Preparation method of manganese-doped nickel molybdate material and application of manganese-doped nickel molybdate material in preparation of nitrate through electro-catalytic ammoxidation

Abstract

The invention discloses a preparation method of a manganese-doped nickel molybdate material and application of the manganese-doped nickel molybdate material in preparation of nitrate through electro-catalytic ammoxidation, and belongs to the field of ammoxidation catalytic materials. A manganese-doped nickel molybdate electrode material is prepared by taking a sodium molybdate (Na2MoO4) aqueous solution as a molybdenum source and a mixed aqueous solution of nickel chloride and manganese chloride as a metal source through a simple chemical precipitation method, the manganese-doped nickel molybdate electrode material is used for synthesizing nitrate through electrocatalytic ammoxidation, and gamma-NiOOH is determined as an active substance in the ammoxidation process. The introduction of manganese accumulates more active Ni < 3 + > species, so that the nucleophilic attack of NH3 to the Ni < 3 + > site becomes more favorable, thereby optimizing the performance of electrocatalytic ammoxidation into nitrate, and the activity and reaction selectivity are far higher than those of a single component. The manganese-doped nickel molybdate material is simple in preparation process, low in cost, good in repeatability, suitable for large-scale industrial production and high in selectivity; the development of a next generation of ammoxidation electrocatalyst can be powerfully promoted.

Description

Technical Field

[0001] The present invention belongs to the field of nano-catalytic materials, and particularly relates to a preparation method of an efficient and stable manganese-doped nickel molybdate electrocatalyst and its application in electrocatalytic ammonia oxidation to nitrate. Background Art

[0002] Electrocatalytic ammonia oxidation plays a crucial role in the fields of environmental remediation and energy storage. The electrochemical oxidation of ammonia can convert ammonia in wastewater into nitrite and nitrate to reduce water pollution. At the same time, nitrate is an important chemical, usually industrially produced by the Ostwald process. This process relies on precious metals (such as platinum and rhodium) and is carried out under high temperature (600 - 800 °C) and high pressure (410 - 1000 kPa) conditions, accompanied by a large amount of energy consumption and carbon dioxide emissions. The electrocatalytic ammonia oxidation reaction provides a more energy-saving and environmentally friendly alternative. At normal temperature and pressure, NH3 is oxidized at the anode to produce the value-added chemical NO3 - , while H2 can be produced at the cathode as a useful by-product. Therefore, designing a catalyst with high activity, high selectivity, and high stability is the key to solving this problem.

[0003] Abundant transition metals (TM) in the earth's crust (such as Fe, Co, and Ni) have unique electronic structures, with adjustable d orbitals and rich outer d electrons. Among them, solid-state material catalysts have the advantages of being easy to fix on the electrode surface, having high catalytic activity, and large current density. The most common solid-state material catalysts are non-precious metal transition metal oxides, and among non-precious metal transition metal oxides, nickel molybdate is the most common. It has rich reserves, low cost, and great potential for application in future industrialization. However, the poor conductivity and intrinsic activity of nickel molybdate itself limit its further development in the catalytic field. Summary of the Invention

[0004] The present invention aims to prepare a manganese-doped nickel molybdate material (Ni 50 Mn 50-s MoO4) and use it for electrocatalytic ammonia oxidation to synthesize nitrate. This catalyst is simple to prepare, the metal content is adjustable, and it has high research value in the field of electrocatalytic synthesis of nitrate. To achieve the above object, the present invention adopts the following specific technical solutions: One object of the present invention is to provide a preparation method of a manganese-doped nickel molybdate catalyst, comprising the following steps (a) Dissolve nickel chloride and manganese chloride in deionized water to form solution A; (b) Dissolve Na2MoO4 in deionized water to form solution B; (c) Rapidly add solution B to solution A and stir for 10 min. Under room temperature conditions, let it stand to obtain a yellowish-green precipitate. Allow the mixture to age for 24 h, wash, centrifuge to collect, and vacuum dry to obtain a yellowish-green powdered Ni 50 Mn 50-s MoO4.

[0005] Furthermore, this solution includes the following steps: (a) Mix nickel chloride and manganese chloride and dissolve them in deionized water to form solution A. The sum of the concentrations of nickel chloride and manganese chloride in solution A is 1 mol L -1 ; (b) Dissolve Na2MoO4 in deionized water to form solution B. The concentration of Na2MoO4 in solution B is 1 molL -1 ; (c) Rapidly add solution B to solution A and stir. Under room temperature conditions, let it stand to obtain a yellowish-green precipitate. At this time, stop stirring. Allow the mixture to age for 24 h, wash, centrifuge to collect, and vacuum dry to obtain a nickel-doped manganese molybdate catalyst. The sample is named Ni x Mn (100-x)-s MoO4 where x is 20, 40, 50, 60, 80; the volume ratio of solution B to solution A is 1:1.

[0006] Preferably, the sum of the concentrations of nickel chloride and manganese chloride in step (a) is 1 mol L -1 , the amount of deionized water used is 10.00 mL, and the dissolution process is ultrasonic for 30 min. The concentration ratio of nickel chloride to manganese chloride is 1:4 - 4:1, and the concentration of nickel chloride is 0.2, 0.4, 0.5, 0.6, 0.8 mol L -1 .

[0007] Preferably, the concentration of Na2MoO4 in step (b) is 1 mol L -1 , the amount of deionized water used is 10.00 mL, and the dissolution process is ultrasonic for 30 min.

[0008] Preferably, in step (c), the volume ratio of solution B to solution A is 1:1, the number of times of washing with methanol and ethanol is three, and the rotational speed of the centrifuge is 8000 - 10000 r min -1 , and the drying time is 12 - 24 h.

[0009] The second object of the present invention is to provide a preparation method of an electrocatalytic synthesis nitrate electrode. The specific steps are as follows: Mix the above nickel-doped manganese molybdate material, isopropanol, and binder, ultrasonically disperse to form a uniform dispersion, and drop-coat it on a polished glassy carbon electrode, and dry at room temperature to obtain an electrocatalytic synthesis nitrate electrode.

[0010] Preferably, the treatment method of the glassy carbon electrode is as follows: Prepare a glass plate, place a layer of chamois leather on the glass plate as a polishing pad, put a small amount of 1.5 μm alumina polishing powder on the polishing pad, and moisten it with distilled water. Hold the glassy carbon electrode with a diameter of 3 mm firmly vertically and polish it in a figure-eight shape. After polishing to a mirror surface, it needs to be ultrasonically cleaned with a 1:1 ethanol and distilled water mixture for 2 - 3 minutes. This can effectively remove surface dirt and impurities and obtain a smooth and uniform electrode surface.

[0011] Preferably, the calibration method of the silver / silver chloride reference electrode is as follows: Prepare an aqueous solution of potassium ferricyanide with a certain concentration. In a three-electrode system with a silver / silver chloride reference electrode, a platinum mesh as the counter electrode, and a polished glassy carbon as the working electrode, perform cyclic voltammetry scanning in the above solution. In the obtained cyclic voltammogram, add the absolute values of the cathodic peak potential and the anodic peak potential and subtract the standard potential of potassium ferricyanide (0.7 V), which is the standard potential of the silver / silver chloride reference electrode.

[0012] Preferably, the ultrasonic time of the above dispersion is 1 h, the binder is Nafion solution, the volume ratio of the binder to isopropanol is 1:20 - 30, the dispersion is drop-coated on the treated glassy carbon electrode 5 times (a total of 10 μL), and the loading amount of the catalyst is 0.2 - 1 mg cm -2 。

[0013] The third object of the present invention is a method for electrocatalytic ammonia oxidation to synthesize nitrate, and the specific steps are as follows: Adopt a three-electrode system, with a silver / silver chloride electrode as the reference electrode, the above electrocatalytic synthesis nitrate electrode as the working electrode, and a platinum mesh as the counter electrode, and perform electrocatalytic ammonia oxidation to synthesize nitrate in an electrolytic cell.

[0014] Preferably, the electrolyte is a mixed solution of 0.137 M (NH4)2SO4 saturated with argon and 1 M NaOH, the reaction potential is 1 - 1.2 V vs. RHE, the reaction time is 1 h, and the reaction temperature is 20 - 30 °C.

[0015] The fourth object of the present invention is the application of the electrocatalytic synthesis nitrate electrode in electrocatalytic ammonia oxidation to synthesize nitrate.

[0016] The beneficial effects obtained by the present invention: (1) Using nickel chloride and manganese chloride as metal sources and Na2MoO4 as a molybdenum source, manganese-doped nickel molybdate (Ni 50 Mn 50-sThe (MoO4) electrode material is obtained by mixing with carbon black (CB), isopropanol and a binder to get a catalyst dispersion with uniform dispersion, which is uniformly coated on a glassy carbon electrode as a working electrode for electrocatalysis. It forms a three-electrode system with a silver / silver chloride electrode and a platinum mesh electrode for electrocatalytic ammonia oxidation to synthesize nitrate.

[0017] (2) Ni 50 Mn 50-s The nanorod-like structure of MoO4 endows the catalyst with a high specific surface area, providing more active sites for ammonia oxidation and improving the mass transfer efficiency during the catalytic process. The Ni element provides active sites for ammonia adsorption, and the Mn element provides active sites for ammonia oxidation. The synergistic effect of the Mn / Ni sites enables Ni 50 Mn 50-s MoO4 combines the advantages of nickel molybdate and manganese molybdate alone, showing the performance of ammonia oxidation to nitrate.

[0018] (3) The electrocatalytic synthesis nitrate electrode prepared above can produce nitrate in the H cell with a Faraday efficiency of 97%, showing the catalytic activity of electrocatalytic ammonia oxidation and having a good nitrate yield.

[0019] In the present invention, introducing metal manganese into nickel molybdate changes its poor conductivity, improves the charge transfer efficiency of nickel molybdate, and at the same time, the two metals play a synergistic role in the oxide, promoting electrocatalytic ammonia oxidation to nitrate. The interaction between the nickel and manganese components affects the electrooxidation behavior of Ni 2+ of which the oxidation potential of Ni 2+ decreases significantly, and γ-NiOOH is determined as the active substance during the ammonia oxidation process. The introduction of manganese accumulates more active Ni 3+ species, making the nucleophilic attack of NH3 on the Ni 3+ sites more favorable, thus optimizing the performance of electrocatalytic ammonia oxidation to nitrate, and the activity and reaction selectivity are far higher than those of single components. Description of the Drawings

[0020] Figure 1 The X-ray diffraction (XRD) patterns of Ni 50 Mn 50-s MoO4 prepared in Example 1 of the present invention and Comparative Example 1, Comparative Example 2 and Comparative Example 3.

[0021] Figure 2 The Raman spectra of Ni 50 Mn 50-s MoO4 prepared in Example 1 of the present invention and Comparative Example 1, Comparative Example 2 and Comparative Example 3.

[0022] Figure 3 The Ni 50 Mn50-s High-resolution field emission scanning electron microscopy (FE-SEM) image of MoO4.

[0023] Figure 4 Ni prepared in Example 1 of the present invention 50 Mn 50-s Transmission electron microscopy (TEM) image of field emission of Ni

[0024] Figure 5 Ni prepared in Example 1 of the present invention 50 Mn 50-s Lattice fringe image of Ni

[0025] Figure 6 Ni prepared in Example 1 of the present invention 50 Mn 50-s High-resolution X-ray photoelectron spectroscopy (XPS) image of O 1s of MoO4.

[0026] Figure 7 LSV curves of Example 3, Comparative Example 7, Comparative Example 8 and Comparative Example 9 of the present invention.

[0027] Figure 8 CV curves of Example 3, Comparative Example 7, Comparative Example 8 and Comparative Example 9 of the present invention.

[0028] Figure 9 Ni prepared in Example 1 of the present invention 50 Mn 50-s Solid ultraviolet diffuse reflectance spectra of Ni

[0029] Figure 10 Ni prepared in Example 1 of the present invention 50 Mn 50-s Approximate band gap energy diagram of Ni

[0030] Figure 11 Potentiostatic electrolysis diagrams of Example 3 of the present invention at different potentials in 0.1 M NH3 buffer solution.

[0031] Figure 12 Potentiostatic electrolysis diagrams of Comparative Example 9 of the present invention at different potentials in 0.1 M NH3 buffer solution.

[0032] Figure 13 Faraday efficiency diagrams of the materials obtained in Example 3, Comparative Example 7 and Comparative Example 8 of the present invention at different potentials in 0.1 M NH3 buffer solution.

[0033] Figure 14Faraday efficiency diagrams of the materials obtained in Comparative Example 9, Comparative Example 7, and Comparative Example 8 of the present invention at different potentials in 0.1 M NH3 buffer solution.

[0034] Figure 15 In-situ Raman spectra of Example 3 of the present invention at different potentials in 0.1 M NH3 buffer solution.

[0035] Figure 16 It is a schematic flow diagram of the preparation method. Detailed implementation manners

[0036] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The specific embodiments described herein are only for explaining and understanding the present invention, and are not used to limit the present invention.

[0037] In the following examples, unless otherwise specified, the specific operation methods and test methods designed are all conventional techniques, and the reagents, drugs, materials, and instruments used can all be obtained through commercial means. Example 1

[0038] In this example, nickel manganese molybdate Ni 50 Mn 50-s MoO4 electrocatalyst was prepared according to the following steps: Accurately weigh 129.59 mg of nickel chloride and 125.84 mg of manganese chloride and add them to 10.00 mL of deionized water. Ultrasonic for 30 min to completely dissolve them, and obtain a green transparent solution denoted as solution A; then use an analytical balance to weigh 205.92 mg of Na2MoO4 and add it to 10.00 mL of deionized water. Ultrasonic for 30 min to completely dissolve it, and obtain a colorless transparent solution denoted as solution B; quickly add solution B to solution A and stir for 10 min. At room temperature, let it stand for 24 h to obtain a yellow-green precipitate. Wash it three times with ethanol, centrifuge to collect the precipitate, and put the obtained yellow-green precipitate into a 60 °C vacuum drying oven to dry overnight to obtain a yellow-green powder denoted as Ni 50 Mn 50-s MoO4.

[0039] Comparative Example 1 In order to prove that the synergistic effect of Mn / Ni elements promotes the performance of ammonia oxidation to synthesize nitrate, the present invention changed the feeding masses of nickel chloride and manganese chloride to 129.59 mg and 0.00 mg respectively to prepare NiMoO4.

[0040] Comparative Example 2 In order to prove that the synergistic effect of Mn / Ni elements promotes the performance of ammonia oxidation to synthesize nitrate, the present invention changed the feeding masses of nickel chloride and manganese chloride to 0.00 mg and 125.84 mg respectively to prepare MnMoO4.

[0041] Comparative Example 3 To prove that the ways (physical mixing and doping) in which Mn / Ni elements play a synergistic role promote the performance of ammonia oxidation to synthesize nitrate, in this invention, the materials synthesized in Comparative Example 1 and Comparative Example 2 were physically mixed together in a 1:1 ratio and ground for 30 min to prepare Ni 50 Mn 50-m MoO4. Example 2

[0042] Ni 50 Mn 50-s Preparation of the Ni Treatment of the glassy carbon electrode: Prepare a glass plate, place a layer of chamois leather on the glass plate as a polishing pad, put a small amount of 1.5 μm alumina polishing powder on the polishing pad, and moisten it with distilled water. Hold the glassy carbon electrode with a diameter of 3 mm firmly vertically and polish it in a figure-eight shape. After polishing to a mirror surface, it needs to be ultrasonically cleaned with a 1:1 ethanol and distilled water mixture for 2 - 3 minutes. This can effectively remove surface dirt and impurities and obtain a smooth and uniform electrode surface.

[0043] Weigh 4.00 mg of the catalyst and put it into a 5.00 mL glass vial. Then add 20.00 μL of Nafion solution (5 wt.%) and 980.00 μL of isopropanol, and ultrasonically disperse for 60 min. Take 10.00 μL of the ultrasonically dispersed liquid and evenly drop-coat it on the treated glassy carbon electrode, five times in total (10.00 μL). After drying the solvent, the Ni 50 Mn 50-s MoO4 electrode is obtained, and the catalyst loading is 0.40 mg cm -2 .

[0044] Comparative Example 4 Preparation of the NiMoO4 electrode, the specific steps are as follows: As a comparative example of Example 2, the electrode preparation process is similar to that of Example 2, except that the catalyst used is the NiMoO4 prepared in Comparative Example 1.

[0045] Comparative Example 5 Preparation of the MnMoO4 electrode, the specific steps are as follows: As a comparative example of Example 2, the electrode preparation process is similar to that of Example 2, except that the catalyst used is the MnMoO4 prepared in Comparative Example 2.

[0046] Comparative Example 6 Ni 50 Mn 50-m Preparation of the MoO4 electrode, the specific steps are as follows: As a comparative example of Example 2, the electrode preparation process was similar to that of Example 2, except that the catalyst used was Ni prepared in Comparative Example 3 50 Mn 50-m MoO4. Example 3

[0047] Electrocatalytic ammonia oxidation to synthesize nitrate.

[0048] All the electrochemical tests in the present invention were collected at room temperature using a CHI 660E electrochemical workstation produced by Shanghai Chenhua, and a standard three-electrode system was adopted. The working electrode was the Ni 50 Mn 50-s MoO4 electrode prepared in Example 2, the reference electrode was an Ag / AgCl electrode (saturated KCl, 0.197 V vs. NHE) produced by Gaushilelian Co., Ltd., and the counter electrode was a platinum mesh electrode. The electrolytic cell used was a closed H-type electrolytic cell provided by Gaushilelian Co., Ltd., and the cathode cell and the anode cell were separated by a Nafion membrane (Nafion 117) produced by DuPont Co., Ltd. The electrolyte was a mixed solution of 0.137 M (NH4)2SO4 saturated with argon and 1 M NaOH, and the reaction temperature was 25 °C.

[0049] Linear sweep voltammetry (LSV) test: At a scanning rate of 10 mV s -1 a linear voltammogram was made in the voltage range of 0-2 V vs. RHE.

[0050] Cyclic voltammetry (CV) test: At a scanning rate of 50 mV s -1 a cyclic voltammogram was made in the voltage range of 0-2 V vs. RHE.

[0051] Electrocatalytic ammonia oxidation test: Constant potential electrolysis was carried out at a potential of 1-1.2 V vs. RHE, the obtained current-time curve (i-t curve) was analyzed, and the nitrate content in the anode cell after electrolysis was quantitatively analyzed by the Gress method.

[0052] Comparative Example 7 As a comparative example of Example 3, the test process was similar to that of Example 3, except that the working electrode was the NiMoO4 electrode prepared in Comparative Example 4.

[0053] Comparative Example 8 As a comparative example of Example 3, the test process was similar to that of Example 3, except that the working electrode was the MnMoO4 electrode prepared in Comparative Example 5.

[0054] Comparative Example 9 As a comparative example of Example 3, the test process is similar to that of Example 3, except that the working electrode is Ni 50 Mn 50-m MoO4 electrode prepared in Comparative Example 6.

[0055] Characterization and electrocatalytic analysis of the catalyst in the example: Figure 1 XRD pattern of Ni 50 Mn 50-s MoO4 prepared in Example 1. The synthesized NiMoO4 and MnMoO4 are consistent with the main diffraction peaks of monoclinic NiMoO4 (PDF#33-0948) and MnMoO4 (PDF#50-1287), indicating the successful preparation of NiMoO4 and MnMoO4. It is observed that after introducing Mn doping, the crystal structure of pure NiMoO4 remains basically unchanged. Some diffraction peaks are masked after physical mixing, indicating that Mn doping does not change the lattice of NiMoO4. Careful observation reveals that the main diffraction peaks of Ni 50 Mn 50-s MoO4 have a slight shift compared with those of NiMoO4, and the lattice shifts towards a small angle, indicating that larger Mn atoms replace Ni atoms, resulting in slight lattice expansion. Figure 2 Raman spectrum of Ni 50 Mn 50-s MoO4 prepared in Example 1. The strong peak observed at 930 cm -1 is due to the symmetric stretching vibration of the Mo=O bond, while the other peaks at 857 and 808 cm -1 are from the asymmetric M=O stretching vibration. The peak observed at 340 cm -1 is attributed to the bending vibration of the Mo-O bond. In addition, there is a certain red shift in the characteristic peaks of Ni 50 Mn 50-s MoO4 compared with NiMoO4, further revealing the fine microstructure changes after successfully doping Mn into the NiMoO4 lattice.

[0056] Figure 3 、 Figure 4 and Figure 5 FE-SEM spectrum and TEM spectrum of Ni 50 Mn 50-s MoO4 prepared in Example 1. The catalyst as a whole presents a nanorod-like structure, indicating that the incorporation of Mn does not significantly change the morphology of NiMoO4. In addition, the synthesized Ni 50 Mn 50- sThe interplanar spacing of MoO4 is 0.36 nm, slightly larger than the typical value of 0.33 nm for NiMoO4. This increase in spacing may be attributed to the lattice expansion caused by Mn doping.

[0057] Figure 6 For the Ni 50 Mn 50-s MoO4 prepared in Example 1, two fitting peaks at approximately 530.2 eV and 532.5 eV can be observed in the high-resolution O 1s XPS spectrum. These two peaks originate from lattice oxygen (O L ) and surface oxygen (O S ), respectively. The concentration of O S increases from 69.7% in NiMoO4 to 74.8% in Ni 50 Mn 50-m MoO4, and then to 81.1% in Ni 50 Mn 50-s MoO4. Therefore, it can be reasonably inferred that the increase in the concentration of O S may be due to more defects with unsaturated compositions on the catalyst surface during the doping process.

[0058] Figure 7 For the LSV curves of Example 3, Comparative Example 7, Comparative Example 8, and Comparative Example 9, in 0.1 M NH3 buffer solution, the onset potential and current density of Ni 50 Mn 50-s MoO4 show obvious negative shifts and increases compared with those of Comparative Example 7, Comparative Example 8, and Comparative Example 9. Figure 8 For the CV curves of Example 3, Comparative Example 7, Comparative Example 8, and Comparative Example 9, in 0.1 M NH3 buffer solution, the catalytic current of Ni 50 Mn 50-s MoO4 increases compared with those of Comparative Example 7, Comparative Example 8, and Comparative Example 9, indicating that Ni 50 Mn 50-s MoO4 has the highest activity for ammonia oxidation.

[0059] Figure 9 For the UV-visible diffuse reflectance spectra of Ni 50 Mn 50-s MoO4 prepared in Example 1 and Comparative Example 1, the strong absorption in the range of 200 - 300 nm is attributed to the tetrahedral coordination charge transfer process from O 2- to Mo 2- in MoO4 6+ . The relatively weak absorption peak at approximately 445 nm may be due to the transition of low-energy electrons of the metal center of Ni 2+ in the material from the highest occupied molecular orbital t 2g * to the lowest unoccupied molecular orbital e g*Caused by. Figure 10 Ni prepared for Example 1 50 Mn 50-s MoO4 and Comparative Example 1 (αhν) 2 Relationship diagram with photon energy (hν), synthesized Ni 50 Mn 50-s Approximate band gap energy (E g = 3.52 eV) of MoO4 is slightly narrower than that of pure NiMoO4 (3.59 eV), which may be caused by the increase of oxygen vacancies. The conclusion obtained is consistent with the above XPS analysis.

[0060] Figure 11 and Figure 12 Are the potentiostatic electrolysis diagrams of Ni 50 Mn 50-s MoO4 and Ni 50 Mn 50-m MoO4 at different potentials in Example 3 and Comparative Example 9, the applied potential range is 1 to 1.2 V vs. RHE, and the electrocatalytic performance is represented by the magnitude of the Faraday efficiency. The greater the Faraday efficiency, the closer it is to 100% and the better the performance. Ni 50 Mn 50-s MoO4 and Ni 50 Mn 50-m The current curves of MoO4 remain stable during the 1-hour electrolysis process, indicating that the catalyst has good stability. Figure 13 and Figure 14 Are the comparison diagrams of the Faraday efficiency of the electrolysis products in the tests of Example 3 and Comparative Example 9 and Comparative Examples 7 and 8. In a mixed solution of 0.137 M (NH4)2SO4 saturated with argon and 1 M NaOH, Ni 50 Mn 50-s MoO4 has a continuous Faraday efficiency exceeding 85% within the potential window of 1 V - 1.2 V vs. RHE, and even reaches an extremely high 97% at 1.05 V vs. RHE. Compared with the samples of Comparative Example 7 and Comparative Example 8, the catalytic activity is significantly improved, and it is also better than the physically mixed Ni 50 Mn 50-m MoO4 in performance, demonstrating the excellent catalytic activity of Ni 50 Mn 50- s MoO4 catalyst.

[0061] Figure 13In-situ Raman spectra of Example 3 and Comparative Example 7 electrolyzed at different potentials in a mixed solution of 0.137 M (NH4)2SO4 and 1 M NaOH saturated with argon. Introducing Mn can effectively adjust the coordination environment of Ni, Mo, and O, which is beneficial to the hybridization between the O 2p orbital and the Ni 3d orbital and the oxidation of nickel ions from Ni 2+ to Ni 3+ . As the applied voltage gradually increases, two obvious characteristic peaks can be detected at 481 and 560 cm -1 above 1.05 V, which are attributed to the E III -bending and A g -stretching vibrations of Ni 1g -O in γ-NiOOH, indicating that the formation of γ-NiOOH has been determined as the active substance in the ammonia oxidation process.

Claims

1. A preparation method of a manganese-doped nickel molybdate catalyst, characterized in that, It includes the following steps: (a) Mix nickel chloride and manganese chloride and dissolve them in deionized water to form solution A. The sum of the concentrations of nickel chloride and manganese chloride in solution A is 1 mol L -1 ; (b) Dissolve Na2MoO4 in deionized water to form Solution B, and the concentration of Na2MoO4 in Solution B is 1 mol L -1 ; (c) Add solution B to solution A and stir. After mixing evenly, stop stirring. Under room temperature conditions, let it stand to obtain a precipitate, age, wash, collect by centrifugation, and dry under vacuum to obtain a nickel molybdate catalyst doped with manganese; the volume ratio of solution B to solution A is 1:

1.

2. The preparation method according to claim 1, characterized in that: In Step 1, the concentration ratio of nickel chloride to manganese chloride is 1:4 - 4:1, and the concentration of nickel chloride is 0.2, 0.4, 0.5, 0.6, 0.8 mol L -1 .

3. A nickel molybdate catalyst doped with manganese, characterized in that: It is prepared by the preparation method described in claim 1 or 2.

4. Application of a manganese-doped nickel molybdate catalyst, characterized in that: The nickel molybdate catalyst doped with manganese is applied to the electrocatalytic ammonia oxidation for synthesizing nitrate.

5. A preparation method of an electrocatalytic synthesis nitrate electrode, characterized in that: The electrode is obtained by loading the nickel molybdate material doped with manganese described in claim 3 onto a glassy carbon electrode; the preparation method comprises the following steps: ultrasonically dispersing the nickel molybdate material doped with manganese, isopropanol and a binder, taking the dispersed liquid after ultrasonic treatment, uniformly drop-coating the dispersed liquid on the glassy carbon electrode, and drying the solvent to obtain a working electrode, and the loading amount of the nickel molybdate material doped with manganese is 0.2-1 mg cm -2 .

6. The preparation method of an electrocatalytic synthesis nitrate electrode according to claim 5, characterized in that: The binder is Nafion solution, and the volume ratio of the binder to isopropanol in the dispersion is 1:20 - 30.

7. An electrocatalytic synthesis nitrate electrode, characterized in that: This electrode is prepared by the method described in claim 5 or 6.

8. Use of an electrode for electrocatalytic ammonia oxidation to synthesize nitrate according to claim 7, characterized in that: The electrocatalytic synthesis nitrate electrode is applied to the electrocatalytic ammonia oxidation for synthesizing nitrate.

9. The application of an electrocatalytic synthesis nitrate electrode according to claim 8, characterized in that: The method for applying the electrocatalytic synthesis nitrate electrode to the electrocatalytic ammonia oxidation for synthesizing nitrate is as follows: A three - electrode system is adopted. The electrocatalytic synthesis nitrate electrode is used as the working electrode, a platinum mesh is used as the counter electrode, and a silver / silver chloride electrode is used as the reference electrode. An ammonium sulfate and sodium hydroxide solution saturated with argon is used as the electrolyte, and electrocatalytic ammonia oxidation is carried out in an electrolytic cell, and the target product is nitrate.

10. The application of an electrocatalytic synthesis nitrate electrode according to claim 9, characterized in that: The electrolytic cell is an H - type electrolytic cell. The cathode chamber and the anode chamber are separated by a proton exchange membrane. The electrolyte is a mixed solution of (NH4)2SO4 and NaOH saturated with argon. The reaction potential is 1 - 1.2 V vs. RHE, the reaction time is 1 h, and the reaction temperature is 20 - 30 °C.

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