Photocatalytic Hydrogen Evolution with a Self-Assembling Reductant–Sensitizer–Catalyst System

Authors

  • Mirco Natali,

    Corresponding author
    1. Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Via Fossato di Mortara 17-19, 44121 Ferrara (Italy)
    2. Centro Interuniversitario per la Conversione Chimica dell'Energia, Solare (SOLARCHEM), sezione di Ferrara, Via L. Borsari 46, 44121 Ferrara (Italy)
    • Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Via Fossato di Mortara 17-19, 44121 Ferrara (Italy)
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  • Dr. Roberto Argazzi,

    1. ISOF-CNR, sezione di Ferrara, Via L. Borsari 46, 44121 Ferrara (Italy)
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  • Dr. Claudio Chiorboli,

    1. ISOF-CNR, sezione di Ferrara, Via L. Borsari 46, 44121 Ferrara (Italy)
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  • Dr. Elisabetta Iengo,

    Corresponding author
    1. Department of Chemical and Pharmaceutical Sciences, University of Trieste, Via L. Giorgeri 1, 34127 Trieste (Italy)
    • Department of Chemical and Pharmaceutical Sciences, University of Trieste, Via L. Giorgeri 1, 34127 Trieste (Italy)
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  • Prof. Dr. Franco Scandola

    Corresponding author
    1. Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Via Fossato di Mortara 17-19, 44121 Ferrara (Italy)
    2. Centro Interuniversitario per la Conversione Chimica dell'Energia, Solare (SOLARCHEM), sezione di Ferrara, Via L. Borsari 46, 44121 Ferrara (Italy)
    • Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Via Fossato di Mortara 17-19, 44121 Ferrara (Italy)
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Abstract

A noble-metal-free system for photochemical hydrogen production is described, based on ascorbic acid as sacrificial donor, aluminium pyridyl porphyrin as photosensitizer, and cobaloxime as catalyst. Although the aluminium porphyrin platform has docking sites for both the sacrificial donor and the catalyst, the resulting associated species are essentially inactive because of fast unimolecular reversible electron-transfer quenching. Rather, the photochemically active species is the fraction of sensitizer present, in the aqueous/organic solvent used for hydrogen evolution, as free species. As shown by nanosecond laser flash photolysis experiments, its long-lived triplet state reacts bimolecularly with the ascorbate donor, and the reduced sensitizer thus formed, subsequently reacts with the cobaloxime catalyst, thereby triggering the hydrogen evolution process. The performance is good, particularly in terms of turnover frequencies (TOF=10.8 or 3.6 min−1, relative to the sensitizer or the catalyst, respectively) and the quantum yield (Φ=4.6 %, that is, 9.2 % of maximum possible value). At high sacrificial donor concentration, the maximum turnover number (TON=352 or 117, relative to the sensitizer or the catalyst, respectively) is eventually limited by hydrogenation of both sensitizer (chlorin formation) and catalyst.

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