Preparation method and application of manganese dioxide / polypyrrole composite electrochromic film

Abstract

The present invention discloses a preparation method and application of a manganese dioxide / polypyrrole composite electrochromic film, belonging to the field of electrochromic technology. The method comprises the following steps: electrodepositing a manganese dioxide film on a conductive substrate, and then immersing the conductive substrate with the manganese dioxide film coated on the surface in a mixed solution of pyrrole and a strong acid to obtain a manganese dioxide / polypyrrole composite electrochromic film. The present invention adopts a two-step method to first electrodeposit a manganese dioxide film on a conductive substrate, and then directly chemically oxidize pyrrole using the manganese dioxide film through immersion treatment to obtain polypyrrole. The operation is simple and the raw materials are easily available. The manganese dioxide / polypyrrole composite film prepared by the method of the present invention has a "coral"-like structural feature, exhibits good electrochromic performance and energy storage characteristics, and has good application prospects in building energy saving, smart windows, electrochromic electronic paper, anti-glare rearview mirrors, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochromism, and in particular to a preparation method and application of a manganese dioxide / polypyrrole composite electrochromic film. Background Art

[0002] The current climate crisis and rapidly growing population have led to energy shortages and environmental pollution, sparking a surge in the development of new energy and energy-saving technologies. Electrochromic materials, due to their environmentally friendly and low energy consumption characteristics, have attracted considerable research attention. Electrochromism refers to the reversible color change caused by an electric field, thereby managing light and heat within a space. Its optical properties are reflected in its color and transmittance. Electrochromic materials are energy-efficient due to their unique bistability. After a certain amount of power is applied, the power supply can be disconnected, and the voltage required for color change is extremely low. Depending on the internal characteristics and combinations of different electrochromic materials, electrochromic films can achieve significant transmittance and reflectance adjustments across the visible and solar spectra, and even in the microwave range. Electrochromic films also offer a range of advantages, including continuously adjustable optical properties, multi-color display, low operating voltage, low energy consumption, zero radiation, wide viewing angle, and open-circuit memory. Therefore, the electrochromic effect holds broad application prospects in building energy conservation, optoelectronic displays, smart windows, infrared control, displays, energy storage batteries, and capacitors.

[0003] Compared to other electrochromic materials, polypyrrole offers advantages such as excellent air stability, high conductivity, environmental stability, and reversible redox properties. Among various organic electrochromic materials, current research on the electrochromism of polypyrrole thin films is still inadequate. Key issues requiring further research include developing simpler, safer, and more environmentally friendly methods for preparing electrochromic polypyrrole thin films, and improving their electrochromic properties by manipulating their structure, including preparing composite films. At present, the main problems in the preparation and performance of polypyrrole electrochromic films are as follows: (1) Complex preparation process: polypyrrole powder prepared by chemical oxidation polymerization is difficult to dissolve and melt, and is not easy to form a film by other methods such as spin coating, and is not conducive to the subsequent assembly of electrochromic devices; (2) The light modulation amplitude and coloring efficiency are not ideal: the common electrochemical preparation method of polypyrrole film in the literature is the constant voltage method. The color change of the film polymerized by this method is single, and the coloring efficiency is not large enough, resulting in unsatisfactory color change performance of the electrochromic device; (3) Slow response time: the coloring and fading switching time of polypyrrole electrochromic films commonly found in the literature is slow, which affects the electrochromic performance. How to solve the above problems is the key to research at this stage. Summary of the Invention

[0004] The present invention aims to provide a method for preparing a manganese dioxide / polypyrrole composite electrochromic film and its application to address the aforementioned problems of the prior art. The present invention employs a two-step process to first electrodeposit a densely packed grid-like manganese dioxide film on a fluorine-doped tin oxide (FTO) transparent conductive glass substrate. Pyrrole is then directly chemically oxidized from the manganese dioxide film via an immersion treatment to obtain polypyrrole. This method is simple to operate and utilizes readily available raw materials. The manganese dioxide / polypyrrole composite film produced by this method exhibits a "coral-like" structure and exhibits excellent electrochromic and energy storage properties.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention: A method for preparing a manganese dioxide / polypyrrole composite electrochromic film, comprising the following steps: electrodepositing a manganese dioxide film on a conductive substrate; then immersing the conductive substrate with the manganese dioxide film coated on its surface in a mixed solution of pyrrole and a strong acid to obtain the manganese dioxide / polypyrrole composite electrochromic film.

[0007] Manganese dioxide is a strong oxidant in an acidic medium, capable of oxidizing pyrrole to polypyrrole, directly forming a manganese dioxide / polypyrrole composite film. During the immersion process, the electrodeposited manganese dioxide film undergoes a chemical redox reaction with pyrrole, directly oxidizing the pyrrole monomer to polypyrrole.

[0008] Furthermore, the manganese dioxide film obtained by electrodeposition has a dense grid-like structure. During the immersion treatment, as the redox reaction between the manganese dioxide film and pyrrole proceeds, the manganese dioxide changes from a dense grid to a loose grid similar to a coral colony.

[0009] Furthermore, the electrodeposition of the manganese dioxide film on the conductive substrate includes: using the conductive substrate as a working electrode, precursor solution A as an electroplating solution, and electrodepositing the manganese dioxide film; the precursor solution A includes a soluble manganese salt, sodium sulfate, and a solvent.

[0010] Furthermore, the solvent is deionized water.

[0011] Furthermore, the conductive substrate is fluorine-doped tin oxide (FTO) conductive glass; and the soluble manganese salt is manganese acetate, manganese sulfate or manganese chloride.

[0012] Furthermore, the electrodeposition adopts a three-electrode system, wherein the working electrode is FTO conductive glass, the reference electrode is a saturated calomel electrode, and the counter electrode is a platinum sheet.

[0013] Furthermore, the precursor solution A is prepared by dissolving soluble manganese salt and sodium sulfate in deionized water, and stirring the mixture magnetically to obtain the precursor solution A.

[0014] Furthermore, the molar concentration of the soluble manganese salt in the precursor solution A is 0.005 to 0.045 mol·L -1 The molar ratio of the soluble manganese salt to the sodium sulfate is 0.9:1 to 1:0.9.

[0015] Furthermore, the voltage of the electrodeposition is 0.6-0.7V, and the deposition time is 100-900s.

[0016] Furthermore, the conductive substrate is pretreated before electrodeposition, including: cutting the FTO conductive glass and washing it with clean water, then placing it in acetone, anhydrous ethanol and deionized water for ultrasonic cleaning for 10 to 30 minutes each, and then drying it in an oven for 4 hours. After drying, it is irradiated with ultraviolet (UV) for 3 to 5 minutes.

[0017] Furthermore, the strong acid is p-toluenesulfonic acid.

[0018] Furthermore, the molar concentration of pyrrole in the mixed solution of pyrrole and strong acid is 0.05 to 0.2 mol·L -1 The molar concentration of strong acid is 0.05~0.15mol·L -1 .

[0019] Furthermore, the solvent of the mixed solution of pyrrole and strong acid is any one of ethylene glycol, ethanol, and deionized water, or a mixture of any two or more thereof. The mixed solution of pyrrole and strong acid is recorded as precursor solution B.

[0020] Furthermore, the precursor solution B is prepared by dissolving a strong acid and pyrrole in a solvent, and uniformly stirring the mixture under magnetic stirring at a low temperature (3 to 15° C.) to obtain the precursor solution B.

[0021] Furthermore, the immersion treatment time is 5 to 30 seconds.

[0022] The second technical solution of the present invention: a manganese dioxide / polypyrrole composite electrochromic film prepared according to the above preparation method, wherein the surface morphology of the manganese dioxide / polypyrrole composite electrochromic film presents a "coral"-like structural feature.

[0023] Furthermore, the morphology of the "coral"-like structure is: polypyrrole nano-spherical particles (size <100nm) are attached to the surface of a loose coral-like grid-like manganese dioxide film, forming a composite film with a "coral"-like structure.

[0024] As an important transition metal oxide, manganese dioxide has good electrochemical properties and is also an anode electrochromic material. 4+It has optical absorption in the visible light range and appears brown, while it is reduced to Mn 3+ Therefore, by combining manganese dioxide with polypyrrole to obtain a coral-like structure, a composite film with good electrochromic properties can be obtained, while also improving the electrochromic properties of single polypyrrole and manganese dioxide.

[0025] The third technical solution of the present invention: an application of the above-mentioned manganese dioxide / polypyrrole composite electrochromic film in building energy saving, smart windows, electrochromic electronic paper or anti-glare rearview mirror.

[0026] The present invention discloses the following technical effects:

[0027] (1) The present invention adopts a two-step method to prepare a manganese dioxide / polypyrrole composite electrochromic film. First, a manganese dioxide film is electrodeposited on a conductive substrate, and then the manganese dioxide film is used to directly oxidize pyrrole into polypyrrole through an immersion treatment. The process is simple, the raw materials are easily available, the preparation conditions are relatively low, and it is green and environmentally friendly.

[0028] (2) In the prior art, most polypyrroles prepared by chemical redox methods are in powder form. Polypyrrole powder is difficult to dissolve and melt, and is difficult to form into a film by spin coating or other methods. However, the preparation method of the manganese dioxide / polypyrrole composite electrochromic film provided by the present invention utilizes manganese dioxide film to chemically oxidize pyrrole in an acidic medium. The generated polypyrrole nano-spherical particles are stably attached to the surface of the manganese dioxide film having a loose grid feature similar to a coral colony, thereby obtaining a manganese dioxide / polypyrrole composite film with a "coral"-like structure, which provides a new approach for further developing high-performance organic / inorganic composite electrochromic materials.

[0029] (3) The manganese dioxide / polypyrrole composite electrochromic film prepared by the method of the present invention has a "coral"-like structural feature. This structure increases the specific surface area of ​​the film, widens the interface, shortens the path of ion insertion and extraction, and makes the electrolyte cation intercalation and deintercalation faster, which is beneficial to improving the electrochromic performance of the material. Secondly, the manganese dioxide / polypyrrole composite film and the FTO substrate intersperse each other to form a larger interface area, which enhances the interface interaction between the composite film and the FTO substrate. The interconnectivity of the "coral"-like structure of the composite film may also help prevent the film from peeling off from the substrate, thereby improving the structural stability of the composite film. In a cheap and easily available KCl electrolyte solution, the electrochromic performance test of the manganese dioxide / polypyrrole composite electrochromic film prepared by the present invention was carried out. The results showed that the light modulation amplitude of the composite film can reach 67%, the coloring time is 2 to 6 seconds, and the fading time is 2 to 6 seconds. Its color can change from black at the time of coloring to dark blue, purple and light yellow, and the coloring efficiency can reach 218.16 cm 2 ·C -1, and 200 electrochemical cyclic voltammetry tests verified the stability of the composite film. This composite film overcomes the shortcomings of single manganese dioxide or polypyrrole materials in the electrochromic process, such as long response time, single color change, and poor cyclic stability.

[0030] (4) The manganese dioxide / polypyrrole composite electrochromic film prepared by the present invention has certain energy storage characteristics, and the electrochromic electrode can reversibly switch between different color states to achieve dynamic monitoring of the energy storage state. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 Phase characterization diagrams of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1; wherein, (a) is the X-ray diffraction (XRD) pattern of the composite film, (b) is the Fourier transform infrared spectrum of the composite film, (c) is the full X-ray photoelectron spectroscopy (XPS) spectrum of the composite film, and (d) is the high-resolution XPS spectrum of Mn 3s of the composite film;

[0033] Figure 2 Scanning electron microscope (SEM) images of the single polypyrrole film prepared in Comparative Example 1 and the single manganese dioxide film obtained after electrodeposition in step (2) of Example 1, wherein (a) is an SEM image of the single polypyrrole film, and (b) is an SEM image of the single manganese dioxide film;

[0034] Figure 3 These are SEM photographs of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1, wherein (a) is a surface SEM photograph of the composite film; (b) is a cross-sectional SEM photograph of the composite film;

[0035] Figure 4 These are scanning electron microscope images of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 2, wherein (a) is a surface SEM image of the composite film; (b) is a cross-sectional SEM image of the composite film;

[0036] Figure 5 These are scanning electron microscope images of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 3, wherein (a) is a surface SEM image of the composite film; (b) is a cross-sectional SEM image of the composite film;

[0037] Figure 6Surface SEM photos of the manganese dioxide / polypyrrole composite electrochromic films prepared in Examples 4 and 5, wherein (a) is Example 4 and (b) is Example 5;

[0038] Figure 7 Surface SEM photographs of the manganese dioxide / polypyrrole composite electrochromic films prepared in Examples 6 and 7, wherein (a) is Example 6 and (b) is Example 7;

[0039] Figure 8 Graph showing transmittance of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1 in the colored and faded states;

[0040] Figure 9 Response time curve of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1;

[0041] Figure 10 Graph showing the coloring efficiency of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1;

[0042] Figure 11 Macroscopic digital images of the electrochromic effect of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1 at different voltages;

[0043] Figure 12 200 cyclic voltammetry curves of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1;

[0044] Figure 13 1 is the constant current charge / discharge (GCD) curve of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1 at different current densities. DETAILED DESCRIPTION

[0045] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0046] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0047] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0048] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the present invention. The present description and examples are intended to be illustrative only.

[0049] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0050] Example 1

[0051] (1) Pretreatment of FTO conductive glass substrate: FTO conductive glass was cut into 50 mm × 25 mm rectangular pieces, and then placed in acetone, ethanol and deionized water in turn, ultrasonically cleaned for 30 min each, and then placed in an oven to dry. After drying, ultraviolet irradiation was performed for 5 min before use.

[0052] (2) Preparation of manganese dioxide film: 0.44 g (0.0025 mol) of manganese acetate and 0.35 g (0.0025 mol) of sodium sulfate were weighed and dissolved in 100 mL of deionized water, and stirred magnetically to obtain 0.025 mol·L -1 Manganese acetate and 0.025 mol·L -1 A mixed solution of sodium sulfate, designated as precursor solution A, was transferred to an electrolytic cell. Using a three-electrode system, a pretreated FTO conductive glass substrate was connected with a wire, with the conductive surface facing the platinum electrode (counter electrode). The substrate was vertically inserted into the precursor solution A, parallel to the saturated calomel electrode (reference electrode), with the FTO conductive glass substrate protruding 10 mm above the liquid surface. The electrochemical workstation was turned on and a constant voltage of 0.6 V was applied for 400 seconds. After the reaction was complete, the FTO conductive glass substrate was removed and rinsed sequentially with ethanol and deionized water. The substrate was then dried in a vacuum drying oven at 60°C for 1 hour. After drying, the substrate was cooled to room temperature in the oven. A manganese dioxide electrochromic film was formed on the surface of the FTO conductive glass substrate, resulting in FTO conductive glass coated with a manganese dioxide film.

[0053] (3) Preparation of manganese dioxide / polypyrrole composite electrochromic film: Weigh 1.72 g of p-toluenesulfonic acid and 670 μL of pyrrole and dissolve them in 100 mL of deionized water. Stir magnetically at 10 °C to obtain 0.1 mol·L -1 p-Toluenesulfonic acid and 0.1 mol·L -1 A mixed solution of pyrrole is recorded as precursor solution B; the FTO conductive glass coated with manganese dioxide obtained in step (2) is placed in the precursor solution B and immersed for 10 seconds, then the FTO conductive glass is taken out, washed with water and ethanol in sequence, and dried at room temperature to generate polypyrrole (PPy) in the form of spherical particles on the surface of the manganese dioxide film to obtain a manganese dioxide / polypyrrole composite electrochromic film.

[0054] Comparative Example 1

[0055] Preparation method of a single polypyrrole film: Weigh 1.72g of p-toluenesulfonic acid, measure 670μL of pyrrole and 100mL of deionized water, dissolve the pyrrole and p-toluenesulfonic acid in deionized water in turn to obtain the precursor solution required for electrodeposition of the polypyrrole film. Use a pretreated FTO conductive glass substrate (pretreatment process is the same as in Example 1) as the working electrode, a platinum sheet and a saturated calomel electrode as the counter electrode and reference electrode, respectively. Immerse these three in the above-mentioned precursor solution, turn on the electrochemical workstation, use the constant voltage method, set the voltage to 0.7V, and the time to 150s to electrodeposit the polypyrrole film.

[0056] Figure 1 The following are phase characterization diagrams of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1, wherein (a) is the XRD pattern of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1. In addition to the diffraction peak of FTO conductive glass (SnO2, JCPDS No.77-0447), the diffraction peaks at 2θ=27.4°, 38.7°, 52.4° and 62.1° belong to the orthorhombic γ-MnO2 phase (JCPDS No.43-1455), indicating that the MnO2 film was successfully coated on the FTO glass. (b) is the infrared spectrum of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1. It can be seen from the figure that the characteristic peak of PPy is at a wave number of 1627cm -1 、1450cm -1 、1064cm -1 The band peaks at 3432cm are related to the C=C, CC and CN stretching vibration absorption peaks on the pyrrole ring. -1 The absorption peak at 607cm is the OH stretching vibration peak. -1The absorption peaks at characterize the presence of manganese dioxide. The positions of these peaks prove that the manganese dioxide / polypyrrole composite film was successfully prepared on the FTO conductive glass substrate. (c) is the full XPS spectrum of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1, showing the electronic structure of the film, such as C1s, O 1s, N 1s, S2p, Mn 2p, and Mn 3s. (d) is the high-resolution XPS spectrum of Mn 3s of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1. Due to the coupling of non-ionized 3s electrons with 3d valence band electrons, the peak shows two split components. The size of the peak splitting can be used to diagnose the oxidation state of manganese; the two peaks are located at 88.7 and 84 eV, respectively. The calculated binding energy shift ΔE = 4.7 eV further confirms that manganese dioxide is still present after the composite.

[0057] Figure 2 The following are scanning electron microscope (SEM) photos of the single polypyrrole film prepared in Comparative Example 1 and the single manganese dioxide film obtained after electrodeposition in step (2) of Example 1. Among them, (a) is a scanning electron microscope photo of the single polypyrrole film prepared in Comparative Example 1, and it can be seen that the polypyrrole film is composed of spherical particles with a size of submicron level; (b) is a scanning electron microscope photo of the manganese dioxide film obtained after electrodeposition in step (2) of Example 1, and it can be seen that the manganese dioxide film has a dense network structure.

[0058] Figure 3 Figures 2 and 3 are SEM photographs of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1, wherein (a) is a surface SEM photograph of the composite film. It can be seen that after the immersion treatment, the dense network structure of manganese dioxide on the surface of the FTO conductive glass is reduced by pyrrole, and its structure becomes loose, forming a grid-like shape similar to a coral colony, while pyrrole is oxidized into polypyrrole in the form of nano-spheres attached to the coral-like grid of the manganese dioxide film. The composite film forms a "coral"-like structure with good uniformity; (b) is a cross-sectional SEM photograph of the composite film, from which it can be seen that the thickness of the composite film prepared in Example 1 is about 216 nm.

[0059] Example 2

[0060] Same as Example 1, except that the molar concentrations of manganese acetate and sodium sulfate in precursor solution A are both 0.015 mol·L -1 .

[0061] Figure 4These are scanning electron microscope images of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 2. (a) is a surface SEM image of the composite film. It can be seen that after the immersion treatment, the dense network of manganese dioxide on the FTO conductive glass surface becomes loose, forming a coral-like grid. Pyrrole is oxidized into polypyrrole nanospheres that adhere to the manganese dioxide film grid, forming a coral-like structure with good uniformity. (b) is a cross-sectional SEM image of the composite film, showing that the composite film prepared in Example 2 is approximately 165 nm thick.

[0062] Example 3

[0063] Same as Example 1, except that the molar concentrations of manganese acetate and sodium sulfate in precursor solution A are both 0.035 mol·L -1 .

[0064] Figure 5 These are scanning electron microscope images of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 3. (a) is a surface SEM image of the composite film. It can be seen that after the immersion treatment, the dense network structure on the FTO conductive glass surface becomes loose, forming a coral-like grid. Pyrrole is oxidized into polypyrrole nanospheres that adhere to the manganese dioxide film grid, forming a coral-like structure with good uniformity. (b) is a cross-sectional SEM image of the composite film, showing that the composite film prepared in Example 3 is approximately 302 nm thick.

[0065] Example 4

[0066] Same as Example 1, except that the molar concentration of pyrrole in precursor solution B is 0.05 mol·L -1 The surface SEM photo of the manganese dioxide / polypyrrole composite electrochromic film prepared in this example is as follows: Figure 6 As shown in (a), the composite film has a "coral"-like structure.

[0067] Example 5

[0068] Same as Example 1, except that the molar concentration of pyrrole in precursor solution B is 0.2 mol·L -1 The surface SEM photo of the manganese dioxide / polypyrrole composite electrochromic film prepared in this example is as follows: Figure 6 As shown in (b), the composite film has a "coral"-like structure.

[0069] Example 6

[0070] Same as Example 1, except that the molar concentrations of manganese acetate and sodium sulfate in the precursor solution A in step (2) are both 0.005 mol·L -1, the electrodeposition voltage is 0.6 V, and the deposition time is 100 s; the molar concentration of pyrrole in the precursor solution B in step (3) is 0.05 mol·L -1 , the concentration of p-toluenesulfonic acid is 0.05 mol·L -1 The surface SEM photos of the manganese dioxide / polypyrrole composite electrochromic film prepared in this embodiment are shown in FIG. Figure 7 As shown in (a), the composite film has a "coral"-like structure.

[0071] Example 7

[0072] Same as Example 1, except that the molar concentrations of manganese acetate and sodium sulfate in the precursor solution A in step (2) are both 0.045 mol·L -1 , the electrodeposition voltage is 0.7 V, and the deposition time is 900 s; the molar concentration of pyrrole in the precursor solution B in step (3) is 0.2 mol·L -1 , the concentration of p-toluenesulfonic acid is 0.15 mol·L -1 The surface SEM photos of the manganese dioxide / polypyrrole composite electrochromic film prepared in this embodiment are shown in FIG. Figure 7 As shown in (b), the composite film has a "coral"-like structure.

[0073] Effect verification

[0074] 1. Characterization of electrochromic properties of composite films

[0075] A three-electrode system was used, in which the prepared manganese dioxide / polypyrrole composite film (actually FTO conductive glass with manganese dioxide / polypyrrole composite film attached to the surface) was used as the working electrode, platinum sheet was used as the counter electrode, and saturated calomel electrode was used as the reference electrode. -1 Using KCl as the electrolyte solution, the electrochromic properties of the composite film were characterized, including light modulation amplitude, response time, and coloring efficiency. The light modulation amplitude is defined as the difference in transmittance between the faded state and the colored state of the electrochromic film or device. The larger the light modulation amplitude, the more obvious the color change of the film or device. The response time is the time taken for the electrochromic process, and is generally defined as the time interval corresponding to when the transmittance difference between the colored state and the faded state reaches 90%. Among them, the response time of the electrochromic film or device from the colored state to the faded state is called the fading response time, and the response time from the faded state to the colored state is called the coloring response time. The coloring efficiency is the change in optical density caused by the charge consumed per unit area.

[0076] Figure 8 This is the transmittance curve of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1, from which it can be calculated that the maximum light modulation amplitude value of the composite film is 67%. Figure 9 This is the response time curve of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1, from which it can be calculated that the coloring response time of the composite film is 4s and the fading response time is 3s. Figure 10 The coloring efficiency diagram of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1 is shown. From it, the coloring efficiency of the composite film can be calculated to be 218.16 cm 2 ·C -1 .

[0077] Figure 11 The following are macroscopic digital images of the electrochromic effect of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1 at different voltages. It can be seen that the composite film initially appears light gray (0V) and changes to different colors when voltage is applied. The film colors when a positive voltage is applied, and changes to dark blue (0.2V) and black (0.5V) when the voltage increases from 0V to 0.5V. The film fades when a negative voltage is applied, and changes to maroon (-0.2V), dark yellow (-0.5V), and light yellow (-1V) when the voltage decreases from 0V to -1V.

[0078] The cyclic stability of the film was tested by cyclic voltammetry using an electrochemical workstation. Figure 12 This is a 200-cycle voltammetry curve of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1. It can be seen that after 200 cycles of coloring and fading, the capacitance does not decrease significantly, indicating that the prepared composite film has high cycle stability.

[0079] The electrochromic properties of Examples 1-7 are shown in Table 1:

[0080] Table 1

[0081]

[0082] 2. Energy storage performance of composite films

[0083] Figure 13 The following are the galvanostatic charge / discharge (GCD) curves of the manganese dioxide / polypyrrole composite electrochromic film prepared in Example 1 at different current densities. As can be seen, all curves are symmetrical isosceles triangles, indicating that the composite film has excellent capacitance and electrochemical reversibility. This indicates that in addition to its excellent electrochromic properties, the composite film also has good energy storage characteristics.

[0084] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a manganese dioxide / polypyrrole composite electrochromic film, characterized in that: The following steps are involved: A manganese dioxide film is electrodeposited on a conductive substrate; the conductive substrate with the manganese dioxide film is then immersed in a mixed solution of pyrrole and a strong acid to obtain a manganese dioxide / polypyrrole composite electrochromic film; The strong acid is p-toluenesulfonic acid; The molar concentration of pyrrole in the mixed solution of pyrrole and strong acid is 0.05-0.2 mol·L -1 The molar concentration of strong acid is 0.05~0.15mol·L -1 ; The immersion time is 5 to 30 seconds; The surface morphology of the manganese dioxide / polypyrrole composite electrochromic film has a "coral-like" structural feature; The morphology of the "coral"-like structure is that polypyrrole nano-spherical particles are attached to the surface of a loose, coral-like grid-like manganese dioxide film, forming a composite film with a "coral"-like structure.

2. The method for preparing the manganese dioxide / polypyrrole composite electrochromic film according to claim 1, wherein: The method of electrodepositing a manganese dioxide film on a conductive substrate comprises: using the conductive substrate as a working electrode, using precursor solution A as an electroplating solution, and electrodepositing the manganese dioxide film; the precursor solution A comprises a soluble manganese salt, sodium sulfate, and a solvent.

3. The method for preparing the manganese dioxide / polypyrrole composite electrochromic film according to claim 2, wherein: The conductive substrate is fluorine-doped tin oxide conductive glass; the soluble manganese salt is manganese acetate, manganese sulfate or manganese chloride.

4. The method for preparing the manganese dioxide / polypyrrole composite electrochromic film according to claim 2, wherein: The molar concentration of the soluble manganese salt in the precursor solution A is 0.005-0.045 mol·L -1 The molar ratio of the soluble manganese salt to the sodium sulfate is 0.9:1 to 1:0.

9.

5. The method for preparing the manganese dioxide / polypyrrole composite electrochromic film according to claim 2, wherein: The voltage of the electrodeposition is 0.6-0.7V, and the deposition time is 100-900s.

6. A manganese dioxide / polypyrrole composite electrochromic film prepared according to the preparation method according to any one of claims 1 to 5.

7. Use of the manganese dioxide / polypyrrole composite electrochromic film as claimed in claim 6 in building energy conservation, smart windows, electrochromic electronic paper or anti-glare rearview mirror.

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