Polybenzimidazole / polyionic liquid composite ionic membrane and preparation method thereof

Abstract

The invention discloses a polybenzimidazole / polyionic liquid composite ionic membrane and a preparation method thereof, and belongs to the technical field of polymer electrolyte membranes. Formaldehyde, glyoxal and at least one diamine which does not contain positive charge or negative charge groups are used as raw materials, a simple Debus-Radziszewski imidazole synthesis reaction is carried out to generate polyion liquid, the polyion liquid is precipitated in an aqueous solution rich in large-volume anions to obtain polyion liquid, the polyion liquid and polybenzimidazole are jointly dissolved in an organic solvent in a blending mode, and the polybenzimidazole / formaldehyde composite material is obtained. And then pouring the mixed membrane liquid to prepare the polybenzimidazole / polyionic liquid composite ionic membrane. The composite ionic membrane prepared by the invention can keep high proton conductivity at both high and low temperatures of a fuel cell, has higher phosphoric acid retention rate, has high proton conductivity and excellent vanadium resistance in a vanadium redox flow battery, and has intrinsic physical characteristics such as excellent heat resistance, mechanical strength, antioxidant stability and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer electrolyte membranes, and particularly relates to a polybenzimidazole / polyionic liquid composite ion membrane and a preparation method thereof. Background Art

[0002] Polybenzimidazole ion membranes are considered to be one of the most promising proton exchange membrane materials because they can be used at high temperatures above 100 °C. At the same time, due to their excellent vanadium resistance, they show great development potential in the field of vanadium redox flow batteries. For hydrogen fuel cells, durability is one of the main technical challenges that have dominated this field in recent years. A large number of studies have shown that the most critical reason for the voltage drop of hydrogen fuel cells is the loss of phosphoric acid in the ion membrane. Therefore, the acid retention analysis of phosphoric acid-doped ion membranes is necessary to evaluate their feasibility in practical applications. Extensive research has shown that the main way for phosphoric acid is to be discharged from the membrane. First, phosphoric acid will be distilled out of the membrane through water and leave with the gas flow because of the interaction between phosphoric acid and water. On the other hand, phosphoric acid migrates from the PEM to other layers (including the catalyst layer, microporous layer, and gas diffusion layer) under external pressure, ultimately corroding the bipolar plate.

[0003] Existing research has recognized the key role of ion pair coordination in membrane acid retention. Among the key representatives, ionic liquids, as fillers, are attractive enough to improve the acid retention of ion membranes. At the same time, numerous literatures have shown that the addition of ionic liquids can significantly improve the electrochemical performance of polybenzimidazole ion membranes. After simple doping, the ion membrane can show higher proton conductivity.

[0004] However, after long-term operation of fuel cells or flow batteries, ionic liquids often leach out from the polymer matrix, resulting in poor electrochemical performance of the blended membrane.

[0005] Based on this, the present patent application is proposed. Summary of the Invention

[0006] For the above reasons, aiming at the problems of low proton conductivity and poor acid retention performance of polybenzimidazole ion membranes in the prior art, the purpose of the present invention is to provide a polybenzimidazole / polyionic liquid composite ion membrane and a preparation method thereof, which are expected to solve or at least optimize the above technical defects existing in the prior art.

[0007] In order to achieve one of the above purposes of the present invention, the technical solution adopted by the present invention is as follows:

[0008] A polybenzimidazole / polyionic liquid composite ion membrane is obtained by fully dissolving a polyionic liquid and polybenzimidazole in an organic solvent, dispersing to form a homogeneous system, and then casting into a film.

[0009] Further, in the above technical solution, the thickness of the polybenzimidazole / polyionic liquid composite ion membrane is between 5 and 100 microns.

[0010] Further, in the above technical solution, the polybenzimidazole in the composite ion membrane comprises one or a mixture of several repeating units in Formula I below, where n is 1 or greater, about 10 or greater, or about 100 or greater;

[0011]

[0012] Formula I.

[0013] Further, in the above technical solution, the organic solvent comprises one or a mixture of several of N,N-dimethylformamide, N,N-dimethylacetamide, 1-methyl-2-pyrrolidone, dimethyl sulfoxide, trifluoroacetic acid, methanesulfonic acid, formic acid. The amount of the organic solvent may not be specifically limited as long as it can achieve uniform and complete dissolution of the polyionic liquid and polybenzimidazole.

[0014] Further, in the above technical solution, the mass ratio of the polyionic liquid to the polybenzimidazole is 5-70:30-95.

[0015] Further, in the above technical solution, the polyionic liquid is obtained by a Debus-Radziszewski imidazole synthesis reaction using formaldehyde, glyoxal, and a diamine without positive or negative charge groups as raw materials, and precipitating the synthesized product in an aqueous solution rich in bulky anions followed by drying.

[0016] Even further, in the above technical solution, the polyionic liquid is prepared by the following method:

[0017] Dissolve equimolar amounts of formaldehyde, glyoxal, at least one diamine without positive or negative charge groups, and acetic acid in deionized water, mix well, heat the resulting mixed reaction solution to 100 °C and react at a constant temperature for 3 hours; after the reaction is completed, transfer the resulting product to an aqueous solution rich in bulky anions, and the polyionic liquid in the product pairs with the bulky anions and precipitates out. Skim off the upper clear liquid, and the lower dark brown product is washed and dried to obtain the polyionic liquid.

[0018] Specifically, the synthesis chemical reaction equation of the above polyionic liquid is shown in Formula II below:

[0019]

[0020] Formula II.

[0021] Preferably, in the above technical solution, the diamine without positive or negative charge groups includes one or a mixture of several of: butanediamine, pentanediamine, hexanediamine, heptanediamine, octanediamine, nonanediamine, decanediamine, p-phenylenediamine, 1,5-diaminonaphthalene, 4,4'-diaminodiphenylsulfone, 2,7-diaminofluorene, 4,4'-diaminobenzophenone, 4,4'-biphenyldiamine.

[0022] Preferably, in the above technical solution, the bulky anion includes one or a mixture of several of: bis(trifluoromethylsulfonyl)imide anion, bis(trifluoromethylphenylsulfonyl)imide anion, trifluoromethanesulfonate anion, trifluoromethylbenzenesulfonate anion, methanesulfonate anion, hexafluorophosphate anion, perchlorate anion, phosphate anion, hydrogen phosphate anion, dihydrogen phosphate anion, phosphotungstate anion, phosphomolybdate anion, silicotungstate anion, silicomolybdate anion.

[0023] Preferably, in the above technical solution, the molar ratio of the diamine without positive or negative charge groups to formaldehyde is 1:1.

[0024] Preferably, in the above technical solution, the molar ratio of acetic acid to formaldehyde is 1:1.

[0025] The second object of the present invention is to provide the preparation method of the above-mentioned polybenzimidazole / polyionic liquid composite ion membrane, and the method specifically includes the following steps:

[0026] Dissolve the polyionic liquid and polybenzimidazole in an organic solvent in proportion to make a membrane solution; then pour the membrane solution on a substrate to form a membrane, and obtain the polybenzimidazole / polyionic liquid composite ion membrane after the solvent volatilizes.

[0027] Further, in the above technical solution, the total solid content in the membrane solution accounts for 3% - 30% of the mass volume fraction of the membrane solution.

[0028] The mechanism involved in the present invention is as follows:

[0029] The present invention introduces polyionic liquid. Due to the polymerization form of the ionic liquid, it is not easy to lose in the ion membrane, and can improve the long-range cycle stability of the ion membrane.

[0030] The imidazole group of the polyionic liquid is a kind of Lewis base, and its basicity is significantly higher than that of benzimidazole, which directly improves the interaction with acid, and improves the acid absorption rate, acid retention rate, and proton conductivity.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] ① The polybenzimidazole / polyionic liquid composite ion membrane provided by the present invention has a higher phosphoric acid retention rate in the hydrogen fuel cell, and the long-range cycle performance decays more slowly.

[0033] ② The proton conductivity of the polybenzimidazole / polyionic liquid composite ion membrane provided by the present invention in a vanadium redox flow battery is higher than that of most ion membranes based on polybenzimidazole. At the same time, due to its excellent vanadium-blocking performance, the Coulomb efficiency, voltage efficiency, and energy efficiency of the flow battery all reach a relatively high level.

[0034] ③ The polyionic liquid provided by the present invention is simple to synthesize, and the preparation method of the polybenzimidazole / polyionic liquid composite ion membrane is simple. The polyionic liquid is formed by one-step polymerization, and after mixing with polybenzimidazole, it is dissolved and dispersed to form a homogeneous system and then cast into a film. The prepared ion membrane has excellent intrinsic physical properties such as heat resistance, mechanical strength, and antioxidant stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is a physical diagram of the polybenzimidazole / polyionic liquid composite ion membrane prepared in Examples 1-3 of the present invention;

[0037] Figure 2 It is a stress-strain curve diagram of the polybenzimidazole / polyionic liquid composite ion membrane prepared in Examples 1-3 of the present invention;

[0038] Figure 3 It is a bar chart of the acid absorption rate of the polybenzimidazole / polyionic liquid composite ion membrane prepared in Examples 1-3 of the present invention and the OPBI control group ion membrane;

[0039] Figure 4 It is a diagram of the acid retention rate of the polybenzimidazole / polyionic liquid composite ion membrane prepared in Examples 1-3 of the present invention and the OPBI control group ion membrane at different times;

[0040] Figure 5 It is a diagram of the conductivity change of the polybenzimidazole / polyionic liquid composite ion membrane prepared in Examples 1-3 of the present invention at different temperatures when applied to a hydrogen fuel cell;

[0041] Figure 6 It is a Nyquist diagram of the polybenzimidazole / polyionic liquid composite ion membrane prepared in Examples 1-3 of the present invention when applied to a vanadium redox flow battery.

[0042] Figure 71H NMR spectra of the poly(ionic liquid) prepared in Examples 1-3 of the present invention. Detailed implementation mode

[0043] To solve the problems existing in the prior art, poly(ionic liquid) has been developed. The poly(ionic liquid) provided by the present invention is a linear polymer, and the repeating unit is usually a bulky cation. After the cations are arranged repeatedly, a linear arrangement of proton acceptors and proton donors is formed, providing a fast pathway for proton conduction. In addition, the polybenzimidazole / poly(ionic liquid) composite membrane provided by the present invention has excellent electrochemical properties and can be used as a separator in the hydrogen fuel cell industry. In addition, the above-mentioned separator can also be used to improve the electrochemical performance of the flow battery.

[0044] The present invention uses formaldehyde, glyoxal and at least one diamine without positive or negative charge groups as raw materials, generates poly(ionic liquid) through a simple Debus–Radziszewski imidazole synthesis reaction and precipitates it in an aqueous solution rich in bulky anions, and co-dissolves it with polybenzimidazole in an organic solvent by blending to form a mixed membrane solution, and then a polybenzimidazole / poly(ionic liquid) composite ion membrane is prepared by casting.

[0045] The polybenzimidazole / poly(ionic liquid) composite ion membrane prepared by the present invention has a wide operating temperature range and can be used in application fields such as hydrogen fuel cells and vanadium flow batteries. At the same time, the preparation method of the present invention has a simple process, and the prepared composite ion membrane can maintain high proton conductivity at high and low temperatures of the fuel cell, and at the same time has a higher phosphoric acid retention rate. At the same time, it has high proton conductivity and excellent vanadium resistance in the vanadium flow battery, and has excellent mechanical strength, antioxidant stability and other intrinsic physical properties.

[0046] The present invention discloses a preparation method of a polybenzimidazole / poly(ionic liquid) composite ion membrane. The preparation process includes the following steps: ① Debus–Radziszewski imidazole synthesis reaction and obtain poly(ionic liquid) through ion exchange; ② Mix and dissolve the synthesized poly(ionic liquid) and polybenzimidazole in an organic solvent according to a certain mass ratio to form a membrane solution; ③ Pour the membrane solution on a smooth substrate to cast a membrane, and a polybenzimidazole / poly(ionic liquid) composite ion membrane is obtained after the solvent volatilizes. The method of the present invention has a simple operation process, and the prepared ion membrane has very excellent proton conductivity and intrinsic physical properties.

[0047] All drugs, raw materials, equipment, etc. used in the present invention can be directly purchased on the market or are commonly used in the energy industry. The numerical values in the examples of the present invention are obtained by the conventional rounding method. The addition amounts of the solid samples in the examples of the present invention are all considered with reference to the purity provided by the original manufacturer.

[0048] In the following embodiments of the present invention, the polybenzimidazole involved is specifically an aromatic ether type polybenzimidazole (OPBI), and the aromatic ether type polybenzimidazole is synthesized by the method of Example 4 in the patent with the authorized announcement number CN 116063679 B. The specific method is as follows:

[0049] (1) Add 3.90 g of phosphorus pentoxide to 25 mL of methanesulfonic acid (CAS No.: 75-75-2), magnetically stir and heat at 120 °C for 5 h. After it becomes clear, cool it to room temperature to obtain a phosphorus pentoxide / methanesulfonic acid solution;

[0050] Add 20 mL of the pre-prepared phosphorus pentoxide / methanesulfonic acid solution to a 100 mL round-bottom flask. Under nitrogen protection, heat and stir to raise the temperature to 40 °C; accurately weigh 5 mmol each of 4,4'-dicarboxydiphenyl ether and 3,3'-diaminobenzidine (the corresponding masses of both monomers are calculated after discounting the purity) and add them to the phosphorus pentoxide / methanesulfonic acid solution; after stirring and mixing completely, obtain a reaction precursor;

[0051] (2) Transfer the reaction precursor to a microwave synthesizer, heat it under microwave with a certain power, set the relevant program parameters to raise the temperature for reaction. The reaction is carried out in two stages: first, raise the temperature to 120 °C and react for 30 min, then raise the temperature to 150 °C and react for 20 min, and the microwave power is 500 W;

[0052] (3) After the reaction is completed, when the temperature of the reaction solution drops to about 80 °C, slowly pour the reaction solution into a glass beaker containing deionized water. Wash the precipitated polymer until it is close to neutral, then add saturated sodium bicarbonate solution for neutralization, filter under reduced pressure, wash it with water many times first, and then wash it with ethanol many times. Vacuum dry the obtained polymer at 120 °C for 24 h and grind it into powder, which is the aromatic ether type polybenzimidazole.

[0053] The present invention will be further described in detail below through implementation cases.

[0054] Example 1

[0055] A method for preparing a polybenzimidazole / polyionic liquid composite ion membrane in this example includes the following steps:

[0056] ① Mix 1,2-bis(2-aminoethoxy)ethane (4.89 g, 33 mmol), analytical grade acetic acid (1.98 g), 40% (mass / volume) glyoxal solution (4.79 mL), 40% (mass / volume) formaldehyde solution (2.48 mL) and deionized water (10 mL) in a 100 mL round-bottom flask and reflux at 100 °C for 3 hours. Subsequently, drop the reaction product into an aqueous solution of lithium bis(trifluoromethanesulfonyl)imide with a total mass of 9.5 g. At this time, the bis(trifluoromethanesulfonyl)imide anion can completely replace the acetate ion, then stir at room temperature for about 10 min, filter the obtained product, wash it thoroughly with deionized water three times, and then place it in a vacuum dryer at 80 °C for 12 h.

[0057] ② Take 0.4 g of the above poly(ionic liquid), mix it with 2 g of polybenzimidazole (OPBI), dissolve it in 20 ml of N,N-dimethylformamide, and heat it to 100 °C and stir at a constant temperature for 12 h to obtain a viscous film solution.

[0058] ③ Pour the above film solution onto a smooth substrate to prepare a polybenzimidazole / poly(ionic liquid) composite ionic membrane with a thickness of 35 microns.

[0059] Example 2

[0060] A preparation method of a polybenzimidazole / poly(ionic liquid) composite ionic membrane in this example includes the following steps:

[0061] ① Mix hexanediamine (3.80 g, 3.3 mmol), analytical grade acetic acid (1.98 g), 40% (mass / volume) glyoxal solution (4.79 mL), 40% (mass / volume) formaldehyde solution (2.48 mL) and deionized water (10 mL) in a 100 mL round-bottom flask and reflux at 100 °C for 3 hours. Subsequently, drop the reaction product into an aqueous solution of lithium bis(trifluoromethanesulfonyl)imide with a total mass of 9.5 g. At this time, the bis(trifluoromethanesulfonyl)imide anion can completely replace the acetate ion, then stir at room temperature for about 10 min, filter the obtained product, wash it thoroughly with deionized water three times, and then place it in a vacuum dryer at 80 °C for 12 h.

[0062] ② Take 0.4 g of the above poly(ionic liquid), mix it with 2 g of polybenzimidazole (OPBI), dissolve it in 20 ml of N,N-dimethylformamide, and heat it to 100 °C and stir at a constant temperature for 12 h to obtain a viscous film solution.

[0063] ③ Pour the above film solution onto a smooth substrate to prepare a polybenzimidazole / poly(ionic liquid) composite ionic membrane with a thickness of 32 microns.

[0064] Example 3

[0065] A preparation method of a polybenzimidazole / polyionic liquid composite ion membrane in this embodiment includes the following steps:

[0066] ① Mix 1,2-bis(2-aminoethoxy)ethane (4.89 g, 3.3 mmol), analytical pure acetic acid (1.98 g), a 40% (mass / volume) glyoxal solution (4.79 mL), a 40% (mass / volume) formaldehyde solution (2.48 mL), and deionized water (10 mL) in a 100 mL round-bottom flask and reflux at 100 °C for 3 hours. Subsequently, drop the reaction product into an aqueous solution of 9.5 g of lithium bis(trifluoromethylsulfonyl)imide. At this time, the bis(trifluoromethylsulfonyl)imide anion can completely replace the acetate ion, and then stir at room temperature for about 10 min. Filter the obtained product, wash it thoroughly with deionized water three times, and then place it in a vacuum dryer at 80 °C for 12 h.

[0067] ② Take 0.8 g of the above polyionic liquid and mix it with 2 g of polybenzimidazole (OPBI) and dissolve them in 20 ml of N,N-dimethylformamide. Heat it to 100 °C and stir at a constant temperature for 12 h to obtain a viscous membrane solution.

[0068] ③ Pour the above membrane solution onto a smooth substrate to prepare a polybenzimidazole / polyionic liquid composite ion membrane with a thickness of 40 microns.

[0069] Performance test:

[0070] (1) The test method for mechanical properties is as follows:

[0071] ① Under the constant temperature and humidity conditions of 25 °C ± 2 °C and relative humidity of 50% ± 5%, quickly measure the thickness of the 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%;

[0072] ② Place the sample in the test fixture of the tensile testing machine so that the longitudinal axis of the sample coincides with the center line connecting the upper and lower fixtures and clamp it. The pressure value of the pneumatic fixture is set at 5.3 MPa;

[0073] ③ The tensile speed of the tensile testing machine is set at 100 mm / min -1 ;

[0074] ④ After the sample breaks, read the corresponding load value. If the sample breaks at a position outside the gauge line, this test is invalid.

[0075] Read the required load, the corresponding film thickness and width according to the measured tensile curve, and calculate the maximum tensile strength of the film according to the formula.

[0076]

[0077] In the formula:

[0078] P —— The maximum tensile strength of the film, unit: megapascal (MPa);

[0079] F —— The maximum load, unit: Newton (N);

[0080] b —— The width of the specimen, unit: millimeter (mm);

[0081] d —— The thickness of the specimen, unit: millimeter (mm).

[0082] Take 3 samples as a group, calculate the average value as the test result.

[0083] (2) The test method for antioxidant stability is as follows:

[0084] The test method for antioxidant stability involved in the present invention is carried out with reference to the "Fenton reagent oxidation method" in Subheading 5.11 "Antioxidant performance" of NB / T 42028 - 2023. The detailed test method is as follows:

[0085] ① Dilute the 30% hydrogen peroxide solution within one month after opening to prepare a 3% hydrogen peroxide solution. Measure 50 ml of the above - prepared 3% hydrogen peroxide solution, and add 0.1 ml of 0.1 M ferrous sulfate solution thereto to obtain Fenton reagent, and ensure that the Fenton reagent is prepared and used immediately;

[0086] ② Cut the pre - treated film fragment to 25 cm 2 , place it in a vacuum drying oven at 110 °C for 2 h, dry it until the mass difference between two consecutive weighings is less than 0.2 mg, and weigh its mass as m 0 ;

[0087] ③ After cutting the dried film fragment into pieces and putting it into a beaker, add the prepared Fenton reagent to ensure that the film is completely immersed, and then keep the beaker at a constant temperature of 60 °C for 3 h;

[0088] ④ Take out the film, put it into a beaker containing 3 M dilute sulfuric acid aqueous solution, soak it for 30 min, then rinse the film sample with deionized water until the pH value of the washing water is neutral. Subsequently, place the rinsed - clean film in a vacuum drying oven at 110 °C for 2 h, dry it until the mass difference between two consecutive weighings is less than 0.2 mg, and weigh its mass as m a ;

[0089] The antioxidant performance of the membrane was characterized by comparing the mass change of the dried membrane before and after treatment with Fenton reagent according to the formula. The larger the value, the more serious the degradation degree of the polymer membrane during the treatment with Fenton reagent, and the worse the antioxidant property of the membrane. The antioxidant coefficient is denoted by S.

[0090]

[0091] In the formula:

[0092] S - The antioxidant coefficient measured by the Fenton reagent oxidation method and characterized by mass change;

[0093] m 0 - The mass of the dried membrane before treatment with Fenton reagent;

[0094] m a - The mass of the dried membrane after treatment with Fenton reagent.

[0095] (3) The test method for the phosphoric acid absorption rate is as follows:

[0096] ① Cut a membrane fragment of 3 cm × 3 cm and place it in a vacuum drying oven at 110 °C for 2 h. Dry it until the mass difference between two consecutive weighings is less than 0.2 mg, and weigh its mass as m 0 ;

[0097] ② Place the completely dried ion-exchange membrane in 30 ml of concentrated phosphoric acid with a purity of 85%. After the ion-exchange membrane is completely immersed in the phosphoric acid, place the whole system in a forced-air drying oven at 120 °C for phosphoric acid absorption, and the acid soaking time is 3 h.

[0098] ③ After 3 h, take out the ion-exchange membrane soaked in acid, gently dry the phosphoric acid on the surface with filter paper until the mass difference between two consecutive weighings is less than 1 mg, and weigh its mass as m 1 .

[0099] The phosphoric acid absorption capacity of the ion-exchange membrane was characterized by comparing the mass change of the ion-exchange membrane before and after phosphoric acid treatment according to the formula. The larger the value, the stronger the acid absorption capacity of the ion-exchange membrane. The acid absorption rate is denoted by A.

[0100]

[0101] In the formula:

[0102] A - The acid absorption rate, used to characterize the ability of the ion-exchange membrane to absorb phosphoric acid;

[0103] m 0 - The mass of the dried membrane before phosphoric acid treatment;

[0104] m 1—— Mass of the wet membrane after soaking in phosphoric acid.

[0105] (4) The test method for phosphoric acid retention rate is as follows:

[0106] ① According to the "test method for phosphoric acid absorption rate", change the soaking time of phosphoric acid to make the acid absorption rate of the ion exchange membrane reach 400 ± 5%, and record the mass of the ion exchange membrane after acid soaking at this time as m a .

[0107] ② Hang the ion exchange membrane after acid soaking in an oven at a temperature of 80 °C and a humidity of 40% RH, take it out and weigh it every 24 h and record the mass as m t , until 240 h.

[0108] Compare the mass change of the ion exchange membrane after acid soaking before and after treatment in the humidifying oven according to the formula to characterize the phosphoric acid retention ability. The larger the value, the stronger the acid absorption ability of the ion exchange membrane. The acid retention rate is represented by R.

[0109]

[0110] In the formula:

[0111] R —— Acid retention rate, used to characterize the ability of the ion exchange membrane to retain phosphoric acid;

[0112] m 0 —— Mass of the dried membrane before phosphoric acid treatment;

[0113] m a —— Mass of the wet membrane after soaking in phosphoric acid;

[0114] m t —— Mass of the wet membrane after treatment in the humidifying oven.

[0115] (5) The test method for proton conductivity of hydrogen fuel cells is as follows:

[0116] The proton conductivity test method involved in the present invention refers to subsection 3.5 "Proton Conductivity Test" in GB / T 20042.3-2009. The detailed test method is as follows:

[0117] Cut a membrane of a certain size as a sample. Under the conditions of a temperature of 25 °C ± 2 °C and a relative humidity of 50 ± 5%, use a thickness gauge to measure the thickness of the sample, and take the average value of three points as the calculated thickness d value. Fix the sample in the conductivity measurement fixture and tighten the bolt with a torque wrench at a torque of 3 N·m. Then place the conductivity measurement fixture in different temperature and different constant humidity environments, and perform the test after 30 minutes of constancy under each temperature and humidity condition. In the frequency range of 1 Hz to 2×10 6The impedance spectrum of the sample was measured using an electrochemical impedance tester under the conditions of Hz and a perturbation voltage of 10 mV. In the measured impedance spectrum, the impedance value (R) of the sample was read from the intersection of the high-frequency part of the spectrum line and the real axis, and the proton conductivity of the sample was calculated according to the following formula:

[0118]

[0119] In the formula:

[0120] σ—the proton conductivity of the sample, in millisiemens per centimeter (mS cm -1 );

[0121] a—the distance between the two electrodes, in centimeters (cm);

[0122] R—the measured impedance of the sample, in kiloohms (kΩ);

[0123] b—the effective length of the membrane in the direction perpendicular to the electrode, in centimeters (cm);

[0124] d—the thickness of the sample, in centimeters (cm).

[0125] Three samples were taken as a group, and the average value was calculated as the test result.

[0126] (6) The test method for the proton conductivity and surface resistance of the vanadium redox flow battery is as follows:

[0127] The test method for the surface resistance and proton conductivity involved in the present invention refers to Subsection 5.7 "Conductivity and Membrane Resistance" in NB / T 42028-2023. The detailed test method is as follows:

[0128] ① Cut the membrane into 3 cm × 3 cm square pieces and immerse them in 3M sulfuric acid solution for 24 h, which is called the pretreatment of the membrane;

[0129] ② Join the two half-cells of the conductivity cell, clamp them tightly with an iron clamp, add 3M sulfuric acid solution to the liquid addition hole of the conductivity cell with a dropper and discharge the air bubbles. The liquid level should be higher than the round holes of the half-cell;

[0130] ③ Clamp the test wires of the counter electrode and reference electrode of the electrochemical workstation on one end electrode of the conductivity cell at the same time, and clamp the working electrode test wire on the other end electrode of the conductivity cell to 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 R of the conductivity cell 1 ;

[0131] ④ Clamp the pretreated membrane sample in the middle of the round holes of the two half-cells, repeat operation step ③, and read the data, which is the impedance R of the conductivity cell installed with the membrane sample 2 ;

[0132] ⑤ Repeat the measurement 3 times, record all impedance data and calculate the average value, denoted as 、 , and calculate according to the following formula:

[0133]

[0134] In the formula

[0135] R 2 —— The impedance value of the conductivity cell installed with the membrane sample, in ohms (Ω);

[0136] R 1 —— The impedance value of the conductivity cell without the membrane sample installed, in ohms (Ω);

[0137] R A —— The membrane surface resistance, in ohm square centimeter (Ω cm 2 );

[0138] A—— The effective area of the membrane, in square centimeter (cm 2 );

[0139]

[0140] In the formula

[0141] σ—— The proton conductivity of the sample, in siemens per centimeter (S cm -1 );

[0142] d—— The average thickness of the membrane, in centimeter (cm);

[0143] Take 3 samples as a group and take the average value as the test result.

[0144] Analysis of test results

[0145] Figure 1 This is the physical diagram of the polybenzimidazole / polyionic liquid composite ion membrane prepared in Examples 1-3 of the present invention, showing the good compatibility between polybenzimidazole and polyionic liquid, without phase separation, and excellent film-forming property.

[0146] Figure 2The stress-strain curve diagram of the polybenzimidazole / polyionic liquid composite ion membrane prepared in Examples 1-3 of the present invention. This diagram shows that the mechanical strength of the composite ion membrane prepared in Example 1 of the present invention reaches 121 MPa, and the elongation at break reaches 50%, meeting the usage requirements; the mechanical strength of the composite ion membrane prepared in Example 2 of the present invention can reach 128 MPa, and the elongation at break reaches 46%, meeting the usage requirements; the mechanical strength of the composite ion membrane prepared in Example 3 of the present invention can reach 132 MPa, and the elongation at break reaches 72%, all meeting the usage requirements.

[0147] Table 1

[0148]

[0149] Table 1 is a list of the antioxidant stability of the polybenzimidazole / polyionic liquid composite ion membrane prepared in Examples 1-3 of the present invention by the Fenton reagent method. This table shows that the antioxidant coefficient of the composite ion membrane prepared in Example 1 of the present invention is 0.73%, meeting the usage requirements; the antioxidant coefficient of the composite ion membrane prepared in Example 2 of the present invention is 0.54%, meeting the usage requirements; the antioxidant coefficient of the composite ion membrane prepared in Example 3 of the present invention is 1.07%, meeting the usage requirements.

[0150] Figure 3 The bar chart of the acid absorption rate of the polybenzimidazole / polyionic liquid composite ion membrane prepared in Examples 1-3 of the present invention and the OPBI control group ion membrane. This diagram shows that under the same conditions, the acid absorption rate of the composite ion membrane prepared in Example 1 of the present invention reaches 324%; the acid absorption rate of the composite ion membrane prepared in Example 2 of the present invention reaches 318%; the acid absorption rate of the composite ion membrane prepared in Example 3 of the present invention reaches 369%, all higher than the OPBI ion membrane of the control group. The reason for the different acid absorption rates between Example 1 and Example 2 is the structural difference of the polyionic liquid; the reason for the different acid absorption amounts between Example 1 and Example 3 is the different addition amounts of the polyionic liquid.

[0151] Figure 4 The acid retention rate diagram of the polybenzimidazole / polyionic liquid composite ion membrane prepared in Examples 1-3 of the present invention and the OPBI control group ion membrane. This diagram shows that after 240 h, the acid retention rate of the composite ion membrane prepared in Example 1 of the present invention reaches 56.23%; the acid absorption rate of the composite ion membrane prepared in Example 2 of the present invention reaches 54.95%; the acid absorption rate of the composite ion membrane prepared in Example 3 of the present invention reaches 64.85%, all higher than the OPBI ion membrane of the control group. Similarly, the differences in the acid absorption rates of Examples 1-3 of the present invention after 240 h are also caused by the different structures and addition amounts of the polyionic liquid.

[0152] Figure 5It is a graph showing the change in conductivity at different temperatures of the polybenzimidazole / polyionic liquid composite ion membrane prepared in Examples 1-3 of the present invention when applied to a hydrogen fuel cell. This graph shows that the conductivity at the optimal temperature of the composite ion membrane prepared in Example 1 of the present invention is 110 mS cm -1 , reaching a relatively high level in the industry; the conductivity at the optimal temperature of the composite ion membrane prepared in Example 2 of the present invention is 145 mS cm -1 , reaching a relatively high level in the industry; the conductivity at the optimal temperature of the composite ion membrane prepared in Example 3 of the present invention is 142 mS cm -1 , reaching a relatively high level in the industry.

[0153] Figure 6 It is a graph showing the change in conductivity at different temperatures of the polybenzimidazole / polyionic liquid composite ion membrane prepared in Examples 1-3 of the present invention when applied to a vanadium redox flow battery. According to this graph, the surface resistance of the composite ion membrane prepared in Example 1 of the present invention is 0.358 Ω cm 2 , reaching a relatively high level in the industry; the surface resistance of the composite ion membrane prepared in Example 2 of the present invention is 0.357 Ω cm 2 , reaching a relatively high level in the industry; the surface resistance of the composite ion membrane prepared in Example 3 of the present invention is 0.345 Ω cm 2 , reaching a relatively high level in the industry.

[0154] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A polybenzimidazole / polyionic liquid composite ion membrane, characterized in that: The polyionic liquid and polybenzimidazole are fully dissolved in an organic solvent, dispersed to form a uniform system, and then cast into a film; the polyionic liquid is prepared by the following method: Dissolve formaldehyde, glyoxal, at least one diamine without positive or negative charge groups and acetic acid in deionized water in equal molar ratios, mix well, and heat the obtained mixed reaction solution to 100° C. for constant temperature reaction for 3 hours; after the reaction, transfer the obtained product to an aqueous solution rich in large-volume anions, and the polyionic liquid in the product is precipitated after pairing with the large-volume anions, skim off the upper clear liquid, and wash and dry the lower dark brown product to obtain the polyionic liquid; Wherein: the diamine without positively or negatively charged groups is 1,2-bis(2-aminoethoxy)ethane or hexamethylenediamine.

2. The polybenzimidazole / polyionic liquid composite ion membrane according to claim 1, characterized in that: The thickness of the polybenzimidazole / polyionic liquid composite ion membrane is between 5 and 100 microns.

3. The polybenzimidazole / polyionic liquid composite ion membrane according to claim 1, characterized in that: The polybenzimidazole in the composite ion membrane is any one of aromatic ether polybenzimidazole OPBI, meta-polybenzimidazole mPBI or para-polybenzimidazole pPBI.

4. The polybenzimidazole / polyionic liquid composite ion membrane according to claim 1, characterized in that: The mass ratio of the polyionic liquid to the polybenzimidazole is 5-70:30-95.

5. The polybenzimidazole / polyionic liquid composite ion membrane according to claim 4, characterized in that: The bulky anion is a bis(trifluoromethylsulfonyl)imide anion.

6. The polybenzimidazole / polyionic liquid composite ion membrane according to claim 4, characterized in that: The molar ratio of the diamine without positive or negative charge groups to formaldehyde is 1:

1.

7. The method for preparing the polybenzimidazole / polyionic liquid composite ion membrane according to any one of claims 1 to 6, characterized in that: The method specifically comprises the following steps: The polyionic liquid and polybenzimidazole are dissolved in an organic solvent in sequence according to a ratio to prepare a membrane liquid; the membrane liquid is then cast on a substrate to form a membrane, and the polybenzimidazole / polyionic liquid composite ion membrane is obtained after the solvent evaporates.

Images