A proton exchange membrane and its preparation method and application

Abstract

The present invention relates to a method for preparing a proton exchange membrane with high strength and high proton conductivity and its application. The membrane material of the proton exchange membrane is a sulfonated polymer, and sulfonated polyimide nanofibers are included in the proton exchange membrane. By blending sulfonated polyimide nanofibers, the present invention enhances the mechanical strength and dimensional stability of the membrane while improving the proton conductivity, and can be used as a proton exchange membrane in hydrogen fuel cells or alcohol fuel cells.

Description

Technical Field

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

[0002] Fuel cells are power generation technologies that have gradually received attention in recent years. Proton exchange membrane fuel cells are one of the most widely used and relatively important types of fuel cells. Currently, commercially available proton exchange membranes are mainly fluorine-containing perfluorosulfonic acid proton membranes (Nafion). However, at high temperatures (>120 °C), the proton conductivity of such membranes will drop sharply due to water loss, thus limiting the operating efficiency of the battery.

[0003] Non-fluorinated proton exchange membranes are a new solution proposed in recent years to replace the Nafion series of proton exchange membranes. Sulfonated polymers with a rigid main chain structure, such as sulfonated polyether ether ketone, sulfonated polysulfone, and sulfonated polyimide, have received sufficient attention. However, the current problem with non-fluorinated proton exchange membranes is that they do not easily form a microphase separation structure within the system like Nafion. Therefore, in the formed homogeneous membrane, it is not easy to form microphase channels inside, and dead zone structures are likely to form between the hydrophilic and hydrophobic phases, resulting in a decrease in proton conduction ability. In order to construct a channel effect, compounds with other positively charged or weakly positively charged structures are often blended with sulfonic acid groups to form acid-base ion pairs, reducing the loss of proton exchange caused by dehydration at high temperatures.

[0004] Patent CN103715438A proposes an organic-inorganic composite method, mixing graphene oxide to improve the performance of the proton exchange membrane. However, due to the high requirement for the uniformity of the homogeneous membrane in the proton exchange membrane, in addition to playing the role of conducting protons, it also has high requirements for blocking gas permeation. Therefore, the compatibility between the blended material and the matrix is also an important factor to be considered.

[0005] Under the existing acid-base composite ion pair mechanism, how to construct an effective proton transport channel and maintain the intrinsic uniformity and stability of the membrane material remains to be further explored. Summary of the Invention

[0006] In order to solve the problem in the prior art that the performance between proton conductivity and membrane anti-swelling property cannot be improved simultaneously when conventional sulfonated polymers are used as proton exchange membranes, the present invention proposes a preparation method and an application of a proton exchange membrane with high strength and high proton conductivity, mainly improving the mechanical properties and proton conductivity of non-fluorinated sulfonic acid proton exchange membranes, and increasing the possibility of applying such proton exchange membranes in high-temperature scenarios.

[0007] One object of the present invention is to provide a proton exchange membrane, wherein the membrane material of the proton exchange membrane is a sulfonated polymer, and the proton exchange membrane contains sulfonated polyimide nanofibers.

[0008] The sulfonated polyimide nanofibers account for 5 to 50 wt% of the sulfonated polymer, preferably 10 to 30 wt%.

[0009] The sulfonated polymer has a molecular weight greater than 70,000 and a sulfonation degree of 50% to 80%, preferably 60% to 70%. Among them, the sulfonated polymer is preferably at least one selected from sulfonated polyether ether ketone, sulfonated benzimidazole, sulfonated polysulfone, sulfonated polyether sulfone, and sulfonated polyimide.

[0010] The sulfonated polyimide nanofibers are prepared by the following steps: pulverize the polyimide nanofiber membrane and add it to a solvent to disperse to obtain a nanofiber dispersion; add the sulfonated polyelectrolyte to a solvent to obtain a sulfonated polyelectrolyte solution; mix the nanofiber dispersion with the sulfonated polyelectrolyte solution.

[0011] In the above steps, the swelling degree of the polyimide nanofiber membrane in an aprotic polar solvent is less than 10%, preferably less than 5%.

[0012] In the above steps, the sulfonated polyelectrolyte is a polymer with sulfonic acid groups or sulfonate groups, and the sulfonation degree is greater than 50%. The polymer with sulfonate groups can be, for example, a polymer with sodium sulfonate groups. Among them, the sulfonated polyelectrolyte is preferably at least one selected from sodium polystyrene sulfonate, sulfonated octaphenyl substituted silsesquioxane, sulfonated polysulfone, and polyether sulfone.

[0013] In the above steps, the molar ratio of the imide groups in the polyimide to the sulfonic acid groups or sulfonate groups in the sulfonated polyelectrolyte is (3:1) to (1:3), preferably (2:1) to (1:2).

[0014] In the above steps, the diameter of the nanofibers is less than 1000 nm, preferably 200 nm to 500 nm; the size distribution coefficient of the diameter distribution is <2.

[0015] In the above steps, the solvent is an aprotic polar solvent or water.

[0016] In the above steps, the nanofiber dispersion is obtained by shear dispersion, where the shear rotation speed is 5000 to 20000 rpm, preferably 8000 to 15000 rpm, and the shear time is 5 min to 120 min, preferably 20 min to 60 min.

[0017] In the above steps, the polyimide nanofiber membrane is obtained by reacting a dianhydride with a diamine in an aprotic polar solvent to obtain a polyamic acid solution, then electrospinning the polyamic acid solution into a nanofiber membrane, and finally performing imidization treatment.

[0018] Among them, the Hansen solubility difference Ra between the solubility parameter of the polymer formed by the dianhydride and the diamine and the solubility parameter of the solvent is greater than 5.5, and preferably Ra is greater than 6.

[0019] Ra is calculated according to the following formula:

[0020] R a = [4(D solv - D poly ) 2 + (P solv - P poly ) 2 + (H solv - H poly ) 2 ) 0.5 ,

[0021] In the formula, D represents the dispersion component, P represents the polar component, H represents the hydrogen bond component, solv represents the solvent, and poly represents the polymer; the solubility parameter of the solvent can be obtained by referring to the Hansen solubility parameter table; the solubility parameter of the polymer is calculated by the group contribution method and the Hoftyzer-Van Krevelen method for each parameter.

[0022] In the present invention, the magnitude of the Ra value represents the compatibility between the solvent and the polymer. The polyimide nanofiber membrane has a low swelling degree in aprotic polar solvents. The combination of dianhydride or diamine monomers for the low-swelling polyimide nanofiber membrane is selected according to the principle of like dissolves like. Among them, the solubility parameter and solubility parameter components (dispersion component, polar component, and hydrogen bond component) of the aprotic polar solvent can be obtained by referring to the Hansen solubility parameter table. The solubility parameter of the polymer system is calculated by the group contribution method and the Hoftyzer-Van Krevelen method for each parameter. Finally, the Ra is obtained by calculating the component parameters of the polymer and the components of the solvent through the Hansen solubility formula.

[0023] On the premise that the Ra value of the solubility parameter meets the requirements, monomers with high symmetry are more preferred, which can provide higher strength and stability of the material. Among the monomer combinations, on the premise of ensuring the solubility parameter, monomers with low molar molecular weight are more preferably used. In this case, the mass ratio of the imine structure in the imide is higher. The monomer combination is not limited to a single combination of dianhydride and diamine, and a multi-component copolymer polymer that meets the low swelling conditions can also be used.

[0024] During the preparation process of the polyimide nanofiber membrane,

[0025] The molar ratio of the dianhydride to the diamine is (0.970 - 0.998):1, preferably (0.98 - 0.99):1;

[0026] The reaction temperature is 0 to 50 °C, and the reaction time is 1 to 12 h;

[0027] The imidization treatment includes staying at 80 to 150 °C for 0.5 to 1 h; heating at a heating rate of 0.5 to 5 °C / min to 230 to 300 °C and staying for 0.5 to 2 h; heating to -30 to +30 °C of the glass transition temperature of the polyimide system and staying for 0.5 to 1 h.

[0028] The proton exchange membrane of the present invention has a tensile strength greater than 100 MPa at room temperature; under the conditions of 60 °C and 100% RH, the proton conductivity is greater than 100 mS / cm.

[0029] The second object of the present invention is to provide a method for preparing the proton exchange membrane. A casting solution is prepared from raw materials including a sulfonated polymer and sulfonated polyimide nanofibers, a liquid film is formed by coating on the surface of a substrate, and then heat treatment is carried out.

[0030] In the preparation method, the dosage of the sulfonated polyimide nanofibers is 5 wt% to 50 wt% of the sulfonated polymer, preferably 10 wt% to 30 wt%.

[0031] In the preparation method, the thickness of the liquid film is 100 to 1000 μm.

[0032] In the preparation method, the temperature of the heat treatment is 180 to 240 °C, preferably 200 to 220 °C.

[0033] In the preparation method, the time of the heat treatment is 0.5 to 4 h.

[0034] The third object of the present invention is to provide the application of the proton exchange membrane or the proton exchange membrane obtained by the preparation method in a hydrogen fuel cell or an alcohol fuel cell.

[0035] The present invention preferably solves the problem that the swelling degree of the material increases while the sulfonation degree of the non-fluorinated proton exchange membrane is improved. By blending nanofiber materials with certain strength and sulfonation degree, the problem that defects or unevenness are easily generated when the sulfonated polymer matrix is directly cast is avoided. The uniform dispersion of the nanomaterials constructs an effective transmission channel, enhances the mechanical strength and dimensional stability of the material while improving the proton conductivity of the material, and can be used as a proton exchange membrane in a hydrogen fuel cell.

[0036] The technical concept of the present invention mainly modifies the non-fluorinated sulfonated polymer matrix by constructing nanofiber materials. On the one hand, the nanofibers play a role in composite reinforcement; on the other hand, they play a role as channels, reducing the mass transfer resistance during proton conduction. Most importantly, anionic and cationic pairs are formed between the nanofibers with polyimide structure and the sulfonated polymer. While water molecules act as proton carriers, the proton transfer pathway is increased in the form of ion pairs, thereby further improving the proton conductivity. The main structure of the proton exchange membrane is a non-fluorinated sulfonated polymer, and polyimide nanofibers are used as reinforcing materials. After sulfonating and modifying the nanofibers and then compounding them with the matrix, the finally obtained proton exchange membrane has good mechanical properties and proton conductivity.

[0037] The present invention solves the compatibility problem between nanofibers and sulfonated polymer matrix by preparing nanofibers with certain strength and proton conductivity, improves the strength of the membrane and at the same time improves the proton conductivity of the membrane, and can be used in high-temperature hydrogen fuel cells and alcohol fuel cell systems.

[0038] The following further elaborates on the present invention through examples. Specific embodiments

[0039] The following specifically describes the present invention in combination with specific examples. It is necessary to point out here that the following examples are only for further illustration of the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0040] If there is no special limitation on the raw materials used in the examples and comparative examples, they are all disclosed in the prior art, for example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0041] According to a preferred embodiment of the present invention, the preparation method of the proton exchange membrane with high strength and high proton conductivity may include the following steps:

[0042] (1) Preparation of a polyimide nanofiber membrane with low swelling degree;

[0043] (2) Composite of nanofibers and sulfonated polyelectrolyte;

[0044] (3) Blend of sulfonated nanofibers and sulfonated polymer for film formation;

[0045] (4) Solution molding process.

[0046] In the above step (1), the polyimide nanofiber membrane with low swelling degree is prepared. The polyimide nanofiber membrane with low swelling degree refers to that polyimide has a low swelling degree in aprotic polar solvents, generally the swelling degree is less than 10%, and preferably the swelling degree is lower than 5%.

[0047] The preparation of the polyimide nanofiber membrane refers to electrospinning a precursor solution, i.e., a polyamic acid solution, into a nanofiber membrane, and then obtaining a polyimide nanofiber membrane through an imidization reaction.

[0048] The monomer combination described is not limited to a single combination of dianhydride and diamine. Multicomponent copolymer polymers that meet the low swelling conditions can also be used. Taking the polymer formed by 3,3,4,4-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA) as an example, according to the Hoftyzer-Van Krevelen method for calculating solubility parameters, the components D, P, and H in the solubility parameter are calculated by the formulas and respectively, where the F di , F pi , E hi and V i values of each group structure are obtained by looking up tables, and then the corresponding superposition calculations are carried out to obtain the solubility parameter of the polymer.

[0049] According to this method, the solubility parameter components of the BPDA-PDA system are: δ d = 14.8, δ p = 6.9, δ h = 8.1; if the solvent selected is N,N-dimethylacetamide, its solubility parameter components are δ d = 16.8, δ p = 11.5, δ h = 10.2; obtained through the Hansen solubility parameter calculation formula, at this time the Ra value is 6.4, meeting the project requirements. From the above calculation formulas, the parameter components are not in a simple mathematical superposition form. Adding new structural units may make the parameter components larger or smaller. Therefore, certain specific polymer structures are not limited. The monomers selected in this patent are only PI polymers or PI copolymers with Ra values meeting the requirements.

[0050] In the preparation of the polyimide nanofiber membrane, electrospinning is used to spin the precursor solution, i.e., the polyamic acid solution, into a nanofiber membrane. The preparation of the polyamic acid solution involves a reaction where a dianhydride and a diamine are first stirred and reacted in an aprotic polar solvent under an inert gas protection atmosphere. The ratio of the dianhydride to the diamine is fed in a ratio of (0.970 - 0.998):1, and preferably the ratio of the dianhydride to the diamine is (0.98 - 0.99):1; the solid content is 10 - 18 wt%, preferably 13 - 15 wt%; the inert gas atmosphere refers to a reaction atmosphere such as nitrogen or argon; the aprotic polar solvent refers to common aprotic polar solvents such as N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, etc.; for the stirring reaction, the temperature condition is 0 - 50 °C, preferably 25 - 40 °C, and the reaction time is 1 - 12 h, preferably 2 - 4 h.

[0051] In the electrospinning process, the precursor solution is spun into a nanofiber membrane. The electrospinning equipment can be a needle-type or needleless electrospinning device. For the nanofiber membrane, the spinning process parameters should be adjusted to control the fiber diameter to be less than 1000 nm, preferably 200 nm - 500 nm, and the diameter distribution size distribution coefficient < 2.

[0052] The imidization treatment refers to placing the sample in an atmosphere heating oven for programmed temperature increase. The atmosphere oven refers to an oven protected by an inert atmosphere, such as nitrogen, argon, etc. The programmed temperature increase is carried out at 80 - 150 °C for a residence time of 0.5 - 1 h. Subsequently, at a certain heating rate, the heating rate is controlled at 0.5 - 5 °C / min, and the temperature is raised to 230 - 300 °C, preferably 250 - 280 °C. After reaching the set temperature, the residence time is 0.5 - 2 h. Subsequently, the temperature is continued to be raised to the complete imidization stage, and the set temperature is set to -30 to +30 °C of the glass transition temperature of the selected polyimide system, preferably -15 to +15 °C of the glass transition temperature, to completely imidize the nanofibers to obtain polyimide nanofibers. After reaching the set temperature, the residence time is 0.5 - 1 h.

[0053] In step (2) described above, the nanofibers are compounded with a sulfonated polyelectrolyte to obtain sulfonated nanofibers. The nanofibers refer to nanofiber dispersions obtained by cutting the nanofiber membrane into pieces and then dispersing them by high-speed shearing in a solution. The solution refers to an aprotic polar solvent or an aqueous solution. The high-speed shearing machine is set with a shearing rotation speed of 5000 - 20000 rpm, preferably 8000 - 15000 rpm, and the shearing time is 5 min - 120 min, preferably 20 min - 60 min.

[0054] The sulfonated polyelectrolyte mentioned above is a polymer with sulfonic acid groups and sulfonate groups, having a sulfonation degree > 50%, and having a certain solubility in polar solvents, such as sodium polystyrene sulfonate, sulfonated octaphenyl substituted silsesquioxane, sulfonated polysulfone, polyethersulfone, etc. The polar solvent is the same as the solvent condition selected in the nanofiber dispersion.

[0055] The compounding mentioned above is to mix and disperse the nanofiber dispersion and the sulfonated electrolyte, filter, wash, and dry after stirring for a certain time to obtain nanofibers compounded with the sulfonated polyelectrolyte. The dosages of the nanofibers and the sulfonated polyelectrolyte are added according to the molar ratio of imine in the imide group to sulfonic acid groups or sulfonate groups in the sulfonated polyelectrolyte of 3:1 to 1:3, and preferably 2:1 to 1:2, such as 3:1, 2.5:1, 2:1, 1.5:1, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, etc.

[0056] In step (3) mentioned above, the sulfonated nanofibers are blended with the sulfonated polymer for film formation. The sulfonated polymer for film formation refers to a sulfonated polymer with a molecular weight > 70000, and its sulfonation degree is 50% - 80%, preferably 60% - 70%. The polymer has good film-forming properties, such as sulfonated polyether ether ketone, sulfonated benzimidazole, sulfonated polysulfone, sulfonated polyethersulfone, sulfonated polyimide, etc. Among them, preferably, sulfonated polyarylether ketone and sulfonated polyimide with a certain rigid structure are selected.

[0057] The blending mentioned above means blending a certain amount of sulfonated nanofibers into the sulfonated polymer for film formation. The dosage of the sulfonated nanofibers is 5wt% - 50wt% of the sulfonated polymer for film formation, preferably 10wt% - 30wt%, such as 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 40wt%, 50wt%, etc.

[0058] In step (4) mentioned above, solution casting processing is carried out. The solution casting processing refers to coating the casting solution on the surface of the substrate to form a liquid film with a certain thickness by means of dip coating, blade coating, spin coating, or spraying, and then removing the solvent by heat treatment to finally obtain a cured proton exchange membrane. The liquid film with a certain thickness is 100μm - 1000μm in thickness. The heat treatment refers to heat treatment at 180 - 240°C, preferably 200 - 220°C for 0.5 - 4h to obtain a cured membrane.

[0059] Example 1

[0060] (1) Preparation of polyimide nanofiber membrane with low swelling degree. 4.09 g of p-phenylenediamine was added to 85 g of N,N-dimethylacetamide solution purged with N2 and stirred until dissolved. Then 10.91 g of 3,3`,4,4`-biphenyltetracarboxylic dianhydride was added, and the reaction temperature was set at 40 °C. After reacting for 4 h, a polyamic acid solution was obtained. The polyamic acid solution was electrospun into a fiber membrane through a needleless electrospinning device to obtain a nanofiber membrane with an average diameter of 200 - 300 nm, and the diameter distribution size distribution coefficient <1.6. Subsequently, it was placed in a high-temperature oven under N2 atmosphere for heat treatment. The programmed temperature was set as follows: starting temperature of 80 °C for 0.5 h, then heating at 3 °C / min to 250 °C and staying for 0.5 h, continuing to heat to 380 °C and staying for 1 h to obtain a polyimide nanofiber membrane. The solubility parameter of the polyimide material obtained from this system (polar, dispersion, and hydrogen bond components are 14.8, 6.9, and 8.1 respectively) and the solubility parameter of N,N-dimethylacetamide (polar, dispersion, and hydrogen bond components are 16.8, 11.5, and 10.2 respectively) were calculated to obtain an Ra value of 6.4, indicating good swelling resistance of the material.

[0061] (2) Composite of nanofibers and sulfonated polyelectrolyte. The obtained nanofiber membrane was cut into pieces and dispersed in N,N-dimethylacetamide solvent. A high-speed shear machine was used to accelerate the dispersion, with the rotation speed set at 10000 rpm and the dispersion time of 30 min. Subsequently, sulfonated polysulfone with a sulfonation degree of 70% was dissolved in N,N-dimethylacetamide. After it was dissolved evenly, it was mixed with the nanofiber dispersion. The addition amounts of the two were such that the molar ratio of imide groups to sulfonic acid groups in polyimide was mixed at 1:1. After mixing evenly, the composite nanofibers were obtained through filtration, solvent washing, filtration, and drying.

[0062] (3) Blending of sulfonated nanofibers and sulfonated polymer for film formation. Sulfonated polyether ether ketone with a sulfonation degree of 70% was selected as the matrix casting solution with a solid content of 20 wt%. Sulfonated nanofibers were added for blending, and the addition amount was 15% of the matrix polymer. It was stirred and dispersed evenly.

[0063] (4) Solution forming process. The mixed casting solution was coated on a glass substrate by doctor blading to obtain a liquid film with a thickness of 300 μm. Subsequently, it was placed in an oven to remove the solvent, with the temperature set at 200 °C and staying for 1 h to finally obtain a proton exchange membrane.

[0064] For the proton exchange membrane obtained by this method, its mechanical strength is 120 MPa, and the proton conductivity is 130 mS / cm under the conditions of 60 °C and 100% RH.

[0065] Example 2

[0066] (1) Preparation of polyimide nanofiber membrane with low swelling degree. 3.91 g of p-phenylenediamine was added to 85 g of N,N-dimethylacetamide solution purged with N2 atmosphere and stirred until dissolved. Then, 11.09 g of 4,4'-biphenyl ether tetracarboxylic dianhydride was added, and the reaction temperature was set at 40 °C. After reacting for 4 h, a polyamic acid solution was obtained. The polyamic acid solution was electrospun into a fiber membrane through a needleless electrospinning device to obtain a nanofiber membrane with an average diameter of 200 - 350 nm, and the diameter distribution coefficient was <1.8. Subsequently, it was placed in a high-temperature oven under N2 atmosphere for heat treatment, and the programmed temperature was set as follows: starting temperature of 80 °C for 0.5 h, then heating at 3 °C / min to 250 °C and staying for 0.5 h, continuing to heat to 380 °C and staying for 1 h to obtain a polyimide nanofiber membrane. The solubility parameter (polar, dispersion, and hydrogen bond components were 15.0, 7.0, and 8.7 respectively) of the polyimide material obtained from this system and the solubility parameter Ra value of N,N-dimethylacetamide was 6.0, indicating good swelling resistance of the material.

[0067] (2) Composite of nanofibers and sulfonated polyelectrolytes. After the obtained nanofiber membrane was cut into pieces, it was dispersed in N,N-dimethylacetamide solvent, and a high-speed shear machine was used to accelerate the dispersion, with the rotation speed set at 10000 rpm and the dispersion time of 30 min. Subsequently, sulfonated polysulfone with a sulfonation degree of 70% was dissolved in N,N-dimethylacetamide. After it was dissolved evenly, it was mixed with the nanofiber dispersion, and the addition amounts of the two were such that the molar ratio of imide groups to sulfonic acid groups in the polyimide was 1:1. After mixing evenly, the composite nanofibers were obtained through filtration, solvent washing, filtration, and drying.

[0068] (3) Blending of sulfonated nanofibers and sulfonated polymers for film formation. Sulfonated polyether ether ketone with a sulfonation degree of 70% was selected as the matrix casting solution with a solid content of 20 wt%, and sulfonated nanofibers were added for blending, with the addition amount being 15% of the matrix polymer, and stirred and dispersed evenly.

[0069] (4) Solution forming process. The mixed casting solution was coated on a glass substrate by doctor blade coating to obtain a liquid film with a thickness of 300 μm, and then placed in an oven to remove the solvent, with the temperature set at 200 °C and staying for 1 h, finally obtaining a proton exchange membrane.

[0070] For the proton exchange membrane obtained by this method, its mechanical strength was 108 MPa, and the proton conductivity was 125 mS / cm under the conditions of 60 °C and 100% RH.

[0071] Example 3

[0072] (1) Preparation of polyimide nanofiber membrane with low swelling degree. 4.06 g of p-phenylenediamine was added to 85 g of N,N-dimethylacetamide solution purged with N2 and stirred until dissolved. Then 10.94 g of 3,3`,4,4`-biphenyltetracarboxylic dianhydride was added. The reaction temperature was set at 40 °C, and after reacting for 4 h, a polyamic acid solution was obtained. The polyamic acid solution was electrospun into a fiber membrane through a needleless electrospinning device to obtain a nanofiber membrane with an average diameter of 300 - 500 nm, and the diameter distribution size distribution coefficient < 1.7. Subsequently, it was placed in a high-temperature oven under N2 atmosphere for heat treatment. The programmed temperature was set as follows: starting temperature of 80 °C for 0.5 h, then heating to 250 °C at a rate of 3 °C / min and staying for 0.5 h, continuing to heat to 380 °C and staying for 1 h to obtain a polyimide nanofiber membrane. The solubility parameter Ra value of the polyimide material obtained from this system with N,N-dimethylacetamide was calculated to be 6.4, and the material had good swelling resistance.

[0073] (2) Composite of nanofibers and sulfonated polyelectrolytes. After the obtained nanofiber membrane was cut into pieces, it was dispersed in N,N-dimethylacetamide solvent, and a high-speed shear machine was used to accelerate the dispersion. The rotation speed was set at 10000 rpm, and the dispersion time was 30 min. Subsequently, sulfonated polysulfone with a sulfonation degree of 70% was dissolved in N,N-dimethylacetamide. After it was dissolved evenly, it was mixed with the nanofiber dispersion. The addition amounts of the two were such that the molar ratio of imide groups to sulfonic acid groups in the polyimide was mixed at 1:1. After mixing evenly, the composite nanofibers were obtained through filtration, solvent washing, filtration, and drying.

[0074] (3) Blending of sulfonated nanofibers and sulfonated polymers for film formation. Sulfonated polyether ether ketone with a sulfonation degree of 70% was selected as the matrix casting solution with a solid content of 20 wt%. Sulfonated nanofibers were added for blending, and the addition amount was 15% of the matrix polymer, and they were stirred and dispersed evenly.

[0075] (4) Solution forming process. The mixed casting solution was coated on a glass substrate by doctor blade coating to obtain a liquid film with a thickness of 300 μm. Subsequently, it was placed in an oven to remove the solvent. The temperature was set at 200 °C and it stayed for 1 h, and finally a proton exchange membrane was obtained.

[0076] For the proton exchange membrane obtained according to this method, its mechanical strength was 105 MPa, and the proton conductivity was 112 mS / cm under the conditions of 60 °C and 100% RH.

[0077] Example 4

[0078] (1) Preparation of polyimide nanofiber membrane with low swelling degree. 3.52 g of p-phenylenediamine was added to 85 g of N,N-dimethylacetamide solution purged with N2 atmosphere and stirred until dissolved. Then, 9.48 g of 3,3`,4,4`-biphenyltetracarboxylic dianhydride was added. The reaction temperature was set at 40 °C, and after reacting for 4 h, a polyamic acid solution was obtained. The polyamic acid solution was electrospun into a fiber membrane through a needleless electrospinning device to reduce the solid content, obtaining a nanofiber membrane with an average diameter of 200 - 380 nm and a diameter distribution size distribution coefficient < 2. Subsequently, it was placed in a high-temperature oven under N2 atmosphere for heat treatment, and the programmed temperature was set as follows: starting temperature of 80 °C for 0.5 h, then heating at 3 °C / min to 250 °C and staying for 0.5 h, continuing to heat to 380 °C and staying for 1 h to obtain a polyimide nanofiber membrane. The solubility parameter Ra value of the polyimide material obtained from this system and N,N-dimethylacetamide was calculated to be 6.4, indicating good swelling resistance of the material.

[0079] (2) Composite of nanofibers and sulfonated polyelectrolytes. After the obtained nanofiber membrane was cut into pieces, it was dispersed in N,N-dimethylacetamide solvent, and a high-speed shear machine was used to accelerate the dispersion, with the rotation speed set at 10000 rpm and the dispersion time of 30 min. Subsequently, sulfonated polysulfone with a sulfonation degree of 70% was dissolved in N,N-dimethylacetamide. After it was dissolved uniformly, it was mixed with the nanofiber dispersion, and the addition amounts of the two were such that the molar ratio of imide groups to sulfonic acid groups in the polyimide was mixed at 1:1. After mixing evenly, the composite nanofibers were obtained through filtration, solvent washing, filtration, and drying.

[0080] (3) Blending of sulfonated nanofibers and sulfonated polymers for film formation. Sulfonated polyether ether ketone with a sulfonation degree of 70% was selected as the matrix casting solution with a solid content of 20 wt%, and sulfonated nanofibers were added for blending, with the addition amount being 15% of the matrix polymer, and stirred and dispersed evenly.

[0081] (4) Solution forming process. The mixed casting solution was coated on a glass substrate by doctor blade coating to obtain a liquid film with a thickness of 300 μm, and then placed in an oven to remove the solvent, with the temperature set at 200 °C and staying for 1 h, finally obtaining a proton exchange membrane.

[0082] For the proton exchange membrane obtained according to this method, its mechanical strength was 130 MPa, and the proton conductivity was 108 mS / cm under the conditions of 60 °C and 100% RH.

[0083] Example 5

[0084] (1) Preparation of polyimide nanofiber membrane with low swelling degree. 4.09 g of p-phenylenediamine was added to 85 g of N,N-dimethylacetamide solution purged with N2 and stirred until dissolved. Then, 10.91 g of 3,3`,4,4`-biphenyltetracarboxylic dianhydride was added. The reaction temperature was set at 40 °C, and after reacting for 4 h, a polyamic acid solution was obtained. The polyamic acid solution was electrospun into a fiber membrane through a needleless electrospinning device to obtain a nanofiber membrane with an average diameter of 200 - 300 nm, and the diameter distribution coefficient was <1.6. Subsequently, it was placed in a high-temperature oven under N2 atmosphere for heat treatment. The programmed temperature was set as follows: starting temperature of 80 °C for 0.5 h, then heating to 250 °C at a rate of 3 °C / min and staying for 0.5 h, continuing to heat to 380 °C and staying for 1 h to obtain a polyimide nanofiber membrane. The solubility parameter Ra value of the polyimide material obtained from this system with N,N-dimethylacetamide was 6.4, and the material had good swelling resistance.

[0085] (2) Composite of nanofibers and sulfonated polyelectrolytes. After the obtained nanofiber membrane was cut into pieces, it was dispersed in N,N-dimethylacetamide solvent, and a high-speed shear machine was used to accelerate the dispersion. The rotation speed was set at 10,000 rpm, and the dispersion time was 30 min. Subsequently, sulfonated polysulfone with a sulfonation degree of 60% was dissolved in N,N-dimethylacetamide. After it was dissolved uniformly, it was mixed with the nanofiber dispersion. The addition amounts of the two were such that the molar ratio of imide groups to sulfonic acid groups in the polyimide was mixed at 1:1. After mixing evenly, the composite nanofibers were obtained through filtration, solvent washing, filtration, and drying.

[0086] (3) Blending of sulfonated nanofibers and sulfonated polymers for film formation. Sulfonated polyether ether ketone with a sulfonation degree of 70% was selected as the matrix casting solution with a solid content of 20 wt%. Sulfonated nanofibers were added for blending, and the addition amount was 30% of the matrix polymer. After stirring and dispersing evenly.

[0087] (4) Solution forming process. The mixed casting solution was coated on a glass substrate by doctor blade coating to obtain a liquid film with a thickness of 300 μm, and then placed in an oven to remove the solvent. The temperature was set at 200 °C and stayed for 1 h to finally obtain a proton exchange membrane.

[0088] For the proton exchange membrane obtained according to this method, its mechanical strength was 112 MPa, and the proton conductivity was 130 mS / cm under the conditions of 60 °C and 100% RH.

[0089] Example 6

[0090] (1) Preparation of polyimide nanofiber membrane with low swelling degree. 4.09 g of p-phenylenediamine was added to 85 g of N,N-dimethylacetamide solution purged with N2 and stirred until dissolved. Then 10.91 g of 3,3`,4,4`-biphenyltetracarboxylic dianhydride was added, and the reaction temperature was set at 40 °C. After reacting for 4 h, a polyamic acid solution was obtained. The polyamic acid solution was electrospun into a fiber membrane through a needleless electrospinning device to obtain a nanofiber membrane with an average diameter of 200 - 300 nm, and the diameter distribution size distribution coefficient <1.6. Subsequently, it was placed in a high-temperature oven under N2 atmosphere for heat treatment, and the programmed temperature was set as follows: starting temperature of 80 °C for 0.5 h, then heating to 250 °C at a rate of 3 °C / min and staying for 0.5 h, continuing to heat to 380 °C and staying for 1 h to obtain a polyimide nanofiber membrane. The solubility parameter Ra value of the polyimide material obtained from this system with N,N-dimethylacetamide was 6.4, and the material had good swelling resistance.

[0091] (2) Composite of nanofibers and sulfonated polyelectrolytes. After the obtained nanofiber membrane was cut into pieces, it was dispersed in N,N-dimethylacetamide solvent, and a high-speed shear machine was used to accelerate the dispersion, with the rotation speed set at 15000 rpm and the dispersion time of 30 min. Subsequently, sulfonated polysulfone with a sulfonation degree of 70% was dissolved in N,N-dimethylacetamide. After it was dissolved evenly, it was mixed with the nanofiber dispersion, and the addition amounts of the two were such that the molar ratio of imide groups to sulfonic acid groups in the polyimide was mixed at 1:1. After mixing evenly, the composite nanofibers were obtained through filtration, solvent washing, filtration, and drying. After high-speed shearing, the aspect ratio of the nanofibers decreased and they were broken into shorter structures.

[0092] (3) Blending of sulfonated nanofibers and sulfonated polymers for film formation. Sulfonated polyether ether ketone with a sulfonation degree of 70% was selected as the matrix casting solution with a solid content of 20 wt%, and sulfonated nanofibers were added for blending, with the addition amount being 15% of the matrix polymer, and stirred and dispersed evenly.

[0093] (4) Solution forming process. The mixed casting solution was coated on a glass substrate by doctor blading to obtain a liquid film with a thickness of 300 μm, and then placed in an oven to remove the solvent, with the temperature set at 200 °C and staying for 1 h to finally obtain a proton exchange membrane.

[0094] For the proton exchange membrane obtained by this method, due to the shorter nanofibers, the mechanical reinforcement effect increased, while the proton transport ability decreased due to the bridging effect of the nanofibers. Its mechanical strength was 136 MPa, and the proton conductivity was 110 mS / cm under the conditions of 60 °C and 100% RH.

[0095] Example 7

[0096] (1) Preparation of polyimide nanofiber membrane with low swelling degree. 4.09 g of p-phenylenediamine was added to 85 g of N,N-dimethylacetamide solution purged with N2 atmosphere and stirred until dissolved. Then 10.91 g of 3,3`,4,4`-biphenyltetracarboxylic dianhydride was added, and the reaction temperature was set at 40 °C. After reacting for 4 h, a polyamic acid solution was obtained. The polyamic acid solution was electrospun into a fiber membrane through a needleless electrospinning device to obtain a nanofiber membrane with an average diameter of 200 - 300 nm, and the diameter distribution size distribution coefficient <1.6. Subsequently, it was placed in a high-temperature oven under N2 atmosphere for heat treatment, and the programmed temperature was set as follows: starting temperature of 80 °C for 0.5 h, then heating to 250 °C at a rate of 3 °C / min and staying for 0.5 h, continuing to heat to 380 °C and staying for 1 h to obtain a polyimide nanofiber membrane. The solubility parameter Ra value of the polyimide material obtained from this system with N,N-dimethylacetamide was 6.4, and the material had good swelling resistance.

[0097] (2) Composite of nanofibers and sulfonated polyelectrolytes. After the obtained nanofiber membrane was cut into pieces, it was dispersed in N,N-dimethylacetamide solvent, and a high-speed shear machine was used to accelerate the dispersion, with the rotation speed set at 10000 rpm and the dispersion time of 30 min. Subsequently, sulfonated polysulfone with a sulfonation degree of 70% was dissolved in N,N-dimethylacetamide. After it was dissolved uniformly, it was mixed with the nanofiber dispersion, and the addition amounts of the two were mixed according to the molar ratio of imide groups to sulfonic acid groups in polyimide of 2:1. After mixing evenly, the composite nanofibers were obtained by filtration, solvent washing, filtration, and drying.

[0098] (3) Blending of sulfonated nanofibers and sulfonated polymers for film formation. Sulfonated polyether ether ketone with a sulfonation degree of 70% was selected as the matrix casting solution with a solid content of 20 wt%, and sulfonated nanofibers were added for blending, with the addition amount being 15% of the matrix polymer, and stirred and dispersed evenly.

[0099] (4) Solution forming process. The mixed casting solution was coated on a glass substrate by doctor blade coating to obtain a liquid film with a thickness of 300 μm, and then placed in an oven to remove the solvent, with the temperature set at 200 °C and staying for 1 h, and finally a proton exchange membrane was obtained.

[0100] For the proton exchange membrane obtained according to this method, due to the excess imide groups in the nanofibers, the number of combined sulfonic acid groups decreased, resulting in a decrease in proton conduction ability. Its mechanical strength was 120 MPa, and the proton conductivity was 106 mS / cm under the conditions of 60 °C and 100% RH.

[0101] Example 8

[0102] (1) Preparation of polyimide nanofiber membrane with low swelling degree. 4.09 g of p-phenylenediamine was added to 85 g of N,N-dimethylacetamide solution purged with N2 and stirred until dissolved. Then, 10.91 g of 3,3`,4,4`-biphenyltetracarboxylic dianhydride was added. The reaction temperature was set at 40 °C, and after reacting for 4 h, a polyamic acid solution was obtained. The polyamic acid solution was electrospun into a fiber membrane through a needleless electrospinning device to obtain a nanofiber membrane with an average diameter of 200 - 300 nm and a diameter distribution size distribution coefficient <1.6. Subsequently, it was placed in a high-temperature oven under N2 atmosphere for heat treatment. The programmed temperature was set as follows: starting temperature of 80 °C for 0.5 h, then heating to 250 °C at a rate of 3 °C / min and staying for 0.5 h, continuing to heat to 380 °C and staying for 1 h to obtain a polyimide nanofiber membrane. The solubility parameter Ra value of the polyimide material obtained from this system with N,N-dimethylacetamide was 6.4, indicating good swelling resistance of the material.

[0103] (2) Composite of nanofibers and sulfonated polyelectrolyte. After the obtained nanofiber membrane was cut into pieces, it was dispersed in N,N-dimethylacetamide solvent, and a high-speed shear machine was used to accelerate the dispersion. The rotation speed was set at 10,000 rpm, and the dispersion time was 30 min. Subsequently, sulfonated polysulfone with a sulfonation degree of 70% was dissolved in N,N-dimethylacetamide. After it was dissolved evenly, it was mixed with the nanofiber dispersion. The addition amounts of the two were such that the molar ratio of imide groups to sulfonic acid groups in the polyimide was mixed at 1:2. After mixing evenly, the composite nanofibers were obtained through filtration, solvent washing, filtration, and drying.

[0104] (3) Blending of sulfonated nanofibers and sulfonated polymer for film formation. Sulfonated polyether ether ketone with a sulfonation degree of 70% was selected as the matrix casting solution with a solid content of 20 wt%. Sulfonated nanofibers were added for blending, and the addition amount was 15% of the matrix polymer. It was stirred and dispersed evenly.

[0105] (4) Solution forming process. The mixed casting solution was coated on a glass substrate by doctor blade coating to obtain a liquid film with a thickness of 300 μm. Subsequently, it was placed in an oven to remove the solvent. The temperature was set at 200 °C and stayed for 1 h to finally obtain a proton exchange membrane.

[0106] For the proton exchange membrane obtained according to this method, due to the excessive sulfonic acid groups loaded in the nanofibers, the proton exchange sites between the nanofibers and the matrix decreased, and more were combined with the sulfonic acid groups that were self-combined. However, due to the additional part of sulfonate ions, the total proton conduction ability decreased slightly. Its mechanical strength was 122 MPa, and the proton conductivity was 128 mS / cm under the conditions of 60 °C and 100% RH.

[0107] Example 9

[0108] (1) Preparation of polyimide nanofiber membrane with low swelling degree. 4.09 g of p-phenylenediamine was added to 85 g of N,N-dimethylacetamide solution purged with N2 atmosphere and stirred until dissolved. Then 10.91 g of 3,3`,4,4`-biphenyltetracarboxylic dianhydride was added, and the reaction temperature was set at 40 °C. After reacting for 4 h, a polyamic acid solution was obtained. The polyamic acid solution was electrospun into a fiber membrane through a needleless electrospinning device to obtain a nanofiber membrane with an average diameter of 200 - 300 nm, and the diameter distribution size distribution coefficient <1.6. Subsequently, it was placed in a high-temperature oven under N2 atmosphere for heat treatment, and the programmed temperature was set as follows: starting temperature of 80 °C for 0.5 h, then heating to 250 °C at a rate of 3 °C / min and staying for 0.5 h, continuing to heat to 380 °C and staying for 1 h to obtain a polyimide nanofiber membrane. The solubility parameter Ra value of the polyimide material obtained from this system with N,N-dimethylacetamide was calculated to be 6.4, and the material had good swelling resistance.

[0109] (2) Composite of nanofibers and sulfonated polyelectrolyte. After the obtained nanofiber membrane was cut into pieces, it was dispersed in N,N-dimethylacetamide solvent, and a high-speed shear machine was used to accelerate the dispersion, with the rotation speed set at 10,000 rpm and the dispersion time of 30 min. Subsequently, sulfonated polysulfone with a sulfonation degree of 70% was dissolved in N,N-dimethylacetamide. After it was dissolved evenly, it was mixed with the nanofiber dispersion, and the addition amounts of the two were mixed according to the molar ratio of imide groups to sulfonic acid groups in polyimide of 1:1. After mixing evenly, the composite nanofibers were obtained through filtration, solvent washing, filtration, and drying.

[0110] (3) Blending of sulfonated nanofibers and sulfonated polymer for film formation. Sulfonated polyether ether ketone with a sulfonation degree of 70% was selected as the matrix casting solution with a solid content of 20 wt%, and sulfonated nanofibers were added for blending, with the addition amount being 10% of the matrix polymer, and stirred and dispersed evenly.

[0111] (4) Solution forming process. The mixed casting solution was coated on a glass substrate by doctor blade coating to obtain a liquid film with a thickness of 300 μm, and then placed in an oven to remove the solvent, with the temperature set at 200 °C and staying for 1 h, and finally a proton exchange membrane was obtained.

[0112] For the proton exchange membrane obtained according to this method, the introduced nanofiber membrane enhanced the mechanical properties and proton conductivity to a certain extent. Its mechanical strength was 112 MPa, and the proton conductivity was 125 mS / cm under the conditions of 60 °C and 100% RH.

[0113] Example 10

[0114] (1) Preparation of polyimide nanofiber membranes with low swelling degree. 4.09 g of p-phenylenediamine was added to 85 g of N,N-dimethylacetamide solution purged with N2 and stirred until dissolved. Then, 10.91 g of 3,3`,4,4`-biphenyltetracarboxylic dianhydride was added. The reaction temperature was set at 40 °C, and after reacting for 4 h, a polyamic acid solution was obtained. The polyamic acid solution was electrospun into a fiber membrane using a needleless electrospinning device to obtain a nanofiber membrane with an average diameter of 200 - 300 nm, and the diameter distribution size distribution coefficient <1.6. Subsequently, it was placed in a high-temperature oven under N2 atmosphere for heat treatment. The programmed temperature was set as follows: starting temperature of 80 °C for 0.5 h, then heating at 3 °C / min to 250 °C and staying for 0.5 h, continuing to heat to 380 °C and staying for 1 h to obtain a polyimide nanofiber membrane. The solubility parameter Ra value of the polyimide material obtained from this system was 6.4 when calculated with the solubility parameter of N,N-dimethylacetamide, indicating good swelling resistance of the material.

[0115] (2) Composite of nanofibers and sulfonated polyelectrolytes. After the obtained nanofiber membrane was cut into pieces, it was dispersed in N,N-dimethylacetamide solvent, and a high-speed shear machine was used to accelerate the dispersion. The rotation speed was set at 10000 rpm, and the dispersion time was 30 min. Subsequently, sulfonated polysulfone with a sulfonation degree of 70% was dissolved in N,N-dimethylacetamide. After it was dissolved evenly, it was mixed with the nanofiber dispersion. The addition amounts of the two were such that the molar ratio of imide groups to sulfonic acid groups in the polyimide was mixed at 1:1. After mixing evenly, the composite nanofibers were obtained by filtration, solvent washing, filtration, and drying.

[0116] (3) Blending of sulfonated nanofibers and sulfonated polymers for film formation. Sulfonated polyether ether ketone with a sulfonation degree of 70% was selected as the matrix casting solution with a solid content of 20 wt%. Sulfonated nanofibers were added for blending, and the addition amount was 30% of the matrix polymer, and it was stirred and dispersed evenly.

[0117] (4) Solution forming process. The mixed casting solution was coated on a glass substrate by doctor blading to obtain a liquid film with a thickness of 300 μm. Subsequently, it was placed in an oven to remove the solvent. The temperature was set at 200 °C and stayed for 1 h to finally obtain a proton exchange membrane.

[0118] For the proton exchange membrane obtained by this method, due to the large amount of nanofibers used, the mechanical properties were negatively affected, and the proton conduction increased due to the reduction of the transfer resistance. Its mechanical strength was 102 MPa, and the proton conductivity was 140 mS / cm under the conditions of 60 °C and 100% RH.

[0119] Comparative Example 1

[0120] Sulfonated polyether ether ketone with a sulfonation degree of 70% was selected as the matrix casting solution. The casting solution was directly coated on a glass substrate by doctor blading to obtain a liquid film with a thickness of 300 μm. Subsequently, it was placed in an oven to remove the solvent. The temperature was set at 200 °C and it was left for 1 h to obtain a proton exchange membrane without doping.

[0121] The mechanical strength of the film was 56 MPa, and the proton conductivity was 65 mS / cm under the conditions of 60 °C and 100% RH.

[0122] Comparative Example 2

[0123] (1) Preparation of polyimide nanofiber membrane. 7.25 g of diaminodiphenyl ether was dissolved in 85 g of N,N-dimethylacetamide, and 7.75 g of pyromellitic dianhydride was added. The reaction temperature was set at 40 °C. After reacting for 4 h, a polyamic acid solution was obtained. The polyamic acid solution was electrospun into a fiber membrane through a needleless electrospinning device to obtain a nanofiber membrane with an average diameter of 200 - 300 nm, and the diameter distribution size distribution coefficient < 1.6. Subsequently, it was placed in a high-temperature oven under N2 atmosphere for heat treatment. The programmed temperature was set as follows: starting temperature of 80 °C for 0.5 h, then heating at 3 °C / min to 250 °C and staying for 0.5 h, continuing to heat to 380 °C and staying for 1 h to obtain a polyimide nanofiber membrane. The solubility parameter Ra value of the polyimide material obtained from this system with respect to N,N-dimethylacetamide by calculating its solubility parameter (PMDA-ODA solubility parameter components 16.5, 7.1, 8.8) was 4.6, and the material had insufficient swelling resistance.

[0124] (2) Composite of nanofibers and sulfonated polyelectrolyte. After the obtained nanofiber membrane was cut into pieces, it was dispersed in N,N-dimethylacetamide solvent, and a high-speed shear machine was used to accelerate the dispersion. The rotation speed was set at 10000 rpm and the dispersion time was 30 min. The swelling resistance of this system was insufficient, and almost all the nanofibers were dissolved after high-speed shearing, and the corresponding product could not be filtered out.

[0125] Comparative Example 3

[0126] (1) Preparation of polyimide nanofiber membrane with low swelling degree. 4.09 g of p-phenylenediamine was added to 85 g of N,N-dimethylacetamide solution purged with N2 atmosphere and stirred until dissolved. Then 10.91 g of 3,3`,4,4`-biphenyltetracarboxylic dianhydride was added. The reaction temperature was set at 40 °C. After reacting for 4 h, a polyamic acid solution was obtained. The polyamic acid solution was electrospun into a fiber membrane by a needleless electrospinning device to obtain a nanofiber membrane with an average diameter of 200 - 300 nm and a diameter distribution size distribution coefficient <1.6. Subsequently, it was placed in a high-temperature oven under N2 atmosphere for heat treatment. The programmed temperature was set as follows: starting temperature of 80 °C for 0.5 h, then heating at 3 °C / min to 250 °C and staying for 0.5 h, continuing to heat to 380 °C and staying for 1 h to obtain a polyimide nanofiber membrane. The solubility parameter Ra value of the polyimide material obtained from this system and N,N-dimethylacetamide was calculated to be 6.4, and the material had good swelling resistance.

[0127] (2) Nanofiber dispersion. Sulfonation composite is not carried out here, only dispersion is done, and nanofibers are obtained after dispersion.

[0128] (3) Blending of nanofibers and sulfonated polymer for film formation. Sulfonated polyether ether ketone with a sulfonation degree of 70% was selected as the matrix casting solution with a solid content of 20 wt%. Untreated nanofibers were added for blending, and the addition amount was 15% of the matrix polymer. After the unsulfonated treated nanofibers were added to the sulfonated polymer matrix solution, a phase separation reaction occurred quickly, changing the uniformity of the solution, and partial precipitation occurred after standing in the solution.

[0129] (4) Solution forming process. Defects were found in the liquid film during the coating process, and some precipitates aggregated on the film surface. Eventually, the obtained film had many defects and electrochemical related tests could not be carried out normally.

[0130] The technical solution of the present invention preferably solves the problem of insufficient swelling resistance of sulfonated polymers when the sulfonation degree is increased. Nanofibers composite with sulfonated polyelectrolytes are selected to reinforce the matrix, which further increases the sulfonation degree in the system. The treated nanofibers have good compatibility with the matrix, and at the same time, the channel effect in the system is increased, improving the proton conductivity of the membrane.

Claims

1. A proton exchange membrane, wherein the membrane material of the proton exchange membrane is a sulfonated polymer, and the proton exchange membrane contains sulfonated polyimide nanofibers; the sulfonated polyimide nanofibers are obtained by adding a polyimide nanofiber membrane to a solvent after pulverization to obtain a nanofiber dispersion; a sulfonated polyelectrolyte is added to a solvent to obtain a sulfonated polyelectrolyte solution, and the nanofiber dispersion is mixed with the sulfonated polyelectrolyte solution; the polyimide nanofiber membrane is obtained by reacting a dianhydride with a diamine in an aprotic polar solvent to obtain a polyamic acid solution, then electrospinning the polyamic acid solution into a nanofiber membrane, and finally performing imidization treatment, wherein, The Hansen solubility difference Ra between the solubility parameter of the polymer formed by the dianhydride and diamine and the solubility parameter of the solvent is greater than 5.5, and Ra is calculated according to the following formula: ， In the formula, D represents the dispersion component, P represents the polar component, H represents the hydrogen bond component, solv represents the solvent, and poly represents the polymer; the solubility parameter of the solvent can be obtained by referring to the Hansen solubility parameter table; the solubility parameter of the polymer is calculated by the group contribution method and the Hoftyzer-Van Krevelen method for each parameter.

2. The proton exchange membrane according to claim 1, wherein: The sulfonated polyimide nanofibers are 5 to 50 wt% of the sulfonated polymer; and / or, The sulfonated polymer has a molecular weight greater than 70,000 and a sulfonation degree of 50% to 80%.

3. The proton exchange membrane according to claim 2, wherein: The sulfonated polyimide nanofibers are 10 to 30 wt% of the sulfonated polymer; and / or, The sulfonation degree of the sulfonated polymer is 60% to 70%; and / or, The sulfonated polymer is selected from at least one of sulfonated polyether ether ketone, sulfonated polybenzimidazole, sulfonated polysulfone, sulfonated polyether sulfone, and sulfonated polyimide.

4. The proton exchange membrane according to claim 1, wherein: The swelling degree of the polyimide nanofiber membrane in the aprotic polar solvent is less than 10%; and / or, The sulfonated polyelectrolyte is a polymer with a sulfonic acid group or a sulfonate group, and the sulfonation degree is greater than 50%; and / or, The molar ratio of the imide group in the polyimide to the sulfonic acid group or sulfonate group in the sulfonated polyelectrolyte is (3:1) to (1:3).

5. The proton exchange membrane according to claim 4, wherein: The swelling degree of the polyimide nanofiber membrane in the aprotic polar solvent is less than 5%; and / or, The sulfonated polyelectrolyte is selected from at least one of sodium polystyrene sulfonate and sulfonated polysulfone; and / or, The molar ratio of the imide group in the polyimide to the sulfonic acid group or sulfonate group in the sulfonated polyelectrolyte is (2:1) to (1:2).

6. The proton exchange membrane according to claim 1, wherein: The diameter of the nanofibers is less than 1000 nm; the size distribution coefficient of the diameter distribution is <2; and / or, The solvent is an aprotic polar solvent or water; and / or, The nanofiber dispersion is obtained by shear dispersion, wherein the shear rotation speed is 5000 to 20000 rpm and the shear time is 5 min to 120 min.

7. The proton exchange membrane according to claim 6, wherein: The diameter of the nanofibers is 200 nm to 500 nm and / or, The shear rotation speed is 8000 to 15000 rpm and the shear time is 20 min to 60 min.

8. The proton exchange membrane according to claim 1, wherein: The Hansen solubility difference Ra between the solubility parameter of the polymer formed by the dianhydride and diamine and the solubility parameter of the solvent is greater than 6.

9. The proton exchange membrane according to claim 1, wherein: The molar ratio of dianhydride to diamine is (0.970~0.998):1; and / or, The reaction temperature is 0~50 °C, and the reaction time is 1~12 h; and / or, The imidization treatment includes staying at 80~150 °C for 0.5~1 h; heating at a rate of 0.5~5 °C / min to 230~300 °C and staying for 0.5~2 h; heating to -30~+30 °C of the glass transition temperature of the polyimide system and staying for 0.5~1 h.

10. The proton exchange membrane according to claim 9, wherein: The molar ratio of dianhydride to diamine is (0.98~0.99):

1.

11. The proton exchange membrane according to any one of claims 1~10, wherein: The tensile strength of the proton exchange membrane at room temperature is greater than 100 MPa; under the conditions of 60 °C and 100% RH, the proton conductivity is greater than 100 mS / cm.

12. A method for preparing the proton exchange membrane according to any one of claims 1~11, comprising formulating a casting solution from raw materials including a sulfonated polymer and sulfonated polyimide nanofibers, coating the surface of a substrate to form a liquid film, and then performing heat treatment.

13. The preparation method according to claim 12, wherein: The thickness of the liquid film is 100~1000 μm; The temperature of the heat treatment is 180~240 °C; The time of the heat treatment is 0.5~4 h.

14. The preparation method according to claim 13, wherein: The temperature of the heat treatment is 200~220 °C.

15. The application of the proton exchange membrane according to any one of claims 1~11 or the proton exchange membrane obtained by the preparation method according to any one of claims 12~14 in a hydrogen fuel cell or an alcohol fuel cell.

Images