Unravelling the pH-dependence of a molecular photocatalytic system for hydrogen production
Gross, Manuela A
Durrant, James R
Royal Society of Chemistry
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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 4855-4859. https://doi.org/10.1039/C5SC01349F
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.
Financial support from the ERC (291482, Intersolar to J. D.), the EPSRC (EP/H00338X/2 to E. R., DTG scholarship to E. P.), the European Commission Marie Curie CIG (303650, PhotoCO2 to A. R.), the Christian Doppler Research Association (Austrian Federal Ministry of Science, Research and Economy and National Foundation for Research, Technology and Development), and the OMV Group (to E. R.) is gratefully acknowledged.
External DOI: https://doi.org/10.1039/C5SC01349F
This record's URL: https://www.repository.cam.ac.uk/handle/1810/248593
Attribution 2.0 UK: England & Wales
Licence URL: http://creativecommons.org/licenses/by/2.0/uk/
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