Composite proton exchange membrane and preparation method and application thereof

Abstract

This invention relates to the field of fuel cells, and more particularly to a composite proton exchange membrane, its preparation method, and its applications. By employing the synergistic effect of staged thermal crosslinking and ePTFE porous membrane reinforcement, the membrane exhibits both high proton conductivity and excellent dimensional stability under high temperature and high pressure liquid water conditions at 110°C; specifically, the proton conductivity under 110°C and high pressure liquid water conditions is not less than 168.3 mS·cm. ‑1 The area swelling ratio under 110℃ and high-pressure liquid water conditions is no higher than 39.29%.

Description

Technical Field

[0001] This invention relates to the field of fuel cells, and more particularly to a composite proton exchange membrane, its preparation method, and its applications. Background Technology

[0002] Under the "dual carbon" goal, the efficient utilization of renewable energy has become a key issue in energy system transformation. Hydrogen production through water electrolysis can convert fluctuating renewable electricity into high-value-added hydrogen energy, representing an important technological path for optimizing the energy structure. Among these technologies, proton exchange membrane electrolysis (PEMWE) has attracted widespread attention due to its advantages such as high hydrogen purity, fast dynamic response, and ability to operate under high current density and high pressure conditions. However, traditional low-temperature PEMWE still suffers from shortcomings in energy efficiency and system cost, hindering its further development.

[0003] High-temperature proton exchange membrane electrolysis (ET-PEMWE) raises the operating temperature of PEMWE to 100-200℃, effectively improving electrode reaction kinetics and reducing thermodynamic decomposition voltage, thus decreasing energy consumption and the amount of precious metal catalysts required. However, under high-temperature conditions, steam feed easily leads to severe water shortage in the membrane electrode assembly, causing a significant increase in ohmic overpotential and concentration polarization, resulting in a rapid decline in electrolysis performance. Studies have shown that by increasing the feed pressure to achieve liquid water supply under high-temperature conditions, sufficient hydration of the membrane and catalyst layer can be maintained, thereby significantly improving electrolysis performance. Therefore, high-temperature, high-pressure liquid water operation is considered a promising operating mode for ET-PEMWE in practical applications.

[0004] Under these conditions, the proton exchange membrane must simultaneously possess high proton conductivity, good thermomechanical stability, and resistance to high-pressure liquid water erosion. Currently, perfluorosulfonic acid (PFSA) membranes, widely used in low-temperature PEMWE, exhibit significant shortcomings under high temperature and pressure conditions: PFSA membranes have a low glass transition temperature, making them prone to irreversible structural changes and chemical degradation near this temperature, resulting in a significant decrease in mechanical strength; simultaneously, the high-pressure liquid water environment exacerbates excessive swelling, leading to hydrogen permeability exceeding 30% and disrupting the hydrophilic / hydrophobic microphase structure balance, resulting in increased proton conduction impedance. Consequently, their service life under long-term testing is less than 300 hours, failing to meet the requirements for long-term stable operation.

[0005] To overcome the temperature adaptability limitations of PFSA membranes, researchers began exploring non-fluorinated proton exchange membrane materials, such as polybenzimidazole (PBI) and sulfonated hydrocarbon polymers (SHPs). Although phosphoric acid (PA)-doped PBI membranes exhibit good stability in high-temperature fuel cells, under water electrolysis conditions, even with steam feed, the PA loss rate remains as high as 0.8 mg / (cm³). 2The rapid degradation of membrane performance due to high hydrogen permeability (·h) limits its application in PEMWE. In contrast, sulfonated hydrocarbon polymer membranes, with their advantages of low cost, good thermal stability, and low hydrogen permeability, have become an important research direction for high-temperature PEMWE membrane materials.

[0006] Among various sulfonated hydrocarbons (SHPs), sulfonated polyether sulfone (SPES) exhibits excellent mechanical properties and thermal and chemical stability due to the flexibility of the ether bonds in its main chain, the rigidity of the aromatic rings, and the conjugated structure formed by the sulfone groups. Compared with other sulfonated hydrocarbon materials, SPES can introduce two sulfonic acid groups into each repeating unit, exhibiting higher sulfonation efficiency and proton conduction potential. However, while high-degree sulfonation of SPES can significantly improve IEC and proton conduction performance, its hydrophilicity is significantly enhanced, and the inter-chain forces of the polymer are weakened, leading to excessive swelling or even dissolution of the membrane in water. This makes it difficult to use directly, especially in high-temperature, high-pressure liquid water environments, becoming a key bottleneck restricting its engineering applications. Summary of the Invention

[0007] The purpose of this invention is to provide a composite proton exchange membrane, its preparation method, and its application. By constructing covalent bonds between molecular chains through thermal crosslinking to improve chemical stability, and by introducing expanded polytetrafluoroethylene (ePTFE) porous membrane as a reinforcing framework to provide physical constraint, the invention aims to simultaneously achieve high proton conductivity and excellent dimensional stability.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] This invention provides a method for preparing a composite proton exchange membrane, comprising the following steps: S1. Dissolve sulfonated polyethersulfone in an alcohol solvent to obtain a casting solution; S2. Pour the casting solution onto the substrate and dry it to obtain a sulfonated polyethersulfone substrate film. S3. Cover one side of the expanded polytetrafluoroethylene porous membrane wetted with an alcohol solvent onto the sulfonated polyethersulfone substrate membrane obtained in step S2. S4. The casting liquid obtained in step S1 is poured onto the other side of the expanded polytetrafluoroethylene porous membrane, and after drying, a composite primary membrane is obtained. S5. The composite primary membrane obtained in step S4 is subjected to a staged thermal crosslinking treatment, then cleaned and dried to obtain the composite proton exchange membrane.

[0010] In the above technical solution, further, in step S1, the degree of sulfonation of the sulfonated polyether sulfone is 80-99%.

[0011] In the above technical solution, further, in step S1, the mass concentration of sulfonated polyethersulfone in the casting solution is 2-20 wt%.

[0012] In the above technical solution, further, in step S1, the alcohol solvent is n-butanol.

[0013] In the above technical solution, further, in step S2, the drying temperature is 30-60℃ and the time is 12h-15h.

[0014] In the above technical solution, further, in step S3, the porosity of the expanded polytetrafluoroethylene porous membrane is 30-90%, and its average pore size is 100-200 nm.

[0015] In the above technical solution, further, in step S3, the alcohol solvent is ethanol.

[0016] In the above technical solution, further, in step S4, the second drying method is: first drying at 50-80℃ for 12-15 hours, and then drying at 70-120℃ for 12-15 hours.

[0017] In the above technical solution, further, in step S5, the staged thermal crosslinking treatment is carried out in a nitrogen-filled environment, with an initial temperature of 120°C, and the temperature is gradually increased to 180-200°C in 4-8 stages, with each stage being held for 2 hours.

[0018] Another aspect of the present invention provides a composite proton exchange membrane prepared by the above-described preparation method, comprising a sulfonated polyethersulfone base membrane, a reinforcing layer, and a sulfonated polyethersulfone top membrane stacked sequentially; wherein the reinforcing layer is an expanded polytetrafluoroethylene porous membrane; The interfaces of the sulfonated polyethersulfone base film, the reinforcing layer, and the sulfonated polyethersulfone top film are connected by covalent bonds.

[0019] In the above technical solution, the thickness of the sulfonated polyethersulfone substrate film is further 10-50 μm; The thickness of the reinforcing layer is 3-20 μm; The thickness of the sulfonated polyethersulfone top film is 10-50 μm.

[0020] The present invention also provides an application of the above-mentioned composite proton exchange membrane in medium-high temperature PEM water electrolysis, wherein the medium-high temperature is 90-140℃.

[0021] In summary, the present invention has the following beneficial effects: 1. This invention uses highly sulfonated polyether sulfone (SPES) as the membrane matrix, which can significantly improve IEC and proton conductivity. Simultaneously, to address the problem of excessive swelling in such membranes, a combination of thermal crosslinking and composite reinforcement layers is employed to effectively control the membrane structure. On one hand, thermal crosslinking introduces covalent bonds between molecular chains, thereby significantly improving the structural stability of the membrane. Since expanded polytetrafluoroethylene (ePTFE) porous membranes possess excellent mechanical strength, high-temperature resistance, and chemical inertness, introducing them as a reinforcement layer effectively limits the volume swelling of the membrane and improves dimensional stability. On the other hand, combining thermal crosslinking with the ePTFE porous membrane, the ePTFE porous membrane acts as a rigid framework. When SPES is filled into the interior, it physically supports and inhibits polymer swelling and deformation, thereby improving tensile strength. Crosslinking, on the other hand, allows polymer segments to be connected by covalent bonds to form a three-dimensional network structure, thereby inhibiting chain slippage and improving tensile strength and creep resistance. Therefore, the composite proton exchange membrane prepared by this invention can effectively suppress excessive swelling of highly sulfonated SPES while maintaining high proton conductivity, thus achieving synergistic optimization of structural stability and electrochemical performance.

[0022] 2. In the preparation method of the present invention, an alcohol solvent is used as the solvent, which has the dual characteristics of being able to dissolve highly sulfonated SPES and efficiently wet expanded polytetrafluoroethylene porous membrane. The alcohol solvent acts as a carrier, allowing the SPES solution to fully penetrate into the porous network of the expanded polytetrafluoroethylene porous membrane. The partially penetrated solvent can also locally dissolve the pre-deposited SPES, thereby promoting the mutual diffusion and entanglement of polymer chains at the interface. This achieves a tight wrapping and firm bonding between the SPES matrix and the fiber skeleton of the expanded polytetrafluoroethylene porous membrane, forming a dense "sandwich" composite structure, which effectively improves the interlayer bonding force.

[0023] 3. In the process of preparing the composite membrane, this invention addresses the low surface energy and strong hydrophobicity of expanded polytetrafluoroethylene (ePTFE) porous membranes by pre-wetting them with alcohol solvents. Compared to conventional polar solvent modification methods, this invention employs simple, mild, near-zero residue alcohol solvents that are highly compatible with the casting solution. Firstly, after pre-wetting with an alcohol solvent, the subsequent casting solution using an alcohol solvent as the solvent can more easily wet and cover the ePTFE porous membrane. This alcohol solvent acts as a "transition solvent" for the casting solution, promoting better "mixing" and contact between the two originally incompatible materials (SPES and ePTFE) at the interface, and penetrating into its porous structure, further strengthening the robust physical interlocking structure between the membrane layers. Secondly, using an alcohol solvent... The solvent wets the expanded PTFE porous membrane, effectively displacing and expelling air from the PTFE pores. This allows the casting solution to flow smoothly into and fill the liquid-occupied pores when poured onto the membrane, significantly reducing the possibility of gas entrainment. Consequently, the surface area of ​​the membrane wetted by the solvent is temporarily enhanced, facilitating more uniform spreading and leveling of the casting solution poured in step S4. This results in a smoother, less defective, and more uniform coating layer, preventing droplets from shrinking and agglomerating on hydrophobic surfaces.

[0024] 4. This invention employs a staged thermal crosslinking strategy, effectively resolving the contradiction between water absorption and swelling rate of PEM membranes in electrolysis applications. This strategy constructs a moderately stable crosslinking network, enabling the membrane to maintain a high water absorption rate to meet proton conduction requirements while effectively suppressing excessive dimensional expansion caused by excessive water absorption. Simultaneously, the resulting controllable swelling rate significantly reduces the risk of catalyst layer detachment due to repeated swelling and contraction of the membrane, and significantly enhances the membrane's mechanical strength and dimensional stability, fundamentally avoiding the pinhole effect caused by decreased mechanical properties. Attached Figure Description

[0025] Figure 1 The images show the surface microstructure and cross-sectional microstructure of the membrane prepared in Example 3, as well as the C, F, and S elements within the membrane. a is the surface image, and b is the cross-sectional image. Figure 2 The graphs show the water absorption and swelling properties of the membranes prepared in Example 3 and Comparative Examples 2-6. Figure 3 The mechanical strength properties of the films prepared in Examples 1, 3, 5-6, and 7 are shown in the diagram. Figure 4 The graphs show the proton conductivity performance of the membranes prepared in Examples 1, 3, and Comparative Examples 5-6, as well as the Nafion-115 commercial membrane, at different temperatures. Detailed Implementation

[0026] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0027] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0028] Example 1 A method for preparing a composite proton exchange membrane specifically includes the following steps: S1. Place 10 g of polyethersulfone (PES) in a vacuum drying oven and dry overnight. The dried PES and 100 mL of sulfuric acid are mechanically stirred at 80 °C for 5 h under a nitrogen atmosphere. After the reaction is complete, the polymer solution is poured into an ice-water mixture to obtain a white precipitate. The precipitate is washed with a large amount of ice water to remove the surface acid. Then the polymer is washed through a dialysis membrane until pH=7. Finally, the dialysis solution is dried to obtain sulfonated polyethersulfone (SPES) with a sulfonation degree of 80%. S2. Dissolve the SPES obtained in step S1 in n-propanol to prepare a 2wt% casting solution. Filter the casting solution with a 0.45μm needle filter and then degas for 30 min. Then pour the casting solution onto a glass plate and dry it in a vacuum oven at 30℃ for 15 h to form a sulfonated polyethersulfone substrate film. S3. Rinse the commercially available expanded polytetrafluoroethylene porous membrane (porosity 30%, pore size 200nm) with ethanol, and then lay one side of the polytetrafluoroethylene porous membrane flat on the sulfonated polyethersulfone substrate membrane obtained in step S2 to form a reinforcing layer. S4. The casting solution obtained in step S2 is poured onto the other side of the expanded polytetrafluoroethylene porous membrane, dried at 50 ℃ for 15 h, and then kept at 70 ℃ for 15 h to remove excess solution, thus obtaining the composite primary membrane. S5. The composite primary membrane is subjected to staged thermal crosslinking treatment in a nitrogen-filled oven, namely, thermal crosslinking treatment is carried out at 120℃ for 2h, 140℃ for 2h, 160℃ for 2h, and 180℃ for 2h respectively. The membrane is then immersed in 0.5 M sulfuric acid at 80℃ for 3h, followed by immersion in a large amount of 80℃ deionized water for 3h to clean the membrane. Finally, the membrane is air-dried for later use. The resulting composite proton exchange membrane is named CSSPES / PTFE-180.

[0029] In the composite proton exchange membrane prepared in this embodiment, the thickness of the sulfonated polyethersulfone base membrane is 11.2 μm, the thickness of the reinforcing layer is 3.4 μm, and the thickness of the sulfonated polyethersulfone top membrane is 10.6 μm.

[0030] Example 2 A method for preparing a composite proton exchange membrane specifically includes the following steps: S1. Place 10 g of PES in a vacuum drying oven and dry overnight. The dried PES and 100 mL of sulfuric acid are mechanically stirred at 70 °C for 6 h under a nitrogen atmosphere. After the reaction is complete, the polymer solution is poured into an ice-water mixture to obtain a white precipitate. The precipitate is washed with a large amount of ice water to remove the surface acid. Then the polymer is washed through a dialysis membrane until pH=7.3. Finally, the dialysis solution is dried to obtain sulfonated polyether sulfone (SPES) with a sulfonation degree of 88%. S2. Dissolve the SPES from step S1 in n-propanol to prepare a 20wt% casting solution. Filter the casting solution with a 0.45μm needle filter and then degas for 40 min. Then pour the casting solution onto a glass plate and dry it in a vacuum oven at 60℃ for 12 h to form a sulfonated polyethersulfone substrate film. S3. Rinse the commercially available expanded polytetrafluoroethylene porous membrane (porosity 90%, pore size 100nm) with ethanol, and then lay one side of the expanded polytetrafluoroethylene porous membrane flat on the sulfonated polyethersulfone substrate membrane of step S2 to form a reinforcing layer. S4. The casting solution obtained in step S2 is poured onto the other side of the expanded polytetrafluoroethylene porous membrane, dried at 80 ℃ for 12 h, and then kept at 120 ℃ for 12 h to remove excess solution, thus obtaining the composite primary membrane. S5. The composite primary membrane is subjected to staged thermal crosslinking treatment in a nitrogen-filled oven, that is, thermal crosslinking treatment is carried out sequentially at 120℃ for 2h, 140℃ for 2h, 160℃ for 2h, 180℃ for 2h, and 200℃ for 2h. After the membrane is removed from the oven, it is immersed in 0.5M sulfuric acid at 80℃ for 3h, and then immersed in a large amount of 80℃ deionized water for 3h to clean the membrane. Finally, the membrane is air-dried for later use to obtain the composite proton exchange membrane.

[0031] In the composite proton exchange membrane prepared in this embodiment, the thickness of the sulfonated polyethersulfone base membrane is 46.2 μm, the thickness of the reinforcing layer is 17.8 μm, and the thickness of the sulfonated polyethersulfone top membrane is 48.9 μm.

[0032] Example 3 A method for preparing a composite proton exchange membrane specifically includes the following steps: S1. Place 10 g of PES in a vacuum drying oven and dry overnight. The dried PES and 100 mL of sulfuric acid are mechanically stirred at 80 °C for 7 h under a nitrogen atmosphere. After the reaction is complete, the polymer solution is poured into an ice-water mixture to obtain a white precipitate. The precipitate is washed with a large amount of ice water to remove the surface acid. Then the polymer is washed through a dialysis membrane until pH=7. Finally, the dialysis solution is dried to obtain sulfonated polyether sulfone (SPES) with a sulfonation degree of 95%. S2. Dissolve the SPES obtained in step S1 in n-propanol to prepare a 6wt% casting solution. Filter the casting solution with a 0.45μm needle filter and then degas for 30 min. Then pour the casting solution onto a glass plate and dry it in a vacuum oven at 50℃ for 12 h to form a sulfonated polyethersulfone substrate film. S3. Rinse the commercially available expanded polytetrafluoroethylene porous membrane (porosity 60%, pore size 150nm) with ethanol, and then lay one side of the polytetrafluoroethylene porous membrane flat on the sulfonated polyethersulfone substrate membrane of step S2 to form a reinforcing layer. S4. The casting solution obtained in step S2 is poured onto the other side of the expanded polytetrafluoroethylene porous membrane, dried at 50 ℃ for 12 h, and then maintained at 70 ℃ for 12 h to remove excess solution, thus obtaining the composite primary membrane. S5. The composite primary membrane is subjected to staged thermal crosslinking treatment in a nitrogen-filled oven, namely, maintaining thermal crosslinking treatment at 120℃ for 2h, 140℃ for 2h, 160℃ for 2h, 180℃ for 2h, and 200℃ for 2h respectively. After removing the membrane from the oven, the membrane is immersed in 0.5M sulfuric acid at 80℃ for 3h, and then immersed in a large amount of 80℃ deionized water for 3h to clean the membrane. Finally, the membrane is air-dried for later use. The resulting composite proton exchange membrane is named CSSPES / PTFE-200.

[0033] In the composite proton exchange membrane obtained in this embodiment, the thickness of the sulfonated polyethersulfone base membrane is 31.2 μm, the thickness of the reinforcing layer is 10.5 μm, and the thickness of the sulfonated polyethersulfone top membrane is 33.1 μm.

[0034] like Figure 1 As shown in Figure a, the surface microstructure of the composite proton exchange membrane was examined using a scanning electron microscope (SEM, JSM-IT300). Figure 1 As shown in b, the cross-section of the composite proton exchange membrane prepared in Example 3 was examined using a scanning electron microscope (SEM, SU8020). It can be seen that both the surface and cross-section of the composite proton exchange membrane exhibit density, with no defects or cracks observed. The cross-sectional morphology presents a typical "sandwich" structure: SPES is uniformly covered on both sides of the expanded polytetrafluoroethylene (ePTFE) porous membrane reinforcement layer, and the interfaces between the layers are tightly bonded. Elemental energy dispersive spectroscopy analysis results show that F is mainly concentrated in the middle expanded polytetrafluoroethylene porous membrane reinforcement layer, while C and S are uniformly distributed throughout the interface, further confirming that SPES fully wets and fills the ePTFE porous structure.

[0035] Comparative Example 1 A method for preparing a proton exchange membrane, using the same preparation method as in Example 1, except that it does not include a reinforcing layer, specifically including the following steps: S1. Place 10 g of PES in a vacuum drying oven and dry overnight. The dried PES and 100 mL of H2SO4 are mechanically stirred at 80 °C for 5 h under a nitrogen atmosphere. After the reaction is complete, the polymer solution is poured into an ice-water mixture to obtain a white precipitate. The precipitate is washed with a large amount of ice water to remove the surface acid. Then the polymer is washed through a dialysis membrane until pH=7. Finally, the dialysis solution is dried to obtain sulfonated polyethersulfone with a sulfonation degree of 80%. S2. Dissolve the SPES polymer obtained in step S1 in n-propanol to prepare a 2wt% casting solution. Filter the casting solution with a 0.45μm needle filter and then degas for 30 min. Then pour the casting solution onto a glass plate and dry it in a vacuum oven at 30℃ for 15 h to form a sulfonated polyethersulfone film. S3. The sulfonated polyethersulfone membrane was subjected to staged thermal crosslinking treatment in a nitrogen-filled oven, that is, the thermal crosslinking treatment was carried out sequentially at 120℃ for 2h, 140℃ for 2h, 160℃ for 2h, and 180℃ for 2h. After the membrane was removed from the oven, it was immersed in 0.5 M sulfuric acid at 80℃ for 3h, and then immersed in a large amount of 80℃ deionized water for 3h to clean the membrane. Finally, the membrane was air-dried for use. The obtained proton exchange membrane was named CSSPES-180.

[0036] Comparative Example 2 A method for preparing a proton exchange membrane, using the same method as in Example 3, except that it does not include a reinforcing layer, specifically including the following steps: S1. Place 10 g of PES in a vacuum drying oven and dry overnight. The dried PES and 100 mL of sulfuric acid are mechanically stirred at 80 °C for 7 h under a nitrogen atmosphere. After the reaction is complete, the polymer solution is poured into an ice-water mixture to obtain a white precipitate. The precipitate is washed with a large amount of ice water to remove the surface acid. Then the polymer is washed through a dialysis membrane until pH=7. Finally, the dialysis solution is dried to obtain sulfonated polyether sulfone (SPES) with a sulfonation degree of 95%. S2. Dissolve the SPES polymer obtained in step S1 in n-propanol to prepare a 6wt% casting solution. Filter the casting solution with a 0.45μm needle filter and then degas for 30 min. Then pour the casting solution onto a glass plate and dry it in a vacuum oven at 50℃ for 12 h to form a sulfonated polyethersulfone film. S3. The sulfonated polyethersulfone membrane was subjected to staged thermal crosslinking treatment in a nitrogen-filled oven, namely, thermal crosslinking treatment was carried out sequentially at 120℃ for 2h, 140℃ for 2h, 160℃ for 2h, 180℃ for 2h, and 200℃ for 2h. After the membrane was removed from the oven, it was immersed in 0.5 M sulfuric acid at 80℃ for 3h, and then immersed in a large amount of 80℃ deionized water for 3h to clean the membrane. Finally, the membrane was air-dried for later use. The resulting proton exchange membrane was named CSSPES-200.

[0037] Comparative Example 3 A method for preparing a proton exchange membrane, using the same preparation method as Comparative Example 2, differs in that the thermal crosslinking parameters in step S3 are as follows: sequentially maintaining thermal crosslinking treatments at 120℃ for 2h, 140℃ for 2h, 160℃ for 2h, 180℃ for 2h, 200℃ for 2h, and 220℃ for 2h, respectively. The resulting proton exchange membrane is named CSSPES-220.

[0038] Comparative Example 4 A method for preparing a proton exchange membrane, using the same preparation method as Comparative Example 2, differs in that the thermal crosslinking parameters in step S3 are as follows: sequentially maintaining thermal crosslinking treatments at 120℃ for 2h, 140℃ for 2h, 160℃ for 2h, 180℃ for 2h, 200℃ for 2h, 220℃ for 2h, and 240℃ for 2h, respectively. The resulting proton exchange membrane is named CSSPES-240.

[0039] Comparative Example 5 A method for preparing a composite proton exchange membrane is adopted, which is the same as the preparation method in Example 3. The difference is that the thermal crosslinking parameters in step S5 are as follows: thermal crosslinking treatment is maintained at 120°C for 2 hours, 140°C for 2 hours, 160°C for 2 hours, 180°C for 2 hours, 200°C for 2 hours, and 220°C for 2 hours respectively. The resulting composite proton exchange membrane is named CSSPES / PTFE-220.

[0040] Comparative Example 6 A method for preparing a composite proton exchange membrane is adopted, which is the same as the preparation method in Example 3. The difference is that the thermal crosslinking parameters in step S5 are as follows: the thermal crosslinking treatment is maintained at 120°C for 2 hours, 140°C for 2 hours, 160°C for 2 hours, 180°C for 2 hours, 200°C for 2 hours, 220°C for 2 hours, and 240°C for 2 hours respectively. The resulting composite proton exchange membrane is named CSSPES / PTFE-240.

[0041] Comparative Example 7 A method for preparing a composite proton exchange membrane specifically includes the following steps: S1. 10 g of PES was placed in a vacuum drying oven and dried overnight. The dried PES and 100 mL of H2SO4 were mechanically stirred at 80 °C for 7 h under a nitrogen atmosphere. After the reaction was completed, the polymer solution was poured into an ice-water mixture to obtain a white precipitate. The precipitate was washed with plenty of ice water to remove the surface acid. The polymer was then washed through a dialysis membrane until pH=7. Finally, the dialysis solution was dried to obtain sulfonated polyethersulfone (SPES). S2. Dissolve the SPES polymer from S1 in n-propanol to prepare a 6wt% casting solution. Filter the casting solution with a 0.45μm needle filter and then degas for 30 min. Then pour the casting solution onto a glass plate and dry it in a vacuum oven at 50℃ for 12 h to form a sulfonated polyethersulfone substrate film. S3. Porous polytetrafluoroethylene (PTFE) rinsed with ethanol is spread on the sulfonated polyethersulfone (PES) substrate membrane of S2 to form a reinforcing layer. The casting solution of S2 is then poured a second time onto the porous PTFE. The composite membrane is then dried at 50 °C for 12 h, followed by maintaining it at 70 °C for 12 h to remove excess solution. After removing the membrane from the oven, it is soaked in 0.5 M sulfuric acid at 80 °C for 3 h, and then soaked in a large amount of 80 °C deionized water for 3 h to clean the membrane. Finally, the membrane is air-dried for later use. The resulting composite membrane is denoted as SPES / PTFE.

[0042] Test Example 1 The membranes prepared in Examples 1, 3, and Comparative Examples 1-6 were subjected to hydrolysis resistance tests at 80 °C and 110 °C for 72 h, respectively. The test results are recorded in Table 1 below.

[0043] Table 1. Stability of the membrane after 72 hours in water baths or DMSO at different temperatures.

[0044] Notes: ×: Dissolves; √: Swells and disintegrates; √√: Swells but retains its shape; √√√: Slightly absorbs water, size stable; √√√√: Stable.

[0045] Tests showed that CSSPES-180 dissolved due to excessive swelling in a 90℃ water bath environment; CSSPES-200 swelled severely at 110℃, failing to meet the requirements of electrolysis; CSSPES / PTFE-200, CSSPES / PTFE-220, and CSSPES / PTFE-240 remained stable at all three temperature gradients.

[0046] Test Example 2 In a simulated electrolysis environment, the membranes from Example 3 and Comparative Examples 2-6 were placed in a high-pressure reactor and maintained at 110°C for 12 hours. The tests were then conducted, and the results are as follows: Figure 2 As shown.

[0047] Depend on Figure 2It is evident that the water absorption and volume swelling of the CSSPES membrane decrease with increasing crosslinking degree, with CSSPES-200 exhibiting a swelling rate as high as 157.2%, failing to meet the requirements of high-temperature and high-pressure electrolysis. After reinforcement with an ePTFE porous membrane, the area swelling rate and water absorption rate of the CSSPES / PTFE-200 membrane in Example 3 were significantly reduced by 75% and 71.6%, respectively, compared to the unreinforced CSSPES-200 membrane. This significant improvement is mainly attributed to the strong physical constraint effect of the ePTFE network; its hydrophobic and high-strength microfiber skeleton effectively limits the expansion of the hydrophilic SPES matrix during hydration, thereby significantly improving the dimensional stability of the composite membrane. This confirms that introducing an ePTFE porous membrane reinforcement layer is an effective strategy to suppress excessive swelling of high-sulfonation SPES. The water absorption and swelling of CSSPES-220 and CSSPES-240 composites before and after the ePTFE reinforcement layer showed little change, possibly due to the increased crosslinking degree resulting from higher crosslinking temperature.

[0048] Test Example 3 Tensile strength tests were conducted on the films from Examples 1, 3, Comparative Examples 5-6, Comparative Example 7, and SPES. The tensile strength and elongation at break of the composite films were characterized using a universal testing machine (WDW-100) at a tensile rate of 2 mm / min. Figure 3 It is evident that after reinforcement and crosslinking treatment with ePTFE porous membranes, the tensile stress of the membranes significantly increases, while the elongation decreases. Specifically, the tensile strength of CSSPES / PTFE-240 decreases slightly due to partial thermal decomposition. Furthermore, the composite membrane reinforced with ePTFE porous membranes exhibits a slow stress release during fracture, with the stress reaching a peak and then gradually decreasing. This means that the ePTFE porous membrane, acting as a rigid porous framework, often improves tensile strength by physically supporting and inhibiting polymer swelling and deformation when SPES is filled into it. Crosslinking allows polymer segments to be connected by covalent bonds to form a three-dimensional network structure, thereby inhibiting segment slippage and enhancing tensile strength and creep resistance.

[0049] Test Example 4 Conductivity tests were performed on the films from Examples 1 and 3, Comparative Examples 5-6, and the Nafion-115 commercial membrane. The proton conductivity of the membranes was measured using electrochemical impedance spectroscopy (EIS) on an electrochemical workstation (Gamry Interface 5000E). The test frequency range was 5 MHz–1 Hz, and the test potential amplitude was 10 mV. The test results are as follows: Figure 4 As shown.

[0050] Figure 4The proton conductivity of CSSPES / PTFE composite membranes in the temperature range of 60-110℃ was demonstrated. CSSPES / PTFE-180 exhibited high swelling at 90℃, making testing impossible, while CSSPES-PTFE-200 showed a conductivity of 168.3 mS·cm at 110℃. -1 The proton conductivity is higher than that of the Nafion-115 commercial membrane, at 136.3 mS·cm under the same conditions. -1 When the crosslinking temperature is greater than 200℃, the degree of crosslinking of the polymer is relatively large, and it exhibits extremely low proton conductivity, which is consistent with its water absorption and swelling rate.

[0051] In summary, this invention provides a composite proton exchange membrane suitable for medium- and high-temperature PEM water electrolysis. Through the synergistic effect of thermal crosslinking and ePTFE porous membrane reinforcement, and by developing the most suitable thermal crosslinking temperature, namely 120-200℃, the membrane exhibits both high proton conductivity (168.3 mS / cm) and excellent dimensional stability in a high-temperature and high-pressure liquid water environment at 110℃.

[0052] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for preparing a composite proton exchange membrane, characterized in that: Includes the following steps: S1. Dissolve sulfonated polyethersulfone in an alcohol solvent to obtain a casting solution; S2. Pour the casting solution onto the substrate and dry it to obtain a sulfonated polyethersulfone substrate film. S3. Cover one side of the expanded polytetrafluoroethylene porous membrane wetted with an alcohol solvent onto the sulfonated polyethersulfone substrate membrane obtained in step S2. S4. The casting liquid obtained in step S1 is poured onto the other side of the expanded polytetrafluoroethylene porous membrane, and after drying, a composite primary membrane is obtained. S5. The composite primary membrane obtained in step S4 is subjected to a staged thermal crosslinking treatment, then cleaned and dried to obtain the composite proton exchange membrane.

2. The preparation method according to claim 1, characterized in that: In step S1, the degree of sulfonation of the sulfonated polyether sulfone is 80-99%; The mass concentration of sulfonated polyethersulfone in the casting solution is 2-20 wt%.

3. The preparation method according to claim 1, characterized in that: In step S2, the drying temperature is 30-60℃ and the time is 12-15h.

4. The preparation method according to claim 1, characterized in that: In step S3, the porosity of the expanded polytetrafluoroethylene porous membrane is 30-90%, and its average pore size is 100-200 nm.

5. The preparation method according to claim 1, characterized in that: In step S4, the second drying method is as follows: first, dry at 50-80℃ for 12-15 hours, and then dry at 70-120℃ for 12-15 hours.

6. The preparation method according to claim 1, characterized in that: In step S5, the staged thermal crosslinking treatment is carried out in a nitrogen-filled environment with an initial temperature of 120°C. The temperature is gradually increased to 180-200°C in 4-8 stages, and each stage is held for 2 hours.

7. A composite proton exchange membrane prepared by the method according to any one of claims 1-6, characterized in that: It comprises a sulfonated polyethersulfone base film, a reinforcing layer, and a sulfonated polyethersulfone top film stacked sequentially; the reinforcing layer is an expanded polytetrafluoroethylene porous membrane; The interfaces of the sulfonated polyethersulfone base film, the reinforcing layer, and the sulfonated polyethersulfone top film are connected by covalent bonds.

8. The composite proton exchange membrane according to claim 1, characterized in that: The thickness of the sulfonated polyethersulfone substrate film is 10-50 μm; The thickness of the reinforcing layer is 3-20 μm; The thickness of the sulfonated polyethersulfone top film is 10-50 μm.

9. An application of a composite proton exchange membrane prepared by the preparation method according to any one of claims 1-6, characterized in that: The application is in the medium-high temperature PEM water electrolysis, where the medium-high temperature is 90-140℃.

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