Electric Double Layer Organization of Proton-Transfer Pathways Regulates Alkaline Hydrogen Evolution.

Constructing bifunctional catalysts with synergistic interfaces is a promising strategy to overcome the sluggish kinetics of the hydrogen evolution reaction (HER) in alkaline media, where interfacial proton transfer plays a critical role in the reaction kinetics. However, how bifunctional interfaces regulate the interfacial environment governing proton transfer remains poorly understood, particularly at the nanoscale. Here, using well-defined Pt/Ni and Pt/NiO model systems, we integrate spatially resolved scanning electrochemical microscopy, hydration force measurements, and ab initio molecular dynamics simulations across multiple length scales to establish a correlation among local HER kinetics, interfacial electrostatics, and hydration structure. Specifically, the Pt/NiO-derived interface exhibits a lower potential of zero charge (PZC) that is closer to the HER operating potential together with a more interconnected interfacial hydrogen-bond network. In contrast, the Pt/Ni-derived interface exhibits a higher PZC and a less-interconnected hydration structure. These results identify interfacial electrostatics and hydration organization within the electric double layer (EDL) as important factors governing the enhanced HER kinetics at bifunctional interfaces.