Polymer electrolyte membrane based on phosphoric acid doped quaternary ammonium polyphenyl ether cross-linked polybenzimidazole and preparation method thereof

Abstract

The application belongs to the field of high polymer materials, and relates to a polymer electrolyte membrane for high-temperature phosphoric acid fuel cells, in particular to a polymer electrolyte membrane based on phosphoric acid doped quaternary ammonium polyphenyl ether cross-linked polybenzimidazole and a preparation method thereof. Polyphenyl ether is first brominated, the brominated polyphenyl ether is then partially quaternized, polybenzimidazole is prepared, then an electrolyte membrane of quaternary ammonium polyphenyl ether cross-linked polybenzimidazole is prepared, and finally phosphoric acid doping treatment is performed to obtain the polymer electrolyte membrane based on phosphoric acid doped quaternary ammonium polyphenyl ether cross-linked polybenzimidazole. The introduction of quaternary ammonium groups is more conducive to the absorption of phosphoric acid, thereby improving the conductivity of the electrolyte membrane. Polybenzimidazole is cross-linked with quaternary ammonium polyphenyl ether, and the introduction of the cross-linked structure can guarantee excellent size stability, chemical stability and mechanical properties of the electrolyte membrane. Moreover, the preparation cost is relatively low, and the process is simple and safe.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of high polymer materials, and relates to a polymer electrolyte membrane for high-temperature phosphoric acid fuel cells, in particular to a polymer electrolyte membrane based on phosphoric acid-doped quaternary ammonium polyphenyl ether cross-linked polybenzimidazole and a preparation method thereof. BACKGROUND

[0002] In recent decades, high-temperature proton exchange membrane fuel cells (HT-PEMFC) have attracted extensive attention due to their simple water / thermal management system, high tolerance to fuel impurities and higher electrode kinetics. The electrolyte membrane is the core component of the HT-PEMFC. So far, the polymer electrolyte membrane widely considered to have the most promising application is the perfluorosulfonic acid type proton exchange membrane represented by Nafion membrane developed by the American Dupont Company in the 1960s. Due to its unique molecular structure (polytetrafluoroethylene hydrophobic skeleton, perfluoroether side chain and hydrophilic -SO3H group), the Nafion membrane has many remarkable advantages, such as strong acidic sulfonic acid groups and obvious micro-phase separation structure. Such structure is conducive to the transmission of protons. However, the conductivity of the Nafion membrane is extremely dependent on water, and the loss of water at high temperature will cause the conductivity of the membrane to drop sharply, which limits its application in high-temperature environments (above 100℃). At the same time, the high cost of the Nafion membrane greatly affects the competitiveness of fuel cells in the field of power energy and mobile power sources.

[0003] The working temperature of the HT-PEMFC is generally higher than 100℃, so a suitable proton conductor needs to be selected to replace water. Phosphoric acid is currently the most widely used non-aqueous proton conducting material. The phosphoric acid (PA) doped polybenzimidazole (PA-PBI) membrane has high mechanical properties, excellent chemical and thermal stability and is widely used in high-temperature phosphoric acid proton exchange membrane fuel cells. Since the proton conductivity of polybenzimidazole (PBI) itself is very low, only 10 -9 mS cm -1 , it cannot be used as an independent solid electrolyte. Therefore, the phosphoric acid doping amount greatly affects the conductivity of the membrane and is generally considered to be an important performance indicator of high-temperature phosphoric acid doped membranes. The traditional PBI structure relies on the acid-base interaction between the H on the imidazole and the phosphoric acid molecules to achieve the absorption and retention of phosphoric acid. However, with the increase of the phosphoric acid doping amount, on the one hand, it will exacerbate the weakening of the interaction between the polymer molecules, making the swelling degree of the membrane too large, and on the other hand, it will exacerbate the plasticizing effect of phosphoric acid on the membrane, ultimately leading to the decline of the dimensional stability of the membrane and the loss of mechanical properties. Therefore, there is an urgent need to develop a phosphoric acid doped polymer electrolyte membrane with high acid absorption rate and high stability. SUMMARY

[0004] The application aims to provide a phosphoric acid doped quaternary ammonium based polyphenyl ether cross-linked polybenzimidazole polymer electrolyte membrane for high temperature phosphoric acid fuel cell to overcome the shortcomings of the prior art. The polyphenyl ether is a low-cost engineering plastic with excellent film forming property, thermal stability and mechanical strength. The quaternary ammonium treatment is beneficial to the absorption and retention of the polyphenyl ether membrane to the phosphoric acid, thereby obtaining high conductivity. On this basis, the cross-linked polybenzimidazole structure can guarantee the chemical stability and the size stability of the electrolyte membrane after the phosphoric acid doping.

[0005] The polymer provided by the application comprises a repeating unit as shown in formula (1) in the general structure formula of the polymer,

[0006]

[0007] In the formula, x, y and z are the number of each repeating unit of the polyphenyl ether, n is an integer of 1-12, and m is the polymerization degree of the polybenzimidazole.

[0008] The preparation process of the high temperature phosphoric acid membrane is as follows:

[0009] (1) Bromination of polyphenyl ether

[0010] Under the nitrogen environment, the polyphenyl ether is dissolved in 1, 2 dichloroethane to form a homogeneous solution. x-brominated alkyl acid chloride and aluminum chloride (catalyst) are added, and the reaction is continuously stirred for 4-12 hours. The reaction solution is dropped into ethanol for precipitation, and the precipitate is washed with deionized water for multiple times, and then placed in an oven at 80°C for drying to obtain the brominated alkyl acylated polyphenyl ether. Under the nitrogen atmosphere, the brominated alkyl acylated polyphenyl ether is dissolved in 1, 2 dichloroethane to form a homogeneous solution. Triethylsilane and trifluoroacetic acid are added, and the temperature is raised to 105°C for 1-2 days for reduction. After the precipitation by dropping into ethanol, the neutralization with potassium hydroxide and the washing with deionized water for multiple times, the brominated polyphenyl ether is placed in an oven at 80°C for drying.

[0011] The molar ratio of the polyphenyl ether, x-brominated alkyl acid chloride and aluminum chloride is 1: x: 1, and the x-brominated alkyl acid chloride is 4-bromobutyryl chloride, 5-bromovaleryl chloride, 6-bromohexanoyl chloride or 8-bromooctanoyl chloride.

[0012] The molar ratio of the brominated alkyl acylated polyphenyl ether, triethylsilane and trifluoroacetic acid is 1: 5: 10.

[0013] (2) Partial quaternization of the brominated polyphenyl ether

[0014] The brominated polyphenyl ether and 1-methylimidazole are dissolved in N-methylpyrrolidone, and the reaction is carried out at 60°C for 2-4 hours. After the precipitation by dropping into diethyl ether, the washing for multiple times and the drying in an oven, the quaternary ammonium polyphenyl ether is obtained by controlling the ratio of the brominated polyphenyl ether and 1-methylimidazole.

[0015] The molar ratio of brominated polyphenyl ether to 1-methyl imidazole is: 1:0.25-1:0.45.

[0016] (3) Preparation of polybenzimidazole

[0017] 3,3'4,4'-diphenyltetramine and 2,2-bis(4-carboxyphenyl) hexafluoropropane in a molar ratio of 1:1 are used as raw materials, and a solution with a polymer mass fraction of 10% is prepared by dissolving them in polyphosphoric acid. Under nitrogen protection, the solution is subjected to gradient heating (heating speed is 40°C / hour) at 90-180°C, and mechanical stirring polymerization is performed until the reaction material shows obvious "climbing rod" phenomenon, and the reaction is stopped. The product is washed with deionized water and ethanol until it is neutral.

[0018] (4) Preparation of electrolyte membrane of quaternary ammonium polyphenyl ether cross-linked polybenzimidazole

[0019] The electrolyte membrane of quaternary ammonium polyphenyl ether cross-linked polybenzimidazole is prepared by dissolving polybenzimidazole and quaternary ammonium polyphenyl ether in dimethyl sulfoxide in a molar ratio of 2:1 of the bromine in polyphenyl ether to the benzimidazole repeating unit in polybenzimidazole, forming a 5% polymer (a mixture of polybenzimidazole and quaternary ammonium polyphenyl ether) / dimethyl sulfoxide solution, and stirring the reaction liquid at 80°C for 3-6 hours, and then pouring the reaction liquid onto a clean glass plate and drying at 60°C for 48 hours.

[0020] (5) Phosphoric acid doping treatment

[0021] The prepared electrolyte membrane is immersed in an 85% phosphoric acid solution, soaked at 40°C for 24 hours, so that the phosphoric acid is fully absorbed into the membrane, and the residual phosphoric acid on the surface of the cross-linked electrolyte membrane is removed with dust-free paper, and then the test can be performed.

[0022] Thanks to the technical solutions, the present application has the following advantages compared with the prior art:

[0023] The electrolyte membrane based on polybenzimidazole is introduced into the quaternary ammonium group, which is more conducive to the absorption of phosphoric acid and thus improves the conductivity of the electrolyte membrane. The polybenzimidazole is cross-linked with the quaternary ammonium polyphenyl ether, and the introduction of the cross-linked structure can guarantee excellent dimensional stability, chemical stability and mechanical properties of the electrolyte membrane; and the preparation cost is relatively low, and the process is relatively simple and safe. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The structural formula and nuclear magnetic resonance spectrum of completely brominated PPO and quaternary ammonium PPO.

[0025] Figure 2 The structural formula and nuclear magnetic resonance spectrum of polybenzimidazole. DETAILED DESCRIPTION

[0026] The application will be further described in connection with the following examples.

[0027] Example 1

[0028] This example provides a method for preparing a quaternary ammonium polyphenylene ether cross-linked polybenzimidazole polymer electrolyte membrane, which comprises the following steps:

[0029] (a) Preparation of bromohexanoylated polyphenylene ether: 2.00 g of polyphenylene ether is dissolved in 30 ml of 1,2-dichloroethane under a nitrogen atmosphere, and stirred to form a homogeneous solution. 4.98 g of 6-bromohexanoyl chloride and 3.12 g of aluminum chloride are added, and after stirring vigorously at room temperature for 4 hours, precipitated by dropping into ethanol, and washed with deionized water for 3 times (to remove the residual aluminum chloride and solvent in the polymer, and finally obtain a light yellow product), and placed in an oven at 80°C for drying. The polyphenylene ether with a degree of hexanoylation of 100% is obtained, and its molecular formula is:

[0030]

[0031] (b) Reduction of brominated polyphenylene ether: 1.00 g of hexanoylated polyphenylene ether is dissolved in 6.67 ml of 1,2-dichloroethane, and stirred to form a homogeneous solution. 1.65 ml of triethylsilane and 1.71 ml of trifluoroacetic acid are added, and the temperature is raised to 105°C for reaction for 2 days, precipitated by dropping into ethanol, and washed with potassium hydroxide until neutral, and then washed with deionized water for 3 times (to remove the residual triethylsilane and trifluoroacetic acid, and finally obtain a light yellow solid). Placed in an oven at 80°C for drying to obtain polyphenylene ether with a degree of bromination of 100%. Its molecular formula is:

[0032] (see the preparation method of other brominated polyphenylene ethers described below);

[0033] (c) Preparation of quaternary ammonium polyphenylene ether: 1.00 g of brominated polyphenylene ether is dissolved in N-methylpyrrolidone with 0.072 g of 1-methylimidazole, and reacted at 60°C for 4 hours, precipitated by dropping into diethyl ether, and washed for 3 times until a light yellow powder is formed, and then placed in an oven for drying to obtain quaternary ammonium polyphenylene ether with a degree of quaternary ammonium of 25%;

[0034] (d) 0.15 g of polybenzimidazole (polybenzimidazole is prepared as follows: a clean three-necked flask is selected, 27.00 g of polyphosphoric acid is added into the three-necked flask under the nitrogen environment at 90 °C, and stirred until no bubbles are generated. After uniform stirring, 1.20 g of 3,3'4,4'-diphenyltetramine is added and stirred for half an hour, and finally 1.3 g of 2,2-bis(4-carboxyphenyl) hexafluoropropane is added, and after uniform stirring, the nitrogen is removed. The temperature is increased by 20 °C every half an hour until the temperature is increased to 180 °C, and the reaction is stopped after the reactants show obvious "climbing rod" phenomenon. The product is washed with deionized water and ethanol until neutral) and 0.20 g of polyphenyl ether with a quaternary ammonium degree of 25% are dissolved in dimethyl sulfoxide, and stirred at 80 °C for 3 hours, and then the reaction liquid is poured onto a clean glass plate, and dried at 60 °C for 48 hours, to prepare a cross-linked polymer electrolyte membrane (the structure formula and nuclear magnetic resonance spectrum of the quaternary ammonium polyphenyl ether and polybenzimidazole are shown in Figure 1 、 Figure 2 ).

[0035] (e) The prepared cross-linked polymer electrolyte membrane is immersed in an 85% phosphoric acid solution, soaked at 40 °C for 24 hours, so that the phosphoric acid is fully absorbed into the membrane, and the residual phosphoric acid on the surface of the cross-linked polymer electrolyte membrane is removed with a dust-free paper, and the structure formula is as follows:

[0036] The performance parameters of the cross-linked electrolyte membrane are measured as follows: the phosphoric acid absorption rate is 119.56%, the swelling degree is 103.62%, the phosphoric acid retention rate is 83.36% after being placed at 100 °C for 120 hours, the tensile strength after acid soaking is 20.31 MPa, and the proton conductivity at 80 °C can reach 44.78 mS cm -1 , and the proton conductivity at 160 °C is 74.46 mS cm -1 ; the membrane is soaked in Fenton reagent (4 ppm Fe 2+ , 3% H2O2) at 80 °C for 120 hours, and the residual weight is measured again as 81.21%, which proves that it has good oxidation stability.

[0037] Example 2

[0038] The preparation method of the quaternary ammonium polyphenyl ether cross-linked polybenzimidazole polymer electrolyte membrane provided in this embodiment is basically the same as that in Example 1, except that 4.33 g of 4-bromobutyryl chloride is used in step (a).

[0039] The performance parameters of the polymer electrolyte membrane are measured as follows: the phosphoric acid absorption rate is 102.58%, the swelling degree is 88.03%, the phosphoric acid retention rate is 81.17% after being placed at 100 °C for 120 hours, the tensile strength after acid soaking is 30.58 MPa, and the proton conductivity at 80 °C can reach 35.74 mS cm -1The proton conductivity at 160°C is 63.84 mS cm -1 The membrane was immersed in Fenton's reagent (4ppmFe 2+ , 3% H2O2), placed at 80°C for 120 hours, and its remaining weight was measured again to be 84.02%, proving that it has good oxidation stability.

[0040] Example 3

[0041] This embodiment provides a method for preparing a polymer electrolyte membrane of quaternized polyphenylene ether cross-linked polybenzimidazole, which is basically the same as that in Example 1, except that 4.65 g of 5-bromovaleryl chloride is used in step (a).

[0042] The performance parameters of the polymer electrolyte membrane were measured as follows: phosphoric acid absorption rate of 111.35%, swelling degree of 91.27%; phosphoric acid retention rate of 82.65% after 120 hours at 100°C; tensile strength after acid soaking of 26.84 MPa; proton conductivity of 40.89 mS cm at 80°C. -1 The proton conductivity at 160°C is 69.93 mS cm -1 The membrane was immersed in Fenton's reagent (4ppmFe 2+ , 3% H2O2), placed at 80°C for 120 hours, and its remaining weight was measured again to be 82.97%, proving that it has good oxidation stability.

[0043] Example 4

[0044] This embodiment provides a method for preparing a polymer electrolyte membrane of quaternized polyphenylene ether cross-linked polybenzimidazole, which is basically the same as that in Example 1, except that 5.63 g of 8-bromooctanoyl chloride is used in step (a).

[0045] The performance parameters of the polymer electrolyte membrane were measured as follows: phosphoric acid absorption rate of 143.28%, swelling degree of 122.65%, phosphoric acid retention rate of 84.42% after 120 hours at 100°C, tensile strength after acid soaking of 11.78 MPa, and proton conductivity of 52.81 mS cm at 80°C. -1 The proton conductivity at 160°C is 80.79 mS cm -1 The membrane was immersed in Fenton's reagent (4ppmFe 2+ , 3% H2O2), placed at 80°C for 120 hours, and its remaining weight was measured again to be 79.35%, proving that it has good oxidation stability.

[0046] Example 5

[0047] The present example provides a preparation method of a quaternary ammonium polyphenyl ether cross-linked polybenzimidazole polymer electrolyte membrane, which is basically the same as that in Example 1, except that the mass of 1-methylimidazole prepared in step (c) is 0.101 g, and a polyphenyl ether with a quaternization degree of 35% is obtained (the molar ratio of brominated PPO to 1-methylimidazole is 1:0.35).

[0048] The performance parameters of the polymer electrolyte membrane are measured as follows: phosphoric acid absorption rate is 125.72%, swelling degree is 112.84%; phosphoric acid retention rate is 84.15% after being placed at 100°C for 120 hours; tensile strength after acid soaking is 15.73 MPa; proton conductivity at 80°C is up to 53.64 mS cm -1 , and proton conductivity at 160°C is 87.73 mS cm -1 ; the membrane is soaked in Fenton reagent (4 ppm Fe 2+ , 3% H2O2) and placed at 80°C for 120 hours, and the remaining weight is measured again as 79.54%, proving that it has good oxidation stability.

[0049] Example 6

[0050] The present example provides a preparation method of a quaternary ammonium polyphenyl ether cross-linked polybenzimidazole polymer electrolyte membrane, which is basically the same as that in Example 1, except that the mass of 1-methylimidazole prepared in step (c) is 0.130 g. A polyphenyl ether with a quaternization degree of 45% is obtained (the molar ratio of brominated PPO to 1-methylimidazole is 1:0.45).

[0051] The performance parameters of the polymer electrolyte membrane are measured as follows: phosphoric acid absorption rate is 134.83%, swelling degree is 123.54%; phosphoric acid retention rate is 85.72% after being placed at 100°C for 120 hours; tensile strength after acid soaking is 11.87 MPa; proton conductivity at 80°C is up to 64.91 mS cm -1 , and proton conductivity at 160°C is 96.94 mS cm -1 ; the membrane is soaked in Fenton reagent (4 ppm Fe 2+ , 3% H2O2) and placed at 80°C for 120 hours, and the remaining weight is measured again as 78.91%, proving that it has good oxidation stability.

[0052] Example 7

[0053] The present example provides a preparation method of a quaternary ammonium polyphenyl ether cross-linked polybenzimidazole polymer electrolyte membrane, which is basically the same as that in Example 1, except that: the mass of 6-bromohexanoyl chloride prepared in step (a) is 1.743 g, and the mass of aluminum chloride is 1.089 g. The bromination degree of PPO is 35% (control PPO: 6-bromohexanoyl chloride: 1:0.35).

[0054] The performance parameters of the polymer electrolyte membrane are measured as follows: the phosphoric acid absorption rate is 84.65%, the swelling degree is 95.75%; the phosphoric acid retention rate is 80.53% after being placed at 100°C for 120 hours; the tensile strength after acid soaking is 26.87 MPa; the proton conductivity at 80°C can reach 35.43 mS cm -1 , and the proton conductivity at 160°C is 59.36 mS cm -1 ; the residual weight of the membrane immersed in Fenton reagent (4 ppm Fe 2+ , 3% H2O2) and placed at 80°C for 120 hours is measured again as 84.54%, proving that it has good oxidation stability.

[0055] Example 8

[0056] The present example provides a preparation method of a quaternary ammonium polyphenyl ether cross-linked polybenzimidazole polymer electrolyte membrane, which is basically the same as that in Example 1, except that: the mass of 6-bromohexanoyl chloride prepared in step (a) is 1.743 g, and the mass of aluminum chloride is 1.089 g. The bromination degree of PPO is 35% (control PPO: 6-bromohexanoyl chloride: 1:0.35).

[0057] The performance parameters of the polymer electrolyte membrane are measured as follows: the phosphoric acid absorption rate is 84.65%, the swelling degree is 95.75%; the phosphoric acid retention rate is 80.53% after being placed at 100°C for 120 hours; the tensile strength after acid soaking is 26.87 MPa; the proton conductivity at 80°C can reach 35.43 mS cm -1 , and the proton conductivity at 160°C is 59.36 mS cm -1 ; the residual weight of the membrane immersed in Fenton reagent (4 ppm Fe 2+ , 3% H2O2) and placed at 80°C for 120 hours is measured again as 84.54%, proving that it has good oxidation stability.

[0058] Comparative Example 1

[0059] The present example provides a preparation method of a polymer electrolyte membrane, which selects a polyphenyl ether with a bromination degree of 100% for 25% quaternary ammonium treatment to prepare a non-cross-linked PPO-based polymer electrolyte membrane, and the structural formula is as follows:

[0060]

[0061] Under the same experimental conditions, the performance parameters of the polymer electrolyte membrane were measured as follows: proton conductivity at 80°C was 34.68 mS cm -1 , it can reach 73.76mS cm at 160℃ -1 After acid soaking, the tensile strength is 3.04Mpa, which is relatively weak; the acid absorption rate at 40°C is 98.23%, and the swelling degree is 215.77%, which is relatively large.

[0062] Comparative Example 2

[0063] This embodiment provides a method for preparing a polymer electrolyte membrane, in which polybenzimidazole is used alone to prepare a non-cross-linked polybenzimidazole membrane. The specific synthesis process of the polybenzimidazole membrane is as follows: Use a clean three-necked flask, add 27g of polyphosphoric acid to the three-necked flask under a nitrogen environment at 90°C, and stir until there are no bubbles. Add 4g of phosphorus pentoxide to remove moisture from the reaction. After stirring evenly, add 1.2g of 3,3'4,4'-diphenyltetramine and stir for half an hour. Finally, add 1.3g of 2,2-bis(4-carboxyphenyl)hexafluoropropane, stir evenly, and remove the nitrogen. Raise the temperature by 20°C every half hour until it reaches 180°C. Stop the reaction when the reactants show obvious "pole climbing" phenomenon. Wash the product with deionized water and ethanol until it is neutral. Specific film formation process: weigh 0.2g of polybenzimidazole and dissolve it in 4ml of dimethyl sulfoxide at 80℃. After stirring for 24 hours until it is completely dissolved, drop it on a clean glass plate and bake it in an 80℃ oven for 24 hours to obtain a polybenzimidazole film. Its structural formula is:

[0064]

[0065] Under the same experimental conditions, the performance parameters of the polymer electrolyte membrane were measured as follows: phosphoric acid absorption rate of 71.36%, swelling degree of 85.64%, and pure PBI had a lower acid absorption rate. After 120 hours at 100°C, the phosphoric acid retention rate was 73.64%. The tensile strength after acid soaking was 31.16 MPa. The proton conductivity at 80°C was 17.58 mS cm -1 The proton conductivity at 160°C is 35.81 mS cm -1 The membrane was immersed in Fenton reagent (4ppm Fe 2+ , 3% H2O2), and placed at 80°C for 120 hours. The remaining weight was measured again and was 85.63%.

[0066] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A polymer electrolyte membrane based on phosphoric acid-doped quaternized polyphenylene ether cross-linked polybenzimidazole, characterized in that: The structural formula of the polymer is shown in formula (1), ， （1）； Wherein, x, y and z are the number of repeating units of polyphenylene ether, n is an integer of 1 to 12, and m is the degree of polymerization of polybenzimidazole.

2. A method for preparing a polymer electrolyte membrane based on phosphoric acid-doped quaternized polyphenylene ether cross-linked polybenzimidazole according to claim 1, characterized in that: The preparation method comprises the following steps: (1) Bromination of polyphenylene ether Under a nitrogen atmosphere, polyphenylene ether is dissolved in 1,2-dichloroethane and stirred to form a homogeneous solution; x-bromoalkyl chloride and aluminum trichloride catalyst are added, stirred and reacted at room temperature for 4-12 hours, the reaction solution is dropped into ethanol for precipitation, the precipitate is washed with deionized water, and dried in an oven at 80°C to obtain brominated alkyl acylated polyphenylene ether; under a nitrogen atmosphere, the brominated alkyl acylated polyphenylene ether is dissolved in 1,2-dichloroethane and stirred to form a homogeneous solution, triethylsilane and trifluoroacetic acid are added, and the temperature is raised to 105°C for reaction for 1-2 days for reduction; the precipitate is dropped into ethanol, washed with potassium hydroxide until neutral, then washed with deionized water, and dried in an oven at 80°C to obtain brominated polyphenylene ether; (2) Partial quaternization of brominated polyphenylene ether The brominated polyphenylene ether and 1-methylimidazole were dissolved in N-methylpyrrolidone, reacted at 60°C for 2-4 hours, and then added dropwise to ether for precipitation. After washing, the mixture was placed in an oven for drying, and the ratio of brominated polyphenylene ether to 1-methylimidazole was controlled to obtain quaternized polyphenylene ether. (3) Preparation of polybenzimidazole Dissolve 3,3'4,4'-benzyltetramine and 2,2-bis(4-carboxyphenyl)hexafluoropropane in polyphosphoric acid, increase the temperature gradually from 90 to 180°C under nitrogen protection, and polymerize with mechanical stirring until the reactants show obvious "pole climbing" phenomenon. Stop the reaction, and wash the product with deionized water and ethanol until it is neutral. (4) Preparation of electrolyte membrane of quaternized polyphenylene ether cross-linked polybenzimidazole Polybenzimidazole and quaternized polyphenylene ether were dissolved in dimethyl sulfoxide to form a polymer / dimethyl sulfoxide solution with a mass fraction of 5%. The solution was heated to 80°C, stirred and reacted for 3 to 6 hours, and then poured onto a clean glass plate and dried at 60°C for 48 hours to prepare an electrolyte membrane of quaternized polyphenylene ether cross-linked polybenzimidazole. (5) Phosphoric acid doping treatment The prepared electrolyte membrane was immersed in a phosphoric acid solution with a mass fraction of 85% at 40°C for 24 hours so that the phosphoric acid was fully absorbed into the membrane. The residual phosphoric acid on the surface of the cross-linked electrolyte membrane was removed with dust-free paper to obtain the product.

3. The method for preparing a polymer electrolyte membrane based on phosphoric acid-doped quaternized polyphenylene ether cross-linked polybenzimidazole according to claim 2, wherein: The molar ratio of polyphenylene ether, x-bromoalkyl chloride and aluminum trichloride is 1:x:1, and the x-bromoalkyl chloride is 4-bromobutyryl chloride, 5-bromovaleryl chloride, 6-bromohexanoyl chloride and 8-bromooctanoyl chloride.

4. The method for preparing a polymer electrolyte membrane based on phosphoric acid-doped quaternized polyphenylene ether cross-linked polybenzimidazole according to claim 2, wherein: The molar ratio of bromoalkyl acylated polyphenylene ether, triethylsilane and trifluoroacetic acid is 1:5:

10.

5. The method for preparing a polymer electrolyte membrane based on phosphoric acid-doped quaternized polyphenylene ether cross-linked polybenzimidazole according to claim 2, wherein: The molar ratio of brominated polyphenylene ether to 1-methylimidazole is 1:0.25-1:0.

45.

6. The method for preparing a polymer electrolyte membrane based on phosphoric acid-doped quaternized polyphenylene ether cross-linked polybenzimidazole according to claim 2, wherein: 3,3'4,4'-diphenyltetramine and 2,2'-bis(4-carboxyphenyl)hexafluoropropane at a molar ratio of 1:1 were dissolved in polyphosphoric acid to prepare a solution with a polymer mass fraction of 10%.

7. The method for preparing a polymer electrolyte membrane based on phosphoric acid-doped quaternized polyphenylene ether cross-linked polybenzimidazole according to claim 2, wherein: The molar ratio of the bromide in the polyphenylene ether to the benzimidazole repeating unit in the polybenzimidazole is controlled to be 2:

1.

8. An application of the polymer electrolyte membrane based on phosphoric acid-doped quaternized polyphenylene ether cross-linked polybenzimidazole as claimed in claim 1, characterized in that: The electrolyte membrane is used as an electrolyte membrane of a high-temperature phosphoric acid fuel cell.

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