(Invited) Role of Chemical Heterogeneities on Oxygen Reduction Kinetics on the Surface of Thin Film Cathodes

Abstract

We investigated the effects of annealing and A-site stoichiometry on the surface heterostructures at (La0.8Sr0.2)yMnO3 (LSM, y≤1) dense thin films. While annealing at high temperatures induces cation segregation on LSM, A-site deficiency is hypothesized to reduce the level of Sr enrichment on the surface by providing more space in the bulk of LSM for this relatively large cation. Localized chemical analysis by Auger electron spectroscopy revealed the strong enrichment of Sr and Zr in annealing-induced particles on LSM surfaces. By systematically varying y from 1.0 to 0.95, A-site deficiency in LSM films was shown to suppress Sr segregation and decrease the density of these secondary phases on annealed LSM surfaces, suggesting a higher chemical stability of LSM surfaces with A-site deficiency. Our results contribute to understanding the elastic energy contributions to cation segregation on perovskite cathode surfaces, and to elucidating the role of surface chemical heterogeneities to the ORR kinetics.