Elucidating the Dynamic Changes in the Mechanism of the Potential-Dependent Alkaline Hydrogen Evolution Reaction on Platinum

Platinum is widely regarded as the most efficient catalyst for the hydrogen evolution reaction (HER). However, as the overpotential increases, the kinetics of the HER significantly declines and the mechanism exhibits potential-dependent behavior. Through a combination of theoretical simulations and experimental testing, we investigated the changes in the HER mechanism and the underlying kinetic reasons within the kinetic control potential region. The results revealed that at a low cathodic overpotential, the HER follows the Volmer–Tafel mechanism at the Pt(111)/water interface, while at a high cathodic overpotential, it follows the Volmer–Heyrovsky mechanism. The transition and shift in the rate-determining step from the Tafel step to the Volmer step are attributed to the reduced density of active sites and the accumulation of OH generated from water dissociation. Excessive accumulation of OH can promote the desorption of H₂ but can also raise the energy barrier of the Volmer step. This occurs because it weakens the adsorption of species and disrupts the orientation of interfacial water on the Pt(111) surface, thus hindering the HER. These findings clarify the significant role of local OH enrichment and its effect on interfacial water in modulating the HER mechanism and enhancing HER kinetics under kinetic control conditions.