Bridging Microscopic Interfacial Water and Macroscopic Wettability for Enhanced Hydrogen Evolution Reaction

Electrocatalytic hydrogen evolution reaction (HER) necessitates managing both macroscopic wettability for bubble release and microscopic water structure for proton transfer. However, highly hydrophilic surfaces, while beneficial for bubble transport, tend to induce strongly hydrogen‐bonded water networks that hinder proton dynamics, presenting a fundamental conflict in advancing electrocatalyst design. Herein, we leverage polymeric modifiers to tune the surface electronic structure of platinum electrodes and investigate the synergistic influence of macroscopic wettability and microscopic interfacial water structure on HER performance. We demonstrate that peak HER performance is achieved on polyethylenimine (PEI)‐modified Pt electrode, which uniquely affords moderate hydrophilicity (contact angle: ∼15°) alongside a disordered, weakly hydrogen‐bonded interfacial water network. This dual optimization enhances bubble release and proton‐transfer kinetics, reducing the overpotential by 229 mV at 10 mA cm −2 compared to pristine Pt. In situ Raman spectroscopy confirms an increase in weakly hydrogen‐bonded water species under PEI modification compared to the superhydrophilic electrode. This study bridges interfacial water dynamics with electrode wettability, guiding the design of advanced electrocatalytic interfaces.