Preparation And Characterized Research On La_1-xSr_xCo_1-yFe_yO_3-δ Cathode For IT-SOFC

Decreasing electrolyte layer and developing new electrode material are two majormethods for reducing solid oxide fuel cells （SOFC） operating temperature （500⁸00C）,which is the focus of research in recent years. The main performance loss in SOFC withthin electrolyte layer is caused by the polarization of cathode due to the high activationenergy and low electrode reaction rate for the redox reaction that occurred at the threephase boundary of cathode. Therefore, many reaserchers pay more attention todeveloping a series of cathodes with the high activation energy and mixed ionic andelectronic conductivity （MIEC）. La_1-xSr_xCo_1-yFe_yO_3-δ（LSCF） with high catalytic activityfor the redox reaction are regarded as the MIEC cathode materials for IT-SOFC.However, LSCF with high coefficient of thermal expansion isn’t match to YSZ, and thereaction beween LSCF and YSZ form a resistive phase at high temperature. To avoid thephenomenon, Gd_xCe_1-xO_1.95（GDC） with a proper coefficient of thermal expansion is usedas electrolyte or interlayer. So LSCF cathode powders and GDC electrolyte layer arestudied in this paper.1) LSCF cathode nano-powders for SOFC were prepared by EDTA-citratecompound complexation method. EDTA and citric acid have strong complexing power,absolutely complex metal ion to avoid metal ion segregation, meanwhile reducecalcinations temperature and particle size. The optimum conditions of EDTA-citratecompound complexation method are summarized as follow: the mol ratio of metal ionand EDTA is1:1.25; the mol ratio of citric acid to EDTA is1:1; the concentrationtemperature is80C; the pH value of the solution is between7and10. The powders atdifferent calcinations temperature are characterized by TG-DTA, XRD, TEM. This LSCFpowders sintered at800C was with the particle size range only from20nm to30nm andits shape appears spherical, less aggregate.2) GDC electrolyte powders for SOFC were prepared by EDTA-citrate compoundcomplexation method and coprecipitation method, which were charactered by XRD,SEM and TEM testing. The results revealed that GDC powders prepared by the twomethods were both nano-sizes. The grain with the average size30⁴0nm had noagglomeration by EDTA-citrate compound complexation method. The grain with theaverage size～50nm had a certain degree of aggregation by using NH4HCO3as theprecipitant. The powders with a nonuniform distribution by using carbamide as theprecipitant had serious aggregation. The relative sintered density of GDC powders byEDTA-citrate compound complexation method sintered at1400C was96%. 3) The catalytic performance of different composite cathode（LSCF-GDC10%、LSCF-GDC20%、LSCF-GDC30%） is superior to pure LSCF cathode by three electrodemethod. The electrode polarization resistances are1.93cm²ã€1.28cm²ã€1.40cm²for LSCF cathode at700C、750C、800C, respectively. The electrode polarizationresistances of different composite cathode are higher than that of LSCF.