Electrochromism in CuWO4 and WO3 thin films synthesized by combined electrochemical and chemical methods

This paper presents a comparative analysis of electrochromic properties of nonstoichiometric hydrated films CuWO3.7·2H2O, WO2.5·2H2O, and α-WO2.9·H2O obtained by combined electrochemical and chemical methods. The use of EDAX X-ray diffraction and UV VIS spectroscopy and the Smacula-Dexter equation helped to determine that of differences in spectral and electrochemical characteristics CuWO3.7·2H2O, WO2.5·2H2O, and α-WO2.9·H2O electrochromic process as results chemical composition, stoichiometry, and the structure films based on W oxide compounds, where the contribution to the electrochromic film coloration is mainly done using localized states of W5+, W4+, and additionally Cu+ in the case of CuWO3.7·2H2O. This allows CuWO3.7·2H2O extending light absorption at the electrochromic coloration in the 450–650 nm visible region spectrum. At the same time, diffusion processes are slowed down due to the complementary electrochromic coloration of copper oxide compounds, which reduces the rate and efficiency CuWO3.7·2H2O film compared to WO2.5·2H2O and α-WO2.9·H2O. This helped to establish that the metal tungstates can be effective electrochromic material as is WO3 with an additional absorption band provided that the dimensionally diffusion rates of protons or lithium ions in both oxide components are achieved.