Method for preparing tungsten oxide electrochromic film with high visible light transmittance at low temperature based on chemical bath method

Abstract

The invention belongs to the technical field of electrochromic films, and discloses a method for preparing a high-visible-light-transmittance tungsten oxide electrochromic film at low temperature based on a chemical bath method.The method comprises the steps that sodium tungstate is dissolved in water to obtain a sodium tungstate solution, the sodium tungstate solution and an oxalic acid solution are added into deionized water, stirring is conducted, and then the high-visible-light-transmittance tungsten oxide electrochromic film is obtained; adding hydrochloric acid to obtain a mixed solution, immersing FTO conductive glass into the mixed solution, and carrying out ultrasonic oscillation; and heating the reaction system at 60 DEG C for reaction, and washing, drying and annealing the FTO conductive glass on which the yellow film grows to obtain the tungsten oxide electrochromic layer. According to the method, the reaction conditions are mild, growth of the precursor film is completed through low temperature and raw material matching cooperation, and the tungsten oxide electrochromic film with high light transmittance and excellent electrochromic performance is finally prepared.

Description

Technical Field

[0001] The invention belongs to the field of electrochromic film preparation, and in particular relates to a tungsten oxide electrochromic film prepared based on a chemical bath method. Background Art

[0002] At present, commercial electrochromic films mainly use tungsten oxide materials, and their preparation methods mostly rely on magnetron sputtering. Although the magnetron sputtering method can effectively control the thickness of the film, its preparation process has high requirements on reaction conditions and requires a high degree of vacuum and cleanliness, so its preparation cost is relatively high.

[0003] Another commonly used method for preparing the electrochromic layer is the hydrothermal / solvothermal method, in which tungsten oxide is grown on the conductive layer through a hydrothermal / solvothermal reaction in a reactor. The reaction conditions of this method are milder than those of magnetron sputtering, but the temperature generally reaches above 100°C. For example, CN202110344207.0 discloses a method for preparing a tungsten oxide / ammonium molybdate composite film for electrochromism, (1) dissolving sodium tungstate in deionized water, adding potassium oxalate, adding hydrochloric acid to adjust the pH and stirring for a period of time to prepare a tungsten oxide precursor reaction solution; (2) placing the FTO glass obliquely with the conductive surface facing downward into a hydrothermal reactor, and after a hydrothermal reaction at a certain temperature for a certain period of time, drying the reacted sample. The FTO glass is transferred to a muffle furnace for treatment to obtain a tungsten oxide film attached to the FTO conductive glass. The temperature and time of the thermal reaction are 120-150°C and 1-2h respectively. The heating temperature is high and the reaction kettle is required. The area of ​​the prepared electrochromic layer is small, and the visible light transmittance of the tungsten oxide film is not studied. CN201510724443.X A method for preparing a WO3 nanosheet array film and its application research, under water bath conditions, peroxytungstic acid is slowly reduced to tungstic acid and slowly precipitated on the FTO film to obtain a tungstic acid film, the water bath conditions are 75-95°C for 120-220 minutes, although the temperature is lower than that of other hydrothermal reactions, the thickness of the prepared WO3 nanosheet is thicker, and the visible light transmittance of the obtained sample is lower.

[0004] In view of the volume limitation of the existing hydrothermal / solvothermal material reactor, the electrochromic layer prepared by this method has a small area. In addition, the hydrothermal reaction has the characteristics of high temperature and high pressure, which is dangerous. In addition, the tungsten oxide film obtained by hydrothermal reaction is thicker, which is not conducive to improving the electrochromic properties such as film color change speed, coloring efficiency and cycle stability, and also affects the visible light transmittance of the tungsten oxide film.

[0005] The technical problem to be solved by the present invention is how to adopt mild reaction conditions, only requiring a low temperature of about 60°C to complete the growth of the precursor film, the entire reaction does not require a high-pressure reactor, does not require high vacuum, high pressure and other reaction conditions, and is conducive to obtaining a thinner tungsten oxide film, which is conducive to improving the optical properties of the film and is conducive to improving the electrochromic properties such as the film's color change speed, coloring efficiency and cycle stability. Summary of the invention

[0006] In order to solve the problems in the background technology, the present invention proposes a method for preparing a tungsten oxide electrochromic film with high visible light transmittance at low temperature based on a chemical bath method. The reaction conditions of this method are mild. The growth of the precursor film can be completed through the coordination of low temperature and raw material ratio. The subsequent calcination can be carried out in a normal atmosphere. The preparation method of the tungsten oxide electrochromic film does not require high vacuum, high pressure and other reaction conditions. The method is suitable for large-area preparation of tungsten oxide electrochromic layers, and can obtain good optical properties and electrochromic properties.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] (1) Sodium tungstate (Na2WO4·2H2O) is dissolved in deionized water to obtain a sodium tungstate solution, wherein the concentration of the sodium tungstate solution is 0.1-3 mol / L; oxalic acid (H2C2O4) is dissolved in deionized water to obtain an oxalic acid solution, wherein the concentration of the oxalic acid solution is 0.3-0.5 mol / L;

[0009] (2) Prepare FTO conductive glass and use acetone, ethanol, and deionized water to ultrasonically clean it to remove surface impurities;

[0010] (3) Sodium tungstate solution and oxalic acid solution are added to deionized water, and then hydrochloric acid (2 mol / L) is added to mix to obtain a mixed solution; wherein the volume ratio of sodium tungstate solution: oxalic acid solution: deionized water: hydrochloric acid is 0.3-0.6: 0.2-0.4: 2.2-2.4: 1.5-2.5, and more preferably 0.5: 0.3: 2.3: 2; wherein the volume ratio mainly controls the relative concentration of oxalic acid, sodium tungstate and hydrochloric acid. The concentration relationship of the three directly affects the film forming rate and thickness.

[0011] (4) immersing the FTO conductive glass after cleaning in step (2) into the mixed solution of step (3) and subjecting it to ultrasonic oscillation; then heating the reaction system to 50-70° C. for 2-4 hours; taking out the FTO conductive glass with the yellow film grown thereon, rinsing it with deionized water to remove excess ions, and wiping off the precipitate deposited on the non-conductive surface;

[0012] Further preferred reaction conditions are: heating reaction at 60° C. for 3 hours. Below 60° C., the reaction will basically not proceed or proceed very slowly, and above 60° C., the reaction rate will accelerate, resulting in decreased uniformity of film formation and decreased visible light transmittance.

[0013] (5) placing the above FTO conductive glass in an oven at 70-90° C. and drying for 10-14 hours; annealing the dried sample and naturally cooling it to room temperature to obtain a tungsten oxide electrochromic layer.

[0014] The annealing treatment is: calcining at 450-550°C for 1.5-3 hours, more preferably calcining at 500°C for 2 hours.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The present invention optimizes the preparation conditions and controls the microscopic morphology, and the film finally formed has a morphology of nanosheets. This morphology can effectively increase the contact area between the electrochromic layer and the conductive layer, increase the ion deintercalation area, and improve the cycle stability of the electrochromic film;

[0017] (2) The chemical bath method of the present invention is that the prepared tungstic acid film is self-generated on the FTO conductive glass, and the two are connected by chemical bonds, which has a strong interface bonding force. The subsequent calcination further increases the interface bonding force. Therefore, the tungsten oxide film prepared by this method has a higher interface bonding force;

[0018] (3) The present invention needs to explore the experimental scheme to achieve a thinner (several hundred nanometers) and more uniform tungsten acid film at a lower temperature. By controlling the reaction conditions, such as reaction temperature, reaction time, and reaction concentration, the prepared film can finally have a high visible light transmittance. The transmittance of the electrochromic material (tungsten oxide / FTO / white glass three-layer structure) in visible light (600nm) can reach more than 66%, while general electrochromic materials mainly focus on the color change of the material, and the overall transmittance is relatively low. The tungsten oxide film prepared by conventional methods has a low transmittance in visible light (600nm). BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the tungsten oxide film preparation process;

[0020] Figure 2 Scanning electron microscope image of tungsten oxide thin film sample of Example 1;

[0021] Figure 3 The images of tungsten acid film and tungsten oxide film samples with good film formation;

[0022] Figure 4The UV-visible transmission spectra of tungstate film (a) and tungsten oxide film (b);

[0023] Figure 5 is a scanning electron micrograph of sample No. 3-11;

[0024] Figure 6 is a scanning electron micrograph of the cross section of sample No. 3-11;

[0025] Figure 7 Sample images of tungsten oxide films after bias coloring for sample No. 3-11;

[0026] Figure 8 In situ UV-visible spectroscopic images of the samples stabilized during bias staining. DETAILED DESCRIPTION

[0027] Example 1

[0028] (1) Prepare reactant solution A: 6.6 g sodium tungstate Na2WO4·2H2O is dissolved in 100 mL deionized water, and the concentration of sodium tungstate solution is 0.2 mol / L;

[0029] (2) Prepare reactant solution B: 3.6 g oxalic acid H2C2O4 dissolved in 100 mL deionized water, the concentration of oxalic acid solution is 0.4 mol / L;

[0030] (3) Prepare FTO conductive glass and use acetone, ethanol, and deionized water to ultrasonically clean it to remove surface impurities;

[0031] (4) adding 0.5 mL of solution A and 0.5 mL of solution B to 2.0 mL of deionized water, and then adding 2.0 mL of 2 mol / L hydrochloric acid to obtain a mixed solution;

[0032] (5) immersing the FTO conductive glass in the above mixed solution, ultrasonically oscillating for 10 min, and then heating the reaction system at 60° C. for 3 hours;

[0033] (6) Obtain FTO conductive glass with a yellow film grown thereon, rinse with deionized water to remove excess ions, and wipe off the precipitate deposited on the non-conductive surface; place in an oven at 80°C and dry for 12 hours; anneal the dried sample: calcined at 500°C for 2 hours, and naturally cooled to room temperature to obtain a tungsten oxide electrochromic layer.

[0034] Example 2

[0035] Compared with Example 1, the preparation method is the same, except that the volumes of sodium tungstate solution: oxalic acid solution: deionized water: hydrochloric acid are different, that is, the mass of the reactants in the mixed solution is different, and the influence on the tungsten oxide electrochromic layer and visible light transmittance is studied.

[0036] Table 1:

[0037]

[0038]

[0039] Figure 4 The UV-visible transmission spectra of (a) tungstic acid film and (b) tungsten oxide film samples 3-11, from which it can be obtained that samples 3 and 4 have higher visible light transmittance.

[0040] Figure 5 (a)-(i) are scanning electron micrographs of samples 3-11, from which it can be seen that as the amount of oxalic acid added increases, the size of the nanosheets constituting the film increases in three dimensions. Specifically, the thickness of the nanosheets increases, and the length of the nanosheets increases.

[0041] Figure 7 The following are sample images of tungsten oxide films after bias coloring. Bias voltages of +1.0V, 0V, -0.2V, -0.4V, -0.6V, -0.8V, and -1.0V were applied to each sample for more than 60 seconds until the film color did not change. As can be seen from the figure, samples 3-7 changed color significantly after coloring. Figure 3 The beige color in the sample was changed to dark blue, the coloring was uniform and the sample stability was good, and there was no obvious peeling before and after coloring. Samples 8-10 also changed color under the bias, but the stability was poor, and the film was damaged and peeled off. Sample 11 had uneven color after coloring.

[0042] Figure 8 The electrochemical workstation was used in conjunction with a UV-visible spectrophotometer to perform in-situ coloration tests on the samples. Samples 3-5 correspond to Figure 8 (a) Figure 8 (b) Figure 8 (c), sample No. 6 is Figure 8 (d) Sample No. 7 is Figure 8 (e) Sample No. 11 is Figure 8 (f) The specific detection method is to use a dual-electrode system, with a platinum mesh as the counter electrode and the prepared sample as the working electrode. The reaction is carried out in a quartz reaction cell, with 1M LiClO4 / PC as the electrolyte, and the reaction cell is placed in the light path of the UV-visible spectrophotometer, with the light path facing the sample to be measured. The sample is biased by +1.0V, -0.2V, -0.4V, -0.6V, -0.8V, and -1.0V through an electrochemical workstation to change the color of the sample, and the UV-visible transmission spectrum of the sample is tested immediately.

[0043] Figure 8As can be seen, samples 3-5 have a large transmittance change between the colored state and the faded state, and the transmittance of the color-changing layer can be effectively modulated by voltage change. The transmittance of samples 6 and 7 is low before and after coloring, and the transmittance of the color-changing layer cannot be effectively modulated. The transmittance of sample 11 is high before and after modulation, and the transmittance of the color-changing layer cannot be effectively modulated.

Claims

1. A method for preparing a tungsten oxide electrochromic film with high visible light transmittance at low temperature based on a chemical bath method, characterized in that: (1) Sodium tungstate is dissolved in deionized water to obtain a sodium tungstate solution, wherein the concentration of the sodium tungstate solution is 0.1-3 mol / L; oxalic acid is dissolved in deionized water to obtain an oxalic acid solution, wherein the concentration of the oxalic acid solution is 0.3-0.5 mol / L; (2) Prepare FTO conductive glass and use acetone, ethanol, and deionized water to ultrasonically clean it to remove surface impurities; (3) adding sodium tungstate solution and oxalic acid solution into deionized water, and then adding hydrochloric acid, and mixing to obtain a mixed solution; wherein the volume ratio of sodium tungstate solution: oxalic acid solution: deionized water: hydrochloric acid is 0.3-0.6: 0.2-0.4: 2.2-2.4: 1.5-2.5; (4) immersing the FTO conductive glass cleaned in step (2) into the mixed solution in step (3) and subjecting it to ultrasonic oscillation; Then the reaction system is heated at 50-70°C for 2-4 hours; the FTO conductive glass with the yellow film is taken out, rinsed with deionized water to remove excess ions, and the precipitate deposited on the non-conductive surface is wiped off; (5) placing the above FTO conductive glass in an oven at 70-90° C. and drying for 10-14 hours; annealing the dried sample and naturally cooling it to room temperature to obtain a tungsten oxide electrochromic layer.

2. The method for preparing a tungsten oxide electrochromic film with high visible light transmittance at low temperature based on a chemical bath method according to claim 1, characterized in that: The concentration of sodium tungstate solution is 0.2mol / L, the concentration of oxalic acid solution is 0.4mol / L, the concentration of hydrochloric acid is 2mol / L, and the volume ratio of sodium tungstate solution, oxalic acid solution, deionized water and hydrochloric acid is 0.5:0.3:2.3:

2.

3. The method for preparing a tungsten oxide electrochromic film with high visible light transmittance at low temperature based on a chemical bath method according to claim 1, characterized in that: The hydrothermal reaction in step (4) is carried out by heating at 60° C. for 3 h.

4. The method for preparing a tungsten oxide electrochromic film with high visible light transmittance at low temperature based on a chemical bath method according to claim 1, characterized in that: The annealing treatment is performed by calcining at 450 to 550° C. for 1.5 to 3 hours, more preferably calcining at 500° C. for 2 hours.

5. A tungsten oxide electrochromic film with high visible light transmittance prepared according to the method according to any one of claims 1 to 4.

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