Linear quaternary ammonium side chain fluorenyl polymers, methods of making and high phosphoric acid retention proton exchange membranes based thereon and applications

Abstract

Linear quaternary ammonium side chain fluorenyl polymer, its preparation method and high phosphoric acid retention proton exchange membrane based on it and application. The invention belongs to the technical field of high-temperature proton exchange membranes for fuel cells. The purpose of the invention is to solve the technical problem of serious phosphoric acid loss of the existing proton exchange membrane. The invention develops a new type of high-temperature proton exchange membrane with high phosphoric acid retention, and the strong ion pair action between the multi-quaternary ammonium side chain and the phosphoric acid molecules makes the multi-quaternary ammonium side chain form a new limited action on the phosphoric acid, thereby improving the phosphoric acid retention rate of the membrane after phosphoric acid doping. Therefore, it can be applied to the working environment of medium-high temperature and high humidity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high temperature proton exchange membrane (HT-PEMFCs) for fuel cells, and particularly relates to a linear quaternary ammonium side chain fluorenyl polymer, a preparation method thereof, and a high phosphoric acid retention proton exchange membrane based on the same and applications. BACKGROUND

[0002] Proton exchange membrane fuel cells (PEMFCs) have attracted a great deal of research due to their high energy conversion efficiency and diverse fuel supply routes, especially hydrogen-oxygen fuel cells using hydrogen as raw material have been the research focus in recent years. The proton exchange membrane is a key component of hydrogen-oxygen fuel cells; however, the high cost and complex preparation process of the existing commercial perfluorosulfonic acid membrane (such as Nafion) limit its wide application in the field of hydrogen-oxygen fuel cells. At the same time, due to the high humidity dependence of proton transmission in the perfluorosulfonic acid membrane, the temperature use range of hydrogen-oxygen fuel cells is usually lower than 80℃ (i.e. medium-low temperature fuel cells), which not only makes the water and heat management system of hydrogen-oxygen fuel cells more complex, but also puts higher requirements on the activity, usage amount of electrode catalysts and the purity of fuel hydrogen. Therefore, the development of new high-temperature stable proton transmission medium and high-temperature proton exchange membrane fuel cell (HT-PEMFC) system provides a new idea and solution to overcome the above-mentioned shortcomings of medium-low temperature hydrogen-oxygen fuel cells. On the one hand, due to the operating environment above 120℃, it is beneficial to improve the poisoning tolerance of catalyst to carbon monoxide and the electrode reaction kinetics; on the other hand, under this condition, the water and heat management of the fuel cell system is greatly simplified, and therefore, high-temperature fuel cells show great commercial application prospects. Generally, high-temperature fuel cells usually use phosphoric acid as the carrier or medium for proton transmission, which can achieve efficient proton transmission under water-free conditions. The existing developed phosphoric acid doped proton exchange membranes usually include polybenzimidazole type, imidazole type, etc., among which polybenzimidazole (PBI) has become one of the most studied membranes due to its good thermal stability and chemical stability.

[0003] Generally, in order to obtain higher proton conduction efficiency, a sufficient amount of phosphoric acid needs to be doped in the PBI membrane. However, a higher phosphoric acid doping amount usually causes the following problems: 1) the PBI membrane is highly swollen or even loses mechanical properties, which is not conducive to the long-term operation stability of the fuel cell; 2) the phosphoric acid in the PBI membrane is severely lost, which significantly reduces the fuel cell performance of the membrane. After years of development, researchers have carried out research work in the preparation of crosslinked membranes, blended membranes and doped membranes, and have made significant progress in improving the mechanical properties of PBI membranes; however, there is still a lack of effective methods and strategies to inhibit the loss of phosphoric acid in PBI membranes. Therefore, it is of great significance to develop a new type of high phosphoric acid retention proton exchange membrane. SUMMARY

[0004] The present application aims at providing a linear quaternary ammonium side chain fluorenyl polymer, a preparation method thereof, and a high phosphoric acid retention proton exchange membrane based on the linear quaternary ammonium side chain fluorenyl polymer and an application thereof.

[0005] The present application is achieved by the following technical solutions.

[0006] One of the objectives of the present application is to provide a linear quaternary ammonium side chain fluorenyl polymer, the structure of which is represented by the general formula:

[0007]

[0008] In the formula, m is greater than or equal to 10, x is greater than or equal to 0.2 and less than or equal to 0.6, n is greater than or equal to 0 and less than or equal to 3, Ar is an aromatic group, and R includes but is not limited to one of the following structures:

[0009]

[0010] Further, m is greater than or equal to 20, x is equal to 0.4, and n is equal to 2.

[0011] Further, Ar includes but is not limited to one of the following structures:

[0012]

[0013] The second objective of the present application is to provide a preparation method of a linear quaternary ammonium side chain fluorenyl polymer, the preparation method of which is performed according to the following steps:

[0014] S1: reacting bromo dialkyl fluorene, aromatic monomer, and trifluoroacetone in the presence of an acid catalyst for a certain period of time, pouring the reaction product into ethanol to precipitate and vacuum drying to obtain a linear polymer;

[0015] S2: re-dissolving the linear polymer in an organic solvent, adding a quaternary ammonium reagent, and reacting for a certain period of time, pouring the reaction product into diethyl ether to precipitate and vacuum drying to obtain a linear quaternary ammonium side chain fluorenyl polymer.

[0016] Further, the reaction in S1 is performed for 0.5 to 1 hours.

[0017] Further, the reaction temperature in S2 is 30 to 80 degrees Celsius, and the reaction time is 8 to 12 hours.

[0018] The third objective of the present application is to provide a preparation method of a high phosphoric acid retention proton exchange membrane, the preparation method of which is as follows:

[0019] The linear quaternary ammonium side chain fluorenyl polymer is dissolved in a polar solvent at room temperature to obtain a polymer solution, then a film is prepared by a casting method, and then immersed in a phosphoric acid solution for phosphoric acid doping at different temperatures, and after reaching adsorption equilibrium, it is taken out and vacuum dried to obtain a high phosphoric acid retention proton exchange membrane.

[0020] Further limitation, the polar solvent includes one or more of dimethyl sulfoxide, N, N-dimethylacetamide and N, N-dimethylformamide.

[0021] Further limitation, the solid content of the polymer solution is 5-8wt%.

[0022] Further limitation, the film preparation temperature is 70-80℃.

[0023] Further limitation, the concentration of the phosphoric acid solution is 70-85wt%.

[0024] Further limitation, the phosphoric acid doping temperature is 30-80℃.

[0025] Further limitation, the film thickness is 10-100μm.

[0026] The fourth object of the present application is to provide a high phosphoric acid retention proton exchange membrane prepared by the above method.

[0027] The fifth object of the present application is to provide the application of a high phosphoric acid retention proton exchange membrane prepared by the above method in a high temperature fuel cell.

[0028] Compared with the prior art, the present application has the following remarkable effects:

[0029] (1) The present application develops a new type of high temperature proton exchange membrane with high phosphoric acid retention, which utilizes the strong ion pair interaction between the multi-quaternary ammonium side chain and the phosphoric acid molecules to form a new confinement effect of the multi-quaternary ammonium side chain on phosphoric acid, thereby improving the phosphoric acid retention rate of the membrane after phosphoric acid doping. Therefore, it can be applied to medium-high temperature and high humidity working environment.

[0030] (2) The comparison research results of the phosphoric acid retention rate of the new type of high temperature proton exchange membrane and the common polybenzimidazole (PBIs) membrane show that: under the condition of 80℃, 40RH%, the phosphoric acid retention rate of the new type of membrane with three quaternary ammonium groups is increased by 2-3 times ( Figure 3 ), and the phosphoric acid loss rate is greatly reduced; under the condition of 100℃, 49RH%, 0.2A cm -2 High temperature fuel cell operating conditions, the long-term stability of the new type of membrane with three quaternary ammonium groups is increased by 5-6 times ( Figure 4 ). The calculation results show that the ion pair binding energy between the multi-quaternary ammonium ion and H2PO4 - is 186.8 kilocalories per mole, which is higher than that between the single quaternary ammonium ion and H2PO4- The binding energy of the ion pairs between them (97.6 kcal / mol) was nearly doubled. This is the real reason why multi-quaternary ammonium ions can provide excellent phosphoric acid retention properties. Attached Figure Description

[0031] Figure 1 The 1H NMR spectra of the linear quaternary ammonium side-chain fluorene polymers in Examples 1-3;

[0032] Figure 2 The proton conductivity curves of the high phosphate-retaining proton exchange membranes in Examples 1-5 are shown.

[0033] Figure 3 Phosphoric acid retention rate of the high phosphate retention proton exchange membranes in Examples 1-5 (80°C / 40% RH);

[0034] Figure 4 The stability (100°C / 49%RH) results of the high phosphate retention proton exchange membranes of Examples 1-3 and the commercial membranes of Comparative Examples 1-2 in hydrogen-oxygen fuel cells;

[0035] Figure 5 The performance of high-temperature fuel cells based on the high phosphate retention proton exchange membranes of Examples 3 and 6 is presented. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0037] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. The materials, reagents, methods, and instruments used, unless otherwise specified, are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0038] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used in the following embodiments, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such a composition, step, method, article, or apparatus.

[0039] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range. In this specification and claims, range definitions may be combined and / or interchanged, unless otherwise stated, these ranges include all subranges contained therein.

[0040] The indefinite articles “a” and “an” preceding an element or component of this invention do not impose any limitation on the quantity (i.e., number of times) of the element or component. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers only to the singular form.

[0041] In this invention, "an embodiment" or "embodiment" refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments.

[0042] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0043] Example 1

[0044] The preparation route of the high-phosphate-retaining proton exchange membrane in this embodiment is as follows:

[0045]

[0046] The specific preparation method is carried out according to the following steps:

[0047] (1) In a 100 mL pressure bottle, bromo bis-alkyl fluorene 1.86 g (4 mmol), biphenyl 0.92 g (6 mmol) and trifluoroacetone 1.25 g (11.2 mmol) were added as reactants, dichloromethane 8 mL was added as solvent and trifluoromethanesulfonic acid 8 mL was added as catalyst for polymerization, the reaction temperature was 0°C, and the polymerization time was 40 minutes. After the reaction was completed, the reaction solution was poured into ethanol to precipitate, and linear polymer was obtained after vacuum drying.

[0048] (2) Linear polymer 3.02 g (bromine content 6.5 mmol) was dissolved in 100 mL N,N-dimethylacetamide, and 30 wt% aqueous trimethylamine solution 2 g was added as a quaternary ammonium reagent. After 8 hours of reaction at 30°C, the reaction solution was poured into diethyl ether to precipitate the polymer, and linear single-quaternary ammonium side-chain fluorenyl polymer was obtained after vacuum drying. The structure was proved by nuclear magnetic hydrogen spectrum (see Figure 1 ).

[0049] (3) The linear single-quaternary ammonium side-chain fluorenyl polymer was dissolved in N,N-dimethylacetamide at room temperature to obtain a polymer solution with a solid content of 5%, and then a film was prepared by evaporation of the solvent at 70°C using a casting method. The film was immersed in an 85 wt% phosphoric acid solution, and the phosphoric acid doping amount was allowed to reach adsorption equilibrium by doping at 30°C for 24 hours. After being taken out, the film was dried in a vacuum drying oven at 80°C for 24 hours to obtain a high phosphoric acid retention proton exchange membrane.

[0050] Example 2

[0051] The preparation route of the high phosphoric acid retention proton exchange membrane of this example is as follows:

[0052]

[0053] The specific preparation method was carried out according to the following steps:

[0054] (1) In a 100 mL pressure bottle, bromo bis-alkyl fluorene 0.93 g (2 mmol), biphenyl 1.23 g (8 mmol) and trifluoroacetone 1.25 g (11.2 mmol) were added as reactants, dichloromethane 8 mL was added as solvent and trifluoromethanesulfonic acid 8 mL was added as catalyst for polymerization, the reaction temperature was 0°C, and the polymerization time was 48 minutes. After the reaction was completed, the reaction solution was poured into ethanol to precipitate, and linear polymer was obtained after vacuum drying.

[0055] (2) Take the above linear polymer 3.10 g (bromine content is 4.0 mmol) dissolved in 100 mL of N,N-dimethylacetamide, and add 6-(dimethylamino)-N,N,N-trimethylhexylammonium salt 1.89 g (6 mmol) as a quaternary ammonium reagent and anhydrous potassium carbonate 0.83 g (6 mmol), after reacting at 80°C for 12 hours, pour the reaction solution into ether to precipitate the polymer, and after drying in vacuum, linear double quaternary ammonium side chain fluorenyl polymer is obtained. The structure is proved by nuclear magnetic hydrogen spectrum (see Figure 1 ).

[0056] (3) The above linear double quaternary ammonium side chain fluorenyl polymer is dissolved in N,N-dimethylacetamide at room temperature to obtain a polymer solution with a solid content of 5 wt%, then the solvent is evaporated by casting method at 70°C to form a film, and then immersed in an 85 wt% phosphoric acid solution, and the phosphoric acid doping amount reaches adsorption equilibrium after phosphoric acid doping at 30°C for 24 h, and then dried in a vacuum drying oven at 80°C for 24 h to obtain a high phosphoric acid retention proton exchange membrane.

[0057] Example 3

[0058] The preparation route of the high phosphoric acid retention proton exchange membrane of this example is as follows:

[0059]

[0060] The specific preparation method is carried out in the following steps:

[0061] (1) In a 100 mL pressure-resistant bottle, brominated bisalkylfluorene 0.56 g (1.2 mmol), biphenyl 1.38 g (8.8 mmol) and trifluoroacetone 1.25 g (11.2 mmol) are added as reactants, dichloromethane 8 mL is added as a solvent, and trifluoromethanesulfonic acid 8 mL is added as a catalyst for polymerization, the reaction temperature is 0°C, and the polymerization time is 50 minutes. After the reaction is completed, the reaction solution is poured into ethanol to precipitate, and after drying in vacuum, a linear polymer is obtained.

[0062] (2) Take the above linear polymer 3.01 g (bromine content is 2.5 mmol) dissolved in 100 mL of N,N-dimethylacetamide, and add N1-{6-(dimethylamino)-hexyl}-N1,N1,N6,N6-pentamethylhexane-1,6-diammonium salt 1.80 g (3.8 mmol) as a quaternary ammonium reagent and anhydrous potassium carbonate 0.53 g (3.8 mmol), after reacting at 80°C for 12 hours, pour the reaction solution into ether to precipitate the polymer, and after drying in vacuum, linear three quaternary ammonium side chain fluorenyl polymer is obtained. The structure is proved by nuclear magnetic hydrogen spectrum (see Figure 1 ).

[0063] (3) The linear triquaternary ammonium side chain fluorenyl polymer is dissolved in N,N-dimethylacetamide at room temperature to obtain a polymer solution with a solid content of 5 wt%, then a film is prepared by evaporation of the solvent at 70°C using a casting method, and then immersed in an 85 wt% phosphoric acid solution, and phosphoric acid doping is carried out at 80°C for 24 hours to reach the adsorption equilibrium of phosphoric acid doping, and then dried in a vacuum drying oven at 80°C for 24 hours to obtain a high phosphoric acid retention proton exchange membrane.

[0064] Example 4

[0065] The difference between this example and Example 1 is that the phosphoric acid doping temperature is 80°C. The other steps and parameters are the same as those of Example 1.

[0066] Example 5

[0067] The difference between this example and Example 2 is that the phosphoric acid doping temperature is 80°C. The other steps and parameters are the same as those of Example 2.

[0068] Example 6

[0069] The preparation method of the high phosphoric acid retention proton exchange membrane of this example is carried out according to the following steps:

[0070] (1) In a 100 mL pressure-resistant bottle, brominated bisalkyl fluorene 0.93 g (2 mmol), biphenyl 1.23 g (8 mmol) and trifluoroacetone 1.25 g (11.2 mmol) are added as reactants, dichloromethane 8 mL is added as a solvent, and trifluoromethanesulfonic acid 8 mL is added as a catalyst for polymerization, the reaction temperature is 0°C, and the polymerization time is 48 minutes. After the reaction is completed, the reaction liquid is poured into ethanol to precipitate, and then vacuum dried to obtain a linear polymer.

[0071] (2) The linear polymer 3.10 g (bromine content 4.0 mmol) is dissolved in 100 mL N,N-dimethylacetamide, and N1-{6-(dimethylamino)-hexyl}-N1,N1,N6,N6-pentamethylhexane-1,6-diammonium salt 2.84 g (6 mmol) is added as a quaternary ammonium reagent and anhydrous potassium carbonate 0.83 g (6 mmol), and then the reaction is carried out at 80°C for 12 hours. After the reaction is completed, the reaction liquid is poured into diethyl ether to precipitate the polymer, and then vacuum dried to obtain a linear triquaternary ammonium side chain fluorenyl polymer.

[0072] (3) The linear triquaternary ammonium side chain fluorenyl polymer is dissolved in N,N-dimethylacetamide at room temperature to obtain a polymer solution with a solid content of 5 wt%, then a film is prepared by evaporation of the solvent at 70°C using a casting method, and then immersed in an 85 wt% phosphoric acid solution, and phosphoric acid doping is carried out at 80°C for 24 hours to reach the adsorption equilibrium of phosphoric acid doping, and then dried in a vacuum drying oven at 80°C for 24 hours to obtain a high phosphoric acid retention proton exchange membrane.

[0073] Example 7

[0074] The preparation method of the high phosphoric acid retention proton exchange membrane of this example was carried out in the following steps:

[0075] (1) In a 100 mL pressure-resistant bottle, bromo-dialkyl fluorene 1.39 g (3 mmol), diphenyl 1.08 g (7 mmol), and trifluoroacetone 1.25 g (11.2 mmol) were added as reactants, dichloromethane 8 mL was added as a solvent, and trifluoromethanesulfonic acid 8 mL was added as a catalyst for polymerization, the reaction temperature was 0°C, and the polymerization time was 40 minutes. After the reaction was completed, the reaction solution was poured into ethanol for precipitation, and the linear polymer was obtained after vacuum drying.

[0076] (2) The linear polymer 2.76 g (bromine content 4.9 mmol) was dissolved in 100 mL N,N-dimethylacetamide, and N1-{6-(dimethylamino)-hexyl}-N1,N1,N6,N6-pentamethylhexane-1,6-diammonium salt 3.45 g (7.3 mmol) was added as a quaternary ammonium reagent and anhydrous potassium carbonate 1.01 g (7.3 mmol), and the reaction was carried out at 80°C for 12 hours. After the reaction was completed, the reaction solution was poured into diethyl ether for precipitation, and the linear triquaternary ammonium side chain fluorenyl polymer was obtained after vacuum drying.

[0077] (3) The linear triquaternary ammonium side chain fluorenyl polymer was dissolved in N,N-dimethylacetamide at room temperature to obtain a polymer solution with a solid content of 5 wt%, then the solvent was evaporated at 70°C by casting to form a film, and then the film was immersed in a 85 wt% phosphoric acid solution. The phosphoric acid doping amount reached adsorption equilibrium after being doped with phosphoric acid at 80°C for 24 hours, and then dried in a vacuum drying oven at 80°C for 24 hours to obtain a high phosphoric acid retention proton exchange membrane.

[0078] Comparative Example 1

[0079] The commercial polybenzimidazole membrane OPBI was immersed in phosphoric acid at 80°C for 12 hours, and after vacuum drying, a phosphoric acid doped OPBI membrane was obtained, and the phosphoric acid doping rate was maintained at 136%. Under the same test conditions, the phosphoric acid retention rate was maintained at about 40% (consistent with the reported data).

[0080] Comparative Example 2

[0081] The commercial Nafion 212 membrane (DuPont, USA) was treated with 3% hydrogen peroxide and 3% dilute sulfuric acid solution at 80°C for 12 hours, respectively. There was no alkaline group, and no phosphoric acid retention rate test was performed.

[0082] Data Comparison

[0083] The doping rate and swelling rate of the high phosphoric acid retention proton exchange membranes prepared in Examples 1-7 are shown in Table 1.

[0084] The proton conductivity of the high phosphoric acid retention proton exchange membranes prepared in Examples 1-5 is shown in Table 2. Figure 2

[0085] The phosphoric acid retention rate of the high phosphoric acid retention proton exchange membranes prepared in Examples 1-5 is shown in Table 3, and the figure shows that the phosphoric acid retention rate of the phosphoric acid doped membrane with quaternary ammonium groups is the highest, and the phosphoric acid retention rate of the new type membrane with quaternary ammonium groups is increased by 2-3 times. Figure 3

[0086] In the stability test of the fuel cell based on the high phosphoric acid retention proton exchange membranes prepared in Examples 1-3 and the commercial membranes of Comparative Examples 1-2, under the condition of 100℃ and 49% relative humidity, as shown in Table 4, the figure shows that compared with the commercial Nafion and OPBI membranes, the phosphoric acid doped membrane with quaternary ammonium groups has the longest running time, and shows excellent stability, and the power density of the new type membrane with quaternary ammonium groups is increased by 5-6 times. Figure 4 -2 Under the operating conditions of high temperature fuel cell, the long-term stability of the new type membrane with quaternary ammonium groups is increased by 5-6 times.

[0087] The performance test results of the fuel cell based on the high phosphoric acid retention proton exchange membranes prepared in Examples 3 and 6 are shown in Table 5, and the figure shows that under the condition of 160℃ and 0% relative humidity, through the control of ion exchange capacity, the power density of the new type membrane with quaternary ammonium groups is increased by 1.4 times. Figure 5

[0088] Table 1, doping rate and swelling rate of phosphoric acid doped membranes under different conditions

[0089]

[0090]

[0091] The above merely illustrates the preferred embodiments of the present application, and these embodiments are different implementations based on the overall concept of the present application, and the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.​​​​

Claims

1. A method for preparing a high-phosphate-retaining proton exchange membrane, characterized in that, The preparation method is as follows: A linear quaternary ammonium side-chain fluorene polymer was dissolved in a polar solvent at room temperature to obtain a polymer solution. Then, a membrane was formed by casting. The membrane was then immersed in a phosphoric acid solution and phosphoric acid doping was performed at different temperatures. After reaching adsorption equilibrium, the membrane was removed and vacuum dried to obtain a high phosphoric acid retention proton exchange membrane. The general structural formula of linear quaternary ammonium side-chain fluorene polymers is: ； In the formula, m ≥ 10, 0.2 ≤ x ≤ 0.6, 0 < n ≤ 3, and Ar is selected from one of the following structures: ； R is selected from one of the following structures: .

2. The preparation method according to claim 1, characterized in that, m≥20, x=0.4, n=2.

3. The preparation method according to claim 1, characterized in that, The preparation method of linear quaternary ammonium side-chain fluorene polymer is carried out according to the following steps: S1: Bromodialkylfluorene, aromatic monomer and trifluoroacetone are reacted in the presence of an acid catalyst for a certain time. After the reaction is completed, the mixture is poured into ethanol to precipitate and then dried under vacuum to obtain a linear polymer. S2: The linear polymer is redissolved in an organic solvent, then a quaternizing agent is added, and the reaction is allowed to proceed for a certain period of time. After the reaction is complete, the polymer is poured into diethyl ether to precipitate and then dried under vacuum to obtain a linear quaternary ammonium side-chain fluorene polymer.

4. The preparation method according to claim 3, characterized in that, The reaction in S1 takes 0.5 to 1 hour, and the reaction in S2 takes 8 to 12 hours at a temperature of 30 to 80°C.

5. The preparation method according to claim 1, characterized in that, The polymer solution has a solid content of 5-8 wt% and the film-forming temperature is 70-80℃.

6. The preparation method according to claim 1, characterized in that, The phosphoric acid solution concentration is 70~85wt%, and the phosphoric acid doping temperature is 30~80℃.

7. The high-phosphate-retaining proton exchange membrane prepared by the method according to any one of claims 1-6.

8. The application of the high-phosphate-retaining proton exchange membrane prepared by the method of any one of claims 1-6 in a high-temperature fuel cell.

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