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 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 H 2 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.