Platinum–Water Interaction Induced Interfacial Water Orientation That Governs the pH-Dependent Hydrogen Oxidation Reaction

Understanding the electrode–water interface structure in acid and alkali is crucial to unveiling the underlying mechanism of pH-dependent hydrogen oxidation reaction (HOR) kinetics. In this work, we construct the explicit Pt(111)–H2O interface models in both acid and alkali to investigate the relationship between the HOR mechanism and electrode–electrolyte interface structure using ab initio molecular dynamics and density functional theory. We find that the interfacial water orientation in the outer Helmholtz layer (OHP) induced by the Pt–water interaction governs the pH-dependent HOR kinetics on Pt(111). In alkali, the strong Pt–interfacial water electrostatic interaction behaves as a narrow OHP, which increases the proportion of “H-down” interfacial water and leads to less adsorbed water entering the inner Helmholtz plane (IHP), decreasing the work function of Pt(111). Furthermore, the more “H-down” interfacial water stabilizes the Had adsorption, prevents Had desorption, and suppresses the Volmer step of HOR by forming the solvated [Had···H2O···H2O] complex. Our work provided a visualized molecular-level mechanism to understand the nature of pH-dependent HOR kinetics