Covalent organic framework film with sandwich structure as well as preparation method and application of covalent organic framework film

Abstract

The invention belongs to the technical field of energy storage, and discloses a covalent organic framework film with a sandwich structure as well as a preparation method and application of the covalent organic framework film. The preparation method comprises the following steps: carrying out condensation reaction on 2, 2 '-benzidine disulfonic acid and trialdehyde phloroglucinol to prepare a self-supporting covalent organic framework membrane, dip-coating the self-supporting covalent organic framework membrane in a polybenzimidazole solution, and carrying out phase inversion to prepare the covalent organic framework membrane with a sandwich structure. According to the invention, selective transfer of protons is realized by using a pore structure and a sulfonic acid group in the covalent organic framework, vanadium ion permeation is hindered, and meanwhile, in the battery assembly and operation process, the polybenzimidazole layers on the two sides play a role in protecting the covalent organic framework membrane. The prepared membrane has high proton selectivity and battery efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage, and relates to a "sandwich" - structured covalent organic framework membrane, a preparation method thereof, and an application thereof. Background Art

[0002] Driven by the goal of energy security, each country regards the development of renewable energy as the core path. However, the characteristics of new renewable energies such as wind energy and solar energy, such as non - steady - state and intermittency, seriously restrict their reliability as base - load energy. Flow batteries, with advantages such as fast response speed, high energy density, easy scalability, and flexible configuration, have become the key technology to support the grid connection of renewable energy. The all - vanadium flow battery has become one of the most mature flow - battery systems because its active substances are of the same element, reducing the cost of electrolyte regeneration. The separator is a key component of the battery, which plays the role of separating the positive and negative electrodes, preventing battery short - circuit, conducting protons, and connecting the battery circuit. Currently, the non - fluorinated ion - exchange membranes that have been widely studied achieve proton conduction by introducing hydrophilic functional groups into the polymer main chain to induce the formation of a microphase - separation structure. However, the swelling effect of flexible polymer chains leads to dynamic changes in the channel size, so it faces a trade - off effect between ionic conductivity and selectivity.

[0003] Covalent organic frameworks (COFs) are porous crystalline polymer materials formed by arranging rigid organic units in a periodic structure, with highly ordered and interconnected pores. The key advantage of COFs is the ability to select appropriate organic units from a vast library of organic building blocks to design the desired channel structure, so as to selectively transport or exclude according to the size and properties of ions. In 2020, we first proposed incorporating COF particles into a polymer matrix to achieve the sieving of H + / V + and improve the efficiency of the battery (Chemical Engineering Journal, 2020, 399, 125833). Subsequently, COF - and - polymer - doped membranes for flow - battery systems have been widely studied. However, doped membranes have problems such as discontinuous COF and limited COF doping amount. Therefore, it is necessary to prepare composite membranes with a continuous COF layer. Composite membranes with continuous COF nanosheet layers can be simply prepared by methods such as spin - coating, spraying, or vacuum - assisted filtration. However, the composite membranes prepared by these methods have problems such as poor flexibility of the COF nanosheet layers and easy detachment during long - term flushing of flowing electrolytes, resulting in unstable composite structures, which limit their flow - battery performance and the possibility of large - scale preparation. Summary of the Invention

[0004] The present invention aims to improve the flexibility, structural stability, proton conductivity and battery performance of covalent organic framework membranes, and provides a method for preparing a "sandwich"-structured covalent organic framework membrane: using an amine monomer and an aldehyde monomer containing sulfonic acid groups to condense to prepare a flexible, continuous and self-supporting COF membrane, then dip-coating the COF membrane with a polybenzimidazole (PBI) solution, and finally obtaining a "sandwich"-integrated structured covalent organic framework membrane with porous PBI layers on both sides and a dense COF layer in the middle through a phase inversion method. By combining a continuous covalent organic framework membrane with a polymer, the present invention solves the problems of discontinuity of COF, limited COF doping amount, poor flexibility of the COF composite membrane, easy shedding of the COF layer and unstable structure of the composite membrane in the existing COF-doped membranes.

[0005] The technical solution of the present invention:

[0006] A "sandwich"-structured covalent organic framework membrane, comprising a middle sandwich layer and two side membrane layers; the middle sandwich layer is a self-supporting COF membrane (m-TpBDSA) with a thickness of 30-50 μm; both side membrane layers are polybenzimidazole (PBI) membranes with a thickness of 20-65 μm; wherein, the structure of the self-supporting COF membrane m-TpBDSA is as follows:

[0007]

[0008] The structure of polybenzimidazole is as follows:

[0009]

[0010] Wherein, the degree of polymerization 1 < n < 500.

[0011] A method for preparing a "sandwich"-structured covalent organic framework membrane, the steps are as follows:

[0012] (1) Preparation of polybenzimidazole solution: Dissolve the polybenzimidazole polymer in N,N-dimethylacetamide and heat and stir at 80 °C until completely dissolved;

[0013] The concentration of the N,N-dimethylacetamide solution of polybenzimidazole is 80 mg / mL;

[0014] (2) Preparation of self-supporting covalent organic framework m-TpBDSA membrane: Mix the N-methylpyrrolidone solution of phloroglucinol trialdehyde and the dimethyl sulfoxide solution of 2,2'-benzidine disulfonic acid, carry out ultrasonic reaction for 60 min and then centrifuge, and take the upper clear liquid for casting to obtain a self-supporting covalent organic framework membrane;

[0015] The concentration of the N-methylpyrrolidone solution of phloroglucinol trialdehyde is 7-11.6 mg / mL;

[0016] The concentration of the dimethyl sulfoxide solution of 2,2'-benzidine disulfonic acid is 22.5 - 37.5 mg / mL;

[0017] The molar ratio of the triformylphloroglucinol and 2,2'-benzidine disulfonic acid is 2:3;

[0018] The rotation speed of the centrifugation is 8000 rmp;

[0019] The heating temperature during the casting process is 45 - 50 °C, and the time is 48 - 60 hours.

[0020] (3) Preparation of the "sandwich" integrated structure COF membrane: Immerse the dried self-supporting covalent organic framework membrane in the polybenzimidazole solution for 10 - 30 seconds, take it out and let it stand in the air for 30 - 120 seconds, then immerse it in methanol for 5 - 10 minutes to undergo a phase inversion process, thus obtaining the "sandwich" structure covalent organic framework membrane.

[0021] A "sandwich" structure covalent organic framework membrane prepared by the above preparation method is applied to an all-vanadium redox flow battery.

[0022] Advantages of the present invention: The present invention selects an amine monomer with sulfonic acid groups in the meta-position of the amino group to prepare a flexible, continuous, and self-supporting COF membrane, solving the problem of discontinuous COF in the doped membrane. At the same time, the double sulfonic acid groups in the meta-position of the amino group shorten the distance, which is beneficial for establishing a continuous dynamic hydrated hydrogen bond network, thereby improving the proton conductivity, battery voltage efficiency, and energy efficiency of the self-supporting COF membrane. At the same time, after immersing the self-supporting COF membrane in the PBI solution and then undergoing the phase inversion to solid PBI, this process enables a tight integrated combination between the sandwich-layer COF and the PBI layers on both sides. On the one hand, it overcomes the problem that the COF layer is easily peeled off due to being washed by the flowing electrolyte in the COF composite membrane. On the other hand, the PBI layers on both sides can serve as "buffer pads", solving the problem that the self-supporting COF membrane is not resistant to extrusion in the flow battery, which improves the structural stability of the separator and thus enhances the performance of the COF membrane in the flow battery. Description of the Drawings

[0023] Figure 1 It is the result diagram of the self-supporting m-TPBDSA membranes of Example 1 and Example 2. Among them, (a) is the digital photo of Example 2, (b) is the microscopic morphology of the surface of the membrane in Example 1, (c) is the microscopic morphology of the cross-section of the membrane in Example 1, and (d) is the sulfur element distribution diagram of the cross-section of the membrane in Example 1;

[0024] Figure 2Results of the "sandwich" structure P / m-TpBDSA / P-30 film of Example 4, where (a) is the cross-sectional microscopic morphology of the film, (b) is the sulfur element distribution map of the film cross-section, (c) is the carbon element distribution map of the film cross-section, and (d) is the oxygen element distribution map of the film cross-section;

[0025] Figure 3 Conductivities of the self-supporting m-TPBDSA film of Example 1 and the commercial Nafion 212 film;

[0026] Figure 4 V battery efficiency diagrams of the "sandwich" structure P / m-TpBDSA / P films of Example 6 and Example 7, where (a) is the battery Coulomb efficiency, (b) is the battery voltage efficiency, and (c) is the battery energy efficiency. Detailed implementation mode

[0027] The present invention will be further described in detail below in combination with implementation cases, but the implementation modes of the present invention are not limited thereto.

[0028] Example 1

[0029] Preparation of sulfonic acid type self-supporting COF (m-TpBDSA) film: Dissolve 0.042 g of phloroglucinol trialdehyde in 6 mL of N-methylpyrrolidone, and use an ultrasonic crusher to ultrasonicate it for 10 minutes to ensure its full dissolution, while maintaining an ice-water bath condition during the ultrasonic process. Similarly, dissolve 0.135 g of 2,2'-biphenylenediamine disulfonic acid in 6 mL of dimethyl sulfoxide, and use an ultrasonic crusher to ultrasonicate it for 10 minutes to ensure its full dispersion. Then, mix the above phloroglucinol trialdehyde / N-methylpyrrolidone solution and 2,2'-biphenylenediamine disulfonic acid / dimethyl sulfoxide solution, and ultrasonicate for 60 minutes to form a casting solution, keeping the whole process in an ice-water bath. Then, centrifuge the ultrasonically treated solution at 8000 rmp, take the upper clear liquid, and cast it on a glass plate of 6×6 cm 2 and dry it in an oven at 50 °C for 60 hours to obtain a self-supporting m-TpBDSA film.

[0030] Tests show that the thickness of the sulfonic acid type self-supporting m-TPBDSA film in this example is 30 μm, the tensile strength is 49.6 Mpa, and the elongation at break reaches 13%, indicating that the flexibility and strength of the self-supporting COF film are good. The proton conductivity of the m-TPBDSA film at 30 °C is 196 mS cm -1 , and the proton conductivity at 80 °C is 332 mS cm -1 , much higher than that of the commercial perfluorosulfonic acid Nafion 212 film (68 mS cm -1 @30 °C; 137 mS cm -1 @80 °C).

[0031] Example 2

[0032] Preparation of sulfonic acid-based self-supporting COF (m-TpBDSA) membrane: Dissolve 0.117 g of phloroglucinol trialdehyde in 16 mL of N-methylpyrrolidone, and sonicate it with a sonicator for 10 minutes to ensure its complete dissolution, while maintaining an ice-water bath during the sonication process. Similarly, dissolve 0.378 g of 2,2'-benzidine disulfonic acid in 16 mL of dimethyl sulfoxide, and sonicate it with a sonicator for 10 minutes to ensure its full dispersion. Then, mix the above phloroglucinol trialdehyde / N-methylpyrrolidone solution and 2,2'-benzidine disulfonic acid / dimethyl sulfoxide solution, and sonicate for 60 minutes to form a casting solution, keeping the whole process in an ice-water bath. Then centrifuge the sonicated solution at 8000 rmp, take the upper clear liquid, and cast it on a glass plate of 10×10 cm 2 and dry it in an oven at 50 °C for 60 hours to obtain a self-supporting m-TpBDSA membrane.

[0033] Tests show that the thickness of the sulfonic acid-based self-supporting m-TPBDSA membrane in this example is 30 μm, and the membrane area is 100 cm 2 , compared with Example 1, this example only changes the mass and area of the m-TpBDSA membrane, indicating that the m-TpBDSA self-supporting membrane can be prepared on a large scale by changing the monomer mass and mold size.

[0034] Example 3

[0035] Preparation of sulfonic acid-based self-supporting COF (m-TpBDSA) membrane: Dissolve 0.056 g of phloroglucinol trialdehyde in 6 mL of N-methylpyrrolidone, and sonicate it with a sonicator for 10 minutes to ensure its complete dissolution, while maintaining an ice-water bath during the sonication process. Similarly, dissolve 0.180 g of 2,2'-benzidine disulfonic acid in 6 mL of dimethyl sulfoxide, and sonicate it with a sonicator for 10 minutes to ensure its full dispersion. Then, mix the above phloroglucinol trialdehyde / N-methylpyrrolidone solution and 2,2'-benzidine disulfonic acid / dimethyl sulfoxide solution, and sonicate for 60 minutes to form a casting solution, keeping the whole process in an ice-water bath. Then centrifuge the sonicated solution at 8000 rmp, take the upper clear liquid, and cast it on a glass plate of 6×6 cm 2 and dry it in an oven at 50 °C for 60 hours to obtain a self-supporting m-TpBDSA membrane.

[0036] Tests show that the thickness of the sulfonic acid-based self-supporting m-TPBDSA membrane in this example is 40 μm. Compared with Example 1, this example only changes the mass and thickness of the m-TpBDSA membrane, indicating that the thickness of the m-TpBDSA self-supporting membrane can be simply regulated by changing the monomer mass, and the proton conductivity of the membrane does not change due to the change in thickness.

[0037] Example 4

[0038] Preparation of sulfonic acid-based self-supporting COF (m-TpBDSA) membrane: The same as Example 1

[0039] Preparation of "sandwich" integrated covalent organic framework membrane (P / m-TpBDSA / P): Add 8 g of polybenzimidazole (PBI) material into a 250 mL flask, then add 100 mL of N,N-dimethylacetamide to it, and heat and stir at 80 °C until the PBI is completely dissolved to form a homogeneous PBI solution. Then immerse the m-TpBDSA membrane with a size of 6×6 cm 2 vertically into the PBI solution and keep it for 10 seconds to ensure that the surface of the m-TpBDSA membrane is coated with PBI. Then take out the membrane impregnated with PBI and let it stand for 30 seconds. Subsequently, quickly immerse the membrane in methanol and keep it for 5 minutes to complete the phase change process. Finally, the P / m-TpBDSA / P-1 membrane is prepared.

[0040] Tests show that the structure of the "sandwich" structure P / m-TpBDSA / P-1 membrane in this example is that there is a dense m-TPBDSA layer with a thickness of 30 μm in the middle, and porous PBI layers with a thickness of 60 - 65 μm on both sides. The vanadium battery assembled with the P / m-TpBDSA / P-1 membrane has a Coulombic efficiency (CE) of 98.7%, a voltage efficiency of 80.4%, and an energy efficiency of 79.4% at 200 mA cm -2 under.

[0041] Example 5

[0042] Preparation of sulfonic acid-based self-supporting COF (m-TpBDSA) membrane: The same as Example 1

[0043] Preparation of "sandwich" integrated covalent organic framework membrane (P / m-TpBDSA / P): Add 8 g of polybenzimidazole (PBI) material into a 250 mL flask, then add 100 mL of N,N-dimethylacetamide to it, and heat and stir at 80 °C until the PBI is completely dissolved to form a homogeneous PBI solution. Then immerse the m-TpBDSA membrane with a size of 6×6 cm 2The m-TpBDSA membrane was vertically immersed in the PBI solution for 10 seconds to ensure that the surface of the m-TpBDSA membrane was coated with PBI. Then, the membrane impregnated with PBI was taken out and left standing for 9 seconds. Subsequently, the membrane was quickly immersed in methanol and kept for 5 minutes to complete the phase transition process. Finally, the P / m-TpBDSA / P-2 membrane was prepared.

[0044] Tests showed that the structure of the "sandwich" structure P / m-TpBDSA / P-2 membrane in this example was that there was a dense m-TPBDSA layer with a thickness of 30 μm in the middle, and porous PBI layers with a thickness of 30 - 35 μm on both sides. The vanadium battery assembled with the P / m-TpBDSA / P-2 membrane had a Coulombic efficiency (CE) of 98.2% at 200 mA cm -2 and a voltage efficiency of 83.4% and an energy efficiency of 82.0%.

[0045] Example 6

[0046] Preparation of sulfonic acid-based self-supporting COF (m-TpBDSA) membrane: The same as Example 1

[0047] Preparation of the "sandwich" integrated structure covalent organic framework membrane (P / m-TpBDSA / P): 8 g of polybenzimidazole (PBI) material was added to a 250 mL flask, and then 100 mL of N,N-dimethylacetamide was added thereto. It was heated and stirred at 80 °C until the PBI was completely dissolved to form a uniform PBI solution. Then, the m-TpBDSA membrane with a size of 6×6 cm 2 was vertically immersed in the PBI solution for 10 seconds to ensure that the surface of the m-TpBDSA membrane was coated with PBI. Then, the membrane impregnated with PBI was taken out and left standing for 120 seconds. Subsequently, the membrane was quickly immersed in methanol and kept for 5 minutes to complete the phase transition process. Finally, the P / m-TpBDSA / P-3 membrane was prepared.

[0048] Tests showed that the structure of the "sandwich" structure P / m-TpBDSA / P-3 membrane in this example was that there was a dense m-TPBDSA layer with a thickness of 30 μm in the middle, and porous PBI layers with a thickness of 20 - 25 μm on both sides. The vanadium battery assembled with the P / m-TpBDSA / P-3 membrane had a Coulombic efficiency (CE) of 97.5% at 200 mA cm -2 and a voltage efficiency of 84.5% and an energy efficiency of 82.5%.

[0049] Example 7

[0050] Preparation of sulfonic acid-based self-supporting COF (m-TpBDSA) membrane: The same as Example 3

[0051] Preparation of "sandwich" - type integrated covalent organic framework membrane (P / m - TpBDSA / P): Add 8 g of polybenzimidazole (PBI) material into a 250 mL flask, then add 100 mL of N,N - dimethylacetamide to it. Heat and stir at 80 °C until PBI is completely dissolved to form a uniform PBI solution. Then vertically immerse the m - TpBDSA membrane with a size of 6×6 cm 2 into the PBI solution and keep it for 10 seconds to ensure that the surface of the m - TpBDSA membrane is coated with PBI. Then take out the membrane impregnated with PBI and let it stand for 120 seconds. Subsequently, quickly immerse the membrane into methanol and keep it for 5 minutes to complete the phase - change process. Finally, the P / m - TpBDSA / P - 4 membrane is prepared.

[0052] Tests show that the structure of the "sandwich" - structured P / m - TpBDSA / P - 4 membrane in this example is that there is a dense m - TPBDSA layer with a thickness of 40 μm in the middle, and porous PBI layers with a thickness of 20 - 25 μm on both sides. The vanadium battery assembled with the P / m - TpBDSA / P - 4 membrane has a Coulombic efficiency (CE) of 98.6%, a voltage efficiency of 84.4%, and an energy efficiency of 83.2% at 200 mA cm -2 .

[0053] Comparative Example 1

[0054] Preparation of sulfonic acid - type self - supported COF (m - TpBDSA) membrane: The same as Example 1

[0055] Preparation of "sandwich" - type integrated covalent organic framework membrane (P / m - TpBDSA / P): Add 8 g of polybenzimidazole (PBI) material into a 250 mL flask, then add 100 mL of N,N - dimethylacetamide to it. Heat and stir at 80 °C until PBI is completely dissolved to form a uniform PBI solution. Then vertically immerse the m - TpBDSA membrane with a size of 6×6 cm 2 into the PBI solution and keep it for 10 seconds to ensure that the surface of the m - TpBDSA membrane is coated with PBI. Then take out the membrane impregnated with PBI and let it stand for 150 seconds, and it is found that the membrane curls. Analyzing this situation, due to the presence of N,N - dimethylacetamide solvent in the PBI solution, when the m - TpBDSA membrane contacts the solvent for a certain time, swelling or deformation will occur. Therefore, in the present invention, the time between immersing the m - TpBDSA membrane in the PBI solution and the phase - transformation to the methanol solution is controlled within 30 - 120 seconds.

Claims

1. A "sandwich" - structured covalent organic framework membrane, characterized in that, The "sandwich" - structured covalent organic framework membrane includes a middle sandwich layer and two side membrane layers; the middle sandwich layer is a self - supported COF membrane m - TpBDSA with a thickness of 30 - 50 μm; both side membrane layers are polybenzimidazole membranes with a thickness of 20 - 65 μm.

2. The "sandwich" - structured covalent organic framework membrane according to claim 1, wherein, The structure of the self - supported COF membrane m - TpBDSA is as follows: The structure of polybenzimidazole is as follows: Among them, the degree of polymerization 1 < n < 500.

3. A method for preparing the "sandwich" - structured covalent organic framework membrane according to claim 1 or 2, characterized in that, The steps are as follows: (1) Preparation of polybenzimidazole solution: Dissolve polybenzimidazole polymer in N,N - dimethylacetamide and heat - stir at 80 °C until completely dissolved; (2) Preparation of self - supported covalent organic framework m - TpBDSA membrane: Mix the N - methylpyrrolidone solution of phloroglucinol tri - aldehyde and the dimethyl sulfoxide solution of 2,2'-biphenylenediamine disulfonic acid, carry out ultrasonic reaction for 60 min and then centrifuge. Take the upper clear liquid and cast it to obtain the self - supported covalent organic framework membrane; (3) Preparation of "sandwich" - structured COF membrane: Immerse the dried self - supported covalent organic framework membrane in the polybenzimidazole solution for 10 - 30 seconds, take it out and let it stand in the air for 30 - 120 seconds, then immerse it in methanol for 5 - 10 minutes to undergo a phase - inversion process, and thus obtain the "sandwich" - structured covalent organic framework membrane.

4. According to the preparation method described in claim 3, it is characterized in that In step (1), The concentration of the N,N - dimethylacetamide solution of polybenzimidazole is 80 mg / mL.

5. According to the preparation method described in claim 3, it is characterized in that In step (2), The concentration of the N - methylpyrrolidone solution of phloroglucinol tri - aldehyde is 7 - 11.6 mg / mL; The concentration of the dimethyl sulfoxide solution of 2,2'-biphenylenediamine disulfonic acid is 22.5 - 37.5 mg / mL; The molar ratio of phloroglucinol tri - aldehyde to 2,2'-biphenylenediamine disulfonic acid is 2:3; The rotation speed of the centrifugation is 8000 rmp; The heating temperature during the casting process is 45 - 50 °C and the time is 48 - 60 hours.

6. A "sandwich" - structured covalent organic framework membrane described in claim 1 or 2 is applied to a vanadium redox flow battery.

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