Photocatalytic Production of Hydrogen by Disproportionation of One-Electron-Reduced Rhodium and Iridium-Ruthenium Complexes in Water

摘要

Photocatalytic production of hydrogen (H2) has attracted increasing attention, because H2 is a clean energy source for the future to reduce dependence on fossil fuels and emissions of greenhouse gases in the long term. Extensive efforts have explored the development of photocatalytic H2 evolution systems, which consist of an electron donor, a photo-sensitizer, an electron mediator such as methyl viologen (MV~(2+)), and a hydrogen-evolution catalyst. Both heterogeneous catalysts such as platinum nanoclusters and molecular homogeneous catalysts have been used for the photocatalytic hydrogen evolution. Organorhodium complexes were found to be useful in place of colloidal platinum for TiO2 photosensitized hydrogen evolution. However, the detailed photocatalytic mechanism of one-electron transfer among components has yet to be elucidated, because the two-electron reduction of protons is required for H2 production. In particular, it should be clarified how photoinduced electron transfer of a photosensitizer (a one-electron process) leads to H2 production (a two-electron process) to improve the photocatalytic efficiency of H2 production.