Modified porous polymer membrane, preparation method and composite proton exchange membrane

Abstract

The present application relates to the field of battery materials, and in particular to a kind of modified porous polymer film, preparation method and composite proton exchange membrane.The modified porous polymer film is that porous polymer film surface modification has formula I compound to form, #imgabsO#(I), wherein R includes nitrogen onium cation and sulfonate, and n is 200 2000, wherein porous polymer film is selected from following one or more:Porous polyethylene film, porous polyarylether film, porous polypropylene film, porous polyvinyl fluoride film, porous polyvinylidene fluoride film.The present application embodiment uses the composite proton exchange membrane prepared by the porous polymer film modified by specific betaine compound and perfluorosulfonic acid resin to have an intensity greater than 63Mpa, elongation at break is greater than 80%, and specific conductivity is greater than 0.102mS / cm, is better than import Gore proton exchange membrane, has broad application prospect in proton exchange membrane field.

Description

Technical Field

[0001] The present application relates to the field of battery materials, and in particular to a modified porous polymer membrane, a preparation method and a composite proton exchange membrane. Background Art

[0002] Proton exchange membrane (PEM) is a key material for proton exchange membrane fuel cells. An ideal proton exchange membrane needs to have good chemical durability and mechanical durability. Initially, perfluorosulfonic acid resin was mostly used to prepare proton exchange membranes. However, this material is expensive and has low inherent strength, which has certain limitations. In related technologies, Gore further proposed a composite proton exchange membrane using a porous polytetrafluoroethylene membrane as a reinforcement layer, which reduced the cost of the proton exchange membrane and improved its mechanical properties. However, porous polytetrafluoroethylene has strong hydrophobicity, and perfluorosulfonic acid resin is a strong water-based material. The combination of the two is unstable, and tearing and delamination may occur under harsh conditions. Therefore, the composite PEM made of the two has problems such as reduced durability and potential safety hazards.

[0003] Therefore, there is an urgent need to provide a modified polymer membrane that can be closely combined with perfluorosulfonic acid resin to improve the performance of the composite proton exchange membrane. Summary of the Invention

[0004] The present invention solves at least one of the problems of the related art from the following aspects.

[0005] The embodiment of the first aspect of the present invention provides a modified porous polymer membrane, wherein the modified porous polymer membrane is formed by modifying the surface of the porous polymer membrane with a compound of formula I.

[0006] (I), wherein R comprises a nitrogen onium cation and a sulfonate radical, and n is 200-2000,

[0007] The porous polymer membrane is selected from one or more of the following: porous polyethylene membrane, porous polyarylether membrane, porous polypropylene membrane, porous polyvinyl fluoride membrane, porous polyvinylidene fluoride membrane.

[0008] In some embodiments, R is selected from one or more of the group consisting of:

[0009] 、 、 、 、 、 、 、 、 、 .

[0010] In some embodiments, the porous polymer membrane is a porous polytetrafluoroethylene membrane.

[0011] A second aspect of the present invention provides a method for preparing a modified porous polymer membrane according to any one of the first aspects, comprising: subjecting the porous polymer membrane to plasma treatment; and contacting a reaction solution containing a betaine compound and a free radical initiator with the plasma-treated porous polymer membrane to perform surface modification, wherein the betaine compound is selected from one or more of the following groups:

[0012] 、 、 、 、 、 、 、 、 、 .

[0013] In some embodiments, plasma treating the porous polymer membrane comprises: contacting the porous polymer membrane with an acidic solution for pretreatment; and plasma treating the pretreated porous polymer membrane at a power of 10-50 W, a frequency of 1-16 MHz, and a time of 1-10 s, wherein the acidic solution is ethanol, acetic acid, and water in a mass ratio of (2-4):(0.5-1.5):(0.5-1.5).

[0014] In some embodiments, the free radical initiator is selected from one or more of the following: azobisisobutyronitrile, diacyl peroxide, ammonium peroxodisulfate, and cumene hydroperoxide.

[0015] In some embodiments, contacting a reaction solution comprising a betaine compound and a free radical initiator with a plasma-treated porous polymer membrane for surface modification comprises contacting a reaction solution comprising a betaine compound and a free radical initiator with a plasma-treated porous polymer membrane at 70-90° C. for 3-5 hours for surface modification.

[0016] The third aspect of the present invention provides a composite proton exchange membrane, comprising: a modified porous polymer membrane and a perfluorosulfonic acid resin membrane as described in any embodiment of the first aspect, or a modified porous polymer membrane and a perfluorosulfonic acid resin membrane obtained by the preparation method of any embodiment of the second aspect.

[0017] Compared with the related art, the embodiments of the present application achieve at least the following beneficial effects:

[0018] The examples of this application use a specific betaine compound to modify a porous polymer membrane, significantly changing its surface properties and the effect of its composite with a perfluorosulfonic acid resin membrane. The composite proton exchange membranes prepared using a porous polymer membrane modified with a specific betaine compound and a perfluorosulfonic acid resin in the examples of this application have a strength greater than 63 MPa, an elongation at break greater than 80%, and a conductivity greater than 0.102 S / cm, which is superior to imported Gore proton exchange membranes and has broad application prospects in the field of proton exchange membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the SEM image of the unmodified ePTFE membrane surface.

[0020] Figure 2 This is the SEM image of the surface of the modified ePTFE membrane 5 in Example 1.

[0021] Figure 3 The contact angle test results of unmodified ePTFE membrane and aqueous solution.

[0022] Figure 4 1 is the contact angle test result between the modified ePTFE membrane 5 and the aqueous solution in Example 1.

[0023] Figure 5 This is a cross-sectional SEM image of the composite proton exchange membrane 5 in Example 2. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below in conjunction with specific embodiments. The examples provided are only for illustrating the present invention and are not intended to limit the scope of the present invention. The examples provided below can serve as a guide for further improvements by those skilled in the art and are not intended to limit the present invention in any way.

[0025] Ion exchange membranes are currently widely used as proton exchange membranes in fuel cells, requiring excellent chemical and mechanical durability. Perfluorosulfonic acid resin is known as "resin gold," and PEMs of equivalent quality made from it are more expensive than gold. Consequently, major companies are considering how to reduce PEM thickness without compromising performance. Advances in scientific research have seen PEM thickness gradually evolve from 50 microns in the last century to a commercially viable 18 microns. Gore's introduction of a 12-micron proton exchange membrane a few years ago further advanced this field. Gore's approach involves transforming pure resin membranes into composite membranes reinforced with expanded polytetrafluoroethylene (ePTFE). This approach not only conserves resin but also improves membrane mechanical properties.

[0026] Polytetrafluoroethylene (PTFE), as a fully fluorinated polymer material, has impressive properties such as high chemical resistance, low surface energy, good thermal stability, low dielectric constant, and low water absorption. It is widely used in the electronics, chemical, medical, construction, energy and other industries. However, its extreme inertness and hydrophobicity limit its performance in applications. The polytetrafluoroethylene molecular chain can be regarded as all the H atoms in PE replaced by F atoms. However, because the volume of F atoms is much larger than that of H atoms, the C-F bond length is short. The negative charges of the F atoms in adjacent molecules repel each other, resulting in the molecular chain being arranged in a spiral shape so that the larger F atoms can be tightly arranged and stacked around the CC skeleton. Therefore, the carbon backbone of PTFE is protected from any external acid and alkali corrosion, giving it good chemical corrosion resistance and making it difficult to be modified by common methods.

[0027] In order to improve the performance of polytetrafluoroethylene and expand its application range. Currently, most surface curing research is more on glass or metal oxides. Related technologies introduce hydrophilic groups such as hydroxyl groups, sulfonic acid groups or amino groups on the surface of polytetrafluoroethylene to improve its hydrophilicity or ion exchange properties. Due to its excellent chemical resistance, PTFE membranes can be used under strict conditions, such as strong acid / strong base. Porous PTFE membranes have strong hydrophobicity and no flux in water systems. Therefore, it is of great significance to improve the hydrophilicity of polytetrafluoroethylene membranes. Modified ePTFE membranes can be modified by physical means such as ultraviolet light or KrF excimer laser, radiation grafting, and ion beam irradiation, which all require relatively expensive equipment and complex processes. Moreover, it is difficult for the pretreated porous ePTFE membrane surface to produce enough free radicals to initiate the polymerization of vinyl monomers.

[0028] Due to the significant difference in surface energy between the ePTFE membrane and perfluorosulfonic acid resin (large contact angles in actual measurements), the filling and contact between the two materials are not particularly harmonious. As a result, tearing and delamination often occur under harsh testing conditions, especially in dry and wet conditions. This severely reduces the durability of the PEM and may even cause direct contact between the anode and cathode gases, leading to explosion. Therefore, there is an urgent need to improve the compatibility of the ePTFE membrane and perfluorosulfonic acid resin and reduce the contact angle. To address this issue, the present invention proposes a modified porous polymer membrane and a composite proton exchange membrane.

[0029] The first embodiment of the present application provides a modified porous polymer membrane, wherein the modified porous polymer membrane is formed by modifying the surface of the porous polymer membrane with a compound of formula I.

[0030] (I), wherein R comprises a nitrogen onium cation and a sulfonate radical, and n is 200-2000 (any integer between 200-2000, such as 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 125 0, 1300, 1350, 1400, 1450, 1500, 1550, 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950, 2000), wherein the porous polymer membrane is selected from one or more of the following: porous polyethylene membrane, porous polyarylether membrane, porous polypropylene membrane, porous polyvinyl fluoride membrane, porous polyvinylidene fluoride membrane.

[0031] It is understood that the first end of the compound of formula I is connected to the porous polymer membrane and the second end of the compound of formula I is connected to the H atom.

[0032] In some embodiments, the first end of the compound of Formula I is attached to the porous polymer membrane through an oxygen atom, and the second end of the compound of Formula I is attached to an H atom.

[0033] In some embodiments, R is selected from one or more of the group consisting of:

[0034] 、 、 、 、 、 、 、 、 、 .

[0035] In some embodiments, the porous polymer membrane is a porous polytetrafluoroethylene membrane.

[0036] A second aspect of the present application provides a method for preparing a modified porous polymer membrane according to any one of the first aspects, comprising: plasma-treating the porous polymer membrane; and contacting a reaction solution containing a betaine compound and a free radical initiator with the plasma-treated porous polymer membrane to perform surface modification, wherein the betaine compound is selected from one or more of the following groups:

[0037] (Compound 1), (Compound 2), (Compound 3), (Compound 4), (Compound 5), (Compound 6), (Compound 7), (Compound 8), (Compound 9), (Compound 10).

[0038] In the examples of this application, an ePTFE membrane is treated in an atmospheric environment with a plasma of appropriate power to activate its surface. Plasma treatment is crucial for ePTFE membrane surface activation because it breaks the inert C—H chemical bonds on the ePTFE surface, generating reactive groups such as -H, -OH, and -O. These functional groups increase the wettability of the monomer solution and, more importantly, serve as initiators for covalent grafting via free radical polymerization. A zwitterionic compound solution (a nitrogen-sulfonate ion compound) is then grafted onto the plasma-treated ePTFE membrane surface by spraying or solution infiltration. This reaction is convenient and simple to carry out in a water bath or at relatively low temperatures. The free radical initiator is typically selected from azobisisobutyronitrile, diacyl peroxide, ammonium peroxodisulfate, or cumene hydroperoxide. Grafting the betaine compound onto the ePTFE membrane surface significantly reduces the contact angle between the ePTFE membrane and the PFSA resin, improves the strength and conductivity of the composite ion exchange membrane prepared using the modified ePTFE membrane, and enhances the overall performance of the resulting composite ion exchange membrane. The PEM composite membrane based on the modified porous polymer membrane of the embodiment of the present application has high stacking density and high strength as the compatibility of the reinforcement layer and the ion exchange resin is improved, and is more suitable for application in fuel cell proton exchange membranes.

[0039] In some embodiments, the plasma treatment of the porous polymer membrane comprises: contacting the porous polymer membrane with an acidic solution for pretreatment; and plasma-treating the porous polymer membrane at a power of 10-50 W (e.g., 15 W, 20 W, 25 W, 30 W, 35 W, 40 W, 45 W, 50 W), preferably 20-30 W, a frequency of 1-16 MHz (e.g., 2 MHz, 3 MHz, 4 MHz, 5 MHz, 6 MHz, 7 MHz, 8 MHz, 9 MHz, 10 MHz, 11 MHz, 12 MHz, 13 MHz, 14 MHz, 15 MHz, 16 MHz), and a duration of 2-10 s (e.g., 3 s, 4 s, 5 s, 6 s, 7 s, 8 s, 9 s, 10 s). The pretreated porous polymer membrane is plasma treated for a period of 4-8 s, preferably 4-8 s, wherein the acidic solution comprises ethanol, acetic acid and water in a mass ratio of (2-4):(0.5-1.5):(0.5-1.5) (e.g., 2.5:0.5:0.5, 3:0.5:0.5, 3.5:0.5:0.5, 2.5:1:0.5, 3:1:0.5, 3.5:1:0.5, 2.5:1.5:0.5, 3:1.5:0.5, 3.5:1.5:0.5, 2.5:0.5:1, 3:0.5:1, 3.5:0.5:1, 2.5:1:1, 3:1:1, 3.5:1:1, 2.5:1.5:1.5, 3:1.5:1.5, 3.5:1.5:1.5).

[0040] In some embodiments, the free radical initiator is selected from one or more of the following: azobisisobutyronitrile, diacyl peroxide, ammonium peroxodisulfate, and cumene hydroperoxide.

[0041] In some embodiments, contacting a reaction solution comprising a betaine compound and a free radical initiator with a plasma-treated porous polymer membrane for surface modification comprises contacting a reaction solution comprising 0.05-0.5 g / mL (e.g., 0.06 g / mL, 0.07 g / mL, 0.08 g / mL, 0.09 g / mL, 0.1 g / mL, 0.15 g / mL, 0.2 g / mL, 0.25 g / mL, 0.3 g / mL, 0.35 g / mL, 0.4 g / mL, 0.45 g / mL, 0.5 g / mL) of the betaine compound and 0.005-0.05 g / mL (e.g., 0.006 g / mL, 0.007 g / mL, 0.008 g / mL, 0.009 g / mL, 0.01 g / mL, 0.011 g / mL, 0.012 g / mL, 0.013 g / mL, 0.014 g / mL) of the betaine compound. The reaction solution of the free radical initiator of 0.5 g / mL, 0.015 g / mL, 0.016 g / mL, 0.017 g / mL, 0.018 g / mL, 0.019 g / mL, 0.02 g / mL, 0.025 g / mL, 0.03 g / mL, 0.035 g / mL, 0.04 g / mL, 0.045 g / mL, 0.05 g / mL) is contacted with the plasma-treated porous polymer membrane at 70-90°C (e.g., 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C, 90°C) for 3-5 hours (e.g., 3.5 hours, 4 hours, 4.5 hours, 5 hours) to perform surface modification.

[0042] A third aspect of the present application provides a composite proton exchange membrane, comprising the modified porous polymer membrane of any one of the first aspects and a perfluorosulfonic acid resin membrane; or

[0043] The modified porous polymer membrane and perfluorosulfonic acid resin membrane are obtained according to the preparation method of any embodiment of the second aspect.

[0044] The following examples are used to further illustrate the advantages and characteristics of the present method, but are not intended to limit the present invention. The experimental methods in the following examples, unless otherwise specified, are conventional methods and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions.

[0045] Unless otherwise specified, the quantitative analysis experiments in the following examples were performed three times, and the results were averaged.

[0046] Detection methods used in the examples:

[0047] Mechanical properties are tested according to GB / T 1040-2006 standard.

[0048] Conductivity: The electrochemical workstation Metrohm Autolab PGSTAT302N was used to measure the AC impedance of the film and calculate the proton conductivity. The AC frequency was 1~10 5 Hz, with a sweep amplitude of 10 mV. The film was clamped according to the four-electrode method, with two custom clamps used to measure the conductivity normal to the membrane (σ⊥) and the conductivity parallel to the membrane (σ∥), respectively.

[0049] Preparation Example 1 Betaine Compound

[0050] In this preparation example, the first compound and the second compound are used to synthesize the betaine compound. The specific chemical formula is shown in Table 1 below.

[0051] The first compound (nitrogen-containing heterocyclic compound): 4-vinylpyridine, 2-vinylpyridine, 3-vinylpyridine, N-4-vinylbenzyl-N,N-dimethylamine, N-vinylimidazole; the second compound (sultone compound): 1,3-propane sultone, 1,4-butane sultone and 2,4-butane sultone.

[0052] Betaine compounds: Compounds 1-10, see Table 1 below for their specific structures.

[0053] 1.1 Preparation of compound 5

[0054] The first compound is N-4-vinylbenzyl-N,N-dimethylamine, and the second compound is 1,3-propane sultone, to prepare compound 5.

[0055] Dissolve 160 mmol of N-4-vinylbenzyl-N,N-dimethylamine in 100 mL of ethyl acetate (EtOAc) with constant stirring. Then, slowly add 192 mmol of 1,3-propane sultone in 200 mL of ethyl acetate and stir at 50°C for 20 hours. The suspension is filtered to obtain a white powder. Multiple recrystallizations from ethanol yield the product, compound 5, as white, shiny crystals.

[0056] 1.2 Preparation of compound 8

[0057] The first compound is N-4-vinylbenzyl-N,N-dimethylamine, and the second compound is 1,4-butane sultone, to prepare compound 8.

[0058] Dissolve 160 mmol of N-4-vinylbenzyl-N,N-dimethylamine in 100 mL of ethyl acetate (EtOAc) with constant stirring. Dissolve 192 mmol of 1,4-butane sultone in 200 mL of ethyl acetate and slowly add the resulting mixture dropwise. Stir at 50°C for 20 hours. Filter the suspension to obtain a white powder. Recrystallize the product several times from ethanol to obtain compound 8, a white, shiny crystal.

[0059] 1.3 Referring to the methods in 1.1 and 1.2 above, the remaining betaine compounds were synthesized. The structures of the obtained betaine compounds are shown in Table 1 below.

[0060] Table 1

[0061]

[0062] Preparation Example 2 Plasma-treated ePTFE membrane

[0063] 2.1 Soak the Gore (or Donaldson) ePTFE membrane in a solution of ethanol:acetic acid:water = 3:1:1 for 24 h, then rinse with deionized water in an ultrasonic machine, and then place it in an 80°C oven to remove the residual solution. Repeat this process twice to obtain a pretreated ePTFE membrane.

[0064] 2.2 The pretreated ePTFE membrane was plasma treated under the following conditions:

[0065] Treatment group 1: treated with 10W power for 6 seconds in air, then exposed to air for 5 minutes;

[0066] Treatment group 2: treated with 25W power for 6 seconds in air, then exposed to air for 5 minutes;

[0067] Treatment group 3: treated with 40W power for 6 seconds in air, then exposed to air for 5 minutes;

[0068] Treatment group 4: treated with 50W power for 6 seconds in air, and then exposed to air for 5 minutes.

[0069] Mechanical properties testing

[0070] The test results of the mechanical properties of the plasma-treated ePTFE membrane are shown in Table 2 below.

[0071] Table 2

[0072]

[0073] It can be seen from Table 2 that with the increase of plasma treatment energy, the performance of the ePTFE membrane can be retained to the greatest extent before 25w, and it decreases significantly after 25w, especially the strength data decreases by about 15%, and decreases further to 19% after 50w. Therefore, 25w plasma is selected to treat the ePTFE membrane.

[0074] Example 1 Betaine-modified ePTFE membrane

[0075] 10 g of each betaine compound (Compounds 1-10) shown in Table 1 and 1 g of ammonium peroxodisulfate were respectively weighed and dissolved in 100 mL of water to prepare a solution containing 0.1 g / mL of the betaine compound and 0.01 g / mL of ammonium peroxodisulfate. The solution was then evenly sprayed onto the plasma-treated ePTFE membrane prepared in Treatment Group 2 of Preparation Example 2 and polymerized at 80° C. for 4 hours. The membrane was then washed multiple times with deionized water and ethyl acetate to obtain betaine compound-modified ePTFE membranes 1-10 (ePTFE membranes modified with Compounds 1-10, respectively).

[0076] SEM inspection

[0077] Taking modified ePTFE membrane 5 (ePTFE membrane modified with compound 5) as an example, the surface fiber structure and contact angle of the ePTFE membrane to aqueous solution before and after modification were detected using a scanning electron microscope and a German Krügers contact angle measuring instrument DSA-100E, including a high-resolution CCD camera. Single-frame shooting was adopted, and the instrument's built-in software fitted the angle. The results are as follows: Figure 1-4 shown.

[0078] Figure 1 Figure 1 is a SEM image of the ePTFE membrane before modification, which shows the surface fiber structure of the ePTFE membrane. Figure 1 It can be clearly seen that the ePTFE membrane has uneven fiber distribution, many nodes, uneven fiber thickness, and a wide distribution of short fibers and broken fibers, so the microstructure is not ideal. Figure 2 3 is a SEM image of the ePTFE membrane modified with compound 5 prepared in this preparation example, which shows the surface fiber structure of the ePTFE membrane modified with betaine compound 5. Figure 2 The results of grafting modification are clearly shown. The membrane fibers are uniform in thickness, with few breakpoints and broken fibers. Figure 1 It has been greatly improved compared.

[0079] Figure 3 and Figure 4 The contact angles of the ePTFE membrane to aqueous solution before and after modification are shown. Figure 3 and Figure 4 It can be seen that the contact angle of the ePTFE membrane to the aqueous solution changed significantly before and after grafting.

[0080] Mechanical properties testing

[0081] The thickness, strength, elastic modulus and elongation at break of each betaine-modified ePTFE membrane prepared in this example were tested, and the results are shown in Table 3 below, where the unmodified Gore ePTFE membrane was used as a control group.

[0082] Table 3

[0083]

[0084] Example 2 Composite membrane based on betaine-modified ePTFE membrane

[0085] Composite membranes were prepared based on the betaine-modified ePTFE membranes (modified ePTFE membranes 1-10) prepared in Example 1, respectively, including the following steps SS1-SS3.

[0086] SS1 Preparation of perfluorosulfonic acid solution: 3M perfluorosulfonic acid resin is completely dissolved in a mixed solution of ethanol: water: isopropanol 5:2:3 by mass ratio to prepare a first coating solution with a solid content of 9% and a viscosity of 90mPa·s and a second coating solution with a solid content of 25% and a viscosity of 80mPa·s.

[0087] SS2 single-coat proton membrane: Set the scraping speed of the doctor coater (Hefei Kejing) to 25 and the scraper height to 11 μm. Place the Daicel PET base film (cut into A4 paper size) on the doctor coater, add 10 mL of the single-coat solution prepared in step SS1, start the equipment to scrape the resin solution evenly, then cut the betaine-modified ePTFE membrane prepared in Example 1 into A4 size and cover it on the single-coat solution. Wait for 5 minutes at room temperature to allow the solution to completely penetrate the ePTFE membrane modified with the betaine compound, and then dry it at 60°C for 20 minutes to remove it.

[0088] Preparation of SS3-modified proton membrane: Reset the scraper height to 8 μm and continue dripping 8 mL of the second coating solution onto the membrane prepared in step SS2 above. Continue scraping at the same speed and apply another coat. After the coating is complete, place the membrane in an oven at 160°C for 10 minutes to remove the solvent. This completes the preparation of composite proton exchange membranes based on betaine-modified ePTFE membranes, yielding composite proton exchange membranes 1-10.

[0089] SEM inspection

[0090] Taking the composite proton exchange membrane 5 based on the modified ePTFE membrane 5 as an example, SEM detection was carried out, and the results are as follows Figure 5 shown. Figure 5 The SEM cross-sectional view of the composite proton exchange membrane is shown in FIG. Figure 5It can be seen that the middle layer is grafted ePTFE (i.e. modified ePTFE membrane 5), and the upper and lower layers are perfluorosulfonic acid resin after the solvent of the first and second coating resin solutions are evaporated. Figure 5 It can be seen that in the composite proton exchange membrane prepared in the examples of the present application, the ePTFE membrane is tightly filled with the resin after being grafted onto compound 5, thereby improving the strength of the composite membrane.

[0091] Electrochemical and mechanical properties testing

[0092] The conductivity, thickness, strength, elastic modulus, and elongation at break of composite proton exchange membranes based on each betaine compound-modified ePTFE membrane prepared in Example 1 were tested, and the results are shown in Tables 4-5 below. As can be seen in Table 4, compared to composite membranes based on unmodified ePTFE membranes, the electrochemical performance of composite membranes based on modified ePTFE membranes grafted with betaine compounds was greatly improved, surpassing that of imported membranes (Gore's ePTFE / perfluorosulfonate composite proton exchange membrane) by more than 40%. The modified ePTFE membranes provided in the examples of this application significantly improve the electrochemical performance of proton exchange membranes.

[0093] Table 4

[0094]

[0095] Table 5

[0096]

[0097] Comparative Example 1 Composite membrane based on ePTFE membrane modified with sodium styrenesulfonate

[0098] The preparation of the modified ePTFE is basically the same as that in Example 1, except that sodium styrene sulfonate is used instead of Compound 1-10 of the present application to prepare the modified ePTFE membrane.

[0099] The modified ePTFE membrane of this comparative example was used to prepare a comparative composite proton exchange membrane 1, and the preparation steps were the same as those in Example 2.

[0100] The comparative composite proton exchange membrane 1 has a thickness of 12±1 μm, a strength of 61 MPa, an elastic modulus of 320.32 MPa, an elongation at break of 290.54%, and an electrical conductivity of 0.112 S / cm.

[0101] Comparative Example 2 Composite membrane based on N,N-dimethylacetamide modified ePTFE membrane

[0102] The preparation of the modified ePTFE is basically the same as that in Example 1, except that N,N-dimethylacetamide is used instead of Compound 1-10 of the present application to prepare the modified ePTFE membrane.

[0103] The modified ePTFE membrane of this comparative example was used to prepare a comparative composite proton exchange membrane 2, and the preparation steps were the same as those in Example 2.

[0104] The comparative composite proton exchange membrane 2 has a thickness of 12±1 micrometers, a strength of 63 MPa, an elastic modulus of 316.22, an elongation at break of 310.26%, and an electrical conductivity of 0.103 S / cm.

[0105] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0106] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a modified porous polymer membrane, characterized in that: The preparation method comprises: plasma treating the porous polymer membrane; and contacting a reaction solution comprising a betaine compound and a free radical initiator with a plasma-treated porous polymer membrane for surface modification, The modified porous polymer membrane is formed by modifying the surface of the porous polymer membrane with a compound of formula I. (I), wherein R comprises a nitrogen onium cation and a sulfonate, n is 200-2000, wherein R is selected from one or more of the group consisting of: 、 、 、 、 、 、 、 、 、 , wherein the betaine compound is selected from one or more of the group consisting of: 、 、 、 、 、 、 、 、 、 ， The porous polymer membrane is selected from one or more of the following: porous polyethylene membrane, porous polyarylether membrane, porous polypropylene membrane, porous polyvinyl fluoride membrane, porous polyvinylidene fluoride membrane.

2. The preparation method according to claim 1, wherein The plasma treatment of the porous polymer film comprises: contacting the porous polymer membrane with an acidic solution for pretreatment; and The pretreated porous polymer membrane is subjected to plasma treatment at a power of 10-50 W, a frequency of 1-16 MHz and a time of 1-10 s. The acidic solution is ethanol, acetic acid and water in a mass ratio of (2-4):(0.5-1.5):(0.5-1.5).

3. The preparation method according to claim 1, characterized in that The free radical initiator is selected from one or more of the following: azobisisobutyronitrile, diacyl peroxide, ammonium peroxodisulfate, and cumene hydroperoxide.

4. The preparation method according to claim 1, characterized in that The contacting of a reaction solution comprising a betaine compound and a free radical initiator with a plasma-treated porous polymer membrane for surface modification comprises: A reaction solution containing 0.05-0.5 g / mL of a betaine compound and 0.005-0.05 g / mL of a radical initiator is brought into contact with the plasma-treated porous polymer membrane at 70-90° C. for 3-5 hours to perform surface modification.

5. The preparation method according to claim 1, characterized in that The porous polymer membrane is a porous polytetrafluoroethylene membrane.

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