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.