Electron Transfer in Dye‐Sensitised Semiconductors Modified with Molecular Cobalt Catalysts: Photoreduction of Aqueous Protons

A visible‐light driven H₂ evolution system comprising of a Ru^II dye ( RuP ) and Co^III proton reduction catalysts ( CoP ) immobilised on TiO₂ nanoparticles and mesoporous films is presented. The heterogeneous system evolves H₂ efficiently during visible‐light irradiation in a pH‐neutral aqueous solution at 25 °C in the presence of a hole scavenger. Photodegradation of the self‐assembled system occurs at the ligand framework of CoP , which can be readily repaired by addition of fresh ligand, resulting in turnover numbers above 300 mol H₂ (mol CoP )^?1 and above 200,000 mol H₂ (mol TiO₂ nanoparticles)^?1 in water. Our studies support that a molecular Co species, rather than metallic Co or a Co‐oxide precipitate, is responsible for H₂ formation on TiO₂. Electron transfer in this system was studied by transient absorption spectroscopy and time‐correlated single photon counting techniques. Essentially quantitative electron injection takes place from RuP into TiO₂ in approximately 180 ps. Thereby, upon dye regeneration by the sacrificial electron donor, a long‐lived TiO₂ conduction band electron is formed with a half‐lifetime of approximately 0.8 s. Electron transfer from the TiO₂ conduction band to the CoP catalysts occurs quantitatively on a 10 μs timescale and is about a hundred times faster than charge‐recombination with the oxidised RuP . This study provides a benchmark for future investigations in photocatalytic fuel generation with molecular catalysts integrated in semiconductors.     

Selective reduction of aqueous protons to hydrogen with a synthetic cobaloxime catalyst in the presence of atmospheric oxygen

Protons preferred: A cobalt catalyst is reported that evolves H(2) electro- and photocatalytically at room temperature, in pH-neutral water, and in the presence of atmospheric O(2) . The catalyst shows respectable Faradaic efficiencies under N(2) and 21?% O(2) in N(2) , and can be used under both homogeneous and heterogeneous conditions.     

Photocatalytic H2 evolution from neutral water with a molecular cobalt catalyst on a dye-sensitised TiO2 nanoparticle

We report on a self-assembled system comprising of a molecular H(2) production cobalt catalyst attached on a ruthenium dye-sensitised TiO(2) nanoparticle. Visible light irradiation of the dispersed nanoparticles in the presence of the sacrificial electron donor triethanolamine produces H(2) photocatalytically in pH neutral water and at room temperature.