Color Adjustment And Electrochromic Properties Of Composite Film Based On Polyoxometalate

In recent years,the environmental pollution and energy consumption are becoming more and more serious,and people’s demand for environmental protection and energy-saving materials is gradually increasing.Electrochromic material is a green and energy-saving material with reversible changes in optical properties,such as transmittance and color.As an inorganic electrochromic material,polyoxometalates have good redox property,transfer and store electrons or protons,and obtain electrons without changing the structure.Combining polyoxometalate with other materials can improve the electrochromic properties of the material,such as light contrast,response time,coloring efficiency and stability.But,coloration states of polyoxometalate electrochromic materials are relatively monotonous.In this paper,three kinds of polyoxometalate/dye composite films have been prepared by the layer-by-layer self-assembly method,and characterized by ultraviolet-visible-absorption spectroscopy（UV-vis）,infrared spectroscopy（FTIR）,scanning electron microscopy（SEM）,atomic force microscopy（AFM）,X-ray photoelectron spectrometer（XPS）,and cyclic voltammetry（CV）.The electrochromic properties have been studied by electrochemical workstation and UV-vis spectroscopy.The films have been enriched the color of materials based on polyoxometalate and improved their electrochromic properties.The main research contents are as follows:1.A composite film based on vanadium-substituted polyoxometalate anion[P₂W₁₅V₃O₆₂]^9-(P₂W₁₅V₃)and dye Congo red（MR）has been prepared by the layer-by-layer self-assembly method.At 600 nm,the optical contrast is 22.55%,the response time is 2.02/12.67 s,and the coloring efficiency is 122.67 cm²·C^-1.After 200 cycles,the optical contrast retention rate is 91.18%,the composite film has good stability and reversibility.It has reversible adjustment of color from light red to blue-purple,and the assembled device also has the same color adjustment ability.The composite film enriches the color modulation of materials and maintains the electrochromic properties of polyoxometalate.2.A composite film based on polyoxometalate anion[P₂W₁₈O₆₂]^6-(P₂W₁₈)and dye Alizarin red（AR）obtains different initial colors by adjusting the p H of the dye Alizarin red solution,and improves the electrochromic properties though changing the test conditions.The composite film（the p H of solution is 2.00）has a faster response time（2.37/5.57 s）at smaller voltages and a better optical contrast at larger voltages（39.71%）,while the adjustment of color can from yellow,green to blue-green.The composite film（the p H of solution is 6.00）has better performance at larger voltages,of which the optical contrast retention rate after 1000 cycles is 82.09%,and the color can be adjusted from light purple,blue-purple to dark purple.The material provides a new strategy for the preparation of multi-color materials.3.A bifunctional composite film based on the Preyssler type polyoxometalate anion[P₅W₃₀O₁₁₀]^15-(P₅W₃₀)and dye Methyl red（MR）by polycation connection has been prepared.The composite film has electrochromic properties and energy storage performance.The fiber structure dominated of the dye Methyl red makes the structure of the material more three-dimensional,which is more conducive to the transmission of electrons,and improves the electrochromic performance and energy storage performance.Compared with the simple polyoxometalate film,the optical contrast of the composite film is increased by 31.58%,and the specific capacitance is increased by 86.39%at the current density of 0.20 m A/cm².The color of the composite film can be adjusted from red to blue-purple.The device based on the composite film also has the same color adjustment,and can light a diode.This work provides a reference for the development of multi-color materials based on polyoxometalate in the field of electrochromic and energy storage.