Photo-electrochemical properties of amorphous WO 3 supported on TiO 2 hybrid catalysts
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Catalysis Letters Vol. 101, Nos. 1–2, May 2005 ( 2005) DOI: 10.1007/s10562-004-3748-7
Photo-electrochemical properties of amorphous WO3 supported on TiO2 hybrid catalysts Shinya Higashimoto*, Nobuya Kitahata, Kohichi Mori, and Masashi Azuma Department of Applied Chemistry, College of Engineering Osaka Institute of Technology, 5-16-1 Omiya, Asahi-ku, Osaka 535-8585, Japan
Received 26 November 2004; accepted 03 December 2004
In this work, we have carried out ivestigations on photo-electrochemical energy conversion and storage on WO3/TiO2 hybrid materials. The band gap excitation of the hybrid WO3/TiO2 having an amorphous WO3 phase led to an effective photo-charging to form a tungsten bronze structure by the intercalation of protons while a reversible discharging through de-intercalation could also be observed. KEY WORDS: photo-charging; discharging; WO3/TiO2; amorphous WO3.
Introduction The photo-electrochemical conversion and storage of solar (photo) energy using semiconductors have attracted considerable interest over the last decades. Tungsten trioxide (WO3) is especially interesting as a photo-anode and electro- or photo-chromic material [1–6]. On the other hand, the bicomponent WO3/TiO2 has been found to exhibit higher photocatalytic reactivity for the decomposition of organic compounds than either TiO2 or WO3 itself [7]. Moreover, the WO3/TiO2 system, with its energy storage ability, could also be applied for anticorrosion or bactericidal effects [8–10]. The photoinduced charge separation on WO3/TiO2 to produce a hole and an electron initiates the oxidation and slow reduction of the substrates even under dark conditions, respectively. Our aim is to design such photo-functional devices as photo-chargeable batteries using a hybrid WO3/TiO2 that can operate as an effective UV-light driven photo-anode for charge separation as well as charge accumulation. Here, we report on the effects of the crystallinity of WO3, i.e., polycrystalline or amorphous, on its photo-charging and discharging abilities using hybrid WO3/TiO2 materials.
Experimental A polycrystalline WO3 (referred to as c-WO3) and an amorphous WO3 (a-WO3) were prepared by the thermal decomposition of ammonium tungstate at 873 K for 6 h and tungstic acid (H2WO4) at 573 K for 1 h, respectively. An a-WO3/TiO2 and c-WO3/TiO2 with 20 wt% WO3 were prepared by the impregnation of ammonium tungstate into TiO2 (anatase structure, Kanto Chemi* To whom correspondence should be addressed. E-mail: [email protected]
cals), and by a physical mixing of c-WO3 with TiO2, respectively. Each sample was spread over a conductive indium tin oxide glass (ITO, 10 W) with triethyleneglycol as the binder, and was then calcinated in air at 773 K for 15 min. The powder X-ray diffraction (XRD) patterns of all the samples were obtained with a RIGAKU RINT2000 using Cu Ka radiation (k=1.5417 A˚). The charge–discharge characteristics of these materials were measured by a potentiostat (HA-501, HOKUTO DENKO) used as a potentiometer. A black light (UV-light: 365 nm, 0.50 mW/cm2) was
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