Direct anodic growth of thick WO3 mesosponge layers and characterization of their photoelectrochemical response

Abstract

Thick mesoporous tungsten oxide (WO3) layers can be formed by anodization of tungsten in a 10 wt% K2HPO4/glycerol electrolyte, if the electrolyte temperature is around 80-100 °C. At 90 °C, a regular mesoporous WO3 layer was grown up to a thickness of approximately 9 μm. This WO3 mesosponge layer consists of typical feature sizes of 20-30 nm and pore widths of 10-30 nm. The photoresponse of different layer thicknesses and different annealing treatments was characterized in a photoelectrochemical cell. The highest photocurrents were observed with a 2.5 μm thick WO3 layer annealed at 550 °C consisting of a mixture of orthorhombic, triclinic and monoclinic phases. Incident photon to current efficiencies (IPCEs) of the samples were 73.4% in a 1 M HClO4 electrolyte and 167.5% for methanol photo-oxidation in 0.1 M CH3OH/1 M HClO4 electrolyte, at 1 V vs. Ag/AgCl under illumination at a wavelength of 420 nm. © 2010 Elsevier Ltd. All rights reserved.