High-temperature proton exchange membrane for fuel cell and preparation method therefor

Abstract

The present invention provides a high-temperature proton exchange membrane (HT-PEM) for a fuel cell and a preparation method therefor. The HT-PEM is prepared by means of a cross-linking reaction of specific polybenzimidazole and imidazole ionic liquid. By means of the structural design of a nitrogen-containing bulky group in the polybenzimidazole and the introduction of the bulky side group-substituted imidazole ionic liquid, the free volume is improved, the phosphoric acid doping amount and the phosphoric acid retention amount are increased, and proton conduction is promoted. A cross-linked network is constructed by using the cross-linking method, so that the phosphoric acid doping amount and the retention capacity are improved while the creep resistance, mechanical properties, and swelling resistance of the membrane material are enhanced. The dependence of the membrane material on the phosphoric acid doping amount is reduced by utilizing the promoting effect of the polyionic liquid on proton conduction, so that high proton conductivity can be obtained at a low phosphoric acid doping amount; and in addition, by means of the ionic interaction between the polyionic liquid and the phosphoric acid, the interaction between phosphoric acid molecules and a system is enhanced, thereby obtaining a HT-PEM having excellent phosphoric acid retention capacity.

Description

High temperature proton exchange membrane for fuel cell and preparation method thereof TECHNICAL FIELD

[0001] The present application belongs to the technical field of fuel cells, and more particularly relates to a high temperature proton exchange membrane for fuel cells and a preparation method thereof. BACKGROUND

[0002] Proton exchange membrane fuel cells (PEMFC) combine high power density, high energy efficiency and environmental friendliness, and are considered one of the most promising energy conversion technologies. However, strict operating conditions lead to complex heat / water management and low catalyst efficiency, limiting the application of proton exchange membrane fuel cells. At present, high temperature proton exchange membrane fuel cells (HT-PEMFC) operate in a water-free environment at high temperatures of 100-200℃, which can effectively solve these problems and thus provide a possible way for the development of fuel cells. As a core component, the high temperature proton exchange membrane (HT-PEM) has the functions of conducting protons and blocking fuel, and it must have sufficient mechanical strength, thermal stability and proton conductivity to meet the use requirements in a water-free environment.

[0003] The high temperature proton exchange membrane (PA-PBI) prepared by doping phosphoric acid in polybenzimidazole polymer has become the most potential candidate membrane material for HT-PEMFC due to its high proton conductivity, excellent thermal mechanical properties and thermal chemical stability in high temperature and low humidity operating environment. In order to obtain excellent proton conduction capacity in a high temperature and low humidity environment, PBI membrane material usually needs to be treated with a large amount of phosphoric acid doping. However, a very high level of phosphoric acid doping often leads to a decrease in the mechanical properties of the membrane material due to the "strong plasticizing" effect of phosphoric acid molecules. In addition, the incorporation of a large amount of phosphoric acid makes the phosphoric acid supersaturated and in a free state. The free state phosphoric acid molecules are prone to migrate and lose under external force, which leads to a significant decrease in proton conductivity and seriously affects the durability of the equipment. In summary, the key to the current commercial application research of HT-PEM is to develop a membrane with both high proton conductivity and good mechanical properties, and to improve its retention capacity for phosphoric acid.

[0004] Patent CN202211268613.4 uses fluoroalkene, perfluoro vinyl phosphonate monomer and two different structure perfluoro vinyl ether sulfuryl fluoride monomers for tetramer copolymerization, and combines porous fibers and antioxidant additives to prepare a high-temperature perfluoro sulfonic acid proton exchange membrane. The structure of this membrane fixes the phosphonic acid group on the side chain of the polymer, which can improve the phosphonic acid retention capacity, but the skeleton structure of the fluorine-containing alkene determines that it is only suitable for medium temperature (120-150℃), and the size changes greatly when it runs at higher temperature. In addition, the cost of fluorine-containing polymer is high, which is not conducive to industrial production. Patent CN202211706565.2 uses 2,6-pyridine dimethyl alcohol to crosslink polybenzimidazole to prepare a phosphoric acid doped polybenzimidazole proton exchange membrane. The introduction of pyridine ring with Lewis base N atom in the crosslinked structure can form interaction with phosphoric acid molecules, and the crosslinked structure can greatly improve the mechanical properties and dimensional stability of the membrane, which can effectively improve the phosphoric acid doping amount and retention capacity. Simply fixing the phosphonic acid group on the side chain of the polymer has strong phosphonic acid retention capacity, but it greatly reduces the movement ability of the phosphonic acid group, which is not conducive to proton conduction in the membrane, resulting in low proton conductivity. Patent CN202310326448.1 crosslinks poly(pentenyl 1,4-diazabicyclo[2.2.2]octane-1-ium bromide) and bromomethyl polyarylether ketone to prepare a polyarylether ketone / polyionic liquid crosslinked composite high-temperature proton exchange membrane. The strong adsorption of ionic liquid to phosphoric acid improves the phosphoric acid retention capacity. In addition, the crosslinked structure greatly improves the mechanical properties and dimensional stability of the membrane. At present, the traditional small molecule crosslinking agent for PBI crosslinking modification has certain shortcomings. When it consumes the basic imidazole site on the PBI molecular chain, the crosslinking network is often too tight due to the small molecular volume. Although this can improve the mechanical properties of the material, it will significantly reduce the proton conductivity, which may cause serious performance degradation in actual battery applications. SUMMARY

[0005] The purpose of the present application is to overcome the above shortcomings, provide a high-temperature proton exchange membrane for fuel cells and a preparation method thereof. The structure design of the polybenzimidazole bulky group and the introduction of the bulky side group substituted imidazole ionic liquid improve the free volume, increase the phosphoric acid doping amount and retention amount, and promote proton conduction. The crosslinking method is used to construct a crosslinking network, increase the anti-creep property of the membrane material, further improve the mechanical properties of the membrane, and improve the phosphoric acid doping amount and retention capacity.

[0006] To achieve the above purpose, the present application is realized by the following technical scheme:

[0007] The present application provides a high-temperature proton exchange membrane for fuel cells, which is prepared by crosslinking reaction of polybenzimidazole and imidazole ionic liquid. The crosslinking reaction is composed of substitution reaction of halogenated alkyl and N-H and polymerization reaction of olefin bond.

[0008] The polybenzimidazole has a general structure of:

[0009] wherein p = 50-200; R is any one of preferably R is

[0010] The imidazole ionic liquid has a general structure of:

[0011] wherein R1, R2, R3 are independently selected from H, C1-C6 alkyl group, any one of m, n is any integer of 0, 1, 2, 3.

[0012] It is to be noted that in the above general structure of the present application, the dotted line on the benzene ring represents a covalent bond.

[0013] Further, the polybenzimidazole is prepared by reacting 3,3'-diaminobenzidine, polyphosphoric acid, dicarboxylic acid and phosphorus pentoxide, wherein the dicarboxylic acid has a general structure of HOOC-R-COOH.

[0014] Further, the imidazole ionic liquid is prepared by reacting bromoalkylamine, diketone, aldehyde, ammonium acetate, sodium dihydrogen phosphate and bromoalkene; wherein:

[0015] The diketone has a general structure of:

[0016] The aldehyde has a general structure of R1-CHO.

[0017] The present application also provides a preparation method of the high-temperature proton exchange membrane for fuel cells, comprising:

[0018] Dissolving the polybenzimidazole and the imidazole ionic liquid in DMSO (dimethyl sulfoxide), and heating to 75-85℃ for 24-30h;

[0019] Adding an initiator to obtain a mixed solution;

[0020] Casting the mixed solution on a flat plate and drying for 24-30h to prepare a membrane.

[0021] Further, the prepared membrane needs to be further dried at 110℃; then, the membrane is soaked in 5M NaOH for alkalization treatment, taken out after 24h, and soaked in deionized water for 24h to remove excess NaOH; finally, the membrane is soaked in 85wt% phosphoric acid solution at 160℃ for 24h for phosphoric acid doping treatment.

[0022] Further, the mass ratio of the polybenzimidazole and the imidazole ionic liquid is (2.5-10):1.

[0023] Further, the preparation method of the polybenzimidazole comprises:

[0024] 3,3'-diaminobenzidine is dissolved in polyphosphoric acid under the atmosphere of N2 at 130-150°C, then dicarboxylic acid and phosphorus pentoxide are added under continuous stirring to obtain a mixture;

[0025] The temperature of the mixture is orderly heated to 190-200°C and kept for 5-6h to obtain a polymer solution. The obtained polymer solution is poured into distilled water, neutralized by sodium bicarbonate (NaHCO3), filtered, and then dried in an oven for standby.

[0026] Further, the molar ratio of the 3,3'-diaminobenzidine, the dicarboxylic acid and the phosphorus pentoxide is (1-1.5):(1-1.5):(1.3-1.7), preferably 1:1:1.3.

[0027] Further, the synthesis route of the imidazole ionic liquid is as shown below:

[0028] wherein, m, n = 0, 1, 2, 3;

[0029] The preparation method comprises:

[0030] The bromoalkyl amine, the diketone, the aldehyde, the ammonium acetate and the sodium dihydrogen phosphate are dissolved in an organic solvent, stirred at 0°C for 1.5-2.5h, and then continuously stirred at 55-65°C for 22-28h to synthesize the bromoimidazole compound.

[0031] The bromoimidazole compound is dissolved in tetrahydrofuran, the bromoalkene is added, and the reaction is stirred at 55-65°C for 22-28h to synthesize the imidazole ionic liquid.

[0032] Further, after the synthesis reaction of the bromoimidazole compound is completed, the reaction solution needs to be cooled to room temperature, filtered, and the filtrate is concentrated under reduced pressure, and then purified by extraction and recrystallization.

[0033] Further, the molar ratio of the bromoalkyl amine, the diketone, the aldehyde, the ammonium acetate, the sodium dihydrogen phosphate and the bromoalkene is (0.5-0.75):(1-1.5):(1-1.5):(1-1.5):(0.2-0.3):(1-1.5), preferably 0.5:1:1:1:0.2:1.

[0034] Further, the molar ratio of the bromoimidazole compound and the bromoalkene is (1-1.5):(1-1.5), preferably 1:1.

[0035] Further, the reaction solution needs to be cooled to room temperature after the synthesis reaction of the imidazole ionic liquid is completed, and the solvent is removed by reduced pressure distillation.

[0036] Preferably, the preparation method of the high-temperature proton exchange membrane for fuel cells specifically comprises the following steps:

[0037] (1) Synthesis of imidazole ionic liquid:

[0038] The bromoalkyl amine, diketone, aldehyde, ammonium acetate, and sodium dihydrogen phosphate are dissolved in a methanol solvent to synthesize an imidazole compound substituted with a bromoalkyl group through a Radziszewski reaction: first, the reaction mixture is stirred at 0°C for 2 h, and then stirred at 60°C for 24 h. After the reaction is completed, the reaction solution is cooled to room temperature, filtered, and the filtrate is concentrated under reduced pressure to obtain a crude imidazole precursor. The crude imidazole precursor is further purified by extraction and recrystallization to obtain an imidazole precursor for use in the next step.

[0039] The imidazole precursor is dissolved in THF, and then a bromoalkene is added for quaternary ammonium reaction to synthesize an imidazole ionic liquid. The reaction solution is stirred at 60°C for 24 h. After the reaction is completed, the reaction solution is cooled to room temperature, and the solvent is removed by reduced pressure distillation to obtain the imidazole ionic liquid.

[0040] (2) Synthesis of polybenzimidazole:

[0041] 3,3'-diaminobenzidine (DAB) is dissolved in polyphosphoric acid (PPA) at 140°C under N2 atmosphere, and then dicarboxylic acid and phosphorus pentoxide (P2O5) are added under continuous stirring. The temperature of the mixture is sequentially heated to 190-200°C and maintained for 5-6 h. It is observed that the solution becomes viscous, and then poured into distilled water. The polymer is neutralized with sodium bicarbonate (NaHCO3), filtered, and then placed in an oven to dry the water.

[0042] (3) Preparation of high-temperature proton exchange membrane:

[0043] A certain amount of polybenzimidazole (PBI) and imidazole ionic liquid (imidazole ionic liquid:PBI = 10wt%, 20wt%, 30wt%, 40wt%) are dissolved in DMSO; then, the solution is transferred to a flask under stirring, and the temperature is raised to 80°C for 24 h; subsequently, 1wt% of initiator (AIBN) is mixed, and the solution is cast on a glass plate at 90°C for drying for 24 h to prepare a membrane; the prepared membrane needs to be further dried at 110°C; then, the membrane is soaked in 5M NaOH for alkalization treatment, taken out after 24 h, and soaked in deionized water for 24 h to remove excess NaOH; finally, the membrane is soaked in an 85wt% phosphoric acid solution at 160°C for 24 h.

[0044] Compared with the prior art, the application has the following beneficial effects:

[0045] The high-temperature proton exchange membrane for fuel cells provided by the application is crosslinked by specific polybenzimidazole and imidazole ionic liquid, the structure design of the nitrogen bulky group of the polybenzimidazole modifies the main chain of the polymer, can provide a twisted three-dimensional structure for the polymer chain to increase the free volume, thereby obviously inhibiting the size swelling caused by the increase of the phosphoric acid doping amount; the imidazole ionic liquid with the bulky side group is combined to increase the free volume, increase the phosphoric acid doping amount and the phosphoric acid retention amount, and promote the proton conduction; meanwhile, the crosslinking method is used to construct a crosslinking network, the phosphoric acid doping amount and the retention capacity are increased while the anti-creep property, the mechanical property and the anti-swelling capacity of the membrane material are enhanced;

[0046] The imidazole ionic liquid with a double bond is synthesized by the reaction of a bromoalkene and a bromoimidazole compound, and the reaction site is provided for the next crosslinking reaction; the polyionic liquid (imidazole ionic liquid) is used to promote the proton conduction, the dependence of the membrane material on the phosphoric acid doping amount is reduced, and the high proton conductivity under the low phosphoric acid doping amount is obtained; meanwhile, the polyionic liquid and the phosphoric acid are ionically interacted, the interaction force between the phosphoric acid molecules and the system is increased, and the HT-PEM with excellent phosphoric acid retention capacity is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0047] Fig. 1 is a structural formula of the imidazole ionic liquid crosslinked PA-PBI high-temperature proton exchange membrane provided by the application, wherein x = 50-200;

[0048] Fig. 2 is a nuclear magnetic hydrogen spectrum of the imidazole ionic liquid 1-bromoethyl-2-methyl-3-alkenylbutyl-4,5-diphenylimidazole bromide salt described in Example 1. DETAILED DESCRIPTION

[0049] The preferred embodiments of the application will be described in more detail below with reference to the drawings and specific examples.

[0050] The application provides a high-temperature proton exchange membrane for fuel cells, which is an imidazole ionic liquid crosslinked PA-PBI high-temperature proton exchange membrane prepared by crosslinking reaction of polybenzimidazole and imidazole ionic liquid, and a structural formula thereof is shown in Fig. 1, wherein m, n = 0, 1, 2, 3.

[0051] R: any one selected from the group consisting of

[0052] R1, R2, R3 are independently selected from any one of H, C1-C6 alkyl group,

[0053] Specifically, the following examples can be referred to. ​​

[0054] Example 1

[0055] This example provides a high temperature proton exchange membrane for fuel cells (HTPEM-1), which is prepared as follows:

[0056] (1) Synthesis of polybenzimidazole (m-PBI) (R is derived from isophthalic acid):

[0057] 3,3'-diaminobenzidine (DAB) (2.14 g, 0.01 mol) was dissolved in polyphosphoric acid (PPA) (200 g) at 140 °C under N2atmosphere; then isophthalic acid (PIA) (1.66 g, 0.01 mol) and phosphorus pentoxide (1.89 g, 0.013 mol) were added under continuous stirring; the temperature of the mixture was sequentially heated to 200 °C and maintained for 5 h; it was observed that the solution became viscous, which was then poured into distilled water; the polymer was then neutralized with a bicarbonate solution, filtered, and then placed in an oven to dry the water.

[0058] (2) Synthesis of imidazole ionic liquid 1-bromoethyl-2-methyl-3-alkenylbutyl-4,5- diphenylimidazole bromide salt:

[0059] Acetaldehyde (0.88 g, 0.02 mol), benzil (4.2 g, 0.02 mol), bromoethylamine (1.24 g, 0.01 mol), ammonium acetate (1.51 g, 0.02 mol) and sodium dihydrogen phosphate (0.48 g, 0.004 mol) were dissolved in methanol (80 mL), then the reaction mixture was stirred at 0 °C for 2 h, and then at 60 °C for 24 h. After the reaction was completed, the reaction liquid was cooled to room temperature, filtered, and the filtrate was concentrated under reduced pressure to obtain the imidazole precursor 1-bromoethyl-2-methyl-4,5-diphenylimidazole, which was further purified by extraction and recrystallization.

[0060] 1-bromoethyl-2-methyl-4,5-diphenylimidazole (6.82 g, 0.02 mol) was dissolved in THF, and then 6-bromobutene (2.70 g, 0.02 mol) was added to synthesize the imidazole ionic liquid by quaternary ammonium reaction. The reaction liquid was stirred at 60 °C for 24 h. After the reaction was completed, the reaction liquid was cooled to room temperature, and the solvent was removed by distillation under reduced pressure to obtain the imidazole ionic liquid 1-bromoethyl-2-methyl-3-alkenylbutyl-4,5-diphenylimidazole bromide salt. Its nuclear magnetic hydrogen spectrum is shown in Figure 2.

[0061] (3) Preparation of high temperature proton exchange membrane (HTPEM-1): 1 g of m-PBI and 0.1 g of 1-bromoethyl-2-methyl-3-alkylbutyl-4,5-diphenylimidazole bromide salt were dissolved in DMSO; then, the solution was transferred to a flask under stirring, the temperature was raised to 80 °C for 24 h; subsequently, 1 wt% of initiator (AIBN) was mixed, and the solution was cast on a glass plate at 90 °C for 24 h to prepare a film; the prepared film needs to be further dried at 110 °C; then, the film was soaked in 5M NaOH for alkalization treatment, taken out after 24 h, and soaked in deionized water for 24 h to remove excess NaOH; finally, it was soaked in 85 wt% phosphoric acid solution at 160 °C for 24 h.

[0062] Example 2

[0063] This example provides a high temperature proton exchange membrane (HTPEM-2) for fuel cells, which is prepared as follows:

[0064] (1) Synthesis of polybenzimidazole (3,5-PPBI):

[0065] 3,3'-diaminobenzidine (DAB) (2.14 g, 0.01 mol) was dissolved in polyphosphoric acid (PPA) (200 g) at 140 °C under N2 atmosphere; then pyridine-3,5-dicarboxylic acid (1.67 g, 0.01 mol) and phosphorus pentoxide (1.89 g, 0.013 mol) were added under continuous stirring. The temperature of the mixture was sequentially heated to 200 °C and maintained for 5 h. It was observed that the solution became viscous, then poured into distilled water; the polymer was neutralized with sodium bicarbonate, filtered, and then placed in an oven to dry the water.

[0066] (2) Synthesis of imidazole ionic liquid 1-bromohexyl-2-phenyl-3-alkylhexyl-4,5- dimethylimidazole bromide salt:

[0067] Benzaldehyde (2.12 g, 0.02 mol), 2,3-butanedione (1.72 g, 0.02 mol), 6-bromohexylamine (3.60 g, 0.01 mol), ammonium acetate (1.51 g, 0.02 mol) and sodium dihydrogen phosphate (0.48 g, 0.004 mol) were dissolved in methanol (80 mL), then the reaction mixture was stirred at 0 °C for 2 h, and then continued to be stirred at 60 °C for 24 h. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, and the filtrate was concentrated under reduced pressure to obtain the imidazole precursor 1-bromohexyl-2-phenyl-4,5-dimethylimidazole, which was further purified by extraction and recrystallization.

[0068] The imidazolium ionic liquid was synthesized by dissolving 1-bromohexyl-2-phenyl-4,5-dimethylimidazole (6.68 g, 0.02 mol) in THF and then adding 6-bromohexene (3.26 g, 0.02 mol) for quaternary ammonium reaction. The reaction solution was stirred at 60°C for 24 h. After the reaction was completed, the reaction solution was cooled to room temperature, and the solvent was removed by distillation under reduced pressure to obtain the imidazolium ionic liquid 1-bromohexyl-2-phenyl-3-alkenylhexyl-4,5-dimethylimidazole bromide.

[0069] (3) Preparation of high temperature proton exchange membrane (HTPEM-2): 1 g of 3,5-PPBI and 0.2 g of 1-bromohexyl-2-phenyl-3-alkenylhexyl-4,5-dimethylimidazole bromide bromide were dissolved in DMSO; then, the solution was transferred to a flask under stirring, the temperature was raised to 80°C for 24 h; subsequently, 1 wt% of initiator (AIBN) was mixed, and the solution was cast on a glass plate at 90°C for 24 h to prepare a film; the prepared film needs to be dried at 110°C; then, the film was soaked in 5M NaOH for alkalization treatment, taken out after 24 h, and soaked in deionized water for 24 h to remove excess NaOH; finally, it was soaked in 85 wt% phosphoric acid solution at 160°C for 24 h.

[0070] Example 3

[0071] This example provides a high temperature proton exchange membrane (HTPEM-3) for fuel cells, which is prepared as follows:

[0072] (1) Synthesis of polybenzimidazole (BPY-PBI):

[0073] 3,3'-diaminobenzidine (DAB) (2.14 g, 0.01 mol) was dissolved in polyphosphoric acid PPA (250 g) at 140°C under N2 atmosphere; then, 4,4-[(4,4-bipyridine)-2,6-diyl]dibenzoic acid monomer (3.96 g, 0.01 mol) and phosphorus pentoxide (1.89 g, 0.013 mol) were added under continuous stirring. The temperature of the mixture was sequentially heated to 200°C and maintained for 5 h; it was observed that the solution became viscous, and then it was poured into distilled water; the polymer was neutralized with sodium bicarbonate, filtered, and then placed in an oven to dry the water.

[0074] (2) Synthesis of imidazolium ionic liquid 1-bromobutyl-2-butyl-3-alkenylhexyl-4,5-dimethylimidazole bromide:

[0075] Butyraldehyde (1.44 g, 0.02 mol), 2,3-butanedione (1.72 g, 0.02 mol), bromobutylamine (1.52 g, 0.01 mol), ammonium acetate (1.51 g, 0.02 mol) and sodium dihydrogen phosphate (0.48 g, 0.004 mol) were dissolved in methanol (100 mL), then the reaction mixture was stirred at 0 °C for 2 h, and then at 60 °C for 24 h. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, and the filtrate was concentrated under reduced pressure to obtain the imidazole precursor 1-bromobutyl-2-butyl-4,5-dimethylimidazole, which was further purified by extraction and recrystallization.

[0076] 1-bromobutyl-2-butyl-4,5-dimethylimidazole (5.72 g, 0.02 mol) was dissolved in THF, and then 6-bromohexene (3.26 g, 0.02 mol) was added to perform quaternary ammonium reaction to synthesize the imidazole ionic liquid. The reaction solution was stirred at 60 °C for 24 h. After the reaction was completed, the reaction solution was cooled to room temperature, and the solvent was removed by distillation under reduced pressure to obtain the imidazole ionic liquid 1-bromobutyl-2-butyl-3-alkenylhexyl-4,5-dimethylimidazole bromide.

[0077] (3) Preparation of high temperature proton exchange membrane (HTPEM-3): 1 g of BPY-PBI and 0.4 g of 1-bromobutyl-2-butyl-3-alkenylhexyl-4,5-dimethylimidazole bromide were dissolved in DMSO; then, the solution was transferred to a flask under stirring, the temperature was raised to 80 °C, and maintained for 24 h; subsequently, 1 wt% of initiator (AIBN) was mixed, and the solution was cast on a glass plate at 90 °C and dried for 24 h to prepare a film; the prepared film was further dried at 110 °C; subsequently, the film was soaked in 5 M NaOH for alkalization treatment, taken out after 24 h, and soaked in deionized water for 24 h to remove excess NaOH. Finally, the film was soaked in 85 wt% phosphoric acid solution at 160 °C for 24 h.

[0078] Comparative Example 1

[0079] This comparative example provides a high temperature proton exchange membrane (HTPEM-0) for fuel cells, which is prepared as follows:

[0080] (1) Synthesis of polybenzimidazole (m-PBI):

[0081] DAB (2.14 g, 0.01 mol) was dissolved in polyphosphoric acid (PPA) (200 g) at 140 °C under N2atmosphere. Then, isophthalic acid (PIA) (1.66 g, 0.01 mol) and phosphorus pentoxide (1.89 g, 0.013 mol) were added under continuous stirring. The temperature of the mixture was sequentially heated to 200 °C and kept for 5 h. Subsequently, the solution became viscous and was poured into distilled water. The polymer was neutralized with bicarbonate solution, filtered, and then put into an oven to dry the water.

[0082] (2) Preparation of high temperature proton exchange membrane (HTPEM-0): 1 g of m-PBI was dissolved in DMSO, the solution was cast on a glass plate at 90 °C and dried for 24 h, finally, the prepared membrane needs to be further dried at 110 °C. Subsequently, the membrane was soaked in 5 M NaOH for alkalization treatment, taken out after 24 h, and then soaked in deionized water for 24 h to remove excess KOH. Finally, it was soaked in 85 wt% phosphoric acid solution at 160 °C for 24 h.

[0083] The high temperature proton exchange membranes prepared in the above examples and comparative examples were tested for performance, and the test methods were as follows:

[0084] 1. Mechanical property test:

[0085] Test method: Before testing, all samples were cut into 3 mm x 5 cm pieces. In the test, sandpaper was added to the clamps at both ends of the sample to increase friction. The tensile rate of the phosphoric acid doped membrane sample was 5 mm min -1 .

[0086] Instrument used: MTSC MT 8535 tensile testing machine

[0087] 2. Proton conductivity test:

[0088] Test method: The test used a four-electrode alternating current impedance method, with deionized water as the medium, a test frequency range of 1 Hz to 1 MHz, an amplitude of 10 mV, and a temperature of 170 °C.

[0089] The phosphoric acid doped membrane sample was cut into a size of 5 cm x 1 cm for proton conductivity testing.

[0090] Calculation formula: σ = L / (A x R), where L is the distance between the two electrodes, and A is the cross-sectional area of the membrane sample.

[0091] Instrument used: PARSTAT 3000A electrochemical workstation

[0092] 3. Phosphoric acid retention test:

[0093] The phosphoric acid doped membrane sample was exposed in a vacuum oven at 160℃, and was taken out after 400 hours, weighed, and the mass change was recorded.

[0094] The results of the above performance tests are shown in Table 1.

[0095] Table 1 Performance data of high temperature proton exchange membranes prepared in examples and comparative examples

[0096] As can be seen from the table, the tensile strength, proton conductivity and phosphoric acid retention capacity of the high temperature proton exchange membranes prepared in the examples of the present application all have obvious advantages compared with the comparative examples.

[0097] The above has described various embodiments of the present application, the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and technical principles of the described embodiments, and these modifications and changes should also be considered as the protection scope of the present application.

Claims

1. A high-temperature proton exchange membrane for fuel cells, characterized by, The high-temperature proton exchange membrane is made by cross-linking reaction of polybenzimidazole and imidazole ionic liquid, and the cross-linking reaction is composed of substitution reaction of haloalkyl and N-H and polymerization reaction of olefin bond. The polybenzimidazole has a general structure of: wherein p = 50-200; R is The general structure of the imidazole ionic liquid is: wherein R1, R2, R3are independently selected from H, C1-C6 alkyl groups, Any one of 0, 1, 2, 3; m, n is any integer of 0, 1, 2, 3.

2. The high-temperature proton exchange membrane for fuel cells according to claim 1, characterized by, The polybenzimidazole is prepared by reaction of 3,3'-diaminobenzidine, polyphosphoric acid, dicarboxylic acid and phosphorus pentoxide, wherein the dicarboxylic acid has a structural formula of HOOC-R-COOH.

3. The high-temperature proton exchange membrane for fuel cells according to claim 1, characterized by, The imidazole ionic liquid is prepared by reaction of bromoalkyl amine, diketone, aldehyde, ammonium acetate, sodium dihydrogen phosphate and bromoalkene; wherein: The structural formula of the diketone is: The aldehyde has a structural formula of R1-CHO.

4. A method for producing the high-temperature proton exchange membrane for fuel cells as claimed in any one of claims 1 to 3, characterized by, Comprising: Dissolve the polybenzimidazole and the imidazole ionic liquid in dimethyl sulfoxide, and heat to 75-85 DEG C, and keep for 24-30 h; Add an initiator to obtain a mixed solution; Pour the mixed solution on a flat plate and dry for 24-30 h to prepare a film.

5. The method for producing a high-temperature proton exchange membrane for fuel cells according to claim 4, characterized by, The mass ratio of the polybenzimidazole and the imidazole ionic liquid is (2.5-10):

1.

6. The method for producing a high-temperature proton exchange membrane for fuel cells according to claim 4, characterized by, The preparation method of the polybenzimidazole comprises: Dissolve 3,3'-diaminobenzidine in polyphosphoric acid at 130-150 DEG C under N2 atmosphere, then add dicarboxylic acid and phosphorus pentoxide under continuous stirring to obtain a mixture; Heat the temperature of the mixture to 190-200 DEG C and keep for 5-6 h to obtain the polybenzimidazole.

7. The method for producing a high-temperature proton exchange membrane for fuel cells according to claim 6, characterized by, The molar ratio of the 3,3'-diaminobenzidine, the dicarboxylic acid and the phosphorus pentoxide is (1-1.5):(1-1.5):(1.3-1.7).

8. The method for producing a high-temperature proton exchange membrane for fuel cells according to claim 6, characterized by, The preparation method of the imidazole ionic liquid comprises: Dissolve bromoalkyl amine, diketone, aldehyde, ammonium acetate and sodium dihydrogen phosphate in an organic solvent, stir at 0 DEG C for 1.5-2.5 h, then continue to stir at 55-65 DEG C for 22-28 h to synthesize a bromoimidazole compound; Dissolve the bromoimidazole compound in tetrahydrofuran, add bromoalkene, and stir at 55-65 DEG C for 22-28 h to synthesize the imidazole ionic liquid.

9. The method for producing a high-temperature proton exchange membrane for fuel cells according to claim 8, characterized by, The molar ratio of the bromoalkyl amine, the diketone, the aldehyde, the ammonium acetate, the sodium dihydrogen phosphate and the bromoalkene is (0.5-0.75):(1-1.5):(1-1.5):(1-1.5):(0.2-0.3):(1-1.5).

10. The method for producing a high-temperature proton exchange membrane for fuel cells according to claim 8, characterized by, The molar ratio of the bromoimidazole compound and the bromoalkene is (1-1.5):(1-1.5).

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