High‐Entropy Oxysulfide for High‐Performance Oxygen Evolution Reactions Electrocatalyst

Hydrogen energy is considered as a significant clean, green, and renewable energy technology. Oxygen evolution reaction (OER) plays an important role in hydrogen production through overall electrochemical water splitting. Herein, novel transition‐ and rare‐earth metal‐based high‐entropy oxysulfides (HEOS) are synthesized via low‐temperature hydrothermal method to overcome the immiscibility issue of sulfur. HEOS with systematically varying sulfur content are investigated as electrocatalysts in the OER for the first time. To assess the contribution of sulfur toward OER, the electrocatalytic performance of oxysulfides is compared with high‐entropy oxides (not containing sulfur). HEOS with higher sulfur content shows superior electrocatalytic activity and outperforms the high‐entropy oxides. The considerable amount of sulfate left in the structure during electrolysis contributes to the catalytic activity. The HEOS exhibits a reasonable overpotential of 348 mV at a current density of 10 mA cm −2 and outstanding electrochemical stability of 100 h of testing. The extraordinary OER activity of complex HEOS demonstrates its viability in rational design of highly efficient oxysulfide catalyst for overall water‐splitting.