Engineering Sulfur Vacancies in a High-Entropy Sulfide to Generate Defective Multimetal Oxyhydroxide Catalysts for the Oxygen Evolution Reaction

Alkaline water electrolysis is a promising route for hydrogen production, yet its widespread application is hindered by the sluggish kinetics of the oxygen evolution reaction (OER) and the insufficient durability of electrocatalysts. Herein, we investigate a pyrite-type high-entropy sulfide, (FeCoNiZnV)S 2, as a precatalyst for alkaline OER. Under anodic polarization, the material undergoes in situ surface reconstruction characterized by the preferential leaching of Zn and V species, the formation of sulfur vacancies, and the development of a defective multimetal oxyhydroxide layer. The resulting reconstructed phase, denoted as FeCoNiZnVOOH-S, exhibits an enlarged electrochemically active surface area and a tailored local coordination environment. As a result, the catalyst achieves an overpotential of 244 mV at 100 mA cm −2 in 1.0 M KOH. When employed as both anode and cathode in a two-electrode configuration, the electrolyzer delivers a cell voltage of only 1.52 V at 10 mA cm −2 and demonstrates stability for over 200 h at 1000 mA cm −2 in a flow-cell system. Post-operando analysis confirms that the reconstructed oxyhydroxide phase is preserved during prolonged electrolysis. This work underscores the critical role of dynamic surface reconstruction in high-entropy materials and offers a rational design strategy for developing robust OER electrocatalysts toward large-scale alkaline water electrolysis.