Preparation Method and Application of Quaternized Polyimide Film

Abstract

The present invention discloses the preparation and application of a quaternized polyimide membrane. First, a polyimide polymer is synthesized by a monomer polymerization strategy. Secondly, the polyimide polymer is dissolved in N,N-dimethylformamide, and 2,3-epoxypropyltrimethylammonium chloride is added for reaction to obtain a casting solution. The casting solution is poured onto a glass plate, cast into a film, and dried. Finally, the quaternized polyimide membrane is immersed in absolute ethanol, washed, and dried; the dried quaternized polyimide membrane is immersed in a KOH solution, washed, and dried, and then used as a separator in an electrocatalytic CO2 reduction device. The present invention uses polyimide as the hydrophobic polymer backbone of an anion exchange membrane, and modifies the backbone with a hydrophilic side chain containing a quaternary ammonium group to construct a polyimide-based anion exchange membrane with a novel molecular structure and high efficiency in electrocatalytic CO2 reduction, providing a new choice for membrane materials for electrocatalytic CO2 reduction applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of anion exchange membranes for electrocatalytic reduction of CO2. More specifically, the present invention relates to a preparation method and application of a quaternized polyimide membrane. Background Art

[0002] How to effectively reduce the concentration of CO2 in the atmosphere has become an important research topic at present. There are mainly two solutions: the first is energy conservation and emission reduction to reduce CO2 emissions from the source; the second is to collect CO2 gas in the atmosphere and utilize it. In recent years, researchers have been continuously exploring the reduction and conversion methods of CO2. According to different driving energies, the existing CO2 reduction reactions can be divided into four categories: biocatalysis, thermal catalysis, photocatalysis, and electrocatalysis. Among them, the electrocatalytic CO2 reduction reaction is convenient to operate and has a simple device, and can be catalyzed by green electricity generated from renewable energy sources such as wind energy, solar energy, and tidal energy, so it has received extensive attention.

[0003] The electrocatalytic CO2 reduction technology is a technology that uses electrocatalysis to convert CO2 into hydrocarbons, hydrocarbon compounds, or other carbon-containing organic compounds. It uses electrocatalytic methods to replace traditional chemical catalytic processes, which can significantly reduce environmental pollution and boost the development of a low-carbon society. The electrocatalytic CO2 reduction technology has many advantages. (1) Environmentally friendly and sustainable: It can convert CO2 into useful chemicals, reduce greenhouse gas emissions, and contribute to addressing climate change. (2) High energy efficiency: Compared with traditional chemical synthesis methods, the electrocatalytic CO2 reduction process requires less energy and has a short reaction time, which can reduce production costs. (3) Product diversity: By adjusting factors such as electrode materials and reaction conditions, various organic compounds can be selectively synthesized, having broad application prospects. (4) Strong controllability: The electrocatalytic reaction can precisely control the reaction process by adjusting parameters such as potential and current density, improving the purity and yield of products.

[0004] The ion exchange membrane is the core component of the electrocatalytic CO2 reduction device. Using the ion exchange membrane can separate the anode and cathode of the electrolytic cell, which not only effectively prevents the oxidation of the reduction product at the anode but also maintains a good ion balance in the whole system. There are two types of ion exchange membranes used for CO2 reduction, one is a cation exchange membrane (CEM), and the other is an anion exchange membrane (AEM). The cation exchange membrane realizes charge transfer through the transport of H + in the electrolyte; the anion exchange membrane transfers charge by combining cationic groups on the membrane with OH - in the electrolyte. When using CEM, H + flows from the anode to the cathode, causing the pH of the cathode to change, and at the same time, it will also promote the occurrence of the hydrogen evolution reaction, increasing production costs. AEM transports OH- The direction is consistent with the direction of the reduction product of CO2 and is more suitable for electrocatalytic CO2 reduction than CEM. As an important component for conducting anions and isolating the two electrodes, the anion exchange membrane should have high OH - conductivity, good stability, strong mechanical properties, and good alkali stability, etc. Summary of the Invention

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

[0006] To achieve these objects and other advantages according to the present invention, a quaternized polyimide membrane is provided, and its structural formula is:

[0007]

[0008] A preparation method of a quaternized polyimide membrane includes the following steps:

[0009] Step 1: Add 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl and 2-(4-aminophenyl)-1H-benzo[d]imidazol-5-amine into a reaction vessel, add N,N-dimethylacetamide, and stir at room temperature; then add 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and continue to react at room temperature;

[0010] Step 2: After the reaction in the previous step is completed, add triethylamine and acetic anhydride to the reaction system in Step 1 to make the reaction system continue to react. Finally, after the reaction solution is cooled to room temperature, slowly pour it into ethanol, filter to obtain a fibrous product, and dry it to obtain a polyimide polymer;

[0011] Step 3: Weigh the polyimide polymer and dissolve it in N,N-dimethylformamide to prepare a brown viscous liquid. Add 2,3-epoxypropyltrimethylammonium chloride and continuously stir in an oil bath to obtain a casting solution. Then pour the casting solution onto a dry and clean glass plate to cast a film, and then dry it in an oven to obtain a chloride-ionized quaternized polyimide membrane;

[0012] Step 4: Immerse the prepared chloride-ionized quaternized polyimide membrane in ethanol for 24 h to remove the residual solvent, and then wash it with deionized water and dry it;

[0013] Step 5: Immerse the chloride-ionized quaternized polyimide membrane in 0.1 mol L -1 KOH solution for 24 h to achieve the exchange of chloride ions and hydroxide ions; finally, wash it with deionized water and dry it.

[0014] Preferably, in step 1, the preparation method of 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl includes:

[0015] S1. Prepare the intermediate 4,4-bis(4-nitrophenoxy)octafluorobiphenyl. The specific method includes: adding decafluorobiphenyl, p-nitrophenol and anhydrous potassium carbonate into a reaction vessel, and adding toluene and N,N-dimethylacetamide; subsequently, stirring the reaction system at 30°C for 1 h, then heating to 80°C and reacting for 24 h; after the reaction is completed, pouring the mixture into deionized water, filtering to collect the yellow solid, and drying it at 40°C for 24 h; finally, obtaining the intermediate 4,4-bis(4-nitrophenoxy)octafluorobiphenyl; wherein the mass-volume ratio of decafluorobiphenyl, p-nitrophenol, anhydrous potassium carbonate, toluene, N,N-dimethylacetamide and deionized water is 8.35 g:6.96 g:10.35 g:10.0 mL:100.0 mL:500.0 mL;

[0016] S2. Add the 4,4-bis(4-nitrophenoxy)octafluorobiphenyl, activated carbon, ferric chloride and absolute ethanol synthesized in the previous step into a reaction vessel, and carry out reflux condensation at 80°C for 0.5 h; then cool down to 70°C, and dropwise add hydrazine hydrate to the reaction system, and continue to react for 12 h; after the reaction is completed, filter off the activated carbon and collect the filtrate; pour the filtrate into deionized water, filter to collect the white solid, and dry it at 40°C for 24 h to obtain the final product 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl; wherein the mass-volume ratio of activated carbon, ferric chloride, absolute ethanol, hydrazine hydrate and deionized water is 2.0 g:0.25 g:150.0 mL:30.0 mL:500.0 mL.

[0017] Preferably, in step 1, the mass-volume ratio of 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl, 2-(4-aminophenyl)-1H-benzimidazol-5-amine, and N,N-dimethylacetamide is 0.61 - 1.02 g:0.46 - 0.63 g:20.0 mL:1.78 g; the stirring time at room temperature is 1 h, and the continued reaction time at room temperature is 24 h.

[0018] Preferably, in step 2, the volume ratio of triethylamine and acetic anhydride is 1:2; after adding triethylamine and acetic anhydride, the reaction system continues to react at 60°C for 2 h, at 90°C for 1 h, and at 100°C for 0.5 h; the drying temperature is 80°C, and the drying time is 24 h.

[0019] Preferably, in the step 3, the mass-volume ratio of the polyimide polymer, N,N-dimethylformamide, and 2,3-epoxypropyltrimethylammonium chloride is 1.00 g: 20.0 mL: 0.12 - 0.16 g; the oil bath temperature is 80 °C, the continuous stirring time is 24 h; the drying temperature in the oven is 80 °C, and the drying time is 24 h.

[0020] Preferably, the step 5 is replaced by: soaking the chlorinated quaternized polyimide membrane in KOH solutions with gradient concentrations, and the concentrations of the KOH solutions with gradient concentrations are 0.05 mol L -1 、0.15 mol L -1 、0.2 mol L -1 、0.25 mol L -1 、0.3 mol L -1 、0.35 mol L -1 in sequence. The soaking time of the chlorinated quaternized polyimide membrane in KOH at each concentration is 4 h, and the soaking temperatures are 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, and 40 °C in sequence.

[0021] An application of a quaternized polyimide membrane, where the quaternized polyimide membrane is applied as a diaphragm in an H-type electrolytic cell for electrocatalytic reduction of CO2.

[0022] Preferably, the specific application method of the quaternized polyimide membrane includes: adding an electrolyte solution to the H-type electrolytic cell, and introducing CO2 into the electrolyte solution at a flow rate of 50 - 70 mL min -1 for half an hour to saturate the electrolyte solution with CO2; using a silver foil with a larger specific surface area as the working electrode, an Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode; continuously introducing CO2 into the electrolyte solution at a speed of 35 - 55 mL min -1 and then applying a voltage between the two electrodes to cause the reduction reaction of CO2 on the surface of the working electrode.

[0023] Preferably, the process of making the silver foil have a larger specific surface area is as follows: using a 0.5-mm-thick silver foil as the cathode catalytic material, using the constant voltage electrolysis function of a CHI660E electrochemical workstation, oxidizing the surface of the silver foil for 3 min under the condition of 2.6 V, and then reducing it for 3 min under the condition of -2.6 V to form a microporous structure on the surface of the silver foil. After the microporous structure is formed on the surface of the silver foil, it is clamped with a glassy carbon electrode clamp to form a working electrode.

[0024] Preferably, the electrolyte solution is a KHCO3 solution with a concentration of 0.1 mol L -1 ;

[0025] The thickness of the quaternized polyimide membrane is 10 - 50 μm;

[0026] In the cathode electrolyte of the H-type electrolytic cell, a magnetic stir bar is added, and the rotation speed of the magnetic stir bar is 100 - 140 r / min -1 .

[0027] The present invention has at least the following beneficial effects: By adopting the molecular structure design and modification strategy, using polyimide as the hydrophobic polymer backbone of the anion exchange membrane, and modifying the backbone with hydrophilic side chains containing quaternary ammonium groups, a polyimide-based anion exchange membrane with a novel molecular structure and high efficiency in electrocatalytic CO2 reduction can be constructed, which can improve the OH- conductivity and CO Faraday efficiency of the anion exchange membrane, providing a new choice for membrane materials for electrocatalytic CO2 reduction applications.

[0028] Other advantages, objectives, and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through the research and practice of the present invention. Brief Description of the Drawings

[0029] Figure 1 It is a schematic diagram of the synthesis route of the quaternized polyimide membrane of the present invention;

[0030] Figure 2 It is the infrared spectrogram of the polyimide membrane and the quaternized polyimide membrane of the present invention;

[0031] Figure 3 It is the 1 1H-NMR spectrogram of the polyimide membrane and the quaternized polyimide membrane of the present invention;

[0032] Figure 4 It is the mechanical strength and elongation at break diagram of Examples 1 - 3 and Comparative Examples 1 - 3 of the present invention;

[0033] Figure 5 It is the CO Faraday efficiency diagram of the quaternized polyimide membranes of Examples 1 - 3 of the present invention;

[0034] Figure 6 It is the CO current density diagram of the quaternized polyimide membranes of Examples 1 - 3 of the present invention;

[0035] Figure 7 It is the CO current density diagram of the quaternized polyimide membranes prepared in Example 2, Example 4, and Example 5 of the present invention. Detailed Description of the Embodiments

[0036] The following further detailed description of the present invention is provided in conjunction with the drawings, so that those skilled in the art can implement it according to the description in the specification.

[0037] It should be understood that terms such as "having", "comprising", and "including" used herein do not preclude the presence or addition of one or more other elements or combinations thereof.

[0038] Example 1

[0039] As Figure 1 shown, this example provides a method for preparing a quaternized polyimide film, comprising the following steps:

[0040] Step 1: Add 1.02 g of 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl (OFBAPB) and 0.46 g of 2-(4-aminophenyl)-1H-benzo[d]imidazol-5-amine (APABI) into a 250 mL three-necked flask, and add 20.0 mL of N,N-dimethylacetamide. Stir at room temperature for 1 h. Subsequently, add 1.78 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and continue to react at room temperature for 24 h;

[0041] Step 2: After the reaction in the previous step is completed, add 5.0 mL of triethylamine and 10.0 mL of acetic anhydride to the reaction system, and make the reaction system continue to react at 60 °C for 2 h, at 90 °C for 1 h, and at 100 °C for 0.5 h. Finally, after the reaction solution is cooled to room temperature, slowly pour it into ethanol, filter to obtain a fibrous product, and dry it at 80 °C for 24 h to obtain polyimide (PI) polymer;

[0042] Step 3: Weigh 1.00 g of polyimide polymer and dissolve it in 20.0 mL of N,N-dimethylformamide to prepare a brown viscous liquid. Add 0.12 g of 2,3-epoxypropyltrimethylammonium chloride, and continuously stir in an 80 °C oil bath for 24 h to obtain a casting solution. Then pour the casting solution onto a dry and clean glass plate to form a film by casting, and then dry it in an 80 °C oven for 24 h to obtain a chloride-ionized quaternized polyimide film;

[0043] Step 4: Immerse the prepared chloride-ionized quaternized polyimide film in ethanol for 24 h to remove the residual solvent, and then wash it with deionized water and dry it;

[0044] Step 5: Immerse the chloride-ionized quaternized polyimide film in a 0.1 mol L -1 KOH solution for 24 h to achieve the exchange of chloride ions and hydroxide ions; finally, wash it with deionized water and dry it. The structural formula of the quaternized polyimide film prepared in this example is:

[0045]

[0046] Among them, in step one, the preparation method of 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl includes:

[0047] S1. Prepare the intermediate 4,4-bis(4-nitrophenoxy)octafluorobiphenyl. The specific method includes: adding 8.35 g of decafluorobiphenyl, 6.96 g of p-nitrophenol, and 10.35 g of anhydrous potassium carbonate into a 250 mL three-necked flask, and adding 10.0 mL of toluene and 100.0 mL of N,N-dimethylacetamide; then, stirring the reaction system at 30 °C for 1 h, and then heating to 80 °C for reaction for 24 h; after the reaction is completed, pouring the mixture into 500.0 mL of deionized water, filtering to collect the yellow solid, and drying it at 40 °C for 24 h; finally, obtaining the intermediate 4,4-bis(4-nitrophenoxy)octafluorobiphenyl;

[0048] S2. Add the synthesized 4,4-bis(4-nitrophenoxy)octafluorobiphenyl, 2.0 g of activated carbon, 0.25 g of ferric chloride, and 150.0 mL of absolute ethanol into a 250 mL three-necked flask, and reflux under condensation at 80 °C for 0.5 h; then cool down to 70 °C, and add 30.0 mL of hydrazine hydrate dropwise to the reaction system, and continue the reaction for 12 h; after the reaction is completed, filter off the activated carbon and collect the filtrate; pour the filtrate into 500.0 mL of deionized water, filter to collect the white solid, and dry it at 40 °C for 24 h to obtain the final product 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl.

[0049] The quaternized polyimide film prepared in this example is denoted as QAPI-50.

[0050] Example 2

[0051] This example provides a preparation method of a quaternized polyimide film, including the following steps:

[0052] Step one: Add 0.82 g of 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl (OFBAPB) and 0.54 g of 2-(4-aminophenyl)-1H-benzo[d]imidazol-5-amine (APABI) into a 250 mL three-necked flask, and add 20.0 mL of N,N-dimethylacetamide, and stir at room temperature for 1 h. Then add 1.78 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and continue the reaction at room temperature for 24 h;

[0053] Step 2: After the previous reaction is completed, add 5.0 mL of triethylamine and 10.0 mL of acetic anhydride to the reaction system, and continue to react the reaction system at 60 °C for 2 h, at 90 °C for 1 h, and at 100 °C for 0.5 h. Finally, after the reaction solution is cooled to room temperature, slowly pour it into ethanol, filter to obtain a fibrous product, and dry it at 80 °C for 24 h to obtain polyimide (PI) polymer;

[0054] Step 3: Weigh 1.00 g of polyimide polymer and dissolve it in 20.0 mL of N,N-dimethylformamide to prepare a brown viscous liquid. Add 0.14 g of 2,3-epoxypropyltrimethylammonium chloride, and continuously stir in an 80 °C oil bath for 24 h to obtain a casting solution. Then pour the casting solution onto a dry and clean glass plate to cast a film, and then dry it in an 80 °C oven for 24 h to obtain a chlorinated quaternized polyimide film;

[0055] Step 4: Immerse the prepared chlorinated quaternized polyimide film in ethanol for 24 h to remove the residual solvent, and then wash it with deionized water and dry it;

[0056] Step 5: Immerse the chlorinated quaternized polyimide film in 0.1 mol L -1 of KOH solution for 24 h to achieve the exchange of chloride ions and hydroxide ions; finally, wash it with deionized water and dry it.

[0057] The quaternized polyimide film prepared in this example is denoted as QAPI-60.

[0058] Example 3

[0059] This example provides a method for preparing a quaternized polyimide film, including the following steps:

[0060] Step 1: Add 0.61 g of 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl (OFBAPB) and 0.63 g of 2-(4-aminophenyl)-1H-benzo[d]imidazol-5-amine (APABI) to a 250 mL three-necked flask, and add 20.0 mL of N,N-dimethylacetamide, and stir at room temperature for 1 h. Subsequently, add 1.78 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and continue to react at room temperature for 24 h;

[0061] Step 2: After the previous reaction is completed, add 5.0 mL of triethylamine and 10.0 mL of acetic anhydride to the reaction system, and continue to react the reaction system at 60 °C for 2 h, at 90 °C for 1 h, and at 100 °C for 0.5 h. Finally, after the reaction solution is cooled to room temperature, slowly pour it into ethanol, filter to obtain a fibrous product, and dry it at 80 °C for 24 h to obtain a polyimide (PI) polymer;

[0062] Step 3: Weigh 1.00 g of the polyimide polymer and dissolve it in 20.0 mL of N,N-dimethylformamide to prepare a brown viscous liquid. Add 0.16 g of 2,3-epoxypropyltrimethylammonium chloride, and continuously stir in an 80 °C oil bath for 24 h to obtain a casting solution. Then pour the casting solution onto a dry and clean glass plate to cast a film, and then dry it in an 80 °C oven for 24 h to obtain a chloride-ionized quaternized polyimide film;

[0063] Step 4: Immerse the prepared chloride-ionized quaternized polyimide film in ethanol for 24 h to remove the residual solvent, and then wash it with deionized water and dry it;

[0064] Step 5: Immerse the chloride-ionized quaternized polyimide film in a 0.1 mol L -1 KOH solution for 24 h to achieve the exchange of chloride ions and hydroxide ions; finally, wash it with deionized water and dry it.

[0065] The quaternized polyimide film prepared in this example is denoted as QAPI-70.

[0066] Example 4

[0067] This example provides a method for preparing a quaternized polyimide film, including the following steps:

[0068] Step 1: Add 0.82 g of 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl (OFBAPB) and 0.54 g of 2-(4-aminophenyl)-1H-benzimidazol-5-amine (APABI) to a 250 mL three-necked flask, and add 20.0 mL of N,N-dimethylacetamide, and stir at room temperature for 1 h. Subsequently, add 1.78 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and continue to react at room temperature for 24 h;

[0069] Step 2: After the previous reaction is completed, add 5.0 mL of triethylamine and 10.0 mL of acetic anhydride to the reaction system, and continue to react the reaction system at 60 °C for 2 h, at 90 °C for 1 h, and at 100 °C for 0.5 h. Finally, after the reaction solution is cooled to room temperature, slowly pour it into ethanol, filter to obtain a fibrous product, and dry it at 80 °C for 24 h to obtain a polyimide (PI) polymer;

[0070] Step 3: Weigh 1.00 g of the polyimide polymer and dissolve it in 20.0 mL of N,N-dimethylformamide to prepare a brown viscous liquid. Add 0.14 g of 2,3-epoxypropyltrimethylammonium chloride, and continuously stir in an 80 °C oil bath for 24 h to obtain a casting solution. Then pour the casting solution onto a dry and clean glass plate to cast a film, and then dry it in an 80 °C oven for 24 h to obtain a chloride ionized quaternized polyimide film;

[0071] Step 4: Immerse the prepared chloride ionized quaternized polyimide film in ethanol for 24 h to remove the residual solvent, and then wash it with deionized water and dry it;

[0072] Step 5: Immerse the chloride ionized quaternized polyimide film in KOH solutions with equal gradient concentrations. The concentrations of the KOH solutions with equal gradient concentrations are 0.05 mol L -1 、0.15 mol L -1 、0.2 mol L -1 、0.25 mol L -1 、0.3 mol L -1 、0.35 mol L -1 in turn. The immersion time of the chloride ionized quaternized polyimide film in KOH at each concentration is 4 h, and the immersion temperatures are 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, and 40 °C in turn to achieve the exchange of chloride ions and hydroxide ions; finally, wash it with deionized water and dry it.

[0073] The quaternized polyimide film prepared in this example is denoted as QAPI-80.

[0074] Example 5

[0075] This example provides a method for preparing a quaternized polyimide film, including the following steps:

[0076] Step 1: Add 0.61 g of 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl (OFBAPB) and 0.63 g of 2-(4-aminophenyl)-1H-benzo[d]imidazol-5-amine (APABI) into a 250 mL three-necked flask, and add 20.0 mL of N,N-dimethylacetamide. Stir for 1 h at room temperature. Subsequently, add 1.78 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and continue the reaction at room temperature for 24 h;

[0077] Step 2: After the reaction in the previous step is completed, add 5.0 mL of triethylamine and 10.0 mL of acetic anhydride to the reaction system, and continue the reaction at 60 °C for 2 h, at 90 °C for 1 h, and at 100 °C for 0.5 h. Finally, after the reaction solution is cooled to room temperature, slowly pour it into ethanol, filter to obtain a fibrous product, and dry it at 80 °C for 24 h to obtain a polyimide (PI) polymer;

[0078] Step 3: Weigh 1.00 g of the polyimide polymer and dissolve it in 20.0 mL of N,N-dimethylformamide to prepare a brown viscous liquid. Add 0.16 g of 2,3-epoxypropyltrimethylammonium chloride, and continuously stir in an 80 °C oil bath for 24 h to obtain a casting solution. Then pour the casting solution onto a dry and clean glass plate to form a film by casting, and then dry it in an 80 °C oven for 24 h to obtain a chlorinated quaternized polyimide film;

[0079] Step 4: Immerse the prepared chlorinated quaternized polyimide film in ethanol for 24 h to remove the residual solvent, and then wash it with deionized water and dry it;

[0080] Step 5: Immerse the chlorinated quaternized polyimide film in KOH solutions with gradient concentrations. The concentrations of the KOH solutions with gradient concentrations are 0.05 mol L -1 、0.15 mol L -1 、0.2 mol L -1 、0.25 mol L -1 、0.3 mol L -1 、0.35 mol L -1 in turn. The immersion time of the chlorinated quaternized polyimide film in each concentration of KOH is 4 h, and the immersion temperatures are 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, and 40 °C in turn to achieve the exchange of chloride ions and hydroxide ions; finally, wash it with deionized water and dry it.

[0081] Denote the quaternized polyimide film prepared in this example as QAPI-90.

[0082] Comparative Example 1

[0083] This comparative example provides a method for preparing a polyimide film, and the steps are as follows:

[0084] Step 1: Add 1.02 g of 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl (OFBAPB) and 0.46 g of APABI into a 250 mL three-necked flask, and add 20.0 mL of N,N-dimethylacetamide. Stir at room temperature for 1 h. Subsequently, add 1.78 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and continue to react at room temperature for 24 h;

[0085] Step 2: After the reaction in the previous step is completed, add 5.0 mL of triethylamine and 10.0 mL of acetic anhydride to the reaction system, and make the reaction system continue to react at 60 °C for 2 h, at 90 °C for 1 h, and at 100 °C for 0.5 h. Finally, after the reaction solution is cooled to room temperature, slowly pour it into ethanol, filter to obtain a fibrous product, and dry it at 80 °C for 24 h to obtain polyimide (PI) polymer;

[0086] Step 3: Weigh 1.00 g of polyimide polymer and dissolve it in 20.0 mL of N,N-dimethylformamide to prepare a casting solution with a mass ratio of 5 wt%. Then pour the casting solution onto a dry and clean glass plate to cast a film, and then dry it in an 80 °C oven for 24 h to obtain a polyimide film; Immerse the prepared polyimide film in ethanol for 24 h, wash it with deionized water, and dry it.

[0087] The polyimide film prepared in this comparative example is denoted as PI-50.

[0088] Comparative Example 2

[0089] This comparative example provides a method for preparing a polyimide film, and the steps are as follows:

[0090] Step 1: Add 0.82 g of 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl (OFBAPB) and 0.54 g of 2-(4-aminophenyl)-1H-benzo[d]imidazol-5-amine (APABI) into a 250 mL three-necked flask, and add 20.0 mL of N,N-dimethylacetamide. Stir at room temperature for 1 h. Subsequently, add 1.78 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and continue to react at room temperature for 24 h;

[0091] Step 2: After the previous reaction is completed, add 5.0 mL of triethylamine and 10.0 mL of acetic anhydride to the reaction system, and continue to react the reaction system at 60 °C for 2 h, at 90 °C for 1 h, and at 100 °C for 0.5 h. Finally, after the reaction solution is cooled to room temperature, slowly pour it into ethanol, filter to obtain a fibrous product, and dry it at 80 °C for 24 h to obtain polyimide (PI) polymer;

[0092] Step 3: Weigh 1.00 g of polyimide polymer and dissolve it in 20.0 mL of N,N-dimethylformamide to prepare a casting solution with a mass ratio of 5 wt%. Then pour the casting solution onto a dry and clean glass plate to cast a film, and then dry it in an 80 °C oven for 24 h to obtain a polyimide film; Immerse the prepared polyimide film in ethanol for 24 h, wash it with deionized water, and dry it.

[0093] The polyimide film prepared in this comparative example is denoted as PI-60.

[0094] Comparative Example 3

[0095] This comparative example provides a method for preparing a polyimide film, and the steps are as follows:

[0096] Step 1: Add 0.61 g of 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl (OFBAPB) and 0.63 g of 2-(4-aminophenyl)-1H-benzo[d]imidazol-5-amine (APABI) to a 250 mL three-necked flask, and add 20.0 mL of N,N-dimethylacetamide, and stir at room temperature for 1 h. Then add 1.78 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and continue to react at room temperature for 24 h;

[0097] Step 2: After the previous reaction is completed, add 5.0 mL of triethylamine and 10.0 mL of acetic anhydride to the reaction system, and continue to react the reaction system at 60 °C for 2 h, at 90 °C for 1 h, and at 100 °C for 0.5 h. Finally, after the reaction solution is cooled to room temperature, slowly pour it into ethanol, filter to obtain a fibrous product, and dry it at 80 °C for 24 h to obtain polyimide (PI) polymer;

[0098] Step 3: Weigh 1.00 g of polyimide polymer and dissolve it in 20.0 mL of N,N-dimethylformamide to prepare a casting solution with a mass ratio of 5 wt%. Then pour the casting solution onto a dry and clean glass plate to cast a film, and then dry it in an 80 °C oven for 24 h to obtain a polyimide film; Immerse the prepared polyimide film in ethanol for 24 h, wash it with deionized water, and dry it.

[0099] The polyimide film prepared in this comparative example was denoted as PI-70.

[0100] The chemical structures of Examples 1 to 3 and Comparative Examples 1 to 3 were characterized by Fourier transform attenuated total reflection infrared (ATR-FTIR) spectroscopy and nuclear magnetic resonance. Figure 2 ATR-FTIR spectra of the polyimide (PI) films prepared in Comparative Examples 1 to 3 and the quaternized polyimide films (QAPI) prepared in Examples 1 to 3. The characteristic peak at 1367 cm -1 was attributed to the symmetric stretching vibration of C-N on the imide ring; the characteristic peaks at 1720 cm -1 and 1780 cm -1 were attributed to the symmetric and asymmetric stretching vibrations of C=O on the imide ring; the stretching vibration peak of -O- was located at 1249 cm -1 ; the absorption peak at 1143 cm -1 came from the vibration of -CF3 in 6FDA; the new characteristic peak appearing at 1621 cm -1 was attributed to the in-plane bending vibration of O-H after the ring-opening reaction; the characteristic peak at 950 cm -1 could be attributed to the quaternary ammonium group, indicating that the side chain containing the quaternary ammonium group had been successfully grafted onto the polyimide high molecular main chain. Figure 3 was the 1 1H-NMR spectra of the polyimide film and the quaternized polyimide film. After the grafting reaction was completed, the N-H chemical shift at 13.26 ppm on the imidazole completely disappeared; the chemical shifts at 7.20 - 8.40 ppm came from the hydrogen of the aromatic ring of the polyimide main chain; the chemical shift peak at 4.35 ppm was the hydrogen on the hydroxyl group after the ring-opening substitution reaction; the peaks at 3.12 ppm and 3.28 ppm were the hydrogens of the methylene and methyl groups in the side chain, indicating that the side chain containing the quaternary ammonium group had been successfully grafted onto the polyimide main chain. The above results indicated that the quaternized polyimide film was successfully prepared.

[0101] The physical and chemical properties of the quaternized polyimide films prepared in the examples and comparative examples were tested respectively, and the methods were as follows:

[0102] (1) Membrane water absorption rate, swelling rate and ion exchange capacity

[0103] The test methods for the membrane water absorption rate (abbreviation: WU) and swelling rate (abbreviation: SR) were as follows: A membrane sample of a certain size was taken out after being dried at 50 °C for 12 h, and the mass and thickness of the dry membrane were measured; then it was immersed in deionized water for 24 h. After taking out the membrane, the water attached to the membrane surface was quickly blotted dry with filter paper, and the mass and thickness of the wet membrane were measured. The calculation formulas for WU and SR were as follows:

[0104]

[0105]

[0106] Among them, W wet and W dry are the masses (g) of the wet film and the dry film respectively, and d wet and d dry are the thicknesses (μm) of the wet film and the dry film respectively.

[0107] The ion exchange capacity (abbreviation: IEC) represents the number of ion exchange groups in the membrane. After drying a 2×4 cm membrane sample at 50 °C for 12 h, take it out and weigh it. Then, soak it in 0.1 mol L -1 HCl solution for 24 h to make all the OH - on the active exchange groups in the membrane be exchanged by Cl - and enter the solution. Finally, using phenolphthalein as an indicator, titrate the solution with 0.1 mol L -1 NaOH, and calculate the ion exchange capacity of the separator through the volume of NaOH consumed. The calculation formula is as follows:

[0108]

[0109] Among them, C HCl represents the concentration of the HCl solution (mol L -1 ), V HCl represents the volume of the HCl solution, C NaOH represents the concentration of the NaOH solution (mol L -1 ), and V NaOH represents the volume of the NaOH solution consumed during the titration process (mL).

[0110] (2) Hydroxide conductivity

[0111] OH - conductivity (abbreviation: σ) reflects the conduction ability of the anion exchange membrane to OH - . Use an anion exchange membrane soaked in 1.0 mol L -1 KOH solution for 24 h to separate the H electrolytic cell into two compartments, and fill 1.0 mol L -1 KOH solution into both compartments. Under a constant current of 5.0 mA and a frequency range of 1.0 Hz to 100 kHz, use the CHI660E electrochemical workstation produced by Shanghai Chenhua Instrument Co., Ltd. to measure the impedance of the conductance cell with the membrane installed as R1. Use the same conductance cell, keep the distance between the two electrodes and the volume of the electrolyte in the two compartments consistent, and use the same test method to measure the impedance of the conductance cell without the membrane as R0. The calculation formula for the hydroxide conductivity of the separator is as follows:

[0112]

[0113] Among them, σ is the OH⁻ conductivity of the membrane (mS cm -1 ), A is the effective area of the separator (cm 2 ), and d is the thickness of the separator (cm).

[0114] The physical and chemical property results are shown in Table 1:

[0115] Table 1

[0116]

[0117] (3) Mechanical properties

[0118] The mechanical properties of the separator can be tested by an electronic universal testing machine at room temperature, and the tensile rate is 10 mm / min -1 . In the experiment, the membrane is tested at least three times, and the average value is taken. The calculation formulas for the maximum tensile strength (S) and elongation at break (E) of the membrane are as follows:

[0119]

[0120]

[0121] Among them, S is the maximum tensile strength of the membrane (MPa), F is the maximum stress of the membrane at break (N), d and L respectively represent the thickness (μm) and length (mm) in the middle of the membrane; E represents the elongation at break of the membrane (%), and L’ represents the absolute elongation at break of the membrane (mm). The mechanical strength and elongation at break of the quaternized polyimide membranes prepared in Examples 1 - 3 and the polyimide membranes prepared in Comparative Examples 1 - 3 obtained by testing are as Figure 4 shown.

[0122] (4) Test of electrocatalytic CO₂ reduction performance

[0123] After wetting the anion exchange membrane with deionized water, it is installed in the middle of an H-type electrolytic cell as a separator. Add 0.1 mol / L -1 KHCO₃ solution as the electrolyte in the H-type electrolytic cell, and pass CO₂ into the electrolyte at a flow rate of 40 mL / min -1 to discharge the oxygen in the electrolyte and make the electrolyte reach a CO₂-saturated state; clamp a glassy carbon electrode with a silver foil with a microporous structure on its surface as the working electrode (wherein, the process of forming a microporous structure on the surface of the silver foil is: using the constant voltage electrolysis function of a CHI660E electrochemical workstation produced by Shanghai Chenhua Instrument Co., Ltd., oxidize the surface of the silver foil for 3 min under the condition of 2.6 V, and then reduce it for 3 min under the condition of -2.6 V to form a microporous structure on the surface of the silver foil), use Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode; at 20 mL / min-1 Continuously introduce CO2 into the electrolyte at a certain rate, and then apply different voltages to promote the reduction reaction of CO2 on the surface of the working electrode for 15 minutes of electrolysis time; the gas product is introduced into a 9790Plus type gas chromatograph produced by Fuli Instrument Co., Ltd. of Fuzhou for testing to obtain the ppm value of CO in the product.

[0124] The calculation formulas for the CO Faraday efficiency and the total cathode current density are as follows:

[0125]

[0126] Among them, α is the number of electrons transferred when CO2 is reduced to CO, which is 2, n is the molar amount of CO (mol), F is the Faraday constant (96485 C mol -1 ), and Q is the total Coulomb quantity transferred at the cathode (C);

[0127] j CO = FE co × j total

[0128] Among them, j total is the total cathode current density (mA cm -2 ), FE CO is the CO Faraday efficiency (%), and j co is the partial current density of CO. The CO Faraday efficiency diagrams of the quaternized polyimide membranes in Examples 1 to 3 are as shown in Figure 5 shown, and the CO current density is as shown in Figure 6 shown. The CO current density diagrams of the quaternized polyimide membranes prepared in Examples 2, 4, and 5 are as shown in Figure 7 shown. The results show that the magnitude relationship of the CO current density of the quaternized polyimide membranes is QAPI-80 > QAPI-90 > QAPI-60.

[0129] The equipment quantities and processing scales described here are used to simplify the description of the present invention. Applications, modifications, and variations of the present invention are obvious to those skilled in the art.

[0130] Although the embodiments of the present invention have been disclosed above, they are not limited to only the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details and the examples shown and described here.

Claims

1. A quaternized polyimide film, characterized in that, The structural formula of the quaternized polyimide film is as follows: ； The preparation method of the quaternized polyimide film includes: Step 1: Add 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl and 2-(4-aminophenyl)-1 H -benzo d imidazolyl-5-amine into a reaction vessel, add N,N-dimethylacetamide, and stir at room temperature; then add 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and continue the reaction at room temperature; Step 2: After the previous reaction is completed, add triethylamine and acetic anhydride to the reaction system in Step 1 to make the reaction system continue to react. Finally, after the reaction solution is cooled to room temperature, slowly pour it into ethanol, filter to obtain a fibrous product, and dry it to obtain polyimide polymer. Step 3: Weigh the polyimide polymer and dissolve it in N,N-dimethylformamide to obtain a brown viscous liquid. Add 2,3-epoxypropyltrimethylammonium chloride and continuously stir in an oil bath to obtain a casting solution. Then pour the casting solution onto a dry and clean glass plate to cast a film, and then dry it in an oven to obtain a chloride-ionized quaternized polyimide film. Step 4: Immerse the prepared chloride-ionized quaternized polyimide film in ethanol for 24 h to remove the residual solvent, and then wash it with deionized water and dry it. Step 5. Immerse the chlorinated and quaternized polyimide membrane in 0.1 mol L -1 KOH solution for 24 h to achieve the exchange of chloride ions and hydroxide ions; finally, wash it with deionized water and dry it.

2. A method for preparing the quaternized polyimide film according to claim 1, characterized in that, It includes the following steps: Step 1. Add 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl and 2-(4-aminophenyl)-1 H -benzo d imidazol-5-amine into a reaction vessel, add N,N-dimethylacetamide, and stir at room temperature; then add 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and continue the reaction at room temperature; Step 2: After the previous reaction is completed, add triethylamine and acetic anhydride to the reaction system in Step 1 to make the reaction system continue to react. Finally, after the reaction solution is cooled to room temperature, slowly pour it into ethanol, filter to obtain a fibrous product, and dry it to obtain polyimide polymer. Step 3: Weigh the polyimide polymer and dissolve it in N,N-dimethylformamide to obtain a brown viscous liquid. Add 2,3-epoxypropyltrimethylammonium chloride and continuously stir in an oil bath to obtain a casting solution. Then pour the casting solution onto a dry and clean glass plate to cast a film, and then dry it in an oven to obtain a chloride-ionized quaternized polyimide film. Step 4: Immerse the prepared chloride-ionized quaternized polyimide film in ethanol for 24 h to remove the residual solvent, and then wash it with deionized water and dry it. Step 5. Immerse the chlorinated quaternized polyimide membrane in 0.1 mol L -1 KOH solution for 24 h to achieve the exchange of chloride ions and hydroxide ions; finally, wash it with deionized water and dry it.

3. The method for preparing the quaternized polyimide film according to claim 2, characterized in that, In the said Step 1, the preparation method of 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl includes: S1: Prepare the intermediate 4,4-bis(4-nitrophenoxy)octafluorobiphenyl. The specific method includes: Add decafluorobiphenyl, p-nitrophenol and anhydrous potassium carbonate into a reaction vessel, and add toluene and N,N-dimethylacetamide. Subsequently, stir the reaction system at 30 °C for 1 h, and then heat it to 80 °C and react for 24 h. After the reaction is completed, pour the mixture into deionized water, filter to collect the yellow solid, and dry it at 40 °C for 24 h. Finally, obtain the intermediate 4,4-bis(4-nitrophenoxy)octafluorobiphenyl. The mass-volume ratio of decafluorobiphenyl, p-nitrophenol, anhydrous potassium carbonate, toluene, N,N-dimethylacetamide and deionized water is 8.35 g:6.96 g:10.35 g:10.0 mL:100.0 mL:500.0 mL. S2. Add the synthesized 4,4-bis(4-nitrophenoxy)octafluorobiphenyl, activated carbon, ferric chloride, and absolute ethanol into a reaction vessel, and carry out reflux condensation at 80 °C for 0.5 h; then cool down to 70 °C, and drop hydrazine hydrate into the reaction system, and continue the reaction for 12 h; after the reaction is completed, filter out the activated carbon and collect the filtrate; pour the filtrate into deionized water, filter to collect the white solid, and dry it at 40 °C for 24 h to obtain the final product 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl; wherein, the mass-volume ratio of activated carbon, ferric chloride, absolute ethanol, hydrazine hydrate, and deionized water is 2.0 g:0.25 g:150.0 mL:30.0 mL:500.0 mL.

4. The method for preparing the quaternized polyimide film according to claim 2, characterized in that, In the first step, the mass-volume ratio of 2,2',3,3',5,5',6,6'-octafluoro-4,4'-bis(4-aminophenoxy)biphenyl, 2-(4-aminophenyl)-1 H -benzo d imidazolyl-5-amine, and N,N-dimethylacetamide is 0.61~1.02 g:0.46~0.63 g:20.0 mL:1.78 g; the stirring time at room temperature is 1 h, and the continued reaction time at room temperature is 24 h.

5. The method for preparing the quaternized polyimide film according to claim 2, characterized in that, In the second step, the volume ratio of triethylamine to acetic anhydride is 1:2; after adding triethylamine and acetic anhydride, the reaction system continues to react at 60 °C for 2 h, at 90 °C for 1 h, and at 100 °C for 0.5 h; the drying temperature is 80 °C, and the drying time is 24 h.

6. The method for preparing the quaternized polyimide film according to claim 2, characterized in that, In the third step, the mass-volume ratio of polyimide polymer, N,N-dimethylformamide, and 2,3-epoxypropyltrimethylammonium chloride is 1.00 g:20.0 mL:0.12 - 0.16 g; the oil bath temperature is 80 °C, and the continuous stirring time is 24 h; the drying temperature in the oven is 80 °C, and the drying time is 24 h.

7. The method for preparing the quaternized polyimide film according to claim 2, characterized in that, Step 5 is replaced by: Soak the chlorinated quaternized polyimide film in KOH solutions with gradually increasing concentrations. The concentrations of the KOH solutions with gradually increasing concentrations are 0.05 mol L -1 , 0.15 mol L -1 , 0.2 mol L -1 , 0.25 mol L -1 , 0.3 mol L -1 , 0.35mol L -1 respectively. The soaking time of the chlorinated quaternized polyimide film in KOH at each concentration is 4 h, and the soaking temperatures are 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, and 40 °C in sequence.

8. An application of the quaternized polyimide film according to claim 1, characterized in that, The quaternized polyimide membrane is applied to the diaphragm of an H-type electrolytic cell for electrocatalytic reduction of CO2; The specific application method includes: adding an electrolyte into an H-shaped electrolytic cell, and introducing CO2 into the electrolyte at a flow rate of 50 - 70 mL min -1 for half an hour to saturate the electrolyte with CO2; using silver foil with a larger specific surface area as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode; continuously introducing CO2 into the electrolyte at a rate of 35 - 55 mL min -1 , and then applying a voltage across the two electrodes to cause the reduction reaction of CO2 on the surface of the working electrode.

9. The application of the quaternized polyimide film according to claim 8, characterized in that, The process of making the silver foil have a larger specific surface area is as follows: Use a silver foil with a thickness of 0.5 mm as the cathode catalytic material, use the constant voltage electrolysis function of a CHI660E electrochemical workstation, and oxidize the surface of the silver foil for 3 min under the condition of 2.6 V, and then reduce it for 3 min under the condition of -2.6 V to form a microporous structure on the surface of the silver foil. After the microporous structure is formed on the surface of the silver foil, use a glassy carbon electrode clamp to hold it to form a working electrode.

10. The application of the quaternized polyimide film according to claim 8, characterized in that, The electrolyte is a KHCO3 solution with a concentration of 0.1 mol L -1 ; The thickness of the quaternized polyimide membrane is 10 - 50 μm; A magnetic stir bar is added to the cathode electrolyte in the H-type electrolytic cell, and the rotation speed of the magnetic stir bar is 100~140 r min -1 .

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