Preparation method of column [5] arene / polybenzimidazole high-temperature proton exchange membrane

Abstract

The invention relates to a preparation method of a column [5] arene / polybenzimidazole high-temperature proton exchange membrane, and belongs to the technical field of polymer chemistry and membrane materials. The method comprises the following steps: synthesizing functionalized pillararene through a strategy of first cyclization and then modification, and embedding the functionalized pillararene into a polybenzimidazole main chain through a condensation polymerization reaction to prepare the high-temperature proton exchange membrane, X-CP5-PBI mol% (X = 0, 2, 2.5, 3), and forming a continuous proton transmission channel to improve the proton conductivity. In addition, the column [5] arene cavity can contain phosphate to improve acid absorption and has excellent dimensional stability, and the problem that existing original PBI is high in acid absorption rate but large in swelling is solved. The prepared high-temperature proton exchange membrane has excellent proton conductivity, thermal stability and chemical stability and proper swelling ratio. The membrane has a wide application prospect in the aspect of practical application of fuel cells.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-temperature proton exchange membrane fuel cells and supramolecular macrocycles, and particularly relates to a preparation method and application of a functionalized pillar[5]arene modified polybenzimidazole high-temperature proton exchange membrane. TECHNICAL BACKGROUND

[0002] Fuel cells (PEMFC) are considered as one of the most potential energy conversion devices due to their clean, pollution-free, high energy conversion efficiency and other advantages. Among them, high-temperature proton exchange membrane fuel cells (HT-PEMFCs) have the advantages of simplified water and heat management, no need for complex humidification and drainage system, can avoid the problem of membrane dehydration at low temperature, and strong CO poisoning resistance of catalyst. High-temperature proton exchange membrane (HT-PEM) is an important component of high-temperature proton exchange membrane fuel cell (HT-PEMFC).

[0003] Polybenzimidazole (PBI) is a kind of high-performance aromatic heterocyclic polymer, which has excellent high-temperature resistance, mechanical strength and chemical stability, and is an ideal material for preparing high-temperature proton exchange membrane. However, the proton conduction sites of pure polybenzimidazole membrane are limited, and proton transmission groups need to be introduced through functional modification to improve the proton conduction performance under high-temperature conditions. In addition, although the proton conduction can be improved by increasing acid absorption, too high phosphoric acid absorption will lead to an increase in membrane volume and swelling rate. In recent years, significant progress has been made in the research on modification strategies for polybenzimidazole high-temperature proton exchange membrane.

[0004] Pillar arene as a new type of supramolecular macrocyclic compound has the advantages of rigid cavity structure, easy functional modification and good thermal stability, and its unique molecular structure can construct host-guest interaction and ion transmission channel, providing a new way for proton exchange membrane modification. In the prior art, functionalized pillar arene is introduced into the polymer matrix mainly through physical blending, which has the problems of uneven dispersion and poor interfacial compatibility. Therefore, embedding pillar arene into the polybenzimidazole main chain through condensation reaction is a preparation method for realizing the synergistic optimization of structure and performance.

[0005] The reason why we choose pillar[5]arene to improve the performance of PA-PBI membrane is that research has found that by introducing different molar ratios of pillar arene to obtain modified membranes with different proton conduction, the proton conduction of PA-PBI membrane is improved to 1.9 times that of the original membrane, especially the introduction of pillar arene forms a continuous proton transmission channel, which effectively improves the proton conduction performance. The improvement of proton migration significantly improves the performance of the battery. Overall, pillar arene enhances the proton conductivity and battery performance.

[0006] Although the existing high-temperature proton exchange membrane improves the PA absorption rate and the proton conduction performance through modification strategies, it still cannot meet the long-term use requirements in terms of size stability and the like while having high phosphoric acid absorption. Therefore, it is urgent to develop a relatively optimal high-temperature proton exchange membrane. SUMMARY

[0007] In view of the existing situation, the application provides a high-temperature proton exchange membrane, a preparation method and application thereof, and at least one of the above technical problems is solved.

[0008] The technical scheme provided by the application is: a high-temperature proton exchange membrane, which realizes chemical combination of a pillar arene and a polybenzimidazole through a main chain copolymerization strategy, significantly improves the high-temperature proton conduction performance, phosphoric acid absorption capacity and size stability of the membrane material.

[0009] The pillar [5] arene is functionalized to obtain a carboxyl pillar [5] arene.

[0010] Further, different proportions of pillar arenes can be introduced to be chemically combined with the polybenzimidazole.

[0011] Further, the proportion of the pillar arene in the polybenzimidazole is 0%, 2%, 2.5%, 3% or 5% of the molar ratio, respectively.

[0012] The technical scheme provided by the application is: a preparation method of the high-temperature proton exchange membrane applicable in the hydrogen-oxygen fuel cell, comprising the following steps:

[0013] (1) Synthesis of carboxyl pillar [5] arene monomer: a strategy of "ring formation first and then modification" is adopted, full-methoxyl pillar [5] arene is prepared first by bridging reaction of dimethoxybenzene and polyformaldehyde, then quinone is prepared by oxidation, phenolic hydroxyl is further reduced from quinone, ester group pillar arene is synthesized by nucleophilic substitution esterification reaction, and finally carboxyl pillar [5] arene is converted by alkaline hydrolysis reaction. The purity of the carboxyl pillar arene monomer is ensured, laying a foundation for the subsequent polymerization reaction.

[0014] (2) Further, the carboxyl pillar [5] arene is used as a comonomer to perform a polycondensation reaction with diphenyl diamine and isophthalic acid in a high-temperature environment, so that the pillar [5] arene is firmly embedded into the polybenzimidazole main chain through a covalent bond to improve the performance of the membrane.

[0015] (3) A preparation method of a pillar [5] arene / polybenzimidazole high-temperature proton exchange membrane, in the first step, the pillar [5] arene-containing polybenzimidazole polymer is dissolved in DMSO at room temperature to obtain a casting solution; in the second step, the casting solution obtained in the first step is spread on a film.

[0016] (4) Casting the casting solution on a clean glass plate of 8 cm x 8 cm, drying in an oven at 90 DEG C for 24 h to evaporate the solvent, to obtain a column [5] arene / polybenzimidazole high-temperature proton exchange membrane.

[0017] The second technical solution provided in the application is: application of the high-temperature proton exchange membrane in a hydrogen-oxygen fuel cell.

[0018] The application improves the conduction of the polybenzimidazole high-temperature proton exchange membrane. Because the column arene is introduced, the cavity has the ability to contain phosphate molecules, thereby enhancing the phosphate absorption capacity and proton conduction capacity of the polybenzimidazole high-temperature proton exchange membrane. At the same time, it can also promote the formation of a continuous proton transmission channel, and form a favorable environment for proton conduction. Compared with the conventional membrane, this unique supramolecular macrocycle structure helps to form a proton transmission channel to promote rapid proton transfer, while reducing the swelling of the membrane.

[0019] Compared with the prior art, the application has the following advantages: (1) Structural innovation, the column arene is embedded in the polybenzimidazole molecular chain by main chain copolymerization, realizing uniform distribution and chemical bonding of functional groups, solving the interface compatibility problem existing in physical blending, and improving the structural stability of the membrane material. (2) Performance synergy, the rigid cavity structure of the carboxyl column [5] arene constructs a continuous proton transmission channel, so that the proton conductivity of the membrane at 180 DEG C is 1.9 times that of the conventional membrane, the phosphate absorption rate is 398.15%, and the swelling is only 77.64%, improving the dimensional stability. (3) Process feasibility, the preparation process does not require special equipment, the prepared membrane material has a high thermal decomposition temperature, excellent thermal stability, high proton transmission capacity and phosphate absorption capacity, improves the dimensional stability of the membrane, and meets the application of high-temperature proton exchange membrane fuel cells. BRIEF DESCRIPTION OF DRAWINGS The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments of the present application and, together with the description, serve to explain the principles of the application. The drawings in the following description are some embodiments of the present application, not all embodiments.

[0020] Figure 1 SEM of a column [5] arene / polybenzimidazole high-temperature proton exchange membrane;

[0021] Figure 2 Thermogravimetric curve of a column [5] arene / polybenzimidazole high-temperature proton exchange membrane;

[0022] Figure 3 Phosphate absorption curve of a column [5] arene / polybenzimidazole high-temperature proton exchange membrane;

[0023] Figure 4 AFM image of a pillar[5]arene / polybenzimidazole high temperature proton exchange membrane;

[0024] Figure 5 Proton conductivity and activation energy of a pillar[5]arene / polybenzimidazole high temperature proton exchange membrane at different temperatures;

[0025] Figure 6 Hydrogen-oxygen fuel cell peak power density curve of a pillar[5]arene / polybenzimidazole high temperature proton exchange membrane;

[0026] Figure 7 Volume swelling ratio of a pillar[5]arene / polybenzimidazole high temperature proton exchange membrane; Specific implementation method:

[0027] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0028] Embodiment 1 includes the following steps:

[0029] 1. Dissolve 1,4-dimethoxybenzene (11.04 g, 79.9 mmol) and 7.2 g of paraformaldehyde ((CH2O)n) in dichloromethane (DCM, 500 ml) and place in a 1000 ml round bottom flask. After the reaction mixture is stirred for 30 min, carefully add boron trifluoride etherate (BF3·OEt2) (10 ml, 81.03 mmol) at 0°C and monitor by TLC spotting; when the reaction is completed, quench the reaction by adding sodium hydroxide (NaOH) and deionized water for 4 hours. After the quenching is completed, extract and wash with DCM three times, and then purify the crude product by silica gel column chromatography (PE:DCM=1:2) to obtain a white solid product. n

[0030] 2. Dissolve the product in step 1 (5 g, 6.7 mmol) in DCM (300 ml) and stir for activation. Then, add a solution of cerium ammonium nitrate (CAN) (7.4 g, 13.5 mmol) dropwise to the reaction solution. After the addition is completed, stop the reaction after stirring at room temperature for another 30 min. After the reaction is completed, extract with DCM, wash, and further purify by silica gel column chromatography (PE:DCM:EA=20:4:1) to obtain a red powder product. ​

[0031] 3. Dissolve the product of step 2 (5g, 7mmol) in DCM (200ml). Then, under vigorous stirring, add sodium dithionite (Na2S2O4) aqueous solution to the above solution. Stir until the solution turns white, stop the reaction, and wash and extract three times with DCM to remove the solvent. After obtaining the white powder product compound, weigh (12.6g, 17.5mmol), add it together with K2CO3 (46g, 0.33mol), a small spoon of KI and 120ml of acetonitrile into a 250ml double-necked flask. After removing water and oxygen from the reaction, fill the entire reaction system with nitrogen gas, add ethyl bromoacetate (8ml, 72mmol) dropwise under N2 protection, and reflux the reaction at 70℃ for 3 days. After the reaction stops, filter the impurities and wash with DCM to remove acetonitrile. Then, further purify by silica gel column chromatography (PE:DCM:EA = 20:1:1) to obtain column aromatics containing ester functional groups [5].

[0032] 4. In a pressure-resistant bottle, the ester-based [5] aromatic hydrocarbon (1.5 g, 1.7 mmol) obtained in step 3 was mixed with 30% NaOH (16 ml) and 16 ml ethanol, and then reacted at 90 °C for 24 hours. After the reaction was completed, deionized water was added, and the solution turned brownish-red and transparent. After removing the ethanol from the solution, hydrochloric acid was added dropwise to the solution, and a solid precipitate was produced. The reaction was stopped when no more solid precipitate was produced after adding hydrochloric acid. After centrifugation at 10000 r / min for 3 min and vacuum drying, the grayish-white powder product carboxyl [5] aromatic hydrocarbon (CP5) was finally obtained.

[0033] 5. First, under a nitrogen atmosphere, 77g of polyphosphoric acid (PPA) was poured into a four-necked flask, and the temperature was gradually increased to 140℃ with stirring to ensure the polyphosphoric acid was fully heated and stirred. Then, 3g of 3,3′,4,4′-biphenyltetramine (DAB) was added, and the mixture was stirred for 2 hours to ensure homogeneity. Next, functionalized carboxylated columnar aromatics (CP5), isophthalic acid (IPA, 99%), and phosphorus pentoxide (P2O5, 98.5%) were added, and after thorough mixing, the temperature was increased to 200℃ until polymerization was complete. The product in the flask was poured into a saturated sodium bicarbonate (NaHCO3) solution and boiled in deionized water for 3 days to remove residual PPA and balance the pH. Finally, it was dried in an oven to obtain the final polymer X-CP5-PBI. Where X (X = 2%, 2.5%, 3%) represents the molar percentage of CP5. X = 0% corresponds to a pure membrane without the introduction of CP5, with a meta-polybenzimidazole (m-PBI) as the control group.

[0034] 6. A homogeneous casting solution was prepared by dissolving X-CP5-PBI (0.25 g) from step 5 in 15 ml of dimethyl sulfoxide (DMSO) at room temperature.

[0035] 7. The membranes were cast by slowly pouring the casting solution on a 8 cm x 8 cm smooth glass plate and dried in an oven at 90 °C for 24 h to evaporate the solvent and obtain the p- quaterphenyl / polybenzimidazole high temperature proton exchange membranes.

[0036] The SEM images of the surface and cross-section of the p-quaterphenyl / polybenzimidazole high temperature proton exchange membranes prepared in Example 1 are shown in Figure 1 From the SEM images, it can be observed that the surface of the obtained membranes is uniform, smooth and flat without obvious aggregation or surface defects, and the introduction of CP5 does not damage the integrity of the membranes. After the membranes are brittle fractured, it is found that the membranes exhibit a fish scale-like dense cross-section, which is a typical feature of PBI membranes.

[0037] The thermogravimetric curve of the p-quaterphenyl / polybenzimidazole high temperature proton exchange membranes prepared in Example 1 is shown in Figure 2 The test was carried out under nitrogen flow with a temperature range of 30 °C to 800 °C and a temperature rising rate of 10 °C / min. From the graph, it can be seen that the PBI membrane after the addition of p-quaterphenyl has excellent thermal stability.

[0038] The phosphoric acid absorption of the p-quaterphenyl / polybenzimidazole high temperature proton exchange membranes prepared in Example 1 is shown in Figure 3 From the graph, it can be seen that as the CP5 content increases, the PA absorption rate of the membranes also increases. The PA absorption rate of the 3% -CP5-PBI membrane is 398.15%, which is nearly 2 times the PA absorption rate of the m-PBI membrane. This is because the CP5 supramolecular cavity structure we introduced can accommodate most of the phosphoric acid molecules. The increase in CP5 content leads to an increase in the ability to absorb PA.

[0039] The AFM of the p-quaterphenyl / polybenzimidazole high temperature proton exchange membranes prepared in Example 1 is shown in Figure 4 From the graph, it can be seen that due to the introduction of CP5, the membranes have obvious continuous ion transmission channels, which can improve the proton transmission efficiency.

[0040] The conductivity and activation energy of the p-quaterphenyl / polybenzimidazole high temperature proton exchange membranes prepared in Example 1 are shown in Figure 5 The test was completed on a SP-300 electrochemical workstation. From the graph, it can be seen that the proton conductivity of all the membranes increases with the increase of temperature. In addition, the proton conductivity of the m-PBI membrane at 180 °C is 46.26 mS cm -1With the increase of the content of CP5, the proton conductivity of the membrane is enhanced. The proton conductivity of the 3%-CP5-PBI membrane with the highest content of CP5 reaches 90.10 mS cm-1, which is almost twice that of the m-PBI membrane. In addition, the activation energy Ea of the 3%-CP5-PBI membrane is 19.16 kJ / mol, and the activation energy Ea of the m-PBI membrane is 19.86 kJ / mol. The activation energy value of the 3%-CP5-PBI membrane is lower, the proton jump of the membrane is easier, and the proton is more easily transmitted.

[0041] The hydrogen-oxygen fuel cell of the pillar [5] arene / polybenzimidazole high-temperature proton exchange membrane prepared in Embodiment 1 is shown in Figure 6 The open-circuit voltage of all the membranes is higher than 0.9 V, which indicates that the membranes have good gas tightness, and the open-circuit voltage of the obtained membrane is improved after the introduction of CP5, which can effectively prevent the penetration of gas. At 160℃, the peak power density of the m-PBI membrane is 151.72 mW cm -2 , and the peak power density is improved after the introduction of CP5. Among them, the peak power density of the 3%-CP5-PBI membrane is the largest, which is 355.47 mW cm -2 at a current density of 1116.1 mA cm -2 , which is 2.3 times that of the m-PBI membrane. The advantage of the X-CP5-PBI (X=2%, 2.5% and 3%) series of membranes in the power density is due to the fact that the CP5 cavity can accommodate phosphoric acid molecules, which helps to absorb and retain PA, thereby enhancing the proton conductivity and improving the peak power density.

[0042] The volume swelling rate of the pillar [5] arene / polybenzimidazole high-temperature proton exchange membrane prepared in Embodiment 1 is shown in Figure 7 From the figure, it can be seen that the volume swelling rate of m-PBI is too high (141.15%). This is because a large number of PA molecules enter the membrane, increasing the spacing between the molecular chains of the polymer, resulting in significant swelling of the membrane. However, after the introduction of CP5, the supramolecular macrocyclic cavity of the pillar arene does not significantly increase the spacing between the molecular chains of PBI, thereby reducing the swelling of the membrane, and the swelling rate is only 77.64%.

[0043] In summary, a pillar [5] arene / polybenzimidazole type high-temperature proton exchange membrane is prepared in the present application. By introducing the pillar arene, a continuous ion transmission channel is formed, which effectively enhances the proton conductivity and acid absorption capacity of the membrane, while reducing the volume swelling of the membrane.

[0044] The above-described content can be implemented individually or in various combinations, and these variations are within the scope of protection of the present application.

[0045] The above is further detailed description of the present application in combination with specific preferred embodiments, and cannot be deemed as limitation of the specific embodiments of the present application. For those skilled in the art of the present application, without departing from the concept of the present application, a number of simple deductions or substitutions can be made, which shall be deemed as falling within the protection scope of the present application.

Claims

1. A method for preparing a pillar[5]arene / polybenzimidazole high-temperature proton exchange membrane, characterized by The method comprises the following steps: I. Preparation of functional carboxyl pillar[5]arene: The carboxyl pillar[5]arene is prepared by the strategy of "forming ring first and then modifying", which lays the foundation for subsequent polymerization. II. Embedding pillar[5]arene into polybenzimidazole polymerization by condensation polymerization: Under nitrogen atmosphere, 77g of polyphosphoric acid (PPA) is poured into a four-necked flask and heated to 140℃ under stirring to heat and stir the polyphosphoric acid. Then 3g of 3,3',4,4'-diaminobiphenyl (DAB) is added and the mixture is stirred for 2 hours to mix uniformly. Next, the functional carboxyl pillar[5]arene (CP5), isophthalic acid (IPA, 99%) and phosphorus pentoxide (P2O5, 98.5%) are added, and the mixture is heated to 200℃ until the polymerization is completed. The product in the flask is poured into a saturated sodium bicarbonate (NaHCO3) solution, and deionized water is boiled for 3 days to remove residual PPA to balance the pH value. Finally, the oven is used to dry the final polymer X-CP5-PBI. Wherein X (X=2%, 2.5%, 3%) represents the molar percentage of CP5. X=0% corresponds to a pure film without CP5, and a meta-polybenzimidazole (m-PBI) is used as a control group. III. Preparation of a pillar[5]arene / polybenzimidazole high-temperature proton exchange membrane: The first step is to prepare a pillar[5]arene / polybenzimidazole casting solution; the second step is to cast and lay the film of the casting solution prepared in the first step to obtain a series of high-temperature proton exchange membranes X-CP5-PBI (X=0%, 2%, 2.5%, 3%).

2. The synthesis of a high temperature proton exchange membrane, a pillar[5]arene / polybenzimidazole proton exchange membrane according to claim 1, characterized by The raw materials in step II are 77g of polyphosphoric acid (PPA), 3g of 3,3',4,4'-diaminobiphenyl (DAB), isophthalic acid (IPA, 99%), phosphorus pentoxide (P2O5, 98.5%) and sodium bicarbonate (NaHCO3), all of which are from Aladdin Pharmaceutical.

3. The method for preparing a pillar[5]arene / polybenzimidazole high-temperature proton exchange membrane according to claim 1, characterized in that, The solvent used in step III above is DMSO.

4. The method for preparing a pillar[5]arene / polybenzimidazole high-temperature proton exchange membrane according to claim 1, characterized in that, The specific operation steps for laying the film in step III above are as follows: The casting solution is slowly poured onto a smooth glass plate of 8cm×8cm using the casting method, and dried in an oven at 90℃ for 24h to evaporate the solvent, thereby obtaining a pillar[5]arene / polybenzimidazole high-temperature proton exchange membrane.

5. The molar ratio of pillar[5]arene in the proton exchange membrane mentioned in claim 1 is 0%, 2%, 2.5% and 3% respectively.

6. The high-temperature proton exchange membrane according to any one of claims 1-5 is used in a hydrogen-oxygen fuel cell.

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