Crystalline WO3 nanoparticles were made with hot-wire chemical vapor deposition. The powder was heat-treated at 300, 400, 500, and 600 degrees C in air. The structural properties were measured with X-ray photoelectron spectroscopy, X-ray diffraction. and Raman spectroscopy. Thin-film electrodes of the powder were made by ultrasonic spray deposition onto conducting substrates. The photocurrent was measured at wavelengths greater than 400 nm as the voltage was scanned from 0.2 to 1.8 V in an aqueous environment. A correlation was seen between the photocurrent and dye decomposition and the results were most favorable for the monoclinic (I) gamma-phase of WO3. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3484474] All rights reserved.