A method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl ketone copolymer and its application.

Abstract

This invention belongs to the field of proton exchange membrane preparation technology, specifically relating to a method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl ketone copolymer and its application. The preparation method includes the following steps: (1) copolymer synthesis: Decafluorobiphenyl ketone, hydroquinone and N,N-dimethylacetamide are mixed and stirred until dissolved; dry potassium carbonate is added, heated to 120-160℃, and stirred for 3-5 hours under nitrogen protection, and cooled to room temperature; added to a stirred acetic acid solution, filtered, washed with deionized water, and vacuum dried to obtain copolymer powder; (2) sulfonation to obtain sulfonated product; (3) casting the sulfonated product into a membrane. The perfluorosulfonic acid proton exchange membrane prepared by this invention has a polyarylene ether polymer as its backbone, low water absorption, good mechanical properties, and high proton conductivity, and can be applied to flow batteries, fuel cells and water electrolysis for hydrogen production.

Description

Technical Field

[0001] This invention belongs to the field of proton exchange membrane preparation technology, specifically relating to a method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl copolymerization and its application. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are one of the most promising sources of electrical energy for electric vehicles. The proton exchange membrane (PEM), as its core functional component, plays a crucial role in the continuous conversion of electrochemical energy through the directional conduction of protons, thus determining the battery's performance.

[0003] Currently, commercially available PEMs are mainly fluorosulfonic acid membranes, represented by Nafion. These membranes use fluorocarbon chains as a hydrophobic framework and sulfonic acid groups as proton conduction sites, achieving a proton conductivity of 0.1 S cm⁻¹ at 25 °C. -1 However, it suffers from high production costs, easy water loss above 100 °C, and chemical degradation, leading to a significant decrease in proton conductivity. Furthermore, the cost of Nafion membranes as proton exchange membranes is approximately 1000-2000 RMB / m³. 2 PEMs account for 20%-30% of the total battery cost. Therefore, developing inexpensive PEMs suitable for higher temperatures is one of the challenges in the development of PEMFC technology.

[0004] Non-fluorinated proton exchange membranes using sulfonated polyarylether ketone polymers, with aromatic polymers as the main chain and proton-conducting groups introduced through sulfonation, possess advantages such as high proton conductivity and a cost that is only 1 / 5 to 1 / 10 that of Nafion membranes, making them promising proton exchange membrane materials. However, the proton conductivity, size, and mechanical properties of non-fluorinated polymers are highly dependent on their degree of sulfonation, and there is an inherent contradiction among these three aspects, making it impossible to achieve optimal performance simultaneously. This is the most fundamental problem. For example, the contradiction between high sulfonation degree and low stability is manifested in the fact that in order to improve proton conductivity, the sulfonation degree needs to be increased (introducing more hydrophilic groups), but high sulfonation degree will cause the membrane to absorb water and swell excessively. The water absorption rate usually exceeds 35% or even more than 50%, which will cause two major problems. First, the membrane dimensional stability is poor, and the lateral and longitudinal swelling rates can reach 15~30%, far exceeding the requirements of fuel cells for membrane swelling rate (<10%), which leads to the membrane peeling off from the catalyst layer and gas diffusion layer in the membrane electrode assembly (MEA) and battery failure. Second, the mechanical properties of the membrane will drop sharply, with the tensile strength dropping from 30~40MPa at low sulfonation degree to below 10MPa, which cannot withstand the fuel cell assembly pressure (0.5~2MPa) and long-term dry and wet cycles (moisture fluctuations during start-up and shutdown), and is prone to cracking and damage. Essentially, the high degree of sulfonation disrupts the hydrophilic-hydrophobic microphase separation balance of the membrane, weakens the supporting role of the hydrophobic main chain, and causes the structure to collapse due to excessive expansion of the hydrophilic region. Its stability is far inferior to that of fluorosulfonic acid membranes. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for preparing a fluorinated sulfonated polyarylether ketone proton exchange membrane based on decafluorobiphenyl ketone copolymer and its application. The fluorinated sulfonated proton exchange membrane uses polyarylether polymer as the backbone material. By introducing fluorine groups, not only can the water absorption rate be reduced, but the effects of the hydrophilic and hydrophobic parts of the sulfonated polyarylether ketone are also enhanced, promoting the separation of the membrane microphase and thus providing high proton conductivity.

[0006] A method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl copolymer includes the following steps: (1) Copolymer synthesis: (1.1) Mix decafluorobenzyl ketone, hydroquinone, and N,N-dimethylacetamide and stir until dissolved; (1.2) Add dry potassium carbonate to it, heat to 120-160℃, stir for 3-5 hours under nitrogen protection, and cool to room temperature; (1.3) Add the mixture from step (1.2) to a stirred acetic acid solution, filter, wash with deionized water, and vacuum dry to obtain copolymer powder; preferably, the vacuum drying temperature is 100-120℃; (2) Sulfonation to obtain the sulfonated product; (3) Cast the sulfonated product into a film.

[0007] Preferably, the copolymer powder has the following structural formula: , where n is between 30 and 70.

[0008] Preferably, the molar ratio of decafluorobenzyl ketone, hydroquinone, N,N-dimethylacetamide, and potassium carbonate is 1:(1-3):(30-50):(1-5).

[0009] Preferably, the sulfonation is specifically as follows: (2.1) Mix the copolymer powder with chloroform, then add sulfonation solvent to it, stir at 60-65°C for 0.5-5h, and after the reaction is completed, stop the sulfonation by adding it dropwise into an ice-water bath; (2.2) Centrifuge and wash until the pH of the centrifuged liquid is 7, filter and dry the solid obtained by centrifugation to obtain the sulfonated product; preferably, the drying temperature is 100-105℃.

[0010] Preferably, the sulfonating solvent is any one of concentrated sulfuric acid, fuming sulfuric acid, or chlorosulfonic acid.

[0011] Preferably, the ratio of the copolymer powder to the sulfonating solvent is (5-10) g: 100 mL.

[0012] Preferably, the casting process is as follows: (3.1) The sulfonated product is added to a solvent and stirred at 60-70°C to form a copolymer solution; (3.2) Stir the copolymer solution at room temperature for 12-14 h to obtain a film-forming solution; (3.3) The film-forming solution is added to a glass mold for casting and drying to obtain the proton exchange membrane; preferably, the drying temperature is 80-100℃.

[0013] Preferably, in step (3.1), the solvent is any one of dimethylacetamide, dimethylformamide, acetone and dimethyl sulfoxide; the concentration of the copolymer solution is 10-15%.

[0014] Preferably, the concentration of the acetic acid solution is 1-5 wt%.

[0015] An application of a perfluorosulfonic acid proton exchange membrane in flow batteries, fuel cells, and water electrolysis for hydrogen production is characterized in that: the perfluorosulfonic acid proton exchange membrane is prepared by the preparation method described in this invention, and the perfluorosulfonic acid proton exchange membrane is activated in a 2-3 mol / L dilute sulfuric acid solution for 12-24 h before use.

[0016] Advantages of this invention: The perfluorosulfonic acid proton exchange membrane prepared by this invention has a polyarylene ether polymer as its backbone, low water absorption, good mechanical properties, and high proton conductivity. It can be applied to flow batteries, fuel cells, and water electrolysis for hydrogen production. Attached Figure Description

[0017] Figure 1 The NMR F-spectrum of the copolymer powder is shown. Detailed Implementation

[0018] Example 1: A method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl copolymer, comprising the following steps: (1) Copolymer synthesis: (1.1) Mix decafluorobenzyl ketone, hydroquinone and N,N-dimethylacetamide in a molar ratio of 1:1:30 and stir until dissolved; (1.2) Add dry potassium carbonate, the molar amount of which is 3 times that of the decafluorobenzyl ketone, heat to 120°C, stir for 5 hours under nitrogen protection, and cool to room temperature. (1.3) The mixture from step (1.2) was added to a 1 wt% acetic acid solution under stirring, filtered, washed with deionized water, and vacuum dried at 100°C for 24 h to obtain copolymer powder with the following structural formula: Where n is between 30 and 70; Its NMR F-spectrum is shown below Figure 1 As shown, based on the molecular formula, different F molecules are labeled F1, F2, F3, F4, F5, F6, F7, F8, F9, and F1, respectively. 10 The chemical shifts of different F values ​​are indicated: F6 and F8 are -154 ppm, F1 and F3 are -144.8 ppm, F5 and F7 are -138.7 ppm, and F2 and F4 are -141 ppm and -139.5 ppm, respectively. (2) Sulfonation to obtain the sulfonated product: (2.1) Add 2g of the copolymer powder and 20mL of chloroform to a flask equipped with a magnetic stirrer and a condenser. Inject fuming sulfuric acid (containing 28%~33% SO3) into the flask within 5 minutes. Stir at 60℃ and 900rpm for 0.5h. After the reaction is complete, transfer the liquid to a constant pressure dropping funnel and then drop it dropwise into an ice-water bath to stop sulfonation. The ratio of the copolymer powder to the fuming sulfuric acid is 5g:100mL. (2.2) Centrifuge and wash until the pH of the centrifuged liquid is 7. Filter the solid obtained by centrifugation and dry it at 100°C to obtain spherical sulfonated products. (3) Casting the sulfonated product into a film: (3.1) The sulfonated product is added to dimethylacetamide and stirred at 60°C to form a 13wt% copolymer solution; (3.2) The copolymer solution was stirred at room temperature for 12 hours to obtain a film-forming solution; (3.3) The film-forming solution is added to a glass mold for casting and drying at 80°C to obtain the proton exchange membrane.

[0019] Example 2: In step (2.1), the mixture was stirred at 60°C and 900 rpm for 1.5 h, and the rest was the same as in Example 1.

[0020] Example 3: In step (2.1), the mixture was stirred at 60°C and 900 rpm for 4 hours, and the rest was the same as in Example 1.

[0021] Example 4: A method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl copolymer, comprising the following steps: (1) Copolymer synthesis: (1.1) Mix decafluorobenzyl ketone, hydroquinone and N,N-dimethylacetamide in a molar ratio of 1:3:50 and stir until dissolved; (1.2) Add dry potassium carbonate to it, heat to 160°C, stir for 3 hours under nitrogen protection, and cool to room temperature; wherein the molar amount of potassium carbonate is equal to that of the decafluorobenzyl ketone. (1.3) Add the mixture from step (1.2) to a 5 wt% acetic acid solution under stirring, filter, wash with deionized water, and vacuum dry at 120°C to obtain copolymer powder; (2) Sulfonation to obtain the sulfonated product: (2.1) Add 2g of the copolymer powder and 20mL of chloroform to a flask equipped with a magnetic stirrer and a condenser. Add concentrated sulfuric acid to the flask within 5 minutes. Stir at 65°C and 900rpm for 4 hours. After the reaction is complete, transfer the liquid to a constant pressure dropping funnel and then add it dropwise to an ice-water bath to stop sulfonation. The ratio of the copolymer powder to concentrated sulfuric acid is 10g:100mL. (2.2) Centrifuge and wash until the pH of the centrifuged liquid is 7. Filter the solid obtained by centrifugation and dry it at 105℃ to obtain the sulfonated product, which is a spherical substance. (3) Casting the sulfonated product into a film: (3.1) The sulfonated product is added to dimethylformamide and stirred at 70°C to form a 10 wt% copolymer solution; (3.2) The copolymer solution was stirred at room temperature for 12 hours to obtain a film-forming solution; (3.3) The film-forming solution is added to a glass mold for casting and drying at 85°C to obtain the proton exchange membrane.

[0022] Example 5: A method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl copolymer, comprising the following steps: (1) Copolymer synthesis: (1.1) Mix decafluorobenzyl ketone, hydroquinone and N,N-dimethylacetamide in a molar ratio of 1:3:40 and stir until dissolved; (1.2) Add dry potassium carbonate to it, heat to 140°C, stir for 4 hours under nitrogen protection, and cool to room temperature; wherein the molar amount of potassium carbonate is 5 times that of the decafluorobiphenyl ketone. (1.3) Add the mixture from step (1.2) to a 3 wt% acetic acid solution under stirring, filter, wash with deionized water, and vacuum dry at 120°C to obtain copolymer powder; (2) Sulfonation to obtain the sulfonated product: (2.1) Add 2g of the copolymer powder and 20mL of chloroform to a flask equipped with a magnetic stirrer and a condenser. Inject chlorosulfonic acid into the flask within 5 minutes. Stir at 60°C and 900rpm for 5 hours. After the reaction is complete, transfer the liquid to a constant pressure dropping funnel and then drop it dropwise into an ice-water bath to stop sulfonation. The ratio of the copolymer powder to chlorosulfonic acid is 8g:100mL. (2.2) Centrifuge and wash until the pH of the centrifuged liquid is 7. Filter the solid obtained by centrifugation and dry it at 105℃ to obtain the sulfonated product, which is a spherical substance. (3) Casting the sulfonated product into a film: (3.1) The sulfonated product is added to N,N-dimethylformamide and stirred at 65°C to form a 15wt% copolymer solution; (3.2) The copolymer solution was stirred at room temperature for 14 hours to obtain a film-forming solution; (3.3) The film-forming solution is added to a glass mold for casting and drying at 100°C to obtain the proton exchange membrane.

[0023] Comparative Example 1: A method for preparing a sulfonic acid proton exchange membrane based on the copolymerization of difluorobenzophenone and hydroquinone (1) Synthesis of polyetheretherketone copolymer powder Difluorobenzophenone was used instead of decafluorobenzyl ketone, and everything else was the same as in Example 1; (1.1) Mix difluorobenzophenone, hydroquinone and N,N-dimethylacetamide in a molar ratio of 1:1:30 and stir until dissolved; (1.2) Add dry potassium carbonate, the molar amount of which is 3 times that of the difluorobenzophenone, heat to 120°C, stir for 5 hours under nitrogen protection, and cool to room temperature; (1.3) Add the mixture from step (1.2) to a 1 wt% acetic acid solution under stirring, filter, wash with deionized water, and vacuum dry at 100°C for 24 h to obtain copolymer powder, which is polyether ether ketone powder; (2) Sulfonation to obtain sulfonated products (2.1) Take 2g of the polyetheretherketone powder and 20mL of chloroform and add them to a flask equipped with a magnetic stirrer and a condenser. Add fuming sulfuric acid (containing 28%~33% SO3) to the flask within 5 minutes and stir at 60℃ and 900rpm for 1.5h. After the reaction is completed, place the resulting orange liquid in a constant pressure dropping funnel and then slowly drop it into an ice water bath to stop sulfonation and obtain a uniform white spherical product. The ratio of the polyetheretherketone powder to the fuming sulfuric acid is 5g:100mL. (2.2) Centrifuge and wash until the pH of the centrifuged liquid is 7. Filter the solid obtained by centrifugation and dry it at 100°C to obtain the sulfonated product, which is a yellow spherical product SPEEK. (3) Casting the sulfonated product into a film (3.1) The sulfonated product SPEEK was added to dimethylacetamide and stirred at 60°C to form a 13wt% copolymer solution; (3.2) The copolymer solution was stirred at room temperature for 12 hours to obtain a film-forming solution; (3.3) The film-forming solution is added to a glass mold for casting and drying at 80°C to obtain the proton exchange membrane.

[0024] Performance testing 1. Detection of proton conductivity Test method: The proton conductivity of the membrane sample was measured using the AC impedance method, with a test frequency range of 1 Hz to 5 × 10⁻⁶. 6 Hz. Before testing, the membrane sample needs to be cut into a rectangle of 2 cm × 1 cm, and the membrane thickness should be measured using a thickness gauge. The membrane is then activated by immersing it in a 2 M sulfuric acid solution for 24 h. Before testing, the membrane is rinsed with deionized water to remove any residual sulfuric acid solution from the surface. During testing, the sample membrane is placed between two platinum electrodes, and the entire testing setup is placed in a constant temperature and humidity chamber at 80 ℃ and 100% humidity. The proton conductivity of the sample membrane is calculated using the following formula: σ = L / (R × d × b); Where σ represents proton conductivity, in units of S / cm; L is the distance between the two electrodes, in units of cm; b is the effective width of the membrane in the direction perpendicular to the electrodes, in units of cm; d is the thickness of the membrane, in units of cm; and R is the measured resistance of the membrane, in units of Ω. The results are shown in Table 1; Table 1. Proton conductivity test results , As shown in Table 1, Examples 1-3 have outstanding conductivity advantages. Compared with the non-perfluorosulfonic acid polymer membrane of Comparative Example 1, their conductivity is improved and belongs to the category of high conductivity, which can be used for proton exchange membranes.

[0025] 2. Mechanical performance testing According to the national standard GB / T 20042.3-2022, the mechanical properties of the proton exchange membrane were evaluated by testing its initial tensile strength. The results are shown in Table 2. Table 2 Initial Tensile Strength , As shown in Table 2, the proton exchange membrane prepared in this invention has a much higher tensile strength than that of Comparative Example 1. This is because the monomer used in this invention is decafluorobenzyl ketone, which contains more fluorinated groups (hydrophobic groups) and occupies more reaction sites. Therefore, during the sulfonation reaction, the number of sulfonated groups (hydrophilic groups) added is relatively reduced. Thus, in this invention, the hydrophobic region of the membrane is dominant, the molecular chains are more tightly packed, the crystallinity is high, and the tensile strength is generally higher. In contrast, the monomer in Comparative Example 1 is difluorobenzophenone, which contains fewer fluorinated groups. The polyether ether ketone obtained after reacting with hydroquinone is essentially fluorine-free. Therefore, during the sulfonation reaction, more sulfonic acid groups can be added, the hydrophilic region is dominant, the membrane swells severely after absorbing water, the molecular chain slip resistance decreases significantly, and the tensile strength decreases sharply. Excessive swelling may even lead to membrane structure damage, resulting in low tensile strength and rendering it impractical.

[0026] 3. Water absorption rate test After drying the sample in an oven for 24 hours, cool it to room temperature and measure its initial mass m0. Test the water absorption rate at 100 °C by immersing the sample in boiling distilled water at 100 °C for 2 hours, then removing the sample, absorbing surface moisture, and measuring its mass m1. The water absorption rate of the sample membrane is calculated using the following formula: Δm = (m1 - m0) / m0 × 100%, and the calculation results are shown in Table 3. Table 3 Water absorption test results , As shown in Table 3, the fluorinated polyarylene ether polymer with low sulfonation degree in this invention has a low water absorption rate. In the comparative example, because the sulfonated polyether ether ketone backbone has a weakly hydrophobic aromatic group and lacks the strong hydrophobicity of the fluorinated backbone, it expands more easily after hydration in the hydrophilic water, thus resulting in a higher water absorption rate under the same sulfonation time. Since sulfonic acid groups are strongly hydrophilic groups, their number directly determines the upper limit of the membrane's water absorption rate. Therefore, the water absorption capacity of the proton exchange membrane is essentially determined by the sulfonic acid groups on the molecular chain. Thus, the high water absorption rate also verifies that in Examples 1-3, the presence of fluorine element results in a lower and more uniform sulfonation degree; while Comparative Example 1, which does not contain fluorine element, has a higher water absorption rate due to its high sulfonation degree.

Claims

1. A method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl copolymer, characterized in that: Includes the following steps: (1) Copolymer synthesis: (1.1) Mix decafluorobenzyl ketone, hydroquinone, and N,N-dimethylacetamide and stir until dissolved; (1.2) Add dry potassium carbonate to it, heat to 120-160℃, stir for 3-5 hours under nitrogen protection, and cool to room temperature; (1.3) Add the mixture from step (1.2) to a stirred acetic acid solution, filter, wash with deionized water, and vacuum dry to obtain copolymer powder; (2) Sulfonation to obtain the sulfonated product; (3) Cast the sulfonated product into a film.

2. The method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl copolymer according to claim 1, characterized in that: The structural formula of the copolymer powder is as follows: , where n is between 30 and 70.

3. The method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl copolymer according to claim 2, characterized in that: The molar ratio of decafluorobenzyl ketone, hydroquinone, N,N-dimethylacetamide, and potassium carbonate is 1:(1-3):(30-50):(1-5).

4. The method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl copolymer according to claim 1, characterized in that: The sulfonation process is as follows: (2.1) Mix the copolymer powder with chloroform, then add sulfonation solvent to it, stir at 60-65°C for 0.5-5h, and after the reaction is completed, stop the sulfonation by adding it dropwise into an ice-water bath; (2.2) Centrifuge and wash until the pH of the centrifuged liquid is 7. Filter the solid obtained by centrifugation and dry it to obtain the sulfonated product.

5. The method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl copolymer according to claim 4, characterized in that: The sulfonating solvent is any one of concentrated sulfuric acid, fuming sulfuric acid, or chlorosulfonic acid.

6. The method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl copolymer according to claim 5, characterized in that: The ratio of the copolymer powder to the sulfonation solvent is (5-10) g: 100 mL.

7. The method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl copolymer according to claim 1, characterized in that: The film casting process is as follows: (3.1) The sulfonated product is added to a solvent and stirred at 60-70°C to form a copolymer solution; (3.2) Stir the copolymer solution at room temperature for 12-14 h to obtain a film-forming solution; (3.3) The film-forming solution is added to a glass mold for casting and drying to obtain the proton exchange membrane.

8. The method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl copolymer according to claim 7, characterized in that: In step (3.1), the solvent is any one of dimethylacetamide, dimethylformamide, acetone and dimethyl sulfoxide; the concentration of the copolymer solution is 10-15%.

9. The method for preparing a perfluorosulfonic acid proton exchange membrane based on decafluorobiphenyl copolymer according to claim 1, characterized in that: The concentration of the acetic acid solution is 1-5 wt%.

10. An application of a perfluorosulfonic acid proton exchange membrane in flow batteries, fuel cells, and water electrolysis for hydrogen production, characterized in that: The perfluorosulfonic acid proton exchange membrane is prepared by the preparation method described in claims 1-9, and the perfluorosulfonic acid proton exchange membrane is activated in a 2-3 mol / L dilute sulfuric acid solution for 12-24 h before use.

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