Vanadium-tungsten bimetallic oxide electrochromic thin film and preparation method thereof

Abstract

The application discloses a vanadium-tungsten bimetal oxide electrochromic film and a preparation method thereof, and the preparation method comprises the following steps: S1, dissolving ammonium paratungstate hydrate, ammonium metavanadate and oxalic acid dihydrate in deionized water to obtain a hydrothermal reaction precursor solution after stirring; and S2, performing a hydrothermal reaction on conductive glass, and thus the vanadium-tungsten bimetal oxide electrochromic film is obtained. The controllable synthesis of the vanadium-tungsten bimetal oxide film is realized by controlling the molar ratio of vanadium and tungsten in the precursor solution. The application further discloses a vanadium-tungsten bimetal oxide electrochromic film prepared by the method and an electrochromic device comprising the film. The vanadium-tungsten oxide film prepared by the application has a unique nano hexagonal star structure, high specific surface area and excellent structural stability, can not only improve the rich electrochemical reaction active sites and significantly improve the area capacitance of the film material, but also improve the cycle stability, and has a high light modulation amplitude and a high coloring efficiency.

Description

Technical Field

[0001] This invention relates to the field of electrochromic thin film technology, specifically to a vanadium-tungsten bimetallic oxide electrochromic thin film and its preparation method. Background Technology

[0002] Electrochromism refers to the continuous and reversible change in the optical properties of certain materials caused by the simultaneous insertion and extraction of ions and electrons under an applied voltage, which visually manifests as a change in the material's color. Electrochromic materials can be classified into inorganic and organic types. Inorganic electrochromic materials mainly include transition metal oxides, Prussian blue, and polyoxometalates, which have been widely studied due to their rich composition, tunable structure, and outstanding electrochemical performance.

[0003] As is well known, electrochromism typically aims to achieve large optical modulation with a small amount of charge injection, thereby providing high coloring efficiency and achieving high energy efficiency. Electrochemical energy storage, on the other hand, requires a large charge density to obtain a high energy storage capacity. WO3, as the most widely studied inorganic electrochromic material, possesses excellent color-changing properties such as large optical modulation amplitude, high coloring efficiency, and fast response speed, but its energy storage capacity is relatively low. For example, Zhao et al. ‎ A nanostructured WO3 electrode for electrochromic energy storage applications is reported, exhibiting optical modulation amplitudes of 70.8% and 71.7% at 633 / 1200 nm, respectively, and at 1 A·m -2 The areal capacitance at the given current density is only 40.6 mAh·m. -2 ( Chem. Eng. J 2024, 485, 149350, Cathode / Anode electrodes for large-area bifunctional electrochemical devices prepared by a novel Na3Cit-assisted chemical deposition method). Roy et al. synthesized WO3·H2O thin films using a hydrothermal method, achieving a light modulation amplitude of 42% at 700 nm and at 0.4 A·m. -2 The surface capacitance is 45 mAh·m -2 ( ACS Appl. Mater. Interfaces2024, 16(30), 39539-39550, Electrochromic and Energy Storage Performance Enhancement by IntroducingJahn–Teller Distortion: Experimental and Theoretical Study). Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a vanadium-tungsten bimetallic oxide electrochromic thin film and its preparation method. A one-step hydrothermal method is used to prepare a self-assembled hexagonal star-shaped vanadium-tungsten bimetallic oxide thin film with a multi-level structure. This unique structure combines the advantages of a large active specific surface area and better structural stability, providing more electrochemical reaction active sites, increasing areal capacitance, enhancing cycling stability, and maintaining a high optical modulation amplitude. The preparation method of the present invention is simple and yields a vanadium-tungsten bimetallic oxide electrochromic thin film with high bonding strength and uniformity.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing a vanadium-tungsten bimetallic oxide electrochromic thin film, comprising the following steps:

[0007] S1. Dissolve ammonium paratungstate hydrate, ammonium metavanadate and oxalate dihydrate in deionized water and stir to obtain a hydrothermal reaction precursor solution.

[0008] S2. A hydrothermal reaction is carried out on conductive glass to obtain the product.

[0009] As some specific embodiments of the present invention, in step S1, the concentration of ammonium metavanadate in the hydrothermal reaction precursor solution is 0.045~0.1 mol / L.

[0010] As some specific embodiments of the present invention, in step S1, the molar ratio of vanadium to tungsten in the hydrothermal reaction precursor solution is 3:1 to 7:1.

[0011] As some specific embodiments of the present invention, in step S1, the molar ratio of ammonium metavanadate to oxalate dihydrate in the hydrothermal reaction precursor solution is 1:2 to 2:1.

[0012] As some specific embodiments of the present invention, in step S1, the stirring is heating stirring, and the heating stirring temperature is 70~90 ℃.

[0013] As some specific embodiments of the present invention, in step S2, the temperature of the hydrothermal reaction is 150~180 ℃; the time of the hydrothermal reaction is 1~4 h.

[0014] As some specific embodiments of the present invention, in step S2, the conductive glass is selected from any one of FTO (fluorine-doped tin dioxide) conductive glass, ITO conductive glass, and AZO conductive glass.

[0015] As some specific embodiments of the present invention, step S2 specifically includes the following steps:

[0016] S21. Transfer the hydrothermal reaction precursor solution obtained in step S1 to a hydrothermal reactor, and place a piece of conductive glass obliquely into the hydrothermal reactor with its conductive surface facing down, and seal the hydrothermal reactor.

[0017] S22. Place the sealed hydrothermal reactor into a constant temperature drying oven to carry out the hydrothermal reaction. After the reaction is completed, allow it to cool naturally to room temperature.

[0018] S23. Remove the conductive glass from the hydrothermal reactor, clean and dry it to obtain vanadium-tungsten bimetallic oxide.

[0019] Secondly, the present invention provides a vanadium-tungsten bimetallic oxide electrochromic thin film, which is prepared by any of the preparation methods described above.

[0020] Thirdly, the present invention provides an electrochromic device comprising the aforementioned vanadium-tungsten bimetallic oxide electrochromic thin film.

[0021] The vanadium-tungsten bimetallic oxide thin film prepared on FTO conductive glass by this invention has a nano-hexagonal star-shaped surface microstructure and exhibits a good electrochromic effect.

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

[0023] 1) This invention achieves controllable synthesis of vanadium-tungsten bimetallic oxide thin films by controlling the molar ratio of vanadium to tungsten in the precursor solution;

[0024] 2) The vanadium-tungsten oxide thin film prepared by this invention has a unique nano-hexagonal star structure, which has both high specific surface area and excellent structural stability. It can not only enhance the rich electrochemical reaction active sites and significantly improve the areal capacitance of the thin film material, but also improve the cycle stability.

[0025] 3) The preparation process of this invention is simple, requires little equipment, uses inexpensive and readily available raw materials, and has low cost; it also has low requirements for the experimental environment, does not produce volatile gases, and is harmless to the human body.

[0026] 4) The vanadium-tungsten bimetallic oxide thin film prepared by the present invention has a high light modulation amplitude and a high coloring efficiency. Attached Figure Description

[0027] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0028] Figure 1 SEM image of the vanadium-tungsten bimetallic oxide thin film prepared in Example 1;

[0029] Figure 2 The XRD pattern of the vanadium-tungsten bimetallic oxide thin film prepared in Example 1;

[0030] Figure 3 Cyclic voltammetry curves of the vanadium-tungsten bimetallic oxide thin film prepared in Example 1;

[0031] Figure 4 The images show the color-changing effect of the vanadium-tungsten bimetallic oxide thin film prepared in Example 1, where (a) is the colored state and (b) is the faded state.

[0032] Figure 5 The transmittance curve of the vanadium-tungsten bimetallic oxide thin film prepared in Example 1;

[0033] Figure 6 The response time curve of the vanadium-tungsten bimetallic oxide thin film prepared in Example 1;

[0034] Figure 7 The coloring efficiency curve of the vanadium-tungsten bimetallic oxide thin film prepared in Example 1;

[0035] Figure 8 The constant current charge-discharge curve of the vanadium-tungsten bimetallic oxide thin film prepared in Example 1;

[0036] Figure 9 SEM image of the vanadium-tungsten bimetallic oxide thin film prepared in Example 2;

[0037] Figure 10 The images show the color-changing effect of the vanadium-tungsten bimetallic oxide thin film prepared in Example 2, where (a) is the colored state and (b) is the faded state.

[0038] Figure 11 SEM image of the vanadium-tungsten bimetallic oxide thin film prepared in Example 3;

[0039] Figure 12 The images show the color-changing effect of the vanadium-tungsten bimetallic oxide thin film prepared in Example 3, where (a) is the colored state and (b) is the faded state.

[0040] Figure 13SEM image of the vanadium-tungsten bimetallic oxide thin film prepared for Comparative Example 1;

[0041] Figure 14 The images show the color-changing effect of the vanadium-tungsten bimetallic oxide thin film prepared in Comparative Example 1, where (a) is the colored state and (b) is the faded state.

[0042] Figure 15 SEM image of the vanadium-tungsten bimetallic oxide thin film prepared for Comparative Example 2;

[0043] Figure 16 The image shows the color change effect of the vanadium-tungsten bimetallic oxide film prepared in Comparative Example 2, where (a) is the colored state and (b) is the faded state. Detailed Implementation

[0044] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0045] The inorganic compounds added in the following examples can be commercially available products with similar performance. The size of the FTO conductive glass can be adjusted according to the volume of the hydrothermal reactor liner and is suitable for other conductive glass substrate materials. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of this invention are considered equivalent substitutions and are included within the protection scope of this invention.

[0046] Example 1

[0047] First, weigh 0.3510 g of NH4VO3 into a beaker, add 40 mL of ultrapure water, and heat to 70 °C while stirring until a clear yellow solution is obtained. Next, add 0.7564 g of C2H2O4·2H2O to the above solution at a molar ratio of NH4VO3 to C2H2O4·2H2O of 1:2, and heat and stir until the solution turns blue. Finally, add 0.1530 g of (NH4)2O4 to the blue solution. 10 H2(W2O7)6 was stirred at room temperature for 10 min to obtain a hydrothermal precursor solution. The resulting solution was transferred to a polytetrafluoroethylene (PTFE) reactor liner, and a clean piece of material measuring 2.5 × 5 cm was placed inside the reactor. 2 The FTO conductive glass was tilted so that the conductive surface faced down. The reactor was sealed and placed in a constant temperature drying oven. It was reacted at 150 °C for 2 hours and then naturally cooled to room temperature.

[0048] Remove the FTO conductive glass from the reactor, rinse it with deionized water and anhydrous ethanol, and then air dry it naturally to obtain a vanadium-tungsten bimetallic oxide film on the FTO conductive glass.

[0049] like Figure 1 The image shows a SEM image of the vanadium-tungsten bimetallic oxide film prepared in this embodiment. As can be seen from the image, the film is composed of a nano-hexagonal star-shaped vanadium-tungsten bimetallic oxide structure. This hexagonal star structure is assembled from a central polyhedral prism and six peripheral branches. The size of the branch units gradually decreases from the bottom to the top of the central polyhedral prism, forming a multi-level stepped hierarchical structure. This gradient stacking method creates a unique pyramid-like three-dimensional architecture with excellent structural stability, which can improve the electrochemical cycling stability of the film.

[0050] like Figure 2 The figure shows the XRD pattern of the vanadium-tungsten bimetallic oxide thin film prepared in this embodiment. As shown in the figure, the diffraction peaks at 14.5°, 24.9°, 27.2°, 37.3°, 50.7°, and 56.8° are highly consistent with the standard diffraction data (JCPDF 24-1397) of vanadium-tungsten oxide V2WO7; at 2 θ The characteristic peaks observed at 23.8°, 28.8°, and 48.4° are WO 2.90 Typical diffraction peaks of phase (JCPDF 18-1417) indicate that the prepared vanadium-tungsten bimetallic oxide thin film is composed of two phases.

[0051] The vanadium-tungsten bimetallic oxide thin film obtained in this embodiment was subjected to 0.5 mol·L⁻¹ -1 In a ZnSO4 electrolyte solution, a three-electrode system was used for performance testing, in which the prepared thin film was the working electrode, the platinum sheet was the counter electrode, and the Ag / AgCl electrode was the reference electrode. Figure 3 At a scan rate of 5 mV·s -1 Cyclic voltammetry (CV) curves were obtained. A clear color change was observed during the test, at a rate of 5 mV·s. -1 When the scan rate is reduced to -1.1 V, the film gradually turns deep blue; when the voltage is reversed to 0.8 V, the film gradually turns yellowish-brown. The obvious redox peaks in the figure are due to the charge storage kinetics of the vanadium-tungsten bimetallic oxide, which is related to pseudocapacitive behavior (Faraday redox reaction), a behavior associated with Zn. 2+ It relates to embedding and de-embedding.

[0052] Figure 4 Digital photographs of the film in its colored and faded states, where (a) is the colored state and (b) is the faded state. The colored state is blue and the faded state is yellowish-brown.

[0053] An electrochemical workstation was connected to a UV spectrophotometer to test the transmittance curves of its colored and faded states in the wavelength range of 400–1250 nm. The results are as follows: Figure 5 As shown, the optical modulation amplitude at a wavelength of 1200 nm is 33.6%.

[0054] The electrochromic response time curve of the thin film was further tested at 1200 nm, and the test results are as follows: Figure 6 As shown, the response time is defined as the time required to reach 90% of the change in light modulation amplitude. The coloring time of the vanadium-tungsten bimetallic oxide film obtained in this embodiment is calculated to be approximately 20.8 s, and the fading time is approximately 31.2 s.

[0055] Figure 7 The graph shows the change in optical density at 1200 nm as a function of current density for the vanadium-tungsten bimetallic oxide thin film obtained in this embodiment. The calculated coloring efficiency of this film is 60.1 cm⁻¹. 2 / C.

[0056] Figure 8 The vanadium-tungsten bimetallic oxide thin film obtained in this embodiment is at 0.2 mA·cm⁻¹ -2 The constant current charge-discharge curves at the current density yielded a calculated areal capacity of 73.2 mAh·m³. -2 .

[0057] Example 2

[0058] First, weigh 0.2106 g of NH4VO3 into a beaker, add 40 mL of ultrapure water, and heat to 80 °C while stirring until a clear yellow solution is obtained. Next, add 0.2269 g of C2H2O4·2H2O to the above solution at a molar ratio of NH4VO3 to C2H2O4·2H2O of 1:1, and heat and stir until the solution turns blue. Finally, add 0.1530 g of (NH4)2O4 to the blue solution. 10 H2(W2O7)6 was stirred at room temperature for 10 min to obtain a hydrothermal precursor solution. The resulting solution was transferred to a polytetrafluoroethylene (PTFE) reactor liner, and a clean piece of material measuring 2.5 × 5 cm was placed inside the reactor. 2 The FTO conductive glass was placed at an angle with its conductive surface facing down. The reactor was then sealed and placed in a constant temperature drying oven. The reaction was carried out at 150 °C for 4 hours and then allowed to cool naturally to room temperature.

[0059] The FTO conductive glass was removed from the reactor, rinsed with deionized water and anhydrous ethanol, and then air-dried to obtain a vanadium-tungsten bimetallic oxide film with the properties to be tested on the FTO conductive glass. The vanadium-tungsten bimetallic oxide film prepared in this embodiment was subjected to the same microstructure and performance tests as in Example 1. Compared with Example 1, the hydrothermal reaction time was increased by 2 hours, resulting in a larger nano-hexagonal star structure in the vanadium-tungsten bimetallic oxide film prepared in this embodiment compared to Example 1 (e.g., ...). Figure 9 As shown), the thickness of the resulting film increases. Therefore, the colors of both the colored and faded states are deeper than those of Example 1 (as shown). Figure 10 As shown in Table 1, the corresponding transmittance will also decrease, and the difference between the two, i.e., the light modulation amplitude, is not much different from that in the example.

[0060] Example 3

[0061] First, weigh 0.4679 g of NH4VO3 into a beaker, add 40 mL of ultrapure water, and heat to 90 °C while stirring until a clear yellow solution is obtained. Next, add 0.2536 g of C2H2O4·2H2O to the above solution at a molar ratio of NH4VO3 to C2H2O4·2H2O of 2:1, and heat and stir until the solution turns blue. Finally, add 0.1457 g of (NH4)2O4 to the blue solution. 10 H2(W2O7)6 was stirred at room temperature for 10 min to obtain a hydrothermal precursor solution. The resulting solution was transferred to a polytetrafluoroethylene (PTFE) reactor liner, and a clean piece of material measuring 2.5 × 5 cm was placed inside the reactor. 2 The FTO conductive glass was tilted so that the conductive surface faced down. The reactor was sealed and placed in a constant temperature drying oven. It was reacted at 180 °C for 1 hour and then naturally cooled to room temperature.

[0062] The FTO conductive glass was removed from the reactor, rinsed with deionized water and anhydrous ethanol, and then air-dried to obtain a vanadium-tungsten bimetallic oxide film with the properties to be tested on the FTO conductive glass. The vanadium-tungsten bimetallic oxide film prepared in this embodiment was subjected to the same microstructure and performance tests as in Example 1. Due to the increased molar ratio of vanadium to tungsten and the increased reaction temperature, the nano-hexagonal structure of the vanadium-tungsten bimetallic oxide film prepared in this embodiment is also larger than that in Example 1 (e.g., ...). Figure 11 As shown), and is more dense. Therefore, the colors of the colored and faded states are deeper than those of Examples 1 and 2 (as shown). Figure 12 As shown in Table 1, the corresponding transmittance will also decrease. The difference between the two, i.e., the light modulation amplitude, is not much different from that in Examples 1 and 2.

[0063] Comparative Example 1

[0064] In this comparative example, the molar concentration of ammonium metavanadate in the hydrothermal precursor solution was adjusted to 0.015 mol / L.

[0065] First, weigh 0.0702 g of NH4VO3 into a beaker, add 40 mL of ultrapure water, and heat to 70 °C while stirring until a clear yellow solution is obtained. Next, add 0.1513 g of C2H2O4·2H2O to the above solution at a molar ratio of NH4VO3 to C2H2O4·2H2O of 1:2, and heat and stir until the solution turns blue. Finally, add 0.0306 g of (NH4)2O4 to the blue solution. 10 H2(W2O7)6 was stirred at room temperature for 10 min to obtain a hydrothermal precursor solution. The resulting solution was transferred to a polytetrafluoroethylene (PTFE) reactor liner, and a clean piece of material measuring 2.5 × 5 cm was placed inside the reactor. 2 The FTO conductive glass was tilted so that the conductive surface faced down. The reactor was sealed and placed in a constant temperature drying oven. It was reacted at 150 °C for 2 hours and then naturally cooled to room temperature.

[0066] The FTO conductive glass was removed from the reactor, rinsed with deionized water and anhydrous ethanol, and then air-dried. This yielded a vanadium-tungsten bimetallic oxide film with the properties to be tested on the FTO conductive glass. Compared to Example 1, the concentration of ammonium metavanadate was reduced to 1 / 5, resulting in a significant reduction in the size of the hexagonal star-shaped vanadium-tungsten bimetallic oxide film and a sparser distribution (e.g., ...). Figure 13 As shown), the thin and uneven film results in a lighter and more uneven color in both the colored and faded states (e.g. Figure 14 As shown in Table 1), the optical modulation amplitude is significantly reduced.

[0067] Comparative Example 2

[0068] In this comparative example, the molar ratio of vanadium to tungsten in the hydrothermal precursor solution was adjusted to 1:1.

[0069] First, weigh 0.3510 g of NH4VO3 into a beaker, add 40 mL of ultrapure water, and heat to 70 °C while stirring until a clear yellow solution is obtained. Next, add 0.7564 g of C2H2O4·2H2O to the above solution at a molar ratio of NH4VO3 to C2H2O4·2H2O of 1:2, and heat and stir until the solution turns blue. Finally, add 0.7651 g of (NH4)2O4 to the blue solution. 10 H2(W2O7)6 was stirred at room temperature for 10 min to obtain a hydrothermal precursor solution. The resulting solution was transferred to a polytetrafluoroethylene (PTFE) reactor liner, and a clean piece of material measuring 2.5 × 5 cm was placed inside the reactor. 2The FTO conductive glass was tilted so that the conductive surface faced down. The reactor was sealed and placed in a constant temperature drying oven. It was reacted at 150 °C for 2 hours and then naturally cooled to room temperature.

[0070] The FTO conductive glass was removed from the reactor, rinsed with deionized water and anhydrous ethanol, and then air-dried. This yielded a vanadium-tungsten bimetallic oxide film with the properties to be tested on the FTO conductive glass. Compared to Example 1, the significantly reduced molar ratio of vanadium to tungsten in this comparative example resulted in a smaller hexagonal star-shaped size and a sparser distribution of the prepared vanadium-tungsten bimetallic oxide film (e.g., ...). Figure 15 As shown), the film thickness will decrease. Furthermore, the faded yellowish-brown color of the film in Example 1 originated from vanadium. In this comparative example, the molar ratio of vanadium to tungsten is significantly reduced, therefore the faded yellowish-brown color of the film almost disappears. Thus, the film's coloring and faded state are relatively light (e.g., as shown). Figure 16 As shown in Table 1), the optical modulation amplitude is only 7.7%.

[0071] Comparative Example 3

[0072] In this comparative example, the vanadium source is vanadium oxysulfate, and the tungsten source is sodium tungstate dihydrate.

[0073] First, 0.4891 g of VOSO4 was weighed into a beaker and 40 mL of ultrapure water was added. The mixture was heated to 70 °C and stirred until dissolved. Next, 0.7564 g of C2H2O4·2H2O was added to the solution at a molar ratio of VOSO4 to C2H2O4·2H2O of 1:2. The mixture was heated and stirred to obtain a blue solution. Finally, 0.1979 g of Na2WO4·2H2O was added to the blue solution, and the mixture was stirred at room temperature for 10 min to obtain a hydrothermal precursor solution. The resulting solution was transferred to a polytetrafluoroethylene (PTFE) reactor liner. A clean 2.5 × 5 cm piece of [material / material] was then placed inside the reactor. 2 The FTO conductive glass was tilted so that the conductive surface faced down. The reactor was sealed and placed in a constant temperature drying oven. It was reacted at 150 °C for 2 h and then naturally cooled to room temperature.

[0074] The FTO conductive glass was removed from the reactor, rinsed with deionized water and anhydrous ethanol, and allowed to air dry. It was found that no thin film had formed on the surface of the FTO conductive glass, and the solution in the reactor lining remained blue. A possible reason is that the vanadium in the vanadium source NH4VO3 used in Example 1 has a +5 valence, while the vanadium in VOSO4 used in Comparative Example 3 has a +4 valence. This shows that changing the vanadium and tungsten sources alters the reaction in the reactor under the same conditions, and a vanadium-tungsten bimetallic oxide thin film cannot be obtained.

[0075] Table 1. Comparison of electrochromic properties of vanadium-tungsten bimetallic oxide films prepared in each example and comparative example.

[0076]

[0077] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a vanadium-tungsten bimetallic oxide electrochromic thin film, characterized in that, Includes the following steps: S1. Dissolve ammonium paratungstate hydrate, ammonium metavanadate and oxalate dihydrate in deionized water and stir to obtain a hydrothermal reaction precursor solution. S2. A hydrothermal reaction is carried out on conductive glass to obtain the product; In step S1, the concentration of ammonium metavanadate in the hydrothermal reaction precursor solution is 0.045~0.1 mol / L; In step S1, the molar ratio of vanadium to tungsten in the hydrothermal reaction precursor solution is 3:1 to 7:

1. In step S1, the molar ratio of ammonium metavanadate to oxalate dihydrate in the hydrothermal reaction precursor solution is 1:2 to 2:

1. Step S2 specifically includes the following steps: S21. Transfer the hydrothermal reaction precursor solution obtained in step S1 to a hydrothermal reactor, and place a piece of conductive glass obliquely into the hydrothermal reactor with its conductive surface facing down, and seal the hydrothermal reactor. S22. Place the sealed hydrothermal reactor into a constant temperature drying oven to carry out the hydrothermal reaction. After the reaction is completed, allow it to cool naturally to room temperature. S23. Remove the conductive glass from the hydrothermal reactor, clean and dry it to obtain vanadium-tungsten bimetallic oxide.

2. The preparation method according to claim 1, characterized in that, In step S1, the stirring is heating stirring, and the heating stirring temperature is 70~90 ℃.

3. The preparation method according to claim 1, characterized in that, In step S2, the temperature of the hydrothermal reaction is 150~180 ℃; the time of the hydrothermal reaction is 1~4 h.

4. The preparation method according to claim 1, characterized in that, In step S2, the conductive glass is selected from any one of FTO conductive glass, ITO conductive glass, and AZO conductive glass.

5. A vanadium-tungsten bimetallic oxide electrochromic thin film, characterized in that, It is prepared by the preparation method described in any one of claims 1-4.

6. An electrochromic device, characterized in that, Including the vanadium-tungsten bimetallic oxide electrochromic thin film as described in claim 5.

Images