Amine-modified copper gas diffusion electrode and its application in pulse electrocatalytic CN coupling

Abstract

The present invention belongs to the field of material science and electrocatalysis technology, and discloses an amine-modified copper gas diffusion electrode and its pulse electrocatalytic C-N coupling application, wherein firstly, copper nanoparticles are sprayed on the surface of carbon paper to obtain a copper gas diffusion electrode, and then amines are sprayed on the surface of the copper gas diffusion electrode to obtain an amine-modified copper gas diffusion electrode. The method of the present invention is simple to operate, the obtained gas diffusion electrode has a stable structure, and the amine modification is uniform and effective. It can be used in electrocatalytic C-N coupling to achieve the microenvironment of the catalyst surface regulated by pulse potential, promote the occurrence of C-N coupling reaction, and has a high urea yield and Faraday efficiency.

Description

Technical Field

[0001] The invention relates to the field of material science and electrocatalysis technology, and in particular to an amine-modified copper gas diffusion electrode and a pulse electrocatalytic CN coupling application thereof. Background Art

[0002] At present, the Bosch-Meiser method is mainly used in the industry to synthesize urea. This method couples CO2 and NH3 under high temperature and high pressure reaction conditions to achieve urea production. The electrocatalytic synthesis of urea can occur under mild conditions and has attracted widespread attention as a solution that can replace traditional synthesis methods. Copper-based catalysts have been widely used in electrochemical CO2 reduction reactions and NO3 - The unique catalytic activity exhibited in the reduction reaction has attracted extensive attention in the design and selection of catalysts for electrocatalytic synthesis of urea. However, copper-based catalysts still have problems such as low urea yield, poor selectivity, unclear synthesis path, and severe hydrogen evolution when synthesizing urea by electrocatalytic CN coupling. Therefore, further design and improvement of copper-based catalysts are needed to achieve more efficient electrochemical urea synthesis.

[0003] The introduction of amines into the CO2 electrocatalytic reduction system of copper-based catalysts has been proven to be an effective way to regulate the reduction reaction products. However, various methods of introducing amines also bring certain problems. For example, although the addition of ethanolamine to the electrolyte can increase the solubility of CO2 in the electrolyte and increase the electrocatalytic reduction reaction rate, it also brings about the separation problem of liquid products; amines can be introduced into the catalyst using chemical methods such as hydrothermal method and electrodeposition method, but these methods cannot effectively regulate the microenvironment of the catalyst surface and the preparation process is complicated and the operation is cumbersome; mixing amines with catalysts to prepare slurry and then spraying to prepare gas diffusion electrodes will affect the conductivity of the gas diffusion electrodes and cannot ensure the uniform distribution of amines. Therefore, it is imperative to explore an amine modification method that is simple to operate and does not bring the above problems. Summary of the invention

[0004] Based on the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a simple method for preparing an amine-modified copper gas diffusion electrode, so that it can be used in pulse electrocatalytic CN coupling reactions such as the preparation of urea.

[0005] In order to achieve the purpose, the present invention adopts the following technical solution:

[0006] The present invention discloses a method for preparing an amine-modified copper gas diffusion electrode, which is achieved by a layered spraying method, and is characterized in that: first, copper nanoparticles are sprayed on the surface of carbon paper to obtain a copper gas diffusion electrode; then, amine is continuously sprayed on the surface of the copper gas diffusion electrode to obtain an amine-modified copper gas diffusion electrode. Specifically, the method comprises the following steps:

[0007] Step 1, dispersing copper nanoparticles in a mixture of isopropanol, water, and 5wt% Nafion solution (the volume ratio of the three is 4:1:0.005) to form a slurry, and then spraying the slurry on carbon paper to obtain a copper gas diffusion electrode;

[0008] Step 2: dissolving amine in a mixture of isopropanol and 5 wt % Nafion solution (the volume ratio of the two is 1:0.001), and then spraying the obtained solution on the copper gas diffusion electrode obtained in step 1 to obtain an amine-modified copper gas diffusion electrode.

[0009] Preferably, in step 1, the particle size of the copper nanoparticles is 25-50 nm.

[0010] Preferably, in step 1, the loading amount of copper nanoparticles on the gas diffusion electrode is 0.5-1.5 mg·cm -2 .

[0011] Preferably, in step 2, the amine is phenazine, 1-aminoanthraquinone, N-phenyl-1-naphthylamine, 4,4'-azopyridine or azobenzene.

[0012] Preferably, in step 2, the loading amount of amine on the gas diffusion electrode is 0.02-0.20 mg·cm -2 .

[0013] The present invention also discloses the application of the prepared amine-modified copper gas diffusion electrode in pulse electrocatalytic CN coupling synthesis of urea. The application method can be: in a flow electrolytic cell system, nickel foam is used as a counter electrode, Ag / AgCl is used as a reference electrode, the amine-modified copper gas diffusion electrode is used as a working electrode, and potassium nitrate aqueous solution is used as a cathode electrolyte, CO2 is introduced into the flow electrolytic cell system, a pulse potential is applied to react, and CO2 and nitrate are co-reduced to obtain urea.

[0014] Preferably, the pulse potential is applied by applying a periodic potential consisting of an oxidation potential and a reduction potential. The oxidation potential is 0.2 to 0.4 V vs. RHE, and the reduction potential is -0.1 to -0.5 V vs. RHE. The duration of applying the oxidation potential in each cycle is 4 to 6 s, and the duration of applying the reduction potential is 5 to 15 s.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] 1. The present invention obtains an amine-modified copper gas diffusion electrode by a layered spraying method, which has a simple operation method, few equipment requirements, and mild conditions. The obtained gas diffusion electrode has a stable structure, uniform amine modification, and will not affect the conductivity of the gas diffusion electrode. The liquid product catalyzed in the pulse electrocatalytic CN coupling reaction is easy to separate.

[0017] 2. The amine modified on the copper gas diffusion electrode of the present invention is a water-insoluble electrochemical redox active amine, which can electrochemically adsorb CO2 when a reduction potential is applied, and can electrochemically desorb and release CO2 when an oxidation potential is applied. Modifying it on the surface of the catalyst and applying a periodic redox potential (i.e., a pulse potential) can effectively regulate the microenvironment of the catalyst surface in an aqueous electrolyte, which is beneficial to CN coupling.

[0018] 3. The pulse electrocatalysis method used in the present invention is simple to operate, and the equipment used is the same as that used in the commonly used constant potential or constant current electrocatalysis, and can be widely promoted.

[0019] 4. The amine-modified copper gas diffusion electrode of the present invention can convert NO3 - Pulse electrochemical coupling with CO2 was used to achieve urea synthesis, with a urea synthesis yield and Faraday efficiency of 1.76 μmol h -1 cm -2 and 58.20%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a cross-sectional SEM image of the phenazine-modified copper gas diffusion electrode obtained in Example 1.

[0021] Figure 2 This is the XRD pattern of the phenazine modified copper gas diffusion electrode obtained in Example 1.

[0022] Figure 3 The Faraday efficiency and yield of the phenazine-modified copper gas diffusion electrode obtained in Example 1 in the pulse electrocatalytic CN-coupled urea synthesis reaction ( Figure 3 (a) ) and UV-vis spectra ( Figure 3 (b) in the figure).

[0023] Figure 4 This is the XRD pattern of the 1-aminoanthraquinone modified copper gas diffusion electrode obtained in Example 2.

[0024] Figure 5 This is the Faradaic efficiency and yield diagram of the 1-aminoanthraquinone modified copper gas diffusion electrode obtained in Example 2 in the pulse electrocatalytic CN coupled urea synthesis reaction ( Figure 5 (a) ) and UV-vis spectra ( Figure 5 (b) in the figure).

[0025] Figure 6 This is the XRD pattern of the N-phenyl-1-naphthylamine modified copper gas diffusion electrode obtained in Example 3.

[0026] Figure 7 This is the Faradaic efficiency and yield diagram of the N-phenyl-1-naphthylamine modified copper gas diffusion electrode obtained in Example 3 in the pulse electrocatalytic CN coupled urea synthesis reaction ( Figure 7 (a) ) and UV-vis spectra ( Figure 7 (b) in the figure).

[0027] Figure 8 This is the XRD pattern of the 4,4'-azopyridine modified copper gas diffusion electrode obtained in Example 4.

[0028] Fig. 9 The Faraday efficiency and yield of the 4,4'-azopyridine modified copper gas diffusion electrode obtained in Example 4 in the pulse electrocatalytic CN coupled urea synthesis reaction ( Fig. 9 (a) ) and UV-vis spectra ( Fig. 9 (b) in the figure).

[0029] Fig.10 This is the XRD pattern of the azobenzene modified copper gas diffusion electrode obtained in Example 5.

[0030] Fig.11 The Faraday efficiency and yield of the azobenzene-modified copper gas diffusion electrode obtained in Example 5 in the pulse electrocatalytic CN coupling synthesis of urea ( Fig.11 (a) ) and UV-vis spectra ( Fig.11 (b) in the figure). DETAILED DESCRIPTION

[0031] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail in combination with the embodiments below. The following content is only an example and explanation of the concept of the present invention. The technicians in the relevant technical field make various modifications or supplements to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

[0032] Example 1

[0033] In this example, a phenazine-modified copper gas diffusion electrode was prepared according to the following steps and used in the pulse electrocatalytic CN coupling reaction for synthesizing urea:

[0034] Step 1: Disperse copper nanoparticles with a particle size of about 25 nm in a mixture of isopropanol, water, and 5 wt% Nafion solution (the volume ratio of the three is 4:1:0.005) to form a slurry, and then spray the slurry on carbon paper to obtain a copper nanoparticle loading of 1.0 mg cm -2 The copper gas diffusion electrode is denoted as Cu / C.

[0035] Step 2: Dissolve phenazine (PhN) in a mixture of isopropanol and 5 wt% Nafion solution (the volume ratio of the two is 1:0.001), and then spray the resulting solution on the copper gas diffusion electrode obtained in step 1 to obtain a phenazine loading of 0.05 mg cm -2 The phenazine-modified copper gas diffusion electrode is denoted as PhN / Cu / C.

[0036] Step 3: In a flow electrolytic cell system, nickel foam is used as a counter electrode, Ag / AgCl is used as a reference electrode, the phenazine-modified copper gas diffusion electrode obtained in step 2 is used as a working electrode, and 0.1 mol·L -1 A potassium nitrate aqueous solution was used as the anode and cathode electrolyte, CO2 was introduced into the flow electrolysis cell system at a flow rate of 20 sccm, and oxidation potential and reduction potential were applied for 1 h with a cycle of 15 s, where: the oxidation potential was 0.3 V vs. RHE, and the time in each cycle was 5 s; the reduction potential was (-0.1, -0.2, -0.3, -0.4 or -0.5 V (vs. RHE)), and the time in each cycle was 10 s.

[0037] Figure 1 This is a cross-sectional SEM image of the phenazine-modified copper gas diffusion electrode obtained in this example. It can be seen that the phenazine-modified copper gas diffusion electrode has an obvious layered structure, which includes a phenazine modification layer, a copper catalyst layer, and a carbon paper layer from top to bottom.

[0038] Figure 2 3 and 4 are XRD patterns of the copper gas diffusion electrode and the phenazine-modified copper gas diffusion electrode obtained in this example. It can be seen that the copper gas diffusion electrode is effectively modified by phenazine after layered spraying.

[0039] The electrolyte flowing through the cathode chamber in step 3 was collected, and the electrolyte after the reaction was quantitatively analyzed by UV-vis-NIR spectrophotometer. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that the urea synthesis yield and Faradaic efficiency reached the highest values ​​under the pulse potential condition of -0.3 V (vs. RHE), which were 1.65 μmol h -1 cm -2and 58.28%, demonstrating that the obtained phenazine-modified copper gas diffusion electrode has the ability to efficiently CN-couple to synthesize urea under pulse electrocatalytic conditions.

[0040] Example 2

[0041] In this example, 1-aminoanthraquinone modified copper gas diffusion electrode was prepared according to the following steps and used in the pulse electrocatalytic CN coupling reaction for synthesizing urea:

[0042] Step 1: Disperse copper nanoparticles with a particle size of about 25 nm in a mixture of isopropanol, water, and 5 wt% Nafion solution (the volume ratio of the three is 4:1:0.005) to form a slurry, and then spray the slurry on carbon paper to obtain a copper nanoparticle loading of 1.5 mg cm -2 The copper gas diffusion electrode is denoted as Cu / C.

[0043] Step 2: Dissolve 1-aminoanthraquinone (AAQ) in a mixture of isopropanol and 5 wt% Nafion solution (volume ratio of the two is 1:0.001), and then spray the resulting solution onto the copper gas diffusion electrode obtained in step 1 to obtain a 1-aminoanthraquinone loading of 0.10 mg cm -2 1-aminoanthraquinone modified copper gas diffusion electrode, denoted as AAQ / Cu / C.

[0044] Step 3: In a flow electrolytic cell system, nickel foam is used as a counter electrode, Ag / AgCl is used as a reference electrode, the 1-aminoanthraquinone modified copper gas diffusion electrode obtained in step 2 is used as a working electrode, and 0.1 mol·L -1 A potassium nitrate aqueous solution was used as the anode and cathode electrolyte, CO2 was introduced into the flow electrolysis cell system at a flow rate of 20 sccm, and oxidation potential and reduction potential were applied for 1 h with a cycle of 14 s, where: the oxidation potential was 0.2 V vs. RHE, and the time in each cycle was 4 s; the reduction potential was (-0.1, -0.2, -0.3, -0.4 or -0.5 V (vs. RHE)), and the time in each cycle was 10 s.

[0045] Figure 4 1-aminoanthraquinone modified copper gas diffusion electrode and the copper gas diffusion electrode obtained in this example have XRD patterns. It can be seen that after layered spraying, 1-aminoanthraquinone effectively modified the copper gas diffusion electrode.

[0046] The electrolyte flowing through the cathode chamber in step 3 was collected, and the electrolyte after the reaction was quantitatively analyzed by UV-vis-NIR spectrophotometer. The results are as follows: Figure 5 As shown. Figure 5It can be seen that the urea synthesis yield and Faradaic efficiency reached the highest values ​​under the pulse potential condition of -0.3 V (vs. RHE), which were 1.59 μmol h -1 cm -2 and 54.40%, demonstrating that the obtained 1-aminoanthraquinone modified copper gas diffusion electrode has the ability of efficient CN coupling to synthesize urea under pulse electrocatalytic conditions.

[0047] Example 3

[0048] In this example, the N-phenyl-1-naphthylamine modified copper gas diffusion electrode was prepared according to the following steps and used in the pulse electrocatalytic CN coupling reaction for synthesizing urea:

[0049] Step 1: Disperse copper nanoparticles with a particle size of about 25 nm in a mixture of isopropanol, water, and 5 wt% Nafion solution (the volume ratio of the three is 4:1:0.005) to form a slurry, and then spray the slurry on carbon paper to obtain a copper nanoparticle loading of 0.5 mg cm -2 The copper gas diffusion electrode is denoted as Cu / C.

[0050] Step 2: Dissolve N-phenyl-1-naphthylamine (ArNA) in a mixture of isopropanol and 5 wt% Nafion solution (the volume ratio of the two is 1:0.001), and then spray the resulting solution on the copper gas diffusion electrode obtained in step 1 to obtain an N-phenyl-1-naphthylamine loading of 0.10 mg cm -2 The N-phenyl-1-naphthylamine modified copper gas diffusion electrode is denoted as ArNA / Cu / C.

[0051] Step 3: In a flow electrolytic cell system, nickel foam is used as a counter electrode, Ag / AgCl is used as a reference electrode, the N-phenyl-1-naphthylamine modified copper gas diffusion electrode obtained in step 2 is used as a working electrode, and 0.1 mol·L -1 A potassium nitrate aqueous solution was used as the anode and cathode electrolyte, CO2 was introduced into the flow electrolysis cell system at a flow rate of 20 sccm, and oxidation potential and reduction potential were applied for 1 h with a cycle of 10 s, where: the oxidation potential was 0.4 V vs. RHE, and the time in each cycle was 5 s; the reduction potential was (-0.1, -0.2, -0.3, -0.4 or -0.5 V (vs. RHE)), and the time in each cycle was 5 s.

[0052] Figure 6 3 and 4 are XRD patterns of the copper gas diffusion electrode and the copper gas diffusion electrode modified with N-phenyl-1-naphthylamine obtained in this example. It can be seen that the copper gas diffusion electrode is effectively modified by N-phenyl-1-naphthylamine after layered spraying.

[0053] The electrolyte flowing through the cathode chamber in step 3 was collected, and the electrolyte after the reaction was quantitatively analyzed by UV-vis-NIR spectrophotometer. The results are as follows: Figure 7 As shown. Figure 7 It can be seen that the urea synthesis yield and Faradaic efficiency reached the highest values ​​under the pulse potential condition of -0.4 V (vs. RHE), which were 1.61 μmol h -1 cm -2 and 52.61%, demonstrating that the obtained N-phenyl-1-naphthylamine modified copper gas diffusion electrode has the ability of efficient CN coupling to synthesize urea under pulse electrocatalytic conditions.

[0054] Example 4

[0055] In this example, the 4,4'-azopyridine modified copper gas diffusion electrode was prepared according to the following steps and used in the pulse electrocatalytic CN coupling reaction for synthesizing urea:

[0056] Step 1: Disperse copper nanoparticles with a particle size of about 25 nm in a mixture of isopropanol, water, and 5 wt% Nafion solution (the volume ratio of the three is 4:1:0.005) to form a slurry, and then spray the slurry on carbon paper to obtain a copper nanoparticle loading of 1.0 mg cm -2 The copper gas diffusion electrode is denoted as Cu / C.

[0057] Step 2: Dissolve 4,4'-azopyridine (AzPy) in a mixture of isopropanol and 5 wt% Nafion solution (the volume ratio of the two is 1:0.001), and then spray the resulting solution on the copper gas diffusion electrode obtained in step 1 to obtain a 4,4'-azopyridine loading of 0.15 mg cm -2 The 4,4'-azopyridine modified copper gas diffusion electrode was denoted as AzPy / Cu / C.

[0058] Step 3: In a flow electrolytic cell system, nickel foam is used as the counter electrode, Ag / AgCl is used as the reference electrode, the 4,4'-azopyridine-modified copper gas diffusion electrode obtained in step 2 is used as the working electrode, and 0.1 mol·L -1 A potassium nitrate aqueous solution was used as the anode and cathode electrolyte, CO2 was introduced into the flow electrolysis cell system at a flow rate of 20 sccm, and oxidation potential and reduction potential were applied for 1 h with a cycle of 21 s, where: the oxidation potential was 0.3 V vs. RHE, and the time in each cycle was 6 s; the reduction potential was (-0.1, -0.2, -0.3, -0.4 or -0.5 V (vs. RHE)), and the time in each cycle was 15 s.

[0059] Figure 8 : These are the XRD patterns of the copper gas diffusion electrode obtained in this example and the copper gas diffusion electrode modified with 4,4'-azopyridine. It can be seen that after layered spraying, 4,4'-azopyridine has effectively modified the copper gas diffusion electrode.

[0060] The electrolyte flowing through the cathode chamber in step 3 was collected, and the electrolyte after the reaction was quantitatively analyzed by UV-vis-NIR spectrophotometer. The results are as follows: Fig. 9 As shown. Fig. 9 It can be seen that the urea synthesis yield and Faradaic efficiency reached the highest values ​​under the pulse potential condition of -0.4 V (vs. RHE), which were 1.76 μmol h -1 cm -2 and 58.20%, demonstrating that the obtained 4,4'-azopyridine modified copper gas diffusion electrode has the ability of efficient CN coupling to synthesize urea under pulse electrocatalytic conditions.

[0061] Example 5

[0062] In this example, an azobenzene-modified copper gas diffusion electrode was prepared according to the following steps and used in the pulse electrocatalytic CN coupling reaction for synthesizing urea:

[0063] Step 1: Disperse copper nanoparticles with a particle size of about 25 nm in a mixture of isopropanol, water, and 5 wt% Nafion solution (the volume ratio of the three is 4:1:0.005) to form a slurry, and then spray the slurry on carbon paper to obtain a copper nanoparticle loading of 0.5 mg cm -2 The copper gas diffusion electrode is denoted as Cu / C.

[0064] Step 2: Dissolve azobenzene (AzB) in a mixture of isopropanol and 5 wt% Nafion solution (the volume ratio of the two is 1:0.001), and then spray the resulting solution on the copper gas diffusion electrode obtained in step 1 to obtain an azobenzene loading of 0.20 mg cm -2 Azobenzene modified copper gas diffusion electrode, denoted as AzB / Cu / C.

[0065] Step 3: In a flow electrolytic cell system, nickel foam is used as a counter electrode, Ag / AgCl is used as a reference electrode, the azobenzene-modified copper gas diffusion electrode obtained in step 2 is used as a working electrode, and 0.1 mol·L -1A potassium nitrate aqueous solution was used as the anode and cathode electrolyte, CO2 was introduced into the flow electrolysis cell system at a flow rate of 20 sccm, and oxidation potential and reduction potential were applied for 1 h with a cycle of 15 s, where: the oxidation potential was 0.4 V vs. RHE, and the time in each cycle was 5 s; the reduction potential was (-0.1, -0.2, -0.3, -0.4 or -0.5 V (vs. RHE)), and the time in each cycle was 10 s.

[0066] Fig.10 2 are XRD patterns of the copper gas diffusion electrode and the azobenzene-modified copper gas diffusion electrode obtained in this example. It can be seen that after layered spraying, azobenzene has effectively modified the copper gas diffusion electrode.

[0067] The electrolyte flowing through the cathode chamber in step 3 was collected, and the electrolyte after the reaction was quantitatively analyzed by UV-vis-NIR spectrophotometer. The results are as follows: Fig.11 As shown. Fig.11 It can be seen that the Faradaic efficiency of urea synthesis under the pulse potential condition of -0.3 V (vs. RHE) reaches the highest value, which is 44.64%. The urea synthesis yield under the pulse voltage of -0.4 V (vs. RHE) reaches the highest value, which is 1.30 μmol h -1 cm -2 The results showed that the azobenzene-modified copper gas diffusion electrode has the ability to efficiently synthesize urea by CN coupling under pulse electrocatalytic conditions.

[0068] The above contents are merely examples and explanations of the concept of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A method for preparing an amine-modified copper gas diffusion electrode, characterized in that: First, copper nanoparticles are sprayed on the surface of carbon paper to obtain a copper gas diffusion electrode; then, amines are sprayed on the surface of the copper gas diffusion electrode to obtain an amine-modified copper gas diffusion electrode; the specific steps include: Step 1, dispersing copper nanoparticles in a mixture of isopropanol, water, and 5 wt% Nafion solution to form a slurry, and then spraying the slurry on carbon paper to obtain a copper gas diffusion electrode; Step 2: dissolving amine in a mixture of isopropanol and 5 wt % Nafion solution, and then spraying the resulting solution on the copper gas diffusion electrode obtained in step 1 to obtain an amine-modified copper gas diffusion electrode.

2. The method for preparing an amine-modified copper gas diffusion electrode according to claim 1, characterized in that: In step 1, the particle size of the copper nanoparticles is 25-50 nm.

3. The method for preparing an amine-modified copper gas diffusion electrode according to claim 1, characterized in that: In step 1, the loading amount of copper nanoparticles on the gas diffusion electrode is 0.5~1.5 mg cm -2 .

4. The method for preparing an amine-modified copper gas diffusion electrode according to claim 1, characterized in that: In step 2, the amine is phenazine, 1-aminoanthraquinone, N-phenyl-1-naphthylamine, 4,4'-azopyridine or azobenzene.

5. The method for preparing an amine-modified copper gas diffusion electrode according to claim 1, characterized in that: In step 2, the loading amount of amine on the gas diffusion electrode is 0.02~0.20 mg cm -2 .

6. An amine-modified copper gas diffusion electrode prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the amine-modified copper gas diffusion electrode according to claim 6 in pulse electrocatalytic CN coupling synthesis of urea.

8. The use according to claim 7, characterized in that: In a flow electrolytic cell system, nickel foam is used as a counter electrode, Ag / AgCl is used as a reference electrode, the amine-modified copper gas diffusion electrode is used as a working electrode, and potassium nitrate aqueous solution is used as a cathode electrolyte. CO2 is introduced into the flow electrolytic cell system, and a pulse potential is applied to react, so that CO2 and nitrate are co-reduced to obtain urea.

9. The use according to claim 8, characterized in that: The applied pulse potential refers to applying a periodic potential consisting of an oxidation potential and a reduction potential; the oxidation potential value is 0.2~0.4 V vs. RHE, and the reduction potential value is -0.1~-0.5 V vs. RHE; the duration of applying the oxidation potential in each cycle is 4~6 s, and the duration of applying the reduction potential is 5~15 s.

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