Cross-linked anion exchange membrane and preparation method thereof

Abstract

The invention relates to the technical field of fuel cell anion exchange membranes, in particular to a cross-linked anion exchange membrane and a preparation method thereof. The preparation method comprises the following steps: in the presence of a first organic solvent and a free radical initiator, polymerizing 4-vinyl benzyl chloride monomers to prepare poly 4-vinyl benzyl chloride; in the presence of a second organic solvent, N-methylpiperidone, N-methylpiperidine and poly (4-vinylbenzyl chloride) are subjected to a reaction, and a quaternized poly (4-vinylbenzyl chloride) solution is prepared; in the presence of a third organic solvent and hydrochloric acid, polyvinyl alcohol and the quaternized poly (4-vinylbenzyl chloride) solution are subjected to ketal reaction, and the cross-linked anion exchange membrane is obtained after solvent volatilization and alkali exchange. The cross-linked anion exchange membrane disclosed by the invention is simple in preparation process and uniform and transparent in formed membrane, has the characteristics of low swelling rate, high ionic conductivity, rigid and soft mechanical properties and strong alkali resistance, and can be used for effectively improving the electrolytic properties of fuel cells and water.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of fuel cell anion exchange membranes, and in particular to a crosslinked anion exchange membrane and a preparation method thereof. BACKGROUND

[0002] In hydrogen-oxygen fuel cells, water electrolysis, carbon dioxide electrolysis, flow batteries and electrodialysis devices, anion exchange membranes (AEM) mainly play the role of ion conduction and separation of positive and negative electrodes, and play an irreplaceable role in improving the performance of the battery. Anion exchange membrane is a kind of polymer electrolyte composed of free-moving anions and cations fixed on the polymer. In the research of improving the performance of fuel cells and water electrolysis, an important point is how to obtain anion exchange membranes with excellent performance, that is, high ionic conductivity, high mechanical properties and excellent alkali resistance. Therefore, at present, how to obtain anion exchange membranes with high comprehensive performance is particularly important.

[0003] Hydroxide as the carrier of charge conduction of anion exchange membrane, increasing its content helps to improve the ionic conductivity of the anion exchange membrane, however, too high ion content will lead to excessive water absorption and swelling of the anion exchange membrane, and thus reduce the mechanical properties of the wet membrane. In order to limit the problem of poor dimensional stability of the wet membrane caused by the increase of ion content, introducing crosslinking structure into the polymer network becomes a common method to solve the above-mentioned "trade-off" relationship. However, the formation of crosslinking network will hinder the conduction of ions on the one hand, and dilute the ion concentration of the original anion exchange membrane on the other hand, so that the common crosslinking strategy will reduce the ionic conductivity while improving the dimensional stability of the anion exchange membrane.

[0004] Hydroxide is a strong nucleophile, which will cause the degradation of the anion exchange membrane. The alkali resistance of the anion exchange membrane can be improved from the aspects of electronic effect and steric effect. The current mainstream research idea for preparing high-alkali-resistant anion exchange membranes is to use oxygen-free main chain and heterocyclic quaternary ammonium cation. For example, polyaryl piperidine synthesized based on terphenyl and N-methyl piperidone, and anion exchange membrane synthesized based on functionalized polyolefin and quaternary ammonium cation. However, the acid dosage of super-acid polymerization reaction is large, and the functional modification reaction condition of polyolefin is harsh, so a more mild way is needed to prepare high-alkali-resistant anion exchange membranes. In addition, the polymer main chain of the former is composed of rigid benzene ring structure units, and the prepared anion exchange membrane is not flexible enough; the polymer main chain of the latter is composed of flexible structure units, and the prepared anion exchange membrane is low in strength.

[0005] Document (ACS Applied Polymer Materials 2024, 6, 5039−5048) in order to prepare anion exchange membranes with excellent mechanical properties, based on a flexible polystyrene-b-(ethylene-co-butylene)-b-styrene (SEBS) main chain and a rigid poly(m- triphenylpiperidine) (TPIP) as the main chain, by crosslinking TPIP with SEBS grafted with 1-methyl-1,4-diazabicyclo[2.2.2]octane-1-iodonium ammonium, a crosslinked anion exchange membrane was synthesized. The product SEBS-C6-MDA-TPIP20% has the characteristics of high strength and high flexibility, for example, the tensile strength of SEBS-C6-MDA-TPIP20% is 24.61 MPa, and the elongation at break is 284.66%. With the increase of crosslinking degree, although the swelling rate of the anion exchange membrane is decreasing, for example, the swelling rate of SEBS-C6-MDA-TPIP10% at 80 o C is 25.4%, and the swelling rate of SEBS-C6-MDA-TPIP20% at 80 o C is 19.11%, but because the crosslinking site will sacrifice part of the cationic grafting site, and the crosslinking network structure hinders ion conduction, therefore, the ionic conductivity will also decrease. For example, the ionic conductivity of SEBS-C6-MDA-TPIP10% at 30 o C is 38.04 mS / cm (ion exchange capacity is 3.42 mmol / g), and the swelling rate of SEBS-C6-MDA-TPIP20% at 30 °C is 31.72 mS / cm (ion exchange capacity is 2.91 mmol / g).

[0006] Document (Journal of Membrane Science 2022, 655, 120578) a kind of polydianaphthylpiperidine-based anion exchange membrane (QABNP) with twisted 1,1'-dianaphthyl and piperidine cation as main body is synthesized by using super acid catalysis polymerization reaction. The prepared anion exchange membrane is composed of oxygen-free main chain and heterocyclic quaternary ammonium cation, so the film material shows excellent alkali resistance. After soaking in 2 M NaOH, 80 °C for 1080 hours, the retention rate of QABNP ionic conductivity is still about 90%. Due to the strong rigidity of the four-ring aromatic dianaphthyl, the prepared anion exchange membrane has high tensile strength (more than 30 MPa), but the elongation at break is less than 7.5%. In addition, because of super acid polymerization, a higher content of trifluoroacetic acid and trifluoromethanesulfonic acid is used as catalyst, 0.5 mL of trifluoroacetic acid and 5 mL of trifluoromethanesulfonic acid are consumed for 1 g of monomer (1,1'-dianaphthyl monomer) involved in polymerization.

[0007] Journal of Membrane Science 2022, 661, 120921 synthesized a copolymer polyolefin-based anion exchange membrane based on ethylene and propylene structural units. This type of anion exchange membrane has excellent alkali resistance and stability. After soaking in 1M NaOH at 80°C for 1680 hours, no loss of ionic conductivity was observed. Because the polymer is composed of flexible structural units, the prepared anion exchange membrane has excellent flexibility, and the optimal breaking elongation rate is as high as 191% (PEI-20-C70-QA). However, the strength of this material is low, and the optimal tensile strength is not more than 12 MPa. In addition, the polymerization of polyolefin needs to be carried out in a strict water-free and oxygen-free environment, and the reaction process uses the toxic solvent toluene and the expensive catalyst rac-ethylene bis(1-indenyl) zirconium(IV) dichloride.

[0008] In view of the problems of the above-mentioned anion exchange membrane or the preparation method thereof, the reaction conditions are severe, and the performance of ion conductivity, mechanical property and alkali resistance stability cannot be considered, and there is an urgent need for an anion exchange membrane prepared by a more moderate reaction condition, which has rigidity and flexibility, high alkali resistance and high ion conductivity, so as to improve the performance of battery and water electrolysis. SUMMARY

[0009] Therefore, the present application provides a cross-linked anion exchange membrane and a preparation method thereof, so as to solve the technical problem that the existing battery anion exchange membrane cannot consider the performance of ion conductivity, mechanical property and alkali resistance stability.

[0010] N-methyl piperidine and N-methyl piperidone are grafted on polyvinyl benzyl chloride by means of the door show gold reaction, and then the ketone group and the hydroxyl group on the polyvinyl alcohol (PVA) undergo ketal reaction under the catalysis of a small amount of acid, so as to realize the cross-linking between the polymer chains and prepare a new type of cross-linked anion exchange membrane with good compatibility. The rigid polyvinyl benzyl chloride gives the anion exchange membrane high strength, and the flexible polyvinyl alcohol gives the anion exchange membrane high flexibility. The ether-free main chain and the quaternized N-methyl piperidine cation give the anion exchange membrane the characteristics of high alkali resistance. Because the cross-linking sites are generated by the ketal reaction on the quaternized N-methyl piperidone, the cation grafting sites are not sacrificed, so the high cation grafting degree gives the anion exchange membrane the characteristics of high ion conductivity.

[0011] The technical scheme of the present application is as follows: In a first aspect, the present application provides an anion exchange membrane, and the structure of the anion exchange membrane is shown as formula (I): ; In formula (I), x, y, z, m and n all represent the proportion of each structural unit.

[0012] Preferably, the value of x is 0.1-0.4; the value of y is 0.2-0.7; the value of z is 0.2-0.4; the value of m is 0.1-0.4; and the value of n is 0.2-0.8.

[0013] Further preferably, x is 0.2, y is 0.4, z is 0.4, m is 0.2, and n is 0.6.

[0014] In a second aspect, a preparation method of the anion exchange membrane is provided, comprising the following steps: S1, a mixture II containing N-methyl piperidone, N-methyl piperidine, poly 4-vinyl benzyl chloride and a second organic solvent is subjected to a Grignard reaction to obtain a solution of N-methyl piperidone and N-methyl piperidine grafted quaternary ammonium poly 4-vinyl benzyl chloride; S2, polyvinyl alcohol and hydrochloric acid are dissolved in a third organic solvent, and then the quaternary ammonium poly 4-vinyl benzyl chloride solution in step S1 is added to undergo a ketal reaction to obtain a film-forming mixed solution; S3, the film-forming mixed solution in step S2 is dried to obtain a halogen type anion exchange membrane; S4, the halogen type anion exchange membrane in step S3 is subjected to ion exchange with an alkali solution to obtain an anion exchange membrane.

[0015] In the present application, poly 4-vinyl benzyl chloride and polyvinyl alcohol are selected as the main chain, quaternary ammonium N-methyl piperidine is selected as the cation, and quaternary ammonium N-methyl piperidone is selected as both the cation and the crosslinking agent to synthesize the crosslinked anion exchange membrane. The tertiary amine of N-methyl piperidone reacts with benzyl chloride, and the ketone group reacts with the hydroxyl group. On the one hand, the crosslinking between the rigid main chain and the flexible main chain is realized, which helps to obtain an anion exchange membrane with good compatibility, high strength and high flexibility; on the other hand, the crosslinking site occurs on the cation group, which does not consume additional benzyl chloride functional sites, and helps to obtain an anion exchange membrane with high ion content. In addition, the excess hydroxyl groups on the polyvinyl alcohol can promote the rapid transfer of hydroxyl ions. The above factors help to improve the ionic conductivity of the anion exchange membrane. Secondly, the main chain does not contain polar groups, the quaternary ammonium N-methyl piperidine cation and the ketal have strong alkali resistance, which ensures that the anion exchange membrane has high alkali resistance.

[0016] Preferably, in step S1, the mass-volume ratio of N-methyl piperidone, N-methyl piperidine, poly 4-vinyl benzyl chloride, and the second organic solvent is (0.0148-0.0593 g):(0.0260-0.0520 g):0.2 g:(10-15 mL).

[0017] More preferably, the mass-to-volume ratio of N-methylpiperidone, N-methylpiperidine, poly(4-vinylbenzyl chloride), and the second organic solvent is 0.0296 g: 0.0520 g: 0.2 g: 13 mL.

[0018] Based on the above technical solutions, preferably, the poly(4-vinylbenzyl chloride) is obtained by polymerizing a mixture I containing 4-vinylbenzyl chloride monomer, an initiator, and a first organic solvent under an inactive atmosphere.

[0019] Based on the above technical solutions, preferably, the mass-to-volume ratio of the 4-vinylbenzyl chloride monomer, the initiator, and the first organic solvent is (4~8 g):(0.15~0.30 g):(35~70 mL); more preferably, the mass-to-volume ratio of the 4-vinylbenzyl chloride monomer, the initiator, and the first organic solvent is 6 g:0.2 g:50 mL.

[0020] Based on the above technical solutions, preferably, the first organic solvent is tetrahydrofuran.

[0021] Based on the above technical solutions, preferably, the initiator is a free radical initiator.

[0022] Based on the above technical solutions, preferably, the free radical initiator is azobisisobutyronitrile.

[0023] Based on the above technical solutions, preferably, the inactive atmosphere is selected from at least one of nitrogen, argon, and helium; more preferably, the inactive atmosphere is nitrogen.

[0024] Based on the above technical solutions, preferably, the polymerization reaction time is 8-12 h and the temperature is 55-65℃; more preferably, the polymerization reaction time is 10 h and the temperature is 60℃.

[0025] Based on the above technical solutions, preferably, in step S1, the second organic solvent is dimethyl sulfoxide; the reaction time of the methyl sulfoxide is 4-6 h and the temperature is 40-60 ℃; more preferably, the reaction time of the methyl sulfoxide is 5 h and the temperature is 60 ℃.

[0026] Based on the above technical solutions, preferably, in step S2, the mass-to-volume ratio of polyvinyl alcohol to the third organic solvent is 0.0577 g: (5~10 mL); more preferably, the mass-to-volume ratio of polyvinyl alcohol to the third organic solvent is 0.0577 g: 7 mL.

[0027] Based on the above technical solutions, preferably, in step S2, the third organic solvent is dimethyl sulfoxide; the ketal reaction time is 4-6 h and the temperature is 40-60 ℃; more preferably, the ketal reaction time is 4 h and the temperature is 60 ℃.

[0028] Based on the above technical solutions, preferably, in step S2, the hydrochloric acid is added to adjust the pH value of mixture I to 3~4.

[0029] Based on the above technical solutions, preferably, in step S3, the drying time is 8~12 h and the temperature is 70~90 ℃; more preferably, the drying time is 10 h and the temperature is 80 ℃.

[0030] Based on the above technical solutions, preferably, in step S4, the alkaline solution is selected from one or both of KOH solution and NaOH solution; the concentration of the alkaline solution is 1~2 mol / L and the temperature is 40~80 ℃.

[0031] More preferably, the alkaline solution is selected from KOH solution; the concentration of the alkaline solution is 1 mol / L and the temperature is 60℃.

[0032] Based on the above technical solutions, preferably, in step S4, the halogen anion exchange membrane undergoes ion exchange with the alkaline solution by immersing the halogen anion exchange membrane in the alkaline solution.

[0033] Based on the above technical solutions, preferably, the soaking time is 12-24 hours; more preferably, the soaking time is 12 hours.

[0034] Based on the above technical solutions, preferably, the number of times the fresh alkali solution is replaced during soaking is 3 to 5 times; more preferably, the number of times the fresh alkali solution is replaced is 3 times.

[0035] The cross-linked anion exchange membrane and its preparation method of the present invention have the following advantages over the prior art: The anion exchange membrane of the present invention crosslinks poly(4-vinylbenzyl chloride) and polyvinyl alcohol by N-methylpiperidone, so that the prepared anion exchange membrane has the mechanical characteristics of low swelling ratio and a combination of rigidity and flexibility.

[0036] The anion exchange membrane of the present invention has a high ion content and the characteristic of hydroxyl-assisted hydroxide ion conduction, which helps to improve the ionic conductivity of the anion exchange membrane.

[0037] The anion exchange membrane of the present invention is composed of a main chain without polar groups, highly alkali-resistant cations and ketal groups, and has high chemical stability.

[0038] The anion exchange membrane of the present invention has uniform and transparent film formation and good film formation performance.

[0039] The anion exchange membrane of this invention has excellent overall performance and has broad application prospects in fields such as batteries and water electrolysis.

[0040] The anion exchange membrane preparation method of the present invention can achieve adjustable physicochemical properties by adjusting the grafting degree of N-methylpiperidone and N-methylpiperidine; the anion exchange membrane preparation process is simple and mild, the raw materials are inexpensive and readily available, it is easy to achieve large-scale production, and it has wide applicability. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a photograph of the cross-linked anion exchange membrane of the present invention. Figure 2 This is a scanning electron microscope image of the cross-linked anion exchange membrane of Example 4 of the present invention; Figure 3 The X-ray photoelectron spectrum of the cross-linked anion exchange membrane N(1s) of Example 4 of the present invention is shown. Figure 4 Fourier transform infrared spectra of the cross-linked anion exchange membranes of Examples 1-6 of the present invention; Figure 5 The graph shows the water electrolysis performance of the cross-linked anion exchange membrane of Example 4 of the present invention at 60 °C and 80 °C. Figure 6 This is a synthetic route diagram of the cross-linked anion exchange membrane of Comparative Example 1 of the present invention; Figure 7 This is a synthetic route diagram of the cross-linked anion exchange membrane of Comparative Example 1 of the present invention; Figure 8 This is a schematic diagram of the synthetic route for preparing the cross-linked anion exchange membrane of the present invention. Detailed Implementation

[0043] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0044] The 4-vinylbenzyl chloride, N-methyl-4-piperidinone, N-methylpiperidine, and polyvinyl alcohol (hydrolysis rate: 98-99 mol%, Mw: 190000) used in the embodiments of the present invention were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0045] The test methods for the test items involved in the embodiments and comparative examples of this invention are as follows: (1) Ion exchange capacity: The ion exchange capacity of AEM was determined using the Mohr titration method, and the calculation formula is shown below:

[0046] in c (AgNO3) It refers to the concentration of the AgNO3 solution. v (AgNO3) This is the volume of AgNO3 solution consumed. m dry(Cl-) This is the dry weight of AEM, and IEC is the ion exchange capacity.

[0047] (2) Gel content test: The gel strength (GF) of AEM was calculated by recording the mass change after immersion in dimethyl sulfoxide at 80°C for 24 h. The dry weight before measurement was [missing data]. m before The mass obtained after soaking, washing, and drying is m after The ratio of the two is the gel strength. A higher gel strength indicates a more complete degree of cross-linking.

[0048] GF% represents gel strength.

[0049] (3) Dimensional stability: First, record the dry film size. x dry(OH) Then test the OH ion. - The dimensions of the AEM after it fully absorbs water and swells at different temperatures are recorded as follows: x hyd(OH) The formula for calculating dimensional stability is shown below:

[0050] SD represents the swelling ratio.

[0051] (4) Moisture content: Take the anion as OH - The AEM was dried by wiping its surface with filter paper and then weighed in a saturated water state. Whyd The membrane was then placed in a vacuum drying oven at 65 °C for 12 hours to dry thoroughly until the membrane mass no longer decreased, after which its mass was weighed. W dry The formula for calculating water content is shown below: .

[0052] (5) Ionic conductivity: The present invention uses AC impedance method to measure the ionic resistance of anion exchange membrane. The measurement frequency range is 1Hz-5MHz, the potential amplitude is 5mV, and the measured resistance Nyquist curve is fitted. The intersection of the curve with the real axis Z' is the ionic resistance value R of the anion exchange membrane.

[0053] The formula for calculating conductivity is shown below:

[0054] σ It is the ionic conductivity. l The distance between the two electrodes. R The ionic resistance of the sample being measured is... S Let be the cross-sectional area of ​​the membrane.

[0055] (6) Mechanical strength: The mechanical performance test includes two aspects: the tensile strength and elongation at break of the polymer to be tested. The instrument's stretching speed is 5 mm / min.

[0056] (7) Alkali resistance stability: The stability test conditions in the example were 80 °C and soaking in 1 mol / L KOH solution for 720 hours.

[0057] Example 1 (1) Under nitrogen protection, 6 g of 4-vinylbenzyl chloride was dissolved in 50 mL of tetrahydrofuran. After heating to 60 °C, 0.2 g of azobisisobutyronitrile was added, and the reaction was continued for 10 hours until the solution became viscous. The product was precipitated in methanol and filtered to obtain a crude product. The crude product was then washed four times with methanol and dried in a vacuum drying oven at 40 °C to obtain poly(4-vinylbenzyl chloride).

[0058] (2) Weigh 2 g of poly(4-vinylbenzyl chloride) dissolved in 100 mL of DMSO, then add 0.148 g of N-methylpiperidone and 0.260 g of N-methylpiperidine to the above solution, and react at 60 °C for 5 h to obtain a quaternized poly(4-vinylbenzyl chloride) solution.

[0059] (3) Weigh 0.577 g of polyvinyl alcohol and dissolve it in 50 mL of DMSO. Then adjust the pH of the system to 3-4 with hydrochloric acid. Add the quaternized poly(4-vinylbenzyl chloride) solution prepared in step 2 above to the solution and react at 60 °C for 4 hours to obtain the film-forming mixture.

[0060] (4) Pour the above membrane-forming mixture onto a flat and clean glass plate of 6 cm × 6 cm and place it in an oven at 70°C for 12 hours to obtain a dry halogen-type anion exchange membrane.

[0061] (5) The above-mentioned halogen-type anion exchange membrane was immersed in a 1 mol / L potassium hydroxide solution at 60 °C for 12 hours, during which the alkali solution was replaced 3 times. Finally, the membrane surface was rinsed with deionized water to remove residual alkali until the pH of the aqueous solution was 7, thus obtaining a cross-linked anion exchange membrane with hydroxide ions as the anion. Wherein, x is 0.1, y is 0.7, z is 0.2, m is 0.1, and n is 0.8.

[0062] The anion exchange capacity of the membrane was measured to be 1.28 mmol / g; the gelation degree was 92.1%; the swelling ratio at 80℃ was 1.8%; the water content was 55.1%; and the ionic conductivity was 55.2 mS / cm. The tensile strength and elongation at break under fully wet conditions were 7.2 MPa and 25.1%, respectively. After immersion in 1M hot alkali (80℃, KOH) for 720 h, the retention rates of mass and ionic conductivity at 80℃ were 88.1% and 91.2%, respectively.

[0063] Example 2 (1) Under nitrogen protection, 6 g of 4-vinylbenzyl chloride was dissolved in 50 mL of tetrahydrofuran. After heating to 60 °C, 0.2 g of azobisisobutyronitrile was added, and the reaction was continued for 10 hours until the solution became viscous. The product was precipitated in methanol and filtered to obtain a crude product. The crude product was then washed four times with methanol and dried in a vacuum drying oven at 40 °C to obtain poly(4-vinylbenzyl chloride).

[0064] (2) Weigh 2 g of poly(4-vinylbenzyl chloride) dissolved in 130 mL of DMSO, then add 0.148 g of N-methylpiperidone and 0.520 g of N-methylpiperidine to the above solution, and react at 60 °C for 5 h to obtain a quaternized poly(4-vinylbenzyl chloride) solution.

[0065] (3) Weigh 0.577 g of polyvinyl alcohol and dissolve it in 50 mL of DMSO. Then adjust the pH of the system to 3-4 with hydrochloric acid. Add the quaternized poly(4-vinylbenzyl chloride) solution prepared in step 2 above to the solution and react at 60 °C for 4 hours to obtain the film-forming mixture.

[0066] (4) Pour the above membrane-forming mixture onto a flat and clean glass plate of 6 cm × 6 cm and place it in an oven at 70 ℃ for 12 hours to obtain a dry halogen-type anion exchange membrane.

[0067] (5) The above-mentioned halogen-type anion exchange membrane was immersed in a 1 mol / L potassium hydroxide solution at 60 °C for 12 hours, during which the alkali solution was replaced 3 times. Finally, the membrane surface was rinsed with deionized water to remove residual alkali until the pH of the aqueous solution was 7, thus obtaining a cross-linked anion exchange membrane with hydroxide ions as the anion. Wherein, x is 0.1, y is 0.5, z is 0.4, m is 0.1, and n is 0.8.

[0068] The anion exchange membrane was found to have an ion exchange capacity of 1.89 mmol / g, a gel strength of 91.5%, a swelling ratio of 4.5% at 80 °C, a water content of 69.3%, and an ionic conductivity of 83.2 mS / cm. Its tensile strength and elongation at break were 4.2 MPa and 39.6%, respectively. After immersion in 1M hot alkali (80 °C, KOH) for 720 h, the retention rates of mass and ionic conductivity at 80 °C were 83.6% and 89.9%, respectively.

[0069] Example 3 (1) Under nitrogen protection, 6 g of 4-vinylbenzyl chloride was dissolved in 50 mL of tetrahydrofuran. After heating to 60 °C, 0.2 g of azobisisobutyronitrile was added, and the reaction was continued for 10 hours until the solution became viscous. The product was precipitated in methanol and filtered to obtain a crude product. The crude product was then washed four times with methanol and dried in a vacuum drying oven at 40 °C to obtain poly(4-vinylbenzyl chloride).

[0070] (2) Weigh 2 g of poly(4-vinylbenzyl chloride) dissolved in 130 mL of DMSO, then add 0.296 g of N-methylpiperidone and 0.260 g of N-methylpiperidine to the above solution, and react at 60 °C for 5 h to obtain a quaternized poly(4-vinylbenzyl chloride) solution.

[0071] (3) Weigh 0.577 g of polyvinyl alcohol and dissolve it in 70 mL of DMSO. Then adjust the pH of the system to 3-4 with hydrochloric acid. Add the quaternized poly(4-vinylbenzyl chloride) solution prepared in step 2 above to the solution and react at 60 °C for 4 hours to obtain the film-forming mixture.

[0072] (4) Pour the above membrane-forming mixture onto a flat and clean glass plate of 6 cm × 6 cm and place it in an oven at 80 ℃ for 10 hours to obtain a dry halogen-type anion exchange membrane.

[0073] (5) The above-mentioned halogen-type anion exchange membrane was immersed in a 1 mol / L potassium hydroxide solution at 60 °C for 12 hours, during which the alkali solution was replaced 3 times. Finally, the membrane surface was rinsed with deionized water to remove residual alkali until the pH of the aqueous solution was 7, thus obtaining a cross-linked anion exchange membrane with hydroxide ions as the anion. Wherein, x is 0.2, y is 0.6, z is 0.2, m is 0.2, and n is 0.6.

[0074] The anion exchange membrane was found to have an ion exchange capacity of 1.58 mmol / g, a gel strength of 92.6%, a swelling ratio of 1.5% at 80 °C, a water content of 40.1%, and an ionic conductivity of 62.5 mS / cm. Its tensile strength and elongation at break were 23.6 MPa and 12.4%, respectively. After immersion in 1M hot alkali (80 °C, KOH) for 720 h, the retention rates of mass and ionic conductivity at 80 °C were 88.4% and 94.1%, respectively.

[0075] Example 4 (1) Under nitrogen protection, 6 g of 4-vinylbenzyl chloride was dissolved in 50 mL of tetrahydrofuran. After heating to 60 °C, 0.2 g of azobisisobutyronitrile was added, and the reaction was continued for 10 hours until the solution became viscous. The product was precipitated in methanol and filtered to obtain a crude product. The crude product was then washed four times with methanol and dried in a vacuum drying oven at 40 °C to obtain poly(4-vinylbenzyl chloride).

[0076] (2) Weigh 2 g of poly(4-vinylbenzyl chloride) dissolved in 130 mL of DMSO, then add 0.296 g of N-methylpiperidone and 0.520 g of N-methylpiperidine to the above solution, and react at 60 °C for 5 h to obtain a quaternized poly(4-vinylbenzyl chloride) solution.

[0077] (3) Weigh 0.577 g of polyvinyl alcohol and dissolve it in 70 mL of DMSO. Then adjust the pH of the system to 3-4 with hydrochloric acid. Add the quaternized poly(4-vinylbenzyl chloride) solution prepared in step 2 above to the solution and react at 60 °C for 4 hours to obtain the film-forming mixture.

[0078] (4) Pour the above membrane-forming mixture onto a flat and clean glass plate of 6 cm × 6 cm and place it in an oven at 80 ℃ for 10 hours to obtain a dry halogen-type anion exchange membrane.

[0079] (5) The above-mentioned halogen-type anion exchange membrane was immersed in a 1 mol / L potassium hydroxide solution at 60 °C for 12 hours, during which the alkali solution was replaced 3 times. Finally, the membrane surface was rinsed with deionized water to remove residual alkali until the pH of the aqueous solution was 7, thus obtaining a cross-linked anion exchange membrane with hydroxide ions as the anion. Wherein, x is 0.2, y is 0.4, z is 0.4, m is 0.2, and n is 0.6.

[0080] The anion exchange membrane was found to have an ion exchange capacity of 2.09 mmol / g, a gel strength of 92.5%, a swelling ratio of 3.5% at 80℃, a water content of 62.4%, and an ionic conductivity of 120.4 mS / cm. Its tensile strength and elongation at break were 10.5 MPa and 22.3%, respectively. After immersion in 1M hot alkali (80℃, KOH) for 720 h, the retention rates of mass and ionic conductivity at 80℃ were 85.2% and 92.4%, respectively.

[0081] Example 5 (1) Under nitrogen protection, 6 g of 4-vinylbenzyl chloride was dissolved in 50 mL of tetrahydrofuran. After heating to 60 °C, 0.2 g of azobisisobutyronitrile was added, and the reaction was continued for 10 hours until the solution became viscous. The product was precipitated in methanol and filtered to obtain a crude product. The crude product was then washed four times with methanol and dried in a vacuum drying oven at 40 °C to obtain poly(4-vinylbenzyl chloride).

[0082] (2) Weigh 2 g of poly(4-vinylbenzyl chloride) dissolved in 130 mL of DMSO, then add 0.593 g of N-methylpiperidone and 0.260 g of N-methylpiperidine to the above solution, and react at 40 °C for 5 h to obtain a quaternized poly(4-vinylbenzyl chloride) solution.

[0083] (3) Weigh 0.577 g of polyvinyl alcohol and dissolve it in 100 mL of DMSO. Then adjust the pH of the system to 3-4 with hydrochloric acid. Add the quaternized poly(4-vinylbenzyl chloride) solution prepared in step 2 above to the solution and react at 40 °C for 6 hours to obtain the film-forming mixture.

[0084] (4) Pour the above membrane-forming mixture onto a flat and clean glass plate of 6 cm × 6 cm and place it in an oven at 90 ℃ for 8 hours to obtain a dry halogen-type anion exchange membrane.

[0085] (5) The above-mentioned halogen-type anion exchange membrane was immersed in a 2 mol / L potassium hydroxide solution at 40 °C for 24 hours, during which the alkali solution was replaced 3 times. Finally, the membrane surface was rinsed with deionized water to remove residual alkali until the pH of the aqueous solution was 7, thus obtaining a cross-linked anion exchange membrane with hydroxide ions as the anion. Wherein, x is 0.4, y is 0.4, z is 0.2, m is 0.4, and n is 0.2.

[0086] The anion exchange membrane was found to have an ion exchange capacity of 2.01 mmol / g, a gel strength of 93.3%, a swelling ratio of 3.0% at 80 °C, a water content of 56.9%, and an ionic conductivity of 70.8 mS / cm. Its tensile strength and elongation at break were 13.0 MPa and 41.2%, respectively. After immersion in 1M hot alkali (80 °C, KOH) for 720 h, the retention rates of mass and ionic conductivity at 80 °C were 85.4% and 94.5%, respectively.

[0087] Example 6 (1) Under nitrogen protection, 6 g of 4-vinylbenzyl chloride was dissolved in 50 mL of tetrahydrofuran. After heating to 60 °C, 0.2 g of azobisisobutyronitrile was added, and the reaction was continued for 10 hours until the solution became viscous. The product was precipitated in methanol and filtered to obtain a crude product. The crude product was then washed four times with methanol and dried in a vacuum drying oven at 40 °C to obtain poly(4-vinylbenzyl chloride).

[0088] (2) Weigh 2 g of poly(4-vinylbenzyl chloride) dissolved in 130 mL of DMSO, then add 0.593 g of N-methylpiperidone and 0.520 g of N-methylpiperidine to the above solution, and react at 50 °C for 6 h to obtain a quaternized poly(4-vinylbenzyl chloride) solution.

[0089] (3) Weigh 0.577 g of polyvinyl alcohol and dissolve it in 100 mL of DMSO. Then adjust the pH of the system to 3-4 with hydrochloric acid. Add the quaternized poly(4-vinylbenzyl chloride) solution prepared in step 2 above to the solution and react at 50 °C for 5 hours to obtain the film-forming mixture.

[0090] (4) Pour the above membrane-forming mixture onto a flat and clean glass plate of 6 cm × 6 cm and place it in an oven at 90 ℃ for 8 hours to obtain a dry halogen-type anion exchange membrane.

[0091] (5) The above-mentioned halogen-type anion exchange membrane was immersed in a 1 mol / L potassium hydroxide solution at 80 °C for 16 hours, during which the alkali solution was replaced 3 times. Finally, the membrane surface was rinsed with deionized water to remove residual alkali until the pH of the aqueous solution was 7, thus obtaining a cross-linked anion exchange membrane with hydroxide ions as the anion. Wherein, x is 0.4, y is 0.2, z is 0.4, m is 0.4, and n is 0.2.

[0092] The anion exchange membrane was found to have an ion exchange capacity of 2.69 mmol / g, a gel strength of 95.4%, a swelling ratio of 6.5% at 80℃, a water content of 75.5%, and an ionic conductivity of 100.1 mS / cm. Its tensile strength and elongation at break were 7.9 MPa and 33.4%, respectively. After immersion in 1M hot alkali (80℃, KOH) for 720 h, the retention rates of mass and ionic conductivity at 80℃ were 82.4% and 93.6%, respectively.

[0093] The test results for the above embodiments are summarized as follows: (1) Ion exchange capacity: The ion exchange capacity of each of the above embodiments is greater than 1.0 mmol / g, and increases with the increase of cross-linking agent and cation content.

[0094] (2) Gel degree test: The gel degree of each of the above embodiments is greater than 90%, and the higher the crosslinking agent content, the greater the gel degree.

[0095] (3) Dimensional stability: The swelling rate of each of the above embodiments at 80 °C is less than 7%. A low swelling rate means high dimensional stability, which helps to improve the wet mechanical properties of the anion exchange membrane.

[0096] (4) Moisture content: The moisture content of each of the above examples at 80 °C is distributed between 40% and 80%. The higher the swelling rate, the higher the corresponding moisture content.

[0097] (5) Ionic conductivity: The ionic conductivity of each of the above examples at 80 °C is distributed in the range of 55~121 mS / cm.

[0098] Mechanical strength: The tensile strength of the above embodiments under fully wet conditions is 4.2~23.6 MPa, and the elongation at break is 12.4~41.2%. These mechanical properties support the use of anion exchange membranes as membrane materials in electrochemical devices.

[0099] (7) Alkali resistance stability: The mass retention rate of the above examples is 82.4~88.4%, and the ionic conductivity retention rate is 89.9~94.5%, which proves that the anion exchange membrane has good alkali resistance stability.

[0100] A photograph of the cross-linked anion exchange membrane prepared in Example 4 is shown below. Figure 1 As shown, the film is uniform and has a transparent pale yellow color, possessing both strength and flexibility.

[0101] The cross-sectional scanning electron microscope image of the cross-linked anion exchange membrane prepared in Example 4 is shown below. Figure 2 As shown, the image exhibits a flat, non-porous, and dense morphology, indicating that the two components constituting the cross-linked membrane have excellent compatibility.

[0102] The X-ray photoelectron spectroscopy (XPS) spectrum of the cross-linked anion exchange membrane prepared in Example 4 is shown below. Figure 3 As shown, the electron binding energies of N(1s) in the anion exchange membrane prepared in Example 4 show peaks at 401.7 eV and 398.9 eV. 401.7 eV corresponds to the electron binding energy of quaternary ammonium N, and 398.9 eV corresponds to the electron binding energy of tertiary amine N, with the signal peak of quaternary ammonium N being significantly stronger than that of tertiary amine. The spectral results indicate that most tertiary amines participate in the Menshoukin reaction, generating quaternary ammonium cations.

[0103] The Fourier transform infrared (FTIR) spectra of the cross-linked anion exchange membranes prepared in Examples 1-6 are shown below. Figure 4 As shown, the anion exchange membranes prepared in Examples 1-6 can be seen to have a wavelength of 1720 cm⁻¹. -1 At wavenumbers around 1051 cm⁻¹, the infrared absorption peak of the carbonyl group is almost unobservable, while at 1051 cm⁻¹... -1 The presence of a distinct COC absorption peak at the wavenumber indicates that the carbonyl group undergoes a cross-linking reaction via a ketal condensation. The XPS and FTIR results described above confirm the chemical structure of the cross-linked anion exchange membrane described in the examples.

[0104] Water electrolysis performance test of the cross-linked anion exchange membrane prepared in Example 4 in a zero-gap electrolyzer: The cathode used a Pt / C catalyst, the anode used a NiFe₂O₄ catalyst, and the membrane electrode ionomer used a QAPPT ionomer. The anion exchange membrane prepared in Example 4 was used as the electrolyte membrane in the water electrolyzer. The electrolyte solution in the electrolyzer was a 1 M KOH solution. The LSV scan rate was 10 mV / s, and the scan range was 1.4–2.2 V. The results are as follows: Figure 5 As shown, the current density at 60 ℃ and 2.0 V is 1.03 A cm⁻¹. -2 When the temperature rises to 80 °C, the current density at a voltage of 2.0 V increases to 1.65 A cm⁻¹. -2 .

[0105] Comparative Example 1 The comparative example is described in the literature (ACS Applied Polymer Materials 2024, 6, 5039−5048). Similarly, the comparative example synthesized a flexible-rigid crosslinked anion exchange membrane, SEBS-C6-MDA-TPIPx, using flexible polystyrene-ethylene-butene-styrene (SEBS) and rigid poly(m-triphenylpiperidine) (TPIP). The specific synthetic route is as follows: Figure 6 and Figure 7As shown in the diagram, firstly, the cationic precursor 1-methyl-1,4-diazohexacyclooctane-1-ammonium iodide (MDA) was synthesized. Then, SEBS was functionalized via Friedel-Crafts acylation, and SEBS-C6-Br, grafted with long-chain aliphatic alkane bromine, was generated via reduction. On the other hand, using trifluoroacetic acid and trifluoromethanesulfonic acid as catalysts, poly(m-terphenylpiperidine) (TPIP) was generated via a superacid polymerization reaction based on m-terphenyl and ketone groups. The pathway is as follows: Figure 6 As shown; finally, crosslinking is achieved using the Menthol reaction between SEBS-C6-Br and TPIP, as shown in the diagram. Figure 7 As shown.

[0106] The optimal experimental example, SEBS-C6-MDA-TPIP15%, was selected as Comparative Example 1 of this invention.

[0107] The comparative example, SEBS-C6-MDA-TPIP15%, has a tensile strength of 18.75 MPa and an elongation at break of 395.5%.

[0108] The comparative SEBS-C6-MDA-TPIP15% had an ion exchange capacity of 3.11 mmol / g.

[0109] The comparative example, SEBS-C6-MDA-TPIP15%, had a swelling rate of 23.22% at 80 °C.

[0110] The comparative example, SEBS-C6-MDA-TPIP15%, had a moisture content of 88.81% at 80 °C.

[0111] The comparative example, SEBS-C6-MDA-TPIP 15%, exhibited an ionic conductivity of 86.76 mS / cm at 80 °C. -1 .

[0112] After immersing the comparative example SEBS-C6-MDA-TPIP15% in 2M NaOH solution at 80 °C for 2200 hours, the loss rate of ionic conductivity was 20.81%.

[0113] Comparative Example 2 This comparative example is the same as Example 4, except that in step (2), 2 g of poly(4-vinylbenzyl chloride) was weighed and dissolved in 80 mL of DMSO, and then 0.8891 g of N-methylpiperidone and 0.5200 g of N-methylpiperidine were added to the above solution. The mixture was reacted at 60 °C for 4 h to obtain a quaternized poly(4-vinylbenzyl chloride) solution. 0.577 g of polyvinyl alcohol was weighed and dissolved in 100 mL of DMSO, and then the pH of the system was adjusted to 3-4 with hydrochloric acid. The quaternized poly(4-vinylbenzyl chloride) solution prepared above was added to the solution, and an attempt was made to react at 40 °C to obtain a film-forming mixture. However, due to the excessive grafting of N-methylpiperidone on poly(4-vinylbenzyl chloride), the crosslinking between it and PVA under acid catalysis was too large. Therefore, the quaternized poly(4-vinylbenzyl chloride) solution quickly formed a gel during the mixing with the acid solution of polyvinyl alcohol, and a film-forming solution could not be obtained.

[0114] Table 1 summarizes the test results for the anion exchange membrane prepared in Example 4 and the comparative example SEBS-C6-MDA-TPIP15% (Comparative Example 1), as shown below: The ion exchange capacity, ionic conductivity, swelling ratio, water content, and mechanical properties of Comparative Example 1 and Example 4 were tested under the same conditions. The alkali resistance stability test conditions for this patent example were immersion in a 1 mol / L KOH solution at 80°C for 720 hours.

[0115] Table 1 Comparison of Test Results

[0116] Compared to the synthesis process of the comparative example, the preparation process of the embodiments of this invention has simpler reaction steps and milder conditions. As can be seen from the performance data in Table 1 above, compared to Comparative Example 1, the cross-linked anion exchange membrane prepared by the optimal Example 4 of this invention has a lower ion exchange capacity, lower swelling ratio, lower water content, and higher ionic conductivity. This may be due to the rapid conduction of abundant hydroxyl-assisted ions in the structure of Example 4. Although the mechanical properties of Example 4 in the wet state are lower than those of the comparative example, they are still sufficient for its use in electrochemical devices. Example 4 exhibited good alkali resistance after being immersed in a 1 mol / L KOH solution at 80 °C for 720 hours.

[0117] Compared to Comparative Example 2, further increasing the degree of crosslinking would cause the film-forming process to rapidly generate gel, thus making it impossible to obtain the target film product.

[0118] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An anion exchange membrane, characterized in that: The structure of the anion exchange membrane is shown in formula (I): ； In equation (I), x, y, z, m, and n all represent the proportion of each structural unit; The value of x ranges from 0.1 to 0.4; the value of y ranges from 0.2 to 0.7; the value of z ranges from 0.2 to 0.4; the value of m ranges from 0.1 to 0.4; and the value of n ranges from 0.2 to 0.

8.

2. A method for preparing an anion exchange membrane, characterized in that, Includes the following steps: S1, a mixture II containing N-methylpiperidone, N-methylpiperidine, poly(4-vinylbenzyl chloride) and a second organic solvent is subjected to a Mensoukin reaction to obtain a quaternized poly(4-vinylbenzyl chloride) solution grafted with N-methylpiperidone and N-methylpiperidine; wherein the mass-to-volume ratio of N-methylpiperidone, N-methylpiperidine, poly(4-vinylbenzyl chloride) and the second organic solvent is (0.0148~0.0593 g): (0.0260~0.0520 g): 0.2 g: (10~15 mL); S2, polyvinyl alcohol and hydrochloric acid are dissolved in a third organic solvent, and then the quaternized poly(4-vinylbenzyl chloride) solution from step S1 is added to undergo a ketal reaction to obtain a film-forming mixture; S3, dry the membrane-forming mixture in step S2 to obtain a halogen-type anion exchange membrane; S4. The halogen-type anion exchange membrane from step S3 is subjected to ion exchange with an alkaline solution to obtain an anion exchange membrane.

3. The method for preparing the anion exchange membrane as described in claim 2, characterized in that: In step S1, the poly(4-vinylbenzyl chloride) is obtained by polymerizing a mixture I containing 4-vinylbenzyl chloride monomer, an initiator, and a first organic solvent under an inactive atmosphere.

4. The method for preparing the anion exchange membrane as described in claim 2, characterized in that: In step S1, the second organic solvent is dimethyl sulfoxide; the reaction time of the methyl sulfoxide is 4-6 h and the temperature is 40-60 °C.

5. The method for preparing the anion exchange membrane as described in claim 2, characterized in that: In step S2, the mass-to-volume ratio of polyvinyl alcohol to the third organic solvent is 0.0577 g: (5~10 mL).

6. The method for preparing the anion exchange membrane as described in claim 2, characterized in that: In step S2, the third organic solvent is dimethyl sulfoxide; the ketal reaction takes 4-6 h and is carried out at a temperature of 40-60 °C.

7. The method for preparing the anion exchange membrane as described in claim 2, characterized in that: In step S3, the drying time is 8-12 h and the temperature is 70-90 ℃.

8. The method for preparing the anion exchange membrane as described in claim 2, characterized in that: In step S4, the alkaline solution is selected from one or both of KOH solution and NaOH solution; the concentration of the alkaline solution is 1~2 mol / L and the temperature is 40~80℃.

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