Bi2o3 / cof heterojunction composite material and preparation method and application thereof

Abstract

The application discloses a Bi2O3 / COF heterojunction composite material and a preparation method and application thereof. The preparation method of the Bi2O3 / COF heterojunction composite material comprises the following steps: (1) synthesizing a covalent organic framework COF-1 by reacting cyanuric chloride and anhydrous piperazine at room temperature; (2) dissolving bismuth salt and urea in a solvent, adding the COF-1, and growing Bi2O3 nanosheets on the COF-1 framework in situ through a solvothermal reaction to obtain the Bi2O3 / COF heterojunction composite material. The Bi2O3 / COF heterojunction composite material and the preparation method and application thereof are characterized in that the Bi2O3 nanosheets are grown on the COF framework in situ through a one-step solvothermal method, a close heterojunction interface is formed, the porous network of the COF is utilized to inhibit the agglomeration of the Bi2O3, a built-in electric field is formed through Fermi level difference, the working voltage window of an electrode is widened, and the technical problems existing when the Bi2O3 material is used as a negative electrode material are solved.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage materials technology, specifically relating to a Bi2O3 / COF heterojunction composite material, its preparation method, and its application. Background Technology

[0002] Supercapacitors have attracted much attention due to their high power density, rapid charge / discharge capability, and long cycle life. However, compared to batteries, supercapacitors have a lower energy density, limiting their large-scale application. According to the energy density formula... Improving specific capacitance and widening the operating voltage window are key to increasing energy density.

[0003] Bismuth oxide (Bi2O3), as a typical pseudocapacitive material, has advantages such as high theoretical specific capacitance, low cost, environmental friendliness, and abundant resources, making it an ideal anode material. However, Bi2O3 exhibits severe volume expansion and is prone to agglomeration during charge and discharge, resulting in poor rate performance and cycle stability.

[0004] Covalent organic frameworks (COFs) are a class of porous crystalline materials with tunable pore size, high specific surface area, and designable functional groups, giving them unique advantages in the field of electrochemical energy storage. However, the inherently low conductivity and limited accessibility of active sites in COFs restrict their performance as electrode materials on their own.

[0005] To address the limitations of single-material applications, constructing heterojunctions is an effective strategy. When two materials at different energy levels come into contact, a built-in electric field spontaneously forms at the interface, promoting charge transfer and reaction kinetics.

[0006] In view of this, the present invention proposes a novel heterojunction composite material, its preparation method, and its application. By combining Bi₂O₃ with COFs having different electronic structures to construct a heterojunction, the operating voltage window of the electrode is broadened, allowing the same electrode to be used simultaneously as the positive and negative electrodes of a supercapacitor. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing Bi2O3 / COF heterojunction composite materials. By using a one-step solvothermal method, Bi2O3 nanosheets are grown in situ on a COF framework to form a tight heterojunction interface. This method utilizes the porous network of COF to suppress Bi2O3 aggregation and forms a built-in electric field through the Fermi level difference. This widens the working voltage window of the electrode and solves the technical problems existing when Bi2O3 is used as a negative electrode material.

[0008] To achieve the above objectives, the technical solution adopted is as follows:

[0009] A method for preparing a Bi2O3 / COF heterojunction composite material includes the following steps:

[0010] (1) Covalent organic framework COF-1 was synthesized by reacting cyanuric chloride and anhydrous piperazine at room temperature;

[0011] (2) Dissolve bismuth salt and urea in a solvent, add COF-1, and grow Bi2O3 nanosheets in situ on the COF-1 framework through a solvothermal reaction to obtain the Bi2O3 / COF-1 heterojunction composite material.

[0012] Furthermore, in step (1), the synthesis method of COF-1 is as follows: cyanuric chloride is dissolved in 1,4-dioxane, and then triethylamine and piperazine in 1,4-dioxane solution are added in sequence. After stirring the reaction at room temperature, the mixture is centrifuged, washed, and dried to obtain COF-1.

[0013] Furthermore, the bismuth salt is bismuth nitrate, with a concentration of 0.01-0.1 mol / L;

[0014] The urea concentration is 0.01-0.1 mol / L;

[0015] The mass ratio of Bi2O3 to COF-1 in the Bi2O3 / COF-1 heterojunction composite material is 1:1, 5:1, 10:1, or 15:1.

[0016] The solvothermal reaction is carried out at a temperature of 140-160℃ for 8-12 hours.

[0017] Furthermore, the solvothermal reaction is carried out at a temperature of 150°C for 10 hours.

[0018] Furthermore, the solvent is a mixed solution of equal volumes of ethylene glycol and deionized water.

[0019] Another objective of this invention is to provide a Bi2O3 / COF-1 heterojunction composite material with excellent rate performance and good cycle stability.

[0020] To achieve the above objectives, the technical solution adopted is as follows:

[0021] A Bi2O3 / COF heterojunction composite material was prepared using the above-described preparation method.

[0022] Furthermore, the composite material has a nanosheet anchoring structure, wherein COF-1 is a porous framework.

[0023] Furthermore, the working voltage window of the composite material is -1.0 to 0.5 V.

[0024] Another objective of this invention is to provide applications of the aforementioned Bi2O3 / COF-1 heterojunction composite material, which, by utilizing the wide voltage window characteristics of this composite material, can be used in supercapacitors.

[0025] To achieve the above objectives, the technical solution adopted is as follows:

[0026] The above-mentioned Bi2O3 / COF heterojunction composite material is used in supercapacitor electrodes.

[0027] Furthermore, the Bi2O3 / COF heterojunction composite material is coated onto nickel foam as an active material for assembling symmetrical supercapacitors.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] Currently, there are no reports on constructing heterojunctions by combining Bi2O3 with COFs (Chemical Element Materials) with different electronic structures and using them in wide-voltage-window supercapacitors. This invention suppresses Bi2O3 aggregation through the porous network of COF and utilizes the Fermi level difference at the interface to create a built-in electric field, enabling electron transfer from Bi2O3 to COF. This broadens the operating voltage window of the electrode (-1.0~0.5 V), allowing the same electrode to be used as both the positive and negative electrodes of a supercapacitor. The resulting composite material, as a supercapacitor electrode, exhibits a high specific capacitance of 675.4 F / g, excellent rate performance, and good cycle stability. Specific advantages are as follows:

[0030] (1) One-step in-situ growth method to construct a dense heterogeneous interface

[0031] This invention utilizes a one-step solvothermal method to directly grow Bi2O3 nanosheets in situ on a COF-1 framework, forming a tight heterogeneous interface and avoiding phase separation caused by physical mixing. The porous network of COF-1 provides confined space for Bi2O3, effectively suppressing nanosheet aggregation and volume expansion during charge and discharge processes.

[0032] (2) The Fermi level difference drives the formation of the built-in electric field.

[0033] The optical and electronic properties were investigated using UV-Vis absorption spectroscopy and Mott-Schottky analysis. The Bi₂O₃ / COF₁ heterojunction forms a built-in electric field based on the spontaneous alignment of the Fermi levels at the interface. Figure 6 The built-in electric field promotes interfacial charge transfer and ion diffusion kinetics, significantly improving the capacitance and rate performance of the electrode, providing strong evidence for the successful construction of heterojunctions.

[0034] (3) Wide voltage window and dual-function electrode characteristics

[0035] Pure COF-1 operates in the positive potential window (0~0.5 V), while pure Bi2O3 operates in the negative potential window (-1.0~0 V). After recombination, the Bi2O3 / COF-1 heterojunction integrates both potential ranges, achieving a wide voltage window of -1.0~0.5 V. This characteristic allows the same electrode to be used simultaneously as both the positive and negative electrode in a symmetrical supercapacitor, simplifying device assembly.

[0036] (4) Excellent electrochemical performance

[0037] In 6 M KOH electrolyte, the Bi₂O₃ / COF₁ electrode exhibits a specific capacitance of 675.4 F / g at 1 A / g, significantly higher than that of pure Bi₂O₃ (474.0 F / g) and pure COF₁ (256.4 F / g). It retains 77% of its capacitance at 20 A / g, demonstrating excellent rate performance. The assembled symmetrical supercapacitor achieves an energy density of 30.8 Wh / kg (power density 750 W / kg). After 10,000 cycles, the capacitance retention is 95.7%. Attached Figure Description

[0038] Figure 1 (a) X-ray diffraction pattern and (b) Fourier transform infrared spectrum of COF-1, Bi2O3 and Bi2O3 / COF-1.

[0039] Figure 2 Scanning electron microscope images of COF-1, Bi2O3 and Bi2O3 / COF-1: (a) COF-1; (b) Bi2O3; (c) Bi2O3 / COF-1.

[0040] Figure 3 (a) High-resolution transmission electron microscopy image of Bi2O3 / COF-1; (bc) IFFT maps of different phases in the high-resolution transmission electron microscopy (HRTEM) image; (d) Selected area electron diffraction pattern; (e) Elemental distribution map.

[0041] Figure 4 The three-electrode electrochemical performance of Bi2O3 / COF-1 is shown below, including: (a) cyclic voltammetry curves of Bi2O3 / COF-1-X at a scan rate of 20 mV / s; (b) galvanostatic charge-discharge curves of Bi2O3 / COF-1-X at a current density of 1 A / g; (c) cyclic voltammetry curves of COF-1, Bi2O3, and Bi2O3 / COF-1 at a scan rate of 20 mV / s; (d) galvanostatic charge-discharge curves of COF-1, Bi2O3, and Bi2O3 / COF-1 at a current density of 1 A / g; (e) cyclic voltammetry curves of Bi2O3 / COF-1 at different scan rates; and (f) galvanostatic charge-discharge curves of Bi2O3 / COF-1 at different current densities.

[0042] Figure 5 The electrochemical performance of the Bi2O3 / COF-1 assembled into a symmetrical supercapacitor is shown in the following figures: (a) Schematic diagram of Bi2O3 / COF-1 / / Bi2O3 / COF-1 SSC; (b) Cyclic voltammetry curves of Bi2O3 / COF-1 at different operating voltages with a scan rate of 20 mV / s; (c) Constant current discharge curves at different operating voltages with a current density of 1 A / g; (d) Voltammetry curves at different scan rates; (e) Constant current discharge curves at different current densities; (f) Comparison of the supercapacitor with previously reported Ragone plots; and (g) Cyclic stability test.

[0043] Figure 6 (a) are the UV-Vis absorption spectra of Bi₂O₃, COF₁, and Bi₂O₃ / COF₁, and (b) are the UV-Vis absorption spectra of Bi₂O₃, COF₁, and Bi₂O₃ / COF₁. With photon energy The relationship diagrams. (c) Mott-Schottky diagrams of Bi2O3, (d) COF-1 and (e) Bi2O3 / COF-1. (f) Possible band diagrams of Bi2O3 and COF-1 before and after contact. Detailed Implementation

[0044] To further illustrate the Bi2O3 / COF heterojunction composite material, its preparation method, and its applications according to the present invention, and to achieve the intended objectives of the invention, the following detailed description, in conjunction with preferred embodiments, details the specific implementation methods, structures, features, and effects of the Bi2O3 / COF heterojunction composite material, its preparation method, and its applications based on the present invention. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable manner.

[0045] The following will provide a detailed description of the Bi2O3 / COF heterojunction composite material, its preparation method, and its applications, with reference to specific embodiments:

[0046] This invention utilizes the porous network of COF-1 to suppress Bi2O3 aggregation and forms a built-in electric field through the Fermi level difference at the interface, enabling electron transfer from Bi2O3 to COF-1. This broadens the operating voltage window of the electrode (-1.0~0.5 V), allowing the same electrode to be used as both the positive and negative electrodes of a supercapacitor. The resulting composite material, as a supercapacitor electrode, exhibits a high specific capacitance of 675.4 F / g, excellent rate performance, and good cycle stability. The technical solution adopted is as follows:

[0047] A method for preparing a Bi2O3 / COF heterojunction composite material includes the following steps:

[0048] (1) Covalent organic framework COF-1 was synthesized by reacting cyanuric chloride and anhydrous piperazine at room temperature;

[0049] (2) Dissolve bismuth salt and urea in a solvent, add COF-1, and grow Bi2O3 nanosheets in situ on the COF-1 framework through a solvothermal reaction to obtain the Bi2O3 / COF-1 heterojunction composite material.

[0050] In the above technical solution, the abundant N sites in the COF-1 backbone are used for anchoring. Then, Bi2O3 is fixed onto the COF-1 framework through an in-situ solvothermal reaction, forming a tight heterojunction structure of Bi2O3 and COF-1.

[0051] Preferably, in step (1), the synthesis method of COF-1 is as follows: cyanuric chloride is dissolved in 1,4-dioxane, and then triethylamine and piperazine in 1,4-dioxane solution are added in sequence. After stirring at room temperature, the mixture is centrifuged, washed, and dried to obtain COF-1.

[0052] Preferably, the bismuth salt is bismuth nitrate with a concentration of 0.01-0.1 mol / L;

[0053] The urea concentration is 0.01-0.1 mol / L;

[0054] In the Bi2O3 / COF-1 heterojunction composite material, the mass ratio of c to COF-1 is 1:1, 5:1, 10:1, and 15:1.

[0055] The solvothermal reaction is carried out at a temperature of 140-160℃ for 8-12 hours.

[0056] More preferably, the temperature of the solvothermal reaction is 150°C and the reaction time is 10 hours.

[0057] Preferably, the solvent is a mixed solution of equal volumes of ethylene glycol and deionized water.

[0058] A Bi2O3 / COF heterojunction composite material was prepared using the above-described preparation method.

[0059] Preferably, the composite material has a nanosheet anchoring structure, wherein COF-1 is a porous framework and Bi2O3 nanosheets are uniformly anchored on the surface of the COF framework; a tight heterogeneous interface is formed between the two phases. Due to the difference in Fermi levels between COF-1 and Bi2O3, electrons are transferred from Bi2O3 to COF-1, forming a built-in electric field at the interface pointing from Bi2O3 to COF-1.

[0060] Preferably, the working voltage window of the composite material is -1.0 to 0.5 V, and it can be used as a bifunctional electrode (serving as both a positive and a negative electrode).

[0061] The above-mentioned Bi2O3 / COF heterojunction composite material is used in supercapacitor electrodes.

[0062] Furthermore, the Bi2O3 / COF heterojunction composite material, used as the active material, is mixed with a conductive agent and a binder and then coated onto nickel foam for assembling symmetrical supercapacitors. Utilizing its wide voltage window characteristics, symmetrical supercapacitors (using the same composite material for both positive and negative electrodes) can be assembled to achieve high energy density and power density.

[0063] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0064] Example 1: Synthesis of COF-1

[0065] 0.46 g of cyanuric chloride (TC, 0.0025 mol) was dissolved in 15 mL of 1,4-dioxane, and 0.25 mL of triethylamine (TEA) was added. This solution was then quickly poured into 35 mL of a 1,4-dioxane solution containing 0.3225 g of piperazine (PA, 0.00375 mol). The reaction mixture was stirred at room temperature for 30 minutes. The resulting precipitate was separated by centrifugation, washed successively with water, 1,4-dioxane (once), and tetrahydrofuran (twice), and dried to obtain COF-1.

[0066] Example 2: Synthesis of Bi2O3 materials

[0067] Weigh out 0.4368 g 0.1920 g of urea was dissolved in a 60 mL mixture of ethylene glycol and deionized water (1:1 v / v) and stirred until completely dissolved. The clear solution was transferred to a 100 mL PTFE-lined autoclave and kept at 150 °C for 10 hours. After naturally cooling to room temperature, the product was washed three times with ethanol and deionized water and dried at 60 °C to obtain Bi₂O₃.

[0068] Example 3: Preparation of Bi2O3 / COF-1 composite material

[0069] (1) Taking a mass ratio of Bi2O3 to COF-1 of 10:1 as an example, the specific process is as follows:

[0070] Weigh out 0.4368 g Dissolve 0.1920 g of urea in 60 mL of a 1:1 v / v mixture of ethylene glycol and deionized water, and stir until completely dissolved.

[0071] Then add the COF-1 prepared in Example 1 (theoretical Bi2O3 yield is about 210 mg, and the amount of COF-1 added is about 21 mg based on a mass ratio of 10:1), and continue stirring for 1 hour until the mixture is homogeneous. Transfer the mixture to a 100 mL polytetrafluoroethylene-lined autoclave and react at 150 °C for 10 hours.

[0072] Finally, after natural cooling, the product was collected by centrifugation, washed three times with ethanol and deionized water, and dried at 60°C to obtain the Bi2O3 / COF-1 composite material, denoted as Bi2O3 / COF-1-10.

[0073] (2) Following the same method as in step (1), adjust the amount of COF-1 added to obtain composite materials with a Bi2O3:COF-1 mass ratio of 1:1, 5:1, 10:1, and 15:1, which are respectively denoted as Bi2O3 / COF-1-1, Bi2O3 / COF-1-5, Bi2O3 / COF-1-10, and Bi2O3 / COF-1-15.

[0074] Comparative experiment: Pure Bi2O3 and pure COF-1 electrodes (i.e., Examples 1-2, respectively) were prepared as comparisons.

[0075] Example 4.

[0076] The specific operating steps are as follows:

[0077] Weigh out 0.001 mol Dissolve 0.001 mol of urea in 60 mL of a 1:1 v / v mixture of ethylene glycol and deionized water, and stir until completely dissolved.

[0078] Then add the COF-1 prepared in Example 1 (Bi2O3 to COF-1 mass ratio 10:1), and continue stirring for 1 hour until homogeneous. Transfer the mixture to a 100 mL polytetrafluoroethylene-lined autoclave and react at 140 °C for 12 h.

[0079] Finally, after natural cooling, the product was collected by centrifugation, washed three times with ethanol and deionized water, and dried at 60°C to obtain the Bi2O3 / COF-1 composite material.

[0080] Example 5.

[0081] The specific operating steps are as follows:

[0082] Weigh out 0.01 mol Dissolve 0.01 mol of urea in 60 mL of a 1:1 v / v mixture of ethylene glycol and deionized water, and stir until completely dissolved.

[0083] Then add the COF-1 prepared in Example 1 (Bi2O3 to COF-1 mass ratio 10:1), and continue stirring for 1 hour until homogeneous. Transfer the mixture to a 100 mL polytetrafluoroethylene-lined autoclave and react at 160 °C for 8 hours.

[0084] Finally, after natural cooling, the product was collected by centrifugation, washed three times with ethanol and deionized water, and dried at 60°C to obtain the Bi2O3 / COF-1 composite material.

[0085] Example 6: Material Characterization

[0086] The COF-1, Bi2O3, and Bi2O3 / COF-1-10 prepared in Examples 1-3 were characterized by XRD, FT-IR, SEM, and TEM. The results are as follows: Figure 1 As shown.

[0087] XRD ( Figure 1 a) The spectrum shows that the composite material simultaneously exhibits characteristic diffraction peaks of both amorphous COF-1 and Bi2O3. This indicates that the two phases coexist.

[0088] FT-IR spectroscopy ( Figure 1 b) shows the characteristic absorption peak of COF-1 in the composite material: 1563. (C–N stretching vibration) and 793 The presence of the triazine ring breathing vibration indicates successful COF-1 framework formation. Simultaneously, the characteristic absorption peak of Bi2O3 is observed at 843°C. (Bi–O–Bi stretching vibration) and 1384 The (Bi–O stretching vibration) also appeared clearly, indicating that Bi2O3 maintained its structural integrity during the recombination process. The coexistence of the two sets of characteristic peaks proves the successful recombination of the two phases, and the peak positions did not shift significantly, indicating the existence of strong interactions at the heterogeneous interface.

[0089] SEM ( Figure 2 ) and TEM ( Figure 3 HRTEM showed that Bi2O3 nanosheets were uniformly anchored on the COF-1 framework, forming a tight heterogeneous interface. Figure 3 lattice fringes of Bi₂O₃ (0.28 nm and 0.32 nm) were observed using SAED (ac). Figure 3 d) shows the polycrystalline diffraction rings of Bi2O superimposed on the diffuse halo of COF-1, EDS-mapping ( Figure 3e) The distribution of C, N, Bi, and O elements is uniform.

[0090] Example 7: Electrochemical Performance Testing

[0091] A three-electrode system was used, with 6 M KOH as the electrolyte, Pt as the counter electrode, and Hg / HgO as the reference electrode. The Bi2O3 / COF-1-X (X is 1, 5, 10, 15) composite material prepared in Example 3 was coated on nickel foam as the working electrode (active material loading is approximately 2). ).

[0092] like Figure 4 As shown in Figure a, the Bi₂O₃ content plays a crucial role in energy storage performance. With increasing Bi₂O₃ content, the integral area of ​​the cyclic voltammetry (CV) curve first increases and then decreases. Based on the constant current charge-discharge (GCD) curve (… Figure 4 (b) The calculated specific capacitance further confirms this trend. Further increases in Bi₂O₃ loading may lead to impaired ion transport and capacitance decay, highlighting the crucial role of the COF framework as a support material in improving overall performance. The Bi₂O₃ / COF-1-10 sample exhibited the highest capacitance. Figure 4 The CD-ROM displays the CV and GCD curves for Bi2O3 / COF-1, Bi2O3, and COF-1. Compared to Bi2O3 and COF-1, the larger integral area of ​​Bi2O3 / COF-1 indicates its higher specific capacitance. GCD testing shows that Bi2O3 / COF-1-10 has a specific capacitance of 675.4 F / g at 1 A / g, significantly higher than pure Bi2O3 (474.0 F / g) and pure COF-1 (256.4 F / g). Rate performance: 77% capacitance is maintained at 20 A / g.

[0093] Example 8: Assembly and Testing of Symmetrical Supercapacitors

[0094] A symmetrical supercapacitor was assembled using Bi2O3 / COF-1-10 prepared in Example 3 as both positive and negative electrodes, 6 M KOH as the electrolyte, and melamine foam as the separator.

[0095] The results are as follows Figure 5 As shown, CV and GCD tests were performed at different voltage windows. Figure 5 bc) indicates a stable operating voltage window of up to 1.6 V. Figure 5 d shows that the CV curves at different scan rates maintain a good shape, and the GCD ( Figure 5 e) The calculated device energy density is 30.8 Wh / kg (power density 750 W / kg). Ragone diagram ( Figure 5f(Table 1) shows that the Bi2O3 / COF-1 symmetric supercapacitor (SSC) outperforms many previously reported symmetric and asymmetric supercapacitors, including other bismuth-based materials and other materials in this invention, highlighting the superior energy storage capability of the Bi2O3 / COF-1 heterostructure. Figure 5 The g-display shows that the Bi2O3 / COF-1 symmetrical supercapacitor (SSC) retains approximately 95.7% of its capacitance after 10,000 cycles.

[0096] This also demonstrates that the Bi2O3 / COF-1 heterojunction integrates two potential ranges, achieving a wide voltage window of -1.0 to 0.5 V. This characteristic allows the same electrode to be used simultaneously as both the positive and negative electrode in a symmetrical supercapacitor, simplifying device assembly.

[0097] Table 1

[0098]

[0099] Example 9: Electronic Properties

[0100] The optical and electronic properties were investigated using UV-Vis absorption spectroscopy and Mott-Schottky analysis. For example... Figure 6 As shown in b, the band gap of Bi₂O₃ / COF₁ (3.19 eV) is significantly lower than that of Bi₂O₃ (3.35 eV) and COF₁ (3.96 eV), which facilitates electron transition from the valence band to the conduction band and improves conductivity. Linear extrapolation of the Mott-Schottky diagrams (Figures 6c-e) yields the following flat band potentials: –0.66 V for COF₁, –0.71 V for Bi₂O₃, and –0.34 V for Bi₂O₃ / COF₁ (relative to Ag / AgCl). The positive slope confirms their n-type semiconductor characteristics. Accordingly, the conduction band (CB) positions are calculated to be –0.46 V, –0.51 V, and –0.14 V (relative to NHE), respectively. Using the relationship... From this, the valence band (VB) potential energies of COF-1, Bi2O3, and Bi2O3 / COF-1 can be derived to be approximately 3.50 eV, 2.84 eV, and 3.05 eV, respectively. Based on these data, a band structure diagram was constructed and... Figure 6 As shown in f, the band structure exhibits a type II staggered arrangement. This heterojunction is based on the spontaneous alignment of the Fermi levels at the interface, thus forming an equilibrium state that promotes efficient interfacial charge transport and optimizes charge storage dynamics. This synergistic effect significantly improves the capacitance and rate performance of the electrode, providing strong evidence for the successful formation of a heterojunction between COF-1 and Bi2O3.

[0101] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a Bi2O3 / COF heterojunction composite material, characterized in that, Includes the following steps: (1) Covalent organic framework COF-1 was synthesized by reacting cyanuric chloride and anhydrous piperazine at room temperature; (2) Dissolve bismuth salt and urea in a solvent, add COF-1, and grow Bi2O3 nanosheets in situ on the COF-1 framework through a solvothermal reaction to obtain the Bi2O3 / COF-1 heterojunction composite material.

2. The preparation method according to claim 1, characterized in that, In step (1), the synthesis method of COF-1 is as follows: cyanuric chloride is dissolved in 1,4-dioxane, and then triethylamine and piperazine in 1,4-dioxane solution are added in sequence. After stirring at room temperature, the mixture is centrifuged, washed, and dried to obtain COF-1.

3. The preparation method according to claim 1, characterized in that, The bismuth salt is bismuth nitrate, with a concentration of 0.01-0.1 mol / L; The urea concentration is 0.01-0.1 mol / L; The mass ratio of Bi2O3 to COF-1 in the Bi2O3 / COF-1 heterojunction composite material is 1:1, 5:1, 10:1, or 15:

1. The solvothermal reaction is carried out at a temperature of 140-160℃ for 8-12 hours.

4. The preparation method according to claim 3, characterized in that, The solvothermal reaction was carried out at a temperature of 150°C for 10 hours.

5. The preparation method according to claim 1, characterized in that, The solvent is a mixed solution of equal volumes of ethylene glycol and deionized water.

6. A Bi₂O₃ / COF heterojunction composite material, characterized in that, It is prepared by the preparation method described in any one of claims 1-5.

7. The Bi₂O₃ / COF heterojunction composite material according to claim 6, characterized in that, The composite material has a nanosheet anchoring structure, wherein COF-1 is a porous framework.

8. The Bi₂O₃ / COF heterojunction composite material according to claim 6, characterized in that, The working voltage window of the composite material is -1.0 to 0.5 V.

9. The application of the Bi2O3 / COF heterojunction composite material according to any one of claims 6-8 in the electrode of a supercapacitor.

10. The application according to claim 9, characterized in that, The Bi2O3 / COF heterojunction composite material is coated onto nickel foam as an active material for assembling symmetrical supercapacitors.

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