Surface structural changes of perovskite oxides during oxygen evolution in alkaline electrolyte

Abstract

Perovskite oxides such Ba0.5Sr0.5Co0.8Fe0.8O3-6 (BSCF82) are among the most active catalysts for the oxygen evolution reaction (OER) in alkaline solution reported to date. In this work it is shown via high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy that oxides such as BSCF82 rapidly undergoes amorphization at its surface under OER conditions, which occurs simultaneously with an increase in the pseudocapacitive current and OER activity. This amorphization was not detected at potentials below those where significant OER current was observed. Lower concentrations of Sr²- and Ba²- are found in the amorphous regions of BSCF82. Perovskite oxides with lower OER activities such as LaCoO₃ (LCO) and LaMnO₃ (LMO) remained crystalline under identical electrochemical conditions. In addition, the OER activity and tendency for amorphization are found to correlate with the oxygen p-band center as calculated using density functional theory. This work illustrates that the surface structure and stoichiometry of oxide catalysts can differ significantly from the bulk during catalysis, and that understanding these phenomena is critical for designing highly active and stable catalysts for the OER.