Photochemical cleavage of water by photocatalysis

A bifunctional redox catalyst, composed of Pt and RuO 2 co-deposited on a colloidal TiO 2 carrier, is a highly potent mediator for water decomposition by visible light 1 . The system contains apart from the sensitizer (Ru(bipy) 2+ 3 ) an electron relay—methylviologen. The latter is reduced on light excitation, and the photoreaction is coupled with catalytic steps 2 generating H 2 and O 2 from water. To rationalize the surprisingly high efficiency of this photoredox system, we proposed a mechanism involving species adsorbed at the TiO 2 surface. This led us to explore sensitizers which through suitable functionalization show an enhanced affinity for adsorption at the particle–water interface. We describe here the performance of electron relay-free systems capable of efficiently decomposing water into H 2 and O 2 under visible light illumination. A bifunctional redox catalyst composed of RuO 2 and Pt co-supported on colloidal TiO 2 particles is used. The only other component present is a sensitizer. Amphiphilic surfactant derivatives of Ru(bipy) 2+ 3 exhibit extremely high activity in promoting the water cleavage process. Adsorption of the sensitizer at the TiO 2 particle–water interface and electron ejection into the TiO 2 conduction band are evoked to explain the observations. Exposure to UV radiation leads to efficient water cleavage in the absence of sensitizer.