A two-step photoexcitation system for photocatalytic water splitting into hydrogen and oxygen under visible light irradiation

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 (Zscheme) 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 (∼460 nm for H₂ evolution and ∼600 nm for O₂evolution) from that in conventional water splitting systems (∼460 nm) based on one-step photoexcitation in single semiconductor material.