Nb-Doped Hematite Nanorods for Efficient Solar Water Splitting: Electronic Structure Evolution versus Morphology Alteration

In this study, Nb-doped α-Fe₂O₃ nanorod photoanodes were prepared via a facile solution-based process by directly adding NbCl₅ in the aqueous solution. The morphology and electronic structure of Nb-doped α-Fe₂O₃ films depended strongly on the dopant concentrations. Compared with the undoped sample, the optimal Nb-doped α-Fe₂O₃ film showed an approximately 4-fold photocurrent increase under solar light at 1.0 V versus Ag/AgCl, and the incident photon-to-current conversion efficiency was increased by 2.5 times, reaching 13.7 % at 350 nm and 1.23 V versus RHE. The enhancement in PEC activity, as induced by moderate Nb doping, was attributed to the increased charge carrier density for promoted charge transfer ability as well as the smaller nanorod diameter for shortened charge transfer distance. However, superfluous Nb dopants would destroy the nanorod structure and greatly reduce the thickness of α-Fe₂O₃ films, leading to poor optical absorption and thus decreased photoelectrochemical performance.