Co-reporter:Yukwon Jeon;Jae-ha Myung;Sang-hoon Hyun;Yong-gun Shul
Journal of Materials Chemistry A 2017 vol. 5(Issue 8) pp:3966-3973
Publication Date(Web):2017/02/21
DOI:10.1039/C6TA08692F
An efficient cathode for solid oxide fuel cells (SOFC) is mainly determined by the oxygen reduction reaction (ORR) activity of mixed materials. We demonstrate a new microstructure design through a nanofibrous electrode based on a unique corn-cob structure. A one-step process to produce corn-cob ceramic nanofibers of La0.8Sr0.2MnO3 (LSM) and Y2O3-stabilized ZrO2 (YSZ) is introduced using an electrospinning system equipped with a coaxial nozzle. From the microscope analysis, perfect corn-cob nanofibers are finely produced with a diameter of 350 nm for the core and nanoparticles (30–40 nm) stacked on the surface similar to a core–shell structure. The cathode fabricated using nanofibers with LSM outside and YSZ inside (YSZ@LSM) shows the best maximum power density of 1.15 W cm−2 at 800 °C with low polarization resistance, which is higher than that of the reverse core and shell positions (LSM@YSZ) and even the commercial LSM–YSZ. This better outcome is more prominent at elevated temperatures due to its accelerated catalytic activity. Therefore, insight into the key factors that enhance ORR activity and single cell performance is obtained in terms of not only the nanofibrous core@shell structure but also more reaction active sites from the optimum catalyst position at the designed corn-cob nanofiber based cathodes.
Co-reporter:Cairong Jiang;Jianjun Ma;Gael Corre;Sneh L. Jain
Chemical Society Reviews 2017 vol. 46(Issue 10) pp:2889-2912
Publication Date(Web):2017/05/22
DOI:10.1039/C6CS00784H
A direct carbon fuel cell (DCFC) can produce electricity with both superior electrical efficiency and fuel utilisation compared to all other types of fuel cells. Although the first DCFC prototype was proposed in 1896, there was, until the 1970s, little sustained effort to investigate further, because of technology development issues. Interest in DCFCs has recently been reinvigorated as a possible method of replacing conventional coal-fired power plants to meet the demands for lower CO2 emissions, and indeed for efficient utilisation of waste derived chars. In this article, recent developments in direct carbon conversion are reviewed, with the principal emphasis on the materials involved. The development of electrolytes, anodes and cathodes as well as fuel sources is examined. The activity and chemical stability of the anode materials are a critical concern addressed in the development of new materials. Redox media of molten carbonate or molten metal facilitating the transportation of ions offer promising possibilities for carbon oxidation. The suitability of different carbon fuels in various DCFC systems, in terms of crystal structure, surface properties, impurities and particle size, is also discussed. We explore the influence of a variety of parameters on the electrochemical performance of DCFCs, with regard to their open circuit voltage, power output and lifetime. The challenges faced in developing DCFCs are summarised, and potential prospects of the system are outlined.
Co-reporter:Jianing Hui;Guan Zhang;Chengsheng Ni
Chemical Communications 2017 vol. 53(Issue 72) pp:10038-10041
Publication Date(Web):2017/09/05
DOI:10.1039/C7CC05144A
Cation defects in La and Cr co-doped SrTiO3 have been specifically studied for elucidating correlations between defect concentration, electronic properties, structural properties and photocatalytic activity for H2 production. A moderate cation deficiency can promote the photocatalytic activity by ca. 3 fold, which can be mainly linked to the enhancement of the charge carrier mobility.
Co-reporter:Elena Stefan, Dragos Neagu, Peter Blennow Tullmar, Åsa Helen Persson, Bhaskar R. Sudireddy, David Miller, Ming Chen, John Irvine
Materials Research Bulletin 2017 Volume 89(Volume 89) pp:
Publication Date(Web):1 May 2017
DOI:10.1016/j.materresbull.2017.02.003
•A successful method of solution infiltration is used for coating porous metals.•Continuous spinel coatings were successfully prepared on porous metal scaffolds.•Traces of Si favoured infiltration of aqueous solutions and forming spinel coatings.Metal supports and metal supported half cells developed at DTU are used for the study of a solution infiltration approach to form protective coatings on porous metal scaffolds. The metal particles in the anode layer, and sometimes even in the support may undergo oxidation in realistic operating conditions leading to severe cell degradation. Here, a controlled oxidation of the porous metal substrate and infiltration of Mn and/or Ce nitrate solutions are applied for in situ formation of protective coatings. Our approach consists of scavenging the FeCr oxides formed during the controlled oxidation into a continuous and well adhered coating. The effectiveness of coatings is the result of composition and structure, but also of the microstructure and surface characteristics of the metal scaffolds.Download high-res image (204KB)Download full-size image
Co-reporter:X. Yue;J. T. S. Irvine
Journal of Materials Chemistry A 2017 vol. 5(Issue 15) pp:7081-7090
Publication Date(Web):2017/04/11
DOI:10.1039/C6TA09421J
Extensive efforts have been made to find new fuel electrode materials for solid oxide cells with high activity and durability to provide more robust materials than state-of-the-art materials, Ni-cermets. In the present study, a Ni-free cathode with competitive performance and higher durability than a well performing Ni–YSZ cermet for CO2 electrolysis using SOECs is prepared. A (La, Sr)(Cr, Mn)O3/(Gd, Ce)O2 (LSCM/GDC) cathode fabricated by vacuum infiltration of GDC nitrate solutions into a LSCM/YSZ (8 mol% yttria stabilised zirconia) skeleton is reported. A porous YSZ layer introduced between the dense electrolyte and this cathode helps to maintain a good cathode/electrolyte interface, whilst the nano-structured GDC phase introduced on the surface of the LSCM/YSZ backbone is advantageous to boost the electrochemical and catalytic properties of the cathode towards CO2 reduction using SOECs. Vacuum impregnation therefore offers an effective means to modify the microstructure of the LSCM/GDC material used as a cathode for high temperature CO2 electrolysis. With the doping of a Pd co-catalyst after GDC impregnation, the cathodic activity of the GDC impregnated LSCM material is further enhanced for high temperature CO2 electrolysis, and the 0.5 wt% Pd and GDC co-impregnated LSCM cathode achieves an Rp value of 0.24 Ω cm2 at OCV at 900 °C in a CO2–CO 70–30 mixture, a comparable level to that of a high performance Ni–YSZ cathode operated under identical conditions.
Co-reporter:M. Naeem Khan, C.D. Savaniu, A.K. Azad, Peter Hing, J.T.S. Irvine
Solid State Ionics 2017 Volume 303(Volume 303) pp:
Publication Date(Web):1 May 2017
DOI:10.1016/j.ssi.2017.01.001
Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3 − δ (BSCZGY) proton conducting electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs) has been synthesized by a sol-gel modified Pechini process and its sinterability, thermal expansion, microstructure, ionic conductivity and chemical stability have been investigated. Ionic conductivity at 700 °C was measured to be ~ 8 × 10− 3 S cm− 1 in wet 5 vol.% H2/Ar atmospheres. Chemical stability test in pure CO2 up to 1200 °C shows that the material is highly stable; better than the stability of BaZr0.3Ce0.5Y0.1Yb0.1O3 − δ.
Co-reporter:Jun Zhou, Tae-Ho Shin, Chengsheng Ni, Gang Chen, Kai Wu, Yonghong Cheng, and John T. S. Irvine
Chemistry of Materials 2016 Volume 28(Issue 9) pp:2981
Publication Date(Web):April 11, 2016
DOI:10.1021/acs.chemmater.6b00071
Compared to traditional deposition techniques, in situ growth of nanoparticles on material surfaces is one of the more time- and cost-effective ways to design new catalysts. The B-site transition-metal cations in perovskite lattice could be partially exsolved as nanoparticles under reducing conditions, greatly enhancing catalytic activity. Here, we demonstrate that growing nanoparticles on the surface of a layered perovskite La0.8Sr1.2Fe0.9Co0.1O4±δ (LSFC), which could be applied as a redox stable and active electrode for intermediate-temperature symmetrical solid oxide fuel cells (IT-SSOFCs). Substitution of a proper amount of Co into the layered perovskite can thus optimize cathode and anode performance simultaneously. For example, the polarization resistances (Rp) of LSFC electrode at 800 °C are 0.29 and 1.14 Ω cm2 in air and in 5% H2/N2 respectively, which are much smaller compared with the Rp of Co-free La0.8Sr1.2FeO4±δ. The lower polarization resistance for LSFC in air can be mainly attributed to the enhanced electrical conductivity through the partial substitution of iron by cobalt in La0.8Sr1.2FeO4±δ. Meanwhile, the electrocatalytic activity of H2 greatly improved, because of the formation of exsolved homogeneous Co0 nanoparticles on the surface of LSFC, which appears to promote hydrogen oxidation reaction. Lower polarization resistance of 0.21 Ω cm2 in air and 0.93 Ω cm2 in 5% H2/N2 at 800 °C could be obtained further by examining an LSFC–Gd0.1Ce0.9O2−δ (CGO) composite as an electrode for IT-SSOFCs.
Co-reporter:Lanying Lu, Chengsheng Ni, Mark Cassidy and John T. S. Irvine
Journal of Materials Chemistry A 2016 vol. 4(Issue 30) pp:11708-11718
Publication Date(Web):28 Jun 2016
DOI:10.1039/C6TA04074H
Perovskite electrodes have been considered as an alternative to Ni-YSZ cermet-based anodes as they afford better tolerance towards coking and impurities and due to redox stability can allow very high levels of fuel utilisation. Unfortunately performance levels have rarely been sufficient, especially for a second generation anode supported concept. A-site deficient lanthanum and calcium co-doped SrTiO3, La0.2Sr0.25Ca0.45TiO3 (LSCTA-) shows promising thermal, mechanical and electrical properties and has been investigated in this study as a potential anode support material for SOFCs. Flat multilayer ceramics cells were fabricated by aqueous tape casting and co-sintering, comprising a 450 μm thick porous LSCTA- scaffold support, a dense YSZ electrolyte and a thin layer of La0.8Sr0.2CoO3−δ (LSC)-La0.8Sr0.2FeO3−δ (LSF)-YSZ cathode. Impregnation of a small content of Ni significantly enhanced fuel cell performance over naked LSCTA-. Use of ceria as a co-catalyst was found to improve the microstructure and stability of impregnated Ni and this in combination with the catalytic enhancement from ceria significantly improved performance over Ni impregnation alone. With addition of CeO2 and Ni to a titanate scaffold anode that had been pre-reduced at 1000 °C, a maximum powder density of 0.96 W cm−2 can be achieved at 800 °C using humidified hydrogen as fuel. The encouraging results show that an oxide anode material, LSCTA- can be used as anode support with YSZ electrolyte heralding a new option for SOFC development.
Co-reporter:Amit Sinha, David N. Miller and John T. S. Irvine
Journal of Materials Chemistry A 2016 vol. 4(Issue 28) pp:11117-11123
Publication Date(Web):21 Jun 2016
DOI:10.1039/C6TA03404G
Solid oxide fuel cells (SOFC) offer a clean technology to electrochemically generate electricity and heat from hydrogen or hydrocarbon based fuel at high efficiencies. All the active components of the SOFC unit cell comprise of rare-earth or low abundant elements. An increase in the cost of rare-earths is likely to jeopardize the commercialization prospects of SOFC based technologies. Hence, a greater scientific effort should be focused on the development of rare-earth free SOFC materials. The previous research works on electrode-supported intermediate temperature solid oxide fuel cells (IT-SOFCs) indicate that the anode supported concept provides better electro-chemical performance than the cathode supported one. Therefore, the total material cost of anode-supported SOFC is largely governed by the cost of the anode material. The objective of the present investigation was, therefore, the development of a rare-earth free anode material for IT-SOFC. The present work envisages application of titanium oxycarbide as a possible rare-earth free anode material for intermediate temperature solid oxide fuel cells. Titanium oxycarbide samples (TiOxC1−x with x = 0.2–0.8) were prepared by reaction-sintering of TiO and TiC powders under vacuum at 1500 °C for 5 h. Basic studies on TiOxC1−x (x = 0.2–0.8) with respect to phase purity and stability under oxidizing and reducing environments were carried out. The compatibility of titanium oxycarbide with intermediate-temperature electrolyte material (Ce0.9Gd0.1O3−δ) was studied. The electrochemical properties of planar cells using Ce0.9Gd0.1O3−δ as electrolyte and employing TiO0.2C0.8 and La0.8Sr0.2Co0.2Fe0.8O3−δ based anode and cathode materials were investigated. The present study indicates that titanium oxycarbide is an alternative anode material for IT-SOFC. This is the first report on the possibility of application of a rare-earth free ceramic in the form of titanium oxycarbide as a potential fuel electrode in IT-SOFC.
Co-reporter:Guan Zhang, Chengsheng Ni, Xiubing Huang, Aakash Welgamage, Linda A. Lawton, Peter K. J. Robertson and John T. S. Irvine
Chemical Communications 2016 vol. 52(Issue 8) pp:1673-1676
Publication Date(Web):07 Dec 2015
DOI:10.1039/C5CC09075J
Photocatalytic conversion of cellulose to sugars and carbon dioxide with simultaneous production of hydrogen assisted by cellulose decomposition under UV or solar light irradiation was achieved upon immobilization of cellulose onto a TiO2 photocatalyst. This approach enables production of hydrogen from water without using valuable sacrificial agents, and provides the possibility for recovering sugars as liquid fuels.
Co-reporter:Alfredo Damiano Bonaccorso, Cairong Jiang, Jianjun Ma, John T.S. Irvine
International Journal of Hydrogen Energy 2016 Volume 41(Issue 41) pp:18788-18796
Publication Date(Web):2 November 2016
DOI:10.1016/j.ijhydene.2016.01.115
•Current collection configurations show to be a crucial aspect for a tubular HDCFC.•Good cell performance was improved using current collector with high surface contact.•Ea of anodic reactions was studied depending on the current collector configurations.•Toku P-24 composite shows high resistance to carbonate and high sealing performance.Direct Carbon Fuel Cells (DCFC) offer efficient conversion of coal or biomass derived carbons to electricity. A Hybrid Direct Carbon Fuel Cell (HDCFC) is a type of DCFCs that combines solid oxide cell geometry with a molten carbonate fuel cell electrode. This study focused on investigating different current collection configurations and sealant for tubular HDCFC concept. A HDCFC used a gadolinia doped ceria (GDC) or a YSZ as the electrolyte, in composites with NiO and LSM as the anode and the cathode, respectively. Three different current collection configurations of HDCFC were investigated by AC impedance in order to study the electrochemical phenomena that occur at the electrodes surface. The AC impedance results showed that both the surface area and the position of the current collector inside of the anode chamber affect drastically both the series resistance (Rs) and the polarisation resistance (Rp) values. The lowest total resistance (Rtot) was achieved on Configuration b with silver wire interwoven nickel mesh attached to the side of the anode wall by silver paste (Rtot = 2.98 Ω) and while the highest Rtot was achieved on the configuration c with silver wire interwoven nickel mesh inserted into the mixture of carbon and carbonate (Rtot = 149 Ω). The leak test carried out on several sealants demonstrated that composite sealants of Toku P-24 paste and an alumina silicate disc produced a low degree of leaks due to both the high resistance to the carbonate mixture and high density sealing after curing compared to the ceramabond.
Co-reporter:Cairong Jiang, Jianjun Ma, Ana Arenillas, A. Damiano Bonaccorso, John T.S. Irvine
International Journal of Hydrogen Energy 2016 Volume 41(Issue 41) pp:18797-18806
Publication Date(Web):2 November 2016
DOI:10.1016/j.ijhydene.2016.04.047
•Raw anthracite coals and raw bituminous coals are investigated as the fuel for hybrid direct carbon fuel cells.•Mechanical mixing is an efficient way to mix carbonate with carbon.•The short-term and long-term durability of the HDCFCs are evulated.•A HDCFC with bituminous coal shows slower performance drop in the first 10 h.•HDCFC with 1.6 g anthracite coal has been operating for 160 h.Direct carbon fuel cells offer the opportunity of generating energy from coal at high efficiency as an alternative to the procedure of conventional power plants. In this study, raw anthracite coal and raw bituminous coal were investigated in a hybrid direct carbon fuel cell (HDCFC), which was a combination of a solid oxide fuel cell and a molten carbonate fuel cell. Mechanical mixing was confirmed to be an efficient method of mixing coal with carbonate. The coal samples had different properties, for example, carbon content, hydrogen content, volatile matter and impurities. The results showed that the maximum power density obtained by the cell with anthracite coal was similar to that obtained by the cell with bituminous coal. It was found that the total power output from coal in HDCFCs mostly depended on the carbon content, while volatile matter, hydrogen content, moisture, etc. had an effect on the short-term durability. HDCFCs were kept operating for more than 120 h with 1.6 g coal. This study demonstrates that energy can be generated efficiently by employing anthracite and bituminous coal in hybrid direct carbon fuel cells.
Co-reporter:Federica Fina, Samantha K. Callear, George M. Carins, and John T. S. Irvine
Chemistry of Materials 2015 Volume 27(Issue 7) pp:2612
Publication Date(Web):March 23, 2015
DOI:10.1021/acs.chemmater.5b00411
Graphitic carbon nitride (g-C3N4) has, since 2009, attracted great attention for its activity as a visible-light-active photocatalyst for hydrogen evolution. Since it was synthesized in 1834, g-C3N4 has been extensively studied both catalytically and structurally. Although its 2D structure seems to have been solved, its 3D crystal structure has not yet been confirmed. This study attempts to solve the 3D structure of graphitic carbon nitride by means of X-ray diffraction and of neutron scattering. Initially, various structural models are considered and their XRD patterns compared to the measured one. After selecting possible candidates as g-C3N4 structure, neutron scattering is employed to identify the best model that describes the 3D structure of graphitic carbon nitride. Parallel chains of tri-s-triazine units organized in layers with an A–B stacking motif are found to describe the structure of the synthesized graphitic carbon nitride well. A misalignment of the layers is favorable because of the decreased π–π repulsive interlayer interactions.
Co-reporter:Xiubing Huang, Tae Ho Shin, Jun Zhou and John T. S. Irvine
Journal of Materials Chemistry A 2015 vol. 3(Issue 25) pp:13468-13475
Publication Date(Web):28 May 2015
DOI:10.1039/C5TA00983A
Hierarchically nanoporous materials based on layered perovskite oxides La1.7Ca0.3NixCu1−xO4−δ (x = 0, 0.25, 0.50 or 0.75) have been synthesized by a facile citrate-modified evaporation-induced self-assembly (EISA) method. These La1.7Ca0.3NixCu1−xO4−δ oxides have been evaluated as potential cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs) with Ni–YSZ cermet supported type cells. It was found that La1.7Ca0.3CuO4−δ cathode exhibits the maximum power density at high temperature (e.g., 1.5 W cm−2 at 850 °C), while La1.7Ca0.3Ni0.75Cu0.25O4−δ cathode shows the highest power density at intermediate temperature (e.g. 0.71 W cm−2 at 750 °C) using humidified H2 and air as the fuel and oxidant, respectively. The electrochemical performance of single cells with La1.7Ca0.3Ni0.75Cu0.25O4−δ cathode materials with different morphologies demonstrated better performance in the intermediate temperature range when using the cathode prepared by the citrate-modified EISA method, which has a bigger grain size, but with higher surface area and pore volumes.
Co-reporter:Jianjun Ma, Cairong Jiang, Paul A. Connor, Mark Cassidy and John T. S. Irvine
Journal of Materials Chemistry A 2015 vol. 3(Issue 37) pp:19068-19076
Publication Date(Web):2015/08/18
DOI:10.1039/C5TA06421J
Solid oxide fuel cells (SOFCs) afford an opportunity for the direct electrochemical conversion of biogas with high efficiency; however, direct utilisation of biogas in nickel-based SOFCs is a challenge as it is subject to carbon deposition. A biogas composition representative of a real operating system of 36% CH4, 36% CO2, 20% H2O, 4% H2 and 4% CO used here was derived from an anode recirculation method. A BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BCZYYb) infiltrated Ni-YSZ anode was investigated for biogas conversion. The infiltration of BCZYYb significantly promoted the electrochemical reactions and the cells exhibited high power output at the operational temperatures of 850, 800 and 750 °C. At 800 °C, supplied with a 20 ml min−1 biogas, the cell with a BCZYYb-Ni-YSZ anode, generated 1.69 A cm−2 at 0.8 V with an optimal amount of 0.6 wt% BCZYYb, whereas only 0.65 A cm−2 was produced with a non-infiltrated Ni-YSZ in the same conditions. At 750 °C, a maximum power density of 1.43 W cm−2 was achieved on a cell with a BCZYYb-Ni-YSZ anode, a 3 μm dense YSZ film electrolyte, a Gd0.1Ce0.9O2 (GDC) buffer layer and a La0.6Sr0.4Co0.2Fe0.8O3–Gd0.1Ce0.9O2 (LSCF-GDC) composite cathode. The cell remained stable, while operating at 0.8 V for 50 hours with a current density of 1.25 A cm−2. A well-designed cell structure and selected components made it possible to obtain excellent performance at good fuel utilisation. The analysis of gases in open-circuit conditions or under various current loads suggested that the prevalent reaction was reforming of methane without coking. This study demonstrates that the BCZYYb-Ni-YSZ is a promising electrode for carbon-containing fuel.
Co-reporter:Guan Zhang, Chengsheng Ni, Lingjuan Liu, Guixia Zhao, Federica Fina and John T. S. Irvine
Journal of Materials Chemistry A 2015 vol. 3(Issue 30) pp:15413-15419
Publication Date(Web):03 Jul 2015
DOI:10.1039/C5TA03628C
We have demonstrated that resorcinol–formaldehyde resin polymers are good visible light responsive photocatalysts, with band gap energies ranging from ca. 1.80 to 2.00 eV. They were found to be photoactive in terms of decomposition of organic substrates under visible light irradiation. The photocatalytic performance of resins could be markedly enhanced by coupling with electron conducting materials such as reduced graphene oxide. Photocatalytic water oxidation was also achievable on the hybrid reduced graphene oxide/resin catalyst with a sacrificial agent. These industrial widely-used resins exhibit many merits as photocatalysts such as low-cost, high surface area, large pore size and volume, facile preparation and scalability for development of eco-friendly commercial products with “self-cleaning” properties, based on their capability for the oxidative removal of organic pollutants under visible light.
Co-reporter:Guixia Zhao, Xiubing Huang, Xiangke Wang, Paul Connor, Jiaxing Li, Shouwei Zhang and John T. S. Irvine
Journal of Materials Chemistry A 2015 vol. 3(Issue 1) pp:297-303
Publication Date(Web):31 Oct 2014
DOI:10.1039/C4TA05376A
In this report, a novel method is proposed to prepare MnO/reduced graphene oxide (rGO) composites via calcining the precursors (i.e. δ-MnO2/graphene oxide composites) at 500 °C in Ar using no external reducing gas, in which graphene oxide (GO) successfully serves as a reductant by releasing CO during its thermolysis for the first time. By controlling the initial ratios of GO to KMnO4, differently composed precursors can be obtained via the redox reaction between GO and KMnO4, then leading to the formation of composites with different MnO/rGO ratios and dispersion of MnO on the rGO surface (denoted as MGC1 and MGC2). When applied as an active material in lithium ion batteries, MGC1 shows excellent cycling performance and capacity retention. Under 100 and 200 mA g−1, MGC1 could deliver reversible capacities as high as 900 and 750 mA h g−1, respectively, after more than 100 cycles. Considering the simple operation and low energy consumption in the whole material synthesis processes, the present strategy is feasible and effective for practical application. Even more importantly, the reductibility of graphene oxide upon thermolysis is utilized for the first time, which is meaningful for its extension in synthesis of functional nanomaterials.
Co-reporter:Xiubing Huang, Chengsheng Ni, Guixia Zhao and John T. S. Irvine
Journal of Materials Chemistry A 2015 vol. 3(Issue 24) pp:12958-12964
Publication Date(Web):12 May 2015
DOI:10.1039/C5TA01361E
Fast and reversible oxygen diffusion in solid oxides depending on oxygen partial pressure at low temperatures is a promising strategy for improving the overall performance and service lifetime of many energy-related materials. However, the high energy required for the redox reaction of cations and their high thermodynamic barriers have impeded the realization of fast oxygen diffusion at low temperatures. Herein, we report enhanced oxygen diffusion and storage capacity of monoclinic crednerite CuMnO2 at a lower temperature by surface modification with CeO2. The fast and reversible oxygen uptake/release can be attributed to CeO2 that serves as a fast oxygen diffusion channel between bulk CuMnO2 and the surrounding atmospheres. Importantly, the amount of CeO2 in the CuMnO2–CeO2 composite system has a great effect on the total oxygen storage capacity and redox behaviour. Our findings could provide useful information for developing effective oxygen storage materials for wide energy-related applications.
Co-reporter:Guixia Zhao, Xiubing Huang, Federica Fina, Guan Zhang and John T. S. Irvine
Catalysis Science & Technology 2015 vol. 5(Issue 6) pp:3416-3422
Publication Date(Web):28 Apr 2015
DOI:10.1039/C5CY00379B
In this work, two photocatalysts (i.e., C3N4 and WO3) were successfully combined into a heterojunction structure by a facile hydrothermal method for mediator-free overall water splitting, analogous to the natural photosynthesis over a two-step photoexcitation Z-scheme system. Hydrogen and oxygen are evolved with a 2:1 ratio by irradiating the C3N4-WO3 composites loaded with Pt under visible light (λ > 420 nm) without any redox mediator. Introducing reduced graphene oxide (rGO) into the C3N4-WO3 composites enhances the water splitting efficiency. Through optimizing the mass ratio in the C3N4-WO3 composites, rGO content, amount of loaded Pt and pH value of the reacting system, the highest H2/O2 evolution rates of 2.84 and 1.46 μmol h−1 can be obtained, with a quantum yield of 0.9%. Our findings demonstrate that the hydrothermal method is a promising strategy for constructing intimate heterostructures for Z-scheme water-splitting systems without using any redox mediator, and that rGO can be used to further enhance the performance in optimized conditions.
Co-reporter:F. Fina, H. Ménard and J. T. S. Irvine
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 21) pp:13929-13936
Publication Date(Web):30 Apr 2015
DOI:10.1039/C5CP00560D
Loading of a co-catalyst on the surface of a semiconductor photocatalyst is often carried out without considering the effect of the loading procedure on the final product. The present study looks in detail at the effect that the loading method has on the morphology and final composition of platinum-based nanoparticles by means of XPS and TEM analysis. Additionally, reduction pre-treatments are performed to investigate how the coverage, crystallinity and composition of the NPs affect the photocatalytic H2 evolution. The activity of Pt–g-C3N4 can significantly be enhanced by controlling the properties of the co-catalyst NPs.
Co-reporter:Ahmed D. Aljaberi and John T. S. Irvine
Dalton Transactions 2015 vol. 44(Issue 23) pp:10828-10833
Publication Date(Web):04 Mar 2015
DOI:10.1039/C5DT00238A
The crystal structures of several members of the solid solution perovskite La0.2Sr0.7−xCaxTiO3 were investigated using the Rietveld analysis of neutron powder diffraction patterns collected in ambient conditions and high temperatures. At room temperature, samples showed a tetragonal I4/mcm symmetry for compositions with 0.1 ≤ x ≤ 0.35 followed by a phase transition to the orthorhombic Pbnm symmetry for compositions with 0.4 ≤ x ≤ 0.7. Samples with the orthorhombic symmetry showed two reversible phase transitions in the temperature range 20 °C–900 °C. The first phase transition was a discontinuous Pbnm–I4/mcm around 300 °C and the second was a continuous I4/mcm–Pmm transition around 900 °C. The lower symmetries resulted from very small distortions and changes in tilts of the BO6 octahedra of this perovskite material; which was a direct result from the A-site ionic radius mismatch.
Co-reporter:Jae-ha Myung, Tae Ho Shin, Xiubing Huang, George Carins, John T.S. Irvine
International Journal of Hydrogen Energy 2015 Volume 40(Issue 35) pp:12003-12008
Publication Date(Web):21 September 2015
DOI:10.1016/j.ijhydene.2015.05.029
•Metal dopants (Ni, Cu, Co, Mn, Ti, Zr) were soluble in ceria lattice without secondary phases.•Metal doped ceria oxide enhanced the oxygen storage capacity and electrical conductivity.•Ni doped ceria anode for solid oxide fuel cell showed 0.15 W/cm2 at 800 °C.Various metal oxide materials have been actively investigated to improve energy efficiency as exhaust-catalyst as well as electrodes in electrochemical devices such as fuel cells, ceramic sensors, photo-catalyst etc. Ceria-based materials are of great interest due to their wide applications; such as redox or oxygen storage promoter in automotive catalyst and solid state conductor in fuel cells. Here we report redox and electrical properties for Ce1−xMxO2−δ (M = Ni, Cu, Co, Mn, Ti, Zr) by X-ray diffraction (XRD) and simultaneous thermo-gravimetric analysis (TGA). Among various system, Ce1−xCuxO2−δ and Ce1−xNixO2−δ indicated relatively reversible redox behavior, although Cu2+ and Ni2+ had limited solid solubility in CeO2. The enhancement of oxygen carrier concentration and electrical conductivity as well as electrochemical activity in the ceria lattice by the introduction of small amounts transition metal cations have been considered in this study. Ce0.7Cu0.3O2−δ showed about 1015 μmol[O2]/g of oxygen storage capacity (OSC) with high redox stability at 700 °C. We also demonstrated that Ce0.9Ni0.1O2−δ was used as an anode of the YSZ electrolyte supported SOFC single cell; the maximum power density was 0.15 W/cm2 at 850 °C with hydrogen fuel.
Co-reporter:Tae Ho Shin, Jae-ha Myung, Khan M. Naeem, Cristian Savaniu, John T.S. Irvine
Solid State Ionics 2015 Volume 275() pp:106-109
Publication Date(Web):July 2015
DOI:10.1016/j.ssi.2015.03.015
•CMF–LSFM composite was used for improving CO2 reduction in proton conducting SOECs.•The electrolysis cell, Ni–Fi|BCZYYZ|LSCF–GDC|CMF–LSF, showed 0.5 A/cm2 at 1.3 V at 700 °C.•The CMF–LSFM containing cell presented a lower polarisation resistance value.A solid oxide electrolysis cell concept for reducing CO2 to CO was studied using a proton conducting mixed oxide — BaCe0.7Zr0.1Y0.1Yb0.06Zn0.04O3 − δ (BCZYYZ) as an electrolyte. The oxide composite mixture: Ce0.6Mn0.3Fe0.1O2–La0.6Sr0.4Fe0.9Mn0.1O3 (12.5–87.5 wt.%) was examined as enhancing catalyst electrode for CO2 reduction and proton oxidation reaction on the cathode side for avoiding coke formation. Here we demonstrate the successful electrochemical reduction of CO2 in proton conducting SOECs. During electrochemical reduction of CO2 at 700 °C, current densities as high as 0.5 A/cm2 and 1 A/cm2 at 1.3 V and 2.2 V respectively, were withdrawn even though the cell employed a 400 μm thick BCZYYZ electrolyte support.
Co-reporter:Elena Stefan, Paul A. Connor, Abul K. Azad and John T. S. Irvine
Journal of Materials Chemistry A 2014 vol. 2(Issue 42) pp:18106-18114
Publication Date(Web):19 Sep 2014
DOI:10.1039/C4TA03633F
Novel electrode scaffold materials based on chromium-rich spinels, such as MgMxCr2−xO4, (M = Li, Mg, Ti, Fe, Cu, Ga) have been investigated for solid oxide fuel cell (SOFC) applications, in terms of conductivity and chemical stability when operated in fuel environments. Cation distributions were obtained by Rietveld refinement from X-ray diffraction data (XRD), with cation site preference considered in agreement with literature, and correlated with electrical properties determined experimentally. The substitutions with cations such as Li and Cu on B site improved the conductivity of the materials in air, while introducing Fe and Ga in the structure led to a decrease in conductivity in air. However, Fe had a positive contribution under reducing conditions, generating a change in the conductivity mechanism from p-type in air, to n-type. Conductivity measurements indicated that MgFexCr2−xO4 spinels exhibit faster reduction kinetics, in comparison with other substituted cations at the B site which is desirable in fuel cell application, for a reasonably fast response of a cell or a stack to reach its full functional potential. MgFeCrO4 showed fast reduction kinetics, with increase of the conductivity in reducing conditions from 0.014 S cm−1 to 0.4 S cm−1 and equilibration time for reaching the maximum conductivity value of 10 hours, under dry 5% H2/Ar at 850 °C.
Co-reporter:C. S. Ni, J. M. Vohs, R. J. Gorte and J. T. S. Irvine
Journal of Materials Chemistry A 2014 vol. 2(Issue 45) pp:19150-19155
Publication Date(Web):06 Oct 2014
DOI:10.1039/C4TA04789C
Infiltration of ceramic materials into a pre-formed ceramic scaffold is an effective way of fabricating a solid oxide fuel cell with nano-structured ceramic electrodes by avoiding detrimental interfacial reactions through low-temperature processing for achieving high performance using hydrogen as well as a carbonaceous fuel. However, there are significant concerns about the applicability of this method because of the difficulty in fabricating a large-area gas-tight but thin electrolyte between two highly porous ceramic and the multiple repetitions of infiltration process. Here, a large-area (5 cm by 5 cm) scaffold with a thin yttria-stabilized zirconia (YSZ) electrolyte sandwiched between two identical porous structures is prepared by tape casting and co-firing, and then solution precursors are impregnated into the porous scaffolds to prepare nano-structured La0.8Sr0.2FeO3 (LSF) and La0.7Sr0.3VO3−δ (LSVred). The thus prepared solid oxide fuel cell with 10 wt% ceria + 1 wt% Pd as a catalyst in anodes shows a peak power of 489 mW cm−2 (∼6 W per cell) at 800 °C using H2 as a fuel and air as an oxidant. This large-area fuel cell retained the integrity of the thin electrolyte and high performance after the reducing-oxidation cycle at 900 °C, showing superiority over the conventional Ni(O)-YSZ based support.
Co-reporter:George Tsekouras, Dragos Neagu and John T. S. Irvine
Energy & Environmental Science 2013 vol. 6(Issue 1) pp:256-266
Publication Date(Web):22 Nov 2012
DOI:10.1039/C2EE22547F
B-site doped, A-site deficient perovskite oxide titanates with formula La0.4Sr0.4Mn+xTi1−xO3−γ−δ (M = Fe3+ or Ni2+; x = 0.06; γ = (4 − n)x/2) were employed as solid oxide electrolysis cell (SOEC) cathodes for hydrogen production via high temperature steam electrolysis at 900 °C. A-site deficiency provided additional driving force for the exsolution of a proportion of B-site dopants at the surface in the form of metallic nanoparticles under reducing SOEC cathode operating conditions. In the case of La0.4Sr0.4Fe0.06Ti0.94O2.97, this represents the first time that Fe0 has been exsolved from a perovskite in such a way. Exsolution was due in part to the inability of the host lattice to accommodate vacancies (introduced (δ) oxygen vacancies () and fixed A-site () and inherent (γ) oxygen vacancies) beyond a certain limit. The presence of electrocatalytically active Fe0 or Ni0 nanoparticles and higher concentrations dramatically lowered the activation barrier to steam electrolysis compared to the parent material (x = 0). The use of defect chemistry to drive the exsolution of less reducible dopant cations could conceivably be extended to produce new catalytically active perovskites with unique properties.
Co-reporter:Ahmed D. Aljaberi and John T. S. Irvine
Journal of Materials Chemistry A 2013 vol. 1(Issue 19) pp:5868-5874
Publication Date(Web):20 Mar 2013
DOI:10.1039/C3TA10844A
Samples from across the solid solution series La0.2Sr0.7−xCaxTiO3, were successfully synthesised by solid state reaction. Structural properties were determined at room temperature using X-ray powder diffraction and conductivity measurements were performed using the four probe DC and van der Pauw techniques at different temperatures and atmospheres. On increasing x, the perovskite phase lattice symmetry changes from cubic Pmm to tetragonal I4/mcm at x = 0.05 and tetragonal to orthorhombic Pbnm at x = 0.425. The lattice also shrinks as x increases. Samples showed only a slight 0.3% increase in lattice volume after reduction at 900 °C in 5% H2. On increasing calcium doping, conductivity in reduced samples and equilibrated at 900 °C in 5%H2 increased markedly reaching 27.53 S cm−1 at x = 0.45, but decreased as x increased further.
Co-reporter:Elena Stefan, Paul A. Connor and John T. S. Irvine
Journal of Materials Chemistry A 2013 vol. 1(Issue 28) pp:8262-8269
Publication Date(Web):07 Jun 2013
DOI:10.1039/C3TA11496A
Composite anodes for solid oxide fuel cells (SOFC) developed on yttria stabilised zirconia (YSZ) porous supports by infiltration of electrode materials has been successfully applied for various anode and cathode compositions, resulting in high performance SOFC devices. The focus of this study is the performance of the chromium-rich spinel (MgFeCrO4) as an electrode support material when used alone or impregnated. The composite anodes were prepared by aqueous infiltration of nitrate salts to produce (La0.75Sr0.25)0.97Cr0.5Mn0.5O3−δ, Ce0.9Gd0.1O2−δ, CeO2 or Pd into a MgFeCrO4 scaffold with 45% porosity and studied by electrochemical impedance spectroscopy in symmetrical cell configuration. The performance was evaluated in humidified 5% H2/Ar in order to quantify their stability and performance up to 850 °C with respect to the MgFeCrO4 porous substrate. It was found that all the impregnated phases adhere very well to the spinel and considerably enhance performance and stability to a level required for SOFC applications. MgFeCrO4/LSCM/CGO and MgFeCrO4/LSCM/CGO/Pd showed the most substantial improvement in comparison to the scaffold’s performance, with ASR values of 1.74 Ω cm2 and 0.91 Ω cm2, respectively.
Co-reporter:Paraskevi Efstathiou, Xiaoxiang Xu, Hervé Ménard and John T. S. Irvine
Dalton Transactions 2013 vol. 42(Issue 22) pp:7880-7887
Publication Date(Web):18 Apr 2013
DOI:10.1039/C3DT32064B
Sr1−xNbO3 is an unusual material that displays both metallic type conduction and photocatalytic activity, despite being an NbIV oxide, and it sustains photo-oxidation without degradation. The influence of crystal structure, surface area and surface chemistry on the photocatalytic activity of strontium niobate has been investigated. The crystal structure of strontium niobate depends on the Sr content of the A site, with cubic symmetry for Sr ≤ 0.92 and orthorhombic symmetry for 0.92 < Sr ≤ 0.97. The change of crystal structure from cubic to orthorhombic symmetry seems to have a negative effect on the photocatalytic activity, as the NbO6 octahedra become distorted and unfavourable for d-orbital overlapping. The photocatalytic activity increased significantly by enlarging the surface area through ball milling, nevertheless, a clear trend for the surface area effect on activity is not obtained among samples with different Sr content. An enrichment of Sr on the surface of strontium niobate was observed by XPS, which seems to be a governing factor for improving stability.
Co-reporter:Andrew C. Chien, Gale Corre, Rui Antunes, John T.S. Irvine
International Journal of Hydrogen Energy 2013 Volume 38(Issue 20) pp:8497-8502
Publication Date(Web):9 July 2013
DOI:10.1016/j.ijhydene.2012.10.097
A hybrid direct carbon fuel cell (HDCFC), combining molten carbonate fuel cell (MCFC) and solid oxide fuel cell (SOFC) technologies, is capable of converting solid carbon directly into electrical energy without intermediate reforming. The performance level achieved on small-scale cells (area <4 cm2) suggests that engineering developments should now be undertaken to scale up and demonstrate the feasibility of practical systems. The scaling up of the HDCFC through the design and test of single stack repeat unit with realistic cell sizes was investigated in this study. A single cell of ∼12.56 cm2 active area produced a maximum power of ∼1.2 W at 800 °C and a current density of ∼200 mA cm2 at 0.6 V, using wood-based pyrolyzed medium density fiberboard (p-MDF) as fuel. In comparison, the HDCFC with activated carbon as fuel produced a maximum power density of 36 and 53 mW cm−2 at 700 and 800 °C, respectively, and an electric efficiency of ∼40% evaluated under 0.7 V for 17 h at 700 °C. These results demonstrated the applicability of HDCFC to practical systems while stack units were operated in batch mode and an appropriate fuel feeding mechanism has to be designed. Moreover, more engineering advances should be done to enhance power output since a HDCFC stack unit involves multiple challenges that have not been addressed yet, including system configuration and corrosion protection, and durability.Graphical abstractHighlights► The HDCFC applies fuel cell technologies to coal conversion for power generation. ► A bench-scale HDCFC of ∼12.56 cm2 produced 1.2 W at 800 °C with p-MDF as fuel. ► With activated carbon as fuels, an energy efficiency of 40% was obtained at 700 °C.
Co-reporter:E. Ruiz-Trejo, J.T.S. Irvine
Solid State Ionics 2013 Volume 252() pp:157-164
Publication Date(Web):1 December 2013
DOI:10.1016/j.ssi.2013.05.021
•Simultaneous electrolysis of steam and CO2 in a proton conductor.•Syn-gas production rates of H2 ≈ 0.14 mmol/cm2s and CO ≈ 0.05 mmol/cm2s.•At 600 °C a 30 mA/cm2 current at 1.5 V can be passed using Fe as cathode.•Small additions of Pt improves the performance of the Fe and Cu electrodes.The electrolysis of CO2 is examined in a proton conducting solid electrolyser using BaCe0.5Zr0.3Y0.16Zn0.04O3 − δ as the electrolyte, nickel as the anode to oxidize H2O/H2 and copper, nickel or iron as the cathode to reduce CO2. The electrolyte and porous scaffolds were prepared by tape casting and the electrodes by impregnation. During electrolysis at 600 °C, currents as high as 35 mA/cm2 (iron), 20 mA/cm2 (copper) or 15 mA/cm2 (nickel) at 1.5 V pass through the 200 μm thick electrolytes. Small additions of Pt improve considerably the performance of the electrodes. For iron based cathodes Faradaic efficiencies up to 100% are achieved with production rates of H2 ≈ 0.14 μmol/cm2 s, H2O ≈ 0.25 μmol/cm2 s and CO ≈ 0.05 μmol/cm2 s. The possibilities of increasing these yields are discussed.
Co-reporter:Li Peng, John T.S. Irvine
Progress in Natural Science: Materials International 2013 Volume 23(Issue 3) pp:302-307
Publication Date(Web):June 2013
DOI:10.1016/j.pnsc.2013.05.004
With a view to produce intermediate temperature SOFCs, yttria and scandia doped zirconia with a core–shell structure was prepared, then an anode supported fuel cell was fabricated by a spray method. The influences of the scandia content in the electrolyte and atmosphere conditions used in the testing experiments on phase composition, microstructure and fuel cell performance were investigated. The electrolyte was composed of cubic and tetragonal phases and SEM pictures revealed very fine grain sizes and a smooth surface of the electrolyte film, though some defects were observed in samples with high Scandia content. Coating scandia on partially stabilized zirconium particles improves both ionic conductivity of the electrolyte and power density of the fuel cell distinctly below 750 °C. Anodes were pre-sintered at 1200 °C before co-sintering with the electrolyte film to ensure that the shrinkage percentage was close to that of the electrolyte during co-sintering, avoiding warping of cell.
Co-reporter:Cairong Jiang, Jianjun Ma, Alfredo D. Bonaccorso and John T. S. Irvine
Energy & Environmental Science 2012 vol. 5(Issue 5) pp:6973-6980
Publication Date(Web):13 Feb 2012
DOI:10.1039/C2EE03510C
Direct carbon fuel cells offer highly efficient means of converting carbon from waste, biomass or coal to electricity producing an exhaust stream that is well-suited to CO2 sequestration and, hence could underpin a new, clean carbon economy. If this technology is to contribute significantly to improving our impending global energy crisis, three aspects must first be addressed: competitive performance with extant fuel cell technologies, development of practical systems to handle available carbon resources and demonstration of sufficient durability, i.e. 40000 hours minimum for system. In the present study, we demonstrate excellent performance from a hybrid direct carbon fuel cell based upon an yttrium-stabilised zirconia electrolyte to use solid carbons as fuels directly. Good stability of the zirconia is observed during and after fuel cell testing and in corrosion tests under reducing conditions; however, significant intergrain erosion is observed under oxidising conditions. The carbon fuel chosen is a waste product, Medium Density Fibreboard, which is widely available and difficult to recycle. Cells exhibit excellent electrochemical performance at 750 °C, with a maximum power density of 390 mW cm−2 using a lanthanum doped strontium manganite (LSM) cathode and 878 mW cm−2 using a lanthanum doped strontium cobalt (LSC) cathode under flowing air. This is comparable with current commercial Solid Oxide Fuel Cell and significantly in excess of commercial Molten Carbonate Fuel Cell (MCFC) performance. This hybrid direct carbon fuel cell therefore offers the clean utilisation of coal, waste and renewable carbon sources and hence merits development as a realistic alternative technology.
Co-reporter:A. Damiano Bonaccorso, John TS. Irvine
International Journal of Hydrogen Energy 2012 Volume 37(Issue 24) pp:19337-19344
Publication Date(Web):December 2012
DOI:10.1016/j.ijhydene.2012.02.104
The hybrid direct carbon fuel cell is a direct carbon fuel cell concept that combines a solid oxide fuel cell with a molten carbonate fuel cell electrode. This offers efficient conversion of coal or biomass derived carbons to electricity. In this study we aim to improve the electrical performance of this cell by using gadolinia doped ceria (GDC) as either a protection layer over a YSZ electrolyte or as the electrolyte itself. In our study, the electrical performance of several tubular cell geometries were investigated using impedance spectroscopy both with and without gas flows of carbon dioxide or nitrogen. Integrity of microstructure including possible layer delamination effects were investigated by SEM. Promising values of power and resistance were observed using a GDC material as electrolyte at intermediate temperature reducing the operation temperature compared to YSZ, doubling the power of each cell.Highlights► Carbon solid fuel has an energy density 10 times higher than hydrogen fuel. ► Carbon solid fuel is easily available compared to hydrogen. ► Tubular cell decreases in size of the final stack and improves continuous fuelling. ► GDC material shows higher stability and ions conductivity than YSZ. ► H-DCFC obtained a level of power twice higher than YSZ electrolyte.
Co-reporter:Kui Xie, Yaoqing Zhang, Guangyao Meng and John T. S. Irvine
Energy & Environmental Science 2011 vol. 4(Issue 6) pp:2218-2222
Publication Date(Web):28 Apr 2011
DOI:10.1039/C1EE01035B
Synthetic fuels produced from CO2/H2O are an attractive alternative energy carrier. Here we demonstrate a novel strategy to electrochemically convert CO2/H2O into hydrocarbon in a single step in an oxygen-ion conducting solid oxide electrolyser. Methane was directly synthesized in an efficient electrolyser with configuration of (anode) (La0.8Sr0.2)0.95MnO3−δ/YSZ/La0.2Sr0.8TiO3+δ (cathode) by combining coelectrolysis of CO2/H2O and in situ Fischer–Tropsch-type synthesis. We demonstrate a high Faradaic yield of CO/H2 and lower methane yield, which shows that the limit on conversion efficiency comes from the heterogeneous catalysis process. Electrochemical results also show that the electrochemical reduction of La0.2Sr0.8TiO3+δ cathode is the main process at low electrical voltages while the coelectrolysis is the main process at high voltages.
Co-reporter:Jung Hyun Kim, David Miller, Harald Schlegl, Damien McGrouther, and John T. S. Irvine
Chemistry of Materials 2011 Volume 23(Issue 17) pp:3841
Publication Date(Web):August 16, 2011
DOI:10.1021/cm2007318
The microstructural and electrochemical properties of La0.4Sr0.6Ti0.8Mn0.2O3±δ (LSTM) fabricated via liquid-phase impregnation have been investigated for solid oxide fuel cell (SOFC) applications. Scanning electron micrography (SEM) showed that LSTM uniformly covers the porous scaffold when heated in an oxidizing atmosphere, which transforms to fine particles when reduced. The electrical conductivity of a 10 wt % CeO2–50 wt % LSTM–8 mol % yttria-stabilized zirconia (8YSZ) composite anode was higher than that of a 50 wt % LSTM–8YSZ anode and was stable at 700, 800, and 900 °C under reducing conditions. When the 50 wt % LSTM-8YSZ was used as an anode, power densities of the sample were <100 mW cm–2 over the entire measured temperature range. The addition of 10 wt % of CeO2 and 1 wt % of Pd as catalysts increased the power density to 150 and 210 mW cm–2 at 800 and 850 °C, respectively.Keywords: anode; dual beam focused ion beam; impregnation; solid oxide fuel cell; tape cast;
Co-reporter:Kui Xie, Yaoqing Zhang, Guangyao Meng and John T. S. Irvine
Journal of Materials Chemistry A 2011 vol. 21(Issue 1) pp:195-198
Publication Date(Web):22 Oct 2010
DOI:10.1039/C0JM02205E
Synthetic hydrocarbon fuels from CO2/H2O are proposed as alternatives to hydrogen as an energy carrier to enable a carbon neutral energy cycle, given their inherent advantages of high H/C ratio and convenience of storage and transportation. Here we demonstrate the successful electrochemical reduction of CO2 into CO and CH4 in a proton conducting solid oxide electrolyser based on BaCe0.5Zr0.3Y0.16Zn0.04O3 − δ (BCZYZ) electrolyte and a composite iron/iron oxide cathode. The production of CH4 and CO reaches 0.07 and 3.25 ml min−1 cm−2, respectively, with 1.5 A cm−2 at 614 °C. The overall CO2 conversion rate in the electrochemical reduction process is 65%.
Co-reporter:Cairong Jiang, John T.S. Irvine
Journal of Power Sources 2011 Volume 196(Issue 17) pp:7318-7322
Publication Date(Web):1 September 2011
DOI:10.1016/j.jpowsour.2010.11.066
The hybrid direct carbon fuel cell (HDCFC), combining molten carbonate fuel cell and solid oxide fuel cell technology, is capable of converting solid carbon directly into electrical energy without intermediate reforming. Here, we report the investigation of the HDCFC with yttria stabilized zirconia (YSZ) electrolyte, NiO-YSZ anode and lanthanum strontium manganite (LSM) cathode using the eutectic mixture of 62 mol% Li2CO3 and 38 mol% K2CO3. An open circuit voltage (OCV) of 0.71 V at 800 °C is recorded without the carbonate which increases to 1.15–1.23 V in the presence of the carbonate at the same temperature. In addition, the cell's OCV is enhanced not only by the thermal history but also by the carbonate, which is in excess of 1.57 V after the high temperature treatment. Electrochemical performance analysis indicates a suitable amount of the carbonate enhanced the carbon oxidation. With 1 mm robust thick electrolyte and commercial carbon, the cell (1.13 cm2 active area) generates the peak density of 50 mW cm−2 at 800 °C. There are significant losses from electrolyte resistance, which would be overcome by the application of a thinner electrolyte.
Co-reporter:Xiaoxiang Xu, Gang Liu, Chamnan Randorn, John T.S. Irvine
International Journal of Hydrogen Energy 2011 Volume 36(Issue 21) pp:13501-13507
Publication Date(Web):October 2011
DOI:10.1016/j.ijhydene.2011.08.052
A highly active photocatalyst based on g-C3N4 coated SrTiO3 has been synthesized simply by decomposing urea in the presence of SrTiO3 at 400 °C. The catalyst demonstrates a high H2 production rate ∼440 μmol h−1/g catalyst in aqueous solution under visible light irradiation, which is much higher than conventional anion doped SrTiO3 or physical mixtures of g-C3N4 and SrTiO3. The improved photocatalytic activity can be ascribed to the close interfacial connections between g-C3N4 and SrTiO3 where photo-generated electron and holes are effectively separated. The newly synthesized catalyst also exhibited a stable performance in the repeated experiments.Highlights► Synthesis of a photocatalyst based on g-C3N4 coated SrTiO3. ► The catalyst shows high activity for H2 production. ► The special structure is responsible for high activity.
Co-reporter:Stephen R. Gamble, John T.S. Irvine
Solid State Ionics 2011 Volume 192(Issue 1) pp:394-397
Publication Date(Web):16 June 2011
DOI:10.1016/j.ssi.2010.11.024
Pressurised operation of solid oxide fuel cells (SOFC) has been shown to significantly improve their performance (Singhal, 2000) [1], however little work has been done on the effects of pressure on SOFC cathodes. The effect of pressurised oxygen on the area specific polarisation resistance (ASRp) of (La0.8Sr0.2)0.95MnO3–δ/8YSZ SOFC cathodes was determined by electrochemical impedance spectroscopy (EIS). Pellets of 8YSZ were pressed and sintered at 1350 °C, and screen printed layers of LSM/8YSZ cathode and LSM current collector were applied and sintered at 1300 °C and 1200 °C respectively. EIS was carried out between 1 and 3 bar oxygen at 800–1000 °C. One process dominated the spectra, and was identified as process C, (Jorgensen and Morgensen, 2001) [2] by comparison of measured and reference frequency maxima, the dependence of polarisation resistance on PO2, the capacitance, and the activation energy. It is suggested that this represents the physical process of dissociative adsorption of oxygen at the triple phase boundaries of the electrode. A second process, with a magnitude almost independent of PO2, is observed, which may be process B [2], related to transport of oxygen ions in the YSZ.Research Highlights► We test LSM-YSZ SOFC cathode symmetrical half cells by EIS in pressurised oxygen. ► EIS spectra are modeled with an electrical equivalent circuit, showing two arcs. ► EIS arcs are compared to literature, large arc is dissociative adsorption of oxygen. ► The small arc is transport of oxide ions through YSZ. ► Polarisation resistance decreases with increasing oxygen pressure from 1 to 3 bar.
Co-reporter:Jung Hyun Kim, Mark Cassidy, John T.S. Irvine and Joongmyeon Bae
Chemistry of Materials 2010 Volume 22(Issue 3) pp:883
Publication Date(Web):November 23, 2009
DOI:10.1021/cm901720w
The electrochemical characteristics of the samarium and strontium doped layered perovskite (SmBa1−xSrxCo2O5+δ, x = 0.5) have been investigated for possible application as a cathode material for an intermediate temperature-operating solid oxide fuel cell (IT-SOFC). The cathodic polarization of single-phase and composite cathodes with 10 mol % gadolinia-doped ceria (Ce0.9Gd0.1O2−δ, CGO91) shows that a weight ratio between SmBa0.5Sr0.5Co2O5+δ (SBSCO) and CGO91 of 1:1 (50 wt % SBSCO and 50 wt % CGO91, SBSCO:50) gives the lowest area specific resistance (ASR) of 0.10 Ω cm2 at 600 °C and 0.013 Ω cm2 at 700 °C. The maximum and minimum electrical conductivity in SBSCO are 1280 S cm−1 at 50 °C and 280 S cm−1 at 900 °C, with the influence of oxygen partial pressure indicating p-type conduction. The maximum power density of SBSCO:50 in an anode supported SOFC was 1.31 W cm−2 at 800 °C and 0.75 W cm−2 at 700 °C.
Co-reporter:Chamnan Randorn and John T. S. Irvine
Journal of Materials Chemistry A 2010 vol. 20(Issue 39) pp:8700-8704
Publication Date(Web):06 Sep 2010
DOI:10.1039/C0JM01370F
High temperature stable yellow TiO2 synthesized by a simple and organic free combustion method using TiN as precursor exhibits an interesting property of being photoactive under visible light.
Co-reporter:Abul K. Azad and John T. S. Irvine
Chemistry of Materials 2009 Volume 21(Issue 2) pp:215
Publication Date(Web):December 19, 2008
DOI:10.1021/cm8031847
Structural studies from X-ray and high-resolution neutron powder diffraction data collected on deuterated and nondeuterated BaCe0.4Zr0.4Sc0.2O2.9·x(D2O) have been carried out. Although X-ray diffraction suggested that a sample of the nominal composition was single phase cubic, neutron diffraction showed the structure as single phase orthorhombic in the space group Pbnm. The structural distortion can be related to the determination of accurate oxygen positions in the structure by neutron diffraction. Rietveld refinement of the neutron diffraction data and subsequent Fourier nuclear density maps have proved to be successful in locating the deuterium (D) positions despite the low occupancies present, with a final composition of BaCe0.4Zr0.4Sc0.2O2.90·0.10(D2O) and the D position associated with the O1 position in the Ba-containing plane. TGA analysis in dry air on the deuterated sample shows the 0.70% weight loss for heating from room temperature to 900 °C which corresponds to the D2O loss of 0.10/formula unit. The unit-cell volume for the deuterated phase was found to be higher than the nondeuterated phase (i.e., dry) at 295 K, i.e., V = 311.59(5) Å3 compared with 310.91(5) Å3. The O1−D distance was found to be 1.06(1) Å. The presence of anisotropic displacements for oxygen was observed during the refinement.
Co-reporter:Cristian-Daniel Savaniu and John T. S. Irvine
Journal of Materials Chemistry A 2009 vol. 19(Issue 43) pp:8119-8128
Publication Date(Web):21 Sep 2009
DOI:10.1039/B912305A
Here we report a study of the properties of A-site deficient lanthanum-doped SrTiO3 (La0.2Sr0.7TiO3) in order to establish its potential as an anode component material for intermediate temperature SOFCs. The behaviour of the material in reducing atmosphere has been investigated and results of thermal expansion and conductivity dependence of the oxygen partial pressures are presented revealing a strong dependence of the material's thermal and electrical properties on temperature and atmosphere. From thermogravimetry, dilatometry and conductivity measurements it seems that reduction may become more facile as the extent of reduction increases. Two types of fuel cells, electrolyte supported and electrode supported, were produced using yttria-stabilized zirconia (YSZ) electrolyte, a porous, conductive backbone of La0.2Sr0.7TiO3 impregnated via solutions with catalytically active 20 mol% gadolinia-doped ceria and copper, for improved current collection as anode, and thin films of La0.6Sr0.4CoO3 produced in situ in the fuel cell test experiment as cathode. Fuel cell tests using pure, humidified H2 as fuel demonstrated that power densities in excess of 0.5 W cm−2 at 750 °C can be achieved using these cells with suitable pre-reduction of the titanate material.
Co-reporter:Jung Hyun Kim, Yongmin Kim, Paul A. Connor, John T.S. Irvine, Joongmyeon Bae, Wuzong Zhou
Journal of Power Sources 2009 Volume 194(Issue 2) pp:704-711
Publication Date(Web):1 December 2009
DOI:10.1016/j.jpowsour.2009.06.024
The synthesis, conductivity properties, area specific resistance (ASR) and thermal expansion behaviour of the layered perovskite SmBaCo2O5+d (SBCO) are investigated for use as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The SBCO is prepared and shows the expected orthorhombic pattern. The electrical conductivity of SBCO exhibits a metal–insulator transition at about 200 °C. The maximum conductivity is 570 S cm−1 at 200 °C and its value is higher than 170 S cm−1 over the whole temperature range investigated. Under variable oxygen partial pressure SBCO is found to be a p-type conductor. The ASR of a composite cathode (50 wt% SBCO and 50 wt% Ce0.9Gd0.1O2−d, SBCO:50) on a Ce0.9Gd0.1O2−d (CGO91) electrolyte is 0.05 Ω cm2 at 700 °C. An abrupt increase in thermal expansion is observed in the vicinity of 320 °C and is ascribed to the generation of oxygen vacancies. The coefficients of thermal expansion (CTE) of SBCO is 19.7 and 20.0 × 10−6 K−1 at 600 and 700 °C, respectively. By contrast, CTE values for SBCO:50 are 12.3, 12.5 and 12.7 × 10−6 K−1 at 500, 600 and 700 °C, that is, very similar to the value of the CGO91 electrolyte.
Co-reporter:Yuta Nabae, Kevin D. Pointon and John T. S. Irvine
Energy & Environmental Science 2008 vol. 1(Issue 1) pp:148-155
Publication Date(Web):17 Jun 2008
DOI:10.1039/B804785E
The hybrid direct carbon fuel cell (HDCFC) with solid oxide and molten carbonate binary electrolyte merges solid oxide fuel cell (SOFC) and molten carbonate fuel cell technologies to achieve direct conversion of solid carbon to electric power. The purpose of this study is to investigate in detail the electrochemistry of the oxidation of solid carbon in the carbon/carbonate slurry in the HDCFC. A planar test cell has been fabricated employing conventional SOFC materials and a eutectic carbonate mixture of lithium carbonate and potassium carbonate. The HDCFC with a model fuel, carbon black XC-72R, shows very high open circuit voltages (OCVs), approximately 1.5 V at 550–700 °C, especially after a high temperature operation at 900 °C, where carbonate decomposes to O2− and CO2. The carbon/carbonate slurry increases the active reaction zone from a two-dimensional Ni/YSZ anode to a three-dimensional slurry and significantly enhances the carbon oxidation. The high OCV is probably due to the low activity of CO2 in the slurry, which results from the recombination of CO2 and O2−. Gaseous products were analysed using an online gas chromatograph, and CO2 and CO were detected, with their selectivity found to be dependent on temperature. Solid carbon is electrochemically oxidised to CO2 and the final distribution of the products is dominated by the equilibrium of the Boudouard reaction (C + CO2 ⇄ 2CO).
Co-reporter:Sneh L. Jain, Yuta Nabae, Barry J. Lakeman, Kevin D. Pointon, John T.S. Irvine
Solid State Ionics 2008 Volume 179(27–32) pp:1417-1421
Publication Date(Web):30 September 2008
DOI:10.1016/j.ssi.2008.01.078
In direct carbon fuel cells (DCFCs), elemental carbon is electrochemically oxidised to generate electrical power. Carbon is readily available, easily transported and stored and, therefore, affordable to the global energy economy. Further operational advantages include the use of fully renewable solid bio-carbon fuel sources and the opportunity for scale-up. Herein we discuss a DCFC which utilises a molten mixed alkali metal carbonate eutectic as a secondary electrolyte, contained within a solid oxide fuel cell. The operation of small cells working as semi-fuel cells has been successfully demonstrated over an extended temperature range (525–900 °C) using a range of carbons derived from fossil, renewable and waste sources. Preliminary mechanistic studies demonstrate open circuit voltages (OCVs) well in excess of 1 V and indicate that direct oxidation and Boudouard conversion both contribute to the conversion process, with the dominant process changing with both temperature and extent of molten electrode/electrolyte component.
Co-reporter:Juan C. Ruiz-Morales, Jesús Canales-Vázquez, Cristian Savaniu, David Marrero-López, Pedro Núñez, Wuzong Zhou and John T. S. Irvine
Physical Chemistry Chemical Physics 2007 vol. 9(Issue 15) pp:1821-1830
Publication Date(Web):21 Mar 2007
DOI:10.1039/B617266K
A new SOFC anode material based upon oxygen excess perovskite related phases has been synthesised. The material shows better electrochemical performance than other alternative new anodes and comparable performance to the state-of-art of the electrodes, Ni–YSZ cermets, under pure hydrogen. Furthermore, this material shows an enhanced performance under methane operation with high open circuit voltages, i.e. 1.2–1.4 V at 950 °C, without using steam excess. The effect of the anode configuration was tested in one and four layer configurations. The optimised electrode polarisation resistances were just 0.12 Ω cm2 and 0.36 Ω cm2, at 950 °C, in humidified H2 and humidified CH4, respectively. Power densities of 0.5 W cm−2 and 0.35 W cm−2 were obtained in the same conditions. A very low anodic overpotential of 100 mV at 1 A cm−2 was obtained under humidified H2 at 950 °C. Samples were tested for two days in reducing and oxidising conditions, alternating heating and cooling processes from 850 °C to 950 °C, showing stable electrode performance and open circuit voltages. The results show that the substituted strontium titanates are very promising anode materials for SOFC.
Co-reporter:H.D.A.L. Viana, J.T.S. Irvine
Solid State Ionics 2007 Volume 178(7–10) pp:717-722
Publication Date(Web):April 2007
DOI:10.1016/j.ssi.2007.02.029
The proton conductors Sr3CaZr0.5Ta1.5O8.75 (SCZT), BaCe0.9Y0.1O2.95 (BCY10) and Ba3Ca1.18Nb1.82O8.73(BCN18) have been shown to be active heterogeneous catalysts for the reverse water gas shift (RWGS) reaction. Catalytic characterisation was conducted in a quartz fixed-bed reactor with a silica fritted disk and monitored by a gas chromatograph. X-ray diffraction and TGA + MS were used to characterise samples before and after catalytic tests. BCY10 reaches 45% CO2 conversion at 900 °C, 3% more than BCN18 (42% total conversion) at 900 °C. SCZT reaches 36% CO2 conversion at 900 °C, but has the lowest conversion onset temperature and activation energy of the materials studied.
Co-reporter:Sneh L. Jain;Barry Lakeman;Kevin D. Pointon
Ionics 2007 Volume 13( Issue 6) pp:413-416
Publication Date(Web):2007 December
DOI:10.1007/s11581-007-0161-4
Carbon is an exceptionally versatile fuel source, with excellent conductivity properties and an extraordinarily high energy density. This paper describes the evolution of carbon–air fuel cells to produce electrical energy, the use of renewable carbon in carbon-neutral processes and greenhouse gas reduction and the long-term future of such cells.
Co-reporter:A.K. Azad, J.T.S. Irvine
Solid State Ionics 2007 Volume 178(7–10) pp:635-640
Publication Date(Web):April 2007
DOI:10.1016/j.ssi.2007.02.004
Rare-earth-doped BaCeO3 and BaZrO3 electrolytes with perovskite structure have been studied extensively in developing intermediate temperature SOFC. Traditional solid state sintering has been used to prepare the perovskite type proton conductors Ba(Ce,Zr)1−xScxO3 − δ (x = 0.1, 0.2). Rietveld refinement of the XRD data shows the materials as cubic in the space group Pm-3m. The unit cell parameter a decreases with Sc concentration. Thermogravimetric analysis (TGA) traces obtained for dehydrated samples on heating in a 3% H2O/5% H2/Ar atmosphere show that, on heating, initially the sample weight remains constant up to 400 °C and then decreases. TGA in pure CO2 shows that Sc doping increases the chemical stability. AC impedance measurements under wet 5% H2/Ar show that these materials are good conductors and stable under H2 atmosphere. It also shows that bulk and grain boundary resistances decrease with Sc doping. The total conductivity increases from 2.58 × 10− 4 Scm− 1 to 1.06 × 10− 3 Scm− 1 for x = 0.1 and 0.2 respectively at 600 °C.
Co-reporter:S. W. Tao;J. T. S. Irvine
Advanced Materials 2006 Volume 18(Issue 12) pp:1581-1584
Publication Date(Web):19 MAY 2006
DOI:10.1002/adma.200502098
For proton-conducting oxides to be used in fuel cell and related technologies, sintering to form dense ceramics at low temperatures and avoiding carbonation of BaCeO3-based oxides is required. A new strategy that allows densification at much reduced temperatures (see figure) and provides high total conductivity, with the additional benefit of stabilization against degradation, is reported.
Co-reporter:S. W. Tao;J. T. S. Irvine;J. A. Kilner
Advanced Materials 2005 Volume 17(Issue 14) pp:
Publication Date(Web):8 JUL 2005
DOI:10.1002/adma.200402007
An all-perovskite solid oxide fuel cell has been achieved using LSCM ((La0.75Sr0.25)0.95Cr0.5Mn0.5O3–δ) as the anode, LSGMCo (La0.8Sr0.2Ga0.8Mg0.15-Co0.05O3–δ) as the electrolyte, and GSC (Gd0.4Sr0.6CoO3–δ) as the cathode (see Figure). The all-perovskite design enhances structural integrity and minimizes interface polarization losses.
Co-reporter:J. Canales-Vázquez;M. J. Smith;J. T. S. Irvine;W. Zhou
Advanced Functional Materials 2005 Volume 15(Issue 6) pp:
Publication Date(Web):27 MAY 2005
DOI:10.1002/adfm.200400362
Perovskite titanates with nominal stoichiometry ABO3+δ often exhibit quite interesting properties, but their structural characterization is not always rigorous. Herein, we demonstrate how excess oxygen can be incorporated in a titanate perovskite-based lattice. A new family of layered perovskites La4Srn–4TinO3n+2 has been investigated by means of X-ray diffraction, neutron diffraction, transmission electron microscopy, thermogravimetric analysis, and density and magnetic measurements. Such layered perovskites are known to be able to accommodate extra oxygen beyond the parental ABO3 perovskite in crystallographic shears. The structure evolves with increasing n. Firstly, the perovskite blocks become more extensive and the oxygen intergrowth layers move further apart; then the spacing between the intergrowth layers increases further and their repetition becomes more sporadic. Finally, the layered structure is lost for the n = 12 member (La2Sr4Ti6O19–δ). In this structure, excess oxygen is accommodated within the perovskite framework in randomly distributed short-range linear defects. These defects become more dilute as the cubic perovskite, that is, n = ∞, composition is approached.
Co-reporter:Cristian D. Savaniu, Jesus Canales-Vazquez and John T. S. Irvine
Journal of Materials Chemistry A 2005 vol. 15(Issue 5) pp:598-604
Publication Date(Web):22 Nov 2004
DOI:10.1039/B410958A
Barium zirconate shows better chemical and mechanical stability than the corresponding cerate, but lower protonic conductivity largely due to resistive grain boundary contributions. In this work we attempted to reduce the grain boundary resistance of BaZr0.9Y0.1O2.95 starting from a core–shell modification of its grain with a thin film of BaCe0.9Y0.1O2.95. The resultant core–shell material was characterised by X-ray powder diffraction (XRD), thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM). Impedance spectroscopy performed on the material in wet 5% H2/Ar atmosphere showed a significant reduction in terms of both bulk and grain boundary resistances of the initial barium zirconate when modified with a thin film of barium cerate. As by thin films modification the total conductivity of the sample increases by about one order of magnitude, this surface modification concept appears to be a promising way to control the grain boundary properties for a given material.
Co-reporter:Angela Kruth, Glenn C. Mather, José Ramón Jurado, John T.S. Irvine
Solid State Ionics 2005 Volume 176(7–8) pp:703-712
Publication Date(Web):28 February 2005
DOI:10.1016/j.ssi.2004.10.014
Doped cerate perovskite oxides are potential candidates for application as proton conducting electrolytes in solid protonic fuel cells. Previous reports suggested nonsystematic variations of structural parameters in several doped cerate systems and that solid solution formation on substitution or removal of cations does not obey Vegard's law. In this paper, we show that the anomalies are, in fact, a wide-ranging phenomenon in this class of materials. Several different systems have been investigated with different compositions prepared under comparable conditions in air. In all cases, deviations of oxygen stoichiometry from that determined by cation stoichiometry were very small, <0.01% per perovskite formula unit. In ACe1−xMxO3−x/2 and A1−zCe0.9Y0.1O2.95−z, anomalies occur at oxygen stoichiometry 2.94, corresponding to an overall oxygen vacancy concentration of ca. 2%. In systems with constant oxygen vacancy concentrations, such as Ba1−xLaxCe0.9−xM0.1+xO2.95 and Ba1−xLaxCe0.85−xM0.15+xO2.925, structural parameters show anomalous variations at lanthanum contents around x=0.05. Possible factors that might lead to the occurrence of anomaly regions are discussed: oxygen vacancy ordering at vacancy concentrations above 1 in 48, cross-substitution of dopant ions at high doping levels or A-cation deficiency and the formation of defect clusters. Possibly, the most important factor may relate to the high degree of octahedral distortion associated with the unusual axial metric in most of the investigated compositions.
Co-reporter:Jesús Canales-Vázquez, John T.S. Irvine, Wuzong Zhou
Journal of Solid State Chemistry 2004 Volume 177(Issue 6) pp:2039-2043
Publication Date(Web):June 2004
DOI:10.1016/j.jssc.2004.02.014
Layered compounds have been synthesized and structurally characterized for the n=5 and 6 members of the perovskite-related family La4Srn−4TinO3n+2 by combining X-ray diffraction and transmission electron microscopy. Their structure can be regarded as comprising [(La,Sr)5Ti5O17] and [(La,Sr)6Ti6O20] perovskite blocks joined by crystallographic shears along the a-axis, with consecutive blocks shifted by 1/2 [100]p. The n=5 member is similar to the previously reported n=5 member of other AnBnO3n+2-related series. The n=6 member, which has only been briefly reported in other systems previously, is also a well-behaved member of this AnBnO3n+2 series.
Co-reporter:Shanwen Tao;John T.S. Irvine
The Chemical Record 2004 Volume 4(Issue 2) pp:
Publication Date(Web):1 APR 2004
DOI:10.1002/tcr.20003
The search for alternative anode materials for solid oxide fuel cells (SOFCs) has been reviewed in the light of structure, stability, conductivity, chemical and thermal compatibility with electrolyte YSZ. In this review, we have presented the advantages and disadvantages of the traditional Ni-YSZ anode for SOFCs. The development of alternative anode for SOFCs with fluorite, rutile, tungsten bronze, pyrochlore, perovskite and spinel structures has been reviewed and discussed in detail. Among the reported materials systems, materials with perovskite structure are promising particularly where two ions with complimentary function are present on the B-site at high concentration. We have recently found a good redox stable anode (La0.75Sr0.25)1−xCr0.5Mn0.5O3 (0 ≤ x ≤ 0.1) using this approach. These materials exhibit comparable performance to the traditional Ni-YSZ anode. Therefore, we can use nickel-free redox stable anode for SOFCs. With further optimisation of the composition and microstructure, the performance of these materials may be further improved and hopefully replace the traditional Ni-YSZ anode in the future. © 2004 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 4: 83–95; 2004: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20003
Co-reporter:Shanwen Tao and John T. S. Irvine
Journal of Materials Chemistry A 2002 vol. 12(Issue 8) pp:2356-2360
Publication Date(Web):07 Jun 2002
DOI:10.1039/B204248G
The new non-stoichiometric mixed perovskite SrMn0.5Nb0.5O3−δ has a cubic double perovskite structure similar to that of Sr2CrNbO6 with space group Fmm
(225), a
= 7.9338(3)
Å, V
= 499.39(6)
Å3 according to X-ray diffraction. The material is redox stable and maintains its structure in a reducing atmosphere. After reducing in 5% H2 at 900 °C for 6 hours, SrMn0.5Nb0.5O3−δ still exhibits a cubic structure with space group Pmm
(221), a
= 4.0022(5)
Å, V
= 64.10(8)
Å3. A lattice volume expansion of 2.7% was observed during the reduction. TGA analysis indicates SrMn0.5Nb0.5O3−δ
loses 0.125 oxygen per formula unit from 500 to 950 °C in 5% H2. This weight change is consistent with a reduction from SrMn0.5Nb0.5O3 to SrMn0.5Nb0.5O2.875. The morphology of this material does not significantly change on reduction according to SEM observation. A.c. impedance measurements indicate that electronic conduction is probably dominant both in air and 5% H2. The conductivities of this material in air, humidified 5% H2 and 5% H2 were 1.23, 6.4 × 10−2 and 3.1 × 10−2 S cm−1 respectively at 900 °C. The decrease of d.c. conductivity of SrMn0.5Nb0.5O3−δ at pO2 below 10−12 atm indicates p-type electronic conduction. The higher apparent conduction activation energy and lower conductivity
in H2 than in air may be due to the contribution of lattice expansion which results in poorer overlap of both σ and π bonds, which makes the hopping of electron holes more difficult. The d.c. conductivity of SrMn0.5Nb0.5O3−δ at low pO2 exhibits a pO21/6 dependence that is interpreted by a simple defect chemistry model.
Co-reporter:F. Belliard, J.T.S. Irvine
Journal of Power Sources 2001 Volumes 97–98() pp:219-222
Publication Date(Web):July 2001
DOI:10.1016/S0378-7753(01)00544-4
ZnO displays similar redox and alloying chemistry to the tin oxides on Li insertion. It might, therefore, be expected to be an interesting network modifier for tin oxides. ZnO/SnO2 composites show degradation in cycling performance, however, for low ZnO levels, cyclability is improved by some milling, however, for high ZnO levels milling degrades performance, probably due to the increase of ZnO activity. On testing ZnO, it is found that it cycles very poorly. Both electrochemical and X-ray studies indicate that highly crystalline LixZn alloys are formed. It seems that the high degree of crystallisation on insertion is the determinant factor leading to the poor performance of ZnO and ZnO/SnO2 composites compared to SnO2.
Co-reporter:P.A. Connor, J.T.S. Irvine
Journal of Power Sources 2001 Volumes 97–98() pp:223-225
Publication Date(Web):July 2001
DOI:10.1016/S0378-7753(01)00545-6
In this study, a series of inverse spinel M2SnO4 (M=Mg, Mn, Co) oxides were produced and tested to probe the effect the oxide matrix has on the electrochemical performance of tin oxides. Generally, these new oxides show similar behaviour to SnO2 with the formation of a more complicated mixed metal oxide matrix affecting the potentials of tin reduction and lithium insertion. A reasonable correlation is observed between the potential of the initial reduction of the spinel oxide to metallic tin and the enthalpy of formation of the metal oxide (MO). Amongst the spinels, Mn2SnO4 exhibits the best reversibility and Mg2SnO4 the worst.
Co-reporter:Lorena L. Garza Tovar, Paul A. Connor, Frédérique Belliard, Leticia M. Torres-Martı́nez, John T.S. Irvine
Journal of Power Sources 2001 Volumes 97–98() pp:258-261
Publication Date(Web):July 2001
DOI:10.1016/S0378-7753(01)00533-X
Lead tin fluorides are well known fast ion conductors. In this study the electrochemical behaviour of materials as negative electrodes in lithium rechargeable batteries was investigated. The initial reduction with lithium occurs at much higher potentials for fluorides than oxides. This correlates well with the standard energies of formation of metals and lithium oxide/fluoride on lithium insertion. Lead rich compounds present a greater degree of crystallinity than tin rich materials and it is also observed that fluoride matrices exhibit greater crystallinity after cycling than their oxide counterparts. Tin oxide exhibits the best cycling performance and this seems to correlate with the low degree of crystallinity observed in this system.
Co-reporter:Shanwen Tao, John T.S Irvine
Materials Research Bulletin 2001 Volume 36(7–8) pp:1245-1258
Publication Date(Web):May–June 2001
DOI:10.1016/S0025-5408(01)00625-0
Recent reports have indicated good fast oxide ion conductivity in apatite silicates. In this article we report on the successful low temperature synthesis of the apatite-type lanthanum silicates, La10(SiO4)6O3 and La9.33(SiO4)6O2, via a sol-gel process. The properties of the resulting apatite phases have been characterised by thermal analysis (TGA-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and conductivity measured by both a.c. impedance spectroscopy (IS) and d.c. methods. The apatite phases may be obtained at 800°C. On further reaction at 1400°C, crystallinity improved, with the apatite structure retained. The room-temperature structure is hexagonal, space group P63 or P63/m, with a = 9.722(1), c = 7.182(1)Å for La10(SiO4)6O3 and a = 9.717(2), c = 7.177(1)Å for La9.33(SiO4)6O2, i.e., the cell volume of La10(SiO4)6O3 is a little greater than that of La9.33(SiO4)6O2. Both compositions exhibit high ionic conductivity, although the grain boundary resistance is the dominant feature in the impedance spectrum of both. At 1000K the total conductivity is 10-3Scm-1. In general, the conductivity of La10(SiO4)6O3 is higher than La9.33(SiO4)6O2 indicating that oxygen interstitials may be introduced into the apatite lattice for La10(SiO4)6O3, which may benefit the oxygen ion transportation. The a.c. and d.c. conductivitis are comparable for La10(SiO4)6O3 but not for La9.33(SiO4)6O2.
Co-reporter:Li Peng, John T.S. Irvine
Progress in Natural Science: Materials International (June 2013) Volume 23(Issue 3) pp:302-307
Publication Date(Web):1 June 2013
DOI:10.1016/j.pnsc.2013.05.004
With a view to produce intermediate temperature SOFCs, yttria and scandia doped zirconia with a core–shell structure was prepared, then an anode supported fuel cell was fabricated by a spray method. The influences of the scandia content in the electrolyte and atmosphere conditions used in the testing experiments on phase composition, microstructure and fuel cell performance were investigated. The electrolyte was composed of cubic and tetragonal phases and SEM pictures revealed very fine grain sizes and a smooth surface of the electrolyte film, though some defects were observed in samples with high Scandia content. Coating scandia on partially stabilized zirconium particles improves both ionic conductivity of the electrolyte and power density of the fuel cell distinctly below 750 °C. Anodes were pre-sintered at 1200 °C before co-sintering with the electrolyte film to ensure that the shrinkage percentage was close to that of the electrolyte during co-sintering, avoiding warping of cell.
Co-reporter:Guan Zhang, Gang Liu, Lianzhou Wang and John T. S. Irvine
Chemical Society Reviews 2016 - vol. 45(Issue 21) pp:NaN5984-5984
Publication Date(Web):2016/09/08
DOI:10.1039/C5CS00769K
The development and utilization of solar energy in environmental remediation and water splitting is being intensively studied worldwide. During the past few decades, tremendous efforts have been devoted to developing non-toxic, low-cost, efficient and stable photocatalysts for water splitting and environmental remediation. To date, several hundreds of photocatalysts mainly based on metal oxides, sulfides and (oxy)nitrides with different structures and compositions have been reported. Among them, perovskite oxides and their derivatives (layered perovskite oxides) comprise a large family of semiconductor photocatalysts because of their structural simplicity and flexibility. This review specifically focuses on the general background of perovskite and its related materials, summarizes the recent development of perovskite photocatalysts and their applications in water splitting and environmental remediation, discusses the theoretical modelling and calculation of perovskite photocatalysts and presents the key challenges and perspectives on the research of perovskite photocatalysts.
Co-reporter:Yukwon Jeon, Jae-ha Myung, Sang-hoon Hyun, Yong-gun Shul and John T. S. Irvine
Journal of Materials Chemistry A 2017 - vol. 5(Issue 8) pp:NaN3973-3973
Publication Date(Web):2017/01/09
DOI:10.1039/C6TA08692F
An efficient cathode for solid oxide fuel cells (SOFC) is mainly determined by the oxygen reduction reaction (ORR) activity of mixed materials. We demonstrate a new microstructure design through a nanofibrous electrode based on a unique corn-cob structure. A one-step process to produce corn-cob ceramic nanofibers of La0.8Sr0.2MnO3 (LSM) and Y2O3-stabilized ZrO2 (YSZ) is introduced using an electrospinning system equipped with a coaxial nozzle. From the microscope analysis, perfect corn-cob nanofibers are finely produced with a diameter of 350 nm for the core and nanoparticles (30–40 nm) stacked on the surface similar to a core–shell structure. The cathode fabricated using nanofibers with LSM outside and YSZ inside (YSZ@LSM) shows the best maximum power density of 1.15 W cm−2 at 800 °C with low polarization resistance, which is higher than that of the reverse core and shell positions (LSM@YSZ) and even the commercial LSM–YSZ. This better outcome is more prominent at elevated temperatures due to its accelerated catalytic activity. Therefore, insight into the key factors that enhance ORR activity and single cell performance is obtained in terms of not only the nanofibrous core@shell structure but also more reaction active sites from the optimum catalyst position at the designed corn-cob nanofiber based cathodes.
Co-reporter:X. Yue and J. T. S. Irvine
Journal of Materials Chemistry A 2017 - vol. 5(Issue 15) pp:NaN7090-7090
Publication Date(Web):2017/03/13
DOI:10.1039/C6TA09421J
Extensive efforts have been made to find new fuel electrode materials for solid oxide cells with high activity and durability to provide more robust materials than state-of-the-art materials, Ni-cermets. In the present study, a Ni-free cathode with competitive performance and higher durability than a well performing Ni–YSZ cermet for CO2 electrolysis using SOECs is prepared. A (La, Sr)(Cr, Mn)O3/(Gd, Ce)O2 (LSCM/GDC) cathode fabricated by vacuum infiltration of GDC nitrate solutions into a LSCM/YSZ (8 mol% yttria stabilised zirconia) skeleton is reported. A porous YSZ layer introduced between the dense electrolyte and this cathode helps to maintain a good cathode/electrolyte interface, whilst the nano-structured GDC phase introduced on the surface of the LSCM/YSZ backbone is advantageous to boost the electrochemical and catalytic properties of the cathode towards CO2 reduction using SOECs. Vacuum impregnation therefore offers an effective means to modify the microstructure of the LSCM/GDC material used as a cathode for high temperature CO2 electrolysis. With the doping of a Pd co-catalyst after GDC impregnation, the cathodic activity of the GDC impregnated LSCM material is further enhanced for high temperature CO2 electrolysis, and the 0.5 wt% Pd and GDC co-impregnated LSCM cathode achieves an Rp value of 0.24 Ω cm2 at OCV at 900 °C in a CO2–CO 70–30 mixture, a comparable level to that of a high performance Ni–YSZ cathode operated under identical conditions.
Co-reporter:Jianjun Ma, Cairong Jiang, Paul A. Connor, Mark Cassidy and John T. S. Irvine
Journal of Materials Chemistry A 2015 - vol. 3(Issue 37) pp:NaN19076-19076
Publication Date(Web):2015/08/18
DOI:10.1039/C5TA06421J
Solid oxide fuel cells (SOFCs) afford an opportunity for the direct electrochemical conversion of biogas with high efficiency; however, direct utilisation of biogas in nickel-based SOFCs is a challenge as it is subject to carbon deposition. A biogas composition representative of a real operating system of 36% CH4, 36% CO2, 20% H2O, 4% H2 and 4% CO used here was derived from an anode recirculation method. A BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BCZYYb) infiltrated Ni-YSZ anode was investigated for biogas conversion. The infiltration of BCZYYb significantly promoted the electrochemical reactions and the cells exhibited high power output at the operational temperatures of 850, 800 and 750 °C. At 800 °C, supplied with a 20 ml min−1 biogas, the cell with a BCZYYb-Ni-YSZ anode, generated 1.69 A cm−2 at 0.8 V with an optimal amount of 0.6 wt% BCZYYb, whereas only 0.65 A cm−2 was produced with a non-infiltrated Ni-YSZ in the same conditions. At 750 °C, a maximum power density of 1.43 W cm−2 was achieved on a cell with a BCZYYb-Ni-YSZ anode, a 3 μm dense YSZ film electrolyte, a Gd0.1Ce0.9O2 (GDC) buffer layer and a La0.6Sr0.4Co0.2Fe0.8O3–Gd0.1Ce0.9O2 (LSCF-GDC) composite cathode. The cell remained stable, while operating at 0.8 V for 50 hours with a current density of 1.25 A cm−2. A well-designed cell structure and selected components made it possible to obtain excellent performance at good fuel utilisation. The analysis of gases in open-circuit conditions or under various current loads suggested that the prevalent reaction was reforming of methane without coking. This study demonstrates that the BCZYYb-Ni-YSZ is a promising electrode for carbon-containing fuel.
Co-reporter:Cristian-Daniel Savaniu and John T. S. Irvine
Journal of Materials Chemistry A 2009 - vol. 19(Issue 43) pp:NaN8128-8128
Publication Date(Web):2009/09/21
DOI:10.1039/B912305A
Here we report a study of the properties of A-site deficient lanthanum-doped SrTiO3 (La0.2Sr0.7TiO3) in order to establish its potential as an anode component material for intermediate temperature SOFCs. The behaviour of the material in reducing atmosphere has been investigated and results of thermal expansion and conductivity dependence of the oxygen partial pressures are presented revealing a strong dependence of the material's thermal and electrical properties on temperature and atmosphere. From thermogravimetry, dilatometry and conductivity measurements it seems that reduction may become more facile as the extent of reduction increases. Two types of fuel cells, electrolyte supported and electrode supported, were produced using yttria-stabilized zirconia (YSZ) electrolyte, a porous, conductive backbone of La0.2Sr0.7TiO3 impregnated via solutions with catalytically active 20 mol% gadolinia-doped ceria and copper, for improved current collection as anode, and thin films of La0.6Sr0.4CoO3 produced in situ in the fuel cell test experiment as cathode. Fuel cell tests using pure, humidified H2 as fuel demonstrated that power densities in excess of 0.5 W cm−2 at 750 °C can be achieved using these cells with suitable pre-reduction of the titanate material.
Co-reporter:Chamnan Randorn and John T. S. Irvine
Journal of Materials Chemistry A 2010 - vol. 20(Issue 39) pp:NaN8704-8704
Publication Date(Web):2010/09/06
DOI:10.1039/C0JM01370F
High temperature stable yellow TiO2 synthesized by a simple and organic free combustion method using TiN as precursor exhibits an interesting property of being photoactive under visible light.
Co-reporter:Cairong Jiang, Jianjun Ma, Gael Corre, Sneh L. Jain and John T. S. Irvine
Chemical Society Reviews 2017 - vol. 46(Issue 10) pp:NaN2912-2912
Publication Date(Web):2017/04/19
DOI:10.1039/C6CS00784H
A direct carbon fuel cell (DCFC) can produce electricity with both superior electrical efficiency and fuel utilisation compared to all other types of fuel cells. Although the first DCFC prototype was proposed in 1896, there was, until the 1970s, little sustained effort to investigate further, because of technology development issues. Interest in DCFCs has recently been reinvigorated as a possible method of replacing conventional coal-fired power plants to meet the demands for lower CO2 emissions, and indeed for efficient utilisation of waste derived chars. In this article, recent developments in direct carbon conversion are reviewed, with the principal emphasis on the materials involved. The development of electrolytes, anodes and cathodes as well as fuel sources is examined. The activity and chemical stability of the anode materials are a critical concern addressed in the development of new materials. Redox media of molten carbonate or molten metal facilitating the transportation of ions offer promising possibilities for carbon oxidation. The suitability of different carbon fuels in various DCFC systems, in terms of crystal structure, surface properties, impurities and particle size, is also discussed. We explore the influence of a variety of parameters on the electrochemical performance of DCFCs, with regard to their open circuit voltage, power output and lifetime. The challenges faced in developing DCFCs are summarised, and potential prospects of the system are outlined.
Co-reporter:F. Fina, H. Ménard and J. T. S. Irvine
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 21) pp:NaN13936-13936
Publication Date(Web):2015/04/30
DOI:10.1039/C5CP00560D
Loading of a co-catalyst on the surface of a semiconductor photocatalyst is often carried out without considering the effect of the loading procedure on the final product. The present study looks in detail at the effect that the loading method has on the morphology and final composition of platinum-based nanoparticles by means of XPS and TEM analysis. Additionally, reduction pre-treatments are performed to investigate how the coverage, crystallinity and composition of the NPs affect the photocatalytic H2 evolution. The activity of Pt–g-C3N4 can significantly be enhanced by controlling the properties of the co-catalyst NPs.
Co-reporter:Guan Zhang, Chengsheng Ni, Xiubing Huang, Aakash Welgamage, Linda A. Lawton, Peter K. J. Robertson and John T. S. Irvine
Chemical Communications 2016 - vol. 52(Issue 8) pp:NaN1676-1676
Publication Date(Web):2015/12/07
DOI:10.1039/C5CC09075J
Photocatalytic conversion of cellulose to sugars and carbon dioxide with simultaneous production of hydrogen assisted by cellulose decomposition under UV or solar light irradiation was achieved upon immobilization of cellulose onto a TiO2 photocatalyst. This approach enables production of hydrogen from water without using valuable sacrificial agents, and provides the possibility for recovering sugars as liquid fuels.
Co-reporter:Guan Zhang, Chengsheng Ni, Lingjuan Liu, Guixia Zhao, Federica Fina and John T. S. Irvine
Journal of Materials Chemistry A 2015 - vol. 3(Issue 30) pp:NaN15419-15419
Publication Date(Web):2015/07/03
DOI:10.1039/C5TA03628C
We have demonstrated that resorcinol–formaldehyde resin polymers are good visible light responsive photocatalysts, with band gap energies ranging from ca. 1.80 to 2.00 eV. They were found to be photoactive in terms of decomposition of organic substrates under visible light irradiation. The photocatalytic performance of resins could be markedly enhanced by coupling with electron conducting materials such as reduced graphene oxide. Photocatalytic water oxidation was also achievable on the hybrid reduced graphene oxide/resin catalyst with a sacrificial agent. These industrial widely-used resins exhibit many merits as photocatalysts such as low-cost, high surface area, large pore size and volume, facile preparation and scalability for development of eco-friendly commercial products with “self-cleaning” properties, based on their capability for the oxidative removal of organic pollutants under visible light.
Co-reporter:Ahmed D. Aljaberi and John T. S. Irvine
Journal of Materials Chemistry A 2013 - vol. 1(Issue 19) pp:NaN5874-5874
Publication Date(Web):2013/03/20
DOI:10.1039/C3TA10844A
Samples from across the solid solution series La0.2Sr0.7−xCaxTiO3, were successfully synthesised by solid state reaction. Structural properties were determined at room temperature using X-ray powder diffraction and conductivity measurements were performed using the four probe DC and van der Pauw techniques at different temperatures and atmospheres. On increasing x, the perovskite phase lattice symmetry changes from cubic Pmm to tetragonal I4/mcm at x = 0.05 and tetragonal to orthorhombic Pbnm at x = 0.425. The lattice also shrinks as x increases. Samples showed only a slight 0.3% increase in lattice volume after reduction at 900 °C in 5% H2. On increasing calcium doping, conductivity in reduced samples and equilibrated at 900 °C in 5%H2 increased markedly reaching 27.53 S cm−1 at x = 0.45, but decreased as x increased further.
Co-reporter:Juan C. Ruiz-Morales, Jesús Canales-Vázquez, Cristian Savaniu, David Marrero-López, Pedro Núñez, Wuzong Zhou and John T. S. Irvine
Physical Chemistry Chemical Physics 2007 - vol. 9(Issue 15) pp:NaN1830-1830
Publication Date(Web):2007/03/21
DOI:10.1039/B617266K
A new SOFC anode material based upon oxygen excess perovskite related phases has been synthesised. The material shows better electrochemical performance than other alternative new anodes and comparable performance to the state-of-art of the electrodes, Ni–YSZ cermets, under pure hydrogen. Furthermore, this material shows an enhanced performance under methane operation with high open circuit voltages, i.e. 1.2–1.4 V at 950 °C, without using steam excess. The effect of the anode configuration was tested in one and four layer configurations. The optimised electrode polarisation resistances were just 0.12 Ω cm2 and 0.36 Ω cm2, at 950 °C, in humidified H2 and humidified CH4, respectively. Power densities of 0.5 W cm−2 and 0.35 W cm−2 were obtained in the same conditions. A very low anodic overpotential of 100 mV at 1 A cm−2 was obtained under humidified H2 at 950 °C. Samples were tested for two days in reducing and oxidising conditions, alternating heating and cooling processes from 850 °C to 950 °C, showing stable electrode performance and open circuit voltages. The results show that the substituted strontium titanates are very promising anode materials for SOFC.
Co-reporter:Elena Stefan, Paul A. Connor and John T. S. Irvine
Journal of Materials Chemistry A 2013 - vol. 1(Issue 28) pp:NaN8269-8269
Publication Date(Web):2013/06/07
DOI:10.1039/C3TA11496A
Composite anodes for solid oxide fuel cells (SOFC) developed on yttria stabilised zirconia (YSZ) porous supports by infiltration of electrode materials has been successfully applied for various anode and cathode compositions, resulting in high performance SOFC devices. The focus of this study is the performance of the chromium-rich spinel (MgFeCrO4) as an electrode support material when used alone or impregnated. The composite anodes were prepared by aqueous infiltration of nitrate salts to produce (La0.75Sr0.25)0.97Cr0.5Mn0.5O3−δ, Ce0.9Gd0.1O2−δ, CeO2 or Pd into a MgFeCrO4 scaffold with 45% porosity and studied by electrochemical impedance spectroscopy in symmetrical cell configuration. The performance was evaluated in humidified 5% H2/Ar in order to quantify their stability and performance up to 850 °C with respect to the MgFeCrO4 porous substrate. It was found that all the impregnated phases adhere very well to the spinel and considerably enhance performance and stability to a level required for SOFC applications. MgFeCrO4/LSCM/CGO and MgFeCrO4/LSCM/CGO/Pd showed the most substantial improvement in comparison to the scaffold’s performance, with ASR values of 1.74 Ω cm2 and 0.91 Ω cm2, respectively.
Co-reporter:Amit Sinha, David N. Miller and John T. S. Irvine
Journal of Materials Chemistry A 2016 - vol. 4(Issue 28) pp:NaN11123-11123
Publication Date(Web):2016/06/21
DOI:10.1039/C6TA03404G
Solid oxide fuel cells (SOFC) offer a clean technology to electrochemically generate electricity and heat from hydrogen or hydrocarbon based fuel at high efficiencies. All the active components of the SOFC unit cell comprise of rare-earth or low abundant elements. An increase in the cost of rare-earths is likely to jeopardize the commercialization prospects of SOFC based technologies. Hence, a greater scientific effort should be focused on the development of rare-earth free SOFC materials. The previous research works on electrode-supported intermediate temperature solid oxide fuel cells (IT-SOFCs) indicate that the anode supported concept provides better electro-chemical performance than the cathode supported one. Therefore, the total material cost of anode-supported SOFC is largely governed by the cost of the anode material. The objective of the present investigation was, therefore, the development of a rare-earth free anode material for IT-SOFC. The present work envisages application of titanium oxycarbide as a possible rare-earth free anode material for intermediate temperature solid oxide fuel cells. Titanium oxycarbide samples (TiOxC1−x with x = 0.2–0.8) were prepared by reaction-sintering of TiO and TiC powders under vacuum at 1500 °C for 5 h. Basic studies on TiOxC1−x (x = 0.2–0.8) with respect to phase purity and stability under oxidizing and reducing environments were carried out. The compatibility of titanium oxycarbide with intermediate-temperature electrolyte material (Ce0.9Gd0.1O3−δ) was studied. The electrochemical properties of planar cells using Ce0.9Gd0.1O3−δ as electrolyte and employing TiO0.2C0.8 and La0.8Sr0.2Co0.2Fe0.8O3−δ based anode and cathode materials were investigated. The present study indicates that titanium oxycarbide is an alternative anode material for IT-SOFC. This is the first report on the possibility of application of a rare-earth free ceramic in the form of titanium oxycarbide as a potential fuel electrode in IT-SOFC.
Co-reporter:C. S. Ni, J. M. Vohs, R. J. Gorte and J. T. S. Irvine
Journal of Materials Chemistry A 2014 - vol. 2(Issue 45) pp:NaN19155-19155
Publication Date(Web):2014/10/06
DOI:10.1039/C4TA04789C
Infiltration of ceramic materials into a pre-formed ceramic scaffold is an effective way of fabricating a solid oxide fuel cell with nano-structured ceramic electrodes by avoiding detrimental interfacial reactions through low-temperature processing for achieving high performance using hydrogen as well as a carbonaceous fuel. However, there are significant concerns about the applicability of this method because of the difficulty in fabricating a large-area gas-tight but thin electrolyte between two highly porous ceramic and the multiple repetitions of infiltration process. Here, a large-area (5 cm by 5 cm) scaffold with a thin yttria-stabilized zirconia (YSZ) electrolyte sandwiched between two identical porous structures is prepared by tape casting and co-firing, and then solution precursors are impregnated into the porous scaffolds to prepare nano-structured La0.8Sr0.2FeO3 (LSF) and La0.7Sr0.3VO3−δ (LSVred). The thus prepared solid oxide fuel cell with 10 wt% ceria + 1 wt% Pd as a catalyst in anodes shows a peak power of 489 mW cm−2 (∼6 W per cell) at 800 °C using H2 as a fuel and air as an oxidant. This large-area fuel cell retained the integrity of the thin electrolyte and high performance after the reducing-oxidation cycle at 900 °C, showing superiority over the conventional Ni(O)-YSZ based support.
Co-reporter:Lanying Lu, Chengsheng Ni, Mark Cassidy and John T. S. Irvine
Journal of Materials Chemistry A 2016 - vol. 4(Issue 30) pp:NaN11718-11718
Publication Date(Web):2016/06/28
DOI:10.1039/C6TA04074H
Perovskite electrodes have been considered as an alternative to Ni-YSZ cermet-based anodes as they afford better tolerance towards coking and impurities and due to redox stability can allow very high levels of fuel utilisation. Unfortunately performance levels have rarely been sufficient, especially for a second generation anode supported concept. A-site deficient lanthanum and calcium co-doped SrTiO3, La0.2Sr0.25Ca0.45TiO3 (LSCTA-) shows promising thermal, mechanical and electrical properties and has been investigated in this study as a potential anode support material for SOFCs. Flat multilayer ceramics cells were fabricated by aqueous tape casting and co-sintering, comprising a 450 μm thick porous LSCTA- scaffold support, a dense YSZ electrolyte and a thin layer of La0.8Sr0.2CoO3−δ (LSC)-La0.8Sr0.2FeO3−δ (LSF)-YSZ cathode. Impregnation of a small content of Ni significantly enhanced fuel cell performance over naked LSCTA-. Use of ceria as a co-catalyst was found to improve the microstructure and stability of impregnated Ni and this in combination with the catalytic enhancement from ceria significantly improved performance over Ni impregnation alone. With addition of CeO2 and Ni to a titanate scaffold anode that had been pre-reduced at 1000 °C, a maximum powder density of 0.96 W cm−2 can be achieved at 800 °C using humidified hydrogen as fuel. The encouraging results show that an oxide anode material, LSCTA- can be used as anode support with YSZ electrolyte heralding a new option for SOFC development.
Co-reporter:Guixia Zhao, Xiubing Huang, Xiangke Wang, Paul Connor, Jiaxing Li, Shouwei Zhang and John T. S. Irvine
Journal of Materials Chemistry A 2015 - vol. 3(Issue 1) pp:NaN303-303
Publication Date(Web):2014/10/31
DOI:10.1039/C4TA05376A
In this report, a novel method is proposed to prepare MnO/reduced graphene oxide (rGO) composites via calcining the precursors (i.e. δ-MnO2/graphene oxide composites) at 500 °C in Ar using no external reducing gas, in which graphene oxide (GO) successfully serves as a reductant by releasing CO during its thermolysis for the first time. By controlling the initial ratios of GO to KMnO4, differently composed precursors can be obtained via the redox reaction between GO and KMnO4, then leading to the formation of composites with different MnO/rGO ratios and dispersion of MnO on the rGO surface (denoted as MGC1 and MGC2). When applied as an active material in lithium ion batteries, MGC1 shows excellent cycling performance and capacity retention. Under 100 and 200 mA g−1, MGC1 could deliver reversible capacities as high as 900 and 750 mA h g−1, respectively, after more than 100 cycles. Considering the simple operation and low energy consumption in the whole material synthesis processes, the present strategy is feasible and effective for practical application. Even more importantly, the reductibility of graphene oxide upon thermolysis is utilized for the first time, which is meaningful for its extension in synthesis of functional nanomaterials.
Co-reporter:Xiubing Huang, Chengsheng Ni, Guixia Zhao and John T. S. Irvine
Journal of Materials Chemistry A 2015 - vol. 3(Issue 24) pp:NaN12964-12964
Publication Date(Web):2015/05/12
DOI:10.1039/C5TA01361E
Fast and reversible oxygen diffusion in solid oxides depending on oxygen partial pressure at low temperatures is a promising strategy for improving the overall performance and service lifetime of many energy-related materials. However, the high energy required for the redox reaction of cations and their high thermodynamic barriers have impeded the realization of fast oxygen diffusion at low temperatures. Herein, we report enhanced oxygen diffusion and storage capacity of monoclinic crednerite CuMnO2 at a lower temperature by surface modification with CeO2. The fast and reversible oxygen uptake/release can be attributed to CeO2 that serves as a fast oxygen diffusion channel between bulk CuMnO2 and the surrounding atmospheres. Importantly, the amount of CeO2 in the CuMnO2–CeO2 composite system has a great effect on the total oxygen storage capacity and redox behaviour. Our findings could provide useful information for developing effective oxygen storage materials for wide energy-related applications.
Co-reporter:Ahmed D. Aljaberi and John T. S. Irvine
Dalton Transactions 2015 - vol. 44(Issue 23) pp:NaN10833-10833
Publication Date(Web):2015/03/04
DOI:10.1039/C5DT00238A
The crystal structures of several members of the solid solution perovskite La0.2Sr0.7−xCaxTiO3 were investigated using the Rietveld analysis of neutron powder diffraction patterns collected in ambient conditions and high temperatures. At room temperature, samples showed a tetragonal I4/mcm symmetry for compositions with 0.1 ≤ x ≤ 0.35 followed by a phase transition to the orthorhombic Pbnm symmetry for compositions with 0.4 ≤ x ≤ 0.7. Samples with the orthorhombic symmetry showed two reversible phase transitions in the temperature range 20 °C–900 °C. The first phase transition was a discontinuous Pbnm–I4/mcm around 300 °C and the second was a continuous I4/mcm–Pmm transition around 900 °C. The lower symmetries resulted from very small distortions and changes in tilts of the BO6 octahedra of this perovskite material; which was a direct result from the A-site ionic radius mismatch.
Co-reporter:Paraskevi Efstathiou, Xiaoxiang Xu, Hervé Ménard and John T. S. Irvine
Dalton Transactions 2013 - vol. 42(Issue 22) pp:NaN7887-7887
Publication Date(Web):2013/04/18
DOI:10.1039/C3DT32064B
Sr1−xNbO3 is an unusual material that displays both metallic type conduction and photocatalytic activity, despite being an NbIV oxide, and it sustains photo-oxidation without degradation. The influence of crystal structure, surface area and surface chemistry on the photocatalytic activity of strontium niobate has been investigated. The crystal structure of strontium niobate depends on the Sr content of the A site, with cubic symmetry for Sr ≤ 0.92 and orthorhombic symmetry for 0.92 < Sr ≤ 0.97. The change of crystal structure from cubic to orthorhombic symmetry seems to have a negative effect on the photocatalytic activity, as the NbO6 octahedra become distorted and unfavourable for d-orbital overlapping. The photocatalytic activity increased significantly by enlarging the surface area through ball milling, nevertheless, a clear trend for the surface area effect on activity is not obtained among samples with different Sr content. An enrichment of Sr on the surface of strontium niobate was observed by XPS, which seems to be a governing factor for improving stability.
Co-reporter:Elena Stefan, Paul A. Connor, Abul K. Azad and John T. S. Irvine
Journal of Materials Chemistry A 2014 - vol. 2(Issue 42) pp:NaN18114-18114
Publication Date(Web):2014/09/19
DOI:10.1039/C4TA03633F
Novel electrode scaffold materials based on chromium-rich spinels, such as MgMxCr2−xO4, (M = Li, Mg, Ti, Fe, Cu, Ga) have been investigated for solid oxide fuel cell (SOFC) applications, in terms of conductivity and chemical stability when operated in fuel environments. Cation distributions were obtained by Rietveld refinement from X-ray diffraction data (XRD), with cation site preference considered in agreement with literature, and correlated with electrical properties determined experimentally. The substitutions with cations such as Li and Cu on B site improved the conductivity of the materials in air, while introducing Fe and Ga in the structure led to a decrease in conductivity in air. However, Fe had a positive contribution under reducing conditions, generating a change in the conductivity mechanism from p-type in air, to n-type. Conductivity measurements indicated that MgFexCr2−xO4 spinels exhibit faster reduction kinetics, in comparison with other substituted cations at the B site which is desirable in fuel cell application, for a reasonably fast response of a cell or a stack to reach its full functional potential. MgFeCrO4 showed fast reduction kinetics, with increase of the conductivity in reducing conditions from 0.014 S cm−1 to 0.4 S cm−1 and equilibration time for reaching the maximum conductivity value of 10 hours, under dry 5% H2/Ar at 850 °C.
Co-reporter:Xiubing Huang, Tae Ho Shin, Jun Zhou and John T. S. Irvine
Journal of Materials Chemistry A 2015 - vol. 3(Issue 25) pp:NaN13475-13475
Publication Date(Web):2015/05/28
DOI:10.1039/C5TA00983A
Hierarchically nanoporous materials based on layered perovskite oxides La1.7Ca0.3NixCu1−xO4−δ (x = 0, 0.25, 0.50 or 0.75) have been synthesized by a facile citrate-modified evaporation-induced self-assembly (EISA) method. These La1.7Ca0.3NixCu1−xO4−δ oxides have been evaluated as potential cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs) with Ni–YSZ cermet supported type cells. It was found that La1.7Ca0.3CuO4−δ cathode exhibits the maximum power density at high temperature (e.g., 1.5 W cm−2 at 850 °C), while La1.7Ca0.3Ni0.75Cu0.25O4−δ cathode shows the highest power density at intermediate temperature (e.g. 0.71 W cm−2 at 750 °C) using humidified H2 and air as the fuel and oxidant, respectively. The electrochemical performance of single cells with La1.7Ca0.3Ni0.75Cu0.25O4−δ cathode materials with different morphologies demonstrated better performance in the intermediate temperature range when using the cathode prepared by the citrate-modified EISA method, which has a bigger grain size, but with higher surface area and pore volumes.
Co-reporter:Kui Xie, Yaoqing Zhang, Guangyao Meng and John T. S. Irvine
Journal of Materials Chemistry A 2011 - vol. 21(Issue 1) pp:NaN198-198
Publication Date(Web):2010/10/22
DOI:10.1039/C0JM02205E
Synthetic hydrocarbon fuels from CO2/H2O are proposed as alternatives to hydrogen as an energy carrier to enable a carbon neutral energy cycle, given their inherent advantages of high H/C ratio and convenience of storage and transportation. Here we demonstrate the successful electrochemical reduction of CO2 into CO and CH4 in a proton conducting solid oxide electrolyser based on BaCe0.5Zr0.3Y0.16Zn0.04O3 − δ (BCZYZ) electrolyte and a composite iron/iron oxide cathode. The production of CH4 and CO reaches 0.07 and 3.25 ml min−1 cm−2, respectively, with 1.5 A cm−2 at 614 °C. The overall CO2 conversion rate in the electrochemical reduction process is 65%.
Co-reporter:Guixia Zhao, Xiubing Huang, Federica Fina, Guan Zhang and John T. S. Irvine
Catalysis Science & Technology (2011-Present) 2015 - vol. 5(Issue 6) pp:NaN3422-3422
Publication Date(Web):2015/04/28
DOI:10.1039/C5CY00379B
In this work, two photocatalysts (i.e., C3N4 and WO3) were successfully combined into a heterojunction structure by a facile hydrothermal method for mediator-free overall water splitting, analogous to the natural photosynthesis over a two-step photoexcitation Z-scheme system. Hydrogen and oxygen are evolved with a 2:1 ratio by irradiating the C3N4-WO3 composites loaded with Pt under visible light (λ > 420 nm) without any redox mediator. Introducing reduced graphene oxide (rGO) into the C3N4-WO3 composites enhances the water splitting efficiency. Through optimizing the mass ratio in the C3N4-WO3 composites, rGO content, amount of loaded Pt and pH value of the reacting system, the highest H2/O2 evolution rates of 2.84 and 1.46 μmol h−1 can be obtained, with a quantum yield of 0.9%. Our findings demonstrate that the hydrothermal method is a promising strategy for constructing intimate heterostructures for Z-scheme water-splitting systems without using any redox mediator, and that rGO can be used to further enhance the performance in optimized conditions.
