Defining the Role of Excess Electrons in the Surface Chemistry of TiO2

Abstract

Understanding and quantifying the principles governing surface-to-adsorbate charge transfer is of utmost importance because excess electrons in n-type oxides alter significantly surface binding and reactivity. We performed a systematic study using density functional theory (DFT) of the role of excess electrons in rutile TiO2, which can result from point defects such as oxygen vacancies, bridging row hydroxyls, and interstitial Ti species. These defects create excess electrons within the Ti sublattice which can perform redox chemistry on adsorbates. We show the similarity of these defects in their ability to donate electrons to surface adsorbates, indicating that experimentally distinguishing the nature of the defects may be difficult. We examined the adsorption and reactivity of O2 in detail and also present a generalization of these findings for a variety of species. A characterization of the redox properties of the surface/adsorbate complex indicates that when the electronegativity of the adsorbate is g...