The roles and mechanism of cocatalysts in photocatalytic water splitting to produce hydrogen

Photocatalytic hydrogen (H2) evolution via water spilling over semiconductors has been considered to be one of the most promising strategies for sustainable energy supply in the future to provide non-pollution and renewable energy. The key to efficient conversion of solar-chemical energy is the design of an efficient structure for high charge separation and transportation. Therefore, cocatalysts are necessary in boosting photocatalytic H2 evolution. To date, semiconductor photocatalysts have been modified by various cocatalysts due to the extended light harvest, enhanced charge carrier separation efficiency and improved stability. This review focuses on recent developments of cocatalysts in photocatalytic H2 evolution, the roles and mechanism of the cocatalysts are discussed in detail. The cocatalysts can be divided into the following categories: metal/alloy cocatalysts, metal phosphides cocatalysts, metal oxide/hydroxide cocatalysts, carbon-based cocatalysts, dual cocatalysts, Z-scheme cocatalysts and MOFs cocatalysts. The future research and forecast for photocatalytic hydrogen generation are also suggested.