Dual cocatalysts for photocatalytic hydrogen evolution: Categories, synthesis, and design considerations

To enable a low-carbon economy, it is vital to develop clean and renewable energy sources such as hydrogen energy. One promising strategy is to sustainably generate H2 by solar-driven photocatalytic water splitting using semiconductors. However, the bottleneck in the industrialization of photocatalysis technology lies in the high recombination rate of photogenerated charge carriers in the semiconductors. Fortunately, introducing dual cocatalysts into the semiconductor can promote the development of three-phase interfaces that enable the efficient transfer of interfacial charges, thereby enhancing the photocatalytic H2-evolution efficiency. In this review, we provide a detailed and systematic description of the development of ternary composite photocatalysts with high H2-evolution efficiencies by loading dual cocatalysts onto semiconductors. First, we categorize dual cocatalysts into two types: dual-reductive pairs and reductive-oxidative pairs, and then summarize four advantages of the dual-cocatalyst-based systems for H2 production. Subsequently, the synthesis strategies for dual cocatalyst-semiconductor photocatalysts and their design considerations are presented in detail. Finally, the current status, challenges, and future developmental directions of dual cocatalysts for photocatalytic H2 production are summarized.