High‐Entropy Oxide Toward Practical Hydrogen Production From Alkaline Fresh and Seawater

High-entropy oxides (HEOs) emerge as versatile electrocatalysts due to their tunable compositions, defect-rich structures, and robust stability. In this study, non-equimolar (VCrMnFeCo)O HEO microstructures were synthesized via mechanical alloying, a scalable and cost-effective route for catalyst design. When evaluated for hydrogen evolution reaction (HER), these materials exhibited excellent activity and durability in both commercial alkaline electrolyte (6 m KOH) and low-alkaline seawater (1 m KOH). While 6 m KOH is widely employed in commercial alkaline water electrolysis (AWE), catalyst stability under such concentrated conditions remains a critical challenge. Similarly, seawater electrolysis is hindered by chloride-induced corrosion, making durability a key bottleneck. The developed catalyst exhibited low HER overpotentials and high stability during the accelerated durability test (ADT) for 5000 CV cycles. A detailed structural analysis of recovered catalysts after ADT indicated in situ reduction and redistribution of elements under operational conditions that resulted in an enhancement in activity during continuous electrocatalysis cycling. This study establishes mechanically alloyed HEOs as promising candidates for sustainable hydrogen generation, bridging fundamental materials design with practical electrolysis applications in freshwater and seawater systems.