Factors that Influence Cation Segregation at the Surfaces of Perovskite Oxides

摘要

As the oxygen reduction reaction (ORR) becomes more critical for development of solid oxide fuel cells (SOFCs) that operate at 500-700 °C, the correlation between the surface chemistry and electrochemical performance is important to understand and enable design of cathode materials with optimal surface chemistry. Recently we demonstrated that elastic and electrostatic interactions of the dopant with the host lattice drive dopant segregation, a detrimental process on the surface of perovskite cathodes [1]. Motivated by those results, here we investigated the effects of A-site stoichiometry in La0.8Sr0.2MnO3 (LSM) thin films on the surface chemistry and electrochemical activity. Angle-resolved X-ray photoelectron spectroscopy was employed to identify the surface cation content and chemical bonding states. A-site deficient LSM films showed higher chemical stability against Sr segregation and secondary phase formation upon annealing. This was correlated with a higher electrochemical activity measured by AC impedance spectroscopy. Given the insulating nature of secondary phases created on the surface upon annealing, observed higher electrochemical stability in A-site deficient LSM films can be ascribed to the suppressed surface segregation and phase separation.