Cross-linked sulfonated polybenzimidazole membrane as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of a cross-linked sulfonated polybenzimidazole membrane, which comprises the following steps: in a nitrogen atmosphere, adding polybenzimidazole into a first solvent, reacting, adding anhydrous potassium carbonate powder, slowly adding a sulfonating agent, reacting, and carrying out post-treatment to obtain sulfonated polybenzimidazole; the sulfonated polybenzimidazole is dissolved in a second solvent, a cross-linking agent is added, the mixture is heated for a reaction, and cross-linked sulfonated polybenzimidazole is obtained after aftertreatment; and dissolving the cross-linked sulfonated polybenzimidazole in a third solvent, drying to obtain a cross-linked sulfonated polybenzimidazole membrane, and activating to obtain the activated cross-linked sulfonated polybenzimidazole membrane. The cross-linked sulfonated polybenzimidazole membrane provided by the invention has excellent proton conductivity and ion selectivity, has excellent coulombic efficiency and voltage efficiency in an all-vanadium redox flow battery, and has optimal battery performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of diaphragms for liquid flow batteries, and in particular, relates to a cross-linked sulfonated polybenzimidazole membrane and a preparation method and application thereof. Background Art

[0002] Among energy storage technologies, electrochemical energy storage technology has received extensive attention and has developed rapidly. In particular, redox flow batteries (RFBs) are considered to be an ideal choice for large-scale long-term energy storage due to their overall safety, flexible design, high conversion efficiency and long cycle life. At present, all-vanadium redox flow batteries (VRFBs) have been commercialized and have good development prospects.

[0003] The diaphragm is the core component of VRFB and must meet the requirements of high proton conductivity, low vanadium permeation, good mechanical properties and excellent chemical stability. In all-vanadium flow batteries, the most widely used is DuPont's Nafion series membrane, which has good mechanical stability and proton conductivity. However, the high water absorption rate of perfluorosulfonic acid membrane (PFSA) exacerbates the permeability of vanadium ions, resulting in its low ion selectivity; and the cost of Nafion membrane accounts for more than 40% of the total cost of a 1 kW battery stack. Such high material costs also hinder the widespread commercialization of VRFB. Therefore, there is an urgent need to develop low-cost, high-performance new flow battery diaphragms.

[0004] As one of the most promising non-fluorinated ion-conducting membranes, polybenzimidazole (PBI) membrane has excellent vanadium resistance and chemical stability and has been widely used in VRFB. However, the PBI membrane lacks ion exchange groups, resulting in very low conductivity. In the past few years, researchers have explored the effects of various ionic groups on the conductivity of PBI. Among them, the proton dissociation ability of sulfonic acid groups is much higher than that of other proton-conducting groups. The introduction of sulfonic acid groups is an effective way to improve the ionic conductivity of PBI membranes. However, it may potentially reduce the mechanical strength, chemical stability and ion selectivity of the membrane. In order to solve these problems, other modification strategies can be used simultaneously to achieve optimal performance. Among them, covalent cross-linking is the main means to improve the mechanical and chemical stability of the membrane, which can effectively reduce the excessive swelling of the PBI membrane and the cross-contamination of the electrolyte to balance the mass transfer capacity and stability of the sulfonated PBI membrane. In addition, the use of suitable cross-linking agents can form a wide cross-linking network inside the membrane, broaden the ion transport channel and optimize the pore structure, ensuring that the ionic conductivity of the PBI membrane is improved while maintaining its high ion selectivity and chemical stability. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a cross-linked sulfonated polybenzimidazole membrane.

[0006] Another object of the present invention is to provide an application of the cross-linked sulfonated polybenzimidazole membrane prepared by the method in the preparation of a liquid flow battery.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The first aspect of the present invention provides a method for preparing a cross-linked sulfonated polybenzimidazole membrane, comprising the following steps:

[0009] The first step is to add polybenzimidazole to the first solvent under a nitrogen atmosphere, stir for 1 to 3 h (preferably 2 h) at a temperature of 60 to 100 ° C (preferably 80 ° C), add anhydrous potassium carbonate powder, the molar ratio of polybenzimidazole to anhydrous potassium carbonate powder is 1:1 to 2 (preferably 1:1.5), and then slowly add a sulfonating agent, the molar ratio of polybenzimidazole to the sulfonating agent is 8 to 20:1 (preferably 10:1), react at a temperature of 30 to 50 ° C (preferably 40 ° C) for 1 to 48 h (preferably 24 h), and obtain sulfonated polybenzimidazole through post-treatment;

[0010] The sulfonating agent is selected from at least one of 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, vinyl sultone, benzene sultone, ethylene sultone, and functionalized sultone derivatives;

[0011] The second step is to dissolve the sulfonated polybenzimidazole in a second solvent to obtain a solution with a mass fraction of 1-10% (preferably 2%), add a crosslinking agent, and the molar ratio of the sulfonated polybenzimidazole to the crosslinking agent is 1-20:1 (preferably 10:1, 5:1), heat to 60-100°C (preferably 80°C) for reaction for 1-48 h (preferably 24 h), and obtain a crosslinked sulfonated polybenzimidazole after post-treatment;

[0012] The cross-linking agent is selected from at least one of glycerol triglycidyl ether (GTE), ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, and pentaerythritol glycidyl ether;

[0013] The third step is to dissolve the cross-linked sulfonated polybenzimidazole in a third solvent, dry to obtain a cross-linked sulfonated polybenzimidazole membrane, and activate to obtain an activated cross-linked sulfonated polybenzimidazole membrane.

[0014] The first solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, and methanesulfonic acid.

[0015] The post-treatment step in the first step is as follows: the mixture is poured into acetone to precipitate the polymer, and washed with water and ethanol several times until the solution becomes colorless, and dried.

[0016] In the first step of drying, the precipitate is dried under vacuum at a temperature of 50-70°C (preferably 60°C) for 1-48 h (preferably 24 h).

[0017] The preparation method of the polybenzimidazole comprises the following steps:

[0018] Under a nitrogen atmosphere, phosphorus pentoxide and methane sulfonic acid in a mass ratio of 1:1-20 (preferably 1:10) are mixed, and 3,3'-diaminobenzidine (DAB) and 4,4'-dicarboxy diphenyl ether (OBA) in a molar ratio of 1:1-2 (preferably 1:1) are added, and the mass ratio of phosphorus pentoxide to 3,3'-diaminobenzidine is 1-5:1 (preferably 3.1:1). Under stirring conditions, the reaction system is heated to 90-110°C (preferably 100°C) and stirred for 1-3 h (preferably 2 h), and then the temperature is raised to 130-150°C (preferably 140°C) and reacted for 1-5 h (preferably 4 h) to obtain the polybenzimidazole.

[0019] The number average molecular weight (Mn) of the polybenzimidazole is 34175 g·mol -1 , weight average molecular weight (Mw) is 57958 g·mol -1 , the polydispersity index (PDI) is 1.69.

[0020] The second solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, and methanesulfonic acid.

[0021] The post-treatment step in the second step is as follows: the mixture is poured into acetone to precipitate the polymer, and washed with water and ethanol several times until the solution becomes colorless, and dried.

[0022] The drying in the second step is to dry the precipitate under vacuum at a temperature of 50-70°C (preferably 60°C) for 1-48 h (preferably 24 h).

[0023] The cross-linked sulfonated polybenzimidazole is dissolved in the third solvent to obtain a solution with a mass fraction of 1-10% (preferably 2%).

[0024] The drying step in the third step is: drying the above solution at a temperature of 60-100°C (preferably 80°C) for 1-48 h (preferably 24 h).

[0025] The third solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, and methanesulfonic acid.

[0026] The thickness of the cross-linked sulfonated polybenzimidazole membrane is 20-30 μm (preferably 25 μm).

[0027] The activation step in the third step is as follows: placing the prepared membrane in a phosphoric acid solution with a mass concentration of 85 wt% and standing for 1 to 48 h (preferably 24 h) for activation pretreatment, and washing with deionized water for multiple times.

[0028] The second aspect of the present invention provides a cross-linked sulfonated polybenzimidazole membrane, wherein the cross-linked sulfonated polybenzimidazole membrane is prepared by the preparation method.

[0029] The third aspect of the present invention provides a use of the cross-linked sulfonated polybenzimidazole membrane in the preparation of a liquid flow battery.

[0030] The flow battery is selected from at least one of an all-vanadium flow battery, a lithium-ion flow battery, a zinc-bromine flow battery, a zinc-cerium flow battery, a zinc-nickel flow battery, a lead flow battery, an iron-chromium flow battery, a sodium polysulfide / bromine flow battery or an all-iron flow battery.

[0031] Due to the adoption of the above technical solution, the present invention has the following advantages and beneficial effects:

[0032] The cross-linked sulfonated polybenzimidazole membrane provided by the present invention modifies the molecular structure of PBI by grafting and cross-linking reaction, and the grafted hydrophilic sulfonic acid groups provide more proton transfer sites for the membrane, and a dynamic hydrogen bond network conducive to proton transfer is constructed by cross-linking reaction, which provides a good ion transfer channel for protons and significantly improves the proton conductivity of the membrane. At the same time, the continuous cross-linked network formed by covalent bonds effectively limits the diffusion of active substances, so that it maintains excellent ion selectivity. The cross-linked sulfonated polybenzimidazole membrane provided by the present invention can show excellent performance in VRFB.

[0033] The preparation method of the cross-linked sulfonated polybenzimidazole membrane provided by the present invention is to graft a sulfonic acid group with high conductivity on the main chain of PBI as an ion exchange group, and use glycerol triglycidyl ether (GTE) as a covalent cross-linking agent to prepare the cross-linked sulfonated polybenzimidazole membrane. On the one hand, the synergistic effect of the sulfonic acid group and the protonated imidazole group provides more ion exchange sites for protons. On the other hand, the dynamic hydrogen bond network formed by the ether bond and hydroxyl group between the chain segments provides a good ion transmission channel for protons, which significantly improves the proton conductivity of the membrane. At the same time, the tight cross-linking network also enables the membrane to maintain excellent ion selectivity and chemical stability. The all-vanadium liquid flow battery assembled with it shows excellent electrochemical performance and stability. The present invention provides an effective strategy for the design of high-performance PBI membranes, thereby improving the competitiveness of PBI membranes in the field of all-vanadium liquid flow batteries.

[0034] The cross-linked sulfonated polybenzimidazole membrane provided by the present invention has both excellent proton conductivity and ion selectivity, excellent coulombic efficiency and voltage efficiency in an all-vanadium liquid flow battery, and optimal battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of the vanadium ion penetration test.

[0036] Figure 2 It is OPBI-SO 3 XRD patterns of H-GTE membrane and pure OPBI membrane.

[0037] Figure 3 It is OPBI-SO 3 Schematic diagram of SEM image and EDS elemental spectrum of H-GTE membrane.

[0038] Figure 4 OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO 3 Schematic diagram of the water absorption and swelling rate test results of H-GTE membrane.

[0039] Figure 5 It is Nafion212 membrane, OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO 3 Schematic diagram of IEC of H-GTE membrane.

[0040] Figure 6 OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO 3 Schematic diagram of water contact angle of H-GTE membrane.

[0041] Figure 7It is Nafion212 membrane, OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO 3 Schematic diagram of proton conductivity and surface resistance of H-GTE membrane.

[0042] Figure 8 It is Nafion212 membrane, OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO 3 Schematic diagram of vanadium ion permeability of H-GTE membrane.

[0043] Fig. 9 It is Nafion212 membrane, OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO 3 Schematic diagram of the variable current performance of H-GTE membrane.

[0044] Fig.10 It is OPBI-SO 3 H-GTE membrane at 200 mA·cm -2 Long term cycling performance diagram below.

[0045] Fig.11 It is Nafion212 membrane, OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO 3 Schematic diagram of the self-discharge curve of H-GTE membrane. DETAILED DESCRIPTION

[0046] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0047] The present invention can improve the proton conductivity of the PBI membrane while maintaining its high chemical stability by rationally selecting modification strategies and carefully regulating the structure and properties of the polymer side chains. The present invention uses 1,3-propane sultone, which is inexpensive and highly reactive, as the sulfonation reagent of PBI, performs epoxy ring opening at a temperature of 40°C, and grafts sulfonic acid groups on the PBI side chains. The process is simple and stable. In addition, propylene glycol triglycidyl ether (GTE) is used as a covalent crosslinking agent, which has abundant epoxy active sites, can ensure the crosslinking effect, and the numerous ether bonds and hydroxyl groups between the chain segments after crosslinking not only broaden the free volume of the membrane, but also form a dynamic hydrogen bond network that provides more ion transport channels for protons, further improving the mass transfer capacity of the membrane.

[0048] Example 1

[0049] Preparation of aryl ether polybenzimidazole (OPBI)

[0050] 10 g of phosphorus pentoxide and 100 g of methane sulfonic acid were added to a three-necked flask, the mass ratio of phosphorus pentoxide to methane sulfonic acid was 1:10, and 3,3'-diaminobenzidine (DAB) (15 mmol, 3.21 g) and 4,4'-dicarboxy diphenyl ether (OBA) (15 mmol, 3.87 g) were added under nitrogen atmosphere, the molar ratio of 3,3'-diaminobenzidine (DAB) to 4,4'-dicarboxy diphenyl ether (OBA) was 1:1, and the mass ratio of phosphorus pentoxide to 3,3'-diaminobenzidine was 3.1:1. Under stirring conditions, the reaction system was heated to 100 °C and stirred for 2 h, and then the temperature was raised to 140 °C for 4 h. After the reaction was completed, the solution was slowly poured into saturated NaHCO 3 The OPBI polymer was precipitated in water to neutralize the residual methane sulfonic acid in the product. The precipitated product was cut into pieces and filtered and washed with water and ethanol several times until the solution was neutral. Finally, the OPBI polymer was vacuum dried at 120 °C for 24 h to obtain 4.97 g OPBI. The number average molecular weight (Mn) was 34175 g·mol -1 , weight average molecular weight (Mw) is 57958 g·mol -1 , the calculated polydispersity index (PDI) was 1.69.

[0051]

[0052] Sulfonated polybenzimidazole (OPBI-SO 3 H) Membrane preparation

[0053] Under nitrogen atmosphere, OPBI (2.5 mmol, 1 g) was added to 50 g of dimethyl sulfoxide and stirred at 80 °C for 2 h. After complete dissolution, anhydrous K 2 CO 3 powder (3.75 mmol, 0.52 g) was used as the reaction catalyst, and OPBI was reacted with anhydrous K 2 CO 3 The molar ratio of the powder was 1:1.5, and then 1,3-propane sultone (0.25 mmol, 0.03 g) was slowly added. The molar ratio of OPBI to 1,3-propane sultone was 10:1. The reaction was carried out at 40 °C for 24 h. After the reaction, the mixture was poured into acetone to precipitate the polymer, and washed with water and ethanol several times until the solution became colorless. Finally, the precipitate was vacuum dried at 60 °C for 24 h to obtain 0.84 g OPBI-SO 3 H.

[0054] 0.5 g OPBI-SO 3 The H solid was dissolved in 25 g of dimethyl sulfoxide to obtain a solution with a mass fraction of 2%. 2.0 mL of the solution was added to an ultra-flat dish (Japanese Flat-glass Petri dish, FS-30, diameter 32 mm, height 15 mm) and dried in an oven at 80 °C for 24 h to obtain OPBI-SO with a thickness of 25 μm and a uniform surface. 3 The prepared membrane was placed in 10 mL of 85 wt% phosphoric acid solution and left to stand for 24 h for activation pretreatment. After being taken out, it was washed several times with deionized water to obtain the activated OPBI-SO 3 H membrane.

[0055] Cross-linked sulfonated polybenzimidazole (OPBI-SO 3 Preparation of H-GTE membrane

[0056] OPBI-SO 3 H (0.95 mmol, 0.5 g) solid was dissolved in 25 g of dimethyl sulfoxide to obtain a 2% solution, and glycerol triglycidyl ether (GTE) (0.095 mmol, 0.025 g) and OPBI-SO 3 The molar ratio of H to GTE was 10:1. The temperature was raised to 80 °C for 24 h. After the reaction, the mixture was poured into acetone to precipitate the polymer and washed with water and ethanol several times until the solution became colorless. Finally, the precipitate was vacuum dried at 60 °C for 24 h to obtain 0.42 g OPBI-SO 3 H-GTE product.

[0057] 0.5 g OPBI-SO 3 H-GTE solid was dissolved in 25 g of dimethyl sulfoxide to obtain a 2% solution. 2.0 mL of the solution was added to an ultra-flat dish and dried in an oven at 80 °C for 24 h to obtain OPBI-SO with a thickness of 25 μm and a uniform surface. 3 The prepared membrane was placed in 10 mL of 85 wt% phosphoric acid solution and left to stand for 24 h for activation pretreatment. After being taken out, it was washed several times with deionized water to obtain the activated OPBI-SO 3 H-GTE membrane.

[0058]

[0059] Comparative Example 1

[0060] Preparation of OPBI pure membrane

[0061] 0.5 g of OPBI solid was dissolved in 25 g of dimethyl sulfoxide to obtain a solution with a mass fraction of 2%. 2.0 mL of the solution was added to an ultra-flat dish and placed in an oven at 80 °C for 24 h to obtain a PBI membrane with a thickness of 25 μm and a uniform surface. The prepared membrane was placed in 10 mL of 85 wt% phosphoric acid solution and allowed to stand for 24 h for activation pretreatment. After being taken out, it was washed several times with deionized water to obtain an activated OPBI membrane.

[0062] Comparative Example 2

[0063] Commercially available Nafion 212 membrane.

[0064] Test methods for samples prepared in Example 1 and Comparative Examples 1-2

[0065] Swelling rate and water absorption

[0066] The membranes used in the preparation of the membrane samples below are all activated membranes.

[0067] The cut film samples were placed in a vacuum drying oven at 60 °C and dried for 24 h. The mass of the dry film was weighed immediately after the samples were taken out of the oven and recorded as M. dry , and measure its diameter, recorded as D dry After immersion in deionized water for 24 h, the surface water of the membrane was removed with filter paper, and the mass of the wet membrane was immediately weighed. wet and diameter D wet In order to ensure the accuracy of the data and reduce the error, each membrane sample was measured three times and the average value was taken. The SR (swelling rate) and WU (water absorption rate) of the membrane were obtained by the following two equations:

[0068]

[0069] Among them, M dry is the dry weight of the membrane, M wet It is the wet weight of the membrane after absorbing water. dry is the diameter of the membrane in dry state, D wet is the diameter of the membrane in the wet state.

[0070] Ion exchange capacity

[0071] The prepared membrane sample was placed in a vacuum drying oven at 60 °C for 24 h. The mass m of the dry membrane was accurately weighed after the sample was taken out of the oven. The sample was placed in 10 mL of 1 mol / L sulfuric acid for 24 h. After the soaking, the free acid on the membrane surface was rinsed with deionized water and the water on the membrane surface was wiped with filter paper. Phenolphthalein was used as an indicator and titrated with a NaOH standard solution with a concentration of 0.01 mol / L. The volume of the standard solution consumed was recorded. The ion exchange capacity (IEC) was calculated as follows:

[0072] Where, m is the dry weight of the membrane, C NaOH is the molar concentration of NaOH, V' and V are the volume readings after and before titration, respectively.

[0073] Proton conductivity

[0074] The proton conductivity (σ) and surface resistance (AR) of various membranes were measured by electrochemical workstation using the AC impedance method. The frequency range was 10 -2 -10 6 Hz, and the AC amplitude is 5 mV. The calculation formulas for proton conductivity and surface resistance are as follows:

[0075] AR=A×R

[0076] Where σ is the proton conductivity of the membrane (mS·cm -1 ), L is the thickness of the membrane between the positive and negative electrode plates (cm), A is the cross-sectional area of ​​the membrane sample (cm 2 ), R is the actual test value of membrane impedance (Ω), AR is the surface resistance of the membrane (Ω·cm 2 ).

[0077] Vanadium Ion Penetration Test

[0078] The penetration of vanadium ions was tested by diffusion. First, vanadium sulfate (VOSO 4 ) dissolved in 3.0 MH 2 SO 4 Prepare standard vanadium sulfate solution with a concentration of 0.1 mol·L -1 , 0.075 mol·L -1 , 0.03 mol·L -1 、 0.015 mol·L -1 , 0.005 mol·L -1 and 0.0025 mol·L -1 , used to calibrate VOSO 4 Medium V 4+The concentration-absorbance standard curve of Figure 1 As shown, Figure 1 The prepared membrane was sandwiched in a diffusion cell with 50 mL [1.5 M VOSO 4 +3.0 MH 2 SO 4 solution] and 50 mL [1.5 M MgSO 4 +3.0 MH 2 SO 4 ] To avoid concentration polarization, magnetic stirring was maintained on both sides and the same rotation speed was maintained. Every 24 h, a 4 Take a 4 mL sample from one side of the solution and replenish it with 4 mL [1.5 M MgSO 4 +3.0 MH 2 SO 4 ] solution to maintain ion balance. The absorbance of the solution obtained by UV-visible spectrophotometer is then used to obtain the corresponding V according to the calibrated standard curve. 4+ Finally, the permeability of vanadium ions was calculated by the following formula.

[0079]

[0080] Among them, V B is the volume of the solution (mL), t is the time (min), A is the tested membrane area (cm 2 ), L is the thickness of the membrane (cm), P is the vanadium ion permeability of the membrane (cm 2 ·min -1 ), C A For VOSO 4 V in solution 4+ Concentration (mol·L -1 ), C B (t) is MgSO 4 V in solution 4+ Concentration (mol·L -1 ).

[0081] Basic Characterization of Membranes

[0082] Figure 2 It is OPBI-SO 3 XRD patterns of H-GTE film and pure OPBI film. It can be seen from the figure that the pure OPBI film with dense structure only presents a single strong diffraction peak at 2θ=23.6° due to π-π stacking, and its segment spacing corresponds to 4.21 Å. 3Compared with the OPBI membrane, in addition to the diffraction peak at 2θ=22.8°, a new diffraction peak at 2θ=16.9° (5.45 Å) was observed in the H-GTE membrane, which indicates that in the local space where grafting and cross-linking reactions occur, the distance between molecules is expanded due to the presence of long side chains, resulting in an increase in the free volume of the polymer chain.

[0083] Figure 3 It is OPBI-SO 3 SEM image and EDS elemental spectrum diagram of H-GTE membrane, where (a) is SEM surface image; (b) is SEM cross-sectional image; (c) is EDS elemental spectrum diagram. It can be seen from the figure that the membrane is smooth, transparent and dense, with a thickness of about 25 μm, and the S element is evenly distributed in the membrane.

[0084] Figure 4 OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO 3 Schematic diagram of the water absorption and swelling rate test results of H-GTE membrane. It can be seen from the figure that OPBI-SO 3 The water absorption rate of H-GTE membrane is 25.35%, which is 2.4 times that of pure OPBI membrane (10.52%). 3 The anti-swelling property of H membrane is enhanced. This is because the grafted sulfonic acid group has good hydrophilicity, and the grafting and cross-linking of the long side chain expands the free volume of the chain, which can accommodate more water molecules inside the membrane, which will significantly enhance the proton transport process with water as the carrier. After the cross-linking reaction occurs, a continuous cross-linking network is formed in the membrane, and the anti-swelling property of the membrane is enhanced.

[0085] Figure 5 It is Nafion212 membrane, OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO 3 IEC schematic diagram of H-GTE membrane. It can be seen from the figure that OPBI-SO 3 The H-GTE membrane has the highest IEC value (1.57 mmol / g), which is significantly higher than that of Nafion212 membrane (0.84 mmol / g) and OPBI membrane (0.45 mmol / g). 3 - The anion is H + Provides abundant ion exchange sites, resulting in high ion exchange capacity of the membrane. After cross-linking, the long side chains expand the ion conduction channels of the membrane, allowing it to absorb more water molecules and promote ion transport.

[0086] Figure 6 OPBI membrane, OPBI-SO3 H membrane and OPBI-SO 3 Schematic diagram of the water contact angle of H-GTE membrane. The water contact angle of the membrane after grafting and cross-linking decreased from 80.69° to 28.6°, which further illustrates that the hydrophilic sulfonic acid groups, ether bonds and hydroxyl groups in the membrane can adsorb more water molecules and significantly improve its ion transport capacity.

[0087] Figure 7 It is Nafion212 membrane, OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO 3 Schematic diagram of the proton conductivity and surface resistance of H-GTE membrane. It can be seen from the figure that the proton conductivity of pure OPBI membrane is only 30.27 mS·cm -1 , lower than Nafion212 membrane (47.3 mS·cm -1 ), after grafting and cross-linking reaction, OPBI-SO 3 The conductivity of H-GTE membrane reached 74.86 mS·cm -1 , and its surface resistance is as low as 13.40 Ω·cm 2 , which is much lower than the surface resistance of Nafion212 membrane (21.18 Ω·cm 2 ). This is because the introduction of sulfonic acid groups increases the hydrophilicity of the membrane and provides more proton transfer sites, thereby promoting the transfer of protons; after cross-linking, the content of hydroxyl and ether bonds in the membrane is increased, and these hydroxyl and ether bonds form a dynamic hydrogen bond network that is conducive to proton transfer, providing a good ion transfer channel for protons and greatly reducing the surface resistance of the membrane.

[0088] Figure 8 It is Nafion212 membrane, OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO 3 Schematic diagram of vanadium ion permeability of H-GTE membrane. It can be seen from the figure that OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO 3 The vanadium ion permeability of H-GTE membrane is much lower than that of Nafion212 membrane. 3 The H-GTE membrane exhibited a lower vanadium ion permeability (12.63×10 -8 cm 2 ·min -1 ), which indicates that the cross-linked network formed by covalent bonds can effectively limit membrane swelling and reduce the molecular gap, thereby hindering the transmembrane transfer of vanadium ions.

[0089] Flow battery performance

[0090] The membrane performance was tested at room temperature using a flow battery device. The flow battery device mainly consists of the following components: an effective area of ​​4 cm 2 The membrane, two activated carbon felt electrodes, two graphite conductive plates, several gaskets, several bolts and nuts, and two PTFE shells. The structure of the vanadium battery from left to right is: PTFE shell, gasket, graphite conductive plate, gasket, electrode frame, carbon felt electrode, diaphragm. The structure on the right is consistent with the structure on the left and is symmetrically distributed. The above components are fixed by bolts and nuts across both ends. The membrane sample is firmly clamped between the two electrodes in the battery to isolate the positive and negative electrolytes. The positive and negative electrolytes are both vanadium ion solutions dissolved in sulfuric acid.

[0091] After the flow battery is assembled, the variable current charge and discharge performance test is carried out, and the variable current density range is 80-220 mA cm -2 , interval is 20 mA·cm -2 , the cut-off voltage is 0.8-1.7 V. At 200 mA·cm -2 Long-term cycle test was carried out under , and the end voltage was the same as the variable current test. Self-discharge test was carried out at 50% state of charge (SOC), and the change of voltage with shelf time during the test was recorded. The coulombic efficiency (CE), energy efficiency (EE) and voltage efficiency (VE) of the flow battery were calculated using the following formulas.

[0092]

[0093]

[0094]

[0095] Among them, I c is the battery charging current (mA), I d is the battery discharge current (mA), V c is the battery charging voltage (V), V d is the battery discharge voltage (V), and t is the time (s).

[0096] Fig. 9 It is Nafion212 membrane, OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO 3 Schematic diagram of the variable current performance of H-GTE membrane, where (a) is Nafion212 membrane, OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO 3 Schematic diagram of the Coulombic efficiency (CE) of H-GTE membrane, (b) Nafion212 membrane, OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO3 Schematic diagram of voltage efficiency (VE) of H-GTE membrane, (c) Nafion212 membrane, OPBI membrane, OPBI-SO 3 H membrane and OPBI-SO 3 Schematic diagram of the energy efficiency (EE) of H-GTE membrane. As can be seen from the figure, OPBI-SO 3 The coulombic efficiency of H-GTE membrane (98.49%-99.68%) is the highest, which indicates that the tight cross-linked network formed in the membrane effectively enhances the ion selectivity of the membrane. The voltage efficiency test results are consistent with the surface resistance results of various membranes. 3 The voltage efficiency of H-GTE membrane (91.98%-78-95%) is significantly better than other membranes. This is due to the presence of efficient proton transport channels. On the one hand, the presence of sulfonic acid groups and protonated imidazole provides more transport sites for protons. On the other hand, the presence of flexible side chains not only broadens the free volume of the membrane, but also the dynamic hydrogen bond network formed by the ether bonds and hydroxyl groups between the chain segments provides more ion transport channels for protons, thereby improving its voltage efficiency. Based on the excellent coulombic efficiency and voltage efficiency, OPBI-SO 3 The H-GTE membrane showed the best comprehensive performance, with an energy efficiency of 90.60%-78.34%, while the OPBI-SO 3 The comprehensive performance of H membrane (87.48%-74.74%) is better than that of OPBI-SO 3 The H-GTE membrane has certain disadvantages, but it is still higher than the pure OPBI membrane (86.36%-72.45%) and the commercial Nafion212 (90.60%-78.34%) membrane, which also shows that the cross-linked sulfonated polybenzimidazole membrane has a good application scenario in VRFB.

[0097] Fig.10 It is OPBI-SO 3 H-GTE membrane at 200 mA·cm -2 Long-term cycling performance diagram using OPBI-SO 3 The all-vanadium liquid flow battery assembled with H-GTE membrane cycled for a total of about 1,200 times with a cycle time of 720 h. Its good ion selectivity gave it an excellent coulombic efficiency (>99%), and its energy efficiency was almost constant throughout the test, remaining at around 80%. This indicates that the cross-linked sulfonated polybenzimidazole membrane with grafted and cross-linked structure can not only efficiently conduct protons during the dynamic charge and discharge process of VRFB, but also has excellent long-term chemical stability under the strong acidity and strong oxidizing conditions of the electrolyte.

[0098] Fig.11 It is Nafion212 membrane, OPBI membrane, OPBI-SO3 H membrane and OPBI-SO 3 Schematic diagram of the self-discharge curve of H-GTE membrane. 3 The self-discharge time of H-GTE membrane can reach 54 h, which is much longer than that of OPBI membrane (34 h) and Nafion212 membrane (24 h). 2+ The ion permeation results are consistent with the coulombic efficiency of the battery, which proves that the cross-linked sulfonated polybenzimidazole membrane prepared in the present invention has excellent ion selectivity.

[0099] Example 2

[0100] Sulfonated polybenzimidazole (OPBI-SO 3 H) Membrane preparation

[0101] Under nitrogen atmosphere, OPBI (2.5 mmol, 1 g) was added to 50 g of dimethyl sulfoxide and stirred at 80 °C for 2 h. After complete dissolution, anhydrous K 2 CO 3 powder (3.75 mmol, 0.52 g) was used as the reaction catalyst, and OPBI was reacted with anhydrous K 2 CO 3 The molar ratio of the powder was 1:1.5, and then 1,4-butane sultone (0.25 mmol, 0.034 g) was slowly added. The molar ratio of OPBI to 1,4-butane sultone was 10:1. The reaction was carried out at 40 °C for 24 h. After the reaction, the mixture was poured into acetone to precipitate the polymer, and washed with water and ethanol several times until the solution became colorless. Finally, the precipitate was vacuum dried at 60 °C for 24 h to obtain 0.86 g OPBI-SO 3 H.

[0102] Cross-linked sulfonated polybenzimidazole (OPBI-SO 3 Preparation of H-GTE membrane

[0103] OPBI-SO 3 H (0.93 mmol, 0.5 g) solid was dissolved in 25 g of dimethyl sulfoxide to obtain a 2% solution, and glycerol triglycidyl ether (GTE) (0.093 mmol, 0.024 g) and OPBI-SO 3 The molar ratio of H to GTE was 10:1. The temperature was raised to 80 °C for 24 h. After the reaction, the mixture was poured into acetone to precipitate the polymer and washed with water and ethanol several times until the solution became colorless. Finally, the precipitate was vacuum dried at 60 °C for 24 h to obtain 0.43 g OPBI-SO 3 H-GTE product.

[0104] 0.5 g OPBI-SO 3 H-GTE solid was dissolved in 25 g of dimethyl sulfoxide to obtain a 2% solution. 2.0 mL of the solution was added to an ultra-flat dish and dried in an oven at 80 °C for 24 h to obtain OPBI-SO with a thickness of 25 μm and a uniform surface. 3 The prepared membrane was placed in 10 mL of 85 wt% phosphoric acid solution and left to stand for 24 h for activation pretreatment. After being taken out, it was washed several times with deionized water to obtain the activated OPBI-SO 3 H-GTE membrane.

[0105] Example 3

[0106] Sulfonated polybenzimidazole (OPBI-SO 3 H) Membrane preparation

[0107] Under nitrogen atmosphere, OPBI (2.5 mmol, 1 g) was added to 50 g of dimethyl sulfoxide and stirred at 80 °C for 2 h. After complete dissolution, anhydrous K 2 CO 3 powder (3.75 mmol, 0.52 g) was used as the reaction catalyst, and OPBI was reacted with anhydrous K 2 CO 3 The molar ratio of the powder was 1:1.5, and then 1,3-propane sultone (0.25 mmol, 0.03 g) was slowly added. The molar ratio of OPBI to 1,3-propane sultone was 10:1. The reaction was carried out at 40 °C for 24 h. After the reaction, the mixture was poured into acetone to precipitate the polymer, and washed with water and ethanol several times until the solution became colorless. Finally, the precipitate was vacuum dried at 60 °C for 24 h to obtain 0.84 g OPBI-SO 3 H.

[0108] Cross-linked sulfonated polybenzimidazole (OPBI-SO 3 Preparation of H-GDE membrane

[0109] OPBI-SO 3 H (0.95 mmol, 0.5 g) solid was dissolved in 25 g of dimethyl sulfoxide to obtain a 2% solution, and ethylene glycol diglycidyl ether (GDE) (0.095 mmol, 0.016 g) and OPBI-SO 3The molar ratio of H to GDE was 10:1. The temperature was raised to 80 °C for 24 h. After the reaction, the mixture was poured into acetone to precipitate the polymer and washed with water and ethanol several times until the solution became colorless. Finally, the precipitate was vacuum dried at 60 °C for 24 h to obtain 0.41 g OPBI-SO 3 H-GDE product.

[0110] 0.5 g OPBI-SO 3 The H-GDE solid was dissolved in 25 g of dimethyl sulfoxide to obtain a 2% solution. 2.0 mL of the solution was added to an ultra-flat dish and dried in an oven at 80 °C for 24 h to obtain an OPBI-SO with a thickness of 25 μm and a uniform surface. 3 The prepared membrane was placed in 10 mL of 85 wt% phosphoric acid solution and left to stand for 24 h for activation pretreatment. After being taken out, it was washed several times with deionized water to obtain the activated OPBI-SO 3 H-GDE membrane.

[0111] Example 4

[0112] Sulfonated polybenzimidazole (OPBI-SO 3 H) Membrane preparation

[0113] Under nitrogen atmosphere, OPBI (2.5 mmol, 1 g) was added to 50 g of dimethyl sulfoxide and stirred at 80 °C for 2 h. After complete dissolution, anhydrous K 2 CO 3 powder (3.75 mmol, 0.52 g) was used as the reaction catalyst, and OPBI was reacted with anhydrous K 2 CO 3 The molar ratio of the powder was 1:1.5, and then 1,3-propane sultone (0.5 mmol, 0.061 g) was slowly added. The molar ratio of OPBI to 1,3-propane sultone was 5:1. The reaction was carried out at 40 °C for 24 h. After the reaction, the mixture was poured into acetone to precipitate the polymer, and washed with water and ethanol several times until the solution became colorless. Finally, the precipitate was vacuum dried at 60 °C for 24 h to obtain 0.92 g OPBI-SO 3 H.

[0114] Cross-linked sulfonated polybenzimidazole (OPBI-SO 3 Preparation of H-GTE membrane

[0115] OPBI-SO 3H (0.95 mmol, 0.5 g) solid was dissolved in 25 g of dimethyl sulfoxide to obtain a 2% solution, and glycerol triglycidyl ether (GTE) (0.095 mmol, 0.025 g) and OPBI-SO 3 The molar ratio of H to GTE was 10:1. The temperature was raised to 80 °C for 24 h. After the reaction, the mixture was poured into acetone to precipitate the polymer, and then washed with water and ethanol several times until the solution became colorless. Finally, the precipitate was vacuum dried at 60 °C for 24 h to obtain 0.44 g OPBI-SO 3 H-GTE product.

[0116] 0.5 g OPBI-SO 3 H-GTE solid was dissolved in 25 g of dimethyl sulfoxide to obtain a 2% solution. 2.0 mL of the solution was added to an ultra-flat dish and dried in an oven at 80 °C for 24 h to obtain OPBI-SO with a thickness of 25 μm and a uniform surface. 3 The prepared membrane was placed in 10 mL of 85 wt% phosphoric acid solution and left to stand for 24 h for activation pretreatment. After being taken out, it was washed several times with deionized water to obtain the activated OPBI-SO 3 H-GTE membrane.

[0117] Example 5

[0118] Sulfonated polybenzimidazole (OPBI-SO 3 H) Membrane preparation

[0119] Under nitrogen atmosphere, OPBI (2.5 mmol, 1 g) was added to 50 g of dimethyl sulfoxide and stirred at 80 °C for 2 h. After complete dissolution, anhydrous K 2 CO 3 powder (3.75 mmol, 0.52 g) was used as the reaction catalyst, and OPBI was reacted with anhydrous K 2 CO 3 The molar ratio of the powder was 1:1.5, and then 1,3-propane sultone (0.25 mmol, 0.03 g) was slowly added. The molar ratio of OPBI to 1,3-propane sultone was 10:1. The reaction was carried out at 40 °C for 24 h. After the reaction, the mixture was poured into acetone to precipitate the polymer, and washed with water and ethanol several times until the solution became colorless. Finally, the precipitate was vacuum dried at 60 °C for 24 h to obtain 0.84 g OPBI-SO 3 H.

[0120] Cross-linked sulfonated polybenzimidazole (OPBI-SO3 Preparation of H-GTE membrane

[0121] OPBI-SO 3 H (0.95 mmol, 0.5 g) solid was dissolved in 25 g of dimethyl sulfoxide to obtain a 2% solution, and glycerol triglycidyl ether (GTE) (0.19 mmol, 0.049 g) and OPBI-SO 3 The molar ratio of H to GTE was 5:1. The temperature was raised to 80 °C for 24 h. After the reaction, the mixture was poured into acetone to precipitate the polymer, and then washed with water and ethanol several times until the solution became colorless. Finally, the precipitate was vacuum dried at 60 °C for 24 h to obtain 0.44 g OPBI-SO 3 H-GTE product.

[0122] 0.5 g OPBI-SO 3 H-GTE solid was dissolved in 25 g of dimethyl sulfoxide to obtain a 2% solution. 2.0 mL of the solution was added to an ultra-flat dish and dried in an oven at 80 °C for 24 h to obtain OPBI-SO with a thickness of 25 μm and a uniform surface. 3 The prepared membrane was placed in 10 mL of 85 wt% phosphoric acid solution and left to stand for 24 h for activation pretreatment. After being taken out, it was washed several times with deionized water to obtain the activated OPBI-SO 3 H-GTE membrane.

[0123] Table 1 shows the performance results of the membranes prepared in the examples of the present invention and the comparative examples.

[0124] Table 1

[0125] From the data in Table 1, it can be seen that Example 1 has the best comprehensive performance, thanks to OPBI-SO 3 The H-GTE membrane has efficient proton transport channels and cross-linked networks, with coulombic efficiency and voltage efficiency of 200 mA cm -2 The energy efficiency of the membrane was 99.40% and 80.73% respectively, which was better than the pure OPBI membrane in comparative example 1 (98.73%, 75.36%) and the Nafion212 membrane in comparative example 2 (97.54%, 75.60%). Based on the excellent coulombic efficiency and voltage efficiency, its energy efficiency was 80 mA·cm -2 and 200 mA·cm -2 The OPBI pure membrane of Comparative Example 1 and the Nafion212 membrane of Comparative Example 2 reached 90% and 80% respectively at 200 mA·cm-2 The energy efficiency at high current density is only 74.41% and 73.74%. This shows that the cross-linked sulfonated polybenzimidazole membrane prepared by the present invention has higher ionic conductivity while maintaining its excellent selectivity and stability, showing great application potential.

[0126] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment, it is not used to limit the present invention. Any technician familiar with this patent can make some changes or modify the technical contents suggested above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the solution of the present invention.

Claims

1. A method for preparing a cross-linked sulfonated polybenzimidazole membrane, characterized in that: The following steps are involved: The first step is to add polybenzimidazole to the first solvent under a nitrogen atmosphere, stir for 1 to 3 hours at a temperature of 60 to 100 ° C, add anhydrous potassium carbonate powder, the molar ratio of polybenzimidazole to anhydrous potassium carbonate powder is 1:1 to 2, and then slowly add a sulfonating agent, the molar ratio of polybenzimidazole to the sulfonating agent is 8 to 20:1, react at a temperature of 30 to 50 ° C for 1 to 48 hours, and obtain sulfonated polybenzimidazole after post-treatment; The sulfonating agent is selected from at least one of 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, vinyl sultone, benzene sultone, ethylene sultone, and functionalized sultone derivatives; The second step is to dissolve the sulfonated polybenzimidazole in a second solvent to obtain a solution with a mass fraction of 1-10%, add a crosslinking agent, and the molar ratio of the sulfonated polybenzimidazole to the crosslinking agent is 1-20:1, heat to 60-100 °C for reaction for 1-48 h, and obtain a crosslinked sulfonated polybenzimidazole after post-treatment; The cross-linking agent is selected from at least one of glycerol triglycidyl ether, ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, and pentaerythritol glycidyl ether; The third step is to dissolve the cross-linked sulfonated polybenzimidazole in a third solvent, dry to obtain a cross-linked sulfonated polybenzimidazole membrane, and activate to obtain an activated cross-linked sulfonated polybenzimidazole membrane.

2. The method for preparing a cross-linked sulfonated polybenzimidazole membrane according to claim 1, characterized in that: The first solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, and methanesulfonic acid; The post-treatment step in the first step is as follows: the mixture is poured into acetone to precipitate the polymer, and washed with water and ethanol several times until the solution becomes colorless, and dried.

3. The method for preparing a cross-linked sulfonated polybenzimidazole membrane according to claim 1, characterized in that: The preparation method of the polybenzimidazole comprises the following steps: Under a nitrogen atmosphere, phosphorus pentoxide and methane sulfonic acid in a mass ratio of 1:1-20 are mixed, 3,3'-diaminobenzidine and 4,4'-dicarboxy diphenyl ether in a molar ratio of 1:1-2 are added, and the mass ratio of phosphorus pentoxide to 3,3'-diaminobenzidine is 1-5:

1. Under stirring conditions, the reaction system is heated to 90-110°C and stirred for 1-3 hours, and then the temperature is raised to 130-150°C for reaction for 1-5 hours to obtain the polybenzimidazole.

4. The method for preparing a cross-linked sulfonated polybenzimidazole membrane according to claim 1, characterized in that: The second solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, and methanesulfonic acid; The post-treatment step in the second step is as follows: the mixture is poured into acetone to precipitate the polymer, and washed with water and ethanol several times until the solution becomes colorless, and dried.

5. The method for preparing a cross-linked sulfonated polybenzimidazole membrane according to claim 1, characterized in that: The cross-linked sulfonated polybenzimidazole is dissolved in the third solvent to obtain a solution with a mass fraction of 1 to 10%.

6. The method for preparing a cross-linked sulfonated polybenzimidazole membrane according to claim 1, characterized in that: The third solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, and methanesulfonic acid.

7. The method for preparing a cross-linked sulfonated polybenzimidazole membrane according to claim 1, characterized in that: The thickness of the cross-linked sulfonated polybenzimidazole membrane is 20-30 μm; The activation step in the third step is as follows: placing the prepared membrane in a phosphoric acid solution with a mass concentration of 85 wt% and standing for 1 to 48 hours for activation pretreatment, and washing with deionized water for multiple times.

8. A cross-linked sulfonated polybenzimidazole membrane, characterized in that: The cross-linked sulfonated polybenzimidazole membrane is prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the cross-linked sulfonated polybenzimidazole membrane according to claim 8 in preparing a liquid flow battery.

10. The use according to claim 9, characterized in that: The flow battery is selected from at least one of an all-vanadium flow battery, a lithium-ion flow battery, a zinc-bromine flow battery, a zinc-cerium flow battery, a zinc-nickel flow battery, a lead flow battery, an iron-chromium flow battery, a sodium polysulfide / bromine flow battery or an all-iron flow battery.

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