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 N2, 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 ≈823 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.