Fuel cell proton exchange membrane and preparation method thereof

Abstract

The invention relates to a fuel cell proton exchange membrane and a preparation method thereof, and the preparation method comprises the following steps: uniformly mixing a neutral Nafion solution and organic alcohol, and carrying out heat preservation treatment at 200-240 DEG C to obtain a resin solution; coating a first layer of resin solution on a substrate, covering the porous membrane on the first layer of resin solution, pre-drying, then coating a second layer of resin solution on the porous membrane, and pre-drying to obtain a composite membrane; and performing drying, heat treatment and post-treatment on the composite membrane to obtain the fuel cell proton exchange membrane. According to the invention, the organic alcohol is added into the neutral Nafion solution, and the resin solution meeting the requirements of the subsequent process can be obtained at one time through heat preservation treatment; the composite film is prepared by coating, so that the defect that bubbles are easily generated by negative-pressure impregnation is avoided; the proton exchange membrane is simple in preparation steps, low in cost and high in efficiency; the obtained proton exchange membrane is good in conductivity performance and excellent in mechanical performance.

Description

Technical Field

[0001] This invention relates to the field of fuel cell proton exchange membrane preparation technology, specifically to a fuel cell proton exchange membrane and its preparation method. Background Technology

[0002] Proton exchange membrane (PEM) is a key material used in devices such as fuel cells and water electrolysis. Especially in the field of fuel cells, PEM, as the core material of fuel cells, directly affects the performance and lifespan of the cell. Its main functions include the following: (1) Proton conduction: In the hydrated state, sulfonic acid groups release protons, which migrate within the membrane to form an electric current; (2) Electron barrier: Prevents electrons from passing directly through the membrane, ensuring that the current passes through the external circuit; (3) Gas barrier: Blocks hydrogen and oxygen, preventing direct reaction and improving efficiency; (4) Mechanical support: Provides structural support for the cell and maintains the separation between the electrodes. Due to the above functions of PEM, it must have high proton conductivity, good thermal and chemical stability, and low gas permeability; at the same time, it must have sufficiently high mechanical and structural strength, as well as the ability of the membrane surface to bond with the catalyst.

[0003] Due to the need for high mechanical strength, composite proton exchange membranes are generally used in the market instead of traditional single-component perfluorosulfonic acid membranes. This involves adding an ePTFE support layer in the middle of the resin to stabilize the resin structure, reduce swelling, and increase mechanical strength. This significantly reduces the thickness of the proton exchange membrane. However, during preparation, the filling rate of the proton exchange membrane needs to be carefully monitored to ensure that the resin is completely immersed in the porous ePTFE structure, thereby obtaining better electrochemical performance. Traditional pilot production, especially small-batch production, generally uses a negative pressure impregnation method, increasing the resin filling rate through a vacuum environment. However, this requires a vacuum environment, and the resulting proton exchange membrane is prone to bubble formation, necessitating the addition of surfactants for control. This results in relatively harsh and complex preparation conditions and high costs. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a proton exchange membrane for fuel cells and its preparation method, thereby solving the technical problems of complex conditions and easy bubble generation in the preparation of proton exchange membranes by negative pressure impregnation method in the prior art.

[0005] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows: In a first aspect, the present invention provides a method for preparing a proton exchange membrane for a fuel cell, comprising the following steps: S1, mixing a neutral Nafion solution and an organic alcohol uniformly to obtain a mixture, and heat-treating the mixture at 200-240°C to obtain a resin solution; S2, coating a first layer of resin solution onto a substrate, covering the first layer of resin solution with a porous membrane, pre-drying, and then coating a second layer of resin solution onto the porous membrane, and pre-drying to obtain a composite membrane; S3, subjecting the composite membrane to drying, heat treatment, and post-treatment to obtain a proton exchange membrane for a fuel cell.

[0006] Secondly, the present invention provides a proton exchange membrane for a fuel cell prepared by the above-described preparation method.

[0007] Compared with the prior art, the beneficial effects of the present invention include: This invention involves adding an organic alcohol to a neutral Nafion solution and then heat-treating it to obtain a resin solution that meets the requirements of subsequent processes in one step, reducing the need for adding surfactants and other steps required by conventional methods such as negative pressure impregnation. A composite membrane is then prepared by coating, avoiding the bubble-generating defects of negative pressure impregnation. Finally, a proton exchange membrane is obtained through heat treatment and post-treatment. The preparation steps are simple, low-cost, and highly efficient. The resulting proton exchange membrane exhibits good electrical conductivity, excellent mechanical properties, and a tensile strength exceeding 40 MPa. Attached Figure Description

[0008] Figure 1 This is a schematic flowchart of the preparation method of the proton exchange membrane of the present invention; Figure 2 This is a comparison chart of the membrane electrode performance prepared by the proton exchange membrane obtained in Example 1 of the present invention and the commercial proton exchange membrane in Comparative Example 2. Figure 3 This is a physical image of the proton exchange membrane obtained in Comparative Example 3; Figure 4 This is a physical image of the proton exchange membrane obtained in Embodiment 1 of the present invention; Figure 5 This is a surface SEM image of the proton exchange membrane obtained in Example 1 of the present invention; Figure 6 This is a cross-sectional SEM image of the proton exchange membrane obtained in Example 1 of the present invention. Detailed Implementation

[0009] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0010] To address the shortcomings of current methods for preparing proton exchange membranes using negative pressure impregnation, which involve complex conditions, bubble generation, and the need for surfactants, this invention provides a fuel cell proton exchange membrane and its preparation method. This method is a coating process under ambient temperature and pressure, which greatly simplifies the preparation steps of the proton exchange membrane. The resulting proton exchange membrane is uniform and bubble-free, making it particularly suitable for small-batch trial production and providing a new process for the production of proton exchange membranes.

[0011] In a first aspect, the present invention provides a method for preparing a proton exchange membrane for a fuel cell, comprising the following steps: S1, a neutral Nafion solution and an organic alcohol are mixed evenly to obtain a mixture. The mixture is then subjected to heat and pressure treatment at 200-240℃ and 10-20MPa to obtain a resin solution. S2, a first layer of resin solution is coated on the substrate, a porous membrane is covered on the first layer of resin solution, and after pre-drying, a second layer of resin solution is coated on the porous membrane and pre-dried to obtain a composite membrane. S3, the composite membrane is dried, heat-treated and post-treated to obtain the proton exchange membrane for the fuel cell.

[0012] This invention involves adding an organic alcohol to a neutral Nafion (perfluorosulfonic acid) solution and mixing it thoroughly under high temperature and high pressure. This allows for the preparation of a resin solution that meets the requirements of subsequent processes in a single step, reducing the need for steps such as adding surfactants required by conventional negative pressure impregnation methods. A composite membrane is prepared by coating a porous membrane as a reinforcement, followed by heat treatment and post-treatment to obtain a proton exchange membrane. This invention features simple preparation steps, low cost, and high efficiency. The resulting proton exchange membrane exhibits good electrical conductivity, excellent mechanical properties, and a tensile strength exceeding 40 MPa.

[0013] Specifically, in the heat preservation and pressure preservation process, the heat preservation temperature includes, but is not limited to, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, 235℃, 240℃, etc.; the heat preservation pressure includes, but is not limited to, 10MPa, 12MPa, 14MPa, 15MPa, 16MPa, 18MPa, 20MPa, etc.

[0014] Preferably, in step S1, the neutral Nafion solution is prepared by adding alkali to the Nafion solution to adjust the pH value to 7; the mass concentration of the Nafion solution is 15-30%, including but not limited to 15%, 16%, 18%, 20%, 25%, 30%, etc.

[0015] More preferably, the alkali used is a NaOH solution with a concentration of 0.1 mol / L.

[0016] Preferably, in step S1, the organic alcohol includes n-propanol.

[0017] Preferably, in step S1, the volume ratio of the neutral Nafion solution to the organic alcohol is 1:(0.8 to 1.2), including but not limited to 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, etc.

[0018] This invention ensures the yield of the obtained proton exchange membrane by controlling the amount of organic alcohol added. Adding too much or too little organic alcohol will lead to a decrease in the yield.

[0019] Preferably, in step S1, the heat preservation treatment time is 18 to 22 hours, including but not limited to 18 hours, 18.5 hours, 19 hours, 19.5 hours, 20 hours, 20.5 hours, 21 hours, 21.5 hours, and 22 hours.

[0020] The total insulation time of this invention is shorter than that of traditional processes (which are generally more than 24 hours); and it uses a single-stage insulation process, making it simple to operate.

[0021] Preferably, in step S2, the substrate is a vacuum adsorption plate.

[0022] In this invention, a vacuum adsorption plate is used to provide a certain suction force, which allows the resin solution to better adhere to the substrate to form a resin layer, thus avoiding uneven coating or the resin layer detaching from the substrate.

[0023] Preferably, in step S2, the pre-drying time is 15 to 25 minutes, including but not limited to 15 minutes, 18 minutes, 20 minutes, 22 minutes, and 25 minutes.

[0024] This invention involves coating a resin solution on a vacuum adsorption plate. The doctor blade height is set as needed to form a first resin solution layer. A fixed porous membrane is then placed on top of this resin solution layer. After 15-25 minutes, a second layer of resin solution is applied to form a second layer. After another 15-25 minutes, a composite membrane is formed. This invention achieves a smooth, single-sided proton exchange membrane through vacuum adsorption plate coating. Furthermore, this method is performed at room temperature and pressure, avoiding air bubbles generated during vacuuming steps such as negative pressure impregnation. The lower layer coating is performed first, reducing the likelihood of air bubbles being trapped at the bottom and increasing the resin filling rate.

[0025] Preferably, in step S2, the porous membrane is an ePTFE (expanded polytetrafluoroethylene) membrane; the thickness of the porous membrane is 2 to 4 μm, including but not limited to 2 μm, 3 μm, 4 μm, etc.

[0026] Preferably, in step S3, the drying process involves heating to 90–100°C at a rate of 0.5–2°C / min and holding at that temperature for 25–35 min. Specifically, the heating rate includes, but is not limited to, 0.5°C / min, 1°C / min, 1.5°C / min, and 2°C / min; the holding temperature includes, but is not limited to, 90°C, 92°C, 95°C, 98°C, and 100°C; and the holding time includes, but is not limited to, 25 min, 30 min, and 35 min.

[0027] Preferably, in step S3, the heat treatment involves heating to 100–280°C at a heating rate of 8–12°C / min and holding at that temperature for at least 60 minutes. Specifically, the heating rate includes, but is not limited to, 8°C / min, 8.5°C / min, 9°C / min, 9.5°C / min, 10°C / min, 10.5°C / min, 11°C / min, 11.5°C / min, and 12°C / min; the holding temperature includes, but is not limited to, 100°C, 110°C, 120°C, 140°C, 150°C, 160°C, 180°C, 190°C, 200°C, 220°C, 230°C, 240°C, 260°C, 265°C, 270°C, and 280°C; and the holding time includes, but is not limited to, 60 minutes, 70 minutes, 80 minutes, 90 minutes, 100 minutes, and 120 minutes.

[0028] Further preferably, the heat treatment holding time is 60–90 min.

[0029] In this invention, heat treatment conditions are controlled to enhance the performance of the resulting proton exchange membrane. If the heat treatment time is too short or the temperature is too low, the mechanical strength of the prepared proton exchange membrane will be insufficient. The heat treatment holding time should not be less than 1 hour, and can be appropriately increased, but excessive time will increase the preparation cost. The heat treatment temperature should not exceed 280℃, otherwise defects will occur.

[0030] Preferably, in step S3, the post-treatment includes acid immersion and washing; the acid immersion is performed by soaking in a 0.5–1.5 mol / L sulfuric acid solution for 1.5–2.5 hours. Specifically, the concentration of the sulfuric acid solution includes, but is not limited to, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, etc.; the soaking time includes, but is not limited to, 1.5 hours, 1.8 hours, 2.0 hours, 2.2 hours, 2.5 hours, etc.

[0031] A further preferred method is to use deionized water for rinsing.

[0032] Secondly, the present invention provides a proton exchange membrane for a fuel cell prepared by the above-described preparation method.

[0033] The present invention will be further described in detail below through specific embodiments.

[0034] Example 1 A method for preparing a proton exchange membrane for a fuel cell includes the following steps: S1. Add 0.1 mol / L NaOH solution dropwise to a 20 wt% Nafion solution to adjust the pH to 7, thus obtaining a neutral Nafion solution. Mix the neutral Nafion solution and n-propanol at a volume ratio of 1:1 to obtain a mixed solution. Incubate the mixed solution at 220℃ and 20MPa for 20 hours to obtain a resin solution. S2, coat the first layer of resin solution on the vacuum adsorption plate, cover the first layer of resin solution with ePTFE, wait for 20 minutes, then coat the second layer of resin solution on the ePTFE, wait for 20 minutes to obtain the composite film. S3. The composite membrane is placed in an oven and heated to 100℃ at a rate of 1℃ / min, and dried for 30 min. Then, it is heated to 220℃ at a rate of 10℃ / min and held for 1 h. Finally, it is soaked in 1 mol / L sulfuric acid solution for 2 h and rinsed with deionized water to obtain the finished proton exchange membrane sheet for fuel cells.

[0035] Comparative Example 1 The only difference from Example 1 is that the coating order in step S2 is different. Specifically, ePTFE is placed on the vacuum adsorption plate first, the first layer of resin solution is coated on one side of the ePTFE, and after waiting for 20 minutes, it is flipped over and the second layer of resin solution is coated on the other side of the ePTFE. After waiting for 20 minutes, the composite film is obtained. Other steps and conditions are the same as in Example 1.

[0036] Comparative Example 2 Commercial proton exchange membranes (GORE 12μm proton exchange membranes) were used directly.

[0037] Comparative Example 3 The only difference from Example 1 is that in step S2, the composite membrane is obtained using a conventional negative pressure impregnation method; all other steps and conditions are the same as in Example 1. The difference lies in: S2: Place the resin solution in a glass dish (e.g., Figure 3 The glass dish (which can be replaced with containers of different sizes) is used to evacuate the entire vacuum chamber to -0.06 MPa. The ePTFE is then immersed in the glass dish for 6 minutes, then flipped over and immersed for another 4 minutes. The dish is then pulled out of the resin and kept in the vacuum chamber for 2 hours. The vacuum chamber is then allowed to return to normal pressure before the composite membrane is removed.

[0038] Performance testing Conductivity test: According to Section 5 "Proton conductivity test" of GB / T 20042.3 "Proton exchange membrane fuel cells Part 3: Proton exchange membrane test method".

[0039] Polarization performance test: According to Section 6 "Single cell polarization curve test" of GB / T 20042.5 "Proton exchange membrane fuel cells Part 5: Membrane electrode test method", the pressure test is adopted in section 6.7.1.2.

[0040] Tensile property test: According to Section 5 "Tensile property test" of GB / T 20042.3 "Proton exchange membrane fuel cells Part 3: Proton exchange membrane test methods".

[0041] (1) The conductivity of the proton exchange membranes obtained in Example 1 and Comparative Example 1 was tested, and the results are shown in Table 1 below.

[0042] Table 1. Conductivity of proton exchange membranes prepared by different process sequences

[0043] As shown in Table 1, Comparative Example 1 and Example 1 were prepared using the same parameters but different process sequences. However, the conductivity of Comparative Example 1 was lower than that of Example 1. Conductivity can also characterize the resin filling situation, which indicates that the resin filling rate of Example 1 was higher. The present invention effectively reduces the situation where air bubbles are pressed at the bottom and improves the conductivity of the obtained proton exchange membrane.

[0044] (2) The proton exchange membranes of Example 1 and Comparative Example 2 were assembled into membrane electrodes at 2 A / cm 2 Polarization performance was tested at a current density, and the results are as follows: Figure 2 As shown, in Example 1, the voltage is 0.628V (denoted as 0.628V@2A / cm). 2 ), compared to the mature commercial membrane of Comparative Example 1 (0.632V@2A / cm) 2 )near.

[0045] (3) A physical image of the proton exchange membrane obtained in Comparative Example 3 of the present invention is shown below. Figure 3 As shown, a physical image of the proton exchange membrane obtained in Example 1 is shown below. Figure 4 As shown.

[0046] Depend on Figure 3 It can be seen that Comparative Example 3 uses the traditional vacuum impregnation method, and the vacuuming process easily leads to the generation of bubbles in the final proton exchange membrane, and the operation steps are cumbersome; while the present invention does not require vacuum impregnation, and the proton exchange membrane obtained by direct coating has a smooth surface without bubbles. Figure 4 ).

[0047] The surface and cross-section of the proton exchange membrane obtained in Example 1 were scanned by electron microscopy, and the results are as follows: Figure 5 and Figure 6 As shown, Figure 5This further demonstrates that the proton exchange membrane prepared by this invention has a smooth surface free of bubbles. Figure 6 It can be seen that the ePTFE used in this invention has a thickness of about 3 μm, and the thickness of the resin layers on both sides is between 5.6 and 6.3 μm.

[0048] (4) The tensile properties of the proton exchange membrane obtained in Example 1 of the present invention were tested.

[0049] The results showed that the proton exchange membrane obtained in Example 1 of the present invention had a tensile strength of 46 MPa and an elongation at break of 170.82%, indicating excellent mechanical properties.

[0050] This invention first prepares a proton exchange membrane resin solution, then uses a vacuum adsorption plate to coat a smooth composite membrane, followed by heat treatment and post-treatment to obtain the proton exchange membrane. This invention can prepare sheet-like proton exchange membranes of various sizes, and the prepared proton exchange membranes exhibit good conductivity, with low preparation cost and high preparation efficiency. Furthermore, by adjusting certain parameters, such as the solid content of the resin solution, the ePTFE thickness, or the coating thickness, proton exchange membranes of different thicknesses can be prepared to meet various application requirements.

[0051] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a proton exchange membrane for a fuel cell, characterized in that, Includes the following steps: S1, a neutral Nafion solution and an organic alcohol are mixed evenly to obtain a mixture, and the mixture is kept at 200-240°C to obtain a resin solution; S2, a first layer of resin solution is coated on the substrate, a porous membrane is covered on the first layer of resin solution, and after pre-drying, a second layer of resin solution is coated on the porous membrane and pre-dried to obtain a composite membrane. S3, the composite membrane is dried, heat-treated and post-treated to obtain a proton exchange membrane for a fuel cell.

2. The method for preparing the proton exchange membrane for a fuel cell according to claim 1, characterized in that, In step S1, the neutral Nafion solution is prepared by adding alkali to the Nafion solution to adjust the pH value to 7; the mass concentration of the Nafion solution is 15-30%.

3. The method for preparing the proton exchange membrane for a fuel cell according to claim 1, characterized in that, In step S1, the organic alcohol includes n-propanol.

4. The method for preparing the proton exchange membrane for a fuel cell according to claim 1, characterized in that, In step S1, the volume ratio of the neutral Nafion solution to the organic alcohol is 1:(0.8 to 1.2).

5. The method for preparing the proton exchange membrane for a fuel cell according to claim 1, characterized in that, In step S1, the heat preservation treatment time is 18 to 22 hours.

6. The method for preparing a proton exchange membrane for a fuel cell according to claim 1, characterized in that, In step S2, the substrate is a vacuum adsorption plate; and / or, The pre-drying time is 15–25 min; and / or, The porous membrane is an ePTFE membrane.

7. The method for preparing the proton exchange membrane for a fuel cell according to claim 1, characterized in that, In step S3, the drying process involves heating the temperature to 90-100°C at a rate of 0.5-2°C / min and holding it at that temperature for 25-35 minutes.

8. The method for preparing a proton exchange membrane for a fuel cell according to claim 1, characterized in that, In step S3, the heat treatment involves heating the temperature to 100-280°C at a rate of 8-12°C / min and holding it at that temperature for at least 60 minutes.

9. The method for preparing a proton exchange membrane for a fuel cell according to claim 1, characterized in that, In step S3, the post-treatment includes acid immersion and cleaning; the acid immersion is performed by soaking in a 0.5-1.5 mol / L sulfuric acid solution for 1.5-2.5 hours; the cleaning is performed by rinsing with deionized water.

10. The proton exchange membrane for a fuel cell prepared by any one of claims 1-9.

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