Issue 8, 2015

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

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 RuPNiP 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 RuPNiP photocatalytic system, which can be widely applied to other photocatalytic systems.

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

Supplementary files

Article information

Article type
Edge Article
Submitted
14 Apr 2015
Accepted
27 May 2015
First published
28 May 2015
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2015,6, 4855-4859

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

A. Reynal, E. Pastor, M. A. Gross, S. Selim, E. Reisner and J. R. Durrant, Chem. Sci., 2015, 6, 4855 DOI: 10.1039/C5SC01349F

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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