Composite cation exchange membrane, method for preparing the same, and use thereof

Abstract

This invention provides a composite cation exchange membrane, its preparation method, and its application. The composite cation exchange membrane includes a substrate and a resin layer distributed inside and on the surface of the substrate; the substrate contains polar groups; the resin layer is made of perfluorosulfonic acid resin and / or sulfonated non-fluorinated resin material; the sulfonic acid group loading per unit volume of the resin layer is 1.6 × 10⁻⁶. ‑3 ~4.8×10 ‑3 mol / cm 3 The composite cation exchange membrane provided by this invention can achieve a good balance between mechanical properties and ionic conductivity.

Description

Technical Field

[0001] This invention belongs to the field of cation exchange membrane technology, and relates to a composite cation exchange membrane, its preparation method, and its application. Background Technology

[0002] Currently, existing cation exchange membranes typically consist of a solution of perfluorosulfonic acid resin, which is then infused or laminated into the pores of a substrate membrane to form a composite structure. While reducing the membrane thickness can lower membrane resistance, balancing high ionic conductivity and high mechanical strength is challenging. Furthermore, the resin and substrate are only physically bonded, making them susceptible to delamination under high temperature and humidity conditions or during prolonged operation. In practical applications such as flow batteries, water electrolysis for hydrogen production, and hydrogen fuel cells, these methods are prone to performance degradation and safety issues such as hydrogen-oxygen crosstalk due to delamination. Therefore, there is a need for a cation exchange membrane that balances high mechanical performance and high ionic conductivity. Summary of the Invention

[0003] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a composite cation exchange membrane, its preparation method and application.

[0004] To achieve this objective, the present invention employs the following technical solution: In a first aspect, the present invention provides a composite cation exchange membrane, the composite cation exchange membrane comprising a substrate and a resin layer distributed inside and on the surface of the substrate; The substrate contains polar groups; The resin layer is made of perfluorosulfonic acid resin and / or sulfonated non-fluorinated resin material. The sulfonic acid group loading per unit volume of resin layer is 1.6 × 10⁻⁶. -3 ~4.8×10 -3 mol / cm 3 For example, 1.6 × 10 - 3 mol / cm 3 1.8×10 -3 mol / cm 3 2×10 -3 mol / cm 3 2.2×10 -3 mol / cm 3 2.4×10 -3 mol / cm 3 2.5×10 -3 mol / cm 3 2.6×10 -3 mol / cm 3 2.8×10 -3 mol / cm3 2.9×10 -3 mol / cm 3 3×10 -3 mol / cm 3 3.2×10 -3 mol / cm 3 3.4×10 -3 mol / cm 3 3.5×10 -3 mol / cm 3 3.6×10 -3 mol / cm 3 3.8×10 -3 mol / cm 3 4×10 -3 mol / cm 3 4.2×10 -3 mol / cm 3 4.4×10 -3 mol / cm 3 4.5×10 -3 mol / cm 3 4.6×10 -3 mol / cm 3 4.8×10 -3 mol / cm 3 or a range consisting of any two of them.

[0005] The composite cation exchange membrane provided by this invention can improve the problems of insufficient mechanical strength and poor interfacial bonding of current composite membrane materials. By controlling the presence of polar groups on the substrate, the substrate material can be made more hydrophilic, improving the permeation effect. Furthermore, by adding some hydrophilic groups to the substrate material, hydrogen bonds and other forces can be formed between it and the resin material, enhancing the bonding force. By controlling the sulfonic acid group loading per unit volume of the resin layer within a specific range, the composite cation exchange membrane can achieve a balance between superior mechanical properties and ionic conductivity.

[0006] In this invention, the method for controlling the sulfonic acid group loading per unit volume of resin layer includes: First, determine the number of sulfonic acid groups in the resin repeating unit (e.g., determine the degree of sulfonation of the sulfonated non-fluorinated resin material). Adjust the solid content of the resin solution, and calculate the amount of resin needed based on the porosity of the substrate and the coating thickness. Combine this with the degree of sulfonation of the resin to calculate the theoretical sulfonic acid group loading. Finally, by controlling the coating process and parameters to ensure that the resin fully penetrates the substrate and forms a uniform coating on the surface, the ideal sulfonic acid group loading can be obtained.

[0007] In this invention, the sulfonic acid group loading per unit volume of resin layer can be tested using acid-base titration or elemental analysis. Acid-base titration involves displacing hydrogen ions from the sulfonic acid groups and then using sodium hydroxide solution to determine the hydrogen ion concentration; elemental analysis involves determining the mass fraction of sulfur using ion chromatography or inductively coupled plasma atomic emission spectrometry.

[0008] Preferably, the sulfonic acid group loading per unit volume of resin layer is 2.9 × 10⁻⁶. -3 ~4.2×10 -3 mol / cm 3 .

[0009] Preferably, the polar group includes any one or a combination of at least two of the following: hydroxyl (-OH), carboxyl (-COOH), carbonyl (C=O), amino (-NH2, -NH-), epoxy (-CH(O)CH-), sulfonic acid (-SO3H), phosphate (-PO3H2), cyano (-CN), and amide (-CONH-).

[0010] Preferably, the sulfonated non-fluorinated resin material contains at least one benzene ring, and each benzene ring contains 1 to 4 (e.g., 1, 2, 3 or 4) sulfonic acid groups.

[0011] Preferably, the sulfonated non-fluorinated resin material includes at least one of sulfonated non-fluorinated polymers, sulfonated copolymers (such as random copolymers of sulfonated monomers and non-sulfonated monomers, block copolymers), or products obtained by crosslinking sulfonated non-fluorinated polymers. Existing methods for obtaining sulfonated non-fluorinated resin materials include polymerization using monomers modified with sulfonic acid groups, or post-treatment such as sulfonation of non-fluorinated polymers.

[0012] Preferably, the degree of sulfonation of the sulfonated non-fluorinated resin material is 0.4 to 0.85, for example, a range of 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85 or any two thereof, preferably 0.6 to 0.8.

[0013] Preferably, the sulfonated non-fluorinated resin material includes any one or a combination of at least two of the following: sulfonated polysulfone material, sulfonated polyethersulfone material, sulfonated polyarylene ethersulfone material, sulfonated polyamide material, sulfonated polyimide material, sulfonated polyetherimide material, sulfonated polyetheretherketone material, sulfonated polyarylene etherketone material, sulfonated polyphenylene sulfide material, sulfonated polyphenylene ether material, sulfonated polybenzimidazole material, and sulfonated polyphosphonic nitrile material.

[0014] Preferably, the substrate can be a reinforcing substrate. A reinforcing substrate refers to a porous / fibrous support material used to improve the mechanical strength of the composite cation exchange membrane, inhibit membrane deformation (such as high-temperature swelling), and form a stable interface with the resin layer. Its core function is to provide mechanical support for the resin layer, while simultaneously achieving resin permeation and filling through a porous structure or surface modification, ensuring the overall structural integrity of the composite membrane. Its characteristics include a porous structure, which can be in the form of non-woven fabric, woven fabric, porous membrane, fiber felt, etc., ensuring sufficient mechanical strength, and possessing resistance to solvents (such as NMP, DMF, ethanol, etc.), acid and alkali corrosion, high temperature resistance, and excellent electrochemical stability. It exhibits no significant swelling, degradation, or precipitation, and does not chemically react with the resin.

[0015] Preferably, the substrate material includes any one or a combination of at least two of expanded polytetrafluoroethylene (ePTFE), polyethylene terephthalate (PET), polyimide (PI), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polysulfone (PSU), polyethylene (PE), and polypropylene (PP).

[0016] Preferably, the substrate is any one of porous membrane, nonwoven fabric, woven fabric, or fiber felt.

[0017] Preferably, the thickness of the substrate is 5~40μm, for example, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm or any two of these ranges; the porosity is 40%~90%, for example, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or any two of these ranges; and the pore size is 50nm~5μm, for example, 50nm, 80nm, 100nm, 200nm, 300nm, 500nm, 800nm, 1μm, 2μm, 3μm, 4μm, 5μm or any two of these ranges.

[0018] Preferably, the thickness of the composite cation exchange membrane is 30~100μm, for example, a range of 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm or any combination thereof.

[0019] In a second aspect, the present invention provides a method for preparing a composite cation exchange membrane as described in the first aspect, the method comprising the following steps: (1) Provide a substrate with polar groups; (2) Dissolve the material of the resin layer in a solvent to obtain a resin solution; (3) The resin solution is cast onto the substrate surface on one or both sides, and then vacuum impregnation and filling, vacuum drying, conventional drying and biaxial stretching are performed in sequence to obtain the composite cation exchange membrane.

[0020] This invention improves the preparation method to control the content of sulfonic acid groups on the resin layer per unit volume within a certain range. The vacuum impregnation and filling process reduces the surface tension of the resin solution, promotes its penetration into the substrate pores, reduces residual air bubbles in the pores, and increases the contact area between the resin and the inner wall of the substrate. At the same time, vacuum drying avoids the "pore shrinkage" caused by solvent evaporation in conventional drying, ensuring that the resin forms a continuous and dense filling structure in the pores and enhances the physical interlocking effect. The final biaxial stretching process can induce "conformal deformation" between the resin and the substrate through mechanical force, causing the resin molecular chains to align along the three-dimensional structure of the substrate pores, forming a mechanical interlocking structure similar to "anchors". Moreover, biaxial stretching helps the orientation and crystallization of polymer materials, further improving the mechanical properties of the composite cation exchange membrane.

[0021] Preferably, step (1) specifically includes: performing a hydrophilic modification pretreatment on the substrate.

[0022] Preferably, the hydrophilic modification pretreatment of the substrate includes hydrophilic modification pretreatment of the substrate using a treatment agent, wherein the treatment agent includes at least one of surfactants, polar materials, or hydrophilic solvents; Preferably, the surfactant is a nonionic surfactant, including any one or a combination of at least two of the following: polyoxyethylene vinyl phenyl ether surfactants, polyoxyethylene-polyoxypropylene block copolymer surfactants, polyoxyethylene fatty alcohol ether surfactants, polyoxyethylene sorbitan fatty acid ester surfactants, and alkyl polyglycoside surfactants.

[0023] Preferably, the nonionic surfactant includes, but is not limited to, any one or a combination of at least two of Triton X-100, poloxamer (such as Poloxamer 188, Poloxamer 407), octylphenol polyoxyethylene ether (OP-10), lauryl alcohol polyoxyethylene ether (AEO-9), Tween 80, and dodecyl glucoside (APG 1214).

[0024] Preferably, the polar material includes polyvinyl alcohol (PVA).

[0025] Preferably, the hydrophilic solvent includes isopropanol.

[0026] Preferably, the hydrophilic modification pretreatment of the substrate using a treatment agent specifically includes: The substrate is immersed in a solution or dispersion of surfactant and / or polar material or in a hydrophilic solvent, or a solution or dispersion of surfactant and / or polar material is coated onto the substrate surface, or a hydrophilic solvent is directly coated onto the substrate surface, ensuring complete wetting of the substrate. Then, excess solution on the substrate surface is absorbed with filter paper and dried.

[0027] This invention uses solutions or dispersions of surfactants and / or polar materials, or directly uses hydrophilic solvents to treat the substrate. These modifiers can penetrate along the pores through capillary action, directly contacting the internal pore walls of the substrate, so that the polar groups are distributed throughout the inner surface of the porous structure, resulting in coverage from the outside to the inside. This improves the overall wettability of the substrate and ensures more uniform and thorough resin filling. The treatment conditions of surfactants, polar materials, or hydrophilic solvents are mild, applicable to a wider range of materials, and have low equipment requirements, resulting in high cost-effectiveness. By selecting different types of surfactants, polar materials, or hydrophilic solvents, the modification effect can be flexibly adjusted to meet the matching requirements of different resin systems.

[0028] Preferably, the mass fraction of the surfactant and / or polar material solution or dispersion is 1% to 5%, for example, a range of 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any combination thereof. The solution may be, for example, an aqueous solution, an organic solution, etc.

[0029] Preferably, the drying temperature is 50~70℃, for example, a range of 50℃, 55℃, 60℃, 65℃, 70℃ or any combination thereof.

[0030] Preferably, the solvent in step (2) includes any one or a combination of at least two of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), ethanol, methanol, n-propanol, isopropanol, and water.

[0031] Preferably, the solid content of the resin solution in step (2) is 5% to 40%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or any two of these, preferably 15% to 30%.

[0032] Preferably, the vacuum impregnation filling in step (3) is performed at 20~40°C (e.g., a range of 20°C, 25°C, 30°C, 35°C, 40°C or any combination thereof). The vacuum impregnation filling process allows the resin solution to fully wet the pores of the filling substrate.

[0033] Preferably, the vacuum drying in step (3) specifically includes: heating from 20 to 40°C (e.g., a range of 20°C, 25°C, 30°C, 35°C, 40°C or any two thereof) at a rate of 0.4 to 0.6°C / min (e.g., a range of 0.4°C / min, 0.5°C / min, 0.6°C / min or any two thereof) to 50 to 70°C (e.g., a range of 50°C, 55°C, 60°C, 65°C, 70°C or any two thereof) under vacuum, and drying at 50 to 70°C (e.g., a range of 50°C, 55°C, 60°C, 65°C, 70°C or any two thereof) for no less than 1 hour (e.g., 1 hour, 2 hours, 3 hours or any two thereof).

[0034] Preferably, the conventional drying in step (3) specifically includes: exiting the vacuum state and adjusting the temperature from 50~70℃ (e.g., a range of 50℃, 55℃, 60℃, 65℃, 70℃ or any combination thereof) at a rate of 4~6℃ / min (e.g., 4℃ / min, 4.2℃ / min, 4.4℃ / min, 4.5℃ / min, 4.6℃ / min, 4.8℃ / min, 5℃ / min, 5.2℃ / min, 5.4℃ / min, 5.5℃ / min, 5.6℃ / min, 5.8℃ / min). The temperature is increased to 80~120℃ (e.g., 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃ or any two of these) at a rate of 6℃ / min, and dried at 80~120℃ for no less than 2 hours (e.g., 2 hours, 3 hours, 4 hours or any two of these) for no less than 2 hours.

[0035] Preferably, the biaxial stretching in step (3) is performed at a temperature not lower than 120°C (e.g., a range of 120°C, 130°C, 140°C, 150°C, 160°C or any combination thereof).

[0036] Preferably, the biaxial stretching ratio in step (3) is 1% to 5%, for example, a range consisting of 1%, 2%, 3%, 4%, 5% or any two of them.

[0037] Preferably, after the biaxial stretching in step (3), the following steps are also included: naturally cooling down while maintaining the stretched state until it drops to room temperature.

[0038] Thirdly, the present invention provides an application of the composite cation exchange membrane as described in the first aspect in flow batteries, water electrolysis for hydrogen production, or hydrogen fuel cells.

[0039] Compared with the prior art, the present invention has the following beneficial effects: The composite cation exchange membrane provided by this invention can improve the problems of insufficient mechanical strength and poor interfacial bonding of current composite membrane materials, while having a high ionic conductivity (0.015~0.079S / cm, preferably 0.045~0.075S / cm). First, by improving the preparation method, the sulfonic acid group loading per unit volume of the resin layer is controlled within a certain range. The vacuum impregnation and filling process can reduce the surface tension of the resin solution, promote its penetration into the substrate pores, reduce residual bubbles in the pores, and increase the contact area between the resin and the inner wall of the substrate. At the same time, vacuum drying can avoid the "pore shrinkage" caused by solvent evaporation in conventional drying, ensuring that the resin forms a continuous and dense filling structure in the pores and enhancing the physical interlocking effect. Second, by controlling the presence of polar groups on the substrate, the reinforcing material can be made more hydrophilic, improving the penetration effect. It also allows the substrate material to carry some hydrophilic groups, enabling it to form hydrogen bonds and other forces with the resin material, thus enhancing the bonding force. Finally, the biaxial stretching process can induce "conformal deformation" between the resin and the substrate through mechanical force, causing the resin molecular chains to align along the three-dimensional structure of the substrate pores, forming a mechanical interlocking structure similar to an "anchor". Moreover, biaxial stretching helps the orientation and crystallization of polymer materials, further improving the mechanical properties of the composite cation exchange membrane (dry tensile strength: 20~60MPa, preferably 40~60MPa). Detailed Implementation

[0040] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0041] Example 1 This embodiment provides a composite cation exchange membrane, which includes a substrate and a resin layer distributed inside and on the surface of the substrate.

[0042] The preparation method includes the following steps: (1) Apply the treatment agent (an aqueous solution of PVA with a mass fraction of 3%) to the substrate surface to ensure that the substrate is completely wetted. Then, use filter paper to absorb the excess solution on the substrate surface and dry it at 60°C. (2) Dissolve the material of the resin layer (sulfonated polysulfone, sulfonation degree of 0.85) in a solvent (DMSO) to obtain a resin solution with a solid content of 5%; (3) The resin solution is cast onto the surface of the hydrophilically modified pretreated substrate on one side, and then undergoes a programmed temperature rise film formation process, specifically including: the first stage, vacuum impregnation and filling at 35°C, so that the resin solution fully wets and fills the pores of the substrate; the second stage, under vacuum, the temperature is raised from 35°C to 60°C at a rate of 0.5°C / min, and dried at 60°C for 6 hours; the third stage, the vacuum state is removed, and the temperature is raised from 60°C to 100°C at a rate of 5°C / min, and dried at 100°C for 3 hours; the fourth stage, high temperature biaxial stretching post-treatment process, the above membrane is biaxially stretched at a temperature of 130°C with a stretching ratio of 5%; then, under the stretching state, it is naturally cooled until it drops to room temperature to obtain the composite cation exchange membrane.

[0043] The substrate is a porous membrane made of expanded polytetrafluoroethylene, with a thickness of 40 μm, a porosity of 90%, and a pore size of 3 μm. The sulfonic acid group loading per unit volume of resin layer is 4.07 × 10⁻⁶. -3 mol / cm 3 The thickness of the composite cation exchange membrane is 50 μm.

[0044] Examples 2-13, Comparative Examples 1-2 The difference from Example 1 is that the types and / or parameters of the substrate, treatment agent, and resin layer material, as well as the preparation conditions, are different, as shown in Tables 1-3.

[0045] Table 1 Table 2 PVA was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with the brand name P139540. Sulfonated polysulfone material was purchased from Shanghai Chenyihui Plastics Co., Ltd. The sulfonated polyether ether ketone materials were purchased from Dongguan Tianzhihong Plastic Co., Ltd.

[0046] Table 3 The performance of the composite cation exchange membranes provided in the embodiments and comparative examples of the present invention was tested using the following methods: (1) Ionic conductivity (room temperature): The ionic conductivity test is performed according to GB / T 20042.3-2022. The membrane sample is fixed in the conductivity measurement cell, and then the device is placed in the constant temperature and humidity test chamber. The test conditions are set. After the test chamber reaches the set test conditions and stabilizes for 30 minutes, the test is performed in the frequency range of 1 Hz to 2×10⁻⁶. 6The ionic conductivity of a sample can be calculated by measuring its impedance spectrum using an electrochemical impedance spectroscopy instrument under conditions of Hz and a perturbation voltage of 10 mV.

[0047] (2) Tensile strength (dry state): The tensile strength test shall be performed in accordance with GB / T 20042.3-2022. Place the sample in the test fixture, align the longitudinal axis of the sample with the line connecting the centers of the upper and lower fixtures, and clamp it. Use a tensile speed of 50 mm / min until the sample breaks, and read the corresponding load value.

[0048] (3) Sulfonic acid group loading per unit volume of resin layer: Refer to GB / T 20042.3-2022, cut a dry sample of the composite cation exchange membrane to be tested, and record the volume V1 of the composite cation exchange membrane. Place the sample in a sealed reagent bottle containing saturated sodium chloride solution and stir for 24 hours, then use NaOH standard solution (concentration C) NaOH Titrate to neutral using an automatic potentiometric titrator and record the volume V of NaOH solution consumed. NaOH The sulfonic acid group loading per unit volume of resin layer is: V NaOH ×C NaOH / V1.

[0049] The performance test results are shown in Table 4.

[0050] Table 4 As can be seen from Table 4, the composite cation exchange membranes provided in the embodiments of the present invention all have high room temperature ionic conductivity (0.015~0.079S / cm, preferably 0.045~0.075S / cm) and dry tensile strength (20~60MPa, preferably 40~60MPa).

[0051] Compared with Example 3, the room temperature ionic conductivity of the composite cation exchange membrane provided in Comparative Example 1 decreased significantly, and the dry tensile strength of the composite cation exchange membrane provided in Comparative Example 2 decreased significantly.

[0052] The applicant declares that the present invention is illustrated by the above embodiments to demonstrate the composite cation exchange membrane, its preparation method, and its application. However, the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A composite cation exchange membrane, characterized in that, The composite cation exchange membrane includes a substrate and a resin layer distributed inside and on the surface of the substrate; The substrate contains polar groups; The resin layer is made of perfluorosulfonic acid resin and / or sulfonated non-fluorinated resin material. The sulfonic acid group loading per unit volume of resin layer is 1.6 × 10⁻⁶. -3 ~4.8×10 -3 mol / cm 3 .

2. The composite cation exchange membrane according to claim 1, characterized in that, The sulfonic acid group loading per unit volume of resin layer is 2.9 × 10⁻⁶. -3 ~4.2×10 -3 mol / cm 3 ; Preferably, the polar group includes any one or a combination of at least two of the following: hydroxyl, carboxyl, carbonyl, amino, epoxy, sulfonic acid, phosphate, cyano, and amide. Preferably, the sulfonated non-fluorinated resin material contains at least one benzene ring, and each benzene ring contains 1 to 4 sulfonic acid groups; Preferably, the sulfonated non-fluorinated resin material includes at least one of sulfonated non-fluorinated polymers, sulfonated copolymers, or products obtained by crosslinking sulfonated non-fluorinated polymers; Preferably, the degree of sulfonation of the sulfonated non-fluorinated resin material is 0.4~0.85; Preferably, the sulfonated non-fluorinated resin material includes any one or a combination of at least two of the following: sulfonated polysulfone material, sulfonated polyethersulfone material, sulfonated polyarylene ethersulfone material, sulfonated polyamide material, sulfonated polyimide material, sulfonated polyetherimide material, sulfonated polyetheretherketone material, sulfonated polyarylene etherketone material, sulfonated polyphenylene sulfide material, sulfonated polyphenylene ether material, sulfonated polybenzimidazole material, and sulfonated polyphosphonic nitrile material.

3. The composite cation exchange membrane according to claim 1 or 2, characterized in that, The substrate material includes any one or a combination of at least two of expanded polytetrafluoroethylene, polyethylene terephthalate, polyimide, polyetheretherketone, polyphenylene sulfide, polysulfone, polyethylene, and polypropylene. Preferably, the substrate is any one of porous membrane, nonwoven fabric, woven fabric, and fiber felt; Preferably, the substrate has a thickness of 5~40μm, a porosity of 40%~90%, and a pore size of 50nm~5μm.

4. The composite cation exchange membrane according to any one of claims 1-3, characterized in that, The thickness of the composite cation exchange membrane is 30~100μm.

5. A method for preparing a composite cation exchange membrane as described in any one of claims 1-4, characterized in that, The preparation method includes the following steps: (1) Provide a substrate with polar groups (2) Dissolve the material of the resin layer in a solvent to obtain a resin solution; (3) The resin solution is cast onto the substrate surface on one or both sides, and then vacuum impregnation and filling, vacuum drying, conventional drying and biaxial stretching are performed in sequence to obtain the composite cation exchange membrane.

6. The preparation method according to claim 5, characterized in that, Step (1) specifically includes: performing hydrophilic modification pretreatment on the substrate; Preferably, the hydrophilic modification pretreatment of the substrate includes hydrophilic modification pretreatment of the substrate using a treatment agent, wherein the treatment agent includes at least one of surfactants, polar materials, or hydrophilic solvents; Preferably, the surfactant is a nonionic surfactant, including any one or a combination of at least two of the following: polyoxyethylene vinyl phenyl ether surfactants, polyoxyethylene-polyoxypropylene block copolymer surfactants, polyoxyethylene fatty alcohol ether surfactants, polyoxyethylene sorbitan fatty acid ester surfactants, and alkyl polyglycoside surfactants. Preferably, the polar material comprises polyvinyl alcohol; Preferably, the hydrophilic solvent includes isopropanol; Preferably, the pretreatment of the substrate with a treatment agent for hydrophilic modification specifically includes: The substrate is immersed in a solution or dispersion of surfactant and / or polar material or in a hydrophilic solvent, or a solution or dispersion of surfactant and / or polar material is coated onto the substrate surface, or a hydrophilic solvent is directly coated onto the substrate surface and then dried. Preferably, the mass fraction of the surfactant and / or polar material solution or dispersion is 1% to 5%; Preferably, the drying temperature is 50~70℃.

7. The preparation method according to claim 5 or 6, characterized in that, The solvent in step (2) includes any one or a combination of at least two of N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, ethanol, methanol, n-propanol, isopropanol, and water; Preferably, the solid content of the resin solution in step (2) is 5% to 40%, more preferably 15% to 30%.

8. The preparation method according to any one of claims 5-7, characterized in that, The vacuum impregnation filling in step (3) is carried out at 20~40℃; Preferably, the vacuum drying in step (3) specifically includes: heating from 20~40℃ to 50~70℃ at a rate of 0.4~0.6℃ / min under vacuum, and drying at 50~70℃ for not less than 1 hour; Preferably, the conventional drying in step (3) specifically includes: exiting the vacuum state and raising the temperature from 50~70℃ to 80~120℃ at a rate of 4~6℃ / min, and drying at 80~120℃ for no less than 2 hours.

9. The preparation method according to any one of claims 5-8, characterized in that, The biaxial stretching in step (3) is performed at a temperature not lower than 120°C; Preferably, the biaxial stretching ratio in step (3) is 1% to 5%; Preferably, after the biaxial stretching in step (3), the following steps are also included: naturally cooling down while maintaining the stretched state until it drops to room temperature.

10. The application of a composite cation exchange membrane as described in any one of claims 1-4 in a flow battery, water electrolysis for hydrogen production, or a hydrogen fuel cell.

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