Modification of Ti-doped hematite nanowires with a NiO_x buffer layer for improved photoelectrochemical performance

Hematite (α-Fe₂O₃) is a promising photoanode material for photoelectrochemical (PEC) water splitting due to its appropriate bandgap, good stability, and earth-abundance. However, the poor charge transfer property and sluggish kinetics of water oxidation limit the PEC performance of α-Fe₂O₃ photoanodes. Herein, a thin NiO_x buffer layer was introduced between the Ti doped α-Fe₂O₃ (Fe₂O₃-Ti) layer and the fluorine-doped tin oxide (FTO) substrate without affecting the nanowire morphology and light absorption property of Fe₂O₃-Ti. This buffer layer can apparently suppress the charge recombination by mitigating the lattice mismatching between the Fe₂O₃-Ti film and the FTO substrate. In addition, the good conductivity of the NiO_x film from the non-stoichiometric composition is also beneficial to the charge transfer. As a consequence, the photocurrent density was greatly improved by adding the NiO_x layer in the Fe₂O₃-Ti photoanode, reaching 1.32 mA·cm⁻² at 1.23 V_RHE without any co-catalyst and sacrificial agent. This work gives a detailed analysis of the back contact in the hematite-based photoanode and provides an effective strategy for underlayer interface optimization.