A method for preparing a cross-linked proton exchange membrane for water electrolysis

Abstract

This invention relates to a method for preparing a cross-linked proton exchange membrane for water electrolysis, belonging to the field of PEM water electrolysis membrane materials. The main chain of the exchange membrane is made of arylpyridine polymer, and cesium salts of heteropolyacids are doped into the membrane, which has excellent alkali resistance, strong mechanical strength, and proton conductor adsorption sites, effectively improving ionic conductivity and reducing acid loss during operation. Simultaneously, the cesium salts of heteropolyacids are formed into a gel state and layered with a casting solution to fully cover the membrane. Then, by heating, the gel state melts, and during the liquid vaporization / solvent evaporation process, the cesium salts of heteropolyacids can more comprehensively penetrate into the unformed membrane, finally forming along with the membrane. This ensures a very comprehensive and uniform distribution and binding of the cesium salts of heteropolyacids within the membrane, greatly guaranteeing the uniformity of the finished membrane.

Description

Technical Field

[0001] This invention relates to a method for preparing a cross-linked proton exchange membrane for water electrolysis, belonging to the field of PEM water electrolysis membrane materials. Background Technology

[0002] The global energy shortage is becoming increasingly severe. Traditional fossil fuels are non-renewable and cause serious environmental pollution during their use. However, the vast majority of energy conversion is achieved through heat engine processes, which have low conversion efficiency. The ever-increasing global energy consumption and the demand for "energy conservation and emission reduction" are the main driving forces for the development of renewable energy. Hydrogen, with its advantages of zero emissions and high energy density, is considered an ideal energy carrier for the future energy society. Hydrogen production through water electrolysis can not only balance loads and smooth peak flows in smart grids, but also widely utilize hydrogen in transportation, methane synthesis, and as input into natural gas supply networks. In recent years, fuel cells have made significant progress and have been practically applied in various fields. Fuel cells are not limited by the Carnot cycle, have a high theoretical energy conversion rate, and use hydrogen-rich substances such as hydrogen, methanol, and hydrocarbons as fuels, making them environmentally friendly. Therefore, fuel cells (PEMFCs) have broad application prospects. Proton exchange membrane water electrolysis (PEMWE) technology is widely studied and is being demonstrated on a large scale due to its advantages such as high current density, small footprint, fast dynamic response, wide operating range, high hydrogen purity (up to 99.99%), and high-pressure operation.

[0003] High-temperature PEM water electrolysis (100–180°C, HT-PEMWE), a revolutionary technology, also has a promising market potential. Combined with PBI polymer-based materials, it has demonstrated significant effectiveness and feasibility as a high-temperature proton exchange membrane in HT-PEMFCs. However, PBI membrane materials inevitably degrade at high temperatures (T≥150°C). In alkaline environments, the presence of strong nucleophiles OH- within the membrane, particularly ion-conducting groups with unstable end groups such as quaternary ammonium salts containing β-H or α-C, or functional groups containing ether bonds, can also lead to degradation of the polymer backbone and functional groups within the membrane. Therefore, arylpyridine polymers are also used as polymeric backbones in this field. These ether-free polymers effectively address the degradation problem and offer advantages such as good film-forming properties, chemical stability, and thermal stability. However, due to limitations in the functional groups of arylpyridine polymers and severe swelling after impregnation with phosphoric acid, the impregnation amount is usually limited, thus affecting conductivity and membrane mechanical strength.

[0004] In addition, the casting method is commonly used in this field for the preparation of proton exchange membranes. Generally, multiple materials are directly mixed to form a casting solution. Then, during the casting process, heating is used to combine the materials in the casting solution to achieve membrane formation. This method is widely used because of its simplicity. However, if the formulation of the casting solution is complex and the casting solution has a certain fluidity, molecular structures may agglomerate in some places or have uneven distribution due to insufficient quantity in some areas. This will prevent some polymer structures from combining smoothly to form a membrane, resulting in poor membrane formation and affecting the uniformity of the finished membrane. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a cross-linked proton exchange membrane for water electrolysis, thereby effectively improving the uniformity of molecular material distribution within the membrane and ensuring the homogeneity of the finished membrane.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for preparing a cross-linked proton exchange membrane for water electrolysis includes the following steps:

[0008] Step 1) The aryl hydrocarbon is copolymerized with 4-acetylpyridine to obtain an arylpyridine polymer. The arylpyridine polymer is mixed with a haloalkanes to undergo a nucleophilic substitution reaction to obtain a quaternized arylpyridine polymer. The quaternized arylpyridine polymer is dissolved in a high-boiling-point solvent to form a casting solution.

[0009] Step 2), disperse the heteropolyacid cesium salt in a high-boiling-point solvent to form a mixed solution;

[0010] Step 3): Add a crosslinking agent to the mixed solution in step 2), and stir at room temperature to form a gel-state mixed solution; the amount of crosslinking agent added is 0.5-2 times the mass of the quaternized arylpyridine polymer, and the gel state is from liquid to non-flowing state; the gel state of the heteropolyacid cesium salt is controlled by the amount of crosslinking agent added.

[0011] Step 4), film is formed by casting: first, the gel-state mixed solution is laid on a flat plate, then a release paper with pores is laid on the gel-state mixed solution, and then a casting solution is laid on the release paper to form a multilayer film structure.

[0012] Step 5): Heat the multilayer film structure from step 4) until the gel-state mixed solution is completely melted, then remove the release paper to obtain the formed film.

[0013] Step 6): Immerse the formed membrane obtained in step 5) in phosphoric acid solution, and dry it to obtain the desired cross-linked proton exchange membrane.

[0014] In the above technical solution, further, in step 1), the preparation method of the casting solution is specifically as follows:

[0015] a. Add 4-acetylpyridine and aryl hydrocarbons to dichloromethane solvent, add catalyst and protonating agent at -5 to 5℃, then return to room temperature, react for 2-50 h and then purify to obtain arylpyridine polymer;

[0016] The aryl hydrocarbon is selected from one or more of biphenyl, p-terphenyl, m-terphenyl, p-tetraphenyl, 9,9-dimethyl-9H-fluorene, triphenylmethane, and 1,3,5-triphenylbenzene;

[0017] The molar ratio of 4-acetylpyridine to aryl hydrocarbon is (1:1)-(1.5:1);

[0018] The molar ratio of the arylpyridine polymer to the haloalkane is (1:2)-(1:5);

[0019] The aryl hydrocarbon is present in dichloromethane at a concentration of 0.001-0.01 mol / ml;

[0020] The molar ratio of 4-acetylpyridine to the catalyst is (1:3)-(1:6);

[0021] The molar ratio of 4-acetylpyridine to the protonating agent is (1:4)-(1:10);

[0022] The catalyst is selected from trifluoroacetic acid and trichloroacetic acid, and the protonating agent is selected from trifluoromethanesulfonic acid and trinitrobenzenesulfonic acid;

[0023] b. Dissolve the arylpyridine polymer from step a in a high-boiling-point solvent, add a haloalkane, heat to 60-90℃, react for 4-70 h, and then purify to obtain the quaternized arylpyridine polymer.

[0024] The high-boiling-point solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone;

[0025] The haloalkanes are any one or more selected from 1,2-dibromoethane, 1,3-dibromopropane, 1,4-dibromobutane, 1,5-dibromopentane, 1,6-dibromohexane, 1,7-dibromoheptane, 1,8-dibromooctane, or 1,9-dibromononane;

[0026] The arylpyridine polymer has a concentration of 0.1-0.5 mol / L in a high-boiling-point solvent;

[0027] c. Mix the quaternized arylpyridine polymer with a high-boiling-point solvent and stir at room temperature to form a casting solution;

[0028] The mass fraction of the casting solution is 0.1%-20%.

[0029] In the above technical solution, further, in step 2), the synthesis step of the heteropolyacid cesium salt is specifically as follows:

[0030] Cesium carbonate and heteropoly acid are dissolved in deionized water, mixed, heated to 50-75℃ and reacted for 10-30 hours, rinsed with deionized water 1-3 times, and dried at 80-110℃.

[0031] The heteropolyacid is selected from one or more of phosphomolybdic acid, phosphotungstic acid, silicotungstic acid, and silicotomolybdic acid;

[0032] The molar ratio of cesium carbonate to heteropolyacid is 1.25:1.

[0033] In the above technical solution, further, in step 2), the organic high-boiling point solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone;

[0034] The mass ratio of the heteropolyacid cesium salt to the quaternized arylpyridine polymer is 0.005-0.015:1;

[0035] The mass fraction of the mixed solution is 0.1%-1%.

[0036] In the above technical solution, further, in step 3), the crosslinking agent includes one or more of N,N,N′,N′-tetramethylmethyldiamine (TMMDA), N,N,N′,N′-tetramethylethylenediamine (TMEDA), and N,N,N′,N′-tetramethyl-1,6-hexanediamine (TMHDA).

[0037] In the above technical solution, further, in step 5), the heating temperature is 120℃-160℃, the heating time is 10-50h, and the thickness of the formed film is 50-150μm.

[0038] In the above technical solution, further, in step 6), the mass fraction of the phosphoric acid solution is 1%-85%; the soaking time is 20-80h; and the drying temperature is 60-120℃.

[0039] In summary, the present invention has the following beneficial effects:

[0040] 1. This invention first selects arylpyridine polymers without unstable end groups such as ether bonds as the polymeric framework of the proton exchange membrane, which exhibits excellent alkali resistance and has a simple synthesis method and process. The polymer contains highly chemically stable nitrogen heterocyclic functional groups, and due to steric hindrance, degradation of the polymer backbone and functional groups within the membrane can be effectively avoided, thus exhibiting excellent chemical stability; at the same time, the numerous nitrogen-containing sites readily form hydrogen bonds with phosphoric acid, thereby adsorbing a large amount of phosphoric acid.

[0041] 2. In this invention, cesium heteropolyacid salts are prepared into a gel state and then laid out in a manner that completely covers the casting solution. The gel-state cesium heteropolyacid salts do not exhibit significant flow during this process, ensuring their proper positioning. Subsequently, heating melts the gel state, and during the liquid vaporization / solvent evaporation process, the cesium heteropolyacid salts can more comprehensively penetrate into the unformed membrane, ultimately forming along with the membrane. Therefore, the distribution and bonding of the cesium heteropolyacid salts within the membrane are very comprehensive and uniform, greatly ensuring the uniformity of the finished membrane. Furthermore, the addition of anti-sticking paper during this process ensures a smoother layup between the gel layer and the casting solution layer, thereby improving tensile strength, without affecting the bonding between the gel state after heating and vaporization and the casting solution.

[0042] 3. After adding a cross-linking agent, cesium salts of heteropolyacids can not only form a gel state, but also a cross-linked structure, which can effectively improve the phosphoric acid adsorption rate, conductivity, and reduce swelling. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to specific embodiments.

[0044] Example 1

[0045] (1) Add 0.02 mol 4-acetylpyridine and 0.02 mol biphenyl to 20 ml dichloromethane, add 0.06 mol trifluoroacetic acid and 0.08 mol trifluoromethanesulfonic acid at -5℃, then return to room temperature and react for 2 h. Pour the reaction solution into methanol aqueous solution to precipitate solid. Wash the solid with potassium carbonate solution at 50℃, then wash with deionized water until neutral, and dry to obtain arylpyridine polymer. Dissolve the obtained 0.01 mol arylpyridine polymer in 100 ml N-methylpyrrolidone, add 0.02 mol 1,2-dibromoethane, heat to 60℃ and react for 4 h. Pour into diethyl ether solution to precipitate solid. Wash the solid with deionized water 3 times and dry to obtain quaternized arylpyridine polymer. Finally, take 1 g of quaternized arylpyridine polymer and prepare a 0.1% mass fraction casting solution with N-methylpyrrolidone.

[0046] (2) Dissolve 0.0125 mol of cesium carbonate and 0.01 mol of phosphomolybdic acid in deionized water, mix and heat to 50°C for 10 h, then rinse three times with deionized water and dry at 80°C to obtain heteropolyacid cesium salt.

[0047] (3) Take 5 mg of heteropolyacid cesium salt and disperse it in 5 g of N-methylpyrrolidone to form a mixed solution;

[0048] (4) Add 0.5g of N,N,N′,N′-tetramethylmethyldiamine to the mixed solution and stir at room temperature to form a gel-like mixed solution;

[0049] (5) First, a gel-state mixed solution is laid on a plate, then a pore-filled release paper is laid on the gel-state mixed solution, and then a casting solution is laid on the release paper to form a multilayer film structure.

[0050] (6) Heat to 120°C for 10 hours until the gel-state mixed solution is completely melted. Remove the release paper to obtain a 50μm molded film.

[0051] (7) The prepared membrane is soaked in a 1% phosphoric acid solution for 20 hours and dried at 60°C to obtain a cross-linked proton exchange membrane, as shown in formula (I).

[0052]

[0053] Example 2

[0054] (1) Add 0.03 mol 4-acetylpyridine and 0.02 mol triphenylmethane to 2 ml dichloromethane, add 0.18 mol trifluoroacetic acid and 0.3 mol trifluoromethanesulfonic acid at 5 °C, then return to room temperature and react for 50 h. Pour the reaction solution into methanol aqueous solution to precipitate solid. Wash the solid with potassium carbonate solution at 50 °C, then wash with deionized water until neutral, and dry to obtain arylpyridine polymer. Dissolve the obtained 0.01 mol arylpyridine polymer in 20 ml N,N-dimethylformamide, add 0.05 mol 1,3-dibromopropane and heat to 90 °C for 70 h. Pour into diethyl ether solution to precipitate solid. Wash the solid with deionized water 3 times and dry to obtain quaternized arylpyridine polymer. Finally, take 3 g of quaternized arylpyridine polymer and place it in N,N-dimethylformamide to prepare a 20% mass fraction casting solution.

[0055] (2) Dissolve 0.0125 mol of cesium carbonate and 0.01 mol of phosphotungstic acid in deionized water, mix and heat to 75°C for 30 h, then rinse three times with deionized water and dry at 110°C to obtain heteropolyacid cesium salt.

[0056] (3) Take 45 mg of heteropolyacid cesium salt and disperse it in 4.5 g of N,N-dimethylformamide to form a mixed solution;

[0057] (4) Add 6g of N,N,N′,N′-tetramethylmethyldiamine to the mixed solution and stir at room temperature to form a gel-like mixed solution;

[0058] (5) First, the gel-state mixed solution is laid on a plate, then a porous release paper is laid on the gel-state mixed solution, and then a casting liquid is laid on the release paper to form a multilayer film structure.

[0059] (6) Heat to 160°C for 50 hours until the gel-state mixed solution is completely melted. Remove the release paper to obtain a 150μm molded film.

[0060] (7) The prepared membrane is soaked in 85% phosphoric acid solution for 80 hours and dried at 120°C to obtain the desired cross-linked proton exchange membrane.

[0061] Example 3

[0062] (1) 0.025 mol of 4-acetylpyridine and 0.02 mol of 9,9-dimethyl-9H-fluorene were added to 10 ml of dichloromethane. 0.11 mol of trichloroacetic acid and 0.18 mol of trinitrobenzenesulfonic acid were added at 0 °C. The mixture was then brought back to room temperature and reacted for 25 h. The resulting solution was poured into a methanol aqueous solution to precipitate a solid. The solid was washed with potassium carbonate solution at 50 °C and then washed with deionized water until neutral. After drying, an arylpyridine polymer was obtained. 0.01 mol of the obtained arylpyridine polymer was dissolved in 50 ml of dimethyl sulfoxide. 0.04 mol of 1,4-dibromobutane was added and heated to 75 °C for 35 h. The mixture was then poured into an ether solution to precipitate a solid. The solid was washed three times with deionized water and dried to obtain a quaternized arylpyridine polymer. Finally, 2 g of the quaternized arylpyridine polymer was placed in a 5% mass fraction casting solution with dimethyl sulfoxide.

[0063] (2) Dissolve 0.0125 mol of cesium carbonate and 0.01 mol of silicotungstic acid in deionized water, mix and heat to 75°C for 30 h, then rinse three times with deionized water and dry at 110°C to obtain heteropolyacid cesium salt.

[0064] (3) Take 20 mg of heteropolyacid cesium salt and disperse it in 4 g of N,N-dimethylformamide to form a mixed solution;

[0065] (4) Add 2g of N,N,N′,N′-tetramethylmethyldiamine and stir at room temperature to form a gel-like mixed solution;

[0066] (5) First, the gel-state mixed solution is laid on a plate, then a porous release paper is laid on the gel-state mixed solution, and then a casting liquid is laid on the release paper to form a multilayer film structure.

[0067] (6) Heat to 140°C for 30 hours until the gel-state mixed solution is completely melted. Remove the release paper to obtain a 100μm molded film.

[0068] (7) The prepared membrane is soaked in 40% phosphoric acid solution for 50 hours and dried at 100°C to obtain the desired cross-linked proton exchange membrane.

[0069] Comparative Example 1

[0070] The difference from Example 1 is that the film is not formed by gelation, but by directly mixing solutions:

[0071] (1) Add 0.02 mol 4-acetylpyridine and 0.02 mol biphenyl to 20 ml dichloromethane, add 0.06 mol trifluoroacetic acid and 0.08 mol trifluoromethanesulfonic acid at -5℃, then return to room temperature and react for 2 h. Pour the reaction solution into methanol aqueous solution to precipitate solid. Wash the solid with potassium carbonate solution at 50℃, then wash with deionized water until neutral, and dry to obtain arylpyridine polymer. Dissolve the obtained 0.01 mol arylpyridine polymer in 100 ml N-methylpyrrolidone, add 0.02 mol 1,2-dibromoethane, heat to 60℃ and react for 4 h. Pour into diethyl ether solution to precipitate solid. Wash the solid with deionized water 3 times and dry to obtain quaternized arylpyridine polymer. Finally, take 1 g of quaternized arylpyridine polymer and prepare a 0.1% mass fraction casting solution with N-methylpyrrolidone.

[0072] (2) Dissolve 0.0125 mol of cesium carbonate and 0.01 mol of phosphomolybdic acid in deionized water, mix and heat to 50°C for 10 h, then rinse three times with deionized water and dry at 80°C to obtain heteropolyacid cesium salt.

[0073] (3) Take 5 mg of heteropolyacid cesium salt and 0.5 g of N,N,N′,N′-tetramethyldiamine, add them to the casting solution, sonicate and stir to mix evenly;

[0074] (4) Cast film in an oven and heat at 120°C for 10 hours to obtain a 50μm shaped film;

[0075] (5) The prepared membrane is soaked in 1% phosphoric acid solution for 20 hours and dried at 60°C to obtain the desired cross-linked proton exchange membrane.

[0076] Comparative Example 2

[0077] The difference from Example 1 is that no release paper is added, and the gel layer and the casting solution layer are in direct contact:

[0078] (1) Add 0.02 mol 4-acetylpyridine and 0.02 mol biphenyl to 20 ml dichloromethane, add 0.06 mol trifluoroacetic acid and 0.08 mol trifluoromethanesulfonic acid at -5℃, then return to room temperature and react for 2 h. Pour the reaction solution into methanol aqueous solution to precipitate solid. Wash the solid with potassium carbonate solution at 50℃, then wash with deionized water until neutral, and dry to obtain arylpyridine polymer. Dissolve the obtained 0.01 mol arylpyridine polymer in 100 ml N-methylpyrrolidone, add 0.02 mol 1,2-dibromoethane, heat to 60℃ and react for 4 h. Pour into diethyl ether solution to precipitate solid. Wash the solid with deionized water 3 times and dry to obtain quaternized arylpyridine polymer. Finally, take 1 g of quaternized arylpyridine polymer and prepare a 0.1% mass fraction casting solution with N-methylpyrrolidone.

[0079] (2) Dissolve 0.0125 mol of cesium carbonate and 0.01 mol of phosphomolybdic acid in deionized water, mix and heat to 50°C for 10 h, then rinse three times with deionized water and dry at 80°C to obtain heteropolyacid cesium salt.

[0080] (3) Take 5 mg of heteropoly acid cesium salt and disperse it in 5 g of N-methylpyrrolidone to form a mixed solution. Add 0.5 g of N,N,N′,N′-tetramethylmethyldiamine and stir at room temperature to form a gel-like mixed solution.

[0081] (4) First, the gel-state mixed solution is laid on the plate, and then the casting solution is laid on the gel-state mixed solution to form a multilayer film structure;

[0082] (5) The multilayer film structure was heated to 120℃ for 10h to obtain a 50μm shaped film;

[0083] (6) The prepared membrane is soaked in 1% phosphoric acid solution for 20 hours and dried at 60°C to obtain the desired cross-linked proton exchange membrane.

[0084] Comparative Example 3

[0085] The difference from Example 1 is that no heteropoly acid was added; instead, the crosslinking agent and casting solution were directly mixed.

[0086] (1) Add 0.02 mol 4-acetylpyridine and 0.02 mol biphenyl to 20 ml dichloromethane, add 0.06 mol trifluoroacetic acid and 0.08 mol trifluoromethanesulfonic acid at -5℃, then return to room temperature and react for 2 h. Pour the reaction solution into methanol aqueous solution to precipitate solid. Wash the solid with potassium carbonate solution at 50℃, then wash with deionized water until neutral, and dry to obtain arylpyridine polymer. Dissolve the obtained 0.01 mol arylpyridine polymer in 100 ml N-methylpyrrolidone, add 0.02 mol 1,2-dibromoethane, heat to 60℃ and react for 4 h. Pour into diethyl ether solution to precipitate solid. Wash the solid with deionized water 3 times and dry to obtain quaternized arylpyridine polymer. Finally, take 1 g of quaternized arylpyridine polymer and prepare a 0.1% mass fraction casting solution with N-methylpyrrolidone.

[0087] (2) Add 0.5g of N,N,N′,N′-tetramethylmethyldiamine, sonicate and stir to mix evenly;

[0088] (3) Cast film in an oven and heat to 120℃ for 10h to obtain a 50μm shaped film;

[0089] (4) The prepared membrane is soaked in 1% phosphoric acid solution for 20 hours and dried at 60°C to obtain the desired cross-linked proton exchange membrane.

[0090] The acid retention rate, chemical stability, electrical conductivity, tensile strength, dimensional change rate, and chemical stability of the proton exchange membranes prepared in the test examples and comparative examples were evaluated. The electrical conductivity was tested at 120°C and 40% humidity, and at 100°C and 30% humidity. The tensile strength was tested using the national standard method (GB / T20042.3-2009). The chemical stability was tested using the Fenton method.

[0091] The proton exchange membranes prepared in Examples 1-3 and Comparative Examples 1-3 of this invention were weighed after adsorbing acids and alkalis, and then immersed in pure water to test the mass residue rate after a certain period of time, to detect the ability to retain acids and alkalis, and to test the conductivity retention rate before and after immersion. The results are shown in the table below.

[0092] Table 1

[0093]

[0094] Comparative Example 1, which does not use the gel-state method to form a film, but directly mixes the solution to form a film, and Comparative Example 2, which does not add release paper and the gel layer and the casting liquid layer are in direct contact, show the importance of film uniformity. If the formed film is not flat and uniform, the tensile strength and chemical stability will be reduced.

[0095] In Comparative Example 3, without adding heteropoly acids, directly mixing the crosslinking agent and casting solution resulted in a poorer acid-fixing ability and a much lower conductivity of the membrane.

[0096] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for preparing a cross-linked proton exchange membrane for water electrolysis, characterized in that, Includes the following steps: Step 1) The aryl hydrocarbon is copolymerized with 4-acetylpyridine to obtain an arylpyridine polymer. The arylpyridine polymer is mixed with a haloalkanes to undergo a nucleophilic substitution reaction to obtain a quaternized arylpyridine polymer. The quaternized arylpyridine polymer is dissolved in a high-boiling-point solvent to form a casting solution. Step 2), disperse the heteropolyacid cesium salt in a high-boiling-point solvent to form a mixed solution; Step 3): Add a crosslinking agent to the mixed solution in step 2), and stir at room temperature to form a gel-like mixed solution; the amount of crosslinking agent added is 0.5-2 times the mass of the quaternized arylpyridine polymer; Step 4), film is formed by casting: first, the gel-state mixed solution is laid on a flat plate, then a release paper with pores is laid on the gel-state mixed solution, and then a casting solution is laid on the release paper to form a multilayer film structure. Step 5): Heat the multilayer film structure from step 4) until the gel-state mixed solution is completely melted, then remove the release paper to obtain the formed film. Step 6): Immerse the formed membrane obtained in step 5) in phosphoric acid solution, and dry it to obtain the desired cross-linked proton exchange membrane.

2. The preparation method according to claim 1, characterized in that: In step 1), the specific method for preparing the casting solution is as follows: a. Add 4-acetylpyridine and aryl hydrocarbons to dichloromethane solvent, add catalyst and protonating agent at -5 to 5℃, then return to room temperature, react for 2-50 h and then purify to obtain arylpyridine polymer; The aryl hydrocarbon is selected from one or more of biphenyl, p-terphenyl, m-terphenyl, p-tetraphenyl, 9,9-dimethyl-9H-fluorene, triphenylmethane, and 1,3,5-triphenylbenzene; The molar ratio of 4-acetylpyridine to aryl hydrocarbon is (1:1)-(1.5:1); The molar ratio of the arylpyridine polymer to the haloalkane is (1:2)-(1:5); The aryl hydrocarbon is present in dichloromethane at a concentration of 0.001-0.01 mol / ml; The molar ratio of 4-acetylpyridine to the catalyst is (1:3)-(1:6); The molar ratio of 4-acetylpyridine to the protonating agent is (1:4)-(1:10); The catalyst is selected from trifluoroacetic acid and trichloroacetic acid, and the protonating agent is selected from trifluoromethanesulfonic acid and trinitrobenzenesulfonic acid; b. Dissolve the arylpyridine polymer from step a in a high-boiling-point solvent, add a haloalkane, heat to 60-90℃, react for 4-70 h, and then purify to obtain the quaternized arylpyridine polymer. The high-boiling-point solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; The haloalkanes are any one or more selected from 1,2-dibromoethane, 1,3-dibromopropane, 1,4-dibromobutane, 1,5-dibromopentane, 1,6-dibromohexane, 1,7-dibromoheptane, 1,8-dibromooctane, or 1,9-dibromononane; The arylpyridine polymer has a concentration of 0.1-0.5 mol / L in a high-boiling-point solvent; c. Mix the quaternized arylpyridine polymer with a high-boiling-point solvent and stir at room temperature to form a casting solution; The mass fraction of the casting solution is 0.1%-20%.

3. The preparation method according to claim 1, characterized in that: In step 2), the synthesis steps of the heteropolyacid cesium salt are specifically as follows: Cesium carbonate and heteropoly acid are dissolved in deionized water, mixed, heated to 50-75℃ and reacted for 10-30 hours, rinsed with deionized water 1-3 times, and dried at 80-110℃. The heteropolyacid is selected from one or more of phosphomolybdic acid, phosphotungstic acid, silicotungstic acid, and silicotomolybdic acid; The molar ratio of cesium carbonate to heteropolyacid is 1.25:

1.

4. The preparation method according to claim 1, characterized in that: In step 2), the high-boiling solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; The mass ratio of the heteropolyacid cesium salt to the quaternized arylpyridine polymer is 0.005-0.015:1; The mass fraction of the mixed solution is 0.1%-1%.

5. The preparation method according to claim 1, characterized in that: In step 3), the crosslinking agent includes one or more of N,N,N′,N′-tetramethylmethyldiamine (TMMDA), N,N,N′,N′-tetramethylethylenediamine (TMEDA), and N,N,N′,N′-tetramethyl-1,6-hexanediamine (TMHDA).

6. The preparation method according to claim 1, characterized in that: In step 5), the heating temperature is 120℃-160℃, the heating time is 10-50h, and the thickness of the formed film is 50-150μm.

7. The preparation method according to claim 1, characterized in that: In step 6), the phosphoric acid solution has a mass fraction of 1%-85%; the soaking time is 20-80 hours; and the drying temperature is 60-120°C.

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