A Bidentate Hydrogen-Bond Molecular Vise Activates Interfacial Water for Universal Hydrogen Electrocatalysis.

Growing evidence indicates that modulation of the catalyst surface microenvironment provides an effective route to optimize electrocatalytic performance, serving as a valuable complement to the traditional emphasis on electronic effects. Yet, despite recent progress in probing interfacial water activation under low-proton conditions, our understanding of this process remains far from complete. Herein, we selected 2,6-diacetylpyridine (DAcPy), a representative molecule with pronounced electrocatalytic enhancement effects, to systematically elucidate the mechanism of interfacial water activation. DAcPy universally enhances reaction kinetics across diverse hydrogen electrocatalytic systems on both Pt and Cu surfaces. Combined scanning tunneling microscope (STM) imaging and theoretical calculations reveal that the symmetric diacetyl groups of DAcPy form a geometrically matched V-shaped molecular vise. This bidentate C═O···H-O hydrogen bonding configuration precisely captures water molecules, and the resulting cooperative polarization effect weakens the H-OH bond, increasing the interfacial water dissociation constant (Kw) by a factor of 2. In situ attenuated total reflection-surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) measurements directly confirm the formation of a strengthened hydrogen-bond network upon DAcPy modification, in agreement with theoretical predictions. Electrochemical impedance spectroscopy with distribution of relaxation times (EIS-DRT) analysis further reveals that this molecular strategy selectively accelerates the water-involved Volmer and Heyrovsky steps without affecting the Tafel step. Notably, the DAcPy-enabled enhancement applies broadly, significantly boosting rates across various low-proton electrocatalytic systems, including alkaline HER/HOR, CO/CO2 electroreduction to methane/ethylene, and selective acetylene hydrogenation.