Preparation and photoelectrocatalytic activity of a nano-structured WO3 platelet film

A tungsten trioxide (WO3) film was prepared by calcination from a precursor paste including suspended ammonium tungstate and polyethylene glycol (PEG). The ammonium tungstate suspension was yielded by an acid-base reaction of tungstic acid and an ammonium solution followed by deposition with ethanol addition. Thermogravimetric (TG) analysis showed that the TG profile of PEG is significantly influenced by deposited ammonium tungstate, suggesting that PEG is interacting strongly with deposited ammonium tungstate in the suspension paste. X-ray diffraction (XRD) data indicated that the WO3 film is crystallized by sintering over 400 degrees C. The scanning electron microscopic (SEM) measurement showed that the film is composed of the nano-structured WO3 platelets. The semiconductor properties of the film were examined by Mott-Schottky analysis to give flat band potential E-FB = 0.30 V vs. saturated calomel reference electrode (SCE) and donor carrier density N-D = 2.5 x 10(22) cm(-3), latter of which is higher than previous WO3 films by two orders of magnitude. The higher ND was explained by the large interfacial heterojunction area caused by the nano-platelet structure, which apparently increases capacitance per a unit electrode area. The WO3 film sintered at 550 degrees C produced 3.7 mAcm(-2) of a photoanodic current at 1.2 V vs. SCE under illumination with a 500 W xenon lamp due to catalytic water oxidation. This photocurrent was 4.5-12.8 times higher than those for the other control WO3 films prepared by similar but different procedures. The high catalytic activity could be explained by the nano-platelet structure. The photocurrent was generated on illumination of UV and visible light below 470 nm, and the maximum incident photon-to-current conversion efficiency (IPCE) was 47% at 320 nm at 1.2 V. Technically important procedures for preparation of nano-structured platelets were discussed. (c) 2007 Elsevier Inc. All rights reserved.