CuO-CeO2-loaded foamed nickel electrode as well as preparation method and application thereof

Abstract

The invention relates to electrocatalytic reduction of nitrate, and particularly discloses a CuO-CeO2-loaded foamed nickel electrode and a preparation method and application thereof.The preparation method of the CuO-CeO2-loaded foamed nickel electrode comprises the steps that Cu (NO3) 2.3 H2O, Ce (NO3) 3.3 H2O and urea are taken and dissolved in water, and a first mixture is obtained; the foamed nickel is pretreated, the pretreated foamed nickel is added into the first mixture for a hydrothermal reaction, the foamed nickel is taken out after the reaction, and post-treatment is carried out; and roasting the post-treated foamed nickel, cooling to room temperature after roasting, and taking out to obtain the CuO-CeO2-loaded foamed nickel electrode. According to the method, the electrode cost of nitrate electrocatalytic reduction can be reduced, the catalytic reduction efficiency can be improved, meanwhile, the method is suitable for high-concentration nitrate wastewater, and harmless treatment of the high-concentration nitrate wastewater is achieved due to the fact that the target product is harmless nitrogen.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic reduction of nitrate, and more particularly to a nickel foam electrode loaded with CuO-CeO2, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous deepening of water environmental protection work in China, the treatment of water eutrophication has become an urgent problem to be solved in water environmental protection work. Among the pollutants causing water eutrophication, the treatment of nitrate pollution still lacks a process with high treatment efficiency, good stability, low investment and operation costs, and is currently a research hotspot in the industry.

[0003] At present, the main methods for treating nitrate pollution include reverse osmosis method, ion exchange method, biological treatment method, chemical catalysis method, and electrocatalytic method. Among them, the reverse osmosis method and the ion exchange method only separate nitrate from wastewater and do not reduce nitrate. The biological treatment method mainly uses the denitrification of microorganisms to reduce nitrate, but the biological treatment method has a low reaction rate, is greatly affected by the environment, and there are also problems such as excess sludge. The chemical catalysis method realizes the reduction of nitrate by introducing hydrogen or formic acid into water as a reducing agent, but there are safety problems and cost problems. At present, the electrocatalytic reduction technology has become the most promising treatment technology in the field of nitrate treatment due to its simple process and low electric energy cost.

[0004] The electrocatalytic reduction of nitrate is a heterogeneous reaction that occurs at the phase interface between an electronic conductor (i.e., an electrode) and an ionic conductor (i.e., an electrolyte). The process is very complex and involves the adsorption of nitrate, products such as nitrite obtained after the reduction of nitrate, and ions in the electrolyte on the electrode surface, as well as the direct oxidation and reduction of the above substances on the electrode surface and the indirect oxidation and reduction in the electrolyte. Specifically, the main steps are first the adsorption of nitrate on the electrode surface and its reduction to nitrite, and then the adsorbed nitrite is respectively in two different active intermediates, namely adsorbed NO and free NO2 -, the final products nitrogen or ammonia are generated via mechanisms such as the Vooys-Koper mechanism and the Duca-Feliu-Koper mechanism. Therefore, from the perspective of products, the electrocatalytic reduction of nitrate technology can be divided into two categories. One is from the perspective of chemical synthesis, using nitrate to generate chemical raw materials and energy carriers - ammonia; the other is from the perspective of harmless denitrification, converting nitrate into nitrogen to achieve complete denitrification. The current mainstream nitrate removal technology is to reduce nitrate to ammonia in the lowest valence state. On the one hand, reducing nitrate to the lowest valence state does not require precise control of the reaction endpoint, which can reduce the reaction difficulty; on the other hand, ammonia can be recycled as an energy source. However, there are still problems such as the difficulty of recycling the ammonia produced by electrocatalytic reduction. Therefore, reducing nitrate to harmless nitrogen is a better choice compared to reducing it to ammonia.

[0005] In addition, electrolytes such as sodium chloride generally exist in the electrolyte to enhance conductivity, and chloride ions can also affect the electrode potential through adsorption, form active chlorine, hypochlorite and other substances, and oxidize substances in the system such as ammonia into various products including nitrogen, etc., thereby having an impact. The high concentration of chloride ions and their products in the solution can undergo strong redox reactions, further increasing the difficulty of electrocatalytic reduction of nitrate and making the product trend unpredictable. It can be seen that environmental conditions such as the electrode and electrolyte have a decisive influence on the product trend during the electrocatalytic reduction of nitrate. In other words, different target products (nitrogen or ammonia) require different electrodes, that is, the selectivity of the electrode for a certain product is the key factor in electrode preparation.

[0006] In the research field of electrocatalytic reduction of nitrate to produce nitrogen, CN115287693A discloses the preparation of a cerium oxide vacancy-supported bimetallic nanoparticle and its application in electrocatalytic reduction of nitrate. This patent prepares a cerium oxide vacancy-supported bimetallic nanoparticle through a series of steps such as hydrothermal-calcination-impregnation, and then this particle and nickel foam are used as the cathode, and a ruthenium-iridium titanium oxide electrode is used as the anode to form a two-electrode system and place it in a reaction solution of nitrate, sodium sulfate and sodium chloride for electrocatalytic reduction of nitrate. However, the cerium oxide vacancy-supported bimetallic nanoparticle prepared in this patent is not used as an electrocatalytic cathode, but is only added to the reaction system in a way similar to a filler, and is only suitable for use at a nitrate concentration of 50 mg / L or less. In addition, CN106040239A discloses that it uses a mesoporous composite material (nano-zero-valent iron / mesoporous carbon) to prepare an electrocatalyst, and the nitrate concentration that can be treated is between 20 and 500 mg / L, but its removal rate is low and the selectivity of nitrogen is poor.

[0007] Therefore, it is necessary to design a new nickel foam electrode loaded with CuO-CeO2 to solve the problems of low nitrate concentration that the electrode can handle in electrocatalytic reduction of nitrate, poor nitrogen selectivity, and inapplicability to high-salt environments. Summary of the Invention

[0008] In view of this, the present invention proposes a preparation method of a nickel foam electrode loaded with CuO-CeO2, aiming to solve the problems of low nitrate concentration that the electrode can handle in electrocatalytic reduction of nitrate, poor nitrogen selectivity, and inapplicability to high-salt environments.

[0009] On the one hand, the present invention proposes a preparation method of a nickel foam electrode loaded with CuO-CeO2, comprising the following steps:

[0010] Dissolve Cu(NO3)2·3H2O, Ce(NO3)3·3H2O and urea in water to obtain a first mixture;

[0011] Pretreat the nickel foam, add the pretreated nickel foam to the first mixture for hydrothermal reaction, take out the nickel foam after the reaction, and perform post-treatment;

[0012] Calcine the post-treated nickel foam, cool it and take it out after completion to obtain a nickel foam electrode loaded with CuO-CeO2.

[0013] Further, the concentration of Cu(NO3)2 in the first mixture is 0.04 - 0.08 mol / L, the concentration of Ce(NO3)3 is 0.02 - 0.04 mol / L, and the concentration of urea is 0.1 - 0.2 mol / L.

[0014] Further, the pretreatment method is: cut the nickel foam into a sheet structure of 50 mm × 50 mm, and ultrasonically impregnate it in HCl solution, water and absolute ethanol for 5 minutes respectively to obtain the pretreated nickel foam.

[0015] Further, the hydrothermal reaction temperature is 100 - 120 °C, and the reaction time is 8 - 10 hours.

[0016] Further, the post-treatment is: rinse the nickel foam taken out after the hydrothermal reaction with water for 5 - 10 minutes, then wash it with absolute ethanol 2 - 3 times, 3 - 5 minutes each time. After completion, vacuum-dry the washed nickel foam, the drying temperature is 60 - 80 °C, the vacuum degree is 0.08 - 0.1 MPa, and the drying time is 2 - 4 hours.

[0017] Further, the calcination method is: heat the post-treated nickel foam to 300 - 500 °C at a heating rate of 3 - 5 °C / minute and keep it warm for 1 - 2 hours.

[0018] Further, the concentration of the HCl solution is 1.2 mol / L.

[0019] On the one hand, the present invention also provides a CuO-CeO₂ supported nickel foam electrode obtained by the preparation method of the CuO-CeO₂ supported nickel foam electrode.

[0020] On the other hand, the present invention provides an application of a CuO-CeO₂ supported nickel foam electrode, including: using the CuO-CeO₂ supported nickel foam electrode as the cathode and a ruthenium-iridium-titanium plate as the anode, controlling the plate spacing to be 2 cm, and the effective reaction area of the plates to be 20 cm 2 , assembling a single-chamber electrocatalytic reactor, adding nitrate wastewater into the electrolyte, and performing electrolysis after adjusting the electrolysis parameters; wherein the nitrate concentration in the nitrate wastewater is above 1000 mg / L.

[0021] Furthermore, the electrolysis parameters are: the current density is 5-35 mA / cm 2 , and the electrolysis time is 3-6 hours.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: by using nickel foam as the electrode substrate, the specific surface area of the electrode is greatly increased, so that more reactive sites can be exposed on the electrode surface; by using a series of steps such as hydrothermal method and post-treatment to prepare the catalyst, a nano-sized catalyst with a smaller particle size is synthesized, increasing the reactive sites and improving the catalytic reduction performance; by loading Ce, oxygen vacancies are introduced on the electrode surface, further improving the electrode catalytic reduction performance and having good nitrogen selectivity, realizing the efficient and harmless treatment of high-concentration nitrate wastewater in a high-salt environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0024] Figure 1 is a flow chart of the preparation method of the CuO-CeO₂ supported nickel foam electrode of the present invention.

[0025] Figure 2 is a scanning electron microscope image of the CuO-CeO₂ supported nickel foam electrode prepared in Example ② of the present invention.

[0026] Figure 3 is an energy spectrum analysis chart of the spectrum Figure 3 position in the scanning electron microscope image of the CuO-CeO₂ supported nickel foam electrode prepared in Example ② of the present invention.

[0027] Figure 4Energy spectrum analysis diagram of the spectrum at the Figure 4 position in the scanning electron microscope image of the CuO-CeO2 supported nickel foam electrode prepared in Example 2 of the present invention.

[0028] Figure 5 Energy spectrum analysis diagram of the spectrum at the Figure 5 position in the scanning electron microscope image of the CuO-CeO2 supported nickel foam electrode prepared in Example 2 of the present invention.

[0029] Figure 6 X-ray photoelectron spectrometer test diagram of the CuO-CeO2 supported nickel foam electrode prepared in Example 2 of the present invention.

[0030] Figure 7 Diagram of nitrate concentration change, nitrate removal rate, and nitrogen selectivity during electrocatalytic reduction of nitrate in Application Example 1 of the present invention.

[0031] Figure 8 Diagram of nitrate concentration change, nitrate removal rate, and nitrogen selectivity during electrocatalytic reduction of nitrate in Application Example 2 of the present invention. Detailed implementation manners

[0032] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present invention can be fully conveyed to those skilled in the art. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0033] At present, due to its simple process and low electric energy cost, electrocatalytic reduction technology has become the most promising treatment technology in the field of nitrate reduction. In the prior art, CN115287693A discloses the preparation of vacancy cerium oxide supported bimetallic nanoparticles and their application in electrocatalytic reduction of nitrate. This patent prepares vacancy cerium oxide supported bimetallic nanoparticles through a series of steps such as hydrothermal-calcination-impregnation. Then, the nanoparticles and nickel foam are used as the cathode, and the ruthenium-iridium titanium oxide electrode is used as the anode to form a two-electrode system placed in a reaction solution of nitrate, sodium sulfate, and sodium chloride for electrocatalytic reduction of nitrate. However, the prepared vacancy cerium oxide supported bimetallic nanoparticles in this patent are not used as the electrocatalytic cathode, but are only added to the reaction system in a manner similar to a filler, and are only suitable for use when the nitrate concentration is below 50 mg / L and the chloride ion concentration is below 1000 mg / L. In addition, CN106040239A discloses that it uses a mesoporous composite material (nano-zero valent iron / mesoporous carbon) to prepare an electrocatalyst, which can treat nitrate concentrations in the range of 20 to 500 mg / L, but its removal rate is low and the selectivity of nitrogen is poor.

[0034] On the one hand, as Figure 1 shown, in some embodiments of the present application, a method for preparing a CuO-CeO2 supported nickel foam electrode includes the following steps:

[0035] Take Cu(NO3)2·3H2O, Ce(NO3)3·3H2O, and urea and dissolve them in deionized water to obtain a first mixture;

[0036] Pretreat the nickel foam, add the pretreated nickel foam to the first mixture for hydrothermal reaction, take out the nickel foam after the reaction, and perform post-treatment;

[0037] Calcine the post-treated nickel foam, and after cooling, take it out to obtain a CuO-CeO2 supported nickel foam electrode.

[0038] Specifically, when performing the hydrothermal reaction, transfer the pretreated nickel foam and the first mixture to a polytetrafluoroethylene inner liner, assemble a hydrothermal reaction kettle for hydrothermal reaction; use a muffle furnace to calcine the post-treated nickel foam during calcination.

[0039] It can be understood that using nickel foam as the electrode substrate greatly increases the specific surface area of the electrode, increases the reaction active sites, and improves the catalytic reduction performance; using the hydrothermal method to prepare the catalyst synthesizes a catalyst with a smaller nanoscale particle size, further improving the electrode catalytic reduction performance. At the same time, the product of catalytic reduction is nitrogen, realizing the efficient and harmless treatment of high-concentration nitrate wastewater in a high-salt environment.

[0040] As Figure 1As shown, in some embodiments of the present invention, the pretreatment method is as follows: Cut the nickel foam into a sheet structure of 50 mm × 50 mm, and ultrasonically immerse it in HCl solution, water, and absolute ethanol for 5 minutes respectively to remove the surface oxide layer, obtaining the pretreated nickel foam; the water is deionized water.

[0041] Specifically, the ultrasonic immersion can adopt the parameters well-known to those skilled in the art.

[0042] It can be understood that during the storage and processing of nickel foam, an oxide layer is easily formed on its surface. These oxide layers will hinder the deposition and reaction of subsequent active substances on the surface of nickel foam. By ultrasonically immersing in HCl, deionized water, and absolute ethanol, the surface oxide layer can be effectively removed to facilitate the subsequent loading of catalytic metals.

[0043] As Figure 1 shown, in some embodiments of the present invention, the concentration of Cu(NO3)2 in the first mixture is preferably 0.04 - 0.08 mol / L, the concentration of Ce(NO3)3 is preferably 0.02 - 0.04 mol / L, and the concentration of urea is preferably 0.1 - 0.2 mol / L; the concentration of Cu(NO3)2 is further preferably 0.08 mol / L, the concentration of Ce(NO3)3 is further preferably 0.04 mol / L, and the concentration of urea is further preferably 0.2 mol / L;

[0044] As Figure 1 shown, in some embodiments of the present invention, the hydrothermal reaction temperature is 100 - 120 °C, and the reaction time is 8 - 10 hours; the hydrothermal reaction temperature is preferably 120 °C, and the reaction time is preferably 10 hours.

[0045] As Figure 1 shown, in some embodiments of the present invention, the calcination is specifically as follows: Heat the post-treated nickel foam to 300 - 500 °C at a heating rate of 3 - 5 °C / minute and then hold for 1 - 2 hours; the heating rate is preferably 3 °C / minute, the maximum temperature is preferably 500 °C, and the holding time is preferably 2 hours.

[0046] It can be understood that slow heating can enable the orderly migration and arrangement of atoms, avoid the generation of crystal defects, and thus improve the crystallinity of the material. The well-crystallized CuO - CeO2 crystal has a more regular lattice structure and more stable chemical properties, which is beneficial for it to exhibit better performance in applications such as catalysis. Moreover, a suitable heating rate and calcination time can enable the active substances to be better fixed on the surface of nickel foam, enhancing the binding strength between them. In this way, during subsequent use (such as catalytic reactions or other application scenarios), the active substances are not easily detached from the nickel foam, ensuring the stability of the material performance.

[0047] As Figure 1 shown, in some embodiments of the present invention, the post-treatment is as follows: the nickel foam taken out after the hydrothermal reaction is rinsed with water for 5 - 10 minutes, then washed with absolute ethanol 2 - 3 times, 3 - 5 minutes each time. After that, the washed nickel foam is dried in vacuum, the drying temperature is 60 - 80 °C, the vacuum degree is 0.08 - 0.1 MPa, and the drying time is 2 - 4 hours.

[0048] Preferably, the rinsing time is 10 minutes, the number of times of washing with absolute ethanol is preferably 3 times, the washing time each time is preferably 5 minutes, the drying temperature is preferably 80 °C, the vacuum degree is preferably 0.1 MPa, and the drying time is preferably 4 hours.

[0049] It can be understood that rinsing with a large amount of deionized water first can initially remove the unreacted raw materials that may adhere to the surface of the nickel foam, and finally washing with absolute ethanol can dissolve some organic impurities and absolute ethanol is volatile, which is beneficial to the subsequent drying process.

[0050] As Figure 1 shown, in some embodiments of the present invention, the concentration of the HCl solution is 1.2 mol / L.

[0051] On the one hand, in some embodiments of the present application, a CuO-CeO₂ supported nickel foam electrode prepared by the preparation method of the CuO-CeO₂ supported nickel foam electrode described above is also provided.

[0052] On the other hand, as Figure 1 shown, in some embodiments of the present application, an application of the CuO-CeO₂ supported nickel foam electrode is provided, including: using the CuO-CeO₂ supported nickel foam electrode as the cathode, and a ruthenium-iridium-titanium plate as the anode, controlling the plate spacing to be 2 cm, and the effective reaction area of the plate to be 20 cm 2 , assembling into a single-chamber electrocatalytic reactor, adding nitrate wastewater into the electrolyte, and performing a catalytic reduction reaction after adjusting the electrolysis parameters.

[0053] Specifically, the concentration of nitrate in the nitrate wastewater is 1000 mg / L or more.

[0054] The electrolyte is preferably one of an NaCl solution or a Na₂SO₄ solution; the concentration of the NaCl solution is preferably 2000 mg / L; the concentration of the Na₂SO₄ solution is preferably 0.3 mol / L.

[0055] Specifically, the ruthenium-iridium-titanium plate is a commercially available ruthenium-iridium-titanium plate purchased, and a DC regulated power supply is used to control the electrolysis parameters;

[0056] As Figure 1As shown, in some embodiments of the present invention, the electrolysis parameters are, the current density is 5-35mA / cm 2 The electrolysis time is 3-6 hours; the current density is preferably 35 mA / cm 2 , the electrolysis time is preferably 6 hours.

[0057] Example 1

[0058] S1. Take Cu(NO3)2·3H2O, Ce(NO3)3·3H2O, and urea and dissolve them in water to obtain a first mixture, in which the concentration of Cu(NO3)2 in the mixture is 0.04 mol / L, the concentration of Ce(NO3)3 is 0.02 mol / L, and the concentration of urea is 0.1 mol / L.

[0059] S2. Cut the nickel foam into a 50 mm × 50 mm sheet structure, and ultrasonically immerse it in HCl solution, deionized water, and anhydrous ethanol for 5 minutes respectively to obtain pretreated nickel foam.

[0060] S3, adding the pretreated nickel foam to the first mixture, then transferring the nickel foam and the first mixture into a polytetrafluoroethylene liner, reacting at a temperature of 100° C. for 8 hours, and then taking out the nickel foam after the reaction.

[0061] S4. Rinse the nickel foam taken out after the hydrothermal reaction with water for 5 minutes, then wash it twice with anhydrous ethanol for 3 minutes each time. After that, vacuum dry the cleaned nickel foam at a drying temperature of 60° C., a vacuum degree of 0.08 MPa, and a drying time of 2 hours.

[0062] S5. Place the post-treated nickel foam in a muffle furnace, heat the temperature to 500° C. at a heating rate of 3° C. / min, and keep the temperature for 2 hours. After the temperature is raised, cool the furnace and take out the nickel foam electrode loaded with CuO—CeO 2 to obtain the CuO—CeO 2 -loaded nickel foam electrode.

[0063] Example 2

[0064] S1. Take Cu(NO3)2·3H2O, Ce(NO3)3·3H2O, and urea and dissolve them in water to obtain a first mixture. The concentration of Cu(NO3)2 in the first mixture is 0.08 mol / L, the concentration of Ce(NO3)3 is 0.04 mol / L, and the concentration of urea is 0.2 mol / L.

[0065] S2. Cut the nickel foam into a 50 mm × 50 mm sheet structure, and ultrasonically immerse it in HCl solution, deionized water, and anhydrous ethanol for 5 minutes respectively to obtain pretreated nickel foam.

[0066] S3. Add the pretreated nickel foam to the first mixture, then transfer the nickel foam and the first mixture to a polytetrafluoroethylene inner container, react at a temperature of 120 °C for 10 hours, and take out the nickel foam after completion.

[0067] S4. Rinse the nickel foam taken out after the hydrothermal reaction with water for 10 minutes, then wash it 3 times with absolute ethanol for 5 minutes each time. After completion, vacuum-dry the washed nickel foam at a drying temperature of 80 °C, a vacuum degree of 0.1 MPa, and a drying time of 4 hours.

[0068] S5. Put the post-treated nickel foam into a muffle furnace, heat it to 500 °C at a heating rate of 3 °C / minute and keep it warm for 2 hours. After completion, cool it and take it out to obtain the CuO-CeO2-loaded nickel foam electrode.

[0069] Application Example 1

[0070] Use the CuO-CeO2-loaded nickel foam electrode prepared in Example 2 as the cathode, and a commercially available ruthenium-iridium-titanium plate as the anode. Control the plate spacing to be 2 cm, and the effective reaction area of the plate to be 20 cm 2 , configure a 2000 mg / L NaCl solution as the electrolyte, use a DC regulated power supply to control the output current density to be 35 mA / cm 2 , add a solution with a nitrate concentration of 1000 mg / L to the electrolyte, and electrocatalytically reduce for 6 hours.

[0071] Application Example 2

[0072] Use the CuO-CeO2-loaded nickel foam electrode prepared in Example 2 as the cathode, and a commercially available ruthenium-iridium-titanium plate as the anode. Control the plate spacing to be 2 cm, and the effective reaction area of the plate to be 20 cm 2 , configure a 0.3 mol / L Na2SO4 solution as the electrolyte, use a DC regulated power supply to control the output current density to be 35 mA / cm 2 , add a solution with a nitrate concentration of 1000 mg / L to the electrolyte, and electrocatalytically reduce for 6 hours.

[0073] Effect Test

[0074] Conduct scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) tests on the CuO-CeO2-loaded nickel foam electrode prepared in Example 2. The results are as Figures 2 - 5 shown. It can be observed that flaky aggregates of Cu appear on the electrode surface, while Ce is more evenly distributed on the surface of the nickel foam, and the diameter of the cerium oxide particles is about 200 nm. It can also be observed that the diameter of the copper oxide particles in the flaky aggregates of Cu is also about 150 nm.

[0075] The CuO-CeO2 supported nickel foam electrode prepared in Example 2 was tested by X-ray photoelectron spectroscopy (XPS). The results are as Figure 6 shown. In the high-resolution spectrum of Ce 3d, the characteristic peaks in the Ce 3d orbital can be divided into v peaks and u peaks, corresponding to the 3d 5 / 2 and 3d 3 / 2 orbitals of the multiplet spin-orbit, respectively. From low binding energy to high binding energy, they are v 0 , v’, v’, v”, v”’, u 0 , u’, u”, u”’, respectively. Among them, v’ and u’ are related to Ce 3+ , and the remaining six sub-peaks are related to Ce 4+ . Judging by the peak area, the peak areas of v’ and u’ are small, so Ce mainly exists in the form of Ce 4+ . Compared with Ce 4+ , the existence of Ce 3+ has higher reaction activity, which can promote the formation of vacant oxygen, increase oxygen vacancies, improve the transfer rate of oxygen on the electrode surface, generate more unsaturated chemical bonds, and thus accelerate the catalytic reduction process of nitrate. In the high-resolution spectrum of O 1s, it can be decomposed into three peaks, namely O α at 533.44 eV, O β at 531.39 eV and O γ at 529.55 eV, corresponding to lattice oxygen, vacant oxygen and surface hydroxyl oxygen (such as OH - , CO3 2- , adsorbed O2, etc.). The discovery of vacant oxygen in the O 1s spectrum can also assist in verifying the analysis in the Ce 3d spectrum, that is, the appearance of oxygen vacancies is related to the doping of Ce ions. Generally, it is considered that O β can reduce the dissociation energy of N-O, contribute to accelerating the reduction of NO to a lower valence state, and thus promote the electrocatalytic reduction process of nitrate and improve the reaction activity.

[0076] The results of nitrate concentration, nitrate removal rate and nitrogen selectivity during electrocatalytic reduction in Application Example 1 and Application Example 2 are as Figure 7 and Figure 8 shown. Figure 7 It shows that when the electrolyte is a 2000 mg / L NaCl solution, for 1000 mg / L nitrate, the nitrate removal rate can reach 83.4% within 6 hours of electrolysis time, and the nitrogen selectivity is always close to 100%; Figure 8 It shows that when the electrolyte is a 0.3 mol / L Na2SO4 solution, the nitrate removal rate is 86.4%, and the nitrogen selectivity decreases slightly, but still remains stable above 81%.

Claims

1. A preparation method of a CuO-CeO2 supported nickel foam electrode, characterized in that, It includes the following steps: Dissolve Cu(NO3)2·3H2O, Ce(NO3)3·3H2O and urea in water to obtain a first mixture; Pretreat the nickel foam, add the pretreated nickel foam into the first mixture for hydrothermal reaction, take out the nickel foam after the reaction, and perform post-treatment; Calcine the post-treated nickel foam, cool it to room temperature and take it out after completion to obtain a nickel foam electrode loaded with CuO-CeO2.

2. The preparation method of the CuO-CeO2 supported nickel foam electrode according to claim 1, characterized in that, In the first mixture, the concentration of Cu(NO3)2 is 0.04 - 0.08 mol / L, the concentration of Ce(NO3)3 is 0.02 - 0.04 mol / L, and the concentration of urea is 0.1 - 0.2 mol / L.

3. The preparation method of the CuO-CeO2 supported nickel foam electrode according to claim 1, characterized in that, The pretreatment method is: cut the nickel foam into a sheet structure of 50mm×50mm, and ultrasonically impregnate it in HCl solution, water and absolute ethanol for 5 minutes respectively to obtain the pretreated nickel foam.

4. The preparation method of the CuO-CeO2 supported nickel foam electrode according to claim 1, characterized in that, The hydrothermal reaction temperature is 100 - 120 °C, and the reaction time is 8 - 10 hours.

5. The preparation method of the CuO-CeO2 supported nickel foam electrode according to claim 1, characterized in that, The post-treatment is: rinse the nickel foam taken out after the hydrothermal reaction with water for 5 - 10 minutes, then wash it with absolute ethanol 2 - 3 times, 3 - 5 minutes each time. After completion, vacuum-dry the washed nickel foam at a drying temperature of 60 - 80 °C, a vacuum degree of 0.08 - 0.1 MPa, and a drying time of 2 - 4 hours.

6. The preparation method of the CuO-CeO2 supported nickel foam electrode according to claim 1, characterized in that, The specific conditions for the calcination are: heat the post-treated nickel foam at a heating rate of 3 - 5 °C per minute to 300 - 500 °C and hold for 1 - 2 hours.

7. The preparation method of the CuO-CeO2 supported nickel foam electrode according to claim 1, characterized in that, The concentration of the HCl solution is 1.2 mol / L.

8. The nickel foam electrode loaded with CuO-CeO2 obtained by the preparation method of the nickel foam electrode loaded with CuO-CeO2 according to any one of claims 1 to 7.

9. Use of the CuO-CeO2 supported nickel foam electrode according to claim 8, characterized in that, Using the CuO-CeO2 supported nickel foam electrode as the cathode and the ruthenium-iridium-titanium plate as the anode, controlling the plate spacing to be 2 cm and the effective reaction area of the plates to be 20 cm 2 , adding the nitrate wastewater to the electrolyte, and carrying out electrolysis after adjusting the electrolysis parameters.

10. Use of the CuO-CeO2 supported nickel foam electrode according to claim 9, characterized in that, The electrolysis parameters are as follows: the current density is 5 - 35 mA / cm 2 , and the electrolysis time is 3 - 6 hours.

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