Insight into the enhanced photocatalytic activity of SrTiO3 in the presence of a (Ni, V/Nb/Ta/Sb) pair

Increasing applications of SrTiO3 as a photocatalyst in recent times drive the development of various strategies through doping with foreign elements to improve its efficiency under sunlight. Motivated by the recent experimental observation of increased lifetime of photogenerated charge carriers due to codoping of Ta into Ni-doped SrTiO3 (R. Niishiro et al., Phys. Chem. Chem. Phys., 2005, 7, 2241-2245, and A. Yamakata et al., J. Phys. Chem. C, 2016, 120, 7997-8004), we systematically investigate the detailed electronic structure of Ni-doped SrTiO3 in the presence and absence of Ta. The present theoretical study reveals that Ni-doping reduces the effective band gap by introducing unoccupied Ni-3d states in the forbidden region, while addition of Ta passivates these states. Here, we have properly explained the fact that improved photoconversion efficiency can be achieved only when the proportion of Ta is double with respect to that of Ni. The defect formation energy for the 1:2 type (Ni, Ta)-codoped SrTiO3 is energetically more favourable than that of the 1:1 type variety. The present study also explored the possibility of using V, Nb, and Sb in place of Ta to aim at better utilization of visible light activity. Interestingly, we arrive at a conclusion that V and Nb may be better choices over experimentally reported Ta for achieving enhanced photocatalytic activity of Ni-doped SrTiO3 under visible light. Finally, applicability of all these codoped systems for the generation of hydrogen and oxygen through water splitting has been checked by inspecting their band edge levels with respect to water redox levels.