Hydrated Tungsten Oxide Nano-Electrochromic Films

Electrochromic means that the material has reversible color when applied voltage. Materials that can undergo reversible changes in optical properties (e.g., color) based on electrochemical redox reactions are called electrochromic materials. Tungsten oxide has become a hotspot in electrochromic research due to its excellent electrochromic properties.

In order to solve the technical problems, some scholars have adopted a method of preparing nest-like hydrated tungsten oxide nano-electrochromic films grown by self-crystal seeds. The operation process of the film includes the following contents:

The FTO conductive glass was soaked in detergent, deionized water, acetone and ethanol for 15 minutes respectively, and then dried. 5 g tungstic acid was dissolved in 60 mL hydrogen peroxide, heated to 95 ℃, and cooled to obtain transparent sol. The transparent sol was diluted to 200 mL with deionized water. Among them, 10.5 ml transparent sol, 3.5 ml hydrochloric acid (3 mol/L), 10.5 ml deionized water and 31.5 ml ethylene glycol were poured into the kettle. The FTO conductive glass is immersed in a hydrothermal kettle, kept at 120 ℃ for 2 hours, then cooled to room temperature naturally. The FTO conductive glass is taken out and washed with water and ethanol in turn and dried. WO₃ 0.3 3H₂O films with orthorhombic crystalline phase were prepared. Scanning electron microscopy (SEM) photos of the films show that the films have a bird's nest-like morphology consisting of two-dimensional nanosheets.

The electrochromic properties of hydrated tungsten oxide nanostructured thin films were measured by three-electrode system combined with electrochemical workstation and solid ultraviolet-visible spectrophotometer. The change of light transmittance and electrochromic response speed of hydrated tungsten oxide nanostructured thin films were determined and the coloring efficiency was calculated. The results show that the blue color of the hydrated tungsten oxide nanostructured films gradually deepens when different negative pressures are applied, and the discoloration of the hydrated tungsten oxide nanostructured films will occur when positive pressures are applied. The transmittance of the films varies significantly in the 400-900 nm band, reaching 40.8% and 57.6% at the wavelength of lambda=632 nm, and has a high discoloration rate and dyeing efficiency because its unique nanostructure not only shortens the diffusion path of ions in the films, but also makes full use of its active surface, thus effectively improving the dyeing efficiency of the films.

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