(Oxy)nitrides with d0-electronic configuration as photocatalysts and photoanodes that operate under a wide range of visible light for overall water splitting

Water splitting to form H2 and O2 using semiconductor photocatalysts under sunlight is a possible means of clean energy production from renewable resources. (Oxy)nitrides are regarded as suitable candidates for the application, because of their suitable band edge positions, small band gaps (<3 eV), and stability under irradiation. Since early reports published in 2002 by Domen et al., it has been demonstrated that several (oxy)nitrides are active photocatalysts capable of reducing and oxidizing water in the presence of suitable electron donors and acceptors, respectively, under visible light (λ > 400 nm). Some have achieved direct water splitting into H2 and O2 with good reproducibility. (Oxy)nitrides are also attractive as water-splitting photoelectrodes, and highly efficient photoelectrochemical water splitting has been accomplished using tantalum-based (oxy)nitrides under visible light with good stability. However, there still remain a lot of challenges that have to be addressed in this research field. This perspective highlights recent progress in the development of (oxy)nitride materials for application in photocatalytic and photoelectrochemical water splitting made by the author and his colleagues, especially in the last 5 years.