Preparation method of copper nanoparticles with controllable size and crystal surface and its application

Abstract

This invention discloses a method for preparing copper nanoparticles with controllable size and crystal planes, and its application. Using commercial copper powder as a precursor, the method utilizes controlled ultrasound time, followed by electrochemical reduction, to produce copper nanoparticles with controllable size and crystal planes and excellent electrocatalytic performance. The method utilizes a wide range of raw materials and is simple to operate. The prepared copper nanoparticles not only achieve a specific size and crystal plane, but can also be used as a catalyst in the electrocatalytic reduction of carbon dioxide. The catalytic activity and selectivity for ethylene production are significantly improved compared to conventional copper catalysts.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanoparticle preparation, and in particular relates to a method for converting copper powder into copper nanoparticles with controllable size and crystal surface, and an application thereof in the field of electrocatalytic reduction of carbon dioxide. Background Art

[0002] In order to overcome the greenhouse effect, people have invested a lot of energy in developing different carbon dioxide conversion technologies. Researchers have developed various methods (e.g., biological, thermochemical, electrochemical, and photochemical conversions) to use carbon dioxide as a carbon source to electrochemically synthesize high-value fuels / chemicals (e.g., CO, CH4, HCOOH, C2H4, and C2H5OH). At the same time, the synthesis of carbon products by electrochemical CO2 reduction (ECR) has also aroused great interest among researchers because it can achieve CO2 electrosynthesis by integrating electricity generated by renewable energy sources (such as solar, wind, and tidal energy) at ambient temperature and pressure in modular, compact, flexible, and scalable devices.

[0003] Copper catalysts for the electroreduction of carbon dioxide to produce hydrocarbons and C 2+ Oxygen-containing compounds have unique properties. Their adsorption energy for the intermediate *CO is negative, and the adsorption energy for *H is positive. Therefore, they tend to reduce CO2 to hydrocarbons and alcohols. This has attracted scientists to study for decades. At present, when using copper-based catalysts, CO2 electroreduction can be achieved at current densities as high as 1A cm -2 Electrochemical synthesis of C 2+ However, the use of Cu catalysts for ECR still faces many challenges, such as poor selectivity, slow electron transfer kinetics, low current density, and poor stability.

[0004] The size and shape of the material directly determine the number of active sites of the electrocatalyst in ECR. Existing studies generally believe that the smaller the size of the catalyst, the more active sites it will expose during the reaction. Therefore, smaller electrocatalysts usually exhibit better catalytic activity. In addition to size regulation, controlling various metal nanostructures and shapes to regulate the active sites and specific crystal faces exposed during the catalytic process is another effective means to regulate catalytic activity. For example, in copper catalysts, the exposure of different crystal faces during the reaction directly affects the catalytic selectivity. When the exposed crystal face is the (111) crystal face, the main catalytic product is CH4, while when the exposed crystal face is the (100) crystal face, the main catalytic product is converted into C2H4.

[0005] Copper-based materials used for the electrocatalytic reduction of carbon dioxide primarily consist of elemental copper, copper oxide, cuprous oxide, or alloys containing copper. Current methods for preparing copper-based catalysts primarily utilize raw materials containing copper metal salts or copper-containing templates, which can generate significant pollution during the reaction. Furthermore, most current methods require the presence of precipitants such as sodium hydroxide and urea, resulting in complex and variable reactions, demanding reaction conditions, and strict equipment requirements. Furthermore, the resulting catalyst materials often lack control over both size and crystal surface.

[0006] In summary, most existing methods for preparing copper-based materials have complex processes or high requirements for equipment and raw materials. Summary of the Invention

[0007] In response to the shortcomings of the above-mentioned existing preparation methods, the present invention provides a method for preparing copper nanoparticles with controllable size and crystal surface, aiming to enable them to have excellent electrocatalytic reduction of carbon dioxide to produce ethylene performance.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for preparing copper nanoparticles with controllable size and crystal planes, characterized by using commercial copper powder as a precursor and converting it into copper nanoparticles with controllable size and crystal planes through ultrasonic and electrochemical reduction. The specific method is as follows:

[0010] Commercial copper powder is dispersed in an ultrasonic solution to form a dispersion; the obtained dispersion is ultrasonically treated, and a sample after ultrasonic treatment is collected to obtain copper nanoparticles of a desired size; and the obtained nanoparticles are then electrochemically reduced to obtain copper nanoparticles with a desired crystal surface.

[0011] Furthermore, the ultrasonic power is 400W and the ultrasonic time is 8 to 20 hours.

[0012] Furthermore, the potential of the electrochemical reduction is (-0.1) to (-1.0) V vs. RHE, and the reduction time is 0 to 40 min.

[0013] Furthermore, the usage ratio of the commercial copper powder to the ultrasonic solution is 0.1-1000 mg:100 mL.

[0014] Furthermore, the ultrasonic solution is a mixture of one or more liquids selected from N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), isopropyl alcohol (IPA), ethanol and water.

[0015] Compared with the existing technology, the beneficial effects of the present invention are embodied in:

[0016] 1. Compared with previous methods for preparing copper nanoparticles, the method mentioned in the present invention regulates the size of copper nanoparticles by controlling the ultrasonic time. Copper nanoparticles of different sizes expose different crystal faces after electrochemical reduction, thereby achieving simultaneous control of size and crystal face.

[0017] 2. The copper nanoparticles prepared by the present invention can be used as catalysts in the electrocatalytic reduction of carbon dioxide and have excellent performance. Their catalytic activity for producing ethylene is very high. The maximum Faradaic efficiency of commercial copper powder for producing ethylene is only 24%, and the current density of the ethylene portion is only ~0.023A cm -2 The maximum Faraday efficiency of the copper nanoparticles prepared by the present invention in producing ethylene can reach 80%, and the partial current density of ethylene can reach 1.1A cm -2 .

[0018] 3. The present invention provides a novel method for preparing copper nanoparticles with controllable size and crystal plane, which can directly convert commercial copper powder into copper nanoparticles with controllable size and crystal plane. The raw material source is wide and the method is simple, which provides a new idea for the subsequent preparation of copper nanoparticles with different sizes and crystal planes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the SEM image of the commercial copper powder used in Example 1 ( Figure 1 (a)) and TEM images, HRTEM images and particle size distribution images of the prepared copper nanoparticles ( Figure 1 (b,c,d) in the figure.

[0020] Figure 2 This is the SEM image of the commercial copper powder used in Example 2 ( Figure 2 (a)) and TEM images, HRTEM images and particle size distribution images of the prepared copper nanoparticles ( Figure 2 (b,c,d) in the figure.

[0021] Figure 3 This is the SEM image of the commercial copper powder used in Example 3 ( Figure 3 (a)) and TEM images, HRTEM images and particle size distribution images of the prepared copper nanoparticles ( Figure 3 (b,c,d) in the figure.

[0022] Figure 4 This is the SEM image of the commercial copper powder used in Example 4 ( Figure 4 (a)) and TEM images, HRTEM images and particle size distribution images of the prepared copper nanoparticles ( Figure 4 (b,c,d) in the figure.

[0023] Figure 5This is the SEM image of the commercial copper powder used in Example 5 ( Figure 5 (a)) and TEM images, HRTEM images and particle size distribution images of the prepared copper nanoparticles ( Figure 5 (b,c,d) in the figure.

[0024] Figure 6 The product efficiency distribution diagram and current diagram of the electrocatalytic reduction of carbon dioxide by the commercial copper powder used in each example are shown.

[0025] Figure 7 (a) to (d) are the product efficiency distribution diagrams and current diagrams of the electrocatalytic reduction of carbon dioxide by the copper nanoparticles prepared in Examples 1-4, respectively.

[0026] Figure 8 (a) to (d) are diagrams showing the adsorption states of *CO intermediates on the surface of the copper nanoparticles prepared in Examples 1-4 during the electrocatalytic reduction process. DETAILED DESCRIPTION

[0027] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0028] The ultrasonic solution used in the following examples is a mixed solution of isopropyl alcohol and water in a volume ratio of 1:1.

[0029] The electrochemical reduction method in the following examples is as follows: first, the prepared catalyst powder is weighed, and then dispersed in a mixed solution of isopropyl alcohol and water (volume ratio 3:1) to form a dispersion, and then the dispersion is ultrasonically homogenized to prepare a catalyst slurry. The catalyst slurry is sprayed onto carbon paper by air spraying to obtain a catalyst electrode, and then the prepared catalyst electrode is used as the working electrode, the Ag / AgCl electrode is used as the reference electrode, and the nickel mesh is used as the counter electrode. A three-electrode electrochemical reduction is performed using a constant potential method, and the electrolyte is 1 molL -1 of potassium hydroxide solution.

[0030] Example 1

[0031] In this example, commercial copper powder was used as raw material to prepare copper nanoparticles. The specific steps are as follows:

[0032] Weigh 1g of commercial copper powder and disperse it in 200mL of ultrasonic solution to form a dispersion. The resulting dispersion was ultrasonicated at 400W for 8 hours. The sonicated sample was collected and electrochemically reduced at a potential of -1.0V vs. RHE to produce copper nanoparticles of the appropriate size and crystal plane.

[0033] The SEM images of the commercial copper powder used in this example are as follows: Figure 1As shown in (a), the TEM image, HRTEM image and particle size distribution of the prepared copper nanoparticles are shown in Figure 1 As shown in (b, c, d), it can be seen that the product is copper nanoparticles with a particle size of 50 nm and exposed (111) crystal plane.

[0034] Example 2

[0035] In this example, commercial copper powder was used as raw material to prepare copper nanoparticles. The specific steps are as follows:

[0036] Weigh 1g of commercial copper powder and disperse it in 200mL of ultrasonic solution to form a dispersion. The resulting dispersion was ultrasonicated at 400W for 12 hours. The sonicated sample was collected and electrochemically reduced at -1.0V vs. RHE to produce copper nanoparticles of the appropriate size and crystal plane.

[0037] The SEM images of the commercial copper powder used in this example are as follows: Figure 2 As shown in (a), the TEM image, HRTEM image and particle size distribution of the prepared copper nanoparticles are shown in Figure 2 As shown in (b, c, d), it can be seen that the product is copper nanoparticles with a particle size of 25 nm and exposed (111) crystal plane.

[0038] Example 3

[0039] In this embodiment, commercial copper powder is used as raw material to prepare copper nanoparticles. The specific steps are as follows:

[0040] Weigh 1g of commercial copper powder and disperse it in 200mL of ultrasonic solution to form a dispersion. The resulting dispersion was ultrasonicated at 400W for 16 hours. The sonicated sample was collected and electrochemically reduced at a potential of -1.0V vs. RHE to produce copper nanoparticles of the appropriate size and crystal plane.

[0041] The SEM images of the commercial copper powder used in this example are as follows: Figure 3 As shown in (a), the TEM image, HRTEM image and particle size distribution of the prepared copper nanoparticles are shown in Figure 3 As shown in (b, c, d), it can be seen that the product is copper nanoparticles with a particle size of 15 nm and exposed (110) crystal plane.

[0042] Example 4

[0043] In this example, commercial copper powder was used as raw material to prepare copper nanoparticles. The specific steps are as follows:

[0044] Weigh 1g of commercial copper powder and disperse it in 200mL of ultrasonic solution to form a dispersion. The resulting dispersion was ultrasonicated at 400W for 20 hours. The sonicated sample was collected and electrochemically reduced at -1.0V vs. RHE to produce copper nanoparticles of the appropriate size and crystal plane.

[0045] The SEM images of the commercial copper powder used in this example are as follows: Figure 4 As shown in (a), the TEM image, HRTEM image and particle size distribution of the prepared copper nanoparticles are shown in Figure 4 As shown in (b, c, d), it can be seen that the product is copper nanoparticles with a particle size of 5 nm and exposed (100) crystal plane.

[0046] Example 5

[0047] In this example, commercial copper powder was used as raw material to prepare copper nanoparticles. The specific steps are as follows:

[0048] Weigh 1g of commercial copper powder and disperse it in 200mL of ultrasonic solution to form a dispersion. The resulting dispersion was ultrasonicated at 400W for 20 hours. The sonicated sample was collected and electrochemically reduced at -0.8V vs. RHE to produce copper nanoparticles of the appropriate size and crystal plane.

[0049] The SEM images of the commercial copper powder used in this example are as follows: Figure 5 As shown in (a), the TEM image, HRTEM image and particle size distribution of the prepared copper nanoparticles are shown in Figure 5 As shown in (b, c, d), it can be seen that the product is copper nanoparticles with a particle size of 5 nm and exposed (100) crystal plane.

[0050] The performance of the sample in electrocatalytic reduction of CO2 was tested using a flow reactor, in which the prepared copper nanoparticles were used as the working electrode, the Ag / AgCl electrode was used as the reference electrode, the nickel mesh was used as the counter electrode, and the electrolyte was 1 molL -1 During the electrochemical test, chronopotentiometry was used. The gas products produced by the reaction at different potentials were directly tested by a gas chromatograph connected to the reactor, and the liquid products were subsequently tested by a superconducting nuclear magnetic resonance spectrometer.

[0051] Figure 6 The product efficiency distribution diagram and current diagram of the electrocatalytic reduction of CO2 by the commercial copper powder used in each embodiment are shown in the figure. It can be seen from the figure that in the electrocatalytic reduction of carbon dioxide reaction, the maximum Faradaic efficiency of ethylene of the commercial copper powder is only 24%, and the partial current density of ethylene at this efficiency is only 0.023A cm -1, as the reaction proceeds, the Faradaic efficiency of hydrogen increases dramatically, reaching 58%, eventually leading to catalyst deactivation.

[0052] Figure 7 The product efficiency distribution and current diagrams for the electrocatalytic reduction of CO2 using copper nanoparticles prepared in each example show that copper nanoparticles of different sizes and crystal faces exhibit different catalytic performance. In terms of selectivity, the maximum Faradaic efficiencies for ethylene produced by the copper nanoparticles prepared in Examples 1-4 were 50%, 53%, 56%, and 79%, respectively, corresponding to ethylene partial currents of 0.30 A cm -1 , 0.49A cm -1 、0.63A cm -1 and 1.1A cm -1 , from which it can be seen that the catalytic activity of copper nanoparticles is affected by their size and crystal surface.

[0053] During the reaction, the adsorption state of the *CO intermediate on the sample surface will affect its catalytic performance. Figure 8 (ad) are the results related to the adsorption state of *CO intermediates on the surface of each sample. In general, as the sample particle size decreases, the total *CO intermediate adsorption intensity increases. When the sample particle size is 50nm and 25nm, *CO only appears when the test voltage is large. bridge and *CO atop signal peaks, and the intensities of these two signal peaks are relatively weak; when the sample particle size is 15nm, there is *CO at the beginning of the test bridge and *CO atop The signal peak is much higher than that of the samples with particle sizes of 50nm and 25nm. When the sample particle size is 5nm, the *CO bridge and *CO atop The signal peak will also appear at the beginning of the test, and when the signal peak intensity is high, it can be clearly found that the proportion of the *COatop signal has increased. This also explains why different sample particle sizes will expose different crystal faces during the reaction. Relevant studies have shown that in the electrocatalytic reduction of carbon dioxide, the type of reaction intermediates may affect the reconstruction process of the catalyst, causing the catalyst to expose different crystal faces. From the above test results, the adsorption intensity of *CO intermediates in samples with a particle size of 50nm and 25nm is generally low during the reaction. The adsorption intensity of *CO intermediates in samples with a particle size of 15nm is relatively high during the reaction. The adsorption intensity of *CO intermediates in samples with a particle size of 5nm is the highest during the reaction. Different *CO adsorption intensities can adjust the crystal faces exposed by the sample during the reaction. Ultimately, the difference in *CO intermediate adsorption intensity causes samples of different particle sizes to expose different crystal faces during the electrochemical reduction process.

[0054] The above embodiments are typical examples of the present invention and are not intended to limit the present invention in any way. For example, the type of copper powder, ultrasonic solution, the ratio of copper powder to ultrasonic solution, ultrasonic conditions, and electrochemical reduction parameters can all be further adjusted. Therefore, based on the overall concept of the present invention, any adjustments and modifications made by those skilled in the art to the described process parameters shall fall within the scope of protection of the present invention as long as they do not deviate from the concept of the invention or exceed the scope defined by the claims.

Claims

1. A method for preparing copper nanoparticles with controllable size and crystal surface, characterized in that: Using commercial copper powder as a precursor, the commercial copper powder is converted into copper nanoparticles with controllable size and crystal surface through ultrasonic and electrochemical reduction. The specific steps include: Commercial copper powder is dispersed in an ultrasonic solution to form a dispersion; the resulting dispersion is ultrasonically treated at a power of 400 W and a time of 8 to 20 h, and a sample after ultrasonic treatment is collected to obtain copper nanoparticles of the desired size; the resulting nanoparticles are then electrochemically reduced at a potential of -0.1 to -1.0 V vs. RHE and a reduction time of 0 to 40 min to obtain copper nanoparticles with the desired crystal plane; the size of the copper nanoparticles is regulated by controlling the ultrasonic time, so that copper nanoparticles of different sizes expose different crystal planes after electrochemical reduction, thereby achieving simultaneous control of both size and crystal plane.

2. The preparation method according to claim 1, wherein: The usage ratio of the commercial copper powder to the ultrasonic solution is 0.1-1000 mg:100 mL.

3. Copper nanoparticles with controllable size and crystal surface obtained by the preparation method according to claim 1 or 2.

4. Use of the copper nanoparticles according to claim 3 as a catalyst in an electrocatalytic reduction of carbon dioxide reaction.

5. The use according to claim 4, characterized in that: Used for electrocatalytic reduction of carbon dioxide to produce ethylene.

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