Proton exchange membrane for hydrogen fuel cell, preparation method of proton exchange membrane and hydrogen fuel cell

Abstract

The invention provides a proton exchange membrane for a hydrogen fuel cell, a preparation method of the proton exchange membrane and the hydrogen fuel cell, and the method comprises the following steps: S1, reducing an aldehyde group in diaminobenzaldehyde through sodium borohydride, and reacting with thionyl chloride to obtain chloromethylated aromatic diamine; s2, carrying out a reaction on the chloromethylated aromatic diamine and aromatic diacyl chloride to obtain chloromethylated aromatic polyamide; s3, the chloromethylated aromatic polyamide reacts with an imidazole compound, a hydroxyl phosphonic acid compound and a hydroxyl phosphonate compound, and modified aromatic polyamide is obtained; and S4, dissolving the modified aromatic polyamide in an organic solvent to obtain slurry, and carrying out film casting on the slurry to obtain the proton exchange membrane. The proton exchange membrane prepared by the steps can keep good proton conductivity in normal-temperature and high-temperature environments, and is suitable for stable operation of a hydrogen fuel cell in a relatively wide working temperature range.

Description

Technical Field

[0001] The present application relates to the technical field of hydrogen fuel cells, and in particular to a proton exchange membrane for a hydrogen fuel cell, a preparation method thereof, and a hydrogen fuel cell. Background Art

[0002] The proton exchange membrane (PEM) is a core component of hydrogen fuel cells. Its primary function is to conduct protons between the anode and cathode while blocking electrons and the fuel gas. Its performance directly impacts the fuel cell's energy conversion efficiency, operating temperature window, and service life. Currently, commercial fuel cells widely use perfluorosulfonic acid resins (such as Nafion®) as PEMs, which exhibit excellent proton conductivity and chemical stability in low-temperature and high-humidity environments.

[0003] However, existing perfluorosulfonic acid-based proton exchange membranes primarily rely on the hydration mechanism of sulfonic acid groups for proton conduction. This results in a significant decrease in proton conductivity at high temperatures (>100°C) or in low humidity environments, severely limiting the operating temperature window and cold-start performance of hydrogen fuel cells. Furthermore, the microstructure of these membranes is highly uncontrollable, and their thermal stability and mechanical properties degrade rapidly. These membranes are prone to dehydration cracking and ion channel collapse during actual service.

[0004] To overcome these challenges, researchers have attempted to develop sulfonic acid-modified aromatic polymer membranes or composite membranes (such as sulfonated polyetheretherketone and sulfonated polybenzimidazole). However, these systems still rely heavily on hydration, making their proton conduction mechanisms difficult to maintain under high-temperature, anhydrous conditions. Other technologies have employed non-hydrated proton donor structures to enhance high-temperature performance. However, these systems lack synergistic structural design for the proton-conducting segments, resulting in a lack of continuity and separation-driven mechanisms for the ion channels, often resulting in limited conductivity gains.

[0005] Therefore, how to improve the proton conductivity of proton exchange membranes in high-temperature environments while ensuring their thermal stability and structural integrity is a technical problem that needs to be urgently solved in this field. Summary of the Invention

[0006] The present application provides a proton exchange membrane for a hydrogen fuel cell, a preparation method thereof, and a hydrogen fuel cell, aiming to solve the problem that the proton conductivity of existing proton exchange membranes decreases significantly under high temperature or low humidity environments. The provided proton exchange membrane can still maintain a high proton conductivity under normal temperature and high temperature conditions, thereby improving the operating performance and stability of hydrogen fuel cells in a wider temperature range.

[0007] In a first aspect, the present application provides a method for preparing a proton exchange membrane for a hydrogen fuel cell, comprising the following steps: S1: The aldehyde group in diaminobenzaldehyde is reduced with sodium borohydride and then reacted with thionyl chloride to convert the aldehyde group in diaminobenzaldehyde into chloromethyl to obtain chloromethylated aromatic diamine; S2: reacting the chloromethylated aromatic diamine with aromatic diacyl chloride to cause a polycondensation reaction between the chloromethylated aromatic diamine and the aromatic diacyl chloride to obtain a chloromethylated polyaromatic amide; S3: reacting the chloromethylated polyaromatic amide with an imidazole compound, a hydroxyphosphonic acid compound, and a hydroxyphosphonate compound, so that the imidazole compound, the hydroxyphosphonic acid compound, and the hydroxyphosphonate compound undergo a nucleophilic substitution reaction with the chloromethyl group on the chloromethylated polyaromatic amide to obtain a modified polyaromatic amide; S4: dissolving the modified polyaromatic amide in an organic solvent to obtain a slurry, and casting the slurry into a membrane to obtain a proton exchange membrane.

[0008] According to the present application, the proton exchange membrane prepared by the above steps can maintain good proton conductivity at both room temperature and high temperature environments, and is suitable for the stable operation of hydrogen fuel cells in a wide operating temperature range.

[0009] Specifically, in step S1, the aldehyde groups in diaminobenzaldehyde are reduced with sodium borohydride and then reacted with thionyl chloride to convert the aldehyde groups on the diaminobenzaldehyde into chloromethyl groups, yielding a chloromethylated aromatic diamine. This step, by first reducing the aldehyde groups to hydroxymethyl groups and then reacting with thionyl chloride to generate chloromethyl groups, imparts a controlled distribution of side chain reaction sites to the aromatic diamine. This step lays the foundation for the subsequent grafting of side chain functional groups, allowing the proton-conducting structure to retain active sites prior to main chain polymerization, improving grafting efficiency and reaction uniformity.

[0010] In step S2, a rigid aromatic amide backbone is formed by polycondensation of an aromatic diamine and an aromatic diacyl chloride. This polymer backbone possesses high thermal stability and chemical inertness, which helps the membrane maintain structural integrity and dimensional stability in a high-temperature, anhydrous environment. Furthermore, the chloromethyl side groups retained on the polymer backbone provide controllable active sites for grafting proton-conducting structures.

[0011] Step S3 is the key to achieving high proton conductivity. By grafting three types of compounds containing proton-conducting functions onto the side chains of the polymer main chain, a multi-point collaborative proton-conducting structure is formed inside the membrane material. Among them, the imidazole structure has proton-accepting ability and can adsorb and transfer protons through hydrogen bonds under anhydrous or low-humidity conditions. The dynamic proton hopping path formed between its cyclic nitrogen atoms is the core of maintaining conductivity under high temperature conditions. The hydroxyphosphonic acid structure provides a stable proton donor. The ionizable hydrogen on the phosphonic acid group forms a hydrogen bond coupling system with the imidazole, allowing protons to be efficiently transferred between the donor-acceptor system, thereby increasing the available proton concentration in the membrane. While providing a source of protons, the hydroxyphosphonate structure's flexible chain segments can adjust the distribution and spacing of various proton-conducting groups in the membrane, helping to induce the formation of a microphase separation structure, promoting the local enrichment of polar proton-conducting groups, and constructing a continuous and accessible ion migration channel.

[0012] Therefore, in the modified polyaramid, the modified imidazole and phosphonic acid form a proton "acid-base pair" complex structure, realizing short-range and medium-range proton hopping; at the same time, the flexible chain segments of the phosphonic acid ester regulate the arrangement and orientation of the local chain segments, improving the continuity of the proton migration direction; the combination of the three constructs a stable and directional proton-conducting network inside the membrane, so that the membrane material still maintains excellent proton conductivity under high temperature and low humidity environments.

[0013] In step S4, a dense, continuous membrane is formed on the macroscale through solution casting, while retaining the enriched structure of polar segments on the microscale, thereby constructing a multi-scale, cooperative proton-conducting network. This structure ensures the uniformity and mechanical strength of the membrane during the film formation process, and further promotes the morphological stability and conduction efficiency of the ion channels.

[0014] In summary, this application uses the main chain-side chain partitioning structure and the coordinated grafting design of three types of proton-conducting groups to make the resulting proton exchange membrane have both high thermal stability and high-temperature proton conductivity, which is suitable for the efficient operation of hydrogen fuel cells in a wide temperature range.

[0015] In some embodiments, in step S1, the molar ratio of diaminobenzaldehyde, sodium borohydride, and thionyl chloride is 1:(1.01-1.1):(1.01-1.2).

[0016] In some of the above embodiments, the molar ratio of diaminobenzaldehyde to sodium borohydride is controlled within the range of 1:1.01 to 1.1 to reduce the aldehyde groups to hydroxyl groups. Simultaneously, the molar ratio of thionyl chloride is controlled within the range of 1.01 to 1.2 to ensure efficient introduction of the chloromethyl groups and avoid side reactions (such as incomplete reaction or excessive halogenation) caused by excess thionyl chloride. This controlled molar ratio ensures efficient and controllable reaction efficiency at each step, ensuring the purity and uniformity of the resulting chloromethylated aromatic diamine structure.

[0017] In some embodiments, step S1 includes: Diaminobenzaldehyde is dissolved in methanol, sodium borohydride is added under ice bath conditions, and the reaction is carried out at 20-30°C for 1-3 hours. After the reaction, the pH is adjusted to 6.5-7.5, and the solvent is removed by rotary evaporation to obtain diaminobenzyl alcohol; the diaminobenzyl alcohol is dissolved in dichloromethane, thionyl chloride and a catalytic amount of N,N-dimethylformamide are added under ice bath conditions, and the reaction is carried out at 30-50°C for 2-4 hours to obtain a chloromethylated aromatic diamine.

[0018] In some of the above embodiments, the aldehyde group in diaminobenzaldehyde is effectively reduced to a hydroxymethyl group through a sodium borohydride reduction reaction. This process is carried out under mild temperature conditions (20~30°C), avoiding side reactions of the amino group, maintaining the activity of the amino group, and providing highly reactive raw materials for subsequent reactions; subsequently, under the action of thionyl chloride, the hydroxymethyl group is effectively converted into a chloromethyl group. The reaction is carried out at 30~50°C and is catalyzed by N,N-dimethylformamide. Chloromethylation can be achieved efficiently and selectively, and excessive chlorination or side reactions can be avoided by controlling the reaction conditions. Ultimately, a chloromethylated aromatic diamine is obtained, providing a high-quality starting material for subsequent polymerization reactions.

[0019] In some embodiments, in step S2, the molar ratio of the chloromethylated aromatic diamine to the aromatic diacyl chloride is 1:(1-1.1).

[0020] In some of the above embodiments, by controlling the molar ratio of chloromethylated aromatic diamine to aromatic diacyl chloride within the range of 1: (1 to 1.1), it is beneficial to achieve a high conversion rate of the polymerization reaction and linear regulation of the main chain structure. When the aromatic diacyl chloride is slightly excessive, the residual terminal amino group can be effectively reduced, the cross-linking tendency at the end of the reaction is reduced, and the resulting polyaramid structure is more regular and the molecular weight distribution is narrower. In addition, the chloromethylated aromatic diamine contains side chain active sites. To ensure that the chloromethyl side groups do not undergo side reactions or cross-linking during the polycondensation process, it is necessary to control the polycondensation balance. A slight excess of acyl chloride can play an end-capping role, thereby improving the uniformity of the main chain and the retention rate of the chloromethyl sites. The above molar ratio not only improves the polymerization efficiency, but also significantly improves the thermal stability of the polymer and the controllability of the subsequent graft modification reaction, thereby being more conducive to obtaining a proton exchange membrane with high proton conductivity.

[0021] In some embodiments, step S2 includes: The chloromethylated aromatic diamine and aromatic dichloride are respectively dissolved in N,N-dimethylacetamide to obtain a diamine solution and a dichloride solution. Triethylamine is added to the diamine solution, and then the dichloride solution is added in an ice bath. The mixture is reacted at 20-30° C. for 8-12 hours to obtain a chloromethylated polyaromatic amide.

[0022] In some of the above-mentioned embodiments, dissolving the diamine and the diacyl chloride separately in the highly polar aprotic solvent N,N-dimethylacetamide (DMAc) helps maintain the activity and uniform dispersion of the reaction monomers and improves the controllability of the polymerization reaction. At the same time, the use of triethylamine as an acid scavenger can effectively absorb the hydrochloric acid generated during the condensation process of the acyl chloride, prevent the occurrence of side reactions, and ensure the integrity of the main chain structure.

[0023] Controlling the initial reaction under ice bath conditions can reduce the reaction rate and inhibit side reactions, especially the premature reaction of chloromethyl groups, thereby better retaining the active sites required for subsequent grafting; and controlling the main reaction temperature in a mild range of 20~30℃ is conducive to the smooth progress of the polycondensation reaction, and ultimately forms a linear aromatic amide main chain with chloromethyl side groups, which provides high reaction efficiency and spatial site accessibility for the subsequent selective grafting of imidazole, phosphonic acid groups, and phosphonate groups, thereby enhancing the structural stability and modification efficiency of the final membrane material.

[0024] In some embodiments, in step S3, the imidazole compound includes 1-(2-hydroxyethyl)imidazole; The hydroxyphosphonic acid compound includes 2-hydroxyethanephosphonic acid; The hydroxyphosphonate compound includes 1,3-propylene glycol grafted 2-bromoethylphosphonate diethyl, and the 1,3-propylene glycol grafted 2-bromoethylphosphonate diethyl is obtained by a nucleophilic substitution reaction between a hydroxyl group at one end of 1,3-propylene glycol and 2-bromoethylphosphonate diethyl.

[0025] In some of the above embodiments, the imidazole compound is preferably 1-(2-hydroxyethyl)imidazole, in which the imidazole ring does not have an NH structure, and it undergoes nucleophilic substitution reaction only through the hydroxyl group on the side chain and the chloromethyl group on the polymer backbone. Compared with imidazole or 4-hydroxyethylimidazole, its reaction pathway is simpler and more controllable, avoiding the problem of unbalanced grafting ratio due to the higher reactivity of NH than hydroxy in the co-grafting system, thereby facilitating the uniform grafting of the three proton-conducting structures and forming a proton-conducting network with reasonable distribution and structural synergy.

[0026] The hydroxyphosphonic acid compound is preferably 2-hydroxyethanephosphonic acid, which contains both ionizable phosphonic acid groups and hydroxyl groups in its molecular structure. The phosphonic acid group acts as a stable proton donor and can maintain efficient proton release under anhydrous or low-humidity conditions. The hydroxyl group can react with a chloromethyl group to be introduced into the side chain to achieve covalent anchoring of the phosphonic acid group, thereby avoiding the problems of proton source migration and loss in traditional phosphonic acid doping systems.

[0027] The hydroxyphosphonate compound is preferably 1,3-propylene glycol grafted with diethyl 2-bromoethylphosphonate, obtained by a nucleophilic substitution reaction between the hydroxyl group at one end of 1,3-propylene glycol and diethyl 2-bromoethylphosphonate. Compared with using ethylene glycol and 1,4-butanediol as nucleophilic substitution reagents, 1,3-propylene glycol has a more suitable flexible chain segment length and spatial configuration. While ensuring moderate spacing between phosphonate groups, it can induce proton-conducting groups to form a local enrichment structure in the membrane, enhance microphase separation drive, and thus construct a more continuous proton migration channel. The short ethylene glycol chain segment is not conducive to regulating the spacing between polar domains and making it difficult to guide orderly arrangement. The excessively long 1,4-butanediol chain segment may cause the polar groups to disperse too far, weakening the continuity of the conduction path. The use of a 1,3-propylene glycol structure can achieve a better balance between proton conduction ability and structural order, thereby improving the conductivity and stability of the proton exchange membrane under high temperature conditions.

[0028] In summary, the synergistic grafting of the three structures not only ensures the stable coexistence of proton donors and acceptors in the membrane material, but also realizes the uniform construction and synergistic conduction of the microscopic conductive network through structural selectivity, reaction path separation and flexible chain segment regulation, thereby significantly improving the proton conductivity of the membrane under room temperature and high temperature conditions.

[0029] In some embodiments, the 1,3-propylene glycol-grafted diethyl 2-bromoethylphosphonate is prepared by the following method: 1,3-propylene glycol and diethyl 2-bromoethylphosphonate are added in a molar ratio of 1.01 to 1.1 to an anhydrous polar solvent (such as N,N-dimethylformamide or N-methylpyrrolidone) containing a basic catalyst (such as potassium carbonate, added in an amount of 1.5 to 2 times the molar amount of diethyl 2-bromoethylphosphonate); the reaction is stirred at 60 to 80°C under nitrogen for 8 to 12 hours, causing the hydroxyl group of the 1,3-propylene glycol to undergo nucleophilic substitution reaction with the bromoethyl group in the phosphonate. By controlling the amount of 1,3-propylene glycol and using potassium carbonate as a catalyst, the main product is a single-end grafted phosphonate structure. After the reaction, the solvent is removed by vacuum distillation or rotary evaporation, the reactants are dissolved in ethyl acetate, the inorganic salts are filtered off, and then dried to obtain the 1,3-propylene glycol-grafted diethyl 2-bromoethylphosphonate.

[0030] In some embodiments, step S3 specifically includes: 10 parts of the chloromethylated polyaromatic amide are dispersed in 150-300 parts of N-methylpyrrolidine, 2-4 parts of an imidazole compound, 2-4 parts of a hydroxyphosphonic acid compound and 3-5 parts of a hydroxyphosphonate compound are added, and then 4-6 parts of potassium carbonate are added. The mixture is reacted at 60-80° C. under a nitrogen atmosphere for 10-14 hours to obtain a modified polyaromatic amide.

[0031] In some of the above embodiments, the reaction process parameters can effectively ensure the uniform grafting of the three types of functional groups on the side groups of the polyaromatic amide main chain. N-methylpyrrolidine has high polarity and solubility, which can stably disperse the polyaromatic amide matrix containing chlorine functional groups and promote the balanced concentration of imidazoles, hydroxyphosphonic acids and hydroxyphosphonate compounds around the polymer chain. Controlling the addition ratio of various nucleophiles within a reasonable range can effectively avoid the phenomenon of excessive or insufficient grafting of a certain type of group due to competitive reactions, ensuring the coordinated distribution and functional complementarity of the proton-conducting structure in the membrane; the reaction temperature is controlled in the range of 60-80°C, which is conducive to activating the nucleophilic substitution reaction of the chloromethyl group; the reaction time is controlled in the range of 10-14 hours, which can fully carry out the grafting reaction and improve the efficiency and stability of the group grafting. The addition of potassium carbonate as a mild alkaline catalyst can not only promote the deprotonation of alcohols and imidazoles to generate nucleophiles, but also inhibit the occurrence of side reactions, which helps to improve the functional group grafting selectivity and the chemical stability of the membrane.

[0032] Through the above-mentioned process conditions, efficient covalent grafting of three types of proton-conducting structures can be achieved, further improving the distribution uniformity of proton-conducting segments in modified polyarylamide and the efficiency of constructing migration channels, thereby enhancing the proton conductivity of the proton exchange membrane.

[0033] In some embodiments, the diaminobenzaldehyde includes 2,4-diaminobenzaldehyde.

[0034] In some embodiments, the aromatic dichloride includes at least one of terephthaloyl chloride and isophthaloyl chloride. Based on the above embodiments, different aromatic dichloride structures will affect the segment configuration and orientation of the polyaramid. Terephthaloyl chloride can form linear rigid segments, improving the thermal and dimensional stability of the polymer; isophthaloyl chloride imparts a certain degree of twist to the segments, which helps enhance the flexibility and solubility of the main chain, facilitates a more uniform segment distribution during the cast film process, and improves the processability and density of the film. Selecting the type of aromatic dichloride according to specific application requirements can optimize its film-forming performance and adaptability to the proton-conducting structure while maintaining the strength of the film skeleton.

[0035] In some embodiments, the solid content of the slurry is 10wt%~15wt%, and the wet film thickness obtained by the slurry casting is 150~200μm. Based on the above embodiment, controlling the solid content and wet film thickness of the slurry can effectively adjust the dry film thickness and microstructural density of the final film. A solid content of 10wt%~15wt% helps to form a suitable viscosity range, ensure uniform spreading and good leveling during the casting process, and avoid defects such as holes or uneven thickness in the film; if the wet film thickness is controlled in the range of 150~200μm, a final film thickness of 25~40μm can be obtained after drying, which has both low resistance and mechanical support capabilities, and is suitable for the assembly requirements of fuel cells. Reasonable film thickness control can also enhance the directional arrangement of the proton-conducting segments inside the membrane, which helps to build a more continuous proton migration path.

[0036] In a second aspect, the present application provides a proton exchange membrane for a hydrogen fuel cell, which is a proton exchange membrane prepared according to the method described in any embodiment of the first aspect.

[0037] According to the present application, the proton exchange membrane maintains high proton conductivity at both room and high temperatures, making it suitable for stable operation of hydrogen fuel cells over a wide operating temperature range. In the membrane structure, the polyaramid backbone forms a skeletal framework with excellent thermal and dimensional stability. The grafted imidazole, hydroxyphosphonic acid, and hydroxyphosphonate groups form a synergistic proton-conducting network within the membrane, enhancing the efficiency and path continuity of proton migration, resulting in excellent proton conductivity.

[0038] In a third aspect, the present application provides a hydrogen fuel cell, characterized in that it includes the proton exchange membrane described in any embodiment of the second aspect.

[0039] According to the present application, the hydrogen fuel cell uses the proton exchange membrane constructed by the above-mentioned synergistic grafting structure as the electrolyte membrane layer to achieve efficient and stable proton conduction between the anode and the cathode. In high temperature or low humidity working environments, the ion channels at the membrane-electrode interface can still be maintained unobstructed and the internal resistance is low, which significantly improves the energy conversion efficiency and environmental adaptability of the fuel cell. The fuel cell is suitable for high-temperature proton exchange membrane fuel cell systems, and can also be used in special scenarios that require long-term high-temperature operation or high cold start performance requirements, such as vehicles, backup power supplies, and distributed energy systems.

[0040] Compared with the prior art, the present invention has the following advantages: 1. This application adopts a main chain-side chain structure design. The main chain provides a thermally stable skeleton, and three types of side chain proton-conducting structures (imidazole, hydroxyphosphoric acid, and hydroxyphosphoric acid ester) synergistically construct a proton conduction network to achieve stability and directionality control of the conduction path at the molecular scale.

[0041] 2. All the grafted proton-conducting groups in this application are covalently anchored, which avoids the common problems of proton-conducting material loss and migration in the doping system, and significantly improves the stability and durability of the proton exchange membrane.

[0042] 3. Each proton-conducting structure is uniformly grafted through molecular structure design and reaction path separation. The arrangement of conductive groups is regulated by flexible chain segments, which effectively induces microphase separation and enhances the continuity of proton migration channels, making the proton exchange membrane have better proton conductivity. DETAILED DESCRIPTION

[0043] The various embodiments or implementation schemes in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments.

[0044] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with an embodiment or example is included in at least one embodiment or example of the present application. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0045] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0046] In the description of this specification, unless otherwise specified, "parts" refer to "parts by mass".

[0047] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0048] 1-(2-Hydroxyethyl)imidazole, CAS number 1615-14-1; 4-Hydroxyethylimidazole, CAS number 872-82-2; Diethyl 2-bromoethylphosphonate, CAS number 5324-30-1; Dimethyl 2-hydroxyethylphosphonate, CAS number 54731-72-5.

[0049] Preparation Example 1 Preparation of 1,3-propylene glycol grafted diethyl 2-bromoethylphosphonate: In a 250 mL three-necked flask, 50 mL of N-methylpyrrolidone (NMP) was added as the reaction solvent. 10.0 g (approximately 40.8 mmol) of diethyl 2-bromoethylphosphonate and 3.27 g (approximately 42.8 mmol) of 1,3-propylene glycol were then added sequentially. Subsequently, 10.1 g (approximately 73.4 mmol) of potassium carbonate was added as a catalyst. The reaction system was stirred at 70°C under a nitrogen atmosphere for 10 h. After completion of the reaction, the system was cooled to room temperature, and the solvent was removed by rotary evaporation under reduced pressure. The residue was dissolved in excess ethyl acetate, filtered to remove inorganic salts, and the filtrate was concentrated under reduced pressure and dried to yield diethyl 2-bromoethylphosphonate grafted onto 1,3-propylene glycol.

[0050] Preparation Example 2 Preparation of ethylene glycol grafted diethyl 2-bromoethylphosphonate: In a 250 mL three-necked flask, 50 mL of N-methylpyrrolidone (NMP) was added as the reaction solvent. 10.0 g (approximately 40.8 mmol) of diethyl 2-bromoethylphosphonate and 2.65 g (approximately 42.8 mmol) of ethylene glycol were then added sequentially. Subsequently, 10.1 g (approximately 73.4 mmol) of potassium carbonate was added as a catalyst. The reaction system was stirred at 70°C under a nitrogen atmosphere for 10 h. After completion of the reaction, the system was cooled to room temperature, and the solvent was removed by rotary evaporation under reduced pressure. The residue was dissolved in excess ethyl acetate, and the inorganic salts were removed by filtration. The filtrate was concentrated under reduced pressure and dried to obtain ethylene glycol-grafted diethyl 2-bromoethylphosphonate.

[0051] Preparation Example 3 Preparation of 1,4-butanediol grafted diethyl 2-bromoethylphosphonate: In a 250 mL three-necked flask, 50 mL of N-methylpyrrolidone (NMP) was added as the reaction solvent. 10.0 g (approximately 40.8 mmol) of diethyl 2-bromoethylphosphonate and 3.86 g (approximately 42.8 mmol) of 1,4-butanediol were then added sequentially. Subsequently, 10.1 g (approximately 73.4 mmol) of potassium carbonate was added as a catalyst. The reaction system was stirred at 70°C under a nitrogen atmosphere for 10 h. After completion of the reaction, the system was cooled to room temperature, and the solvent was removed by rotary evaporation under reduced pressure. The residue was dissolved in excess ethyl acetate, filtered to remove inorganic salts, and the filtrate was concentrated under reduced pressure and dried to yield diethyl 2-bromoethylphosphonate grafted onto 1,4-butanediol.

[0052] Example 1

[0053] Preparation of proton exchange membranes for hydrogen fuel cells: In a 500 mL three-necked flask, 13.6 g of 2,4-diaminobenzaldehyde (molecular weight 136.15 g / mol, approximately 0.1 mol) and 160 mL of methanol were added and dissolved under stirring. In an ice bath, 3.8 g of sodium borohydride (molecular weight 37.83 g / mol, approximately 0.105 mol) was slowly added. After complete addition, the mixture was stirred at 25°C for 2 h. After completion of the reaction, the pH of the reaction system was adjusted to 7.0 with dilute hydrochloric acid, and the methanol solvent was removed by vacuum rotary evaporation to obtain the intermediate product, 2,4-diaminobenzyl alcohol. This product was redissolved in 100 mL of dichloromethane, and 13 g of thionyl chloride (molecular weight 118.97 g / mol, 0.109 mol) and 0.4 mL of N,N-dimethylformamide were slowly added dropwise in an ice bath. After complete addition, the reaction temperature was raised to 40°C, and the mixture was stirred for 3 h. After the reaction is completed, the reaction solution is poured into 400 mL of ice water and stirred to precipitate a solid, which is then washed thoroughly with cold water until the pH of the washing solution is close to neutral. The resulting solid is purified by suction filtration and recrystallization from ethanol, and then dried in a vacuum drying oven at 50 ° C for 8 h to obtain a chloromethylated phenylenediamine solid.

[0054] Weigh 7.85 g (approximately 0.05 mol) of the chloromethylated phenylenediamine obtained above and dissolve it in 80 mL of N,N-dimethylacetamide. Cool in an ice bath. Add dropwise a solution of 10.5 g (approximately 0.052 mol) of phthaloyl chloride in 30 mL of N,N-dimethylacetamide. Add 10.1 g (approximately 0.10 mol) of triethylamine as an acid acceptor. After the addition is complete, stir and react at 25°C for 10 h. The resulting polymer is precipitated with ethanol and filtered. The filter cake is washed with diethyl ether to obtain chloromethylated poly(o-phthalamide), which is then vacuum-dried for later use.

[0055] 10 g of the chloromethylated poly(o-phthalamide) obtained above was weighed and dispersed in 200 mL of N-methylpyrrolidine. 2.24 g of 1-(2-hydroxyethyl)imidazole, 2.6 g of 2-hydroxyethanephosphonic acid, and 3.24 g of 1,3-propylene glycol-grafted diethyl 2-bromoethylphosphonate were added and mixed thoroughly. 5 g of potassium carbonate was then added and stirred at 70°C under a nitrogen atmosphere for 12 hours. After the reaction solution cooled, the N-methylpyrrolidine was recovered by rotary evaporation. 300 mL of ethyl acetate was poured into the concentrated solution to precipitate the polymer. The solid was isolated by filtration, washed with ethyl acetate and then anhydrous ether, and finally dried under vacuum to obtain the modified polyarylamide.

[0056] Weigh 4g of the modified polyarylamide obtained above and dissolve it in 30g of N-methylpyrrolidine. Stir overnight to form a uniform slurry. Apply the slurry evenly to a clean glass plate using a 200μm wet film caster. Allow to stand at room temperature for 30 minutes, then vacuum dry at 60°C for 4 hours. Heat treat at 120°C for 2 hours to form a proton exchange membrane approximately 25μm thick.

[0057] Example 2

[0058] Preparation of proton exchange membranes for hydrogen fuel cells: The process is substantially the same as Example 1, except that an equal amount of imidazole is used instead of 1-(2-hydroxyethyl)imidazole.

[0059] Example 3

[0060] Preparation of proton exchange membranes for hydrogen fuel cells: The process is substantially the same as Example 1, except that an equal amount of 4-hydroxyethylimidazole is used instead of 1-(2-hydroxyethyl)imidazole.

[0061] Example 4

[0062] Preparation of proton exchange membranes for hydrogen fuel cells: The process is substantially the same as Example 1, except that an equal mass of ethylene glycol-grafted diethyl 2-bromoethylphosphonate is used instead of 1,3-propylene glycol-grafted diethyl 2-bromoethylphosphonate.

[0063] Example 5

[0064] Preparation of proton exchange membranes for hydrogen fuel cells: The process is substantially the same as Example 1, except that an equal mass of 1,4-butanediol-grafted diethyl 2-bromoethylphosphonate is used instead of 1,3-propylene glycol-grafted diethyl 2-bromoethylphosphonate.

[0065] Example 6

[0066] Preparation of proton exchange membranes for hydrogen fuel cells: The process is substantially the same as Example 1, except that an equal amount of dimethyl 2-hydroxyethylphosphonate is used instead of 1,3-propylene glycol to graft diethyl 2-bromoethylphosphonate.

[0067] Comparative Example 1 Preparation of proton exchange membranes for hydrogen fuel cells: The method is substantially the same as Example 1, except that the preparation process of the modified polyaramid is different, specifically: 10 g of the chloromethylated poly(o-phthalamide) obtained above was dispersed in 200 mL of N-methylpyrrolidine. 2.24 g of 1-(2-hydroxyethyl)imidazole and 5.84 g of 2-hydroxyethanephosphonic acid were added and mixed thoroughly. 5 g of potassium carbonate was then added and stirred at 70°C under a nitrogen atmosphere for 12 hours. After the reaction solution cooled, the N-methylpyrrolidine was recovered by rotary evaporation. 300 mL of ethyl acetate was poured into the concentrated solution to precipitate the polymer. The solid was isolated by filtration, washed with ethyl acetate and then anhydrous ether, and finally dried under vacuum to obtain the modified polyarylamide.

[0068] Comparative Example 2 Preparation of proton exchange membranes for hydrogen fuel cells: The method is substantially the same as Example 1, except that the preparation process of the modified polyaramid is different, specifically: 10g of the chloromethylated poly(o-phthalamide) obtained above was weighed and dispersed in 200mL of N-methylpyrrolidine. 2.24g of 1-(2-hydroxyethyl)imidazole and 5.84g of 1,3-propylene glycol grafted diethyl 2-bromoethylphosphonate were added and mixed thoroughly. 5g of potassium carbonate was then added and stirred at 70°C under a nitrogen atmosphere for 12 hours. After the reaction solution cooled, the N-methylpyrrolidine was recovered by rotary evaporation. 300mL of ethyl acetate was poured into the concentrated solution to precipitate the polymer. The solid was isolated by filtration, washed with ethyl acetate and then anhydrous ether, and finally dried under vacuum to obtain the modified polyarylamide.

[0069] Comparative Example 3 Preparation of proton exchange membranes for hydrogen fuel cells: The method is substantially the same as Example 1, except that the preparation process of the modified polyaramid is different, specifically: 10 g of the chloromethylated poly(o-phthalamide) obtained above was weighed and dispersed in 200 mL of N-methylpyrrolidine. 4.84 g of 2-hydroxyethanephosphonic acid and 3.24 g of 1,3-propylene glycol-grafted diethyl 2-bromoethylphosphonate were added and mixed thoroughly. 5 g of potassium carbonate was then added and stirred at 70°C under a nitrogen atmosphere for 12 hours. After the reaction solution cooled, the N-methylpyrrolidine was recovered by rotary evaporation. 300 mL of ethyl acetate was poured into the concentrated solution to precipitate the polymer. The solid was isolated by filtration, washed with ethyl acetate and then anhydrous ether, and finally dried under vacuum to obtain the modified polyarylamide.

[0070] Test section With reference to GB / T 20042.3-2022 "Proton exchange membrane fuel cells - Part 3: Test methods for proton exchange membranes", the proton conductivity σ1 of the proton exchange membranes prepared in each embodiment and comparative example was tested at 25°C and a relative humidity of 50%, and the proton conductivity σ2 at 80°C and a relative humidity of 30%. The results are shown in Table 1.

[0071] Table 1 <![CDATA[σ1(mS / cm)]]> <![CDATA[σ2(mS / cm) <!-- 8 -->]]> Example 1 147 165 Example 2 111 134 Example 3 122 140 Example 4 136 151 Example 5 116 133 Example 6 125 142 Comparative Example 1 75 92 Comparative Example 2 85 99 Comparative Example 3 82 95 According to Table 1, each embodiment shows higher proton conductivity than comparative examples 1 to 3 under both room temperature and high temperature conditions, indicating that the proton exchange membrane provided by the present application has better proton conductivity under both room temperature and high temperature conditions, and is suitable for wide temperature range fuel cell applications. The possible reasons are: in comparative example 1, the lack of phosphate structure causes the proton conduction path in the membrane to mainly rely on the "acid-base pair" between imidazole and phosphonic acid, lacks segment flexibility regulation and conductive channel structure construction, and the proton migration efficiency is limited; in comparative example 2, the lack of phosphate groups to provide a stable proton source, although phosphate is grafted, the lack of donor-acceptor synergistic mechanism limits the proton concentration and migration efficiency; in comparative example 3, the lack of imidazole proton acceptor structure means that there is only a weak hydrogen bond conduction path between phosphoric acid and phosphate groups in the membrane, and the proton conduction efficiency is significantly reduced.

[0072] In addition, the proton conductivity of the proton exchange membrane provided by this application at 80°C and 30% RH is generally higher than that at 25°C and 50% RH, in contrast to conventional proton membranes that rely on hydration, demonstrating the excellent high-temperature anhydrous proton conductivity of this membrane material. The main reason for this may be that this application constructs a proton-conducting network by synergistically grafting imidazole structures, phosphate structures, and phosphate flexible chain segments. Under high temperature environments, these structural units can form stable hopping migration paths through non-aqueous hydrogen bond coupling mechanisms, and the proton migration rate is accelerated due to increased temperature, thereby improving overall conductivity. In contrast, traditional proton membranes such as Nafion mainly rely on the migration of hydrated proton clusters formed by sulfonic acid groups and water. Under high temperature and low humidity conditions, water loss causes migration chain breakage and a sharp drop in proton migration efficiency. However, the structural design of this membrane weakens its dependence on hydration and instead relies on covalently anchored proton-conducting structures and the continuous polar channels they construct to achieve conduction. Therefore, it actually exhibits higher proton conductivity under high temperature and low humidity environments.

[0073] Examples 1-3 show that when the imidazole structure is replaced by imidazole (Example 2) or 4-hydroxyethylimidazole (Example 3), the membrane's proton conductivity decreases significantly, indicating that the preferred use of 1-(2-hydroxyethyl)imidazole can improve the overall conductivity of the proton exchange membrane. This is because the 1-(2-hydroxyethyl)imidazole structure lacks NH sites, resulting in a single, controllable reaction pathway. Under co-grafting conditions, competitive preferential grafting is avoided, preventing an imbalance in the proportions of the various groups. This results in a uniform distribution of the three proton-conducting structures throughout the membrane and enhances the synergistic conductivity. In contrast, imidazole and 4-hydroxyethylimidazole, due to their NH content and high reactivity, can lead to a disordered grafting sequence and reduced structural uniformity.

[0074] Examples 1, 4, and 6 demonstrate that, while maintaining the imidazole and phosphoric acid structures, the selection of phosphonate groups with different structures significantly influences membrane performance. Example 1 (1,3-propylene glycol grafting) exhibits the highest conductivity, demonstrating that its chain segment flexibility and spatial configuration are more suitable for inducing localized enrichment of polar groups. Example 4 (ethylene glycol grafting) exhibits slightly lower conductivity due to its relatively short chain segments and weaker structural regulation. Example 5 (1,4-butanediol grafting) exhibits relatively long chain segments, resulting in a dispersed distribution of polar groups and poor channel connectivity. Example 6 (phosphate monomer) lacks flexible chain segment regulation, resulting in a random distribution of polar groups and discontinuous proton-conducting pathways, resulting in lower conductivity. This suggests that selecting a phosphonate structure with moderately flexible chain length and spatial configuration can achieve a balance between conductivity and structural order in the construction of a proton-conducting network, thereby improving the proton conductivity of the proton exchange membrane.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a proton exchange membrane for a hydrogen fuel cell, characterized in that: The following steps are involved: S1: The aldehyde group in diaminobenzaldehyde is reduced with sodium borohydride and then reacted with thionyl chloride to convert the aldehyde group in diaminobenzaldehyde into chloromethyl to obtain chloromethylated aromatic diamine; S2: reacting the chloromethylated aromatic diamine with aromatic diacyl chloride to cause a polycondensation reaction between the chloromethylated aromatic diamine and the aromatic diacyl chloride to obtain a chloromethylated polyaromatic amide; S3: reacting the chloromethylated polyaromatic amide with an imidazole compound, a hydroxyphosphonic acid compound, and a hydroxyphosphonate compound, so that the imidazole compound, the hydroxyphosphonic acid compound, and the hydroxyphosphonate compound undergo a nucleophilic substitution reaction with the chloromethyl group on the chloromethylated polyaromatic amide to obtain a modified polyaromatic amide; S4: dissolving the modified polyaromatic amide in an organic solvent to obtain a slurry, and casting the slurry into a membrane to obtain a proton exchange membrane.

2. The method according to claim 1, characterized in that In step S1, the molar ratio of diaminobenzaldehyde, sodium borohydride and thionyl chloride is 1:(1.01-1.1):(1.01-1.2).

3. The method according to claim 2, characterized in that The step S1 comprises: Diaminobenzaldehyde is dissolved in methanol, sodium borohydride is added under ice bath conditions, and the reaction is carried out at 20-30°C for 1-3 hours. After the reaction, the pH is adjusted to 6.5-7.5, and the solvent is removed by rotary evaporation to obtain diaminobenzyl alcohol; the diaminobenzyl alcohol is dissolved in dichloromethane, thionyl chloride and a catalytic amount of N,N-dimethylformamide are added under ice bath conditions, and the reaction is carried out at 30-50°C for 2-4 hours to obtain a chloromethylated aromatic diamine.

4. The method according to claim 1, wherein In the step S2, the molar ratio of the chloromethylated aromatic diamine to the aromatic diacyl chloride is 1:(1-1.1).

5. The method according to claim 4, characterized in that The step S2 comprises: The chloromethylated aromatic diamine and aromatic dichloride are respectively dissolved in N,N-dimethylacetamide to obtain a diamine solution and a dichloride solution. Triethylamine is added to the diamine solution, and then the dichloride solution is added in an ice bath. The mixture is reacted at 20-30° C. for 8-12 hours to obtain a chloromethylated polyaromatic amide.

6. The method according to claim 1, characterized in that In step S3, the imidazole compound includes 1-(2-hydroxyethyl)imidazole; The hydroxyphosphonic acid compound includes 2-hydroxyethanephosphonic acid; The hydroxyphosphonate compound includes 1,3-propylene glycol grafted 2-bromoethylphosphonate diethyl, and the 1,3-propylene glycol grafted 2-bromoethylphosphonate diethyl is obtained by a nucleophilic substitution reaction between a hydroxyl group at one end of 1,3-propylene glycol and 2-bromoethylphosphonate diethyl.

7. The method according to claim 6, characterized in that The step S3 specifically includes: 10 parts of the chloromethylated polyaromatic amide are dispersed in 150-300 parts of N-methylpyrrolidine, 2-4 parts of an imidazole compound, 2-4 parts of a hydroxyphosphonic acid compound and 3-5 parts of a hydroxyphosphonate compound are added, and then 4-6 parts of potassium carbonate are added. The mixture is reacted at 60-80° C. under a nitrogen atmosphere for 10-14 hours to obtain a modified polyaromatic amide.

8. The method according to any one of claims 1 to 7, characterized in that The method satisfies at least one of the following conditions: 1) The diaminobenzaldehyde includes 2,4-diaminobenzaldehyde; 2) The aromatic diacyl chloride comprises at least one of terephthaloyl chloride and isophthaloyl chloride; 3) In step S4, the solid content of the slurry is 10 wt% to 15 wt%, and the thickness of the wet film obtained by the slurry casting is 150 to 200 μm.

9. A proton exchange membrane for a hydrogen fuel cell, characterized in that: A proton exchange membrane prepared according to the method according to any one of claims 1 to 8.

10. A hydrogen fuel cell, characterized in that: Comprising the proton exchange membrane according to claim 9.