A metal element-doped modified Cu2O catalyst, its preparation method, and its application in electrocatalytic carbon dioxide to ethylene production.

Abstract

This invention discloses a metal element-doped modified Cu2O catalyst, its preparation method, and its application. The catalyst uses Cu2O as a substrate, with Zn doped into the Cu2O lattice in an atomically dispersed form to form a Zn-O-Cu dual-site synergistic structure. The preparation method is as follows: (1) Dissolve soluble copper salt and polyvinylpyrrolidone in water, then adjust the pH value of the system, and the solution color changes from blue-green to dark brown; (2) Add soluble zinc salt to the suspension and mix evenly; (3) Add a reducing agent and react in a water bath at 50~80℃ for 2~6 hours. After the reaction, separate the product, wash and dry it. This invention promotes the formation of oxygen vacancies in the Cu2O lattice by doping Zn into the cuprous oxide lattice, strengthens CO2 activation and C-C coupling, and effectively inhibits the excessive reduction of Cu during the reaction process, maintaining the stability of the active sites.

Description

Technical Field

[0001] This invention relates to a carbon dioxide reduction catalyst, its preparation method and application, and particularly to a metal element-doped modified Cu2O catalyst, its preparation method and its application in electrocatalytic carbon dioxide to ethylene production. Background Technology

[0002] With the acceleration of global industrialization and the continuous consumption of fossil fuels, the concentration of carbon dioxide (CO2) in the atmosphere is constantly rising, and the resulting greenhouse effect has become a global challenge. Against this backdrop, utilizing CO2 as a cheap, non-toxic, and abundant carbon resource to achieve "carbon neutrality" has become an international consensus. Among numerous carbon capture and utilization technologies, electrocatalytic carbon dioxide reduction reaction (CO2RR) technology is considered a key pathway to achieving a sustainable carbon cycle because it can utilize electricity generated from renewable energy sources to convert CO2 into high-value-added fuels and chemicals under mild conditions. It combines the dual significance of carbon resource utilization and intermittent electricity storage. Among CO2RR products, multi-carbon products (such as ethylene and ethanol) have higher energy density and commercial value than C1 products (such as carbon monoxide, methane, and formic acid). Ethylene, as one of the world's largest-produced chemical raw materials, has a broad market demand.

[0003] Among the various known electrocatalysts, copper (Cu)-based catalysts have attracted much attention from researchers due to their moderate adsorption energy for *CO intermediates, which promotes the C-C coupling reaction. They are among the few metallic materials capable of efficiently converting CO2 into multi-carbon products. Cuprous oxide (Cu2O), in particular, is considered a highly promising CO2RR catalytic material due to its unique electronic structure and abundant active sites.

[0004] However, copper-based catalysts still face several key challenges in practical applications. First, the formation of multi-carbon products involves complex multi-step proton-coupled electron transfer processes. The high energy barrier of the C-C coupling step makes precise control of the reaction pathway difficult, leading to unsatisfactory selectivity for the target product. Second, during electrocatalytic reduction, the catalyst surface is prone to reconstruction, making it difficult to maintain the stability of the active site structure, resulting in a significant decline in catalytic performance over time. This is especially true at more negative operating potentials, where high-valence copper species (such as Cu) in the catalyst... + It is easily over-reduced to elemental copper (Cu), leading to the deactivation of active sites. In addition, on the surface of traditional hydrophilic electrodes, water molecules tend to accumulate and compete with CO2 for active sites, resulting in the competitive hydrogen evolution reaction (HER) becoming dominant, which severely limits the Faraday efficiency of the target product.

[0005] To overcome these limitations, researchers have developed various modification strategies. Nanomorphic modification optimizes the distribution of active sites by exposing specific crystal faces, but it is often difficult to effectively control the reaction microenvironment. Elemental doping can adjust the electronic structure of catalysts, but dopants are easily lost during the reaction, leading to insufficient long-term stability. Although alloying strategies can optimize the adsorption energy of intermediates, metal leaching is still difficult to avoid.

[0006] Therefore, optimizing the electronic structure of Cu2O and reducing the CC coupling energy barrier to improve the selectivity of catalytic CO2 to ethylene production while maintaining the long-term stability of the catalyst has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] Objectives of the Invention: The first objective of this invention is to provide a metal-doped modified Cu2O catalyst that improves the selectivity and stability of catalytic CO2 to ethylene production; the second objective of this invention is to provide a method for preparing the metal-doped modified Cu2O catalyst; and the third objective of this invention is to provide the application of the metal-doped modified Cu2O catalyst in electrocatalytic CO2 to ethylene production.

[0008] Technical solution: The metal element doped modified Cu2O catalyst of the present invention uses Cu2O as a substrate, and Zn is doped in the Cu2O lattice in an atomically dispersed form to form a Zn-O-Cu dual-site synergistic structure, wherein the doping amount of Zn is 10.6 at% to 26.4 at%.

[0009] When the Zn doping concentration in the catalyst is low (10.6 at%), appropriate Zn doping promotes electron transfer and oxygen vacancy formation, resulting in electron-rich Cu sites, while maintaining a regular cubic morphology and high specific surface area. When the doping concentration increases to 26.4 at%, the catalytic performance decreases. This may be due to excess Zn leading to phase separation, active site coverage, decreased Cu₂O crystallinity, and Cu… + The reduction is intensified, which leads to a decrease in performance.

[0010] Preferably, the Cu2O-Zn 0.1 O x The catalyst has a cubic structure with an average particle size of 300-500 nm. Smaller particle sizes result in a higher specific surface area, which is beneficial for exposing more active sites, promoting CO2 adsorption and intermediate mass transfer, and thus exhibiting higher ethylene selectivity and reaction kinetics. However, excessively small particle sizes can lead to nanoparticle aggregation, which is detrimental to performance improvement. Therefore, the preferred catalyst particle size range is 300-500 nm, within which the optimal balance between active site exposure and structural stability can be achieved.

[0011] The preparation method of the metal element doped modified Cu2O catalyst of the present invention includes the following steps:

[0012] (1) Dissolve soluble copper salt and polyvinylpyrrolidone (PVP) in water until completely dissolved, then adjust the pH of the system to form a blue-green suspension. Continue the reaction, and the solution color changes from blue-green to dark brown.

[0013] (2) Add soluble zinc salt to the suspension obtained in step (1) and mix well;

[0014] (3) Add a reducing agent to the suspension obtained in step (2) and react in a water bath at 50~80℃ for 2~6 hours. After the reaction, separate the product, wash and dry it to obtain a Zn-doped cuprous oxide catalyst.

[0015] Preferably, the reducing agent is ascorbic acid or glucose, the molar ratio of soluble copper salt to reducing agent is 1:40-80, and the concentration of reducing agent is 0.1-0.3 M. Preferably, the reducing agent is added dropwise at a rate of 1-3 mL / min.

[0016] In step (3), ascorbic acid acts as a mild reducing agent, gradually reducing the Cu(OH)₂ precursor to Cu₂O. The reduction process follows a dissolution-crystallization mechanism: Cu(OH)₂ is slightly soluble under alkaline conditions, releasing Cu₂O. 2+ Ions; electrons provided by ascorbic acid will convert Cu 2+ Reduced to Cu + Cu + It then reacts with OH in the system - Cu₂O crystal nuclei are formed and further grown into cubic Cu₂O nanoparticles. The introduction of Zn doping occurs during the Cu₂O nucleation and growth stages. Zn in solution... 2+ Ionic radius (0.74 Å) and Cu + With similar ionic radii (0.77 Å), Zn 2+ Can replace Cu + It enters the Cu₂O crystal lattice, or adsorbs onto the surface of the crystal nucleus and is subsequently encapsulated within the lattice. Due to Zn... 2+ The charge of Cu + Different, Zn 2+ Doping introduces localized charge compensation into the crystal lattice, inducing the formation of oxygen vacancies and adjusting the electron cloud density at Cu sites. Simultaneously, Zn... 2+ The coordination with PVP and its selective adsorption on crystal planes further modulate the doping uniformity and distribution of Zn in the Cu₂O lattice. By controlling the amount of zinc salt added, the Zn doping level can be precisely controlled.

[0017] Preferably, the concentration of the soluble copper salt is 0.5-5 mM. Preferably, the soluble copper salt is copper chloride, copper sulfate, or copper nitrate.

[0018] Preferably, the concentration of the soluble zinc salt is 0.13-0.51 mM. Preferably, the soluble zinc salt is zinc sulfate monohydrate, zinc chloride, or zinc nitrate.

[0019] Preferably, the pH is 9.0 to 11.0.

[0020] Preferably, the pH-adjusting sodium hydroxide solution has a concentration of 0.1-0.5 M and a dropping rate of 4-6 mL / min.

[0021] Preferably, the molar mass ratio of the soluble copper salt to polyvinylpyrrolidone is 1 mmol: 9~18 g.

[0022] Preferably, the product separation method in step (3) is centrifugation, with a centrifugation speed of 8000-10000 rpm; the washing is performed by washing with ethanol and deionized water three times each to remove impurities; and the drying is performed by drying in a vacuum drying oven for 6-12 hours at a temperature of 60-80℃.

[0023] The electrode of the present invention contains the aforementioned metal element-doped modified Cu2O catalyst.

[0024] The application of the metal element doped modified Cu2O catalyst or the electrode described in this invention in the electrocatalytic production of ethylene from carbon dioxide.

[0025] The application method of the metal element doped modified Cu2O catalyst includes the following steps:

[0026] (1) Disperse the catalyst in ethanol and add Nafion solution to prepare catalyst ink;

[0027] (2) The catalyst ink is drop-coated onto the surface of the gas diffusion electrode and dried to obtain the catalyst electrode;

[0028] (3) Using the catalytic electrode as the working electrode, the platinum mesh as the counter electrode, and the silver-silver chloride electrode as the reference electrode, the electrocatalytic carbon dioxide reduction reaction is carried out in a flow cell or an H-type electrolytic cell.

[0029] Preferably, in step (2), the catalyst loading on the catalytic electrode is 0.8-1.5 mg / cm³. 2 The preferred electrode substrate is carbon paper, carbon cloth, or a gas diffusion electrode.

[0030] Preferably, in step (3), a flow-through cell is used as the electrolytic cell in the CO2 electroreduction conversion system, and 0.1 M KHCO3 solution is used as the electrolyte in the cathode and anode chambers. The cathode and anode chambers are isolated by anion exchange membranes. High-purity CO2 gas is continuously introduced, and the gas flow rate is controlled at 10-30 mL / min. The electrocatalytic CO2 reduction reaction is carried out in constant potential mode using an electrochemical workstation. The back end of the device is connected to an online gas chromatograph (GC) for real-time analysis of the gas phase products. Preferably, the carbon dioxide gas flow rate is 10~30 mL / min, and the reaction potential is -0.6 V to -1.2 V (vs. RHE).

[0031] Preferably, at a potential of -1.1 V (vs. RHE), the ethylene Faradaic efficiency is not less than 75.8%, the total Faradaic efficiency of C2 products is not less than 82%, and the ethylene bias current density is not less than 235 mA cm⁻¹. -2 .

[0032] Preferably, the catalyst is at 350 mA cm⁻¹ -2 It can operate continuously and stably for more than 80 hours under high current density, and the ethylene Faraday efficiency remains above 70%.

[0033] The electrocatalytic carbon dioxide reduction system of the present invention includes the catalytic electrode, the electrolytic cell, the gas supply device, and the electrochemical workstation.

[0034] More preferably, the system further includes an online gas chromatograph and / or nuclear magnetic resonance spectrometer for real-time monitoring of reaction products.

[0035] Invention Mechanism:

[0036] This invention, by doping zinc into a cubic cuprous oxide lattice, has the following advantages:

[0037] (1) Extremely high ethylene selectivity and activity

[0038] Appropriate Zn doping significantly promotes the formation of oxygen vacancies in the Cu₂O lattice. Abundant oxygen vacancies enhance CO₂ activation and CC coupling. Therefore, appropriate Zn doping induces electron-deficient states at Cu sites, enhancing the adsorption capacity for the key intermediate *CO, while stabilizing the *CO adsorption configuration at bridge sites and significantly lowering the energy barrier of the CC coupling reaction. Furthermore, an appropriate amount of oxygen vacancies can modulate the electronic structure of adjacent Cu sites, optimizing the adsorption energy of the *CO intermediate; this is beneficial for stabilizing Cu… + Species, inhibiting its irreversible reduction to Cu 0 In a 0.1 MKHCO3 electrolyte, at a potential of -1.1 V (vs. RHE), the ethylene Faradaic efficiency reached 75.8%, the total Faradaic efficiency of C2 products reached 82%, and the ethylene bias current density reached 235 mA cm⁻¹.-2 .

[0039] (2) Excellent long-term operational stability

[0040] Zn doping effectively suppressed excessive reduction of Cu during the reaction process, maintaining the stability of the active sites. At 350 mA / cm², -2 At high current densities, this catalyst can operate stably for more than 80 hours, maintaining an ethylene Faraday efficiency of over 70%, far exceeding that of pure Cu2O catalysts (whose performance significantly declines within hours).

[0041] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The present invention improves the selectivity and stability of catalytic CO2 to ethylene production by doping zinc into the cuprous oxide lattice; (2) When the zinc doping amount is around 10.6 at%, in 0.1 MKHCO3 electrolyte, at a potential of -1.1 V (vs. RHE), the ethylene Faradaic efficiency is as high as 75.8%, the total Faradaic efficiency of C2 products is as high as 82%, and the ethylene bias current density reaches 235 mA cm⁻¹. -2 (3) The catalyst of this invention involves only three elements: Cu, Zn and O. It does not rely on precious metals or rare earth elements. Cu and Zn are both metal elements that are abundant in the earth's crust. They are inexpensive and have a stable supply. The catalyst has a simple composition, is environmentally friendly and has a low cost. (4) After long-term operation, the catalyst can be recycled after simple centrifugal washing and drying. The recovery rate is greater than 90%, which further reduces the overall cost of use and shows good prospects for industrial application. (5) The preparation method is simple and has industrial potential: The preparation method is based on conventional liquid phase reduction process. The raw materials are readily available, the conditions are mild, the controllability is strong, and it is easy to scale up production. (6) The preparation process does not use toxic or harmful reagents. The reaction byproducts are only sodium chloride and water. There is no need for complicated waste liquid treatment facilities. It can be completed in a conventional laboratory environment. (7) The catalyst of this invention exhibits high current density and excellent stability in the flow cell, indicating that it has the potential to be integrated into industrial electrolysis devices. Attached Figure Description

[0042] Figure 1 These are scanning electron microscope images from Embodiment 1 of the present invention;

[0043] Figure 2 These are scanning electron microscope images from Embodiment 2 of the present invention;

[0044] Figure 3 These are scanning electron microscope images from Embodiment 3 of the present invention;

[0045] Figure 4 This is a scanning electron microscope image of Comparative Example 1 of the present invention;

[0046] Figure 5 This is a scanning electron microscope image of Comparative Example 3 of the present invention;

[0047] Figure 6 The electron paramagnetic resonance (EPR) spectra of the catalysts in Examples 1-3 of this invention are shown below.

[0048] Figure 7 The nitrogen adsorption-desorption isotherms of the catalysts in Example 1 and Comparative Example 1 of this invention are shown below.

[0049] Figure 8 This is a comparison graph of the current density of C2H4 in the catalysts of Example 1 and Comparative Example 1.

[0050] Figure 9 The graph shows a comparison of the Faraday efficiency and partial current density of the electrocatalytic reduction of CO2 to C2H4 in Examples 1, 2, 3, and Comparative Example 1.

[0051] Figure 10 This is a graph showing the long-term stability test results for Example 1;

[0052] Figure 11 This is a comparison of the long-term stability of the two catalysts in Example 1 and Comparative Example 1 at -1.1 V vs. RHE potential.

[0053] Figure 12 The graph shows the performance test results of the electrode prepared by the catalyst in Example 1 at different potentials. Detailed Implementation

[0054] The technical solution of the present invention will be further described below with reference to the embodiments.

[0055] Example 1

[0056] The metal element-doped modified Cu₂O catalyst of the present invention contains 10.6 at% zinc doped into cuprous oxide (denoted as Cu₂O-Zn). 0.1 O x The preparation method includes the following steps:

[0057] (1) Dissolve 342 mg (0.2 mmol) CuCl2·2H2O and 3.6 g PVP (Mw=58000) in 200 mL of deionized water and stir until completely dissolved. While stirring continuously, add 20 mL of NaOH solution (0.2 M) dropwise to the above solution. The solution color turns dark red. Stir for 30 minutes to make the reaction uniform.

[0058] (2) Then add 50 mg (0.028 mmol) zinc sulfate monohydrate (ZnSO4·H2O) and stir well;

[0059] (3) Using a syringe pump, slowly add 20 mL of 0.2 M ascorbic acid solution at a rate of 2 mL / min. The solution turns into a turbid red color. Transfer the reaction solution to a 60℃ water bath and heat for 4 hours. After the reaction is complete, allow the mixture to cool naturally. Centrifuge at 8000 rpm to collect the product. Wash the product three times alternately with deionized water and anhydrous ethanol. Finally, dry the product in a 60℃ vacuum drying oven for 12 hours to obtain Cu2O-Zn. 0.1 O x catalyst.

[0060] Example 2

[0061] The metal element-doped modified Cu2O catalyst of the present invention contains 15.8 at% zinc doped into cuprous oxide (denoted as Cu2O-Zn). 0.2 O x The preparation method includes the following steps:

[0062] Based on Example 1, the amount of zinc sulfate monohydrate (ZnSO4·H2O) in step (2) was changed to 100 mg, while the other conditions remained unchanged to obtain Cu2O-Zn. 0.2 O x catalyst.

[0063] Example 3

[0064] The metal element-doped modified Cu2O catalyst of the present invention contains 26.4 at% zinc doped into cuprous oxide (denoted as Cu2O-Zn). 0.2 O x The preparation method includes the following steps:

[0065] Based on Example 1, the amount of zinc sulfate monohydrate (ZnSO4·H2O) in step (2) was changed to 200 mg, while the other conditions remained unchanged to obtain Cu2O-Zn. 0.2 O x catalyst.

[0066] Example 4

[0067] Based on Example 1, the mass of PVP was changed to 1.8 g, while the other conditions remained unchanged.

[0068] Example 5

[0069] Based on Example 1, the concentration of ascorbic acid solution was changed to 0.1 M, while other conditions remained unchanged.

[0070] Example 6

[0071] Based on Example 1, the concentration of the ascorbic acid solution was changed to 0.3 M, while the other conditions remained unchanged.

[0072] Comparative Example 1

[0073] Preparation of pure Cu₂O cubes:

[0074] 172 mg (1 mmol) CuCl₂·2H₂O and 1.8 g PVP (Mw=58000) were dissolved in 100 mL of deionized water and stirred until completely dissolved, yielding a clear, bright green solution. While stirring continuously, 10 mL of NaOH solution (0.2 M) was added dropwise to the above solution, causing the solution to turn a turbid blue-green, then a dark brown. The mixture was stirred for 30 minutes to ensure homogeneity. Then, 10 mL of ascorbic acid solution (0.2 M) was slowly added at a rate of 2 mL / min using a syringe pump, causing the solution to turn a turbid red. The reaction solution was transferred to a 55°C water bath and heated for 3 hours. After the reaction was complete, the mixture was allowed to cool naturally, and the resulting orange-red solid was collected by centrifugation at 8000 rpm. The solid was washed three times alternately with deionized water and anhydrous ethanol, and finally dried in a vacuum drying oven at 60°C for 12 hours to obtain pure Cu₂O cubic powder.

[0075] Comparative Example 2

[0076] Based on Example 1, the zinc sulfate monohydrate (ZnSO4·H2O) in step (2) was changed to 25 mg, while the other conditions remained unchanged.

[0077] Comparative Example 3

[0078] Based on Example 1, the mass of PVP was changed to 0 g, while all other conditions remained unchanged.

[0079] Structural characterization

[0080] The catalyst morphologies of Examples 1-4, Comparative Examples 1 and 3 were characterized, and the results are as follows: Figures 1-5 As shown.

[0081] Depend on Figure 1 It can be seen that the catalyst prepared in Example 1 has a regular cubic morphology and a particle size of 300-500 nm.

[0082] Depend on Figure 2 As can be seen, the catalyst prepared in Example 2 has an irregular morphology.

[0083] Depend on Figure 3 As can be seen, the catalyst prepared in Example 3 has an irregular morphology.

[0084] Examples 2 and 3 are due to excessive Zn 2+ Not all Zn can enter the Cu2O lattice, and some Zn... 2+The ZnO or Zn(OH)2 precipitates on the surface, forming an amorphous or nanoparticle-like second phase, which disrupts the regular growth of the Cu2O cubic crystal planes; secondly, Zn 2+ With Cu + Differences in ionic radius and charge lead to increased lattice stress, inducing crystal plane distortion and increased defects, reducing the anisotropic growth capability of the crystal, and thus resulting in an irregular cubic structure.

[0085] Depend on Figure 4 It can be seen that the pure Cu2O prepared in Comparative Example 1 has a spherical morphology.

[0086] Depend on Figure 5 It can be seen that the catalyst prepared in Comparative Example 3 exhibits an irregular morphology. This is because when the system does not contain PVP, the selective adsorption of crystal faces disappears, the growth rate of each crystal face tends to be uniform, and the product tends to have a thermodynamically stable polyhedral morphology. At the same time, due to the lack of steric hindrance effect of PVP, the nanoparticles are prone to agglomeration during nucleation and growth, making it difficult to form a cubic structure with uniform size and good dispersion.

[0087] The Zn doping content in the catalysts prepared in Examples 1-6 and Comparative Examples 2-3 was tested. The zinc contents of Examples 1-6 and Comparative Examples 2-3 were 10.6%, 15.8%, 26.4%, 10.6%, 10.6%, 10.6%, 0%, and 10.6%, respectively. No Zn doping was detected in Comparative Example 2, possibly because the amount of hydrated zinc sulfate added was too low, resulting in an insufficient absolute concentration of Zn in the synthesis system to achieve effective doping in the Cu₂O lattice. 2+ When the concentration is below the critical threshold for lattice doping, Zn 2+ Cannot replace Cu + Instead of entering the Cu₂O lattice, PVP exists as a surface adsorption or impurity in extremely low concentrations, making it difficult to form stable Zn-O-Cu structural units. Examples 1, 4, and Comparative Example 3 demonstrate that PVP does not affect the zinc doping level. Examples 1 and 5-6 demonstrate that the concentration of ascorbic acid solution does not affect the zinc doping level.

[0088] The electron paramagnetic resonance spectra of the catalysts in Examples 1-3 and Comparative Example 1 are as follows: Figure 6 As shown in the figure, the signal intensity of the catalysts in Examples 1-3 at g=2.003 is significantly higher than that of pure Cu2O, indicating that the catalysts in Examples 1-3 have more oxygen vacancies. Oxygen vacancies have multiple beneficial effects: they can serve as activation sites for CO2 molecules, lowering the conversion energy barrier from CO2 to *COOH; they can regulate the electronic structure of adjacent Cu sites, optimizing the adsorption energy of the *CO intermediate; and they are beneficial for stabilizing Cu. + Species, inhibiting its irreversible reduction to Cu 0It is noteworthy that there is a linear decreasing relationship between oxygen vacancy concentration and ZnO doping amount, as observed in the Cu2O-Zn catalyst of Example 1. 0.1 O x It has the highest oxygen vacancy concentration, and excessive doping will inhibit oxygen vacancy formation due to excessive lattice distortion.

[0089] The nitrogen adsorption-desorption isotherms of the catalysts in Example 1 and Comparative Example 1 are shown below. Figure 7 As shown in the figure, it can be seen from the entire relative pressure range that Cu2O-Zn 0.1 O x The nitrogen adsorption capacity of (Example 1) was significantly higher than that of pure Cu2O (Comparative Example 1), indicating that appropriate Zn doping effectively increased the specific surface area of ​​the catalyst. A higher specific surface area facilitates the exposure of more active sites, promoting CO2 adsorption and mass transfer of reaction intermediates, which is beneficial for Cu2O-Zn catalysts. 0.1 O x An important structural basis for achieving excellent ethylene selectivity.

[0090] The comparison graph of the current density of C2H4 in the catalysts of Example 1 and Comparative Example 1 is shown in the figure. Figure 8 As shown in the figure, it can be seen from the entire test potential range that Cu2O-Zn 0.1 O x The current densities of the two samples were significantly higher than those of pure Cu₂O, and the onset potential was more positive, indicating that appropriate Zn doping effectively reduced the overpotential of CO₂ reduction and promoted reaction kinetics. This electrochemical activity advantage is characteristic of Cu₂O-Zn. 0.1 O x This is an important prerequisite for achieving high ethylene selectivity and high bias current density.

[0091] Example 7

[0092] Preparation of the catalytic electrode: 3 mg of catalyst powder from Examples 1-6, Comparative Examples 1 and 3 were mixed with 500 μL of anhydrous ethanol and 30 μL of 5 wt% Nafion solution, respectively. The mixtures were sonicated for at least 30 minutes to form a uniform catalyst ink. The ink was uniformly coated onto pre-treated 1 cm x 1 cm carbon paper (YLS-30T) using a micropipette, controlling the catalyst loading to be approximately 1 mg / cm². 2 The coated electrode was allowed to air dry overnight at room temperature to obtain the working electrode.

[0093] Example 8

[0094] Electrocatalytic CO2 reduction performance test:

[0095] Electrochemical tests were performed in an H-type electrolytic cell or a self-assembled flow cell. The electrode prepared in Example 7 was used as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode (all potentials were converted to reversible hydrogen electrode, RHE). The cathode and anode chambers were separated by an anion exchange membrane, and the electrolyte was 30 mL of 0.1 MkHCO3 solution. High-purity CO2 gas was continuously introduced into the cathode chamber at a flow rate of 30 sccm. Potentiostatic measurements were performed using an electrochemical workstation (CHI760E), with a potential range of -0.6 V to -1.2 V (vs. RHE). Gas phase products were analyzed by automated online gas chromatography (GC-2014C, Shimadzu) every 25 minutes, and liquid phase products were analyzed by 1H NMR after the reaction. The test results are as follows: Figure 9 As shown.

[0096] Depend on Figure 9 It was found that the ethylene Faradaic efficiency of the pure Cu2O cube in Comparative Example 1 was 32.2%, the total Faradaic efficiency of the C2 products (C2H4, C2H5OH, CH3COOH) was 48.1%, and the ethylene partial current density was 50 mA cm⁻¹. -2 In Example 1, the catalyst exhibited an ethylene Faradaic efficiency of 75.8%, a total Faradaic efficiency of 82% for C2 products (C2H4, C2H5OH, CH3COOH), and an ethylene partial current density of 285 mA cm⁻¹. -2 In Example 2, the catalyst exhibited an ethylene Faradaic efficiency of 56.8%, a total Faradaic efficiency of 69.1% for C2 products (C2H4, C2H5OH, CH3COOH), and an ethylene bias current density of 145 mA cm⁻¹. -2 In Example 3, the catalyst exhibited an ethylene Faradaic efficiency of 36.7%, a total Faradaic efficiency of 51.5% for C2 products (C2H4, C2H5OH, CH3COOH), and an ethylene bias current density of 190 mA cm⁻¹. -2 In Examples 1-3, the ethylene Faradaic efficiencies of the zinc-doped catalysts were all higher than those of pure Cu₂O in Comparative Example 1. As the Zn doping amount increased, the ethylene Faradaic efficiency gradually decreased, and the performance was optimal when the Zn doping amount was 10.6 at%.

[0097] Depend on Figure 9 It was found that the ethylene Faradaic efficiency of the catalyst in Example 4 was 58.6%, the total Faradaic efficiency of the C2 products (C2H4, C2H5OH, CH3COOH) was 65.3%, and the ethylene bias current density was 180 mA cm⁻¹. -2 The catalyst in Comparative Example 3 exhibited an ethylene Faradaic efficiency of 45.6%, a total Faradaic efficiency of 57.3% for C2 products (C2H4, C2H5OH, CH3COOH), and an ethylene bias current density of 165 mA cm⁻¹. -2The data from Example 1 show that different amounts of PVP significantly affect the morphology, structure, and catalytic performance of the C catalyst. The amide groups and carbonyl oxygen atoms on the PVP molecular chain can react with Cu... 2+ and Zn 2+ PVP interacts with Cu₂O crystals, regulating the release rate of metal ions and thus controlling the formation and growth kinetics of crystal nuclei. Simultaneously, PVP selectively adsorbs onto specific crystal faces of Cu₂O, inhibiting the rapid growth of certain facets through steric hindrance and inducing the formation of a regular cubic morphology. Furthermore, the steric hindrance effect of PVP effectively prevents nanoparticle aggregation, ensuring uniform Zn doping within the Cu₂O lattice, avoiding localized ZnO phase separation, and maximizing the exposure of catalytic active sites. Therefore, the amount of PVP added is a key factor in achieving catalyst morphology control, structural optimization, and performance improvement.

[0098] Depend on Figure 9 It was found that the ethylene Faradaic efficiency of the catalyst in Example 5 was 56.7%, the total Faradaic efficiency of C2 products (C2H4, C2H5OH, CH3COOH) was 64.8%, and the ethylene bias current density was 185 mA cm⁻¹. -2 In Example 6, the catalyst exhibited an ethylene Faradaic efficiency of 50.8%, a total Faradaic efficiency of 62.7% for C2 products (C2H4, C2H5OH, CH3COOH), and an ethylene bias current density of 175 mA cm⁻¹. -2 The data from Example 1 show that different concentrations of the reducing agent ascorbic acid significantly affect the crystal growth, morphology, and electrocatalytic performance of the catalyst. Ascorbic acid, as a reducing agent, determines the concentration of Cu... 2+ Reduced to Cu + The reduction rate, and consequently the nucleation and growth process of Cu₂O crystal nuclei, are influenced by the ascorbic acid concentration. When the ascorbic acid concentration is moderate, the reduction rate and nucleation rate are optimally matched, which is beneficial for forming uniformly sized and regularly morphologically regular Cu₂O nanocubes and ensuring uniform Zn doping into the crystal lattice. If the ascorbic acid concentration is too low, the reduction rate is slow, and Cu₂O nuclei will not form uniformly. + Insufficient supply leads to incomplete crystal nucleus formation, resulting in low crystallinity and irregular morphology of the product. If the ascorbic acid concentration is too high, the reduction rate is too fast, causing a large number of crystal nuclei to form and grow rapidly, easily leading to uneven particle size and increased agglomeration. Simultaneously, the excessively rapid reduction process may inhibit effective Zn doping. Therefore, the ascorbic acid concentration is a key parameter for controlling the crystal structure, morphological regularity, and Zn doping uniformity of the catalyst; an appropriate concentration is a prerequisite for achieving excellent catalytic performance.

[0099] Example 9

[0100] Long-term stability testing:

[0101] In the flow cell system described in Example 8, Cu2O-Zn is used. 0.1 O x The electrode (the electrode prepared from the catalyst in Example 1) was used as the working electrode at 350 mA cm⁻¹. -2 Continuous electrolysis tests were conducted at a constant current density, and the products were continuously monitored online by GC. The results are as follows: Figures 10-11 As shown.

[0102] Depend on Figure 10 and 11 It can be seen that after 80 hours of continuous operation, the ethylene Faraday efficiency of the catalyst electrode in Example 1 remained above 70%, and the electrode structure remained intact. In contrast, the performance of the pure Cu2O electrode showed a significant decline after only 8 hours of operation under the same conditions.

[0103] Example 10

[0104] Effect of different potentials on product selectivity

[0105] The Cu2O-Zn prepared in Example 1 0.1 O x The catalyst was used to prepare the electrode according to the method in Example 7, and tested at different potentials (-0.6 V to -1.2 V vs. RHE) according to the method in Example 8. The results are as follows. Figure 12 As shown.

[0106] Depend on Figure 12 It can be seen that the ethylene Faradaic efficiency reaches its peak (75.8%) at -1.1V vs. RHE potential, and the ratio of C2 product Faradaic efficiency to C1 product Faradaic efficiency reaches its maximum at this potential. At excessively positive potentials, CO2 activation is insufficient, while at excessively negative potentials, the increased proton supply rate leads to intensified deep hydrogenation and hydrogen evolution reactions.

[0107] The above examples fully demonstrate that the ZnO-doped cuprous oxide catalyst provided by the present invention, by precisely controlling the Zn doping amount to the optimal level of 10.6 at%, exhibits extremely high selectivity, activity, and stability in the electrocatalytic reduction of CO2 to ethylene, showing great application potential.

Claims

1. A metal element-doped modified Cu2O catalyst, characterized in that, The modified Cu2O catalyst uses Cu2O as a substrate, with Zn doped in the Cu2O lattice in an atomically dispersed form to form a Zn-O-Cu dual-site synergistic structure; wherein the doping amount of Zn is from 10.6 at% to 26.4 at%.

2. The metal element-doped modified Cu2O catalyst according to claim 1, characterized in that, The Cu2O has a cubic structure with an average particle size of 200-500 nm.

3. A method for preparing a metal element-doped modified Cu₂O catalyst according to any one of claims 1 or 2, characterized in that, Includes the following steps: (1) Dissolve soluble copper salt and polyvinylpyrrolidone in water, then adjust the pH of the system to form a blue-green suspension. Continue the reaction, and the solution color changes from blue-green to dark brown. (2) Add soluble zinc salt to the suspension obtained in step (1) and mix well; (3) Add a reducing agent to the suspension obtained in step (2) and react in a water bath at 50-80℃ for 2-6 hours. After the reaction, separate the product, wash and dry it to obtain a Zn-doped cuprous oxide catalyst.

4. The method for preparing the metal element-doped modified Cu2O catalyst according to claim 3, characterized in that, The reducing agent is ascorbic acid or glucose, the molar ratio of soluble copper salt to reducing agent is 1:40-80, and the concentration of reducing agent is 0.1-0.3 M.

5. The method for preparing the metal element-doped modified Cu2O catalyst according to claim 3, characterized in that, In step (1), the concentration of the soluble copper salt is 0.5-5 mM.

6. The method for preparing the metal element-doped modified Cu2O catalyst according to claim 5, characterized in that, The concentration of the soluble zinc salt is 0.13-0.51 mM.

7. The method for preparing the metal element-doped modified Cu2O catalyst according to claim 3, characterized in that, The pH is 9.0-11.

0.

8. The method for preparing the metal element-doped modified Cu2O catalyst according to claim 3, characterized in that, In step (1), the molar mass ratio of the soluble copper salt and polyvinylpyrrolidone added is 1 mmol: 9-18 g.

9. An electrode, characterized in that, The catalyst containing the metal element doping modified Cu2O as described in claim 1 or 2.

10. The application of a metal element-doped modified Cu2O catalyst according to claim 1 or 2 or the electrode according to claim 9 in the selective electrocatalytic production of ethylene from carbon dioxide.

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