Preparation and Application of a Crosslinked Quaternized Polybenzimidazole Anion Exchange Membrane

Abstract

The present invention discloses the preparation and application of a cross-linked quaternized polybenzimidazole anion exchange membrane. A grafted modified quaternized polybenzimidazole precursor is dissolved in dimethyl sulfoxide, and dichloroalkane is added for reaction to obtain a viscous casting solution. The solution is then poured onto a dry and clean glass plate, cast into a film, and dried. Finally, the obtained cross-linked quaternized polybenzimidazole anion exchange membrane is immersed in anhydrous ethanol, washed, and dried. The dried cross-linked quaternized polybenzimidazole anion exchange membrane is immersed in a KOH solution, washed with deionized water, and dried to serve as a membrane diaphragm for a membrane electrode in electrocatalytic reduction of carbon dioxide (CO2). The present invention uses dichloroalkane as a cross-linking agent to react with hydroxyl groups on the side chains of the quaternized polybenzimidazole to cross-link the main chain, thereby obtaining a cross-linked quaternized polybenzimidazole anion exchange membrane. The cross-linked quaternized polybenzimidazole anion exchange membrane can improve the ionic conductivity and the Faradaic efficiency of carbon monoxide (CO) of the anion exchange membrane.

Description

Technical Field

[0001] The invention belongs to the field of anion exchange membranes for organic synthesis and electrocatalytic reduction of CO2, and relates to a preparation method and application of a cross-linked quaternized polybenzimidazole anion exchange membrane. Background Art

[0002] With the development of social economy, CO2 emissions are increasing, causing global warming and greenhouse effect, and leading to the occurrence of extreme weather. In order to maintain the natural environment on which human beings depend for survival, it is urgent to reduce the content of CO2 in the atmosphere. Converting CO2 into high-value-added products such as CO, methanol or dimethyl ether is crucial to the high-value utilization of CO2 and carbon cycle. At present, there are mainly the following methods for high-value utilization of CO2: (1) Biochemical method - green plants convert CO2 into organic matter through photosynthesis; (2) Photocatalysis - under the action of light, electrons escape from the surface of the photocatalyst, forming holes on the surface of the catalyst, providing binding sites for CO2 reduction, and reducing CO2 to high-value-added products such as CO, formic acid and methane; (3) Electrocatalysis - CO2 is reduced at the cathode of the electrolytic cell through electrolysis to obtain a series of products with economic value. At the same time, the type and purity of the products of CO2 electroreduction can be controlled by adjusting the cathode catalytic material and reduction potential. Among the above methods, electrocatalytic reduction of CO2 is an efficient and environmentally friendly technology with the following advantages: (1) electrocatalytic reduction can be carried out at room temperature and atmospheric pressure, and the reaction conditions are relatively mild; (2) the electrocatalytic reduction process only consumes CO2. Based on these factors, electrocatalytic reduction of CO2 is regarded as a promising CO2 conversion technology.

[0003] At present, electrocatalytic reduction of CO2 devices are mainly divided into two types: H-type electrolytic cell and membrane electrode device. Among them, the main components of the membrane electrode are ion exchange membrane, gas diffusion layer, catalyst, flow field (i.e. bipolar plate, its function is to guide the gas flow, ensure uniform contact between gas and catalyst, and reduce the pressure drop of gas. The common flow fields currently include: straight-through type, serpentine type, bionic leaf vein type, etc.). The schematic diagram of the membrane electrode structure is shown in the figure below. Figure 1 As shown. The catalyst is dispersed in a Nafion solution or other polymer solution, and the catalyst is loaded on the gas diffusion layer by drop coating or other methods to form a catalyst layer. Ideally, after the catalyst is loaded, the catalyst layer has a uniform thickness and a microscopic porous structure. Compared with the H-type electrolytic cell, the membrane electrode assembly can greatly shorten the distance between the anode and cathode, and the cathode does not need to use an electrolyte, which reduces the system ohmic consumption caused by the electrolyte. At the same time, one side of the membrane electrode is the gas diffusion layer, and the other side is the electrolyte. The presence of the electrolyte can keep the membrane in a wet state for a longer time, which is beneficial to the transmission of ions in the membrane, improves the ion conductivity and the anion transfer rate, and thus enhances the effect of electrocatalytic reduction of CO2.

[0004] In a membrane electrode assembly (MEA), the diaphragm performs two primary functions: first, it separates the cathode and anode, preventing oxygen generated by anodic oxidation from affecting the CO2 reduction reaction at the cathode; second, it allows ions, such as protons and hydroxide, to pass through, creating a complete pathway. The membrane's efficient ion exchange capacity effectively suppresses the increase in the cathode electrolyte pH, thereby improving CO2 utilization. Ion exchange membrane materials, which transport ions and separate the anode and cathode, are primarily classified into anion exchange membranes, cation exchange membranes, and bipolar membranes. Anion exchange membranes are polymer membranes containing alkaline active groups that are selectively permeable to anions. Ideal anion exchange membranes should exhibit excellent anion conductivity, high mechanical strength, low swelling rate, and good chemical stability. In addition, the anion exchange membrane can selectively transfer hydroxide, thereby reducing the hydroxide concentration at the cathode, inhibiting the hydrogen evolution reaction at the cathode, and improving the Faraday efficiency of the electrocatalytic reduction of CO2; at the same time, it can effectively prevent the generated hydroxide from having a negative impact on the cathode catalyst, causing the peeling and precipitation of the metal catalyst and the loss of CO2; however, the ionic conductivity and Faraday effect of CO of the anion exchange membrane in the existing technology are not high, which seriously affects the effect of the electrocatalytic reduction of CO2. Summary of the Invention

[0005] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0006] In order to achieve these purposes and other advantages according to the present invention, a cross-linked quaternized polybenzimidazole anion exchange membrane is provided. The cross-linked quaternized polybenzimidazole anion exchange membrane has the structural formula:

[0007]

[0008] The present invention also embodies the use of the cross-linked quaternized polybenzimidazole anion exchange membrane as claimed in claim 1 in the electrocatalytic reduction of CO2, wherein the cross-linked quaternized polybenzimidazole anion exchange membrane is used as a diaphragm of a membrane electrode in the electrocatalytic reduction of CO2.

[0009] Preferably, the preparation method of the membrane electrode is: taking nano silver powder and adding it to ethanol, deionized water and Nafion117 solution, ultrasonicating to obtain catalyst ink, and then evenly drop-coating it on hydrophobic carbon paper, and drying it at 50-70°C to form a cathode; then taking iridium oxide and adding it to ethanol, deionized water and Nafion117 solution, ultrasonicating, and evenly drop-coating the obtained solution on hydrophobic carbon paper, drying to form an anode; finally, assembling the cathode, cross-linked quaternized polybenzimidazole anion exchange membrane, and anode to obtain a membrane electrode.

[0010] Preferably, the mass volume ratio of the nano silver powder to ethanol, deionized water and Nafion 117 solution is: 1 mg: 150 μL: 50 μL: 12 μL; the size of the cross-linked quaternized polybenzimidazole anion exchange membrane is 2×2 cm 2 The mass volume ratio of the iridium oxide to ethanol, deionized water and Nafion 117 solution is: 1 mg: 150 μL: 50 μL: 12 μL; the amount of iridium oxide in the anode is 0.5 to 1.5 mg cm -2 .

[0011] Preferably, 0.1 to 1 mol L -1 KHCO3 is used as the electrolyte, and the electrolyte is transported to the anode for flow through a peristaltic pump. The dry CO2 is humidified by a gas humidifier and then transported to the cathode for flow. Then, voltage is applied for electrolysis to promote electrocatalytic reduction of CO2.

[0012] Preferably, the rotation speed of the peristaltic pump is 30-80 rpm; the flow rate of the CO2 is 10-30 mL min -1 .

[0013] Preferably, the preparation method of the cross-linked quaternized polybenzimidazole anion exchange membrane comprises the following steps:

[0014] Step 1: dissolving the grafted modified quaternized polybenzimidazole precursor in dimethyl sulfoxide, stirring at 70-85°C until completely dissolved, adding dichloroalkane and continuously stirring at 85-95°C, reacting for 18-36 hours to obtain a viscous liquid, then pouring the viscous liquid onto a dry and clean glass plate to cast a film, and then drying at 50-70°C for 20-30 hours to obtain a cross-linked quaternized polybenzimidazole anion exchange membrane;

[0015] Step 2: Soak the prepared cross-linked quaternized polybenzimidazole anion exchange membrane in anhydrous ethanol for 18 to 28 hours, wash with deionized water, and dry;

[0016] Step 3: Place the membrane dried in step 2 in a 1 mol L -1 The membrane was immersed in KOH solution for 18 to 28 hours to carry out ion exchange, and then washed with deionized water and dried to obtain a cross-linked quaternary ammonium polybenzimidazole anion exchange membrane that can be used for electrocatalytic reduction of CO2.

[0017] Preferably, in step 1, dimethyl sulfoxide is replaced by one or a mixture of N,N'-diaminoacetamide, N,N'-diaminoformamide, diethylene glycol dimethyl ether, and N-methyl-2-pyrrolidone; in step 3, anhydrous ethanol is replaced by one or a mixture of methanol, acetone, and isopropanol.

[0018] Preferably, the chain length of the dichloroalkane is 4 to 10; the mass volume ratio of the quaternized polybenzimidazole precursor to dimethyl sulfoxide is 5 to 10 w / v%; and the mass molar ratio of the quaternized polybenzimidazole precursor to the dichloroalkane is 1 g: 2 to 3 mmol.

[0019] Preferably, the thickness of the cross-linked quaternized polybenzimidazole anion exchange membrane obtained in step 4 is 20 to 50 μm.

[0020] The present invention has at least the following beneficial effects:

[0021] (1) The present invention uses polybenzimidazole as the polymer backbone, which can improve the chemical stability and mechanical properties of the anion exchange membrane;

[0022] (2) The present invention uses 2,3-epoxypropyltrimethylammonium chloride as a grafting agent to react with imidazole in the polybenzimidazole main chain to modify the main chain to obtain a polybenzimidazole main chain containing quaternary ammonium groups, which can improve the ion conductivity of the anion exchange membrane and the Faraday effect of CO;

[0023] (3) The present invention uses dichloroalkane as a cross-linking agent to react with the hydroxyl groups on the polybenzimidazole side chains to cross-link the main chain to obtain a cross-linked quaternized polybenzimidazole anion exchange membrane, which can improve the ion conductivity of the anion exchange membrane and the Faradaic efficiency of CO.

[0024] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the membrane electrode structure of the present invention;

[0026] Figure 2 ATR-FTIR spectra of PBI, QAPBI and cQAPBI-nC films of the present invention;

[0027] Figure 3 The cQAPBI-6C membrane of the present invention 1 H-NMR spectroscopy;

[0028] Figure 4 The Faraday efficiency diagram FE of the cQAPBI-6C membrane of the present invention, the commercial anion exchange membrane (FAA-3-PK-130, Fumasep, Germany), and the Nafion 117 membrane CO ;

[0029] Figure 5Graphs showing the CO current density of the cQAPBI-6C membrane of the present invention, a commercial anion exchange membrane (FAA-3-PK-130, Fumasep, Germany), and a Nafion 117 membrane.

[0030] Figure 6 The synthetic route of the cross-linked quaternized polybenzimidazole anion exchange membrane of the present invention is shown in FIG. DETAILED DESCRIPTION

[0031] The present invention will be described in further detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0032] It should be understood that terms such as “having,” “including,” and “comprising” used herein do not prescribe the existence or addition of one or more other elements or combinations thereof.

[0033] Example 1:

[0034] A method for preparing a cross-linked quaternized polybenzimidazole anion exchange membrane comprises the following steps:

[0035] Step 1: Weigh 1.00 g of polybenzimidazole and place it in a three-necked flask. Add 40.0 mL of dimethyl sulfoxide and stir in an 80 ° C oil bath until completely dissolved. Add 5 mmol of 2,3-epoxypropyltrimethylammonium chloride and continue stirring at 80 ° C for 24 hours to obtain a brown viscous solution. Pour it into 200.0 mL of acetone for precipitation. After suction filtration and washing with deionized water for 3 to 5 times, it is vacuum dried at room temperature for 48 hours to obtain a quaternized polybenzimidazole precursor.

[0036] Step 2: Weigh 1.00 g of quaternized polybenzimidazole precursor and dissolve it in 20.0 mL of dimethyl sulfoxide to obtain a brown viscous solution. Add 2.5 mmol of 1,4-dichlorobutane and stir continuously in a 90 ° C oil bath for 24 hours to obtain a brown viscous solution. Pour the viscous solution onto a dry and clean glass plate and cast it into a film. Then dry it at 60 ° C for 24 hours to obtain a cross-linked quaternized polybenzimidazole anion exchange membrane.

[0037] Step 3: Soak the prepared cross-linked quaternized polybenzimidazole anion exchange membrane in ethanol for 24 hours, wash with deionized water, and dry;

[0038] Step 4: Cross-linked quaternized polybenzimidazole anion exchange membrane was added to 1 mol L -1 The membrane was immersed in a KOH solution for 24 hours to achieve the exchange of chloride ions and hydroxide ions; finally, it was washed with deionized water and dried to obtain a cross-linked quaternary ammonium polybenzimidazole anion exchange membrane (cQAPBI-4C) that can be used for electrocatalytic reduction of CO2.

[0039] Example 2:

[0040] A method for preparing a cross-linked quaternized polybenzimidazole anion exchange membrane comprises the following steps:

[0041] Step 1: Weigh 1.00 g of polybenzimidazole and place it in a three-necked flask. Add 40.0 mL of dimethyl sulfoxide and stir in an 80 ° C oil bath until completely dissolved. Add 5 mmol of 2,3-epoxypropyltrimethylammonium chloride and continue stirring at 80 ° C for 24 hours to obtain a brown viscous solution. Pour it into 200.0 mL of acetone for precipitation. After suction filtration and washing with deionized water for 3 to 5 times, it is vacuum dried at room temperature for 48 hours to obtain a quaternized polybenzimidazole precursor.

[0042] Step 2: Weigh 1.00 g of quaternized polybenzimidazole precursor and dissolve it in 20.0 mL of dimethyl sulfoxide to obtain a brown viscous solution. Add 2.5 mmol of 1,6-dichlorohexane and stir continuously in a 90 ° C oil bath for 24 hours to obtain a brown viscous solution. Pour the viscous solution onto a dry and clean glass plate and cast it into a film. Then dry it at 60 ° C for 24 hours to obtain a cross-linked quaternized polybenzimidazole anion exchange membrane.

[0043] Step 3: Soak the prepared cross-linked quaternized polybenzimidazole anion exchange membrane in ethanol for 24 hours, wash with deionized water, and dry;

[0044] Step 4: Cross-linked quaternized polybenzimidazole anion exchange membrane was added to 1 mol L -1 The membrane was immersed in a KOH solution for 24 hours to achieve the exchange of chloride ions and hydroxide ions; finally, it was washed with deionized water and dried to obtain a cross-linked quaternary ammonium polybenzimidazole anion exchange membrane (cQAPBI-6C) that can be used for electrocatalytic reduction of CO2.

[0045] Example 3:

[0046] A method for preparing a cross-linked quaternized polybenzimidazole anion exchange membrane comprises the following steps:

[0047] Step 1: Weigh 1.00 g of polybenzimidazole and place it in a three-necked flask. Add 40.0 mL of dimethyl sulfoxide and stir in an 80 ° C oil bath until completely dissolved. Add 5 mmol of 2,3-epoxypropyltrimethylammonium chloride and continue stirring at 80 ° C for 24 hours to obtain a brown viscous solution. Pour it into 200.0 mL of acetone for precipitation. After suction filtration and washing with deionized water for 3 to 5 times, it is vacuum dried at room temperature for 48 hours to obtain a quaternized polybenzimidazole precursor.

[0048] Step 2: Weigh 1.00 g of quaternized polybenzimidazole precursor and dissolve it in 20.0 mL of dimethyl sulfoxide to obtain a brown viscous solution. Add 2.5 mmol of 1,8-dichlorooctane and stir continuously in a 90 ° C oil bath for 24 hours to obtain a brown viscous solution. Pour the viscous solution onto a dry and clean glass plate and cast it into a film. Then dry it at 60 ° C for 24 hours to obtain a cross-linked quaternized polybenzimidazole anion exchange membrane.

[0049] Step 3: Soak the prepared cross-linked quaternized polybenzimidazole anion exchange membrane in ethanol for 24 hours, wash with deionized water, and dry;

[0050] Step 4: Cross-linked quaternized polybenzimidazole anion exchange membrane was added to 1 mol L -1 The membrane was immersed in a KOH solution for 24 hours to achieve the exchange of chloride ions and hydroxide ions; finally, it was washed with deionized water and dried to obtain a cross-linked quaternary ammonium polybenzimidazole anion exchange membrane (cQAPBI-8C) that can be used for electrocatalytic reduction of CO2.

[0051] Example 4:

[0052] A method for preparing a cross-linked quaternized polybenzimidazole anion exchange membrane comprises the following steps:

[0053] Step 1: Weigh 1.00 g of polybenzimidazole and place it in a three-necked flask. Add 40.0 mL of dimethyl sulfoxide and stir in an 80 ° C oil bath until completely dissolved. Add 5 mmol of 2,3-epoxypropyltrimethylammonium chloride and continue stirring at 80 ° C for 24 hours to obtain a brown viscous solution. Pour it into 200.0 mL of acetone for precipitation. After suction filtration and washing with deionized water for 3 to 5 times, it is vacuum dried at room temperature for 48 hours to obtain a quaternized polybenzimidazole precursor.

[0054] Step 2: Weigh 1.00 g of quaternized polybenzimidazole precursor and dissolve it in 20.0 mL of dimethyl sulfoxide to obtain a brown viscous solution. Add 2.5 mmol of 1,10-dichlorodecane and stir continuously in a 90 ° C oil bath for 24 hours to obtain a brown viscous solution. Pour the viscous solution onto a dry and clean glass plate and cast it into a film. Then dry it at 60 ° C for 24 hours to obtain a cross-linked quaternized polybenzimidazole anion exchange membrane.

[0055] Step 3: Soak the prepared cross-linked quaternized polybenzimidazole anion exchange membrane in ethanol for 24 hours, wash with deionized water, and dry;

[0056] Step 4: Cross-linked quaternized polybenzimidazole anion exchange membrane was added to 1 mol L -1The membrane was immersed in a KOH solution for 24 hours to achieve the exchange of chloride ions and hydroxide ions; finally, it was washed with deionized water and dried to obtain a cross-linked quaternary ammonium polybenzimidazole anion exchange membrane (cQAPBI-10C) that can be used for electrocatalytic reduction of CO2.

[0057] Comparative Example 1:

[0058] Step 1: Weigh 1.00 g of polybenzimidazole and place it in a three-necked flask. Add 40.0 mL of dimethyl sulfoxide and stir in an 80 ° C oil bath until completely dissolved. Add 5 mmol of 2,3-epoxypropyltrimethylammonium chloride and continue stirring at 80 ° C for 24 hours to obtain a brown viscous solution. Pour it into 200.0 mL of acetone for precipitation. After suction filtration and washing with deionized water for 3 to 5 times, it is vacuum dried at room temperature for 48 hours to obtain a quaternized polybenzimidazole precursor.

[0059] Step 2: Weigh 1.00 g of quaternized polybenzimidazole precursor and dissolve it in 20.0 mL of dimethyl sulfoxide. Stir at 60 ° C to obtain a brown viscous liquid. Pour the viscous liquid onto a dry and clean glass plate and cast it into a film. Then dry it at 60 ° C for 24 h to obtain a quaternized polybenzimidazole (QAPBI) anion exchange membrane.

[0060] Step 3: Soak the prepared quaternized polybenzimidazole anion exchange membrane in ethanol for 24 hours, rinse with deionized water, and dry;

[0061] Step 4: quaternized polybenzimidazole anion exchange membrane in 1 mol L -1 Soak in KOH solution for 24 hours to achieve the exchange of chloride ions and hydroxide ions; finally wash with deionized water and dry.

[0062] Comparative Example 2:

[0063] A method for preparing a polybenzimidazole (PBI) membrane comprises:

[0064] 1.00 g of polybenzimidazole was weighed and placed in a three-necked flask. 40.0 mL of dimethyl sulfoxide was added and stirred in an 80 °C oil bath until completely dissolved. The mixture was then poured onto a dry and clean glass plate and cast into a film. The film was then dried at 120 °C for 24 h to obtain a novel polybenzimidazole membrane. The prepared polybenzimidazole membrane was immersed in ethanol for 24 h, washed with deionized water, and dried. The polybenzimidazole membrane was then immersed in 1 mol L -1 Soak in KOH solution for 24 hours to achieve the exchange of chloride ions and hydroxide ions; finally wash with deionized water and dry.

[0065] Figure 2As shown in the ATR-FTIR spectra of PBI, QAPBI, and cQAPBI-nC films, the NH bond on the imidazole group appears at 1543 cm -1 , which disappears after grafting with EPTMA-Cl (2,3-epoxypropyltrimethylammonium chloride). 1419cm -1 The characteristic peaks at 1036 cm are identified as CH stretching vibrations of methyl and methylene groups. -1 The characteristic peak at 950 cm is attributed to the stretching vibration of OH on the flexible alkane side chain after the ring-opening reaction, and the characteristic peak of hydroxyl disappears after cross-linking, indicating that alkane chains of different lengths are successfully cross-linked through nucleophilic substitution reaction. -1 The characteristic peak at is the quaternary ammonium group. ATR-FTIR results demonstrate that EPTMA-Cl has been grafted onto the imidazole groups of the PBI polymer via the expected ring-opening reaction, and cQAPBI-nC membranes have been successfully prepared by cross-linking.

[0066] Figure 3 For cQAPBI-6C membrane 1 H-NMR spectrum; after the grafting and cross-linking reactions were completed, the NH chemical shift of 13.00 ppm on the imidazole completely disappeared; the chemical shift of 6.50-8.50 ppm came from the hydrogen of the aromatic ring of the PBI main chain; the chemical shift peak of 5.40 ppm was the hydroxyl group obtained after the ring-opening substitution reaction; the doublet at 4.50 ppm was the hydrogen of the methylene group, indicating that the flexible alkyl side chain had been successfully grafted onto the PBI main chain; the chemical shift peak at 1.55 ppm was the methyl group on the quaternary ammonium group; the quintet at 1.18-1.35 ppm was the methylene group on the cross-linker; the chemical shift peak at 1.06 ppm was the methylene group connected to the hydroxyl group; and the triplet at 0.85 ppm was the methylene group on the ether bond; the above results also showed that the cQAPBI-6C membrane was successfully prepared using PBI, EPTMA-Cl and 1,6-dichlorohexane as raw materials.

[0067] The performance tests of the polybenzimidazole quaternary ammonium salt anion exchange membranes prepared in the examples and comparative examples were performed as follows:

[0068] (1) Ion exchange capacity (IEC) test:

[0069] IEC of anion exchange membrane (mmol g -1 ) reflects the content of ion exchange groups in the membrane. Generally speaking, the more ion exchange groups in the membrane, the better the ion conductivity of the membrane. The IEC test method is to take 1×5cm 2 The anion exchange membrane was washed and dried in a 50℃ oven for 36 hours until the weight remained constant. The weight of the dry membrane was measured as m dry The membrane was placed in a 0.1 mol L-1 Soak in HCl solution for 24 h to exchange hydroxide ions into the solution, and then use 1 mol L - 1 The volume of NaOH solution consumed in titration is V2. The IEC calculation formula of anion exchange membrane is as follows:

[0070]

[0071] Where C1 is the concentration of HCl and C2 is the concentration of NaOH.

[0072] The IEC of the anion exchange membranes of Examples 1 to 4 and Comparative Example 1 are shown in Table 1;

[0073] (2) Swelling (SR) test:

[0074] The swelling rate of anion exchange membrane reflects the change in the physical dimensions of the membrane before and after water absorption, thereby evaluating the stability of the membrane. 2 The anion exchange membrane was cleaned and dried in a 50°C oven for 36 hours until the weight remained constant. The length of the dry membrane was measured as L1. The membrane was soaked in 30°C deionized water for 24 hours, and the surface of the membrane was wiped dry with filter paper. The length of the wet membrane was measured as L2. The swelling ratio of the membrane was calculated as follows:

[0075]

[0076] The SR of the anion exchange membranes of Examples 1 to 4 and Comparative Example 1 is shown in Table 1;

[0077] (3) Water absorption (WU) test:

[0078] The water absorption rate of anion exchange membrane is affected by the content of ion exchange groups and membrane structure, and is closely related to ion conductivity. The water absorption rate of anion exchange is determined by dry-wet weight method. 2 Wash the anion exchange membrane and dry it in a 50°C oven for 36 hours until the weight remains constant. Weigh the mass of the dry membrane as m1. Soak the membrane in 30°C deionized water for 24 hours, remove it, wipe the water off the membrane surface with filter paper, and weigh the mass of the wet membrane as m2. The formula for the membrane's water absorption is as follows:

[0079]

[0080] The WU of the anion exchange membranes of Examples 1 to 4 and Comparative Example 1 are shown in Table 1.

[0081] Table 1

[0082]

[0083] (4) Hydroxide conductivity (σ) test:

[0084] Ionic conductivity reflects the anion exchange membrane's ability to conduct hydroxide ions. Higher hydroxide conductivity indicates better CO2 electrocatalytic reduction. An H-type electrolytic cell was divided into two compartments using a soaked anion exchange membrane. Both compartments were filled with 25°C deionized water. Finally, the impedance of the H-type electrolytic cell with the membrane installed was measured using a CHI660E electrochemical workstation manufactured by Shanghai Chenhua Instrument Co., Ltd. at a constant current of 5.0 mA and a frequency range of 1.0 Hz to 100 kHz. The impedance of the conductivity cell without the membrane was measured using the same test method, maintaining the same distance between the two electrodes and the same volume of electrolyte in the two compartments. The proton conductivity of the membrane was calculated as follows:

[0085]

[0086] Where σ is the hydroxide conductivity of the membrane (mS cm -1 ), A is the effective area of the diaphragm (cm 2 ), d is the thickness of the diaphragm (cm).

[0087] The σ of the anion exchange membranes of Examples 1 to 4 and Comparative Example 1 are shown in Table 2;

[0088] Table 2

[0089]

[0090] (5) Electrocatalytic reduction of CO2 test:

[0091] Anion exchange membranes are used as separators in the electrocatalytic reduction of CO2. Current density (j) and Faraday effect (FE) are the main parameters for evaluating the performance of the membrane. The membrane electrode preparation method is as follows: 5 mg of nanosilver powder is weighed, 750 μL of ethanol, 250 μL of deionized water, and 60 μL of Nafion 117 solution are added to obtain a catalyst ink. The catalyst ink is then ultrasonicated for 1 hour and evenly sprayed onto a 2×2 cm2 surface in a 60°C oven. 2 Then, 5 mg of iridium oxide was added to 750 μL of ethanol, 250 μL of deionized water and 60 μL of Nafion 117 solution, and ultrasonicated to obtain a solution uniformly sprayed on the SGL hydrophobic carbon paper (the amount of iridium oxide in the anode is 1 mg cm -2 ), drying to form an anode; finally, assembling the cathode, cross-linked quaternary ammonium polybenzimidazole anion exchange membrane, and anode to obtain a membrane electrode. -1 KHCO3 was used as the electrolyte, and the electrolyte was transported to the anode by a peristaltic pump for flow. The dry CO2 was humidified by a gas humidifier and then heated at a rate of 20 mL min-1 The gas was delivered to the cathode at a flow rate of 100 nm. Using the IT curve function of a CHI660E electrochemical workstation manufactured by Shanghai Chenhua Instrument Co., Ltd., electrolysis was performed at different voltages for 1 h. The gas products were then passed through a 9790Plus gas chromatograph manufactured by Fuzhou Fuli Instrument Co., Ltd. to measure the ppm values of CO and hydrogen in the products. The Faraday effect calculation formula for CO is as follows:

[0092]

[0093] Where α is the number of electrons transferred when CO2 is reduced to CO2, n is the molar amount of CO (mol), and F is the Faraday constant (96485mol C -1 ), Q is the total coulomb amount transferred to the cathode (C).

[0094] jCO=FEco×jt ota l

[0095] Among them, j total is the total cathode current density (mA cm -2 ), FE CO is the Faraday effect of CO (%).

[0096] FE of the anion exchange membranes of Example 2 and Comparative Example 1 CO and j CO As shown in Table 3.

[0097] Table 3

[0098]

[0099] Figure 4 The Faraday efficiency diagram FE of the cQAPBI-6C membrane of the present invention, the commercial anion exchange membrane (FAA-3-PK-130, Fumasep, Germany), and the Nafion 117 membrane CO ; As can be seen from the figure, the Faradaic efficiency of cQAPBI-6C is better than that of commercial anion exchange membrane.

[0100] Figure 5 The figure shows the CO current density of the cQAPBI-6C membrane of the present invention, a commercial anion exchange membrane (FAA-3-PK-130, Fumasep, Germany), and a Nafion 117 membrane. As can be seen from the figure, the CO current density of the cQAPBI-6C is better than that of the commercial anion exchange membrane.

[0101] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. Application of a cross-linked quaternized polybenzimidazole anion exchange membrane in electrocatalytic reduction of CO2, characterized in that: The structural formula of the cross-linked quaternized polybenzimidazole anion exchange membrane is: ； The cross-linked quaternized polybenzimidazole anion exchange membrane is used as a diaphragm for a membrane electrode in the electrocatalytic reduction of CO2.

2. Use of the cross-linked quaternized polybenzimidazole anion exchange membrane according to claim 1 in electrocatalytic reduction of CO2, characterized in that: The membrane electrode preparation method comprises the following steps: adding nanosilver powder to a solution of ethanol, deionized water, and Nafion 117, ultrasonically treating the solution to obtain a catalyst ink, and then uniformly drop-coating the ink on hydrophobic carbon paper and drying the ink at 50-70°C to form a cathode; then adding iridium oxide to a solution of ethanol, deionized water, and Nafion 117, ultrasonically treating the solution to obtain a catalyst ink, and uniformly drop-coating the ink on the hydrophobic carbon paper and drying the ink to form an anode; and finally assembling the cathode, a cross-linked quaternized polybenzimidazole anion exchange membrane, and an anode to obtain a membrane electrode.

3. Use of the cross-linked quaternized polybenzimidazole anion exchange membrane according to claim 2 in electrocatalytic reduction of CO2, characterized in that: The mass volume ratio of the nano-silver powder to ethanol, deionized water and Nafion 117 solution is: 1 mg: 150 μL: 50 μL: 12 μL; the size of the cross-linked quaternary ammonium polybenzimidazole anion exchange membrane is 2×2 cm 2 The mass volume ratio of the iridium oxide to ethanol, deionized water and Nafion 117 solution is: 1 mg:150 μL:50 μL:12 μL; the amount of iridium oxide in the anode is 0.5~1.5 mg cm -2 .

4. Use of the cross-linked quaternized polybenzimidazole anion exchange membrane according to claim 2 in electrocatalytic reduction of CO2, characterized in that: Use 0.1~1 mol L -1 KHCO3 is used as the electrolyte, and the electrolyte is transported to the anode for flow through a peristaltic pump. The dry CO2 is humidified by a gas humidifier and then transported to the cathode for flow. Then, voltage is applied for electrolysis to promote electrocatalytic reduction of CO2.

5. Use of the cross-linked quaternized polybenzimidazole anion exchange membrane according to claim 4 in electrocatalytic reduction of CO2, characterized in that: The rotation speed of the peristaltic pump is 30-80 rpm; the flow rate of the CO2 is 10-30 mL min -1 .

6. Use of the cross-linked quaternized polybenzimidazole anion exchange membrane according to claim 1 in electrocatalytic reduction of CO2, characterized in that: The preparation method of the cross-linked quaternized polybenzimidazole anion exchange membrane comprises the following steps: Step 1: dissolving the grafted modified quaternized polybenzimidazole precursor in dimethyl sulfoxide, stirring at 70-85°C until completely dissolved, adding dichloroalkane and continuously stirring at 85-95°C, reacting for 18-36 hours to obtain a viscous liquid, then pouring the viscous liquid onto a dry and clean glass plate to cast a film, and then drying at 50-70°C for 20-30 hours to obtain a cross-linked quaternized polybenzimidazole anion exchange membrane; Step 2: Soak the prepared cross-linked quaternized polybenzimidazole anion exchange membrane in anhydrous ethanol for 18 to 28 hours, rinse with deionized water, and dry; Step 3: Place the membrane dried in step 2 in 1 mol L -1 The membrane was immersed in KOH solution for 18 to 28 hours for ion exchange, and then washed with deionized water and dried to obtain a cross-linked quaternary ammonium polybenzimidazole anion exchange membrane that can be used for electrocatalytic reduction of CO2.

7. Use of the cross-linked quaternized polybenzimidazole anion exchange membrane according to claim 6 in electrocatalytic reduction of CO2, characterized in that: In the step 1, dimethyl sulfoxide is replaced by one or a mixture of N,N'-diaminoacetamide, N,N'-diaminoformamide, diethylene glycol dimethyl ether, and N-methyl-2-pyrrolidone; in the step 3, anhydrous ethanol is replaced by one or a mixture of methanol, acetone, and isopropanol.

8. Use of the cross-linked quaternized polybenzimidazole anion exchange membrane according to claim 6 in electrocatalytic reduction of CO2, characterized in that: The chain length of the dichloroalkane is 4 to 10; the mass volume ratio of the quaternized polybenzimidazole precursor to dimethyl sulfoxide is 5 to 10 w / v; and the mass molar ratio of the quaternized polybenzimidazole precursor to the dichloroalkane is 1 g:2 to 3 mmol.

9. Use of the cross-linked quaternized polybenzimidazole anion exchange membrane according to claim 6 in electrocatalytic reduction of CO2, characterized in that: The thickness of the cross-linked quaternized polybenzimidazole anion exchange membrane obtained in step three is 20-50 μm.

Images