High‐Entropy Oxychalcogenide for Hydrogen Spillover Enhanced Hydrogen Evolution Reaction in Proton and Anion Exchange Membrane Water Electrolyzers

Abstract The hydrogen spillover phenomenon provides an expeditious reaction pathway via hydrogen transfer from a strong H adsorption site to a weak H adsorption site, enabling a cost‐efficient hydrogen evolution reaction (HER) analogous to platinum with moderate H adsorption energy. Here, a high‐entropy oxychalcogenide (HEOC) comprising Co, Ni, Mo, W, O, Se, and Te is prepared by a two‐step electrochemical deposition for hydrogen spillover‐enhanced HER in acidic and alkaline water electrolysis. The anodic–cathodic reversal current enables the co‐deposition of cations and aliovalent anions, facilitating a glass structure with multiple active sites for hydrogen spillover. The HEOC exhibits low overpotentials of 52 and 57 mV to obtain a current density of 10 mA cm ⁻² in acidic and alkaline media, respectively, and long‐term stability for 500 h. The electrochemical and analytical approaches elucidate the hydrogen transfer toward Mo/W−O sites in both acid and alkaline HERs. Meanwhile, the other sites act as hydrogen adsorption or water dissociation‐derived hydroxide adsorption sites, showing accommodable behavior in acidic and alkaline media. The HEOC exhibits a practically high current of 1 A cm ⁻² at cell voltages of 1.78 and 1.89 V and long‐term stability for 100 h in proton and anion exchange membrane water electrolyzers, respectively.