High-Entropy Oxides for Efficient Oxygen Evolution Reaction: Structural Design, Reaction Mechanisms, and Future Perspectives.

The oxygen evolution reaction (OER) is a kinetically demanding anodic process in water electrolysis and related electrochemical energy-conversion systems. Its multistep proton-coupled electron-transfer kinetics and catalyst degradation under strongly oxidizing conditions limit overall efficiency and durability. High-entropy oxides (HEOs), which combine multicomponent configurational disorder, lattice distortion, broad distributions of local coordination environments, and element-specific electronic interactions, have emerged as a versatile platform for OER catalyst design. This review summarizes the definitions and physicochemical characteristics of HEOs, OER reaction pathways, theoretical and data-driven methods, synthesis strategies, representative crystal structures, and recent progress in acidic OER and proton-exchange-membrane water electrolysis (PEMWE). Particular attention is given to rutile-type Ir/Ru-based HEOs, including their phase formation, local electronic-structure regulation, degradation behavior, and device-level validation. Current challenges in composition-space exploration, operando mechanism identification, long-term stability, noble-metal utilization, reproducible scale-up, and standardized device testing are discussed, together with directions for future research.