All-Oxide α-Fe2O3/H:TiO2Heterojunction Photoanode: A Platform for Stable and Enhanced Photoelectrochemical Performance through Favorable Band Edge Alignment

To improve the photoelectrochemical (PEC) performance of hematite thin-film photoanode, we report a novel heterostructure based on Fe2O3/TiO2and hydrogenated Fe2O3/TiO2(Fe2O3/H:TiO2) for faster charge transfer owing to passivation of surface states in Fe2O3via TiO2overlayer and favorable band alignment using hydrogen annealing of TiO2overlayer. The valence band offset, band gap and work function values have been measured using X-ray photoelectron spectroscopy, optical absorption, and Kelvin probe force microscopy to construct the energy band diagram of the heterostructure photoanodes. The results confirm the upshift in the valence band edge of TiO2over Fe2O3after hydrogen treatment of TiO2overlayer, which leads to the formation of type II band edge alignment in Fe2O3/H:TiO2heterojunction and improved PEC performance compared to Fe2O3/TiO2, pristine Fe2O3and TiO2thin-film photoelectrodes. The well-straddled and improved band alignment in Fe2O3/H:TiO2heterostructure gives rise to substantial enhancement in photocurrent density, up to 3.36 mA/cm2at 1.23 V (vs reversible hydrogen electrode (RHE)) with a low onset potential of 0.1 V (vs RHE), under AM1.5 illumination condition. The observed photocurrent density in Fe2O3/H:TiO2heterostructure is 15-fold higher than bare Fe2O3(0.22 mA/cm2) photoanode. This work shows how a simple bilayer junction and its hydrogen treatment can be used to enhance the PEC response of heterojunctions and offers valuable insights into the further development of all-oxide heterojunctions.