A novel proton exchange membrane with high proton conductivity and a preparation method thereof

Abstract

This invention discloses a novel proton exchange membrane with high proton conductivity and its preparation method. The COF-polymer composite membrane consists of a COF host framework and post-modified polymer guest molecules; wherein the COF host framework, formed by solvent casting of amino monomers and aldehyde monomers, serves as the continuous phase, and the post-modified polymer serves as the dispersed phase; after forming the COF membrane, confined polymerization is carried out within the pores of the COF host framework to form the COF-polymer composite membrane. This invention enhances proton selective transport by introducing polymers containing sulfonic acid groups into the pores and combining them with the sub-nanometer one-dimensional channels of the COF itself; simultaneously, the introduction of fluorinated guest molecules into the pores significantly increases the chemical stability of the composite membrane, with fluorinated segments forming stable hydrogen bonds with secondary amine groups to reduce oxide attack. The preparation conditions disclosed in this patent are mild and have a wide range of applications; the COF-polymer composite membrane prepared by this invention exhibits good mechanical properties and high proton conductivity.

Description

Technical Field

[0001] This invention relates to the field of separation membrane materials technology, and discloses a novel proton exchange membrane with high proton conductivity and its preparation method, and uses the proton exchange membrane as a battery separator in an all-vanadium redox flow battery. Background Technology

[0002] With the acceleration of industrialization, one of the major challenges facing modern society and humanity is finding sustainable, abundant, and inexpensive clean energy to control carbon emissions. Developing new energy technologies and their key materials is a crucial step in achieving zero-carbon energy restructuring, aiming to develop energy storage and conversion technologies with high energy density, high conversion efficiency, and long service life. Among these, ion exchange membranes, as the core of many new energy devices, determine the efficiency of energy storage and conversion in energy systems. In these devices, the membrane must act as a separator to prevent cross-contamination of chemical substances while also promoting the conduction of target ions to achieve circuit connection—that is, achieving ion selective transfer. Although ion exchange membranes have broad application prospects, developing ion exchange membranes that combine high ion selectivity, ion conductivity, and chemical stability remains a significant challenge.

[0003] To achieve precise ion sieving of target ions using ion exchange membranes, the pore structure and chemical microenvironment of the membrane must be designed at the molecular level. Covalent organic frameworks (COFs) are a class of pre-designable crystalline polymers linked by covalent bonds, with the formation of crystalline microporous frameworks guided by their topological structure. This molecular design principle differs from that of polymers, enhancing the ability to design pore structures. COF materials possess abundant and uniform nanopores and customizable physicochemical environments, making them ideal materials for separation membranes. Furthermore, the abundant rigid nanochannels (0.5-6.5 nm) and readily reactive functional sites endow COFs with excellent ion-selective separation and transport properties. However, limited by the solubility of COF materials and the limited understanding of monomer diffusion kinetics and reaction thermodynamics, the preparation of ion-exchange COF membranes is still in its early stages of development. Summary of the Invention

[0004] The problem to be solved by the present invention is to overcome the preparation problems of existing ionic covalent organic framework membranes and provide a simple method for preparing covalent organic framework composite membranes.

[0005] To solve the technical problem, the solution of the present invention is:

[0006] This invention provides a novel proton exchange membrane with high proton conductivity and its preparation method. The COF-polymer composite membrane of this invention consists of a COF host framework and post-modified polymer guest molecules. The COF host framework, formed by solvent casting of amino monomers and aldehyde groups, serves as the continuous phase, while the post-modified polymer serves as the dispersed phase. After forming the COF membrane, confined polymerization is carried out within the pores of the COF host framework to form the COF-polymer composite membrane.

[0007] The present invention discloses a novel proton exchange membrane with high proton conductivity and its preparation method, comprising the following steps:

[0008] Step A: The aldehyde monomer is dissolved in dimethyl sulfoxide to obtain precursor solution A. The amino monomer is dissolved in N-methylpyrrolidone and ultrasonically dispersed to obtain precursor solution B. The molar ratio of the aldehyde monomer to the amino monomer is 1:1.

[0009] Step B: Mix precursor solutions A and B thoroughly and add them dropwise into a glass bath. Evaporate slowly at 60°C for 3 days to obtain a COF membrane.

[0010] Step C: Dissolve 2,2,2-trifluoroethyl acrylate, 2-acrylamido-2-methylpropanesulfonic acid, and azobisisobutyronitrile in anhydrous methanol, and sonicate for 10 minutes to obtain a clear mixed solution. Add the COF membrane prepared in Step B to the mixed solution and soak for 10 hours to allow the monomers (referring to 2,2,2-trifluoroethyl acrylate, 2-acrylamido-2-methylpropanesulfonic acid, and azobisisobutyronitrile in the mixed solution) to fully enter the pores. Heat the COF membrane in the mixed solution at 85°C for 12 hours to obtain a COF-polymer composite membrane.

[0011] In this invention, the amino monomer is 2,5-diaminobenzenesulfonic acid, 2,5-diaminobenzene, 4,4'-diaminobiphenyl, 1,3,5-tris(4-aminophenyl)benzene, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, tetra(4-aminophenyl)porphyrin, or tetra(4-aminophenyl)methane.

[0012] The aldehyde monomers used in this invention are terephthalaldehyde, 2,5-dihydroxyterephthalaldehyde, trialdehyde-resorcinol, or 4,4'-biphenyldialdehyde.

[0013] The method of using a novel proton exchange membrane with high proton conductivity as described in this invention includes the following steps:

[0014] The COF-polymer composite membrane obtained after the reaction was washed with methanol and ethanol to remove unreacted monomers (which may include amino monomers, aldehyde monomers, 2,2,2-trifluoroethyl acrylate, 2-acrylamido-2-methylpropanesulfonic acid and azobisisobutyronitrile) to obtain a composite membrane; the composite membrane was dried at room temperature to obtain a covalent organic framework composite membrane containing fluorine groups and sulfonic acid groups; the covalent organic framework composite membrane was used as a separator for a vanadium redox flow battery.

[0015] Description of the invention principle:

[0016] This invention involves forming a COF membrane using solution casting, then encapsulating vinyl-containing polymer monomers (2,2,2-trifluoroethyl acrylate and 2-acrylamido-2-methylpropanesulfonic acid) within an organic framework. The vinyl monomers (2,2,2-trifluoroethyl acrylate and 2-acrylamido-2-methylpropanesulfonic acid) undergo confined radical polymerization initiated by azobisisobutyronitrile (AIBN), constructing a multifunctional ionic COF-polymer composite membrane material through a top-down host-guest assembly approach. On one hand, introducing polymers containing sulfonic acid groups into the pores, combined with the sub-nanometer one-dimensional channels of the COF itself, enhances proton selective transport. On the other hand, introducing fluorinated guest molecules into the pores significantly increases the chemical stability of the composite membrane, with fluorinated segments forming stable hydrogen bonds with secondary amine groups to reduce oxide attack.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] 1. This invention innovatively employs a confined polymerization strategy to achieve the preparation of a covalent organic framework-based high-efficiency proton exchange membrane.

[0019] 2. This invention can prepare composite films of different thicknesses by adjusting the concentrations of amino monomers and aldehyde monomers to adapt to more application scenarios.

[0020] 3. By using the aforementioned composite membrane as a separator in a vanadium redox flow battery, the vanadium redox flow battery can achieve a higher discharge capacity and a discharge rate of 300 mA / cm². -2 It was stable after 600 constant current charge-discharge cycles at a current density. Attached Figure Description

[0021] Figure 1 The chemical structures of the amino monomer and aldehyde monomer used in this invention are shown.

[0022] Figure 2 The chemical structure of the COF membrane synthesized in the examples is shown. Detailed Implementation

[0023] The invention will be further described in detail below with reference to specific embodiments. These embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the invention, but do not limit the invention in any way.

[0024] A novel proton exchange membrane with high proton conductivity and its preparation method, comprising the following steps:

[0025] Step 1: Preparation of monomer solution

[0026] The aldehyde monomer was dissolved in dimethyl sulfoxide to obtain precursor solution A. The amino monomer was dissolved in N-methylpyrrolidone and ultrasonically dispersed to obtain precursor solution B. The molar ratio of the aldehyde monomer to the amino monomer was 1:1. The chemical structures of the amino monomer and the aldehyde monomer used in this invention are as follows: Figure 1 As shown.

[0027] Step 2: Preparation of COF membrane by solvent casting method

[0028] After solutions A and B are mixed evenly, they are added dropwise into a glass trough and slowly evaporated at 60°C for 3 days to obtain a COF membrane.

[0029] Step 3: Preparation of composite membrane by confined polymerization

[0030] 2,2,2-Trifluoroethyl acrylate, 2-acrylamido-2-methylpropanesulfonic acid, and azobisisobutyronitrile were dissolved in anhydrous methanol and sonicated for 10 minutes to obtain a clear solution. The COF membrane prepared in step B was added to the mixed solution and soaked for 10 hours to allow the monomers to fully enter the pores. The COF membrane was then heated in the solution at 85°C for 12 hours to obtain the Polymer@COF membrane.

[0031] In this invention, the process of constructing the composite membrane by solution casting is carried out under normal pressure, and the reaction time is 3 days.

[0032] Step 4: Use of the membrane:

[0033] The reacted membrane was washed with methanol and ethanol to remove unreacted monomers to obtain a composite membrane; the composite membrane was dried at room temperature to obtain a covalent organic framework composite membrane containing fluorine groups and sulfonic acid groups; the composite membrane was used as a separator for a vanadium redox flow battery.

[0034] The following five embodiments illustrate the preparation method of the covalent organic framework composite membrane of the present invention. The experimental data of each embodiment are detailed in Table 1 below.

[0035] Example 1:

[0036] 28.5 mg of trialdehyde phloroglucinol was dissolved in 1 mL of dimethyl sulfoxide to obtain precursor solution A. 37.6 mg of 2,5-diaminobenzenesulfonic acid was dissolved in 1 mL of N-methylpyrrolidone and ultrasonically dispersed to obtain precursor solution B. The molar ratio of the aldehyde group of trialdehyde phloroglucinol to the amino group of 2,5-diaminobenzenesulfonic acid was 1:1. Solutions A and B were mixed thoroughly and added dropwise to a glass bath. The mixture was slowly evaporated at 60 °C for 3 days to obtain a COF membrane with a thickness of 22.1 μm. 412 mg of 2,2,2-trifluoroethyl acrylate, 210 mg of 2-acrylamido-2-methylpropanesulfonic acid, and 10 mg of azobisisobutyronitrile were dissolved in 5 mL of anhydrous methanol and ultrasonicated for 10 minutes to obtain a clear solution. The COF membrane prepared in step B was added to the mixed solution and soaked for 10 hours to allow the monomers to fully enter the pores. A Polymer@COF membrane was obtained by heating the COF membrane in solution at 85°C for 12 hours. The reacted membrane was then washed with methanol and ethanol to remove unreacted monomers, yielding a composite membrane. The composite membrane was dried at room temperature to obtain a covalent organic framework composite membrane containing fluorine and sulfonic acid groups. This composite membrane was then used as a separator in a vanadium redox flow battery. Figure 2 The chemical structure of the COF membrane synthesized in this embodiment is partially shown.

[0037] Example 2:

[0038] 28.5 mg of trialdehyde phloroglucinol was dissolved in 1 mL of dimethyl sulfoxide to obtain precursor solution A. 37.5 mg of 4,4'-diaminobiphenyl was dissolved in 1 mL of N-methylpyrrolidone and ultrasonically dispersed to obtain precursor solution B. The molar ratio of the aldehyde group of trialdehyde phloroglucinol to the amino group of 4,4'-diaminobiphenyl was 1:1. Solutions A and B were mixed thoroughly and added dropwise to a glass bath. The mixture was slowly evaporated at 60 °C for 3 days to obtain a COF membrane with a thickness of 23.4 μm. 412 mg of 2,2,2-trifluoroethyl acrylate, 210 mg of 2-acrylamido-2-methylpropanesulfonic acid, and 10 mg of azobisisobutyronitrile were dissolved in 5 mL of anhydrous methanol and ultrasonicated for 10 minutes to obtain a clear solution. The COF membrane prepared in step B was added to the mixed solution and soaked for 10 hours to allow the monomers to fully enter the pores. Polymer@COF membrane was obtained by heating the COF membrane in solution at 85°C for 12 hours. The reacted membrane was washed with methanol and ethanol to remove unreacted monomers, resulting in a composite membrane. The composite membrane was dried at room temperature to obtain a covalent organic framework composite membrane containing fluorine and sulfonic acid groups. The composite membrane was used as a separator in a vanadium redox flow battery.

[0039] Example 3:

[0040] 28.5 mg of trialdehyde-resorcinol was dissolved in 1 mL of dimethyl sulfoxide to obtain precursor solution A. 47.3 mg of 1,3,5-tris(4-aminophenyl)benzene was dissolved in 1 mL of N-methylpyrrolidone and ultrasonically dispersed to obtain precursor solution B. The molar ratio of the aldehyde group of trialdehyde-resorcinol to the amino group of 1,3,5-tris(4-aminophenyl)benzene was 1:1. Solutions A and B were mixed thoroughly and added dropwise to a glass bath. The mixture was slowly evaporated at 60 °C for 3 days to obtain a COF membrane with a thickness of 22.9 μm. 412 mg of 2,2,2-trifluoroethyl acrylate, 210 mg of 2-acrylamido-2-methylpropanesulfonic acid, and 10 mg of azobisisobutyronitrile were dissolved in 5 mL of anhydrous methanol and ultrasonicated for 10 minutes to obtain a clear solution. The COF membrane prepared in step B was added to the mixed solution and soaked for 10 hours to allow the monomers to fully enter the pores. Polymer@COF membrane was obtained by heating the COF membrane in solution at 85°C for 12 hours. The reacted membrane was washed with methanol and ethanol to remove unreacted monomers, resulting in a composite membrane. The composite membrane was dried at room temperature to obtain a covalent organic framework composite membrane containing fluorine and sulfonic acid groups. The composite membrane was used as a separator in a vanadium redox flow battery.

[0041] Example 4:

[0042] 27.3 mg of terephthalaldehyde was dissolved in 1 mL of dimethyl sulfoxide to obtain precursor solution A. 67.9 mg of tetrakis(4-aminophenyl)porphyrin was dissolved in 1 mL of N-methylpyrrolidone and ultrasonically dispersed to obtain precursor solution B. The molar ratio of the aldehyde group of terephthalaldehyde to the amino group of tetrakis(4-aminophenyl)porphyrin was 1:1. Solutions A and B were mixed thoroughly and added dropwise to a glass bath. The mixture was slowly evaporated at 60 °C for 3 days to obtain a COF membrane with a thickness of 24.1 μm. 412 mg of 2,2,2-trifluoroethyl acrylate, 210 mg of 2-acrylamido-2-methylpropanesulfonic acid, and 10 mg of azobisisobutyronitrile were dissolved in 5 mL of anhydrous methanol and ultrasonicated for 10 minutes to obtain a clear solution. The COF membrane prepared in step B was added to the mixed solution and soaked for 10 hours to allow the monomers to fully enter the pores. Polymer@COF membrane was obtained by heating the COF membrane in solution at 85°C for 12 hours. The reacted membrane was washed with methanol and ethanol to remove unreacted monomers, resulting in a composite membrane. The composite membrane was dried at room temperature to obtain a covalent organic framework composite membrane containing fluorine and sulfonic acid groups. The composite membrane was used as a separator in a vanadium redox flow battery.

[0043] Example 5:

[0044] 27.3 mg of terephthalaldehyde was dissolved in 1 mL of dimethyl sulfoxide to obtain precursor solution A. 38.1 mg of tetrakis(4-aminophenyl)methane was dissolved in 1 mL of N-methylpyrrolidone and ultrasonically dispersed to obtain precursor solution B. The molar ratio of the aldehyde group of terephthalaldehyde to the amino group of tetrakis(4-aminophenyl)methane was 1:1. Solutions A and B were mixed thoroughly and added dropwise to a glass bath. The mixture was slowly evaporated at 60 °C for 3 days to obtain a COF membrane with a thickness of 24.1 μm. 412 mg of 2,2,2-trifluoroethyl acrylate, 210 mg of 2-acrylamido-2-methylpropanesulfonic acid, and 10 mg of azobisisobutyronitrile were dissolved in 5 mL of anhydrous methanol and ultrasonicated for 10 minutes to obtain a clear solution. The COF membrane prepared in step B was added to the mixed solution and soaked for 10 hours to allow the monomers to fully enter the pores. Polymer@COF membrane was obtained by heating the COF membrane in solution at 85°C for 12 hours. The reacted membrane was washed with methanol and ethanol to remove unreacted monomers, resulting in a composite membrane. The composite membrane was dried at room temperature to obtain a covalent organic framework composite membrane containing fluorine and sulfonic acid groups. The composite membrane was used as a separator in a vanadium redox flow battery.

[0045] Table 1. Experimental data of covalent organic framework composite membranes in the examples.

[0046]

[0047] Technical effect verification

[0048] For the COF-based composite membrane examples prepared as described above, proton conductivity testing, vanadium redox flow battery rate performance testing, and vanadium redox flow battery cycle testing were performed according to the following procedures. These results are recorded in Table 2.

[0049] Table 2. Experimental results of ion-type COF-based composite membranes in the examples.

[0050]

[0051] The test methods for each verification test are described below:

[0052] 1. Proton conductivity

[0053] In-plane resistivity was measured using a two-point probe technique (CHI 660E electrochemical workstation) with an EIS frequency range of 1 MHz to 1 Hz. The membrane sample was placed in a Teflon conductivity cell with platinum electrodes and immersed in deionized water. Membrane conductivity was calculated using the following method:

[0054]

[0055] Where L is the distance between the potential sensing electrodes, R is the absolute ohmic resistance measured according to the Nyquist curve, T is the thickness of the film, and W is the width of the film.

[0056] 2. Performance evaluation of single-cell vanadium redox flow batteries

[0057] In a single-cell module, the effective area is 1 cm². 2 The membrane is sandwiched between the activated carbon felt electrode and the graphite plate, and is completely clamped by the outer casing. The initial positive and negative electrode electrolytes contain 1.7 MV. 3.5+ A 3M H₂SO₄ solution was used. Before the test, the reservoir was thoroughly purged with inert gas at 100 mA cm⁻¹. –2 Electrolyte activation was performed twice using a current of 100-400 mA cm⁻¹. Charge-discharge tests were conducted at 100-400 mA cm⁻¹. –2 The current density was measured at 0.8V and 1.7V, with cutoff voltages of 0.8V and 1.7V. The capacity utilization (CU) was calculated using the following formula:

[0058]

[0059] This invention has been described in detail herein and specific embodiments of the invention have been illustrated by way of example in the Embodiments section. However, various modifications and alternatives can be made to the invention. It should be understood, however, that this invention is not intended to limit the invention to the specific forms disclosed. Rather, the invention covers all modifications, equivalents, and alternatives that fall within the spirit and scope of the invention as defined by the appended claims.

Claims

1. A novel proton exchange membrane with high proton conductivity, characterized in that, The COF-polymer composite membrane consists of a COF host framework and post-modified polymer guest molecules. The COF host framework, formed by solvent casting of amino and aldehyde monomers, serves as the continuous phase, while the post-modified polymer serves as the dispersed phase. After forming the COF membrane, confined polymerization occurs within the pores of the COF host framework to form the COF-polymer composite membrane. The preparation of this exchange membrane is achieved as follows: The aldehyde monomer was dissolved in dimethyl sulfoxide to obtain precursor solution A; the amino monomer was dissolved in N-methylpyrrolidone and ultrasonically dispersed to obtain precursor solution B. After thoroughly mixing precursor solutions A and B, the mixture was added dropwise into a glass trough and slowly evaporated at 60 °C for 3 days to obtain a COF membrane. 2,2,2-trifluoroethyl acrylate, 2-acrylamido-2-methylpropanesulfonic acid and azobisisobutyronitrile were dissolved in anhydrous methanol and sonicated for 10 minutes to obtain a clear mixed solution. The COF membrane prepared in step 2 was added to the mixed solution and soaked for 10 hours to allow the monomers to fully enter the pores. The COF membrane was then heated in the mixed solution at 85 °C for 12 h to obtain a COF-polymer composite membrane.

2. The method for preparing a novel proton exchange membrane with high proton conductivity according to claim 1, characterized in that, Includes the following steps: Step 1: Dissolve the aldehyde monomer in dimethyl sulfoxide to obtain precursor solution A; The amino monomer was dissolved in N-methylpyrrolidone and ultrasonically dispersed to obtain precursor solution B; Step 2: Mix precursor solutions A and B thoroughly and add them dropwise into a glass trough. Evaporate slowly at 60 °C for 3 days to obtain a COF membrane. Step 3: Dissolve 2,2,2-trifluoroethyl acrylate, 2-acrylamido-2-methylpropanesulfonic acid and azobisisobutyronitrile in anhydrous methanol, and sonicate for 10 minutes to obtain a clear mixed solution; add the COF membrane prepared in Step 2 to the mixed solution and soak for 10 hours to allow the monomers to fully enter the pores; heat the COF membrane in the mixed solution at 85 °C for 12 h to obtain a COF-polymer composite membrane.

3. The method for preparing a novel proton exchange membrane with high proton conductivity according to claim 2, characterized in that, In step 1, the molar ratio of aldehyde monomer to amino monomer is 1:

1.

4. A method for preparing a novel proton exchange membrane with high proton conductivity according to claim 2 or 3, characterized in that, The amino monomer is 2,5-diaminobenzenesulfonic acid, 2,5-diaminobenzene, 4,4'-diaminobiphenyl, 1,3,5-tris(4-aminophenyl)benzene, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, tetra(4-aminophenyl)porphyrin, or tetra(4-aminophenyl)methane.

5. A method for preparing a novel proton exchange membrane with high proton conductivity according to claim 2 or 3, characterized in that, The aldehyde monomer is terephthalaldehyde, 2,5-dihydroxyterephthalaldehyde, trialdehyde-resorcinol, or 4,4'-biphenyldialdehyde.

6. A method of using a novel proton exchange membrane with high proton conductivity as described in claim 1, characterized in that, Includes the following steps: The COF-polymer composite membrane obtained after the reaction was washed with methanol and ethanol to remove unreacted monomers and obtain a composite membrane. The composite membrane was dried at room temperature to obtain a covalent organic framework composite membrane containing fluorine groups and sulfonic acid groups. The covalent organic framework composite membrane was used as a separator for a vanadium redox flow battery.

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