Electrode for electrocatalytic synthesis of urea and method for its production and use

Abstract

The application belongs to the field of urea catalytic preparation, and particularly relates to an electrode for electrocatalytic synthesis of urea and a preparation method and application thereof. The preparation method of the electrode for electrocatalytic synthesis of urea comprises the following steps: performing solvothermal treatment on a mixed solution containing graphene oxide, a water-soluble copper source and a water-soluble bismuth source to realize reduction of the graphene oxide and loading of a Bi2O3 / Cu2O composite heterojunction, thereby obtaining a Bi2O3 / Cu2O-rGO active material; compounding the Bi2O3 / Cu2O-rGO active material on a current collector to form a precursor electrode; and performing electro-reduction on the precursor electrode in a modified electrolyte to obtain the electrode; the modified electrolyte is an aqueous solution of a water-soluble carbonate and a nitrate; and the potential of the electro-reduction is -0.4 to -0.7 V. The electrode has excellent urea catalytic performance, the Faraday efficiency of which can reach 45%, and the yield can reach 550 µg h ‑1 mg cat ‑1 .

Description

Technical Field

[0001] This invention belongs to the field of electrocatalysis and energy chemical technology, specifically relating to the electrocatalytic synthesis of urea. Background Technology

[0002] Urea (CO(NH2)2) is the world's most produced nitrogen fertilizer and an important bulk chemical. Traditional industrial synthesis relies on the tandem Haber-Bosch and Bosch-Meiser processes, which require high temperatures (150-200℃) and high pressures (150-250 bar), resulting in enormous energy consumption and large CO2 emissions. Electrocatalytic co-reduction of CO2 and nitrogen-containing pollutants (such as NO3) is a promising approach. - Synthesizing urea can realize CO2 resource utilization and synergistic treatment of "dual pollution" under normal temperature and pressure, which is a green and sustainable synthesis path.

[0003] However, existing electrocatalytic urea synthesis technologies still face significant challenges: the CO2 reduction reaction (CO2RR) and the nitrate reduction reaction (NO3RR) need to occur synergistically at similar potentials, but their kinetics differ significantly, resulting in low CN bond formation efficiency. Simultaneously, side reactions such as hydrogen evolution reaction (HER) and ammonia (NH3) formation compete fiercely, severely limiting the selectivity and yield of urea. Furthermore, existing catalysts mostly employ precious metals or single-component systems, leading to high costs and difficulty in achieving bifunctional synergy. For example, patent document CN120625100A discloses a method for preparing a Cu3Sn alloy electrocatalyst and its application in urea synthesis. The specific preparation steps are as follows: glucose, dicyandiamine, copper chloride, and stannous chloride dihydrate are ground and mixed evenly to obtain material A; the obtained material A is transferred to a tube furnace and sintered at 420~500℃ for 2h under a hydrogen / argon mixed atmosphere, and then naturally cooled to room temperature to obtain material B; the obtained material B is ground evenly to obtain a Cu3Sn alloy electrocatalyst, which can be used in the reaction system of electrocatalytic co-reduction of nitrate and carbon dioxide to urea. Patent document CN120138705A discloses a method for preparing a cobalt-based nanofoam hybrid catalyst and its application in the electrocatalytic synthesis of urea. The method includes dissolving glucose, urea, cobalt nitrate, and other metal salts in deionized water and stirring to form a homogeneous solution; heating the solution to form porous foam; placing the porous foam in a tube furnace, heating it in an air atmosphere, cooling it to room temperature, and then heat-treating it in an argon-hydrogen mixture to form a cobalt-based nanofoam hybrid catalyst.

[0004] Although some methods for electrocatalytic urea production have been disclosed in the prior art, most of these methods employ high reduction potentials (-1.0 V to -1.2 V vs. RHE or lower) for catalyst pre-reduction or reaction, which has the following drawbacks: (1) the hydrogen evolution reaction (HER) is intense at high potentials, resulting in low current efficiency; (2) nitrate ions are easily over-reduced to NH3 or NO2. - It is difficult to remain in the intermediate stage required for coupling with CO2; (3) Catalyst structure destruction: Rapid reduction of metal oxides at high potential easily leads to sintering of the active phase and Cu + Completely reduced to Cu 0 Loss of synergy, or Bi 0 Particle aggregation disrupts the carefully designed heterogeneous interface; (4) At high potentials, a large number of hydrogen atoms are easily adsorbed on the catalyst surface, occupying active sites and inhibiting CN coupling. Therefore, it is urgent to develop a new method to construct an active phase and maintain stable catalysis through in-situ reduction at low potential. Summary of the Invention

[0005] To address the problems of single-function catalyst active sites, poor CN coupling selectivity, and severe side reactions caused by harsh reaction conditions in existing technologies, this invention provides an electrode for the electrocatalytic synthesis of urea, aiming to provide an electrode with urea electrocatalytic activity and selectivity.

[0006] The second objective of this invention is to provide an electrode prepared by the aforementioned method and its application in the electrocatalytic synthesis of urea.

[0007] An electrode for electrocatalytic synthesis of urea, comprising the following steps:

[0008] Step 1:

[0009] A mixed solution containing graphene oxide, a water-soluble copper source, and a water-soluble bismuth source was subjected to solvothermal treatment to reduce graphene oxide and load a Bi₂O₃ / Cu₂O composite heterostructure, thus preparing a Bi₂O₃ / Cu₂O-rGO active material; wherein the weight ratio of Bi / Cu metal elements in the water-soluble copper source and the water-soluble bismuth source is 0.34~0.55:1.

[0010] Step 2:

[0011] Bi2O3 / Cu2O-rGO active material is composited onto the current collector to form a precursor electrode;

[0012] Step 3:

[0013] The electrode is prepared by electroreduction of the precursor electrode in a modified electrolyte.

[0014] The modified electrolyte is an aqueous solution of water-soluble carbonates and nitrates; the electroreduction potential is -0.4 to -0.7 V.

[0015] This invention innovatively deposits a Bi₂O₃ / Cu₂O composite heterojunction with a specific Bi / Cu ratio on reduced graphene, forms it as a precursor electrode, and then performs in-situ electroreduction under the modified electrolyte and a specific potential. This allows for the confined and selective conversion of Bi and Cu in the Bi₂O₃ / Cu₂O composite heterojunction into a Bi-Cu composite alloy phase. Furthermore, Cu selectively retains a portion of its 1 valence state. Research in this invention indicates that the specific Bi₂O₃ / Cu₂O-rGO precursor electrode, the electroreduction process, and the combined control of parameters such as the Bi / Cu ratio, the modified electrolyte, and the electroreduction potential contribute to the synergistic optimization of the electrode structure and active sites, reduces active particle shedding and aggregation, and significantly improves the activity and stability of urea electrocatalytic synthesis.

[0016] In this invention, graphene oxide and a water-soluble copper source are first dispersed in a solvent to obtain a dispersion. Then, the pH is adjusted to alkaline and a water-soluble bismuth salt is added to obtain a mixed solution.

[0017] The water-soluble copper source and the water-soluble bismuth source are at least one of the nitrate, sulfate, chloride, and acetate of their respective metals;

[0018] The weight ratio of Bi / Cu elements in the water-soluble copper source and the water-soluble bismuth source is 0.4~0.45:1;

[0019] The weight ratio of the total metals in graphene oxide and water-soluble copper and bismuth sources is 1:1 to 5; it can be further 1:2 to 3.

[0020] The solvent in the mixed solution includes at least one of water and C1-C4 alcohols;

[0021] The concentration of graphene oxide in the mixed solution is 1~5 g / L.

[0022] In this invention, the solvothermal temperature is 150℃~200℃, and can be further 160~180℃;

[0023] The solvothermal reaction time is 5 to 15 hours, and can be further extended to 10 to 12 hours.

[0024] In this invention, in step 2, the Bi2O3 / Cu2O-rGO active material and binder are mixed and then composited onto the current collector, followed by drying to obtain the precursor electrode.

[0025] The adhesive includes at least one of CMC, PVDF, and Nafion;

[0026] The weight ratio of Bi2O3 / Cu2O-rGO active material to binder is 6~9:1;

[0027] The current collector is at least one of copper foil, carbon paper, and carbon cloth.

[0028] In this invention, the water-soluble carbonate in the modified electrolyte is at least one of sodium carbonate, sodium bicarbonate, and potassium bicarbonate.

[0029] The nitrate mentioned is sodium nitrate;

[0030] In the modified electrolyte, the concentration of water-soluble carbonate is 0.1~0.3M; the concentration of sodium nitrate is 0.05~0.2M; further, the concentration of water-soluble carbonate is 0.2~0.25M; and the concentration of sodium nitrate is 0.1~0.15M.

[0031] The modified electrolyte contains saturated carbon dioxide.

[0032] In this invention, the electroreduction is a three-electrode constant potential electroreduction; the three electrodes include the working electrode of the precursor electrode, the platinum plate counter electrode, and the Ag / AgCl reference electrode;

[0033] The present invention also provides an electrode for electrocatalytic synthesis of urea prepared by a method thereof.

[0034] In this invention, the preparation method can endow the prepared material with special physicochemical characteristics, and the electrode prepared by the method can be unexpectedly adapted to the electrocatalytic synthesis characteristics of urea, exhibiting excellent urea electrocatalytic synthesis activity and stability.

[0035] In this invention, the electrode contains Bi with a valence of 0; the valence state of Cu includes Cu... + / Cu 0 Mixed valence state; total metal loading of Bi and copper is 0.5–1 mg cm⁻¹ -2 .

[0036] The present invention also provides an application of the electrode prepared by the method for electrocatalytic synthesis of urea, which is used as an electrode for electrocatalytic synthesis of urea.

[0037] The electrolyte in the electrocatalytic synthesis of urea is an aqueous solution of water-soluble carbonates and nitrates;

[0038] Preferably, the water-soluble carbonate is at least one of sodium carbonate, sodium bicarbonate, and potassium bicarbonate;

[0039] Preferably, the nitrate is sodium nitrate;

[0040] Preferably, in the electrolyte, the concentration of water-soluble carbonate is 0.1~0.3M; and the concentration of sodium nitrate is 0.05~0.2M.

[0041] The electrolyte contains saturated carbon dioxide;

[0042] The potential for electrocatalytic synthesis of urea is -0.8 V to -1.2 V vs. RHE.

[0043] In this invention, the special pre-in-situ electroreduction electrode is used for subsequent urea catalysis. Based on the potential gradient control, the physicochemical structure of the electrode can be pre-reconstructed, which is beneficial to improving the catalytic activity and stability of subsequent urea.

[0044] Beneficial effects

[0045] This invention innovatively performs in-situ electroreduction conversion on a special Bi2O3 / Cu2O-rGO precursor electrode with Bi and Cu, combined with a modified electrolyte for in-situ electroreduction and potential control. This allows for confined and controllable conversion, preparing an electrode suitable for the electrocatalytic synthesis of urea. Research by this invention shows that the electrode prepared by the method exhibits excellent urea electrocatalytic activity and stability. Attached Figure Description

[0046] Figure 1 The XRD pattern of the Bi2O3 / Cu2O(3 / 7)-rGO precursor prepared in Example 1;

[0047] Figure 2 Bi / CuO obtained by in-situ electroreduction in Example 1 x XRD pattern of (3 / 7)-rGO;

[0048] Figure 3 A comparison of the urea Faraday efficiency of different catalysts at different potentials;

[0049] Figure 4 Bi / CuO prepared in Example 1 x Cyclic stability test plot of (3 / 7)-rGO at -0.8 V vs. RHE;

[0050] Figure 5 Bi / CuO prepared in the in-situ electroreduction process of Example 1 x In-situ Raman spectra of species changes on the surface of (3 / 7)-rGO catalyst; Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0052] The present invention provides an optional method for preparing a composite catalyst for the electrocatalytic synthesis of urea, comprising the following steps:

[0053] (1) Graphene oxide (GO) was ultrasonically dispersed in anhydrous ethanol to obtain a uniform dispersion;

[0054] (2) Add copper salt to the above dispersion, adjust the pH to alkaline to precipitate and anchor the copper species, then add bismuth source and continue stirring to form a precursor mixture;

[0055] (3) The mixture obtained in step (2) is subjected to hydrothermal reaction to crystallize copper and bismuth species to form Cu2O / Bi2O3 heterojunction, while GO is partially reduced to obtain Bi2O3 / Cu2O-rGO composite oxide precursor.

[0056] (4) Coat the precursor obtained in step (3) onto the surface of carbon paper, and then place it in a CO2-saturated atmosphere containing NO3. - In the electrolyte, in-situ electrochemical reduction was performed at a potential of -0.4 to -0.7 V vs. RHE to completely reduce Bi₂O₃ to metallic Bi. 0 Cu2O is partially reduced to Cu + / Cu 0 Mixed valence state (CuO) x Finally, Bi / CuO was obtained. x -rGO composite catalyst.

[0057] The copper salt mentioned in step (2) is copper nitrate, copper chloride or copper sulfate, and the bismuth source is Bi2O3 powder; the mass ratio of Bi2O3 to Cu2O is 3:7.

[0058] In step (2), the pH is adjusted to 7-9, and the alkaline solution is a NaOH, KOH or NaHCO3 solution with a concentration of 4-8 M.

[0059] The hydrothermal reaction temperature in step (3) is 150℃~200℃, and the reaction time is 5~15 hours.

[0060] The in-situ electrochemical reduction described in step (4) specifically involves: using carbon paper coated with the precursor as the working electrode, a platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode in an H-type electrolytic cell, in a mixed electrolyte containing 0.2 M KHCO3 and 0.1 M KNO3, CO2 is first introduced to saturate the electrolyte, followed by constant potential reduction at -0.8 V vs. RHE for 1 hour to construct Bi in situ. 0 -CuO x Heterogeneous structure.

[0061] This invention also provides a method for electrocatalytic synthesis of urea, using the Bi / CuO method described in this invention. x -rGO composite catalyst as working electrode includes the following reaction condition control features that differ from existing technologies:

[0062] (a) Potential window control: Constant potential electrolysis is performed at a mild reduction potential of -0.8 V to -1.2 V vs. RHE to avoid hydrogen evolution side reaction and deep reduction of nitrate due to overpotential;

[0063] (b) Co-current supply of reactants: The cathode electrolyte is a CO2-saturated solution of bicarbonate and nitrate, with CO2 continuously supplied as a carbon source at a flow rate of 20 mL / min. -1 NO3 - As a nitrogen source, at a concentration of 0.1 M, it reacts with CuO through Bi sites. x Spatial separation and interfacial coupling of sites enable CO2 activation and NO3 activation. - The restoration process is carried out in a coordinated manner;

[0064] (c) In-situ dynamic activation mode: catalyst active phase Bi 0 with CuO x It is generated in situ at the reaction potential and participates in the reaction simultaneously, maintaining Cu + / Cu 0 The dynamic equilibrium of mixed valence states promotes the formation of CN-coupled intermediates.

[0065] The preparation of the working electrode includes: Bi / CuO x -rGO catalyst powder was ultrasonically dispersed with Nafion solution, ethanol, and ultrapure water to form an ink, which was then drop-coated onto hydrophobic carbon paper. The catalyst loading was 0.5–1 mg / cm³. -2 .

[0066] The method of this invention innovatively uses Bi2O3 / Cu2O-rGO as a precursor active ingredient for in-situ electroreduction, and controls the electroreduction conditions in combination to achieve synergy and induce the confined construction of the active ingredient. This "dynamic activation" mode avoids the problem of pre-reduction catalyst oxidation and deactivation in air, and ensures the true exposure of active sites.

[0067] 2. Catalyst structure retention: The reduction rate is controllable at low potentials (-0.6 V ~ -0.7 V), Bi 0 Uniform nanoparticle size, CuO x Retain an appropriate amount of Cu + Maintain Bi 0 -CuO x The heterogeneous interface facilitates the directional transfer of electrons from Bi to Cu and the regulation of intermediate adsorption. Furthermore, the high potential (-1.2 V) results in a large reduction current for Bi. 0 Rapid nucleation and growth lead to grain coarsening, Cu + Excessive reduction to Cu 0 Loss of Cu + / Cu 0 Redox cycling capacity, heterostructure disruption, and insufficient exposure of active sites.

[0068] 3. Spatial separation and interface coupling control of bifunctional sites: By precisely controlling the Bi / Cu element mass ratio of Bi2O3 to Cu2O in the precursor to 3:7, the Bi sites and CuO sites are spatially separated and their interface coupling is controlled. x Sites form a spatially separated but electronically coupled configuration on the rGO surface. rGO has a high defect density (I0). D / I G = 1.25) not only provides an electron transport channel, but also anchors metal species through surface oxygen-containing functional groups, preventing particle agglomeration during the electroreduction process.

[0069] 4. Three-phase interface optimization: Hydrophobic carbon paper was used as the substrate, and the catalyst loading was controlled at 0.5~1 mg cm⁻¹. -2 The H-type electrolyzer design, combined with Nafion 117 membrane separation, ensures efficient contact at the three-phase interface of CO2 (gas phase), electrolyte (liquid phase) and catalyst (solid phase), promoting the continuous activation of CO2 at Bi sites.

[0070] Example 1: Bi / CuO at low potential x Preparation of (3 / 7)-rGO catalyst and electrocatalytic synthesis of urea

[0071] (1) Preparation of precursor: 50 mg GO was ultrasonically dispersed in 15 mL of anhydrous ethanol for 1 h; 0.4270 g of copper nitrate trihydrate was added, stirred and dissolved, and 6 M NaOH was added dropwise until pH 8-9; then 5 mL of ethanol dispersion containing 0.0542 g Bi2O3 was added, and stirring was continued for 0.5 h; the mixture was transferred to a 100 mL hydrothermal reactor and reacted at 180 °C for 12 h; after centrifugation, washing with water, washing with alcohol, and vacuum drying at 60 °C for 12 h, Bi2O3 / Cu2O(3 / 7)-rGO precursor (Bi / Cu element weight ratio of 3:7) was obtained.

[0072] (2) Preparation of working electrode: 5 mg of the above precursor and Nafion (the weight ratio of precursor to Nafion is 8:1), 880 μL of ethanol and 100 μL of ultrapure water were ultrasonically dispersed for 30 min. 20 μL was then dropped onto carbon paper (0.5 cm × 1 cm) and dried at room temperature.

[0073] (3) In-situ electroreduction and urea synthesis: In an H-type electrolytic cell (Nafion 117 membrane separator), carbon paper coated with the precursor was used as the working electrode (the electrode in step 2), a platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode. 30 mL of electrolyte containing 0.2 M KHCO3 and 0.1 M KNO3 were added to the cathode and anode chambers, respectively. Initially, 20 mL of electrolyte was used as the starting solution. -1 The solution was passed through a CO2-saturated cathode electrolyte at a flow rate of 30 min, followed by constant potential reduction at -0.7 V vs. RHE (electroreduction potential) for 1 hour (in-situ construction of Bi / CuO). x Urea synthesis was carried out by electrolysis at -0.8 V (active phase) for 30 minutes using RHE electrolysis. The catholyte was then analyzed by diacetyl monooxime colorimetric method; the absorbance at 525 nm corresponded to the urea concentration. The calculated urea Faradaic efficiency was 45%, and the yield was 550 µg / h. -1 mg cat -1 .

[0074] Example 2

[0075] Compared to Example 1, the only difference is the Bi / Cu ratio in step 1. The total amount of Bi / Cu metal elements is the same as in Example 1, specifically, the Bi / Cu elemental weight ratio is 0.45:1, and the amount of graphene oxide relative to the total metal element weight ratio is 1:3.5; the hydrothermal temperature is 160℃, and the hydrothermal time is 15h; all other conditions are the same, and the reaction is carried out again. The urea Faradaic efficiency is 41%, and the yield is 511 µg / h. -1 mg cat -1 .

[0076] Example 3

[0077] Compared with Example 1, the only difference is that the conditions of the in-situ electroreduction activation stage in step 3 are changed; all other operations and parameters are the same as in Example 1. The experimental groups are as follows:

[0078] Group A: The electrolyte consisted of 0.25 M KHCO3 and 0.15 M KNO3. All other operations and parameters were the same as in Example 1; the calculated urea Faradaic efficiency was 42%, and the yield was 543 µg / h. -1 mg cat -1 .

[0079] Group B: The electroreduction potential was -0.6 V vs. RHE, the electroreduction time was 1.5 h, and the potential in the subsequent urea catalytic process was 0.9 V vs. RHE. All other operations and parameters were the same as in Example 1; the urea Faradaic efficiency was 43%, and the yield was 508 µg / h.-1 mg cat -1 .

[0080] Comparative Example 1

[0081] Compared with Example 1, the only difference is that the electroreduction potential in step 3 is -1.2 V vs. RHE; all other operations and parameters are the same as in Example 1.

[0082] The urea Faradaic efficiency was low across the entire testing range, with a rate of 12.7% and a yield of 110 µg h at -0.8 V vs. RHE. -1 mg cat -1 .

[0083] Comparative Example 2

[0084] Compared with Example 1, the only difference is that the Bi / Cu ratio in step 1 is changed, while the total amount of Bi / Cu metal elements is the same as in Example 1. The experimental groups are as follows:

[0085] Group A: The elemental weight ratio of Bi / Cu is 1:1, and all other conditions are the same (this electrode is labeled Bi / CuO). x (5 / 5)-rGO). The urea Faradaic efficiency was 22%, and the yield was 326 µg h. -1 mg cat -1 .

[0086] Group B: Bi / Cu elemental weight ratio is 3:1, all other conditions are the same. Urea Faraday efficiency is 15%, yield is 180 µg / h. -1 mg cat -1 The production of NH3 byproducts increases.

[0087] All other operations and parameters are the same as in Example 1.

[0088] Comparative Example 3: CuO x -rGO single-component catalyst

[0089] Compared with Example 1, the only difference is that Bi raw material is missing in step 1, while the total metal oxide content and other operations and parameters are the same as in Example 1.

[0090] At -0.8 V vs. RHE, the urea Faraday efficiency is <5%, and the main products are NH3 and NO2. - This indicates that the lack of Bi sites leads to insufficient CO2 activation capacity, making it impossible to effectively couple CN.

[0091] Comparative Example 4: Bi 0-rGO single-component catalyst

[0092] Compared with Example 1, the only difference is that in step 1, copper raw material is missing, while the total metal oxide content and other operations and parameters are the same as in Example 1.

[0093] At -0.8 V vs. RHE, the urea Faraday efficiency was <5%, and the main product was formic acid, indicating that the lack of Cu sites resulted in insufficient NO3RR activation and inability to effectively perform CN coupling.

[0094] Comparative Example 5: Bi / CuO x (3 / 7) Catalyst

[0095] Compared to Example 1, the only difference is that GO was not added in step 1 of the preparation process. At -0.8 V vs. RHE, the urea Faradaic efficiency was 13%, and the yield was 223 µg h⁻¹. -1 mg cat -1 This indicates that the oxygen-containing functional group defects in rGO can anchor metal ions and inhibit particle migration and aggregation during the reduction process. It confirms that the graphene support is an essential component for constructing a highly efficient and stable active phase.

[0096] Comparative Example 6: Direct testing of Bi2O3 / Cu2O(3 / 7)-rGO precursor

[0097] Compared to Example 1, the only difference is that the in-situ electroreduction process at -0.7 V vs. RHE in step 3 was omitted; instead, urea was directly synthesized under catalytic conditions at -0.8 V vs. RHE, with a urea Faradaic efficiency of 27% and a yield of 370 µg / h. -1 mg cat -1 XRD analysis showed that Bi2O3 and Cu2O were still the main precursors, indicating that the oxide precursors themselves had low activity and must be converted into metal / oxide heterojunctions through in-situ electroreduction to achieve higher activity.

[0098] Comparative Example 7:

[0099] Compared with Example 1, the only difference is that the electrolyte in step 3 is a 0.3 M KHCO3 solution, which lacks nitrate. All other operations and parameters are the same as in Example 1. The urea Faraday efficiency was almost 0, and the main products were formic acid, H2 and CO.

[0100] As can be seen from Examples 1-3 and Comparative Examples 1-7, by performing in-situ electroreduction conversion on the Bi2O3 / Cu2O-rGO precursor electrode, and by controlling the Bi / Cu ratio and the in-situ reduction conditions, a confined and controllable conversion can be achieved to prepare an electrode suitable for the electrocatalytic synthesis of urea. The research of this invention shows that the electrode prepared by the method can exhibit excellent urea electrocatalytic activity and stability.

Claims

1. A method for preparing an electrode for electrocatalytic synthesis of urea, characterized in that the step... include: Step 1: A mixed solution containing graphene oxide, a water-soluble copper source, and a water-soluble bismuth source was subjected to solvothermal treatment to reduce graphene oxide and load a Bi₂O₃ / Cu₂O composite heterostructure, thus preparing a Bi₂O₃ / Cu₂O-rGO active material; wherein the weight ratio of Bi / Cu metal elements in the water-soluble copper source and the water-soluble bismuth source is 0.34~0.55:

1. Step 2: Bi2O3 / Cu2O-rGO active material is composited onto the current collector to form a precursor electrode; Step 3: The electrode is prepared by electroreduction of the precursor electrode in a modified electrolyte. The modified electrolyte is an aqueous solution of water-soluble carbonates and nitrates; the electroreduction potential is -0.4 to -0.7 V.

2. The method for preparing the electrode for electrocatalytic synthesis of urea as described in claim 1, characterized in that, Graphene oxide and a water-soluble copper source were first dispersed in a solvent to obtain a dispersion. Then, the pH was adjusted to alkaline and a water-soluble bismuth salt was added to obtain a mixed solution. The water-soluble copper source and the water-soluble bismuth source are at least one of the nitrate, sulfate, chloride, and acetate of their respective metals; The weight ratio of Bi / Cu elements in the water-soluble copper source and the water-soluble bismuth source is 0.4~0.45:1; The weight ratio of the total metals in graphene oxide and water-soluble copper and bismuth sources is 1:1 to 5. The solvent in the mixed solution includes at least one of water and C1-C4 alcohols; The concentration of graphene oxide in the mixed solution is 1~5 g / L.

3. The method for preparing the electrode for electrocatalytic synthesis of urea as described in claim 1, characterized in that, The solvothermal temperature is 150℃~200℃; The solvothermal reaction time is 5 to 15 hours.

4. The method for preparing the electrode for electrocatalytic synthesis of urea as described in claim 1, characterized in that, In step 2, the Bi2O3 / Cu2O-rGO active material and binder are mixed and then composited onto the current collector, followed by drying to obtain the precursor electrode. The adhesive includes at least one of CMC, PVDF, and Nafion; The weight ratio of Bi2O3 / Cu2O-rGO active material to binder is 6~9:1; The current collector is at least one of copper foil, carbon paper, and carbon cloth.

5. The method for preparing the electrode for electrocatalytic synthesis of urea as described in claim 1, characterized in that, In the modified electrolyte, the water-soluble carbonate is at least one of sodium carbonate, sodium bicarbonate, and potassium bicarbonate. The nitrate mentioned is sodium nitrate; In the modified electrolyte, the concentration of water-soluble carbonate is 0.1~0.3M; the concentration of sodium nitrate is 0.05~0.2M. The modified electrolyte contains saturated carbon dioxide.

6. The method for preparing the electrode for electrocatalytic synthesis of urea as described in claim 1, characterized in that, Electroreduction is a three-electrode constant potential electroreduction; the three electrodes include the working electrode of the precursor electrode, the platinum plate counter electrode, and the Ag / AgCl reference electrode.

7. An electrode for electrocatalytic synthesis of urea prepared by any one of claims 1 to 6.

8. The electrode as claimed in claim 7, characterized in that, Bi has a valence of 0; Cu has valence states including Cu + / Cu 0 Mixed valence state; total metal loading of Bi and copper is 0.5–1 mg cm⁻¹ -2 .

9. The application of an electrode for electrocatalytic synthesis of urea prepared by any one of claims 1 to 6, characterized in that, It was used as an electrode for the electrocatalytic synthesis of urea.

10. The application as described in claim 9, characterized in that, The electrolyte in the electrocatalytic synthesis of urea is an aqueous solution of water-soluble carbonates and nitrates; Preferably, the water-soluble carbonate is at least one of sodium carbonate, sodium bicarbonate, and potassium bicarbonate; Preferably, the nitrate is sodium nitrate; Preferably, in the electrolyte, the concentration of water-soluble carbonate is 0.1~0.3M; and the concentration of sodium nitrate is 0.05~0.2M. The electrolyte contains saturated carbon dioxide; The potential in the electrocatalytic synthesis of urea is -0.8 V to -1.2 V vs. RHE.

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