Cwo nanocrystals, electrochromic thin films, electrochromic devices, methods of preparation and applications

Abstract

The application provides CWO nanocrystals, an electrochromic film, an electrochromic device, a preparation method and application, and relates to the technical field of electrochromic technology.The preparation method of the CWO nanocrystals comprises the following steps: taking water and ethylene glycol as solvents, stirring and adding a reducing agent and a precursor to prepare a precursor solution; adding an HCl solution to the precursor solution to adjust the pH; performing high-temperature reflux on the precursor solution after the pH is adjusted to prepare a suspension, and performing dialysis on the suspension; centrifuging the suspension after the dialysis, separating supernatant, and drying to obtain the CWO nanocrystals.The CWO nanocrystals are used in the preparation of a double-waveband zinc-type electrochromic device ZECD for the first time, and the CWO nanocrystals exhibit excellent independent control ability of near-infrared heat and visible light transmittance and optimal cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of electrochromic technology, and particularly relates to CWO nanocrystals, electrochromic thin films, electrochromic devices, preparation methods and applications. Background Technology

[0002] Buildings account for a large proportion of global energy consumption, with nearly half used for regulating indoor heating, cooling, and lighting. Forecasts indicate that building energy consumption will continue to increase from 2010 to 2050. Therefore, developing low-energy building energy-saving technologies is imperative. Electrochromic smart windows (ESWs) offer a promising solution by dynamically adjusting the light entering a room, potentially reducing building energy consumption by up to 20%.

[0003] However, traditional ESWs require external power, which complicates installation, increases costs, and limits energy efficiency. Our previously established solar-charged smart window strategy integrates an innovative zinc-type electrochromic device (ZECD) platform and photovoltaic (PV) equipment to address the intermittent sunlight issue for both electrochromic devices and PV equipment that require external power. However, some current work, particularly PV-ESWs utilizing Prussian blue (PB) materials, limits the modulation of near-infrared (NIR) light, hindering energy efficiency and indoor comfort. Furthermore, the inherent capacity and energy density of ZECDs result in low PV power conversion efficiency, leading to solar energy waste and ZECD overcharging.

[0004] The technology of integrating IoT devices into smart windows in green buildings is rapidly developing and will transform the operation and use of windows. Furthermore, this approach enables the integration of smart windows into solar building systems to address the lack of basic grid connectivity. Therefore, the combination of PV-ZECD windows with IoT devices allows for real-time monitoring of the ZECD window's optical status and, as needed, the discharge of the solar-charged ZECD window, thus enabling the continuous transmission of electricity generated by the PV to indoor electrical appliances. This method improves energy efficiency, increases user comfort, and prevents ZECD overcharging.

[0005] While ZECD windows play a crucial role in PV-ZECD-IoT systems through intelligent dimming, their energy storage function prioritizes efficient energy recovery over large-scale energy storage due to the low mass load of electrochromic materials. Therefore, ZECDs primarily function as channels for transmitting electricity generated by the PV system to indoor devices, dynamically modulating VIS and NIR during power transmission. Thus, developing ZECDs with intelligent near-infrared and visible light control, high cycle energy utilization efficiency, and cycle stability is key to PV-ZECD-IoT systems. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, this invention provides CWO nanocrystals, electrochromic thin films, electrochromic devices, preparation methods, and applications. For the first time, CWO nanocrystals are used to prepare dual-band zinc-type electrochromic devices (ZECDs). CWO nanocrystals exhibit excellent independent control over near-infrared thermal and visible light transmittance, as well as optimal cycling stability, showing no capacity decay after 10,000 cycles, which surpasses existing ZECDs in this respect.

[0007] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0008] The first aspect of this invention provides a method for preparing CWO nanocrystals.

[0009] The preparation method of CWO nanocrystals includes the following steps:

[0010] A precursor solution was prepared by stirring and adding a reducing agent and a precursor using water and ethylene glycol as solvents.

[0011] Add HCl solution to the precursor solution to adjust the pH;

[0012] The precursor solution after pH adjustment was subjected to high-temperature reflux to obtain a suspension, and the suspension was dialyzed.

[0013] The dialyzed suspension was centrifuged, the supernatant was separated, and then dried to obtain CWO nanocrystals.

[0014] Optional:

[0015] The reducing agent is hydrazine hydrate, with a volume fraction of 0.5%-5%;

[0016] The ratio of water to ethylene glycol in the solvent is 3:1;

[0017] The precursors are Na2WO4·2H2O and Cs2CO3, with concentration ranges of 80-200 mmol / L and 10-50 mmol / L, respectively.

[0018] The pH range of the precursor solution is 0.1-2;

[0019] The high-temperature reflux temperature range is 80-150℃, and the reflux time is 2-10h.

[0020] A second aspect of the present invention provides a CWO nanocrystal.

[0021] A CWO nanocrystal is prepared based on the CWO nanocrystal preparation method described in the first aspect.

[0022] A third aspect of the present invention provides an electrochromic thin film.

[0023] An electrochromic thin film includes a conductive substrate and a CWO nanocrystal layer sprayed onto the conductive substrate, wherein the CWO nanocrystal layer is prepared based on the CWO nanocrystals described in the second aspect.

[0024] The fourth aspect of this invention provides a method for preparing an electrochromic thin film.

[0025] A method for preparing the electrochromic thin film according to the third aspect includes the following steps:

[0026] Clean the conductive substrate before spraying;

[0027] At an appropriate temperature, the CWO nanocrystal solution is sprayed onto a clean conductive substrate;

[0028] The coated conductive substrate is annealed at high temperature to obtain an electrochromic film.

[0029] Optionally, the conductive substrate is ITO / glass.

[0030] Optionally, CWO nanocrystals can be dissolved in water to prepare a CWO nanocrystal solution with a concentration of 10-50 mg / mL.

[0031] The spraying temperature of CWO nanocrystal solution is 50-100℃, preferably 60-90℃;

[0032] The annealing temperature is 90-150℃, and the time is 10-30h.

[0033] The fifth aspect of the present invention provides an electrochromic device.

[0034] An electrochromic device, comprising:

[0035] The working electrode uses an electrochromic thin film as described in the third aspect;

[0036] The counter electrode, or a counter electrode and a reference electrode, is made of zinc foil.

[0037] The electrolyte is a mixed solution using propylene carbonate as solvent and zinc perchlorate-aluminum perchlorate or zinc sulfate-aluminum sulfate as solute.

[0038] Optionally, the concentration of zinc sulfate is 0.1-0.9 mol / L, and the concentration of aluminum sulfate is 0.1-2.0 mol / L; the concentration of zinc perchlorate is 0.1-0.9 mol / L, and the concentration of aluminum perchlorate is 0.1-2.0 mol / L.

[0039] The fifth aspect of the present invention provides an application.

[0040] The application of the electrochromic thin film described in the third aspect in converting solar energy into power for indoor devices.

[0041] The above one or more technical solutions have the following beneficial effects:

[0042] 1. This invention uses hydrazine hydrate as a reducing agent to prepare electrochromic CWO nanocrystals for ZECD. Gram-level production can be achieved in the laboratory, and the scale-up can be scaled up for mass production to meet potential practical applications.

[0043] 2. This is the first time CWO nanocrystals have been used in a dual-band ZECD. These nanocrystals exhibit excellent independent control over near-infrared thermal and visible light transmittance (ΔT = 73.0% at 700 nm; ΔT = 83.7% at 1200 nm). Furthermore, they demonstrate superior cycling stability, showing no capacity decay after 10,000 cycles, surpassing existing ZECDs in this respect (e.g., Adv. Mater., 2023, 2301141; Angew. Chem. Int. Ed., 2024, 63, e2023179).

[0044] 3. The ZECD has the ability to self-charge quickly, comparable to the performance of advanced self-charging batteries (e.g., Adv. Mater., 2024, 2314050; Adv. Energy Mater., 2024, 14, 2303475). This excellent self-charging capability indicates that the ZECD can also generate electricity at night.

[0045] 4. This ZECD offers superior insulation with a 10°C difference between "bright" and "dark" modes. This level of insulation is comparable to dynamic windows utilizing reversible metal deposition (e.g., Nat. Sustain., 2023, 6, 428; ACS Energy Lett., 2021, 6, 3906).

[0046] 5. The integration of a dual-band ZECD and a self-developed IoT control device enables continuous transmission of photovoltaic power, supplying power to indoor devices while also intelligently controlling visible and near-infrared light transmission. Using an improved Joule thief circuit integrated with a commercial WiFi control system, the dual-operation IoT control device achieves intelligent dimming by adjusting a smartphone between 0.7V (“cool” mode) and 0.18V (“dark” mode).

[0047] 6. The PV-ZECD-I0T platform can serve as a blueprint for future glass curtain wall designs. In the future, curtain walls are envisioned as transparent displays that intelligently control VIS and NIR, while seamlessly transmitting the electricity generated by PV to power indoor electrical equipment.

[0048] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0049] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0050] Figure 1 The prepared CWO nanocrystalline structure.

[0051] Figure 2(a) is the XRD pattern of the CWO electrochromic film prepared in Example 1.

[0052] Figure 2(b) shows the morphology of the CWO electrochromic film prepared in Example 1.

[0053] Figure 3 This is a macroscopic diagram of the reversible color switching process of the CWO electrochromic thin film prepared in Example 1.

[0054] Figure 4 The transmittance curves of the CWO electrochromic film prepared in Example 1 at different voltages are shown.

[0055] Figure 5(a) shows the transmittance of CWO during the self-coloring process at a wavelength of 700 nm as a function of time.

[0056] Figure 5(b) shows the transmittance of CWO thin film during the coloring / fading process at a wavelength of 1200 nm as a function of time.

[0057] Figure 6(a) shows the test results of the CWO electrochromic thin film prepared in Example 1 after 10,000 CV cycles.

[0058] Figure 6(b) shows the transmittance spectrum of the CWO electrochromic thin film prepared in Example 1 before and after 10,000 cycles at wavelengths of 700 nm and 1200 nm.

[0059] Figure 7(a) shows the CV curve of the CWO electrochromic film prepared in Example 2 in pure zinc perchlorate-propylene carbonate electrolyte.

[0060] Figure 7(b) shows the transmittance curves of the CWO electrochromic film prepared in Example 2 at different voltages.

[0061] Figure 7(c) shows the response time of the CWO electrochromic film prepared in Example 2 at 700 nm.

[0062] Figure 7(d) shows the response time of the CWO electrochromic film prepared in Example 2 at 1200 nm.

[0063] Figure 8 The transmittance curves of the CWO electrochromic film prepared for Comparative Example 2 at different voltages in aqueous electrolytes (zinc sulfate, aluminum sulfate).

[0064] Figure 9 This is a diagram of the electrochromic process of CWO / / Zn / / CWO ZECD.

[0065] Figure 10 This is a diagram illustrating the thermal insulation effect of CWO / / Zn / / CWO ZECD.

[0066] Figure 11 A schematic diagram illustrating the use of a CWO / / Zn / / CWO ZECD in conjunction with a self-made IoT device for remote control.

[0067] Figure 12 The circuit structure and schematic diagram of a self-made Internet of Things (IoT) controller.

[0068] Figure 13 A schematic diagram illustrating how CWO / / Zn / / CWO ZECD, photovoltaic cells, and self-made IoT devices can be used to achieve modular and efficient conversion of solar energy to power indoor devices. Detailed Implementation

[0069] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0070] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0071] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0072] The overall concept proposed in this invention is as follows:

[0073] Integrated solar cells and electrochromic windows have made significant contributions to green building, with solar-charged zinc anode electrochromic devices (ZECDs) playing a crucial role. S This presents an opportunity to solve the problem of intermittent solar charging. However, ZECD S Limited energy storage capacity leads to inefficient use of solar energy and ZECD S Overcharging. This invention employs a spectrally selective dual-band ZECD to continuously deliver solar energy to indoor devices through remote control of the daytime repeating bleach-color (i.e., charge-discharge) cycle.

[0074] The method of this invention utilizes synthesized h-Cs 0.32 WO3 (CWO) nanocrystals were used to prepare CWO / / Zn / / CWO ZECDs. The CWO / / Zn / / CWO ZECD platform demonstrated excellent dynamic modulation of VIS and NIR. By integrating with PV cells and IoT systems, it enables remote transmission of photovoltaic power to indoor devices, prevents ZECD overcharging, and improves the energy efficiency of window systems. This comprehensive approach not only ensures optimized lighting conditions but also guarantees efficient energy management throughout the building.

[0075] This invention:

[0076] (1) In a first aspect, a method for preparing CWO nanocrystals is provided, comprising the following steps:

[0077] Na₂WO₄·2H₂O and Cs₂CO₃ were added sequentially to a mixed solution of water, ethylene glycol, and hydrazine hydrate under magnetic stirring to prepare a precursor solution. After the mixture formed a clear and transparent solution, the pH was adjusted with HCl and stirring continued. Subsequently, the precursor solution was transferred to a round-bottom flask and refluxed at high temperature, and then the suspension was transferred to a dialysis bag for dialyzing. Then, the suspension was centrifuged to separate large particles, and the supernatant was used as ink for spraying.

[0078] (2) In a second aspect, the present invention provides a method for preparing a CWO electrochromic thin film, comprising the following steps:

[0079] ITO / glass was treated with a plasma cleaner. Then, a CWO nanocrystalline solution was sprayed onto the cleaned ITO / glass at an appropriate temperature. High-temperature annealing was then performed to obtain a CWO electrochromic film, which improves near-infrared transmittance.

[0080] (3) In a third aspect, the present invention provides a method for remote control by integrating a PV-ZECD with an Internet of Things system, including the following:

[0081] An IoT system based on a commercial WiFi control system was designed. We propose an improved Joule-stealing circuit that can independently control the visible and near-infrared light of a CWO / / Zn / / CWO ZECD prototype device. A PNP germanium switching transistor is used to achieve a low on-state voltage of 0.18V to block visible and near-infrared light.

[0082] This invention is the first to use hexagonal cesium-tungsten bronze (h-Cs) 0.32Dual-band ZECDs were fabricated using WO3 (CWO) nanocrystals. Due to their significant ability to independently control near-infrared (NIR) and visible light (VIS) transmittance (ΔT = 73.0%, 700 nm; ΔT = 83.7%, 1200 nm) and excellent cycling stability (optical contrast at 1200 nm decreased by 0.8% after 10,000 cycles).

[0083] The prototype device proposed in this invention (i.e., CWO / / Zn / / CWO ZECD) has exceptional thermal insulation capabilities, exhibiting a 10°C difference between "bright" and "dark" modes.

[0084] Furthermore, this invention designs an Internet of Things (IoT) controller that allows independent control of the NIR and VIS of the CWO / / Zn / / CWO ZECD window via a smartphone, enabling the solar-charged window to remotely and continuously discharge during the day. Such a window represents an interesting potential technology with significant implications for future green building.

[0085] More specifically:

[0086] (1) First aspect:

[0087] This invention discloses a method for preparing CWO nanocrystals, which are synthesized via a one-pot wet chemical doping route. Specifically, it includes:

[0088] Using water and ethylene glycol as solvents, a reducing agent and a precursor were added sequentially to a mixed solvent under magnetic stirring to prepare a precursor solution. After the precursor solution became clear and transparent, the pH was adjusted with HCl while stirring continued. Subsequently, the precursor solution was transferred to a round-bottom flask and refluxed at high temperature. The suspension was then transferred to a dialysis bag for dialyzing. Large particles were then separated by centrifugation, and the supernatant was dried to obtain CWO nanocrystals. The supernatant was used as ink for spray painting.

[0089] Going further:

[0090] The reducing agent is hydrazine hydrate, with a volume fraction of 0.5%-5%, preferably 1%-3%;

[0091] The ratio of solvent water to ethylene glycol is 3:1;

[0092] The precursors are Na2WO4·2H2O and Cs2CO3, with the concentration of Na2WO4·2H2O ranging from 80 to 200 mmol / L, preferably 100 to 150 mmol / L; and the concentration of Cs2CO3 ranging from 10 to 50 mmol / L, preferably 30 to 40 mmol / L.

[0093] After the precursor solution becomes clear and transparent, adjust the pH with HCl and continue stirring. The pH adjustment range is 0.1-2, preferably 0.5-1.

[0094] The mixing time is 10-60 min, preferably 20-40 min;

[0095] The precursor solution was transferred to a round-bottom flask and refluxed at a temperature of 80-150°C for 2-10 hours.

[0096] After high-temperature reflux, the suspension is transferred to a dialysis bag for dialysis. The dialysis time is 3-14 days, and the water is changed every 3-6 hours.

[0097] The dialyzed suspension was centrifuged to separate large particles, and the supernatant was used as ink for spraying. The centrifugation speed was 1000-4000 rpm, and the centrifugation time was 10-30 minutes.

[0098] (2) Second aspect:

[0099] A CWO nanocrystal is prepared based on the above-described method for preparing CWO nanocrystals.

[0100] (3) The third aspect:

[0101] An electrochromic thin film includes a conductive substrate and a CWO nanocrystal layer sprayed onto the conductive substrate, wherein the CWO nanocrystal layer is prepared based on the CWO nanocrystals.

[0102] (4) Fourth aspect:

[0103] A method for preparing an electrochromic thin film includes the following steps:

[0104] The conductive substrate, which is ITO / glass, is treated with a plasma cleaner for 50-150 seconds.

[0105] CWO nanocrystal solutions were prepared by dissolving CWO nanocrystals in water. The concentration of the CWO nanocrystal solution was 10-50 mg / mL, and the volume was 1-5 mL.

[0106] CWO nanocrystal solution is sprayed onto cleaned ITO / glass at an appropriate temperature. The spraying temperature is 50-100℃, preferably 60-90℃; the effective area of ​​ITO / glass is 5-10 cm². 2 ;

[0107] The coated film is annealed at high temperature to obtain a CWO electrochromic film. The annealing temperature is 90-150℃ and the time is 10-30h.

[0108] (5) Fifth aspect:

[0109] like Figure 12 As shown, an electrochromic thin film is provided for the application of solar energy conversion to power indoor devices.

[0110] The following examples, comparative examples, and application examples are provided:

[0111] In addition, the experimental methods described in the following embodiments are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0112] Example 1

[0113] A method for preparing a CWO electrochromic thin film includes the following steps:

[0114] (1) Preparation of CWO materials

[0115] In a mixture of 120 mL H₂O, 60 mL ethylene glycol, and 1.8 mL hydrazine hydrate, Na₂WO₄·2H₂O (100 mmol / L) and Cs₂CO₃ (40 mmol / L) were added sequentially under magnetic stirring to prepare a precursor solution, which was stirred for 0.5 h. After the mixture formed a clear and transparent solution, the pH was adjusted to 0.9 with HCl and stirred for another 0.5 h. Subsequently, the precursor solution was transferred to a round-bottom flask and refluxed at 80 °C for 3 h. The suspension was then transferred to a dialysis bag and dialyzed for 3 days, with the water changed every 3 hours. The suspension was then centrifuged at 1000 rpm for 10 minutes to separate large particles, and the supernatant was used as ink for spraying.

[0116] (2) Preparation of CWO electrochromic thin film

[0117] ITO / glass was treated with a plasma cleaner for 100 seconds before spraying. Then, CWO nanosheet colloid (3.0 mL, 15 mg / mL; ethanol as solvent) was sprayed onto the cleaned ITO / glass (effective area 3 x 3 cm) at 60°C. 2 Then, CWO electrochromic films were obtained by annealing at 100°C for 24 hours to improve near-infrared transmittance.

[0118] (3) Preparation of organic electrolytes

[0119] Zn was prepared by dissolving zinc perchlorate and aluminum perchlorate in propylene carbonate at a molar ratio of 1:9. 2+ -A1 3+ Mixed electrolytes.

[0120] The electrochromic properties of the obtained electrochromic CWO electrochromic thin film were characterized:

[0121] (4) The thin film prepared in step (2) is used as the working electrode, and the zinc foil is used as the counter electrode and reference electrode, and is placed in the electrolyte prepared in step (3). The electrochemical performance is characterized by connecting an electrochemical workstation to the two-electrode system. At the same time, the electrochemical workstation is coupled with a UV-Vis spectrometer to characterize the electrochromic performance.

[0122] The structure of the CWO nanocrystals of the present invention was determined by X-ray diffraction, as shown in Figure 2(a). The XRD pattern shows that the composition of the obtained material is Cs. 0.32 WO3. The morphology of the material was observed using transmission electron microscopy, as shown in Figure 2(b). The CWO morphology is that of a nanoplate. When different voltages between 0.1 and 1.8 V were applied using an electrochemical workstation, the film exhibited different colors, such as... Figure 3 As shown, when a voltage of 0.1V is applied, the film is dark blue; when a voltage of 0.7V is applied, the film is light blue; and when a voltage of 1.8V is applied, the film is colorless, clearly illustrating three optical states: bright, cool, and dark. Applying different voltages will result in films with different states.

[0123] When performing in-situ monitoring of color switching using a UV-Vis spectrometer, the transmittance curves for different colors are as follows: Figure 4 As shown, the tunable visible and near-infrared transmittance of the CWO electrode is demonstrated, showcasing the special optical modulation (ΔT = 73.0% at 700 nm and ΔT = 83.7% at 1200 nm).

[0124] Color switching time t during bleaching and coloring processes b and t c Defined as the time required to achieve 90% transmittance, the kinetics of the CWO thin film were evaluated on a CWO / / Zn / / CWO platform for dynamic optical transmittance measurement between different operating modes (i.e., bright, cold, and dark states). The switching speed (1.8–0.1 V) from the "bright" mode to the "dark" mode was measured at 700 nm (Fig. 5(a)) and yielded a t of 18.4 s. c and 15.2s t b The switching speed measured at 1200nm (Figure 5(b)) was t. c =6.7s,t b =111.3s.

[0125] The cycle life of the film was determined by cyclic voltammetry. The CWO film retained almost all of its initial capacity (Fig. 6(a)) and after 10,000 CV cycles, the optical contrast decreased by only 0.8% (at 1200 nm) (Fig. 6(b)), demonstrating excellent reversibility and repeatability.

[0126] Example 2

[0127] A method for preparing a CWO electrochromic thin film includes the following steps:

[0128] (1) Preparation of CWO materials

[0129] In a mixture of 120 mL H₂O, 60 mL ethylene glycol, and 3.6 mL hydrazine hydrate, Na₂WO₄·2H₂O (120 mmol / L) and Cs₂CO₃ (35 mmol / L) were added sequentially under magnetic stirring to prepare a precursor solution, which was stirred for 0.5 h. After the mixture formed a clear and transparent solution, the pH was adjusted to 0.9 with HCl and stirred for another 0.5 h. Subsequently, the precursor solution was transferred to a round-bottom flask and refluxed at 80 °C for 3 h. The suspension was then transferred to a dialysis bag and dialyzed for 3 days, with the water changed every 3 hours. The suspension was then centrifuged at 3000 rpm for 10 minutes to separate large particles, and the supernatant was used as ink for spraying.

[0130] (2) Preparation of CWO electrochromic thin film

[0131] ITO / glass was treated with a plasma cleaner for 100 seconds before spraying. Then, CWO nanosheet colloid (1.0 mL, 40 mg / mL; ethanol as solvent) was sprayed onto the cleaned ITO / glass (effective area 3 x 3 cm) at 50°C. 2 Then, CWO electrochromic films were obtained by annealing at 100°C for 24 hours to improve near-infrared transmittance.

[0132] (3) Preparation of organic electrolytes

[0133] A Zn-containing compound was prepared by dissolving zinc perchlorate in propylene carbonate at a molar concentration of 1M. 2+ Electrolytes.

[0134] The electrochromic properties of the obtained electrochromic CWO electrochromic thin film were characterized:

[0135] (4) The electrochromic performance characterization method is the same as in Example 1. When different voltages between 0.1-1.8V are applied by an electrochemical workstation, the film still exhibits reversible color switching (colorless, light blue, dark blue).

[0136] Its electrochemical activity and optical modulation ( Figures 7(a)-7(b) The performance of the CWO electrode is inferior to that tested in zinc perchlorate, aluminum perchlorate, and propylene carbonate electrolytes. Figure 4 -Figure 5), this is attributed to the CWO on Zn 2+The CWO film exhibits low electrochemical activity. The kinetics of the CWO / / Zn / / CWO film between different operating modes (i.e., bright, cold, and dark) were evaluated on a CWO / / Zn / / CWO platform with dynamic optical transmittance measurements. The switching speed (1.8–0.1 V) from the "bright" mode to the "dark" mode, measured at 700 nm (Fig. 7(c)), yielded a tc of 57.8 s and a tb of 23.2 s, while at 1200 nm (Fig. 7(d)), the switching speed was tc = 28.2 s and tb = 153.6 s.

[0137] The cycle life of the film was determined by cyclic voltammetry, and the CWO film retained almost all of its initial capacity. Figure 6a Furthermore, after 10,000 CV cycles, the optical contrast decreased by only 0.8% (at 1200 nm). Figure 6b It exhibits excellent reversibility and repeatability.

[0138] Comparative Example 1

[0139] A method for preparing a CWO electrochromic thin film includes the following steps:

[0140] (1) Preparation of CWO materials

[0141] In a mixture of 120 mL H₂O, 60 mL ethylene glycol, and 5.4 mL hydrazine hydrate, Na₂WO₄·2H₂O (150 mmol / L) and Cs₂CO₃ (50 mmol / L) were added sequentially under magnetic stirring to prepare a precursor solution, which was stirred for 0.5 h. After the mixture formed a clear and transparent solution, the pH was adjusted to 0.8 with HCl and stirred for another 0.5 h. Subsequently, the precursor solution was transferred to a round-bottom flask and refluxed at 90 °C for 5 h. The suspension was then transferred to a dialysis bag and dialyzed for 3 days, with the water changed every 3 hours. The suspension was then centrifuged at 1000 rpm for 20 minutes to separate large particles, and the supernatant was used as ink for spraying.

[0142] (2) The preparation of the CWO electrochromic film is the same as in Example 1.

[0143] (3) Preparation of aqueous electrolytes

[0144] Zn was prepared by dissolving zinc sulfate and aluminum sulfate in water at a molar ratio of 1:9. 2+ -A1 3+ Mixed aqueous electrolytes.

[0145] The electrochromic properties of the obtained electrochromic CWO electrochromic thin film were characterized:

[0146] (4) The electrochromic performance characterization method is the same as in Example 1. When different voltages between 0.1-1.8V are applied by an electrochemical workstation, the film still exhibits reversible color switching (colorless, light blue, dark blue).

[0147] Its light modulation ( Figure 8 The performance of the CWO electrode is inferior to that tested in zinc perchlorate, aluminum perchlorate, and propylene carbonate electrolytes. Figure 4 -5), and almost no modulation in the near-infrared region (1400-2000nm), which is attributed to the low activity of the CWO electrochromic film in aqueous electrolytes.

[0148] Application Example 1

[0149] Dual-band electrochromic smart window based on zinc anode

[0150] The preparation steps are as follows:

[0151] (1) Component assembly

[0152] Cleaning: Take two 5×5cm pieces 2 The ITO glass was treated with a plasma cleaner for 100 seconds and then dried with nitrogen for later use.

[0153] Film formation: As described in step (2) of Example 1, a 3×3cm film is sprayed onto the center of each of the two glass plates. 2 CWO electrochromic film;

[0154] Assembly: Apply 2mm wide conductive copper tape around the edges of two prepared ITO glass pieces and press them firmly. Then, apply two layers of 3M transparent double-sided tape over the conductive copper tape, ensuring the tape completely covers the copper tape without contacting the electrolyte. Next, cut out a zinc foil frame, ensuring that when the zinc frame is attached to the double-sided tape on the glass, 3-5mm of its edges protrude inwards without obstructing the CWO film. Finally, place another ITO glass piece without the zinc frame on top and press the two pieces together to form a CWO / / Zn / / CWO electrochromic device.

[0155] Compaction: Place the device under a heavy object and compact it for 4-6 days;

[0156] Preparation of gel electrolyte: as described in step (3) of Example 1, and add polymethyl methacrylate (PMMA, 1.2 mg / mL) to it and stir until clear and transparent;

[0157] Electrolyte injection: Remove the compacted electrochromic device and inject the gel electrolyte into the cavity of the device using a syringe;

[0158] (2) Electrochromic process of CWO / / Zn / / CWO electrochromic device

[0159] Digital photographs of the CWO / / Zn / / CWO ZECD prototype device in three different modes, as shown below. Figure 9 As shown, it has good light transmission in "cool" mode and effective privacy in "dark" mode.

[0160] (3) Thermal insulation performance of CWO / / Zn / / CWO electrochromic devices

[0161] In addition to its excellent self-charging performance, CWO / / Zn / / CWO ZECD also has superior thermal insulation properties, such as... Figure 10 As shown, the CWO / / Zn / / CWO ZECD was placed on a heating plate set to 40°C, demonstrating the variation in surface temperature depending on the CWO / / Zn / / CWO ZECD's operating mode. In "Bright" mode, the CWO / / Zn / / CWO ZECD's high light transmittance allows more heat to pass through the heating plate, reaching a surface temperature of 34.0°C. Switching to "Cold" mode blocks some heat, causing the surface temperature to drop to 27.6°C. Subsequently, switching to "Dark" mode restricts heat transfer through the device, causing the surface temperature to drop to 23.8°C. The significant surface temperature difference (10.2°C) between "Bright" and "Dark" modes indicates that the CWO / / Zn / / CWO ZECD prototype device exhibits significant thermal insulation capabilities. The CWO / / Zn / / CWO ZECD has great potential for regulating indoor temperature and reducing building energy consumption.

[0162] (4) CWO / / Zn / / CWO ZECD is used in conjunction with a self-made IoT device to realize remote control of color change of photos.

[0163] like Figure 11 As shown, this embodiment provides a self-made WiFi control system. Figure 12 This is a schematic diagram of the circuit structure and principle of a homemade WiFi control system. The WiFi control system consists of three parts: a Joule thief circuit, a WiFi controller, and an LED. The WiFi controller allows for easy control of the Joule thief circuit, thereby controlling the CWO / / Zn / / CWOZECD device.

[0164] A light tap on the "0.7V" (i000) power switch on the phone screen triggers the activation of relay K2 via the homemade WiFi control system. The 0.7V LED indicator lights up, initiating the discharge of the CWO / / Zn / / CWO ZECD device prototype from "on" to "cold" mode. To fully discharge the device prototype in "cold" mode, the relay K1 must be activated by pressing the "0.18V" (i002) power switch on the phone screen. Figure 12At this point, the 0.18V LED indicator lights up. Therefore, the prototype device switches to "dark" mode, which also involves energy recovery. Subsequent energy transfer occurs when the "dark" prototype device is connected to a commercial solar panel for charging and then switches back to "bright" mode. Simultaneously, it stores and transports electricity generated by the photovoltaic system. In short, the prototype device's round-trip bleaching and coloring process enables dynamic control of VIS and NIR.

[0165] (5) Smart window for continuous solar energy conversion integrating CWO / / Zn / / CWO ZECD and IoT system

[0166] like Figure 13 The diagram shows a modular and efficient conversion of solar energy to power indoor devices, achieved by using CWO / / Zn / / CWO ZECD and photovoltaic cells in conjunction with a self-made IoT device.

[0167] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing hexagonal cesium-doped tungsten bronze (CWO) nanocrystals, characterized in that, Includes the following steps: A precursor solution was prepared by stirring and adding a reducing agent and a precursor using water and ethylene glycol as solvents. Add HCl solution to the precursor solution to adjust the pH; The precursor solution after pH adjustment was subjected to high-temperature reflux to obtain a suspension, and the suspension was dialyzed. The dialyzed suspension was centrifuged, the supernatant was separated, and dried to obtain hexagonal cesium-doped tungsten bronze (CWO) nanocrystals. The reducing agent is hydrazine hydrate, with a volume fraction of 0.5%-5%; The volume ratio of water to ethylene glycol in the solvent is 2:1; The pH range of the precursor solution is 0.1-2.

2. The method for preparing hexagonal cesium-doped tungsten bronze (CWO) nanocrystals as described in claim 1, characterized in that: The precursors are Na2WO4·2H2O and Cs2CO3, with concentration ranges of 80-200 mmol / L and 10-50 mmol / L, respectively; The high-temperature reflux temperature range is 80-150°C, and the reflux time is 2-10 h.

3. A hexagonal cesium-doped tungsten bronze (CWO) nanocrystal, characterized in that, It was prepared according to the preparation method of hexagonal phase cesium-doped tungsten bronze (CWO) nanocrystals as described in any one of claims 1-2.

4. An electrochromic thin film, characterized in that, The invention includes a conductive substrate and a hexagonal cesium-doped tungsten bronze (CWO) nanocrystal layer sprayed onto the conductive substrate, wherein the hexagonal cesium-doped tungsten bronze (CWO) nanocrystal layer is prepared based on the hexagonal cesium-doped tungsten bronze (CWO) nanocrystals described in claim 3.

5. A method for preparing the electrochromic thin film according to claim 4, characterized in that, Includes the following steps: Clean the conductive substrate before spraying; At an appropriate temperature, a solution of hexagonal cesium-doped tungsten bronze (CWO) nanocrystals was sprayed onto a clean conductive substrate. The coated conductive substrate is annealed at high temperature to obtain an electrochromic film.

6. The method for preparing an electrochromic thin film as described in claim 5, characterized in that, The conductive substrate is ITO glass.

7. The method for preparing an electrochromic thin film as described in claim 5, characterized in that: A hexagonal cesium-doped tungsten bronze (CWO) nanocrystal solution was prepared by dissolving hexagonal cesium-doped tungsten bronze (CWO) nanocrystals in water, with a concentration of 10-50 mg / mL. The spraying temperature for hexagonal cesium-doped tungsten bronze (CWO) nanocrystal solution is 50-100°C. The annealing temperature is 90-150°C, and the time is 10-30 h.

8. The method for preparing an electrochromic thin film as described in claim 7, characterized in that: The spraying temperature for hexagonal cesium-doped tungsten bronze (CWO) nanocrystal solution is 60-90°C.

9. An electrochromic device, characterized in that, include: The working electrode uses the electrochromic thin film as described in claim 4; The counter electrode, or both the counter electrode and the reference electrode, is made of zinc foil. The electrolyte is a mixed solution using propylene carbonate as solvent and zinc perchlorate-aluminum perchlorate or zinc sulfate-aluminum sulfate as solute.

10. The electrochromic device as described in claim 9, characterized in that, The concentration of zinc sulfate is 0.1-0.9 mol / L, and the concentration of aluminum sulfate is 0.1-2.0 mol / L; the concentration of zinc perchlorate is 0.1-0.9 mol / L, and the concentration of aluminum perchlorate is 0.1-2.0 mol / L.

11. The application of the electrochromic thin film of claim 4 in converting solar energy into power for indoor devices.

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