Development of a New System for Photocatalytic Water Splitting into H2 and O2 under Visible Light Irradiation

Photocatalytic water splitting using semiconductor materials has attracted considerable interest due to its potential for clean production of H-2 from water by utilizing abundant solar light. The developments of water-splitting systems that can efficiently use visible light have been a major challenge for many years in order to realize efficient conversion of solar light. We have developed a new type of photocatalysis system that can split water into H-2 and O-2 under visible light irradiation, which was inspired by the two-step photoexcitation (Z-scheme) mechanism of natural photosynthesis in green plants. In this system, the water-splitting reaction is broken up into two stages: one for H-2 evolution and the other for O-2 evolution; these are combined by using a shuttle redox couple (Red/Ox) in the solution. The introduction of a Z-scheme mechanism reduces the energy required to drive each photocatalysis process, extending the usable wavelengths significantly (approximate to 660 nm for H-2 evolution and approximate to 600 nm for O-2 evolution) from that in conventional water splitting systems (approximate to 460 nm) based on one-step photoexcitation in single semiconductor material.