Doped and Core/Shell Structured Hematite Nanorods for Improved Photoanodic Performance for Solar Water Splitting

In this study, a facile solution-based method was developed to fabricate hematite nanorods coated with ultrathin overlayer of TiO2 or AgxFe2-xO3, as well as doped with Ta5+. The core/shell nanorod structures of α-Fe2O3/TiO2 and α-Fe2O3/AgxFe2-xO3 were obtained by annealing solution-fabricated β-FeOOH nanorod arrays which were first ultrasonicated in TiO2 sol and Ag+ aqueous solution, respectively. In the α-Fe2O3/TiO2 nanorod structure, TiO2 overlayer could extract photogenerated holes from α-Fe2O3 core via the quantum-mechanical tunneling process, resulting in promoted charge carrier separation, and hence greatly improved photoelectrochemical performance for water splitting, with IPCE increased by a factor of 4.5 from ~2.0% to 9.0% at 400 nm. In the α-Fe2O3/AgxFe2-xO3 nanorod structure, the surface doping of Ag+ ions gave rise to increased electron donor density, which also led to the enhancement in photoelectrochemical performance with IPCE at 400 nm increased from ~2.0% to ~7.5%. Ta5+ doping was found to effectively enhance the PEC performace for water splitting, due to the improved conductivity, increased donor density and reduced charge recombination. However, excessive Ta doping will reduce the PEC acitivity, by forming insulating layer of Ta-rich oxide over the hematite surface.