A CuN-OCH3 catalyst, its preparation method, and its application in the electrochemical reduction of carbon dioxide.

Abstract

This invention relates to the field of carbon dioxide recycling technology, disclosing a CuN-OCH3 catalyst, its preparation method, and its application in the electrochemical reduction reaction of carbon dioxide. The preparation method of the CuN-OCH3 catalyst includes the following steps: dispersing a copper salt and a methoxy-substituted pyridazine ligand in a solvent, followed by a hydrothermal reaction, and then separating and drying to obtain the CuN-OCH3 catalyst. In this invention, a methoxy-substituted pyridazine ligand and a copper salt are synergistically constructed in an organic solvent to form a CuN coordination structure. This ligand not only provides N coordination sites to stably form a well-defined CuN local configuration, but its methoxy substituents also introduce additional regulation at the electronic and structural levels, thereby inducing a microenvironment on the catalyst surface that is more suitable for the CO2RR to ethylene production process. It exhibits a very high ethylene fractional current density at high current densities and also has a high ethylene Faradaic efficiency.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide recycling technology, specifically to a CuN-OCH3 catalyst, its preparation method, and its application in the electrochemical reduction reaction of carbon dioxide. Background Technology

[0002] To achieve the effective coupling of carbon dioxide resource utilization and renewable energy storage, the electrochemical reduction reaction of carbon dioxide (CO2RR) to produce high-value-added products such as ethylene has attracted widespread attention. Ethylene, as a basic chemical feedstock, suffers from high energy consumption and strong carbon emissions from traditional petrochemical routes; however, CO2RR can convert carbon dioxide and electricity into ethylene under mild conditions, achieving efficient coupling of "carbon source—electricity—chemicals." However, CO2RR to ethylene production involves multi-electron, multi-proton processes and C / C bond construction. The pathway is highly sensitive to catalytic site configuration, surface electronic structure, and interfacial microenvironment, and is easily competitive with side reactions such as hydrogen evolution, leading to limited selectivity and energy efficiency. Furthermore, at high current densities, engineering bottlenecks such as insufficient carbon dioxide supply, local pH drift, mass transfer / ion conduction polarization, and water management hinder long-term stability and large-scale application. Therefore, it is urgent to optimize the system synergistically at multiple scales: at the catalyst level, improve the regulation of key intermediates and C / C coupling capabilities; at the interfacial level, optimize the local carbon dioxide concentration and pH microenvironment; and at the system level, improve membrane electrode components, flow fields, and operational control strategies to promote the development of CO2RR to ethylene production towards high efficiency, stability, and scalability.

[0003] With the development of CO2RR ethylene production technology, various copper-based / copper composite catalysts or electrode systems have been disclosed in existing technologies. However, they still have significant shortcomings in terms of ethylene Faradaic efficiency at industrial-grade current densities, process simplicity, and scalability, making it difficult to meet the needs of large-scale applications. For example, CN114990606A obtains a catalytic electrode by electrochemically cyclically activating a copper substrate. Under -1.5 V (vs RHE) conditions, the highest ethylene Faradaic efficiency is 42.1%, but the corresponding ethylene bias current density is only -17 mA·cm. -2 The overall yield is low, making it difficult to support the high current density operation required for industrialization.

[0004] CN115418666A employs a catalyst system constructed using methods such as "mixing cuprous oxide with a nitrogen-rich precursor—in-situ calcination," disclosing an ethylene Faradaic efficiency of up to 55.97%, but with a reaction current density of only -12.8 mA·cm⁻¹. -2Similarly, it falls within the low current density range, making it difficult to achieve high-throughput ethylene production. CN116288474A constructs a CuO@Cu2O composite structure through multiple wet chemical / solventricular steps, achieving an ethylene Faradaic efficiency of 43.5%, but the corresponding current density is also relatively low, and the preparation steps are numerous, severely limiting the feasibility of this catalyst in industrial applications.

[0005] In summary, existing technologies generally suffer from the following problems: (1) although the ethylene Faraday efficiency has been improved, the corresponding current density is relatively low; (2) some routes involve multiple steps / high temperatures or harsh system conditions, resulting in problems such as unfavorable scale-up consistency and energy consumption costs. Therefore, it is urgent to develop a catalyst system that is simpler to synthesize, has a controllable structure, and can achieve high ethylene selectivity and high ethylene partial current density at high current densities. Summary of the Invention

[0006] This invention addresses the problem of low current density in the electrochemical reduction of carbon dioxide for the preparation of ethylene by providing a CuN-OCH3 catalyst. This catalyst can effectively improve catalytic activity and achieve high ethylene fractional current density in the application of carbon dioxide electrochemical reduction.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a CuN-OCH3 catalyst includes the following steps: dispersing a copper salt and a methoxylated pyridazine ligand in a solvent and then carrying out a hydrothermal reaction, followed by separation and drying to obtain the CuN-OCH3 catalyst.

[0008] The copper salt includes one or more of copper nitrate, copper chloride, copper sulfate, copper acetylacetonate, or copper acetate.

[0009] The methoxypyridazine ligands include one or more of 4-methoxypyridazine, 3,6-dimethoxypyridazine, and 3,5-dimethoxypyridazine.

[0010] The hydrothermal reaction temperature is 100℃~130℃, and the time is 15-30h; The solvent includes any one of anhydrous acetonitrile, N,N-dimethylformamide, ethanol, or a mixture of N,N-dimethylformamide and water.

[0011] The molar ratio of the copper salt to the methoxylated pyridazine ligand is 1:1-2.

[0012] The present invention also provides a CuN-OCH3 catalyst obtained by the preparation method described above.

[0013] The present invention also provides the application of the CuN-OCH3 catalyst in the electrochemical reduction of carbon dioxide to prepare ethylene.

[0014] In this invention, a methoxy-substituted pyridazine ligand is used in conjunction with a copper salt in an organic solvent to construct a CuN coordination structure. This ligand not only provides N coordination sites to stably form a well-defined CuN local configuration, but its methoxy substituents also introduce additional regulation at the electronic and structural levels, thereby inducing a microenvironment on the catalyst surface that is more suitable for CO2RR to ethylene production.

[0015] Specifically, methoxy groups possess certain electron-donating characteristics and can influence the electron distribution of the ligand skeleton through inductive / conjugation effects. This allows for fine-tuning of the electron density and ligand field strength at the Cu center, potentially optimizing the adsorption strength and coverage of key carbon-containing intermediates (such as *CO and subsequent CC coupling-related intermediates) at the Cu site, achieving favorable matching of the CC coupling window. Simultaneously, methoxy substitution may alter the local polarity and interfacial solvation environment around the ligand, thereby potentially suppressing other side reactions and improving the utilization efficiency of electrons and protons for carbon reduction channels. This is reflected in the very high ethylene fractional current density at high current densities and the relatively high ethylene Faraday efficiency.

[0016] Preferably, in the electrochemical reduction reaction of carbon dioxide, the working electrode (cathode) is a CuN-OCH3 catalyst; the counter electrode (anode) includes one or more of nickel foam, platinum mesh, and iridium-plated titanium mesh. The solute in the catholy solution includes one or more of KOH, KHCO3, KCl, K2SO4, NaOH, NaHCO3, NaCl, and Na2SO4, with a molar concentration of 0.1–1.0 mol·L⁻¹. -1 ; The solute in the anolyte is selected from one or more of KHCO3, K2SO4, KOH, NaHCO3, Na2SO4, and NaOH, and the molar concentration of the solute is 0.1~1.0 mol·L. -1 .

[0017] Preferably, the current density in the electrochemical reduction reaction of carbon dioxide is -100 to -900 mA·cm. -2 .

[0018] Preferably, the partial current density of ethylene in the electrochemical reduction reaction of carbon dioxide is -250 to -450 mA·cm⁻¹. -2 .

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, a methoxy-substituted pyridazine ligand is used to synergistically construct a CuN coordination structure with a copper salt in an organic solvent. This ligand not only provides N coordination sites to stably form a well-defined CuN local configuration, but its methoxy substituents also introduce additional regulation at the electronic and structural levels, thereby inducing a microenvironment on the catalyst surface that is more suitable for CO2RR to produce ethylene. This enables the high selectivity and high throughput of ethylene production at high current densities, which is closer to the comprehensive requirements of "high selectivity + high current density" for industrial-grade high-load operation.

[0020] (2) The CuN-OCH3 catalytic preparation method of the present invention only requires the raw materials to be mixed and dispersed, and then separated and dried by hydrothermal reaction. The route is simple and clear, which is very conducive to direct industrial application. Attached Figure Description

[0021] Figure 1 This is a transmission electron microscope (TEM) image of the CuN-4-OCH3 catalyst prepared in Example 1.

[0022] Figure 2 The image shows the lattice pattern of the CuN-4-OCH3 catalyst prepared in Example 1.

[0023] Figure 3 The Cu K-edge extended X-ray absorption fine structure (EXAFS) spectrum of the CuN-4-OCH3 catalyst prepared in Example 1 is shown in the R-space Fourier transform spectrum.

[0024] Figure 4 The infrared spectrum of the CuN-4-OCH3 catalyst prepared in Example 1.

[0025] Figure 5 Catalysts prepared for different embodiments and comparative examples were tested at 700 mA·cm⁻¹. -2 Faraday efficiency diagram of electrocatalytic carbon dioxide to ethylene production.

[0026] Figure 6 The image shows the Faraday efficiency of the CuN-4-OCH3 catalyst prepared in Example 1 for the electrocatalytic production of ethylene from carbon dioxide at different current densities. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0028] All raw materials used in the following specific implementation methods were purchased from the market.

[0029] Example 1 This example provides a method for preparing a CuN-4-OCH3 catalyst, comprising: 3 mmol CuCl2·2H2O and 3 mmol 4-methoxypyridazine were co-dispersed in 60 mL N,N-dimethylformamide and mechanically stirred for 30 minutes to ensure thorough mixing. The resulting suspension was then transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 120 °C for 24 hours. After the reaction, the mixture was allowed to cool naturally to room temperature, and the precipitate was collected by centrifugation and freeze-dried for 12 hours to obtain CuN-4-OCH3.

[0030] The transmission electron microscope image of the CuN-4-OCH3 catalyst prepared in Example 1 is shown below. Figure 1 As shown, this CuN-4-OCH3 catalyst has a sandwich-like structure. The lattice pattern of the CuN-4-OCH3 catalyst prepared in Example 1 is shown below. Figure 2 As shown, Cu(002) lattice fringes are locally visible. The R-space Fourier transform spectrum of Cu K-edge EXAFS is shown below. Figure 3 As shown, the catalyst exhibits Cu-N dominant coordination, indicating that Cu sites are primarily dispersed in a coordinated state rather than aggregated with metal. The infrared spectrum is shown below. Figure 4 As shown, the infrared light appears at 1453 cm. -1 (CH3), 1020 / 1263 cm -1 Characteristic peaks such as (CO / Ar-O) prove that the methoxy group was successfully introduced.

[0031] Carbon dioxide electrocatalytic reduction activity test: The CuN-4-OCH3 catalyst obtained in this embodiment was dispersed on carbon paper for electrocatalytic reduction reaction testing. The catalytic activity of the catalyst was observed. Using the CuN-4-OCH3 catalyst as the working electrode, carbon dioxide was reduced under constant current with an applied current density of -700 mA·cm⁻¹. -2 The reaction time was 300 s, and the carbon dioxide flow rate was 20 mL / min. -1 The cathode solution is 1.0 mol·L⁻¹ -1 A saturated KOH solution containing carbon dioxide, with an anolyte concentration of 1.0 mol·L⁻¹. -1 Using KOH solution and nickel foam as the counter electrode, hydrogen, carbon monoxide, and ethylene were produced. The Faraday efficiency for ethylene was 57.9%, and the partial current density of ethylene was -405.3 mA·cm⁻¹. -2 .

[0032] Comparative Example 1 3 mmol CuCl2·2H2O and 3 mmol pyridazine were co-dispersed in 60 mL of N,N-dimethylformamide and mechanically stirred for 30 minutes to ensure thorough mixing. The resulting suspension was then transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 120 °C for 24 hours. After the reaction, the mixture was allowed to cool naturally to room temperature, and the precipitate was collected by centrifugation and freeze-dried for 12 hours to obtain CuN.

[0033] Analysis of the experimental results showed that the Faraday current efficiency of ethylene in Comparative Example 1 was 25.46%, and the partial current density of ethylene was -178.2 mA·cm⁻¹. -2 The efficiency of the catalyst prepared in Example 1 is significantly lower than that of the ethylene Faradaic current. This indicates that the lack of methoxy groups to synergistically regulate the ligand field and interfacial microenvironment leads to a greater bias in the electronic state and solvation environment of the Cu-N sites towards *CO generation and desorption, limiting further coupling and deep reduction of *CO. This results in a decrease in ethylene Faradaic efficiency and a significant increase in CO selectivity.

[0034] Example 2 This embodiment provides a method for preparing a CuN-3,5-OCH3 catalyst, specifically including the following steps: Step 1: 3 mmol CuCl2·2H2O and 3 mmol 3,5-dimethoxypyridazine were co-dispersed in 60 mL N,N-dimethylformamide and mechanically stirred for 30 minutes to ensure thorough mixing. The resulting suspension was then transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 120 °C for 24 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The precipitate was collected by centrifugation and freeze-dried for 12 hours to obtain CuN-3,5-OCH3.

[0035] Carbon dioxide electrocatalytic reduction activity test: The CuN-3,5-OCH3 catalyst obtained in this embodiment was dispersed on carbon paper for electrocatalytic reduction reaction testing to observe the catalytic activity. Using the CuN-3,5-OCH3 catalyst as the working electrode, carbon dioxide was reduced under constant current with an applied current density of -700 mA·cm⁻¹. -2 The reaction time was 300 s, and the carbon dioxide flow rate was 20 mL / min. -1 The cathode solution is 1.0 mol·L⁻¹ -1 A saturated KOH solution containing carbon dioxide, with an anolyte concentration of 1.0 mol·L⁻¹. -1 Using a KOH solution with a nickel foam counter electrode, hydrogen, carbon monoxide, ethylene, and ethanol were produced, with a Faraday efficiency of 41.71% for ethylene. The partial current density of ethylene was -292.0 mA·cm⁻¹. -2 .

[0036] Example 3 This embodiment provides a method for preparing a CuN-3,6-OCH3 catalyst, specifically including the following steps: Step 1: 3 mmol CuCl2·2H2O and 3 mmol 3,6-dimethoxypyridazine were co-dispersed in 60 mL N,N-dimethylformamide and mechanically stirred for 30 minutes to ensure thorough mixing. The resulting suspension was then transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 120 °C for 24 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The precipitate was collected by centrifugation and freeze-dried for 12 hours to obtain CuN-3,6-OCH3.

[0037] Carbon dioxide electrocatalytic reduction activity test: The CuN-3,6-OCH3 catalyst obtained in this example was dispersed on carbon paper for electrocatalytic reduction reaction testing. The catalytic activity of the catalyst was observed. Using the CuN-3,6-OCH3 catalyst as the working electrode, carbon dioxide was reduced under constant current with an applied current density of -700 mA·cm⁻¹. -2 The reaction time was 300 s, and the carbon dioxide flow rate was 20 mL / min. -1 The cathode solution is 1.0 mol·L⁻¹ -1 A saturated KOH solution containing carbon dioxide, with an anolyte concentration of 1.0 mol·L⁻¹. -1 Using a KOH solution with a nickel foam counter electrode, hydrogen, carbon monoxide, ethylene, and ethanol were produced, with a Faraday efficiency of 43.36% for ethylene. The partial current density of ethylene was -303.5 mA·cm⁻¹. -2 .

[0038] The catalysts prepared in Examples 1-3 and Comparative Example 1 were applied to the electrocatalytic reduction of carbon dioxide, with an applied current density of -700 mA·cm⁻¹. -2 The Faraday efficiency of ethylene under a reaction time of 300 s is summarized as follows: Figure 5 As shown.

[0039] Application examples The CuN-4-OCH3 catalyst prepared in Example 1 was used as the cathode (working electrode), and nickel foam was used as the counter electrode (anode). Carbon dioxide was reduced under constant current, with applied current densities ranging from -100 to -900 mA·cm⁻¹. -2 The test was conducted with a reaction time of 300 s and a carbon dioxide flow rate of 20 mL / min. -1 The cathode solution is 1.0 mol·L⁻¹ -1 A saturated KOH solution containing carbon dioxide, with an anolyte concentration of 1.0 mol·L⁻¹. -1KOH solution was used to produce hydrogen, carbon monoxide, and ethylene. The Faradaic efficiencies of the electrocatalytic production of ethylene from carbon dioxide at different current densities are as follows: Figure 6 As shown, it can be seen that the range is -400 to -900 mA·cm -2 The effects are all quite good, including -700 mA·cm -2 The best results are achieved this way.

[0040] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a CuN-OCH3 catalyst, characterized in that, The process includes the following steps: dispersing copper salt and methoxylated pyridazine ligands in a solvent and then carrying out a hydrothermal reaction, followed by separation and drying to obtain the CuN-OCH3 catalyst.

2. The method for preparing the CuN-OCH3 catalyst according to claim 1, characterized in that, The copper salt includes one or more of copper nitrate, copper chloride, copper sulfate, copper acetylacetonate, or copper acetate.

3. The method for preparing the CuN-OCH3 catalyst according to claim 1, characterized in that, The methoxypyridazine ligands include one or more of 4-methoxypyridazine, 3,6-dimethoxypyridazine, and 3,5-dimethoxypyridazine.

4. The method for preparing the CuN-OCH3 catalyst according to claim 1, characterized in that, The hydrothermal reaction temperature is 100℃~130℃, and the time is 15-30h; The solvent includes any one of anhydrous acetonitrile, N,N-dimethylformamide, ethanol, or a mixture of N,N-dimethylformamide and water.

5. The method for preparing the CuN-OCH3 catalyst according to claim 1, characterized in that, The molar ratio of the copper salt to the methoxylated pyridazine ligand is 1:1-2.

6. The CuN-OCH3 catalyst obtained by the preparation method according to any one of claims 1-5.

7. The application of the CuN-OCH3 catalyst according to claim 6 in the electrochemical reduction of carbon dioxide to prepare ethylene.

8. The application according to claim 7, characterized in that, In the electrochemical reduction reaction of carbon dioxide, the working electrode is a CuN-OCH3 catalyst; the counter electrode includes one or more of nickel foam, platinum mesh, and iridium-plated titanium mesh. The solute in the catholy solution includes one or more of KOH, KHCO3, KCl, K2SO4, NaOH, NaHCO3, NaCl, and Na2SO4, with a molar concentration of 0.1–1.0 mol·L⁻¹. -1 ; The solute in the anolyte is selected from one or more of KHCO3, K2SO4, KOH, NaHCO3, Na2SO4, and NaOH, and the molar concentration of the solute is 0.1~1.0 mol·L. -1 .

9. The application according to claim 7, characterized in that, The current density in the electrochemical reduction reaction of carbon dioxide is -100 to -900 mA·cm. -2 .

10. The application according to claim 7, characterized in that, The partial current density of ethylene in the electrochemical reduction reaction of carbon dioxide is -250 to -450 mA·cm⁻¹ -2 .

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