A proton exchange membrane for a hydrogen fuel cell and a method of manufacturing the same, and a hydrogen fuel cell

Abstract

The application provides a proton exchange membrane for a hydrogen fuel cell and a preparation method thereof and the hydrogen fuel cell, and the method comprises the following steps: S1: after an aldehyde group in diaminobenzaldehyde is reduced by sodium borohydride, the diaminobenzaldehyde is reacted with thionyl chloride to obtain a chloromethylated aromatic diamine; S2: the chloromethylated aromatic diamine is reacted with aromatic dichloride to obtain a chloromethylated polyaromatic amide; S3: the chloromethylated polyaromatic amide is reacted with an imidazole compound, a hydroxyphosphonic acid compound and a hydroxyphosphonate compound to obtain a modified polyaromatic amide; and S4: the modified polyaromatic amide is dissolved in an organic solvent to obtain a slurry, and the slurry is cast into a membrane to obtain the proton exchange membrane. The proton exchange membrane prepared through the above steps can maintain good proton conductivity in normal temperature and high temperature environments, and is suitable for stable operation of the hydrogen fuel cell in a wide working temperature range.

Description

TECHNICAL FIELD

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

[0002] Proton exchange membrane (PEM) is a core component in hydrogen fuel cells, and its main function is to conduct protons between the anode and the cathode while blocking electrons and fuel gas. Its performance directly affects the energy conversion efficiency, working temperature window and service life of the fuel cell. The current commercialized fuel cell widely uses perfluorosulfonic acid resin (such as Nafion®) as the proton exchange membrane, which exhibits good proton conductivity and chemical stability in low temperature and high humidity environments.

[0003] However, the existing perfluorosulfonic acid type proton exchange membrane mainly relies on the hydration mechanism of sulfonic acid groups to realize proton conduction, which leads to a significant decrease in proton conduction ability in high temperature (> 100℃) or low humidity environments, severely limiting the working temperature window and system cold start performance of the hydrogen fuel cell. In addition, the micro-phase structure of such membranes is highly uncontrollable, and the thermal stability and mechanical properties of the membrane body decrease rapidly, which can easily cause problems such as dehydration and brittle fracture, and ion channel collapse during actual service.

[0004] In order to overcome the above problems, some research has attempted to develop sulfonic acid modified aromatic polymer membranes or composite membranes (such as sulfonated polyether ether ketone, sulfonated polybenzimidazole, etc.), but these systems still rely on hydration, and their proton conduction mechanism is difficult to maintain under high temperature and water-free conditions. Some other technologies use non-hydrated proton donor structures to improve high temperature performance, but the proton conduction chain segments in these systems lack coordinated structural design, and the ion channels lack continuity and separation driving mechanism, which usually limits the improvement of conductivity.

[0005] Therefore, how to improve the proton conductivity of the proton exchange membrane in high temperature environments while ensuring its thermal stability and structural integrity is a technical problem that needs to be solved in the current field. SUMMARY

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

[0007] In a first aspect, the present application provides a method for preparing a proton exchange membrane for hydrogen fuel cells, comprising the following steps:

[0008] S1: reducing the aldehyde group in the diaminobenzaldehyde with sodium borohydride and then reacting with thionyl chloride to convert the aldehyde group on the diaminobenzaldehyde into a chloromethyl group, thereby obtaining a chloromethylated aromatic diamine;

[0009] S2: reacting the chloromethylated aromatic diamine with an aromatic diacyl chloride to cause a polycondensation reaction between the chloromethylated aromatic diamine and the aromatic diacyl chloride, thereby obtaining a chloromethylated polyaramide;

[0010] S3: reacting the chloromethylated polyaramide with an imidazole compound, a hydroxyphosphonic acid compound, and a hydroxyphosphonate compound to cause a nucleophilic substitution reaction between the imidazole compound, the hydroxyphosphonic acid compound, and the hydroxyphosphonate compound and the chloromethyl group on the chloromethylated polyaramide, thereby obtaining a modified polyaramide;

[0011] S4: dissolving the modified polyaramide in an organic solvent to obtain a slurry, and casting the slurry into a film to obtain a proton exchange membrane.

[0012] According to the present application, the proton exchange membrane prepared through the above steps can maintain good proton conductivity in both normal temperature and high temperature environments, and is suitable for stable operation of a hydrogen fuel cell in a wide working temperature range.

[0013] Specifically, in step S1, the aldehyde group in the diaminobenzaldehyde is reduced with sodium borohydride and then reacted with thionyl chloride to convert the aldehyde group on the diaminobenzaldehyde into a chloromethyl group, thereby obtaining a chloromethylated aromatic diamine. This step first reduces the aldehyde group to a hydroxymethyl group, and then reacts with thionyl chloride to generate a chloromethyl group, thereby imparting the aromatic diamine with controllable distribution of side chain reaction sites. This step lays the foundation for the subsequent grafting of side chain functional groups, so that the proton conducting structure can retain active sites before the main chain polymerization, thereby improving the grafting efficiency and reaction uniformity.

[0014] In step S2, the aromatic diamine is polycondensed with the aromatic diacyl chloride to form a rigid aromatic amide skeleton, and the polymer main chain has high thermal stability and chemical inertness, which is conducive to maintaining the structural integrity and dimensional stability of the membrane material in a high-temperature and water-free environment. At the same time, the chloromethyl side group remaining on the polymer main chain provides controllable active sites for grafting the proton conducting structure.

[0015] Step S3 is the key to achieve high proton conductivity. By grafting three types of compounds containing proton-conducting functional groups onto the side chains of the polymer main chain, a multi-point synergistic proton-conducting structure is formed inside the membrane material; among them, the imidazole structure has proton accepting ability, can adsorb and transfer protons under anhydrous or low humidity conditions, and forms a dynamic proton hopping path between the ring nitrogen atoms, which is the core of maintaining the conductivity under high temperature conditions; the hydroxyphosphonic acid structure provides a stable proton donor, and through the hydrogen ionizable on the phosphonic acid group and the imidazole to form a hydrogen bond coupling system, the proton can be efficiently transferred between the donor-acceptor system, and the available concentration of protons in the membrane is improved; the hydroxyphosphonate structure not only provides a source of protons, but also its flexible segment can adjust the distribution and spacing of various proton-conducting groups in the membrane, which helps to induce the formation of a microphase separation structure, promotes the local enrichment of polar proton-conducting groups, and constructs a continuous ion migration channel.

[0016] Thus, in the modified polyarylamide, the modified imidazole and phosphonic acid form a proton "acid-base pair" complex structure to achieve short-range and medium-range proton hopping; at the same time, the flexible segment of the phosphonate adjusts the arrangement and orientation of the local segment, improving the continuity of the proton migration direction; the three are combined to build a stable and directional proton-conducting network inside the membrane body, so that the membrane material still maintains excellent proton conductivity in a high-temperature, low-humidity environment.

[0017] In step S4, a dense and continuous membrane body is formed on a macroscopic scale by a solution casting method, while the enrichment structure of the polar segment on a microscopic scale is retained, realizing the construction of a multi-scale synergistic proton-conducting network. This structure ensures the uniformity and mechanical strength of the membrane during film formation, and further promotes the stability and conduction efficiency of the ion channel morphology.

[0018] In summary, through the synergistic grafting design of main chain-side chain partition structure and three types of proton-conducting groups, the obtained proton exchange membrane has high thermal stability and high-temperature proton conductivity, and is suitable for efficient operation of hydrogen fuel cells in a wide temperature range.

[0019] In some embodiments, in step S1, the molar ratio of the diaminobenzaldehyde, sodium borohydride and thionyl chloride is 1:(1.01-1.1):(1.01-1.2).

[0020] In some of the above embodiments, the molar ratio of diaminobenzaldehyde to sodium borohydride is controlled in the range of 1:1.01-1.1 to reduce the aldehyde group to a hydroxyl group; at the same time, the molar ratio of thionyl chloride is controlled in the range of 1.01-1.2 to ensure the effective introduction of chloromethyl group and avoid side reactions caused by excessive thionyl chloride (such as incomplete reaction or excessive halogenation). The control of the molar ratio makes each step of the reaction efficient and controllable, ensuring the purity and reaction uniformity of the final chloromethylated aromatic diamine structure.

[0021] In some embodiments, the step S1 comprises:

[0022] The diaminobenzaldehyde is dissolved in methanol, sodium borohydride is added under ice bath conditions, and the reaction is carried out at 20-30°C for 1-3h. After the reaction is completed, 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, and thionyl chloride and a catalytic amount of N,N-dimethylformamide are added under ice bath conditions. The reaction is carried out at 30-50°C for 2-4h to obtain a chloromethylated aromatic diamine.

[0023] In some of the above embodiments, the aldehyde group in diaminobenzaldehyde is effectively reduced to a hydroxymethyl group by sodium borohydride reduction reaction. This process is carried out at a mild temperature condition (20-30°C), avoiding side reactions of amino groups and maintaining the activity of amino groups, thus providing high-reactivity raw materials for subsequent reactions. Subsequently, the hydroxymethyl group is effectively converted to a chloromethyl group under the action of thionyl chloride. This reaction is carried out at 30-50°C with N,N-dimethylformamide as catalyst, which can efficiently and selectively realize chloromethylation and avoid over-chlorination or side reactions by controlling the reaction conditions. Finally, a chloromethylated aromatic diamine is obtained, which provides high-quality starting materials for subsequent polymerization reactions.

[0024] In some embodiments, in the step S2, the molar ratio of the chloromethylated aromatic diamine to the aromatic diacyl chloride is 1:(1-1.1).

[0025] In some of the above embodiments, by controlling the molar ratio of the chloromethylated aromatic diamine to the aromatic diacyl chloride within the range of 1:(1-1.1), high conversion rate of the polymerization reaction and linearization control of the main chain structure are facilitated. When the aromatic diacyl chloride is slightly excessive, the residual end amino groups can be effectively reduced, the crosslinking tendency at the end of the reaction can be reduced, and the resulting polyaramide structure can be more regular and have a narrower molecular weight distribution. In addition, the chloromethylated aromatic diamine contains side chain active sites. To ensure that the chloromethyl side groups do not undergo side reactions or crosslinking during the polycondensation process, the polycondensation equilibrium needs to be controlled. A slight excess of acyl chloride can act as an end-capping agent to improve 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 subsequent graft modification reactions, thereby facilitating the obtaining of a proton exchange membrane with high proton conductivity.

[0026] In some embodiments, the step S2 comprises:

[0027] 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.

[0028] 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.

[0029] 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.

[0030] In some embodiments, in step S3, the imidazole compound includes 1-(2-hydroxyethyl)imidazole;

[0031] The hydroxyphosphonic acid compound includes 2-hydroxyethanephosphonic acid;

[0032] 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.

[0033] 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.

[0034] The hydroxyphosphonic acid compound is preferably 2-hydroxyethane phosphonic acid, which contains both an ionizable phosphonic acid group and a hydroxyl group in the molecular structure. The phosphonic acid group acts as a stable proton donor, which can maintain high proton release efficiency under anhydrous or low humidity conditions. The hydroxyl group can react with the chloromethyl group to introduce it into the side chain, achieving covalent anchoring of the phosphonic acid group, thereby avoiding the problems of proton source migration and loss in traditional phosphonic acid doping systems.

[0035] The hydroxyphosphonic acid compound is preferably 1,3-propanediol grafted 2-bromoethyl phosphonic acid diethyl ester, which is obtained by nucleophilic substitution reaction of the hydroxyl group at one end of 1,3-propanediol with 2-bromoethyl phosphonic acid diethyl ester. Compared with using ethylene glycol or 1,4-butanediol as a nucleophilic substitution reagent, 1,3-propanediol has a more suitable flexible segment length and spatial configuration, which can ensure a moderate distance between phosphonate groups while inducing the formation of a local enrichment structure of the proton-conducting group in the membrane body, enhancing the driving force of microphase separation, and further constructing a more continuous proton migration channel. The ethylene glycol segment is too short to be conducive to the regulation of the distance between the polar domains, making it difficult to guide the ordered arrangement. The 1,4-butanediol segment is too long, which may cause the polar groups to be dispersed too far apart, weakening the continuity of the conduction path. The use of 1,3-propanediol structure can achieve a better balance between proton conduction ability and structural order, thereby improving the proton conductivity and stability of the proton exchange membrane under high temperature conditions.

[0036] 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 micro-conduction network through structural selectivity, reaction path separation and flexible segment adjustment, thereby significantly improving the proton conductivity of the membrane under normal and high temperature conditions.

[0037] In some embodiments, the 1,3-propanediol grafted 2-bromoethyl phosphonic acid diethyl ester is prepared by the following method: 1,3-propanediol and 2-bromoethyl phosphonic acid diethyl ester are added to an anhydrous polar solvent (such as N,N-dimethylformamide or N-methyl pyrrolidone) containing a basic catalyst at a molar ratio of (1.01-1.1):1, the catalyst is potassium carbonate, and the addition amount is 1.5-2 times the molar amount of 2-bromoethyl phosphonic acid diethyl ester; the reaction is carried out under nitrogen protection at 60-80°C for 8-12h, the hydroxyl group of 1,3-propanediol undergoes nucleophilic substitution reaction with the bromoethyl group in the phosphonate, and by controlling the amount of 1,3-propanediol and using potassium carbonate as the catalyst, the main product is a single-end grafted phosphonate structure. After the reaction is completed, the solvent is removed by reduced pressure distillation or rotary evaporation, the reactants are dissolved in ethyl acetate, the inorganic salt is filtered off, and then dried to obtain 1,3-propanediol grafted 2-bromoethyl phosphonic acid diethyl ester.

[0038] In some embodiments, the step S3 specifically comprises:

[0039] The 10 parts of the chloromethylated polyarylamide 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 4-6 parts of potassium carbonate is added, and the reaction is carried out at 60-80°C for 10-14 hours under a nitrogen atmosphere to obtain the modified polyarylamide.

[0040] In some of the above embodiments, the reaction process parameters can effectively ensure uniform grafting of the three types of functional groups on the side groups of the polyarylamide main chain. N-methylpyrrolidine has high polarity and solubility, can stably disperse the chloro-functional group-containing polyarylamide matrix, and promote the concentration balance of imidazole, hydroxyphosphonic acid, and hydroxyphosphonate compounds around the polymer chain, control the addition ratio of each type of nucleophile in a reasonable range, and effectively avoid the phenomenon of excessive or insufficient grafting of a certain type of group due to competition reaction, ensuring that the proton-conducting structure achieves synergistic distribution and functional complementation in the membrane body; the reaction temperature is controlled in the range of 60-80°C, which is beneficial to activate the nucleophilic substitution reaction of chloromethyl; the reaction time is controlled in the range of 10-14h, which can make the grafting reaction proceed fully, improve the grafting efficiency and stability of the groups. The addition of potassium carbonate as a mild basic catalyst not only promotes the deprotonation of alcohols and imidazoles to generate nucleophiles, but also inhibits the occurrence of side reactions, which helps to improve the grafting selectivity of functional groups and the chemical stability of the membrane body.

[0041] Through the above process conditions, covalent and efficient grafting of the three types of proton-conducting structures can be achieved, further improving the uniformity of the distribution of the proton-conducting segments in the modified polyarylamide and the construction efficiency of the migration channel, thereby enhancing the proton conductivity of the proton exchange membrane.

[0042] In some embodiments, the diamino benzaldehyde includes 2,4-diamino benzaldehyde.

[0043] In some embodiments, the aromatic diacyl chloride includes at least one of terephthaloyl chloride and isophthaloyl chloride. Based on the above embodiments, different aromatic diacyl chloride structures will affect the segment configuration and orientation of the polyarylamide, terephthaloyl chloride can form linear rigid segments, improve the thermal stability and dimensional stability of the polymer; isophthaloyl chloride imparts a certain degree of twist to the segments, which is beneficial to enhancing the flexibility and solubility of the main chain, and helps to achieve more uniform segment distribution in the casting film forming process, improving the processability and density of the film. According to the specific application requirements, the type of aromatic diacyl chloride can be selected to optimize the film forming performance and adaptability of the proton-conducting structure while maintaining the strength of the membrane body skeleton.

[0044] In some embodiments, the solid content of the slurry is 10wt%-15wt%, and the wet film thickness obtained by casting the slurry into a film is 150-200 μm. Based on the above embodiments, the solid content and the wet film thickness of the slurry are controlled to effectively adjust the dry film thickness and the microstructure compactness of the final film. The solid content of 10wt%-15wt% helps to form a suitable viscosity range, ensuring uniform spreading and good leveling during the casting process, and avoiding defects such as holes or uneven thickness in the film. The wet film thickness is controlled in the range of 150-200 μm, so that the final film thickness of 25-40 μm can be obtained after drying, which has low resistance and mechanical support capability, 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 film, which helps to build a more continuous proton migration path.

[0045] In a second aspect, the application provides a proton exchange membrane for a hydrogen fuel cell, which is prepared by the method according to any one of the embodiments of the first aspect.

[0046] According to the application, the proton exchange membrane can maintain a high proton conductivity at room temperature and high temperature environments, and is suitable for stable operation of the hydrogen fuel cell in a wide working temperature range. In the membrane structure, the polyaramid main chain constructs a skeleton framework with excellent thermal stability and dimensional stability, and the grafted imidazole, hydroxyphosphonic acid and hydroxyphosphonate groups form a synergistic proton-conducting network in the film, which improves the efficiency and continuity of the proton migration path, and thus has a good proton conductivity.

[0047] In a third aspect, the application provides a hydrogen fuel cell, characterized in that it comprises the proton exchange membrane according to any one of the embodiments of the second aspect.

[0048] According to the application, the hydrogen fuel cell uses the above-mentioned proton exchange membrane constructed by a synergistic grafting structure as an electrolyte membrane layer, which realizes efficient and stable proton conduction between the anode and the cathode. In high-temperature or low-humidity working environments, the ion channel of the membrane-electrode interface can still be unobstructed and have a low internal resistance, 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 have high requirements for cold start performance, such as vehicles, backup power sources and distributed energy systems.

[0049] Compared with the prior art, the application has at least the following beneficial effects:

[0050] 1. The 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, hydroxyphosphonic acid and hydroxyphosphonate) synergistically construct a proton-conduction network, which realizes stability and directionality control of the conduction path at the molecular scale.

[0051] 2、All the grafted proton-conducting groups in this application are covalently anchored, avoiding the loss and migration of the proton-conducting materials commonly seen in doped systems, significantly improving the stability and durability of the proton exchange membrane.

[0052] 3、Each proton-conducting structure is uniformly grafted by separating the molecular structure design and reaction path, combined with the regulation of flexible chain segments to control the arrangement of conductive groups, effectively inducing the continuity of microphase separation and proton migration channels, making the proton exchange membrane have better proton conductivity. DETAILED DESCRIPTION

[0053] Each embodiment or implementation in the specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments.

[0054] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the implementation or example are included in at least one implementation or example of the present application. In the specification, the exemplary description of the above terms does not necessarily refer to the same implementation or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more implementations or examples in a suitable manner.

[0055] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise specifically limited.

[0056] In the description of the specification, "parts" refers to "mass parts" unless otherwise specified.

[0057] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If the specific technology or condition is not specified in the embodiments, it is carried out according to the technology or condition described in the literature in the art or according to the product manual. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.

[0058] 1-(2-hydroxyethyl)imidazole, CAS No. 1615-14-1;

[0059] 4-hydroxyethyl imidazole, CAS No. 872-82-2;

[0060] 2-bromoethylphosphonic acid diethyl ester, CAS No. 5324-30-1;

[0061] 2-hydroxyethylphosphonic acid dimethyl ester, CAS No. 54731-72-5.

[0062] Preparation Example 1

[0063] Preparation of 1,3-propanediol grafted 2-bromoethylphosphonic acid diethyl ester:

[0064] In a 250 mL three-necked flask, 50 mL of N-methyl pyrrolidone (NMP) was added as a reaction solvent, followed by the addition of 2-bromoethylphosphonic acid diethyl ester 10.0 g (about 40.8 mmol) and 1,3-propanediol 3.27 g (about 42.8 mmol), and then potassium carbonate 10.1 g (about 73.4 mmol) was added as a catalyst. The reaction system was stirred at 70 °C under a nitrogen atmosphere for 10 h, after the reaction was completed, the system was cooled to room temperature, the solvent was removed by rotary evaporation under reduced pressure, the residue was dissolved in excess ethyl acetate, inorganic salts were removed by filtration, and the filtrate was concentrated and dried under reduced pressure to obtain 1,3-propanediol grafted 2-bromoethylphosphonic acid diethyl ester.

[0065] Preparation Example 2

[0066] Preparation of ethylene glycol grafted 2-bromoethylphosphonic acid diethyl ester:

[0067] In a 250 mL three-necked flask, 50 mL of N-methyl pyrrolidone (NMP) was added as a reaction solvent, followed by the addition of 2-bromoethylphosphonic acid diethyl ester 10.0 g (about 40.8 mmol) and ethylene glycol 2.65 g (about 42.8 mmol), and then potassium carbonate 10.1 g (about 73.4 mmol) was added as a catalyst. The reaction system was stirred at 70 °C under a nitrogen atmosphere for 10 h, after the reaction was completed, the system was cooled to room temperature, the solvent was removed by rotary evaporation under reduced pressure, the residue was dissolved in excess ethyl acetate, inorganic salts were removed by filtration, and the filtrate was concentrated and dried under reduced pressure to obtain ethylene glycol grafted 2-bromoethylphosphonic acid diethyl ester.

[0068] Preparation Example 3

[0069] Preparation of 1,4-butanediol grafted 2-bromoethylphosphonic acid diethyl ester:

[0070] In a 250 mL three-necked flask, 50 mL of N-methyl pyrrolidone (NMP) was added as a reaction solvent, 2-bromoethyl phosphonic acid diethyl ester 10.0 g (about 40.8 mmol) and 1,4-butanediol 3.86 g (about 42.8 mmol) were added in sequence, followed by the addition of potassium carbonate 10.1 g (about 73.4 mmol) as a catalyst. The reaction system was stirred at 70 °C under a nitrogen atmosphere for 10 h, after the reaction was completed, the system was cooled to room temperature, the solvent was removed by rotary evaporation under reduced pressure, the residue was dissolved in excess ethyl acetate, the inorganic salt was removed by filtration, the filtrate was concentrated under reduced pressure and dried to obtain 1,4-butanediol grafted 2-bromoethyl phosphonic acid diethyl ester.

[0071] Example 1

[0072] Preparation of a proton exchange membrane for a hydrogen fuel cell:

[0073] In a 500 mL three-necked flask, 2,4-diaminobenzaldehyde 13.6 g (molecular weight 136.15 g / mol, about 0.1 mol) and methanol 160 mL were dissolved under stirring. Under ice bath conditions, sodium borohydride 3.8 g (molecular weight 37.83 g / mol, about 0.105 mol) was slowly added, after the addition was completed, the reaction was continuously stirred at 25 °C for 2 h, after the reaction was completed, the pH of the reaction system was adjusted to 7.0 with dilute hydrochloric acid, and the methanol solvent was removed by rotary evaporation under reduced pressure to obtain the intermediate product 2,4-diaminobenzyl alcohol; the above product was redissolved in 100 mL of dichloromethane, and under ice bath conditions, thionyl chloride 13 g (molecular weight 118.97 g / mol, 0.109 mol) and N,N-dimethylformamide 0.4 mL were slowly added dropwise, after the addition was completed, the reaction temperature was raised to 40 °C, and the stirring reaction was continued for 3 h. After the reaction was completed, the reaction liquid was poured into 400 mL of ice water to precipitate the solid, which was washed with cold water until the pH of the washing liquid was close to neutral, and the obtained solid was purified by filtration and recrystallization with ethanol, and then dried in a vacuum drying oven at 50 °C for 8 h to obtain chloromethylated phenylenediamine solid.

[0074] The above obtained chloromethylated phenylenediamine 7.85 g (about 0.05 mol) was dissolved in N,N-dimethylacetamide 80 mL under ice bath cooling. To the solution, a solution of phthaloyl chloride 10.5 g (about 0.052 mol) in N,N-dimethylacetamide 30 mL was added dropwise, and triethylamine 10.1 g (about 0.10 mol) was added as an acid acceptor, after the addition was completed, the reaction was stirred at 25 °C for 10 h, the obtained polymer was precipitated with ethanol, filtered, and the filter cake was washed with diethyl ether to obtain chloromethylated polyphthaloyl amide, which was dried under vacuum for later use.

[0075] The chloromethylated polyphthalamide 10 g obtained above was weighed out and dispersed in 200 mL of N-methylpyrrolidine, 2.24 g of 1-(2-hydroxyethyl)imidazole, 2.6 g of 2-hydroxyethane phosphonic acid, and 3.24 g of 1,3-propanediol-grafted diethyl 2-bromoethylphosphonate were added and mixed, and then 5 g of potassium carbonate was added. The mixture was stirred at 70°C for 12 h under a nitrogen atmosphere. After the reaction solution was cooled, N-methylpyrrolidine was recovered by rotary evaporation, 300 mL of ethyl acetate was poured into the concentrated solution, and the polymer was precipitated. The solid was separated by filtration, washed with ethyl acetate and anhydrous diethyl ether, and finally dried under vacuum to obtain a modified polyaramide.

[0076] The modified polyaramide 4 g obtained above was dissolved in N-methylpyrrolidine 30 g, and stirred overnight to form a uniform slurry. The slurry was uniformly coated on a clean glass plate using a 200 μm wet film coater, left to stand at room temperature for 30 min, and then dried at 60°C for 4 h under vacuum, and then heated to 120°C for 2 h to form a proton exchange membrane having a thickness of about 25 μm.

[0077] Example 2

[0078] Preparation of a proton exchange membrane for a hydrogen fuel cell:

[0079] The procedure was substantially the same as in Example 1, except that an equal amount of imidazole was used instead of 1-(2-hydroxyethyl)imidazole.

[0080] Example 3

[0081] Preparation of a proton exchange membrane for a hydrogen fuel cell:

[0082] The procedure was substantially the same as in Example 1, except that an equal amount of 4-hydroxyethyl imidazole was used instead of 1-(2-hydroxyethyl)imidazole.

[0083] Example 4

[0084] Preparation of a proton exchange membrane for a hydrogen fuel cell:

[0085] The procedure was substantially the same as in Example 1, except that an equal amount of ethylene glycol-grafted diethyl 2-bromoethylphosphonate was used instead of 1,3-propanediol-grafted diethyl 2-bromoethylphosphonate.

[0086] Example 5

[0087] Preparation of a proton exchange membrane for a hydrogen fuel cell:

[0088] The procedure was substantially the same as in Example 1, except that an equal amount of 1,4-butanediol-grafted diethyl 2-bromoethylphosphonate was used instead of 1,3-propanediol-grafted diethyl 2-bromoethylphosphonate.

[0089] Example 6

[0090] Preparation of proton exchange membranes for hydrogen fuel cells:

[0091] 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.

[0092] Comparative Example 1

[0093] Preparation of proton exchange membranes for hydrogen fuel cells:

[0094] The method is substantially the same as Example 1, except that the preparation process of the modified polyaramid is different, specifically:

[0095] 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.

[0096] Comparative Example 2

[0097] Preparation of proton exchange membranes for hydrogen fuel cells:

[0098] The method is substantially the same as Example 1, except that the preparation process of the modified polyaramid is different, specifically:

[0099] 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.

[0100] Comparative Example 3

[0101] Preparation of proton exchange membranes for hydrogen fuel cells:

[0102] The method is substantially the same as Example 1, except that the preparation process of the modified polyaramid is different, specifically:

[0103] The chloromethylated polyphthalamide 10 g obtained above was weighed into 200 mL N-methylpyrrolidine, 4.84 g 2-hydroxyethane phosphonic acid and 3.24 g 1,3-propanediol grafted 2-bromoethyl phosphonic acid diethyl ester were added and mixed, then 5 g potassium carbonate was added, and the reaction was stirred at 70°C for 12 h under a nitrogen atmosphere. After the reaction solution was cooled, N-methylpyrrolidine was recovered by rotary evaporation, 300 mL ethyl acetate was poured into the concentrated solution, and the polymer was precipitated. The solid was separated by filtration, washed with ethyl acetate and anhydrous ethyl ether in sequence, and finally dried in vacuum to obtain the modified polyaramide.

[0104] Test section

[0105] The proton exchange membranes prepared in each example and comparative example were tested for proton conductivity σ1 at 25°C and 50% relative humidity, and for proton conductivity σ2 at 80°C and 30% relative humidity, according to GB / T 20042.3-2022 “Proton Exchange Membrane Fuel Cells Part 3: Test Method for Proton Exchange Membrane”, and the results are shown in Table 1.

[0106] Table 1

[0107] <![CDATA[σ1(mS / cm)]]> 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

[0108] According to Table 1, each example exhibits higher proton conductivity at room temperature and high temperature conditions compared to Comparative Examples 1-3, indicating that the proton exchange membrane provided by the present application has more excellent proton conductivity at room temperature and high temperature conditions, and is suitable for wide temperature range fuel cell applications. The possible reason is that in Comparative Example 1, the lack of phosphate ester structure results in that the proton conduction path in the membrane mainly depends on the “acid-base pair” between imidazole-phosphonic acid, and lacks segment flexibility regulation and conduction channel structure construction, so the proton migration efficiency is limited; in Comparative Example 2, the lack of phosphonic acid group provides stable proton source, although the phosphate ester is grafted, but the donor-acceptor synergistic mechanism is lacking, which limits the proton concentration and migration efficiency; in Comparative Example 3, the lack of imidazole proton acceptor structure, only the weak hydrogen bond conduction path between phosphonic acid and phosphate ester groups exists in the membrane, and the proton conduction efficiency is significantly reduced.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate 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: dissolving diaminobenzaldehyde in methanol, adding sodium borohydride in an ice bath, reacting at 20-30°C for 1-3 hours, adjusting the pH to 6.5-7.5 after the reaction, and removing the solvent by rotary evaporation to obtain diaminobenzyl alcohol; dissolving the above product in dichloromethane, adding thionyl chloride and a catalytic amount of N,N-dimethylformamide in an ice bath, and reacting at 30-50°C for 2-4 hours to obtain chloromethylated aromatic diamine; wherein the molar ratio of diaminobenzaldehyde, sodium borohydride, and thionyl chloride is 1:(1.01-1.1):(1.01-1.2); S2: dissolving the chloromethylated aromatic diamine and aromatic dichloride in N,N-dimethylacetamide to obtain a diamine solution and a dichloride solution, respectively; adding triethylamine to the diamine solution; and then adding the dichloride solution in an ice bath; reacting at 20-30° C. for 8-12 hours to obtain a chloromethylated polyarylamide; wherein the molar ratio of the chloromethylated aromatic diamine to the aromatic dichloride is 1:(1-1.1); 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 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.

3. The method according to claim 2, 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.

4. The method according to any one of claims 1 to 3, characterized in that The method satisfies at least one of the following conditions: 1) The diaminobenzaldehyde includes 2,4-diaminobenzaldehyde; 2) The aromatic dichloride 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.

5. 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 4.

6. A hydrogen fuel cell, characterized in that: Comprising the proton exchange membrane according to claim 5.