Effect of oxygen deficiency on the excited state kinetics of WO3 and implications for photocatalysis

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Title: Effect of oxygen deficiency on the excited state kinetics of WO3 and implications for photocatalysis
Authors: Sachs, M
Park, JS
Pastor, E
Kafizas, A
Wilson, AA
Francàs, L
Gul, S
Ling, M
Blackman, C
Yano, J
Walsh, A
Durrant, JR
Item Type: Journal Article
Abstract: Oxygen vacancies are widely used to tune the light absorption of semiconducting metal oxides, but a photophysical framework describing the impact of such point defects on the dynamics of photogenerated charges, and ultimately on catalysis, is still missing. We herein use WO3 as a model material and investigate the impact of significantly different degrees of oxygen deficiency on its excited state kinetics. For highly oxygen-deficient films, photoelectron spectroscopy shows an over 2 eV broad distribution of oxygen vacancy states within the bandgap which gives rise to extended visible light absorption. We examine the nature of this distribution using first-principles defect calculations and find that defects aggregate to form clusters rather than isolated vacancy sites. Using transient absorption spectroscopy, we observe trapping of photogenerated holes within 200 fs after excitation at high degrees of oxygen deficiency, which increases their lifetime at the expense of oxidative driving force. This loss in driving force limits the use of metal oxides with significant degrees of sub-stoichiometry to photocatalytic reactions that require low oxidation power such as pollutant degradation, and highlights the need to fine-tune vacancy state distributions for specific target reactions.
Issue Date: 14-Jun-2019
Date of Acceptance: 12-Apr-2019
URI: http://hdl.handle.net/10044/1/70979
DOI: https://doi.org/10.1039/c9sc00693a
ISSN: 2041-6520
Publisher: Royal Society of Chemistry
Start Page: 5667
End Page: 5677
Journal / Book Title: Chemical Science
Volume: 10
Issue: 22
Copyright Statement: © 2019 The Authors. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (https://creativecommons.org/licenses/by/3.0/).
Sponsor/Funder: Engineering and Physical Sciences Research Council
Publication Status: Published
Open Access location: https://pubs.rsc.org/en/content/articlepdf/2019/sc/c9sc00693a
Online Publication Date: 2019-05-09
Appears in Collections:Materials
Centre for Environmental Policy
Faculty of Natural Sciences

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