Preparation method and application of a proton exchange membrane for water electrolysis and fuel cell

Abstract

This invention relates to a method for preparing a proton exchange membrane for water electrolysis and fuel cells, and its application, belonging to the technical field of proton exchange membrane materials. First, a main chain containing an arylpyridine polymer is prepared. Then, diamine-functionalized graphene oxide is introduced into the side chain. Next, cesium salts of heteropoly acids are doped during membrane fabrication. The main chain of the exchange membrane of this invention uses an arylpyridine polymer, which has excellent alkali resistance and a simple synthesis method and process. The side chain contains diamine-functionalized graphene oxide, and the doping of cesium salts of heteropoly acids within the membrane provides strong mechanical strength and proton conductor adsorption sites, effectively improving ionic conductivity and reducing acid loss during operation. The proton exchange membrane prepared by this invention is applied to high-temperature water electrolysis and medium-high temperature fuel cells.

Description

Technical Field

[0001] This invention relates to a method for preparing a proton exchange membrane for water electrolysis and fuel cells and its application, belonging to the field of proton exchange membrane material technology. 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] In high-temperature water electrolysis and fuel cell applications, the operating temperature of high-temperature proton exchange membrane fuel cells is mainly determined by the high-temperature proton exchange membrane, and the proton conductor is the core. Existing commercial high-temperature proton exchange membranes all use phosphoric acid as the proton conductor, but as the operating temperature increases, the loss of phosphoric acid accelerates, leading to an increase in the rate of battery performance degradation.

[0004] Considering the gas barrier properties, durability, and safety factors of proton exchange membranes (PEMs), most PEMs currently used in the industry are thick-film membranes (such as Nafion 117 and Nafion 115), typically exceeding 100 μm in thickness. This leads to an increase in the internal resistance of the electrolyzer and higher energy consumption for hydrogen production via water electrolysis. Therefore, reducing the thickness of the exchange membrane is a future development direction. However, due to the pressure difference in the electrolyte during water electrolysis for hydrogen production, reducing the membrane thickness will decrease its gas barrier properties and mechanical strength, potentially causing safety issues. Furthermore, decreased gas barrier properties can cause hydrogen peroxide and various free radicals to be generated on the catalyst, which in turn attack the PEM and degrade it. On the other hand, the material cost of PEM water-electrolyte PEMs is high, far exceeding that of PEMs used in fuel cells; therefore, reducing manufacturing costs is also a crucial issue.

[0005] 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. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a proton exchange membrane for water electrolysis and fuel cells and its application. First, a main chain containing an arylpyridine polymer is prepared, and then diamine-functionalized graphene oxide is introduced into the side chain. Second, cesium salts of heteropoly acids are doped during membrane preparation to reduce acid loss at high temperatures.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] This invention provides a method for preparing a proton exchange membrane, comprising the following steps:

[0009] Step 1) The aryl hydrocarbon is copolymerized with 4-acetylpyridine to obtain an arylpyridine polymer;

[0010] Step 2) Introduce diamine into graphene oxide to obtain diamine-functionalized graphene oxide;

[0011] Step 3) The diamine-functionalized graphene oxide and the haloalkane from step 2) are subjected to nucleophilic addition to obtain a side-chain cation;

[0012] Step 4) The arylpyridine polymer obtained in step 1) and the side-chain cation obtained in step 3) are subjected to a quaternization reaction to obtain a quaternized arylpyridine polymer, wherein the molar ratio of the arylpyridine polymer to the side-chain cation is (100:1)-(10:1).

[0013] Step 5): Dissolve the quaternized arylpyridine polymer obtained in step 4) in organic high-boiling solvent 1 to form solution 1, disperse the heteropolyacid cesium salt in organic high-boiling solvent 2 to form solution 2, mix solution 1 and solution 2 again to form casting solution, cast into a film and dry.

[0014] Step 6): Immerse the membrane obtained in step 5) in phosphoric acid solution and dry it to obtain the proton exchange membrane.

[0015] In the above technical solution, further, in step 1), the synthesis step of the arylpyridine polymer specifically includes:

[0016] 4-Acetylpyridine and aryl hydrocarbons were added to dichloromethane solvent, and a catalyst and protonating agent were added at -20 to 5°C. The mixture was then returned to room temperature and reacted for 2 to 72 hours before purification to obtain arylpyridine polymers.

[0017] 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;

[0018] The catalyst is selected from trifluoroacetic acid and trichloroacetic acid, and the protonating agent is selected from trifluoromethanesulfonic acid and trinitrobenzenesulfonic acid.

[0019] The molar ratio of 4-acetylpyridine to aryl hydrocarbon is (1:1)-(1.6:1);

[0020] The aryl hydrocarbon is present in dichloromethane at a concentration of 0.001-0.1 g / ml;

[0021] The molar ratio of 4-acetylpyridine to the catalyst is (1:5)-(1:10);

[0022] The molar ratio of 4-acetylpyridine to the protonating agent is (1:5)-(1:20).

[0023] In the above technical solution, further, in step 2), the synthesis step of the diamine-functionalized graphene oxide is specifically as follows:

[0024] Graphene oxide was dispersed in a solvent and placed in an ice bath. Then, N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide were added. After reacting for 0.5-3 h, the ice bath was removed. When the reaction system returned to room temperature, diamine was added and the mixture was stirred. After reacting for 10-50 h, the mixture was purified to obtain diamine-functionalized graphene oxide.

[0025] The diamine is selected from any one of N,N-dimethyl-1,3-diaminopropane, 3-diethylaminopropylamine, N,N-diethylbutane-1,4-diamine, 5-(diethylaminopentamine), 6-(dimethylamino)hexylamine, and (7-aminoheptyl)dimethylamine;

[0026] The solvent is either toluene or tetrahydrofuran;

[0027] The concentration of the graphene oxide in the solvent is 0.001-0.1 g / ml;

[0028] The molar ratio of graphene oxide to N-hydroxysuccinimide is (1:20)-(1:50);

[0029] The molar ratio of the graphene oxide to 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide is (1:20)-(1:50);

[0030] The molar ratio of graphene oxide to diamine is (1:3)-(1:5).

[0031] In the above technical solution, further, in step 3), the synthesis step of the side-chain cation is specifically as follows:

[0032] The diamine-functionalized graphene oxide and haloalkanes prepared in step 2) were added to a solvent and heated to 60-100℃ for 8-50 h to obtain a solid precipitate; the precipitate was filtered, purified with ethyl acetate to remove excess reactants, and dried under vacuum to obtain a side-chain cation.

[0033] The haloalkane is selected from any one of 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;

[0034] The solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone;

[0035] The molar ratio of the diamine-functionalized graphene oxide to the haloalkane is (1:2)-(1:5);

[0036] The molar ratio of the arylpyridine polymer to the haloalkane is (1:1)-(1:5);

[0037] The concentration of the diamine-functionalized graphene oxide in the solvent is 0.001-0.1 g / ml.

[0038] In the above technical solution, further, in step 4), the synthesis step of the quaternized arylpyridine polymer is specifically as follows:

[0039] The arylpyridine polymer obtained in step 1) and the side-chain cation obtained in step 3) are added to a solvent, heated to 80-120℃ for 20-50 h, precipitated in ethyl acetate, washed multiple times with deionized water, filtered, and dried at 60-120℃ to obtain the quaternized arylpyridine polymer.

[0040] The solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone;

[0041] The arylpyridine polymer has a concentration of 0.001-0.1 g / ml in the solvent.

[0042] In the above technical solution, further, in step 5), the mass ratio of the heteropolyacid cesium salt and the quaternized arylpyridine polymer is (1:1000)-(1:100);

[0043] The organic high-boiling-point solvent one and organic high-boiling-point solvent two are independently one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone;

[0044] The concentration of the solution is 0.01-0.1 g / ml;

[0045] The concentration of the solution is 0.001-0.01 g / ml;

[0046] The drying temperature is 60-120℃;

[0047] The film thickness is 30-100 μm.

[0048] In the above technical solution, further, in step 5), the synthesis step of the heteropolyacid cesium salt is specifically as follows:

[0049] Cesium carbonate and heteropoly acid are dissolved in deionized water, mixed, heated to 60-80℃, and reacted for 20-40 hours. After the reaction, the mixture is rinsed with deionized water 1-3 times and dried at 60-120℃.

[0050] The heteropolyacid is selected from one or more of phosphomolybdic acid, phosphotungstic acid, silicotungstic acid, and silicotomolybdic acid;

[0051] The molar ratio of cesium carbonate to heteropolyacid is 1.25:1.

[0052] In the above technical solution, further, in step 6), the mass fraction of the phosphoric acid solution is 0.1-85%; the soaking time is 20-80h; and the drying temperature is 60-120℃.

[0053] In another aspect, the present invention provides a proton exchange membrane prepared by the above method.

[0054] The present invention also provides an application of an upper proton exchange membrane in high-temperature water electrolysis (80-190℃) and medium-high temperature fuel cells (80-190℃).

[0055] The present invention has the following beneficial effects:

[0056] 1. This invention first selects an arylpyridine polymer without unstable end groups such as ether bonds as the polymeric backbone of the proton exchange membrane, which exhibits excellent alkali resistance and 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 is effectively prevented, thus resulting in excellent chemical stability. Simultaneously, the numerous nitrogen-containing sites readily form hydrogen bonds with phosphoric acid, thereby adsorbing a large amount of phosphoric acid.

[0057] 2. Because diamines have abundant electrons, they can neutralize the phenomenon of electron transfer from graphene oxide to pyridine polymers, thereby effectively avoiding the reduction in the number of electrons transferred from graphene, which leads to graphene shedding and decreased stability. At the same time, it eliminates the influence of the addition of unmodified graphene on the membrane's proton-carrying capacity. Therefore, the proton exchange membrane of the present invention has good film-forming properties and conductivity. In addition, the present invention also increases the quaternary ammonium group when introducing diamine-functionalized graphene oxide as a side chain into the backbone, which also improves the retention capacity of phosphoric acid.

[0058] 3. Diamine-functionalized graphene oxide can overcome the limitation of the number of proton conductors adsorbed, not only providing a large number of active sites and improving conductivity, but also effectively avoiding problems such as increased membrane resistance caused by the addition of graphene after functionalization modification; it can also effectively increase the content of basic groups such as imidazole and increase the compatibility of graphene with polymers, so that graphene oxide inorganic materials can be added into the membrane in a timely manner, thereby obtaining better film-forming performance and conductivity.

[0059] 4. [The text abruptly shifts to a seemingly unrelated topic:] ...containing larger cations Cs... + The cesium salt of heteropolyacids is doped into the membrane, which can effectively conduct protons. At the same time, the membrane prepared by this invention is impregnated with phosphoric acid during the preparation process. The phosphoric acid and the cesium salt of heteropolyacids are used to conduct protons together. The solid heteropolyacid can be stably present in the membrane because it is solid, while the phosphoric acid adsorbed by graphene can effectively fix the phosphoric acid and slow down the loss of phosphoric acid. Through the above methods, the conductivity value and the long-term stability of the battery during operation are effectively improved. Detailed Implementation

[0060] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0061] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0062] Example 1

[0063] (1) Add 0.02 mol of biphenyl and 0.02 mol of 4-acetylpyridine to 2 ml of dichloromethane, cool to -20 °C, add 0.1 mol of trifluoroacetic acid dropwise, then add 0.1 mol of trifluoromethanesulfonic acid dropwise. After the addition is complete, return to room temperature and react for 2 h. Pour the reaction solution into methanol aqueous solution to precipitate a white solid. Wash the white solid with potassium carbonate solution at 50 °C, then wash with deionized water until neutral, and dry to obtain arylpyridine polymer.

[0064] (2) 0.01 mol of graphene oxide was dispersed in 10 ml of toluene and placed in an ice bath. Then, 0.2 mol of N-hydroxysuccinimide and 0.2 mol of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide were added in a molar ratio to graphene oxide. After reacting for 0.5 h, the ice bath was removed. When the reaction system returned to room temperature, 0.03 mol of N,N-diethylbutane-1,4-diamine was added and the mixture was stirred. After reacting for 10 h, the diamine-functionalized graphene oxide was purified.

[0065] (3) 10 mmol of the prepared diamine-functionalized graphene oxide and 20 mmol of 1,2-dibromoethane were added to 10 ml of N,N-dimethylformamide, heated to 60 °C and reacted for 8 h to obtain a solid precipitate. The precipitate was filtered, purified with ethyl acetate to remove excess reactants, and dried under vacuum to obtain a side-chain cation.

[0066] (4) The 0.01 mol of arylpyridine polymer and 0.1 mmol of side-chain cation were added to 10 ml of N,N-dimethylformamide, heated to 80 °C and reacted for 20 h. The polymer was then precipitated in ethyl acetate, washed multiple times with deionized water, filtered, and dried in a vacuum oven at 60 °C to obtain the quaternized arylpyridine polymer.

[0067] (5) Dissolve 0.0125 mol of cesium carbonate and 0.01 mol of phosphomolybdic acid in deionized water, mix and heat to 60°C for 20 h, then rinse three times with deionized water and dry to obtain heteropolyacid cesium salt.

[0068] (6) Dissolve the 0.01 mol quaternized arylpyridine polymer in 10 ml dimethyl sulfoxide to form solution one, disperse the 0.1 mmol heteropolyacid cesium salt in 10 ml dimethyl sulfoxide to form solution two, mix solution one and solution two again to form casting solution, cast into a film and dry in a vacuum oven at 60 °C to obtain a film with a thickness of 30 μm;

[0069] (7) The prepared membrane is soaked in a 1% phosphoric acid solution for 20 hours and then dried in a vacuum oven at 120°C to obtain a proton exchange membrane.

[0070] The reaction process of Example 1 is as follows:

[0071]

[0072] Example 2

[0073] (1) Add 0.02 mol of m-terphenyl and 0.032 mol of 4-acetylpyridine to 200 ml of dichloromethane and cool to 5 °C; add 0.2 mol of trichloroacetic acid dropwise, then add 0.4 mol of trifluoromethanesulfonic acid dropwise. After the addition is complete, return to room temperature and react for 72 h. Pour the solution after the reaction into a methanol aqueous solution to precipitate a white solid. Wash the white solid with potassium carbonate solution at 50 °C, then wash with deionized water until neutral, and dry to obtain arylpyridine polymer.

[0074] (2) 0.01 mol of graphene oxide was dispersed in 100 ml of tetrahydrofuran and placed in an ice bath. Then, 0.5 mol of N-hydroxysuccinimide and 0.5 mol of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide were added. After reacting for 3 h, the ice bath was removed. When the reaction system returned to room temperature, 0.05 mol of N,N-dimethyl-1,3-diaminopropane was added and the mixture was stirred. After reacting for 50 h, the diamine-functionalized graphene oxide was purified.

[0075] (3) 10 mmol of the prepared diamine-functionalized graphene oxide and 50 mmol of 1,3-dibromopropane were added to 100 ml of N,N-dimethylacetamide and heated to 100 °C for 50 h to obtain a solid precipitate. The precipitate was filtered, purified with ethyl acetate to remove excess reactants, and dried under vacuum to obtain a side-chain cation.

[0076] (4) 10 mmol of the prepared arylpyridine polymer and 1 mmol of the side-chain cation were added to 100 ml of N,N-dimethylacetamide, heated to 120 °C and reacted for 50 h. The polymer was then precipitated in ethyl acetate, washed multiple times with deionized water, filtered, and dried in a vacuum oven at 120 °C to obtain the quaternized arylpyridine polymer.

[0077] (5) Dissolve 0.0125 mol of cesium carbonate and 0.01 mol of phosphotungstic acid in deionized water, mix and heat to 60°C for 20 h, then rinse with deionized water 3 times and dry to obtain heteropolyacid cesium salt;

[0078] (6) Dissolve the 0.03 mol quaternized arylpyridine polymer in 1 ml dimethyl sulfoxide to form solution one, disperse the 0.3 mmol heteropolyacid cesium salt in dimethyl sulfoxide to form solution two, mix solution one and solution two again to form casting solution, cast into a film and dry in a vacuum oven at 120 °C to obtain a film with a thickness of 100 μm;

[0079] (7) The prepared membrane was soaked in a phosphoric acid solution with a mass fraction of 85% for 80 hours and then dried in a vacuum oven at 60°C to obtain a proton exchange membrane.

[0080] Example 3

[0081] (1) Add 0.02 mol of p-terphenyl and 0.022 mol of 4-acetylpyridine to 50 ml of dichloromethane and cool to -10 °C; add 0.132 mol of trichloroacetic acid dropwise, then add 0.176 mol of trinitrobenzenesulfonic acid dropwise. After the addition is complete, return to room temperature and react for 6 h. Pour the solution after reaction into methanol aqueous solution to precipitate a white solid. Wash the white solid with potassium carbonate solution at 50 °C, then wash with deionized water until neutral, and dry to obtain arylpyridine polymer.

[0082] (2) 0.01 mol of graphene oxide was dispersed in 500 ml of toluene and placed in an ice bath. Then, 0.3 mol of N-hydroxysuccinimide and 0.3 mol of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide were added in a molar ratio to graphene oxide. After reacting for 1 h, the ice bath was removed. When the reaction system returned to room temperature, 0.035 mol of N,N-diethylbutane-1,4-diamine was added and the mixture was stirred. After reacting for 15 h, the diamine-functionalized graphene oxide was purified.

[0083] (3) 10 mmol of the prepared diamine-functionalized graphene oxide and 25 mmol of 1,4-dibromobutane were added to 500 ml of dimethyl sulfoxide and heated to 70 °C for 12 h to obtain a solid precipitate. The precipitate was filtered, purified with ethyl acetate to remove excess reactants, and dried under vacuum to obtain a side-chain cation.

[0084] (4) 10 mmol of the prepared arylpyridine polymer and 0.125 mmol of side-chain cation were added to 10 ml of dimethyl sulfoxide, heated to 85 °C and reacted for 25 h. The polymer was then precipitated in ethyl acetate, washed multiple times with deionized water, filtered, and dried in a vacuum oven at 85 °C to obtain the quaternized arylpyridine polymer.

[0085] (5) Dissolve 0.0125 mol of cesium carbonate and 0.01 mol of silicotungstic acid in deionized water, mix and heat to 65°C for 25 h, then rinse three times with deionized water and dry to obtain heteropolyacid cesium salt;

[0086] (6) Dissolve the 0.01 mol quaternized arylpyridine polymer in dimethyl sulfoxide to form 20 ml of solution one, disperse the 1 mmol heteropolyacid cesium salt in dimethyl sulfoxide to form 20 ml of solution two, mix solution one and solution two again to form casting solution, cast into a film and dry in a vacuum oven at 90 °C to obtain a film with a thickness of 40 μm.

[0087] (7) The prepared membrane is soaked in a 5% phosphoric acid solution for 25 hours and then dried in a vacuum oven at 70°C to obtain a proton exchange membrane.

[0088] Example 4

[0089] (1) Add 0.02 mol of p-tetraphenyl and 0.028 mol of 4-acetylpyridine to 10 ml of dichloromethane and cool to -5 °C; add 0.196 mol of trifluoroacetic acid dropwise, then add 0.28 mol of trifluoromethanesulfonic acid dropwise. After the addition is complete, return to room temperature and react for 15 h. Pour the solution after reaction into methanol aqueous solution to precipitate a white solid. Wash the white solid with potassium carbonate solution at 50 °C, then wash with deionized water until neutral, and dry to obtain arylpyridine polymer.

[0090] (2) 0.01 mol of graphene oxide was dispersed in 70 ml of toluene and placed in an ice bath. Then, 0.4 mol of N-hydroxysuccinimide and 0.4 mol of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide were added. After reacting for 1 h, the ice bath was removed. When the reaction system returned to room temperature, 0.04 mol of 5-(diethylaminopentylamine) was added and the mixture was stirred. After reacting for 20 h, the diamine-functionalized graphene oxide was purified.

[0091] (3) 10 mmol of the prepared diamine-functionalized graphene oxide and 30 mmol of 1,5-dibromopentane were added to 70 ml of dimethyl sulfoxide and heated to 80 °C for 20 h to obtain a solid precipitate. The precipitate was filtered, purified with ethyl acetate to remove excess reactants, and dried under vacuum to obtain a side-chain cation.

[0092] (4) 10 mmol of the prepared arylpyridine polymer and 0.2 mmol of side-chain cation were added to 20 ml of N-methylpyrrolidone, heated to 90 °C and reacted for 30 h. The polymer was then precipitated in ethyl acetate, washed multiple times with deionized water, filtered, and dried in a vacuum oven at 90 °C to obtain the quaternized arylpyridine polymer.

[0093] (5) Dissolve 0.0125 mol of cesium carbonate and 0.01 mol of molybdic acid in deionized water, mix and heat to 70°C for 30 h, then rinse three times with deionized water and dry to obtain heteropolyacid cesium salt;

[0094] (6) Dissolve the 0.012 mol quaternized arylpyridine polymer in 6 ml of N-methylpyrrolidone to form solution one, disperse the 1.2 mmol heteropolyacid cesium salt in 6 ml of N-methylpyrrolidone to form solution two, mix solution one and solution two again to form casting solution, cast into a film and dry in a vacuum oven at 100 °C to obtain a film with a thickness of 60 μm;

[0095] (7) The prepared membrane was soaked in a 25% phosphoric acid solution for 30 hours and dried in a vacuum oven at 80°C to obtain a proton exchange membrane.

[0096] Example 5

[0097] (1) 0.02 mol of 9,9-dimethyl-9H-fluorene and 0.028 mol of 4-acetylpyridine were added to 5 ml of dichloromethane and cooled to 0 °C. 0.252 mol of trifluoroacetic acid was added dropwise, followed by 0.448 mol of trifluoromethanesulfonic acid. After the addition was complete, the mixture was returned to room temperature and reacted for 50 h. The solution after the reaction was poured into a methanol aqueous solution to precipitate a white solid. The white solid was washed with potassium carbonate solution at 50 °C, then washed with deionized water until neutral, and dried to obtain arylpyridine polymer.

[0098] (2) 0.01 mol of graphene oxide was dispersed in 50 ml of toluene and placed in an ice bath. Then, 0.45 mol of N-hydroxysuccinimide and 0.45 mol of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide were added. After reacting for 2.5 h, the ice bath was removed. When the reaction system returned to room temperature, 0.045 mol of 6-(dimethylamino)hexylamine was added and the mixture was stirred. After reacting for 40 h, the diamine-functionalized graphene oxide was purified.

[0099] (3) 10 mmol of the prepared diamine-functionalized graphene oxide and 35 mmol of 1,6-dibromohexane were added to 50 ml of N,N-dimethylacetamide and heated to 90 °C for 40 h to obtain a solid precipitate. The precipitate was filtered, purified with ethyl acetate to remove excess reactants, and dried under vacuum to obtain a side-chain cation.

[0100] (4) 10 mmol of the prepared arylpyridine polymer and 0.5 mmol of side-chain cation were added to 10 ml of N-methylpyrrolidone, heated to 95 °C and reacted for 35 h. The polymer was then precipitated in ethyl acetate, washed multiple times with deionized water, filtered, and dried in a vacuum oven at 110 °C to obtain the quaternized arylpyridine polymer.

[0101] (5) Dissolve 0.0125 mol of cesium carbonate and 0.01 mol of phosphomolybdic acid in deionized water, mix and heat to 75°C for 40 h, then rinse three times with deionized water and dry to obtain heteropolyacid cesium salt.

[0102] (6) Dissolve the 0.02 mol quaternized arylpyridine polymer in 8 ml of dimethyl sulfoxide to form solution one, disperse the 0.5 mmol heteropolyacid cesium salt in 8 ml of dimethyl sulfoxide to form solution two, mix solution one and solution two again to form casting solution, cast into a film and dry in a vacuum oven at 110 °C to obtain a film with a thickness of 80 μm;

[0103] (7) The prepared membrane was soaked in a 50% phosphoric acid solution for 40 hours and then dried in a vacuum oven at 95°C to obtain a proton exchange membrane.

[0104] Comparative Example 1

[0105] Films are formed directly using arylpyridine polymers without introducing diamine-functionalized graphene oxide into the framework:

[0106] (1) Add 0.02 mol of biphenyl and 0.02 mol of 4-acetylpyridine to 2 ml of dichloromethane and cool to -20 °C; add 0.1 mol of trifluoroacetic acid dropwise, then add 0.1 mol of trifluoromethanesulfonic acid dropwise. After the addition is complete, return to room temperature and react for 2 h. Pour the solution after reaction into methanol aqueous solution to precipitate a white solid. Wash the white solid with potassium carbonate solution at 50 °C, then wash with deionized water until neutral, and dry to obtain arylpyridine polymer.

[0107] (2) Dissolve 0.0125 mol of cesium carbonate and 0.01 mol of phosphomolybdic acid in deionized water, mix and heat to 60°C for 20 h, then rinse with deionized water 3 times and dry to obtain heteropolyacid cesium salt;

[0108] (3) Dissolve the 0.01 mol quaternized arylpyridine polymer in 10 ml dimethyl sulfoxide to form solution one, disperse the 0.1 mmol heteropolyacid cesium salt in 10 ml dimethyl sulfoxide to form solution two, mix solution one and solution two again to form casting solution, cast into a film and dry in a vacuum oven at 60 °C to obtain a film with a thickness of 30 μm;

[0109] (4) The prepared membrane is soaked in a 1% phosphoric acid solution for 20 hours and then dried in a vacuum oven at 120°C to obtain a proton exchange membrane.

[0110] Comparative Example 2

[0111] Excessive introduction of diamine-functionalized graphene oxide:

[0112] (1) Add 0.02 mol of biphenyl and 0.02 mol of 4-acetylpyridine to 2 ml of dichloromethane and cool to -20 °C; add 0.1 mol of trifluoroacetic acid dropwise, then add 0.1 mol of trifluoromethanesulfonic acid dropwise. After the addition is complete, return to room temperature and react for 2 h. Pour the solution after reaction into methanol aqueous solution to precipitate a white solid. Wash the white solid with potassium carbonate solution at 50 °C, then wash with deionized water until neutral, and dry to obtain arylpyridine polymer.

[0113] (2) 0.01 mol of graphene oxide was dispersed in 10 ml of toluene and placed in an ice bath. Then, 0.2 mol of N-hydroxysuccinimide and 0.2 mol of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide were added in a molar ratio to graphene oxide. After reacting for 0.5 h, the ice bath was removed. When the reaction system returned to room temperature, 0.03 mol of N,N-diethylbutane-1,4-diamine was added and the mixture was stirred. After reacting for 10 h, the diamine-functionalized graphene oxide was purified.

[0114] (3) 10 mmol of the prepared diamine-functionalized graphene oxide and 20 mmol of 1,2-dibromoethane were added to 10 ml of N,N-dimethylformamide and heated to 60 °C for 8 h to obtain a solid precipitate. The precipitate was filtered, purified with ethyl acetate to remove excess reactants, and dried under vacuum to obtain a side-chain cation.

[0115] (4) 10 mmol of the prepared arylpyridine polymer and 10 mmol of side-chain cation were added to 10 ml of N,N-dimethylformamide, heated to 80 °C and reacted for 20 h. The polymer was then precipitated in ethyl acetate, washed multiple times with deionized water, filtered, and dried in a vacuum oven at 60 °C to obtain the quaternized arylpyridine polymer.

[0116] (5) Dissolve 0.0125 mol of cesium carbonate and 0.01 mol of phosphomolybdic acid in deionized water, mix and heat to 60°C for 20 h, then rinse three times with deionized water and dry to obtain heteropolyacid cesium salt.

[0117] (6) Dissolve the 0.01 mol quaternized arylpyridine polymer in 10 ml dimethyl sulfoxide to form solution one, disperse the 0.1 mmol heteropolyacid cesium salt in 10 ml dimethyl sulfoxide to form solution two, mix solution one and solution two again to form casting solution, cast into a film and dry in a vacuum oven at 60 °C to obtain a film with a thickness of 30 μm;

[0118] (7) The prepared membrane is soaked in a 1% phosphoric acid solution for 20 hours and then dried in a vacuum oven at 120°C to obtain a proton exchange membrane.

[0119] Comparative Example 3

[0120] No heteropolyacid cesium salts added:

[0121] (1) Add 0.02 mol of biphenyl and 0.02 mol of 4-acetylpyridine to 2 ml of dichloromethane and cool to -20 °C; add 0.1 mol of trifluoroacetic acid dropwise, then add 0.1 mol of trifluoromethanesulfonic acid dropwise. After the addition is complete, return to room temperature and react for 2 h. Pour the solution after reaction into methanol aqueous solution to precipitate a white solid. Wash the white solid with potassium carbonate solution at 50 °C, then wash with deionized water until neutral, and dry to obtain arylpyridine polymer.

[0122] (2) 0.01 mol of graphene oxide was dispersed in 10 ml of toluene and placed in an ice bath. Then, 0.2 mol of N-hydroxysuccinimide and 0.2 mol of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide were added in a molar ratio to graphene oxide. After reacting for 0.5 h, the ice bath was removed. When the reaction system returned to room temperature, 0.03 mol of N,N-diethylbutane-1,4-diamine was added and the mixture was stirred. After reacting for 10 h, the diamine-functionalized graphene oxide was purified.

[0123] (3) 10 mmol of the prepared diamine-functionalized graphene oxide and 20 mmol of 1,2-dibromoethane were added to 10 ml of N,N-dimethylformamide and heated to 60 °C for 8 h to obtain a solid precipitate. The precipitate was filtered, purified with ethyl acetate to remove excess reactants, and dried under vacuum to obtain a side-chain cation.

[0124] (4) The 0.01 mol of arylpyridine polymer and 0.1 mmol of side-chain cation were added to 10 ml of N,N-dimethylformamide, heated to 80 °C and reacted for 20 h. The polymer was then precipitated in ethyl acetate, washed multiple times with deionized water, filtered, and dried in a vacuum oven at 60 °C to obtain the quaternized arylpyridine polymer.

[0125] (5) Dissolve the 0.01 mol quaternized arylpyridine polymer in 10 ml of dimethyl sulfoxide to form a casting solution, cast the solution into a film, and dry it in a vacuum oven at 60 °C to obtain a film with a thickness of 30 μm.

[0126] (6) The prepared membrane is soaked in a 1% phosphoric acid solution for 20 hours and then dried in a vacuum oven at 120°C to obtain a proton exchange membrane.

[0127] The acid retention rate, chemical stability, electrical conductivity, tensile strength, dimensional change rate, and chemical stability of the proton exchange membranes prepared in Examples 1-5 and Comparative Examples 1-3 were tested.

[0128] The conductivity test conditions are: 120℃, 40% humidity and 100℃, 30% humidity. The tensile strength test method is the national standard method (GB / T20042.3-2009). The hydrogen permeation current test method is the electrochemical method.

[0129] The ionic conductivity of the membrane was tested, and the results are shown in the table below. The results show that the membrane exhibits proton conductivity after impregnation with acid, and the membrane with high conductivity and high mechanical strength is also achieved by appropriately introducing diamine-functionalized graphene oxide.

[0130] Table 1. Conductivity and tensile strength of the membrane

[0131]

[0132] Comparative Example 1: The film was formed directly using arylpyridine polymer without introducing diamine-functionalized graphene oxide into the framework. The results showed low acid adsorption and low conductivity.

[0133] Comparative Example 2: Excessive introduction of diamine-functionalized graphene oxide resulted in low conductivity due to its inherent resistance.

[0134] Comparative Example 3, without the addition of heteropolyacid cesium salts, showed poor acid retention and poor conductivity stability.

[0135] Comparative Example 4

[0136] Films can be formed directly using polybenzimidazole (OPBI) polymers containing ether bonds, without introducing diamine-functionalized graphene oxide into the framework:

[0137] (1) Dissolve 0.02 mol of commercial OPBI in N-methylpyrrolidone (NMP) to form a casting solution, cast the solution into a film, and dry it in a vacuum oven at 60°C to obtain a film with a thickness of 30 μm.

[0138] (2) The prepared membrane was soaked in a 1% phosphoric acid solution for 20 hours and then dried in a vacuum oven at 120°C to obtain a proton exchange membrane.

[0139] The proton exchange membranes prepared in Examples 1-5 and Comparative Examples 1-4 of this invention were immersed in Fenton's reagent for durability testing, and the results are shown in the table below. Due to the excellent chemical stability of the framework, the membranes in this series also exhibit excellent chemical stability.

[0140] Table 2. Membrane Residual Rate Test

[0141] Case 200h membrane mass residue rate / % Example 1 99.5 Example 2 99.3 Example 3 99.0 Example 4 99.4 Example 5 98.9 Comparative Example 1 86.0 Comparative Example 2 70.6 Comparative Example 3 60.5 Comparative Example 4 50.1

[0142] The proton exchange membranes prepared in Examples 1-5 and Comparative Examples 1-4 of this invention were weighed after adsorbing acid, and then immersed in pure water for a certain period of time to test the residual mass rate, thus detecting their ability to retain acid. The conductivity retention rate before and after immersion was also tested, and the results are shown in the table below. Adding cesium salts of heteropolyacids significantly improves the membrane's acid retention capacity and conductivity retention rate.

[0143] Table 3. Acid absorption capacity, acid retention capacity, and conductivity retention rate of the membrane.

[0144]

[0145] 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 proton exchange membrane, characterized in that, Includes the following steps: Step 1) The aryl hydrocarbon is copolymerized with 4-acetylpyridine to obtain an arylpyridine polymer; Step 2) Introduce diamine into graphene oxide to obtain diamine-functionalized graphene oxide; Step 3) The diamine-functionalized graphene oxide and the haloalkane from step 2) are subjected to nucleophilic addition to obtain a side-chain cation; Step 4) The arylpyridine polymer obtained in step 1) and the side-chain cation obtained in step 3) are subjected to a quaternization reaction to obtain a quaternized arylpyridine polymer, wherein the molar ratio of the arylpyridine polymer to the side-chain cation is (100:1)-(10:1). Step 5): Dissolve the quaternized arylpyridine polymer obtained in step 4) in organic high-boiling solvent 1 to form solution 1, disperse the heteropolyacid cesium salt in organic high-boiling solvent 2 to form solution 2, mix solution 1 and solution 2 again to form casting solution, cast into a film and dry. Step 6): Immerse the membrane obtained in step 5) in phosphoric acid solution, and then dry it to obtain the proton exchange membrane.

2. The preparation method according to claim 1, characterized in that: In step 1), the synthesis steps of the arylpyridine polymer are specifically as follows: 4-Acetylpyridine and aryl hydrocarbons were added to dichloromethane solvent, and a catalyst and protonating agent were added at -20 to 5°C. The mixture was then returned to room temperature and reacted for 2 to 72 hours before purification to obtain arylpyridine polymers. 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 catalyst is selected from trifluoroacetic acid and trichloroacetic acid, and the protonating agent is selected from trifluoromethanesulfonic acid and trinitrobenzenesulfonic acid. The molar ratio of 4-acetylpyridine to aryl hydrocarbon is (1:1)-(1.6:1); The aryl hydrocarbon is present in dichloromethane at a concentration of 0.001-0.1 g / ml; The molar ratio of 4-acetylpyridine to the catalyst is (1:5)-(1:10); The molar ratio of 4-acetylpyridine to the protonating agent is (1:5)-(1:20).

3. The preparation method according to claim 1, characterized in that: In step 2), the synthesis steps of the diamine-functionalized graphene oxide are specifically as follows: Graphene oxide was dispersed in a solvent and placed in an ice bath. Then, N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide were added. After reacting for 0.5-3 h, the ice bath was removed. When the reaction system returned to room temperature, diamine was added and the mixture was stirred. After reacting for 10-50 h, the mixture was purified to obtain diamine-functionalized graphene oxide. The diamine is selected from any one of N,N-dimethyl-1,3-diaminopropane, 3-diethylaminopropylamine, N,N-diethylbutane-1,4-diamine, 5-(diethylaminopentamine), 6-(dimethylamino)hexylamine, and (7-aminoheptyl)dimethylamine; The solvent is either toluene or tetrahydrofuran; The concentration of the graphene oxide in the solvent is 0.001-0.1 g / ml; The molar ratio of graphene oxide to N-hydroxysuccinimide is (1:20)-(1:50); The molar ratio of the graphene oxide to 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide is (1:20)-(1:50); The molar ratio of graphene oxide to diamine is (1:3)-(1:5).

4. The preparation method according to claim 1, characterized in that: In step 3), the specific steps for synthesizing the side-chain cation are as follows: The diamine-functionalized graphene oxide and haloalkanes prepared in step 2) were added to a solvent and heated to 60-100℃ for 8-50 h to obtain a solid precipitate; the precipitate was filtered, purified with ethyl acetate to remove excess reactants, and dried under vacuum to obtain a side-chain cation. The haloalkane is selected from any one of 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 solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; The molar ratio of the diamine-functionalized graphene oxide to the haloalkane is (1:2)-(1:5); The molar ratio of the arylpyridine polymer to the haloalkane is (1:1)-(1:5); The concentration of the diamine-functionalized graphene oxide in the solvent is 0.001-0.1 g / ml.

5. The preparation method according to claim 1, characterized in that: In step 4), the specific steps for synthesizing the quaternized arylpyridine polymer are as follows: The arylpyridine polymer obtained in step 1) and the side-chain cation obtained in step 3) are added to a solvent, heated to 80-120℃ for 20-50 h, precipitated in ethyl acetate, washed multiple times with deionized water, filtered, and dried at 60-120℃ to obtain the quaternized arylpyridine polymer. The solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; The arylpyridine polymer has a concentration of 0.001-0.1 g / ml in the solvent.

6. The preparation method according to claim 1, characterized in that: In step 5), the mass ratio of the heteropolyacid cesium salt to the quaternized arylpyridine polymer is (1:1000)-(1:100); The organic high-boiling solvent one and organic high-boiling solvent two are independently one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; The concentration of the solution is 0.01-0.1 g / ml; The concentration of the solution is 0.001-0.01 g / ml; The drying temperature is 60-120℃; The film thickness is 30-100 μm.

7. The preparation method according to claim 1, characterized in that: In step 5), the specific steps for synthesizing the heteropolyacid cesium salt are as follows: Cesium carbonate and heteropoly acid are dissolved in deionized water, mixed, heated to 60-80℃, and reacted for 20-40 hours. After the reaction, the mixture is rinsed with deionized water 1-3 times and dried at 60-120℃. 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.

8. The preparation method according to claim 1, characterized in that: In step 6), the phosphoric acid solution has a mass fraction of 0.1-85%; the soaking time is 20-80 hours; and the drying temperature is 60-120°C.

9. A proton exchange membrane prepared by the method according to any one of claims 1-8.

10. The application of the proton exchange membrane according to claim 9 in high-temperature water electrolysis and medium-high temperature fuel cells.

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