A covalent organic framework composite polyphenylene ether anion exchange membrane and its preparation method

Abstract

This invention relates to a covalent organic framework composite polyphenylene ether anion exchange membrane, which is an organic membrane constructed using quaternized polyphenylene ether of structural formula (I) as the membrane matrix and a mixed alkyl-linked COF-TpBpy framework as the filler. This invention, by introducing COF-TpBpy framework ion channels into polyphenylene ether, constructs a novel covalent organic framework composite polyphenylene ether anion exchange membrane with excellent structural stability and significantly improves OH- ion exchange efficiency. ‑ Its high ionic conductivity shows great potential in high-performance ion conduction channel structures.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials technology, and relates to a membrane material, particularly an anion exchange membrane based on a covalent organic framework structure and its preparation method. Background Technology

[0002] With increasing global energy consumption and rising energy service costs, energy supply, climate, and local air quality are all negatively impacted. To meet the needs of sustainable development, hydrogen energy, as a recognized low-carbon and zero-carbon energy source, has received widespread attention.

[0003] Electrolysis of water can produce green hydrogen with zero carbon emissions, meeting the needs of global energy development. Furthermore, water electrolysis is a reliable, simple, and easy-to-maintain technology that produces high-purity hydrogen without pollution, making it a mature technology with promising development prospects. Technically, water electrolysis uses low-cost, non-precious metal catalysts and highly efficient and stable anion exchange membranes (AEMs), significantly reducing the cost of key raw materials.

[0004] However, the AEMs currently in use have not yet reached an ideal state in some key characteristics, and their efficiency and stability still need to be improved.

[0005] The challenges faced by AEMs mainly stem from two aspects: Firstly, while increasing ionic conductivity can improve the hydrogen production efficiency of electrolyzers, this process increases the water absorption and swelling rate of the membrane, reducing its mechanical properties and stability. Therefore, it is urgent to solve the trade-off between ionic conductivity and membrane mechanical properties. Secondly, the ether and ester bonds in the main chain of AEMs and the amino and quaternary ammonium salt cationic groups in the side chains are easily converted to OH groups under alkaline conditions. - Hydrolysis occurs due to nucleophilic attack, leading to the breakage of membrane molecular chains and the detachment of ion exchange groups. Therefore, overcoming the susceptibility of cationic groups and the polymer backbone to nucleophilic OH groups under alkaline conditions is crucial. - The problem of attack by substances such as alkaline anion exchange membranes is one of the important topics in the research and development of alkaline anion exchange membranes.

[0006] Low electrical conductivity is one of the main challenges faced by AEMs (Alternating Electrolytes), directly affecting the current efficiency and energy consumption of electrolyzers, and is a limiting factor in improving the hydrogen production efficiency of current electrolyzers. An effective way to increase ionic conductivity is to optimize the polymer matrix of AEMs by introducing conductive fillers to increase ion migration channels, adjusting the membrane structure to optimize ion migration paths, and developing AEMs with high conductivity and good mechanical properties.

[0007] Covalent organic frameworks (COFs) connect molecular constituent units into predetermined periodic structures using strong bonds, exhibiting excellent porosity, chemical stability, and thermodynamic stability. These properties make them promising for the separation and transport of small molecules. Therefore, constructing COF "ion channel" nanostructures within AEMs for assisted transport can enable AEMs to possess both good ion selectivity and low water absorption and swelling rates.

[0008] Although COFs have made significant progress in the application of membrane materials, some problems still need to be solved. For example, the lack of sufficient conductive sites on the surface of COFs restricts their development in AEMs. Surface modification of COFs to improve their properties is a very effective strategy for enhancing the ionic conductivity of AEMs.

[0009] Fengxiang Zhang et al. (Mixed matrix anion exchange membrane containing covalent organic frameworks: Ultra-low IEC but medium conductivity. Applied Surface Science (2021, 560, 0169-4332.) Quaternized COF (QCOF) was synthesized using a mechanochemical method and combined with a hydroxyl-functionalized polysulfone matrix to prepare hybrid matrix AEMs (or MMAEMs) with abundant hydrogen bonding networks and micropores. The synergistic effect enhanced the conductivity of the hydroxide, achieving an ion exchange capacity (IEC) of 0.38 mmol / g and an expansion rate of 2.5% at 20% QCOF content. However, the conductivity of these MMAEMs at 30 °C was only 14.3 mS / cm. -1 This is related to the fact that the side chains of its COF framework are not modified with diverse functions, resulting in low conductivity and limiting its use in devices.

[0010] Side chain functionalization is one of the effective methods to improve the conductivity of COFs. By introducing diverse functional groups that can promote hydroxide conduction on the side chains of COFs, their conductivity can be enhanced, thereby improving their performance in applications such as energy storage and conversion. Summary of the Invention

[0011] The purpose of this invention is to provide a covalent organic framework composite polyphenylene ether anion exchange membrane and its preparation method. By improving the ion conductivity of the COFs framework, the migration channels and pathways of ions are further enhanced, thereby improving the transport performance of AEMs and providing a more efficient solution for applications such as water electrolysis for hydrogen production.

[0012] The covalent organic framework composite polyphenylene ether anion exchange membrane of the present invention is an organic membrane composed of quaternary ammonium polyphenylene ether as shown in the following structural formula (I) as the membrane matrix and COF-TpBpy framework with alkyl linkages as shown in the following structural formula (II) as the filler. The mass percentage of the membrane matrix is ​​95-99%, and the mass percentage of the filler is 1-5%.

[0013]

[0014]

[0015] Among them, the quaternized polyphenylene ether shown in structural formula (I) is a copolymer QAPPO composed of quaternized polyphenylene ether structural units and polyphenylene ether structural units obtained by the quaternization reaction of polyphenylene ether, and the molar ratio of its quaternized polyphenylene ether structural units is... x =0.4~0.5.

[0016] The COF-TpBpy framework with alkyl-linked branches shown in structural formula (II) serves as an ion channel and is simply referred to as QAxSLCOF-TpBpy. Furthermore, the covalent organic framework composite polyphenylene ether anion exchange membrane of the present invention is simply referred to as QAxSLCOF-TpBpy@PPO, where x represents different R groups.

[0017] Specifically, R is C 1～3 Alkyl or fluorine-substituted alkyl groups.

[0018] More specifically, the fluorine substitution can be monofluorine substitution, polyfluorine substitution, or perfluorine substitution.

[0019] In the QAxSLCOF-TpBpy ion channel of this invention, the R-group iodide acts as a nucleophile to attack the nitrogen atom (N site) on the pyridine ring, resulting in a nucleophilic substitution reaction. The R-group is chemically bonded to the nitrogen atom, giving the nitrogen a positive charge and forming N... + Cations; simultaneously, iodine atoms detach and form iodide ions (I- ions). - N surrounding the positive charge + To create a stable environment.

[0020] The QAxSLCOF-TpBpy@PPO membrane of this invention employs a nanostructured COF-TpBpy ion channel. Based on its advantages such as large specific surface area, adjustable pore size and structure, convenient functional customization, and flexible covalent combination of building units, a highly arranged and oriented ion channel structure can be obtained in the matrix membrane.

[0021] Furthermore, QAPPO, as a polymer with excellent mechanical properties and chemical stability, can combine its toughness with the rigid structure of the QAxSLCOF-TpBpy ion channel to achieve an enriched state of transport tracks in the rigid structure of QAxSLCOF-TpBpy, thereby forming a high-performance hybrid matrix membrane with abundant ion transport channels to enhance its ion conduction performance.

[0022] Furthermore, the present invention also provides a method for preparing the covalent organic framework composite polyphenylene ether anion exchange membrane, which involves dissolving brominated polyphenylene ether (BPPO) as shown in structural formula (III) in its good solvent, adding a required amount of COF-TpBpy framework with alkyl linkages as shown in structural formula (II), dispersing it evenly, and then passing trimethylamine through it to carry out a quaternization reaction. After the reaction solution is dried to form a film, the anion exchange membrane is prepared.

[0023]

[0024] The brominated polyphenylene ether is a copolymer composed of brominated polyphenylene ether structural units and polyphenylene ether structural units, wherein the molar ratio of the brominated polyphenylene ether structural units is... x =0.4~0.5.

[0025] More specifically, the good solvent for the brominated polyphenylene ether can be any organic solvent that has good solubility and stability for the brominated polyphenylene ether, and the present invention does not have any particular limitation on it.

[0026] Preferably, the good solvent described in this invention can be N-methylpyrrolidone or dimethylformamide.

[0027] More specifically, the present invention involves coating the reaction solution after the quaternization reaction into a membrane, placing it under vacuum at 80°C for no less than 30 hours, and slowly drying the solvent and unreacted trimethylamine to obtain the covalent organic framework composite polyphenylene ether anion exchange membrane. The thickness of the membrane is controlled at approximately 60±5μm.

[0028] Furthermore, the present invention also provides a typical preparation method for the COF-TpBpy framework with alkyl linkages as fillers, which uses the covalent organic framework material COF-TpBpy as raw material and performs an iodination reaction with an iodide of structural formula RI in its good dispersion solvent to obtain COF-TpBpy frameworks with alkyl linkages of different structures.

[0029] R is C 1～3 The alkyl or fluorinated alkyl group, wherein the fluorine substitution can be monofluorinated, polyfluorinated or perfluorinated.

[0030] More specifically, the covalent organic framework material COF-TpBpy described in this invention can be COF-TpBpy prepared using various reported preparation methods, and this invention does not impose any particular limitation on it.

[0031] However, preferably, the COF-TpBpy of the present invention can be an ion channel COF-TpBpy structure obtained by condensation reaction of trialdehyde phloroglucinol and 5,5'-diamino-2,2'-bipyridine as raw materials in an N,N-dimethylaniline / 1,2-dichlorobenzene solvent system in an aqueous acetic acid solution.

[0032] Specifically, the preferred molar ratio of trialdehyde phloroglucinol to 5,5'-diamino-2,2'-bipyridine is 1:1.5 to 2.

[0033] Furthermore, the present invention further refines the COF-TpBpy material through ultrasonication. Specifically, the covalent organic framework material COF-TpBpy is dispersed in a dimethylformamide or N-methylpyrrolidone solvent system to form a suspension. The suspension is then broken up using an ultrasonic cell disruptor, and after removing the solvent, it is dried to obtain the refined SLCOF-TpBpy material. The refined SLCOF-TpBpy material is more conducive to the subsequent iodination reaction for grafting alkyl chains.

[0034] By employing the aforementioned ultrasonic disruption method, this invention assists in achieving high dispersibility and encapsulation of QAxSLCOF-TpBpy, thereby further improving the controllability of ion channel arrangement and transport sites in the membrane.

[0035] This invention innovatively introduces ion channels with highly aligned transport sites and tunable multi-cation sites into polyphenylene ether, synthesizing a novel covalent organic framework composite polyphenylene ether anion exchange membrane. This membrane not only possesses excellent structural stability but also significantly improves OH- ion exchange capacity. - Its high ionic conductivity makes it a promising candidate for high-performance ion conduction channel structures.

[0036] The covalent organic framework composite polyphenylene ether anion exchange membrane of the present invention has a simple preparation method, low cost, and superior electrochemical performance. It can be applied in alkaline fuel cells, carbon dioxide reduction and water electrolysis devices, and has broad application prospects.

[0037] QAxSLCOF-TpBpy possesses a highly ordered pore structure. By introducing this material, the pore structure and functional groups of the matrix membrane can be adjusted, thereby improving the ion transport performance of the matrix membrane. Simultaneously, based on the high chemical and thermodynamic stability of QAxSLCOF-TpBpy, the acid and alkali resistance, high temperature resistance, and other properties of the matrix membrane can be enhanced, thus improving its chemical stability. Furthermore, the intrinsic rigidity of QAxSLCOF-TpBpy allows AEMs to maintain a low water absorption and swelling rate while improving ion conduction. Attached Figure Description

[0038] Figure 1 This is the 1H NMR spectrum of brominated polyphenylene oxide (BPPO).

[0039] Figure 2 These are the 1H NMR spectra of a polyphenylene ether anion exchange membrane (QAPPO) and the 1H NMR spectra of brominated polyphenylene ether (BPPO).

[0040] Figure 3 This is a comparison of the infrared spectra of SLCOF-TpBpy and QAxSLCOF-TpBpy with different structures.

[0041] Figure 4 This is a comparison of the infrared spectra of QAPPO, SLCOF-TpBpy@PPO, and QAxSLCOF-TpBpy@PPO films with different structures.

[0042] Figure 5 This is an IEC comparison curve of QAPPO, SLCOF-TpBpy@PPO and QAxSLCOF-TpBpy@PPO membranes with different structures.

[0043] Figure 6 These are the ionic conductivity versus temperature curves for QAPPO, SLCOF-TpBpy@PPO, and QAxSLCOF-TpBpy@PPO membranes with different structures.

[0044] Figure 7 This is a comparison curve of the water absorption rates of QAPPO and QAxSLCOF-TpBpy@PPO membranes.

[0045] Figure 8 This is a comparison curve of the swelling rates of QAPPO and QAxSLCOF-TpBpy@PPO membranes.

[0046] Figure 9 This is a comparison curve of the mechanical properties of QAPPO, COF-TpBpy@PPO, QAmSLCOF-TpBpy@PPO and QAmCOF-TpBpy@PPO films. Implementation

[0047] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention, so that those skilled in the art can better understand and utilize the present invention, and are not intended to limit the scope of protection of the present invention.

[0048] Unless otherwise specified, the production processes, experimental methods, or testing methods involved in the embodiments and comparative examples of this invention are all conventional methods in the prior art, and their names and / or abbreviations are all conventional names in the art, which are very clear and distinct in the relevant application fields. Those skilled in the art can understand the conventional process steps based on the names and apply the corresponding equipment, and implement them according to conventional conditions or the conditions recommended by the manufacturer.

[0049] The various instruments, equipment, raw materials or reagents used in the embodiments of this invention are not subject to any special restrictions on their source. They are all conventional products that can be purchased through regular commercial channels and can be prepared according to conventional methods known to those skilled in the art.

[0050] The covalent organic framework composite polyphenylene ether anion exchange membrane of the present invention is prepared according to the following method:

[0051] Brominated polyphenylene ether (BPPO) was prepared by reacting polyphenylene ether, N-bromosuccinimide, and azobisisobutyronitrile in a chlorobenzene solvent system under inert protection.

[0052] The COF-TpBpy ion channel structure was synthesized by condensation reaction of trialdehyde phloroglucinol and 5,5'-diamino-2,2'-bipyridine in a mixed solution system of N,N-dimethylaniline / 1,2-dichlorobenzene.

[0053] COF-TpBpy was ground and ultrasonically crushed to obtain fine SLCOF-TpBpy dispersed in N-methylpyrrolidone or dimethylformamide solvent system. Alkylating agents with different structures were added under inert protection, and grafting reaction was carried out to obtain rigid ion channel QAxSLCOF-TpBpy with the structure shown in formula (II).

[0054] Add the required amount of QAxSLCOF-TpBpy to the brominated polyphenylene ether solvent system, and carry out the quaternization reaction with trimethylamine to obtain a homogeneous solution of mixed membrane;

[0055] The homogeneous solution was poured onto a clean glass plate and slowly dried to prepare the covalent organic framework composite polyphenylene ether anion exchange membrane of the present invention.

[0056] Specifically, the brominated polyphenylene ether is prepared by dissolving polyphenylene ether, N-bromosuccinimide, and azobisisobutyronitrile in chlorobenzene and refluxing at 135–140 °C.

[0057] More specifically, the molar ratio of polyphenylene ether to N-bromosuccinimide in the reflux reaction is 1:3.

[0058] Furthermore, the dried polyphenylene ether is preferably dissolved in chlorobenzene at a concentration of 6.5% (w / v); the reflux reaction time is preferably 6 to 7 hours.

[0059] The product obtained from the reflux reaction was washed with methanol and then dried by forced air to obtain brominated polyphenylene ether.

[0060] Specifically, in the condensation reaction, the molar ratio of the raw material trialdehyde phloroglucinol to 5,5'-diamino-2,2'-bipyridine is 1:1.5.

[0061] More specifically, a 6 mol / L aqueous solution of acetic acid is also added to the condensation reaction system.

[0062] After the condensation reaction was completed, the precipitate was collected by centrifugation and dried under vacuum at 80°C to obtain the COF-TpBpy ion channel structure.

[0063] Furthermore, in this invention, the obtained COF-TpBpy is first ground for 2 hours, then dispersed in a solvent, and then broken down using an ultrasonic cell disruptor with a power of 100-200W to obtain SLCOF-TpBpy. The preferred disruption time is 1.5-2 hours.

[0064] More preferably, the suspension can be cooled during the crushing process to maintain the temperature of the suspension at around 30°C.

[0065] The grafting reaction requires the alkylating agent to be added dropwise and carried out under inert and light-protected conditions.

[0066] Furthermore, the grafting reaction time is preferably 24 to 30 hours.

[0067] Preferably, the present invention involves fully dissolving brominated polyphenylene ether in a solvent to obtain a 2% (w / v) solution for quaternization reaction.

[0068] Specifically, the present invention involves laying the quaternization reaction product into a membrane and placing it under vacuum at 80°C for 30 hours. After slowly drying the solvent and unreacted trimethylamine, a covalent organic framework composite polyphenylene ether anion exchange membrane with a membrane thickness controlled at approximately 60±5μm is obtained. Example

[0069] Example 1

[0070] Under argon protection, polyphenylene ether (1.8 g, 15 mmol, Mn = 50000~58000), N-bromosuccinimide (1.3623 g, 7.65 mmol) and azobisisobutyronitrile (0.0753 g, 0.46 mmol) were dissolved in 28 mL of chlorobenzene and refluxed at 135 °C for 6 h.

[0071] After the reaction solution cools to room temperature, slowly add 20 mL of continuously sonicated methanol to precipitate the reactants and prevent clumping.

[0072] The precipitate was repeatedly washed with methanol (10×4mL), and the washed product was dried overnight in a 50℃ forced-air drying oven to obtain brominated polyphenylene ether (BPPO). The bromination rate was found to be 40-50%.

[0073] Nuclear magnetic resonance analysis was performed on the prepared BPPO to obtain... Figure 1 The hydrogen spectrum is shown. The hydrogen atom signals on the benzene ring appear around 6.6 ppm, labeled a and b. Due to the presence of the bromine substituent, the two hydrogen atoms originally in the meta position on the benzene ring no longer have equivalence, causing them to appear in... 1 The signal positions in the 1H NMR spectra differed. Furthermore, the signal at 2.09 ppm (c) was attributed to a hydrogen atom on the benzylmethyl group, while the peak at 4.3 ppm (h) represented a hydrogen atom on the methylene group, indicating that the methyl group in the polymer had been replaced by a bromine atom, thus confirming the success of the bromomethylation reaction. Simultaneously, the chemical shifts and integral ratios of the hydrogen atoms in the spectra were consistent with those of the target product.

[0074] Example 2

[0075] Trialdehyde phloroglucinol (208 mg, 1 mmol) and 5,5'-diamino-2,2'-bipyridine (279 mg, 1.5 mmol) were dissolved in 20 mL of a mixed solution of N,N-dimethylaniline / 1,2-dichlorobenzene (1:1 v / v), placed in a 50 mL Teflon-lined high-pressure reactor, and sonicated for 5 min to ensure uniform dispersion. Then, 2.7 mL of a 6 mol / L solution was added. -1 An aqueous solution of acetic acid was stirred magnetically for 2 hours, then sealed and heated to 120°C for 72 hours.

[0076] The precipitate was collected by centrifugation, washed with anhydrous tetrahydrofuran (6×4mL) and acetone (3×4mL), and then dried under vacuum at 80℃ overnight to prepare orange-red COF-TpBpy with a yield of 65%.

[0077] The prepared COF-TpBpy was ground into powder and dispersed in 50 mL of dimethylformamide solvent to form a suspension. The suspension was disrupted for 2 hours using an ultrasonic cell disruptor at a power of 150 W. During the process, the ultrasonic on / off time was set to 2 s and 3 s respectively, and the suspension was circulated and cooled to maintain the temperature of the suspension at about 30 °C.

[0078] The suspension was vacuum filtered, washed with methanol (15×3mL), and vacuum dried overnight at 80℃ to prepare a finer orange-red SLCOF-TpBpy powder.

[0079] Example 3

[0080] Weigh 30 mg of dried SLCOF-TpBpy and disperse it in 2 mL of N-methylpyrrolidone under argon protection. Circulate and condense to 0 °C, then add iodomethane (2.13 g, 15 mmol) dropwise. React at room temperature in the dark for 24 h.

[0081] After the reaction was complete, the product was washed with methanol (15×3mL) and dried overnight in a vacuum drying oven at 80℃ to obtain the product QAmSLCOF-TpBpy.

[0082] Under argon protection, the prepared BPPO (0.21 g, containing 0.5 mmol of brominated functional group) was dissolved in 10 ml of N-methylpyrrolidone and sonicated for 5 min to obtain a homogeneous solution.

[0083] Weigh 2.5% of QAmSLCOF-TpBpy in the mixed membrane solution and disperse it in the above homogeneous solution. Add trimethylamine (0.15 ml, 0.16 mmol) dropwise to carry out the quaternization reaction. After 24 h of reaction, the mixed membrane solution is obtained.

[0084] The mixed membrane solution was poured into a clean petri dish and slowly dried at 80°C to prepare a covalent organic framework composite polyphenylene ether anion exchange membrane, denoted as QAmSLCOF-TpBpy@PPO.

[0085] Example 4

[0086] Weigh 30 mg of dried SLCOF-TpBpy and disperse it in 2 mL of N-methylpyrrolidone under argon protection. Add iodopropane (2.55 g, 15 mmol) dropwise and react at room temperature for 24 h.

[0087] After the reaction was complete, the product was washed with methanol (15×3mL) and dried overnight in a vacuum drying oven at 80℃ to obtain the product QAprSLCOF-TpBpy.

[0088] Under argon protection, the prepared BPPO (0.21 g, containing 0.5 mmol of brominated functional group) was dissolved in 10 ml of N-methylpyrrolidone and sonicated for 5 min to obtain a homogeneous solution.

[0089] Weigh 2.5% of QAprSLCOF-TpBpy from the mixed membrane solution and disperse it in the above homogeneous solution. Add trimethylamine (0.15 ml, 0.16 mmol) dropwise to carry out the quaternization reaction. After 24 h of reaction, the mixed membrane solution is obtained.

[0090] The mixed membrane solution was poured into a clean petri dish and slowly dried at 80°C to prepare a covalent organic framework composite polyphenylene ether anion exchange membrane, denoted as QAprSLCOF-TpBpy@PPO.

[0091] Example 5

[0092] Weigh 30 mg of dried SLCOF-TpBpy and disperse it in 1 mL of dimethylformamide under argon protection. Circulate and condense to 0 °C, then add 11.75 g of 25% trifluoroiodide aqueous solution (15 mmol) dropwise. React at 30 °C for 24 h in the dark.

[0093] After the reaction was complete, the product was washed with methanol (15×3mL) and dried overnight in a vacuum drying oven at 80℃ to obtain the product QAF3SLCOF-TpBpy.

[0094] Under argon protection, the prepared BPPO (0.21 g, containing 0.5 mmol of brominated functional group) was dissolved in 10 ml of dimethylformamide and sonicated for 5 min to obtain a homogeneous solution.

[0095] Weigh 2.5% of QAF3SLCOF-TpBpy from the mixed membrane solution and disperse it in the above homogeneous solution. Add trimethylamine (0.15 ml, 0.16 mmol) dropwise to carry out the quaternization reaction. After 24 h of reaction, the mixed membrane solution is obtained.

[0096] The mixed membrane solution was poured into a clean petri dish and slowly dried at 80°C to prepare a covalent organic framework composite polyphenylene ether anion exchange membrane, denoted as QAF3SLCOF-TpBpy@PPO.

[0097] Comparative Example 1

[0098] Under argon protection, polyphenylene ether (1.8 g, 15 mmol, Mn = 50000~58000), N-bromosuccinimide (1.3623 g, 7.65 mmol) and azobisisobutyronitrile (0.0753 g, 0.46 mmol) were dissolved in 28 mL of chlorobenzene and refluxed at 135 °C for 6 h.

[0099] After the reaction solution cools to room temperature, slowly add 20 mL of continuously sonicated methanol to precipitate the reactants and prevent clumping.

[0100] The precipitate was repeatedly washed with methanol (10×4mL), and the washed product was dried overnight in a 50℃ forced-air drying oven to obtain brominated polyphenylene ether (BPPO). The bromination rate was found to be 40-50%.

[0101] Under argon protection, the prepared BPPO (0.21 g, containing 0.5 mmol brominated functional groups) was dissolved in 10 ml of N-methylpyrrolidone and sonicated for 5 min to obtain a homogeneous solution. Trimethylamine (0.15 ml, 0.16 mmol) was added dropwise to carry out a quaternization reaction. After 24 h of reaction, a membrane solution was obtained.

[0102] The membrane solution was poured into a clean petri dish and dried slowly at 80°C to prepare a quaternary ammonium polyphenylene ether anion exchange membrane, denoted as QAPPO.

[0103] Nuclear magnetic resonance analysis was performed on the prepared QAPPO anion exchange membrane to obtain... Figure 2 The hydrogen spectrum shown is shown. (Compared to...) Figure 1 compared to, Figure 2 The QAPPO peaks exhibited new characteristic peaks, indicating structural differences, particularly the unique QAPPO peaks associated with nitrogen ions (N). + The methyl hydrogen atom signal peak (d) connected to the target product appeared at 3.1 ppm, and the chemical shift and integral ratio of the hydrogen atoms in the spectrum were also consistent with those of the target product.

[0104] Comparative Example 2

[0105] Under argon protection, the prepared BPPO (0.21 g, containing 0.5 mmol of brominated functional group) was dissolved in 10 ml of N-methylpyrrolidone and sonicated for 5 min to obtain a homogeneous solution.

[0106] Weigh 2.5% of SLCOF-TpBpy in the mixed membrane solution and disperse it in the above homogeneous solution. Add trimethylamine (0.15 ml, 0.16 mmol) dropwise to carry out the quaternization reaction. After 24 h of reaction, the mixed membrane solution is obtained.

[0107] The mixed membrane solution was poured into a clean petri dish and slowly dried at 80°C to prepare a covalent organic framework composite polyphenylene ether anion exchange membrane, denoted as SLCOF-TpBpy@PPO.

[0108] Comparative Example 3

[0109] Weigh 30 mg of dried SLCOF-TpBpy and disperse it in 2 mL of N-methylpyrrolidone under argon protection. Circulate and condense to 0 °C, then add iodopentane (2.97 g, 15 mmol) dropwise. React at room temperature in the dark for 24 h.

[0110] After the reaction was complete, the product was washed with methanol (15×3mL) and dried overnight in a vacuum drying oven at 80℃ to obtain the product QApSLCOF-TpBpy.

[0111] Under argon protection, the prepared BPPO (0.21 g, containing 0.5 mmol of brominated functional group) was dissolved in 10 ml of N-methylpyrrolidone and sonicated for 5 min to obtain a homogeneous solution.

[0112] Weigh 2.5% of QApSLCOF-TpBpy from the mixed membrane solution and disperse it in the above homogeneous solution. Add trimethylamine (0.15 ml, 0.16 mmol) dropwise to carry out the quaternization reaction. After 24 h of reaction, the mixed membrane solution is obtained.

[0113] The mixed membrane solution was poured into a clean petri dish and slowly dried at 80°C to prepare a covalent organic framework composite polyphenylene ether anion exchange membrane, denoted as QApSLCOF-TpBpy@PPO.

[0114] Comparative Example 4

[0115] Weigh 30 mg of dried SLCOF-TpBpy and disperse it in 2 mL of dimethylformamide under argon protection. Circulate and condense to 0 °C, then add heptafluoro-5-iodopentane (4.86 g, 15 mmol) dropwise. React at room temperature (40 °C) for 30 h in the dark.

[0116] After the reaction was complete, the product was washed with methanol (15×3mL) and dried overnight in a vacuum drying oven at 80℃ to obtain the product QAF7SLCOF-TpBpy.

[0117] Under argon protection, the prepared BPPO (0.21 g, containing 0.5 mmol of brominated functional group) was dissolved in 10 ml of dimethylformamide and sonicated for 5 min to obtain a homogeneous solution.

[0118] Weigh 2.5% of QAF7SLCOF-TpBpy from the mixed membrane solution and disperse it in the above homogeneous solution. Add trimethylamine (0.15 ml, 0.16 mmol) dropwise to carry out the quaternization reaction. After 24 h of reaction, the mixed membrane solution is obtained.

[0119] The mixed membrane solution was poured into a clean petri dish and slowly dried at 80°C to prepare a covalent organic framework composite polyphenylene ether anion exchange membrane, denoted as QAF7SLCOF-TpBpy@PPO.

[0120] Figure 3 The image shows the infrared spectra of COF-TpBpy frameworks with different microstructures, including SLCOF-TpBpy, QAmSLCOF-TpBpy, QAprSLCOF-TpBpy, QAF3SLCOF-TpBpy, QApSLCOF-TpBpy, and QAF7SLCOF-TpBpy. They all share a common feature: a wavelength of 1646 cm⁻¹. -1 and 1440cm -1 The peak at 1450–1350 cm⁻¹ corresponds to the stretching vibration of the CN bond in the quaternary ammonium salt. -1 The infrared spectral data within the range reflect the bending vibrations of methyl and methylene groups, thus proving the successful grafting of carbon chains induced by the quaternization reaction.

[0121] Figure 4 Infrared spectra of anion exchange membranes containing different microstructures of COF-TpBpy frameworks are presented. Due to the low doping concentration of the ion channel QAxSLCOF-TpBpy, only the asymmetric and symmetric vibrations of the C=O bonds in its molecule are clearly visible in the spectrum, corresponding to 1658 cm⁻¹, respectively. -1 and 1711cm -1 The absorption peak at that location.

[0122] Application Example 1

[0123] The relationship between IEC (Extended Ion Exchange Rate) and ion conductivity is very close. A higher IEC value means that there are more active groups in the material that can participate in ion exchange, which usually leads to higher ion conductivity. This is because more active groups can release and absorb ions, thereby promoting ion migration within the material.

[0124] This application example demonstrates IEC performance testing on different QAxSLCOF-TpBpy@PPO membranes, including the anion exchange membranes QAmSLCOF-TpBpy@PPO, QAprSLCOF-TpBpy@PPO, and QAF3SLCOF-TpBpy@PPO prepared in Examples 3, 4, and 5 above, as well as the anion exchange membranes QAPPO, SLCOF-TpBpy@PPO, QApSLCOF-TpBpy@PPO, and QAF7SLCOF-TpBpy@PPO prepared in Comparative Examples 1-4. The results are as follows: Figure 5 As shown.

[0125] It can be seen that as the length of the quaternized alkyl chain of QAxSLCOF-TpBpy increases, the IEC values ​​of different QAxSLCOF-TpBpy@PPO membranes show a gradually decreasing trend.

[0126] For different simple alkyl grafts, QAmSLCOF-TpBpy@PPO (2.07 mmol g) -1 ), QAprSLCOF-TpBpy@PPO (2.03mmol g -1 ) and QApSLCOF-TpBpy@PPO (1.67mmol g) -1 The three types of membranes, with their intertwined long alkyl chains and excessive hydrophobicity, hinder ion transport, demonstrating the negative impact of this phenomenon on ion transport. However, the first two membranes, compared to the original QAPPO membrane (1.96 mmol g), showed better performance. -1 In terms of IEC, there is still a certain degree of improvement, proving that grafting with appropriate carbon chain length has a certain improvement effect on IEC.

[0127] Furthermore, although the fluorine-substituted QAF3SLCOF-TpBpy@PPO has a lower IEC due to its hydrophobicity, its 1.95 mmol / g... -1 The IEC value was almost identical to that of the original membrane QAPPO (1.96 mmol g). -1 The values ​​are consistent. However, due to its longer carbon chain and the hydrophobicity of the fluorine substituents, QAF7SLCOF-TpBpy@PPO has the lowest IEC value (1.63 mmol g). -1 This demonstrates that carbon chain length plays a dominant role in ion transport efficiency.

[0128] The SLCOF-TpBpy@PPO membrane without quaternization modification did not provide more active sites, resulting in a lower IEC value of 1.85 mmol g. -1 This also indirectly proves the necessity of quaternization modification of COF-TpBpy framework materials in terms of ion transport.

[0129] Application Example 2

[0130] The ionic conductivity of the QAxSLCOF-TpBpy@PPO membrane described in this invention was tested in a pure water electrolyte at a temperature range of 20–80°C, as follows: Figure 6 As shown.

[0131] Figure 6 In the process, as the alkyl chain length of the quaternizing reagent increases, its variation pattern is almost consistent with the IEC trend, and the ionic conductivity also gradually decreases. Similarly, the ionic conductivity of QAmSLCOF-TpBpy@PPO and QAprSLCOF-TpBpy@PPO is worse than that of the original QAPPO membrane. However, QApSLCOF-TpBpy@PPO with a longer alkyl chain is worse than QAPPO. The ionic conductivity of unmodified SLCOF-TpBpy@PPO is also worse than that of QAPPO.

[0132] However, the fluorine-substituted QAF3SLCOF-TpBpy@PPO exhibits the highest ionic conductivity at 65.54 ms / cm, which is 27.42 ms / cm higher than the ionic conductivity of QAPPO (38.12 ms / cm). This is attributed to the fact that the fluorine group helps to increase the ion concentration of the AEMs material by reducing the hydration and expansion ratio, thereby improving the conductivity.

[0133] In contrast, although QAF7SLCOF-TpBpy@PPO also contains more fluorine groups, the alkyl chain length is also greatly increased, which blocks ion transport. This again proves that the grafting of appropriate carbon chain length should be the primary consideration in terms of ion transport.

[0134] The above results demonstrate that the quaternized QAxSLCOF-TpBpy of the present invention, containing different lengths and structures, has ordered ion transport channels and a robust support structure that enriches it in QAPPO, thus solving the problem of low ionic conductivity of AEMs to a certain extent. At the same time, with an appropriate carbon chain length, the channel structure containing fluorine groups can further enhance ionic conductivity by increasing the ion concentration in the local microenvironment, thereby improving the electrochemical performance of batteries.

[0135] Application Example 3

[0136] The water absorption and swelling rates of QAxSLCOF-TpBpy@PPO membranes, which exhibit improved ionic conductivity compared to QAPPO membranes, were further investigated. These included QAmSLCOF-TpBpy@PPO, QAprSLCOF-TpBpy@PPO, and QAF3SLCOF-TpBpy@PPO. The results are as follows: Figure 7 , Figure 8 As shown.

[0137] Due to the stability of the QAxSLCOF-TpBpy structure and the interaction between the phenyl ether side chain and the quaternary ammonium cation in the matrix membrane, the water absorption and swelling ratio of QAmSLCOF-TpBpy@PPO and QAprSLCOF-TpBpy@PPO also tend to be higher than those of the QAPPO membrane. The QAF3SLCOF-TpBpy@PPO membrane, due to the hydrophobicity of fluorine atoms, has a water absorption rate almost identical to that of the QAPPO membrane, only with a slightly lower swelling ratio. These results indicate that the anion exchange membrane prepared in this invention possesses good dimensional stability, allowing the membrane to maintain its morphology and structure in more demanding environments.

[0138] Application Example 4

[0139] Furthermore, due to the poor compatibility between COF-TpBpy and the polymer, it affects polymer chain entanglement, causing stress concentration points at the locations of COF-TpBpy, thus increasing the probability of fracture during tensile testing. This invention improves the mechanical properties of the membrane by processing multilayer COF-TpBpy into a single-layer SLCOF-TpBpy.

[0140] Under argon protection, the prepared BPPO (0.21 g, containing 0.5 mmol of brominated functional group) was dissolved in 10 ml of dimethylformamide and sonicated for 5 min to obtain a homogeneous solution.

[0141] Weigh 2.5% COF-TpBpy of the mixed membrane solution and grind it into powder in a mortar until uniform. Disperse the powder in the above homogeneous solution and add trimethylamine (0.15 ml, 0.16 mmol) dropwise to carry out the quaternization reaction. After 24 h of reaction, the mixed membrane solution is obtained.

[0142] The mixed membrane solution was poured into a clean petri dish and slowly dried at 80°C to prepare a covalent organic framework composite polyphenylene ether anion exchange membrane, denoted as COF-TpBpy@PPO.

[0143] Mechanical properties were tested on the above-mentioned COF-TpBpy@PPO membrane, as well as QAPPO and QAmSLCOF-TpBpy@PPO membranes, and the results were obtained. Figure 9 The tensile strength and elongation at break of different films are shown.

[0144] from Figure 9 The results showed that, under the premise of consistent enrichment, the mechanical properties of QAPPO and QAmSLCOF-TpBpy@PPO did not change significantly, but the tensile strength of COF-TpBpy@PPO membrane dropped sharply from 26.61 MPa of QAPPO membrane to 10.26 MPa.

[0145] The above embodiments of the present invention do not describe all details exhaustively, nor do they limit the present invention to the embodiments described above. Various changes, modifications, substitutions, and variations made by those skilled in the art to these embodiments without departing from the principles and spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A covalent organic framework composite polyphenylene ether anion exchange membrane, comprising an organic membrane using quaternized polyphenylene ether as shown in structural formula (I) as the membrane matrix and a COF-TpBpy framework with alkyl-linked branches as shown in structural formula (II) as the filler: ； The quaternized polyphenylene ether represented by structural formula (I) is a copolymer QAPPO obtained by the quaternization reaction of polyphenylene ether, consisting of quaternized polyphenylene ether structural units and polyphenylene ether structural units. The molar ratio of its quaternized polyphenylene ether structural units is... x =0.4~0.5; ； In the COF-TpBpy framework with alkyl linkages shown in structural formula (II), R is C 1～3 Alkyl or fluorinated alkyl groups.

2. The covalent organic framework composite polyphenylene ether anion exchange membrane according to claim 1, characterized in that: Thin film substrate The mass percentage content is 95-99%, and the mass percentage content of the filler is 1-5%.

3. The covalent organic framework composite polyphenylene ether anion exchange membrane according to claim 1, characterized in that: The fluorine substitution is monofluorine substitution, polyfluorine substitution, or perfluorine substitution.

4. The method for preparing the covalent organic framework composite polyphenylene ether anion exchange membrane according to claim 1 comprises dissolving the brominated polyphenylene ether shown in structural formula (III) in a well-soluble solvent, adding a required amount of the COF-TpBpy framework with alkyl-linked branches shown in structural formula (II), dispersing it evenly, and then passing trimethylamine through it to carry out a quaternization reaction. The reaction solution is then dried to form the anion exchange membrane. ； in, The brominated polyphenylene ether is a copolymer composed of brominated polyphenylene ether structural units and polyphenylene ether structural units, wherein the molar ratio of the brominated polyphenylene ether structural units is... x =0.4~0.

5.

5. The method for preparing the covalent organic framework composite polyphenylene ether anion exchange membrane according to claim 4, characterized in that: The brominated polyphenylene ether is well soluble in N-methylpyrrolidone or dimethylformamide.

6. The method for preparing the covalent organic framework composite polyphenylene ether anion exchange membrane according to claim 4, characterized in that: The reaction solution after the quaternization reaction was laid into a membrane and placed under vacuum at 80°C for no less than 30 hours to prepare a covalent organic framework composite polyphenylene ether anion exchange membrane with a membrane thickness of 60±5μm.

7. The method for preparing the covalent organic framework composite polyphenylene ether anion exchange membrane according to claim 4, characterized in that: The COF-TpBpy framework with alkyl linkages shown in structural formula (II) is obtained by iodination of the covalent organic framework material COF-TpBpy with an iodide of structural formula RI in a well-dispersed solvent, resulting in COF-TpBpy frameworks with different alkyl linkage structures, where R is C 1～3 The alkyl or fluorinated alkyl group, wherein the fluorine substitution is monofluorinated, polyfluorinated or perfluorinated.

8. The method for preparing the covalent organic framework composite polyphenylene ether anion exchange membrane according to claim 7, characterized in that: The covalent organic framework material COF-TpBpy is an ion channel COF-TpBpy structure obtained by condensation reaction of trialdehyde phloroglucinol and 5,5'-diamino-2,2'-bipyridine as raw materials in an N,N-dimethylaniline / 1,2-dichlorobenzene solvent system in an aqueous acetic acid solution.

9. The method for preparing the covalent organic framework composite polyphenylene ether anion exchange membrane according to claim 8, characterized in that: The molar ratio of trialdehyde phloroglucinol to 5,5'-diamino-2,2'-bipyridine is 1:1.5 to 2.

10. The method for preparing the covalent organic framework composite polyphenylene ether anion exchange membrane according to claim 8, characterized in that: The covalent organic framework material COF-TpBpy was dispersed in a dimethylformamide or N-methylpyrrolidone solvent system to form a suspension. The suspension was then broken down and refined using an ultrasonic cell disruptor. After removing the solvent, the refined SLCOF-TpBpy material was obtained.

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