Ti-doped hematite films coupled with ultrathin nickel-borate layer as photoanode for enhanced photoelectrochemical water oxidation

Hematite (α-Fe₂O₃) is a very attractive photoanode material for photoelectrochemical (PEC) water oxidation application due to its remarkable chemical stability and appropriate bandgap. However, the low charge separation efficiency, poor conductivity, and sluggish water oxidation kinetics still severely limit its expected performance. In this study, we constructed a photo-electrodeposited amorphous nickel-borate (Ni-B_i) thin layer on Ti-doped α-Fe₂O₃ photoanode. The fabricated heterostructure photoanode developed a built-in electric field, which will accelerate charge transport and improve the water oxidation kinetics significantly, resulting in the greatly enhanced photocurrent density of about 348% at 1.23 V vs. reversible hydrogen electrode (RHE) and the improvement of onset potential advance of ~ 80 mV. The surface morphology of samples was characterized with field-emission scanning electron microscope (FE-SEM) and high-resolution transmission electron microscope (HRTEM). The Mott–Schottky (M-S) and electrochemical impedance spectroscopy (EIS) results confirmed the donor density and the conductivity of photoanodes with Ti-doping and Ni-B_i coated. This work provides a novel strategy to develop various heterojunction photoanodes for practical PEC application of α-Fe₂O₃.