Rough electrochromic phosphotungstic acid (PWA) films were fabricated by spraying a gel of phosphotungstate anions with a molar ratio of P:W = 1: 12 onto glass substrates. The substrates were coated with transparent and electrically conducting SnO2:F at 300degreesC. Analysis by X-ray photoelectron spectroscopy determined that the P:W molar ratio in the films was approximately 1:14. Infrared spectroscopy and X-ray diffraction showed that the film is a form of polycrystalline phosphotungstic acid. SEM micrographs showed that the films have a rough morphology based on fiber-shape bridges. Optoelectrochernical measurements demonstrated pronounced electrochromism in the PWA films upon H+ intercalation/ deintercalation with a high diffuse reflectance (R-d) and transmittance (T-d). We found for as-deposited films that R-d/total reflectance (R-t) and T-d/total transmittance (T-t) at 550 nm was around 0.83 and 0.68, respectively. This ratio decreases at bleached state to 0.74 and 0.41 for R-d/R-t and T-d/T-t , respectively. (C) 2003 Elsevier B.V. All rights reserved.