Enhanced photoelectrochemical performance of anatase TiO2 for water splitting via surface codoping

Codoping can effectively engineer the band structures of photocatalysts (e.g. TiO2) to enhance their photoelectrochemical performance, however, previous investigations mainly focused on codoped bulk materials. In this work, we explore the (Rh + F) surface codoping effect on anatase TiO2 (101) and (001) facets for solar water splitting by performing extensive density functional theory calculations. According to the calculated defect formation energies, we find that the noble metal (Rh) atoms can be stably doped at the anatase TiO2 (101) surface with the aid of the codoped F atoms, thus can act as active sites for photocatalytic H-2 evolution, which also provides the possibility of single-atom Rh catalysis on the (Rh + F) codoped anatase TiO2 (101) surface. The band gap of the codoped system is narrowed to about 2.14 eV through introducing several occupied and delocalized intermediate states which prevent the recombination of photogenerated carriers. Remarkably, the valence band maximum and conduction band minimum of the (Rh + F) codoped anatase TiO2 (101) surface match well with the water redox potentials and the visible light absorption is significantly enhanced. These findings imply that this kind of surface codoping is an effective approach to obtain visible light photocatalysts for water splitting.