Preparation method and application of iron-doped cuprous oxide catalytic electrode based on copper-iron double active sites

Abstract

The invention relates to a preparation method and application of an iron-doped cuprous oxide catalytic electrode based on copper-iron double active sites, and belongs to the technical field of electrochemical catalysis. The iron-copper double-active-site iron-doped cuprous oxide catalytic electrode with a three-dimensional conical structure is prepared through an electroplating-oxidation-electroreduction coupling process. The iron-doped cuprous oxide catalytic electrode based on the copper-iron double active sites has excellent ammonia preparation catalytic activity and structural stability; the problems of low ammonia preparation efficiency, poor selectivity and the like caused by too strong adsorption energy of a nitrogen-containing intermediate product and too slow hydrogenation reaction rate of a traditional copper-based catalytic material in the process of preparing ammonia through nitrate electroreduction can be solved.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of an iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites, belonging to the technical field of electrocatalytic technology. Background Art

[0002] Ammonia is an energy carrier with a relatively high energy density. At present, the production of industrial ammonia mainly relies on the Haber-Bosch process, which has huge energy consumption and carbon dioxide emissions. Therefore, sustainable ammonia (NH3) synthesis pathways such as biological nitrogen fixation, photocatalytic nitrogen reduction, and electrocatalytic nitrogen reduction have been proposed. The electrocatalytic nitrogen reduction reaction (eNRR) for preparing NH3 has good environmental conditions and high selectivity. However, due to the relatively high dissociation energy of the N≡N bond (i.e., 941 kJ / mol -1 ), the ammonia production efficiency of eNRR is low and the energy consumption is high. Compared with N2, the dissociation energy of nitrate (NO3 - ) is much lower, which is 204 kJ / mol -1 , so it is recognized as a very promising nitrogen source for electrochemical synthesis of NH3. In addition, nitrate (NO3 - ) in domestic and industrial wastewater is harmful to the environment and human health. Therefore, it is of great significance to "turn waste into treasure" by using the electrocatalytic reduction of nitrate technology to reduce and convert nitrate into recyclable and high-value ammonia under mild conditions.

[0003] However, the electrochemical NO3 - reduction reaction (eNO3 - RR), as the most promising alternative process to the Haber-Bosch process for NH3 synthesis, involves 8 electron couplings and 9 proton transfer steps, which reduces the selectivity and ammonia production efficiency in this reaction. In addition, in the cathodic hydrogen evolution reaction (HER), the dimerization of *H to produce H2 competes viciously with the supply of hydrogen intermediates (*H) required for eNO3 - RR, resulting in low ammonia production efficiency and Faraday efficiency. Therefore, it is crucial to develop an electrocatalyst that can effectively generate *H and inhibit the dimerization of *H and has high ammonia production catalytic activity. Compared with metal copper catalysts, cuprous oxide (Cu2O) catalysts have higher selectivity and NH3 Faraday efficiency. This is to some extent because the active Cu + promotes the generation of *H in the Volmer reaction and inhibits HER. However, the poor conductivity of p-type Cu2O inhibits the transfer of electrons from the catalyst to the electrolyte, reducing the catalytic performance of eNO3 - RR. Summary of the Invention

[0004] Aiming at the problems of the existing Cu2O electrode material, such as the too strong adsorption energy of nitrogen-containing intermediates and poor hydrogenation ability during the electroreduction of nitrate to ammonia, resulting in low ammonia production efficiency and weak selectivity, the present invention proposes a preparation method and application of an iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites. Through the "electroplating-oxidation-electroreduction" coupling process, an iron-doped cuprous oxide catalytic electrode with a three-dimensional conical structure and copper-iron dual active sites is prepared. By doping heteroatom iron into Cu2O, the traditional single copper active site is transformed into a copper-iron dual active site, and the effective regulation of the Cu + active site in the electroreduction of NO3 - to NH3 is achieved by the copper-iron dual active sites, so as to strengthen the ammonia production selectivity and efficiency of Cu2O.

[0005] A preparation method of an iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites is as follows:

[0006] (1) Immerse the copper plate and the copper foam substrate into an acidic solution respectively, and perform ultrasonic treatment at room temperature to obtain an ultrasonically pretreated copper plate and an ultrasonically pretreated copper foam substrate;

[0007] (2) The ultrasonically pretreated copper plate and the ultrasonically pretreated copper foam substrate are successively ultrasonically cleaned with absolute ethanol and ultrasonically cleaned with deionized water to obtain a copper electrode and a copper foam substrate electrode;

[0008] (3) Using the copper foam substrate electrode as the cathode and the copper electrode as the anode, electroplate in a ferrous electrolyte. After the cathode is cleaned with deionized water, an iron-copper / copper foam substrate electrode is obtained;

[0009] (4) Place the iron-copper / copper foam substrate electrode in an air atmosphere and uniformly heat it to a temperature of 500-600 °C and oxidize it for 100-150 min to obtain an oxidized (iron-copper / copper foam) substrate electrode;

[0010] (5) Using the oxidized (iron-copper / copper foam) substrate electrode as the working electrode, a platinum sheet as the counter electrode, and a mercury / mercuric oxide electrode as the reference electrode, perform an electrochemical reduction reaction in an alkaline electrolyte. After the working electrode is washed with deionized water and dried, an iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites is obtained.

[0011] Preferably, the acidic solution in step (1) is a hydrochloric acid solution with a concentration of 2.5-3.5 mol / L, the ultrasonic power is 170-190 W, and the ultrasonic treatment time is 4-10 min.

[0012] Preferably, the ferrous electrolyte in step (3) contains 0.05-0.15 mol / L of sodium sulfate, 0.05-0.15 mol / L of ferrous sulfate, and 0.03-0.05 mol / L of sulfuric acid.

[0013] More preferably, the temperature of electroplating in step (3) is 55-65°C, and the current density is 180-200 mA / cm 2 , and the electroplating time is 0.5-1.5 h.

[0014] Preferably, the alkaline electrolyte in step (5) is a potassium hydroxide solution with a concentration of 0.05-0.15 mol / L.

[0015] More preferably, the temperature of the electrochemically reduction reaction in step (5) is 20-30°C, the electrochemically reduction potential is -1.12 to -1.32 V vs. Hg / HgO, and the electrochemically reduction reaction time is 1.5-2.5 h.

[0016] The iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites has a three-dimensional "conical structure".

[0017] Application of the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites in electroreduction of nitrate to ammonia: the concentration of sodium nitrate in the cathode chamber of the electroreduction of ammonia reaction is 0.10 mol / L.

[0018] Preferably, the applied potential for the electroreduction of ammonia reaction is -0.2 to -0.4 V vs. RHE.

[0019] The beneficial effects of the present invention are as follows:

[0020] (1) Aiming at the problems of poor conductivity of traditional p-type cuprous oxide, too strong adsorption ability for nitrogen-containing intermediates and slow hydrogenation rate, resulting in low ammonia production catalytic activity, the present invention introduces heteroatom Fe into Cu2O, changes the local electron coordination environment of Cu2O, converts the single Cu active site into a Cu-Fe dual active site, can effectively change the conductivity of Cu2O, regulate and optimize its adsorption energy for nitrogen-containing intermediates and hydrogenation reaction, thereby improving its ammonia production efficiency and Faraday efficiency;

[0021] (2) The method of the present invention to "enhance the number of active sites" to change the catalytic activity of the catalyst enables the prepared iron-doped cuprous oxide catalytic electrode with copper-iron dual active sites to exhibit excellent ammonia production catalytic activity. Under the condition of -0.3 V vs. RHE, the highest ammonia production rate reaches 10.37 mg h -1 cm -2 , the Faraday efficiency is as high as 93.50%, and under the 20-h cyclic test, the ammonia production performance is still strong, showing extremely strong catalytic stability. Compared with the cuprous oxide electrode, its Faraday efficiency is increased by nearly 45%;

[0022] (3) The iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites of the present invention has excellent ammonia synthesis catalytic activity and structural stability, and can solve the problems of low ammonia synthesis efficiency and poor selectivity of traditional copper-based catalytic materials due to the too strong adsorption energy of nitrogen-containing intermediate products and the too slow hydrogenation reaction rate during the electroreduction of nitrate to ammonia. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is the process flow chart of the present invention;

[0024] Figure 2 is the XRD pattern of the catalytic electrodes of Comparative Example 1 and Example 2;

[0025] Figure 3 is the Raman pattern of the catalytic electrodes of Comparative Example 1 and Example 2;

[0026] Figure 4 is the scanning electron microscope image and energy spectrum diagram of the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites of Example 2;

[0027] Figure 5 is the CV comparison diagram of the catalytic electrodes of Comparative Example 1 and Example 2 before and after adding sulfate cyanide ions to the electrolyte;

[0028] Figure 6 is the linear sweep curve comparison diagram of the catalytic electrodes of Comparative Example 1 and Examples 1-3;

[0029] Figure 7 is the Faraday and ammonia production rate comparison diagram of the catalytic electrodes of Comparative Example 1 and Examples 1-3;

[0030] Figure 8 is the linear sweep curve comparison diagram of the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites of Example 2 before and after adding sodium nitrate to the alkaline electrolyte;

[0031] Figure 9 is the Faraday and ammonia production rate comparison diagram of the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites of Example 2 at different potentials;

[0032] Figure 10 is the cyclic test diagram of the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites of Example 2 at an applied voltage of -0.3V vs. RHE. DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention will be further described in detail below in conjunction with the specific embodiments, but the protection scope of the present invention is not limited to the content described.

[0034] Example 1: A preparation method of an iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites (see Figure 1), the specific steps are as follows:

[0035] (1) Immerse the copper plate (2 cm × 2 cm × 0.1 cm) and the copper foam substrate (1 cm × 2 cm × 0.1 cm) separately into an acidic solution (hydrochloric acid solution with a concentration of 2.5 mol / L), and perform ultrasonic treatment for 4 min at room temperature to obtain the ultrasonically pretreated copper plate and the ultrasonically pretreated copper foam substrate; the ultrasonic power is 170 W;

[0036] (2) The ultrasonically pretreated copper plate and the ultrasonically pretreated copper foam substrate are successively ultrasonically cleaned with absolute ethanol and ultrasonically cleaned with deionized water to obtain a copper electrode and a copper foam substrate electrode;

[0037] (3) Using the copper foam substrate electrode as the cathode and the copper electrode as the anode, in a ferrous electrolyte solution, electroplate at a temperature of 55 °C for 0.5 h. After the cathode is cleaned with deionized water, an iron / copper foam substrate electrode is obtained; the ferrous electrolyte solution contains 0.05 mol / L of sodium sulfate, 0.05 mol / L of ferrous sulfate, and 0.03 mol / L of sulfuric acid; the current density of the electroplating is 180 mA / cm 2 ;

[0038] (4) Place the iron / copper foam substrate electrode in an air atmosphere, and uniformly heat it at a heating rate of 5 °C / min to a temperature of 500 °C and oxidize it for 100 min to obtain an oxidized (iron / copper foam) substrate electrode;

[0039] (5) Using the oxidized (iron / copper foam) substrate electrode as the working electrode, a platinum sheet as the counter electrode, and a mercury / mercuric oxide electrode as the reference electrode, perform an electrochemical reduction reaction for 1.5 h in an alkaline electrolyte solution (0.05 mol / L potassium hydroxide solution) at a temperature of 20 °C. After the working electrode is washed with deionized water and dried, an iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites is obtained; the electrochemical reduction potential is -1.12 V vs. Hg / HgO.

[0040] Example 2: A method for preparing an iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites (see Figure 1 ), the specific steps are as follows:

[0041] (1) Immerse the copper plate (2 cm × 2 cm × 0.1 cm) and the copper foam substrate (1 cm × 2 cm × 0.1 cm) separately into an acidic solution (hydrochloric acid solution with a concentration of 3.0 mol / L), and perform ultrasonic treatment for 7.0 min at room temperature to obtain the ultrasonically pretreated copper plate and the ultrasonically pretreated copper foam substrate; the ultrasonic power is 180 W;

[0042] (2) The ultrasonically pretreated copper plate and the ultrasonically pretreated copper foam substrate are successively ultrasonically cleaned with absolute ethanol and ultrasonically cleaned with deionized water to obtain a copper electrode and a copper foam substrate electrode;

[0043] (3) Using the copper foam matrix electrode as the cathode and the copper electrode as the anode, in the ferrous electrolyte, electroplate for 1.0 h at a temperature of 60 °C to obtain an iron / copper foam matrix electrode after the cathode is washed with deionized water; the ferrous electrolyte contains 0.10 mol / L of sodium sulfate, 0.10 mol / L of ferrous sulfate, and 0.04 mol / L of sulfuric acid; the current density of the electroplating is 190 mA / cm 2 ;

[0044] (4) Place the iron copper / copper foam matrix electrode in an air atmosphere, heat it uniformly at a heating rate of 5 °C / min to a temperature of 550 °C and oxidize for 120 min to obtain an oxidized (iron copper / copper foam) matrix electrode;

[0045] (5) Using the oxidized (iron copper / copper foam) matrix electrode as the working electrode, the platinum sheet as the counter electrode, and the mercury / mercuric oxide electrode as the reference electrode, carry out an electrochemical reduction reaction for 2.0 h in an alkaline electrolyte (0.10 mol / L potassium hydroxide solution) at a temperature of 25 °C. Wash the working electrode with deionized water and dry it to obtain an iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites; the electrochemical reduction potential is -1.22 V vs. Hg / HgO.

[0046] Comparative Example 1: The difference between this comparative example and Example 2 is that the ferrous electrolyte in step (3) is replaced with an electrolyte containing only 0.10 mol / L of sodium sulfate and 0.04 mol / L of sulfuric acid to prepare an undoped cuprous oxide catalytic electrode;

[0047] The XRD patterns of the catalytic electrodes of Comparative Example 1 and Example 2 are shown in Figure 2 , from Figure 2 it can be seen that doping the heteroatom Fe into Cu2O does not change the main phase of cuprous oxide, but the position of the diffraction peak corresponding to the Cu2O (111) crystal plane shifts to a higher angle after the incorporation of iron, and the positions of other peaks do not change, indicating that the heteroatom iron has been successfully incorporated into the lattice of cuprous oxide;

[0048] The Raman spectra of the catalytic electrodes of Comparative Example 1 and Example 2 are shown in Figure 3 , from Figure 3 it can be seen that the position of the Cu-O bond of cuprous oxide (148.7 cm -1 ) shows a red shift phenomenon after the incorporation of iron, and the corresponding peak width becomes wider, further proving the successful preparation of the iron-doped cuprous oxide catalytic electrode;

[0049] The scanning electron microscope images and energy spectrum diagrams of the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites in Example 2 are shown in Figure 4 , from Figure 4It can be seen that the apparent morphology of the iron-doped cuprous oxide catalytic electrode material is a uniformly distributed conical structure. In addition, the corresponding energy spectrum EDS proves the uniform distribution of copper, iron, and oxygen elements on the surface of the catalytic electrode, demonstrating the successful preparation of the iron-doped cuprous oxide catalytic electrode.

[0050] Example 3: A preparation method of an iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites (see Figure 1 ), and the specific steps are as follows:

[0051] (1) Immerse the copper plate (2 cm × 2 cm × 0.1 cm) and the copper foam substrate (1 cm × 2 cm × 0.1 cm) separately into the acidic solution (hydrochloric acid solution with a concentration of 3.5 mol / L), and perform ultrasonic treatment for 10.0 min at room temperature to obtain the ultrasonically pretreated copper plate and the ultrasonically pretreated copper foam substrate; the ultrasonic power is 190 W;

[0052] (2) The ultrasonically pretreated copper plate and the ultrasonically pretreated copper foam substrate are successively ultrasonically cleaned with absolute ethanol and ultrasonically cleaned with deionized water to obtain the copper electrode and the copper foam substrate electrode;

[0053] (3) Using the copper foam substrate electrode as the cathode and the copper electrode as the anode, in the ferrous electrolyte, electroplate at a temperature of 65 °C for 1.5 h. After the cathode is cleaned with deionized water, the iron / copper foam substrate electrode is obtained; the ferrous electrolyte contains 0.15 mol / L of sodium sulfate, 0.15 mol / L of ferrous sulfate, and 0.05 mol / L of sulfuric acid; the current density of the electroplating is 200 mA / cm 2 ;

[0054] (4) Place the iron-copper / copper foam substrate electrode in an air atmosphere, and uniformly heat it at a heating rate of 5 °C / min to a temperature of 600 °C and oxidize for 150 min to obtain the oxidized (iron-copper / copper foam) substrate electrode;

[0055] (5) Using the oxidized (iron-copper / copper foam) substrate electrode as the working electrode, a platinum sheet as the counter electrode, and a mercury / mercuric oxide electrode as the reference electrode, perform an electrochemical reduction reaction in the alkaline electrolyte (0.15 mol / L potassium hydroxide solution) at a temperature of 30 °C for 2.5 h. After the working electrode is washed with deionized water and dried, the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites is obtained; the electrochemical reduction potential is -1.32 V vs. Hg / HgO.

[0056] Performance detection of the iron-doped cuprous oxide catalytic electrode material based on copper-iron dual active sites for electro-reducing nitrate to ammonia:

[0057] The catalytic electrode materials obtained from Comparative Example 1, Example 1, Example 2, and Example 3 were respectively used for the performance test of nitrate reduction to ammonia. This test was carried out in an H-type electrolytic cell with a Nafion 117 proton exchange membrane through a standard three-electrode system. The prepared catalytic electrode was used as the working electrode, the Hg / HgO electrode was used as the reference electrode, and the Pt sheet was used as the counter electrode. The cathode cell was filled with a mixed solution of 1.0 mol / L -1 KOH + 0.1 mol / L -1 NaNO3, and the anode cell was filled with 1.0 mol / L -1 KOH solution. It should be noted that high-purity argon gas was introduced into the cathode cell electrolyte for 30 min before the reaction and each test result was repeated three times to ensure the accuracy of the test results. Electrochemical characterization was required to test the linear sweep curve, the constant current polarization curve, and the cyclic voltammetry curve. Among them, in the linear sweep curve, the sweep rate was 5 mV / s -1 , and the applied voltage window was 0.52 V - 1.1 V vs. RHE; the test results are shown in Figures 5 - 10 ;

[0058] The CV comparison diagrams of the catalytic electrodes of Comparative Example 1 and Example 2 before and after adding thiocyanate ions to the electrolyte are shown in Figure 5 . Before and after adding 0.1 mol / L thiocyanate to the electrolyte, the current density of the catalytic electrode of Comparative Example 1 decreased sharply during the nitrate reduction to ammonia process, indicating that the metal sites with catalytic activity for nitrate reduction to ammonia in the catalytic electrode of Comparative Example 1 were mainly Cu. The same phenomenon also occurred in the catalytic electrode of Example 2, but the current density shown by the catalytic electrode of Example 2 was larger, indicating that the incorporated Fe had a promoting effect on the ammonia production performance of the catalytic electrode, and also proved the existence of the Cu-Fe bimetallic active sites in the catalytic electrode of Example 2;

[0059] The comparison diagrams of the linear sweep curves of the catalytic electrodes of Comparative Example 1 and Examples 1 - 3 are shown in Figure 6 ; the comparison diagrams of the Faraday and ammonia production rates of the catalytic electrodes of Comparative Example 1 and Examples 1 - 3 are shown in Figure 7 ; at the same applied voltage, compared with the catalytic electrodes of Comparative Example 1, Example 1, and Example 3, the current density of the catalytic electrode of Example 2 was larger, proving that the doping concentration of Fe had a very important influence on the ammonia production performance of Cu2O; and the ammonia production rate (10.37 mg / h - 1 cm -2 ) and the Faraday efficiency (93.50%) corresponding to the catalytic electrode of Example 2 were also the highest, indicating that the doping concentration of Fe in the catalytic electrode of Example 2 was the best;

[0060] Figure for comparing linear sweep curves of the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites before and after adding sodium nitrate in an alkaline electrolyte, as shown in Figure 8 , figure for comparing Faraday and ammonia production rates of the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites at different potentials in Example 2, as shown in Figure 9 , in the KOH electrolyte without adding NO3 - , compared with the catalytic electrode of Comparative Example 1, the catalytic electrode of Example 2 has a larger current density, indicating that the catalytic electrode of Example 2 has a stronger ability to generate hydrogen intermediates; after adding NO3 - , the increase in the current density of the catalytic electrode of Example 2 is greater than that of the catalytic electrode of Comparative Example 1, indicating that the catalytic electrode of Example 2 has a stronger NO3 - reduction performance; in addition, as the applied voltage increases, the ammonia production rate and Faraday efficiency of the catalytic electrode of Example 2 show a trend of first increasing and then decreasing. When the applied potential is -0.3 V vs. RHE, the ammonia production rate and Faraday efficiency reach the maximum, indicating that the applied potential at this time is the optimal potential;

[0061] Figure for cyclic voltammetry test of the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites at an applied voltage of -0.3 V vs. RHE in Example 2, as shown in Figure 10 , under the condition of the optimal applied potential of -0.3 V vs. RHE, after continuously performing 10 cycles, the catalytic electrode of Example 2 still exhibits strong and stable NO3 - ammonia production performance, demonstrating its strong catalytic stability.

[0062] The specific embodiments of the present invention have been described in detail above, but the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A preparation method of an iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites, characterized in that, The specific steps are as follows: (1) Immerse the copper plate and the copper foam substrate in an acidic solution respectively, and perform ultrasonic treatment at room temperature to obtain an ultrasonically pretreated copper plate and an ultrasonically pretreated copper foam substrate; (2) The ultrasonically pretreated copper plate and the ultrasonically pretreated copper foam substrate are successively ultrasonically cleaned with absolute ethanol and ultrasonically cleaned with deionized water to obtain a copper electrode and a copper foam substrate electrode; (3) Using the copper foam substrate electrode as the cathode and the copper electrode as the anode, electroplate in a ferrous electrolyte. After the cathode is cleaned with deionized water, an iron-copper / copper foam substrate electrode is obtained; (4) Place the iron / copper foam substrate electrode in an air atmosphere and uniformly heat it to a temperature of 500-600 °C and oxidize it for 100-150 min to obtain an oxidized (iron-copper / copper foam) substrate electrode; (5) Using the oxidized (iron-copper / copper foam) substrate electrode as the working electrode, a platinum sheet as the counter electrode, and a mercury / mercuric oxide electrode as the reference electrode, perform an electrochemical reduction reaction in an alkaline electrolyte. After the working electrode is washed with deionized water and dried, an iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites is obtained.

2. The preparation method of the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites according to claim 1, characterized in that: In step (1), the acidic solution is a hydrochloric acid solution with a concentration of 2.5-3.5 mol / L, the ultrasonic power is 170-190 W, and the ultrasonic treatment time is 4-10 min.

3. The preparation method of the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites according to claim 1, wherein: In step (3), the ferrous electrolyte contains 0.05-0.15 mol / L of sodium sulfate, 0.05-0.15 mol / L of ferrous sulfate, and 0.03-0.05 mol / L of sulfuric acid.

4. The preparation method of the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites according to claim 3, characterized in that: The temperature of electroplating in step (3) is 55 to 65 °C, the current density is 180 to 200 mA / cm 2 , and the electroplating time is 0.5 to 1.5 h.

5. The preparation method of the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites according to claim 1, characterized in that: In step (5), the alkaline electrolyte is a potassium hydroxide solution with a concentration of 0.05-0.15 mol / L.

6. The preparation method of the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites according to claim 5, wherein: In step (5), the temperature of the electrochemical reduction reaction is 20-30 °C, the electrochemical reduction potential is -1.12 to -1.32 V vs. Hg / HgO, and the electrochemical reduction reaction time is 1.5-2.5 h.

7. The iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites prepared by the method according to any one of claims 1 to 6, characterized in that: The iron-doped cuprous oxide catalytic electrode has a three-dimensional "conical structure".

8. Application of the iron-doped cuprous oxide catalytic electrode based on copper-iron dual active sites according to claim 7 in the electroreduction of nitrate to ammonia.

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