Design And Optimization Of The Co-based Perovskite Cathode Materials

Lowering the operating temperature to intermediate-temperature(IT), 500-800℃, which can extend the choice range of solid oxide fuel cell materials, decrease production cost and speeding up the commercialization process. However, the reduction of operating temperature leads to a significant decrease for cathode catalytic activity. Therefore, the development of new cathode materials with high electrocatalytic activities is the key to improve the performance of IT-SOFCs.In this thesis, a series samples of YBaCo2-x Cux O5+δ(YBCCO, x = 0.0, 0.0, 0.2, 0.6, 0.8) cathode materials in intermediate-temperature of solid oxide fuel cell(IT- SOFC) were prepared by sol-gel method, the aim is studying the microstructure, the conductivity, the chemical compatibility with electrolyte, the thermal expansion coefficient and the electrochemical properties of the cathode material. After sintering at 1000 ℃ about 10 h, the YBCCO samples has a single phase and a good chemical compatibility with LSGM electrolyte which is prepared by using the glycine- nitrate method(GNP). Within the temperature range of 30-850 ℃, the conductivity decreased with the copper content increase and showed a good regularity. The thermal expansion coefficient(TEC) of YBCCO is from 17.8x10-6 K-1 to 13.4x10-6 K-1 with increasing Cu content. For electrochemical performance of YBCCO, it were studied by the Ac impedance spectroscopy with the LSGM as electrolyte, combining the SEM image, we got the best electrochemical performance when the doping ratio is 0.6, After sintering at 950℃, the polarization resistance of YBCCO(x = 0.6) is 0.041 ? cm2 at 800℃, the power density is 644 mw/cm2.The samples of SrCo0.7Fe0.2Nb0.1O3-δ(SCFN) were synthesized by a solid state reaction and the SDC electrolyte was synthesized using the glycine-nitrate. SCFN cathode showed a high conductivity above 100 cm-1 at the temperature range of 30-850℃. The thermal expansion coefficient of SCFN is 25.06 x 10-6 K-1 at 30-850℃, it is not a good match with Ce0.8Sm0.2O1.9(SDC) electrolyte(12.39 x 10-6 K-1, in laboratory test), So we adopted SCFN-xSDC(x = 0, 20, 30, 40, 50, 60, wt %) composite materials for the cathode, then studyed the microstructure, the thermodynamic properties, and the electrochemical performance of composite materials.