An Examination of LSM-LSCo Mixtures for Use in SOFC Cathodes

Composites of yttria-stabilized zirconia (YSZ) and mixed perovskites with the average compositions La 0.8 Sr 0.2 Mn (1-x) Co x O 3 (x = 0, 0.1, 0.25, and 0.5) and with total loadings of 40 wt % perovskite were prepared by impregnation of aqueous salt solutions into a porous YSZ cathode matrix and examined for their use as cathodes in solid oxide fuel cells (SOFCs) at 973 K. For calcination at 1173 K, the cathode made from La 0.8 Sr 0.2 Mn 0.75 Co 0.25 O 3 showed the best performance of the mixed perovskites, although the improvement over La 0.8 Sr 0.2 MnO 3 (LSM) was only modest. After calcination at 1373 K, LSM-YSZ performed better than any of the mixed perovskites. X-ray diffraction showed that Co-containing mixed perovskites undergo a solid-state reaction with YSZ at 1373 K to form insulating phases that decrease the electrochemical performance. While the addition of 10 wt % COO x to an LSM-YSZ composite was found to have no effect on cathode performance, the addition of 10 wt % La 0.8 Sr 0.2 CoO 3 to an LSM-YSZ composite dramatically decreased the cathode area-specific resistance from 0.45 Ω cm 2 to approximately 0.1 Ω cm 2 . Based on these results, the possibilities for improving the performance of LSM-based cathodes through doping with Co-containing compounds are discussed.