Branched anion exchange membrane based on tetraphenyl ethylene as well as preparation method and application of branched anion exchange membrane

Abstract

The invention discloses a tetraphenylethylene-based branched anion exchange membrane and a preparation method and application thereof, tetraphenylethylene is used as a branching agent, the tetraphenylethylene, an aromatic monomer and piperidone are subjected to superacid catalytic polymerization to prepare polyaryl piperidine with a star-shaped branched structure, and then quaternary ammonium functionalization and post-treatment are performed to obtain the branched anion exchange membrane (AEM). The branched structure can reduce the stacking density of polymer chains in the membrane, form a high-proportion free volume to improve the water absorption rate, reduce the OH <-> transmission resistance and improve the ionic conductivity; the rigid aromatic branched skeleton can inhibit excessive water swelling of the membrane; the free volume fraction of the membrane can be optimized by regulating and controlling the molar percentage of tetraphenyl ethylene in the copolymerized aromatic monomer, the AEM with high ionic conductivity and dimensional stability is obtained, and the AEM can be applied to an anion exchange membrane water electrolysis cell.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electrochemical energy materials and membrane separation technology, and particularly relates to a branched anion exchange membrane based on tetraphenyl ethylene as well as a preparation method and application thereof. BACKGROUND

[0002] To solve the problem of high carbon emission in the hydrogen production process, relying on renewable energy power driven hydrogen production technology has become the core research direction to realize environmentally friendly hydrogen production. Among them, water electrolysis cell is considered as a potential carbon neutral hydrogen production technology due to its zero pollution emission, high hydrogen purity and simple operation. Among various water electrolysis cells, anion exchange membrane water electrolyzer (AEMWE) is of great concern in the industry because of its green alternative advantages. Compared with traditional alkaline electrolyzers, AEMWE has the following advantages: first, the gapless structure design based on polymer membrane can improve the response adaptability to renewable energy power input fluctuation; second, it is compatible with renewable energy power supply mode, has high efficient start-stop ability and electrolysis efficiency; third, in the alkaline operating environment, the oxidation electrode reaction has high kinetic activity and low oxidation potential characteristics, which can adapt to low-cost non-noble metal catalysts and significantly reduce the device cost.

[0003] Anion exchange membrane (AEM) is the core functional component of AEMWE, and its core role is to block the mutual penetration of hydrogen and oxygen generated by the anode and cathode, and to realize the selective transmission of OH - to the anode. Currently, the performance optimization of AEM faces the core bottleneck of how to balance high ionic conductivity and structural stability. In the existing technology path to improve conductivity, one mainstream solution is to increase the ion exchange capacity (IEC) of the polymer membrane, but too high IEC will cause the membrane material to swell due to excessive water absorption, thereby degrading the mechanical properties. Another effective idea is to improve the free volume fraction (FFV) of the polymer, which can strengthen the conductivity by reducing the ion transmission resistance.

[0004] However, there is no existing technology that can simultaneously achieve high FFV regulation, moderate water absorption rate and excellent structural stability. Traditional membrane materials are difficult to meet the stringent requirements of long-term service performance of AEMWE in actual application, so the development of new anion exchange membranes with high conductivity and structural stability has become a key breakthrough for the industrialization of AEMWE technology. SUMMARY

[0005] The present application aims to solve the technical bottleneck that the high conductivity and structural stability of the existing anion exchange membrane (AEM) are difficult to be considered together, and provides a branched anion exchange membrane based on tetraphenyl ethylene as well as a preparation method and application thereof, and the core purpose is to make the anion exchange membrane have high ionic conductivity and excellent dimensional stability by regulating the free volume fraction of the polymer.

[0006] To achieve the purpose, the present application adopts the following technical solutions: In a first aspect, the present application provides a preparation method of a branched anion exchange membrane based on tetraphenyl ethylene, comprising the following steps: Step 1, preparing branched polyaryl piperidine copolymer The aromatic monomer, tetraphenyl ethylene and piperidone monomer are dissolved in a first solvent to obtain a first mixed solution; under ice bath conditions, a catalyst is added to the first mixed solution to perform a polymerization reaction, and branched polyaryl piperidine copolymer is prepared; wherein, based on 100% of the total moles of the aromatic monomer and the tetraphenyl ethylene, the mole percentage of tetraphenyl ethylene is not more than 5%.

[0007] Step 2, preparing quaternized polyaryl piperidine The branched polyaryl piperidine copolymer is dissolved in a second solvent to obtain a second mixed solution; an alkali catalyst and a quaternization reagent are added to the second mixed solution to perform a quaternization reaction, and quaternized polyaryl piperidine is prepared.

[0008] Step 3, preparing branched anion exchange membrane based on tetraphenyl ethylene The quaternized polyaryl piperidine is dissolved in a third solvent to obtain a polymer casting solution; the polymer casting solution is formed by flow casting, pouring or coating to obtain a branched anion exchange membrane based on tetraphenyl ethylene.

[0009] Further, in step 1, the aromatic monomer is selected from at least one of biphenyl, triphenyl and diphenyl ethane, wherein the triphenyl can be p-triphenyl or m-triphenyl; the piperidone monomer is selected from at least one of 4-piperidone, N-methyl-4-piperidone, N-ethyl-4-piperidone, N-propyl-4-piperidone, N-isopropyl-4-piperidone, N-butyl-4-piperidone, N-pentyl-4-piperidone, N-hexyl-4-piperidone, piperidine trifluoromethyl ketone and N-benzyl-4-piperidone.

[0010] Further, in step 1, the catalyst is a mixture of trifluoroacetic acid and trifluoromethane sulfonic acid, wherein the molar ratio of trifluoroacetic acid and trifluoromethane sulfonic acid to the aromatic monomer is 1:1.8~1.9 and 1:9~11, respectively.

[0011] Further, in step 1, the polymerization reaction time is 4 h~6 h.

[0012] Further, in step 1, after the end of the polymerization reaction, a purification treatment step is further included: adding excess sodium hydroxide to the reaction system to precipitate a precipitate; after the precipitate is washed to neutral with deionized water, it is dried at 40-50 DEG C for 20-24 h to obtain a purified branched polyaryl piperidine copolymer.

[0013] Further, in step 2, the concentration of the branched polyaryl piperidine copolymer in the second mixed solution is 4.5-5.5 g / mL. Further, in step 2, the base catalyst is selected from one of potassium carbonate, potassium hydroxide, and sodium hydroxide, and the quaternary ammonium reagent is selected from at least one of iodoalkyl compounds, bromoalkyl compounds, and chloroalkyl compounds.

[0014] Further, in step 2, the quaternary ammonium reaction is carried out in the dark at 40-50 DEG C water bath, and the reaction time is 10-15 min, wherein the molar ratio of base catalyst to branched polyaryl piperidine copolymer is 1-1.1:1, and the molar ratio of quaternary ammonium reagent to branched polyaryl piperidine copolymer is 1-1.1:1.

[0015] Further, in step 3, the concentration of the quaternary ammonium polyaryl piperidine in the polymer casting solution is 4.5-5.5 g / mL.

[0016] In a second aspect, the present application provides a tetraphenyl ethylene-based branched anion exchange membrane made by the preparation method described above. The branched anion exchange membrane constructs a branched structure with tetraphenyl ethylene, and can adjust the free volume fraction of the membrane by adjusting the molar percentage of tetraphenyl ethylene, achieving the synergistic combination of high ionic conductivity and excellent dimensional stability.

[0017] In a third aspect, the present application provides a tetraphenyl ethylene-based branched anion exchange membrane as described above for use in the field of anion exchange membrane water electrolysis cells, and is particularly suitable for green hydrogen production scenarios.

[0018] The preparation method of the branched anion exchange membrane of the present application realizes the following significant beneficial effects by precisely designing the preparation process and structure control strategy: The star-shaped branched polyarylpiperidine material is prepared by copolymerization of tetraphenyl ethylene with aromatic monomers and piperidone through superacid catalytic low-temperature polymerization reaction, with tetraphenyl ethylene as a branching agent; and the target anion exchange membrane is finally prepared through quaternary ammonium functionalization and post-treatment of film formation. Firstly, by adjusting the mole percentage of tetraphenyl ethylene in the total aromatic monomers, the branching degree and the free volume fraction in the membrane can be precisely controlled, the star-shaped branched structure can effectively weaken the close packing of polymer chains, form a high proportion of free volume area, significantly reduce the OH - transport resistance, and further improve the ionic conductivity; secondly, by adjusting the functionalization reaction process, the ion exchange capacity (IEC) of the membrane can be controlled within a reasonable range, the water absorption rate is simultaneously improved on the premise of avoiding excessive water absorption and swelling of the membrane and ensuring excellent dimensional stability, so as to provide sufficient channels for efficient OH - transport. In summary, the present application successfully realizes the simultaneous consideration of high ionic conductivity and excellent dimensional stability, and precisely solves the core technical bottleneck that the existing anion exchange membrane is difficult to achieve both high conductivity and stability.

[0019] The present application will be further described in detail below in combination with the drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The preparation flow chart of the branched anion exchange membrane in the embodiments of the present application is shown in the figure; Figure 2 The synthesis schematic diagram of the quaternary ammonium polyarylpiperidine in Example 1 of the present application is shown in the figure; Figure 3 The nuclear magnetic resonance hydrogen spectrum of the polymer obtained in step (1) in Examples 2-4 and Comparative Example 1 of the present application is shown in the figure; Figure 4 The nuclear magnetic resonance hydrogen spectrum of the quaternary ammonium polyarylpiperidine obtained in step (2) in Examples 2-4 and Comparative Example 1 of the present application is shown in the figure; Figure 5 The scanning electron microscope (SEM) images of the anion exchange membranes prepared in Examples 2-4 and Comparative Example 1 of the present application are shown in the figures, wherein: Figure 5 (a) is the SEM image of the membrane obtained in Comparative Example 1, Figure 5 (b)-(d) are the SEM images of the membranes obtained in Examples 2-4; Figure 6 The free volume fraction (FFV) comparison chart of the anion exchange membranes prepared in Examples 2-4 and Comparative Example 1 of the present application is shown in the figure; Figure 7 The water absorption rate-temperature change curve of the anion exchange membranes prepared in Examples 2-4 and Comparative Example 1 of the present application is shown in the figure; Figure 8 The swelling rate-temperature change curve of the anion exchange membranes prepared in Examples 2-4 and Comparative Example 1 of the present application is shown in the figure; Figure 9 Transmission electron microscope images of the anion exchange membranes prepared in Examples 2-4 and Comparative Example 1 of this invention, wherein: Figure 9 (a) is a SEM image of the membrane obtained in Comparative Example 1. Figure 9 (b) to (d) are SEM images of the membranes obtained in Examples 2 to 4; Figure 10 The OH groups of the anion exchange membranes prepared in Examples 2-4 and Comparative Example 1 of this invention are... - The curve of electrical conductivity as a function of temperature.

[0021] Figure 11 The curves are for testing the water electrolysis cell performance of the anion exchange membranes prepared in Example 2 and Comparative Example 1 of this invention. Detailed Implementation

[0022] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0023] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the description of this application is for the purpose of describing particular embodiments only and is not intended to limit this application. like Figure 1 As shown in the figure, an embodiment of the present invention provides a method for preparing a branched anion exchange membrane based on tetraphenylethylene, comprising the following steps: Step 1: Preparation of branched polyarylpiperidine copolymer Aromatic monomers, tetraphenylethylene and piperidone monomers are dissolved in a first solvent to obtain a first mixture. A catalyst is added to the first mixture under ice bath conditions to carry out a polymerization reaction, which generates a branched polyarylpiperidine copolymer. The total molar amount of the aromatic monomers and the tetraphenylethylene is 100%, and the molar percentage of the tetraphenylethylene does not exceed 5%, that is, the molar percentage of the tetraphenylethylene is greater than 0 and less than or equal to 5%.

[0024] Step 2: Preparation of quaternized polyarylpiperidine The branched polyarylpiperidine copolymer is dissolved in a second solvent to obtain a second mixture; an alkaline catalyst and a quaternization reagent are added to the second mixture to carry out a quaternization reaction to obtain quaternized polyarylpiperidine.

[0025] Step 3, preparation of branched anion exchange membrane based on tetraphenyl ethylene The quaternary ammonium polyarylpipehdine is dissolved in a third solvent to obtain a polymer casting solution, and the polymer casting solution is shaped by way of casting, pouring or coating to obtain a branched anion exchange membrane based on tetraphenyl ethylene.

[0026] In this embodiment, tetraphenyl ethylene is an aromatic monomer containing carbon-carbon double bonds, and the four benzene rings in its molecular structure are connected to the carbon atoms at both ends of the double bond by single bonds. This bulky and rigid benzene ring skeleton has a dual core effect: on the one hand, it can significantly increase the scale of hydrophilic-hydrophobic phase separation, promoting regular hydrophilic-hydrophobic microphase separation morphology, and the continuous hydrophilic-hydrophobic channels formed by this morphology can accelerate the transport process of water molecules carrying OH - , thereby improving the ionic conductivity of the anion exchange membrane (AEM); on the other hand, by regulating its molar percentage in the total aromatic monomer (the sum of aromatic monomers and tetraphenyl ethylene), the free volume fraction (FFV) inside the membrane material can be precisely controlled. FFV refers to the unoccupied space within the polymer skeleton of the membrane material. Higher FFV can effectively reduce the packing density between polymer chains, providing more channels for the migration of OH - , thereby optimizing the overall performance of the AEM. In the anion exchange membrane system, the increase in FFV is usually accompanied by an increase in water absorption, because more free volume can provide sufficient space for water molecule adsorption; and a moderate increase in water absorption can further promote the transport of OH - , thereby enhancing the ionic conductivity. At the same time, since water molecules preferentially fill these unoccupied free volumes, they do not cause significant deformation of the overall structure of the membrane, thus ensuring the dimensional stability of the membrane during water absorption, avoiding excessive swelling or deformation.

[0027] It should be particularly noted that FFV is not the higher the better: if FFV is too large, it will lead to excessive water absorption of the membrane material, thereby producing a dilution effect - the excess water is equivalent to a solvent, which will reduce the OH - concentration in the membrane, thereby inhibiting the efficiency of ion transport. Therefore, regulating FFV to a reasonable range is the key to achieving a balance between "dimensional stability guarantee" and "water absorption and conductivity improvement", and ultimately achieving a balance between high ionic conductivity and excellent dimensional stability of the AEM.

[0028] The present application is based on a large number of experimental researches, and it is found that, taking the total mole number of aromatic monomers and tetraphenyl ethylene as 100%, the mole ratio of tetraphenyl ethylene directly affects the film-forming performance and comprehensive performance of the film material: when the mole ratio of tetraphenyl ethylene exceeds 5%, the polymer is prone to excessive crosslinking, resulting in deterioration of film-forming performance; when the mole ratio of tetraphenyl ethylene does not exceed 5%, the film material prepared can have good film-forming performance and excellent comprehensive performance, realizing the coordination and unity of moderate water swelling and high ionic conductivity.

[0029] Based on the above research, the present application preferably limits that the mole ratio of tetraphenyl ethylene is 1% to 5%, and within this range, especially when reaching 5%, the comprehensive performance of the prepared branched anion exchange film is optimal, and the related conclusion will be verified by experimental data of subsequent examples.

[0030] The above technical solution of the present application also includes the following optional limitations: I. Monomer selection (1) Piperidone monomer Preferably, the piperidone monomer is selected from at least one of 4-piperidone, N-methyl-4-piperidone, N-ethyl-4-piperidone, N-propyl-4-piperidone, N-isopropyl-4-piperidone, N-butyl-4-piperidone, N-pentyl-4-piperidone, N-hexyl-4-piperidone, piperidine trifluoromethyl ketone and N-benzyl-4-piperidone. Such piperidone monomers can adjust the solubility of the polymer by introducing different alkyl or phenyl substituents, so that the product has better solubility in the target solvent; at the same time, its suitable reactivity and nucleophilicity can significantly improve the polymerization reaction efficiency and product yield.

[0031] (2) Aromatic monomer Preferably, the aromatic monomer is selected from at least one of biphenyl, terphenyl (including p-terphenyl, m-terphenyl), diphenyl ethane, and the rigid structure of such monomers can further strengthen the skeleton stability of the film material, and form synergy with the branching effect of tetraphenyl ethylene.

[0032] II. Catalyst selection (1) Polymerization catalyst Preferably, the polymerization catalyst is a mixed system of trifluoroacetic acid (TFA) and trifluoromethanesulfonic acid (TFSA). Such fluorinated super acid can efficiently catalyze Friedel-Crafts alkylation reaction, significantly improve the polymerization reaction rate and selectivity, and promote directional polymerization of monomers.

[0033] (2) Quaternization catalyst Preferably, the base catalyst is selected from one of potassium carbonate, potassium hydroxide and sodium hydroxide, which can provide a suitable alkaline environment for the quaternization reaction and ensure efficient functionalization reaction.

[0034] III. Selection of quaternization reagent Preferably, the quaternization reagent is selected from at least one of alkyl iodide, alkyl bromide, and alkyl chloride. Among them, alkyl iodide can be selected from methyl iodide, ethyl iodide, propyl iodide, butyl iodide, pentyl iodide, hexyl iodide, 1,2-diiodoethane, 1,3-diiodopropane, 1,4-diiodobutane, 1,5-diiodopentane, 1,6-diiodohexane, etc.; alkyl bromide can be selected from ethyl bromide, propyl bromide, butyl bromide, pentyl bromide, hexyl bromide, bromocyclopropane, bromocyclobutane, bromocyclopentane, bromocyclohexane, 1,2-dibromoethane, 1,3-dibromopropane, 1,4-dibromobutane, 1,5-dibromopentane, 1,6-dibromohexane, etc. Such quaternization reagent can undergo nucleophilic substitution reaction with nitrogen atoms in branched polyaryl piperidine copolymer, efficiently introducing quaternary ammonium groups, and endowing the membrane material with anion exchange function, providing active sites for OH - transport.

[0035] IV. Selection of solvent (1) First solvent (polymerization reaction solvent) Preferably, the first solvent is selected from dichloromethane, chloroform, tetrachloroethane, toluene, etc. commonly used organic solvents, or fluorine-containing organic solvents such as trifluoroacetic acid and trifluoromethanesulfonic acid, which can be used alone or in combination. Such solvents can ensure that aromatic monomers, tetraphenyl ethylene, and piperidone monomers are fully dissolved, providing a homogeneous reaction environment for polymerization reaction, and promoting uniform reaction.

[0036] (2) Second solvent (quaternization reaction solvent) Preferably, the second solvent is selected from at least one of dimethyl sulfoxide (DMSO), dimethylformamide, dimethylacetamide, and 1-methyl-2-pyrrolidone, which has excellent solubility for branched polyaryl piperidine copolymer and can ensure the uniformity of quaternization reaction.

[0037] (3) Third solvent (casting solution solvent) Preferably, the third solvent is selected from at least one of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and 1-methyl-2-pyrrolidone, which can be the same as or different from the second solvent, and can make quaternized polyaryl piperidine form a stable homogeneous casting solution, providing protection for subsequent film formation.

[0038] V. Limitation of reaction parameters (1) Polymerization reaction time Preferably, the polymerization reaction time is 4 h to 6 h. Combined with low-temperature conditions of ice bath (0℃), on the one hand, the reaction selectivity can be improved, and side reactions can be inhibited; on the other hand, the polymerization degree can be accurately controlled, and incomplete reaction or over-polymerization can be avoided, thereby ensuring the purity and structural stability of the product.

[0039] (2) Polymerization post-processing step Preferably, after the polymerization reaction, a purification treatment is further included: adding an excess of sodium hydroxide solution to the reaction system to precipitate a precipitate; washing the precipitate with deionized water until it is neutral, and drying at 40°C for 24 hours. This step can effectively remove residual solvents, catalysts and impurities in the reaction, obtaining branched polyaryl piperidine copolymer with high purity and stable structure, laying a foundation for subsequent functionalization reaction and film quality.

[0040] (3) Quaternization reaction conditions Preferably, the quaternization reaction is carried out in the dark under water bath conditions at 40°C-50°C, and the reaction time is 10 min-15 min; wherein the molar ratio of base catalyst to branched polyaryl piperidine copolymer is 1-1.1:1, and the molar ratio of quaternary ammonium reagent to branched polyaryl piperidine copolymer is 1-1.1:1. This condition can ensure that the quaternization reaction is efficient and controllable, accurately control the ion exchange capacity, and avoid excessive functionalization leading to unstable membrane structure.

[0041] Six, concentration parameter limitation (1) Concentration of the second mixed solution Preferably, the concentration of the branched polyaryl piperidine copolymer in the second mixed solution is 4.5 g / mL-5.5 g / mL. This concentration can keep the polymer solution at an appropriate viscosity, ensure that the quaternary ammonium reagent and the polymer molecules are in full contact, and avoid uneven reaction due to too high concentration or reduced reaction efficiency due to too low concentration.

[0042] (2) Concentration of the casting solution Preferably, the concentration of the quaternary ammonium polyaryl piperidine in the polymer casting solution is 4.5 g / mL-5.5 g / mL. This concentration makes the casting solution have ideal fluidity and film-forming property, and can form a thin film with uniform thickness and dense structure through flow casting, pouring or coating process.

[0043] The present application adopts Friedel-Crafts alkylation reaction catalyzed by super acid to prepare polymer, which has the advantages of simple operation, high polymerization efficiency and controllable product structure; the core innovation is to use tetraphenyl ethylene as a branching agent, which has a dual synergistic effect: on the one hand, it weakens the aggregation tendency of polymer chain segments, expands the hydrophilic-hydrophobic phase separation scale, and forms a wider hydrophilic domain channel; on the other hand, it accurately controls the free volume fraction inside the membrane material, improves the water absorption rate on the premise of ensuring dimensional stability, and provides OH -The high-efficiency transmission provides double protection. In addition, experiments prove that when the mole ratio of tetraphenyl ethylene is in the range of 1% to 5%, the film material has the optimal comprehensive performance, wherein the branched film with a 5% mole ratio has the highest water absorption rate, moderate swelling rate and optimal ion conductivity, and perfectly realizes the synergistic consideration of high conductivity and dimensional stability.

[0044] The embodiment of the present application also provides a branched anion exchange film based on tetraphenyl ethylene, which is prepared by the above preparation method. The anion exchange film inherits all the technical advantages brought by the above preparation method, specifically, the synergistic consideration of high ion conductivity and excellent dimensional stability, regular hydrophilic-hydrophobic microphase separation structure, controllable free volume fraction and excellent film-forming performance, and the like. The related advantages have been described in detail in the foregoing, and will not be repeated here.

[0045] The embodiment of the present application further provides the application of the above branched anion exchange film based on tetraphenyl ethylene in the field of electrochemical energy devices, preferably in an anion exchange membrane water electrolysis cell. When the anion exchange film is used as a core functional film assembly to assemble an anion exchange membrane water electrolysis cell, the electrolysis cell can fully rely on the excellent performance of the film material to realize the advantages of high electrolysis efficiency, stable operation and adaptation to non-noble metal catalysts, and effectively improve the comprehensive performance and economy of the device. The advantages embodied by the application are consistent with the core advantages of the above film material and preparation method, and will not be repeated here.

[0046] The present application will be further described below in conjunction with specific examples.

[0047] Example 1 A synthesis method of a branched anion exchange film based on tetraphenyl ethylene, the specific steps are as follows: 1) Preparation of branched polyaryl piperidine copolymer (BPTP): Dichloromethane (V DCM ≈0.9 V TFSA) was added slowly. After the addition was completed, the polymerization reaction was continued. After 5 h, the system was sticky and tended to agglomerate. Excess sodium hydroxide was added, and the mixture was stirred for 4 h to precipitate the product. The white precipitate was collected, washed repeatedly with deionized water until the washing liquid was neutral, and then dried in a vacuum oven at 40°C for 24 h to obtain a branched polyarylpipehdine copolymer (BPTP) in the form of white fibers. In this embodiment, x = 0.01-0.05 (i.e., the mole percentage of tetraphenyl ethylene was 1%-5%), and 1-x = 0.95-0.99 (i.e., the mole percentage of biphenyl was 95%-99%).

[0048] 2) Preparation of quaternary ammonium polyarylpipehdine (QBPTP): The BPTP prepared in step 1 was taken and dissolved in dimethyl sulfoxide (DMSO) to obtain a homogeneous second mixture with a concentration of about 5 g / mL. The mixture was placed in a 40°C water bath, and K2CO3 (1 equiv.) and CH3I (1 equiv.) were added to the mixture under light shielding and stirred for 10 min. After the reaction was completed, the system was poured into excess ethyl acetate to precipitate the product. The precipitate was collected and washed with deionized water three times to remove residual impurities. The product was dried in a vacuum oven at 40°C for 24 h to obtain a white solid quaternary ammonium polyarylpipehdine (QBPTP). As shown in FIG. 2, the QBPTP was obtained by quaternization of the BPTP. Figure 2

[0049] 3) Preparation of branched anion exchange membrane: The QBPTP prepared in step 2 was taken and dissolved in DMSO to obtain a homogeneous polymer casting solution with a concentration of about 5 g / mL. The transparent casting solution was uniformly cast on a clean glass plate, and the glass plate was placed on a heating table at 60°C to dry the solvent. After the solvent was completely volatilized, the glass plate was immersed in deionized water, and the primary membrane in the form of I - was carefully peeled off. The primary membrane was immersed in a 1 mol / L NaOH solution for ion exchange. After the ion exchange was completed, the membrane surface was washed with deionized water to remove residual ions, and a tetraphenyl ethylene-based branched anion exchange membrane in the form of OH - was obtained.

[0050] Example 2 In this example, a branched anion exchange membrane was prepared according to the steps of Example 1. The amounts of the raw materials used in each step are as follows: ​(1) Synthesis of poly(biphenyltetraphenylstyrene piperidinium) copolymer BPTP-5: Biphenyl (0.293 g, 1.90 mmol), tetraphenylstyrene (0.033 g, 0.10 mmol), dichloromethane (1.5 mL), N-methyl-4-piperidone (0.284 mL, 2.31 mmol), TFA (0.28 mL, 3.66 mmol), TFSA (1.6 mL, 18 mmol).

[0051] (2) Preparation of quaternized BPTP-5 (QBPTP-5): BPTP-5 (0.233 g, 0.879 mmol), DMSO (4.66 mL), K2CO3 (0.121 g, 0.879 mmol), CH3I (55 μL, 0.879 mmol).

[0052] (3) Preparation of QBPTP-5 AEMs: QBPTP-5 (0.1 g), DMSO (2 mL).

[0053] In this example, the mole percentage of tetraphenylstyrene is 5%, i.e., the ratio of the mole amount of tetraphenylstyrene to the total mole amount of aromatic monomers, the total mole amount of aromatic monomers being the sum of the mole amount of tetraphenylstyrene and the mole amount of biphenyl. Exemplarily, the mole percentage of tetraphenylstyrene = n1 / (n1+n2), n1=0.05, n2=0.95. In order to distinguish the product prepared from the product prepared in subsequent examples or Comparative Example 1, the product prepared is represented by a simple English name and the corresponding mole percentage of tetraphenylstyrene x 100, for example, poly(biphenyltetraphenylstyrene piperidinium) copolymer is represented by “BPTP-5”.

[0054] Example 3 In this example, a branched anion exchange membrane was prepared according to the steps of Example 1, and the amounts of raw materials used in each step are as follows: (1) Synthesis of poly(biphenyltetraphenylstyrene piperidinium) copolymer BPTP-5: Biphenyl (0.293 g, 1.90 mmol), tetraphenylstyrene (0.033 g, 0.10 mmol), dichloromethane (1.5 mL), N-methyl-4-piperidone (0.284 mL, 2.31 mmol), TFA (0.28 mL, 3.66 mmol), TFSA (1.6 mL, 18 mmol).

[0055] (2) Preparation of quaternized BPTP-1 (QBPTP-1): BPTP-1 (0.233 g, 0.917 mmol), DMSO (4.66 mL), K2CO3 (0.127 g, 0.917 mmol), CH3I (57 μL, 0.917 mmol).

[0056] (3) Preparation of QBPTP-1 AEMs: QBPTP-1 (0.1 g), DMSO (2 mL).

[0057] Example 4 This example prepared branched anion exchange membranes according to the procedure of Example 1, with the following amounts of reagents used in each step: (1) Synthesis of polydiphenyltetraphenylstyrene piperidine copolymer BPTP-2.5: Diphenyl (0.3007 g, 1.95 mmol), tetraphenylstyrene (0.0166 g, 0.05 mmol), dichloromethane (1.5 mL), N-methyl-4-piperidone (0.277 mL, 2.255 mmol), TFA (0.28 mL, 3.66 mmol), TFSA (1.6 mL, 18 mmol).

[0058] (2) Preparation of quaternized BPTP-2.5 (QBPTP-2.5): BPTP-2.5 (0.233 g, 0.903 mmol), DMSO (4.66 mL), K2CO3 (0.125 g, 0.903 mmol), CH3I (56 μL, 0.903 mmol).

[0059] (3) Preparation of QBPTP-2.5 AEMs: QBPTP-2.5 (0.1 g), DMSO (2 mL).

[0060] Comparative Example 1 This comparative example prepared branched anion exchange membranes according to the procedure of Example 1, with the following amounts of reagents used in each step: (1) Synthesis of polydiphenyl piperidine copolymer PBP: Diphenyl (0.3084 g, 2.00 mmol), dichloromethane (1.5 mL), N-methyl-4-piperidone (0.270 mL, 2.00 mmol), TFA (0.28 mL, 3.66 mmol), TFSA (1.6 mL, 18 mmol).

[0061] (2) Preparation of quaternized PBP (QBP): PBP (0.233 g, 0.937 mmol), DMSO (4.66 mL), K2CO3 (0.129 g, 0.937 mmol), CH3I (58 μL, 0.937 mmol).

[0062] (3) Preparation of QBP AEMs: QBP (0.1 g), DMSO (2 mL).

[0063] The samples obtained in each example were characterized and tested as follows: 1. Nuclear magnetic resonance (NMR) 1 H NMR test The polymers BPTP-x (branched type) and PBP (linear type) prepared in step 1 of Examples 2-4 and Comparative Example 1 were subjected to... 1 HNMR testing, results as follows Figure 3 As shown. By Figure 3 It can be seen that: 7.3~7.8 ppm (Ha-b) is the characteristic resonance peak of the proton of the biphenyl benzene ring, and 6.55~7.3 ppm (Hc-d) is the characteristic peak of the proton of the tetraphenylethylene benzene ring. The area of ​​this characteristic peak increases with the increase of tetraphenylethylene content. The peaks near 2.25, 2.8, 3.1 and 3.5 ppm correspond to the proton signal of the methylene group of the piperidine ring, and the signal at 2.7 ppm is the proton signal of the methyl group of the piperidine ring. The above characteristic peaks confirm the successful synthesis of BPTP-x polymer.

[0064] The quaternized polyarylepiperidines prepared in Step 2 of Examples 2-4 and Comparative Example 1 were subjected to... 1 H NMR test, results as follows Figure 4 As shown. With Figure 3 The comparison shows that the α and β-H (c, d) splitting peaks of the piperidine ring in the product of Comparative Example 1 disappeared, and a new characteristic peak appeared at 3.1 ppm (He), indicating that the linear polymer was fully functionalized; the products of Examples 2-4 showed N at 3.1 ppm (Hl). + The presence of a quaternary ammonium salt characteristic peak at 2.2–3.4 ppm (He-m) confirms that QBPTP-x has achieved partial functionalization. The partial functionalization design employed in Examples 2–4 avoids the problems of excessively high water absorption (WU) and swelling ratio (SR) caused by full functionalization, thus ensuring the mechanical properties of the membrane.

[0065] 2. Scanning Electron Microscopy (SEM) Testing SEM tests were performed on the anion exchange membranes of Examples 2-4 and Comparative Example 1, and the results are as follows: Figure 5 As shown, where: Figure 5 (a) is a SEM image of the membrane obtained in Comparative Example 1. Figure 5 Images (b) to (d) are SEM images of the membranes obtained in Examples 2 to 4, with the inset in the upper right corner showing the cross-sectional morphology. Figure 5 It can be seen that the polymers prepared in Examples 2-4 have excellent film-forming properties, and the film surface and cross-section are smooth, dense and flat with no obvious pores; and the film thickness is controlled at 20-30 μm, which confirms that this type of polymer can be used to prepare independently formed films.

[0066] 3. Free Volume Fraction (FFV) Test The FFV test results of the anion exchange membranes (AEMs) prepared in Examples 2-4 and Comparative Example 1 are as follows:Figure 6 As shown in Figure 6 It can be seen that the FFV of the membrane material increases significantly with the increase of the content of tetraphenyl ethylene, and the FFV of the QBPTP-5 AEM reaches 35.5%, which is much higher than 21.8% of the QBP AEM of Comparative Example 1. The improvement of FFV can expand the hydrophilic-hydrophobic phase separation scale to form a wider hydrophilic domain; at the same time, the rigid skeleton of the branched structure can inhibit the excessive water swelling of the membrane to realize the coordination of the improvement of water absorption and the guarantee of dimensional stability.

[0067] 4. Water absorption and swelling performance test Test conditions: at 30-80℃, immerse the AEM in deionized water for 12h, calculate the water uptake (WU) and swelling ratio (SR) through the change of membrane mass and length, and the results are shown in Figure 7 (WU-temperature curve), Figure 8 (SR-temperature curve).

[0068] It can be seen from Figure 7 , 8 that within the range of 30-80℃, the WU and SR of all membranes increase with the increase of temperature; at 80℃, the WU (267%) and SR (53.1%) of the QBP linear membrane of Comparative Example 1 are much higher than the WU (106%-173%) and SR (27%-46%) of the QBPTP-x branched membrane of Examples 2-4, because high temperature is beneficial to the thermal motion of molecules. And in the QBPTP-x branched membrane, the WU and SR of the AEM increase with the increase of the content of the branched agent, which shows that the appropriate rigid tetraphenyl ethylene unit helps to enhance the FFV of the membrane, thereby increasing its water absorption.

[0069] The hydration number (λ) is defined as the number of water molecules absorbed around each quaternary ammonium cation group, and after calculation, the λ of the linear membrane QBP and the branched membrane QBPTP-x at 30℃ is 23.6 and 5.8-10.9 respectively, and the ion exchange capacity (IEC) of the linear membrane QBP and the branched membrane QBPTP-x is 3.84 mmol g -1 and 2.35-2.47 mmol g -1The high λ value (23.6) of the linear membrane QBP is mainly due to its ultra-high density of hydrophilic groups, but the absorbed water may contain a large amount of free water that is weakly bound to the ion sites, leading to severe swelling. Among the branched membranes, QBPTP-5 exhibits the highest λ value (10.9), indicating that each ion site has a stronger water molecule binding capacity, enabling the formation of a more stable hydration layer. This efficient hydration characteristic allows QBPTP-5 to absorb a relatively large number of water molecules while confining their movement within a microscopic region using its rigid three-dimensional branched network, thus exhibiting excellent macroscopic dimensional stability.

[0070] 5. Transmission electron microscopy (TEM) testing TEM tests were performed on the AEMs of Examples 2-4 and Comparative Example 1, and the results are as follows: Figure 9 As shown in the diagram (bright areas represent hydrophobic waters, dark areas represent hydrophilic waters). (From...) Figure 9 It can be seen that the introduction of branched structure enables AEM to form a clearer hydrophilic and hydrophobic microphase separation structure, and the size and connectivity of the hydrophilic water area increase with the increase of tetraphenylethylene content. This is because the large-volume rigid structure of tetraphenylethylene hinders the close packing of the polymer backbone and forms a cavity structure, which is conducive to the aggregation of water molecules around the ionic functional groups to form a continuous hydrophilic water area, confirming that tetraphenylethylene can construct a wide and continuous ion transport channel.

[0071] 6. OH - Electrical conductivity (OH) - Conductivity test AEM's OH − Conductivity-temperature curve as shown Figure 10 As shown. By Figure 10 It can be seen that: OH in all membranes - The conductivity of all samples increased with increasing temperature. Although the IEC of the linear membrane in Comparative Example 1 was much higher than that of the branched membranes in Examples 2-4, its OH... - The conductivity is significantly lower: the linear QBP membrane has a conductivity of 38.3 mS / cm at 30 °C. -1 At 80℃, it is 92.7 mS cm. -1 The branched membrane QBPTP-x exhibits a conductivity of 78.9-95.4 mS / cm at 30℃. -1 Within the range of 125.8-165.4 mS / cm at 80℃. -1 The above results confirm that branched structures can improve FFV, optimize microphase separation morphology, and significantly reduce OH. - Reduces transport resistance and increases ionic conductivity.

[0072] 7. Performance testing of water electrolysis cells Using the membrane electrode assembly (MEA) of Example 2 and Comparative Example 1, and selecting fully functionalized QBPTP-5 ionomer as the anode catalyst binder, the performance of the water electrolyzer at different temperatures was tested, and the results are as follows: Figure 11 As shown. By Figure 11 It can be seen that under the conditions of 60℃ and 2V, the current density of the QBPTP-5 AEM is 0.510 A cm⁻¹. -2 The value is significantly higher than that of linear QBP AEM (0.195A cm). -2 When the temperature rises to 80℃, the electrolysis efficiency of both increases, and the current density of QBP and QBPTP-5 AEM reaches 0.252 A cm⁻¹ under 2 V conditions. -2 0.641 A cm -2 This indicates that QBPTP-5 AEM can improve ion transport efficiency and electrode reaction kinetics, significantly optimizing the performance of water electrolyzers.

[0073] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for preparing a branched anion exchange membrane based on tetraphenyl ethylene, characterized by, Comprising the following steps: Step 1, preparing branched polyaryl piperidine copolymer The aromatic monomer, tetraphenyl ethylene and piperidone monomer are dissolved in a first solvent to obtain a first mixed solution; a catalyst is added to the first mixed solution under ice bath conditions to carry out a polymerization reaction to prepare branched polyaryl piperidine copolymer; wherein, based on 100% of the total moles of the aromatic monomer and the tetraphenyl ethylene, the mole percentage of tetraphenyl ethylene is not more than 5%; Step 2, preparing quaternary ammonium polyaryl piperidine The branched polyaryl piperidine copolymer is dissolved in a second solvent to obtain a second mixed solution; a base catalyst and a quaternary ammonium reagent are added to the second mixed solution to carry out a quaternary ammonium reaction to prepare quaternary ammonium polyaryl piperidine; Step 3, preparing branched anion exchange membrane based on tetraphenyl ethylene The quaternary ammonium polyaryl piperidine is dissolved in a third solvent to obtain a polymer casting solution; the polymer casting solution is formed by casting, pouring or coating to obtain a branched anion exchange membrane based on tetraphenyl ethylene.

2. The method of claim 1, wherein: In step 1, the mole percentage of tetraphenyl ethylene is 1%-5%.

3. The method of claim 1, wherein: In step 1, the aromatic monomer is selected from at least one of biphenyl, terphenyl and diphenyl ethane; the piperidone monomer is selected from at least one of 4-piperidone, N-methyl-4-piperidone, N-ethyl-4-piperidone, N-propyl-4-piperidone, N-isopropyl-4-piperidone, N-butyl-4-piperidone, N-pentyl-4-piperidone, N-hexyl-4-piperidone, piperidine trifluoromethyl ketone and N-benzyl-4-piperidone; and the catalyst is a mixture of trifluoroacetic acid and trifluoromethane sulfonic acid.

4. The method of claim 1, wherein: In step 1, the polymerization reaction time is 4 h-6 h.

5. The method of claim 1, wherein, In step 1, after the polymerization reaction is completed, a purification treatment step is further included: excess sodium hydroxide is added to the reaction system to precipitate a precipitate; after the precipitate is washed to neutral with deionized water, it is dried.

6. The method of claim 1, wherein: In step 2, the concentration of the branched polyaryl piperidine copolymer in the second mixed solution is 4.5 g / mL-5.5 g / mL.

7. The method of claim 1, wherein: In step 2, the base catalyst is selected from one of potassium carbonate, potassium hydroxide and sodium hydroxide, and the quaternary ammonium reagent is selected from at least one of iodoalkyl compounds, bromoalkyl compounds and chloroalkyl compounds.

8. The method of claim 1, wherein: In step 2, the quaternary ammonium reaction is carried out in the dark under a water bath condition of 40℃-45℃, and the reaction time is 10 min-15 min, wherein the molar ratio of base catalyst to branched polyaryl piperidine copolymer is 1-1.1:1, and the molar ratio of quaternary ammonium reagent to branched polyaryl piperidine copolymer is 1-1.1:

1.

9. A tetraphenyl-ethene-based branched anion exchange membrane, characterized in that, Made by the preparation method of any one of claims 1-8.

10. The branched anion exchange membrane of claim 9 in the field of anion exchange membrane water electrolysis cells.

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