Application of COF structure confinement metal catalyst in electro-catalysis of carbon dioxide reduction reaction

Abstract

The invention discloses an application of a COF structure confinement metal catalyst in an electro-catalysis carbon dioxide reduction reaction, and relates to the technical field of electro-catalysis carbon dioxide reduction. The COF structure confinement metal catalyst comprises a cationic polymer with a crystalline periodic distribution network structure and a metal catalyst existing in the cationic polymer through a confinement effect, so that the electrostatic repulsion effect of the COF structure supported metal catalyst cooperates with the confinement effect to electrically catalyze a carbon dioxide reduction reaction. The COF structure confinement metal catalyst is applied to electrocatalytic carbon dioxide reduction reaction, hydrogen evolution side reaction under the acidic electrolyte condition and the corrosion degree of the metal catalyst can be remarkably reduced, and then the carbon loss and energy consumption of carbon dioxide are reduced.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic carbon dioxide reduction reaction technology, specifically to the application of COF-structure-confined metal catalysts in electrocatalytic carbon dioxide reduction reactions. Background Art

[0002] In the field of electrocatalytic carbon dioxide electrochemical reduction reaction (eCO2RR), compared to traditional alkaline media, the high proton concentration in acidic media can effectively alleviate carbonate formation and deposition, thereby significantly reducing carbon loss and energy consumption. However, in acidic media, eCO2RR is kinetically inferior to the hydrogen evolution reaction (HER). Precise control of proton concentrations (H... + Mass transfer kinetics are improved to suppress competitive adsorption between eCO2 molecules and CO2 molecules at active sites on the catalyst surface, thereby effectively blocking the occurrence of hydrogen evolution side reaction (HER) and simultaneously improving the reactivity and product selectivity of eCO2RR.

[0003] In existing technologies, potassium (K) is typically added to the electrolyte. + 、Cs + Alkali metal cations accumulate near the Outer Helmholtz Plane (OHP) and repel foreign H+ ions through electrostatic interactions. + H is continuously consumed inside the double layer. + The generation of OH- ions leads to the formation of a locally high pH microenvironment at the catalyst interface, inhibiting H+. + Reduction. The activity of acidic eCO2RR is usually highly dependent on the concentration of alkali metal cations in the electrolyte, but higher local alkalinity can still cause salting out, affecting stability.

[0004] To completely eliminate the salting-out effect, organic cationic polymers were used to replace the addition of alkali metal cations. This surface modification strategy not only replaces free alkali metal cations to maintain the cationic effect, but the resulting dense organic cationic layer can also effectively block H+. + The migration kinetics of organic cationic polymers. However, the ion exchange capacity (IEC) of organic cationic polymers is a key parameter. At higher IEC values, densely immobilized cation sites, while enhancing electrostatic repulsion of protons (H+), also contribute to the migration dynamics. +While the IEC value is high, the large number of hydrophilic groups causes the polymer layer to absorb water and swell, expanding the pore size and forming proton transport channels. However, at lower IEC values, although the water absorption rate decreases and the pore size remains small, the insufficient number of cation sites significantly weakens the electrostatic repulsion effect. This interrelationship between IEC value and water absorption rate means that the proton blocking ability begins to decrease after the cation grafting amount reaches a critical value, ultimately limiting the HER inhibition effect.

[0005] Therefore, current technologies that use cationic polymers to replace traditional alkali metal cations are only suitable for electrocatalytic CO2 reduction reactions in weakly acidic electrolyte environments and under low current density conditions. Furthermore, during long-term operation under pure acid conditions, the metal catalyst inevitably corrodes, leading to reduced activity and decreased stability. Summary of the Invention

[0006] One objective of this invention is to provide an application of a COF-structured confined metal catalyst in the electrocatalytic carbon dioxide reduction reaction, thereby solving the technical problems of severe hydrogen evolution side reactions and easy corrosion of metal catalysts in the existing electrocatalytic carbon dioxide reduction reaction in acidic electrolyte solutions.

[0007] Another objective of this invention is to further suppress proton transport / HER competing reactions.

[0008] According to the purpose of this invention, the present invention provides an application of a COF-structured confined metal catalyst in the electrocatalytic reduction of carbon dioxide. The COF-structured confined metal catalyst comprises a cationic polymer having a crystalline periodically distributed network structure and a metal catalyst confined within the cationic polymer through a confinement effect, such that the electrostatic repulsion of the COF-structured confined metal catalyst synergistically enhances the confinement effect in the electrocatalytic reduction of carbon dioxide.

[0009] Optionally, the cationic polymer is a piperidine salt ion polymer, an imidazole salt ion polymer, or a trimethylammonium salt ion polymer.

[0010] Optionally, the preparation method of the COF-structured confined metal catalyst includes:

[0011] Polyaldehyde phenol monomers are mixed with cationic hydrazine monomers, and a reaction solvent is added. After mixing evenly, the first reaction solution is obtained.

[0012] A reaction catalyst is added to the first reaction solution, and the reaction is carried out at a preset temperature for a preset time to obtain a second reaction solution;

[0013] The second reaction solution was sequentially subjected to washing, solvent exchange, and drying to prepare a cationic polymer.

[0014] The COF-structured confined metal catalyst is prepared by reacting the cationic polymer with a metal catalyst.

[0015] Optionally, the molar ratio of the polyaldehyde phenol monomer to the cationic hydrazine monomer in the first reaction solution is any value between 1:1 and 2.

[0016] Optionally, the cationic hydrazine monomer is any one of 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(1-methylpiperidin-1-onium), 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(1-methylimidazol-3-onium), and 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(N,N,N-trimethylbut-1-ammonium).

[0017] Optionally, the polyaldehyde phenol monomer is any one of 1,3,5-tricarboxymethyl-retrophenol, 1,3,5-tricarboxymethyl-retrophenol, or 1,3,5-tricarboxymethyl-retrophenol.

[0018] Optionally, the preparation method of 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(1-methylpiperidine-1-onium) includes:

[0019] Diethyl 2,5-bis(4-bromobutoxy)terephthalate was dissolved in an organic solvent, N-methylpiperidine was added, and the reaction solution was evaporated to dryness to obtain the reaction intermediate.

[0020] The reaction intermediate was dissolved in water, silver chloride was added, and after the reaction was completed, the mixture was cooled, filtered, and the filtrate was evaporated to obtain the reaction precursor.

[0021] The reaction precursor was dissolved in ethanol, hydrazine hydrate was added, and after the reaction was cooled, the solvent was evaporated, and the mixture was dried under vacuum to prepare 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(1-methylpiperidine-1-onium).

[0022] Optionally, the mass ratio of the cationic polymer to the metal catalyst is any value between 1 and 3:1.

[0023] Optionally, the metal catalyst is any one of Cu(OAc)2·H2O, CuSO4, CuCl2 or Cu(NO3)2.

[0024] Optionally, the COF-structured confined metal catalyst is coated onto the surface of hydrophobic carbon paper as a catalyst slurry to construct the working electrode for the electrocatalytic carbon dioxide reduction reaction.

[0025] This invention utilizes a COF-structured confined metal catalyst obtained by confining a metal catalyst within a cationic polymer for the electrocatalytic reduction of carbon dioxide. Specifically, the π-conjugated COF framework in the cationic polymer forms a strong electronic coupling with the active metal center, while simultaneously confining metal nanoparticles or single atoms within regular channels, preventing migration and aggregation. The two-dimensional crystalline framework, composed of rigid covalent bonds, maintains sub-nanometer pore size stability even under high-density cation grafting conditions, precisely anchoring cationic groups and exhibiting excellent anti-swelling properties. Furthermore, the high-density arrangement of cations within the framework in the cationic polymer results in a high interfacial electric field strength, directly electrostatically repelling protons, thereby significantly improving the electrochemical stability of the metal sites and enhancing the catalytic activity and product selectivity of the electrocatalytic carbon dioxide reduction reaction. By utilizing the confinement effect, proton electrostatic repulsion, and the rigidity of the framework, the COF-structured confined metal catalyst possesses high activity, high Faradaic efficiency, long-term acid corrosion resistance, and salting-out resistance.

[0026] Furthermore, the three types of cationic polymers used in this invention—piperidine salt, imidazole salt, and trimethylammonium salt—achieve covalent intercalation and ordered arrangement of cations with the COF backbone through structural design, which can enhance carbon dioxide activation and adsorption and suppress proton transport / HER competitive reactions in different electrochemical environments.

[0027] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0028] The following sections will describe some specific embodiments of the invention in a detailed manner by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or portions. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0029] Figure 1 This is a schematic flowchart of a method for preparing a COF-structured confined metal catalyst according to an embodiment of the present invention;

[0030] Figure 2 This is the molecular structural formula of DQA-Pip according to an embodiment of the present invention;

[0031] Figure 3 This is the molecular structural formula of a COF structure according to an embodiment of the present invention;

[0032] Figure 4 This is a molecular structure diagram of a COF-structured confined metal catalyst according to an embodiment of the present invention;

[0033] Figure 5 This is a scanning electron microscope image of a cationic polymer according to an embodiment of the present invention;

[0034] Figure 6 This is a scanning electron microscope image of a COF-structured confined metal catalyst according to an embodiment of the present invention;

[0035] Figure 7 This is a schematic structural diagram of the working electrode prepared according to Embodiment 1 of the present invention;

[0036] Figure 8 This is a graph showing the electrochemical performance test of the working electrode prepared according to Example 1 of the present invention;

[0037] Figure 9 This is a graph showing the electrochemical performance test results of the working electrode prepared according to Comparative Example 1 of the present invention. Detailed Implementation

[0038] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] Figure 1 This is a schematic flowchart of a method for preparing a COF-structured confined metal catalyst according to an embodiment of the present invention. Figure 2 This is the molecular structural formula of DQA-Pip according to an embodiment of the present invention. Figure 3 This is the molecular structural formula of a COF structure according to an embodiment of the present invention. Figure 4 This is a molecular structure diagram of a COF-structured confined metal catalyst according to an embodiment of the present invention. Figure 5 This is a scanning electron microscope image of a cationic polymer according to an embodiment of the present invention. Figure 6 This is a scanning electron microscope image of a COF-structured confined metal catalyst according to an embodiment of the present invention. Figure 7 This is a schematic structural diagram of the working electrode prepared according to Embodiment 1 of the present invention.

[0043] This invention provides an application of a COF-structured confined metal catalyst in the electrocatalytic reduction of carbon dioxide. The COF-structured supported metal catalyst comprises a cationic polymer with a crystalline, periodically distributed network structure and a metal catalyst confined within the cationic polymer through a confinement effect. This allows the electrostatic repulsion of the COF-structured confined metal catalyst to synergistically enhance the confinement effect in the electrocatalytic reduction of carbon dioxide. Here, the cationic polymer has a two-dimensional porous, crystalline, periodically distributed network structure.

[0044] In this embodiment, a COF-structured confined metal catalyst obtained by confining a metal catalyst within a cationic polymer is applied to the electrocatalytic carbon dioxide reduction reaction. Specifically, the π-conjugated COF framework in the cationic polymer forms a strong electronic coupling with the metal active center, while simultaneously confining metal nanoparticles or single atoms within regular channels, preventing migration and aggregation. The two-dimensional crystalline framework, composed of rigid covalent bonds, maintains sub-nanometer pore size stability even under high-density cation grafting conditions, precisely anchoring cationic groups and exhibiting excellent anti-swelling properties. Furthermore, the high-density arrangement of cations within the framework in the cationic polymer results in a high interfacial electric field strength, directly electrostatically repelling protons, thereby significantly improving the electrochemical stability of the metal sites and enhancing the catalytic activity and product selectivity of the electrocatalytic carbon dioxide reduction reaction. In other words, by utilizing the confinement effect, proton electrostatic repulsion, and the rigidity of the framework, the COF-structured confined metal catalyst possesses high activity, high Faradaic efficiency, long-term acid corrosion resistance, and salting-out resistance. Furthermore, the cationic polymer not only synergistically suppresses hydrogen evolution side reactions and stabilizes the size and distribution of metal catalysts through its electrostatic repulsion and confinement effects, but also, due to the abundance of cationic sites in its backbone, can enrich and activate carbon dioxide molecules at the interface, significantly enhancing the adsorption capacity of carbon dioxide and the density of conversion active sites, thereby achieving higher catalytic efficiency and selectivity. This structural design endows the cationic polymer with multifunctional synergistic catalytic properties, significantly promoting both the reaction rate and product selectivity in the electrocatalytic carbon dioxide reduction reaction.

[0045] In this embodiment, by confining the metal catalyst within the cationic polymer through strong electronic coupling, the metal nanoparticles or single atoms in the metal catalyst are confined to specific positions in the pores or framework of the cationic polymer, and a strong electronic coupling is formed between the π-conjugated system in the cationic polymer framework and the confined metal. This restricts the size migration and aggregation of the metal nanoparticles in the metal catalyst, thereby improving the thermal stability, catalytic activity, and selectivity of the COF structure-confined metal catalyst.

[0046] In this embodiment, the cationic polymer constructs a two-dimensional crystalline framework through rigid covalent bonds. Its regularly arranged pore structure maintains sub-nanometer pore size stability even under high-density cation grafting conditions. This allows the cationic polymer to achieve precise anchoring of high-density cationic groups while effectively suppressing structural expansion caused by water molecule permeation, significantly reducing the surface water content of the COF-confined metal catalyst, and suppressing proton transport to alleviate hydrogen evolution in the acidic carbon dioxide reduction system. Simultaneously, a high-intensity electric field is formed at the interface between the high-density cations and the catalyst, enabling carbon dioxide reduction in a purely acidic environment without the assistance of alkali metal ions, thus avoiding stability issues caused by salting-out effects.

[0047] In a further embodiment, the cationic polymer is a piperidine salt ionic polymer, an imidazole salt ionic polymer, or a trimethylammonium salt ionic polymer. In this embodiment, the three types of cationic polymers—piperidine salt, imidazole salt, and trimethylammonium salt—achieve covalent intercalation and ordered arrangement of cations with the COF framework through structural design. These polymers can enhance carbon dioxide activation and adsorption, suppress proton transport / HER competition reactions, improve the catalyst's electronic structure regulation capability and metal site stability, and maintain framework stability and pore integrity in different electrochemical environments. Furthermore, the three polymers possess differentiated advantages in structural rigidity, electronic coupling ability, and electrostatic interaction strength, making them suitable for different types of metal catalyst systems.

[0048] like Figure 1 As shown, in a further embodiment, the preparation method of the COF-structured confined metal catalyst includes:

[0049] Step S100: Mix the polyaldehyde phenol monomer with the cationic hydrazine monomer, add the reaction solvent, and mix thoroughly to obtain the first reaction solution (refer to...). Figure 2 );

[0050] Step S200: Add a reaction catalyst to the reaction solution and react for a preset time at a preset temperature to obtain a second reaction solution;

[0051] Step S300: The second reaction solution is sequentially subjected to washing, solvent exchange, and drying to prepare the cationic polymer (refer to...). Figure 3 );

[0052] Step S400: React the cationic polymer with a metal catalyst to prepare a COF-structured confined metal catalyst (refer to...). Figure 4 ).

[0053] like Figure 1 As shown, in this embodiment, the preparation method of the COF structure-confined metal catalyst first involves mixing a polyaldehyde phenol monomer with a cationic hydrazine monomer, and adding 1,4-dioxane and mesitylene as reaction solvents. After mixing evenly, a first reaction solution is obtained. An aqueous acetic acid solution is then added to the first reaction solution as a reaction catalyst, and the reaction is carried out at a preset temperature for a preset time to obtain a second reaction solution. The second reaction solution is then subjected to washing, solvent exchange, and drying processes to prepare a dark red powdery cationic polymer (see reference). Figure 5 Finally, the cationic polymer was reacted with a metal catalyst to prepare a COF-structured confined metal catalyst. Here, the COF-structured confined metal catalyst is a dark green solid (see reference). Figure 6 The concentration of the acetic acid aqueous solution was 3 mol / L, and the addition volumes of 1,4-dioxane and mesitylene were 1.6 mL and 0.4 mL, respectively.

[0054] In this embodiment, 1,4-dioxane in the reaction solvent provides strong solubility and an inert reaction medium environment, promoting the uniform dispersion and orderly assembly of the framework monomers. Trimethylbenzene, as a low-polarity co-solvent, can adjust the solution polarity, helping to control the nucleation rate and crystal growth kinetics, thereby improving the crystallinity and pore regularity of the product. The introduction of acetic acid aqueous solution as a catalyst provides moderate acidic conditions to catalyze the hydrazine-aldehyde condensation reaction, promoting the formation of acylhydrazone bonds and framework crosslinking. Furthermore, the post-processing steps (washing, solvent exchange, and drying) remove unreacted monomers and oligomers, improving purity, increasing the porosity and usable surface area of ​​the material, ensuring that the COF pore structure does not collapse, and obtaining a dry and structurally complete cationic polymer. In other words, the above-mentioned multiple solvents work together synergistically to achieve the hydrazine-aldehyde condensation reaction to construct acylhydrazone bonds, forming a highly crystalline two-dimensional or three-dimensional cationic organic framework with a π-conjugated structure.

[0055] In this embodiment, the solvent for the washing process is N,N-dimethylformamide. That is, during the washing process, N,N-dimethylformamide solvent is mixed with the second reaction solution for washing until the supernatant is colorless, so as to remove unreacted monomers and oligomers and improve the purity of the reactants.

[0056] In this embodiment, the solvents used in the solvent exchange treatment are tetrahydrofuran and n-hexane. That is, tetrahydrofuran and n-hexane are used for multiple exchanges to promote the replacement of small molecules in the pores with the solvent, thereby increasing the porosity and usable surface area of ​​the material.

[0057] In this embodiment, the material is dried under vacuum at 80°C for 12 hours to obtain a deep red cationic polymer solid powder, ensuring that the COF pore structure does not collapse and obtaining a dry and structurally complete cationic polymer COF structure.

[0058] In a further embodiment, the molar ratio of the polyaldehyde phenol monomer to the cationic hydrazine monomer in the first reaction solution is any value between 1:1 and 2. That is, in the process of constructing the acylhydrazone linkage in the hydrazine-aldehyde condensation reaction, the molar ratio of the two reactants can be 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, or 1:2, or any other value between 1:1 and 2. In this embodiment, by controlling the molar ratio of the polyaldehyde phenol monomer to the cationic hydrazine monomer within the range of 1:1 to 2, the synthesis process can achieve both the highly ordered and periodic structure construction of the COF skeleton and the introduction of an appropriate amount of high-density cationic groups into the skeleton. This enhances the electrostatic repulsion, confinement ability, and electronic coupling strength of the material, effectively improving the confinement stability and catalytic selectivity of the metal catalyst, while optimizing the processability and structural stability of the COF. In a preferred embodiment, the molar ratio of the polyaldehyde phenol monomer to the cationic hydrazine monomer is 1:1.5.

[0059] In a further embodiment, the cationic hydrazine monomer is any one of 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(1-methylpiperidin-1-onium), 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(1-methylimidazol-3-onium), and 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(N,N,N-trimethylbut-1-ammonium). In this embodiment, by selecting 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl)) derivatives with the same backbone but different terminal cationic groups as cationic hydrazine monomers, the controllable construction and functional fine-tuning of the COF cationic polymer structure can be achieved. This not only ensures the crystallinity and pore size stability of the material, but also effectively regulates the electrostatic environment and electronic structure of the metal confinement region within the backbone, thereby enhancing the confinement and coupling ability of the COF structure to metal catalytic sites.

[0060] In a further embodiment, the polyaldehyde phenol monomer is any one of 1,3,5-tricarboxymethyl-resorcinol, 1,3,5-tricarboxymethyl-resorcinol, or 1,3,5-tricarboxymethyl-resorcinol. In this embodiment, by selecting 1,3,5-tricarboxymethyl-resorcinol monomers with different aromatic structures as polyaldehyde phenol monomers, the crystallinity, pore size, and π-conjugation degree of the obtained COF framework can be effectively controlled, thereby enhancing the spatial confinement and electronic coupling of the COF structure in the confined metal catalyst.

[0061] In a further embodiment, the preparation method of 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(1-methylpiperidine-1-onium) includes:

[0062] Step S700: Dissolve 2,5-bis(4-bromobutoxy)terephthalate in an organic solvent, add N-methylpiperidine, and evaporate the reaction solution to dryness after the reaction to obtain the reaction intermediate;

[0063] Step S800: Dissolve the reaction intermediate in water, add silver chloride, and after the reaction is complete, cool, filter, and evaporate the filtrate to obtain the reaction precursor;

[0064] Step S900: Dissolve the reaction precursor in ethanol, add hydrazine hydrate, cool after reaction, evaporate the solvent, and dry under vacuum to prepare 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(1-methylpiperidine-1-onium).

[0065] In this embodiment, the preparation method of 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(1-methylpiperidine-1-onium) involves first dissolving 1.386 mmol of 2,5-bis(4-bromobutoxy) terephthalate in 15 mL of ethanol, then adding 13.2 mmol of N-methylpiperidine. The resulting mixture is refluxed at 80 °C for 48 h. After the reaction, the intermediate is obtained by evaporation of the solution. The intermediate is then dissolved in 40 mL of water, and 3 mmol of silver chloride is added. The mixture is stirred at 90 °C for 7 h under nitrogen protection. After cooling, the mixture was filtered, and the filtrate was evaporated to obtain a pink solid reaction precursor. Finally, 1.36 mmol of the reaction precursor was dissolved in 18 mL of ethanol, and 2 mL of hydrazine hydrate was added. After the reaction was cooled and the solvent was evaporated, the mixture was dried under vacuum at 45 °C for 12 h to obtain a white solid 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(1-methylpiperidine-1-onium).

[0066] In a further embodiment, the mass ratio of the cationic polymer to the metal catalyst is any value between 1 and 3:1, i.e., the mass ratio of the cationic polymer to the metal catalyst is 1:1, 1.5:1, 2:1, 2.5:1, or 3:1, or any other value between 1 and 3:1. In this embodiment, by controlling the mass ratio of the cationic polymer to the metal catalyst within the range of 1-3:1, the distribution density and confinement strength of the metal active sites can be effectively adjusted, achieving high dispersion and high stability of the confined metal, enhancing the electronic coupling and interfacial synergy between the COF framework and the metal, and thus significantly improving the catalytic efficiency, Faraday selectivity, and reaction stability of the catalyst in the electrocatalytic carbon dioxide reduction reaction.

[0067] In a further embodiment, the metal catalyst is any one of Cu(OAc)2·H2O, CuSO4, CuCl2 or Cu(NO3)2, which not only broadens the preparation method and application range of the catalyst, but also achieves efficient confinement and uniform dispersion of the metal active center by controlling the ionic environment and coordination state of the copper source.

[0068] In a further embodiment, a highly efficient electrocatalytic carbon dioxide reduction working electrode is constructed by uniformly coating a COF-structured confined metal catalyst onto the surface of hydrophobic carbon paper in the form of a catalyst slurry. This significantly improves the electrode's catalytic activity, electron conduction, and gas transport performance, effectively optimizes the gas-liquid-solid three-phase interface reaction environment, and enhances the catalyst's utilization rate and durability. Here, the coating method can be any one of spraying, dripping, or dip coating.

[0069] The present application will be further described in detail below with reference to specific embodiments.

[0070] Example 1

[0071] In the COF-structured confined metal catalyst, the cationic polymer monomers are 1,3,5-tricarboxymethyl-m-triphenol and 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(1-methylpiperidin-1-onium), with a molar ratio of 1:1.5. The metal catalyst is Cu(OAc)₂·H₂O, with a mass ratio of cationic polymer to Cu(OAc)₂·H₂O of 2:1. The working electrode of the COF-structured confined metal catalyst is fabricated by spraying onto 3×1.5 cm hydrophobic carbon paper (see reference). Figure 7 It is used as the cathode in a flowing electrolytic cell made of polyetheretherketone material for electrocatalytic CO2 reduction.

[0072] Comparative Example 1

[0073] The only difference between Comparative Example 1 and Example 1 is that the working electrode is a copper electrode.

[0074] Figure 8 This is a graph showing the electrochemical performance test results of the working electrode prepared according to Example 1 of the present invention. Figure 9 This is a graph showing the electrochemical performance test results of the working electrode prepared according to Comparative Example 1 of the present invention.

[0075] Electrocatalytic carbon dioxide reduction reaction was tested on the working electrodes prepared in Example 1 and Comparative Example 1, respectively. The electrolyte was a pure acid aqueous solution containing 0.01 M H2SO4, the electrolyte flow rate was controlled at 20 mL / min, and the CO2 supply gas rate was 30 mL / min. The gaseous products of CO2 electroreduction were analyzed by gas chromatography, and the results were as follows: Figure 8 and Figure 9 The performance test results are shown.

[0076] like Figure 8 and Figure 9 As shown, the working electrode prepared using a COF-structured confined metal catalyst exhibits performance at 50 mA / cm². 2 100mA / cm 2 and 150mA / cm 2 At a current density of 100 mA / cm², CO₂ is converted into CO, C₂H₄, CH₄ and a small amount of H₂, and the working electrode of Example 1 operates at 100 mA / cm². 2 At a current density of 50 mA / cm², the highest Faraday efficiency is 47%, while when the copper electrode prepared in Comparative Example 1 is used as the working electrode, the efficiency is 47%. 2 100mA / cm 2 and 150mA / cm 2 Under current density conditions, more than 90% of CO2 is converted to H2, indicating that the working electrode has high catalytic activity and product selectivity under the catalytic action of the COF structure-confined metal catalyst, and can significantly reduce the probability of hydrogen evolution in the electrochemical CO2 reduction system under acidic electrolyte conditions.

[0077] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0078] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. The application of a COF-structured confined metal catalyst in the electrocatalytic reduction of carbon dioxide, characterized in that, The COF-structured confined metal catalyst comprises a cationic polymer having a crystalline periodically distributed network structure and a metal catalyst confined within the cationic polymer through a confinement effect, such that the electrostatic repulsion of the COF-structured confined metal catalyst synergistically enhances the confinement effect to electrocatalyze the carbon dioxide reduction reaction.

2. The application of the COF-structured confined metal catalyst according to claim 1 in the electrocatalytic reduction of carbon dioxide, characterized in that, The cationic polymer is a piperidine salt ion polymer, an imidazole salt ion polymer, or a trimethylammonium salt ion polymer.

3. The application of the COF-structured confined metal catalyst according to claim 2 in the electrocatalytic reduction of carbon dioxide, characterized in that, The preparation method of the COF-structured confined metal catalyst includes: Polyaldehyde phenol monomers are mixed with cationic hydrazine monomers, and a reaction solvent is added. After mixing evenly, the first reaction solution is obtained. A reaction catalyst is added to the first reaction solution, and the reaction is carried out at a preset temperature for a preset time to obtain a second reaction solution; The second reaction solution was sequentially subjected to washing, solvent exchange, and drying to prepare a cationic polymer. The COF-structured confined metal catalyst is prepared by reacting the cationic polymer with a metal catalyst.

4. The application of the COF-structured confined metal catalyst according to claim 3 in the electrocatalytic reduction of carbon dioxide, characterized in that, The molar ratio of the polyaldehyde phenol monomer to the cationic hydrazine monomer in the first reaction solution is any value between 1:1 and 2.

5. The application of the COF-structured confined metal catalyst according to claim 4 in the electrocatalytic reduction of carbon dioxide, characterized in that, The cationic hydrazine monomer is any one of 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(1-methylpiperidin-1-onium), 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(1-methylimidazol-3-onium), and 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(N,N,N-trimethylbut-1-ammonium).

6. The application of the COF-structured confined metal catalyst according to claim 5 in the electrocatalytic carbon dioxide reduction reaction, characterized in that, The polyaldehyde phenol monomer is any one of 1,3,5-tricarboxymethyl-retrophenol, 1,3,5-tricarboxymethyl-retrophenol, or 1,3,5-tricarboxymethyl-retrophenol.

7. The application of the COF-structured confined metal catalyst according to claim 6 in the electrocatalytic reduction of carbon dioxide, characterized in that, The preparation method of the 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(1-methylpiperidine-1-onium) includes: Diethyl 2,5-bis(4-bromobutoxy)terephthalate was dissolved in an organic solvent, N-methylpiperidine was added, and the reaction solution was evaporated to dryness to obtain the reaction intermediate. The reaction intermediate was dissolved in water, silver chloride was added, and after the reaction was completed, the mixture was cooled, filtered, and the filtrate was evaporated to obtain the reaction precursor. The reaction precursor was dissolved in ethanol, hydrazine hydrate was added, and after the reaction was cooled, the solvent was evaporated, and the mixture was dried under vacuum to prepare 1,1'-(((2,5-di(hydrazine carbonyl)-1,4-phenylene)bis(oxy))bis(butane-4,1-diyl))bis(1-methylpiperidine-1-onium).

8. The application of the COF-structured confined metal catalyst according to any one of claims 1-7 in the electrocatalytic reduction of carbon dioxide, characterized in that, The mass ratio of the cationic polymer to the metal catalyst is any value between 1 and 3:

1.

9. The application of the COF-structured confined metal catalyst according to claim 8 in the electrocatalytic reduction of carbon dioxide, characterized in that, The metal catalyst is any one of Cu(OAc)2·H2O, CuSO4, CuCl2 or Cu(NO3)2.

10. The application of the COF-structured confined metal catalyst according to claim 9 in the electrocatalytic reduction of carbon dioxide, characterized in that, The COF-structured confined metal catalyst is coated onto the surface of hydrophobic carbon paper as a catalyst slurry to construct the working electrode for the electrocatalytic carbon dioxide reduction reaction. The coating method can be any one of spraying, dripping, or dipping.

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