A polybenzofuran indole type anion exchange membrane and a preparation method thereof

Abstract

The application belongs to the technical field of anion exchange membranes, aims to improve the ion transfer performance and size stability of anion exchange membranes, and provides a polyoxafluorene indole type anion exchange membrane and a preparation method thereof.The preparation method synthesizes polyoxafluorene indole type materials with good stability and electrical conductivity, then ion liquid is grafted to the polymer to obtain polyoxafluorene indole type quaternary ammonium polymer, and a membrane is prepared.Through testing, the prepared membrane better balances the problem between stability and electrical conductivity, and can be applied to neutral flow batteries.The polyoxafluorene indole type anion exchange membrane prepared by the method can exhibit very excellent battery performance, the energy efficiency is much better than that of a commercial membrane AMVN, and the stability is very good, and the efficiency does not obviously decrease after 1000 cycles of battery circulation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of anion exchange membranes, and relates to a polyoxylfluorene indole type anion exchange membrane and a preparation method thereof. BACKGROUND

[0002] Due to the increasingly serious energy crisis and carbon emission burden, the development of renewable energy has attracted more and more attention. Among various energy storage technologies, a liquid flow battery has the characteristics of high safety, long cycle life and high efficiency, and is very suitable for being combined with renewable energy to realize stable output and wide application.

[0003] A neutral organic liquid flow battery uses a cheap sodium chloride salt as a supporting electrolyte, has low cost and low corrosion, is more safe and environmentally friendly, a diaphragm is an anion exchange membrane, conducts chloride ions, and prevents cross mixing of active substances at two poles. Since the neutral liquid flow battery has low corrosion to equipment and pipelines, the stability requirement of the membrane is relatively low, but the chloride ion conductivity requirement is relatively high.

[0004] At present, some commercial membranes are applied to the neutral aqueous liquid flow battery (NAORFB). Hu et al. studied some commonly used anion exchange membranes for NAORFB, including commercial membranes Selemion AMV, ASV and DSV. It is proved by electrochemical impedance spectroscopy that the ohmic resistance of the ion membrane is the main component of the battery resistance. After a series of commercial membranes and electrolytes are optimally combined, the results show that the thinnest membrane DSV (90 mu m) shows the best battery performance and capacity utilization. When the current density is 60 mA cm -2 -2, the coulombic efficiency is above 99%, but the voltage efficiency is only about 76%, which still has a high space for improvement. Increasing the ion exchange capacity in the membrane is beneficial to the improvement of the conductivity, but will cause excessive water swelling, and the mechanical stability cannot be well guaranteed. In view of the problem that the ion exchange membrane cannot be compatible in terms of conductivity and stability, the modification of the membrane is still a difficult problem to be solved. SUMMARY

[0005] The application aims to improve the ion transfer performance of the anion exchange membrane under the premise of maintaining the dimensional stability of the membrane. By introducing a rigid in-plane linked benzene monomer oxylfluorene, the chemical stability and mechanical stability of the ion membrane are maintained, and then a flexible quaternary ammonium side chain is further grafted. The hydrophobic main chain and the hydrophilic side chain together form a good microphase separation morphology, and construct an ion conduction channel. Through testing, the prepared membrane has good stability and high ion conductivity, and can be applied to a neutral liquid flow battery.

[0006] The technical scheme of the application:

[0007] A polyoxylfluorene indole type anion exchange membrane has the following structure:

[0008]

[0009] Where 1 > x > 0, n = 1 to 10 positive integers, and R is H or quaternary ammonium, spirocyclic quaternary ammonium, imidazolium, piperidinium, pyridinium, or pyrrolomunium cations.

[0010] A method for preparing a polyoxyfluorene indole-type anion exchange membrane, comprising the following steps:

[0011] (1) Synthesis of polyoxyfluorene indole material: Under ice-water bath conditions, fluorene and indigo were added to solvent A and mechanically stirred until completely dissolved. Trifluoroacetic acid was added, followed by trifluoromethanesulfonic acid under ice bath conditions. After reacting for 1 hour under ice bath conditions, the temperature was gradually raised to room temperature to continue the reaction. The reaction produced a brown viscous solid until the mechanical stirring could no longer be performed. The reaction time was controlled to be 3-10 hours depending on the amount of trifluoromethanesulfonic acid added. The reaction time was shortened as the amount of trifluoromethanesulfonic acid added increased. The reactants were poured into precipitant A, filtered, washed, and dried to obtain polyoxyfluorene indole material.

[0012] The molar ratio of fluorene:indigo:trifluoromethanesulfonic acid:trifluoroacetic acid is 1:1.1:4:0.67;

[0013] The fluorene:indigo in solvent A has a w / v ratio of 0.2288 to 0.2540.

[0014] The volume ratio of trifluoroacetic acid to solvent A is 0.1031:1;

[0015] Solvent A is dichloromethane or trichloromethane;

[0016] The precipitant A is ice water or a 5wt%-10wt% aqueous solution of sodium hydroxide;

[0017] (2) Synthesis of ionic liquid: The dibromo monomer containing aliphatic chain and the ionizing reagent are dissolved in solvent B and reacted at 20-60℃ for 48h. The precipitated solid product is washed repeatedly with solvent B 3-5 times and dried under vacuum to obtain the ionic liquid.

[0018] The structure of the dibromo monomer containing the aliphatic chain is as follows: Where n is a positive integer from 1 to 10;

[0019] The molar ratio of the dibromo monomer containing aliphatic chains to the ionizing reagent is 2-3:1;

[0020] The total mass of the dibromo monomer containing aliphatic chains and the ionizing reagent in solvent B is 10-30% by w / v.

[0021] Solvent B is ethyl acetate or acetonitrile;

[0022] the ionization reagent is one of N-methylpiperidine, N-methylpyrrolidine, 1-methylimidazole, 2-methylimidazole, 1,2-dimethylimidazole, N-methylmorpholine;

[0023] (3) Preparation of polyoxylfluorene indole type anion exchange membrane: dissolve the polyoxylfluorene indole type material in DMSO at 80℃, then add potassium carbonate, and then add ionic liquid, and react at 80℃ for 36-48h, pour the reaction solution into precipitant B, filter, wash, and dry; then dissolve the product in solvent C, prepare a casting solution, and then cast into a membrane; soak the membrane in 3mol / L sodium chloride solution for 24-48h, soak in deionized water until neutral, and dry, to obtain a polyoxylfluorene indole type functionalized anion exchange membrane;

[0024] the molar ratio of the repeating unit in the polyoxylfluorene indole type material: K2CO3: ionic liquid is 1:0.8-2:0.8-2;

[0025] the w / v of the polyoxylfluorene indole type material in solvent C is 3-10%;

[0026] the solvent C is one of N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide;

[0027] the precipitant B is acetone or ethyl acetate;

[0028] the w / v of the casting solution is 3-10%;

[0029] the w / v of the polyoxylfluorene indole type material and DMSO is 2-10%;

[0030] the units of the above w / v are g / ml.

[0031] In step (1), the drying is vacuum drying, the temperature is 40-100℃, and the time is more than 6h.

[0032] In step (2), the vacuum drying temperature is 30-60℃, and the time is more than 12h.

[0033] In step (3), the drying is vacuum drying, the temperature is 40-80℃, and the time is more than 8h.

[0034] The drying temperature for the membrane formed by casting is 50-80℃, and the time is 24-48h.

[0035] The effect and benefit of the present application is that a polyoxylfluorene indole type anion exchange membrane applied in neutral flow battery is designed and prepared through condensation and grafting reaction, the introduction of monomer with rigid in-plane linked benzene structure ensures the chemical stability and dimensional stability of the membrane material, then the flexible side chain quaternary ammonium salt is introduced for ion conduction, while the stability and conductivity of the ion membrane are ensured. The polyoxylfluorene indole type anion exchange membrane prepared in this way can exhibit very excellent battery performance, and the energy efficiency is much better than that of commercial membrane AMVN, and has very good stability, and the efficiency does not decrease obviously after 1000 cycles of battery cycle. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 (a) is the nuclear magnetic hydrogen spectrum of QPDFI-100;

[0037] Figure 1 (b) is the nuclear magnetic hydrogen spectrum of PDFI.

[0038] Figure 2 is the energy efficiency of the membrane of the example under different current densities. DETAILED DESCRIPTION

[0039] The present application will be further described in detail below in combination with examples, but the embodiments of the present application are not limited to this.

[0040] Example 1

[0041] Synthesis of polyoxylfluorene indole type material: 1.3730 g (8 mmol) of oxylfluorene and 1.5240 g (13.2 mmol) of indigo were dissolved in 6 mL of dichloromethane, 0.9214 g (0.6667 equivalent) of trifluoroacetic acid and 7.2761 g (4.0000 equivalent) of trifluoromethanesulfonic acid were added under ice bath condition, the ice bath was removed after 1 h, and the mechanical stirring was continued for about 3 h to obtain a viscous product. After the reaction was completed, the product was crushed with tweezers under mechanical stirring and placed in methanol to obtain a block-shaped polymer. After repeated washing and soaking with deionized water, the polymer was dried to obtain a product ready for use.

[0042] Synthesis of 6-Br-N,N,N-trimethylhexane ionic liquid: 13.2770 g of 1,6-dibromohexane was added to a 250 mL single-neck flask, and then 80 mL of trimethylamine tetrahydrofuran solution was added, and stirred at room temperature for 48 h to obtain a white powder precipitate. The product was repeatedly washed with tetrahydrofuran for 3-5 times, and vacuum dried at 60°C for 12 h to obtain a white powder ionic liquid.

[0043] Preparation of functionalized quaternary ammonium polymer: The polymer 1 g obtained from the previous step was dissolved in 30 mL of DMSO, and after the polymer was dissolved, 0.3689 g (0.8 equivalent) of K2CO3 and 0.9062 g (0.8 equivalent) of 6-Br-N,N,N-trimethylhexane were added, and the reaction was carried out at 80 °C for 48 h; the above mixture was first centrifuged to remove K2CO3, and then precipitated with ethyl acetate, washed quickly with deionized water, filtered, and dried in an 80 °C oven for 24 h for standby use.

[0044] Preparation of polyoxadiphenylindole anion exchange membrane: The quaternary ammonium functionalized polymer synthesized in the previous step was dissolved in the casting solution DMSO to form a casting solution of 26.67 g / L; the casting solution was dropped onto the casting plate and dried in an oven to form a polyoxadiphenylindole anion exchange membrane; the polyoxadiphenylindole anion exchange membrane was gently peeled off from the casting glass plate; the polyoxadiphenylindole anion exchange membrane was soaked in deionized water at room temperature for 12 h to remove impurities; then, the polyoxadiphenylindole anion exchange membrane was soaked in alkali for 12 h to allow it to undergo sufficient ion exchange; and the polyoxadiphenylindole anion exchange membrane was soaked in deionized water to remove excess alkali.

[0045] The structure of the anion exchange membrane obtained in this example is as follows (x = 0.7; n = 6):

[0046]

[0047] Tests show that the polyoxadiphenylindole anion exchange membrane prepared in this example has an ion conductivity of 10.31 mS cm-1 at 25 °C -1 , a water absorption rate of 14.42% and a swelling degree of 5.71% in a 3M NaCl solution. In a neutral flow battery, the CE is 99.36% and the EE is 87.07% at 40 mA cm-2. -2

[0048] Example 2

[0049] Synthesis of polyoxadiphenylindole material: same as Example 1.

[0050] Synthesis of 6-Br-N,N,N-trimethylhexane ionic liquid: same as Example 1.

[0051] ​Preparation of functionalized quaternary ammonium polymer: The polymer 1 g obtained from the previous step was dissolved in 30 mL of DMSO, and after the polymer was dissolved, 0.7049 g (1 equivalent) of K2CO3 and 1.1327 g (1 equivalent) of 6-Br-N,N,N-trimethylhexane were added, and the reaction was carried out at 80 °C for 48 h; the above mixture was first centrifuged to remove K2CO3, and then precipitated with ethyl acetate, washed with deionized water, filtered, and dried in an 80 °C oven for 24 h for standby use.

[0052] Preparation of polyoxafluorene indole type anion exchange membrane: The quaternary ammonium functionalized polymer synthesized in the previous step was dissolved in the casting solution DMSO to form a casting solution of 26.67 g / L; the casting solution was dropped onto the casting plate and dried in an oven to form a polyoxafluorene indole type anion exchange membrane; the polyoxafluorene indole type anion exchange membrane was gently peeled off from the casting glass plate; the polyoxafluorene indole type anion exchange membrane was soaked in deionized water at room temperature for 12 h to remove impurities; then, the polyoxafluorene indole type anion exchange membrane was soaked in alkali for 12 h to allow it to undergo sufficient ion exchange; and finally, the polyoxafluorene indole type anion exchange membrane was soaked in deionized water to remove excess alkali.

[0053] The structure of the anion exchange membrane obtained in this example is as follows (x = 0.8; n = 6):

[0054]

[0055] Tests show that the polyoxafluorene indole type anion exchange membrane prepared in this embodiment has an ion conductivity of 13.33 mS cm-1 at 25 °C, a water absorption rate of 20.03% in a 3M NaCl solution, and a swelling degree of 6.59%. In a neutral flow battery, the CE is 99.19% and the EE is 88.03% at 40 mA cm-2. -1 -2

[0056] Example 3

[0057] Synthesis of polyoxafluorene indole type material: same as Example 1.

[0058] Synthesis of 6-Br-N,N,N-trimethylhexane ionic liquid: same as Example 1.

[0059] ​​Preparation of functionalized quaternary ammonium polymer: The polymer 1 g obtained from the previous step was dissolved in 30 mL of DMSO, and after the polymer was dissolved, 1.0573 g (1.5 equivalent) of K2CO3 and 1.6990 g (1.5 equivalent) of 6-Br-N,N,N-trimethylhexane were added, and the reaction was carried out at 80 °C for 48 h; the above mixture was first centrifuged to remove K2CO3, and then precipitated with ethyl acetate, washed with deionized water, filtered, and dried in an 80 °C oven for 24 h for standby use.

[0060] Preparation of polyoxadiphenyl indole type anion exchange membrane: The quaternary ammonium functionalized polymer synthesized in the previous step was dissolved in the casting solution DMSO to form a casting solution of 26.67 g / L; the casting solution was dropped onto the casting plate and dried in an oven to form a polyoxadiphenyl indole type anion exchange membrane; the polyoxadiphenyl indole type anion exchange membrane was gently peeled off from the casting glass plate; the polyoxadiphenyl indole type anion exchange membrane was soaked in deionized water at room temperature for 12 h to remove impurities; then, the porous quaternary ammonium functionalized anion exchange membrane was soaked in alkali for 12 h to allow sufficient ion exchange; the polyoxadiphenyl indole type anion exchange membrane was then soaked in deionized water to remove excess alkali.

[0061] The structure of the anion exchange membrane obtained in this example is as follows (x = 0.9; n = 6):

[0062]

[0063] Tests show that the polyoxadiphenyl indole type anion exchange membrane prepared in this embodiment has an ion conductivity of 18.97 mS cm-1 at 25 °C -1 , a water absorption rate of 23.68% and a swelling degree of 7.84% in a 3M NaCl solution. In a neutral flow battery, the CE is 99.03% and the EE is 89.25% at 40 mA cm-2. -2

[0064] Example 4

[0065] Synthesis of polyoxadiphenyl indole type material: same as Example 1.

[0066] Synthesis of 6-Br-N,N,N-trimethylhexane ionic liquid: same as Example 1.

[0067] ​Preparation of functionalized quaternary ammonium onion polymer: 1g of the reaction product polymer obtained in the previous step was dissolved in 30mL of DMSO. After the polymer was decomposed, 1.4098g (2 equivalents) of K2CO3 and 2.2654g (2 equivalents) of 6-Br-N,N,N-trimethylhexane were added, and the mixture was reacted at 80℃ for 48h. The K2CO3 was removed by centrifugation, and then precipitated with ethyl acetate. The mixture was then quickly washed with deionized water, filtered, and dried in an oven at 80℃ for 24h for later use.

[0068] Preparation of polyoxyfluorene-indole anion exchange membrane: The quaternary ammonium-onium functionalized polymer synthesized in the previous step was dissolved in DMSO casting solution to obtain a casting solution of 26.67 g / L; the casting solution was dropped onto the casting plate and thoroughly dried in an oven to prepare the polyoxyfluorene-indole anion exchange membrane; the polyoxyfluorene-indole anion exchange membrane was gently peeled off from the casting glass plate; at room temperature, the polyoxyfluorene-indole anion exchange membrane was immersed in deionized water for 12 h to remove impurities; then, the polyoxyfluorene-indole anion exchange membrane was immersed in alkali for 12 h to allow for sufficient ion exchange; finally, the polyoxyfluorene-indole anion exchange membrane was immersed in deionized water to remove excess alkali.

[0069] The structure of the anion exchange membrane obtained in this example is as follows (x = 1, n = 6):

[0070]

[0071] Tests showed that the polyoxyfluorene indole anion exchange membrane prepared in this embodiment has an ion conductivity of 23.42 mS / cm at 25°C. -1 In 3M NaCl solution, the water absorption rate is 29.27%, and the swelling degree is 9.89%. In a neutral flow cell, at 40 mA cm⁻¹... -2 When electrically secure, CE is 99.16% and EE is 89.94%.

Claims

1. A method for preparing a polyoxyfluorene indole-type anion exchange membrane, characterized in that, The structure of the polyoxyfluorene indole anion exchange membrane is as follows: ； Where 1 > x > 0, n = 1 to 10 positive integers, and R is H or quaternary ammonium, spirocyclic quaternary ammonium, imidazolium, piperidinium, pyridinium, or pyrrolomunium cations; The steps are as follows: (1) Synthesis of polyoxyfluorene indole material: Under ice-water bath conditions, fluorene and indigo were added to solvent A and mechanically stirred until completely dissolved. Trifluoroacetic acid was added, and then trifluoromethanesulfonic acid was added under ice bath conditions. After reacting for 1 hour under ice bath conditions, the temperature was gradually raised to room temperature to continue the reaction. The reaction produced a brown viscous solid until the mechanical stirring could no longer be performed. The reaction time was controlled to be 3-10 hours depending on the amount of trifluoromethanesulfonic acid added. The reaction time was shortened as the amount of trifluoromethanesulfonic acid added increased. The reactants were poured into precipitant A, filtered, washed, and dried to obtain polyoxyfluorene indole material. The molar ratio of fluorene:indigo:trifluoromethanesulfonic acid:trifluoroacetic acid is 1:1.1:4:0.67; The fluorene:indigo in solvent A has a w / v ratio of 0.2288~0.2540; The volume ratio of trifluoroacetic acid to solvent A is 0.1031:1; Solvent A is dichloromethane or trichloromethane; The precipitant A is ice water or a 5wt%-10wt% aqueous solution of sodium hydroxide; (2) Synthesis of ionic liquid: The dibromo monomer containing aliphatic chain and the ionizing reagent are dissolved in solvent B and reacted at 20-60℃ for 48h. The precipitated solid product is washed repeatedly with solvent B 3-5 times and dried under vacuum to obtain the ionic liquid. The structure of the dibromo monomer containing the aliphatic chain is as follows: , where n is a positive integer from 1 to 10; The molar ratio of the dibromo monomer containing aliphatic chains to the ionizing reagent is 2-3:1; The total mass of the dibromo monomer containing aliphatic chains and the ionizing reagent in solvent B is 10-30% by w / v. Solvent B is ethyl acetate or acetonitrile; The ionizing agent is one of N-methylpiperidine, N-methylpyrrolidine, 1-methylimidazolium, 2-methylimidazolium, 1,2-dimethylimidazolium, and N-methylmorpholine; (3) Preparation of polyoxyfluorene indole anion exchange membrane: At 80℃, polyoxyfluorene indole material was dissolved in DMSO, then potassium carbonate was added, followed by ionic liquid. The reaction was carried out at 80℃ for 36-48h. The reaction solution was poured into precipitant B, filtered, washed, and dried. The product was then dissolved in solvent C to prepare a casting solution and cast into a membrane. The membrane was immersed in 3mol / L sodium chloride solution for 24-48h, then immersed in deionized water until neutral, and dried to obtain polyoxyfluorene indole functionalized anion exchange membrane. The molar ratio of repeating unit K2CO3 to ionic liquid in the polyoxyfluorene indole material is 1:0.8~2:0.8~2; The polyoxyfluorene indole-type material has a w / v of 3-10% in solvent C; The solvent C is one of N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide; The precipitant B is acetone or ethyl acetate; The casting solution has a w / v ratio of 3-10%; The polyoxyfluorene indole type material has a w / v ratio of 2-10% to DMSO; All w / v values ​​mentioned above are in g / ml.

2. The preparation method according to claim 1, characterized in that, In step (1), the drying is vacuum drying, the temperature is 40-100℃, and the time is more than 6 hours.

3. The preparation method according to claim 1, characterized in that, In step (2), the vacuum drying temperature is 30-60°C and the time is more than 12 hours.

4. The preparation method according to claim 1, characterized in that, In step (3), the drying is vacuum drying, the temperature is 40-80℃, and the time is more than 8 hours.

5. The preparation method according to claim 1, characterized in that, The drying temperature for the casting film is 50–80℃, and the drying time is 24–48 hours.

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