Synthesis and characterization of rough electrochromic phosphotungstic acid films obtained by spray-gel process

Abstract

Abstract 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 SnO 2 :F at 300°C. 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. Optoelectrochemical 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.