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

Abstract

The invention relates to the field of battery materials, in particular to a modified porous polymer membrane, a preparation method and a composite proton exchange membrane. The modified porous polymer membrane is formed by modifying the surface of a porous polymer membrane with a compound shown in a formula I, # imgabs0 # (I), R comprises azonium positive ions and sulfonate radicals, n is 200-2000, and the porous polymer membrane is selected from one or more of a porous polyethylene membrane, a porous polyarylether membrane, a porous polypropylene membrane, a porous polyvinyl fluoride membrane and a porous polyvinylidene fluoride membrane. The strength of the composite proton exchange membrane prepared from the porous polymer membrane modified by the specific betaine compound and the perfluorinated sulfonic acid resin is larger than 63 Mpa, the elongation at break is larger than 80%, the conductivity is larger than 0.102 mS / cm, the composite proton exchange membrane is superior to an imported Gore proton exchange membrane, and the composite proton exchange membrane has wide application prospects in the field of proton exchange membranes.

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 the related art, 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 one of the problems of the related art from at least 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, (I), wherein R comprises a nitrogen onium cation and a sulfonate group, and n is 200-2000, 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.

[0006] In some embodiments, R is selected from one or more of the group consisting of: , , , , , , , , , .

[0007] In some embodiments, the porous polymer membrane is a porous polytetrafluoroethylene membrane.

[0008] The 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: , , , , , , , , , .

[0009] 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).

[0010] In some embodiments, the free radical initiator is selected from one or more of the following: azobisisobutyronitrile, diacyl peroxide, ammonium peroxodisulfate, and cumene hydroperoxide.

[0011] 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.

[0012] 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 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.

[0013] Compared with the related art, the embodiments of the present application achieve at least the following beneficial effects: The examples of the present application use a specific betaine compound to modify a porous polymer membrane, which significantly changes its surface properties and the effect of compounding with a perfluorosulfonic acid resin membrane. The composite proton exchange membrane prepared by using a porous polymer membrane modified with a specific betaine compound and a perfluorosulfonic acid resin in the examples of the present application has a strength greater than 63 Mpa, an elongation at break greater than 80%, and a conductivity greater than 0.102 S / cm, which is better than the imported Gore proton exchange membrane and has broad application prospects in the field of proton exchange membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the SEM image of the unmodified ePTFE membrane surface.

[0015] Figure 2 This is the SEM image of the surface of the modified ePTFE membrane 5 in Example 1.

[0016] Figure 3 The contact angle test results of unmodified ePTFE membrane and aqueous solution.

[0017] Figure 4 The contact angle test results of the modified ePTFE membrane 5 in Example 1 and the aqueous solution.

[0018] Figure 5 This is a cross-sectional SEM image of the composite proton exchange membrane 5 in Example 2. DETAILED DESCRIPTION

[0019] The present invention is 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 be used as a guide for further improvements by those of ordinary skill in the art and are not intended to limit the present invention in any way.

[0020] Ion exchange membranes are currently widely used in proton exchange membranes for fuel cells, and they need to have good chemical and mechanical durability. As we all know, perfluorosulfonic acid resin is called "resin gold", and PEM of the same quality prepared from it is more expensive than gold, so major companies are thinking about how to reduce the thickness of PEM without affecting performance. With the development of scientific research, PEM has gradually developed from 50 microns in the last century to 18 microns for commercial use. A few years ago, Gore launched a 12-micron proton exchange membrane, which pushed this field forward a big step. The approach taken by Gore is to make the pure resin membrane into a composite membrane with a porous polytetrafluoroethylene membrane (expanded polytetrafluoroethylene, ePTFE) as the reinforcement layer, which not only saves resin but also improves the mechanical properties of the membrane.

[0021] As a fully fluorinated polymer material, polytetrafluoroethylene (PTFE) has impressive properties such as high chemical resistance, low surface energy, good thermal stability, low dielectric constant, low water absorption, etc. It is widely used in electronics, chemical, medical, construction, energy and other industries. However, extreme inertness and hydrophobicity limit their performance in applications. The polytetrafluoroethylene molecular chain can be regarded as all H atoms in PE replaced by F atoms, but because the volume of F atoms is much larger than that of H atoms, the CF bond length is short, and the negative charges of adjacent molecular F atoms repel each other, resulting in the molecular chain can only be arranged in a spiral shape so that the larger F atoms can be closely arranged and accumulated around the CC skeleton. Therefore, the carbon main chain of PTFE is protected from any external acid and alkali corrosion, which makes it have good chemical corrosion resistance and is difficult to be modified by common methods.

[0022] In order to improve the performance of polytetrafluoroethylene and expand its application range. At present, most of the surface curing research is more on glass or metal oxides. Related technologies introduce hydrophilic groups such as hydroxyl, sulfonic acid 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 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.

[0023] Due to the large surface energy difference between the ePTFE membrane and the perfluorosulfonic acid resin (the contact angle is large in actual measurement), the filling and contact of the two materials are not particularly harmonious, so that under harsh test conditions, especially in dry and wet conditions, tearing and delamination often occur, resulting in a serious reduction in the durability of the PEM, and may even cause the anode and cathode gases to directly contact and cause an explosion. Therefore, it is urgent to improve the compatibility of the ePTFE membrane and the perfluorosulfonic acid resin and reduce the contact angle. In order to solve the above problems, the embodiments of the present application propose a modified porous polymer membrane and a composite proton exchange membrane.

[0024] The first aspect 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. (I), wherein R comprises a nitrogen onium cation and a sulfonate group, 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.

[0025] 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.

[0026] 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.

[0027] In some embodiments, R is selected from one or more of the group consisting of: , , , , , , , , , .

[0028] In some embodiments, the porous polymer membrane is a porous polytetrafluoroethylene membrane.

[0029] The 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: 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: (Compound 1), (Compound 2), (Compound 3), (Compound 4), (Compound 5), (Compound 6), (Compound 7), (Compound 8), (Compound 9), (Compound 10).

[0030] In the embodiment of the present application, the ePTFE membrane is treated in an atmospheric environment with a plasma of suitable power to activate its surface. Plasma treatment is crucial for the activation of the ePTFE membrane surface because it can break the inert CF chemical bonds on the ePTFE surface to generate active groups such as -H, -OH, and -O. These functional groups increase the wettability of the monomer aqueous solution, and more importantly, can be used as primer groups for covalent grafting of free radical polymerization. Then, the zwitterionic compound solution (nitrogenium ion-sulfonate ion compound) is grafted onto the surface of the plasma-treated ePTFE membrane by spraying or solution infiltration. The above reaction is convenient and simple to carry out in a water bath or at a lower temperature. The free radical initiator is generally selected from azobisisobutyronitrile or diacyl peroxide or ammonium persulfate or isopropylbenzene hydroperoxide, etc. After the betaine compound is grafted on the surface of the ePTFE membrane, the contact angle between the ePTFE membrane and the PFSA resin is greatly reduced, and the strength and conductivity of the composite ion exchange membrane prepared using the modified ePTFE membrane are improved, thereby improving the comprehensive 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 with the ion exchange resin is improved, and is more suitable for application in proton exchange membranes of fuel cells.

[0031] In some embodiments, the porous polymer membrane is subjected to plasma treatment, comprising: contacting the porous polymer membrane with an acidic solution for pretreatment; and plasma-treating the porous polymer membrane with 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 time 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 time (s) preferably 4-8s, 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) (for example, 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).

[0032] In some embodiments, the free radical initiator is selected from one or more of the following: azobisisobutyronitrile, diacyl peroxide, ammonium peroxodisulfate, and cumene hydroperoxide.

[0033] 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 a 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 a free radical initiator with a plasma-treated porous polymer membrane for surface modification. The reaction solution of 0.05 g / mL, 0.014 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) of the free radical initiator 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) for surface modification.

[0034] A third aspect of the present application provides a composite proton exchange membrane, comprising a modified porous polymer membrane and a perfluorosulfonic acid resin membrane according to any one of the first aspects above; or The modified porous polymer membrane and perfluorosulfonic acid resin membrane are obtained by the preparation method of any embodiment of the second aspect.

[0035] The following examples are used to further illustrate the advantages and features 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 art or according to the product instructions.

[0036] Unless otherwise specified, the quantitative analysis experiments in the following examples were performed three times and the results were averaged.

[0037] Detection methods used in the examples: The mechanical properties are tested according to GB / T 1040-2006 standard.

[0038] 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, scanning amplitude 10mV. The film was clamped according to the four-electrode method, and two custom clamps were used to measure the conductivity in the normal direction (σ⊥) and the conductivity in the parallel direction (σ∥).

[0039] Preparation Example 1 Betaine Compound 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.

[0040] 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.

[0041] Betaine compounds: Compounds 1-10, see Table 1 below for their specific structures.

[0042] 1.1 Preparation of compound 5 The first compound is N-4-vinylbenzyl-N,N-dimethylamine, and the second compound is 1,3-propane sultone, to prepare compound 5.

[0043] 160mmol of N-4-vinylbenzyl-N,N-dimethylamine was dissolved in 100mL of ethyl acetate (EtOAc) solution and stirred continuously. 192mmol of 1,3-propane sultone was dissolved in 200mL of ethyl acetate and then slowly added to the solution and stirred at 50°C for 20h. Finally, the suspension was filtered to obtain a white powder. After recrystallization with ethanol for several times, a white bright crystal product was obtained: Compound 5.

[0044] 1.2 Preparation of compound 8 The first compound is N-4-vinylbenzyl-N,N-dimethylamine, and the second compound is 1,4-butane sultone, to prepare compound 8.

[0045] 160 mmol of N-4-vinylbenzyl-N,N-dimethylamine was dissolved in 100 mL of ethyl acetate (EtOAc) solution and stirred continuously. 192 mmol of 1,4-butane sultone was dissolved in 200 mL of ethyl acetate and then slowly added to the solution and stirred at 50°C for 20 h. Finally, the suspension was filtered to obtain a white powder. After recrystallization with ethanol for several times, a white bright crystal product was obtained: Compound 8.

[0046] 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.

[0047] Table 1

[0048] Preparation Example 2 Plasma-treated ePTFE membrane 2.1 Soak the Gore (or Donaldson) ePTFE membrane in a solution of ethanol: acetic acid: water = 3:1:1 for 24 h, then clean it with deionized water in an ultrasonic machine, and then put it in an 80°C oven to remove the solution residue. Repeat this process twice to obtain a pretreated ePTFE membrane.

[0049] 2.2 The pretreated ePTFE membrane was plasma treated under the following conditions: Treatment group 1: treated with 10W power for 6s in air, then exposed to air for 5min; Treatment group 2: treated with 25W power for 6s in air, then exposed to air for 5min; Treatment group 3: treated with 40W power for 6s in air, then exposed to air for 5min; Treatment group 4: treated with 50W power for 6s in air, and then exposed to air for 5min.

[0050] Mechanical properties testing The test results of the mechanical properties of the plasma-treated ePTFE membrane are shown in Table 2 below.

[0051] Table 2

[0052] It can be seen from Table 2 that with the increase of plasma treatment energy, the performance of the ePTFE membrane can retain the performance of the membrane to the greatest extent before 25w, and it will be greatly reduced after 25w, especially the strength data will drop by about 15%, and it will drop more to 19% after 50w. Therefore, 25w plasma is selected to treat the ePTFE membrane.

[0053] Example 1 Betaine modified ePTFE membrane 10 g of each betaine compound (compound 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 betaine compound and 0.01 g / mL ammonium peroxodisulfate, which was evenly sprayed on the plasma-treated ePTFE membrane prepared in Treatment Group 2 in Preparation Example 2 by spraying and polymerized at 80°C for 4 hours, and then washed with deionized water and ethyl acetate for multiple times to finally obtain betaine compound-modified ePTFE membranes 1-10 (respectively ePTFE membranes modified with compounds 1-10).

[0054] SEM inspection Taking modified ePTFE membrane 5 (ePTFE membrane modified by 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 Krueger contact angle measuring instrument DSA-100E, including a high-resolution CCD camera, using a single shot, and the instrument's built-in software fitting angle. The results are as follows: Figure 1-4 shown.

[0055] Figure 1 Figure 2 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 Compared to the previous version, it has been greatly improved.

[0056] Figure 3 and Figure 4 The contact angles of the ePTFE membrane to the aqueous solution before and after modification are shown respectively. 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.

[0057] Mechanical properties testing The thickness, strength, elastic modulus and elongation at break of each betaine-modified ePTFE membrane prepared in this example were tested respectively. The results are shown in Table 3 below, where the unmodified Gore ePTFE membrane was used as the control group.

[0058] Table 3

[0059] Example 2 Composite membrane based on betaine modified ePTFE membrane 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.

[0060] 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.

[0061] SS2 one-coat proton membrane: set the scraping speed of the scraper (Hefei Kejing) to 25 and the scraper height to 11 μm, place the Daicel PET base film (cut into A4 paper size) on the scraper, add 10 mL of the one-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 one-coat solution, wait for 5 min at room temperature to allow the solution to completely infiltrate the ePTFE membrane modified with the betaine compound, and then dry it at 60°C for 20 min to remove it.

[0062] Preparation of SS3 modified proton membrane: reset the scraper height to 8 μm, continue to drip 8 mL of the second coating solution on the membrane prepared in the above step SS2, keep the scraper speed unchanged, and scrape once more. After the end, place it in an oven at 160°C for 10 minutes to remove the solvent. In summary, the composite proton exchange membrane prepared based on betaine modified ePTFE membrane is completed, and composite proton exchange membranes 1-10 are obtained respectively.

[0063] SEM inspection 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. Figure 5 It 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 is evaporated. Figure 5 It can be seen that in the composite proton exchange membrane prepared in the example 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.

[0064] Electrochemical and mechanical properties testing The conductivity, thickness, strength, elastic modulus and elongation at break of the composite proton exchange membrane of each betaine compound modified ePTFE membrane prepared in Example 1 were tested respectively, and the results are shown in Tables 4-5 below. According to Table 4, it can be seen that compared with the composite membrane based on the unmodified ePTFE membrane, the electrochemical performance of the composite membrane based on the modified ePTFE membrane grafted with betaine compounds has been greatly improved, and has completely opened up the imported membrane (Gore's ePTFE / perfluorosulfonate composite proton exchange membrane) by more than 40%. The modified ePTFE membrane provided in the embodiment of the present application significantly improves the electrochemical performance of the proton exchange membrane.

[0065] Table 4

[0066] Table 5

[0067] Comparative Example 1 Composite membrane based on ePTFE membrane modified by sodium styrene sulfonate The preparation of the modified ePTFE is basically the same as that of Example 1, except that sodium styrene sulfonate is used instead of compound 1-10 of the present application to prepare the modified ePTFE membrane.

[0068] 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.

[0069] The comparative composite proton exchange membrane 1 has a thickness of 12±1 micrometers, 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.

[0070] Comparative Example 2 Composite membrane based on N,N-dimethylacetamide modified ePTFE membrane The preparation of the modified ePTFE is basically the same as that of Example 1, except that N,N-dimethylacetamide is used instead of the compounds 1-10 of the present application to prepare the modified ePTFE membrane.

[0071] 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 of Example 2.

[0072] 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 a conductivity of 0.103 S / cm.

[0073] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means 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 may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0074] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A modified porous polymer membrane, characterized in that: 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 group, and n is 200-2000, 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 modified porous polymer membrane according to claim 1, characterized in that R is selected from one or more of the group consisting of: 、 、 、 、 、 、 、 、 、 。 3. The modified porous polymer membrane according to claim 1 or 2, characterized in that The porous polymer membrane is a porous polytetrafluoroethylene membrane.

4. The method for preparing a modified porous polymer membrane according to any one of claims 1 to 3, characterized in that: include: Plasma treatment of a 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, Wherein the betaine compound is selected from one or more of the group consisting of: 、 、 、 、 、 、 、 、 、 。 5. The preparation method according to claim 4, characterized in that 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 film 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).

6. The preparation method according to claim 4, characterized in that: The free radical initiator is selected from one or more of the following: azobisisobutyronitrile, diacyl peroxide, ammonium peroxodisulfate, and cumene hydroperoxide.

7. The preparation method according to claim 4, 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 for surface modification.

8. A composite proton exchange membrane, characterized in that: Include: The modified porous polymer membrane and perfluorosulfonic acid resin membrane according to any one of claims 1 to 3, or A modified porous polymer membrane and a perfluorosulfonic acid resin membrane obtained by the preparation method according to any one of claims 4 to 7.

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