High‐Entropy Materials for Water Splitting: An Atomic Nanoengineering Approach to Sustainable Hydrogen Production

Abstract Green hydrogen production via water electrolysis is pivotal for achieving energy sustainability. However, the inherently sluggish kinetics of the hydrogen evolution reaction and oxygen evolution reaction impede the progress of water‐splitting technology. Recently, high‐entropy materials (HEMs) composed of at least five elements have garnered significant attention as promising electrocatalysts for water splitting, owing to their compositional versatility, structural robustness, and synergistic interactions among elements. This review comprehensively explores the development of HEMs, tracing their emergence and structural evolution via atomic nanoengineering strategies (i.e., from bulk to nanostructuring, from random distributions to relatively ordered architectures, from bare HEMs to reconstructed HEMs, from intact HEMs to defective structures, from pristine HEMs to functionalized variants) and revealing how these evolutionary steps contribute to the properties and enhance catalytic performance in water splitting. The fundamental roles of individual elements (e.g., active sites, promoters, stabilizers) in shaping the structure, stability, and catalytic activity of HEMs are examined, laying a foundation for the rational design of efficient HEM‐based electrocatalysts. The review also highlights recent advances in HEM‐based catalysts for water splitting, emphasizing desirable properties and elemental contributions. Finally, the remaining challenges and perspectives on the future directions of HEM‐based materials in energy conversion technologies are discussed.