Novel proton exchange membrane with high proton conductivity and preparation method thereof

Abstract

The invention discloses a novel proton exchange membrane with high proton conductivity and a preparation method thereof. The COF-polymer composite film is composed of a COF main body framework and a post-modified polymer guest molecule. Wherein a COF main body frame formed by casting an amino monomer and an aldehyde monomer through a solvent is used as a continuous phase, and a post-modified polymer is used as a dispersed phase; after the COF film is formed, the COF-polymer composite film is formed in the pore channels of the COF main body frame through confinement polymerization. According to the invention, by introducing a polymer containing a sulfonic acid group into a pore channel and combining with a sub-nano-scale one-dimensional channel of COF, selective transmission of protons can be enhanced; meanwhile, fluorine-containing guest molecules are introduced into the pore channels, so that the chemical stability of the composite membrane can be greatly improved, and a fluorinated chain segment and a secondary amine group form a stable hydrogen bond to reduce attack of oxides. The preparation conditions disclosed by the invention are mild, the application range is wide, and the prepared COF-polymer composite membrane has good mechanical properties and relatively high proton conductivity.

Description

Technical Field

[0001] The invention relates to the technical field of separation membrane materials, and discloses a novel proton exchange membrane with high proton conductivity and a preparation method thereof. The proton exchange membrane is used as a battery separator in an all-vanadium redox flow battery. Background Art

[0002] With the acceleration of industrialization, one of the major challenges facing modern society and humanity is to find sustainable, abundant and cheap clean energy to control carbon emissions. The development of new energy technologies and their key materials is a key link in achieving zero-carbon energy reconstruction. Its goal is to develop energy storage and conversion technologies with high energy density, high conversion efficiency and long service life. Among them, ion exchange membranes, as the core of various new energy devices, determine the efficiency of energy storage and conversion in energy systems. In these devices, the membranes must act as separators to prevent cross-contamination of chemical substances and promote the conduction of target ions to achieve circuit connectivity, that is, to achieve ion-selective transfer. Although the application prospects of ion exchange membranes are broad, the development of ion exchange membranes with high ion selectivity, ion conductivity and chemical stability still faces huge challenges.

[0003] In order to achieve accurate screening of target ions by ion exchange membranes, the pore structure and chemical microenvironment of the ion exchange membrane must be designed at the molecular level. Covalent organic frameworks (COFs) are a class of pre-designed crystalline polymers that are connected by covalent bonds and guide the formation of crystalline microporous frameworks based on topological structures. This molecular design principle is different from the design principle of polymers and enhances the ability to design pore structures. COF materials have the characteristics of rich and uniform nanopores and customizable physicochemical environments, making them ideal materials for separation membranes. In addition, the rich rigid nanochannels (0.5-6.5nm) and easily reactive functional sites give COF excellent ion selective separation and transport properties. However, due to the solubility of COF materials and the limited understanding of monomer diffusion kinetics and reaction thermodynamics, the preparation of ionic 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 preparation method of covalent organic framework composite membranes.

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

[0006] Provided are a novel proton exchange membrane with high proton conductivity and a method for preparing the same. The COF-polymer composite membrane comprises a COF framework and post-modified polymer guest molecules. The COF 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 the COF membrane is formed, confined polymerization occurs within the pores of the COF framework to form the COF-polymer composite membrane.

[0007] The novel proton exchange membrane with high proton conductivity and the preparation method thereof described in the present invention comprise the following steps:

[0008] Step A: Dissolve the aldehyde monomer in dimethyl sulfoxide to obtain a precursor solution A. Dissolve the amino monomer in N-methylpyrrolidone and disperse it evenly by ultrasonication to obtain a precursor solution B. The molar ratio of the aldehyde monomer to the amino monomer is 1:1.

[0009] Step B: Precursor solutions A and B were mixed evenly and then added dropwise to a glass tank, and slowly evaporated at 60°C for 3 days to obtain a COF film.

[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. The COF membrane prepared in Step B is added to the mixed solution and soaked 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. The COF membrane is heated in the mixed solution at 85°C for 12 hours to obtain a COF-polymer composite membrane.

[0011] In the present 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, tetrakis(4-aminophenyl)porphyrin or tetrakis(4-aminophenyl)methane.

[0012] The aldehyde monomer of the present invention is terephthalaldehyde, 2,5-dihydroxyterephthalaldehyde, trialdehyde phloroglucinol or 4,4'-biphenyldicarboxaldehyde.

[0013] The method for using a novel proton exchange membrane with high proton conductivity described in the present invention comprises the following steps:

[0014] The COF-polymer composite membrane obtained after the reaction is washed with methanol and ethanol to remove unreacted monomers (possibly including amino monomers, aldehyde monomers, 2,2,2-trifluoroethyl acrylate, 2-acrylamido-2-methylpropanesulfonic acid and azobisisobutyronitrile) to obtain a composite membrane; the composite membrane is 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 is used as an all-vanadium redox flow battery membrane.

[0015] Description of the invention principle:

[0016] After forming a COF membrane via solution casting, the present invention encapsulates vinyl-containing polymer monomers (2,2,2-trifluoroethyl acrylate and 2-acrylamido-2-methylpropanesulfonic acid) within an organic framework. This vinyl monomer (2,2,2-trifluoroethyl acrylate and 2-acrylamido-2-methylpropanesulfonic acid) undergoes confined free radical polymerization initiated by the initiator azobisisobutyronitrile. A multifunctional ionic COF-polymer composite membrane material is constructed via a top-down host-guest assembly process. The introduction of sulfonic acid-containing polymers into the pores, combined with the subnanometer-scale one-dimensional channels of the COF itself, enhances proton selective transport. Furthermore, the introduction of fluorinated guest molecules into the pores significantly increases the chemical stability of the composite membrane, with the fluorinated segments forming stable hydrogen bonds with secondary amine groups to reduce oxide attack.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

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

[0019] 2. The present 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 above composite membrane as a diaphragm in the all-vanadium redox flow battery, the all-vanadium redox flow battery can achieve a higher discharge capacity and a current of 300mAcm -2 The constant current charge and discharge cycle stability was achieved for 600 times at a current density of . BRIEF DESCRIPTION OF THE DRAWINGS

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

[0022] Figure 2 : The chemical structure of the COF film synthesized in the example. DETAILED DESCRIPTION

[0023] The invention will be further described in detail below with reference to specific examples. The examples may help professionals in this field to understand the invention more comprehensively, but they do not limit the invention in any way.

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

[0025] Step 1: Preparation of monomer solution

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

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

[0028] Solutions A and B were mixed evenly and then added dropwise to a glass tank and slowly evaporated at 60 °C for 3 days to obtain a COF film.

[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 penetrate the pores. The COF membrane was heated in the solution at 85°C for 12 hours to obtain a Polymer@COF membrane.

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

[0032] Step 4: Use of membrane:

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

[0034] The following five examples are used to specifically illustrate the method for preparing the covalent organic framework composite membrane of the present invention. The experimental data in each example are detailed in Table 1 below.

[0035] Example 1:

[0036] Precursor solution A was prepared by dissolving 28.5 mg of trialdehyde phloroglucinol in 1 mL of dimethyl sulfoxide. Precursor solution B was prepared by dissolving 37.6 mg of 2,5-diaminobenzenesulfonic acid in 1 mL of N-methylpyrrolidone and homogenizing by ultrasonic dispersion. 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 and added dropwise to a glass tank. 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 penetrate the pores. The COF membrane was heated in a solution at 85°C for 12 hours to obtain a Polymer@COF membrane. The membrane after the reaction 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 vanadium redox flow battery separator. Figure 2 Part of the figure shows the chemical structure of the COF film synthesized in this example.

[0037] Example 2:

[0038] Precursor solution A was prepared by dissolving 28.5 mg of trialdehyde phloroglucinol in 1 mL of dimethyl sulfoxide. Precursor solution B was prepared by dissolving 37.5 mg of 4,4'-diaminobiphenyl in 1 mL of N-methylpyrrolidone and homogenizing by ultrasonication. 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 and added dropwise to a glass tank. 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 penetrate the pores. The COF membrane was heated in a solution at 85°C for 12 hours to obtain a Polymer@COF membrane. The membrane was then washed with methanol and ethanol to remove unreacted monomers, yielding a composite membrane. The composite membrane was then dried at room temperature to obtain a covalent organic framework composite membrane containing fluorine and sulfonic acid groups. The composite membrane was then used as a separator for an all-vanadium redox flow battery.

[0039] Example 3:

[0040] Precursor solution A was prepared by dissolving 28.5 mg of trialdehyde phloroglucinol in 1 mL of dimethyl sulfoxide. Precursor solution B was prepared by dissolving 47.3 mg of 1,3,5-tris(4-aminophenyl)benzene in 1 mL of N-methylpyrrolidone and homogenizing by ultrasonic dispersion. The molar ratio of the aldehyde groups of trialdehyde phloroglucinol to the amino groups of 1,3,5-tris(4-aminophenyl)benzene was 1:1. Solutions A and B were mixed and added dropwise to a glass tank. 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 penetrate the pores. The COF membrane was heated in a solution at 85°C for 12 hours to obtain a Polymer@COF membrane. The membrane was then washed with methanol and ethanol to remove unreacted monomers, yielding a composite membrane. The composite membrane was then dried at room temperature to obtain a covalent organic framework composite membrane containing fluorine and sulfonic acid groups. The composite membrane was then used as a separator for an all-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 dispersed homogeneously by ultrasonication 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 tank. 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 penetrate the pores. The COF membrane was heated in a solution at 85°C for 12 hours to obtain a Polymer@COF membrane. The membrane was then washed with methanol and ethanol to remove unreacted monomers, yielding a composite membrane. The composite membrane was then dried at room temperature to obtain a covalent organic framework composite membrane containing fluorine and sulfonic acid groups. The composite membrane was then used as a separator for an all-vanadium redox flow battery.

[0043] Example 5:

[0044] Precursor solution A was prepared by dissolving 27.3 mg of terephthalaldehyde in 1 mL of dimethyl sulfoxide. Precursor solution B was prepared by dissolving 38.1 mg of tetrakis(4-aminophenyl)methane in 1 mL of N-methylpyrrolidone and homogenizing by ultrasonication. The molar ratio of the aldehyde groups of terephthalaldehyde to the amino groups of tetrakis(4-aminophenyl)methane was 1:1. Solutions A and B were mixed thoroughly and added dropwise to a glass tank. 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 penetrate the pores. The COF membrane was heated in a solution at 85°C for 12 hours to obtain a Polymer@COF membrane. The membrane was then washed with methanol and ethanol to remove unreacted monomers, yielding a composite membrane. The composite membrane was then dried at room temperature to obtain a covalent organic framework composite membrane containing fluorine and sulfonic acid groups. The composite membrane was then used as a separator for an all-vanadium redox flow battery.

[0045] Table 1 Example covalent organic framework composite membrane test data table

[0046]

[0047] Technical effect verification

[0048] The COF-based composite membrane prepared as described above was subjected to proton conductivity testing, rate performance testing of an all-vanadium redox flow battery, and cycle testing of an all-vanadium redox flow battery according to the following procedures.

[0049] Table 2 Example ionic COF-based composite membrane test results

[0050]

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

[0052] 1. Proton conductivity

[0053] In-plane resistance 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. The 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 from the Nyquist plot, T is the thickness of the membrane, and W is the width of the membrane.

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

[0057] In a single cell module, the effective area is 1cm 2 The membrane is sandwiched between the activated carbon felt electrode and the graphite plate, all clamped by the shell. The initial positive and negative electrolytes contain 1.7MV 3.5+ 3M H2SO4 solution. Before the test, the reservoir was fully purged with inert gas and the –2 The electrolyte was activated twice with a current of 100-400 mA cm –2 The test was carried out at a current density of 1.5 V and a cut-off voltage of 0.8 V and 1.7 V. The capacity utilization (CU) was calculated using the following formula:

[0058]

[0059] While the present invention has been described in detail herein and specific embodiments thereof have been illustrated by way of example in the Examples, various modifications and alternatives are possible. However, it should be understood that this disclosure is not intended to limit the invention to the specific forms disclosed. On the contrary, the present invention encompasses all modifications, equivalents, and alternatives falling 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 is composed of a COF main framework and post-modified polymer guest molecules; the COF main 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 the COF membrane is formed, confined polymerization occurs within the pores of the COF main framework to form 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: The following steps are involved: Step 1: dissolving the aldehyde monomer in dimethyl sulfoxide to obtain a precursor solution A; The amino monomer is dissolved in N-methylpyrrolidone and dispersed uniformly by ultrasonication to obtain a precursor solution B; Step 2: Precursor solutions A and B were mixed evenly and then added dropwise to a glass tank. The mixture was slowly evaporated at 60°C for 3 days to obtain a COF film. Step 3: Dissolve 2,2,2-trifluoroethyl acrylate, 2-acrylamido-2-methylpropanesulfonic acid and azobisisobutyronitrile in anhydrous methanol, and obtain a clear mixed solution after ultrasonic treatment for 10 minutes; add the COF membrane prepared in step 2 to the mixed solution and soak it for 10 hours to allow the monomer 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.

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 the aldehyde monomer to the amino monomer is 1:

1.

4. The 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, tetrakis(4-aminophenyl)porphyrin or tetrakis(4-aminophenyl)methane.

5. The 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 phloroglucinol or 4,4'-biphenyldicarboxaldehyde.

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

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