Stability of composite cathode consisting of doped bismuth oxide (Y _0.25Bi_0.75O_1.5) and Conducting Perovskite La_1-xSr_XMeO₃-δ (Me=Mn, Cu)

The mixed conducting cathodes for solid oxide fuel cells usually consist of a mixture of oxygen ion conductor and a conducting perovskite oxide. Bismuth oxide based materials are known to exhibit high ionic conductivity. Among them, Y_0.25Bi_0.75O_1.5 (25YSB) is a typical example. On the other hand, La_0.8Sr_0.2MnO₃-δ (20LSM) and La_0.75Sr_0.25CuO₃-δ (25LSCu) are well known cathodes for SOFC applications. In this study, the phase stability of composite cathode consisting of 25LSCu or 20LSM and 25YSB mixed powders was examined. No additional phase other than LSM and YSB was observed at temperatures as high as 1000°C for 8h. However, 25LSCu tends to react with 25YSB and additional phases belonging to La_0.3Bi_0.7O _1.5, La₂CuO₄, CuO and Bi₂Sr ₂CuO₆ appeared after heat treatment at 800°C for 20h. The conductivity of 20LSM-25YSB composite electrode increases with increasing volume fraction of 20LSM. The thermal expansion of 20LSM-25YSB composite electrode was also measured as a function of 25YSB content. Based on these results, 20LSM+25YSB is believed to be the desired composite cathode for SOFC application.