Thiophene macrocyclic three-dimensional covalent organic framework material, preparation method thereof and electrocatalyst

Abstract

The invention relates to the technical field of covalent organic framework materials, in particular to a thiophene macrocyclic three-dimensional covalent organic framework material, a preparation method thereof and an electrocatalyst. The thiophene macrocyclic three-dimensional covalent organic framework material is formed by bonding an aldehyde group of an aldehyde group-containing 6-linked cyclic thiophene oligomer and an amino group of a 4-linked amino monomer, the structural formula of the aldehyde group-containing 6-linked cyclic thiophene oligomer is shown in the specification: # imgabs 0 # 4-linked amino monomer is shown in the specification: # imgabs 1 #, p is 1 or 2, and R represents hydrogen or metal ions. The thiophene macrocyclic three-dimensional covalent organic framework material has efficient electrocatalytic oxygen reduction reaction activity and 2e <-> H2O2 production selectivity.

Description

Technical Field

[0001] The present invention relates to the technical field of covalent organic framework materials, and in particular, to a thiophene macrocycle-based three-dimensional covalent organic framework material, a preparation method thereof, and an electrocatalyst. Background Art

[0002] Hydrogen peroxide (H 2 O 2 ) is a multifunctional chemical substance with both oxidizing and reducing properties. The electrocatalytic oxygen reduction reaction (ORR) technology provides an efficient, controllable, and environmentally friendly approach for the generation of H 2 O 2 . Catalysts play a crucial role in the ORR process and can significantly affect the activity and selectivity of the reaction. So far, various catalysts have been developed. However, in order to obtain a high H 2 O 2 Faraday efficiency (FE), the current density of most catalysts is still limited to below 100 mA cm -2 , which seriously hinders their practical applications. Therefore, it is still crucial to develop and explore new catalysts with good activity and selectivity at industrially relevant current densities (100 mA cm -2 ).

[0003] Three-dimensional covalent organic frameworks (3D COFs) show unique advantages in this field due to their special structures and chemical properties. Specifically, 3D COFs usually have a large specific surface area and open pore structures, which can effectively enhance the exposure of catalytic active sites. The 3D connected structure is conducive to oxygen mass transfer, thereby increasing the contact area between the active sites and the reactants. In addition, the designability of COFs at the molecular level enables precise manipulation of specific catalytic active sites. So far, there is a lack of COFs with excellent 2e- electrocatalytic ORR performance at high current densities.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a thiophene macrocycle-based three-dimensional covalent organic framework material, a preparation method thereof, and an electrocatalyst. The thiophene macrocycle-based three-dimensional covalent organic framework material provided by the embodiments of the present invention has high electrocatalytic oxygen reduction reaction activity and 2e- H 2 O 2 production selectivity.

[0006] The present invention is implemented as follows:

[0007] In a first aspect, the present invention utilizes the unique structure and electrocatalytic ORR activity of the thiophene unit to construct a functional three-dimensional COF. Specifically, the present invention provides a three-dimensional covalent organic framework material based on a thiophene macrocycle, which is formed by bonding the aldehyde group of a 6-connected cyclic thiophene oligomer containing an aldehyde group and the amino group of a 4-connected amino monomer. The structural formula of the 6-connected cyclic thiophene oligomer containing an aldehyde group is as follows:

[0008] The structural formula of the 4-connected amino monomer is as follows: Wherein, p is 1 or 2, and R represents hydrogen or a metal ion.

[0009] In a second aspect, the present invention provides a method for preparing the three-dimensional covalent organic framework material based on a thiophene macrocycle described in the foregoing embodiment, including: mixing a 6-connected cyclic thiophene oligomer containing an aldehyde group and a 4-connected amino monomer to carry out a Schiff base reaction.

[0010] In a third aspect, an embodiment of the present invention provides an electrocatalyst, which includes the foregoing three-dimensional covalent organic framework material based on a thiophene macrocycle.

[0011] The present invention has the following beneficial effects: The three-dimensional covalent organic framework material based on a thiophene macrocycle provided by the embodiment of the present invention is connected by covalent bonds and has good stability. This material has a three-dimensional interconnected fully conjugated structure and rich electron-rich thiophene units, which is conducive to the exposure of active sites, promotes mass transfer and electron delocalization. It can be used as an electrocatalyst for the oxygen reduction reaction. This material has excellent 2e - catalytic reaction activity and selectivity, and can achieve a COF-based electrocatalyst for highly efficient electrocatalytic ORR at a high current density. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0013] Figure 1 Powder X-ray diffraction patterns of COF-NUST-67 and its organic monomers provided by the embodiments of the present invention;

[0014] Figure 2 Powder X-ray diffraction pattern of COF-NUST-67 provided by the embodiments of the present invention;

[0015] Figure 3 Fourier transform infrared spectra of COF-NUST-67 and its organic monomers provided by the embodiments of the present invention;

[0016] Figure 4 This is the thermogravimetric curve of COF-NUST-67 provided by the embodiments of the present invention;

[0017] Figure 5 This is the N 2 adsorption-desorption and pore size distribution diagram of COF-NUST-67 provided by the embodiments of the present invention;

[0018] Figure 6 This is the scanning electron micrograph of COF-NUST-67 provided by the embodiments of the present invention;

[0019] Figure 7 This is the CV curve of the COF-NUST-67 catalyst provided by the embodiments of the present invention under different atmospheres;

[0020] Figure 8 This is the LSV curve collected by RRDE of the COF-NUST-67 catalyst provided by the embodiments of the present invention, as well as the number of electron transfers and H 2 O 2 selectivity result diagram provided by the embodiments of the present invention;

[0021] Figure 9 This is the H 2 O 2 yield and Faraday efficiency FE of the material obtained by converting the COF-NUST-67 catalyst provided by the embodiments of the present invention through a standard flow electrolytic cell test at different current densities. Detailed implementation manners

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products available on the market.

[0023] In a first aspect, the present invention provides a thiophene macrocycle-based three-dimensional covalent organic framework material, which is formed by bonding the aldehyde group of an aldehyde group-containing 6-connected cyclic thiophene oligomer and the amino group of a 4-connected amino monomer.

[0024] Among them, the structural formula of the aldehyde group-containing 6-connected cyclic thiophene oligomer is as follows:

[0025] The structural formula of the 4-connected amino monomer is as follows:

[0026] Among them, p is 1 or 2, and R represents hydrogen or a metal ion. That is, the porphyrin ring can be connected to the amino group through a biphenyl, or the porphyrin ring can be connected to the amino group through a phenyl group. Secondly, the porphyrin ring can be a metal porphyrin ring chelated with a metal, or it can be an unchelated pure porphyrin ring. Specifically, R represents hydrogen, iron, copper or nickel.

[0027] Specifically, the thiophene macrocyclic-based three-dimensional covalent organic framework material can be a compound represented by the following structural formula:

[0028]

[0029]

[0030]

[0031]

[0032] The embodiments of the present invention are only illustrated by the compounds represented by the following structural formula.

[0033]

[0034] In a second aspect, the present invention provides a method for preparing the thiophene macrocyclic-based three-dimensional covalent organic framework material described in the foregoing embodiment, including: mixing a 6-connected cyclic thiophene oligomer containing an aldehyde group and a 4-connected amino monomer to carry out a Schiff base reaction.

[0035] Specifically, referring to the following synthetic route to synthesize a 6-connected cyclic thiophene oligomer containing an aldehyde group (hereinafter also abbreviated as CDHt-6CHO):

[0036]

[0037] Referring to the following synthetic route to synthesize a 4-connected amino monomer (hereinafter also abbreviated as) Por-NH 2 ;

[0038]

[0039] Specifically, the preparation steps of the thiophene macrocyclic-based three-dimensional covalent organic framework material include: mixing the 6-connected cyclic thiophene oligomer containing an aldehyde group, the 4-connected amino monomer, an organic solvent and a catalyst, and then performing freeze-thaw-degassing cyclically for multiple times, and then heating up for reaction. Specifically, the aldehyde group compound of the 6-connected cyclic thiophene oligomer and the 4-connected amino monomer are added to a glass tube in a certain proportion, an organic solvent is added, a catalyst is added, the glass tube is frozen in liquid nitrogen, evacuated and flame-sealed, heated to room temperature, and placed in an oven at 120-140 °C for heating reaction for 5-7 days to obtain the thiophene macrocyclic-based three-dimensional covalent organic framework material.

[0040] Among them, the molar ratio of the aldehyde group-containing 6-linked cyclic thiophene oligomer to the 4-linked amine monomer is 2:(2.9-3.1). The organic solvent is selected from at least one of alcohol solvents and halogenated phenyls; for example, the organic solvent is selected from at least one of o-dichlorobenzene and n-butanol; the volume ratio of the o-dichlorobenzene to the n-butanol is 1:(6-9). The catalyst is acetic acid, preferably an aqueous acetic acid solution, and the concentration of the aqueous acetic acid solution is 6-9M; the volume ratio of the catalyst to the organic solvent is 1:(8-12).

[0041] In a third aspect, an embodiment of the present invention provides an electrocatalyst, which includes the aforementioned thiophene macrocycle-based three-dimensional covalent organic framework material.

[0042] The features and properties of the present invention will be further described in detail below in conjunction with examples.

[0043] Example 1

[0044] An embodiment of the present invention provides a method for preparing a thiophene macrocycle-based three-dimensional covalent organic framework material, including:

[0045] S1. Synthesize an aldehyde group-containing 6-linked cyclic thiophene oligomer;

[0046] Synthesis is carried out with reference to the following synthetic route:

[0047]

[0048] , specifically,[[]]

[0049] Synthesis of Compound 1: Add 3-thiopheneboronic acid (1.27 g, 10 mmol), anhydrous potassium carbonate (4.14 g, 30 mmol) and tetrakis(triphenylphosphine)palladium (231 mg) to a 250 mL dry Schlenk flask. The reaction system is evacuated for 30 min, and Ar is replenished three times during this period. Under Ar protection, add 50 mL of anaerobic tetrahydrofuran, 15 mL of anaerobic water and 3-bromothiophene (1.55 g, 9.5 mmol). Then transfer the reaction system to an oil bath at 100 °C, stir and reflux the reaction in the dark for 24 h. After the reaction is completed, naturally cool to room temperature, remove the solvent under reduced pressure, add 100 mL of dichloromethane for extraction, wash the organic phase with water, dry it with anhydrous sodium sulfate, and remove the solvent under reduced pressure to obtain a crude product. Using petroleum ether as an eluent, separate and purify by silica gel column chromatography to obtain a white flaky solid compound 1, with a yield of 1.46 g and a yield of 93%.

[0050] Synthesis of Compound 2: Weigh Compound 1 (3.32 g, 20 mmol) and add it to a 250 mL dry Schlenk flask. Under Ar protection, add 80 mL of chloroform, N-bromosuccinimide (NBS, 7.15 g, 40.1 mmol), and 20 mL of glacial acetic acid (HOAc). Stir the reaction system in the dark at room temperature for 8 h. After the reaction is completed, pour the reaction solution into 100 mL of water, separate the organic phase, and wash the organic phase successively with water and saturated sodium bicarbonate solution. Add anhydrous sodium sulfate to dry the organic phase, remove the solvent under reduced pressure to obtain the crude product. Then, use petroleum ether as the eluent and separate and purify it by silica gel column chromatography to obtain Compound 2 in the form of a white powder, with a yield of 5.7 g and a yield rate of 88%.

[0051] Synthesis of Compound 3: Under Ar protection, add 15 mL of diethyl ether to a 100 mL dry Schlenk flask, and slowly add anhydrous and anaerobic diisopropylamine (3.3 mL, 23 mmol) dropwise thereto. Place the reaction flask in an ice-water bath and keep the system temperature at about 0 °C. Under Ar protection, slowly add n-BuLi (9.2 mL, 22 mmol) dropwise and stir the reaction in the ice-water bath for 30 min to prepare the lithium diisopropylamide (LDA) solution required for the reaction. Weigh Compound 2 (3.24 g, 10 mmol) into a 250 mL dry Schlenk flask, add 80 mL of diethyl ether under Ar protection, cool it to 0 °C, and then slowly add the prepared LDA dropwise and stir the reaction at 0 °C for 2 h. Then, transfer the reaction system to a cryostat, cool it to -78 °C, and slowly add an anhydrous and anaerobic trimethylchlorosilane solution (5.43 g, 50 mmol) dropwise under Ar protection, and keep stirring the reaction at -78 °C for 2 h. Let it warm up to room temperature naturally and stir overnight. After the reaction is completed, slowly add water dropwise to quench the reaction at 0 °C. Remove the solvent under reduced pressure, add dichloromethane to dilute the concentrated solution, and use a separatory funnel to separate the aqueous phase and the organic phase. Extract the aqueous phase with dichloromethane and combine the organic phases. Wash the organic phase successively with water and saturated sodium bicarbonate solution. Dry the organic phase with anhydrous sodium sulfate, filter, remove the solvent under reduced pressure to obtain the crude product, use petroleum ether as the eluent, and separate and purify it by silica gel column chromatography to obtain the white solid product Compound 3, with a yield of 3.93 g and a yield rate of 84%.

[0052] Synthesis of CDHt-6TMS: Weigh compound 3 (5.62 g, 12 mmol) and add it to a 250 mL dry Schlenk flask. Vacuum the reaction system for 30 min, and purge with Ar three times during this period. Add 120 mL of anhydrous and anaerobic diethyl ether under Ar protection and stir until dissolved. Cool the reaction system to -78 °C, and dropwise add n-BuLi (10.5 mL, 25.2 mmol) drop by drop under Ar protection. Stir and react at -78 °C for 2 h. Subsequently, add anhydrous copper chloride (4.84 g, 30 mmol) under Ar atmosphere and continue to stir and react at -78 °C for 2 h. Then, let the reaction system naturally warm to room temperature and stir overnight. After the reaction is completed, slowly add water dropwise to quench the reaction at low temperature. Remove the solvent under reduced pressure, add dichloromethane for extraction, separate the organic phase, and extract the aqueous phase with dichloromethane. Combine the organic phases and wash with water and saturated ammonium chloride solution. Dry the organic phase with anhydrous sodium sulfate, remove the solvent under reduced pressure to obtain the crude product, and use petroleum ether as the eluent to separate and purify by silica gel column chromatography to obtain a pale yellow oily product CDHt-6TMS with a yield of 1.26 g and a yield of 34%.

[0053] Synthesis of CDHt: Weigh compound CDHt-6TMS (2.0 g, 2.16 mmol) into a 100 mL round-bottom flask, add 60 mL of chloroform to dissolve the sample, and dropwise add trifluoroacetic acid (3.0 mL) under stirring. Stir and react at room temperature in the dark for 30 min, and monitor the reaction progress using a TLC plate. After the reaction is completed, add 30 mL of water to quench the reaction, separate the aqueous phase and the organic phase, extract the aqueous phase with dichloromethane, combine the organic phases, and wash successively with water and saturated sodium bicarbonate solution. Add anhydrous sodium sulfate to dry the organic phase and remove the solvent under reduced pressure. Use dichloromethane and methanol for rapid precipitation to obtain an off-white powder product CDHt with a yield of 0.99 g and a yield of 93%.

[0054] Synthesis of CDHt-6Br: Weigh compound CDHt (985 mg, 2.0 mmol) into a 100 mL round-bottom flask, add 50 mL of N,N-dimethylformamide, and add N-bromosuccinimide (3.58 g, 20 mmol) in batches under stirring. Then stir at room temperature overnight until the reaction system becomes a milky yellow emulsion, and end the reaction. Remove the solvent under reduced pressure, add 100 mL of methanol, ultrasonically disperse for 5 min, vacuum filter, collect the filter cake, and repeatedly wash the solid product with ethanol. The obtained solid is dried in vacuo at 60 °C to obtain an off-white powder product CDHt-6Br with a yield of 1.65 g and a yield of 85%.

[0055] Synthesis of CDHt-6CHO: In a 250 mL dry Schlenk flask, add compound CDHt-6Br (1.93 g, 2.0 mmol), 4-formylphenylboronic acid (2.40 g, 16.0 mmol), tetrakis(triphenylphosphine)palladium (416 mg, 0.36 mmol) and anhydrous potassium carbonate (4.97 g, 36 mmol). Evacuate the reaction system for 30 min, during which Ar is evacuated and replaced three times. Under Ar protection, add 100 mL of anaerobic tetrahydrofuran and 20 mL of anaerobic water, and stir until dissolved. Transfer the reaction system to an oil bath and stir the reaction in the dark at 100 °C for 48 h. After the reaction is completed, cool it to room temperature naturally. Remove the solvent under reduced pressure, add chloroform for extraction, separate the aqueous phase and the organic phase, extract the aqueous phase with chloroform, combine the organic phases, and wash with water. Add anhydrous sodium sulfate to dry the organic phase and remove the solvent under reduced pressure. Use ethyl acetate and dichloromethane as eluents, and separate and purify by silica gel column chromatography to obtain a bright yellow solid product CDHt-6CHO with a yield of 1.46 g and a yield of 66%.

[0056] S2. Synthesis of the 4-linked amino monomer Por-NH 2 ;

[0057] Synthesize the 4-linked amino monomer Por-NH with reference to the following synthetic route 2 :

[0058] Specifically,

[0059] Synthesis of Por-Br: Weigh 4-bromobenzaldehyde (3.7 g, 20 mmol) and add it to a 250 mL dry two-necked flask. Add 150 mL of propionic acid and heat to reflux. Under reflux, add pyrrole (1.34 g, 20 mmol). Keep the reaction system stirring under reflux for 3 h. After the reaction is completed, cool it to room temperature naturally. Filter under vacuum, separate the solid product, wash the solid repeatedly with methanol, and dry it under vacuum at 60 °C to obtain a purple product Por-Br with a yield of 1.23 g and a yield of 26%.

[0060] Por-NH 2Synthesis: Weigh the compound Por-Br (1.21g, 1.3mmol), 4-aminophenylboronic acid pinacol ester (1.71g, 7.8mmol), anhydrous potassium carbonate (2.15g, 15.6mmol) and tetrakis(triphenylphosphine) palladium (277mg, 0.24mmol) and add them to a 250mL dry Schlenk bottle. The reaction system was evacuated for 30min, and Ar was added 3 times during the period. Under Ar protection, 60mL of oxygen-free tetrahydrofuran and 10mL of oxygen-free water were added to the reaction bottle, and the reaction was stirred at 100℃ in the dark for 48h. After the reaction was completed, it was naturally cooled to room temperature, the organic solvent was removed under reduced pressure, and dichloromethane was added for extraction. The organic phase and the aqueous phase were separated, the aqueous phase was extracted with dichloromethane, and the organic phase was combined. The organic phase was washed with water. The organic phase was dried over anhydrous sodium sulfate, and the solvent was removed under reduced pressure to obtain a crude product. The crude product was washed with methanol and water several times, dried, and purified by silica gel column chromatography using dichloromethane as the eluent to obtain a dark purple solid product Por-NH 2 The yield was 0.91 g and the yield was 71%.

[0061] S3. Synthesize thiophene macrocyclic three-dimensional covalent organic framework materials; synthesize according to the following synthesis route:

[0062]

[0063]

[0064] Specifically,

[0065] CDHt-6CHO (22.3 mg, 0.02 mmol) and Por-NH2 (29.4 mg, 0.03 mmol) were added to a pressure-resistant ampoule in sequence, and 3.6 mL of o-dichlorobenzene) and 0.4 mL of n-butanol were added, and the mixture was mixed evenly by ultrasonication for 5 min. 0.4 mL of 9 MHOAc solution was added as a catalyst. Liquid nitrogen was used to quickly freeze the mixture in the ampoule, and vacuum was applied for 3 min. The mixture was degassed by freezing-thawing for a total of three times, and then the tube mouth was sealed with a flame gun. After naturally rising to room temperature, the ampoule was placed in a 120 ° C oven for 6 days. The reaction bottle was taken out, cooled naturally to room temperature, the solid was separated by filtration, and then the solid powder was subjected to Soxhlet extraction for 24 h with N, N-dimethylformamide to remove unreacted monomers or catalyst residues. Finally, the powder sample was soaked and filtered with water, methanol and acetone in turn, and then dried in a vacuum drying oven at 80°C for 24 hours to obtain a dark brown solid powder thiophene macrocyclic three-dimensional covalent organic framework material (abbreviated as COF-NUST-67) with a yield of 44 mg and a yield of 89%.

[0066] Characterization

[0067] The thiophene macrocycle-based three-dimensional covalent organic framework material prepared in Example 1 was characterized, and the results are shown in Figures 1-6 . Among them, Figure 1 is the powder X-ray diffraction pattern of COF-NUST-67 and its organic monomers provided in the examples of the present invention. From Figure 1 , it can be seen that the thiophene macrocycle-based three-dimensional covalent organic framework material shows diffraction peaks different from those of the monomers, indicating that a new type of three-dimensional organic framework material has been successfully synthesized through the examples of the present invention.

[0068] Figure 2 is the powder X-ray diffraction pattern of COF-NUST-67 provided in the examples of the present invention. From Figure 2 , it can be seen that by comparing the experimental curve with the X-ray diffraction pattern obtained by simulated refinement, it is determined that the new three-dimensional organic framework material provided by the examples of the present invention has an stp topological structure, and the unit cell parameters are: α = 90°, β = 89°, γ = 153°, and the diffraction peaks at 3.73°, 4.08° and 8.16° correspond to the (010), (100) and (021) Bragg crystal planes respectively.

[0069] Figure 3 is the Fourier transform infrared spectrum of COF-NUST-67 and its organic monomers provided in the examples of the present invention. From Figure 3 , it can be seen that COF-NUST-67 shows a stretching vibration peak of C=N near 1624 cm -1 , indicating that the organic monomers have successfully reacted to form C=N.

[0070] Figure 4 is the thermogravimetric curve of COF-NUST-67 provided in the examples of the present invention. According to Figure 4 , it can be seen that the thiophene macrocycle-based three-dimensional covalent organic framework material does not show obvious weight loss before 450 °C, indicating excellent thermal stability.

[0071] Figure 5 is the N 2 adsorption-desorption and pore size distribution diagram of COF-NUST-67 provided in the examples of the present invention. According to Figure 5 , it can be seen that the BET specific surface area of COF-NUST-67 reaches 2769 m 2 g -1 , and the pore size is microporous, distributed around 1.80 nm.

[0072] Figure 6 is the scanning electron microscope image of COF-NUST-67 provided in the examples of the present invention. According to Figure 6 , it can be seen that COF-NUST-67 has a lamellar morphology.

[0073] Electrocatalytic Oxidation-Reduction Performance Test

[0074] (1) Rotating Ring-Disk Electrode (RRDE) Test of Thiophene Macrocycle-Based Three-Dimensional Covalent Organic Framework Material as an Electrocatalyst: The electrochemical test of RRDE was carried out using a four-electrode system connected to a CHI 760E electrochemical workstation. The catalyst loading used in the experiment was 5 mg mL -1 . To prepare the working electrode, 5 mg of the thiophene macrocycle-based three-dimensional covalent organic framework material and 1 mg of acetylene black were weighed, and 750 μL of isopropanol, 210 μL of deionized water, and 40 μL of Nafion solution were added. After ultrasonic treatment for 1 h, a uniformly mixed catalyst ink was obtained. Then, 10 μL of the ink was dropped on the surface of the RRDE and dried naturally under ambient conditions. The disk electrode was used as the working electrode, the ring electrode as the second working electrode, the carbon rod as the counter electrode, and the Ag / AgCl electrode (3M KCl) as the reference electrode. The electrolyte used in this device was 0.5 M K 2 SO 4 . The test environment included two different gas environments of saturated Ar and O 2 . The scanning rate of cyclic voltammetry (CV) was 10 mV s -1 . The scanning rate of linear sweep voltammetry (LSV) was 5 mV s -1 . The electrocatalytic activity of the thiophene macrocycle-based three-dimensional covalent organic framework material was obtained from the CV curve, and the average number of electron transfers (n) and H 2 O 2 selectivity of the electrocatalysis of the thiophene macrocycle-based three-dimensional covalent organic framework material were obtained from the LSV curve.

[0075] (2) Standard Flow Cell Electrochemical Performance Test of Thiophene Macrocycle-Based Three-Dimensional Covalent Organic Framework Material as an Electrocatalyst: The working area of the working electrode used was 1 cm 2 , the loading of the thiophene macrocycle-based three-dimensional covalent organic framework material was 2.5 mg cm -2 . The counter electrode used was a titanium anode coated with iridium oxide (DSA), the reference electrode was Ag / AgCl (3M KCl), the electrolyte was 50 mL of 0.5 M K 2 SO 4 , and the diaphragm was Nafion 115. The flow rate of the electrolyte was 40 mL·min -1 , and the gas flow rate was 40 mL·min -1 . The scanning rate of LSV was 5 mV s -1 .

[0076] The results are shown in Figures 7-9 . Among them, Figure 7 is the CV curve of the COF-NUST-67 catalyst provided in the embodiment of the present invention under different atmospheres. According toFigure 7 It can be seen that under Ar conditions, no oxygen reduction peak was observed in the CV curve of COF-NUST-67. However, under O 2 saturated electrolyte test conditions, an obvious oxygen reduction peak appeared at 0.23 V (vs. RHE) in the CV curve of COF-NUST-67, indicating that COF-NUST-67 has ORR activity.

[0077] Figure 8 The LSV curve collected by RRDE and the electron transfer number and H 2 O 2 selectivity calculated from the LSV for the COF-NUST-67 catalyst provided in the examples of the present invention. According to Figure 8 it can be seen that the average electron transfer number of the thiophene macrocycle-based three-dimensional covalent organic framework material is 2.1, which is more inclined to a 2e - transfer reaction and has excellent H 2 O 2 selectivity, basically higher than 95%.

[0078] Figure 9 The H 2 O 2 yield and Faraday efficiency FE of the material converted from the standard flow electrolytic cell test for the COF-NUST-67 catalyst provided in the examples of the present invention. According to Figure 9 it can be seen that COF-NUST-67 maintains an FE of more than 92% in the current density range of 50 to 350 mA cm -2 . At 250 mA cm -2 , the FE of COF-NUST-67 reaches 97%, and the H 2 O 2 yield is 155.4 mg cm -2 h -1 (1828 mmol g -1 h -1 ). When the current density reaches 400 mA cm -2 , COF-NUST-67 still maintains good electrochemical performance, and the H 2 O 2 yield is 223.5 mg cm -2 h -1 , and the FE value of H 2 O 2 is 88%. This excellent electrochemical activity and selectivity at high current densities are superior to most reported 2e - ORR electrocatalysts.

[0079] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A thiophene macrocyclic three-dimensional covalent organic framework material, characterized in that: It is formed by bonding the aldehyde group of a 6-connected cyclic thiophene oligomer containing an aldehyde group and the amine group of a 4-connected amine monomer. The structural formula of the 6-connected cyclic thiophene oligomer containing an aldehyde group is shown below: The structural formula of the 4-linked amino monomer is as follows: Wherein, p is 1 or 2, and R represents hydrogen or a metal ion.

2. The thiophene macrocyclic three-dimensional covalent organic framework material according to claim 1, characterized in that: R represents hydrogen, iron, copper or nickel.

3. The thiophene macrocyclic three-dimensional covalent organic framework material according to claim 1, characterized in that: It is selected from the compounds represented by the following structural formula:

4. A method for preparing the thiophene macrocyclic three-dimensional covalent organic framework material according to claim 1, characterized in that: include: A 6-linked cyclic thiophene oligomer containing an aldehyde group and a 4-linked amine monomer are mixed to carry out a schiff base reaction.

5. The preparation method according to claim 4, characterized in that: include: The 6-linked cyclic thiophene oligomer containing aldehyde groups, the 4-linked amine monomer, an organic solvent and a catalyst are mixed, and then freeze-thaw-degassing is performed in a cycle for multiple times, and then the temperature is raised to react.

6. The preparation method according to claim 5, characterized in that: include: The 6-linked cyclic thiophene oligomer containing aldehyde groups, the 4-linked amine monomer, an organic solvent and a catalyst are mixed, and then freeze-thaw-degassing is performed in a cycle for multiple times, and then the temperature is raised to room temperature, and then reacted at 120-140° C. for 5-7 days.

7. The preparation method according to claim 4, characterized in that: The molar ratio of the 6-linked cyclic thiophene oligomer containing aldehyde groups to the 4-linked amine monomer is 2:(2.9-3.1).

8. The preparation method according to claim 5, characterized in that: The organic solvent is selected from at least one of an alcohol solvent and a halogen phenyl; Preferably, the organic solvent is selected from at least one of o-dichlorobenzene and n-butanol; Preferably, the volume ratio of the o-dichlorobenzene to the n-butanol is 1:(6-9).

9. The preparation method according to claim 5, characterized in that: The catalyst is acetic acid, preferably an acetic acid aqueous solution, and the concentration of the acetic acid aqueous solution is 6-9M; Preferably, the volume ratio of the catalyst to the organic solvent is 1:(8-12).

10. An electrocatalyst, characterized in that It comprises the thiophene macrocyclic three-dimensional covalent organic framework material according to claim 1.

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