Development of Novel Photocatalyst and Cocatalyst Materials for Water Splitting under Visible Light

Overall water splitting using a semiconductor photocatalyst with sunlight has long been viewed as a potential means of large-scale H2 production from renewable resources. In general, the reaction can be accomplished when a photocatalyst is modified with a suitable cocatalyst that efficiently promotes water reduction. It is therefore essential to develop both photocatalysts and cocatalysts in harmony. Certain metal (oxy)nitrides are potential candidates as water-splitting photocatalysts because of their suitable band edge positions for water reduction/oxidation, small band gaps (<3 eV), and stability under irradiation. However, efficient water splitting using visible-light-responsive oxynitrides has still remained a challenge. This account describes our recent developments over the last 10 years of new oxynitrides as well as cocatalysts for overall water splitting under visible light.