Amino acid modified copper-based catalysts, methods of making and using the same

Abstract

The application belongs to the technical field of electrocatalytic materials and carbon dioxide emission reduction resource utilization, and particularly relates to an amino acid modified copper-based catalyst and a preparation method and application thereof. The catalyst is prepared by modifying the surface of cuprous oxide with rhombic section half cubic morphology with L-cysteine to form a composite structure with a special interface microenvironment. The sulfhydryl in L-cysteine can form a strong coordination with copper species on the surface of cuprous oxide, promote water decomposition and CO protonation, stabilize the surface structure, and be beneficial to asymmetric coupling, and the amino group can provide an electron-rich environment to strengthen the capture of carbon dioxide, and synergistically regulate the selectivity and stability of electrocatalytic carbon dioxide reduction to ethylene.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electrocatalytic materials and carbon dioxide emission reduction and resource utilization, and particularly relates to an amino acid modified copper-based catalyst for electrocatalytic reduction of carbon dioxide to ethylene as well as a preparation method and application thereof. BACKGROUND

[0002] The rapid development of modern industrial level and the continuous acceleration of global industrialization process cannot be separated from huge fossil energy consumption, and the concentration of carbon dioxide (CO2) emitted into the atmosphere by burning fossil energy is also rising day by day, which has caused the greenhouse effect to become a global challenge. CO2 is a cheap, non-toxic and abundant carbon resource, and its conversion into valuable chemicals has dual significance of rational utilization of carbon resources and environmental protection. Therefore, it is also a top priority to develop efficient carbon capture, utilization and storage technology. Among various carbon capture and utilization technologies, electrocatalytic carbon dioxide reduction reaction (CO2RR) technology can utilize the electric energy generated by renewable energy sources such as wind energy or solar energy to drive the conversion of CO2 into formic acid (HCOOH), ethylene (C2H4) and other high economic value products under relatively mild reaction conditions, realize the resource utilization of CO2, and store intermittent electric energy in the form of chemical energy, which is a clean and energy-saving green and sustainable technology path.

[0003] Among various electrocatalyst materials known at present, copper (Cu) based catalysts are widely concerned because they can efficiently reduce CO2 to multi-carbon products. Among them, copper oxides such as cuprous oxide (Cu2O) are widely studied because of their low cost, wide source and certain catalytic activity for CO2 reduction. Generally speaking, the morphology and surface chemical state of the catalyst play a crucial role in its catalytic activity and selectivity. In the process of electrocatalytic reduction of CO2, Cu2O will be reduced to metallic Cu in situ, and its initial morphology and structure are difficult to maintain, resulting in poor stability of the catalyst and undesirable product selectivity.

[0004] Therefore, it is of great significance to develop a Cu-based electrocatalyst with high stability and effective product selectivity. SUMMARY

[0005] The present application aims to overcome the deficiencies of the prior art, and provides an amino acid modified copper-based catalyst with unique morphology, high stability and high selectivity, which uses amino acid as a surface modifier to modify Cu2O, regulates the surface electronic structure, improves the capture and adsorption of CO2, and realizes the high selectivity of C2H4 generation.

[0006] To achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0007] In a first aspect, the present application provides an amino acid modified copper-based catalyst, which is composed of Cu2O with cubic or rhombic truncated cubic morphology and natural amino acid modified on the surface of Cu2O.

[0008] Preferably, the natural amino acid is L-cysteine, glycine or lysine.

[0009] Preferably, the natural amino acid is L-cysteine. L-cysteine (L-cys) is a natural amino acid containing sulfhydryl (-SH) and amino (-NH2), which has strong interaction between sulfhydryl and Cu species, can be used as a surface modifier to stabilize nanoparticles and regulate the surface electronic structure, and the amino functional group can provide an electron-rich environment to promote the adsorption and activation of CO2, which is beneficial to the capture of CO2.

[0010] In a second aspect, the present application provides a preparation method of an amino acid modified copper-based catalyst, which comprises adding amino acid into cuprous oxide suspension with rhombic truncated cubic morphology, allowing the amino acid to fully modify the surface of cuprous oxide, and collecting the product after reaction, thereby obtaining the amino acid modified copper-based catalyst.

[0011] Preferably, the preparation method of cuprous oxide suspension with rhombic truncated cubic morphology comprises adding alkaline solution into copper salt solution, adjusting the pH value of the reaction system to 9.0-11.0 to obtain a mixed solution, and adding reducing agent into the mixed solution and stirring to obtain cuprous oxide suspension.

[0012] Preferably, the copper salt is copper sulfate pentahydrate, copper chloride dihydrate or copper nitrate.

[0013] Preferably, the alkaline solution is sodium hydroxide solution with a concentration of 0.1-0.5M.

[0014] Preferably, the reducing agent is glucose or ascorbic acid solution.

[0015] Preferably, the basic solution is added to the copper salt solution, and the reaction is carried out at a stirring speed of 400-800 rpm, and the pH value of the reaction system is adjusted to 9.0-11.0 to obtain a mixed solution; the reducing agent is added to the mixed solution, and the reaction is carried out at a stirring speed of 400-800 rpm to obtain a cuprous oxide suspension.

[0016] Preferably, the basic solution is added to the copper salt solution at a speed of 2-6 ml / min, the reaction is carried out at a stirring speed of 400-800 rpm, and the pH value of the reaction system is adjusted to 9.0-11.0 to obtain a mixed solution; the reducing agent is added to the mixed solution at a speed of 2-4 ml / min, and the reaction is carried out at a stirring speed of 500-1000 rpm to obtain a cuprous oxide suspension.

[0017] Preferably, the amino acid is L-cysteine, glycine or lysine, and the loading mode of the amino acid on the surface of the cuprous oxide is ultrasonic normal temperature stirring, oil bath heating stirring or hydrothermal loading.

[0018] Preferably, the molar ratio of the copper salt to the amino acid is 5-20:1. More preferably, the molar ratio of the copper salt to the amino acid is 5-10:1.

[0019] As a preferred embodiment, the present application provides an amino acid modified Cu-based catalyst for electrocatalytic conversion of CO2 to C2H4, and a preparation method of the catalyst is as follows:

[0020] (1) A soluble copper salt is dissolved in deionized water to form a divalent copper solution under stirring;

[0021] (2) A basic solution is added dropwise to the divalent copper solution in step (1) to react under stirring, and the pH value of the reaction system is adjusted to obtain a mixed solution;

[0022] (3) A reducing agent is added dropwise to the mixed solution in step (2) to react under stirring, and the divalent copper is reduced to monovalent copper to obtain an orange yellow Cu2O suspension. The stirring is continued until the color of the solution no longer changes obviously, and it is ensured that the reaction is fully carried out;

[0023] (4) An amino acid is added to the Cu2O suspension obtained in step (3) to disperse under ultrasonic and react under stirring, so that the amino acid is fully modified on the surface of the Cu2O. The reaction is completed to obtain a product;

[0024] (5) The product after the reaction in step (4) is subjected to centrifugal separation, washing and drying to obtain an amino acid modified Cu-based catalyst.

[0025] Preferably, in step (1), the soluble copper salt is copper sulfate pentahydrate, copper chloride dihydrate or copper nitrate, and the solution concentration is 0.5-5 mM.

[0026] Preferably, in step (2), the alkaline solution is sodium hydroxide solution with a concentration of 0.1-0.5M, and is added at a speed of 2-6ml / min using a syringe pump, the pH value of the reaction system is adjusted to 9.0-11.0, and the stirring speed is 400-800rpm at room temperature.

[0027] Preferably, in step (3), the reducing agent is a reducing agent such as glucose or ascorbic acid solution, and the molar ratio of copper salt to reducing agent is 1:(1-4); the reducing agent is added at a speed of 2-4ml / min using a syringe pump, and the stirring speed is 600-1000rpm at a temperature of 25-60℃ for 1-3h.

[0028] Preferably, in step (4), the amino acid is L-cys, glycine (Gly) or lysine (Lys), and the molar ratio to the soluble copper salt in step (1) is (1-10):20; the ultrasonic time is 30-60min, the stirring speed is 500-1000rpm, and the reaction is carried out at room temperature for 1-3h.

[0029] Preferably, in step (5), the centrifugal speed is 5000-10000rpm; the impurities are removed by washing with ethanol and deionized water for 3 times respectively; and the drying is vacuum drying in a vacuum drying oven for 4-12h at a temperature of 50-80℃.

[0030] In a third aspect, the present application provides a use of the above-mentioned catalyst in preparing an electrode for electrocatalytic conversion of carbon dioxide to ethylene.

[0031] The amino acid-modified copper-based catalyst is mixed with a perfluorosulfonic acid type polymer to prepare catalyst ink; the catalyst ink is coated on the surface of an electrode substrate to obtain a copper-based catalytic electrode.

[0032] In a fourth aspect, the present application provides a method for electrocatalytic conversion of carbon dioxide to ethylene, wherein the above-mentioned catalyst is mixed with a perfluorosulfonic acid type polymer to prepare catalyst ink; the catalyst ink is coated on the surface of an electrode substrate to obtain a copper-based catalytic electrode; the copper-based catalytic electrode is used as a working electrode, a platinum mesh or a platinum sheet is used as a counter electrode, and a silver-silver chloride electrode or a saturated calomel electrode is used as a reference electrode to form a three-electrode system, and carbon dioxide is reduced to obtain ethylene.

[0033] As a preferred embodiment, the present application provides a use of a Cu-based catalyst for electro-reduction of CO2 to C2H4. The aforementioned amino acid-modified copper-based catalyst, i.e., amino acid-modified Cu2O catalyst particles, are uniformly dispersed in an appropriate amount of ethanol, and an appropriate amount of Nafion (perfluorosulfonic acid type polymer) is added to prepare catalyst ink. After ultrasonic dispersion, the catalyst ink is drop-coated on the surface of an electrode substrate until the catalyst loading reaches 0.5-3mg / cm 2The Cu-based catalyst electrode is made into a working electrode, a platinum mesh, a platinum sheet or the like is used as a counter electrode, a silver-silver chloride electrode, a saturated calomel electrode or the like is used as a reference electrode, a three-electrode system is formed, a negative potential is applied through an electrochemical workstation, and CO2 is reduced and converted into HCOOH, C2H4 or the like in an H cell or a flow cell with an acidic, neutral or alkaline solution as an electrolyte.

[0034] Preferably, the catalyst loading is 0.6-2 mg / cm 2 .

[0035] Preferably, the electrode substrate is a carbon cloth, a carbon paper, a gas working electrode or the like.

[0036] Preferably, a flow cell electrolysis cell is used in the CO2 electro-reduction conversion system, a platinum mesh is used as a counter electrode, a silver-silver chloride electrode is used as a reference electrode, a 0.1-1 M neutral potassium bicarbonate (KHCO3) solution or an alkaline potassium hydroxide (KOH) solution is used as an electrolyte in a cathode chamber and an anode chamber, a proton exchange membrane (PEM) or an anion exchange membrane (AEM) is used to isolate the cathode chamber and the anode chamber, high-purity CO2 gas is continuously introduced, the gas flow rate is controlled at 10-40 mL / min, the gas-liquid contact is realized through a peristaltic pump, the electro-catalytic CO2 reduction reaction is carried out in a constant potential or constant current mode through an electrochemical workstation, and an online gas chromatograph (GC) is connected at the rear end of the device to support the analysis of gaseous products. Under suitable potential or current conditions, the Cu-based catalyst can efficiently reduce CO2 into C2H4.

[0037] Principle: The present application modifies the surface of cuprous oxide with an orthorhombic truncated cubic morphology by L-cysteine, forming a composite structure with a special interface microenvironment. The thiol group in L-cysteine can form a strong coordination with the copper species on the surface of cuprous oxide, promoting water decomposition and CO protonation, stabilizing the surface structure, and facilitating asymmetric coupling. Meanwhile, the amino group can provide an electron-rich environment, strengthening the capture of carbon dioxide, and synergistically regulating the selectivity and stability of electrocatalytic reduction of carbon dioxide to ethylene.

[0038] Advantages: Compared with the prior art, the present application has the following remarkable advantages:

[0039] 1. High ethylene selectivity: The present application uses amino acid modified Cu-based catalysts, regulates the feedstock input ratio, regulates the rotation speed at different nucleation stages, and regulates the feed speed to obtain special orthorhombic truncated cubic structure Cu2O. L-cys in the amino acid provides an electron-rich environment through the amino group, promotes the adsorption and activation of CO2, captures CO2, and at the same time, the strong coordination of its sulfhydryl group with the copper species on the surface of Cu2O forms Cu-S to promote water decomposition and CO protonation, which is beneficial to subsequent asymmetric coupling and synergistically catalyzes the reduction of CO2 to C2H4. The catalyst exhibits high C2H4 Faraday efficiency in neutral or alkaline electrolyte, which can reach more than 60%, which is better than traditional Cu-based catalysts.

[0040] 2. Long-term stability: In the present application, L-cys is used to modify Cu2O, which stabilizes the orthorhombic truncated cubic structure through strong coordination of Cu-S, and can still maintain high C2H4 Faraday efficiency in a test lasting up to 50h, which is better than the orthorhombic truncated cubic Cu2O without L-cys modification.

[0041] 3. High industrialization potential: The L-cys modified orthorhombic truncated cubic Cu2O catalyst in the present application can achieve high C2H4 selectivity under industrial current density (>-0.25 A / cm 2 ) in a flow cell, and has the potential for industrial scale application. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The scanning electron microscope pictures of the present application Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 1; wherein (a) is B-C-Cu2O, (b) is B-GR-Cu2O, (c) is L-S-Cu2O, and (d) is L-GR-Cu2O;

[0043] Figure 2 The Faraday efficiency comparison of Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 1 for electrocatalytic reduction of CO2 to C2H4 under a current density of-250 mA / cm²;

[0044] Figure 3 The Faraday efficiency comparison of three electrodes of different amino acid types in Example 3 for electrocatalytic reduction of CO2 to C2H4 under a current density of-200 mA / cm²;

[0045] Figure 4 The Faraday efficiency comparison of three electrodes with different segmented reaction speeds of 400 / 600, 500 / 700, and 800 / 1000 rpm in Example 2 for electrocatalytic reduction of CO2 to C2H4 under a current density of-200 mA / cm²;

[0046] Figure 5Comparison of selectivity of three electrodes in different loading modes of L-cys in Example 4 for electrocatalytic reduction of CO2 to C2H4 at a potential of -1.2 V vs. RHE;

[0047] Figure 6 Comparison of selectivity of three electrodes in Example 5 for electrocatalytic reduction of CO2 to C2H4 at a potential of -1.2 V vs. RHE when the molar ratio of Cu2O:L-cys is 20:1, 10:1 and 5:1;

[0048] Figure 7 Comparison of long-term stability of L-cys modified Cu2O catalysts in different ratios in Example 1, Example 5, Comparative Example 1 and Comparative Example 2 at a potential of -1.2 V vs. RHE. DETAILED DESCRIPTION

[0049] The technical solutions of the present application are further described below by specific examples, and the protection scope of the present application includes the following examples but is not limited to the following examples, and any variation related to the present application is within the protection scope.

[0050] The drugs used in the following examples and comparative examples are all conventional commercially available drugs. In the following examples, the L-cys modified rhombic truncated cube Cu2O, the rhombic truncated cube Cu2O modified by different types of amino acids, the L-cys modified Cu2O, the rhombic truncated cube Cu2O with different L-cys loading modes, and the rhombic truncated cube Cu2O modified by L-cys in different ratios are all amino acid modified copper-based catalysts of the present application.

[0051] Example 1

[0052] This example provides a preparation method of an L-cys modified rhombic truncated cube Cu2O electrode:

[0053] (1-1) Dissolve 2 mmol of copper chloride dihydrate in 500 ml of deionized water, stir until uniform, and the solution is light blue;

[0054] (1-2) Use a syringe pump to add 30 ml of 0.3 M sodium hydroxide solution at a uniform speed of 3 ml / min, adjust the pH value of the reaction system to about 9.5, generate a light blue flocculent precipitate, and control the rotation speed to be maintained at 500 rpm, and carry out the reaction at room temperature;

[0055] (1-3) Use a syringe pump to add 20 ml of 0.2 M ascorbic acid solution at a uniform speed of 2 ml / min, reduce the divalent copper to monovalent copper, the solution color changes to orange yellow or brown yellow, control the rotation speed to be maintained at 700 rpm, and carry out the reaction at a temperature of 50°C for 1 h;

[0056] (1-4) The mixed solution after the reaction is cooled to room temperature, 0.2 mmol of L-cys powder is added, ultrasonic dispersion is carried out at a power of 40 W for 30 min, and then reaction is carried out at room temperature for 2 h under stirring, so that the L-cys is fully modified on the Cu2O particles;

[0057] (1-5) The solid product after the reaction is completed is centrifuged at a speed of 8000 rpm, washed with ethanol and deionized water respectively for 3 times to remove impurities, and placed in a vacuum drying box for drying at 60℃ for 12 h, to obtain the L-cys modified rhombic truncated cubic Cu2O particles, which are amino acid modified copper-based catalysts;

[0058] (1-6) 100 mg of the L-cys modified rhombic truncated cubic Cu2O particles are dispersed in 4 ml of ethanol, 100 microliters of Nafion are added to prepare catalyst ink, the prepared catalyst ink is ultrasonic dispersed for 1 h, and then dropped and coated on a gas diffusion electrode with an area of 1.5 x 1.5 cm 2 , so that the catalyst loading weight is 1.0 mg / cm 2 , to obtain the L-cys modified rhombic truncated cubic Cu2O electrode, which is recorded as L-GR-Cu2O.

[0059] Comparative Example 1

[0060] The present comparative example provides a preparation of a cubic Cu2O catalyst electrode without amino acid modification:

[0061] (2-1) 1 mmol of copper acetate is dissolved in 500 ml of deionized water, and stirred uniformly, and the solution is light blue;

[0062] (2-2) 30 ml of 0.3M sodium hydroxide solution is added dropwise, a light blue flocculent precipitate is formed, the speed is controlled to be kept at 500 rpm, and the reaction is carried out at room temperature;

[0063] (2-3) 20 ml of 0.2M ascorbic acid solution is added dropwise within 10 min, the divalent copper is reduced to monovalent copper, the solution color changes to brown yellow, and the reaction is carried out at room temperature for 3 h;

[0064] (2-4) The solid product after the reaction is completed is centrifuged at a speed of 8000 rpm, washed with ethanol and deionized water respectively for 3 times to remove impurities, and placed in a vacuum drying box for drying at 60℃ for 12 h, to obtain cubic Cu2O particles;

[0065] (2-5) 50 mg of the cubic Cu2O particles are dispersed in 2 ml of ethanol, 50 microliters of Nafion are added to prepare catalyst ink, the catalyst ink is ultrasonic dispersed for 1 h, and then dropped and coated on a gas diffusion electrode with an area of 1.5 x 1.5 cm 2On the gas diffusion electrode, the catalyst loading weight is 1.0 mg / cm³. 2 A cubic Cu2O particle electrode without amino acid modification was obtained, denoted as BC-Cu2O.

[0066] Comparative Example 2

[0067] This comparative example provides the preparation of an orthorhombic semi-cubic Cu2O catalyst electrode without amino acid modification:

[0068] The specific method is the same as steps (1-1) to (1-3) in Example 1, without subsequent L-cys modification. The dried rhombic semi-cubic Cu2O particles are ground, 50 mg is taken, dispersed in 2 ml of ethanol, 50 μL of Nafion is added, and the mixture is sonicated for 1 h to prepare catalyst ink. 92.2 μL of catalyst ink is then drop-coated onto an area of ​​1.5 x 1.5 cm using a pipette. 2 On the gas diffusion electrode, the catalyst loading weight is 1.0 mg / cm³. 2 An unmodified rhombic semi-cubic Cu2O electrode, denoted as B-GR-Cu2O, was obtained.

[0069] Comparative Example 3

[0070] This comparative example provides the preparation of an L-cys-modified spherical Cu2O electrode:

[0071] (3-1) Dissolve 1 mmol of copper acetate in 100 ml of deionized water, stir well, add to a three-necked flask placed in a water bath, place a rotor, connect the inlet to nitrogen gas, connect the outlet to a bubbler to pass through the waste liquid bottle, seal the main port with a rubber stopper, turn on the nitrogen switch, adjust the flow rate and bubble for 10 minutes to displace the air in the container and form nitrogen protection, set the speed to 500 rpm;

[0072] (3-2) Dissolve 3.4g of sodium hydroxide in 20ml of deoxygenated water (pre-bubbled with nitrogen to remove deionized water). Add the prepared solution to a three-necked flask using a syringe, heat to 60℃ and react for 10min. A yellow-brown precipitate will gradually form.

[0073] (3-2) Dissolve 0.54g of glucose in 30ml of deoxygenated water (purged with nitrogen), add the prepared solution to a three-necked flask using a syringe, and react for 30min. The precipitate changes from yellow-brown to dark brown.

[0074] (3-3) Dissolve 0.2 mmol of L-cys powder in 20 ml of deoxygenated water and add it to a three-necked flask using a syringe. Stir and react for 3 h to modify the surface of Cu2O with L-cys.

[0075] (3-4) After the reaction is completed, stop heating, and after the mixed solution is cooled to room temperature, perform suction filtration under continuous nitrogen purging to obtain a solid product, which is placed in a vacuum drying box for drying at 60°C for 12h to obtain L-cys-modified spherical Cu2O particles;

[0076] (3-5) Take 50mg of L-cys-modified spherical Cu2O particles, disperse them in 2ml of ethanol, add 50 microliters of Nafion to prepare a catalyst ink, ultrasonically disperse the prepared catalyst ink for 1h, and then drop coat it on a gas diffusion electrode with an area of 1.5x1.5cm 2 , so that the catalyst loading weight is 1.0mg / cm 2 , to obtain an L-cys-modified spherical Cu2O electrode, which is denoted as L-S-Cu2O.

[0077] The surface SEM pictures of the catalytic electrodes prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1 are shown in Figure 1 , Figure 1 (a) is a cubic Cu2O catalyst electrode B-C-Cu2O without amino acid modification, and the Cu2O particles obtained without adjusting the rotation speed and feeding speed in the nucleation stage are in cubic morphology with an average particle size of 50nm and are prone to agglomeration. Figure 1 (b) is a Cu2O catalytic electrode B-GR-Cu2O without L-cys modification, which presents a unique rhombic truncated cubic morphology by adjusting the raw material feeding ratio, rotation speed and feeding speed in different nucleation stages, and has an average particle size of about 120nm, but the particle size is not uniform. Figure 1 (c) is an L-cys-modified Cu2O electrode L-S-Cu2O, which has an approximate spherical morphology with an average particle size of about 400nm and uniform size but is prone to agglomeration. Figure 1 (d) is an L-cys-modified Cu2O electrode L-GR-Cu2O, which also has a unique rhombic truncated cubic morphology, and the amino and thiol groups in L-cys synergistically catalyze the reduction of CO2, with an average particle size of about 150nm. As can be seen from Figure 1 , L-GR-Cu2O has the advantages of large specific surface area, uniform dispersion and uniform size.

[0078] Application of Cu-based catalyst electrode for electroreduction of CO2 to C2H4: The performance of the Cu-based catalytic electrode was tested in a flow electrolyzer. Catalytic electrodes prepared in Examples 1, 1, 2, and 3 were used as working electrodes, a platinum mesh as the counter electrode, and a silver-silver chloride electrode as the reference electrode. The cathode electrolyte was 1M KHCO3, and the anolyte was 1M KOH. The cathode and anolyte chambers were separated by an ion-exchange membrane. High-purity CO2 was introduced at a flow rate of 30 sccm, and the downstream end was connected to an online gas chromatograph. Constant current testing was performed at a current density of -250 mA / cm² using an electrochemical workstation. The gaseous products generated by the reaction were measured and analyzed by online GC, and the liquid products were analyzed by 1H NMR spectroscopy. After electrolysis for 25 min, the Faraday efficiency of the main gaseous product C2H4 was calculated based on the amount of C2H4 detected by online GC. Results are shown below. Figure 2 Electrodes prepared from BC-Cu2O, B-GR-Cu2O, LS-Cu2O, and L-GR-Cu2O exhibited Faradaic efficiencies of 20.74%, 33.37%, 36.84%, and 61.22% for C2H4 at a current density of -250 mA / cm², respectively. Figure 1 , Figure 2 The results show that L-cys-modified Cu2O and L-GR-Cu2O, by adjusting the raw material input ratio and precisely controlling the dripping rate of the reducing agent using an injection pump at different nucleation stages, and adjusting the rotation speed at each reaction stage, produced a uniform rhombic semi-cubic morphology with 26 faces, 24 vertices, and 48 edges. The amino groups in the modified L-cys provide an electron-rich environment, promoting CO2 adsorption and activation, facilitating CO2 capture. The thiol groups also strongly coordinate with Cu species on the Cu2O surface to form Cu-S, promoting water decomposition, promoting *CO protonation, stabilizing the rhombic semi-cubic structure, providing more adsorption sites and reactive sites for the reaction, which is beneficial for subsequent asymmetric coupling. Compared with the cubic Cu2O and the unmodified rhombic semi-cubic Cu2O, the cubic Cu2O showed higher selectivity for C2H4.

[0079] Example 2

[0080] This invention provides the preparation and application of orthorhombic semi-cubic Cu2O electrodes modified with different types of amino acids. The specific steps are as follows:

[0081] 1) Preparation of rhombic semi-cubic Cu2O electrodes modified with different types of amino acids:

[0082] The steps (1-1) to (1-3) in Example 1 are basically the same, except that 0.2 mmol L-cys in step (1-4) is replaced by 0.3 mmol of L-cys, Gly and Lys, and the subsequent centrifugation, washing, drying and electrode preparation process is the same as that in Example 1, and L-cys, Gly and Lys modified rhombic truncated cube Cu2O electrodes are obtained, respectively, and are denoted as L-cys-Cu2O, Gly-Cu2O and Lys-Cu2O.

[0083] 2) Application of rhombic truncated cube Cu2O electrodes modified by different types of amino acids: constant current test was carried out at a current density of -200 mA / cm2, the test equipment and process were the same as in Example 1, online GC was used for product content measurement and analysis, after electrolysis for 25 min, the results are shown in Table 2 Figure 3 , the faradic efficiency of C2H4 gas product of L-cys-Cu2O, Gly-Cu2O and Lys-Cu2O electrodes modified by three different amino acids is 51.27%, 35.06% and 22.16%, respectively. Compared with Gly and Lys, L-cys shows strong superiority in improving the performance of Cu2O for electrocatalytic CO2 to C2H4 due to the synergistic regulation of its thiol and amino functional groups.

[0084] Example 3

[0085] The present application provides the preparation and application of L-cys modified Cu2O electrodes prepared by different segmented reaction rotation speeds, and the specific steps are as follows:

[0086] 1) Preparation of L-cys modified Cu2O electrodes with different reaction rotation speeds: 2 mmol of copper chloride dihydrate was dissolved in 500 ml of deionized water, and stirred uniformly. The solution was light blue. 30 ml of 0.3 M sodium hydroxide solution was added at a speed of 3 ml / min using a syringe pump, and a light blue flocculent precipitate was formed. The rotation speed was controlled to be 400, 500, 800 rpm, and the reaction was carried out at room temperature. 20 ml of 0.2 M ascorbic acid solution was added at a speed of 2 ml / min using a syringe pump, and the color changed to orange yellow or brown yellow. The rotation speed was controlled to be 600, 700, 1000 rpm, and the reaction was carried out at a temperature of 50°C for 1 h. After the reaction was completed, the solution was naturally cooled to room temperature, and 0.2 mmol of L-cys was added. The L-cys was completely dispersed in the solution by ultrasonic treatment for 30 min. The reaction was continuously stirred at 500 rpm at room temperature for 2 h. After the L-cys was fully modified, the solid product was separated by centrifugation at a rotation speed of 8000 rpm, and washed with ethanol and deionized water for 3 times each to remove impurities. The product was placed in a vacuum drying oven and dried at 60°C for 12 h. L-cys modified rhombic truncated cubic Cu2O particles prepared at different reaction rotation speeds were obtained. 50 mg of L-cys modified Cu2O particles were dispersed in 2 ml of ethanol, 50 microliters of Nafion were added to prepare a catalyst ink, and the catalyst ink was ultrasonically dispersed for 1 h. The catalyst ink was dropped and coated on a gas diffusion electrode with an area of 1.5 x 1.5 cm 2 , so that the catalyst loading weight was 1.0 mg / cm 2 . L-cys modified Cu2O electrodes prepared at different reaction rotation speeds were obtained.

[0087] 2) Application of L-cys modified Cu2O electrodes with different reaction rotation speeds:

[0088] The above three kinds of Cu2O electrodes were tested in a flow type electrolysis cell. A platinum mesh was used as the counter electrode, a silver-silver chloride electrode was used as the reference electrode, 1 M KHCO3 was used as the cathode electrolyte, 1 M KOH was used as the anode electrolyte, the cathode chamber and the anode chamber were separated by an ion exchange membrane, high purity CO2 was introduced at a flow rate of 30 sccm, a current density of -200 mA / cm² was applied by an electrochemical workstation for constant current test, and an online GC was used for product content measurement and analysis. After electrolysis for 25 min, the test results of the GC were obtained, and were recorded in Figure 4 . The faraday efficiency of C2H4 was 40.71%, 53.44% and 43.48%, respectively. From the results of Figure 4 , it can be seen that when the front and rear reaction rotation speeds are 500 and 700 rpm, respectively, the best performance is shown.

[0089] Example 4

[0090] This invention provides the preparation and application of rhombic semi-cubic Cu2O electrodes with different L-cys loading methods. The specific steps are as follows:

[0091] Fabrication of rhombohedral semi-cubic Cu2O electrodes with different L-cys loading methods:

[0092] 1) Preparation of L-cys-modified Cu2O electrode loaded with ultrasonic stirring at room temperature

[0093] 2 mmol of copper chloride dihydrate was dissolved in 500 ml of deionized water and stirred until homogeneous, resulting in a light blue solution. 30 ml of 0.3 M sodium hydroxide solution was added dropwise at a rate of 3 ml / min using a syringe pump, producing a light blue flocculent precipitate. The reaction was carried out at room temperature with the stirring speed maintained at 500 rpm. 20 ml of 0.2 M ascorbic acid solution was then added dropwise at a rate of 2 ml / min, resulting in an orange-yellow or brownish-yellow color. The reaction was carried out at 50°C for 1 h with the stirring speed maintained at 700 rpm. After the solution cooled naturally to room temperature, 0.2 mmol of L-cys was added, and the mixture was sonicated at 40 W for 30 min to ensure complete dispersion. The mixture was stirred continuously at 500 rpm for 2 h at room temperature until fully modified with L-cys. The solid product was then centrifuged at 8000 rpm and washed three times each with ethanol and deionized water to remove impurities. The product was then dried in a vacuum drying oven at 60°C for 12 h, yielding ultrasonically stirred Cu₂O particles modified with L-cys.

[0094] 2) Preparation of L-cys-modified Cu2O electrode by oil bath heating

[0095] 2 mmol of copper chloride dihydrate was dissolved in 500 ml of deionized water and stirred until homogeneous, resulting in a light blue solution. 30 ml of 0.3 M sodium hydroxide solution was added dropwise at a rate of 3 ml / min using a syringe pump, producing a light blue flocculent precipitate. The reaction was carried out at room temperature with the stirring speed maintained at 500 rpm. 20 ml of 0.2 M ascorbic acid solution was then added dropwise at a rate of 2 ml / min using a syringe pump, resulting in an orange-yellow or brownish-yellow color. The reaction was carried out at 50°C for 1 h with the stirring speed maintained at 700 rpm. 0.2 mmol of L-cys was added, and the reaction was continued at 50°C with stirring at 500 rpm for 2 h. After sufficient L-cys modification, the solid product was separated by centrifugation at 8000 rpm and washed three times each with ethanol and deionized water to remove impurities. The product was then dried in a vacuum drying oven at 60°C for 12 h, yielding L-cys-modified Cu₂O particles heated in an oil bath.

[0096] 3) Preparation of hydrothermally loaded L-cys modified Cu2O electrode

[0097] Dissolve 2 mmol of copper chloride dihydrate in 500 ml of deionized water, stir until uniform, and the solution is light blue; use a syringe pump to add 20 ml of 0.2 M ascorbic acid solution at a speed of 2 ml / min, the color changes to orange yellow or brown yellow, control the rotation speed to keep at 700 rpm, react at a temperature of 50℃ for 3h; centrifuge the solid product after the reaction is completed at a speed of 8000 rpm, wash with ethanol and deionized water for 3 times respectively, and put into a vacuum drying box to dry at 60℃ for 12h; grind the dried solid product, dissolve in 20 ml of deionized water, add 0.2 mmol of L-cys powder, transfer the solution into a 50 ml reaction kettle, and place in a blast drying oven to carry out hydrothermal reaction at 120℃, maintain for 12h, then stop heating, centrifuge the solid product after the reaction kettle is naturally cooled to room temperature, wash with ethanol and deionized water for 3 times, and the obtained solid product is placed in a vacuum drying box to dry at 60℃ for 12h, to obtain hydrothermal loaded L-cys modified Cu2O particles.

[0098] Application of rhombic truncated cubic Cu2O electrodes with different L-cys loading methods:

[0099] Take 50 mg of each of the three kinds of L-cys modified Cu2O particles, disperse in 2 ml of ethanol, add 50 microliters of Nafion to prepare a catalyst ink, ultrasonic dispersion for 1h, and then drop coat on a gas diffusion electrode with an area of 1.5x1.5cm 2 , so that the catalyst loading weight is 1.0mg / cm 2 , and the performance test is carried out in a flow cell, the test equipment and process are the same as in Example 1, a potential of-1.2V vs.RHE is applied by an electrochemical workstation for constant potential test, an online GC is used for product content measurement and analysis, after electrolysis for 25 min, the test results of the GC are obtained, recorded in Figure 5 , and the Faraday efficiency of the C2H4 gas product of the Cu2O electrode loaded by ultrasonic stirring at room temperature, oil bath heating and hydrothermal method is 60.06%, 39.12% and 48.56% respectively, among which the loading method of ultrasonic stirring at room temperature shows the best performance.

[0100] Example 5

[0101] The embodiments of the present application provide preparation and application of rhombic truncated cubic Cu2O electrodes modified by different proportions of L-cys, and the specific steps are as follows:

[0102] 1) Preparation of rhombic truncated cubic Cu2O electrodes modified by different proportions of L-cys:

[0103] Dissolve 2 mmol of copper chloride dihydrate in 500 ml of deionized water, stir until uniform, and the solution is light blue; use a syringe pump to add 30 ml of 0.3 M sodium hydroxide solution at a uniform speed of 3 ml / min, generate a light blue flocculent precipitate, control the rotation speed to keep at 500 rpm, and react at room temperature; use a syringe pump to add 20 ml of 0.2 M ascorbic acid solution at a uniform speed of 2 ml / min, the color changes to orange yellow or brown yellow, control the rotation speed to keep at 700 rpm, and react at a temperature of 50°C for 1 h; after the solution is naturally cooled to room temperature, add 0.1 mmol, 0.2 mmol, and 0.4 mmol of L-cys (the molar ratio of Cu2O to L-cys is 20:1, 10:1, and 5:1, respectively), and ultrasonic for 30 min at a power of 40 W to make the L-cys completely dispersed in the solution; continue to stir at 500 rpm at room temperature for 2 h, and after the L-cys is fully modified, centrifugal separate the solid product at a rotation speed of 8000 rpm, and wash with ethanol and deionized water for 3 times each to remove impurities, and put into a vacuum drying oven to dry at 60°C for 12 h; obtain rhombic truncated cubic Cu2O particles modified with different proportions of L-cys. Take 50 mg of rhombic truncated cubic Cu2O particles modified with L-cys, disperse in 2 ml of ethanol, add 50 microliters of Nafion to prepare a catalyst ink, ultrasonic for 1 h, and then drop coat on a gas diffusion electrode with an area of 1.5 x 1.5 cm 2 , so that the catalyst loading weight is 1.0 mg / cm 2 , to obtain rhombic truncated cubic Cu2O electrodes modified with different proportions of L-cys.

[0104] 2) Application of rhombic truncated cubic Cu2O electrodes modified with different proportions of L-cys: test the performance of the above three Cu-based catalytic electrodes in a flow-type electrolytic cell, and the operation steps are the same as in Example 1, apply a potential of -1.2 V vs. RHE by an electrochemical workstation for constant potential test, and use an online GC for product content measurement and analysis, after electrolysis for 25 min, obtain the test results of GC, which are recorded in Figure 4 , and the faradic efficiencies of the three electrodes for the gas product C2H4 are 39.08%, 60.06%, and 46.36% respectively when the molar ratio of Cu2O to L-cys is 20:1, 10:1, and 5:1. Figure 6 From the results, it can be seen that the rhombic truncated cubic Cu2O electrodes modified with L-cys show a volcano-type trend that the selectivity of the target product C2H4 first increases and then decreases due to the change of the molar ratio of Cu2O to L-cys, and the best performance is shown when the molar ratio of Cu2O to L-cys is 10:1.

[0105] Three different ratios of L-cys modified Cu-based catalysts in Comparative Example 1, Comparative Example 2, Example 1 and Example 5 were selected to conduct long-term current-time (i-t) tests at a constant potential of -1.2 V vs. RHE, and the gas-phase products were analyzed using online GC to record the long-term stability. The results are shown in Table 1. Figure 7 Comparative Examples 1 and 2 could only be maintained for 8 h and 12 h, respectively, without more than 20% performance decay, while the three Cu-based catalysts in Example 5 could be maintained for 24 h, 45 h and 36 h, respectively, without more than 20% C2H4faradaic efficiency decay, and Example 1 still had a C2H4faradaic efficiency of 50.5% at 50 h, indicating that the sulfhydryl group in L-cys could stabilize the half-cubic structure of the catalyst by Cu-S bonds, and had strong long-term stability.

[0106] The above results fully demonstrate that by adjusting the raw material input ratio and precisely controlling the dropping speed of the reducing agent and the stirring speed of the reaction at different stages of nucleation using a syringe pump, the morphology of the Cu2O half-cubic truncated octahedron can be effectively controlled, and the L-cys in the modified amino acid can strongly coordinate with the Cu species on the surface of Cu2O to form Cu-S, which promotes water splitting and *CO protonation, stabilizes the surface structure, while the amino group can provide an electron-rich environment to strengthen the capture of CO2, synergistically regulate the local microenvironment of the reaction, promote asymmetric coupling, and using ultrasonic normal temperature stirring can ensure sufficient loading of L-cys without denaturation of the amino acid due to high temperature, and can avoid agglomeration, maintain the uniformity of the particle size, and increase the specific surface area, thereby significantly improving the selectivity and stability of the electrocatalytic CO2 reduction to C2H4.

Claims

1. An amino acid-modified copper-based catalyst characterized in that, The catalyst is composed of Cu2O with rhombic truncated cuboid morphology and natural amino acid modified on the surface of Cu2O, and the natural amino acid is L-cysteine.

2. A process for the preparation of the amino acid-modified copper-based catalyst of claim 1, characterized in that, The amino acid is added into the suspension of cuprous oxide with rhombic truncated cuboid morphology, and the amino acid is fully modified on the surface of cuprous oxide by the loading method of ultrasonic stirring at room temperature, and the product after reaction is collected, which is the amino acid modified copper-based catalyst.

3. The method for preparing the amino acid-modified copper-based catalyst according to claim 2, characterized in that, The preparation method of the suspension of cuprous oxide with rhombic truncated cuboid morphology is as follows: a basic solution is added into a copper salt solution, the pH value of the reaction system is adjusted to 9.0-11.0 to obtain a mixed solution; a reducing agent is added into the mixed solution to obtain the suspension of cuprous oxide by stirring reaction.

4. The process for preparing an amino acid-modified copper-based catalyst according to claim 3, characterized by, The copper salt is copper sulfate pentahydrate, copper chloride dihydrate or copper nitrate; or, the basic solution is sodium hydroxide solution; or, the reducing agent is glucose or ascorbic acid solution.

5. The process for preparing an amino acid-modified copper-based catalyst according to claim 3, characterized by, The basic solution is added into the copper salt solution, and the reaction is carried out at a stirring speed of 400-800 rpm, the pH value of the reaction system is adjusted to 9.0-11.0 to obtain the mixed solution; the reducing agent is added into the mixed solution, and the reaction is carried out at a stirring speed of 400-800 rpm to obtain the suspension of cuprous oxide.

6. The process for preparing an amino acid-modified copper-based catalyst according to claim 5, characterized in that, The method for adding the basic solution into the copper salt solution is that the basic solution is added into the copper salt solution at a uniform and slow speed of 2-6 ml / min; and the method for adding the reducing agent into the mixed solution is that the reducing agent solution is added into the mixed solution at a uniform and slow speed of 2-4 ml / min.

7. The process for preparing an amino acid-modified copper-based catalyst according to claim 3, characterized by, The molar ratio of the copper salt to the amino acid is 5-20:

1.

8. Use of the catalyst of claim 1 in the preparation of an electrode for electrocatalytic conversion of carbon dioxide into ethylene.

9. Use according to claim 8, characterized in that, The amino acid modified copper-based catalyst is mixed with a perfluorosulfonic acid type polymer to prepare catalyst ink; the catalyst ink is coated on the surface of an electrode substrate to obtain a copper-based catalytic electrode.

10. A method of electrocatalytic conversion of carbon dioxide to ethylene, characterized in that, The catalyst of claim 1 is mixed with a perfluorosulfonic acid type polymer to prepare catalyst ink; the catalyst ink is coated on the surface of an electrode substrate to obtain a copper-based catalytic electrode; the copper-based catalytic electrode is used as a working electrode, a platinum mesh or a platinum sheet is used as a counter electrode, and a silver-silver chloride electrode or a saturated calomel electrode is used as a reference electrode to form a three-electrode system, and carbon dioxide is reduced to obtain ethylene.

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