Polybenzimidazole proton exchange membrane modified by sulfonyl imide cross-linking agent as well as preparation method and application of polybenzimidazole proton exchange membrane

Abstract

The invention discloses a polybenzimidazole proton exchange membrane modified by a sulfimide cross-linking agent, and a preparation method and application thereof, and belongs to the technical field of proton exchange membranes. According to the invention, a cross-linking agent sulfimide participates in cross-linking, so that a cross-linked structure is formed between polybenzimidazole and sulfimide groups, and the dimensional stability and mechanical strength of the proton exchange membrane are improved; meanwhile, the proton conductivity of the proton exchange membrane is favorably improved by the strongly acidic sulfimide group; according to a screening mechanism, an ethanol solution of potassium hydroxide is used as a solvent to pre-treat the sulfimide grafted polybenzimidazole, the free volume between chains is expanded, permeation of electrolyte ions is avoided on the premise of ensuring free passing of protons, and the method can be applied to an all-vanadium redox flow battery. The sulfonyl imide grafted polybenzimidazole proton exchange membrane provided by the invention has an internal cross-linked structure, so that the sulfonyl imide grafted polybenzimidazole proton exchange membrane has good dimensional stability and mechanical strength; and the proton conductivity is improved by introducing the strongly acidic sulfimide group.

Description

Technical Field

[0001] The present invention belongs to the technical field of proton exchange membranes, and specifically relates to a polybenzimidazole proton exchange membrane modified by a sulfonyl imide crosslinking agent, a preparation method and application thereof, in particular to applications in liquid flow batteries and high-temperature proton exchange membrane fuel cells. Background Art

[0002] Proton exchange membrane, also known as proton membrane or hydrogen ion exchange membrane, is an ion-selective permeable membrane that provides channels for proton migration and transmission, separates gas reactants and blocks electrolytes in batteries (electrolyzers). Traditional commercial Nafion membranes have disadvantages such as high prices and poor ion selectivity. However, polybenzimidazole proton exchange membranes with low cost, stable chemical properties and high mechanical strength have made great progress in practical applications. However, there are still several key issues to be resolved, especially the poor proton conductivity. Sulfonation modification to graft proton-conductive strongly acidic sulfonic acid groups onto the polybenzimidazole main chain is the main solution to this problem. The higher the degree of sulfonation, the higher the proton conductivity, even higher than Nafion membrane, but its dimensional stability, mechanical strength and vanadium barrier effect are also significantly deteriorated.

[0003] Based on the above reasons, this application is filed. Summary of the invention

[0004] Based on the above reasons, in view of the problems or defects in the prior art, the purpose of the present invention is to provide a polybenzimidazole proton exchange membrane modified by a sulfonimide crosslinking agent, a preparation method and application thereof, to solve or at least partially solve the above technical defects in the prior art:

[0005] The acidity of sulfonyl imide group is higher than that of sulfonic acid group, and it is introduced into polybenzimidazole as a cross-linking agent to form a cross-linking structure, which can achieve the best balance between the proton conductivity and dimensional stability of polybenzimidazole proton exchange membrane. At the same time, potassium hydroxide ethanol solution is used as a solvent to pretreat sulfonyl imide grafted polybenzimidazole. Its application in all-vanadium redox flow batteries can not only prevent vanadium penetration, but also further improve its proton conductivity.

[0006] In order to achieve one of the above purposes of the present invention, the technical solution adopted by the present invention is as follows:

[0007] A method for modifying a polybenzimidazole proton exchange membrane using a sulfonimide crosslinking agent, the method specifically comprising the following steps:

[0008] A sulfonimide cross-linking agent is prepared by using sulfonamide compounds and sulfonyl halide compounds as main reactants;

[0009] The polybenzimidazole is dissolved in an organic solvent, and then an activator is added to activate the polybenzimidazole to obtain a polybenzimidazole membrane solution, and the prepared sulfonimide crosslinking agent is added to the membrane solution, and the mixture is stirred and reacted continuously to form a crosslinked polybenzimidazole;

[0010] The prepared cross-linked polybenzimidazole is dissolved in an ethanol solution of potassium hydroxide to obtain a uniform and stable film casting solution;

[0011] The casting solution is cast into a membrane, dried, immersed in deionized water, and washed to neutrality to obtain a polybenzimidazole proton exchange membrane modified by a sulfonyl imide crosslinking agent.

[0012] Furthermore, in the above technical solution, the specific preparation method of the sulfonimide cross-linking agent is as follows:

[0013] Under inert atmosphere conditions, a sulfonamide compound solution and a sulfonyl halide compound solution are prepared respectively; then, an inorganic base is added to the sulfonamide compound solution under stirring conditions, and after mixing, the sulfonyl halide compound solution is continuously added dropwise to the reaction system, and the obtained mixed reactant is reacted at 30° C. for 12 hours; after the reaction is completed, the obtained product is filtered, rotary evaporated, washed, and dried to obtain the sulfonyl imide cross-linking agent.

[0014] Furthermore, in the above technical solution, the sulfonamide compound is one or a mixture of chloromethanesulfonamide, aminosulfonyl chloride, and 4-bromomethylbenzenesulfonamide.

[0015] Furthermore, in the above technical solution, the sulfonyl halide compound is one or a mixture of 3-chloropropanesulfonyl chloride, 4-chloro-1-butanesulfonyl chloride, 2-(3-chlorophenyl)ethanesulfonyl chloride, 4-bromomethylbenzenesulfonyl chloride, and 4-chloromethylbenzenesulfonyl fluoride.

[0016] Furthermore, in the above technical solution, the molar ratio of the sulfonamide compound to the sulfonyl halide compound is 75-25:25-75.

[0017] Furthermore, in the above technical solution, the inorganic base is sodium hydroxide or potassium hydroxide.

[0018] Furthermore, in the above technical solution, the mass ratio of the sulfonamide compound to the inorganic base is 95:5 to 80:20.

[0019] Further, in the above technical solution, the polybenzimidazole comprises one or more of the following formula-repeating units; wherein: n is 1 or greater, about 10 or greater, or about 100 or greater;

[0020]

[0021] Furthermore, in the above technical solution, the organic solvent is one or a mixture of methanol, ethanol, isopropanol, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0022] Furthermore, in the above technical solution, the activator is one of lithium hydride, calcium hydride, sodium hydride, lithium aluminum hydride, etc.

[0023] Furthermore, in the above technical solution, the activation time is 3-5h.

[0024] Furthermore, in the above technical solution, the mass ratio of the activator to the polybenzimidazole is (1-5):100.

[0025] Furthermore, in the above technical solution, the molar ratio of the polybenzimidazole to the sulfonimide crosslinking agent is 1-25:75-99.

[0026] Furthermore, in the above technical solution, in a preferred embodiment of the present invention, the reaction temperature of the polybenzimidazole and the sulfonimide cross-linking agent is 120° C., and the reaction time is 12 hours.

[0027] Furthermore, in the above technical solution, the method for preparing the potassium hydroxide ethanol solution is to add solid potassium hydroxide to anhydrous ethanol in a stirring state, and stir until it is completely dissolved to obtain the potassium hydroxide ethanol solution.

[0028] Furthermore, in the above technical solution, the mass fraction of potassium hydroxide in the potassium hydroxide ethanol solution is 2.5% to 5%.

[0029] Furthermore, in the above technical solution, the solid content of the casting solution is 5wt% to 25wt%.

[0030] Furthermore, in the above technical solution, the drying temperature is 20°C to 60°C.

[0031] The second object of the present invention is to provide a polybenzimidazole proton exchange membrane modified with a sulfonyl imide crosslinking agent prepared by the above method.

[0032] Furthermore, in the above technical solution, the thickness of the polybenzimidazole proton exchange membrane modified by the sulfonyl imide cross-linking agent is 5 μm to 70 μm.

[0033] The third object of the present invention is to provide the use of the polybenzimidazole proton exchange membrane modified by the sulfonyl imide crosslinking agent or the polybenzimidazole proton exchange membrane modified by the sulfonyl imide crosslinking agent prepared by the above method in high-temperature proton exchange membrane fuel cells and liquid flow batteries.

[0034] Furthermore, in the above technical solution, the liquid flow battery is preferably an all-vanadium liquid flow battery.

[0035] The present invention also provides a high-temperature proton exchange membrane fuel cell or liquid flow battery, comprising a polybenzimidazole proton exchange membrane modified with the sulfonimide crosslinking agent described above or a polybenzimidazole proton exchange membrane modified with the sulfonimide crosslinking agent obtained by the method described above.

[0036] The mechanism involved in the present invention is as follows:

[0037] The present invention utilizes a cross-linking agent sulfonyl imide to participate in cross-linking, so that a cross-linking structure is formed between polybenzimidazole and the sulfonyl imide group, thereby improving the dimensional stability and mechanical strength of the proton exchange membrane; at the same time, the strongly acidic sulfonyl imide group helps to improve the proton conductivity of the proton exchange membrane; according to the screening mechanism, an ethanol solution of potassium hydroxide is used as a solvent to pretreat the sulfonyl imide grafted polybenzimidazole, expand the free volume between chains, ensure the free passage of protons, and avoid the penetration of electrolyte ions, and can be applied to all-vanadium liquid flow batteries.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The present invention uses potassium hydroxide ethanol solution as solvent, which can deprotonate the imidazole ring on the PBI chain, and by removing part of the hydrogen bonding between the PBI chains, loose accumulation is formed between the PBI chain segments, the free volume is expanded, and water molecules are promoted to enter between the chains, and water molecule chains are established in the PBI membrane, thereby significantly improving the proton conductivity. In addition, the solvent potassium hydroxide ethanol solution used is low in price, saving costs; ethanol evaporates quickly and can be completely evaporated at medium and low temperatures, saving energy consumption.

[0040] (2) The polybenzimidazole proton exchange membrane modified by the sulfonimide crosslinking agent provided by the present invention has an internal crosslinking structure, which enables it to have good dimensional stability and mechanical strength; the introduction of strongly acidic sulfonimide groups improves proton conductivity.

[0041] (3) The preparation method of the polybenzimidazole proton exchange membrane modified by the sulfonyl imide crosslinking agent of the present invention is simple, has a low dissolution temperature, a short process flow, and is easy to achieve scale-up production; the prepared proton exchange membrane has a good vanadium barrier effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1 This is a physical picture of the polybenzimidazole proton exchange membrane modified by the sulfonimide crosslinking agent prepared in Example 1 of the present invention;

[0044] Figure 2 is a stress-strain curve of the polybenzimidazole proton exchange membrane modified by the sulfonimide crosslinking agent prepared in Example 2 of the present invention;

[0045] Figure 3 (a), (b), and (c) are respectively graphs of the proton conductivity of the polybenzimidazole proton exchange membrane modified with the sulfonimide crosslinker prepared in Examples 1-3 of the present invention and applied to a high-temperature proton exchange membrane fuel cell.

[0046] Figure 4 This is the H NMR spectrum of the sulfonimide cross-linking agent prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0047] The present invention adopts a simple synthesis method, firstly prepares a sulfonyl imide crosslinking agent, and grafts it onto a polybenzimidazole side chain to form a crosslinked polybenzimidazole. An ethanol solution of potassium hydroxide is used as a solvent to prepare a crosslinked polybenzimidazole membrane liquid, and the crosslinked polybenzimidazole membrane liquid is cast into a membrane to prepare the sulfonyl imide grafted polybenzimidazole proton exchange membrane. The proton exchange membrane prepared by the present invention has high proton conductivity at both high and low temperatures, and has good size and chemical stability and high mechanical strength.

[0048] The present invention discloses a polybenzimidazole proton exchange membrane modified by a sulfonyl imide crosslinking agent, a preparation method and application thereof, wherein the preparation process comprises the following steps: (1) using a sulfonamide compound and a sulfonyl halide compound as reactants to prepare a sulfonyl imide crosslinking agent; (2) dissolving polybenzimidazole in a solvent, activating the polybenzimidazole membrane liquid, adding the prepared sulfonyl imide crosslinking agent to the membrane liquid, stirring and continuously reacting to form a crosslinked polybenzimidazole; (3) dissolving the prepared crosslinked polybenzimidazole in an ethanol solution of potassium hydroxide to obtain a uniform and stable casting liquid; (4) casting the casting liquid into a membrane, drying and soaking it in deionized water, washing to neutrality, and obtaining a sulfonyl imide grafted polybenzimidazole proton exchange membrane. The method of the present invention has a simple operation process, and the prepared sulfonyl imide grafted polybenzimidazole proton exchange membrane has good size and chemical stability, high proton conductivity, obvious vanadium blocking effect, and high mechanical strength.

[0049] The present invention is further described in detail below through implementation cases.

[0050] In order to better understand the present invention but not to limit the scope of the present invention, all the numbers used in this application to express the amount, percentage, and other numerical values ​​should be understood as modified by the word "about" in all cases. Therefore, unless otherwise specified, the numerical parameters listed in the specification are approximate values, which may be changed according to the different ideal properties attempted to be obtained. Each numerical parameter should at least be regarded as obtained based on the reported significant figures and by conventional rounding methods.

[0051] The equipment and raw materials used in the present invention can be purchased from the market or are commonly used in the art. The methods in the following embodiments are all conventional methods in the art unless otherwise specified.

[0052] The aromatic ether polybenzimidazole (OPBI) used in the following Examples 1 and 2 of the present invention is synthesized by the method of Example 4 in the patent with authorization announcement number CN 116063679 B. The specific method is as follows:

[0053] (1) Add 3.90 g of phosphorus pentoxide to 25 mL of methanesulfonic acid (CAS No.: 75-75-2), heat at 120° C. with magnetic stirring for 5 h, dissolve and cool to room temperature to obtain a phosphorus pentoxide / methanesulfonic acid solution;

[0054] Add 20 mL of the pre-prepared phosphorus pentoxide / methanesulfonic acid solution to a 100 mL round-bottom flask, heat and stir to 40° C. under nitrogen protection; accurately weigh 5 mmol each of 4,4'-dicarboxy diphenyl ether and 3,3'-diaminobenzidine (the corresponding masses of both monomers are calculated based on the purity) and add them to the phosphorus pentoxide / methanesulfonic acid solution; stir and mix thoroughly to obtain a reaction precursor;

[0055] (2) transferring the reaction precursor to a microwave synthesizer, heating it under a microwave of a certain power, setting relevant program parameters for temperature increase reaction, and the reaction is carried out in two stages: first, the temperature is raised to 120° C. for reaction for 30 min, and then the temperature is raised to 150° C. for reaction for 20 min, and the microwave power is 500 W;

[0056] (3) After the reaction is completed, when the temperature of the reaction liquid drops to about 80° C., the reaction liquid is slowly poured into a glass beaker containing deionized water, the precipitated polymer is washed with water until it is nearly neutral, and then a saturated sodium bicarbonate solution is added for neutralization, and the mixture is filtered under reduced pressure, first washed with water for multiple times, and then washed with ethanol for multiple times, and the obtained polymer is vacuum dried at 120° C. for 24 hours, and ground into powder, i.e., the aromatic ether type polybenzimidazole.

[0057] The meta-fully aromatic polybenzimidazole (mPBI) used in the following Example 3 of the present invention is synthesized by the method of Example 3 in the patent with the authorization announcement number CN116063679 B, and the specific method is as follows:

[0058] (1) Add 3.85 g of phosphorus pentoxide to 25 mL of methanesulfonic acid (CAS No.: 75-75-2), heat with magnetic stirring at 120° C. for 5 h, and cool to room temperature after dissolving to obtain a phosphorus pentoxide / methanesulfonic acid solution;

[0059] Add 20 mL of the pre-prepared phosphorus pentoxide / methanesulfonic acid solution to a 100 mL round-bottom flask, heat and stir to 40° C. under nitrogen protection; accurately weigh 5 mmol of isophthalic acid and 3,3'-diaminobenzidine (the corresponding masses of both monomers are calculated based on their purity) and add them to the phosphorus pentoxide / methanesulfonic acid solution; stir and mix thoroughly to obtain a reaction precursor;

[0060] (2) transferring the reaction precursor to a microwave synthesizer, heating it under a certain power of microwave, setting relevant program parameters for temperature rise reaction, and the reaction is carried out in two stages: first, the temperature is raised to 120° C. for reaction for 20 min, and then the temperature is raised to 160° C. for reaction for 40 min, and the microwave power is 300 W;

[0061] (3) After the reaction is completed, when the temperature of the reaction liquid drops to about 80° C., the reaction liquid is slowly poured into a glass beaker containing deionized water, the precipitated polymer is washed with water until it is nearly neutral, and then a saturated sodium bicarbonate solution is added for neutralization, and the mixture is filtered under reduced pressure, first washed with water for multiple times, and then washed with ethanol for multiple times, and the obtained polymer is vacuum dried at 120° C. for 24 hours, and ground into powder to obtain the meta-aromatic polybenzimidazole.

[0062] Example 1

[0063] The method for preparing a polybenzimidazole proton exchange membrane modified by a sulfonimide crosslinking agent of the present embodiment comprises the following steps:

[0064] 1) Under argon protection, 6g of chloromethanesulfonamide was dissolved in 100mL of anhydrous acetonitrile and placed in a 500mL double-necked glass bottle. 5g of potassium hydroxide was added under stirring and stirred for 30 minutes. A solution of 8.5g of 3-chloropropanesulfonyl chloride dissolved in 100mL of anhydrous acetonitrile was added through a constant pressure funnel and reacted at 30°C for 12h. After the reaction was completed, the system was filtered, and the filtrate was completely dried using a rotary evaporator, and then dichloromethane was added for washing to fully wash off the unreacted raw materials, and a sulfonimide cross-linking agent with a molecular weight of 256g / mol was obtained by filtration.

[0065] 2) Weigh 5g of aromatic ether polybenzimidazole and dissolve it in 150ml of N,N-dimethylacetamide. Add lithium hydride at 120°C and stir thoroughly for 4h, then continue to add 11g of the sulfonyl imide crosslinker prepared in step 1), and keep the temperature at 120°C for 12h. Pour the product into distilled water while hot to form a flocculent gel. Wash the gel thoroughly with hydrochloric acid and then use sodium carbonate to wash away the excess hydrochloric acid. Dry in a forced air oven at 120°C for 12h to obtain a crosslinked polybenzimidazole.

[0066] 3) 1.5 g of the dried product prepared in step 2) was dissolved in 20 mL of 2.5% potassium hydroxide ethanol solution, and the temperature was raised to 65° C. and stirred at constant temperature for 2 h to obtain a film-forming solution with a mass volume fraction of 7.5%.

[0067] 4) Casting the membrane-forming solution in step 2) into a membrane, drying to obtain a dry membrane with a thickness of 35 μm, soaking the dry membrane in deionized water, washing to neutrality, and obtaining a polybenzimidazole proton exchange membrane modified by a sulfonyl imide crosslinking agent.

[0068] Figure 1 This is a physical picture of the polybenzimidazole proton exchange membrane modified by the sulfonimide crosslinking agent prepared in Example 1 of the present invention; it can be seen from the figure that the cross-linked polybenzimidazole membrane prepared by the present invention has good film-forming properties.

[0069] Example 2

[0070] The method for preparing a polybenzimidazole proton exchange membrane modified by a sulfonimide crosslinking agent of the present embodiment comprises the following steps:

[0071] 1) Under argon protection, 12g of 4-bromomethylbenzenesulfonamide was dissolved in 100mL of anhydrous acetonitrile and placed in a 500mL double-necked glass bottle. 5g of potassium hydroxide was added under stirring and stirred for 30 minutes. A solution of 8g of 4-chloro-1-butanesulfonyl chloride dissolved in 100mL of anhydrous acetonitrile was added through a constant pressure funnel and reacted at 30°C for 12h. After the reaction was completed, the system was filtered, and the filtrate was completely dried using a rotary evaporator, and then dichloromethane was added for washing to fully wash off the unreacted raw materials, and a sulfonimide cross-linking agent with a molecular weight of 405g / mol was obtained by filtration.

[0072] 2) Weigh 4g of aromatic ether polybenzimidazole and dissolve it in 150ml of N,N-dimethylacetamide. Add lithium hydride at 120°C and stir thoroughly for 4h, then continue to add 7.8g of sulfonyl imide crosslinker prepared in step 1), and keep at 120°C for 12h. Pour the product into distilled water while hot to form a flocculent gel. Wash the gel thoroughly with hydrochloric acid and then use sodium carbonate to wash off the excess hydrochloric acid. Dry in a forced air oven at 120°C for 12h to obtain a crosslinked polybenzimidazole.

[0073] 3) 3 g of the dried product prepared in step 2) was dissolved in 20 mL of a 4% potassium hydroxide ethanol solution, and the temperature was raised to 65° C. and stirred at a constant temperature for 2 h to obtain a film-forming solution with a mass volume fraction of 15%.

[0074] 4) Casting the membrane-forming solution in step 2) into a membrane, drying to obtain a dry membrane with a thickness of 40 μm, soaking the dry membrane in deionized water, washing to neutrality, and obtaining a polybenzimidazole proton exchange membrane modified with a sulfonyl imide crosslinking agent.

[0075] Example 3

[0076] The method for preparing a polybenzimidazole proton exchange membrane modified by a sulfonimide crosslinking agent of the present embodiment comprises the following steps:

[0077] 1) Under argon protection, 9g of 4-bromomethylbenzenesulfonamide was dissolved in 100mL of anhydrous acetonitrile and placed in a 500mL double-necked glass bottle. 5g of potassium hydroxide was added under stirring and stirred for 30 minutes. A solution of 5.5g of 2-(3-chlorophenyl)ethanesulfonyl chloride dissolved in 100mL of anhydrous acetonitrile was added through a constant pressure funnel and reacted at 30°C for 12h. After the reaction was completed, the system was filtered, and the filtrate was completely dried using a rotary evaporator, and then dichloromethane was added for washing to fully wash off the unreacted raw materials, and a sulfonimide cross-linking agent with a molecular weight of 452g / mol was obtained by filtration.

[0078] 2) Weigh 8.6g of meta-wholly aromatic polybenzimidazole and dissolve it in 150ml of N,N-dimethylacetamide. Add lithium hydride at 120°C and stir thoroughly for 4h, then continue to add 12.5g of sulfonyl imide crosslinker prepared in step 1), and keep at 120°C for 12h. Pour the product into distilled water while hot to form a flocculent gel. Wash the gel thoroughly with hydrochloric acid and then use sodium carbonate to wash off the excess hydrochloric acid. Dry in a forced air oven at 120°C for 12h to obtain a crosslinked polybenzimidazole.

[0079] 3) 5 g of the dried product prepared in step 2) was dissolved in 20 mL of a 3.6% potassium hydroxide ethanol solution, and the temperature was raised to 65° C. and stirred at this temperature for 2 h to obtain a film-forming solution with a mass volume fraction of 25%.

[0080] 4) Casting the membrane-forming solution in step 2) into a membrane, drying to obtain a dry membrane with a thickness of 61 μm, soaking the dry membrane in deionized water, washing to neutrality, and obtaining a polybenzimidazole proton exchange membrane modified by a sulfonyl imide crosslinking agent.

[0081] Performance Test:

[0082] The polybenzimidazole proton exchange membrane modified by the sulfonimide crosslinking agent prepared in Examples 1-3 was subjected to mechanical property, proton conductivity and vanadium permeation tests, wherein:

[0083] (I) The test methods for mechanical properties are as follows:

[0084] a) Under constant temperature and humidity conditions of 25℃±2℃ and 50%±5%, quickly measure the thickness of the pretreated sample. The thickness and width of each sample should be measured at three points within the gauge length and the average value should be taken. The thickness measurement accuracy is ±0.2% and the width measurement accuracy is ±0.5%.

[0085] b) Place the sample in the test fixture of the tensile testing machine, make the longitudinal axis of the sample coincide with the center line of the upper and lower fixtures, and clamp it. The pressure value of the pneumatic fixture is selected within the range of 0.3MPa to 0.7MPa.

[0086] c) The tensile speed of the tensile testing machine is selected within the range of 50 mm / min to 200 mm / min.

[0087] d) After the sample breaks, read the corresponding load value. If the sample breaks outside the marked line, the test is invalid.

[0088] The required load and the corresponding film thickness and width are read according to the measured tensile curve, and the maximum tensile strength of the film is calculated according to formula (4).

[0089] The formula is: σ=p / (b×d)

[0090] Where:

[0091] σ——The maximum tensile strength of the membrane, in megapascals (MPa);

[0092] p——maximum load, in Newton (N);

[0093] b——specimen width, in millimeters (mm);

[0094] d——specimen thickness, in millimeters (mm).

[0095] Take 3 samples as a group and calculate the average value as the test result.

[0096] (II) The specific test method of proton conductivity is as follows:

[0097] The proton conductivity test method involved in the application examples 1-3 of the present invention refers to Section 7 "Conductivity and Membrane Surface Resistance" of "Part 5: Proton Exchange Membrane Test Method" in GB / T42080-2023. The detailed test method is as follows:

[0098] a) Wet the inner chamber of the H-type conductivity cell with 3.0 mol / L H2SO4 solution;

[0099] b) Connect the two half slots of the H-type conductivity cell and press them tightly with an iron clamp. Add 3.0 mol / L H2SO4 solution into the conductivity cell and expel the bubbles. The liquid level should be higher than the circular hole of the half slot.

[0100] c) Clamp the test wires of the reference electrode and working electrode of the electrochemical workstation to the electrodes at both ends of the conductivity cell, and ensure that the distance between the electrodes on both sides and the membrane is the same; measure the impedance of the conductivity cell. After the test is completed, read the resistance value in the high-frequency region that intersects the real axis, which is the blank impedance R1 of the conductivity cell:

[0101] d) Place the pretreated membrane sample between the two circular holes, repeat steps b) to c), and read the data, which is the impedance R2 of the conductivity cell with the membrane sample installed:

[0102] e) Repeat the measurement 8 times, record all impedance data and remove the highest and lowest values ​​to calculate the average value, recorded as

[0103] f) Use a micrometer to measure the thickness of the film after the resistance is measured, and record it as d.

[0104] Calculated by the formula:

[0105] a) The membrane resistance is calculated according to the formula as follows:

[0106]

[0107] R m ——Membrane resistance, in ohms (Ω);

[0108] ——Impedance value of the conductivity cell with the membrane sample installed, in ohms (Ω):

[0109] The resistivity of a conductivity cell without a membrane sample installed, in ohms (Ω).

[0110] b) The membrane surface resistance is calculated according to the formula as follows

[0111] R A =R m A

[0112] R A —Film surface resistance, in ohm square centimeter (Ω·cm 2 ):

[0113] R m ——membrane resistance in ohms (92);

[0114] A – effective area of ​​the membrane, in square centimeters (cm2).

[0115] c) The conductivity of the ion-conducting membrane is calculated according to the formula:

[0116]

[0117] σ——membrane conductivity, in Siemens per centimeter (S / cm);

[0118] R A - Film surface resistance, in ohm square centimeters (Ω·cm2);

[0119] d is the average thickness of the film, in centimeters (cm).

[0120] Take 3 samples as a group and take the average value as the test result.

[0121] The proton conductivity test method involved in the application examples 1-3 of the present invention refers to Section 5 "Proton Conductivity Test" of "Part 3: Proton Exchange Membrane Test Method" in GB / T20042.3-2009. The detailed test method is as follows:

[0122] Cut a film of a certain size as a sample, measure the thickness of the sample with a thickness gauge at a temperature of 25℃±2℃ and a relative humidity of 50±5%, and take the average value of three points as the value for calculating the thickness d. Fix the sample in a conductivity measurement fixture, and tighten the bolts with a torque wrench at a torque of 3N·m. Then place the conductivity measurement fixture in a constant humidity environment with different temperatures, and test it after keeping it constant for 30 minutes under each temperature and humidity condition. The impedance spectrum of the sample is measured with an electrochemical impedance tester under the conditions of a frequency range of (1~2×106)Hz and a disturbance voltage of 10mV. In the measured impedance spectrum, read the impedance value (R) of the sample from the intersection of the high-frequency part of the spectrum line and the real axis.

[0123] The proton conductivity of the sample was calculated according to the following formula:

[0124] σ——proton conductivity of the sample, in Siemens per centimeter (S / cm);

[0125] a——the distance between the two electrodes, in centimeters (cm);

[0126] R——Measurement impedance of the sample, in ohms;

[0127] b——The effective length of the membrane in the direction perpendicular to the electrode, in centimeters (cm);

[0128] d is the thickness of the sample in centimeters (cm).

[0129] Take 3 samples as a group and calculate the average value as the test result.

[0130] (III) The specific test method for vanadium ion permeability is as follows:

[0131] a) Place the membrane soaked in 3 mol / L H2SO4 for 24 hours in the middle of the H-type conductivity cell and press it tightly with an iron clamp.

[0132] b) Pour an aqueous solution of 1.5 mol / LMgSO4 and 3.0 mol / LH2SO4 into one side of the H-type conductivity cell as a blank reference solution; measure an aqueous solution of 1.5 mol / LVOSO4 and 3.0 mol / LH2SO4 of the same volume as the blank reference solution as an electrolyte, and pour it into the other chamber so that the solution heights on both sides remain consistent and completely immerse the effective area of ​​the membrane sample to be tested, and the bubbles on both sides are discharged.

[0133] c) Place the stirring bars into the chambers on both sides of the conduction cell and turn on the power of the magnetic stirrer.

[0134] d) At specific time intervals, 3 mL of the blank solution was taken out with a pipette and VO was detected using a UV-visible spectrometer. 2+ ion.

[0135] The permeability (ρ) was calculated according to the following formula:

[0136]

[0137] ρ——Permeability, in square centimeters per minute (cm 2 / min)

[0138] L——film thickness, in centimeters (cm)

[0139] V R ——The volume of blank reference solution taken out, in milliliters (ml)

[0140] A——Effective membrane area, in square centimeters (cm 2 )

[0141] C L ——is VO in the electrolyte 2+ Initial concentration, in moles per liter (mol / L)

[0142] C R ——VO in blank reference solution 2+ Initial concentration, in moles per liter (mol / L)

[0143] The last item - blank reference liquid side VO 2+ The slope of the quasi-linear trend of concentration over time.

[0144] Test result analysis:

[0145] Table 1

[0146] <![CDATA[Sheet Resistance (Ωcm 2 )]]> Conductivity (mS / cm) Permeability (cm / min) Example 1 0.042 54 <![CDATA[2.71×10 -9 ]]> Example 2 0.085 35 <![CDATA[3.44×10 -9 ]]> Example 3 0.064 47 <![CDATA[3.29×10 -9 ]]>

[0147] The proton conductivity and surface resistance of the polybenzimidazole proton exchange membrane modified by sulfonyl imide crosslinking agent prepared in Examples 1-3 of the present invention applied in the field of all-vanadium redox flow batteries are shown in Table 1. As can be seen from Table 1, the surface resistance of the crosslinked polybenzimidazole proton exchange membrane prepared in Example 1 of the present invention is 0.042Ωcm 2 The conductivity is 54 mS / cm, which meets the use requirements. The surface resistance of the cross-linked polybenzimidazole proton exchange membrane prepared in Example 2 of the present invention is 0.085 Ωcm 2 The conductivity is 35 mS / cm, which meets the use requirements. The surface resistance of the cross-linked polybenzimidazole proton exchange membrane prepared in Example 3 of the present invention is 0.023 Ωcm 2 The conductivity is 47mS / cm, which meets the use requirements.

[0148] Figure 2 is a stress-strain curve of the polybenzimidazole proton exchange membrane modified by the sulfonimide crosslinking agent prepared in Example 2 of the present invention; Figure 2 It can be seen that the mechanical strength of the cross-linked polybenzimidazole proton exchange membrane prepared in Example 2 of the present invention can reach 61MPa, and the elongation at break is 102%, which meets the use requirements. The mechanical strength and elongation at break of the polybenzimidazole proton exchange membrane modified by the sulfonimide crosslinker prepared in Examples 1 and 3 of the present invention are similar to those of Example 2, wherein the mechanical strength of the proton exchange membrane in Example 1 can reach 55MPa, and the elongation at break is 122%, which meets the use requirements; the mechanical strength of the proton exchange membrane in Example 3 can reach 60MPa, and the elongation at break is 116%, which meets the use requirements.

[0149] Figure 3 The proton conductivity diagram of the polybenzimidazole proton exchange membrane modified by the sulfonimide crosslinking agent prepared in Examples 1-3 of the present invention applied to a high-temperature proton exchange membrane fuel cell; Figure 3 It can be seen that: Example 1, at a temperature of 160°C, its proton conductivity is 148mS / cm, and the proton conductivity decays slightly above 160°C, meeting the use requirements. Example 2, at a temperature of 160°C, its proton conductivity is 142mS / cm, meeting the use requirements. Example 3, at a temperature of 160°C, its proton conductivity is 131mS / cm, and the proton conductivity decays slightly above 160°C, meeting the use requirements.

[0150] Figure 4 is the H NMR spectrum of the sulfonimide crosslinking agent prepared in Example 2 of the present invention; Figure 4It can be seen that the characteristic peak at 8.61 ppm is generated by NH in the sulfonyl imide crosslinker. According to the analysis of the H-NMR spectrum, we have successfully prepared the sulfonyl imide crosslinker in Example 2.

[0151] In the absence of conflict, the above embodiments and features of the embodiments of the present invention may be combined with each other.

[0152] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection of the present invention.

Claims

1. A method for modifying a polybenzimidazole proton exchange membrane using a sulfonimide crosslinking agent, characterized in that: The method specifically comprises the following steps: A sulfonimide cross-linking agent is prepared by using sulfonamide compounds and sulfonyl halide compounds as main reactants; The polybenzimidazole is dissolved in an organic solvent, and then an activator is added to activate the polybenzimidazole to obtain a polybenzimidazole membrane solution, and the prepared sulfonimide crosslinking agent is added to the membrane solution, and the mixture is stirred and reacted continuously to form a crosslinked polybenzimidazole; The prepared cross-linked polybenzimidazole is dissolved in an ethanol solution of potassium hydroxide to obtain a uniform and stable film casting solution; The casting solution is cast into a membrane, dried and then immersed in deionized water, and washed to neutrality to obtain a sulfonimide-grafted polybenzimidazole proton exchange membrane.

2. The method according to claim 1, characterized in that: The specific preparation method of the sulfonimide cross-linking agent is as follows: Under inert atmosphere conditions, a sulfonamide compound solution and a sulfonyl halide compound solution are prepared respectively; then, an inorganic base is added to the sulfonamide compound solution under stirring conditions, and after mixing, the sulfonyl halide compound solution is continuously added dropwise to the reaction system, and the obtained mixed reactant is reacted at 30° C. for 12 hours; after the reaction is completed, the obtained product is filtered, rotary evaporated, washed, and dried to obtain the sulfonyl imide cross-linking agent.

3. The method according to claim 2, characterized in that: The sulfonamide compound is one of chloromethanesulfonamide, aminosulfonyl chloride, and 4-bromomethylbenzenesulfonamide, or a mixture of several thereof; the sulfonyl halide compound is one of 3-chloropropanesulfonyl chloride, 4-chloro-1-butanesulfonyl chloride, 2-(3-chlorophenyl)ethanesulfonyl chloride, 4-bromomethylbenzenesulfonyl chloride, and 4-chloromethylbenzenesulfonyl fluoride, or a mixture of several thereof.

4. The method according to claim 2, characterized in that: The molar ratio of the sulfonamide compound to the sulfonyl halide compound is 75-25:25-75.

5. The method according to claim 1, characterized in that: The polybenzimidazole comprises one or more of the following formula-repeating units; wherein: n is 1 or greater, about 10 or greater, or about 100 or greater; 6. The method according to claim 1, characterized in that: The molar ratio of the polybenzimidazole to the sulfonimide crosslinking agent is 1-25:75-99.

7. The sulfonimide-grafted polybenzimidazole proton exchange membrane prepared by the method according to any one of claims 1 to 5.

8. The sulfonimide-grafted polybenzimidazole proton exchange membrane according to claim 7, characterized in that: The thickness of the sulfonimide grafted polybenzimidazole proton exchange membrane is 5 μm to 70 μm.

9. Use of the sulfonimide grafted polybenzimidazole proton exchange membrane prepared by the method according to any one of claims 1 to 5 or the sulfonimide grafted polybenzimidazole proton exchange membrane according to claim 6 or 7 in high-temperature proton exchange membrane fuel cells and liquid flow batteries.

10. A high temperature proton exchange membrane fuel cell or liquid flow battery, characterized in that: The invention comprises the sulfonimide grafted polybenzimidazole proton exchange membrane prepared by the method according to any one of claims 1 to 5 or the sulfonimide grafted polybenzimidazole proton exchange membrane according to claim 6 or 7.

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