Electron transfer in dye-sensitised semiconductors modified with molecular cobalt catalysts: Photoreduction of aqueous protons

Fezile Lakadamyali, Anna Reynal, Masaru Kato, James R. Durrant, Erwin Reisner

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    77 Citations (Scopus)

    Abstract

    A visible-light driven H2 evolution system comprising of a RuII dye (RuP) and CoIII 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. Long-lived charge separation! Photoexcitation of a ruthenium dye (RuP) on TiO2 results in ultrafast electron injection into the semiconductor, and the resulting long-lived conduction-band electron has sufficient time to reach co-attached cobalt catalysts (CoP) for H 2 evolution in a pH-neutral solution and at room temperature (see figure).

    Original languageEnglish
    Pages (from-to)15464-15475
    Number of pages12
    JournalChemistry - A European Journal
    Volume18
    Issue number48
    DOIs
    Publication statusPublished - 26 Nov 2012

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