Nanostructuring Bi-Doped α-Fe₂O₃ Thin-Layer Photoanode to Advance the Water Oxidation Performance

A nanograin α-Fe2O3 thin-film photoanode with Bi dopant was successfully synthesized with a simple electrodeposition method on indium tin oxide (ITO) glass and annealing at 550 °C for 3 h. The thin-film photoanodes were characterized and evaluated for their capabilities in oxidizing water. Incorporating Bi dopant into the photoanode could cathodically shift the onset potential to 0.43 V at 0.6 mA/cm2 under a 150 W solar light illumination. Interestingly, the incident photon-to-electron (IPCE) and applied bias photon-to-current efficiency (ABPE) could achieve 22.2 and 0.63%, respectively. On the basis of the experimental data, the low onset potential is notably supported by the nanosized α-Fe2O3 with substitutional defects of Bife+ and oxygen vacancy (VO) to overcome the limitation of natural α-Fe2O3. A density functional theory (DFT) calculation also indicated that the water adsorption step on the modified 5%-bismuth-doped Fe2O3 (BF-5) photoanode was thermodynamically favorable compared to the pristine α-Fe2O3. As a result, the BF-5 photoanode could support the water-splitting process close to a stoichiometric ratio with Pt as the cathode. This work demonstrated an exciting strategy to overcome the short diffusion length of α-Fe2O3 in separating excitons during photoreaction.