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Mechanism of photocatalytic water splitting in TiO2. Reaction of water with photoholes, importance of charge carrier dynamics, and evidence for four-hole chemistry

Tang, JW; Durrant, JR; Klug, DR; (2008) Mechanism of photocatalytic water splitting in TiO2. Reaction of water with photoholes, importance of charge carrier dynamics, and evidence for four-hole chemistry. J AM CHEM SOC , 130 (42) 13885 - 13891. 10.1021/ja8034637.

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Abstract

We show for the first time that the photogenerated hole lifetime in TiO2 is a strong determinant of the ability of TiO2 to split water. Hole lifetimes were measured using transient absorption spectroscopy over a range of excitation intensities. The lifetimes of the holes were modulated by the use of exogenous scavengers and were also found to vary systematically with the excitation intensity. In all cases the quantum yield of oxygen production is found to be linked to the light intensity used, ranging from below 1 sun equivalent to nearly 1 sun equivalent. We also provide evidence that oxygen production requires four photons for each molecule of oxygen, which is reminiscent of the natural photosynthetic water-splitting mechanism. This in turn suggests a mechanism for oxygen production which requires four-hole chemistry, presumably via three, as yet unidentified intermediates. It is also shown that at excitation densities on the order of 1 sun, nongeminate electron-hole recombination limits the quantum yield significantly.

Type: Article
Title: Mechanism of photocatalytic water splitting in TiO2. Reaction of water with photoholes, importance of charge carrier dynamics, and evidence for four-hole chemistry
DOI: 10.1021/ja8034637
Keywords: VISIBLE-LIGHT IRRADIATION, TRANSIENT ABSORPTION-SPECTROSCOPY, PHOTOINDUCED HYDROGEN-PRODUCTION, ELECTRON-PARAMAGNETIC-RES, PHOTOPHYSICAL PROPERTIES, NANOCOMPOSITE FILMS, PHOTOSYSTEM-II, TRAPPED HOLES, OXYGEN, NANOPARTICLES
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering
URI: http://discovery.ucl.ac.uk/id/eprint/171991
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