Fast-switching electrochromic response of WO3 • 2H2O of plate-like particles synthesized by liquid phase deposition

WO3 center dot 2H(2)O with the layered crystal structure was grown into films consisting of plate-like particles on indium doped tin oxide substrates by the liquid phase deposition at room temperature. The [WOF5](-) complex was prepared by dissolving 0.015 mol tungstic acid in 86 cc of a 2.34 wt% hydrofluoric acid solution. The hydrolysis of [WOF5](-) species in the presence of boric acid at room temperature was studied by F-19 NMR spectroscopy to gain insight into the formation mechanism of WO3 center dot 2H(2)O. Microstructural studies revealed that the plate-like particles are single crystals with well-developed facets in octagonal shapes. The basal plane of the plate-like particles is parallel to the corner-sharing WO6 octahedra layers. The films showed a 92.7 +/- 7.5 cm(2)/C coloration efficiency and fast response electrochromic properties with a bleaching time and a coloration time of 0.6 s and 2.0 s, respectively. Such a fast electrochromic response was attributed to the facile migration of proton ions through the layered crystal structure of WO3 center dot 2H(2)O and the plate-like morphology of the films. (C) 2021 Elsevier B.V. All rights reserved.