Polypropylene-based cross-linked quaternary ammonium anion exchange membrane, its preparation method and application in hydrogen production by electrolysis of water

Abstract

The application belongs to the technical field of anion exchange membranes for water electrolysis hydrogen production, and discloses a polypropylene-based cross-linked quaternary ammonium anion exchange membrane, a preparation method thereof and application thereof in water electrolysis hydrogen production. The polypropylene is used as a polymer main chain, a benzyl chloride active reaction site is given to an intermediate film through radiation grafting, and then precise cross-linking is realized between polymer segments through a Menshutkin reaction. Two different flexible cross-linking agents are selected to form different cross-linking networks, effectively solving the defects of weak mechanical properties and poor dimensional stability of uncross-linked membranes. Meanwhile, by precisely controlling the ratio of amination and cross-linking, the coupling optimization of the ion conductivity, mechanical properties and dimensional stability of the membrane material is realized. Due to the structural matching of the main chain and the side chain, the multiple gains of cross-linking and the synergistic balance of multiple properties, the anion exchange membrane material exhibits excellent comprehensive performance and good application potential in related electrochemical applications.

Description

Technical Field

[0001] This invention belongs to the technical field of anion exchange membranes for hydrogen production by water electrolysis. Specifically, it relates to a polypropylene-based cross-linked quaternary ammonium anion exchange membrane, its preparation method, and its application in hydrogen production by water electrolysis. Background Technology

[0002] Since the beginning of the 21st century, the energy crisis and environmental pollution have intensified, prompting a sustained increase in global demand for clean energy. Hydrogen energy, with its clean and efficient energy conversion and utilization characteristics, is widely recognized as a core carrier for promoting energy structure transformation. However, current global hydrogen production is still dominated by fossil fuel reforming processes, which are accompanied by large amounts of carbon dioxide emissions, severely restricting the environmental benefits of hydrogen energy throughout its entire life cycle. In contrast, green hydrogen produced by water electrolysis technology driven by renewable energy sources has become a key technological path for achieving hydrogen economic transformation and contributing to the achievement of "dual carbon" goals due to its outstanding advantage of zero carbon emissions across the entire chain. Among existing water electrolysis hydrogen production technologies, anion exchange membrane electrolysis (AEMWE) technology has attracted much attention due to its unique performance advantages: this technology not only inherits the low-cost characteristics of traditional alkaline water electrolysis (AWE) using non-precious metal catalysts, but also combines the advantages of efficient and compact equipment configuration of proton exchange membrane electrolysis (PEMWE), and is considered one of the optimal development directions for next-generation water electrolysis hydrogen production technology.

[0003] Anion exchange membranes (AEMs), as the core component of anion exchange membrane electrolysis (AEMWE), are composed of a polymer backbone and cationic groups. Their core function is to mediate the exchange of OH-. - The oxygen evolves from the cathode to the anode, participating in the oxygen evolution reaction. Simultaneously, the H2 and O2 generated at the anode and cathode are strictly separated to avoid safety hazards and electrolysis efficiency losses caused by cross-mixing of gases. The chemical structure and aggregate structure of the polymer backbone determine the membrane's mechanical strength, oxidation resistance, and dimensional stability, while the number, distribution, and dissociation ability of cationic groups directly regulate the membrane's anion conduction efficiency. However, current performance bottlenecks in ionic conductivity and stability of AEMs severely limit their practical applications. Ionic conductivity is closely related to ion exchange capacity (IEC), hydration degree, and the microphase separation structure of the membrane material. Increasing IEC is a direct way to improve ionic conductivity, but it easily leads to excessive water absorption and swelling of the membrane, significantly reducing mechanical strength and dimensional stability, thereby degrading the performance of AEMWE.

[0004] Inter-chain crosslinking of polymers is an effective means of suppressing membrane swelling, but traditional crosslinking strategies require the introduction of additional crosslinking agents or rely on high-temperature heat treatment, which not only increases the complexity of the process but may also cause degradation of cationic groups. Simultaneously, the free volume of the crosslinked membrane decreases, water absorption is reduced, and OH groups are degraded. -Decreased mobility often makes it difficult to improve or even weakens ionic conductivity. Therefore, how to simultaneously improve the dimensional stability and alkali stability of AEMs while ensuring high ionic conductivity, and thus optimize their electrolytic performance and lifespan in AEMWE, is a core challenge that urgently needs to be overcome in the current research and application of AEMs materials. It is also the key to promoting the development of AEMWE technology towards low cost, high reliability, and large-scale production. Summary of the Invention

[0005] This invention focuses on solving the problems of coupled regulation of ionic conductivity, dimensional stability, mechanical properties, and water electrolysis performance of polypropylene-based anion exchange membranes. It provides a cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane and its preparation method. This invention uses polypropylene (PP) as the main chain and adopts side chains containing benzyltrimethylammonium chloride anion groups, so that there is a clear microphase separation structure between the hydrophobic polymer main chain and the hydrophilic ionic domains containing functional groups, which helps to form ion-conducting channels and improve ionic conductivity. The cross-linking of the hydrophilic ionic regions not only improves the dimensional stability of the membrane, but also aims to increase the aggregation of ion clusters, thereby forming a microphase separation structure and ion-conducting channels.

[0006] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0007] According to one aspect of the present invention, a polypropylene-based cross-linked quaternized anion exchange membrane is provided, the chemical structural formula of which is as follows:

[0008] ;

[0009] The main chain of this anion exchange membrane is one of polypropylene (PP); where N... + (CH3)3 represents a quaternary ammonium group; in the formula, the number of functionalized structural units is xm1+ym2, and the number of non-functionalized structural units z is 1-(xm1+ym2); the functionalized structural unit contains cross-linked parts with different molar proportions, xm1 / (xm1+ym2)=4-50%; the molar proportion of the non-cross-linked part, i.e., the cationic side chain part, is ym2 / (xm1+ym2)=1-xm1 / (xm1+ym2); in the formula, the value of n is 100-35000, and the values ​​of m1 and m2 are both 1-500.

[0010] Preferably, the polypropylene in step (1) is isotactic polypropylene or biaxially oriented polypropylene (BOPP).

[0011] According to another aspect of the present invention, a method for preparing the above-described polypropylene-based crosslinked quaternized anion exchange membrane is provided, comprising the following steps:

[0012] (1) Using polypropylene film as a precursor film;

[0013] (2) The precursor film was irradiated with an electron beam and then stored at low temperature.

[0014] (3) First, chloromethyl vinylbenzene (VBC), surfactant and ultrapure water are added to the reactor, and an inert gas is introduced at room temperature to make the reactor an inert atmosphere environment, while chloromethyl vinylbenzene (VBC) and surfactant are uniformly mixed in ultrapure water to form an emulsion.

[0015] Then, the irradiated film obtained in step (2) is added to the reactor, and then an inert gas is introduced;

[0016] After introducing an inert gas for 0.5-2 hours, the reaction system is transferred to a water bath and the reaction is carried out under heating.

[0017] After the reaction was completed, the film was washed with solvent A and then dried in a vacuum oven to obtain the grafted intermediate film.

[0018] (4) The grafted intermediate film obtained in step (3) is added to the trimethylamine solution for reaction. After the reaction is completed, it is washed with solvent B to obtain the amination intermediate film.

[0019] (5) The amination intermediate film obtained in step (4) is added to a mixed solution of crosslinking agent and N-methylpyrrolidone (NMP) for reaction. After the reaction is completed, it is washed with solvent B to obtain a crosslinked quaternary ammonium functionalized polypropylene anion exchange membrane.

[0020] (6) The cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane synthesized in step (5) was immersed in sodium chloride solution and washed with water to obtain the anion with the form Cl. - A cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane is used for long-term storage under humid conditions.

[0021] Preferably, the dose of electron beam radiation in step (2) is 50-150 kGy.

[0022] Preferably, the temperature for low-temperature preservation in step (2) is less than or equal to -30°C.

[0023] Preferably, the surfactant in step (3) is 1-octyl-2-pyrrolidone (NOP).

[0024] Preferably, the volume ratio of chloromethyl vinylbenzene (VBC) to surfactant in step (3) is 1-10:1.

[0025] Preferably, the reaction is carried out under the heating state described in step (3), the reaction temperature should be 40-60℃, and the reaction time should be 6-10h.

[0026] Preferably, the cleaning solvent A in step (3) is at least one of methanol, ethanol, isopropanol, and deionized water.

[0027] Preferably, the grafted intermediate film in step (4) is an aromatic side chain film containing chloromethyl groups.

[0028] Preferably, the trimethylammonium solution concentration in step (4) is 30-35 wt%.

[0029] Preferably, the reaction described in step (4) is carried out at room temperature for 2-8 hours to regulate the degree of amination, which is controlled at 50%-96%.

[0030] Preferably, the grafted intermediate film in step (5) is a film containing a side chain structure of benzyltrimethylammonium chloride anionic group.

[0031] Preferably, the crosslinking agent in step (5) is dissolved in N-methylpyrrolidone (NMP) to form a crosslinking agent solution with a mass fraction of 5-15%.

[0032] Preferably, the crosslinking agent solution in step (5) is one of N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) solution and bis(dimethylaminoethyl ether) (BDMAEE) solution.

[0033] Preferably, the reaction in step (5) is carried out at 70-80°C for 24-48 hours to ensure that the remaining chloromethyl sites react fully.

[0034] Preferably, the solvent B in step (5) is at least one of ethanol and deionized water.

[0035] According to another aspect of the present invention, the application of the above-described polypropylene-based cross-linked quaternized anion exchange membrane in water electrolysis for hydrogen production is provided.

[0036] The beneficial effects of this invention are:

[0037] This invention provides a cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane and its preparation method. Polypropylene (PP) is used as the polymer backbone, combined with side chains containing benzyltrimethylammonium chloride anionic groups. A cross-linked structure is introduced into the polymer structural unit, with the degree of cross-linking controlled within the range of 4%-50%. On one hand, an intermediate membrane containing chloromethyl aromatic side chains is synthesized, wherein the cross-linkable functional groups undergo Menshutkin reactions with two different flexible cross-linking agents. The resulting cross-linked structure effectively solves the problems of weak mechanical properties and poor dimensional stability of uncross-linked membranes. On the other hand, by adjusting the degree of cross-linking to 4%-50%, the "trade-off" between ionic conductivity, mechanical properties, and dimensional stability is resolved, providing a high-performance ion exchange membrane material for alkaline water electrolyzers. Among them, the non-ether-containing flexible crosslinking agent enables the polypropylene-based anion exchange membrane to improve its mechanical properties by at least 1.26 times while maintaining good ion transport performance, and significantly optimizes its dimensional stability. At 80℃, the water absorption rate of the crosslinked membrane is reduced by more than 55% compared to the non-crosslinked membrane, and the swelling rate is reduced by more than 50% compared to the non-crosslinked membrane, so that the electrolysis performance meets the actual operation requirements. On the other hand, the ether-containing flexible crosslinking structure enables the biaxially stretched polypropylene-based anion exchange membrane to achieve mechanical properties of more than 40 MPa while ensuring hydroxide ion conductivity >100 mS / cm. The dimensional stability is also improved. At 80℃, the water absorption rate and swelling rate of the crosslinked membrane are reduced by more than 25% and 20% respectively compared to the non-crosslinked membrane. In the electrolysis test, it shows lower electrolysis energy consumption and better electrolysis reaction kinetics. Attached Figure Description

[0038] Figure 1 The graph shows a comparison of the mechanical properties of the anion exchange membranes prepared in Example 1, Example 2, and Comparative Example 1.

[0039] Figure 2 The OH groups of the anion exchange membranes prepared in Examples 1, 2, and 1 are... - Conductivity comparison chart.

[0040] Figure 3 The thickness swelling comparison diagram shows the thickness swelling of the anion exchange membranes prepared in Example 1, Example 2, and Comparative Example 1.

[0041] Figure 4 This is a comparison chart of the water absorption rates of the anion exchange membranes prepared in Example 1, Example 2, and Comparative Example 1.

[0042] Figure 5 The graph shows a comparison of linear sweep voltammetric curves of the water electrolysis performance of the anion exchange membranes prepared in Example 1, Example 2, and Comparative Example 1.

[0043] Figure 6The graph shows a comparison of the mechanical properties of the anion exchange membranes prepared in Examples 3, 4, and 2.

[0044] Figure 7 The OH groups of the anion exchange membranes prepared in Examples 3, 4, and 2 are... - Conductivity comparison chart.

[0045] Figure 8 The thickness swelling comparison diagram shows the thickness swelling of the anion exchange membranes prepared in Examples 3, 4, and 2.

[0046] Figure 9 The graph shows a comparison of the water absorption rates of the anion exchange membranes prepared in Examples 3, 4, and 2.

[0047] Figure 10 The image shows a comparison of linear sweep voltammetric curves of the water electrolysis performance of the anion exchange membranes prepared in Example 3 and Comparative Example 2. Detailed Implementation

[0048] The specific implementation of the present invention will be described in more detail below with reference to the accompanying drawings and embodiments, so as to better understand the solution of the present invention and the advantages of its various aspects. It should be noted that the specific implementation methods and embodiments described below are for illustrative purposes only and are not intended to limit the present invention.

[0049] This invention provides a polypropylene-based cross-linked quaternized anion exchange membrane, the chemical structural formula of which is as follows:

[0050] ;

[0051] The main chain of this anion exchange membrane is one of polypropylene (PP); where N... + (CH3)3 represents a quaternary ammonium group; in the formula, the number of functionalized structural units is xm1+ym2, and the number of non-functionalized structural units z is 1-(xm1+ym2); the functionalized structural unit contains cross-linked parts with different molar proportions, xm1 / (xm1+ym2)=4-50%; the molar proportion of the non-cross-linked part, i.e., the cationic side chain part, is ym2 / (xm1+ym2)=1-xm1 / (xm1+ym2); in the formula, the value of n is 100-35000, and the values ​​of m1 and m2 are both 1-500.

[0052] As some preferred embodiments of the present invention, the polypropylene in step (1) is isotactic polypropylene or biaxially oriented polypropylene (BOPP).

[0053] The present invention also provides a method for preparing the above-mentioned polypropylene-based crosslinked quaternized anion exchange membrane, comprising the following steps:

[0054] (1) Using polypropylene film as a precursor film;

[0055] (2) The precursor film was irradiated with an electron beam and then stored at low temperature.

[0056] (3) First, chloromethyl vinylbenzene (VBC), surfactant and ultrapure water are added to the reactor, and an inert gas is introduced at room temperature to make the reactor an inert atmosphere environment, while chloromethyl vinylbenzene (VBC) and surfactant are uniformly mixed in ultrapure water to form an emulsion.

[0057] Then, the irradiated film obtained in step (2) is added to the reactor, and then an inert gas is introduced;

[0058] After introducing an inert gas for 0.5-2 hours, the reaction system is transferred to a water bath and the reaction is carried out under heating.

[0059] After the reaction was completed, the film was washed with solvent A and then dried in a vacuum oven to obtain the grafted intermediate film.

[0060] (4) The grafted intermediate film obtained in step (3) is added to the trimethylamine solution for reaction. After the reaction is completed, it is washed with solvent B to obtain the amination intermediate film.

[0061] (5) The amination intermediate film obtained in step (4) is added to a mixed solution of crosslinking agent and N-methylpyrrolidone (NMP) for reaction. After the reaction is completed, it is washed with solvent B to obtain a crosslinked quaternary ammonium functionalized polypropylene anion exchange membrane.

[0062] (6) The cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane synthesized in step (5) was immersed in sodium chloride solution and washed with water to obtain the anion with the form Cl. - A cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane is used for long-term storage under humid conditions.

[0063] As some preferred embodiments of the present invention, the dose of electron beam radiation in step (2) is 50-150 kGy.

[0064] As some preferred embodiments of the present invention, the temperature for low-temperature storage in step (2) is less than or equal to -30°C.

[0065] As some preferred embodiments of the present invention, the surfactant in step (3) is 1-octyl-2-pyrrolidone (NOP).

[0066] As some preferred embodiments of the present invention, the volume ratio of chloromethyl vinylbenzene (VBC) to surfactant in step (3) is 1-10:1.

[0067] As some preferred embodiments of the present invention, the reaction is carried out under the heating state in step (3), the reaction temperature should be 40-60℃, and the reaction time should be 6-10h.

[0068] As some preferred embodiments of the present invention, the cleaning solvent A in step (3) is at least one of methanol, ethanol, isopropanol, and deionized water.

[0069] As some preferred embodiments of the present invention, the grafted intermediate film in step (4) is an aromatic side chain film containing chloromethyl groups.

[0070] As some preferred embodiments of the present invention, the concentration of trimethylammonium solution in step (4) is 30-35 wt%.

[0071] As some preferred embodiments of the present invention, the reaction in step (4) is carried out at room temperature for 2-8 hours, thereby regulating the degree of amination to be controlled at 50%-96%.

[0072] As some preferred embodiments of the present invention, the grafted intermediate film in step (5) is a film containing a side chain structure of benzyltrimethylammonium chloride anionic group.

[0073] As some preferred embodiments of the present invention, the crosslinking agent in step (5) is dissolved in N-methylpyrrolidone (NMP) to form a crosslinking agent solution with a mass fraction of 5-15%.

[0074] As some preferred embodiments of the present invention, the crosslinking agent solution in step (5) is one of N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) solution and bis(dimethylaminoethyl ether) (BDMAEE) solution.

[0075] As some preferred embodiments of the present invention, the reaction in step (5) is carried out at 70-80°C for 24-48 hours to ensure that the remaining chloromethyl sites react fully.

[0076] As some preferred embodiments of the present invention, the solvent B in step (5) is at least one of ethanol and deionized water.

[0077] The polypropylene-based cross-linked quaternized anion exchange membrane with the above structure and preparation exhibits excellent comprehensive performance and good application potential in the application of water electrolysis for hydrogen production.

[0078] Example 1

[0079] A cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane is prepared by the following steps:

[0080] A 45 μm thick isotactic polypropylene (PP) precursor film was irradiated with an electron beam at a dose of 150 kGy and then stored in dry ice after irradiation.

[0081] Add 17 ml of chloromethylvinylbenzene (VBC), 3.4 ml of 1-octyl-2-pyrrolidone (NOP), and 319.6 ml of ultrapure water to a Schlenk tube, and purge with argon gas at room temperature for 30 min. The liquid will turn into a milky white, uniform emulsion.

[0082] Cut the precursor film PP to 10*10cm, place it in a Schlenk tube, and continue to purge with argon gas for 2 hours to allow VBC and NOP droplets in the reaction solution to adhere to the film surface.

[0083] Remove the vent tube, seal the Schlenk tube, and heat in an inert gas atmosphere at 50°C in a water bath for 5 hours.

[0084] After the reaction was complete, the liquid in the Schlenk tube was removed, isopropanol was added for washing, and the mixture was heated and stirred in a 50°C water bath for 1 hour. The washed film was then dried in an oven at 60°C for 4 hours to obtain the grafted intermediate film. Its mass increased by approximately 78.8%.

[0085] The grafted intermediate film was added to a 35 wt% trimethylamine solution and stirred at room temperature for 4 hours. After the reaction was completed, it was washed with ultrapure water for 1 hour to obtain a film containing a benzyltrimethylammonium chloride anion group side chain structure.

[0086] The amination-treated intermediate membrane was added to a mixed solution of N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) and N-methylpyrrolidone (NMP) and reacted. The mass fraction of N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) in the solution was 15%. The mixture was stirred at 80°C for 24-48 h. After the reaction was completed, the membrane was washed with ultrapure water and stirred for 1 h to obtain a cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane.

[0087] The prepared cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane was immersed in a sodium chloride solution (1 mol / L) and stirred at room temperature for 48 hours to convert the ions to Cl. - form.

[0088] The structural formula of the anion exchange membrane obtained in this embodiment is:

[0089] ;

[0090] In the formula, the number of functionalized structural units is xm1 + ym2 = 0.16, and the number of non-functionalized structural units is z = 0.84; the functionalized structural unit contains cross-linked parts with different molar proportions, xm1 / (xm1 + ym2) = 5%; the molar proportion of the non-cross-linked part, i.e., the cationic side chain part, is ym2 / (xm1 + ym2) = 95%. In the formula, n is 100-35000, and m1 and m2 are 1-500.

[0091] Example 2

[0092] A cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane is prepared by the following steps:

[0093] A 45 μm thick isotactic polypropylene (PP) precursor film was irradiated with an electron beam at a dose of 150 kGy and then stored in dry ice after irradiation.

[0094] Add 17 ml of chloromethylvinylbenzene (VBC), 3.4 ml of 1-octyl-2-pyrrolidone (NOP), and 319.6 ml of ultrapure water to a Schlenk tube, and purge with argon gas at room temperature for 30 min. The liquid will turn into a milky white, uniform emulsion.

[0095] Cut the precursor film PP to 10*10cm, place it in a Schlenk tube, and continue to purge with argon gas for 2 hours to allow VBC and NOP droplets in the reaction solution to adhere to the film surface.

[0096] Remove the vent tube, seal the Schlenk tube, and heat in an inert gas atmosphere at 50°C in a water bath for 5 hours.

[0097] After the reaction was complete, the liquid in the Schlenk tube was removed, isopropanol was added for washing, and the mixture was heated and stirred in a 50°C water bath for 1 hour. The washed film was then dried in an oven at 60°C for 4 hours to obtain the grafted intermediate film. Its mass increased by approximately 78.8%.

[0098] The grafted intermediate film was added to a 35 wt% trimethylamine solution and stirred at room temperature for 3 hours. After the reaction was completed, it was washed with ultrapure water for 1 hour to obtain a film containing a benzyltrimethylammonium chloride anion group side chain structure.

[0099] The amination-treated intermediate membrane was added to a mixed solution of N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) and N-methylpyrrolidone (NMP) and reacted. The mass fraction of N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) in the solution was 15%. The mixture was stirred at 80°C for 24-48 h. After the reaction was completed, the membrane was washed with ultrapure water and stirred for 1 h to obtain a cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane.

[0100] The prepared cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane was immersed in a sodium chloride solution (1 mol / L) and stirred at room temperature for 48 hours to convert the ions to Cl. - form.

[0101] The structural formula of the anion exchange membrane obtained in this embodiment is:

[0102] ;

[0103] In the formula, the number of functionalized structural units is xm1 + ym2 = 0.16, and the number of non-functionalized structural units is z = 0.84; the functionalized structural unit contains cross-linked parts with different molar proportions, xm1 / (xm1 + ym2) = 30%; the molar proportion of the non-cross-linked part, i.e., the cationic side chain part, is ym2 / (xm1 + ym2) = 70%. In the formula, n is 100-35000, and m1 and m2 are 1-500.

[0104] Example 3

[0105] A cross-linked quaternary ammonium functionalized biaxially oriented polypropylene anion exchange membrane is prepared by the following steps:

[0106] A 25 μm thick biaxially oriented polypropylene (BOPP) precursor film was irradiated with an electron beam at a dose of 150 kGy and then stored in dry ice after irradiation.

[0107] Add 17 ml of chloromethylvinylbenzene (VBC), 3.4 ml of 1-octyl-2-pyrrolidone (NOP), and 319.6 ml of ultrapure water to a Schlenk tube, and purge with argon gas at room temperature for 30 min. The liquid will turn into a milky white, uniform emulsion.

[0108] The precursor film BOPP was cut to 10*10cm and placed in a Schlenk tube. Argon gas was continued to be passed through for 2 hours to allow VBC and NOP droplets in the reaction solution to adhere to the film surface.

[0109] Remove the vent tube, seal the Schlenk tube, and heat in an inert gas atmosphere at 50°C in a water bath for 5 hours.

[0110] After the reaction was complete, the liquid in the Schlenk tube was removed, isopropanol was added for washing, and the mixture was heated and stirred in a 50°C water bath for 1 hour. The washed film was dried in an oven at 60°C for 4 hours to obtain the grafted intermediate film. Its mass increased by approximately 93%.

[0111] The grafted intermediate film was added to a 35 wt% trimethylamine solution and stirred at room temperature for 4 hours. After the reaction was completed, it was washed with ultrapure water for 1 hour to obtain a film containing a benzyltrimethylammonium chloride anion group side chain structure.

[0112] The amination-treated intermediate membrane was added to a mixed solution of bis(dimethylaminoethyl ether) (BDMAEE) and N-methylpyrrolidone (NMP) and reacted. The mass fraction of BDMAEE in the solution was 15%. The mixture was stirred at 80°C for 24-48 hours. After the reaction was completed, the membrane was washed with ultrapure water for 1 hour to obtain a cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane.

[0113] The prepared cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane was immersed in a sodium chloride solution (1 mol / L) and stirred at room temperature for 48 hours to convert the ions to Cl. - form.

[0114] The structural formula of the anion exchange membrane obtained in this embodiment is:

[0115] ;

[0116] In the formula, the number of functionalized structural units is xm1 + ym2 = 0.19, and the number of non-functionalized structural units z is 0.81; the functionalized structural unit contains cross-linked parts with different molar proportions, xm1 / (xm1 + ym2) = 5%; the molar proportion of the non-cross-linked part, i.e., the cationic side chain part, is ym2 / (xm1 + ym2) = 95%. In the formula, n is 100-35000, and m1 and m2 are 1-500.

[0117] Example 4

[0118] A cross-linked quaternary ammonium functionalized biaxially oriented polypropylene anion exchange membrane is prepared by the following steps:

[0119] A 25 μm thick biaxially oriented polypropylene (BOPP) precursor film was irradiated with an electron beam at a dose of 150 kGy and then stored in dry ice after irradiation.

[0120] Add 17 ml of chloromethylvinylbenzene (VBC), 3.4 ml of 1-octyl-2-pyrrolidone (NOP), and 319.6 ml of ultrapure water to a Schlenk tube, and purge with argon gas at room temperature for 30 min. The liquid will turn into a milky white, uniform emulsion.

[0121] The precursor film BOPP was cut to 10*10cm and placed in a Schlenk tube. Argon gas was continued to be passed through for 2 hours to allow VBC and NOP droplets in the reaction solution to adhere to the film surface.

[0122] Remove the vent tube, seal the Schlenk tube, and heat in an inert gas atmosphere at 50°C in a water bath for 5 hours.

[0123] After the reaction was complete, the liquid in the Schlenk tube was removed, isopropanol was added for washing, and the mixture was heated and stirred in a 50°C water bath for 1 hour. The washed film was dried in an oven at 60°C for 4 hours to obtain the grafted intermediate film. Its mass increased by approximately 93%.

[0124] The grafted intermediate film was added to a 35 wt% trimethylamine solution and stirred at room temperature for 3 hours. After the reaction was completed, it was washed with ultrapure water for 1 hour to obtain a film containing a benzyltrimethylammonium chloride anion group side chain structure.

[0125] The amination-treated intermediate membrane was added to a mixed solution of bis(dimethylaminoethyl ether) (BDMAEE) and N-methylpyrrolidone (NMP) and reacted. The mass fraction of BDMAEE in the solution was 15%. The mixture was stirred at 80°C for 24-48 hours. After the reaction was completed, the membrane was washed with ultrapure water for 1 hour to obtain a cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane.

[0126] The prepared cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane was immersed in a sodium chloride solution (1 mol / L) and stirred at room temperature for 48 hours to convert the ions to Cl. - form.

[0127] The structural formula of the anion exchange membrane obtained in this embodiment is:

[0128] ;

[0129] In the formula, the number of functionalized structural units is xm1 + ym2 = 0.19, and the number of non-functionalized structural units z is 0.81; the functionalized structural unit contains cross-linked parts with different molar proportions, xm1 / (xm1 + ym2) = 35%; the molar proportion of the non-cross-linked part, i.e., the cationic side chain part, is ym2 / (xm1 + ym2) = 65%. In the formula, n is 100-35000, and m1 and m2 are 1-500.

[0130] Comparative Example 1:

[0131] A non-crosslinked polypropylene anion exchange membrane comprising a benzyltrimethylammonium chloride anion group side chain structure is prepared by the following steps:

[0132] A 45 μm thick isotactic polypropylene (PP) precursor film was irradiated with an electron beam at a dose of 150 kGy and then stored in dry ice after irradiation.

[0133] Add 17 ml of chloromethylvinylbenzene (VBC), 3.4 ml of 1-octyl-2-pyrrolidone (NOP), and 319.6 ml of ultrapure water to a Schlenk tube, and purge with argon gas at room temperature for 30 min. The liquid will turn into a milky white, uniform emulsion.

[0134] Cut the precursor film PP to 10*10cm, place it in a Schlenk tube, and continue to purge with argon gas for 2 hours to allow VBC and NOP droplets in the reaction solution to adhere to the film surface.

[0135] Remove the vent tube, seal the Schlenk tube, and heat in an inert gas atmosphere at 50°C in a water bath for 5 hours.

[0136] After the reaction was complete, the liquid in the Schlenk tube was removed, isopropanol was added for washing, and the mixture was heated and stirred in a 50°C water bath for 1 hour. The washed film was then dried in an oven at 60°C for 4 hours to obtain the grafted intermediate film. Its mass increased by approximately 78.8%.

[0137] The grafted intermediate membrane was added to a 35 wt% trimethylamine solution and stirred at room temperature for 24 hours. After the reaction was completed, it was washed with ultrapure water for 1 hour to obtain a non-crosslinked polypropylene anion exchange membrane containing benzyltrimethylammonium chloride anion group side chain structure.

[0138] The prepared polypropylene-based anion exchange membrane was immersed in a sodium chloride solution (1 mol / L) and stirred at room temperature for 48 hours to convert the ions to Cl. - form.

[0139] The structural formula of the anion exchange membrane obtained in this embodiment is:

[0140] ;

[0141] In the formula, the number of functional structural units is ym2 = 0.16, and the number of non-functional structural units is z = 0.84; the value of n is 100-35000, and the values ​​of m1 and m2 are 1-500.

[0142] Comparative Example 2:

[0143] A non-crosslinked biaxially stretched polypropylene anion exchange membrane comprising a benzyltrimethylammonium chloride anion group side chain structure is prepared by the following steps:

[0144] A 25 μm thick biaxially oriented polypropylene (BOPP) precursor film was irradiated with an electron beam at a dose of 150 kGy and then stored in dry ice after irradiation.

[0145] Add 17 ml of chloromethylvinylbenzene (VBC), 3.4 ml of 1-octyl-2-pyrrolidone (NOP), and 319.6 ml of ultrapure water to a Schlenk tube, and purge with argon gas at room temperature for 30 min. The liquid will turn into a milky white, uniform emulsion.

[0146] The precursor film BOPP was cut to 10*10cm and placed in a Schlenk tube. Argon gas was continued to be passed through for 2 hours to allow VBC and NOP droplets in the reaction solution to adhere to the film surface.

[0147] Remove the vent tube, seal the Schlenk tube, and heat in an inert gas atmosphere at 50°C in a water bath for 5 hours.

[0148] After the reaction was complete, the liquid in the Schlenk tube was removed, isopropanol was added for washing, and the mixture was heated and stirred in a 50°C water bath for 1 hour. The washed film was dried in an oven at 60°C for 4 hours to obtain the grafted intermediate film. Its mass increased by approximately 93%.

[0149] The grafted intermediate membrane was added to a 35 wt% trimethylamine solution and stirred at room temperature for 24 hours. After the reaction was completed, it was washed with ultrapure water for 1 hour to obtain a non-crosslinked biaxially stretched polypropylene anion exchange membrane containing benzyltrimethylammonium chloride anion group side chain structure.

[0150] The prepared polypropylene-based anion exchange membrane was immersed in a sodium chloride solution (1 mol / L) and stirred at room temperature for 48 hours to convert the ions to Cl. - form.

[0151] The structural formula of the anion exchange membrane obtained in this embodiment is:

[0152] ;

[0153] In the formula, the number of functional structural units is ym2=0.19, and the number of non-functional structural units is z=0.81; the value of n is 100-35000, and the values ​​of m1 and m2 are 1-500.

[0154] Performance testing:

[0155] The polypropylene-based anion exchange membranes prepared in Examples 1 and 2 above, with N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) as the crosslinking agent and crosslinking degrees of 5% and 30% respectively, were subjected to common basic performance and water electrolysis performance tests compared with the non-crosslinked polypropylene-based anion exchange membrane prepared in Comparative Example 1. The basic performance test data are shown in Table 1.

[0156] Table 1. Performance test results of polypropylene-based anion exchange membranes prepared in Examples 1 and 2 and Comparative Example 1.

[0157]

[0158] See Figure 1 The mechanical strength and elongation of the cross-linked films of Examples 1 and 2 of the present invention, and the uncross-linked film of Comparative Example 1, were measured. Figure 1 As can be seen, after crosslinking, the mechanical strengths of the membranes of Example 1, Example 2, and Comparative Example 1 of the present invention were measured to be 26.73 MPa, 33.13 MPa, and 11.82 MPa, respectively. Compared with the uncrosslinked membrane of Comparative Example 1, the mechanical strengths of Example 1 and Example 2 increased by approximately 1.26 times and 1.8 times, respectively. The main reason may be that after radiation grafting, the chloromethyl groups in the membrane can undergo nucleophilic substitution reactions with the tertiary amine groups of the crosslinking agent to generate stable CN covalent crosslinking bonds; at the same time, each crosslinking agent molecule has two reaction sites, and a bisquaternary ammonium salt is generated after the reaction. The formation of a crosslinked network in the anion exchange membrane restricts the mobility of the polymer chains and hinders chain segment slippage, which can be macroscopically manifested as a significant increase in mechanical strength.

[0159] Table 1 shows that the IEC of the prepared membranes ranged from 1.8 to 2.14 mmol / g. The presence of cations promotes ion conduction, so the hydroxide ion conductivity increases with increasing IEC. However, excessively high effective ion exchange capacity can easily lead to membrane swelling and dimensional changes, causing mechanical stress and non-uniform failure in the membrane electrode assembly. It also reduces the membrane's hydration dependence and degrades its mechanical properties. Figure 2 The figures show that the hydroxide ion conductivity of the membranes in Examples 1 and 2 of this invention is 150.85 mS / cm and 127.4 mS / cm, respectively, indicating that they possess good ion transport performance. Figure 3 and Figure 4 The dimensional stability of Examples 1 and 2 was significantly better than that of Comparative Example 1. Excessive water absorption can easily cause swelling of the membrane material, leading to a decrease in its mechanical properties. As shown in Table 1, the water absorption rate and swelling rate of Examples 1 and 2 were both lower than those of Comparative Example 1, indicating that the water absorption and swelling of the membranes were significantly improved. As the degree of crosslinking increased by 30% from 5%, the water absorption rate decreased from 34.23% to 25.28% at 80°C, and the swelling rate decreased from 13.19% to 11.99% at 80°C. This is attributed to the formation of a crosslinked network structure between the polymer chains in the membranes of Examples 1 and 2, which restricts the movement of the polymer chains and effectively inhibits the water absorption and swelling of the membranes.

[0160] Figure 5 For the hydrogen production test results via water electrolysis, in the water electrolysis test, the anode used was 1 mg / cm³. 2 RuO2 catalyst, cathode concentration 1 mg / cm 2The platinum-carbon catalyst (20% Pt) was tested at 60°C with 1M KOH as the electrolyte. The test results show that when the current density reaches 1 A / cm², the membrane voltage of Example 1 is 1.74 V, which is better than the voltage of Comparative Example 1 (1.77 V). The membrane voltage of Example 2 is 1.81 V, also exhibiting good electrolysis performance. Therefore, crosslinking degrees of 5% and 30% can effectively improve the water absorption and swelling behavior of polypropylene-based anion exchange membranes. While ensuring the basic requirements of ion exchange capacity and hydroxide conductivity, both water absorption and swelling rates are significantly reduced, and mechanical strength is greatly improved, enabling the water electrolysis performance to meet actual operational requirements.

[0161] The biaxially oriented polypropylene-based anion exchange membranes prepared in Examples 3 and 4 above, with bis(dimethylaminoethyl) ether (BDMAEE) as the crosslinking agent and crosslinking degrees of 5% and 35% respectively, were compared with the non-crosslinked polypropylene-based anion exchange membrane prepared in Comparative Example 2. Common basic performance and water electrolysis performance tests were conducted. The basic performance test data are shown in Table 2.

[0162] Table 2 shows the performance test results of the biaxially stretched polypropylene-based anion exchange membranes prepared in Examples 3 and 4 and Comparative Example 2.

[0163]

[0164] See Figure 6 The mechanical strength and elongation of the cross-linked membranes of Examples 3 and 4 of the present invention and the uncross-linked membrane of Comparative Example 2 were measured. After cross-linking, the mechanical strengths of the membranes of Examples 3, 4, and Comparative Example 2 were measured to be 50.39 MPa, 41.09 MPa, and 31.72 MPa, respectively. Compared with the uncross-linked membrane of Comparative Example 2, the mechanical strengths of Examples 3 and 4 increased by approximately 0.61 times and 0.31 times, respectively. This is mainly attributed to the introduction of the cross-linking structure, which effectively improved the mechanical properties of the membrane.

[0165] As shown in Table 2, the membrane prepared in Comparative Example 2 had the highest IEC (intersection over ionization), at 2.09 mmol / g. The IEC gradually decreased with increasing crosslinking degree. The IEC values ​​for Examples 3 and 4 were 2.04 mmol / g and 1.96 mmol / g, respectively, ensuring the membrane's basic ion transport capacity. Figures 7-9Analysis shows that the presence of this cross-linked structure effectively balances the contradiction between ion conduction and water absorption / swelling of the membrane. With increasing cross-linking degree, both the swelling rate and water absorption rate of the membrane decrease. The cross-linking degree of the membrane in Example 3 is only 5%. Although the IEC of the membranes in Example 3 and Comparative Example 2 are very similar, the water absorption rate and swelling degree are significantly reduced. The swelling rate is about 0.21 times lower than that of Comparative Example 2, and the water absorption rate is about 0.29 times lower. As the cross-linking degree increases from 5% to 35%, the water absorption rate decreases from 124.63% to 89.37% at 80°C, and the swelling rate decreases from 87.31% to 51.58% at 80°C. Figure 7 The hydroxide ion conductivity was tested in the temperature range of 25-80℃. Example 3 showed the best ion conduction performance, with a hydroxide ion conductivity as high as 230.14 mS / cm at 80℃. The hydroxide ion conductivity of Example 4 was 128.71 mS / cm, indicating that it has good ion transport performance. This is due to the presence of ether bonds in the cross-linked structure, which can provide an effective channel for hydroxide ion transport.

[0166] Figure 10 The results of the water electrolysis hydrogen production test are shown. This test aims to evaluate the water electrolysis application performance of the membranes in Example 4 and Comparative Example 2. In the water electrolysis test, the anode used 1 mg / cm³. 2 RuO2 catalyst, cathode concentration 1 mg / cm 2 The platinum-carbon catalyst (20% Pt) was tested at 60°C with 1M KOH as the electrolyte. The test data show that when the current density reaches 1 A / cm², the electrolysis voltage corresponding to Example 4 is 1.73 V, significantly better than the 1.79 V of Comparative Example 2, exhibiting lower electrolysis energy consumption and better water electrolysis reaction kinetics. Therefore, both 5% and 35% crosslinking degrees can effectively improve the water absorption and swelling behavior of the biaxially oriented polypropylene-based anion exchange membrane. While maintaining a comparable ion exchange capacity, both water absorption and swelling rates are significantly reduced, mechanical strength is significantly improved, and ionic conductivity and water electrolysis performance are simultaneously optimized.

[0167] In summary, by comparing the basic performance and water electrolysis performance of the membranes from Examples 1 and 2 (with TMDHA as the crosslinking agent and crosslinking degrees of 5% and 30%, respectively) with the non-crosslinked Comparative Example 1 membrane, it can be further verified that polypropylene-based anion exchange membranes with a crosslinking degree of 4%-50% can achieve a balance and optimization of comprehensive performance. Within this crosslinking degree range, the formation of the crosslinked network restricts the movement of polymer chains in the anion exchange membrane, inhibits water absorption and swelling, and the mechanical strength and dimensional stability of the membrane are continuously optimized with the increase of the crosslinking degree. Controlling the crosslinking degree between 4% and 50% can also maintain the membrane's key electrochemical performance such as IEC and hydroxide ion conductivity, making it meet the practical application requirements in the water electrolysis hydrogen production process. Similarly, by comparing the basic properties and water electrolysis performance of the membranes from Examples 3 and 4 (with BDMAEE as the crosslinking agent and crosslinking degrees of 5% and 35%, respectively) with the non-crosslinked comparative example 2 membrane, it can be further verified that the biaxially oriented polypropylene anion exchange membrane with a crosslinking degree of 4%-50% can, while ensuring the effective concentration of cationic conductive groups in the polymer units, limit the inter-chain spacing of polymers, reduce membrane water absorption and swelling, and enhance the mechanical strength of the membrane. This achieves a good balance between structural stability and electrochemical performance, thus meeting the application requirements for alkaline water electrolysis to produce hydrogen. Therefore, through appropriate crosslinking, the coupled optimization of ionic conductivity, mechanical properties, and dimensional stability is achieved. With the structural adaptation of the main chain and side chains, the multiple gains from crosslinking, and the synergistic balance of multiple properties, the anion exchange membrane can exhibit excellent comprehensive performance and application potential in relevant electrochemical applications.

[0168] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many specific modifications under the guidance of the present invention without departing from the spirit of the invention and the scope of protection of the claims, and these modifications all fall within the scope of protection of the present invention.

Claims

1. A polypropylene-based cross-linked quaternized anion exchange membrane, characterized in that, The chemical structural formula of the anion exchange membrane is as follows: ； The main chain of this anion exchange membrane is one of polypropylene (PP); where N... + (CH3)3 represents a quaternary ammonium group; in the formula, the number of functionalized structural units is xm1+ym2, and the number of non-functionalized structural units z is 1-(xm1+ym2); the functionalized structural unit contains cross-linked parts with different molar proportions, xm1 / (xm1+ym2)=4-50%; the molar proportion of the non-cross-linked part, i.e., the cationic side chain part, is ym2 / (xm1+ym2)=1-xm1 / (xm1+ym2); in the formula, the value of n is 100-35000, and the values ​​of m1 and m2 are both 1-500.

2. The polypropylene-based cross-linked quaternized anion exchange membrane according to claim 1, characterized in that, The polypropylene in step (1) is isotactic polypropylene or biaxially oriented polypropylene (BOPP).

3. A method for preparing a polypropylene-based cross-linked quaternized anion exchange membrane as described in any one of claims 1 or 2, characterized in that, Includes the following steps: (1) Using polypropylene film as a precursor film; (2) The precursor film was irradiated with an electron beam and then stored at low temperature. (3) First, chloromethyl vinylbenzene (VBC), surfactant and ultrapure water are added to the reactor, and an inert gas is introduced at room temperature to make the reactor an inert atmosphere environment, while chloromethyl vinylbenzene (VBC) and surfactant are uniformly mixed in ultrapure water to form an emulsion. Then, the irradiated film obtained in step (2) is added to the reactor, and then an inert gas is introduced; After introducing an inert gas for 0.5-2 hours, the reaction system is transferred to a water bath and the reaction is carried out under heating. After the reaction was completed, the film was washed with solvent A and then dried in a vacuum oven to obtain the grafted intermediate film. (4) The grafted intermediate film obtained in step (3) is added to the trimethylamine solution for reaction. After the reaction is completed, it is washed with solvent B to obtain the amination intermediate film. (5) The amination intermediate film obtained in step (4) is added to a mixed solution of crosslinking agent and N-methylpyrrolidone (NMP) for reaction. After the reaction is completed, it is washed with solvent B to obtain a crosslinked quaternary ammonium functionalized polypropylene anion exchange membrane. (6) The cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane synthesized in step (5) was immersed in sodium chloride solution and washed with water to obtain the anion with the form Cl. - A cross-linked quaternary ammonium functionalized polypropylene anion exchange membrane is used for long-term storage under humid conditions.

4. The method for preparing the polypropylene-based cross-linked quaternized anion exchange membrane according to claim 3, characterized in that, The dose of electron beam radiation in step (2) is 50-150 kGy; the temperature for cryopreservation in step (2) is less than or equal to -30℃.

5. The method for preparing a polypropylene-based cross-linked quaternized anion exchange membrane according to claim 3, characterized in that, The surfactant mentioned in step (3) is 1-octyl-2-pyrrolidone (NOP); the volume ratio of chloromethyl vinylbenzene (VBC) to surfactant in step (3) is 1-10:

1.

6. The method for preparing the polypropylene-based cross-linked quaternized anion exchange membrane according to claim 3, characterized in that, The reaction is carried out under the heating state described in step (3), the reaction temperature should be 40-60℃, and the reaction time should be 6-10h; the cleaning solvent A described in step (3) is at least one of methanol, ethanol, isopropanol, and deionized water.

7. The method for preparing a polypropylene-based cross-linked quaternized anion exchange membrane according to claim 3, characterized in that, The grafted intermediate film in step (4) is an aromatic side chain film containing chloromethyl; the trimethylammonium solution concentration in step (4) is 30-35 wt%; the reaction in step (4) is carried out at room temperature for 2-8 hours, thereby regulating the degree of amination to 50%-96%.

8. The method for preparing a polypropylene-based cross-linked quaternized anion exchange membrane according to claim 3, characterized in that, The grafted intermediate film in step (5) is a film containing a side chain structure of benzyltrimethylammonium chloride anionic group; the crosslinking agent in step (5) is dissolved in N-methylpyrrolidone (NMP) to form a crosslinking agent solution with a mass fraction of 5-15%; the crosslinking agent solution in step (5) is one of N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) solution and bis(dimethylaminoethyl ether) (BDMAEE) solution.

9. The method for preparing a polypropylene-based cross-linked quaternized anion exchange membrane according to claim 3, characterized in that, The reaction described in step (5) is carried out at 70-80°C for 24-48 hours to ensure that the remaining chloromethyl sites react fully; the solvent B described in step (5) is at least one of ethanol and deionized water.

10. The application of a polypropylene-based cross-linked quaternized anion exchange membrane as described in any one of claims 1 or 2 in hydrogen production by water electrolysis.

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