Iridium‐Free High‐Entropy Alloy for Acidic Water Oxidation at High Current Densities

Abstract Designing active and cost‐effective catalysts for acidic oxygen evolution reaction (OER) is critically important for improving proton exchange membrane water electrolyzers (PEMWEs) used in hydrogen production. In this study, we introduce a rapid and straightforward method to synthesize a quinary high‐entropy ruthenium‐based alloy (RuMnFeMoCo) for acidic OER. This iridium‐free catalyst demonstrates a low overpotential of 170 mV and exceptional stability, enduring a 1000‐hour durability test at 10 mA cm −2 in 0.5 M H 2 SO 4 . Microstructural analyses and density functional theory (DFT) calculations reveal that the incorporation of corrosion‐resistant elements such as Ru, Mo, and Co enhances the overall stability of the catalyst under acidic conditions. Concurrently, the presence of Mn, Fe, and Co significantly reduces the energy barrier of the rate‐determining step in the OER process, thus accelerating the OER kinetics and lowering the overpotential. The PEMWE employing the RuMnFeMoCo catalyst operates stably at high current densities of 500 and 1000 mA cm −2 for over 300 hours with negligible performance degradation. This work illustrates a strategy for designing high‐performance OER electrocatalysts by synergistically integrating the benefits of multiple elements, potentially overcoming the activity‐stability trade‐off typically encountered in the catalyst development.