Enhancing\nAlkaline Hydrogen Evolution Electrocatalysis\nthrough Hydrogen Spillover in a Ni<sub>3</sub>S<sub>2</sub>@Cu<sub>2</sub>S Heterostructure

Efficient electrocatalysts based on transition metal\ncompounds\n(TMCs) are essential for advancing water electrolysis technology by\nfacilitating the hydrogen evolution reaction (HER). However, achieving\noptimal adsorption energy that promotes both hydrogen adsorption and\ndesorption at a single active site is challenging due to significant\ndeviations of the hydrogen adsorption Gibbs free energy (Δ<i>G</i><sub>H</sub>) in most transition metals from thermal neutrality.\nTo address this challenge, the hydrogen spillover effect provides\na solution by spatially separating hydrogen adsorption and desorption\nsites. This separation breaks the Sabatier principle and enables catalysts\nto overcome the constraints imposed by Δ<i>G</i><sub>H</sub>, resulting in enhanced catalytic activity. In this study,\nwe examined the triggering conditions for the hydrogen spillover effect\nand made theoretical predictions indicating that, at the Cu<sub>2</sub>S/Ni<sub>3</sub>S<sub>2</sub> interface, the internal polarization\nfield (IPF) and the weakened thermodynamic barrier for hydrogen migration\ncan induce this effect. To validate our theoretical predictions, we\nprepared catalysts with abundant Cu<sub>2</sub>S@Ni<sub>3</sub>S<sub>2</sub> heterointerfaces for the hydrogen elution reaction (HER).\nNotably, the catalyst exhibited remarkable performance in a 1.0 M\nKOH electrolyte, achieving a current density of 10 mA cm<sup>–2</sup> with a mere 39 mV overpotential. This study confirms, both theoretically\nand experimentally, the feasibility of utilizing the hydrogen spillover\neffect to enhance the catalytic activity of TMCs toward the HER.