Properties Of Layered Perovskite LaBaCuCo（Fe）O_5+δ Based Cathodes For Intermediate-temperature Solid Oxide Fuel Cells

Solid oxide fuel cells （SOFCs） are considered as the most promising powergenerating technologies in the future, which convert chemical energy directly intoelectrical energy. Their striking advantages are substantially high conversionefficiency, excellent fuel flexibility and very low levels of emission of pollutants.However, the traditional SOFC system is operated at high temperature of8001000°C, which can lead to highly cost of the materials and interfacial diffusion betweenelectrolytes and electrodes, thus limiting the commercial use of SOFCs. As aconsequence, significant efforts have been devoted to the development ofintermediate-temperature SOFCs （IT-SOFCs） capable of operating at600800°C.However, the polarization resistance of the cathode significantly increased withdecreasing operation temperature. Therefore, the development of new cathodematerials with high electrochemical performance is indispensable to thecommercialization of IT-SOFCs. Our previous works have demonstrated thatLaBaCuFeO_5+δand LaBaCuCoO_5+δlayered perovskites showed high electrochemicalperformance, which were suitable cathode candidates for application in IT-SOFCs. Toextend our research work, we investigated the feasibility of Sr-doped LaBaCuMO_5+δ（M=Fe,Co） as cathode materials. The cell performance was also evaluated for use inIT-SOFCs.The layered perovskite cathode materials, LaBa_1-xSr_xCuFeO_5+δ（LBSCuFx,x=0.25and0.50） were prepared with a solid-state reaction. The LBSCuF oxidessintered at1050oC for24h crystallized in a single phase layered-perovskite structure.The LBSCuF materials had a good chemical compatibility with the SDCelectrolyte for temperatures up to950°C. The lattice parameters and cell volumes ofthe LBSCuF decreased with increasing Sr content. The average TEC was18.1×10^-6K^-1and17.6×10^-6K^-1for LBSCuF samples with x=0.25and0.50in the temperaturerange of30850°C, respectively. The electrical conductivities of LBSCuF samplesattained101163S cm^-1for x=0.25and130208S cm^-1for x=0.50in the temperature range of600800°C, respectively. The polarization resistances ofLBSCuF cathodes with x=0.25and0.50were0.193Ω cm²and0.173cm²at700oC, respectively. The peak power densities of a single-cell for x=0.25and0.50cathodes were614and661mW cm2at800oC, respectively. The resultsdemonstrated that the LBSCuF oxides were very promising cathode materials for usein IT-SOFCs.The layered-perovskite cathode materials, LaBa_1-xSr_xCuCoO_5+δ（LBSCuCx,x=0.25and0.50） were prepared with a solid-state reaction. The LBSCuC oxidessintered at1050oC for24h crystallized in a single phase layered-perovskite structure.The materials displayered a good chemical compatibility with the SDC electrolytefor temperatures up to950°C for2h. The lattice parameters and cell volumes of theLBSCuC decreased with increasing Sr content. The average TEC was19.5×10^-6K^-1and19.1×10^-6K^-1for the LBSCuC cathodes with x=0.25and0.50in thetemperature range of30850°C, respectively. The electrical conductivities of theLBSCuC cathodes attained237338S cm^-1for x=0.25and321460S cm^-1for x=0.50in the temperature range of500800°C, respectively. The polarizationresistances of the LBSCuC cathodes with x=0.25and0.50on SDC electrolyte were0.059cm²and0.042cm²at800oC, respectively. The maximum power densitiesof a single-cell with x=0.25and0.50LBSCuC cathodes were563and573mW cm`（-2）at800oC, respectively. The results demonstrated that the LBSCuC oxides exhibitedgood cathode performances for application in IT-SOFCs.The LBSCuF0.50-SDCx composites were assessed as IT-SOFC cathodes. TheLBSCuF0.50-SDC40composite cathode presented the smallest TEC, in which theaverage TEC was14.9×10^-6K^-1in the temperature range of30850°C. Theelectrical conductivities of LBSCuF0.50-SDCx samples decreased as the SDC contentincreased. The introduction of SDC into LBSCuF0.50cathode improved theelectrochemical performance of the composite cathodes. The LBSCuF0.50-SDC30composite cathode exhibited the smallest polarization resistance of0.030and0.113cm²at800and700oC, respectively. The peak power densities of a single-cell withLBSCuF0.50-SDC30composite cathode were778and329mW cm2at800and700 oC, respectively. The results indicated that the LBSCuF0.50-SDCx compositematerials are promising for application as cathodes for SDC electrolyte IT-SOFCs.