Performance Of SrCo_0.7Fe_0.2Ta_0.1O_3-δ And A₂FeNbO_6-δ（A=Ba,Sr） Electrode Materials For Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) have attracted great attention owing to their highenergy conversion efficiency, low environment pollution and various fuel resources.The traditional SOFCs operate at relatively high temperature (1000oC). The highoperating temperature can lead to many complex material problems, such as electrodesintering, interfacial diffusion between electrolyte and electrodes, and high costs ofmaterials and SOFC fabrication. All of these thus limit the commercial application ofSOFCs. Therefore, it is necessary to reduce the operating temperature of SOFCs tothe intermediate temperature (IT) range (600-800oC) in order to improve materialcompatibility and reduce SOFC costs. However, the electrochemical performance oftraditional cathode naterials (such as Sr-doped LaMnO3) decreases dramatically witha decrease in operating temperature. Therefore, the new cathode materials with highelectrocatalytical activities should be developed to meet the requirement ofIT-SOFCs. The perovskite oxide SrCo0.7Fe0.2Ta0.1O3-(SCFT) was synthesized by asolid-state reaction. The single phase SCFT having a cubic perovskite structure wasobtained by sintering the sample at1200oC for10h in air. The SCFT exhibited agood chemical compatibility with the La0.9Sr0.1Ga0.8Mg0.2O3-(LSGM) andCe0.8Sm0.2O1.9(SDC) electrolytes at950oC for10h. The average thermal expansioncoefficient was23.8×10-6K-1between30and1000oC in air. The electricalconductivities of the SCFT sample were71-119S cm-1in the600-800oC temperaturerange in air, and the maximum conductivity reached247S cm-1at325oC. Thepolarization resistance of the SCFT cathode on the LSGM and SDC electrolytes was0.159and0.060Ω cm2at700oC. The maximum power density of a single-cell withthe SCFT cathode on a300μm-thick LSGM and SDC electrolytes reached652.9and468.0mW cm-2at800oC, repectively. The SCFT cathode had shown a goodelectrochemical stability over a period of20h short-term testing. These findingsindicated that the SCFT could be a suitable alternative cathode material for IT-SOFCs.In searching for the anode materials which can resist carbon deposition andtolerate sulfur contamination, the perovskite-type materials have received extensiveattention because of its structural stability in wide range of oxygen partial presure.Type of double Perovskite A2BB′O6oxide, especially Sr2MgMoO6-has been studiedas a new anode material for SOFCs. This material not only has high ionic-electronicconductivity and hign catalytic activity, but also has a high carbon-and sulfur-telerantperformance. Therefore, it is important for developing a SOFC running onhydrocarbon fuel. The double perovskite oxide A2FeNbO6-(A=Ba， Sr) wassynthesized by a solid-state reaction. The SFNO exhibits a tetragonal structure bysintering the sample at1200oC for10h in H2; the BFNO having a cubic perovskitestructure was obtained by sintering the sample at1250oC for10h in H2. The averagethermal expansion coefficient of the SFNO and BFNO were12.0×10-6K-1and17.1×10-6K-1between30and1000oC in H2. The maximum electrical conductivitiesof SFNO and BFNO were2.601and3.114S cm-1in the200-900oC temperature rangein H2, repectively. The polarization resistance of the SFNO and BFNO anode on theLSGM electrolytes were0.816and0.441Ω cm2at800oC in H2. The maximumpower densities of single-cells with the SFNO and BFNO anode on a300mm-thickLSGM electrolyte reached647and513mW cm-2at800oC with H2as the fuel,repectively. This finding may indicate that further improvement is still needed toimprore the SFNO and BFNO want to be the anode performances for SOFCs.