Electrochromic device based on salt-free polyacrylic acid gel and preparation method thereof

Abstract

The present invention relates to the field of material technology, and in particular to an electrochromic device based on a salt-free polyacrylic acid gel and a preparation method thereof. The present invention comprises the following steps: firstly, a crosslinking agent N,N-methylenebisacrylamide and an initiator ammonium persulfate are mixed and dissolved with deionized water, and after uniform dissolution by magnetic stirring, an acrylic acid monomer is added to obtain a precursor solution; then, the precursor solution is injected into the cavity of a Prussian blue / tungsten oxide electrochromic device, and a polymerization reaction is carried out at a set temperature; after completion of the reaction, the device is naturally cooled to room temperature to obtain a Prussian blue / tungsten oxide electrochromic device containing an in-situ polymerized salt-free polyacrylic acid gel electrolyte; the gel electrolyte prepared by the present invention has a pore size of 20 to 80 μm, good ionic conductivity, and high transmittance, and can be applied to electrochromic devices and related fields.

Description

Technical Field

[0001] The present invention relates to the field of material technology, and in particular to an electrochromic device based on salt-free polyacrylic acid gel and a preparation method thereof. Background Art

[0002] With energy conservation and environmental protection becoming increasingly important, electrochromic smart windows, which can dynamically adjust optical properties to regulate the flow of light and heat between buildings and the environment, are a crucial research area. Electrolytes are a key component of electrochromic smart windows. Functionally, the electrolyte layer provides and transports ions. Structurally, it prevents direct electrical contact between electrodes. Performance-wise, the electrolyte primarily determines the conductivity, resistivity, and voltage window of electrochromic smart windows. Current research on electrolytes focuses on liquid, solid, and gel electrolytes. Liquid electrolytes offer high conductivity but also have a narrow voltage window and the risk of leakage. Even with the use of organic solvents to increase the electrolyte's voltage window, challenges such as high resistivity, low specific capacitance, toxicity, and flammability persist. Solid electrolytes address the leakage, toxicity, and flammability issues of liquid electrolytes, but they also come with reduced conductivity, increased cost, and interfacial contact issues. Polymer gel electrolytes combine the advantages of easy processing and packaging of solid electrolytes with the high ionic conductivity of liquid electrolytes. In addition, they also have the advantages of light weight and good viscoelasticity. They provide a strong guarantee for the development of electrochromic devices towards lightness, thinness, flexibility, wearability and large area, and have become a class of electrolyte materials with the greatest application potential. The electrochromic process is accompanied by the insertion and extraction of electrons and ions, so the transport dynamics of electrolyte ions plays an extremely critical role in the electrochromic performance. Electrochromic devices have evolved from the initial limited electrolyte ion drive (H + 、Li + ) to various electrolyte ion drives (H + 、Li + 、Na + , K + Mg 2+ , Ca 2+ 、Zn 2+ 、Al 3+ For example, Li et al. synthesized a polyacrylic acid hydrogel using a chemical crosslinker of hydroxypropyl methylcellulose and an ionic crosslinker of CaCl2 and immersed it in 2 mol·L -1Li2SO4 solution was used in a single-layer tungsten oxide electrochromic device (A Self-Healing Polyacrylic Acid-Based Hydrogel Electrolyte for Flexible Quasi-Solid-State Electrochromic Device, Solar Energy Materials and Solar Cells, 2023, 250). Lv et al. added LiClO4 electrolyte to a mixed solvent containing polyvinyl alcohol and polyacrylic acid for use in a thiophene polymer / poly(3,4-ethylenedioxythiophene) electrochromic device (An electrochromic device based on polyvinyl alcohol-polyacrylic acid hydrogel electrolyte and its preparation method and application, CN202110018875.4). These methods increase ionic conductivity by adding different inorganic salts to the polymer matrix, which not only increases the manufacturing cost of the electrolyte but also reduces the transmittance of the electrolyte itself. Adding inorganic salts to the solution affects the concentration of the solution, and changes in the solution concentration directly affect the transmittance; when the solubility is low, crystals will appear in the solution, which will block light and also reduce the transmittance. Summary of the Invention

[0003] In order to overcome the deficiencies of the prior art, the present invention provides an electrochromic device based on a salt-free polyacrylic acid gel electrolyte, electrodeposited Prussian blue, and electrodeposited tungsten oxide, and a preparation method thereof.

[0004] The first aspect of the present invention discloses an electrochromic device, comprising a salt-free polyacrylic acid gel electrolyte and an electrochromic material.

[0005] Preferably, the electrochromic material is electrodeposited Prussian blue and / or electrodeposited tungsten oxide.

[0006] The second aspect of the present invention discloses a method for preparing the electrochromic device, comprising the following steps:

[0007] S1: Mix and dissolve N,N-methylenebisacrylamide, ammonium persulfate, acrylic acid and deionized water to obtain a reaction precursor solution;

[0008] S2: Electrodeposition of Prussian blue film: In a three-electrode system, potassium ferrocyanide, ferric chloride, and potassium chloride with set concentrations were used as the electrolyte, FTO glass was used as the working electrode, platinum sheet was used as the counter electrode, and Ag / AgCl electrode was used as the reference electrode. Prussian blue film was prepared by constant current electrodeposition to obtain FTO glass with Prussian blue film;

[0009] S3: Electrodeposition of tungsten oxide thin film: In a three-electrode system, sodium tungstate dihydrate, nitric acid, and hydrogen peroxide with set concentrations are used as the electrolyte, transparent conductive substrate FTO glass is used as the working electrode, platinum sheet is used as the counter electrode, and Ag / AgCl electrode is used as the reference electrode. FTO glass with tungsten oxide thin film is prepared by constant voltage electrodeposition;

[0010] S4: The FTO glass with the Prussian blue film prepared in S2 and the FTO glass with the tungsten oxide film prepared in S3 were bonded together using 1 mm thick double-sided tape to obtain a Prussian blue / tungsten oxide electrochromic device containing a cavity;

[0011] S5: injecting the reaction precursor solution obtained in S1 into the cavity of the Prussian blue / tungsten oxide electrochromic device described in S4, performing a polymerization reaction at a set temperature, and naturally cooling to room temperature after the reaction to obtain a Prussian blue / tungsten oxide electrochromic device containing an in-situ polymerized salt-free polyacrylic acid gel electrolyte.

[0012] Preferably, in the S1 reaction precursor solution, the mass ratio of acrylic acid to deionized water is 1:2-10.

[0013] Preferably, in the S1 reaction precursor solution, the mass ratio of acrylic acid, N,N-methylenebisacrylamide and ammonium persulfate is 400:1-4:2-10.

[0014] More preferably, the deionized water described in S1 is at least Cl - 、SO4 2- 、NO3 - 、NO2 - PO4 3- 、HPO4 2- Mg 2+ , Ca 2+ 、Fe 3+ and Fe 2+ of water.

[0015] Preferably, the concentration ratio of potassium ferrocyanide, ferric chloride and potassium chloride in S2 is 1:1:5.

[0016] More preferably, 10 mmol·L -1 Potassium ferrocyanide, 10 mmol·L -1 Ferric chloride, 50mmol·L -1 Potassium chloride is the electrolyte.

[0017] Preferably, the constant current electrodeposition method in S2 is specifically -40 to -60 μA·cm -2 Electrodeposition was performed at a constant current density for 280 to 320 seconds.

[0018] More preferably, constant current electrodeposition is used at -50 μA cm -2 Electrodeposition was performed at a constant current density for 300 s.

[0019] Preferably, the polymerization reaction temperature in S5 is 60-80° C., and the polymerization reaction time is 1-4 h.

[0020] Preferably, the polyacrylic acid gel obtained in S5 has a pore size of 20 to 80 μm, a microporous surface structure, and good ionic conductivity and high transmittance.

[0021] The third aspect of the present invention discloses the use of the salt-free polyacrylic acid gel electrolyte in electrochromic devices, including color-changing devices used in fields such as smart glass and displays.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention provides an electrochromic device based on salt-free polyacrylic acid gel electrolyte, electrodeposited Prussian blue, and electrodeposited tungsten oxide, and a preparation method thereof, which forms an electrochromic device that is simple to manufacture, low in cost, highly transparent, and has free-moving H + A salt-free polyacrylic acid gel electrolyte with high ionic conductivity. When this gel electrolyte is combined with electrodeposited Prussian blue and electrodeposited tungsten oxide to form an electrochromic device, it produces an electrochromic device with large light modulation amplitude and fast response time. By adjusting experimental parameters, the controllable preparation of polyacrylic acid gel with high ionic conductivity and high transmittance is achieved.

[0024] (2) The preparation method of the present invention controls the polymerization time, the polymerization degree of the gel and the pore size; the prepared polyacrylic acid gel has good ionic conductivity and high transmittance; the prepared polyacrylic acid gel has good stability and high compatibility with the Prussian blue / tungsten oxide electrochromic device; the prepared Prussian blue / tungsten oxide electrochromic device containing the polyacrylic acid gel has a faster response speed; at the same time, the gel preparation process is simple, no inorganic salts need to be added, the raw materials are cheap and easy to obtain, the cost is low, the experimental environment requirements are low, and it is harmless to the human body. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Scanning electron microscope photograph of the salt-free polyacrylic acid gel prepared in Example 1 of the present invention.

[0026] Figure 2 Transmittance curve of the salt-free polyacrylic acid gel prepared in Example 1 of the present invention.

[0027] Figure 3 Fourier transform infrared spectrum of the salt-free polyacrylic acid gel prepared in Example 1 of the present invention.

[0028] Figure 4 Cyclic voltammetry curve of the Prussian blue / tungsten oxide electrochromic device containing salt-free polyacrylic acid gel prepared by Example 1 of the present invention.

[0029] Figure 5 Effect diagrams of the faded state (a) and colored state (b) of the Prussian blue / tungsten oxide electrochromic device containing salt-free polyacrylic acid gel prepared by Example 1 of the present invention.

[0030] Figure 6 Transmittance curve of the Prussian blue / tungsten oxide electrochromic device containing salt-free polyacrylic acid gel prepared by Example 1 of the present invention.

[0031] Figure 7 Response time curve of the Prussian blue / tungsten oxide electrochromic device containing salt-free polyacrylic acid gel prepared by Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0033] Example 1

[0034] (1) In a three-electrode system, 10 mmol·L -1 Potassium ferrocyanide, 10 mmol·L -1 Ferric chloride, 50mmol·L -1 Potassium chloride was used as the electrolyte; FTO glass was used as the working electrode, platinum sheet was used as the counter electrode, and Ag / AgCl electrode was used as the reference electrode. Constant current electrodeposition was used at -50 μA·cm -2 FTO glass with Prussian blue film was obtained by electrodeposition at constant current density for 300s.

[0035] (2) In the three-electrode system, 50 mmol·L -1 Sodium tungstate dihydrate, 0.6 mL of hydrogen peroxide was added to each liter of the solution system, and the pH of the solution was adjusted to 1 with nitric acid as the electrolyte. A transparent conductive substrate FTO glass was used as the working electrode, a platinum sheet was used as the counter electrode, and an Ag / AgCl electrode was used as the reference electrode. The FTO glass with a tungsten oxide film was prepared by constant voltage electrodeposition. The FTO glass with a tungsten oxide film was obtained by constant current electrodeposition at a constant voltage of -0.7 V for 400 s. The Prussian blue / tungsten oxide electrochromic device was obtained by double-sided bonding with the FTO glass with a Prussian blue film obtained in (1).

[0036] (3) Dissolve 0.0125 g of N,N-methylenebisacrylamide and 0.025 g of ammonium persulfate in 10 mL of deionized water.

[0037] (4) Add 2.5 g of acrylic acid to the solution obtained in (3), and then inject it into the cavity of the Prussian blue / tungsten oxide electrochromic device adhered with double-sided tape obtained in (2), place it in an oven at 70°C for polymerization for 2 hours, and naturally cool to room temperature to obtain a Prussian blue / tungsten oxide electrochromic device containing polyacrylic acid gel with the performance to be tested.

[0038] The scanning electron microscope photo of the salt-free polyacrylic acid gel prepared in this example is as follows: Figure 1 As shown, it is a micron pore structure; the free movement of ions is relatively easy, which is suitable for fields such as electrochromic electrolytes. Figure 2 The transmittance curve of the salt-free polyacrylic acid gel prepared in this example is shown in Figure 2. The scanning cyclic voltammetry (CV) curve of the Prussian blue / tungsten oxide electrochromic device containing the salt-free polyacrylic acid gel obtained in this example is shown in Figure 3. Figure 4 As shown, 0.9V was selected as the coloring voltage and -2.4V was selected as the fading voltage. The electrochemical workstation was connected to the UV-visible spectrophotometer and tested in the wavelength range of 400-1100nm. The transmittance was adjusted at a wavelength of 660nm to reach the maximum amplitude. The light response curve formed by the electrochromic device transitioned between 0.9V and -2.4V every 20s. All data were measured at 660nm. Figure 5 These are the fading (a) and coloring (b) changes of the Prussian blue / tungsten oxide electrochromic device containing polyacrylic acid gel prepared in this example. Figure 7 The response time curves are shown in the figure. As can be seen, the device rapidly changes to blue at a voltage of 0.9V, and then switches from blue to colorless when a positive voltage of -2.4V is applied. The maximum change in transmittance between the colored and faded states occurs at 660nm, at approximately 72.7%. Calculations show that the coloring time for the Prussian blue / tungsten oxide electrochromic device containing salt-free polyacrylic acid gel to achieve a 90% change in light modulation amplitude is approximately 2.6 seconds, and the fading time is approximately 2.2 seconds.

[0039] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing an electrochromic device, characterized in that: The following steps are involved: S1: Mix and dissolve N,N-methylenebisacrylamide, ammonium persulfate, acrylic acid and deionized water to obtain a reaction precursor solution; S2: Electrodeposition of Prussian blue film: In a three-electrode system, potassium ferrocyanide, ferric chloride, and potassium chloride with set concentrations were used as the electrolyte, fluorine-doped tin oxide (FTO) transparent conductive glass was used as the working electrode, platinum was used as the counter electrode, and Ag / AgCl electrode was used as the reference electrode. Prussian blue film was prepared by constant current electrodeposition to obtain FTO glass with Prussian blue film; S3: Electrodeposition preparation of hydrated tungsten oxide thin film: In a three-electrode system, sodium tungstate dihydrate, nitric acid, and hydrogen peroxide with set concentrations are used as the electrolyte, transparent conductive substrate FTO glass is used as the working electrode, platinum sheet is used as the counter electrode, and Ag / AgCl electrode is used as the reference electrode. FTO glass with hydrated tungsten oxide thin film is prepared by constant voltage electrodeposition; S4: Laminating the FTO glass with the Prussian blue film prepared in S2 and the FTO glass with the hydrated tungsten oxide film prepared in S3 together to obtain a Prussian blue / hydrated tungsten oxide electrochromic device; S5: injecting the reaction precursor solution obtained in S1 into the cavity of the Prussian blue / hydrated tungsten oxide electrochromic device described in S4, performing a polymerization reaction at a set temperature, and naturally cooling to room temperature after the reaction is completed to obtain a Prussian blue / hydrated tungsten oxide electrochromic device containing an in-situ polymerized salt-free polyacrylic acid gel electrolyte.

2. The preparation method according to claim 1, characterized in that In the S1 reaction precursor solution, the mass ratio of acrylic acid to deionized water is 1:2~10.

3. The preparation method according to claim 1, characterized in that In the S1 reaction precursor solution, the mass ratio of acrylic acid, N,N-methylenebisacrylamide and ammonium persulfate is 400:1-4:2-10.

4. The preparation method according to claim 1, characterized in that The concentration ratio of potassium ferrocyanide, ferric chloride and potassium chloride in S2 is 1:1:5; the Prussian blue film constant current electrodeposition method described in S2 is specifically at -40 to -60 μA·cm -2 Electrodeposition was performed at a constant current density for 280 to 320 s.

5. The preparation method according to claim 1, characterized in that The concentration of sodium tungstate dihydrate in S3 is 50 mmol·L -1 , 0.6 mL of hydrogen peroxide, and adjusting the pH of the solution to 1 with nitric acid. The constant voltage electrodeposition method of the hydrated tungsten oxide thin film described in S3 is specifically electrodeposition at a constant voltage of -0.7 V for 400 s.

6. The preparation method according to claim 1, characterized in that The polymerization reaction temperature in S5 is 60-80° C., and the polymerization reaction time is 1-4 h.

7. The preparation method according to claim 1, characterized in that The polyacrylic acid gel obtained in S5 has a pore size of 20 to 80 μm.

8. An electrochromic device, characterized in that: Prepared by the preparation method according to any one of claims 1 to 7.

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