Preparation method of bromine beta cyclodextrin and polybenzimidazole composite proton exchange membrane

Abstract

The application relates to a preparation method of a bromo-beta cyclodextrin and polybenzimidazole composite proton exchange membrane and relates to the technical field of high-temperature proton exchange membrane fuel cells. In order to solve the technical problem that the existing method improves the PA absorption amount but cannot optimize the PA retention capacity, resulting in the decline of the proton conductivity in a short time, the application is characterized by the following steps: 2,2'-(m-phenyl)-5,5'-diphenylbenzimidazole is prepared; bromo-beta cyclodextrin is prepared; and a bromo-beta cyclodextrin and PBI composite membrane is prepared. The prepared proton exchange membrane has multifunctional quaternary ammonium salt, provides more proton hopping sites, can absorb more PA to improve the proton conductivity of the membrane, and has certain acid retention capacity. The application is used for preparing a proton exchange membrane.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature proton exchange membrane fuel cells, in particular to a multi-functional quaternary ammonium salt composite poly[2,2'-(m-phenyl)-5,5'-bibenzimidazole] proton exchange membrane with high proton conductivity. Background Art

[0002] Proton exchange membrane (PEM) has the advantages of environmental friendliness, high energy conversion efficiency, and rapid response. It is one of the clean energy sources with lower cost and longer life. These characteristics have made it attract widespread attention.

[0003] Currently, research on proton exchange membranes has matured, and various types of proton exchange membranes have achieved certain results, but they still face some aspects that need improvement and optimization. For example, proton exchange membranes doped with high phosphoric acid have better proton transfer capabilities, and quaternary ammonium anions can effectively fix phosphoric acid (PA). In the past, the number of quaternary ammonium anions on quaternary ammonium proton exchange membranes was relatively small, resulting in a limited amount of PA that could be bound and anchored, which to some extent restricted the PA absorption capacity and proton conductivity. Secondly, the proton exchange membrane's ability to retain PA also needs to be improved. Current research often increases PA absorption but fails to optimize PA retention, resulting in a short-term decrease in proton conductivity and limiting the scope and application of proton exchange membranes. Therefore, solving the above problems has become a new challenge for the application of high-temperature proton exchange membranes. Summary of the Invention

[0004] In order to solve the technical problem that the existing method improves the PA absorption but cannot optimize the PA retention capacity, resulting in a decrease in proton conductivity in a short period of time, the present invention provides a method for preparing a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane.

[0005] A method for preparing a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane is specifically carried out according to the following steps:

[0006] Step 1: Preparation of 2,2'-(m-phenyl)-5,5'-bibenzimidazole

[0007] Dissolve diaminobenzidine and isophthalic acid in polyphosphoric acid, control the temperature between 120 and 140°C, and mechanically stir under nitrogen protection; after complete dissolution, raise the temperature to 200°C and continue the reaction until the product becomes viscous;

[0008] The viscous product is poured into a sodium bicarbonate solution, washed repeatedly until neutral, and dried to obtain 2,2'-(m-phenyl)-5,5'-bibenzimidazole;

[0009] Step 2: Preparation of brominated β-cyclodextrin

[0010] β-cyclodextrin and N-bromosuccinimide are dissolved in NN-dimethylacetamide, and a polymerization initiator, triphenylphosphine, is added. The reaction is carried out under nitrogen protection at a temperature of 80°C for 20 to 24 hours. The mixture is then poured into methanol and stirred to obtain a precipitate. The precipitate is then washed with a methanol-water solution until the washing liquid is colorless. The mixture is then dried to obtain brominated β-cyclodextrin.

[0011] Step 3: Preparation of phosphoric acid / bromo-β-cyclodextrin / PBI composite membrane

[0012] The 2,2'-(m-phenyl)-5,5'-bibenzimidazole obtained in step 1 and the brominated β-cyclodextrin obtained in step 2 were dissolved in NN-dimethylacetamide, stirred for 24 hours at a temperature of 60-80°C under nitrogen protection, and then poured onto a horizontal glass plate, cast into a film, and dried to obtain a brominated β-cyclodextrin and PBI composite film;

[0013] The brominated β-cyclodextrin and PBI composite membrane is immersed in a trimethylamine solution to carry out a quaternization reaction, and then the surface of the composite membrane is rinsed with distilled water, dried, and immersed in a phosphoric acid solution with a mass concentration of 85% for 48 hours to obtain the brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane.

[0014] The synthetic reaction formula of 2,2'-(m-phenyl)-5,5'-bibenzimidazole (PBI) is:

[0015]

[0016] The synthetic reaction formula of brominated β-cyclodextrin (Br-CD) is:

[0017]

[0018] Beneficial effects of the present invention:

[0019] The proton exchange membrane has multi-functional quaternary ammonium salts, which provide more proton hopping sites. Since each quaternary ammonium salt ion can bind to a PA, and the PAs are anchored to each other through hydrogen bonds to form a continuous proton transfer channel, the proton exchange membrane can absorb more PAs, thereby improving the proton conductivity of the membrane, and has a certain acid retention capacity.

[0020] The invention is used for preparing a proton exchange membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1SEM images of 2,2'-(m-phenyl)-5,5'-bibenzimidazole (PBI) prepared in the control example and the brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane (PBI-BC-X) prepared in the example, wherein Figure (a) is a cross-sectional SEM image of PBI, Figure (b) is a cross-sectional SEM image of PBI-BC-10%, Figure (c) is a cross-sectional SEM image of PBI-BC-20%, Figure (d) is a cross-sectional SEM image of PBI-BC-30%, Figure (e) is a surface SEM image of PBI, Figure (f) is a surface SEM image of PBI-BC-10%, Figure (g) is a surface SEM image of PBI-BC-20%, and Figure (h) is a surface SEM image of PBI-BC-30%;

[0022] Figure 2 The infrared spectra of 2,2'-(m-phenyl)-5,5'-bibenzimidazole (PBI) prepared in the control example and the brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane (PBI-BC-X) prepared in the example are shown;

[0023] Figure 3 The acid loss diagrams are for 2,2'-(m-phenyl)-5,5'-bibenzimidazole (PBI) prepared in the control example and the brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane (PBI-BC-X) prepared in the example;

[0024] Figure 4 The proton conductivity diagram of 2,2'-(m-phenyl)-5,5'-bibenzimidazole (PBI) prepared in the control example and the brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane (PBI-BC-X) prepared in the example. DETAILED DESCRIPTION

[0025] Specific embodiment 1: This embodiment is a method for preparing a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane, which is specifically carried out according to the following steps:

[0026] Step 1: Preparation of 2,2'-(m-phenyl)-5,5'-bibenzimidazole

[0027] Dissolve diaminobenzidine and isophthalic acid in polyphosphoric acid, control the temperature between 120 and 140°C, and mechanically stir under nitrogen protection; after complete dissolution, raise the temperature to 200°C and continue the reaction until the product becomes viscous;

[0028] The viscous product is poured into a sodium bicarbonate solution, washed repeatedly until neutral, and dried to obtain 2,2'-(m-phenyl)-5,5'-bibenzimidazole;

[0029] Step 2: Preparation of brominated β-cyclodextrin

[0030] β-cyclodextrin and N-bromosuccinimide are dissolved in NN-dimethylacetamide, and a polymerization initiator, triphenylphosphine, is added. The reaction is carried out under nitrogen protection at a temperature of 80°C for 20 to 24 hours. The mixture is then poured into methanol and stirred to obtain a precipitate. The precipitate is then washed with a methanol-water solution until the washing liquid is colorless. The mixture is then dried to obtain brominated β-cyclodextrin.

[0031] Step 3: Preparation of phosphoric acid / bromo-β-cyclodextrin / PBI composite membrane

[0032] The 2,2'-(m-phenyl)-5,5'-bibenzimidazole obtained in step 1 and the brominated β-cyclodextrin obtained in step 2 were dissolved in NN-dimethylacetamide, stirred for 24 hours at a temperature of 60-80°C under nitrogen protection, and then poured onto a horizontal glass plate, cast into a film, and dried to obtain a brominated β-cyclodextrin and PBI composite film;

[0033] The brominated β-cyclodextrin and PBI composite membrane is immersed in a trimethylamine solution to carry out a quaternization reaction, and then the surface of the composite membrane is rinsed with distilled water, dried, and immersed in a phosphoric acid solution with a mass concentration of 85% for 48 hours to obtain the brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane.

[0034] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the mass ratio of diaminobenzidine, isophthalic acid and polyphosphoric acid in step 1 is 5.6:4.3:80. Other aspects are the same as specific embodiment 1.

[0035] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the mechanical stirring speed in step 1 is 200-300 rpm. Other aspects are the same as specific embodiment 1 or 2.

[0036] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the concentration of the sodium bicarbonate solution in step 1 is 2 mol / L. Other aspects are the same as those of specific embodiments 1 to 3.

[0037] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the molar ratio of β-cyclodextrin to N-bromosuccinimide in step 2 is 1:14, and the amount of triphenylphosphine used is 1.5 g. Other steps are the same as those of specific embodiments 1 to 4.

[0038] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the stirring speed is controlled to be 500-600 rpm in step 2. The rest is the same as specific embodiments 1 to 5.

[0039] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the volume ratio of distilled water to methanol in the methanol aqueous solution in step 2 is 1:1. Other aspects are the same as specific embodiments 1 to 6.

[0040] Specific embodiment 8: This embodiment differs from Specific embodiments 1 to 7 in that the mass ratio of 2,2'-(m-phenyl)-5,5'-bibenzimidazole, brominated β-cyclodextrin, and NN-dimethylacetamide in step 3 is 1:(0.05-0.3):25. Other steps are the same as Specific embodiments 1 to 7.

[0041] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the thickness of the composite film in step 3 is 80 to 100 μm. Other aspects are the same as specific embodiments 1 to 8.

[0042] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that the quaternization reaction time in step 3 is controlled to be 48 to 72 hours. Other aspects are the same as specific embodiments 1 to 9.

[0043] The content of the present invention is not limited to the content of the above-mentioned embodiments. The combination of one or more specific embodiments can also achieve the purpose of the invention.

[0044] Example 1:

[0045] A method for preparing a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane is specifically carried out according to the following steps:

[0046] Step 1: Preparation of 2,2'-(m-phenyl)-5,5'-bibenzimidazole (PBI)

[0047] Dissolve 5.6 g of diaminobenzidine and 4.3 g of isophthalic acid in 80 g of polyphosphoric acid at 160°C with mechanical stirring under nitrogen. After complete dissolution, raise the temperature to 200°C and continue the reaction until the product becomes viscous.

[0048] The viscous product was poured into a 2 mol / L sodium bicarbonate solution, washed repeatedly until neutral, and dried to obtain 2,2'-(m-phenyl)-5,5'-bibenzimidazole (PBI);

[0049] Step 2: Preparation of brominated β-cyclodextrin (Br-CD)

[0050] β-cyclodextrin and N-bromosuccinimide were dissolved in NN-dimethylacetamide at a molar ratio of β-cyclodextrin to N-bromosuccinimide of 1:14. 1.5 g of triphenylphosphine, a polymerization initiator, was added. The reaction was carried out at 80° C. under nitrogen protection for 24 h. The mixture was then poured into methanol and stirred to obtain a precipitate. The precipitate was then washed with a methanol-water solution until the washing liquid turned from yellow to transparent. The precipitate was then dried in an oven at 60° C. to obtain brominated β-cyclodextrin (Br-CD).

[0051] Step 3: Preparation of phosphoric acid / bromo-β-cyclodextrin / PBI composite membrane (PBI-BC-X)

[0052] 1 g of 2,2'-(m-phenyl)-5,5'-bibenzimidazole obtained in step 1 and 0.05 g of brominated β-cyclodextrin obtained in step 2 were dissolved in 25 g of N-N-dimethylacetamide, and the mixture was reacted at 80° C. under nitrogen protection for 24 h. The mixture was then poured onto a clean glass plate, cast into a film, and dried to obtain a brominated β-cyclodextrin and PBI composite film;

[0053] The brominated β-cyclodextrin and PBI composite membrane was immersed in a trimethylamine solution for 48 hours to carry out a quaternization reaction, and then the surface of the composite membrane was rinsed with distilled water. After drying, the membrane was immersed in a phosphoric acid solution with a mass concentration of 85% for 48 hours to obtain the brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane (PBI-BC-5%).

[0054] The mechanical stirring speed in step 1 is 300 rpm;

[0055] Step 2: Control the stirring speed to 500 rpm;

[0056] The volume ratio of distilled water to methanol in the methanol aqueous solution in step 2 is 1:1;

[0057] The thickness of the composite film in step 3 is 80-90 μm.

[0058] Example 2:

[0059] This embodiment differs from the first embodiment in that the amount of brominated β-cyclodextrin used in step 3 is 0.1 g, and the product obtained is a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane (PBI-BC-10%). Other parameters and steps are the same as those in the first embodiment.

[0060] Example 3:

[0061] This embodiment differs from the first embodiment in that the amount of brominated β-cyclodextrin used in step 3 is 0.15 g, and the product obtained is a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane (PBI-BC-15%). Other parameters and steps are the same as those in the first embodiment.

[0062] Example 4:

[0063] This embodiment differs from the first embodiment in that the amount of brominated β-cyclodextrin used in step 3 is 0.20 g, and the product obtained is a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane (PBI-BC-20%). Other parameters and steps are the same as those in the first embodiment.

[0064] Embodiment 5:

[0065] The difference between this embodiment and embodiment 1 is that the amount of brominated β-cyclodextrin used in step 3 is 0.25 g, and the product obtained is a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane (PBI-BC-25%). Other parameters and steps are the same as those in embodiment 1.

[0066] Example 6:

[0067] The difference between this embodiment and the first embodiment is that the amount of brominated β-cyclodextrin used in step 3 is 0.30 g, and the product obtained is a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane (PBI-BC-30%). The other parameters and steps are the same as those in the first embodiment.

[0068] Comparison example:

[0069] This comparative example is 2,2'-(m-phenyl)-5,5'-bibenzimidazole prepared in Example, which was then prepared into a film (PBI).

[0070] The absorption capacity, ADL, and volume swelling test results of the PBI prepared in the control example and the brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane prepared in the example for PA are shown in Table 1:

[0071] Table 1

[0072] Samples PA uptake (wt.%) ADL Swelling (%) PBI 185.6±5.8 5.8±0.2 125.7±2.0 PBI-BC-5% 226.9±1.3 7.5±0.4 141.0±4.4 PBI-BC-10% 270.3±8.0 9.3±0.3 153.5±3.0 PBI-BC-15% 342.1±9.2 12.4±0.3 173.0±3.5 PBI-BC-20% 419.3±8.5 15.8±0.3 192.2±3.1 PBI-BC-25% 389.7±7.2 15.3±0.3 184.5±3.6 PBI-BC-30% 369.5±1.6 15.1±0.1 178.4±3.0

[0073] Figure 1SEM images of 2,2'-(m-phenyl)-5,5'-bibenzimidazole (PBI) prepared in the control example and the brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane (PBI-BC-X) prepared in the example, wherein Figure (a) is a cross-sectional SEM image of PBI, Figure (b) is a cross-sectional SEM image of PBI-BC-10%, Figure (c) is a cross-sectional SEM image of PBI-BC-20%, Figure (d) is a cross-sectional SEM image of PBI-BC-30%, and Figure (e) is a cross-sectional SEM image of PBI Figure (f) is the surface SEM image of PBI-BC-10%, Figure (g) is the surface SEM image of PBI-BC-20%, and Figure (h) is the surface SEM image of PBI-BC-30%; in the cross-sectional view, each membrane shows a certain degree of roughness, and with the increase of Br-CD content, the roughness becomes more obvious, which is beneficial to improving the absorption content of PA and promoting the enhancement of electrical conductivity; in the plan view, each membrane is smooth, dense, and defect-free, and can be used as a good membrane material.

[0074] Figure 2 Infrared spectra of 2,2'-(m-phenyl)-5,5'-bibenzimidazole (PBI) prepared in the control example and the brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane (PBI-BC-X) prepared in the example; 804 cm -1 The CN stretching vibration peak on the polybenzimidazole ring is 1450 cm -1 The characteristic absorption peak at 1623 cm corresponds to the deformation of the imidazole surface. -1 The peak at 656cm is the C=N stretching vibration peak on the polybenzimidazole ring. -1 The peak at the center is the stretching vibration peak of the bromine bond. It is observed that the peak intensity increases with the increase of Br-CD content, indicating that multifunctional quaternary ammonium salts in different proportions have been successfully introduced into PBI, indicating the successful preparation of the composite membrane PBI-BC-X.

[0075] Figure 3 Acid loss plots for a 2,2'-(m-phenyl)-5,5'-bibenzimidazole (PBI) proton exchange membrane (PBI-BC-X) prepared as a control and a brominated β-cyclodextrin / polybenzimidazole composite proton exchange membrane (PBI-BC-X) prepared as an example. Compared to the original PBI membrane, the composite membrane exhibits better PA retention, attributed to the introduction of Br-CD, which allows it to bind more PA and improves acid retention. The performance of PBI-BC-20% is superior to that of PBI-BC-25% and PBI-BC-30%, both of which have higher Br-CD content. This is due to the high concentration of Br-CD within the membrane, which hinders effective PA absorption. These test results echo those of the acid absorption test.

[0076] Figure 4The proton conductivity graphs for the 2,2'-(m-phenyl)-5,5'-bibenzimidazole (PBI) prepared as a control example and the brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane (PBI-BC-X) prepared as an example. The proton conductivity of the membranes was tested at 100°C to 180°C. The results showed that the proton conductivity of the composite membranes increased with increasing temperature, and the conductivity of the composite membranes was superior to that of the original PBI membrane. This improvement in the conductivity of the composite membranes is attributed to the presence of a large amount of quaternary ammonium salts within the membranes, which aids in the absorption and retention of polyacrylic acid (PA), which provides a pathway for proton transfer. Among the composite membranes, the most conductive one was PBO-BC-20%, with a conductivity of 127 mS / cm at 180°C. This test result is consistent with the results of the acid absorption capacity, ADL, swelling volume test, and acid loss test.

[0077] In summary, the product of the present invention prepares a PBI composite membrane with a multi-functional quaternary ammonium salt. The quaternary ammonium salt can combine with PA through ionic bonds, providing more proton hopping sites and improving the ability of the high-temperature proton exchange membrane in absorbing and retaining PA. At the same time, Br-CD has the cavity structure of β-cyclodextrin, which can fix more PA and thus promote the improvement of electrical conductivity.

Claims

1. A method for preparing a composite proton exchange membrane of brominated β-cyclodextrin and polybenzimidazole, characterized in that The method is specifically carried out in the following steps: Step 1: Preparation of 2,2'-(m-phenyl)-5,5'-bibenzimidazole Dissolve diaminobenzidine and isophthalic acid in polyphosphoric acid, control the temperature between 120 and 140°C, and mechanically stir under nitrogen protection; after complete dissolution, raise the temperature to 200°C and continue the reaction until the product becomes viscous; The viscous product is poured into a sodium bicarbonate solution, washed repeatedly until neutral, and dried to obtain 2,2'-(m-phenyl)-5,5'-bibenzimidazole; Step 2: Preparation of brominated β-cyclodextrin β-cyclodextrin and N-bromosuccinimide are dissolved in NN-dimethylacetamide, and a polymerization initiator, triphenylphosphine, is added. The reaction is carried out under nitrogen protection at a temperature of 80°C for 20 to 24 hours. The mixture is then poured into methanol and stirred to obtain a precipitate. The precipitate is then washed with a methanol-water solution until the washing liquid is colorless. The mixture is then dried to obtain brominated β-cyclodextrin. Step 3: Preparation of phosphoric acid / bromo-β-cyclodextrin / PBI composite membrane The 2,2'-(m-phenyl)-5,5'-bibenzimidazole obtained in step 1 and the brominated β-cyclodextrin obtained in step 2 were dissolved in NN-dimethylacetamide, stirred for 24 hours at a temperature of 60-80°C under nitrogen protection, and then poured onto a horizontal glass plate, cast into a film, and dried to obtain a brominated β-cyclodextrin and PBI composite film; The brominated β-cyclodextrin and PBI composite membrane is immersed in a trimethylamine solution to carry out a quaternization reaction, and then the surface of the composite membrane is rinsed with distilled water, dried, and immersed in a phosphoric acid solution with a mass concentration of 85% for 48 hours to obtain the brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane.

2. The method for preparing a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane according to claim 1, characterized in that The mass ratio of diaminobenzidine, isophthalic acid and polyphosphoric acid in step 1 is 5.6:4.3:

80.

3. The method for preparing a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane according to claim 1, characterized in that The mechanical stirring speed in step 1 is 200-300 rpm.

4. The method for preparing a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane according to claim 1, characterized in that The concentration of the sodium bicarbonate solution in step 1 is 2 mol / L.

5. The method for preparing a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane according to claim 1, characterized in that The molar ratio of β-cyclodextrin to N-bromosuccinimide in step 2 is 1:14, and the amount of triphenylphosphine used is 1.5 g.

6. The method for preparing a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane according to claim 1, characterized in that Step 2: Control the stirring speed to 500-600 rpm.

7. The method for preparing a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane according to claim 1, characterized in that The volume ratio of distilled water to methanol in the methanol aqueous solution in step 2 is 1:

1.

8. The method for preparing a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane according to claim 1, characterized in that The mass ratio of 2,2'-(m-phenyl)-5,5'-bibenzimidazole, brominated β-cyclodextrin and NN-dimethylacetamide in step 3 is 1:(0.05-0.3):

25.

9. The method for preparing a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane according to claim 1, characterized in that The thickness of the composite film in step 3 is 80-100 μm.

10. The method for preparing a brominated β-cyclodextrin and polybenzimidazole composite proton exchange membrane according to claim 1, characterized in that In step 3, the quaternization reaction time is controlled to be 48 to 72 hours.

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