Taming Proton Transfer Through Proton Conductors to Boost Hydrogen Evolution

The hydrogen evolution reaction (HER) is highly sensitive to interfacial pH, which differs from bulk pH due to proton consumption and hydroxide ion formation. However, in situ monitoring and controlling interfacial pH during HER remains challenging. This work develops a novel strategy to modulate interfacial pH by incorporating nitrogen-functionalized carbon as proton-conducting mediators, physically mixed with Pt catalysts to prevent direct Pt-N bonding while enabling systematic variation of nitrogen group density. Electrochemical characterization through open-circuit potential transients, combined with in-situ infrared spectroscopy, establishes a quantitative correlation between nitrogen group density and interfacial proton concentration. During HER operation, continuous proton reduction generates H₂ while hydroxide ion accumulation creates a steep pH gradient near the electrode. The nitrogen moieties address this limitation by facilitating proton transport via a Grotthuss-type mechanism, where reversible protonation/deprotonation of amine/ammonium groups enables efficient proton hopping along the carbon framework. This dynamic process effectively elevates the local proton concentration around the active sites. The demonstrated approach of using nitrogen-doped carbons as tunable proton conductors provides a generalizable platform for optimizing electrocatalytic systems where reaction rates are governed by interfacial pH conditions.