Preparation method of cobalt-based double-site catalyst suitable for wide voltage load

Abstract

The invention discloses a preparation method of a cobalt-based double-site catalyst suitable for wide voltage load, which comprises the following steps of: oxidizing cobalt acetylacetonate serving as a cobalt source, dicyandiamide serving as a carbon source and a nitrogen source and zinc nitrate serving as a pore-forming agent by a grinding oxidation method, and loading CoPc to prepare the cobalt-based double-site catalyst. By changing the applied potential, the Faraday efficiency of all samples can reach 100% within the range of-0.47 to-1.07 V vs.RHE, the catalytic performance of the CoPc / Co3O4 at-NC-400 DEG C prepared at 400 DEG C is the most stable, the H2 / CO Faraday efficiency ratio of the catalytically generated synthesis gas is the most stable and is closest to the industrial application requirement (1-2), the catalyst can be directly used for subsequent Fischer-Tropsch synthesis, and the method is suitable for industrial production. The method provided by the invention has the advantages of simple operation, no need of introducing new gas, provides a new way for more efficient utilization of CO2, and is expected to realize resource utilization of CO2 through a production process route of CO2-synthesis gas-high-energy chemicals.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a cobalt-based dual-site catalyst suitable for a wide voltage load and belongs to the technical field of catalysts. BACKGROUND

[0002] At present, fossil energy is still the main power source for human activities. A series of environmental problems caused by excessive CO2 emission due to large consumption of fossil energy have led to more frequent natural disasters. Reducing CO2 emission and realizing CO2 resource utilization are imminent. The reported CO2 conversion technologies with application prospects include photocatalytic reduction of CO2, electrocatalytic reduction of CO2, biological conversion and thermal catalytic CO2 hydrogenation integration technology. The electrocatalytic reduction of CO2 is one of the most effective and potential technologies, but there are several difficulties in the electrochemical reduction of CO2. First, CO2 is a linear molecule with very high thermodynamic stability, and its dissociation energy is as high as 750 kJ·mol -1 , which is significantly higher than that of C-O bond (327 kJ·mol -1 ), C-C bond (336 kJ·mol -1 ) and C-H (411 kJ·mol -1 ). This makes it difficult for CO2 to undergo reduction. And the potential of CO2 reduction to CO2 ·- is high, reaching-1.90 V compared with the standard hydrogen electrode (RHE) in neutral water medium. CO2 reduction also involves multiple and complex electron transfer / protonation coupling processes, so there are many possible reaction pathways, which can produce various compounds from C l (formaldehyde, methanol, CH, CO), C2 (ethylene, acetate, ethanol, acid salt) to C3 (propanol), which seriously limits the selectivity of the reaction and makes it difficult to produce products with stable content. At present, the electrocatalytic CO2 reduction device mainly has H-type electrolytic cell or flow phase electrolytic cell, and the reaction is carried out in a three-electrode system. Platinum sheet is used as the counter electrode, the catalyst is used as the working electrode, Ag / AgCl or saturated calomel electrode (SCE) is used as the reference electrode, and inorganic salts KCl, KHCO3, Na2SO4, etc. are commonly used electrolytes. In this reaction system, H2O is the most important proton source, but the hydrogen evolution reaction is easy to occur, which is the most important factor leading to the reduction of CO Faraday efficiency. Therefore, it is an important problem to regulate the relative rate of CO2 reduction and hydrogen evolution reaction and realize efficient CO2 reduction to generate stable syngas ratio.

[0003] Fischer-Tropsch synthesis is a chemical process that converts synthesis gas (a mixture of CO and H2, the molar ratio of H2 and CO is controlled at 1-2) into hydrocarbons under the action of catalyst, but due to different fossil raw materials and synthesis routes, the composition and purity of synthesis gas are different, so it is difficult to directly use synthesis gas for Fischer-Tropsch synthesis. If you want to speed up the industrialization stage of CO2 reduction into Fischer-Tropsch synthesis, it is essential to develop high-efficiency electrocatalysts with high activity, high selectivity and high stability. Most of the currently reported catalysts have a large gap between the performance in the reduction of CO2 and the actual industrial application requirements, such as poor product selectivity, poor stability, low Faraday efficiency and other problems. Based on this, the present application develops a cobalt-based double-site catalyst suitable for wide voltage load, which provides a new way for more efficient utilization of CO2, and is expected to realize the resource utilization of CO2 through the production process route of CO2-synthesis gas-high-energy chemicals. SUMMARY

[0004] In view of the shortcomings of the prior art, the purpose of the present application is to provide a preparation method of a cobalt-based double-site catalyst suitable for wide voltage load, which has the most stable Faraday efficiency for catalyzing the generation of synthesis gas and is most promising for industrial application. In the range of 0.47-1.07V vs.RHE, the Faraday efficiency of H2 and CO of CoPc / Co3O4@NC-400℃ is about 100%, the H2 / CO Faraday efficiency ratio is 1-2, and the maximum current density of CO is 12.02mA·cm-2. -2 , which provides a good raw material for subsequent Fischer-Tropsch synthesis.

[0005] In order to achieve the above-mentioned purpose, the technical scheme of the present application is to provide a preparation method of a cobalt-based double-site catalyst suitable for wide voltage load, comprising the following steps:

[0006] (1) Preparation of Co3O4@NC

[0007] Weigh cobalt acetylacetone, dicyandiamide and zinc nitrate, mix, then weigh anhydrous ethanol and acetone, add to the mixture, grind to dryness, and dry; after thorough drying, grind again; put into a tube furnace, pass N2 into the tube furnace, then perform stepwise temperature calcination, cool the furnace to room temperature, take out, and grind; repeat the above steps several times, and mark the obtained product as Co3O4@NC;

[0008] (2) Preparation of Co3O4@NC-T

[0009] Co3O4@NC was added with H2SO4 solution and stirred in oil bath, and then acid washed, cooled to room temperature, centrifuged, washed, and dried to obtain a black powder; the obtained powder was ground, placed into a tube furnace, N2 was passed into the tube furnace, and then calcination was performed, the furnace was cooled to room temperature, taken out, ground, placed into a tube furnace again, and oxidation was performed, and the obtained product was marked as Co3O4@NC-T;

[0010] (3) Preparation of CoPc / Co3O4@NC-T

[0011] Co3O4@NC-T and CoPc were weighed and mixed, anhydrous ethanol and DMF were weighed and added to the mixture, oil bath stirring was performed until evaporation, and then grinding was performed, and the mixture was placed into a tube furnace, N2 was passed into the tube furnace, and then calcination was performed, the furnace was cooled to room temperature, taken out, and a black powder was obtained, which was the catalyst and was marked as CoPc / Co3O4@NC-T.

[0012] Further, in step (1), the molar ratio of cobalt acetylacetonate, dicyanamide, and zinc nitrate was 1:3:0.1, and the volume ratio of anhydrous ethanol and acetone was 4:1.

[0013] Further, in step (1), the method for stage-wise temperature increase calcination was as follows: the temperature was increased from room temperature to 350℃ at a rate of 5℃·min -1 , and then held for 3h, and then increased to 650℃ and held for 3h, and finally increased to 900℃ and held for 1h.

[0014] Further, in step (2), the molar ratio of Co3O4@NC and H2SO4 was 1:1.

[0015] Further, in step (2), the oil bath temperature was 80℃, and the time was 5h; the method for calcination was as follows: the temperature was increased from room temperature to 900℃ at a rate of 5℃·min -1 , and then held for 1h.

[0016] Further, in step (2), the method for oxidation was as follows: the temperature was increased from room temperature to 350-450℃ at a rate of 5℃·min -1 , and then held for 2h, and preferably 400℃.

[0017] Further, in step (3), the mass ratio of Co3O4@NC-T and CoPc was 2:1, and the volume ratio of anhydrous ethanol and DMF was 1:1.

[0018] Further, in step (3), the oil bath temperature was 80℃.

[0019] Further, in step (3), the method for calcination was as follows: the temperature was increased from room temperature to 200℃ at a rate of 5℃·min -1 , and then held for 1h.

[0020] Beneficial effects:

[0021] The present application prepares a series of CoPc / Co3O4@NC-T catalysts by grinding oxidation method, taking cobalt acetylacetonate as cobalt source, dicyandiamide as carbon source and nitrogen source, and zinc nitrate as pore forming agent, controlling the oxidation temperature at 350℃, 400℃ and 450℃, and loading CoPc, and the performance of the catalysts for CO2 electrochemical reduction to prepare synthesis gas is correlated. Due to the different oxidation conditions, Co3O4, carbon nanotube structure and CoPc loading in CoPc / Co3O4@NC-T are different, thereby having different catalytic performance. By changing the applied potential, the Faraday efficiency of all samples can reach 100% in the range of-0.47 to-1.07 V vs. RHE, among which the catalytic performance of CoPc / Co3O4@NC-400℃ prepared at 400℃ is the most stable, and the Faraday efficiency ratio of the synthesis gas H2 / CO generated by catalysis is the most stable and closest to the required industrial application, which can be directly used for subsequent Fischer-Tropsch synthesis without introducing new gas. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 a is the SEM of CoPc / Co3O4@NC-350℃; b is the SEM of CoPc / Co3O4@NC-400℃; c is the SEM of CoPc / Co3O4@NC-450℃; d is the SEM of CoPc / Co@NC.

[0023] Figure 2 FIG. 6 is the XRD spectrum of CoPc / Co3O4@NC-T and the control group.

[0024] Figure 3 FIG. 7 is the Faraday efficiency of CoPc / Co3O4@NC-T and Co3O4@NC-T.

[0025] Figure 4 FIG. 8 is the Faraday efficiency of CoPc / Co@NC.

[0026] Figure 5 FIG. 9 is the jco and jH2 of CoPc / Co3O4@NC-T and Co3O4@NC-T at different voltages. H2 . DETAILED DESCRIPTION

[0027] The specific embodiments of the present application are further described in detail below in conjunction with the examples.

[0028] Example 1

[0029] A preparation method of a cobalt-based dual-site catalyst suitable for wide voltage load, comprising the following steps:

[0030] (1) Preparation of Co3O4@NC

[0031] Co(acac)3(1 mmol), dicyandiamide (3 mmol), and Zn(NO3)2(0.1 mmol) were weighed into a mortar, 8 mL of anhydrous ethanol and 2 mL of acetone were weighed into the mortar, and the mixture was ground to dryness in a fume hood at room temperature. The mixture was placed in a vacuum drying oven at 60°C for drying. After complete drying, the mixture was taken out, ground, and placed in a porcelain boat in a tube furnace. The tube furnace was purged with N2for 1 h to remove air, and then calcination was performed at a ramping rate of 5°C / min -1 . The temperature was first increased from room temperature to 350°C and maintained for 3 h, then increased to 650°C and maintained for 3 h, and finally increased to 900°C and maintained for 1 h. After cooling to room temperature in the tube furnace, the mixture was taken out, ground, and placed in a beaker. The above operation was repeated four times. The obtained product was labeled as Co3O4@NC.

[0032] (2) Preparation of Co3O4@NC-T

[0033] A 2M H2SO4solution was added to Co3O4@NC (molar ratio of Co3O4@NC to H2SO4was 1:1), and the mixture was stirred in an 80°C oil bath for 5 h. After cooling to room temperature, the mixture was centrifuged, washed, and dried to obtain a black powder. The black powder was ground and placed in a porcelain boat in a tube furnace. The tube furnace was purged with N2for 1 h to remove air, and then calcination was performed at a ramping rate of 5°C / min -1 . The temperature was increased to 900°C and maintained for 1 h. After cooling to room temperature in the tube furnace, the mixture was taken out, ground, and obtained as a black powder. The black powder was divided into three parts and placed in a tube furnace for oxidation at a ramping rate of 5°C / min -1 . The temperature was increased to different temperatures (350°C, 400°C, and 450°C) and maintained for 2 h. The obtained products were labeled as Co3O4@NC-T (T represents the oxidation temperature).

[0034] (3) Preparation of CoPc / Co3O4@NC-T

[0035] 40 mg of Co3O4@NC-T and 20 mg of CoPc were weighed into a beaker, and 20 mL of anhydrous ethanol and 20 mL of N,N-dimethylformamide (DMF) were added to the beaker. The mixture was stirred in an 80°C oil bath until it was evaporated. The mixture was taken out, ground, and placed in a porcelain boat in a tube furnace. The tube furnace was purged with N2for 1 h to remove air, and then calcination was performed at a ramping rate of 5°C / min -1 . The temperature was increased to 200°C and maintained for 1 h. After cooling to room temperature, the mixture was taken out, ground, and collected as a black powder. The obtained product was a catalyst and was labeled as CoPc / Co3O4@NC-T.

[0036] Comparative Example 1

[0037] This comparative example is to directly load CoPc on Co3O4@NC prepared in step (1) of Example 1. The specific operation refers to steps (1) and (3) of Example 1, and the obtained product is denoted as CoPc / Co@NC.

[0038] Catalyst characterization and test results:

[0039] I. SEM results and analysis

[0040] The morphology of the samples of CoPc / Co3O4@NC-T and CoPc / Co@NC was analyzed using a scanning electron microscope (SEM), and the results are shown in FIG. 1. Figure 1 It can be seen that the CoPc / Co3O4@NC-T nanoparticles are uniformly distributed, but the carbon nanotube structure in all samples after oxidation has been damaged to varying degrees, Figure 1 a is CoPc / Co3O4@NC-350℃, and it can be seen that the carbon nanotubes exist, Figure 1 b and Figure 1 c are SEM images of CoPc / Co3O4@NC-400℃ and CoPc / Co3O4@NC-450℃, respectively, and the damage to the carbon nanotubes in the images is very serious.

[0041] We conducted a supplementary experiment to study the reason for the collapse of the carbon nanotubes. Since the degree of damage to the carbon nanotubes increases with the increase of the oxidation temperature, CoPc / Co@NC was prepared by removing the oxidation step, and the SEM image is shown in FIG. 2d. Figure 1 It can be seen that the carbon nanotube structure of the sample without oxidation remains intact, and too high an oxidation temperature will cause instability of the carbon element in the sample, further leading to difficulty in maintaining the carbon nanotube structure.

[0042] II. XRD results and analysis

[0043] Figure 2a is the XRD pattern of CoPc / Co3O4@NC-T catalyst obtained at different oxidation temperatures, and the diffraction peak appears near 26° in the figure, indicating that the polymer in the sample is mainly graphite after oxidation. CoPc / Co3O4@NC-350℃ and CoPc / Co3O4@NC-400℃ appear diffraction peaks at 7°, 9.2°, indicating that CoPc is successfully loaded on Co3O4@NC-T, but CoPc / Co3O4@NC-450℃ has no obvious change at this position, and the original diffraction peak at 26° also becomes very inconspicuous. It is preliminarily speculated that the loss of carbon elements in the catalyst caused by the high oxidation temperature destroys the defects that can load CoPc, so that CoPc cannot be normally loaded, and CoPc itself is not stable, and after loading, it will also go through a calcination process. If the loading is unstable, it is easy to cause desorption. In addition, the diffraction peak intensity at 36.8° is increasing with the increase of oxidation temperature, indicating that the preferred growth of Co3O4(311) crystal plane is related to the oxidation temperature, and is positively correlated within the temperature range of this experiment.

[0044] Figure 2 b is the XRD pattern of CoPc / Co3O4@NC-400℃ sample at different stages. Combining the two figures, the sample before oxidation (Co) diffraction peaks appear at 44.2°, 51.5°, 75.8°, corresponding to Co (111), (200), (220) crystal planes. After oxidation at 400℃, obvious diffraction peaks appear at 31.2°, 36.8°, 59.2°, 65.2°, 77.3°, respectively corresponding to Co3O4(JCPDS.no.43-1003) (220), (311), (511), (440), (533) crystal planes, while the original Co diffraction peaks almost disappear. Therefore, after oxidation, almost all the Co in the sample is converted into Co3O4.

[0045] Catalyst electrochemical performance test:

[0046] I. Preparation of working electrode

[0047] Cut the carbon paper into a 1x1.5cm 2 rectangular block. Weigh 5mg of the prepared catalyst into a small centrifuge tube, add 25μL naphthol and 475μL anhydrous ethanol to the tube with a pipette, then ultrasonic for 1h. After ultrasonic, drop it on the 1x1cm 2 area of one side of the carbon paper with an amount of 20μL each time, drop 5 times, a total of 100μL. Wait for the carbon paper to dry before the next drop. After all the drops are completed, dry and prepare for use.

[0048] II. Electrochemical performance test

[0049] Electrochemical measurements were carried out in a H-type electrolysis cell at room temperature and atmospheric pressure using a three-electrode system. Ag / AgCl was used as the reference electrode and the working electrode was the catalyst prepared. Both of them were placed in the cathode chamber and put into a magnetic rotor. A platinum plate (2 x 2 cm 2 ) was used as the counter electrode and placed in the anode chamber. The two chambers were separated by a Nafion 117 proton exchange membrane. KHCO3 solution (0.5 M) was used as the electrolyte solution. Before the electrolysis started, 1 h CO2 and Ar were bubbled into the cathode chamber to remove the air in the electrolyte solution and the cathode chamber cavity and to saturate the CO2 in the electrolyte solution. The pH value of the electrolyte solution after CO2 saturation was 7.3. CO2 was delivered as the gaseous reactant by a flow display instrument (Beijing Qixing Huachuang D08-1F) at a rate of 16.9 seem (milliliters per minute). CO2 and Ar were continuously bubbled during the test. The volume of the electrolyte solution in the cathode and anode chambers was 35 mL, respectively. The electrolysis cell was connected to the sample inlet of a gas chromatograph (Changzhou Pannuo Instrument Co., Ltd., Model A91) by a hose for online quantitative analysis of the gaseous products.

[0050] The i-t curves at different applied potentials were measured by an electrochemical workstation (Wuhan Kechuang Instrument Co., Ltd. CS310MA). The production of CO and H2 was qualitatively and quantitatively detected by the FID and TCD channels of the gas chromatograph. The Faraday efficiency (FE) of the products was calculated according to formula (2-1):

[0051]

[0052] In the formula, z is the number of electrons transferred for the generation of the target product, n is the molar number (mol) of the product analyzed by the gas chromatograph, F is the Faraday constant (96500 C·mol -1 ), and Q (Q = It) is the total charge consumed (C).

[0053] The partial current densities (j CO and j H2 ) of CO and H2 were calculated by formulas (2-2) and (2-3), respectively:

[0054]

[0055] In the formula, j is the total current of the potentiostatic electrolysis (mA), FE CO is the Faraday efficiency of CO, FE H2 is the Faraday efficiency of H2, and A is the area of the working electrode (1 cm 2 ).

[0056] The auxiliary electrode used in this experiment was an Ag / AgCl electrode, which was converted to a reversible hydrogen electrode (RHE) by formula (2-4):

[0057] E(vs.RHE)=E(vs.AgCl)+0.21+0.0591×pH (2-4)

[0058] E represents the electrode potential, where E(vs.RHE) is the electrode potential relative to the reversible hydrogen electrode, and E(vs.Ag / AgCl) is the electrode potential relative to the silver chloride-silver (Ag / AgCl) reference electrode.

[0059] III. FE Test Results and Analysis

[0060] To investigate the application of the catalyst CoPc / Co3O4@NC-T in the electrochemical reduction of CO2 to syngas, this invention measured the Faradaic efficiency of the catalyst. The Faradaic efficiency (FE) test results for each sample are as follows: Figure 3 As shown (the area above the black line represents H2, and the area below it represents CO).

[0061] Depend on Figure 3 It can be seen that within the range of -0.47 to -1.07 V vs. RHE, the main product of the Co3O4@NC-T sample is H2, while the detected CoPc / Co3O4@NC-T products consist only of CO and H2, with no other liquid phase products generated. Within the range of 0.47 to 1.07 V vs. RHE, the Faraday efficiency of H2 and CO in CoPc / Co3O4@NC at -400℃ is approximately 100%, the H2 / CO Faraday efficiency ratio is 1–2, and the highest current density for CO reaches 12.02 mA·cm². -2 The CoPc / Co3O4@NC-350℃ Faraday efficiency of H2 and CO is approximately 100% in the range of 0.47–0.87 V vs. RHE, with an H2 / CO Faraday efficiency ratio of 1–2, and the highest CO current density reaches 12.05 mA·cm⁻¹. -2 Compared to CoPc / Co3O4@NC-400℃, CoPc / Co3O4@NC-350℃ exhibits a narrower voltage range for stable H2 / CO Faradaic efficiency ratio generation. However, at CoPc / Co3O4@NC-450℃, the Faradaic efficiency of H2 to CO is approximately 100% within the range of 0.57–0.87 V vs. RHE, with an H2 / CO Faradaic efficiency ratio of 1–2, and a maximum CO current density reaching 10.02 mA·cm⁻¹. -2Compared with CoPc / Co3O4@NC-400℃, the H2 / CO of CoPc / Co3O4@NC-450℃ is unstable in the catalytic synthesis of synthesis gas, and with the increase of the potential, the H2 / CO faradic efficiency ratio roughly presents a "basin" trend of first decreasing and then increasing. If the potential is too high, the hydrogen evolution reaction will be greatly enhanced, thereby causing the H2 / CO faradic efficiency ratio to greatly increase. In general, through the faradic efficiency test, CoPc / Co3O4@NC-400℃ has more stable catalytic selectivity in a wider voltage range, and has the best catalytic CO2ER effect, and can obtain synthesis gas with H2 / CO faradic efficiency ratio of 1-2 in a wider voltage range, which is very important for the industrial catalytic reaction process driven by unstable renewable energy such as wind power and photovoltaic power, and provides good raw materials for the subsequent Fischer-Tropsch synthesis stage, and has great advantages in actual industrial application.

[0062] At the same time, in order to explore the influence of oxidation on the performance of the catalyst, the present application prepared CoPc / Co@NC without oxidation, and the FE test results are shown in Figure 4 It can be seen that in the range of 0.57-0.77V vs.RHE, the faradic efficiency of H2 and CO of CoPc / Co@NC is about 100%, and the H2 / CO faradic efficiency ratio is 3-5. Compared with CoPc / Co@NC, the product selectivity of the oxidized catalyst CoPc / Co3O4@NC-T is more stable in a wider voltage range, and the catalytic performance (the stability of H2 / CO obtained by catalytic reduction of CO2 under wide voltage load) is better than that of the unoxidized catalyst, which indicates that the synergistic effect of Co3O4 and CoPc is better than that of Co and CoPc in the production of synthesis gas by CO2ER, and the catalytic performance of CoPc / Co3O4@NC-400℃ is the best.

[0063] Four, co With j H2 Test results and analysis

[0064] In order to further explore the catalytic performance of the catalyst at different potentials, the present application tests the partial current density of CO and H2, and the test results are shown in Figure 5 The test results show that when the voltage is in the range of-0.47--0.87V vs.RHE, the jco and j H2 of all samples increase with the increase of the voltage. However, when the applied voltage continues to increase, the jco of CoPc / Co3O4@NC-350℃, CoPc / Co3O4@NC-450℃ and Co3O4@NC-350℃ decreases obviously, and the j H2 rapidly increases. Among all samples, the jco and j H2The rising amplitude is most stable with the increase of the electric potential, and theoretically, the jco / j ratio of the Faraday efficiency should also be very stable, while other samples have more or less catalytic efficiency fluctuations, which corresponds to the FE test results. H2

[0065] In summary, the nanostructure of the catalyst is confirmed by XRD, SEM and other characterization tests, but it is found that the carbon nanotube structure originally used to load the catalyst collapses due to the excessively high oxidation temperature, which theoretically greatly negatively affects the catalytic performance (the stability of H2 / CO obtained by catalytic reduction of CO2 under wide voltage load) of the catalyst. However, the CoPc / Co3O4@NC-350℃ prepared at a lower oxidation temperature has less carbon nanotube collapse, but the catalytic performance is not as good as that of CoPc / Co3O4@NC-400℃. Meanwhile, the actual catalytic performance of CoPc / Co3O4@NC-450℃ prepared at 450℃ is also not ideal. The CoPc / Co3O4@NC-400℃ prepared at 400℃ has the most stable catalytic performance, and the generated synthesis gas H2 / CO value is the most stable and closest to the requirement of industrial application.​

Claims

1. A method for preparing a cobalt-based dual-site catalyst suitable for a wide voltage load, characterized in that, Includes the following steps: (1) Preparation of Co3O4@NC Weigh out cobalt acetylacetone, dicyandiamide, and zinc nitrate, mix them, then weigh out anhydrous ethanol and acetone, add them to the mixture, grind until dry, and dry completely; after drying, grind again; place in a tube furnace, pass N2 into the tube furnace, and then perform stepwise heating and calcination, cool to room temperature with the furnace, take out, and grind. Repeat the above steps several times, and the resulting product is labeled Co3O4@NC; (2) Preparation of Co3O4@NC-T H2SO4 solution was added to Co3O4@NC and the mixture was stirred and acid-washed in an oil bath. After cooling to room temperature, the mixture was centrifuged, washed, and dried to obtain a black powder. The obtained powder was ground and placed in a tube furnace. N2 was introduced into the tube furnace, and the mixture was then calcined. After cooling to room temperature in the furnace, the powder was removed, ground, and then placed back into the tube furnace for oxidation. The resulting product was labeled as Co3O4@NC-T. (3) Preparation of CoPc / Co3O4@NC-T Weigh out Co3O4@NC-T and CoPc, then weigh out anhydrous ethanol and DMF and add them to the mixture. Stir in an oil bath until dry, then grind and place in a tube furnace. Pass N2 into the tube furnace and calcine. After cooling to room temperature in the furnace, remove the mixture to obtain a black powder, which is the catalyst, labeled CoPc / Co3O4@NC-T.

2. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of cobalt acetylacetone, dicyandiamide, and zinc nitrate is 1:3:0.1; the volume ratio of anhydrous ethanol and acetone is 4:

1.

3. The preparation method according to claim 1, characterized in that, The staged heating and calcination method in step (1) is as follows: at 5℃·min -1 The heating rate is as follows: first, the temperature is raised from room temperature to 350℃ and held for 3 hours, then raised to 650℃ and held for 3 hours, and finally raised to 900℃ and held for 1 hour.

4. The preparation method according to claim 1, characterized in that, In step (2), the molar ratio of Co3O4@NC and H2SO4 is 1:

1.

5. The preparation method according to claim 1, characterized in that, In step (2), the oil bath temperature is 80℃ and the time is 5h; the calcination method is: at 5℃·min -1 The heating rate was such that the temperature was raised from room temperature to 900℃ and held for 1 hour.

6. The preparation method according to claim 1, characterized in that, The oxidation method in step (2) is as follows: at 5℃·min -1 The heating rate was such that the temperature was raised from room temperature to 350-450℃ and held for 2 hours.

7. The preparation method according to claim 6, characterized in that, The oxidation method in step (2) is as follows: at 5℃·min -1 The heating rate was such that the temperature was raised from room temperature to 400℃ and held for 2 hours.

8. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of Co3O4@NC-T and CoPc is 2:1; the volume ratio of anhydrous ethanol and DMF is 1:

1.

9. The preparation method according to claim 1, characterized in that, In step (3), the oil bath temperature is 80℃.

10. The preparation method according to claim 1, characterized in that, The calcination method in step (3) is as follows: at 5℃·min -1 The heating rate was such that the temperature was raised from room temperature to 200°C and held for 1 hour.

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