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

Abstract Photocatalytic water splitting using semiconductor materials has attracted considerable interest due to its potential for clean production of H2 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 H2 and O2 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 H2 evolution and the other for O2 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 (≈660 nm for H2 evolution and ≈600 nm for O2 evolution) from that in conventional water splitting systems (≈460 nm) based on one-step photoexcitation in single semiconductor material.