Transition‐Metal‐Based Cocatalysts for Photocatalytic Water Splitting

Recently, semiconductor‐based photocatalytic water splitting has been extensively studied as a promising strategy for converting solar energy into carbon‐neutral and clean H 2 fuel. However, the lack of sufficient active sites for surface redox reactions generally results in unsatisfactory photocatalytic water splitting performances over semiconductors. For this problem, cocatalyst provides an encouraging solution and is of great significance in improving photocatalytic performance. Noble metals and their derivatives are mostly utilized as efficient cocatalytic components, but their scarcity and expensiveness severely hamper large‐scale applications. Thereby, the utilization of noble‐metal‐free cocatalysts has aroused immense research attention. Owing to the facile availability, low cost, large abundance, high stability, and efficient performance, transition‐metal‐based materials have been developed as desirable candidates in the photocatalytic water splitting water splitting process. This review gives an outline of some recent advances in the active transition‐metal‐based water splitting cocatalysts. First, the fundamentals of transition‐metal‐based cocatalysts are presented, including the classification, function mechanisms, loading methods, modification strategies, and design considerations. Second, the various cases of depositing reduction cocatalysts, oxidation cocatalysts, and reduction–oxidation dual cocatalysts for water splitting are further discussed. Finally, the crucial challenges and possible research directions of transition‐metal‐based cocatalysts for photocatalytic water splitting are proposed.