Advancing Photo(Electro)Chemical Water Splitting: The Promise of Atomically Dispersed Single‐, Dual‐, and Alloy‐Site Catalysts

ABSTRACT Single‐atom catalysts (SACs) have rapidly gained prominence as an emerging class of electrocatalysts for water splitting, owing to their uniform and precisely defined active sites. By maintaining uniform reaction pathways, SACs minimize the formation of unwanted byproducts, thus exhibiting extremely high selectivity and atomic efficiency. A key determinant of SAC performance lies in the interfacial interaction between the isolated metal atoms and the supporting material under strong metal–support coordination, which is vital for maintaining long‐term activity. However, despite these benefits, reproducibly synthesizing SACs with high metal loadings while retaining uniform dispersion remains a significant challenge. To address the intrinsic challenges of SACs, recent research has expanded into dual‐atom catalysts (DACs) and single‐atom alloy catalysts (SAACs), providing synergistic active sites and combining the benefits of SACs with bimetallic systems. This review systematically explores the latest advancements in synthesis methods and innovations for SACs for electrochemical water splitting. Additionally, it examines the evolution of catalyst design, emphasizing the unique structural and electronic characteristics of single‐site, dual‐site, and alloyed SAC systems and highlighting their critical roles in accelerating water‐splitting reaction kinetics as well as the prevailing challenges and outlining promising directions for advancing hydrogen production via water electrolysis.