Preparation method and application of polybenzimidazole membrane containing double ion exchange groups

Abstract

The invention discloses a preparation method and application of a polybenzimidazole membrane containing double ion exchange groups, and the preparation method comprises the following steps: firstly, synthesizing an ammonium bromide-containing monomer by using 1, 6-dibromohexane, a tertiary ammonium group-containing reagent and ethyl acetate as raw materials; secondly, carrying out condensation polymerization on a dicarboxylic acid monomer and diaminobenzidine in methanesulfonic acid and P2O5 to prepare a polybenzimidazole polymer; then, the obtained polybenzimidazole polymer and 2, 3-epoxypropyl trimethyl ammonium chloride are subjected to a grafting reaction in dimethyl sulfoxide, then the ammonium bromide-containing monomer is introduced for continuous reaction, and a dicationic polybenzimidazole polymer is obtained; the dicationic polybenzimidazole polymer is dissolved in dimethyl sulfoxide, film casting and drying are carried out, and the polybenzimidazole membrane which has high ionic conductivity and contains double ion exchange groups can be obtained. The polybenzimidazole membrane constructed by the invention is applied to an electro-catalysis CO2 reduction system, and the current density and CO Faraday efficiency can be remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic CO2 reduction anion exchange membranes, and relates to a method for preparing and applying a polybenzimidazole membrane containing two ion exchange groups. Background Technology

[0002] Carbon dioxide (CO2), a major component of greenhouse gases, plays a significant role in global warming. It has been reported that atmospheric CO2 concentrations have increased from 280 ppm to 415 ppm over the past two centuries and are projected to exceed 600 ppm by 2100. This trend is expected to disrupt the carbon balance between the atmosphere and ecosystems. Currently, the main pathways for converting CO2 into useful products include bioconversion, photocatalytic reduction, and electrocatalytic reduction. Bioconversion primarily relies on plant photosynthesis to fix CO2, representing a natural carbon remediation process. Photocatalysis utilizes photosensitive materials to drive CO2 conversion under light, generating a range of economically valuable chemicals. Among these technologies, electrocatalytic CO2 reduction has gained significant attention due to its high energy efficiency and environmental friendliness. This technology uses renewable energy as its power source and, through heterogeneous catalysis, continuously converts CO2 into high-value-added chemicals such as carbon monoxide, formic acid, methanol, methane, ethanol, and dimethyl ether, becoming an important direction for promoting carbon resource recycling and efficient utilization.

[0003] The key to achieving efficient electrocatalytic CO2 reduction lies in the rational design of catalytic materials and the structural optimization of the reactor. Among them, the "zero-gap" membrane electrode reactor stands out with its compact cathode-membrane-anode stack configuration. This structure greatly reduces the electrode spacing and eliminates the need for liquid electrolyte on the cathode side. This design not only overcomes the bottleneck of limited CO2 solubility in electrolyte but also significantly reduces ohmic losses caused by electrolyte, thereby improving the overall efficiency of CO2 reduction and is considered one of the most promising electrocatalytic CO2 reduction devices for industrialization.

[0004] In this type of membrane electrode system, the membrane serves a dual function: first, it isolates the cathode and anode reaction zones, preventing oxygen generated at the anode from re-oxidizing the cathode products; second, it provides an ion transport channel, ensuring the smooth migration of ions required for charge balance (such as protons or hydroxide ions). In recent years, anion exchange membranes that enable anion transport from the cathode to the anode, maintain pH stability in the cathode region, and suppress hydrogen evolution reactions during CO2 reduction have become increasingly popular research topics. High-performance anion exchange membranes should possess high hydroxide conductivity, good mechanical strength, dimensional stability, and chemical durability. Furthermore, the selective permeability of these membranes to hydroxide ions helps reduce the hydroxide concentration at the cathode interface, suppressing competitive hydrogen evolution reactions and thus improving the Faraday efficiency of CO2 reduction, while simultaneously avoiding the adverse effects of hydroxide accumulation on the cathode catalyst and the ineffective consumption of CO2.

[0005] Currently, several commercially available anion exchange membranes are commonly used in electrocatalytic CO2 reduction membrane electrode systems, such as Sustainion X37-50 from Dioxide Materials (USA), the PiperION series from Versogen (USA), and FAA-3-PK-130 from Fumasep (Germany). However, these existing commercial membranes suffer from insufficient hydroxide conductivity, limited ion selectivity, and limited mechanical properties, hindering further improvements in CO2 reduction efficiency. Furthermore, imported membrane materials are expensive, and long-term reliance on imports may pose supply chain risks. Therefore, developing high-performance, low-cost novel anion exchange membrane materials suitable for electrocatalytic CO2 reduction has become a crucial issue requiring breakthroughs in this field. Summary of the Invention

[0006] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0007] To achieve these and other advantages according to the present invention, a polybenzimidazole membrane containing two ion-exchange groups is provided, the structural formula of which is: Where X is , and Any one of the following: Q is 1-methylpiperidine group, 1,4-dimethylpiperazine group, 1-methylpyrrole group, 1-methylimidazolium group, 1-methylpyrrolidinyl group, 1-methylpyrazole group, imidazolonium group, trimethylamine group, triethylamine group, or tripropylamine group.

[0008] This invention also provides a method for preparing a polybenzimidazole membrane containing two ion-exchange groups, comprising the following steps: Step 1: Under a nitrogen atmosphere, add the reagent containing the tertiary ammonium group, dibromohexane and ethyl acetate to the reactor, stir to dissolve, and after the reaction is complete, a white solid is generated. Filter, wash repeatedly with ethyl acetate, and dry under vacuum to obtain the ammonium bromide monomer. Step 2: Under nitrogen protection, methanesulfonic acid and P2O5 are added sequentially to a three-necked flask and stirred until completely dissolved. Then, diaminobenzidine is added and stirred until fully dissolved. After the system becomes clear, dicarboxylic acid monomer is added to initiate a polycondensation reaction. After the reaction is complete, the mixture is slowly poured into deionized water to precipitate the product. The fibrous solid is collected by suction filtration. The crude product is then placed back into deionized water, and NaHCO3 is slowly added to adjust the system to neutrality until no more bubbles are generated. After filtration again, the mixture is vacuum dried to obtain polybenzimidazole polymer.

[0009] Step 3: Under a nitrogen atmosphere, the polybenzimidazole polymer obtained in Step 2 and dimethyl sulfoxide are added to the reactor and stirred to dissolve. 2,3-epoxypropyltrimethylammonium chloride is added to carry out a grafting reaction. Then, the ammonium bromide monomer obtained in Step 1 is added to the reactor to continue the reaction. After the reaction is completed, the reaction solution is poured into a precipitant, filtered, and the yellow fibrous solid is collected and dried to obtain the dicationic polybenzimidazole polymer. Step 4: Add the dicationic polybenzimidazole polymer and dimethyl sulfoxide obtained in Step 3 to the reactor, stir and dissolve to obtain a bright yellow casting solution. Pour the casting solution onto a clean glass plate to cast a film. After drying, immerse the film in ethanol to remove residual solvent and wash with deionized water. Step 5: Immerse the membrane obtained in Step 4 in KOH solution for ion exchange to obtain a polybenzimidazole membrane containing two ion exchange groups.

[0010] Preferably, in step one, the molar ratio of the reagent containing the tertiary ammonium group to dibromohexane is 1:2~10, the molar volume ratio of the reagent containing the tertiary ammonium group to ethyl acetate is 10~30 mmol : 20~50 mL, the reaction temperature is 20~50 ℃, the reaction time is 24~48 h, the vacuum drying temperature is 40~60 ℃, the drying time is 12~36 h, and the reagent containing the tertiary ammonium group is any one of 1-methylpiperidine, 1,4-dimethylpiperazine, 1-methylpyrrole, 1-methylimidazolium, 1-methylpyrrolidine, 1-methylpyrazole, imidazoline, trimethylamine, triethylamine, and tripropylamine.

[0011] Preferably, in step two, the volume-to-mass ratio of methanesulfonic acid to P2O5 is 10 mL : 1~5 g, the volume-to-molar ratio of methanesulfonic acid to diaminobenzidine is 10 mL : 1~3 mmol, and the molar ratio of diaminobenzidine to dicarboxylic acid monomer is 10~30 mmol : 10~30 mmol; the reaction temperature is 80~150 ℃, the reaction time is 24~48 h, the vacuum drying temperature is 40~60 ℃, and the drying time is 12~36 h; the dicarboxylic acid monomer is any one of 2,2-bis(4-carboxyphenyl)hexafluoropropane, 4,4'-dicarboxylic acid diphenyl ether, and terephthalic acid.

[0012] Preferably, in step three, the molar volume ratio of polybenzimidazole polymer to dimethyl sulfoxide is 1 mmol : 5~15 mL, the molar ratio of polybenzimidazole polymer to 2,3-epoxypropyltrimethylammonium chloride is 1 mmol : 1.5~3.0 mmol, the molar ratio of 2,3-epoxypropyltrimethylammonium chloride to ammonium bromide monomer is 0~4 mmol : 0~4 mmol, the reaction temperature is 80~110 ℃, and the reaction time is 24~48 h; the precipitant is one or more of anhydrous ethanol, ethyl acetate, and deionized water.

[0013] Preferably, in step four, the stirring and dissolving temperature is 60-80 °C, and the stirring time is 6-24 h; the drying temperature of the casting solution is 60-100 °C, and the drying time is 12-24 h; the mass-to-volume ratio of the dicationic polybenzimidazole polymer to dimethyl sulfoxide is 0.3-0.8 g:10 mL; and in step five, the concentration of the KOH solution is 0.5-4 mol·L⁻¹. –1 The soaking time is 24~72 hours.

[0014] Preferably, step four is replaced with: S41. Add the dicationic polybenzimidazole polymer and dimethyl sulfoxide obtained in step 3 to the reactor, stir to dissolve, then add carbon nanotubes and stir evenly to obtain a bright yellow casting solution. S42. Add silver nitrate solution to the casting solution and triethylamine to adjust the pH. After stirring the reaction, a modified casting solution is obtained. Pour the modified casting solution onto a clean glass plate to cast a film. After drying, immerse the film in ethanol to remove residual solvent and wash it with deionized water.

[0015] Preferably, in step S41, the amount of carbon nanotubes added is 5-10 wt% of the polybenzimidazole polymer.

[0016] Preferably, in step S42, the concentration of the silver nitrate solution is 0.2~0.3 mol·L⁻¹. –1 The volume ratio of casting solution to copper nitrate solution is 1~2:0.1~0.2. Adjust the pH to 7~8 and stir at 600~800 rpm for 8~12 hours.

[0017] An application of a polybenzimidazole membrane containing dual ion exchange groups, wherein the polybenzimidazole membrane containing dual ion exchange groups is used as a diaphragm in a membrane electrode for electrocatalytic CO2 reduction.

[0018] Preferably, the method for preparing the membrane electrode includes: adding nano-silver powder to a mixed solution of deionized water, anhydrous ethanol, and FAA, ultrasonicating to obtain cathode catalyst ink, then uniformly spraying it onto hydrophobic carbon paper using a spray gun, and drying it at 50-70°C to obtain the cathode; adding iridium oxide to a solution of deionized water, anhydrous ethanol, and FAA, ultrasonicating to obtain anode catalyst ink, then uniformly spraying it onto hydrophobic carbon paper using a spray gun, and drying it at 50-70°C to obtain the anode; and finally assembling the cathode, a polybenzimidazole membrane containing two ion exchange groups, and the anode to obtain the membrane electrode.

[0019] Preferably, the mass-to-volume ratio of nano-silver powder, anhydrous ethanol, deionized water, and FAA solution in the cathode preparation is: 1~3 mg : 100~300 μL : 20~100 μL : 5~20 μL; and the mass-to-volume ratio of iridium oxide, anhydrous ethanol, deionized water, and FAA solution in the anode preparation is: 1~3 mg : 100~300 μL : 20~100 μL : 5~20 μL.

[0020] Preferably, 0.1~1 mol·L⁻¹ is used. –1 KHCO3 is used as the anolyte. A peristaltic pump delivers the electrolyte to the anode for flow. Dry CO2 is humidified using a gas humidification device and then delivered to the cathode for flow. A constant current is then applied for electrolysis, promoting the electrocatalytic reduction of CO2. The peristaltic pump rotates at 20–80 rpm, and the CO2 flow rate is 10–40 mL / min. –1 The thickness of the polybenzimidazole membrane containing dual ion exchange groups is 10~50 μm.

[0021] The present invention has at least the following beneficial effects: (1) The present invention uses polybenzimidazole as the polymer backbone, which can improve the alkaline stability and mechanical properties of the anion exchange membrane; (2) By simultaneously grafting two cationic functional groups, the present invention can significantly improve the ion conductivity of the anion exchange membrane, thereby increasing the current density of the membrane electrode and the CO Faradaic efficiency, and overcoming the disadvantage of excessive surface resistance of polybenzimidazole polymer membrane in use. (3) By designing the molecular structure of the side chain monomer, side chains carrying different functional groups are grafted onto polybenzimidazole to regulate the cationic groups, so that it has better hydroxide conductivity and electrochemical stability, thereby enabling it to meet the application requirements of electrocatalytic CO2 reduction. (4) Adding carbon nanotubes to the casting solution and using silver ions to complex with some polybenzimidazole, the carbon nanotubes further improve the mechanical strength of the film, and at the same time, the carbon nanotubes can also improve the electrochemical performance of the polybenzimidazole film. After the silver ions are complexed with polybenzimidazole, they are used to improve the ion conductivity of the film, which can also improve the electrochemical performance of the polybenzimidazole film.

[0022] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0023] Figure 1 This is a synthetic route diagram of the polybenzimidazole membrane containing two ion-exchange groups in Example 1; Figure 2 This is a synthetic route diagram of the polybenzimidazole membrane containing two ion-exchange groups in Example 2; Figure 3 This is a synthetic route diagram of the polybenzimidazole membrane containing two ion-exchange groups in Example 3; Figure 4 This is a schematic diagram of the membrane electrode structure; Figure 5 The current density diagram is shown for the membrane electrode assembled using the polybenzimidazole membrane containing dual ion exchange groups according to Example 2 of the present invention. Figure 6 The CO Faradaic efficiency diagram is shown for the membrane electrode assembled using the polybenzimidazole membrane containing dual ion exchange groups according to Example 2 of the present invention. Detailed Implementation The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0024] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not imply the presence or addition of one or more other elements or combinations thereof.

[0025] Example 1 A method for preparing a polybenzimidazole membrane containing two ion-exchange groups, the synthetic route of which is shown in the figure below. Figure 1 As shown, the specific steps include: Step 1: Under a nitrogen atmosphere, 5 mL of 30 wt% trimethylamine ethanol solution, 7.32 g of dibromohexane and 30 mL of ethyl acetate were added to the reactor and stirred at 40 °C to dissolve. After reacting for 48 h, a white solid was generated. The solid was filtered, washed repeatedly with ethyl acetate, filtered under vacuum and dried to obtain 1-(6-bromohexyl)trimethylammonium bromide monomer. Step 2: Under nitrogen protection, add 100 mL of methanesulfonic acid and 10.0 g of P2O5 to a three-necked flask in sequence. Stir until completely dissolved, then add 2.14 g of diaminobenzidine and stir until fully dissolved. After the system becomes clear, add 3.97 g of 2,2-bis(4-carboxyphenyl)hexafluoropropane to carry out a polycondensation reaction. After the reaction is complete, slowly pour the mixture into deionized water to precipitate the product. Collect the fibrous solid by vacuum filtration, place the fibrous solid back into deionized water, and slowly add NaHCO3 to adjust the system to neutral until no bubbles are generated. After filtration again, vacuum dry to obtain polybenzimidazole polymer. Step 3: Under a nitrogen atmosphere, 0.43 g of the polybenzimidazole polymer obtained in Step 2 and 10 mL of dimethyl sulfoxide were added to the reactor and stirred at 50 °C to dissolve. 0.23 g of 2,3-epoxypropyltrimethylammonium chloride was added to carry out a grafting reaction for 24 h. Then, 0.44 g of the ammonium bromide monomer obtained in Step 1 was added to the reactor and the reaction was continued for 24 h. After the reaction was completed, the reaction solution was poured into a precipitant, filtered, and the yellow fibrous solid was collected and dried to obtain the dicationic polybenzimidazole polymer. Step 4: Add 0.50 g of the dicationic polybenzimidazole polymer obtained in Step 3 and 10 mL of dimethyl sulfoxide to the reactor, stir and dissolve at 80 °C to obtain a bright yellow casting solution. Pour the casting solution onto a clean glass plate to cast a film. After drying at 80 °C, immerse the film in ethanol to remove residual solvent and wash with deionized water. Step 5: Place the membrane obtained in Step 4 in a 1.0 mol·L⁻¹ solution. –1 Ion exchange was carried out by soaking in KOH solution for 24 h to obtain polybenzimidazole membrane containing two ion exchange groups.

[0026] Example 2 A method for preparing a polybenzimidazole membrane containing two ion-exchange groups, the synthetic route of which is shown in the figure below. Figure 2 As shown, the specific steps include: Step 1: Under a nitrogen atmosphere, 1.98 g of 1-methylpiperidine, 7.32 g of dibromohexane and 30 mL of ethyl acetate were added to the reactor and stirred at 40 °C to dissolve. After reacting for 48 h, a white solid was generated. The solid was filtered, washed repeatedly with ethyl acetate, filtered under vacuum and dried to obtain 1-(6-bromohexyl)-1-methylpiperidine ammonium bromide monomer. Step 2: Under nitrogen protection, add 100 mL of methanesulfonic acid and 10.0 g of P2O5 to a three-necked flask in sequence. Stir until completely dissolved, then add 2.14 g of diaminobenzidine and stir until fully dissolved. After the system becomes clear, add 3.97 g of 2,2-bis(4-carboxyphenyl)hexafluoropropane to carry out a polycondensation reaction. After the reaction is complete, slowly pour the mixture into deionized water to precipitate the product. Collect the fibrous solid by vacuum filtration, place the fibrous solid back into deionized water, and slowly add NaHCO3 to adjust the system to neutral until no bubbles are generated. After filtration again, vacuum dry to obtain polybenzimidazole polymer. Step 3: Under a nitrogen atmosphere, 0.43 g of the polybenzimidazole polymer obtained in Step 2 and 10 mL of dimethyl sulfoxide were added to the reactor and stirred at 50 °C to dissolve. 0.23 g of 2,3-epoxypropyltrimethylammonium chloride was added to carry out a grafting reaction for 24 h. Then, 0.52 g of the ammonium bromide monomer obtained in Step 1 was added to the reactor and the reaction was continued for 24 h. After the reaction was completed, the reaction solution was poured into a precipitant, filtered, and the yellow fibrous solid was collected and dried to obtain the dicationic polybenzimidazole polymer. Step 4: Add 0.50 g of the dicationic polybenzimidazole polymer obtained in Step 3 and 10 mL of dimethyl sulfoxide to the reactor, stir and dissolve at 80 °C to obtain a bright yellow casting solution. Pour the casting solution onto a clean glass plate to cast a film. After drying at 80 °C, immerse the film in ethanol to remove residual solvent and wash with deionized water. Step 5: Place the membrane obtained in Step 4 in a 1.0 mol·L⁻¹ solution. –1 Ion exchange was carried out by soaking in KOH solution for 24 h to obtain polybenzimidazole membrane containing two ion exchange groups.

[0027] Example 3 A method for preparing a polybenzimidazole membrane containing two ion-exchange groups, the synthetic route of which is shown in the figure below. Figure 3 As shown, the specific steps include: Step 1: Under a nitrogen atmosphere, 1.98 g of 1-methylpiperidine, 7.32 g of dibromohexane and 30 mL of ethyl acetate were added to the reactor and stirred at 40 °C to dissolve. After reacting for 48 h, a white solid was generated. The solid was filtered, washed repeatedly with ethyl acetate, filtered under vacuum and dried to obtain 1-(6-bromohexyl)-1-methylpiperidine ammonium bromide monomer. Step 2: Under nitrogen protection, add 100 mL of methanesulfonic acid and 10.0 g of P2O5 to a three-necked flask, stirring until completely dissolved. Then add 2.14 g of diaminobenzidine and stir until fully dissolved. After the system becomes clear, add 2.58 g of 4,4'-dicarboxylic acid diphenyl ether to carry out a polycondensation reaction. After the reaction is complete, slowly pour the mixture into deionized water to precipitate the product. Collect the fibrous solid by vacuum filtration, place the fibrous solid back into deionized water, and slowly add NaHCO3 to adjust the system to neutral until no bubbles are generated. After filtration again, vacuum dry to obtain polybenzimidazole polymer. Step 3: Under a nitrogen atmosphere, 0.43 g of the polybenzimidazole polymer obtained in Step 2 and 10 mL of dimethyl sulfoxide were added to the reactor and stirred at 50 °C to dissolve. 0.23 g of 2,3-epoxypropyltrimethylammonium chloride was added to carry out a grafting reaction for 24 h. Then, 0.52 g of the ammonium bromide monomer obtained in Step 1 was added to the reactor and the reaction was continued for 24 h. After the reaction was completed, the reaction solution was poured into a precipitant, filtered, and the yellow fibrous solid was collected and dried to obtain the dicationic polybenzimidazole polymer. Step 4: Add 0.50 g of the dicationic polybenzimidazole polymer obtained in Step 3 and 10 mL of dimethyl sulfoxide to the reactor, stir and dissolve at 80 °C to obtain a bright yellow casting solution. Pour the casting solution onto a clean glass plate to cast a film. After drying at 80 °C, immerse the film in ethanol to remove residual solvent and wash with deionized water. Step 5: Place the membrane obtained in Step 4 in a 1.0 mol·L⁻¹ solution. –1 Ion exchange was carried out by soaking in KOH solution for 24 h to obtain polybenzimidazole membrane containing two ion exchange groups.

[0028] Example 4 A method for preparing a polybenzimidazole membrane containing two ion-exchange groups. Steps one to three in this embodiment are the same as in Example 2, except that step four is as follows: S41. Add 0.50g of the dicationic polybenzimidazole polymer obtained in step 3 and 10mL of dimethyl sulfoxide to the reactor, stir and dissolve at 80℃, then add 0.025g of carbon nanotubes and stir evenly to obtain a bright yellow casting solution. S42. Add 1 mL of 0.3 mol·L⁻¹ solution to 10 mL of casting solution. –1 A silver nitrate solution was prepared, and triethylamine was added dropwise to adjust the pH to 8. During the dropwise addition, the mixture was continuously stirred at 600 rpm. After the dropwise addition was completed, the mixture was stirred and reacted for another 8 hours to obtain a modified casting solution. The modified casting solution was poured onto a clean glass plate to cast a film. After drying at 80 °C, the film was immersed in ethanol to remove residual solvent and then washed with deionized water. Step 5: Place the membrane obtained in Step 4 in a 1.0 mol·L⁻¹ solution. –1 The modified polybenzimidazole membrane containing two ion-exchange groups was obtained by soaking the membrane in KOH solution for 24 h for ion exchange.

[0029] Example 5 A method for preparing a polybenzimidazole membrane containing two ion-exchange groups. Steps one to three in this embodiment are the same as in Example 2, except that step four is as follows: S41. Add 0.50g of the dicationic polybenzimidazole polymer obtained in step 3 and 10mL of dimethyl sulfoxide to the reactor, stir and dissolve at 80℃, then add 0.025g of carbon nanotubes and stir evenly to obtain a bright yellow casting solution; pour the casting solution onto a clean glass plate to cast a film, dry it at 80℃, immerse the film in ethanol to remove residual solvent, and wash it with deionized water; Step 5: Place the membrane obtained in Step 4 in a 1.0 mol·L⁻¹ solution. –1 Ion exchange was performed by soaking the polybenzimidazole membrane with two ion exchange groups in KOH solution for 24 h, thus obtaining the polybenzimidazole membrane doped with carbon nanotubes.

[0030] Example 6 A method for preparing a polybenzimidazole membrane containing two ion-exchange groups. Steps one to three in this embodiment are the same as in Example 2, except that step four is as follows: S41. Add 0.50g of the dicationic polybenzimidazole polymer obtained in step three and 10mL of dimethyl sulfoxide to the reactor, stir and dissolve at 80℃ to obtain a bright yellow casting solution. S42. Add 1 mL of 0.3 mol·L⁻¹ solution to 10 mL of casting solution. –1 A silver nitrate solution was prepared, and triethylamine was added dropwise to adjust the pH to 8. During the dropwise addition, the mixture was continuously stirred at 600 rpm. After the dropwise addition was completed, the mixture was stirred and reacted for another 8 hours to obtain a modified casting solution. The modified casting solution was poured onto a clean glass plate to cast a film. After drying at 80 °C, the film was immersed in ethanol to remove residual solvent and then washed with deionized water. Step 5: Place the membrane obtained in Step 4 in a 1.0 mol·L⁻¹ solution. –1 Ion exchange was performed by soaking the membrane in KOH solution for 24 h, resulting in a polybenzimidazole membrane with silver ion complexation and containing two ion exchange groups.

[0031] Comparative Example 1 This comparative example provides a method for preparing a polybenzimidazole anion exchange membrane grafted with trimethylamine cationic groups, comprising the following steps: Step 1: Under nitrogen protection, add 100 mL of methanesulfonic acid and 10.0 g of P2O5 to a three-necked flask, stirring until completely dissolved. Then add 2.14 g of diaminobenzidine and stir until fully dissolved. After the system becomes clear, add 3.97 g of 2,2-bis(4-carboxyphenyl)hexafluoropropane to carry out a polycondensation reaction. After the reaction is complete, slowly pour the mixture into deionized water to precipitate the product. Collect the fibrous solid by vacuum filtration. Place the crude product back into deionized water, slowly add NaHCO3 to adjust the system to neutral until no bubbles are generated, filter again, and vacuum dry to obtain polybenzimidazole polymer. Step 2: Under a nitrogen atmosphere, 0.43 g of the polybenzimidazole polymer obtained in Step 1 and 10 mL of dimethyl sulfoxide were added to the reactor and stirred at 50 °C to dissolve. Then, 0.23 g of 2,3-epoxypropyltrimethylammonium chloride was added to carry out a grafting reaction for 24 h. After the reaction was completed, the reaction solution was poured into a precipitant, filtered, and the yellow fibrous solid was collected and dried to obtain trimethylamine cationic polybenzimidazole polymer. Step 3: Add 0.50 g of the trimethylamine cationic polybenzimidazole polymer obtained in Step 2 and 10 mL of dimethyl sulfoxide to the reactor, stir and dissolve at 80 °C to obtain a bright yellow casting solution, pour the casting solution onto a clean glass plate to cast a film, dry at 80 °C, immerse the film in ethanol to remove residual solvent, and wash with deionized water. Step 4: Place the membrane obtained in Step 3 in a 1.0 mol·L⁻¹ solution. –1 The trimethylamine cationic polybenzimidazole anion exchange membrane was obtained by soaking in KOH solution for 24 h for ion exchange.

[0032] Comparative Example 2 This comparative example provides a method for preparing a polybenzimidazole anion exchange membrane grafted with piperidine cationic groups, comprising the following steps: Step 1: Under a nitrogen atmosphere, 1.98 g of 1-methylpiperidine, 7.32 g of dibromohexane and 30 mL of ethyl acetate were added to the reactor and stirred at 40 °C to dissolve. After reacting for 48 h, a white solid was generated. The solid was filtered, washed repeatedly with ethyl acetate, filtered under vacuum and dried to obtain 1-(6-bromohexyl)-1-methylpiperidine ammonium bromide monomer. Step 2: Under nitrogen protection, add 100 mL of methanesulfonic acid and 10.0 g of P2O5 to a three-necked flask in sequence. Stir until completely dissolved, then add 2.14 g of diaminobenzidine and stir until fully dissolved. After the system becomes clear, add 3.97 g of 2,2-bis(4-carboxyphenyl)hexafluoropropane to carry out a polycondensation reaction. After the reaction is complete, slowly pour the mixture into deionized water to precipitate the product. Collect the fibrous solid by vacuum filtration. Place the crude product back into deionized water and slowly add NaHCO3 to adjust the system to neutral until no bubbles are generated. After filtration again, vacuum dry to obtain polybenzimidazole polymer. Step 3: Under a nitrogen atmosphere, 0.43 g of the polybenzimidazole polymer obtained in Step 2 and 10 mL of dimethyl sulfoxide were added to the reactor and stirred at 50 °C to dissolve. Then, 0.52 g of the ammonium bromide monomer obtained in Step 1 was added to carry out the grafting reaction for 24 h. After the reaction was completed, the reaction solution was poured into a precipitant, filtered, and the yellow fibrous solid was collected and dried to obtain the piperidine cationic polybenzimidazole polymer. Step 4: Add 0.50 g of piperidine cationic polybenzimidazole polymer obtained in Step 3 and 10 mL of dimethyl sulfoxide to the reactor, stir and dissolve at 80 °C to obtain a bright yellow casting solution. Pour the casting solution onto a clean glass plate to cast a film. After drying at 80 °C, immerse the film in ethanol to remove residual solvent and wash with deionized water. Step 5: Place the membrane obtained in Step 4 in a 1.0 mol·L⁻¹ solution. –1 Ion exchange was performed by soaking the membrane in KOH solution for 24 h to obtain a piperidine cationic polybenzimidazole anion exchange membrane.

[0033] The electrocatalytic CO2 reduction performance of the polybenzimidazole membranes containing dual ion-exchange groups prepared in Examples 1-3 and the polybenzimidazole anion-exchange membranes prepared in Comparative Examples 1-2 were tested respectively: Anion exchange membranes are used as membrane electrode components in electrocatalytic CO2 reduction, with current density ( j ) and Faraday efficiency ( FE The performance index of the membrane electrode is the main evaluation index. The membrane electrode is prepared as follows: 5 mg of nano-silver powder is added to 0.25 mL of deionized water, 0.75 mL of anhydrous ethanol, and 50 μL of LFA solution, and sonicated for 1 h to obtain cathode catalyst ink, which is then uniformly sprayed onto a 2×2 cm² substrate. 2 The cathode was prepared by drying 39BB hydrophobic carbon paper at 50-70 °C. Then, 5 mg of iridium oxide was added to 0.25 mL of deionized water, 0.75 mL of anhydrous ethanol, and 50 μL of LFAA solution, and sonicated for 1 h to obtain the anode catalyst ink. This ink was then uniformly sprayed onto a 2×2 cm² substrate. 2The anode was prepared by drying the substrate on 39BB hydrophobic carbon paper at 70 °C; finally, the cathode, a polybenzimidazole membrane containing two ion exchange groups, and the anode were assembled to obtain a membrane electrode (e.g., ...). Figure 4 As shown in the diagram, the outer side of the cathode is the gas flow field, and the outer side of the anode is the electrolyte flow field. A 0.1 mol·L⁻¹ solution is used. –1 KHCO3 was used as the electrolyte, which was delivered to the anode by a peristaltic pump. Dry CO2 was then humidified using a gas humidification device at a rate of 20 mL / min. –1 The flow rate was fed to the cathode, and electrolysis was performed for 1 hour under different current conditions using the constant current function of a CHI660E electrochemical workstation manufactured by Shanghai Chenhua Instrument Co., Ltd. The gaseous products were then tested using a 9790Plus gas chromatograph manufactured by Fuzhou Fuli Instrument Co., Ltd. The CO Faraday efficiency was calculated as follows: in, α The number of electrons transferred for the reduction of CO2 to CO is 2. n This represents the molar amount (mol) of CO. F Faraday constant (96485 mol·C) –1 ), Q The total coulombic quantity (C) transferred from the cathode. in, j CO CO current density, j total The total cathode current density (mA·cm) –2 ), FE CO CO Faraday efficiency (%).

[0034] The CO Faradaic efficiencies of the polybenzimidazole membranes containing dual ion-exchange groups prepared in Examples 1-3 and the anion-exchange membranes prepared in Comparative Examples 1 and 2 ( FE CO ) and CO current density ( j CO As shown in the table below: As can be seen from the table above, compared with Comparative Examples 1 and 2, the polybenzimidazole membrane containing dual ion-exchange groups prepared in Example 2, by controlling the content of hydrophilic and hydrophobic side chains, can achieve a higher current density in the membrane electrode reactor. This is because the combined action of the two cations promotes hydroxide ion transport and effectively improves hydroxide ion conductivity. On the other hand, the interaction between the hydrophilic side chains and the hydrophobic main chain promotes the formation of microphase separation within the membrane, thereby giving the membrane excellent performance. Compared with Example 3, the fluorinated main chain in Example 2 has a significantly higher CO Faradaic efficiency, indicating that the fluorinated side chains effectively regulate the microenvironment of the cathode-side catalytic interface, prevent catalyst flooding, and facilitate CO generation. Furthermore, in Example 4, carbon nanotubes were added to the casting solution based on Example 2, and silver ions were used to complex with some polybenzimidazole. The carbon nanotubes helped to improve the mechanical strength of the film and also improved the electrochemical performance of the polybenzimidazole film. After the silver ions were complexed with polybenzimidazole, they were used to improve the ionic conductivity of the film, which also improved the electrochemical performance of the polybenzimidazole film. Its CO current density and CO Faradaic efficiency were significantly improved compared with Example 2. In Example 5, only carbon nanotubes were added, and in Example 6, only silver ions were complexed. The improvement in electrochemical performance of the two examples was not as good as that of Example 4.

[0035] Figure 5 The figure shows the current density of the membrane electrode assembled using the polybenzimidazole membrane containing dual ion-exchange groups according to Example 2 of the present invention. As can be seen from the figure, compared with Comparative Example 1 and Comparative Example 2, the CO current density of Example 2 is significantly improved after adjusting the ratio of hydrophilic and hydrophobic side chains.

[0036] Figure 6 The figure shows the CO Faradaic efficiency of the membrane electrodes assembled using the polybenzimidazole membranes containing dual ion-exchange groups described in Examples 2-3 of this invention. As can be seen from the figure, the current density in Example 2 is 150 mA·cm⁻¹. –2 The corresponding CO Faradaic efficiency was 94.7%, indicating that the membrane has significant advantages in electrocatalytic CO2 reduction applications.

[0037] The number of devices and processing scale described herein are for the purpose of simplifying the description of the invention. Applications, modifications, and variations of the invention will be readily apparent to those skilled in the art.

[0038] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A polybenzimidazole membrane containing dual ion exchange groups, characterized in that, The structure of the double-ion exchange group-containing polybenzimidazole membrane is as follows: wherein X is any one of , and ; Q is any one of a 1-methylpiperidine group, a 1,4-dimethylpiperazine group, a 1-methylpyrrole group, a 1-methylimidazole group, a 1-methylpyrrolidine group, a 1-methylpyrazole group, an imidazolium group, a trimethylamine group, a triethylamine group, a tripropylamine group.

2. A process for the preparation of a polybenzimidazole membrane containing dual ion exchange groups as claimed in claim 1, characterized in that, The method comprises the following steps: Step one: under a nitrogen atmosphere, a tertiary ammonium group-containing reagent, dibromohexane and ethyl acetate are added into a reactor, stirred and dissolved, and a white solid is generated after the reaction, which is filtered, repeatedly washed with ethyl acetate and vacuum dried to obtain an ammonium bromide-containing monomer; Step two: under a nitrogen atmosphere, P2O5 is added into methane sulfonic acid, stirred until completely dissolved, then diamino benzidine is added and stirred until completely dissolved, then dicarboxylic acid monomer is added for condensation reaction, after the reaction, the mixture is slowly poured into deionized water to precipitate the product, the fibrous solid is collected by suction filtration, the fibrous solid is placed in deionized water again, NaHCO3 is slowly added to adjust the system to neutral until no bubbles are generated, the system is filtered again and vacuum dried to obtain a polybenzimidazole polymer; Step three: under a nitrogen atmosphere, the polybenzimidazole polymer obtained in step two and dimethyl sulfoxide are added into a reactor, stirred and dissolved, 2,3-epoxypropyl trimethyl ammonium chloride is added for grafting reaction, then the ammonium bromide-containing monomer obtained in step one is added into the reactor for continuous reaction, after the reaction, the reaction solution is poured into a precipitant, filtered, the yellow fibrous solid is collected and dried to obtain a double-cationic polybenzimidazole polymer; Step four: the double-cationic polybenzimidazole polymer obtained in step three and dimethyl sulfoxide are added into a reactor, stirred and dissolved to obtain a bright yellow casting solution, the casting solution is poured onto a clean glass plate to flow into a membrane, the membrane is dried, then soaked in ethanol to remove residual solvents and washed with deionized water; Step five: the membrane obtained in step four is soaked in a KOH solution for ion exchange to obtain a double-ion exchange group-containing polybenzimidazole membrane.

3. The method for preparing a polybenzimidazole membrane containing two ion-exchange groups as described in claim 2, characterized in that, In step one, the molar ratio of the tertiary ammonium group-containing reagent to dibromohexane is 1:2-10, the molar volume ratio of the tertiary ammonium group-containing reagent to ethyl acetate is 10-30 mmol:20-50 mL, the reaction temperature is 20-50 DEG C, the reaction time is 24-48 h, the vacuum drying temperature is 40-60 DEG C, the drying time is 12-36 h, and the tertiary ammonium group-containing reagent is any one of 1-methylpiperidine, 1,4-dimethylpiperazine, 1-methylpyrrole, 1-methylimidazole, 1-methylpyrrolidine, 1-methylpyrazole, imidazolium, trimethylamine, triethylamine and tripropylamine.

4. The method for preparing a polybenzimidazole membrane containing two ion-exchange groups as described in claim 2, characterized in that, In step two, the volume-mass ratio of methane sulfonic acid to P2O5 is 10 mL:1-5 g, the volume-molar ratio of methane sulfonic acid to diamino benzidine is 10 mL:1-3 mmol, the molar ratio of diamino benzidine to dicarboxylic acid monomer is 10-30 mmol:10-30 mmol, the reaction temperature is 80-150 DEG C, the reaction time is 24-48 h, the vacuum drying temperature is 40-60 DEG C, and the drying time is 12-36 h; the dicarboxylic acid monomer is any one of 2,2-bis(4-carboxyphenyl)hexafluoropropane, 4,4'-dicarboxy diphenyl ether and terephthalic acid.

5. The method for preparing a polybenzimidazole membrane containing two ion-exchange groups as described in claim 2, characterized in that, In the third step, the molar volume ratio of the polybenzimidazole polymer and dimethyl sulfoxide is 1 mmol: 5-15 mL, the molar ratio of the polybenzimidazole polymer and 2,3-epoxypropyltrimethylammonium chloride is 1 mmol: 1.5-3.0 mmol, the molar ratio of 2,3-epoxypropyltrimethylammonium chloride and the monomer containing ammonium bromide is 0-4 mmol: 0-4 mmol, the reaction temperature is 80-110 ℃, and the reaction time is 24-48 h; the precipitant is one or more of anhydrous ethanol, ethyl acetate, and deionized water.

6. The method for preparing a polybenzimidazole membrane containing two ion-exchange groups as described in claim 2, characterized in that, In the fourth step, the stirring and dissolving temperature is 60-80 ℃, the stirring time is 6-24 h; the casting solution drying temperature is 60-100 ℃, the drying time is 12-24 h; the mass-volume ratio of the double-cationic polybenzimidazole polymer and dimethyl sulfoxide is 0.3-0.8 g:10 mL; in the fifth step, the concentration of the KOH solution is 0.5-4 mol·L –1 , and the soaking time is 24-72 h.

7. The process for producing a polybenzimidazole membrane containing dual ion exchange groups according to claim 2, wherein The fourth step is replaced by: S41, adding the dicationic polybenzimidazole polymer obtained in the third step and dimethyl sulfoxide into a reactor, stirring and dissolving, then adding carbon nanotubes and stirring uniformly to obtain a bright yellow casting solution; S42, adding silver nitrate solution dropwise into the casting solution while adding triethylamine to adjust the pH, stirring and reacting to obtain a modified casting solution, pouring the modified casting solution onto a clean glass plate to flow into a film, drying the film, then immersing the film in ethanol to remove residual solvents, and washing with deionized water.

8. Use of a polybenzimidazole membrane containing double ion exchange groups, characterized in that The polybenzimidazole membrane containing the double ion exchange groups is used as a diaphragm in a membrane electrode for electrocatalytic reduction of CO2.

9. Use of a polybenzimidazole membrane containing dual ion exchange groups according to claim 8, characterized in that, The preparation method of the membrane electrode comprises the following steps: adding nano-silver powder into a mixed solution of deionized water, anhydrous ethanol, and FAA, ultrasonicating to obtain a cathode catalyst ink, uniformly spraying the ink onto a hydrophobic carbon paper using an airbrush, drying at 50-70 ℃, and preparing a cathode; adding iridium oxide into a solution of deionized water, anhydrous ethanol, and FAA, ultrasonicating to obtain an anode catalyst ink, uniformly spraying the ink onto a hydrophobic carbon paper using an airbrush, drying at 50-70 ℃, and preparing an anode; and finally assembling the cathode, the polybenzimidazole membrane containing the double ion exchange groups, and the anode to obtain a membrane electrode. In the preparation of the cathode, the mass-volume ratio of the nano-silver powder, the anhydrous ethanol, the deionized water, and the FAA solution is 1-3 mg: 100-300 μL: 20-100 μL: 5-20 μL; and in the preparation of the anode, the mass-volume ratio of the iridium oxide, the anhydrous ethanol, the deionized water, and the FAA solution is 1-3 mg: 100-300 μL: 20-100 μL: 5-20 μL.

10. Use of a polybenzimidazole membrane containing dual ion exchange groups according to claim 9, characterized in that 0.1~1mol·L –1 KHCO3 as an anode electrolyte, the electrolyte is delivered to the anode by a peristaltic pump for flow, dry CO2 is humidified by a gas humidification device and delivered to the cathode for flow, then a constant current is applied for electrolysis to promote the electrocatalytic reduction of CO2; the rotation speed of the peristaltic pump is 20~80 rpm; the flow rate of the CO2 is 10~40 mL·min –1 ; the thickness of the polybenzimidazole membrane containing double ion exchange groups is 10~50 μm.

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