Method for synthesizing carbon fiber loaded nitrogen-doped copper-nickel alloy catalyst based on Joule heat technology and application thereof

Abstract

The invention discloses a method for synthesizing a carbon fiber loaded nitrogen-doped copper-nickel alloy catalyst based on a Joule heat technology and application of the carbon fiber loaded nitrogen-doped copper-nickel alloy catalyst. The carbon fiber-loaded nitrogen-doped copper-nickel alloy catalyst is successfully prepared by taking carbon paper as a substrate through a Joule heat technology, the carbon fiber-loaded nitrogen-doped copper-nickel alloy catalyst as a catalyst shows excellent catalytic performance in a reaction system for synthesizing urea through co-reduction of nitrate and carbon dioxide, and 68% of Faraday efficiency and 544 [mu] g cm <-2 > h <-1 > of urea yield are achieved under-0.5 V v.RHE. The preparation method of the catalyst has the advantages of being simple, rapid, green, environmentally friendly and the like, and a new method and a new idea are provided for the field of electro-catalytic synthesis of urea.

Description

Technical Field

[0001] The present invention belongs to the field of electrocatalysis, and particularly relates to a method for synthesizing a carbon fiber-supported nitrogen-doped copper-nickel alloy catalyst based on Joule heat technology and its application. Background Art

[0002] Urea plays a crucial role in agricultural production and human civilization, contributing approximately 40% of the global food production and solving about 27% of the human survival problems. However, the current industrial synthesis of urea usually uses the Haber-Bosch process (N2 + 3H2 → 2NH3) and the Bosch-Meiser process (2NH3 + CO2 → NH2CONH2 + H2O), which pose challenges to sustainable development due to their high energy consumption and large amount of carbon dioxide emissions. At the same time, nitrate, as a common water pollutant, can cause water eutrophication and threaten human health. In the face of the above challenges, the electrocatalytic coupling synthesis of urea from carbon dioxide and nitrate has become a hot research direction. This green electricity-driven method can convert the greenhouse gas carbon dioxide and nitrogen-containing wastewater into high-value-added urea under ambient conditions, not only significantly reducing energy consumption but also demonstrating great potential for green and sustainable development.

[0003] Research shows that noble metals (such as Ru, Pd, Ag, Au, etc.) exhibit excellent electrocatalytic performance during the urea synthesis process. However, compared with noble metal catalysts, transition metal catalysts have received more attention due to their superior catalytic performance, low cost, and abundant resources. For example, in the field of nitrate reduction to ammonia, Cu shows excellent electrocatalytic reduction ability for nitrates. However, single metal copper cannot catalyze carbon dioxide reduction simultaneously, resulting in low urea yield and Faraday efficiency. In the field of carbon dioxide reduction, Ni single-atom sites show excellent performance for the CO2 reduction reaction and can effectively convert CO2 into CO. Therefore, introducing metal nickel, which is beneficial for carbon dioxide reduction, into metal copper will be conducive to the synthesis of urea.

[0004] The patent document of CN202311210501.8 discloses a nitrogen-doped carbon nanotube-coated copper-nickel alloy catalyst, its preparation method and application. The catalyst includes nitrogen-doped carbon nanotubes and copper-nickel alloy particles coated inside the nitrogen-doped carbon nanotubes. The specific preparation process is as follows: annealing the mixture in an inert atmosphere to obtain a catalyst precursor, and the mixture includes a carbon nitride precursor, an organic copper salt and an organic nickel salt; then performing acid treatment on the catalyst precursor. This catalyst is used for electrocatalytic synthesis of urea. The catalyst prepared by this patent document is a nitrogen-doped carbon nanotube-supported copper-nickel alloy catalyst, and the supported material is a copper-nickel alloy catalyst. At the same time, it is easy to produce particle agglomeration based on the traditional tube furnace heat treatment process, which will affect the catalytic performance of the catalyst to a certain extent. In addition, the heat treatment efficiency of the traditional heat treatment process is relatively low, and the product production cycle is relatively long.

[0005] Based on the above research, the present invention designs a copper-nickel alloy double-site catalyst containing nitrogen doping, which is expected to improve the efficiency of urea synthesis. In the method of synthesizing the catalyst, based on the Joule heat technology, instantaneous heating and cooling are achieved in an extremely short time, effectively preventing the agglomeration and sintering of metal particles. The present invention synthesizes a carbon fiber-supported nitrogen-doped copper-nickel alloy catalyst through a simple Joule heating strategy, which can be applied to the reaction system of electrocatalytic co-reduction of nitrate and carbon dioxide to urea, and there is no relevant report in this regard at present. In addition, this method provides theoretical feasibility for efficient C-N coupling and urea generation. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for synthesizing a carbon fiber-supported nitrogen-doped copper-nickel alloy catalyst based on Joule heat technology, which has easily available raw materials, a simple process, low cost and high catalytic efficiency of the product. This catalyst exhibits excellent catalytic performance in the fields of co-reduction of nitrate and carbon dioxide and synthesis of urea.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is: a method for synthesizing a carbon fiber-supported nitrogen-doped copper-nickel alloy catalyst based on Joule heat technology, and its specific preparation process is as follows: Step S1: Cut the carbon paper and perform hydrophilic treatment. Step S2: Prepare an ethanol mixed solution of copper nitrate trihydrate and nickel nitrate hexahydrate to obtain a metal precursor solution A, and the molar ratio of copper ions to nickel ions in this metal precursor solution A is 4:1. Step S3: Prepare an ethanol solution of 1,2-dimethylimidazole to obtain a precursor solution B. Step S4: Add the precursor solution B obtained in Step S3 to the metal precursor solution A obtained in Step S2 to obtain a precursor solution C. Step S5: Extract 1 mL of the precursor solution C obtained in Step S4 into a spray gun, evenly spray it onto the carbon paper obtained by hydrophilic treatment in Step S1, then dry it under an infrared lamp, and then put it into an oven until the surface of the carbon paper is completely dry to obtain material D; Step S6: Place the material D obtained in Step S5 in a Joule heating device and continuously introduce a hydrogen-argon mixed gas. Conduct three-in and three-out gas washing on the Joule heating device to ensure that there is no air residue in the cavity of the Joule heating device. When introducing the hydrogen-argon mixed gas, maintain the vacuum degree in the cavity of the Joule heating device at 0.04 - 0.05 Mpa, set the carbon thermal shock temperature at 1100 - 1200 °C, and set the carbon thermal shock time at 3 - 5 s to achieve a rapid thermal shock process to obtain a carbon fiber supported nitrogen-doped copper-nickel alloy catalyst. This carbon fiber supported nitrogen-doped copper-nickel-gold catalyst exhibits significant kinetic advantages and excellent electrocatalytic activity in the electrocatalytic co-reduction reaction system of nitrate and carbon dioxide to synthesize urea.

[0008] Further limitation, the specific process of the hydrophilic treatment in Step S1 is to place the cut carbon paper on the outer flame of an alcohol lamp and sinter it for 1 - 2 minutes, so that the subsequent precursor solution can more easily penetrate into the carbon paper and be more evenly dispersed.

[0009] Further limitation, the total concentration of copper nitrate trihydrate and nickel nitrate hexahydrate in the metal precursor solution A in Step S2 is 0.2 mol / L.

[0010] Further limitation, the concentration of 1,2-dimethylimidazole in the precursor solution B in Step S3 is 0.8 mol / L.

[0011] Further limitation, the drying temperature of the oven in Step S5 is 60 °C, and the drying time is 7 h.

[0012] Further limitation, the carbon thermal shock temperature in Step S6 is set at 1130 °C, the mode is selected as the rapid mode, and the specific parameter settings are: the time is set at 3 s, the voltage is set at 40 V, and the current is set at 40 A.

[0013] Further limitation, the volume ratio of hydrogen to argon in the hydrogen-argon mixed gas in Step S6 is 1:9.

[0014] The method for synthesizing a carbon fiber supported nitrogen-doped copper-nickel alloy catalyst based on Joule heat technology described in the present invention, its specific preparation steps are as follows: Step S1: Cut the carbon paper into a rectangle with the required size of 1 cm × 10 cm and place the rectangular carbon paper on the outer flame of an alcohol lamp and sinter it for 1 minute for hydrophilic treatment; Step S2: Prepare an ethanol solution of copper nitrate trihydrate and nickel nitrate hexahydrate with a total concentration of 0.2 mol / L to obtain a metal precursor solution A, where the molar ratio of copper ions to nickel ions is 4:1, and the solvent is 8 mL of ethanol solution; Step S3: Prepare a 1,2-dimethylimidazole solution with a concentration of 0.8 mol / L to obtain a precursor solution B, where the solvent is 8 mL of ethanol solution; Step S4: Slowly add the precursor solution B in Step S3 to the metal precursor solution A obtained in Step S2 to obtain a precursor solution C; Step S5: Take out 1 mL of the precursor solution C obtained in Step S4, spray it on the carbon paper treated by hydrophilic treatment in Step S1 with a spray gun with a pore diameter of 0.5 mm, ensure that the precursor solution C evenly covers the carbon paper, then place it under an infrared lamp for drying and put it into an oven to dry at 60 °C for 7 h until the surface of the carbon paper is completely dry to obtain a material D; Step S6: Place the material D obtained in Step S5 in a Joule heating device and continuously introduce a hydrogen-argon mixed gas, conduct three-in and three-out gas washing on the Joule heating device to ensure that there is no air residue in the cavity of the Joule heating device to avoid the generation of oxides. When introducing the hydrogen-argon mixed gas, maintain the vacuum degree in the cavity of the Joule heating device at 0.04 - 0.05 Mpa, set the carbon thermal shock temperature at 1100 - 1200 °C, and set the carbon thermal shock time at 3 s to achieve a rapid thermal shock process to obtain a carbon fiber supported nitrogen-doped copper-nickel alloy catalyst.

[0015] The application of the carbon fiber supported nitrogen-doped copper-nickel alloy catalyst in the electrocatalytic co-reduction of carbon dioxide and nitrate to synthesize urea is as follows: Place the carbon fiber supported nitrogen-doped copper-nickel alloy catalyst in a Pt sheet electrode clip as the working electrode, use Ag / AgCl as the reference electrode, use a Pt sheet as the counter electrode, and use a 0.1 M KNO3 + 0.1 M KHCO3 mixed solution as the electrolyte to form a three-electrode system. Pass CO2 through the electrolyte for 30 min to saturate it, and then perform CV activation pretreatment on the working electrode for 1000 s. This carbon fiber supported nitrogen-doped copper-nickel alloy catalyst exhibits excellent catalytic performance, with a Faraday efficiency of 68% and an ammonia production rate of 544 μg h -1 cm -2 。

[0016] The present invention has the following advantages and beneficial effects compared with the prior art: 1. The preparation process of the Joule heat technology involved in the present invention is simple, green, and efficient, surpassing traditional heating methods such as muffle furnaces and tube furnaces. It shortens the preparation cycle and improves production efficiency. At the same time, the Joule heat technology promotes the decomposition of the precursor and inhibits the growth of nanoparticles through the rapid heating and cooling process, effectively avoiding particle agglomeration.

[0017] 2. The carbon fiber supported nitrogen-doped copper-nickel alloy catalyst prepared by the present invention has a higher electrochemically active surface area (ECSA) and more active sites, improving the efficiency of the catalyst for synthesizing urea.

[0018] 3. The carbon fiber supported nitrogen-doped copper-nickel alloy catalyst prepared by the present invention has excellent electrocatalytic urea synthesis performance. The carbon fiber supported nitrogen-doped copper-nickel alloy catalyst is placed in a Pt sheet electrode clip as the working electrode, Ag / AgCl as the reference electrode, a Pt sheet as the counter electrode, and a 0.1 M KNO3 + 0.1 M KHCO3 mixed solution as the electrolyte to form a three-electrode system. The urea yield reaches 544 μg cm -2 h -1 , and the Faraday efficiency reaches 68%. Description of the Drawings

[0019] Figure 1 Scanning electron microscope image and energy-dispersive spectroscopy (EDS) elemental map of the product E1 prepared in Example 1.

[0020] Figure 2 X-ray diffraction patterns of the products E1 - E5 prepared in Example 1 and Comparative Examples 1 - 4.

[0021] Figure 3 Linear sweep voltammogram of the product E1 prepared in Example 1 in a 0.1 M KNO3 + 0.1 M KHCO3 electrolyte with and without carbon dioxide.

[0022] Figure 4 Linear sweep voltammograms of the products E1 - E5 prepared in Example 1 and Comparative Examples 1 - 4 in a 0.1 M KNO3 + 0.1 M KHCO3 electrolyte.

[0023] Figure 5 Faraday efficiency of urea synthesis at different potentials shown during the co-reduction of nitrate and carbon dioxide for the product E1 prepared in Example 1.

[0024] Figure 6 Urea yield diagrams at different potentials shown during the co-reduction of nitrate and carbon dioxide for the product E1 prepared in Example 1.

[0025] Figure 7Double-layer capacitance and impedance diagrams of products E1 - E5 prepared in Example 1 and Comparative Examples 1 - 4. Detailed implementation manners

[0026] The following further elaborates on the above content of the present invention through examples. However, it should not be understood that the scope of the above subject matter of the present invention is limited to the following examples. All technologies implemented based on the above content of the present invention fall within the scope of the present invention. Example

[0027] Step S1: Cut the carbon paper into a rectangular shape with the required size of 1 cm × 10 cm and place the rectangular carbon paper in the outer flame of an alcohol lamp for sintering for 1 minute for hydrophilic treatment. Step S2: Prepare a mixed solution of copper nitrate trihydrate and nickel nitrate hexahydrate with a total concentration of 0.2 mol / L to obtain the metal precursor solution A1, where the molar ratio of copper ions to nickel ions is 4:1, and the solvent is 8 mL of ethanol solution. Step S3: Prepare a 1,2-dimethylimidazole solution with a concentration of 0.8 mol / L to obtain the precursor solution B1, where the solvent is 8 mL of ethanol solution. Step S4: Slowly add the precursor solution B1 in Step S3 to the metal precursor solution A1 obtained in Step S2 to obtain the precursor solution C1. Step S5: Take out 1 mL of the precursor solution C1 obtained in Step S4, spray it on the carbon paper obtained by hydrophilic treatment in Step S1 with a 0.5 mm spray gun, ensure that the precursor solution C1 completely covers the carbon paper, then dry it under an infrared lamp and put it into an oven to dry at 60 °C for 7 h until the surface of the carbon paper is completely dry to obtain the material D1. Step S6: Place the material D1 obtained in Step S5 in a Joule heating device and continuously introduce a hydrogen-argon mixed gas (volume ratio of 1:9), perform three-in-three-out gas washing on the Joule heating device to ensure that there is no air residue in the cavity of the Joule heating device to avoid oxide generation. When introducing the hydrogen-argon mixed gas, maintain the vacuum degree in the cavity of the Joule heating device at 0.04 Mpa, set the carbon thermal shock temperature to 1130 °C, and set the carbon thermal shock time to 3 s to achieve a rapid thermal shock process to obtain the carbon fiber supported nitrogen-doped copper-nickel alloy catalyst E1.

[0028] Comparative Example 1 Step S1: Cut the carbon paper into a rectangular shape with the required size of 1 cm × 10 cm and place the rectangular carbon paper in the outer flame of an alcohol lamp for sintering for 1 minute for hydrophilic treatment. Step S2: Prepare a mixed solution of copper nitrate trihydrate and nickel nitrate hexahydrate with a total concentration of 0.2 mol / L to obtain the metal precursor solution A2, where the molar ratio of copper ions to nickel ions is 1:4, and the solvent is 8 mL of ethanol solution. Step S3: Prepare a 1,2-dimethylimidazole solution with a concentration of 0.8 mol / L to obtain precursor solution B2, where the solvent is 8 mL of ethanol solution; Step S4: Slowly add the precursor solution B2 obtained in Step S3 to the metal precursor solution A2 obtained in Step S2 to obtain precursor solution C2; Step S5: Take out 1 mL of the precursor solution C2 obtained in Step S4, spray it on the carbon paper treated by hydrophilic treatment in Step S1 with a 0.5 mm spray gun, ensure that the metal precursor solution C2 completely covers the carbon paper, then dry it under an infrared lamp and place it in an oven to dry at 60 °C for 7 h until the surface of the carbon paper is completely dry to obtain material D2; Step S6: Place the material D2 obtained in Step S5 in a Joule heating device and continuously introduce a hydrogen-argon mixed gas (volume ratio of 1:9), conduct three-in and three-out gas washing on the Joule heating device to ensure that there is no air residue in the cavity of the Joule heating device to avoid the generation of oxides. When introducing the hydrogen-argon mixed gas, keep the vacuum degree in the cavity of the Joule heating device at 0.04 Mpa, set the carbon thermal shock temperature to 1130 °C, and set the carbon thermal shock time to 3 s to achieve a rapid thermal shock process to obtain a carbon fiber supported nitrogen-doped copper-nickel alloy catalyst E2.

[0029] Comparative Example 2 Step S1: Cut the carbon paper into a rectangle with the required size of 1 cm × 10 cm and place the rectangular carbon paper on the outer flame of an alcohol lamp to sinter for 1 minute for hydrophilic treatment; Step S2: Prepare a mixed solution of copper nitrate trihydrate and nickel nitrate hexahydrate with a total concentration of 0.2 mol / L to obtain metal precursor solution A3, where the molar ratio of copper ions to nickel ions is 1:1, and the solvent is 8 mL of ethanol solution; Step S3: Prepare a 1,2-dimethylimidazole solution with a concentration of 0.8 mol / L to obtain precursor solution B3, where the solvent is 8 mL of ethanol solution; Step S4: Slowly add the precursor solution B3 obtained in Step S3 to the metal precursor solution A3 obtained in Step S2 to obtain precursor solution C3; Step S5: Take out 1 mL of the precursor solution C3 obtained in Step S4, spray it on the carbon paper treated by hydrophilic treatment in Step S1 with a 0.5 mm spray gun, ensure that the precursor solution C3 completely covers the carbon paper, then dry it under an infrared lamp and place it in an oven to dry at 60 °C for 7 h until the surface of the carbon paper is completely dry to obtain material D3; Step S6: Place the material D3 obtained in step S5 in a Joule heating device and continuously introduce a hydrogen-argon mixed gas (volume ratio 1:9). Conduct three-in-three-out gas washing on the Joule heating device to ensure that there is no air residue in the cavity of the Joule heating device to avoid oxide generation. When introducing the hydrogen-argon mixed gas, maintain the vacuum degree in the cavity of the Joule heating device at 0.04 Mpa, set the carbon thermal shock temperature to 1130 °C, and set the carbon thermal shock time to 3 s to achieve a rapid thermal shock process and obtain a carbon fiber supported nitrogen-doped copper-nickel alloy catalyst E3.

[0030] Comparative Example 3 Step S1: Cut the carbon paper into a rectangle with the required size of 1 cm × 10 cm and place the rectangular carbon paper on the outer flame of an alcohol lamp for sintering for 1 minute for hydrophilic treatment; Step S2: Prepare a copper nitrate trihydrate solution with a concentration of 0.2 mol / L to obtain a metal precursor solution A4, where the solvent is 8 mL of ethanol solution; Step S3: Prepare a 1,2-dimethylimidazole solution with a concentration of 0.8 mol / L to obtain a precursor solution B4, where the solvent is 8 mL of ethanol solution; Step S4: Slowly add the precursor solution B4 obtained in step S3 to the metal precursor solution A4 obtained in step S2 to obtain a precursor solution C4; Step S5: Take out 1 mL of the precursor solution C4 obtained in step S4, spray it on the carbon paper obtained by hydrophilic treatment in step S1 with a 0.5 mm spray gun, ensure that the precursor solution C4 completely covers the carbon paper, then place it under an infrared lamp for drying and put it in an oven for drying at 60 °C for 7 h until the surface of the carbon paper is completely dry to obtain a material D4; Step S6: Place the material D4 obtained in step S5 in a Joule heating device and continuously introduce a hydrogen-argon mixed gas (volume ratio 1:9). Conduct three-in-three-out gas washing on the Joule heating device to ensure that there is no air residue in the cavity of the Joule heating device to avoid oxide generation. When introducing the hydrogen-argon mixed gas, maintain the vacuum degree in the cavity of the Joule heating device at 0.04 Mpa, set the carbon thermal shock temperature to 1130 °C, and set the carbon heat treatment time to 3 s to achieve a rapid thermal shock process and obtain a carbon fiber supported nitrogen-doped copper metal catalyst E4.

[0031] Comparative Example 4: Step S1: Cut the carbon paper into a rectangle with the required size of 1 cm × 10 cm and place the rectangular carbon paper on the outer flame of an alcohol lamp for sintering for 1 minute for hydrophilic treatment; Step S2: Prepare a nickel nitrate hexahydrate solution with a concentration of 0.2 mol / L to obtain a metal precursor solution A5, where the solvent is 8 mL of ethanol solution; Step S3: Prepare a 1,2-dimethylimidazole solution with a concentration of 0.8 mol / L to obtain the precursor solution B5, where the solvent is 8 mL of ethanol solution; Step S4: Slowly add the precursor solution B5 obtained in Step S3 to the metal precursor solution A5 obtained in Step S2 to obtain the precursor solution C5; Step S5: Take out 1 mL of the precursor solution C5 obtained in Step S4, spray it on the carbon paper hydrophilically treated in Step S1 with a 0.5 mm spray gun, ensure that the precursor solution C5 completely covers the carbon paper, then dry it under an infrared lamp and place it in an oven to dry at 60 °C for 7 h until the surface of the carbon paper is completely dry to obtain the material D5; Step S6: Place the material D5 obtained in Step S5 in a Joule heating device and continuously introduce a hydrogen-argon mixed gas (volume ratio of 1:9), perform three-in and three-out gas washing on the Joule heating device to ensure that there is no air residue in the cavity of the Joule heating device to avoid the generation of oxides. When introducing the hydrogen-argon mixed gas, maintain the vacuum degree in the cavity of the Joule heating device at 0.04 Mpa, set the carbon thermal shock temperature to 1130 °C, and set the carbon thermal shock time to 3 s to achieve a rapid thermal shock process to obtain the carbon fiber supported nitrogen-doped nickel metal catalyst E5.

[0032] Testing process: Place the prepared catalyst (E1 / E2 / E3 / E4 / E5) in a Pt sheet electrode clip as the working electrode (with an area of 0.25 cm 2 ), use Ag / AgCl as the reference electrode, use a Pt sheet as the counter electrode, and use a mixed solution of 0.1 M KNO3 + 0.1 M KHCO3 as the electrolyte. All electrochemical tests are carried out using a three-electrode system. Before testing, pass CO2 through the electrolyte for 30 min to saturate it, and then perform CV activation pretreatment on the working electrode for 1000 s. Subsequently, perform linear sweep voltammetry (LSV) tests, constant voltage electrolysis (it) tests, and electrochemically active surface area (ECSA) tests on the catalysts E1~E5 in sequence. During the LSV test, the sweep rate is set to 5 mV / s, and the potential range is -0~-1 V vs. RHE. During the it test, the potential range is -0.3~-0.5 V vs. RHE, and the time is 1 h. Perform a diacetyl monoxime test on the electrolyte composition through a UV-visible spectrophotometer to obtain their UV-visible spectral curves, and finally obtain the urea concentration in the electrolyte.

[0033] The product E1 prepared in Example 1 showed excellent electrocatalytic activity as an electrocatalyst in the co-reduction of carbon dioxide and nitrate to urea, with a Faraday efficiency of 68% and a urea yield of 544 μg h -1 cm -2Meanwhile, product E1 has the highest double-layer capacitance, and the diameter of the semicircle in the impedance diagram of E1 is the smallest, reflecting the advantages of the catalyst of the present invention in catalytic kinetics.

[0034] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for synthesizing a carbon fiber supported nitrogen-doped copper-nickel alloy catalyst based on Joule heating technology, characterized in that The specific preparation process is as follows: Step S1: Cut the carbon paper and perform hydrophilic treatment. Step S2: Prepare an ethanol mixed solution of copper nitrate trihydrate and nickel nitrate hexahydrate to obtain a metal precursor solution A. The molar ratio of copper ions to nickel ions in the metal precursor solution A is 4:

1. Step S3: Prepare an ethanol solution of 1,2-dimethylimidazole to obtain a precursor solution B. Step S4: Add the precursor solution B obtained in Step S3 to the metal precursor solution A obtained in Step S2 to obtain a precursor solution C. Step S5: Extract 1 mL of the precursor solution C obtained in Step S4 into a spray gun, evenly spray it onto the carbon paper obtained by hydrophilic treatment in Step S1, then dry it under an infrared lamp, and then place it in an oven until the surface of the carbon paper is completely dry to obtain material D. Step S6: Place the material D obtained in Step S5 in a Joule heating device and continuously introduce a hydrogen-argon mixed gas. Perform three-in and three-out gas washing on the Joule heating device to ensure that there is no air residue in the cavity of the Joule heating device. When introducing the hydrogen-argon mixed gas, maintain the vacuum degree in the cavity of the Joule heating device at 0.04 - 0.05 Mpa, set the carbon thermal shock temperature to 1100 - 1200 °C, and set the carbon thermal shock time to 3 - 5 s to achieve a rapid thermal shock process to obtain a carbon fiber supported nitrogen-doped copper-nickel alloy catalyst. This carbon fiber supported nitrogen-doped copper-nickel-gold catalyst exhibits significant kinetic advantages and excellent electrocatalytic activity in the electrocatalytic co-reduction reaction system of nitrate and carbon dioxide to synthesize urea.

2. The method for synthesizing a carbon fiber supported nitrogen-doped copper-nickel alloy catalyst based on the Joule heating technology according to claim 1, wherein: The specific process of the hydrophilic treatment in Step S1 is to place the cut carbon paper on the outer flame of an alcohol lamp and sinter it for 1 - 2 minutes, so that the subsequent precursor solution can more easily penetrate into the carbon paper and be more evenly dispersed.

3. The method for synthesizing a carbon fiber supported nitrogen-doped copper-nickel alloy catalyst based on Joule heating technology according to claim 1, wherein: In the metal precursor solution A in Step S2, the total concentration of copper nitrate trihydrate and nickel nitrate hexahydrate is 0.2 mol / L.

4. The method for synthesizing a carbon fiber supported nitrogen-doped copper-nickel alloy catalyst based on the Joule heating technique according to claim 1, characterized in that: In the precursor solution B in Step S3, the concentration of 1,2-dimethylimidazole is 0.8 mol / L.

5. The method for synthesizing a carbon fiber supported nitrogen-doped copper-nickel alloy catalyst based on the Joule heating technology according to claim 1, wherein: In Step S5, the drying temperature of the oven is 60 °C and the drying time is 7 h.

6. The method for synthesizing a carbon fiber supported nitrogen-doped copper-nickel alloy catalyst based on Joule heating technology according to claim 1, wherein: In Step S6, the carbon thermal shock temperature is set to 1130 °C, the mode is selected as the rapid mode, and the specific parameter settings are: the time is set to 3 s, the voltage is set to 40 V, and the current is set to 40 A.

7. The method for synthesizing a carbon fiber supported nitrogen-doped copper-nickel alloy catalyst based on Joule heating technology according to claim 1, characterized in that: In Step S6, the volume ratio of hydrogen to argon in the hydrogen-argon mixed gas is 1:

9.

8. The method for synthesizing a carbon fiber supported nitrogen-doped copper-nickel alloy catalyst based on Joule heating technology according to claim 1, wherein The specific preparation steps are as follows: Step S1: Cut the carbon paper into a rectangle with the required size of 1 cm × 10 cm and place the rectangular carbon paper on the outer flame of an alcohol lamp and sinter it for 1 minute for hydrophilic treatment. Step S2: Prepare an ethanol solution of copper nitrate trihydrate and nickel nitrate hexahydrate with a total concentration of 0.2 mol / L to obtain a metal precursor solution A, where the molar ratio of copper ions to nickel ions is 4:1 and the solvent is 8 mL of ethanol solution. Step S3: Prepare a 1,2-dimethylimidazole solution with a concentration of 0.8 mol / L to obtain a precursor solution B, where the solvent is 8 mL of ethanol solution. Step S4: Slowly add the precursor solution B in Step S3 to the metal precursor solution A obtained in Step S2 to obtain a precursor solution C. Step S5: Take out 1 mL of the precursor solution C obtained in step S4, spray it on the carbon paper obtained by hydrophilic treatment in step S1 with a spray gun having a pore size of 0.5 mm, ensure that the precursor solution C uniformly covers the carbon paper, then place it under an infrared lamp for drying and put it into an oven for drying at 60 °C for 7 h until the surface of the carbon paper is completely dry to obtain material D; Step S6: Place the material D obtained in step S5 in a Joule heating device and continuously introduce a hydrogen-argon mixed gas. Conduct three-in-three-out gas washing on the Joule heating device to ensure that there is no air residue in the cavity of the Joule heating device to avoid the generation of oxides. When introducing the hydrogen-argon mixed gas, maintain the vacuum degree in the cavity of the Joule heating device at 0.04~0.05 Mpa, set the carbon thermal shock temperature to 1100~1200 °C, and set the carbon thermal shock time to 3 s to achieve a rapid thermal shock process to obtain a carbon fiber supported nitrogen-doped copper-nickel alloy catalyst.

9. Application of the carbon fiber supported nitrogen-doped copper-nickel alloy catalyst prepared by the method according to any one of claims 1~8 in the electrocatalytic co-reduction of carbon dioxide and nitrate to synthesize urea.

10. The application according to claim 9, wherein The specific process is as follows: The carbon fiber supported nitrogen-doped copper-nickel alloy catalyst is placed in a Pt sheet electrode clip as the working electrode, Ag / AgCl is used as the reference electrode, a Pt sheet is used as the counter electrode, and a mixed solution of 0.1 M KNO3 + 0.1 M KHCO3 is used as the electrolyte to form a three-electrode system. CO2 is passed through the electrolyte for 30 min to saturate it, and then the working electrode is pre-treated by CV activation for 1000 s. The carbon fiber supported nitrogen-doped copper-nickel alloy catalyst exhibits excellent catalytic performance, with a Faraday efficiency of 68% and an ammonia production rate of 544 μg h -1 cm -2 。

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