Preparation method of electrode catalyst for preparing ethylene through electrochemical reduction of carbon dioxide

Abstract

The invention discloses a preparation method of an electrode catalyst for preparing ethylene by electrochemical reduction of carbon dioxide, which comprises the following steps: step 1, ultrasonically dispersing a conductive carrier in a dispersant to form a carrier dispersion liquid; step 2, stirring the carrier dispersion liquid obtained in the step 1 under a water bath heating condition until the carrier dispersion liquid is uniformly mixed; step 3, adding mercaptoethylamine, uniformly dispersing, then adding a copper salt trihydrate copper solution precursor, and heating and stirring in a water bath until the mixture is uniformly mixed; and 4, dropwise adding a reducing agent, and heating and stirring in a water bath to obtain the electrode catalyst. According to the catalyst for loading the copper-based nanoparticles on the conductive carrier prepared by the preparation method disclosed by the invention, the problem of relatively large internal resistance caused by stacking of the copper-based nanoparticles is reduced through support expansion of the conductive material.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical reduction of carbon dioxide, and relates to a preparation method of an electrode catalyst for electrochemically reducing carbon dioxide to ethylene. Background Art

[0002] The electroreduction of carbon dioxide has become a highly potential method for utilizing carbon dioxide using renewable energy. When using copper-based catalysts, this process can produce multi-carbon fuels and chemicals with almost net-zero emissions, contributing to closing the anthropogenic carbon cycle. Therefore, the rational design, development, and preparation of copper-based catalysts are crucial for achieving efficient electrochemical reduction of carbon dioxide. A Chinese invention patent with the publication number CN115595607A, publication date January 13, 2023, and title "Composite Catalyst for Regulating Selectivity of Electrochemical Reduction Products of Carbon Dioxide and Applications" discloses a composite catalyst for regulating the selectivity of electrochemical reduction products of carbon dioxide and its applications. By adding carbon black to a cuprous oxide microparticle catalyst to form a composite electrocatalytic electrode, the selectivity of the carbon dioxide reduction product can be regulated from methane to ethylene.

[0003] A Chinese invention patent with the publication number CN115490258A, publication date of December 20, 2022, and title "A Copper Oxide Nanosheet Catalyst and Its Preparation Method and Application in the Electrochemical Reduction of Carbon Dioxide and Carbon Monoxide" discloses a copper oxide nanosheet catalyst and its preparation method and application in the electrochemical reduction of carbon dioxide and carbon monoxide. A certain mass of copper salt is dissolved in water, an alkali solution with a certain concentration is added, and after stirring, a certain volume of ethanol is added and heated to a certain temperature for hydrothermal reaction. After filtration and drying, copper oxide nanosheets are obtained, which are used for the electrochemical reduction of carbon dioxide, carbon monoxide, or the co-electrolysis reaction of carbon monoxide / carbon dioxide, and the C-(2+) Faraday efficiency reaches more than 85%; A Chinese invention patent with the publication number CN111659437A, publication date of May 12, 2023, and title "A Preparation Method of a Nitrogen-Doped Graphene-Supported Core-Shell Copper-Carbon Composite Catalyst for Electrochemical Production of Formic Acid from Carbon Dioxide" discloses a preparation method of a nitrogen-doped graphene-supported core-shell copper-carbon Cu2O / Cu@C composite catalyst for electrochemical production of formic acid from carbon dioxide; A Chinese invention patent with the publication number CN108677179A, publication date of August 4, 2020, and title "Modification of Copper Foil Electrode and Its Method for Electrochemical Reduction of CO2 Reaction" discloses a method for hydrothermally modifying copper foil electrodes using a KHCO3 solution. The CuO generated on the surface of the modified copper foil is beneficial to improving the electrocatalytic performance of copper foil for ethylene; A Chinese invention patent with the publication number CN111229261B, publication date of April 13, 2021, and title "Catalyst for Electroreduction of Carbon Dioxide and Carbon Monoxide to Produce Multi-Carbon Products, Its Preparation Method and Application" discloses a catalyst for electroreduction of carbon dioxide and carbon monoxide to produce multi-carbon products, its preparation method and application, belonging to the field of electrocatalysis. The catalyst is a halogen-modified copper electrocatalyst, and the halogen includes at least one of fluorine, chlorine, bromine, and iodine; The preparation method of the catalyst is as follows: A copper halide precursor is loaded on a gas diffusion layer, and an electroreduction is carried out to obtain a halogen-modified copper electrocatalyst; The copper halide precursor includes at least one of a copper hydroxide fluoride precursor and other copper halide precursors except the copper hydroxide fluoride precursor; The catalyst is applied to the reaction of electroreducing carbon dioxide and carbon monoxide to produce multi-carbon products, with high reaction activity, high selectivity, stable catalytic performance, and maintaining a high multi-carbon product selectivity within a wide current range.

[0004] In the existing preparation technologies of electrode catalysts for electrocatalytic reduction of carbon dioxide, since metallic copper is the only element that can enable carbon-carbon coupling, most of the existing electrode catalysts directly use copper foil or copper nanoparticles as the substrate. When using copper foil as the electrode catalyst mechanism, the electrode metal content is relatively high, resulting in a high cost of the electrode; while using copper nanoparticles as the substrate of the electrode catalyst, due to the difficulty in dispersing nanoparticles during electrode forming, the stacked metal particles will increase the resistance at the electrode conduction interface, thereby increasing the overpotential in electrode testing. In addition, there may be some metal sites that are not in sufficient contact with the reactants during the electrolysis reaction or dissolve in the electrolyte, leading to the deterioration of the electrolyte and affecting the electrolysis efficiency. Summary of the Invention

[0005] The present invention provides a method for preparing an electrode catalyst for electrochemically reducing carbon dioxide to ethylene, which solves the technical problem in the prior art that the stacked metal particles increase the resistance at the electrode conduction interface, thereby increasing the overpotential in electrode testing.

[0006] The technical solution adopted by the present invention is that the method for preparing an electrode catalyst for electrochemically reducing carbon dioxide to ethylene includes the following steps:

[0007] Step 1: Ultrasonically disperse a conductive carrier in a dispersant to form a carrier dispersion.

[0008] Step 2: Under the condition of water bath heating, stir the carrier dispersion obtained in Step 1 until it is evenly mixed.

[0009] Step 3: Add mercaptoethylamine, and after uniform dispersion, add a copper salt copper solution precursor of copper trihydrate, and stir under water bath heating until it is evenly mixed.

[0010] Step 4: Dropwise add a reducing agent, and stir under water bath heating to obtain an electrode catalyst.

[0011] The characteristics of the present invention are as follows:

[0012] The conductive carrier is any one of graphene, C3N4, MOF or MIL-101.

[0013] In Step 1, the dispersant is any one of isopropanol, ethanol or acetone; the concentration of the carrier dispersion in Step 1 is less than or equal to 5 mg / mL.

[0014] In Step 3, the mass ratio of mercaptoethylamine to the conductive carrier is 100:1 - 100:5, and the mercaptoethylamine is Aladdin C106461.

[0015] In Step 3, the copper salt is any one of copper nitrate or copper chloride; the concentration of the copper salt is formulated to be 1 mg / mL - 7 mg / mL.

[0016] In step 3, the concentration of Cu2+ in the copper solution precursor of copper trihydrate salt is 100 mg / mL.

[0017] In step 4, the reducing agent is any one of hydrazine hydrate or hydroxylamine; the concentration of the reducing agent is 60%-85%.

[0018] In steps 2 and 4, the water bath heating temperature is 45°C - 80°C.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. For the catalyst obtained by loading copper-based nanoparticles onto a conductive carrier by the preparation method of the present invention, through the support expansion of the conductive material, the problem of large internal resistance caused by the stacking of copper-based nanoparticles is reduced.

[0021] 2. For the highly dispersed supported copper-based catalyst obtained by the preparation method of the present invention, mercaptoethylamine is used to covalently bond metal particles and the carrier, so that the metal particles are stably loaded on the carrier, and it has better catalyst stability than the physical mixture of copper particles and carbon black. By regulating the addition amount of mercaptoethylamine, the number of loading sites can be increased or decreased. At the same time, by changing the total amount of the metal salt solution, the particle size of the supported copper-based nanoparticles can be adjusted. Description of the Drawings

[0022] Figure 1 is the transmission electron micrograph of the conductive carrier uniformly loaded with copper-based metal nanoparticles prepared by the present invention. Detailed Embodiments

[0023] The present invention will be described in detail below with reference to the drawings and specific embodiments.

[0024] The present invention provides a preparation method of an electrode catalyst for electrochemically reducing carbon dioxide to ethylene, comprising the following steps:

[0025] Step 1, ultrasonically disperse the conductive carrier in a dispersant to form a carrier dispersion;

[0026] Among them, the conductive carrier is any one of graphene, C3N4, MOF or MIL-101; the dispersant is any one of isopropanol, ethanol or acetone; to avoid carrier aggregation, the concentration of the carrier dispersion is preferably not more than 5 mg / mL. The ultrasonic dispersion time is not less than 30 min.

[0027] Step 2, under the condition of water bath heating, stir the carrier dispersion obtained in step 1 until it is uniformly mixed;

[0028] Among them, the water bath heating temperature is 45°C - 80°C.

[0029] Step 3: Add mercaptoethylamine. After uniform dispersion, add the copper salt copper solution precursor of copper trihydrate, and heat and stir in a water bath until evenly mixed.

[0030] Among them, the mass ratio of mercaptoethylamine to the conductive carrier is 100:1 - 100:5. The copper salt is any one of copper nitrate or copper chloride; the concentration of the copper salt is prepared at 1 mg / mL - 7 mg / mL. The concentration of Cu2+ in the copper trihydrate copper solution precursor is 100 mg / mL.

[0031] Step 4: Dropwise add the reducing agent, heat and stir in a water bath to obtain the electrode catalyst.

[0032] Among them, the water bath heating temperature is 45°C - 80°C. The reducing agent is any one of hydrazine hydrate or hydroxylamine; the concentration of the reducing agent is 60% - 85%.

[0033] The conductive carrier of the present invention is prepared and synthesized by using the conductive carrier for electrocatalytic reduction of carbon dioxide and its preparation method with the patent application number 202311274708.1 and the patent name; mercaptoethylamine is selected from Aladdin C106461.

[0034] Example 1

[0035] Step 1: Preparation of the conductive carrier dispersion: Take 200 mg of dry conductive carrier and add it to 90 mL of deionized water, ultrasonically disperse it to a uniform state, transfer the mixed solution to a 100 mL volumetric flask, and make up the volume to 100 mL with deionized water. The concentration of the obtained carrier dispersion solution is 2 mg / mL. Shake well and set aside.

[0036] Step 2: Preparation of the copper precursor solution: Weigh 3.802 g of copper nitrate trihydrate, add it to 9.15 g of deionized water, and fully dissolve it to obtain a dark blue copper nitrate solution, where the concentration of Cu2+ is 100 mg / mL.

[0037] Step 3: Take 50 mL of the carrier mixture, weigh and dissolve 1 mg of mercaptoethylamine in the carrier dispersion, then take 10 μL of the copper solution. After mixing, heat the mixture in a water bath at 65°C, stir evenly for 30 min, then dropwise add 0.5 mL of the reducing agent hydrazine hydrate (85%), and continue to stir at 60°C for 2 h to obtain a 1% Cu@conductive carrier material electrocatalyst.

[0038] Step 4: Catalyst washing: Filter the dispersion obtained in Step 3 by suction filtration, and then wash it with deionized water and ethanol three times or more in sequence. Finally, dry the wet solid sample in a vacuum drying oven at 60 - 80°C overnight, and mark the obtained catalyst as xCu@conductive carrier material.

[0039] Example 2

[0040] Prepare the same carrier dispersion and metal salt solution as in Example 1. Take 50 mL of the carrier dispersion, weigh and dissolve 2 mg of mercaptoethylamine in the carrier dispersion, then take 30 μL of the copper solution. After mixing, heat the mixture in a water bath at 65 °C, stir evenly for 30 min, then dropwise add 1 mL of the reducing agent hydrazine hydrate (85%), and continue to stir at 60 °C for 2 h to obtain a 3% Cu@conductive carrier material electrocatalyst.

[0041] Example 3

[0042] Prepare the same carrier dispersion and metal salt solution as in Example 1. Take 50 mL of the carrier dispersion, weigh and dissolve 3 mg of mercaptoethylamine in the carrier dispersion, then take 50 μL of the copper solution. After mixing, heat the mixture in a water bath at 65 °C, stir evenly for 30 min, then dropwise add 2 mL of the reducing agent hydrazine hydrate (85%), and continue to stir at 60 °C for 2 h to obtain a 5% Cu@conductive carrier material electrocatalyst.

[0043] Example 4

[0044] Prepare the same carrier dispersion and metal salt solution as in Example 1. Take 50 mL of the carrier dispersion, weigh and dissolve 5 mg of mercaptoethylamine in the carrier dispersion, then take 100 μL of the copper solution. After mixing, heat the mixture in a water bath at 65 °C, stir evenly for 30 min, then dropwise add 5 mL of the reducing agent hydrazine hydrate (85%), and continue to stir at 60 °C for 2 h to obtain a 10% Cu@conductive carrier material electrocatalyst.

[0045] Comparative Example

[0046] In the comparative sample of the electrode catalyst, mercaptoethylamine is not added as a riveting agent, but the metal salt solution is mixed into the carrier dispersion, and direct reduction is carried out using hydrazine hydrate. Prepare a contrast agent with the same loading amount. The specific electrochemical test data are shown in the list.

[0047] In the present invention, mercaptoethylamine is used as a riveting agent to connect between the conductive carrier material and the catalyst active phase. By evenly distributing mercaptoethylamine in the carrier material dispersion, the ammonium group end is connected to a conductive material such as GO through hydrogen bonds, increasing the nucleation sites on the carrier for the subsequent loading of the metal active phase. Then, the metal salt solution is added, and active phase nuclei are further formed on the carrier by heating in a water bath. After that, the reducing agent is added dropwise to further form the loaded phase.

[0048] Through the riveting action of mercaptoethylamine, not only the dispersion degree of the loaded metal particles on the carrier surface is increased, but also the valence state shift of the metal phase on the carrier surface is further reduced, enhancing the reducibility of the metal active phase.

[0049] The electrochemical characterization of the above-prepared highly dispersed and low-resistance catalyst is as follows:

[0050] All electrochemical tests were performed on an electrochemical workstation (PARSTST 4000+). Before the CO2RR test, first, N2 gas was introduced into the electrolyte for 1 h, and then CO2 gas was introduced for 30 min to achieve CO2 saturation. We used an H-type electrolytic cell as the test device, separated by a cation exchange membrane (Nafion N117, DuPont) between the cathode and the anode. Electrochemical performance tests were carried out in a three-electrode system, with a graphite rod electrode as the counter electrode, silver / silver chloride (Ag / AgCl) as the reference electrode, a hydrophobic carbon paper loaded with the catalyst as the working electrode, and 0.1 M aqueous KHCO3 as the electrolyte. Under the condition of a scanning rate of 5 mV / s, linear sweep voltammetry (LSV) curves were collected, and the potential value at a current density of 10 mA / cm2 was taken to evaluate the overpotential.

[0051] The overpotential of each catalyst is shown in Table 1:

[0052] Table 1

[0053] Catalyst Overpotential E (vs RHE) Contrast agent 1% Cu@GO 972 mV 998 mV 3% Cu@GO 984 mV 1.02V 5% Cu@GO 1.01V 1.13V 10% Cu@GO 1.23V 1.32V

[0054] The highly dispersed catalyst 1% Cu@GO prepared in the example is as shown in the attached figure.

Claims

1. Preparation method of electrode catalyst for electrochemically reducing carbon dioxide to ethylene, characterized in that, it includes the following steps: Step 1, ultrasonically disperse the conductive carrier in the dispersant to form a carrier dispersion; Step 2, under the condition of water bath heating, stir the carrier dispersion obtained in Step 1 until it is evenly mixed; Step 3, add mercaptoethylamine, after evenly dispersing, then add the copper salt copper solution precursor of copper trihydrate, and stir with water bath heating until it is evenly mixed; Step 4, dropwise add the reducing agent, and stir with water bath heating to obtain the electrode catalyst.

2. The preparation method of the electrode catalyst for electrochemically reducing carbon dioxide to ethylene according to claim 1, characterized in that, the conductive carrier is any one of graphene, C3N4, MOF or MIL-101.

3. The preparation method of the electrode catalyst for electrochemically reducing carbon dioxide to ethylene according to claim 2, characterized in that, in Step 1, the dispersant is any one of isopropanol, ethanol or acetone; the concentration of the carrier dispersion in Step 1 is less than or equal to 5 mg / mL.

4. The preparation method of the electrode catalyst for electrochemically reducing carbon dioxide to ethylene according to claim 1, characterized in that, in Step 3, the mass ratio of mercaptoethylamine to the conductive carrier is 100:1 - 100:5, and the mercaptoethylamine is Aladdin C106461.

5. The preparation method of the electrode catalyst for electrochemically reducing carbon dioxide to ethylene according to claim 1, characterized in that, in Step 3, the copper salt is any one of copper nitrate or copper chloride; the concentration of the copper salt is formulated to be 1 mg / mL - 7 mg / mL.

6. The preparation method of the electrode catalyst for electrochemically reducing carbon dioxide to ethylene according to claim 5, characterized in that, in Step 3, the concentration of Cu2+ in the copper salt copper solution precursor of copper trihydrate is 100 mg / mL.

7. The preparation method of the electrode catalyst for electrochemically reducing carbon dioxide to ethylene according to claim 1, characterized in that, in Step 4, the reducing agent is any one of hydrazine hydrate or hydroxylamine; the concentration of the reducing agent is 60% - 85%.

8. The preparation method of the electrode catalyst for electrochemically reducing carbon dioxide to ethylene according to claim 1, characterized in that, in Step 2 and Step 4, the water bath heating temperature is 45°C - 80°C.

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