A proton exchange membrane suitable for low humidity environment and preparation method thereof

Abstract

The present invention belongs to the field of fuel cell membrane materials, and relates to a proton exchange membrane suitable for low humidity environment and a preparation method thereof. The proton exchange membrane is composited with imidazolium salt crystals, polybenzimidazole, polyvinyl benzyl chloride, and phosphoric acid as raw materials, and the imidazolium salt crystals are formed by using 4,5-disubstituted imidazolium salt as raw materials and fixed in metal organic framework crystal materials. The preparation of the proton exchange membrane is to form a casting liquid by polybenzimidazole, polyethylene derivatives and imidazolium salt crystals, pour the casting liquid into a glass mold, fully dry to obtain a membrane, and then immerse the membrane in a phosphoric acid solution, and dry to obtain a proton exchange membrane; the proton exchange membrane of the present invention has high proton conductivity and mechanical strength, and the addition of a free radical quencher during the preparation process slows down the oxidative degradation of HT-PEM, and the mechanical strength of the membrane is effectively improved by cross-linking, adding nanomaterials, blending with another stable polymer, and improving the membrane structure.

Description

Technical Field

[0001] The invention relates to a proton exchange membrane suitable for a low-humidity environment and a preparation method thereof, and belongs to the field of fuel cell membrane materials. Background Art

[0002] Proton exchange membrane fuel cell (PEMFC) is an efficient clean energy system that converts chemical energy into electrical energy using low-carbon renewable fuels such as hydrogen. In the process of global energy structure adjustment, as an important link in the hydrogen energy industry chain, it has shown great potential in the fields of vehicle power supply, portable power supply, fixed power supply and micro-cogeneration system. Since the by-products are mainly discharged into the environment in the form of water, it has a broad application space in the field of automotive fuel cells. However, the promotion of proton exchange membrane fuel cells is still limited by cost and life issues. Among them, proton exchange membrane, as a key material of fuel cells, accounts for about 20% of the total cost of the stack. Its performance breakthrough will have a profound impact on the development of fuel cells.

[0003] The proton exchange membrane is the core component of PEMFC. PEM is different from the diaphragm used in general chemical power sources. Proton exchange membrane fuel cells have become the most competitive clean alternative power source to gasoline internal combustion engines. The materials used for PEM should meet the following conditions: (1) good proton conductivity; (2) small electrical permeation effect of water molecules in the membrane; (3) as small as possible gas permeability in the membrane; (4) good electrochemical stability; (5) good dry-wet conversion performance; (6) certain mechanical strength; (7) good processability and appropriate price.

[0004] Compared with traditional proton exchange membrane fuel cells (PEMFC), the operating temperature of high temperature and low humidity proton exchange membrane fuel cells (HT-PEMFC) is conducive to improving the catalyst reaction activity and accelerating the reaction rate, improving the catalyst's resistance to carbon monoxide poisoning, and facilitating simple water and heat management. As the core component of HT-PEMFC, the main function of high temperature proton exchange membrane (HT-PEM) is to transfer protons from the anode to the cathode, separate reactants and isolate electrons to avoid short circuits. Phosphoric acid-doped proton exchange membranes have the advantages of high proton conductivity and good chemical stability under high temperature and low humidity or anhydrous conditions, making it a research hotspot for high temperature proton exchange membrane materials. However, some shortcomings of HT-PEM prepared by a series of methods currently limit its further commercialization. For example, although phosphoric acid in the membrane improves proton conductivity, it sacrifices the mechanical strength of the membrane. In addition, after long-term operation, especially when the polymer chain undergoes oxidation and mechanical degradation, phosphoric acid loss is particularly serious. Therefore, how to solve the three main challenges of HT-PEM (phosphoric acid loss, membrane oxidation degradation and membrane mechanical degradation) is of great significance for the commercialization of HT-PEMFC. Summary of the invention

[0005] The purpose of the present invention is to provide a proton exchange membrane suitable for low humidity environment and a preparation method thereof, aiming to solve the problems of phosphoric acid loss, membrane oxidation degradation and membrane mechanical degradation of the proton exchange membrane in low humidity environment.

[0006] The above technical purpose of the present invention is achieved through the following technical solutions:

[0007] On one hand, the present invention provides a proton exchange membrane, which is composited with imidazolium salt crystals, polybenzimidazole, polyvinylbenzyl chloride and phosphoric acid as raw materials. The imidazolium salt crystals are prepared by fixing 4,5-disubstituted imidazolium salt as raw material in a metal organic framework crystal material; the 4,5-disubstituted imidazolium salt is 1-butyl C4, C5 disubstituted imidazolium salt or 1-hexyl C4, C5 disubstituted imidazolium salt.

[0008] In the above technical solution, further, the raw materials of the imidazolium salt crystals also include chloromethylstyrene, polybenzimidazole and a free radical quencher.

[0009] In the above technical scheme, further, the metal-organic framework crystal material is a cubic structure with micropores, and the pore size of the metal-organic framework crystal material is 100-1000nm; the metal-organic framework crystal material is one or more of MIL-101(Fe), MIL-101(Cr), MIL-53(Cr), MIL-53(Fe), ZIF-6, ZIF-8, and ZIF-10; the phosphoric acid is a polypeptide organic phosphoric acid or an inorganic phosphoric acid.

[0010] In the above technical solution, further, the imidazolium salt crystal is synthesized by a low-temperature vacuum method, and the C4 and C5 substituted imidazolium salts are "fixed" in the crystal material of the metal organic framework material with a microporous cubic structure, comprising the following steps:

[0011] (1) placing a metal organic framework crystal material having a microporous cubic structure in a Schlenk tube equipped with a constant pressure funnel, and continuously evacuating the metal organic framework crystal material to place it in a vacuum state;

[0012] (2) under low temperature, mixing a mixture of 4,5-disubstituted imidazolium salt and p-chloromethylstyrene with the metal organic framework crystal material of step (1), stirring for reaction, and then adding polybenzimidazole and a free radical quencher to mix;

[0013] (3) After the reaction is completed, centrifugation is performed, and the precipitate is dried, and the vinyl group in the chloromethylstyrene is self-crosslinked to obtain imidazolium salt crystals.

[0014] In the above technical scheme, further, the vacuum degree of the vacuum state in step (1) is -0.6 to -1.0 MPa; the low-temperature reaction temperature in step (2) is -20 to -10°C, and the stirring time is 48 to 96 hours; the precipitate drying temperature in step (3) is 60 to 100°C, and the drying time is 4 to 8 hours; steps (1) and (2) are in the same vacuum state.

[0015] In the above technical solution, further, the C4 and C5 substituents in the 4,5-disubstituted imidazolium salt are R1 and R2 respectively, and the R1 and R2 are any one of methyl, ethyl, propyl, butyl, isopropyl, and tert-butyl. The structures of the 1-butyl C4, C5 disubstituted imidazolium salt or the 1-hexyl C4, C5 disubstituted imidazolium salt are as follows:

[0016]

[0017] 1-Butyl C4, C5 disubstituted imidazolium salts 1-Hexyl C4, C5 disubstituted imidazolium salts

[0018] The free radical quencher is any one of phosphated cerium dioxide, sulfonated cerium dioxide, sulfonated manganese dioxide, cerium dioxide, and manganese dioxide;

[0019] The added mass ratio of the metal organic framework material, 4,5-disubstituted imidazolium salt, p-chloromethylstyrene, polybenzimidazole and free radical quencher is metal organic framework material: 4,5-disubstituted imidazolium salt: p-chloromethylstyrene: polybenzimidazole: free radical quencher = 0.5:1:0.3-1.5:1-2:0.01-0.05.

[0020] Another aspect of the present invention provides a method for preparing the aforementioned proton exchange membrane, the preparation method comprising the following steps:

[0021] A. prepare a polybenzimidazole high boiling point solution, add polyvinyl benzyl chloride at room temperature, and stir to obtain a mixed solution of polybenzimidazole and polyvinyl benzyl chloride;

[0022] B. adding imidazolium salt crystals to the mixed solution of polybenzimidazole and polyvinylbenzyl chloride obtained in step A, stirring at room temperature to obtain a functionalized film casting solution;

[0023] C. Pour the casting solution prepared in step B into a glass mold, and after sufficient drying, peel the obtained film from the glass mold;

[0024] D. Weigh phosphoric acid and add it to deionized water to prepare a phosphoric acid aqueous solution, soak the membrane obtained in step C in the solution and then remove it;

[0025] E. The membrane fished out in step D is washed with deionized water for more than 5 times, and dried to obtain a proton exchange membrane suitable for a low humidity environment.

[0026] In the above technical solution, further, in step A, the mass concentration of the polybenzimidazole high boiling point solution is 0.5-2wt%, and the high boiling point solvent used to prepare the polybenzimidazole high boiling point solution is one of N-methylpyrrolidone, N,N-dimethylformamide, tetrahydrofuran, and dimethyl sulfoxide.

[0027] In the above technical solution, further, the stirring time of step A is 24-48 hours, and the stirring time of step B is 24-48 hours.

[0028] In the above technical solution, further, the mass ratio of each component in steps A and B is imidazolium salt crystal: polybenzimidazole: polyvinyl benzyl chloride = 1:1-3:1-1.5.

[0029] In the above technical solution, further, the mass concentration of the phosphoric acid aqueous solution is 5-15wt%. In the above technical solution, further, the drying temperature of the casting solution in step C is 60-80°C, and the drying time is 24-48h; the soaking time in step D is 24-48h; and the drying temperature in step E is 40-60°C, and the drying time is 24-48h.

[0030] Beneficial Effects

[0031] 1. The low-humidity proton exchange membrane prepared by the present invention includes polybenzimidazole and polyvinyl benzyl chloride as the skeleton polymer material, and the phosphoric acid compound and the imidazolium salt crystal material have the function of ion transmission. It has excellent mechanical properties and low cost under low humidity operating conditions. On the one hand, the polybenzimidazole material itself has good stability and adsorption of phosphoric acid. On the other hand, the addition of polyvinyl benzyl chloride can improve the toughness of the skeleton material, and the alkane end group of polyvinyl benzyl chloride can further react with polybenzimidazole to form a more stable network structure, thereby improving the stability of the composite membrane;

[0032] The addition of the imidazolium salt crystal structure formed by the imidazolium salt and the metal organic framework constructs an ordered proton transfer channel, so that the phosphoric acid can be evenly and orderly locked in the channel of the crystal structure, thereby reducing the ion transfer resistance, improving the ion transfer efficiency, and further improving the electrochemical performance. The metal organic framework in the imidazolium salt crystal material provides a place to accommodate the vinyl compounds in the imidazolium salt and chloromethylstyrene, so that the prepared anion exchange membrane will not cause chemical degradation of the ion membrane and loss of functionalized ion groups due to changes in the reaction environment;

[0033] Adding imidazolium salt crystal materials to the skeleton polymer material not only increases the active sites for proton conduction, but also achieves effective compatibility between the membrane skeleton polymer material, the crystal material and the phosphate molecules, so that the imidazolium salt crystal material can be evenly dispersed in the polymer material without problems such as agglomeration and loss, thereby improving the uniformity and efficiency of proton conduction in the proton exchange membrane.

[0034] 2. The present invention uses metal organic framework crystal materials and imidazolium salts as functional materials for proton exchange membranes. The imidazolium salt crystals can adsorb phosphate compounds in the imidazole-type MOFs structure and in the pores of the crystal structure, thereby increasing the phosphate adsorption sites and improving the proton conductivity. In addition, when the prepared composite membrane is immersed in a phosphoric acid solution, the phosphoric acid molecules enter the imidazolium salt crystal structure and are fixed in the imidazole microporous structure in the crystal structure, forming a "ship in a bottle" structure. This structure has a large internal space and a macromolecular structure and a small pore structure, so that the internal compounds such as phosphoric acid will not flow out, effectively avoiding the loss of phosphoric acid with the water flow during the operation of the fuel cell. The sulfonated free radical quencher is filled in the polymer skeleton to improve the proton conduction ability, thereby improving the conduction stability and mechanical strength of the resulting proton membrane.

[0035] 3. The present invention slows down the loss of phosphoric acid by preparing capture sites for phosphoric acid molecules or increasing the interaction between polymers and phosphoric acid molecules, and synthesizes polymers with cross-linked and branched structures to protect the polymer skeleton from the attack of free radicals. The addition of free radical quenchers during the preparation process slows down the oxidative degradation of HT-PEM. In addition, the mechanical strength of the membrane is effectively improved by cross-linking, adding nanomaterials, blending with another stable polymer, improving the membrane structure, etc.

[0036] 4. The present invention uses a special molecular structure design and adds different functional particles into the membrane to make the high-temperature proton exchange membrane with phosphoric acid as the proton conductor. The proton conductor filling amount is large, thereby obtaining a higher proton conductivity, and the adsorption force between phosphoric acid and the polymer membrane is increased, thereby improving the chemical stability of the membrane. DETAILED DESCRIPTION

[0037] The present invention is described in further detail below.

[0038] Embodiment 1:

[0039] (1) Weigh 10 g of MIL-101(Fe) and place it in a Schlenk tube equipped with a constant pressure funnel. Continuously evacuate the tube to maintain a vacuum degree of -1.0 MPa and lower the temperature of the Schlenk tube to -10°C.

[0040] (2) Weigh 20 g of a mixture of 1-hexyl-4,5-dimethylimidazolium salt and 6 g of p-chloromethylstyrene and inject it into the Schlenk tube of step (1), continue stirring for 96 hours to allow 1-hexyl-4,5-dimethylimidazolium salt and p-chloromethylstyrene to fully react, then weigh 40 g of polybenzimidazole and 0.2 g of 3 nm phosphated cerium dioxide and add them thereto for mixing;

[0041] (3) After the reaction is completed, the precipitate is centrifuged and then dried at 60° C. for 8 h to allow the vinyl groups to self-crosslink and form imidazolium salt crystals;

[0042] (4) At 25° C., 12 g of polybenzimidazole was dissolved in 2388 g of N-methylpyrrolidone and stirred to obtain a polymer solution with a concentration of 0.5%. Then, 4 g of polyvinylbenzyl chloride was added and stirred for 24 h.

[0043] (5) Weigh 4 g of imidazolium salt crystals and add them to step (4), stir for 24 h until uniform, and obtain a casting solution for later use;

[0044] (6) Add the casting solution obtained in step (5) into a glass mold, dry at 60° C. for 48 h, and peel off the dried film from the glass plate for later use;

[0045] (7) Weigh 5 g of polypeptide phosphate and add it to 95 g of deionized water to obtain a 5% polypeptide phosphate solution;

[0046] (8) The membrane obtained in step (6) is placed in the solution prepared in step (7), soaked for 24 hours, taken out, repeatedly rinsed with deionized water for 5 times, and thoroughly dried at 40° C. for 48 hours to obtain a proton exchange membrane suitable for a low humidity environment.

[0047] Embodiment 2:

[0048] (1) Weigh 5 g of MIL-101(Cr) and place it in a Schlenk tube equipped with a constant pressure funnel. Continuously evacuate the tube to maintain a vacuum degree of -0.8 MPa and lower the temperature of the Schlenk tube to -15°C.

[0049] (2) Weigh 7.5 g of a mixture of 1-hexyl-4,5-ethylmethylimidazolium salt and 7.5 g of p-chloromethylstyrene and inject it into the Schlenk tube of step (1), and continue stirring for 36 h to allow the 1-hexyl-4,5-ethylmethylimidazolium salt and p-chloromethylstyrene to fully react, then weigh 15 g of polybenzimidazole and 0.15 g of 10 nm sulfonated manganese dioxide and add them thereto for mixing;

[0050] (3) After the reaction is completed, the precipitate is centrifuged and then dried at 70° C. for 7 h to allow the vinyl groups to self-crosslink and form imidazolium salt crystals;

[0051] (4) At 25° C., 4 g of polybenzimidazole was dissolved in 396 g of N,N-diformamide and stirred to obtain a polymer solution with a concentration of 1%. Then, 2.4 g of polyvinylbenzyl chloride was added and stirred for 48 h.

[0052] (5) Weigh 2 g of imidazolium salt crystals and add them to step (4), stir for 48 h until uniform, and obtain a casting solution for later use;

[0053] (6) Add the casting solution obtained in step (5) into a glass mold, dry at 70° C. for 36 h, and peel off the dried film from the glass plate for later use;

[0054] (7) Weigh 10 g of polypeptide phosphate and add it to 90 g of deionized water to obtain a 10% phosphoric acid solution;

[0055] (8) The membrane obtained in step (6) is placed in the solution prepared in step (7), soaked for 36 hours, taken out, repeatedly rinsed with deionized water for 5 times, and thoroughly dried at 50° C. for 36 hours to obtain a proton exchange membrane suitable for a low humidity environment.

[0056] Embodiment 3:

[0057] (1) Weigh 4 g of ZIF-8 and place it in a Schlenk tube equipped with a constant pressure funnel. Continuously evacuate the tube to maintain a vacuum degree of -0.6 MPa and lower the temperature of the Schlenk tube to -20 °C.

[0058] (2) Weigh 8 g of a mixture of 1-hexyl-4,5-dimethylimidazolium salt and 12 g of p-chloromethylstyrene and inject it into the Schlenk tube of step (1), continue stirring for 48 h to allow 1-hexyl-4,5-dimethylimidazolium salt and p-chloromethylstyrene to fully react, then weigh 8 g of polybenzimidazole and 0.4 g of 5 nm sulfonated cerium dioxide and add them thereto for mixing;

[0059] (3) After the reaction is completed, the precipitate is centrifuged and then dried at 60° C. for 8 h to allow the vinyl groups to self-crosslink and form imidazolium salt crystals;

[0060] (4) At 25° C., 4 g of polybenzimidazole was dissolved in 196 g of N,N-diformamide and stirred to obtain a polymer solution with a concentration of 2%. Then, 6 g of polyvinylbenzyl chloride was added and stirred for 48 h.

[0061] (5) Weigh 4 g of imidazolium salt crystals and add them to step (4), stir for 36 h until uniform, and obtain a casting solution for later use;

[0062] (6) Add the casting solution obtained in step (5) into a glass mold, dry at 80° C. for 24 h, and peel off the dried film from the glass plate for later use;

[0063] (7) Weigh 15 g of phosphoric acid and add it to 85 g of deionized water to obtain a phosphoric acid solution with a concentration of 15%;

[0064] (8) The membrane obtained in step (6) is placed in the solution prepared in step (7), soaked for 48 hours, taken out, repeatedly rinsed with deionized water for 5 times, and thoroughly dried at 60° C. for 24 hours to obtain a proton exchange membrane suitable for a low humidity environment.

[0065] Comparative Example 1:

[0066] (1) At 25° C., 12 g of polybenzimidazole was dissolved in 2388 g of N-methylpyrrolidone and stirred to obtain a polymer solution with a concentration of 0.5%. Then, 4 g of polyvinylbenzyl chloride was added and stirred for 24 h to obtain a casting solution.

[0067] (2) pouring the casting solution obtained in step (1) into a glass mold, drying at 60° C. for 48 h, and peeling the dried film from the glass plate for later use;

[0068] (3) Weigh 5 g of polypeptide phosphate and add it to 95 g of deionized water to obtain a 5% polypeptide phosphate solution;

[0069] (4) placing the membrane obtained in step (3) in the solution prepared in step (7), soaking for 24 hours, taking it out, repeatedly rinsing it with deionized water for 5 times, and thoroughly drying it at 40° C. for 48 hours to obtain a proton exchange membrane suitable for a low humidity environment.

[0070] Comparative Example 2:

[0071] (1) Weigh 10 g of MIL-101(Fe) and place it in a Schlenk tube equipped with a constant pressure funnel. Continuously evacuate the tube to maintain a vacuum degree of -1.0 MPa and lower the temperature of the Schlenk tube to -10°C.

[0072] (2) Weigh 20 g of a mixture of 1-hexyl-4,5-dimethylimidazolium salt and 6 g of p-chloromethylstyrene, inject the mixture into the Schlenk tube of step (1), and continue stirring for 96 h to allow the 1-hexyl-4,5-dimethylimidazolium salt and p-chloromethylstyrene to react fully, then weigh 40 g of polybenzimidazole and 0.2 g of phosphated cerium dioxide, add the mixture, and continue stirring;

[0073] (3) After the reaction is completed, the precipitate is centrifuged and then dried at 60° C. for 8 h to allow the vinyl groups to self-crosslink and form imidazolium salt crystals;

[0074] (4) weighing 12 g of polybenzimidazole and dissolving it in 2388 g of N-methylpyrrolidone at 25° C., stirring to dissolve, to obtain a polymer solution with a concentration of 0.5%;

[0075] (5) Weigh 4 g of imidazolium salt crystals and add them to step (4), stir evenly to obtain a casting solution for later use;

[0076] (6) Add the casting solution obtained in step (5) into a glass mold, dry at 60° C. for 48 h, and peel off the dried film from the glass plate for later use;

[0077] (7) Weigh 5 g of polypeptide phosphate and add it to 95 g of deionized water to obtain a 5% polypeptide phosphate solution;

[0078] (8) The membrane obtained in step (6) is placed in the solution prepared in step (7), soaked for 24 hours, taken out, repeatedly rinsed with deionized water for 5 times, and thoroughly dried at 40° C. for 48 hours to obtain a proton exchange membrane suitable for a low humidity environment.

[0079] Comparative Example 3:

[0080] (1) Weigh 10 g of MIL-101(Fe) and place it in a Schlenk tube equipped with a constant pressure funnel. Continuously evacuate the tube to maintain a vacuum degree of -1.0 MPa and lower the temperature of the Schlenk tube to -10°C.

[0081] (2) Weighing 20 g of 1-hexyl-4,5-dimethylimidazolium salt and injecting it into the Schlenk tube of step (1), stirring continuously for 96 hours to allow the 1-hexyl-4,5-dimethylimidazolium salt to enter the metal organic framework crystal material, and then weighing 40 g of polybenzimidazole and 0.2 g of phosphated cerium dioxide and adding them thereto, and continuing stirring;

[0082] (3) After the reaction is completed, the precipitate is centrifuged and then dried at 60° C. for 8 h to allow the vinyl groups to self-crosslink and form imidazolium salt crystals;

[0083] (4) At 25° C., 12 g of polybenzimidazole was dissolved in 2388 g of N-methylpyrrolidone and stirred to obtain a polymer solution with a concentration of 0.5%. Then, 4 g of polyvinylbenzyl chloride was added and stirred for 24 h.

[0084] (5) Weigh 4 g of imidazolium salt crystals and add them to step (4), stir for 24 h until uniform, and obtain a casting solution for later use;

[0085] (6) Add the casting solution obtained in step (5) into a glass mold, dry at 60° C. for 48 h, and peel off the dried film from the glass plate for later use;

[0086] (7) Weigh 5 g of polypeptide phosphate and add it to 95 g of deionized water to obtain a 5% polypeptide phosphate solution;

[0087] (8) The membrane obtained in step (6) is placed in the solution prepared in step (7), soaked for 24 hours, taken out, repeatedly rinsed with deionized water for 5 times, and thoroughly dried at 40° C. for 48 hours to obtain a proton exchange membrane suitable for a low humidity environment.

[0088] Comparative Example 4:

[0089] (1) Weigh 10 g of MIL-101(Fe) and place it in a Schlenk tube equipped with a constant pressure funnel. Continuously evacuate the tube to maintain a vacuum degree of -1.0 MPa and lower the temperature of the Schlenk tube to -10°C.

[0090] (2) Weigh 20 g of a mixture of 1-hexyl-4,5-dimethylimidazolium salt and 2 g of p-chloromethylstyrene, inject the mixture into the Schlenk tube of step (1), and continue stirring for 96 h to allow the 1-hexyl-4,5-dimethylimidazolium salt and p-chloromethylstyrene to fully react, then weigh 40 g of polybenzimidazole and 0.2 g of phosphated cerium dioxide, add the mixture, and continue stirring;

[0091] (3) After the reaction is completed, the precipitate is centrifuged and then dried at 60° C. for 8 h to allow the vinyl groups to self-crosslink and form imidazolium salt crystals;

[0092] (4) At 25° C., 12 g of polybenzimidazole was dissolved in 2388 g of N-methylpyrrolidone and stirred to obtain a polymer solution with a concentration of 0.5%. Then, 4 g of polyvinylbenzyl chloride was added and stirred for 24 h.

[0093] (5) Weigh 4 g of imidazolium salt crystals and add them to step (4), stir for 24 h until uniform, and obtain a casting solution for later use;

[0094] (6) Add the casting solution obtained in step (5) into a glass mold, dry at 60° C. for 48 h, and peel off the dried film from the glass plate for later use;

[0095] (7) Weigh 5 g of polypeptide phosphate and add it to 95 g of deionized water to obtain a 5% polypeptide phosphate solution;

[0096] (8) The membrane obtained in step (6) is placed in the solution prepared in step (7), soaked for 24 hours, taken out, repeatedly rinsed with deionized water for 5 times, and thoroughly dried at 40° C. for 48 hours to obtain a proton exchange membrane suitable for a low humidity environment.

[0097] Comparative Example 5:

[0098] (1) Weigh 10 g of MIL-101(Fe) and place it in a Schlenk tube equipped with a constant pressure funnel. Continuously evacuate the tube to maintain a vacuum degree of -1.0 MPa and lower the temperature of the Schlenk tube to -10°C.

[0099] (2) Weigh 20 g of a mixture of 1-hexyl-4,5-dimethylimidazolium salt and 40 g of p-chloromethylstyrene, inject the mixture into the Schlenk tube of step (1), and continue stirring for 96 h to allow the 1-hexyl-4,5-dimethylimidazolium salt and p-chloromethylstyrene to react fully, then weigh 40 g of polybenzimidazole and 0.2 g of phosphated cerium dioxide, add the mixture, and continue stirring;

[0100] (3) After the reaction is completed, the precipitate is centrifuged and then dried at 60° C. for 8 h to allow the vinyl groups to self-crosslink and form imidazolium salt crystals;

[0101] (4) At 25° C., 12 g of polybenzimidazole was dissolved in 2388 g of N-methylpyrrolidone and stirred to obtain a polymer solution with a concentration of 0.5%. Then, 4 g of polyvinylbenzyl chloride was added and stirred for 24 h.

[0102] (5) Weigh 4 g of imidazolium salt crystals and add them to step (4), stir for 24 h until uniform, and obtain a casting solution for later use;

[0103] (6) Add the casting solution obtained in step (5) into a glass mold, dry at 60° C. for 48 h, and peel off the dried film from the glass plate for later use;

[0104] (7) Weigh 5 g of polypeptide phosphate and add it to 95 g of deionized water to obtain a 5% polypeptide phosphate solution;

[0105] (8) The membrane obtained in step (6) is placed in the solution prepared in step (7), soaked for 24 hours, taken out, repeatedly rinsed with deionized water for 5 times, and thoroughly dried at 40° C. for 48 hours to obtain a proton exchange membrane suitable for a low humidity environment.

[0106] Comparative Example 6:

[0107] (1) Weigh 10 g of MIL-101(Fe) and place it in a Schlenk tube equipped with a constant pressure funnel. Continuously evacuate the tube to maintain a vacuum degree of -1.0 MPa and lower the temperature of the Schlenk tube to -10°C.

[0108] (2) Weigh 20 g of a mixture of 1-hexyl-4,5-dimethylimidazolium salt and 6 g of p-chloromethylstyrene, inject the mixture into the Schlenk tube of step (1), and continue stirring for 96 h to allow the 1-hexyl-4,5-dimethylimidazolium salt and p-chloromethylstyrene to react fully, then weigh 80 g of polybenzimidazole and 0.2 g of phosphated cerium dioxide, add the mixture, and continue stirring;

[0109] (3) After the reaction is completed, the precipitate is centrifuged and then dried at 60° C. for 8 h to allow the vinyl groups to self-crosslink and form imidazolium salt crystals;

[0110] (4) At 25° C., 12 g of polybenzimidazole was dissolved in 2388 g of N-methylpyrrolidone and stirred to obtain a polymer solution with a concentration of 0.5%. Then, 4 g of polyvinylbenzyl chloride was added and stirred for 24 h.

[0111] (5) Weigh 4 g of imidazolium salt crystals and add them to step (4), stir for 24 h until uniform, and obtain a casting solution for later use;

[0112] (6) Add the casting solution obtained in step (5) into a glass mold, dry at 60° C. for 48 h, and peel off the dried film from the glass plate for later use;

[0113] (7) Weigh 5 g of polypeptide phosphate and add it to 95 g of deionized water to obtain a 5% polypeptide phosphate solution;

[0114] (8) The membrane obtained in step (6) is placed in the solution prepared in step (7), soaked for 24 hours, taken out, repeatedly rinsed with deionized water for 5 times, and thoroughly dried at 40° C. for 48 hours to obtain a proton exchange membrane suitable for a low humidity environment.

[0115] Comparative Example 7:

[0116] (1) Weigh 10 g of MIL-101(Fe) and place it in a Schlenk tube equipped with a constant pressure funnel. Continuously evacuate the tube to maintain a vacuum degree of -1.0 MPa and lower the temperature of the Schlenk tube to -10°C.

[0117] (2) Weigh 20 g of a mixture of 1-hexyl-4,5-dimethylimidazolium salt and 6 g of p-chloromethylstyrene, inject the mixture into the Schlenk tube of step (1), and continue stirring for 96 h to allow the 1-hexyl-4,5-dimethylimidazolium salt and p-chloromethylstyrene to react fully, then weigh 10 g of polybenzimidazole and 0.2 g of phosphated cerium dioxide, add the mixture, and continue stirring;

[0118] (3) After the reaction is completed, the precipitate is centrifuged and then dried at 60° C. for 8 h to allow the vinyl groups to self-crosslink and form imidazolium salt crystals;

[0119] (4) At 25° C., 12 g of polybenzimidazole was dissolved in 2388 g of N-methylpyrrolidone and stirred to obtain a polymer solution with a concentration of 0.5%. Then, 4 g of polyvinylbenzyl chloride was added and stirred for 24 h.

[0120] (5) Weigh 4 g of imidazolium salt crystals and add them to step (4), stir for 24 h until uniform, and obtain a casting solution for later use;

[0121] (6) Add the casting solution obtained in step (5) into a glass mold, dry at 60° C. for 48 h, and peel off the dried film from the glass plate for later use;

[0122] (7) Weigh 5 g of polypeptide phosphate and add it to 95 g of deionized water to obtain a 5% polypeptide phosphate solution;

[0123] (8) The membrane obtained in step (6) is placed in the solution prepared in step (7), soaked for 24 hours, taken out, repeatedly rinsed with deionized water for 5 times, and thoroughly dried at 40° C. for 48 hours to obtain a proton exchange membrane suitable for a low humidity environment.

[0124] Compared with Examples 1-7, Comparative Example 1 did not add imidazolium salt crystal materials, and Comparative Example 2 did not add polyethylene derivatives. The proton exchange membranes of the embodiments and comparative examples were tested for conductivity and tensile strength, and the results are shown in Table 1. It can be seen from Table 1 that the conductivity and tensile strength of the exchange membrane prepared by the present invention are relatively high, and the effects are better than those of the comparative examples. This is because imidazolium salts are introduced into the proton exchange membrane in two forms, namely, covalent crosslinking and metal organic framework solid fixation, to increase the number of functional groups in the membrane, and to construct regular and orderly ion transfer channels with the help of regular lattice structures, thereby reducing ion transfer resistance; at the same time, polyvinyl benzyl chloride and a crosslinking agent are used for crosslinking reaction to form a skeleton structure, thereby improving the stability and mechanical strength of the ion exchange membrane.

[0125] In Comparative Example 1, no imidazolium salt crystal material was added, and polybenzimidazole was used to lock the phosphoric acid molecules in the preparation of the proton exchange membrane. As the operation time increased, phosphoric acid was seriously lost, resulting in a decrease in its performance;

[0126] In the process of preparing the proton exchange membrane in Comparative Example 2, no polyethylene derivatives were added to the skeleton material, and the skeleton material did not form a cross-linked network structure. On the one hand, the imidazolium salt crystals were not firmly fixed in the skeleton material and were easily lost, resulting in performance impairment. On the other hand, the prepared membrane had poor chemical stability and was easily degraded.

[0127] In Comparative Example 3, no p-chloromethylstyrene was added, and the imidazolium salt could not form a macromolecular solid with p-chloromethylstyrene and be fixed in the metal organic framework crystal material. When the membrane was just prepared, its electrochemical performance was high, but as time went on, the imidazolium salt would gradually be lost, and the performance of the membrane would drop sharply.

[0128] In Comparative Example 4, the amount of p-chloromethylstyrene added is relatively small, and some imidazolium salts cannot form macromolecules with p-chloromethylstyrene and are fixed in the metal organic framework crystal material. During the operation of the prepared proton exchange membrane, the imidazolium salts will gradually be lost, and the performance thereof will also decrease.

[0129] In Comparative Example 5, the amount of p-chloromethylstyrene added is too much, and the polymer structure formed by self-crosslinking of p-chloromethylstyrene covers the crystal structure of the imidazolium salt. The prepared proton exchange membrane has poor performance, but strong mechanical strength.

[0130] In Comparative Example 6, a large amount of polybenzimidazole is added. Since polybenzimidazole has a strong adsorption capacity for phosphate compounds, the prepared proton exchange membrane has excellent performance. However, the proton exchange membrane prepared by polybenzimidazole has insufficient toughness and is prone to defects such as cracks and brittle cracks.

[0131] In Comparative Example 7, the amount of polybenzimidazole added is relatively small, the prepared proton exchange membrane has poor performance, large mechanical tensile strength, and is easily degraded.

[0132] Table 1 Conductivity and tensile strength of proton exchange membrane

[0133]

[0134]

[0135] The proton exchange membranes prepared in the examples of the present invention and the comparative examples were immersed in Fenton's reagent for durability testing, and the results are shown in Table 2. The chemical tolerance of the proton exchange membranes that were not covalently cross-linked and not added with free radical quenchers was significantly poor.

[0136] Table 2 Proton exchange membrane quality residual rate test

[0137] Case 100h exchange membrane mass residual rate / % Example 1 99.2 Example 2 99.1 Example 3 98.9 Comparative Example 1 72 Comparative Example 2 81 Comparative Example 3 67 Comparative Example 4 87.3 Comparative Example 5 77.2 Comparative Example 6 89.9 Comparative Example 7 67

[0138] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

Claims

1. A proton exchange membrane, characterized in that: The proton exchange membrane is composited with imidazolium salt crystals, polybenzimidazole, polyvinylbenzyl chloride and phosphoric acid as raw materials. The imidazolium salt crystals are: a substance formed by using 4,5-disubstituted imidazolium salt as raw material and fixed in a metal organic framework crystal material; the 4,5-disubstituted imidazolium salt is 1-butyl C4, C5 disubstituted imidazolium salt or 1-hexyl C4, C5 disubstituted imidazolium salt; The raw materials of the imidazolium salt crystals also include p-chloromethylstyrene, polybenzimidazole and a free radical quencher; The added mass ratio of the metal organic framework material, 4,5-disubstituted imidazolium salt, p-chloromethylstyrene, polybenzimidazole and free radical quencher is metal organic framework material: 4,5-disubstituted imidazolium salt: p-chloromethylstyrene: polybenzimidazole: free radical quencher = 0.5:1:0.3-1.5:1-2:0.01-0.

05.

2. The proton exchange membrane according to claim 1, characterized in that: The metal organic framework crystal material is a cubic structure with micropores, and the pore size of the micropores is 100-1000nm; the metal organic framework crystal material is one or more of MIL-101 (Fe), MIL-101 (Cr), MIL-53 (Cr), MIL-53 (Fe), ZIF-6, ZIF-8, and ZIF-10; the phosphoric acid is a polypeptide organic phosphoric acid or an inorganic phosphoric acid.

3. The proton exchange membrane according to claim 1, characterized in that: The imidazolium salt crystal is synthesized by a low temperature vacuum method, comprising the following steps: (1) placing the metal organic framework crystal material in a vacuum state; (2) under low temperature, mixing a mixture of 4,5-disubstituted imidazolium salt and p-chloromethylstyrene with the metal organic framework crystal material of step (1), stirring, and then adding polybenzimidazole and a free radical quencher to mix; (3) centrifuging and drying to obtain imidazolium salt crystals; The low temperature reaction temperature in step (2) is -20 to -10°C.

4. The proton exchange membrane according to claim 3, characterized in that: The vacuum degree of the vacuum state in step (1) is -0.6 to -1.0 MPa; the stirring time in step (2) is 48 to 96 hours; the precipitate drying temperature in step (3) is 60 to 100° C. and the drying time is 4 to 8 hours; steps (1) and (2) are in the same vacuum state.

5. The proton exchange membrane according to claim 1, characterized in that: The C4 and C5 substituents in the 4,5-disubstituted imidazolium salt are R1 and R2, respectively, and the R1 and R2 are any one of methyl, ethyl, propyl, butyl, isopropyl, and tert-butyl. The structures of the 1-butyl C4, C5 disubstituted imidazolium salt or the 1-hexyl C4, C5 disubstituted imidazolium salt are as follows: 1-Butyl C4, C5 disubstituted imidazolium salts 1-Hexyl C4, C5 disubstituted imidazolium salts The free radical quencher is any one of phosphated cerium dioxide, sulfonated cerium dioxide, sulfonated manganese dioxide, cerium dioxide, and manganese dioxide.

6. The method for preparing a proton exchange membrane according to any one of claims 1 to 5, characterized in that: The steps include: A. Prepare a polybenzimidazole high boiling point solution, add polyvinyl benzyl chloride at room temperature, stir, and obtain a mixed solution; B. adding imidazolium salt crystals to the mixed solution of step A, stirring at room temperature to obtain a film casting solution; C. pouring the casting solution prepared in step B into a glass mold, and after drying, peeling the obtained film from the glass mold; D. soaking the membrane obtained in step C with an aqueous phosphoric acid solution; E. Wash the membrane in step D with deionized water for more than 5 times and dry it to obtain the proton exchange membrane.

7. The preparation method according to claim 6, characterized in that: The mass concentration of the polybenzimidazole high boiling point solution in step A is 0.5-2wt%, and the high boiling point solvent used to prepare the polybenzimidazole high boiling point solution is one of N-methylpyrrolidone, N,N-dimethylformamide, tetrahydrofuran, and dimethyl sulfoxide; the mass concentration of the phosphoric acid aqueous solution in step D is 5-15wt%.

8. The preparation method according to claim 6, characterized in that: The mass ratio of each component in steps A and B is imidazolium salt crystal: polybenzimidazole: polyvinyl benzyl chloride = 1:1-3:1-1.

5.

9. The preparation method according to claim 6, characterized in that: The stirring time of step A is 24-48h, and the stirring time of step B is 24-48h; the drying temperature of the casting liquid in step C is 60-80°C, and the drying time is 24-48h; the soaking time in step D is 24-48h; the drying temperature in step E is 40-60°C, and the drying time is 24-48h.

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