In Situ Raman Spectroscopic Insight of Hydrogen Spillover in Electrocatalytic Hydrogenation

Given the crucial role of adsorbed hydrogen species (*H) in electrochemical hydrogenation reactions, manipulating hydrogen spillover to facilitate the generation and migration of *H is highly necessary. However, the strong coupling between hydrogen activation sites and hydrogenation sites, together with the coexistence of protons and water molecules in practical electrocatalytic systems, renders a grand challenge for the in situ monitoring of hydrogen spillover. Herein, using single-atom Ru-doped Cu as a model catalyst, the spectroscopic visualization of hydrogen spillover under electrochemical conditions was realized by in situ surface-enhanced Raman spectroscopy. Taking para-nitrothiophenol as the probe molecule, we elucidated that the hydrogen spillover distance was facet-dependent, with Cu(111) being more active for electrocatalytic hydrogenation than Cu(100). Notably, electrochemical hydrogen spillover distances were tunable with the variation of applied potentials, which increased, ranging from 0.8 to 2.6 nm as the potentials shifted negatively. Moreover, by leveraging the hydrogen spillover effect to increase the hydrogen coverage on the Cu(111) surface, we found that the rate-determining step of nitrate electroreduction could be altered, resulting in a significant enhancement of catalytic performance.