Preparation method of amine compound modified copper electrode composite material and application thereof

Abstract

The application discloses a preparation method of amine compound modified copper electrode composite material and application thereof, and relates to the technical field of electrocatalysis. The preparation method comprises the following steps: (1) dissolving copper salt in deionized water to form a uniform solution, then adding alkali solution dropwise, stirring at room temperature, centrifuging, washing, drying, and obtaining alkaline copper salt nanosheets; (2) dispersing the alkaline copper salt nanosheets in an isopropanol solution, then adding an amine compound aqueous solution, and obtaining an amine compound modified alkaline copper composite material. The amine compound rich in sp 3 -N is used for modifying a copper electrode, the local carbon dioxide concentration and pH value of the copper catalyst surface are adjusted, the C 2+ product selectivity of the copper-based catalyst in an acidic electrolyte is improved, and the catalytic conversion efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, specifically to a method for preparing amine-modified copper electrode composite materials and their applications. Background Technology

[0002] Using intermittent renewable electricity such as solar, wind, and tidal power to drive electrocatalytic CO2 reduction reactions can convert electrical energy into chemical energy, which is an effective technology to alleviate the greenhouse effect and energy crisis.

[0003] The selectivity and efficiency of electrocatalytic CO2 reduction reactions depend on the type of catalyst, and different catalysts produce different products. For example, Au, Fe, Co, Ni, and carbon-based catalysts exhibit the highest selectivity for carbon monoxide; Bi, Sn, In, and Pb-based catalysts show the highest selectivity for formic acid; while Cu-based catalysts can convert CO2 into alkanes and alcohols with higher energy density and greater economic value, such as ethylene, ethanol, and n-propanol. This is mainly attributed to the unique electronic structure of copper atoms and the moderate *CO adsorption energy. However, most copper catalysts still face the problem of poor selectivity, with the main products being H2 and CO. Further improving the catalytic activity and selectivity of copper-based catalysts has become a key focus and challenge in this field. To improve C... 2+ To address product selectivity, researchers have proposed a series of modification strategies, among which functionalizing copper electrodes with organic molecules or polymers is an effective activity-regulating strategy. Reported additives, such as pyridine salts, polyaniline, and polypyrrole, can modulate the binding energy of CO2 reduction reaction intermediates on the surface of copper catalysts, thereby controlling product selectivity. However, the selection of such organic compounds remains very limited, and the preparation processes are complex.

[0004] The amine group in amine compounds is a Lewis base, which has an affinity for CO2 and is often used in CO2 permeation membranes and CO2 adsorbents. Polyethyleneimine (PEI) is a commercially available and inexpensive amine polymer whose structure contains a large amount of sp(s) groups. 3 The -N structure effectively adsorbs CO2, thereby increasing the local CO2 concentration and lowering the activation energy of the catalytic reaction. Simultaneously, PEI, as a basic cationic polymer, can increase the local pH of the electrode surface, suppressing the competing reaction for hydrogen evolution in water electrolysis and enhancing catalytic activity. However, there are currently no research reports on the use of amine compounds, especially polyethyleneimine, to modify copper-based catalysts for electrocatalytic CO2 reduction. Therefore, this invention reports a method for preparing amine-modified copper electrode composite materials and their applications, which, by adjusting the local microenvironment on the catalyst surface, suppresses the competing reaction for hydrogen evolution in water electrolysis, thereby improving the catalytic activity and selectivity of CO2 conversion. Summary of the Invention

[0005] In view of the above-mentioned deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a method for preparing amine-modified copper electrode composite materials and their application, which can suppress hydrogen evolution competition reaction and improve CO2 conversion catalytic activity and selectivity by increasing the local CO2 concentration and pH value on the catalyst surface.

[0006] To achieve the above objectives, the present invention provides a method for preparing an amine-modified copper electrode composite material, characterized by comprising the following steps:

[0007] (1) Dissolve copper salt in deionized water to form a homogeneous solution, then add alkaline solution dropwise, stir at room temperature, centrifuge, wash, and dry to obtain basic copper salt nanosheets;

[0008] (2) Disperse basic copper salt nanosheets in isopropanol solution, then add aqueous solution of amine compound, stir vigorously, remove solvent, and obtain amine compound modified basic copper salt composite material.

[0009] In a preferred embodiment of the present invention, in step (1), the copper salt is one of copper nitrate, copper chloride, and copper sulfate.

[0010] In a preferred embodiment of the present invention, in step (1), the alkaline solution is KOH or NaOH.

[0011] In a preferred embodiment of the present invention, in step (1), the molar ratio of the copper salt to the alkaline solution is greater than or equal to 1:1; preferably, the molar ratio of the copper salt to the alkaline solution is 1:1.

[0012] In a preferred embodiment of the present invention, the stirring time in both steps (1) and (2) is 1-10 hours.

[0013] In a preferred embodiment of the present invention, in step (1), during washing, the product is first washed three times with deionized water, and then washed once with ethanol.

[0014] In another preferred embodiment of the present invention, in step (2), 10 mg of basic copper salt nanosheets are dispersed in 5 mL of isopropanol solution, and the concentration of the added amine compound aqueous solution is 10 mg / mL, and the amount added is 0.025 mL.

[0015] In another preferred embodiment of the present invention, in step (2), the amine compound is any one of polyethyleneimine, hydroxyethyl ethylenediamine or tetraethylenepentamine.

[0016] In another preferred embodiment of the present invention, in step (2), the amine compound is polyethyleneimine.

[0017] This invention also discloses the application of a composite material prepared by the method described above in the electrocatalytic reduction of carbon dioxide. Preferably, the composite material is used to electrocatalytically reduce carbon dioxide to ethylene.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This invention uses the basic cationic polymer polyethyleneimine to modify copper electrodes. Since polyethyleneimine is a basic molecule, it can form an alkaline environment in the local electrode to inhibit the hydrogen evolution reaction. After modification with polyethyleneimine, the copper-based catalyst has improved C2+ product selectivity and reduced hydrogen evolution selectivity in acidic electrolyte.

[0020] Polyethyleneimine has an affinity for CO2, which can increase the local CO2 concentration and further enhance the selectivity for C2+ products;

[0021] Currently, most of the organic small molecules used for copper modification have complicated preparation processes and are not easy to apply on a large scale. The polyethyleneimine used in this invention is inexpensive, easy to functionalize and modify, has strong processability, and its abundant amine groups can easily bind to the substrate, enabling large-scale preparation.

[0022] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0023] Figure 1 This is the XRD pattern of the basic copper nitrate nanosheets in Example 1 of this invention;

[0024] Figure 2 This is the infrared spectrum of PEI-Cu in Example 1 of the present invention;

[0025] Figure 3 This is a graph showing the electrocatalytic CO2 reduction performance of PEI-Cu in a near-neutral electrolyte in Example 1 of this invention;

[0026] Figure 4 This is a graph showing the electrocatalytic CO2 reduction performance of PEI-Cu in acidic electrolyte in Example 1 of this invention;

[0027] Figure 5 This is a comparison chart of the electrocatalytic CO2 reduction performance of copper composite materials modified with different amine compounds in Example 1 and Comparative Examples 1 and 2 of this invention. Detailed Implementation

[0028] The following description, with reference to the accompanying drawings, illustrates several preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0029] In the accompanying drawings, components with the same structure are indicated by the same numerical designation, and components with similar structures or functions are indicated by similar numerical designations. The dimensions and thicknesses of each component shown in the drawings are arbitrary, and the present invention does not limit the dimensions and thicknesses of each component. To make the illustrations clearer, the thickness of some components has been appropriately exaggerated in the drawings.

[0030] Example 1

[0031] This embodiment describes the preparation of PEI-modified basic copper nitrate nanoparticle composite material, and the process is as follows:

[0032] (a) Dissolve 374 mg of copper nitrate in 200 mL of deionized water to obtain a 0.01 M copper nitrate solution. Add 20 mL of 0.1 M potassium hydroxide solution to this solution and stir at room temperature for 2 h. After the reaction is complete, centrifuge at 10000 r / min for 10 min, and wash three times with deionized water and once with ethanol. Dry under vacuum at 60 °C to obtain basic copper nitrate particles.

[0033] (b) Take 10 mg of basic copper nitrate particles and disperse them in 5 mL of isopropanol. Then add 0.025 mL of 10 mg / mL PEI aqueous solution and stir vigorously for 2 h. Use a rotary evaporator to evaporate the solvent to dryness. Place it in a vacuum oven at 60 °C and dry for 12 h to obtain PEI-modified basic copper nitrate composite material PEI-Cu.

[0034] Comparative Example 1

[0035] This example describes the preparation of a hydroxyethyl ethylenediamine (AEAE) modified basic copper nitrate nanoparticle composite material, and the process is as follows:

[0036] 10 mg of basic copper nitrate nanoparticles were dispersed in isopropanol (5 ml), followed by the addition of 0.025 mL of 10 mg / mL AEAE aqueous solution. The mixture was stirred vigorously for 2 h, and the solvent was evaporated to dryness using a rotary evaporator. The mixture was then placed in a vacuum oven at 60 °C and dried for 12 h to obtain AEAE-Cu, an AEAE-modified basic copper nitrate nanocomposite material.

[0037] Comparative Example 2

[0038] This example describes the preparation of tetraethylenepentamine (TEP) modified basic copper nitrate nanoparticle composite material, and the process is as follows:

[0039] 10 mg of basic copper nitrate nanoparticles were dispersed in isopropanol (5 ml), followed by the addition of 0.025 mL of 10 mg / mL TEP aqueous solution. The mixture was stirred vigorously for 2 h, and the solvent was evaporated to dryness using a rotary evaporator. The mixture was then placed in a vacuum oven at 60 °C and dried for 12 h to obtain TEP-Cu, a TEP-modified basic copper nitrate nanoparticle composite material.

[0040] The following is a structural characterization of Example 1.

[0041] X-ray diffraction (XRD) was performed on the PEI-Cu sample from Example 1. The generator voltage was 40 kV, the generator current was 40 mA, and the scanning speed was 5° / min. -1 The result is as follows Figure 1 As shown.

[0042] Depend on Figure 1 The XRD pattern shows that the material has obvious diffraction peaks at 2θ = 12.5°, 25.7°, 33.5°, 36.4°, and 40°. By comparing with the standard card, it is confirmed that copper exists in the form of Cu2(NO3)(OH)3.

[0043] Fourier transform infrared spectroscopy was performed on the PEI-Cu in Example 1, and the results are as follows: Figure 2 As shown.

[0044] Depend on Figure 2 The infrared spectrum shows that the material has a wavelength of 1422 cm⁻¹. -1 and 1354cm -1 The presence of a distinct absorption peak indicates that the NH vibration is present, suggesting that PEI-Cu contains a large number of amine groups, and that PEI has been successfully grafted onto the Cu surface.

[0045] The following are the electrocatalytic CO2 reduction performance tests of the samples prepared in Example 1 and each comparative example:

[0046] The electrocatalytic CO2 reduction activity of the PEI-Cu sample prepared in Example 1 was tested. The test electrode was prepared as follows: 5 mg of the PEI-Cu sample was ultrasonically stirred and dispersed in 500 μL of 0.5 wt% Nafion solution to obtain a catalyst slurry. 5 μL of the slurry was pipetted and uniformly dropped onto a glassy carbon electrode, which was then air-dried to obtain the test electrode. The specific testing method was a three-electrode system, where the catalyst-loaded glassy carbon electrode was the working electrode, the silver / silver chloride electrode was the reference electrode, and the platinum sheet was the counter electrode. During the test, the near-neutral electrolyte was 0.1 M KHCO3, and the acidic electrolyte was 0.2 mM H2SO4 / 0.1 M KCl. The gaseous products generated by the reaction were quantitatively analyzed by gas chromatography.

[0047] The electrocatalytic CO2 reduction performance test results of Example 1 are as follows: Figure 3and 4 As shown, this PEI-Cu catalyst exhibits high ethylene selectivity and low hydrogen selectivity in both near-neutral and acidic electrolytes. In a 0.1 M KHCO3 electrolyte, the ethylene selectivity reaches as high as 45.4% at a potential of -1.5 V. In a 0.2 mM H2SO4 / 0.1 M KCl electrolyte, the ethylene selectivity reaches as high as 54.3% at a potential of -1.6 V.

[0048] The results of the electrocatalytic reduction of CO2 to ethylene in Example 1 and the comparative examples in acidic electrolytes are as follows: Figure 5 As shown in the figure, the highest ethylene Faradaic efficiency of Comparative Example 1 was 39.8%, and the highest ethylene Faradaic efficiency of Comparative Example 2 was 20.5%. Therefore, the PEI of Example 1 showed the most significant improvement in CO2 electrocatalytic activity compared to other amine small molecules, providing a new approach for the development of highly efficient electrocatalysts.

[0049] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. The application of an amine-modified basic copper salt composite material in electrocatalytic carbon dioxide conversion, characterized in that, The preparation method of the composite material includes the following steps: (1) Dissolve copper salt in deionized water to form a homogeneous solution, then add alkaline solution dropwise, stir at room temperature, centrifuge, wash, and dry to obtain basic copper salt nanosheets; the copper salt is copper nitrate; the basic copper salt is Cu2(NO3)(OH)3. (2) Basic copper salt nanosheets were dispersed in isopropanol, followed by the addition of an aqueous solution of an amine compound. The mixture was stirred vigorously to remove the solvent, thereby obtaining a basic copper salt composite material modified with an amine compound. The amine compound was polyethyleneimine. In step (2), 10 mg of basic copper salt nanosheets are dispersed in 5 mL of isopropanol, and the concentration of the added amine compound aqueous solution is 10 mg / mL, and the amount added is 0.025 mL.

2. The application according to claim 1, characterized in that, In step (1), the alkaline solution is a KOH solution or a NaOH solution.

3. The application according to claim 2, characterized in that, In step (1), the molar ratio of the copper salt to the alkali in the alkaline solution is greater than or equal to 1:

1.

4. The application according to claim 1, characterized in that, In both steps (1) and (2), the stirring time is 1-10 hours.

5. The application according to claim 1, characterized in that, In step (1), during washing, first wash with deionized water three times, and then wash with ethanol once.

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