A preparation method of a pyrazole type trinuclear cobalt-based catalyst

Abstract

The present application relates to the technical fields of catalyst design and ammonia synthesis, and discloses a preparation method of a pyrazole trinuclear cobalt-based catalyst, which comprises the following steps: step 1, dissolving a metal cobalt compound in water to obtain a first mixed solution, dissolving a pyridine molecule in a mixed organic solution to obtain a second mixed solution, mixing and stirring the first mixed solution and the second mixed solution, and then transferring the mixture to a high-vacuum reaction tube, and then placing the high-vacuum reaction tube in an oil bath to perform a solvothermal reaction; step 2, after the solvothermal reaction is completed, washing, centrifuging and drying the obtained substance to obtain a trinuclear cobalt-based compound powder. The present application uses nitrate as a nitrogen source, a pyrazole cobalt-based compound as a catalyst, and a mixture of potassium sulfate and potassium nitrate as an electrolyte, and effectively synthesizes ammonia through electrochemical reduction. The catalyst exhibits high Faraday efficiency and high yield under high-concentration nitrate conditions.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of catalyst design and ammonia synthesis, and particularly relates to a preparation method of a pyrazole-based trinuclear cobalt catalyst. BACKGROUND

[0002] Ammonia (NH3) is a high-value chemical product, widely used in the fields of nitrogen fertilizer production, drug synthesis, etc., and is a hope for a new generation of hydrogen-rich fuel. Industrial ammonia synthesis mainly uses the Haber-Bosch process technology to realize ammonia synthesis by using nitrogen and hydrogen as raw materials under high temperature and high pressure. However, this not only consumes 1-2% of the global energy, but also emits about 1.5% of the global carbon dioxide, so it is urgent to develop a sustainable alternative route for NH3 synthesis. With industrial pollution and overuse of chemical fertilizers, nitrate is the main pollutant of groundwater and has been accumulating in the water cycle system. As one of the most dangerous pollutants in the environment, incomplete conversion of nitrate in the body can produce nitrosamine, causing liver damage and inducing cancer and other diseases.

[0003] Electrochemical reduction of NO 3− by electricity generated from renewable energy sources such as solar and wind energy can not only provide a double benefit of solving environmental pollution and reducing energy consumption, but also produce high-value chemicals without carbon dioxide emissions, showing an ideal way of resource saving and environmental friendliness. Nitrate reduction involves a 9-proton coupled 8-electron transfer process, which is not only slow in reaction kinetics, but also can generate various nitrogen-containing oxidation state products (such as NO x , NO 2− , N2, hydrazine, hydroxylamine and ammonia). In addition, since the reaction potential of NO 3− conversion to NH3 is usually lower than that of hydrogen evolution reaction (HER), part of the electrons from the donor will be consumed by HER, thereby reducing the NH3 yield and the Faraday efficiency is low. Therefore, in order to achieve high-efficiency catalysis at high current density, it is particularly crucial to optimize the catalyst material and improve the electrocatalytic system to electrochemically reduce nitrate to generate ammonia. Developing high-efficiency new catalysts is not only a key step to accelerate the process of electrochemical reduction of nitrate to ammonia, but also an effective way to promote the strategy of green nitrogen cycle. SUMMARY

[0004] To solve the technical problems proposed in the background, the application provides a preparation method of a pyrazole-based trinuclear cobalt catalyst.

[0005] The application adopts the following technical scheme: a preparation method of a pyrazole-based trinuclear cobalt catalyst

[0006] comprising the following steps:

[0007] Step 1, a metal cobalt compound is dissolved in water to obtain a first mixed solution, and a pyrazole molecule is dissolved in a mixed organic solution to obtain a second mixed solution, the first mixed solution and the second mixed solution are mixed and stirred, and then transferred to a high vacuum reaction tube, and then placed in an oil bath pot for solvothermal reaction;

[0008] Step 2, after the solvothermal reaction is completed, the obtained material is washed, centrifuged and dried to obtain a trinuclear cobalt-based compound powder.

[0009] As a further improvement of the above scheme, the metal cobalt compound is at least one of cobalt chloride, cobalt bromide, cobalt iodide, cobalt sulfate, cobalt acetate, cobalt nitrate, cobalt carbonate and a hydrate thereof;

[0010] The pyrazole molecule is at least one of pyrazole, 4-nitro-pyrazole, 4-methoxy-1H-pyrazole, pyrazole-4-carboxaldehyde, 4-iodopyrazole, 4-chloropyrazole, 4-bromopyrazole, 4-methyl-1H-pyrazole and 4-cyanopyrazole;

[0011] The mixed organic solution is at least one of a mixed solution of ethanol and dichloromethane, a mixed solution of ethanol and N,N-dimethylformamide, a mixed solution of dichloromethane and N,N-dimethylformamide, and a mixed solution of methanol and N,N-dimethylformamide;

[0012] The volume ratio of the water and the mixed organic solution is 5:5:5, 5:6.2:6.2, 5:7.6:7.6 or 5:6.7:6.7;

[0013] The molar ratio of the metal cobalt compound and the pyrazole molecule is 1:0.53, 1:0.73, 1:0.83, 1:0.95 or 1:1;

[0014] In step 1, the stirring time is 0.5-2h, the oil bath heating temperature is 80-140℃, and the solvothermal reaction time is 8-30h;

[0015] In step 2, the washing solution is at least one of ethanol, methanol, dichloromethane and acetone;

[0016] In step 2, the centrifugal speed is 5000-12000rpm, and the centrifugal time is 1-15min.

[0017] The electrode material comprises a pyrazole trinuclear cobalt-based catalyst prepared by the above method, a carbon material and a carbon cloth.

[0018] The application provides a preparation method of the electrode material, and the pyrazole-based trinuclear cobalt catalyst, carbon material and the mixed solution of the organic solvent and Nafion 117 are taken and dispersed in an ultrasonic dispersion machine for 1 h to obtain a uniformly dispersed mixed solution, 50 uL of the uniformly dispersed mixed solution is taken by using a pipette, and the mixed solution is drop-coated on the pretreated carbon cloth with an area of 1x1 cm -2 , and then the carbon cloth coated with the mixed solution is dried to obtain the electrode material.

[0019] Preferably, the organic solvent is at least one selected from ethanol, isopropanol and methanol.

[0020] The mass fraction of the Nafion 117 dispersion solution is 5-20 wt%.

[0021] The ratio of the Nafion 117 dispersion solution, the pyrazole-based trinuclear cobalt catalyst and the carbon material is 20-100 muL:3.5 mg:1.5 mg.

[0022] The application provides an electrochemical catalytic system, the electrode material prepared by the above scheme is used as a working electrode, a platinum sheet electrode and an Ag / AgCl electrode are used as a counter electrode and a reference electrode respectively, and the catalytic system further comprises a reaction electrolyte and a reaction device.

[0023] Preferably, the reaction electrolyte is at least one selected from KOH aqueous solution, K2CO3 aqueous solution, KHCO3 aqueous solution, K2SO4 aqueous solution and Na2SO4 aqueous solution; the concentration of the reaction electrolyte is 0.1-1.0 M; and the reaction device is an H-shaped electrolytic cell.

[0024] The application provides an application of the electrode material, and the electrode material is used as an electrocatalyst to detect and reduce ammonia in a wide range of concentrations.

[0025] A method for efficiently reducing ammonia by using a pyrazole-based trinuclear cobalt catalyst, comprising the following steps.

[0026] Step one, detecting and converting nitrate into ammonia by using a simple and clean electrochemical method;

[0027] Step two, synthesizing a pyrazole-based trinuclear cobalt catalyst by using the above method;

[0028] Step three, the electrode material prepared by using the above method;

[0029] Step four, obtaining a linear graph of nitrate concentration and reduction peak current value by linear sweep voltammetry (LSV) test under a three-electrode system, so as to realize conversion of nitrate in a wide range of concentrations.

[0030] Step five, high Faraday efficiency, high ammonia selectivity and high nitrate electrocatalytic synthesis of ammonia in a wide range of nitrate solution concentration.

[0031] As a further improvement of the above scheme: the electrolyte is a mixture of 0.5M K2SO4 and 0.1M KNO3; the reaction potential is 0~ -1.0V vs. RHE; the reaction time is 0.2~10h. Wherein, the wide range of nitrate concentration is 0.5~200g / L -1 .

[0032] Compared with the prior art, the beneficial effects of the present application are:

[0033] The present application uses nitrate as a nitrogen source, a pyrazole cobalt-based compound as a catalyst, and a mixture of potassium sulfate and potassium nitrate as an electrolyte to effectively synthesize ammonia by electrochemical reduction. The catalyst exhibits high Faraday efficiency and high yield under high concentration of nitrate.

[0034] The flower-shaped catalytic electrode material composed of nanospheres, nanochalices and nanosheets designed in the present application has low cost, high active area, can effectively enrich nitrate, and realize the conversion of ultra-high concentration of nitrate and the efficient synthesis of ammonia.

[0035] The present application provides a solid foundation for the industrialization of ammonia synthesis and the efficient promotion of global nitrogen cycle, and opens up new possibilities for its industrial development. The innovation of using nitrate in wastewater as a nitrogen source not only optimizes the environment, but also has significant commercial potential, and has a profound impact on forming a resource-saving and environment-friendly society. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is the scanning electron microscope (SEM) and transmission electron microscope (TEM) images of Co3(OCH3)3 prepared in the present application. Among them Figure 1 (a) is the SEM image, Figure 1 (b) is the TEM image;

[0037] Figure 2 is the scanning electron microscope (SEM) and transmission electron microscope (TEM) images of Co3(CHO)3 prepared in the present application. Among them Figure 2 (a) is the SEM image, Figure 2 (b) is the TEM image;

[0038] Figure 3 is the scanning electron microscope (SEM) and transmission electron microscope (TEM) images of Co3(NO2)3 prepared in the present application. Among them Figure 3 (a) is the SEM image, Figure 3 (b) is the TEM image;

[0039] Figure 4 X-ray diffraction (XRD) patterns of Co3(OCH3)3, Co3(CHO)3and Co3(NO2)3;

[0040] Figure 5 X-ray photoelectron spectroscopy (XPS) patterns of Co3(OCH3)3, Co3(CHO)3and Co3(NO2)3;

[0041] Figure 6 Ammonia polarization current density plots of Co3(OCH3)3, Co3(CHO)3and Co3(NO2)3;

[0042] Figure 7 Faradaic efficiency plots of Co3(OCH3)3, Co3(CHO)3and Co3(NO2)3;

[0043] Figure 8 Yield plots of Co3(OCH3)3, Co3(CHO)3and Co3(NO2)3.

[0044] Figure 9 Yield and Faradaic efficiency plots of Co3(OCH3)3, Co3(CHO)3and Co3(NO2)3in the catalytic synthesis of NH3at NO3 - concentration of 0.1-200 gL -1 concentration of 0.1-200 gL

[0045] Figure 10 Cycle stability of Co3(OCH3)3, Co3(CHO)3and Co3(NO2)3in the cyclic synthesis of NH3for 10 consecutive cycles, respectively. DETAILED DESCRIPTION

[0046] The application will be further described below in conjunction with the drawings and specific embodiments. It should be noted that the following described embodiments or technical features can be combined in any manner to form new embodiments without conflict.

[0047] The experimental methods in the following examples are all conventional methods, and are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions, unless otherwise specified. The materials, reagents, etc. used in the following examples can be obtained from commercial sources, unless otherwise specified.

[0048] Example 1:

[0049] Taking the preparation of Co3(NO2)3 catalyst as an example, firstly, 200 mg of Co(NO3)2·6H2O was dissolved in 5 mL of deionized water and stirred continuously to form a uniform pink solution. 98 mg of 4-methoxy-1H-pyrazole was dissolved in a mixed solution of 13.4 mL of ethanol and N,N-dimethylformamide. The Co(NO3)2·6H2O solution was slowly added dropwise to the 4-methoxy-1H-pyrazole solution while stirring continuously for 1 h. Then, the solution was transferred to a high-vacuum reaction tube, sealed, and solvated at 100 °C for 12 h, followed by natural cooling to room temperature. Subsequently, the solution was separated by centrifugation, washed multiple times with acetone solution, and vacuum dried at 60 °C for 12 h to obtain an orange-red powder, Co3(OCH3)3.

[0050] Example 2:

[0051] Under the conditions of Example 1, 4-methoxy-1H-pyrazole was replaced with pyrazole-4-carboxaldehyde, and everything else was the same as in Example 1. The resulting catalyst material was analyzed by scanning electron microscopy and high-resolution transmission electron microscopy.

[0052] Example 3:

[0053] Under the conditions of Example 1, 4-methoxy-1H-pyrazole was replaced with 4-nitropyrazole, and everything else was the same as in Example 1. The resulting catalyst material was analyzed by scanning electron microscopy and high-resolution transmission electron microscopy.

[0054] Example 4: Electrochemical Catalytic Synthesis of Ammonia from Nitrate

[0055] This scheme also proposes an electrode preparation method, which involves weighing 3.5 mg of the described electrocatalyst and 1.5 mg of...

[0056] Carbon material was dispersed in a mixed solution of organic solvent and Nafion 117, and ultrasonically dispersed for 1 hour to obtain a uniformly dispersed mixture. 50 μL of the uniformly dispersed mixture was measured using a 100 μL pipette and drop-coated onto a 1 x 1 cm² area. -2 The pretreated carbon cloth was dried at room temperature, with an actual catalyst loading of 0.16 mg / cm³ for each electrode. -2 .

[0057] The organic solvent is selected from at least one of the following: ethanol, isopropanol, methanol, preferably isopropanol;

[0058] The mass fraction of the Nafion 117 dispersion is 5~20wt%;

[0059] The ratio of the Nafion 117 dispersion to the catalyst and carbon material is 20-100 μL: 3.5 mg; 1.5 mg;

[0060] All electrochemical experiments were performed using an electrochemical workstation (CHI760E, Shanghai Chenhua Instrument Co. Ltd.). Electrolysis experiments were carried out in a H-type electrolysis cell with a volume of 100 mL at room temperature under a three-electrode system. The three electrodes were composed of a working electrode, an Ag / AgCl reference electrode and a platinum plate counter electrode. A saturated potassium chloride solution was added to the reference electrode.

[0061] In the experiment, Nafion117 proton exchange membrane was used to separate the cathode and anode. The electrolyte of the anode and cathode was 30 mL of 0.5M K2SO4 and 0.1M KNO3 mixed aqueous solution. The electrolyte was purged with Ar for at least 0.5h to remove oxygen in the electrolyte. The liquid product was detected by ultraviolet spectrophotometer (UV-vis, Shimadzu UV-1900).

[0062] Example 5:

[0063] The method for detecting high-concentration nitrate and efficiently reducing ammonia provided in the present scheme comprises the following steps:

[0064] Step one, using a simple and clean electrochemical method to reduce nitrate to synthesize ammonia;

[0065] Step two, using the electrode as described in Example 4;

[0066] Step three, under a three-electrode system, a linear graph of nitrate concentration and reduction peak current value is obtained by linear sweep voltammetry (LSV) test. The electrolyte in the anode area is kept unchanged, and the electrolyte in the cathode area is configured to contain or not contain nitrate solution, and the test is carried out under room temperature and normal pressure. The main test method is LSV, and the applied voltage range is 0V vs. RHE to-1.0V vs. RHE. As shown in Figure 6 , it is the comparison of LSV curves of different pyrazole-based trinuclear cobalt catalysts catalyzing nitrate reduction. Compared with Co3(NO2)3, Co3(CHO)3, Co3(OCH3)3 and pure ligand, Co3(NO2)3 has larger current density, which indicates that it has good nitrate reduction activity and excellent selectivity to ammonia. By controlling the constant voltage, the electrochemical performance is determined, and the same reaction charge amount is controlled each time. The electrolyte after reaction is diluted within the testable range, and the salicylic acid-hypochlorite colorimetric method is used to determine the concentration of ammonia in the solution. Compared with other materials, the catalytic activity of Co3(NO2)3 is the highest. The faradic efficiency of ammonia can reach 97% at a potential of-0.5V vs. RHE after 0.5h of reaction, and the partial current density of ammonia can reach 315mAcm -2 -2 -1 -2 cat -1 As shown in Figure 7 and Figure 8The high Faraday efficiency and high yield under high current density are realized at the same time.

[0067] It is found by screening different pyrazole substituents that the electron-withdrawing nitro group can promote the conversion of nitrate to nitrite, and further promote the generation of ammonia.

[0068] Result analysis:

[0069] Figure 1 For scanning electron microscope analysis of Co3(OCH3)3 prepared in Example 1, as shown in Figure 1 (a), Co3(OCH3)3 presents a regular spherical shape, as shown in Figure 1 (b), the high-resolution transmission electron microscopy test results show that it is a spherical structure.

[0070] Figure 2 For scanning electron microscope analysis of Co3(CHO)3 catalytic electrode material prepared in Example 2, as shown in Figure 2 (a), Co3(CHO)3 catalytic electrode material presents a sea urchin structure, as shown in Figure 2 (b), the high-resolution transmission electron microscopy test results also confirm the sea urchin structure.

[0071] Figure 3 For scanning electron microscope analysis of Co3(NO2)3 catalytic electrode material prepared in Example 1, as shown in Figure 3 (a), Co3(NO2)3 catalytic electrode material presents a flaky nanoflower structure, as shown in Figure 3 (b), the high-resolution transmission electron microscopy test results also confirm the flaky structure.

[0072] Figure 4 For X-ray diffraction analysis of Co3(OCH3)3, Co3(CHO)3 and Co3(NO2)3 materials prepared in Example 1, Example 2 and Example 3, the results confirm the successful preparation of the three pyrazole cobalt-based catalysts, and the crystal structure and high purity of the catalysts synthesized in Example 1, Example 2 and Example 3.

[0073] Figure 5 For X-ray photoelectron spectroscopy analysis of Co3(OCH3)3, Co3(CHO)3 and Co3(NO2)3 catalytic electrode materials prepared in Example 1, Example 2 and Example 3, the surface composition and chemical state of the obtained product samples are studied, and the Co2p high-resolution XPS spectra of Co3(OCH3)3, Co3(CHO)3 and Co3(NO2)3 catalysts are shown in Figure 5 In Figure 5 , the two peaks of Co3(OCH3)3 at 781.7e and 796.7eV are attributed to Co2+ Co2p 3 / 2 and Co2p 1 / 2 When -OCH3 is replaced by electron-withdrawing -CHO and -NO2, Co 2+ The binding energies shifted positively by approximately 0.858 eV and 0.359 eV, respectively, indicating that the oxidation state of Co decreased and its reducing power increased.

[0074] Figure 6 To compare the LSV curves of the Co3(OCH3)3, Co3(CHO)3 and Co3(NO2)3 catalytic electrode materials and their corresponding ligands prepared in Examples 1, 2 and 3 in 0.5M K2SO4 and 0.1M KNO3 solutions, Co3(NO2)3 showed the highest catalytic activity, indicating that it has excellent electrocatalytic performance in reducing hypernitrate to ammonia.

[0075] Figure 7 and 8 The FE diagram and ammonia production yield diagram are shown for the Co3(OCH3)3, Co3(CHO)3, and Co3(NO2)3 and their corresponding ligand catalytic electrode materials prepared in Examples 1, 2, and 3, after electrolysis in 0.5 Mk2SO4 and 0.1 MkNO3 solutions for 0.5 h. The Faradaic efficiency of ammonia reaches 97% after 0.5 h at a potential of -0.5 V vs. RHE, and the deviatoric current density of ammonia can reach 315 mA / cm². -2 The yield reached 24.4 mgh. -1 mg cat -1 ,like Figure 7 and Figure 8 As shown, this simultaneously achieves high Faradaic efficiency and high yield at high current densities.

[0076] Figure 9 To investigate the effects of the Co3(OCH3)3, Co3(CHO)3, and Co3(NO2)3 catalytic electrode materials prepared in Examples 1, 2, and 3 on NO3... - Concentration range: 0.1–200 g / L -1 The catalytic synthesis of NH3 yield and Faraday results are shown in the figure. The yield and Faraday ratio of NH3 are shown as the nitrate nitrogen concentration increases from 0.1 to 200 g / L. -1 With the increase of [amount], the ammonia production rate and the corresponding FE [product] show an upward trend. (10gL) -1 The maximum FE reached 97%, and the ammonia production rate was 24.4 mgh. -1 mg cat -1. Under the condition of extreme nitrate pollution, it can replace the high-efficiency nitrate reduction solution. In addition, under high nitrate concentration, the conversion rate of the cationic method is usually limited. At higher concentrations, close to the saturation of nitrate in water, the NH3 yield of Co3(NO2)3 (33.20 mgh -1 mg cat -1 .) and FE (90.53%) are limited due to the limited supply of protons, and part of the reduction product NO2 - . Under the condition of ultra-high nitrate concentration (200 gL -1 ), Co3(NO2)3 still maintains a high FE (> 90%) for ammonia, and the NH3 yield (31.06 mgh -1 mg cat -1 ) of Co3(NO2)3. It shows that the catalytic electrode material prepared in the present application can realize the reduction of high-concentration nitrate to produce ammonia.

[0077] Figure 10 The Co3(OCH3)3, Co3(CHO)3 and Co3(NO2)3 prepared in Example 1, Example 2 and Example 3 were subjected to 10 cycles of electrocatalytic reduction of nitrate to synthesize ammonia, as shown in Figure 10 . Figure 10 a is the ammonia yield and Faraday efficiency diagram of Co3(OCH3)3 after 10 cycles of electrocatalytic reduction of nitrate to synthesize ammonia. Figure 10 b is the NH3 yield and Faraday efficiency diagram of Co3(CHO)3 after 10 cycles of electrocatalytic reduction of nitrate to synthesize ammonia. Figure 10 c is the NH3 yield and Faraday efficiency diagram of Co3(NO2)3 after 10 cycles of electrocatalytic reduction of nitrate to synthesize ammonia. The NH4 + concentration was determined by i-t test at a potential of -0.5 V vs. RHE for 10 times, and salicylic acid-hypochlorite colorimetric method was used to evaluate the cycle stability of the material, from Figure 10 It can be seen from the above table that after 10 cycles, the NH3 yield and Faraday efficiency of Co3(NO2)3 catalyst tend to be stable, which can prove that the Co3(NO2)3 catalyst material has good cycle stability.

[0078] The Faraday efficiency and ammonia yield of ammonia in the examples of the present application are determined by salicylic acid-hypochlorite colorimetric method, which involves the following formula: the Faraday efficiency formula of ammonia is FE = (8 x F x C NH3 x V) / (M NH3-N x Q) x 100%, and the ammonia yield formula is NH3 yield = (C NH3 x V / S x t), wherein 8 is the number of transferred electrons, F is the Faraday constant (96485 Cmol-1 ), C NH3 NH3 concentration measured by UV-visible absorption spectrum, V is electrolyte volume (L), M NH3-N is the relative molecular mass of N (gmol -1 ), Q is the charge quantity (C), S is the electrode area (cm -2 ), t is the reaction time (h).

[0079] The above embodiments are only preferred embodiments of the present application, and cannot be used to limit the scope of protection of the present application. Any non-essential changes and substitutions made by those skilled in the art on the basis of the present application shall fall within the scope of protection of the present application.

Claims

1. A method for preparing a pyrazole-based trinuclear cobalt-based catalyst, characterized in that, Includes the following steps: Step 1: Dissolve the cobalt metal compound in water to obtain a first mixture, and dissolve the pyrazole molecules in a mixed organic solution to obtain a second mixture. Mix and stir the first and second mixtures and transfer them to a high vacuum reaction tube, and then place them in an oil bath for a solvothermal reaction. Step 2: After the solvothermal reaction is complete, the obtained substance is washed, centrifuged, and dried to obtain trinuclear cobalt-based compound powder; The cobalt compound is selected as cobalt nitrate hexahydrate; The pyrazole molecule is selected from at least one of 4-nitropyrazole, 4-methoxy-1H-pyrazole, and pyrazole-4-carboxaldehyde; The mixed organic solution is selected from at least one of the following: a mixed solution of ethanol and dichloromethane, a mixed solution of ethanol and N,N-dimethylformamide, a mixed solution of dichloromethane and N,N-dimethylformamide, and a mixed solution of methanol and N,N-dimethylformamide. The volume ratio of the water to the mixed organic solution is 5:5:5, 5:6.2:6.2, 5:7.6:7.6, or 5:6.7:6.

7. The molar ratio of the cobalt metal compound to the pyrazole molecule is 1:0.53, 1:0.73, 1:0.83, 1:0.95 or 1:1; In step 1, the stirring time is 0.5~2h; the oil bath heating temperature is 80~140℃; and the solvothermal reaction time is 8~30h. In step 2, the washing solution is at least one of ethanol, methanol, dichloromethane, and acetone; In step 2, the centrifugation speed is 5000~12000 rpm and the centrifugation time is 1~15 min.

2. An electrode material comprising a pyrazole-based trinuclear cobalt-based catalyst prepared by the method of claim 1, a carbon material, and carbon cloth.

3. A method for preparing the electrode material as described in claim 2, comprising weighing carbon material and the pyrazole-based trinuclear cobalt-based catalyst prepared by the method as described in claim 1, and dispersing them in a mixed solution of organic solvent and Nafion 117, ultrasonically dispersing for 1 h to obtain a uniformly dispersed mixture, and using a pipette to measure 50 μL of the uniformly dispersed mixture and drop-coating it onto an area of ​​1 x 1 cm². -2 The electrode material is prepared by drying the pretreated carbon cloth coated with the mixed solution.

4. The method for preparing the electrode material as described in claim 3, characterized in that, in, The organic solvent is selected from at least one of the following: ethanol, isopropanol, and methanol; The mass fraction of the Nafion 117 dispersion is 5-20 wt%. The ratio of the Nafion 117 dispersion to the pyrazole-based trinuclear cobalt-based catalyst and carbon material is 20-100 μL: 3.5 mg: 1.5 mg.

5. An electrochemical catalytic system, characterized in that, Using the electrode material described in claim 2 as the working electrode, and a platinum sheet electrode and an Ag / AgCl electrode as the counter electrode and specific electrode, respectively, the catalytic system further includes a reaction electrolyte and a reaction apparatus.

6. The electrochemical catalytic system as described in claim 5, characterized in that: The reaction electrolyte is selected from at least one of the following: KOH aqueous solution, K2CO3 aqueous solution, KHCO3 aqueous solution, K2SO4 aqueous solution, and Na2SO4 aqueous solution; the concentration of the reaction electrolyte is 0.1-1.0M; and the reaction apparatus is an H-type electrolytic cell.

7. The application of the electrode material as described in claim 2, characterized in that, As an electrocatalyst, it enables the detection of nitrate ions over a wide range of concentrations and efficient ammonia production through reduction.

8. A method for efficient reduction of ammonia using a pyrazole-based trinuclear cobalt-based catalyst, characterized in that: Includes the following steps: Step 1: Use a simple and clean electrochemical method to detect and convert nitrates into ammonia; Step 2: Synthesize a pyrazole-based trinuclear cobalt-based catalyst using the method described in claim 1; Step 3: Using the electrode material prepared by the method described in claim 3 or 4; Step 4: In a three-electrode system, a linear sweep voltammetry (LSV) test is performed to obtain a linear graph of nitrate concentration versus reduction peak current, thereby achieving the conversion of nitrate concentrations over a wide range. Step 5: Achieve high Faradaic efficiency and high ammonia selectivity in the electrocatalytic synthesis of ammonia from nitrate ions under a wide range of nitrate concentration solutions.

9. The method for efficient reduction of ammonia using a pyrazole-based trinuclear cobalt-based catalyst as described in claim 8, characterized in that: The electrolyte was a mixed solution of 0.5 Mk₂SO₄ and 0.1 MkNO₃; the reaction potential was 0 to -1.0 V vs. RHE; the reaction time was 0.2 to 10 h; and the nitrate concentration ranged from 0.5 to 200 g / L. -1 .

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