A method for preparing a cobalt-based catalyst for electrocatalytic synthesis of ammonia from nitrate

Abstract

The application relates to the technical field of electrochemical catalysis, and particularly discloses a preparation method of a cobalt-based catalyst for electrocatalytic synthesis of ammonia from nitrate. In the method, melamine is placed in the upstream of ZIF-67 powder, and two-step programmed temperature pyrolysis treatment is carried out under a high-purity nitrogen protection atmosphere. After natural cooling, a cobalt-based catalyst with rhombic carbon as a substrate and Co-NC nanoparticles anchored thereon is obtained. Nitrogen atoms in the prepared catalyst are doped on the surface of cobalt clusters to form Co-NC sites, the local electronic structure of cobalt can be accurately controlled, and the Faraday efficiency and yield of electrocatalytic reduction of nitrate to synthesize ammonia can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of electrochemical catalysis technology, and more specifically, to a method for preparing a cobalt-based catalyst for the electrocatalytic synthesis of ammonia from nitrates. Background Technology

[0002] Ammonia is a crucial chemical feedstock and a potential hydrogen carrier. Currently, industrial ammonia synthesis mainly relies on the Haber-Bosch (HB) process, which consumes large amounts of fossil fuels and generates significant CO2 emissions. Therefore, finding a green and low-carbon ammonia synthesis method is of great importance. Electrocatalytic nitrate reduction (eNO3RR) can utilize renewable energy and can be carried out at room temperature, thus it is considered one of the ideal alternatives to the traditional HB process. However, achieving high NH3 yields and high Faradaic efficiency in electrocatalytic nitrate reduction still faces significant challenges due to the complex 8-electron and 9-proton transfer processes involved in the electrocatalytic nitrate reduction reaction (NO3RR). - +9H + +8e - →NH3+3H2O), and easily produces the byproduct NO2. - The nitrate reduction reaction often involves the presence of a competitive hydrogen evolution reaction (HER), which reduces the selectivity and yield of NH3. Cobalt has abundant unoccupied d orbitals, which are beneficial for the adsorption and activation of nitrate. Surface modification is considered an effective strategy for regulating catalyst performance. By introducing non-metallic atoms, the local electronic structure can be adjusted, creating a cooperative interface, thereby optimizing the adsorption energy of nitrogen-containing intermediates and improving electrochemical stability during the electrocatalytic nitrate reduction reaction. Therefore, a structurally stable NH3-containing intermediate suitable for NO3- reduction was designed and prepared. - The development of highly efficient cobalt-based catalysts for ammonia reduction is an important technical problem that needs to be solved in this field. Summary of the Invention

[0003] To overcome the aforementioned deficiencies of existing technologies, this invention provides a method for preparing a cobalt-based catalyst for electrocatalytic nitrate-to-ammonia synthesis. The method involves a two-step programmed pyrolysis process under high-purity nitrogen protection, allowing nitrogen-containing gaseous species generated from melamine decomposition to be in situ doped onto the surface of cobalt clusters, forming Co-NC sites. This yields a cobalt-based catalyst with a rhombic carbon substrate and Co-NC nanoparticles anchored on the rhombic carbon substrate. This method solves the technical problems of low ammonia yield, low Faraday efficiency, and poor selectivity in existing electrocatalytic nitrate reduction reactions.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a cobalt-based catalyst for electrocatalytic synthesis of ammonia from nitrates includes the following steps: Step 1: Place ZIF-67 powder and melamine separately in a tube furnace, with melamine placed upstream and ZIF-67 powder placed downstream along the direction of high-purity nitrogen flow. Step 2: High-purity nitrogen gas is introduced into the tube furnace, and the pyrolysis process is carried out in stages using a two-step temperature program under the protective atmosphere of high-purity nitrogen gas. After that, it is naturally cooled to room temperature to obtain a cobalt-based catalyst with rhombic carbon as the substrate and Co-NC nanoparticles anchored on the rhombic carbon substrate.

[0005] As a further aspect of the present invention, in step two, the specific process of the two-step programmed heating pyrolysis treatment is as follows: First, the tubular furnace is heated from room temperature to 450°C at a heating rate of 3°C / min. During the heating process, the flow rate of high-purity nitrogen is controlled at 80 sccm. After the temperature reaches 450°C, it is held for 1 hour, and the flow rate of high-purity nitrogen is adjusted to 40 sccm. Then, the temperature is further increased to 800°C at a heating rate of 5°C / min and held for 2 hours. During the holding period at 800°C, the flow rate of high-purity nitrogen is controlled at 30 sccm.

[0006] As a further aspect of the present invention, the mass ratio of ZIF-67 powder to melamine is 1:10.

[0007] A cobalt-based catalyst for the electrocatalytic synthesis of ammonia from nitrate is disclosed. The catalyst uses rhombic carbon as a substrate, with Co-NC nanoparticles uniformly anchored on the substrate. Nitrogen atoms are doped onto the surface of the cobalt clusters to form Co-NC sites. Nitrogen doping precisely modulates the local electronic structure of the Co clusters, promoting the formation of key adsorbed hydrogen intermediates during the reaction and lowering the reaction energy barrier of the rate-determining step. The Co-NC sites redistribute the electronic structure of Co, shifting the d-band center down relative to the Fermi level, thereby weakening the adsorption energy of key nitrogen-containing intermediates and promoting the hydrogenation reaction, thus jointly promoting the production of NO3-. - →NH3 reaction kinetics. Due to the high structural stability and large specific surface area of ​​the rhombic carbon substrate, cobalt nanoparticles can be uniformly dispersed. Through the synergistic integration of the spatial confinement and protection effect of the carbon matrix, combined with the precise control of the local electronic structure of Co, stable active sites are provided for the catalytic reaction.

[0008] As a further aspect of the present invention, the average particle size of the Co-NC nanoparticles is 6.61 nm; the average size of the rhombic carbon substrate is 200 nm.

[0009] A method for electrocatalytic synthesis of ammonia from nitrates, wherein the cobalt-based catalyst is used as the cathode catalyst to carry out the electrocatalytic nitrate reduction reaction in an alkaline electrolyte.

[0010] As a further embodiment of the present invention, the alkaline electrolyte is a 1 mol / L potassium hydroxide solution, wherein the concentration of potassium nitrate in the potassium hydroxide solution is 0.1 mol / L.

[0011] As a further aspect of the present invention, a reversible hydrogen electrode is used as a reference electrode, and the application potential range of electrocatalysis is 0.2V to -0.5V.

[0012] A zinc-nitrate battery, wherein the positive electrode is a cobalt-based catalyst with a rhombic carbon substrate and Co-NC nanoparticles anchored on the rhombic carbon substrate, the negative electrode is a zinc plate, and the electrolyte is a solution containing nitrate.

[0013] As a further aspect of the present invention, the battery simultaneously achieves the reduction of nitrate to ammonia and the output of electrical energy during the discharge process.

[0014] This invention involves a two-step programmed pyrolysis process, placing melamine upstream of ZIF-67 powder and performing the process under high-purity nitrogen protection. This allows nitrogen-containing gaseous species generated from melamine decomposition to be transported to the ZIF-67 powder surface via the gas flow, achieving in-situ controllable doping of cobalt clusters with nitrogen atoms and forming Co-NC sites. These Co-NC sites precisely regulate the local electronic structure of cobalt, shifting the d-band center down relative to the Fermi level, thereby effectively promoting the formation of the key adsorbed hydrogen intermediate (*H) and lowering the reaction energy barrier of the rate-determining step. Compared to existing methods that directly pyrolyze ZIF-67 without introducing a nitrogen source, this invention achieves precise control of nitrogen doping through upstream nitrogen source placement, overcoming the shortcomings of existing technologies where excessively strong adsorption energy of nitrogen-containing intermediates hinders hydrogenation reactions, leading to low ammonia yield and Faraday efficiency.

[0015] The cobalt-based catalyst prepared in this invention, using a reversible hydrogen electrode as a reference electrode, exhibits an ammonia Faradaic efficiency as high as 95.82% and an ammonia yield of 0.989 mmol·h⁻¹. -1 ·cm -2 Six cycles of repeated electrolysis experiments (totaling 18 hours) were conducted at -0.4V, and neither the Faradaic efficiency nor the ammonia yield showed significant decline, demonstrating long-term operational stability. Compared to the control sample without nitrogen doping, the Faradaic efficiency and ammonia yield of the catalyst of this invention were significantly improved, proving that the introduction of Co-NC sites has a clear effect on enhancing the activity and selectivity of electrocatalytic nitrate reduction to ammonia synthesis.

[0016] Compared with existing technologies, the beneficial effects of the method for preparing a cobalt-based catalyst for electrocatalytic synthesis of ammonia from nitrates in this invention are as follows: the upstream nitrogen source arrangement enables precise control of nitrogen doping; in the prepared cobalt-based catalyst, Co-NC nanoparticles are uniformly anchored on a rhombic carbon substrate, with an average particle size of approximately 6.61 nm, and are highly dispersed on the surface of the carbon substrate. Transmission electron microscopy and high-resolution transmission electron microscopy characterization results show that the heterostructure of the Co-NC sites did not change significantly after nitrogen doping, indicating that the rhombic carbon substrate can effectively anchor cobalt clusters, thereby inhibiting their migration and aggregation during the electrocatalytic process. Compared with the problems of easy aggregation of cobalt particles and loss of active sites in existing cobalt-based catalysts, the cobalt-based catalyst of this invention has a more stable structure, which is beneficial for maintaining active sites during long-term electrocatalytic operation. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of a method for preparing a cobalt-based catalyst for electrocatalytic synthesis of ammonia from nitrates according to the present invention.

[0018] Figure 2 These are scanning electron microscope (SEM) images, transmission electron microscope (TEM) images, and high-resolution scanning transmission electron microscope (HRTEM) images of the cobalt-based catalyst in Example 1 of this invention.

[0019] Figure 3 This is an X-ray diffraction pattern of the cobalt-based catalyst in Example 1 of the present invention.

[0020] Figure 4 The images show the X-ray photoelectron spectrum, Raman spectrum, and cobalt K-edge X-ray absorption near-edge structure spectrum of the cobalt-based catalyst in Example 1 of this invention.

[0021] Figure 5 This is a graph showing the electrocatalytic performance of the cobalt-based catalyst in Example 1 of this invention for the reduction of nitrate to ammonia.

[0022] Figure 6 This is an electrochemical stability diagram of the cobalt-based catalyst in Example 1 of the present invention for the electrocatalytic nitrate reduction reaction.

[0023] Figure 7 This diagram illustrates the application of the cobalt-based catalyst in a zinc-nitrate battery, as shown in Example 1 of this invention.

[0024] Figure 8 This is a schematic diagram of the mechanism of electrocatalytic nitrate reduction to ammonia synthesis using a Co-NC catalyst, which is used in the preparation method of a cobalt-based catalyst for electrocatalytic nitrate synthesis of ammonia according to the present invention. Detailed Implementation

[0025] The technical solutions of this embodiment will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0026] Unless otherwise specified, the raw materials and reagents used in this invention are commercially available. The following are some of the raw materials used in the preparation of the examples and their descriptions:

[0027] Example 1

[0028] This embodiment prepares a cobalt-based catalyst with rhombic carbon as the substrate and Co-NC nanoparticles anchored on the rhombic carbon substrate according to the following steps.

[0029] First, ZIF-67 powder was prepared. 5.248 g of 2-methylimidazole was dissolved in 50 mL of methanol and stirred at 500 rpm for 30 min at 25 °C to form a first solution. 1.164 g of Co(NO3)2·6H2O was dissolved in 50 mL of methanol and stirred at 500 rpm for 30 min at 25 °C to form a second solution. The first solution was poured into the second solution, and the mixture was stirred at 700 rpm for 24 h at 25 °C. The resulting mixture was centrifuged at 8000 rpm for 3 min, and the precipitate was washed and dried at 60 °C for 12 h to obtain ZIF-67 powder.

[0030] A two-step programmed pyrolysis treatment was then performed. 0.2g of ZIF-67 powder and 2.0g of melamine were placed separately in quartz boats and loaded into a tube furnace. The quartz boat containing melamine was positioned upstream, and the quartz boat containing ZIF-67 powder downstream, along the direction of high-purity nitrogen flow. High-purity nitrogen was introduced into the tube furnace, and a two-step programmed pyrolysis treatment was performed under a high-purity nitrogen protective atmosphere: First, the tube furnace was heated from room temperature to 450℃ at a heating rate of 3℃ / min, with the high-purity nitrogen flow rate controlled at 80 sccm to maintain a stable protective atmosphere during the heating process; after reaching 450℃, the temperature was held for 1 hour, and the high-purity nitrogen flow rate was adjusted to 40 sccm; then, the temperature was further increased to 800℃ at a heating rate of 5℃ / min and held for 2 hours, with the high-purity nitrogen flow rate controlled at 30 sccm during the 800℃ holding period. After the heat preservation was completed, the mixture was naturally cooled to room temperature to obtain a cobalt-based catalyst with rhombic carbon as the substrate and Co-NC nanoparticles anchored on the rhombic carbon substrate, denoted as Co-NC-10.

[0031] The microstructure and structure of the obtained Co-NC-10 cobalt-based catalyst were characterized. Images obtained using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution scanning transmission electron microscopy (HRSTEM) revealed the following features: Figure 2 As shown, the rhombic carbon substrate in Co-NC-10 has a uniform morphological distribution and a diameter of approximately 200 nm. The rhombic carbon substrate anchors the Co-NC nanoparticles, and the average particle size of the Co-NC nanoparticles is approximately 6.61 nm.

[0032] X-ray diffraction (XRD) analysis was performed on Co-NC-10. Figure 3 Plotting intensity on the ordinate and 2θ on the abscissa shows the diffraction peaks of elemental cobalt. Clearly, the diffraction peaks of Co-NC-10 and Co-NC-0 conform to Co (JCPDS PDF#15-0806), indicating that the Co-NC-10 composite material was successfully synthesized without the presence of other impurity phases.

[0033] Chemical valence state and electronic structure analysis of Co-NC-10. Figure 4 The relevant characterization results are presented. In X-ray photoelectron spectroscopy analysis, the horizontal axis represents binding energy, and the vertical axis represents intensity. The spectrum includes Co 2p, representing the inner-shell electronic state of cobalt atoms; N 1s, representing the electronic state of nitrogen atoms; and C 1s, representing the electronic state of carbon atoms. In the Co 2p spectrum, zero-valent cobalt (Co) was observed. 0 Divalent cobalt (Co) 2+And the satellite peak Sat. In the N 1s spectrum, pyrrole nitrogen was fitted at 399.3 eV, cobalt-nitrogen bond at 399.0 eV, graphitic nitrogen at 400.8 eV, and pyridine nitrogen at 398.6 eV. In the C 1s spectrum, CN bond at 285.4 eV, CC bond at 284.8 eV, OC=O at 290.6 eV, and CO bond at 287.1 eV were fitted. The presence of Co-N and CN bonds indicates that nitrogen atoms were successfully doped into the Co-C interface on the surface of the cobalt cluster, forming Co-NC sites. In Raman spectroscopy analysis, the horizontal axis represents Raman shift, and the vertical axis represents intensity. The spectrum shows a distinct D band representing the degree of defect in the carbon material and a G band representing the degree of order in the carbon atoms. The analysis results indicate that the introduction of Co-NC sites brings more defects, which helps to improve electron transport performance and makes it more favorable for catalytic reactions. In X-ray absorption near-edge structure analysis, the horizontal axis represents energy, and the vertical axis represents normalized absorption intensity. In Fourier transform extended X-ray absorption fine structure analysis, the horizontal axis represents distance, and the vertical axis represents Fourier transform intensity. X-ray absorption near-edge structure (XANES) and Fourier transform extended X-ray absorption fine structure (EXAFS) analyses further elucidated the local coordination environment and chemical state of Co in Co-NC-10 and Co-NC-0. The results showed that nitrogen atoms interact strongly with cobalt atoms on the surface of cobalt clusters, leading to charge transfer and redistribution of electronic structure of Co in Co-NC-10.

[0034] In terms of electrochemical performance testing, the electrocatalytic nitrate reduction performance of Co-NC-10 was evaluated using a three-electrode H-type electrolytic cell with a working electrode area of ​​1 cm². 2 The catalyst loading was 3 mg·cm³. -2 The result is as follows Figure 5 As shown. The linear sweep voltammetric characteristic curve is plotted with the potential relative to a standard reversible hydrogen electrode on the x-axis and the current density on the y-axis. The figure shows the Co-NC-0 without NO3. - Co-NC-0 contains NO3 - Co-NC-10 contains no NO3 - and Co-NC-10 containing NO3 - The current response is shown. The Tafel slope curve is plotted with the logarithm of the current density on the x-axis and the potential relative to the standard reversible hydrogen electrode on the y-axis. The figure records the kinetic parameters of different samples, with the slope of Co-NC-0 being 182.8 mV dec. -1 The slope of Co-NC-10 is 122.4 mV dec. -1 The double-layer capacitance curve is plotted with scan rate on the x-axis and current density on the y-axis. Linear fitting calculations show that the slope of Co-NC-10 is 6.58 mF cm⁻¹. -2The slope of Co-NC-0 is 3.19 mF cm. -2 The Faraday efficiency distribution at different potentials is plotted with the potential relative to the standard reversible hydrogen electrode on the x-axis and the percentage of Faraday efficiency on the y-axis. The results show that the ammonia Faraday efficiency of Co-NC-10 is 95.82 ± 1.29% at -0.4 V. The product conversion analysis plot is plotted with the potential relative to the standard reversible hydrogen electrode on the x-axis and the percentage and ammonia yield on the left and right y-axis, respectively. The figure details NO3... - The conversion rate, NH3 selectivity, and specific ammonia yield were as follows: at a potential of -0.4 V, the ammonia yield of Co-NC-10 was 0.989 ± 0.03 mmol·h⁻¹. -1 ·cm -2 It is significantly superior to Co-NC-0. The comprehensive performance comparison chart, with percentages on the vertical axis, visually demonstrates the NO3 content of Co-NC-0 and Co-NC-10. - Conversion rate, NH3 selectivity, and Faraday efficiency.

[0035] In terms of stability testing, Co-NC-10 was subjected to six consecutive cycles of repeated electrolysis at a potential of -0.4V, for a total of 18 hours. The results are as follows: Figure 6 As shown, the concentration versus time graph is plotted with time on the x-axis and concentration on the y-axis. The graph illustrates the NO3 concentration during the reaction process. - -N, NO2 - The concentrations of -N and NH3-N changed over time. The cycle stability analysis plot uses the number of cycles (n) as the x-axis and percentage and NH3 yield as the left and right y-axis, respectively. The plot clearly records the performance of the NH3 ammonia Faradaic efficiency and NH3 yield from cycle 1 to 6. The results show that neither the Faradaic efficiency nor the ammonia yield showed significant decay. The long-term current stability curve uses time as the x-axis and current density as the y-axis. Under a constant potential of -0.4V relative to the standard reversible hydrogen electrode, the current density remained stable during 40 hours of continuous testing. These results collectively demonstrate that Co-NC-10 possesses long-term operational stability.

[0036] In the application of zinc-nitrate batteries, a zinc-nitrate battery was assembled using Co-NC-10 as the positive electrode, a zinc plate as the negative electrode, and a solution containing nitrates as the electrolyte. Its electrochemical performance was then evaluated. Figure 7 As shown in the schematic diagram of battery operation, NO3 is displayed on the positive electrode side. - The reduction to NH3 and the oxidation of Zn to Zn on the negative electrode side 2+ and release e -The process uses an electrolyte containing KOH + KNO3 and KOH. The zinc-nitrate battery assembled with Co-NC-10 and zinc exhibits a stable open-circuit voltage of 1.34V (relative to Zn / Zn). 2+ The open-circuit voltage curve in the figure is plotted with time on the x-axis and the voltage relative to the zinc reference electrode on the y-axis, with corresponding labels for Co-NC-10: 1.34V and Co-NC-0: 1.22V. The discharge polarization curve is plotted with current density on the x-axis and voltage and power density relative to the zinc reference electrode on the left and right y-axis, respectively. The results show that as the potential becomes more negative, the current density gradually increases, reaching 11.6 mA·cm⁻¹. -2 The current density reached 9.25 mW·cm. -2 The peak power density is shown in the figure as 9.25 mW / cm². -2 This is superior to the 6.18 mW·cm² of the Co-NC-0 assembled battery. -2 The corresponding value in the figure is 6.18 mWcm. -2 This indicates that the assembled zinc-nitrate battery has good energy storage capacity. After discharging for 1 hour at different current densities, the relevant performance graphs are plotted with current density on the x-axis and NH3 production and Faraday efficiency on the left and right y-axis, respectively. With increasing current density, the ammonia production gradually increases, reaching a certain level at 10 mA·cm⁻¹. -2 The current density reached 211.45 μmol·h⁻¹. -1 ·cm -2 The maximum ammonia yield is at 8 mA·cm -2 The maximum Faraday efficiency reached 84.58% at a given current density. The assembled zinc-nitrate battery successfully powered an embedded electronic timer for over 24 hours; the application demonstration photos record the operating times at 0h, 6h, 12h, and 24h. This was achieved at a fixed current density of 8mA·cm⁻¹. -2 In a 15-hour discharge test, the discharge curve was plotted with time on the x-axis and voltage relative to the zinc reference electrode on the y-axis. Simultaneously, a stability histogram was plotted with time on the x-axis and NH3 production and Faraday efficiency on the left and right y-axis, respectively, confirming the battery's excellent durability and long-term stability. This zinc-nitrate battery simultaneously achieves nitrate reduction to ammonia synthesis and electrical energy output during discharge, successfully integrating nitrate reduction to ammonia production with chemical energy-to-electrical energy conversion. It can function as a self-powered electrochemical reactor for removing NO3 pollutants from nitrate-containing wastewater. - While converting into the useful chemical NH3, it also generates usable electricity, providing a new approach for sustainable environmental remediation and energy recovery.

[0037] like Figure 8As shown, the Co-NC catalyst prepared in this invention uses rhombic carbon as a substrate, with cobalt nanoparticles uniformly anchored on the surface of the carbon substrate, and converts NO3 under electrocatalytic conditions. - The nitrogen-doped Co-NC-2.0 is reduced to NH3. Compared with undoped Co-C-2.0, the d-band center of nitrogen-doped Co-NC-2.0 shifts downward relative to the Fermi level. Simultaneously, the Hamiltonian population integral of the crystal orbitals, an indicator of the bonding strength between *NOH and cobalt, increases from -2.43 eV to -1.02 eV. This indicates that nitrogen doping weakens the bonding strength between the key nitrogen-containing intermediate *NOH and the Co site, thereby optimizing the adsorption energy of the reaction intermediate and promoting the reduction of NO3. - The conversion to NH3.

[0038] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0039] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a cobalt-based catalyst for the electrocatalytic synthesis of ammonia from nitrates, characterized in that, Includes the following steps: Step 1: Place ZIF-67 powder and melamine separately in a tube furnace, with melamine placed upstream and ZIF-67 powder placed downstream along the direction of high-purity nitrogen flow. Step 2: High-purity nitrogen gas is introduced into the tube furnace, and a two-step programmed temperature rise method is used to carry out staged pyrolysis under the protective atmosphere of high-purity nitrogen gas. After that, it is naturally cooled to room temperature to obtain a cobalt-based catalyst with rhombic carbon as the substrate and Co-NC nanoparticles anchored on the rhombic carbon substrate. The two-step programmed temperature rise pyrolysis process is as follows: first, the tube furnace is heated from room temperature to 450°C and then held at that temperature, and then the heating rate is increased to continue heating to 800°C and then held at that temperature.

2. The method for preparing a cobalt-based catalyst for electrocatalytic synthesis of ammonia from nitrates according to claim 1, characterized in that, In step two, the specific process of the two-step temperature-increasing pyrolysis treatment is as follows: First, the tubular furnace is heated from room temperature to 450℃ at a heating rate of 3℃ / min. During the heating process, the flow rate of high-purity nitrogen is controlled at 80 sccm. After the temperature reaches 450℃, it is held for 1 hour and the flow rate of high-purity nitrogen is adjusted to 40 sccm. Then, the temperature is continued to rise to 800℃ at a heating rate of 5℃ / min and held for 2 hours. During the holding period at 800℃, the flow rate of high-purity nitrogen is controlled at 30 sccm.

3. The method for preparing a cobalt-based catalyst for electrocatalytic synthesis of ammonia from nitrates according to claim 1, characterized in that, The mass ratio of ZIF-67 powder to melamine is 1:

10.

4. A cobalt-based catalyst for the electrocatalytic synthesis of ammonia from nitrates, characterized in that, The cobalt-based catalyst is prepared by the method described in any one of claims 1-3 for preparing a cobalt-based catalyst for electrocatalytic synthesis of ammonia from nitrates. The cobalt-based catalyst uses rhombic carbon as a substrate, with Co-NC nanoparticles anchored on the rhombic carbon substrate and nitrogen atoms doped on the surface of cobalt clusters to form Co-NC sites.

5. A cobalt-based catalyst for electrocatalytic synthesis of ammonia from nitrates according to claim 4, characterized in that, The average particle size of the Co-NC nanoparticles is 6.61 nm; the average size of the rhombic carbon substrate is 200 nm.

6. A cobalt-based catalyst for electrocatalytic synthesis of ammonia from nitrates according to claim 4, characterized in that, The cobalt-based catalyst described above is used as the cathode catalyst to carry out an electrocatalytic nitrate reduction reaction in an alkaline electrolyte, which is used for the electrocatalytic synthesis of ammonia from nitrate.

7. A cobalt-based catalyst for electrocatalytic synthesis of ammonia from nitrates according to claim 6, characterized in that, The alkaline electrolyte is a 1 mol / L potassium hydroxide solution, and the concentration of potassium nitrate in the potassium hydroxide solution is 0.1 mol / L.

8. A cobalt-based catalyst for the electrocatalytic synthesis of ammonia from nitrates according to claim 6, characterized in that, Using a reversible hydrogen electrode as a reference electrode, the application potential range of the electrocatalysis is 0.2V to -0.5V.

9. A zinc-nitrate battery, characterized in that, The positive electrode of the battery uses a cobalt-based catalyst for electrocatalytic synthesis of ammonia from nitrates as described in claim 4, the negative electrode uses a zinc plate, and the electrolyte is a solution containing nitrates.

10. A zinc-nitrate battery according to claim 9, characterized in that, The battery simultaneously achieves the reduction of nitrates to ammonia and the output of electrical energy during the discharge process.

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