PPTA-modified perfluorosulfonic acid proton exchange membrane and its preparation method

Abstract

This invention discloses a PPTA-modified perfluorosulfonic acid proton exchange membrane and its preparation method. The PPTA-modified perfluorosulfonic acid proton exchange membrane has a layered structure, with the middle layer being a mixture of perfluorosulfonic acid polymer and PPTA. The preparation method of the perfluorosulfonic acid polymer and PPTA mixture includes: mixing a pore-forming agent, PPTA resin, and concentrated sulfuric acid, stirring until the pore-forming agent and PPTA resin are uniformly dispersed in the concentrated sulfuric acid, and then vacuum degassing to obtain a PPTA porous casting solution; coating the PPTA porous casting solution onto a substrate, immersing it in pure water, and after solidification, peeling it off from the substrate, and then immersing it in ultrafiltration water to obtain a PPTA porous membrane; immersing the PPTA porous membrane in the perfluorosulfonic acid casting solution, and then drying it to obtain the perfluorosulfonic acid polymer and PPTA mixture layer. The perfluorosulfonic acid polymer and PPTA mixture layer can improve the thermal stability, mechanical strength, and swelling resistance of the membrane, and also has the advantage of reducing methanol permeability. It also increases the proton conductivity of the composite membrane.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a PPTA-modified perfluorosulfonic acid proton exchange membrane and its preparation method. Background Technology

[0002] With the increasing severity of environmental pollution and the energy crisis, green and renewable energy has become an urgent need for society. Proton exchange membrane fuel cells (PEMFCs), as a highly efficient and environmentally friendly energy device, are highly anticipated and have a very broad application prospect. As a current research hotspot, PEMFCs do not involve the combustion of hydrogen and oxygen during power generation, thus avoiding the limitations of the Carnot cycle and exhibiting a high energy conversion rate. Among them, the direct methanol fuel cell, often referred to as the sixth generation of fuel cells, has attracted significant attention from industry and academia. The proton exchange membrane is one of its core components and should possess high proton conductivity, mechanical properties, and resistance to swelling. Currently used perfluorosulfonic acid proton exchange membranes (Nafion) have excellent electrochemical performance, acceptable mechanical strength, and good oxidative stability, but they have poor methanol fuel rejection, high fuel permeability, and significant water swelling. They are also prone to degradation at high temperatures, have low proton conductivity under low humidity conditions, and are expensive, thus failing to fully realize the performance advantages of direct methanol fuel cells. Therefore, increasing research is focused on the development of fluorinated or non-fluorinated proton exchange membranes.

[0003] CN106159301A discloses a method for preparing a perfluorosulfonic acid proton exchange membrane. This invention provides an electrophoretic method for preparing the perfluorosulfonic acid proton exchange membrane. This method is simple, easy to operate, has a short preparation time, and is easy to industrialize. However, this invention fails to improve the mechanical stability of the perfluorosulfonic acid proton exchange membrane. CN104558649A discloses a PVDF-modified perfluorosulfonic acid proton exchange membrane and its preparation method. This invention uniformly composites PVDF into the perfluorosulfonic acid proton exchange membrane through ammonia crosslinking. The resulting PVDF-modified perfluorosulfonic acid proton exchange membrane effectively improves the mechanical stability and dimensional stability of the composite proton exchange membrane and reduces methanol permeability. However, this invention does not significantly improve the proton conductivity, limiting the practical application of this composite proton exchange membrane. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a PPTA-modified perfluorosulfonic acid proton exchange membrane. This method involves compositing perfluorosulfonic acid and a PPTA porous membrane to obtain a mixed layer of perfluorosulfonic acid polymer and PPTA, thereby improving the mechanical strength and swelling resistance of the membrane and reducing methanol permeability. Furthermore, coating the upper and lower sides of the mixed layer with perfluorosulfonic acid casting solution can increase the proton conductivity of the composite membrane to a certain extent.

[0005] Another object of the present invention is to provide a PPTA-modified perfluorosulfonic acid proton exchange membrane. This invention is achieved through the following technical solution.

[0006] A method for preparing a mixed layer of perfluorosulfonic acid polymer and PPTA includes the following steps:

[0007] S1, mix the porogen, PPTA resin (poly(p-phenylene terephthalamide) resin) and concentrated sulfuric acid to obtain a first mixture. Stir the first mixture until the porogen and PPTA resin are uniformly dispersed in the concentrated sulfuric acid to obtain a second mixture. Degas the second mixture under vacuum to obtain a PPTA porous casting solution.

[0008] In S1, the porogen is PEG.

[0009] In S1, the stirring speed is 300-1000 r / min, and the stirring time is 1-5 h.

[0010] In S1, the stirring temperature is 50–100°C.

[0011] In S1, the ratio of the porogen to the PPTA resin by mass parts is (1-5):(1-6).

[0012] In S1, the concentration of the concentrated sulfuric acid is ≥97%.

[0013] In S1, the ratio of the mass fraction of the porogen to the volume fraction of concentrated sulfuric acid is (1-5):(10-25), where the mass fraction is in mg and the volume fraction is in mL.

[0014] S2, the PPTA porous casting solution is scraped onto the substrate, placed in pure water, and after solidification, it is peeled off from the substrate and then soaked in ultrafiltration water for 15-30 hours to obtain a PPTA porous membrane.

[0015] S3, immerse the PPTA porous membrane in a perfluorosulfonic acid casting solution, soak for 0.5 to 1.5 hours, and then dry it under vacuum to obtain a mixed layer of perfluorosulfonic acid polymer and PPTA, wherein the perfluorosulfonic acid casting solution is a solution formed by dissolving Nafion resin in a solvent.

[0016] In S3, the drying temperature is 60–120℃, and the drying time is 5–10 hours.

[0017] In S3, the concentration of Nafion resin in the perfluorosulfonic acid casting solution is 10–30 wt%.

[0018] In S3, Nafion resin is dissolved in the solvent by stirring at 60–120°C for 1–10 hours.

[0019] In S3, the Nafion resin is obtained by drying a Nafion solution at 80–100°C for 4–8 hours.

[0020] In S3, the solvent is one or more of N-methylpyrrolidone, N,N-dimethylformamide, tetrahydrofuran, acetone, and ethanol.

[0021] The above preparation method yields a mixed layer of perfluorosulfonic acid polymer and PPTA.

[0022] A PPTA-modified perfluorosulfonic acid proton exchange membrane has a layered structure, comprising an upper layer, a middle layer, and a lower layer, wherein the upper layer, middle layer, and lower layer are arranged sequentially from top to bottom.

[0023] The intermediate layer is a mixture of perfluorosulfonic acid polymer and PPTA;

[0024] Both the upper and lower layers are Nafion resin layers.

[0025] In the above technical solution, the thickness of the PPTA-modified perfluorosulfonic acid proton exchange membrane is 10–70 μm.

[0026] In the above technical solution, the thickness of the intermediate layer is 10-50 μm.

[0027] A method for preparing a PPTA-modified perfluorosulfonic acid proton exchange membrane includes: coating both sides of the intermediate layer with perfluorosulfonic acid casting solution to obtain a composite membrane, and drying the composite membrane after the perfluorosulfonic acid casting solution has fully impregnated it.

[0028] In the above technical solution, the perfluorosulfonic acid casting solution is fully immersed for 1-2 hours.

[0029] In the above technical solution, the condition for drying the composite film is to place it at a temperature of 60-120°C for 5-10 hours.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. This invention combines perfluorosulfonic acid casting solution and PPTA porous membrane. PPTA resin has excellent mechanical properties, heat resistance and dimensional stability. The perfluorosulfonic acid polymer and PPTA mixed layer can improve the thermal stability, mechanical strength and swelling resistance of the membrane, and also has the advantage of reducing methanol permeability.

[0032] 2. In this invention, perfluorosulfonic acid casting solution is coated on both the upper and lower sides of the perfluorosulfonic acid polymer and PPTA mixed layer, which can increase the proton conductivity of the composite membrane to a certain extent. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0034] The source of the ultrafiltration water was: self-made in the laboratory, and the equipment used was purchased from Qianjing Environmental Protection Equipment Co., Ltd., specifically the Q-20C ultrapure water machine.

[0035] Nafion resin is obtained by drying a commercially available 5 wt% Nafion solution, which was purchased from DuPont.

[0036] The test parameters and methods involved in this embodiment include:

[0037] Swelling rate in water: After drying the membrane, cut it into square pieces and measure the diagonal length D. d Then it was placed in deionized water and soaked at room temperature for 24 hours. After that, it was taken out and the diagonal length was tested again to obtain D. w The formula for calculating the swelling ratio ΔD of a proton exchange membrane in water is as follows:

[0038] ΔD=(D w -D d ) / D d ×100%

[0039] Tensile strength: The test was conducted using an electronic universal testing machine to measure the mechanical strength and tensile strain of the membrane material at a tensile speed of 10 mm / min. A computer-controlled monitoring system connected to the testing machine monitored the magnitude of the force and displacement of the membrane in real time. The test ended upon membrane rupture.

[0040] Proton conductivity: The wet film sample size was cut to 5×40mm. 2 The membrane was immersed in deionized water at room temperature, and its proton conductivity was measured using electrochemical impedance spectroscopy. An electrochemical workstation was used. The sample membrane was placed in a test fixture, which was positioned vertically. The membrane length needed to be greater than the two measuring electrodes in the fixture. The fixture was then connected to the workstation. The membrane fixture was placed in a water bath to measure the proton conductivity of the membrane at 60°C. The proton conductivity measurement frequency was 10⁻¹⁰. 5 Hz to 1Hz.

[0041] Thermal stability analysis: A thermogravimetric analyzer was used in this experiment to detect the thermal stability of the synthesized substances and the proton exchange membrane. The test environment was a nitrogen atmosphere, with a heating rate of 10℃ / min and a temperature range of 30-800℃.

[0042] Limiting current density: The amount of methanol permeation was measured using an electrochemical linear scan method. A potentiostat was used, with 0.2 MPa of high-purity nitrogen flowing through the cathode and a 1 mol / L methanol aqueous solution flowing at a rate of 1 mL / min at the anode. The working electrode was connected to the cathode, and the reference and counter electrodes were connected to the anode. The linear scan range was 0–0.85 V, and the scan rate was 2 mV / s. The limiting current density was used to characterize the amount of methanol permeated.

[0043] Example 1

[0044] A method for preparing a mixed layer of perfluorosulfonic acid polymer and PPTA includes the following steps:

[0045] S1, a porogen, PPTA resin (poly(p-phenylene terephthalamide) resin) and concentrated sulfuric acid are mixed to obtain a first mixture. The first mixture is stirred at 600 r / min for 4 h in a water bath at 80 °C until the porogen and PPTA resin are uniformly dispersed in the concentrated sulfuric acid to obtain a second mixture. The second mixture is then degassed under vacuum (vacuum degassed by removing gas from the second mixture using a vacuum method) to obtain a PPTA porous casting solution. The porogen is PEG, the ratio of porogen to PPTA resin by mass is 2:5, the concentration of concentrated sulfuric acid is 98%, and the ratio of the mass fraction of porogen to the volume fraction of concentrated sulfuric acid is 1:15. The mass fraction is expressed in mg and the volume fraction is expressed in mL.

[0046] S2, the PPTA porous casting solution is scraped onto the substrate, placed in pure water, and after solidification, it is peeled off from the substrate and then soaked in ultrafiltration water for 24 hours to obtain the PPTA porous membrane. The substrate is a glass plate.

[0047] S3, immerse the PPTA porous membrane in a perfluorosulfonic acid casting solution, soak for 1 hour, and then dry at 100°C for 5 hours under vacuum to obtain a 15 μm thick mixed layer of perfluorosulfonic acid polymer and PPTA. The perfluorosulfonic acid casting solution is a solution formed by dissolving Nafion resin in a solvent, which is N-methylpyrrolidone. The concentration of Nafion resin in the perfluorosulfonic acid casting solution is 25 wt%. The Nafion resin is dissolved in the solvent by stirring in a water bath at 100°C for 4 hours. The Nafion resin is obtained by drying a 5 wt% Nafion solution at 80°C for 5 hours.

[0048] A method for preparing a PPTA-modified perfluorosulfonic acid proton exchange membrane includes: coating both sides of a mixture of perfluorosulfonic acid polymer and PPTA using a casting method to obtain a composite membrane by coating with perfluorosulfonic acid casting solution; after the perfluorosulfonic acid casting solution has been immersed for 90 min, the composite membrane is dried in a suspension vacuum drying oven at 120°C for 8 h to obtain a perfluorosulfonic acid proton exchange membrane with a thickness of 51.2 μm.

[0049] Example 2

[0050] A method for preparing a mixed layer of perfluorosulfonic acid polymer and PPTA includes the following steps:

[0051] S1, a porogen, PPTA resin (poly(p-phenylene terephthalamide) resin) and concentrated sulfuric acid are mixed to obtain a first mixture. The first mixture is stirred at 600 r / min for 4 h in a water bath at 80 °C until the porogen and PPTA resin are uniformly dispersed in the concentrated sulfuric acid to obtain a second mixture. The second mixture is then degassed under vacuum (vacuum degassed by removing gas from the second mixture using a vacuum method) to obtain a PPTA porous casting solution. The porogen is PEG, the ratio of porogen to PPTA resin by mass is 3:4, the concentration of concentrated sulfuric acid is 98%, and the ratio of the mass fraction of porogen to the volume fraction of concentrated sulfuric acid is 1:15. The unit of mass fraction is mg, and the unit of volume fraction is mL.

[0052] S2, the PPTA porous casting solution is scraped onto the substrate, placed in pure water, and after solidification, it is peeled off from the substrate and then soaked in ultrafiltration water for 24 hours to obtain the PPTA porous membrane. The substrate is a glass plate.

[0053] S3, a PPTA porous membrane is immersed in a perfluorosulfonic acid casting solution and soaked for 1 hour. Then, it is dried at 100°C for 5 hours under vacuum to obtain a 14.4 μm thick mixed layer of perfluorosulfonic acid polymer and PPTA. The perfluorosulfonic acid casting solution is a solution formed by dissolving Nafion resin in a solvent, which is N-methylpyrrolidone. The concentration of Nafion resin in the perfluorosulfonic acid casting solution is 25 wt%. The Nafion resin is dissolved in the solvent by stirring in a water bath at 100°C for 4 hours. The Nafion resin is obtained by drying a 5 wt% Nafion solution at 80°C for 5 hours.

[0054] A method for preparing a PPTA-modified perfluorosulfonic acid proton exchange membrane includes: coating both sides of a mixture of perfluorosulfonic acid polymer and PPTA using a casting method to obtain a composite membrane by coating with perfluorosulfonic acid casting solution; after the perfluorosulfonic acid casting solution has been immersed for 90 min, the composite membrane is dried in a suspension vacuum drying oven at 120°C for 8 h to obtain a perfluorosulfonic acid proton exchange membrane with a thickness of 52.2 μm.

[0055] Example 3

[0056] A method for preparing a mixed layer of perfluorosulfonic acid polymer and PPTA includes the following steps:

[0057] S1, a porogen, PPTA resin (poly(p-phenylene terephthalamide) resin) and concentrated sulfuric acid are mixed to obtain a first mixture. The first mixture is stirred at 600 r / min for 4 h in a water bath at 80 °C until the porogen and PPTA resin are uniformly dispersed in the concentrated sulfuric acid to obtain a second mixture. The second mixture is then degassed under vacuum (vacuum degassed by removing gas from the second mixture using a vacuum method) to obtain a PPTA porous casting solution. The porogen is PEG, the ratio of porogen to PPTA resin by mass is 5:2, the concentration of concentrated sulfuric acid is 98%, and the ratio of the mass fraction of porogen to the volume fraction of concentrated sulfuric acid is 1:15. The unit of mass fraction is mg, and the unit of volume fraction is mL.

[0058] S2, the PPTA porous casting solution is scraped onto the substrate, placed in pure water, and after solidification, it is peeled off from the substrate and then soaked in ultrafiltration water for 24 hours to obtain the PPTA porous membrane. The substrate is a glass plate.

[0059] S3, immerse the PPTA porous membrane in a perfluorosulfonic acid casting solution, soak for 1 hour, and then dry at 100°C for 5 hours under vacuum to obtain a 14 μm thick mixed layer of perfluorosulfonic acid polymer and PPTA. The perfluorosulfonic acid casting solution is a solution formed by dissolving Nafion resin in a solvent, which is N-methylpyrrolidone. The concentration of Nafion resin in the perfluorosulfonic acid casting solution is 25 wt%. The Nafion resin is dissolved in the solvent by stirring in a water bath at 100°C for 4 hours. The Nafion resin is obtained by drying a 5 wt% Nafion solution at 80°C for 5 hours.

[0060] A method for preparing a PPTA-modified perfluorosulfonic acid proton exchange membrane includes: coating both sides of a mixture of perfluorosulfonic acid polymer and PPTA using a casting method to obtain a composite membrane by coating with perfluorosulfonic acid casting solution; after the perfluorosulfonic acid casting solution has been immersed for 90 min, the composite membrane is dried in a suspension vacuum drying oven at 120°C for 8 h to obtain a perfluorosulfonic acid proton exchange membrane with a thickness of 50.6 μm.

[0061] Comparative Example 1

[0062] A method for preparing a mixed layer of perfluorosulfonic acid polymer and PPTA includes the following steps:

[0063] S1, a porogen, PPTA resin (poly(p-phenylene terephthalamide) resin) and concentrated sulfuric acid are mixed to obtain a first mixture. The first mixture is stirred at 600 r / min for 4 h in a water bath at 80 °C until the porogen and PPTA resin are uniformly dispersed in the concentrated sulfuric acid to obtain a second mixture. The second mixture is then degassed under vacuum (vacuum degassed by removing gas from the second mixture using a vacuum method) to obtain a PPTA porous casting solution. The porogen is PEG, the ratio of porogen to PPTA resin by mass is 3:4, the concentration of concentrated sulfuric acid is 98%, and the ratio of the mass fraction of porogen to the volume fraction of concentrated sulfuric acid is 1:15. The unit of mass fraction is mg, and the unit of volume fraction is mL.

[0064] S2, the PPTA porous casting solution is scraped onto the substrate, placed in pure water, and after solidification, it is peeled off from the substrate and then soaked in ultrafiltration water for 24 hours to obtain the PPTA porous membrane. The substrate is a glass plate.

[0065] S3, a PPTA porous membrane is immersed in a perfluorosulfonic acid casting solution for 1 hour and then dried at 100°C for 5 hours under vacuum to obtain a 15.3 μm thick mixed layer of perfluorosulfonic acid polymer and PPTA. The perfluorosulfonic acid casting solution is a solution formed by dissolving Nafion resin in a solvent, which is N-methylpyrrolidone. The concentration of Nafion resin in the perfluorosulfonic acid casting solution is 25 wt%. The Nafion resin is dissolved in the solvent by stirring in a water bath at 100°C for 4 hours. The Nafion resin is obtained by drying a 5 wt% Nafion solution at 80°C for 5 hours.

[0066] The performance parameter test data of the perfluorosulfonic acid proton exchange membrane or the perfluorosulfonic acid polymer and PPTA mixed layer in the above embodiments and comparative examples are as follows:

[0067]

[0068] A comparison of the three examples shows that when the PPTA content is highest and the porogen PEG content is low, the proton conductivity is low, while the thermal decomposition temperature and tensile strength are high. The swelling ratio in water is also low, and the proton exchange membrane is less prone to deformation. The lowest limiting current density indicates the lowest methanol permeation and better battery performance. As the PPTA content in the composite membrane decreases and the porogen content increases, the swelling ratio and limiting current density in water increase, while the thermal decomposition temperature and tensile strength decrease, but the proton conductivity increases accordingly. Therefore, to consider the overall performance of the composite membrane, appropriate amounts of PPTA and porogen (PEG) need to be added.

[0069] Comparative analysis of Example 2 and Comparative Example 1 shows that, under the same parameter conditions, the proton conductivity is significantly reduced without the addition of the two Nafion resin layers of this invention. Therefore, this invention improves the thermal and mechanical stability of the proton exchange membrane and reduces methanol permeability while maintaining high proton conductivity.

Claims

1. A PPTA-modified perfluorosulfonic acid proton exchange membrane, characterized in that, It has a layered structure, including: an upper layer, a middle layer, and a lower layer, which are arranged sequentially from top to bottom. The intermediate layer is a mixture of perfluorosulfonic acid polymer and PPTA; Both the upper and lower layers are Nafion resin layers; The preparation method of the perfluorosulfonic acid polymer and PPTA mixed layer includes the following steps: S1, mix the porogen, PPTA resin and concentrated sulfuric acid to obtain a first mixture, stir the first mixture until the porogen and PPTA resin are uniformly dispersed in the concentrated sulfuric acid to obtain a second mixture, degas the second mixture under vacuum to obtain a PPTA porous casting solution; S2, the PPTA porous casting solution is scraped onto the substrate, placed in pure water, and after solidification, it is peeled off from the substrate and then soaked in ultrafiltration water for 15-30 hours to obtain a PPTA porous membrane. S3, immerse the PPTA porous membrane in a perfluorosulfonic acid casting solution, soak for 0.5~1.5h and then dry under vacuum to obtain a mixed layer of perfluorosulfonic acid polymer and PPTA, wherein the perfluorosulfonic acid casting solution is a solution formed by dissolving Nafion resin in a solvent.

2. The PPTA-modified perfluorosulfonic acid proton exchange membrane according to claim 1, characterized in that, In S1, the porogen is PEG.

3. The PPTA-modified perfluorosulfonic acid proton exchange membrane according to claim 1, characterized in that, In S1, the ratio of the pore-forming agent to the PPTA resin by mass parts is (1~5):(1~6).

4. The PPTA-modified perfluorosulfonic acid proton exchange membrane according to claim 1, characterized in that, In S1, the ratio of the mass fraction of the pore-forming agent to the volume fraction of concentrated sulfuric acid is (1~5):(10~25), the mass fraction is in mg, the volume fraction is in mL, and the concentration of the concentrated sulfuric acid is ≥97wt%.

5. The PPTA-modified perfluorosulfonic acid proton exchange membrane according to claim 1, characterized in that, In S3, the solvent is one or more of N-methylpyrrolidone, N,N-dimethylformamide, tetrahydrofuran, acetone, and ethanol.

6. The PPTA-modified perfluorosulfonic acid proton exchange membrane according to claim 1, characterized in that, In S3, Nafion resin is dissolved in the solvent by stirring at 60~120℃ for 1~10h.

7. The PPTA-modified perfluorosulfonic acid proton exchange membrane according to claim 1, characterized in that, In S3, the concentration of Nafion resin in the perfluorosulfonic acid casting solution is 10~30wt%.

8. The PPTA-modified perfluorosulfonic acid proton exchange membrane according to claim 1, characterized in that, In S3, the Nafion resin is obtained by drying a Nafion solution at 80-100°C for 4-8 hours.

9. The PPTA-modified perfluorosulfonic acid proton exchange membrane according to claim 1, characterized in that, In S3, the drying temperature is 60~120℃ and the drying time is 5~10h.

10. The PPTA-modified perfluorosulfonic acid proton exchange membrane according to claim 1, characterized in that, In S1, the stirring speed is 300~1000 r / min, the stirring time is 1~5 h, and the stirring temperature is 50~100℃.

11. The PPTA-modified perfluorosulfonic acid proton exchange membrane according to claim 1, characterized in that, The thickness of the PPTA-modified perfluorosulfonic acid proton exchange membrane is 10~70μm; The thickness of the intermediate layer is 10~50μm.

12. The method for preparing the PPTA-modified perfluorosulfonic acid proton exchange membrane according to any one of claims 1 to 11, characterized in that, include: A composite film is obtained by coating both sides of the intermediate layer with perfluorosulfonic acid casting solution. After the perfluorosulfonic acid casting solution has fully impregnated the composite film, it is dried.

13. The preparation method according to claim 12, characterized in that, The perfluorosulfonic acid casting solution should be fully immersed for 1-2 hours.

14. The preparation method according to claim 12, characterized in that, The composite film is dried at 60-120°C for 5-10 hours.

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