Bandgap Engineering of TiO2 for Enhanced Selectivity in Photoelectrochemical Glycerol Oxidation

Abstract

The application of photoelectrochemical cells to the partial oxidation of biomass represents a promising avenue as a sustainable process for obtaining valuable products. However, achieving both efficient conversion rates and high selectivity of desired products remains a great challenge. In this study, the photoelectrochemical oxidation of glycerol is investigated to produce dihydroxyacetone (DHA) as the primary target using TiO₂ nanotubes (NTs) as the photoanode. Nitrogen doping is used to modify the TiO₂ NTs, resulting in enhanced visible light photoactivity in N-doped NTs. These N-doped NTs exhibit a high selectivity toward DHA and show a remarkable faradaic efficiency when irradiated with light at a wavelength of 450 nm, i.e., light that excites N-related states in the band gap of TiO₂. The N-doped material also exhibits remarkable stability over prolonged reaction periods. The superior performance of N-doped NTs can be attributed to the band-engineering effects induced by nitrogen doping. Specifically, N-doping leads to an upward shift of the valence band, thereby adjusting the exit energy levels of photogenerated holes that result in a high selectivity toward glycerol conversion to DHA.