Photocatalytic Seawater Splitting for Hydrogen Production: Recent Advances toward Activity Enhancement, Selectivity Control, and Long‐Term Stability

ABSTRACT Photocatalytic water splitting represents a promising route to convert solar energy into hydrogen as clean fuels. Compared with conventional photocatalytic water splitting that needs high‐purity water, directly using seawater as the reaction solution and proton source can reduce the energy and cost burdens of freshwater treatment, presenting an attractive approach for large‐scale applications. However, seawater contains a complex mixture of ions that affect charge transport at the catalyst surface, trigger side reactions, and induce catalyst deactivation. For instance, chlorine ions (Cl − ) can be oxidized by photogenerated holes, competing with oxygen evolution and generating corrosive chlorine species. Ca 2+ and Mg 2+ can form insoluble deposits such as Mg(OH) 2 and CaCO 3 under localized alkaline conditions, blocking active sites and slowing mass and charge transfer. This review summarizes key principles and recent progress in photocatalytic seawater splitting, with an emphasis on practical strategies to enhance hydrogen evolution activity, improve oxidation selectivity, and ensure long‐term stability, including band and defect regulation, cocatalyst engineering, protective layers, ion‐selective interfaces and floating photothermal‐photocatalytic system. Furthermore, this review provides forward‐looking perspectives on the rational design of next‐generation materials, the strategic assembly of photothermal‐photocatalytic architectures, and the cascading utilization of full‐spectrum solar energy for efficient and durable seawater splitting.