A method for electrocatalytic conversion of carbon dioxide to produce multi-carbon products

Abstract

The present invention discloses a method for preparing multi-carbon products by electrocatalytic conversion of carbon dioxide. The present invention first synthesizes a lanthanide metal-doped copper-based catalyst. The electrode material of the present invention comprises the above-mentioned lanthanide metal-doped copper-based catalyst and a gas diffusion layer. An electrochemical catalytic system comprises the above-mentioned electrode material, a reaction electrolyte and a reaction device. The method of the present invention for electrocatalytic conversion of carbon dioxide to prepare multi-carbon products comprises the following steps: 1) using a constant potential electrolysis method in an electrocatalytic system to pre-activate the electrode material under constant potential conditions; 2) using carbon dioxide as a raw material, and synthesizing multi-carbon products by constant potential electrolysis reaction in an electrolytic cell reaction device through the action of the electrode material and the electrolyte. The present invention uses CO2 as a raw material and a lanthanide metal-doped copper-based catalyst / gas diffusion electrode composite material as an electrode material, can efficiently synthesize multi-carbon products, and has excellent stability.

Description

Technical Field

[0001] The invention belongs to the field of chemistry and chemical engineering, and relates to a method for preparing multi-carbon products by electrocatalytic conversion of carbon dioxide. Background Art

[0002] As a cheap, renewable carbon resource, CO2's resource utilization not only meets the current goal of reducing CO2 emissions but also has significant implications for green and sustainable development. It has become a national strategic need and a frontier of international scientific research. Existing CO2 conversion methods include thermal catalytic conversion, photocatalytic conversion, electrocatalytic conversion, and biological conversion. Electrocatalytic conversion offers advantages such as mild reaction conditions, easily regulated reaction performance, and ease of assembly and scalability. In recent years, the continuous expansion of the distributed power industry (solar, wind, geothermal, etc.) has provided an energy guarantee for low-cost, large-scale, and economical electrocatalytic conversion of CO2, making it increasingly popular.

[0003] Current research on the electrocatalytic conversion of CO₂ primarily focuses on the reaction of CO₂ with H₂O to produce C₁ products such as CO, HCOOH, CH₄, and CH₃OH. However, multi-carbon products such as ethylene, ethanol, and propanol are of greater research interest due to their high added value, high energy density, and crucial role in the chemical industry. For example, ethylene is a fundamental chemical raw material for synthetic fibers, synthetic rubber, and synthetic plastics, and is also used in the manufacture of vinyl chloride, styrene, ethylene oxide, acetic acid, acetaldehyde, and explosives, making it a key indicator of a country's petrochemical development. However, the generation pathways for multi-carbon products are complex, involving multiple competing reactions and intermediates. For example, the reaction to produce ethanol requires the transfer of 12 pairs of electrons and protons, involves at least 10 reaction intermediates, and six competing products. Consequently, the current efficiency of multi-carbon product generation is far below practical requirements. Therefore, developing high-activity, high-efficiency, and high-stability electrocatalytic CO₂ conversion for the production of multi-carbon products remains a major challenge in the field of CO₂ electrocatalytic reduction.

[0004] To improve the efficiency of multi-carbon product formation, a variety of electrocatalysts have been designed. Among them, metallic copper is currently the only metal catalyst capable of electrocatalytically converting CO2 into multi-carbon products, but its activity is less than satisfactory. To this end, a variety of catalyst regulation strategies have been applied to improve the multi-carbon product formation activity of copper-based catalysts, such as crystal face regulation, morphology regulation, defect introduction, surface modification, and heterostructure construction. Among them, doping strategies can effectively improve the binding ability of copper-based catalysts to reaction intermediates, promote carbon-carbon coupling reactions, and generate multi-carbon products. The choice of doping atom is crucial to the effectiveness of the doping strategy, because the introduction of a second metal atom not only changes the activity of the copper-based catalyst for the electrocatalytic reduction of CO2, but also changes the activity of the competing reaction, the hydrogen evolution reaction. Therefore, the ideal doping metal atom should not only promote the formation of multi-carbon products, but also inhibit the occurrence of the hydrogen evolution reaction. The unique properties of lanthanide metals have attracted particular attention as dopant atoms. Due to their unique 4f electrons and unfilled 5d orbitals, lanthanide metals exhibit strong spin-orbit coupling and the lanthanide contraction effect, which can effectively modulate the local electron density of surrounding atoms, changing the binding strength of surrounding atoms to catalytic reaction intermediates, thereby affecting reaction selectivity. Therefore, the introduction of lanthanide metals as dopant atoms into copper-based catalysts is expected to achieve high activity, high efficiency, and high stability for the electrocatalytic reduction of CO2 to multi-carbon products. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing multi-carbon products by electrocatalytic conversion of carbon dioxide.

[0006] The first object of the present invention is to provide a method for preparing a lanthanide metal-doped copper-based catalyst, comprising the following steps:

[0007] 1) dissolving a copper compound and a lanthanide metal compound in a solvent and stirring to obtain a mixed solution;

[0008] 2) placing the mixed solution in a hydrothermal kettle and then reacting by a solvothermal method;

[0009] 3) After the reaction is completed, the precipitate in the reaction system is centrifuged, washed, and dried to obtain a lanthanide metal-doped copper-based catalyst.

[0010] In the above preparation method, the copper compound is selected from at least one of copper sulfate (CuSO4), copper nitrate (CuNO3), copper chloride (CuCl2), copper acetate (Cu(CH3COO)2), copper acetylacetonate (Cu(acac)2) and hydrates thereof, specifically Cu(CH3COO)2 hydrate, more specifically Cu(CH3COO)2·H2O;

[0011] The lanthanide metal compound is selected from at least one of lanthanide metal chlorides, lanthanide metal nitrates, lanthanide metal acetates, lanthanide metal sulfates and hydrates thereof, specifically lanthanum nitrate (La(NO3)3), samarium nitrate (Sm(NO3)3), erbium nitrate (Er(NO3)3), cerium nitrate (Ce(NO3)3) and hydrates thereof, more specifically Gd(NO3)3·6H2O;

[0012] The molar ratio of the copper compound to the lanthanide metal compound may be 100:0.01-1, preferably 10:0.1-1, specifically 5:1;

[0013] said dissolving being performed by ultrasound;

[0014] The solvent is selected from water and / or organic solvent 1;

[0015] The organic solvent 1 is selected from at least one of ethanol, ethylene glycol, acetone, acetonitrile, tetrahydrofuran, and dimethylformamide;

[0016] The molar ratio of the copper compound to the volume of the solvent is 1 mmol:10-80 mL; more specifically, 1 mmol:50 mL;

[0017] The stirring time may be 0.2 to 10 hours, specifically 4 hours.

[0018] According to an embodiment of the present invention, the copper compound is Cu(CH3COO)2·H2O, and the lanthanide metal compound is Gd(NO3)3·6H2O, and the molar ratio of the two can be 10:1, 5:1 or 4:1.

[0019] In the above preparation method, in step 2), the solvent thermal temperature of the solvent thermal reaction can be 90-200° C., specifically 120° C., and the reaction time can be 5-36 h, specifically 16 h.

[0020] In the above preparation method, in step 3), the centrifugal speed can be 1000-10000 rpm, and the time can be 1-60 min, specifically 8000 rpm for 3 min;

[0021] The washing solvent may be at least one of deionized water, ethanol, acetone and methanol;

[0022] The drying temperature may be 30-100° C., and the drying time may be 1-50 h, specifically, drying at 60° C. for 16 h.

[0023] The second object of the present invention is to provide the lanthanide metal-doped copper-based catalyst prepared by the above preparation method.

[0024] The third object of the present invention is to provide an electrode material comprising the above-mentioned lanthanide metal-doped copper-based catalyst and a gas diffusion layer.

[0025] In the above-mentioned electrode material, the method for preparing the electrode material comprises the following steps:

[0026] The lanthanide metal-doped copper-based catalyst is dispersed in an organic solvent 2, and Nafion D-520 dispersion is added as a binder to obtain a dispersion; the dispersion is dropwise coated on the gas diffusion layer to obtain the electrode material.

[0027] In the above-mentioned electrode material, the organic solvent 2 is at least one selected from acetone, ethanol, isopropanol and methanol.

[0028] The ratio of the Nafion D-520 dispersion to the lanthanide metal-doped catalyst may be 5-100 μL:2 mg, specifically 20 μL:2 mg.

[0029] In the above-mentioned electrode materials, the gas diffusion layer can be selected from at least one of carbon fiber paper, carbon fiber woven cloth and carbon black paper with PTFE coating, wherein the PTFE content can be 5% to 20%.

[0030] In the above electrode material, the amount of the catalyst on the gas diffusion layer can be 0.1 to 10 mg·cm -2 , specifically 1 mg cm -2 .

[0031] The fourth object of the present invention is to provide an electrochemical catalytic system, comprising the above-mentioned electrode material, reaction electrolyte and reaction device.

[0032] In the above-mentioned electrochemical catalytic system, the reaction electrolyte is selected from at least one of KOH aqueous solution, KHCO3 aqueous solution, KCl aqueous solution, NaOH aqueous solution, NaHCO3 aqueous solution and NaCl aqueous solution;

[0033] The concentration of the reaction electrolyte may be 0.1 to 10 M; specifically, it may be a 1 M KOH aqueous solution;

[0034] The reaction device is an H-type electrolytic cell, a flow-type electrolytic cell or a membrane electrode electrolytic cell;

[0035] A fifth object of the present invention is to provide the use of the above-mentioned electrode material or the above-mentioned electrochemical catalytic system in the electrocatalytic conversion of carbon dioxide to synthesize multi-carbon products.

[0036] A sixth object of the present invention is to provide a method for electrocatalytically converting carbon dioxide into multi-carbon products, comprising the following steps: 1) preactivating the electrode material using a constant potential electrolysis method in the electrocatalytic system;

[0037] 2) Using carbon dioxide as a raw material, a constant potential electrolysis reaction is performed in the electrolytic cell reaction device through the action of the electrode material and the electrolyte to synthesize a multi-carbon product.

[0038] In the above method, in step 1), the potential selected by the constant potential method can be -1 to -2 V vs. RHE (-1.6 to -2.6 V vs. Hg / HgO), specifically -1.6 V vs. RHE;

[0039] The activation time may be 0.2 to 1 h, specifically 0.4 h.

[0040] In the present invention, the electrolyte used to pre-activate the electrode material in step 1) is selected from at least one of KOH aqueous solution, KHCO3 aqueous solution, KCl aqueous solution, NaOH aqueous solution, NaHCO3 aqueous solution and NaCl aqueous solution;

[0041] In step 2), the electrolyte is not the electrolyte in step 1), but a newly replaced electrolyte.

[0042] In the above method, in step 2), when the electrolytic cell reaction device adopts the H-type electrolytic cell system or the flow-type electrolytic cell system, the potential of the electrolysis reaction can be -0.4 to -2.4 V vs. RHE (-1 to -3.0 V vs. Hg / HgO), specifically -1.6 V vs. RHE;

[0043] When the electrolytic cell reaction device adopts the membrane electrode electrolytic cell system, the electrolytic reaction potential can be 2 to 8V;

[0044] The electrolysis reaction time may be 0.1 to 500 hours, preferably 1 to 300 hours.

[0045] The products of the reaction include CO, hydrogen, ethylene, ethanol, acetic acid, and n-propanol, with ethylene and ethanol being the main multi-carbon products.

[0046] The present invention has the following advantages:

[0047] A method for synthesizing multi-carbon products using CO2 as a raw material under electrocatalytic action. This reaction can be efficiently carried out in flow-type electrolyzers and membrane electrode electrolyzers using a lanthanide metal-doped copper-based catalyst / gas diffusion electrode composite as the electrode material, demonstrating the potential for large-scale application of electrocatalytic CO2 reduction. Furthermore, the catalyst of this invention possesses excellent stability, laying a solid foundation for its industrial development and having far-reaching significance in addressing energy crises and environmental issues. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 6.5%Gd / CuO x Scanning electron microscope (SEM) images of

[0049] Figure 2 6.5%Gd / CuO x X-ray diffraction analysis (XRD) pattern;

[0050] Figure 3 6.5%Gd / CuO x Element distribution map (EDS Mapping);

[0051] Figure 4 6.5%Gd / CuO x Faradaic efficiency diagram of electrochemical reduction of CO2 to multi-carbon products;

[0052] Figure 5 6.5%Gd / CuO x Current density diagram for the electrochemical reduction of CO2 to multi-carbon products. DETAILED DESCRIPTION

[0053] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0054] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0055] Example 1. Preparation and characterization of catalyst:

[0056] The catalyst with a Gd mass fraction of 6.5% (6.5% Gd / CuO x ) preparation as an example.

[0057] First, 0.56 mmol of Gd(NO3)3·6H2O and 2.5 mmol of Cu(COOH)2·H2O were ultrasonically dissolved in 50 mL of ethanol solution and stirred vigorously for 12 hours. The resulting mixed solution was placed in a 100 mL hydrothermal autoclave and maintained at 120°C for 16 hours. After cooling naturally to room temperature, the precipitate was centrifuged at 8000 rpm for 3 minutes to obtain a precipitate. After washing with deionized water and ethanol, the precipitate was placed in a vacuum drying oven at 60°C for 12 hours to obtain 6.5% Gd / CuO x The mass fraction of the elements in the catalyst was measured by inductively coupled plasma emission spectrometry. By adjusting the addition ratio of Gd(NO3)3·6H2O and Cu(COOH)2·H2O, 2.6% Gd / CuO was obtained. x 5.4%Gd / CuO x 、14.1%Gd / CuO x The catalyst, the corresponding amount of Gd(NO3)3·6H2O and Cu(COOH)2·H2O added were: 0.25mmol Gd(NO3)3·6H2O and 2.5mmol Cu(COOH)2·H2O (2.6% Gd / CuO x ), 0.44mmol Gd(NO3)3·6H2O and 2.5mmol Cu(COOH)2·H2O (5.4%Gd / CuO x ); 0.69mmol Gd(NO3)3·6H2O and 2.5mmol Cu(COOH)2·H2O (14.1%Gd / CuO x ).

[0058] Based on the above method, 6.5% La / CuO was prepared using La(NO3)3, Sm(NO3)3, Er(NO3)3, and Ce(NO3)3. x 、6.5%Sm / CuO x 、6.5%Er / CuO x 、6.5%Ce / CuO x catalyst.

[0059] For comparison, CuO was synthesized according to the above method without adding lanthanide metal compounds. x catalyst.

[0060] For 6.5%Gd / CuO x The catalyst was systematically characterized. Scanning electron microscope (SEM) images showed that 6.5% Gd / CuO x The catalyst is a cube with a side length of about 60nm ( Figure 1 ). X-ray diffraction analysis (XRD) showed that 6.5% Gd / CuOx Cu in the catalyst exists in the form of copper and cuprous oxide ( Figure 2 ). Element distribution map (EDS Mapping) research shows that Cu, Gd, and O elements are evenly distributed on the catalyst surface ( Figure 3 ).

[0061] Catalyst prepared above: 6.5% La / CuO x 、6.5%Sm / CuO x 、6.5%Er / CuO x 、6.5%Ce / CuO x The structure of the catalyst is similar to that of 6.5% Gd / CuO x The catalysts are similar.

[0062] The CuO prepared above x The structure of the catalyst is similar to that of 6.5% Gd / CuO x The catalysts are similar, but only Cu and O elements are evenly distributed on the catalyst surface.

[0063] Example 2: Electrocatalytic conversion of carbon dioxide:

[0064] To prepare the working electrode, 2 mg of 6.5% Gd / CuO x Catalyst or CuO x The catalyst (prepared in Example 1 of the present invention) was dispersed in 1 mL of isopropanol along with 20 μL of Nafion D-520 dispersion (5 wt%) and ultrasonicated for 30 min to achieve uniform dispersion. The dispersion was evenly drop-coated on the surface of the carbon fiber paper of the gas diffusion layer and allowed to stand at room temperature for 12 h. The loading of the catalyst on each electrode was 1 mg cm -2 .

[0065] Electrolysis experiments were conducted at 25°C using a three-electrode flow-type electrolytic cell system consisting of the aforementioned working electrode, a nickel foam counter electrode, and a Hg / HgO reference electrode. A 1M KOH aqueous solution was added to the cell. A Fumasep FAA-3-PK-130 membrane served as the anion exchange membrane, separating the cathode and anode. The electrolyte in the anode and cathode compartments was 10 mL of 1M KOH aqueous solution. Prior to the electrolysis experiments, the electrode materials were activated for 0.5 h using potentiostatic electrolysis at -1.6 V vs. RHE (-2.2 V vs. Hg / HgO). The anode and cathode electrolytes were then replaced with fresh electrolytes, and electrocatalytic CO conversion experiments were initiated. The CO2 flow rate was controlled at 40 sccm, and the potential range was -0.2 to -2 V vs. RHE. The electrolysis time was 0.5 h. The gaseous products were collected using a gas bag and analyzed by gas chromatography (GC, HP 4890D), and the liquid products were analyzed by nuclear magnetic resonance ( 1H NMR, Bruker Avance III 400 HD) was used for analysis.

[0066] The experimental results of electrocatalytic CO2 reaction under different catalytic conditions are as follows Figure 4 、 Figure 5 As shown in the figure, the catalytic system of the present invention has excellent multi-carbon product selectivity (Faraday efficiency greater than 80%) and high current density. When the potential is -1.0 V vs. RHE, the current density is greater than 1 A cm -2 , reaching the industrial current density requirements (>500mA cm -2 ), and its activity is much higher than CuO x catalytic activity.

[0067] Example 3: Study on Catalyst Stability

[0068] The reaction was continued at a potential of -0.8 V vs RHE for 100 h to evaluate the 6.5% Gd / CuO x It was found that the Faradaic efficiency and current density of the multi-carbon product did not change significantly (the results are shown in Table 1), indicating that the catalyst has excellent electrochemical stability and potential industrial value.

[0069] Table 1 The Faraday efficiency and current density of multi-carbon products in the stability test of 6.5% Gd / CuOx over time

[0070] Electrolysis time (h) Multi-carbon product Faraday efficiency (%) <![CDATA[Current density (mA cm -2 )]]> 5 82 444 10 83 425 20 80 456 30 83 436 40 81 428 50 79 413 60 80 403 70 78 426 80 76 409 90 80 423 100 81 428

Claims

1. A method for preparing a lanthanide metal-doped copper-based catalyst, comprising the following steps: 1) dissolving a copper compound and a lanthanide metal compound in a solvent and stirring to obtain a mixed solution; The solvent is selected from water and ethanol; 2) placing the mixed solution in a hydrothermal reactor and reacting by a solvothermal method; The solvent thermal temperature of the solvent thermal reaction is 90-120°C; 3) After the reaction is completed, the precipitate in the reaction system is centrifuged, washed, and dried to obtain a lanthanide metal-doped copper-based catalyst.

2. The preparation method according to claim 1, characterized in that The copper compound is selected from at least one of copper sulfate, copper nitrate, copper chloride, copper acetate, copper acetylacetonate and hydrates thereof; The lanthanide metal compound is selected from at least one of lanthanide metal chlorides, lanthanide metal nitrates, lanthanide metal acetates, lanthanide metal sulfates and hydrates thereof; The molar ratio of the copper compound to the lanthanide metal compound is 100:0.01-1; said dissolving being performed by ultrasound; The molar ratio of the copper compound to the solvent volume is 1 mmol: 10-80 mL; The stirring time is 0.2 to 10 h; And / or, in step 2), the solvothermal reaction time is 5 to 36 hours; And / or, in step 3), the centrifugation speed is 1000-10000 rpm and the time is 1-60 min; The washing solvent is at least one of deionized water, ethanol, acetone and methanol; The drying temperature is 30-100° C., and the drying time is 1-50 h.

3. The lanthanide metal-doped copper-based catalyst prepared by the preparation method according to claim 1 or 2.

4. An electrode material comprising the lanthanide metal-doped copper-based catalyst according to claim 3 and a gas diffusion layer.

5. The electrode material according to claim 4, characterized in that The method for preparing the electrode material comprises the following steps: The lanthanide metal-doped copper-based catalyst is dispersed in an organic solvent 2, and Nafion D-520 dispersion is added as a binder to obtain a dispersion; the dispersion is dropwise coated on the gas diffusion layer to obtain the electrode material.

6. The electrode material according to claim 5, characterized in that The organic solvent 2 is selected from at least one of acetone, ethanol, isopropanol and methanol; The ratio of the Nafion D-520 dispersion to the lanthanide metal-doped catalyst is 5-100 μL: 2 mg; The gas diffusion layer may be selected from at least one of carbon fiber paper, carbon fiber woven cloth and carbon black paper with a PTFE coating, wherein the PTFE content is 5% to 20%; On the gas diffusion layer, the catalyst dosage is 0.1~10 mg·cm -2 .

7. An electrochemical catalytic system comprising the electrode material according to any one of claims 4 to 6, a reaction electrolyte and a reaction device.

8. The electrochemical catalytic system according to claim 7, characterized in that: The reaction electrolyte is selected from at least one of a KOH aqueous solution, a KHCO3 aqueous solution, a KCl aqueous solution, a NaOH aqueous solution, a NaHCO3 aqueous solution and a NaCl aqueous solution; The concentration of the reaction electrolyte is 0.1~10 M; The reaction device is an H-type electrolytic cell, a flow-type electrolytic cell or a membrane electrode electrolytic cell.

9. Use of the electrode material according to any one of claims 4 to 6 or the electrochemical catalytic system according to claims 7 and 8 in the electrocatalytic conversion of carbon dioxide to synthesize multi-carbon products.

10. A method for electrocatalytic conversion of carbon dioxide to multi-carbon products, comprising the following steps: 1) using the electrochemical catalytic system of claim 8, using a constant potential electrolysis method to pre-activate the electrode material under constant potential conditions; 2) Using carbon dioxide as a raw material, a constant potential electrolysis reaction is performed in the electrolytic cell reaction device through the action of the electrode material and the electrolyte to synthesize a multi-carbon product.

11. The method according to claim 10, characterized in that: In step 1), the potential selected by the constant potential method is -1~-2 V vs. RHE; The activation time is 0.2~1 h; In step 2), when the electrolytic cell reaction device adopts the H-type electrolytic cell system or the flow-type electrolytic cell system, the potential of the electrolytic reaction is -0.4~-2.4 V vs. RHE; When the electrolytic cell reaction device adopts the membrane electrode electrolytic cell system, the electrolysis reaction potential is 2 to 8 V; The electrolysis reaction time is 0.1 to 500 h.

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