Supersonically sprayed iron oxide nanoparticles with atomic-layer-deposited ZnO/TiO₂ layers for solar water splitting

We demonstrate a promising Fe₂O₃/ZnO/TiO₂ photoanode for photoelectrochemical water splitting. Passivation of the Fe₂O₃ surface with thin layers of ZnO and TiO₂ enhances the water splitting photocurrent density of Fe₂O₃. The increased photoelectrochemical activity of the hematite-based structure with heterojunctions, compared to that of bare Fe₂O₃, results from improved charge separation during water oxidation. The multilayered Fe₂O₃ film exhibits a seven-fold improvement in photocurrent density (to 4.25 mA cm⁻²) compared with bare Fe₂O₃, due to suppression of electron–hole recombination. The transient photocurrent density and impedance were evaluated to assess the effect of the passivation layer thickness and achieve a high photocurrent at low potential (0.7 V vs. Ag/AgCl) through improved light harvesting of the Fe₂O₃ film with an ultrathin ZnO/TiO₂ overlayer.