Covalent organic framework loaded monatomic catalyst and preparation method and application thereof

Abstract

The invention discloses a non-noble metal monatomic catalyst based on a covalent organic framework, a preparation method of the non-noble metal monatomic catalyst and application of the non-noble metal monatomic catalyst in an electro-catalytic oxygen evolution reaction, and belongs to the technical field of electro-catalytic materials. The catalyst comprises a covalent organic framework and non-noble metal atoms which are connected with the covalent organic framework through coordinate bonds and are in a monatomic form, and the catalyst has a repetitive structural unit as shown in a formula (I). The benzobisimidazole-triazine covalent organic framework with a unique tridentate nitrogen coordination structure is constructed, various non-noble metal single atoms can be stably anchored, an active center with a highly uniform and clear structure is formed, and the problems of non-uniform active sites and poor stability of a traditional catalyst are fundamentally solved. The catalyst disclosed by the invention shows high activity and high stability comparable to those of a noble metal catalyst in an alkaline oxygen evolution reaction, and a novel material system is provided for solving the contradiction between the cost and the performance of the oxygen evolution catalyst.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials technology, specifically relating to a single-atom catalyst based on a covalent organic framework, its preparation method, and its application in electrocatalytic water oxidation reaction. Background Technology

[0002] Electrocatalytic water splitting for hydrogen production is a key green energy technology for achieving the "dual carbon" goal. The water oxidation reaction at the anode, namely the electrocatalytic oxygen evolution reaction (OER), is a complex process involving four electron / proton transfers with a high kinetic energy barrier, and has become the rate-determining step restricting the overall energy efficiency of water splitting. Therefore, developing highly active and stable OER catalysts is crucial for promoting the large-scale application of this technology.

[0003] Currently, research frontiers focus on designing non-noble metal-based materials to replace expensive benchmark catalysts such as IrO2 and RuO2. Dispersing transition metals as single atoms on a support can maximize the exposure of active sites and significantly improve atom utilization, making it a highly promising technological approach. However, traditional single-atom catalysts often suffer from problems such as heterogeneous coordination environments at metal sites and the tendency for metal atoms to migrate, aggregate, or leach under harsh electrocatalytic conditions, making it difficult to simultaneously achieve intrinsic activity and long-term stability.

[0004] Covalent organic frameworks (COFs) are a class of periodic crystalline porous materials formed by organic building blocks linked by strong covalent bonds. Their long-range ordered structure, tunable pores, and ease of site engineering provide an ideal platform for precisely constructing well-defined metal single-atom active centers at the atomic scale. However, existing COF-based electrocatalysts still face the following challenges: First, how to stably construct specific metal coordination structures (such as M–N) on the COF framework through molecular-level design, achieving both high activity and high stability. x O Secondly, how to develop a universal COF support that can be widely used to anchor a variety of non-precious metal single atoms and maintain its high efficiency of OER activity and structural integrity in a wide pH range (especially alkaline media).

[0005] Therefore, there is an urgent need in this field for an innovative COF support design that can universally provide a well-defined, stable, and highly active coordination environment for a variety of non-noble metal single atoms, such as structurally defined M–N. x Coordination structures (such as the M–N3 structure of the present invention) are used to simultaneously solve the above-mentioned problems of activity, stability and universality. Summary of the Invention

[0006] In view of the technical problems of heterogeneous active sites, poor stability and dependence on noble metal materials in the existing oxygen evolution catalysts, the purpose of this invention is to provide a class of non-noble metal single-atom catalysts supported by covalent organic frameworks, their preparation methods and applications.

[0007] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention provides a single-atom catalyst supported on a covalent organic framework, characterized in that the catalyst has repeating structural units as shown in formula (I).

[0008] (I) Where M represents a non-noble metal atom in monatomic form, This represents the coordinate bond between the M atom and the N3 coordination structure. This indicates that the repeating structural unit extends periodically in multiple directions within a plane to form a network structure of a two-dimensional covalent organic framework.

[0009] The covalent organic framework-supported single-atom catalyst provided by this invention comprises a covalent organic framework and single-atom non-noble metal atoms connected to the covalent organic framework via coordinate bonds. The covalent organic framework is a two-dimensional covalent organic framework formed by using tetraamino aromatic monomers and triazine carboxylic acid ester monomers as building units, covalently linked through benzobisimidazole structural units. Specifically, the covalent organic framework is a two-dimensional covalent organic framework with a benzobisimidazole-triazine topology formed by the condensation reaction of tetraamino aromatic monomers and triazine carboxylic acid ester monomers. The active center of the catalyst of this invention can be defined by formula M–N3, which specifically represents a non-noble metal single atom M connected to three nitrogen atoms N via three coordinate bonds, forming a tridentate nitrogen coordination structure. The three nitrogen atoms N connected to M via coordinate bonds originate from one nitrogen atom in one triazine structural unit of the covalent organic framework and one nitrogen atom in each of the two benzobisimidazole structural units. The triazine structural unit is formed by the triazine carboxylic acid ester monomers providing the triazine ring core structure in the condensation reaction. As shown in formula (I), the repeating structural unit of the catalyst of the present invention has abundant M–N3 active centers. The M–N3 active center is a well-defined tripentate coordination unit composed of a single M atom and three N atoms; the active center is highly uniformly and stably dispersed on the two-dimensional plane of the covalent organic framework and the inner and outer surfaces of the pores, forming a periodic, high-density array of single-atom active sites on the support framework. Thus, the catalyst of the present invention has the following characteristics: First, the uniform dispersion of single-atom active sites achieves nearly 100% utilization of metal atoms; second, the well-defined M–N3 coordination structure and the stable covalent organic framework together ensure the structural stability and anti-migration and anti-agglomeration ability of the catalyst under harsh electrochemical conditions; finally, the two-dimensional porous structure of the support and the active sites distributed throughout the entire surface provide an ideal pathway for rapid mass transfer between reactants and products and efficient electron conduction, thereby endowing the catalyst with excellent oxygen evolution reaction activity and long-term operational stability.

[0010] As a preferred embodiment of the present invention, the non-precious metal atom M is selected from any one of cobalt (Co), nickel (Ni), iron (Fe), copper (Cu) or manganese (Mn); preferably, M is cobalt (Co).

[0011] In a preferred embodiment of the present invention, the tetraaminoaromatic monomer is 1,2,4,5-phenyltetramine or a salt formed therefrom with an inorganic or organic acid. The organic acid includes, but is not limited to, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and organic acids including, but not limited to, formic acid and acetic acid. Preferably, in a preferred embodiment, the tetraaminoaromatic monomer is 1,2,4,5-phenyltetramine tetrahydrochloride.

[0012] As a preferred embodiment of the present invention, the triazine carboxylic acid ester monomer is selected from trimethyl 1,3,5-triazine-2,4,6-tricarboxylic acid, triethyl 1,3,5-triazine-2,4,6-tricarboxylic acid, or tripropyl 1,3,5-triazine-2,4,6-tricarboxylic acid; preferably, it is triethyl 1,3,5-triazine-2,4,6-tricarboxylic acid.

[0013] As a preferred embodiment of the present invention, the X-ray diffraction pattern of the catalyst exhibits a broadened diffraction peak in the range of 2θ from 26° to 28°.

[0014] A second aspect of the present invention provides a method for preparing the above-mentioned catalyst, comprising the following steps: S1. Carrier construction: Tetraamino aromatic monomers, triazine carboxylic acid ester monomers, the first solvent and condensing agent are mixed and polycondensation reaction is carried out under a protective atmosphere. After the reaction is completed, the mixture is purified and dried to obtain a covalent organic framework material. S2, Metal Coordination: The covalent organic framework material obtained in step S1, the non-precious metal salt, and the second solvent are mixed, and a catalytic amount of organic amine is added. Under a protective atmosphere, ultrasonic dispersion and heating and stirring are performed sequentially to allow the non-precious metal ions to undergo a coordination reaction with the covalent organic framework material. After the reaction is completed, the mixture is washed and dried to obtain the metal-coordinated covalent organic framework precursor. S3. Heat treatment activation: The metal-coordinated covalent organic framework precursor obtained in step S2 is subjected to programmed temperature-controlled heat treatment under an inert atmosphere to obtain a single-atom catalyst.

[0015] As a preferred embodiment of the present invention, in step S1: The first solvent is one of anhydrous N,N-dimethylformamide, anhydrous N,N-dimethylacetamide, and anhydrous N-methyl-2-pyrrolidone; preferably anhydrous N,N-dimethylformamide. The condensing agent is one of polyphosphoric acid, p-toluenesulfonic acid, and phosphorus pentoxide; preferably polyphosphoric acid. The molar ratio of the tetraamino aromatic monomer to the triazine carboxylic acid ester monomer is 1.2:1-1.8:1; The mass ratio of the tetraamino aromatic monomer to the condensing agent is 1:20-30; The polycondensation reaction is carried out at a temperature of 110-130℃ for 20-28 hours. The purification process employs Soxhlet extraction, using methanol as the solvent for continuous extraction over 60-80 hours.

[0016] In step S1, the amount of condensing agent added can be calculated appropriately based on the molar amount of the reactants. In a preferred embodiment, the mass ratio of the tetraamino aromatic monomer to the condensing agent is 1:20-30.

[0017] As a preferred embodiment of the present invention, in step S2: The second solvent is one of anhydrous N,N-dimethylformamide, anhydrous N,N-dimethylacetamide, and anhydrous N-methyl-2-pyrrolidone; preferably anhydrous N,N-dimethylformamide. The non-precious metal salt is an acetate, nitrate, or chloride of the non-precious metal; the non-precious metal salt is preferably a cobalt salt, nickel salt, or iron salt, and more preferably cobalt acetate tetrahydrate. The organic amine is one of ethylenediamine, 1,3-propanediamine, and 1,4-butanediamine; preferably ethylenediamine. The mass ratio of the covalent organic framework material to the metal salt is 1:0.8-1:1.2; The ultrasonic dispersion time is 5-7 hours; The heating and stirring treatment is carried out at a temperature of 70-80℃ for 44-52 hours. The washing process involves washing with ethanol 3-5 times and then washing with deionized water 2-4 times.

[0018] In step S2, the amount of organic amine added is preferably 0.1%-1% of the volume of the second solvent.

[0019] In a preferred embodiment of the present invention, in step S3: The conditions for the programmed temperature-controlled heat treatment are as follows: under an inert atmosphere, the temperature is programmed to rise to 180-220°C at a heating rate of 1-3°C / min, and held at this temperature for 1-3 hours.

[0020] As a preferred embodiment of the present invention, in steps S1 and S2, the drying is vacuum drying, the drying temperature is 70-90℃, and the drying time is 10-14 hours.

[0021] In the preparation method of this invention, a special treatment process is adopted in the metal coordination step (step S2): ultrasonic treatment followed by heating and stirring. Ultrasonic treatment can promote the dispersion of covalent organic framework materials and the initial adsorption of metal salts; then, stirring is carried out under heating for a long time (stirring time up to 44-52 hours). This treatment process is conducive to the formation of stable coordination bonds between metal ions and the pre-set tripentate nitrogen sites in the covalent organic framework. Furthermore, the protective atmosphere can prevent the metal ions from being oxidized during heating, ensuring a high content of single-atom metal active sites.

[0022] A third aspect of the present invention provides the application of the above-described catalyst in the electrocatalytic oxygen evolution reaction.

[0023] In a preferred embodiment of the present invention, the electrocatalytic oxygen evolution reaction is carried out in a 1.0-1.2 M NaOH electrolyte, and the catalyst reaches 10 mA·cm⁻¹.- The overpotential at a given current density is no greater than 269 mV. Furthermore, the catalyst at 10 mA·cm²... - ² It operates stably for 5 hours at current density, and its overpotential decay rate is less than 5%.

[0024] Compared with the prior art, the present invention has the following beneficial effects: 1. Clear and uniform active center: Through precise design of tetraamino aromatic hydrocarbon and triazine carboxylic acid ester monomer, a benzobisimidazole-triazine COF support with a unique tridentate nitrogen coordination structure is constructed. It can stably anchor a variety of non-noble metal single atoms to form a highly uniform and clear M–N3 active center, which fundamentally solves the problems of non-uniformity and poor stability of active sites in traditional catalysts.

[0025] 2. Excellent Support Structure and Function: The benzobisimidazole-triazine COF support of this invention possesses high specific surface area, a large π-conjugated system, and high chemical stability. SEM images show that the catalyst of this invention has a three-dimensional interconnected porous network structure formed by the staggered stacking of two-dimensional nanosheets, exhibiting a cross-scale open pore structure. This regular two-dimensional network and hierarchical pore structure not only promotes electron conduction but also optimizes the mass transfer pathway of reactants / products, significantly improving the kinetics and long-term operational stability of the catalytic reaction.

[0026] 3. The preparation method is universal and controllable: The "support construction-metal coordination-thermal treatment activation" route provided by this invention has clear process parameters, is universally applicable to a variety of non-precious metals, and can precisely optimize the coordination structure and catalytic performance of metal sites by adjusting the heat treatment conditions, making it easy to achieve the controllable preparation of high-performance catalysts.

[0027] 4. Outstanding overall performance: The catalyst provided by this invention exhibits high activity comparable to noble metal catalysts in the alkaline oxygen evolution reaction (η@10 mA·cm). - With a voltage of ≤ 269 mV and high stability (performance degradation < 5% after 5 hours of continuous operation), it maintains the cost advantage of non-precious metals, providing an ideal material solution for resolving the contradiction between cost and performance of oxygen evolution catalysts. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the repeating structural unit represented by the general formula (I) of the catalyst of the present invention; Figure 2 The X-ray diffraction patterns of the COF-Co-Stp catalyst prepared in Example 1 and the comparative sample COF-Stp are shown below. Figure 3 A scanning electron microscope image of the COF-Co-Stp catalyst prepared in Example 1; Figure 4Linear sweep voltammetric curves of the COF-Co-Stp catalyst prepared in Example 1 and the comparative sample COF-Stp in 1.0 M NaOH electrolyte; Figure 5 Chronoamperometry curves of the COF-Co-Stp catalyst prepared in Example 1 at a constant potential of 1.55 V (vs. RHE) in 1.0 M NaOH electrolyte; Figure 6 The image shows the X-ray photoelectron spectrum of the catalyst COF-Co-Stp prepared in Example 1. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0032] Unless otherwise specified, "room temperature" and "normal temperature" in this invention refer to 25±2℃.

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments mainly use cobalt (Co) as a representative of non-precious metals to demonstrate the preferred preparation scheme and excellent performance of the catalyst. Obviously, the embodiments described herein are only some embodiments of the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments prepared by those skilled in the art using other non-precious metals (such as Ni, Fe, etc.) according to this method without creative effort are within the protection scope of the present invention.

[0034] Unless otherwise specified, the following examples and comparative examples were conducted under conventional conditions. Unless otherwise specified, the reagents or instruments used were all commercially available products.

[0035] Performance testing methods: The electrocatalytic oxygen evolution reaction performance of the catalysts prepared in the following examples and comparative examples was tested using the following methods: 1. Preparation of working electrode Accurately weigh 5.0 mg of catalyst sample and uniformly disperse it in a mixed solvent consisting of 480 μL anhydrous ethanol and 20 μL 5% Nafion solution. After ultrasonic treatment for 30 minutes, a homogeneous and stable catalyst slurry is formed. Accurately transfer 100 μL of this slurry and uniformly coat it onto the surface of pretreated 1×1 cm² carbon paper using a drop-coating method. After natural drying at room temperature, it is treated in a vacuum drying oven at 60 ℃ for 2 hours to obtain a catalyst loading of 1.0 mg·cm². - ² Working electrode.

[0036] 2. Electrochemical testing system A standard three-electrode testing system was adopted. Working electrode: Catalyst-supported electrode prepared according to the above method Counter electrode: 1×1 cm² platinum sheet electrode Reference electrode: Hg / HgO electrode (1.0 M KOH filling solution) Electrolyte: 1.0 M NaOH solution All tests were conducted under constant temperature conditions of 25±1 ℃.

[0037] 3. Testing Methods 3.1 Linear Scan Voltammetric Test In 1.0 M NaOH electrolyte, at 50 mV·s - Linear scan voltammetry was performed at a scan rate of ¹, with a potential range of 1.0–1.8 V relative to the reversible hydrogen electrode. The test data were corrected for 90% IR compensation and used to evaluate the catalyst's initial overpotential and catalytic activity.

[0038] 3.2 Timing Current Test The stability of the catalyst was evaluated using a chronoamperometry method. Tests were conducted at a constant potential of 1.55 V (vs. RHE), and the change in current density over time was continuously recorded to assess the long-term operational stability of the catalyst at a fixed operating potential.

[0039] 4. Data Processing All electrochemical test data were acquired using the software accompanying the electrochemical workstation and underwent appropriate IR compensation correction. The overpotential was calculated using the formula η = E(vs. RHE) - 1.23 V.

[0040] Example 1 Preparation of cobalt single-atom catalyst COF-Co-Stp supported on a covalent organic framework: S1: 1,2,4,5-phenyltetramine tetrahydrochloride (120 mg, 0.42 mmol) and triethyl 1,3,5-triazine-2,4,6-tricarboxylic acid (115 mg, 0.31 mmol) were placed in a reaction vessel, and 15 mL of anhydrous N,N-dimethylformamide was added as a solvent. Then, 3.2 g of polyphosphoric acid was added, and the reaction was carried out in an oil bath at 130 °C for 20 hours under argon protection, forming a covalent organic framework through dehydration condensation. After the reaction was completed, the solid product was collected by filtration, washed continuously with methanol using a Soxhlet extractor for 80 hours, and finally dried under vacuum at 90 °C for 10 hours to obtain the covalent organic framework material.

[0041] S2: The covalent organic framework material (100 mg) obtained in step S1, cobalt acetate tetrahydrate (100 mg, 0.40 mmol), and ethylenediamine (0.1 mL) were added to 15 mL of anhydrous N,N-dimethylformamide, wherein the mass ratio of the covalent organic framework material to the cobalt salt was 1:1. The mixture was first sonicated for 6 hours, and then stirred in an oil bath at 75 °C for 48 hours under nitrogen protection to allow the cobalt ions to fully coordinate with the nitrogen sites in the framework. After the reaction was completed, the solid product was collected by filtration, washed 4 times with ethanol and 3 times with deionized water, and finally dried under vacuum at 80 °C for 12 hours to obtain the cobalt-coordinated covalent organic framework material.

[0042] S3: The cobalt-coordinated covalent organic framework material obtained in step S2 is placed in a tube furnace and heated to 200 °C at a heating rate of 2 °C / min under argon protection, and held at this temperature for 2 hours. After natural cooling to room temperature, the final catalyst COF-Co-Stp is obtained.

[0043] The prepared catalyst COF-Co-Stp has the following repeating structural units: .

[0044] Example 2 Preparation of the cobalt single-atom catalyst COF-Co-Stp-1 supported on a covalent organic framework: S1: 1,2,4,5-phenyltetramine tetrahydrochloride (120 mg, 0.42 mmol) and triethyl 1,3,5-triazine-2,4,6-tricarboxylic acid (95 mg, 0.25 mmol) were placed in a reaction vessel, and 15 mL of anhydrous N,N-dimethylformamide was added as a solvent. Then, 2.8 g of polyphosphoric acid was added, and the reaction was carried out in an oil bath at 110 °C for 28 hours under argon protection, forming a covalent organic framework through dehydration condensation. After the reaction was completed, the solid product was collected by filtration, washed continuously with methanol using a Soxhlet extractor for 60 hours, and finally dried under vacuum at 70 °C for 14 hours to obtain the covalent organic framework material.

[0045] S2: The covalent organic framework material (100 mg) obtained in step S1, cobalt acetate tetrahydrate (100 mg, 0.40 mmol), and ethylenediamine (0.1 mL) were added to 15 mL of anhydrous N,N-dimethylformamide, wherein the mass ratio of the covalent organic framework material to the cobalt salt was 1:1. The mixture was first sonicated for 6 hours, and then stirred in an oil bath at 75 °C for 48 hours under nitrogen protection to allow the cobalt ions to fully coordinate with the nitrogen sites in the framework. After the reaction was completed, the solid product was collected by filtration, washed 4 times with ethanol and 3 times with deionized water, and finally dried under vacuum at 80 °C for 12 hours to obtain the cobalt-coordinated covalent organic framework material.

[0046] S3: The material obtained in step S2 is heated to 180 °C at a heating rate of 1 °C / min under argon protection and held at this temperature for 3 hours to obtain catalyst COF-Co-Stp-1.

[0047] Example 3 Preparation of the cobalt single-atom catalyst COF-Co-Stp-2 supported on a covalent organic framework: S1: 1,2,4,5-phenyltetramine tetrahydrochloride (120 mg, 0.42 mmol) and triethyl 1,3,5-triazine-2,4,6-tricarboxylic acid (115 mg, 0.31 mmol) were placed in a reaction vessel, and 15 mL of anhydrous N,N-dimethylformamide was added as a solvent. Then, 3.2 g of polyphosphoric acid was added, and the reaction was carried out in an oil bath at 130 °C for 20 hours under argon protection, forming a covalent organic framework through dehydration condensation. After the reaction was completed, the solid product was collected by filtration, washed continuously with methanol using a Soxhlet extractor for 80 hours, and finally dried under vacuum at 90 °C for 10 hours to obtain the covalent organic framework material.

[0048] S2: The covalent organic framework material (100 mg) obtained in step S1, cobalt acetate tetrahydrate (100 mg, 0.40 mmol), and ethylenediamine (0.1 mL) were added to 15 mL of anhydrous N,N-dimethylformamide, wherein the mass ratio of the covalent organic framework material to the cobalt salt was 1:1. The mixture was first sonicated for 6 hours, and then stirred in an oil bath at 75 °C for 48 hours under nitrogen protection to allow the cobalt ions to fully coordinate with the nitrogen sites in the framework. After the reaction was completed, the solid product was collected by filtration, washed 4 times with ethanol and 3 times with deionized water, and finally dried under vacuum at 80 °C for 12 hours to obtain the cobalt-coordinated covalent organic framework material.

[0049] S3: The material obtained in step S2 is heated to 220 °C at a heating rate of 3 °C / min under argon protection and held at this temperature for 1 hour to obtain the catalyst COF-Co-Stp-2.

[0050] Comparative Example 1 Preparation of cobalt-free COF material COF-Stp: S1: Covalent organic framework materials were prepared according to the same method and raw material ratio as in S1 of Example 1. Specific steps included: reacting 1,2,4,5-phenyltetramine tetrahydrochloride (120 mg, 0.42 mmol) and triethyl 1,3,5-triazine-2,4,6-tricarboxylic acid (115 mg, 0.31 mmol) with 3.0 g of polyphosphoric acid in 15 mL of anhydrous DMF, followed by Soxhlet extraction and purification to obtain the COF material.

[0051] S2: The COF material obtained in step S1 was heat-treated under the same conditions as S3 in Example 1: the temperature was increased to 200 °C at 2 °C / min under argon protection and held for 2 hours to obtain a cobalt-free COF comparison sample, denoted as COF-Stp.

[0052] This comparative example is used to verify the crucial role of single-atom active metal centers in catalytic reactions.

[0053] Comparative Example 2 Preparation of physically mixed cobalt COF materials (COF+Co-mix): S1: COF material was prepared using the same method as in S1 of Example 1.

[0054] S2: The COF material (100 mg) obtained in step S1 and cobalt acetate tetrahydrate (100 mg, 0.40 mmol) are simply mechanically mixed in a mortar for 30 minutes to physically mix the cobalt salt with the COF material.

[0055] S3: The mixed material was heat-treated under the same conditions as S3 in Example 1: the temperature was increased to 200 °C at 2 °C / min under argon protection and held for 2 hours to obtain a comparative sample of physically mixed cobalt, denoted as COF+Co-mix.

[0056] This comparative example is used to demonstrate the fundamental difference in catalytic performance between metal single atoms bonded by coordinate bonds and physically mixed metal species.

[0057] Comparative Example 3 Preparation of CoOx catalyst without COF support: S1: Cobalt acetate tetrahydrate (100 mg, 0.40 mmol) was placed directly in a tube furnace.

[0058] S2: Under argon protection, the temperature is increased to 200 ℃ at 2 ℃ / min and held for 2 hours to obtain a cobalt oxide control sample, denoted as CoOx.

[0059] This comparative example is used to demonstrate the important role of COF supports in dispersing and stabilizing active sites of single metal atoms.

[0060] Comparative Example 4 Preparation of COF-Co-TsOH materials synthesized with different dehydrating agents: S1: 1,2,4,5-phenyltetramine tetrahydrochloride (120 mg, 0.42 mmol) and triethyl 1,3,5-triazine-2,4,6-tricarboxylic acid (105 mg, 0.28 mmol) were placed in a reaction vessel, and 15 mL of anhydrous DMF was added. p-Toluenesulfonic acid (1.0 g) was used as a dehydrating agent instead of polyphosphoric acid, and the reaction was carried out at 120 °C for 24 hours. After the reaction was completed, the solid product was collected by filtration, washed continuously with methanol using a Soxhlet extractor for 80 hours, and finally dried under vacuum at 90 °C for 10 hours to obtain the covalent organic framework material.

[0061] S2: The covalent organic framework material (100 mg) obtained in step S1, cobalt acetate tetrahydrate (100 mg, 0.40 mmol), and ethylenediamine (0.1 mL) were added to 15 mL of anhydrous N,N-dimethylformamide. The mixture was first sonicated for 6 hours, and then stirred in an oil bath at 75 °C for 48 hours under nitrogen protection to allow the cobalt ions to fully coordinate with the nitrogen sites in the framework. After the reaction was complete, the solid product was collected by filtration, washed four times with ethanol and three times with deionized water, and finally dried under vacuum at 80 °C for 12 hours to obtain the cobalt-coordinated covalent organic framework material.

[0062] S3: The material obtained in step S2 is heated to 200 ℃ under argon protection at a heating rate of 2 ℃ / min and held at this temperature for 2 hours to obtain a control sample, denoted as COF-Co-TsOH.

[0063] This comparative example is used to verify the unique effect of polyphosphoric acid in forming specific COF structures.

[0064] Comparative Example 5 Preparation of the catalyst COF-Co-imp using the conventional impregnation method: S1: COF material was prepared using the same method as in S1 of Example 1.

[0065] S2: Immerse the COF material (100 mg) in a cobalt acetate aqueous solution (10 mL, 10 mg / mL) and let it stand at room temperature for 12 hours.

[0066] S3: After drying the sample at 80 ℃, it was calcined in air at 400 ℃ for 4 hours to obtain a comparative sample prepared by the traditional impregnation method, denoted as COF-Co-imp.

[0067] This comparative example is used to demonstrate the advantages of the coordination method described in this invention in forming single-atom dispersed active sites.

[0068] Electrocatalytic water oxidation tests were conducted on the above catalysts, and the results are shown in Table 1.

[0069] Table 1. Different catalysts at 10 mA·cm - ²Oxygen evolution overpotential at current density

[0070] As shown in Table 1, the catalyst provided by this invention has a smaller water oxidation overpotential compared to other catalysts, indicating that it has higher catalytic performance.

[0071] Figure 2 The XRD patterns of the catalyst COF-Co-Stp prepared in Example 1 and COF-Stp prepared in Comparative Example 1 are shown to characterize the crystal structure of the materials. The XRD patterns show that COF-Co-Stp exhibits a broadened diffraction peak at approximately 27°, indicating that the material possesses short-range ordered layered stacking characteristics, reflecting both nanoscale crystal domain size and abundant structural defects, consistent with the structural characteristics of a covalent organic framework. In contrast, COF-Stp also shows a similar broadened diffraction peak near the same position, indicating that the support framework maintains basic structural integrity before and after loading metal single atoms. Simultaneously, the diffraction peak positions and intensities of COF-Co-Stp change slightly, indicating that cobalt atoms were successfully introduced and coordinated with nitrogen sites in the framework, slightly affecting the original interlayer stacking mode.

[0072] Figure 3 The image shows a SEM image of the COF-Co-Stp catalyst prepared in Example 1, used to characterize the microstructure of the material. The SEM image shows that the material is formed by a three-dimensional interconnected porous network of interleaved stacked two-dimensional nanosheets, which has a cross-scale open pore structure, which is beneficial for mass transfer and exposes a rich active interface.

[0073] Figure 4 The electrochemical performance test graphs for the catalyst COF-Co-Stp prepared in Example 1 and the COF-Stp prepared in Comparative Example 1 are used to evaluate the oxygen evolution reaction activity of the catalysts. COF-Co-Stp achieved 10 mA·cm⁻¹ in 1.0 M NaOH. - The overpotential at the given current density is 269 mV, demonstrating high activity comparable to noble metal catalysts in the alkaline oxygen evolution reaction (OER). In contrast, COF-Stp exhibits significantly lower activity under the same test conditions, requiring a much higher overpotential to reach the same current density. This indicates that the pure COF support, lacking metal single atoms, possesses almost no OER catalytic activity, further confirming that the M–N3 coordination center of the metal single atom is the key source of the catalyst's high activity.

[0074] Figure 5 The chronoamperometry results for the COF-Co-Stp catalyst prepared in Example 1 are used to evaluate the catalyst's electrochemical stability. The test was conducted at a constant potential of 1.55 V, and the current density of the catalyst remained stable at 10 mA·cm⁻¹ during the 5-hour test period. - ², exhibiting excellent electrochemical stability.

[0075] Figure 6 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the COF-Co-Stp catalyst prepared in Example 1, used to analyze the surface elemental composition of the catalyst. XPS shows that COF-Co-Stp is composed of C, O, N, and Co elements.

[0076] The above characterization and test results fully demonstrate that the non-noble metal single-atom catalyst based on a specific COF framework provided by this invention possesses a well-defined framework structure, abundant active sites, and excellent electrochemical performance. The preferred embodiment, COF-Co-Stp, exhibits promising application prospects in alkaline electrocatalytic oxygen evolution reaction, fully verifying the feasibility and superiority of the technical solution of this invention.

[0077] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A single-atom catalyst supported on a covalent organic framework, characterized in that, The catalyst comprises a covalent organic framework and single-atom non-noble metal atoms coordinated to the covalent organic framework, and the catalyst has repeating structural units as shown in formula (I): （Ⅰ） Where M represents a non-noble metal atom in monatomic form, This represents the coordinate bond between M and N atoms. This indicates that the repeating structural unit extends periodically in multiple directions within a plane.

2. The catalyst according to claim 1, characterized in that, The non-noble metal atom M is selected from any one of Co, Ni, Fe, Cu or Mn.

3. The catalyst according to claim 1, characterized in that, The covalent organic framework is a two-dimensional periodic network structure formed by the covalent connection of tetraamino aromatic monomers and triazine carboxylic acid ester monomers as building units through benzobisimidazole.

4. The catalyst according to claim 3, characterized in that, The tetraamino aromatic monomer is 1,2,4,5-phenyltetramine or its salt formed with an inorganic or organic acid, and the triazine carboxylic acid ester monomer is selected from trimethyl 1,3,5-triazine-2,4,6-tricarboxylic acid, triethyl 1,3,5-triazine-2,4,6-tricarboxylic acid, or tripropyl 1,3,5-triazine-2,4,6-tricarboxylic acid.

5. A method for preparing a single-atom catalyst supported on a covalent organic framework as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Mix tetraamino aromatic monomers, triazine carboxylic acid ester monomers, the first solvent and condensing agent, and carry out a condensation reaction under a protective atmosphere. Collect the solid reaction product, purify and dry it to obtain a covalent organic framework. S2. The covalent organic framework and non-precious metal salt obtained in step S1 are mixed with the second solvent, and a catalytic amount of organic amine is added. Under a protective atmosphere, ultrasonic dispersion and heating and stirring are performed sequentially to allow the non-precious metal ions to undergo a coordination reaction with the covalent organic framework. After washing and drying, a metal-coordinated covalent organic framework precursor is obtained. S3. The metal-coordinated covalent organic framework precursor obtained in step S2 is heat-treated under an inert atmosphere to obtain the catalyst.

6. The preparation method according to claim 5, characterized in that, In step S1: The molar ratio of the tetraamino aromatic monomer to the triazine carboxylic acid ester monomer is 1.2:1-1.8:1; The first solvent is one of anhydrous N,N-dimethylformamide, anhydrous N,N-dimethylacetamide, and anhydrous N-methyl-2-pyrrolidone, and the condensing agent is one of polyphosphoric acid, p-toluenesulfonic acid, and phosphorus pentoxide. The polycondensation reaction is carried out at a temperature of 110-130℃ for 20-28 hours. The purification process employs Soxhlet extraction, using methanol as the solvent for continuous extraction over 60-80 hours.

7. The preparation method according to claim 5, characterized in that, In step S2: The non-precious metal salt is an acetate, nitrate, or chloride of the non-precious metal; The mass ratio of the carrier to the non-precious metal salt is 1:0.8 to 1:1.2; The organic amine is one of ethylenediamine, 1,3-propanediamine, and 1,4-butanediamine; The second solvent is one of anhydrous N,N-dimethylformamide, anhydrous N,N-dimethylacetamide, and anhydrous N-methyl-2-pyrrolidone; The ultrasonic dispersion time is 5-7 hours; The heating and stirring treatment is carried out at a temperature of 70-80℃ for 44-52 hours.

8. The preparation method according to claim 5, characterized in that, In step S3, the heat treatment conditions include: heating to 180-220°C at a heating rate of 1-3°C / min under an inert atmosphere, and holding at that temperature for 1-3 hours.

9. The application of the single-atom catalyst supported on the covalent organic framework according to any one of claims 1 to 4 in the electrocatalytic oxygen evolution reaction.

10. The application according to claim 9, characterized in that, The electrocatalytic oxygen evolution reaction is carried out in a 1.0-1.2 M NaOH electrolyte.

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