Polybenzimidazole modified ion exchange membrane as well as preparation and application thereof

Abstract

The invention discloses a polybenzimidazole modified ion exchange membrane as well as preparation and application thereof. The polybenzimidazole modified ion exchange membrane comprises a polybenzimidazole-containing porous base membrane, the surface of the porous base membrane is grafted with a sulfonic acid modified layer, and the outer surface of the sulfonic acid modified layer is coated with an aluminum fluoride layer. The preparation method of the membrane comprises the following steps: immersing a polybenzimidazole-based membrane into an ammonium acetate aqueous solution for reaction, taking out the base membrane after the reaction, and drying to obtain a pretreated base membrane; immersing the pretreated base membrane into a sulfonic acid group grafting solution, heating for reaction, cleaning the base membrane after the reaction, and drying to obtain a sulfonic acid modified base membrane; and immersing the sulfonic acid modified base membrane into an ethanol solution of aluminum fluoride for reaction, taking out the membrane after the reaction, cleaning and drying to obtain the membrane. The membrane can be used for assembling a flow battery. According to the invention, the problem that a sulfonic acid modified layer is incompatible with metal fluoride is overcome, and a proper combination of a sulfonating agent and metal fluoride is screened, so that the high-performance ion exchange membrane which can be used for a flow battery is successfully obtained.

Description

Technical Field

[0001] The invention relates to a modification preparation method of an ion exchange membrane, in particular to a polybenzimidazole modified ion exchange membrane and the preparation and application thereof. Background Art

[0002] Polybenzimidazole (PBI) is a class of engineering plastics with excellent properties. It is an aromatic heterocyclic polymer containing a benzimidazole structure in the repeating unit. PBI material is easy to modify, and many functional groups such as sulfonate, sulfone, and phenolic hydroxyl groups can be introduced into its skeleton. The reason why PBI is easy to modify is that its chemical stability is weak, and the weak chemical stability leads to poor corrosion resistance of PBI membrane in acidic environment. However, when PBI membrane is used as an ion exchange membrane in vanadium flow battery, in order to improve the coulombic efficiency and energy efficiency of the battery, the PBI membrane must be loaded with acid before it can be used for the assembly of vanadium flow battery, which makes the disadvantage of PBI membrane not resistant to acid corrosion more prominent and cannot be used on a large scale. In addition, the existing PBI membrane still has the problem of poor hydrophilicity and ionic conductivity when used in the field of flow battery, which further limits its application in flow battery. Summary of the invention

[0003] Purpose of the invention: The purpose of the present invention is to provide a polybenzimidazole modified ion exchange membrane with good chemical stability and excellent electrochemical performance. Another purpose of the present invention is to propose a method for preparing a polybenzimidazole modified ion exchange membrane to solve the problem of how to modify and prepare a polybenzimidazole modified ion exchange membrane. The third purpose of the present invention is to provide an application of a polybenzimidazole modified ion exchange membrane in the preparation of a liquid flow battery to solve the problem of how to prepare a liquid flow battery.

[0004] Technical solution: The polybenzimidazole modified ion exchange membrane described in the present invention comprises a porous base membrane containing polybenzimidazole, a sulfonic acid modified layer is grafted on the surface of the porous base membrane, and an aluminum fluoride layer is coated on the outer surface of the sulfonic acid modified layer.

[0005] The second aspect of the present invention discloses a method for preparing the polybenzimidazole modified ion exchange membrane, comprising the following steps:

[0006] (1) immersing a base film made of polybenzimidazole into an aqueous solution of ammonium acetate for reaction, and after the reaction, taking out the base film and drying it to obtain a pretreated base film;

[0007] (2) immersing the pretreated base membrane in a sulfonic acid group grafting solution, heating for reaction, and after the reaction, washing the base membrane and drying to obtain a sulfonic acid modified base membrane;

[0008] (3) The sulfonic acid modified base membrane is immersed in an ethanol solution of aluminum fluoride for reaction, and the membrane is taken out after the reaction, and the polybenzimidazole modified ion exchange membrane is obtained after washing and drying.

[0009] Preferably, in step (1), the concentration of the ammonium acetate aqueous solution is 0.2 - 1 M, the reaction conditions are reacting at 40 - 80 °C for 10 - 50 min, and the drying conditions are drying at 70 - 90 °C for 30 - 90 min.

[0010] Preferably, in step (2), the sulfonic acid group grafting solution is a mixed solution of concentrated sulfuric acid and chlorosulfonic acid.

[0011] Preferably, the volume ratio of the concentrated sulfuric acid to the chlorosulfonic acid is 1 - 3:1 - 3.

[0012] Preferably, in step (2), the heating reaction conditions are heating to 40 - 60 °C and reacting for 6 - 8 h, with intermittent stirring during the reaction; the cleaning method is to wash the membrane with deionized water until the pH of the membrane returns to neutral; the drying conditions are drying at 40 - 80 °C for 1 - 3 h.

[0013] Preferably, in step (3), the concentration of aluminum chloride in the ethanol solution of aluminum fluoride is 0.5 - 1 M.

[0014] Preferably, in step (3), the reaction conditions are soaking at 50 - 70 °C for 5 - 15 min, the cleaning method is to wash the membrane with deionized water until the pH of the membrane returns to neutral, and the drying conditions are drying and curing at 80 - 100 °C for 30 - 90 min.

[0015] The third aspect of the present invention discloses the application of the above-mentioned polybenzimidazole modified ion exchange membrane in the preparation of a flow battery.

[0016] Preferably, the flow battery is a vanadium redox flow battery.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0018] In the present invention, sulfonic acid groups are grafted onto the surface of the PBI membrane through a grafting reaction, which increases the hydrophilicity and ion exchange capacity of the membrane, improves the ion conductivity of the membrane, and enhances the Coulomb efficiency. By coating aluminum fluoride, a protective layer is formed on the membrane surface, improving the chemical stability of the membrane, especially the corrosion resistance in an acidic environment, further reducing the resistance of the membrane, and improving the voltage efficiency. The present invention overcomes the problem of incompatibility between the sulfonic acid modified layer and metal fluoride, and by screening an appropriate combination of sulfonating agent and metal fluoride, a high-performance ion exchange membrane for flow batteries is successfully obtained. Description of the Drawings

[0019] Figure 1 It is the surface microscopic morphology diagram of the polybenzimidazole modified ion exchange membrane prepared in Example 1. Detailed Embodiments

[0020] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings.

[0021] Example 1: A polybenzimidazole modified ion exchange membrane, comprising a porous base membrane containing polybenzimidazole, a sulfonic acid modified layer is grafted on the surface of the porous base membrane, and an aluminum fluoride layer is coated on the outer surface of the sulfonic acid modified layer.

[0022] The preparation method of the above polybenzimidazole modified ion exchange membrane is as follows:

[0023] (1) Immerse a 54 kDa polybenzimidazole base membrane in an aqueous ammonium acetate solution with a concentration of 0.5 M, react at 60 °C for 30 min, take out the base membrane after the reaction, and dry it at 80 °C for 60 min to obtain a pretreated base membrane;

[0024] (2) Mix concentrated sulfuric acid and chlorosulfonic acid in a volume ratio of 1:1 as the grafting solution, immerse the pretreated base membrane in the grafting solution, heat to 50 °C and react for 7 h, stir once per hour during the reaction, and after the reaction, wash the membrane with deionized water until the pH of the membrane returns to neutral, and dry it at 60 °C for 2 h to obtain a sulfonic acid modified base membrane;

[0025] (3) Dissolve aluminum chloride in absolute ethanol at a concentration of 0.75 M to obtain an ethanol solution of aluminum fluoride; immerse the sulfonic acid modified base membrane in the ethanol solution of aluminum fluoride, soak and react at 60 °C for 10 min, take out the membrane after the reaction, wash the membrane with deionized water until the pH of the membrane returns to neutral, and then dry and cure the membrane at 90 °C for 60 min to obtain a polybenzimidazole modified ion exchange membrane, and its surface morphology is as Figure 1 shown.

[0026] Example 2: Prepare a polybenzimidazole modified ion exchange membrane according to the following method:

[0027] (1) Immerse the polybenzimidazole base membrane in an aqueous ammonium acetate solution with a concentration of 0.2 M, react at 40 °C for 50 min, take out the base membrane after the reaction, and dry it at 70 °C for 90 min to obtain a pretreated base membrane;

[0028] (2) Mix concentrated sulfuric acid and chlorosulfonic acid in a volume ratio of 3:1 as the grafting solution, immerse the pretreated base membrane in the grafting solution, heat to 40 °C and react for 8 h, stir once per hour during the reaction, and after the reaction, wash the membrane with deionized water until the pH of the membrane returns to neutral, and dry it at 40 °C for 3 h to obtain a sulfonic acid modified base membrane;

[0029] (3) Dissolve aluminum chloride in absolute ethanol at a concentration of 0.5 M to obtain an ethanol solution of aluminum fluoride; immerse the sulfonic acid modified base membrane in the ethanol solution of aluminum fluoride, soak and react at 50 °C for 15 min, take out the membrane after the reaction, wash the membrane with deionized water until the pH of the membrane returns to neutral, and then dry and cure the membrane at 80 °C for 90 min to obtain a polybenzimidazole modified ion exchange membrane.

[0030] Example 3: Prepare a polybenzimidazole modified ion exchange membrane by the following method:

[0031] (1) Immerse the polybenzimidazole-based membrane in an aqueous ammonium acetate solution with a concentration of 1 M, react at 80 °C for 10 min, take out the base membrane after the reaction, and dry it at 90 °C for 30 min to obtain a pretreated base membrane;

[0032] (2) Mix concentrated sulfuric acid and chlorosulfonic acid in a volume ratio of 1:3 as the grafting solution, immerse the pretreated base membrane in the grafting solution, heat to 60 °C and react for 6 h, stir once per hour during the reaction, after the reaction, wash the membrane with deionized water until the pH of the membrane returns to neutral, and dry it at 80 °C for 1 h to obtain a sulfonic acid modified base membrane;

[0033] (3) Dissolve aluminum chloride in absolute ethanol to obtain an ethanol solution of aluminum fluoride according to the concentration of aluminum chloride being 1 M; immerse the sulfonic acid modified base membrane in the ethanol solution of aluminum fluoride, soak and react at 70 °C for 5 min, take out the membrane after the reaction, wash the membrane with deionized water until the pH of the membrane returns to neutral, and then dry and cure the membrane at 100 °C for 30 min to obtain a polybenzimidazole modified ion exchange membrane.

[0034] Comparative Example 1: The rest are the same as in Example 1, except that:

[0035] Replace ammonium acetate in step (1) with calcium acetate.

[0036] Comparative Example 2: The rest are the same as in Example 1, except that:

[0037] Replace the polybenzimidazole-based membrane in step (1) with a polyether ether ketone membrane.

[0038] Comparative Example 3: The rest are the same as in Example 1, except that:

[0039] Replace chlorosulfonic acid in step (2) with concentrated sulfuric acid.

[0040] Comparative Example 4: The rest are the same as in Example 1, except that:

[0041] Replace concentrated sulfuric acid in step (2) with chlorosulfonic acid.

[0042] Comparative Example 5: The rest are the same as in Example 1, except that:

[0043] Replace chlorosulfonic acid in step (2) with sulfur trioxide.

[0044] Comparative Example 6: The rest are the same as in Example 1, except that:

[0045] Replace concentrated sulfuric acid in step (2) with sodium sulfite.

[0046] Comparative Example 7: The rest are the same as in Example 1, except that:

[0047] The aluminum fluoride in step (3) is replaced with CaF2.

[0048] Comparative Example 8: The rest are the same as in Example 1, except that:

[0049] The aluminum fluoride in step (3) is replaced with ZrF4.

[0050] All-vanadium redox flow batteries are assembled and prepared using the ion exchange membrane samples prepared in Examples 1-3 and Comparative Examples 1-8. The method is as follows:

[0051] Electrode and ion exchange membrane treatment: Immerse the graphite electrode in dilute sulfuric acid solution for cleaning to remove impurities and oxides on the surface, ensuring that the active sites on the electrode surface are fully exposed. The ion exchange membrane sample also needs to be pretreated in sulfuric acid solution to fully swell the membrane and enhance the ion conduction ability. After pretreatment, rinse the electrode and ion exchange membrane with deionized water to remove the residual acid solution on the surface.

[0052] Assemble the battery body: Inside the battery frame, place the current collector plate, graphite electrode, sealing gasket, ion exchange membrane, sealing gasket, graphite electrode, and current collector plate in sequence. Ensure that each component fits tightly to avoid liquid leakage. The selection of the sealing gasket needs to consider its sealing performance and corrosion resistance in an acidic environment. Gaskets made of acid-resistant materials such as polytetrafluoroethylene can be used.

[0053] Connect the external circulation system: Connect the storage tank to the battery body through a connecting pipeline, and use a peristaltic pump to drive the electrolyte to circulate between the battery and the storage tank. The storage tank needs to be made of acid-resistant materials such as polyethylene or polypropylene to prevent acid corrosion. When connecting the pipeline, ensure that the pipeline is well sealed without liquid leakage, and at the same time ensure the smooth flow of the electrolyte to achieve the efficient operation of the battery.

[0054] The electrolyte is prepared by using vanadium sulfate salts such as vanadyl sulfate (VOSO4) as the vanadium source and dissolving it in sulfuric acid and water. The total vanadium concentration in the electrolyte is 1.8 mol / L, and the sulfuric acid concentration is 2 mol / L.

[0055] Test the electrochemical performance of different all-vanadium redox flow batteries. The results are as follows:

[0056] Table 1 Electrochemical performance test results of all-vanadium redox flow batteries assembled based on different ion-conducting membranes

[0057]

[0058] In the results of Table 1, it can be seen from Comparative Example 1 that when calcium acetate is used as the pore regulator, it will reduce the graft modification effect of the subsequent sulfonic acid groups on the PBI membrane, thereby weakening the ionic conductivity of the membrane. Comparative Example 2 shows that the sulfonic acid group graft modification solution composed of concentrated sulfuric acid and chlorosulfonic acid cannot effectively modify the polyether ether ketone membrane, and this graft modification solution can specifically graft-modify the PBI membrane. Comparative Examples 3-6 show that a single sulfonating agent or an inappropriate combination of multiple sulfonating agents will make it difficult for subsequent metal fluorides to stably bind, unable to form a protective layer, thereby reducing the corrosion resistance of the membrane in an acidic environment and ultimately resulting in poor electrical properties of the membrane. Comparative Examples 7 and 8 show that metal fluorides such as CaF2 cannot stably bind to the sulfonic acid modified layer, resulting in insufficient corrosion resistance of the ion exchange membrane, while aluminum fluoride can stably bind to the sulfonic acid modified layer prepared by a specific sulfonating agent, protecting the sulfonic acid modified layer and the base membrane from corrosion in an acidic environment, effectively improving the ionic conductivity of the membrane and obtaining better comprehensive electrical properties.

Claims

1. A polybenzimidazole modified ion exchange membrane, characterized in that: The invention comprises a porous base film containing polybenzimidazole, a sulfonic acid modified layer is grafted on the surface of the porous base film, and an aluminum fluoride layer is coated on the outer surface of the sulfonic acid modified layer.

2. The method for preparing the polybenzimidazole modified ion exchange membrane according to claim 1, characterized in that: The steps include: (1) immersing a base film made of polybenzimidazole into an aqueous solution of ammonium acetate for reaction, and after the reaction, taking out the base film and drying it to obtain a pretreated base film; (2) immersing the pretreated base membrane in a sulfonic acid group grafting solution, heating for reaction, and after the reaction, washing the base membrane and drying it to obtain a sulfonic acid modified base membrane; (3) The sulfonic acid modified base membrane is immersed in an ethanol solution of aluminum fluoride for reaction, and the membrane is taken out after the reaction, and the polybenzimidazole modified ion exchange membrane is obtained after washing and drying.

3. The method for preparing the polybenzimidazole modified ion exchange membrane according to claim 2, characterized in that: In step (1), the concentration of the aqueous ammonium acetate solution is 0.2-1M, the reaction conditions are 40-80°C for 10-50 min, and the drying conditions are 70-90°C for 30-90 min.

4. The method for preparing the polybenzimidazole modified ion exchange membrane according to claim 2, characterized in that: In step (2), the sulfonic acid group grafting solution is a mixture of concentrated sulfuric acid and chlorosulfonic acid.

5. The method for preparing the polybenzimidazole modified ion exchange membrane according to claim 4, characterized in that: The volume ratio of the concentrated sulfuric acid to chlorosulfonic acid is 1-3:1-3.

6. The method for preparing the polybenzimidazole modified ion exchange membrane according to claim 2, characterized in that: In step (2), the heating reaction conditions are heating to 40-60°C for 6-8h, with intermittent stirring during the reaction; the cleaning method is to use deionized water to clean the membrane until the pH of the membrane returns to neutral; the drying conditions are drying at 40-80°C for 1-3h.

7. The method for preparing the polybenzimidazole modified ion exchange membrane according to claim 2, characterized in that: In step (3), the concentration of aluminum chloride in the ethanol solution of aluminum fluoride is 0.5-1M.

8. The method for preparing the polybenzimidazole modified ion exchange membrane according to claim 2, characterized in that: In step (3), the reaction conditions are immersion at 50-70°C for 5-15 minutes, the cleaning method is to use deionized water to clean the membrane until the pH of the membrane returns to neutral, and the drying conditions are drying and curing at 80-100°C for 30-90 minutes.

9. Use of the polybenzimidazole modified ion exchange membrane according to claim 1 in preparing a liquid flow battery.

10. The use according to claim 9, characterized in that: The liquid flow battery is an all-vanadium liquid flow battery.

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