A method for preparing a fluorine-modified copper-based electrocatalyst and its application in urea electrosynthesis.

Abstract

This invention discloses a method for preparing a fluorine-modified copper-based electrocatalyst and its application in urea electrosynthesis, relating to the field of electrocatalytic urea synthesis technology. The invention involves dispersing a copper source in a solvent, adding a fluorine source, and then performing a solvothermal reaction to obtain an fluorine-modified copper electrocatalyst precursor. This precursor is then loaded onto a conductive substrate and subjected to electrolytic reduction to obtain the fluorine-modified copper-based electrocatalyst. This invention utilizes fluorine modification to regulate the surface charge distribution of copper and construct a strong hydrogen bond network structure, thereby controlling the adsorption of intermediates, water dissociation, and hydrogenation capacity during urea electrosynthesis, promoting the reaction of CO2 and NO3. ‑ The conversion to urea. The fluorine-modified copper-based electrocatalyst prepared in this invention can be used for the electrosynthesis of urea, specifically, at -0.8V. vs. RHE achieved 70.45 mmol / h / g at the specified voltage. cat The urea yield was high, and the urea yield remained almost unchanged after 30 hours of continuous cycling.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic synthesis of urea, and in particular to a method for preparing a fluorine-modified copper-based electrocatalyst and its application in urea electrosynthesis. Background Technology

[0002] Urea, with the chemical formula CO(NH2)2, is an important chemical raw material, nitrogen fertilizer, and energy carrier, widely used in agriculture, industry, and medicine. Traditional urea synthesis requires high temperature (150-200℃), high pressure (100-200 bar), high-purity nitrogen, and hydrogen, making it a highly energy-intensive process that consumes large amounts of fossil fuels and emits the greenhouse gas carbon dioxide. In contrast, electrocatalytic reduction of CO2 and NO3... - The co-reduction preparation of urea achieves carbon-nitrogen coupling through electrochemical reduction at room temperature and pressure, avoiding the energy-intensive Haber-Bosch method. Simultaneously, it can mitigate the effects of greenhouse gas CO2 and water pollutant nitrate (NO3). - The damage to human health and ecological balance caused by [the virus] has become a current research hotspot.

[0003] Electrocatalysts are the core of the urea electrosynthesis reaction. Currently, copper-based catalysts are favored due to their good conductivity, high catalytic activity, and suitability for both the carbon source (CO2) and nitrogen source (NO3) in urea synthesis. - Copper possesses moderate adsorption and good activation capabilities, making it widely used in the field of urea electrosynthesis. Although copper has a good effect on NO3-... - While reduction exhibits high activity, the slow kinetics of the hydrogenation step, which reduces the NO2 intermediate to the NH2 intermediate, at the pure copper interface, and the low CN coupling efficiency due to the easy desorption of the CO intermediate on the bare copper surface, are key bottlenecks limiting urea yield. The fundamental reasons are: the high OH bond dissociation energy of water (approximately 492 kJ / mol) leads to insufficient supply of active hydrogen, and Cu has a weak affinity for binding the CO intermediate.

[0004] Studies have shown that interfacial hydrogen bond networks can act as "proton highways," enabling ultrafast proton transport via the Grothuss mechanism. However, stable hydrogen bond networks alone can only accelerate the proton shuttle process but cannot overcome the kinetic energy barrier of initial water dissociation. Previous studies have promoted water dissociation by introducing heterogeneous transition metal sites, but excessive active hydrogen or overly strong water dissociation inevitably triggers the competitive hydrogen evolution reaction (HER), thus limiting the NH4+ transition metals. x The formation of intermediates. Therefore, the fundamental challenge of urea electrosynthesis lies in coordinating the complex interactions between multiple reactants. Catalysts used for urea electrosynthesis need to simultaneously activate the dissociation of H2O, constructing an efficient hydrogen bond network to achieve rapid proton transport and ensure NO... xHydrogenation of intermediates and optimization of electronic structure to enhance adsorption capacity of CO intermediates.

[0005] Therefore, designing a copper-based catalyst that can simultaneously activate reactants, regulate intermediate adsorption behavior, lower the water dissociation energy barrier, and accelerate proton transport by reconstructing hydrogen bond networks, thereby achieving controllable optimization of reaction kinetics, is a key challenge we currently face. Summary of the Invention

[0006] To address the aforementioned limitations of existing technologies, the present invention aims to provide a method for preparing a fluorine-modified copper-based electrocatalyst and its application in urea electrosynthesis. The present invention disperses a copper source in a solvent, adds a fluorine source, and performs a solvothermal reaction to obtain an fluorine-modified copper electrocatalyst precursor. This precursor is then loaded onto a conductive substrate and subjected to electrolytic reduction to obtain the fluorine-modified copper-based electrocatalyst. The present invention utilizes fluorine modification to regulate the surface charge distribution of copper and construct a strong hydrogen bond network structure, which can regulate the adsorption of intermediates, water dissociation, and hydrogenation capacity during urea electrosynthesis, promoting the reaction of CO2 and NO3. - The conversion to urea. The fluorine-modified copper-based electrocatalyst prepared in this invention can be used for the electrosynthesis of urea. Specifically, at -0.8 V... vs. RHE achieved a voltage of 70.45 mmol / h / g cat The urea yield was high, and the urea yield remained almost unchanged after 30 hours of continuous cycling.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a fluorine-modified copper-based electrocatalyst, comprising the following steps: (1) Disperse the copper source in a solvent to obtain a copper-based dispersion; add a fluorine source to the copper-based dispersion and stir to obtain a mixture; heat the mixture and react it; cool it after the reaction; centrifuge, wash and dry it to obtain the F-modified copper electrocatalyst precursor. (2) The F-modified copper electrocatalyst precursor was loaded onto a conductive substrate to obtain an electrode sheet; an electrolytic cell was constructed using the electrode sheet, and the fluorine-modified copper-based electrocatalyst was obtained by electrolytic reduction treatment.

[0008] Preferably, in step (1), the copper source is one or more of copper nitrate, copper chloride, and copper sulfate; the solvent is one or more of deionized water, ethanol, ethylene glycol, and N,N-dimethylformamide; and the fluorine source is one or more of sodium fluoride, potassium fluoride, ammonium hydrogen fluoride, and ammonium fluoride.

[0009] Preferably, in step (1), the ratio of copper source to solvent is (1.5-2.5) mmol: 50 mL.

[0010] Preferably, in step (1), the molar ratio of copper source to fluorine source is (0.5-3):1.

[0011] Preferably, in step (1), the stirring time is 10-20 min.

[0012] Preferably, in step (1), the heating temperature is 60-180℃ and the reaction time is 1-12h.

[0013] Preferably, in step (2), the conductive substrate is carbon paper or carbon cloth.

[0014] Preferably, in step (2), the specific operation of loading the F-modified copper electrocatalyst precursor onto the conductive substrate is as follows: The F-modified copper electrocatalyst precursor and ethanol solution were mixed at a ratio of (1-2) mg: 1 mL to obtain a slurry; the slurry was coated onto a conductive substrate and dried to obtain an electrode sheet.

[0015] Furthermore, the ethanol solution is prepared by mixing ethanol and water in a volume ratio of (6-8):(2-4); the coating amount of the slurry is 100-200 μL / cm. 2 .

[0016] As a preferred option, in step (2), the specific operation of the electrolytic reduction treatment is as follows: using a Pt sheet or carbon rod as the counter electrode, Ag / AgCl as the reference electrode, and the prepared electrode sheet as the working electrode, an electrolytic cell is constructed in combination with the electrolyte, and electrolysis is performed for 40-70 minutes.

[0017] Furthermore, the electrolyte is a CO2-saturated bicarbonate-nitrate mixture; wherein, in the bicarbonate-nitrate mixture, the concentration of bicarbonate is 0.08-0.12 mol / L and the concentration of nitrate is 0.04-0.06 mol / L; the bicarbonate is sodium bicarbonate and / or potassium bicarbonate, and the nitrate is potassium nitrate and / or sodium nitrate.

[0018] Preferably, in step (2), the electrolytic reduction treatment method is constant current electrolysis or constant potential electrolysis.

[0019] Furthermore, in constant current electrolysis, the current is -10 to -100 mA; in constant potential electrolysis, the voltage is -0.2 to -1.5 V. vs. RHE.

[0020] In a second aspect, the present invention provides the application of the above-mentioned fluorine-modified copper-based electrocatalyst in urea electrosynthesis.

[0021] As a preferred option, the specific application steps are as follows: A fluorine-modified copper-based electrocatalyst was loaded onto a conductive substrate and used as the working electrode. An electrode system was formed by using Ag / AgCl as the reference electrode and a Pt sheet as the counter electrode. The electrode system was then placed in an electrolyte for electrolysis.

[0022] Furthermore, the specific steps for supporting the fluorine-modified copper-based electrocatalyst on the substrate are as follows: Fluorine-modified copper electrocatalyst and ethanol solution were mixed at a ratio of (1-2) mg: 1 mL to obtain a slurry; the slurry was coated onto a conductive substrate and dried to obtain an electrode sheet; The loading of fluorine-modified copper-based electrocatalysts on the substrate was 0.05-0.15 mg / cm³. 2 The conductive substrate is carbon cloth or carbon paper.

[0023] Furthermore, the electrolyte is a CO2-saturated bicarbonate-nitrate mixture; wherein, in the bicarbonate-nitrate mixture, the concentration of bicarbonate is 0.08-0.12 mol / L and the concentration of nitrate is 0.04-0.06 mol / L; the bicarbonate is sodium bicarbonate and / or potassium bicarbonate, and the nitrate is potassium nitrate and / or sodium nitrate.

[0024] Furthermore, during the electrolysis process, the reaction temperature is 20-60℃ and the reaction potential is -0.2 to -1.2 V. vs. RHE, electrolysis time ≥ 0.5h.

[0025] The beneficial effects of this invention are: 1. This invention disperses a copper source in a solvent, adds a fluorine source, and performs a solvothermal reaction to obtain an F-modified copper electrocatalyst precursor. This precursor is then loaded onto a conductive substrate and subjected to electrolytic reduction to obtain a fluorine-modified copper-based electrocatalyst. This invention, through fluorine modification and in-situ electrolytic reduction, can regulate the charge redistribution on the copper surface, enhance the adsorption of CO and NO3 intermediates, lower the water dissociation energy barrier, and accelerate proton transport by reconstructing the hydrogen bond network, thus promoting the reaction of CO2 and NO3. - The conversion of co-reduction to urea.

[0026] The fluorine-modified copper-based electrocatalyst prepared by this invention can be used for urea electrosynthesis. Specifically, at -0.8 V... vs. RHE achieved a voltage of 70.45 mmol / h / g cat The urea yield was high, and the urea yield remained almost unchanged after 30 hours of continuous cycling.

[0027] 2. This invention does not limit itself to a single copper source, fluorine source, or solvent, but provides a broad and selectable space for precursors and reaction pathways, adaptable to various practical production conditions and needs. The entire preparation process is simple and easy to operate, requiring no expensive equipment or stringent vacuum and high-temperature conditions, significantly reducing production costs and possessing certain industrial-scale application value. Attached Figure Description

[0028] Figure 1 a) is a scanning electron microscope image of the fluorine-modified copper-based electrocatalyst prepared in Example 1; b) is a particle size distribution diagram of the fluorine-modified copper-based electrocatalyst prepared in Example 1. Figure 2 High-angle annular dark-field-scanning transmission electron microscope image and F and Cu elemental distribution map of the fluorine-modified copper-based electrocatalyst prepared in Example 1; Figure 3 a) is the X-ray diffraction pattern of the fluorine-modified copper-based electrocatalyst prepared in Example 1; b) is the X-ray photoelectron spectrum of Cu 2p in the fluorine-modified copper-based electrocatalyst prepared in Example 1; c) is the X-ray photoelectron spectrum of F 1s in the fluorine-modified copper-based electrocatalyst prepared in Example 1. Figure 4 Example 1: In-situ attenuated total reflectance surface-enhanced infrared absorption spectrum of the fluorine-modified copper-based electrocatalyst during the electrosynthesis of urea; Figure 5 a) is the in-situ attenuated total reflectance surface-enhanced infrared absorption spectrum of interfacial water in the fluorine-modified copper-based electrocatalyst prepared in Example 1; b) is a diagram showing the distribution of different types of interfacial water in the fluorine-modified copper-based electrocatalyst prepared in Example 1. Figure 6 The graph shows a comparison of the catalytic performance of the fluorine-modified copper-based electrocatalyst prepared in Example 1 and the copper catalyst prepared in Comparative Example 1 in the urea electrosynthesis reaction. In the graph, a is the LSV curve of Cu and Cu-F, b is the urea yield of Cu and Cu-F, and c is the urea yield of Cu-Cl and Cu-Br. Figure 7 a) represents the adsorption energies of the fluorine-modified copper-based electrocatalyst prepared in Example 1 and the copper catalyst prepared in Comparative Example 1 for CO intermediates and NO3 intermediates; b) represents the three-dimensional Bader charge mapping of the fluorine-modified copper-based electrocatalyst prepared in Example 1; and c) represents the three-dimensional Bader charge mapping of the copper electrocatalyst prepared in Comparative Example 1.

[0029] Figure 8 Cyclic performance diagram of the fluorine-modified copper-based electrocatalyst prepared in Example 1. Detailed Implementation

[0030] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0031] While existing technologies disclose the use of copper-based catalysts for the electrosynthesis of urea, they suffer from drawbacks such as slow hydrogenation kinetics of the NO2 intermediate and easy desorption of the CO intermediate from the bare copper surface, leading to low CN coupling efficiency. The root cause lies in the insufficient supply of active hydrogen due to the high OH bond dissociation energy in H2O and the weak adsorption of the CO intermediate by Cu. Therefore, developing a copper-based catalyst that simultaneously possesses the ability to activate reactants, regulate intermediate adsorption behavior, lower the water dissociation energy barrier, and accelerate proton transport through hydrogen bond network reconstruction, thereby achieving controllable optimization of reaction kinetics, is currently crucial.

[0032] Based on this, the present invention provides a fluorine-modified copper-based electrocatalyst, which is prepared by dispersing a copper source in a solvent, adding a fluorine source, and performing a solvothermal reaction to obtain an F-modified copper electrocatalyst precursor; loading the precursor onto a conductive substrate and performing an electrolytic reduction treatment to obtain the fluorine-modified copper-based electrocatalyst.

[0033] This invention utilizes the modification and electroreduction of fluorine (F) to regulate the charge distribution on the copper surface and form a strong hydrogen bond network, thereby optimizing the adsorption of intermediates (CO and NO3 intermediates) during urea electrosynthesis, lowering the water dissociation energy barrier, ensuring proton migration, and thus promoting the adsorption of CO2 and NO3. - The reaction for the co-reduction synthesis of urea involves the introduction of highly electronegative fluorine (F) to extract electrons from adjacent Cu sites, resulting in an electron-deficient Cu surface. This enhances the adsorption of CO intermediates and nitrogen-containing intermediates (NO2 and NO3 intermediates), alleviates CO intermediate desorption, promotes subsequent hydrogenation steps, and ultimately increases the urea yield.

[0034] Furthermore, although existing technologies disclose F-modified copper-based catalysts, their use in electrocatalytic CO2 reduction differs fundamentally from the electrosynthesis of urea. These different reaction mechanisms prevent the catalysts from being converted for practical applications. Specifically: CO2 reduction involves reducing CO2 to products such as CO, C2H4, CH4, HCOOH, and CH3OH, while electrocatalysis reduces CO2 and NO3. - Co-reduction synthesis of urea requires CO2 and NO3. - Co-reduction, the key step is the stable adsorption of the CO intermediate and its reaction with NO3. - The reduction intermediate undergoes CN coupling to regenerate urea (NH2CONH2).

[0035] Most catalysts used for CO2 reduction are designed to promote CO desorption and cannot retain CO intermediates for coupling or NO3. - Its weak activation ability and mismatched intermediate adsorption energy windows can easily lead to CO escape or excessive hydrogenation, which makes it unsuitable for electrosynthesis of urea.

[0036] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0037] The experimental materials used in the embodiments of this invention are all conventional experimental materials in the art and can be purchased through commercial channels.

[0038] Example 1: Preparation of Fluorine-Modified Copper-Based Electrocatalyst (1) Add 2 mmol of copper nitrate to 50 mL of N,N-dimethylformamide and stir at room temperature for 20 min to obtain a copper-based dispersion; add 2 mmol of ammonium bifluoride to the copper-based dispersion and stir for 15 min to mix evenly to obtain a mixture; transfer the mixture to a stainless steel autoclave lined with polytetrafluoroethylene and react at 160 °C for 4 h. After the reaction is completed, cool and centrifuge at 10000 r / min, wash three times alternately with deionized water and ethanol, and dry under vacuum at 60 °C to obtain the F-modified copper electrocatalyst precursor; (2) Mix 0.7 mL of ethanol and 0.3 mL of water to obtain an ethanol solution; weigh 1.2 mg of fluorine-modified copper precursor and disperse it in the above ethanol solution, mix evenly to obtain a slurry; take 100 μL of slurry and drop it onto 1 cm × 1 cm carbon paper (TGPH060) without a gas diffusion layer, and dry to obtain an electrode sheet. The prepared electrode sheet was used as the working electrode, the Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode. A CO2-saturated potassium bicarbonate-potassium nitrate mixture was used as the electrolyte to construct an electrolytic cell. The concentration of potassium bicarbonate in the potassium bicarbonate-potassium nitrate mixture was 0.1 mol / L, and the concentration of potassium nitrate was 0.05 mol / L. A voltage of -0.5 V was applied to the electrolytic cell. vs. Electrolysis of RHE at a constant voltage for 60 min yielded a fluorine-modified copper-based electrocatalyst, denoted as Cu-F catalyst.

[0039] Example 2: Preparation of Fluorine-Modified Copper-Based Electrocatalyst (1) Mix 40 mL of ethanol and 10 mL of deionized water as a solvent; add 1.5 mmol of copper nitrate to 50 mL of the above solvent and stir at room temperature for 30 min to obtain a copper-based dispersion; add 2 mmol of ammonium fluoride to the copper-based dispersion and stir for 10 min to mix evenly to obtain a mixture; transfer the mixture to a stainless steel autoclave lined with polytetrafluoroethylene and react at 60 °C for 12 h. After the reaction is completed, cool and centrifuge at 10000 r / min, wash three times alternately with deionized water and ethanol, and vacuum dry at 60 °C to obtain the F-modified copper electrocatalyst precursor; (2) Mix 0.7 mL of ethanol and 0.3 mL of water to obtain an ethanol solution; weigh 1 mg of fluorine-modified copper precursor and disperse it in the above ethanol solution, mix evenly to obtain a slurry; take 150 μL of slurry and drop it onto a 1 cm × 1 cm carbon cloth (w1s1011) with a gas diffusion layer, and dry it to obtain an electrode sheet. The prepared electrode sheet was used as the working electrode, the Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode. A CO2-saturated potassium bicarbonate-potassium nitrate mixture was used as the electrolyte to construct an electrolytic cell. The concentration of potassium bicarbonate in the potassium bicarbonate-potassium nitrate mixture was 0.08 mol / L, and the concentration of potassium nitrate was 0.04 mol / L. The electrolytic cell was electrolyzed for 40 min under a constant current of -50 mA to obtain a fluorine-modified copper-based electrocatalyst.

[0040] Example 3: Preparation of Fluorine-Modified Copper-Based Electrocatalyst (1) Mix 40 mL of ethanol and 10 mL of deionized water as a solvent; add 2.5 mmol of copper chloride to 50 mL of solvent and stir at room temperature for 30 min to obtain a copper-based dispersion; add 1 mmol of potassium fluoride to the copper-based dispersion and stir for 20 min to mix evenly to obtain a mixture; transfer the mixture to a stainless steel autoclave lined with polytetrafluoroethylene and react at 180 °C for 1 h. After the reaction is completed, cool and centrifuge at 10000 r / min, wash three times alternately with deionized water and ethanol, and vacuum dry at 60 °C to obtain the F-modified copper electrocatalyst precursor. (2) Mix 0.7 mL of ethanol and 0.3 mL of water to obtain an ethanol solution; weigh 2 mg of fluorine-modified copper precursor and disperse it in the above ethanol solution, mix evenly to obtain a slurry; take 200 μL of slurry and drop it onto a 1 cm × 1 cm carbon cloth (w1s1011) with a gas diffusion layer, and dry it to obtain an electrode sheet. An electrolytic cell was constructed using the prepared electrode sheet as the working electrode, the Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode, with a CO2-saturated potassium bicarbonate-potassium nitrate mixture as the electrolyte; wherein the concentration of potassium bicarbonate in the potassium bicarbonate-potassium nitrate mixture was 0.12 mol / L and the concentration of potassium nitrate was 0.06 mol / L. Electrolysis at a constant current of -100mA for 70 minutes yielded a fluorine-modified copper-based electrocatalyst.

[0041] Example 4: Urea Electrosynthesis Method The electrosynthesis of urea was carried out using the Cu-F catalyst prepared in Example 1, and the specific steps are as follows: 0.7 mL of ethanol and 0.3 mL of water were mixed to obtain an ethanol solution; 1.2 mg of the Cu-F catalyst prepared in Example 1 was weighed and dispersed in 1 mL of the ethanol solution, and mixed evenly to obtain a slurry; the slurry was coated onto carbon paper (TGPH060) without a gas diffusion layer, and the coating amount was controlled at 0.1 mg / cm². 2 The electrode sheet is dried. A three-electrode system was constructed using the aforementioned electrode sheet as the working electrode, Ag / AgCl as the reference electrode, and a Pt sheet as the counter electrode. A CO2-saturated potassium bicarbonate-potassium nitrate mixture was used as the electrolyte, and a voltage of -0.5 to -0.9 V was applied. vs. The urea electrosynthesis reaction was carried out at room temperature under a constant voltage of RHE; wherein the potassium bicarbonate-potassium nitrate mixture contained a potassium bicarbonate concentration of 0.1 mol / L and a potassium nitrate concentration of 0.05 mol / L.

[0042] Example 5: Urea Electrosynthesis Method The electrosynthesis of urea was carried out using the Cu-F catalyst prepared in Example 2. The specific steps are as follows: 0.7 mL of ethanol and 0.3 mL of water were mixed to obtain an ethanol solution; 1.0 mg of the Cu-F catalyst prepared in Example 2 was weighed and dispersed in 1 mL of the ethanol solution, and mixed evenly to obtain a slurry; the slurry was coated onto carbon paper (TGPH060) without a gas diffusion layer, and the coating amount was controlled at 0.15 mg / cm². 2 The electrode sheet is dried. A three-electrode system was constructed using the aforementioned electrode sheet as the working electrode, Ag / AgCl as the reference electrode, and a Pt sheet as the counter electrode. The system was placed in a CO2-saturated potassium bicarbonate-potassium nitrate mixture as the electrolyte and subjected to an voltage of -0.5 to -0.9 V. vs. The urea electrosynthesis reaction was carried out at room temperature under a constant voltage of RHE; wherein the potassium bicarbonate-potassium nitrate mixture contained a potassium bicarbonate concentration of 0.1 mol / L and a potassium nitrate concentration of 0.05 mol / L.

[0043] Example 6: Urea Electrosynthesis Method The electrosynthesis of urea was carried out using the Cu-F catalyst prepared in Example 3. The specific steps are as follows: 0.7 mL of ethanol and 0.3 mL of water were mixed to obtain an ethanol solution; 1.0 mg of the Cu-F catalyst prepared in Example 3 was weighed and dispersed in 1 mL of the ethanol solution, and mixed evenly to obtain a slurry; the slurry was coated onto carbon paper (TGPH060) without a gas diffusion layer, and the coating amount was controlled at 0.05 mg / cm². 2 The electrode sheet is dried. A three-electrode system was constructed using the aforementioned electrode sheet as the working electrode, Ag / AgCl as the reference electrode, and a Pt sheet as the counter electrode. The system was placed in a CO2-saturated potassium bicarbonate-potassium nitrate mixture as the electrolyte and subjected to an voltage of -0.5 to -0.9 V. vs. The urea electrosynthesis reaction was carried out at room temperature under a constant voltage of RHE; wherein the potassium bicarbonate-potassium nitrate mixture contained a potassium bicarbonate concentration of 0.1 mol / L and a potassium nitrate concentration of 0.05 mol / L.

[0044] Comparative Example 1: The difference between this comparative example and Example 1 is that no F modification treatment was performed during the preparation of the electrocatalyst. The specific steps are as follows: A copper-based dispersion was prepared according to the method in Example 1. The copper-based dispersion was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and reacted at 160°C for 4 hours. After the reaction was completed, the mixture was cooled, centrifuged at 10,000 r / min, washed three times alternately with deionized water and ethanol, and dried under vacuum at 60°C to obtain a copper electrocatalyst precursor. The copper electrocatalyst precursor was electroreduced according to the method in Example 1 to obtain a copper-based electrocatalyst.

[0045] Comparative Example 2: The difference between this comparative example and Example 1 is that NH4Cl is used instead of ammonium bifluoride to modify copper, thus preparing a modified copper-based electrocatalyst. The specific steps are as follows: A copper-based dispersion was prepared according to the method in Example 1. 2 mmol of NH4Cl was added to the copper-based dispersion and stirred for 15 min to ensure uniform mixing, resulting in a mixed solution. The mixed solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and reacted at 160°C for 4 h. After the reaction, the mixture was cooled, centrifuged at 10000 r / min, washed three times alternately with deionized water and ethanol, and dried under vacuum at 60°C to obtain a chlorine-modified copper electrocatalyst precursor. The chlorine-modified copper electrocatalyst precursor was electroreduced according to the method in Example 1 to obtain a chlorine-modified copper-based electrocatalyst, denoted as Cu-Cl catalyst.

[0046] Comparative Example 3: The difference between this comparative example and Example 1 is that NH4Br is used instead of ammonium bifluoride to modify copper, thus preparing a modified copper-based electrocatalyst. The specific steps are as follows: A copper-based dispersion was prepared according to the method in Example 1. 2 mmol of NH4Br was added to the copper-based dispersion and stirred for 15 min to ensure uniform mixing, resulting in a mixed solution. The mixed solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and reacted at 160°C for 4 h. After the reaction was completed, the mixture was cooled, centrifuged at 10000 r / min, washed three times alternately with deionized water and ethanol, and dried under vacuum at 60°C to obtain a bromine-modified copper electrocatalyst precursor. The bromine-modified copper electrocatalyst precursor was electroreduced according to the method in Example 1 to obtain a bromine-modified copper-based electrocatalyst, denoted as Cu-Br catalyst.

[0047] Experimental Example 1: Structural Characterization 1. The structure of the Cu-F catalyst prepared in Example 1 was characterized, and the results are as follows: Figures 1-3 As shown.

[0048] Depend on Figure 1 As can be seen from 'a', the prepared Cu-F catalyst is in the form of spherical particles. Figure 1 As can be seen from b, the average size of these nanoparticles is approximately 57.8 nm.

[0049] Depend on Figure 2 It can be seen that copper and fluorine elements are uniformly dispersed in the prepared Cu-F catalyst.

[0050] Depend on Figure 3 As can be seen from 'a', the prepared Cu-F catalyst exhibits (111), (200), and (220) diffraction peaks; Figure 3 As can be seen from b, the Cu-F catalyst exhibits a clear zero-valent copper (Cu) at 933 eV. 0 Characteristic peaks, consistent with X-ray diffraction results; by Figure 3 As can be seen from c, the F1s characteristic peak at 685.3 eV can still be clearly detected in the electroreduced Cu-F.

[0051] Experimental Example 2: In-situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) was used to perform in-situ detection of the Cu-F catalyst during urea electrosynthesis in Example 4, in order to monitor the evolution of intermediates during CN coupling. The results are as follows: Figure 4 As shown.

[0052] Meanwhile, understanding the interfacial water behavior on the catalyst surface is crucial for elucidating the reaction mechanism during urea electrosynthesis. Therefore, this invention employs in-situ ATR-SEIRAS technology to study the interfacial water structure on the Cu-F surface during urea electrosynthesis in Example 4. The results are as follows: Figure 5 As shown.

[0053] Depend on Figure 4It can be seen that it is approximately 1637cm -1 The peak at that point corresponds to the bending vibration of the NH2 intermediate. δ NH), 1670cm -1 The peak at approximately 1650 cm⁻¹ belongs to the CO intermediate. It is noteworthy that the peak at approximately 1650 cm⁻¹... -1 The negative peak at approximately 1419 cm⁻¹ is associated with water dissociation, indicating that the introduction of fluorine promotes the water dissociation process. More importantly, at approximately 1419 cm⁻¹... -1 and 1490cm -1 CN stretching vibrations of the NH2CO intermediate and characteristic peaks of the NCN intermediate were detected. Overall, the enhanced intermediate signal observed in in-situ ATR-SEIRAS measurements reflects the presence of NO3- in NO3-. - In the co-reduction process with CO2, the Cu-F catalyst promotes the electrosynthesis of urea by promoting the formation of CN bonds.

[0054] Depend on Figure 5 From 'a', we can see that 3000-3800cm -1 The broad peak within the range corresponds to the stretching vibration mode of the OH bond. Through Gaussian fitting, this broad peak can be decomposed into three sub-peaks located at 3600, 3450, and 3250 cm⁻¹. -1 The water was classified into three types: non-hydrogen-bonded water, weakly hydrogen-bonded water, and strongly hydrogen-bonded water. The proportions of these three types of peaks at different potentials were quantitatively analyzed. For example... Figure 5 As shown in b, with increasing potential, the proportion of weakly and strongly hydrogen-bonded water increases, while isolated water decreases. Simultaneously, a red shift in hydrogen bonds indicates the presence of a strong hydrogen bond network. This evolutionary trend suggests that a more ordered hydrogen bond network has formed on the catalyst surface, facilitating proton transport and supply, thereby promoting the hydrogenation reaction in urea synthesis.

[0055] Experimental Example 3: Electrochemical Performance 1. Urea was electrosynthesized using the electrocatalysts prepared in Example 1 and Comparative Examples 1-3, wherein the specific steps for urea electrosynthesis were the same as in Example 4. Performance parameters during the urea electrosynthesis process were measured, and the results are as follows: Figure 6 As shown.

[0056] Depend on Figure 6 It can be seen that the Cu-F catalyst prepared in Example 1 achieved a urea yield of up to 70.45 mmol / h / g during electrosynthesis. cat When using the copper-based electrocatalyst prepared in Comparative Example 1 for the electrosynthesis of urea, the urea yield can reach a maximum of 11.67 mmol / h / g. cat When using the Cu-Cl catalyst prepared in Comparative Example 2 for the electrosynthesis of urea, the highest urea yield reached 48.83 mmol / h / g. catWhen using the Cu-Br catalyst prepared in Comparative Example 3 for the electrosynthesis of urea, the urea yield reached a maximum of 39.75 mmol / h / g. cat Experimental data show that the Cu-F catalyst has a much higher urea yield than the Cu-Cl catalyst, Cu-Br catalyst, and copper-based electrocatalyst, with the performance order being F>Cl>Br>halogen-free.

[0057] The principle is that fluorine has the strongest electronegativity and the smallest atomic radius, which can moderately modulate the electronic structure of copper surface through strong electron-withdrawing effect, enhance the adsorption of CO intermediate and NO3 intermediate and promote water dissociation to donate proton active hydrogen, thereby significantly promoting CN coupling; while the electronegativity of Cl and Br decreases and the atomic radius increases in turn, and their ability to regulate the electronic structure of copper is insufficient, so the urea generation effect gradually deteriorates.

[0058] 2. Urea was electrosynthesized using the fluorine-modified copper-based electrocatalyst prepared in Example 1, following the same method as in Example 4. Density functional theory calculations were performed, and its electrochemical cycling stability was tested. The results are as follows: Figures 7-8 As shown.

[0059] Density functional theory calculations combined with Bader charge analysis were used to elucidate the electronic mechanism underlying the enhanced catalytic performance of the Cu-F catalyst prepared in this invention. Figure 7 As shown in Figure a, the adsorption energies of two key reaction intermediates (CO intermediate and NO3 intermediate) were compared on the surfaces of copper-based electrocatalysts and Cu-F catalysts, respectively. Compared with the copper-based electrocatalyst, the Cu-F catalyst exhibited a significantly enhanced adsorption affinity for the CO intermediate, effectively inhibiting the desorption of the CO intermediate to gaseous CO, while retaining sufficient carbon source to support the subsequent CN coupling reaction. Similarly, the adsorption capacity of the NO3 intermediate on the Cu-F catalyst surface was also significantly enhanced, which is beneficial for NO3 adsorption. - The initial activation and hydrogenation of the species provide a sufficient nitrogen source for the coupling reaction. Bader charge results further visually demonstrate the electronic regulation effect induced by F, such as... Figure 7 As shown in b and c, compared to copper-based electrocatalysts, the introduction of highly electronegative F atoms leads to a significant charge redistribution on the Cu-F catalyst surface. The three-dimensional charge density distribution map confirms that F atoms extract electrons from neighboring Cu sites, making the copper surface positively charged. This significantly enhances the adsorption affinity of the Cu-F catalyst for electron-rich CO and NO3 intermediates, thereby guiding the reaction pathway towards selective urea formation.

[0060] Depend on Figure 8 It can be seen that the Cu-F catalyst prepared by this invention has good performance stability after 30 hours of electrochemical cycling.

[0061] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A fluorine-modified copper-based electrocatalyst, characterized in that, It is prepared by the following method: (1) Disperse the copper source in a solvent to obtain a copper-based dispersion; add a fluorine source to the copper-based dispersion and stir to obtain a mixture; heat the mixture and react it; cool it after the reaction; centrifuge, wash and dry it to obtain the F-modified copper electrocatalyst precursor. (2) The F-modified copper electrocatalyst precursor was loaded onto a conductive substrate to obtain an electrode sheet; an electrolytic cell was constructed using the electrode sheet, and the fluorine-modified copper-based electrocatalyst was obtained by electrolytic reduction treatment.

2. The fluorine-modified copper-based electrocatalyst as described in claim 1, characterized in that, In step (1), the copper source is one or more of copper nitrate, copper chloride, and copper sulfate; the solvent is one or more of deionized water, ethanol, ethylene glycol, and N,N-dimethylformamide; and the fluorine source is one or more of sodium fluoride, potassium fluoride, ammonium hydrogen fluoride, and ammonium fluoride.

3. The fluorine-modified copper-based electrocatalyst as described in claim 1, characterized in that, In step (1), the ratio of copper source to solvent is (1.5-2.5) mmol: 50 mL; the molar ratio of copper source to fluorine source is (0.5-3):

1.

4. The fluorine-modified copper-based electrocatalyst as described in claim 1, characterized in that, In step (1), the heating temperature is 60-180℃ and the reaction time is 1-12h.

5. The fluorine-modified copper-based electrocatalyst as described in claim 1, characterized in that, In step (2), the specific operation of loading the F-modified copper electrocatalyst precursor onto the conductive substrate is as follows: The F-modified copper electrocatalyst precursor and ethanol solution were mixed at a ratio of (1-2) mg: 1 mL to obtain a slurry; the slurry was coated onto a conductive substrate and dried to obtain an electrode sheet; The ethanol solution is prepared by mixing ethanol and water in a volume ratio of (6-8):(2-4); the coating amount of the slurry is 100-200 μL / cm. 2 .

6. The fluorine-modified copper-based electrocatalyst according to claim 1, characterized in that, In step (2), the specific operation of the electrolytic reduction process is as follows: Using Pt sheets or carbon rods as counter electrodes, Ag / AgCl as reference electrodes, and the prepared electrode sheets as working electrodes, an electrolytic cell is constructed in combination with the electrolyte and electrolyzed for 40-70 minutes.

7. The fluorine-modified copper-based electrocatalyst as described in claim 6, characterized in that, The electrolyte is a CO2-saturated bicarbonate-nitrate mixture; In the bicarbonate-nitrate mixture, the concentration of bicarbonate is 0.08-0.12 mol / L and the concentration of nitrate is 0.04-0.06 mol / L; the bicarbonate is sodium bicarbonate and / or potassium bicarbonate, and the nitrate is potassium nitrate and / or sodium nitrate.

8. The fluorine-modified copper-based electrocatalyst as described in claim 1, characterized in that, In step (2), the electrolytic reduction treatment method is constant current electrolysis or constant potential electrolysis; In constant current electrolysis, the current is -10 to -100 mA; in constant potential electrolysis, the voltage is -0.2 to -1.5 V. vs. RHE.

9. The application of the fluorine-modified copper-based electrocatalyst according to any one of claims 1-8 in the electrosynthesis of urea.

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