Composite proton exchange membrane as well as preparation method and application thereof

Abstract

The invention provides a composite proton exchange membrane as well as a preparation method and application thereof. The preparation method comprises the following steps: filling a hydrophobic substrate with a solution of a hydrophilic two-dimensional nanosheet material, drying, and carrying out a cross-linking reaction to obtain a modified basement membrane; and filling the modified basement membrane with the resin solution, and drying to obtain the single-layer composite proton exchange membrane. The invention also provides the composite proton exchange membrane obtained by the preparation method and application of the composite proton exchange membrane in water electrolysis hydrogen production and / or batteries. According to the preparation method provided by the invention, the interface bonding capacity of the perfluorosulfonic acid resin and the porous film in the composite proton exchange membrane can be improved, the filling and coating capacities of the resin in the film are improved while the stability of the film structure is maintained, and the proton conductivity of the membrane is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of proton exchange membranes, and particularly relates to a composite proton exchange membrane, a preparation method thereof, and an application thereof. Background Art

[0002] Building a new power system with new energy as the main body around wind energy, solar energy, hydrogen energy, etc. is an important means of energy development. Aiming at the prominent problems such as intermittency and volatility of photovoltaic and wind power generation, electrochemical energy storage technologies represented by all-vanadium redox flow batteries and lithium batteries can play an important role in enhancing the electricity storage capacity and ensuring the stable operation of the power system. As a zero-carbon fuel, hydrogen has a high calorific value and a wide range of sources. Developing a hydrogen economy with hydrogen energy as a medium using technologies such as proton exchange membrane electrolysis for hydrogen production and proton exchange membrane fuel cells helps today's society get rid of dependence on fossil energy and achieve low-carbon and green development of the economy and society.

[0003] As a common core component of all-vanadium redox flow batteries, proton exchange membrane fuel cells, and electrolysis for hydrogen production, the proton exchange membrane plays a role in transferring protons and blocking the mixing of cathode and anode chemical substances, and is an important factor determining the performance and cost of the battery. A homogeneous perfluorosulfonic acid proton exchange membrane with a low thickness helps reduce the ohmic loss of the battery, but the increase in membrane swelling rate and the decrease in mechanical properties seriously limit the battery life. An enhanced composite proton exchange membrane prepared by using a chemically stable and high-strength polytetrafluoroethylene porous film as a substrate and filling perfluorosulfonic acid resin into the pores has a low membrane thickness, can reduce the resin usage and membrane cost while ensuring the battery performance. However, due to the difference in hydrophilic and hydrophobic properties, it is difficult to completely fill the resin with proton conduction function in the hydrophobic substrate, resulting in a decrease in membrane proton conduction ability, an increase in gas-liquid permeation, and even battery failure. At the same time, the structural defect of incomplete interfacial composite also brings potential risks to the stability and life of the membrane.

[0004] Currently, the methods for improving the compatibility between polytetrafluoroethylene film and perfluorosulfonic acid resin have the following defects:

[0005] 1. Adding hydrophilic particles to polytetrafluoroethylene powder can improve the hydrophilicity of the porous film, but the hydrophilic particles will affect the porous microstructure of the membrane, and the hydrophilic particles are easily covered by resin particles, affecting the performance;

[0006] 2. Treating the polytetrafluoroethylene porous film by methods such as chemical method, gas thermal oxidation method, and low-temperature plasma will change the chemical structure of polytetrafluoroethylene, affecting the mechanical strength and microstructure of the film.

[0007] Therefore, improving the filling and coating ability of the resin in the porous film is an important problem to be solved in the preparation of high-performance composite proton exchange membranes. Summary of the Invention

[0008] In order to solve the above problems, the purpose of the present invention is to provide a composite proton exchange membrane, a preparation method thereof and an application thereof, to improve the interfacial bonding ability between the perfluorosulfonic acid resin and the porous film in the composite proton exchange membrane, and while maintaining the stability of the film structure, improve the filling and coating ability of the resin in the film, and improve the proton conductivity of the membrane.

[0009] To achieve the above purpose, the present invention provides a preparation method of a composite proton exchange membrane, and the preparation method includes:

[0010] S1. Filling a solution of a hydrophilic two-dimensional nanosheet material into a hydrophobic substrate, drying, and performing a cross-linking reaction to obtain a modified substrate membrane;

[0011] S2. Filling a resin solution into the modified substrate membrane, and drying to obtain a single-layer composite proton exchange membrane.

[0012] In the above preparation method, in S1, during the process of filling the solution of the hydrophilic two-dimensional nanosheet material into the hydrophobic substrate, the two-dimensional nanosheets are physically entangled with the hydrophobic substrate, and the hydrophobic substrate can be physically modified by using the hydrophilic two-dimensional nanosheet material to improve the hydrophilicity of the hydrophobic substrate.

[0013] In the prior art, after mixing the resin and the nanomaterial and then filling them into the hydrophobic substrate, the high-viscosity resin will affect the dispersion of the nanomaterial in the resin solution, resulting in the aggregation of the nanomaterial in the resin and uneven distribution in the substrate. However, in the present invention, by first distributing the nanomaterial in the substrate and then filling the resin into the substrate, it helps to improve the uniformity of the distribution of the nanomaterial in the substrate.

[0014] In the above preparation method, the hydrophilic two-dimensional nanosheet material has hydrophilicity and the morphology of nanosheets, and the specific surface area and strength of the two-dimensional nanosheet material are relatively high. The hydrophilic two-dimensional nanosheet material may include graphene oxide-based materials, and specifically may include graphene oxide and / or graphene oxide derivatives. Graphene oxide and / or its derivatives can be prepared by chemical oxidation, exfoliation, and chemical modification of graphite, and the obtained two-dimensional nanosheet plane has hydrophilic oxygen-containing groups such as carboxyl, hydroxyl, amino, sulfonic acid, carbonyl, and epoxy groups. Due to the relatively high specific surface area and the abundant oxygen-containing groups on the surface, graphene oxide exhibits good hydrophilicity and can effectively hydrophilically modify the hydrophobic substrate membrane.

[0015] In the above preparation method, the graphene oxide may specifically include one or a combination of two or more of hydrophilic oxygen-containing groups such as carboxyl, hydroxyl, carbonyl, and epoxy groups. The graphene oxide derivative may include graphene oxide modified with an organic compound having a polar group. The graphene oxide derivative includes -COOH (carboxyl), -NH 2 (amino), -SO 3Graphene oxide modified with a group of one or more combinations of -SO₃H (sulfonic acid group), -OH (hydroxyl group), etc. In some specific embodiments, the hydrophilic two-dimensional nanosheet material may include -SO₃H 3 modified graphene oxide.

[0016] In the above preparation method, if the concentration of the solution of the hydrophilic two-dimensional nanosheet material is too high, the nanosheets will deposit on the surface of the hydrophobic substrate and cannot enter the interior of the substrate; if the concentration of the solution of the hydrophilic two-dimensional nanosheet material is too low, the hydrophilic modification effect on the hydrophobic substrate is limited. By controlling the concentration of the solution of the hydrophilic two-dimensional nanosheet material within a reasonable range, the present invention can enable the nanosheets to enter the interior of the hydrophobic substrate and effectively improve the hydrophilicity of the hydrophobic substrate. The concentration of the solution of the hydrophilic two-dimensional nanosheet material can be 0.01 - 1 mg / mL, such as specific values of 0.01 mg / mL, 0.03 mg / mL, 0.1 mg / mL, 0.3 mg / mL, 1 mg / mL, etc. and ranges with any two of the above specific values as endpoints. The concentration of the solution of the hydrophilic two-dimensional nanosheet material can further be 0.03 - 0.3 mg / mL, 0.1 - 1 mg / mL, etc. In some specific embodiments, the solvent for dispersing the hydrophilic two-dimensional nanosheet material can be water and / or alcohol. When the solvent is water and ethanol, the preparation method of the solution of the hydrophilic two-dimensional nanosheet material is as follows: First, the hydrophilic two-dimensional nanosheet material is mixed with water to form an aqueous solution, and the mixing process can be treated by stirring, ultrasonic treatment, etc. to promote uniform dispersion; then the aqueous solution is mixed with alcohol to form a uniform solution. The alcohol can be ethanol, etc.

[0017] In the above preparation method, the hydrophobic substrate can be a polytetrafluoroethylene porous membrane. In some specific embodiments, the porosity of the polytetrafluoroethylene porous membrane can be more than 80%.

[0018] In the above preparation method, the preparation method may further include: before filling the solution of the hydrophilic two-dimensional nanosheet material into the substrate, an operation of pre-treating the hydrophobic substrate, and the pre-treatment can improve the hydrophilicity of the hydrophobic substrate in advance. The pre-treatment includes soaking the hydrophobic substrate in alcohol and / or ketone and performing ultrasonic treatment. In some specific embodiments, the alcohol may include one or more combinations of methanol, ethanol, and propanol, and the ketone may include acetone. The temperature of the ultrasonic treatment can be room temperature, and the time of the ultrasonic treatment can be 5 - 20 min, such as 15 min.

[0019] In the above preparation method, in S1, the method of filling the solution of the hydrophilic two-dimensional nanosheet material into the hydrophobic substrate may include one or more combinations of casting, blade coating, dipping.

[0020] In the above preparation method, in S1, the drying temperature can be from room temperature to 40 °C; the drying time can be 15 min - 1 h, for example, it can be 20 min - 1 h.

[0021] In the above preparation method, in S1, the hydrophilic two-dimensional nanosheets generally include graphene oxide and / or its derivatives. The surface of graphene oxide and / or its derivatives contains hydrophilic oxygen-containing groups, such as carboxyl groups dispersed at the edges of the two-dimensional nanosheets and hydroxyl groups on the basal plane, etc. These hydrophilic oxygen-containing groups can undergo irreversible dehydration esterification reactions in a vacuum drying environment, and this reaction can crosslink the two-dimensional nanosheets with each other; and due to physical entanglement between the nanosheets and the fibers of the hydrophobic substrate membrane, the nanosheets are distributed on the surface of the fibers and the surface of the fiber nodes. Therefore, the above crosslinking process can improve the hydrophilicity of the hydrophobic substrate membrane surface while ensuring the structural integrity of the modified material.

[0022] In the above preparation method, in S1, the crosslinking reaction is generally carried out in a vacuum environment. The temperature of the crosslinking reaction can be 80 - 120 °C, for example, 90 - 120 °C; the time of the crosslinking reaction can be 4 - 48 h, for example, 4 - 36 h.

[0023] In the above preparation method, in S1, the dosage of the solution of the hydrophilic two-dimensional nanosheets can be adjusted according to the type and size of the hydrophobic substrate. For example, for a polytetrafluoroethylene porous film with a thickness of 5 - 8 μm and an area of 12 cm 2 When the concentration of the hydrophilic two-dimensional nanosheet solution is 0.1 - 1 mg / mL, the volume of the hydrophilic two-dimensional nanosheet solution can be 1 - 2 mL.

[0024] In the above preparation method, the "filling - drying - crosslinking" process can be carried out 1 - 20 times in S1, or "filling - drying" can be carried out 1 - 20 times and then crosslinking can be carried out to improve the binding effect between the hydrophobic substrate and the hydrophilic two-dimensional nanosheet material.

[0025] In the above preparation method, in S2, by mixing the hydrophilically modified substrate membrane with the resin, the filling effect of the resin in the substrate membrane can be improved through the interaction (such as hydrogen bonding, etc.) between the hydrophilic groups (such as sulfonic acid groups, etc.) of the resin and the hydrophilic groups on the surface of the two-dimensional nanosheet material, thereby improving the binding between the resin particles and the substrate membrane and increasing the membrane proton conductivity. In some specific embodiments, the resin can be distributed in the pores of the modified substrate membrane to achieve uniform dispersion.

[0026] In the above preparation method, in S2, the resin includes Nafion resin (perfluorosulfonic acid resin).

[0027] In the above preparation method, the solvent of the resin solution includes one or more combinations of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and ethanol. The resin solution is generally uniform and bubble-free.

[0028] In the above preparation method, the mass concentration of the resin in the resin solution is 5-30 wt.%, for example, it can be 15-20 wt.%.

[0029] In the above preparation method, in S2, the amount of the resin solution can be adjusted according to the type and size of the hydrophobic substrate. For example, for a polytetrafluoroethylene porous film with a thickness of 5-8 μm and an area of 12 cm 2 When the mass concentration of the resin solution is 15%-20%, the mass of the resin solution can be 1.2-1.6 g.

[0030] In the above preparation method, in S2, the filling method includes one or more combinations of casting, knife coating, and dipping. During the filling process, the above methods can make each surface of the modified substrate film fully contact with the resin solution.

[0031] In the above preparation method, in S2, the drying temperature is 80-150 °C, and the drying time is 5 min-12 h.

[0032] In some specific embodiments, the preparation method further includes stacking and thermocompression of two or more single-layer composite proton exchange membranes to form a multi-layer composite proton exchange membrane.

[0033] In the above preparation method, the thermocompression temperature is 100-160 °C, the thermocompression pressure is 0.3-10 MPa, and the thermocompression time is 30 s-5 min.

[0034] The present invention provides a composite proton exchange membrane obtained by the above preparation method. In some specific embodiments, the composite proton exchange membrane may use a polytetrafluoroethylene porous membrane as the substrate, with a hydrophilic two-dimensional nanosheet material distributed on the inner surface (i.e., in the pore structure) of the polytetrafluoroethylene porous membrane, and the resin is distributed in the pores of the polytetrafluoroethylene porous membrane.

[0035] The present invention also provides the application of the above composite proton exchange membrane in hydrogen production by electrolyzing water and / or batteries. The binding force between the resin and the hydrophobic substrate membrane at the interface of the composite proton exchange membrane provided by the present invention is improved. While maintaining the structural stability of the substrate membrane, it can improve the filling and coating ability of the resin in the substrate membrane, thereby enhancing the proton conductivity of the composite proton exchange membrane, and further enhancing the hydrogen production ability of the composite proton exchange membrane by electrolyzing water and the electrochemical performance of the battery made therefrom. In some specific embodiments, the proton conductivity of the composite proton exchange membrane provided by the present invention can reach more than 37.5 mS / cm, and further reach more than 40 mS / cm.

[0036] The beneficial effects of the present invention are as follows:

[0037] 1. In the present invention, the hydrophilic two-dimensional nanosheet material can adhere to and be fixed on the fibers and nodes of the hydrophobic substrate membrane, improving the hydrophilicity of the hydrophobic substrate membrane while forming a multi-scale reinforcement structure in the membrane. This method avoids the damage to the molecular structure and pore morphology of the hydrophobic substrate membrane caused by modification methods such as chemical treatment, radiation grafting, plasma treatment, and laser treatment in the prior art.

[0038] 2. The present invention can improve the filling effect of the resin at the interface and increase the proton conductivity of the membrane through the interaction between the oxygen-containing groups on the surface of the hydrophilic two-dimensional nanosheet and the surface groups of the resin. In addition, the hydrophilic groups on the surface of the hydrophilic two-dimensional nanosheet material can also serve as proton transfer sites, forming an ion transfer channel along the surface of the fibers of the substrate membrane to reduce the proton transfer resistance.

[0039] 3. In the composite proton exchange membrane prepared by the present invention, pre-distributing the hydrophilic two-dimensional nanosheet on the hydrophobic substrate helps to improve the uniformity of the distribution of the hydrophilic two-dimensional nanosheet in the membrane, avoiding the problem of particle aggregation in the resin and non-uniform distribution in the substrate caused by the co-blending and filling of the resin and nanoparticles in the prior art. On this basis, the two-dimensional sheet structure of the hydrophilic two-dimensional nanosheet can also enhance the inhibition of gas permeation and solute permeation. Detailed Embodiments

[0040] In order to have a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0041] The raw material sources of the following examples and comparative examples are:

[0042] Raw material source: The perfluorosulfonic acid resin is obtained by fully drying the Nafion solution produced by Chemours Company at 60°C.

[0043] The graphene oxide powder is purchased from Nanjing Xianfeng Nano Materials Technology Co., Ltd., and this graphene oxide contains hydroxyl and carboxyl groups.

[0044] The polytetrafluoroethylene porous film is selected from Dongyue Hydrogen Energy Co., Ltd., and a polytetrafluoroethylene porous film with a porosity greater than 80% is used as the film, with a thickness of 5 - 8 μm. During the experiment, the area of the polytetrafluoroethylene porous film is 12 cm 2 .

[0045] Based on the purchased graphene oxide, the preparation method of sulfonated graphene oxide is as follows:

[0046] (1) Mix 180 mg of graphene oxide, 60 mL of deionized water and 60 mL of ethanol, then ultrasonically treat for 30 min, and then place it in an ice - water bath for later use;

[0047] (2) Mix 300 mL of hydrochloric acid aqueous solution, 5.2 g of sulfanilic acid, and 33 mL of sodium nitrite aqueous solution (1 mol / L) in an ice - water bath, magnetically stir for 1 h and then filter the white product (benzenediazonium sulfonate);

[0048] (3) Add benzenediazonium sulfonate to (1), and magnetically stir the solution in an ice - water bath for 8 h;

[0049] (4) Centrifuge the solution and repeatedly wash it with deionized water until the unreacted diazonium salt and other by - products are completely removed.

[0050] The preparation method of the solution of graphene oxide or its derivative is as follows: Add 25 mL of deionized water to 50 mg of graphene oxide or its derivative, stir and mix for 2 h, ultrasonically treat for 30 min to prepare a 2 mg / L aqueous solution of graphene oxide, and then mix the obtained solution with ethanol according to a certain volume ratio, stir evenly and then use.

[0051] Evaluation and analysis method: Use a two - electrode device to test the proton conductivity in the thickness direction of the membrane. During the test, clamp the membrane sample between metal electrodes, then put them together into a closed container filled with deionized water, and ensure that the membrane sample and the metal electrodes do not directly contact with water. Heat the deionized water to 60 °C to fully wet the membrane sample with water vapor. After the test conditions are stable, apply a sinusoidal AC perturbation by an electrochemical workstation for impedance testing, and calculate the membrane proton conductivity according to the obtained membrane resistance value.

[0052] Example 1

[0053] This example provides a composite proton exchange membrane, and its preparation method includes:

[0054] (1) Prepare a porous film modified with graphene oxide:

[0055] Immerse the polytetrafluoroethylene porous film (as a hydrophobic substrate membrane) in ethanol, ultrasonically treat for 15 min, take it out and dry it at room temperature for later use.

[0056] Mix the graphene oxide aqueous solution and ethanol in a volume ratio of 1:9, and obtain a homogeneous solution with a graphene oxide concentration of 0.1 mg / mL through stirring and ultrasonic treatment.

[0057] Then, fix the polytetrafluoroethylene porous film in the spraying device, and spray 1 mL of the graphene oxide solution onto its surface. Keep the vacuum pump on during the spraying process so that the solution can fully contact the fibrils and nodes of the film with the airflow. The film sprayed with graphene oxide is dried at 40 °C for 20 min. After repeating the spraying and drying processes 5 times, the film is treated in a vacuum oven at 100 °C for 24 h for crosslinking to obtain a modified porous film with self-crosslinked graphene oxide.

[0058] (2) Prepare the resin solution:

[0059] Add Nafion resin to N,N-dimethylformamide, and mix and stir for 12 h to prepare a resin solution with a resin content of 15 wt.%. To fully remove air bubbles, the resin solution is allowed to stand at room temperature for 12 h before use.

[0060] (3) Prepare the composite proton exchange membrane:

[0061] Flatten the modified porous film obtained in step (1) on a glass plate and fix the four sides of the film with a polytetrafluoroethylene frame. Pour 1.6 g of the resin solution prepared in step (2) onto the film, dry it at 80 °C for 4 h and at 120 °C for 6 h, and then immerse the glass plate in deionized water for 1 h to allow the membrane to absorb water and swell and then peel it off from the surface of the glass plate to obtain the composite proton exchange membrane.

[0062] Referring to the membrane proton conductivity evaluation and analysis method provided by the present invention, the proton conductivity of the composite proton exchange membrane is 39.1 mS / cm.

[0063] Example 2

[0064] This example provides a composite proton exchange membrane, and its preparation method includes:

[0065] (1) Prepare the porous film modified with graphene oxide:

[0066] Immerse the polytetrafluoroethylene porous film in ethanol, perform ultrasonic treatment for 15 min, take it out and dry it at room temperature for later use.

[0067] Mix the graphene oxide aqueous solution and ethanol in a volume ratio of 1:1, and obtain a homogeneous solution with a graphene oxide concentration of 1 mg / mL through stirring and ultrasonic treatment.

[0068] Then, after fixing the polytetrafluoroethylene porous film in the spraying device, 1 mL of graphene oxide solution was sprayed onto its surface. During the spraying process, the vacuum pump was always turned on to allow the solution to enter the film along with the airflow and make full contact with the fibrils and nodes of the film. The film sprayed with graphene oxide was dried at 30 °C for 45 min. After repeating the spraying and drying processes 3 times, the film was treated in a vacuum oven at 90 °C for 36 h for crosslinking to obtain a modified porous film with self-crosslinked graphene oxide.

[0069] (2) Prepare the resin solution: The same as step (2) of Example 1.

[0070] (3) Prepare the composite proton exchange membrane: The same as step (3) of Example 1.

[0071] Referring to the membrane proton conductivity evaluation and analysis method provided by the present invention, the proton conductivity of the composite proton exchange membrane in this example is 38.7 mS / cm.

[0072] Example 3

[0073] This example provides a composite proton exchange membrane, and its preparation method includes:

[0074] (1) Prepare a sulfonated graphene oxide modified porous film:

[0075] The polytetrafluoroethylene porous film was immersed in ethanol, ultrasonically treated for 15 min, taken out and dried at room temperature for later use.

[0076] A 2 mg / L aqueous solution of sulfonated graphene oxide was mixed with ethanol in a volume ratio of 1:3, and after stirring and ultrasonic treatment, a homogeneous solution with a sulfonated graphene oxide concentration of 0.5 mg / mL was obtained.

[0077] The polytetrafluoroethylene porous film was fixed with a polytetrafluoroethylene frame and immersed in the above sulfonated graphene oxide solution for 5 min. Then, the film adsorbed with sulfonated graphene oxide was dried at room temperature for 1 h, and then treated in a vacuum oven at 120 °C for 4 h for self-crosslinking. The impregnation, drying, and self-crosslinking processes were repeated 8 times to obtain a modified porous film with self-crosslinked sulfonated graphene oxide.

[0078] (2) Prepare the resin solution:

[0079] Nafion resin was added to a mixed solution of N,N-dimethylformamide and dimethyl sulfoxide with a volume ratio of 1:1, and after mixing and stirring for 12 h, a resin solution with a resin content of 20 wt.% was prepared. To fully remove air bubbles, the resin solution was allowed to stand at room temperature for 12 h before use.

[0080] (3) Prepare the composite proton exchange membrane:

[0081] The modified porous film was flattened on a glass plate, and 1.2 g of the resin solution was coated on the porous film using a film applicator. Then, the film was dried at 80 °C for 0.5 h, and then dried at 140 °C for 2 h for shaping. Finally, the film was immersed in deionized water for 1 h to allow the film to absorb water and swell, and then peeled off from the surface of the glass plate to obtain a composite proton exchange membrane.

[0082] Referring to the evaluation and analysis method provided by the present invention, the proton conductivity of the composite proton exchange membrane was 40.3 mS / cm.

[0083] Example 4

[0084] This example provides a composite proton exchange membrane, and its preparation method is similar to that of Example 1. The difference is that: the composite proton exchange membrane in this example is obtained by hot pressing two composite proton exchange membranes in Example 1. The specific process is as follows: A small amount of resin solution was sprayed on one side of the composite proton exchange membrane obtained in Example 1 as a binder, and then the two membranes were stacked and hot pressed. The hot pressing temperature was 100 °C, the hot pressing pressure was 5 MPa, and the hot pressing time was 2 min to obtain a multi-layer composite proton exchange membrane.

[0085] Referring to the evaluation and analysis method provided by the present invention, the proton conductivity of the multi-layer composite proton exchange membrane in this example was 37.8 mS / cm.

[0086] Comparative Example 1

[0087] This comparative example provides a composite proton exchange membrane, and its preparation method is similar to that of Example 1. The difference is that: the resin solution components used in this comparative example are different, and the resin solution contains graphene oxide. The preparation method of this comparative example is as follows:

[0088] The polytetrafluoroethylene porous film was immersed in ethanol, ultrasonically treated for 15 min, taken out and dried at room temperature for later use.

[0089] Graphene oxide and Nafion resin were successively added to N,N-dimethylformamide according to the mass ratio of graphene oxide:Nafion = 0.5:99.5, and then the mixture was stirred for 12 h and then ultrasonically treated for 15 min to prepare a resin solution with a resin content of 15 wt.%. The resin solution was allowed to stand at room temperature for 12 h for later use to remove the bubbles therein.

[0090] The polytetrafluoroethylene porous film was flattened on a glass plate and the film was fixed around the four sides with a polytetrafluoroethylene frame, and then 1.2 g of the resin solution was cast on the film. Finally, the film was dried at 80 °C for 4 h, dried at 120 °C for 6 h, and then immersed in deionized water for 1 h to allow the film to absorb water and swell, and then peeled off from the surface of the glass plate to obtain a composite proton exchange membrane.

[0091] Referring to the evaluation and analysis method provided by the present invention, the proton conductivity of the composite proton exchange membrane is 36.5 mS / cm.

[0092] Comparative Example 2

[0093] This comparative example provides a composite proton exchange membrane. Its preparation method is similar to that of Comparative Example 1, except that: graphene oxide is not added to the resin in this comparative example (and graphene oxide is not contained in the raw materials), and the resin solution cast on the film remains 1.2 g. All other steps are the same as those in Comparative Example 1.

[0094] Referring to the evaluation and analysis method provided by the present invention, the proton conductivity of the composite proton exchange membrane is 37.3 mS / cm.

[0095] It can be seen from the comparison between Comparative Example 2 and Comparative Example 1 that when the resin and graphene oxide are added together, the proton conductivity of the composite proton exchange membrane decreases slightly compared to that of the proton exchange membrane with only resin added. This is because the conductivity of the hydroxyl and carboxyl groups in graphene oxide is poorer than that of the sulfonic acid groups in the resin. When graphene oxide and the resin enter the substrate together, it will reduce the content of sulfonic acid groups per unit thickness of the substrate, thereby reducing the conductivity.

[0096] It can be seen from the comparison of the effects of Comparative Example 2 with those of Examples 1 to 4 that, compared with the composite proton exchange membrane prepared from the porous film without graphene oxide modification, the proton conductivity of the composite proton exchange membrane provided by the present invention is higher. The present invention uses graphene oxide and its derivatives to physically modify the polytetrafluoroethylene porous film. Through the interaction between the surface groups of graphene oxide and the resin groups, the filling effect of the resin in the substrate can be improved, and the conductivity of the proton exchange membrane can be enhanced; moreover, the hydrophilic groups in graphene oxide and its derivatives can also serve as proton transfer sites, reducing the proton transfer resistance.

[0097] It can be seen from the comparison of the effects of Comparative Example 1 with those of Examples 1 to 4 that the present invention can improve the hydrophilicity of the substrate membrane without destroying the molecular structure and pore structure of the substrate membrane by first mixing graphene oxide and its derivatives with the substrate membrane and self-crosslinking, which helps the subsequent filling of resin particles in the substrate membrane and improves the proton conductivity of the membrane.

[0098] It can be seen from the comparison of the effects of Example 1 and Example 3 that, compared with graphene oxide, graphene oxide grafted with sulfonic acid groups can further reduce the proton transfer resistance of the composite proton exchange membrane and improve the proton conductivity.

Claims

1. A preparation method of a composite proton exchange membrane, the preparation method comprises: S1. Filling a solution of a hydrophilic two-dimensional nanosheet material into a hydrophobic substrate, drying, and performing a crosslinking reaction to obtain a modified substrate membrane; S2. Filling a resin solution into the modified substrate membrane, drying, to obtain a single-layer composite proton exchange membrane.

2. The preparation method according to claim 1, wherein, the hydrophilic two-dimensional nanosheet material comprises graphene oxide and / or graphene oxide derivatives.

3. The preparation method according to claim 2, wherein, The groups of the graphene oxide and / or graphene oxide derivatives include -COOH, -NH 2 , -SO 3 H, -OH, or a combination of two or more thereof.

4. The preparation method according to claim 1, wherein, the concentration of the solution of the hydrophilic two-dimensional nanosheet material is 0.01 - 1 mg / mL, preferably 0.1 - 1 mg / mL.

5. The preparation method according to claim 1, the hydrophobic substrate comprises a polytetrafluoroethylene membrane.

6. The preparation method according to claim 1, wherein, the temperature of the crosslinking reaction is 80 - 120 °C, the time of the crosslinking reaction is 4 - 48 h, and the crosslinking reaction is carried out in a vacuum environment.

7. The preparation method according to claim 1, wherein, the resin comprises Nafion resin.

8. The preparation method according to claim 1, wherein, the preparation method further comprises stacking and hot-pressing two or more single-layer composite proton exchange membranes to form a multi-layer composite proton exchange membrane; preferably, the temperature of the hot-pressing is 100 - 160 °C, the pressure of the hot-pressing is 0.3 - 10 MPa, and the time of the hot-pressing is 30 s - 5 min.

9. A composite proton exchange membrane, which is obtained by the preparation method according to any one of claims 1 - 8.

10. Application of the composite proton exchange membrane according to claim 9 in water electrolysis for hydrogen production and / or batteries.