhang, Rui Cai, Yinke Zhou, Zongping Shao, Xiao-Zhen Liao, Zi-Feng Ma
Electrochimica Acta 2010 Volume 55(Issue 8) pp:2653-2661
Publication Date(Web):1 March 2010
DOI:10.1016/j.electacta.2009.12.023
Effects of ball milling way and time on the phase formation, particulate morphology, carbon content, and consequent electrode performance of LiFePO4/C composite, prepared by high-energy ball milling of Li2CO3, NH4H2PO4, FeC2O4 raw materials with citric acid as organic carbon source followed by thermal treatment, were investigated. Three ball milling ways and five different milling durations varied from 0 to 8 h were compared. LiFePO4/C composites could be obtained from all synthesis processes. TEM examinations demonstrated LiFePO4/C from ball milling in acetone resulted in sphere shape grains with a size of ∼60 nm, similar size was observed for LiFePO4/C from dry ball milling but in a more irregular shape. The ball milling in benzene resulted in a much larger size of ∼250 nm. The LiFePO4/C composites prepared from dry ball milling and ball milling in acetone showed much better electrochemical performance than that from ball milling in benzene. SEM examinations and BET measurements demonstrated that the high-energy ball milling effectively reduced the grain size. A ball milling for 4 h resulted in the best electrochemical performance, likely due to the proper amount of carbon and proper carbon structure were created.
Co-reporter:Youmin Guo, Ran Ran, Zongping Shao
International Journal of Hydrogen Energy 2010 Volume 35(Issue 19) pp:10513-10521
Publication Date(Web):October 2010
DOI:10.1016/j.ijhydene.2010.07.179
A proton-conducting solid oxide fuel cells with a dual-layer electrolyte, constructed of a highly protonic conductive BaCe0.8Y0.2O3−δ (BCY) electrolyte and chemically stable BaZr0.4Ce0.4Y0.2O3−δ (BZCY4) electrolyte, was easily fabricated by dry pressing the electrolyte powders onto an NiO + BZCY4 anode substrate, followed by co-sintering at a high temperature. The performance of the as-fabricated cell with the BCY and BZCY4 dual-layer electrolyte was studied. Peak power densities of 249 and 101 mW cm−2 were achieved at 700 and 500 °C, respectively. Zinc was applied as a sintering promoter to increase the relative density of the BZCY4 electrolyte. Cross-sectional micrographs of the as-fabricated, dual-layer electrolyte cells were obtained by scanning electron microscopy. The results showed that the sintering ability of BZCY4 was improved by using zinc as sintering aid. A cell with BCY and zinc-modified BZCY4 dual-layer electrolyte delivered peak power densities of 276 and 247 mW cm−2 and OCVs of 1.03 and 1.02 V at 700 °C under humidified hydrogen and 15% CO2-containing hydrogen atmospheres, respectively. The operation stability of the dual-layer electrolyte cell under a 15% CO2-containing hydrogen atmosphere was also investigated.
Co-reporter:Chunming Zhang, Ye Lin, Ran Ran, Zongping Shao
International Journal of Hydrogen Energy 2010 Volume 35(Issue 15) pp:8171-8176
Publication Date(Web):August 2010
DOI:10.1016/j.ijhydene.2009.12.164
In order to improve the single-chamber performance of a traditional anode-supported single-chamber solid-oxide fuel cell with NiO–ScSZ anode and ScSZ electrolyte, the modification of the anode with a fine nickel catalyst by impregnation method was exploited. Catalytic test demonstrated the nickel catalyst had higher catalytic activity than the severe sintered nickel–cermet anode between 700 and 900 °C, especially at the lower temperature range. SEM examination demonstrated the nickel catalyst impregnation increased the roughness of the nickel grains within the anode. Furthermore, some surfaces of the ScSZ grains are also covered with very fine nickel catalyst. By operating on a methane-air mixture gas with methane to oxygen ratio of 1.3:1, the cell with its anode impregnated with the nickel catalyst showed an open circuit voltage and peak power density of 0.954 V and 119 mW cm−2 at a furnace temperature of 750 °C, respectively, as a comparison of 0.893 V and 79 mW cm−2 for the cell without the nickel catalyst. The improved cell performance was attributed to the higher cell temperature and increased anode catalytic activity for methane partial oxidation.
Co-reporter:Baoming An, Youmin Guo, Ran Ran, Zongping Shao
International Journal of Hydrogen Energy 2010 Volume 35(Issue 14) pp:7608-7617
Publication Date(Web):July 2010
DOI:10.1016/j.ijhydene.2010.04.112
Dual-layer composite electrodes consisting of a layer adjoining to an Sm0.2Ce0.8O1.9 (SDC) electrolyte composed of 70 wt.% SrSc0.2Co0.8O3−δ + 30 wt.% Sm0.2Ce0.8O1.9 (SScC + SDC composite) and a second layer composed of 70 wt.% SrSc0.2Co0.8O3−δ + 30 wt.% Sm0.5Sr0.5CoO3−δ (SScC + SmSC composite) were fabricated and investigated as potential cathodes in intermediate temperature solid-oxide fuel cells. Thermo-mechanical compatibility between the two electrode layers and between the electrode and the electrolyte were examined by SEM, XRD and EIS. After sintering, no clear boundary between SScC + SDC and SScC + SmSC layers was observable by SEM. The repeated thermal cycling didn’t induce the delamination of the electrode from the electrolyte nor the formation of cracks within the electrode. As a result, stable electrode performance was achieved during thermal cycling and long-term operation. Symmetric cell tests demonstrated that the dual-layer electrode with a ∼10-μm SScC + SDC layer and a ∼50-μm SScC + SmSC layer (SScC + SDC/SScC + SmSC (1:5)) had the lowest electrode-polarization resistance among those tested. Anode-supported fuel cells with an SDC electrolyte and SScC + SDC/SScC + SmSC (1:5) cathode were fabricated. Peak power density as high as 1326 mW cm−2 was achieved at 650 °C, which was higher than for similar fuel cells with a single-layer SScC + SDC or an SScC + SmSC composite electrode.
Co-reporter:Baoming An, Wei Zhou, Youmin Guo, Ran Ran, Zongping Shao
International Journal of Hydrogen Energy 2010 Volume 35(Issue 11) pp:5601-5610
Publication Date(Web):June 2010
DOI:10.1016/j.ijhydene.2010.03.044
SSC (70 wt.% SrSc0.2Co0.8O3−δ)–SDC (30 wt.% Sm0.2Ce0.8O1.9) composite was evaluated as cathode for intermediate-temperature solid-oxide fuel cells. The effect of firing temperature on the chemical interaction between SSC and SDC was characterized by oxygen-temperature programmed desorption (O2-TPD) techniques. Certain type of phase reactions occurred between SSC and SDC at calcination temperatures higher than 950 °C. The conductivity of the composite was measured by a four-prober direct current technique. The electro-catalytic activity of the composite electrode for oxygen reduction was measured by electrochemical impedance spectroscopy (EIS) in a symmetric cell configuration. The electrode fired at 950 °C showed the best performance. By applying the SSC + SDC-composite electrode, a cell with a ∼20-μm thick SDC electrolyte delivered a peak power density of 760 mW cm−2 at 600 °C. This suggested that an SSC + SDC-composite electrode may be a promising cathode for intermediate-temperature solid-oxide fuel cells.
Co-reporter:Youmin Guo, Ran Ran, Zongping Shao
International Journal of Hydrogen Energy 2010 Volume 35(Issue 11) pp:5611-5620
Publication Date(Web):June 2010
DOI:10.1016/j.ijhydene.2010.03.039
The effects of zinc modification methods on membrane sintering, electrical conductivity of BaZr0.4Ce0.4Y0.2O3−δ (BZCY4) and the thermo-mechanical match of the BZCY4 electrolyte with anode were systematically investigated. Three modification methods are pursued, including the physical mixing of BZCY4 with a ZnO solid (method 1), introducing zinc during the solution stage of the sol–gel synthesis (method 2) and doping zinc into a perovskite lattice by synthesis of a new compound with a nominal composition of BaZr0.4Ce0.4Y0.16Zn0.04O3−δ (method 3). Method 1 turned out to be the most effective at reducing the sintering temperature, which can mainly be attributed to a reactive sintering although ZnO doping into the BZCY4 lattice also facilitates the sintering. While all three modification methods facilitated the membrane sintering, only the electrolyte from method 3 had similar shrinkage behavior to the anode. An anode-supported thin-film BZCY4-3 electrolyte solid oxide fuel cell (SOFC) was successfully fabricated, and the fuel cell delivered an attractive performance with a peak power density of ∼307 mW cm−2 at 700 °C.
Co-reporter:Ye Lin, Ran Ran, Youmin Guo, Wei Zhou, Rui Cai, Jun Wang, Zongping Shao
International Journal of Hydrogen Energy 2010 Volume 35(Issue 7) pp:2637-2642
Publication Date(Web):April 2010
DOI:10.1016/j.ijhydene.2009.04.019
Anode-supported proton-conducting fuel cell with BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte and Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) cathode was fabricated. Peak power densities of ∼420 and 135 mW/cm2 were achieved, respectively, at 700 and 450 °C for a cell with 35 μm thick electrolyte operating on hydrogen fuel. The endothermic nature of the ammonia decomposition reaction, however, resulted in cell temperature 30–65 °C lower than the furnace when operating on ammonia. Accounting the cooling effect, comparable power density was achieved for the cell operating on ammonia and hydrogen at high temperature. At reduced temperature, the cell demonstrated worse performance when operating on ammonia than on hydrogen due to the poor activity of the anode towards NH3 catalytic decomposition. By applying on-line catalytic decomposition products of N2H4 as the fuel, similar cell performance to that with NH3 fuel was also observed.
Co-reporter:Liangliang Sun, Ran Ran, Zongping Shao
International Journal of Hydrogen Energy 2010 Volume 35(Issue 7) pp:2921-2925
Publication Date(Web):April 2010
DOI:10.1016/j.ijhydene.2009.05.049
An improved fabrication technique for catalyst-coated membrane (CCM), characterized by high-temperature spray deposition and immobilization of the membrane with a pyrex glass via Van der Walt force, was developed. The high heating temperature minimized the adsorption of liquid ethanol by the Nafion membrane and also resulted in the firm adhesion of the membrane to the pyrex glass, both processes suppressed the dimensional change of the membrane during the fabrication. The as-fabricated CCMs were analyzed by I–V polarization, cyclic voltammetry and electrochemical impedance spectroscopy. A comparative study was also made with the conventional hot-pressed membrane-electrode assembly with identical Pt catalyst loading of 0.4 mg cm−2. Higher catalyst utilization and better cell performance were observed for the cell based on the CCM configuration. A peak power density of ∼715 mW cm−2 was achieved when oxygen was the cathode atmosphere and hydrogen was the fuel at ambient pressure.
Co-reporter:Liangliang Sun, Yuqiang Liu, Wei Wang, Ran Ran, Yan Huang, Zongping Shao
International Journal of Hydrogen Energy 2010 Volume 35(Issue 7) pp:2958-2963
Publication Date(Web):April 2010
DOI:10.1016/j.ijhydene.2009.05.069
In this study, 70 wt.% Ni/Al2O3 was prepared via a glycine–nitrate combustion method and applied as the catalyst for decomposing methane into hydrogen and carbon nanotubes that can be applied in polymer-electrolyte-membrane fuel cell (PEMFC). The methane conversion and the hydrogen content in the effluent gas reached 71 and 83%, respectively, at an operating temperature of 700 °C under ambient pressure. I–V tests demonstrated that the methane is inert to the electro-catalyst and acts mainly as a diluting gas. A porous Al2O3-supported thin-film Pd membrane was integrated with the catalytic methane decomposition process. Due to the high initial hydrogen content, even an imperfect Pd membrane, effectively increased the hydrogen content to >98%, which resulted in only a slight performance loss of ∼10% compared to the application of pure hydrogen as the fuel. The advantages, such as continuous hydrogen separation, simple process, high reliability and value-added by-product, all make this process highly attractive for future PEMFC application.
Co-reporter:Ye Lin, Ran Ran, Zongping Shao
International Journal of Hydrogen Energy 2010 Volume 35(Issue 15) pp:8281-8288
Publication Date(Web):August 2010
DOI:10.1016/j.ijhydene.2009.12.017
Electrochemical performance of silver-modified Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF-Ag) as oxygen reduction electrodes for a protonic intermediate-temperature solid-oxide fuel cell (SOFC-H+) with BaZr0.1Ce0.8Y0.1O3 (BZCY) electrolyte was investigated. The BSCF-Ag electrodes were prepared by impregnating the porous BSCF electrode with AgNO3 solution followed by reducing with hydrazine and then firing at 850 °C for 1 h. The 3 wt.% silver-modified BSCF (BSCF-3Ag) electrode showed an area specific resistance of 0.25 Ω cm2 at 650 °C in dry air, compared to around 0.55 Ω cm2 for a pure BSCF electrode. The activation energy was also reduced from 119 kJ mol−1 for BSCF to only 84 kJ mol−1 for BSCF-3Ag. Anode-supported SOFC-H+ with a BZCY electrolyte and a BSCF-3Ag cathode was fabricated. Peak power density up to 595 mW cm−2 was achieved at 750 °C for a cell with 35 μm thick electrolyte operating on hydrogen fuel, higher than around 485 mW cm−2 for a similar cell with BSCF cathode. However, at reduced temperatures, water had a negative effect on the oxygen reduction over BSCF-Ag electrode, as a result, a worse cell performance was observed for the cell with BSCF-3Ag electrode than that with pure BSCF electrode at 600 °C.
Co-reporter:Jia Song, Ran Ran, Zongping Shao
International Journal of Hydrogen Energy 2010 Volume 35(Issue 15) pp:7919-7924
Publication Date(Web):August 2010
DOI:10.1016/j.ijhydene.2010.05.094
Co-reporter:Liangliang Sun, Yong Hao, Chunming Zhang, Ran Ran, Zongping Shao
International Journal of Hydrogen Energy 2010 Volume 35(Issue 15) pp:7971-7981
Publication Date(Web):August 2010
DOI:10.1016/j.ijhydene.2010.05.048
This paper presents a systematic study of a direct-flame solid oxide fuel cell (DF-SOFC) operating on methanol and ethanol flames by SEM, EIS, I-V polarization and mass spectrometer (MS) characterizations and numerical simulation. The experimental study demonstrated that, by adopting a conventional Ni + Sm0.2Ce0.8O1.9 (SDC) anode, irreversible carbon deposition and a drop of cell performance was observed when running the cell on an ethanol flame, while no carbon was deposited by operating on a methanol flame. Fuel cell stability tests indicated significant degradation in performance after 3 h of operation on an ethanol flame, while no degradation was observed after 30 h of operation on a methanol flame. A simple qualitative explanation of the difference observed in the electrochemical performance for the fuel cell operating on a methanol flame and an ethanol flame is presented based on numerical simulation.
Co-reporter:Jing Zhao, Dengjie Chen, Zongping Shao, Shaomin Liu
Separation and Purification Technology 2010 Volume 74(Issue 1) pp:28-37
Publication Date(Web):30 July 2010
DOI:10.1016/j.seppur.2010.05.004
In this work, the effects of CuO addition on sintering behavior, crystal structure and the oxygen permeation of SrCo0.9Nb0.1O3−δ (SCN) membranes have been investigated. XRD characterization demonstrated that copper could incorporate into the perovskite lattices with certain solubility dependent on temperature. Small amount of CuO (5 wt.%) successfully reduced the sintering temperature of the SCN membrane by 180 °C. A relative density of 95.4% was reached for the membrane with 5 wt.% CuO additive after sintering at 1000 °C. The promoting effect on sintering is likely associated with liquid assisted sintering. The incorporation of copper into the SCN lattice has minimal effect on the membrane sintering but a significant effect on the membrane integrity. As compared to the single-phase SCN membranes, the introduction of CuO as a sintering aid does not affect the electronic conductivity of the membrane between 700 and 900 °C, but the oxygen permeability is slightly reduced. Permeation study of the membranes of 0.9 mm thickness demonstrated oxygen fluxes of 1.5, 1.4, 1.3 and 1.2 ml cm−2 min−1 [STP] at 800 °C for the membranes containing 0 (pure SCN), 1, 3 and 5 wt.% CuO, respectively. The results suggest that the introduction of CuO as a sintering aid had a more significant effect on the oxygen surface exchange kinetics than on the oxygen bulk diffusion rate.
Co-reporter:Kun Zhang, Ran Ran, Zongping Shao, Zhonghua Zhu, Yonggang Jin, Shaomin Liu
Ceramics International 2010 Volume 36(Issue 2) pp:635-641
Publication Date(Web):March 2010
DOI:10.1016/j.ceramint.2009.09.040
Abstract
Niobium doping effect on phase structure, phase stability and electrical conductivity of SrCoOx oxides and oxygen permeability of the corresponding membranes were systematically investigated. Niobium was successfully incorporated into A-site, B-site or simultaneously A and B double sites of SrCoOx oxide and stabilized the perovskite structure with a cubic symmetry in air down to room temperature at a proper doping amount. However, the A-site doping could not stabilize the cubic structure under a more reducing atmosphere of nitrogen, as to SrCo1−yNbyO3−δ, y ≥ 0.1 is necessary to sustain the cubic perovskite structure. Simultaneous doping of Nb at A and B sites is the most effective way to stabilize the perovskite structure under nitrogen atmosphere. Irrespective of doping site, the electrical conductivity decreased monotonously with Nb-doping amount. Both NbxSr1−xCoO3−δ and NbzSr1−zCo1−zNbzO3−δ envisaged a decrease in oxygen permeation flux with Nb-doping amount while SrCo1−yNbyO3−δ reached the maximum flux at y = 0.1. Among all the membranes, SrCo0.9Nb0.1O3−δ and Nb0.05Sr0.95Co0.95Nb0.05O3−δ show the highest oxygen fluxes of 3.5 and 2.7 ml cm−2 min−1 at 900 °C under an air/helium gradient, respectively.
Co-reporter:Wei Zhou, Wanqin Jin, Zhonghua Zhu, Zongping Shao
International Journal of Hydrogen Energy 2010 Volume 35(Issue 3) pp:1356-1366
Publication Date(Web):February 2010
DOI:10.1016/j.ijhydene.2009.11.092
SrNb0.1Co0.9O3−δ (SNC) perovskite oxide has been prepared by high-energy ball milling followed by calcination at 1100 °C. According to oxygen temperature-programmed desorption and thermogravimetry analysis results, highly charged Nb5+ successfully stabilizes the perovskite structure to avoid order-disorder phase transition. The electrical conductivity reaches 550 S cm−1 at 300 °C in air and as high as 106 S cm−1 under P(O2) = 1 × 10−5 atm at 900 °C. The high electrical conductivity is beneficial in improving the charge-transfer process for the oxygen reduction reaction on the cathode. Based on the defect chemical analysis, the Nb-doping in SrCoO3−δ perovskite facilitates the formation of Co2+, which increases oxygen nonstoichiometry and, subsequently, the mixed valence of [Co2+]/[Co3+] under lower oxygen partial pressure. A relatively low thermal expansion coefficient of 19.1 × 10−6 K−1 in air was achieved. All above properties show SNC to be a promising cathode material in the practical application of low-temperature solid oxide fuel cells.
Co-reporter:Jing Zhao, Kun Zhang, Dongmei Gao, Zongping Shao, Shaomin Liu
Separation and Purification Technology 2010 Volume 71(Issue 2) pp:152-159
Publication Date(Web):18 February 2010
DOI:10.1016/j.seppur.2009.11.014
Mixed conducting SrCo0.9Nb0.1O3−δ perovskite is a newly developed promising ceramic membrane material for air separation. In this work, SrCo0.9Nb0.1O3−δ was further optimized by the introduction of Ba to partially replace Sr in the A-site of the perovskite structure. The phase structure, phase stability, carbonate formation rate under carbon dioxide atmosphere, electrical conductivity, oxygen desorption properties, and oxygen permeation properties of BaxSr1−xCo0.9Nb0.1O3−δ (BSCNx) with varying Ba2+ doping level were systematically investigated. Pure phase cubic perovskite was formed at x = 0.0–0.8. BSCNx (x = 0.0–0.8) can be stably operated in atmospheres with oxygen partial pressure varying from at least 1 atm to as low as 10−5 atm (Ar atmosphere). The barium doping concentration had a significant effect on electrical conductivity and oxygen permeability of the membranes. BSCN0.6 had the highest oxygen permeation flux of 2.67 × 10−6 mol cm−2 s−1 for 0.87 mm thickness at 900 °C and the highest oxygen ionic conductivity of 1.38 S cm−1 at 900 °C.
Co-reporter:Wei Zhou;Ran Ran;Wanqin Jin;Nanping Xu
Bulletin of Materials Science 2010 Volume 33( Issue 4) pp:371-376
Publication Date(Web):2010 August
DOI:10.1007/s12034-010-0056-2
Nano-sized La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) and La0.8Sr0.2MnO3−δ (LSM) oxides were synthesized by a simple in situ sol-gel derived carbon templating process. Nano-sized LSCF-carbon and LSM-carbon composites were first obtained with a grain size of 20–30 nm. Further calcination of the obtained composites under air resulted in the nano-sized pure-phase perovskites with crystalline size of as small as 14 nm. Such a decrease in crystalline size of perovskite via the indirect calcination process was ascribed to the suppressing effect of carbon in the grain growth of perovskite. Furthermore, when the in situ created carbon was applied as a template for pore forming, a highly porous perovskite sintering body packing from the nano-sized perovskite oxide was obtained.
Co-reporter:Ye Lin, Ran Ran, Chunming Zhang, Rui Cai and Zongping Shao
The Journal of Physical Chemistry A 2010 Volume 114(Issue 11) pp:3764-3772
Publication Date(Web):July 13, 2009
DOI:10.1021/jp9042599
The potential application of PrBaCo2O5+δ (PBC) double perovskite oxide as a cathode for a proton-conducting solid-oxide fuel cell based on a BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte was systematically investigated. XRD and O2-TPD results demonstrated that cation exchange between BZCY and PBC perovskites simultaneously occurs from the formation of Co3+-doped BZCY and Y3+-doped PBC. This event does not significantly change the cathodic polarization resistance. Under real fuel cell conditions, neither the electrolyte nor electrode resistances were significantly affected by the phase reaction and morphologic change of PBC. Anode-supported cells with an electrolyte thickness of ∼30 μm were successfully fabricated via a dual dry pressing process. Relatively high performance of 520 and 407 mW cm−2 at 700 °C was achieved for the cell with a PBC cathode fired at 950 and 1100 °C, respectively. A low electrode polarization resistance of 0.06 Ω cm2 was achieved at 700 °C for the PBC cathode calcined at 950 °C.
Co-reporter:Dengjie Chen, Ran Ran, Kun Zhang, Jun Wang, Zongping Shao
Journal of Power Sources 2009 Volume 188(Issue 1) pp:96-105
Publication Date(Web):1 March 2009
DOI:10.1016/j.jpowsour.2008.11.045
A-site cation-ordered PrBaCo2O5+δ (PrBC) double perovskite oxide was synthesized and evaluated as the cathode of an intermediate-temperature solid-oxide fuel cell (IT-SOFC) on a samarium-doped ceria (SDC) electrolyte. The phase reaction between PrBC and SDC was weak even at 1100 °C. The oxygen reduction mechanism was investigated by electrochemical impedance spectroscopy characterization. Over the intermediate-temperature range of 450–700 °C, the electrode polarization resistance was mainly contributed from oxygen-ion transfer through the electrode–electrolyte interface and electron charge transfer over the electrode surface. An area-specific resistance as low as ∼0.4 Ω cm2 was measured at 600 °C in air, based on symmetric cell test. A thin-film SDC electrolyte fuel cell with PrBC cathode was fabricated which delivered attractive peak power densities of 620 and 165 mW cm−2 at 600 and 450 °C, respectively.
Co-reporter:Lei Ge, Ran Ran, Wei Zhou, Zongping Shao, Shaomin Liu, Wanqin Jin, Nanping Xu
Journal of Membrane Science 2009 Volume 329(1–2) pp:219-227
Publication Date(Web):5 March 2009
DOI:10.1016/j.memsci.2008.12.040
The potential application of combustion synthesis of La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) based on a modified ethylenediaminetetraacetic acid (EDTA)–citrate complexing method with NH4NO3 as combustion aid for ceramic oxygen separation membrane was systematically investigated. Depending on the relative amount of NH4NO3 applied during the synthesis, the combustion can proceed in three different modes: self-propagating combustion, volumetric combustion and smothering combustion. As a whole, electrical conductivity and oxygen permeation fluxes of derived LSCF membrane increased with sintering temperature (1000–1300 °C). Among three different combustion modes, LSCF from self-propagating combustion showed the highest sintering ability, electrical conductivity and oxygen permeability. Under optimized conditions, the derived membrane exhibited the permeation fluxes comparable to that of LSCF membrane prepared from the normal EDTA–citrate complexing method.
Co-reporter:Wei Zhou, Ran Ran, Zongping Shao
Journal of Power Sources 2009 Volume 192(Issue 2) pp:231-246
Publication Date(Web):15 July 2009
DOI:10.1016/j.jpowsour.2009.02.069
Solid-oxide fuel cells (SOFCs) convert chemical energy directly into electric power in a highly efficient way. Lowering the operating temperature of SOFCs to around 500–800 °C is one of the main goals in current SOFC research. The associated benefits include reducing the difficulties associated with sealing and thermal degradation, allowing the use of low-cost metallic interconnectors and suppressing reactions between the cell components. However, the electrochemical activity of the cathode deteriorates dramatically with decreasing temperature for the typical La0.8Sr0.2MnO3-based electrodes. The cathode becomes the limiting factor in determining the overall cell performance. Therefore, the development of new electrodes with high electrocatalytic activity for oxygen reduction becomes a critical issue for intermediate-temperature (IT)-SOFCs. Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) perovskite oxide was first reported as a potential IT-SOFC cathode material in 2004 by Shao and Haile. After that, the BSCF cathode has attracted considerable attention. This paper reviews the current research activities on BSCF-based cathodes for IT-SOFCs. Emphasis will be placed on the understanding and optimization of BSCF-based materials. The issues raised by the BSCF cathode are also presented and analyzed to provide some guidelines in the search for the new generation of cathode materials for IT-SOFCs.
Co-reporter:Wei Zhou, Ran Ran, Rui Cai, Zongping Shao, Wanqin Jin, Nanping Xu
Journal of Power Sources 2009 Volume 186(Issue 2) pp:244-251
Publication Date(Web):15 January 2009
DOI:10.1016/j.jpowsour.2008.10.055
Silver-modified Ba0.5Sr0.5Co0.8Fe0.2O3−δ (Ag/BSCF) electrodes were prepared using an electroless deposition technique. The morphology, microstructure and oxygen reduction reaction activity of the resulted Ag/BSCF electrodes were comparatively studied using Fourier transform infrared spectra, environmental scanning electron microscopy, temperature-programmed oxygen desorption, X-ray diffraction, and electrochemical impedance spectroscopy. An area-specific resistance as low as 0.038 Ω cm2 was achieved for N2H4-reduced Ag/BSCF cathode at 600 °C. Carbonates were detected over the BSCF surface during the reduction of silver, which deteriorated both the charge-transfer process and diffusion process of HCHO-reduced Ag/BSCF cathode for the oxygen electrochemical reduction reaction. An anode-supported single cell with an N2H4-reduced Ag/BSCF cathode showed a peak power of 826 mW cm−2 at 600 °C. In comparison, only 672 mW cm−2 was observed with the HCHO-reduced Ag/BSCF cathode.
Co-reporter:Youmin Guo, Ye Lin, Ran Ran, Zongping Shao
Journal of Power Sources 2009 Volume 193(Issue 2) pp:400-407
Publication Date(Web):5 September 2009
DOI:10.1016/j.jpowsour.2009.03.044
High-temperature proton conductors are promising electrolytes for protonic solid oxide fuel cells (H+-SOFCs). In this study, the relationship between the Zr doping content and structure, chemical stability, carbon dioxide resistivity, sinterability and electrochemical properties of BaZryCe0.8−yY0.2O3−δ (BZCYy), 0.0 ≤ y ≤ 0.8, are studied systemically using XRD, CO2-TPD, SEM, EIS and I–V polarization characterizations. Zr doping suppresses carbonate formation, CO2-TPD demonstrates that the formative rate of carbonate over BZCYy are 7.50 × 10−6 and 8.70 × 10−7 mol m−2 min−1 at y = 0.0 and 0.4, respectively. Investigation of sinterability shows that the anode-supported configuration helps the sintering of the thin-film electrolyte. Peak power densities of 220 and 84 mW cm−2 are obtained at 750 and 450 °C, respectively, with BZCY0.4 electrolyte. Due to the favorable chemical stability against CO2 and good sintering in the thin-film configuration, BZCY0.4 is a potential electrolyte material for H+-SOFCs.
Co-reporter:Chunming Zhang, Yao Zheng, Ye Lin, Ran Ran, Zongping Shao, David Farrusseng
Journal of Power Sources 2009 Volume 191(Issue 2) pp:225-232
Publication Date(Web):15 June 2009
DOI:10.1016/j.jpowsour.2009.02.043
As candidates of cathode materials for single-chamber solid oxide fuel cells, La0.8Sr0.2MnO3 (LSM) and La0.8Sr0.2Sc0.1Mn0.9O3 (LSSM) were synthesized by a combined EDTA-citrate complexing sol–gel process. The solid precursors of LSM and LSSM were calcined at 1000 and 1150 °C, respectively, to obtain products with similar specific surface area. LSSM was found to have higher activity for methane oxidization than LSM due to LSSM's higher catalytic activity for oxygen reduction. Single cells with these two cathodes initialized by ex situ reduction had similar peak power densities of around 220 mW cm−2 at 825 °C. The cell using the LSM cathode showed higher open-circuit-voltage (OCV) at corresponding temperatures due to its reduced activity for methane oxidation relative to LSSM. A negligible effect of methane and CO2 on the cathode performance was observed for both LSM and LSSM via electrochemical impedance spectroscopy analysis. The high phase stability of LSSM under reducing atmosphere allows a more convenient in situ reduction for fuel cell initiation. The resultant cell with LSSM cathode delivered a peak power density of ∼200 mW cm−2 at 825 °C, comparable to that from ex situ reduction.
Co-reporter:Yunbo Zhou, Baoming An, Youmin Guo, Ran Ran, Zongping Shao
Electrochemistry Communications 2009 Volume 11(Issue 11) pp:2216-2219
Publication Date(Web):November 2009
DOI:10.1016/j.elecom.2009.09.034
We propose a new way to develop high-performance cathodes for IT-SOFCs by utilizing the interfacial reactions. SrCoOx was selected as the starting electrode material, which took a vacancy-ordered 2H BaNiO3-type structure and showed negligible ionic conductivity and low electrical conductivity. Phase reactions between SrCoOx and Sm0.2Ce0.8O1.9 happened at 900 °C or higher, resulting in the incorporation of Sm and Ce into its lattice structure. This promoted the phase transition to a cubic perovskite and led to substantial increase in the electrical conductivity and oxygen mobility of the electrode. By utilizing such phase reactions, the SrCoOx + Sm0.2Ce0.8O1.9 composite was developed into a high performance electrode with a low area specific resistance of 0.08 Ω cm−2 at 650 °C. An anode-supported cell with such electrode delivered a peak power density of 795 mW cm−2 at 600 °C.
Co-reporter:Chunming Zhang, Liangliang Sun, Ran Ran, Zongping Shao
Electrochemistry Communications 2009 Volume 11(Issue 8) pp:1563-1566
Publication Date(Web):August 2009
DOI:10.1016/j.elecom.2009.05.048
Initialization is a critical processing step that has thus far limited the application of the single-chamber solid oxide fuel cell (SC-SOFC). In-situ initialization of a SC-SOFC with a nickel-based anode by methane–air mixtures was investigated. Porous Ru–CeO2 was used as a catalyst layer over a Ni-ScSZ cermet anode. Catalytic testing demonstrated Ru–CeO2 had high activity for methane oxidation. The Ru in the catalyst layer catalyzed the formation of syngas, which successfully reduced the nickel oxide to metallic nickel in the anode. Single cells with a La0.8Sr0.2MnO3 (LSM) cathode, initialized by this in-situ reduction method, delivered peak power densities of 205 and 327 mW cm−2 at 800 °C and 850 °C, respectively. Such performances were better than those of the cell without the Ru–CeO2 catalyst layer that was initialized by an ex-situ reduction method were.
Co-reporter:Yuzhou Wu, Chao Su, Chunming Zhang, Ran Ran, Zongping Shao
Electrochemistry Communications 2009 Volume 11(Issue 6) pp:1265-1268
Publication Date(Web):June 2009
DOI:10.1016/j.elecom.2009.04.016
Solid carbon was investigated as the fuel for an intermediate-temperature solid oxide fuel cell (IT-SOFC). An innovative, indirect operating method involving internal catalytic gasification of carbon to gaseous carbon monoxide via the reverse Boudouard reaction (C(s) + CO2(g) → 2CO(g)) was proposed. The carbon gasification reaction rate was greatly enhanced by adopting FemOn–MxO (M = Li, K, Ca) as a catalyst. A peak power density of ∼297 mW cm−2 was achieved at 850 °C for an anode-supported SOFC with scandium-stabilized zirconia electrolyte and a La0.8Sr0.2MnO3 cathode by applying a catalyst-loaded, activated carbon as fuel. This peak power density was only modestly lower than that obtained using gaseous hydrogen as the fuel.
Co-reporter:Wei Wang, Wei Zhou, Ran Ran, Rui Cai, Zongping Shao
Electrochemistry Communications 2009 Volume 11(Issue 1) pp:194-197
Publication Date(Web):January 2009
DOI:10.1016/j.elecom.2008.11.014
Novel γ-Al2O3 supported nickel (Ni/Al2O3) catalyst was developed as a functional layer for Ni–ScSZ cermet anode operating on methane fuel. Catalytic tests demonstrated Ni/Al2O3 had high and comparable activity to Ru–CeO2 and much higher activity than the Ni–ScSZ cermet anode for partial oxidation, steam and CO2 reforming of methane to syngas between 750 and 850 °C. By adopting Ni/Al2O3 as a catalyst layer, the fuel cell demonstrated a peak power density of 382 mW cm−2 at 850 °C, more than two times that without the catalyst layer. The Ni/Al2O3 also functioned as a diffusion barrier layer to reduce the methane concentration within the anode; consequently, the operation stability was also greatly improved without coke deposition.
Co-reporter:Yao Zheng, Chunming Zhang, Ran Ran, Rui Cai, Zongping Shao, D. Farrusseng
Acta Materialia 2009 Volume 57(Issue 4) pp:1165-1175
Publication Date(Web):February 2009
DOI:10.1016/j.actamat.2008.10.047
Abstract
A novel perovskite-type La0.8Sr0.2Sc0.2Mn0.8O3 (LSSM) oxide was synthesized and evaluated as the electrode material of a symmetric solid-oxide fuel cell. Characterization was done by electrical conductivity, crystal structure stability, redox stability, catalytic activity for methane oxidation and oxygen electro-reduction. LSSM shows greater electrical conductivity than the typical La0.8Sr0.2Cr0.5Mn0.5O3 (LSCM) perovskite oxide under both anode and cathode operating conditions. It also shows excellent chemical and structural stability due to the backbone effect of Sc3+ for the perovskite lattice structure. A symmetric electrolyte-supported cell with 0.3 mm thick scandium-stabilized zirconia electrolyte and LSSM as cathode and anode shows peak power densities of 310 and 130 mW cm2 at 900 °C, respectively, when operating on wet H2 and wet CH4. Stable performance is demonstrated.
Co-reporter:Ke Wang, Rui Cai, Tao Yuan, Xing Yu, Ran Ran, Zongping Shao
Electrochimica Acta 2009 Volume 54(Issue 10) pp:2861-2868
Publication Date(Web):1 April 2009
DOI:10.1016/j.electacta.2008.11.012
Co-reporter:Pingying Zeng, Zongping Shao, Shaomin Liu, Zhi Ping Xu
Separation and Purification Technology 2009 Volume 67(Issue 3) pp:304-311
Publication Date(Web):15 June 2009
DOI:10.1016/j.seppur.2009.03.047
In this work, various M cations like Bi5+, Zr4+, Ce4+, Sc3+, La3+, Y3+, Al3+ and Zn2+ were incorporated into SrCoO3−δ (SC) lattices one by one via doping strategy to form a series of new SrCo0.95M0.05O3−δ (SCM) mixed oxides for membrane separation. In general, the M cations have significant effects on the crystal structure, electrical conductivity, sintering behavior and the oxygen permeability of the SCM membranes even though only 5% of Co ions are exchanged. The phase structure of SCMs in the air atmosphere is seemingly determined by the electron configuration in the outer orbits of M cation. In the current cases, the doping of M cation with d10 configuration results in 2H-hexagonal structure while that with p6 gives rise to a cubic perovskite or brownmillerite. The formation of cubic perovskite induced by M cation increases the electrical conductivity and the oxygen permeability by 1–2 orders of magnitude due to the high density of oxygen vacancy. In particular, disk-shaped perovskite SrCo0.95Sc0.05O3−δ membrane demonstrates the highest oxygen flux and theoretical analysis indicates that the oxygen permeation process is rate-determined by the surface reactions.
Co-reporter:Zhihao Chen, Ran Ran, Zongping Shao, Hai Yu, J.C. Diniz da Costa, Shaomin Liu
Ceramics International 2009 Volume 35(Issue 6) pp:2455-2461
Publication Date(Web):August 2009
DOI:10.1016/j.ceramint.2009.02.015
Perovskite Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) is a promising mixed conducting ceramic membrane material for air separation. In this work, BSCF powder was synthesized by a modified Pechini sol–gel technique at relatively lower temperature. The O2 permeation through a series of BSCF membranes has been tested at different temperatures and various O2 partial pressure gradients. Theoretical investigation indicated that bulk diffusion and the O2 exchange reactions on membrane surfaces jointly controlled the O2 permeation through BSCF membranes with thickness of between 1.1 and 0.75 mm. To further improve the O2 fluxes, effective efforts are made on membrane thickness reduction and surface modification by spraying porous BSCF layers on both surfaces. When the membrane thickness was reduced from 0.75 to 0.40 mm, the O2 fluxes were increased by 20–60% depending on the operating conditions. The surface modification further improved the O2 flux by another 20–40%. The high O2 fluxes achieved in this work are quite encouraging with a maximum value reaching 6.0 mL min−1 cm−2 at 900 °C.
Co-reporter:Lei Ge, Ran Ran, Zongping Shao, Zhong Hua Zhu, Shaomin Liu
Ceramics International 2009 Volume 35(Issue 7) pp:2809-2815
Publication Date(Web):September 2009
DOI:10.1016/j.ceramint.2009.03.018
Abstract
La0.6Sr0.4Co0.2Fe0.8O3−δ powder was synthesized by a combined EDTA-citrate complexing process via low-temperature auto-combustion synthesis with NH4NO3 as an oxidizer and a combustion trigger. Two novel methods were explored to improve this auto-combustion technology with reduced NH4NO3 addition: the use of La0.6Sr0.4Co0.2Fe0.8O3−δ as the combustion catalyst and the application of asymmetric sol–gel process to provide the precursor with different NH4NO3 concentrations. The prepared perovskite powder was characterized by BET, SEM, XRD and iodometric titration techniques. The catalytic performance of the powder was also examined in the decomposition of peroxide hydrogen. Experimental results indicate that powders from catalytic combustion and asymmetric precursor routes have more advantages in terms of better crystallites, higher specific surface area, higher B-site valence state, improved sintering capability and better catalytic performance in peroxide hydrogen decomposition than that from the synthesis with uniform NH4NO3 distribution.
Co-reporter:Youmin Guo, Huangang Shi, Ran Ran, Zongping Shao
International Journal of Hydrogen Energy 2009 Volume 34(Issue 23) pp:9496-9504
Publication Date(Web):December 2009
DOI:10.1016/j.ijhydene.2009.09.053
In order to improve the electrical conductivity of the SrSc0.2Co0.8O3−δ (SrScCo) electrode, a composite of 70 wt% SrSc0.2Co0.8O3−δ and 30 wt% Sm0.5Sr0.5CoO3−δ (SrScCo + SmSrCo) was prepared and investigated for electrochemical oxygen reduction at intermediate temperatures. The phase reaction between SrScCo and SmSrCo and its effect on the electrical conductivity, oxygen vacancy concentration and oxygen mobility were examined by XRD, 4-probe DC conductivity measurement, iodometry titration and O2-TPD experiment, respectively. The results showed that the composite reached a maximum conductivity around 123 S cm−1 at 600 °C, nearly five times that of SrScCo. AC impedance results showed that the electron charge-transfer process was greatly improved by forming the composite electrode, while the oxygen-ion charge-transfer process was somewhat deteriorated. By firing at 1000 °C for 2 h, a SOFC with the SrScCo + SmSrCo cathode and thin-film SDC electrolyte delivered peak power densities of 1100 and 366 mW cm−2 at 600 and 500 °C, respectively, which were only modestly lower than those of a similar cell with a pure SrScCo cathode.
Co-reporter:Lei Ge, Zhonghua Zhu, Zongping Shao, Shaobin Wang, Shaomin Liu
Ceramics International 2009 Volume 35(Issue 8) pp:3201-3206
Publication Date(Web):December 2009
DOI:10.1016/j.ceramint.2009.05.024
Abstract
La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) powders were synthesized respectively by an EDTA (ethylenediaminetetraacetic acid)–Citrate sol–gel process and a low-temperature auto-combustion process. The samples were characterized by XRD, SEM, BET, TGA and instant temperature analysis. The iodometric titration was used to determine the average valence of Co and Fe ions and the oxygen nonstoichiometry of the prepare powders. The catalytic properties of the synthesized powders were investigated by the hydrogen peroxide catalytic decomposition. Pure-perovskite structure was formed by both synthesis methods. The oxygen nonstoichiometry of the samples prepared by the auto-combustion process is larger than that by the sol–gel process. The catalytic activities of the powders from two synthesis processes also differed largely due to the different oxygen nonstoichiometry, surface area and crystalline sizes.
Co-reporter:Tao Yuan, Rui Cai, Ke Wang, Ran Ran, Shaomin Liu, Zongping Shao
Ceramics International 2009 Volume 35(Issue 5) pp:1757-1768
Publication Date(Web):July 2009
DOI:10.1016/j.ceramint.2008.10.010
Abstract
Spinel Li4Ti5O12 was synthesized by a simple glycine-nitrate auto-combustion by applying aqueous medium and constricting the reactions in the pores of cellulose fibers. The products from the auto-combustion and further calcination at various temperatures were characterized by XRD, SEM, BET surface area and TEM examinations. Pure phase and well-crystallized nano-Li4Ti5O12 oxides were obtained at a calcination temperature of 700 °C or higher. The 700 °C calcined one shows the best and high electrochemical performance, which reached a capacity of ∼125 mAh/g at 10 C discharge rate with fairly stable cycling performance even at 40 °C. Electrochemical impedance spectroscopy tests demonstrated that the surface reaction kinetics of Li4Ti5O12 was improved significantly with the increase of its electronic conductivity.
Co-reporter:Wei Zhou;Ran Ran;Wanqin Jin
Bulletin of Materials Science 2009 Volume 32( Issue 4) pp:
Publication Date(Web):2009/08/01
DOI:10.1007/s12034-009-0059-z
Conic Ba0·5Sr0·5Co0·8Fe0·2O3−δ (BSCF) functional composite oxide was synthesized via a simple in situ templating process. The treatment of the solid precursor with concentrated nitric acid resulted in the mismatch of ionic radius at A-site and B-site of the ABO3 perovskite, due to the oxidation of cobalt/iron ions, and the formation of Ba0·5Sr0·5(NO3)2 solid solution. Therefore, instead of the direct formation of BSCF oxide, an intermediate phase of Ba0·5Sr0·5CoO3 (BSC) in hexagonal lattice structure and with conic particle shape was preferentially formed during calcination at low temperature. BSCF perovskite was then produced by the in situ templating of BSC with iron diffusing into the BSC lattice during calcination at high temperature. Well-crystallized BSCF particles in conic shape were obtained by the calcination of the nitric acid treated precursor at 900°C.
Co-reporter:Yao Zheng;Ran Ran
Rare Metals 2009 Volume 28( Issue 4) pp:361-366
Publication Date(Web):2009 August
DOI:10.1007/s12598-009-0072-9
La0.75Sr0.25CryMn1−yO3 (LSCM) (y = 0.0–0.6) composite oxides were synthesized by a complexing process of combining ethylene diamine tetraacetic acid (EDTA) and citrate. X-ray diffraction (XRD), temperature-programmed reduction, electrical conductivity, I–V polarization, and impedance spectroscopy were conducted to investigate the Cr doping effect of La0.75Sr0.25MnO3 on its phase stability and electrochemical performance as a solid-oxide fuel cell (SOFC) anode. The chemical and structural stabilities of the oxides increased steadily with increasing Cr doping concentration, while the electrical conductivity decreased on the contrary. At y ≥ 0.4, the basic perovskite structure under the anode operating condition was sustained. a cell with 0.5-mm-thick scandia-stabilized zirconia electrolyte and La0.75Sr0.25CryMn1−yO3 anode delivered a power density of ∼15 mW·cm−2 at 850°C.
Co-reporter:Wei Zhou, Zongping Shao, Ran Ran, Wanqin Jin and Nanping Xu
Chemical Communications 2008 (Issue 44) pp:5791-5793
Publication Date(Web):01 Oct 2008
DOI:10.1039/B813327A
A novel SrNb0.1Co0.9O3−δelectrode material, which possesses not only high electrical conductivity but also large oxygen vacancy concentration at 400–600 °C, shows an excellent performance in the application of reduced temperature solid-oxide fuel cells.
Co-reporter:Kang Wang, Ran Ran, Wei Zhou, Hongxia Gu, Zongping Shao, Jeongmin Ahn
Journal of Power Sources 2008 Volume 179(Issue 1) pp:60-68
Publication Date(Web):15 April 2008
DOI:10.1016/j.jpowsour.2007.12.051
The properties and performance of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) + Sm0.2Ce0.8O1.9 (SDC) (70:30 in weight ratio) composite cathode for intermediate-temperature solid-oxide fuel cells were investigated. Mechanical mixing of BSCF with SDC resulted in the adhesion of fine SDC particles to the surface of coarse BSCF grains. XRD, SEM-EDX and O2-TPD results demonstrated that the phase reaction between BSCF and SDC was negligible, constricted only at the BSCF and SDC interface, and throughout the entire cathode with the formation of new (Ba,Sr,Sm,Ce)(Co,Fe)O3−δ perovskite phase at a firing temperature of 900, 1000, and ≥ 1050 °C, respectively. The BSCF + SDC electrode sintered at 1000 °C showed an area specific resistance of ∼0.064 Ω cm2 at 600 °C, which is a slight improvement over the BSCF (0.099 Ω cm2) owing to the enlarged cathode surface area contributed from the fine SDC particles. A peak power density of 1050 and ∼382 mW cm−2 was reached at 600 and 500 °C, respectively, for a thin-film electrolyte cell with the BSCF + SDC cathode fired from 1000 °C.
Co-reporter:Kun Zhang, Ran Ran, Lei Ge, Zongping Shao, Wanqin Jin, Nanping Xu
Journal of Membrane Science 2008 Volume 323(Issue 2) pp:436-443
Publication Date(Web):15 October 2008
DOI:10.1016/j.memsci.2008.07.002
SrCo1−yNbyO3−δ (y = 0.025–0.4) were synthesized for oxygen separation application. The crystal structure, phase stability, oxygen nonstoichiometry, electrical conductivity, and oxygen permeability of the oxides were systematically investigated. Cubic perovskite, with enhanced phase stability at higher Nb concentration, was obtained at y = 0.025–0.2. However, the further increase in niobium concentration led to the formation of impurity phase. The niobium doping concentration also had a significant effect on electrical conductivity and oxygen permeability of the membranes. SrCo0.9Nb0.1O3−δ exhibited the highest electrical conductivity and oxygen permeability among the others. It reached a permeation flux of ∼2.80 × 10−6 mol cm−2 s−1 at 900 °C for a 1.0-mm membrane under an air/helium oxygen gradient. The further investigation demonstrated the oxygen permeation process was mainly rate-limited by the oxygen bulk diffusion process.
Co-reporter:Ye Lin, Ran Ran, Yao Zheng, Zongping Shao, Wanqin Jin, Nanping Xu, Jeongmin Ahn
Journal of Power Sources 2008 Volume 180(Issue 1) pp:15-22
Publication Date(Web):15 May 2008
DOI:10.1016/j.jpowsour.2008.02.044
The potential application of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) as a cathode for a proton-conducting solid-oxide fuel cell based on BaCe0.9Y0.1O2.95 (BCY) electrolyte was investigated. Cation diffusion from BCY to BSCF with the formation of a perovskite-type Ba2+-enriched BSCF and a Ba2+-deficient BCY at a firing temperature as low as 900 °C was observed, the higher the firing temperature the larger deviation of the A to B ratio from unit for the perovskites. Symmetric cell tests demonstrated the impurity phases did not induce a significant change of the cathodic polarization resistance, however, the ohmic resistance of the cell increased obviously. Anode-supported cells with the electrolyte thickness of ∼50 μm were successfully fabricated via a dual-dry pressing process for the single-cell test. Under optimized conditions, a maximum peak power density of ∼550 and 100 mW cm−2 was achieved at 700 and 400 °C, respectively, for the cell with the BSCF cathode layer fired from 950 °C. At 500 °C, the ohmic resistance is still the main source of cell resistance. A further reduction in membrane thickness would envisage an increase in power density significantly.
Co-reporter:Lei Ge, Ran Ran, Kun Zhang, Shaomin Liu, Zongping Shao
Journal of Membrane Science 2008 Volume 318(1–2) pp:182-190
Publication Date(Web):20 June 2008
DOI:10.1016/j.memsci.2008.02.015
(Ba0.5Sr0.5)(Co0.8Fe0.2)yO3−δ ((BS)(CF)y, 1.00 ≥ y ≥ 0.77) oxides were investigated for oxygen separation application with emphasis on long-term operational stability. Pure phase cubic perovskite was formed at y ≥ 0.83. The oxygen nonstoichiometry increased while electrical conductivity and permeability decreased with the decrease of y. However, the (BS)(CF)0.97 membrane still displayed an attractive oxygen flux as high as 2.4 × 10−6 mol cm−2 s−1 at 900 °C, as compared to 2.5 × 10−6 mol cm−2 s−1 for a cation stoichiometric BSCF membrane. The B-site deficiency greatly restrained the A-site cation diffusion and stabilized the perovskite structure and permeation properties of the membranes. During the long-term operation of the (BS)(CF)0.97 membrane at 850 °C for more than 300 h, a stable permeation flux of (1.8 ± 0.3) × 10−6 mol cm−2 s−1 was achieved. Further investigation demonstrated that the improved importance of oxygen bulk-diffusion regime in the rate-determination of oxygen permeation through the membranes.
Co-reporter:Hongxia Gu, Yao Zheng, Ran Ran, Zongping Shao, Wanqin Jin, Nanping Xu, Jeongmin Ahn
Journal of Power Sources 2008 Volume 183(Issue 2) pp:471-478
Publication Date(Web):1 September 2008
DOI:10.1016/j.jpowsour.2008.05.053
Perovskite-type La0.8Sr0.2ScyMn1−yO3−δ oxides (LSSMy, y = 0.0–0.2) were synthesized and investigated as cathodes for solid-oxide fuel cells (SOFCs) containing a stabilized zirconia electrolyte. The introduction of Sc3+ into the B-site of La0.8Sr0.2MnO3−δ (LSM) led to a decrease in the oxides’ thermal expansion coefficients and electrical conductivities. Among the various LSSMy oxides tested, LSSM0.05 possessed the smallest area-specific cathodic polarization resistance, as a result of the suppressive effect of Sc3+ on surface SrO segregation and the optimization of the concentration of surface oxygen vacancies. At 850 °C, it was only ∼0.094 Ω cm2 after a current passage of 400 mA cm−2 for 30 min, significantly lower than that of LSM (∼0.25 Ω cm2). An anode-supported cell with a LSSM0.05 cathode demonstrated a peak power density of 1300 mW cm−2 at 850 °C. The corresponding value for the cell with LSM cathode was 450 mW cm−2 under the same conditions. The LSSM0.05 oxide may potentially be a good cathode material for IT-SOFCs containing doped zirconia electrolytes.
Co-reporter:Wei Zhou, Huangang Shi, Ran Ran, Rui Cai, Zongping Shao, Wanqin Jin
Journal of Power Sources 2008 Volume 184(Issue 1) pp:229-237
Publication Date(Web):15 September 2008
DOI:10.1016/j.jpowsour.2008.06.021
The wet powder spraying (WPS) technique was used for the deposition of dense and thin (Y2O3)0.08(ZrO2)0.92 (YSZ-8) films on an anode substrate being used for fuel cell applications. Both agglomeration of the powder and the presence of organics in the substrate have a significant effect on the quality and densification of the thin electrolyte layer. High-energy ball milling effectively broke up the agglomerates and enhanced the packing density of the green layer. Pre-calcination of the substrate at ∼1000 °C enhanced the match of sintering shrinkage between the electrolyte layer and the substrate and improved the quality of the YSZ-8 thin film significantly. Crack-free dual-layer assembly with a highly densified YSZ-8 film as thin as 10 μm was successfully fabricated by optimizing the fabrication parameters. The cells with a La0.8Sr0.2MnO3 cathode showed a high open circuit voltage of 1.071 V and a peak power density of 894 mW cm−2 at 850 °C operated with hydrogen fuel.
Co-reporter:Wei Zhou, Ran Ran, Zongping Shao, Wanqin Jin, Nanping Xu
Journal of Power Sources 2008 Volume 182(Issue 1) pp:24-31
Publication Date(Web):15 July 2008
DOI:10.1016/j.jpowsour.2008.04.012
A-site cation-deficient (Ba0.5Sr0.5)1−xCo0.8Fe0.2O3−δ ((BS)1−xCF) oxides were synthesized and evaluated as cathode materials for intermediate-temperature solid-oxide fuel cells (ITSOFCs). The material's thermal expansion coefficient, electrical conductivity, oxygen desorption property, and electrocatalytic activity were measured. A decrease in both the electronic conductivity and the thermal expansion coefficient was observed for increasing values of the stoichiometric coefficient, x. This effect was attributed to the creation of additional oxygen vacancies, the suppression of variation in the oxidation states of cobalt and iron, and the suppression of the spin-state transitions of cobalt ions. The increase in A-site cation deficiency resulted in a steady increase in cathode polarization resistance, because impurities formed at the cathode/electrolyte interface, reducing the electronic conductivity. A single SOFC equipped with a BS0.97CF cathode exhibited peak power densities of 694 and 893 mW cm−2 at 600 and 650 °C, respectively, and these results were comparable with those obtained with a Ba0.5Sr0.5Co0.8Fe0.2O3−δ cathode. Slightly A-site cation-deficient (BS)1−xCF oxides were still highly promising cathodes for reduced temperature SOFCs.
Co-reporter:Chunming Zhang, Yao Zheng, Ran Ran, Zongping Shao, Wanqin Jin, Nanping Xu, Jeongmin Ahn
Journal of Power Sources 2008 Volume 179(Issue 2) pp:640-648
Publication Date(Web):1 May 2008
DOI:10.1016/j.jpowsour.2008.01.030
The initialization of an anode-supported single-chamber solid-oxide fuel cell, with NiO + Sm0.2Ce0.8O1.9 anode and Ba0.5Sr0.5Co0.8Fe0.2O3−δ + Sm0.2Ce0.8O1.9 cathode, was investigated. The initialization process had significant impact on the observed performance of the fuel cell. The in situ reduction of the anode by a methane–air mixture failed. Although pure methane did reduce the nickel oxide, it also resulted in severe carbon coking over the anode and serious distortion of the fuel cell. In situ initialization by hydrogen led to simultaneous reduction of both the anode and cathode; however, the cell still delivered a maximum power density of ∼350 mW cm−2, attributed to the re-formation of the BSCF phase under the methane–air atmosphere at high temperatures. The ex situ reduction method appeared to be the most promising. The activated fuel cell showed a peak power density of ∼570 mW cm−2 at a furnace temperature of 600 °C, with the main polarization resistance contributed from the electrolyte.
Co-reporter:Hongxia Gu, Ran Ran, Wei Zhou, Zongping Shao, Wanqin Jin, Nanping Xu, Jeongmin Ahn
Journal of Power Sources 2008 Volume 177(Issue 2) pp:323-329
Publication Date(Web):1 March 2008
DOI:10.1016/j.jpowsour.2007.11.062
Hydrazine was examined as a fuel for a solid-oxide fuel cell (SOFC) that employed a typical nickel-based anode. An in situ catalytic decomposition of hydrazine at liquid state under room temperature and ambient pressure before introducing to the fuel cell was developed by applying a Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) oxide catalyst. Catalytic testing demonstrated that liquid N2H4 can be decomposed to gaseous NH3 and H2 at a favorable rate and at a temperature as low as 20 °C and H2 selectivity reaching values as high as 10% at 60 °C. Comparable fuel cell performance was observed using either the in situ decomposition products of hydrazine or pure hydrogen as fuel. A peak power density of ∼850 mW cm−2 at 900 °C was obtained with a typical fuel cell composed of scandia-stabilized zirconia and La0.8Sr0.2MnO3 cathode. The high energy and power density, easy storage and simplicity in fuel delivery make it highly attractive for portable applications.
Co-reporter:Kang Wang, Ran Ran, Yong Hao, Zongping Shao, Wanqin Jin, Nanping Xu
Journal of Power Sources 2008 Volume 177(Issue 1) pp:33-39
Publication Date(Web):15 February 2008
DOI:10.1016/j.jpowsour.2007.11.004
A no-chamber solid-oxide fuel cell operated on a fuel-rich ethanol flame was reported. Heat produced from the combustion of ethanol thermally sustained the fuel cell at a temperature of 500–830 °C. Considerable amounts of hydrogen and carbon monoxide were also produced during the fuel-rich combustion which provided the direct fuels for the fuel cell. The location of the fuel cell with respect to the flame was found to have a significant effect on the fuel cell temperature and performance. The highest power density was achieved when the anode was exposed to the inner flame. By modifying the Ni + Sm0.2Ce0.8O1.9 (SDC) anode with a thin Ru/SDC catalytic layer, the fuel cell envisaged not only an increase of the peak power density to ∼200 mW cm−2 but also a significant improvement of the anodic coking resistance.
Co-reporter:Yao Zheng, Ran Ran, Hongxia Gu, Rui Cai, Zongping Shao
Journal of Power Sources 2008 Volume 185(Issue 2) pp:641-648
Publication Date(Web):1 December 2008
DOI:10.1016/j.jpowsour.2008.09.003
Composite electrodes composed of a perovskite-type La0.8Sr0.2Sc0.1Mn0.9O3−δ (LSSM) and a fluorite-type scandium-stabilized zirconia (ScSZ) were prepared and evaluated as potential cathodes for intermediate-temperature solid-oxide fuel cells. Characterization was made by phase reaction, electrochemical impedance spectroscopy, step current polarization and I–V tests. The phase reaction between LSSM and ScSZ occurred at 1150 °C or higher; however, it had a minor effect on the electrode performance. The formation of a composite electrode led to an obvious improvement in both charge transfer and surface-related processes. With the increase of ScSZ content, the rate-limiting step of oxygen reduction reaction steadily changed from mainly a surface diffusion process to an electron transfer process. The optimal ScSZ content and sintering temperature of the electrode layer were found to be 20 wt.% and 1100–1150 °C, respectively. Under optimal conditions, an anode-supported single cell with LSSM + ScSZ composite cathode showed high power densities of ∼1211 and 386 mW cm−2 at 800 and 650 °C, respectively.
Co-reporter:Wei Zhou, Ran Ran, Zongping Shao, Rui Cai, Wanqin Jin, Nanping Xu, Joenmin Ahn
Electrochimica Acta 2008 Volume 53(Issue 13) pp:4370-4380
Publication Date(Web):20 May 2008
DOI:10.1016/j.electacta.2008.01.058
Silver-modified Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) cathodes for intermediate-temperature solid-oxide fuel cells (IT-SOFCs) were prepared by an electroless deposition process using N2H4 as the reducing agent at room temperature. This fabrication technique together with tailored electrode porosity, modified the BSCF electrodes with silver content that varied from 0.3 to 30 wt.% without damaging the electrode microstructure. Both the Ag loading and firing temperatures were found to have a significant impact on the electrode performance, which could facilitate or block the electrochemical processes of the BSCF-based cathodes, processes that include charge-transfer, oxygen adsorption and oxygen electrochemical reduction. At an optimal Ag loading of 3.0 wt.% and firing temperature of 850 °C, an area specific resistance of only 0.042 Ω cm2 at 600 °C was achieved for a modified BSCF cathode.
Co-reporter:Wei Zhou, Ran Ran, Zongping Shao, Wei Zhuang, Jing Jia, Hongxia Gu, Wanqin Jin, Nanping Xu
Acta Materialia 2008 Volume 56(Issue 12) pp:2687-2698
Publication Date(Web):July 2008
DOI:10.1016/j.actamat.2008.02.002
Abstract
(Ba0.5Sr0.5)1+xCo0.8Fe0.2O3−δ, or BSCF(1 + x), (0 ⩽ x ⩽ 0.3) oxides were synthesized and investigated as cathodes for intermediate-temperature solid-oxide fuel cells. The A-site cation excess in BSCF(1 + x) resulted in a lattice expansion and the creation of more active sites for oxygen reduction reaction due to the lowered valence states of the B-site ions and the increased oxygen vacancy concentration, which improved the oxygen adsorption process. On the other hand, the A-site excess could also result in higher resistances for oxygen adsorption (due to the formation of BaO and/or SrO impurities), and oxygen-ion transfer (by facilitating the solid-phase reaction between the cathode and the electrolyte). By taking all these factors into account, we found BSCF1.03 to be the optimal composition, which lead to a peak power density of 1026.2 ± 12.7 mW cm−2 at 650 °C for a single cell.
Co-reporter:Kun Zhang, Lei Ge, Ran Ran, Zongping Shao, Shaomin Liu
Acta Materialia 2008 Volume 56(Issue 17) pp:4876-4889
Publication Date(Web):October 2008
DOI:10.1016/j.actamat.2008.06.004
Abstract
LnBaCo2O5+δ (Ln = La, Pr, Nd, Sm, Gd, and Y) was synthesized via an EDTA–citrate complexing process. The particular Ln3+ dopant had a significant effect on the oxide’s phase structure/stability, oxygen content, electrical conductivity, oxygen permeability, and cathode performance. Stable, cation-ordered oxides with layered lattice structures were obtained with medium-sized Ln3+ ions over a wide range of oxygen partial pressures, a property essential for applications as oxygen separation membranes and solid oxide fuel cell (SOFC) cathodes. PrBaCo2O5+δ demonstrated the highest oxygen flux (∼5.09 × 10−7 mol cm−2 s−1 at 900 °C), but this value was still significantly lower than that of Ba0.5Sr0.5Co0.8Fe0.2O3−δ perovskite (∼3.1 × 10−6 mol cm−2 s−1 at 900 °C). The observed difference was attributed to the much longer diffusion distance through a polycrystalline membrane with a layered lattice structure than through cubic perovskite because bulk diffusion was the rate-limiting step of permeation. An area-specific resistance of ∼0.213 Ω cm2 was achieved at 600 °C with a PrBaCo2O5+δ cathode, suggesting that the layer-structured oxides were promising alternatives to ceramic membranes for SOFC cathodes.
Co-reporter:Pingying Zeng, Ran Ran, Zhihao Chen, Wei Zhou, Hongxia Gu, Zongping Shao, Shaomin Liu
Journal of Alloys and Compounds 2008 Volume 455(1–2) pp:465-470
Publication Date(Web):8 May 2008
DOI:10.1016/j.jallcom.2007.01.144
SrCoO3−δ is a material with multiple phase structures. The influence of Sc3+ doping in the B-site of SrCoO3−δ on its lattice structure/phase stability, electrical conductivity, and cathode performance for intermediate-temperature solid oxide fuel cells (IT-SOFCs) was investigated by X-ray diffraction, four-probe dc conductivity and impedance spectroscopy measurements, respectively. The introduction of large-size Sc3+ (0.745 Å) cation together with the sol–gel synthesis technique, led to a substantial stabilization of the cubic phase of SrCoO3−δ—even at a Sc3+ doping amount as low as 5 mol%. Such stabilization resulted in a sharp increase in the electrical conductivity of the material, which was found to be p-type in nature. A maximum electrical conductivity and favourable cubic phase stability of the material was reached at the Sc3+ doping concentration of 5–10 mol%. A further increase of Sc3+ doping, however, lowered the electrical conductivity due to the blocking effect of Sc3+ for the electron conduction. An area specific resistance (ASR) as low as 0.25 Ωcm2 was reached at 600 °C for SrSc0.1Co0.9O3−δ as a cathode material based on Sm0.15Ce0.85O1.925 electrolyte.
Co-reporter:Yazhong Chen, Zongping Shao and Nanping Xu
Energy & Fuels 2008 Volume 22(Issue 3) pp:1873-1879
Publication Date(Web):March 26, 2008
DOI:10.1021/ef700576f
Hydrogen production for application to proton exchange membrane fuel cells (PEMFCs) has been a focus of investigation globally. Ethanol as a H2 source benefits from the ready availability of infrastructure and environmental benignity in comparison with those of other hydrocarbon fuels. Thus, H2 production from ethanol has gained much attention worldwide. In this work, H2 production from ethanol steam reforming (ESR) was investigated over Pt catalysts supported on CexZr1−xO2 (x = 0.2, 0.4, 0.6, or 0.8) developed via a glycine nitrate process. The supports or catalysts were characterized by low temperature N2 physical adsorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), H2 temperature-programmed reduction, temperature-programmed desorption of ethanol, and catalytic performance measurements for ESR at 350–550 °C. Initial catalyst stability was also investigated. The results indicated that Pt/CexZr1−xO2 catalysts were highly active for ESR at lower temperatures, only yielding H2, CO, CH4, and CO2 as products. However, selectivity to CH4 was found around 50.0% at 350–400 °C, while selectivity of products at 450–550 °C was found close to thermodynamic control values, indirectly suggesting that ethanol first dehydrogenates on the metallic surface and then aldehyde undergoes decarbonylation, forming CO and CH4. The function of steam was to establish thermodynamic equilibria for methane steam reforming and water gas shift reactions. The high activity and good initial stability made the catalysts suitable for application to portable power generation by using a PEMFC combined with a solid oxide fuel cell or a methane internal combustion engine for capturing the energy in methane.
Co-reporter:Yao Zheng, Ran Ran and Zongping Shao
The Journal of Physical Chemistry C 2008 Volume 112(Issue 47) pp:18690-18700
Publication Date(Web):2017-2-22
DOI:10.1021/jp806941d
Electrochemical impedance spectroscopy, step current polarization, and cyclic voltammetry were applied to investigate the activation and deactivation kinetics of oxygen reduction over a novel La0.8Sr0.2Sc0.1Mn0.9O3 (LSSM) cathode material. Oxygen vacancies were created after cathodic polarization for a certain period of time. The generating rate was closely related with oxygen partial pressure of surrounding atmosphere (PO2), polarization time, temperature, and voltage. The in situ created oxygen vacancies could propagate both over the surface and into the bulk of the LSSM electrode after a high cathodic polarization. Both chemical oxidation by ambient air and electrochemical oxidation by anodic polarization were exploited to demonstrate the deactivation mechanism of these in situ created oxygen vacancies. The rate-determining step of oxygen reduction reaction over LSSM electrode before and after the activation was also investigated. It was by oxygen ion surface diffusion at 800 °C in air, while a steady change to an electron-transfer process was observed with decreasing temperature and PO2.
Co-reporter:Guixin Wang, Jingjing Xu, Ming Wen, Rui Cai, Ran Ran, Zongping Shao
Solid State Ionics 2008 Volume 179(21–26) pp:946-950
Publication Date(Web):15 September 2008
DOI:10.1016/j.ssi.2008.03.032
High-energy ball milling (HEBM) was applied for the synthesis of spinel Li4Ti5O12 and the influence of milling time was investigated systematically. With the increase of ball-milling time, the average particle size of the as-synthesized Li4Ti5O12 powder decreased from ~ 900 nm to ~ 150 nm, while the particle morphology changed little. At the same time, the main particle size distribution peak split up into two parts, which were narrowed and moved to a smaller range. Electrochemical testing results showed that the Li4Ti5O12 with precursor milled for 60 min at 500 rpm rotational speed showed a favorable discharge capacity of ~ 146.9 mAh/g with corresponding coulombic efficiency of 99.9% at 1 C rate. The rate performance was improved with the increase of milling time because of the smaller particle size of the resulted Li4Ti5O12. The voltage change between oxidation peak and reduction peak of Li4Ti5O12 also became wider with milling time increasing.
Co-reporter:Wei Zhou, Zongping Shao, Ran Ran, Pingying Zeng, Hongxia Gu, Wanqin Jin, Nanping Xu
Journal of Power Sources 2007 Volume 168(Issue 2) pp:330-337
Publication Date(Web):1 June 2007
DOI:10.1016/j.jpowsour.2007.03.041
A novel Ba0.5Sr0.5Co0.8Fe0.2O3 − δ + LaCoO3 (BSCF + LC) composite oxide was investigated for the potential application as a cathode for intermediate-temperature solid-oxide fuel cells based on a Sm0.2Ce0.8O1.9 (SDC) electrolyte. The LC oxide was added to BSCF cathode in order to improve its electrical conductivity. X-ray diffraction examination demonstrated that the solid-state reaction between LC and BSCF phases occurred at temperatures above 950 °C and formed the final product with the composition: La0.316Ba0.342Sr0.342Co0.863Fe0.137O3 − δ at 1100 °C. The inter-diffusion between BSCF and LC was identified by the environmental scanning electron microscopy and energy dispersive X-ray examination. The electrical conductivity of the BSCF + LC composite oxide increased with increasing calcination temperature, and reached a maximum value of ∼300 S cm−1 at a calcination temperature of 1050 °C, while the electrical conductivity of the pure BSCF was only ∼40 S cm−1. The improved conductivity resulted in attractive cathode performance. An area-specific resistance as low as 0.21 Ω cm2 was achieved at 600 °C for the BSCF (70 vol.%) + LC (30 vol.%) composite cathode calcined at 950 °C for 5 h. Peak power densities as high as ∼700 mW cm−2 at 650 °C and ∼525 mW cm−2 at 600 °C were reached for the thin-film fuel cells with the optimized cathode composition and calcination temperatures.
Co-reporter:Lei Ge, Wei Zhou, Ran Ran, Shaomin Liu, Zongping Shao, Wanqin Jin, Nanping Xu
Journal of Membrane Science 2007 Volume 306(1–2) pp:318-328
Publication Date(Web):1 December 2007
DOI:10.1016/j.memsci.2007.09.004
(Ba0.5Sr0.5)1−xCo0.8Fe0.2O3−δ (BSCF) (x = 0–0.3) oxides were prepared by a combined EDTA–citrate complexing method. The crystal structure, electrical conductivity, sintering behavior and oxygen desorption property of the oxides were studied by X-ray diffraction (XRD), four-probe direct current (DC) conductivity, environmental scanning electron microscopy (ESEM) and oxygen temperature-programmed desorption (O2-TPD) technologies, respectively. At x = 0.0–0.15, BSCF had a cubic perovskite structure, the lattice parameter and electrical conductivity both decreased steadily with increasing A-site deficiency. The A-site deficiency resulted in the increasing oxygen vacancy concentration in the lattice structure and improved the sintering of the oxides. BSCF (x = 0.03) showed the highest oxygen permeability with the flux reaching 3.5 × 10−6 mol cm−2 s−1 [STP: standard temperature and pressure] at 900 °C through a 1.0 mm thickness membrane. Long-term stability test of BSCF (x = 0.03) membrane at 850 °C indicated a slight deterioration of the permeation flux, which was attributed in part to the increased A-site deficiency of the bulk from Ba2+ and Sr2+ segregation over the membrane surface.
Co-reporter:Pingying Zeng, Ran Ran, Zhihao Chen, Hongxia Gu, Zongping Shao, J.C. Diniz da Costa, Shaomin Liu
Journal of Membrane Science 2007 Volume 302(1–2) pp:171-179
Publication Date(Web):15 September 2007
DOI:10.1016/j.memsci.2007.06.047
In this work, the effects of sintering temperature on the phase structure, oxygen nonstoichiometry, microstructure, electrical conductivity, and oxygen permeation behavior of perovskite La0.6Sr0.4Co0.2Fe0.8O3−δ membranes were systematically studied. The sintering temperature has negligible effect on the bulk properties of the phase structure and the oxygen nonstoichiometry, but has significant influence on the microstructure and electrical conductivity of the membranes, and therefore imposes large impact on its oxygen permeability. With an increase in the sintering temperature, the grain size increased steadily from 0.3 μm at 1000 °C to 3.5 μm at 1300 °C, accompanied with the substantial enhancement of electrical conductivity but the decrease of activation energy for the electrical conduction. Results indicate that the grain boundary had a much lower electrical conductivity than that of the bulk. The oxygen permeation process was mainly rate-determined by the slow oxygen diffusion over the grain boundary. Higher sintering temperature lowers the activation energy for oxygen permeation and accordingly gives rise to higher oxygen permeation flux. The oxygen permeation flux could be improved more than 10 times if the sintering temperature increased from 1000 to 1300 °C.
Co-reporter:Wei Zhou, Ran Ran, Zong Ping Shao, Hong Xia Gu, Wan Qin Jin, Nan Ping Xu
Journal of Power Sources 2007 Volume 174(Issue 1) pp:237-245
Publication Date(Web):22 November 2007
DOI:10.1016/j.jpowsour.2007.08.087
Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) perovskite was synthesized by the sol–gel process based on EDTA–citrate (EC) complexing method, nitric acid modified EC route (NEC) and nitric acid aided EDTA–citrate combustion process (NECC). A crystallite size of 27, 38 and 42 nm, respectively, was observed for the powders of NECC-BSCF, NEC-BSCF and EC-BSCF calcined at 1000 °C, suggesting the suppression effect of nitric acid on the crystallite size growth of BSCF. The smaller crystallite size of the powders resulted in the higher degree of sintering of the cathode. Oxygen permeation study of the corresponding membranes demonstrated that in the powder synthesis, nitric acid also had a noticeable detrimental effect on the oxygen surface exchange kinetics and on the oxygen bulk diffusion rate of the BSCF oxides. The effect of powder synthesis route on the bulk properties of the oxide was validated by the oxygen temperature-programmed desorption technique. On the whole, a decreasing cathode performance in the sequence of EC-BSCF, NEC-BSCF and NECC-BSCF was observed. A peak power density of 693 mW cm−2 was achieved for an anode-supported cell with an EC-BSCF cathode at 600 °C, which was significantly higher than that with an NEC-BSCF cathode (571 mW cm−2) or an NECC-BSCF cathode (543 mW cm−2) under similar operation conditions.
Co-reporter:Hongxia Gu, Ran Ran, Wei Zhou, Zongping Shao
Journal of Power Sources 2007 Volume 172(Issue 2) pp:704-712
Publication Date(Web):25 October 2007
DOI:10.1016/j.jpowsour.2007.07.056
The potential application of combined EDTA–citrate complexing process (ECCP) in intermediate-temperature solid-oxide fuel cells (IT-SOFCs) processing was investigated. ECCP-derived scandia-stabilized-zirconia (ScSZ) powder displayed low packing density, high surface area and nano-crystalline, which was ideal material for thin-film electrolyte fabrication based on dual dry pressing. A co-synthesis of NiO + ScSZ anode based on ECCP was developed, which showed reduced NiO(Ni) and ScSZ grain sizes and improved homogeneity of the particle size distribution, as compared with the mechanically mixed NiO + ScSZ anode. Anode-supported ScSZ electrolyte fuel cell with the whole cell materials synthesized from ECCP was successfully prepared. The porous anode and cathode exhibited excellent adhesion to the electrolyte layer. Fuel cell with 30 μm thick ScSZ electrolyte and La0.8Sr0.2MnO3 cathode showed a promising maximum peak power density of 350 mW cm−2 at 800 °C.
Co-reporter:Zhihao Chen, Ran Ran, Wei Zhou, Zongping Shao, Shaomin Liu
Electrochimica Acta 2007 Volume 52(Issue 25) pp:7343-7351
Publication Date(Web):September 2007
DOI:10.1016/j.electacta.2007.06.010
The influence of iron doping level in Ba0.5Sr0.5Co1−yFeyO3−δ (y = 0.0–1.0) (BSCF) oxides on their phase structure, oxygen nonstoichiometry, electrical conductivity, performance as symmetrical cell electrode and oxygen permeating membranes was systematically investigated. A cubic perovskite structure was observed for all the compositions with the presence of iron. The increase of iron doping level resulted in the decrease of the lattice constant, room-temperature oxygen nonstoichiometry, total electrical conductivity, and the increase of area specific resistance (ASR) as cathode with samaria doped ceria electrolyte. However, promising cathode performance with an ASR as low as 0.613 Ω cm2 was still obtained at 600 °C for Ba0.5Sr0.5FeO3−δ (BSF). The ceramic membranes composing of BSCF with various iron doping level are all oxygen semi-permeable at elevated temperatures. The increase of iron doping level resulted in the decrease of oxygen permeation flux from JO2JO2 = 2.28 μmol cm−2 s−1 (STP) for Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF5582) to ∼0.45 μmol cm−2 s−1 (STP) at 900 °C for BSF (y = 1.0) with the same membrane thickness of 1.1 mm, alongside with the change of the rate-determination step from the oxygen surface exchange to the slow oxygen bulk diffusion. The formation of composite oxide with a proper electronic conducting phase and the thin film technology are important for their prospective application as cathode in IT-SOFCs and oxygen permeating membrane, respectively.
Co-reporter:Yazhong Chen, Zongping Shao, Nanping Xu
Journal of Natural Gas Chemistry (March 2008) Volume 17(Issue 1) pp:75-80
Publication Date(Web):1 March 2008
DOI:10.1016/S1003-9953(08)60029-8
Dimethyl ether (DME) is a non-toxic fuel with high H/C ratio and high volumetric energy density, and could be served as an ideal source of H2/syngas production for application in solid oxide fuel cells (SOFC). This study presents results of DME partial oxidation over a 1.5 wt% Pt/Ce0.4Zr0.6O2 catalyst under the condition of gas hourly space velocity (GHSV) of 15000-60000 ml/(g·h), molar ratio of O2/DME of 0.5 and 500-700 °C, and this temperature range was also the operation temperature range for intermediate temperature SOFC. The results indicated that the catalyst showed good activity for the selective partial oxidation of DME to H2/syngas. Under the working conditions investigated, DME was completely converted. Increase in reaction temperature enhanced the amount of syngas, but lowered the H2/CO ratio and yield of methane; while increase in reaction GHSV resulted in only slight variation in the distribution of products. The good catalytic activity of Pt supported on Ce0.4Zr0.6O2 for the partial oxidation of DME may be directly associated with the good oxygen storage capacity of the support, which is worth of further investigation to develop materials for application in SOFC.
Co-reporter:Jing Zhao, Dengjie Chen, Zongping Shao, Shaomin Liu
Separation and Purification Technology (30 July 2010) Volume 74(Issue 1) pp:28-37
Publication Date(Web):30 July 2010
DOI:10.1016/j.seppur.2010.05.004
In this work, the effects of CuO addition on sintering behavior, crystal structure and the oxygen permeation of SrCo0.9Nb0.1O3−δ (SCN) membranes have been investigated. XRD characterization demonstrated that copper could incorporate into the perovskite lattices with certain solubility dependent on temperature. Small amount of CuO (5 wt.%) successfully reduced the sintering temperature of the SCN membrane by 180 °C. A relative density of 95.4% was reached for the membrane with 5 wt.% CuO additive after sintering at 1000 °C. The promoting effect on sintering is likely associated with liquid assisted sintering. The incorporation of copper into the SCN lattice has minimal effect on the membrane sintering but a significant effect on the membrane integrity. As compared to the single-phase SCN membranes, the introduction of CuO as a sintering aid does not affect the electronic conductivity of the membrane between 700 and 900 °C, but the oxygen permeability is slightly reduced. Permeation study of the membranes of 0.9 mm thickness demonstrated oxygen fluxes of 1.5, 1.4, 1.3 and 1.2 ml cm−2 min−1 [STP] at 800 °C for the membranes containing 0 (pure SCN), 1, 3 and 5 wt.% CuO, respectively. The results suggest that the introduction of CuO as a sintering aid had a more significant effect on the oxygen surface exchange kinetics than on the oxygen bulk diffusion rate.
Co-reporter:Chao Su, Zongping Shao, Ye Lin, Yuzhou Wu and Huanting Wang
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 35) pp:NaN12181-12181
Publication Date(Web):2012/07/26
DOI:10.1039/C2CP41166K
An intriguing cell concept by applying proton-conducting oxide as the ionic conducting phase in the anode and taking advantage of beneficial interfacial reaction between anode and electrolyte is proposed to successfully achieve both high open circuit voltage (OCV) and power output for SOFCs with thin-film samarium doped ceria (SDC) electrolyte at temperatures higher than 600 °C. The fuel cells were fabricated by conventional route without introducing an additional processing step. A very thin and dense interfacial layer (2–3 μm) with compositional gradient was created by in situ reaction between anode and electrolyte although the anode substrate had high surface roughness (>5 μm), which is, however, beneficial for increasing triple phase boundaries where electrode reactions happen. A fuel cell with Ni–BaZr0.4Ce0.4Y0.2O3 anode, thin-film SDC electrolyte and Ba0.5Sr0.5Co0.8Fe0.2O3–δ (BSCF) cathode has an OCV as high as 1.022 V and delivered a power density of 462 mW cm−2 at 0.7 V at 600 °C. It greatly promises an intriguing fuel cell concept for efficient power generation.
Co-reporter:Yingjie Niu, Wei Zhou, Jaka Sunarso, Lei Ge, Zhonghua Zhu and Zongping Shao
Journal of Materials Chemistry A 2010 - vol. 20(Issue 43) pp:NaN9622-9622
Publication Date(Web):2010/09/27
DOI:10.1039/C0JM02816A
Bi doping of SrFeO3−δ results in the formation of a structure with high symmetry and extraordinary electrochemical performance for Bi0.5Sr0.5FeO3-δ, which is capable of competing effectively with the current Co-based cathode benchmark with additional advantages of lower thermal expansion and cost.
Co-reporter:Wei Zhou, Zongping Shao, Fengli Liang, Zhi-Gang Chen, Zhonghua Zhu, Wanqin Jin and Nanping Xu
Journal of Materials Chemistry A 2011 - vol. 21(Issue 39) pp:NaN15351-15351
Publication Date(Web):2011/08/30
DOI:10.1039/C1JM12660A
As highly efficient energy conversion devices with the capability for power/heat co-generation and fuel flexibility, solid-oxide fuel cells (SOFCs) have received considerable attention recently as a keystone of the future energy economy. Nowadays, lack of a proper cathode with high performance at intermediate temperature (IT) has become the main obstacle in realizing this fascinating technology. Here we present (La0.8Sr0.2)0.95Ag0.05MnO3−δ as a novel CO2 tolerant cathode of IT-SOFCs, which shows silver intercalation/de-intercalation capability. Under cathodic polarization, silver can be extracted from perovskite lattice to form a 5–15 nm silver modified A-site cation deficient (La0.8Sr0.2)0.95MnO3−δelectrode with superior electrocatalytic activity and improved stability. Any performance degradation due to silver sintering can be easily in situ restored by re-intercalating silver into the perovskite lattice under anodic polarization. Through electrochemically adjusting the oxidation state and location of silver, we introduce a way for the development of high-performance silver-modified cathode for IT-SOFCs, which may contribute significantly to a sustainable future.
Co-reporter:Feifei Dong, Dengjie Chen, Yubo Chen, Qing Zhao and Zongping Shao
Journal of Materials Chemistry A 2012 - vol. 22(Issue 30) pp:NaN15079-15079
Publication Date(Web):2012/05/28
DOI:10.1039/C2JM31711G
Cobalt-free small La3+-doped BaFeO3−δ is synthesized and systematically characterized towards application as an oxygen reduction electrode material for intermediate temperature solid oxide fuel cells (IT-SOFCs) with oxygen-ion conducting electrolyte. The formation of an oxygen vacancy-disordered perovskite oxide with cubic lattice symmetry is demonstrated by XRD, after the doping of only 5 mol% La3+ into BaFeO3−δ parent oxide with the formation of Ba0.95La0.05FeO3−δ (BLF). The structural, thermal, electrical and electrochemical properties of BLF have been evaluated. High structural stability, high thermal expansion coefficient, high oxygen vacancy concentration, and relatively low electrical conductivity, are demonstrated. BLF shows a superior electrocatalytic activity, which is comparable to those state-of-the-art cobalt-based mixed conducting cathodes, in addition, it demonstrates a favorable long-term operational stability. It thus promises as a new cathode candidate for IT-SOFCs with oxygen-ion conducting electrolyte.
Co-reporter:Yujing Sha, Bote Zhao, Ran Ran, Rui Cai and Zongping Shao
Journal of Materials Chemistry A 2013 - vol. 1(Issue 42) pp:NaN13243-13243
Publication Date(Web):2013/09/09
DOI:10.1039/C3TA12620J
As a lithium-intercalation material, high crystallinity is important for Li4Ti5O12 to achieve good capacity and cycling stability, while a large surface area and a short lithium diffusion distance are critical to increase rate capacity. In this study, well-crystallized Li4Ti5O12 nanoplates with outstanding electrochemical performance were facially prepared through a two-step hydrothermal preparation with benzyl alcohol–NH3·H2O (BN) as the solvent and a subsequent intermediate-temperature calcination at 500 °C for 2 h in air. To support the superiority of benzyl alcohol–NH3·H2O (BN) for hydrothermal synthesis, ethanol–NH3·H2O (EN) was also comparatively studied as solvent. In addition, different hydrothermal reaction times were tried to locate the optimal reaction time. The nature of as-prepared Li4Ti5O12–BN (LTO–BN) and Li4Ti5O12–EN (LTO–EN) was characterized by XRD, N2 adsorption/desorption tests, SEM, TEM and TGA-DSC. Compared with EN, the BN hydrothermal solvent facilitated the formation of nanosheet-Li4Ti5O12 with wall thicknesses of 8–15 nm and better crystallization. After a 6 h hydrothermal reaction at 180 °C and subsequent calcination, well-crystallized Li4Ti5O12–BN nanoplates were produced, which demonstrate a superior discharge capacity of 160 mA h g−1, even at 40 C, maintaining a capacity of 88.8% compared with that at 1 C. The nanoplates also exhibited excellent cycling stability, retaining a discharge capacity of 153 mA h g−1 after 1000 charge–discharge cycles at 10 C.
Co-reporter:Feifei Dong, Yubo Chen, Ran Ran, Dengjie Chen, Moses O. Tadé, Shaomin Liu and Zongping Shao
Journal of Materials Chemistry A 2013 - vol. 1(Issue 34) pp:NaN9791-9791
Publication Date(Web):2013/06/04
DOI:10.1039/C3TA11447C
Cobalt-free perovskite BaNb0.05Fe0.95O3−δ (BNF) is synthesized and characterized towards application as a cathode material for intermediate temperature solid oxide fuel cells. In situ X-ray diffraction and transmission electron microscopy are applied to study the crystal structure and thermally induced phase transformation. BNF exists as a multiphase structure composed of a monoclinic phase and a cubic phase at room temperature, and then undergoes a phase transformation to a cubic structure starting at ∼400 °C, which is maintained at temperatures up to 900 °C during a thermal cycle between room temperature and 900 °C; while it retains the cubic perovskite lattice structure on cooling from 900 °C to room temperature. Oxygen temperature-programmed desorption, combined thermal expansion and thermo-gravimetric analysis are used to clarify the thermal reducibility of BNF. A relatively good stability of BNF is demonstrated by electrical conductivity and electrochemical impedance spectroscopy measurements. The activity of BNF for oxygen reduction reaction is probed by symmetrical cell and single fuel cell tests. Favorable electrochemical activities at intermediate temperature, e.g. very low interfacial resistance of only ∼0.016 Ω cm2 and maximum power density of 1162 mW cm−2 at 750 °C, are demonstrated, which could be attributed to the cubic lattice structure of BNF within the temperature range of cell operation.
Co-reporter:Chao Su, Wei Wang, Ran Ran, Zongping Shao, Moses O. Tade and Shaomin Liu
Journal of Materials Chemistry A 2013 - vol. 1(Issue 18) pp:NaN5627-5627
Publication Date(Web):2013/03/05
DOI:10.1039/C3TA10538E
The feasibility of renewable acetic acid as a direct fuel of SOFCs for sustainable electric power generation was investigated. To solve the problem of carbon deposition over conventional nickel cermet anodes, an advanced catalyst for acetic acid catalytic decomposition/internal reforming reaction was exploited. A comparative study of coke formation over Ni/Al2O3, Ni/MgO–Al2O3 and Ni–YSZ catalysts was conducted by oxygen-temperature programmed oxidation analysis. We found that the Ni/MgO–Al2O3 catalyst is much superior to the other two catalysts in suppressing carbon deposition, especially under the condition of the presence of steam in the acetic acid fuel. Various cells were fabricated and tested under different conditions. The differences in OCVs and power outputs of the cells caused by the usage of hydrogen and acetic acid as fuels were studied and explained based on the thermodynamic calculation and EIS measurement. After optimization, a peak power density of 1325 mW cm−2 at a furnace temperature of 800 °C was achieved for the cell with a catalyst layer operating on acetic acid fuel. The cell was successfully operated continuously on acetic acid–steam fuel for a period of at least 200 h without any noticeable performance degradation, delamination of the catalyst layer and carbon deposition. The promising results of this work show the possibility of better utilization of the abundant bio-mass or bio-oil for future energy generation.
Co-reporter:Yixin Sun, Jie Wang, Bote Zhao, Rui Cai, Ran Ran and Zongping Shao
Journal of Materials Chemistry A 2013 - vol. 1(Issue 15) pp:NaN4746-4746
Publication Date(Web):2013/02/07
DOI:10.1039/C3TA01285A
We demonstrate a facile and effective way for the fabrication of a flexible, homogeneous and neat α-MoO3 thin-film electrode for lithium-ion batteries with high performance without using any binder and conductive additives. Single-crystalline α-MoO3 nanobelts with uniform width of around 200 nm and length at the micrometer level are first synthesized by a simple water-based hydrothermal route. The as-obtained α-MoO3 slurry is then directly deposited onto a copper foil current collector by the doctor blade method. The formation of the α-MoO3 film and its good adhesion to the current collector is realized via van der Waals attraction forces through a drying process. The structure and morphology of the α-MoO3 nanobelt particles and thin-film electrode are systematically characterized by XRD, Raman spectra, TEM, SEM and XPS techniques, and the electrochemical properties are investigated by CV and constant current discharge–charge test techniques. The α-MoO3 film electrode exhibits a reversible specific capacity of ∼1000 mA h g−1 at 50 mA g−1 and a stable capacity retention of 387–443 mA h g−1 at 2000 mA g−1, indicating its high Li storage capacity, superior rate performance and good cycling stability. The electrode material, as well as the fabrication technique, is highly promising for practical use in high energy and power density lithium-ion batteries.
Co-reporter:Wei Zhou, Zongping Shao, Ran Ran, Wanqin Jin and Nanping Xu
Chemical Communications 2008(Issue 44) pp:NaN5793-5793
Publication Date(Web):2008/10/01
DOI:10.1039/B813327A
A novel SrNb0.1Co0.9O3−δelectrode material, which possesses not only high electrical conductivity but also large oxygen vacancy concentration at 400–600 °C, shows an excellent performance in the application of reduced temperature solid-oxide fuel cells.
Co-reporter:Yingke Zhou, Jie Wang, Yuanyuan Hu, Ryan O’Hayre and Zongping Shao
Chemical Communications 2010 - vol. 46(Issue 38) pp:NaN7153-7153
Publication Date(Web):2010/08/02
DOI:10.1039/C0CC01721C
A novel composite electrode structure with highly-conductive 3D nanotube networks superimposed into interlaced porous LiFePO4 media was designed and realized via an in situ sol–gel process, yielding a high-performance multidimensional composite cathode for high-energy and high-power lithium-ion batteries.
Co-reporter:Zhenbao Zhang, Yubo Chen, Moses O. Tade, Yong Hao, Shaomin Liu and Zongping Shao
Journal of Materials Chemistry A 2014 - vol. 2(Issue 25) pp:NaN9674-9674
Publication Date(Web):2014/04/24
DOI:10.1039/C4TA00926F
In this study, we propose a new tin-doped perovskite oxide, BaCo0.7Fe0.2Sn0.1O3−δ (BCFSn0.1), as a promising alternative material for a ceramic oxygen-permeating membrane. A high energy ball milling-assisted solid-state reaction method is used for the material synthesis. The effect of tin doping on the structure, electrical conductivity, oxygen activity, oxygen bulk diffusivity and surface exchange properties of the materials, sintering behaviour, and oxygen permeability of the related membranes is systematically investigated via transmission electron microscopy (TEM), environmental scanning electron microscopy (E-SEM), thermo-gravimetric analysis (TGA), oxygen temperature-programmed desorption (O2-TPD) and electrical conductivity relaxation (ECR), and oxygen permeation test. The minor substitution of B-site cations in BaCo0.7Fe0.3O3−δ (BCF) with tin is found to be highly effective in improving oxygen flux of the resultant membrane. Under an oxygen gradient created by air/helium, BCFSn0.1 membrane reaches fluxes of 9.62 × 10−7 and 3.55 × 10−7 mol m−2 s−1 Pa−1 [STP], respectively, at 900 and 700 °C, in sharp contrast with the flux values of 4.42 × 10−7 and 2.84 × 10−8 mol m−2 s−1 Pa−1 for BCF membrane with the same thickness of 1 mm. Favorable permeation stability is also demonstrated for the tin-doped membrane, and oxygen bulk diffusion is the main rate-limiting step for oxygen permeation, indicating a further increase in fluxes by reducing the membrane thickness.
Co-reporter:Shanshan Jiang, Jaka Sunarso, Wei Zhou and Zongping Shao
Journal of Materials Chemistry A 2013 - vol. 1(Issue 36) pp:NaN11032-11032
Publication Date(Web):2013/07/16
DOI:10.1039/C3TA12376F
Layered oxides of Sr4Fe4Co2O13 (SFC2) which contains alternating perovskite oxide octahedral and polyhedral oxide double layers are attractive for their mixed ionic and electronic conducting and oxygen reduction reaction properties. In this work, we used the EDTA–citrate synthesis technique to prepare SFC2 and vary the calcination temperature between 900 and 1100 °C to obtain SFC2, containing different phase content of perovskite (denoted as SFC-P) and (Fe,Co) layered oxide phases (SFC-L). Rietveld refinements show that the SFC-P phase content increased from ∼39 wt% to ∼50 wt% and ∼61 wt% as the calcination temperature increased from 900 °C (SFC2-900) to 1000 °C (SFC2-1000) and 1050 °C (SFC2-1050). At 1100 °C (SFC2-1100), SFC-P became the dominant phase. The oxygen transport properties (e.g. oxygen chemical diffusion coefficient and oxygen permeability), electrical conductivity and oxygen reduction reaction activity is enhanced in the order of SFC2-1000, SFC2-1100 and SFC2-1050. The trend established here therefore negates the hypothesis that the perovskite phase content correlates with the oxygen transport property enhancement. The results suggest instead that there is an optimum composition value (e.g. 61 wt% of SFC-L for SFC2-1050 in this work) on which synergistic effects take place between the SFC-P and SFC-L phase.
Co-reporter:Bote Zhao, Simin Jiang, Chao Su, Rui Cai, Ran Ran, Moses O. Tadé and Zongping Shao
Journal of Materials Chemistry A 2013 - vol. 1(Issue 39) pp:NaN12320-12320
Publication Date(Web):2013/08/08
DOI:10.1039/C3TA12770B
To develop high-power and fast energy storage devices, electrode materials with superior ionic and electronic transport properties should be developed. Herein, a novel composite electrode with TiO2 nanotubes connected onto a conductive carbon nanofiber network is designed and realized through a general route. The carbon matrix is first synthesized using an electrospinning technique and heat-treatment, and the embedded rutile TiO2 nanoparticles are formed in situ as the starting materials for the hydrothermal reaction. After hydrothermal treatment, a three-dimensional (3D) porous architecture is developed. The mechanistic analysis demonstrates that the raw embedded rutile TiO2 nanoparticles react with NaOH solution and go out around the carbon nanofiber matrix to form a well-connected 3D porous nanotube/nanofiber architecture. By using the as-prepared films as electrodes for lithium-ion batteries (LIBs) without the application of any additional conductive agent or binder, high initial capacity and excellent rate performance (214 mA h g−1 at 5 C rate, 180 mA h g−1 at 10 C rate, 138 mA h g−1 at 20 C rate and 112 mA h g−1 at 30 C rate) are achieved. Moreover, the electrode shows stable cycling performance, especially at a high rate of 30 C, without undergoing decay after 1000 cycles.
Co-reporter:Bote Zhao, Xing Yu, Rui Cai, Ran Ran, Huanting Wang and Zongping Shao
Journal of Materials Chemistry A 2012 - vol. 22(Issue 7) pp:NaN2907-2907
Publication Date(Web):2011/12/22
DOI:10.1039/C1JM14362J
A facile way for the synthesis of LiFePO4 composite using a solution combustion technique based on the glycine–nitrate process with inexpensive iron (III) as the raw material is introduced. Pure phase LiFePO4 was obtained at an optimal glycine to LiFePO4 ratio of 4:1. To further increase the electrode performance, sucrose is applied as an organic carbon source. The introduction of sucrose after the auto-combustion is found to be the most effective way in improving electrode performance. The as-synthesized LiFePO4/C sample contained about 2.86 wt.% carbon shows an attractive discharge capacity of about 160 mA h g−1 at a 0.1 C rate and retains a capacity of 110 mA h g−1 at a 5 C rate. In addition, the electrodes show excellent cycling performance during the 90 cycles at various rates. The rate limiting step for the electrode reaction is explored with the chronoamperometry technique and it demonstrates the surface kinetics is effectively improved for the LiFePO4 electrode modified with a proper amount of carbon.
Co-reporter:Shanshan Jiang, Fengli Liang, Wei Zhou and Zongping Shao
Journal of Materials Chemistry A 2012 - vol. 22(Issue 32) pp:NaN16218-16218
Publication Date(Web):2012/06/27
DOI:10.1039/C2JM33311B
A 3D hierarchical porous ceramic electrode is fabricated directly from a carbon-oxides precursor by a general, cost-effective, and facile method. The oxygen reduction reaction activity of the electrode is significantly enhanced due to enlarged active areas and optimized gas transport channels. For the first time, this study demonstrates that a cobalt-free cathode is able to reach the target area specific resistance value of 0.15 Ω cm2 at 600 °C. The new material has been successfully used as the cathode for a SOFC and shows high power generation ability below 600 °C.
Co-reporter:Zinan Wan, Rui Cai, Simin Jiang and Zongping Shao
Journal of Materials Chemistry A 2012 - vol. 22(Issue 34) pp:NaN17781-17781
Publication Date(Web):2012/07/06
DOI:10.1039/C2JM33346E
It is believed that a TiN coating can increase the electrical conductivity, and consequently the performance, of an electrode. In this work, a simple one-step synthesis of nitrogen- and TiN-modified Li4Ti5O12, i.e. solid-state reaction of Li2CO3 and TiO2 anatase in an ammonia-containing atmosphere, is introduced. The reducing ammonia atmosphere could cause the partial reduction of Ti4+ to Ti3+ and the doping of nitrogen into the Li4Ti5O12 lattice, in addition to the formation of the TiN phase. By controlling the ammonia concentration of the atmosphere and using a slight Ti excess in the reactants, Li4Ti5O12, nitrogen-doped Li4Ti5O12, or TiN-coated nitrogen-doped Li4Ti5O12 were obtained. Both the electrical conductivity and the TiN thickness were closely related to the ammonia concentration in the atmosphere. Synthesis under reducing atmosphere also resulted in powders with a different plate shape particulate morphology from that synthesized in air, and such plate-shape powders had an ultrahigh tap density of ∼1.9 g cm−3. Interestingly, the formation of TiN was not beneficial for capacity improvement due to its insulation towards lithium ions, unlike the nitrogen doping. The sample prepared under 3% NH3–N2, which was free of TiN coating, showed the best electrode performance with a capacity of 103 mA h g−1 even at 20 C with only 3% capacity decay after cycling 100 times.
Co-reporter:Rui Cai, Simin Jiang, Xing Yu, Bote Zhao, Huanting Wang and Zongping Shao
Journal of Materials Chemistry A 2012 - vol. 22(Issue 16) pp:NaN8021-8021
Publication Date(Web):2012/03/14
DOI:10.1039/C2JM15731D
An amenable method for improving rate performance of Li4Ti4.85Al0.15O12 electrode by post-synthesis treatment in formaldehyde aqueous solution at room temperature is introduced. The as-prepared samples are characterized by XRD, BET, SEM, HR-TEM, XPS and electronic conductivity measurement. The treatment causes no noticeable change on the phase structure and has only little effect on the specific surface area and particulate morphologies. It also only slightly decreases the lithium ion diffusion coefficient. However, it substantially increases the electronic conductivity due to the creation of Ti3+ in the oxide lattice. The post-synthesis treatment for a period of 4 h effectively increases the capacity at 10 C rate for Li4Ti4.85Al0.15O12 from 125 mA h g−1 for the untreated sample to 160 mA h g−1, and the electrode performance is also fairly stable. This method is highly attractive for synthesis of high-performance Li4Ti5O12 electrodes owing to its simplicity, energy saving and efficiency. As a general method, post-synthesis treatment using formaldehyde may be applicable to other electrodes.
