A method for preparing a magnetic nanoparticle loaded phosphotungstic acid-sulfonated polyether ether ketone composite proton exchange membrane

Abstract

This invention discloses a method for preparing a magnetic nanoparticle-supported phosphotungstic acid-sulfonated polyetheretherketone (PEE ketone) composite proton exchange membrane. The membrane is formed by mixing magnetic nanoparticles loaded with phosphotungstic acid with a sulfonated PEEK solution under a magnetic field. The preparation method includes: preparing sulfonated PEEK from PEEK; synthesizing magnetic nanoparticles by co-precipitation with ferric chloride and ferrous sulfate; coating the magnetic nanoparticles with polydopamine to introduce amine groups onto the particle surface; immersing the polydopamine-coated magnetic nanoparticles in a phosphotungstic acid solution to obtain phosphotungstic acid-loaded magnetic nanoparticles; mixing the phosphotungstic acid-loaded magnetic nanoparticles with sulfonated PEEK, and heating under a magnetic field to form a membrane, resulting in a composite proton exchange membrane with ordered magnetic nanoparticle arrangement. The raw materials of this invention are readily available, the operation is simple, and it is relatively easy to construct proton transport channels perpendicular to the membrane surface. The prepared composite proton exchange membrane is used in fuel cells and exhibits good proton conduction performance.

Description

Technical Field

[0001] This invention relates to a method for preparing a magnetic nanoparticle-supported phosphotungstic acid-sulfonated polyether ether ketone composite proton exchange membrane, belonging to the field of proton exchange membrane fuel cells. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs), as electrochemical devices, convert hydrogen and oxygen into water and generate electricity in the process, offering advantages such as high efficiency and environmental friendliness. The proton exchange membrane, as one of the core components of the fuel cell membrane electrode assembly, requires high proton conductivity, good thermal and chemical stability, and low gas permeability. Common proton exchange membrane materials mainly include perfluorosulfonic acid membranes (such as...). Sulfonated aromatic hydrocarbon polymer membranes (such as sulfonated polyether ether ketone, sulfonated polyarylether sulfone, and sulfonated polyimide), etc. Currently used perfluorosulfonic acid membranes are expensive and require processing into ultrathin films to reduce proton transport resistance, which leads to a decrease in membrane mechanical strength and an increase in fuel permeability. Phosphotungstic acid (chemical formula H3PW) 12 O 40As a strong acid among heteropoly acids, phosphotungstic acid has a Hammett acidity function H0 = -13.16, reaching the standard of a superacid. Even at low pH values, the three protons of phosphotungstic acid are completely dissociated. Incorporating phosphotungstic acid into polymer membrane materials to prepare composite proton exchange membranes can provide additional proton transport sites and improve proton conductivity. Simultaneously, phosphotungstic acid has strong water absorption properties, allowing the composite proton exchange membrane to maintain a certain proton conductivity under low humidity conditions. However, phosphotungstic acid is readily soluble in water, and it is easily lost when the proton exchange membrane operates in an aqueous environment, leading to a decrease in the membrane's proton conductivity. To prevent phosphotungstic acid loss, researchers have made many beneficial attempts. For example, phosphotungstic acid is filled into carbon nanotubes and then blended with Nafion to prepare composite proton exchange membranes. The carbon nanotubes both physically immobilize the phosphotungstic acid and form long-range ion transport channels (Nano Energy 2016, 23, 114–121). For example, by using acid-base interactions, phosphotungstic acid is loaded onto nanotubes or nanosheets rich in amine groups on the surface, and then blended with sulfonated polymers to form a membrane, effectively improving the proton conductivity of the membrane (Polymer Testing 2019, 73: 242–249; International Journal of Hydrogen Energy 2020, 45(35): 17782–17794). The proton transport channels of the composite proton exchange membrane composed of phosphotungstic acid prepared above are randomly arranged, that is, the proton conductivity is basically the same in the horizontal and vertical directions of the membrane. If vertical channels are constructed along the direction perpendicular to the membrane surface, the proton transport path can be shortened, which is beneficial to improving the performance of fuel cells. Therefore, this study synthesized magnetic nanoparticles rich in amine groups on the surface and loaded them with phosphotungstic acid. These nanoparticles were then blended with sulfonated polyether ether ketone and a vertical magnetic field was applied to form a membrane. Under the action of the magnetic field, the magnetic nanoparticles were arranged in an orderly manner, forming proton transport channels in the direction perpendicular to the membrane surface, shortening the proton transport path and improving the proton conductivity. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing a magnetic nanoparticle-supported phosphotungstic acid-sulfonated polyether ether ketone composite proton exchange membrane. This preparation method is simple, and the prepared composite proton exchange membrane exhibits low proton transport resistance in the direction perpendicular to the membrane surface, thus demonstrating good proton conductivity when used in proton exchange membrane fuel cells.

[0004] This invention is achieved through the following technical solution: a magnetic nanoparticle-supported phosphotungstic acid-sulfonated polyether ether ketone composite proton exchange membrane. The membrane is formed by magnetic nanoparticles loaded with phosphotungstic acid and sulfonated polyether ether ketone with a sulfonation degree of 50-60% at a mass ratio of 0.05-5:100, under the action of a magnetic field, resulting in a composite proton exchange membrane with a thickness of 30-60 μm. The diameter of the magnetite nanoparticles is 20-50 nm, the polydopamine coating layer thickness is 10-30 nm, the loading amount of phosphotungstic acid on the magnetic nanoparticles is 10-30 wt%, and the magnetic induction intensity of the applied magnetic field is 0.05-0.5 T.

[0005] The preparation method of the above-mentioned phosphotungstic acid-loaded magnetic nanoparticle-sulfonated polyether ether ketone composite proton exchange membrane includes the following steps:

[0006] (1) Preparation of sulfonated polyether ether ketone:

[0007] Fully dried polyether ether ketone powder was added to 98% concentrated sulfuric acid at a mass ratio of 5–15:100. The mixture was stirred at room temperature until completely dissolved, and then heated to 50–60°C for sulfonation reaction for 1–3 hours. After cooling, the mixture was poured into ice water to precipitate the precipitate. The precipitate was washed repeatedly with deionized water until neutral, and then dried under vacuum at 60°C for 24 hours to obtain sulfonated polyether ether ketone with a sulfonation degree of 50–60%.

[0008] (2) Preparation of magnetic nanoparticles loaded with phosphotungstic acid:

[0009] a. Preparation of Fe3O4 nanoparticles. Fe3O4 nanoparticles were prepared by coprecipitation. FeCl3 and FeSO4 were dissolved in deoxygenated deionized water at a molar ratio of 2:1 to obtain an iron salt solution. The total iron salt to water mass ratio was 5–10:100. The solution was mechanically stirred and heated to 80°C under a nitrogen atmosphere. Concentrated ammonia was rapidly added to the iron salt solution and reacted for 5 minutes. The volume ratio of concentrated ammonia to iron salt solution was 10–20:100. Then, 1 mol / L sodium citrate solution was added to prevent particle agglomeration. The volume ratio of sodium citrate solution to iron salt solution was 2–5:100. After continuous stirring for 2–5 hours, the precipitate was collected using a permanent magnet and washed repeatedly with deionized water until neutral. Finally, the black precipitate was washed twice with ethanol and dried under vacuum at 60°C to obtain Fe3O4 magnetic nanoparticles.

[0010] b. Polydopamine-coated magnetic nanoparticles. Fe3O4 magnetic nanoparticles were ultrasonically dispersed in water to obtain a 1-3% (w / w) dispersion. 10 mL of this dispersion was then added to 90 mL of a 10 mmol / L Tris buffer solution. The pH was adjusted to 8.5 with 0.1 mol / L dilute hydrochloric acid, and the nanoparticles were ultrasonically dispersed uniformly. 0.1-0.3 g of dopamine hydrochloride was added, and the mixture was vigorously stirred at 30°C in air for 6 hours to ensure complete coating of the magnetic nanoparticles with polydopamine. The nanoparticles were washed repeatedly with deionized water and ethanol, and then vacuum-dried at 60°C to obtain polydopamine-coated magnetic nanoparticles.

[0011] c. Loading with phosphotungstic acid. Polydopamine-coated magnetic nanoparticles were dispersed in a 5–10% (w / w) solution of phosphotungstic acid and N,N-dimethylformamide. After the phosphotungstic acid reacted fully with the amine groups on the surface of the magnetic nanoparticles, the magnetic nanoparticles were separated using a strong magnet. Excess phosphotungstic acid was removed by washing with N,N-dimethylformamide, and finally, the nanoparticles were washed twice with ethanol and dried under vacuum at 60°C to obtain magnetic nanoparticles loaded with phosphotungstic acid.

[0012] (3) Preparation of composite proton exchange membranes:

[0013] The sulfonated polyether ether ketone prepared in step (1) was dissolved in N-methylpyrrolidone to obtain a sulfonated polyether ether ketone solution with a mass fraction of 8-10%. The magnetic nanoparticles loaded with phosphotungstic acid prepared in step (2) were ultrasonically dispersed in N-methylpyrrolidone to obtain a dispersion with a mass fraction of 0.5-2%. The dispersion of magnetic nanoparticles loaded with phosphotungstic acid was mixed with the sulfonated polyether ether ketone solution, with a mass ratio of magnetic nanoparticles to sulfonated polyether ether ketone of 0.05-5:100. The mixture was mechanically stirred and ultrasonically dispersed to ensure uniform mixing. After standing for 2 hours to remove bubbles, a casting solution was obtained. The casting solution was poured into a petri dish and placed under a magnetic field perpendicular to the liquid surface. The mixture was dried at 60°C to form a film. The magnetic field was controlled using a magnetic field generator, with the magnetic induction intensity controlled at 0.05-0.5T. The prepared membrane was acidified in 2 mol / L hydrochloric acid solution for 24 h, then washed with water until neutral, and dried to obtain a magnetic nanoparticle-supported phosphotungstic acid-sulfonated polyether ether ketone composite proton exchange membrane with a thickness of 30-60 μm.

[0014] The magnetic nanoparticle-supported phosphotungstic acid-sulfonated polyether ether ketone composite proton exchange membrane prepared by this invention can be used as a proton exchange membrane for fuel cells.

[0015] The advantages of this invention are: the raw materials used are readily available, the operation is simple, and the magnetic induction intensity is controllable and easily achieved. By forming a film of magnetic nanoparticles loaded with phosphotungstic acid and sulfonated polyether ether ketone under a magnetic field, a proton transport channel perpendicular to the membrane surface is constructed, shortening the proton transport path. The prepared composite proton exchange membrane, when used in fuel cells, exhibits good proton conductivity. Attached Figure Description

[0016] Figure 1 This is a cross-sectional field emission scanning electron microscope (FESEM) image of the magnetic nanoparticle-supported phosphotungstic acid-sulfonated polyether ether ketone composite proton exchange membrane prepared under a magnetic field in Example 1.

[0017] Figure 2 Cross-sectional field emission scanning electron microscope (FESEM) image of the magnetic nanoparticle-supported phosphotungstic acid-sulfonated polyether ether ketone composite proton exchange membrane prepared under conditions without a magnetic field, for Comparative Example 1.

[0018] Figure 3 A cross-sectional field emission scanning electron microscope (FESEM) image of the pure sulfonated polyether ether ketone membrane prepared in Example 2.

[0019] Figure 4 The results shown are the proton conductivity test results of membranes 1 and 2 prepared in Examples 1 and 2, and membranes 3 and 4 prepared in Comparative Examples 1 and 2. Detailed Implementation

[0020] Example 1

[0021] Polyether ether ketone powder was vacuum dried at 80℃ for 24h. 10g of the powder was added to 100mL of 98% concentrated sulfuric acid and mechanically stirred at 20℃ for 12h to dissolve. The temperature was then raised to 50℃ and reacted for 1.5h. The reaction was immediately terminated by cooling with cold water. The reaction solution was slowly poured into a large amount of ice water for precipitation to obtain a fibrous product. The product was washed repeatedly with deionized water until the washing water was close to neutral. Finally, the product was placed in a vacuum oven at 60℃ and dried for 24h to obtain sulfonated polyether ether ketone with a sulfonation degree of 50%.

[0022] 100 mL of deoxygenated deionized water was added to a three-necked flask, followed by FeCl3·6H2O (5.4 g, 20 mmol) and FeSO4·7H2O (2.8 g, 10.07 mmol). The mixture was mechanically stirred and heated to 80 °C under a nitrogen atmosphere. 16 mL of concentrated ammonia was rapidly added to the mixture, and the reaction was allowed to proceed for 5 minutes. Then, 2 mL of 1 mol / L sodium citrate solution was added to prevent particle agglomeration. After continuous stirring for 2 hours, the precipitate was collected using a permanent magnet and washed repeatedly with deionized water until neutral. Finally, the black precipitate was washed twice with ethanol and dried under vacuum at 60 °C to obtain Fe3O4 magnetic nanoparticles. 0.2 g of Fe3O4 magnetic nanoparticles were ultrasonically dispersed in 10 mL of deionized water, then added to 90 mL of 10 mmol / L Tris buffer solution. The pH was adjusted to 8.5 with 0.1 mol / L dilute hydrochloric acid, and the Fe3O4 magnetic nanoparticles were ultrasonically dispersed uniformly. Add 0.2 g of dopamine hydrochloride and react vigorously at 30 °C in air for 6 h. Separate the product with a magnet, wash repeatedly with deionized water and ethanol alternately, and dry under vacuum at 60 °C to obtain polydopamine-coated magnetic nanoparticles. Take 0.05 g of polydopamine-coated magnetic nanoparticles and disperse them in 10 mL of N,N-dimethylformamide solution containing 5% phosphotungstic acid. Stir for 12 h to allow the phosphotungstic acid to fully react with the amine groups on the surface of the magnetic nanoparticles. Separate the magnetic nanoparticles with a strong magnet, wash with N,N-dimethylformamide to remove excess phosphotungstic acid, and finally wash twice with ethanol. Dry under vacuum at 60 °C to obtain magnetic nanoparticles loaded with phosphotungstic acid, with a phosphotungstic acid loading of 20 wt%.

[0023] 0.05 g of magnetic nanoparticles loaded with phosphotungstic acid were dispersed in N-methylpyrrolidone to obtain a 1% (w / w) dispersion. 0.3 g of sulfonated polyetheretherketone (PEEK) with a sulfonation degree of 50% was dissolved in 2.5 g of N-methylpyrrolidone to obtain a sulfonated PEEK solution. 0.6 g of the dispersion (containing 0.006 g of solids) was then mixed with the sulfonated PEEK solution, mechanically stirred, and ultrasonically dispersed to ensure uniform mixing. The mixture was allowed to stand for 2 hours to remove bubbles, yielding a casting solution. The casting solution was poured into an 8 cm diameter petri dish and placed in a vertical magnetic field with a magnetic induction intensity of 0.3 T. The mixture was dried at 60 °C for 24 hours to form a membrane. The prepared membrane was acidified in a 2 mol / L hydrochloric acid solution for 24 hours, then washed with water until neutral, and dried to obtain a composite proton exchange membrane (membrane 1.M-SP / PWA-MNPs-2) with a thickness of approximately 52 μm, consisting of magnetic nanoparticles loaded with phosphotungstic acid and sulfonated PEEK.

[0024] Example 2

[0025] Polyether ether ketone powder was vacuum dried at 80℃ for 24h. 15g of the powder was added to 100mL of 98% concentrated sulfuric acid and mechanically stirred at 20℃ for 12h to dissolve. The temperature was then raised to 50℃ for 2h, and the reaction was immediately stopped by cooling with cold water. The reaction solution was slowly poured into a large amount of ice water for precipitation to obtain a fibrous product. The product was washed repeatedly with deionized water until the washing water was close to neutral. Finally, the product was placed in a vacuum oven at 60℃ and dried for 24h to obtain sulfonated polyether ether ketone with a sulfonation degree of 55%.

[0026] 100 mL of deoxygenated deionized water was added to a three-necked flask, followed by FeCl3·6H2O (5.4 g, 20 mmol) and FeSO4·7H2O (2.8 g, 10.07 mmol). The mixture was mechanically stirred and heated to 80 °C under a nitrogen atmosphere. 16 mL of concentrated ammonia was rapidly added to the mixture, and the reaction was allowed to proceed for 5 minutes. Then, 2 mL of 1 mol / L sodium citrate solution was added to prevent particle agglomeration. After continuous stirring for 2 hours, the precipitate was collected using a permanent magnet and washed repeatedly with deionized water until neutral. Finally, the black precipitate was washed twice with ethanol and dried under vacuum at 60 °C to obtain Fe3O4 magnetic nanoparticles. 0.3 g of Fe3O4 magnetic nanoparticles were ultrasonically dispersed in 100 mL of deionized water. 10 mL of the dispersion was then added to 90 mL of 10 mmol / L Tris buffer solution. The pH was adjusted to 8.5 with 0.1 mol / L dilute hydrochloric acid, and the Fe3O4 magnetic nanoparticles were ultrasonically dispersed uniformly. Add 0.3 g of dopamine hydrochloride and react vigorously at 30 °C in air for 6 h. Separate the product with a magnet, wash the product repeatedly with deionized water and ethanol alternately, and dry under vacuum at 60 °C to obtain polydopamine-coated magnetic nanoparticles. Take 0.1 g of polydopamine-coated magnetic nanoparticles and disperse them in 15 mL of N,N-dimethylformamide solution containing 5% phosphotungstic acid. Stir for 10 h to allow the phosphotungstic acid to fully react with the amine groups on the surface of the magnetic nanoparticles. Separate the magnetic nanoparticles with a strong magnet, wash with N,N-dimethylformamide to remove excess phosphotungstic acid, and finally wash twice with ethanol. Dry under vacuum at 60 °C to obtain magnetic nanoparticles loaded with phosphotungstic acid, with a phosphotungstic acid loading of 18 wt%.

[0027] 0.1 g of magnetic nanoparticles loaded with phosphotungstic acid were dispersed in N-methylpyrrolidone to obtain a 1% (w / w) dispersion. 0.3 g of sulfonated polyetheretherketone (PEEK) with a sulfonation degree of 55% was dissolved in 2.5 g of N-methylpyrrolidone to obtain a sulfonated PEEK solution. 1.2 g of the dispersion (containing 0.012 g of solids) was then mixed with the sulfonated PEEK solution, mechanically stirred, and ultrasonically dispersed to ensure uniform mixing. The mixture was allowed to stand for 2 hours to remove bubbles, yielding a casting solution. The casting solution was poured into an 8 cm diameter petri dish and placed in a vertical magnetic field with a magnetic induction intensity of 0.2 T. The mixture was then dried at 60 °C for 24 hours to form a membrane. The prepared membrane was acidified in a 2 mol / L hydrochloric acid solution for 24 hours, washed with water until neutral, and dried to obtain a composite proton exchange membrane (membrane 2.M-SP / PWA-MNPs-4) with a thickness of approximately 55 μm, consisting of magnetic nanoparticles loaded with phosphotungstic acid and sulfonated PEEK.

[0028] Comparative Example 1

[0029] Polyether ether ketone powder was vacuum dried at 80℃ for 24h. 10g of the powder was added to 100mL of 98% concentrated sulfuric acid and mechanically stirred at 20℃ for 12h to dissolve. The temperature was then raised to 50℃ and reacted for 1.5h. The reaction was immediately terminated by cooling with cold water. The reaction solution was slowly poured into a large amount of ice water for precipitation to obtain a fibrous product. The product was washed repeatedly with deionized water until the washing water was close to neutral. Finally, the product was placed in a vacuum oven at 60℃ and dried for 24h to obtain sulfonated polyether ether ketone with a sulfonation degree of 50%.

[0030] Add 100 mL of deoxygenated deionized water to a three-necked flask, then add FeCl3·6H2O (5.4 g, 20 mmol) and FeSO4·7H2O (2.8 g, 10.07 mmol). Stir mechanically and heat to 80 °C under a nitrogen atmosphere. Quickly add 16 mL of concentrated ammonia to the mixture and react for 5 minutes. Then add 2 mL of 1 mol / L sodium citrate solution to prevent particle agglomeration. After continuous stirring for 2 hours, collect the precipitate with a permanent magnet and wash repeatedly with deionized water until neutral. Finally, wash the black precipitate twice with ethanol and vacuum dry at 60 °C to obtain Fe3O4 magnetic nanoparticles. Disperse 0.2 g of Fe3O4 magnetic nanoparticles ultrasonically in 100 mL of deionized water. Add 10 mL of the dispersion to 90 mL of 10 mmol / L Tris buffer solution. Adjust the pH to 8.5 with 0.1 mol / L dilute hydrochloric acid and sonicate to ensure uniform dispersion of the Fe3O4 magnetic nanoparticles. Add 0.2 g of dopamine hydrochloride and react vigorously at 30 °C in air for 6 h. Separate the product with a magnet, wash the product repeatedly with deionized water and ethanol alternately, and then dry it under vacuum at 60 °C to obtain polydopamine-coated magnetic nanoparticles. Take 0.05 g of polydopamine-coated magnetic nanoparticles and disperse them in 10 ml of N,N-dimethylformamide solution containing 5% phosphotungstic acid. Stir for 12 h to allow the phosphotungstic acid to fully react with the amine groups on the surface of the magnetic nanoparticles. Separate the magnetic nanoparticles with a strong magnet, wash with N,N-dimethylformamide to remove excess phosphotungstic acid, and finally wash twice with ethanol. Dry under vacuum at 60 °C to obtain magnetic nanoparticles loaded with phosphotungstic acid, with a phosphotungstic acid loading of 20 wt%.

[0031] 0.05 g of magnetic nanoparticles loaded with phosphotungstic acid were dispersed in N-methylpyrrolidone to obtain a 1% (w / w) dispersion. 0.3 g of sulfonated polyetheretherketone (PEEK) with a sulfonation degree of 50% was dissolved in 2.5 g of N-methylpyrrolidone to obtain a sulfonated PEEK solution. 0.6 g of the dispersion (containing 0.006 g of solids) was then mixed with the sulfonated PEEK solution, mechanically stirred, and ultrasonically dispersed to ensure uniform mixing. The mixture was allowed to stand for 2 hours to remove bubbles, yielding a casting solution. The casting solution was poured into an 8 cm diameter petri dish and dried directly at 60 °C for 24 hours without applying a magnetic field to form a membrane. The prepared membrane was acidified in a 2 mol / L hydrochloric acid solution for 24 hours, then washed with water until neutral, and dried to obtain a magnetic nanoparticle-loaded phosphotungstic acid-sulfonated PEEK composite proton exchange membrane (membrane 3.SP / PWA-MNPs-2) with a thickness of approximately 54 μm.

[0032] Comparative Example 2

[0033] Polyether ether ketone powder was vacuum dried at 80℃ for 24h. 10g of the powder was added to 100mL of 98% concentrated sulfuric acid and mechanically stirred at 20℃ for 12h to dissolve. The temperature was then raised to 50℃ and reacted for 1.5h. The reaction was immediately terminated by cooling with cold water. The reaction solution was slowly poured into a large amount of ice water for precipitation to obtain a fibrous product. The product was washed repeatedly with deionized water until the washing water was close to neutral. Finally, the product was placed in a vacuum oven at 60℃ and dried for 24h to obtain sulfonated polyether ether ketone with a sulfonation degree of 50%.

[0034] 0.3 g of sulfonated polyether ether ketone (50% sulfonation degree) was dissolved in 3 g of N-methylpyrrolidone and allowed to stand for 2 h to remove bubbles, yielding a casting solution. The casting solution was poured into a petri dish with a diameter of 8 cm and placed in a vertical magnetic field with a magnetic induction intensity of 0.3 T at 60 °C for 24 h to form a film. The prepared membrane was acidified in 2 mol / L hydrochloric acid solution for 24 h, then washed with water until neutral, and dried to obtain a pure sulfonated polyether ether ketone membrane with a thickness of approximately 55 μm (membrane 4.SPEEK).

[0035] Matters not covered in this invention are common knowledge.

[0036] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a magnetic nanoparticle-supported phosphotungstic acid-sulfonated polyetheretherketone composite proton exchange membrane, characterized in that, This membrane is a composite proton exchange membrane with a thickness of 30-60 μm, formed by magnetic nanoparticles loaded with phosphotungstic acid and sulfonated polyether ether ketone with a sulfonation degree of 50-60% at a mass ratio of 0.05-5:100 under a magnetic field. The magnetic nanoparticles of iron oxide have a diameter of 20-50 nm, the polydopamine coating layer has a thickness of 10-30 nm, the loading of phosphotungstic acid on the magnetic nanoparticles is 10-30 wt%, and the magnetic induction intensity of the applied magnetic field is 0.05-0.5 T. This membrane preparation method The process includes the following: Preparation of sulfonated polyether ether ketone: Fully dried polyether ether ketone powder was added to concentrated sulfuric acid with a mass fraction of 98%, and the mass ratio of polyether ether ketone to concentrated sulfuric acid was 5-15:

100. The mixture was stirred at room temperature until it was completely dissolved, and then heated to 50-60°C for sulfonation reaction for 1-3 hours. After cooling, the mixture was poured into ice water to precipitate the precipitate. The precipitate was washed several times with deionized water until neutral, and then dried under vacuum at 60°C for 24 hours to obtain sulfonated polyether ether ketone with a sulfonation degree of 50-60%. Preparation of magnetic nanoparticles loaded with phosphotungstic acid: (1) FeCl3 and FeSO4 were dissolved in deoxygenated deionized water at a molar ratio of 2:1 to obtain an iron salt solution. The total iron salt to water mass ratio was 5-10:

100. The solution was mechanically stirred and heated to 80°C under a nitrogen atmosphere. Concentrated ammonia was quickly added to the iron salt solution and reacted for 5 minutes. The volume ratio of concentrated ammonia to iron salt solution was 10-20:

100. 1 mol / L sodium citrate solution was added to prevent particle agglomeration. The volume ratio of sodium citrate solution to iron salt solution was 2-5:

100. After continuous stirring for 2-5 hours, the precipitate was collected with a permanent magnet to obtain Fe3O4 magnetic nanoparticles. (2) The Fe3O4 magnetic nanoparticles prepared in step (1) were ultrasonically dispersed in water to obtain a dispersion with a mass fraction of 1-3%. 10 mL of the dispersion was then added to 90 mL of Tris buffer solution with a pH of 8.

5. 0.1-0.3 g of dopamine hydrochloride was added, and the mixture was stirred vigorously at 30°C in air for 6 h to fully coat the surface of the magnetic nanoparticles with polydopamine, thus obtaining polydopamine-coated magnetic nanoparticles. (3) The polydopamine-coated magnetic nanoparticles prepared in step (2) are dispersed in a solution of N,N-dimethylformamide containing 5-10 wt% phosphotungstic acid. After the phosphotungstic acid reacts fully with the amino groups on the surface of the magnetic nanoparticles, the magnetic nanoparticles are separated by a strong magnet, and excess phosphotungstic acid is removed by washing with N,N-dimethylformamide. The nanoparticles are washed twice with ethanol and dried to obtain magnetic nanoparticles loaded with phosphotungstic acid. Preparation of composite proton exchange membranes: The prepared sulfonated polyether ether ketone was dissolved in N-methylpyrrolidone to obtain a sulfonated polyether ether ketone solution with a mass fraction of 8-10%. Magnetic nanoparticles loaded with phosphotungstic acid were ultrasonically dispersed in N-methylpyrrolidone to obtain a dispersion with a mass fraction of 0.5-2%. The dispersion was mixed with the sulfonated polyether ether ketone solution, with a mass ratio of magnetic nanoparticles to sulfonated polyether ether ketone of 0.05-5:

100. The mixture was mechanically stirred and ultrasonically dispersed to ensure uniform mixing. After standing for 2 hours to remove bubbles, a casting solution was obtained. The casting solution was poured into a petri dish and dried at 60°C under a vertical magnetic field. The magnetic field was controlled using a magnetic field generator, with the magnetic induction intensity controlled at 0.05-0.5T. The prepared membrane was acidified in a 2 mol / L hydrochloric acid solution for 24 hours, then washed with water until neutral, and dried to obtain a magnetic nanoparticle-loaded phosphotungstic acid-sulfonated polyether ether ketone composite proton exchange membrane with a thickness of 30-60 μm, which was used in fuel cells.

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