Preparation Of WO₃Porous Films And Their Photoelectrochemical Properties

The low light quantum yield and limited visible spectral response prombles of WO3compact photoanode hold back its utilization in the application. In this paper, arrayed WO3porous films were prepared via electrophoretic deposition using polystyrene spheres as templates. CdS was assembled onto WO3porous films by electrodepositon in a nonanqueous solution and used as sensitizer of a photoelectrode. The surface morphology, crystalline phase and surface chemical composition of the samples were characterized by field emission scanning electron microscope (FESEM), transmission elelctoron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS). The photoelectrochemical properties of the samples were also further investigated.The peroxo-tungsten acid as WO3precursor was obtained by sol-gel route using tungsten powder. The arrayed WO3porous films with diameter of250nm were obtained by combinating template the method and the electrophoretic deposition method. The porous films are monoclinic WO3and the average crystal size is34.6nm. A small portion of carbon was doped into WO3lattice in the process of removing the PS templates, resulting in a decrease of the band gap of the porous WO3from2.8eV to2.3eV. The porous srucrture and carbon doping are found to be important factors in affecting photoelectrochemical property. When controlling the ethanol/acetic acid ratio of3:1, deposition time of2min and annealing temperature of450℃, the WO3porous film demonstrated the best photoelectrochemical property. The photocurrent density of the porous film is1.93mA·cm-2, which is1fold enhancement compared with the compact WO3film prepared under the same conditions.The CdS sensitized WO3porous films were prepared by electrodepositon in a nonanqueous solution containing Cd(NO3)2and sulfur. In comparison with WO3porous film, the CdS sensitized WO3films prepared at a deposition voltage of2.5V and calcined at350℃exhibited an enhanced visible light absorption and the bandgap was reduced to1.8eV. The CdS sensitized WO3film showed higer photoelectrochemical propertiy. The carrier concentration of CdS sensitized WO3film is about2times of that generated by WO3porous film, the photocurrent density of CdS/WO3is1.2mA·cm-2at0V(vs.Ag/AgCl sat.).