Design and Development of Oxynitride Photocatalysts for Overall Water Splitting under Visible Light Irradiation

Photocatalytic overall water splitting into H-2 and O-2 is expected to be a promising method for the efficient utilization of solar energy. The design of optimal photocatalyst structures is a key to efficient overall water splitting. The photocatalyst used is generally a composite of particulate semiconductor and cocatalyst nanoparticles. Thus, the photocatalyst has the properties of both a semiconductor and a catalyst. In the design of photocatalysts for water splitting, both of these aspects should be taken into consideration. In the present article, we introduce key approaches that have led to the recent progress in oxynitride photocatalysts for visible-light-driven water splitting. In particular, band engineering of semiconductors by compositional modification and effective surface coating, which has a molecular sieving function to control the surface redox reactions, are explained through recent advances in our studies as examples.