A proton exchange membrane for fuel cells and its preparation method and use

Abstract

This invention relates to a proton exchange membrane for fuel cells, its preparation method, and its application, belonging to the field of proton exchange membrane fuel cell technology. The method involves copolymerizing aryl hydrocarbons with 2-acetylpyrimidine to obtain an arylpyrimidine polymer; dissolving the arylpyrimidine polymer in a high-boiling-point organic solvent to form a casting solution, casting it into a membrane, and drying it; then placing the obtained membrane in a phosphonate aqueous solution for crosslinking by heating; finally, immersing the crosslinked membrane in a phosphoric acid solution and drying it to obtain the proton exchange membrane. The proton exchange membrane of this invention uses an arylpyrimidine polymer as its framework, which has a higher phosphoric acid adsorption capacity compared to arylpiperone and arylpyridine polymers; the use of phosphonate crosslinking forms a dense surface layer, reducing the loss of phosphoric acid from the membrane interior; phosphonate enhances the proton co-conduction capability with phosphoric acid; and phosphonate can form hydrogen bonds with nitrogen-containing heterocycles in the framework, thereby enhancing conductivity.

Description

Technical Field

[0001] This invention relates to a proton exchange membrane for fuel cells, its preparation method, and its application, belonging to the field of proton exchange membrane fuel cell technology. Background Technology

[0002] In high-temperature fuel cell (100-180℃) applications, the operating temperature of high-temperature proton exchange membrane fuel cells is mainly determined by the high-temperature proton exchange membrane, and the proton conductor is the core. Existing commercial high-temperature proton exchange membranes all use phosphoric acid as the proton conductor, but as the operating temperature increases, the loss of phosphoric acid accelerates, leading to an increase in the rate of battery performance degradation.

[0003] PBI polymer-based materials have demonstrated significant effectiveness and feasibility in use as high-temperature proton exchange membranes in HT-PEMFCs. However, PBI membrane materials inevitably degrade at high temperatures (T≥150℃). In alkaline environments, the presence of strong nucleophiles OH- within the membrane can also lead to degradation of the polymer backbone and functional groups if they are connected to unstable end groups, such as quaternary ammonium salts containing β-H or α-C, or functional groups containing ether bonds. Therefore, arylpyridine polymers have also been used as polymeric backbones in this field. These ether-free polymers effectively address the degradation problem and offer advantages such as good film-forming properties, chemical stability, and thermal stability. However, due to limitations in the functional groups of arylpyridine polymers and severe swelling after impregnation with phosphoric acid, the impregnation amount is usually limited, thus affecting conductivity and membrane mechanical strength. Summary of the Invention

[0004] The purpose of this invention is to provide a proton exchange membrane for fuel cells, its preparation method, and its application. The proton exchange membrane framework is made of arylpyrimidine polymers, which have a higher phosphoric acid adsorption capacity compared to arylpiperone and arylpyridine polymers. The use of phosphonate crosslinking can form a dense surface layer, reducing the loss of phosphoric acid inside the membrane. Phosphonate can enhance the proton co-conduction ability with phosphoric acid. Phosphonate can form hydrogen bonds with nitrogen-containing heterocycles in the framework, thereby enhancing the conductivity.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] This invention provides a method for preparing a proton exchange membrane, comprising the following steps:

[0007] Step 1) The aryl hydrocarbon is copolymerized with 2-acetylpyrimidine to obtain an arylpyrimidine polymer;

[0008] Step 2): Dissolve the arylpyrimidine polymer obtained in step 1) in an organic high-boiling-point solvent to form a casting solution, cast it into a film, and then dry it.

[0009] Step 3): Place the membrane obtained in step 2) into a phosphonate aqueous solution and heat for crosslinking;

[0010] Step 4): Immerse the cross-linked membrane obtained in step 3) in phosphoric acid solution and dry it to obtain a proton exchange membrane.

[0011] In the above technical solution, further, in step 1), the synthesis step of the arylpyridine polymer specifically includes:

[0012] 2-Acetylpyrimidine and aryl hydrocarbons were added to dichloromethane solvent, and a catalyst and protonating agent were added at -15 to 5°C. The mixture was then returned to room temperature and reacted for 2 to 72 hours before purification to obtain arylpyridine polymers.

[0013] The aryl hydrocarbon is selected from one or more of biphenyl, p-terphenyl, m-terphenyl, p-tetraphenyl, 9,9-dimethyl-9H-fluorene, triphenylmethane, and 1,3,5-triphenylbenzene;

[0014] The catalyst is selected from either trifluoroacetic acid or trichloroacetic acid.

[0015] The protonating agent is selected from any one of trifluoromethanesulfonic acid and trinitrobenzenesulfonic acid;

[0016] The molar ratio of the 2-acetylpyrimidine to the aryl hydrocarbon is (1:1) to (1.4:1);

[0017] The aryl hydrocarbon is present in dichloromethane at a concentration of 0.001-0.01 mol / ml;

[0018] The molar ratio of 2-acetylpyrimidine to the catalyst is (1:4)-(1:8);

[0019] The molar ratio of 2-acetylpyrimidine to the protonating agent is (1:5)-(1:12).

[0020] In the above technical solution, further, in step 2), the high-boiling-point solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and dioxane;

[0021] The mass concentration of the casting solution is 1%-10%;

[0022] The drying temperature is 80-110℃, and the drying time is 15-30 hours;

[0023] The thickness of the membrane is 40-80 μm.

[0024] In the above technical solution, further, in step 3), the phosphonate is selected from one or more of the following: trimethyl phosphoroacetate; trimethyl phosphoroacetate; tetraethylmethylene diphosphate; and tetraisopropyl methylene diphosphate.

[0025] The mass concentration of the phosphonate aqueous solution is 5%-10%;

[0026] The heating temperature is 70-90℃, and the heating time is 5-10 hours;

[0027] In the above technical solution, further, in step 4), the mass fraction of the phosphoric acid solution is 1%-85%;

[0028] The soaking time is 10-30 hours;

[0029] The drying temperature is 60-120℃.

[0030] Another aspect of the present invention provides the application of the proton exchange membrane prepared by the above-described method in a fuel cell.

[0031] In summary, the present invention has the following beneficial effects:

[0032] 1. Firstly, this invention synthesizes arylpyrimidine polymers without unstable end groups such as ether bonds as the polymer backbone for proton exchange membranes, exhibiting excellent alkali resistance and simple synthesis methods and processes. Because the nitrogen atom content of the pyrimidine ring in the pyrimidine polymer is higher than that of arylpiperone and arylpyridine, it can provide more phosphate adsorption sites, thus exhibiting a higher phosphate adsorption capacity compared to arylpiperone and arylpyridine polymers.

[0033] 2. Secondly, this invention employs phosphonate crosslinking, which forms a dense surface layer and reduces the loss of phosphoric acid from the membrane. The method used in this invention enables the membrane to construct a multi-layered composite crosslinked structure. The middle layer is a dense layer of pyrimidine polymer, while the two sides are crosslinked by hydrothermal heating, allowing the phosphonate to polymerize with the pyrimidine polymer on the membrane surface to form a dense surface layer. The abundant sulfate groups in the phosphate ester contribute to the high conductivity of the membrane. The multi-layered crosslinked structure formed by the phosphate ester and the pyrimidine polymer can effectively improve the mechanical strength of the membrane. The phosphonate can enhance the proton co-conduction ability with phosphoric acid. The phosphonate can form hydrogen bonds with nitrogen-containing heterocycles in the backbone, which can further improve the bonding degree of the multi-layered structure. The hydrogen bonds formed between the multi-layered structures can enhance the conductivity. The crosslinked structure effectively alleviates the membrane swelling problem caused by impregnation with phosphoric acid. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to specific embodiments.

[0035] Example 1

[0036] (1) Add 0.01 mol of m-terphenyl and 0.01 mol of 2-acetylpyrimidine to 10 ml of dichloromethane and cool to -15 °C; add 0.04 mol of trifluoroacetic acid dropwise, then add 0.05 mol of trifluoromethanesulfonic acid dropwise. After the addition is complete, return to room temperature and react for 2 h. Pour the solution after reaction into methanol aqueous solution to precipitate a white solid. Wash the white solid with potassium carbonate solution at 50 °C, then wash with deionized water until neutral, and dry to obtain arylpyrimidine polymer.

[0037] (2) Take 0.1g of the prepared arylpyrimidine polymer and dissolve it in 10g of N,N-dimethylformamide to form a casting solution. Cast the solution into a film and dry it in a vacuum oven at 80°C for 15h to obtain a film with a thickness of 40μm.

[0038] (3) The prepared membrane was placed in a 5% trimethyl phosphoroacetate aqueous solution and heated at 70°C for 5 hours before being removed.

[0039] (4) The cross-linked membrane is soaked in a 1% phosphoric acid solution for 10 hours and then dried at 60°C to obtain a proton exchange membrane.

[0040] Example 2

[0041] (1) 0.01 mol of m-9,9-dimethyl-9H-fluorene, triphenylmethane and 0.14 mol of 2-acetylpyrimidine were added to 100 ml of dichloromethane and cooled to -15 °C; 0.08 mol of trichloroacetic acid was added dropwise, followed by 0.12 mol of trifluoromethanesulfonic acid. After the addition was completed, the mixture was returned to room temperature and reacted for 2 h. The solution after the reaction was poured into a methanol aqueous solution to precipitate a white solid. The white solid was washed with potassium carbonate solution at 50 °C, then washed with deionized water until neutral, and dried to obtain an arylpyrimidine polymer.

[0042] (2) Take 0.1g of the prepared arylpyrimidine polymer and dissolve it in 10g of N,N-dimethylformamide to form a casting solution. Cast the solution into a film and dry it in a vacuum oven at 80°C for 15h to obtain a film with a thickness of 40μm.

[0043] (3) The prepared membrane was placed in a 10% trimethyl phosphoroacetate aqueous solution and heated at 70°C for 5 hours before being removed.

[0044] (4) The cross-linked membrane is soaked in a phosphoric acid solution with a mass fraction of 85% for 30 hours and then dried at 120°C to obtain a proton exchange membrane.

[0045] Example 3

[0046] (1) Add 0.01 mol of m-1,3,5-triphenylbenzene and 0.12 mol of 2-acetylpyrimidine to 50 ml of dichloromethane and cool to -15 °C; add 0.05 mol of trifluoroacetic acid dropwise, then add 0.10 mol of trifluoromethanesulfonic acid dropwise. After the addition is complete, return to room temperature and react for 2 h. Pour the solution after reaction into methanol aqueous solution to precipitate a white solid. Wash the white solid with potassium carbonate solution at 50 °C, then wash with deionized water until neutral, and dry to obtain arylpyrimidine polymer.

[0047] (2) Take 0.1g of the prepared arylpyrimidine polymer and dissolve it in 10g of N,N-dimethylacetamide to form a casting solution. Cast the solution into a film and dry it in a vacuum oven at 70°C for 15h to obtain a film with a thickness of 40μm.

[0048] (3) The prepared membrane was placed in a 5% trimethyl phosphoroacetate aqueous solution and heated at 80°C for 5 hours, and then removed.

[0049] (4) The cross-linked membrane is soaked in a phosphoric acid solution with a mass fraction of 80% for 10 hours and then dried at 120°C to obtain a proton exchange membrane.

[0050] Comparative Example 1

[0051] The difference from Example 1 is that arylpyridine is used as the skeleton:

[0052] (1) Add 0.01 mol of m-terphenyl and 0.01 mol of 4-acetylpyridine to 10 ml of dichloromethane and cool to -15 °C; add 0.04 mol of trifluoroacetic acid dropwise, then add 0.05 mol of trifluoromethanesulfonic acid dropwise. After the addition is complete, return to room temperature and react for 2 h. Pour the solution after reaction into methanol aqueous solution to precipitate a white solid. Wash the white solid with potassium carbonate solution at 50 °C, then wash with deionized water until neutral, and dry to obtain arylpyrimidine polymer.

[0053] (2) Take 0.1g of the prepared arylpyrimidine polymer and dissolve it in 10g of N,N-dimethylformamide to form a casting solution. Cast the solution into a film and dry it in a vacuum oven at 80°C for 15h to obtain a film with a thickness of 40μm.

[0054] (3) The prepared membrane was placed in a 5% trimethyl phosphonoacetate aqueous solution and heated at 70°C for 5 hours before being removed.

[0055] (4) The cross-linked membrane is soaked in 1% phosphoric acid solution for 10 hours and dried at 60°C to obtain the proton exchange membrane.

[0056] Comparative Example 2

[0057] The difference from Example 1 is that phosphonate crosslinking is not performed:

[0058] (1) Add 0.01 mol of m-terphenyl and 0.01 mol of 2-acetylpyrimidine to 10 ml of dichloromethane and cool to -15 °C; add 0.04 mol of trifluoroacetic acid dropwise, then add 0.05 mol of trifluoromethanesulfonic acid dropwise. After the addition is complete, return to room temperature and react for 2 h. Pour the solution after reaction into methanol aqueous solution to precipitate a white solid. Wash the white solid with potassium carbonate solution at 50 °C, then wash with deionized water until neutral, and dry to obtain arylpyrimidine polymer.

[0059] (2) Take 0.1g of the prepared arylpyrimidine polymer and dissolve it in 10g of N,N-dimethylformamide to form a casting solution. Cast the solution into a film and dry it in a vacuum oven at 80°C for 15h to obtain a film with a thickness of 40μm.

[0060] (3) The prepared membrane was placed in a 5% trimethyl phosphate aqueous solution for 5 hours without heating and then removed.

[0061] (4) The cross-linked membrane is soaked in a 1% phosphoric acid solution for 10 hours and then dried at 60°C to obtain a proton exchange membrane.

[0062] Comparative Example 3

[0063] The difference from Example 1 is that tetramethylhexanediamine (TMHDA) is used for crosslinking:

[0064] (1) Add 0.01 mol of m-terphenyl and 0.01 mol of 2-acetylpyrimidine to 10 ml of dichloromethane and cool to -15 °C; add 0.04 mol of trifluoroacetic acid dropwise, then add 0.05 mol of trifluoromethanesulfonic acid dropwise. After the addition is complete, return to room temperature and react for 2 h. Pour the solution after reaction into methanol aqueous solution to precipitate a white solid. Wash the white solid with potassium carbonate solution at 50 °C, then wash with deionized water until neutral, and dry to obtain arylpyrimidine polymer.

[0065] (2) Take 0.1g of the prepared arylpyrimidine polymer and dissolve it in 10g of N,N-dimethylformamide to form a casting solution. Cast the solution into a film and dry it in a vacuum oven at 80°C for 15h to obtain a film with a thickness of 40μm.

[0066] (3) Place the prepared membrane in immersion in tetramethylhexanediamine (TMHDA) for 5 hours and then remove it.

[0067] (4) The cross-linked membrane is soaked in a 1% phosphoric acid solution for 10 hours and then dried at 60°C to obtain a proton exchange membrane.

[0068] The acid retention rate, chemical stability, electrical conductivity, tensile strength, dimensional change rate, and chemical stability of the proton exchange membranes prepared in Examples 1-3 and Comparative Examples 1-3 were tested.

[0069] The conductivity test conditions are: 120℃, 40% humidity and 100℃, 30% humidity. The tensile strength test method is the national standard method (GB / T20042.3-2009). The hydrogen permeation current test method is the electrochemical method.

[0070] The ionic conductivity of the membrane was tested, and the results are shown in the table below. The results show that the membrane exhibits proton conductivity after impregnation with acid, and the membrane with high conductivity and high mechanical strength is also achieved by appropriately introducing diamine-functionalized graphene oxide.

[0071] The proton exchange membranes prepared in the embodiments and comparative examples of the present invention were weighed after adsorbing acid, and then immersed in pure water to test the mass residue rate after a certain period of time to detect the ability to retain acid. The conductivity retention rate before and after immersion was also tested. The results are shown in the table below.

[0072] Table 1

[0073]

[0074] Comparative Example 1: A film was formed directly using arylpyridine as the framework, without using the pyrimidine polymer used in this invention. The results showed that the acid adsorption was low and the conductivity was low.

[0075] In Comparative Example 2, no phosphonate heating crosslinking was performed during the membrane process. Instead, the phosphonate was directly immersed in the membrane and dried. No crosslinked structure or dense layer was formed. The results showed that the membrane of Comparative Example 2 suffered severe phosphoric acid loss and low conductivity.

[0076] Comparative Example 3, which used tetramethylhexanediamine (TMHDA) for crosslinking, did not form hydrogen bonds with the polymer or form a dense layer. The results showed poor acid retention, poor conductivity stability, and low conductivity value.

[0077] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for producing a proton exchange membrane, characterized by, Includes the following steps: Step 1) The aryl hydrocarbon is copolymerized with 2-acetylpyrimidine to obtain an arylpyrimidine polymer; Step 2): Dissolve the arylpyrimidine polymer obtained in step 1) in an organic high-boiling-point solvent to form a casting solution, cast it into a film, and then dry it. Step 3): Place the membrane obtained in step 2) into a phosphonate aqueous solution and heat for crosslinking; Step 4): Immerse the cross-linked membrane obtained in step 3) in phosphoric acid solution and dry it to obtain a proton exchange membrane.

2. The preparation method according to claim 1, characterized in that: In step 1), the synthesis steps of the arylpyrimidine polymer are specifically as follows: 2-Acetylpyrimidine and aryl hydrocarbons were added to dichloromethane solvent, and a catalyst and protonating agent were added at -15 to 5°C. The mixture was then returned to room temperature and reacted for 2 to 72 hours before purification to obtain arylpyrimidine polymers. The aryl hydrocarbon is selected from one or more of biphenyl, p-terphenyl, m-terphenyl, p-tetraphenyl, 9,9-dimethyl-9H-fluorene, triphenylmethane, and 1,3,5-triphenylbenzene; The catalyst is selected from either trifluoroacetic acid or trichloroacetic acid. The protonating agent is selected from any one of trifluoromethanesulfonic acid and trinitrobenzenesulfonic acid; The molar ratio of the 2-acetylpyrimidine to the aryl hydrocarbon is (1:1) to (1.4:1); The aryl hydrocarbon is present in dichloromethane at a concentration of 0.001-0.01 mol / ml; The molar ratio of 2-acetylpyrimidine to the catalyst is (1:4)-(1:8); The molar ratio of 2-acetylpyrimidine to the protonating agent is (1:5)-(1:12).

3. The preparation method according to claim 1, characterized in that: In step 2), the high-boiling solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and dioxane; The mass concentration of the casting solution is 1%-10%; The drying temperature is 80-110℃, and the drying time is 15-30 hours; The thickness of the membrane is 40-80 μm.

4. The preparation method according to claim 1, characterized in that: In step 3), the phosphonate is selected from one or more of trimethyl phosphoroacetate, trimethyl phosphoroacetate, tetraethylmethylene diphosphate, and tetraisopropyl methylene diphosphate; The mass concentration of the phosphonate aqueous solution is 5%-10%; The heating temperature is 70-90℃, and the heating time is 5-10 hours.

5. The preparation method according to claim 1, characterized in that: In step 4), the phosphoric acid solution has a mass fraction of 1%-85%; the soaking time is 10-30 hours; and the drying temperature is 60-120°C.

6. The application of a proton exchange membrane prepared by any one of claims 1-5 in a fuel cell.

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