SPBI and antioxidant doped SPEEK proton exchange membrane, and preparation method and application thereof

Abstract

The application relates to the technical field of proton exchange membrane preparation, and discloses a SPBI and antioxidant-doped SPEEK proton exchange membrane as well as a preparation method and application thereof, which comprises the following steps: a phenolic monomer containing a sulfonic acid group, a bisphenol monomer and a dihalide monomer are mixed and subjected to nucleophilic substitution polymerization in the presence of a catalyst and a solvent to generate sulfonated polyether ether ketone through a monomer polymerization method; meanwhile, sulfonation treatment is conducted on polybenzimidazole to obtain sulfonated polybenzimidazole; the sulfonated polyether ether ketone, the sulfonated polybenzimidazole and an antioxidant 1330 are dissolved in an organic solvent to prepare a composite proton exchange membrane through a solution casting method. The application solves the problems of difficult control of sulfonation degree and poor batch stability of a traditional post-sulfonation process from the source; an acid-base crosslinking network is constructed through the introduction of SPBI, so that the membrane swelling is effectively inhibited; free radicals are captured through the antioxidant 1330, so that the antioxidant stability of the membrane is significantly improved, and the obtained composite membrane has wide application prospects in the field of fuel cells.

Description

Technical Field

[0001] This invention relates to the field of proton exchange membrane preparation technology, and particularly to a SPBI and antioxidant-doped SPEEK proton exchange membrane, its preparation method and application. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs), as a highly efficient and clean energy conversion device, are one of the core technologies of the future hydrogen society. The proton exchange membrane (PEM), as the core component of a PEMFC, directly determines the power density, efficiency, and lifespan of the fuel cell. Currently, commercially available perfluorosulfonic acid membranes (Nafion membranes) dominate due to their excellent chemical stability and proton conductivity. However, perfluorosulfonic acid membranes have inherent drawbacks such as high cost, complex synthesis processes, significant conductivity degradation under high temperature and low humidity conditions, and environmental unfriendliness, which severely restrict the large-scale commercial application of fuel cells.

[0003] In search of alternatives to Nafion membranes, researchers have turned their attention to sulfonated aromatic polymers, among which sulfonated polyether ether ketone (SPEEK) has attracted considerable attention due to its low raw material cost, relatively simple synthesis process, and good thermal stability and mechanical properties. SPEEK is typically produced from polyether ether ketone (PEEK) through a post-sulfonation reaction; however, existing post-sulfonation processes suffer from the following insurmountable technical problems:

[0004] Sulfonation degree is difficult to control precisely: Post-sulfonation reaction is a heterogeneous reaction or a homogeneous but difficult-to-control reaction. Sulfonic acid groups are prone to random distribution on polymer chains and are prone to over-sulfonation or uneven local sulfonation, resulting in large differences in sulfonation degree and molecular weight distribution between different batches of products, which seriously affects the consistency and reliability of membrane materials.

[0005] The "trade-off" effect between proton conductivity and swelling resistance: Increasing the degree of sulfonation can increase the number of proton conduction sites, thereby improving proton conductivity; however, excessively high sulfonation will significantly enhance the hydrophilicity of the polymer, leading to excessive swelling of the membrane in the hydrated state, resulting in poor dimensional stability and a sharp decrease in mechanical strength. This illustrates the contradiction that higher conductivity leads to more severe swelling.

[0006] Poor antioxidant stability: The aromatic backbone of SPEEK, especially the sites where ether bonds and sulfonic acid groups are connected, is prone to chain breakage and degradation under the attack of hydroxyl radicals and peroxy radicals generated during fuel cell operation (especially during start-up and shutdown or local hydrogen deficiency), leading to chemical degradation and performance degradation of the membrane and shortened lifespan.

[0007] Therefore, how to precisely control the structure of SPEEK, break the constraint between proton conductivity and size stability, and improve its antioxidant stability are key technical problems that need to be solved by those skilled in the art. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the purpose of this invention is to provide a SPBI and antioxidant-doped SPEEK proton exchange membrane, its preparation method and application, aiming to solve the problems of uncontrollable degree of sulfonation and uneven distribution of sulfonic acid groups in SPEEK proton exchange membranes prepared by the traditional post-sulfonation method, as well as the resulting technical problems of difficulty in balancing proton conductivity and dimensional stability and poor antioxidant stability.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for preparing an SPBI and antioxidant-doped SPEEK proton exchange membrane includes the following steps: mixing a sulfonic acid-containing phenolic monomer, a bisphenol monomer, and a dihalogen monomer in the presence of a catalyst and a solvent, and generating sulfonated polyether ether ketone through a nucleophilic substitution polymerization reaction; sulfonating polybenzimidazole to obtain sulfonated polybenzimidazole; dissolving the sulfonated polyether ether ketone, sulfonated polybenzimidazole, and antioxidant 1330 in an organic solvent to form a casting solution; and preparing the casting solution into a membrane to obtain the SPBI and antioxidant-doped SPEEK proton exchange membrane.

[0011] The method for preparing SPBI and antioxidant-doped SPEEK proton exchange membranes includes the following steps: sulfonate-containing phenolic monomers, bisphenol monomers, and dihalogen monomers are subjected to nucleophilic substitution polymerization in the presence of a catalyst and solvent to generate sulfonated polyether ether ketones. The steps include: adding an aprotic polar solvent to a reaction vessel; starting the stirring system and controlling the stirring rate at 100-150 rpm; sequentially adding bisphenol monomers, sulfonate-containing phenolic monomers, dihalogen monomers, and the catalyst; and finally adding an aprotic nonpolar solvent to rinse the vessel wall; the reaction vessel is then heated... Nitrogen gas is continuously introduced during the process to maintain an inert atmosphere. When the temperature rises to 150-170℃, the reaction is maintained for 1-3 hours. Then, the temperature is further increased to 180-190℃ and the reaction is maintained for 140-160 hours. After the reaction is completed, the reaction solution is quickly poured into ice water to allow the polymer to precipitate and solidify. The resulting solid is soaked in ice water, then crushed by a crusher, washed with distilled water to remove residual impurities, and then the moisture is removed by a press to obtain a wet material. The wet material is then placed in an oven to dry, and finally the target polymer product, sulfonated polyether ether ketone, is obtained.

[0012] The method for preparing SPBI and antioxidant-doped SPEEK proton exchange membranes includes the following step: in the preparation of sulfonated polyether ether ketone, the phenolic monomer containing sulfonic acid groups is potassium 2,5-dihydroxybenzenesulfonate or sodium 2,5-dihydroxybenzenesulfonate; 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 dimethyl sulfoxide and the aprotic nonpolar solvent is xylene.

[0013] The method for preparing SPBI and antioxidant-doped SPEEK proton exchange membranes includes a step in which the degree of sulfonation of the sulfonated polyether ether ketone is controlled by adjusting the molar ratio of phenolic monomers containing sulfonic acid groups to bisphenol monomers; the degree of sulfonation of the sulfonated polyether ether ketone is 60%-80%.

[0014] The method for preparing the SPBI and antioxidant-doped SPEEK proton exchange membrane includes the following steps: sulfonation treatment of polybenzimidazole to obtain sulfonated polybenzimidazole.

[0015] Polybenzimidazole powder was dispersed in concentrated sulfuric acid and reacted at 60-100℃ for 3-6 hours. The reaction product was then precipitated, washed, neutralized and dried to obtain sulfonated polybenzimidazole.

[0016] The method for preparing the SPBI and antioxidant-doped SPEEK proton exchange membrane includes a step in which the sulfonated polyether ether ketone, sulfonated polybenzimidazole, and antioxidant 1330 are dissolved in an organic solvent, wherein the mass ratio of the sulfonated polyether ether ketone, sulfonated polybenzimidazole, and antioxidant 1330 is 1:(0.05-0.15):(0.01-0.05).

[0017] The method for preparing the SPBI and antioxidant-doped SPEEK proton exchange membrane includes a step of dissolving the sulfonated polyether ether ketone, sulfonated polybenzimidazole, and antioxidant 1330 in an organic solvent, wherein the organic solvent is one or more of N-methylpyrrolidone, dimethylformamide, and dimethylacetamide.

[0018] The method for preparing the SPBI and antioxidant-doped SPEEK proton exchange membrane includes the following steps: Preparing the casting solution into a membrane.

[0019] The casting solution is uniformly coated on the surface of a glass plate and dried in an oven at 40-80℃ for 24-36 hours to obtain SPBI and antioxidant-doped SPEEK proton exchange membranes.

[0020] A SPBI and antioxidant-doped SPEEK proton exchange membrane is provided, wherein it is prepared by the method for preparing SPBI and antioxidant-doped SPEEK proton exchange membranes described in this invention.

[0021] An application of SPBI and antioxidant-doped SPEEK proton exchange membrane, wherein the SPBI and antioxidant-doped SPEEK proton exchange membrane described in this invention are used to prepare a fuel cell.

[0022] Beneficial Effects: The preparation method and application of SPBI and antioxidant 1330-doped SPEEK proton exchange membrane provided by this invention have the following beneficial effects compared with the prior art:

[0023] 1) Achieving precise and controllable SPEEK structure from the source: This invention uses monomer polymerization to prepare SPEEK. Through the copolymerization reaction of phenolic monomers containing sulfonic acid groups and bisphenol monomers, the degree of sulfonation is precisely adjustable and the sulfonic acid groups are evenly distributed. Compared with the traditional post-sulfonation method, this method avoids the problems of main chain breakage and uneven distribution of sulfonic acid groups during the sulfonation process. The resulting SPEEK molecular chains are complete, with high molecular weight and narrow distribution, laying an ideal material foundation for subsequent modification. This innovative method fundamentally solves the common industry problems of uncontrollable post-sulfonation process and large batch-to-batch product differences.

[0024] 2) Constructing a uniform and dense acid-base crosslinking network: This invention introduces sulfonated polybenzimidazole (SPBI) as a blending component. It utilizes the strong ionic crosslinking and hydrogen bond interaction between the imidazole ring (basic) in its molecular structure and the sulfonic acid group (acidic) of SPEEK. Since the sulfonic acid group of SPEEK is uniformly distributed in this invention, SPBI can find crosslinking sites at nearly equal intervals on the molecular scale, forming a uniform and dense three-dimensional physical crosslinking network. This network effectively binds the SPEEK molecular chain and significantly inhibits the excessive swelling of the membrane in the hydrated state.

[0025] 3) Achieving efficient free radical capture and antioxidant protection: This invention introduces antioxidant 1330 as a third component. The multiple hindered phenolic hydroxyl groups in its molecular structure can efficiently capture hydroxyl radicals and peroxy radicals generated during fuel cell operation, terminate the oxidation chain reaction, and work synergistically with the SPEEK main chain and SPBI crosslinking network. Antioxidant 1330 comprehensively improves the durability of the membrane from a chemical perspective.

[0026] 4) Achieving Synergistic Effects of Multiple Components: This invention, for the first time, combines monomer polymerization SPEEK, SPBI, and antioxidant 1330 to construct a multifunctional synergistic system with a controllable matrix, acid-base crosslinking network, and free radical capture. Data comparison shows that the performance of this ternary system far exceeds the simple summation of single or binary modifications: SPBI solves the swelling problem, antioxidant 1330 solves the oxidation problem, and the uniformly distributed sulfonic acid groups ensure high conductivity. The three components work synergistically in the optimal ratio (approximately 10:1:0.3), achieving significant technical effects.

[0027] The SPEEK composite proton exchange membrane prepared by this invention possesses high proton conductivity, low swelling ratio, and excellent oxidation stability, with overall performance far exceeding that of existing SPEEK membrane materials. Its preparation process is simple and controllable, raw materials are widely available, and costs are relatively low, making it suitable for large-scale production. This membrane material can be widely used in proton exchange membrane fuel cells, direct methanol fuel cells, vanadium redox flow batteries, and water electrolysis for hydrogen production, demonstrating significant industrial value. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the preparation method of SPBI and antioxidant-doped SPEEK proton exchange membranes according to the present invention. Detailed Implementation

[0029] This invention provides SPBI and antioxidant-doped SPEEK proton exchange membranes, their preparation methods, and applications. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the following examples provide further detailed description of the invention. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the scope of protection of the invention.

[0030] Please see Figure 1 , Figure 1 A flowchart of a method for preparing SPBI and antioxidant-doped SPEEK proton exchange membranes provided by this invention is shown in the figure, which includes the following steps:

[0031] S1. Phenolic monomers containing sulfonic acid groups, bisphenol monomers and dihalogen monomers are mixed in the presence of a catalyst and a solvent, and sulfonated polyether ether ketones are generated through nucleophilic substitution polymerization.

[0032] S2. Sulfonate polybenzimidazole to obtain sulfonated polybenzimidazole;

[0033] S3. Dissolve the sulfonated polyether ether ketone, sulfonated polybenzimidazole and antioxidant 1330 in an organic solvent to form a casting solution;

[0034] S4. The casting solution is used to prepare a membrane, that is, an SPBI and antioxidant-doped SPEEK proton exchange membrane is obtained.

[0035] Specifically, this invention employs a nucleophilic substitution stepwise polymerization reaction to synthesize SPEEK. The chemical essence of this reaction is as follows: under the action of an alkaline catalyst, a nucleophile (phenolic monomers containing sulfonic acid groups and bisphenol monomers) undergoes a nucleophilic substitution reaction with an electrophile (dihalogen monomer), forming an ether bond to become the polymer backbone. Taking bisphenol monomer as an example, firstly, the bisphenol monomer forms a bisphenol salt anion under the action of a catalyst (alkali metal carbonate), enhancing its nucleophilicity; subsequently, the bisphenol salt anion attacks the partially positively charged carbon atom on the dihalogen monomer (the carbon atom bonded to the fluorine atom), undergoing a nucleophilic substitution reaction. The fluorine atom leaves in the form of potassium fluoride, forming an ether bond.

[0036] The core difference between this invention and the traditional post-sulfonation method lies in the fact that the sulfonic acid groups are covalently bonded to the monomers before the polymerization reaction begins. Specifically, this invention uses phenolic monomers containing sulfonic acid groups and bisphenol monomers without sulfonic acid groups to copolymerize with dihalogen monomers. In this system, the positions of the sulfonic acid groups are fixed and do not migrate or disappear during polymerization; the polymerization reaction simply connects the various monomers sequentially. Therefore, by precisely controlling the molar ratio of phenolic monomers containing sulfonic acid groups to bisphenol monomers, this invention can precisely control the content of sulfonic acid groups in the final polymer.

[0037] The sulfonated polyether ether ketone prepared by the monomer polymerization method of this invention has the following molecular structure characteristics: uniform distribution of sulfonic acid groups: due to the random copolymerization of phenolic monomers and bisphenol monomers containing sulfonic acid groups in the polymerization reaction, the sulfonic acid groups are uniformly distributed along the molecular chain, avoiding the problem of local over-sulfonation or unsulfonation in the post-sulfonation method. This uniform distribution is conducive to the formation of a uniform hydrophilic-hydrophobic microphase separation structure and promotes the formation of proton conduction channels; intact molecular chains: the polymerization reaction is carried out under relatively mild alkaline conditions, without the presence of strong oxidizing sulfonating agents, which will not attack the already formed polymer backbone. Therefore, the product has intact and defect-free molecular chains, high molecular weight and narrow distribution, which is conducive to the formation of effective molecular chain entanglement and enhances the mechanical strength of the film.

[0038] This invention introduces sulfonated polybenzimidazole (SPBI) as a blending component for proton exchange membranes. The PBI molecule contains an imidazole ring, in which the nitrogen atom is basic. The sulfonated PBI (SPBI) contains both sulfonic acid groups (acidic) and imidazole ring nitrogen atoms (basic), making it an amphoteric polymer. This structural feature allows it to form multiple interactions with the sulfonic acid groups of SPEEK when blended with SPEEK. Specifically, firstly, the imidazole ring (basic) on the SPBI molecular chain forms a strong ionic crosslinking or hydrogen bond interaction with the sulfonic acid group (acidic) of SPEEK. This physical crosslinking network acts as an anchor point, effectively binding the SPEEK molecular chain and significantly inhibiting its free movement and swelling in the hydrated state. This mechanism maintains the proton conductivity of high-sulfonated SPEEK while greatly improving the dimensional stability of the membrane. Secondly, SPBI itself contains sulfonic acid groups, which can participate in proton conduction and make a positive contribution to the proton conductivity of the membrane. This has a significant advantage compared with existing technologies using unsulfonated PBI. Thirdly, the acid-base interaction promotes good compatibility between the two polymers, forming a uniform and dense membrane structure, which helps to reduce the permeability of fuels (such as methanol).

[0039] This invention also selects antioxidant 1330 as the third component of the proton exchange membrane. Its chemical name is 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, and its chemical structural formula is as follows: It is a phenolic antioxidant with significant steric hindrance.

[0040] The molecular structure of antioxidant 1330 has the following characteristics: the molecular center is a trimethylbenzene ring, and three benzyl groups are respectively connected to three side chains containing 3,5-di-tert-butyl-4-hydroxyphenyl groups. This structure endows it with the following functions: free radical scavenging function: the multiple phenolic hydroxyl groups in the molecular structure can efficiently capture and remove reactive oxygen free radicals generated during fuel cell operation. The capture mechanism is: the phenolic hydroxyl groups react with free radicals to generate stable phenolic oxygen free radicals (stabilized by the conjugated system and steric hindrance), transforming the active free radicals into a stable structure, thereby breaking the chain reaction of polymer main chain oxidation; multiple capture sites: each antioxidant 1330 molecule contains three phenolic hydroxyl groups, which can capture multiple free radicals and have high antioxidant efficiency; good thermal stability: the tert-butyl groups in the molecule provide steric hindrance protection, enhancing the thermal stability of the antioxidant itself, enabling it to maintain its activity under the high temperature conditions of membrane preparation and use. The molecular structure of antioxidant 1330 enables it to perform the following functions in the composite membrane of this invention: 1) Protecting the SPEEK backbone: It captures free radicals that attack the ether bonds and sulfonic acid group linkages of the SPEEK molecular chain, inhibits the oxidative breakage of the polymer backbone, and slows down the chemical degradation of the membrane; 2) Protecting the SPBI component: It also protects the SPBI molecular chain from free radical attacks and maintains the integrity of the acid-base crosslinking network; 3) Synergistic stabilizing effect: It works synergistically with the physical crosslinking network formed by SPBI to comprehensively improve the durability of the membrane from both chemical stability (antioxidation) and physical stability (anti-swelling).

[0041] In summary, the use of sulfonated polyether ether ketone (PEEK) in this invention to prepare proton exchange membranes fundamentally solves the problem of unstable product quality caused by traditional post-sulfonation processes. Unlike the traditional method of polymerization followed by sulfonation, this method introduces sulfonated monomers during the polymerization reaction stage, achieving controllable distribution of sulfonic acid groups in the molecular chain. This significantly improves the uniformity and repeatability of sulfonation, reduces batch variations, and enhances the consistency and stability of the membrane material. Simultaneously, this precursor control strategy helps optimize the polymer's microstructure, enhances the overall regularity of the molecular chain, and further improves its mechanical strength and chemical durability. To further enhance the overall performance of the SPEEK membrane, this invention also introduces sulfonated polybenzimidazole (SPBI) as a blending component, supplemented with antioxidant 1330 for synergistic modification. SPBI possesses excellent proton conductivity and good dimensional stability. The imidazole ring in its molecular structure can form an acid-base interaction with the sulfonic acid groups in SPEEK, constructing a stable cross-linked network that effectively inhibits excessive swelling of the membrane in the hydrated state, thereby balancing the contradiction between proton conductivity and swelling resistance. Meanwhile, antioxidant 1330 can capture hydroxyl and peroxide free radicals generated during fuel cell operation, slow down the oxidative degradation process of the polymer backbone, and significantly improve the durability of membrane materials under long-term working conditions.

[0042] In some embodiments, sulfonate-containing phenolic monomers, bisphenol monomers, and dihalogen monomers are subjected to nucleophilic substitution polymerization in the presence of a catalyst and a solvent to generate sulfonated polyether ether ketones, including the following steps:

[0043] S11. Add aprotic polar solvent to the reactor, start the stirring system, control the stirring speed to 100-150 rpm, and add bisphenol monomer, phenolic monomer containing sulfonic acid group, dihalogen monomer and catalyst in sequence. Finally, add aprotic nonpolar solvent to rinse the reactor wall.

[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, the stirring rate is controlled at 100-150 rpm, which ensures that the materials are fully mixed and avoids polymer degradation that may be caused by excessive shear force. The viscosity of the system is low in the early stage of the polymerization reaction, and the viscosity of the system increases in the later stage as the molecular weight increases. It is necessary to adjust the stirring rate in a timely manner according to the reaction progress.

[0046] In this step, the present invention preferably uses dimethyl sulfoxide (DMSO) as the reaction solvent. DMSO is a strongly polar aprotic solvent with a boiling point of 189°C and has the following advantages: strong solubility for monomers and catalysts, enabling the formation of a homogeneous reaction system; high boiling point, suitable for polymerization reactions at high temperatures; and good solubility for polymerization products, preventing premature precipitation of polymers.

[0047] The role of aprotic nonpolar solvents: In this invention, xylene is preferred as a dehydrating agent. Xylene has the following functions: it forms an azeotrope with water, carrying away the water generated in the reaction from the system and promoting the forward polymerization reaction; it has a moderate boiling point (137-140.5℃), and can reflux to remove water when reacting at 170℃, and can evaporate and leave the system at 185℃; it is chemically inert to the reaction system and does not participate in side reactions, making it very suitable for the reaction system of this invention.

[0048] S12. Nitrogen gas is continuously introduced into the reactor during the heating process to maintain an inert atmosphere. When the temperature reaches 150-170℃, the reaction is held at this temperature for 1-3 hours. Then, the temperature is further increased to 180-190℃ and the reaction is held at this temperature for 140-160 hours.

[0049] This step adopts a two-stage heating design principle. The first stage is to keep the temperature at 150-170℃ for 1-3 hours. The main purpose of this stage is to remove the water generated in the reaction system by azeotropic reaction of xylene and water. Water is generated during the salt formation of bisphenol. If it is not removed in time, it will inhibit the reaction. Xylene is refluxed at this temperature and the water is separated by a water separator to ensure that the reaction system is in an anhydrous state.

[0050] The second stage involves holding the reaction at 180-190℃ for 140-160 hours. After the xylene is distilled off, the reaction proceeds in pure DMSO, with the temperature increased to 180-190℃. Higher temperatures are beneficial for increasing the reaction rate and the final polymer molecular weight. Gradual polymerization requires a longer time to reach a high molecular weight; a reaction time of 150 hours is sufficient to ensure the required degree of polymerization is achieved. Continuous nitrogen flow removes oxygen from the reaction system, preventing oxidative degradation of the polymer at high temperatures. Simultaneously, the nitrogen flow helps remove water and byproducts generated during the reaction, promoting the forward reaction.

[0051] 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 to obtain a wet material. The wet material is then placed in an oven to dry, and finally the target polymer product, sulfonated polyether ether ketone, is obtained.

[0052] This step is a post-processing step. The reaction solution is poured into ice water, and the polymer is precipitated and solidified by taking advantage of the fact that the solubility of the polymer in cold water decreases sharply. Thorough soaking and washing can remove residual solvents, catalysts and inorganic salts. After drying to remove moisture, a pure polymer product is obtained.

[0053] In some specific embodiments, the sulfonic acid-containing phenolic monomer is potassium 2,5-dihydroxybenzenesulfonate or sodium 2,5-dihydroxybenzenesulfonate; 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 dimethyl sulfoxide and the aprotic nonpolar solvent is xylene.

[0054] In the preparation step of sulfonated SPEEK, this invention selects materials specifically. Potassium 2,5-dihydroxybenzenesulfonate or sodium 2,5-dihydroxybenzenesulfonate is chosen as the phenolic monomer containing sulfonic acid groups. This is because the two hydroxyl groups are located at the 2 and 5 positions of the benzene ring, exhibiting appropriate reactivity and enabling successful nucleophilic substitution polymerization. The sulfonic acid groups are located on the benzene ring and directly connected to the polymer backbone, resulting in structural stability and preventing them from easily detaching during subsequent film formation and use. The potassium or sodium salt form enhances the thermal stability of the monomer, facilitating storage and use.

[0055] The bisphenol monomer chosen in this invention is bisphenol A because it is a widely used bisphenol monomer in industry, with abundant sources and low cost; the two benzene rings of bisphenol A are connected by isopropylidene groups, which endows the polymer backbone with a certain degree of flexibility, which is beneficial to film formation and mechanical properties; bisphenol A has a symmetrical structure and moderate reactivity, which is beneficial to obtaining high molecular weight polymers.

[0056] The dihalogen monomer chosen in this invention is 4,4'-difluorobenzophenone because fluorine atoms are good leaving groups, which are conducive to nucleophilic substitution reactions; the two fluorine atoms are located at the 4,4' position of benzophenone, with a symmetrical structure and consistent reactivity; the carbonyl group in the benzophenone structure is conjugated with the benzene rings on both sides, which improves the thermal and chemical stability of the polymer.

[0057] The catalyst of this invention is an alkali metal carbonate, preferably a mixture of potassium carbonate and sodium carbonate. Alkali metal carbonates can salt bisphenol monomers, improving their nucleophilicity; the mixture of potassium carbonate and sodium carbonate has a synergistic effect, which can more effectively promote the reaction; the carbonate generates carbon dioxide gas during the reaction and escapes, so it will not remain in the polymer and affect its performance.

[0058] The solvents used in this invention are a combination of aprotic polar solvent (dimethyl sulfoxide, DMSO) and aprotic nonpolar solvent (xylene). DMSO has a strong ability to dissolve monomers and polymers and provides a homogeneous reaction environment; DMSO has a high boiling point (189°C), making it suitable for high-temperature polymerization; xylene acts as a dehydrating agent, azeotropically dehydrating water and promoting the forward reaction. The combination of the two solvents achieves a functional division of labor between dissolution and dehydration, which is a key design for optimizing the polymerization process.

[0059] In some embodiments, the degree of sulfonation of the sulfonated polyether ether ketone is controlled by adjusting the molar ratio of the sulfonate-containing phenolic monomer to the bisphenol monomer in the preparation step; the degree of sulfonation of the sulfonated polyether ether ketone is 60%-80%.

[0060] This embodiment precisely controls the content of sulfonic acid groups in the final polymer by accurately controlling the molar ratio of phenolic monomers containing sulfonic acid groups to bisphenol monomers without sulfonic acid groups. This is a typical copolymer composition control principle, which falls under the category of chemometrics.

[0061] The specific calculation formula is as follows:

[0062] Degree of sulfonation (DS) = [Moles of phenolic monomers containing sulfonic acid groups / (Moles of phenolic monomers containing sulfonic acid groups + Moles of bisphenol monomers)] × 100%

[0063] For example, when the molar ratio of phenolic monomers containing sulfonic acid groups to bisphenol monomers is 80:20, the degree of sulfonation is 80%; when the ratio is 60:40, the degree of sulfonation is 60%. The advantage of this control method is that the degree of sulfonation is determined by the formulation design, not by the reaction conditions. As long as the purity of the two monomers meets the requirements, the weighing is accurate, and the polymerization reaction conditions are properly controlled, the degree of sulfonation of different batches of products will have a high degree of consistency. This fundamentally solves the common industry problem of large fluctuations in the degree of sulfonation and significant batch-to-batch differences in post-sulfonation methods.

[0064] In this embodiment, the sulfonation degree of SPEEK is controlled within the range of 60%-80%. This choice is based on the following considerations: When the sulfonation degree is below 60%, the content of sulfonic acid groups in the polymer is insufficient, resulting in a limited number of proton conduction sites and a low proton conductivity of the membrane, which makes it difficult to meet the power density requirements of fuel cells. In addition, when the sulfonation degree is too low, the hydrophilicity of the polymer is insufficient, making it difficult to form interconnected hydrated proton conduction channels in the membrane, further limiting the improvement of conductivity. When the sulfonation degree is above 80%, although the proton conductivity is expected to be further improved, the water absorption rate and swelling rate of the membrane increase sharply. The strong hydrophilicity of the high-density sulfonic acid groups leads to excessive water absorption by the membrane, severe volume expansion, and a significant decrease in dimensional stability. Excessive swelling not only weakens the mechanical strength of the membrane but may also cause the membrane to deform and wrinkle during battery assembly and operation, damaging the interfacial contact of the membrane electrode.

[0065] In the system of this invention, the sulfonation degree range of 60%-80% has been proven to be the region in which the best balance between proton conductivity and dimensional stability can be achieved. Within this range, the SPEEK membrane has sufficient proton conductivity. At the same time, through subsequent modification with SPBI and antioxidant 1330, swelling can be effectively suppressed, resulting in a composite membrane with excellent comprehensive performance.

[0066] In some embodiments, polybenzimidazole is sulfonated to obtain sulfonated polybenzimidazole, including the steps of: dispersing polybenzimidazole powder in concentrated sulfuric acid, reacting at 60-100°C for 3-6 hours, and obtaining sulfonated polybenzimidazole after precipitation, washing, neutralization and drying of the reaction product.

[0067] In this embodiment, the sulfonation reaction of polybenzimidazole (PBI) is essentially an electrophilic substitution reaction. Concentrated sulfuric acid, acting as the sulfonating agent, provides SO3H+ electrophilic species to attack the benzene ring portion of the benzimazole ring on the PBI molecular chain, introducing sulfonic acid groups into the PBI molecular chain. The sulfonation reaction requires a certain temperature to proceed, but excessively high temperatures may lead to polymer degradation or over-sulfonation. A temperature range of 60-100°C ensures that the sulfonation reaction proceeds at an appropriate rate while avoiding damage to the PBI backbone from high temperatures. A reaction time of 3-6 hours is sufficient to obtain SPBI products with moderate sulfonation and excellent performance.

[0068] In some embodiments, in the step of dissolving the sulfonated polyether ether ketone, sulfonated polybenzimidazole and antioxidant 1330 in an organic solvent, the mass ratio of the sulfonated polyether ether ketone, sulfonated polybenzimidazole and antioxidant 1330 is 1:(0.05-0.15):(0.01-0.05).

[0069] Specifically, in this embodiment, the mass ratio of sulfonated polyether ether ketone (PEEK) to sulfonated polybenzimidazole (PBBE) is 1:(0.05-0.15). Within this range, the SPBI content is moderate, forming a sufficiently dense cross-linked network to effectively suppress swelling without excessively affecting the proton conductivity of SPEEK. Simultaneously, the sulfonic acid groups of SPBI itself contribute to proton conduction without significantly reducing conductivity. If the SPBI content is too low, the density of the formed acid-base cross-linked network will be insufficient, limiting its inhibitory effect on membrane swelling and making it difficult to effectively improve dimensional stability. If the SPBI content is too high, excessive discontinuous phase may disrupt the continuity of the SPEEK matrix, and an overly dense cross-linked network may hinder proton transport channels, leading to a decrease in proton conductivity. Furthermore, SPBI is more expensive than SPEEK, and an excessively high proportion increases material costs.

[0070] In this embodiment, the mass ratio of sulfonated polyether ether ketone to antioxidant 1330 is 1:(0.01-0.05). Within this range, the antioxidant content is moderate, which can effectively capture free radicals generated during operation and significantly improve the antioxidant stability of the membrane, while preventing significant aggregation or phase separation in the membrane. If the antioxidant content is too low, the free radical capture ability is insufficient, and the improvement on the antioxidant stability of the membrane is limited. If the antioxidant content is too high, it may cause aggregation in the membrane, forming defects. At the same time, excessive small molecule antioxidants may plasticize the membrane material and affect mechanical properties.

[0071] In some embodiments, the step of dissolving the sulfonated polyether ether ketone, sulfonated polybenzimidazole, and antioxidant 1330 in an organic solvent, wherein the organic solvent is one or more of N-methylpyrrolidone, dimethylformamide, and dimethylacetamide, but is not limited thereto.

[0072] In this embodiment, all organic solvents are polar aprotic solvents, which have good solubility for SPEEK, SPBI and antioxidant 1330. Among them, NMP has a high boiling point (202℃) and a moderate evaporation rate, making it suitable for preparing defect-free homogeneous films by solution casting. DMF and DMAc are also commonly used solvents and can be selected according to process requirements.

[0073] In some embodiments, the casting solution is prepared into a membrane by the following steps: uniformly coating the casting solution onto the surface of a glass plate and drying it in an oven at a temperature of 40-80°C for 24-36 hours to obtain an SPBI and antioxidant-doped SPEEK proton exchange membrane.

[0074] In this embodiment, the temperature is selected as 40-80℃. If the temperature is too low (<40℃), the solvent will evaporate too slowly, the film formation cycle will be too long, and the efficiency will be affected. If the temperature is too high (>80℃), the solvent will evaporate too quickly, which may cause the film surface to form a skin quickly, and the internal solvent will not be able to escape in time, forming bubbles or defects. At the same time, the high temperature may cause thermal degradation of the components. 24-36 hours can ensure that the solvent is fully evaporated and obtain a film material with a dense structure and stable performance.

[0075] In some embodiments, an SPBI and antioxidant-doped SPEEK proton exchange membrane is also provided, which is prepared by the method for preparing SPBI and antioxidant-doped SPEEK proton exchange membranes described in this invention.

[0076] In some embodiments, an application of SPBI and antioxidant-doped SPEEK proton exchange membranes is also provided, in which the SPBI and antioxidant-doped SPEEK proton exchange membranes described in this invention are used to prepare fuel cells.

[0077] The present invention will be further explained and illustrated below through specific embodiments:

[0078] The reagents used in the examples were sourced from the following sources: Bisphenol A, potassium 2,5-dihydroxybenzenesulfonate, 4,4'-difluorobenzophenone, dimethyl sulfoxide, xylene, potassium carbonate, and sodium carbonate were provided by Shanghai Maclean Biochemical Technology Co., Ltd.

[0079] The concentrated sulfuric acid was provided by Shanghai Guoyao Group, PBI was provided by Kunshan Primis Polymer Materials Co., Ltd., and antioxidant 1330 was provided by Tangshan Keao Chemical Additives Co., Ltd.

[0080] Example 1

[0081] A method for preparing SPEEK (SPEEK-80) with a sulfonation degree of 80% includes the following steps:

[0082] 1. Take a 30 L glass reactor and heat it to 100 °C. Purge with nitrogen for 30 min to remove residual moisture. Then add 10.5 mol of dimethyl sulfoxide as a solvent and start the stirring system, controlling the stirring speed at 120 rpm. Add 0.20 mol of bisphenol A, 0.80 mol of potassium 2,5-dihydroxybenzenesulfonate, 1.00 mol of 4,4'-difluorobenzophenone, 2.45 mol of potassium carbonate, and 0.6 mol of sodium carbonate in sequence. Finally, add 2.3 mol of xylene to rinse the reactor walls, ensuring complete material transfer.

[0083] 2. Nitrogen gas is continuously introduced into the reactor during the heating process to maintain an inert atmosphere. When the temperature reaches 170℃, the reaction is held at this temperature for 2 hours. Then, the temperature is further increased to 185℃ and the reaction is held at this temperature for 150 hours.

[0084] 3. 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 soaked in ice water for 24 hours, crushed by a crusher, and washed 10 times with distilled water to remove residual impurities. Subsequently, most of the water is removed by a press, and the wet material is dried in an 80°C oven for 120 hours to finally obtain the target polymer product SPEEK-80.

[0085] The chemical reaction process involved in Example 1 is shown below:

[0086] .

[0087] Example 2

[0088] The preparation method of SPEEK (SPEEK-80) with a sulfonation degree of 60% is the same as that in Example 1, except that the feeding ratio of sulfonating monomer and bisphenol monomer is adjusted: bisphenol A is 0.40 mol, potassium 2,5-dihydroxybenzenesulfonate is 0.60 mol, and the amount and steps of other components are the same as in Example 1. Finally, SPEEK-60 with a sulfonation degree of about 60% is obtained.

[0089] Example 3

[0090] A method for preparing sulfonated polybenzimidazole (SPBI) includes the following steps:

[0091] 1. Take a 1 L three-necked flask, add a magnetic stir bar, then add 100 mL of concentrated sulfuric acid, and start stirring at 100 rpm. Under continuous stirring, slowly add 15 g of PBI powder in batches to avoid agglomeration. Then rinse the inner wall of the flask with 30 mL of concentrated sulfuric acid to ensure that any residual material is completely incorporated into the reaction system;

[0092] 2. Heat the mixture to 80℃ and stir continuously for 5 h. After the reaction is complete, let it cool naturally to room temperature. Then slowly pour the reaction solution into ice water to precipitate the solid product. After filtration, wash with water. Adjust the crude product to neutral with 1 mol / L sodium hydroxide solution, and then wash repeatedly with deionized water until the washing solution is neutral (tested with pH paper). Finally, dry it under vacuum and transfer it to an 80℃ oven to dry for 12 h to obtain the target product SPBI.

[0093] Example 4

[0094] A method for preparing a SPEEK-80 / SPBI / antioxidant 1330 composite membrane (mass ratio 10:1:0.3) includes the following steps:

[0095] Take a 250 mL beaker, add 85 g of N-methylpyrrolidone (NMP), place a magnetic stir bar in the beaker, and heat to 80 °C while stirring at 400 rpm; then slowly add 20 g of SPEEK-80 powder prepared in Example 1, 2 g of SPBI powder prepared in Example 3, and 0.6 g of antioxidant 1330 powder in sequence (mass ratio of SPEEK:SPBI:1330 = 10:1:0.3). After the addition is complete, continue stirring at 80 °C for 24 hours until a uniform, transparent, bubble-free casting solution is formed.

[0096] The obtained casting solution was uniformly coated on the surface of a clean glass plate and placed in a 50°C forced-air oven to dry for 30 hours to allow the solvent to evaporate slowly. After drying, the glass plate was removed, cooled to room temperature, and the film was peeled off the glass plate to obtain a composite film with uniform thickness, which was denoted as sample S1.

[0097] Example 5

[0098] The preparation method of SPEEK-80 / SPBI / antioxidant 1330 composite membrane (mass ratio 10:1:0.1) differs from that in Example 4 only in that the amount of SPEEK-80 remains unchanged at 20 g, and the amounts of SPBI and antioxidant 1330 are adjusted to 2 g and 0.2 g respectively. The resulting composite membrane is designated as sample S2.

[0099] Example 6

[0100] The preparation method of SPEEK-80 / SPBI / antioxidant 1330 composite membrane (mass ratio 10:1:0.5) differs from that in Example 4 only in that the amount of SPEEK-80 remains unchanged at 20 g, and the amounts of SPBI and antioxidant 1330 are adjusted to 2 g and 1 g respectively. The resulting composite membrane is designated as sample S3.

[0101] Example 7

[0102] The preparation method of SPEEK-80 / SPBI / antioxidant 1330 composite membrane (mass ratio 10:0.5:0.3) differs from that of Example 4 only in that the amount of SPEEK-80 remains unchanged at 20 g, and the amounts of SPBI and antioxidant 1330 are adjusted to 1 g and 0.6 g respectively. The resulting composite membrane is designated as sample S4.

[0103] Example 8

[0104] The preparation method of SPEEK-80 / SPBI / antioxidant 1330 composite membrane (mass ratio 10:1.5:0.3) differs from that in Example 4 only in that the amount of SPEEK-80 remains unchanged at 20 g, and the amounts of SPBI and antioxidant 1330 are adjusted to 3 g and 0.6 g respectively. The resulting composite membrane is designated as sample S5.

[0105] Example 9

[0106] The preparation method of SPEEK-60 / SPBI / antioxidant 1330 composite membrane (mass ratio 10:1:0.3) is different from that of Example 4 only in that the SPEEK-80 powder is replaced with the SPEEK-60 powder prepared in Example 2, and the resulting composite membrane is denoted as sample S6.

[0107] Comparative Example 1

[0108] The preparation method of pure SPEEK-80 membrane (without SPBI and antioxidant 1330) includes the following steps: Take a 250 mL beaker, add 85 g of NMP, and heat to 80°C while stirring at 400 rpm. Add 20 g of SPEEK-80 powder prepared in Example 1, and continue stirring for 24 hours to form a homogeneous solution; uniformly coat the solution onto the surface of a glass plate, and dry it in a 50°C oven for 30 hours to obtain a pure SPEEK-80 membrane, denoted as sample D1.

[0109] Comparative Example 2

[0110] The preparation method of pure SPEEK-60 membrane (without SPBI and antioxidant 1330) includes the following steps: Take a 250 mL beaker, add 85 g of NMP, and heat to 80 °C while stirring at 400 rpm. Add 20 g of SPEEK-60 powder prepared in Example 2, and continue stirring for 24 hours to form a homogeneous solution; uniformly coat the solution onto the surface of a glass plate, and dry it in a 50 °C oven for 30 hours to obtain a pure SPEEK-60 membrane, denoted as sample D2.

[0111] Comparative Example 3

[0112] A membrane with only SPBI added (without antioxidant 1330) was prepared by dissolving 20 g of SPEEK-80 and 2 g of SPBI in NMP, following the steps of Example 4, without adding antioxidant 1330. This composite membrane was denoted as sample D3 (mass ratio SPEEK:SPBI=10:1).

[0113] Comparative Example 4

[0114] A membrane with only antioxidant 1330 added (without SPBI) was prepared by dissolving 20 g of SPEEK-80 and 0.6 g of antioxidant 1330 in NMP, following the steps of Example 4, without adding SPBI. This composite membrane was denoted as sample D4 (mass ratio SPEEK:1330 = 10:0.3).

[0115] Comparative Example 5

[0116] The method for preparing a composite membrane from post-sulfonated SPEEK includes the following steps:

[0117] Preparation of post-sulfonated SPEEK: 100 mL of chlorosulfonic acid was placed in a 500 mL beaker, a magnetic stir bar was added, and the mixture was stirred at 100 rpm. Under continuous stirring, 15 g of PEEK powder was slowly added in batches. The reaction system was then heated to 80 °C and stirred for 5 hours. After the reaction was completed, 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 1 mol / L potassium hydroxide solution and soaked at room temperature for 2 hours to remove residual acidic impurities. The solid 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 SPEEK.

[0118] Composite membrane preparation: Referring to the steps in Example 4, SPEEK-80 was replaced with an equal mass of post-sulfonated SPEEK, and the feed ratio was post-sulfonated SPEEK:SPBI:1330=10:1:0.3. The composite membrane was prepared and denoted as sample D5.

[0119] Comparative Example 6

[0120] The composite membrane was prepared using the method of non-sulfonated PBI doping, referring to the steps of Example 4. SPBI was replaced with an equal mass of non-sulfonated PBI (purchased from Kunshan Primis Polymer Materials Co., Ltd.), and the feed ratio was SPEEK-80:PBI:1330 =10:1:0.3. The composite membrane was prepared and denoted as sample D6.

[0121] The membrane samples prepared in Examples 4-9 and Comparative Examples 1-6 were subjected to the following performance tests:

[0122] 8.1 Proton conductivity test

[0123] Test Method: The proton transport performance of the membrane samples was characterized using electrochemical 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 1Hz to 5×10⁻⁶. 6 Hz, AC disturbance voltage is set to 10mV.

[0124] Test principle: By measuring the impedance response of the membrane sample at different frequencies, the bulk resistance (R) of the membrane can be separated. The proton conductivity (σ) is calculated according to the formula σ=L / (R × A), where L is the membrane thickness and A is the effective electrode area.

[0125] 8.2 Swelling Rate Test

[0126] 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%.

[0127] 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.

[0128] 8.3 Antioxidant stability test

[0129] Test Method: Accelerated chemical degradation experiments were used to evaluate the antioxidant stability of the membrane samples. A 3cm × 3cm sample of the membrane to be tested was immersed in Fenton's reagent (composed of 3% hydrogen peroxide aqueous solution and 2 ppm Fe) at a constant temperature of 70℃. 2+ In ), Fenton's reagent in Fe. 2+ Catalytic decomposition of H₂O₂ generates hydroxyl radicals (·OH), simulating the oxidative environment during fuel cell operation. The evolution of the macroscopic morphology of the samples is observed through periodic sampling. When the membrane surface first shows visually identifiable rupture characteristics, the cumulative treatment time at this point is recorded as the membrane's critical breakage time, thus characterizing the membrane's tolerance to strong oxidative environments. A longer breakage time indicates better antioxidant stability of the membrane.

[0130] The performance test results are shown in Table 1.

[0131] Table 1 Performance test results of composite membrane

[0132]

[0133] Analyzing the data in Table 1 and observing the data of examples S1-S6 as a whole, the following general patterns can be summarized: First, using SPEEK prepared by monomer polymerization as the matrix is ​​a prerequisite for achieving excellent comprehensive performance. All examples (S1-S6) are based on monomer-polymerized SPEEK, and their data show good performance adjustability and consistency. In particular, S1 (SPEEK-80 / SPBI / 1330=10:1:0.3) exhibits excellent comprehensive performance: the proton conductivity reaches 72.1 mS / cm, which is basically the same as that of pure SPEEK-80 (D1, 75.0 mS / cm); the area swelling ratio is as low as 11.8%, which is much lower than D1's 35.0%; and the antioxidant stability reaches 152 minutes, which is more than 20 times that of D1. This indicates that, based on the excellent performance of the monomer polymerization method SPEEK, subsequent modification can achieve a significant performance improvement. Secondly, the synergistic effect of SPBI and antioxidant 1330 is the key to overcoming the performance bottleneck. As can be seen from the data gradient of S1-S5, when the ratio of SPBI to 1330 changes within a reasonable range (SPEEK:SPBI:1330=1:0.05-0.15:0.01-0.05), the performance of the composite membrane exhibits a regular change: as SPBI increases, the swelling rate decreases but the conductivity may be impaired; as 1330 increases, the antioxidant capacity improves but the swelling rate may increase. This indicates that there exists an optimal synergistic ratio range (approximately 10:1:0.3) within which the best performance balance can be achieved. Furthermore, the choice of sulfonation degree is crucial. Comparing S1 (SPEEK-80 matrix) and S6 (SPEEK-60 matrix), it can be seen that, under the same modification ratio, the high sulfonation degree matrix (80%) provides a higher proton conduction potential (72.1 mS / cm vs. 41.5 mS / cm), while the modifier is responsible for addressing the swelling and oxidation issues caused by the high sulfonation degree. This reveals the core design concept of this invention: the high sulfonation degree matrix provides conductivity, the modifier solves the swelling rate and stability issues, and the two work synergistically to achieve a performance breakthrough.

[0134] The comparative examples reveal the shortcomings of the existing technology, as shown below:

[0135] Comparative Example 1 (D1, pure SPEEK-80): As a benchmark for high-sulfonated SPEEK, its proton conductivity is as high as 75.0 mS / cm, demonstrating the potential of SPEEK materials in proton conduction. However, its area swelling ratio is as high as 35.0%, and its breakage time in Fenton reagent is only 7 minutes. These two data reveal two major inherent defects of high-sulfonated SPEEK: poor dimensional stability due to excessive swelling, and poor chemical stability due to the main chain being susceptible to free radical attack. This is the core technical problem that this application aims to solve.

[0136] Comparative Example 2 (D2, pure SPEEK-60): As a benchmark for low-sulfonated SPEEK, its swelling ratio (11.3%) was significantly improved compared to D1, but its conductivity (38.0 mS / cm) decreased sharply, only about half that of D1. This indicates that while simply reducing the degree of sulfonation can alleviate the swelling problem, it comes at the cost of sacrificing proton conductivity, and a balanced optimization of performance cannot be achieved. Although the antioxidant properties of D2 (20 minutes) are better than those of D1, they are still at a low level.

[0137] D1 and D2 together illustrate that pure SPEEK membranes have a fundamental contradiction between conductivity and swelling rate, and regardless of the degree of sulfonation, their antioxidant stability cannot meet the requirements of practical applications. This provides a clear direction for the technical improvement of this application.

[0138] Comparative Example 3 (D3, SPBI only, without 1330): Compared to D1, the swelling rate of D3 decreased from 35.0% to 10.0%, an improvement of 71.4%, demonstrating that the cross-linking network formed by SPBI through acid-base interaction can effectively inhibit membrane swelling. This is a direct effect of SPBI modification. However, the conductivity of D3 decreased from 75.0 mS / cm to 67.6 mS / cm, a decrease of approximately 10%, indicating that the addition of SPBI consumed some of the sulfonic acid groups used for proton conduction. More importantly, its antioxidant capacity only improved to 98 minutes (compared to 7 minutes for D1), which, although an improvement, is still not ideal. The data from D3 reveals two key pieces of information: First, SPBI modification can indeed solve the swelling problem, verifying the effectiveness of the acid-base cross-linking strategy; second, SPBI modification alone provides limited improvement in antioxidant capacity and has a certain negative impact on conductivity. This indicates that SPBI modification alone cannot achieve comprehensive optimization of overall performance.

[0139] Comparative Example 4 (D4, 1330 only, no SPBI): Compared to D1, the antioxidant activity of D4 increased from 7 minutes to 29 minutes, an improvement of more than 3 times, proving that 1330 can effectively capture free radicals, which is a direct effect of antioxidant modification. However, the swelling rate of D4 was still as high as 34.3%, almost the same as D1's 35.0%, indicating that 1330 alone cannot solve the swelling problem. At the same time, although its antioxidant activity (29 minutes) has improved, it is far from meeting the requirements of practical applications.

[0140] The comparison between D3 and D4 fully demonstrates that a single SPBI modification or a single 1330 modification can only solve one of the swelling problem and the oxidation problem, respectively, and cannot achieve a comprehensive improvement in overall performance. This provides a basis for comparison of the synergistic effect of the ternary system of this invention.

[0141] Comparative Example 5 (D5, post-sulfonated SPEEK as the matrix, same proportions as S1): This is the most direct comparison with Example 4 (S1) of the present invention. D5 uses SPEEK prepared by post-sulfonation as the matrix, with the same proportions of SPBI and 1330 added. Its proton conductivity (72.0 mS / cm) is comparable to that of S1 (72.1 mS / cm), but its area swelling ratio is as high as 41.0% (far exceeding 11.8% of S1), and its oxidation resistance is extremely poor (<5 minutes, far lower than 152 minutes of S1). This comparative data reveals a fundamental problem: even with the exact same modifiers and proportions, the structural quality of the matrix material determines the upper limit of the final performance. Due to inherent defects in post-sulfonated SPEEK, such as main chain breakage and uneven distribution of sulfonic acid groups during sulfonation, even with the subsequent addition of SPBI and 1330, a uniform and effective cross-linked network cannot be formed, making it difficult to effectively suppress swelling. Simultaneously, structural defects in the main chain become priority targets for free radical attack, hindering effective protection by antioxidants. Data from D5 indicates that the technical contribution of this invention lies not only in discovering the synergistic modifying effect of SPBI and 1330, but also in recognizing that only by establishing this synergistic modification on the superior structural foundation of monomer-polymerized SPEEK can its potential be fully realized. This is the core idea of ​​this invention, starting from the design of the original structure.

[0142] Comparative Example 6 (D6, unsulfonated PBI instead of SPBI): D6 uses unsulfonated PBI instead of SPBI, with the same ratio as S1. Comparing D6 with S1 in Example 4, it can be found that the proton conductivity of D6 (55.6 mS / cm) is 22.9% lower than that of S1 (72.1 mS / cm). This difference illustrates the dual function of SPBI: SPBI itself contains sulfonic acid groups, which can participate in crosslinking in the blend film and also serve as proton conduction sites, thus making a positive contribution to conductivity.

[0143] The single-function limitation of PBI: Unsulfonated PBI lacks sulfonic acid groups and can only form acid-base interactions with the sulfonic acid groups of SPEEK through the imidazole ring. This consumes some of the sulfonic acid groups that would otherwise be used for proton conduction, without providing additional conduction sites. The integrity of the conduction network: The sulfonic acid groups of SPBI in S1 help maintain the continuity of hydrophilic channels; the consumption effect of PBI in D6 may lead to the interruption or distortion of some hydrophilic channels. This comparison directly proves that using PBI after sulfonation treatment can significantly improve the proton conduction performance of the composite membrane.

[0144] The swelling rate of D6 (10.9%) was at the same level as that of S1 (11.8%), or even slightly better. This indicates that unsulfonated PBI can also form an acid-base interaction with the sulfonic acid group of SPEEK through the imidazole ring to build a cross-linking network and effectively inhibit membrane swelling. Under the same mass ratio, PBI and SPBI provide a similar number of cross-linking sites, so their effects on inhibiting swelling are similar. The control of swelling rate mainly depends on the cross-linking effect of the imidazole ring, and the presence or absence of the sulfonic acid group has little effect on this.

[0145] The antioxidant properties of D6 (155 minutes) were almost identical to those of S1 (152 minutes), indicating that the antioxidant properties mainly come from the free radical scavenging function of 1330 and the cross-linking effect between SPEEK and the imidazole ring. Under the same amount of 1330 added, the antioxidant properties of the two should be similar. In addition, the cross-linking networks formed by PBI and SPBI can provide a good dispersion matrix for 1330, which helps to exert its antioxidant function. Under the effective protection of 1330, the intrinsic differences of the SPEEK backbone (the complete backbone of the monomer polymerization method and the defective backbone of the post-sulfonation method) were not reflected in the comparison between D6 and S1, because both use SPEEK-80 of monomer polymerization as the matrix.

[0146] Furthermore, comparing the performance of S1 (SPEEK-80 / SPBI / 1330=10:1:0.3) in Example 4 with D1 (pure SPEEK-80) in Comparative Example 1, D3 (SPBI only) in Comparative Example 3, and D4 (1330 only) in Comparative Example 4, it can be found that the performance of adding both SPBI and antioxidant 1330 (10:1:0.3) is far superior to the simple sum of D3 and D4. If the effect of S1 is the simple sum of D3 and D4, the expected swelling rate should be close to the average of D3 and D4 (about 22%), and the expected antioxidant activity should be 98+29=127 minutes. However, in reality, the actual swelling rate of S1 (11.8%) is better than that of D3 (10.0%), and the actual antioxidant activity (152 minutes) far exceeds 127 minutes. This indicates a positive synergistic effect between SPBI and 1330: the uniform cross-linked network constructed by SPBI provides an ideal dispersion matrix for 1330, enabling 1330 to function more effectively; at the same time, 1330 protects the SPBI and SPEEK backbone from free radical attacks, maintaining the integrity of the cross-linked network.

[0147] Based on the above analysis, existing SPEEK membranes have consistently faced technical bottlenecks, including difficulty in balancing conductivity and swelling rate, and poor oxidation resistance. While pure SPEEK-80 (D1) exhibits high conductivity, it suffers from severe swelling and extremely poor oxidation resistance; pure SPEEK-60 (D2), although its swelling is controllable, experiences a significant decrease in conductivity. This invention, through the ternary synergy of monomer-polymerized SPEEK with SPBI and 1330, successfully achieves simultaneous optimization of high conductivity (72.1 mS / cm), low swelling rate (11.8%), and high oxidation resistance (152 minutes), breaking through this performance ceiling. Comparisons between S1 and D3 / D4 show that the synergistic effect of SPBI and 1330 far exceeds the simple sum of their components; comparisons between S1 and D5 indicate that monomer-polymerized SPEEK is a necessary prerequisite for the synergistic effect to take effect; and comparisons between S1 and D6 demonstrate that sulfonation treatment of SPBI is a necessary condition for achieving optimal performance.

[0148] 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 SPBI and antioxidant-doped SPEEK proton exchange membrane, characterized in that, Including the following steps: A sulfonated polyether ether ketone is generated by mixing phenolic monomers containing sulfonic acid groups, bisphenol monomers, and dihalogen monomers in the presence of a catalyst and solvent and then undergoing a nucleophilic substitution polymerization reaction. Sulfonation of polybenzimidazole yields sulfonated polybenzimidazole. The sulfonated polyether ether ketone, sulfonated polybenzimidazole, and antioxidant 1330 are dissolved in an organic solvent to form a casting solution; The casting solution is used to prepare a membrane, thereby obtaining an SPBI and antioxidant-doped SPEEK proton exchange membrane.

2. The method for preparing the SPBI and antioxidant-doped SPEEK proton exchange membrane according to claim 1, characterized in that, Sulfonated polyether ether ketones are produced by nucleophilic substitution polymerization of phenolic monomers containing sulfonic acid groups, bisphenol monomers, and dihalogen monomers in the presence of a catalyst and solvent. The steps include: Add an aprotic polar solvent to the reactor, start the stirring system, control the stirring speed at 100-150 rpm, and add bisphenol monomer, phenolic monomer containing sulfonic acid group, dihalogen monomer and catalyst in sequence. Finally, add an aprotic nonpolar solvent to rinse the reactor wall. Nitrogen gas is continuously introduced into the reactor during the heating process to maintain an inert atmosphere. When the temperature reaches 150-170℃, the reaction is held at this temperature for 1-3 hours. Then, the temperature is further increased to 180-190℃ and the reaction is held at this temperature for 140-160 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 to obtain a wet material. The wet material is then placed in an oven to dry, and finally the target polymer product, sulfonated polyether ether ketone, is obtained.

3. The method for preparing the SPBI and antioxidant-doped SPEEK proton exchange membrane according to claim 1 or 2, characterized in that, In the step of preparing sulfonated polyether ether ketone, the phenolic monomer containing sulfonic acid groups is potassium 2,5-dihydroxybenzenesulfonate or sodium 2,5-dihydroxybenzenesulfonate; 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 dimethyl sulfoxide and the aprotic nonpolar solvent is xylene.

4. The method for preparing the SPBI and antioxidant-doped SPEEK proton exchange membrane according to claim 1 or 2, characterized in that, In the preparation of sulfonated polyether ether ketone, the degree of sulfonation of the sulfonated polyether ether ketone is controlled by adjusting the molar ratio of phenolic monomers containing sulfonic acid groups to bisphenol monomers; the degree of sulfonation of the sulfonated polyether ether ketone is 60%-80%.

5. The method for preparing the SPBI and antioxidant-doped SPEEK proton exchange membrane according to claim 1, characterized in that, The sulfonation of polybenzimidazole to obtain sulfonated polybenzimidazole includes the following steps: Polybenzimidazole powder was dispersed in concentrated sulfuric acid and reacted at 60-100℃ for 3-6 hours. The reaction product was then precipitated, washed, neutralized and dried to obtain sulfonated polybenzimidazole.

6. The method for preparing the SPBI and antioxidant-doped SPEEK proton exchange membrane according to claim 1, characterized in that, In the step of dissolving the sulfonated polyether ether ketone, sulfonated polybenzimidazole and antioxidant 1330 in an organic solvent, the mass ratio of the sulfonated polyether ether ketone, sulfonated polybenzimidazole and antioxidant 1330 is 1:(0.05-0.15):(0.01-0.05).

7. The method for preparing the SPBI and antioxidant-doped SPEEK proton exchange membrane according to claim 1, characterized in that, In the step of dissolving the sulfonated polyether ether ketone, sulfonated polybenzimidazole and antioxidant 1330 in an organic solvent, the organic solvent is one or more of N-methylpyrrolidone, dimethylformamide and dimethylacetamide.

8. The method for preparing the SPBI and antioxidant-doped SPEEK 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 is uniformly coated on the surface of a glass plate and dried in an oven at 40-80℃ for 24-36 hours to obtain SPBI and antioxidant-doped SPEEK proton exchange membranes.

9. A SPBI and antioxidant-doped SPEEK proton exchange membrane, characterized in that, The SPBI and antioxidant-doped SPEEK proton exchange membranes described in any one of claims 1-8 were prepared using the same method.

10. An application of an SPBI and antioxidant-doped SPEEK proton exchange membrane, characterized in that, The SPBI and antioxidant-doped SPEEK proton exchange membrane described in claim 9 are used to prepare fuel cells.

Images