•Ag nanoparticles grown on LSC substrate as a novel electrode for supercapacitors.•Ag/LSC displays a large areal capacitance of 14.8 F cm−2 at 1 mA cm−2.•Ag/LSC shows an outstanding stability (85.6% retention) at 50 mA cm−2.•The asymmetric supercapacitor shows an energy density of 21.9 mWh cm−3.Supercapacitors have potential for many emerging energy storage applications because of their excellent power density and long cycling stability. However, their applicability is often limited by the relatively low energy density. Here we report our findings in design, fabrication, and testing of a composite electrode composed of Ag nanoparticles grown directly on a porous perovskite-type material La0.7Sr0.3CoO3−δ (LSC) substrate. When tested in KOH aqueous electrolyte, the electrode (with a high mass loading of Ag nanoparticles of 28.6 mg cm−2) demonstrates an areal capacity of 14.8 F cm−2 (specific capacitance of 517.5 F g−1 and volumetric capacitance of 262.5 F cm−3) at 1 mA cm−2, while maintaining outstanding cycle stability (85.6% retention after 3000 cycles at 50 mA cm−2). An asymmetric supercapacitor (Ag/LSC//carbon cloth) with a wide voltage of 1.8 V displays a high energy density of 21.9 mWh cm−3 and an excellent stability. The superior capacitive performance can be ascribed to the porous, conductive and stable LSC framework, the uniform distribution and high mass loading of Ag nanoparticles on LSC, and the effective unitization of redox process.Download high-res image (392KB)Download full-size image

•Silver-based anode enables SOFCs to directly operate on propane without reforming.•A SOFC with Ag-GDC anode maintains a stable output at 62 mW cm−2 for 160 h at 800 °C.•Carbon layer is built on surface of Ag-GDC anode of SOFCs operated on propane.•The breakages on the carbon layer enable the stable operation of Ag-GDC-anode cell.A cermet of sliver and gadolinium-doped ceria (GDC) is investigated as the anode material of solid oxide fuel cells (SOFCs). The SOFCs are operated with hydrogen and dry propane as the fuel and ambient air as the oxidant. Their electrochemical and durability performances are tested and compared to those of SOFCs with conventional Ni-GDC anode. Experimental results show that performances of the SOFCs, respectively with Ag-GDC and Ni-GDC anode, are similar when operated on hydrogen, while quite different on propane. The open circuit voltage (OCV) of a SOFC with Ag-GDC anode is stable at ∼1 V while that with Ni-GDC anode continuously drops from the initial 1.2 V–0.85 V in 140 min. A SOFC with Ag-GDC anode has been stably operated on propane at a constant current density of 103 mA cm−2 for more than 160 h while that with Ni-GDC anode for only 50 h. SEM examination shows Ni-GDC anode is destroyed by carbon deposition during operation on propane, while Ag-GDC anode is well conserved and has a carbon layer, with some breakages, built on its surface. Mechanisms of the stable operation of SOFCs with Ag-GDC anode on dry propane is investigated and analyzed.Download high-res image (369KB)Download full-size image

•Ca-loaded activated carbon is developed as fuel for DC-SOFCs.•Ca significantly improves the DC-SOFC output from 258 to 373 mW cm−2 at 850 °C.•The catalytic activity of Ca is even better than that of Fe.•5 wt. % Ca-loaded activated carbon is the optimal carbon fuel for DC-SOFC.•Agglomeration of CaO reduces the fuel utilization of DC-SOFC.Ca-loaded activated carbon is developed as fuel for direct carbon solid oxide fuel cells (DC-SOFCs), operating without any carrier gas and liquid medium. Ca is loaded on activated carbon through impregnation technique in the form of CaO, which exhibits excellent catalytic activity and significantly promotes the output performance of DC-SOFCs. DC-SOFCs fueled by activated carbon with different Ca loading content (0, 1, 3, 5 and 7 wt. %) are tested and the performances are compared with the DC-SOFC running on the conventional Fe-loaded activated carbon. It is found that the performance of the DC-SOFC with 5 wt. % (373 mW cm−2) and 7 wt. % (378 mW cm−2) Ca-loaded activated carbon is significantly higher than that of the cells operated on 5 wt. % Fe-loaded activated carbon, 1 wt. % and 3 wt. % Ca-loaded activated carbon. The discharging time and fuel utilization of the DC-SOFC with 5 wt. % Ca-loaded activated carbon are also the optimal ones among all the cells. The microstructure, element distribution and carbon conversion rate of the Ca-loaded carbon, the impedance spectra of the corresponding DC-SOFCs are measured. The reasons for the reduced fuel utilization of 7 wt. % Ca-loaded carbon fuel are analyzed and the advantage of Ca-loaded carbon for DC-SOFCs is demonstrated in detail.

•Ni1-xFexOδ-YSZ anode-supported DC-SOFCs are systematically investigated.•Anode of DC-SOFCs can be reduced in situ by CO generated from Boudouard reaction.•A proper amount of Fe addition in anode can improve DC-SOFC performance.•A DC-SOFC with optimal anode of x = 0.1 gives MPD of 529 mW cm−2 at 800 °C.•DC-SOFC of x = 0.1 run at 0.1 A cm−2 shows a stable plateau of 0.86 V of 15 h.Solid oxide fuel cells (SOFCs) with thin yttrium-stabilized-zirconia (YSZ) electrolyte supported on composite anode of nickel-iron bimetal and YSZ are prepared and operated directly on Fe-loaded activated carbon fuel, without any liquid medium or purging gas. The composition of the anode is represented as Ni1-xFexOδ (x = 0, 0.05, 0.1, 0.2, 0.3)-YSZ. Experiment result shows that such kind of all-solid-state direct carbon solid oxide fuel cells (DC-SOFCs) perform well at 800 °C, giving maximum output power densities in the range of 425–529 mW cm−2. Similar to the case of a SOFC operated on hydrogen fuel, a small amount of Fe addition into the Ni-based anode can improve the performance of a DC-SOFC and the optimum composition is x = 0.1. A DC-SOFC with Ni0.9Fe0.1Oδ-YSZ anode, loaded with 2.5 g Fe-loaded activated carbon fuel, is steadily operated at a constant current density of 0.1 A cm−2 for 15 h at 800 °C. The anodes and the DC-SOFCs are characterized through XRD, AC impedance spectroscopy, and SEM measurements. The superior performance of the Fe-added anode is analyzed accordingly.

•Proper amount of Al2O3 doping can improve sintering and electrical properties of YSZ.•Particle size of doping Al2O3 powder affects the doping effects of Al2O3-doped YSZ.•Al2O3 particle distribution in YSZ determines the grain size of Al2O3-doped YSZ.•Larger mass of Al2O3 with larger particle size is needed to get optimum performance.•1 wt.% Al2O3doping into YSZ electrolyte enhances the SOFC output by 20%.The effects of doping amount and particle size of alumina on the sintering behavior and electrical performance of 8 mol% yttria-stabilized zirconia (YSZ) are investigated through microstructure and impedance spectroscopy analysis. Initial results show that a proper amount of Al2O3 doping can effectively improve the sintering behavior and the electrical performance of YSZ, and the optimum doping amount varies with the particle size of Al2O3. When a raw Al2O3 powder (modal particle size: 0.28 μm) is used as dopant, the optimal doping amount for electrical and sintering improvement is 0.7 wt.% and 3 wt.%, respectively, while that with 1400 °C-calcined-Al2O3 (0.45 μm), 1 wt.% and 4 wt.%. A concept of space distribution distance of the doping particles is introduced to interpret the improvement effect.

A direct carbon solid oxide fuel cell (DC-SOFC) is an all-solid-state electricity generation device that operates directly with solid carbon as fuel, without any liquid medium and feeding gas. Tubular electrolyte-supported solid oxide fuel cells (SOFCs), with silver-gadolinium doped ceria (Ag-GDC) as both anode and cathode materials, are fabricated and operated directly with activated carbon as fuel. The kinetics of the DC-SOFCs is carried out through analyzing the correlations of the cell reaction rates to the emitting rates of CO and CO2. It turns out that higher operating current corresponds to higher rates of consuming and producing CO, through electrochemical oxidation at the anode and the Boudouard reaction at the carbon fuel, respectively. The rate of consuming CO can be maintained constant by controlling the operating current while the rate of producing CO decreases with time because of carbon consumption. When the CO producing rate becomes smaller than the CO consuming rate, the operation will be terminated. Compared to the rates of the chemical reactions, the diffusion rates of CO and CO2 are so fast that their impeding effect on the cell performance can be neglected.

•A wet agglomeration process is developed to make Fe-loaded carbon fuel for DC-SOFCs.•The process improves the DC-SOFC output from 134 to 196 mW cm−2 at 850 °C.•Carbon fuel prepared by agglomeration enables longer DC-SOFC discharging time.•Agglomeration process is superior to others in cost, time, and environment.•DC-SOFC with the agglomerated carbon gives high fuel utilization.A wet agglomeration process is developed for preparing Fe-loaded carbon fuel for direct carbon solid oxide fuel cells (DC-SOFCs). This technique involves a simple mechanical mixing of carbon and Fe2O3 powder, along with a proper amount of polyvinylbutyral (PVB) ethanol solution as binder. A DC-SOFC with carbon fuel prepared by this technique is tested and its performance is compared with DC-SOFCs, respectively operated with pure carbon, carbon mechanically mixed with Fe2O3, and carbon prepared with the conventional impregnation technique. Experimental results show that its output performance is comparable to that of the cell with carbon fuel prepared by the impregnation technique and is better than those of cells, respectively with pure carbon and carbon mechanically mixed with Fe oxide as the fuels. The microstructures of the variety of carbon, the impedance spectra of the corresponding DC-SOFCs are measured and the superiority of the wet agglomeration process in preparing the Fe-loaded carbon for DC-SOFCs is analyzed in detail.

•In anode-supported SOFCs, Al2O3 is doped into YSZ electrolyte as sintering aid.•1 wt.% Al2O3 doping can reduce the sintering temperature of YSZ to 1573 K.•The output of cell is improved with reduced sintering temperature.•A buffer layer is introduced between the Al2O3-doped-YSZ electrolyte and anode.•Buffer layer prevents Al2O3 and NiO from forming non-conductive NiAl2O4.In order to reduce the sintering temperature of Ni-based anode-supported thin 8 mol% yttria-stabilized zirconia (YSZ) elsectrolyte solid oxide fuel cells (SOFCs), alumina, with a weight percent of 1, 3, 5, and 7, is respectively doped into YSZ as sintering aid. A pure YSZ buffer layer is introduced between the Al2O3-doped-YSZ electrolyte and Ni–YSZ anode, to prevent Al2O3 and NiO from forming non-conductive spinel NiAl2O4. The experimental results show that doping proper amount of Al2O3 doping can reduce the sintering temperature of YSZ, e.g., 1 wt.% doping decreases the temperature from 1673 K to 1573 K. Anode-supported SOFCs are prepared with Al2O3-doped-YSZ electrolytes sintered at different temperatures. Electrochemical characterization of the SOFCs shows that the single cell with 1 wt.% alumina-doped YSZ electrolyte sintered at 1573 K gives the highest output. The effect of alumina doping on sintering behavior and electrical performance of YSZ is discussed in detail.

•Carbon deposits on Ni–YSZ anode of SOFCs operated on CH4 or CO.•Deposition is limited by kinetics at low and thermodynamics at high temperature.•Effects of C formation on anode correlates strongly between each other.•High C solubility in Ni and strong C–Ni interaction cause the anode deactivation.•Carbon formation on anode can be avoided by O2− flux through electrolyte of SOFC.Deactivation of Ni–YSZ (yttrium stabilized zirconia) anode of SOFCs operated on CH4 and CO, respectively, is investigated systematically. Experiments show that the rate of carbon deposition on Ni–YSZ substrate from CH4 increases with temperature in the whole testing temperature range (550–800 °C), while the rate from CO increases with temperature at lower temperatures but decreases at higher temperatures. Larger amount of carbon deposit results in more significant substrate deformation and destruction, which can be explained by the mechanism of carbon fiber growth on Ni exposed to carbon-containing gases. Carbon deposition can be avoided by oxygen ion flux through the electrolyte of SOFCs operated on either CH4 or CO.

•La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) can be used as electrolyte of direct carbon SOFCs.•DC-SOFC with LSGM electrolyte gives higher performance than that with YSZ.•LSGM-electrolyte DC-SOFC gives maximum power density of 383 mW cm−2 at 850 °C.•Operation of LSGM-DC-SOFC at 210 mA cm−2 lasts 72 min, with fuel utilization of 60%.Perovskite-type La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) is synthesized by conventional solid state reaction. Its phase composition, microstructure, relative density, and oxygen-ionic conductivity are investigated. Tubular electrolyte-supported solid oxide fuel cells (SOFCs) are prepared with the LSGM as electrolyte and gadolinia doped ceria (GDC) mixed with silver as anode. The SOFCs are operated with Fe-loaded activated carbon as fuel and ambient air as oxidant. A typical single cell gives a maximum power density of 383 mW cm−2 at 850 °C, which is nearly 1.3 times higher than that of the similar cell with YSZ as electrolyte. A stability test of 72 min is carried out at a constant current density of 210 mA cm−2, with a fuel utilization of 60%, indicating that LaGaO3-based electrolyte is promising to be applied in direct carbon SOFCs (DC-SOFCs).

•Cone-shaped tubular anode-supported SOFCs are fabricated by LPIM technique.•The anode substrates are with high accuracy in size and low deformation in shape.•Anode substrates with enough porosity can be obtained with 15 wt.% paraffin used.•A two-cell-stack (without graphite) presents an output power of 5.32 W at 800 °C.A low pressure injection molding (LPIM) technique is successfully developed to fabricate porous NiO–YSZ anode substrates for cone-shaped tubular anode-supported solid oxide fuel cells (SOFCs). The porosity and microstructure of the anode samples prepared with different amount of pore formers are investigated through the Archimedes method and SEM analysis. Experimental results show that with 15 wt.% paraffin as plasticizer, porosity of the NiO–YSZ substrates sintered at 1400 °C is proportional to the amount of graphite as pore former, and proper porosities can be obtained with or without 5 wt.% graphite. NiO–YSZ/YSZ/LSM–YSZ single cells are assembled and tested to demonstrate the feasibility of the LPIM technique. At 800 °C, with moist hydrogen (75 ml min−1) as fuel and ambient air as oxidant, the cell with the anode substrate fabricated with 5 wt.% pore former shows a maximum power density of 531 mW cm−2, while the cell without any pore former, 491 mW cm−2. Two of the single cells (without graphite) are applied to assemble a two-cell-stack which gives an open circuit voltage of 1.75 V and a maximum output power of 5.32 W, at operating temperature of 800 °C.

Anode-supported tubular solid oxide fuel cells (SOFCs) with Cu–CeO2–yttria-stabilized zirconia (YSZ) anode, YSZ electrolyte film, and silver cathode were fabricated. The cells were tested with 5 wt% Fe-loaded activated carbon and dry CO, respectively, and their performances were compared to verify the reaction mechanism of direct carbon SOFCs (DC-SOFCs). The corresponding current–voltage curves and impedance characteristics of the cells operating on these two different fuels were found to be almost the same at high temperatures, demonstrating the presumed mechanism that the anode reaction of a DC-SOFC is the electrochemical oxidation of CO, just as in a SOFC operated directly on CO. Some experimental evidences including the difference in open circuit voltage at different temperatures and the operating stability of the cells were analyzed in detail.

Anode-supported cone-shaped tubular solid oxide fuel cells (SOFCs) are successfully fabricated by a phase inversion method. During processing, the two opposite sides of each cone-shaped anode tube are in different conditions--one side is in contact with coagulant (the corresponding surface is named as “W-surface”), while the other is isolated from coagulate (I-surface). Single SOFCs are made with YSZ electrolyte membrane coated on either W-surface or I-surface. Compared to the cell with YSZ membrane on W-surface, the cell on I-surface exhibits better performance, giving a maximum power density of 350 mW cm−2 at 800 °C, using wet hydrogen as fuel and ambient air as oxidant. AC impedance test results are consistent with the performance. The sectional and surface structures of the SOFCs were examined by SEM and the relationship between SOFC performance and anode structure is analyzed. Structure of anodes fabricated at different phase inversion temperature is also investigated.Highlights► Cone-shaped anode-supported SOFCs are fabricated by phase inversion. ► Microstructures of the two opposite sides of the anode wall are different. ► Performance of SOFC with YSZ on the surface isolated from coagulant is good. ► The side contacting water is a typical asymmetric structure by phase inversion. ► 20–50 °C is a suitable inversion temperature range for fabricating anode supports.

(Ni0.75Fe0.25–xMgO)/YSZ samples—with a varying weight percentage x (0, 5%, 10%) of MgO with respect to Ni0.75Fe0.25—were prepared and studied as anodes for intermediate temperature solid oxide fuel cells (SOFCs) operated on humidified methane (3% H2O). Among the cells with different anode compositions, it was found that the cell with the (Ni0.75Fe0.25–5%MgO)/YSZ anode showed the highest power density, giving 648 mW cm−2 at 800 °C. The cells with MgO-doped anodes were able to operate stably for 20 h under a current density of 0.53 A cm−2 at 700 °C without observed degradation, while the cells without MgO degraded rapidly. The mechanisms responsible for the superior performance and duration of the (Ni0.75Fe0.25–5%MgO)/YSZ anode were analyzed.Highlights► Novel SOFC anode material (Ni0.75Fe0.25–xMgO)/YSZ is investigated in methane fuel. ► Electrochemical performance of the novel anode is much better than Ni/YSZ anode. ► SOFC with the MgO-doped novel anode can operate stably on methane fuel. ► Failure of traditional anode in hydrocarbon fuel is caused by carbon fiber growth. ► MgO in Ni-based anode can suppress carbon fiber growth or strengthen the anode.

Anode-supported cone-shaped tubular solid oxide fuel cells (SOFCs) and segmented-in-series (SIS) SOFCs stack based on gadolinia-doped ceria (GDC) electrolyte film direct utilization methane as fuel are successfully developed in this study. The single cell exhibits maximum power densities of 484 mWcm−2 and 414 mWcm−2 at 600 °C by using moist hydrogen and moist methane as fuel, respectively. A durability test of the single NiO–GDC/GDC/LSCF-GDC cell is performed at a constant current density of 0.4 Acm−2 direct fueled with methane for about 140 h at 600 °C. It stabilizes with no apparent degradation during the durability test. Very little carbon is detected on the anodes, suggesting that carbon deposition is limited during cell operation. The results show that the stability and dependability of as-prepared single cell is good and it is very significant for portable application of low-temperature SOFCs (LT-SOFCs). A three-cell-stack based on the above-mentioned SOFCs is fabricated and tested by direct utilization of methane. Its typical electrochemical performance is investigated. And the stack has experienced 5 times thermal cycling test. Good thermo-mechanical properties and stability are observed and that the developed segmented-in-series LT-SOFCs stack with GDC electrolyte film is highly promising for portable application.

In this paper, La0.8Sr0.2MnO3-Ba0.1Bi0.9O1.5-δ (LSM-BSB) composite cathode was prepared and characterized for intermediate temperature solid oxide fuel cells (IT-SOFCs). XRD results show that no reaction occurred between LSM and BSB at 900°C. SEM results show that the LSM-BSB composite cathode formed good contact with YSZ electrolyte after sintered at 900°C for 2 h, which significantly reduced the sintering temperature of cathode. Compared with the LSM-YSZ electrode sintered at 1200°C for 2 h, LSM-BSB electrode exhibits better electrochemical performance. At 800°C, the area specific resistance (ASR) of the LSM-BSB30 electrode is about 0.168 Ωcm2, which is nearly 1.5 times lower than that of LSM-YSZ composite cathode.

Anode-supported solid oxide fuel cells (SOFCs) with a trilayered yttria-doped bismuth oxide (YDB), strontium- and magnesium-doped lanthanum gallate (LSGM) and lanthanum-doped ceria (LDC) composite electrolyte film are developed. The cell with a YDB (18 μm)/LSGM (19 μm)/LDC (13 μm) composite electrolyte film (designated as cell-A) shows the open-circuit voltages (OCVs) slightly higher than that of a cell with an LSGM (31 μm)/LDC (17 μm) electrolyte film (designated as cell-B) in the operating temperature range of 500–700 °C. The cell-A using Ag-YDB composition as cathode exhibits lower polarization resistance and ohmic resistance than those of a cell-B at 700 °C. The results show that the introduction of YDB to an anode-supported SOFC with a LSGM/LDC composite electrolyte film can effectively block electronic transport through the cell and thus increased the OCVs, and can help the cell to achieve higher power output.

Operation of cone-shaped anode-supported segmented-in-series solid oxide fuel cell (SIS-SOFC) stack directly on methane is studied. A cone-shaped solid oxide fuel cell stack is assembled by connecting 11 cone-shaped anode-supported single cells in series. The 11-cell-stack provides a maximum power output of about 8 W (421.4 mW cm−2 calculated using active cathode area) at 800 °C and 6 W (310.8 mW cm−2) at 700 °C, when operated with humidified methane fuel. The maximum volumetric power density of the stack is 0.9 W cm−3 at 800 °C. Good stability is observed during 10 periods of thermal cycling test. SEM-EDX measurements are taken for analyzing the microstructures and the coking degrees.

Tubular electrolyte-supporting solid oxide fuel cells directly operated on carbon fuel were fabricated and tested. Gadolinia doped ceria (GDC) mixed with silver was used as the anode to catalyze the electrochemical oxidation of CO while Fe-based catalyst was loaded on the carbon fuel to enhance the Boudouard reaction. The performance was significantly improved, with a maximum power density of 45 mW cm−2, 10 times higher than that of the cell without any catalyst. Impedance measurements showed that the polarization resistance was decreased by tens of times through applying catalysts in the cell. An operation life of 10 h was observed at a constant current of 70 mA. The mechanism of the cell reaction was analyzed.

Anode-supported solid oxide fuel cells (SOFCs) with strontium- and magnesium-doped lanthanum gallate (LSGM) have been developed. A novel buffer layer, yttria-doped bismuth oxide (YDB), has been introduced between the cathode and electrolyte interface, while a conventional buffer layer, lanthanum-doped ceria (LDC), has been used between the anode and electrolyte interface. A cell with a YDB (18 μm)/LSGM (19 μm)/LDC (13 μm) composite electrolyte film showed an open-circuit voltage (OCV) 1.07–1.0 V in the operating temperature range of 500–700 °C. The cell using Ag–YDB composite cathode can achieve 701 mW cm−2 maximum power density at 700 °C.

A phase-inversion method was successfully developed to fabricate tubular NiO–YSZ anode-supported solid oxide fuel cells (SOFCs). The microstructure and the sintering shrinkage of the anode samples made by different pore-formers were investigated through SEM and TGA analysis. Compared with graphite pore-former, flour pore-former shows a more severe sintering shrinkage and easily introduces some bigger pores which are very detrimental to the mechanical strength of the anode supports. Experimental results show that the porosity should be less than 55%, otherwise, it will severely affect the resistance of the anode. Four single cells were fabricated at different locations on the same 15 cm long tubular NiO–YSZ anode-support; the maximum power output of the cells depended on their distance from the anode current collecting point (848, 774, 680 and 645 mW/cm2 at 800 °C, using wet hydrogen as fuel and ambient air as oxidant). Electrochemical impedance measurements reveal that change of the ohmic resistance is one of the main factors affecting power output of the presented tubular anode-supported SOFCs.

A novel design of cone-shaped tubular segmented-in-series solid oxide fuel cell (SOFC) stack is presented in this paper. The cone-shaped tubular anode substrates are fabricated by slip casting technique and the yttria-stabilized zirconia (YSZ) electrolyte films are deposited onto the anode tubes by dip coating method. After sintering at 1400 °C for 4 h, a dense and crack-free YSZ film with a thickness of about 7 μm is successfully obtained. The single cell, NiO–YSZ/YSZ (7 μm)/LSM–YSZ, provides a maximum power density of 1.78 W cm−2 at 800 °C, using moist hydrogen (75 ml min−1) as fuel and ambient air as oxidant.A two-cell-stack based on the above-mentioned cone-shaped tubular anode-supported SOFC is fabricated. Its typical operating characteristics are investigated, particularly with respect to the thermal cycling test. The results show that the two-cell-stack has good thermo-mechanical properties and that the developed segmented-in-series SOFC stack is highly promising for portable applications.

A simple and feasible technique is developed successfully to fabricate the cone-shaped tubular segmented-in-series solid oxide fuel cell (SOFC) stack. The cone-shaped tubular anode substrates and yttria-stabilized zirconia (YSZ) electrolyte films are fabricated by dip coating technique. After sintering at 1400 °C for 4 h, a dense and crack-free YSZ film with a thickness of about 35.9 μm is successfully obtained. The single cell, NiO–YSZ/YSZ/LSM–YSZ, provides a maximum power density of 1.08 and 1.35 W cm−2 at 800 and 850 °C, respectively, using moist hydrogen (75 ml/min) as fuel and ambient air as oxidant.A two-cell-stack based on the above-mentioned cone-shaped tubular anode-supported SOFC was assembled and tested. The maximum total power at 800 °C was about 3.7 W.

The composite cathodes consisting of perosvkite material La0.6Sr0.4Co0.8Fe0.2O3−δ (LSCF) and La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) were prepared, and then studied for potential applications in intermediate temperature solid oxide fuel cells (SOFCs) with LSGM electrolyte. Both ac impedance spectroscopy and dc polarization measurements were performed in air within the temperature range of 600–800 °C under open circuit potential. The results showed that the addition of 40 wt% LSGM to LSCF (LSCF–LSGM40) resulted in lower interfacial resistance (0.24 Ω cm2 at 800 °C) than other composite cathodes and was slightly lower than the single-phase LSCF cathode (0.28 Ω cm2 at 800 °C). Although adding LSGM electrolyte material to the LSCF electrode did not improve the electrode performance much, it could buffer the thermal expansion coefficient (TEC) of LSCF, which is larger than that of LSGM electrolyte.

An La0.6Sr0.4Co0.2Fe0.8O3–La0.8Sr0.2MnO3 (LSCF–LSM) multi-layer composite cathode for solid oxide fuel cells (SOFCs) was prepared on an yttria-stabilized zirconia (YSZ) electrolyte by the screen-printing technique. Its cathodic polarization curves and electrochemical impedance spectra were measured and the results were compared with those for a conventional LSM/LSM–YSZ cathode. While the LSCF–LSM multi-layer composite cathode exhibited a cathodic overpotential lower than 0.13 V at 750 °C at a current density of 0.4 A cm−2, the overpotential for the conventional LSM–YSZ cathode was about 0.2 V. The electrochemical impedance spectra revealed a better electrochemical performance of the LSCF–LSM multi-layer composite cathode than that of the conventional LSM/LSM–YSZ cathode; e.g., the polarization resistance value of the multi-layer composite cathode was 0.25 Ω cm2 at 800 °C, nearly 40% lower than that of LSM/LSM–YSZ at the same temperature. In addition, an encouraging output power from an YSZ-supported cell using an LSCF–LSM multi-layer composite cathode was obtained.

Novel cathode materials, Ba2−xSrxFeO4+δ (x = 0.5, 0.6, 0.7, 0.8, 1.0), for intermediate-temperature solid oxide fuel cells on a samaria-doped ceria (SDC) electrolyte were prepared by the glycine–nitrate route and characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric (TG) analysis, electrochemical impedance spectroscopy and steady-state polarization measurement. SEM results showed that the electrode formed a good contact with the SDC electrolyte after sintering at 1000 °C for 2 h. The value of δ in Ba1.0Sr1.0FeO4+δ materials was calculated from the TG results. The electrochemical impedance spectra revealed that Ba2−xSrxFeO4+δ had a better electrochemical performance than that of Ln2NiO4 (Ln = La, Pr, Nd, Sm). In the Ba2−xSrxFeO4+δ (x = 0.5, 0.6, 0.7, 0.8, 1.0) family, the composition Ba1.0Sr1.0FeO4+δ exhibited the best electrochemical activity for oxygen reduction. The polarization resistance of Ba1.0Sr1.0FeO4+δ on SDC electrolyte was 1.11 Ω cm2 at 700 °C, which was less than half that reported for Ln2NiO4 at the same temperature.

A gas-tight yttria-stabilized zirconia (YSZ) electrolyte film was fabricated on porous NiO–YSZ anode substrates by a modified slurry coating, i.e., a pressure-assisted slurry-casting technique. The SEM results showed that the YSZ film was fully dense with a thickness of 26μm. Combined with a screen-printed La0.7Sr0.3MnO3La0.7Sr0.3MnO3 (LSM)–YSZ cathode, a single fuel cell was tested in a temperature range from 650 to 850∘C with humidified hydrogen as fuel and ambient air as oxidant. The open circuit voltage (OCV) of over 1.0 V was observed, which suggested that the fuel leakage across YSZ film was negligible. The maximum power density at 650, 700, 750, 800 and 850∘C were 208, 513, 837, 1116 and 1234mW/cm2, respectively. The results of impedance measurements revealed that the activation energy for the total ohmic resistance of the cell and for the total electrode polarization was 66.1 and 101.7 kJ/mol, respectively. The cell performance was essentially governed by the electrode polarization. A short-term stability testing of the cell for 5 h showed that the fuel cell was quite stable in the testing procedure.

Four kinds of nickel oxide powder with different microstructure were used as the anode materials for anode-supported solid oxide fuel cells (SOFCs). The microstructure of the powders was evaluated using scanning electron microscopy (SEM). The performance of the anode-supported SOFCs was investigated through measuring and analyzing the current–voltage characteristics, electrochemical impedance spectra (EIS) and microstructure images. It was found that the performance of a Ni–YSZ anode-supported SOFC depends strongly upon the anode microstructure which is decided by the characteristics of nickel oxide powder. The highest SOFC performance was obtained from the cell with the finest nickel oxide powder synthesized by glycine-nitrate combustion method while the lowest performance was with the coarsest powder purchased from a general chemical supplier.

A screen printing technique was developed to deposit Sm0.2Ce0.8O1.9 (SDC) electrolyte films onto NiO/SDC anode substrates. After co-firing the anode/film bilayers at 1400 °C for 4 h, pure Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF), BSCF/SDC and BSCF/Ag were screen-printed onto the sintered SDC films, respectively, to complete the single SOFC fabrication. Impedance measurements show that the area-specific resistance (ASR) for BSCF, BSCF/Ag and BSCF/SDC is 0.08, 0.12 and 0.22 Ωcm2 at 600 °C, respectively. The cell with pure BSCF cathode provides a maximum power density of 1.08 Wcm− 2 at 600 °C using hydrogen as fuel and stationary air as oxidant. The cells with BSCF/SDC and BSCF/Ag composite cathodes give the maximum power densities of 0.54 and 0.59 Wcm− 2 at 600 °C, respectively. The results indicate that the SOFCs with BSCF-based cathodes show excellent performance below 600 °C. Screen printing is a promising approach for thin electrolyte film fabrication. The effect of cathode materials on the cell performance is electrochemically tested and discussed.

Pure YSZ (8 mol% yttria stabilized zirconia) and Fe-doped (2 mol% and 4 mol%) YSZ electrolytes were prepared and sintered at 1200 °C and 1400 °C, respectively by solid state method. Their crystal structure, microstructure, sintering behavior, electrical conductivity, and performance as SOFC electrolyte were investigated. Fe can be dissolved into YSZ lattice and decrease the lattice parameter. When sintered at 1200 °C, Fe dopant can make the YSZ electrolyte denser and increase its total conductivity. When sintered at 1400 °C, the total conductivities of samples decrease for higher Fe dopant concentrations though the densities of samples increase. All the SOFCs with Fe-doped YSZ electrolytes show better performance than those with Fe-free electrolytes. The mechanisms of the effect of Fe doping on the properties of YSZ were analyzed.

Sm0.1Ce0.9O1.95 (SDC) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) were synthesized by a glycine–nitrate process. A composite LSCF–SDC–Ag cathode was prepared and its structure was analyzed by X-ray diffraction. No chemical reactions among LSCF, SDC, and Ag in the composite cathode were found. The composite cathode was applied onto SDC electrolyte and the microstructure of the electrolyte–electrode interface was examined by SEM. The overpotential of the interface was measured. A single SOFC was prepared by using LSCF–SDC–Ag as cathode, SDC as electrolyte, and Ni–SDC as anode and its performance was measured. Compared to a similar SOFC with LSCF–SDC cathode, it is found that adding Ag in the cathode improved the SOFC performance significantly.