Covalent organic framework-polymer hybrid porous membranes, their preparation methods and applications

Abstract

This invention relates to the field of flow battery membrane technology, and particularly to a covalent organic framework-polymer hybrid porous membrane, its preparation method, and its application. The method includes the following steps: preparing a porous support layer; preparing a sulfonated polymer hybrid covalent organic framework dispersion; and preparing the covalent organic framework-polymer hybrid composite membrane by electrochemical deposition. The sulfonated polymer enters the framework of the covalent organic framework, reducing its effective pore size and providing abundant proton-conducting groups, thereby improving the coulombic efficiency and voltage efficiency of the vanadium battery. Furthermore, the membrane's vanadium barrier properties and ion selectivity are improved through a combination of pore size sieving and charge repulsion, further enhancing the coulombic efficiency and capacity retention of the vanadium battery.

Description

Technical Field

[0001] This invention relates to the field of flow battery membrane technology, and in particular to a covalent organic framework-polymer hybrid porous membrane, its preparation method and application. Background Technology

[0002] A vanadium redox flow battery (hereinafter referred to as a vanadium battery) is an electrochemical energy storage device that stores and releases electrical energy based on the reversible valence state change of a single transition metal, vanadium. Its core components include a separator, bipolar plates, an electrolyte tank, graphite felt, and a circulation pump. Among these, the separator, as the core functional unit inside the battery, plays a crucial role in isolating the positive and negative electrode electrolytes, suppressing the transpolar migration of vanadium ions, and facilitating proton conduction. Its performance directly determines the long-term operational stability and energy conversion efficiency of the vanadium battery.

[0003] Vanadium battery electrolyte contains V 2+ V 3+ VO 2+ VO2 + Vanadium ions exist in four valence states, with hydrated ions having diameters of only about 0.6-0.8 nm. However, traditional polymer membranes cannot easily reduce pore sizes to below 1 nm through conventional modification and design, failing to meet the requirements for efficient vanadium ion sieving and thus hindering their direct application in vanadium battery separators. Currently, perfluorosulfonic acid ion exchange membranes, widely used in vanadium batteries, consist of hydrophilic polymer side chains and a hydrophobic polymer backbone, enabling efficient proton conduction through micellar channels and exhibiting high ionic conductivity and excellent electrochemical stability. However, the micellar channel size of these membranes remains at the nanometer level, significantly larger than the hydrated diameter of vanadium ions. This results in insufficient ion selectivity and poor vanadium blocking performance, leading to problems such as decreased coulombic efficiency and accelerated capacity decay, severely restricting the commercialization of vanadium batteries.

[0004] Covalent organic frameworks (COFs), as a novel class of organic porous materials possessing both excellent crystallinity and high designability, can be constructed by covalently linking various types and structures of small organic molecules through copolymerization or self-polymerization reactions. Their structural characteristics include low density, high porosity, continuously tunable pore size, and precisely controllable microenvironment within the pores, showing broad application prospects in adsorption separation, catalysis, and energy storage. However, most reported COF membranes currently have pore sizes generally larger than 1 nm, and their actual vanadium blocking effect has not yet reached an ideal level. Furthermore, unmodified intrinsic COF materials typically lack proton-conducting active sites, making it difficult to simultaneously achieve a synergistic improvement in coulombic efficiency and voltage efficiency solely relying on intrinsic pore structure. This bottleneck significantly limits their practical application in flow batteries. Summary of the Invention

[0005] This invention provides a covalent organic framework-polymer hybrid porous membrane, its preparation method, and its application. A polymer containing sulfonic acid groups is added to a mixed dispersion of positively charged amine monomers, aldehyde monomers, and a catalyst. The polymer-hybridized covalent organic framework dispersion is prepared via microwave-assisted synthesis. The sulfonic acid group-containing polymer segments tightly bind to the cationic covalent organic framework through electrostatic interactions, penetrating its interlayer and pore interior, thus aiding in exfoliation and pore size reduction. After dialysis, this dispersion is deposited onto the surface of a porous substrate membrane via electrochemical driving, rapidly preparing a covalent organic framework-polymer hybrid porous membrane, which is then used in a vanadium redox flow battery.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a covalent organic framework-polymer hybrid porous membrane, comprising the following steps:

[0007] S1. Dissolve the polymer in the first solvent, remove bubbles, and obtain a casting solution; pour the casting solution onto a clean glass plate, spread it evenly with a scraper, then immerse it in pure water, and after 20~120s, take out the obtained porous base film, wash it with deionized water, and obtain a porous support layer.

[0008] S2. Disperse 1-4 parts by mass of the first monomer, 2-8 parts by mass of the second monomer, 10-40 parts by mass of the sulfonic acid group-containing polymer and 1-8 parts by mass of the catalyst in 1000-4000 parts by mass of the second solvent, carry out microwave reaction, centrifuge after the reaction is completed, take the supernatant and dialyze to obtain polymer hybrid covalent organic framework dispersion.

[0009] S3. Using the polymer hybrid covalent organic framework dispersion as the electrolyte and the porous support layer as the negative electrode, electrochemical deposition is performed to obtain a covalent organic framework-polymer hybrid porous membrane.

[0010] In one embodiment, the polymer in step S1 is selected from at least one of polysulfone, cellulose acetate, polyacrylonitrile, polyhydroxyalkanoate, and polystyrene; the first solvent is selected from at least one of tetrahydrofuran, acetone, dioxane, N-methylpyrrolidone, and dimethyl sulfoxide; the mass fraction of the polymer in the casting solution is 8-25%; the defoaming method is to let it stand at room temperature for 8-12 hours; and the doctor blade height is 100-400 μm.

[0011] In one embodiment, the first monomer in step S2 is selected from at least one of 1,3,5-tris(4-aldehydephenyl)benzene, 1,3,5-trialdehydephenyl, 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine, tetra(4-aldehydephenyl)methane, and 2,4,6-trialdehydepyridine.

[0012] In one embodiment, the second monomer in step S2 is selected from at least one of ethidium bromide, guanidine triaminohydrochloride, 2,5-diaminophenoxyethanol hydrochloride, 1-(3-trimethylaminopropoxy)-4-hydrazylformylphenyl hydrochloride, and 1,1'-bis(4-aminophenyl)-[4,4'-bipyridine]-1,1'-diammonium chloride.

[0013] In one embodiment, the sulfonic acid group-containing polymer in step S2 is selected from at least one of sulfonated polyacrylonitrile, sulfonated polyethersulfone, sulfonated polysulfone, sulfonated polyacrylamide, and polystyrene sulfonate.

[0014] In one embodiment, the catalyst in step S2 is selected from at least one of acetic acid, trifluoroacetic acid, scandium trifluoromethanesulfonate, copper sulfate, and trichloroacetic acid; the second solvent is selected from at least one of N,N-dimethylformamide, mesitylene, dioxane, ethyl acetate, and glycerol.

[0015] In one embodiment, the power of the microwave reaction in step S2 is 50~400W, and the time is 10~40min; the centrifugation speed is 5000~9000rpm, and the time is 10~20min; the dialysis time is 12~48h.

[0016] In one embodiment, the electrochemical deposition method in step S3 involves pouring the polymer hybrid covalent organic framework dispersion into an electrolytic cell, using indium tin oxide conductive glass as the positive electrode and indium tin oxide conductive glass with the porous support layer attached as the negative electrode. The distance between the positive and negative electrodes is 1-4 cm, the DC voltage is 40-150 V, and the electrochemical deposition time is 1-10 min. Afterward, the porous support layer is removed and cleaned with ethanol and pure water.

[0017] A second aspect of the present invention provides a covalent organic framework-polymer hybrid porous membrane, which is prepared by the preparation method described above.

[0018] A third aspect of the present invention provides an application of a covalent organic framework-polymer hybrid porous membrane, wherein the covalent organic framework-polymer hybrid porous membrane prepared by the above-described preparation method or the covalent organic framework-polymer hybrid porous membrane described above is applied to an all-vanadium redox flow battery.

[0019] The beneficial effects of this invention are as follows:

[0020] The cationic covalent organic framework and sulfonic acid group-containing polymer used in this invention are tightly bound together through electrostatic attraction, which enhances the encapsulation effect and improves the operational stability of vanadium batteries.

[0021] The sulfonic acid-containing polymer used in this invention enters the interlayer and pores of the covalent organic framework, reducing the size of the covalent organic framework, improving its dispersibility and dispersion uniformity, reducing its effective pore size, and providing abundant proton-conducting groups, thereby improving the coulombic efficiency and voltage efficiency of vanadium batteries.

[0022] The cationic covalent organic framework used in this invention has nanoscale positively charged channels, which improve the vanadium barrier properties and ion selectivity of the membrane through the dual effects of pore size sieving and charge repulsion, thereby improving the coulombic efficiency and capacity retention of vanadium batteries. Attached Figure Description

[0023] Figure 1 This is a schematic flowchart of the preparation method of the covalent organic framework-polymer hybrid porous membrane of the present invention;

[0024] Figure 2 These are scanning electron microscope (SEM) images of the polymer hybrid covalent organic framework dispersions in Example 2 and Comparative Example 1 of the present invention.

[0025] Figure 3 The pore size distribution diagrams are shown for the covalent organic frameworks of Embodiment 2 and Comparative Example 1 of the present invention.

[0026] Figure 4 This is a SEM image of the surface and cross-section of the covalent organic framework-polymer hybrid porous membrane in Example 1 of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0028] A method for preparing a covalent organic framework-polymer hybrid porous membrane includes the following steps:

[0029] S1. Preparation of the porous support layer: The polymer is dissolved in the first solvent to prepare a solution with a mass fraction of 8-25%. After standing at room temperature for 8-12 hours to remove air bubbles, a casting solution is obtained. The solution is evenly spread using a doctor blade with a height of 100-400 μm, and then a glass plate is quickly immersed in pure water. After 20 seconds to 2 minutes, the porous base membrane is removed, thoroughly washed with deionized water, and stored. The resulting porous base membrane serves as the porous support layer for a covalent organic framework-polymer hybrid porous membrane used in vanadium batteries, providing mechanical strength and electrodeposition sites. The polymer is selected from one of polysulfone, cellulose acetate, polyacrylonitrile, polyhydroxyalkanoates, and polystyrene; the first solvent is selected from one of tetrahydrofuran, acetone, dioxane, N-methylpyrrolidone, and dimethyl sulfoxide.

[0030] S2. Preparation of polymer hybrid covalent organic framework dispersion by microwave-assisted method: 1-4 parts by mass of the first monomer, 2-8 parts by mass of the second monomer, 10-40 parts by mass of the sulfonic acid-containing polymer, and 1-8 parts by mass of the catalyst are dispersed in 1000-4000 parts by mass of the second solvent. The mixture is then placed in a microwave reactor and sealed. The reaction is carried out at 80-140℃ and 50-400W microwave power for 10-40 min. After the reaction, the dispersion is centrifuged at 5000-9000 rpm for 10-20 min. The supernatant is dialyzed with ethanol for 12-48 h to obtain the polymer hybrid covalent organic framework dispersion for electrochemical deposition. The first monomer is selected from 1,3,5-tris(4-aldehydephenyl)benzene, trialdehyde phloroglucinol, 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine, tetra(4-aldehydephenyl)methane, and 2,4,6-trialdehydepyridine; the second monomer is selected from ethidium bromide, triaminoguanidine hydrochloride, ethidium bromide, 1,4-diamino-2-trimethylaminomethoxybenzene hydrochloride, trimethylaminopropoxyterephthalohydrazide hydrochloride, and 1,1' The polymer containing sulfonic acid groups is selected from one of bis(4-aminophenyl)-[4,4'-bipyridine]-1,1'-diammonium chloride; the polymer containing sulfonic acid groups is selected from one of sulfonated polyacrylonitrile, sulfonated polyethersulfone, sulfonated polysulfone, sulfonated polyacrylamide, and polystyrene sulfonate; the catalyst is selected from one of acetic acid, trifluoroacetic acid, scandium trifluoromethanesulfonate, copper sulfate, and trichloroacetic acid; the second solvent is selected from one of N,N-dimethylformamide, mesitylene, dioxane, ethyl acetate, and glycerol.

[0031] S3. Preparation of covalent organic framework-polymer hybrid porous membrane by electrochemical deposition: The polymer hybrid covalent organic framework dispersion is poured into an electrolytic cell. The positive electrode is indium tin oxide (ITO) conductive glass, and the negative electrode is ITO conductive glass with the porous support layer attached. The distance between the two electrodes is 1-4 cm, the DC voltage is 40-150 V, and the electrochemical deposition time is 1-10 min. After electrochemical deposition, the porous support layer is removed, washed with ethanol and pure water, and stored in pure water to obtain the covalent organic framework-polymer hybrid porous membrane.

[0032] The mechanism involved in this invention is as follows:

[0033] 1. Non-solvent-induced phase separation. When a polymer solution encounters a non-solvent, microphase separation occurs, and the polymer precipitates from the solvent. Therefore, when the casting solution is spread on a glass surface, phase separation occurs, and the polymer precipitates in the form of a porous flat sheet membrane. Due to the rapid solvent exchange rate, the self-supporting membrane quickly detaches from the glass plate surface, thus obtaining a supporting substrate film layer for electrodeposition.

[0034] 2. Interaction between polymer segments and covalent organic frameworks. In the microwave synthesis of cationic covalent organic frameworks, polymers containing sulfonic acid groups are added. The positively charged cationic monomers and the negatively charged polymer segments containing sulfonic acid groups combine through charge attraction. During the growth of the covalent organic framework, the polymer segments containing sulfonic acid groups are encapsulated and packaged within its framework structure, entering its interlayer and pore structures. On one hand, the polymer segments entering the interlayer structure increase the interlayer spacing, aiding in exfoliation. Combined with the self-exfoliation effect of the charge repulsion between the interlayer layers of the ionic covalent organic framework, the covalent organic framework product exists as a dispersion with a size of only tens of nanometers, unlike the insoluble covalent organic framework precipitates obtained by traditional solvothermal synthesis. Therefore, the dispersibility of the covalent organic framework in the solvent is improved, and the stability of the dispersion is also enhanced. On the other hand, the polymer segments entering the pore structure act as a mask and shield, reducing the actual effective pore size of the covalent organic framework. Combined with the charge repulsion between the cationic covalent organic framework and vanadium ions, this enhances the ion sieving ability.

[0035] 3. Electrochemical Deposition Process. A small number of negatively charged polymer segments are encapsulated within a positively charged covalent organic framework. The overall structure still exhibits a significant positive charge, allowing the covalent organic framework particles to move directionally under an electric field, from the positive electrode to the negative electrode, and deposit onto the porous substrate surface of the negative electrode. Although the particles are only tens of nanometers in size, due to the reversibility of the Schiff base reaction, the covalent organic framework deposited on the porous substrate surface can undergo self-repair, repairing defects within the deposition layer. This ultimately forms a continuous, complete, and defect-free covalent organic framework separation layer, achieving the electrochemical deposition preparation of covalent organic framework separation membranes. Membrane preparation can be completed within 10 minutes, significantly improving the preparation efficiency of covalent organic framework membranes.

[0036] 4. Application of covalent organic framework-polymer hybrid porous membranes in vanadium batteries: The prepared composite membrane has a reduced effective pore size and exhibits significant positive charge. Through the combined effects of pore size sieving and charge repulsion, it effectively blocks vanadium ions of various valence states, significantly reducing vanadium ion shuttle behavior and improving the coulombic efficiency and capacity retention of the vanadium battery. Furthermore, the introduced polymer contains abundant sulfonic acid groups, which can play a role in proton conduction, improving the voltage efficiency and energy efficiency of the vanadium battery.

[0037] Example 1: The following technical solution is adopted.

[0038] S1. Polysulfone was dissolved in dioxane to prepare an 8% (w / w) solution. After standing at room temperature for 12 hours to remove air bubbles, a casting solution was obtained. The casting solution was poured onto a clean glass plate and spread evenly using a 100 μm high scraper. The glass plate was then quickly immersed in pure water. After 2 minutes, the porous base membrane was removed, thoroughly rinsed with deionized water, and stored.

[0039] S2. Disperse 1 part by mass of trialdehyde phloroglucinol, 2 parts by mass of triaminoguanidine hydrochloride, 40 parts by mass of sulfonated polyacrylonitrile, and 1 part by mass of acetic acid in 1000 parts by mass of N,N-dimethylformamide. Then, place the mixture in a microwave reactor and seal it. React at 140°C and 400W microwave power for 30 min. After the reaction is complete, centrifuge the dispersion at 5000 rpm for 15 min. Take the supernatant and dialyze it with ethanol for 48 h to obtain a polymer hybrid covalent organic framework dispersion for electrochemical deposition.

[0040] S3. Pour the polymer-hybrid covalent organic framework dispersion into an electrolytic cell. The positive electrode is indium tin oxide (ITO) conductive glass, and the negative electrode is ITO conductive glass with the porous support layer attached. The distance between the two electrodes is 1 cm, the DC voltage is 60 V, and the electrochemical deposition time is 10 min. After electrochemical deposition, remove the porous support layer, wash it with ethanol and pure water, and store it in pure water to obtain the covalent organic framework-polymer hybrid porous membrane.

[0041] Example 2: The following technical solution is adopted.

[0042] S1. Dissolve cellulose acetate in acetone to prepare a 13% (w / w) solution. Let it stand at room temperature for 11 hours to remove air bubbles, obtaining the casting solution. Pour the casting solution onto a clean glass plate and spread it evenly using a 150 μm high scraper. Then, quickly immerse the glass plate in pure water. After 1 minute, remove the porous base membrane, thoroughly rinse it with deionized water, and store it.

[0043] S2. Disperse 2 parts by mass of tetra(4-aldehydephenyl)methane, 4 parts by mass of ethidium bromide, 30 parts by mass of sulfonated polyethersulfone, and 3 parts by mass of trifluoroacetic acid in 1500 parts by mass of mesitylene. Then, place the mixture in a microwave reactor and seal it. React at 120°C and 300W microwave power for 40 min. After the reaction is complete, centrifuge the dispersion at 7000 rpm for 10 min. Take the supernatant and dialyze it with ethanol for 36 h to obtain a polymer hybrid covalent organic framework dispersion for electrochemical deposition.

[0044] S3. Pour the polymer hybrid covalent organic framework dispersion into an electrolytic cell. The positive electrode material is a polymer porous base membrane, and the negative electrode material is a polymer porous base membrane with the porous support layer from S1 attached. The distance between the two electrodes is 2 cm, the DC voltage is 40 V, and the electrochemical deposition time is 8 min. After electrochemical deposition, remove the porous support layer, wash with ethanol and pure water, and store it in pure water to obtain the covalent organic framework-polymer hybrid porous membrane.

[0045] Example 3: The following technical solution is adopted.

[0046] S1. Polyacrylonitrile was dissolved in dimethyl sulfoxide to prepare an 18% (w / w) solution. After standing at room temperature for 10 hours to remove air bubbles, a casting solution was obtained. The casting solution was poured onto a clean glass plate and spread evenly using a 200 μm high scraper. The glass plate was then quickly immersed in pure water. After 30 seconds, the porous base membrane was removed, thoroughly rinsed with deionized water, and stored.

[0047] S2. 2.5 parts by mass of 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine, 5 parts by mass of 1-(3-trimethylaminopropoxy)-4-hydrazinoformylbenzene hydrochloride, 20 parts by mass of sulfonated polysulfone, and 5 parts by mass of scandium trifluoromethanesulfonate were dispersed in 2000 parts by mass of dioxane. The mixture was then placed in a microwave reactor and sealed. The reaction was carried out at 80°C and 200W microwave power for 20 min. After the reaction, the dispersion was centrifuged at 9000 rpm for 20 min. The supernatant was dialyzed against ethanol for 24 h to obtain a polymer hybrid covalent organic framework dispersion for electrochemical deposition.

[0048] S3. Pour the polymer-hybrid covalent organic framework dispersion into an electrolytic cell. The positive electrode is indium tin oxide (ITO) conductive glass, and the negative electrode is ITO conductive glass with the porous support layer attached. The distance between the two electrodes is 2.5 cm, the DC voltage is 100 V, and the electrochemical deposition time is 6 min. After electrochemical deposition, remove the porous support layer, wash it with ethanol and pure water, and store it in pure water to obtain the covalent organic framework-polymer hybrid porous membrane.

[0049] Example 4: The following technical solution is adopted.

[0050] S1. Dissolve polyhydroxyalkanoates in N-methylpyrrolidone to prepare a 22% (w / w) solution. Let it stand at room temperature for 9 hours to remove air bubbles, obtaining the casting solution. Pour the casting solution onto a clean glass plate and spread it evenly using a 300 μm high scraper. Then, quickly immerse the glass plate in pure water. After 40 seconds, remove the porous base membrane, thoroughly rinse it with deionized water, and store it.

[0051] S2. Disperse 3 parts by mass of 1,3,5-tris(4-aldehydephenyl)benzene, 6 parts by mass of 2,5-diaminophenoxyethanol hydrochloride, 10 parts by mass of sulfonated polyacrylamide, and 8 parts by mass of copper sulfate in 2500 parts by mass of ethyl acetate. Then, place the mixture in a microwave reactor and seal it. React at 100°C and 100W microwave power for 5 min. After the reaction is complete, centrifuge the dispersion at 8000 rpm for 15 min. Take the supernatant and dialyze it with ethanol for 12 h to obtain a polymer hybrid covalent organic framework dispersion for electrochemical deposition.

[0052] S3. Pour the polymer-hybrid covalent organic framework dispersion into an electrolytic cell. The positive electrode is indium tin oxide (ITO) conductive glass, and the negative electrode is ITO conductive glass with the porous support layer attached. The distance between the two electrodes is 3.5 cm, the DC voltage is 125 V, and the electrochemical deposition time is 3 min. After electrochemical deposition, remove the porous support layer, wash it with ethanol and pure water, and store it in pure water to obtain the covalent organic framework-polymer hybrid porous membrane.

[0053] Example 5: The following technical solution is adopted.

[0054] S1. Dissolve polystyrene in tetrahydrofuran to prepare a 25% (w / w) solution. Let it stand at room temperature for 8 hours to remove air bubbles, obtaining the casting solution. Pour the casting solution onto a clean glass plate and spread it evenly using a 400 μm high scraper. Then, quickly immerse the glass plate in pure water. After 20 seconds, remove the porous base membrane, thoroughly rinse it with deionized water, and store it.

[0055] S2. Disperse 4 parts by mass of 2,4,6-trialdehyde pyridine, 8 parts by mass of 1,1'-bis(4-aminophenyl)-[4,4'-bipyridine]-1,1'-diammonium chloride, 25 parts by mass of polystyrene sulfonate, and 4 parts by mass of trichloroacetic acid in 4000 parts by mass of glycerol. Then place the mixture in a microwave reactor and seal it. React at 95°C and 50W microwave power for 10 min. After the reaction is complete, centrifuge the dispersion at 6000 rpm for 10 min. Take the supernatant and dialyze it with ethanol for 12 h to obtain a polymer hybrid covalent organic framework dispersion for electrochemical deposition.

[0056] S3. The polymer-polymer hybrid covalent organic framework dispersion is poured into an electrolytic cell. The positive electrode is indium tin oxide (ITO) conductive glass, and the negative electrode is ITO conductive glass with the porous support layer attached. The distance between the two electrodes is 4 cm, the DC voltage is 150 V, and the electrochemical deposition time is 1 min. After electrochemical deposition, the porous support layer is removed, washed with ethanol and pure water, and stored in pure water to obtain the covalent organic framework-polymer hybrid porous membrane.

[0057] Comparative Example 1: The following technical solution is adopted.

[0058] The difference from Example 2 is that no polymer sulfonated polyethersulfone is added in step S2. The solid powder obtained in S2 is ultrasonically treated in ethanol to obtain a covalent organic framework dispersion, and the subsequent electrodeposition film formation process is the same as S3 in Example 2.

[0059] Comparative Example 2: The following technical solution is adopted.

[0060] The difference from Example 2 is that in step S2, the monomer ethidium bromide is replaced with p-phenylenediamine to synthesize a covalent organic framework with similar size but exhibiting electronegativity, while other preparation conditions remain unchanged.

[0061] The characterization tests employed in this invention are as follows:

[0062] 1. Pore size distribution: The covalent organic framework dispersion was heated and evaporated to dryness. The powder was collected, washed with ethanol and pure water, dried, and then the nitrogen adsorption-desorption isotherm of the polymer hybrid covalent organic framework was tested using a surface area and porosity analyzer (Micrometrics ASAP 2460). The pore size distribution was fitted using nonlocal density functional theory (NLDFT).

[0063] 2. Microscopic Morphology Characterization: The hybrid covalent organic framework dispersion was dropped onto a clean silicon wafer surface, dried, and then characterized using SEM (ZEISS Gemini SEM360). Surface and cross-sectional SEM characterizations were performed on the polymer-covalent organic framework hybrid composite film. Prior to characterization, the samples were sputter-coated with gold to enhance conductivity for 40 seconds at an accelerating voltage of 5 kV.

[0064] 3. Battery performance testing: The membranes from Examples 1-5 and Comparative Examples 1-2 were assembled into battery stacks for testing. Coulombic efficiency, voltage efficiency, energy efficiency, and capacity retention after 300 cycles were tested and recorded under the same operating conditions.

[0065] The test results are shown in Table 1.

[0066] Table 1 Battery performance test results

[0067]

[0068] The preparation flow charts of covalent organic framework-polymer hybrid porous membranes in Examples 1-5 are shown below. Figure 1 As shown in Table 1, the covalent organic framework-polymer hybrid porous membranes prepared in Examples 1-5 all maintained a capacity retention of over 80% after 300 cycles in vanadium battery testing, while the capacity retention of Comparative Example 1, which did not use polymer hybridization, was less than 70%. This indicates that the cationic covalent organic framework and the sulfonic acid-containing polymer used in this invention are tightly bonded through electrostatic attraction, enhancing the encapsulation effect and improving the operational stability of the vanadium battery. Figure 2It can be seen that the particle size in the polymer hybrid covalent organic framework dispersions of Example 2 and Comparative Example 1 is significantly different: Example 2 used a polymer containing sulfonic acid groups, which acted as an auxiliary exfoliant, and its average particle size was approximately 30 nm; Comparative Example 1 did not use a polymer containing sulfonic acid groups and could only be dispersed by ultrasonic exfoliation, resulting in larger particles (~70 nm). This indicates that the polymer containing sulfonic acid groups used enters the structure of the covalent organic framework, reducing the size of the covalent organic framework and improving its dispersibility and dispersion uniformity. Figure 3 It can be seen that after adding a sulfonic acid-containing polymer rich in sulfonic acid groups during the synthesis process, the effective pore size of the hybrid covalent organic framework decreased slightly, from ~0.84 nm in Comparative Example 1 to ~0.73 nm in Example 2. This indicates that the sulfonic acid-containing polymer used in this invention enters the channels of the covalent organic framework, reducing its effective pore size. This also explains why the vanadium battery assembled from it has higher coulombic efficiency and voltage efficiency. Figure 4 It can be seen that the electrochemically deposited covalent organic framework-polymer hybrid film has a thinner thickness and a defect-free separation layer, which is due to the self-healing reaction between monomers, further reducing vanadium ion shuttle. In Comparative Example 2, the positively charged monomers used in Example 2 were replaced with neutral monomers to prepare a neutral covalent organic framework. Consequently, there is a lack of charge interaction between this framework and the sulfonic acid-containing polymer, resulting in weaker encapsulation capacity and limited encapsulation amount. Therefore, it has little effect on pore size, cannot achieve the effect of pore reduction, and cannot enhance the selectivity for vanadium ions through charge repulsion. Consequently, the coulombic efficiency and capacity retention of the assembled vanadium battery are reduced. This indicates that the cationic covalent organic framework used in this invention has nanoscale positively charged channels, which improve the vanadium barrier properties and ion selectivity of the membrane through a dual effect of pore size sieving and charge repulsion, thereby improving the coulombic efficiency and capacity retention of the vanadium battery.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a covalent organic framework-polymer hybrid porous membrane, characterized in that, Includes the following steps: S1. Dissolve the polymer in the first solvent, remove bubbles, and obtain a casting solution; pour the casting solution onto a clean glass plate, spread it evenly with a scraper, then immerse it in pure water, and after 20~120s, take out the obtained porous base film, wash it with deionized water, and obtain a porous support layer. S2. Disperse 1-4 parts by mass of the first monomer, 2-8 parts by mass of the second monomer, 10-40 parts by mass of the polymer containing sulfonic acid groups, and 1-8 parts by mass of the catalyst in 1000-4000 parts by mass of the second solvent, and perform a microwave reaction. After the reaction is completed, centrifuge and dialyze the supernatant to obtain a polymer hybrid covalent organic framework dispersion; the first monomer is selected from 1,3,5-tris(4-aldehydephenyl)benzene, 1,3,5-trialdehydephenyl, 2,4 The second monomer is selected from at least one of 6-tris(4-aldehydephenyl)-1,3,5-triazine, tetra(4-aldehydephenyl)methane, and 2,4,6-trialdehydepyridine; the second monomer is selected from at least one of ethidium bromide, guanidine triaminohydrochloride, 2,5-diaminophenoxyethanol hydrochloride, 1-(3-trimethylaminopropoxy)-4-hydrazylformylphenyl hydrochloride, and 1,1'-bis(4-aminophenyl)-[4,4'-bipyridine]-1,1'-diammonium chloride. S3. Using the polymer hybrid covalent organic framework dispersion as the electrolyte and the porous support layer as the negative electrode, electrochemical deposition is performed to obtain a covalent organic framework-polymer hybrid porous membrane.

2. The preparation method according to claim 1, characterized in that, The polymer in step S1 is selected from at least one of polysulfone, cellulose acetate, polyacrylonitrile, polyhydroxyalkanoate, and polystyrene; the first solvent is selected from at least one of tetrahydrofuran, acetone, dioxane, N-methylpyrrolidone, and dimethyl sulfoxide; the mass fraction of the polymer in the casting solution is 8-25%; the defoaming method is to let it stand at room temperature for 8-12 hours; the doctor blade height is 100-400 μm.

3. The preparation method according to claim 1, characterized in that, The sulfonic acid group-containing polymer in step S2 is selected from at least one of sulfonated polyacrylonitrile, sulfonated polyethersulfone, sulfonated polysulfone, sulfonated polyacrylamide, and polystyrene sulfonate.

4. The preparation method according to claim 1, characterized in that, The catalyst in step S2 is selected from at least one of acetic acid, trifluoroacetic acid, scandium trifluoromethanesulfonate, copper sulfate, and trichloroacetic acid; the second solvent is selected from at least one of N,N-dimethylformamide, mesitylene, dioxane, ethyl acetate, and glycerol.

5. The preparation method according to claim 1, characterized in that, In step S2, the power of the microwave reaction is 50~400W and the time is 10~40min; the centrifugation speed is 5000~9000rpm and the time is 10~20min; the dialysis time is 12~48h.

6. The preparation method according to claim 1, characterized in that, The electrochemical deposition method in step S3 involves pouring the polymer hybrid covalent organic framework dispersion into an electrolytic cell. The positive electrode is indium tin oxide conductive glass, and the negative electrode is indium tin oxide conductive glass with the porous support layer attached. The distance between the positive and negative electrodes is 1-4 cm, the DC voltage is 40-150 V, and the electrochemical deposition time is 1-10 min. Afterward, the porous support layer is removed and cleaned with ethanol and pure water.

7. A covalent organic framework-polymer hybrid porous membrane, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 6.

8. An application of a covalent organic framework-polymer hybrid porous membrane, characterized in that, The covalent organic framework-polymer hybrid porous membrane prepared by the preparation method according to any one of claims 1 to 6, or the covalent organic framework-polymer hybrid porous membrane according to claim 7, is applied to an all-vanadium redox flow battery.

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