High‐Entropy Electrocatalysts for Water Splitting: A Review on Structures, Synthesis, Scale‐Up Challenges and Rational Designs

ABSTRACT High‐entropy alloys (HEAs) and their derivatives, defined by their near‐equimolar ratios of five or more principal elements, are endowed with unique synergistic effects, entropy‐driven stabilization, and tunable electronic structures. They have thus emerged as transformative electrocatalysts for electrochemical water splitting. This review systematically outlines recent advances in HEA synthesis, morphology control (0D/1D/2D nanostructures), and design of their derivatives (oxides, chalcogenides, phosphates, etc.). Their superior performances in HER and OER are critically examined through an elucidation of the active sites, element interactions, and catalytic mechanisms. Rational design strategies such as composition modulation, strain engineering, defect engineering, heterostructure engineering and machine learning are highlighted to bridge structure‐activity relationships. Key challenges are addressed alongside promising directions for industrial scale‐up and PEMWE or AEMWE integration, as well as seawater splitting. This work consolidates the potential of HEAs and their derivatives to revolutionize sustainable electrochemical water splitting.