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

This work reports a facile method for preparing highly photoactive alpha-Fe2O3 films as well as their implementation as photoanodes for water oxidation. Transparent alpha-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 degrees C in air. Ti-doped alpha-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 alpha-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 alpha-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 alpha-Fe2O3 film achieved the highest photocurrent density (1.83 mA/cm(2)). and IPCE values at 1.02 V vs RHE for alpha-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.