Facile Solvothermal Method for Fabricating Arrays of Vertically Oriented α-Fe₂O₃ Nanowires and Their Application in Photoelectrochemical Water Oxidation

Abstract

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 80À120 °C, following by annealing to form α-Fe 2 O 3 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-Fe 2 O 3 nanowire arrays provide an effective pathway for electron transport, demonstrating increased photocurrents, up to 1.3 mA/cm 2 under air mass 1.5 global (AM 1.5G) illumination, in photoelectrochemical water oxidation.

Cobalt Phosphate Group Modified Hematite Nanorod Array as Photoanode for Efficient Solar Water Splitting

“…However the reported efficiencies of hematite are relatively lower than theoretically predicted value of 12.4%, mainly because of the extremely short photogenerated charge carriers' lifetime and diffusion length, chemically inert oxygen evolution reaction, and low flat band potential [7][8][9]. Various approaches, i.e., manipulating nanostructure [5,10,11], chemical composition doping [8,9,[12][13][14], and surface modification [7,15] have been adopted to enhance the photoelectrochemical efficiency of ␣-Fe 2 O 3 .…”

“…Works related to the nanostructure manipulating mainly focus on the nanorod/nanowire structure, which behaves as preferable structure for photoelectrocatalyst in solar water splitting [11,16,17]. Such morphology could satisfy both effective light harvest with the long optical path and excellent charge transport with the short diffusion distance.…”

Nanocube-based hematite photoanode produced in the presence of Na 2 HPO 4 for efficient solar water splitting

“…Although efficiency of hematite is theoretically predicted as a value of 12.4%, there are still some obstacles for hematite as photoanode in PEC water splitting, mainly because of the extremely short hole diffusion length, slow carrier mobility [7][8] and low rate constant for water oxidation [9]. Various methods, such as manipulating nanostructure [10][11][12], element doping [13][14][15], and surface modification [16][17][18][19] have been developed to enhance the photoelectrochemical performance of α-Fe 2 O 3 .…”

“…The preferable nanostructures manipulated for photoelectrocatalyst mainly focus on the nanoparticle and nanorod/nanowire structure which would shorten the charge-transport pathway and increase the accessible surface area [20][21] (Figure 1). Numerous techniques including spray pyrolysis [22,23], atomic layer deposition [24], and APCVD [25] have been reported for developing ultrathin hematite films which were employed as photoanodes for PEC water oxidation.…”

Growth of textured iron oxyhydroxide nanorod arrays on glass substrate

“…In addition, these integrated nanostructures show interesting magnetic properties [5] or improved quantum efficiency [6,7]. Particularly, arrays of 1D iron (oxyhydr)oxide nanostructure have attracted much attention owing to their potential for serving as template [8][9][10] and wide applications in solar cells, gas sensors, catalysts, as well as cathodes for lithium-ion batteries [11][12][13][14].…”