In recent years, the electrochemical water splitting using renewable energy has attracted considerable attention for the production and utilization of hydrogen gas as a fuel. However, the high overpotential for the oxygen evolution reaction increases the electrical power expense and induces degradation of the electrode materials. In order to promote the oxygen evolution reaction by lowering the overpotential and suppressing the side reactions, noble metals and their alloys or oxides have been typically employed as catalysts. Nevertheless, alternative catalysts have been sought in recent years in view of the high cost and limited resources of noble metals. In this review, the recently developed oxygen evolution reaction catalysts are presented, and the requirements for the development of such highly active catalysts have also been discussed.
