A Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic thin film and its preparation method

Abstract

This invention relates to a layer-by-layer composite electrochromic thin film of Mo-WO3 and Bi-WO3 and its preparation method. The method includes: dissolving tungstic acid in hydrogen peroxide solution to obtain a peroxytungstic acid solution; adding a Bi-containing substance to the peroxytungstic acid solution and heating until the Bi-containing substance is completely dissolved to obtain a bismuth-doped peroxytungstic acid sol; adding a Mo-containing substance to the peroxytungstic acid solution and heating until the Mo-containing substance is completely dissolved to obtain a molybdenum-doped peroxytungstic acid sol; spin-coating the bismuth-doped peroxytungstic acid sol onto a conductive glass substrate and calcining to obtain a bismuth-doped WO3 thin film; and spin-coating the molybdenum-doped peroxytungstic acid sol onto the bismuth-doped WO3 thin film and calcining to obtain a Mo-WO3 / Bi-WO3 thin film. This invention employs a layer-by-layer composite structure design. The Bi-WO3 bottom layer significantly enhances the film-substrate adhesion and improves cycle stability; the Mo-WO3 surface layer ensures high optical modulation rate, fast response, and memory effect, achieving a synergistic performance improvement.

Description

Technical Field

[0001] This invention relates to the field of electrochromic materials technology, specifically to a Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic thin film and its preparation method. Background Technology

[0002] Electrochromic materials can achieve reversible control of their optical properties under the action of an applied electric field, and have important application value in fields such as smart windows, energy-saving buildings, and display devices. Tungsten trioxide (WO3), as a typical cathode electrochromic material, has advantages such as a large optical modulation range, high coloring efficiency, and good chemical stability, and is currently the most widely studied inorganic electrochromic material.

[0003] Existing research shows that Mo doping can significantly improve the charge transport capability and ion diffusion kinetics of WO3 films, effectively enhancing their electrochromic properties. However, Mo-doped WO3 (Mo-WO3) films are prone to structural collapse and rapid performance degradation during long-term cycling, making their cycling stability insufficient for practical applications. Bi-doped WO3 (Bi-WO3) films, on the other hand, are not only simple to process but also possess excellent electrochromic properties, especially superior cycling stability. They can enhance the adhesion between the film and the conductive substrate, optimize the ion diffusion path, and mitigate structural damage caused by ion insertion and extraction. However, single Bi-WO3 films have limited optical modulation capabilities and poor memory effect, making it difficult to simultaneously meet the dual requirements of high optical modulation and long cycle life.

[0004] Therefore, developing a Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic film that combines high optical modulation rate, fast response, excellent cycling stability and memory effect is of great significance for promoting the practical application of electrochromism. Summary of the Invention

[0005] The purpose of this invention is to provide a layer-by-layer composite electrochromic film of Mo-WO3 and Bi-WO3. The film is constructed by a sol-gel spin coating process to form a layer-by-layer composite structure with Bi-WO3 as the substrate and Mo-WO3 as the surface layer. This achieves synergistic optimization of electrochromic performance and cycling stability. The prepared composite film has high optical modulation rate, fast response, excellent memory effect and long cycle life.

[0006] The second objective of this invention is to provide a method for preparing a Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic thin film.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic thin film, characterized by comprising the following steps: S1: Dissolve tungstic acid in hydrogen peroxide solution to obtain peroxytungstic acid solution; S2: Add a substance containing Bi to the peroxytungstic acid solution in S1, and heat until the substance containing Bi is completely dissolved to obtain bismuth-doped peroxytungstic acid sol; add a substance containing Mo to the peroxytungstic acid solution in S1, and heat until the substance containing Mo is completely dissolved to obtain molybdenum-doped peroxytungstic acid sol. S3: Spin-coat the bismuth-doped peroxytungstic acid sol obtained in S2 onto a conductive glass substrate, and then calcine it to obtain a bismuth-doped WO3 thin film; in this step, the spin-coating-calcine process is repeated 1 to 5 times. S4: The molybdenum-doped peroxytungstic acid sol obtained in S2 is spin-coated onto the bismuth-doped WO3 film obtained in S4. After calcination, a Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic film is obtained. In this step, the spin-coating-calcination is repeated 1 to 3 times.

[0008] The concentration of the peroxytungstic acid solution described in S1 is 0.1 to 1 M.

[0009] The ratio of bismuth atoms to tungsten atoms in the bismuth-doped peroxytungstic sol described in S2 is 1:10 to 1:100.

[0010] The substance containing Bi in S2 is one or more of the following: metallic bismuth powder, bismuth chloride, bismuth nitrate pentahydrate, and bismuth oxide; the heating method for heating until the substance containing Bi is completely dissolved is water bath heating, and the heating temperature is 40–100 °C.

[0011] The molybdenum-doped peroxytungstic acid sol described in S2 has a molybdenum atom to tungsten atom ratio of 1:1 to 1:100.

[0012] The substance containing Mo in S2 is one or more of molybdenum sulfide, molybdic acid, molybdenum dioxide, and molybdenum trioxide; the heating method for heating until the substance containing Mo is completely dissolved is water bath heating, and the heating temperature is 30-100 ℃.

[0013] In S3, the spin coating rate is 1500–3500 rpm, and the spin coating time is 20–45 s.

[0014] In S4, the spin coating rate is 1000–3000 rpm, and the spin coating time is 15–55 s.

[0015] The calcination temperature in S3 and S4 is 50–500 °C, and the calcination time is 1–10 h.

[0016] The electrochromic thin film was prepared by the method for preparing Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic film as described in claim 1.

[0017] The beneficial effects of this invention are: (1) The present invention adopts a sol-gel spin coating process, which does not require extreme environmental conditions such as vacuum or precision and complex equipment. The operation process is simple and suitable for large-scale production. In addition, the raw materials and preparation process used in this method are low cost. They mainly use common chemicals such as tungstic acid, hydrogen peroxide, and bismuth oxide. The precursor solution can be stored at room temperature for several months without deterioration or precipitation, which reduces the preparation cost and storage difficulty and is beneficial to practical production applications.

[0018] (2) The Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic film of the present invention has high transmittance and transparency in the faded state, and is deep blue in the colored state, exhibiting strong shielding ability against visible and near-infrared light. It has a fast response speed in sulfuric acid solution, good memory effect, and good cycling stability within a suitable potential window, giving it a comparative advantage over previously reported products.

[0019] (3) This invention adopts a layer-by-layer composite structure design, and the layered structure achieves coordinated performance: the Bi-WO3 bottom layer significantly enhances the film-substrate adhesion, inhibits film shedding during cycling, optimizes ion transport channels, and improves cycling stability; the surface Mo-WO3 provides high optical modulation rate and excellent proton capture capability, ensuring high coloring efficiency and long-term memory performance. Among them, the number of Bi-WO3 bottom layer spin coatings has a significant impact on film performance: too few bottom layers result in insufficient film-substrate adhesion, poor ion channel continuity, low modulation rate, and poor color retention; too many bottom layers result in excessive film thickness, pore blockage, a surge in ion migration resistance, slower response, and aggravated cycling decay. Attached Figure Description

[0020] Figure 1 The images shown are scanning electron microscope (SEM) and atomic force microscope (AFM) images of the Mo-WO3 / Bi-WO3 layer-by-layer composite electrochromic film in Example 2. Figure 2 The transmittance curves of the Mo-WO3 / Bi-WO3 layer-by-layer composite electrochromic films in Examples 1-3 are shown in the -0.4 V colored state and the 0.6 V bleached state. Figure 3 The in-situ response curves of the Mo-WO3 / Bi-WO3 layer-by-layer composite electrochromic films in Examples 1-3 at potentials of -0.4 / 0.6 V are shown. Figure 4 The stability test curves of the Mo-WO3 / Bi-WO3 layer-by-layer composite electrochromic film in Example 2 at potentials of -0.4 / 0.6 V are shown. Figure 5 The coloring efficiency of the Mo-WO3 / Bi-WO3 layer-by-layer composite electrochromic film in Example 2; Figure 6 The graphs show the memory effect curves of the Mo-WO3 / Bi-WO3 layer-by-layer composite electrochromic films in Examples 1-3. Figure 7 The transmittance curves of the Mo-WO3 / Bi-WO3 layer-by-layer composite electrochromic film in Example 4 are shown in the initial state, the -0.4 V colored state, and the 0.6 V fading state. Figure 8 The transmittance curves of the Bi-WO3 electrochromic film in Comparative Example 1 are shown in the initial state, the -0.4 V colored state, and the 0.6 V bleached state. Figure 9 The transmittance curves of the Mo-WO3 electrochromic film in Comparative Example 2 are shown in the initial state, the -0.4 V colored state, and the 0.6 V fading state. Figure 10 The in-situ response curves of the 3B3M, Bi-WO3, and Mo-WO3 electrochromic films at potentials of -0.4 / 0.6 V are shown in Example 4, Comparative Example 1, and Comparative Example 2. Figure 11 The image shows the memory effect curves of the 3B3M, Bi-WO3, and Mo-WO3 electrochromic films in Example 4, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0021] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0022] Example 1 (1) Pretreatment of fluorine-doped tin oxide (FTO) glass substrate An FTO glass substrate was ultrasonically cleaned for 15 minutes each with deionized water, anhydrous ethanol, and deionized water to remove surface organic matter, and the surface liquid was blown away. The dimensions of the FTO glass substrate were 3 cm × 2 cm.

[0023] (2) Preparation of Bi-WO3 sol and Mo-WO3 sol Includes the following steps: 15 g of tungstic acid (H2WO4) was dissolved in 100 mL of 30% hydrogen peroxide (H2O2). The solution was stirred at 300 rpm for 4 days at room temperature and then allowed to stand for 6 hours to obtain a clear and transparent peroxytungstic acid solution with a concentration of 0.3 M.

[0024] Bismuth oxide (Bi2O3) was added to a tungsten peroxide solution to make the ratio of Bi atoms to W atoms in the solution 1:30. The tungsten peroxide solution with added bismuth oxide was then sealed and heated in a water bath at 80°C for 5 h until Bi2O3 was completely dissolved, thus obtaining bismuth-doped peroxytungstate sol (Bi-WO3 sol, i.e., Bi-PTA).

[0025] Molybdic acid (H2MoO4) was added to the tungsten peroxide solution to make the ratio of Mo atoms to W atoms in the solution 1:5. The tungsten peroxide solution with added molybdic acid was then sealed and heated in a water bath at 80°C for 6 h until H2MoO4 was completely dissolved, thus obtaining molybdenum-doped peroxytungstic acid sol (Mo-WO3 sol, i.e., Mo-PTA).

[0026] (3) Preparation of Mo-WO3 / Bi-WO3 electrochromic thin films The Bi-WO3 sol obtained in step (2) was spin-coated onto an FTO glass substrate at 3000 rpm for 35 s to form a film, followed by calcination at 300°C for 2 h to obtain a bismuth-doped WO3 (Bi-WO3) thin film. Then, the Mo-doped WO3 sol obtained in step (2) was spin-coated onto the above Bi-WO3 thin film at 2000 rpm for 35 s, followed by calcination at 250°C for 2 h to obtain a Mo-WO3 / Bi-WO3 thin film (1 BM).

[0027] The Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic film of Example 1 was prepared using the method described above.

[0028] Example 2 (1) Pretreatment of fluorine-doped tin oxide (FTO) glass substrate An FTO glass substrate was ultrasonically cleaned for 15 minutes each with deionized water, anhydrous ethanol, and deionized water to remove surface organic matter, and the surface liquid was blown away. The dimensions of the FTO glass substrate were 3 cm × 2 cm.

[0029] (2) Preparation of Bi-WO3 sol and Mo-WO3 sol Includes the following steps: 15 g of tungstic acid (H2WO4) was dissolved in 100 mL of 30% hydrogen peroxide (H2O2). The solution was stirred at 300 rpm for 4 days at room temperature and then allowed to stand for 6 hours to obtain a clear and transparent peroxytungstic acid solution with a concentration of 0.3 M.

[0030] Bismuth oxide (Bi2O3) was added to a tungsten peroxide solution to make the ratio of Bi atoms to W atoms in the solution 1:30. The tungsten peroxide solution with added bismuth oxide was then sealed and heated in a water bath at 80°C for 5 h until Bi2O3 was completely dissolved, thus obtaining bismuth-doped peroxytungstate sol (Bi-WO3 sol, i.e., Bi-PTA).

[0031] Molybdic acid (H2MoO4) was added to the tungsten peroxide solution to make the ratio of Mo atoms to W atoms in the solution 1:5. The tungsten peroxide solution with added molybdic acid was then sealed and heated in a water bath at 80°C for 6 h until H2MoO4 was completely dissolved, thus obtaining molybdenum-doped peroxytungstic acid sol (Mo-WO3 sol, i.e., Mo-PTA).

[0032] (3) Preparation of Mo-WO3 / Bi-WO3 electrochromic film of composite three-layer Bi-WO3 film The Bi-WO3 sol obtained in step (2) was spin-coated onto an FTO glass substrate at 3000 rpm for 35 s to form a film, followed by calcination at 300°C for 2 h. This spin-coating-calcination operation was repeated three times to obtain a composite three-layer bismuth-doped WO3 (Bi-WO3) film. Then, the Mo-doped WO3 sol obtained in step (2) was spin-coated onto the above Bi-WO3 film at 2000 rpm for 35 s, followed by calcination at 250°C for 2 h to obtain a Mo-WO3 / Bi-WO3 film (3BM) with a composite three-layer Bi-WO3 film.

[0033] The Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic film of Example 2 was prepared using the above method.

[0034] Scanning electron microscopy (SEM) image of the Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic thin film prepared in Example 2 is shown below. Figure 1 As shown.

[0035] The stability test curves of the Mo-WO3 / Bi-WO3 layer-by-layer composite electrochromic film prepared in Example 2 at potentials of -0.4 / 0.6 V are shown in the figure. Figure 4 As shown.

[0036] The coloring efficiency of the Mo-WO3 / Bi-WO3 layer-by-layer composite electrochromic film prepared in Example 2 is as follows: Figure 5 As shown.

[0037] Example 3 An FTO glass substrate was ultrasonically cleaned for 15 minutes each with deionized water, anhydrous ethanol, and deionized water to remove surface organic matter, and the surface liquid was blown away. The dimensions of the FTO glass substrate were 3 cm × 2 cm.

[0038] (2) Preparation of Bi-WO3 sol and Mo-WO3 sol Includes the following steps: 15 g of tungstic acid (H2WO4) was dissolved in 100 mL of 30% hydrogen peroxide (H2O2). The solution was stirred at 300 rpm for 4 days at room temperature and then allowed to stand for 6 hours to obtain a clear and transparent peroxytungstic acid solution with a concentration of 0.3 M.

[0039] Bismuth oxide (Bi2O3) was added to a tungsten peroxide solution to make the ratio of Bi atoms to W atoms in the solution 1:30. The tungsten peroxide solution with added bismuth oxide was then sealed and heated in a water bath at 80°C for 5 h until Bi2O3 was completely dissolved, thus obtaining bismuth-doped peroxytungstate sol (Bi-WO3 sol, i.e., Bi-PTA).

[0040] Molybdic acid (H2MoO4) was added to the tungsten peroxide solution to make the ratio of Mo atoms to W atoms in the solution 1:5. The tungsten peroxide solution with added molybdic acid was then sealed and heated in a water bath at 80°C for 6 h until H2MoO4 was completely dissolved, thus obtaining molybdenum-doped peroxytungstic acid sol (Mo-WO3 sol, i.e., Mo-PTA).

[0041] (3) Preparation of Mo-WO3 / Bi-WO3 electrochromic film with composite five-layer Bi-WO3 film The Bi-WO3 sol obtained in step (2) was spin-coated onto an FTO glass substrate at 3000 rpm for 35 s to form a film, followed by calcination at 300°C for 2 h. This spin-coating-calcination operation was repeated five times to obtain a composite five-layer bismuth-doped WO3 (Bi-WO3) film. Then, the Mo-doped WO3 sol obtained in step (2) was spin-coated onto the above Bi-WO3 film at 2000 rpm for 35 s, followed by calcination at 250°C for 2 h to obtain a Mo-WO3 / Bi-WO3 film (5BM) with a composite five-layer Bi-WO3 film.

[0042] The Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic film of Example 3 was prepared using the above method.

[0043] Example 4 An FTO glass substrate was ultrasonically cleaned for 15 minutes each with deionized water, anhydrous ethanol, and deionized water to remove surface organic matter, and the surface liquid was blown away. The dimensions of the FTO glass substrate were 3 cm × 2 cm.

[0044] (2) Preparation of Bi-WO3 sol and Mo-WO3 sol Includes the following steps: 15 g of tungstic acid (H2WO4) was dissolved in 100 mL of 30% hydrogen peroxide (H2O2). The solution was stirred at 300 rpm for 4 days at room temperature and then allowed to stand for 6 hours to obtain a clear and transparent peroxytungstic acid solution with a concentration of 0.3 M.

[0045] Bismuth oxide (Bi2O3) was added to a tungsten peroxide solution to make the ratio of Bi atoms to W atoms in the solution 1:30. The tungsten peroxide solution with added bismuth oxide was then sealed and heated in a water bath at 80°C for 5 h until Bi2O3 was completely dissolved, thus obtaining bismuth-doped peroxytungstate sol (Bi-WO3 sol, i.e., Bi-PTA).

[0046] Molybdic acid (H2MoO4) was added to the tungsten peroxide solution to make the ratio of Mo atoms to W atoms in the solution 1:5. The tungsten peroxide solution with added molybdic acid was then sealed and heated in a water bath at 80°C for 6 h until H2MoO4 was completely dissolved, thus obtaining molybdenum-doped peroxytungstic acid sol (Mo-WO3 sol, i.e., Mo-PTA).

[0047] (3) Preparation of Mo-WO3 / Bi-WO3 electrochromic films composed of three layers of Bi-WO3 and three layers of Mo-WO3 The Bi-WO3 sol obtained in step (2) was spin-coated onto an FTO glass substrate at 3000 rpm for 35 s to form a film, followed by calcination at 300°C for 2 h. This spin-coating-calcination operation was repeated three times to obtain a composite three-layer bismuth-doped WO3 (Bi-WO3) film. Then, the Mo-doped WO3 sol obtained in step (2) was spin-coated onto the above Bi-WO3 film at 2000 rpm for 35 s, followed by calcination at 250°C for 2 h. This spin-coating-calcination operation was repeated three times to obtain a Mo-WO3 / Bi-WO3 film (3B3M) that combines a composite three-layer Bi-WO3 film and a three-layer Mo-WO3 film.

[0048] The Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic film of Example 4 was prepared using the above method.

[0049] Example 5 (1) Pretreatment of fluorine-doped tin oxide (FTO) glass substrate An FTO glass substrate was ultrasonically cleaned for 15 minutes each with deionized water, anhydrous ethanol, and deionized water to remove surface organic matter, and the surface liquid was blown away. The dimensions of the FTO glass substrate were 3 cm × 2 cm.

[0050] (2) Preparation of Bi-WO3 sol and Mo-WO3 sol Includes the following steps: 15 g of tungstic acid (H2WO4) was dissolved in 100 mL of 30% hydrogen peroxide (H2O2). The solution was stirred at 300 rpm for 4 days at room temperature and then allowed to stand for 6 hours to obtain a clear and transparent peroxytungstic acid solution with a concentration of 0.1 M.

[0051] Bismuth powder was added to a tungsten peroxide solution to make the ratio of Bi atoms to W atoms in the solution 1:10. The tungsten peroxide solution with added bismuth oxide was then sealed and heated in a water bath at 80°C until Bi2O3 was completely dissolved, thus obtaining bismuth-doped peroxytungstate sol (Bi-WO3 sol, i.e., Bi-PTA).

[0052] Molybdenum sulfide was added to the tungsten peroxide solution to make the ratio of Mo atoms to W atoms in the solution 1:1. Then the tungsten peroxide solution with added molybdic acid was sealed and heated in a water bath at 30°C until H2MoO4 was completely dissolved to obtain molybdenum-doped peroxytungstic acid sol (Mo-WO3 sol, i.e. Mo-PTA).

[0053] (3) Preparation of Mo-WO3 / Bi-WO3 electrochromic thin films The Bi-WO3 sol obtained in step (2) was spin-coated onto an FTO glass substrate at 1500 rpm for 45 s to form a film, followed by calcination at 50°C for 10 h to obtain a bismuth-doped WO3 (Bi-WO3) film. Then, the Mo-doped WO3 sol obtained in step (2) was spin-coated onto the above Bi-WO3 film at 1000 rpm for 55 s, followed by calcination at 50°C for 10 h to obtain a Mo-WO3 / Bi-WO3 film. The spin-coating-calcination operation was repeated twice.

[0054] The Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic film of Example 5 was prepared using the above method.

[0055] Example 6 (1) Pretreatment of fluorine-doped tin oxide (FTO) glass substrate An FTO glass substrate was ultrasonically cleaned for 15 minutes each with deionized water, anhydrous ethanol, and deionized water to remove surface organic matter, and the surface liquid was blown away. The dimensions of the FTO glass substrate were 3 cm × 2 cm.

[0056] (2) Preparation of Bi-WO3 sol and Mo-WO3 sol Includes the following steps: 15 g of tungstic acid (H2WO4) was dissolved in 100 mL of 30% hydrogen peroxide (H2O2). The solution was stirred at 300 rpm for 4 days at room temperature and then allowed to stand for 6 hours to obtain a clear and transparent peroxytungstic acid solution with a concentration of 0.1 M.

[0057] Bismuth chloride was added to a tungsten peroxide solution to make the ratio of Bi atoms to W atoms in the solution 1:10. The tungsten peroxide solution with added bismuth oxide was then sealed and heated in a water bath at 40°C until Bi2O3 was completely dissolved, thus obtaining bismuth-doped peroxytungstate sol (Bi-WO3 sol, i.e., Bi-PTA).

[0058] Molybdenum dioxide was added to a tungsten peroxide solution to make the ratio of Mo atoms to W atoms in the solution 1:1. Then, the tungsten peroxide solution with added molybdic acid was sealed and heated in a water bath at 30°C until H2MoO4 was completely dissolved to obtain molybdenum-doped peroxytungstic acid sol (Mo-WO3 sol, i.e., Mo-PTA).

[0059] (3) Preparation of Mo-WO3 / Bi-WO3 electrochromic thin films The Bi-WO3 sol obtained in step (2) was spin-coated onto an FTO glass substrate at 1500 rpm for 45 s to form a film, followed by calcination at 50°C for 10 h to obtain a bismuth-doped WO3 (Bi-WO3) film. Then, the Mo-doped WO3 sol obtained in step (2) was spin-coated onto the above Bi-WO3 film at 1000 rpm for 55 s, followed by calcination at 50°C for 10 h to obtain a Mo-WO3 / Bi-WO3 film.

[0060] The Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic film of Example 6 was prepared using the above method.

[0061] Example 7 (1) Pretreatment of fluorine-doped tin oxide (FTO) glass substrate An FTO glass substrate was ultrasonically cleaned for 15 minutes each with deionized water, anhydrous ethanol, and deionized water to remove surface organic matter, and the surface liquid was blown away. The dimensions of the FTO glass substrate were 3 cm × 2 cm.

[0062] (2) Preparation of Bi-WO3 sol and Mo-WO3 sol Includes the following steps: 15 g of tungstic acid (H2WO4) was dissolved in 100 mL of 30% hydrogen peroxide (H2O2). The solution was stirred at 300 rpm for 4 days at room temperature and then allowed to stand for 6 hours to obtain a clear and transparent peroxytungstic acid solution with a concentration of 1 M.

[0063] Bismuth nitrate pentahydrate was added to a tungsten peroxide solution to make the ratio of Bi atoms to W atoms in the solution 1:30. The tungsten peroxide solution with added bismuth oxide was then sealed and heated in a water bath at 80°C until Bi2O3 was completely dissolved, thus obtaining bismuth-doped peroxytungstate sol (Bi-WO3 sol, i.e., Bi-PTA).

[0064] Molybdenum trioxide was added to the tungsten peroxide solution to make the ratio of Mo atoms to W atoms in the solution 1:5. Then the tungsten peroxide solution with added molybdic acid was sealed and heated in a water bath at 80°C until H2MoO4 was completely dissolved to obtain molybdenum-doped peroxytungstic acid sol (Mo-WO3 sol, i.e. Mo-PTA).

[0065] (3) Preparation of Mo-WO3 / Bi-WO3 electrochromic thin films The Bi-WO3 sol obtained in step (2) was spin-coated onto an FTO glass substrate at 3000 rpm for 35 s to form a film, followed by calcination at 300°C for 2 h to obtain a bismuth-doped WO3 (Bi-WO3) film. Then, the Mo-doped WO3 sol obtained in step (2) was spin-coated onto the above Bi-WO3 film at 2000 rpm for 35 s, followed by calcination at 250°C for 2 h to obtain a Mo-WO3 / Bi-WO3 film.

[0066] The Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic film of Example 7 was prepared using the above method.

[0067] Example 8 (1) Pretreatment of fluorine-doped tin oxide (FTO) glass substrate An FTO glass substrate was ultrasonically cleaned for 15 minutes each with deionized water, anhydrous ethanol, and deionized water to remove surface organic matter, and the surface liquid was blown away. The dimensions of the FTO glass substrate were 3 cm × 2 cm.

[0068] (2) Preparation of Bi-WO3 sol and Mo-WO3 sol Includes the following steps: 15 g of tungstic acid (H2WO4) was dissolved in 100 mL of 30% hydrogen peroxide (H2O2). The solution was stirred at 300 rpm for 4 days at room temperature and then allowed to stand for 6 hours to obtain a clear and transparent peroxytungstic acid solution with a concentration of 1 M.

[0069] Bismuth chloride and bismuth oxide were added to a tungsten peroxide solution to make the ratio of Bi atoms to W atoms in the solution 1:30. The tungsten peroxide solution with added bismuth oxide was then sealed and heated in a water bath at 80°C until Bi2O3 was completely dissolved, thus obtaining bismuth-doped peroxytungstate sol (Bi-WO3 sol, i.e., Bi-PTA).

[0070] Molybdic acid and molybdenum trioxide were added to a tungsten peroxide solution to make the ratio of Mo atoms to W atoms in the solution 1:5. The tungsten peroxide solution with added molybdic acid was then sealed and heated in a water bath at 80°C until H2MoO4 was completely dissolved, thus obtaining molybdenum-doped peroxytungstic acid sol (Mo-WO3 sol, i.e., Mo-PTA).

[0071] (3) Preparation of Mo-WO3 / Bi-WO3 electrochromic thin films The Bi-WO3 sol obtained in step (2) was spin-coated onto an FTO glass substrate at 3000 rpm for 35 s to form a film, followed by calcination at 300°C for 2 h to obtain a bismuth-doped WO3 (Bi-WO3) film. Then, the Mo-doped WO3 sol obtained in step (2) was spin-coated onto the above Bi-WO3 film at 2000 rpm for 35 s, followed by calcination at 250°C for 2 h to obtain a Mo-WO3 / Bi-WO3 film.

[0072] The Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic film of Example 8 was prepared using the above method.

[0073] In all the above embodiments, the conductive glass uses an FTO glass substrate. In other embodiments, transparent conductive oxide glasses known in the art, such as indium-doped tin oxide (ITO) glass or aluminum-doped zinc oxide (AZO) glass, can also be used.

[0074] Comparative Example 1 An FTO glass substrate was ultrasonically cleaned for 15 minutes each with deionized water, anhydrous ethanol, and deionized water to remove surface organic matter, and the surface liquid was blown away. The dimensions of the FTO glass substrate were 3 cm × 2 cm.

[0075] (2) Preparation of Bi-WO3 sol Includes the following steps: 15 g of tungstic acid (H2WO4) was dissolved in 100 mL of 30% hydrogen peroxide (H2O2). The solution was stirred at 300 rpm for 4 days at room temperature and then allowed to stand for 6 hours to obtain a clear and transparent peroxytungstic acid solution with a concentration of 0.3 M.

[0076] Bismuth oxide (Bi2O3) was added to a tungsten peroxide solution to make the ratio of Bi atoms to W atoms in the solution 1:50. The tungsten peroxide solution with added bismuth oxide was then sealed and heated in a water bath at 90°C for 8 h until Bi2O3 was completely dissolved, thus obtaining bismuth-doped peroxytungstate sol (Bi-WO3 sol, i.e., Bi-PTA).

[0077] (3) Preparation of monolayer Bi-WO3 electrochromic thin film The Bi-WO3 sol obtained in step (2) was spin-coated on an FTO glass substrate at a speed of 3000 rpm for 35 s to form a film, and then calcined at 300℃ for 2 h to obtain a Bi-WO3 thin film.

[0078] The Bi-WO3 electrochromic film of Comparative Example 1 was prepared using the above method.

[0079] Comparative Example 2 An FTO glass substrate was ultrasonically cleaned for 15 minutes each with deionized water, anhydrous ethanol, and deionized water to remove surface organic matter, and the surface liquid was blown away. The dimensions of the FTO glass substrate were 3 cm × 2 cm.

[0080] (2) Preparation of Mo-WO3 sol Includes the following steps: 15 g of tungstic acid (H2WO4) was dissolved in 100 mL of 30% hydrogen peroxide (H2O2). The solution was stirred at 300 rpm for 4 days at room temperature and then allowed to stand for 6 hours to obtain a clear and transparent peroxytungstic acid solution with a concentration of 0.3 M.

[0081] Molybdic acid (H2MoO4) was added to the tungsten peroxide solution to make the ratio of Mo atoms to W atoms in the solution 1:5. The tungsten peroxide solution with added molybdic acid was then sealed and heated in a water bath at 80°C for 6 h until H2MoO4 was completely dissolved, thus obtaining molybdenum-doped peroxytungstic acid sol (Mo-WO3 sol, i.e., Mo-PTA).

[0082] (3) Preparation of monolayer Mo-WO3 electrochromic thin film The Mo-WO3 sol obtained in step (2) was spin-coated on an FTO glass substrate at a speed of 3000 rpm for 35 s to form a film, and then calcined at 300℃ for 2 h to obtain a Mo-WO3 thin film.

[0083] The Mo-WO3 electrochromic film of Comparative Example 2 was prepared using the above method.

[0084] Experimental Example Using the 1BM, 3BM, and 5BM composite films prepared in Examples 1-3 as working electrodes, a platinum sheet as the counter electrode, and saturated Ag / AgCl as the reference electrode, and 0.5 M H₂SO₄ solution as the electrolyte, the electrochromic performance was tested using a three-electrode electrochemical workstation and a UV-Vis-NIR spectrophotometer. The test results are shown in [Figure 1]. Figures 2-6 .from Figure 2 It can be seen that, using 0.5 M H₂SO₄ solution as the electrolyte and a wavelength of 633 nm, the 3BM film prepared in Example 2 exhibits an 84.5% change in transmittance between the -0.4 V colored state and the 0.6 V bleached state, possessing the largest optical modulation range among Examples 1-3. Figure 3 It can be seen that the 3BM film of Example 2 has the fastest fading time and coloring time, with coloring time and fading time of 3.5 s and 2.7 s respectively, which are significantly shorter than those of the 1BM and 5BM samples. It has the best ion insertion and extraction kinetics and the best color change kinetics. Figure 4 The results show that the 3BM film prepared in Example 2 retains over 80% of its performance in more than 3000 fading cycles, demonstrating good stability. Figure 5 It can be seen that the coloring efficiency of the 3BM film is 52.8 cm⁻¹. 2 C -1 High coloring efficiency means that a unit amount of embedded charge can produce a stronger change in optical absorption. From Figure 6 It can be seen that the 3BM film exhibits excellent color state maintenance ability. In the open circuit state, after 450 min, it is far superior to 1BM (48.1%) and 5BM (11.5%), and has excellent optical memory effect. Relying on the synergistic binding effect of Bi bottom layer and Mo surface layer, it can effectively imprison protons embedded in the crystal lattice and has excellent color retention memory characteristics when power is off.

[0085] The thickness of the Bi-WO3 substrate directly determines the interfacial adhesion, pore structure, and ion migration ability of the thin film. A 1BM substrate that is too thin results in insufficient film-substrate adhesion, a lack of continuous ion channels, fewer active sites, insufficient proton traps, and weak modulation and color retention properties; a 5BM substrate that is too thick leads to grain stacking and pore blockage, resulting in H… + Diffusion resistance soars, intrafilm stress is high, and pulverization is easy during cycling. Excessive lattice defects randomly trap protons, making fading difficult. The 3BM three-layer Bi bottom layer can firmly anchor the substrate and construct a through ion channel with appropriate density. Combined with a single-layer Mo surface layer, relying on Bi to optimize the energy band and Mo to provide polaron sites, it takes into account both reversible ion insertion and extraction and long-term proton binding, resulting in the best overall performance.

[0086] A three-electrode test system was constructed using the 3B3M, Bi-WO3, and Mo-WO3 thin films from Examples 4, 1, and 2. Electrode and electrolyte parameters were identical to those described above. Electrochromic performance tests were performed simultaneously, and the test data were summarized in [the table / document / etc.]. Figures 7-11 .from Figure 7 , 8 Spectroscopy results show that, using 0.5 M H₂SO₄ solution as the electrolyte and at a wavelength of 633 nm, the optical modulation rate of the Bi-WO₃ thin film prepared in Comparative Example 1 is 51.3%, while the 3B₃M and monolayer Mo-WO₃ thin films exhibit irreversible intercalation / deintercalation defects. Applying a positive voltage cannot completely deintercalate the intercalated hydrogen ions, making it difficult to restore the initial high transmittance state during the fading stage. Figure 10 It can be seen that the coloring and fading times of the Bi-WO3 film are 1.8 s and 3 s, respectively, showing excellent response times. However, the fading of 3B3M and Mo-WO3 is incomplete, and the transmittance of the faded state continues to decrease after multiple cycles, indicating poor electrochemical reversibility and cycle stability. Figure 11 It can be seen that the Mo-WO3 film exhibits excellent color state maintenance ability. In the open circuit state, after 450 min, it is far superior to 3B3M (30%) and Bi-WO3 (98%), demonstrating excellent optical memory effect and good memory effect.

[0087] Bi-WO3 thin films exhibit high ion conductivity and excellent electrochromic reversibility, with thorough coloring and fading reactions. However, they suffer from limited coloring depth, small optical modulation amplitude, weak proton binding capacity of the lattice, easy hydrogen ion escape in the open-circuit state, and poor memory performance. Mo-WO3 thin films can undergo redox reactions synergistically with Mo and W, resulting in large coloring depth, outstanding optical modulation capability, abundant lattice trap sites, strong hydrogen ion retention capacity, and excellent memory effect. However, they are prone to incomplete fading due to excessive ion retention. Given the complementary advantages and disadvantages of the two single-component thin films, this patent employs a layer-by-layer composite process to construct a 3BM composite structure consisting of a three-layer Bi-WO3 bottom layer and a single-layer Mo-WO3 top layer. The bottom Bi-WO3 layer strengthens the film-substrate bonding, optimizes ion transport pathways, and improves cycle stability, while the top Mo-WO3 layer provides high optical modulation and long-term memory characteristics, thus maximizing performance while minimizing its weaknesses. In contrast, the 3B3M structure, consisting of a three-layer Bi-WO3 composite with a three-layer Mo-WO3 layer, suffers from excessive film thickness and a surge in interlayer interfaces due to the multiple Mo layers, resulting in a significant increase in ion migration dynamics resistance and the generation of a large amount of H₂. + Trapped in the crystal lattice, it is difficult to escape, resulting in incomplete fading and significantly deteriorated cycle stability. Therefore, its overall performance is far inferior to that of 3BM.

[0088] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This disclosure is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be determined by the claims. Similarly, any equivalent structural changes made based on the content of the present invention's specification shall also be included within the scope of protection of the present invention.

Claims

1. A method for preparing a Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic thin film, characterized in that: Includes the following steps: S1: Dissolve tungstic acid in hydrogen peroxide solution to obtain peroxytungstic acid solution; S2: Add a substance containing Bi to the peroxytungstic acid solution in S1, and heat until the substance containing Bi is completely dissolved to obtain bismuth-doped peroxytungstic acid sol; add a substance containing Mo to the peroxytungstic acid solution in S1, and heat until the substance containing Mo is completely dissolved to obtain molybdenum-doped peroxytungstic acid sol. S3: Spin-coat the bismuth-doped peroxytungstic acid sol obtained in S2 onto a conductive glass substrate, and then calcine it to obtain a bismuth-doped WO3 thin film; in this step, the spin-coating-calcine process is repeated 1 to 5 times. S4: The molybdenum-doped peroxytungstic acid sol obtained in S2 is spin-coated onto the bismuth-doped WO3 film obtained in S3. After calcination, a Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic film is obtained. In this step, the spin-coating-calcination is repeated 1 to 3 times.

2. The method for preparing the Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic thin film according to claim 1, characterized in that: The concentration of the peroxytungstic acid solution described in S1 is 0.1 to 1 M.

3. The method for preparing the Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic thin film according to claim 1, characterized in that: The ratio of bismuth atoms to tungsten atoms in the bismuth-doped peroxytungstic sol described in S2 is 1:10 to 1:

100.

4. The method for preparing the Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic thin film according to claim 1, characterized in that: The substance containing Bi in S2 is one or more of the following: metallic bismuth powder, bismuth chloride, bismuth nitrate pentahydrate, and bismuth oxide; the heating method for heating until the substance containing Bi is completely dissolved is water bath heating, and the heating temperature is 40–100 °C.

5. The method for preparing the Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic thin film according to claim 1, characterized in that: The molybdenum-doped peroxytungstic acid sol described in S2 has a molybdenum atom to tungsten atom ratio of 1:1 to 1:

100.

6. The method for preparing the Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic thin film according to claim 1, characterized in that: The substance containing Mo in S2 is one or more of molybdenum sulfide, molybdic acid, molybdenum dioxide, and molybdenum trioxide; the heating method for heating until the substance containing Mo is completely dissolved is water bath heating, and the heating temperature is 30-100℃.

7. The method for preparing the Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic thin film according to claim 1, characterized in that: In S3, the spin coating rate is 1500–3500 rpm, and the spin coating time is 20–45 s.

8. The method for preparing the Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic thin film according to claim 1, characterized in that: In S4, the spin coating rate is 1000–3000 rpm, and the spin coating time is 15–55 s.

9. The method for preparing a Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic thin film according to claim 1, characterized in that: The calcination temperature in S3 and S4 is 50–500 °C, and the calcination time is 1–10 h.

10. A Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic thin film, characterized in that: The electrochromic thin film was prepared by the method for preparing Mo-WO3 and Bi-WO3 layer-by-layer composite electrochromic film as described in claim 1.

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