Phosphotungstic acid modified perfluorosulfonic acid proton membrane, and preparation method and application thereof

Abstract

This invention relates to the field of vanadium redox flow battery membrane technology, and discloses a phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane, its preparation method, and its application. The method includes the following steps: an ether monomer is ring-opened with dopamine under alkaline conditions to generate a tertiary amine-containing intermediate, followed by a nucleophilic substitution reaction. An ester monomer is ring-opened and linked to an amine group to generate a molecule containing a quaternary ammonium salt and a sulfonic acid group. The phosphotungstic acid is then fixed by electrostatic interactions and hydrogen bonding with the phosphotungstic acid. Finally, the mixture is uniformly mixed with perfluorosulfonic acid resin to form a casting solution, which is then cast into a membrane. The phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane prepared by this invention can not only effectively reduce vanadium ion permeation but also improve the coulombic efficiency and voltage efficiency of vanadium batteries.

Description

Technical Field

[0001] This invention relates to the field of vanadium battery separator technology, and particularly to a phosphotungstic acid modified perfluorosulfonic acid proton exchange membrane, its preparation method, and its application. Background Technology

[0002] Vanadium redox flow batteries (VRBs) have attracted widespread attention as a widely adopted energy storage system. The separator, a key material in VRBs, needs to prevent cross-mixing of the positive and negative electrolytes while also transporting ions. An ideal separator should possess good ionic conductivity, excellent vanadium barrier properties, and chemical stability. Perfluorosulfonic acid proton exchange membranes (PFOMs) exhibit high ionic conductivity and good chemical stability, but their low ion selectivity results in high vanadium ion permeability, leading to rapid capacity decay and hindering the long-term stable operation of energy storage systems. This significantly limits the large-scale operation of VRBs. Therefore, developing a separator with low vanadium ion permeability is an urgent problem to be solved. Summary of the Invention

[0003] The purpose of this invention is to provide a phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane, its preparation method, and its application, so as to overcome the shortcomings of the prior art.

[0004] This invention provides the following technical solution:

[0005] In a first aspect, a method for preparing a phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane is disclosed, comprising the following steps:

[0006] Step S1: Dissolve the ether monomer and dopamine in deionized water, adjust the pH, heat the reaction, and dialyze to purify. Then add the ester monomer, heat the reaction again, dialyze to purify, and dry to obtain the quaternary ammonium salt.

[0007] Step S2: Dissolve phosphotungstic acid in ethanol to obtain a phosphotungstic acid alcohol solution; uniformly disperse the quaternary ammonium salt in the phosphotungstic acid alcohol solution to obtain a phosphotungstic acid modifier;

[0008] Step S3: Dissolve the perfluorosulfonic acid resin in N,N-dimethylformamide to obtain a perfluorosulfonic acid resin solution; add the perfluorosulfonic acid resin solution to the phosphotungstic acid modifier and stir to obtain a casting solution;

[0009] Step S4: Pour the casting solution into a grooved glass plate to cast a film, heat it in a gradient, and after the glass plate cools, obtain a phosphotungstic acid modified perfluorosulfonic acid proton exchange membrane.

[0010] In one implementation, in step S1:

[0011] The mass ratio of the ether monomer, the dopamine, the deionized water and the ester monomer is (1~5):(1~5):50:(1~5).

[0012] In one implementation, in step S1:

[0013] The ether monomer is selected from at least one of ethylene glycol diglycidyl ether, glycerol triglycidyl ether, and 1,4-butanediol diglycidyl ether;

[0014] The ester monomer is selected from at least one of 1,3-propanesulfonyl lactone, 2,4-butanesulfonyl lactone, and γ-valerol.

[0015] In one implementation, in step S1:

[0016] The pH is 9-11;

[0017] The heating reaction is carried out at a temperature of 40°C for 6-8 hours.

[0018] The reheating reaction is carried out at a temperature of 40°C for 8-12 hours.

[0019] The drying method is to dry in a vacuum oven at 60°C for 24 hours.

[0020] Ether monomers undergo ring-opening reactions with dopamine under alkaline conditions to form intermediates containing tertiary amines, followed by nucleophilic substitution reactions. Esters then undergo ring-opening reactions to link to amine groups, generating molecules containing quaternary ammonium salts and sulfonic acid groups. Finally, phosphotungstic acid is fixed by electrostatic interactions and hydrogen bonds with phosphotungstic acid.

[0021] In one implementation, in step S2:

[0022] The mass ratio of quaternary ammonium salt to phosphotungstic acid alcohol solution added during the preparation of the phosphotungstic acid modifier is 1:(5~20);

[0023] The phosphotungstic acid in the phosphotungstic acid alcohol solution has a mass concentration of 5% to 25%.

[0024] When phosphotungstic acid combines with quaternary ammonium salts, it can not only act as an electrostatic hydrogen bond crosslinking center, but also act as a proton carrier to provide protons, thereby improving the proton conduction performance and voltage efficiency of the membrane.

[0025] Quaternary ammonium salts, with their positively charged nitrogen-containing groups, generate the Donnan effect with vanadium ions in the vanadium battery electrolyte. The diffusion of vanadium ions is inhibited by electrostatic repulsion, thereby reducing the vanadium ion permeability.

[0026] In one implementation, in step S3:

[0027] The mass ratio of perfluorosulfonic acid resin solution to phosphotungstic acid modifier added during the preparation of the casting solution is (95~99):1.

[0028] In one implementation, in step S3:

[0029] The mass concentration of perfluorosulfonic acid resin in the perfluorosulfonic acid resin solution is 5%~15%;

[0030] The stirring time is 2-4 hours.

[0031] In one implementation, in step S4:

[0032] The gradient heating method is as follows: the glass plate after casting is placed on a heating stage, heated at 60~80℃ for 1~2 hours, and then heated at 100~140℃ for 2~4 hours.

[0033] Secondly, a phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane is disclosed, wherein the phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane is prepared by the above-described preparation method of the phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane.

[0034] Thirdly, an application of a phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane is disclosed, wherein the phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane prepared according to the above preparation method or the above phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane is applied to a vanadium redox flow battery.

[0035] The beneficial effects of the present invention include at least the following:

[0036] When phosphotungstic acid combines with quaternary ammonium salts, it not only acts as an electrostatic hydrogen bond crosslinking center but also as a proton carrier, thereby improving the membrane's proton conductivity and voltage efficiency.

[0037] The Donnan effect between the positively charged nitrogen-containing groups in quaternary ammonium salts and vanadium ions reduces the permeability of vanadium ions.

[0038] In ethers, the ether bond, and in esters, the hydroxyl and sulfonic acid groups after the hydrolysis of sulfonyl lactones can also form hydrogen bonds with water molecules, further improving coulombic efficiency. Attached Figure Description

[0039] Figure 1 This is a SEM image of the phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane prepared in Example 4 of this invention;

[0040] Figure 2 This is a comparison curve of the vanadium blocking ability of the proton exchange membranes obtained in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0041] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0042] A method for preparing a phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane includes the following steps:

[0043] Step S1: Dissolve the ether monomer and dopamine in deionized water, adjust the pH to 9-11, heat at 40°C for 6-8 hours, dialysis for purification, then add the ester monomer, heat again at 40°C for 8-12 hours, dialysis for purification, and dry in a vacuum oven at 60°C for 24 hours to obtain the quaternary ammonium salt; the mass ratio of the ether monomer, dopamine, deionized water, and ester monomer is (1-5):(1-5):50:(1-5). The ether monomer is selected from at least one of ethylene glycol diglycidyl ether, glycerol triglycidyl ether, and 1,4-butanediol diglycidyl ether; the ester monomer is selected from at least one of 1,3-propanesulfonyl lactone, 2,4-butanesulfonyl lactone, and γ-valerolactone.

[0044] Step S2: Dissolve phosphotungstic acid in ethanol to obtain a phosphotungstic acid alcoholic solution with a mass concentration of 5%~25%; uniformly disperse quaternary ammonium salt in the phosphotungstic acid alcoholic solution, with a mass ratio of quaternary ammonium salt to phosphotungstic acid alcoholic solution of 1:(5~20), to obtain a phosphotungstic acid modifier.

[0045] Step S3: Dissolve perfluorosulfonic acid resin in N,N-dimethylformamide to obtain a perfluorosulfonic acid resin solution with a mass concentration of 5%~15%; add the perfluorosulfonic acid resin solution to a phosphotungstic acid modifier, with a mass ratio of resin solution to phosphotungstic acid modifier of (95~99):1, and stir for 2~4 hours to obtain a casting solution.

[0046] Step S4: Pour the casting solution into a grooved glass plate to cast a film. Place the cast glass plate on a heating table and heat it at 60~80℃ for 1~2 hours, then heat it at 100~140℃ for 2~4 hours. After the glass plate cools down, a phosphotungstic acid modified perfluorosulfonic acid proton exchange membrane is obtained.

[0047] Example 1: The following technical solution is adopted.

[0048] Step S1: Dissolve 1g of ethylene glycol diglycidyl ether and 1g of dopamine in 50g of deionized water, add sodium hydroxide to adjust the pH to 9, heat at 40℃ for 6h to fully react, dialyze to purify, add 1g of 1,3-propanesulfonyl lactone to the purified product, heat at 40℃ again for 8h to fully react, dialyze to purify, and dry in a vacuum oven at 60℃ for 24h to obtain quaternary ammonium salt;

[0049] Step S2: Dissolve phosphotungstic acid in ethanol to prepare a 5% (w / w) phosphotungstic acid alcohol solution; add 5g of quaternary ammonium salt to 25g of phosphotungstic acid alcohol solution, stir and disperse to obtain phosphotungstic acid modifier;

[0050] Step S3: Dissolve perfluorosulfonic acid resin in N,N-dimethylformamide to prepare a 5% (w / w) perfluorosulfonic acid resin solution; add 1g of phosphotungstic acid modifier to 99g of perfluorosulfonic acid resin solution and stir for 2h to obtain casting solution;

[0051] Step S4: Pour the casting solution into a grooved glass plate to cast a film. Place the glass plate on a 60°C heating stage for 1 hour, then raise the temperature to 100°C and heat for 2 hours. After the glass plate cools down, scrape off the film to obtain a phosphotungstic acid modified perfluorosulfonic acid proton exchange membrane.

[0052] Example 2: The following technical solution is adopted.

[0053] Step S1: Dissolve 5g of glycerol triglycidyl ether and 5g of dopamine in 50g of deionized water, add sodium hydroxide to adjust the pH to 11, heat at 40℃ for 8h to fully react, dialysis to purify, add 5g of 2,4-butanesulfonyl lactone to the purified product, heat at 40℃ again for 12h to fully react, dialysis to purify, and dry in a vacuum oven at 60℃ for 24h to obtain quaternary ammonium salt;

[0054] Step S2: Dissolve phosphotungstic acid in ethanol to prepare a 25% (w / w) phosphotungstic acid alcohol solution; add 5g of quaternary ammonium salt to 100g of phosphotungstic acid alcohol solution, stir and disperse to obtain phosphotungstic acid modifier;

[0055] Step S3: Dissolve perfluorosulfonic acid resin in N,N-dimethylformamide to prepare a 15% perfluorosulfonic acid resin solution; add 1g of phosphotungstic acid modifier to 95g of perfluorosulfonic acid resin solution and stir for 4h to obtain casting solution;

[0056] Step S4: Pour the casting solution into a grooved glass plate to cast a film. Place the glass plate on an 80°C heating stage for 1-2 hours, then raise the temperature to 140°C and heat for 2-4 hours. After the glass plate cools, scrape off the film to obtain a phosphotungstic acid modified perfluorosulfonic acid proton exchange membrane.

[0057] Example 3: The following technical solution is adopted.

[0058] Step S1: Dissolve 2g of 1,4-butanediol diglycidyl ether and 2g of dopamine in 50g of deionized water, add sodium hydroxide to adjust the pH to 10, heat at 40℃ for 7h to fully react, dialysis to purify, add 2g of γ-valerolactone to the purified product, heat at 40℃ again for 10h to fully react, dialysis to purify, and dry in a vacuum oven at 60℃ for 24h to obtain quaternary ammonium salt;

[0059] Step S2: Dissolve phosphotungstic acid in ethanol to prepare a 10% (w / w) phosphotungstic acid alcohol solution; add 5g of quaternary ammonium salt to 50g of phosphotungstic acid alcohol solution, stir and disperse to obtain phosphotungstic acid modifier;

[0060] Step S3: Dissolve perfluorosulfonic acid resin in N,N-dimethylformamide to prepare a 10% perfluorosulfonic acid resin solution; add 1g of phosphotungstic acid modifier to 97g of perfluorosulfonic acid resin solution and stir for 3h to obtain casting solution;

[0061] Step S4: Pour the casting solution into a grooved glass plate to cast a film. Place the glass plate on a 70°C heating stage for 1.5 hours, then raise the temperature to 120°C and heat for 3 hours. After the glass plate cools down, scrape off the film to obtain a phosphotungstic acid modified perfluorosulfonic acid proton exchange membrane.

[0062] Example 4: The following technical solution is adopted.

[0063] Step S1: Dissolve 3g of ethylene glycol diglycidyl ether and 3g of dopamine in 50g of deionized water, add sodium hydroxide to adjust the pH to 10, heat at 40℃ for 8h to fully react, dialyze to purify, add 3g of 1,3-propanesulfonyl lactone to the purified product, heat again at 40℃ for 12h to fully react, dialyze to purify, and dry in a vacuum oven at 60℃ for 24h to obtain quaternary ammonium salt;

[0064] Step S2: Dissolve phosphotungstic acid in ethanol to prepare a 15% (w / w) phosphotungstic acid alcohol solution; add 5g of quaternary ammonium salt to 75g of phosphotungstic acid alcohol solution, stir and disperse to obtain phosphotungstic acid modifier;

[0065] Step S3: Dissolve perfluorosulfonic acid resin in N,N-dimethylformamide to prepare a 10% perfluorosulfonic acid resin solution; add 1g of phosphotungstic acid modifier to 96g of perfluorosulfonic acid resin solution and stir for 4h to obtain casting solution;

[0066] Step S4: Pour the casting solution into a grooved glass plate to cast a film. Place the glass plate on a 60°C heating stage for 1 hour, then raise the temperature to 140°C and heat for 2 hours. After the glass plate cools down, scrape off the film to obtain a phosphotungstic acid modified perfluorosulfonic acid proton exchange membrane.

[0067] like Figure 1 The image shown is an SEM image of the phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane prepared in this embodiment. It can be seen that the phosphotungstic acid modifier is uniformly distributed on the membrane surface.

[0068] Comparative Example 1: The following technical solution is adopted.

[0069] The blank control group used perfluorosulfonic acid proton exchange membranes prepared directly from perfluorosulfonic acid resin solution.

[0070] Comparative Example 2: The following technical solution is adopted.

[0071] The preparation process is the same as in Example 1, except that no ether monomers are involved in step S1.

[0072] Comparative Example 3: The following technical solution is adopted.

[0073] The preparation process is the same as in Example 1, except that phosphotungstic acid is not involved in step S1.

[0074] Proton exchange membrane vanadium blocking performance test: The separators obtained in Example 1 and Comparative Example 1 were assembled into a vanadium battery stack. Under the same operating conditions, the battery was first charged to 95% SOC, and then the electrolyte circulation pump was kept on. The open-circuit voltage of the battery was tested, as the open-circuit voltage directly reflects the self-discharge rate of the battery. The test results are as follows: Figure 2 As shown, the vanadium blocking performance of the proton exchange membrane prepared in Example 1 is significantly better than that of the blank proton exchange membrane in Comparative Example 1.

[0075] Battery testing: The proton exchange membranes prepared in the examples and comparative examples were assembled into fuel cell stacks and subjected to charge-discharge cycle tests under the same operating conditions. The coulombic efficiency, energy efficiency, and voltage efficiency of the fuel cell stacks were recorded. The test results are shown in Table 1.

[0076] Table 1. Performance test results of membranes prepared in the examples and comparative examples.

[0077]

[0078] The test results above show that, compared with Comparative Example 1, the coulombic efficiency and voltage efficiency of Examples 1-4 are all increased. This is because the combination of phosphotungstic acid and quaternary ammonium salt not only facilitates proton transport but also effectively prevents vanadium permeation. Compared with Comparative Example 2, the coulombic efficiency of Examples 1-4 is higher. This is because the Donnan effect between the positively charged nitrogen-containing groups in the quaternary ammonium salt and vanadium ions reduces the vanadium ion permeation rate. Compared with Comparative Example 3, Examples 1-4 have higher coulombic efficiency and voltage efficiency. This is because the combination of phosphotungstic acid and quaternary ammonium salt allows phosphotungstic acid to not only act as an electrostatic hydrogen bond crosslinking center but also as a proton carrier, providing protons and thus improving the proton conduction performance and voltage efficiency of the membrane.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane, characterized in that, Includes the following steps: Step S1: Dissolve the ether monomer and dopamine in deionized water, adjust the pH, heat the reaction, and dialyze to purify. Then add the ester monomer, heat the reaction again, dialyze to purify, and dry to obtain the quaternary ammonium salt. The ether monomer is selected from at least one of ethylene glycol diglycidyl ether, glycerol triglycidyl ether, and 1,4-butanediol diglycidyl ether. The ester monomer is selected from at least one of 1,3-propanesulfonyl lactone and 2,4-butanesulfonyl lactone. Step S2: Dissolve phosphotungstic acid in ethanol to obtain a phosphotungstic acid alcohol solution; uniformly disperse the quaternary ammonium salt in the phosphotungstic acid alcohol solution to obtain a phosphotungstic acid modifier; Step S3: Dissolve the perfluorosulfonic acid resin in N,N-dimethylformamide to obtain a perfluorosulfonic acid resin solution; add the perfluorosulfonic acid resin solution to the phosphotungstic acid modifier and stir to obtain a casting solution; Step S4: Pour the casting solution into a grooved glass plate to cast a film, heat it in a gradient, and after the glass plate cools, obtain a phosphotungstic acid modified perfluorosulfonic acid proton exchange membrane.

2. The preparation method according to claim 1, characterized in that, In step S1: The mass ratio of the ether monomer, the dopamine, the deionized water and the ester monomer is (1~5):(1~5):50:(1~5).

3. The preparation method according to claim 1, characterized in that, In step S1: The pH is 9-11; The heating reaction is carried out at a temperature of 40°C for 6-8 hours. The reheating reaction is carried out at a temperature of 40°C for 8-12 hours. The drying method is to dry in a vacuum oven at 60°C for 24 hours.

4. The preparation method according to claim 1, characterized in that, In step S2: The mass ratio of quaternary ammonium salt to phosphotungstic acid alcohol solution added during the preparation of the phosphotungstic acid modifier is 1:(5~20); The phosphotungstic acid in the phosphotungstic acid alcohol solution has a mass concentration of 5% to 25%.

5. The preparation method according to claim 1, characterized in that, In step S3: The mass ratio of perfluorosulfonic acid resin solution to phosphotungstic acid modifier added during the preparation of the casting solution is (95~99):

1.

6. The preparation method according to claim 1, characterized in that, In step S3: The mass concentration of perfluorosulfonic acid resin in the perfluorosulfonic acid resin solution is 5%~15%; The stirring time is 2-4 hours.

7. The preparation method according to claim 1, characterized in that, In step S4: The gradient heating method is as follows: the glass plate after casting is placed on a heating stage, heated at 60~80℃ for 1~2 hours, and then heated at 100~140℃ for 2~4 hours.

8. A phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane, characterized in that, The phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane is prepared using the preparation method of the phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane as described in any one of claims 1-7.

9. An application of a phosphotungstic acid-modified perfluorosulfonic acid proton exchange membrane, characterized in that, The phosphotungstic acid modified perfluorosulfonic acid proton exchange membrane as described in claim 8 is applied to a vanadium redox flow battery.

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