A zwitterionic ion exchange membrane containing sulfonic acid side chains and fluoranthene branching, preparation method and application

Abstract

This invention relates to a zwitterionic exchange membrane containing sulfonic acid side chains and fluoranthene branching, its preparation method, and its application. The polymer used in the zwitterionic exchange membrane containing sulfonic acid side chains and fluoranthene branching comprises repeating units as shown in Formula 1: Formula 1; wherein, Ar is selected from biaryl compound structural units; A is a substituted indigo monomer; B is a nitrogen-containing heterocyclic cationic group; x, y, and z are the molar percentages of the corresponding repeating units; x = 1–20%, y = 60–80%, x+y+z = 100%; the group Q is bonded to the nitrogen atoms of A and B, and Q is an alkyl sulfonate ion group. This invention exhibits excellent ion selectivity and comprehensive electrochemical performance in both VRFB and ICRFB.

Description

Technical Field

[0001] This invention belongs to the field of zwitterionic exchange membrane materials, specifically relating to a zwitterionic exchange membrane containing sulfonic acid side chains and fluoranthene branching, its preparation method, and its application. Background Technology

[0002] Electrochemical flow batteries, especially vanadium redox flow batteries (VRFB) and iron-chromium redox flow batteries (ICRFB), have become an important choice for large-scale energy storage technology due to their high safety, long lifespan, and flexible capacity design. In these two types of batteries, the ion exchange membrane is one of the core components, its function being to prevent cross-permeation of the active materials at the positive and negative electrodes while allowing ion-supporting membranes (such as...) to pass through. , (etc.) By forming a current loop, it directly affects the battery's coulombic efficiency, energy efficiency, and cycle life.

[0003] Currently, the most widely used commercial ion exchange membranes are perfluorosulfonic acid membranes (such as the Nafion series), which possess excellent proton conductivity and chemical stability. However, in VRFB, they face problems such as high vanadium ion permeability, leading to severe self-discharge and capacity decay; in ICRFB, they suffer from poor resistance to iron ions (…). ) and chromium ions ( Insufficient selective blocking capability of perfluorinated materials can also lead to capacity decay and efficiency reduction. In addition, the high cost and environmentally unfriendly preparation process of perfluorinated materials limit their economic application in large-scale energy storage.

[0004] To replace perfluorinated membranes, researchers have developed non-fluorinated polymer membranes, mainly including sulfonated cation exchange membranes (CEMs), quaternized anion exchange membranes (AEMs), and the recently emerging zwitterionic exchange membranes (AIEMs). Among these, zwitterionic exchange membranes, containing both positive and negative ion groups within the same membrane, can theoretically achieve efficient blocking of multivalent metal ions while maintaining high ion conductivity through electrostatic interactions and microscopic phase separation structures, thus showing potential in VRFBs and ICRFBs. However, existing zwitterionic membranes still face the following common problems: 1. Insufficient membrane structure stability: Most polymer backbones contain aromatic ether bonds, which are prone to chemical degradation in strong oxidizing and strong acidic electrolytes; 2. Difficulty in balancing performance: High ion exchange capacity often leads to excessive water absorption and swelling, reducing mechanical strength and dimensional stability; it often fails to achieve efficient blocking of multivalent metal ions while maintaining high ion conductivity, and its long-term chemical stability is insufficient, thus making it difficult to maintain the battery's coulombic efficiency (CE), voltage efficiency (VE) and energy efficiency (EE) at a high level simultaneously. 3. Complex preparation process: Multi-step functionalization reactions or complex post-modification processes increase preparation costs and process uncertainty; 4. Limited research on its application in ICRFB: Existing membrane materials are mostly optimized for VRFB, and there is insufficient research on the selective blocking mechanism of Fe / Cr ions and their long-term tolerance. Therefore, their applicability in different systems is limited.

[0005] Therefore, developing a zwitterionic exchange membrane with a stable main chain, precisely tunable side chains, high ion selectivity, low swelling, and excellent chemical stability is of great significance for promoting the development and practical application of flow battery technologies such as VRFB and ICRFB. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects in the prior art and provide a zwitterionic exchange membrane containing sulfonic acid side chains and fluoranthene branching, its preparation method and application, which can simultaneously improve the coulombic efficiency, voltage efficiency and energy efficiency of vanadium redox flow batteries and iron-chromium redox flow batteries.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A zwitterionic exchange membrane containing sulfonic acid side chains and fluoranthene branching, wherein the polymer used comprises repeating units as shown in Formula 1: ; Formula 1; Wherein, Ar is selected from the structural unit of a biaryl compound; B is a nitrogen-containing heterocyclic cationic group; x, y, and z represent the molar percentages of the corresponding repeating units; x = 1–20%, y = 60–80%, x + y + z = 100%; As a further technical solution, A is a substituted indigo monomer; Q is bonded to the nitrogen atoms of A and B, and Q is an alkyl sulfonate ion group.

[0008] As a further technical solution, the biaryl compound structural unit is selected from... or .

[0009] As a further technical solution, the nitrogen-containing heterocyclic cation group is selected from... , , , , , Any one of them.

[0010] As a further technical solution, A is R1, R2, R3 and R4 are each independently selected from any one of methyl, alkyl, haloalkyl, H substituent, F substituent, Cl substituent and Br substituent.

[0011] As a further technical solution, A is selected from... , , , , , , , , Any one of them.

[0012] As a further technical solution, Q is selected from... , , , , Any one of them.

[0013] As a further technical solution, a zwitterion exchange membrane containing sulfonic acid side chains and fluoranthene branching is provided, wherein the polymer used comprises repeating units as shown in Formula 2: ; Formula 2; Wherein, Ar is selected from the structural unit of a biaryl compound; B is a nitrogen-containing heterocyclic cationic group; x, y, and z represent the molar percentages of the corresponding repeating units; x = 1–20%, y = 60–80%, x + y + z = 100%; Q is an alkyl sulfonate ion group, and Q is bonded to the nitrogen atom of B.

[0014] A method for preparing the zwitterionic exchange membrane containing sulfonic acid side chains and fluoranthene branching includes the following steps: Step 1: Add biaryl monomers, fluoranthene, substituted indigo, and carbonyl-containing saturated nitrogen heterocyclic compounds to the first solvent and stir for 30-60 min. Then, under ice-water bath and nitrogen conditions, add trifluoroacetic acid (TFA) and trifluoromethanesulfonic acid (TFSA) dropwise. After the addition is complete, react for 3-12 h to obtain a viscous solution. Then, pour the obtained viscous solution into a 50% ethanol aqueous solution (volume concentration) to obtain a solid polymer. Then, crush the solid polymer, filter and collect the fragments, and wash with the first alkaline solution at 40-60 °C with stirring for 8-12 h. Then wash with deionized water until neutral and dry in a vacuum oven at 60-80 °C for 12-24 h to obtain fluoranthene branched polyaryl polymer. Step 2: Add the fluoranthene branched polyaryl polymer to the second solvent and stir at 80°C for 1-2 hours until a homogeneous solution is formed. Then add the sulfonylating agent and continue stirring at 80°C for 8-12 hours until a homogeneous and clear solution is obtained. Then, under stirring, pour the homogeneous and clear solution into a precipitant to precipitate a solid product. Then, wash the solid product repeatedly with deionized water several times, filter it, and dry it in a vacuum oven at 60-80°C for 12-24 hours to obtain the sulfonic acid side chain functionalized fluoranthene branched polyaryl polymer. Step 3: Dissolve the sulfonic acid side-chain functionalized fluoranthene branched polyaryl polymer obtained in Step 2 in a third solvent, then filter it through a 0.25-0.45 μm polytetrafluoroethylene filter, cast it onto a clean glass plate, and then vacuum dry it at 80-100℃ for 12-36 h to completely remove the residual solvent, thus obtaining a zwitterion exchange membrane containing sulfonic acid side chains.

[0015] As a further technical solution, the carbonyl-containing saturated nitrogen heterocyclic compound is selected from 1-methyl-4-piperidinone. 3-quinine cyclohexanone 1,3-Dimethyl-4-piperidinone 1-Methyl-3-piperidinone 1-Methyl-4-piperidinecarboxaldehyde 1-Methyl-3-piperidinecarboxaldehyde Any one of them.

[0016] As a further technical solution, the substitute indigo is selected from indigo. 5-Methylindigo 5-Fluoroin 6-Fluoroin 5,7-Methylindigo 5,6-Difluoroindigo 7-Bromoindigo 5-Chloroindopur 5-Bromoindigo Any one of them.

[0017] As a further technical solution, the sulfonylating agent is selected from 1,3-propanesulfonyl lactone. 1,4-Butyryl lactone Sodium 2-bromoethylsulfonate Sodium 4-(2-bromoethyl)benzenesulfonate 3-Chloro-2-hydroxy-1-propanesulfonate sodium salt hydrate Any one of them.

[0018] As a further technical solution, in step 1, the molar ratio of the fluoranthene to the biaryl monomer is (1-20):100; The total molar ratio of the substituted indigo and the saturated carbonyl-containing saturated nitrogen-heterocyclic compound to the biaryl compound is 1 to 2:1; The molar ratio of the trifluoroacetic acid and the saturated carbonyl-containing nitrogen heterocyclic compound is (1-2):1; The molar ratio of the trifluoromethanesulfonic acid and the carbonyl-containing saturated nitrogen heterocyclic compound is (8-12):1; The first solvent is a halogenated hydrocarbon solvent, which includes one or more of dichloromethane and 1,2-dichloroethane; The first alkaline solution is KOH, NaOH or The solution has a concentration of 0.5–2.0 M. As a further technical solution, in step 2, the second solvent is one or more of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone; The precipitant includes one or more of diethyl ether, ethanol, methanol, ethyl acetate, deionized water, and methyl tert-butyl ether, and is used to precipitate the polymer in the filtrate. The ratio of the fluoranthene branched polyaryl polymer to the second solvent is 1g:7ml~30ml; The molar ratio of the fluoranthene branched polyaryl polymer to the sulfonylating agent is 1:(2-4); As a further technical solution, in step 3, the ratio of the amount of the sulfonic acid side-chain functionalized fluoranthene branched polyaryl polymer to the third solvent is 1g:(10-100)mL. The third solvent includes one or more of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylformamide, or N,N-dimethylacetamide.

[0019] Application of the zwitterionic exchange membrane containing sulfonic acid side chains and fluoranthene branching in vanadium redox flow batteries and / or iron-chromium redox flow batteries.

[0020] To address the challenge of synergistically optimizing key performance aspects of existing flow battery separators—specifically, the inability of traditional membrane materials to maintain high ionic conductivity while simultaneously achieving efficient blocking of multivalent metal ions, and their insufficient long-term chemical stability—results in difficulties in simultaneously maintaining high levels of coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE), particularly limiting their applicability in different systems (such as VRFB and ICRFB). This invention proposes the following improvement scheme: 1) Main chain structure design: This invention uses biaryl compounds, saturated nitrogen-containing heterocyclic ketones, and aldehydes as a rigid main chain backbone, and introduces fluoranthene units as branched structures. The fluoranthene units are connected to the polymer main chain through symmetrical sites at both ends. Compared to other connection sites, this method achieves better synergistic effects, thereby constructing a highly stable polymer main chain. This polymer main chain is entirely composed of aromatic and rigid heterocyclic structures, without easily degradable aryl ether bonds. Furthermore, the introduction of the fluoranthene branched structure and substituted indigo units significantly enhances the chemical stability and antioxidant properties of the main chain. Compared to the main chain structures formed by the polymerization of linear or simply branched single / binary monomers in existing technologies, the rigidity, stability, and controllability of the main chain structure are greatly improved.

[0021] 2) Side-chain functionalization design: This invention grafts sulfonylating agents onto the nitrogen atoms of saturated nitrogen-containing heterocyclic ketones, aldehydes, and substituted indigo, forming a dense side-chain network with amphiphilic properties and a more uniform charge distribution. This not only enhances the connectivity of ion conduction channels within the membrane but also efficiently blocks multivalent metal ions (such as...) in the electrolyte through the synergistic effect of intramolecular / intermolecular interactions of positive and negatively charged groups and the Donnan repulsion effect. Compared to existing technologies that introduce only a single type of ionic group at a single site, this method greatly enhances the spatial order and synergy of functional groups.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: Regarding ion selectivity, the zwitterionic ion exchange membrane of this invention features synchronously constructed anion and cation side chains that synergistically form an effective ion sieving network. In terms of ion conductivity, the unique hydrophilic side chains and continuous phase structure provide an efficient channel for proton transport, significantly reducing the membrane's sheet resistance. This directly translates into higher voltage efficiency (VE), especially at higher current densities, effectively reducing ohmic polarization and maintaining a good discharge voltage plateau. This results in a high and stable EE value in the VRFB system. Furthermore, its unique zwitterionic structure lays the foundation for subsequent parameter adjustments to adapt to the ICRFB system, broadening the technological application scope of the material.

[0023] In summary, the sulfonic acid side-chain functionalized branched polyaryl polymer of this invention constructs a rigid main chain backbone through the aromatic structure of the biaryl compound to replace the indigo unit and regulate hydrophobicity, and introduces fluoranthene as a branching structure to enhance intermolecular crosslinking and packing density. Simultaneously, by utilizing saturated azo-heterocyclic ketone and aldehyde structures as cation centers and functionalizing grafting of the substituted indigo unit with the sulfonic acid side chain, an amphiphilic side chain structure containing both quaternary ammonium cations and sulfonate anions is constructed. Under the synergistic effect of the biaryl rigid backbone, the bi-terminal symmetrically connected fluoranthene branched structure, the substituted indigo hydrophobic unit, the saturated azo-heterocyclic ketone and aldehyde cation centers, and the sulfonic acid side chain, it exhibits excellent ion selectivity and comprehensive electrochemical performance in both VRFB and ICRFB, meeting the application requirements of high-performance electrochemical devices such as vanadium redox flow batteries and iron-chromium flow batteries. Attached Figure Description

[0024] Figure 1 Fourier transform infrared spectrum of PSFPA-10 prepared in Example 1 of this invention; Figure 2 The proton nuclear magnetic resonance spectrum of PSFPA-10 prepared in Example 1 of this invention ( 1 H-NMR); Figure 3 Fourier transform infrared spectrum of BSFPA-20 prepared in Example 2 of this invention; Figure 4 The graph shows the coulombic efficiency, voltage efficiency, and energy efficiency of the PSFPA-10 prepared in Example 1 of this invention at different current densities in a full vanadium redox flow battery. Figure 5 The coulombic efficiency, voltage efficiency, and energy efficiency of PSFPA-10 prepared for Comparative Example 1 in a full vanadium redox flow battery at different current densities are plotted. Figure 6 The graph shows the coulombic efficiency, voltage efficiency, and energy efficiency of the PSFPA-10 prepared in Example 1 of this invention at different current densities in an iron-chromium redox flow battery. Figure 7 The graph shows the coulombic efficiency, voltage efficiency, and energy efficiency of PSFPA-10 prepared for Comparative Example 1 in an iron-chromium flow battery at different current densities. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0027] The synthetic route for zwitterion exchange membranes containing sulfonic acid side chains and fluoranyl anthracene branching, as shown in Formula 1, is as follows:

[0028] The following detailed description is based on specific embodiments.

[0029] Example 1 A method for preparing a zwitterion exchange membrane containing sulfonic acid side chains and fluoranthene branching includes the following steps: Step 1: 13.5 mmol (3.11 g), fluoranthene (1.5 mmol (0.30 g), 5-fluoroindigo (1.5 mmol (0.25 g), and N-methyl-4-piperidinone (13.5 mmol (1.53 g)) were added to 10 mL of dichloromethane. After stirring for 30 minutes, trifluoroacetic acid (14.85 mmol (1.1 mL) was added at 0 °C, followed by dropwise addition of trifluoromethanesulfonic acid (135 mmol (11.95 mL)). After the addition was complete, the reaction was stirred for another 4 hours to obtain an orange viscous solution. The orange viscous solution was poured into a potassium carbonate solution, precipitating an orange polymer to obtain a solid polymer. The solid polymer was crushed, the fragments were collected by filtration, and then subjected to 1 M at 60 °C. The solution was stirred and washed for 8–12 h, then washed with deionized water until neutral, and dried in a vacuum oven at 80 °C for 12 h to obtain fluoranthene branched polyaryl polymer (FPA-10), the structure of which is shown in Formula 3, where x=10, y=80, z=10.

[0030] Step 2: Add FPA-10 (0.97 mmol, 1 g) to 10 mL of DMSO and stir at 80 °C for 1 hour. The solution becomes a turbid emulsion. Then, add 1,3-propanesulfonic acid lactone (2.91 mmol, 0.36 g) in portions and continue stirring at 80 °C. As the reaction proceeds, the emulsion gradually becomes clear. After reacting at 80 °C for 12 hours, a uniform, clear, orange-red solution is obtained. Slowly pour the orange-red solution into stirred methyl tert-butyl ether, and a solid product precipitates. Wash the solid product repeatedly with deionized water several times, filter, and dry in a vacuum oven at 80 °C for 12 hours to obtain a sulfonic acid side-chain functionalized fluoranthene branched polyaryl polymer (PSFPA-10), with the structure shown in Formula 4, where x = 10, y = 80, and z = 10.

[0031] (3) Dissolve 0.5g of PSFPA-10 in 15mL of DMSO solution, filter it using a 0.45μm polytetrafluoroethylene filter, cast it onto a clean glass plate, and then vacuum dry it at 80℃ for 24h to completely remove the residual solvent, to obtain a sulfonic acid side chain functionalized fluoranthene branched polyarylpiperidine membrane, i.e. a zwitterion exchange membrane containing sulfonic acid side chains, with a membrane thickness of 40μm.

[0032] In this embodiment, FT-IR spectral analysis was performed to confirm the structure of PSFPA-10. The results are shown below. Figure 1 ; like Figure 1 As shown, compared with FPA-10, the PSFPA-10 spectrum shows a new absorption peak at 2930 cm⁻¹. -1 The characteristic absorption band at this point is due to the stretching vibration of -CH- in the side chain. Additionally, a 1169 cm⁻¹ band can be observed in the FT-IR spectrum of PSFPA-10. -1 and 1025cm -1 Two new absorption peaks were observed, which can be attributed to the characteristic absorption peaks of O=S=O in the side chain of PSFPA-10. The FT-IR results confirm the successful synthesis of PSFPA-10.

[0033] To improve the solubility of PSFPA-10, a small amount of TFA (5%) was added to DMSO-d6 as a solvent, and 1H NMR spectroscopy was performed. 1 H-NMR analysis, results are shown in Figure 2 ; like Figure 2 As shown, the hydrogen shifts on the terphenyl and fluoranthene rings appear between 7.0 and 8.0 ppm (Ha, Hb, Hc, Hd, He), while the characteristic peaks of hydrogen on the piperidine ring and the methyl group appear between 1.8 and 3.7 ppm (Hf-Hk). These characteristic peaks further confirm the successful synthesis of PSFPA-10.

[0034] Example 2 A method for preparing a zwitterion exchange membrane containing sulfonic acid side chains and fluoranthene branching includes the following steps: Step 1: 15 mmol (3.45 g), fluoranthene (3 mmol, 0.61 g), 5-fluoroindigo (1.25 mmol, 0.20 g), and N-methyl-4-piperidinone (13.75 mmol, 1.55 g) were added to 10 mL of dichloromethane. After stirring for 30 minutes, trifluoroacetic acid (15.13 mmol, 1.00 mL) was added at 0 °C, followed by dropwise addition of trifluoromethanesulfonic acid (137.50 mmol, 12.17 mL). After the addition was complete, the reaction was stirred for another 4 hours to obtain an orange viscous solution. The obtained orange viscous solution was poured into a potassium carbonate solution, precipitating an orange polymer to obtain a solid polymer. The solid polymer was crushed, the fragments were collected by filtration, and then subjected to 1 M at 60 °C. The solution was stirred and washed for 8–12 h, then washed with deionized water until neutral, and dried in a vacuum oven at 80 °C for 12 h to obtain fluoranthene branched polyaryl polymer (FPA-20), the structure of which is shown in Formula 3, where x=20, y=70, z=10.

[0035] Step 2: Add FPA-20 (0.97 mmol, 1 g) to 10 mL of DMSO and stir at 80 °C for 1 hour. After the reaction product forms a uniform pale yellow emulsion, add 1,4-butyrosulactone (2.91 mmol, 0.4 g) and continue stirring at 80 °C. As the reaction proceeds, the emulsion gradually becomes clear. After reacting at 80 °C for 12 hours, a uniform, clear, pale yellow solution is obtained. Slowly pour the pale yellow solution into stirred methyl tert-butyl ether, and a solid product precipitates. Wash the solid product repeatedly with deionized water several times, filter, and dry in a vacuum oven at 80 °C for 12 hours to obtain a sulfonic acid side-chain functionalized fluoranthene branched polyaryl polymer (BSFPA-20), with the structure shown in Formula 4, where x = 20, y = 70, and z = 10.

[0036] Step 3: Dissolve 0.5g of BSFPA-20 in 15mL of DMSO solution, filter using a 0.45μm polytetrafluoroethylene filter, cast onto a clean glass plate, and then vacuum dry at 100℃ for 24h to completely remove residual solvent, to obtain a sulfonic acid side-chain functionalized fluoranthene branched polyarylpiperidine membrane, i.e., a zwitterion exchange membrane containing sulfonic acid side chains, with a membrane thickness of 40μm.

[0037] In this embodiment, FT-IR spectral analysis was performed to confirm the structure of BSFPA-20. The results are shown below. Figure 3 ; like Figure 3 As shown, compared with FPA-20, the BSFPA-20 spectrum shows a new absorption peak at 2930 cm⁻¹. -1The characteristic absorption band at this point is due to the stretching vibration of -CH- in the side chain. Additionally, a value at 1163 cm⁻¹ can be observed in the FT-IR spectrum of BSFPA-20. -1 and 1030cm -1 Two new absorption peaks were observed, which can be attributed to the characteristic absorption peaks of O=S=O in the side chain of BSFPA-20. The FT-IR results confirm the successful synthesis of BSFPA-20.

[0038] Comparative Example 1 A method for preparing a zwitterionic ion exchange membrane includes the following steps: Step 1: 13.5 mmol (3.11 g), anthracene (1.5 mmol (0.27 g), 5-fluoroindigo (1.5 mmol (0.25 g), and N-methyl-4-piperidinone (13.5 mmol (1.53 g)) were added to 10 mL of dichloromethane. After stirring for 30 minutes, trifluoroacetic acid (14.85 mmol (1.1 mL) was added at 0 °C, followed by dropwise addition of trifluoromethanesulfonic acid (135 mmol (11.95 mL)). After the addition was complete, the reaction was stirred for another 4 hours to obtain a viscous solution. The viscous solution was poured into a potassium carbonate solution, precipitating a yellow polymer to obtain a solid polymer. The solid polymer was crushed, the fragments were collected by filtration, and then subjected to 1 M reaction at 60 °C. The solution was stirred and washed for 8–12 hours, then washed with deionized water until neutral, and dried in a vacuum oven at 80°C for 12 hours to obtain anthracene-branched polyaryl polymer.

[0039] Step 2: Add 0.99 mmol (1 g) of anthracene-branched polyaryl polymer to 10 mL of DMSO and stir at 80 °C for 1 hour. The solution becomes a turbid emulsion. Then, add 2.98 mmol (0.36 g) of 1,3-propanesulfonic acid lactone in portions and continue stirring at 80 °C. As the reaction proceeds, the emulsion gradually becomes clear. After reacting at 80 °C for 12 hours, a uniform, clear, orange-red solution is obtained. Slowly pour the orange-red solution into stirred methyl tert-butyl ether, and a solid product precipitates. Wash the solid product repeatedly with deionized water several times, filter, and dry in a vacuum oven at 80 °C for 12 hours to obtain a sulfonic acid side-chain functionalized anthracene-branched polyaryl polymer (PSFPA-10) with the structure shown in Formula 5.

[0040] Step 3: Dissolve 0.5g of sulfonic acid side-chain functionalized polyaryl polymer in 15mL of DMSO solution. Filter the polymer solution through a 0.45μm polytetrafluoroethylene filter, cast it onto a clean glass plate, and then vacuum dry it at 80℃ for 24h to completely remove residual solvent, thus obtaining a sulfonic acid side-chain functionalized anthracene-branched polyarylpiperidine membrane, i.e., a zwitterionic exchange membrane, with the structural formula shown in Formula 5. The membrane thickness is 40μm.

[0041] Formula 5;

[0042] Example 1: Application effect in vanadium redox flow batteries: The zwitterionic exchange membranes prepared in Example 1 and Comparative Example 1 were used in a vanadium redox flow battery to test their coulombic efficiency, voltage efficiency, and energy efficiency. The test methods were as follows: tests were conducted at a series of current densities of 110, 150, 200, 250, and 300 mA / cm², with four consecutive cycles performed at each density to evaluate the membrane's efficiency and repeatability under different operating intensities. The results are shown in [Figure number missing]. Figure 4-5 ; from Figure 4 It is evident that the zwitterionic exchange membrane prepared in Example 1 maintains a consistently high coulombic efficiency in the vanadium redox flow battery across a wide current density range of 110 to 300 mA / cm², particularly approaching or exceeding 99% at 150 mA / cm² and above. This demonstrates the excellent barrier capability of the zwitterionic exchange membrane prepared in Example 1 for vanadium ions, effectively suppressing cross-permeation between the positive and negative electrode active materials, which is the foundation for the high energy retention rate of the vanadium redox flow battery. Simultaneously, the voltage efficiency of the vanadium redox flow battery exhibits the expected trend of moderately decreasing with increasing current density, but it still maintains above 72.5% at a high current density of 300 mA / cm². Based on the aforementioned high coulombic and high voltage efficiencies, the energy efficiency of the vanadium redox flow battery performs excellently under all test conditions. From approximately 87% at 110 mA / cm² to approximately 72.5% at 300 mA / cm², the energy efficiency changes smoothly with current density, and good repeatability is demonstrated in four cycles at each fixed current density, with minimal data fluctuations.

[0043] And from Figure 5It can be seen that the zwitterionic exchange membrane prepared using Comparative Example 1 exhibits lower CE values ​​than that of Example 1 at all tested current densities. Comparative Example 1's CE value at 300 mA / cm² is approximately 76.7-95.6%, a difference of about 1-2 percentage points compared to Example 1 (approximately or exceeding 99%), indicating a weaker vanadium ion blocking ability. The VE value of Comparative Example 1 decreases even more significantly, reaching only 66.9-67.2% at 300 mA / cm², far lower than the over 76.1% of Example 1, indicating a higher membrane resistance and more severe ohmic polarization. Due to the combined effects of low CE and low VE, the EE value of Comparative Example 1 is only 51.4-64.0% at 300 mA / cm², a significant difference compared to approximately 75.6% of Example 1.

[0044] From the comparison between Example 1 and Comparative Example 1 above, it can be seen that: Example 1 uses a fluoranthene branched structure, while Comparative Example 1 uses an anthracene branched structure. Both have similar polymer backbone compositions (using p-terphenyl, 5-fluoroindigo, and N-methyl-4-piperidinone as comonomers) and the same sulfonation grafting conditions, but their performance in vanadium redox flow batteries differs. The main reason for this is: Fluoranthracene is a non-planar, cyclically fused aromatic hydrocarbon, with its five-membered ring fused with a naphthalene ring to form a three-dimensional spatial configuration. Using fluoranthracene as a branching point, symmetrical introduction of fluoranthracene into the polymer backbone at both ends can induce the formation of a more compact three-dimensional network structure, increasing interchain packing density, reducing free volume, and thus enhancing the resistance to vanadium ions (…). The physical screening capability of (e.g.) Figure 4 As shown, the coulombic efficiency (CE) of Example 1 is close to or exceeds 99% at 300 mA / cm²; while Figure 5 The results show that the anthracene used in Comparative Example 1 has a linear fused-ring structure with weak branching ability and loose molecular chain arrangement. Its CE (efficiency coefficient) is only 97.5-98.0% at the same current density, indicating that the branched structure of fluoranthene imparts superior ion barrier ability to the membrane. The VE (efficiency value) of Example 1 decreases gradually with increasing current density, remaining at a high level at 300 mA / cm², indicating that the branched structure of fluoranthene has stronger antioxidant capacity, resulting in lower membrane resistance and ohmic polarization loss. Therefore, Example 1 maintains high CE while minimizing VE loss, ultimately achieving an energy efficiency (EE) of approximately 75.6% at 300 mA / cm². Figure 4 ), while the EE of Comparative Example 1 was only 51.4-64.0% ( Figure 5 ).

[0045] In summary, compared to the anthracene branched structure, the fluoranthracene branched structure used in this invention, with its optimized ion channel morphology through the three-dimensional network stacking effect, is the key structural feature that enables the zwitterionic exchange membrane of this invention to achieve excellent comprehensive electrochemical performance.

[0046] Example 2: Application effect in iron-chromium redox flow batteries The zwitterionic exchange membranes prepared in Example 1 and Comparative Example 1 were used in an iron-chromium redox flow battery to test their coulombic efficiency, voltage efficiency, and energy efficiency. The test methods were as follows: tests were conducted at current densities of 40, 60, 80, and 100 mA / cm², with four consecutive cycles performed at each density point to evaluate the membrane's efficiency and operational stability in the system. The results are shown in [Figure number missing]. Figure 6-7 ; like Figure 6 As shown, the coulombic efficiency of the iron-chromium redox flow battery increases systematically with increasing operating current density, significantly improving from approximately 80%-90% at 40 mA / cm² to over 96% at 100 mA / cm². The voltage efficiency of the iron-chromium redox flow battery decreases as expected with increasing current density, gradually decreasing from over 85% at 40 mA / cm² to around 65% at 100 mA / cm². The energy efficiency of the iron-chromium redox flow battery remains between 62% and 74% within the test range of 40 to 100 mA / cm². Figure 6 The results show that the zwitterionic exchange membrane of Example 1 can operate normally in the iron-chromium redox flow battery, with a coulombic efficiency of 80-96% and an energy efficiency of 62-74% in the range of 40-100 mA / cm². This proves that the membrane has a basic barrier capability against iron and chromium ions and has the potential for application in iron-chromium redox flow batteries.

[0047] Comparative Example 1, tested under the same conditions using an iron-chromium redox flow battery, yielded the following results: Figure 7 As shown. At a current density of 4 mA / cm², its coulombic efficiency (CE) is approximately 96.6%, voltage efficiency (VE) is approximately 74.6-78.4%, and energy efficiency (EE) is approximately 72.1-75.5%. As the current density increases to 100 mA / cm², its CE rises to approximately 98.2-98.4%, but VE drops sharply to approximately 54.1-54.5%, and EE correspondingly drops to approximately 53.1-53.6%. (Compared to Example 1...) Figure 6 In comparison, although the EE of Comparative Example 1 was slightly higher at 40 mA / cm² (approximately 72-75% vs. 62-74% of Example 1), its EE at 100 mA / cm² was significantly lower than that of Example 1 (approximately 53% compared to approximately 65% ​​of Example 1). This indicates that the film resistance of Comparative Example 1 increased more significantly with increasing current density, and the ohmic polarization loss was more severe.

[0048] Combination Figure 6 and Figure 7Although the energy efficiency of Example 1 at low current density is slightly lower than that of Comparative Example 1, at higher current densities (100 mA / cm²), the energy efficiency of Example 1 (approximately 65%) is significantly better than that of Comparative Example 1 (approximately 53%). While the energy efficiency of Example 1 at low current densities is not optimal, it still maintains a considerable energy efficiency (approximately 65%) at higher current densities and operates stably overall, fully demonstrating the practical application potential of the fluoranthracene branched zwitterionic exchange membrane of this invention in iron-chromium flow batteries.

[0049] The embodiments described above are merely preferred embodiments of the present invention, and not an exhaustive list of all possible implementations of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A zwitterion exchange membrane containing sulfonic acid side chains and fluoranthene branching, characterized in that, The polymer used comprises repeating units as shown in Formula 1: Formula 1; Wherein, Ar is selected from the structural unit of a biaryl compound; B is a nitrogen-containing heterocyclic cationic group; x, y, and z represent the molar percentages of the corresponding repeating units; x = 1–20%, y = 60–80%, x + y + z = 100%.

2. The zwitterionic exchange membrane containing sulfonic acid side chains and fluoranthene branching according to claim 1, characterized in that, A is a substituted indigo monomer; The Q is bonded to the nitrogen atoms of A and B, and the Q is an alkyl sulfonate ion group.

3. The zwitterionic exchange membrane containing sulfonic acid side chains and fluoranthene branching according to claim 1, characterized in that, The biaryl compound structural units are selected from... or ; The nitrogen-containing heterocyclic cationic group is selected from... , , , , , Any one of them.

4. The zwitterionic exchange membrane containing sulfonic acid side chains and fluoranthene branching according to claim 1, characterized in that, The A is R1, R2, R3 and R4 are each independently selected from any one of methyl, alkyl, haloalkyl, H substituent, F substituent, Cl substituent and Br substituent.

5. The zwitterionic exchange membrane containing sulfonic acid side chains and fluoranthene branching according to claim 1, characterized in that, The A is selected from , , , , , , , , Any one of them.

6. The zwitterionic exchange membrane containing sulfonic acid side chains and fluoranthene branching according to claim 1, characterized in that, The Q is selected from , , , , Any one of them.

7. A method for preparing a zwitterion exchange membrane containing sulfonic acid side chains and fluoranthene branching as described in any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Add biaryl monomers, fluoranthene, substituted indigo, and carbonyl-containing saturated nitrogen heterocyclic compounds to the first solvent and stir for 30-60 min. Then, under ice-water bath and nitrogen conditions, add trifluoroacetic acid and trifluoromethanesulfonic acid dropwise. After the addition is complete, react for 3-12 h to obtain a viscous solution. Then, pour the obtained viscous solution into a 50% ethanol aqueous solution to obtain a solid polymer. Then, crush the solid polymer, filter and collect the fragments, and wash with the first alkaline solution at 40-60 °C with stirring for 8-12 h. Then wash with deionized water until neutral, and dry in a vacuum oven at 60-80 °C for 12-24 h to obtain fluoranthene branched polyaryl polymer. Step 2: Add the fluoranthene branched polyaryl polymer to the second solvent and stir at 80°C for 1-2 hours until a homogeneous solution is formed. Then add the sulfonylating agent and continue stirring at 80°C for 8-12 hours until a homogeneous and clear solution is obtained. Then, under stirring, pour the homogeneous and clear solution into a precipitant to precipitate a solid product. Then, wash the solid product repeatedly with deionized water several times, filter it, and dry it in a vacuum oven at 60-80°C for 12-24 hours to obtain the sulfonic acid side chain functionalized fluoranthene branched polyaryl polymer. Step 3: Dissolve the sulfonic acid side-chain functionalized fluoranthene branched polyaryl polymer obtained in Step 2 in a third solvent, then filter it through a 0.25-0.45 μm polytetrafluoroethylene filter, cast it onto a clean glass plate, and then vacuum dry it at 80-100℃ for 12-36 h to completely remove the residual solvent, thus obtaining a zwitterion exchange membrane containing sulfonic acid side chains.

8. The method for preparing a zwitterionic exchange membrane containing sulfonic acid side chains and fluoranthene branching according to claim 7, characterized in that, The carbonyl-containing saturated nitrogen heterocyclic compound is selected from 1-methyl-4-piperidinone. 3-quinine cyclohexanone 1,3-Dimethyl-4-piperidinone 1-Methyl-3-piperidinone 1-Methyl-4-piperidinecarboxaldehyde 1-Methyl-3-piperidinecarboxaldehyde Any one of them; The substituted indigo is selected from indigo. 5-Methylindigo 5-Fluoroin 6-Fluoroin 5,7-Methylindigo 5,6-Difluoroindigo 7-Bromoindigo 5-Chloroindopurine 5-Bromoindigo Any one of them; The sulfonylating agent is selected from 1,3-propanesulfonyl lactone. 1,4-Butyryl lactone Sodium 2-bromoethylsulfonate Sodium 4-(2-bromoethyl)benzenesulfonate 3-Chloro-2-hydroxy-1-propanesulfonate sodium salt hydrate Any one of them.

9. The method for preparing a zwitterionic exchange membrane containing sulfonic acid side chains and fluoranthene branching according to claim 7, characterized in that, In step 1, the molar ratio of fluoranthene to biaryl monomers is (1-20):100; The total molar ratio of the substituted indigo and the saturated carbonyl-containing saturated nitrogen heterocyclic compound to the biaryl compound is 1 to 2:1; The molar ratio of the trifluoroacetic acid and the saturated carbonyl-containing nitrogen heterocyclic compound is (1-2):1; The molar ratio of the trifluoromethanesulfonic acid and the carbonyl-containing saturated nitrogen heterocyclic compound is (8-12):1; The first solvent is a halogenated hydrocarbon solvent, and the first alkaline solution is a K2CO3, KOH, NaOH or NaHCO3 solution with a concentration of 0.5-2.0M; In step 2, the second solvent is one or more of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; The precipitant includes one or more of diethyl ether, ethanol, methanol, ethyl acetate, deionized water, and methyl tert-butyl ether; The ratio of the fluoranthene branched polyaryl polymer to the second solvent is 1g:7mL to 30mL; The molar ratio of the fluoranthracene branched polyaryl polymer to the sulfonylating agent is 1:(2-4); In step 3, the ratio of the sulfonic acid side-chain functionalized fluoranthene branched polyaryl polymer to the third solvent is 1g:(10-100)mL; The third solvent includes one or more of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylformamide, or N,N-dimethylacetamide.

10. The application of the zwitterionic exchange membrane containing sulfonic acid side chains and fluoranthene branching as described in any one of claims 1-6 in vanadium redox flow batteries and / or iron-chromium redox flow batteries.

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