Facile Synthesis of Highly Photoactive α-Fe2O3-Based Films for Water Oxidation

Abstract

This work reports a facile method for preparing highly photoactive α-Fe₂O₃ films as well as their implementation as photoanodes for water oxidation. Transparent α-Fe₂O₃ films were prepared by a new deposition–annealing (DA) process using nontoxic iron(III) chloride as the Fe precursor, followed by annealing at 550 °C in air. Ti-doped α-Fe₂O₃ films were prepared by the same method, with titanium butoxide added as the Ti precursor. Impedance measurements show that the Ti-dopant serves as an electron donor and increases the donor density by 2 orders of magnitude. The photoelectrochemical performance of undoped and Ti-doped α-Fe₂O₃ photoanodes was characterized and optimized through controlled variation of the Fe and Ti precursor concentration, annealing conditions, and the number of DA cycles. Compared to the undoped sample, the photocurrent onset potential of Ti-doped α-Fe₂O₃ is shifted about 0.1–0.2 V to lower potential, thus improving the photocurrent and incident photon to current conversion efficiency (IPCE) at lower bias voltages. Significantly, the optimized Ti-doped α-Fe₂O₃ film achieved the highest photocurrent density (1.83 mA/cm²) and IPCE values at 1.02 V vs RHE for α-Fe₂O₃ photoanode. The enhanced photocurrent is attributed to the improved donor density and reduced electron–hole recombination at the time scale beyond a few picoseconds, as a result of Ti doping.