High temperature proton exchange membrane based on polyimide / sulfonated covalent organic framework and preparation method thereof

Abstract

This invention belongs to the field of polymer materials technology, specifically relating to a high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework and its preparation method. First, a proton-type ionic liquid is synthesized, followed by the synthesis of sulfonated COF. Then, both are added to a polyamic acid solution to obtain a membrane solution. The membrane solution is dried on a glass plate to form a film, which is then subjected to thermal imidization treatment to obtain the ion exchange membrane. This invention introduces sulfonated COF into the COF to prepare sulfonated COF. This sulfonated COF can form a hydrogen bond network with the PI framework, which not only improves the mechanical strength of the PI membrane but also enhances the compatibility between the two, promotes the uniform distribution of sulfonated COF in the PI, constructs continuous proton transport channels, and improves the membrane's conductivity. Furthermore, the hydrogen bonds formed between the sulfonated COF and the ionic liquid promote the absorption and retention of the ionic liquid. A high-temperature proton exchange membrane with high conductivity, high mechanical strength, and high chemical stability is thus prepared.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework and its preparation method. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) have broad application prospects in stationary power plants and transportation due to their high energy conversion efficiency, zero emissions, and fast start-up. Based on operating temperature, PEMFCs can be divided into low-temperature (60~90 ℃) and high-temperature (100~200 ℃) types. Compared to low-temperature PEMFCs, high-temperature proton exchange membrane fuel cells (HT-PEMFCs) have significant advantages such as fast electrode reaction kinetics, strong catalyst resistance to CO poisoning, and simplified hydrothermal management systems, making them an important development direction in this field. As the core component of HT-PEMFCs, the proton exchange membrane directly determines the battery's performance and lifespan. Developing proton exchange membrane materials that possess high conductivity, excellent thermal stability, and chemical stability at high temperatures is currently a key research focus.

[0003] Nafion membranes, based on perfluorosulfonic acid, are currently the most commercially successful proton exchange membranes. The numerous sulfonic acid groups within the membrane can form hydrated protons with water molecules, giving Nafion membranes excellent conductivity. However, when the operating temperature exceeds 100 °C, the water molecules within the membrane rapidly evaporate, drastically reducing the membrane's conductivity. Phosphoric acid has a high boiling point (212 °C), and phosphoric acid-doped polybenzimidazole membranes are currently the most widely used material in high-temperature proton exchange membranes. However, on the one hand, the complex synthesis and poor film-forming properties of polybenzimidazole limit its widespread commercial application; on the other hand, the extremely high plasticizing effect of phosphoric acid molecules on polymer membranes can lead to a loss of the membrane material's mechanical properties. Furthermore, due to the strong acidity of phosphoric acid, the polymer backbone degrades at high temperatures, making it difficult to meet the long-term stable use requirements of HT-PEMFCs. Therefore, there is an urgent need to develop novel polymer membrane materials and conductive media to meet the application needs of HT-PEMFCs.

[0004] Proton-type ionic liquids typically possess high vapor pressure and boiling point, exhibiting excellent thermal stability. Simultaneously, they possess good electrical conductivity, making them widely used in electrochemistry. Replacing phosphoric acid with proton-type ionic liquids holds promise for reducing the plasticizing effect on polymer electrolyte membranes.

[0005] Polyimide (PI) is a class of high-performance polymers with imide rings in the main chain, commonly used in gas separation and insulation materials. Due to its excellent thermal stability, chemical stability, mechanical strength, and film-forming properties, PI is a potential high-temperature proton exchange membrane material. However, research on modifying PI for use as a high-temperature proton exchange membrane material is still limited. This is because pure PI exhibits extremely high impedance, and its dense, conjugated framework structure is also unfavorable for the doping and retention of conductive media (such as phosphoric acid or proton-type ionic liquids). Summary of the Invention

[0006] The purpose of this invention is to provide a high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework and its preparation method. To achieve the above objective, the structural schematic of the high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework provided by this invention is shown in the following formula:

[0007] .

[0008] The specific preparation process is as follows:

[0009] (1) Synthesis of proton-type ionic liquids

[0010] 1-Ethylimidazole and dichloromethane as solvent were added to a round-bottom flask. Trifluoromethanesulfonic acid was slowly added (1 mL / min) under an ice-water bath. The reaction was continued for 2 h under the same conditions. Dichloromethane was removed by rotary evaporation. The crude product was then washed with anhydrous diethyl ether and finally dried to obtain 1-ethylimidazole trifluoromethanesulfonic acid ([EIM][TfO]), a proton-type ionic liquid. The molar ratio of 1-ethylimidazole to trifluoromethanesulfonic acid was 1:1.

[0011] (2) Synthesis of sulfonated COF

[0012] Terephthalaldehyde and melamine were dissolved in anhydrous dimethyl sulfoxide (DMSO) to prepare a reaction solution. The reaction solution was then stirred at high temperature under a nitrogen atmosphere. The crude product was subsequently washed sequentially with acetone, tetrahydrofuran, and dichloromethane, and centrifuged to obtain the COF structure of the target compound. The molar ratio of terephthalaldehyde to melamine was 3:2.

[0013] The prepared COF was then stirred and dispersed in an acetone solution of 1,4-butanesulfonyl lactone for reaction. The reaction solution was centrifuged to obtain a solid product, which was further washed with acetone and dried. The solid product was then stirred and dispersed in a sulfuric acid solution (0.05 mM, pH=4), and finally washed with deionized water until neutral. The target compound, sulfonated COF, was obtained. By changing the ratio of 1,4-butanesulfonyl lactone to COF, sulfonated COF with different degrees of sulfonation could be obtained; the molar ratio of 1,4-butanesulfonyl lactone to COF ranged from 4:1 to 1:1.

[0014] (3) Synthesis of polyamic acid

[0015] Under ice-water bath conditions, equimolar amounts of 5-amino-2-(4-aminophenyl)benzimidazole (APABI) and pyromellitic anhydride (PMDA) were mechanically stirred and dissolved in N,N dimethylacetamide (DMAc). The reaction was carried out under N2 protection. After the reaction solution became highly viscous, it was poured into deionized water to precipitate, yielding polyamic acid (PAA), an intermediate product of polyimide.

[0016] (4) Preparation of high-temperature proton exchange membranes based on polyimide / sulfonated covalent organic framework

[0017] The PAA from step (3) was redissolved in DMAc to obtain a 3 wt% polymer / DMAc solution. Then, the sulfonated COF from step (2) (1%–8% of the polymer mass) and the proton-type ionic liquid from step (1) (50%–200% of the polymer mass) were added to the polymer solution. After thorough stirring, a membrane solution was obtained. The membrane solution was poured onto a clean glass plate and dried to form a membrane. Finally, the membrane was subjected to thermal imidization under N2 protection to obtain a high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework. The thermal imidization treatment was controlled by a programmed temperature rise, with sintering at 100 °C, 200 °C, and 250 °C for 1 h each.

[0018] Covalent organic frameworks (COFs) possess high porosity and an ordered pore distribution. This invention introduces sulfonated COFs by introducing sulfonic acid groups. On one hand, this allows for the formation of a hydrogen bond network with the polyimide (PI) framework, enhancing the mechanical strength of the PI membrane and improving their compatibility. It also promotes the uniform distribution of sulfonated COFs within the PI, creating continuous proton transport channels and improving membrane conductivity. On the other hand, sulfonated COFs form hydrogen bonds with proton-type ionic liquids, promoting the absorption and retention of ionic liquids. This results in the preparation of a high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework, exhibiting high conductivity, high mechanical strength, and high chemical stability.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) By confining and anchoring ionic liquids through sulfonated covalent organic framework channels, a continuous proton transport channel is constructed, while the formation of hydrogen bonds inhibits the loss of ionic liquids and improves the conductivity of polymer films.

[0021] (2) Introducing sulfonated covalent organic frameworks into polyimide allows for hydrogen bonding between the two, thereby improving compatibility. Sulfonated covalent organic frameworks have a large porosity, which is beneficial for the absorption of ionic liquids. This overcomes the problem of insufficient ionic liquid doping caused by the excessively high density of traditional polyimide.

[0022] (3) Replacing the traditional phosphoric acid-type conductive medium with a proton-type ionic liquid reduces the plasticizing effect of the conductive medium on the polymer membrane. Using polyimide with excellent film-forming properties as the polymer substrate, and doping with sulfonated covalent organic frameworks, a high-temperature proton exchange membrane with high electrical conductivity, high mechanical strength and high chemical stability is obtained. Attached Figure Description

[0023] Figure 1 The structural formula and NMR spectrum of the proton-type ionic liquid prepared in Example 1 are shown.

[0024] Figure 2 Fourier transform infrared (FT-IR) spectra of COF and sulfonated COF prepared in Example 1. Detailed Implementation

[0025] The present invention will now be described in detail with reference to specific embodiments.

[0026] Example 1

[0027] (1) Preparation of proton-type ionic liquid: 15 g of 1-ethylimidazolium was added to a round-bottom flask, and 80 mL of dichloromethane was added as solvent. 22.94 g of trifluoromethanesulfonic acid was slowly added dropwise (1 mL / min) at a molar ratio of 1:1. The reaction was carried out in an ice-water bath for 2 h to obtain crude product. Dichloromethane was removed by rotary evaporation. Then, the raw material was washed twice with diethyl ether to remove the unreacted raw material. Diethyl ether was removed by rotary evaporation. The pale yellow liquid was placed in a vacuum oven at 80 °C for 8 h to remove water, thus obtaining [EIM][TfO] ionic liquid.

[0028] (2) Preparation of sulfonated COF: 3.50 g of terephthalaldehyde and 2.20 g of melamine were dissolved in 100 mL of anhydrous DMSO to prepare a reaction solution. The reaction solution was stirred at 180 °C for 72 h under N2 atmosphere to obtain a white solid product. The product was washed successively with acetone, tetrahydrofuran and dichloromethane, and the pale yellow precipitate separated by centrifugation was dried at 60 °C for 24 h to obtain the product COF.

[0029] 0.50 g of COF and 0.11 g of 1,4-butane sulfonyl lactone were reacted in 200 mL of acetone at room temperature for 24 h. After washing with acetone and drying, the product was dispersed in 100 mL of H₂SO₄ solution (0.05 mM, pH=4) and stirred at room temperature for 1 h. The product was washed with deionized water until neutral (pH=7) and then centrifuged to obtain a pale yellow sulfonated COF. The molar ratio of 1,4-butane sulfonyl lactone to COF was 1:1. The resulting structural formula is as follows:

[0030]

[0031] (3) Synthesis of polyamic acid: 6 mL of DMAc was added to a three-necked flask and N2 was introduced while stirring with a mechanical stirrer to keep the flask under an N2 atmosphere. Then, 0.78 g of APABI and 0.76 g of PMDA were added under an ice-water bath and mechanically stirred. The molar ratio of the two was 1:1. After reacting for 5 h, the reaction solution became highly viscous and was poured into deionized water to precipitate, thus obtaining polyamic acid (PAA), an intermediate product of polyimide.

[0032] (4) High-temperature proton exchange membrane based on polyimide / sulfonated covalent organic framework and its preparation method: 0.775 g of PAA from step (3) was weighed and redissolved in DMAc to obtain a 3 wt% polymer / DMAc solution. Then, 0.0078 g (1% of the mass of polyimide) of sulfonated COF was dispersed in 4 mL of DMAc and added to the polymer / DMAc solution. After stirring for 2 h to form a homogeneous solution, 0.3875 g of proton-type ionic liquid (50% of the mass of polyimide) was added. After stirring for 2 h, a homogeneous solution was formed. The homogeneous membrane solution was then cast into a membrane and dried in an oven to prepare a homogeneous polyamic acid membrane. The membrane was then subjected to thermal imidization treatment under N2 protection to obtain a high-temperature proton exchange membrane based on polyimide / sulfonated covalent organic framework. The thermal imidization treatment was controlled by programmed temperature rise (sintering at 100 ℃, 200 ℃ and 250 ℃ for 1 h each).

[0033] The measured performance parameters of the electrolyte membrane are: conductivity of 9.56 mS / cm at 80 ℃. -1 The conductivity at 160℃ is 22.80 mS / cm. -1 The tensile strength is 48.91 MPa. This membrane exhibits both good electrical conductivity and good mechanical properties. The membrane was immersed in Fenton's reagent (4 ppm Fe). 2+ After being placed at 80 °C for 120 h (containing 3% H2O2), its remaining weight was measured again and found to be 98.87%, proving that it has good stability.

[0034] Example 2

[0035] The high-temperature proton exchange membrane based on polyimide / sulfonated covalent organic framework and its preparation method provided in this embodiment are basically the same as those in Example 1. The difference is that in step (4), 0.062 g (8% of the mass of polyimide) of sulfonated COF is added and dispersed in 4 mL of DMAc, and then added to the polymer / DMAc solution. After stirring for 2 h to generate a uniform solution, 1.55 g of proton-type ionic liquid (200% of the mass of polyimide) is added.

[0036] The measured performance parameters of the electrolyte membrane are: conductivity of 24.36 mS / cm at 80 ℃. -1 The conductivity at 160 ℃ is 45.43 mS / cm. -1 The tensile strength is 27.43 MPa. This membrane exhibits good electrical conductivity and good mechanical properties. Oxidative stability is also observed. The membrane was immersed in Fenton's reagent (4 ppm Fe). 2+ After being placed at 80 °C for 120 h (containing 3% H2O2), its remaining weight was measured again and found to be 95.43%, proving that it has good stability.

[0037] Example 3

[0038] The high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework and its preparation method provided in this embodiment are basically the same as those in Example 1, except that in step (2), 0.50 g of COF and 0.27 g of 1,4-butane lactone are reacted in 200 mL of acetone at room temperature for 24 h, and the molar ratio of 1,4-butane sulfonate lactone to COF is 2:1. The resulting structural formula is as follows:

[0039]

[0040] In step (4), 0.0233 g (3% of the mass of polyimide) of sulfonated COF was added and dispersed in 4 mL of DMAc, and then added to the polymer / DMAc solution. After stirring for 2 h to form a homogeneous solution, 0.0078 g of proton-type ionic liquid (100% of the mass of polyimide) was added.

[0041] The measured performance parameters of the electrolyte membrane are: conductivity of 12.94 mS / cm at 80 ℃. -1 Conductivity at 160℃: 26.95 mS / cm -1 The tensile strength is 46.34 MPa. This membrane exhibits both good electrical conductivity and good mechanical properties. The membrane was immersed in Fenton's reagent (4 ppm Fe). 2+ After being placed at 80 °C for 120 h (containing 3% H2O2), its remaining weight was measured again and found to be 96.96%, proving that it has good stability.

[0042] Example 4

[0043] The high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework and its preparation method provided in this embodiment are basically the same as those in Example 1, except that in step (2), 0.50 g of COF and 0.27 g of 1,4-butane lactone are reacted in 200 mL of acetone at room temperature for 24 h, and the molar ratio of 1,4-butane sulfonate lactone to COF is 2:1:

[0044] In step (4), 0.062 g (8% of the mass of polyimide) of sulfonated COF was added and dispersed in 4 mL of DMAc, and then added to the polymer / DMAc solution. After stirring for 2 h to form a homogeneous solution, 0.3875 g of proton-type ionic liquid (50% of the mass of polyimide) was added.

[0045] The measured performance parameters of the electrolyte membrane are: conductivity of 16.45 mS / cm at 80 ℃. -1 The conductivity at 160℃ is 27.95 mS / cm. -1 The tensile strength is 45.71 MPa. This membrane exhibits both good electrical conductivity and good mechanical properties. The membrane was immersed in Fenton's reagent (4 ppm Fe). 2+ After being placed at 80 °C for 120 h (containing 3% H2O2), its remaining weight was measured again and found to be 96.45%, proving that it has good stability.

[0046] Example 5

[0047] The high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework and its preparation method provided in this embodiment are basically the same as those in Example 1, except that: in step (2), 0.50 g of COF and 0.34 g of 1,4-butane lactone are reacted in 200 mL of acetone at room temperature for 24 h, and the molar ratio of 1,4-butane sulfonate lactone to COF is 3:1. The resulting structural formula is as follows:

[0048]

[0049] In step (4), 0.0388 g (5% of the mass of polyimide) of sulfonated COF was added and dispersed in 4 mL of DMAc. Then, after stirring the polymer / DMAc solution for 2 h to form a homogeneous solution, 1.1625 g of proton-type ionic liquid (150% of the mass of polyimide) was added.

[0050] The measured performance parameters of the electrolyte membrane are: conductivity of 22.18 mS / cm at 80 ℃. -1 The conductivity at 160℃ is 42.47 mS / cm. -1 The tensile strength is 30.02 MPa. This membrane exhibits both good electrical conductivity and good mechanical properties. The membrane was immersed in Fenton's reagent (4 ppm Fe). 2+ After being placed at 80 °C for 120 h (containing 3% H2O2), its remaining weight was measured again and found to be 93.21%, proving that it has good stability.

[0051] Example 6

[0052] The high-temperature proton exchange membrane based on polyimide / sulfonated covalent organic framework and its preparation method provided in this embodiment are basically the same as those in Example 1. The difference is that in step (2), 0.50 g of COF and 0.34 g of 1,4-butane lactone are reacted in 200 mL of acetone at room temperature for 24 h, and the molar ratio of 1,4-butane sulfonate lactone to COF is 3:1.

[0053] In step (4), 0.0078 g (1% of the mass of polyimide) of sulfonated COF was added and dispersed in 4 mL of DMAc, and then added to the polymer / DMAc solution. After stirring for 2 h to form a homogeneous solution, 1.55 g of proton-type ionic liquid (200% of the mass of polyimide) was added.

[0054] The measured performance parameters of the electrolyte membrane are: conductivity of 20.51 mS / cm at 80 ℃. -1 The conductivity at 160℃ is 41.88 mS / cm. -1 The tensile strength is 34.73 MPa. This membrane exhibits both good electrical conductivity and good mechanical properties. The membrane was immersed in Fenton's reagent (4 ppm Fe). 2+ After being placed at 80 °C for 120 h (containing 3% H2O2), its remaining weight was measured again and found to be 94.47%, proving that it has good stability.

[0055] Example 7

[0056] The high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework and its preparation method provided in this embodiment are basically the same as those in Example 1, except that: in step (2), 0.50 g of COF and 0.45 g of 1,4-butane lactone are reacted in 200 mL of acetone at room temperature for 24 h, and the molar ratio of 1,4-butane sulfonate lactone to COF is 4:1. The resulting structural formula is as follows:

[0057]

[0058] In step (4), 0.062 g (8% of the mass of polyimide) of sulfonated COF was added and dispersed in 4 mL of DMAc, and then added to the polymer / DMAc solution. After stirring for 2 h to form a homogeneous solution, 1.55 g of proton-type ionic liquid (200% of the mass of polyimide) was added.

[0059] The measured performance parameters of the electrolyte membrane are: conductivity of 28.43 mS / cm at 80 ℃. -1 The conductivity at 160℃ is 49.58 mS / cm. -1The tensile strength is 15.64 MPa. This membrane exhibits both good electrical conductivity and good mechanical properties. The membrane was immersed in Fenton's reagent (4 ppm Fe). 2+ After being placed at 80 °C for 120 h (containing 3% H2O2), its remaining weight was measured again and found to be 92.87%, proving that it has good stability.

[0060] Example 8

[0061] The high-temperature proton exchange membrane based on polyimide / sulfonated covalent organic framework and its preparation method provided in this embodiment are basically the same as those in Example 1. The difference is that in step (2), 0.50 g COF and 0.45 g 1,4-butane lactone are reacted in 200 mL acetone at room temperature for 24 h, and the molar ratio of 1,4-butane sulfonate lactone to COF is 4:1.

[0062] In step (4), 0.0078 g (1% of the mass of polyimide) of sulfonated COF was added and dispersed in 4 mL of DMAc, and then added to the polymer / DMAc solution. After stirring for 2 h to form a homogeneous solution, 0.3875 g of proton-type ionic liquid (50% of the mass of polyimide) was added.

[0063] The measured performance parameters of the electrolyte membrane are: conductivity of 12.81 mS / cm at 80 ℃. -1 The conductivity at 160℃ is 24.51 mS / cm. -1 The tensile strength is 48.04 MPa; this membrane exhibits both good electrical conductivity and good mechanical properties. The membrane was immersed in Fenton's reagent (4 ppm Fe). 2+ After being placed at 80 °C for 120 h (containing 3% H2O2), its remaining weight was measured again and found to be 95.26%, proving that it has good stability.

[0064] Example 9

[0065] The high-temperature proton exchange membrane based on polyimide / sulfonated covalent organic framework and its preparation method provided in this embodiment are basically the same as those in Example 1. The difference is that in step (2), 0.50 g COF and 0.45 g 1,4-butane lactone are reacted in 200 mL acetone at room temperature for 24 h, and the molar ratio of 1,4-butane sulfonate lactone to COF is 4:1.

[0066] In step (4), 0.0078 g (1% of the mass of polyimide) of sulfonated COF was added and dispersed in 4 mL of DMAc, and then added to the polymer / DMAc solution. After stirring for 2 h to form a homogeneous solution, 1.55 g of proton-type ionic liquid (200% of the mass of polyimide) was added.

[0067] The measured performance parameters of the electrolyte membrane are: conductivity of 26.13 mS / cm at 80 ℃. -1 The conductivity at 160℃ is 47.88 mS / cm. -1 The tensile strength is 25.47 MPa; this membrane exhibits both good electrical conductivity and good mechanical properties. The membrane was immersed in Fenton's reagent (4 ppm Fe). 2+ After being placed at 80 °C for 120 h (containing 3% H2O2), its remaining weight was measured again and found to be 94.06%, proving that it has good stability.

[0068] Example 10

[0069] The high-temperature proton exchange membrane based on polyimide / sulfonated covalent organic framework and its preparation method provided in this embodiment are basically the same as those in Example 1. The difference is that in step (2), 0.50 g COF and 0.45 g 1,4-butane lactone are reacted in 200 mL acetone at room temperature for 24 h, and the molar ratio of 1,4-butane sulfonate lactone to COF is 4:1.

[0070] In step (4), 0.062 g (8% of the mass of polyimide) of sulfonated COF was added and dispersed in 4 mL of DMAc, and then added to the polymer / DMAc solution. After stirring for 2 h to form a homogeneous solution, 0.3875 g of proton-type ionic liquid (50% of the mass of polyimide) was added.

[0071] The measured performance parameters of the electrolyte membrane are: conductivity at 80 ℃ is 13.44 mS / cm. -1 The conductivity at 160℃ is 29.35 mS / cm. -1 The tensile strength is 39.04 MPa; this membrane exhibits both good electrical conductivity and good mechanical properties. The membrane was immersed in Fenton's reagent (4 ppm Fe). 2+ After being placed at 80 °C for 120 h (containing 3% H2O2), its remaining weight was measured again and found to be 93.45%, proving that it has good stability.

[0072] Comparative Example 1

[0073] The high-temperature proton exchange membrane based on polyimide and its preparation method provided in this comparative example are basically the same as those in Example 1. The difference is that the sulfonated COF prepared in (2) is not required, and the sulfonated COF is not required in step (4). Only 1.55 g of proton-type ionic liquid (which is 200% of the mass ratio of polyimide) needs to be added.

[0074] Under the same experimental conditions, the performance parameters of the polymer electrolyte membrane were measured as follows: conductivity at 80 ℃ was 7.81 mS / cm. -1 The conductivity at 160℃ is 18.94 mS / cm. -1 The tensile strength is 45.14 MPa. This membrane exhibits low electrical conductivity but good mechanical properties. The membrane was immersed in Fenton's reagent (4 ppm Fe). 2+ After being placed at 80 °C for 120 h (containing 3% H2O2), its remaining weight was measured again and found to be 98.86%, proving that it has good stability.

[0075] Comparative Example 2

[0076] The high-temperature proton exchange membrane based on polyimide / covalent organic framework and its preparation method provided in this comparative example are basically the same as those in Example 1. The difference is that (2) the prepared covalent organic framework does not need to be sulfonated. In step (4), 0.0388 g of COF (5% of the mass of polyimide) is added directly, and then 1.55 g of proton-type ionic liquid (200% of the mass of polyimide) is added.

[0077] Under the same experimental conditions, the performance parameters of the polymer electrolyte membrane were measured as follows: conductivity at 80 ℃ was 8.96 mS / cm. -1 The conductivity at 160℃ is 21.70 mS / cm. -1 The tensile strength is 37.48 MPa. This membrane exhibits low electrical conductivity but good mechanical properties. The membrane was immersed in Fenton's reagent (4 ppm Fe). 2+ After being placed at 80 °C for 120 h (containing 3% H2O2), its remaining weight was measured again and found to be 98.93%, proving that it has good stability.

[0078] Comparative Example 3

[0079] The high-temperature proton exchange membrane based on polyimide / covalent organic framework and its preparation method provided in this comparative example are basically the same as those in Example 1, except for step (3) synthesis of polyamic acid: 6 mL of DMAc was added to a three-necked flask, and N2 was introduced while stirring with a mechanical stirrer to keep the flask under an N2 atmosphere. Then, 0.38 g of p-phenylenediamine (PDA) and 0.76 g of PMDA were added under an ice-water bath and mechanically stirred. The molar ratio of the two was 1:1. After reacting for 5 hours, the reaction solution became highly viscous and was poured into deionized water to precipitate, obtaining polyamic acid (PAA), an intermediate product of polyimide. The structural formula of the obtained polyimide is:

[0080]

[0081] The preparation method of the high-temperature proton exchange membrane based on polyimide / covalent organic framework is the same as in Example 1.

[0082] The measured performance parameters of the electrolyte membrane are: conductivity of 2.81 mS / cm at 80 ℃. -1 The conductivity at 160 ℃ is 13.11 mS / cm. -1 The tensile strength is 47.55 MPa; the membrane has low electrical conductivity but good mechanical properties. The membrane was immersed in Fenton's reagent (4 ppm Fe). 2+ After being placed at 80 °C for 120 h (containing 3% H2O2), its remaining weight was measured again and found to be 91.63%, proving that it has good stability.

[0083] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit 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 high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework, characterized in that, The preparation method steps are as follows: (1) Synthesis of proton-type ionic liquids and polyamic acid (2) Synthesis of sulfonated COF First, COF was obtained, and then the COF was stirred and dispersed in an acetone solution of 1,4-butanesulfonyl lactone for reaction. After centrifugation and drying of the reaction solution, the solid product was stirred and dispersed in a sulfuric acid solution, and then the product was washed until neutral to obtain sulfonated COF. (3) Preparation of high-temperature proton exchange membranes based on polyimide / sulfonated covalent organic framework Polyamic acid was dissolved in DMAc to obtain a polymer solution. Then, sulfonated COF and proton-type ionic liquid were added to the polymer solution. After thorough stirring, a membrane solution was obtained. The membrane solution was poured onto a clean glass plate and dried to form a membrane. Finally, the membrane was subjected to thermal imidization under N2 protection to obtain a high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework.

2. The method for preparing a high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework as described in claim 1, characterized in that, In step (1), the method for synthesizing the proton-type ionic liquid is as follows: 1-ethylimidazolium and dichloromethane are added to a round-bottom flask, trifluoromethanesulfonic acid is added dropwise under an ice-water bath, and the reaction is continued for 2 h. Dichloromethane is removed by rotary evaporation, the crude product is washed with anhydrous diethyl ether, and finally dried to obtain 1-ethylimidazolium trifluoromethanesulfonic acid ([EIM][TfO]) proton-type ionic liquid; wherein, the molar ratio of 1-ethylimidazolium to trifluoromethanesulfonic acid is 1:1, and the dropping rate of trifluoromethanesulfonic acid is 1 mL / min.

3. The method for preparing a high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework as described in claim 1, characterized in that, In step (1), the method for synthesizing polyamic acid is as follows: 5-amino-2-(4-aminophenyl)benzimidazole and pyromellitic anhydride are mechanically stirred and dissolved in N,N dimethylacetamide under an ice-water bath. The reaction is carried out under N2 protection. After the reaction solution becomes highly viscous, it is poured into deionized water to precipitate and obtain polyamic acid, an intermediate product of polyimide. The molar ratio of 5-amino-2-(4-aminophenyl)benzimidazole and pyromellitic anhydride is 1:

1.

4. The method for preparing a high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework as described in claim 1, characterized in that, In step (2), the synthesis method of COF is as follows: terephthalaldehyde and melamine are dissolved in anhydrous dimethyl sulfoxide to prepare a reaction solution; the reaction solution is stirred at high temperature under N2 atmosphere, and then the crude product is washed with acetone, tetrahydrofuran and dichloromethane in sequence and centrifuged to obtain COF; wherein, the molar ratio of terephthalaldehyde and melamine is 3:

2.

5. The method for preparing a high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework as described in claim 1, characterized in that, In step (2), the molar ratio of 1,4-butanesulfonyl lactone to COF is 4:1 to 1:1; the sulfuric acid solution concentration is 0.05 mM and pH=4.

6. The method for preparing a high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework as described in claim 1, characterized in that, In step (3), the mass concentration of the polymer solution is 3 wt%; the sulfonated COF accounts for 1% to 8% of the polymer mass; and the proton-type ionic liquid accounts for 50% to 200% of the polymer mass.

7. The method for preparing a high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework as described in claim 1, characterized in that, In step (3), the thermal imidization treatment is controlled by programmed temperature rise, and sintering is carried out at 100 °C, 200 °C and 250 °C for 1 h each.

8. A high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework prepared by the method according to any one of claims 1-7, characterized in that, The structure of the high-temperature proton exchange membrane based on the polyimide / sulfonated covalent organic framework is shown in the following formula: 。 9. An application of the high-temperature proton exchange membrane based on a polyimide / sulfonated covalent organic framework as described in claim 8, characterized in that, The high-temperature proton exchange membrane is suitable for proton exchange membrane fuel cells with an operating temperature of 100-200℃, and is used in stationary power plants, power supplies for heavy vehicles, and portable emergency power supplies that use reformed hydrogen or low-carbon alcohol reformed gas.

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