A graft crosslinking strategy for the preparation of polybenzimidazole membranes and its application

Abstract

This invention discloses a method for preparing a polybenzimidazole membrane regulated by a grafting and crosslinking strategy, comprising the following steps: First, at a temperature of 60-100°C, a polybenzimidazole compound is dissolved in a first solvent, a solution containing a quaternary ammonium salt grafting agent is added, and the mixture is sonicated to obtain grafted polybenzimidazole powder; Second, the grafted polybenzimidazole powder obtained in the first step is dissolved in a second solvent, and sonicated at a temperature of 40-80°C for 0.1-2 h, a sulfonating agent is added dropwise, and the mixture is sonicated until homogeneous to obtain a sulfonated polybenzimidazole casting solution; Third, the mixture is dried to obtain a polybenzimidazole membrane regulated by the grafting and crosslinking strategy. The grafted and crosslinked polybenzimidazole membrane prepared by the method of this invention exhibits ideal proton conductivity, high selectivity, and chemical stability, which is of great significance for promoting the large-scale application of polybenzimidazole membranes in vanadium redox flow batteries.

Description

Technical Field

[0001] This invention belongs to the field of ion conduction membrane technology for flow batteries, specifically, it relates to a method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy and its application. Background Technology

[0002] Faced with global energy supply and demand imbalances and the challenges of climate change, the replacement of traditional fossil fuels with renewable energy sources such as wind and solar power has become an inevitable trend in energy transformation. However, the inherent intermittency and instability of renewable energy urgently necessitate the development of energy storage technologies. Redox flow batteries (RFBs), as a key component of emerging electrochemical energy storage systems, have attracted considerable attention due to their scalability, environmental compatibility, safety, and cost-effectiveness. Among them, vanadium redox flow batteries (VRFBs) utilize redox reactions between different vanadium ion valence states to achieve bidirectional conversion between chemical and electrical energy, offering advantages such as excellent performance, recyclable electrolytes, and controllable costs. The ion-conducting membrane (ICM) is a crucial component in VRFBs, serving a dual function: physically separating the positive and negative electrode electrolytes to prevent cross-mixing of active materials, while simultaneously transporting protons to form a circuit. An ideal membrane must possess high proton conductivity, high selectivity, excellent mechanical strength, and chemical stability. Commercial perfluorosulfonic acid (PFSA) membranes have exhibited satisfactory proton conductivity and stability, but their severe vanadium ion cross-mixing, high price, and potential environmental hazards hinder their further application.

[0003] Non-fluoropolymers have developed rapidly in recent years, providing cost-effective alternatives to perfluorosulfonic acid proton exchange membranes (PFSA membranes), including sulfonated polyether ether ketone (SPEEK), polybenzimidazole (PBI), sulfonated polyimide (SPI), and sulfonated polysulfone (SPSF). Among these, the dense molecular structure of PBI effectively inhibits vanadium permeation. However, its tightly packed polymer chains hinder continuous proton conduction pathways. Acid doping strategies (phosphoric acid swelling or sulfuric acid treatment) are used to break the intermolecular hydrogen bonds between =N– and –NH– groups, thereby increasing the free volume, improving the original dense structure, and enhancing proton conductivity. However, even acid-treated PBI membranes struggle to achieve the excellent conductivity expected as a fluorine-free alternative, falling short of Nafion's performance. Therefore, further development of polybenzimidazole membranes is needed to improve proton conductivity while maintaining the selectivity and stability of PBI membranes. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy.

[0005] Another object of the present invention is the application of the polybenzimidazole membrane prepared by the method described above in the preparation of flow batteries.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a polybenzimidazole membrane by controlling a graft crosslinking strategy, comprising the following steps:

[0008] Step 1, grafting reaction: Under the condition of 60~100 ℃ (preferably 80 ℃), polybenzimidazole compounds are dissolved in the first solvent, and a solution containing quaternary ammonium salt grafting agent is added. The molar ratio of polybenzimidazole compounds to quaternary ammonium salt grafting agent is 1:0.1~3 (preferably 1:2, 1:1). The mixture is sonicated, and the solution is poured into acetone to precipitate flocculent matter. The precipitate is separated by filtration, and the precipitate is soaked and washed with pure water and anhydrous ethanol. After filtration, the precipitate is dried to obtain grafted polybenzimidazole powder.

[0009] The polybenzimidazole compound is selected from at least one of poly(m-phenyl)-5,5'-bibenzimidazole (mPBI), poly(p-phenyl)-5,5'-bibenzimidazole (pPBI), poly(p-diphenyl ether)-5,5'-bibenzimidazole (OPBI), and poly(2,5-benzimidazole) (ABPBI);

[0010] The quaternary ammonium salt grafting agent is selected from at least one of glycidyltrimethylammonium chloride (GTA), glycidyltriethylammonium chloride, glycidylbenzyldimethylammonium chloride, glycidyldimethyldodecylammonium chloride, diglycidyldimethylammonium chloride, and glycidylpyridineammonium chloride derivatives.

[0011] The second step, sulfonation and cross-linking reaction: The grafted polybenzimidazole powder obtained in the first step is dissolved in a second solvent to obtain a solution with a concentration of 1~10% g / mL (preferably 2% g / mL). The solution is ultrasonicated at a temperature of 40~80 ℃ (preferably 60 ℃) for 0.1~2 h (preferably 0.5 h). A sulfonating agent is added dropwise, and the mass ratio of the sulfonating agent to the grafted polybenzimidazole powder obtained in the first step is 1:0.5~20 (preferably 1:2.1, 1:3.9, 1:4.5, 1:5, 1:10). The solution is ultrasonically vibrated until homogeneous to obtain a sulfonated polybenzimidazole casting solution.

[0012] The sulfonating agent is selected from at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, vinylsulfonate lactone, benzosulfonate lactone, ethylenesulfonate lactone, and functionalized sulfonate lactone derivatives.

[0013] The third step is membrane preparation: the sulfonated polybenzimidazole casting solution obtained in the second step is dried to obtain a polybenzimidazole membrane controlled by the graft crosslinking strategy.

[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] In the first step, the conditions for drying the precipitate are: drying at a temperature of 100~150 ℃ (preferably 120 ℃) ​​for 1~48 h (preferably 24 h).

[0016] Preparation of the solution containing the quaternary ammonium salt grafting agent: Dissolve the quaternary ammonium salt grafting agent in dimethyl sulfoxide to a concentration of 0.01~1 g / mL (preferably 0.02, 0.022, 0.024, 0.05, or 0.046 g / mL).

[0017] The conditions for ultrasound in the first step are: a temperature of 60~100 ℃ (preferably 80 ℃) and 100 W ultrasound for 0.1~2 h (preferably 0.5 h).

[0018] The second solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, and methanesulfonic acid.

[0019] The conditions for uniform ultrasonic oscillation in the second step are: a temperature of 50~70 ℃ (preferably 60 ℃) and 100 W ultrasound for 0.1~2 h (preferably 0.5 h).

[0020] In the third step, the drying conditions are: drying at a temperature of 60~100 ℃ (preferably 80 ℃) for 1~48 h (preferably 24 h).

[0021] The drying in the third step is carried out in a casting dish (a superplate with a diameter of 46 mm).

[0022] The grafting and crosslinking strategy controls the thickness of the polybenzimidazole membrane to be 10~50 μm (preferably 25 μm).

[0023] The grafting rate of the grafted polybenzimidazole is 100-200% (preferably 100% or 200%).

[0024] In a second aspect, the present invention provides a graft crosslinking strategy for regulating polybenzimidazole membranes prepared by the method described above.

[0025] A second aspect of the present invention provides an application of the polybenzimidazole membrane in the preparation of a flow battery.

[0026] The flow battery is selected from vanadium redox flow batteries, lithium-ion flow batteries, zinc-bromine flow batteries, zinc-cerium flow batteries, zinc-nickel flow batteries, lead flow batteries, iron-chromium flow batteries, sodium polysulfide / bromine flow batteries, or all-iron flow batteries.

[0027] By adopting the above technical solution, the present invention has the following advantages and beneficial effects:

[0028] The grafting and crosslinking strategy for polybenzimidazole membranes prepared by the method of this invention provides grafted side chains and a crosslinked structure. Quaternary ammonium groups and hydroxyl groups are introduced through an N-substitution ring-opening reaction, and a sulfonating agent is added to the hydroxyl sites on the grafted side chains. The crosslinked structure is formed simultaneously during the introduction of sulfonic acid groups. The coexistence of quaternary ammonium groups and sulfonic acid groups creates a rich hydrophilic network, inducing the formation of different microphase separation structures and ion transport channels. Simultaneously, the continuous crosslinked network significantly improves the mechanical strength of the polybenzimidazole membrane. The grafting and crosslinking strategy for polybenzimidazole membranes prepared by the method of this invention exhibits ideal proton conductivity, high selectivity, and chemical stability, which is of great significance for promoting the large-scale application of polybenzimidazole membranes in vanadium redox flow batteries.

[0029] The method of the present invention is simple and easy to industrialize, and the reaction can be completed simply by mixing and heating. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the grafting reaction.

[0031] Figure 2 This is a schematic diagram of the synthesis of sulfonated substituted hydroxyl groups.

[0032] Figure 3 This is a schematic diagram of cross-linking synthesis.

[0033] Figure 4 This is a scanning electron microscope (SEM) schematic diagram of the surface and cross-section of the PBI-GTA-PS film.

[0034] Figure 5 This is a schematic diagram of the infrared spectra of the PBI-GTA-PS film and the PBI-GTA film.

[0035] Figure 6 These are the XPS spectra of the PBI-GTA-PS membrane and the PBI-GTA membrane.

[0036] Figure 7 These are tensile strength diagrams for PBI membrane, PBI-GTA membrane, and PBI-GTA-PS membrane.

[0037] Figure 8 PBI-GTA membrane, PBI-GTA-PS membrane, and Nafion 212 membrane are used in the range of 80-220 mA cm⁻¹. -2 The efficiency of a single vanadium redox flow cell at current density is shown in the figure.

[0038] Figure 9 It is a PBI-GTA-PS membrane at 160 mA cm⁻¹ -2 A schematic diagram of the long-cycle performance at current density. Detailed Implementation

[0039] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0040] Example 1

[0041] A method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy includes the following steps:

[0042] Step 1, Grafting reaction: In a round-bottom flask, 100 mL of dimethyl sulfoxide and 3 g of poly(2,2'-(p-diphenyl ether)-5,5'-bibenzimidazole (OPBI) powder (7.5 mmol (based on repeating units)) were added. The mixture was heated in an oil bath with stirring at 80 °C to form a dark reddish-brown solution. Then, 50 mL of a dimethyl sulfoxide solution containing 15 mmol (2.3 g) of glycidyltrimethylammonium chloride (GTA) was added. The mixture was sonicated at 100 W for 0.5 h at 80 °C. The reaction process is as follows: Figure 1 As shown, Figure 1 This is a schematic diagram of the grafting reaction. The solution was poured into acetone, and a milky white flocculent substance precipitated. The precipitate was separated by filtration. The precipitate was soaked and washed with pure water and anhydrous ethanol, filtered, and dried in a vacuum drying oven at 120 °C for 24 h to obtain 5.3 g of grafted polybenzimidazole powder, with a yield of 100% and a grafting rate of 200%.

[0043] The second step, sulfonation and cross-linking reaction: 0.5 g of the grafted polybenzimidazole powder obtained in the first step was dissolved in 25 mL of dimethyl sulfoxide to obtain a solution with a concentration of 2% g / mL. The solution was sonicated at 60 ℃ for 0.5 h. Then, 0.8 mmol (0.1 g) of 1,3-propanesulfonic acid lactone was added dropwise, and the solution was sonicated at 100 W for 0.5 h at 60 ℃ to obtain 25 mL of sulfonated polybenzimidazole, i.e., PBI-GTA-PS casting solution. The reaction process is as follows: Figure 2 and Figure 3 As shown. Figure 2 This is a schematic diagram of the synthesis of sulfonated substituted hydroxyl groups. Figure 3 This is a schematic diagram of cross-linking synthesis.

[0044] The third step is membrane preparation: 3 mL of sulfonated polybenzimidazole, i.e., PBI-GTA-PS casting solution obtained in the second step is added to a casting dish (a 46 mm diameter ultraplate, manufacturer: Flat glass, the same device used below), and dried in an oven at 80 ℃ for 24 h to remove the solvent, resulting in a 25 μm thick graft crosslinking strategy-controlled polybenzimidazole membrane, i.e., PBI-GTA-PS membrane, which is a deep yellow and transparent color.

[0045] Comparative Example 1

[0046] In the first step, 100 mL of dimethyl sulfoxide and 3 g of poly(2,2'-(p-diphenyl ether)-5,5'-bibenzimidazole (OPBI) powder (7.5 mmol (based on repeating units)) were added to a round-bottom flask. The mixture was heated and stirred in an oil bath at 80 °C to form a dark reddish-brown solution. Then, 50 mL of a dimethyl sulfoxide solution containing glycidyltrimethylammonium chloride (GTA) (15 mmol, 2.3 g) was added. The mixture was sonicated at 100 W for 0.5 h at 80 °C. The solution was then poured into acetone to precipitate a milky-white flocculent substance. The precipitate was separated by filtration. The precipitate was soaked and washed with pure water and anhydrous ethanol, filtered, and dried in a vacuum drying oven at 120 °C for 24 h to obtain 5.3 g of grafted polybenzimidazole powder, with a yield of 100% and a grafting rate of 200%.

[0047] In the second step, 0.5 g of the grafted polybenzimidazole powder obtained in the first step was dissolved in 25 mL of dimethyl sulfoxide to obtain a solution with a concentration of 2% g / mL. The solution was then sonicated at 60 ℃ for 0.5 h to obtain 25 mL of PBI-GTA casting solution.

[0048] The third step is membrane preparation: 3 mL of the PBI-GTA casting solution obtained in the second step is added to a casting dish, and the solution is dried in an oven at 80 ℃ for 24 h to remove the solvent, resulting in a polybenzimidazole membrane, i.e., the PBI-GTA membrane. The membrane has a thickness of 25 μm and is yellow and transparent.

[0049] Comparative Example 2

[0050] In a round-bottom flask, 100 mL of dimethyl sulfoxide and OPBI powder (7.5 mmol (based on repeating units), 3 g) were added. The mixture was heated and stirred in an oil bath at 80 °C to form a dark reddish-brown solution. 3 mL of the solution was added to a casting dish and dried in an oven at 80 °C for 24 h to remove the solvent, resulting in a 25 μm thick polybenzimidazole membrane, i.e., a PBI membrane, which was pale yellow and transparent.

[0051] Membrane structural characterization

[0052] Scanning electron microscope images and surface morphology of the PBI-GTA-PS film prepared in Example 1 are shown below. Figure 4 As shown, Figure 4 This is a scanning electron microscope (SEM) schematic diagram of the surface and cross-section of the PBI-GTA-PS film. As can be seen from the image, the PBI-GTA-PS film exhibits a uniform and dense structure with no obvious defects.

[0053] To confirm the successful preparation of the PBI-GTA membrane in Comparative Example 1 and the PBI-GTA-PS membrane in Example 1, their chemical structures were verified using FTIR, and the results are as follows: Figure 5 As shown, Figure 5 This is a schematic diagram of the infrared spectra of the PBI-GTA-PS film and the PBI-GTA film. As can be seen from the figure, in the PBI-GTA film, at 962 cm⁻¹... -1 The appearance of a characteristic peak confirms the successful grafting of the quaternary ammonium group (-CH2N). + (CH3)3). After sulfonation, the PBI-GTA-PS membrane prepared in Example 1 was subjected to a reaction at 1168 cm⁻¹. -1 and 1038 cm -1 The peak at that location corresponds to the characteristic absorption of the O=S=O group, confirming the presence of the sulfonic acid group.

[0054] XPS results are as follows Figure 6 As shown, Figure 6 These are the XPS spectra of the PBI-GTA-PS and PBI-GTA films. XPS analysis provides further evidence for the chemical structures of the PBI-GTA and PBI-GTA-PS films. The N1s spectrum shows three distinct peaks at 401.33 eV, 398.65 eV, and 396.70 eV, corresponding to -N, respectively. + The PBI-GTA-PS membrane exhibits a small characteristic double peak near 160 eV, identified as an S2p signal, indicating the successful introduction of sulfonic acid groups.

[0055] The tensile strength of the membrane is characterized, such as... Figure 7 As shown, Figure 7 The figures show the tensile strength of the PBI membrane, PBI-GTA membrane, and PBI-GTA-PS membrane. The tensile strength of the unmodified pure PBI membrane (prepared in Comparative Example 2) is 76 MPa. After grafting (prepared in Comparative Example 1), its strength decreases to 50 MPa. However, after sulfonation and crosslinking (prepared in Example 1), the membrane strength significantly increases to 94 MPa, indicating that the grafting strategy can effectively improve the mechanical properties of the membrane.

[0056] Characterization of membrane battery performance

[0057] The 25 μm thick PBI-GTA-PS membrane prepared in Example 1 was used for performance testing in a vanadium redox flow battery. The flow battery device mainly consists of the following components: a 25 μm thick 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 redox flow battery from left to right is as follows: PTFE shell, gasket, graphite conductive plate, gasket, electrode frame, carbon felt electrode, and separator. The structure on the right side is consistent with the structure on the left side and is symmetrically distributed. All components are fixed by bolts and nuts passing through both ends. The membrane sample is firmly clamped between the two electrodes inside the battery to isolate the positive and negative electrolytes. The positive electrolyte in the vanadium redox system is 1.5 M VOCs. 2+ / VO2 + And 3 MH2SO4, the negative electrode is 1.5 MV 2+ / V 3+ The system contained 3 M H₂SO₄ and required inert gas protection during testing. Charge-discharge tests were performed at constant current density and cutoff voltages of 0.8 V and 1.7 V. All tests were conducted at room temperature.

[0058] In 80-220 mA cm -2 The coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) were evaluated at the specified current density, and the test methods were in accordance with NB / T 42081-2016. Figure 8 PBI-GTA membrane, PBI-GTA-PS membrane, and Nafion 212 membrane are used in the range of 80-220 mA cm⁻¹. -2 The graph shows the efficiency of a single vanadium redox flow cell at various current densities. The Nafion 212 membrane is a perfluorosulfonic acid membrane manufactured by DuPont. The left graph shows the efficiency of the PBI-GTA membrane, PBI-GTA-PS membrane, and Nafion 212 membrane at current densities ranging from 80 to 220 mA / cm². -2 A schematic diagram illustrating the coulombic efficiency results at current densities ranging from 80 to 220 mA cm⁻¹. The middle figure shows the coulombic efficiency of the PBI-GTA membrane, PBI-GTA-PS membrane, and Nafion 212 membrane at current densities ranging from 80 to 220 mA cm⁻¹. -2 The diagram illustrates the energy efficiency results at current densities ranging from 80 to 220 mA cm⁻¹. The right figure shows the PBI-GTA membrane, PBI-GTA-PS membrane, and Nafion 212 membrane at these current densities. -2 A schematic diagram showing the voltage efficiency results at a given current density.

[0059] As shown in the figure, all membranes exhibited higher CE (ce) with increasing current density. This is due to the shorter cycle time per charge-discharge cycle, which minimizes vanadium ion cross-linking. Simultaneously, ohmic and concentration polarization induced by high current density led to varying degrees of EE (exchange rate reduction). Notably, the PBI-GTA-PS membrane prepared in Example 1 exhibited the best CE and EE performance. Regarding CE enhancement, the formation of the cross-linked network ensured the structural stability of the continuous proton transport channels in the PBI-GTA-PS membrane, where the introduction of long side chains maintained the integrity of the main chain while promoting improved selectivity. In terms of VE (velocity-enhancing) performance, the abundant hydrophilic groups induced different microphase separation structures in the PBI-GTA-PS membrane, thereby achieving high VE in VRFB operation without acid swelling pretreatment. In contrast, the PBI membrane prepared in Comparative Example 2 failed to charge and discharge normally under these test conditions, demonstrating the effectiveness of the graft cross-linking strategy. Similarly, the CE, VE, and EE of the PBI-GTA membrane prepared in Comparative Example 1 were all lower than those of the PBI-GTA-PS membrane prepared in Example 1, indicating that the introduction of the crosslinking network can simultaneously improve the barrier properties and selectivity of the membrane, and is expected to overcome the trade-off effect of the separator.

[0060] At 160 mA cm -2 A vanadium redox flow battery equipped with a PBI-GTA-PS membrane was subjected to cycle testing at a current density of [value missing] to evaluate the long-term stability of the membrane. The test method followed NB / T 42081-2016. The results are as follows: Figure 9 As shown, Figure 9 It is a PBI-GTA-PS membrane at 160 mA cm⁻¹ -2 A schematic diagram of the long-cycle performance at the specified current density is shown. As can be seen from the figure, the PBI-GTA-PS membrane prepared in Example 1 of this invention maintains excellent capacity retention and exhibits superior durability exceeding 1000 cycles, further validating the advantages of the cross-linked structure. These results collectively confirm the structural advantages of the PBI-GTA-PS membrane in terms of balanced ion selectivity, proton conductivity, and operational stability in VRFB applications.

[0061] Example 2

[0062] A method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy includes the following steps:

[0063] Step 1, Grafting reaction: In a round-bottom flask, 100 mL of dimethyl sulfoxide and poly(p-phenyl)-5,5'-bibenzimidazole (pPBI) powder (7.5 mmol (based on repeating units), 2.3 g) were added. Under oil bath heating and stirring at 80 °C, a dark reddish-brown solution was formed. 50 mL of dimethyl sulfoxide solution containing glycidyltrimethylammonium chloride (GTA) (15 mmol, 2.3 g) was added. The solution was sonicated at 100 W for 0.5 h at 80 °C. The solution was poured into acetone, and a white flocculent precipitate was formed. The precipitate was separated by filtration. The precipitate was soaked and washed with pure water and anhydrous ethanol, filtered, and dried in a vacuum drying oven at 120 °C for 24 h to obtain 4.6 g of grafted polybenzimidazole powder, with a yield of 100% and a grafting rate of 200%.

[0064] The second step, sulfonation and crosslinking reaction: 0.5 g of the grafted polybenzimidazole powder obtained in the first step was dissolved in 25 mL of dimethyl sulfoxide to obtain a solution with a concentration of 2% g / mL. The solution was sonicated at 60 ℃ for 0.5 h, and 1,3-propanesulfonic acid lactone (0.9 mmol, 0.11 g) was added dropwise. The solution was sonicated at 60 ℃ and 100 W for 0.5 h to obtain 25 mL of sulfonated polybenzimidazole casting solution.

[0065] The third step is the preparation of the membrane: 3 mL of sulfonated polybenzimidazole casting solution obtained in the second step is added to the casting dish and dried in an oven at 80 ℃ for 24 h to remove the solvent, resulting in a 25 μm thick polybenzimidazole membrane controlled by the grafting and crosslinking strategy. The membrane is dark yellow and transparent.

[0066] Example 3

[0067] A method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy includes the following steps:

[0068] Step 1, Grafting reaction: In a round-bottom flask, 100 mL of dimethyl sulfoxide and poly(2,2'-(m-phenyl)-5,5'-bibenzimidazole) powder (7.5 mmol (based on repeating units), 2.3 g) were added. Under oil bath heating and stirring at 80 °C, a dark reddish-brown solution was formed. 50 mL of dimethyl sulfoxide solution containing glycidyltrimethylammonium chloride (GTA) (15 mmol, 2.3 g) was added. The solution was sonicated at 100 W for 0.5 h at 80 °C. The solution was poured into acetone, and a white flocculent precipitate was formed. The precipitate was separated by filtration. The precipitate was soaked and washed with pure water and anhydrous ethanol, filtered, and dried in a vacuum drying oven at 120 °C for 24 h to obtain 4.6 g of grafted polybenzimidazole powder, with a yield of 100% and a grafting rate of 200%.

[0069] The second step, sulfonation and crosslinking reaction: 0.5 g of the grafted polybenzimidazole powder obtained in the first step was dissolved in 25 mL of dimethyl sulfoxide to obtain a solution with a concentration of 2% g / mL. The solution was sonicated at 60 ℃ for 0.5 h, and 1,3-propanesulfonic acid lactone (0.9 mmol, 0.11 g) was added dropwise. The solution was sonicated at 60 ℃ and 100 W for 0.5 h to obtain 25 mL of sulfonated polybenzimidazole casting solution.

[0070] The third step is the preparation of the membrane: 3 mL of sulfonated polybenzimidazole casting solution obtained in the second step is added to the casting dish and dried in an oven at 80 ℃ for 24 h to remove the solvent, resulting in a 25 μm thick polybenzimidazole membrane controlled by the grafting and crosslinking strategy. The membrane is dark yellow and transparent.

[0071] Example 4

[0072] A method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy includes the following steps:

[0073] Step 1, Grafting reaction: In a round-bottom flask, 100 mL of dimethyl sulfoxide and poly(2,5-benzimidazole) (ABPBI) powder (7.5 mmol (based on repeating units), 0.9 g) were added. Under oil bath heating and stirring at 80 °C, a dark reddish-brown solution was formed. 50 mL of dimethyl sulfoxide solution containing glycidyltrimethylammonium chloride (GTA) (7.5 mmol, 1.1 g) was added. Under sonication at 100 W for 0.5 h at 80 °C, the solution was poured into acetone, and a white flocculent precipitate was formed. The precipitate was separated by filtration. The precipitate was soaked and washed with pure water and anhydrous ethanol, filtered, and dried in a vacuum drying oven at 120 °C for 24 h to obtain 2 g of grafted polybenzimidazole powder, with a yield of 100% and a grafting rate of 100%.

[0074] The second step, sulfonation and crosslinking reaction: 0.5 g of the grafted polybenzimidazole powder obtained in the first step was dissolved in 25 mL of dimethyl sulfoxide to obtain a solution with a concentration of 2% g / mL. The solution was sonicated at 60 ℃ for 0.5 h. Then, 1,3-propanesulfonic acid lactone (2 mmol, 0.24 g) was added dropwise, and the solution was sonicated at 100 W for 0.5 h at 60 ℃ to obtain 25 mL of sulfonated polybenzimidazole casting solution.

[0075] The third step is the preparation of the membrane: 3 mL of sulfonated polybenzimidazole casting solution obtained in the second step is added to the casting dish and dried in an oven at 80 ℃ for 24 h to remove the solvent, resulting in a 25 μm thick polybenzimidazole membrane controlled by the grafting and crosslinking strategy. The membrane is dark yellow and transparent.

[0076] Example 5

[0077] A method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy includes the following steps:

[0078] Step 1, Grafting reaction: In a round-bottom flask, 100 mL of dimethyl sulfoxide and 3 g of poly(2,2'-(p-diphenyl ether)-5,5'-bibenzimidazole (OPBI) powder (7.5 mmol (based on repeating units)) were added. The mixture was heated and stirred in an oil bath at 80 °C to form a dark reddish-brown solution. Then, 50 mL of a dimethyl sulfoxide solution containing glycidyltrimethylammonium chloride (GTA) (7.5 mmol, 1.2 g) was added. The mixture was sonicated at 100 W for 0.5 h at 80 °C. The solution was then poured into acetone to precipitate a milky-white flocculent substance. The precipitate was separated by filtration. The precipitate was soaked and washed with pure water and anhydrous ethanol, filtered, and dried in a vacuum drying oven at 120 °C for 24 h to obtain 4.2 g of grafted polybenzimidazole powder, with a yield of 100% and a grafting rate of 100%.

[0079] The second step, sulfonation and crosslinking reaction: 0.5 g of the grafted polybenzimidazole powder obtained in the first step was dissolved in 25 mL of dimethyl sulfoxide to obtain a solution with a concentration of 2% g / mL. The solution was sonicated at 60 ℃ for 0.5 h. Then, 1,3-propanesulfonic acid lactone (1 mmol, 0.13 g) was added dropwise, and the solution was sonicated at 100 W for 0.5 h at 60 ℃ to obtain 25 mL of sulfonated polybenzimidazole casting solution.

[0080] The third step is the preparation of the membrane: 3 mL of sulfonated polybenzimidazole casting solution obtained in the second step is added to the casting dish and dried in an oven at 80 ℃ for 24 h to remove the solvent, resulting in a 25 μm thick polybenzimidazole membrane controlled by the grafting and crosslinking strategy. The membrane is dark yellow and transparent.

[0081] Example 6

[0082] A method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy includes the following steps:

[0083] Step 1, Grafting reaction: In a round-bottom flask, 100 mL of dimethyl sulfoxide and 3 g of poly(2,2'-(p-diphenyl ether)-5,5'-bibenzimidazole (OPBI) powder (7.5 mmol (based on repeating units)) were added. Under oil bath heating and stirring at 80 °C, a dark reddish-brown solution was formed. 50 mL of dimethyl sulfoxide solution containing glycidyltrimethylammonium chloride (GTA) (15 mmol, 2.3 g) was added. The solution was sonicated at 100 W for 0.5 h at 80 °C. The solution was poured into acetone, and a white flocculent precipitate was formed. The precipitate was separated by filtration. The precipitate was soaked and washed with pure water and anhydrous ethanol, filtered, and dried in a vacuum drying oven at 120 °C for 24 h to obtain 5.3 g of grafted polybenzimidazole powder, with a yield of 100% and a grafting rate of 200%.

[0084] The second step, sulfonation and crosslinking reaction: 0.5 g of the grafted polybenzimidazole powder obtained in the first step was dissolved in 25 mL of dimethyl sulfoxide to obtain a solution with a concentration of 2% g / mL. The solution was sonicated at 60 ℃ for 0.5 h. Then, 1,3-propanesulfonic acid lactone (0.4 mmol, 0.05 g) was added dropwise, and the solution was sonicated at 100 W for 0.5 h at 60 ℃ to obtain 25 mL of sulfonated polybenzimidazole casting solution.

[0085] The third step is the preparation of the membrane: 3 mL of sulfonated polybenzimidazole casting solution obtained in the second step is added to the casting dish and dried in an oven at 80 ℃ for 24 h to remove the solvent, resulting in a 25 μm thick polybenzimidazole membrane controlled by the grafting and crosslinking strategy. The membrane is dark yellow and transparent.

[0086] Example 7

[0087] A method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy includes the following steps:

[0088] Step 1, Grafting reaction: In a round-bottom flask, 100 mL of dimethyl sulfoxide and 3 g of poly(2,2'-(p-diphenyl ether)-5,5'-bibenzimidazole (OPBI) powder (7.5 mmol (based on repeating units)) were added. Under oil bath heating and stirring at 80 °C, a dark reddish-brown solution was formed. 50 mL of dimethyl sulfoxide solution containing glycidyltriethylammonium chloride (15 mmol, 2.5 g) was added. The solution was sonicated at 100 W for 0.5 h at 80 °C. The solution was poured into acetone, and a white flocculent precipitate was formed. The precipitate was separated by filtration. The precipitate was soaked and washed with pure water and anhydrous ethanol, filtered, and dried in a vacuum drying oven at 120 °C for 24 h to obtain 3.5 g of grafted polybenzimidazole powder, with a yield of 100% and a grafting rate of 200%.

[0089] The second step, sulfonation and crosslinking reaction: 0.5 g of the grafted polybenzimidazole powder obtained in the first step was dissolved in 25 mL of dimethyl sulfoxide to obtain a solution with a concentration of 2% g / mL. The solution was sonicated at 60 ℃ for 0.5 h. Then, 0.8 mmol (0.1 g) of 1,3-propanesulfonic acid lactone was added dropwise, and the solution was sonicated at 100 W for 0.5 h at 60 ℃ to obtain 25 mL of sulfonated polybenzimidazole casting solution.

[0090] The third step is the preparation of the membrane: 3 mL of sulfonated polybenzimidazole casting solution obtained in the second step is added to the casting dish and dried in an oven at 80 ℃ for 24 h to remove the solvent, resulting in a 25 μm thick polybenzimidazole membrane controlled by the grafting and crosslinking strategy. The membrane is dark yellow and transparent.

[0091] Example 8

[0092] A method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy includes the following steps:

[0093] Step 1, Grafting reaction: In a round-bottom flask, 100 mL of dimethyl sulfoxide and 3 g of poly(2,2'-(p-diphenyl ether)-5,5'-bibenzimidazole (OPBI) powder (7.5 mmol (based on repeating units)) were added. Under oil bath heating and stirring at 80 °C, a dark reddish-brown solution was formed. 50 mL of dimethyl sulfoxide solution containing glycidyltrimethylammonium chloride (GTA) (15 mmol, 2.3 g) was added. The solution was sonicated at 100 W for 0.5 h at 80 °C. The solution was poured into acetone, and a white flocculent precipitate was formed. The precipitate was separated by filtration. The precipitate was soaked and washed with pure water and anhydrous ethanol, filtered, and dried in a vacuum drying oven at 120 °C for 24 h to obtain 5.3 g of grafted polybenzimidazole powder, with a yield of 100% and a grafting rate of 200%.

[0094] The second step, sulfonation and crosslinking reaction: 0.5 g of the grafted polybenzimidazole powder obtained in the first step was dissolved in 25 mL of dimethyl sulfoxide to obtain a solution with a concentration of 2% g / mL. The solution was sonicated at 60 ℃ for 0.5 h. Then, 0.8 mmol (0.1 g) of 1,3-propenesulfonyl lactone was added dropwise, and the solution was sonicated at 100 W for 0.5 h at 60 ℃ to obtain 25 mL of sulfonated polybenzimidazole casting solution.

[0095] The third step is the preparation of the membrane: 3 mL of sulfonated polybenzimidazole casting solution obtained in the second step is added to the casting dish and dried in an oven at 80 ℃ for 24 h to remove the solvent, resulting in a 25 μm thick polybenzimidazole membrane controlled by the grafting and crosslinking strategy. The membrane is dark yellow and transparent.

[0096] Table 1 shows the performance results of the membranes prepared in the embodiments and comparative examples of the present invention.

[0097] Table 1

[0098]

[0099] As can be seen from the data in Table 1, Examples 1-4, using polybenzimidazoles with different molecular structures, compared to the unmodified pure PBI membrane that could not be properly charged and discharged (Comparative Example 2), demonstrate that the grafting crosslinking strategy of this invention can effectively optimize the membrane performance at 80 mA cm⁻¹. -2 The energy efficiency at the specified current densities was all above 83%, demonstrating the effectiveness of the strategy. Furthermore, the amount and structure of the grafting agent both affected the membrane performance. When the grafting rate was 100% (Example 5), the performance of the product prepared in Example 5 was lower than that of the product prepared in Example 1 when the grafting rate was 200%. Performance decreased when the grafting agent was replaced with glycidyltrimethylammonium chloride (Example 7). Similarly, the amount and structure of the sulfonating agent also affected the membrane structure. Membrane performance decreased when the amount was reduced (Example 6) or when 1,3-propanesulfonate lactone was replaced with 1,3-propenesulfonate lactone (Example 8). However, the performance of the products prepared in the examples of this invention was superior to that of the product prepared in Comparative Example 2.

[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing polybenzimidazole membranes using a grafting and crosslinking strategy, characterized in that, Includes the following steps: The first step involves dissolving a polybenzimidazole compound in a first solvent at a temperature of 60-100 ℃, then adding a solution containing a quaternary ammonium salt grafting agent. The molar ratio of the polybenzimidazole compound to the quaternary ammonium salt grafting agent is 1:0.1-3. The mixture is then sonicated, and the solution is poured into acetone to precipitate flocculent matter. The precipitate is separated by filtration, and the precipitate is soaked and washed with pure water and anhydrous ethanol. After filtration and drying, the precipitate is obtained as grafted polybenzimidazole powder. The polybenzimidazole compound is selected from at least one of poly2,2'-(m-phenyl)-5,5'-bibenzimidazole, poly2,2'-(p-phenyl)-5,5'-bibenzimidazole, poly2,2'-(p-diphenyl ether)-5,5'-bibenzimidazole, and poly(2,5-benzimidazole). The quaternary ammonium salt grafting agent is selected from at least one of glycidyltrimethylammonium chloride, glycidyltriethylammonium chloride, glycidylbenzyldimethylammonium chloride, glycidyldimethyldodecylammonium chloride, diglycidyldimethylammonium chloride, and glycidylpyridineammonium chloride derivatives. The second step involves dissolving the grafted polybenzimidazole powder obtained in the first step in a second solvent to obtain a solution with a concentration of 1-10% g / mL. The solution is then sonicated at a temperature of 40-80 ℃ for 0.1-2 h. A sulfonating agent is added dropwise, with a mass ratio of sulfonating agent to the grafted polybenzimidazole powder obtained in the first step of 1:0.5-20. The solution is then sonicated until homogeneous to obtain a sulfonated polybenzimidazole casting solution. The sulfonating agent is selected from at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, vinylsulfonate lactone, benzosulfonate lactone, and ethylenesulfonate lactone. The third step is to dry the sulfonated polybenzimidazole casting solution obtained in the second step to obtain a polybenzimidazole membrane controlled by the grafting crosslinking strategy.

2. The method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy 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; In the first step, the conditions for drying the precipitate are: drying at a temperature of 100~150 ℃ for 1~48 h.

3. The method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy according to claim 1, characterized in that, Preparation of the solution containing the quaternary ammonium salt grafting agent: Dissolve the quaternary ammonium salt grafting agent in dimethyl sulfoxide to a concentration of 0.01~1g / mL; The ultrasound conditions in the first step are: a temperature of 60~100 ℃ and 100 W ultrasound for 0.1~2 h.

4. The method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy 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.

5. The method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy according to claim 1, characterized in that, The conditions for uniform ultrasonic oscillation in the second step are: a temperature of 50~70 ℃ and 100 W ultrasound for 0.1~2 h.

6. The method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy according to claim 1, characterized in that, In the third step, the drying conditions are: drying at a temperature of 60~100 ℃ for 1~48 h.

7. The method for preparing polybenzimidazole membranes by controlling the grafting and crosslinking strategy according to claim 1, characterized in that, The grafting and crosslinking strategy controls the thickness of the polybenzimidazole membrane to be 10~50 μm; The grafting rate of the grafted polybenzimidazole is 100-200%.

8. A grafting and crosslinking strategy for preparing a polybenzimidazole membrane according to any one of claims 1 to 7.

9. The application of the polybenzimidazole membrane according to claim 8 in the preparation of a flow battery.

10. The application according to claim 9, characterized in that, The flow battery is selected from vanadium redox flow batteries, lithium-ion flow batteries, zinc-bromine flow batteries, zinc-cerium flow batteries, zinc-nickel flow batteries, lead flow batteries, iron-chromium flow batteries, sodium polysulfide / bromine flow batteries, or all-iron flow batteries.

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