Unravelling the pH-dependence of a molecular photocatalytic system for hydrogen production

Anna Reynal, Ernest Pastor, Manuela A. Gross, Shababa Selim, Erwin Reisner, James R. Durrant

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    Abstract

    Photocatalytic systems for the reduction of aqueous protons are strongly pH-dependent, but the origin of this dependency is still not fully understood. We have studied the effect of different degrees of acidity on the electron transfer dynamics and catalysis taking place in a homogeneous photocatalytic system composed of a phosphonated ruthenium tris(bipyridine) dye (RuP) and a nickel bis(diphosphine) electrocatalyst (NiP) in an aqueous ascorbic acid solution. Our approach is based on transient absorption spectroscopy studies of the efficiency of photo-reduction of RuP and NiP correlated with pH-dependent photocatalytic H2 production and the degree of catalyst protonation. The influence of these factors results in an observed optimum photoactivity at pH 4.5 for the RuP-NiP system. The electron transfer from photo-reduced RuP to NiP is efficient and independent of the pH value of the medium. At pH <4.5, the efficiency of the system is limited by the yield of RuP photo-reduction by the sacrificial electron donor, ascorbic acid. At pH >4.5, the efficiency of the system is limited by the poor protonation of NiP, which inhibits its ability to reduce protons to hydrogen. We have therefore developed a rational strategy utilising transient absorption spectroscopy combined with bulk pH titration, electrocatalytic and photocatalytic experiments to disentangle the complex pH-dependent activity of the homogenous RuP-NiP photocatalytic system, which can be widely applied to other photocatalytic systems.

    Original languageEnglish
    Pages (from-to)4855-4859
    Number of pages5
    JournalChemical Science
    Volume6
    Issue number8
    DOIs
    Publication statusPublished - 1 Aug 2015

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  • Cite this

    Reynal, A., Pastor, E., Gross, M. A., Selim, S., Reisner, E., & Durrant, J. R. (2015). Unravelling the pH-dependence of a molecular photocatalytic system for hydrogen production. Chemical Science, 6(8), 4855-4859. https://doi.org/10.1039/c5sc01349f