Electrocatalysts for the oxygen evolution reaction in alkaline and neutral media. A comparative review

Hydrogen can be produced in a clean way from water by its electrochemical splitting. Water electrolysis consists of two half-reactions, of which the oxygen evolution reaction (OER) is the major source of energy loss. In the case of the alkaline water electrolysis, the spectrum of materials that are stable under the conditions of the OER is significantly broader than in the case of an acidic route. This review compares systematically different materials classes based on reported overpotential at current density 10 mA cm−2. Plethora of studies was gathered to accomplish this task and the OER catalysts reported in the literature to date are summarized. In addition, we have provided an insight into the catalyst activity descriptors allowing theoretical identification of the most active materials. In order to assist the reader in gaining a better understanding of this complex subject, the catalysts are classified into three main groups in agreement with their chemical composition as transition metal oxides, phosphides and selenides. Less frequently used materials are reported in a separate group. Near-neutral or neutral pH conditions are considered as well.