A diatomic catalyst based on covalent organic frameworks and a preparation method and application thereof

Abstract

The application discloses a preparation method and application of a diatomic catalyst based on a covalent organic framework. The diatomic catalyst based on the covalent organic framework prepared by the application has a clear structure, and the distance between the bimetallic active centers is clear and adjustable, which is beneficial to the research on the synergistic effect of the diatomic catalyst. The application also provides an excellent catalyst for electrochemically preparing hydrogen peroxide, which has the advantages of stable structure, high specific surface area, high repeatability, simple preparation and hydrogen peroxide selectivity of more than 90%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of catalyst preparation, and particularly relates to a preparation method and application of a covalent organic framework-based diatomic catalyst. BACKGROUND

[0002] Hydrogen peroxide is widely used in industrial, civil and other fields as a carbon-free energy carrier and green and environmentally friendly oxidant. According to statistics, the global utilization rate of hydrogen peroxide is about 4 million tons per year, and it is expected to continue to grow in the future. Currently, 95% of the world's hydrogen peroxide production comes from the anthraquinone oxidation method, which is also a relatively mature preparation method, and can achieve high yield and large-scale preparation of hydrogen peroxide. However, this method has high cost and complex process, and generates toxic by-products. In contrast, the electrocatalytic oxygen reduction reaction (ORR) for preparing hydrogen peroxide provides a simple, efficient and environmentally friendly preparation method. However, this method is limited by the catalytic performance of the two-electron ORR catalyst, so there is an urgent need to design a 2e-ORR catalyst with excellent performance to achieve green synthesis of hydrogen peroxide.

[0003] Diatomic catalyst is a supported catalyst with metal atoms as active centers. There is often a synergistic effect between the two metal atoms, and it has high atom utilization rate, high stability, reaction diversity and adjustability, etc. It is a research hotspot in the field of catalysis. Recently, Sun et al. used pyrolysis to introduce Co and Mn metal elements on a ZIF-8 derived carbon substrate to prepare a CoMn-NC diatomic catalyst (Adv. Funct. Mater. 2024, 2315862). Zhang et al. also used pyrolysis to prepare a Mg / Fe-N-C diatomic catalyst on a nitrogen-doped carbon substrate (Angew. Chem. Int. Ed. 2023, 62, e202314303). Yao et al. also used high-temperature pyrolysis to prepare a Fe / Pt diatomic catalyst (CN117691137A). Most of the reported diatomic catalysts are prepared by pyrolysis of carbon precursors. Although the pyrolysis method is simple and easy to obtain, this preparation method is uncontrollable, and the distance between diatomic atoms and the existence form of diatomic atoms are uncontrollable, and the synergistic effect is not clear. It is difficult to establish the structure-performance relationship of diatomic catalysts. Therefore, designing diatomic catalysts with clear structure and establishing the structure-performance relationship of diatomic structure and performance is the research focus in the field of catalysis. SUMMARY

[0004] Based on the above, the present application relates to the content mainly includes the following three aspects: (1) in the structural aspect, a series of novel adjustable double atomic spacing and double atomic species of covalent organic framework-based electrocatalyst is designed, in the series of structures, two kinds of metal species can be freely switched, the spacing between double metal single atoms can be adjusted, has clear framework structure, clear double metal spacing and active site. While having the above characteristics, it also has the advantages of covalent organic framework itself, such as high specific surface area, high stability, rich pore structure, etc. (2) A preparation method of covalent organic framework-based double atomic catalyst is provided, which has high specific surface area, rich pore structure, high stability, simple preparation method, high repeatability and no complex operation. (3) By utilizing the synergistic effect of the active center in the double atomic catalyst, combining the high specific surface area and rich pore size of the covalent organic framework, the green synthesis of hydrogen peroxide is realized by electrocatalysis, which is used to solve the problems of high cost, complex process, low safety and environmental pollution in the current industrial synthesis of hydrogen peroxide.

[0005] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0006] The present application provides a series of novel adjustable double atomic spacing and double atomic species of covalent organic framework-based electrocatalyst, the specific structure of the double atomic covalent organic framework is shown as formula I or formula II:

[0007]

[0008] The double atomic covalent organic framework shown in the above figure has the following characteristics:

[0009] The double atomic covalent organic framework shown in the above figure has high crystallinity and stability. The two-dimensional lateral long-range order is AA stacking.

[0010] The double atomic covalent organic framework shown in the above figure, M1 or M2 in formula I or formula II includes a series of transition metals such as manganese, iron, cobalt, nickel, copper and zinc.

[0011] The double atomic covalent organic framework shown in the above figure, the distance between the double atoms M1 and M2 is different, the spacing between M1 and M2 in formula I is The spacing between M1 and M2 in formula II is

[0012] The double atomic covalent organic framework shown in the above figure, the M1 site is M1N4 structure, and the M2 site is M2N2 structure, which depends on the metal salt species.

[0013] The double atomic covalent organic framework shown in the above figure, the valence state of M1M2 is +2.

[0014] The diatomic covalent organic frameworks shown in the above figure have a high specific surface area of 600-1000 m2 / g.

[0015] The diatomic covalent organic frameworks shown in the above figure have a pore volume of 0.5-0.9 cm3 / g.

[0016] The diatomic covalent organic frameworks shown in the above figure have a pore size distribution of 1-2.5 nm.

[0017] The diatomic covalent organic frameworks shown in the above figure are named M1N4-M2N2-COF according to Formula I and M1N4-(M2N2)2-COF according to Formula II.

[0018] The diatomic covalent organic framework-based catalysts according to Formula I or Formula II described above, and a preparation method thereof, include the following steps:

[0019] 1) Heating and stirring the reaction of tetraaminophenyl porphyrin and transition metal salt in solution, and obtaining tetraaminophenyl porphyrin coordinated with a single atom of metal (TAPP-M1) after the reaction is completed.

[0020] 2) Solvothermal reaction of TAPP-M1 and 2,2'-dipyridyl-5,5'-diformaldehyde or 3,3'-dipyridyl-6,6'-diformaldehyde dispersed in solution. Obtaining a single atom M1 covalent organic framework after the reaction is completed.

[0021] 3) Uniformly mixing and dispersing the single atom M1 covalent organic framework described above and metal salt in solution, heating and stirring the reaction, and obtaining the covalent organic framework-based diatomic catalyst according to Formula I or Formula II described above after the reaction is completed.

[0022] In step 1) of the above preparation method, the metal salt and tetraaminophenyl porphyrin react in a solvent, and the metal salt includes transition metal chloride or transition metal acetate.

[0023] In step 1) of the above preparation method, the metal salt and tetraaminophenyl porphyrin react in a solvent, and the metal salt includes hydrate and anhydrous.

[0024] In step 1) of the above preparation method, the metal salt and tetraaminophenyl porphyrin react in a solvent, and the molar ratio of tetraaminophenyl porphyrin to metal salt is 1-2:3-4.

[0025] In step 1) of the above preparation method, the metal salt and tetraaminophenyl porphyrin react in a solvent, and the solvent is a mixed solvent of methanol, N,N-dimethylformamide, and chloroform. The volume ratio of methanol, N,N-dimethylformamide, and chloroform is 1-2:3:9.

[0026] In the above preparation method step 1), the tetraaminophenyl porphyrin and the transition metal salt are heated and stirred in solution under a nitrogen or argon atmosphere at a temperature of 70-90°C for 12-48 hours.

[0027] In the above preparation method 1), as preferred, the metal salt is selected from transition metal acetate hydrate. As preferred, the volume ratio of methanol, DMF and chloroform is 1:3:9.

[0028] In the above preparation method 2), the TAPP-M1 and 2,2'-bipyridine-5,5'-dicarboxaldehyde or 3,3'-bipyridine-6,6'-dicarboxaldehyde are dispersed in a mixed solvent for solvothermal reaction, and the molar ratio of TAPP-M1 to 2,2'-bipyridine-5,5'-dicarboxaldehyde or 3,3'-bipyridine-6,6'-dicarboxaldehyde is 1:2.

[0029] In the above preparation method 2), the TAPP-M1 and 2,2'-bipyridine-5,5'-dicarboxaldehyde or 3,3'-bipyridine-6,6'-dicarboxaldehyde are dispersed in a mixed solvent for solvothermal reaction, and the solvent is o-dichlorobenzene / n-butanol mixed solvent or mesitylene / dioxane mixed solvent or ethanol / o-dichlorobenzene mixed solvent.

[0030] In the above preparation method step 2), the TAPP-M1 and 2,2'-bipyridine-5,5'-dicarboxaldehyde or 3,3'-bipyridine-6,6'-dicarboxaldehyde are dispersed in a mixed solvent for solvothermal reaction, and 3M or 6M acetic acid is added as a reaction catalyst.

[0031] In the above preparation method step 2), the TAPP-M1 and 2,2'-bipyridine-5,5'-dicarboxaldehyde or 3,3'-bipyridine-6,6'-dicarboxaldehyde are dispersed in a mixed solvent for solvothermal reaction, and the reaction is carried out under vacuum at a temperature of 120-160°C for 72-120 hours.

[0032] In the above preparation method step 2), as preferred, the mixed solvent is o-dichlorobenzene / n-butanol mixed solution, and the solvothermal reaction catalyst is 6M acetic acid.

[0033] In the above preparation method step 3), the monatomic M1 covalent organic framework prepared in step 2) is uniformly mixed and dispersed with a metal salt in solution and heated and stirred. The solvent includes any one of methanol, ethanol, tetrahydrofuran, ultrapure water and dichloromethane.

[0034] In the above preparation method step 3), the monatomic M1 covalent organic framework prepared in step 2) is uniformly mixed and dispersed with a metal salt in solution and heated and stirred. The reaction is carried out under an inert gas atmosphere.

[0035] In the above preparation method step 3), the monatomic M1 covalent organic framework prepared in step 2) is uniformly mixed and dispersed with the metal salt in solution and heated and stirred. The reaction temperature is 60-90°C.

[0036] In the above preparation method step 3), the monatomic M1 covalent organic framework prepared in step 2) is uniformly mixed and dispersed with the metal salt in solution and heated and stirred. The reaction time is 6-15h.

[0037] In the above preparation method step 3), as preferred, the reaction is carried out under a nitrogen atmosphere, the reaction temperature is 60°C, and the reaction time is 12h.

[0038] The present application uses the above series of covalent organic framework-based catalysts with adjustable double atom spacing and double atom types as the working electrode for two-electron oxygen reduction reactions.

[0039] According to the covalent organic framework-based double atom catalyst as described above, when M1 is Co, M2 is Ni, and the spacing between Co and Ni is , it is denoted as CoN4-NiN2-COF, which has the best two-electron oxygen reduction reaction performance, and the selectivity for hydrogen peroxide can be as high as 95%.

[0040] The present application has the following beneficial effects: The novel covalent organic framework-based catalyst with adjustable double atom spacing and double atom types prepared by the present application has a clear structure, and the distance between the double metal active centers is clear and adjustable, which is conducive to the study of the synergistic effect of double atom catalysts. The present application simultaneously provides an excellent catalyst for electrochemically preparing hydrogen peroxide, which has a stable structure, a high specific surface area, high repeatability, simple preparation, and a selectivity for hydrogen peroxide >90%. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative labor. Among them:

[0042] Figure 1 The infrared spectrum of TAPP and TAPP-Co in Example 1 of the present application.

[0043] Figure 2 The XRD pattern of the catalyst prepared in Example 1 of the present application.

[0044] Figure 3 The nitrogen adsorption-desorption isotherm pattern of the catalyst prepared in Example 1 of the present application.

[0045] Figure 4An infrared spectrum of the catalyst prepared in Example 1 of the present application.

[0046] Figure 5 An XPS full spectrum of the catalyst prepared in Example 1 of the present application.

[0047] Figure 6 A LSV polarization curve of the catalyst in Example 2 of the present application.

[0048] Figure 7 A plot of hydrogen peroxide selectivity vs. voltage of the catalyst in Example 2 of the present application.

[0049] Figure 8 An XRD of the single metal covalent organic framework prepared in Comparative Example 1 of the present application.

[0050] Figure 9 LSV polarization curves of each catalyst in Comparative Example 2 of the present application.

[0051] Figure 10 LSV polarization curves of each catalyst in Comparative Example 3 of the present application.

[0052] Figure 11 A plot of hydrogen peroxide selectivity vs. voltage of each catalyst in Comparative Example 2 of the present application.

[0053] Figure 12 A plot of hydrogen peroxide selectivity vs. voltage of each catalyst in Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0054] In order to make the above objects, features and advantages of the present application more clear and comprehensible, the specific embodiments of the present application will be described in detail below with specific examples.

[0055] Example 1:

[0056] (1) Preparation of TAPP-Co:

[0057] Take 0.3 mmol of tetraaminophenyl porphyrin and 1.2 mmol of cobalt acetate tetrahydrate in a 250 ml round-bottom flask, and sequentially add 20 ml of methanol, 30 ml of N, N-dimethylformamide, and 90 ml of chloroform. Place a condenser and a three-way gas exhaust joint on the upper part of the round-bottom flask. Use a double-tube nitrogen gas-exhaust cycle three times to maintain a closed nitrogen environment inside the round-bottom flask. Then place the reaction system in an oil bath heating device, set the temperature to 80°C, start the magnetic stirring and condensation circulating water, and react for 24 h. After the reaction is completed, pour the dark green solution into a separatory funnel, add a large amount of deionized water to separate the solution, collect the lower organic phase, and repeat three times to remove the DMF solution and uncoordinated metal salts in the system. Centrifuge the lower organic phase and wash it once with methanol. Then dry it at 80°C overnight under vacuum to obtain the final product.

[0058] As shown in the infrared spectrum shown in Figure 1 Compared with TAPP, the TAPP-Co has a N-H vibration peak at 965 cm -1 , and a Co-N vibration peak at 1000 cm -1 , which indicates that Co is successfully coordinated to the center of the porphyrin ring, and TAPP-Co is successfully synthesized.

[0059] (2) Preparation of CoN4-2, 2'-Bp-COF:

[0060] Take 0.022 mmol of TAPP-Co and 0.044 mmol of 2, 2'-dipyridyl-5, 5'-diformaldehyde in a 15 ml heat-resistant reaction bottle, add 0.5 ml of o-dichlorobenzene, 0.5 ml of n-butanol, and 0.1 ml of 6M acetic acid, and ultrasonic for 15 min. Seal the reaction tube and place it in a 120°C oil bath device for a solvothermal reaction under vacuum for three days. After the reaction is completed, centrifuge and wash with acetone three times and tetrahydrofuran five times, and then dry at 80°C under vacuum overnight to obtain a single-metal Co-coordinated covalent organic framework, which is recorded as CoN4-2, 2'Bp-COF.

[0061] (3) Synthesis of CoN4-NiN2-COF:

[0062] Disperse 30 mg of CoN4-2, 2'-Bp-COF in 20 ml of methanol, and add 80 mg of nickel acetate. Reflux at 70°C under nitrogen atmosphere for 12 h. After the reaction is completed, wash with a large amount of methanol and deionized water, and dry at 80°C under vacuum overnight to obtain the final product CoN4-NiN2-COF.

[0063] As shown in the infrared spectrum shown in Figure 2As shown, the crystallinity of the single metal covalent organic framework is not destroyed after the coordination of the second metal Ni atom, and a sharp peak appears at about 2.9°, indicating that it still maintains a high degree of crystallinity. In addition Figure 3 The nitrogen adsorption-desorption isotherm graphs of the two COFs are shown in FIG. 2, which, combined with the infrared spectrum shown in FIG. 3, prove the successful synthesis of CoN4-NiN2-COF. Figure 4 The nitrogen adsorption-desorption isotherm graphs of the two COFs are shown in FIG. 2, which, combined with the infrared spectrum shown in FIG. 3, prove the successful synthesis of CoN4-NiN2-COF.

[0064] (4) Catalyst ink preparation:

[0065] 1 mg of CoN4-NiN2-COF was dispersed in a mixed solution containing 0.9 mL of isopropanol, 0.1 mL of deionized water, and 0.02 mL of Nafion 117 perfluorinated resin solution (Macklin-N831951), and ultrasonicated for 2 h to obtain the catalyst ink.

[0066] Example 2:

[0067] The application of the catalyst in the 2e-ORR was tested: 10 μL of the catalyst ink prepared in Example 1 was coated on the surface of a glassy carbon electrode (0.2475 cm -2 ) to prepare a working electrode.

[0068] The 2e-ORR activity of the catalyst was tested by linear sweep voltammetry. A three-electrode system was used, with a rotating disc electrode coated with the catalyst as the working electrode, a platinum wire as the counter electrode, and Ag / AgCl as the reference electrode, and the electrolyte was 0.1 M KOH. Oxygen was passed to saturate the electrolyte with oxygen. The rotating disc electrode was rotated at 1600 rpm. The voltage scan range was 0.1-1.1 V vs. SHE.

[0069] The LSV polarization curve of the catalyst in Example 1 is shown in FIG. 4, which reflects the 2e-ORR catalytic performance of the catalyst. Figure 6 The 2e-ORR activity of the catalyst was tested by linear sweep voltammetry. A three-electrode system was used, with a rotating disc electrode coated with the catalyst as the working electrode, a platinum wire as the counter electrode, and Ag / AgCl as the reference electrode, and the electrolyte was 0.1 M KOH. Oxygen was passed to saturate the electrolyte with oxygen. The rotating disc electrode was rotated at 1600 rpm. The voltage scan range was 0.1-1.1 V vs. SHE. Figure 7 The 2e-ORR activity of the catalyst was tested by linear sweep voltammetry. A three-electrode system was used, with a rotating disc electrode coated with the catalyst as the working electrode, a platinum wire as the counter electrode, and Ag / AgCl as the reference electrode, and the electrolyte was 0.1 M KOH. Oxygen was passed to saturate the electrolyte with oxygen. The rotating disc electrode was rotated at 1600 rpm. The voltage scan range was 0.1-1.1 V vs. SHE. Figure 6 The 2e-ORR activity of the catalyst was tested by linear sweep voltammetry. A three-electrode system was used, with a rotating disc electrode coated with the catalyst as the working electrode, a platinum wire as the counter electrode, and Ag / AgCl as the reference electrode, and the electrolyte was 0.1 M KOH. Oxygen was passed to saturate the electrolyte with oxygen. The rotating disc electrode was rotated at 1600 rpm. The voltage scan range was 0.1-1.1 V vs. SHE.

[0070] Comparative Example 1:

[0071] (1) 0.022 mmol TAPP-Co and 0.044 mmol 2,2'-bipyridine-5,5'-dicarboxaldehyde were weighed into a 15 mL heat-resistant reaction bottle, 0.5 mL mesitylene, 0.5 mL dioxane, 0.1 mL 6M acetic acid were added, and ultrasonic treatment was performed for 15 min. The reaction tube was sealed and placed in a 120°C oil bath device for solvothermal reaction for three days. After the reaction was completed, centrifugation was performed and washing was performed three times with acetone and five times with tetrahydrofuran, followed by vacuum drying at 80°C overnight. A red-brown powder was obtained. XRD characterization showed that the powder obtained by combining mesitylene and dioxane solvents had low crystallinity.

[0072] (2) 0.022 mmol TAPP-Co and 0.044 mmol 2,2'-bipyridine-5,5'-dicarboxaldehyde were weighed into a 15 mL heat-resistant reaction bottle, 0.25 mL o-dichlorobenzene, 0.75 mL benzaldehyde, 0.1 mL 6M acetic acid were added, and ultrasonic treatment was performed for 15 min. After three cycles of freeze-pumping-thaw, the reaction tube was sealed and placed in a 120°C oil bath device for solvothermal reaction for three days. After the reaction was completed, centrifugation was performed and washing was performed three times with acetone and five times with tetrahydrofuran, followed by vacuum drying at 80°C overnight. A red-brown powder was obtained. XRD characterization showed that the combination of o-dichlorobenzene and benzaldehyde solvents did not result in a crystalline covalent organic framework.

[0073] Comparative Example 2:

[0074] (1) Synthesis and electrochemical test of CoN4-MnN2-COF

[0075] 30 mg of CON4-2,2'-Bp-COF was dispersed in 20 mL of methanol, and 80 mg of manganese acetate was added. The reaction was carried out under reflux at 70°C in a nitrogen atmosphere for 12 h. After the reaction was completed, washing was performed with a large amount of methanol and deionized water, and vacuum drying was performed at 80°C overnight to obtain CoN4-MnN2-COF. 1 mg of CoN4-MnN2-COF was dispersed in a mixture solution of 0.9 mL of isopropanol, 0.1 mL of deionized water, and 0.02 mL of Nafion, and ultrasonic treatment was performed for 2 h to obtain a catalyst ink. The electrochemical performance test of CoN4-MnN2-COF was performed by the same test method as in Example 2.

[0076] (2) Synthesis and electrochemical test of CoN4-FeN2-COF

[0077] Take 30 mg of CoN4-2,2'-Bp-COF and disperse it in 20 mL of methanol, and add 80 mg of iron acetate. Reflux the reaction under a nitrogen atmosphere at 70°C for 12 h. After the reaction is completed, wash it with a large amount of methanol and deionized water, and dry it at 80°C under vacuum overnight to obtain CoN4-FeN2-COF. Disperse 1 mg of CoN4-FeN2-COF in a mixture solution of 0.9 mL of isopropanol, 0.1 mL of deionized water, and 0.02 mL of Nafion, and ultrasonic it for 2 h to obtain a catalyst ink. Perform electrochemical performance testing on the CoN4-FeN2-COF using the same testing method as in Example 2.

[0078] (3) Synthesis and electrochemical testing of CoN4-CoN2-COF

[0079] Take 30 mg of CoN4-2,2'-Bp-COF and disperse it in 20 mL of methanol, and add 80 mg of iron acetate. Reflux the reaction under a nitrogen atmosphere at 70°C for 12 h. After the reaction is completed, wash it with a large amount of methanol and deionized water, and dry it at 80°C under vacuum overnight to obtain CoN4-FeN2-COF. Disperse 1 mg of CoN4-FeN2-COF in a mixture solution of 0.9 mL of isopropanol, 0.1 mL of deionized water, and 0.02 mL of Nafion, and ultrasonic it for 2 h to obtain a catalyst ink. Perform electrochemical performance testing on the CoN4-FeN2-COF using the same testing method as in Example 2.

[0080] (4) Synthesis and electrochemical testing of CoN4-CuN2-COF

[0081] Take 30 mg of CoN4-2,2'-Bp-COF and disperse it in 20 mL of methanol, and add 80 mg of copper acetate. Reflux the reaction under a nitrogen atmosphere at 70°C for 12 h. After the reaction is completed, wash it with a large amount of methanol and deionized water, and dry it at 80°C under vacuum overnight to obtain CoN4-CuN2-COF. Disperse 1 mg of CoN4-CuN2-COF in a mixture solution of 0.9 mL of isopropanol, 0.1 mL of deionized water, and 0.02 mL of Nafion, and ultrasonic it for 2 h to obtain a catalyst ink. Perform electrochemical performance testing on the CoN4-CuN2-COF using the same testing method as in Example 2.

[0082] Comparative Example 3:

[0083] (1) Synthesis of CoN4-3,3'-Bp-COF

[0084] Take 0.022 mmol of TAPP-Co and 0.044 mmol of 3,3'-bipyridine-6,6'-diformaldehyde in a 15 mL heat-resistant reaction bottle, add 0.5 mL of o-dichlorobenzene, 0.5 mL of n-butanol, 0.1 mL of 6M acetic acid, and ultrasonic for 15 min. After three cycles of freeze-pumping-thaw, the reaction tube is sealed and placed in a 120°C oil bath device for solvothermal reaction for three days. After the reaction is completed, centrifugal and washed with acetone three times, tetrahydrofuran five times, and then vacuum dried at 80°C overnight to obtain a coordination monometallic Co covalent organic framework, denoted as CoN4-3,3'-Bp-COF.

[0085] (2) Synthesis and electrochemical test of CoN4-(MnN2)2-COF

[0086] Take 30 mg of CON4-3,3'-Bp-COF and disperse it in 20 mL of methanol, and add 80 mg of manganese acetate. Reflux the reaction under a nitrogen atmosphere at 70°C for 12 h. After the reaction is completed, wash with a large amount of methanol and deionized water, and vacuum dry at 80°C overnight to obtain CoN4-(MnN2)2-COF. Disperse 1 mg of CoN4-(MnN2)2-COF into a mixed solution of 0.9 mL of isopropyl alcohol, 0.1 mL of deionized water, and 0.02 mL of Nafion, and ultrasonic for 2 h to obtain a catalyst ink. Perform electrochemical performance test on CoN4-(MnN2)2-COF by the same test method as in Example 2.

[0087] (3) Synthesis and electrochemical test of CoN4-(FeN2)2-COF

[0088] Take 30 mg of CoN4-3,3'-Bp-COF and disperse it in 20 mL of methanol, and add 80 mg of iron acetate. Reflux the reaction under a nitrogen atmosphere at 70°C for 12 h. After the reaction is completed, wash with a large amount of methanol and deionized water, and vacuum dry at 80°C overnight to obtain CoN4-(FeN2)2-COF. Disperse 1 mg of CON4-(FeN2)2-COF into a mixed solution of 0.9 mL of isopropyl alcohol, 0.1 mL of deionized water, and 0.02 mL of Nafion, and ultrasonic for 2 h to obtain a catalyst ink. Perform electrochemical performance test on CON4-(FeN2)2-COF by the same test method as in Example 2.

[0089] (4) Synthesis and electrochemical test of CoN4-(CoN2)2-COF

[0090] Take 30 mg of CoN4-3,3'-Bp-COF and disperse it in 20 mL of methanol, and add 80 mg of cobalt acetate. Reflux the reaction under a nitrogen atmosphere at 70 °C for 12 h. After the reaction is complete, wash it with a large amount of methanol and deionized water, and dry it at 80 °C under vacuum overnight to obtain CoN4-(CoN2)2-COF. Disperse 1 mg of CoN4-(CoN2)2-COF in a mixture of 0.9 mL of isopropanol, 0.1 mL of deionized water, and 0.02 mL of Nafion, and ultrasonic it for 2 h to obtain a catalyst ink. Perform electrochemical performance testing on the CoN4-(CoN2)2-COF using the same testing method as in Example 2.

[0091] (5) Synthesis and electrochemical testing of CoN4-(NiN2)2-COF

[0092] Take 30 mg of CoN4-3,3'-Bp-COF and disperse it in 20 mL of methanol, and add 80 mg of nickel acetate. Reflux the reaction under a nitrogen atmosphere at 70 °C for 12 h. After the reaction is complete, wash it with a large amount of methanol and deionized water, and dry it at 80 °C under vacuum overnight to obtain CoN4-(NiN2)2-COF. Disperse 1 mg of CON4-(NiN2)2-COF in a mixture of 0.9 mL of isopropanol, 0.1 mL of deionized water, and 0.02 mL of Nafion, and ultrasonic it for 2 h to obtain a catalyst ink. Perform electrochemical performance testing on the CON4-(NiN2)2-COF using the same testing method as in Example 2.

[0093] (6) Synthesis and electrochemical testing of CON4-(CuN2)2-COF

[0094] Take 30 mg of CoN4-3,3'-Bp-COF and disperse it in 20 mL of methanol, and add 80 mg of copper acetate. Reflux the reaction under a nitrogen atmosphere at 70 °C for 12 h. After the reaction is complete, wash it with a large amount of methanol and deionized water, and dry it at 80 °C under vacuum overnight to obtain CoN4-(CuN2)2-COF. Disperse 1 mg of CoN4-(CuN2)2-COF in a mixture of 0.9 mL of isopropanol, 0.1 mL of deionized water, and 0.02 mL of Nafion, and ultrasonic it for 2 h to obtain a catalyst ink. Perform electrochemical performance testing on the CoN4-(CuN2)2-COF using the same testing method as in Example 2.

[0095] Figure 1 In the present application, when TAPP is coordinated with a metal, the N-H absorption peak at 968 cm -1 is replaced by an M-N absorption peak at 1000 cm -1 , indicating that the metal has replaced the H in the N-H in the porphyrin ring to form a stable porphyrin metal complex TAPP-Co.

[0096] Figure 2 The XRD curves of CoN4-2,2-Bp-COF and CoN4-NiN2-COF in Example 1 are shown in FIG. 2. It can be seen that the two COFs have a sharp peak at about 2.9°, indicating that they have high crystallinity.

[0097] Figure 3 The data in FIG. 3 are the nitrogen adsorption-desorption curves of CoN4-2,2-Bp-COF and CoN4-NiN2-COF in Example 1. After coordination of the second metal Ni, the specific surface area of CoN4-2,2-Bp-COF decreases.

[0098] Figure 4 FIG. 4 is an infrared spectrum of CoN4-2,2-Bp-COF and CoN4-NiN2-COF in Example 1, and the C=N absorption peak at 1621 cm -1 proves the formation of the imine bond. Combined with Figure 1 and Figure 2 , it indicates that the two COFs are successfully synthesized.

[0099] Figure 5 The XPS full spectra of CoN4-2,2-Bp-COF and CoN4-NiN2-COF in Example 1 are shown in FIG. 5, and the Ni metal element peak at 850-880 eV indicates the successful coordination of the second metal Ni.

[0100] Figure 6 FIG. 6 is a linear sweep voltammetry curve of CoN4-NiN2-COF as a catalyst in the voltage range of 0.2 V-0.9 V, and the starting potential is 0.75 V. The curve intuitively reflects the catalytic performance of the catalyst.

[0101] Figure 7 It can be seen in FIG. 7 that the hydrogen peroxide selectivity of CoN4-NiN2-COF as a catalyst in a certain voltage range is more than 90%.

[0102] Figure 8 FIG. 8 is an XRD curve of CoN4-2,2-Bp-COF powder prepared in different solvents (Example 1 (2), Comparative Example 1). It can be seen that different solvents have a great influence on the crystallinity of CoN4-2,2-Bp-COF. Through experimental exploration, it is found that the combination of n-butanol and o-dichlorobenzene solvents (1:1) can obtain CoN4-2,2-Bp-COF with the highest crystallinity.

[0103] Figure 9The linear sweep voltammetry curves of the five catalysts CoN4-MnN2-COF, CoN4-FeN2-COF, CoN4-CoN2-COF, CoN4-NiN2-COF and CoN4-CuN2-COF in the voltage range of 0.2V-0.9V are shown.

[0104] Figure 10 The linear sweep voltammetry curves of the five catalysts CoN4-(MnN2)2-COF, CoN4-(FeN2)2-COF, CoN4-(CoN2)2-COF, CoN4-(NiN2)2-COF and CoN4-(CuN2)2-COF in the voltage range of 0.2V-0.9V are shown. The ring current related to hydrogen peroxide production can be observed Figure 9 which is significantly lower than that of the five catalysts.

[0105] Figure 11 and Figure 12 The hydrogen peroxide selectivity of each catalyst (Example 1, Comparative Example 2, Comparative Example 3) prepared in the present application in the voltage range of 0.2V-0.6V is shown. Among them, CoN4-NiN2-COF has the highest hydrogen peroxide selectivity.

[0106] It is worth noting that among the six covalent organic framework-based bimetallic catalysts prepared in the present application, the distance between the two metals has a certain influence on the ORR reaction path. In comparison between CoN4-NiN2-COF and CoN4-(NiN2)2-COF, the shortening of the distance between the two metals leads to a sharp decrease in hydrogen peroxide selectivity, and the reaction half-wave potential increases from 0.57V to 0.72V, and the reaction changes from two-electron (2e-ORR) dominated to four-electron (4e - ORR) dominated. This trend also exists in the remaining catalysts.

[0107] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, which should be covered in the scope of the claims of the present application.

Claims

1. A diatomic catalyst based on covalent organic frameworks, characterized in that: A diatomic catalyst based on covalent organic frameworks capable of adjusting the distance between diatomic atoms and the type of diatomic atoms has a monomer structure as shown in Formula I or Formula II: ， wherein M1 represents one of manganese, iron, cobalt, nickel, copper and zinc, and has a valence of +2; M2 represents one of manganese, iron, cobalt, nickel, copper and zinc, and has a valence of +2; and M1 and M2 are different atoms; the distance between M1 and M2 in Formula I is 15 Å; and the distance between M1 and M2 in Formula II is 11 Å; The specific surface area of the covalent organic framework-based diatomic catalyst is 600-1000 m 2 / g, the pore volume is 0.5-0.9 cm 3 / g, and the pore size distribution is 1-2.5 nm.

2. The method of claim 1, wherein the covalent organic framework-based diatomic catalyst is prepared by: comprising the following steps, Step 1) heating and stirring a tetraaminophenyl porphyrin and a salt of metal M1 in a solution to obtain a tetraaminophenyl porphyrin coordinated with a single atom of metal M1, TAPP-M1; Step 2) dispersing TAPP-M1 and 2,2'-bipyridine-5,5'-dicarboxaldehyde or 3,3'-bipyridine-6,6'-dicarboxaldehyde in a solvent to perform a solvothermal reaction to obtain a single atom M1 covalent organic framework; Step 3) uniformly mixing the single atom M1 covalent organic framework and a salt of metal M2 in a solution, heating and stirring to react, and obtaining the diatomic catalyst based on covalent organic frameworks as shown in Formula I or Formula II.

3. The method of claim 2, wherein the covalent organic framework-based diatomic catalyst is prepared by: In Step 1), the molar ratio of tetraaminophenyl porphyrin to the salt of metal M1 is 1-2:3-5.

4. The method of claim 2, wherein the covalent organic framework-based diatomic catalyst is prepared by: In Step 1), the solution is a mixed solution of methanol, N,N-dimethylformamide and chloroform, and the volume ratio is 1-2:3:

9.

5. The method of claim 2-4, wherein the method is characterized by: In Step 1), the reaction conditions are nitrogen or argon atmosphere, the reaction temperature is 70-90 ℃, and the reaction time is 12-48 h.

6. The method of claim 2-4, wherein the method comprises: In Step 2), the molar ratio of TAPP-M1 to 2,2'-bipyridine-5,5'-dicarboxaldehyde or 3,3'-bipyridine-6,6'-dicarboxaldehyde is 1:

2.

7. The method of claim 2-4, wherein the method is characterized by: In Step 2), 3-6 M acetic acid is added as a reaction catalyst, and the solvent includes one of o-dichlorobenzene / n-butanol mixed solvent, dioxane / mesitylene mixed solvent or ethanol / o-dichlorobenzene mixed solvent.

8. The method of claim 2-4, wherein the method is characterized by: In Step 2), the reaction is performed under vacuum conditions, the reaction temperature is 120-160 ℃, and the reaction time is 72-120 h.

9. The method of claim 2-4, wherein the method is characterized by: In Step 3), the reaction solution is selected from one of methanol, ethanol, ultrapure water, dichloromethane and tetrahydrofuran; the reaction is performed under inert atmosphere, the reaction temperature is 60-90 ℃, and the reaction time is 6-15 h.

10. Use of the diatomic catalyst prepared according to the process of claim 2 in the electrocatalytic two-electron oxygen reduction reaction for the production of hydrogen peroxide, characterized by: The diatomic catalyst is coated on the surface of a glassy carbon electrode as a working electrode, a platinum wire is used as a counter electrode, Ag / AgCl is used as a reference electrode, the electrolyte is 0.1 M KOH, and oxygen is passed to saturate the electrolyte with oxygen.

Images