Perovskite related cuprate phases as potential cathode materials for solid oxide fuel cells

The electrical properties of the perovskite-related cuprate materials YSr2CU2FeO7+y and YSr2Cu2CoO7+y have been investigated for possible use as cathodes in solid oxide fuel cells. Both phases were shown to be stable at high temperatures (1173 K) under N-2, and their conductivities were determined with varying temperature and oxygen partial pressure. Interesting variations of the conductivity with temperature were seen for both samples. In the case of YSr2Cu2FeO7+y, the conductivity showed semiconductor behaviour up to approximate to823 K, with a decrease in conductivity then being observed for higher temperatures. This decrease is believed to be due to a reduction in the number of charge carriers, which is supported by TGA studies, which show oxygen loss above this temperature. For YSr2Cu2CoO7+y, the sample showed semiconducting behaviour over the entire range of temperatures studied, although a steeper increase in conductivity was seen above 1073 K. High temperature XRD studies show that a phase change (orthorhombic-tetragonal) occurs in this temperature region. Chemical compatibility studies (at temperatures between 1173 and 1273 K) of these phases with SOFC electrolytes are also reported.