Effects of Nb Doping on the Photocatalytic Performance of Rutile TiO2 Single Crystals

We characterized the photocatalytic performance of rutile TiO2 single crystals with Nb doping (0.01-0.05 wt%) for water splitting and then observed the effects of doping. Although Nb doping induces additional optical absorption below the bandgap energy, it does not contribute to photocatalytic performance. Moreover, Nb doping enhances carrier recombination and donor concentration, resulting in reduction of the hole diffusion length and depletion of the layer width. Furthermore, it reduces the existing holes generated by light for photocatalysis because of the difficulty of charge separation by an internal electric field. In addition, comparison of the theoretically calculated photocurrents indicates that high Nb doping has other negative effects on the photocatalytic performance. These results suggest that, although Nb doping enhances the electrical conduction by increasing the donor concentration, it has negative effects on other important characteristics for photocatalysis. Therefore, Nb doping has optimum concentrations depending on structures of the photoelectrode. (c) 2019 The Electrochemical Society.