Connectivity of Hydrogen Bond Networks in EDL Dominates the Kinetical pH Effect of Hydrogen Electrocatalysis on Pt

Abstract The hydrogen evolution reaction (HER) on Pt and other noble metals often undergo ~2 orders of magnitude decrease in reaction kinetics when changing the electrolyte pH from acid to alkaline regime. The origin of this kinetic pH effect remains far from a consensus, hindering the rational design of pH-specific electrocatalysts. Herein, by meticulously comparing the electric double layer (EDL) structures of acid and alkaline interfaces from the ab initio molecular dynamics (AIMD) simulations, and the computational vibration spectra of water molecules in the AIMD-simulated interfaces with the results of in situ surface-enhanced infrared absorption spectroscopy (SEIRAS), we conclude that neither the hydrogen adsorption strength nor the water dissociation barrier is responsible for the greatly reduced HER kinetics on Pt in alkaline media, because the alkaline interface could have more favorite hydrogen adsorption strength and lower barriers for individual Volmer reactions; it is the significantly different connectivity of hydrogen bond networks in EDL that cause the huge kinetic pH effect of HER. What’s further, using Pt-Ru alloy as model, our results reveal an unprecedented role of OH adsorption in improving the kinetics of alkaline hydrogen electrocatalysis on Pt-based catalysts, namely, by increasing the connectivity of hydrogen bond networks in EDL rather than by directly affecting the energetics of surface steps. These findings should add significant new insights into the key roles of EDL structures in electrocatalysis. Meanwhile, this study offers a referential research paradigm for exploring the atomic structures of electrochemical interfaces by combining AIMD simulations, computational spectroscopy, and experimental spectroscopy.