Reduced TiO₂ with prolonged electron lifetime for improving photocatalytic water reduction activity

Abstract

The reduction of anatase TiO2 with NaBH4 under argon atmosphere at a high temperature resulted in a longer electron lifetime and a larger electron population. The reduced gray anatase sample with disorder layer showed a higher evolution rate of H2 (130.2 μmol h−1 g−1) compared to pristine TiO2 (24.1 μmol h−1 g−1) in the presence of Pt co-catalyst in an aqueous glucose solution under exposure to ultraviolet light (λ ⩽ 400 nm). Ti3+ and oxygen vacancy defects were proposed to exist in the reduced TiO2. A continuum tail forms above the valence band edge top as a result of these two defects, which contribute to the lattice disorder. This is presumably also the case with the conduction band, which has a continuum tail composed of mid-gap states as a result of the defects. The Ti3+ and oxygen vacancy defects operate as shallow traps for photoexcited electrons, thereby preventing recombination. Since the defects are primarily located at the surface, i.e. in the disorder layer, the photoexcited electrons in shallow traps hence become readily available for the reduction of H3O+ into H2. The prolonged electron lifetime increases the photoexcited electron population in the reduced TiO2, resulting in enhanced water reduction activity.