Solvothermal-Etching Process Induced Ti-Doped Fe₂O₃ Thin Film with Low Turn-On Voltage for Water Splitting

In this work, a thinning process of hematite film accompanied by simultaneous titanium (Ti) doping has been demonstrated. Ti⁴⁺ ion was incorporated into ultrathin Fe₂O₃ film by solvothermally etching a hematite film fabricated on titanium nanorod array substrate. As a consequence, the onset potential (<i>V</i>_on) of oxygen evolution reaction for final ultrathin Ti-doped Fe₂O₃ film shifted toward cathodic substantially, a very low <i>V</i>_on of 0.48 V_RHE was realized, approximately 0.53 V cathodic shift of the hematite film. Working mechanisms were investigated from both kinetic and thermodynamic ways. The ultrathin Ti-doped Fe₂O₃ film exhibited reduced Tafel slope and higher generated photovoltage than the pristine Fe₂O₃ electrode. Moreover, the highly doped Fe₂O₃ resulted in significant reduction of charge-transfer resistance at the Fe₂O₃∥electrolyte interface. The drastic cathodic-shift <i>V</i>_on is believed to be a result of combined factors including thermodynamic contribution, improved surface reaction kinetics, as well as facilitated charge transfer across bulk and interface