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Electron Transfer in Dye‐Sensitised Semiconductors Modified with Molecular Cobalt Catalysts: Photoreduction of Aqueous Protons
Author(s) -
Lakadamyali Fezile,
Reynal Anna,
Kato Masaru,
Durrant James R.,
Reisner Erwin
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201202149
Subject(s) - photocatalysis , photochemistry , electron transfer , catalysis , aqueous solution , photodegradation , nanoparticle , chemistry , visible spectrum , materials science , cobalt , electron donor , inorganic chemistry , nanotechnology , organic chemistry , optoelectronics
A visible‐light driven H 2 evolution system comprising of a Ru II dye ( RuP ) and Co III proton reduction catalysts ( CoP ) immobilised on TiO 2 nanoparticles and mesoporous films is presented. The heterogeneous system evolves H 2 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 H 2 (mol CoP ) −1 and above 200,000 mol H 2 (mol TiO 2 nanoparticles) −1 in water. Our studies support that a molecular Co species, rather than metallic Co or a Co‐oxide precipitate, is responsible for H 2 formation on TiO 2 . 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 TiO 2 in approximately 180 ps. Thereby, upon dye regeneration by the sacrificial electron donor, a long‐lived TiO 2 conduction band electron is formed with a half‐lifetime of approximately 0.8 s. Electron transfer from the TiO 2 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.