Chemical compatibility of alternative perovskite oxide SOFC cathodes with doped lanthanum gallate solid electrolyte

This paper reports on the investigations of the chemical compatibility between SOFC cathode materials with compositions Pr0.8Sr0.2Co0.2Mn0.8O3−δ, Pr0.8Sr0.2Co0.2Fe0.8O3−δ, Pr0.8Sr0.2Co0.3Mn0.7O3−δ and Pr0.75Sr0.2Co0.2Mn0.8O3−δ and the electrolyte materials with compositions La0.8Sr0.2Ga0.9Mg0.1O3−δ, and La0.9Sr0.1Ga0.8Mg0.2O3−δ. The lanthanum gallate electrolyte with 20 mol.% Sr contained two additional phases, namely, LaSrGa3O7 and LaSrGaO4, while that with 10 mol.% Sr was formed in nearly single phase. Two types of experiments were performed: (a) reactivity experiments of powder mixtures and (b) diffusion experiments in cathode/electrolyte double-layer pellets. No reaction products were detected by XRD. High Co diffusion into the electrolyte was identified with SEM/EDX in all diffusion experiments examined. The transition metals diffuse in the order Mn<Fe<Co. La, Pr and Ga show a smaller tendency for diffusion. The diffusion of transition metal cations into the electrolyte La0.8Sr0.2Ga0.9Mg0.1O3−δ caused the destabilisation and disappearance of the second phases in the interdiffusion zone. In the case of the A-site deficient cathode, the formation of LaSrGa3O7 second phase was identified on the electrolyte side, near the interdiffusion zone.