CHAPTER 5: Particulate Oxynitrides for Photocatalytic Water Splitting Under Visible Light

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 chapter describes recent research progress in the development of visible light-driven photocatalysts, focusing on the refinement of (oxy)nitride materials. They harvest visible photons (∼450–700 nm) and work as stable photocatalysts for water reduction and oxidation under visible light. Oxynitrides with d⁰ electronic configuration can be successfully applied to a two-step water-splitting system, which can harvest a wide range of visible photons (∼660 nm), in the presence of an iodate/iodide shuttle redox mediator. Also d¹⁰-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. Highly efficient photoelectrochemical water splitting is also achievable using TaON and Ta₃N₅ as anode materials, with incident photon to current conversion efficiencies of several tens of percent in visible light region.