Composite proton exchange membrane and preparation method thereof

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to a composite proton exchange membrane and a preparation method thereof. According to the prepared composite proton exchange membrane, the perfluorosulfonic acid resin capable of being industrially applied is selected as a base membrane material, and the modified polybenzimidazole polymer resin is added, so that the problem of high ion permeation rate of a perfluorosulfonic acid proton exchange membrane in the prior art is solved; interpenetration and permeation of the electrolyte in the use process of the perfluorosulfonic acid proton exchange membrane can be reduced, cross contamination of positive and negative electrolyte is greatly reduced, and the service life of the electrolyte is prolonged. The PBI is functionalized, so that the proton transmission capacity of the PBI is improved, and the proton exchange membrane formed by blending the functionalized PBI and the perfluorinated sulfonic acid resin can keep excellent vanadium resistance, excellent proton transmission capacity and relatively high ion selectivity at the same time. The preparation process is simple, and the prepared proton exchange membrane can meet the performance and long-term stability use requirements of a flow battery.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and in particular relates to a composite proton exchange membrane and a preparation method thereof. Background Art

[0002] To achieve safe, clean, and large-scale renewable energy storage systems, liquid flow batteries (RFBs) have attracted significant attention in both the electrical and chemical energy fields due to their excellent battery efficiency, rapid response, long cycle life, and unique modular design, enabling the storage and release of electricity. As a key component of all-vanadium redox flow battery (VRFB) systems, the proton exchange membrane (PEM) serves as a barrier between the positive and negative electrolytes and provides the necessary proton transport pathways. An excellent PEM should possess high proton conductivity, low vanadium ion permeability, excellent physical and chemical stability, and low cost. Therefore, research on PEMs with superior overall performance has become a hot topic in the flow battery field.

[0003] Perfluorosulfonic acid resin is currently the only proton exchange membrane material capable of industrial application. Its unique molecular structure imparts excellent mechanical and chemical stability, while its highly hygroscopic surface side chains also provide excellent proton conductivity. Nafion series membranes, produced by DuPont in the United States, are currently the most widely used proton exchange membranes in flow batteries. They exhibit excellent proton conductivity, but their rapid ion permeation rate causes cross-contamination between the positive and negative electrolytes, reducing battery efficiency and membrane lifespan, increasing battery operating costs, and severely limiting the effective use of sulfonic acid resin proton exchange membranes in flow batteries.

[0004] Chinese patent document CN117457953A discloses a perfluorosulfonic acid resin slurry and a proton exchange membrane for a flow battery and a preparation method thereof. The preparation method of the perfluorosulfonic acid resin slurry comprises the following steps: (1) dissolving and dispersing the perfluorosulfonic acid resin in a mixed solvent to obtain a semi-finished perfluorosulfonic acid resin slurry; (2) adding the semi-finished perfluorosulfonic acid resin slurry to a high-pressure homogenizer for high-pressure homogenization to obtain a perfluorosulfonic acid resin slurry. By subjecting the semi-finished perfluorosulfonic acid resin slurry to high-pressure homogenization, the perfluorosulfonic acid resin molecular segments in the obtained perfluorosulfonic acid resin slurry are uniformly distributed and oriented, thereby making the perfluorosulfonic acid resin slurry highly uniformly dispersed, with low viscosity and good fluidity. However, it uses a high-pressure homogenizer to disperse the semi-finished perfluorosulfonic acid resin slurry. The high shear force brought by the high-pressure homogenizer will cause the molecular chain of the polymer resin to break, resulting in mechanical / shear degradation, reducing the molecular chain and affecting the film-forming performance of the product; secondly, the high-pressure homogenizer will bring a significant thermal effect. The high pressure and shear force are converted into heat, causing the material solvent to volatilize, affecting the solution system, and then affecting the metal ion permeability performance of the proton exchange membrane.

[0005] The method of preparing composite proton exchange membranes by adding inorganic materials is an effective way to improve the proton exchange membrane's ability to block metal ion penetration, but the dispersion and solubility problems of inorganic materials limit the application of this method.

[0006] It can be seen that providing a flow battery proton exchange membrane with low metal ion permeability and a preparation method thereof has positive practical significance for improving the service life of the electrolyte and the cycle stability of the battery. Summary of the Invention

[0007] In order to solve the problem of high metal ion permeability of perfluorosulfonic acid resin proton exchange membrane, the present invention provides a composite proton exchange membrane and a preparation method thereof.

[0008] In order to achieve the above object, the present invention provides the following technical solutions: A composite proton exchange membrane consists of perfluorosulfonic acid resin and functionalized polybenzimidazole, wherein the content of the functionalized polybenzimidazole is 0.1%-60% by mass.

[0009] Preferably, the thickness of the proton exchange membrane is 10-250 μm.

[0010] Further preferably, the thickness of the proton exchange membrane is 40-60 μm.

[0011] Preferably, the perfluorosulfonic acid resin has an ion exchange capacity of 0.5-2.5 mmol / g and a molecular weight of 150,000-800,000; more preferably, the ion exchange capacity is 0.8-1.8 mmol / g and the molecular weight is 200,000-600,000; most preferably, the ion exchange capacity is 0.9-1.1 mmol / g and the molecular weight is 250,000-350,000.

[0012] Preferably, the functionalized polybenzimidazole includes one or more of phosphoric acid-doped polybenzimidazole, fluorinated polybenzimidazole and alkylated polybenzimidazole.

[0013] Preferably, the molecular weight of the polybenzimidazole is 50,000-400,000, more preferably 300,000-400,000.

[0014] Further preferably, the phosphoric acid-doped polybenzimidazole is prepared by mixing PBI with a high-concentration phosphoric acid aqueous solution, heating under a nitrogen atmosphere to form a homogeneous solution, and drying and cooling to prepare the phosphoric acid-doped PBI.

[0015] More preferably, in the preparation of the phosphoric acid-doped polybenzimidazole, the mass ratio of PBI to high-concentration phosphoric acid aqueous solution is 1:2-1:4, the mass concentration of phosphoric acid in the high-concentration phosphoric acid aqueous solution is ≥85%, and the reaction temperature is 180-200°C.

[0016] Further preferably, the fluorinated polybenzimidazole is prepared by adding PBI to pentafluorobenzoyl chloride, reacting at 80-180° C. for 8-48 hours under a nitrogen atmosphere, filtering and drying to obtain fluorinated PBI, wherein the mass ratio of PBI to pentafluorobenzoyl chloride is 1:1-1:5.

[0017] Further preferably, the preparation of the alkylated polybenzimidazole is as follows: PBI powder is mixed with NMP under a nitrogen atmosphere, stirred and dissolved at 80-180° C., NaH is added for dispersion, 1-bromohexane is added after dispersion is completed, and the reaction is heated for 8-32 hours. After the reaction is completed, the reaction is cooled to room temperature, methanol is added to precipitate the product, and the precipitate is washed with methanol and deionized water, and dried to obtain alkylated PBI, wherein PBI accounts for 5-15wt% of the mass of NMP, the mass ratio of PBI to NaH is 1:2-1:5, and the mass ratio of PBI to 1-bromohexane is 1:1-1:3.

[0018] Preferably, the composite proton exchange membrane has a functionalized polybenzimidazole content of 15% to 50% by mass.

[0019] Further preferably, the composite proton exchange membrane has a phosphoric acid-doped polybenzimidazole content of 20%-50% by mass.

[0020] Further preferably, the composite proton exchange membrane has a content of fluorinated polybenzimidazole of 15% to 25% by mass.

[0021] Further preferably, the composite proton exchange membrane has an alkylated polybenzimidazole content of 15% to 25% by mass.

[0022] The present invention also provides a method for preparing the composite proton exchange membrane, comprising the following steps: (1) dissolving perfluorosulfonic acid resin and functionalized polybenzimidazole in an organic solvent to obtain a film-forming dispersion; (2) The film-forming dispersion liquid of step (1) is evenly scraped onto the surface of the substrate by solution casting to form a liquid film, and then dried by heating at a gradient increasing temperature of 25-200°C to form a film.

[0023] Preferably, the film-forming dispersion in step (1) has a solid content of 5-60% and a viscosity of 30-2000 mPa / s; the coating speed in step (2) is 10-100 cm / min, the liquid film thickness is 50-300 μm, and the substrate is a glass plate.

[0024] Further preferably, the solid content of the film-forming dispersion in step (1) is 20-30%, and the viscosity is 100-300 mPa / s; the coating speed in step (2) is 40-60 cm / min, and the liquid film thickness is 190-210 μm.

[0025] Preferably, the organic solvent in step (1) is one or more of alcohol, N,N-dimethylformamide DMF, N,N-dimethylacetamide DMAC, N-methylpyrrolidone NMP, and dimethyl sulfoxide DMSO.

[0026] Compared with the prior art, the present invention has at least the following advantages: 1. The present invention functionalizes polybenzimidazole and then mixes it with a perfluorosulfonic acid resin to prepare a composite proton exchange membrane by solution casting. This solves the problem of high ion permeation rate of perfluorosulfonic acid proton exchange membranes in the prior art and can effectively reduce the cross-penetration of metal ions, thereby improving the charge and discharge efficiency and long-term cycle stability of the proton exchange membrane; reduces electrolyte cross-contamination, thereby reducing the cost of electrolyte use, facilitating application in the industrialization of liquid flow battery stacks, and is conducive to achieving the long life and high performance requirements of the proton exchange membrane, thereby reducing the cost of the stack.

[0027] 2. The present invention improves the proton transport capacity of PBI by functionalizing PBI, so that the proton exchange membrane formed by blending functionalized PBI with perfluorosulfonic acid resin can maintain excellent proton transport capacity and high ion selectivity while maintaining excellent vanadium resistance. Among them, phosphorylated PBI and alkylated PBI not only improve the solubility and proton conductivity of pure PBI, but also retain the vanadium resistance of the imidazole ring backbone of PBI. The fluorinated PBI has improved hydrophobicity and vanadium resistance, so the proton exchange membrane formed by mixing fluorinated PBI with perfluorosulfonic acid resin exhibits better performance in blocking vanadium ion penetration.

[0028] 3. The present invention proposes for the first time a method for preparing three different functional PBIs. The preparation method is simple and convenient, can be completed in one step, and can control the reaction time and reaction temperature, control the degree of functionalization, and achieve controllable modification of functional PBI. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The samples of Examples 2, 5, 8 and Comparative Examples 1 and 2 are at 80-200 mA / cm 2 Below is a comparison chart of battery performance tests. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be noted that the following examples are intended to facilitate understanding of the present invention and do not have any limiting effect on the present invention.

[0031] Preparation of phosphoric acid-doped PBI: PBI was mixed with a high-concentration phosphoric acid aqueous solution, heated to 180°C under nitrogen protection to form a homogeneous solution, and then dried and cooled to prepare phosphoric acid-doped PBI, wherein the mass ratio of PBI to the high-concentration phosphoric acid aqueous solution was 1:2, and the mass concentration of the high-concentration phosphoric acid aqueous solution was 85%.

[0032] Preparation of fluorinated PBI: PBI was added to pentafluorobenzoyl chloride, reacted at 150°C for 24 h under a nitrogen atmosphere, and filtered and dried to obtain fluorinated PBI, wherein the mass ratio of PBI to pentafluorobenzoyl chloride was 1:4.

[0033] Preparation of alkylated PBI: Under a nitrogen atmosphere, PBI powder was mixed with a certain amount of NMP (PBI accounting for 5 wt% of the NMP mass), stirred and dissolved at 80°C, and a certain amount of NaH was slowly added. The mass ratio of PBI to NaH was 1:2. After dispersion, a certain amount of 1-bromohexane was slowly added. The mass ratio of PBI to 1-bromohexane was 1:2. The reaction was heated for 24 hours. After the reaction, the mixture was cooled to room temperature and 500 ml of methanol was added to precipitate the product. The precipitate was washed with methanol and deionized water and dried to obtain alkylated PBI.

[0034] In all the following examples and comparative examples, the molecular weight M of the perfluorosulfonic acid resin used is n The molecular weight of polybenzimidazole is M n It is 350,000.

[0035] Example 1 20g of perfluorosulfonic acid resin and 5g of phosphoric acid-doped polybenzimidazole were added to 75g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 110mPa / s. The film-forming dispersion was evenly scraped onto the surface of a glass plate by solution casting to form a liquid film. The scraping speed was 50cm / min and the liquid film thickness was 200μm. After gradient heating from 25℃ (6min) to 50℃ (6min) to 80℃ (6min) to 140℃ (6min) to 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0036] Example 2 20g of perfluorosulfonic acid resin and 10g of phosphoric acid-doped polybenzimidazole were added to 90g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 128mPa / s. The film-forming dispersion was evenly scraped onto the surface of a glass plate by solution casting to form a liquid film at a scraping speed of 50cm / min and a liquid film thickness of 200μm. After gradient heating from 25℃ (6min) to 50℃ (6min) to 80℃ (6min) to 140℃ (6min) to 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0037] Example 3 20g of perfluorosulfonic acid resin and 20g of phosphoric acid-doped polybenzimidazole were added to 120g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 155mPa / s. The film-forming dispersion was evenly scraped onto the surface of a glass plate by solution casting to form a liquid film. The scraping speed was 50cm / min and the liquid film thickness was 200μm. After gradient heating from 25℃ (6min) to 50℃ (6min) to 80℃ (6min) to 140℃ (6min) to 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0038] Example 4 20g of perfluorosulfonic acid resin and 5g of fluorinated polybenzimidazole were added to 75g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 130mPa / s. The film-forming dispersion was evenly scraped onto the surface of a glass plate by solution casting to form a liquid film. The scraping speed was 50cm / min and the liquid film thickness was 200μm. After gradient heating from 25℃ (6min) to 50℃ (6min) to 80℃ (6min) to 140℃ (6min) to 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0039] Example 5 20g of perfluorosulfonic acid resin and 10g of fluorinated polybenzimidazole were added to 90g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 162mPa / s. The film-forming dispersion was evenly scraped onto the surface of a glass plate by solution casting to form a liquid film. The scraping speed was 50cm / min and the liquid film thickness was 200μm. After gradient heating from 25℃ (6min) to 50℃ (6min) to 80℃ (6min) to 140℃ (6min) to 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0040] Example 6 20 g of perfluorosulfonic acid resin and 20 g of fluorinated polybenzimidazole were added to 120 g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 210 mPa / s. The film-forming dispersion was evenly scraped onto the surface of a glass plate by solution casting to form a liquid film. The scraping speed was 50 cm / min and the liquid film thickness was 200 μm. After gradient heating from 25°C (6 min) to 50°C (6 min) to 80°C (6 min) to 140°C (6 min) to 180°C (6 min), a composite proton exchange membrane with a thickness of 50 μm was prepared.

[0041] Example 7 20g of perfluorosulfonic acid resin and 5g of alkylated polybenzimidazole were added to 75g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 122mPa / s. The film-forming dispersion was evenly scraped onto the surface of a glass plate by solution casting to form a liquid film. The scraping speed was 50cm / min and the liquid film thickness was 200μm. After gradient heating from 25℃ (6min) to 50℃ (6min) to 80℃ (6min) to 140℃ (6min) to 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0042] Example 8 20 g of perfluorosulfonic acid resin and 10 g of alkylated polybenzimidazole were added to 90 g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 145 mPa / s. The film-forming dispersion was evenly scraped onto the surface of a glass plate by solution casting to form a liquid film. The scraping speed was 50 cm / min and the liquid film thickness was 200 μm. After gradient heating from 25°C (6 min) to 50°C (6 min) to 80°C (6 min) to 140°C (6 min) to 180°C (6 min), a composite proton exchange membrane with a thickness of 50 μm was prepared.

[0043] Example 9 20 g of perfluorosulfonic acid resin and 20 g of alkylated polybenzimidazole were added to 120 g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 190 mPa / s. The film-forming dispersion was evenly scraped onto the surface of a glass plate by solution casting to form a liquid film. The scraping speed was 50 cm / min and the liquid film thickness was 200 μm. After gradient heating from 25°C (6 min) to 50°C (6 min) to 80°C (6 min) to 140°C (6 min) to 180°C (6 min), a composite proton exchange membrane with a thickness of 50 μm was prepared.

[0044] Comparative Example 1 20g of perfluorosulfonic acid resin and 10g of polybenzimidazole PBI were added to 90g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 160mPa / s. The film-forming dispersion was evenly scraped onto the surface of a glass plate by solution casting to form a liquid film. The scraping speed was 50cm / min and the liquid film thickness was 200μm. After gradient heating from 25℃ (6min) to 50℃ (6min) to 80℃ (6min) to 140℃ (6min) to 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0045] Comparative Example 2 25 g of perfluorosulfonic acid resin was added to 75 g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 105 mPa / s. The film-forming dispersion was evenly scraped onto the surface of a glass plate by solution casting to form a liquid film. The scraping speed was 50 cm / min and the liquid film thickness was 200 μm. After gradient heating from 25°C (6 min) to 50°C (6 min) to 80°C (6 min) to 140°C (6 min) to 180°C (6 min), a composite proton exchange membrane with a thickness of 50 μm was prepared.

[0046] Comparative Example 3 25 g of polybenzimidazole was added to 75 g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 250 mPa / s. The film-forming dispersion was evenly scraped onto the surface of a glass plate by solution casting to form a liquid film. The scraping speed was 50 cm / min and the liquid film thickness was 200 μm. After gradient heating from 25°C (6 min) to 50°C (6 min) to 80°C (6 min) to 140°C (6 min) to 180°C (6 min), a composite proton exchange membrane with a thickness of 50 μm was prepared.

[0047] Comparative Example 4 25g of phosphoric acid-doped polybenzimidazole was added to 75g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 185mPa / s. The film-forming dispersion was evenly scraped onto the surface of a glass plate by solution casting to form a liquid film. The scraping speed was 50cm / min and the liquid film thickness was 200μm. After gradient heating from 25℃ (6min) to 50℃ (6min) to 80℃ (6min) to 140℃ (6min) to 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0048] Comparative Example 5 25 g of fluorinated polybenzimidazole was added to 75 g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 270 mPa / s. The film-forming dispersion was evenly scraped onto the surface of a glass plate by solution casting to form a liquid film. The scraping speed was 50 cm / min and the liquid film thickness was 200 μm. After gradient heating from 25°C (6 min) to 50°C (6 min) to 80°C (6 min) to 140°C (6 min) to 180°C (6 min), a composite proton exchange membrane with a thickness of 50 μm was prepared.

[0049] Comparative Example 6 25 g of alkylated polybenzimidazole was added to 75 g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 223 mPa / s. The film-forming dispersion was evenly scraped onto the surface of a glass plate by solution casting to form a liquid film. The scraping speed was 50 cm / min and the liquid film thickness was 200 μm. After gradient heating from 25°C (6 min) to 50°C (6 min) to 80°C (6 min) to 140°C (6 min) to 180°C (6 min), a composite proton exchange membrane with a thickness of 50 μm was prepared.

[0050] Table 1 shows the proton conductivity, vanadium ion permeability, and ion selectivity of examples and comparative examples doped with different functionalized PBIs. Compared to pure perfluorosulfonic acid resin, the addition of functionalized PBI significantly improves the vanadium ion permeability and ion selectivity of the proton exchange membrane, demonstrating superior overall performance.

[0051] The test methods for proton conductivity and vanadium ion permeability are based on the industry standard NB / T 42080-2023.

[0052] Table 1 Basic physical properties of different membrane samples

[0053] Figure 1 For the samples of Examples 2, 5, 8 and Comparative Examples 1 and 2, the current is 80-200 mA / cm 2 The following chart compares battery performance tests. At all current densities, the Coulombic efficiency (CE) and energy efficiency (EE) of Examples 2, 5, and 8 are superior to those of Comparative Examples 1 and 2, demonstrating that the proton exchange membranes of Examples 2, 5, and 8 exhibit superior performance across the board. These test results generally correspond to the physicochemical properties. Example 5 has the lowest vanadium ion permeability, resulting in the highest Coulombic efficiency (CE); Example 2 has the highest ion selectivity, resulting in the highest energy efficiency (EE).

[0054] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A composite proton exchange membrane, characterized in that: The proton exchange membrane is composed of perfluorosulfonic acid resin and functionalized polybenzimidazole, and the content of the functionalized polybenzimidazole is 0.1%-60% by mass.

2. The composite proton exchange membrane according to claim 1, wherein The thickness of the proton exchange membrane is 10-250 μm.

3. The composite proton exchange membrane according to claim 1, wherein The functionalized polybenzimidazole includes one or more of phosphoric acid-doped polybenzimidazole, fluorinated polybenzimidazole and alkylated polybenzimidazole.

4. The composite proton exchange membrane according to claim 3, characterized in that Preparation of the phosphoric acid-doped polybenzimidazole: PBI is mixed with a high-concentration phosphoric acid aqueous solution, heated under a nitrogen atmosphere to form a homogeneous solution, and then dried and cooled to prepare phosphoric acid-doped PBI; Preparation of the fluorinated polybenzimidazole: PBI is added to pentafluorobenzoyl chloride, reacted at 80-180° C. for 8-48 hours under a nitrogen atmosphere, filtered and dried to obtain fluorinated PBI, wherein the mass ratio of PBI to pentafluorobenzoyl chloride is 1:1-1:5; The preparation of the alkylated polybenzimidazole comprises the following steps: mixing PBI powder with NMP under a nitrogen atmosphere, stirring and dissolving at 80-180° C., adding NaH for dispersion, adding 1-bromohexane after dispersion, heating for reaction for 8-32 hours, cooling to room temperature after the reaction, adding methanol to precipitate the product, washing the precipitate with methanol and deionized water, and drying to obtain the alkylated PBI, wherein the PBI accounts for 5-15 wt % of the mass of the NMP, the mass ratio of PBI to NaH is 1:2-1:5, and the mass ratio of PBI to 1-bromohexane is 1:1-1:

3.

5. The composite proton exchange membrane according to claim 4, characterized in that In the preparation of the phosphoric acid-doped polybenzimidazole, the mass ratio of PBI to high-concentration phosphoric acid aqueous solution is 1:2-1:4, the mass concentration of phosphoric acid in the high-concentration phosphoric acid aqueous solution is ≥85%, and the reaction temperature is 180-200°C.

6. The composite proton exchange membrane according to claim 1, wherein The composite proton exchange membrane has a functionalized polybenzimidazole content of 15% to 50% by mass.

7. The composite proton exchange membrane according to claim 3, wherein: The composite proton exchange membrane has a phosphoric acid-doped polybenzimidazole content of 20%-50% by mass; the composite proton exchange membrane has a fluorinated polybenzimidazole content of 15%-25% by mass; and the composite proton exchange membrane has an alkylated polybenzimidazole content of 15%-25% by mass.

8. The method for preparing a composite proton exchange membrane according to any one of claims 1 to 7, wherein: The following steps are involved: (1) dissolving perfluorosulfonic acid resin and functionalized polybenzimidazole in an organic solvent to obtain a film-forming dispersion; (2) The film-forming dispersion liquid of step (1) is evenly scraped onto the surface of the substrate by solution casting to form a liquid film, and then dried by heating at a gradient increasing temperature of 25-200°C to form a film.

9. The preparation method according to claim 8, wherein The film-forming dispersion in step (1) has a solid content of 5-60% and a viscosity of 30-2000 mPa / s; the coating speed in step (2) is 10-100 cm / min, and the liquid film thickness is 50-300 mm.

10. The preparation method according to claim 8, characterized in that The organic solvent in step (1) is one or more of alcohol, N,N-dimethylformamide DMF, N,N-dimethylacetamide DMAC, N-methylpyrrolidone NMP, and dimethyl sulfoxide DMSO.

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