Composite anion exchange membrane and method for producing the same

Abstract

The application relates to the technical field of membranes, in particular to a composite anion exchange membrane and a preparation method thereof. The composite anion exchange membrane comprises a modified metal organic framework and a quaternary ammonium polytriphenylpiperidine polymer which is compounded with the modified metal organic framework; wherein the modified metal organic framework comprises a metal organic framework with a flexible long side chain grafted with a piperidine functional group and a surface-introduced adhesion medium containing polyphenol. The composite anion exchange membrane provided by the application has excellent compatibility between fillers and polymers, can ensure uniform distribution of the fillers in the membrane, and has good long-term stability.

Description

Technical Field

[0001] This invention relates to the field of membrane technology, specifically to a composite anion exchange membrane and its preparation method. Background Technology

[0002] Anion exchange membrane electrolysis (AEMWEs), as an emerging energy conversion technology, uses anion exchange membranes as solid electrolyte membranes to electrolyze water for hydrogen production, showing great potential in hydrogen production. The anion exchange membrane (AEM), as the core material of AEMWEs, plays a dual role as a charge carrier and an electro / gas barrier. These membranes ensure efficient flow of charged ions while also playing an indispensable role in preventing cross-permeation of electrolytes, significantly influencing the efficiency and reaction rate of hydrogen production from water electrolysis.

[0003] AEMs consist of a polymer backbone, fixed cationic groups, and free anions (such as OH-) that balance the charge of the cationic groups. In practical applications, achieving high ionic conductivity, high dimensional stability, and excellent chemical stability simultaneously has become a major challenge in developing novel AEMs.

[0004] To improve these performance characteristics, introducing advanced fillers to prepare composite AEMs is a common practice in existing research. For example, invention patent CN118431526A reports an organic-organic hybrid anion exchange membrane formed by crosslinking PTP-FM-N copolymers with organic nanotubes to create a series of composite membranes. However, existing technologies still have some drawbacks in preparing composite AEMs, mainly including poor compatibility between the filler and the polymer matrix, uneven distribution of the filler within the membrane, and a gradual decrease in membrane stability during long-term use. These problems limit the performance of AEMs in the field of electrochemical energy conversion. Summary of the Invention

[0005] To address the aforementioned problems, the first aspect of this invention aims to provide a composite anion exchange membrane in which the filler and polymer exhibit excellent compatibility, ensuring uniform distribution of the filler within the membrane, and possessing high ion conductivity and good long-term stability.

[0006] The second objective of this invention is to provide a method for preparing a composite anion exchange membrane.

[0007] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution:

[0008] According to a first aspect of the present invention, the present invention provides a composite anion exchange membrane, characterized in that it comprises a modified metal-organic framework and a quaternized poly(terphenyl piperidine) polymer (PTPip) composite with the modified metal-organic framework; wherein the modified metal-organic framework comprises a metal-organic framework (MOF) with a surface-introduced adhesive medium containing polyphenols and grafted with flexible long side chains having piperidine functional groups.

[0009] Preferably, the polyphenol-containing adhesive medium includes tannic acid (TA).

[0010] Preferably, the flexible long side chain with piperidine functional group comprises 4-(6-bromohexyl)-1,1-dimethylpiperidine-1-onium (6Brpip).

[0011] Preferably, the metal-organic framework comprises a zeolite imidazole framework (ZIF-8).

[0012] The presence of piperidine cations on flexible long side chains increases the ion exchange capacity of the composite membrane, making the hydrophilic area on the membrane more pronounced, thereby significantly improving the overall performance of the membrane. In this application, by attaching flexible long side chains with piperidine functional groups to the basic stable ZIF-8, the density of piperidine cations in the filler is very high, promoting the free exchange of OH- ions and significantly improving the ion conductivity of the membrane. This improved method enhances the compatibility between the filler and the polymer, which is beneficial to the uniform dispersion of the filler, thereby improving the overall performance of the prepared AEM.

[0013] According to a second aspect of the present invention, the present invention also provides a method for preparing the composite anion exchange membrane as described above, characterized in that it includes the following steps:

[0014] S1. Metal-organic framework modified with binder: The metal-organic framework was dispersed in deionized water, a binder containing polyphenols was added, and after standing, it was centrifuged and washed to obtain product A.

[0015] S2. Flexible long side chain modified product A: Product A and a flexible long side chain with piperidine functional group were dissolved in a solvent. After complete dissolution, a strong basic auxiliary agent was added, centrifuged, washed and dried to obtain product B.

[0016] S3. Preparation of composite anion exchange membrane: Quaternized poly(terphenylpiperidine) polymer is dissolved in a solvent, stirred and dispersed, and then product B is added. After uniform mixing, a mixed solution is obtained. The mixed solution is used to prepare an anion exchange membrane by solution casting. The anion exchange membrane is then vacuum dried to obtain a composite anion exchange membrane.

[0017] Preferably, in step S1, the metal-organic framework is prepared by the following steps: At room temperature, a clean beaker is taken, 2-methylimidazole is added, and dissolved in methanol, labeled as solution A. In another container, a certain amount of zinc salt is dissolved in methanol, labeled as solution B. Solution B is quickly poured into solution A, stirred, a certain amount of sodium borohydride is added, stirred, centrifuged, and washed with ethanol. The resulting solid is dried to obtain ZIF-8.

[0018] Preferably, in solution A, the ratio of 2-methylimidazole to methanol is (32-33) g: (100-400) ml.

[0019] Preferably, in solution B, the ratio of zinc salt to methanol is (14-15) g: (50-200) ml.

[0020] Preferably, in step S1, the volume of deionized water is 5 to 10 mL.

[0021] Preferably, in step S1, the ratio of the metal-organic framework to the polyphenol-containing adhesive medium is (8-12) g: (1-5) mg.

[0022] Preferably, in step S1, the settling time is 3 to 6 minutes.

[0023] Preferably, in step S2, the flexible long side chain with piperidine functional groups is prepared by the following steps: 1,6-dibromohexane is added to ethyl acetate in a single-necked flask and stirred until homogeneous to prepare solution C. N-methylpiperidine is poured into ethyl acetate in a beaker and stirred until homogeneous to prepare solution D. Solution D is slowly added dropwise to solution C and mixed thoroughly. After reacting for 24 hours, a large amount of white precipitate is generated. The reactants are allowed to stand for 10 minutes, and the supernatant is discarded. The collected solid is repeatedly washed with ethyl acetate to obtain product 6Brpip.

[0024] Preferably, in the solution C, the ratio of 1,6-dibromohexane to ethyl acetate is (0.15-0.25) mol: (130-160) mL.

[0025] Preferably, in the solution D, the ratio of N-methylpiperidine to ethyl acetate is (0.05-0.15) mol: (40-70) mL.

[0026] Preferably, in step S2, the strongly alkaline auxiliary agent includes potassium carbonate.

[0027] Preferably, in step S2, the ratio of product A to the flexible long side chain with piperidine functional group is (80-100) mg: (280-320) mg.

[0028] Preferably, in step S2, the solvent includes N,N-dimethylformamide (DMF).

[0029] Preferably, in step S2, the ratio of the strong alkaline auxiliary agent to the flexible long side chain with piperidine functional group is (20-35) mg: (80-320) mg.

[0030] Preferably, in step S3, the quaternized poly(terphenylpiperidine) polymer is prepared by the following steps: adding poly(terphenylpiperidine) (PTP), iodomethane, dimethyl sulfoxide and 1-methyl-2-pyrrolidone into a container, shielding the container from light, stirring, precipitating in diethyl ether, washing several times, filtering and drying to obtain the quaternized poly(terphenylpiperidine) polymer.

[0031] Preferably, the ratio of PTP to iodomethane is (1-1.5) g: (0.4-1) mL.

[0032] Preferably, the ratio of dimethyl sulfoxide to 1-methyl-2-pyrrolidone is (10-15) mL: (40-60) mL.

[0033] More preferably, the PTP is prepared by the following steps: N-methyl-4-piperidinone, p-terphenyl, and dichloromethane are added to a three-necked flask equipped with a mechanical stirrer. After complete dissolution, trifluoroacetic acid and trifluoromethanesulfonic acid are added dropwise. After reacting for a certain period of time, the viscous solution is poured into a sodium bicarbonate solution and stirred vigorously. Finally, the solution is filtered and washed to obtain a white fibrous product, which is then vacuum dried to obtain the PTP polymer.

[0034] Preferably, the ratio of N-methyl-4-piperidinone to p-terphenyl is (50-60) mmol: (40-50) mmol.

[0035] Preferably, the volume of dichloromethane is 15–30 mL.

[0036] Preferably, the ratio of trifluoroacetic acid to trifluoromethanesulfonic acid is (2-5) mL: (20-40) mL.

[0037] Preferably, the concentration of the sodium bicarbonate solution is 1–3 mol / L.

[0038] Preferably, the polymerization temperature is 0°C.

[0039] Preferably, the polymerization time is 8 to 14 hours.

[0040] Preferably, in step S3, the solvent includes dimethyl sulfoxide. More preferably, the ratio of PTPip to dimethyl sulfoxide is (0.1–0.4) g : (6–15) mL.

[0041] Preferably, in step S3, the ratio of product B to PTPip is (1-40) mg:(0.1-0.4) g.

[0042] Preferably, in step S3, the anion exchange membrane is vacuum dried at a temperature of 60~80°C.

[0043] The beneficial effects of this invention are as follows:

[0044] 1. The composite anion exchange membrane provided by the present invention is prepared by introducing a polyphenol-containing tannic acid adhesive medium onto the surface of an alkaline stable ZIF-8, then introducing flexible long side chains with piperidine functional groups, and then combining this modified ZIF-8 functional cluster with a highly alkaline stable PTPip polymer. The filler and the polymer have excellent compatibility, which is conducive to the uniform dispersion of the filler, thus exhibiting high ion conductivity and good long-term stability.

[0045] 2. Since both Pip-TA@ZIF-8 filler and PTPip are soluble in common organic solvents, this invention uses a physical mixing and stirring method for doping. This preparation method has the advantage of simple process and high yield of up to 85%. Attached Figure Description

[0046] Figure 1 The graphs show the conductivity of the anion exchange membranes prepared in Examples 1-3 and Comparative Example 1 of this invention as a function of temperature.

[0047] Figure 2 Images showing the water absorption rates of the anion exchange membranes prepared in Examples 1-3 and Comparative Example 1 of this invention at different temperatures;

[0048] Figure 3 Images showing the swelling rates of the anion exchange membranes prepared in Examples 1-3 and Comparative Example 1 of this invention at different temperatures;

[0049] Figure 4 Images showing the mechanical properties of the anion exchange membranes prepared in Examples 1-3 and Comparative Example 1 of this invention;

[0050] Figure 5 Images showing the water electrolysis hydrogen production performance of the anion exchange membranes and FAA-3-50 prepared in Examples 1-3 and Comparative Example 1 of this invention. Detailed Implementation

[0051] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0052] Example 1

[0053] I. Synthesis and Preparation of ZIF-8

[0054] At room temperature, dissolve 300 mg of 2-methylimidazole in 40 mL of methanol in a clean beaker, labeling this solution A. Dissolve 650 mg of Zn(NO3)2-6H2O in 40 mL of methanol in another clean beaker, labeling this solution B. Quickly pour solution B into solution A, stir for 5 minutes, then slowly add 200 mg of NaBH4 using a microprobe, stirring for 10 minutes. Finally, centrifuge the white product and wash with ethanol. Dry the ZIF-8 powder at 100 °C and activate it overnight before use.

[0055] II. Synthesis and Preparation of 6BrPip

[0056] Solution C was prepared by adding 1,6-dibromohexane to ethyl acetate in a single-necked flask and stirring until homogeneous. Solution D was prepared by adding N-methylpiperidine to ethyl acetate in a beaker and stirring until homogeneous. Solution D was slowly added dropwise to solution C and mixed thoroughly. After 24 hours of reaction, a large amount of white precipitate was formed. The reaction mixture was allowed to stand for 10 minutes, and the supernatant was discarded. The collected solid was washed repeatedly with ethyl acetate to obtain the product 6Brpip.

[0057] III. Synthesis and Preparation of PTPip Polymers

[0058] PTP (1 g), methyl iodoforme (2.28 g, 15.6 mmol), dimethyl sulfoxide (5 mL), and 1-methyl-2-pyrrolidone (25 mL) were added to a single-necked flask, and the flask was shielded from light. After stirring at 80 °C for 24 hours, the precipitate was formed in diethyl ether and washed several times with deionized water. After filtration, the precipitate was dried in a vacuum oven at 60 °C for 24 hours to obtain the PTPip polymer.

[0059] PTP was prepared by the following steps: N-methyl-4-piperidinone (6.44 g, 57 mmol), p-terphenyl (10.1 g, 43.8 mmol), and dichloromethane (20 mL) were added to a three-necked flask equipped with a mechanical stirrer. After complete dissolution, trifluoroacetic acid (3 mL) and trifluoromethanesulfonic acid (30 mL) were added dropwise. After reacting for a certain period of time, the viscous solution was poured into a sodium bicarbonate solution (1 mol / L, 1000 mL) and stirred vigorously. Finally, the solution was filtered and washed to obtain a white fibrous product. The polymer was dried in a vacuum oven at 60 °C for 24 hours to obtain the PTP polymer.

[0060] IV. Synthesis and Preparation of Composite Anion Exchange Membranes

[0061] Synthesis of S1.TA-modified ZIF-8 (TA@ZIF-8): ZIF-8 (10 mg) was dispersed in 5 mL of deionized water. Then, 2 mL of tannic acid solution (10 g / L) was added to the ZIF-8 suspension, and the mixture was allowed to stand for 5 minutes. After centrifugation and washing with water, TA@ZIF-8 was obtained.

[0062] Synthesis of S2.6BrPip-modified TA@ZIF-8 (Pip-TA@ZIF-8): TA@ZIF-8 (100 mg) and 6Br-Pip (300 mg) were dissolved in 60 mL of N,N-dimethylformamide. After complete dissolution, potassium carbonate (24 mg) was added, and the mixture was stirred for 48 hours. Finally, the gray-green product was centrifuged, washed with water, and dried at 100 °C.

[0063] Preparation of S3.PTPip-1 composite anion exchange membrane: PTPip (0.2 g) was dissolved in dimethyl sulfoxide and stirred at room temperature for 24 hours. Then, Pip-TA@ZIF-8 (0.002 g) was added, and the mixture was sonicated for 48 hours to obtain a homogeneous solution. Anion exchange membranes were prepared on glass plates by solution casting and dried in a vacuum oven at 80°C to obtain the PTPip-1 composite anion exchange membrane.

[0064] Example 2

[0065] This embodiment is basically the same as Example 1, except that: PTPip (0.2 g) was dissolved in dimethyl sulfoxide and stirred at room temperature for 24 hours. Pip-TA@ZIF-8 (0.01 g) was added, and the mixture was sonicated for 48 hours to obtain a homogeneous solution. An exchange membrane was prepared on a glass plate by solution casting, and the exchange membrane was dried in a vacuum oven at 80°C to obtain a PTPip-5 composite anion exchange membrane.

[0066] Example 3

[0067] This embodiment is basically the same as Example 1, except that: PTPip (0.2 g) was dissolved in dimethyl sulfoxide and stirred at room temperature for 24 hours. Pip-TA@ZIF-8 (0.018 g) was added, and the mixture was sonicated for 48 hours to obtain a homogeneous solution. An exchange membrane was prepared on a glass plate by solution casting, and the exchange membrane was dried in a vacuum oven at 80°C to obtain a PTPip-9 composite anion exchange membrane.

[0068] Comparative Example 1

[0069] This comparative example is essentially the same as Example 1, except that: PTPip (0.2 g) was dissolved in dimethyl sulfoxide and stirred at room temperature for 24 hours. The polymer solution was then sonicated for 48 hours to obtain a homogeneous solution. A membrane was prepared on a glass plate by solution casting, and the mixed membrane was dried in a vacuum oven at 80°C to obtain the PTPip anion exchange membrane.

[0070] Test

[0071] The conductivity versus temperature curves of Examples 1-3 and Comparative Example 1 are summarized in the attached figure. Figure 1 The conductivity, specifically the in-plane OH- conductivity, was measured using a four-electrode probe method with an Autolab (AUT86925) electrochemical workstation via AC impedance spectroscopy in the frequency range of 0.1 Hz to 1 MHz. The membrane was cut into rectangular pieces (40 × 10 mm). 2 The tests were conducted at different temperatures, and the experiments were performed in water and exposed to air. The conductivity (σ) was calculated as follows: σ = L / RS, where L is the distance between the two electrodes, R is the resistance of the membrane, and S is the cross-sectional area of ​​the membrane.

[0072] Depend on Figure 1 It is known that the filler Pip-TA@ZIF-8 significantly improves the conductivity of PTPip, and the anion exchange membrane provided in this application has high conductivity. Among them, the PTPip-1 obtained in Example 1 is the embodiment with the highest conductivity.

[0073] The water absorption rate (WU) and swelling rate (SR) curves as a function of temperature for Examples 1-3 and Comparative Example 1 are summarized in the attached figure. Figure 2 and attached Figure 3 Test methods for water absorption and swelling rate: Weigh the dried membrane (W) in OH- form. dry ) and thickness (L) dry Subsequently, the dried membrane was immersed in deionized water for 24 hours at different temperatures (30-80℃) to ensure complete hydration. Excess moisture was then wiped off the membrane surface with filter paper, and the weight (W) of the fully hydrated membrane was measured.wet ) and thickness (L) wet The formulas for calculating WU and SR are as follows: WU (%) = (W wet -W dry ) / W dry ×100%, SR (%) = (L wet -L dry ) / L dry ×100%.

[0074] Depend on Figure 2 and Figure 3 It can be seen that the Pip-TA@ZIF-8 filler improved the water absorption and swelling rate of PTPip. The composite membranes obtained in Examples 1-3 all maintained a certain swelling rate and good water absorption, providing certain conditions for the dimensional stability of the membrane. Among them, the PTPip-1 obtained in Example 1 still showed a good water absorption rate (17.7%, see Example 1) at 80℃. Figure 2 ) and resistance to expansion (<8%, see Figure 3 ).

[0075] The mechanical property diagrams of the anion exchange membranes of Examples 1-3 and Comparative Example 1 are summarized as follows: Figure 4 Mechanical property testing method for anion exchange membranes: The tensile modulus of the samples was evaluated using a tensile testing instrument (Instron 5965) at a tensile rate of 1 mm / min at room temperature. Before testing, the samples were cut into strips of 5 mm × 5 cm and stored immersed in deionized water. Before the test, the surface moisture of the membrane was wiped off. Each sample was tested five times under the same test conditions for analysis.

[0076] Depend on Figure 4 It is evident that the composite anion exchange membrane prepared in this application exhibits good Young's modulus performance. Among them, PTPip-1 obtained in Example 1 represents the embodiment with the best mechanical properties among Examples 1-3.

[0077] The water electrolysis hydrogen production performance diagrams of Examples 1-3, Comparative Example 1, and FAA-3-50 are compiled as follows: Figure 5 FAA-3-50 is a commonly used commercial anion exchange membrane. The assembled membrane electrode was constructed using NiFe catalyst, PTPip-1, and Pt / C catalyst. The NiFe or Pt / C catalyst was uniformly mixed with 20 wt% FAA-3-50 ion-exchange polymer in an isopropanol / DI-water (1:1) solution. After thorough dispersion, the ink was sprayed onto a fluid collector (4 cm²). 2 The catalyst was applied to a nickel foam anode and a carbon paper diffusion layer cathode. The catalyst loading was 5.0 mg / cm³ of NiFe. 2 Pt / C 0.4 mg / cm 2The performance of AEMWE based on Examples 1-3 and Comparative Example 1 in 1 M KOH solution and pure water was investigated. Polarization curves were recorded using a NEWWAR battery test station over a temperature range of 50–80 °C and a voltage range of 0–2.0 V.

[0078] Depend on Figure 5 It can be seen that the Pip-TA@ZIF-8 packing material improves the alkaline water electrolysis hydrogen production performance of PTPip. Specifically, the PTPip-1 membrane water obtained in Example 1 showed significantly improved electrolysis performance, achieving stable high energy input (2.31 A / cm² at 2 V). 2 ).

Claims

1. A composite anion exchange membrane, characterized in that, The film is prepared by solution casting of a modified metal-organic framework and a quaternized poly(terphenylpiperidine) polymer; wherein the modified metal-organic framework comprises a metal-organic framework with a polyphenol-containing adhesive medium introduced on its surface and grafted with flexible long side chains with piperidine functional groups; the flexible long side chains with piperidine functional groups include 4-(6-bromohexyl)-1,1-dimethylpiperidine-1-onium.

2. The composite anion exchange membrane according to claim 1, characterized in that, The polyphenol-containing adhesive medium includes tannic acid.

3. The composite anion exchange membrane according to claim 1, characterized in that, The metal-organic framework includes a zeolite imidazole framework.

4. A method for preparing a composite anion exchange membrane as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Metal-organic framework modified with binder: The metal-organic framework was dispersed in deionized water, a binder containing polyphenols was added, and after standing, it was centrifuged and washed to obtain product A. S2. Flexible long side chain modified product A: Product A and a flexible long side chain with piperidine functional group were dissolved in a solvent. After complete dissolution, a strong basic auxiliary agent was added, centrifuged, washed and dried to obtain product B. S3. Preparation of composite anion exchange membrane: Quaternized poly(terphenylpiperidine) polymer is dissolved in a solvent, stirred and dispersed, then product B is added, and after uniform mixing, a mixed solution is obtained. Anion exchange membrane is prepared by solution casting, and the anion exchange membrane is vacuum dried to obtain composite anion exchange membrane.

5. The method for preparing the composite anion exchange membrane according to claim 4, characterized in that, In step S2, the strongly alkaline auxiliary agent includes potassium carbonate.

6. The method for preparing the composite anion exchange membrane according to claim 4, characterized in that, In step S2, the ratio of product A to the flexible long side chain with piperidine functional group is (80-100) mg: (280-320) mg.

7. The method for preparing the composite anion exchange membrane according to claim 4, characterized in that, In step S3, the quaternized poly(terphenylpiperidine) polymer is prepared by the following steps: poly(terphenylpiperidine), iodomethane, dimethyl sulfoxide and 1-methyl-2-pyrrolidone are added to a container, the container is shielded from light, stirred, precipitated in diethyl ether, washed several times, filtered and dried to obtain the quaternized poly(terphenylpiperidine) polymer.

8. The method for preparing the composite anion exchange membrane according to claim 4, characterized in that, In step S3, the ratio of product B to quaternized poly(terphenylpiperidine) polymer is (1-40) mg: (0.1-0.4) g.

9. The method for preparing the composite anion exchange membrane according to claim 4, characterized in that, In step S3, the anion exchange membrane is vacuum dried at a temperature of 60–80°C.

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