Diatomic catalyst based on covalent organic framework as well as preparation method and application of diatomic catalyst

Abstract

The invention discloses a preparation method and application of a diatomic catalyst based on a covalent organic framework, the prepared diatomic catalyst based on the covalent organic framework has a clear structure, the bimetal active center distance is clear and adjustable, and research on the synergistic effect of the diatomic catalyst is facilitated. The invention also provides an excellent catalyst for electrochemical preparation of hydrogen peroxide, and the catalyst 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 invention belongs to the field of catalyst preparation, and specifically relates to a preparation method and application of a covalent organic framework-based diatomic catalyst. Background Art

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

[0003] A diatomic catalyst is a supported catalyst with a metal atom as the active center. There is often a synergistic effect between dimetallic atoms, with the characteristics of high atomic utilization, high stability, reaction diversity and adjustability, and is a research hotspot in the current catalysis field. Recently, Sun et al. used a pyrolysis method to introduce Co and Mn metal elements on a carbon substrate derived from ZIF-8 to prepare a CoMn-NC diatomic catalyst (Adv. Funct. Mater. 2024, 2315862). Zhang et al. also used a pyrolysis method to prepare a Mg / Fe-NC diatomic catalyst on a nitrogen-doped carbon substrate (Angew. Chem. Int. Ed. 2023, 62, e202314303). Yao et al. also used a high-temperature pyrolysis method to prepare a Fe / Pt diatomic catalyst (CN117691137A). At present, most of the reported diatomic catalysts are prepared by pyrolysis of carbon precursors. Although the pyrolysis method is simple and easy to prepare, this preparation method is uncontrollable. The distance between the diatoms and the existence form of the diatoms are uncontrollable, and the synergistic effect is unclear. It is difficult to establish the structure-performance relationship between the structure and performance of diatomic catalysts. Therefore, designing diatomic catalysts with clear structures and clarifying the structure-performance relationship between diatomic structures and performance are the current research focuses in the field of catalysis. Summary of the invention

[0004] Based on the above, the present invention mainly includes the following three aspects: (1) In terms of structure, a series of novel covalent organic framework-based electrocatalysts with adjustable distance between diatoms and diatomic types are designed. In this series of structures, both metal types can be switched freely, the distance between dimetallic single atoms is adjustable, and it has a clear framework structure, clear bimetallic distance and active sites. While having the above characteristics, it also has the advantages of the covalent organic framework itself, such as high specific surface area, high stability, rich pore structure, etc. (2) A preparation method of a covalent organic framework-based diatomic catalyst is provided, which has a high specific surface area, rich pore structure, high stability, simple preparation method, high repeatability, and no complicated operation. (3) The synergistic effect of the active center in the diatomic catalyst is utilized, combined with the characteristics of the covalent organic framework such as high specific surface area and rich pore size, to achieve the electrocatalytic green synthesis of hydrogen peroxide, which is used to solve the current problems of high cost, complex process, low safety, and environmental pollution in the industrial synthesis of hydrogen peroxide.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a series of novel covalent organic framework-based electrocatalysts capable of adjusting the distance between diatoms and the types of diatoms. The specific structure of the diatomic covalent organic framework is shown in Formula I or Formula II:

[0007]

[0008] The diatomic covalent organic framework of the present invention as shown in the figure above has the following characteristics:

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

[0010] The diatomic covalent organic framework shown in the figure above, 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 diatomic covalent organic framework shown in the figure above has different distances between diatomic M1 and M2. The distance between M1 and M2 in formula I is In formula II, the distance between M1 and M2 is

[0012] The diatomic covalent organic framework shown in the figure above has an M1N4 structure at the M1 site and an M2N2 structure at the M2 site, depending on the type of metal salt.

[0013] The diatomic covalent organic framework shown in the figure above has a M1M2 valence state of +2.

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

[0015] The diatomic covalent organic framework shown above has a pore volume of 0.5-0.9 cm3 / g.

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

[0017] The diatomic covalent organic framework shown in the figure above, formula I is named M1N4-M2N2-COF, and formula II is named M1N4-(M2N2)2-COF.

[0018] The preparation method of the covalent organic framework-based diatomic catalyst of the structure of Formula I or Formula II of the present invention comprises the following steps:

[0019] 1) Tetraaminophenylporphyrin and a transition metal salt are heated and stirred in a solution for reaction, and after the reaction is completed, tetraaminophenylporphyrin (TAPP-M1) coordinated with a single metal atom is obtained.

[0020] 2) Dispersing TAPP-M1 and 2,2'-bipyridine-5,5'-dicarboxaldehyde or 3,3'-bipyridine-6,6'-dicarboxaldehyde in a solution for solvothermal reaction. After the reaction, a single-atom M1 covalent organic framework is obtained.

[0021] 3) The above-mentioned single-atom M1 covalent organic framework and metal salt are uniformly mixed and dispersed in a solution, heated and stirred for reaction, and the covalent organic framework-based diatomic catalyst shown in the above formula I or formula II is obtained after the reaction is completed.

[0022] In step 1) of the above preparation method, a metal salt reacts with tetraaminophenylporphyrin in a solvent, and the type of the metal salt includes transition metal chloride or transition metal acetate.

[0023] In step 1) of the above preparation method, a metal salt reacts with tetraaminophenylporphyrin in a solvent, and the metal salt includes a hydrate and an anhydrate.

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

[0025] In step 1) of the above preparation method, the metal salt reacts with tetraaminophenylporphyrin 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 step 1) of the above preparation method, tetraaminophenylporphyrin and transition metal salt are heated and stirred in a solution for reaction, the reaction conditions are nitrogen or argon atmosphere, the reaction temperature is 70-90° C., and the reaction time is 12-48 hours.

[0027] In the above preparation method 1): preferably, the metal salt is a transition metal acetate hydrate. Preferably, the volume ratio of methanol, DMF and chloroform is 1:3:9.

[0028] In the above preparation method 2), 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), 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 step 2) of the above preparation method, 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 step 2) of the above preparation method, 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. The reaction is carried out under vacuum conditions at a reaction temperature of 120-160° C. for a reaction time of 72-120 h.

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

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

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

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

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

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

[0038] The present invention uses the above series of covalent organic framework-based catalysts capable of adjusting the distance between diatoms and the types of diatoms as working electrodes for two-electron oxygen reduction reactions.

[0039] According to the covalent organic framework-based diatomic catalyst described above, when M1 is Co, M2 is Ni and the Co Ni distance is When it is recorded as CoN4-NiN2-COF, its two-electron oxygen reduction reaction performance is optimal, and the hydrogen peroxide selectivity can reach up to 95%.

[0040] Beneficial effects of the present invention: The novel covalent organic framework-based catalyst prepared by the present invention, which can adjust the distance between diatoms and the types of diatoms, has a clear structure, and the distance between the dimetallic active centers is clear and adjustable, which is conducive to the study of the synergistic effect of diatomic catalysts. The present invention also provides an excellent catalyst for electrochemical preparation of hydrogen peroxide, which has a stable structure, a high specific surface area, high repeatability, simple preparation, and a selectivity for hydrogen peroxide of more than 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0042] Figure 1 This is the infrared spectra of TAPP and TAPP-Co in Example 1 of the present invention.

[0043] Figure 2 This is the XRD pattern of the catalyst prepared in Example 1 of the present invention.

[0044] Figure 3 This is a nitrogen adsorption-desorption isotherm diagram of the catalyst prepared in Example 1 of the present invention.

[0045] Figure 4This is the infrared spectrum of the catalyst prepared in Example 1 of the present invention.

[0046] Figure 5 This is the full XPS spectrum of the catalyst prepared in Example 1 of the present invention.

[0047] Figure 6 This is the LSV polarization curve diagram of the catalyst in Example 2 of the present invention.

[0048] Figure 7 This is a graph showing the correlation between the hydrogen peroxide selectivity and voltage of the catalyst in Example 2 of the present invention.

[0049] Figure 8 This is the XRD pattern of the single metal covalent organic framework prepared in Comparative Example 1 of the present invention.

[0050] Fig. 9 It is the LSV polarization curve diagram of each catalyst in the comparative example 2 of the present invention.

[0051] Fig.10 It is the LSV polarization curve diagram of each catalyst in comparative example 3 of the present invention.

[0052] Fig.11 Graph showing the correlation between the hydrogen peroxide selectivity and voltage of each catalyst in Comparative Example 2 of the present invention.

[0053] Fig.12 Graph showing the correlation between the hydrogen peroxide selectivity and voltage of each catalyst in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0054] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with specific embodiments.

[0055] Embodiment 1:

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

[0057] Weigh 0.3mmol tetraaminophenylporphyrin and 1.2mmol cobalt acetate tetrahydrate in a 250ml round-bottom flask, and add 20mL methanol, 30mL N,N-dimethylformamide, and 90mL chloroform in turn. Place a condenser and a three-way exhaust joint on the top of the round-bottom flask. Use a double-row pipe to pass nitrogen-vacuum three times to keep the inside of the round-bottom flask in a closed nitrogen environment. Then place the reaction system in an oil bath heating device, set the temperature to 80°C, turn on magnetic stirring and condensation circulating water, and the reaction time is 24h. 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. The lower organic phase is centrifuged and washed once with methanol. Then dry it overnight in vacuum at 80°C to obtain the final product.

[0058] like Figure 1 In the infrared spectrum shown in the figure, TAPP-Co is located at 965cm -1 The NH vibration peak disappears, and the peak at 1000 cm -1 This result shows 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] Weigh 0.022mmol TAPP-Co and 0.044mmol 2,2'-bipyridine-5,5'-dicarboxaldehyde in a 15mL heat-resistant reaction bottle, add 0.5mL o-dichlorobenzene, 0.5mL n-butanol, 0.1mL 6M acetic acid, and ultrasonicate for 15min. Seal the reaction tube and place it in a 120℃ oil bath for three days under vacuum conditions for solvothermal reaction. After the reaction, centrifuge and wash three times with acetone, five times with tetrahydrofuran, and then dry overnight at 80℃ in vacuum to obtain a covalent organic framework with coordinated monometallic Co, which is recorded as CoN4-2,2'Bp-COF.

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

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

[0063] like Figure 2As shown in the figure, the coordination of the second metal Ni atom in the single metal covalent organic framework does not destroy its original crystallinity, and a sharp peak appears at around 2.9°, indicating that a high degree of crystallinity is still maintained. Figure 3 The nitrogen adsorption-desorption isotherms of the two COFs are shown in Figure 4 The infrared spectrum of CoN4-NiN2-COF proves the successful synthesis.

[0064] (4) Preparation of catalyst ink:

[0065] 1 mg of CoN4-NiN2-COF was dispersed into a mixed solution containing 0.9 mL of isopropanol, 0.1 mL of deionized water, and 0.02 mL of Nafion117 perfluorinated resin solution (Macklin-N831951), and ultrasonicated for 2 h to obtain a catalyst ink.

[0066] Embodiment 2:

[0067] Test the application of Example 1 as a catalyst in 2e-ORR: Take 10 μl of the catalyst ink prepared in Example 1 and coat it on the surface of the glassy carbon electrode (0.2475 cm -2 ) was prepared as the working electrode.

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

[0069] The rotating disk electrode was scanned from 1.1 V to 0.1 V vs. RHE at a scan rate of 10 mV / s at 1600 rpm. Figure 6 The LSV polarization curve of the catalyst in Example 1 is shown, which reflects the 2e-ORR catalytic performance of the catalyst. Figure 7 Shown by Figure 6 The 2e-selectivity and voltage correlation diagram of the catalyst was calculated, and it can be seen that the catalyst in Example 1 has excellent performance, and the overall hydrogen peroxide selectivity is greater than 90%, and can reach up to 95%.

[0070] Comparative Example 1:

[0071] (1) Weigh 0.022mmol TAPP-Co and 0.044mmol 2,2'-bipyridine-5,5'-dicarboxaldehyde into a 15mL heat-resistant reaction bottle, add 0.5mL mesitylene, 0.5mL dioxane, and 0.1mL 6M acetic acid, and ultrasonicate for 15min. Seal the reaction tube and place it in a 120℃ oil bath for solvent thermal reaction for three days. After the reaction, centrifuge and wash with acetone three times, tetrahydrofuran five times, and then vacuum dry at 80℃ overnight. A reddish brown powder is obtained. XRD characterization shows that the powder obtained by combining mesitylene and dioxane solvent has low crystallinity.

[0072] (2) Weigh 0.022mmol TAPP-Co and 0.044mmol 2,2'-bipyridine-5,5'-dicarboxaldehyde into a 15mL heat-resistant reaction bottle, add 0.25mL o-dichlorobenzene, 0.75mL benzaldehyde, and 0.1mL 6M acetic acid, and ultrasonicate for 15min. After three cycles of freezing-evacuation-thawing, the reaction tube is sealed and placed in a 120℃ oil bath for solvothermal reaction for three days. After the reaction, centrifuge and wash with acetone three times, tetrahydrofuran wash five times, and then vacuum dry at 80℃ overnight. A reddish brown powder is obtained. XRD characterization shows that the combination of o-dichlorobenzene and benzaldehyde solvents will not produce a crystalline covalent organic framework.

[0073] Comparative Example 2:

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

[0075] Weigh 30 mg CON4-2,2'-Bp-COF and disperse it in 20 mL methanol, and add 80 mg manganese acetate. Reflux reaction at 70 ° C in nitrogen atmosphere for 12 hours. After the reaction, wash with a large amount of methanol and deionized water, and vacuum dry at 80 ° C overnight to obtain CoN4-MnN2-COF. Disperse 1 mg CoN4-MnN2-COF in 0.9 mL isopropanol, 0.1 mL deionized water, and 0.02 mL Nafion mixed solution, ultrasonic for 2 hours, and obtain catalyst ink. The electrochemical performance of CoN4-MnN2-COF was tested using the same test method as in Example 2.

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

[0077] Weigh 30 mg of CoN4-2,2'-Bp-COF and disperse it in 20 mL of methanol, and add 80 mg of ferric acetate. Reflux reaction at 70 ° C in a nitrogen atmosphere for 12 hours. 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-COF. Disperse 1 mg of CoN4-FeN2-COF in a mixed solution of 0.9 mL of isopropanol, 0.1 mL of deionized water, and 0.02 mL of Nafion, and ultrasonicate for 2 hours to obtain the catalyst ink. The electrochemical performance of CoN4-FeN2-COF was tested using the same test method as in Example 2.

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

[0079] Weigh 30 mg CON4-2,2'-Bp-COF and disperse it in 20 mL methanol, and add 80 mg cobalt acetate. Reflux reaction at 70 ° C in nitrogen atmosphere for 12 hours. After the reaction, wash with a large amount of methanol and deionized water, and vacuum dry at 80 ° C overnight to obtain CoN4-CoN2-COF. Disperse 1 mg CoN4-CoN2-COF in 0.9 mL isopropanol, 0.1 mL deionized water, and 0.02 mL Nafion mixed solution, ultrasonic for 2 hours, and obtain catalyst ink. The electrochemical performance of CoN4-CoN2-COF was tested using the same test method as in Example 2.

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

[0081] Weigh 30 mg CoN4-2,2'-Bp-COF and disperse it in 20 mL methanol, and add 80 mg copper acetate. Reflux reaction at 70 ° C in a nitrogen atmosphere for 12 hours. 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-CuN2-COF. Disperse 1 mg CoN4-CuN2-COF in a mixed solution of 0.9 mL isopropanol, 0.1 mL deionized water, and 0.02 mL Nafion, and ultrasonicate for 2 hours to obtain catalyst ink. The electrochemical performance of CoN4-CuN2-COF was tested using the same test method as in Example 2.

[0082] Comparative Example 3:

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

[0084] Weigh 0.022mmol TAPP-Co and 0.044mmol 3,3'-bipyridine-6,6'-dicarboxaldehyde in a 15mL heat-resistant reaction bottle, add 0.5mL o-dichlorobenzene, 0.5mL n-butanol, 0.1mL 6M acetic acid, and ultrasonicate for 15min. After three cycles of freezing-evacuation-thawing, the reaction tube is sealed and placed in a 120℃ oil bath for solvothermal reaction for three days. After the reaction, centrifuge and wash three times with acetone, five times with tetrahydrofuran, and then vacuum dry at 80℃ overnight to obtain a covalent organic framework of coordinated monometallic Co, recorded as CoN4-3,3'-Bp-COF.

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

[0086] Weigh 30 mg CON4-3,3'-Bp-COF and disperse it in 20 mL methanol, and add 80 mg manganese acetate. Reflux reaction at 70 ° C in nitrogen atmosphere for 12 hours. 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 CoN4-(MnN2)2-COF in 0.9 mL isopropanol, 0.1 mL deionized water, and 0.02 mL Nafion mixed solution, ultrasonic for 2 hours, and obtain catalyst ink. The electrochemical performance of CoN4-(MnN2)2-COF was tested using the same test method as in Example 2.

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

[0088] Weigh 30 mg CoN4-3,3'-Bp-COF and disperse it in 20 mL methanol, and add 80 mg ferric acetate. Reflux reaction at 70 ° C in nitrogen atmosphere for 12 hours. 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 CON4-(FeN2)2-COF in 0.9 mL isopropanol, 0.1 mL deionized water, and 0.02 mL Nafion mixed solution, ultrasonic for 2 hours, and obtain catalyst ink. The electrochemical performance of CON4-(FeN2)2-COF was tested using the same test method as in Example 2.

[0089] (4) Synthesis and electrochemical testing of CON4-(CoN2)2-COF

[0090] Weigh 30 mg of CoN4-3,3'-Bp-COF and disperse it in 20 mL of methanol, and add 80 mg of cobalt acetate. Reflux reaction at 70 ° C in a nitrogen atmosphere for 12 hours. 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-(CoN2)2-COF. Disperse 1 mg of CoN4-(CoN2)2-COF in a mixed solution of 0.9 mL of isopropanol, 0.1 mL of deionized water, and 0.02 mL of Nafion, and ultrasonicate for 2 hours to obtain a catalyst ink. The electrochemical performance of CoN4-(CoN2)2-COF was tested using the same test method as in Example 2.

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

[0092] Weigh 30 mg CoN4-3,3'-Bp-COF and disperse it in 20 mL methanol, and add 80 mg nickel acetate. Reflux reaction at 70 ° C in a nitrogen atmosphere for 12 hours. 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-(NiN2)2-COF. Disperse 1 mg CON4-(NiN2)2-COF in a mixed solution of 0.9 mL isopropanol, 0.1 mL deionized water, and 0.02 mL Nafion, and ultrasonicate for 2 hours to obtain a catalyst ink. The electrochemical performance of CON4-(NiN2)2-COF was tested using the same test method as in Example 2.

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

[0094] Weigh 30 mg CON4-3,3'-Bp-COF and disperse it in 20 mL methanol, and add 80 mg copper acetate. Reflux reaction at 70 ° C in nitrogen atmosphere for 12 hours. 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-(CuN2)2-COF. Disperse 1 mg CoN4-(CuN2)2-COF in 0.9 mL isopropanol, 0.1 mL deionized water, and 0.02 mL Nafion mixed solution, ultrasonic for 2 hours, and obtain catalyst ink. The electrochemical performance of CoN4-(CuN2)2-COF was tested using the same test method as in Example 2.

[0095] Figure 1 When TAPP is coordinated with metal, 968cm -1 The NH absorption peak at 1000 cm -1 The MN absorption peak at is replaced, indicating that the metal replaces the H in the NH 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. It can be seen that the two COFs have a peak at about 2.9°, indicating high crystallinity.

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

[0098] Figure 4 The infrared spectra of CoN4-2,2-Bp-COF and CoN4-NiN2-COF in Example 1 are shown at 1621 cm -1 The C=N absorption peak at 1000 nm proves the formation of imine bond. Figure 1 and Figure 2 , indicating that the two COFs were successfully synthesized.

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

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

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

[0102] Figure 8 The XRD curves of powders of CoN4-2,2-Bp-COF prepared in different solvents (Example 1 (2), Control Example 1) show that different solvents have a great influence on the crystallinity of CoN4-2,2-Bp-COF. Through experimental exploration, it was found that the combination of n-butanol and o-dichlorobenzene solvent (1:1) can obtain CoN4-2,2-Bp-COF with the highest crystallinity.

[0103] Fig. 9The linear sweep voltammetric curves of 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] Fig.10 The linear sweep voltammetric curves of 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. It can be observed that the ring current related to the formation of hydrogen peroxide is Fig. 9 It is significantly lower than the other five catalysts.

[0105] Fig.11 and Fig.12 The hydrogen peroxide selectivity of each catalyst prepared by the present invention (Example 1, Comparative Example 2, Comparative Example 3) in the voltage range of 0.2 V to 0.6 V. 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 invention, the distance between the bimetallic catalysts has a certain influence on the ORR reaction path. Compared with CON4-(NiN2)2-COF, the shortening of the distance between the bimetallic catalysts leads to a sharp decrease in the hydrogen peroxide selectivity, and the reaction half-wave potential increases from the original 0.57V to 0.72V, and the reaction is dominated by four electrons (4e-ORR) instead of two electrons (2e-ORR). - ORR) is dominant. This trend also exists in other catalysts.

[0107] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A diatomic catalyst based on a covalent organic framework, characterized in that: The diatomic catalyst based on a covalent organic framework capable of adjusting the distance between diatoms and the types of diatoms 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 The distance between M1 and M2 in formula II The specific surface area of ​​the diatomic catalyst based on the covalent organic framework is 600 to 1000 m 2 / g, pore volume is 0.5~0.9cm 3 / g, and the pore size distribution is 1 to 2.5 nm.

2. The method for preparing a diatomic catalyst based on a covalent organic framework according to claim 1, characterized in that: It consists of the following steps: Step 1) heating and stirring tetraaminophenylporphyrin and a salt of metal M1 in a solution to react, to obtain tetraaminophenylporphyrin TAPP-M1 coordinated with a metal single atom M1; Step 2) dispersing TAPP-M1 and 2,2'-bipyridine-5,5'-dicarboxaldehyde or 3,3'-bipyridine-6,6'-dicarboxaldehyde in a solvent for solvothermal reaction to obtain a single-atom M1 covalent organic framework; Step 3) The single-atom M1 covalent organic framework and the salt of the metal M2 are uniformly mixed and dispersed in the solution, heated and stirred for reaction, and the covalent organic framework-based diatomic catalyst as shown in the above formula I or formula II is obtained after the reaction is completed.

3. The method for preparing a diatomic catalyst based on a covalent organic framework according to claim 2, characterized in that: In step 1), the molar ratio of tetraaminophenylporphyrin to the salt of metal M1 is 1-2:3-5.

4. The method for preparing a diatomic catalyst based on a covalent organic framework according to claim 2, characterized in that: In step 1), the solution is a mixed solution of methanol, N,N-dimethylformamide and chloroform, with a volume ratio of 1 to 2:3:

9.

5. The method for preparing a diatomic catalyst based on a covalent organic framework according to claim 1 or 2, characterized in that: In step 1), the reaction conditions are nitrogen or argon atmosphere, the reaction temperature is 70-90° C., and the reaction time is 12-48 h.

6. The method for preparing a diatomic catalyst based on a covalent organic framework according to claim 1 or 2, characterized in that: 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 for preparing a diatomic catalyst based on a covalent organic framework according to claim 1 or 2, characterized in that: In step 2), 3-6 M acetic acid is added as a reaction catalyst, and the solvent includes one of an o-dichlorobenzene / n-butanol mixed solvent, a dioxane / mesitylene mixed solvent, or an ethanol / o-dichlorobenzene mixed solvent.

8. The method for preparing a diatomic catalyst based on a covalent organic framework according to claim 1 or 2, characterized in that: In step 2), the reaction is carried out under vacuum conditions, the reaction temperature is 120-160° C., and the reaction time is 72-120 h.

9. The method for preparing a diatomic catalyst based on a covalent organic framework according to claim 1 or 2, characterized in that: In step 3), the reaction solution is selected from one of methanol, ethanol, ultrapure water, dichloromethane, and tetrahydrofuran; the reaction is carried out under an inert atmosphere, the reaction temperature is 60-90° C., and the reaction time is 6-15 h.

10. Use of the diatomic catalyst prepared by the preparation method according to claim 1 in preparing hydrogen peroxide by electrocatalytic two-electron oxygen reduction reaction, characterized in that: The diatomic catalyst is coated on the surface of a glassy carbon electrode as a working electrode, a platinum wire is a counter electrode, Ag / AgCI is a reference electrode, the electrolyte is 0.1M KOH, and oxygen is passed through to saturate the electrolyte with oxygen.

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