Preparation method of conductive material, catalytic electrode and application thereof, and method for electrocatalytic reduction of co2 to formic acid

Abstract

The application relates to the technical field of bimetallic catalysts, and discloses a preparation method of conductive material, a catalytic electrode and application thereof, and a method for preparing formic acid by electrocatalytic reduction of CO2. The application discloses a preparation method of conductive material for a catalytic electrode, which comprises the following steps: first mixing a carbon nanotube solution and a precursor solution to obtain a mixture I; second mixing the mixture I and sodium hydroxide to obtain a supported bimetallic catalyst; and third mixing the supported bimetallic catalyst, ethanol and a Nafion solution to obtain the conductive material for the catalytic electrode. The conductive material for the catalytic electrode is prepared by loading an indium copper bimetal on a carbon nanotube catalyst through metal elements Cu and In, the hydrogen evolution reaction is reduced by using the indium element, the selectivity and catalytic stability of the product can be improved, and the adsorption amount of CO2 can be improved.

Description

Technical Field

[0001] This invention relates to the field of bimetallic catalyst technology, specifically to a method for preparing a conductive material for a catalytic electrode, the catalytic electrode and its application, and a method for electrocatalytic reduction of CO2 to formic acid. Background Technology

[0002] CO2 electrocatalytic reduction boasts advantages such as being green, energy-efficient, and reusable. However, due to the stability of CO2, it suffers from drawbacks including high overpotential, low Faraday efficiency, and insufficient catalyst absorption of CO2. Currently, metal electrodes, especially copper-based ones, are widely used in CO2 electrocatalytic reduction research. Copper electrodes can electrocatalyze the production of various products, including carbon monoxide, formates, hydrocarbons, and alcohols, and are inexpensive and widely available, making them a promising area for research. However, with current technology, the CO2 reduction reaction requires high overvoltages, necessitating metal catalysts to lower the reduction potential. Using only copper as the catalytic electrode results in excessively broad selectivity and insufficient stability, while the hydrogen evolution reaction leads to a decrease in overall reaction efficiency and selectivity. Introducing a second element into copper-based CO2 electrocatalytic nanomaterials and creating heterojunctions can improve the effective utilization of CO2.

[0003] CN112176359A discloses a bimetallic gas diffusion electrode, comprising a gas diffusion electrode body and a carbon dioxide electrochemical reduction catalyst supported on the gas diffusion electrode body. The carbon dioxide electrochemical reduction catalyst is a gold-based bimetal supported on multi-walled carbon nanotubes, wherein the gold-based bimetal is composed of two metals: one selected from silver, copper, nickel, bismuth, zinc, iron, indium, and cobalt, and gold. The gas diffusion electrode body is selected from carbon paper, carbon cloth, or carbon felt. This gas diffusion electrode can improve the Faradaic efficiency of carbon monoxide produced in the electrochemical reduction of carbon dioxide and can also effectively suppress the hydrogen evolution reaction. However, the gold-based bimetallic catalyst requires the use of expensive chloroauric acid tetrahydrate in its preparation, resulting in high production costs for the diffusion electrode.

[0004] CN113073345A discloses a bismuth-based composite catalyst for the electroreduction of CO2 to formic acid, characterized by comprising elemental metal M1 and oxide metal M2, wherein M1 and M2 are each independently one or more of the following metals: bismuth, zinc, tin, silver, indium, lead, or copper, and M2 includes at least metallic bismuth. This bismuth-based composite catalyst maintains high formic acid selectivity while also improving acid resistance and resistance to the inhibition effect of high-concentration formic acid, thereby enhancing chemical stability. However, the catalyst also suffers from the problem of high cost of chloroauric acid during preparation, and the electrode product is singular, while the Faraday efficiency for the conversion of carbon dioxide to ethanol is low. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of high production cost, low Faraday efficiency, and insufficient CO2 adsorption capacity of existing copper bimetallic catalysts.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a conductive material for a catalytic electrode, the method comprising the following steps:

[0007] (1) Copper nitrate and indium nitrate are dissolved in water to form a precursor solution, wherein the mass ratio of copper nitrate to indium nitrate in the precursor solution is 0.1-10:1; and

[0008] Carbon nanotubes are dispersed in water under ultrasonic conditions to obtain a carbon nanotube solution with a concentration of 1-10 mg / mL.

[0009] (2) The carbon nanotube solution and the precursor solution are mixed for the first time to obtain mixture I;

[0010] (3) Mix the mixture I with sodium hydroxide for a second mixing to obtain a supported bimetallic catalyst;

[0011] (4) The supported bimetallic catalyst is mixed with ethanol and Nafion solution in a third mixing process to obtain the conductive material used for the catalytic electrode;

[0012] The carbon nanotubes are multi-walled carbon nanotubes, with an outer diameter (OD) of 8-15 nm, an inner diameter (ID) of 3-5 nm, a length of 30-60 μm, a resistivity of 800-1200 μΩ·m, and a specific surface area ≥250 m². 2 / g.

[0013] A second aspect of the present invention provides a catalytic electrode comprising a conductive material for use as a catalytic electrode prepared by the method described in the first aspect.

[0014] A third aspect of the present invention provides an application of the catalytic electrode described in the second aspect in the electrochemical reduction of CO2.

[0015] A fourth aspect of the present invention provides a method for the electrocatalytic reduction of CO2 to formic acid, the method comprising the following steps:

[0016] Using an H-type electrolytic cell as a reactor, the catalytic electrode described in the second aspect is used as the working electrode, and the Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are placed in the anode chamber, and the Pt electrode is placed in the cathode chamber. A Nafion 117 proton exchange membrane is used to separate the anode chamber and the cathode chamber. A 0.1-0.15 mol / L KHCO3 solution is used as the electrolyte for the anode chamber and the cathode chamber.

[0017] CO2 was introduced into the cathode chamber to saturate the KHCO3 solution, and then CO2 was continuously introduced at a rate of 20 mL / min to carry out electrocatalytic reduction in constant voltage mode.

[0018] The conductive material for catalytic electrodes provided by this invention is prepared by using the metal elements Cu and In to prepare an indium copper bimetallic supported carbon nanotube catalyst. This material has low production cost and can utilize indium to reduce the hydrogen evolution reaction. When used in the catalytic reduction of CO2 in the catalytic electrode, it can improve the selectivity and catalytic stability of the reduction products. At the same time, the use of carbon nanotubes as a support can increase the adsorption capacity of the material for CO2 and the reactive sites, thereby improving its utilization rate of CO2. It can promote the selective generation of CO and HCOOH according to different product requirements, and has high Faraday efficiency and strong adsorption capacity for CO2. Attached Figure Description

[0019] Figure 1 The concentrations of CO produced by different catalytic electrodes at voltages of -1.2V, -1.4V, -1.6V, -1.8V, and -2V are shown.

[0020] Figure 2 It shows the current graphs of different catalytic electrodes at voltages of -1.2V, -1.4V, -1.6V, -1.8V, and -2V.

[0021] Figure 3 This is a graph showing the pH changes after reactions at different catalytic electrodes with voltages of -1.2V, -1.4V, -1.6V, -1.8V, and -2V.

[0022] Figure 4 This is the XRD pattern of the conductive material A1 and the catalytic electrode S1 after an electrocatalytic reduction reaction.

[0023] Figure 5 These are transmission electron microscopy (TEM) images and elemental mapping diagrams of conductive material A1.

[0024] Figure 6 This is the XPS spectrum of conductive material A1.

[0025] Figure 7 It is the Raman spectrum of the conductive material A1 and the catalytic electrode S1 after the electrocatalytic reduction reaction. Detailed Implementation

[0026] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0027] As described above, a first aspect of the present invention provides a method for preparing a conductive material for a catalytic electrode, the method comprising the following steps:

[0028] (1) Copper nitrate and indium nitrate are dissolved in water to form a precursor solution, wherein the mass ratio of copper nitrate to indium nitrate in the precursor solution is 0.1-10:1; and

[0029] Carbon nanotubes are dispersed in water under ultrasonic conditions to obtain a carbon nanotube solution with a concentration of 1-10 mg / mL.

[0030] (2) The carbon nanotube solution and the precursor solution are mixed for the first time to obtain mixture I;

[0031] (3) Mix the mixture I with sodium hydroxide for a second mixing to obtain a supported bimetallic catalyst;

[0032] (4) The supported bimetallic catalyst is mixed with ethanol and Nafion solution in a third mixing process to obtain the conductive material used for the catalytic electrode;

[0033] The carbon nanotubes are multi-walled carbon nanotubes, with an outer diameter (OD) of 8-15 nm, an inner diameter (ID) of 3-5 nm, a length of 30-60 μm, a resistivity of 800-1200 μΩ·m, and a specific surface area of ​​≥250 m². 2 / g.

[0034] Preferably, in step (1), the mass ratio of copper nitrate to indium nitrate in the precursor solution is 8-10:1. The inventors have found that, under this preferred condition, the obtained conductive material, when used in a catalytic electrode, can improve the Faraday efficiency during the electrocatalytic reduction of CO2.

[0035] The present invention does not specifically limit the ultrasonic conditions for dispersing the carbon nanotubes in water under ultrasonic conditions in step (1), and those skilled in the art can select them as needed.

[0036] Preferably, in step (1), the amount of water used is 40-60 mL relative to 100 mg of copper nitrate.

[0037] Preferably, in step (2), the volume ratio of the carbon nanotube solution to the precursor solution is 1:0.8-1.2.

[0038] In a preferred embodiment, the method further includes: after the second mixing, sequentially filtering, washing, drying, and grinding the material obtained after the second mixing to obtain the supported bimetallic catalyst. It should be noted that the present invention does not impose special requirements on the specific operations of filtering, washing, drying, and grinding; those skilled in the art can perform these operations according to known methods in the field.

[0039] In a preferred embodiment, in step (3), the mass of sodium hydroxide is 1-2 g, based on a total mass of 1 g of copper nitrate and indium nitrate in mixture I. More preferably, the mass of sodium hydroxide is 1.8-2 g, based on a total mass of 1 g of copper nitrate and indium nitrate in mixture I. The inventors have found that, in this preferred embodiment, the obtained conductive material, when used in a catalytic electrode, can improve the catalyst's adsorption capacity for CO2 during the electrocatalytic reduction of CO2.

[0040] Preferably, in step (4), the amount of the supported bimetallic catalyst is 9-11 mg, with a total volume of ethanol and Nafion solution of 1 mL.

[0041] In a preferred embodiment, in step (4), the volume ratio of ethanol to Nafion solution is 45-50:1, and the concentration of Nafion solution is 4-6 wt%.

[0042] According to a preferred embodiment, the first mixing is performed under ultrasonic conditions for a duration of 0.5-1 hour.

[0043] According to another preferred embodiment, the conditions for the second mixing include: a stirring speed of 400-500 rpm and a time of 3-5 h.

[0044] In a preferred embodiment, the third mixing is performed under ultrasonic conditions for 7-10 minutes.

[0045] Preferably, the supported bimetallic catalyst includes a support and an active component supported on the surface of the support, wherein the support of the catalyst is a carbon nanotube; and the active component includes CuO and a bimetallic oxide Cu2In2O5.

[0046] In a preferred embodiment, the mass ratio of the support to the active component in the supported bimetallic catalyst is 1:1-1.5.

[0047] Preferably, in the supported bimetallic catalyst, copper accounts for 10-20 wt% of the supported bimetallic catalyst, and indium accounts for 3-4 wt% of the supported bimetallic catalyst; and the mass ratio of copper to indium is 4-5:1.

[0048] As previously described, a second aspect of the present invention provides a catalytic electrode comprising a conductive material for use as a catalytic electrode prepared by the method described in the first aspect.

[0049] Preferably, the catalytic electrode is prepared by a method comprising the following steps: coating the conductive material for the catalytic electrode onto carbon paper to obtain the catalytic electrode;

[0050] The carbon paper is a hydrophobic carbon paper, and the size of the carbon paper is 1cm×1cm-2cm×2cm;

[0051] The amount of material used for the catalytic electrode is controlled such that the loading of the conductive material for the catalytic electrode on each sheet of carbon paper is 1-1.5 mg / cm². 2 .

[0052] Preferably, the method further includes: naturally drying the carbon paper coated with the conductive material for the catalytic electrode in air to obtain the catalytic electrode.

[0053] As previously stated, a third aspect of the present invention provides the application of the catalytic electrode described in the second aspect in the electrochemical reduction of CO2.

[0054] Preferably, the application is the electrocatalytic reduction of carbon dioxide in bicarbonate solution to produce formic acid and carbon monoxide using the catalytic electrode.

[0055] The catalytic electrode provided by this invention is applied to the electrocatalytic reduction of CO2, which can effectively solve the problem of excessive carbon emissions.

[0056] As previously described, a fourth aspect of the present invention provides a method for the electrocatalytic reduction of CO2 to formic acid, the method comprising the following steps:

[0057] Using an H-type electrolytic cell as a reactor, the catalytic electrode described in the second aspect is used as the working electrode, and the Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are placed in the anode chamber, and the Pt electrode is placed in the cathode chamber. A Nafion 117 proton exchange membrane is used to separate the anode chamber and the cathode chamber. A 0.1-0.15 mol / L KHCO3 solution is used as the electrolyte for the anode chamber and the cathode chamber.

[0058] CO2 was introduced into the cathode chamber to saturate the KHCO3 solution, and then CO2 was continuously introduced at a rate of 20 mL / min to carry out electrocatalytic reduction in constant voltage mode.

[0059] In a preferred embodiment, the conditions for the electrocatalytic reduction include: the operating voltage of the electrolytic cell is -2V to -1.2V, and the electrocatalytic reduction time is 25-35min.

[0060] Preferably, the electrocatalytic reduction reaction described in this invention is carried out at room temperature.

[0061] Preferably, the method further includes activating the catalytic electrode before using it.

[0062] To further improve the CO2 adsorption capacity of the catalytic electrode, the activation is performed using a method comprising the following steps:

[0063] The dried catalytic electrode was used as the working electrode. A 0.1 mol / L KHCO3 solution was used as the electrolyte in the anode and cathode chambers of the H-type electrolytic cell. The working electrode and the Ag / AgCl reference electrode were placed in the cathode chamber, and the Pt electrode was placed in the anode chamber. The Pt electrode was connected to the red electrode, the working electrode to the green electrode, and the Ag / AgCl reference electrode to the white electrode. The electrolytic cell was connected to the electrochemical workstation. The cyclic voltammetry (CV) scan rate was 10 mV / s, and the potential was from -0.8 V to 0.8 V. The sample was scanned until the cyclic voltammetry curve stabilized.

[0064] This invention utilizes a combination of chemical coprecipitation and electrochemical reduction to incorporate Cu and In bimetallic catalysts in the catalytic electrode, thus solving problems such as poor stability of copper-based catalytic materials in CO2 reduction, insufficient CO2 adsorption capacity, wide distribution and low selectivity of catalytic reduction products, and excessively high CO2 catalytic reduction potential.

[0065] The electrocatalytic reduction of CO2 to formic acid provided by this invention maintains high current and stable Faradaic efficiency even under long-term continuous measurement. By adjusting the copper-indium mass ratio in the supported bimetallic catalyst, the catalytic selectivity of the products HCOOH and CO can be changed. Catalytic electrode materials with higher indium content produce a higher amount of HCOOH.

[0066] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, all raw materials used are commercially available products.

[0067] Nafion solution: 5 wt% concentration, purchased from Sinopharm Chemical Reagent Co., Ltd., product number K7016001;

[0068] Carbon nanotube I: outer diameter 8-15 nm, inner diameter (ID) 3-5 nm, length 8-14 μm, resistivity 800-1200 μΩ·m, specific surface area ≥250 m² 2 / g, purchased from Shenzhen Suiheng Graphene Technology Co., Ltd.;

[0069] Carbon nanotubes II: Diameter 10-30 nm, length 10-30 μm, specific surface area 150-200 m² 2 / g, purchased from Jiacai Technology Co., Ltd.

[0070] Preparation Example 1

[0071] This embodiment provides a method for preparing a conductive material for a catalytic electrode, which includes the following steps:

[0072] (1) Weigh 100mg of carbon nanotubes I and place it in a 250mL beaker. Add 50mL of deionized water, stir evenly with a glass rod, and then sonicate for 1h to obtain a carbon nanotube solution with a concentration of 2mg / mL.

[0073] Weigh 100 mg of copper nitrate and 10 mg of indium nitrate compound into a 100 mL beaker, add 50 mL of deionized water, stir to dissolve completely, and prepare a precursor solution.

[0074] (2) Mix 50 mL of precursor solution prepared in step (1) with 50 mL of carbon nanotube solution and sonicate for 1 h to ensure thorough mixing, to obtain mixture I;

[0075] (3) Weigh 0.2g of sodium hydroxide and place it in mixture I. Add a magnetic spool and stir at 500rpm for 4h to allow the copper indium compound to precipitate fully. Remove the magnetic spool from the above solution, filter it with a Buchner funnel, wash it three times with water, filter it, and place the filtered product in an oven to dry at 60℃ for 12h. Grind it into powder to obtain a supported bimetallic catalyst.

[0076] (4) Weigh 10 mg of supported bimetallic catalyst into a 50 mL beaker, add 980 μL of ethanol and 20 μL of Nafion solution, sonicate for 8 min, and the solution forms a uniform ink-like state to obtain conductive material A1 for the catalytic electrode.

[0077] Preparation Example 2

[0078] This embodiment provides a method for preparing a conductive material for a catalytic electrode, which includes the following steps:

[0079] (1) Weigh 100mg of carbon nanotubes I and place it in a 250mL beaker. Add 50mL of deionized water, stir evenly with a glass rod, and then sonicate for 1h to obtain a carbon nanotube solution with a concentration of 2mg / mL.

[0080] Weigh 90 mg of copper nitrate and 10 mg of indium nitrate compound into a 100 mL beaker, add 50 mL of deionized water, stir to dissolve completely, and prepare a precursor solution.

[0081] (2) Take 50 mL of carbon nanotube solution obtained in step (1) and pour it into 40 mL of precursor solution. Stir with a glass rod and sonicate for 1 h to mix it thoroughly to obtain mixture I.

[0082] (3) Weigh 0.18g of sodium hydroxide and place it in mixture I. Add a magnetic spool and stir at 400rpm for 5h to allow the copper-indium compound to precipitate fully. Remove the magnetic spool from the solution and filter it with a Buchner funnel. Wash the solution three times with water and filter it. Place the filtered product in an oven and dry it at 60℃ for 12h. Grind it into powder to obtain a supported bimetallic catalyst.

[0083] (4) Weigh 10 mg of supported bimetallic catalyst in a 50 mL beaker, add 980 μL of ethanol and 20 μL of Nafion solution, sonicate for 10 min to form a uniform ink-like substance, and obtain conductive material A2 for the catalytic electrode.

[0084] Preparation Example 3

[0085] This preparation example was carried out using a method similar to that of Preparation Example 1, except that 100 mg of copper nitrate and 100 mg of indium nitrate were required.

[0086] The remaining steps are the same as in Preparation Example 1, to obtain conductive material A3 for use in the catalytic electrode.

[0087] Preparation Example 4

[0088] This preparation example was carried out using a method similar to that of Preparation Example 1, except that: 10 mg of copper nitrate and 100 mg of indium nitrate were required.

[0089] The remaining steps are the same as in Preparation Example 1, to obtain conductive material A4 for the catalytic electrode.

[0090] Preparation Example 5

[0091] This preparation example is carried out using a method similar to that of Preparation Example 1, except that in step (2), 50 mL of the precursor solution is poured into 35 mL of the carbon nanotube solution; that is, the volume ratio of the carbon nanotube solution to the precursor solution is 1:1.42.

[0092] The remaining steps are the same as in Preparation Example 1, to obtain conductive material A5 for use in the catalytic electrode.

[0093] Preparation Example 6

[0094] This preparation example is carried out using a method similar to that of Preparation Example 1, except that in step (1), 100 mg of copper nitrate and 150 mg of indium nitrate compound are weighed into a 100 mL beaker, 50 mL of deionized water is added, and the mixture is stirred to dissolve it completely, thus preparing a precursor solution.

[0095] The remaining steps are the same as in Preparation Example 1, to obtain conductive material A6 for the catalytic electrode.

[0096] Comparative Preparation Example 1

[0097] This comparative preparation example was prepared using a method similar to that of preparation example 1, except that the carbon nanotubes I in step (1) were replaced with carbon nanotubes II of equal mass.

[0098] The remaining steps are the same as in Preparation Example 1, to obtain the conductive material DA1 for the catalytic electrode.

[0099] Comparative Preparation Example 2

[0100] This comparative preparation example was prepared using a method similar to that of preparation example 1, except that the copper nitrate in step (1) was replaced with bismuth nitrate by mass.

[0101] The remaining steps are the same as in Preparation Example 1, to obtain the conductive material DA2 for the catalytic electrode.

[0102] Comparative preparation example 3

[0103] This comparative preparation example was prepared using a method similar to that of preparation example 1, except that the indium nitrate in step (1) was replaced with silver nitrate by mass.

[0104] The remaining steps are the same as in Preparation Example 1, to obtain the conductive material DA3 for the catalytic electrode.

[0105] Comparative preparation example 4

[0106] This comparative preparation example was prepared using a method similar to that of preparation example 1. The difference is that in step (1), 120 mg of copper nitrate and 10 mg of indium nitrate compound were weighed into a 100 mL beaker, 50 mL of deionized water was added, and the mixture was stirred to dissolve it completely, thus preparing a precursor solution.

[0107] The remaining steps are the same as in Preparation Example 1, to obtain the conductive material DA4 for the catalytic electrode.

[0108] Comparative preparation example 5

[0109] This comparative preparation example was prepared using a method similar to that of Preparation Example 1, except that in step (1), 100 mg of copper nitrate was weighed into a 100 mL beaker, 50 mL of deionized water was added, and the mixture was stirred to dissolve it completely, thus preparing a precursor solution.

[0110] The remaining steps are the same as in Preparation Example 1, to obtain the conductive material DA5 for the catalytic electrode.

[0111] Comparative preparation example 6

[0112] This comparative preparation example was prepared using a method similar to that of Preparation Example 1, except that in step (1), 100 mg of indium nitrate was weighed into a 100 mL beaker, 50 mL of deionized water was added, and the mixture was stirred to dissolve it completely, thus preparing a precursor solution.

[0113] The remaining steps are the same as in Preparation Example 1, to obtain the conductive material DA6 for the catalytic electrode.

[0114] Example 1

[0115] The conductive material A1 used for the catalytic electrode was coated on a hydrophobic carbon paper with a size of 2cm×2cm and dried naturally in the air to obtain the catalytic electrode S1 (i.e., the Cu58.6In3.32 sample).

[0116] The amount of conductive material used for the catalytic electrode is controlled such that the loading of the conductive material on each sheet of carbon paper is 1 mg / cm². 2 .

[0117] Example 2

[0118] The conductive material A2 used for the catalytic electrode is coated on a hydrophobic carbon paper with a size of 1cm×1cm and dried naturally in air to obtain the catalytic electrode S2.

[0119] The amount of conductive material used for the catalytic electrode is controlled such that the loading of the conductive material on each sheet of carbon paper is 1.5 mg / cm². 2 .

[0120] Example 3

[0121] This embodiment uses a method similar to that in Example 1 to prepare the catalytic electrode, except that the conductive material A1 used for the catalytic electrode is replaced with the conductive material A3 used for the catalytic electrode.

[0122] The remaining steps are the same as in Example 1, and the catalytic electrode S3 (i.e., Cu58.6In33.2 sample) is obtained.

[0123] Example 4

[0124] This embodiment uses a method similar to that in Example 1 to prepare the catalytic electrode, except that the conductive material A1 used for the catalytic electrode is replaced with the conductive material A4 used for the catalytic electrode.

[0125] The remaining steps are the same as in Example 1, and the catalytic electrode S4 (i.e., Cu5.86In33.2 sample) is obtained.

[0126] Example 5

[0127] This embodiment uses a method similar to that in Example 1 to prepare the catalytic electrode, except that the conductive material A1 used for the catalytic electrode is replaced with the conductive material A5 used for the catalytic electrode.

[0128] The remaining steps are the same as in Example 1, and the catalytic electrode S5 is obtained.

[0129] Example 6

[0130] This embodiment uses a method similar to that in Example 1 to prepare the catalytic electrode, except that the conductive material A1 used for the catalytic electrode is replaced with the conductive material A6 used for the catalytic electrode.

[0131] The remaining steps are the same as in Example 1, and the catalytic electrode S6 is obtained.

[0132] Comparative Examples 1-6

[0133] Comparative Examples 1-6 used the conductive materials (DA1, DA2, DA3, DA4, DA5, DA6) prepared in Comparative Preparation Examples 1-6 to prepare catalytic electrodes according to the preparation method of Example 1, except that the conductive materials used for the catalytic electrodes were different.

[0134] The remaining steps are the same as in Example 1, and catalytic electrodes DS1, DS2, DS3, DS4, DS5 (i.e., Cu-100 samples) and DS6 (i.e., In-100 samples) are prepared respectively.

[0135] Test case

[0136] The catalytic electrode prepared in the above example is activated or pure carbon paper is used for the electrocatalytic reduction of CO2 to HCOOH and CO. The method includes the following steps:

[0137] Using an H-type electrolytic cell as a reactor, the catalytic electrode or pure carbon paper prepared in the examples or comparative examples is used as the working electrode, and the Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are placed in the anode chamber, and a gas inlet and a sampling port are provided in the anode chamber. The Pt electrode is placed in the cathode chamber. The anode chamber and the cathode chamber are separated by a Nafion 117 proton exchange membrane. 60 mL of 0.1 mol / L KHCO3 solution (pH 8.53) is added to the anode chamber and the cathode chamber as the electrolyte.

[0138] CO2 was first introduced into the cathode chamber at a rate of 20 mL / min to saturate the KHCO3 solution. Then, CO2 was continuously introduced at a rate of 20 mL / min. The test was conducted in constant voltage mode on an electrochemical workstation, with different bias voltages applied: -1.2V, -1.4V, -1.6V, -1.8V, and -2V, for electrocatalytic reduction for 30 min. After 30 min, 5 mL of the gaseous product from the cathode chamber was extracted using a sampling needle and injected into a CO detector (manufacturer: SIMA Instruments, model AS8700A). The Faraday efficiency was then calculated based on the measured gas content, current density, and injection rate.

[0139] The formula for calculating the Faraday efficiency is as follows:

[0140]

[0141] Cdl=△j / a

[0142] Where V is the volume concentration of CO in ppm; v is the gas flow rate of CO2 in mL / min; i is the constant current in A; and Cdl is the electrochemical double-layer capacitance in mF / cm². 2 Δj is the difference in current density, in mA / cm². 2 'a' represents the scan rate in mV / s. The test results are shown in Table 1, where the CO concentration and the pH value after the reaction were obtained under -2V conditions.

[0143] Table 1

[0144]

[0145] As can be seen from the results in Table 1, the catalytic electrode prepared using the embodiments of the present invention has a strong CO2 adsorption capacity and high Faraday efficiency when used for electrocatalytic reduction of CO2 to HCOOH and CO.

[0146] The present invention provides, by way of example, material characterization diagrams of conductive material A1 and catalytic electrode S1 after electrocatalytic reduction of CO2 by X-ray diffraction (XRD, model ESCALAB) and Raman spectroscopy; transmission electron microscopy (TEM) image and X-ray photoelectron spectroscopy (XPS, model LabRAM HR Evolution) image of conductive material A1; and graphs showing the changes in concentration, current and pH of CO obtained by different catalytic electrodes at different voltages.

[0147] Depend on Figure 1It can be seen that when using the Cu58.6In3.32 sample (catalytic electrode S1) for electrocatalytic reduction of CO2, the CO concentration can reach up to 509 ppm, while when using pure carbon paper for electrocatalytic reduction, about 200 ppm of CO is produced at -2V, indicating that the Cu58.6In3.32 sample has a good ability to catalytically reduce CO2 to produce CO.

[0148] Depend on Figure 2 It can be seen that the current of the Cu58.6In3.32 sample (catalytic electrode S1) is second only to that of the Cu-100 sample (catalytic electrode DS5), reaching a maximum of 23.2 mA, indicating that the Cu58.6In3.32 sample has the largest current and the best CO generation effect.

[0149] Depend on Figure 3 It can be seen that the original pH value of the electrolytic cell was 8.53. After the catalytic electrode was used for the electrocatalytic reduction of CO2, the pH of the Cu58.6In3.32 (catalytic electrode S1), Cu58.6In33.2 (catalytic electrode S3), and Cu-100 (catalytic electrode DS5) samples decreased to around 6.5-7. The pH decrease was most significant in the Cu5.86In33.2 (catalytic electrode S4) and In-100 (catalytic electrode DS6) samples, reaching a minimum of 5.5, indicating the formation of more acidic substances. This corresponds to the fact that the In material primarily controls the reduction of CO2 to HCOOH. The above tests show that the higher the indium content of the material, the more significant the pH decrease. This demonstrates that the selective formation of more acidic substances can be controlled by increasing the amount of indium nitrate in the precursor solution.

[0150] Depend on Figure 4 As can be seen, by comparing the XRD spectra of the conductive material A1 and the catalytic electrode S1 after the reaction with the standard card, it can be determined that the sample is composed of mixed oxide (Cu2In2O5), copper oxide and carbon nanotubes. The small peaks at 18.0° and 22.2° can be attributed to the mixed oxide phase (Cu2In2O5), corresponding to the (002) and (-103) crystal planes of Cu2In2O5, respectively; the peaks at 35.5° and 38.8° belong to the copper oxide phase, corresponding to the (11-1) and (111) crystal planes of CuO; and the remaining peaks belong to carbon nanotubes.

[0151] Depend on Figure 5 It can be seen that the surface of the conductive material A1 mainly contains four elements: O (green), In (yellow), C (red), and Cu (purple), and they are evenly distributed, which confirms the presence of Cu, In, as well as copper oxide and indium oxide substances in the sample.

[0152] Figure 6 The XPS spectrum of conductive material A1 is shown below. Figure 6It can be clearly seen that the surface of the material before the reaction has characteristic peaks of Cu2p, Cu3p, Cu3s, O1s, In3d, and C1s, and the surface of the material contains Cu, In, O, and C elements.

[0153] Figure 7 These are the Raman spectra of conductive material A1 and catalytic electrode S1 after the reaction, from Figure 7 It can be seen that at 285.45cm -1 and 615cm -1 The two Raman peaks at the point are mainly related to the vibrational modes of Cu-O bonds in CuO, proving the presence of CuO.

[0154] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a conductive material for a catalytic electrode, characterized in that, The method includes the following steps: (1) Copper nitrate and indium nitrate are dissolved in water to form a precursor solution, wherein the mass ratio of copper nitrate to indium nitrate in the precursor solution is 0.1-10:1, and the mass ratio of copper nitrate to indium nitrate is not 1:1; and Carbon nanotubes are dispersed in water under ultrasonic conditions to obtain a carbon nanotube solution with a concentration of 1-10 mg / mL. (2) The carbon nanotube solution and the precursor solution are mixed for the first time to obtain mixture I; (3) Mix the mixture I with sodium hydroxide for a second mixing, and then dry the material obtained after the second mixing at 60°C for 12 hours to obtain a supported bimetallic catalyst; (4) The supported bimetallic catalyst is mixed with ethanol and Nafion solution in a third mixing process to obtain the conductive material for the catalytic electrode; The carbon nanotubes are multi-walled carbon nanotubes, with an outer diameter of 8-15 nm, an inner diameter of 3-5 nm, a length of 8-14 μm, a resistivity of 800-1200 μΩ·m, and a specific surface area ≥250 m². 2 / g.

2. The method according to claim 1, wherein, In step (1), the mass ratio of copper nitrate to indium nitrate in the precursor solution is 8-10:1; and / or In step (2), the volume ratio of the carbon nanotube solution to the precursor solution is 1:0.8-1.

2.

3. The method according to claim 1 or 2, wherein, In step (3), the total mass of copper nitrate and indium nitrate in mixture I is 1g, and the mass of sodium hydroxide is 1-2g; and / or In step (4), the amount of the supported bimetallic catalyst is 9-11 mg, with a total volume of ethanol and Nafion solution of 1 mL.

4. The method according to claim 1 or 2, wherein, The first mixing is performed under ultrasonic conditions for a duration of 0.5-1 hour; and / or The conditions for the second mixing include: a stirring speed of 400-500 rpm and a time of 3-5 hours; and / or The third mixing is performed under ultrasonic conditions for 7-10 minutes.

5. The method according to claim 1 or 2, wherein, The supported bimetallic catalyst includes a support and an active component supported on the surface of the support. The support for the catalyst is carbon nanotubes. The active component includes CuO and bimetallic oxide Cu2In2O5. In the supported bimetallic catalyst, the mass ratio of the support to the active component is 1:1-1.5; In the supported bimetallic catalyst, copper accounts for 10-20 wt% of the supported bimetallic catalyst, and indium accounts for 3-4 wt% of the supported bimetallic catalyst; and the mass ratio of copper to indium is 4-5:

1.

6. A catalytic electrode, characterized in that, The catalytic electrode contains a conductive material for use as a catalytic electrode prepared by the method described in any one of claims 1-5.

7. The catalytic electrode according to claim 6, wherein, The catalytic electrode is prepared by a method including the following steps: coating the conductive material for the catalytic electrode onto carbon paper to obtain the catalytic electrode; The carbon paper is a hydrophobic carbon paper, and the size of the carbon paper is 1cm×1cm-2cm×2cm; The amount of conductive material used in the catalytic electrode is controlled such that the loading of the conductive material on each sheet of carbon paper is 1-1.5 mg / cm². 2 .

8. The application of the catalytic electrode according to claim 6 or 7 in the electrochemical reduction of CO2.

9. A method for electrocatalytic reduction of CO2 to formic acid, characterized in that, The method includes the following steps: Using an H-type electrolytic cell as a reactor, the catalytic electrode described in claim 6 or 7 is used as the working electrode, and the Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are placed in the anode chamber, and the Pt electrode is placed in the cathode chamber. A Nafion 117 proton exchange membrane is used to separate the anode chamber and the cathode chamber. A 0.1-0.15 mol / L KHCO3 solution is used as the electrolyte for the anode chamber and the cathode chamber. CO2 was introduced into the cathode chamber to saturate the KHCO3 solution, and then CO2 was continuously introduced at a rate of 20 mL / min to carry out electrocatalytic reduction in constant voltage mode.

10. The method according to claim 9, wherein, The method further includes: activating the catalytic electrode before using it; and / or The conditions for the electrocatalytic reduction include: the working voltage of the electrolytic cell is -2V to -1.2V, and the electrocatalytic reduction time is 25-35min.

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