Competitive Adsorption of OH* and H* Intermediates in Electrocatalytic Hydrogen Evolution: Origins, Mitigation Strategies, and Analytical Techniques

The hydrogen evolution reaction (HER) stands as a fundamental electrochemical process for sustainable hydrogen production through water splitting. While the hydrogen binding energy descriptor has traditionally guided HER catalyst design, this established framework fails to adequately represent the complexity of operational electrocatalytic interfaces, especially in nonacidic environments where hydroxyl species (OH*) competitively adsorb and substantially influence reaction pathways. This concept systematically examines the competitive adsorption behavior between OH* and H* intermediates during HER. The analysis covers the fundamental origins through which OH* blocks active sites and impedes H* adsorption kinetics. A comprehensive overview is provided of recent advances in catalyst design strategies aimed at mitigating OH* interference, including spatial separation of adsorption sites, promotion of OH* spillover, facilitation of proton exchange processes, and creation of unfavorable binding sites for OH* species. The application of advanced characterization techniques, theoretical computations, and electrochemical methods for probing these interfacial phenomena is thoroughly discussed. Finally, the concept outlines remaining challenges and suggests future research directions to advance the fundamental understanding of electrocatalytic interfaces and guide the development of efficient HER catalysts.