(617fo) First-Principles Study for Controlling the Cation Segregation on the Surface of Perovskite Oxide Catalysts

Controlling the surface chemistry of perovskite oxide is a key challenge for enhancing the oxygen reduction reaction (ORR) kinetics of solid oxide fuel cell (SOFC) cathodes. However, segregation of A-site cation often generates secondary phase on the perovskite oxide surface, thereby deteriorating the reactivity and stability in ORR. Although the issue for suppressing the cation segregation has been raised by many researchers, the underlying mechanism is still not clear.

In this study, a key driving force of A-site cation segregation was elucidated for the two classes of perovskite-type materials using density functional theory (DFT) calculations; alkaline earth metal (Ba, Sr, and Ca)-doped LaBO₃ (B = Cr_0.50Mn_0.50, Mn, Fe, Co_0.25Fe_0.75, Co, and Ni) and SrTi_1-xFe_xO₃. In both cases, elastic energy of A-site cation is a dominant factor governing the segregation phenomena, which depends on the size of constituent ions in the perovskite oxide. Based on these results, we suggest simple ways how to suppress the cation segregation by reducing the elastic energy. We believe that our results will be useful to rationally design the SOFC cathodes.