American Chemical Society Acta Medica Okayama 1932-7447 126 22 2022 Role of Oxygen Vacancy in the Photocarrier Dynamics of WO3 Photocatalysts: The Case of Recombination Centers 9257 9263 EN Kosaku Kato Graduate School of Natural Science and Technology, Okayama University Yohei Uemura Institute for Molecular Science Kiyotaka Asakura Institute for Catalysis, Hokkaido University Akira Yamakata Graduate School of Natural Science and Technology, Okayama University Defects in powder photocatalysts determine the photocatalytic activity. The addition of defects sometimes enhances the activity, but sometimes decreases it. However, the factors determining the difference between these cases have not been fully elucidated yet. Herein, we investigated the effects of oxygen vacancies on photocarrier dynamics in WO3 powder using broadband transient absorption spectroscopy. It was found that the decay of deeply trapped electrons was accelerated when the number of oxygen vacancies was increased by H-2 reduction. This result suggests that oxygen vacancies in WO3 mainly act as recombination centers. This is in contrast to many other photocatalysts such as TiO2 and SrTiO3, where the carrier lifetime increases with increasing oxygen vacancy concentration. These differences can be attributed to the difference in the distance between oxygen vacancies. When defects are dispersed, trapped electrons need to travel over long distances by repeatedly hopping and tunneling between defects to combine with holes, resulting in decelerated recombination. In contrast, when the defects are connected or located close together, the trapped electrons can readily migrate among defects, leading to enhanced recombination. Control of the distance between defects is thus important for enhancing photocatalytic activity. No potential conflict of interest relevant to this article was reported.