A fluorine-containing polybenzimidazole membrane and a preparation method and application thereof

Abstract

The application discloses a fluorine-containing polybenzimidazole membrane and a preparation method and application thereof. The fluorine-containing polybenzimidazole membrane is formed by a fluorine-containing polybenzimidazole copolymer, and a chemical structure general formula of the fluorine-containing polybenzimidazole copolymer is shown in the following formula: the fluorine-containing polybenzimidazole copolymer is prepared by polymerization reaction of a first phenyl tetramine monomer, a second phenyl tetramine monomer, a first phenyl diacid monomer and a second phenyl diacid monomer; based on a fluorine-containing twisted molecular structure, molecular chain loose accumulation is promoted, a molecular chain spacing is increased, a connected ultramicropore channel with high ion sieving capacity is formed, a counterbalancing effect of ion conductivity and ion selectivity in the membrane is broken, and the fluorine-containing polybenzimidazole membrane has high ion conductivity, high ion selectivity and high stability; meanwhile, the preparation process of the fluorine-containing polybenzimidazole membrane is simple, the cost is low, and the fluorine-containing polybenzimidazole membrane has a good application prospect in the fields of liquid flow batteries, fuel cells and water electrolysis hydrogen production.

Description

Technical Field

[0001] This invention relates to a method for preparing a polybenzimidazole membrane, specifically to a fluorinated polybenzimidazole membrane and its preparation method and application, belonging to the field of ion exchange membrane technology. Background Technology

[0002] The large-scale application of clean energy electrochemical devices urgently requires high-performance, low-cost ion exchange membranes. However, existing ion exchange membranes struggle to simultaneously possess high ion selectivity, high ion conductivity, and high stability. In recent years, polybenzimidazole (PBI) has emerged as a promising membrane material due to its well-known excellent chemical stability and high mechanical strength. PBI refers to a series of polymer engineering plastics with benzimidazole groups as structural repeating units. PBI can be partially or entirely aromatic, making it particularly suitable for various harsh high-temperature applications. Over the past two decades, the application range of PBI has expanded significantly, especially functionalized PBI derivatives, which have been widely used as electrolyte membranes in clean energy electrochemical devices, such as acidic or alkaline fuel cells, water electrolyzers, and flow batteries. This is mainly due to its high mechanical stability, thermal stability at high temperatures, high operating temperature, and ability to be doped with acid / alkaline solutions to achieve high ion conductivity. Because the PBI structure is tightly connected through hydrogen bonds and stacked π-π interactions, its ion conductivity is relatively low. Therefore, designing the microstructure of ion conduction channels within the PBI membrane and regulating the ion-selective conduction process is crucial to improving its performance in clean energy electrochemical devices.

[0003] Among the existing modification strategies based on PBI, charged hydrophilic structure design can construct hydrophilic channels within the membrane to enhance mass transfer, but its charge characteristics will change the distribution of the main chain electron cloud, leading to a decrease in its stability; porous structure design can reduce its mass transfer resistance without changing the original stability of the membrane, but it is difficult to achieve precise control of the morphology; non-charged hydrophilic structure design can promote ion conduction without changing the charge distribution within the membrane, but its ion conductivity still needs to be improved to meet the application requirements of clean energy electrochemical devices. Summary of the Invention

[0004] The main objective of this invention is to provide a fluorinated polybenzimidazole membrane and its preparation method, so as to overcome the shortcomings of the prior art.

[0005] Another object of the present invention is to provide the application of the fluorinated polybenzimidazole membrane.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0007] This invention provides a fluorinated polybenzimidazole membrane, which is formed from a fluorinated polybenzimidazole copolymer, the general chemical formula of which is shown in formula (I):

[0008] Equation (I);

[0009] Wherein, n is 10~1000, R1 is a second group, or a combination of a first group and a second group, and the first group is selected from any one or more combinations of the following structural formulas:

[0010] ;

[0011] The second group is selected from any one or a combination of the following structural formulas:

[0012] ;

[0013] R2 is a fourth group, or a combination of a third group and a fourth group, wherein the third group is selected from any one or more combinations of the following structural formulas:

[0014] ;

[0015] The fourth group is selected from any one or a combination of the following structural formulas:

[0016] .

[0017] This invention also provides a method for preparing a fluorinated polybenzimidazole membrane, comprising:

[0018] A fluorinated polybenzimidazole copolymer is prepared by polymerizing a tetraamine monomer, a selectively added or absent first phenyl diacid monomer, and a second phenyl diacid monomer. The tetraamine monomer includes a second phenyltetramine monomer or a combination of a first phenyltetramine monomer and a second phenyltetramine monomer.

[0019] The fluorinated polybenzimidazole copolymer is mixed with a polar solvent to obtain a casting solution. The casting solution is applied to a substrate, and after film formation and drying, a fluorinated polybenzimidazole film is obtained.

[0020] Wherein, the first phenyltetramine monomer is selected from any one or a combination of two of the following formulas (1) to (2):

[0021] Equation (1) Equation (2);

[0022] The second phenyltetramine monomer is selected from any one or a combination of formulas (3) to (10):

[0023] Equation (3) Equation (4)

[0024] Equation (5) Equation (6)

[0025] Equation (7) Equation (8)

[0026] Equation (9) Equation (10);

[0027] The first phenyl diacid monomer is selected from any one or a combination of formulas (11) to (15):

[0028] Equation (11) Equation (12)

[0029] Equation (13) Equation (14)

[0030] Equation (15);

[0031] The second phenyl diacid monomer is selected from any one or a combination of formulas (16) to (25):

[0032] Equation (16) Equation (17)

[0033] Equation (18) Equation (19)

[0034] Equation (20) Equation (21)

[0035] Equation (22) Equation (23)

[0036] Equation (24) Equation (25).

[0037] This invention also provides a fluorinated polybenzimidazole membrane prepared by the aforementioned method.

[0038] This invention also provides applications of the fluorinated polybenzimidazole membrane in flow batteries, fuel cells, or water electrolysis for hydrogen production.

[0039] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0040] This invention utilizes the polymerization reaction of a first phenyltetramine monomer, a second phenyltetramine monomer, a first phenyl diacid monomer, and a second phenyl diacid monomer. Based on the fluorine-containing twisted molecular structure, it promotes the loose stacking of molecular chains, increases the inter-chain spacing, and forms interconnected ultraporous channels with strong ion sieving capabilities. This breaks the balance between intramembrane ion conductivity and ion selectivity, achieving a fluorinated polybenzimidazole membrane with high ion conductivity, high ion selectivity, and high stability. Furthermore, the preparation process of this fluorinated polybenzimidazole membrane is simple and inexpensive, showing promising application prospects in flow batteries, fuel cells, and water electrolysis for hydrogen production. Detailed Implementation

[0041] In view of the deficiencies in the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. Inspired by zwitterionic selective channels, this invention proposes a fluorinated polybenzimidazole membrane design from the perspective of molecular structure design. Through the polymerization reaction of the first phenyltetramine monomer, the second phenyltetramine monomer, the first phenyldiacetic acid monomer, and the second phenyldiacetic acid monomer, based on the fluorinated twisted molecular structure, loosely stacking of molecular chains is promoted, increasing the inter-chain spacing and forming interconnected ultraporous channels with strong ion sieving ability. Therefore, its ion conductivity is significantly improved while maintaining high ion selectivity, and the fluorinated structure significantly enhances the stability of the membrane.

[0042] The following will further explain the technical solution, its implementation process, and its principles. However, it should be understood that within the scope of this invention, the above-mentioned technical features of this invention and the technical features specifically described below (in embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, they will not be described in detail here.

[0043] As one aspect of the technical solution of the present invention, a fluorinated polybenzimidazole membrane is formed from a fluorinated polybenzimidazole copolymer, the general chemical structure of which is shown in formula (I):

[0044] Equation (I);

[0045] Wherein, n is 10~1000, R1 is a second group, or a combination of a first group and a second group, and the first group is selected from any one or more combinations of the following structural formulas:

[0046] ;

[0047] The second group is selected from any one or a combination of the following structural formulas:

[0048] ;

[0049] R2 is a fourth group, or a combination of a third group and a fourth group, wherein the third group is selected from any one or more combinations of the following structural formulas:

[0050] ;

[0051] The fourth group is selected from any one or a combination of the following structural formulas:

[0052] .

[0053] In some embodiments, the fluorinated polybenzimidazole membrane comprises interconnected ultraporous channels with ion sieving capabilities, the channel size being 0.3~1 nm.

[0054] In some embodiments, the thickness of the fluorinated polybenzimidazole film is 5 to 100 µm.

[0055] As another aspect of the technical solution of the present invention, it also relates to a method for preparing a fluorinated polybenzimidazole membrane, comprising:

[0056] Fluorinated polybenzimidazole copolymers are prepared by polymerizing tetraamine monomers, selectively added or omitted first phenyl diacid monomers (also known as "Type I phenyl diacid monomers"), and second phenyl diacid monomers (also known as "Type II phenyl diacid monomers"); wherein the tetraamine monomers include second phenyltetramine monomers (also known as "Type II phenyltetramine monomers"), or combinations of first phenyltetramine monomers (also known as "Type I phenyltetramine monomers") and second phenyltetramine monomers.

[0057] The fluorinated polybenzimidazole copolymer is mixed with a polar solvent to obtain a casting solution. The casting solution is applied to a substrate, and after film formation and drying, a fluorinated polybenzimidazole film is obtained.

[0058] In some preferred embodiments, the first phenyltetramine monomer is selected from any one or a combination of two of the following formulas (1) to (2):

[0059] Equation (1) Equation (2);

[0060] In some preferred embodiments, the second phenyltetramine monomer is selected from any one or a combination of formulas (3) to (10):

[0061] Equation (3) Equation (4)

[0062] Equation (5) Equation (6)

[0063] Equation (7) Equation (8)

[0064] Equation (9) Equation (10);

[0065] In some preferred embodiments, the first phenyl diacid monomer is selected from any one or a combination of formulas (11) to (15):

[0066] Equation (11) Equation (12)

[0067] Equation (13) Equation (14) Equation (15);

[0068] In some preferred embodiments, the second phenyl diacid monomer is selected from any one or a combination of formulas (16) to (25):

[0069] Equation (16) Equation (17)

[0070] Equation (18) Equation (19)

[0071] Equation (20) Equation (21)

[0072] Equation (22) Equation (23)

[0073] Equation (24) Equation (25).

[0074] In some embodiments, the preparation method includes: mixing a first phenyltetramine monomer, a second phenyltetramine monomer, a first phenyl diacid monomer and a second phenyl diacid monomer, a specified solvent and a dehydrating condensing agent uniformly to form a polymerization reaction system, and carrying out a polymerization reaction at 100~200℃ for 1~24h to obtain a fluorinated polybenzimidazole copolymer.

[0075] In some preferred embodiments, the polymerization reaction can be carried out in stages with stepped heating.

[0076] In some preferred embodiments, the specified solvent includes polyphosphoric acid and / or methanesulfonic acid, etc. When polyphosphoric acid is used as the specified solvent, the dehydrating condensing agent can be omitted; when methanesulfonic acid is used, a dehydrating condensing agent needs to be added.

[0077] In some preferred embodiments, the dehydrating condensing agent comprises phosphorus pentoxide.

[0078] Furthermore, the mass ratio of the specified solvent to the dehydrating condensing agent is 8:1 to 10:1.

[0079] In some embodiments, the molar ratio of the first phenyltetramine monomer, the second phenyltetramine monomer, the first phenyl diacid monomer, and the second phenyl diacid monomer is x:(1-x):y:(1-y), where 0≤x<1 and 0≤y<1.

[0080] In some more preferred embodiments, the fluorinated polybenzimidazole copolymer is prepared by polymerization reaction using polyphosphoric acid or methanesulfonic acid as solvent and phosphorus pentoxide as dehydrating condensing agent, wherein type I phenyltetramine monomer, type II phenyltetramine monomer, type I phenyl diacid monomer and type II phenyl diacid monomer are fed in a feeding ratio of x:(1-x):y:(1-y), wherein 0≤x<1 and 0≤y<1.

[0081] Furthermore, when the first phenyltetramine monomer and the second phenyltetramine monomer are added simultaneously, the increase in the second phenyltetramine monomer can effectively promote the rigid twisting of polymer chain segments, increase free volume, and reduce mass transfer resistance.

[0082] Compared to using only diphenyl diacid monomer, when diphenyl diacid monomer and diphenyl diacid monomer are added simultaneously, especially when diphenyl diacid monomer is used alone, the membrane exhibits better ion conductivity, ion selectivity, and membrane stability. The mechanism is explained as follows: as the content of diphenyl diacid monomer increases, the stereostructure of polymer chain segments can be effectively controlled, increasing the free volume within the membrane and reducing mass transfer resistance.

[0083] In some embodiments, the total concentration of the first phenyltetramine monomer, the second phenyltetramine monomer, the first phenyl diacid monomer, and the second phenyl diacid monomer in the polymerization reaction system is 10-35 wt%.

[0084] In some embodiments, the polar solvent may include, but is not limited to, one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and methanesulfonic acid.

[0085] In some embodiments, the content of fluorinated polybenzimidazole copolymer in the casting solution is 1 to 30 wt%.

[0086] In some embodiments, the preparation method includes applying the casting liquid to a substrate using at least a casting method or a scraping method.

[0087] Furthermore, the fluorinated polybenzimidazole membrane is obtained by dissolving the fluorinated polybenzimidazole copolymer in a polar solvent to obtain a casting solution, and then forming the casting solution on a substrate by casting or scraping and drying to obtain a dense homogeneous membrane.

[0088] Furthermore, the drying temperature is 40~100℃, and the time is 1~48h.

[0089] As another aspect of the technical solution of the present invention, the method for preparing the fluorinated polybenzimidazole membrane can also be:

[0090] A fluorinated polybenzimidazole copolymer is prepared by polymerizing a tetraamine monomer and a second phenyl diacid monomer; wherein the tetraamine monomer is a first phenyltetraamine monomer, which is of formula (2), or a combination of formula (1) and formula (2); the second phenyl diacid monomer is selected from any one or more combinations of formulas (16) to (25);

[0091] The fluorinated polybenzimidazole copolymer is mixed with a polar solvent to obtain a casting solution. The casting solution is applied to a substrate, and after film formation and drying, a fluorinated polybenzimidazole film is obtained.

[0092] As another aspect of the technical solution of the present invention, the method for preparing the fluorinated polybenzimidazole membrane can also be:

[0093] A fluorinated polybenzimidazole copolymer is prepared by polymerizing a tetraamine monomer, a first phenyl diacid monomer, and a second phenyl diacid monomer; wherein the tetraamine monomer is a first phenyltetraamine monomer, which is of formula (2), or a combination of formula (1) and formula (2); the first phenyl diacid monomer is any one or a combination of formulas (11) to (15); and the second phenyl diacid monomer is selected from any one or a combination of formulas (16) to (25).

[0094] The fluorinated polybenzimidazole copolymer is mixed with a polar solvent to obtain a casting solution. The casting solution is applied to a substrate, and after film formation and drying, a fluorinated polybenzimidazole film is obtained.

[0095] As another aspect of the technical solution of the present invention, it also relates to a fluorinated polybenzimidazole membrane prepared by the above preparation method.

[0096] As another aspect of the technical solution of the present invention, it also relates to the application of the aforementioned fluorinated polybenzimidazole membrane. Specifically, as an ion exchange membrane, it can be applied to fields such as flow batteries, fuel cells, or water electrolysis for hydrogen production.

[0097] The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present invention, and do not constitute any limitation thereof. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or according to the conditions recommended by the manufacturer.

[0098] The flow battery structures in Examples 1-8 below are as follows: The effective area is 3×3 cm. 2 The performance of the assembled flow battery was tested by sandwiching a fluorinated polybenzimidazole membrane between a carbon felt electrode and a graphite plate, using two separate circulation pumps to deliver 45 mL of 1.7 MV fluid. 3.5+ / 3 M H2SO4 solution, using a LANHE battery tester (CT2001A, 5 V / 3 A, Wuhan Landian Electronics Co., Ltd.) at 40-200 mA cm⁻¹ -2 The flow battery was subjected to charge-discharge tests at 160 mA cm⁻¹ to evaluate its electrochemical performance. The cutoff voltage during the charge-discharge process ranged from 1 V to 1.55 V. -2 The charge-discharge cycle performance was tested with a cutoff voltage set from 1 V to 1.55 V to minimize corrosion of the carbon felt electrode and graphite plate. During the charge-discharge cycle test, when the discharge capacity decreased to below 30% of the initial value, the electrolyte was replaced and the test continued.

[0099] The fuel cell structure in Example 1 below is as follows: The performance of the fuel cell containing the fluorinated polybenzimidazole membrane was tested using an 890e Multi Range fuel cell test bench (Shanghai Qunyi). 1.5 g of polybenzimidazole was weighed and dissolved in 30 mL of dimethyl sulfoxide, heated to dissolve, and then centrifuged to obtain the polybenzimidazole solution. The anode catalyst used was a commercial Pt / Ru / C (40% w / w / w Pt component), and the cathode catalyst used was a commercial Pt / C (40% w / w Pt component). 10 mg of each catalyst powder was dispersed in 3 mL of a water / isopropanol mixed solution (V... 水 V 异丙醇 The ratio of the catalyst solution to the cathode solution was 1:9. After ultrasonic treatment for 30 min, the above-mentioned polybenzimidazole solution was added, and ultrasonication was repeated for 30 min to obtain uniformly mixed anolyte and cathode catalyst solutions. Subsequently, the anolyte and cathode catalyst solutions were sprayed onto both sides of the fluorinated polybenzimidazole membrane (effective area 5 cm²) at 70°C. 2The loading of both the cathode and anode catalysts on both sides of the fluorinated polybenzimidazole membrane is 0.6 mg cm⁻¹. -2 A fluorinated polybenzimidazole membrane with supported anode and cathode catalysts was placed between two sheets of carbon paper (AVCARB GDS3250) to form a membrane electrode assembly. The prepared membrane electrode assembly was assembled onto an 890e Multi Range fuel cell test bench (Shanghai Qunyi), and the fuel cell performance was measured at 80°C, with an H2 / O2 (100% humidity) flow rate of 0.2 L / min and a back pressure of 0.1 MPa.

[0100] The structure of the water electrolysis battery in Example 1 is as follows:

[0101] Fabrication of the membrane electrode assembly: First, the carbon paper and nickel foam used as the gas diffusion layer were pretreated. The anode and cathode were carbon paper (Avcarb P75, 232 µm thick) and nickel foam (0.6 mm thick), respectively. The nickel foam was cut into 2.25 cm × 2.25 cm pieces, washed with acetone and ethanol to remove surface impurities and oxide layers, and dried in a 60°C oven for 12 h. The carbon paper required no treatment and was simply cut to the same size as the nickel foam. The fluorinated polybenzimidazole membrane was soaked in 1 MKOH solution for 24 hours, and then the alkaline solution was removed from the surface with pure water. 1.5 g of polybenzimidazole was dissolved in 30 mL of dimethyl sulfoxide, heated to dissolve, and then centrifuged to obtain the polybenzimidazole solution. Pt / C and IrO2 were used as the cathode and anode catalysts, respectively. 10 mg of each catalyst powder was dispersed in 3 mL of a water / isopropanol mixed solution (V... 水 V 异丙醇 The ratio of the catalyst solution to the anode catalyst solution was 1:9. After ultrasonic treatment for 30 min, the above-mentioned polybenzimidazole solution was added, and ultrasonication was repeated for 30 min to obtain uniformly mixed cathode and anode catalyst solutions. Subsequently, the cathode and anode catalyst solutions were sprayed onto carbon paper and nickel foam (effective area 5 cm²) at 70 °C, respectively. 2 The loading amounts of the cathode catalyst on carbon paper and the anode catalyst on nickel foam were both 2 mg / cm³. -2 After spraying, the coating is dried using residual heat on a film scraper. Finally, a fluorinated polybenzimidazole membrane is placed between carbon paper supporting the cathode catalyst layer and nickel foam supporting the anode catalyst layer. The fluorinated polybenzimidazole membrane is in contact with the cathode catalyst layer and the anode catalyst layer on both sides, forming a membrane electrode assembly. A flow field plate and a bipolar plate are then placed sequentially from the inside to the outside on both sides of the membrane electrode assembly, and the assembled assembly yields an electrolytic water battery for electrochemical testing.

[0102] Electrolysis performance testing: The water electrolysis apparatus was used to evaluate the performance of the electrolytic cell. A multi-channel Ivium electrochemical workstation was used to control the battery voltage and current. During testing, an electrolyte solution preheated to 50°C was introduced into the anode side at a flow rate of 5 mL / min. The polarization curve (current density versus battery voltage curve) was measured, with a scanning voltage range of 1.3–2.5 V and a scanning rate of 5 mV / s. Before recording the first polarization curve, the battery was activated for a period of time under varying current. The test was conducted at 60°C and 600 mA / cm². 2 The stability of the battery was tested under a constant current density.

[0103] Example 1

[0104] Methylsulfonic acid and phosphorus pentoxide were added to a three-necked flask in a mass ratio of 9:1. Nitrogen gas was introduced to remove oxygen. 2,2-bis(3,4-aminophenyl)hexafluoropropane (as shown in formula (2)) and 3,3'-diaminobenzidine (as shown in formula (1)) were added to the three-necked flask in a molar ratio of 9:1. The mixture was heated and stirred to dissolve. After the tetraamine monomer was completely dissolved, 4,4-biphenyldicarboxylic acid (as shown in formula (15)) and 2,6-naphthalenedicarboxylic acid (as shown in formula (19)) were added in a molar ratio of 7:3, so that the total concentration of the four monomers was 20 wt%, and the molar ratio of the sum of 2,2-bis(3,4-aminophenyl)hexafluoropropane and 3,3'-diaminobenzidine to the sum of 4,4-biphenyldicarboxylic acid and 2,6-naphthalenedicarboxylic acid was 1:1. The polymerization reaction was carried out using a stepped heating method: first, the temperature was raised to 100℃ and reacted for 1 hour, then raised to 150℃ and reacted for 12 hours, and finally cooled to room temperature. The high-viscosity reaction solution was precipitated in water to obtain filamentous polymer. After neutralization with excess NaHCO3, the polymer was washed repeatedly with water and dried to obtain a solid fluorinated polybenzimidazole copolymer. The obtained copolymer was dissolved in dimethyl sulfoxide to form a 3wt% transparent solution. The casting solution was poured onto a glass plate and dried at 80℃ for 24 hours to form a film. The film was then immersed in a 1mol / L dilute sulfuric acid solution for 24 hours, followed by immersion in deionized water and washing until neutral to obtain the fluorinated polybenzimidazole membrane.

[0105] The fluorinated polybenzimidazole membrane obtained in this embodiment was assembled in a flow battery and tested at 160 mA cm⁻¹. -2 The lower coulombic efficiency is 99%, the voltage efficiency is 81%, and the energy efficiency is 80%. This fluorinated polybenzimidazole membrane was assembled into a fuel cell for testing at 80°C, and the maximum output power was 0.3 W / cm². 2 The fluorinated polybenzimidazole membrane was assembled into a water electrolysis battery for testing. At 80℃ and 2V, the current reached 0.6 A / cm. 2 .

[0106] Example 2

[0107] Methylsulfonic acid and phosphorus pentoxide were added to a three-necked flask in a mass ratio of 8:1. Nitrogen gas was introduced to remove oxygen. 2,2-bis(3,4-aminophenyl)-1,1,1-trifluoropropane (as shown in formula (3)) and 3,3'-diaminobenzidine (as shown in formula (1)) were added to the three-necked flask in a molar ratio of 3:1. The mixture was heated and stirred to dissolve. After the tetraamine monomer was completely dissolved, 4,4'-biphenyldicarboxylic acid (as shown in formula (15)) and terphenyldicarboxylic acid (as shown in formula (23)) were added in a molar ratio of 1:1, so that the total concentration of the four monomers was 25 wt%, wherein the molar ratio of the sum of 2,2-bis(3,4-aminophenyl)-1,1,1-trifluoropropane and 3,3'-diaminobenzidine to the sum of 4,4-biphenyldicarboxylic acid and terphenyldicarboxylic acid was 1:1. The polymerization reaction was carried out using a stepped heating method: the temperature was raised to 100℃ for 1 hour, then raised to 150℃ for 12 hours, and finally cooled to room temperature. The high-viscosity reaction solution was precipitated in water to obtain filamentous polymer. After neutralization with excess NaHCO3, the polymer was washed repeatedly with water and dried to obtain a solid fluorinated polybenzimidazole copolymer. The obtained copolymer was dissolved in dimethyl sulfoxide to form a 3wt% transparent solution. The casting solution was poured onto a glass plate and dried at 80℃ for 24 hours to form a film. The film was then immersed in a 1mol / L dilute sulfuric acid solution for 24 hours, followed by immersion in deionized water and washing until neutral to obtain the fluorinated polybenzimidazole membrane.

[0108] The fluorinated polybenzimidazole membrane obtained in this embodiment was assembled in a flow battery and tested at 160 mA cm⁻¹. -2 The lower coulomb efficiency is 99%, the voltage efficiency is 80%, and the energy efficiency is 79%.

[0109] Example 3

[0110] Methylsulfonic acid and phosphorus pentoxide were added to a three-necked flask in a mass ratio of 10:1. Nitrogen gas was introduced to remove oxygen. 2,2-bis(3,4-aminophenyl)-1,1,1-trifluorobutane (as shown in formula (4)) and 3,3'-diaminobenzidine (as shown in formula (1)) were added to the three-necked flask in a molar ratio of 1:1. The mixture was heated and stirred to dissolve. After the tetraamine monomer was completely dissolved, 2,2-bis(4-carboxyphenyl)hexafluoropropane (as shown in formula (12)) and m-terphenyldicarboxylic acid (as shown in formula (25)) were added in a molar ratio of 4:6, so that the total concentration of the four monomers was 30 wt%. The molar ratio of the sum of 2,2-bis(3,4-aminophenyl)-1,1,1-trifluorobutane and 3,3'-diaminobenzidine to the sum of 2,2-bis(4-carboxyphenyl)hexafluoropropane and m-terphenyldicarboxylic acid was 1:1. The polymerization reaction was carried out using a stepped heating method: the temperature was raised to 100℃ for 1 hour, then raised to 150℃ for 12 hours, and finally cooled to room temperature. The high-viscosity reaction solution was precipitated in water to obtain filamentous polymer. After neutralization with excess NaHCO3, the polymer was washed repeatedly with water and dried to obtain a solid fluorinated polybenzimidazole copolymer. The obtained copolymer was dissolved in dimethyl sulfoxide to form a 3wt% transparent solution. The casting solution was poured onto a glass plate and dried at 80℃ for 24 hours to form a film. The film was then immersed in a 1mol / L dilute sulfuric acid solution for 24 hours, followed by immersion in deionized water and washing until neutral to obtain the fluorinated polybenzimidazole membrane.

[0111] The fluorinated polybenzimidazole membrane obtained in this embodiment was assembled in a flow battery and tested at 160 mA cm⁻¹. -2 The lower coulomb efficiency is 99%, the voltage efficiency is 82%, and the energy efficiency is 81%.

[0112] Example 4

[0113] Add 85% polyphosphoric acid to a three-necked flask, purge with nitrogen to remove oxygen, and add 2,2-bis(3,4-aminophenyl)-1,1,1-trifluoropropane-2-phenyl (as shown in formula (5)) and 3,3'-diaminobenzidine (as shown in formula (1)) to the three-necked flask in a molar ratio of 1:1. Heat and stir to dissolve. After the tetraamine monomer is completely dissolved, add 4,4'-diphenyl ether dicarboxylic acid (as shown in formula (11)) and 2,6-naphthalene dicarboxylic acid (as shown in formula (19)) in a molar ratio of 1:1, so that the total concentration of the four monomers is 15 wt%, wherein the molar ratio of the sum of 2,2-bis(3,4-aminophenyl)-1,1,1-trifluoropropane-2-phenyl and 3,3'-diaminobenzidine to the sum of 4,4'-diphenyl ether dicarboxylic acid and 2,6-naphthalene dicarboxylic acid is 1:1. The polymerization reaction was carried out using a stepped heating method: the temperature was raised to 140℃ for 2 hours, then to 160℃ for 2 hours, and finally to 200℃ for 12 hours. The polymerization ended when the reaction solution became very viscous and began to climb the rod. The high-viscosity reaction solution was precipitated in water to obtain filamentous polymer. After neutralization with excess NaHCO3, the polymer was washed repeatedly with water and dried to obtain a solid fluorinated polybenzimidazole copolymer. The obtained copolymer was dissolved in dimethyl sulfoxide to form a 3wt% transparent solution. The casting solution was poured onto a glass plate and dried at 70℃ for 24 hours to form a film. The film was then immersed in a 1mol / L dilute sulfuric acid solution for 24 hours, followed by immersion in deionized water and washing until neutral to obtain the fluorinated polybenzimidazole membrane.

[0114] The fluorinated polybenzimidazole membrane obtained in this embodiment was assembled in a flow battery and tested at 160 mA cm⁻¹. -2 The lower coulomb efficiency is 99%, the voltage efficiency is 78%, and the energy efficiency is 77%.

[0115] Example 5

[0116] Add 85% polyphosphoric acid to a three-necked flask, purge with nitrogen to remove oxygen, and add 2,2-bis(3,4-aminophenyl)-1,1,1-trifluoropropane-2-(4-fluorophenyl) (as shown in formula (6)) and 3,3'-diaminobenzidine (as shown in formula (1)) to the three-necked flask in a molar ratio of 3:7. Heat and stir to dissolve. After the tetraamine monomer is completely dissolved, add 4,4'-biphenyldicarboxylic acid (as shown in formula (15)) and 2,6-naphthalenedicarboxylic acid (as shown in formula (19)) in a molar ratio of 4:6, so that the total concentration of the four monomers is 16wt%, wherein the molar ratio of the sum of 2,2-bis(3,4-aminophenyl)-1,1,1-trifluoropropane-2-(4-fluorophenyl) and 3,3'-diaminobenzidine to the sum of 4,4'-biphenyldicarboxylic acid and 2,6-naphthalenedicarboxylic acid is 1:1. The polymerization reaction was carried out using a stepped heating method: the temperature was raised to 140℃ for 2 hours, then to 160℃ for 2 hours, and finally to 200℃ for 12 hours. The polymerization ended when the reaction solution became very viscous and began to climb the rod. The high-viscosity reaction solution was precipitated in water to obtain filamentous polymer. After neutralization with excess NaHCO3, the polymer was washed repeatedly with water and dried to obtain a solid fluorinated polybenzimidazole copolymer. The obtained copolymer was dissolved in dimethyl sulfoxide to form a 3wt% transparent solution. The casting solution was poured onto a glass plate and dried at 60℃ for 24 hours to form a film. The film was then immersed in a 1mol / L dilute sulfuric acid solution for 24 hours, followed by immersion in deionized water and washing until neutral to obtain the fluorinated polybenzimidazole membrane.

[0117] The fluorinated polybenzimidazole membrane obtained in this embodiment was assembled in a flow battery and tested at 160 mA cm⁻¹. -2 The lower coulomb efficiency is 99%, the voltage efficiency is 77%, and the energy efficiency is 76%.

[0118] Example 6

[0119] Add 85% polyphosphoric acid to a three-necked flask, purge with nitrogen to remove oxygen, and add 2,2-bis(3,4-aminophenyl)-1,1,1-trifluoropropane-2-(4-trifluoromethyl)phenyl (as shown in formula (9)) and 3,3'-diaminobenzidine (as shown in formula (1)) to the three-necked flask in a molar ratio of 2:8. Heat and stir to dissolve. After the tetraamine monomer was completely dissolved, 2,2-bis(4-carboxyphenyl)hexafluoropropane (as shown in formula (12)) and 1,4-naphthalenedicarboxylic acid (as shown in formula (18)) were added in a molar ratio of 3:7, so that the total concentration of the four monomers was 10 wt%, wherein the molar ratio of the sum of 2,2-bis(3,4-aminophenyl)-1,1,1-trifluoropropane-2-(4-trifluoromethyl)phenyl and 3,3'-diaminobenzidine to the sum of 2,2-bis(4-carboxyphenyl)hexafluoropropane and 1,4-naphthalenedicarboxylic acid was 1:1. The polymerization reaction was carried out by stepwise heating: the temperature was raised to 140℃ for 2 hours, then raised to 160℃ for 2 hours, and then raised to 200℃ for 12 hours. The polymerization reaction ended when the reaction solution became very viscous and climbed the rod. The high-viscosity reaction solution was precipitated in water to obtain filamentous polymer. After neutralization with excess NaHCO3, the mixture was washed repeatedly with water and dried to obtain a solid fluorinated polybenzimidazole copolymer. The obtained copolymer was dissolved in dimethyl sulfoxide to form a 3 wt% transparent solution. The casting solution was poured onto a glass plate and dried at 60°C for 24 hours to form a film. The film was then immersed in a 1 mol / L dilute sulfuric acid solution for 24 hours, followed by immersion in deionized water and washing until neutral to obtain the fluorinated polybenzimidazole membrane.

[0120] The fluorinated polybenzimidazole membrane obtained in this embodiment was assembled in a flow battery and tested at 160 mA cm⁻¹. -2 The lower coulomb efficiency is 99%, the voltage efficiency is 79%, and the energy efficiency is 78%.

[0121] Example 7

[0122] The difference between this embodiment and Example 2 is that only 2,2-bis(3,4-aminophenyl)-1,1,1-trifluoropropane (as shown in formula (3)) was added to the tetraamine monomer, and 3,3'-diaminobenzidine was not added.

[0123] The obtained fluorinated polybenzimidazole copolymer was dissolved in dimethyl sulfoxide to form a 1 wt% transparent solution. The casting solution was poured onto a glass plate and dried at 40°C for 48 hours to form a film. The film was then immersed in a 1 mol / L dilute sulfuric acid solution for 24 hours, and then soaked and washed with deionized water until neutral to obtain the fluorinated polybenzimidazole membrane.

[0124] The fluorinated polybenzimidazole membrane obtained in this embodiment was assembled in a flow battery and tested at 160 mA cm⁻¹. -2The lower coulomb efficiency is 99%, the voltage efficiency is 81%, and the energy efficiency is 80%.

[0125] Example 8

[0126] The difference between this embodiment and embodiment 2 is that only terphenyl dicarboxylic acid (as shown in formula (23)) is added to the dicarboxylic acid monomer, and 4,4'-biphenyl dicarboxylic acid is not added.

[0127] The obtained fluorinated polybenzimidazole copolymer was dissolved in dimethyl sulfoxide to form a 30 wt% transparent solution. The casting solution was then poured onto a glass plate and dried at 100 °C for 1 hour to form a film. The film was then immersed in a 1 mol / L dilute sulfuric acid solution for 24 hours, and then soaked and washed with deionized water until neutral to obtain the fluorinated polybenzimidazole membrane.

[0128] The fluorinated polybenzimidazole membrane obtained in this embodiment was assembled in a flow battery and tested at 160 mA cm⁻¹. -2 The lower coulomb efficiency is 99%, the voltage efficiency is 82%, and the energy efficiency is 79%.

[0129] Comparative Example 1

[0130] Methylsulfonic acid and phosphorus pentoxide were added to a three-necked flask at a mass ratio of 9:1. Nitrogen gas was introduced to purge oxygen. 3,3'-Diaminobenzidine was then added to the flask, and the mixture was heated and stirred until dissolved. After the tetraamine monomer was completely dissolved, 4,4'-biphenyldicarboxylic acid and 2,6-naphthalenedicarboxylic acid were added at a molar ratio of 7:3, resulting in a total monomer concentration of 20 wt%, with the molar ratio of 3,3'-diaminobenzidine to the sum of 4,4'-biphenyldicarboxylic acid and 2,6-naphthalenedicarboxylic acid being 1:1. The polymerization reaction was carried out using a stepped heating method: the temperature was raised to 100℃ for 1 h, then raised to 150℃ for 12 h, and finally cooled to room temperature. The high-viscosity reaction solution was precipitated in water to obtain filamentous polymer. After neutralization with excess NaHCO3, the polymer was washed repeatedly with water and dried to obtain a solid polymer. The obtained polymer was dissolved in dimethyl sulfoxide to form a 3 wt% transparent solution. The casting solution was poured onto a glass plate and dried at 80°C for 24 hours to form a film. The film was then immersed in a 1 mol / L dilute sulfuric acid solution for 24 hours, followed by immersion in deionized water and washing until neutral to obtain the polybenzimidazole film.

[0131] The polybenzimidazole membrane obtained in this comparative example was assembled in a flow battery at 160 mA cm⁻¹. -2 The lower coulomb efficiency is 99%, the voltage efficiency is 74%, and the energy efficiency is 73%.

[0132] Comparative Example 2

[0133] Methylsulfonic acid and phosphorus pentoxide were added to a three-necked flask in a mass ratio of 9:1. Nitrogen gas was introduced to purge oxygen. 2,2-bis(3,4-aminophenyl)hexafluoropropane and 3,3'-diaminobenzidine were added to the flask in a molar ratio of 9:1, and the mixture was heated and stirred until dissolved. After the tetraamine monomer was completely dissolved, 4,4-diphenyl ether dicarboxylic acid was added to bring the total monomer concentration to 20 wt%, with the molar ratio of the sum of 2,2-bis(3,4-aminophenyl)hexafluoropropane and 3,3'-diaminobenzidine to 4,4-diphenyl ether dicarboxylic acid being 1:1. The polymerization reaction was carried out using a stepped heating method: the temperature was raised to 100℃ for 1 hour, then raised to 140℃ for 3 hours, and finally cooled to room temperature. The high-viscosity reaction solution was precipitated in water to obtain filamentous polymer. After neutralization with excess NaHCO3, the polymer was washed repeatedly with water and dried to obtain a solid polymer. The obtained polymer was dissolved in dimethyl sulfoxide to form a 3wt% transparent solution. The casting solution was poured onto a glass plate and dried at 80°C for 24 hours to form a film. The film was then immersed in a 1mol / L dilute sulfuric acid solution for 24 hours, followed by immersion in deionized water and washing until neutral to obtain a fluorinated polybenzimidazole membrane.

[0134] The fluorinated polybenzimidazole membrane obtained in this comparative example was assembled in a flow battery at 160 mA cm⁻¹. -2 The lower coulomb efficiency is 99%, the voltage efficiency is 75%, and the energy efficiency is 74%.

[0135] In summary, the fluorinated polybenzimidazole membrane prepared by this invention plays an extremely important role in promoting its commercial application in fields such as fuel cells, water electrolysis, and flow batteries.

[0136] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a fluorinated polybenzimidazole membrane, characterized in that, include: The first phenyltetramine monomer, the second phenyltetramine monomer, the first phenyl diacid monomer, the second phenyl diacid monomer, a specified solvent, and a dehydrating condensing agent are mixed evenly to form a polymerization reaction system. The polymerization reaction is carried out at 100~200℃ for 1~24h to obtain a fluorinated polybenzimidazole copolymer. The specified solvent is polyphosphoric acid and / or methanesulfonic acid, and the mass ratio of the specified solvent to the dehydrating condensing agent is 8:1~10:

1. The molar ratio of the first phenyltetramine monomer, the second phenyltetramine monomer, the first phenyl diacid monomer, and the second phenyl diacid monomer is x:(1-x):y:(1-y), where 0≤x<1, 0≤y<1. The fluorinated polybenzimidazole copolymer is mixed with a polar solvent to obtain a casting solution. The casting solution is applied to a substrate, and after film formation and drying, a fluorinated polybenzimidazole membrane is obtained. The fluorinated polybenzimidazole membrane contains interconnected ultramicroporous channels with ion sieving capabilities, and the channel size is 0.3~1nm. Wherein, the first phenyltetramine monomer is selected from any one or a combination of two of the following formulas (1) to (2): Equation (1) Equation (2); The second phenyltetramine monomer is selected from any one or a combination of formulas (3) to (10): Equation (3) Equation (4) Equation (5) Equation (6) Equation (7) Equation (8) Equation (9) Equation (10); The first phenyl diacid monomer is selected from any one or a combination of formulas (11) to (15): Equation (11) Equation (12) Equation (13) Equation (14) Equation (15); The second phenyl diacid monomer is selected from any one or a combination of formulas (16) to (25): Equation (16) Equation (17) Equation (18) Equation (19) Equation (20) Equation (21) Equation (22) Equation (23) Equation (24) Equation (25).

2. The preparation method according to claim 1, characterized in that: The dehydrating condensing agent is phosphorus pentoxide.

3. The preparation method according to claim 1, characterized in that: In the polymerization reaction system, the total concentration of the first phenyltetramine monomer, the second phenyltetramine monomer, the first phenyl diacid monomer, and the second phenyl diacid monomer is 10~35wt%.

4. The preparation method according to claim 1, characterized in that: The polar solvent is selected from one or more combinations of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and methanesulfonic acid.

5. The preparation method according to claim 1, characterized in that: The content of fluorinated polybenzimidazole copolymer in the casting solution is 1~30wt%.

6. The preparation method according to claim 1, characterized in that... include: The casting solution is applied to the substrate by at least casting or scraping methods.

7. The preparation method according to claim 1, characterized in that: The drying temperature is 40~100℃, and the time is 1~48h.

8. A fluorinated polybenzimidazole membrane prepared by any one of claims 1-7, characterized in that, The fluorinated polybenzimidazole membrane is formed from a fluorinated polybenzimidazole copolymer, and the general chemical structure of the fluorinated polybenzimidazole copolymer is shown in Formula (I): Equation (I); Wherein, n is 10~1000, R1 is a second group, or a combination of a first group and a second group, and the first group is selected from any one or more combinations of the following structural formulas: ； The second group is selected from any one or a combination of the following structural formulas: ； R2 is a fourth group, or a combination of a third group and a fourth group, wherein the third group is selected from any one or more combinations of the following structural formulas: ； The fourth group is selected from any one or a combination of the following structural formulas: 。 9. The fluorinated polybenzimidazole membrane according to claim 8, characterized in that: The thickness of the fluorinated polybenzimidazole film is 5~100µm.

10. The application of the fluorinated polybenzimidazole membrane according to any one of claims 8-9 in the fields of flow batteries, fuel cells or water electrolysis for hydrogen production.

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