pH-Induced Potential Shifts Modulate HER Activity Via Interfacial Hydrogen-Bond Networks: First-Principles Molecular Dynamics Simulations.

Renewable-electricity-driven hydrogen technologies are central to a sustainable hydrogen economy, with the HER serving as key interfacial reaction associated with kinetic losses. However, the kinetics of HER exhibit a pronounced pH dependence, with activities often decreasing by several orders of magnitude when moving from acidic to alkaline or neutral media. Despite extensive studies, the microscopic origin of this pH effect remains unclear. Here, first-principles molecular dynamics simulations are employed to elucidate how the pH-regulated Pt(111)/water interfacial microenvironment governs proton transfer and HER kinetics. We revealed that acidic media induce a larger population of chemisorbed interfacial water molecules and a denser and stronger hydrogen-bond network on Pt (111) than alkaline media. This robust network enables Grotthuss-type proton hopping during the HER reaction, leading to a concerted multiproton transfer pathway. Such a pathway minimizes solvent reorganization and charge-separation penalties, thereby lowering the proton-transfer barrier and accelerating HER kinetics. These findings identify the pH-regulated interfacial hydrogen-bond network as a key microscopic origin of pH-dependent HER activity.