Preparation method and application of beta-functionalized cobalt phthalocyanine axial connection carbon nanotube electrocatalyst

Abstract

The invention discloses a preparation method and application of a beta-functionalized cobalt phthalocyanine axial connection carbon nanotube electrocatalyst, and relates to a preparation method and application of an electrocatalyst. The invention aims to solve the problem of low selectivity of glycolaldehyde synthesis in the prior art, the CoPcX-CNT electrocatalyst is prepared by adopting a method of combining organic synthesis and diazo treatment, and CoPcCN-CNT containing cyano-functionalized cobalt phthalocyanine has optimal H2O2 selectivity. The Faraday efficiency of 95.7% and the H2O2 yield of 20320 mmol.g <-1 >. H <-1 > can be achieved in a flowing electrolytic tank under the industrial current density of 300 mA. Cm <-2 >. And finally, adjusting the permeability of H2O2 by using an ion exchange membrane, and finding that the AEM system with proper permeability of H2O2 has the highest glycolaldehyde selectivity (63.5%). The method is applied to the field of H2O2 in-situ production and efficient utilization.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of a beta functionalized phthalocyanine cobalt axially connected carbon nanotube electrocatalyst and application thereof. BACKGROUND

[0002] Glycolaldehyde (GD) is the smallest natural aldehyde sugar, widely used as a basic molecular building block and intermediate for the manufacture of perfumes, dyes and pharmaceuticals. The synthesis of GD mainly relies on the selective oxidation of ethylene glycol (EG) under harsh conditions, such as high reaction temperature or the use of inorganic bases. One strategy to address the above issues is to develop an electrochemical process to produce GD at ambient temperature and pressure by renewable electricity. Lum et al. synthesized a gold-doped palladium catalyst as an anode material, which oxidized ethylene to EG by a direct one-step method, in which GD was also produced with low selectivity (5-13%). Therefore, it is crucial to enhance the oxidation process of EG to GD by introducing a non-toxic, low-cost strong oxidant. Hydrogen peroxide (H2O2) is an environmentally friendly strong oxidant, which has an energy density (3.0 MJ·L-1 at 60% solubility) comparable to that of compressed H2 (2.8 MJ·L-1 at 40 MPa). Therefore, H2O2 can be a promising environmentally friendly energy carrier to promote GD synthesis. Currently, the industrial production of H2O2 mainly adopts the energy-intensive and environmentally unfriendly anthraquinone oxidation process. At the same time, there are still safety hazards in the transportation and storage process of H2O2. The electrochemical synthesis of H2O2 by 2e-ORR pathway has the advantages of environmental protection and energy saving, and is considered as a promising alternative process. Thermodynamically, the 4e-ORR pathway competing with 2e-ORR is more favorable for the generation of H2O. Therefore, it is crucial to develop electrocatalysts with high activity and selectivity for the electrochemical synthesis of H2O2. -1 -1 - - - SUMMARY

[0003] The present application aims to solve the problem of low selectivity in the synthesis of glycolaldehyde, and provides a preparation method of a beta functionalized phthalocyanine cobalt axially connected carbon nanotube electrocatalyst and application thereof.

[0004] The present application relates to a preparation method of a beta functionalized phthalocyanine cobalt axially connected carbon nanotube electrocatalyst, which is carried out according to the following steps:

[0005] I. Under the condition of ice water bath, NaNO2, 4-aminopyridine and purified carbon nanotubes are mixed to obtain pyridine functionalized carbon nanotubes, which are then added into N,N-dimethylformamide to obtain solution A;

[0006] ​​​​​II. Put 1,2,4,5-tetracyanobenzene, CoCl2·6H2O, sulfolane and 1,8-diazabicyclo[5.4.0]undec-7-ene into a reaction kettle for mixing and heating to obtain CoPcCN; then add into N,N-dimethylformamide to obtain solution B;

[0007] III. Mix solution A and solution B and then ultrasonic treatment to obtain a mixed solution; then freeze-drying to obtain CoPcCN-CNT electrocatalyst.

[0008] CoPcH-CNT is prepared by axially connecting pyridine grafted CNT with CoPc (cobalt phthalocyanine), wherein the Co-N coordination configuration is changed into Co-N5 coordination, which is beneficial to enrich the electron of Co active center, thereby enhancing the adsorption strength between Co atom and O2 molecule. In order to further adjust the H2O2 selectivity on the basis of high ORR activity of CoPcH-CNT catalyst, a new solution for accurately adjusting electronic properties is provided. Previous studies have confirmed that the beta substituent with different electronic properties can further adjust the charge density of Co active center, which is beneficial to the high selective electro-synthesis of H2O2. Therefore, electron-donating methoxy (OMe), electron-withdrawing amino (NH2) and cyano (CN) are used to replace the H atom at the beta position of CoPc(H). Subsequently, the obtained beta functionalized cobalt phthalocyanine (CoPcX, X=OMe, NH2, CN) is axially connected with pyridine grafted CNT to prepare CoPcX-CNT electrocatalyst.

[0009] The CoPcX-CNT electrocatalyst (X=OMe, NH2, CN, H) is prepared by the method combining organic synthesis with diazo treatment in the application, the beta functionalized CoPcX is axially connected to the surface of CNT through pyridine group, under the synergistic effect of the electron conduction ability of pyridine group and the electron-withdrawing property of cyano (CN), the CN functionalized CoPcCN-CNT shows the best ORR activity-H2O2 selectivity combination. The CoPcCN-CNT cathode and Pt / C anode are used for 2e - -ORR and ethylene oxidation reaction, the H2O2 permeability is adjusted by changing the ion exchange membrane, thereby improving the selectivity and economic benefit of ethylene oxidation synthesis of glycolaldehyde. The catalyst with target activity and selectivity in the application is helpful to the practical application of H2O2 electro-synthesis technology in high-value product synthesis.

[0010] The beneficial effects of the application are as follows:

[0011] The CoPcCN-CNT cathode and Pt / C anode are used in the application to carry out 2e -- ORR and ethylene oxidation reaction, in-situ production of H2O2 and synthesis of glycolaldehyde in alkaline electrolyte. Three substituents with different electron transfer properties were introduced into the β position of cobalt phthalocyanine (CoPc) molecules by organic synthesis method, replacing the H atoms on it, to prepare β-functionalized cobalt phthalocyanine (CoPcX, X = OMe, NH2, CN). Subsequently, pyridine groups were introduced into carbon nanotubes (CNT) by diazonium treatment method, and CoPcX molecules were connected by axial coordination. Among them, CoPcCN-CNT containing cyanide functionalized cobalt phthalocyanine has the best H2O2 selectivity (95.2%). In a flow electrolysis cell under an industrial current density of 300 mA·cm-2, a Faraday efficiency of 95.7% and an H2O2 yield of 20320 mmol·g-1·h-1 can be achieved. Finally, ion exchange membranes are used to adjust the H2O2 permeability, and it is found that the AEM system with appropriate H2O2 permeability has the highest glycolaldehyde selectivity (63.5%). The present application provides a new perspective for the preparation of cobalt phthalocyanine loaded carbon nanotube electrocatalyst and its application in the field of glycolaldehyde synthesis. -2 -1 -1 BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 TEM images of pur-CNT and PF-CNT catalysts;

[0013] Figure 2 N1s XPS spectrum of PF-CNT catalyst;

[0014] Figure 3 UV-vis spectrum of CoPcX catalysts;

[0015] Figure 4 XRD spectrum of CNT, CoPc and CoPcX-CNT catalysts;

[0016] Figure 5 FTIR spectrum of CNT, CoPc and CoPcX-CNT catalysts;

[0017] Figure 6 Co 2p XPS spectrum of CoPc and CoPcX-CNT catalysts;

[0018] Figure 7 Structural characterization of CoPcCN-CNT catalyst; aberration-corrected HAADF-STEM image (a); EDX image (b); aberration-corrected atomic resolution HAADF-STEM image (c);

[0019] Figure 8 ​​​Structure characterization of CoPcOMe-CNT catalyst; aberration-corrected HAADF-STEM image (a); EDX image (b); aberration-corrected atomic resolution HAADF-STEM image (c);

[0020] Figure 9 Structure characterization of CoPcNH2-CNT catalyst; aberration-corrected HAADF-STEM image (a); EDX image (b); aberration-corrected atomic resolution HAADF-STEM image (c);

[0021] Figure 10 Structure characterization of CoPcH-CNT catalyst; aberration-corrected HAADF-STEM image (a); EDX image (b); aberration-corrected atomic resolution HAADF-STEM image (c);

[0022] Figure 11 Normalized Co K-edge XANES spectra of CoPcX-CNT (X = CN, OMe, NH2, H) and CoPcCN / CNT;

[0023] Figure 12 EXAFS spectra of CoPcCN-CNT, CoPcCN / CNT and reference Co foil, CoO, Co2O3 and CoPc;

[0024] Figure 13 FT-EXAFS spectra fitting curves of CoPcCN-CNT, CoPcCN / CNT catalyst;

[0025] Figure 14 N1s XPS spectra of CoPcCN-CNT, CoPcCN / CNT catalyst;

[0026] Figure 15 Fitting EXAFS spectra of CoPcOMe-CNT;

[0027] Figure 16 Fitting EXAFS spectra of CoPcNH2-CNT;

[0028] Figure 17 Fitting EXAFS spectra of CoPcH-CNT;

[0029] Figure 18 Comparison of ORR activity (lower part) and H2O2 current density (upper part) of CoPcX-CNT catalysts under alkaline electrolyte (X = CN, OMe, NH2, H);

[0030] Figure 19Faradaic efficiency of CoPcX-CNT catalysts (X = CN, OMe, NH2, H) for H2O2 in alkaline electrolyte;

[0031] Figure 20 Selectivity of CoPcX-CNT catalysts (X = CN, OMe, NH2, H) for H2O2 in alkaline electrolyte;

[0032] Figure 21 CV curves of CoPc, CNT and CoPcX-CNT catalysts (X = CN, OMe, NH2, H);

[0033] Figure 22 Tafel slopes of CoPcX-CNT catalysts (X = CN, OMe, NH2, H) for ORR;

[0034] Figure 23 LSV curves of CoPc, CNT and CoPcX-CNT catalysts (X = CN, OMe, NH2, H);

[0035] Figure 24 Current density of CoPcX-CNT catalysts (X = CN, OMe, NH2, H) at 0.5 vs. RHE;

[0036] Figure 25 H2O2 production rate, corresponding faradaic efficiency and TOF values of CoPcCN-CNT catalyst at different current densities;

[0037] Figure 26 Faradaic efficiency of CoPc, CNT and CoPcX-CNT catalysts (X = CN, OMe, NH2, H) for H2O2 at different current densities;

[0038] Figure 27 TOF values of CoPc, CNT and CoPcX-CNT catalysts (X = CN, OMe, NH2, H) at different current densities;

[0039] Figure 28 Comparison of H2O2 production rate and faradaic efficiency of CoPcX-CNT catalysts (X = CN, OMe, NH2, H) with previous publications;

[0040] Figure 29 H2O2 electrosynthesis of CoPcX-CNT catalysts (X = CN, OMe, NH2, H) in a two-electrode flow cell;

[0041] Figure 30 Stability test of CoPcCN-CNT catalyst in a two-electrode flow cell;

[0042] Figure 31 To predict the working energy and current of the electrolyzer by the intersection of the LSV curves of Pt / C and CoPcCN-CNT;

[0043] Figure 32 For ethylene oxidation stability test;

[0044] Figure 33 For 13 Electrochemical oxidation products of C-labeled ethylene 13 CH2 13 CH2) in the presence of CoPcCN-CNT 1 HNMR spectra;

[0045] Figure 34 For selectivity of ethylene oxidation products and H2O2 in a flow cell system;

[0046] Figure 35 For the synergistic mechanism of ethylene oxidation and H2O2 production;

[0047] Figure 36 For H2O2 production in the electrolyte after reaction;

[0048] Figure 37 For the effect of H2O2 permeability on the selectivity of ethylene oxidation products;

[0049] Figure 38 For technical and economic analysis of H2O2 electrosynthesis;

[0050] Figure 39 For technical and economic analysis of ORR electrosynthesis of H2O2 under different conditions;

[0051] Figure 40 For energy cost of a two-electrode flow cell;

[0052] Figure 41 For a series of representative results based on H2O2 permeability. DETAILED DESCRIPTION

[0053] The technical solutions of the present application are not limited to the specific embodiments listed below, but also include any combination of the specific embodiments.

[0054] Embodiment one: a method for preparing a β-functionalized cobalt phthalocyanine axially connected carbon nanotube electrocatalyst according to the present application:

[0055] I. Under the condition of an ice water bath, mix NaNO2, 4-aminopyridine and purified carbon nanotubes to obtain pyridine-functionalized carbon nanotubes, and then add them into N,N-dimethylformamide to obtain solution A;

[0056] II. Put 1,2,4,5-tetracyanobenzene, CoCl2·6H2O, sulfolane and 1,8-diazabicyclo[5.4.0]undec-7-ene into a reaction kettle and heat to obtain CoPcCN; then add into N,N-dimethylformamide to obtain solution B;

[0057] III. Mix solution A and solution B and then ultrasonic treatment to obtain a mixed solution; then freeze-drying to obtain CoPcCN-CNT electrocatalyst.

[0058] In the embodiment, the preparation method of purifying carbon nanotubes is as follows: purifying CNT at 400℃ in air, and then acid washing in 5M HCl at 80℃ for 12 hours. Then annealing treatment in argon environment at 800℃ to remove the residual oxygen-containing functional groups and adsorbed gas or solvent on the surface of CNT to obtain purified CNT (pur-CNT).

[0059] Specific embodiment two: different from the specific embodiment one, the mass ratio of NaNO2, 4-aminopyridine and purified carbon nanotubes in step one is 2.58-2.68g: 2.42-2.52g: 33.2-34.7mg. The difference is that the other aspects are the same as the specific embodiment one.

[0060] Specific embodiment three: different from the specific embodiment one or two, the mass-volume ratio of NaNO2 and N,N-dimethylformamide in step one is 2.58-2.68g: 10-30mL. The other aspects are the same as the specific embodiment one or two.

[0061] Specific embodiment four: different from one of the specific embodiments one to three, the temperature of the ice bath in step one is 0℃. The other aspects are the same as one of the specific embodiments one to three.

[0062] Specific embodiment five: different from one of the specific embodiments one to four, the mass-volume ratio of 1,2,4,5-tetracyanobenzene and N,N-dimethylformamide in step two is 1.5-4.5g: 10-30mL. The other aspects are the same as one of the specific embodiments one to four.

[0063] Specific embodiment six: different from one of the specific embodiments one to five, the mass-volume ratio of CoCl2·6H2O and N,N-dimethylformamide in step two is 1.0-1.4g: 10-30mL. The other aspects are the same as one of the specific embodiments one to five.

[0064] Specific embodiment 7: This embodiment differs from Specific embodiments 1 to 6 in that the volume ratio of sulfolane, 1,8-diazabicyclo[5.4.0]undec-7-ene, and N,N-dimethylformamide in step 2 is 30-50 mL:0.1-0.3 mL:10-30 mL. Other processes are the same as Specific embodiments 1 to 6.

[0065] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that the reactor is heated to 120-160° C. and maintained at this temperature for 6-8 hours in step 2. The rest is the same as specific embodiments 1 to 7.

[0066] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that solution A and solution B are mixed and ultrasonically treated for 20 to 40 minutes. Other aspects are the same as specific embodiments 1 to 8.

[0067] Specific embodiment 10: This embodiment is the application of β-functionalized cobalt phthalocyanine axially connected carbon nanotube electrocatalyst as the cathode catalytic material of the electrolytic cell.

[0068] Specific embodiment 11: This embodiment differs from specific embodiment 10 in that β-functionalized cobalt phthalocyanine axially connected carbon nanotube electrocatalyst is used as the cathode catalytic material of the electrolytic cell to in-situ produce H2O2 and promote the synthesis of glycolaldehyde at the anode. Other aspects are the same as specific embodiment 10.

[0069] Specific embodiment 12: The difference between this embodiment and specific embodiment 11 is that the method of using CoPcCN-CNT electrocatalyst as cathode catalytic material to prepare CoPcCN-CNT cathode is as follows: CoPcCN-CNT electrocatalyst powder is dispersed in 0.25wt.% Nafion solution to make the catalyst concentration reach 3.5mg·mL -1 After ultrasonic treatment for 60 minutes, the CoPcCN-CNT electrocatalyst ink was heated to 0.5 mg·cm -2 The mass load is per unit area of ​​1.5 x 1.5 cm 2 The CoPcCN-CNT cathode is obtained on the gas diffusion layer outside the cathode plate of the electrolytic cell. Other aspects are the same as those of the eleventh embodiment.

[0070] The following examples are used to verify the beneficial effects of the present invention:

[0071] Example 1: A method for preparing a β-functionalized cobalt phthalocyanine axially connected carbon nanotube electrocatalyst is carried out according to the following steps:

[0072] I. Synthesis of CN-functionalized phthalocyanine cobalt axial coordination carbon nanotube (CoPcCN-CNT): pyridine-functionalized carbon nanotube (PF-CNT) was prepared by mixing 2.63 g of NaNO2, 2.47 g of 4-aminopyridine and 34.7 mg of purified carbon nanotube (pur-CNT) in an ice water bath at 0°C, and then 30 mg of PF-CNT was dissolved in 20 mL of N,N-dimethylformamide to obtain solution A;

[0073] II. CoPcCN was prepared by adding 3.0 g of 1,2,4,5-tetracyano benzene, 1.2 g of CoCl2·6H2O, 40 mL of sulfolane and 0.2 mL of 1,8-diazabicyclo[5.4.0]undec-7-ene into a round-bottom flask with a stirring rod, and then the mixed solution was heated to 140°C in a reaction kettle for 7 hours, and then 3.0 mg of CoPcCN was dissolved in 20 mL of N,N-dimethylformamide to obtain solution B, and solution A and solution B were mixed and ultrasonically treated for 30 minutes. Finally, the mixed solution was freeze-dried to obtain the CoPcCN-CNT electrocatalyst.

[0074] The method for preparing the CoPcCN-CNT cathode by using the CoPcCN-CNT electrocatalyst as the cathode catalytic material is as follows: CoPcCN-CNT electrocatalyst powder was dispersed in a 0.25 wt.% Nafion solution to make the catalyst concentration reach 3.5 mg·mL-1, and then the solution was ultrasonically treated for 60 minutes to obtain a CoPcCN-CNT electrocatalyst ink. -1 The CoPcCN-CNT electrocatalyst ink was loaded on the gas diffusion layer outside the cathode plate of the electrolytic cell at a mass loading of 0.5 mg·cm-2 per unit area of 1.5×1.5 cm2, and a CoPcCN-CNT cathode was obtained. -2 2 The method for preparing the CoPcCN-CNT cathode by using the CoPcCN-CNT electrocatalyst as the cathode catalytic material is as follows: CoPcCN-CNT electrocatalyst powder was dispersed in a 0.25 wt.% Nafion solution to make the catalyst concentration reach 3.5 mg·mL-1, and then the solution was ultrasonically treated for 60 minutes to obtain a CoPcCN-CNT electrocatalyst ink.

[0075] ​Example 1, Preparation of NH2functionalized cobalt phthalocyanine axially coordinated carbon nanotubes (CoPcNH2-CNT): 4-nitrophthalonitrile (7.04 g), CoCl2-6H2O (1.47 g), 1,8-diazabicyclo[5.4.0]undec-7-ene (0.6 mL), and 50 mL of n-pentanol as solvent were mixed in a 100 mL three-necked flask and reacted in an N2atmosphere oil bath at 140 °C for 6 h. After the reaction was completed, 30 mL of methanol was added and the mixture was stirred thoroughly before being filtered using a Buchner funnel. Subsequently, the filter cake was washed repeatedly with methanol, ethanol, and dichloromethane until the filtrate was colorless. After drying in a vacuum environment at 70 °C, the CoPcNO2compound was obtained as a dark green solid. The synthesized CoPcNO2(3.15 g), Na2S-9H2O (6.74 g), 1 mL of deionized water, and 25 mL of N,N-dimethylformamide were mixed in a 100 mL three-necked flask as solvent and reacted in an N2atmosphere oil bath at 140 °C for 6 h. After cooling to room temperature, the filter cake was filtered and washed with a large amount of deionized water until it was neutral. Finally, NH2functionalized cobalt phthalocyanine (CoPcNH2) was obtained by drying in a vacuum at 70 °C. Next, PF-CNT was axially coordinated with CoPcNH2using the same method as in Example 1 to prepare the CoPcNH2-CNT electrocatalyst.

[0076] Example 2, Preparation of OMe functionalized cobalt phthalocyanine axially coordinated carbon nanotubes (CoPcOMe-CNT): 4-nitrophthalic acid (6.4 g), K2CO3(9.3 g), and 13.3 mL of methanol were added to 75 mL of N,N-dimethylformamide, and the reaction mixture was heated to 70 °C and maintained for 3 h under magnetic stirring and argon protection. The obtained black mixture was dispersed in a mixed solution of water (160 mL) and dichloromethane (160 mL), and the product was purified using dichloromethane as the eluent to obtain 4-methoxyphthalonitrile. Then, 4-methoxyphthalonitrile (3.1 g), CoCl2-6H2O (1.62 g), sulfolane (54 mL), and 1,8-diazabicyclo[5.4.0]undec-7-ene (0.6 mL) were added to a round-bottom flask with a stirring bar. The mixture was heated to 170 °C and maintained for 9 h. Next, the solid powder was precipitated from methanol (500 mL) using a Soxhlet extractor, and further removed from the solvent in an N,N-dimethylformamide solution to obtain OMe functionalized cobalt phthalocyanine (CoPcOMe). Finally, PF-CNT was axially coordinated with CoPcOMe using the same method as in Example 1 to prepare the CoPcOMe-CNT electrocatalyst.

[0077] Comparative Example 3: Preparation of CoPcH-CNT: CoPcH-CNT electrocatalyst was prepared by axial coordination of PF-CNT with CoPc using the same method as in Example 1.

[0078] Comparative Example 4: Preparation of CoPcCN / CNT electrocatalyst: CoPcCN / CNT electrocatalyst was prepared by physical mixing of 3.0 mg of CoPcCN and 30 mg of pur-CNT in a mortar.

[0079] From the HRTEM images (Fig. 2(a) and (b)), it can be observed that the surface of the pur-CNT substrate is smooth, indicating a high purity of the substrate (Fig. 2(a)). Figure 1 Figure 1 (a)). Figure 1 The HRTEM images in (b) show surface protrusions of PF-CNT along the sidewalls, which prove the successful grafting of covalent pyridyl groups. From the Nls XPS spectra (Fig. 3(b)), it can be observed that PF-CNT shows a distinct Nls peak at 399 eV, which is attributed to pyridyl N. This result further confirms the pyridyl functionalization of CNTs. From the UV-vis spectra (Fig. 3(c)), Soret peaks corresponding to different β substituents can be observed in CoPcX catalysts, which indicates the successful preparation of β-functionalized CoPc (CoPcX). Figure 2 Figure 3 Figure 4 XRD patterns of CNT, CoPc and CoPcX-CNT catalysts are shown. The CNT substrate has two broad characteristic peaks at 25.2° and 43.8°, which correspond to the (002) and (100) planes of standard graphite card (JCPDS NO. 26-1079), respectively. In addition, for CoPcX-CNT catalyst, two characteristic peaks corresponding to CoPc are observed at 12.4° and 19.2°, indicating that CoPcX-CNT catalyst is composed of carbon and CoPc molecules. As shown in Fig. 4(b), the FT-IR spectrum of PF-CNT shows characteristic peaks corresponding to C-N stretching and C-H / C-N stretching at 1098 cm Figure 5 -1 and 1420 cm -1 , which prove the presence of pyridyl groups. While CoPcX-CNT catalyst shows characteristic peaks at 730 cm -1 , 910 cm -1 and 1295-1520 cm -1 ​​​​The characteristic peaks at correspond to CH bending, Co-N and CH / CN stretching, respectively. The positions of the above characteristic peaks are highly consistent with those of CoPc, indicating that the molecular structure of CoPcX attached to CNTs is not damaged. In addition, the interaction between the Co active center in CoPcX and the CNT substrate was studied by high-resolution XPS spectroscopy. Figure 6 As shown, the CoPc catalyst has two characteristic peaks at 780.5eV and 796.3eV, corresponding to the Co 2p 3 / 2 and Co 2p 1 / 2 Co 2p of CoPcX-CNT catalyst 3 / 2 The peak shifted negatively (binding energy decreased), indicating that the valence of Co atoms in CoPcX-CNT is lower than that of CoPc. The pyridine functional groups in CoPcX-CNT have electron conduction function, which leads to an increase in the electron density around Co atoms. 3 / 2 The negative shift in peak binding energy (1.1 eV) is greater than that of CoPcH-CNT (0.6 eV), indicating that the OMe substituent has electron-donating properties. The negative shifts in binding energy of CoPcNH2-CNT and CoPcCN-CNT are 0.2 eV and 0.4 eV, respectively, indicating that the NH2 substituent has stronger electron-withdrawing ability than the CN substituent.

[0080] Aberration-corrected HAADF-STEM image ( Figure 7 (a)) and the corresponding EDX images ( Figure 7 (b) The results show that Co and N atoms are evenly distributed on the CNT surface of the CoPcCN-CNT catalyst. Atomic resolution HAADF-STEM image ( Figure 7 (c) shows that the single Co atoms in the CoPcCN molecules on the CNT surface are clearly visible as bright spots, indicating that the CoPcCN is evenly distributed and there are no phthalocyanine aggregates. Similarly, the CoPcX molecules (X = OMe, NH2, H) in the CoPcOMe-CNT, CoPcNH2-CNT and CoPcH-CNT catalysts are evenly distributed on the CNT surface ( Figures 8-10 ), so the dispersion of CoPcX is not affected by the change of β-substituents.

[0081] In order to compare the differences in Co-N coordination between samples prepared by different preparation methods, CoPcCN and CNT were mixed by mechanical method (the prepared samples were denoted as CoPcCN / CNT). First, the regulatory effect of pyridine groups and β-substituents on the detailed electronic structure of CoPcCN-CNT catalysts was determined by X-ray absorption near-edge structure (XANES) spectroscopy ( Figure 11). For the normalized Co K-edge XANES spectra of CoPc and CoPcCN / CNT, the pre-edge peaks at 7718 eV and 7723 eV (1s→4p transition) indicate the D 4h symmetry. In contrast, the transition of the Co active center electrons from 1s to 3d and 4p in CoPcX-CNT (X = CN, OMe, NH2, H) results in the change of the pre-edge peak position (7715-7717 eV). This local electric quadrupole and electric dipole transition is related to the asymmetric electron distribution of the Co active site in CoPcX-CNT. According to the results of Figure 11 , the absorption edge of CoPcX-CNT is lower than that of CoO, indicating that the valence state of Co atom is lower than that of Co 2+ . The absorption edge of CoPcCN / CNT is higher than that of Co2O3, indicating that the valence state of Co atom is higher than that of CoPcX-CNT. This can be due to the pyridine group with electron conduction function in CoPcX-CNT catalyst can enrich the electrons of Co atom, thereby reducing the valence state. According to the above results, the valence state of Co atom in CoPcX-CNT catalyst is arranged as follows: CoPcNH2-CNT > CoPcCN-CNT > CoPcH-CNT > CoPcOMe-CNT, which is consistent with the electron transfer properties of β substituents obtained in high-resolution Co 2p XPS spectra Figure 6 ).

[0082] The k 3 weighted extended X-ray absorption fine structure (FT-EXAFS) and EXAFS spectra Figure 12 , Figure 13 ) confirm the axial coordination connection structure in CoPcCN-CNT catalyst. As shown in Figure 12 , there is no Co-Co characteristic peak (usually at ) related to Co atom aggregation in CoPcCN-CNT and CoPcCN / CNT, further confirming the uniform dispersion of Co single atoms distributed on the surface of CNT. CoPcCN-CNT and CoPcCN / CNT catalysts detect a characteristic peak corresponding to Co-N bond at and , respectively, indicating that the coordination number of Co-N is different in CoPcCN-CNT and CoPcCN / CNT. The FT-EXAFS spectrum results Figure 13 ) of different samples show that the Co-N coordination number (CN) of CoPcCN-CNT is close to 5, while the Co-N coordination number of CoPcCN / CNT is close to 4. According to the N1s XPS spectrum Figure 14), the binding energy of the characteristic peak corresponding to the Co-N bond in CoPcCN-CNT is 1.3 eV higher than that in CoPcCN / CNT, indicating that the metal ligand coordination strategy in CoPcCN-CNT is stronger. Based on the above results, the Co atom in CoPcCN-CNT coordinates with five N atoms to form a Co-N5 coordination bond. Considering that the original CoPc and CoPcCN / CNT only contain Co-N4 coordination bonds, it can be reasonably inferred that the N atom in the pyridine functional group forms an additional axial coordination. At the same time, the CoPcX-CNT catalysts with H, OMe and NH2 substituents all exhibited similar Co-N peaks. The Co-N5 coordination bond of the CoPcX-CNT catalyst is not affected by the β-substituent. Figures 15-17 ).

[0083] 2e - Electrochemical measurements of the redox reaction (ORR) were performed using a conventional three-electrode electrolysis cell configuration with a RRDE system and a custom-made flow cell (collection efficiency N = 0.375, via Fe(CN)6 2+ / 3+ The cathode and anode were separated by a Nafion 117 membrane. The electrochemical response was recorded using an Autolab potentiostat. 2 ) and platinum ring electrode (0.1866cm 2 ) as the working electrode. The CoPcCN-CNT catalyst powder was dispersed in a 0.08 wt.% Nafion solution to make the catalyst concentration reach 0.9 mg mL -1 After the solution was ultrasonically treated for 60 min, the CoPcCN-CNT electrocatalyst ink was dropped onto the glassy carbon disk of the RRDE electrode and dried to obtain 0.01 mg·cm -2 Before measurement, the electrochemical cell was immersed in 0.2-0.8 M H2SO4 for 10 minutes and then boiled in deionized water to remove trace impurities. The working electrode was also mechanically polished with an alumina suspension and rinsed. Ag / AgCl electrodes and Pt mesh (1×1 cm 2 ) as the reference electrode and counter electrode. All potentials of the measured data were calibrated to the reversible hydrogen electrode (RHE). In order to compare the inherent 2e - -ORR performance. All catalysts were first evaluated in a standard RRDE setup. Before ORR measurement, the -1A pre-cycling step from 0.05 to 1.0 V (vs. RHE) was performed in an air-saturated 0.1 M KOH and 0.1 M HClO4 electrolyte until a stable voltammogram was obtained. The catalyst electrode was then transferred to an O2-saturated electrolyte and the charge was tested at 5 mV·s -1 The polarization was performed from 1.0 V to 0.1 V at a scan rate of 1000 rpm and a rotation speed of 1600 rpm, while the potential of the platinum ring electrode was maintained at 1.2 V. The polarization curve was corrected by subtracting the current obtained in Ar saturated electrolyte from the current measured under O2 saturated conditions. The obtained ring current was also corrected using the collection efficiency to evaluate the overall performance. The H2O2 Faradaic efficiency (FE, %) and H2O2 selectivity (%) under the RRDE configuration were calculated according to the following formula: FE (%) = (I r / N) / |I d |×100%, H2O2 selectivity (%)=200×(I r / N) / (|I d |+I r / N), where I r and I d denote the ring current and disk current, respectively. N is the collection efficiency of the Pt ring. Based on the reduction reaction of K3[Fe(CN)6] / K4[Fe(CH)6], N was determined to be 0.375. The Tafel slope was calculated according to the following formula: η = b·log(j / j o ), where η is the overpotential, b is the Tafel slope, j is the current density, and j o is the exchange current density. First, we sourced the current by holding the potential at each point for 20 seconds to ensure steady-state conditions. We then obtained the Tafel slope for each sample from the JV plot by performing a linear fit at each point in the Tafel zone. Following these steps, we investigated the electrocatalytic performance of the CoPcCN-CNT catalyst.

[0084] like Figure 18 As shown, at a voltage of 0.48 V vs. RHE, the disk current densities of CoPcCN-CNT and CoPcH-CNT are -3.55 mA·cm -2 and -3.37 mA·cm -2 , higher than CoPcOMe-CNT (-2.41mA·cm -2 ) and CoPcNH2-CNT(-2.02mA·cm -2 Compared with the standard equilibrium potential of 0.76 V vs. RHE in alkaline solution, the onset overpotentials of CoPcCN-CNT and CoPcH-CNT are 13 mV and 36 mV, respectively, showing a rapid 2e --ORR kinetics. In contrast, CoPcOMe-CNT and CoPcNH2-CNT showed larger onset overpotentials (46 mV and 61 mV), indicating their poor ORR activity. Therefore, the ORR activity trend of different β-substituents is as follows: CN>H>OMe>NH2.

[0085] Next, in Figure 19 and Figure 20 The H2O2 selectivity of CoPcX-CNT catalyst was further evaluated in the paper. The ring current density of CoPcCN-CNT at 0.48V vs.RHE voltage (1.21mA·cm -2 ) is higher than CoPcH-CNT (0.74 mA·cm -2 ), and its H2O2 Faradaic efficiency (FE = 91.2%) is significantly higher than that of CoPcH-CNT (FE = 58.7%). In addition, the H2O2 selectivity of CoPcX-CNT is as follows: CoPcNH2-CNT (96.1%) > CoPcCN-CNT (95.2%) > CoPcH-CNT (73.9%) > CoPcOMe-CNT (62.4%) ( Figure 20 ). In summary, the CoPcCN-CNT catalyst exhibits the best combination of ORR activity and H2O2 selectivity.

[0086] In order to verify that the Co active center is in 2e - -ORR process, CV curves were used to analyze the Co center electronic state of different samples ( Figure 21 The results show that both CoPc and CoPcX-CNT show the same 2+ / Co + In addition, CoPc also has a characteristic peak at +0.03V, corresponding to the reduction reaction of Co + / Co 2+ Oxidation reaction. After the introduction of pyridine groups, Co in CoPcH-CNT + / Co 2+ The oxidation peak shifted positively to +0.17 V, indicating that the Co center accumulated more electrons. Based on the electron-donating ability of the OMe substituent, the electron-rich Co center promoted the Co + / Co 2+ The oxidation peak shifts positively to +0.23 V. In addition, the electron-withdrawing substituents of NH2 and CN lead to the partial depletion of electrons enriched in the Co center, so the Co + / Co 2+The oxidation peaks shifted negatively by +0.08 V and +0.13 V, respectively. The Co + / Co 2+ The negative shift of the oxidation peaks was greater than that of CoPcCN-CNT, which confirmed that the NH2substituent had stronger electron-withdrawing ability than the CN substituent. Then, the kinetic performance of CoPcX-CNT was further evaluated by Tafel analysis Figure 22 ). The Tafel slopes of CoPcX-CNT from large to small were as follows: CoPcOMe-CNT (253 mV·dec -1 )> CoPcNH2-CNT (199 mV·dec -1 )> CoPcH-CNT (127 mV·dec -1 )> CoPcCN-CNT (119 mV·dec -1 ). Therefore, CoPcCN-CNT had the smallest Tafel slope (119 mV·dec -1 ), indicating that its fastest O2adsorption kinetics promoted the synthesis of H2O2. In contrast, CoPcOMe-CNT had the highest Tafel slope.

[0087] For the electro-synthesis of H2O2, two kinds of flow cells were first configured, including a three-electrode flow cell and a two-electrode flow cell. CoPcCN-CNT loaded on a GDL was used as the cathode. A 0.5-1.5 M KOH solution was selected as the electrolyte. During the reaction, O2was injected into the cathode electrolysis tank at a flow rate of 20 mL·min -1 . The concentration of H2O2was determined by spectroscopic titration using a Ce(SO4)2reagent, and the Faraday efficiency (FE, %) and H2O2production rate (mmol·h -1 ·g -1 ) were calculated according to the following formulae: FE = 2C H2O2 ·v·F·t / Q·100%, and H2O2production rate = C H2O2 ·(v·10 -3 ) / (A·m), where v is the flow rate of ultrapure water, t is the reaction time, Q is the cumulative charge, A is the electrode area, and m is the catalyst loading mass. Next, the turnover frequency (TOF, s -1 ) value of the catalyst was calculated to evaluate the efficiency of the 2e - -ORR pathway to produce H2O2: TOF (s -1 ) = (j / 2F) / n, where n is the number of active sites, j is the H2O2production current density measured from the ring electrode at a given overpotential using the RRDE setup, and F is the Faraday constant (96485 C·mol -1Finally, the utilization rate of H2O2 products, energy cost, and production cost were analyzed to further evaluate the economic benefits of H2O2 production.

[0088] The 2e efficiency of CoPcX-CNT catalysts for H2O2 production in alkaline electrolyte at high current density was examined in a three-electrode flow electrolysis cell configuration. - -ORR performance. Figure 23 As shown in the figure, the current density of CNT, CoPc and CoPcX-CNT gradually increases as the applied voltage decreases from 0.7V to 0.1V. The thermodynamic onset potential of H2O2 in alkaline solution (0.76V vs. RHE) is used as a standard to detect the onset overpotential of different electrocatalysts. The H2O2 onset overpotential of pyridine-linked CoPcH-CNT catalyst is 93mV, which is lower than that of CNT (180mV) and CoPc (171mV), indicating that its 2e - The ORR kinetics were faster. In addition, CoPcH-CNT, CoPcNH2-CNT, and CoPcOMe-CNT achieved peak current densities of 380 mV, 450 mV, and 530 mV, respectively. In contrast, the CoPcCN-CNT catalyst exhibited a higher peak current density (443 mA cm-3) at a lower overpotential (310 mV). -2 ) shows that it has the fastest 2e - -ORR kinetics. In order to further study the catalytic activity of CoPcX-CNT catalyst, its current density ( Figure 24 Among the CoPcX-CNT catalysts, the CoPcCN-CNT catalyst has the highest current density (300 mA cm -2 ). In summary, the CoPcCN-CNT catalyst has the fastest 2e - -ORR kinetics, showing the best catalytic activity in a practical alkaline environment.

[0089] Next, in a three-electrode flow electrolysis cell system loaded with CoPcCN-CNT cathode, the electrosynthesis of H2O2 at different current densities was studied by time potentiometry. Based on the H2O2 concentration in the cathode electrolyte after 15 minutes of electrolysis, the H2O2 production rate, the corresponding Faradaic efficiency (FE) and turnover efficiency (TOF) were calculated. Figure 25 As shown in Figure 2, with the increase of current density on CoPcCN-CNT, the production of H2O2 first increases and then decreases. -2 At a current density of 1.5 mol·g, the H2O2 yield reached 20.32 mol·g -1 cat ·h -1 The peak value, FE value is 95.7%, TOF value is 18.7s-1 Compared with CoPcNH2-CNT (92.0% / 15.9s -1 )、CoPcOMe-CNT(63.2% / 11.8s -1 ) and CoPcH-CNT (45.9% / 9.1s -1 ), CoPcCN-CNT with the highest FE and TOF values ​​exhibited the best catalytic activity ( Figure 26 , Figure 27 Furthermore, the H2O2 productivity, FE, and TOF values ​​of CoPcCN-CNT are higher than those of the reported state-of-the-art electrocatalysts ( Figure 28 ).

[0090] Then, a two-electrode flow cell configuration was used for H2O2 electrosynthesis. The Pt / C catalyst material supported on the anode was 2e - -ORR process provides H + .like Figure 29 As shown, as the full battery voltage (E cell As the current density of CNT, CoPc and CoPcX-CNT increases from 1.0 V to 3.5 V, the current density of CoPcCN-CNT catalyst increases gradually. cell To reach 300mA·cm -2 At the same voltage, the current densities of CoPcH-CNT, CoPcNH2-CNT, and CoPcOMe-CNT are 254, 163, and 102 mA cm, respectively. -2 , which further confirms that the CoPcCN-CNT catalyst has a - -Excellent performance in ORR process. Figure 30 As shown, at 300mA·cm -2 The stability of the CoPcCN-CNT catalyst was investigated at a constant current density of 1.5 Å. During the 100 h operation, E cell The value is between 2.51V and 2.55V, and the Faraday efficiency of H2O2 is between 93.4% and 95.7%. At the same time, the H2O2 concentration increases continuously to 1.78-1.82 mol·L within 20 hours. -1 , for 5 cycles.

[0091] For ethylene oxidation reaction, a typical three-electrode flow cell was configured with Nafion 117 separating the cathode and anode. CoPcCN-CNT catalyst supported on GDL was used as the cathode, and Pt / C catalyst supported on carbon paper was used as the anode. The Pt / C anode was prepared by dispersing 4 mg of commercial Pt / C catalyst and 8 μL of Nafion solution in 0.8 mL of ethanol and sonicating for 30 min to form a uniform ink. Then the catalyst ink was loaded onto a hydrophilic carbon paper with an area of 1 x 1 cm -2 at a mass loading of 0.5 mg·cm 2 , and dried in ambient atmosphere to prepare the Pt / C anode. The product content of ethylene oxidation was detected by 1 HNMR and 13 C NMR spectroscopy using water suppression technique, and the selectivity of different oxidation products was calculated by high performance liquid chromatography (HPLC): selectivity (%) = N D / N T x 100%, where N T is the sum of desired product and undesired product content, and N D is the desired product content. Finally, the effect of H2O2 permeability on the enhancement of glycolaldehyde synthesis was further evaluated by changing the ion exchange membrane to adjust the H2O2 permeability, and analyzing the glycolaldehyde yield, glycolaldehyde selectivity, ethylene glycol selectivity, H2O2 concentration, and economic benefit in systems with different membranes (cation exchange membrane CEM, anion exchange membrane AEM, no membrane NoM).

[0092] The ethylene oxidation and H2O2 synthesis experiments were performed simultaneously in a typical three-electrode flow cell with Nafion 117 membrane (cation exchange membrane, CEM) separating the CoPcCN-CNT cathode and Pt / C anode. Figure 31 The LSV curves of Pt / C and CoPcCN-CNT are shown. The predicted initial operating current and voltage of the anode and cathode are ~230 mA and ~0.53 V RHE , respectively. As shown in Figure 32 , the Pt / C anode in this system showed stable performance when the electrolyte was refreshed. After the experiment, the products accumulated in the anode chamber were quantitatively detected using 1 HNMR spectroscopy. It can be observed that the products generated from ethylene oxidation include ethylene glycol (EG), glycolaldehyde (GD), and glycolic acid (GA) Figure 33 . The selectivity of ethylene oxidation products was detected using high performance liquid chromatography (HPLC). As shown in Figure 34 , the selectivity of glycolaldehyde remained in the range of 40.1-41.4%.

[0093] The production of H2O2 can be used to improve the selectivity of ethylene oxidation products, followed by the regulation of H2O2 permeability into the anolyte compartment by membranes. Three systems were compared: CEM, anion exchange membrane (AEM), and no membrane (NoM) ( Figure 35 ). The H2O2 production in the system using CEM (0.89-0.92 mol·L -1 ) was higher than that of the AEM system (0.7-0.76 mol·L -1 ) ( Figure 36 ). This is because H2O2 exists in the form of HO2 - in alkaline solution, which is difficult to permeate CEM. Then, the effect of H2O2 permeability on the selectivity of ethylene oxidation products was studied ( Figure 37 ). In the electrocatalytic system using CEM, the low permeability of H2O2 resulted in a selectivity of glycolaldehyde of only 41.4%. In the electrocatalytic system using AEM, the moderate permeability of H2O2 increased the selectivity of glycolaldehyde to 63.5%. However, the excessive permeability of H2O2 in the NoM system led to the deep oxidation of ethylene to glycolic acid, resulting in a low selectivity of glycolaldehyde (40.3%). Therefore, it is crucial to use an appropriate concentration of H2O2 oxidant to promote the production of glycolaldehyde.

[0094] Finally, a techno-economic analysis of ethylene oxidation and H2O2 production was performed. Figure 38 The production cost predicted by a plant-levelization cost model using CoPcCN-CNT catalyst for the production of H2O2 is shown. At a current density of 300 mA·cm -2 and E cell of 2.55 V, the production cost of electro-synthesized H2O2 (US$550 tonne -1 ) is only half of the market price of H2O2 (US$550 tonne -1 ). At the same time, the system can achieve an energy efficiency (EE) of 23%, thus achieving economic and renewable electro-synthesis of H2O2. In contrast, the cost of producing H2O2 is higher than the market price of H2O2 at 50 mA·cm -2 / 2.55 V and 50 mA·cm -2 / 5.62 V ( Figure 39 ). Energy analysis shows that the energy required for H2O2 electro-synthesis using CoPcCN-CNT catalyst (39 GJ·tonne -1 ) is lower than that of the anthraquinone process (68 GJ·tonne -1 ) ( Figure 40 ). A series of representative results based on H2O2 permeability are shown in Figure 41As shown in Figure 2, the economic benefits (EP) of the ethylene oxidation process were further analyzed by comparing the price of the ethylene oxidation product produced to the price of ethylene consumed in the CEM, AEM and NoM systems. The realization of high EP value depends on high glycolaldehyde yield (Yield GD ) and glycolaldehyde selectivity GD ) is achieved because glycolaldehyde (300.25$·mol -1 ) is more expensive than ethylene glycol (0.043$·mol -1 ) or glycolic acid (7.61$·mol -1 The AEM system showed the highest yield of 224 μmol. GD and the highest Selectivity of 63.5% GD , and the system showed relatively low ethylene glycol selectivity EG =9.4%). Furthermore, the AEM system also exhibited the highest EP of 7695, indicating that the oxidation product value of this system is over 7000 times higher than that of ethylene. Compared to the CEM system, the H2O2 production in the AEM system was not significantly reduced. This result suggests that only a small amount of H2O2 is required to improve the selectivity of glycolaldehyde in the AEM system, while the remaining H2O2 can be used for other applications.

Claims

1. A method for preparing a β-functionalized cobalt phthalocyanine axially connected carbon nanotube electrocatalyst, characterized in that: The preparation method is carried out according to the following steps:

1. In an ice-water bath, NaNO2, 4-aminopyridine and purified carbon nanotubes were mixed to obtain pyridine-functionalized carbon nanotubes, which were then added to N,N-dimethylformamide to obtain solution A.

2. 1,2,4,5-tetracyanobenzene, CoCl2·6H2O, sulfolane and 1,8-diazabicyclo[5.4.0]undec-7-ene were placed in a reaction kettle, mixed and heated to obtain CoPcCN; and then added to N,N-dimethylformamide to obtain solution B; 3. Solution A and solution B are mixed and ultrasonically treated to obtain a mixed solution; and then freeze-dried to obtain the CoPcCN-CNT electrocatalyst.

2. The method for preparing a β-functionalized cobalt phthalocyanine axially connected carbon nanotube electrocatalyst according to claim 1, characterized in that: In step 1, the mass ratio of NaNO2, 4-aminopyridine and purified carbon nanotubes is 2.58-2.68 g: 2.42-2.52 g: 33.2-34.7 mg.

3. The method for preparing a β-functionalized cobalt phthalocyanine axially connected carbon nanotube electrocatalyst according to claim 1, characterized in that: In step 1, the mass volume ratio of NaNO2 to N,N-dimethylformamide is 2.58-2.68 g:10-30 mL.

4. The method for preparing a β-functionalized cobalt phthalocyanine axially connected carbon nanotube electrocatalyst according to claim 1, characterized in that: The temperature of the ice bath in step 1 is 0°C.

5. The method for preparing a β-functionalized cobalt phthalocyanine axially connected carbon nanotube electrocatalyst according to claim 1, characterized in that: In step 2, the mass volume ratio of 1,2,4,5-tetracyanobenzene to N,N-dimethylformamide is 1.5-4.5 g:10-30 mL.

6. The method for preparing a β-functionalized cobalt phthalocyanine axially connected carbon nanotube electrocatalyst according to claim 1, characterized in that: In step 2, the mass volume ratio of CoCl2·6H2O to N,N-dimethylformamide is 1.0-1.4 g:10-30 mL.

7. The method for preparing a β-functionalized cobalt phthalocyanine axially connected carbon nanotube electrocatalyst according to claim 1, characterized in that: In step 2, the volume ratio of sulfolane, 1,8-diazabicyclo[5.4.0]undec-7-ene and N,N-dimethylformamide is 30-50 mL: 0.1-0.3 mL: 10-30 mL.

8. The method for preparing a β-functionalized cobalt phthalocyanine axially connected carbon nanotube electrocatalyst according to claim 1, characterized in that: In step 2, the reactor is heated to 120-160° C. and maintained at this temperature for 6-8 hours.

9. Use of the β-functionalized cobalt phthalocyanine axially connected carbon nanotube electrocatalyst prepared as claimed in claim 1 as a cathode catalytic material in an electrolytic cell.

10. The use according to claim 9, characterized in that β-functionalized cobalt phthalocyanine axially connected carbon nanotube electrocatalyst is used as the cathode catalytic material of the electrolytic cell to in situ produce H2O2 and promote the synthesis of ethanolaldehyde at the anode.

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