Preparation method of organic-inorganic nanofiber composite proton exchange membrane

Abstract

The invention relates to the technical field of fuel cells, and particularly discloses a preparation method of an organic-inorganic nanofiber composite proton exchange membrane. The preparation method comprises the following steps: 1) carrying out hydrophilization treatment on the surface of a porous nanofiber through polydopamine; 2) growing a metal organic framework (ZIF-8) on the porous fiber treated by the polydopamine in situ; (3) carrying out surface modification on the metal organic framework growing on the surface of the porous fiber by using ionic liquid; and 4) preparing a sulfonated aromatic polymer filling liquid, carrying out impregnation filling on the ionic liquid-metal organic framework functionalized porous nanofiber substrate, drying, and carrying out ionic crosslinking in a dilute sulfuric acid solution to obtain the organic-inorganic nanofiber composite proton exchange membrane. The composite proton exchange membrane prepared by the invention has excellent proton conductivity and mechanical properties, and has a good application prospect in direct methanol fuel cells.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a method for preparing an organic-inorganic nanofiber composite proton exchange membrane. Background Art

[0002] Over the past few decades, proton exchange membrane fuel cells (PEM fuel cells) have been extensively studied for their high energy conversion efficiency, environmental friendliness, and high power density. In particular, PEM fuel cells using hydrogen as the anode fuel have been used in fuel cell electric vehicles (e.g., the Toyota Mirai and Hyundai Nexo). However, the high cost of PEMs and Pt-based catalysts has limited the widespread application of hydrogen-powered vehicles. Currently, direct methanol fuel cells (DMFCs) offer significant safety advantages over hydrogen fuel cells because liquid methanol is easier to store and transport. However, currently known commercial PEMs (Nafion) face very serious methanol permeation and low cell durability problems in DMFCs, despite their good proton conductivity and chemical stability. Therefore, the development of low-cost PEMs with high methanol barrier properties and high durability while maintaining high proton conductivity is urgent.

[0003] In recent years, metal-organic frameworks (MOFs) have attracted widespread interest as a promising proton conductor because they have long-range ordered nanopore structures, high specific surface areas, and controllable pore surfaces, which can encapsulate or graft a large number of guest molecules as proton carriers, thereby further improving their proton conductivity. In addition, the small pore size of MOFs can effectively prevent the penetration of methanol fuel, thereby improving selectivity. However, the biggest obstacle to the practical application of MOFs as proton exchange membranes is their high brittleness and difficulty in forming independent membranes. Therefore, MOFs are usually combined with polymers to prepare composite membranes to overcome the above difficulties. In addition to the traditional method of combining MOFs as functional nanofillers with polymer matrices, in situ growth of MOFs on highly flexible three-dimensional nanofibers is another effective method to solve their processing difficulties. Specifically, this new idea provides the following advantages: (1) In situ growth of MOFs on the surface of nanofibers can greatly improve the processability of MOFs, thereby significantly improving the flexibility of proton exchange membranes. (2) Due to the inherent long-distance structure of nanofibers and the excellent porous structure of metal-organic frameworks, they can provide fast conduction channels for protons and significantly reduce the dimensional changes of filled polyelectrolytes. (3) Metal-organic framework-modified nanofibers can further improve the chemical stability and methanol barrier properties of PEMs. However, this single metal-organic framework-modified nanofiber composite membrane still has some defects, such as low proton conductivity and low mechanical strength due to poor interfacial compatibility with the subsequent filled sulfonated polymer. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the present invention aims to provide a method for preparing an organic-inorganic nanofiber composite proton exchange membrane.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing an organic-inorganic nanofiber composite proton exchange membrane comprises the following steps: using a porous nanofiber mat as a starting material, subjecting the surface of the porous nanofiber to polydopamine treatment to obtain a polydopamine-coated porous nanofiber mat; then in-situ growing a metal organic framework on the surface of the polydopamine-coated porous nanofiber to obtain a metal organic framework-modified porous nanofiber; then subjecting the surface of the porous nanofiber to ionic liquid-metal organic framework functionalized porous nanofiber; and finally impregnating a sulfonated aromatic polymer into the pores of the ionic liquid-metal organic framework functionalized porous nanofiber via solution to obtain the organic-inorganic nanofiber composite proton exchange membrane, wherein the porous nanofiber mat is a porous mat formed by interweaving multiple strands of nanofibers.

[0007] Furthermore, the nanofiber is any one of polyvinylidene fluoride electrospun fiber, polytetrafluoroethylene electrospun fiber, polyimide electrospun fiber, and polyacrylonitrile electrospun fiber.

[0008] Furthermore, the preparation method comprises the following steps:

[0009] (1) Soaking the purified porous nanofiber mat (preferably purified with anhydrous ethanol for 0.5 to 1 h) in Tris-HCl buffer, then adding dopamine hydrochloride, and mechanically stirring at room temperature for 6 to 24 h to obtain a polydopamine-coated porous nanofiber mat;

[0010] (2) transferring the polydopamine-coated porous nanofiber mat obtained in step (1) to a Zn(NO3)2·6H2O / methanol solution, then adding a 2-methylimidazole / methanol solution, stirring at room temperature for 12 to 24 hours to allow the metal organic framework (ZIF-8) to in situ grow on the surface of the polydopamine-coated porous nanofibers, washing, and placing in an oven at 60 to 80°C for 12 to 24 hours to obtain ZIF-8 modified porous nanofibers;

[0011] (3) soaking the ZIF-8 modified porous nanofibers obtained in step (2) in a solution containing an ionic liquid, stirring at room temperature for 18 to 24 hours, washing, and placing in a vacuum drying oven at 60 to 80° C. for 18 to 24 hours to obtain ionic liquid-metal organic framework functionalized porous nanofibers;

[0012] (4) using a first solvent to dissolve the sulfonated polyetheretherketone, and then adding a second solvent to dilute it, and impregnating the obtained sulfonated polyetheretherketone solution into the ionic liquid-metal organic framework functionalized porous nanofibers obtained in step (3); after drying, soaking in a 0.5-1.0 mol / L sulfuric acid solution at room temperature for 6-8 hours, washing to remove the residual sulfuric acid on the surface, and obtaining the final organic-inorganic nanofiber composite proton exchange membrane.

[0013] Furthermore, the mass ratio of the purified porous nanofiber mat to dopamine hydrochloride is 0.88-1.76:0.8 (preferably 1.32:0.8); and / or

[0014] The mass ratio of the dopamine-coated polyvinylidene fluoride nanofiber mat to 2-methylimidazole is 0.2-1:1 (preferably 0.48:1); and / or

[0015] The mass ratio of ZIF-8 modified porous nanofibers to ionic liquid is 0.27:0.4-1.2 (preferably 0.27:1.0);

[0016] Furthermore, the ionic liquid preparation method is as follows: slowly add 1,3-propane sultone with the same molar number as imidazole to the imidazole / anhydrous ethanol solution, stir at room temperature for 18 to 24 hours, then filter the reaction solution, repeatedly wash with anhydrous ethanol, and dry the obtained white precipitate in a vacuum oven at 60 to 80°C for 18 to 24 hours to obtain the ionic liquid.

[0017] Furthermore, in step (1), the concentration of Tris-HCl buffer is 1 to 10 mmol / L, preferably 10 mmol / L, and the pH is 8.0 to 9.0, preferably 8.5; the preferred ratio between dopamine hydrochloride and buffer is 2 mg:1 mL;

[0018] Furthermore, the mechanical stirring time at room temperature in step (1) is 12 to 24 hours, most preferably 24 hours;

[0019] Furthermore, in step (2), the amount of Zn(NO3)2·6H2O in the Zn(NO3)2·6H2O / methanol solution is 7-11 mg / mL, most preferably 9 mg / mL; the concentration of the 2-methylimidazole / methanol solution is preferably 8-12 mg / mL, most preferably 10 mg / mL; the volume ratio of the Zn(NO3)2·6H2O / methanol solution to the 2-methylimidazole / methanol solution is 1:1;

[0020] Furthermore, the concentration of the imidazole / anhydrous ethanol solution is 0.8 to 1.0 mol / L, most preferably 1.0 mol / L;

[0021] Furthermore, the concentration of the ionic liquid solution in step (3) is 2-6 g / L, and the solvent is anhydrous ethanol and water with the same volume, and the preferred concentration is 5 g / L.

[0022] Furthermore, the degree of sulfonation of the sulfonated polyetheretherketone in step (4) is 60-80%, preferably 70%; the first solvent is selected from any one of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; the second solvent is deionized water; the preferred volume ratio of the first solvent to the second solvent is 1:3, and the concentration of the sulfonated polyetheretherketone solution is 1wt%-3wt%, preferably 2wt%.

[0023] Furthermore, the drying in step (4) is: first drying at 40°C for 24 hours, and then continuing drying at 80°C for 24 hours.

[0024] The present invention also provides the use of the organic-inorganic nanofiber composite proton exchange membrane obtained by the above preparation method in the preparation of a direct methanol fuel cell.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] (1) With the help of flexible porous nanofibers, the problem of brittleness and difficulty in forming membranes of metal organic frameworks was effectively solved. The prepared organic-inorganic nanofiber composite membrane showed excellent mechanical properties (tensile strength up to 39 MPa, elongation at break up to 126%).

[0027] (2) The modification of ionic liquid further improves the conductivity of the composite membrane. For example, compared with the conductivity of the metal organic framework-polyvinylidene fluoride-sulfonated polyetheretherketone composite membrane (80℃, 125.08mS / cm), the conductivity of the ionic liquid-metal organic framework functionalized polyvinylidene fluoride nanofiber composite proton exchange membrane is increased to 161.92mS / cm.

[0028] (3) The modification of ionic liquid also improves the interfacial compatibility between sulfonated aromatic polymer and porous nanofibers. The prepared ionic liquid-metal organic framework functionalized polyvinylidene fluoride nanofiber composite proton exchange membrane exhibits excellent methanol barrier performance. Under 2M methanol fuel, its methanol cross current density is only 81.70mA / cm 2 , which is about the same as that of sulfonated polyetheretherketone (208.13mA / cm 2 ) of 40%.

[0029] In summary, the ionic liquid-metal organic framework functionalized polyvinylidene fluoride nanofiber composite proton exchange membrane prepared by the present invention has great application prospects in the field of DMFCs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 and Figure 2 They are the Zn 2p and N1s high-resolution X-ray photoelectron spectra of the ZIF-8 modified polyvinylidene fluoride nanofiber mat (represented by ZIF-8@PVDF) in step (2) of Example 1 and the ionic liquid-metal organic framework functionalized polyvinylidene fluoride nanofiber mat (represented by IL-ZIF-8@PVDF) in step (3), respectively.

[0031] Figure 3 These are scanning electron microscope images of the ZIF-8 modified polyvinylidene fluoride nanofiber mat in step (2) of Example 1 and the ionic liquid-metal organic framework functionalized polyvinylidene fluoride nanofiber mat in step (3).

[0032] Figure 4 and Figure 5 They are scanning electron microscope images of the cross sections of the metal organic framework-polyvinylidene fluoride-sulfonated polyetheretherketone composite membrane in Comparative Example 4 and the ionic liquid-metal organic framework functionalized polyvinylidene fluoride composite proton exchange membrane in step (4) of Example 1, respectively.

[0033] from Figure 1 In ZIF-8@PVDF, the peaks of Zn 2p3 and Zn 2p3 belonging to ZIF-8 appear at 1021.8eV and 1045.5eV respectively; compared with ZIF@PVDF, the intensity of Zn 2p peak of IL-ZIF-8@PVDF is significantly reduced due to the introduction of ionic liquid. Figure 2 It can be seen from the N1s graphs of ZIF-8@PVDF and IL-ZIF-8@PVDF that the CN peak intensity of IL-ZIF-8@PVDF is significantly weakened compared with the CN peak of ZIF-8@PVDF. At the same time, a new peak appears at 401.6 eV, which is consistent with the N + -(CH2)4 related. Figure 3 It can be seen that the ZIF-8 nanoparticles on the ZIF-8@PVDF are clearly attached to the fiber surface. After further introduction of ionic liquid, the surface of the IL-ZIF-8@PVDF fiber becomes smooth. Figure 4 It can be seen that the cross section of the metal organic framework-polyvinylidene fluoride-sulfonated polyetheretherketone composite membrane has many pore defects. This is because the incorporation of hydrophobic ZIF-8 greatly reduces the compatibility between the porous substrate and the filler, resulting in visible pore defects at the interface. Figure 5 It can be seen that further modification using ionic liquids results in a very dense cross-section of the ionic liquid-metal organic framework functionalized polyvinylidene fluoride composite proton exchange membrane and significantly improved interfacial compatibility. DETAILED DESCRIPTION

[0034] The applicant will now provide a further detailed description of the technical solution of the present invention in conjunction with specific embodiments and accompanying drawings, with the aim of enabling those skilled in the art to have a clearer understanding and recognition of the present application.

[0035] The following specific embodiments should not be understood or interpreted in any way as limiting the scope of protection requested by the claims of this application.

[0036] The polyvinylidene fluoride (HSV900) used in the following examples was purchased from Aquamarine of France. The polyvinylidene fluoride was dissolved in N,N-dimethylacetamide / acetone (the mass ratio of N,N-dimethylacetamide to acetone was 7:3) to form a polymer solution with a mass fraction of 16 wt%. The resulting polymer solution was added to the syringe of the electrospinning device at a solution feed rate of 0.5 ml / h. The distance between the spinneret and the aluminum collector was fixed at 15 cm. Electrospinning was performed at room temperature (20-25 ° C) to obtain polyvinylidene fluoride electrospun nanofiber mats, hereinafter referred to as polyvinylidene fluoride nanofiber mats.

[0037] The polyetheretherketone PEEK (brand 021P) used in the following examples comes from Jilin University. Other reagents and raw materials are conventional commercial products. The preparation steps of the sulfonated polyetheretherketone used are as follows: heat 200mL concentrated sulfuric acid (98wt%) to 50°C, evenly add 10g of PEEK to the sulfuric acid solution within 1 minute, and stir with a mechanical stirrer, and react at 50°C for 5.5h. After the reaction is completed, the obtained mixture is slowly poured into ice water and stirred continuously, and then the obtained precipitate is washed with deionized water until the pH of the filtrate is 7.0. Finally, the sample is vacuum dried at 60°C for 24h to obtain sulfonated polyetheretherketone. The degree of sulfonation is 70% calculated by nuclear magnetic resonance. Example 1: A method for preparing an ionic liquid-metal organic framework functionalized polyvinylidene fluoride nanofiber composite proton exchange membrane, comprising the following steps:

[0038] (1) Purify polyvinylidene fluoride nanofiber mats (each piece is about 8×8 cm, 0.22 g) in anhydrous ethanol for 0.5 h, wash with deionized water, and prepare a 10 mmol / L tris-hydroxymethylaminomethane (Tris-HCl) buffer solution with a pH of 8.5. Soak the purified polyvinylidene fluoride nanofiber mats (6 pieces, 1.32 g) in 400 mL of the buffer solution, then add dopamine hydrochloride at a ratio of 2 mg:1 mL of dopamine hydrochloride to the buffer solution. Mechanically stir at room temperature (25°C, the same below) for 24 h. Finally, wash the nanofiber mats repeatedly with deionized water (washing end point: the nanofiber mat is placed in deionized water, the liquid is clear and transparent, and there is no impurities visible to the naked eye) and dry in a 60°C oven for 6 h to obtain polydopamine-coated polyvinylidene fluoride nanofiber mats.

[0039] (2) The obtained polydopamine-coated polyvinylidene fluoride nanofiber mat (2 pieces, 0.48 g) was transferred to 100 mL of Zn(NO3)2 / methanol solution (900 mg of Zn(NO3)2·6H2O dissolved in 100 mL of methanol), and then 100 mL of 10 mg / mL 2-methylimidazole / methanol solution was added. The mixture was stirred at room temperature for 24 h to allow the metal organic framework (ZIF-8) to grow in situ on the surface of the polydopamine-coated polyvinylidene fluoride nanofiber mat. Finally, after repeated washing with anhydrous ethanol (washing end point: the nanofiber was placed in anhydrous ethanol, the liquid color was clear and transparent, and there was no visible impurities, the same below), it was placed in an oven at 80°C for 24 h to obtain a ZIF-8 modified polyvinylidene fluoride nanofiber mat.

[0040] (3) Prepare 100 mL of 1.0 mol / L imidazole / anhydrous ethanol solution, then slowly add 1,3-propane sultone in the same molar number as imidazole to the solution and stir at room temperature for 24 h. Then filter the reaction solution, wash it repeatedly with anhydrous ethanol, and dry the obtained white precipitate in a vacuum oven at 60 ° C for 24 h to obtain an ionic liquid. The obtained ZIF-8 modified polyvinylidene fluoride nanofiber mat (1 piece, 0.27 g) is soaked in an ionic liquid solution with a concentration of 5 g / L (the mass of the ionic liquid is 1 g, the solvent is anhydrous ethanol and water, the volume ratio is 1:1, and the total volume is 200 mL). Stir at room temperature for 24 h, wash the nanofiber mat after the reaction is completed with anhydrous ethanol repeatedly, and place it in a vacuum drying oven at 80 ° C for 24 h to obtain an ionic liquid-metal organic framework functionalized polyvinylidene fluoride nanofiber mat.

[0041] (4) Finally, the sulfonated polyetheretherketone with a sulfonation degree of 70% was dissolved in the first solvent (N,N-dimethylformamide), and then the second solvent deionized water was added to dilute it to form a sulfonated polyetheretherketone mixed solution with a concentration of 2wt% (the volume ratio of the first solvent to the second solvent was 1:3). The obtained ionic liquid-metal organic framework functionalized polyvinylidene fluoride nanofiber mat was placed on a clean glass plate, and the sulfonated polyetheretherketone mixed solution was impregnated into the nanofiber mat. It was first dried at 40℃ for 24h, and then dried at 80℃ for another 24h. The obtained membrane was placed in a 0.5mol / L sulfuric acid solution at room temperature for 6h, and repeatedly washed with deionized water to remove the residual sulfuric acid on the membrane surface to obtain the final ionic liquid-metal organic framework functionalized polyvinylidene fluoride nanofiber composite proton exchange membrane (thickness of 73±1.8μm).

[0042] For comparison: the sulfonated polyetheretherketone with a sulfonation degree of 70% prepared in this example was dissolved in N,N-dimethylformamide to form a polymer solution with a mass fraction of 3.5wt%, and cast into a film on a clean glass plate. The film was first dried at 40°C for 24h and then dried at 80°C for another 24h to obtain a sulfonated polyetheretherketone film with a thickness of 56±0.5μm (Comparative Example 1).

[0043] In addition, the polyvinylidene fluoride nanofiber mat prepared in the example was placed on a clean glass plate, and the 2 wt% sulfonated polyetheretherketone mixed solution in step (4) of Example 1 was used to impregnate and fill the nanofiber mat. The mixture was first dried at 40°C for 24 h and then dried at 80°C for another 24 h to obtain a polyvinylidene fluoride-sulfonated polyetheretherketone composite membrane with a thickness of 77±0.8 μm (Comparative Example 2).

[0044] In addition, the polydopamine-coated polyvinylidene fluoride nanofiber mat prepared in step (1) of Example 1 was placed on a clean glass plate, and the 2 wt% sulfonated polyetheretherketone mixed solution in step (4) of Example 1 was impregnated and filled into the nanofiber mat. The mixture was first dried at 40°C for 24 h and then dried at 80°C for another 24 h to obtain a polydopamine-polyvinylidene fluoride-sulfonated polyetheretherketone composite membrane with a thickness of 70±3.5 μm (Comparative Example 3).

[0045] In addition, the ZIF-8 modified polyvinylidene fluoride nanofiber mat prepared in step (2) of Example 1 was placed on a clean glass plate, and the 2 wt% sulfonated polyetheretherketone mixed solution in step (4) of Example 1 was impregnated and filled into the nanofiber mat. The mixture was first dried at 40°C for 24 h and then dried at 80°C for another 24 h to obtain a metal organic framework-polyvinylidene fluoride-sulfonated polyetheretherketone composite membrane with a thickness of 78±0.7 μm (Comparative Example 4).

[0046] The performance test results of the sulfonated polyetheretherketone membrane, polyvinylidene fluoride-sulfonated polyetheretherketone composite membrane, polydopamine-polyvinylidene fluoride-sulfonated polyetheretherketone composite membrane, metal organic framework-polyvinylidene fluoride-sulfonated polyetheretherketone and the composite membrane prepared in Example 1 are shown in Table 1:

[0047] Table 1

[0048]

[0049]

[0050] From the results in Table 1, it can be seen that the proton conductivity of the ionic liquid-metal organic framework functionalized polyvinylidene fluoride nanofiber composite proton exchange membrane prepared in Example 1 at 20°C and 80°C is higher than that of other comparative samples, especially the proton conductivity at 80°C is 2.08 times that of sulfonated polyetheretherketone under the same conditions; at the same time, the composite membrane also maintains good tensile strength and toughness, which is sufficient to meet the use requirements of direct methanol fuel cells. In addition, it can be seen that the composite proton exchange membrane prepared in Example 1 has excellent methanol barrier performance (methanol cross current density is only 81.70mA / cm 2 ).

[0051] Example 2: Preparation method of an ionic liquid-metal organic framework functionalized polyvinylidene fluoride nanofiber composite proton exchange membrane

[0052] The preparation method of this example is the same as that of Example 1, with the only difference being that the ZIF-8 modified polyvinylidene fluoride nanofiber mat in step (3) is immersed in an ionic liquid solution with a concentration of 2 g / L (total volume of 200 mL). Example 3: Preparation method of an ionic liquid-metal organic framework functionalized polyvinylidene fluoride nanofiber composite proton exchange membrane

[0053] The preparation method of this example is the same as that of Example 1, with the only difference being that the ZIF-8 modified polyvinylidene fluoride nanofiber mat in step (3) is immersed in an ionic liquid solution with a concentration of 3 g / L (total volume of 200 mL). Example 4: Preparation method of an ionic liquid-metal organic framework functionalized polyvinylidene fluoride nanofiber composite proton exchange membrane

[0054] The preparation method of this example is the same as that of Example 1, with the only difference being that the ZIF-8 modified polyvinylidene fluoride nanofiber mat in step (3) is immersed in an ionic liquid solution with a concentration of 4 g / L (total volume of 200 mL). Example 5: Preparation method of an ionic liquid-metal organic framework functionalized polyvinylidene fluoride nanofiber composite proton exchange membrane

[0055] The preparation method of this example is the same as that of Example 1, except that the ZIF-8 modified polyvinylidene fluoride nanofiber mat in step (3) is immersed in an ionic liquid solution with a concentration of 6 g / L (total volume of 200 mL).

[0056] Table 2 lists the performance index data of the ionic liquid-metal organic framework functionalized polyvinylidene fluoride nanofiber composite proton exchange membranes prepared in Examples 2-5.

[0057] Table 2

[0058]

[0059]

[0060] It can be seen from Table 2 and the results of Example 1 that with the increase of ionic liquid concentration (2g / L-5g / L), the proton conductivity increases significantly. When the ionic liquid concentration rises to 5g / L, the proton conductivity reaches the highest value. However, when the ionic liquid concentration is further increased to 6g / L, the proton conductivity decreases. In addition, the tensile strength (≥37MPa) and elongation at break (≥118%) of Examples 2 to 5 are maintained at a high level. All membrane samples have good methanol barrier properties (methanol cross current density ≤86.78mA / cm 2 ).

[0061] The test conditions for the membrane performance prepared in the above examples are uniformly described as follows:

[0062] (1) Proton conductivity: Electrochemical impedance spectroscopy (EIS) was recorded on an electrochemical workstation (frequency range: 1 Hz-10 6 The proton conductivity of the membrane in a fully wetted state was measured (Hz). The membrane (width × length = 2 × 3 cm) was immersed in deionized water at room temperature for 24 hours, and then its resistance (R) was measured at different temperatures. The proton conductivity (σ) was calculated using the following formula:

[0063] σ=L / (R×A)

[0064] Where L is the distance between the two electrodes (cm), R is the resistance of the test membrane sample (Ω), and A is the effective cross-sectional area of ​​the membrane (cm 2 ).

[0065] (2) Tensile strength and elongation at break: All film samples with a width of 1×4 cm were subjected to tensile tests at room temperature at a speed of 10 mm / min using a tensile testing machine.

[0066] (3) Methanol permeability test: The methanol crossover current density (mA / cm2) of the membrane sample was measured by linear sweep voltammetry (LSV) at 80°C and 2M methanol fuel. 2 ) to evaluate the methanol permeability of the membrane.

Claims

1. A method for preparing an organic-inorganic nanofiber composite proton exchange membrane, characterized in that: A porous nanofiber mat was used as a starting material and surface treated with polydopamine to obtain a polydopamine-coated porous nanofiber mat; The metal organic framework is then in situ grown on the surface of the polydopamine-coated porous nanofiber to obtain the metal organic framework-modified porous nanofiber; the surface is then modified with ionic liquid to obtain the ionic liquid-metal organic framework functionalized porous nanofiber; finally, the sulfonated aromatic polymer is impregnated into the pores of the ionic liquid-metal organic framework functionalized porous nanofiber through solution impregnation to obtain the organic-inorganic nanofiber composite proton exchange membrane, and the porous nanofiber mat is a porous mat formed by interweaving multiple strands of nanofibers.

2. The preparation method according to claim 1, characterized in that The nanofiber is any one of polyvinylidene fluoride electrospun fiber, polytetrafluoroethylene electrospun fiber, polyimide electrospun fiber, and polyacrylonitrile electrospun fiber.

3. The preparation method according to claim 1, characterized in that The preparation method comprises the following steps: (1) Soaking the purified porous nanofiber mat in Tris-HCl buffer, then adding dopamine hydrochloride, and mechanically stirring at room temperature for 6 to 24 hours to obtain a polydopamine-coated porous nanofiber mat; (2) transferring the polydopamine-coated porous nanofiber mat obtained in step (1) to a Zn(NO3)2·6H2O / methanol solution, adding a 2-methylimidazole / methanol solution, and stirring at room temperature for 12 to 24 hours to allow the metal organic framework ZIF-8 to grow in situ on the surface of the polydopamine-coated porous nanofibers. After washing, the mixture was placed in an oven at 60 to 80°C for 12 to 24 hours to obtain ZIF-8 modified porous nanofibers; (3) soaking the ZIF-8 modified porous nanofibers obtained in step (2) in a solution containing an ionic liquid, stirring at room temperature for 18 to 24 hours, washing, and placing in a vacuum drying oven at 60 to 80° C. for 18 to 24 hours to obtain ionic liquid-metal organic framework functionalized porous nanofibers; (4) using a first solvent to dissolve the sulfonated polyetheretherketone, and then adding a second solvent to dilute it, and impregnating the obtained sulfonated polyetheretherketone solution into the ionic liquid-metal organic framework functionalized porous nanofibers obtained in step (3); after drying, soaking in a 0.5-1.0 mol / L sulfuric acid solution at room temperature for 6-8 hours, washing to remove residual sulfuric acid on the surface, and obtaining an organic-inorganic nanofiber composite proton exchange membrane.

4. The preparation method according to claim 3, characterized in that The mass ratio of the purified porous nanofiber mat to dopamine hydrochloride is 0.88-1.76:0.8; and / or The mass ratio of the dopamine-coated polyvinylidene fluoride nanofiber mat to 2-methylimidazole is 0.2-1:1; and / or The mass ratio of ZIF-8 modified porous nanofibers to ionic liquid is 0.27:0.4-1.

2.

5. The preparation method according to claim 3, characterized in that The preparation method of the ionic liquid is as follows: slowly adding 1,3-propane sultone in the same molar number as imidazole to an imidazole / anhydrous ethanol solution, stirring at room temperature for 18 to 24 hours, then filtering the reaction solution, repeatedly washing with anhydrous ethanol, and drying the obtained white precipitate in a vacuum oven at 60 to 80° C. for 18 to 24 hours to obtain the ionic liquid.

6. The preparation method according to claim 3, characterized in that In step (1), the concentration of Tris-HCl buffer is 1 to 10 mmol / L, and the pH is 8.0 to 9.0; the ratio between dopamine hydrochloride and buffer is 2 mg:1 mL.

7. The preparation method according to claim 3, characterized in that The mechanical stirring time at room temperature in step (1) is 12 to 24 hours.

8. The preparation method according to claim 3, characterized in that In step (2), the amount of Zn(NO3)2·6H2O in the Zn(NO3)2·6H2O / methanol solution is 7-11 mg / mL; the concentration of the 2-methylimidazole / methanol solution is 8-12 mg / mL; the volume ratio of the Zn(NO3)2·6H2O / methanol solution to the 2-methylimidazole / methanol solution is 1:1; and / or The concentration of the imidazole / anhydrous ethanol solution is 0.8 to 1.0 mol / L; and / or The concentration of the ionic liquid solution in step (3) is 2 to 6 g / L, and the solvent is a mixture of anhydrous ethanol and water in equal volumes; and / or The degree of sulfonation of the sulfonated polyetheretherketone in step (4) is 60-80%; the first solvent is selected from any one of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; the second solvent is deionized water; the volume ratio of the first solvent to the second solvent is 1:3, and the concentration of the sulfonated polyetheretherketone solution is 1wt%-3wt%.

9. The preparation method according to claim 3, characterized in that The drying in step (4) is as follows: first drying at 40°C for 24 hours, and then continuing drying at 80°C for 24 hours.

10. Use of the organic-inorganic nanofiber composite proton exchange membrane obtained by the preparation method according to any one of claims 1 to 9 in the preparation of a direct methanol fuel cell.

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