Resolving Proton Diffusion Kinetics in Electrolytic Hydrogen Evolution

Abstract

Although the hydrogen-bond network within the electrical double layer (EDL) is crucial for proton diffusion in the hydrogen evolution reaction (HER), its exact role remains controversial. This debate stems from the experimental difficulty in determining the proton diffusion kinetics during the HER. Here, we employ electrochemical impedance spectroscopy (EIS) at ultramicroelectrodes to quantify the potential dependence of the non-steady-state diffusion coefficient of protons. By scanning the effect of applied potential and solute species independently, we reconcile contradictory reports by revealing that the determining factor for proton diffusion shifts from hydrogen-bond connectivity to rigidity with increasing polarization. This work provides the principles for regulating proton-coupled electron transfer (PCET) in electrocatalysis.