Developments and Perspectives in 3d Transition-Metal-Based Electrocatalysts for Neutral and Near-Neutral Water Electrolysis

Technology for producing highly pure hydrogen (99.999%) by water electrolysis is a field of importance in terms of the planets' current energy scenario. A much needed transition from a carbon economy to a hydrogen economy further adds importance to the field of hydrogen generation from water for a sustainable future. To avoid energy losses in the production process, the use of highly acidic (Proton Exchange Membrane (PEM) water electrolyzer) and alkaline (alkaline water electrolyzer) electrolytes is conventional practice in this field. Unfortunately, there are several other issues associated with the use of acidic and alkaline electrolytes such as the requirement of specific ion exchanging membranes with good stability, acid or alkali stable catalysts and corrosive environment withstanding cell stacks, etc. To overcome these issues, researchers have shown interest in the field of electrochemical water splitting in neutral and near-neutral conditions. In this review, the chronological development of 3d transition-metal-based electrocatalysts for neutral and near-neutral water splitting is extensively discussed with emphases on screening methodologies, mechanisms, structure-activity correlations, and detailed catalyst specific evolution. In addition, catalysts reported so far, are also benchmarked based on their performance separately for different electrolytes used.