Transformation mechanism of high-valence metal sites for the optimization of Co- and Ni-based OER catalysts in an alkaline environment: recent progress and perspectives.

As an important semi-reaction process in electrocatalysis, oxygen evolution reaction (OER) is closely associated with electrochemical hydrogen production, CO electroreduction, electrochemical ammonia synthesis and other reactions, which provide electrons and protons for the related applications. Considering their fundamental mechanism, metastable high-valence metal sites have been identified as real, efficient OER catalytic sites from the recent observation by characterization technology. Herein, we review the transformation mechanism of high-valence metal sites in the OER process, particularly transition metal materials (Co- and Ni-based). In particular, research progress in the transformation process and role of high-valence metal sites to optimize OER performance is summarized. The key challenges and prospects of the design of high-efficiency OER catalysts based on the above-mentioned mechanism and some new characterizations are also discussed.