Subtle structure matters: boosting surface-directed photoelectron transfer via the introduction of specific monovalent oxygen vacancies in TiO2

Abstract

Oxygen vacancies (O_v) are widely considered to play crucial roles in photocatalysis, but how and why they contribute to improved performances remains controversial. In this work, we studied the promotional effect of O_v on photoelectron transfer in TiO₂, using first-principles density functional theory calculations with correction for on-site Coulomb interactions. We explicitly identified three types of O_v with different charge states (i.e., charge-neutral , monovalent , divalent O_v²⁺) via electronic structure analysis. Electron transfer energy calculations revealed that the ionized O_v in anatase TiO₂ are able to collect excess electrons whereas those in the rutile phase are not. The presence of ionized O_v further endows anatase TiO₂ with directional electron transfer along the [100] orientation, in favor of anatase TiO₂(101) for photocatalytic reduction surpassing the (001) termination. After examining various combination modes of ionized O_v involving different charge states and spatial distributions, we demonstrated that the vertical chain in anatase TiO₂(101) is the most catalytically effective O_v pattern in TiO₂. These results signify the importance of subtle defects in photocatalysis and may assist future photocatalyst design toward higher photocatalytic efficiency.