Covalent organic framework anionic polymer as well as preparation method and application thereof

Abstract

The invention provides a covalent organic framework anionic polymer as well as a preparation method and application thereof, and belongs to the field of covalent organic framework materials. The covalent organic framework anionic polymer has an imine type skeleton, the imine type skeleton is formed by a condensation reaction of a fluorine-substituted aromatic aldehyde monomer and a triarylamine monomer containing a triazine structure, and the imine type skeleton contains a fluorine substituent group and a triazine structure unit. And an acidic anion functional group existing in a salt form is grafted. According to the covalent organic framework anionic polymer obtained by the invention, through a synergistic structure and functional design, the K < + > enrichment capacity is favorably improved, the interface CO2 / H2O balance is maintained at the same time, and relatively high CO2 reduction reaction selectivity and electrode stability are realized in an acidic electrolyte system; the problems of poor stability caused by high K < + > concentration and hydrogen evolution caused by insufficient K < + > enrichment capacity in the prior art are solved.

Description

[Technical Field]

[0001] This application relates to the field of covalent organic framework materials, specifically to a covalent organic framework anionic polymer, its preparation method, and its application. [Background Technology]

[0002] Electrocatalytic carbon dioxide reduction reaction systems can be classified as alkaline, neutral, and acidic. Compared to alkaline and neutral systems, acidic systems have a higher CO2 utilization rate because CO2 readily reacts with OH- under alkaline conditions. - The reaction produces CO3 2- Under the influence of an electric field, carbon is lost through the membrane to the anode, thus limiting the carbon conversion efficiency. However, under acidic conditions, there are problems such as high proton concentration and intense competition for hydrogen evolution reaction, resulting in low selectivity of CO2 reduction products.

[0003] To suppress hydrogen evolution reaction under acidic conditions, existing technologies increase the concentration of alkali metal cations (such as K+) in the electrolyte. + The concentration of H+ in the electrolyte forms a tight electrical double layer, repelling H+ from the electrolyte. + Migration, thereby improving the selectivity of CO2 reduction. However, excessive K... + It will react with CO3 on the cathode surface 2- The combination of these factors leads to salt precipitation, which blocks the gas diffusion layer and obstructs CO2 transport, resulting in a significant decrease in the operational stability of the electrolyzer.

[0004] Researchers further proposed coating the cathode surface with K-adsorbable material. + Anionic polymers, to be used at low K + Enrichment of K at concentration + And reject H + This approach aims to suppress hydrogen evolution while avoiding salting out. However, the use of existing anionic polymers has several limitations. For example, the positive correlation between water absorption and anionic grafting amount makes it difficult to increase K0. + While enhancing enrichment capabilities, this process also leads to increased water content at the electrode interface, thus inhibiting CO2 transport. Furthermore, limitations in synthesis make precise functionalization difficult, hindering accurate control of the electrode surface microenvironment. These issues prevent anionic ionomers from simultaneously and efficiently enriching K+. + It also maintains the balance of gas-liquid transport and limits the selectivity of CO2 reduction products in acidic systems. [Summary of the Invention]

[0005] To address the above problems, according to a first aspect of this application, a covalent organic framework anionic polymer is provided, having an imine-type skeleton, wherein the imine-type skeleton is formed by a condensation reaction of a fluorine-substituted aromatic aldehyde monomer and a triarylamine monomer containing a triazine structure, wherein the imine-type skeleton contains fluorine-substituted groups and triazine structural units, and is grafted with acidic anionic functional groups present in the form of salts.

[0006] Optionally, the fluorinated aromatic aldehyde monomer is selected from 2,3,5,6-tetrafluoro-p-dibenzaldehyde, 2,5-difluoro-p-phenylenedialdehyde, 3,5-difluorobenzaldehyde, 2,4,6-trifluorobenzaldehyde, 2,3,5,6-tetrafluoro-biphenylenedialdehyde, or fluorinated structural analogs having the same aromatic aldehyde structural characteristics.

[0007] Optionally, the triarylamine monomer containing the triazine structure is selected from 4,4',4”-(1,3,5-triazine-2,4,6-triyl)triphenylamine, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, or structural analogs having the same triazine core structure and having an amino substituent at the aryl position.

[0008] Optionally, the acidic anionic functional group is selected from at least one of sulfonate, phosphate, acetate, or hydrosulfide.

[0009] Optionally, the cation portion of the salt is selected from at least one of sodium, magnesium, iron, or potassium.

[0010] Optionally, the general formula of the imine-type skeleton is as follows:

[0011]

[0012] Where X represents the acidic anionic functional group and Y represents the cation part of the salt.

[0013] According to a second aspect of this application, a method for preparing the covalent organic framework anionic polymer as described above is provided, comprising the following steps:

[0014] A condensation reaction is carried out between a fluorine-substituted aromatic aldehyde monomer and a triazine-containing aromatic amine monomer in the presence of a first organic solvent and an acidic catalyst to generate a fluorine-containing imine-linked triazine-type covalent organic framework material.

[0015] The triazine-type covalent organic framework material is treated in a reducing agent and a second organic solvent to reduce the imine bonds to the corresponding reduction products, thereby obtaining the covalent organic framework skeleton.

[0016] A halogenated organic reagent containing an acidic anionic functional group precursor is grafted onto the covalent organic framework, and a cationic source and a basic auxiliary agent are added to the reaction system to obtain the covalent organic framework anionic polymer.

[0017] Optionally, the first organic solvent is a mixture of an aromatic organic solvent and an alcohol solvent, and the acidic catalyst is an organic carboxylic acid, an inorganic acid, or a mixture thereof.

[0018] Optionally, the reducing agent is an organic or inorganic reducing agent that can selectively reduce imine bonds to amine groups, and the second organic solvent is a mixed solvent of ethers and carboxylic acids.

[0019] Optionally, the halogenated organic reagent is a halogenated alkyl compound having an acidic anionic functional group as a precursor.

[0020] Optionally, the cation source is selected from inorganic salts capable of providing alkali metal or alkaline earth metal ions, and the basic auxiliary agent is selected from tertiary amine nonnucleophilic bases.

[0021] Optionally, the molar ratio of the fluorinated aromatic aldehyde monomer, the aromatic amine monomer, the first organic solvent, and the acidic catalyst is any value in the range of 1:(1-100).

[0022] The molar ratio of the triazine-type covalent organic framework material, the reducing agent, and the second organic solvent is any value in the range of 1:(1-8000);

[0023] The molar ratio of the covalent organic framework, halogenated organic reagent, cationic source and basic auxiliary agent is any value in the range of 1:(1-1500).

[0024] According to a third aspect of this application, a catalytic electrode is provided, the catalytic electrode comprising the aforementioned covalent organic framework anionic polymer.

[0025] According to a fourth aspect of this application, a CO2 electrocatalytic reduction system is also provided, including the aforementioned catalytic electrode, wherein the catalytic electrode serves as a cathode.

[0026] Optionally, the CO2 electrocatalytic reduction system uses a titanium mesh loaded with iridium oxide as the anode, Ag / AgCl as the reference electrode, an aqueous solution of H2SO4 as the anolyte, and an acidic aqueous solution of K2SO4 as the cathode electrolyte. The concentration of the anolyte is any value between 0.3M and 0.7M, and the concentration of K2SO4 in the cathode electrolyte is any value between 0.05M and 0.15M.

[0027] According to the present invention, acidic anionic functional groups (such as sulfonates) grafted into the imine-type covalent organic framework can react with cations (K+, K ... + Electrostatic interaction occurs, enhancing K + The localized enrichment ability on the electrode surface forms a tight electrical bilayer structure, thereby effectively repelling H. +Transport to the catalytic interface inhibits the hydrogen evolution reaction. Furthermore, the imine-type covalent organic framework possesses highly ordered and stable porosity. This structure facilitates rapid diffusion and transport of CO2 molecules, improving the reaction efficiency at the electrode interface. On the other hand, its rigid planar configuration avoids coating the active sites of the catalyst, thus preserving the active surface of the catalyst and enhancing overall electrocatalytic activity. Simultaneously, the triazine structural units introduced into the imine-type framework exhibit excellent CO2 affinity, enabling CO2 enrichment at the electrode surface and significantly increasing the local CO2 concentration, which helps enhance the reduction reaction rate. Fluorine substituents impart significant hydrophobicity to the framework, reducing the water content at the electrode surface and further increasing the CO2 / H2O ratio, synergistically inhibiting the hydrogen evolution reaction. This synergistic structural and functional design helps improve Kc. + While maintaining interfacial CO2 / H2O balance, it achieves high CO2 reduction selectivity and electrode stability in acidic electrolyte systems, solving the problem of K-related issues in existing technologies. + High concentration leads to poor stability and K + Hydrogen evolution problem caused by insufficient enrichment capacity. [Attached Image Description]

[0028] Figure 1 This is a schematic diagram of a method for preparing a covalent organic framework anionic polymer according to an embodiment of the present invention.

[0029] Figure 2 This is a bar chart showing the electrocatalytic CO2 reduction performance of the catalytic electrode prepared in Comparative Example 1 of this invention under different current densities.

[0030] Figure 3 This is a bar chart showing the electrocatalytic CO2 reduction performance of the catalytic electrode prepared in Example 1 of this invention at different current densities.

Detailed Implementation Methods

[0031] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not the entire structure. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0032] The terms “comprising” and “having”, and any variations thereof, used in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0033] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0034] This invention provides a covalent organic framework anionic polymer having an imine-type backbone. The imine-type backbone is formed by the condensation reaction of a fluorine-substituted aromatic aldehyde monomer and a triarylamine monomer containing a triazine structure. The imine-type backbone contains fluorine-substituted groups and triazine structural units, as well as acidic anionic functional groups grafted in the form of salts.

[0035] According to the present invention, acidic anionic functional groups (such as sulfonates) grafted into the imine-type covalent organic framework can react with cations (K+, K ... + Electrostatic interaction occurs, enhancing K + The localized enrichment ability on the electrode surface forms a tight electrical bilayer structure, thereby effectively repelling H. + Transport to the catalytic interface inhibits the hydrogen evolution reaction. Furthermore, the imine-type covalent organic framework possesses highly ordered and stable porosity. This structure facilitates rapid diffusion and transport of CO2 molecules, improving the reaction efficiency at the electrode interface. On the other hand, its rigid planar configuration avoids coating the active sites of the catalyst, thus preserving the active surface of the catalyst and enhancing overall electrocatalytic activity. Simultaneously, the triazine structural units introduced into the imine-type framework exhibit excellent CO2 affinity, enabling CO2 enrichment at the electrode surface and significantly increasing the local CO2 concentration, which helps enhance the reduction reaction rate. Fluorine substituents impart significant hydrophobicity to the framework, reducing the water content at the electrode surface and further increasing the CO2 / H2O ratio, synergistically inhibiting the hydrogen evolution reaction. This synergistic structural and functional design helps improve Kc. + While maintaining interfacial CO2 / H2O balance, it achieves high CO2 reduction selectivity and electrode stability in acidic electrolyte systems, solving the problem of K-related issues in existing technologies. + High concentration leads to poor stability and K + Hydrogen evolution problem caused by insufficient enrichment capacity.

[0036] The mechanism of action of this covalent organic framework anionic polymer is as follows: First, the high electronegativity of fluorine reduces the surface energy of the framework, creating a hydrophobic microenvironment on the catalytic electrode surface, blocking water molecules and inhibiting hydrogen evolution; second, the sp... 2 Hybridized nitrogen atoms and rigid structure provide ample adsorption sites for CO2 enrichment; finally, the presence of anions creates a densely charged negative charge region on the electrode surface, enabling efficient local enrichment of potassium ions at low electrolyte concentrations and effectively suppressing hydrogen evolution.

[0037] In one embodiment, the fluorinated aromatic aldehyde monomer is selected from 2,3,5,6-tetrafluoro-p-diphenylaldehyde, 2,5-difluoro-p-phenylenedialdehyde, 3,5-difluorobenzaldehyde, 2,4,6-trifluorobenzaldehyde, 2,3,5,6-tetrafluoro-biphenylenedialdehyde, or fluorinated structural analogs with the same aromatic aldehyde structural characteristics. It should be explained that "fluorinated structural analogs with the same aromatic aldehyde structural characteristics" refers to fluorinated aromatic aldehyde derivatives that retain the core structure of the aromatic aldehyde (containing at least one aldehyde group and an aromatic ring skeleton), have one or more fluorine atoms substituted on the aromatic ring, and whose aldehyde group position and fluorine substitution mode are substantially the same as or equivalent to the aforementioned representative compounds, such as 2-fluorobenzaldehyde or 4-fluorobenzaldehyde. The aromatic ring structure in the fluorinated aromatic aldehyde monomer provides rigidity, which helps maintain the porosity and stability of the material. Simultaneously, the aldehyde group in the fluorinated aromatic aldehyde monomer, as a highly reactive functional group, readily undergoes condensation reactions (such as Schiff base reactions) with amine monomers to form stable imine bonds. In addition, fluorine substitution makes the material hydrophobic through the high electronegativity of the fluorine atom itself, effectively reducing the adsorption and diffusion of water molecules on the electrode surface, thereby inhibiting the occurrence of hydrogen evolution reaction.

[0038] In one embodiment, the triazine-containing triarylamine monomer is selected from 4,4',4”-(1,3,5-triazine-2,4,6-triyl)triphenylamine, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, or structural analogs having the same triazine core structure but with an amino substituent at the aryl position. It should be explained that "structural analogs having the same triazine core structure but with an amino substituent at the aryl position" refers to compounds obtained by derivatizing, substituting, or extending the substituents on the aryl group without changing the 1,3,5-triazine core and its connection with the aromatic amine. For example, the benzene ring may be replaced with a naphthalene ring, a biphenyl ring, or an alkyl group or halogen may be introduced onto the aromatic ring. The triazine ring in the triazine-containing triarylamine monomer has a nitrogen-rich structure, giving the monomer high porosity and specific surface area. Simultaneously, the nitrogen atom exhibits a dipole-quadrupole interaction with carbon dioxide molecules, enabling the triazine group to effectively interact with carbon dioxide molecules. These properties are beneficial for improving the adsorption capacity for carbon dioxide.

[0039] In one embodiment, the acidic anionic functional group is selected from at least one of sulfonate, phosphate, acetate, or hydrosulfide. This acidic anionic functional group can create a negatively charged region on the electrode surface, which adsorbs cations (K+). + This creates a tight electrical double-layer structure on the electrode surface, effectively repelling H. + Transported to the catalytic interface.

[0040] In one embodiment, the cation portion of the salt is selected from at least one of sodium, magnesium, iron, or potassium.

[0041] In one embodiment, the general formula of the imine-type skeleton is as follows:

[0042]

[0043] Where X represents the acidic anionic functional group and Y represents the cation part of the salt.

[0044] Figure 1 A method for preparing a covalent organic framework anionic polymer according to an embodiment of the present invention is shown. Figure 1 As shown, the preparation method includes:

[0045] S1, a condensation reaction is carried out between a fluorine-substituted aromatic aldehyde monomer and an aromatic amine monomer containing a triazine structure in the presence of a first organic solvent and an acidic catalyst to generate a fluorine-containing imine-linked triazine covalent organic framework material.

[0046] S2, the triazine-type covalent organic framework material is treated in a reducing agent and a second organic solvent to reduce the imine bonds to the corresponding reduction products to obtain the covalent organic framework skeleton;

[0047] S3, a halogenated organic reagent containing an acidic anionic functional group precursor is grafted onto the covalent organic framework skeleton, and a cationic source and a basic auxiliary agent are added to the reaction system to obtain the covalent organic framework anionic polymer.

[0048] In step S1, the aldehyde group in the fluorinated aromatic aldehyde monomer reacts with the amino group in the triazine-containing aromatic amine monomer to form an imine bond, constructing the basic framework of the covalent organic framework. The first organic solvent used in step S1 is a mixture of an aromatic organic solvent and an alcohol solvent, such as a mixture of any one of o-dichlorobenzene, dichloromethane, and 1,2-dichloroethane with any one of n-butanol, methanol, and acetone. This mixture provides an environment conducive to the condensation reaction, ensuring its stable progress. In some embodiments, the acidic catalyst used is an organic carboxylic acid, an inorganic acid, or a mixture thereof, such as at least one of acetic acid, hydrochloric acid, and p-toluenesulfonic acid. The acidic catalyst lowers the activation energy of the reaction, increasing the yield of the target product. In addition, in one embodiment, the molar ratio of the fluorinated aromatic aldehyde monomer, the aromatic amine monomer, the first organic solvent, and the acidic catalyst is any value of 1:(1-100), such as 1:1, 1:10, 1:20, 1:30, 1:50, 1:70, 1:80, or 1:100, within which the yield of the reaction product can be ensured. The processing conditions for the condensation reaction are as follows: the mixture of the above monomer and the reaction reagent is ultrasonically treated at a temperature of 23°C-27°C, for example, any value of 23°C, 25°C, or 27°C; unreacted solvent is removed by vacuum freezing and sealing; and then the reaction is carried out at a temperature of 100°C-140°C for 60-80 hours, for example, the reaction temperature can be any value of 100°C, 120°C, or 140°C, and the reaction time can be any value of 60 hours, 65 hours, 70 hours, 72 hours, or 80 hours, within which the reaction is carried out to ensure sufficient reaction.

[0049] In step S2, a reducing agent is used to reduce the imine bond to a secondary amine bond, which has higher chemical stability and reactivity, providing a stable platform for subsequent grafting reactions. The reducing agent used in step S2 is an organic or inorganic reducing agent that can selectively reduce the imine bond to an amine group, such as sodium cyanoborohydride or lithium borohydride. In some embodiments, the second organic solvent is a mixed solvent of ethers and carboxylic acids, such as a mixture of tetrahydrofuran, 1,3-dioxolane, or diethyl ether with glacial acetic acid, trifluoroacetic acid, or benzenesulfonic acid. This mixture provides an environment conducive to the reduction reaction, ensuring its stable progress. Furthermore, in one embodiment, the molar ratio of the triazine-type covalent organic framework material, the reducing agent, and the second organic solvent is any value within the range of 1:(1-8000), such as 1:1, 1:50, 1:120, 1:150, 1:1000, 1:4000, 1:6000, or 1:8000. Within this range, the yield of the reaction product can be ensured. The processing conditions for this reduction reaction are as follows: the triazine-type covalent organic framework material, the reducing agent, and the second organic solvent are mixed and reacted for 20-28 hours, for example, 20 hours, 24 hours, or 28 hours; after the reaction, the mixture is washed with dimethylformamide, tetrahydrofuran, and deionized water to remove residual solvent.

[0050] In step S3, the acidic anionic functional groups are effectively grafted onto the abundant grafting sites of the covalent organic framework material. The halogenated organic reagent used in step S3 is a halogenated alkyl compound containing precursors of acidic anionic functional groups. For example, it can be a tribromopropane derivative containing precursors of sulfonate, phosphate, acetate, or hydrosulfide, or a trichloropropane derivative containing precursors of sulfonate, phosphate, acetate, or hydrosulfide. This compound is used to functionalize the covalent organic framework polymer, introducing acidic anionic functional groups. The cation source is selected from inorganic salts capable of providing alkali metal or alkaline earth metal ions, such as potassium iodide, sodium chloride, potassium nitrate, potassium sulfate, magnesium sulfate, ferric sulfonate, or potassium chloride. These serve as counterions to form stable ion pairs with the anionic functional groups, maintaining the electroneutrality of the polymer. In some embodiments, the basic auxiliary is selected from tertiary amine nonnucleophilic bases, such as triethylamine, pyridine, or morpholine, to neutralize acidic substances generated during the reaction, maintain the pH of the reaction system, and improve the yield and purity of the product. Furthermore, in one embodiment, the molar ratio of the covalent organic framework, halogenated organic reagent, cation source, and basic auxiliary is any value within the range of 1:(1-1500), such as 1:1, 1:50, 1:100, 1:500, 1:750, 1:1000, or 1:1500. Within this range, the yield of the reaction product can be ensured. The grafting reaction is performed under the following conditions: the covalent organic framework, halogenated organic reagent, cationic source, and basic auxiliary agent are mixed and reacted at a temperature of 100℃-140℃ for 40h-56h. The reaction temperature can be any value among 100℃, 120℃, or 140℃, and the reaction time can be any value among 40h, 48h, or 56h. Within this temperature and time range, the reaction can be ensured to be complete. After the reaction is completed, the mixture is washed with methanol and deionized water to remove residual solvent. Then, after drying, the covalent organic framework anionic polymer is obtained.

[0051] The above scheme combines fluorine, triazine rings and anionic functional groups through a covalent organic framework to construct a "hydrophobic-enrichment-ion regulation" synergistic chain, achieving efficient integration of the CO2 electrocatalytic reduction process.

[0052] All compounds used in the above steps are those described above and will not be repeated here.

[0053] In one embodiment, the covalent organic framework anionic polymer prepared according to the present invention is sprayed onto the surface of a catalytic electrode and used as a cathode in a CO2 electrocatalytic reduction system.

[0054] In one embodiment, the CO2 electrocatalytic reduction system uses a titanium mesh loaded with iridium oxide as the anode, Ag / AgCl as the reference electrode, an aqueous solution of H2SO4 as the anolyte, and an acidic aqueous solution of K2SO4 as the cathode electrolyte, and performs electrocatalytic carbon dioxide reduction under a carbon dioxide atmosphere. The concentration of the anolyte is any value between 0.3M and 0.7M, for example, 0.3M, 0.4M, and 0.7M; the concentration of the K2SO4 in the cathode electrolyte is any value between 0.05M and 0.15M, for example, 0.05M, 0.1M, and 0.15M. Within this concentration range, the cathode electrolyte provides sufficient ionic strength to maintain the required detection current while avoiding salting out due to excessive potassium ion concentration, thereby preventing blockage of the cathode gas diffusion layer and impeded CO2 mass transfer.

[0055] Example 1

[0056] Example 1 of the present invention provides a covalent organic framework anionic polymer having an imine-type backbone. The backbone is formed by Schiff base reaction of 2,3,5,6-tetrafluoro-p-diphenylaldehyde monomer and 4,4',4”-(1,3,5-triazine-2,4,6-triyl)triphenylamine monomer, and contains fluorine substituent groups and triazine structural units, as well as sulfonate ions grafted onto it.

[0057] The above-mentioned covalent organic framework anionic polymers have the structure shown in the following formula:

[0058]

[0059] The above-mentioned covalent organic framework anionic polymer was prepared by the following method:

[0060] (1) 0.059 mmol of 4,4',4”-(1,3,5-triazine-2,4,6-triyl)triphenylamine and 0.089 mmol of 2,3,5,6-tetrafluoro-p-dibenzaldehyde were added to a Pyrex tube containing o-dichlorobenzene and n-butanol, with 0.5 mL each of o-dichlorobenzene and n-butanol. The mixture was sonicated at room temperature, and then 0.6 mmol of aqueous acetic acid solution was added. After vacuum degassing, the mixture was sealed and reacted in an oven at 120 °C for 72 h. The mixture was then washed with N,N-dimethylformamide, tetrahydrofuran, and n-hexane, and vacuum dried overnight at 80 °C to obtain a fluorinated imine-linked triazine covalent organic framework material.

[0061] (2) 0.051 mmol of a fluorinated imine-linked triazine covalent organic framework was suspended in 308 mmol of anhydrous tetrahydrofuran (25 mL). 0.61 mmol of glacial acetic acid was added, and the mixture was stirred at 25 °C for 10 min. Then, 1.05 mmol of sodium cyanoborohydride was added in batches, and stirring was continued at 25 °C for 24 h. After the reaction was complete, the mixture was washed with N,N-dimethylformamide, tetrahydrofuran, and deionized water to obtain the covalent organic framework.

[0062] (3) 0.457 mmol of covalent organic framework, 6.857 mmol of sodium tribromopropanesulfonate, 0.456 mmol of potassium iodide, 9.138 mmol of triethylamine and 563 mmol of dimethyl sulfoxide were added to a round-bottom flask containing a condenser and reacted at 120 °C for 48 h. Finally, the mixture was washed several times with methanol and water and dried under vacuum at 60 °C overnight to obtain a covalent organic framework anionic polymer.

[0063] Embodiment 1 of the present invention also provides a catalytic electrode, which is made by mixing the above-mentioned covalent organic framework anionic polymer with polytetrafluoroethylene powder and spraying it onto a vapor-deposited copper surface, using carbon paper as a substrate. The polytetrafluoroethylene powder mainly acts as a binder, stably binding the covalent organic framework anionic polymer to the electrode surface.

[0064] Example 1 of this invention also provides a CO2 electrocatalytic reduction system. The electrocatalytic reduction of CO2 is tested in a flow cell using a three-electrode system of an electrochemical workstation. The above-mentioned catalytic electrode is used as the cathode, the titanium mesh loaded with iridium oxide is used as the anode, and Ag / AgCl is used as the reference electrode. The anode electrolyte is an aqueous solution of 0.5M H2SO4, and the cathode electrolyte is 0.1M K2SO4 (pH adjusted to 2). CO2 is continuously passed through the system during the reaction at a gas flow rate of 30 mL / min.

[0065] Comparative Example 1

[0066] Comparative Example 1 provides an ionic polymer, Nafion, having a perfluorosulfonic acid structure formed by free radical polymerization of a perfluorovinyl ether sulfonic acid monomer, containing perfluoro substituent groups and sulfonic acid functional units.

[0067] The Nafion ionomer described above has the structure shown in the following formula:

[0068]

[0069] Comparative Example 1 also provides a catalytic electrode in which the above-mentioned Nafion ionomer is sprayed onto a vapor-deposited copper surface, with carbon paper as the substrate.

[0070] Comparative Example 1 also provides a CO2 electrocatalytic reduction system. The electrocatalytic reduction of CO2 was tested in a flow cell using a three-electrode system of an electrochemical workstation. The catalytic electrode described above was used as the cathode, a titanium mesh loaded with iridium oxide was used as the anode, and Ag / AgCl was used as the reference electrode. The anode electrolyte was an aqueous solution of 0.5 M H2SO4, and the cathode electrolyte was 0.1 M K2SO4 (pH adjusted to 2). CO2 was continuously passed through the system during the reaction at a gas flow rate of 30 mL / min.

[0071] Comparative Example 2

[0072] The only difference between Comparative Example 2 and Example 1 is that steps (2) to (3) are not performed.

[0073] Comparative Example 3

[0074] The only difference between Comparative Example 3 and Example 1 is that the 2,3,5,6-tetrafluoro-p-diphenylaldehyde monomer in step (1) is replaced with terephthalaldehyde.

[0075] Comparative Example 4

[0076] The only difference between Comparative Example 4 and Example 1 is that the 4,4',4”-(1,3,5-triazine-2,4,6-trimethyl)triphenylamine monomer in step (1) is replaced with triphenylamine.

[0077] Table 1 below shows the catalytic electrodes in Example 1 and Comparative Examples 2-4 at 600 mA·cm⁻¹ -1 The Faraday efficiency of electrocatalytic CO2 reduction products at current density.

[0078] Table 1

[0079]

[0080] Table 1 above at 600mA·cm -1The selectivity of the electrocatalytic reduction of carbon dioxide products in Examples 1 and Comparative Examples 2-4 was tested at different current densities. Table 1 shows that Comparative Example 2 exhibited the highest hydrogen selectivity (32.31%). This is because Comparative Example 2 lacked grafted anionic functional groups, resulting in insufficient potassium ion enrichment on the electrode surface. In contrast, Example 1 showed a hydrogen selectivity of only 5.94% and a hydrocarbon product selectivity of 85.85%. This demonstrates that in low-concentration acidic electrolysis systems, anionic functional groups can significantly enhance potassium ion enrichment on the electrode surface, thereby effectively suppressing hydrogen evolution and improving the selectivity of carbon dioxide reduction products. Comparative Example 3, rich in anionic functional groups and triazine groups, also contributed to suppressing hydrogen evolution to some extent. However, due to the absence of strongly hydrophobic fluorine substituents in its covalent organic framework, it could not suppress the diffusion of water molecules on the electrode surface, thus its hydrogen evolution suppression effect was not comparable to that of Example 1. Compared to Comparative Examples 2-3, Comparative Example 4, although possessing fluorine-substituted groups and anionic functional groups, exhibits a hydrogen selectivity of 15.39%, demonstrating some inhibition of hydrogen evolution. However, the absence of triazine groups in its covalent organic framework reduces its adsorption efficiency for carbon dioxide, resulting in a hydrocarbon product selectivity of only 55.67%. Therefore, this invention constructs a "hydrophobic-enrichment-ion-regulation" synergistic chain by combining a covalent organic framework with fluorine-substituted groups, triazine structural units, and anionic functional groups. This synergistic structural and functional design facilitates achieving high CO2 reduction selectivity and electrode stability in acidic electrolyte systems, solving the problem of K... + High concentration leads to poor stability and K + Hydrogen evolution problem caused by insufficient enrichment capacity.

[0081] Figure 2 and Figure 3 The bar charts showing the electrocatalytic CO2 reduction performance of the catalytic electrode prepared in Comparative Example 1 and the catalytic electrode prepared in Example 1 under different current densities are shown. Figure 2 The results showed that in a low-concentration potassium ion acidic electrolyte system, the catalytic electrode prepared in Comparative Example 1 exhibited increasing hydrogen selectivity during the catalytic reduction of CO2 with increasing current density, ultimately reaching a maximum at 400 mA·cm⁻¹. -1 The selectivity for hydrogen evolution reached 78.34%, indicating that the existing technology of coating the Cu electrode with Nafion ionomer cannot effectively suppress hydrogen evolution. In comparison, Figure 3 The catalytic electrode prepared in Example 1 of this application, as shown, performs catalytic reduction of CO2 when the current density is 100 mA·cm⁻¹. -1 Up to 600mA·cm -1Within the specified range, the selectivity for hydrogen remained consistently below 10%, indicating a significant inhibition of hydrogen evolution. Furthermore, at a current density of 600 mA·cm⁻¹, this effect was observed. -1 At that time, C 2+ The product selectivity was as high as 78.95%, while the hydrogen selectivity was only 5.94%. This indicates that the covalent organic framework anionic polymer prepared in this invention can effectively improve the efficiency of potassium ion enrichment on the cathode surface in a low-concentration potassium ion acidic electrolyte system to suppress the hydrogen evolution reaction. Simultaneously, it also improves the adsorption and catalytic efficiency of CO2 on the electrode surface, promotes carbon-carbon coupling, and enhances C... 2+ Product selectivity.

[0082] In summary, this invention provides a covalent organic framework anionic polymer that constructs a "hydrophobic-enrichment-ion regulation" synergistic chain by combining a covalent organic framework with fluorine, triazine rings, and anionic functional groups. This synergistic structure and functional design helps achieve high selectivity and electrode stability in acidic electrolyte systems, solving the problem of K+ ion regulation in existing technologies. + High concentration leads to poor stability and K + Hydrogen evolution problem caused by insufficient enrichment capacity.

[0083] The above is only one specific implementation of this application, and any other improvements made based on the concept of this application shall be considered within the scope of protection of this application.

Claims

1. A covalent organic framework anionic polymer, characterized in that, It has an imine-type skeleton, which is formed by the condensation reaction of a fluorine-substituted aromatic aldehyde monomer and a triarylamine monomer containing a triazine structure. The imine-type skeleton contains fluorine-substituted groups and triazine structural units, as well as acidic anionic functional groups grafted in the form of salts.

2. The covalent organic framework anionic polymer according to claim 1, characterized in that, The fluorinated aromatic aldehyde monomer is selected from 2,3,5,6-tetrafluoro-p-diphenylaldehyde, 2,5-difluoro-p-phenylenedialdehyde, 3,5-difluorobenzaldehyde, 2,4,6-trifluorobenzaldehyde, 2,3,5,6-tetrafluoro-biphenylenedialdehyde, or fluorinated structural analogs having the same aromatic aldehyde structural characteristics. The triarylamine monomer containing the triazine structure is selected from 4,4',4”-(1,3,5-triazine-2,4,6-triyl)triphenylamine, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, or structural analogs having the same triazine core structure and having an amino substituent at the aryl position. The acidic anionic functional group is selected from at least one of sulfonate, phosphate, acetate, or hydrosulfide.

3. The covalent organic framework anionic polymer according to claim 2, characterized in that, The cation portion of the salt is selected from at least one of sodium, magnesium, iron, or potassium.

4. The covalent organic framework anionic polymer according to any one of claims 1-3, characterized in that, The general formula of the imine-type skeleton is as follows: Where X represents the acidic anionic functional group and Y represents the cation part of the salt.

5. A method for preparing a covalent organic framework anionic polymer as described in any one of claims 1-4, characterized in that, Includes the following steps: A condensation reaction is carried out between a fluorine-substituted aromatic aldehyde monomer and a triazine-containing aromatic amine monomer in the presence of a first organic solvent and an acidic catalyst to generate a fluorine-containing imine-linked triazine-type covalent organic framework material. The triazine-type covalent organic framework material is treated in a reducing agent and a second organic solvent to reduce the imine bonds to the corresponding reduction products, thereby obtaining the covalent organic framework skeleton. A halogenated organic reagent containing an acidic anionic functional group precursor is grafted onto the covalent organic framework, and a cationic source and a basic auxiliary agent are added to the reaction system to obtain the covalent organic framework anionic polymer.

6. The preparation method according to claim 5, characterized in that, The first organic solvent is a mixture of an aromatic organic solvent and an alcohol solvent, and the acidic catalyst is an organic carboxylic acid, an inorganic acid, or a mixture thereof; Optionally, the reducing agent is an organic or inorganic reducing agent that can selectively reduce imine bonds to amine groups, and the second organic solvent is a mixed solvent of ethers and carboxylic acids; Optionally, the halogenated organic reagent is a halogenated alkyl compound having an acidic anionic functional group as a precursor; Optionally, the cation source is selected from inorganic salts capable of providing alkali metal or alkaline earth metal ions, and the basic auxiliary agent is selected from tertiary amine nonnucleophilic bases.

7. The preparation method according to claim 5 or 6, characterized in that, The molar ratio of the fluorine-substituted aromatic aldehyde monomer, aromatic amine monomer, first organic solvent, and acidic catalyst is any value in the range of 1:(1-100). The molar ratio of the triazine-type covalent organic framework material, the reducing agent, and the second organic solvent is any value in the range of 1:(1-8000); The molar ratio of the covalent organic framework, halogenated organic reagent, cationic source and basic auxiliary agent is any value in the range of 1:(1-1500).

8. A catalytic electrode, characterized in that, The catalytic electrode contains the covalent organic framework anionic polymer as described in any one of claims 1-4.

9. A CO2 electrocatalytic reduction system, characterized in that, It includes the catalytic electrode of claim 8, wherein the catalytic electrode serves as a cathode.

10. The CO2 electrocatalytic reduction system according to claim 9, characterized in that, The CO2 electrocatalytic reduction system uses a titanium mesh loaded with iridium oxide as the anode, Ag / AgCl as the reference electrode, an aqueous solution of H2SO4 as the anolyte, and an acidic aqueous solution of K2SO4 as the catholyte. The concentration of the anolyte is any value between 0.3M and 0.7M, and the concentration of K2SO4 in the catholyte is any value between 0.05M and 0.15M.

Images