Laser-Induced Photoreduction for Selective Tuning of the Oxidation State and Crystal Structure of Hematite Nanorods

The laser-induced photoreduction process is proposed to obtain patterned magnetite (Fe3O4) nanorod (NR) arrays or the oxygen vacancy (OV) engineering of the hematite (α-Fe2O3) NRs. A continuous-wave laser beam, with a wavelength of 532 nm, is focused on the hematite NRs that are in contact with a liquid reducing agent to provide the thermal energy for triggering the reduction reaction. The path of the laser beam can be controlled through computer software, enabling the reduction reaction to occur in the arbitrary desired area. At lower laser powers than that at which the direct transformation of hematite into magnetite occurs, hematite NRs with a high concentration of OV are produced. The high OV concentration contributes to improving the electrical conductivity of the hematite NRs by increasing the donor density. The OV-abundant hematite NR array is applied to a photoanode in a photoelectrochemical (PEC) water-splitting cell. It exhibits an enhanced PEC performance due to its donor density being higher in comparison with the bare hematite NRs.