Tannic acid-bonded covalent organic framework composite proton exchange membrane and its preparation method

Abstract

This invention discloses a tannic acid-bonded covalent organic framework composite proton exchange membrane. First, tannic acid nanoaggregates and covalent organic framework nanosheets are prepared using thermal polymerization and phase transfer polymerization, respectively. Then, through a vacuum-assisted co-assembly process, the two are uniformly mixed in a specific ratio and filtered to obtain the covalent organic framework composite proton exchange membrane. By changing the preparation conditions and content of the tannic acid nanoaggregates, the hydrogen bonding interactions within the membrane can be precisely controlled. This process introduces highly dynamic and reversible hydrogen bonding interactions within the covalent organic framework membrane, endowing the membrane with excellent mechanical strength and toughness; simultaneously, it constructs a highly interconnected hydrogen bond network within the membrane, improving its proton conductivity. The preparation method of this invention is mild, controllable, simple, and efficient. The prepared membrane possesses excellent mechanical strength, toughness, and proton conductivity, which is beneficial for its widespread application in hydrogen energy conversion technology.

Description

Technical Field

[0001] This invention belongs to the field of polymer membrane technology, and specifically relates to a tannic acid-bonded covalent organic framework composite proton exchange membrane and its preparation method. Background Technology

[0002] Hydrogen energy boasts numerous advantages, including high energy density (142 kJ / kg), safe storage, and clean renewability, holding a crucial strategic position in the nation's energy transition. The development of hydrogen energy urgently requires improving the energy conversion efficiency of hydrogen production, compression, storage, transportation, and end-use applications, encompassing technological advancements in industries such as water electrolysis for hydrogen production, electrochemical hydrogen compression, and fuel cells. Proton exchange membranes (PEMs), which function as both proton transfer agents and electrode separators, are core components in these technologies, and their performance directly determines the energy conversion efficiency of the processes. Currently, the proton conductivity and mechanical strength of commercially available PEMs (such as Nafion membranes) are constrained by a trade-off efficiency where one increases while the other decreases, preventing simultaneous improvements and severely limiting the energy conversion efficiency of the processes. Furthermore, PEMs should possess high toughness to meet the mechanical assembly requirements of practical applications. Therefore, there is an urgent need to develop high-performance PEMs that simultaneously possess excellent mechanical strength, toughness, and proton conductivity.

[0003] Covalent organic frameworks (COFs), composed of periodically linked strong covalent bonds, offer advantages such as customizable structures, orderly pores, and good stability. They hold promise for overcoming the trade-off effect while simultaneously achieving high proton conductivity and high mechanical strength, bringing new opportunities for the development of PEM materials. However, due to their rigid framework structure, COF films often exhibit hardness, brittleness, and poor toughness, making them unsuitable for practical applications. Hydrogen bonding interactions possess high dynamic reversibility, absorbing significant stress during repeated fracture and formation processes, thus endowing the material with extremely high toughness. Therefore, introducing hydrogen bonding interactions into COF films is expected to improve their toughness. Combined with the high proton conductivity and high mechanical strength of COF films, this will fully realize their application potential in hydrogen energy conversion technologies. Summary of the Invention

[0004] To address the demand for high-performance PEMs in the aforementioned background technology, this invention proposes a tannic acid-bonded covalent organic framework (COF) composite proton exchange membrane and its preparation method. The prepared COF membrane simultaneously possesses excellent mechanical strength, toughness, and proton conductivity.

[0005] To address the aforementioned technical problems, this invention proposes a method for preparing a tannic acid-bonded covalent organic framework composite proton exchange membrane. The method involves using covalent organic framework nanosheets as the main body, adding tannic acid nanoaggregates, and then mixing and vacuum co-assembling them. First, tannic acid nanoaggregates and covalent organic framework nanosheets are prepared using thermal polymerization and phase transfer polymerization methods, respectively. Then, through a vacuum-assisted co-assembly process, the two are uniformly mixed at a solute mass ratio of 0.25–1.0:1 and filtered to obtain the covalent organic framework composite proton exchange membrane. The specific steps are as follows:

[0006] Step 1: Preparation of tannic acid nano-aggregate aqueous dispersion: Tannic acid was ultrasonically dissolved in deionized water at a mass-volume concentration of 1.2 mg / mL. The pH of the solution was adjusted to 3.0–12.0 with dilute hydrochloric acid or sodium hydroxide to obtain an aqueous tannic acid solution. The above aqueous tannic acid solution was subjected to polymerization at 90°C for 72 h to obtain an aqueous dispersion of tannic acid nano-aggregates.

[0007] Step 2, Preparation of covalent organic framework nanosheet aqueous dispersion: 2,4,6-trihydroxytriphenyltricarboxaldehyde and 2-sulfo-p-phenylenediamine were ultrasonically dissolved in octanoic acid and deionized water respectively at a molar volume concentration of 0.005 mmol / mL to obtain an aldehyde monomer oil phase and an amine monomer aqueous phase; the aldehyde monomer oil phase was added dropwise to the amine monomer aqueous phase at a volume ratio of 2:3, and the reaction was carried out at 16℃ for 72 h. The dark red aqueous phase was then dialyzed in deionized water for 72 h to obtain the covalent organic framework nanosheet aqueous dispersion.

[0008] Step 3: Preparation of covalent organic framework composite proton exchange membrane: The aqueous dispersion of tannic acid nanoaggregates obtained in Step 1 and the aqueous dispersion of covalent organic framework nanosheets obtained in Step 2 are uniformly mixed at a solute mass ratio of 0.25 to 1.0:1 to obtain a casting solution; the casting solution is filtered through a polyacrylonitrile substrate to obtain a covalent organic framework composite proton exchange membrane attached to a polyacrylonitrile substrate.

[0009] Step 4: Immerse the covalent organic framework composite proton exchange membrane attached to the polyacrylonitrile base membrane obtained in Step 3 in N,N-dimethylformamide; peel the membrane off from the polyacrylonitrile base, first acidify it by soaking in dilute sulfuric acid, and then wash it with a large amount of water until neutral to obtain a self-supporting covalent organic framework composite proton exchange membrane.

[0010] Furthermore, in the preparation method described in this invention:

[0011] Preferably, in step 1, the pH value of the tannic acid aqueous solution is 3.0-7.0.

[0012] Preferably, in step 3, the mass ratio of solute in the aqueous dispersion of tannic acid nanoaggregates and the aqueous dispersion of covalent organic framework nanosheets is 0.5 to 1.0:1.

[0013] The tannic acid-bonded COF composite proton exchange membrane prepared by the above method is obtained by mixing and vacuum co-assembly of COF nanosheets as the main body and adding tannic acid nano-aggregates.

[0014] Compared with COF membranes prepared by existing technologies, the preparation method provided by this invention can introduce highly dynamic and reversible hydrogen bonding interactions within the COF membrane, endowing it with excellent mechanical strength and toughness. Simultaneously, the abundant hydroxyl groups of tannic acid possess excellent water retention properties, enabling the construction of a highly interconnected hydrogen bond network within the membrane. This lowers the energy barrier for proton transfer via hopping mechanisms, thereby improving the membrane's proton conductivity. The prepared COF composite proton exchange membrane exhibits great application potential in hydrogen energy conversion technologies, including but not limited to water electrolysis for hydrogen production, electrochemical hydrogen compression, and fuel cells. Attached Figure Description

[0015] Figure 1 This is a scanning electron microscope cross-sectional view of composite membrane 1 in Example 1;

[0016] Figure 2 This is a scanning electron microscope cross-sectional image of composite membrane 2 in Example 2;

[0017] Figure 3 This is a scanning electron microscope cross-sectional image of composite membrane 3 in Example 3;

[0018] Figure 4 This is a scanning electron microscope cross-sectional view of the composite membrane 4 in Example 4;

[0019] Figure 5 This is a scanning electron microscope cross-sectional view of the composite membrane 5 in Example 5;

[0020] Figure 6 This is a scanning electron microscope cross-sectional view of the composite membrane 6 in Example 6;

[0021] Figure 7 This is a scanning electron microscope cross-sectional view of the composite membrane 7 in Example 7;

[0022] Figure 8 This is a scanning electron microscope cross-sectional view of the composite membrane 8 in Example 8;

[0023] Figure 9 The graph shows a comparison of the mechanical strength, toughness, and proton conductivity of composite membranes 1-5 and the comparative examples.

[0024] Figure 10 The graphs show a comparison of the mechanical strength, toughness, and proton conductivity of composite membranes 4 and 6-8, as well as comparative examples. Detailed Implementation

[0025] The design concept of the tannic acid-bonded COF composite proton exchange membrane proposed in this invention is as follows: This self-supporting covalent organic framework composite proton exchange membrane is based on COF nanosheets, with tannic acid nanoaggregates added and then mixed and vacuum co-assembled. Its preparation process mainly includes: preparation of tannic acid nanoaggregates, preparation of COF nanosheets, vacuum co-assembly of tannic acid nanoaggregates and covalent organic framework nanosheets, and post-treatment of the composite membrane. Tannic acid nanoaggregates were prepared by thermal polymerization. The pH of the solution affected the reactivity of tannic acid, thus altering the hydroxyl content of the tannic acid nanoaggregates. COF nanosheets were prepared by phase transfer polymerization. Through a vacuum-assisted co-assembly process, the tannic acid nanoaggregates and COF nanosheets were uniformly mixed and filtered onto a polyacrylonitrile substrate, resulting in a COF composite proton exchange membrane attached to the polyacrylonitrile substrate. The polyacrylonitrile substrate was then peeled off by immersion in N,N-dimethylformamide, followed by acidification with dilute sulfuric acid and washing with a large amount of water until neutral, yielding a self-supporting COF composite proton exchange membrane. This COF composite proton exchange membrane exhibits excellent mechanical strength, toughness, and proton conductivity. In the preparation method of this invention, the hydrogen bonding interactions within the membrane can be precisely controlled by changing the preparation conditions and content of the tannic acid nanoaggregates. The above process introduces highly dynamic and reversible hydrogen bonding interactions within the covalent organic framework membrane, endowing the membrane with excellent mechanical strength and toughness; simultaneously, it constructs a highly interconnected hydrogen bond network within the membrane, improving its proton conductivity. The preparation method of this invention is mild, controllable, simple and efficient. The prepared membrane has excellent mechanical strength, toughness and proton conductivity, as well as good thermal, chemical and long-term operational stability, which is conducive to its wide application in hydrogen energy conversion technology.

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are for illustrative purposes only and should not be considered as any limitation on the present invention.

[0027] Example 1

[0028] The steps for preparing a tannic acid-bonded COF composite proton exchange membrane are as follows:

[0029] Step 1: Preparation of tannic acid nano-aggregate aqueous dispersion: 48 mg of tannic acid was ultrasonically dissolved in 40 mL of deionized water, and the pH of the solution was adjusted to 12.0 with sodium hydroxide to obtain an aqueous tannic acid solution; the above aqueous tannic acid solution was placed at 90 °C for 72 h to react and polymerize, thereby obtaining an aqueous dispersion of tannic acid nano-aggregates.

[0030] Step 2, Preparation of COF nanosheet aqueous dispersion: 21 mg of 2,4,6-trihydroxytrimethylbenzaldehyde and 28.2 mg of 2-sulfo-p-phenylenediamine were ultrasonically dissolved in 20 mL of octanoic acid and 30 mL of deionized water, respectively, to obtain an aldehyde monomer oil phase and an amine monomer aqueous phase; the aldehyde monomer oil phase was added dropwise to the amine monomer aqueous phase, and the reaction was carried out at 16 °C for 72 h. The dark red aqueous phase was then dialyzed in deionized water for 72 h to obtain a COF nanosheet aqueous dispersion. The COF nanosheet aqueous dispersion was standardized by drying and weighing, and its mass-volume concentration was 1.2 mg / mL.

[0031] Step 3, Preparation of COF composite proton exchange membrane: 1.5 mL of the tannic acid nano-aggregate aqueous dispersion obtained in Step 1 and 2.0 mL of the COF nanosheet aqueous dispersion obtained in Step 2 (i.e., the solute mass ratio of the two is 0.75:1) are mixed uniformly to obtain a casting solution; the casting solution is filtered through a polyacrylonitrile substrate to obtain composite membrane 1 attached to the polyacrylonitrile substrate.

[0032] Step 4: Immerse the composite membrane 1, which is attached to the polyacrylonitrile base membrane and prepared in step 3 above, in N,N-dimethylformamide. The membrane is peeled off from the polyacrylonitrile base. First, it is acidified by soaking in dilute sulfuric acid, and then washed with a large amount of water until neutral to obtain the self-supporting composite membrane 1.

[0033] Figure 1 The image shows a scanning electron microscope cross-sectional image of composite membrane 1, revealing a uniform and continuous cross-section without obvious defects. The mechanical strength and toughness of composite membrane 1 were tested using a multi-stage testing machine at 25℃ and a tensile rate of 1 mm / min. -1 Under these conditions, the mechanical strength is 59.7 MPa and the toughness is 3.79 MJ / m. -3 The proton conductivity of composite membrane 1 was tested using an electrochemical workstation. Under conditions of 80℃ and 100% relative humidity, the proton conductivity was 381.8 mS / cm. -1 ,like Figure 9 As shown.

[0034] Example 2

[0035] The preparation process of the tannic acid-bonded COF composite proton exchange membrane is basically the same as that in Example 1, except that the pH value of the solution is adjusted to 9.0 with sodium hydroxide in step 1. The final COF composite proton exchange membrane is referred to as composite membrane 2.

[0036] Figure 2 The image shows a scanning electron microscope cross-sectional image of composite membrane 2, revealing a uniform and continuous cross-section without obvious defects. The mechanical strength and toughness of composite membrane 2 were tested using a multi-stage testing machine at 25℃ and a tensile rate of 1 mm / min. -1Under these conditions, the mechanical strength is 60.1 MPa and the toughness is 3.83 MJ / m. -3 The proton conductivity of composite membrane 2 was tested using an electrochemical workstation. Under conditions of 80℃ and 100% relative humidity, the proton conductivity was 384.4 mS / cm. -1 ,like Figure 9 As shown.

[0037] Example 3

[0038] The preparation process of the tannic acid-bonded COF composite proton exchange membrane is basically the same as that in Example 1, except that the pH value of the solution is adjusted to 7.0 with sodium hydroxide in step 1. The final COF composite proton exchange membrane is referred to as composite membrane 3.

[0039] Figure 3 The image shows a scanning electron microscope cross-sectional image of composite membrane 3, revealing a uniform and continuous cross-section without obvious defects. The mechanical strength and toughness of composite membrane 3 were tested using a universal testing machine at 25℃ and a tensile rate of 1 mm / min. -1 Under these conditions, the mechanical strength is 86.4 MPa and the toughness is 7.25 MJ / m. -3 The proton conductivity of composite membrane 3 was tested using an electrochemical workstation. Under conditions of 80℃ and 100% relative humidity, the proton conductivity was 424.9 mS / cm. -1 ,like Figure 9 As shown.

[0040] Example 4

[0041] The preparation process of the tannic acid-bonded COF composite proton exchange membrane is basically the same as that in Example 1, except that the pH value of the solution is adjusted to 5.0 with sodium hydroxide in step 1. The final COF composite proton exchange membrane is referred to as composite membrane 4.

[0042] Figure 4 The image shows a scanning electron microscope cross-sectional image of composite membrane 4, revealing a uniform and continuous cross-section without obvious defects. The mechanical strength and toughness of composite membrane 4 were tested using a universal testing machine at 25℃ and a tensile rate of 1 mm / min. -1 Under these conditions, the mechanical strength is 101.9 MPa and the toughness is 9.82 MJ / m. -3 The proton conductivity of composite membrane 4 was tested using an electrochemical workstation. Under conditions of 80℃ and 100% relative humidity, the proton conductivity was 491.3 mS / cm. -1 ,like Figure 9 , 10 As shown.

[0043] Example 5

[0044] The preparation process of the tannic acid-bonded COF composite proton exchange membrane is basically the same as that in Example 1, except that the pH value of the solution is adjusted to 3.0 with hydrochloric acid in step 1. The final COF composite proton exchange membrane is referred to as composite membrane 5.

[0045] Figure 5 The image shows a scanning electron microscope cross-sectional image of composite membrane 5, revealing a uniform and continuous cross-section without obvious defects. Mechanical strength and toughness tests were performed on composite membrane 5 using a multi-stage testing machine at 25℃ and a tensile rate of 1 mm / min. -1 Under these conditions, the mechanical strength is 100.9 MPa and the toughness is 9.77 MJ / m. -3 The proton conductivity of composite membrane 5 was tested using an electrochemical workstation. Under conditions of 80℃ and 100% relative humidity, the proton conductivity was 489.9 mS / cm. -1 ,like Figure 9 As shown.

[0046] Example 6

[0047] The preparation process of the tannic acid-bonded COF composite proton exchange membrane is basically the same as that in Example 4, except that in step 3, the mass ratio of the solute in the aqueous dispersion of tannic acid nano-aggregates and the aqueous dispersion of COF nanosheets is changed to 0.25:1 (0.5 mL of the aqueous dispersion of tannic acid nano-aggregates obtained in step 1 and 2.0 mL of the aqueous dispersion of COF nanosheets obtained in step 2 are mixed evenly); the final COF composite proton exchange membrane is referred to as composite membrane 6.

[0048] Figure 6 The image shows a scanning electron microscope cross-sectional image of composite membrane 6, revealing a uniform and continuous cross-section without obvious defects. The mechanical strength and toughness of composite membrane 6 were tested using a universal testing machine at 25℃ and a tensile rate of 1 mm / min. -1 Under these conditions, the mechanical strength is 74.3 MPa and the toughness is 4.76 MJ / m. -3 The proton conductivity of composite membrane 6 was tested using an electrochemical workstation. Under conditions of 80℃ and 100% relative humidity, the proton conductivity was 388.1 mS / cm. -1 ,like Figure 10 As shown.

[0049] Example 7

[0050] The preparation process of the tannic acid-bonded COF composite proton exchange membrane is basically the same as that in Example 4, except that the mass ratio of solute in the aqueous dispersion of tannic acid nano-aggregates and the aqueous dispersion of COF nanosheets is changed to 0.5:1 in step 3 (1.0 mL of the aqueous dispersion of tannic acid nano-aggregates obtained in step 1 and 2.0 mL of the aqueous dispersion of COF nanosheets obtained in step 2 are mixed evenly). The final COF composite proton exchange membrane is referred to as composite membrane 7.

[0051] Figure 7 The image shows a scanning electron microscope cross-sectional image of composite membrane 7, revealing a uniform and continuous cross-section without obvious defects. Mechanical strength and toughness tests were performed on composite membrane 7 using a universal testing machine at 25℃ and a tensile rate of 1 mm / min. -1 Under these conditions, the mechanical strength is 86.6 MPa and the toughness is 7.40 MJ / m. -3 The proton conductivity of composite membrane 7 was tested using an electrochemical workstation. Under conditions of 80℃ and 100% relative humidity, the proton conductivity was 429.2 mS / cm. -1 ,like Figure 10 As shown.

[0052] Example 8

[0053] The preparation process of the tannic acid-bonded COF composite proton exchange membrane is basically the same as that in Example 4, except that the mass ratio of solute in the aqueous dispersion of tannic acid nano-aggregates and the aqueous dispersion of COF nanosheets is changed to 1:1 in step 3 (2.0 mL of the aqueous dispersion of tannic acid nano-aggregates obtained in step 1 and 2.0 mL of the aqueous dispersion of COF nanosheets obtained in step 2 are mixed evenly). The final COF composite proton exchange membrane is referred to as composite membrane 8.

[0054] The figure shows a scanning electron microscope cross-sectional image of composite membrane 8, revealing a uniform and continuous cross-section without obvious defects. The mechanical strength and toughness of composite membrane 8 were tested using a universal testing machine at 25℃ and a tensile rate of 1 mm / min. -1 Under these conditions, the mechanical strength is 87.9 MPa and the toughness is 10.96 MJ / m. -3 The proton conductivity of composite membrane 8 was tested using an electrochemical workstation. Under conditions of 80℃ and 100% relative humidity, the proton conductivity was 450.3 mS / cm. -1 ,like Figure 10 As shown.

[0055] Comparative Example

[0056] The steps for preparing a pure COF membrane are as follows:

[0057] Step 1: Preparation of COF nanosheet aqueous dispersion: 21 mg of 2,4,6-trihydroxytrimethylbenzaldehyde and 28.2 mg of 2-sulfo-p-phenylenediamine were ultrasonically dissolved in 20 mL of octanoic acid and 30 mL of deionized water, respectively, to obtain an aldehyde monomer oil phase and an amine monomer aqueous phase. The aldehyde monomer oil phase was added dropwise to the amine monomer aqueous phase, and the reaction was carried out at 16 °C for 72 h. The dark red aqueous phase was then dialyzed in deionized water for 72 h to obtain a COF nanosheet aqueous dispersion. The COF nanosheet aqueous dispersion was standardized by drying and weighing, and its mass-volume concentration was 1.2 mg / mL.

[0058] Step 2, Preparation of pure COF membrane: 2.0 mL of the COF nanosheet aqueous dispersion obtained in step 1 was filtered through a polyacrylonitrile substrate to obtain a pure COF membrane attached to the polyacrylonitrile substrate.

[0059] Step 3: Immerse the pure COF membrane attached to the polyacrylonitrile base membrane prepared in Step 2 in N,N-dimethylformamide. The membrane is peeled off from the polyacrylonitrile base. First, acidify it by soaking in dilute sulfuric acid, and then wash it with a large amount of water until neutral to obtain a self-supporting pure COF membrane.

[0060] The mechanical strength and toughness of the pure COF membrane were tested using a multi-testing machine at 25°C and a tensile rate of 1 mm / min. -1 Under these conditions, the mechanical strength is 58.7 MPa and the toughness is 3.44 MJ / m. -3 The proton conductivity of the comparative sample was tested using an electrochemical workstation. Under conditions of 80℃ and 100% relative humidity, the proton conductivity was 352.5 mS / cm. -1 ,like Figure 9 , 10 As shown.

[0061] Table 1 shows the preparation process conditions and the properties of the resulting membrane.

[0062]

[0063] In Table 1, A refers to the aqueous dispersion of tannic acid nanoaggregates, and B refers to the aqueous dispersion of covalent organic framework nanosheets.

[0064] Comparing Examples 1-8 and the comparative examples, it can be concluded that the mechanical strength, toughness, and proton conductivity of composite membranes 1-8 are significantly improved compared to pure COF membranes. Comparing Examples 1-5 and the comparative examples, it can be concluded that when the pH value is 5.0-9.0, the number of hydroxyl groups on the surface of tannic acid nanoaggregates increases with decreasing pH, introducing more hydrogen bond interactions within the membrane, thus improving the performance of the composite membrane. Referring to Table 1, comparing Examples 1 and 2 or 4 and 5, it can be concluded that when pH > 9.0 or pH < 5.0, further increasing or decreasing the pH value has little effect on the performance of the composite membrane. Comparing Examples 4 and 6-8 and the comparative examples, it can be concluded that increasing the amount of tannic acid nanoaggregates gradually increases the toughness of the composite membrane, while the mechanical strength and proton conductivity initially increase and then decrease. When the amount of tannic acid nanoaggregates added is too large, due to the low strength of tannic acid itself and the prolonged proton transport path within the membrane, the mechanical strength and proton conductivity of the composite membrane decrease.

[0065] In summary, this invention utilizes COF nanosheets as the main body, adding tannic acid nanoaggregates and then co-assembling them under vacuum to obtain a tannic acid-bonded COF composite proton exchange membrane. By adjusting the pH value to control the hydroxyl content of the tannic acid nanoaggregates, and then changing the content of tannic acid nanoaggregates within the membrane, the hydrogen bonding interactions within the membrane can be precisely controlled. This process introduces highly dynamic and reversible hydrogen bonding interactions within the COF membrane, endowing it with excellent mechanical strength and toughness. Simultaneously, it constructs a highly interconnected hydrogen bond network within the membrane, reducing the energy barrier for proton transfer via hopping mechanisms and improving the membrane's proton conductivity.

[0066] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many modifications under the guidance of the present invention without departing from the spirit of the present invention, and these modifications are all within the protection scope of the present invention.

Claims

1. A method for preparing a tannic acid-bonded covalent organic framework composite proton exchange membrane, characterized in that, The specific steps are as follows: Step 1: Preparation of tannic acid nano-aggregate aqueous dispersion: Tannic acid was ultrasonically dissolved in deionized water at a mass-volume concentration of 1.2 mg / mL. The pH of the solution was adjusted to 3.0~12.0 with dilute hydrochloric acid or sodium hydroxide to obtain an aqueous tannic acid solution. The above aqueous tannic acid solution was placed at 90 °C for 72 h to react and polymerize, thereby obtaining an aqueous dispersion of tannic acid nano-aggregates. Step 2, Preparation of covalent organic framework nanosheet aqueous dispersion: 2,4,6-trihydroxypyromellitic aldehyde and 2-sulfo-p-phenylenediamine were ultrasonically dissolved in octanoic acid and deionized water, respectively, at a molar volume concentration of 0.005 mmol / mL, to obtain an aldehyde monomer oil phase and an amine monomer aqueous phase; the aldehyde monomer oil phase was added dropwise to the amine monomer aqueous phase at a volume ratio of 2:3, and the reaction was carried out at 16 °C for 72 h. The dark red aqueous phase was then dialyzed in deionized water for 72 h to obtain the covalent organic framework nanosheet aqueous dispersion. Step 3: Preparation of covalent organic framework composite proton exchange membrane: The aqueous dispersion of tannic acid nanoaggregates obtained in step 1 and the aqueous dispersion of covalent organic framework nanosheets obtained in step 2 are uniformly mixed at a solute mass ratio of 0.25~1.0:1 to obtain a casting solution; the casting solution is filtered through a polyacrylonitrile substrate to obtain a covalent organic framework composite proton exchange membrane attached to a polyacrylonitrile substrate. Step 4: Immerse the covalent organic framework composite proton exchange membrane attached to the polyacrylonitrile base membrane obtained in Step 3 in N,N-dimethylformamide; peel the membrane off from the polyacrylonitrile base, first acidify it by soaking in dilute sulfuric acid, and then wash it with a large amount of water until neutral to obtain a self-supporting covalent organic framework composite proton exchange membrane.

2. The preparation method according to claim 1, characterized in that, In step 1, the pH value of the tannic acid aqueous solution is 3.0-7.

0.

3. The preparation method according to claim 1, characterized in that, In step 3, the mass ratio of solute in the aqueous dispersion of tannic acid nanoaggregates and the aqueous dispersion of covalent organic framework nanosheets is 0.5~1.0:

1.

4. A tannic acid-bonded covalent organic framework composite proton exchange membrane, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 3.

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