Rigid Na-OH ionic-bond framework in the Helmholtz layer induces the kinetic pH effect in hydrogen electrocatalysis on Pt

Abstract

A large challenge in hydrogen electrocatalysis is the great decrease in catalytic activity of noble metals when moving from acidic electrolytes to basic ones. Based on first-principles calculations, we report that the Pt/electrolyte interface undergoes a transformation from a highly mobile hydrogen-bond network of water in acid to a solid-state and rigid Na-OH ionic-bond framework in base. Meanwhile, the hydrogen coverage decreases from 100 % to 16 %. This transformation leads to a barrierless water dissociation process, challenging the traditional belief that water splitting is the primary obstacle. The solid-state NaOH layer impedes proton migration towards the interface and retards hydrogen desorption, resulting in the sluggish kinetics. Incorporation of Ni atoms at the interface builds a proton transfer channel through the NaOH layer, enhancing the proton transfer kinetics. We suggest that electron-donor dopants can enhance the kinetics of both the interfacial reactions and the proton transfer in solution.