First-principles insights into role of hydrogen atom in black titania

Abstract

We employ first-principles calculations to investigate hydrogen doping at the (101) surface of the anatase TiO2, as the most stable surface of black titania. Interstitial sites at the surface as well as substitutional sites at the surface and subsurface are considered as possible doping configurations. In the framework of first-principles thermodynamics, it is shown that surface adsorption is more probable in normal environment, while substitutional doping at the surface is feasible in a low oxygen pressure environment, in agreement with experimental observations. It is found that the adsorbed hydrogen impurity creates delocalized electron carriers with Ti-3d character at the bottom of the conduction band, which may enhance light absorption in the infrared and visible regions. On the contrary, the substituted hydrogen impurity results in a localized mid gap state, which reduces oxidation states of the neighboring Ti atom from 4+ to 3+. This localized state may act as a trapping center for electron-hole recombination and thus reducing the photocatalytic efficiency of the system.