Electroreduction nitrate ammonia synthesis CuOx / CoOx nano material with oxygen vacancy defect, and preparation method and application thereof

Abstract

The invention discloses an electroreduction nitrate synthesis ammonia CuOx / CoOx nano material with an oxygen vacancy defect, and a preparation method and application thereof. In the CuOx / CoOx nano material, the molar ratio of a copper element to a cobalt element is 30: (1-8); the particle surface of the CuOx / CoOx nano material is provided with a nano-scale microporous structure; in the microstructure of the CuOx / CoOx nano material, the copper element coexists in the form of a Cu phase, a Cu2O phase and a CuO phase, and the cobalt element exists in the form of a CoO phase and a Co2O3 phase; the CuOx / CoOx nano material is prepared by adopting a coprecipitation method, a hydrothermal method and a calcination method. The CuOx / CoOx nano material is loaded on a cathode of an electrocatalytic reduction nitrate electrolytic tank for electrocatalytic reduction nitrate synthesis ammonia, and the efficiency of the electrolytic tank for catalyzing nitrate synthesis ammonia can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of nitrate-containing wastewater treatment. Specifically, it is a CuOx / CoOx nanomaterial with oxygen vacancy defects for electro-reducing nitrate to synthesize ammonia, a preparation method and uses thereof. Background Art

[0002] Due to advantages such as a relatively high hydrogen storage capacity (17.6 wt%), mass energy density (22.5 MJ / kg), and volume energy density (11.5 MJ / L) of ammonia, ammonia has received extensive attention in the field of renewable clean energy.

[0003] According to the source of hydrogen in the raw material for synthesizing ammonia, the ammonia prepared by electrochemically reducing nitrate is green ammonia, which is a type of ammonia with zero carbon emissions. At the same time, ammonia has a wide range of uses as a new energy source. It can be used in ammonia internal combustion engines, ammonia-fired steam turbines, ammonia-fired boilers, and ammonia fuel cells, etc. Ammonia fuel cells are an important technology for the energy utilization of ammonia and can directly convert chemical energy into electrical energy. Solid oxide fuel cells are currently the most promising type of ammonia fuel cells.

[0004] Using electrocatalytic reduction of nitrate in nitrate-containing wastewater to prepare ammonia is an ammonia fuel production route with great economic value. Currently, the reactors used for electrocatalytic reduction of nitrate to prepare ammonia include H-type electrolytic cells and flow-through electrolytic cells. For the H-type electrolytic cell, a membrane component is used inside the device. Due to the presence of the membrane, the current density and mass transfer efficiency of the electrolytic cell will be affected, thereby reducing the overall reaction efficiency. At the same time, the relatively large ohmic resistance and low current density are not suitable for practical applications. For the flow-through electrolytic cell, the flow channels engraved on the electrodes are too small and not suitable for treating nitrate-containing sewage with a large amount of particulate impurities, which is prone to causing blockage of the flow channels, and the device structure is complex and not suitable for frequent disassembly and treatment. In addition, for sewage containing metal ions, during the long-term operation of the electrodes, the metal ions react with the electrodes and adhere to the electrode surface, which is likely to reduce the efficiency of the working electrode.

[0005] Therefore, it is necessary to develop a membrane-free flow-through electrolytic cell that is convenient for replacing electrodes to solve the problems existing in the above-mentioned electrocatalytic reduction nitrate electrolytic cell when treating nitrate-containing wastewater. At the same time, combined with ammonia fuel cell power generation, the electrolytic cell is combined with an ammonia fuel cell to realize the conversion of nitrate wastewater into new energy and power generation utilization.

[0006] In an electrolytic cell for electrocatalytic reduction of nitrate, the choice of catalyst is directly related to the production efficiency of ammonia. At present, copper-based catalysts are one of the most selective materials in the reaction of electrocatalytic reduction of nitrate to ammonia, and they have an inhibitory effect on the hydrogen evolution reaction. However, copper-based catalysts have a strong adsorption effect on intermediates during the electrocatalytic nitrate reduction reaction, and there is also a problem of poor H2O dissociation activity, which is not conducive to the progress of the electrocatalytic reaction. Therefore, for copper-based catalysts, there is still room for exploration to improve their selectivity for ammonia and reduce the activity of competitive reactions. Summary of the Invention

[0007] To this end, the technical problem to be solved by the present invention is to provide an electro-reduced nitrate synthesis ammonia CuOx / CoOx nanomaterial with oxygen vacancy defects, a preparation method and uses thereof. The CuOx / CoOx nanomaterial can be used as an efficient electrocatalyst for electro-reduced nitrate synthesis ammonia. The present invention also provides a dual-cathode flow-type electrolytic cell combined ammonia fuel cell power generation system and method that can efficiently reduce nitrate in nitrate-containing wastewater to ammonia and integrate an ammonia collection device for ammonia fuel cell power generation.

[0008] To solve the above technical problems, the present invention provides the following technical solutions: An electro-reduced nitrate synthesis ammonia CuOx / CoOx nanomaterial with oxygen vacancy defects, wherein the molar ratio of copper element to cobalt element in the CuOx / CoOx nanomaterial is 30:(1-8); the particle surface of the CuOx / CoOx nanomaterial has a nanoscale microporous structure; in the microstructure of the CuOx / CoOx nanomaterial, the copper element coexists in the forms of Cu phase, Cu2O phase and CuO phase, and the cobalt element exists in the forms of CoO and Co2O3 phases; the Cu phase promotes the hydrolysis dissociation to generate active hydrogen, and the Cu2O phase is used to accelerate the reaction step of NO3 − to NO2 − in the electro-reduced nitrate synthesis ammonia, and the CoO phase and Co2O3 phase are used to accelerate the reaction step of NO2 − to NH3 in the electro-reduced nitrate synthesis ammonia, and the Cu phase and CuO phase play a promoting role in the whole reaction process of electro-reduced nitrate synthesis ammonia.

[0009] Since CuO often has a multiphase structure and oxygen vacancies with rich phase interfaces, and the oxygen vacancies can have a strong interaction with the O atoms in nitrate to improve the selectivity of ammonia. The mechanism of the electro-reduced nitrate synthesis ammonia CuOx / CoOx nanomaterial with oxygen vacancy defects in the present invention for catalyzing nitrate synthesis ammonia is as follows: the Cu phase in the CuOx / CoOx nanomaterial promotes the hydrolysis dissociation to generate active hydrogen (the active hydrogen will participate in the reaction step of NO3 − to NO2 − and the reaction step of NO2 −to the reaction step of NH3), the Cu2O phase in the CuOx / CoOx nanomaterial catalyzes the active hydrogen to promote NO3 − reduction to NO2 − , NO2 − is indirectly transferred through the electrolyte. Subsequently, the CoO phase and Co2O3 phase in the CuOx / CoOx nanomaterial can catalyze the active hydrogen to promote NO2 - reduction to NH3; that is, the Cu2O phase mainly accelerates NO3 − to NO2 − reaction, and the CoOx phase mainly accelerates the step of NO2 − to NH3; in addition, the presence of Cu / CuO promotes the entire catalytic reaction process.

[0010] In the pathway of electroreductive nitrate synthesis of ammonia mediated by active hydrogen (H （ads） ), electrons first reduce the water adsorbed on the cathode surface to generate H （ads） (H2O + e - → H (ads) + OH - ); then, under the direct action of H （ads） , NO3 - gradually dehydrogenates and reduces to NH3 through a series of intermediates (mainly including NO 2(ads) , NO (ads) , N (ads) , NH (ads) and NH 2(ads) ). Therefore, the Cu phase promotes the hydrolysis dissociation to generate active hydrogen (H （ads） ) and promotes the entire reduction process in this pathway.

[0011] The above-mentioned electroreductive nitrate synthesis of ammonia CuOx / CoOx nanomaterial with oxygen vacancy defects is characterized in that the molar ratio of the Cu2O phase, CuO phase and Cu phase is 1:(2.0 - 2.5):(1.0 - 1.2), preferably, the molar ratio of the Cu2O phase, CuO phase and Cu phase is 1:2.48:1.03; the molar ratio of the CoO phase to the Co2O3 phase is 1:(1.3 - 1.6), preferably, the molar ratio of the CoO phase to the Co2O3 phase is 1:1.53. When the molar ratio between each CuOx and each CoOx in the nanomaterial is within the above range, the CuOx / CoOx nanomaterial has better catalytic activity for driving the reaction of electroreductive nitrate synthesis of ammonia in a cascade manner.

[0012] A preparation method of an electroreductive nitrate synthesis of ammonia CuOx / CoOx nanomaterial with oxygen vacancy defects includes the following steps: Step (1): Add cupric acetate monohydrate and cobalt acetate tetrahydrate into glycerol to obtain a mixed dispersion. The reason for choosing cupric acetate monohydrate and cobalt acetate tetrahydrate as the copper source and cobalt source in the present invention is as follows: both have low solubility in glycerol, and the catalyst precursor formed by their reaction is more likely to aggregate and precipitate in glycerol, so as to obtain a catalyst precursor with ideal morphology and degree of aggregation, which is beneficial to obtaining CuOx / CoOx nanomaterials with oxygen vacancy defects by subsequent calcination for electro-reducing nitrate to synthesize ammonia. If cupric acetate or cobalt acetate without crystal water, or organic copper salts or cobalt salts such as copper oxalate or cobalt oxalate are selected as reaction raw materials, the morphology, degree of aggregation, etc. of the finally prepared nanomaterials will change, resulting in changes in the tandem structure formed by the coupling of CuOx and CoOx in the prepared nanomaterials, and further affecting the catalytic activity and catalytic selectivity of the nanomaterials for NO3 - and so on.

[0013] Step (2): Stir the mixed dispersion thoroughly at room temperature, and then transfer it to a reaction kettle for heating to react fully. After the reaction is completed, a mixed suspension is obtained. Stirring thoroughly at room temperature before hydrothermal reaction can better control the ratio between CuOx, CoOx, and between CuOx and CoOx in the generated nanomaterials, and is beneficial to the formation of CuOx / CoOx nanomaterials with a higher specific surface area. If the mixed dispersion does not undergo the coprecipitation reaction at room temperature in the present invention, or directly undergoes subsequent washing, drying and calcination treatment without hydrothermal reaction after thorough stirring at room temperature, it will lead to an unreasonable ratio between the oxides in the finally prepared nanomaterials and affect its catalytic activity for nitrate.

[0014] Step (3): Wash the solid precipitate obtained by centrifuging the mixed suspension with absolute ethanol, and then dry it in a vacuum drying oven to obtain a catalyst precursor; Step (4): Calcinate the catalyst precursor, and after the calcination treatment, naturally cool it to room temperature and crush it to obtain the above-mentioned CuOx / CoOx nanomaterials with oxygen vacancy defects for electro-reducing nitrate to synthesize ammonia.

[0015] The present invention prepares a CuOx / CoOx nanomaterial with oxygen vacancy defects (i.e., CuOx / CoOx tandem catalyst) by coprecipitation method-hydrothermal method-calcination method, and this CuOx / CoOx nanomaterial is used as an efficient electrocatalyst for electro-reducing nitrate to synthesize ammonia.

[0016] For the preparation method of the above-mentioned CuOx / CoOx nanomaterial with oxygen vacancy defects for electrocatalytic reduction of nitrate to ammonia, in step (1), the molar ratio of copper acetate monohydrate to cobalt acetate tetrahydrate is 30: (1-8); glycerol mainly acts as a solvent, reducing agent and stabilizer. Adding glycerol as a reaction medium can achieve the full mixing of reactants and the dispersion of the catalyst precursor generated during the reaction, which is beneficial to the progress of the whole reaction; and the presence of glycerol in the reaction system is conducive to the formation of a tandem structure between CuO and CoO to prepare a CuOx / CoOx nanomaterial that can fully exert the catalytic activity of the dual active sites; the molar concentration of copper acetate monohydrate in the mixed dispersion is 0.08-0.15 mol / L; the concentration of the reactants will affect the structure of the synthesized catalyst precursor, thereby affecting the catalytic performance of the finally synthesized catalyst. By controlling the molar concentration of copper acetate monohydrate in the mixed dispersion within the above range and selecting appropriate reaction conditions, the present invention can enable the organic coupling of two different catalytic sites in the prepared CuOx / CoOx nanomaterial, so that the dual active sites can synergistically drive the reaction in a cascade manner in the reaction of electrocatalytic reduction of nitrate to ammonia, improving the ammonia production efficiency.

[0017] For the preparation method of the above-mentioned CuOx / CoOx nanomaterial with oxygen vacancy defects for electrocatalytic reduction of nitrate to ammonia, in step (2), the stirring rate is 500-1000 rpm and the stirring time is 1-2 h; the heating temperature is 150-200 °C and the reaction time is 20-25 h; under these reaction conditions, it can ensure that the reaction raw materials react to form a catalyst precursor with a tandem structure, and at the same time will not damage the structure of the already formed catalyst precursor.

[0018] For the preparation method of the above-mentioned CuOx / CoOx nanomaterial with oxygen vacancy defects for electrocatalytic reduction of nitrate to ammonia, in step (3), the drying temperature is 60-80 °C and the drying time is 8-12 h.

[0019] For the preparation method of the above-mentioned CuOx / CoOx nanomaterial with oxygen vacancy defects for electrocatalytic reduction of nitrate to ammonia, in step (4), the conditions for calcination treatment are: first, heat from room temperature to 350-400 °C at a heating rate of 5-10 °C / min, and then keep it at 350-400 °C for 1-2 h. The heating rate, calcination temperature and calcination time will all affect the formation of the microporous structure and the crystal phase structure in the CuOx / CoOx nanomaterial; by reasonably controlling the heating rate, calcination temperature and calcination time during the calcination treatment, the present invention enables the catalyst precursor to form a CuOx / CoOx nanomaterial with a stable nanoscale microporous structure and rich oxygen vacancies on the surface after calcination treatment, thereby effectively improving the electrocatalytic performance of the CuOx / CoOx nanomaterial.

[0020] In the preparation method of the above-mentioned CuOx / CoOx nanomaterial for electro-reducing nitrate to synthesize ammonia with oxygen vacancy defects, in step (1), the molar ratio of copper acetate monohydrate to cobalt acetate tetrahydrate is 15:2; the molar concentration of copper acetate monohydrate in the mixed dispersion is 0.1 mol / L; In step (2), the stirring rate is 500 rpm and the stirring time is 1 h; the heating temperature is 180 °C and the reaction time is 24 h; In step (3), the drying temperature is 60 °C and the drying time is 12 h; In step (4), the conditions for the calcination treatment are: first, heat from room temperature to 350 °C at a heating rate of 5 °C / min, and then hold at 350 °C for 2 h.

[0021] The CuOx / CoOx tandem catalyst synthesized by using the synthesis process and parameter conditions of the present invention (including the ratio between reaction raw materials, the ratio between reaction raw materials and solvents, coprecipitation reaction conditions, hydrothermal reaction conditions, and calcination conditions, etc.) can promote and balance the reaction activities of NO3 − to NO2 − and NO2 − to NH3; this is because the CuOx / CoOx tandem catalyst synthesized by the present invention has a high specific surface area, there are abundant oxygen vacancies on its surface, and the ratio between each CuOx, each CoOx, and between CuOx and CoOx in the nanomaterial is reasonable, which is conducive to the CuOx / CoOx tandem catalyst to synergistically drive the reaction in a cascade manner, enabling the coupling of two different catalytic sites to respectively accelerate the steps of NO3 − to NO2 − and NO2 − to NH3, thereby improving the overall efficiency of NO3RR (electrochemical nitrate reduction reaction) to NH3.

[0022] A use of the CuOx / CoOx nanomaterial for electro-reducing nitrate to synthesize ammonia with oxygen vacancy defects is to load the above-mentioned CuOx / CoOx nanomaterial for electro-reducing nitrate to synthesize ammonia with oxygen vacancy defects onto the cathode of an electrocatalytic reduction nitrate electrolytic cell for electrocatalytic reduction of nitrate to synthesize ammonia; the method for loading the CuOx / CoOx nanomaterial onto the cathode of the electrocatalytic reduction nitrate electrolytic cell is: adding the CuOx / CoOx nanomaterial and acetylene black into an isopropyl alcohol aqueous solution and mixing evenly to obtain a catalyst dispersion; adding a Nafion solution to the catalyst dispersion and ultrasonically dispersing evenly to obtain an ink dispersion; evenly dripping the ink dispersion onto the cathode of the electrocatalytic reduction nitrate electrolytic cell and air-drying naturally.

[0023] Use of the CuOx / CoOx nanomaterial for electro-reducing nitrate to synthesize ammonia with oxygen vacancy defects. The mass ratio of the CuOx / CoOx nanomaterial to acetylene black is 8:1. The mass-volume ratio of the CuOx / CoOx nanomaterial to the isopropanol aqueous solution in the catalyst dispersion is 8 g / L, and the volume ratio of water to isopropanol in the isopropanol aqueous solution is 3:1. The volume ratio of the catalyst dispersion to the Nafion solution in the ink dispersion is 1:0.04. The ultrasonic dispersion time is 30 min. The resin solid content in the Nafion solution is 5 wt%. The conductivity of the catalyst itself is relatively low. The purpose of adding acetylene black is to improve the conductivity of the material. Isopropanol is used as the solvent of the catalyst to evenly coat the dispersed catalyst on the cathode material carbon sheet. Too little isopropanol is not conducive to the dispersion of the catalyst, while too much is not conducive to the coating of the catalyst (isopropanol is volatile and needs to be air-dried naturally for a period of time after coating, and then the catalyst can be loaded on the carbon sheet). The Nafion solution is used as a binder. Too much or too little is not suitable for the performance of the catalyst. By controlling the ratio of acetylene black to the CuOx / CoOx nanomaterial and the concentration and dosage of the isopropanol solution and the Nafion solution, the present invention prepares a uniformly dispersed ink dispersion, which is loaded on the cathode, and can effectively improve the reduction efficiency of nitrate near the cathode.

[0024] Use of the CuOx / CoOx nanomaterial for electro-reducing nitrate to synthesize ammonia with oxygen vacancy defects. The electrocatalytic reduction nitrate electrolytic cell is an H-type electrolytic cell or a flow-type electrolytic cell.

[0025] The technical solution of the present invention has achieved the following beneficial technical effects: 1. The present invention uses copper acetate monohydrate and cobalt acetate tetrahydrate with specific ratios as raw materials, uses glycerol as the reaction medium, and adopts the co-precipitation method - hydrothermal method - calcination method. By controlling the concentration of the co-precipitation raw materials, the stirring rate and time at room temperature, the hydrothermal reaction temperature and time, and the heating rate, calcination temperature and calcination time of the calcination treatment, a nano-scale CuO and CoO coupled catalyst CuOx / CoOx nanomaterial (i.e., CuOx / CoOx tandem catalyst) with the best ratio and tandem structure is synthesized. Through the tandem catalysis of the double oxides, the CuOx / CoOx nanomaterial can achieve the efficient and highly selective removal of NO3 - , so as to realize the selective electro-reduction of nitrate to ammonia. The CuOx / CoOx tandem catalyst prepared by the synthesis method of the present invention has good selectivity, Faraday efficiency and stability, which benefits from the synergistic effect of the double active sites and the oxygen vacancy defects of the catalyst.

[0026] 2. The electro-reduced nitrate-synthesized ammonia CuOx / CoOx tandem catalyst with oxygen vacancy defects prepared by the present invention is used for electrocatalytic reduction of nitrate to synthesize ammonia in a dual-cathode flow-type electrolytic cell combined with an ammonia fuel cell power generation system, which can effectively improve the efficiency of catalytic nitrate synthesis of ammonia in the dual-cathode flow-type electrolytic cell. Moreover, by using the flow-type membrane-free electrochemical treatment method in the present invention, the mass transfer efficiency of ions can be effectively increased, and the use of ion exchange membranes can be avoided. Combining the design of a membrane-free flow-type electrolytic cell combined with an ammonia fuel cell for power generation can simultaneously achieve the removal of nitrate in nitrate-containing wastewater and the resource collection of ammonia, and use ammonia for power generation, thus realizing resource utilization. Description of the Drawings

[0027] Figure 1 Schematic diagram of the synthesis route of the electro-reduced nitrate-synthesized ammonia CuOx / CoOx nanomaterial with oxygen vacancy defects in Example 1 of the present invention; Figure 2 When the CuOx / CoOx tandem catalyst prepared in Example 1 of the present invention is used for electrocatalytic reduction of nitrate-containing wastewater, at -0.58 V vs. RHE, with and without NO3 added in 0.2 mol / L K2SO4 electrolyte - NH3 production rate; Figure 3a SEM image (2μm) of the CuOx / CoOx nanomaterial in Example 1 of the present invention; Figure 3b SEM image (1μm) of the CuOx / CoOx nanomaterial in Example 1 of the present invention; Figure 3c SEM image (500nm) of the CuOx / CoOx nanomaterial in Example 1 of the present invention; Figure 3d Transmission electron microscope image of the CuOx / CoOx nanomaterial in Example 1 of the present invention (the inset is the EDX spectrum); Figure 3e HR-TEM image of the CuOx / CoOx nanomaterial in Example 1 of the present invention; Figure 3f Magnified image of the dashed box in the HR-TEM image of the CuOx / CoOx nanomaterial in Example 1 of the present invention; Figure 3g HAADF-STEM image of the CuOx / CoOx nanomaterial in Example 1 of the present invention; Figure 3h EELS elemental mapping image (oxygen element) of the CuOx / CoOx nanomaterial in Example 1 of the present invention; Figure 3iEELS elemental mapping image (copper element) of the CuOx / CoOx nanomaterial in Example 1 of the present invention; Figure 3j EELS elemental mapping image (cobalt element) of the CuOx / CoOx nanomaterial in Example 1 of the present invention; Figure 4a XRD patterns of the CuOx / CoOx nanomaterial and CuOx in Example 1 of the present invention; Figure 4b XPS full spectra of the CuOx / CoOx nanomaterial and CuOx in Example 1 of the present invention; Figure 4c XPS spectrum of Cu 2p of the CuOx / CoOx nanomaterial in Example 1 of the present invention; Figure 4d XPS spectrum of Cu LMM of the CuOx / CoOx nanomaterial in Example 1 of the present invention; Figure 4e XPS spectrum of Co 2p of the CuOx / CoOx nanomaterial in Example 1 of the present invention; Figure 4f XPS spectrum of O 1s of the CuOx / CoOx nanomaterial in Example 1 of the present invention; Figure 5 Schematic structural diagram of the dual-cathode flow-through electrolytic cell combined ammonia fuel cell power generation system in Example 2 of the present invention; Figure 6 Schematic structural diagram of the dual-cathode flow-through electrolytic cell in Example 2 of the present invention; Figure 7a Front view of the dual-cathode flow-through electrolytic cell in Example 2 of the present invention; Figure 7b Left view of the dual-cathode flow-through electrolytic cell in Example 2 of the present invention; Figure 7c Top view of the dual-cathode flow-through electrolytic cell in Example 2 of the present invention; Figure 8 Schematic structural diagram of the ammonia fuel cell in Example 2 of the present invention; Figure 9 Faraday efficiency and selectivity test result graph of the CuOx / CoOx nanomaterial in Example 1 of the present invention; Figure 10 Catalytic product distribution of 3-CuOx / CoOx in the NO3RR process for 7 consecutive cycle tests of the CuOx / CoOx nanomaterial in Example 1 of the present invention under the condition of -0.58 V vs. RHE; Figure 11 Mechanism of catalytic reduction of nitrate to synthesize ammonia by the CuOx / CoOx nanomaterial in Example 1 of the present invention.

[0028] The reference numerals in the figure are represented as follows: 1 - the first cathode plate; 2 - the anode plate; 3 - the separator; 4 - the second cathode plate; 5 - the second peristaltic pump; 6 - the electrochemical workstation; 7 - the first peristaltic pump; 8 - the cathode liquid storage tank; 9 - the anode liquid storage tank; 10 - the hose flow regulator; 11 - the water bath heating device; 12 - the ammonia collection device; 13 - the anode of the ammonia fuel cell; 14 - the solid oxide electrolyte; 15 - the cathode of the ammonia fuel cell; 101 - the first water inlet; 102 - the first water outlet; 103 - the second water outlet; 104 - the second water inlet; 105 - the dual-cathode flow-through electrolytic cell; 201 - the first air inlet; 202 - the first air outlet; 203 - the second air inlet; 204 - the second air outlet; 205 - the ammonia fuel cell. Detailed implementation mode

[0029] Example 1 As Figure 1 shown, a preparation method of a CuOx / CoOx nanomaterial for electro-reducing nitrate to synthesize ammonia with oxygen vacancy defects includes the following steps: Step (1): Add 3 mmol of copper acetate monohydrate and 0.4 mmol of cobalt acetate tetrahydrate to 30 mL of glycerol to obtain a mixed dispersion. Step (2): Stir the mixed dispersion at a stirring rate of 500 rpm at room temperature for 1.0 h, and then transfer it to a reaction kettle and react at a temperature of 180 °C for 24 h. After the reaction, a mixed suspension is obtained. Step (3): Wash the solid precipitate obtained by centrifuging the mixed suspension with anhydrous ethanol 3 times, and then dry it in a vacuum drying oven at 60 °C for 12 h to obtain a catalyst precursor. Step (4): Perform calcination treatment on the catalyst precursor. First, heat it from room temperature to 350 °C at a heating rate of 5 °C / min, and then keep it at 350 °C for 2 h. After the calcination treatment, it is naturally cooled to room temperature to obtain a CuOx / CoOx nanomaterial for electro-reducing nitrate to synthesize ammonia with oxygen vacancy defects.

[0030] The chemical formula of the CuOx / CoOx nanomaterial for electro-reducing nitrate to synthesize ammonia with oxygen vacancy defects prepared in this example is 3CuO-CoO, denoted as "3-CuOx / CoOx".

[0031] Using the same method and preparation conditions as in this example, by changing the amount of cobalt acetate tetrahydrate in step (1) to 0, 0.1 mmol, 0.2 mmol, and 0.8 mmol respectively, the materials prepared are denoted as 0-CuOx, 1-CuOx / CoOx, 2-CuOx / CoOx, and 4-CuOx / CoOx respectively.

[0032] ByFigure 2 It can be seen that the CuOx / CoOx tandem catalyst prepared by the method of this embodiment has the performance of catalytically reducing nitrate to ammonia, and has good selectivity for the nitrate reduction to ammonia reaction.

[0033] The 3-CuOx / CoOx nanomaterial was coated on the negative electrode of the H-type electrolytic cell for application test evaluation. The test results of its Faraday efficiency, selectivity and stability are shown in Figure 9 and Figure 10 . It can be seen from the figure that the 3-CuOx / CoOx nanomaterial prepared in this embodiment has good selectivity, Faraday efficiency and stability for the nitrate reduction to ammonia reaction. Therefore, it can be used for electrocatalytic reduction of nitrate wastewater in an electrolytic cell.

[0034] From Figures 3a to 3j it can be seen that: the CuOx / CoOx tandem catalyst prepared by the method of this embodiment has a granular porous morphology, with many pores on the surface, the ligaments are rough but the internal structure is uniform (see Figures 3a to 3c ). The transmission electron microscope (TEM) image is as shown in Figure 3d . This figure shows that there is a rich microporous structure on the surface of the CuOx / CoOx tandem catalyst material. The high-resolution TEM (HRTEM) images (see Figure 3e and Figure 3f ) show that the fringe patterns with lattice spacings of 0.208, 0.253 and 0.301 nm correspond to the Cu(111), CuO(002) and Cu2O(110) surfaces, and the patterns with spacings of 0.262 nm and 0.232 nm correspond to the CoO(111) and Co2O3(102) surfaces respectively; from Figure 3f it can be seen that in addition to cobalt oxide, Co2O3 was also detected in this tandem catalyst. This indicates that the CuOx / CoOx tandem catalyst has a multiphase structure and phase interface, which can effectively promote the movement of electrons and the generation of the intermediate product *NOH, while inhibiting HER (electrocatalytic hydrogen evolution reaction), thereby improving the selectivity and Faraday efficiency of NH3. Figures 3g to 3j is the high-angle annular dark-field scanning TEM image and its corresponding EELS elemental mapping; this result shows that CuOx / CoOx contains Cu, Co and O elements, and the distribution is uniform.

[0035] The crystal structure of 3-CuOx / CoOx was characterized by XRD ( Figure 4a ). It can be observed from the figure that Cu, Cu2O and CuO coexist in the prepared 3-CuOx / CoOx. This is consistent with the results of HRTEM and electron diffraction analysis. Among them, the specific 2 of 3-CuOx / CoOx θThe peaks at = 43.317, 50.449, and 74.126 correspond to the (111), (200), and (220) crystal planes of Cu (PDF#04 - 0836), located at 2 θ The peaks at = 35.555, 38.75, and 48.751 correspond to the (-111), (111), and (-202) crystal planes of CuO (PDF#05 - 0667), located at 2 θ The peaks at = 29.568, 36.424, 42.308, 61.376, 73.518, and 77.378 correspond to the (110), (111), (200), (221), (311), and (222) crystal planes of Cu2O (PDF#05 - 0667).

[0036] Figure 4a XRD characterization was also carried out on 0 - CuOx, 1 - CuOx / CoOx, 2 - CuOx / CoOx, and 4 - CuOx / CoOx. From Figure 4a it can be seen that as the proportion of CoO increases, the characteristic peaks of Cu gradually decrease, while the characteristic peaks of Cu2O gradually increase. This fully demonstrates the successful preparation of the CuOx / CoOx tandem catalyst. At the same time, the Cu2O peak of 3 - CuOx / CoOx is sharper than that of other materials, indicating that the Cu2O grains in the prepared sample are smaller and the crystallinity is better.

[0037] The types of elements contained in the catalyst and the valence bands of each element were determined by XPS analysis. The XPS spectra of 3 - CuOx / CoOx and 0 - CuOx are shown in Figure 4b and then further analyzed using XPSPEAK41 peak software. Figure 4e It was proved that CoO was successfully tandem with CuOx in 3 - CuOx / CoOx.

[0038] As shown in the Cu 2p spectrum of Figure 4c, the two fitting peaks with binding energies of 932.48 and 952.45 eV respectively belong to Cu + &Cu 0 substances, and also show two peaks at 934.2 eV (Cu 2p 3 / 2 ) and 954.5 eV (Cu 2p 1 / 2 ), and these two fitting peaks belong to the characteristic peaks of Cu 2+ . Three peaks also appear at 941.40, 943.85, and 962.00 eV, belonging to the satellite peaks of Cu 2+ .

[0039] Compared with the Cu + &Cu 0Peaks (932.56 eV and 952.86 eV) and Cu 2+ peaks (955.19 eV) ( Figure 4b ), the Cu + &Cu 0 peaks and Cu 2+ peaks in 3-CuOx / CoOx showed a negative shift, indicating that the tandem of CoOx is beneficial to electron transfer and the regulation of the Cu d-band center.

[0040] Figure 4d The Cu + Auger peak at 920.1 eV was shown, as well as the weak Cu 2+ (918.1 eV) and Cu 0 (917.1 eV) Auger peaks, indicating that the surface of 3-CuOx / CoOx mainly contains oxidized Cu 2+ and Cu + . The presence of Cu2O can effectively improve the electrocatalytic activity of NO3RR and the selectivity of NH3 production.

[0041] Figure 4e It can be seen that the two peaks located at 783.3 and 798.4 eV belong to Co 2+ 2p 3 / 2 and Co 2+ 2p 1 / 2 . The two peaks located at 780.1 and 794.3 eV belong to the characteristic peaks of Co 3+ , and the peaks at 788.43 and 806.32 eV are the satellite peaks of Co 2+ .

[0042] Figure 4f The fitting peaks are for O 1s, where the characteristic peaks at 529.87, 531.70 and 533.36 eV represent lattice oxygen, oxygen vacancies and surface adsorbed oxygen respectively. The area of the oxygen vacancy peak indicates the presence of abundant oxygen vacancies in 3-CuOx / CoOx. Oxygen vacancies, as active sites, improve the electrocatalytic performance of the catalyst.

[0043] According to the XPS spectra of 3-CuOx / CoOx, it can be calculated that in the electro-reduced nitrate-synthesized ammonia CuOx / CoOx nanomaterial 3-CuOx / CoOx with oxygen vacancy defects prepared in this example, the molar ratio of Cu2O phase, CuO phase and Cu phase is 1:2.48:1.03; the molar ratio of CoO phase to Co2O3 phase is 1:1.53.

[0044] The catalytic mechanism of the electro-reduced nitrate-synthesized ammonia CuOx / CoOx nanomaterial with oxygen vacancy defects prepared in this example for the catalytic reduction of nitrate to synthesize ammonia is shown inFigure 11 As Figure 11 shown, the Cu phase in the CuOx / CoOx nanomaterial mainly promotes the hydrolysis dissociation to generate active hydrogen, and the Cu2O phase catalyzes the active hydrogen to accelerate the reaction step of NO3 − to NO2 − in the electroreduction of nitrate to ammonia. The CoO phase and Co2O3 phase catalyze the active hydrogen to accelerate the reaction step of NO2 − to NH3 in the electroreduction of nitrate to ammonia; while the Cu phase and CuO phase play a promoting role in the whole reaction process of electroreduction of nitrate to ammonia.

[0045] Example 2 In this example, the electroreduction of nitrate to ammonia CuOx / CoOx nanomaterial with oxygen vacancy defects prepared in Example 1 is used in the dual-cathode flow electrolyzer combined ammonia fuel cell power generation system to catalyze the reduction of nitrate to ammonia.

[0046] As Figure 5 and Figure 6 shown, in this example, the dual-cathode flow electrolyzer combined ammonia fuel cell power generation system includes an anode liquid storage tank 9, a first peristaltic pump 7, a dual-cathode flow electrolyzer 105, a second peristaltic pump 5, a cathode liquid storage tank 8, and an ammonia fuel cell module; the fluid outlet of the anode liquid storage tank 9 is fluidly connected to the fluid inlet of the first peristaltic pump 7, the fluid outlet of the first peristaltic pump 7 is fluidly connected to the first water inlet 101 of the dual-cathode flow electrolyzer 105, and the first water outlet 102 of the dual-cathode flow electrolyzer 105 is fluidly connected to the fluid inlet of the anode liquid storage tank 9; the second water outlet 103 of the dual-cathode flow electrolyzer 105 is fluidly connected to the fluid inlet of the second peristaltic pump 5, the fluid outlet of the second peristaltic pump 5 is fluidly connected to the fluid inlet of the cathode liquid storage tank 8, and the first fluid outlet of the cathode liquid storage tank 8 is fluidly connected to the second water inlet 104 of the dual-cathode flow electrolyzer 105; the second fluid outlet of the cathode liquid storage tank 8 is fluidly connected to the fluid inlet of the ammonia fuel cell module; In the dual-cathode flow electrolyzer 105, a first cathode plate 1, an anode plate 2, a separator 3, and a second cathode plate 4 are sequentially arranged from the first end to the second end of the dual-cathode flow electrolyzer 105; the first cathode plate 1, the anode plate 2, the separator 3, and the second cathode plate 4 are arranged in a staggered and parallel manner in the dual-cathode flow electrolyzer 105 to form a serpentine flow channel; the first cathode plate 1 and the second cathode plate 4 are respectively electrically connected to the negative electrode of the electrochemical workstation 6, and the anode plate 2 is electrically connected to the positive electrode of the electrochemical workstation 6; As Figure 6 and Figures 7a to 7cAs shown, the first water inlet 101 is opened on the outer wall of the dual-cathode flow-through electrolytic cell 105 adjacent to the first cathode plate 1 and away from the anode plate 2. The first water outlet 102 is opened on the outer wall of the dual-cathode flow-through electrolytic cell 105 between the anode plate 2 and the partition plate 3. The second water outlet 103 is opened on the outer wall of the dual-cathode flow-through electrolytic cell 105 adjacent to the second cathode plate 4 and away from the partition plate 3. The second water inlet 104 is also opened on the outer wall of the dual-cathode flow-through electrolytic cell 105 adjacent to the second cathode plate 4 and away from the partition plate 3.

[0047] The ammonia fuel cell module includes a water bath heating device 11, an ammonia collection device 12, and an ammonia fuel cell 205; as Figure 8 shown, the ammonia fuel cell 205 is an oxygen ion conducting electrolyte-based solid oxide fuel cell; the second fluid outlet of the cathode liquid storage tank 8 is in fluid communication with the liquid inlet of the water bath heating device 11. The gas outlet of the water bath heating device 11 is in fluid communication with the gas inlet of the ammonia collection device 12. The ammonia outlet of the ammonia collection device 12 is in fluid communication with the first air inlet 201 of the ammonia fuel cell 205. The gas generated after the decomposition of ammonia by the ammonia fuel cell anode 13 and the unreacted ammonia are discharged through the first air outlet 202 of the ammonia fuel cell 205. Oxygen is introduced into the second air inlet 203 of the ammonia fuel cell. Oxygen forms oxygen anions at the ammonia fuel cell cathode 15, and the unreacted oxygen is discharged through the second air outlet 204 of the ammonia fuel cell 205.

[0048] In this embodiment, the first cathode plate 1 is a graphite electrode plate; the anode plate 2 is a platinum sheet electrode plate; the partition plate 3 is a polytetrafluoroethylene plate; the second cathode plate 4 is a carbon sheet electrode plate loaded with the CuOx / CoOx nanomaterial prepared in Example 1; the solid oxide electrolyte 14 of the ammonia fuel cell 205 is yttria-stabilized zirconia (YSZ); the ammonia fuel cell anode 13 is a Ni-YSZ cermet anode, and the ammonia fuel cell cathode 15 is a Sr / LaMnO3 cathode. The first cathode plate 1, the anode plate 2, the partition plate 3, and the second cathode plate 4 are all commercially purchased electrodes, cut into squares with a size of 4 cm × 4 cm, and the area of each is 16 cm 2 ; the length, width, and height of the dual-cathode flow-through electrolytic cell are 5 cm × 5 cm × 5 cm, and the volume is 125 cm 3 .

[0049] Since ammonia gas is produced during the nitrate reduction reaction, a top cover and nuts are used in the dual-cathode flow-through electrolytic cell to ensure the tightness of the device and prevent the leakage of liquids and gases. The height of the anode liquid storage tank should be lower than that of the dual-cathode flow-through electrolytic cell to ensure that the liquid in the dual-cathode flow-through electrolytic cell can flow back to the anode liquid storage tank by gravity. The height of the cathode liquid storage tank should be higher than that of the electrolytic cell to ensure that the sewage in the cathode liquid storage tank can flow back into the electrolytic cell by gravity.

[0050] In this embodiment, the method for loading the CuOx / CoOx nanomaterial prepared in Example 1 on the second cathode plate is as follows: 8 mg of the CuOx / CoOx nanomaterial powder prepared in Example 1 and 1 mg of acetylene black are added to 1 mL of an isopropyl alcohol aqueous solution (the volume ratio of water to isopropyl alcohol is 3:1) and mixed evenly to obtain a catalyst dispersion; 40 μL of Nafion solution is added to the catalyst dispersion as a binder and ultrasonicated for 30 min to make it evenly dispersed, obtaining an ink dispersion; the ink dispersion is evenly dripped onto a carbon sheet and air-dried naturally to obtain the second cathode plate loaded with the CuOx / CoOx nanomaterial; the resin solid content in the Nafion solution is 5 wt% (the Nafion solution used in this embodiment is from DuPont, model D-520, produced by Shanghai Chuxi Industry Co., Ltd. The water content of the Nafion solution is 45 ± 3%, the volatile organic compound content is 50 ± 3%, the exchange capacity is 1.03 - 1.12, and the resin solid content is 5%).

[0051] In this embodiment, the method for generating electricity by the dual-cathode flow-through electrolytic cell combined with an ammonia fuel cell is as follows: the dual-cathode flow-through electrolytic cell 105 injects the nitrate-containing wastewater in the anode liquid storage tank 9 into the dual-cathode flow-through electrolytic cell 105 through the first peristaltic pump 7, and reduces the nitrate in the nitrate-containing wastewater to generate ammonia-containing liquid in the dual-cathode flow-through electrolytic cell 105. The ammonia-containing liquid is injected into the cathode liquid storage tank 8 through the second peristaltic pump 5; the ammonia fuel cell module converts the ammonia in the ammonia-containing liquid in the cathode liquid storage tank 8 into electrical energy, and its working method specifically includes the following working stages: The first stage: Inject nitrate-containing wastewater into the anode liquid storage tank 9, and turn on the first peristaltic pump 7, so that the nitrate-containing wastewater in the anode liquid storage tank 9 is pumped into the dual-cathode flow-through electrolytic cell 105 through the first water inlet 101 at a flow rate of 150 mL / min. Wait until the nitrate-containing wastewater fills the dual-cathode flow-through electrolytic cell 105 (about 50 s), then turn on the power supply of the electrochemical workstation 6 to make the dual-cathode flow-through electrolytic cell 105 start to work, and immediately turn on the second peristaltic pump 5, so that the treated nitrate-containing wastewater in the dual-cathode flow-through electrolytic cell 105 is pumped into the cathode liquid storage tank 8 through the second water outlet 103 at a flow rate of 120 mL / min. After the cathode liquid storage tank 8 is filled with the treated nitrate-containing wastewater, adjust the hose flow regulator 10 at the first fluid outlet of the cathode liquid storage tank 8, so that the nitrate-containing wastewater in the cathode liquid storage tank 8 flows into the dual-cathode flow-through electrolytic cell 105 through the second water inlet 104 at a flow rate of 120 mL / min. At the same time, open the first water outlet 102 so that the nitrate-containing wastewater in the dual-cathode flow-through electrolytic cell 105 flows back to the anode liquid storage tank 9 under the action of gravity. Stop injecting the nitrate-containing wastewater into the anode liquid storage tank 9 after the system is stable; The second stage: When the inlet flow rate of the first water inlet 101 is balanced with the outlet flow rate of the first water outlet 102, the nitrate-containing wastewater near the anode plate 2 no longer flows towards the vicinity of the second cathode plate 4, and the nitrate-containing wastewater in the pretreatment module and the nitrate treatment module both realizes self-circulation. Maintain the self-circulation of the nitrate treatment module until the nitrate content in the nitrate-containing wastewater in the nitrate treatment module drops to less than 30% of the initial content, then turn off the second peristaltic pump 5 and the hose flow regulator 10, and open the switch of the second fluid outlet of the cathode liquid storage tank 8, so that the ammonia-containing liquid in the cathode liquid storage tank 8 flows into the ammonia fuel cell module. The ammonia fuel cell module generates electricity using the ammonia in the ammonia-containing liquid; Specifically, first, the ammonia-containing liquid collected by the cathode liquid storage tank 8 enters the water bath heating device 11. The water bath heating device 11 uses the water bath heating method to cause the ammonia in the ammonia-containing liquid to escape. The escaped ammonia enters the ammonia collection device 12, and other gases in the gas are discharged from the system to collect ammonia (since ammonia has a small density, it will be at the upper end of the gas collecting bottle); finally, the ammonia collected by the ammonia collection device 12 enters the ammonia fuel cell 205 through the first air inlet 201. At the same time, oxygen is introduced through the second air inlet 203, and the ammonia fuel cell heating device is started to raise the temperature to 750 °C. At this time, the ammonia fuel cell starts to generate electricity; ammonia reacts and decomposes into hydrogen on the surface of the anode 13 of the ammonia fuel cell, and hydrogen reacts with oxygen anions at the anode 13 of the ammonia fuel cell, ultimately realizing the conversion of ammonia energy into electrical energy. The oxygen anions are formed by introducing oxygen through the second air inlet 203 and reacting on the cathode 15 of the ammonia fuel cell. In this embodiment, the temperature of the water bath heating device is 80 °C (in some other embodiments, it can also be other temperatures from 60 °C to 100 °C), and the ammonia collection device is at 25 °C under standard atmospheric pressure.

[0052] The third stage: After the ammonia-containing liquid in the cathode liquid storage tank 8 is emptied, the nitrate-containing wastewater is re-injected into the anode liquid storage tank 9, and at the same time, the second peristaltic pump 5 is turned on, so that the treated nitrate-containing wastewater in the dual-cathode electrolytic cell is pumped into the cathode liquid storage tank 8 through the second water outlet 103 at a flow rate of 120 mL / min; after the cathode liquid storage tank 8 is filled with the treated nitrate-containing wastewater, the hose flow regulator 10 is adjusted so that the nitrate-containing wastewater in the cathode liquid storage tank 8 flows into the dual-cathode flow-through electrolytic cell 105 through the second water inlet 104 at a flow rate of 120 mL / min; at the same time, the first water outlet 102 is opened so that the nitrate-containing wastewater in the dual-cathode flow-through electrolytic cell 105 flows back to the anode liquid storage tank 9 under the action of gravity; after the system is stable, the injection of the nitrate-containing wastewater into the anode liquid storage tank 9 is stopped; when the water inlet flow rate of the first water inlet 101 is balanced with the water outlet flow rate of the first water outlet 102, the second stage is repeated.

[0053] During the liquid self - circulation process of the nitrate treatment module in the second stage, the nitrate - containing wastewater is pumped into the cathode liquid storage tank 8 by the second peristaltic pump 5 at the second water outlet 103, and then flows back to the second water inlet 104. During the liquid self - circulation process of the pretreatment module in the second stage, the nitrate - containing wastewater flows into the anode liquid storage tank 9 at the first water outlet 102, and then is pumped into the first water inlet 101 by the first peristaltic pump 7. In the ammonia fuel cell module of the second stage, ammonia enters through the first air inlet 201, decomposes into nitrogen and hydrogen at the anode 13 of the ammonia fuel cell, hydrogen reacts with oxygen anions to form water, and the unreacted ammonia, hydrogen, and the product nitrogen and water are all discharged from the first air outlet 202. In the ammonia fuel cell module of the second stage, oxygen enters through the second air inlet 203, forms oxygen anions on the cathode of the ammonia fuel cell, and the unreacted oxygen is discharged from the second air outlet 204.

[0054] In this embodiment, the first peristaltic pump 7 is connected to the anode liquid storage tank 9 and the dual - cathode flow - through electrolytic cell 105. The flow rate of the electrolyte can be controlled by adjusting the first peristaltic pump 7 to ensure that the electrodes are always immersed in the electrolyte. The second peristaltic pump 5 is connected to the cathode liquid storage tank 8 and the dual - cathode flow - through electrolytic cell 105. The ammonia - containing liquid in the cathode liquid storage tank 8 can be continuously collected by adjusting the second peristaltic pump 5. At the same time, a hose flow regulator 10 is provided on the connecting hose between the cathode liquid storage tank 8 and the dual - cathode flow - through electrolytic cell to control the flow rate into the dual - cathode flow - through electrolytic cell.

[0055] In this embodiment, the electrochemical reaction occurring at the first cathode plate of the dual - cathode flow - through electrolytic cell is: M n+ +ne - →M (1); The electrochemical reaction occurring at the second cathode plate of the dual - cathode flow - through electrolytic cell is: NO3 - +6H2O + 8e - → NH3+ 9OH - (2); 4OH - →O2+2H2O+4e - (3); NO3 - +6H2O+8e - →NH3+9OH - (4); NO3 - +H2O+2e - →NO2 - +2OH - (5); NO2 - +5H2O+6e - →NH3+7OH- (6); The electrochemical reaction occurring at the anode plate of the dual-cathode flow-through electrolytic cell is as follows: 2H2O → O2 + 4H + + 4e - (7); In this embodiment, the reaction occurring at the anode of the ammonia fuel cell is as follows: H2 + O 2- → H2O + 2e - (8); The reaction occurring at the cathode of the ammonia fuel cell is as follows: 1 / 2O2 + 2e - → O 2- (9); At the anode surface of the ammonia fuel cell, the cracking of ammonia to generate hydrogen occurs, and the reaction is: 2NH3 → N2 + 3H2 (10); In this embodiment, the concentration of nitrate in the nitrate-containing wastewater used is 400 ppm NO3 − , the concentration of potassium sulfate is 0.2 mol / L, and it also contains metal ions, zinc ions. In order to reduce the occurrence of side reactions such as hydrogen evolution in the first cathode plate and at the same time control the rate of degradation of metal ions in the first cathode plate, the applied voltage range of the dual-cathode flow-through electrolytic cell in this embodiment is controlled at -0.3 to -0.9 V vs. RHE.

[0056] Using the dual-cathode flow-through electrolytic cell combined with the ammonia fuel cell power generation system of this embodiment, the electro-reduced nitrate-synthesized ammonia CuOx / CoOx nanomaterial with oxygen vacancy defects prepared in Example 1 is used to catalyze the synthesis of ammonia from nitrate in the nitrate-containing wastewater, and the ammonia yield is high and the system operation stability is good.

[0057] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the claims of this patent application.

Claims

1. A CuOx / CoOx nanomaterial for electroreductive nitrate synthesis of ammonia with oxygen vacancy defects, characterized in that, The molar ratio of copper to cobalt in the CuOx / CoOx nanomaterial is 30:(1-8); the particle surface of the CuOx / CoOx nanomaterial has a nanoscale microporous structure; in the microstructure of the CuOx / CoOx nanomaterial, copper coexists in the forms of Cu phase, Cu2O phase and CuO phase, and cobalt exists in the forms of CoO phase and Co2O3 phase; the Cu phase promotes the hydrolysis dissociation to generate active hydrogen, and the Cu2O phase is used to accelerate the reaction step from NO3 − to NO2 − in the electroreduction of nitrate to ammonia, and the CoO phase and Co2O3 phase are used to accelerate the reaction step from NO2 − to NH3 in the electroreduction of nitrate to ammonia, and the Cu phase and CuO phase play a promoting role in the whole reaction process of the electroreduction of nitrate to ammonia.

2. The CuOx / CoOx nanomaterial for electrochemically reducing nitrate to ammonia with oxygen vacancy defects according to claim 1, wherein The molar ratio of the Cu2O phase, CuO phase and Cu phase is 1:(2.0 - 2.5):(1.0 - 1.2); the molar ratio of the CoO phase and Co2O3 phase is 1:(1.3 - 1.6).

3. Preparation method of CuOx / CoOx nanomaterial for electro-reducing nitrate to synthesize ammonia with oxygen vacancy defects, characterized in that, It includes the following steps: Step (1), adding copper acetate monohydrate and cobalt acetate tetrahydrate into glycerol to obtain a mixed dispersion; Step (2), fully stirring the mixed dispersion at room temperature, and then transferring it to a reaction kettle for heating to react fully. After the reaction ends, a mixed suspension is obtained; Step (3), washing the solid precipitate obtained by centrifuging the mixed suspension with absolute ethanol, and then drying it in a vacuum drying oven to obtain a catalyst precursor; Step (4), performing a calcination treatment on the catalyst precursor. After the calcination treatment ends, it is naturally cooled to room temperature and pulverized to obtain the CuOx / CoOx nanomaterial with oxygen vacancy defects for electro-reducing nitrate to synthesize ammonia as described in claim 1 or 2.

4. The preparation method of the CuOx / CoOx nanomaterial for electro-reducing nitrate to synthesize ammonia with oxygen vacancy defects according to claim 3, characterized in that, In step (1), the molar ratio of copper acetate monohydrate and cobalt acetate tetrahydrate is 30:(1 - 8); the molar concentration of copper acetate monohydrate in the mixed dispersion is 0.08 - 0.15 mol / L.

5. The preparation method of the CuOx / CoOx nanomaterial for electro-reducing nitrate to synthesize ammonia with oxygen vacancy defects according to claim 3, characterized in that, In step (2), the stirring rate is 500 - 1000 rpm, and the stirring time is 1 - 2 h; the heating temperature is 150 - 200 °C, and the reaction time is 20 - 25 h.

6. The preparation method of the CuOx / CoOx nanomaterial for electro-reducing nitrate to synthesize ammonia with oxygen vacancy defects according to claim 3, characterized in that, In step (3), the drying temperature is 60 - 80 °C, and the drying time is 8 - 12 h.

7. The preparation method of the CuOx / CoOx nanomaterial for electro-reducing nitrate to synthesize ammonia with oxygen vacancy defects according to claim 3, characterized in that, In step (4), the conditions for the calcination treatment are: first heating from room temperature to 350 - 400 °C at a heating rate of 5 - 10 °C / min, and then holding at 350 - 400 °C for 1 - 2 h.

8. The preparation method of the CuOx / CoOx nanomaterial for electro-reducing nitrate to synthesize ammonia with oxygen vacancy defects according to claim 3, characterized in that, In step (1), the molar ratio of copper acetate monohydrate and cobalt acetate tetrahydrate is 15:2; the molar concentration of copper acetate monohydrate in the mixed dispersion is 0.1 mol / L; In step (2), the stirring rate is 500 rpm, and the stirring time is 1 h; the heating temperature is 180 °C, and the reaction time is 24 h; In step (3), the drying temperature is 60 °C, and the drying time is 12 h; In step (4), the conditions for the calcination treatment are: first heating from room temperature to 350 °C at a heating rate of 5 °C / min, and then holding at 350 °C for 2 h.

9. Use of a CuOx / CoOx nanomaterial with oxygen vacancy defects for electroreduction of nitrate to ammonia, characterized in that, Loading the CuOx / CoOx nanomaterial with oxygen vacancy defects for electro-reducing nitrate to synthesize ammonia as described in claim 1 or 2 onto the cathode of an electrocatalytic reduction nitrate electrolytic cell for electrocatalytic reduction of nitrate to synthesize ammonia; the method for loading the CuOx / CoOx nanomaterial onto the cathode of the electrocatalytic reduction nitrate electrolytic cell is: adding the CuOx / CoOx nanomaterial and acetylene black into an isopropyl alcohol aqueous solution and mixing evenly to obtain a catalyst dispersion; adding a Nafion solution to the catalyst dispersion and ultrasonic dispersing evenly to obtain an ink dispersion; evenly dripping the ink dispersion onto the cathode of the electrocatalytic reduction nitrate electrolytic cell and naturally drying it.

10. Use of the CuOx / CoOx nanomaterial with oxygen vacancy defects for electro-reducing nitrate to synthesize ammonia according to claim 9, characterized in that, The mass ratio of the CuOx / CoOx nanomaterial to acetylene black is 8:1; the mass-volume ratio of the CuOx / CoOx nanomaterial to the isopropanol aqueous solution in the catalyst dispersion is 8 g / L, and the volume ratio of water to isopropanol in the isopropanol aqueous solution is 3:1; the volume ratio of the catalyst dispersion to the Nafion solution in the ink dispersion is 1:0.04; the ultrasonic dispersion time is 30 min; the resin solid content in the Nafion solution is 5 wt%; the electrocatalytic reduction nitrate electrolytic cell is an H-type electrolytic cell or a flow-type electrolytic cell.

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