An amphoteric copolymer, a high-temperature proton exchange membrane, and a preparation method and application thereof

Abstract

The present invention relates to an amphoteric copolymer, a high-temperature proton exchange membrane, and a preparation method and application thereof. The amphoteric copolymer has a structure shown in formula (I): wherein, 0 < X < 1; Ar is a structure containing an aromatic ring; R is a structure in which a nitrogen-containing heterocyclic quaternary ammonium cation and an anion are combined through ion-pair interaction. The amphoteric copolymer of the present invention is used to prepare a high-temperature proton exchange membrane, and the obtained high-temperature proton exchange membrane has three acids with different acidities at the same time. The combined action of the three acids with different acidities can endow the membrane with good proton conduction performance and mechanical properties, and a high phosphoric acid retention rate.

Description

Technical Field

[0001] The present invention relates to the field of fuel cells, and more specifically, to an amphoteric copolymer, a high-temperature proton exchange membrane, and a preparation method and application thereof. Background Art

[0002] The high-temperature proton exchange membrane is the core component of a high-temperature proton exchange membrane fuel cell, which functions to transfer protons, block electrons, and prevent gas fuel permeation. The high-temperature proton exchange membrane operating under high-temperature and low-humidity conditions relies on phosphoric acid electrolyte to construct a dense and connected proton transport channel in the membrane, thereby playing the role of proton transport.

[0003] Currently, alkaline polymers are commonly used to prepare high-temperature proton exchange membranes. For example, Intermolecular Acid-Base-Pairs Containing Poly(p-Terphenyl-co-Isatin Piperidinium) for High Temperature Proton Exchange Membrane Fuel Cells, Xiaofeng Hao etc. For this type of high-temperature proton exchange membrane, in order to improve the proton conduction performance in the membrane, it is usually necessary to increase the amount of phosphoric acid doping in the membrane. However, the plasticizing effect of phosphoric acid will weaken the mechanical properties of the membrane and affect the service life of the fuel cell. In addition, there is a strong interaction between the water vapor generated in the fuel cell system and the free phosphoric acid in the membrane, which will increase the loss rate of phosphoric acid. The phosphoric acid that leaks into the membrane electrode will poison the catalyst and corrode the battery system, thereby shortening the service life of the fuel cell. Therefore, it is necessary to solve the problems that it is difficult to balance the proton conduction performance and mechanical properties in the current high-temperature proton exchange membrane and the high phosphoric acid loss rate. Summary of the Invention

[0004] The primary object of the present invention is to overcome the problems that it is difficult to balance the proton conduction performance and mechanical properties in the existing high-temperature proton exchange membrane and the easy loss of phosphoric acid, and to provide an amphoteric copolymer.

[0005] A further object of the present invention is to provide a preparation method of the above amphoteric copolymer.

[0006] A further object of the present invention is to provide an application of the above amphoteric copolymer in the preparation of a high-temperature proton exchange membrane.

[0007] A further object of the present invention is to provide a preparation method of a high-temperature proton exchange membrane.

[0008] A further object of the present invention is to provide a high-temperature proton exchange membrane.

[0009] A further object of the present invention is that the application of the above high-temperature proton exchange membrane in the preparation of fuel cells is also within the protection scope of the present invention.

[0010] The above object of the present invention is achieved by the following technical solutions:

[0011] An amphoteric copolymer has a structure shown in formula (I):

[0012]

[0013] Wherein, 0 < X < 1; Ar is a structure containing an aromatic ring; R is a structure in which a quaternary ammonium cation of a nitrogen-containing heterocycle and an anion are combined by ion pair interaction;

[0014] The anion is at least one of a halide ion, a hydroxide ion or a dihydrogen phosphate ion;

[0015] The intrinsic viscosity of the amphoteric copolymer is 1 to 3 dL / g.

[0016] In the present invention, the intrinsic viscosity of the amphoteric copolymer is measured by an Ubbelohde viscometer at 30 °C.

[0017] It should be understood that X in formula (I) of the present invention refers to the molar amount of the ratio to the sum of the molar amounts of

[0018] Conventionally, polymers used for preparing high-temperature proton exchange membranes often introduce organic phosphonic acid groups. As an intrinsic proton conductor, the organic phosphonic acid groups can be self-ionized at high temperature and 0 RH%, contributing a certain proton conductivity, and the microstructure formed by clusters provides an additional channel for the rapid transport of protons; in addition, the covalently fixed organic phosphonic acid groups are not easily lost and have weak corrosion to the internal components of the battery. However, the organic phosphonic acid groups have weak acidity and low ionization degree, and their proton conductivity at high temperature and low humidity is low. If the proton conductivity is further improved by introducing basic groups to significantly increase the amount of phosphoric acid doping, it will have a negative impact on the mechanical properties and phosphoric acid retention rate of the high-temperature proton exchange membrane.

[0019] The inventors of the present invention introduced organic phosphonic acid groups and nitrogen-containing heterocyclic quaternary ammonium cations into an amphoteric copolymer and used the amphoteric copolymer to prepare a high-temperature proton exchange membrane. On the one hand, the nitrogen-containing heterocyclic quaternary ammonium cations form ion pairs with dihydrogen phosphate through ion-pair interactions to bind acids. The strong force of the ion pairs can reduce the loss rate of phosphoric acid (dihydrogen phosphate). On the other hand, the organic phosphonic acid groups and ion-pair bound acids in the prepared high-temperature proton exchange membrane can regulate the doping amount and distribution of free phosphoric acid in the membrane. This can not only reduce the doping amount of free phosphoric acid and further reduce the loss of phosphoric acid, improving the phosphoric acid retention rate in the membrane, but also, when the doping amount of phosphoric acid is small, enhance the proton transport rate by constructing a dense and connected hydrogen bond network in the membrane, so that the membrane has good proton conduction performance and mechanical properties (tensile strength) at the same time.

[0020] That is, the amphoteric copolymer of the present invention is used to prepare a high-temperature proton exchange membrane, and the obtained high-temperature proton exchange membrane has three different acids with different acidities (organic phosphonic acid groups, ion-pair bound acids and free phosphoric acid) at the same time. The combined action of the three different acids with different acidities can make the membrane have good proton conduction performance and mechanical properties at the same time, and the phosphoric acid retention rate is high. In addition, the amphoteric copolymer of the present invention also enables the high-temperature proton exchange membrane to have good peak power density and voltage decay rate. Therefore, the amphoteric copolymer of the present invention can be widely used in the field of high-temperature proton exchange membrane fuel cells, including fields such as hydrogen production by electrolyzing water and flow batteries.

[0021] Preferably, Ar is any one of the following structures:

[0022]

[0023] Preferably, each R contains a nitrogen-containing heterocyclic quaternary ammonium cation.

[0024] Preferably, R is any one of the following structures: Y - represents an anion.

[0025] Preferably, 0.2 ≤ X ≤ 0.8.

[0026] Preferably, 0.4 ≤ X ≤ 0.6. By regulating X within this range, when the obtained amphoteric copolymer is used to prepare a high-temperature proton exchange membrane, the mechanical properties of the high-temperature proton exchange membrane are better and the phosphoric acid retention rate is higher.

[0027] Preferably, 0.2 ≤ X ≤ 0.4. By regulating X within this range, when the obtained amphoteric copolymer is used to prepare a high-temperature proton exchange membrane, the proton conductivity of the high-temperature proton exchange membrane is higher.

[0028] Preferably, the halide ion is at least one of bromide ion or iodide ion.

[0029] The preparation method of the amphoteric copolymer comprises the following steps:

[0030] S1. Mix isatin, a nitrogen-containing heterocyclic monomer containing a carbonyl group, and an aromatic ring-containing monomer, and then carry out a Friedel-Crafts reaction for polycondensation to obtain a terpolymer;

[0031] S2. The terpolymer obtained in step S1 undergoes a quaternization reaction with a nucleophile to convert the nitrogen-containing heterocycle in the terpolymer into a quaternary ammonium cation, obtaining a quaternary ammonium-terpolymer;

[0032] S3. The quaternary ammonium-terpolymer obtained in step S2 undergoes a phosphorylation reaction and a hydrolysis reaction to introduce an organic phosphonic acid group, thus obtaining the amphoteric copolymer;

[0033] In the amphoteric copolymer, the anion of R is a halide ion.

[0034] Preferably, the nitrogen-containing heterocyclic monomer containing a carbonyl group in step S1 is at least one of N-methylpiperidone, 4-imidazolecarboxaldehyde, and quinuclidone.

[0035] Preferably, the aromatic ring-containing monomer in step S1 is at least one of biphenyl, 2,2'-dihydroxybiphenyl, p-terphenyl, m-terphenyl, and o-terphenyl.

[0036] Preferably, a solvent is further added during the mixing process in step S1; the solvent includes but is not limited to dichloromethane.

[0037] Preferably, the mixing temperature in step S1 is 10-25°C.

[0038] Preferably, the ratio of the sum of the amounts of substances of isatin and the nitrogen-containing heterocyclic monomer containing a carbonyl group to the amount of substance of the aromatic ring-containing monomer in step S1 is (1.1-1.4):1.

[0039] Preferably, the Friedel-Crafts reaction in step S1 is carried out in the presence of an organic strong acid catalyst; the organic strong acid catalyst includes trifluoroacetic acid and trifluoromethanesulfonic acid with a molar ratio of 1:(1-20). The molar ratio of the aromatic ring-containing monomer to the organic strong acid catalyst is 1:(1-30).

[0040] Preferably, the reaction temperature of the Friedel-Crafts reaction in step S1 is 0-5°C, and the reaction time is 5-10 h.

[0041] Preferably, after the Friedel-Crafts reaction in step S1, there are also steps of sedimentation, washing, and drying.

[0042] More preferably, the reagent used for sedimentation is a poor solvent. The poor solvent includes but is not limited to at least one of water, methanol, ethanol, and n-propanol.

[0043] More preferably, the detergent for washing is water and ethanol.

[0044] More preferably, the temperature for drying is 60 - 100 °C and the time is 12 - 48 h.

[0045] Preferably, the nucleophilic reagent in step S2 is at least one of methyl iodide, ethyl iodide, propyl iodide, methyl bromide, ethyl bromide or propyl bromide.

[0046] Preferably, the molar ratio of the nucleophilic reagent in step S2 to the carbonyl-containing cyclic tertiary amine monomer in step S1 is (1 - 20):1.

[0047] Preferably, the reaction temperature of the quaternization reaction in step S2 is 0 - 25 °C and the reaction time is 12 - 24 h.

[0048] Preferably, after the quaternization reaction in step S2, there are also steps of sedimentation, washing and drying.

[0049] More preferably, the reagent used for sedimentation is a poor solvent. The poor solvent includes but is not limited to diethyl ether.

[0050] More preferably, the detergent for washing is at least one of methanol, ethanol and ethylene glycol.

[0051] More preferably, the temperature for drying is 60 - 100 °C and the time is 12 - 48 h.

[0052] Preferably, the specific process of the phosphorylation reaction in step S3 is: adding the quaternary ammonium - terpolymer into an organic solvent and carrying out the phosphorylation reaction with a phosphorylation reagent under a catalyst.

[0053] More preferably, the organic solvent includes but is not limited to N - methylpyrrolidone. The concentration of the quaternary ammonium - terpolymer in the organic solvent is preferably 0.01 - 0.1 g / mL.

[0054] More preferably, the phosphorylation reagent includes but is not limited to phosphorus oxychloride; the molar ratio of the quaternary ammonium - terpolymer to the phosphorylation reagent is 1:(1 - 10).

[0055] More preferably, the catalyst includes but is not limited to pyridine; the molar ratio of the catalyst to the quaternary ammonium - terpolymer is (1 - 10):1.

[0056] More preferably, the temperature of the phosphorylation reaction is 0 - 10 °C and the reaction time is 12 - 24 h.

[0057] Preferably, the temperature of the hydrolysis is 0 - 30 °C and the time is 24 - 48 h.

[0058] Preferably, after the hydrolysis in step S3, there are also steps of washing and drying.

[0059] More preferably, the reagent for washing is at least one of water, methanol or ethanol.

[0060] More preferably, the temperature for drying is 60 - 100 °C and the time is 12 - 48 h.

[0061] A method for preparing a high-temperature proton exchange membrane includes the following steps:

[0062] S4. Prepare the above amphoteric copolymer into a casting solution, cast and dry to obtain a film;

[0063] S5. Immerse the film in an alkaline solution, stir (to displace halogen ions), dry, then immerse it in a phosphoric acid solution for phosphoric acid adsorption, and then perform rearrangement of phosphoric acid in the film to obtain the high-temperature proton exchange membrane.

[0064] In step S5, when the film is immersed in the alkaline solution, the halogen ions of the amphoteric copolymer can be replaced by hydroxide ions; then when immersed in the phosphoric acid solution for phosphoric acid adsorption, the hydroxide ions of the amphoteric copolymer can be replaced by dihydrogen phosphate ions.

[0065] It should be noted that after the amphoteric copolymer is prepared into a high-temperature proton exchange membrane, the anion in R is dihydrogen phosphate. And the conversion of the halogen ions in R of the amphoteric copolymer into dihydrogen phosphate can be carried out either before the film is prepared or after the film is prepared (i.e., the preparation method provided by the present invention). If the halogen ions in R are converted into dihydrogen phosphate before the film is prepared, the amphoteric copolymer needs to be crushed into small enough particles so that the halogen ions can be fully displaced; while the preparation method of the present invention converts the halogen ions in R into dihydrogen phosphate after the film is prepared. Since the thickness of the film applied to the high-temperature proton exchange membrane is very small (usually 15 - 40 μm), the amphoteric copolymer can fully contact and react with the alkaline solution and the phosphoric acid solution, thereby enabling the anion in R to be fully converted into dihydrogen phosphate, and the whole process does not require crushing treatment of the amphoteric copolymer, which is simpler and more convenient.

[0066] Preferably, the solvent of the casting solution in step S4 is at least one of N-methylpyrrolidone, dimethyl sulfoxide, dimethylacetamide or dimethylformamide; the concentration (w / v) of the casting solution is 2 - 5%; the thickness of the film is 15 - 40 μm.

[0067] Preferably, the base of the alkaline solution in step S5 is at least one of potassium hydroxide, sodium hydroxide or lithium hydroxide; the concentration of the alkaline solution is 0.5 - 3 mol / L; the temperature for stirring is 25 - 50 °C and the time is 6 - 24 hours.

[0068] Preferably, in step S5, the concentration of the phosphoric acid solution is 50-85 wt%, the temperature for phosphoric acid adsorption is 80-120 °C, and the time is 12-24 h.

[0069] Preferably, the temperature for the rearrangement of phosphoric acid in the membrane is 10-25 °C, and the time is 3-5 days.

[0070] A high-temperature proton exchange membrane is prepared by the above preparation method.

[0071] The application of the above amphoteric copolymer in the preparation of a high-temperature proton exchange membrane is also within the protection scope of the present invention.

[0072] The application of the above high-temperature proton exchange membrane in the preparation of a fuel cell is also within the protection scope of the present invention.

[0073] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0074] (1) The amphoteric copolymer of the present invention is used to prepare a high-temperature proton exchange membrane. The obtained high-temperature proton exchange membrane simultaneously has three acids with different acidities (organic phosphonic acid groups, ion-pair binding acids, and free phosphoric acid). The combined action of the three acids with different acidities can endow the membrane with good proton conduction performance and mechanical properties, and a high phosphoric acid retention rate. In addition, the amphoteric copolymer of the present invention also enables the high-temperature proton exchange membrane to have good peak power density and voltage decay rate. Therefore, the amphoteric copolymer of the present invention can be widely used in the field of high-temperature proton exchange membrane fuel cells.

[0075] (2) By regulating the ratio of the synthesis monomers of the amphoteric copolymer of the present invention (i.e., the value of X), the contents of the three acids with different acidities in the high-temperature proton exchange membrane can be regulated, so that the phosphoric acid adsorption amount in the membrane can be accurately controlled, the retention rate of the phosphoric acid electrolyte can be improved, and the physical properties and electrochemical properties in the high-temperature proton exchange membrane can be balanced.

[0076] (3) The preparation method of the amphoteric copolymer of the present invention is simple and low in cost. Description of the Drawings

[0077] Figure 1 It is a preparation flow chart of the amphoteric copolymer obtained in step 3) of Example 1.

[0078] Figure 2 It is the 1 1H-NMR spectrum of the amphoteric copolymer obtained in step 3) of Example 1.

[0079] Figure 3 It is the 31 31P-NMR spectrum of the amphoteric copolymer obtained in step 3) of Example 1.

[0080] Figure 4 AFM spectrum of the high-temperature proton exchange membrane of Example 1.

[0081] Figure 5 TFM spectrum of the high-temperature proton exchange membrane of Example 1.

[0082] Figure 6 Obtained in step 3) of Example 2 1 1H-NMR spectrum

[0083] Figure 7 Obtained in step 3) of Example 2 31 31P-NMR spectrum

[0084] Figure 8 Obtained in step 3) of Example 3 1 1H-NMR spectrum

[0085] Figure 9 Obtained in step 3) of Example 3 31 31P-NMR spectrum Detailed implementation manners

[0086] In order to describe the technical solutions of the present invention more clearly and completely, the present invention will be further described in detail below through specific examples. It should be understood that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention. Various changes can be made within the scope defined by the claims of the present invention.

[0087] Example 1

[0088] This example provides an amphoteric copolymer and a high-temperature proton exchange membrane prepared therefrom. The preparation method includes the following steps:

[0089] 1) Add p-terphenyl (14.6 mmol), N-methyl-4-piperidone (12.88 mmol), isatin (3.22 mmol) and 14 mL of anhydrous dichloromethane to the reaction flask in sequence. Stir mechanically at 25 °C for 1 h and at 0 °C for 0.5 h. While maintaining the condition of 0 °C, add trifluoroacetic acid (1 mL) and trifluoromethanesulfonic acid (17 mL) dropwise into the flask in sequence. After the addition is completed, continue to stir for 6 h until the solution viscosity increases to obtain a viscous liquid. Pour the viscous liquid into 400 mL of deionized water for sedimentation to obtain a fibrous product. The fibrous product is dried in an oven at 80 °C for 12 h to obtain a terpolymer (P1).

[0090] 2) Dissolve the terpolymer P1 (1.0 g) in N-methylpyrrolidone (17 mL), and stir at 80 °C until completely dissolved; add methyl iodide (24 mmol), and stir at room temperature in the dark for 12 h. After the reaction is completed, pour the reaction solution into diethyl ether to precipitate a yellow solid. Wash the yellow solid with a large amount of deionized water and ethanol, and then dry it in an oven at 80 °C to obtain the quaternary ammonium salt-terpolymer (P2).

[0091] 3) Take the quaternary ammonium salt-terpolymer P2 (1.0 g) and dissolve it in N-methylpyrrolidone (30 mL), and stir at 80 °C until completely dissolved; at 0 °C, dropwise add POCl3 (6 mmol) and pyridine (6 mmol) into the flask, and end the reaction after 12 h. Then, dropwise add 60 mL of deionized water into the flask, and then pour the entire mixed solution into 400 mL of deionized water, stir for 3 days, separate the reactants from the water, wash the product with a large amount of deionized water and ethanol, and dry it in an oven at 80 °C to obtain the amphoteric copolymer.

[0092] 4) Weigh the amphoteric copolymer (1.0 g) and dissolve it in 25 mL of dimethyl sulfoxide, and stir at 80 °C for 12 h until completely dissolved to obtain a casting solution. Pour the casting solution onto a glass plate, and volatilize the solvent at 70 °C to obtain an M1 film with a thickness of 25 μm.

[0093] 5) Immerse the M1 film in a 0.1 mol / L NaOH dilute solution, and keep it at 40 °C with stirring for 12 h. Then, wash it with deionized water multiple times, and dry it at 80 °C until the mass no longer changes to obtain an M2 film.

[0094] 6) Place the M2 film in an 85 wt% phosphoric acid solution, soak it at 100 °C for 12 h, take it out and place it in a sealed bag and keep it at room temperature for 3 days to obtain a high-temperature proton exchange membrane.

[0095] In this example, the intrinsic viscosity of the amphoteric copolymer obtained in step 3) was measured to be 1.47 dL / g at 30 °C by an Ubbelohde viscometer, and its structure is shown as follows:

[0096]

[0097] Figure 1 It is the preparation flow chart of the amphoteric copolymer obtained in step 3) of Example 1.

[0098] Figure 2 It is for the amphoteric copolymer obtained in step 3) of Example 1 1 1H-NMR spectrum Figure 3 It is for the amphoteric copolymer obtained in step 3) of Example 1 31 31P-NMR spectrum Figure 2 andFigure 3 Indicates the successful synthesis of the amphoteric copolymer obtained in step 3).

[0099] Figure 4 AFM spectrum of the high-temperature proton exchange membrane of Example 1.

[0100] Figure 5 TFM spectrum of the high-temperature proton exchange membrane of Example 1.

[0101] Example 2

[0102] This example provides an amphoteric copolymer and a high-temperature proton exchange membrane prepared therefrom. The preparation method includes the following steps:

[0103] 1) Add p-terphenyl (14.6 mmol), N-methyl-4-piperidone (9.66 mmol), isatin (6.44 mmol) and 14 mL of anhydrous dichloromethane to the reaction flask in sequence. Stir mechanically at 25 °C for 1 h and at 0 °C for 0.5 h. While maintaining the 0 °C condition, add trifluoroacetic acid (1 mL) and trifluoromethanesulfonic acid (17 mL) to the flask drop by drop in sequence. After the addition is complete, continue stirring for 5 h until the solution viscosity increases to obtain a viscous liquid. Pour the viscous liquid into 400 mL of deionized water for sedimentation to obtain a fibrous product. The fibrous product is dried in an oven at 80 °C for 12 h to obtain a terpolymer (P1).

[0104] 2) Dissolve the terpolymer P1 (1.0 g) in N-methylpyrrolidone (17 mL), and stir at 80 °C until completely dissolved; add methyl iodide (18 mmol), and stir at room temperature in the dark for 12 h. After the reaction ends, pour the reaction solution into ether for sedimentation to obtain a yellow solid. Wash the yellow solid with a large amount of deionized water and ethanol, and then dry it in an oven at 80 °C to obtain a quaternary ammonium salt-terpolymer (P2).

[0105] 3) Take the quaternary ammonium salt-terpolymer P2 (1.0 g) and dissolve it in N-methylpyrrolidone (30 mL), and stir at 80 °C until completely dissolved; at 0 °C, add POCl3 (12 mmol) and pyridine (12 mmol) drop by drop to the flask, and end the reaction after 12 h. Then add 60 mL of deionized water drop by drop to the flask, and then pour the mixed solution into 400 mL of deionized water, stir for 3 days, and then separate the reactants from the water. Wash the product with a large amount of deionized water and ethanol, and dry it in an oven at 80 °C to obtain the amphoteric copolymer.

[0106] 4) Weigh the amphoteric copolymer (1.0 g) and dissolve it in 25 mL of dimethyl sulfoxide, and stir at 80 °C for 12 h until completely dissolved to obtain a casting solution. Pour the casting solution onto a glass plate, and volatilize the solvent at 70 °C to obtain an M1 film with a thickness of 25 μm.

[0107] 5) Immerse the M1 film in a 0.1 mol / L dilute NaOH solution, keep it for 12 h under stirring and at 40 °C, then wash it with deionized water multiple times and dry it at 80 °C until the mass no longer changes to obtain the M2 film.

[0108] 6) Place the M2 film in an 85 wt% phosphoric acid solution and soak it at 100 °C for 12 h. After taking it out, place it in a sealed bag and keep it at room temperature for 3 days to obtain the high-temperature proton exchange membrane.

[0109] In this example, the intrinsic viscosity of the amphoteric copolymer obtained in step 3) measured by an Ubbelohde viscometer at 30 °C is 1.98 dL / g, and its structure is as follows:

[0110]

[0111] Figure 6 For the 1 1H-NMR spectrum; Figure 7 For the 31 31P-NMR spectrum, Figure 6 and Figure 7 indicates the successful synthesis of the amphoteric copolymer obtained in step 3).

[0112] Example 3

[0113] This example provides an amphoteric copolymer and a high-temperature proton exchange membrane prepared therefrom, and its preparation method includes the following steps:

[0114] 1) Add biphenyl (14.6 mmol), N-methyl-4-piperidone (6.44 mmol), isatin (9.66 mmol) and 14 mL of anhydrous dichloromethane into the reaction flask in sequence, stir mechanically at 25 °C for 1 h, and stir at 0 °C for 0.5 h; under the condition of keeping 0 °C, add trifluoroacetic acid (1 mL) and trifluoromethanesulfonic acid (17 mL) into the flask drop by drop in sequence. After the dropping is completed, continue to stir for 7 h and the viscosity of the solution increases to obtain a viscous liquid. Pour the viscous liquid into 400 mL of deionized water for sedimentation to obtain a fibrous product, and dry the fibrous product in an 80 °C oven for 12 h to obtain a terpolymer (P1).

[0115] 2) Dissolve the terpolymer P1 (1.0 g) in N-methylpyrrolidone (17 mL), stir at 80 °C until completely dissolved; add methyl iodide (12 mmol), stir at room temperature in the dark for 12 h. After the reaction is completed, pour the reaction solution into ether for sedimentation to obtain a yellow solid, wash the yellow solid with a large amount of deionized water and ethanol, and then dry it in an 80 °C oven to obtain a quaternary ammonium salt-terpolymer (P2).

[0116] 3) Quaternary ammonium salt - terpolymer P2 (1.0 g) was dissolved in N - methylpyrrolidone (30 mL), and stirred at 80 °C until completely dissolved; at 0 °C, POCl3 (18 mmol) and pyridine (18 mmol) were added dropwise into the flask, and the reaction ended after 12 h. Then 60 mL of deionized water was added dropwise into the flask, and then the mixed solution was poured into 400 mL of deionized water, stirred for 3 days, and then the reactants were separated from the water, washed with a large amount of deionized water and ethanol, and dried in an oven at 80 °C to obtain the amphoteric copolymer.

[0117] 4) Weigh the amphoteric copolymer (1.0 g) and dissolve it in 25 mL of dimethyl sulfoxide, stir at 80 °C for 12 h until completely dissolved to obtain a casting solution. The casting solution was cast on a glass plate, and after volatilizing the solvent at 70 °C, an M1 film with a thickness of 25 μm was obtained.

[0118] 5) The M1 film was immersed in a 0.1 mol / L NaOH dilute solution, kept at 40 °C with stirring for 12 h, then washed with deionized water multiple times, and dried at 80 °C until the mass no longer changed to obtain the M2 film.

[0119] 6) The M2 film was placed in an 85 wt% phosphoric acid solution, immersed at 100 °C for 12 h, taken out and placed in a sealed bag and kept at room temperature for 3 days to obtain a high - temperature proton exchange membrane.

[0120] In this example, the intrinsic viscosity of the amphoteric copolymer obtained in step 3) was measured to be 2.96 dL / g at 30 °C by an Ubbelohde viscometer, and its structure is as follows::

[0121]

[0122] Figure 8 For the 1 1H - NMR spectrum obtained in step 3) of Example 3; Figure 9 For the 31 31P - NMR spectrum obtained in step 3) of Example 3, Figure 8 and Figure 9 indicated the successful synthesis of the amphoteric copolymer obtained in step 3).

[0123] Example 4

[0124] This example provides an amphoteric copolymer and a high - temperature proton exchange membrane prepared therefrom, and its preparation method includes the following steps:

[0125] 1) 2,2'-Dihydroxybiphenyl (14.6 mmol), N-methyl-4-piperidone (3.22 mmol), isatin (12.88 mmol) and 14 mL of anhydrous dichloromethane were successively added to a reaction flask. The mixture was mechanically stirred at 25 °C for 1 h and then at 0 °C for 0.5 h. Under the condition of maintaining 0 °C, trifluoroacetic acid (1 mL) and trifluoromethanesulfonic acid (17 mL) were successively added dropwise into the flask. After the addition was completed, the mixture was stirred for another 10 h and the solution viscosity increased to obtain a viscous liquid. The viscous liquid was poured into 400 mL of deionized water for sedimentation to obtain a fibrous product, and the fibrous product was dried in an oven at 80 °C for 12 h to obtain a terpolymer (P1).

[0126] 2) The terpolymer P1 (1.0 g) was dissolved in N-methylpyrrolidone solution (30 mL) and stirred at 80 °C until completely dissolved. Methyl iodide (26 mmol) was added, and the mixture was stirred at room temperature in the dark for 12 h. After the reaction was completed, the reaction solution was poured into ether for sedimentation to obtain a yellow solid, which was washed with a large amount of deionized water and ethanol, and then dried in an oven at 80 °C to obtain a quaternary ammonium salt-terpolymer (P2).

[0127] 3) Take the quaternary ammonium salt-terpolymer P2 (1.0 g) and dissolve it in N-methylpyrrolidone (30 mL), and stir at 80 °C until completely dissolved. At 0 °C, POCl3 (0.162 mol) and pyridine (0.162 mol) were added dropwise into the flask, and the reaction ended after 12 h. Then 60 mL of deionized water was added dropwise into the flask for hydrolysis reaction. Subsequently, the mixed solution was all poured into 400 mL of deionized water, stirred for 3 days, and then the reactant was separated from the water, washed with a large amount of deionized water and ethanol, and dried in an oven at 80 °C to obtain an amphoteric copolymer.

[0128] 4) Weigh 1.0 g of the amphoteric copolymer and dissolve it in 25 mL of dimethyl sulfoxide, and stir at 80 °C for 12 h until completely dissolved to obtain a casting solution. The casting solution was cast on a glass plate, and after the solvent was volatilized at 70 °C, an M1 film with a thickness of 25 μm was obtained.

[0129] 5) The M1 film was soaked in a 0.1 mol / L NaOH dilute solution, kept at 40 °C with stirring for 12 h, then washed with deionized water multiple times, and dried at 80 °C until the mass no longer changed to obtain an M2 film.

[0130] 6) The M2 film was placed in an 85 wt% phosphoric acid solution and soaked at 100 °C for 12 h. After taking it out, it was placed in a sealed bag and kept at room temperature for 3 days to obtain a high-temperature proton exchange membrane.

[0131] In this example, the intrinsic viscosity of the amphoteric copolymer obtained in step 3) was measured to be 1.05 dL / g at 30 °C by an Ubbelohde viscometer, and its structure is shown as follows:

[0132]

[0133] The successful synthesis of the amphoteric copolymer of this example was proven by nuclear magnetic resonance hydrogen spectroscopy and nuclear magnetic resonance phosphorus spectroscopy.

[0134] Example 5

[0135] This example provides an amphoteric copolymer and a high-temperature proton exchange membrane prepared therefrom, and its preparation method includes the following steps:

[0136] 1) Add o-terphenyl (14.6 mmol), 4-imidazolecarboxaldehyde (3.22 mmol), isatin (12.88 mmol) and 14 mL of anhydrous dichloromethane to the reaction flask in sequence, stir mechanically at 25 °C for 1 h, and stir at 0 °C for 0.5 h; while maintaining the condition of 0 °C, add trifluoroacetic acid (1 mL) and trifluoromethanesulfonic acid (17 mL) to the flask drop by drop in sequence. After the addition is complete, continue to stir for 6 h, and the viscosity of the solution increases to obtain a viscous liquid. Pour the viscous liquid into 400 mL of deionized water for sedimentation to obtain a fibrous product, and dry the fibrous product in an oven at 80 °C for 12 h to obtain a terpolymer (P1).

[0137] 2) Dissolve the terpolymer P1 (1.0 g) in N-methylpyrrolidone solution (30 mL), and stir at 80 °C until completely dissolved; add methyl iodide (19 mmol), and stir at room temperature in the dark for 12 h. After the reaction is completed, pour the reaction solution into ether for sedimentation to obtain a yellow solid, wash the yellow solid with a large amount of deionized water and ethanol, and then dry it in an oven at 80 °C to obtain a quaternary ammonium salt-terpolymer (P2).

[0138] 3) Take the quaternary ammonium salt-terpolymer (1.0 g) and dissolve it in N-methylpyrrolidone (30 mL), and stir at 80 °C until completely dissolved; at 0 °C, add POCl3 (4.9 mmol) and pyridine (4.9 mmol) drop by drop into the flask, and the reaction ends after 12 h. Then add 60 mL of deionized water drop by drop into the flask for hydrolysis reaction. Subsequently, pour the mixed solution into 400 mL of deionized water, stir for 3 days, then separate the reactants from the water, wash the product with a large amount of deionized water and ethanol, and dry it in an oven at 80 °C to obtain the amphoteric copolymer.

[0139] 4) Weigh the amphoteric copolymer (1.0 g) and dissolve it in 25 mL of dimethyl sulfoxide, and stir at 80 °C for 12 h until completely dissolved to obtain a casting solution. Pour the casting solution onto a glass plate, and volatilize the solvent at 70 °C to obtain an M1 film with a thickness of 25 μm.

[0140] 5) Immerse the M1 film in a 0.1 mol / L dilute NaOH solution, keep it for 12 h under stirring and at 40 °C, then wash it with deionized water multiple times and dry it at 80 °C until the mass no longer changes to obtain the M2 film.

[0141] 6) Place the M2 film in an 85 wt% phosphoric acid solution and immerse it at 100 °C for 12 h. After taking it out, place it in a sealed bag and keep it at room temperature for 3 days to obtain the high-temperature proton exchange membrane.

[0142] In this example, the amphoteric copolymer obtained in step 3) has an intrinsic viscosity of 1.25 dL / g measured by an Ubbelohde viscometer at 30 °C, and its structure is as follows:

[0143]

[0144] The successful synthesis of the amphoteric copolymer in this example is proved by nuclear magnetic resonance hydrogen spectrum and nuclear magnetic resonance phosphorus spectrum.

[0145] Comparative Example 1

[0146] This comparative example provides a phosphonic acid group copolymer and a high-temperature proton exchange membrane prepared therefrom, and its preparation method includes the following steps:

[0147] 1) Add p-terphenyl (14.6 mmol), N-methyl-4-piperidone (12.88 mmol), isatin (3.22 mmol) and 14 mL of anhydrous dichloromethane to the reaction flask in sequence, mechanically stir at 25 °C for 1 h, and stir at 0 °C for 0.5 h; keep at 0 °C, and add trifluoroacetic acid (1.0 mL) and trifluoromethanesulfonic acid (17 mL) to the flask drop by drop in sequence. After the addition is complete, continue to stir for 6 h and the solution viscosity increases to obtain a viscous liquid. Pour the viscous liquid into 400 mL of deionized water for sedimentation to obtain a fibrous product, and dry the fibrous product in an 80 °C oven for 12 h to obtain a terpolymer (P1).

[0148] 2) Take the terpolymer P1 (1.0 g) and dissolve it in N-methylpyrrolidone (30 mL), stir at 80 °C until completely dissolved; at 0 °C, add POCl3 (6 mmol) and pyridine (6 mmol) drop by drop to the flask, and end the reaction after 12 h. Then add 60 mL of deionized water drop by drop to the flask, and then pour the mixed solution into 400 mL of deionized water, stir for 3 days, then separate the reactants from the water, wash the product with a large amount of deionized water and ethanol, and dry it in an 80 °C oven to obtain the phosphonic acid group copolymer.

[0149] 3) Weigh the phosphonic acid group copolymer (1.0 g) and dissolve it in 25 mL of dimethyl sulfoxide, stir at 80 °C for 12 h until completely dissolved to obtain a casting solution. Pour the casting solution onto a glass plate, and after volatilizing the solvent at 70 °C, obtain an M1 film with a thickness of 25 μm.

[0150] 4) Immerse the M1 film in an 85 wt% phosphoric acid solution at 100 °C for 12 h. After taking it out, place it in a sealed bag and keep it at room temperature for 3 days to obtain a high-temperature proton exchange membrane.

[0151] In this example, the intrinsic viscosity of the phosphonic acid group copolymer obtained in step 2) measured by an Ubbelohde viscometer at 30 °C is 1.43 dL / g, and its structure is as follows:

[0152]

[0153] The literature "Intermolecular Acid-Base-Pairs Containing Poly(p-Terphenyl-co-Isatin Piperidinium) for High Temperature Proton Exchange Membrane Fuel Cells" is used to prove that steps 1) and 2) of this comparative example can synthesize the phosphonic acid group copolymer with the corresponding structure.

[0154] Performance test

[0155] Take the high-temperature proton exchange membranes of Examples 1 to 5 and Comparative Example 1 for performance testing, and the results are shown in Table 1.

[0156] Table 1

[0157]

[0158] As can be seen from Table 1:

[0159] Compared with Comparative Example 1, the amphoteric copolymer of Example 1 introduces a nitrogen-containing heterocyclic quaternary cation. When used to prepare a high-temperature proton exchange membrane for a fuel cell, it can effectively reduce the phosphoric acid adsorption amount in the high-temperature proton exchange membrane (low phosphoric acid adsorption amount and volume swelling rate), thereby improving the mechanical properties of the high-temperature proton exchange membrane (high tensile strength); and, at 140 °C, the high-temperature proton exchange membrane of Example 1 has higher proton conduction performance under the condition of a lower phosphoric acid adsorption amount, that is, the amphoteric copolymer of the present invention enables the membrane to have both good proton conduction performance and mechanical properties; in addition, the phosphoric acid retention rate of the high-temperature proton exchange membrane of Example 1 is higher; and, at 140 °C, the peak power density and voltage decay rate of the high-temperature proton exchange membrane of Example 1 are also better, indicating that the amphoteric copolymer of the present invention can make the membrane have high performance and long life.

[0160] Comparing Examples 1 to 3, it can be seen that by regulating the value of X (i.e., regulating the ratio of the organic phosphonic acid group and the ion-pairing acid in the polymer), precise regulation of the phosphoric acid adsorption amount of the high-temperature proton exchange membrane can be achieved, and further simultaneous regulation of the mechanical strength and electrochemical performance can be realized.

[0161] Comparing Examples 1, 4 to 5, it can be seen that conventional monomers of Ar or R can be used to prepare the amphoteric copolymer of the present invention, and have a certain influence on the performance of the high-temperature proton exchange membrane. When the monomer-derived structures and their ratios of the amphoteric copolymer are the same, by introducing a nitrogen-containing heterocyclic quaternary ammonium cation, the performance of the membrane can be superior to that of the membrane prepared from the copolymer without the introduction of the nitrogen-containing heterocyclic quaternary ammonium cation.

[0162] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. An amphoteric copolymer for preparing a high-temperature proton exchange membrane, characterized in that: It is the structure shown in formula (Ⅰ): Wherein, 0.2≤X≤0.4; Ar is a structure containing an aromatic ring; R is a structure in which a nitrogen-containing heterocyclic quaternary ammonium cation and an anion are bound by an ion pair force; The anion is dihydrogen phosphate; The intrinsic viscosity of the amphoteric copolymer is 1 to 3 dL / g; The R structure is as follows: Y - represents the anion.

2. The amphoteric copolymer according to claim 1, characterized in that The Ar is any one of the following structures:

3. Use of the amphoteric copolymer according to any one of claims 1 to 2 in the preparation of a high-temperature proton exchange membrane.

4. A method for preparing a high-temperature proton exchange membrane, characterized in that: The steps include: S1. mixing indigo carmine, a carbonyl-containing nitrogen-containing heterocyclic monomer and an aromatic ring-containing monomer, and then subjecting the mixture to a Friedel-Crafts reaction polycondensation to obtain a terpolymer; S2. The terpolymer in step S1 undergoes a quaternization reaction with a nucleophilic reagent to convert the nitrogen-containing heterocycle in the terpolymer into a quaternary ammonium cation to obtain a quaternary ammonium-terpolymer; S3. The quaternary ammonium-terpolymer in step S2 undergoes a phosphating reaction and a hydrolysis reaction to introduce an organic phosphonic acid group to obtain a halide-containing amphoteric copolymer; S4. The halide-containing amphoteric copolymer of step S3 is formulated into a casting solution, cast, and dried to obtain a film; S5. The film is immersed in an alkaline solution, stirred, dried, and then immersed in a phosphoric acid solution for phosphoric acid adsorption, and then the phosphoric acid in the membrane is rearranged to obtain the high temperature proton exchange membrane; The high temperature proton exchange membrane contains the amphoteric copolymer according to any one of claims 1 to 2.

5. A high temperature proton exchange membrane, characterized in that: It is prepared by the preparation method described in claim 4.

Images