Oxynitride materials for solar water splitting

Water splitting to form hydrogen and oxygen over a heterogeneous photocatalyst using solar energy is a promising process for clean and renewable hydrogen production. In recent years, numerous attempts have been made for the development of photocatalysts that work under visible light irradiation to efficiently utilize solar energy. This article reviews recent research progress in the development of visible light-driven photocatalysts, focusing on the refinement of oxynitride materials. They harvest visible photons (similar to 450-700 nm) and work as stable photocatalysts for water reduction and oxidation under visible light. Oxynitrides with d(0) electronic configuration can be successfully applied to a two-step water-splitting system, which can harvest a wide range of visible photons (similar to 660 nm), in the presence of an iodate/iodide shuttle redox mediator. Also d(10)-type oxynitrides of GaN-ZnO and ZnGeN2-ZnO solid solutions can achieve functionality as photocatalysts for overall water-splitting under visible light without noticeable degradation.