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

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 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 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.