Reversible Hydrogen Spillover: Adsorption-Desorption Site Reversal in HER

The shift to a sustainable economy relies heavily on green hydrogen production. The elevated energy barrier of water dissociation precludes hydrogen generation in alkaline medium. To circumvent the inherent limitations of conventional catalysts governed by the Sabatier principle, Reversible Hydrogen Spillover has emerged as a powerful design strategy. This approach spatially decouples catalytic function by allocating water dissociation to a designed support, followed by hydrogen recombination and desorption to a neighboring metallic site, establishing a synergistic pathway that skips traditional kinetic bottleneck. This perspective provides a comprehensive understanding of the material design principles that enable reversible hydrogen spillover. Four key strategies are critically examined: 1) Structurally tuning the support for the intrinsic water dissociation activity, 2) integrating oxophilic species to create dedicated water scissoring hotspots, 3) implanting single-atomic metal sites to suppress the interfacial transfer barriers, 4) leveraging interatomic interaction in multi-metallic systems to synergistically boost both water dissociation and H₂ evolution. The operando spectroscopic and electrochemical techniques (CO-stripping, scanning electrochemical microscopy, in situ Raman/infra-red) are further discussed for the molecular-level understanding of the spillover pathways. The study establishes a systematic framework that emphasizes reversible hydrogen spillover as a pivotal idea capable advancing the development of high-performance electrocatalyst.