High-Entropy Alloy-Catalyzed Bifunctional Electrocatalysis of H 2 and O 2 Involving Reactions

High-entropy alloys (HEAs), composed of five or more principal elements in near-equiatomic ratios, have emerged as transformative electrocatalysts for energy conversion due to their exceptional compositional flexibility, thermodynamic stability, and tunable surface chemistry. This review authoritatively analyzes recent advances in HEA-based electrocatalysts for reactions, including hydrogen evolution (HER), hydrogen oxidation (HOR), oxygen evolution (OER), and oxygen reduction (ORR), crucial to water electrolyzers, fuel cells, and metal–air batteries (MABs). Fundamental aspects governing HEA formation (configurational entropy, lattice distortion, and sluggish diffusion) are outlined alongside synthetic strategies. The electrochemical performance of HEAs in acidic and alkaline media is critically discussed, emphasizing structure–activity–stability correlations and multielement synergistic effects. Despite major progress, challenges persist in compositional precision, identification of active sites, and large-scale fabrication. The review concludes by outlining future research directions toward the rational design of HEA electrocatalysts for efficient, scalable, and sustainable energy technologies.