Functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane as well as preparation method and application thereof

Abstract

The invention belongs to the field of proton exchange membrane water electrolysis hydrogen production, and particularly relates to a functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane as well as a preparation method and application thereof, which are used for solving the technical problems of high cost, low mechanical strength, swelling at high temperature and low conductivity of a Nafion composite membrane. A PVDF / Nafion solution is subjected to functionalized ionic liquid modification to obtain a membrane casting solution, and then the membrane casting solution is coated and dried to obtain the functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane. According to the ionic liquid modified PVDF / Nafion composite proton exchange membrane disclosed by the invention, the usage amount of Nafion resin is reduced, the cost is reduced, and meanwhile, the proton conductivity is improved by adding the ionic liquid; the ionic liquid functionalized by different cations can form a hydrogen bond network with sulfonic acid groups of Nafion and fluorine atoms of PVDF, so that the mechanical property and the thermal stability of the proton exchange membrane are improved, and the proton exchange membrane has a good application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of proton exchange membrane electrolysis of water to produce hydrogen, and particularly relates to a functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane as well as a preparation method and application thereof. BACKGROUND

[0002] Hydrogen is considered as a new energy with great potential, which has high energy density and is suitable for large-scale hydrogen energy storage. Green hydrogen can be prepared by using renewable energy to electrolyze water, which can not only reduce the production cost of hydrogen, but also realize zero carbon emission. Proton exchange membrane water electrolysis (PEMWE) technology is pollution-free, high-purity, fast start and stop, small in size, and flexible in operation during hydrogen production, and is very suitable for combination with distributed renewable energy such as wind energy and solar energy. Therefore, PEMWE technology has been widely concerned at home and abroad in the field of green hydrogen production.

[0003] The proton exchange membrane (PEM) in the PEMWE membrane electrode is one of the core components, which plays a role in blocking hydrogen and oxygen and transmitting protons, and accounts for about 20% of the cost of the membrane electrode. At present, the proton exchange membrane used in PEMWE is perfluorosulfonic acid membrane (PFSA) Nafion membrane, which has excellent proton conductivity, good chemical stability and mechanical stability, but has problems such as high production cost, swelling and conductivity reduction at high temperature.

[0004] Chinese patent CN117107296A discloses a composite high-temperature proton exchange membrane for water electrolysis and a preparation method and application thereof. The proton exchange membrane comprises Nafion resin and 0.1-1.0 wt% boron nitride. The composite membrane has good mechanical stability and excellent conductivity, maintains a certain water content at a high temperature of 100-200 ℃, and avoids the problem of proton conductivity reduction caused by water deficiency. The conductivity and tensile strength of the composite membrane are relatively low, and the water absorption rate is relatively high.

[0005] Chinese patent CN115763921A discloses a preparation method of a fuel cell proton exchange membrane, and particularly relates to a conductive polyaniline / graphene oxide modified Nafion composite proton exchange membrane and application thereof. The graphene oxide in the invention has various hydrophilic groups with good compatibility with the high molecular film, which improves the water retention of the Nafion membrane and ensures that the Nafion composite membrane has good proton conductivity. The surface groups of the conductive polyaniline combine with the Nafion membrane to form a conductive network, which strengthens the proton conductivity of the composite membrane and enhances the conduction capacity. The dispersion of graphene in the composite membrane is difficult, the preparation process of the composite membrane is complex, and the proton exchange capacity and proton conductivity of the composite membrane are low.

[0006] A method for functionalizing a PVDF proton exchange membrane with UiO-66-NH2 / UiO-66-SO3H is disclosed in Chinese patent CN116779925A. The method combines in-situ growth and electrospinning to grow UiO MOF on the surface of PVDF nanofibers and to prepare a proton exchange membrane by compounding with Nafion. The MOF material provides proton transport sites and has higher proton conductivity; compounding PVDF in Nafion improves the durability and mechanical properties of the proton exchange membrane and reduces the cost of the membrane, but the preparation process is complex. SUMMARY

[0007] In view of the technical problems of high cost, low mechanical strength, high temperature swelling and low conductivity of Nafion composite membrane, a functional ionic liquid modified PVDF / Nafion composite proton exchange membrane and its preparation method and application are proposed.

[0008] To achieve the above-mentioned purposes, the technical solutions of the present application are as follows: A method for preparing a functional ionic liquid modified PVDF / Nafion composite proton exchange membrane, comprising the following steps: (1) After drying Nafion D2020 20wt% solution to form Nafion resin, the Nafion resin is dissolved in a polar aprotic solvent to prepare a Nafion solution with a certain concentration for standby use; (2) A PVDF solution with a certain concentration is prepared, and the PVDF solution is compounded with the Nafion solution obtained in step (1) to form a uniform PVDF / Nafion solution; (3) Different functional ionic liquids are added to modify the PVDF / Nafion solution obtained in step (2) to form a uniform casting solution; (4) The solution obtained in step (3) is coated on a coating machine for coating and drying to obtain a functional ionic liquid modified PVDF / Nafion composite proton exchange membrane.

[0009] In step (1), the temperature for drying the Nafion D2020 20wt% solution is 50-100 ℃, and the time is 12-72h.

[0010] In step (1), the polar aprotic solvent is any one of acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide and hexamethylphosphoramide; the dissolving temperature is 40-120 ℃, and the time is 12-72h.

[0011] In step (1), the content of Nafion resin in the Nafion solution is 1-20wt%.

[0012] The solvent in the step (2) is any one of acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide and hexamethylphosphoramide, and the mass percentage of the solute PVDF is 5-20 wt%.

[0013] The mass ratio of the Nafion solution to the PVDF solution in the step (2) is (1-10):1; the PVDF solution and the Nafion solution are stirred at 40-120 ℃ for 12-72 h to form a uniform PVDF / Nafion solution.

[0014] The functionalized ionic liquid in the step (3) refers to any one of a cation hydroxyl (-OH) functionalized ionic liquid, a cation carboxyl (-COOH) functionalized ionic liquid, a cation ether (-ROR) functionalized ionic liquid, a cation sulfonic acid (-SO3H) functionalized ionic liquid and a cation benzyl (-Benzyl) functionalized ionic liquid.

[0015] Specifically, the cation hydroxyl functionalized ionic liquid in the step (3) is 1-hydroxyethyl-3-methylimidazole chloride ([HOETMIM][Cl]), the cation carboxyl functionalized ionic liquid is 1-carboxymethyl-3-methylimidazole chloride ([HOOCMIM][Cl]), the cation ether functionalized ionic liquid is 1-ethyl methyl ether-3-methylimidazole chloride ([EOMIM][Cl]), the cation sulfonic acid (-SO3H) functionalized ionic liquid is 1-propane sulfonic acid-3-methylimidazole chloride ([PrSO3HMIM][Cl]) and the cation benzyl (-Benzyl) functionalized ionic liquid is 1-benzyl-3-methylimidazole chloride ([BzMIM][Cl]).

[0016] The mass of the functionalized ionic liquid in the step (3) is 0.5-50 wt% of the mass of the Nafion resin; and the modification condition is stirring at 40-120 ℃ for 12-72 h.

[0017] The coating thickness in the step (4) is 20-1000 μm; the drying temperature is 30-250 ℃, and the drying time is 6-72 h, and then the product is cooled to room temperature.

[0018] The functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane is prepared by the above preparation method.

[0019] The functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane is prepared by the above preparation method.

[0020] The present application has the following beneficial effects: (1) The present application adds PVDF as a coating liquid in a Nafion dispersion liquid to form a composite film. PVDF is a good polymer material, has excellent film-forming performance, and is low in price. As a hydrophobic polymer with high mechanical strength and chemical stability, PVDF has good chemical compatibility with Nafion, which has a perfluoro structure in the main chain, and is low in cost, and is one of the candidate raw materials for modifying proton exchange membranes. The addition of PVDF in Nafion can improve its stability, mechanical properties and swelling.

[0021] (2) The ionic liquid (ILs) in the present application is used as a green medium, and has excellent thermal stability, ionic conductivity and electrochemical stability, and can control the stability and proton conductivity of the PEM film. At present, the application is concentrated in the field of proton exchange membrane fuel cells. The ionic liquid has high proton conductivity. The functionalized ionic liquid with different functional groups (-OH, -COOH, -ROR, -SO3H, -Benzyl, etc.) introduced into PVDF / Nafion forms a hydrogen bond network with the sulfonic acid groups of Nafion, which improves the proton conductivity and significantly increases the thermal stability and mechanical stability of the composite film (when the addition amount of the sulfonic acid group functionalized ionic liquid [PrSO3HMIM][Cl] is 5 wt%, 10 wt% and 20 wt% of the mass of Nafion resin, the strength of the sulfonic acid group functionalized ionic liquid [PrSO3HMIM][Cl] composite PVDF / Nafion proton exchange membrane can reach 22.446 MPa, 22.644 MPa and 19.668 MPa, respectively).

[0022] (3) The functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane process described in the present application has good stability and low cost, which lays a solid foundation for large-scale preparation of composite membranes. The composite proton exchange membrane prepared has low swelling even at high temperature (80℃), slightly decreased water absorption rate (at high temperature 80℃), high proton conductivity, thermal stability and mechanical strength, which improves the electrolysis efficiency and service life of the proton exchange membrane in water electrolysis. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the description of the embodiments or the prior art will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0024] Figure 1 SEM image of the functionalized ionic liquid modified PVDF / Nafion composite membrane prepared in Example 1.

[0025] Figure 2 The conductivity of PVDF / Nafion composite membranes modified with different cationic functionalized ionic liquids prepared in Examples 1-5 is shown.

[0026] Figure 3 The conductivity of the composite proton exchange membranes prepared in Examples 1, 6, 7 and Comparative Examples 1-4.

[0027] Figure 4 The swelling ratio and water absorption rate of the composite proton exchange membranes prepared in Examples 1, 6, 7 and Comparative Examples 1-4.

[0028] Figure 5 Tensile tests were performed on the composite proton exchange membranes prepared in Examples 1, 6, 7 and Comparative Examples 1-4.

[0029] Figure 6 Thermogravimetric analysis of the composite proton exchange membranes prepared in Examples 1, 6, 7 and Comparative Examples 1-4 is compared. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1 The preparation method of the functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane in this embodiment includes the following steps: 1) Preparation of Nafion solution: Place 10 g of Nafion D2020 solution in an 80 ℃ drying oven for 24 h to obtain colorless and transparent Nafion resin. Weigh 2 g of Nafion resin and dissolve it in dimethyl sulfoxide. Stir at 80 ℃ for 12 h to obtain a 20 wt% Nafion solution. 2) Preparation of PVDF solution: Dissolve 1 g of PVDF in dimethyl sulfoxide and stir at 80 °C for 24 h to obtain a 10 wt% PVDF solution; 3) Preparation of casting solution: Weigh 4 g of Nafion solution and 2 g of PVDF solution respectively, and add 0.08 g of [PrSO3HMIM][Cl] to them. Stir thoroughly at 80 ℃ for 8 h, and let it stand to remove air bubbles; 4) Membrane preparation: Automatic coating was performed with a 750 μm doctor blade, and the membrane was dried at 80 °C for 12 h and then at 100 °C for 24 h. After cooling to room temperature, the functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane was peeled off.

[0032] Figure 1 The scanning electron microscope image of the composite proton exchange membrane prepared in this example shows that the composite proton exchange membrane surface is flat and exhibits a uniform microporous structure.

[0033] Example 2 The preparation method of the functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane of this example is as follows: 1) Nafion solution preparation: 10 g of Nafion D2020 solution was dried in a 80 °C drying oven for 24 h to obtain colorless transparent Nafion resin. 2 g of Nafion resin was dissolved in dimethyl sulfoxide and stirred at 80 °C for 12 h to obtain a 20 wt% Nafion solution; 2) PVDF solution preparation: 1 g of PVDF was dissolved in dimethyl sulfoxide and stirred at 80 °C for 24 h to obtain a 10 wt% PVDF solution; 3) Casting solution preparation: 4 g of Nafion solution and 2 g of PVDF solution were weighed, and 0.08 g of [HOOCMIM][CI] was added on this basis. The mixture was stirred at 80 °C for 8 h, and then bubbles were removed by standing; 4) Membrane preparation: Automatic coating was performed with a 750 μm doctor blade, and the membrane was dried at 80 °C for 12 h and then at 100 °C for 24 h. After cooling to room temperature, the functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane was peeled off.

[0034] Example 3 The preparation method of the functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane of this example is as follows: 1) Nafion solution preparation: 10 g of Nafion D2020 solution was dried in a 80 °C drying oven for 24 h to obtain colorless transparent Nafion resin. 2 g of Nafion resin was dissolved in dimethyl sulfoxide and stirred at 80 °C for 12 h to obtain a 20 wt% Nafion solution; 2) PVDF solution preparation: 1 g of PVDF was dissolved in dimethyl sulfoxide and stirred at 80 °C for 24 h to obtain a 10 wt% PVDF solution; 3) Casting solution preparation: 4 g of Nafion solution and 2 g of PVDF solution were weighed, and 0.08 g of [EOMIM][Cl] was added on this basis. The mixture was stirred at 80 °C for 8 h, and then left to stand to remove bubbles; 4) Membrane preparation: automatic coating was performed with a 750 pm doctor blade, and the membrane was dried at 80 °C for 12 h and then at 100 °C for 24 h. After cooling to room temperature, the functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane with uniform thickness and smooth surface was peeled off.

[0035] Example 4 The preparation method of the functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane of this example is as follows: 1) Nafion solution preparation: 10 g of Nafion D2020 solution was placed in a 80 °C drying oven and dried for 24 h to obtain colorless transparent Nafion resin. 2 g of Nafion resin was dissolved in dimethyl sulfoxide and stirred at 80 °C for 12 h to obtain a 20 wt% Nafion solution; 2) PVDF solution preparation: 1 g of PVDF was dissolved in dimethyl sulfoxide and stirred at 80 °C for 24 h to obtain a 10 wt% PVDF solution; 3) Casting solution preparation: 4 g of Nafion solution and 2 g of PVDF solution were weighed, and 0.08 g of [HOETMIM][Cl] was added on this basis. The mixture was stirred at 80 °C for 8 h, and then left to stand to remove bubbles; 4) Membrane preparation: automatic coating was performed with a 750 pm doctor blade, and the membrane was dried at 80 °C for 12 h and then at 100 °C for 24 h. After cooling to room temperature, the functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane with uniform thickness and smooth surface was peeled off.

[0036] Example 5 The preparation method of the functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane of this example is as follows: 1) Nafion solution preparation: 10 g of Nafion D2020 solution was placed in a 80 °C drying oven and dried for 24 h to obtain colorless transparent Nafion resin. 2 g of Nafion resin was dissolved in dimethyl sulfoxide and stirred at 80 °C for 12 h to obtain a 20 wt% Nafion solution; 2) PVDF solution preparation: 1 g of PVDF was dissolved in dimethyl sulfoxide and stirred at 80 °C for 24 h to obtain a 10 wt% PVDF solution; 3) Casting solution preparation: 4 g of Nafion solution and 2 g of PVDF solution were weighed, and 0.08 g of [BzMIM][CI] was added on this basis. After being fully stirred at 80 °C for 8 h, it was left to stand to remove bubbles; 4) Membrane preparation: automatic coating was performed with a 750 pm doctor blade, and after drying at 80 °C for 12 h and increasing the temperature to 100 °C for 24 h, the temperature was cooled to room temperature. The functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane with uniform thickness and smooth surface was obtained by peeling.

[0037] Example 6 The preparation method of the functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane of this example is as follows: 1) Nafion solution preparation: 10 g of Nafion D2020 solution was placed in a 80 °C drying oven for 24 h to obtain colorless transparent Nafion resin. 2 g of Nafion resin was dissolved in dimethyl sulfoxide and stirred at 80 °C for 12 h to obtain a 20 wt% Nafion solution; 2) PVDF solution preparation: 1 g of PVDF was dissolved in dimethyl sulfoxide and stirred at 80 °C for 24 h to obtain a 10 wt% PVDF solution; 3) Casting solution preparation: 4 g of Nafion solution and 2 g of PVDF solution were weighed, and 0.04 g of [PrSO3HMIM][CI] was added on this basis. After being fully stirred at 80 °C for 8 h, it was left to stand to remove bubbles; 4) Membrane preparation: automatic coating was performed with a 750 pm doctor blade, and after drying at 80 °C for 12 h and increasing the temperature to 100 °C for 24 h, the temperature was cooled to room temperature. The functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane with uniform thickness and smooth surface was obtained by peeling.

[0038] Example 7 The preparation method of the functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane of this example is as follows: 1) Nafion solution preparation: 10 g of Nafion D2020 solution was placed in a 80 °C drying oven for 24 h to obtain colorless transparent Nafion resin. 2 g of Nafion resin was dissolved in dimethyl sulfoxide and stirred at 80 °C for 12 h to obtain a 20 wt% Nafion solution; 2) PVDF solution preparation: 1 g of PVDF was dissolved in dimethyl sulfoxide and stirred at 80 °C for 24 h to obtain a 10 wt% PVDF solution; 3) Casting solution preparation: 4 g of Nafion solution and 2 g of PVDF solution were weighed, and 0.16 g of [PrSO3HMIM][CI] was added on this basis. The mixture was stirred at 80 °C for 8 h, and then left to stand to remove bubbles; 4) Membrane preparation: automatic coating was performed using a 750 pm doctor blade. After drying at 80 °C for 12 h and then at 100 °C for 24 h, the temperature was lowered to room temperature, and a functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane with uniform thickness and smooth surface was obtained by peeling.

[0039] Example 8 The preparation method of the functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane of this example is as follows: 1) Nafion solution preparation: 10 g of Nafion D2020 solution was dried in a 50 °C drying oven for 72 h to obtain colorless transparent Nafion resin. 2 g of Nafion resin was dissolved in N,N-dimethylformamide and stirred at 120 °C for 12 h to obtain a 10 wt% Nafion solution; 2) PVDF solution preparation: 1 g of PVDF was dissolved in N,N-dimethylformamide and stirred at 120 °C for 12 h to obtain a 5 wt% PVDF solution; 3) Casting solution preparation: 2 g of Nafion solution and 2 g of PVDF solution were weighed, and 0.1 g of [PrSO3HMIM][CI] was added on this basis. The mixture was stirred at 120 °C for 12 h, and then left to stand to remove bubbles; 4) Membrane preparation: automatic coating was performed using a 20 pm doctor blade. After drying at 250 °C for 6 h, the temperature was lowered to room temperature, and a functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane with uniform thickness and smooth surface was obtained by peeling.

[0040] Example 9 The preparation method of the functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane of this example is as follows: 1) Nafion solution preparation: 10 g of Nafion D2020 solution was dried in a 100 °C drying oven for 12 h to obtain colorless transparent Nafion resin. 2 g of Nafion resin was dissolved in acetonitrile and stirred at 40 °C for 72 h to obtain a 1 wt% Nafion solution; 2) PVDF solution preparation: 1 g of PVDF was dissolved in acetonitrile and stirred at 40 °C for 72 h to obtain a 20 wt% PVDF solution; 3) Casting solution preparation: 20 g of Nafion solution and 2 g of PVDF solution were weighed, and 0.01 g of [PrSO3HMIM][Cl] was added on this basis. After being fully stirred at 40 °C for 72 h, it was left to stand to remove bubbles; 4) Membrane preparation: automatic coating was performed with a 1000 μm doctor blade, and after drying at 30 °C for 72 h and further drying at 100 °C for 24 h, the temperature was cooled to room temperature. A functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane with uniform thickness and smooth surface was obtained by peeling.

[0041] Comparative Example 1 The preparation method of the [PrSO3HMIM][Cl] / Nafion composite membrane of the present comparative example comprises the following steps: 1) Nafion solution preparation: 10 g of Nafion D2020 solution was placed in a 80 °C drying oven and dried for 24 h to obtain colorless transparent Nafion resin. 2 g of Nafion resin was dissolved in dimethyl sulfoxide and stirred at 80 °C for 12 h to obtain a 20wt% Nafion solution; 2) Casting solution preparation: 4 g of Nafion solution was weighed, and 0.04 g of [PrSO3HMIM][Cl] was added on this basis. After being fully stirred at 80 °C for 8 h, it was left to stand to remove bubbles; 3) Membrane preparation: automatic coating was performed with a 750 μm doctor blade, and after drying at 80 °C for 12 h and further drying at 100 °C for 24 h, the temperature was cooled to room temperature. A [PrSO3HMIM][Cl] / Nafion composite membrane with uniform thickness and smooth surface was obtained by peeling.

[0042] Comparative Example 2 The preparation method of the [PrSO3HMIM][Cl] / Nafion composite membrane of the present comparative example comprises the following steps: 1) Nafion solution preparation: 10 g of Nafion D2020 solution was placed in a 80 °C drying oven and dried for 24 h to obtain colorless transparent Nafion resin. 2 g of Nafion resin was dissolved in dimethyl sulfoxide and stirred at 80 °C for 12 h to obtain a 20wt% Nafion solution; 2) Casting solution preparation: 4 g of Nafion solution was weighed, and 0.08 g of [PrSO3HMIM][Cl] was added on this basis. After being fully stirred at 80 °C for 8 h, it was left to stand to remove bubbles; 3) Film preparation: automatic coating was performed with a 750 μm doctor blade, and the film was dried at 80 °C for 12 h and then at 100 °C for 24 h, after which it was cooled to room temperature, and the [PrSO3HMIM][Cl] / Nafion composite film was peeled off. Comparative Example 3 The preparation method of the [PrSO3HMIM][Cl] / Nafion composite film of the present comparative example comprises the following steps: 1) Preparation of Nafion solution: 10 g of Nafion D2020 solution was placed in a drying oven at 80 °C and dried for 24 h to obtain colorless transparent Nafion resin, 2 g of Nafion resin was dissolved in dimethyl sulfoxide, and stirred at 80 °C for 12 h to obtain a 20 wt% Nafion solution; 2) Preparation of casting solution: 0.16 g of [PrSO3HMIM][Cl] was added to 4 g of the Nafion solution, and stirred at 80 °C for 8 h, and then the bubbles were removed by standing. 3) Film preparation: automatic coating was performed with a 750 μm doctor blade, and the film was dried at 80 °C for 12 h and then at 100 °C for 24 h, after which it was cooled to room temperature, and the [PrSO3HMIM][Cl] / Nafion composite film was peeled off. Comparative Example 4 The preparation method of the PVDF / Nafion composite film of the present comparative example comprises the following steps: 1) Preparation of Nafion solution: 10 g of Nafion D2020 solution was placed in a drying oven at 80 °C and dried for 24 h to obtain colorless transparent Nafion resin, 2 g of Nafion resin was dissolved in dimethyl sulfoxide, and stirred at 80 °C for 12 h to obtain a 20 wt% Nafion solution; 2) Preparation of PVDF solution: 1 g of PVDF was dissolved in dimethyl sulfoxide and stirred at 80 °C for 24 h to obtain a 10 wt% PVDF solution; 3) Preparation of casting solution: 4 g of the Nafion solution and 2 g of the PVDF solution were weighed out and stirred at 80 °C for 8 h, and then the bubbles were removed by standing.

[0043] 4) Film preparation: automatic coating was performed with a 750 μm doctor blade, and the film was dried at 80 °C for 12 h and then at 100 °C for 24 h, after which it was cooled to room temperature, and the [PrSO3HMIM][Cl] / Nafion composite film was peeled off.

[0044] Test Example The conductivity of the PVDF / Nafion composite membranes modified by different cationic functionalized ionic liquids prepared in Examples 1-5 and the conductivity, swelling rate, water absorption rate, mechanical strength and thermal stability of the composite proton exchange membranes prepared in Examples 1, 6, 7 and Comparative Examples 1-4 were tested, and the results are as follows.

[0045] Figure 2 The conductivity of the PVDF / Nafion composite membranes modified by different cationic functionalized ionic liquids prepared in Examples 1-5, as can be seen from the figure, the PVDF / Nafion composite membrane modified by [PrSO3HMIM][CI] in Example 1 showed higher conductivity, and the conductivity of the composite membrane reached 0.05464 S cm -1 and 0.12488 S cm -1 at 30 ℃ and 80 ℃, respectively. Figure 3 The conductivity of the composite proton exchange membranes prepared in Examples 1, 6, 7 and Comparative Examples 1-4, as can be seen from the figure, compared with Comparative Examples 1-3, the addition of PVDF in Examples 1, 6 and 7 reduced the conductivity to some extent, and when the amount of [PrSO3HMIM][CI] was less than 5 wt%, the conductivity did not increase significantly; when the amount was more than 10 wt%, the conductivity was higher than that of Comparative Example 4.

[0046] Figure 4 The swelling rate and water absorption rate of the composite proton exchange membranes prepared in Examples 1, 6, 7 and Comparative Examples 1-4, as can be seen from the figure, the swelling rate of Examples 1, 6 and 7 was significantly lower than that of Comparative Examples 1-4, showing good dimensional stability, and the swelling rate of the composite proton exchange membrane prepared in Example 1 was 2.5% at 80 ℃, which was much lower than that of Comparative Examples 1-4; at the same time, the water absorption rate of Example 1 also decreased slightly.

[0047] Figure 5 The tensile test comparison of the composite proton exchange membranes prepared in Examples 1, 6, 7 and Comparative Examples 1-4, as can be seen from the figure, compared with Comparative Examples 1-4, the tensile strength of Examples 1, 6 and 7 was obviously improved, reaching 22.644 MPa, 22.446 MPa and 19.668 MPa, respectively, and the elongation rate decreased slightly.

[0048] Figure 6 The thermal gravimetric test comparison of the composite proton exchange membranes prepared in Examples 1, 6, 7 and Comparative Examples 1-4, as can be seen from the figure, compared with Comparative Examples 1-4, under the same [PrSO3HMIM][CI] ratio, the PVDF / Nafion composite membrane modified by [PrSO3HMIM][CI] showed better stability than [PrSO3HMIM][CI] / Nafion.

[0049] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane, characterized in that, The steps are as follows: (1) dissolving Nafion resin in a solvent to prepare a Nafion solution; (2) adding a PVDF solution to the Nafion solution obtained in step (1) to form a PVDF / Nafion solution; (3) modifying the PVDF / Nafion solution obtained in step (2) with a functionalized ionic liquid to obtain a casting solution; (4) coating and drying the casting solution obtained in step (3) to obtain a functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane.

2. The method for preparing a functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane according to claim 1, characterized in that, In step (1), the Nafion resin is obtained by drying a Nafion D2020 solution; the solvent is any one of acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide and hexamethylphosphoramide; the content of Nafion resin in the Nafion solution is 1-20 wt%.

3. The method for preparing a functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane according to claim 2, characterized in that, In step (2), the solvent in the PVDF solution is any one of acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide and hexamethylphosphoramide, and the mass percentage of the solute PVDF is 5-20 wt%.

4. The method for preparing a functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane according to any one of claims 1-3, characterized in that, In step (2), the mass ratio of the Nafion solution to the PVDF solution is (1-10):

1.

5. The method for preparing the functionalized ionic liquid-modified PVDF / Nafion composite proton exchange membrane according to claim 3, characterized in that, In step (3), the functionalized ionic liquid refers to any one of a cationic hydroxyl functionalized ionic liquid, a cationic carboxyl functionalized ionic liquid, a cationic ether functionalized ionic liquid, a cationic sulfonic acid functionalized ionic liquid and a cationic benzyl functionalized ionic liquid.

6. The method for preparing the functionalized ionic liquid-modified PVDF / Nafion composite proton exchange membrane according to claim 5, characterized in that, The cationic hydroxyl functionalized ionic liquid is 1-hydroxyethyl-3-methylimidazole chloride, the cationic carboxyl functionalized ionic liquid is 1-carboxymethyl-3-methylimidazole chloride, the cationic ether functionalized ionic liquid is 1-ethyl methyl ether-3-methylimidazole chloride, the cationic sulfonic acid functionalized ionic liquid is 1-propane sulfonic acid-3-methylimidazole chloride, and the cationic benzyl functionalized ionic liquid is 1-benzyl-3-methylimidazole chloride.

7. The method for preparing the functionalized ionic liquid-modified PVDF / Nafion composite proton exchange membrane according to claim 5, characterized in that, In step (3), the mass of the functionalized ionic liquid is 0.5-50 wt% of the mass of the Nafion resin; the modification conditions are stirring at 40-120 ℃ for 12-72 h.

8. The method for preparing the functionalized ionic liquid-modified PVDF / Nafion composite proton exchange membrane according to claim 7, characterized in that, In step (4), the coating thickness is 20-1000 μm; the drying temperature is 30-250 ℃, and the drying time is 6-72 h.

9. A functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane prepared by the preparation method of claim 1.

10. The use of the functionalized ionic liquid modified PVDF / Nafion composite proton exchange membrane of claim 9 in electrolytic water hydrogen production.

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