A Cu-doped CeO2-CN x Catalyst, preparation method and application thereof in nitrate reduction

Abstract

The present invention provides a Cu-doped CeO2-CN x The catalyst, preparation method and application in nitrate reduction significantly enhance the interaction between reactants and catalysts through activation and multiple heat treatments, optimize the electron transfer capacity, and simultaneously enhance the adsorption capacity for nitrate, optimize the synergistic effect of oxygen vacancies and Cu active sites, and the obtained catalyst for electrocatalytic reduction of nitrate to ammonia has high activity, high selectivity and stability.

Description

Technical Field

[0001] The present invention belongs to the field of electrocatalysis technology and relates to a Cu-doped CeO2-CN x The invention relates to a catalyst, a preparation method and application thereof in nitrate reduction; in particular, to a preparation method and application of a porous catalytic material with high activity, high selectivity and high stability. Background Art

[0002] With fossil energy depletion and a growing global population, environmental challenges and energy crises are constantly emerging, necessitating the development of sustainable energy resources. Most countries are committed to adopting green chemical production in industry to reduce fossil fuel consumption and achieve the international mandate of "carbon neutrality." Ammonia (NH3) is the world's second-largest chemical by volume, with a global market value exceeding 185 million tons annually. NH3 is also essential in industrial production and agricultural life. Approximately 50% of global food production relies on ammonia-based fertilizers, feeding nearly 7 billion people. NH3 is also widely used in pharmaceuticals, textiles, fuels, wastewater treatment, and other fields. Achieving a stable and affordable food supply for a growing global population requires sufficient and cost-effective NH3 production. NH3 is also an ideal zero-carbon energy carrier and hydrogen storage medium. It is easily liquefied, has a high energy density, high-quality hydrogen content, and low transportation and storage costs, and is currently being explored as a future renewable energy alternative. Due to its use as a carbon-free fuel, demand for NH3 production is expected to further increase.

[0003] In nature, biological nitrogen fixation provides essential nutrients for organisms, but the reaction is slow. Inspired by the conversion of N₂ to NH₃ by nitrogenase, the electrocatalytic nitrogen reduction reaction (NRR), utilizing N₂ from water and air as feedstock, has become a leading research frontier as an environmentally friendly method for producing NH₃. Compared to the HB process, electrocatalytic NRR offers advantages such as low energy consumption, mild reaction conditions, and zero carbon emissions. It also enables decentralized ammonia production, supporting distributed long-term energy storage and fuel production, making it a promising alternative to the HB process for a circular economy.

[0004] Electrochemical nitrate reduction reaction (e-NO3RR) is considered a promising pathway for ambient NH3 production because NO3 − It has low N=O bond dissociation energy, which ensures faster reaction kinetics; at the same time, its excellent solubility makes NO3 −The electrocatalyst surface can be fully contacted; and the more positive reaction potential reduces the interference of the competitive HER. Therefore, e-NO3RR is easier than NRR in terms of thermodynamics and kinetics, and is expected to provide a practical green route for NH3 electrosynthesis under ambient conditions. On the other hand, NO3 − It is widely present in industrial wastewater and groundwater. Its excessive discharge and accumulation will destroy the ecological balance and nitrogen cycle system. In addition, NO3 − It will directly threaten human health and cause a variety of diseases. Therefore, from the perspective of "turning waste into treasure", NO3 − The conversion of nitrogen dioxide into value-added NH3 is of great significance to environmental protection, public health, and restoring the balance of the nitrogen cycle. Similar to NRR, e-NO3RR uses water as the hydrogen source and is powered by sustainable energy (solar, wind, and tidal energy), reducing consumption and greenhouse gas emissions.

[0005] Excellent e-NO3RR performance is closely related to the catalyst, which is mainly reflected in the intrinsic activity of each active site and the density of active sites. The morphology, structure, defects and synergistic effects of electrocatalysts are the main factors affecting the activity of e-NO3RR. For example, different crystal structures can be used for NO3 − Activation provides a large number of defect sites and coordination conditions. By adjusting the band gap or intrinsic conductivity, heteroatom doping can maximize the absorption free energy of electrocatalysts for different intermediates. In the e-NO3RR process, the interaction between the reaction intermediates and the catalyst surface directly affects the subsequent hydrogenation ability and the kinetics of the reaction. The selectivity of the final product is largely affected by the electrode material. In order to achieve efficient e-NO3RR, researchers have studied electrocatalysts including non-metallic, precious metal and transition metal-based materials. Transition metal-based materials include Cu-based, Fe-based, Ni-based and Co-based catalysts. In the e-NO3RR process, NO3 − Reduction to NO2 − The kinetics are slower, which may be attributed to the lowest unoccupied molecular π * The orbital has high energy, which is not conducive to the entry of charges. Cu has a unique 3d 10 configuration, whose high d orbital occupancy is similar to the LUMOπ of nitrate * The similar energy levels can promote the e-NO3RR and help to become NO3 − Highly active center for reduction reaction.

[0006] For example, CN118513042A discloses a preparation method and application of a single-atom transition metal catalyst CeO2 rich in oxygen vacancies. The preparation method is as follows: weighing phthalocyanine molecules containing single-atom transition metal sites and trimesic acid, polyvinylpyrrolidone and Ce(NO3)3; dissolving them in a mixed solution of ethanol and N,N-dimethylformamide; reacting the mixed solution at 100-140°C to form MPc / Ce-MOF powder; finally, placing the MPc / Ce-MOF powder in a muffle furnace and calcining it at a temperature of 350-550°C in an air atmosphere for 2 hours to obtain an M1 / CeO2 catalyst; the obtained catalyst improves the utilization rate of active sites, generates a large number of oxygen vacancies, enhances the adsorption of nitric acid and intermediates, can effectively improve the activity of electrocatalytic reduction of nitrate ions and the selectivity of ammonia production, and has a better ammonia production effect. Summary of the Invention

[0007] Based on the above content, the present invention provides a Cu-doped CeO2-CN x The catalyst, preparation method, and application in nitrate reduction significantly enhance the interaction between reactants and catalysts through multiple heat treatments, optimize electron transport capacity, enhance nitrate adsorption capacity, and optimize the synergistic effect of oxygen vacancies and Cu active sites. The resulting catalyst has high dispersion, high selectivity, and stability, providing an innovative strategy for the development of efficient nitrate reduction catalysts, as follows:

[0008] A Cu-doped CeO2-CN x The preparation method of the catalyst includes the following preparation method:

[0009] (1) Preparation of bimetallic MOF materials:

[0010] Solution A: Add copper nitrate and cerium nitrate solids into methanol solution and stir magnetically to fully dissolve;

[0011] Solution B: Add dimethylimidazole solid and citric acid to methanol solution and stir magnetically to fully dissolve;

[0012] Pour solution A into solution B, adjust the pH to 5.5±0.2 with sodium hydroxide or ammonia water, stir magnetically at 500-800 rpm for 12-36 hours at a water bath temperature of 25-30°C, filter, wash, and dry to obtain a copper-cerium bimetallic MOF material;

[0013] (2) Preparation of nitrogen-doped carbon materials: The product obtained in step (1) is mixed with melamine in a certain proportion and ground thoroughly, and then calcined in nitrogen in a tube furnace, cooled naturally to room temperature, and then ground thoroughly;

[0014] (3) Activation: The product prepared in step (2) was placed in a hydrothermal reactor containing 6-8 wt% KOH, and activated at 170-180°C for 4-5 h. After cooling, the mixture was filtered and dried to obtain a nitrogen-doped porous carbon support with a high specific surface area.

[0015] (4) After secondary nitrogen calcination treatment, the mixture was ground evenly to obtain Cu-doped CeO2-CN x catalyst.

[0016] In certain embodiments, 0.06-0.08 mol of copper nitrate and 0.03-0.04 mol of cerium nitrate solids are added to 100-150 mL of methanol solution and magnetically stirred for 5-10 minutes to fully dissolve.

[0017] In certain embodiments, 0.8-1.2 mol of dimethylimidazole solid and 0.04-0.06 mol of citric acid are added to 140-160 mL of methanol solution and magnetically stirred for 5-10 minutes to fully dissolve.

[0018] In certain embodiments, the weight ratio of the product obtained in step (1) to melamine is 2:(1.2-1.4).

[0019] In some embodiments, the tubular furnace is subjected to a nitrogen calcination treatment once: the temperature is increased at 3-5°C / min to 490-510°C and held at this temperature for 50-70 minutes, and then the temperature is increased at 3-5°C / min to 950-1000°C and held at this temperature for 110-130 minutes.

[0020] In certain embodiments, the secondary nitrogen calcination treatment is performed by heating the temperature at 3-5°C / min to 200-500°C and maintaining the temperature for 120-140 minutes.

[0021] In certain embodiments, a Cu-doped CeO2-CN x Catalyst used in the electrochemical reduction of nitrate to synthesize ammonia.

[0022] An electrode material, wherein the electrode material is formed by Cu doping CeO2-CN x The catalyst is prepared by compounding with a conductive substrate, and the conductive substrate is selected from one of foamed nickel, carbon paper and carbon cloth.

[0023] A method for preparing an electrode material by doping Cu with CeO2-CN x The catalyst and Nafion dispersion are dispersed in an organic solvent, the obtained dispersion is drop-coated on carbon paper, and dried to obtain the product.

[0024] The present invention first prepares Cu-Ce bimetallic MOF materials, and uses citric acid instead of oxalic acid as a complexing agent. Citric acid regulates the size distribution of metal clusters through steric hindrance, wherein the tricarboxylic acid structure can simultaneously chelate Cu 2+and Ce 3+ , to avoid heterogeneous precipitation or phase separation, see the attached Figure 1 The prepared bimetallic MOF material has a hexagonal morphology and a smooth surface, indicating that the bimetallic MOF was successfully prepared without any technical problems of dual-phase deposition.

[0025] Next, the nitrogen-doped carbon material is prepared: During the calcination process, the MOF organic ligand (dimethylimidazole) is carbonized at high temperature to form a porous carbon matrix that retains some of the MOF's pore structure, which is primarily micro-mesoporous. A nitrogen source, melamine, is also introduced during the calcination process, ultimately resulting in a porous nitrogen-doped carbon support. The nitrogen-doped carbon material serves as a catalyst support. During the electroreduction of nitrate to ammonia, the catalytic efficiency and reaction performance are significantly improved through structural modification, enhanced conductivity, and intermediate state stabilization. This material not only accelerates the reaction rate but also ensures the effective stability of the intermediate substances, making the overall reaction process more efficient and reliable.

[0026] Activation: The original specific surface area of the bimetallic MOF material is relatively high, which decreases significantly after calcination and carbonization, but the porous carbon still retains a relatively high value. However, in order to obtain a higher specific surface area, pore expansion activation is required. KOH reacts with carbon in the following way, etching the carbon skeleton to generate new pores, forming a rough or porous structure, and enhancing the surface active sites.

[0027] Finally, the second nitrogen calcination process plays multiple key roles in the preparation of the catalyst and has significant technical advantages in improving the performance of the electrochemical reduction of nitrate to ammonia: (1) The second calcination can further form and stabilize oxygen vacancies in the CeO2 lattice. Oxygen vacancies serve as key active sites for nitrate adsorption and activation, which can significantly enhance the interaction between the reactants and the catalyst; (2) Since the present invention does not require subsequent precious metal impregnation loading, the second calcination can effectively remove the residual oxygen-containing groups (such as -COOH) after KOH activation, reduce inactive sites, and improve conductivity; (3) The second calcination induces electron rearrangement, enhances the charge transfer efficiency at the Cu-CeO2 heterogeneous interface, and promotes the conversion of the intermediate in the rate-determining step; (4) The heat treatment can eliminate the internal stress formed during the pre-treatment of the porous carbon, avoid the structural collapse of the carbon skeleton during the electrochemical cycle, and relieve the volume expansion stress during the electrochemical cycle, thereby improving the stability and life of the catalyst.

[0028] See attached Figure 1 and attached Figure 2 , of which Figure 1 (C) and (d) are the morphologies after activation and secondary nitrogen calcination heat treatment, which are porous morphologies. Figure 1 Zhonghe Fu Figure 2From the TEM-Mapping results, it can be seen that the copper and cerium are evenly dispersed and coupled in the form of an alloy, with a lattice spacing of 0.27nm, and the C, N, O, Cu, and Ce species elements are evenly distributed in the catalyst.

[0029] Beneficial technical effects: The present invention significantly enhances the interaction between reactants and catalysts through multiple heat treatments, optimizes electron transfer capacity, and simultaneously enhances the adsorption capacity of nitrate ions, optimizes the synergistic effect of oxygen vacancies and Cu active sites, and the obtained catalyst has high NH3 yield and high NH3 selectivity and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Attachment Figure 1 Bimetallic MOF materials and Cu-doped CeO2-CN x Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of the catalyst, and the corresponding elemental mapping images.

[0031] Attachment Figure 2 Cu-doped CeO2-CN x Elemental mapping diagram of multiple elements in catalyst.

[0032] Attachment Figure 3 Faradaic efficiency and yield of NH3 of the catalyst at different secondary calcination temperatures.

[0033] Attachment Figure 4 Linear sweep voltammetry (LSV), chronoamperometry (CA) curves and Faradaic efficiency and yield of NH3 of different sample catalysts.

[0034] Attachment Figure 5 Catalyst spectral testing.

[0035] Attachment Figure 6 Catalyst stability testing. DETAILED DESCRIPTION

[0036] Example 1

[0037] A Cu-doped CeO2-CN x The preparation method of the catalyst includes the following preparation method:

[0038] (1) Preparation of bimetallic MOF materials.

[0039] Solution A: Add 0.06 mol copper nitrate and 0.03 mol cerium nitrate solids into 100 mL methanol solution and stir magnetically for 5 minutes to fully dissolve.

[0040] Solution B: Add 0.8 mol of dimethylimidazole solid and 0.04 mol of citric acid to 140 mL of methanol solution and stir magnetically for 5 minutes to fully dissolve.

[0041] Solution A was poured into solution B, and the pH value was adjusted to 5.5±0.2 using sodium hydroxide or ammonia water. The solution was stirred magnetically at 500 rpm for 12 h at a water bath temperature of 25°C, filtered, washed, and dried to obtain a copper-cerium bimetallic MOF material.

[0042] (2) Preparation of nitrogen-doped carbon materials: The product obtained in step (1) was mixed with melamine in a weight ratio of 2:(1.2) and ground thoroughly. The mixture was then subjected to nitrogen calcination in a tubular furnace: the temperature was raised to 490°C at a rate of 3°C / min and kept constant for 50 min. The temperature was then raised to 950°C at a rate of 3°C / min and kept constant for 110 min. The mixture was then naturally cooled to room temperature and ground thoroughly.

[0043] (3) Activation: The product prepared in step (2) was placed in a hydrothermal reactor containing 6 wt% KOH and activated at 170°C for 4 h. After cooling, it was filtered and dried to obtain a nitrogen-doped porous carbon support with a high specific surface area.

[0044] (4) Secondary nitrogen calcination treatment: heating at 3°C / min to 200°C and maintaining constant temperature for 120 min. After calcination, grinding is carried out to obtain Cu-doped CeO2-CN. x catalyst.

[0045] Example 2

[0046] A Cu-doped CeO2-CN x The preparation method of the catalyst includes the following preparation method:

[0047] (1) Preparation of bimetallic MOF materials.

[0048] Solution A: Add 0.07 mol copper nitrate and 0.035 mol cerium nitrate solids into 125 mL methanol solution and stir magnetically for 7.5 min to fully dissolve.

[0049] Solution B: Add 1.0 mol of dimethylimidazole solid and 0.05 mol of citric acid to 150 mL of methanol solution and stir magnetically for 7.5 min to fully dissolve.

[0050] Solution A was poured into solution B, and the pH value was adjusted to 5.5±0.2 using sodium hydroxide or ammonia water. The solution was stirred magnetically at 650 rpm for 24 h at a water bath temperature of 27.5°C, filtered, washed, and dried to obtain a copper-cerium bimetallic MOF material.

[0051] (2) Preparation of nitrogen-doped carbon materials: The product obtained in step (1) was mixed with melamine in a weight ratio of 2: (1.3) and ground thoroughly. The mixture was then subjected to nitrogen calcination in a tubular furnace: the temperature was raised to 500°C at 4°C / min and kept constant for 60 min. The temperature was then raised to 975°C at 4°C / min and kept constant for 120 min. The mixture was then naturally cooled to room temperature and ground thoroughly.

[0052] (3) Activation: The product prepared in step (2) was placed in a hydrothermal reactor containing 7 wt% KOH and activated at 175°C for 4.5 h. After cooling, it was filtered and dried to obtain a nitrogen-doped porous carbon support with a high specific surface area.

[0053] (4) Secondary nitrogen calcination treatment: heating at 4°C / min to 350°C and maintaining the temperature for 130 min. After calcination, grind evenly to obtain Cu-doped CeO2-CN x catalyst.

[0054] Example 3

[0055] A Cu-doped CeO2-CN x The preparation method of the catalyst includes the following preparation method:

[0056] (1) Preparation of bimetallic MOF materials.

[0057] Solution A: Add 0.08 mol copper nitrate and 0.04 mol cerium nitrate solids into 150 mL methanol solution and stir magnetically for 10 minutes to fully dissolve.

[0058] Solution B: Add 1.2 mol of dimethylimidazole solid and 0.06 mol of citric acid to 160 mL of methanol solution and stir magnetically for 10 minutes to fully dissolve.

[0059] Solution A was poured into solution B, and the pH value was adjusted to 5.5±0.2 using sodium hydroxide or ammonia water. The mixture was stirred magnetically at 800 rpm for 36 h at a water bath temperature of 30° C., filtered, washed, and dried to obtain a copper-cerium bimetallic MOF material.

[0060] (2) Preparation of nitrogen-doped carbon materials: The product obtained in step (1) was mixed with melamine in a weight ratio of 2: (1.4) and ground thoroughly. The mixture was then subjected to nitrogen calcination in a tubular furnace: the temperature was raised at 5°C / min to 510°C and held constant for 70 min, then the temperature was further raised at 5°C / min to 1000°C and held constant for 130 min, and the mixture was naturally cooled to room temperature and ground thoroughly.

[0061] (3) Activation: The product prepared in step (2) was placed in a hydrothermal reactor containing 8 wt% KOH and activated at 180°C for 5 h. After cooling, it was filtered and dried to obtain a nitrogen-doped porous carbon support with a high specific surface area.

[0062] (4) Secondary nitrogen calcination treatment: Heating at 5°C / min to 500°C and maintaining constant temperature for 140 min. After calcination, grinding is carried out to obtain Cu-doped CeO2-CN. x catalyst.

[0063] Comparative Example 1

[0064] A method for preparing a Cu / C catalyst comprises the following preparation method:

[0065] (1) Preparation of bimetallic MOF materials.

[0066] Solution A: Add 0.07 mol of copper nitrate solid to 125 mL of methanol solution and stir magnetically for 7.5 minutes to fully dissolve.

[0067] Solution B: Add 1.0 mol of dimethylimidazole solid and 0.05 mol of citric acid to 150 mL of methanol solution and stir magnetically for 7.5 min to fully dissolve.

[0068] Solution A was poured into solution B, and the pH value was adjusted to 5.5±0.2 using sodium hydroxide or ammonia water. The mixture was stirred magnetically at 650 rpm for 24 h at a water bath temperature of 27.5°C, filtered, washed, and dried to obtain the MOF material.

[0069] (2) The product obtained in step (1) was subjected to a nitrogen calcination treatment in a tubular furnace: the temperature was raised to 500°C at 4°C / min and kept constant at that temperature for 60 min, and then the temperature was further raised to 975°C at 4°C / min and kept constant at that temperature for 120 min. After naturally cooling to room temperature, the product was fully ground to obtain a Cu / C catalyst.

[0070] Electrochemical measurements: Three-electrode system tests were performed on a CHI 660E electrochemical workstation. A platinum sheet was used as the counter electrode, and a saturated Hg / HgO electrode was used as the reference electrode. The potential was converted to that relative to the reversible hydrogen electrode (RHE): E(RHE) = E(Hg / HgO) + 0.197 + 0.0591*pH. The working electrode was prepared by drop-coating 150 μL of catalyst ink (2 mg of the catalyst prepared in the examples and comparative examples, 240 μL of isopropanol, 60 μL of water, and 25 μL of Nafion solution) onto carbon paper (area: 1 cm). 2 )superior.

[0071] The catalyst prepared in Example 2 was used as the reference, and the secondary nitrogen calcination treatment was adjusted: the temperature was raised to 200°C, 300°C, 400°C, and 500°C at 4°C / min, and the mixture was ground evenly after calcination to obtain Cu-doped CeO2-CN. x Catalyst, see attached Figure 3 The FE and yield of NH3 of the catalyst at different secondary calcination temperatures are as follows. When the calcination temperature is modified to 500°C in Example 2, the corresponding catalyst has the best catalytic performance.

[0072] See attached Figure 4 , tested based on Example 2 and Comparative Example 1, wherein the attached Figure 4 (a) is the preparation of Cu-doped CeO2-CN in Example 2 xThe chronoamperometric CA curve of (Ce-Cu / C) catalyst; Figure 4 (b) is the CA curve of the Cu / C catalyst prepared in Comparative Example 1. The following conclusions can be drawn: (1) the current density increases significantly after Ce doping; (2) the FE of Example 2 NH3 The overall yield is higher than that of comparative example 1, and the highest can reach 96.01%; (3) The yield of example 2 is much higher than that of Cu / C, and the highest can reach 25.12 μmol . h -1 cm -2 .

[0073] See attached Figure 5 , UV spectrum of catalyst (a) N2H4 (b) NO2 - UV spectrum of (c) N2H4, NO2 - , FE of NH3, it can be concluded that the catalyst of the present invention has high selectivity, that is, the yield of the corresponding by-products and the Faradaic efficiency are very low.

[0074] See attached Figure 6 It can be seen that in the ten cycle tests, the FE of NH3 always remained above 93%, and the absorbance curve of NH3 after each test was very close. The IT curve and NH3 yield also remained stable during the cycle, which proved the stability of the catalyst.

[0075] It should be noted that the above example is merely one preferred embodiment of the present invention. It is readily possible for a skilled person to modify or alter some of its parameters. Therefore, meaningless modifications based solely on the underlying design principles of the present invention are futile and ineffective; such modifications remain within the scope of protection of the present invention.

Claims

1. A Cu-doped CeO2-CN x The method for preparing a catalyst is characterized in that The invention comprises the following preparation methods: (1) Preparation of bimetallic MOF materials: Solution A: Add copper nitrate and cerium nitrate solids into methanol solution and stir magnetically to fully dissolve; Solution B: Add dimethylimidazole solid and citric acid to methanol solution and stir magnetically to fully dissolve; Pour solution A into solution B, adjust the pH to 5.5±0.2 with sodium hydroxide or ammonia water, stir magnetically at 500-800 rpm for 12-36 hours at a water bath temperature of 25-30°C, filter, wash, and dry to obtain a copper-cerium bimetallic MOF material; (2) Preparation of nitrogen-doped carbon materials: The product obtained in step (1) is mixed with melamine in a certain proportion and ground thoroughly, and then calcined in nitrogen in a tube furnace, cooled naturally to room temperature, and then ground thoroughly; (3) Activation: The product prepared in step (2) was placed in a hydrothermal reactor containing 6-8 wt% KOH, and activated at 170-180°C for 4-5 h. After cooling, the mixture was filtered and dried to obtain a nitrogen-doped porous carbon support with a high specific surface area. (4) After secondary nitrogen calcination treatment, the mixture was ground evenly to obtain Cu-doped CeO2-CN x catalyst.

2. A Cu-doped CeO2-CN as claimed in claim 1 x The method for preparing a catalyst is characterized in that Add 0.06-0.08 mol of copper nitrate and 0.03-0.04 mol of cerium nitrate solids into 100-150 mL of methanol solution and stir magnetically for 5-10 minutes to fully dissolve.

3. A Cu-doped CeO2-CN as claimed in claim 1 x The method for preparing a catalyst is characterized in that Add 0.8-1.2 mol of dimethylimidazole solid and 0.04-0.06 mol of citric acid to 140-160 mL of methanol solution and stir magnetically for 5-10 minutes to fully dissolve.

4. A Cu-doped CeO2-CN as claimed in claim 1 x The method for preparing a catalyst is characterized in that The weight ratio of the product obtained in step (1) to melamine is 2:(1.2-1.4).

5. A Cu-doped CeO2-CN as claimed in claim 1 x The method for preparing a catalyst is characterized in that Tubular furnace nitrogen calcination treatment: heating at 3-5 ° C / min to 490-510 ° C and holding at this temperature for 50-70 min, then continue heating at 3-5 ° C / min to 950-1000 ° C and holding at this temperature for 110-130 min.

6. A Cu-doped CeO2-CN as claimed in claim 1 x The method for preparing a catalyst is characterized in that Secondary nitrogen calcination treatment: heat up at 3-5°C / min to 200-500°C and maintain constant temperature for 120-140 minutes.

7. A Cu-doped CeO2-CN x Catalyst, characterized in that A catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. A Cu-doped CeO2-CN as claimed in claim 7 x The use of a catalyst is characterized in that Used in the field of electrochemical reduction of nitrate to synthesize ammonia.

9. An electrode material, comprising the Cu-doped CeO2-CN according to claim 7 x Catalyst, characterized in that The electrode material is Cu doped CeO2-CN x The catalyst is prepared by compounding with a conductive substrate, and the conductive substrate is selected from one of foamed nickel, carbon paper and carbon cloth.

10. A method for preparing an electrode material, characterized in that The Cu-doped CeO2-CN prepared in claim 7 x The catalyst and Nafion dispersion are dispersed in an organic solvent, the obtained dispersion is drop-coated on carbon paper, and dried to obtain the product.

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