Preparation method of covalent organic framework composite membrane for all-vanadium redox flow battery

Abstract

The invention discloses a preparation method of a covalent organic framework composite membrane for an all-vanadium redox flow battery. The covalent organic framework composite membrane is composed of a COF main body framework and sulfonated polymer guest molecules. Wherein COF-TPTAM formed by casting tetra (4-aminophenyl) methane and trialdehyde phloroglucinol through a solvent is used as a continuous phase, and a sulfonated polymer is used as a dispersed phase. The preparation method comprises the following steps: 1, dissolving trialdehyde phloroglucinol in dimethyl sulfoxide to obtain a precursor solution A; 2, dissolving tetra (4-aminophenyl) methane in dimethyl sulfoxide, adding the linear sulfonated polymer, and ultrasonically dispersing uniformly to obtain a precursor solution B; 3, fully mixing the precursor solution A and the precursor solution B, ultrasonically dispersing, dropwise adding into a glass tank, heating to 60 DEG C, and slowly evaporating for 24 hours; and heating to 80 DEG C, and slowly evaporating for 48 hours to obtain the covalent organic framework composite membrane. The preparation conditions are mild, the application range is wide, and the prepared composite membrane has good mechanical performance and proton conductivity.

Description

Technical Field

[0001] The invention relates to the technical field of all-vanadium redox flow battery diaphragm materials, discloses a method for preparing a covalent organic framework composite membrane for an all-vanadium redox flow battery, and uses the composite membrane as a battery diaphragm in the all-vanadium redox flow battery. Background Art

[0002] Proton exchange membranes are currently urgently needed for some electrochemical devices, such as redox flow batteries, fuel cells, and water electrolyzers. In these devices, the membrane acts as a separator, preventing chemical species from crossing each other while promoting ion conduction to achieve circuit connectivity, that is, to achieve selective ion transfer. At the nanoscale, the selective transport of protons in the membrane depends on the nanoconfinement effect and the physical and chemical environment within the pores. The efficiency of ion transport across the membrane surface depends on the overall energy barrier. In aqueous systems, proton transfer mainly occurs on the water-hydrate hydrogen bond network, so creating a water-mediated proton transfer pathway with a higher carrier concentration has always been an ideal pursuit. The sulfonic acid groups in the composite membrane act as excellent hydrophilic ligands and proton carriers, which can promote the high proton conductivity of the membrane.

[0003] Covalent organic frameworks (COFs) are crystalline porous materials formed by covalently bonding organic precursors. They possess excellent chemical and thermal stability. Composed of lightweight elements, they have low density and, as crystalline materials, exhibit more regular structures and uniform pores than conventional porous materials. These exceptional properties have attracted significant attention for applications in a wide range of fields, including ion separation and transport, gas adsorption, catalysis, and optoelectronics. Their atomic-scale designability, robustness, and precise control of the pore environment offer exciting possibilities for achieving both high selectivity and high conductivity. Three-dimensional COFs, in which three-dimensional building blocks serve as nodes and are covalently linked along a topologically guided graph to form a three-dimensional network, often contain richer channels. Unfortunately, non-planar building blocks and building blocks functionalized with ionic groups introduce greater steric hindrance and reduced reactivity during membrane formation. Summary of the Invention

[0004] The problem to be solved by the present invention is to overcome the preparation problem of existing ionic three-dimensional covalent organic framework membranes and provide a preparation method of a covalent organic framework composite membrane for all-vanadium redox flow batteries.

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

[0006] The covalent organic framework composite membrane (COF composite membrane) prepared by the present invention is composed of a COF main framework and a sulfonated polymer. COF-TPTAM, a solvent-cast mixture of tetrakis(4-aminophenyl)methane (TAM) and trialdehyde phloroglucinol (TP), serves as the continuous phase, while the sulfonated polymer serves as the dispersed phase. During solvent evaporation, the sulfonated polymer, acting as a guest molecule, can spontaneously enter the pores of the COF main framework.

[0007] The method for preparing a covalent organic framework composite membrane for an all-vanadium redox flow battery according to the present invention comprises the following steps:

[0008] Step 1: dissolving trialdehyde phloroglucinol (TP) in dimethyl sulfoxide to obtain a precursor solution A.

[0009] Step 2: Tetrakis(4-aminophenyl)methane (TAM) is dissolved in dimethyl sulfoxide, and then an appropriate amount of linear sulfonated polymer is added, and the precursor solution B is obtained after uniform dispersion by ultrasonication.

[0010] The molar ratio of the amino group of tetrakis(4-aminophenyl)methane (TAM) to the sulfonic acid group of the sulfonated polymer is 10:1.

[0011] Step 3: Mix the precursor solutions A and B thoroughly, disperse them ultrasonically for 10 minutes, and then add them dropwise to the glass tank. The glass tank needs to be calibrated with a level. -1 Heat to 60℃ at a speed of 10℃ for 24h. -1 The temperature was raised to 80°C at a rate of 1000 nm and slowly evaporated for 48 h to obtain a Polymer@COF membrane, i.e., a COF composite membrane.

[0012] When the precursor solutions A and B are mixed, the molar ratio of the amino group to the aldehyde group in the mixed solution is (1:1) to (1:1.5).

[0013] In the present invention, the process of constructing the COF composite membrane by the solution casting method is carried out under normal pressure, and the reaction time is 3 days.

[0014] In the present invention, the linear sulfonated polymer is sulfonated polyimide (SPI), sulfonated polyarylethersulfone (SPES), sulfonated polyvinyl alcohol (SPVA), sulfonated polyaryletherketone (SPAEK), sulfonated polyphenylene oxide (SPPO) or sulfonated polyetheretherketone (SPEEK).

[0015] The method for using a covalent organic framework composite membrane for an all-vanadium redox flow battery according to the present invention comprises the following steps:

[0016] The COF composite membrane obtained after the solvent evaporates is taken out, and the unreacted monomers (possibly including trialdehyde phloroglucinol (TP), tetrakis(4-aminophenyl)methane (TAM) and sulfonated polymers) are washed away in methanol and ethanol; the COF composite membrane is dried at room temperature to obtain an ionic three-dimensional covalent organic framework composite membrane; and the COF composite membrane is used as a vanadium redox flow battery membrane.

[0017] Description of the invention principle:

[0018] The introduction of linear sulfonated polymers can play the following roles: 1) The interaction between the sulfonic acid groups and the amine groups drives the TAMs to arrange along the linear polymers; 2) The sulfonic acid groups catalyze the Schiff base reaction, forming a framework with the macromolecular polymer as a long-range template; 3) After the composite membrane is formed, the sulfonic acid groups and their surrounding water areas promote rapid proton transfer.

[0019] This invention employs an in situ host-guest assembly strategy, guided by a long-range template, to construct a highly crystalline three-dimensional covalent organic framework proton exchange membrane. The rigid main framework and interwoven sulfonated polymers create a closed environment, which together enhances the mechanical and chemical stability of the composite membrane and reduces the proton diffusion barrier.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. This invention innovatively adopts a flexible in situ host-guest assembly strategy to achieve the preparation of covalent organic framework-based high-efficiency proton exchange membranes.

[0022] 2. The present invention can prepare composite films of different thicknesses by adjusting the monomer concentration and polymer concentration to adapt to more application scenarios.

[0023] 3. By using the above composite membrane as a diaphragm in an all-vanadium redox flow battery, the all-vanadium redox flow battery can achieve a higher discharge capacity and a stable cycle of 1,000 constant current charge and discharge cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the synthesis and structure of the COF composite membrane prepared in the present invention. DETAILED DESCRIPTION

[0025] 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.

[0026] A method for preparing a covalent organic framework composite membrane for an all-vanadium redox flow battery comprises the following steps:

[0027] Step 1: Preparation of monomer solution

[0028] TP was dissolved in dimethyl sulfoxide to obtain precursor solution A. TAM was dissolved in dimethyl sulfoxide, and 10 equivalents of sulfonated polymer (based on the sulfonic acid groups and amino groups of TAM) were added. After ultrasonic dispersion, precursor solution B was obtained. The molar ratio of amino groups to aldehyde groups was 1:1 to 1:1.5.

[0029] Step 2: Preparation of composite membrane by solvent casting

[0030] The precursor solutions A and B were fully mixed and ultrasonically dispersed for 10 minutes before being added dropwise to the glass tank, which was calibrated with a level. -1 The temperature was raised to 60℃ and evaporated slowly for 24h. Then the temperature was raised to 10℃ for 24h. -1 The temperature was raised to 80°C and slowly evaporated for 48 hours to obtain a Polymer@COF film.

[0031] In the present invention, the process of constructing the composite membrane by the solution casting method is carried out at room temperature and pressure, and the reaction time is 3 days. Figure 1 Figure 2 shows the synthesis and structural diagram of the COF composite membrane prepared in this invention. Using an in situ host-guest self-assembly strategy, COF-TPTAM serves as the host framework and sulfonated polymers (SPI, SPES, SPVA, SPAEK, SPPO, or SPEEK) serve as guest molecules to construct a COF composite membrane with an interwoven structure.

[0032] Step 3: Use of membrane:

[0033] The membrane obtained after the solvent evaporates is taken out, and the unreacted monomers are washed away in methanol and ethanol; the composite membrane is dried at room temperature to obtain an ionic three-dimensional covalent organic framework composite membrane; and the composite membrane is used as a vanadium liquid flow battery diaphragm.

[0034] The following five examples are used to specifically illustrate the method for preparing the ionic three-dimensional 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] Dissolve 3 mg of trialdehyde phloroglucinol (TP) in 1 mL of dimethyl sulfoxide to obtain precursor solution A. Dissolve 6 mg of tetrakis(4-aminophenyl)methane (TAM) in 1 mL of dimethyl sulfoxide, add 1.7 mg of sulfonated polyimide (SPI), and disperse evenly by ultrasonication to obtain precursor solution B. Among them, the molar ratio of the amino group of tetrakis(4-aminophenyl)methane (TAM) and the sulfonic acid group of sulfonated polyimide (SPI) is 10:1, and the molar ratio of the amino group of tetrakis(4-aminophenyl)methane (TAM) and the aldehyde group of trialdehyde phloroglucinol (TP) is 1:1.5. Mix the precursor solutions A and B thoroughly, disperse ultrasonically for 10 minutes, and then add them dropwise to the glass tank. The glass tank needs to be calibrated with a spirit level. Then, heat the mixture at 10°C for 1 h. -1 Heat to 60℃ at a speed of 10℃ for 24h. -1 The temperature was raised to 80°C at a rate of 1000 nm and slowly evaporated for 48 h to obtain the SPI@COF-25 film, which was a COF composite film encapsulating SPI and having a thickness of 25 μm.

[0037] Example 2:

[0038] Dissolve 2 mg of trialdehyde phloroglucinol (TP) in 1 mL of dimethyl sulfoxide to obtain precursor solution A. Dissolve 6 mg of tetrakis(4-aminophenyl)methane (TAM) in 1 mL of dimethyl sulfoxide, add 1.7 mg of sulfonated polyimide (SPI), and disperse evenly by ultrasonication to obtain precursor solution B. Among them, the molar ratio of the amino group of tetrakis(4-aminophenyl)methane (TAM) and the sulfonic acid group of sulfonated polyimide (SPI) is 10:1, and the molar ratio of the amino group of tetrakis(4-aminophenyl)methane (TAM) and the aldehyde group of trialdehyde phloroglucinol (TP) is 1:1. Mix the precursor solutions A and B thoroughly, disperse ultrasonically for 10 minutes, and then add them dropwise to the glass tank. The glass tank needs to be calibrated with a spirit level. Then, heat the mixture at 10°C for 1 h. -1 Heat to 60℃ at a speed of 10℃ for 24h. -1 The temperature was raised to 80°C at a rate of 1000 nm and slowly evaporated for 48 h to obtain the SPI@COF-22 film, which was a COF composite film encapsulating SPI and having a thickness of 22 μm.

[0039] Example 3:

[0040] Dissolve 2 mg of trialdehyde phloroglucinol (TP) in 1 mL of dimethyl sulfoxide to obtain precursor solution A. Dissolve 5 mg of tetrakis(4-aminophenyl)methane (TAM) in 1 mL of dimethyl sulfoxide, add 1.4 mg of sulfonated polyimide (SPI), and disperse evenly by ultrasonication to obtain precursor solution B. Among them, the molar ratio of the amino group of tetrakis(4-aminophenyl)methane (TAM) and the sulfonic acid group of sulfonated polyimide (SPI) is 10:1, and the molar ratio of the amino group of tetrakis(4-aminophenyl)methane (TAM) and the aldehyde group of trialdehyde phloroglucinol (TP) is 1:1.2. Mix the precursor solutions A and B thoroughly, disperse ultrasonically for 10 minutes, and then add them dropwise to the glass tank. The glass tank needs to be calibrated with a spirit level. Then, heat the mixture at 10°C for 1 h. -1 Heat to 60℃ at a speed of 10℃ for 24h. -1 The temperature was raised to 80°C at a rate of 1000 nm and slowly evaporated for 48 h to obtain the SPI@COF-20 film, which was a COF composite film encapsulating SPI and having a thickness of 20 μm.

[0041] Example 4:

[0042] Dissolve 3 mg of trialdehyde phloroglucinol (TP) in 1 mL of dimethyl sulfoxide to obtain precursor solution A. Dissolve 6 mg of tetrakis(4-aminophenyl)methane (TAM) in 1 mL of dimethyl sulfoxide, add 2.3 mg of sulfonated polyetheretherketone (SPEEK), and disperse evenly by ultrasonication to obtain precursor solution B. Among them, the molar ratio of the amino group of tetrakis(4-aminophenyl)methane (TAM) and the sulfonic acid group of sulfonated polyetheretherketone (SPEEK) is 10:1, and the molar ratio of the amino group of tetrakis(4-aminophenyl)methane (TAM) and the aldehyde group of trialdehyde phloroglucinol (TP) is 1:1.5. Mix the precursor solutions A and B thoroughly, disperse ultrasonically for 10 minutes, and then add them dropwise to the glass tank. The glass tank needs to be calibrated with a spirit level. Then, heat the mixture at 10°C for 1 h. -1 Heat to 60℃ at a speed of 10℃ for 24h. -1 The temperature was raised to 80°C at a rate of 1000 nm and slowly evaporated for 48 h to obtain a SPEEEK@COF-25 film, which was a COF composite film encapsulating SPEEEK and having a thickness of 25 μm.

[0043] Example 5:

[0044] Dissolve 2 mg of trialdehyde phloroglucinol (TP) in 1 mL of dimethyl sulfoxide to obtain precursor solution A. Dissolve 6 mg of tetrakis(4-aminophenyl)methane (TAM) in 1 mL of dimethyl sulfoxide, add 2.3 mg of sulfonated polyetheretherketone (SPEEK), and disperse evenly by ultrasonication to obtain precursor solution B. Among them, the molar ratio of the amino group of tetrakis(4-aminophenyl)methane (TAM) and the sulfonic acid group of sulfonated polyetheretherketone (SPEEK) is 10:1, and the molar ratio of the amino group of tetrakis(4-aminophenyl)methane (TAM) and the aldehyde group of trialdehyde phloroglucinol (TP) is 1:1.5. Mix the precursor solutions A and B thoroughly, disperse ultrasonically for 10 minutes, and then add them dropwise to the glass tank. The glass tank needs to be calibrated with a spirit level. Then, heat the mixture at 10°C for 1 h. -1 Heat to 60℃ at a speed of 10℃ for 24h. -1 The temperature was raised to 80°C at a rate of 1000 nm and slowly evaporated for 48 h to obtain a SPEEEK@COF-25 film, which was a COF composite film encapsulating SPEEEK and having a thickness of 25 μm.

[0045] Table 1 Example ionic three-dimensional covalent organic framework composite membrane test data table

[0046]

[0047]

[0048] Technical effect verification

[0049] The ionic 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. The results are shown in Table 2.

[0050] Table 2 Example ionic COF composite membrane test results

[0051]

[0052] The test methods for each verification test are described as follows:

[0053] 1. Proton conductivity

[0054] 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:

[0055]

[0056] 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.

[0057] 2. Performance evaluation of single-cell all-vanadium redox flow battery

[0058] 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 activation was performed 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:

[0059]

[0060] 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 covalent organic framework composite membrane for all-vanadium redox flow battery, characterized in that: This covalent organic framework composite membrane is composed of a COF main framework and a sulfonated polymer, in which COF-TPTAM, which is solvent-casted from tetrakis(4-aminophenyl)methane and trialdehyde phloroglucinol, serves as the continuous phase, and the sulfonated polymer serves as the dispersed phase. During the evaporation of the solvent, the sulfonated polymer can spontaneously enter the pores of the COF main framework as a guest molecule; an in situ host-guest assembly strategy is adopted, guided by a long-range template, to construct a highly crystalline three-dimensional covalent organic framework composite membrane.

2. The method for preparing a covalent organic framework composite membrane for an all-vanadium redox flow battery according to claim 1, characterized in that: The following steps are involved: Step 1, dissolving trialdehyde phloroglucinol in dimethyl sulfoxide to obtain a precursor solution A; Step 2: Tetrakis(4-aminophenyl)methane is dissolved in dimethyl sulfoxide, and then an appropriate amount of linear sulfonated polymer is added, and the precursor solution B is obtained after uniform dispersion by ultrasonication; Step 3: Mix the precursor solutions A and B thoroughly, disperse them ultrasonically for 10 minutes, and then add them dropwise to the glass tank. The glass tank needs to be calibrated with a level. Then, -1 The temperature was raised to 60℃ at a speed of 10℃ h -1 The temperature was raised to 80°C at a rate of 1000 nm and slowly evaporated for 48 h to obtain a Polymer@COF membrane, i.e., a covalent organic framework composite membrane.

3. The method for preparing a covalent organic framework composite membrane for an all-vanadium redox flow battery according to claim 2, characterized in that: In step 2, the molar ratio of the amino groups of tetrakis(4-aminophenyl)methane to the sulfonic acid groups of the sulfonated polymer is 10:

1.

4. The method for preparing a covalent organic framework composite membrane for an all-vanadium redox flow battery according to claim 2 or 3, characterized in that: In step 3, when the precursor solutions A and B are mixed, the molar ratio of amino groups to aldehyde groups in the mixed solution is (1:1) to (1:1.5).

5. The method for preparing a covalent organic framework composite membrane for an all-vanadium redox flow battery according to claim 4, characterized in that: The process of constructing the covalent organic framework composite membrane using the solution casting method is carried out under normal pressure and the reaction time is 3 days.

6. The method for preparing a covalent organic framework composite membrane for an all-vanadium redox flow battery according to claim 4, characterized in that: In step 2, the linear sulfonated polymer is sulfonated polyimide, sulfonated polyarylethersulfone, sulfonated polyvinyl alcohol, sulfonated polyaryletherketone, sulfonated polyphenylene ether or sulfonated polyetheretherketone.

7. A method for using a covalent organic framework composite membrane for an all-vanadium redox flow battery, characterized in that: The following steps are involved: The covalent organic framework composite membrane prepared in claim 1 is taken out after the solvent is evaporated, and the unreacted monomers are washed away in methanol and ethanol; the covalent organic framework composite membrane is then dried at room temperature to obtain an ionic three-dimensional covalent organic framework composite membrane, and the covalent organic framework composite membrane is used as an all-vanadium redox flow battery diaphragm.

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