The Key Role of Proton‐Responsive Groups in Electrochemical Hydrogen Evolution Reaction

Abstract The much‐needed global shift from fossil fuels to sustainable energy is driving significant attention towards hydrogen (H 2 ) as a promising alternative. Proton reduction, a process central to H 2 production, is a key area of research for this transition. Naturally‐occurring [FeFe] and [NiFe]‐hydrogenase enzymes play vital roles in the reversible production and oxidation of H 2 . These enzymes feature a proton‐relay unit comprising of pendant amine and thiol groups in the secondary coordination sphere at the active site. This unit accelerates the rate of H 2 production/oxidation, making it a focal point for scientific exploration. Efforts are concentrated on mimicking the active sites of these enzymes both structurally and functionally. In this pursuit, many synthetic transition metal complexes with proton‐responsive units at the secondary coordination sphere of the active site mimic the enzyme's behavior. These units facilitate intramolecular metal‐hydride (M−H) generation and H 2 ‐elimination via H + /H − s coupling, leveraging the proton from the pendant functional group and the hydride from the M−H intermediate. This review delves into electrocatalysts featuring pendant proton‐responsive units and their roles in the electrochemical hydrogen evolution reaction (eHER).