Preparation And Electrochemical Properties Of Core-shell Cathode Materials

So far,the main obstacles,which affect the commercialization of SOFCs,are the difficulty in selecting the material of the connecting body caused by the high operating temperature,the rapid degradation of performance.Therefore,reducing the operating temperature of SOFC has become the consensus of SOFC researchers.The development of high-performance cathodes has become the key to reduce the operating temperature of SOFC,which has become one of the key issues in SOFC research.In this paper,based on the idea of composite cathode,Sm_0.5Sr_0.5CoO₃?SSC?was coated on Ca₃Co₄O₉?CCO?,which is a cathode material with good thermal matching with cerium oxide based electrolyte Sm_0.2Ce_0.8O_1.925?SDC?.The above process is implemented by two methods:sol-gel method and solution impregnation method combined with low-temperature sintering technology.The microstructure,phase composition and thermal expansion coefficient of cathode powders were studied by means of transmission electron microscope,X-ray diffraction,thermal dilatometer and other means.The electrochemical properties of SSC@CCO composite cathode are studied by dc quadrupole method and impedance spectroscopy.Comparing the electrochemical performance of the composite cathode synthesized by the two methods,the results show that:The composite cathode powders,which is produced by sol-gel method,are core-shell structure and the average particle size is about 400nm.The electronic conductivity of composite cathode materials increases with the increase of SSC cladding amount,especially when the cladding ratio is 4:1,the maximum value is 320S?cm^-1.The thermal expansion coefficient of SSC-coated cathode was slightly increased when it is compared with CCO cathode.However,it has little difference from the thermal expansion coefficient of SDC electrolyte(11.0×10^-6k^-1),and the maximum value was 13.4×10^-6k^-1.Compared with pure CCO cathodes and composite cathodes with mechanical mixing of SSC and CCO with the same molar ratio,the ASR of core-shell cathode materials is significantly reduced.At the same temperature,the ASR of core-shell composite cathodes is 1/4 of that of pure CCO cathodes and it is 40%lower than the polarization plane resistance of the mechanical hybrid cathode.After 20 thermal vibration cycles,the polarization surface resistance of core-shell structure composite cathode does not increase obviously,which shows good stability.When using different cladding amounts of core-shell composites as the cathode,the anode-supported cells with SDC as the electrolyte were tested in turn.It was found that the cathode of the 4SSC@CCO had the best performance,and at 750?,the maximum output power is 496 mW?cm^-2.With the CCO porous skeleton as the primary structure,the polarization surface resistance of the composite cathode prepared by the solution impregnation method is significantly lower than that of the pure CCO cathode.And as the amount of impregnation increases,the polarization resistance gradually decreases.When the amount of impregnation is 40%,its minimum value is 0.35??cm².Impregnated cathode ASR have a close relationship with sintering temperature.When the sintering temperature is 700?,ASR of cathode is the smallest.To optimize the distribution of impregnated material at the cathode skeleton and composite cathode performance,solution impregnation and low temperature hydrothermal treatment are used to assemble the impregnated cathode.Electrochemical test results show that methode of hydrothermal method can significantly reduce the cathode polarization of ASR.The polarization surface resistance of the composite cathode processed by hydrothermal method is about 50%of that of the composite cathode processed by dipping and sintering at high temperature.The above results indicate that the impregnation combined with hydrothermal method is an effective measure to improve the performance of the impregnation cathode.