Efficient charge transfers in hematite photoanode integrated by fluorine and zirconia co-doping for photoelectrochemical water splitting

Dual elemental doping strategies were employed in this study to fabricate fluorine and zirconia co-doped hematite (F–Zr:Fe₂O₃/FTO) photoanodes. Such F–Zr:Fe₂O₃/FTO photoanodes had a (1 1 0)-oriented structure with a remarkable photocurrent density of 1.91 mA cm⁻² without any catalyst support at water oxidation potential of 1.23 V_RHE. The enhancement in net photocurrent density was attributed to the synergistic effect between the two doping elements. When in situ doped Zr⁴⁺ ions were used to substitute iron ions, they increase photogenerated free electrons within the bulk hematite and resulted in lower bulk charge transfer resistance, and a minimal concentration of F was doped into hematite lattice, it would go into the oxygen site rather than the iron site, resulting in more positive charges on iron site. The charge compensation contributed to reduced recombination of free electron–hole pairs and improved surface charge injection efficiency at the semiconductor–electrolyte interface by promoting hole transfer via surface states.