Preparation method and application of single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst

Abstract

The invention discloses a preparation method and application of a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst; the preparation method is as follows: 1. Dissolve dicyanobenzene, tetracyanobenzene and cobalt chloride in a mixed solution of N, N-dimethylformamide and ethylene glycol, fully mix, add a catalyst and stir until fully mixed, and then perform a hydrothermal reaction. 2. Add the solid phase product obtained in step 1 and nitrogen-doped multi-walled carbon nanotubes to a mixed solution of ethanol and nafion solution and fully mix to obtain a carbon paper coating catalyst. 3. The obtained carbon paper coating catalyst is drop-coated on an electrode substrate to obtain an electrocatalyst. The present invention polymerizes 1,2,4,5-tetracyanobenzene and 1,4-dicyanobenzene under the catalysis of 1,8-diazabicyclo[5.4.0]undec-7-ene to form a hole defect, thereby causing the overall charge of the carbon skeleton to be rearranged, so that the active center of the catalyst is increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalysts, and specifically relates to a preparation method and application of a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst. Background Art

[0002] In today's era, energy and environment are the vital material basis and foundation for the survival and development of human society. On the one hand, fossil fuels such as coal, oil, and natural gas still account for more than 80% of all energy, and their reserves are seriously insufficient; and with the growth of the world's population and the development of industrialization, global energy demand is expected to increase from 18 TW in 2013 to 24 or 26 TW in 2040, and the global energy consumption rate is expected to double by 2050. On the other hand, the consumption of these energy sources will produce a large amount of harmful gases such as carbon monoxide, carbon dioxide, sulfur dioxide, and nitrogen oxides, which will cause a series of problems such as the generation of haze, greenhouse effect, and environmental pollution. In particular, the excessive emission of carbon dioxide has attracted more and more attention. Therefore, in the face of energy crisis, especially the shortage and unsustainable supply of oil, it is urgent to develop sustainable and environmentally friendly alternative energy; in the face of environmental pollution, especially the problem of excessive emission of carbon dioxide, it is urgent to develop a development strategy of stable circulation and transformation of waste gas into sustainable energy. The development of renewable electrochemical energy conversion and storage technology and the conversion of CO2 into hydrocarbons are expected to solve the problems of global energy shortage and environmental pollution. At present, oxygen evolution reaction (OER) as the key to water electrolysis technology and photocatalytic CO2 reduction have become key research directions; and Co-based catalysts have become the focus of research due to their excellent OER or CO2 reduction performance. Summary of the invention

[0003] The purpose of the present invention is to provide a method for preparing a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst in order to solve the deficiencies of the prior art.

[0004] In a first aspect, the present invention provides a method for preparing a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst, comprising the following steps:

[0005] Step 1: dissolving dicyanobenzene, tetracyanobenzene and cobalt chloride in a mixed solution of N,N-dimethylformamide and ethylene glycol, and after fully mixing, adding 1,8-diazabicyclo[5.4.0]undec-7-ene and stirring until fully mixed; the mass ratio of dicyanobenzene to tetracyanobenzene is 1:(1-9); and subjecting the obtained solution to a hydrothermal reaction at 150-250° C. for 60-84 hours.

[0006] Step 2: Add the solid phase product obtained in step 1 and nitrogen-doped multi-walled carbon nanotubes into a mixed solution of ethanol and nafion solution and mix them thoroughly to obtain a carbon paper coated catalyst.

[0007] Step 3: drop-coat the obtained carbon paper coating catalyst on the electrode substrate to obtain a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst.

[0008] Preferably, in step 1, dicyanobenzene, tetracyanobenzene and cobalt chloride are added to a mixed solution of N,N-dimethylformamide and ethylene glycol and then ultrasonicated for 0.5 to 1 h;

[0009] Preferably, in step 1, after adding 1,8-diazabicyclo[5.4.0]undec-7-ene, stirring is continued for 12 to 36 hours. Preferably, in step 1, after the hydrothermal reaction is completed, the obtained product is centrifuged and washed 2 to 5 times with a deionized aqueous solution of HCl, ethanol, and deionized water, respectively, and then dried in a vacuum drying oven to obtain a solid product.

[0010] Preferably, in step 1, the heating rate at the beginning of the hydrothermal reaction is 2-10°C / min.

[0011] Preferably, the dicyanobenzene is 1,4-dicyanobenzene; and the tetracyanobenzene is 1,2,4,5-tetracyanobenzene.

[0012] Preferably, the volume ratio of N,N-dimethylformamide to ethylene glycol is 1:(1-9).

[0013] Preferably, the ratio of the total mass of dicyanobenzene and tetracyanobenzene to the mass of cobalt chloride is (2-3):1.

[0014] Preferably, the electrode substrate is carbon paper.

[0015] In a second aspect, the present invention provides the use of the single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst prepared by the aforementioned preparation method in the electrocatalytic reduction of carbon dioxide to produce carbon monoxide.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The present invention polymerizes 1,2,4,5-tetracyanobenzene and 1,4-dicyanobenzene under the catalysis of 1,8-diazabicyclo[5.4.0]undec-7-ene. Since the cyano group in 1,4-dicyanobenzene cannot fully meet the polymerization requirements of 1,2,4,5-tetracyanobenzene, part of the N site will be exposed and a hole defect will be formed, thereby causing the overall charge of the carbon skeleton to be rearranged, so that the active center of the catalyst is increased, and the selective reduction of CO2 is enhanced. In addition, the hole defect makes the catalyst prepared by the present invention have a rich porous structure, a high specific surface area and good electrical conductivity, which can effectively improve the Faraday efficiency of electrocatalytic reduction of carbon dioxide to generate carbon monoxide.

[0018] 2. The phthalocyanine small molecules generated in the preparation process of the present invention can not only serve as active sites to promote CO2 reduction, but also their own abundant coordination active sites are conducive to the adsorption of *CO and its intermediate products; the cobalt single atom in the cobalt phthalocyanine molecule serves as an active site, which reduces the reaction energy barrier of the intermediate product COOH* during CO reduction, and at the same time, the enriched charge at the catalyst tip is conducive to the further reduction of *COOH to the intermediate product CO*, thereby promoting the conversion reaction of CO2 to CO gas product.

[0019] 3. The present invention realizes the single-atom loading of cobalt on nitrogen-doped carbon through a hydrothermal reaction, avoids the appearance of metal clusters, and improves the catalytic efficiency of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flowchart of the preparation method of Example 1 of the present invention.

[0021] Figure 2 This is the XRD pattern of the single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst prepared in Example 1 of the present invention.

[0022] Figure 3 This is a graph showing the changes in FE (CO) and FE (H2) with the working voltage during the electrocatalytic reduction of carbon dioxide using the electrocatalyst prepared in Example 1 of the present invention as a cathode.

[0023] Figure 4 This is a comparison chart of FE (CO) and FE (H2) during the electrocatalytic reduction of carbon dioxide using the electrocatalysts prepared in Example 1 and Comparative Example 1 as cathodes.

[0024] Figure 5 This is a comparison chart of FE (CO) and FE (H2) during the electrocatalytic reduction of carbon dioxide using the electrocatalysts prepared in Example 1 and Comparative Example 2 as cathodes.

[0025] Figure 6 This is a comparison chart of the Faraday efficiencies of carbon monoxide and hydrogen generated in Examples 1-3 at an operating voltage of 1.4V. DETAILED DESCRIPTION

[0026] The present invention is described in detail below in conjunction with specific implementation methods, but is not intended to limit the present invention. The experimental methods used in the following embodiments are all conventional methods unless otherwise specified.

[0027] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0028] Example 1

[0029] like Figure 1As shown, a method for preparing a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst comprises the following steps:

[0030] Step 1: Dissolve 0.05 g of 1,4-dicyanobenzene, 0.2 g of 1,2,4,5-1,2,4,5-tetracyanobenzene, and 0.1225 g of cobalt chloride in a mixed solution of 6 ml of N,N-dimethylformamide and 54 ml of ethylene glycol, sonicate for 0.5 h, add 227.5 μl of 1,8-diazabicyclo[5.4.0]undec-7-ene, and stir for 24 h. Heat the resulting solution to 180° C. in a muffle furnace at a heating rate of 5° C. and perform hydrothermal reaction for 72 h. In this process, 1,4-dicyanobenzene and 1,2,4,5-tetracyanobenzene are catalyzed by 1,8-diazabicyclo[5.4.0]undec-7-ene, and cobalt ions are riveted to the center of metal phthalocyanine to form a two-dimensional metal multi-phthalocyanine conjugated porous framework; then, it is centrifuged and washed three times with HCl and deionized water solution, ethanol, and deionized water in sequence, and then dried in a vacuum drying oven to obtain a catalyst powder containing phthalocyanine Co.

[0031] Step 2: Weigh 1 mg of catalyst powder and 3 mg of nitrogen-doped multi-walled carbon nanotubes and mix them ultrasonically in a mixture of 500 μl of ethanol and 10 μl of Nafion solution (i.e., perfluorosulfonic acid polymer solution, specifically Nafion D520 Dispersion) for 30 minutes to prepare a carbon paper coated catalyst.

[0032] Step 3: Apply the obtained carbon paper coating catalyst dropwise on a 1 cm 2 On carbon paper, its ability to accept electrons was enhanced to produce a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst used as a cathode electrode.

[0033] The X-ray diffraction pattern of the obtained single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst is as follows: Figure 2 shown; from Figure 2 It can be seen that a broad graphite carbon diffraction peak appears at the 27° position of the X-ray diffraction pattern, and no metal diffraction peak is found, indicating that the metal crystallinity in the material is low and Co exists in the material in the form of atoms without forming metal clusters.

[0034] In order to verify the effect of the single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst prepared in this example on the electrocatalytic reduction of carbon dioxide to produce carbon monoxide, the following experiments were conducted:

[0035] An H-type reactor with dual electrolytic cells is provided, and the single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst prepared in this embodiment is installed in one electrolytic cell as a cathode electrode, and an anode electrode and an Ag / AgCl reference electrode are installed in the other electrolytic cell; the anode electrode is a platinum electrode. The dual electrolytic cell reactor is sealed with polytetrafluoroethylene, and the two electrolytic cells are connected by a cation exchange membrane, and the anode electrode and the cathode electrode are connected by wires to form an external circuit; a potassium bicarbonate solution with a concentration of 0.5 mol / L is added to the bipolar chambers of the dual electrolytic cells, CO2 is introduced into the cathode chamber through an aerator, and a working voltage is applied to the anode electrode and the cathode electrode to perform an electrocatalytic reduction reaction of CO2.

[0036] The above reaction was carried out at operating voltages of 0.9 V, 1.1 V, 1.3 V, 1.4 V, 1.5 V and 1.7 V for 2 hours, and the Faraday efficiency of carbon monoxide and hydrogen generation was measured.

[0037] The changes in the Faraday efficiency of H2 and CO under different working voltages are shown in the figure below. Figure 3 shown; from Figure 3 It can be seen that at 1.4 V, the Faraday efficiency of CO reaches the highest, close to 100%; therefore, 1.4 V is the optimal operating voltage for the single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst prepared in this embodiment.

[0038] Example 2

[0039] A method for preparing a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst. The difference between this embodiment and embodiment 1 is only that: 0.025g of 1,4-dicyanobenzene and 0.225g of 1,2,4,5-tetracyanobenzene are added in step 1; the remaining steps are consistent with embodiment 1.

[0040] The Faraday efficiency of carbon monoxide and hydrogen generation of the single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst prepared in this example at different operating voltages was determined using the same method as in Example 1.

[0041] Example 3

[0042] A method for preparing a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst. The difference between this embodiment and Example 1 is only that: 0.125g of 1,4-dicyanobenzene and 0.125g of 1,2,4,5-tetracyanobenzene are added in step 1; the remaining steps are consistent with Example 1.

[0043] The Faraday efficiency of carbon monoxide and hydrogen generation of the single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst prepared in this example at different operating voltages was determined using the same method as in Example 1.

[0044] The comparison of the Faraday efficiency of carbon monoxide and hydrogen generated at an operating voltage of 1.4 V in Example 1-3 is shown in FIG. Figure 6 It can be seen that the Faraday efficiency of carbon monoxide generation of the catalyst prepared when the mass ratio of 1,4-dicyanobenzene to 1,2,4,5-1,2,4,5-tetracyanobenzene is 1:4 is much higher than the Faraday efficiency of carbon monoxide generation of the catalyst prepared when the mass ratio of 1,4-dicyanobenzene to 1,2,4,5-1,2,4,5-tetracyanobenzene is 1:1 and 1:9.

[0045] Example 4

[0046] A method for preparing a single-atom cobalt polymer mixed with nitrogen-doped carbon electrocatalyst. The difference between this embodiment and embodiment 1 is only that the temperature of the hydrothermal reaction in step 1 is 150°C.

[0047] Example 5

[0048] A method for preparing a single-atom cobalt polymer mixed with nitrogen-doped carbon electrocatalyst. The difference between this embodiment and embodiment 1 is only that the temperature of the hydrothermal reaction in step 1 is 250°C.

[0049] Example 6

[0050] A method for preparing a single-atom cobalt polymer mixed with nitrogen-doped carbon electrocatalyst. The difference between this embodiment and embodiment 1 is only that the duration of the hydrothermal reaction in step 1 is 84 hours.

[0051] Example 7

[0052] A method for preparing a single-atom cobalt polymer mixed with nitrogen-doped carbon electrocatalyst. The difference between this embodiment and embodiment 1 is only that the duration of the hydrothermal reaction in step 1 is 60 hours.

[0053] Comparative Example 1:

[0054] A method for preparing an electrocatalyst. The difference between this comparative example and Example 1 is that: in step 1, 0.25 g of 1,2,4,5-tetracyanobenzene is added instead of 1,4-dicyanobenzene; the remaining steps are consistent with Example 1.

[0055] The Faraday efficiency of carbon monoxide and hydrogen generation of the single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst prepared in this example at different operating voltages was determined using the same method as in Example 1.

[0056] When the operating voltage is 1.4V, the Faraday efficiency of this comparative example is compared with that of Example 1. Figure 4As shown; it can be seen that the Faraday efficiency of generating carbon monoxide corresponding to Example 1 is significantly higher than that of Comparative Example 1; this indicates that the hole defects formed by using 1,2,4,5-tetracyanobenzene and 1,4-dicyanobenzene together as nitrogen-doped carbon materials have a greater promoting effect on the electrocatalytic reduction of CO2 to prepare CO.

[0057] Comparative Example 2

[0058] A method for preparing an electrocatalyst, the difference between this comparative example and Example 1 is that: in step 2), nitrogen-doped multi-walled carbon nanotubes are not added; the remaining steps are consistent with Example 1.

[0059] The Faraday efficiency of carbon monoxide and hydrogen generation of the electrocatalyst prepared in this comparative example at different operating voltages was determined in the same manner as in Example 1.

[0060] When the operating voltage is 1.4V, the Faraday efficiency of this comparative example is compared with that of Example 1. Figure 5 As shown; it can be seen that the addition of nitrogen-doped multi-walled carbon nanotubes is a necessary condition for the catalyst to produce a better catalytic effect.

[0061] The above-described embodiment is only a preferred solution of the present invention, and does not limit the present invention. Those skilled in the art can make various changes without departing from the basic method of the present invention. However, if the invention solution is obtained by adopting an equivalent or equivalent replacement method, it is within the protection scope of the present invention.

Claims

1. A method for preparing a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst, characterized in that: Step 1, dissolving dicyanobenzene, tetracyanobenzene and cobalt chloride in a mixed solution of N,N-dimethylformamide and ethylene glycol, and after fully mixing, adding 1,8-diazabicyclo[5.4.0]undec-7-ene and stirring until fully mixed; the mass ratio of dicyanobenzene to tetracyanobenzene is 1:(1-9); hydrothermally reacting the obtained solution at 150-250° C. for 60-84 hours; Step 2: adding the solid phase product obtained in step 1 and nitrogen-doped multi-walled carbon nanotubes into a mixed solution of ethanol and nafion solution and mixing them thoroughly to obtain a carbon paper coated catalyst; Step 3: drop-coat the obtained carbon paper coating catalyst on the electrode substrate to obtain a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst.

2. The method for preparing a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst according to claim 1, characterized in that: In step 1, dicyanobenzene, tetracyanobenzene and cobalt chloride are added to a mixed solution of N,N-dimethylformamide and ethylene glycol and then ultrasonicated for 0.5 to 1 hour.

3. The method for preparing a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst according to claim 1, characterized in that: In step 1, after adding 1,8-diazabicyclo[5.4.0]undec-7-ene, stirring is continued for 12 to 36 hours.

4. The method for preparing a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst according to claim 1, characterized in that: In step 1, the heating rate at the beginning of the hydrothermal reaction is 2-10°C / min; after the hydrothermal reaction is completed, the obtained product is centrifugally washed 2-5 times with a deionized water solution of HCl, ethanol, and deionized water, and then dried in a vacuum drying oven to obtain a solid phase product.

5. The method for preparing a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst according to claim 1, characterized in that: The dicyanobenzene is 1,4-dicyanobenzene; and the tetracyanobenzene is 1,2,4,5-tetracyanobenzene.

6. The method for preparing a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst according to claim 1, characterized in that: The volume ratio of N,N-dimethylformamide to ethylene glycol is 1:(1-9).

7. The method for preparing a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst according to claim 1, characterized in that: The ratio of the total mass of dicyanobenzene and tetracyanobenzene to the mass of cobalt chloride is (2-3):

1.

8. The method for preparing a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst according to claim 1, characterized in that: The electrode substrate is carbon paper.

9. A single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst, characterized in that: It is prepared by the preparation method described in any one of claims 1 to 8.

10. Use of a single-atom cobalt polymer mixed nitrogen-doped carbon electrocatalyst as claimed in claim 9 in the electrocatalytic reduction of carbon dioxide to produce carbon monoxide.

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