Preparation method and application of self-supporting cobalt-doped cuprous oxide double-site cathode electrode

Abstract

The invention belongs to the technical field of environmental functional materials, and discloses a preparation method and application of a self-supporting cobalt-doped cuprous oxide double-site cathode electrode. Foamy copper is used for preparing a substrate, and a cobalt-doped copper hydroxide nanorod composite material is obtained through electrochemical deposition; and carrying out annealing treatment at a certain temperature and in a nitrogen atmosphere to obtain the Co-Cu2O / CF electrode. According to the preparation method of the three-dimensional self-supporting Co-Cu2O / CF cathode electrode, adsorption of nitrate is optimized and decomposition of water is promoted through the synergistic effect between two sites of copper and cobalt, so that selective conversion from nitrate to ammonia is improved. The invention provides the application of the cobalt-doped cuprous oxide self-supporting cathode electrode in the aspect of electrocatalytic nitrate reduction synthesis of ammonia, and the cobalt-doped cuprous oxide self-supporting cathode electrode has excellent Faraday efficiency and ammonia selectivity and good stability. Meanwhile, the preparation method of the catalyst is simple and easy to implement, high electro-catalytic performance is achieved, and the catalyst has a certain potential application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental functional materials, and relates to a preparation method and application of a self-supporting cobalt-doped cuprous oxide dual-site cathode electrode. Background Art

[0002] Ammonia (NH 3 ) is one of the most important chemical raw materials and plays an irreplaceable role in the production of fertilizers, chemicals, and pharmaceuticals. In addition to its main use as a fertilizer, ammonia is also an energy carrier in the emerging global hydrogen economy (i.e., hydrogen 2.0) because it can be reliably transported over long distances using existing logistics infrastructure. Currently, the industrial synthesis of NH 3 mainly relies on the energy-intensive and high-carbon-emission Haber-Bosch process, which reacts nitrogen (N 2 ) and hydrogen (H 2 ) under high temperature (350 - 550 °C) and high pressure (150 - 350 atm) conditions. However, its harsh operating conditions result in high energy consumption and a large amount of carbon dioxide emissions. Therefore, it is urgent to explore green and economical ammonia synthesis processes.

[0003] Due to industrial wastewater discharge and improper use of fertilizers, nitrate (NO 3 - ) pollutants are widely present in surface water and groundwater aquifers, which can cause water eutrophication, massive algal blooms, and harm to aquatic plants, and also pose a serious threat to human health. Nitrate degradation has always been a research focus, and treatment processes include reverse osmosis, ion exchange, and biological denitrification, etc., but they have drawbacks such as secondary pollution that requires post-treatment.

[0004] In recent years, the electrochemical nitrate reduction reaction under ambient temperature and pressure as an environmentally friendly and effective method for synthesizing high-value-added NH 3 has broad application prospects. However, the current catalytic electrodes in this field are mainly noble metals. However, the high cost and limited availability of noble metals greatly limit their further development and application. Non-noble metal electrodes have received increasing attention in the direction of electrochemical nitrate reduction in recent years due to their advantages such as low cost, high activity, and great potential for large-scale application. Cu-based electrodes have attracted great attention because of their high adsorption capacity for nitrate and completely filled Cu 3d orbitals, which inhibit the competitive hydrogen evolution reaction (HER). However, during the reaction process of Cu-based electrodes, due to the accumulation of nitrite, long electrolysis time and high overpotential are required to further reduce NO 2 - to NH 3 , resulting in a relatively low adsorption energy for reaction intermediates and low selectivity for NH 3 . Summary of the Invention

[0005] To overcome the deficiencies of the prior art, the present invention aims to address the deficiencies of low selectivity and Faraday efficiency of non-noble metal electrodes. The present invention provides a preparation method and application of a self-supporting cobalt-doped cuprous oxide dual-site cathode electrode. When the provided electrode is applied to an electrocatalytic nitrate reduction system, in a low-concentration, neutral nitrate solution, the prepared cathode electrode has high NO 3 RR catalytic activity, with a Faraday efficiency of 95.98% and a selectivity of up to 92.45%. The NH 3 production rate is 0.4978 mmol h -1 cm -2 , having high practical application value.

[0006] The above object of the present invention is achieved by the following technical solutions:

[0007] A preparation method of a self-supporting cobalt-doped cuprous oxide dual-site cathode electrode, comprising the following steps:

[0008] S1. Prepare the substrate. Pretreat the copper foam, and ultrasonically treat the copper foam successively with acetone, dilute hydrochloric acid, ethanol, and deionized water. After washing, store it in a vacuum-sealed manner as the electrode substrate for standby;

[0009] S2. Prepare Cu(OH) 2 NRs / CF. Vertically immerse the electrode substrate prepared in step S1 into a solution containing an alkaline solution and persulfate to obtain sky-blue CF. Take it out of the solution, wash it thoroughly with deionized water, and dry it in a vacuum to obtain Cu(OH) 2 NRs / CF;

[0010] S3. Prepare Co-Cu(OH) 2 NRs / CF. Place the Cu(OH) 2 NRs / CF prepared in step S2 into a cobalt nitrate solution. At a predetermined temperature, use a three-electrode system and perform electrodeposition using the potentiostatic method. Take it out, wash it, and store it after drying to obtain Co-Cu(OH) 2 NRs / CF;

[0011] S4. Prepare Co-Cu 2 O / CF. Place the Co-Cu(OH) 2 NRs / CF prepared in step S2 into a tubular furnace. Under the protection of an inert gas, heat it to 300 - 600 °C and maintain it for 0.5 - 4 h. Then cool it to room temperature. Finally, reduce it at a constant voltage of -0.5 to -1 V in a nitrate solution for 1 - 4 h; obtain Co-Cu 2 O / CF.

[0012] Further, in step S1, the size of the copper foam is 1 cm * 1 cm to 4 cm * 4 cm; the concentration of hydrochloric acid is 0.1 to 2 M; the ultrasonic time is 10 to 20 min; deionized water is used for washing.

[0013] Further, in step S2, the persulfate is any one of ammonium persulfate, potassium persulfate or sodium persulfate, and the concentration is 0.05 to 0.5 M; the alkaline solution is potassium hydroxide or sodium hydroxide, and the concentration is 0.5 to 4 M.

[0014] Preferably, the persulfate is ammonium persulfate, the concentration is 0.125 M, and the alkaline solution is sodium hydroxide, and the concentration is 2.5 M.

[0015] Further, in step S3, the predetermined temperature is 20 to 30 °C; the drying temperature is 40 to 60 °C; the drying time is 8 to 12 h.

[0016] Further, in step S3, the concentration of the cobalt nitrate solution is 0.01 to 1 M.

[0017] Further, in step S3, the conditions for electro-deposition using the potentiostatic method are: the deposition potential is -0.6 to -1 V; the deposition time is 5 to 30 min.

[0018] Further, in step S3, the counter electrode of the three-electrode system is any one of a platinum sheet, a platinum mesh, and a graphite rod; the reference electrode is one of Ag / AgCl and a saturated calomel electrode; the working electrode is Cu(OH) 2 NRs / CF.

[0019] Further, in step S4, the inert gas is nitrogen or argon.

[0020] Further, in step S4, the heating rate is 5 - 20 °C / min. Preferably, the heating rate is 5 °C / min.

[0021] The present invention also claims the application of the electrode prepared by the above preparation method in the electrocatalytic reduction of nitrate to prepare NH 3 in.

[0022] The application is specifically as follows: The Co-Cu 2 O / CF electrode prepared by the above preparation method is used as the working electrode, and is assembled together with a Pt sheet counter electrode and an Ag / AgCl reference electrode in an H-type electrolytic cell. The cathode chamber and the anode chamber are separated by a Nafion 117 membrane, and a electrochemical workstation (Chenhua 660E) is used for testing. The cathode chamber is filled with 80 mL of 0.5 M Na containing 200 mg L -1 NO 3 - -N2 SO 4 solution (pH = 7), and the anodic chamber is filled with an equal amount of 0.5 M Na 2 SO 4 solution. Before the test, to ensure an anaerobic environment for the electrolyte, argon gas was introduced into the electrolyte for 30 min to exclude the interference of oxygen on the reaction process. Electrolysis was carried out at a constant potential of -0.7 V vs. RHE and 25 °C for 2 hours, and the magnetic stirring rate was 400 rpm. After the reaction, the NH 3 concentration in the catholyte was determined by the Nessler's reagent spectrophotometry method, and the ammonia production rate was calculated to be 0.4978 mmol h -1 cm -2 , the Faraday efficiency was 95.98%, and the selectivity of ammonia reached 92.45%. Ten consecutive cyclic experiments showed that the Co-Cu 2 O / CF electrode still maintained a high Faraday efficiency and ammonia production rate, demonstrating the excellent stability of the electrode.

[0023] The beneficial effects of the present invention compared with the prior art are as follows:

[0024] A preparation method and application of a self-supporting cobalt-doped cuprous oxide double-site cathode electrode provided by the present invention have the following remarkable advantages compared with the prior art:

[0025] (1) When the self-supporting cobalt-doped cuprous oxide double-site cathode electrode is specifically applied, no binder is required, effectively inhibiting the shedding of active substances during the electrocatalytic nitrate reduction to synthesize ammonia.

[0026] (2) The copper active sites of the self-supporting cobalt-doped cuprous oxide double-site cathode electrode promote the adsorption and conversion of NO 3 - on the catalyst surface. At the same time, the modulation effect of the cobalt active sites on the electronic structure of Cu is beneficial to promoting the decomposition of water, thereby optimizing the decomposition of water and promoting the conversion of NO 2 - to NH 3 . At the same time, the adsorption of H ads prevents the release of H 2 , resulting in a high electrocatalytic activity for NO 3 RR.

[0027] (3) The preparation process of the self-supporting cobalt-doped cuprous oxide double-site cathode electrode of the present invention is simple, has strong repeatability, and is easy to be prepared on a large scale. Under neutral conditions, the self-supporting cobalt-doped cuprous oxide double-site cathode electrode has a Faraday efficiency of up to 95.98% and an ammonia selectivity of 92.45% at -0.7 V vs. RHE, and the ammonia production rate is as high as 0.4978 mmol h -1 cm -2 .

[0028] The self-supported cobalt-doped cuprous oxide dual-site cathode electrode provided by the present invention is an innovative method for electrocatalytic nitrate reduction to synthesize ammonia, providing a new catalytic strategy for electrocatalytic nitrate synthesis of ammonia at normal temperature and pressure.

[0029] The preparation method of the self-supported cobalt-doped cuprous oxide dual-site cathode electrode provided by the present invention is simple and easy to implement, achieving a relatively high NO 3 RR catalytic performance, with certain potential application prospects. Description of the Drawings

[0030] Figure 1 XRD patterns of Co-Cu 2 O / CF prepared in Example 1 of the present invention and Cu prepared in Comparative Example 1 2 O / CF;

[0031] Figure 2 XPS full spectrum of Co-Cu 2 O / CF prepared in Example 1 of the present invention;

[0032] Figure 3 SEM images of Co-Cu 2 O / CF prepared in Example 1 of the present invention and Cu prepared in Comparative Example 1 2 O / CF; where Figure a is the SEM image of Cu 2 O / CF, and Figure b is the SEM image of Co-Cu 2 O / CF.

[0033] Figure 4 TEM and EDS images of Co-Cu 2 O / CF prepared in Example 1 of the present invention; where Figure a is the TEM image of Co-Cu 2 O / CF, Figure b is the EDS image of Cu in Co-Cu 2 O / CF, Figure c is the EDS image of Co in Co-Cu 2 O / CF, and Figure d is the EDS image of O in Co-Cu 2 O / CF.

[0034] Figure 5 Electrochemical reaction device diagram for electrocatalytic nitrate reduction to synthesize ammonia of the present invention;

[0035] Figure 6 Comparison chart of Faraday efficiency and ammonia production rate of the cathode electrode for electrocatalytic reduction of nitrate to synthesize ammonia in Example 1 of the present invention at different applied potentials.

[0036] Figure 7It is the graph of the change of nitrate concentration with time and the graph of product proportion in the electrocatalytic reduction of nitrate to ammonia at the optimal applied potential in Example 1 of the present invention; wherein Figure a is the graph of the change of nitrate concentration with time in the electrocatalytic reduction of nitrate to ammonia at the optimal applied potential by the cathode electrode in Example 1, and Figure b is the graph of the product proportion with time in the electrocatalytic reduction of nitrate to ammonia at the optimal applied potential by the cathode electrode in Example 1.

[0037] Figure 8 is the Co-Cu prepared in Example 1 of the present invention 2 LSV curve graphs of the O / CF cathode electrode with and without nitrate.

[0038] Figure 9 is the Co-Cu prepared in Example 1 of the present invention 2 Results of the performance test of the O / CF cathode electrode prepared in Example 1 of the present invention during 10 consecutive runs in an H-type reactor, ammonia production rate and Faraday efficiency graphs. Detailed implementation manners

[0039] The present invention will be described in detail below through specific examples, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods adopted in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained from commercial channels.

[0040] The present invention provides a preparation method and application of a self-supporting cobalt-doped cuprous oxide dual-site cathode electrode, including the following steps: (1) ultrasonically washing the copper foam with acetone, dilute hydrochloric acid, ethanol and deionized water respectively; (2) vertically placing the copper foam cleaned in step (1) into a mixed solution containing NaOH and (NH 4 ) 2 SO 4 for in-situ wet oxidation; (3) using the cuprous hydroxide nanorods obtained in step (2) as the working electrode and performing electrochemical deposition in a cobalt nitrate solution to obtain a composite material of cobalt-doped cuprous hydroxide nanorods; (4) annealing the composite material obtained in step (3) at a certain temperature and in a nitrogen atmosphere to obtain the Co-Cu 2 O / CF electrode. The preparation method of the three-dimensional self-supporting Co-Cu 2 O / CF cathode electrode of the present invention optimizes the adsorption of nitrate and promotes the decomposition of water through the synergistic effect between copper and cobalt dual sites, thereby improving the selective conversion of nitrate to ammonia. The present invention provides the application of the cobalt-doped cuprous oxide self-supporting cathode electrode in the electrocatalytic reduction of nitrate to ammonia, which has excellent Faraday efficiency and ammonia selectivity, and good stability. At the same time, the catalyst preparation method is simple and easy to implement, achieving high electrocatalytic performance and having certain potential application prospects.

[0041] Example 1

[0042] A method for preparing a self-supporting cobalt-doped cuprous oxide dual-site cathode electrode comprises the following steps:

[0043] (1) Before electrode preparation, the size of copper foam (CF) was cut into 2.5 cm*2.0 cm, and ultrasonically cleaned with 10 mL acetone, 10 mL 1.0 M hydrochloric acid, 10 mL anhydrous ethanol and deionized water for 15 min to remove surface oil and oxide layer. The substrate was then dried in a vacuum oven at 60 °C for 4 h and used as the electrode substrate.

[0044] (2) The electrode substrate obtained in step (1) was vertically immersed in a 2.5 mol·L -1 NaOH and 0.125 mol·L -1 (NH 4 ) 2 S 2 O 8 The obtained sky blue electrode substrate was then taken out of the solution, washed thoroughly with deionized water, and dried in a vacuum oven at 60°C for 12 h. 2 NRs / CF.

[0045] (3) Dissolve 0.4365 g (0.05 M) of cobalt nitrate in 30 mL of deionized water and stir thoroughly until completely dissolved to prepare an electrodeposition precursor solution.

[0046] (4) Cu(OH) obtained in step (2) 2 NRs / CF was placed in the electrodeposition precursor solution obtained in step (3) at 25°C using a three-electrode system with a platinum sheet as the counter electrode and an AgCl / Ag electrode as the reference electrode. The Cu(OH) 2 NRs / CF was used as the working electrode, and the electroplating time was 15 min at -0.8 V using the constant potential method. After being taken out and washed several times, it was dried and stored to obtain Co-Cu(OH) 2 NRs / CF.

[0047] (5) Co-Cu(OH) obtained in step (4) 2 NRs / CF were placed in a porcelain boat in a tube furnace under N 2 In an atmosphere, the temperature was raised at 550°C for 2 h at a heating rate of 5°C / min. Since the key operation in this step is to control the oxygen-free environment, the tube furnace was pre-ventilated for 30 min before heating to exhaust the residual air in the tube. 2 The self-supporting Co-Cu 2The O / CF dual-site cathode electrode can be used as the working electrode in the electrocatalytic nitrate reduction to ammonia system.

[0048] Example 2

[0049] (1) Cut the size of the copper foam (CF) to 2.5 cm * 2.0 cm, and ultrasonically clean it with 10 mL of acetone, 10 mL of 1.0 M hydrochloric acid, 10 mL of absolute ethanol, and deionized water for 15 min in sequence to remove the surface oil stain and oxide layer. Then dry the substrate in a vacuum oven at 60 °C for 4 h and reserve it as the electrode substrate.

[0050] (2) Vertically immerse the electrode substrate CF obtained in step (1) into the alkaline solution containing 2.5 mol·L -1 NaOH and 0.125 mol·L -1 (NH 4 ) 2 S 2 O 8 and let it stand at room temperature for 30 min. Then, take out the obtained sky-blue CF from the solution, wash it thoroughly with deionized water, and dry it in a vacuum oven at 60 °C for 12 h. Obtain Cu(OH) 2 NRs / CF.

[0051] (3) Dissolve 0.087 g (0.01 M) of cobalt nitrate in 30 mL of deionized water, and stir it thoroughly until it is completely dissolved to obtain the electrodeposition precursor solution.

[0052] (4) Place the Cu(OH) 2 NRs / CF obtained in step (2) into the electrodeposition precursor solution obtained in step (3). At 25 °C, using a three-electrode system, with a platinum sheet as the counter electrode and an AgCl / Ag electrode as the reference electrode, the Cu(OH) 2 NRs / CF obtained in step (2) as the working electrode, use the potentiostatic method at -0.8 V for an electrodeposition time of 15 min. After taking it out, wash it several times and dry it for storage to obtain Co-Cu(OH) 2 NRs / CF.

[0053] (5) Place the Co-Cu(OH) 2 NRs / CF obtained in step (4) in a porcelain boat in a tube furnace. Under N 2 atmosphere, heat it at a heating rate of 5 °C / min to 550 °C for 2 h. Since the key operation of this step is to control the anaerobic environment, pre-ventilate the tube furnace for 30 min before heating to exhaust the residual air in the tube. Finally, cool it to the ambient temperature under N 2 atmosphere to obtain the self-supporting Co-Cu 2The O / CF dual-site cathode electrode can be used as a working electrode in the electrocatalytic nitrate reduction ammonia synthesis system.

[0054] Example 3

[0055] (1) Cut the size of copper foam (CF) into 2.5 cm*2.0 cm, and ultrasonically clean it with 10 mL acetone, 10 mL 1.0 M hydrochloric acid, 10 mL anhydrous ethanol and deionized water for 15 min to remove the surface oil and oxide layer. Then dry the substrate in a vacuum oven at 60 °C for 4 h and use it as an electrode substrate.

[0056] (2) The electrode substrate CF obtained in step (1) was vertically immersed in a 2.5 mol·L -1 NaOH and 0.125 mol·L -1 (NH 4 ) 2 S 2 O 8 The obtained sky blue CF was then taken out of the solution, washed thoroughly with deionized water, and dried in a vacuum oven at 60 °C for 12 h. 2 NRs / CF.

[0057] (3) Dissolve 0.8731 g (0.1 M) of cobalt nitrate in 30 mL of deionized water and stir thoroughly until completely dissolved to prepare an electrodeposition precursor solution.

[0058] (4) Cu(OH) obtained in step (2) 2 NRs / CF was placed in the electrodeposition precursor solution obtained in step (3) at 25°C using a three-electrode system with a platinum sheet as the counter electrode and an AgCl / Ag electrode as the reference electrode. The Cu(OH) 2 NRs / CF was used as the working electrode, and the electroplating time was 15 min at -0.8 V using the constant potential method. After being taken out and washed several times, it was dried and stored to obtain Co-Cu(OH) 2 NRs / CF.

[0059] (5) Co-Cu(OH) obtained in step (4) 2 NRs / CF were placed in a porcelain boat in a tube furnace under N 2 In an atmosphere, the temperature was raised at 550°C for 2 h at a heating rate of 5°C / min. Since the key operation in this step is to control the oxygen-free environment, the tube furnace was pre-ventilated for 30 min before heating to exhaust the residual air in the tube. 2 The self-supporting Co-Cu 2The O / CF dual-site cathode electrode can be used as a working electrode in the electrocatalytic nitrate reduction ammonia synthesis system.

[0060] Example 4

[0061] (1) Cut the size of copper foam (CF) into 2.5 cm*2.0 cm, and ultrasonically clean it with 10 mL acetone, 10 mL 1.0 M hydrochloric acid, 10 mL anhydrous ethanol and deionized water for 15 min to remove the surface oil and oxide layer. Then dry the substrate in a vacuum oven at 60 °C for 4 h and use it as an electrode substrate.

[0062] (2) The electrode substrate CF obtained in step (1) was vertically immersed in a 2.5 mol·L -1 NaOH and 0.125 mol·L -1 (NH 4 ) 2 S 2 O 8 The obtained sky blue CF was then taken out of the solution, washed thoroughly with deionized water, and dried in a vacuum oven at 60 °C for 12 h. 2 NRs / CF.

[0063] (3) Dissolve 0.4365 g (0.05 M) of cobalt nitrate in 30 mL of deionized water and stir thoroughly until completely dissolved to prepare an electrodeposition precursor solution.

[0064] (4) Cu(OH) obtained in step (2) 2 NRs / CF was placed in the electrodeposition precursor solution obtained in step (3) at 25°C using a three-electrode system with a platinum sheet as the counter electrode and an AgCl / Ag electrode as the reference electrode. The Cu(OH) 2 NRs / CF was used as the working electrode, and the electroplating time was 15 min at -1 V using the constant potential method. After being taken out and washed several times, it was dried and stored to obtain Co-Cu(OH) 2 NRs / CF.

[0065] (5) Co-Cu(OH) obtained in step (4) 2 NRs / CF were placed in a porcelain boat in a tube furnace under N 2 In an atmosphere, the temperature was raised at 550°C for 2 h at a heating rate of 5°C / min. Since the key operation in this step is to control the oxygen-free environment, the tube furnace was pre-ventilated for 30 min before heating to exhaust the residual air in the tube. 2 The self-supporting Co-Cu 2The O / CF dual-site cathode electrode can be used as the working electrode in the electrocatalytic nitrate reduction to ammonia system.

[0066] Comparative Example 1

[0067] Prepare a catalyst control sample without Co, including the following steps:

[0068] (1) Before electrode preparation, cut the size of copper foam (CF) to 2.5 cm * 2.0 cm, and ultrasonically clean it with 10 mL of acetone, 10 mL of 1.0 M hydrochloric acid, 10 mL of absolute ethanol, and deionized water for 15 min in sequence to remove surface oil stains and oxide layers. Then dry the substrate in a vacuum oven at 60 °C for 4 h and reserve it as the electrode substrate.

[0069] (2) Vertically immerse the electrode substrate obtained in step (1) into an alkaline solution containing 2.5 mol·L -1 NaOH and 0.125 mol·L -1 (NH 4 ) 2 S 2 O 8 and let it stand at room temperature for 30 min. Then, take out the obtained sky-blue electrode substrate from the solution, wash it thoroughly with deionized water, and dry it in a vacuum oven at 60 °C for 12 h. Prepare Cu(OH) 2 NRs / CF.

[0070] (3) Place the Cu(OH) 2 NRs / CF obtained in step (2) in a porcelain boat in a tube furnace, and heat it at 550 °C for 2 h at a heating rate of 5 °C / min under N 2 atmosphere to obtain Cu 2 O / CF for electrocatalytic nitrate reduction to ammonia-related electrochemical tests.

[0071] Use an X-ray diffractometer to characterize the phase composition of Example 1 and Comparative Example 1. The results are as Figure 1 shown. The abscissa is the two-fold diffraction angle (degree), and the ordinate is the intensity of the diffraction peak (a.u.). It can be clearly observed in the figure that there are characteristic peaks of Cu and Cu 2 O, and there are no obvious characteristic peaks of metallic cobalt. Use XPS to analyze the elements on the material surface. The results are as Figure 2 shown, proving that cobalt is successfully doped into Cu 2 O. Characterize the morphology and structure of the composite material obtained in Example 1 using a scanning electron microscope. The results are as Figure 3 shown, showing irregular nanorod shapes, proving the successful synthesis of Co-Cu 2 O. Figure 4High-resolution transmission electron microscope images and elemental distribution maps of Example 1. The results show that Cu, Co, and O elements are uniformly distributed on the material surface.

[0072] Comparative Example 2

[0073] Cut the copper foam into pieces of 1×2 cm -2 , and ultrasonically clean it with 10 mL of acetone, 10 mL of 1.0 M hydrochloric acid, 10 mL of absolute ethanol, and deionized water for 15 min in sequence to remove surface oil stains and oxide layers, and dry it at room temperature for standby; dissolve 3.2 g of sodium hydroxide in 22 ml of deionized water, then dissolve 0.89 g of ammonium persulfate in 8 ml of deionized water, and then mix the two solutions evenly; soak the treated foam copper in the mixed solution and stir for 30 minutes; wash it several times with deionized water and absolute ethanol, and then vacuum dry it at 60 °C overnight to obtain Cu(OH) 2 / CF; then place Cu(OH) 2 / CF in a tubular furnace and calcine it at 250 °C for 180 minutes under an air atmosphere condition, and after natural cooling, obtain the CuO / CF material.

[0074] Comparative Example 3

[0075] Cut the nickel foam into pieces of 1×3 cm -2 , and ultrasonically clean it with 10 mL of acetone, 10 mL of 1.0 M hydrochloric acid, 10 mL of absolute ethanol, and deionized water for 15 min in sequence to remove surface oil stains and oxide layers, and dry it at room temperature for standby; transfer the treated nickel foam to a polytetrafluoroethylene lining containing 60 mL of 4.5 wt.% hydrogen peroxide aqueous solution and 8 mg of copper chloride, assemble the reaction kettle, put it into the oven, react at 160 °C for 6 h, after the reaction is completed, cool it to room temperature, take out the foam electrode, wash it with water and dry it to obtain Cu-Ni(OH) 2 / CF.

[0076] Application Example

[0077] The cathode electrodes prepared in Example 1, Example 2, Example 3, and Example 4 are used in the application of electrocatalytic nitrate reduction to synthesize ammonia, specifically as follows:

[0078] The electrocatalytic nitrate reduction synthesis experiment was tested using an electrochemical workstation (Chenhua 660E). The test adopted a three-electrode system, with a 1cm*1cm platinum sheet as the counter electrode, the electrodes obtained in Example 1, Example 2, Example 3, and Example 4 as the working electrode, and the reference electrode was an Ag / AgCl reference electrode. It was carried out in an H-type electrolytic cell, and the cathode chamber and the anode chamber were separated by a Nafion 117 membrane. 5.682g of anhydrous sodium sulfate (superior purity) and 0.0971g of sodium nitrate (superior purity) were dissolved in 80mL of deionized water as the cathode chamber electrolyte, and the molar concentrations of sulfate and nitrate (in terms of nitrogen) were 0.5M and 200mg L, respectively. -1 The electrolyte in the anode chamber is 0.5 M Na 2 SO 4 Before the test, in order to ensure an oxygen-free environment for the electrolyte, argon was introduced into the electrolyte for 30 minutes to eliminate the interference of oxygen on the reaction process.

[0079] Electrochemical testing process:

[0080] Linear sweep voltammetry (LSV) was used at 5 mV s -1 The scanning rate is carried out within a certain voltage range, and the activity of the catalyst is preliminarily tested based on the current density. The chronoamperometry (it) is used to record the change of the current density of the reaction system over time by applying different potentials to the working electrode, so as to obtain the reaction products and calculate relevant indicators. The cyclic stability is a constant potential test at a certain voltage for a certain period of time. A new electrolyte is replaced after each test; a UV spectrophotometer is used to measure the concentrations of nitrate, nitrite, and ammonia nitrogen after the reaction to understand the distribution of total nitrogen changes. +0.2V~-0.8V (vs RHE) is selected as the potential window for LSV scanning, and the scanning speed is set to 5mV / s; the distribution of product nitrogen species at five points of -0.5V, -0.6V, -0.7V, -0.8V, and -0.9V is measured and the Faraday efficiency is calculated. The test results are shown in Table 1.

[0081] Ammonia yield calculation formula:

[0082] NH 3 yieldrate=(C NH3 ×V) / (M NH3 ×t×S)

[0083] Ammonia selectivity:

[0084] Selectivity = C product / ΔC NO3- ×100%

[0085] Faraday efficiency:

[0086] FENH3 = (8F × C NH3 × V) / (M NH3 × Q)

[0087] where C NH3 is the mass concentration of the aqueous solution of NH 3 , V is the volume of the electrolyte in the cathode chamber (80 mL), M NH3 is the molar mass of NH 3 , t is the electrolysis time (2 h), S is the geometric area of the working electrode (1 cm -2 ), ΔC NO3- is the concentration difference of NO 3 - before and after electrolysis, C 0 is the initial concentration of NO 3 - , C product is the generated concentration of ammonia or nitrite, F is the Faraday constant (96485 C mol -1 ), and Q is the total charge passing through the electrode.

[0088] Application of the comparative example

[0089] The undoped cobalt cathode electrode prepared in Comparative Example 1 was used in the electrocatalytic nitrate reduction for ammonia synthesis application as follows:

[0090] The electrocatalytic nitrate reduction synthesis experiment was tested using an electrochemical workstation (Chenhua 660E). The test adopted a three-electrode system. A 1 cm × 1 cm platinum sheet was used as the counter electrode to compare with Cu 2 O in Comparative Example 1 as the working electrode, and an Ag / AgCl reference electrode was used as the reference electrode. The experiment was carried out in an H-type electrolytic cell, and the cathode chamber and the anode chamber were separated by a Nafion 117 membrane. 5.682 g of anhydrous sodium sulfate (analytical grade) and 0.0971 g of sodium nitrate (analytical grade) were dissolved in 80 mL of deionized water as the cathode chamber electrolyte. The molar concentrations of sulfate and nitrate (calculated as nitrogen) were 0.5 M and 200 mg L -1 , respectively. The anode chamber electrolyte was 0.5 M Na 2 SO 4 solution. Before the test, to ensure an anaerobic environment for the electrolyte, argon was introduced into the electrolyte for 30 min to exclude the interference of oxygen on the reaction process.

[0091] The chronoamperometry (i-t) method was used to record the change in the current density of the reaction system with time when different potentials were applied to the working electrode to obtain the reaction products and calculate the relevant indicators. A UV spectrophotometer was used to measure the concentrations of nitrate, nitrite, and ammonia nitrogen after the reaction to understand the change distribution of total nitrogen. The test results are shown in Table 1.

[0092] Table 1 Performance Results of Electrochemical Nitrate Reduction for Ammonia Synthesis

[0093] Material <![CDATA[FE NH3 > <![CDATA[NH 3 Yield]]> Example 1 <![CDATA[Co-Cu 2 O / CF(-0.8V,0.05MCo(NO 3 ) 2 )]]> 95.98％ <![CDATA[0.498 mmol h -1 cm -2 > Example 2 <![CDATA[Co-Cu 2 O / CF(-0.8V,0.01MCo(NO 3 ) 2 )]]> 89.75％ <![CDATA[0.392 mmol h -1 cm -2 > Example 3 <![CDATA[Co-Cu 2 O / CF(-0.8V,0.1MCo(NO 3 ) 2 )]]> 93.67％ <![CDATA[0.448 mmol h -1 cm -2 > Example 4 <![CDATA[Co-Cu 2 O / CF(-1V,0.05MCo(NO 3 ) 2 )]]> 90.49％ <![CDATA[0.406 mmol h -1 cm -2 > Comparative Example 1 <![CDATA[Cu 2 O / CF]]> 83.32％ <![CDATA[0.358 mmol h -1 cm -2 > Comparative Example 2 CuO / CF 75.3％ <![CDATA[0.243 mmol h -1 cm -2 > Comparative Example 3 <![CDATA[Cu-Ni(OH) 2 / CF]]> 80.2％ <![CDATA[0.294mmolh -1 cm -2 >

[0094] Table 1 shows the comparison of the removal efficiency and ammonia synthesis yield of the electrodes prepared in Examples 1-4 for the electrocatalytic reduction of nitrate to ammonia at an applied potential of -0.7 V vs. RHE. The electrocatalytic test results are shown in Table 1, and the results show that the ammonia yields of Examples 1-4 are as high as 0.498 mmol h -1 cm -2 , much higher than that of the pure cuprous oxide electrode in Comparative Example 1, indicating that cobalt metal doping plays an important role in improving the performance of electrocatalytic nitrate reduction for ammonia synthesis.

[0095] The Co-Cu 2 O / CF dual-site cathode electrode prepared by the preparation method of the present invention can achieve efficient conversion of nitrate pollutants at a lower potential, improve the selectivity and Faraday efficiency of ammonia, compared with the Cu 2 O single catalyst without cobalt doping, the Faraday efficiency of ammonia reaches 95.98%, the selectivity can reach 92.45%, and the ammonia production energy consumption is low. At the same time, the electrode has good reusability and stability. As Figure 9 shown, it still maintains a Faraday efficiency of more than 90% after more than 10 cycles, and has the advantages of simple and easy preparation process and no pollution. It can economically and efficiently and environmentally friendly realize the conversion of nitrate and the ammonia production process, showing potential application value.

[0096] The above-described embodiments are only the preferred embodiments of the present invention, and not all the feasible embodiments of the present invention. For those of ordinary skill in the art, any obvious changes made without departing from the principle and spirit of the present invention should be considered to be included within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a self-supporting cobalt-doped cuprous oxide dual-site cathode electrode, characterized in that: The following steps are involved: S1. Prepare a substrate, pre-treat the copper foam, and sequentially ultrasonically treat the copper foam with acetone, dilute hydrochloric acid, ethanol, and deionized water, and then vacuum seal and store it as an electrode substrate for later use; S2. Prepare Cu(OH)2NRs / CF, immerse the electrode substrate prepared in step S1 vertically in a solution containing an alkaline solution and a persulfate, and obtain a sky blue CF, take it out of the solution, wash it thoroughly with deionized water, and vacuum dry it to obtain Cu(OH)2NRs / CF; S3. Prepare Co-Cu(OH)2NRs / CF, place the Cu(OH)2NRs / CF prepared in step S2 in a cobalt nitrate solution, use a three-electrode system, and perform electrodeposition using a constant potential method at a predetermined temperature, remove the solution, wash it, and dry it to obtain Co-Cu(OH)2NRs / CF; S4. Prepare Co-Cu2O / CF, place the Co-Cu(OH)2NRs / CF prepared in step S2 in a tube furnace, heat it to 300-600°C under inert gas protection, maintain it for 0.5-4h, then cool it to room temperature, and finally reduce it in a nitrate solution at a constant voltage of -0.5-1V for 1-4h; obtain Co-Cu2O / CF.

2. The method for preparing a self-supporting cobalt-doped cuprous oxide dual-site cathode electrode according to claim 1, characterized in that the steps In S1, the size of the foam copper is 1 cm*1 cm to 4 cm*4 cm; the concentration of hydrochloric acid is 0.1 to 2 M; the ultrasonic time is 10 to 20 min; and deionized water is used for washing.

3. The method for preparing a self-supporting cobalt-doped cuprous oxide dual-site cathode electrode according to claim 1, characterized in that: In step S2, the persulfate is any one of ammonium persulfate, potassium persulfate or sodium persulfate, and the concentration is 0.05-0.5M.

4. The method for preparing a self-supporting cobalt-doped cuprous oxide dual-site cathode electrode according to claim 1, characterized in that: In step S2, the alkaline solution is potassium hydroxide or sodium hydroxide, and the concentration is 0.5-4M.

5. The method for preparing a self-supporting cobalt-doped cuprous oxide dual-site cathode electrode according to claim 1, characterized in that: In step S3, the predetermined temperature is 20-30°C; the drying temperature is 40-60°C; and the drying time is 8-12 hours.

6. The method for preparing a self-supporting cobalt-doped cuprous oxide dual-site cathode electrode according to claim 1, characterized in that: In step S3, the concentration of the cobalt nitrate solution is 0.01-1M.

7. The method for preparing a self-supporting cobalt-doped cuprous oxide dual-site cathode electrode according to claim 1, characterized in that: In step S3, the conditions for electro-deposition using the constant potential method are: the deposition potential is -0.6 to -1 V; the deposition time is 5 to 30 min.

8. The method for preparing a self-supporting cobalt-doped cuprous oxide dual-site cathode electrode according to claim 1, characterized in that: In step S4, the heating rate is 5-20°C / min.

9. The method for preparing a self-supporting cobalt-doped cuprous oxide dual-site cathode electrode according to claim 1, characterized in that: In step S4, the inert gas is nitrogen or argon.

10. Use of an electrode prepared by the method for preparing a self-supporting cobalt-doped cuprous oxide dual-site cathode electrode according to any one of claims 1 to 9 in preparing NH3 by electrocatalytic nitrate reduction.

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