Structural Changes of Cobalt-Based Perovskites upon Water Oxidation Investigated by EXAFS

Abstract

While many perovskites remain crystalline during the oxygen evolution reaction (OER) in alkaline media, some highly active perovskites become amorphous. We studied the local structure changes of perovskites LaCoO3, Ba0.5Sr0.5Co0.8Fe0.2O3-δ, and SrCo0.8Fe0.2O3-δ before and after OER by X-ray absorption spectroscopy. No change in either local structure or OER activity was observed for LaCoO3, while considerably enhanced OER activities and the conversion of the local structure from corner-sharing octahedra to edge-sharing octahedra were noted for Ba0.5Sr0.5Co0.8Fe0.2O3-δ and SrCo0.8Fe0.2O3-δ as a result of the OER. Possible processes responsible for the structural change and enhanced OER activities are discussed.