Regularities of Obtaining Electrochromic WO3 Films at the Cathode Polarization of the Electrode

In the article, electrochromic WO₃ films were obtained from 25, 100, and 200 mM peroxytungstic acid (PTA) solution. A chronoamperogram of the cathodic reduction of tungsten oxide (WO₃) through the stages of formation of a precursor film adsorbed on the surface of the ITO electrode and its subsequent staged reduction to WO₃ and side formation of soluble reaction products is presented. The material yield of the WO₃ film on ITO glass was within 50%, which is due to the parallel occurrence of side processes associated with hydrogen evolution and the reduction of tungsten complexes that were in the precipitation solution (WO₃ reduction scheme). In this case, it was taken into account that thin WO₃ films were the final product. The features of the synthesis of peroxytungstic acid have been studied. It has been shown that the reaction of W dissolution in 37% H₂O₂ proceeds exothermically. In this case, the reaction temperature reached 96°C within a few seconds, and its decline varied exponentially with the formation of reaction products. The dependence of the limiting current on the square root is obtained. The presented graphic dependence is characterized by linearity, while the beginning of the straight line does not coincide with the origin. The process of intercalation-deintercalation of protons (H⁺) (cathode-anode branches of CV) was a consequence of structural and reversible changes as a result of H⁺ intercalation. WO₃ films obtained by electrochemical (cathodic) deposition can be recommended as an electrode material for electrochromic devices (cathode) and as a material for electrochemical sensors. Another promising direction is the development of a wide band gap anode based on WO₃ for photovoltaic devices, which are energy efficient hydrogen generation systems.