zwitterion-functionalized cyclodextrin sulfonated polymer proton exchange membrane and its preparation method

Abstract

This invention belongs to the field of membrane technology and discloses a zwitterionic functionalized cyclodextrin sulfonated polymer proton exchange membrane and its preparation method, including the following steps: (1) reacting N-aminoethylpiperazine with 1,3-propylsulfonate lactone to obtain the zwitterionic compound AEPPS; (2) reacting AEPPS with NaOH, β-cyclodextrin, and epichlorohydrin to obtain zwitterionic compound-modified cyclodextrin ZCD; (3) dispersing ZCD in a sulfonated polymer solution to form a casting solution, and finally obtaining the zwitterionic functionalized cyclodextrin sulfonated polymer proton exchange membrane. This invention improves the proton conductivity of the prepared proton exchange membrane by introducing zwitterionic functionalized cyclodextrin (ZCD) to modify the sulfonated polymer proton exchange membrane and controlling the overall process design of the preparation method.

Description

Technical Field

[0001] This invention belongs to the field of membrane technology, and more specifically, relates to a zwitterion-functionalized cyclodextrin sulfonated polymer proton exchange membrane and its preparation method. By introducing zwitterion-functionalized cyclodextrin (ZCD) to modify the sulfonated polymer proton exchange membrane, the proton conductivity of the prepared proton exchange membrane can be effectively improved. Background Technology

[0002] Fuel cell technology has attracted much attention due to its high efficiency and the green and safe characteristics of its reaction products. Among them, proton exchange membrane fuel cells (PEMFCs) have been widely used in portable power sources and new energy vehicles due to their advantages such as high energy conversion rate, high power density, and fast start-up speed, and are considered one of the most promising fuel cells. The proton exchange membrane (PEM), as a key component of the PEMFC, not only provides a channel for proton transport but also blocks fuel between the anode and cathode. Proton conductivity is a core factor determining the performance of PEMFCs, and improving proton conductivity is an effective way to obtain high-performance proton exchange membranes.

[0003] Zwitterionic materials are highly hydrophilic, benefiting from their equivalent anionic and cationic functional groups on a neutral molecule. Compared to nonionic materials, zwitterionic materials exhibit significantly stronger hydration properties. In proton exchange membrane modification, zwitterions can bind to ion exchange sites in the proton exchange membrane through ion exchange interactions, thereby improving proton conductivity, membrane stability, durability, and selectivity. n-Aminoethylpiperazine propane sulfonate (AEPPS) has attracted attention in zwitterionic materials due to its strong water-binding capacity and mild and simple synthesis method, and its application in membrane modification has been reported. The journal *Separation and Purification Technology* (2022, 285: 120298) co-deposited tannic acid (TA) and AEPPS on the surface of a prepared polyvinylidene fluoride (PVDF) / poly(2-hydroxyethyl methacrylate) (PVDF / PHEMA) composite membrane, demonstrating excellent underwater oil adhesion resistance on the bi-anionic surface. The journal *Journal of Membrane Science* (2022, 643: 120050) reported the preparation of a membrane with excellent nanofiltration performance using a low concentration of N-aminoethylpiperazine propanesulfonate (AEPPS) as an aqueous monomer. *Journal of Membrane Science* (2016, 510: 122-130) also reported the preparation of a superhydrophilic antibacterial zwitterionic polyamide composite nanofiltration membrane (ZTFCMs) with excellent water permeability and antibiotic selectivity through interfacial polymerization of AEPPS monomer with trimesoyl chloride (TMC) monomer on a polysulfone ultrafiltration membrane. Currently, the application of zwitterionic compound AEPPS in improving proton conductivity has not been reported; therefore, its application in modifying proton exchange membranes has certain research value.

[0004] β-Cyclodextrin (β-CD) is an organic compound composed of D-glucanose units linked cyclically by α-1,4-glycosidic bonds. Cyclodextrin has a cavity at the center of its cyclic structure, containing oxygen atoms (-CH-) bound to glucosides, exhibiting hydrophobicity. Simultaneously, the -OH groups at the 2, 3, and 6 positions of the glucose group are hydrophilic, making it an organic compound readily suitable for zwitterionic functionalization (Chemical Reviews, 2014, 114(21):10940–10975). Furthermore, the hydroxyl groups on the surface of β-CD can provide more proton conductivity channels. Therefore, an increasing number of β-CD-modified proton exchange membranes have been developed. For example, the *Journal of Power Sources* (2008, 185, 1, 49-54) prepared sodium-based H2O2 proton exchange membranes using a solution casting method. +A proton-conducting composite membrane based on sulfonated β-cyclodextrin (sb-CD) exhibits a proton conductivity of 0.0144 S / cm at 20 °C, which is an improvement over the unmodified membrane (0.0105 S / cm). The *International Journal of Hydrogen Energy* (2011, 36, 9, 5666-5674) prepared and studied a DMFC blend membrane using sulfonated polyether ether ketone (PEEK) and sulfonated cyclodextrin as proton-conducting membranes. This membrane achieved a maximum conductivity of 0.057 S / cm at 80 °C, a significant improvement over Nafion 115 (0.034 S / cm). The journal *Electrochimica Acta* (2018, 286, 350e364) reported the successful development of a composite membrane by incorporating sulfonated β-CD into TGDMP-crosslinked sulfonated PVA. This membrane exhibited a proton conductivity of 0.143 S / cm at 80°C and 100% RH (relative humidity), a significant improvement over the unmodified sulfonated poly(vinyl alcohol) membrane. *Polymer Testing* (2021, 100, 107246) reported the preparation of a SPEEK / β-CD-DHNTs / HPW composite membrane using β-cyclodextrin-anchored phosphotungstic acid. At 25°C and 90% RH, the composite membrane achieved a conductivity of up to 0.090 S / cm, approximately 120% higher than the SPEEK membrane (0.041 S / cm). The *Journal of Materials Chemistry A* (2015, 30, 3, 15607-15615) reported the modification of silica nanoparticles (SNs) with β-CD, followed by the mixing of SN-β-CD into Nafion membranes. The resulting proton exchange membrane exhibited a proton conductivity as high as 0.31 S / cm at 80 °C and 100% RH, almost three times that of the unmodified membrane. Although the proton conductivity of these β-CD-modified membranes was improved, the improved conductivity was not high enough. While a few showed significant improvement, their complex preparation and limited industrial application suggest considerable room for further improvement. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the prior art, the purpose of this invention is to provide a zwitterion-functionalized cyclodextrin sulfonated polymer proton exchange membrane and its preparation method. By improving the structure and composition of key functional components in the proton exchange membrane, modifying the sulfonated polymer proton exchange membrane by introducing zwitterion-functionalized cyclodextrin (ZCD), and controlling the overall process flow design of the preparation method, the proton conduction performance of the prepared proton exchange membrane can be effectively improved.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a zwitterionic functionalized cyclodextrin sulfonated polymer proton exchange membrane is provided, characterized by comprising the following steps:

[0007] (1) Place N-aminoethylpiperazine (AEP) and the first solvent together in a container, and then add the mixture of 1,3-propylsulfonate lactone (1,3-PS) and the second solvent dropwise into the container under a water bath at 20℃~50℃. Stir the reaction, and then separate, wash and dry the product to obtain the corresponding zwitterionic compound, denoted as AEPPS.

[0008] (2) The AEPPS obtained in step (1) is stirred together with a soluble strong base compound (i.e., NaOH), β-cyclodextrin (β-CD) and deionized water in an oil bath at 60℃~100℃. Epichlorohydrin (ECH) is added dropwise to obtain a mixed solution. After connecting a reflux condenser, the solution is heated and refluxed. The product is then separated, washed and dried to obtain the zwitterionic compound-modified cyclodextrin, denoted as ZCD.

[0009] (3) Disperse the ZCD obtained in step (2) in a sulfonated polymer solution and sonicate it to obtain a uniformly dispersed casting solution; then, use the casting solution to form a membrane material, dry it, and then soak it in hydrogen peroxide solution, acid and deionized water in sequence to obtain a zwitterionic functionalized cyclodextrin sulfonated polymer proton exchange membrane.

[0010] As a further preferred embodiment of the present invention, in step (2), the volume of epichlorohydrin added accounts for 5-20% of the total volume of the mixed solution; the reaction temperature of the reflux heating reaction is 60-80°C, and the reaction time is 15-180 min;

[0011] Preferably, the volume of epichlorohydrin added accounts for 5-12% of the total volume of the mixed solution; the reaction temperature of the reflux heating reaction is 65-80°C, and the reaction time is 15-150 min.

[0012] As a further preferred embodiment of the present invention, in step (3), the mass of ZCD accounts for 0.7 to 2.1 wt% of the mass of the polymer matrix contained in the sulfonated polymer solution.

[0013] As a further preferred embodiment of the present invention, in step (1), the molar ratio of the N-aminoethylpiperazine to the 1,3-propylsulfonate lactone corresponding to the stirring reaction is 5:1 to 1:5.

[0014] As a further preferred embodiment of the present invention, in step (1), the first solvent and the second solvent are independently selected from one or a mixture of several of N,N-dimethylformamide (DMF), acetonitrile, N,N-diethylformamide, tetrahydrofuran, pyrrolidone, dimethyl sulfoxide, CH3OH, and C2H5OH;

[0015] The temperature of the water bath is 25–45°C; the reaction time of the stirring reaction is 2–12 h.

[0016] As a further preferred embodiment of the present invention, in steps (1) and (2), the solvents used for cleaning are all low-boiling-point solvents with a boiling point not higher than 80°C, independently selected from one or a mixture of several of CH3OH, C2H5OH, CHCl3, CH2Cl2, CH3Cl, acetone, and butanone.

[0017] As a further preferred embodiment of the present invention, in step (3), the sulfonated polymer solution is one of a homogeneous solution of perfluorosulfonic acid resin, sulfonated polyether ether ketone, sulfonated polybenzimidazole, sulfonated polyether sulfone, or sulfonated polyimide; the concentration of the sulfonated polymer solution is 1 to 40 wt%.

[0018] The casting solution is used to form a film material, specifically by coating the casting solution into a film;

[0019] The drying process involves placing the membrane material in an oven at 50–80°C, raising the temperature to 110–150°C, and then maintaining the temperature for 12–36 hours. Preferably, the heating rate is less than 0.5°C / min, and more preferably 0.1–0.5°C / min.

[0020] As a further preferred embodiment of the present invention, in step (3), the concentration of the hydrogen peroxide aqueous solution is 1 to 10 wt%.

[0021] The acid solution is specifically a mixture of one or more of hydrochloric acid, sulfuric acid, and phosphoric acid, and the concentration of the acid solution is 0.1 to 2 mol / L, more preferably 0.5 to 2 mol / L.

[0022] According to another aspect of the present invention, the present invention provides a zwitterionic functionalized cyclodextrin sulfonated polymer proton exchange membrane prepared by the above preparation method.

[0023] According to another aspect of the present invention, the present invention provides the application of the above-mentioned zwitterionic functionalized cyclodextrin sulfonated polymer proton exchange membrane in a proton exchange membrane fuel cell.

[0024] Compared with the prior art, the above-described technical solutions conceived in this invention can achieve the following results.

[0025] Beneficial effects:

[0026] (1) The above-described technical solution conceived in this invention differs from traditional polymer hybrid proton exchange membranes modified with other materials. The AEPPS used in this invention contains sulfonic acid groups and ammonium ions, exhibiting amphiphilicity and demonstrating excellent application potential in the field of proton exchange membrane fuel cells. The unique annular cavity structure of β-CD itself can reduce proton conductivity steric hindrance. Furthermore, β-CD stands out due to its wide availability, low raw material price, and simple construction process. This invention selects β-CD and synthesized AEPPS to construct a composite proton exchange membrane. Taking its application in Nafion membranes as an example, using it as a filler can effectively improve the water retention of Nafion membranes, thereby enhancing their proton conductivity under high-temperature conditions. This is crucial for the performance of energy conversion devices such as fuel cells.

[0027] The research group of the inventors of this invention previously reported a polymer hybrid proton exchange membrane synergistically modified with zwitterionic functionalized COF and SiO2 spheres (see Chinese patent application CN117380003A). Although it can accelerate proton conduction to a certain extent, it uses inorganic filler such as SiO2, which has poor compatibility with the matrix material, affecting the mechanical properties and service life of the membrane. At the same time, the preparation conditions of zwitterionic functionalized COF are harsh, and the cost of carbon nanotube materials is high, which limits its widespread application in practical applications. In contrast, this invention uses zwitterionic β-cyclodextrin (ZCD) as a filler, which has good compatibility with the matrix material. The raw material β-CD is widely available and has low preparation cost. At the same time, because it has a different proton transport mechanism, it can maintain good proton conductivity, thus having greater application potential.

[0028] (2) Compared with traditional cyclodextrin-modified polymer hybrid proton exchange membranes, zwitterionic β-cyclodextrin (ZCD) exhibits better hydrophilicity, providing more proton transport channels. In the microstructure of the proton exchange membrane, hydrated protons (H3O+) form continuous hydrogen bond pathways through the electrostatic field of sulfonic acid groups, achieving efficient proton conduction. In addition to the sulfonic acid groups modified on the internal cavity of β-CD opening a transport path for protons, the sulfonic acid groups on the sulfonated polymer membrane can form hydrogen bonds with quaternary ammonium ions on AEPPS, further increasing the number of proton conduction sites. This allows for stronger binding of water molecules through electrostatic induction, further reducing the energy barrier for proton transfer from one site to another, thereby improving its proton conduction performance under high-temperature conditions.

[0029] (3) Water molecules act as a solubilizing medium, working together with sulfonic acid groups to construct stable transport channels. Under high humidity, increased free water widens proton channels, promoting proton transition and conduction. Therefore, proton exchange membranes containing the zwitterionic compound AEPPS, due to their good hydrophilicity, can increase the water molecule content in the membrane, causing sulfonic acid groups to ionize and form proton clusters. As the water content increases, the clusters swell and link together to form continuous channels, significantly improving proton conductivity. In particular, when applied to systems such as Nafion membranes, the advantages of AEPPS-modified β-CD proton exchange membranes are even more pronounced. The introduction of ZCD significantly improves the stability and durability of the proton exchange membrane. It not only optimizes the proton conduction mechanism but also significantly enhances the overall performance of the modified proton exchange membrane, providing strong support for applications in proton exchange membrane fuel cells and other fields.

[0030] (4) Compared with existing technologies, the preparation method of this invention is simple to operate, has low production costs, mild preparation conditions, and is easy to mass-produce. The selected materials are biodegradable, meet the requirements of clean energy production, and have a good industrial production foundation and broad application prospects. At the same time, this study provides a forward-looking reference for the design and construction of proton exchange membranes with specific structures.

[0031] In summary, this invention provides a proton exchange membrane with significantly improved proton conductivity through a simple process. By grafting AEPPS onto β-CD, this invention obtains zwitterionic β-cyclodextrin (ZCD), which possesses excellent hydrophilicity. The zwitterionic groups on ZCD provide additional proton conduction sites, enabling stronger binding of water molecules through electrostatic induction, further reducing the energy barrier for proton transfer from one site to another. Using ZCD as a filler effectively improves the membrane's water retention, greatly promoting proton conduction within the proton exchange membrane. The resulting modified proton exchange membrane exhibits excellent performance in both proton conductivity and operational stability. Attached Figure Description

[0032] Figure 1This is a comparison of the temperature-dependent proton conductivity (95% RH, RH: relative humidity) between zwitterionic functionalized β-cyclodextrin (ZCD) hybrid proton exchange membranes (doped at 0.7, 1.4, and 2.1 wt% of the Nafion matrix, respectively) and unhybridized proton exchange membranes obtained in Examples 1, 2, and 3 of this invention. In the figures, “RN” represents the unhybridized proton exchange membrane; “ZCD / RN-0.7” represents a ZCD hybrid proton exchange membrane with ZCD doping at 0.7 wt% of the Nafion matrix (i.e., the sample obtained in Example 1); “ZCD / RN-1.4” represents a ZCD hybrid proton exchange membrane with ZCD doping at 1.4 wt% of the Nafion matrix (i.e., the sample obtained in Example 2); and “ZCD / RN-2.1” represents a ZCD hybrid proton exchange membrane with ZCD doping at 2.1 wt% of the Nafion matrix (i.e., the sample obtained in Example 3).

[0033] Figure 2 The graph shows a comparison of the temperature-dependent proton conductivity (95% RH) of proton exchange membranes hybridized with β-CD and ZCD (both doped at 1.4 wt% of the Nafion matrix mass) and those without hybridization. In the graph, "RN" represents the unhybridized proton exchange membrane; "β-CD / RN-1.4" represents a β-CD hybridized proton exchange membrane with β-CD doping at 1.4 wt% of the Nafion matrix mass (i.e., the sample obtained in Comparative Example 1); and "ZCD / RN-1.4" represents a ZCD hybridized proton exchange membrane with ZCD doping at 1.4 wt% of the Nafion matrix mass (i.e., the sample obtained in Example 2).

[0034] Figure 3 The image shows the proton conductivity-time curve obtained from the proton conductivity stability test of ZCD / RN-1.4. "ZCD / RN-1.4" indicates a ZCD hybrid proton exchange membrane with ZCD doping amount of 1.4 wt% of the Nafion matrix mass (i.e., the sample obtained in Example 2). Detailed Implementation

[0035] 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. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0036] The zwitterionic-functionalized cyclodextrin sulfonated polymer composite proton exchange membrane of this invention is prepared by, in general, first obtaining the zwitterionic compound AEPPS, then grafting it onto cyclodextrin to obtain zwitterionic-functionalized β-cyclodextrin (ZCD), and finally doping it into a polymer to obtain a zwitterionic-functionalized cyclodextrin (ZCD) modified polymer hybrid proton exchange membrane. Specifically, the preparation method includes the following steps:

[0037] (1) N-aminoethylpiperazine (AEP) and 1,3-propylsulfonate lactone (1,3-PS) were mixed and stirred to synthesize the zwitterionic compound AEPPS;

[0038] (2) AEPPS and epichlorohydrin (ECH) were grafted onto cyclodextrin (β-CD) to obtain zwitterionic functionalized β-cyclodextrin (ZCD);

[0039] (3) Add zwitterion-functionalized β-cyclodextrin (ZCD) to the sulfonated polymer solution to obtain a casting solution, thereby obtaining a zwitterion-functionalized cyclodextrin sulfonated polymer composite proton exchange membrane.

[0040] The following are specific examples:

[0041] Example 1

[0042] 1. Place AEP (7.22 g) and acetonitrile (65 mL) into a 250 mL flask equipped with a magnetic stirrer. Then, under a 30 °C water bath, slowly add a mixture of 1,3-PS (5.9 g) and acetonitrile (5 mL) dropwise into the flask. Stir for 6 h under a 30 °C water bath. After cooling, collect the pale yellow crude product by centrifugation, wash thoroughly five times with acetone to remove unreacted monomers, and then vacuum dry at 50 °C for 24 h to obtain the zwitterionic compound AEPPS.

[0043] 2. Prepare 30 mL of a mixed solution of 8 wt% NaOH and 14 wt% β-CD using deionized water, and prepare 20 mL of a 14 wt% AEPPS aqueous solution. Mix the two solutions in a 250 mL round-bottom flask equipped with a magnetic stir bar. Place the flask in an oil bath at 80 °C and stir. Slowly add 4.4 mL of ECH. Connect a reflux condenser and continue the reaction at 80 °C for 1 h. After cooling, centrifuge to remove the supernatant. Wash five times with deionized water to remove unreacted monomers, and then vacuum dry at 30 °C for 24 h to obtain zwitterionic compound-modified cyclodextrin ZCD.

[0044] 3. Accurately weigh ZCD at a ratio of 0.7 wt%, dissolve it in 2 mL of DMF, and sonicate the solution for half an hour to ensure complete dissolution. Take 4 mL of Nafion solution, remove the solvent by rotary evaporation at 43 °C, then add 2 mL of DMF and rotary evaporate at 67 °C to recast Nafion. Then mix the corresponding ZCD solution with the recast Nafion solution and sonicate for 3 hours to ensure homogeneity. Slowly add the mixed solution to a preheated quartz mold and let it stand in a vacuum oven at 120 °C for 24 hours to remove the solvent, obtaining a composite proton exchange membrane with the corresponding ZCD content. Finally, soak the membrane in 3 wt% H2O2 solution at 80 °C for 1 hour, then acidify it with 1 M H2SO4 at 80 °C for 1 hour to convert the membrane to H2O. + The membrane is then rinsed with deionized water to obtain the ZCD-modified proton exchange membrane.

[0045] The proton exchange membrane prepared in this embodiment has a proton conductivity of up to 0.189 S / cm at 90°C and 95% RH, which is about 0.29 times higher than that of the unmodified proton exchange membrane (0.146 S / cm).

[0046] Example 2

[0047] 1. Place AEP (7.22 g) and acetonitrile (65 mL) into a 250 mL flask equipped with a magnetic stirrer. Then, under a 30 °C water bath, slowly add a mixture of 1,3-PS (5.9 g) and acetonitrile (5 mL) dropwise into the flask. Stir for 6 h under a 30 °C water bath. After cooling, collect the pale yellow crude product by centrifugation, wash thoroughly five times with acetone to remove unreacted monomers, and then vacuum dry at 50 °C for 24 h to obtain the zwitterionic compound AEPPS.

[0048] 2. Prepare 30 mL of a mixed solution of 8 wt% NaOH and 14 wt% β-CD using deionized water, and prepare 20 mL of a 14 wt% AEPPS aqueous solution. Mix the two solutions in a 250 mL round-bottom flask equipped with a magnetic stir bar. Place the flask in an oil bath at 80 °C and stir. Slowly add 4.4 mL of ECH. Connect a reflux condenser and continue the reaction at 80 °C for 1 h. After cooling, centrifuge to remove the supernatant. Wash five times with deionized water to remove unreacted monomers, and then vacuum dry at 30 °C for 24 h to obtain zwitterionic compound-modified cyclodextrin ZCD.

[0049] 3. Accurately weigh ZCD at a ratio of 1.4 wt%, dissolve it in 2 mL of DMF, and sonicate the solution for half an hour to ensure complete dissolution. Take 4 mL of Nafion solution, remove the solvent by rotary evaporation at 43 °C, then add 2 mL of DMF and rotary evaporate again at 67 °C to recast Nafion. Then mix the corresponding ZCD solution with the recast Nafion solution and sonicate for 3 hours to ensure homogeneity. Slowly add the mixed solution to a preheated quartz mold and let it stand in a vacuum oven at 120 °C for 24 hours to remove the solvent, obtaining a composite proton exchange membrane with the corresponding ZCD content. Finally, soak the membrane in 3 wt% H2O2 solution at 80 °C for 1 hour, then acidify it with 1 M H2SO4 at 80 °C for 1 hour to convert the membrane to H2O. + The membrane is then rinsed with deionized water to obtain the ZCD-modified proton exchange membrane.

[0050] like Figure 2 As shown, the proton exchange membrane prepared in this embodiment exhibits a proton conductivity as high as 0.243 S / cm at 90°C and 95% RH, which is approximately 0.66 times higher than that of the unmodified proton exchange membrane (0.146 S / cm). Figure 3 As shown, at 90°C and 95%RH for approximately 1020 min, the proton conductivity hardly decreased.

[0051] Example 3

[0052] 1. Place AEP (7.22 g) and acetonitrile (65 mL) into a 250 mL flask equipped with a magnetic stirrer. Then, under a 30 °C water bath, slowly add a mixture of 1,3-PS (5.9 g) and acetonitrile (5 mL) dropwise into the flask. Stir for 6 h under a 30 °C water bath. After cooling, collect the pale yellow crude product by centrifugation, wash thoroughly five times with acetone to remove unreacted monomers, and then vacuum dry at 50 °C for 24 h to obtain the zwitterionic compound AEPPS.

[0053] 2. Prepare 30 mL of a mixed solution of 8 wt% NaOH and 14 wt% β-CD using deionized water, and prepare 20 mL of a 14 wt% AEPPS aqueous solution. Mix the two solutions in a 250 mL round-bottom flask equipped with a magnetic stir bar. Place the flask in an oil bath at 80 °C and stir. Slowly add 4.4 mL of ECH. Connect a reflux condenser and continue the reaction at 80 °C for 1 h. After cooling, centrifuge to remove the supernatant. Wash five times with deionized water to remove unreacted monomers, and then vacuum dry at 30 °C for 24 h to obtain zwitterionic compound-modified cyclodextrin ZCD.

[0054] 3. Accurately weigh ZCD at a ratio of 2.1 wt%, dissolve it in 2 mL of DMF, and sonicate the solution for half an hour to ensure complete dissolution. Take 4 mL of Nafion solution, remove the solvent by rotary evaporation at 43 °C, then add 2 mL of DMF and rotary evaporate again at 67 °C to recast Nafion. Then mix the corresponding ZCD solution with the recast Nafion solution and sonicate for 3 hours to ensure homogeneity. Slowly add the mixed solution to a preheated quartz mold and let it stand in a vacuum oven at 120 °C for 24 hours to remove the solvent, obtaining a composite proton exchange membrane with the corresponding ZCD content. Finally, soak the membrane in 3 wt% H2O2 solution at 80 °C for 1 hour, then acidify it with 1 M H2SO4 at 80 °C for 1 hour to convert the membrane to H2O. + The membrane is then rinsed with deionized water to obtain the ZCD-modified proton exchange membrane.

[0055] The proton exchange membrane prepared in this embodiment has a proton conductivity of up to 0.200 S / cm at 90°C and 95% RH, which is about 0.36 times higher than that of the unmodified proton exchange membrane (0.146 S / cm).

[0056] Comparative Example 1

[0057] β-CD was accurately weighed at a ratio of 1.4 wt%, and dissolved in 2 mL of DMF. The solution was sonicated for half an hour to ensure complete dissolution. 4 mL of Nafion solution was taken, and the solvent was removed by rotary evaporation at 43 °C. Then, 2 mL of DMF was added, and the Nafion was recast by rotary evaporation at 67 °C. The corresponding ZCD solution was then mixed with the recast Nafion solution and sonicated for 3 hours to ensure homogeneity. The mixed solution was slowly added to a preheated quartz mold and allowed to stand in a vacuum oven at 120 °C for 24 hours to remove the solvent, obtaining a composite proton exchange membrane with the corresponding ZCD content. Finally, the membrane was first soaked in 3 wt% H₂O₂ solution at 80 °C for 1 hour, followed by acidification with 1 M H₂SO₄ at 80 °C for 1 hour to convert the membrane to H₂O. + The membrane is then rinsed with deionized water to obtain a β-CD modified proton exchange membrane.

[0058] The proton exchange membrane prepared in this comparative example exhibits a proton conductivity as high as 0.164 S / cm at 90°C and 95% RH, which is approximately 0.12 times higher than that of the unmodified proton exchange membrane (0.146 S / cm).

[0059] The proton conductivity of the proton exchange membrane prepared in Comparative Example 1 at 90°C and 95% RH was lower than that of the proton exchange membrane prepared in Example 2 at 90°C and 95% RH, demonstrating the significant advantage of ZCD in improving the proton conductivity of proton exchange membranes.

[0060] All raw materials used in the above embodiments were commercially available. Furthermore, the proton conductivity testing conditions (temperature and humidity) in the above embodiments are merely examples; depending on the actual situation, testing can also be performed under other temperature and / or humidity conditions. Generally, at higher humidity (greater than or equal to 90% RH), proton conductivity increases with increasing temperature.

[0061] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a zwitterionic functionalized cyclodextrin sulfonated polymer proton exchange membrane, characterized in that, Includes the following steps: (1) Place N-aminoethylpiperazine (AEP) and the first solvent together in a container, and then add the mixture of 1,3-propylsulfonate lactone (1,3-PS) and the second solvent dropwise into the container under a water bath at 20℃~50℃. Stir the reaction, and then separate, wash and dry the product to obtain the corresponding zwitterionic compound, denoted as AEPPS. (2) The AEPPS obtained in step (1) is stirred together with NaOH, β-cyclodextrin (β-CD) and deionized water in an oil bath at 60℃~100℃. Epichlorohydrin (ECH) is added dropwise to obtain a mixed solution. After connecting a reflux condenser, the solution is heated and refluxed. The product is then separated, washed and dried to obtain the zwitterionic compound-modified cyclodextrin, denoted as ZCD. (3) Disperse the ZCD obtained in step (2) in a sulfonated polymer solution and sonicate it to obtain a uniformly dispersed casting solution; then, use the casting solution to form a membrane material, dry it, and then soak it in hydrogen peroxide solution, acid and deionized water in sequence to obtain a zwitterionic functionalized cyclodextrin sulfonated polymer proton exchange membrane; wherein, the sulfonated polymer solution is one of the homogeneous solutions of perfluorosulfonic acid resin, sulfonated polyether ether ketone, sulfonated polybenzimidazole, sulfonated polyether sulfone or sulfonated polyimide.

2. The preparation method according to claim 1, characterized in that, In step (2), the volume of epichlorohydrin added accounts for 5-20% of the total volume of the mixed solution; the reaction temperature of the heating reflux reaction is 60-80°C and the reaction time is 15-180 min.

3. The preparation method according to claim 2, characterized in that, In step (2), the volume of epichlorohydrin added accounts for 5-12% of the total volume of the mixed solution; the reaction temperature of the heating reflux reaction is 65-80°C and the reaction time is 15-150 min.

4. The preparation method according to claim 1, characterized in that, In step (3), the mass of ZCD accounts for 0.7 to 2.1 wt% of the mass of the polymer matrix contained in the sulfonated polymer solution.

5. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of the N-aminoethylpiperazine to the 1,3-propylsulfonate lactone corresponding to the stirring reaction is 5:1 to 1:

5.

6. The preparation method according to claim 1, characterized in that, In step (1), the first solvent and the second solvent are independently selected from one or a mixture of several of N,N-dimethylformamide (DMF), acetonitrile, N,N-diethylformamide, tetrahydrofuran, pyrrolidone, dimethyl sulfoxide, CH3OH, and C2H5OH; The temperature of the water bath is 25~45°C; the reaction time of the stirring reaction is 2~12h.

7. The preparation method according to claim 1, characterized in that, In steps (1) and (2), the solvents used for cleaning are all low-boiling-point solvents with a boiling point not higher than 80°C, independently selected from one or a mixture of several of CH3OH, C2H5OH, CHCl3, CH2Cl2, CH3Cl, acetone, and butanone.

8. The preparation method according to claim 1, characterized in that, In step (3), the concentration of the sulfonated polymer solution is 1 ~ 40 wt%; The casting solution is used to form a film material, specifically by coating the casting solution into a film; The drying process involves placing the membrane material in an oven at 50-80°C, heating it to 110-150°C, and then maintaining the temperature for 12-36 hours; the heating rate is less than 0.5°C / min.

9. The preparation method according to claim 1, characterized in that, In step (3), the concentration of the sulfonated polymer solution is 1 ~ 40 wt%; The casting solution is used to form a film material, specifically by coating the casting solution into a film; The drying process involves placing the membrane material in an oven at 50-80°C, heating it to 110-150°C, and then maintaining the temperature for 12-36 hours; the heating rate is 0.1-0.5°C / min.

10. The preparation method according to claim 1, characterized in that, In step (3), the concentration of the hydrogen peroxide aqueous solution is 1~10 wt%; The acid is specifically one or a mixture of hydrochloric acid, sulfuric acid, and phosphoric acid, and the concentration of the acid is 0.1 ~ 2 mol / L.

11. The preparation method according to claim 10, characterized in that, In step (3), the concentration of the acid is 0.5 ~ 2 mol / L.

12. A zwitterionic functionalized cyclodextrin sulfonated polymer proton exchange membrane prepared by the preparation method according to any one of claims 1-11.

13. The application of the zwitterionic functionalized cyclodextrin sulfonated polymer proton exchange membrane as described in claim 12 in a proton exchange membrane fuel cell.

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