Hydrogen Production by Photocatalytic Water Splitting

Hydrogen gas as a fuel has the potential to alleviate the threat of global climate change and help to avoid various undesirable effects caused by the mass consumption of fossil fuel. Photocatalytic water splitting has been widely studied as a potential method to produce H-2 from renewable solar energy. Photocatalysts that can operate under visible light irradiation (lambda>400 nm), which forms the main part of sunlight, are highly desirable. Successful two-step water splitting systems (Z-scheme) that operate with or without a reversible redox couple have been reported for the application of visible light-driven photocatalysts. The Z-scheme system, which mimics photosynthesis in green plants, consists of two photocatalysts, one for H-2 evolution, and the other for O-2 evolution. The Z-scheme process can utilize a wider range of visible light than the conventional one-step excitation system because the energy required to drive each photocatalyst can be reduced. This review presents recent research progress in the development of visible light-driven photocatalytic materials with a focus on Z-scheme water splitting.