Polyimide and perfluorosulfonic acid composite proton exchange membrane as well as preparation method and application thereof

Abstract

The invention discloses a polyimide and perfluorosulfonic acid composite proton exchange membrane and a preparation method and application thereof, the polyimide and perfluorosulfonic acid composite proton exchange membrane is of a layered structure, and the layered structure sequentially comprises a first perfluorosulfonic acid layer, a polyimide porous membrane and a second perfluorosulfonic acid layer from top to bottom; the first perfluorosulfonic acid layer comprises perfluorosulfonic acid resin, the polyimide porous membrane comprises trifluoromethyl-containing polyimide, and the second perfluorosulfonic acid layer comprises perfluorosulfonic acid resin. The perfluorosulfonic acid and the trifluoromethyl-containing polyimide are compounded, so that the proton exchange membrane has excellent mechanical properties and good chemical stability; meanwhile, by introducing a trifluoromethyl group, the free volume is increased, so that a proton exchange space is provided to enhance the proton conductivity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery separators, and particularly relates to a polyimide and perfluorosulfonic acid composite proton exchange membrane and a preparation method and application thereof. BACKGROUND

[0002] In recent years, due to the exhaustion of fossil fuels and environmental pollution, people's interest in environmentally friendly alternative energy sources is growing, and many countries are working hard to develop renewable energy that can replace fossil fuels. Hydrogen, as the most abundant element in the universe, has the most important advantage of being inexhaustible. Hydrogen fuel cells, as an environmentally friendly energy conversion device, can convert chemical energy into electrical energy through electrochemical reactions of hydrogen fuel and oxidants. As the core component of hydrogen fuel cells, proton exchange membranes not only provide a one-way transmission channel for protons, but also isolate the fuel and oxidants. Therefore, the material used as the proton exchange membrane must have high proton conductivity and excellent chemical and mechanical stability. At present, perfluorosulfonic acid proton exchange membranes are most widely used, among which the Nafion series membranes produced by DuPont Company are the most representative. However, the production of Nafion series membranes is difficult and expensive, which has been criticized by people. Moreover, the proton conductivity of the perfluorosulfonic acid proton exchange membranes in the prior art cannot meet the needs of hydrogen fuel cells. SUMMARY

[0003] In view of the deficiencies in the prior art, the purpose of the present application is to provide a polyimide and perfluorosulfonic acid composite proton exchange membrane.

[0004] Another purpose of the present application is to provide a preparation method of the above-mentioned polyimide and perfluorosulfonic acid composite proton exchange membrane.

[0005] The purpose of the present application is achieved by the following technical solutions.

[0006] A polyimide and perfluorosulfonic acid composite proton exchange membrane, which has a layered structure, and the layered structure comprises, from top to bottom, a first perfluorosulfonic acid layer, a polyimide porous membrane and a second perfluorosulfonic acid layer.

[0007] The first perfluorosulfonic acid layer comprises a perfluorosulfonic acid resin, the polyimide porous membrane comprises a trifluoromethyl-containing polyimide, and the second perfluorosulfonic acid layer comprises a perfluorosulfonic acid resin. The ratio of the perfluorosulfonic acid resin in the first perfluorosulfonic acid layer, the trifluoromethyl-containing polyimide in the polyimide porous membrane and the perfluorosulfonic acid resin in the second perfluorosulfonic acid layer is (4-7):(3-7):(4-7) by mass fraction.

[0008] The trifluoromethyl-containing polyimide is polymerized from the following monomers:

[0009]

[0010] In the above technical solution, the method for preparing the polyimide porous membrane comprises: casting a polyimide solution on a substrate, immersing in a coagulation bath at 25-30℃ (phase inversion), and drying to obtain a polyimide porous membrane, wherein the coagulation bath comprises water and / or N-methyl pyrrolidone, and the polyimide solution comprises a trifluoromethyl-containing polyimide.

[0011] In the above technical solution, the content of the trifluoromethyl-containing polyimide in the polyimide solution is 10-15 wt%.

[0012] In the above technical solution, the time for immersing in the coagulation bath is 3-5 min.

[0013] In the above technical solution, the thickness of the first perfluorosulfonic acid layer is 17-60 μm, the thickness of the polyimide porous membrane is 10-20 μm, and the thickness of the second perfluorosulfonic acid layer is 17-60 μm.

[0014] In the above technical solution, the first perfluorosulfonic acid layer and the second perfluorosulfonic acid layer are the same or different.

[0015] In the above technical solution, the ratio of the perfluorosulfonic acid resin in the first perfluorosulfonic acid layer, the trifluoromethyl-containing polyimide in the polyimide porous membrane, and the perfluorosulfonic acid resin in the second perfluorosulfonic acid layer is preferably (6.5-7):(3-7):(6.5-7) by mass fraction.

[0016] In the above technical solution, the thickness of the first perfluorosulfonic acid layer is preferably 40-50 μm, the thickness of the polyimide porous membrane is preferably 15-18 μm, and the thickness of the second perfluorosulfonic acid layer is preferably 40-50 μm.

[0017] In the above technical solution, the raw material for preparing the trifluoromethyl-containing polyimide comprises: an A substance and a B substance, the A substance is one of hexafluoro dianhydride (6FDA), 9,9-bis(trifluoromethyl)-2,3,6,7-anthracene tetracarboxylic dianhydride (6FCDA), and bisphenol A diether dianhydride (BPADA), the B substance is one of 4,4-diamino diphenyl ether (ODA), 4,4'-diamino benzene anilide (DABA), 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA), and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), and at least one of the A substance and the B substance contains a trifluoromethyl group.

[0018] The preparation method of the polyimide and perfluorosulfonic acid composite proton exchange membrane comprises: casting a perfluorosulfonic acid solution for forming a first perfluorosulfonic acid layer on a substrate, placing a polyimide porous membrane on the liquid surface of the perfluorosulfonic acid solution (so that the lower surface of the polyimide porous membrane is in contact with the perfluorosulfonic acid solution), first heating, then casting a perfluorosulfonic acid solution for forming a second perfluorosulfonic acid layer on the upper surface of the polyimide porous membrane, second heating, obtaining the first perfluorosulfonic acid layer on the lower surface of the polyimide porous membrane and the second perfluorosulfonic acid layer on the upper surface of the polyimide porous membrane, post-processing, and obtaining the polyimide and perfluorosulfonic acid composite proton exchange membrane, wherein the perfluorosulfonic acid solution comprises perfluorosulfonic acid resin (PFSA) and a first solvent, and the mass ratio of the perfluorosulfonic acid resin (PFSA) to the first solvent is (3-10):(90-105), and the post-processing comprises sequentially immersing in sulfuric acid, hydrogen peroxide and water.

[0019] In the technical scheme, the temperature of the first heating is 60-90 DEG C, and the time of the first heating is 2-3 h.

[0020] In the technical scheme, the second heating comprises: first heating at 60-90 DEG C for 7-10 h, and then heating at 100-130 DEG C for 1-2 h.

[0021] In the technical scheme, the post-processing comprises: first immersing in sulfuric acid at 50-80 DEG C for 1.5-3 h, then immersing in hydrogen peroxide at 50-70 DEG C for 0.5-2 h, then washing with water, and finally immersing in water at 50-70 DEG C for 0.5-2 h, taking out, and drying (first drying at 60-90 DEG C for 10-14 h, and then drying at 100-130 DEG C for 1-2 h).

[0022] In the technical scheme, the concentration of the sulfuric acid is 0.5-1.2 mol / L, and the concentration of the hydrogen peroxide is 2.5-3.5 wt%.

[0023] In the technical scheme, the method for obtaining the perfluorosulfonic acid solution comprises: mixing the perfluorosulfonic acid resin (PFSA) and the first solvent uniformly to obtain the perfluorosulfonic acid solution.

[0024] In the technical scheme, the first solvent is N-methyl pyrrolidone (NMP).

[0025] In the technical scheme, the perfluorosulfonic acid resin (PFSA) and the first solvent are mixed and stirred at 140-160 DEG C until uniform to obtain the perfluorosulfonic acid solution. The stirring speed is 400-600 r / min, and the stirring time is 2.5-4 h.

[0026] In the technical scheme, the method for obtaining the polyimide solution comprises the following steps: mixing a reaction solvent, an A substance and a B substance under the condition of nitrogen or inert gas atmosphere and stirring, stirring at 25-30 DEG C for 6-10 hours, stopping the nitrogen or inert gas, adding azeotrope agent and stirring at 110-160 DEG C to remove water produced in the reaction, and obtaining the polyimide solution, wherein the ratio of the reaction solvent and the A substance is (450-650) : (40-60) by mass fraction, and the ratio of the A substance and the B substance is 1:1 by substance amount fraction.

[0027] In the technical scheme, the reaction solvent is added twice, and the reaction solvent added twice is a second solvent and a third solvent, and the ratio of the second solvent and the third solvent is (150-200) : (300-450) by mass fraction.

[0028] In the technical scheme, the method for obtaining the polyimide solution comprises the following steps:

[0029] Step 1, under the condition of stirring, a second solvent is added into a three-necked flask, nitrogen or inert gas is introduced, an A substance is added, a B substance is added in 3-6 times, a third solvent is added, and stirring is continued at 25-30 DEG C for 6-10 hours, and the nitrogen or inert gas is stopped.

[0030] Step 2, azeotrope agent is added into the three-necked flask, the three-necked flask is heated to 110-160 DEG C under the condition of oil bath, and stirring is continued at the temperature to remove water produced in the reaction until no water vapor is generated, and then stirring is continued at room temperature for 3-4 hours, and the solution in the three-necked flask is taken out as the polyimide solution.

[0031] In the technical scheme, the azeotrope agent is toluene.

[0032] In the technical scheme, the reaction solvent is a mixture of one or more of N-methyl pyrrolidone (NMP), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAC).

[0033] Application of polyimide containing trifluoromethyl and perfluorosulfonic acid resin in synergistically improving mechanical property and / or hydrolysis stability of proton exchange membrane.

[0034] Application of polyimide containing trifluoromethyl and perfluorosulfonic acid resin in synergistically improving proton conductivity of proton exchange membrane.

[0035] Compared with the prior art, the polyimide solution preparation method has the following beneficial effects:

[0036] The prior art PFSA separator has poor mechanical properties, and the present application has excellent mechanical properties (tensile strength) and good chemical stability by compounding perfluorosulfonic acid and polyimide containing trifluoromethyl groups; meanwhile, by introducing trifluoromethyl groups, the free volume is increased to provide a space for proton exchange to enhance the proton conductivity. When preparing the polyimide porous membrane, the present application also performs phase inversion by soaking in a coagulation bath to make the polyimide porous membrane have more pores, further improving the performance of the proton exchange membrane. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 SEM image of the polyimide porous membrane prepared in Example 3;

[0038] Figure 2 SEM image of the polyimide membrane prepared in Comparative Example 2;

[0039] Figure 3 SEM image of the proton exchange membrane prepared in Example 3;

[0040] Figure 4 Mechanical property test physical image of the proton exchange membrane prepared in Comparative Example 3;

[0041] Figure 5 Reaction formula for synthesizing polyimide containing trifluoromethyl groups. DETAILED DESCRIPTION

[0042] The technical solutions of the present application will be further described below in combination with specific embodiments.

[0043] The purchase sources of the medicines involved in the following examples and comparative examples are as follows:

[0044] Perfluorosulfonic acid resin (powder), purity 98%;

[0045] N-methyl pyrrolidone (NMP), purity 99.5%;

[0046] Hexafluorodiphthalic anhydride, purity 99%;

[0047] 4,4-diamino diphenyl ether, purity 99%;

[0048] Toluene, purity 99%.

[0049] The model and manufacturer of the equipment involved in the following examples and comparative examples are as follows:

[0050] Scanning electron microscope, Sigma 300, Carl Zeiss Company, Germany;

[0051] Universal tensile testing machine, AGS-X (100N), Shimadzu Corporation, Japan;

[0052] Electrochemical workstation, CHI660E, Demei Instruments Technology Co., Ltd.

[0053] High temperature reactor, JHT-205KJ-C, Weihai Chaoyang Chemical Machinery Co., Ltd.

[0054] The test methods in the following examples are as follows:

[0055] Hydrolytic stability value: the film with a mass of W0(g) dried in advance was immersed in deionized water at 80℃ for 48h, the film after immersion was taken out and dried at 80℃ for 8h, and the mass of the film was tested as W t (g). The hydrolytic stability value of the film W c was calculated by the following formula:

[0056]

[0057] Water absorption rate (the water absorption rate is preferably in the range of 10-30%): the film was dried in an oven at 80℃±2℃ for 24h, taken out and air-dried to room temperature, the mass of the film was measured as m0(g), then the film was immersed in distilled water at 80℃ for 8h, the water on the surface of the film was removed with filter paper, and the mass of the film was measured as m1(g) within 30 seconds, and the water absorption rate Δm value was calculated by the following formula:

[0058]

[0059] The film was made into a rectangular sample with a length of 65mm and a width of 15mm, and a Japanese Shimadzu tensile tester was used to test the mechanical properties and elongation at break, with a tensile speed of 5mm / min and an original gauge length of 20mm:

[0060] The mechanical properties (tensile strength) were calculated by the following formula:

[0061] σ1=p / (b×d), wherein σ1 is the tensile strength (MPa), p is the maximum load (N), b is the width of the rectangular sample (mm), and d is the thickness of the rectangular sample (mm), and the thickness was measured by a thickness gauge.

[0062] The elongation at break was calculated by the following formula:

[0063] wherein e is the elongation at break, l0 is the length of the rectangular sample, and l a is the length of the rectangular sample at break.

[0064] Proton conductivity: tested at a temperature of 60℃ and a humidity of 100% RH.

[0065] The free volume fraction (%) is calculated according to Yang Lei. Research on Free Volume Regulation and Dielectric Properties of Polar Polymer and Its Composite Membrane [D]. China University of Geosciences, 2023. DOI: 10.27492 / d.cnki.gzdzu.2023.000215.

[0066] Embodiments 1-8

[0067] A polyimide and perfluorosulfonic acid composite proton exchange membrane has a layered structure, and the layered structure is sequentially from top to bottom: a first perfluorosulfonic acid layer, a polyimide porous membrane, and a second perfluorosulfonic acid layer. The first perfluorosulfonic acid layer comprises a perfluorosulfonic acid resin. The polyimide porous membrane comprises a trifluoromethyl-containing polyimide. The second perfluorosulfonic acid layer comprises a perfluorosulfonic acid resin. The ratio of the perfluorosulfonic acid resin in the first perfluorosulfonic acid layer, the trifluoromethyl-containing polyimide in the polyimide porous membrane, and the perfluorosulfonic acid resin in the second perfluorosulfonic acid layer is Z in terms of mass fraction. The thicknesses of the first perfluorosulfonic acid layer and the second perfluorosulfonic acid layer are the same, and are X μm. The thickness of the polyimide porous membrane is Y μm.

[0068] A method for preparing a polyimide porous membrane comprises: casting a polyimide solution on a substrate (a 20 cm x 20 cm glass plate), immersing in a coagulation bath at 25°C for 5 min to perform phase inversion, and drying at 80°C for 12 h to obtain a polyimide porous membrane. The coagulation bath is deionized water. The polyimide solution comprises a trifluoromethyl-containing polyimide, a second solvent, and a third solvent. The content of the trifluoromethyl-containing polyimide in the polyimide solution is 12 wt%.

[0069] A method for preparing the above-mentioned polyimide and perfluorosulfonic acid composite proton exchange membrane comprises: casting a perfluorosulfonic acid solution for forming a first perfluorosulfonic acid layer on a substrate (a 20 cm x 20 cm glass plate), placing a polyimide porous membrane on the liquid surface of the perfluorosulfonic acid solution (so that the lower surface of the polyimide porous membrane is in contact with the perfluorosulfonic acid solution), first heating (at 80°C for 3 h), casting a perfluorosulfonic acid solution for forming a second perfluorosulfonic acid layer on the upper surface of the polyimide porous membrane, second heating (first heating at 80°C for 8 h, and then heating at 120°C for 1.5 h), obtaining the first perfluorosulfonic acid layer on the lower surface of the polyimide porous membrane and the second perfluorosulfonic acid layer on the upper surface of the polyimide porous membrane, and post-treatment to obtain the polyimide and perfluorosulfonic acid composite proton exchange membrane. The perfluorosulfonic acid solution for forming the first perfluorosulfonic acid layer and the perfluorosulfonic acid solution for forming the second perfluorosulfonic acid layer are the same.

[0070] The perfluorosulfonic acid solution comprises perfluorosulfonic acid resin (PFSA) and a first solvent, the first solvent is N-methyl pyrrolidone (NMP), the ratio of the perfluorosulfonic acid resin (PFSA) and the first solvent is 5:95 by mass fraction, and the method for obtaining the perfluorosulfonic acid solution (the perfluorosulfonic acid solution used in examples 1-8 is the same) comprises mixing the perfluorosulfonic acid resin (PFSA) and the first solvent, stirring at a high temperature of 150℃ in a reaction kettle at a speed of 500r / min for 4h to be uniform, and obtaining the perfluorosulfonic acid solution.

[0071] The post-treatment comprises soaking in sulfuric acid at 60℃ for 2h, taking out, soaking in hydrogen peroxide at 60℃ for 2h, taking out, washing with water for 3 times, finally soaking in water at 60℃ for 2h, taking out, and drying (first drying at 80℃ for 12h, and then drying at 115℃ for 1.5h), the concentration of the sulfuric acid is 1mol / L, and the concentration of the hydrogen peroxide is 3wt%.

[0072] The trifluoromethyl-containing polyimide is synthesized in the process of preparing the polyimide solution (the trifluoromethyl-containing polyimide is obtained by polymerization of A substance and B substance), as shown in Figure 5 The method for obtaining the polyimide solution (the polyimide solution used in examples 1-8 is the same) specifically comprises the following steps:

[0073] Step 1, under stirring, a second solvent is added to a three-necked flask, nitrogen is introduced, A substance is added, B substance is slowly added in four times, a third solvent is added, stirring is continued at 25℃ for 8h, and the introduction of nitrogen is stopped, wherein, the ratio of the second solvent, A substance and the third solvent is 150:50.354:370 by mass fraction, the ratio of A substance and B substance is 1:1 by amount fraction, and the second solvent and the third solvent are the same (both are N-methyl pyrrolidone (NMP)); A substance is hexafluorodiphthalic anhydride (6FDA) (hexafluorodiphthalic anhydride contains trifluoromethyl), and B substance is 4,4-diaminodiphenyl ether (ODA).

[0074] Step 2, azeotrope is added to the three-necked flask, the three-necked flask is heated to 118℃ under oil bath and stirring at the temperature to remove water produced in the reaction until no water is evaporated (the mixed liquid (azeotrope and water) evaporated is collected by a water trap, and when the mixed liquid in the water trap is clear, it is judged that no water is evaporated), stirring is continued at room temperature for 3h, the solution in the three-necked flask is taken out as the polyimide solution, and the azeotrope is toluene.

[0075] The values of X, Y and Z are shown in Table 1, and the polyimide and perfluorosulfonic acid composite proton exchange membranes of examples 1-8 are obtained by changing the values of X and Y.

[0076] Table 1

[0077]

[0078] SEM of the polyimide porous membrane prepared in Example 3 is shown in FIG. 2. Figure 1 SEM of the proton exchange membrane prepared in Example 3 is shown in FIG. 3. Figure 3 SEM of the proton exchange membrane prepared in Example 3 is shown in FIG. 3.

[0079] Comparative Example 1

[0080] A method for preparing a pure PFSA separator includes: casting the perfluorosulfonic acid solution prepared in Example 1 on a 20 cm x 20 cm glass plate, drying at 80°C for 10 h, then drying at 120°C for 1.5 h, post-processing (immersing in 1 mol / L sulfuric acid at 60°C for 2 h, taking out, immersing in hydrogen peroxide (concentration of 3 wt%) at 60°C for 2 h, taking out, washing with deionized water for 3 times, immersing in deionized water at 60°C for 2 h, taking out, drying at 80°C for 12 h first, then drying at 115°C for 1.5 h), to obtain a pure PFSA separator.

[0081] Comparative Example 2

[0082] A method for preparing a polyimide membrane includes: casting the polyimide solution prepared in Example 1 on a substrate (a 20 cm x 20 cm glass plate), drying at 80°C for 12 h, to obtain a polyimide membrane with a thickness of 16.4 μm. That is, Comparative Example 2 is not immersed in a coagulation bath at 25°C.

[0083] SEM of the polyimide membrane prepared in Comparative Example 2 is shown in FIG. 4. Figure 2 SEM of the polyimide membrane prepared in Comparative Example 2 is shown in FIG. 4.

[0084] Comparative Example 3

[0085] A method for preparing a polyimide and perfluorosulfonic acid composite proton exchange membrane is basically the same as that in Example 1, except that the thicknesses of the first perfluorosulfonic acid layer in Comparative Example 3 and the second perfluorosulfonic acid layer in Comparative Example 3 are different.

[0086] The thickness of the first perfluorosulfonic acid layer in Comparative Example 3 is 17.5 μm, and the thickness of the second perfluorosulfonic acid layer is 35 μm. In Comparative Example 3, the ratio of the perfluorosulfonic acid resin in the first perfluorosulfonic acid layer, the polyimide containing trifluoromethyl in the polyimide porous membrane, and the perfluorosulfonic acid resin in the second perfluorosulfonic acid layer is 4:5:6 by mass fraction.

[0087] Comparative Example 4

[0088] A method for preparing a polyimide and perfluorosulfonic acid composite proton exchange membrane is basically the same as that in Example 1, except that "hexafluorodiphthalic dianhydride (6FDA)" is replaced by "bisphenol A diether dianhydride (BPADA)". Bisphenol A diether dianhydride (BPADA) does not contain trifluoromethyl.

[0089] The polyimide and perfluorosulfonic acid composite proton exchange membrane prepared in Comparative Example 4 has a layered structure, and the layered structure from top to bottom is: a first perfluorosulfonic acid layer, a polyimide porous membrane, and a second perfluorosulfonic acid layer,

[0090] The first perfluorosulfonic acid layer comprises a perfluorosulfonic acid resin, the polyimide porous membrane comprises a polyimide, and the second perfluorosulfonic acid layer comprises a perfluorosulfonic acid resin,

[0091] The ratio of the perfluorosulfonic acid resin in the first perfluorosulfonic acid layer, the polyimide in the polyimide porous membrane, and the perfluorosulfonic acid resin in the second perfluorosulfonic acid layer is 4:5:4 by mass fraction, the thicknesses of the first perfluorosulfonic acid layer and the second perfluorosulfonic acid layer are the same, and are both 17.5 μm, and the thickness of the polyimide porous membrane is 12.3 μm.

[0092] The polyimide and perfluorosulfonic acid composite proton exchange membranes prepared in Examples 1-8, the pure PFSA diaphragm prepared in Comparative Example 1, the polyimide membrane prepared in Comparative Example 2, and the polyimide and perfluorosulfonic acid composite proton exchange membranes prepared in Comparative Examples 3 and 4 were subjected to performance testing, and the results are shown in Table 2.

[0093] Table 2

[0094]

[0095]

[0096] As can be seen from Table 2, the polyimide and perfluorosulfonic acid composite proton exchange membranes prepared in Examples 1-8 have a great improvement in tensile strength compared with Comparative Example 1, which shows that the polyimide can well enhance the mechanical properties of the diaphragm. At the same time, the proton conductivity is also improved to different degrees compared with Comparative Example 1, which shows that the introduction of the polyimide containing trifluoromethyl can effectively improve the transmission rate of protons. As can be seen from Examples 1-8 and Comparative Example 2, the membrane prepared by using the porous polyimide as the skeleton has a higher tensile strength than the membrane prepared by using the simple non-porous polyimide as the skeleton, and is also more conducive to improving the proton conductivity.

[0097] Comparing Example 2 with Comparative Example 3, it can be seen that the polyimide and perfluorosulfonic acid composite proton exchange membrane prepared in Example 2 has better mechanical properties and proton conductivity compared with Comparative Example 3, and at the same time, the thickness of the first perfluorosulfonic acid layer and the second perfluorosulfonic acid layer is the same, which is 17.5 μm, and the thickness of the polyimide porous membrane is 12.3 μm. Figure 4 It can be seen that the polyimide and perfluorosulfonic acid composite proton exchange membrane prepared in Comparative Example 3 will have a fracture and delamination during stretching, while the polyimide and perfluorosulfonic acid composite proton exchange membranes prepared in Examples 1-8 do not have this situation. This shows that the polyimide and perfluorosulfonic acid composite proton exchange membrane has better tensile properties when the thicknesses of the first perfluorosulfonic acid layer and the second perfluorosulfonic acid layer are the same.

[0098] Comparative Example 4 uses a polyimide without trifluoromethyl group as the backbone of the proton exchange membrane. By comparing Example 1 and Comparative Example 4, it can be seen that the introduction of trifluoromethyl group leads to a certain degree of decline in the free volume fraction of the polyimide and the perfluorosulfonic acid composite proton exchange membrane prepared in Comparative Example 4, and the proton conductivity is also lower.

[0099] It is well known that there are two proton conduction mechanisms in proton exchange membranes: Grotthuss mechanism (proton hopping) and Vehicle mechanism (vehicle matrix). Regardless of which mechanism, the movement of H + and H3O + requires space. In polymers, its volume is mainly composed of two parts: one part is the volume occupied by the molecule itself, and the other part is the irregular gap between the molecular chains, i.e. free volume. Therefore, for H + and H3O + , their activities are mainly carried out in the free volume, so increasing the free volume of the proton exchange membrane can effectively improve the proton exchange rate of the membrane, which is also conducive to the improvement of the overall performance of the hydrogen fuel cell. Therefore, the use of polyimides with trifluoromethyl groups can create more movement space for protons by increasing the free volume of the proton exchange membrane, which is conducive to the improvement of proton conductivity and can further improve the performance of the battery.

[0100] The above has exemplarily described the present application, it should be explained that, in the case of not departing from the core of the present application, any simple transformation, modification or other equivalent replacement which can not spend the creative labor of the person skilled in the art falls into the protection scope of the present application.

Claims

1. A polyimide and perfluorosulfonic acid composite proton exchange membrane, characterized in that: The polyimide and perfluorosulfonic acid composite proton exchange membrane is a layered structure, and the layered structure comprises, from top to bottom, a first perfluorosulfonic acid layer, a polyimide porous membrane, and a second perfluorosulfonic acid layer; The first perfluorosulfonic acid layer comprises a perfluorosulfonic acid resin, the polyimide porous membrane comprises a trifluoromethyl-containing polyimide, and the second perfluorosulfonic acid layer comprises a perfluorosulfonic acid resin, wherein the ratio of the perfluorosulfonic acid resin in the first perfluorosulfonic acid layer, the trifluoromethyl-containing polyimide in the polyimide porous membrane, and the perfluorosulfonic acid resin in the second perfluorosulfonic acid layer is (4-7):(3-7):(4-7) by weight. Trifluoromethyl-containing polyimide is polymerized from the following monomers:

2. The polyimide and perfluorosulfonic acid composite proton exchange membrane according to claim 1, characterized in that: The method for preparing a polyimide porous membrane comprises: casting a polyimide solution on a substrate, soaking it in a coagulation bath at 25-30°C, and drying it to obtain the polyimide porous membrane, wherein the coagulation bath comprises water and / or N-methylpyrrolidone, and the polyimide solution comprises trifluoromethyl-containing polyimide.

3. The polyimide and perfluorosulfonic acid composite proton exchange membrane according to claim 1, characterized in that: The thickness of the first perfluorosulfonic acid layer is 17 to 60 μm, the thickness of the polyimide porous membrane is 10 to 20 μm, and the thickness of the second perfluorosulfonic acid layer is 17 to 60 μm.

4. The polyimide and perfluorosulfonic acid composite proton exchange membrane according to claim 2, characterized in that: The content of trifluoromethyl-containing polyimide in the polyimide solution is 10-15 wt %.

5. The polyimide and perfluorosulfonic acid composite proton exchange membrane according to claim 2, characterized in that: The immersion time in the coagulation bath is 3 to 5 minutes.

6. The polyimide and perfluorosulfonic acid composite proton exchange membrane according to claim 2, characterized in that: The raw materials for preparing trifluoromethyl-containing polyimide include: substance A and substance B, wherein substance A is one of hexafluorodianhydride, 9,9-bis(trifluoromethyl)-2,3,6,7-anthracenetetracarboxylic dianhydride and bisphenol A diether dianhydride, and substance B is one of 4,4-diaminodiphenyl ether, 4,4'-diaminobenzanilide, 2-(4-aminophenyl)-5-aminobenzimidazole and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, and at least one of substance A and substance B contains a trifluoromethyl group.

7. A method for preparing a polyimide and perfluorosulfonic acid composite proton exchange membrane, characterized in that: include: A perfluorosulfonic acid solution for forming a first perfluorosulfonic acid layer is cast on a substrate, a polyimide porous membrane is placed on the liquid surface of the perfluorosulfonic acid solution, and the membrane is heated for the first time. Then, a perfluorosulfonic acid solution for forming a second perfluorosulfonic acid layer is cast on the upper surface of the polyimide porous membrane, and the membrane is heated for the second time to obtain the first perfluorosulfonic acid layer on the lower surface of the polyimide porous membrane and the second perfluorosulfonic acid layer on the upper surface of the polyimide porous membrane. Post-treatment is performed to obtain a polyimide and perfluorosulfonic acid composite proton exchange membrane, wherein the perfluorosulfonic acid solution comprises: a perfluorosulfonic acid resin and a first solvent, and the ratio of the perfluorosulfonic acid resin to the first solvent is (3-10): (90-105) by mass. The post-treatment comprises: soaking in sulfuric acid, hydrogen peroxide, and water in sequence.

8. Application of trifluoromethyl-containing polyimide and perfluorosulfonic acid resin to synergistically improve the mechanical properties of proton exchange membranes.

9. Application of trifluoromethyl-containing polyimide and perfluorosulfonic acid resin to synergistically improve the proton conductivity of proton exchange membranes.

10. Application of trifluoromethyl-containing polyimide and perfluorosulfonic acid resin to synergistically improve the hydrolysis stability of proton exchange membranes.

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