A modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane, its preparation method and application

Abstract

This invention relates to the field of proton exchange membrane (PEM) preparation technology, and discloses a modified PAN and quercetin-doped sulfonated polyaryletherketone (PAEK) PEM, its preparation method, and its applications. The method includes the following steps: synthesizing sulfonated PAEK via monomer copolymerization; obtaining modified PAN by carboxyl modification of polyacrylonitrile (PAN); and then blending SPAEK, modified PAN, and quercetin to form a membrane. In this invention, the cyano groups of the modified PAN form an acid-base crosslinking network with the sulfonic acid groups of SPAEK to inhibit swelling, and its carboxyl groups participate in proton conduction; the polyphenolic hydroxyl groups of quercetin construct a hydrogen bond network to enhance structural density and act as a free radical scavenger to improve antioxidant stability. This invention, through the synergistic effect of the three components, successfully solves the technical problems of SPAEK membranes, such as difficulty in balancing proton conductivity and dimensional stability, and poor antioxidant performance. The resulting composite membrane possesses high proton conductivity, low swelling rate, and excellent oxidation stability, making it suitable for vanadium redox flow batteries.

Description

Technical Field

[0001] This invention relates to the field of proton exchange membrane preparation technology, and particularly to a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane, its preparation method, and its application. Background Technology

[0002] As one of the core technologies in the field of long-term energy storage, vanadium redox flow batteries (VFBs) require their proton exchange membranes to simultaneously perform four core functions in a strongly acidic vanadium electrolyte environment: rapid proton conduction, strict vanadium ion blocking, chemical stability and tolerance, and mechanical strength support. This need for balancing multiple performance characteristics has become a key challenge in the research and development of membrane materials.

[0003] In current commercial applications, perfluorosulfonic acid membranes (represented by DuPont Nafion membranes) still hold a dominant position. Their structure, with perfluorocarbon chains as the hydrophobic framework and sulfonic acid groups as hydrophilic ionic sites, can form continuous proton conduction channels. At 25°C, the proton conductivity can reach 0.08-0.1 S / cm, meeting the proton migration requirements of VFB during high-current charging and discharging. Simultaneously, the perfluoro framework effectively resists the strong oxidizing agents in the electrolyte. 5+ With strong reducing properties V 2+ It exhibits extremely high tolerance, maintaining stable operation for thousands of hours in acidic environments, and its mature industrialization process ensures product consistency. However, two major drawbacks of Nafion membranes severely restrict their large-scale application: First, the vanadium ion permeation problem. The size of its hydrophilic channels overlaps with the hydration radius of vanadium ions, causing vanadium ions to penetrate the membrane through electromigration and concentration diffusion, leading to cross-contamination of the positive and negative electrolytes. This reduces the battery's coulombic efficiency from the theoretical 99% to 85%-90%, requiring periodic electrolyte replacement to maintain performance. Second, the high cost; Nafion membranes cost approximately 1000-2000 RMB / m³. 2 It accounts for 20%-30% of the total cost of batteries, and the complex perfluorinated polymerization process makes it difficult to achieve low-cost mass production.

[0004] To overcome the bottleneck of perfluorosulfonic acid membranes, non-fluorinated proton exchange membranes (such as sulfonated polyaryletherketones) have become a research hotspot. These membranes use aromatic polymers as the main chain, introducing sulfonic acid groups through sulfonation. Their cost is only 1 / 5 to 1 / 10 that of Nafion membranes, and the spatial arrangement of the aromatic ring structure and sulfonic acid groups can reduce the ion channel size. Vanadium ion permeability is typically only 1 / 10 to 1 / 100 that of Nafion membranes, significantly improving battery coulombic efficiency. However, non-fluorinated membranes face a difficult-to-reconcile triple contradiction of conductivity, swelling, and stability: increasing the degree of sulfonation to increase proton conduction sites can raise conductivity to above 0.05 S / cm, but excessive sulfonic acid groups enhance the membrane's hydrophilicity, leading to excessive swelling in acidic electrolytes (swelling degree can reach 30%-50%), causing a sharp drop in the membrane's mechanical strength and even rupture; decreasing the degree of sulfonation to control swelling causes the proton conductivity to drop below 0.01 S / cm, failing to meet battery performance requirements. More importantly, the aromatic backbone of non-fluorinated membranes is susceptible to free radical attack in VFB electrolytes, and the strong oxidizing properties of VFB... 5+ It can cause the electrolyte to generate active free radicals such as ·OH. These free radicals can destroy the covalent bonds between aromatic rings, leading to the degradation of the membrane backbone and a decrease in ion exchange capacity. After long-term operation, the conductivity will decrease by more than 30%, and the stability is far inferior to that of perfluorosulfonic acid membranes.

[0005] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane, its preparation method and application, aiming to solve the problems of uncontrollable sulfonation degree and uneven distribution of sulfonic acid groups in SPAEK proton exchange membranes prepared by traditional post-sulfonation method, as well as the resulting technical problems of difficulty in balancing proton conductivity and dimensional stability and poor antioxidant stability.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane, comprising the following steps:

[0009] Sulfonated difluorobenzophenone monomer, bisphenol monomer and dihalogen monomer are subjected to nucleophilic substitution polymerization in the presence of catalyst and solvent to generate sulfonated polyarylether ketone;

[0010] Carboxyl modification of polyacrylonitrile yields carboxyl-modified polyacrylonitrile.

[0011] The sulfonated polyarylether ketone, carboxyl-modified polyacrylonitrile, and quercetin are dissolved in an organic solvent to form a casting solution.

[0012] The casting solution is used to prepare a membrane, thereby obtaining a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane.

[0013] The method for preparing the modified PAN and quercetin-doped sulfonated polyarylether ketone proton exchange membrane includes the following steps: sulfonated difluorobenzophenone monomer, bisphenol monomer, and dihalogen monomer are subjected to a nucleophilic substitution polymerization reaction in the presence of a catalyst and solvent to generate sulfonated polyarylether ketone.

[0014] Add an aprotic polar solvent to the reactor, start the stirring system, control the stirring speed at 200-250 rpm, and add bisphenol monomer, dihalogen monomer, sulfonated difluorobenzophenone monomer and catalyst in sequence. Finally, add an aprotic nonpolar solvent to rinse the reactor wall to ensure complete material transfer.

[0015] Nitrogen gas is continuously introduced into the reactor during the heating process to maintain an inert atmosphere. When the temperature reaches 160-180℃, the reaction is held at this temperature for 1-3 hours. Then, the temperature is further increased to 190-210℃ and the reaction is held at this temperature for 160-200 hours.

[0016] After the reaction is complete, the reaction solution is quickly poured into ice water to precipitate and solidify the polymer. The resulting solid is then soaked in ice water, crushed by a crusher, washed with distilled water to remove residual impurities, and then dehydrated using a press. The wet material is then placed in an oven to dry, finally obtaining the target polymer product, sulfonated polyarylether ketone.

[0017] The method for preparing the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane includes the following steps: in the preparation of the sulfonated polyaryletherketone, the sulfonated difluorobenzophenone monomer is 4,4'-difluorobenzophenone-3,3'-disulfonic acid dipotassium salt; the bisphenol monomer is bisphenol A; the dihalogen monomer is 4,4'-difluorobenzophenone; the catalyst is an alkali metal carbonate; and the solvent includes both aprotic polar solvents and aprotic nonpolar solvents, wherein the aprotic polar solvent is sulfolane and the aprotic nonpolar solvent is toluene.

[0018] The method for preparing the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane, wherein in the step of preparing sulfonated polyaryletherketone, the molar ratio of bisphenol monomer to sulfonated difluorobenzophenone monomer and dihalogen monomer is 1:(0.4-0.5):(0.5-0.6), and the molar ratio of the sum of the molar amounts of sulfonated difluorobenzophenone monomer and dihalogen monomer to the molar amount of bisphenol monomer is 1:1.

[0019] The method for preparing the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane includes the following steps: Carboxyl modification treatment of polyacrylonitrile to obtain carboxyl-modified polyacrylonitrile.

[0020] Polyacrylonitrile powder was dispersed in an alkaline aqueous solution and reacted at 60-100℃ for 20-40 min. The reaction product was then precipitated, washed, neutralized, and dried to obtain carboxyl-modified polyacrylonitrile.

[0021] The method for preparing the modified PAN and quercetin-doped sulfonated polyarylether ketone proton exchange membrane includes a step in which the sulfonated polyarylether ketone, carboxyl-modified polyacrylonitrile, and quercetin are dissolved in an organic solvent, wherein the mass ratio of the sulfonated polyarylether ketone, carboxyl-modified polyacrylonitrile, and quercetin is 10:(0.3-0.7):(0.3-0.7).

[0022] The method for preparing the modified PAN and quercetin-doped sulfonated polyarylether ketone proton exchange membrane includes a step of dissolving the sulfonated polyarylether ketone, carboxyl-modified polyacrylonitrile, and quercetin in an organic solvent, wherein the organic solvent is one or more of dimethyl sulfoxide, N-methylpyrrolidone, dimethylformamide, and dimethylacetamide.

[0023] The method for preparing the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane includes the following steps: Preparing the membrane from the casting solution includes the following steps:

[0024] The casting solution was poured onto a clean substrate and coated into a uniform liquid film using a scraping method. The film was then dried in a constant temperature environment of 40-80℃ for 12-48 hours to obtain a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane.

[0025] A modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane is provided, wherein the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane is prepared by the method described in this invention.

[0026] An application of a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane, wherein the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane of the present invention is used to prepare an all-vanadium redox flow battery.

[0027] Beneficial Effects: This invention successfully prepared a proton exchange membrane with excellent comprehensive performance by combining a monomer copolymerization method to synthesize a regular sulfonated polyaryletherketone matrix with modified PAN / quercetin synergistic doping. The main technical effects are as follows: The acid-base crosslinking network formed by the cyano groups of modified PAN and the sulfonic acid groups of SPAEK effectively inhibits excessive swelling of highly sulfonated SPAEK. Simultaneously, the carboxyl groups of modified PAN and the phenolic hydroxyl groups of quercetin construct multiple proton conduction channels, maintaining high proton conductivity. Quercetin, as a highly efficient free radical scavenger, acts as a sacrificial agent in the membrane, preferentially capturing active free radicals attacking the membrane, significantly extending the membrane's lifespan in strong oxidizing environments. The physical crosslinking network formed by modified PAN also restricts chain segment movement caused by free radical attacks. The synergistic effect of both methods results in a superior antioxidant effect compared to single modification. The monomer copolymerization method ensures precise controllability and batch stability of the SPAEK polymer structure, laying the foundation for large-scale production. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the preparation method of a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane according to the present invention. Detailed Implementation

[0029] This invention provides a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane, its preparation method, and its applications. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the following examples provide further detailed description. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of protection of this invention.

[0030] Please see Figure 1 , Figure 1 The flowchart of a method for preparing a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane provided by the present invention is shown in the figure, and includes the following steps:

[0031] S1. Sulfonated difluorobenzophenone monomer, bisphenol monomer and dihalogen monomer are subjected to nucleophilic substitution polymerization in the presence of catalyst and solvent to generate sulfonated polyarylether ketone.

[0032] S2. Carboxyl modification treatment is performed on polyacrylonitrile to obtain carboxyl-modified polyacrylonitrile;

[0033] S3. Dissolve the sulfonated polyarylether ketone, carboxyl-modified polyacrylonitrile, and quercetin in an organic solvent to form a casting solution;

[0034] S4. The casting solution is used to prepare a membrane, thereby obtaining a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane.

[0035] Specifically, this invention utilizes a nucleophilic substitution polymerization reaction of sulfonated difluorobenzophenone monomer, bisphenol monomer, and dihalogen monomer to prepare sulfonated polyarylether ketone. The reaction mechanism is as follows: In the presence of alkali metal carbonates (such as K2CO3), the phenolic hydroxyl group of the bisphenol monomer (such as bisphenol A) is activated to form a phenoxy anion (nucleophile), which attacks the carbonyl-activated fluorine substituent (electrophilic center) on the dihalogen monomer (such as 4,4'-difluorobenzophenone), forming ether bonds through a stepwise polycondensation reaction, thereby constructing the polymer backbone. This invention innovatively introduces a sulfonated difluorobenzophenone monomer (such as 4,4'-difluorobenzophenone-3,3'-disulfonic acid dipotassium salt) to participate in the polymerization reaction. This monomer has a sulfonic acid group (protected in the form of a potassium salt) pre-introduced on the benzene ring of difluorobenzophenone, which remains stable under the polymerization reaction conditions and can directly participate in the polycondensation reaction to enter the polymer backbone. The chemical reaction process is as follows:

[0036] Traditional post-sulfonation methods for preparing sulfonated polyarylether ketones (PEEKs) involve immersing the finished PEEK in concentrated sulfuric acid or chlorosulfonic acid for sulfonation. Sulfonation is an electrophilic substitution reaction, where sulfonic acid groups tend to attack sites with higher electron density, making site selectivity difficult to achieve. The sulfonation reaction often occurs randomly on multiple benzene rings, and the harsh reaction conditions easily lead to polymer backbone breakage. The core difference between this invention and traditional post-sulfonation methods lies in the monomer copolymerization method employed. In this invention, the sulfonic acid groups are already positioned on specific benzene rings (3,3'-positions) during the monomer stage. After polymerization, the position and number of sulfonic acid groups on the main chain are entirely determined by the proportion of the fed monomers, achieving precise control of the sulfonation sites and ensuring the regularity of the polymer structure and the stability of its properties.

[0037] The sulfonated polyarylether ketones prepared by the monomer polymerization method of this invention have the following characteristics in their molecular structure: precise and controllable structure: the position and density of sulfonic acid groups are completely determined by the fed monomers, enabling precise design at the molecular level; high molecular weight and high regularity: the polymerization reaction is mild and controllable, avoiding main chain degradation and obtaining high molecular weight polymers with regular structures, which is beneficial for forming membrane materials with excellent mechanical properties; good batch consistency: by precisely controlling the feed ratio and reaction conditions, the structural consistency of polymers in different batches can be guaranteed, meeting the requirements of material stability for industrial applications.

[0038] This invention introduces carboxyl-modified polyacrylonitrile (modified PAN) as a blending component of a proton exchange membrane. PAN itself possesses good mechanical strength and chemical stability. The cyano groups on its molecular chain are strong polar groups with Lewis basicity, which can form acid-base pairs with the sulfonic acid groups (Lewis acids) of SPAEK. This non-covalent interaction can form physical cross-linking points in the blended membrane, effectively inhibiting swelling. While blending pure PAN with SPAEK can inhibit swelling through cyano-sulfonic acid group interactions, PAN itself does not contain ion-conducting groups. Excessive addition will dilute the proton-conducting sites in the membrane, leading to a decrease in conductivity.

[0039] This invention introduces carboxyl groups into PAN through partial hydrolysis to obtain carboxyl-modified polyacrylonitrile. On the one hand, the carboxyl group itself is a weakly acidic proton-conducting group, which can participate in the construction of proton transport channels to compensate for the conductivity loss caused by the introduction of PAN. On the other hand, the carboxyl group can serve as an interaction site for subsequent hydrogen bonding with quercetin, enhancing the structural compactness of the membrane. Therefore, the introduction of carboxyl-modified polyacrylonitrile (modified PAN) as a blending component of proton exchange membranes in this invention has the following effects: the cyano group forms an acid-base pair with the SPAEK sulfonic acid group, constructing a stable physical cross-linking network, effectively inhibiting excessive swelling of the membrane in the hydrated state; the hydrophilicity and weak acidity of the carboxyl group can construct additional proton jumping sites, improving the hydrophilicity and proton conductivity of the membrane; the carboxyl group can form hydrogen bonds with the phenolic hydroxyl groups of the subsequently added quercetin, further enhancing the microstructural compactness of the membrane.

[0040] Quercetin is a natural flavonoid compound widely found in vegetables and fruits. Its molecular structure contains multiple phenolic hydroxyl groups, and its chemical structural formula is as follows: The main failure mechanism of SPAEK membranes in a vanadium redox flow battery environment is backbone degradation caused by active free radical attack. This invention selects quercetin as the third component of the proton exchange membrane because quercetin, as a highly efficient free radical scavenger, can preferentially capture and neutralize active free radicals such as ·OH in the electrolyte, thereby protecting the SPAEK backbone from attack. This sacrificial agent protection mechanism is an effective strategy to improve membrane chemical stability. Furthermore, in addition to its antioxidant function, the multiple phenolic hydroxyl groups of quercetin can form a dense hydrogen bond network with the sulfonic acid groups of SPAEK, and the carboxyl and cyano groups of modified PAN. This hydrogen bond network can play the following roles: 1) further enhancing the compactness of the membrane's microstructure, physically restricting polymer chain movement, and synergistically inhibiting swelling; 2) the phenolic hydroxyl groups themselves have a certain degree of hydrophilicity and proton conductivity, and can participate in the proton transfer process; 3) the hydrogen bond network helps improve the compatibility between the three components, avoids phase separation, and forms a uniform and dense membrane structure.

[0041] In summary, to alleviate the antagonistic relationship between proton conductivity, dimensional swelling, and chemical stability in SPAEK membrane materials, this invention introduces carboxyl-modified polyacrylonitrile (PAN) as a blending component and combines it with quercetin for synergistic functionalization modification. Specifically, the cyano groups in the carboxyl-modified PAN molecular structure can form acid-base interactions with the sulfonic acid groups of SPAEK, constructing a stable physical cross-linking network that significantly inhibits excessive swelling of the membrane in the hydrated state. Simultaneously, the carboxyl groups help improve the proton transport capacity within the membrane, thus achieving a good balance between proton conductivity and anti-swelling performance. Furthermore, quercetin, rich in polyphenolic hydroxyl groups, can form extensive hydrogen-bonded cross-linking structures with SPAEK and carboxylic acid-modified PAN, further enhancing the structural stability of the membrane; at the same time, it can inhibit the oxidative degradation of the polymer backbone, significantly improving the durability of the membrane material under long-term operating conditions.

[0042] In some embodiments, sulfonated difluorobenzophenone monomer, bisphenol monomer, and dihalogen monomer are subjected to a nucleophilic substitution polymerization reaction in the presence of a catalyst and a solvent to generate sulfonated polyarylether ketone, including the following steps:

[0043] S11. Add aprotic polar solvent to the reactor, start the stirring system, control the stirring speed to 200-250 rpm, and add bisphenol monomer, dihalogen monomer, sulfonated difluorobenzophenone monomer and catalyst in sequence. Finally, add aprotic nonpolar solvent to rinse the reactor wall to ensure complete material transfer.

[0044] Specifically, before adding the aprotic polar solvent to the reactor, the reactor needs to be heated to 100 °C and purged with nitrogen for 30 minutes to remove residual moisture. This is because the presence of water in the polymerization system consumes the catalyst (potassium carbonate / sodium carbonate reacts with water to form hydroxides), affecting the salt formation process of the bisphenol monomer and thus interfering with the normal progress of the polymerization reaction. Therefore, the reactor must be thoroughly dried before the reaction to remove residual moisture.

[0045] In this step, an aprotic polar solvent (such as sulfolane) is added to provide a medium for the polymerization reaction. The stirring speed is controlled at 200-250 rpm to ensure thorough mixing of the materials while avoiding the introduction of air bubbles or shear degradation due to excessive stirring. The bisphenol monomer, dihalogen monomer, sulfonated difluorobenzophenone monomer, and catalyst are added sequentially, and finally, an aprotic nonpolar solvent (such as toluene) is added. Toluene acts as a dehydrating agent, forming an azeotrope with the water generated in the polymerization reaction. Reflux carries the water out of the reaction system, promoting the forward polycondensation reaction. Rinsing the reactor walls with toluene ensures that all materials are completely transferred to the reaction solution, guaranteeing accurate material addition.

[0046] S12. Nitrogen gas is continuously introduced into the reactor during the heating process to maintain an inert atmosphere. When the temperature reaches 160-180℃, the reaction is held at this temperature for 1-3 hours. Then, the temperature is further increased to 190-210℃ and the reaction is held at this temperature for 160-200 hours.

[0047] In this step, nitrogen gas is continuously introduced to maintain an inert atmosphere and prevent the phenolic oxide anions from being oxidized at high temperatures. A segmented heating process is adopted: first, the temperature is maintained at 160-180℃ for 1-3 hours, at which point the reaction system initially polymerizes to form oligomers; then, the temperature is increased to 190-210℃ and the reaction continues for 160-200 hours. The high-temperature stage promotes chain growth and obtains high molecular weight polymers. This segmented heating strategy can avoid excessively vigorous reactions in the early stage of the reaction, which could lead to chain termination or side reactions.

[0048] S13. After the reaction is complete, the reaction solution is quickly poured into ice water to allow the polymer to precipitate and solidify. The resulting solid is then soaked in ice water, crushed by a crusher, washed with distilled water to remove residual impurities, and then dehydrated using a press. The wet material is then placed in an oven to dry, finally obtaining the target polymer product, sulfonated polyarylether ketone.

[0049] In this step, the reaction solution is poured into ice water to allow the polymer to precipitate and solidify, and the insolubility of SPAEK in water is utilized for separation. Immersion in ice water further removes residual solvents and salts. After pulverization, the polymer is washed multiple times with water to thoroughly remove impurities; pressing and dehydration improve drying efficiency, and finally, the target polymer, sulfonated polyarylether ketone, is obtained.

[0050] In some specific embodiments, the sulfonated difluorobenzophenone monomer is 4,4'-difluorobenzophenone-3,3'-disulfonic acid dipotassium salt; the bisphenol monomer is bisphenol A; the dihalogen monomer is 4,4'-difluorobenzophenone; the catalyst is an alkali metal carbonate; and the solvent includes aprotic polar solvents and aprotic nonpolar solvents, wherein the aprotic polar solvent is sulfolane and the aprotic nonpolar solvent is toluene.

[0051] In this invention, materials were selected specifically for the preparation of sulfonated polyarylether ketones. The sulfonated difluorobenzophenone monomer is 4,4'-difluorobenzophenone-3,3'-disulfonic acid dipotassium salt. This monomer introduces a sulfonic acid group at the 3,3' position, forming a dense sulfonated structure, which is beneficial for constructing efficient proton transport channels. The potassium salt form protects the sulfonic acid group from participating in side reactions during polymerization. Bisphenol A was chosen as the bisphenol monomer because it is inexpensive and widely available. Its isopropyl-C(CH3)2- structure imparts a certain degree of flexibility to the polymer backbone, which is beneficial for film formation and processing. Simultaneously, the benzene ring structure of bisphenol A provides rigidity and thermal stability. 4,4'-difluorobenzophenone was chosen as the dihalogen monomer because the 4,4'-site has high reactivity, the fluorine atom is a good leaving group suitable for nucleophilic substitution reactions, and the ketone group forms a conjugated structure with the ether bond, giving the polymer excellent thermal stability and mechanical properties. The catalyst is alkali metal carbonate. Salts, such as K2CO3 or Na2CO3, can activate phenolic hydroxyl groups to form phenoxy anions, which are commonly used catalysts for nucleophilic substitution polymerization. Sulfolane is chosen as an aprotic polar solvent because it has a high boiling point (285℃), good thermal and chemical stability, and can dissolve various monomers and polymers generated in the polymerization reaction, making it an ideal solvent for high-temperature polycondensation reactions. Toluene is chosen as an aprotic nonpolar solvent because it is immiscible with water and can form an azeotrope (azeotropic point about 84℃), effectively carrying away the water generated in the reaction from the system and promoting the forward polycondensation reaction. Toluene is chosen because of its high water removal efficiency and the fact that it does not undergo side reactions with the reactants.

[0052] In some embodiments, during the preparation of sulfonated polyaryletherketones, the molar ratio of bisphenol monomer to sulfonated difluorobenzophenone monomer and dihalogen monomer is 1:(0.4-0.5):(0.5-0.6), and the sum of the molar amounts of sulfonated difluorobenzophenone monomer and dihalogen monomer is 1:1 with the molar amount of bisphenol monomer. In this embodiment, by adjusting the molar percentage of sulfonated difluorobenzophenone monomer, the ion exchange capacity (IEC) of the polymer can be precisely controlled. The higher the percentage, the higher the density of sulfonic acid groups on the polymer chain, and theoretically the higher the proton conductivity. However, excessive sulfonation can also lead to excessive water absorption and swelling. The 0.4-0.5 range specified in this embodiment is a selected sulfonation range that achieves a good balance between proton conductivity and dimensional stability.

[0053] In some embodiments, polyacrylonitrile is subjected to carboxyl modification treatment to obtain carboxyl-modified polyacrylonitrile, including the steps of: dispersing polyacrylonitrile powder in an alkaline aqueous solution, reacting at 60-100℃ for 20-40 min, and obtaining carboxyl-modified polyacrylonitrile after precipitation, washing, neutralization and drying of the reaction product.

[0054] In this embodiment, the alkaline aqueous solution is usually KOH or NaOH aqueous solution to provide an alkaline hydrolysis environment. The reaction temperature is selected as 60-100℃ and the reaction time is 20-40min. The hydrolysis reaction of PAN is controlled by temperature and time. If the temperature is too low (<60℃) or the time is too short (<20min), the degree of hydrolysis is insufficient, the amount of carboxyl groups introduced is small, and the modification effect is not obvious. If the temperature is too high (>100℃) or the time is too long (>40min), it may lead to excessive hydrolysis, with a large number of cyano groups being converted into carboxyl groups or even further degradation, which weakens the structural strength of PAN itself and loses cyano crosslinking sites. The reaction product is precipitated, washed, neutralized, and dried. After the reaction is completed, the product is precipitated from the alkaline solution (it may need to be neutralized to pH 7 with acid), repeatedly washed with a large amount of deionized water to remove residual alkaline solution, and finally dried to obtain modified PAN. This embodiment achieves partial hydrolysis of PAN by precisely controlling the hydrolysis conditions, simultaneously retaining cyano groups (providing cross-linking sites) and introducing carboxyl groups (providing proton conduction and hydrogen bonding sites) on the molecular chain. This bifunctional modification is key to achieving subsequent synergistic effects. If the hydrolysis conditions are not properly controlled, excessive hydrolysis will lead to the complete conversion of cyano groups, resulting in the loss of the ability to form acid-base cross-links with SPAEK.

[0055] In some embodiments, in the step of dissolving the sulfonated polyarylether ketone, carboxyl-modified polyacrylonitrile, and quercetin in an organic solvent, the mass ratio of the sulfonated polyarylether ketone, carboxyl-modified polyacrylonitrile, and quercetin is 10:(0.3-0.7):(0.3-0.7).

[0056] In this embodiment, the sulfonated polyaryletherketone, carboxyl-modified polyacrylonitrile, and quercetin are limited to a mass ratio of 10:0.3-0.7:0.3-0.7. This maximizes the synergistic effect of the three components, ensuring high proton conductivity while controlling the area swelling ratio at a low level and significantly improving oxidative stability. This range is the preferred range obtained through systematic screening. If the modified PAN content is too low, there will be insufficient cyano-sulfonic acid crosslinking points, resulting in limited swelling inhibition. If the modified PAN content is too high, the nonionic polymer (PAN backbone) occupies too much volume fraction, which will dilute the proton conduction sites, leading to a significant decrease in proton conductivity. Within the range of 0.3-0.7, an effective crosslinking network can be formed, controlling the swelling ratio within the ideal range. If the quercetin content is too low, the antioxidant effect will be insufficient; if the quercetin content is too high, small molecule quercetin may aggregate or crystallize in the membrane, damaging the membrane's compactness, or even acting as an impurity to hinder proton conduction channels, leading to a decrease in conductivity; a quercetin content in the range of 0.3-0.7% can form an effective hydrogen bond network and free radical scavenging ability, significantly improving chemical stability.

[0057] In some embodiments, the step of dissolving the sulfonated polyarylether ketone, carboxyl-modified polyacrylonitrile, and quercetin in an organic solvent, wherein the organic solvent is one or more of dimethyl sulfoxide, N-methylpyrrolidone, dimethylformamide, and dimethylacetamide, but is not limited thereto. The dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), dimethylformamide (DMF), and dimethylacetamide (DMAc) selected in this embodiment are all aprotic polar solvents with the following common characteristics: good solubility for SPAEK, modified PAN, and quercetin, enabling uniform mixing at the molecular level; high boiling points (DMSO 189℃, NMP 202℃, DMF 153℃, DMAc 165℃), suitable for preparing casting solutions at appropriate temperatures and slowly evaporating to form a film at slightly higher temperatures, which is beneficial for forming a dense and uniform film structure; these solvents are miscible with water, facilitating the removal of residual solvent by washing with water after film formation.

[0058] In some embodiments, the casting solution is prepared into a membrane by the following steps: pouring the casting solution onto a clean substrate, coating it into a uniform liquid film using a scraping method, and then drying it in a constant temperature environment of 40-80°C for 12-48 hours to obtain a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane. In this embodiment, the casting solution is coated onto a clean substrate (such as a glass plate) using a scraping method (or solution casting method), the film thickness is controlled by adjusting the scraper height, and the membrane is dried in a constant temperature environment of 40-80°C for 12-48 hours to allow the solvent to evaporate slowly. Slow drying helps to form a dense and uniform membrane structure and avoids surface skinning, internal defects, or pinholes caused by rapid drying. The drying temperature and time need to be optimized according to the boiling point of the solvent and the film thickness to ensure that the solvent is completely removed without causing thermal degradation of the membrane.

[0059] In some embodiments, a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane is also provided, which is prepared by the method for preparing the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane described in this invention.

[0060] In some embodiments, an application of the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane is also provided, in which the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane of the present invention is used to prepare fuel cells.

[0061] The present invention will be further explained and illustrated below through specific embodiments:

[0062] The reagents used in the examples were sourced from the following sources: polyacrylonitrile (PAN), 4,4'-difluorobenzophenone, sulfolane, toluene, potassium carbonate, and quercetin were provided by Shanghai Maclean Biochemical Technology Co., Ltd.

[0063] Example 1: SPAEK-C / Modified PAN / Quercetin = 10 / 0.5 / 0.5

[0064] A method for preparing a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane, comprising:

[0065] Step 1: Preparation of sulfonated monomer 4,4'-difluorobenzophenone-3,3'-disulfonic acid dipotassium salt: Take a 1L three-necked flask, add 250mL of fuming sulfuric acid (containing 50% SO3), and slowly add 100g of 4,4'-difluorobenzophenone in batches under stirring, controlling the addition rate to avoid violent exothermic reactions; after the addition is complete, heat the reaction system to 120℃ and keep stirring at a constant speed of 300 rpm for 8 hours; after the reaction is completed, allow it to cool naturally to room temperature, and then slowly pour the reaction solution into an appropriate amount of ice water while stirring to prevent local overheating; after the mixture cools, add potassium chloride until no more precipitate forms, and a pale yellow solid precipitates; filter and collect the precipitate, and recrystallize it with a mixed solvent of deionized water and ethanol for purification. The obtained white crystals are dried in an oven at 80℃ for 24 hours to obtain the target product;

[0066] Step 2: Preparation of SPAEK-C resin by monomer copolymerization: Take a 2L glass reactor, heat to 80℃, and purge with nitrogen for 60 minutes to remove residual moisture; add sulfolane solvent (1200 mL), start the stirring system, and control the stirring speed at 220 rpm; add bisphenol A (1.0 mol), 4,4'-difluorobenzophenone (0.5 mol), 4,4'-difluorobenzophenone-3,3'-disulfonic acid dipotassium salt (0.5 mol), and potassium carbonate catalyst (2.45 mol) in sequence; finally, add toluene (200 mL). Rinse the reactor walls with mL of water to ensure complete material transfer; continuously purge with nitrogen to maintain an inert atmosphere; the heating process is divided into two stages: first, heat to 170℃ and hold for 2 hours; then continue heating to 200℃ and hold for 180 hours; after the reaction is complete, quickly pour the reaction solution into ice water to allow the polymer to precipitate and solidify; soak the resulting solid in ice water for 24 hours, crush it using a crusher, and wash it 10 times with distilled water to remove residual impurities. Remove most of the moisture using a press, and dry the wet material in an 80℃ oven for 120 hours to obtain the SPAEK-C polymer.

[0067] Step 3: Preparation of carboxyl-modified PAN: Add 10 g of polyacrylonitrile (PAN) powder to 200 mL of 3 mol / L potassium hydroxide (KOH) solution, with a solid-liquid ratio of 1:20 (g / mL), and stir the mixture at a constant temperature of 80℃ for 30 minutes. After the reaction, wash the product repeatedly with a large amount of deionized water until the washing liquid is neutral. Then filter the product and dry the resulting solid in a 60℃ oven for 24 hours to obtain carboxyl-modified PAN.

[0068] Step 4: Preparation of the proton exchange membrane: Take a 500 mL three-necked round-bottom flask, pour in 200 mL of dimethyl sulfoxide (DMSO), install a mechanical stirrer, and heat to 60℃ at 400 rpm; then, add SPAEK-C powder (40 g), carboxyl-modified PAN powder (2 g), and quercetin (2 g) in sequence, keep stirring, and react at a constant temperature for 48 hours until all components are fully dispersed and form a homogeneous and stable solution; pour the solution onto a clean glass plate, and coat it into a uniform liquid film using a coating method, controlling the wet film thickness to be 200 μm; transfer it to a 60℃ constant temperature oven to dry for 24 hours, and after the solvent has completely evaporated, peel off the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane, denoted as SPAEK-C / modified PAN / quercetin = 10 / 0.5 / 0.5.

[0069] Example 2: SPAEK-C / Modified PAN / Quercetin = 10 / 0.5 / 0.3

[0070] A method for preparing a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane differs from that in Example 1 in that the amount of quercetin added in step 4 is adjusted to 1.2 g (i.e., 10 / 0.5 / 0.3), while the rest of the operations remain the same. The resulting modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane is denoted as SPAEK-C / modified PAN / quercetin = 10 / 0.5 / 0.3.

[0071] Example 3: SPAEK-C / Modified PAN / Quercetin = 10 / 0.5 / 0.7

[0072] A method for preparing a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane differs from that in Example 1 in that the amount of quercetin added in step 4 is adjusted to 2.8 g (i.e., 10 / 0.5 / 0.7), while the rest of the operations remain the same. The resulting modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane is denoted as SPAEK-C / modified PAN / quercetin = 10 / 0.5 / 0.7.

[0073] Example 4: SPAEK-C / Modified PAN / Quercetin = 10 / 0.3 / 0.5

[0074] A method for preparing a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane differs from that in Example 1 in that the amount of carboxyl-modified PAN added in step 4 is adjusted to 1.2g, while the amount of quercetin added remains unchanged at 2g (i.e., 10 / 0.3 / 0.5). All other operations are the same. The resulting modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane is denoted as SPAEK-C / modified PAN / quercetin = 10 / 0.3 / 0.5.

[0075] Example 5: SPAEK-C / Modified PAN / Quercetin = 10 / 0.7 / 0.5

[0076] A method for preparing a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane differs from that in Example 1 in that the amount of carboxyl-modified PAN added in step 4 is adjusted to 2.8g, while the amount of quercetin added remains unchanged at 2g (i.e., 10 / 0.7 / 0.5). All other operations are the same. The resulting modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane is denoted as SPAEK-C / modified PAN / quercetin = 10 / 0.7 / 0.5.

[0077] Example 6: SPAEK-B / Modified PAN / Quercetin = 10 / 0.5 / 0.5

[0078] A method for preparing a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane differs from that in Example 1 in that: the molar ratio of the sulfonated monomers in step 2 is adjusted to: bisphenol A (1.0 mol), 4,4'-difluorobenzophenone (0.55 mol), and 4,4'-difluorobenzophenone-3,3'-disulfonic acid dipotassium salt (0.45 mol) to prepare SPAEK-B resin; step 4 is changed to using SPAEK-B resin (40 g) mixed with modified PAN (2 g) and quercetin (2 g) to form a membrane; the remaining operations are the same as in Example 1, and the resulting modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane is denoted as SPAEK-B / modified PAN / quercetin = 10 / 0.5 / 0.5.

[0079] Example 7: SPAEK-A / Modified PAN / Quercetin = 10 / 0.5 / 0.5

[0080] A method for preparing a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane differs from that in Example 1 in that: the molar ratio of the sulfonated monomers in step 2 is adjusted to: bisphenol A (1.0 mol), 4,4'-difluorobenzophenone (0.6 mol), and 4,4'-difluorobenzophenone-3,3'-disulfonic acid dipotassium salt (0.4 mol) to prepare SPAEK-A resin; step 4 is changed to using SPAEK-A resin (40 g) mixed with modified PAN (2 g) and quercetin (2 g) to form a membrane; the remaining operations are the same as in Example 1, and the resulting modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane is denoted as SPAEK-A / modified PAN / quercetin = 10 / 0.5 / 0.5.

[0081] Comparative Example 1: Proton exchange membrane containing only modified PAN (without quercetin)

[0082] A method for preparing a proton exchange membrane, the preparation steps of which differ from those in Example 1 are as follows: in step 4, quercetin is not added, but SPAEK-C (40g) and carboxyl-modified PAN (2g) are co-dissolved in DMSO to form a membrane, and the resulting proton exchange membrane is denoted as SPAEK-C / modified PAN = 10 / 0.5 / 0.

[0083] Comparative Example 2: Proton exchange membrane containing only quercetin (unmodified PAN)

[0084] A method for preparing a proton exchange membrane, the preparation steps of which differ from those in Example 1 are as follows: in step 4, no carboxyl-modified PAN is added, and only SPAEK-C (40g) and quercetin (2g) are co-dissolved in DMSO to form a membrane, and the resulting proton exchange membrane is denoted as SPAEK-C / quercetin = 10 / 0 / 0.5.

[0085] Comparative Example 3: Pure SPAEK-C membrane

[0086] A method for preparing a proton exchange membrane, the preparation steps of which differ from those in Example 1 are as follows: in step 4, modified PAN and quercetin are not added, but SPAEK-C (40 g) is dissolved in DMSO (200 mL), and the membrane is directly scraped and dried. The resulting proton exchange membrane is denoted as SPAEK-C.

[0087] Comparative Example 4: Pure SPAEK-B membrane

[0088] A method for preparing a proton exchange membrane, the preparation steps of which differ from those in Example 6 are as follows: in step 4, modified PAN and quercetin are not added, but SPAEK-B (40 g) is dissolved in DMSO (200 mL), and the membrane is directly scraped and dried. The resulting proton exchange membrane is denoted as SPAEK-B.

[0089] Comparative Example 5: Pure SPAEK-A Membrane

[0090] A method for preparing a proton exchange membrane, the preparation steps of which differ from those in Example 7 are as follows: in step 4, modified PAN and quercetin are not added, but SPAEK-A (40 g) is dissolved in DMSO (200 mL), and the membrane is directly scraped and dried. The resulting proton exchange membrane is denoted as SPAEK-A.

[0091] Comparative Example 6: Post-sulfonation SPAEK pure membrane

[0092] A method for preparing a proton exchange membrane, comprising:

[0093] Step 1: Preparation of Post-Sulfonated SPAEK: Bisphenol A type polyarylether ketone (PAEK, non-sulfonated) was used as the raw material. A 500 mL beaker was filled with 100 mL of chlorosulfonic acid, and a magnetic stir bar was added. The mixture was stirred at 100 rpm. Under continuous stirring, 15 g of bisphenol A type PAEK powder was slowly added in batches. The reaction system was then heated to 80°C and stirred for 5 hours. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The reaction product was slowly poured into ice water, and a solid precipitated. After filtration, the solid was washed several times with deionized water. The obtained solid was further immersed in a 1 mol / L potassium hydroxide solution at room temperature for 2 hours to remove residual acidic impurities. It was then filtered again and washed with deionized water until the filtrate was neutral. The final product was filtered and dried at 80°C for 12 hours to obtain post-sulfonated SPAEK resin.

[0094] Step 2, Preparation of pure membrane: Dissolve 40g of post-sulfonated SPAEK resin in 200mL of DMSO, form a membrane using the scraping method, and dry at 60℃ for 24 hours to obtain a post-sulfonated SPAEK pure membrane.

[0095] Comparative Example 7: Post-sulfonation SPAEK / modified PAN / quercetin = 10 / 0.5 / 0.5

[0096] A method for preparing a proton exchange membrane, the preparation steps of which differ from those of Example 1, is as follows: the SPAEK-C resin synthesized in step 2 is replaced with the post-sulfonated SPAEK resin prepared in Comparative Example 6, that is, post-sulfonated SPAEK (40 g) is blended with carboxyl-modified PAN (2 g) and quercetin (2 g) to form a membrane, and the resulting proton exchange membrane is denoted as post-sulfonated SPAEK / modified PAN / quercetin = 10 / 0.5 / 0.5.

[0097] The membrane samples prepared in Examples 1-7 and Comparative Examples 1-7 were subjected to the following performance tests:

[0098] 8.1 Proton conductivity test

[0099] Test Method: The proton transport performance of the membrane samples was characterized using Alternating Current Impedance Spectroscopy (EIS). Before testing, the membrane was cut to a standard size of 2cm × 2cm and immersed in a 3mol / L sulfuric acid solution for 24 hours to ensure thorough acidification. The membrane was then rinsed with deionized water for 3 minutes to remove residual acid. The sample was then placed in a platinum electrode holder and immersed in a constant-temperature deionized water environment at 30℃ for testing. The test frequency range was 1 Hz to 5 × 10⁻⁵ Hz. 6 Hz, AC disturbance voltage is set to 10mV.

[0100] 8.2 Swelling Rate Test

[0101] Test method: Performed according to national standard GB / T 20042.3-2022. Cut the membrane sample into 3cm × 3cm squares, vacuum dry at 80℃ to constant weight, and measure the dry area (A_dry). Then immerse the sample in deionized water at 30℃ for 24 hours, remove it, and quickly blot the surface moisture with filter paper to measure the wet area (A_wet). The area swelling ratio (SR) is calculated using the formula: SR = (A_wet - A_dry) / A_dry × 100%.

[0102] Significance of the test: The swelling ratio reflects the dimensional stability of the membrane material in the hydrated state; the lower the swelling ratio, the lower the risk of deformation and wrinkling of the membrane in actual use, and the more stable the interface contact with the electrode.

[0103] 8.3 Antioxidant stability test

[0104] Test method: A 3 cm × 3 cm proton exchange membrane sample was placed in an 80 ℃ constant temperature oven for 5 hours to remove moisture. After cooling to room temperature, the initial mass was weighed. The sample was then immersed in a solution containing 1.5 mol·L⁻¹ -1 VO 2+ and 3.0 mol·L -1 The membrane was immersed in a simulated sulfuric acid electrolyte at room temperature in the dark for 30 days. After removal, the membrane surface was thoroughly rinsed with deionized water to remove residual ions, and then dried in an oven at 80°C for 5 hours. After cooling, the final mass was measured. By comparing the mass changes of the samples before and after the experiment, the mass loss rate was calculated to evaluate the oxidative stability of the material.

[0105] The performance test results are shown in Table 1.

[0106] Table 1 Performance test results of composite membrane

[0107]

[0108] Analysis of the data in Table 1 reveals that the composite proton exchange membranes prepared in Examples 1-7 of this invention all exhibit excellent comprehensive performance. Taking Example 1 with the preferred ratio as an example, its proton conductivity reaches 77.5 mS / cm, which, although slightly lower than the 89.3 mS / cm of the pure SPAEK-C membrane (a decrease of approximately 13%), is still within the acceptable high-performance range. Its area swelling ratio drops significantly from 37.0% of the pure SPAEK-C membrane to 18.1% (a decrease of 51%), indicating a significant improvement in dimensional stability. Its mass loss rate after oxidation stability testing decreases from 6.8% to 4.4% (a decrease of 35%), demonstrating a significant enhancement in chemical stability. Examples 2-5 further illustrate the performance variation patterns under different ratios, all achieving an ideal performance balance within the mass ratio range defined by this invention. Examples 6-7 demonstrate that the doping modification strategy of this invention is applicable to SPAEK substrates with different degrees of sulfonation, allowing for the selection of SPAEK substrates with different base sulfonation degrees according to application requirements. Overall, the data from Examples 1-7 of this invention fully demonstrate that by synergistic doping of modified PAN and quercetin, the technical challenge of simultaneously achieving conductivity, swelling, and stability in SPAEK films has been successfully solved, and the three key properties have been optimized synchronously.

[0109] Comparing Comparative Example 1 and Comparative Example 3, it can be found that adding modified PAN alone caused the swelling rate to drop sharply from 37.0% to 16.7% (a decrease of 55%), proving that the acid-base cross-linking network formed by the cyano group and sulfonic acid group of modified PAN is the dominant factor in inhibiting swelling. At the same time, the mass loss rate dropped from 6.8% to 5.2% (a decrease of 24%), indicating that the physical cross-linking network also improved the chemical stability to a certain extent.

[0110] Comparing Comparative Example 2 and Comparative Example 3, it can be seen that adding quercetin alone reduced the mass loss rate from 6.8% to 6.0% (a decrease of 12%), proving that quercetin has free radical scavenging function and can improve chemical stability. However, the swelling rate only decreased from 37.0% to 33.0% (a decrease of 11%), indicating that quercetin has limited ability to inhibit swelling.

[0111] Comparing Example 1 with Comparative Example 1, it can be seen that adding quercetin to the same modified PAN further reduced the mass loss rate from 5.2% to 4.4% (an additional reduction of 15%), demonstrating that the antioxidant function of quercetin and the physical cross-linking network of modified PAN work synergistically to significantly enhance chemical stability. Comparing Example 1 with Comparative Example 2, it can be seen that adding modified PAN to the same modified PAN resulted in a significant reduction in swelling rate from 33.0% to 18.1% (an additional reduction of 45%), demonstrating that the cross-linking network of modified PAN and the hydrogen bond network of quercetin work synergistically to significantly enhance dimensional stability.

[0112] The data from the comparative examples 1 and 1-3 show that the combination of modified PAN and quercetin is not a simple functional superposition, but rather produces a significant synergistic effect. Modified PAN constructs a swelling-resistant physical cross-linked framework, while quercetin not only provides antioxidant function but also works with modified PAN to construct a hydrogen bond network to enhance structural density. The synergistic effect of the two comprehensively optimizes the performance of the membrane.

[0113] Comparing the data from Example 4 (PAN 0.3), Example 1 (PAN 0.5), and Example 5 (PAN 0.7), it can be seen that as the PAN content increases, the area swelling ratio continuously decreases (22.4% → 18.1% → 16.5%), proving that the higher the PAN content, the denser the cross-linked network, and the stronger the swelling inhibition effect. However, the proton conductivity also decreases accordingly (80.1 mS / cm → 77.5 mS / cm → 71.4 mS / cm), proving that excessive non-ionic PAN dilutes the proton conduction sites, and 0.5 is the equilibrium point, balancing swelling inhibition and conductivity maintenance. Comparing the data from Example 2 (quercetin 0.3), Example 1 (quercetin 0.5), and Example 3 (quercetin 0.7), it can be seen that as the quercetin content increases, the mass loss rate continuously decreases (4.8% → 4.4% → 4.2%), proving that the higher the quercetin content, the stronger the free radical scavenging ability and the better the antioxidant effect. However, the proton conductivity also decreased (78.7 mS / cm → 77.5 mS / cm → 75.9 mS / cm), proving that excessive quercetin may cause aggregation or dilution effects. 0.5 is the equilibrium point, which balances antioxidant properties and conductivity maintenance.

[0114] Comparing the data from Examples 3-5 reveals that a higher degree of sulfonation (SPAEK-C>B>A) results in higher proton conductivity, but also higher swelling rate and mass loss rate, exhibiting a typical contradiction between conductivity, swelling, and stability. After modification according to this invention, the performance of all composite membranes is significantly improved. As shown in Examples 1, 6, and 7, the swelling rate of the SPAEK-C composite membrane (Example 1) decreased from 37.0% to 18.1%, and the mass loss rate decreased from 6.8% to 4.4%; the swelling rate of the SPAEK-B composite membrane (Example 6) decreased from 28.0% to 17.1%, and the mass loss rate decreased from 6.1% to 4.3%; the swelling rate of the SPAEK-A composite membrane (Example 7) decreased from 19.0% to 16.2%, and the mass loss decreased from 5.7% to 4.2%; and the swelling rate of the SPAEK-B composite membrane (Example 6) decreased from 28.0% to 17.1%, and the mass loss decreased from 6.1% to 4.3%. This demonstrates that the modification strategy of the present invention is effective for SPAEK matrices with a wide range of sulfonation degrees, and SPAEKs with different base sulfonation degrees can be selected according to application requirements to further optimize performance through modification.

[0115] Comparing the data from Comparative Examples 3 and 6 reveals that, in the pure membrane state, the swelling ratio of the post-sulfonated SPEEK is as high as 48.0%, far exceeding the 37.0% of the monomer copolymerized SPEEK-C, and the mass loss rate is also higher (7.0% vs 6.8%). This demonstrates that the post-sulfonation method suffers from defects such as uneven sulfonation reaction and main chain degradation, resulting in poor membrane structure regularity and performance degradation. Further comparison of the data from Comparative Example 7 and Example 1 shows that even using the same doping modification formula (10 / 0.5 / 0.5), the swelling ratio of the post-sulfonated SPEEK composite membrane (38.5%) is still far higher than that of the SPEEK-C composite membrane (18.1%), and the mass loss rate is also higher (6.2% vs 4.4%). This fully demonstrates that the monomer copolymerization method used in this invention to synthesize a regular SPEEK matrix is ​​the foundation and prerequisite for achieving subsequent efficient modification. If the matrix itself has structural defects, even using the same doping modification strategy, the excellent performance of Example 1 of this invention cannot be obtained.

[0116] In summary, this invention is the first to combine the synthesis of a regular sulfonated polyaryletherketone matrix via monomer copolymerization with synergistic doping of modified PAN / quercetin, systematically resolving the performance contradictions of SPAEK membranes from both matrix synthesis and functional modification perspectives. Specifically, modified PAN provides a crosslinking network to inhibit swelling, while quercetin provides antioxidant function to enhance stability; the two also enhance structural compactness through hydrogen bonding interactions. The composite membrane prepared by this invention, while maintaining high proton conductivity, reduces the swelling ratio of the SPAEK-C membrane from 37.0% to 18.1% (a reduction of 51%) and the mass loss rate from 6.8% to 4.4% (a reduction of 35%), demonstrating a significant performance improvement compared to the comparative example. This invention, through the synergistic effect of modified PAN and quercetin, improves chemical stability without significantly sacrificing proton conductivity and significantly improves dimensional stability, successfully overcoming the technical bias of the difficulty in simultaneously achieving conductivity, swelling, and stability.

[0117] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane, characterized in that, Including the following steps: Sulfonated difluorobenzophenone monomer, bisphenol monomer and dihalogen monomer are subjected to nucleophilic substitution polymerization in the presence of catalyst and solvent to generate sulfonated polyarylether ketone; Carboxyl modification of polyacrylonitrile yields carboxyl-modified polyacrylonitrile. The sulfonated polyarylether ketone, carboxyl-modified polyacrylonitrile, and quercetin are dissolved in an organic solvent to form a casting solution. The casting solution is used to prepare a membrane, thereby obtaining a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane.

2. The method for preparing the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane according to claim 1, characterized in that, The sulfonated difluorobenzophenone monomer, bisphenol monomer, and dihalogen monomer are subjected to a nucleophilic substitution polymerization reaction in the presence of a catalyst and solvent to generate sulfonated polyarylether ketone, including the following steps: Add an aprotic polar solvent to the reactor, start the stirring system, control the stirring speed at 200-250 rpm, and add bisphenol monomer, dihalogen monomer, sulfonated difluorobenzophenone monomer and catalyst in sequence. Finally, add an aprotic nonpolar solvent to rinse the reactor wall to ensure complete material transfer. Nitrogen gas is continuously introduced into the reactor during the heating process to maintain an inert atmosphere. When the temperature reaches 160-180℃, the reaction is held at this temperature for 1-3 hours. Then, the temperature is further increased to 190-210℃ and the reaction is held at this temperature for 160-200 hours. After the reaction is complete, the reaction solution is quickly poured into ice water to precipitate and solidify the polymer. The resulting solid is then soaked in ice water, crushed by a crusher, washed with distilled water to remove residual impurities, and then dehydrated using a press. The wet material is then placed in an oven to dry, finally obtaining the target polymer product, sulfonated polyarylether ketone.

3. The method for preparing the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane according to claim 1 or 2, characterized in that, In the step of preparing sulfonated polyaryletherketone, the sulfonated difluorobenzophenone monomer is 4,4'-difluorobenzophenone-3,3'-disulfonic acid dipotassium salt; the bisphenol monomer is bisphenol A; the dihalogen monomer is 4,4'-difluorobenzophenone; the catalyst is an alkali metal carbonate; and the solvent includes aprotic polar solvents and aprotic nonpolar solvents, wherein the aprotic polar solvent is sulfolane and the aprotic nonpolar solvent is toluene.

4. The method for preparing the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane according to claim 1 or 2, characterized in that, In the step of preparing sulfonated polyarylether ketone, the molar ratio of bisphenol monomer to sulfonated difluorobenzophenone monomer and dihalogen monomer is 1:(0.4-0.5):(0.5-0.6), and the molar ratio of the sum of the molar amounts of sulfonated difluorobenzophenone monomer and dihalogen monomer to the molar amount of bisphenol monomer is 1:

1.

5. The method for preparing the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane according to claim 1, characterized in that, Carboxyl modification of polyacrylonitrile to obtain carboxyl-modified polyacrylonitrile includes the following steps: Polyacrylonitrile powder was dispersed in an alkaline aqueous solution and reacted at 60-100℃ for 20-40 min. The reaction product was then precipitated, washed, neutralized, and dried to obtain carboxyl-modified polyacrylonitrile.

6. The method for preparing the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane according to claim 1, characterized in that, In the step of dissolving the sulfonated polyarylether ketone, carboxyl-modified polyacrylonitrile, and quercetin in an organic solvent, the mass ratio of the sulfonated polyarylether ketone, carboxyl-modified polyacrylonitrile, and quercetin is 10:(0.3-0.7):(0.3-0.7).

7. The method for preparing the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane according to claim 1, characterized in that, In the step of dissolving the sulfonated polyarylether ketone, carboxyl-modified polyacrylonitrile, and quercetin in an organic solvent, the organic solvent is one or more of dimethyl sulfoxide, N-methylpyrrolidone, dimethylformamide, and dimethylacetamide.

8. The method for preparing the modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane according to claim 1, characterized in that, The process of preparing a film from the casting solution includes the following steps: The casting solution was poured onto a clean substrate and coated into a uniform liquid film using a scraping method. The film was then dried in a constant temperature environment of 40-80℃ for 12-48 hours to obtain a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane.

9. A modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane, characterized in that, The proton exchange membrane was prepared using the method described in any one of claims 1-8, which involves modifying PAN and quercetin-doped sulfonated polyaryletherketone.

10. An application of a modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane, characterized in that, The modified PAN and quercetin-doped sulfonated polyaryletherketone proton exchange membrane described in claim 9 are used to prepare an all-vanadium redox flow battery.

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