Facile solvothermal method for fabricating arrays of vertically oriented α-Fe₂O₃ nanowires and their application in photoelectrochemical water oxidation

The controlled growth of highly ordered, [211]-oriented FeOOH nanowire arrays on various substrates, such as Pt, W, Ti, and fluoride-doped tin oxide (FTO) glass, was achieved by a solvothermal method in aqueous acetonitrile solutions at 80-120 °C, following by annealing to form α-Fe ₂O₃ nanowires with their [110] direction perpendicular to the substrate. Adjusting the reaction pH and temperature enables control of the nanowire length. In particular, the pH has a dramatic effect on the nanowire growth, with low pH resulting in the growth of longer wires because of the acid-catalyzed hydrolysis of acetonitrile. Photoactive hematite was prepared by diffusing Ti or Sn into the nanowires during thermal annealing. Processing parameters that influenced the photoelectrochemical performance of these nanowire arrays, including the annealing regime, temperature, and length of nanowires, are discussed in detail. The Ti- and Sn-doped one-dimensional [110]-oriented α-Fe₂O₃ nanowire arrays provide an effective pathway for electron transport, demonstrating increased photocurrents, up to 1.3 mA/cm² under air mass 1.5 global (AM 1.5G) illumination, in photoelectrochemical water oxidation.