Copper nanosheet as well as preparation method and application thereof

Abstract

The invention relates to the technical field of electro-catalysis, in particular to a copper nanosheet and a preparation method and application thereof. The preparation method comprises the following steps: A) mixing copper salt, sodium hydroxide and water, and reacting at 80-120 DEG C to obtain nano flaky copper oxide; b) performing nitrogen plasma treatment on the nano flaky copper oxide to obtain nano flaky copper oxide rich in oxygen vacancies; c) preparing the nano flaky copper oxide rich in oxygen vacancies into a copper oxide electrode; and D) carrying out an electrochemical pre-reduction reaction on the copper oxide electrode to obtain the copper nanosheet with the specifically exposed (100) crystal face. According to the method, the content of oxygen vacancies on the surface of copper oxide is adjusted through plasma treatment, the copper nanosheet obtained after electrochemical pre-reduction specifically exposes a (100) crystal face with high carbon dioxide activity, and the copper nanosheet has good performance of preparing ethylene through electro-catalysis carbon dioxide reduction in a neutral medium.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalysis, and particularly relates to a copper nanosheet, a preparation method thereof, and an application thereof. Background Art

[0002] In 2022, the global market demand for ethylene (C 2 H 4 ) was approximately 224 million tons, far exceeding any other organic chemical demanded annually. It is an important industrial raw material for manufacturing various plastics, cosmetics, and solvents. Traditional C 2 H 4 production relies on steam cracking of long-chain hydrocarbons (such as naphtha or liquefied petroleum gas); unfortunately, this process releases more than 200 million tons of CO 2 annually, accounting for approximately 0.6% of the total anthropogenic carbon dioxide emissions.

[0003] Electrochemical CO 2 reduction (CO 2 R) using renewable electricity and water provides a promising route for low-carbon carbon dioxide production. In the past few years, through adjusting the morphology, oxidation state, surface and defects of the catalyst, introducing molecules and halogens, alloying of copper (Cu) with other metals, and using cascade CO 2 electroreduction, the conversion performance of CO 2 to C 2 H 4 has made substantial progress. In alkaline media, the peak Faraday efficiencies are 70% and >80% at the abrupt Cu interface and Cu-Al alloy, respectively, but the carbon utilization efficiency is low in alkaline media. When switching the electrolyte from an alkaline environment to a neutral environment, an important advantage is that the carbon utilization efficiency can be significantly improved; in addition, the mild reaction environment can reduce the demand for reaction device materials, increase the service life of the device, and reduce the cost of the reaction system.

[0004] Recently, in mild neutral electrolytes, the conversion of CO 2 to C 2 H 4 has shown impressive Faraday efficiencies (FE) on some Cu-based catalysts; however, these catalysts rarely exhibit a high partial current density (product formation rate) of >300 mA cm -2 , and it is difficult to combine high reaction activity, fast reaction rate, and excellent stability. In addition, their performance in actual membrane electrode assembly (MEA) electrolyzers has not been fully studied. Therefore, there is an urgent need to develop highly efficient, fast, and stable catalysts that can more effectively catalyze the reduction of CO 2 to prepare C 2 H 4 in mild neutral media. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a copper nanosheet, a preparation method thereof and an application. The copper nanosheet prepared by the present invention can selectively expose the (100) crystal plane of Cu and is rich in defect sites, and has excellent performance in electrocatalytic reduction of carbon dioxide to ethylene in a neutral medium.

[0006] The present invention provides a method for preparing a copper nanosheet, comprising the following steps:

[0007] A) Mix a copper salt, sodium hydroxide and water, and react at 80-120 °C to obtain nano-sheet copper oxide;

[0008] B) Perform nitrogen plasma treatment on the nano-sheet copper oxide to obtain nano-sheet copper oxide rich in oxygen vacancies;

[0009] C) Fabricate the nano-sheet copper oxide rich in oxygen vacancies into a copper oxide electrode;

[0010] D) Perform an electrochemical pre-reduction reaction on the copper oxide electrode to obtain a copper nanosheet specifically exposing the (100) crystal plane.

[0011] Preferably, in step A), the copper salt is copper chloride dihydrate;

[0012] The molar ratio of the copper salt to sodium hydroxide is 0.5-1.5:55-125;

[0013] The reaction time is 8-15 h.

[0014] Preferably, in step B), in the nitrogen plasma treatment, nitrogen is used as the carrier gas, the power is 100-300 W, the time is 30-90 min, and the temperature is room temperature.

[0015] Preferably, in step B), the thickness of the nano-sheet copper oxide rich in oxygen vacancies is 5-7 nm.

[0016] Preferably, in step D), the current density of the electrochemical pre-reduction reaction is preferably 10-100 mA cm -2 , and the time is 5-30 min.

[0017] Preferably, in step D), during the electrochemical pre-reduction reaction, the cathode electrolyte used is 0.8-1.2 mol / L KCl solution, and the anode electrolyte is 0.8-1.2 mol / L KOH solution.

[0018] Preferably, in step D), during the electrochemical pre-reduction reaction, carbon dioxide is introduced into the electrolyte as the reaction gas.

[0019] The present invention also provides a copper nanosheet prepared by the preparation method described above.

[0020] The present invention also provides an application of the copper nanosheet described above as a catalyst for electrocatalytic reduction of carbon dioxide to prepare ethylene.

[0021] Preferably, the electrocatalytic reduction of carbon dioxide to prepare ethylene is carried out in a flow electrolytic cell;

[0022] or the electrocatalytic reduction of carbon dioxide to prepare ethylene is carried out in a membrane electrode assembly electrolytic cell.

[0023] The present invention provides a method for preparing a copper nanosheet, comprising the following steps: A) mixing a copper salt, sodium hydroxide and water, and reacting at 80-120 °C to obtain nano-sheet copper oxide; B) performing nitrogen plasma treatment on the nano-sheet copper oxide to obtain nano-sheet copper oxide rich in oxygen vacancies; C) fabricating the nano-sheet copper oxide rich in oxygen vacancies into a copper oxide electrode; D) performing an electrochemical pre-reduction reaction on the copper oxide electrode to obtain a copper nanosheet with specific exposure of the (100) crystal plane.

[0024] Compared with the prior art, the present invention realizes the regulation of the oxygen vacancy content on the surface of copper oxide through a simple method of plasma treatment, and the copper nanosheet obtained after electrochemical pre-reduction specifically exposes the (100) crystal plane with high carbon dioxide activity. Therefore, it has good performance in electrocatalytic reduction of carbon dioxide to prepare ethylene in a neutral medium, with a Faraday efficiency as high as 72%, and the performance stability time exceeds 100 h at a current density of 500 mA / cm -2 of the current density.

[0025] Experiments show that the copper nanosheet obtained by pre-reducing the nano-sheet copper oxide rich in oxygen vacancies prepared by the present invention has good performance in electrocatalytic reduction of carbon dioxide to prepare ethylene in a flow electrolytic cell in a neutral medium, with an ethylene Faraday efficiency as high as 72%, and the reaction rate (partial current density) can be as high as 360 mA cm -2 , and can stably and efficiently electrocatalytically reduce carbon dioxide to prepare ethylene for more than 100 h in a neutral medium. In addition, the copper nanosheet prepared by the present invention also has good performance in electrocatalytic reduction of carbon dioxide to prepare ethylene in a membrane electrode assembly electrolytic cell, with an ethylene Faraday efficiency as high as 64%, a total reaction current of 800 mA, and can stably and efficiently electrocatalytically reduce carbon dioxide to prepare ethylene for more than 70 h in a neutral medium. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a TEM image of the nano-sheet copper oxide rich in oxygen vacancies in Example 1 of the present invention;

[0027] Figure 2XRD patterns of the oxygen vacancy-rich flaky copper oxide of Example 1 of the present invention and the flaky copper oxide of Comparative Example 1;

[0028] Figure 3 High-resolution transmission electron microscopy image and electron diffraction pattern of the oxygen vacancy-rich flaky copper oxide of Example 1 of the present invention;

[0029] Figure 4 Electron spin resonance spectra of the oxygen vacancy-rich flaky copper oxide obtained in Example 1 of the present invention and the flaky copper oxide obtained in Comparative Example 1;

[0030] Figure 5 High-angle annular dark-field scanning transmission electron microscopy image of the copper nanosheets obtained in Example 1 of the present invention;

[0031] Figure 6 Electrochemical linear voltammograms of the copper nanosheets obtained in Example 1 and Comparative Example 1 of the present invention;

[0032] Figure 7 Faradaic efficiencies for the electrocatalytic reduction of carbon dioxide to ethylene in a neutral medium in a flow electrolytic cell using the copper nanosheets obtained in Example 1 and Comparative Example 1 of the present invention;

[0033] Figure 8 Partial current densities for the electrocatalytic reduction of carbon dioxide to ethylene in a neutral medium in a flow electrolytic cell using the copper nanosheets obtained in Example 1 and Comparative Example 1 of the present invention;

[0034] Figure 9 Stability test graphs for the electrocatalytic reduction of carbon dioxide to ethylene in a neutral medium in a flow electrolytic cell using the copper nanosheets obtained in Example 1 and Comparative Example 1 of the present invention;

[0035] Figure 10 Faradaic efficiency for the electrocatalytic reduction of carbon dioxide to ethylene in a neutral medium in a membrane electrode assembly electrolytic cell using the copper nanosheets of Example 1 of the invention;

[0036] Figure 11 Energy conversion efficiency for the electrocatalytic reduction of carbon dioxide to ethylene in a neutral medium in a membrane electrode assembly electrolytic cell using the copper nanosheets of Example 1 of the invention;

[0037] Figure 12 Stability test graph for the electrocatalytic reduction of carbon dioxide to ethylene in a neutral medium in a membrane electrode assembly electrolytic cell using the copper nanosheets of Example 1 of the invention;

[0038] Figure 13 TEM image of the oxygen vacancy-rich flaky copper oxide of Example 2 of the present invention;

[0039] Figure 14 TEM image of the oxygen vacancy-rich flaky copper oxide of Example 3 of the present invention;

[0040] Figure 15 TEM image of sheet-like copper oxide rich in oxygen vacancies of Example 4 of the present invention;

[0041] Figure 16 TEM image of sheet-like copper oxide rich in oxygen vacancies of Example 5 of the present invention;

[0042] Figure 17 TEM image of sheet-like copper oxide of Comparative Example 1 of the present invention;

[0043] Figure 18 High-angle annular dark-field scanning transmission electron microscopy photograph of sheet-like copper obtained in step D-2) of Comparative Example 1 of the present invention. Detailed implementation manners

[0044] Next, in combination with the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0045] The present invention provides a method for preparing copper nanosheets, including the following steps:

[0046] A) Mix a copper salt, sodium hydroxide and water, and react at 80-120 °C to obtain nano-sheet-like copper oxide;

[0047] B) Perform nitrogen plasma treatment on the nano-sheet-like copper oxide to obtain nano-sheet-like copper oxide rich in oxygen vacancies;

[0048] C) Fabricate the nano-sheet-like copper oxide rich in oxygen vacancies into a copper oxide electrode;

[0049] D) Perform an electrochemical pre-reduction reaction on the copper oxide electrode to obtain copper nanosheets with specifically exposed (100) crystal planes.

[0050] In step A):

[0051] Mix a copper salt, sodium hydroxide and water, and react at 80-120 °C to obtain nano-sheet-like copper oxide.

[0052] The copper salt is preferably a soluble inorganic copper salt, more preferably copper chloride dihydrate; the water is preferably deionized water.

[0053] The molar ratio of the copper salt to sodium hydroxide is 0.5-1.5:55-125, such as 0.5-1.5:55-65, specifically 1:60. The mass sum of the copper salt and sodium hydroxide and the amount of water used are in a ratio of 4-8 g:60-120 mL.

[0054] The time of the reaction is 8 to 15 h; more preferably 8 to 12 h, and even more preferably 10 h.

[0055] After the reaction ends, it further includes: centrifugation and washing. The washing includes: first washing with deionized water, and then washing with ethanol. The number of times of washing with deionized water is preferably 2 to 4 times, more preferably 3 times; the number of times of washing with ethanol is preferably 2 to 4 times, more preferably 3 times.

[0056] After the washing, it further includes: vacuum drying to obtain nano-sheet copper oxide.

[0057] In step B):

[0058] The nano-sheet copper oxide is subjected to nitrogen plasma treatment to obtain nano-sheet copper oxide rich in oxygen vacancies.

[0059] In the nitrogen plasma treatment, nitrogen is used as the carrier gas; the power is preferably 100 to 300 W, such as 100 W, 200 W or 300 W; the time is preferably 30 to 90 min, such as 30 min, 60 min or 90 min; the temperature is preferably room temperature (25 - 30 °C).

[0060] Specifically, it includes:

[0061] The nano-sheet copper oxide is evenly spread on a quartz boat, placed in a quartz tube, and nitrogen is used as the carrier gas for plasma deposition to obtain nano-sheet copper oxide rich in oxygen vacancies.

[0062] The thickness of the nano-sheet copper oxide rich in oxygen vacancies is 5 to 7 nm.

[0063] In step C):

[0064] The nano-sheet copper oxide rich in oxygen vacancies is made into a copper oxide electrode.

[0065] Specifically, it includes:

[0066] The nano-sheet copper oxide rich in oxygen vacancies, isopropanol and Nafion solution are mixed and then ultrasonically mixed evenly, and the obtained dispersion is evenly sprayed on a gas diffusion carbon paper to prepare a copper oxide gas diffusion electrode (i.e., a copper oxide electrode).

[0067] The mass concentration of the Nafion solution is 4% to 6%, such as 5%.

[0068] The dosage ratio of the nano-sheet copper oxide rich in oxygen vacancies, isopropanol and Nafion solution is 10 mg: 2 mL: 50 μL.

[0069] The size of the gas diffusion carbon paper is 3×3 cm -2 .

[0070] In step D):

[0071] Perform an electrochemical pre-reduction reaction on the copper oxide electrode to obtain copper nanosheets with specifically exposed (100) crystal planes.

[0072] Performing the electrochemical pre-reduction reaction on the copper oxide electrode includes:[[]]

[0073] Using the copper oxide electrode as the working electrode, a titanium mesh coated with iridium oxide and potassium chloride as the counter electrode, and a saturated silver / silver chloride electrode (Ag / AgCl) as the reference electrode, connect to a multi-channel electrochemical workstation equipped with an amplifier to perform the electrochemical pre-reduction reaction.

[0074] The current density of the electrochemical pre-reduction reaction is preferably 10-100 mA cm -2 , more preferably 20 mA cm -2 ; the time is preferably 5-30 min, more preferably 10 min.

[0075] During the electrochemical pre-reduction reaction, the cathode electrolyte used is a 0.8-1.2 mol / L KCl solution, such as 1 mol / L KCl solution; the anode electrolyte is a 0.8-1.2 mol / L KOH solution, such as 1 mol / L KOH solution. The cathode is the copper oxide electrode.

[0076] During the electrochemical pre-reduction reaction, it is preferred to introduce carbon dioxide into the electrolyte as the reaction gas. Specifically, carbon dioxide is introduced into the cathode electrolyte as the reaction gas.

[0077] After the electrochemical pre-reduction reaction, the obtained copper nanosheets specifically expose the (100) crystal plane.

[0078] The present invention also provides copper nanosheets prepared by the preparation method described above. The copper nanosheets specifically expose the (100) crystal plane. The copper nanosheets have good electrocatalytic performance for carbon dioxide reduction to prepare ethylene, with high Faraday efficiency, reaction rate, and excellent stability.

[0079] In the present invention, when the power of nitrogen plasma treatment is low or the reaction time is short, it is not sufficient to significantly reduce the lattice oxygen content of the synthesized flaky copper oxide, and flaky copper oxide rich in oxygen vacancies will not be formed; when the power of nitrogen plasma treatment is high or the time is long, the structure of the flaky copper oxide will be damaged, and the cuprous oxide crystal phase will form and accumulate, and flaky copper oxide rich in oxygen vacancies will not be formed even more; when the power and treatment time of nitrogen plasma treatment are appropriate, flaky copper oxide rich in oxygen vacancies can be synthesized.

[0080] By simply adjusting the power and treatment time of nitrogen plasma treatment, the present invention realizes the regulation of the morphology and structure of copper oxide, and the obtained flaky copper oxide has abundant oxygen vacancy defect sites, thereby inducing the copper nanosheets obtained during the electrochemical pre-reduction reaction to specifically expose the (100) crystal plane. Therefore, it has good electrocatalytic performance for carbon dioxide reduction to ethylene in neutral media, with high Faraday efficiency, reaction rate, and excellent stability.

[0081] The present invention also provides an application of the copper nanosheets described above as a catalyst for electrocatalytic reduction of carbon dioxide to ethylene. Experimental results show that the copper nanosheets provided by the present invention have good electrocatalytic performance for carbon dioxide reduction to ethylene, with high Faraday efficiency, reaction rate, and excellent stability. Therefore, the present invention requests protection for the application of the copper nanosheets as a catalyst for electrocatalytic reduction of carbon dioxide to ethylene.

[0082] In certain embodiments of the present invention, the electrocatalytic reduction of carbon dioxide to ethylene is carried out in a flow electrolytic cell. The electrolyte for electrocatalytic reduction of carbon dioxide to ethylene is preferably a neutral solution, more preferably a potassium salt solution, and still more preferably a potassium chloride solution; the concentration of the potassium chloride solution is preferably 0.8 - 1.2 mol / L, such as 1 mol / L.

[0083] In certain embodiments of the present invention, the electrocatalytic reduction of carbon dioxide to ethylene is carried out in a membrane electrode assembly electrolytic cell. The electrolyte for electrocatalytic reduction of carbon dioxide to ethylene is preferably a neutral solution, more preferably a potassium salt solution, and still more preferably a potassium bicarbonate solution; the concentration of the potassium bicarbonate solution is preferably 0.08 - 0.12 mol / L, such as 0.1 mol / L.

[0084] The present invention places no special restrictions on the sources of the raw materials used above, and they can be commercially available in general.

[0085] To further illustrate the present invention, the following will describe in detail a copper nanosheet, its preparation method and application provided by the present invention in combination with examples, but it should not be construed as a limitation to the protection scope of the present invention.

[0086] The reagents used in the following examples are all commercially available; the examples are carried out under open conditions.

[0087] Example 1

[0088] 1) Mix 0.51 g (3 mmol) of copper chloride dihydrate, 7.2 g (180 mmol) of sodium hydroxide with 120 mL of deionized water, react at 100 °C for 10 h, centrifuge, wash 3 times with deionized water first, and then wash 3 times with ethanol to obtain nano-sheet copper oxide.

[0089] 2) Take 20 mg of the nano-sheet copper oxide and evenly spread it on a 4×20 cm -2 extended quartz boat to form a thin layer, then place it in a quartz tube, use nitrogen as the carrier gas, and perform plasma deposition at room temperature. The power of plasma deposition is 100 W and the time is 30 min to obtain sheet copper oxide rich in oxygen vacancies with a thickness of 5 - 7 nm.

[0090] Analyze the sheet copper oxide rich in oxygen vacancies obtained in Example 1 by transmission electron microscopy to obtain its transmission electron micrograph, as Figure 1 shown, Figure 1 which is the TEM image of the sheet copper oxide rich in oxygen vacancies of Example 1 of the present invention. The results show that the copper oxide obtained in Example 1 is in a sheet structure and its surface is rich in pores.

[0091] Analyze the sheet copper oxide rich in oxygen vacancies obtained in Example 1 by X-ray diffraction to obtain its X-ray crystal diffraction pattern, as Figure 2 shown, Figure 2 which is the XRD pattern of the sheet copper oxide rich in oxygen vacancies of Example 1 of the present invention and the sheet copper oxide of Comparative Example 1. The results show that the phase obtained in Example 1 is copper oxide, which corresponds well to the standard card.

[0092] Analyze the sheet copper oxide rich in oxygen vacancies obtained in Example 1 by high-resolution transmission electron microscopy to obtain its high-resolution transmission electron micrograph and electron diffraction pattern, as Figure 3 shown, Figure 3 which is the high-resolution transmission electron micrograph and electron diffraction pattern of the sheet copper oxide rich in oxygen vacancies of Example 1 of the present invention. The results show that the direction of the zone axis is

[001] .

[0093] Analyze the sheet copper oxide rich in oxygen vacancies obtained in Example 1 by an electron spin resonance spectrometer to obtain its electron spin resonance spectrum, as Figure 4 shown, Figure 4The electron spin resonance spectra of the flaky copper oxide rich in oxygen vacancies obtained in Example 1 of the present invention and the flaky copper oxide obtained in Comparative Example 1 are shown. The results show that the flaky copper oxide obtained in step 2) of Example 1 is rich in oxygen vacancies.

[0094] 3) Weigh 10 mg of the flaky copper oxide rich in oxygen vacancies obtained in step 2), add 2 mL of isopropanol, then add 50 μL of a 5% Nafion solution, sonicate until the catalyst (flaky copper oxide rich in oxygen vacancies) is evenly dispersed, and spray the dispersed droplets evenly on a 3×3 cm -2 A copper oxide gas diffusion electrode (copper oxide electrode) was prepared on a gas diffusion carbon paper.

[0095] 4) The copper oxide electrode was used as the working electrode, iridium oxide and potassium chloride were coated on the titanium mesh as the counter electrode, and a saturated silver / silver chloride electrode (Ag / AgCl) was used as the reference electrode. The electrodes were connected to a multi-channel electrochemical workstation (IM6ex, ZAHNER elektrik, manufactured in Germany) equipped with an amplifier.

[0096] The prepared copper oxide electrode was charged at 20 mA cm-1 using 1 mol / L KCl solution as the cathode electrolyte and 1 mol / L KOH solution as the anode electrolyte. -2 The pre-reduction was carried out for 10 min at a current density of 1.5 %. During the pre-reduction process, CO was continuously introduced into the cathode electrolyte. 2 , and obtain a sheet-like copper electrode (i.e., copper nanosheet).

[0097] Electrochemical hydroxyl adsorption tests were performed in a rotating disk electrode apparatus to analyze the exposed crystal faces of the catalyst (sheet copper electrode), such as Figure 5 As shown, Figure 5 This is a high-angle annular dark field scanning transmission electron microscopy image of the copper nanosheet obtained in Example 1 of the present invention. The results show that after pre-reduction, the copper oxide in Example 1 becomes flaky and porous copper.

[0098] The electrochemical hydroxide adsorption test was performed in a rotating disk electrode apparatus to analyze the exposed crystal surface of the copper nanosheet obtained in step 4). Specifically, the copper nanosheet was subjected to a linear cyclic voltammetry test in a 1 mol / L KOH solution saturated with nitrogen. The linear voltammetry curve was obtained at a voltage range of -0.4 to 0.7 V relative to a standard hydrogen electrode at a scanning rate of 20 mV / s. The data were collected after the scanning current was stable, such as Figure 6 As shown, Figure 6 The electrochemical linear voltammetric curves of the copper nanosheets obtained in Example 1 and Comparative Example 1 are shown. The results show that the main exposed crystal plane of the flaky copper obtained in Example 1 is the Cu (100) crystal plane.

[0099] The electrocatalytic reduction of carbon dioxide to ethylene was tested in a flow electrolytic cell device. The catholyte used in the test was 1 mol / L KCl solution; the anolyte was 1 mol / L KOH solution. The ethylene Faraday efficiency diagram and partial current density diagram at different current densities were obtained, as Figure 7 and 8 shown. Figure 7 This is the Faraday efficiency of the copper nanosheets of Example 1 and Comparative Example 1 of the present invention for electrocatalytic reduction of carbon dioxide to ethylene in a neutral medium of a flow electrolytic cell. Figure 8 This is the partial current density of the copper nanosheets of Example 1 and Comparative Example 1 of the present invention for electrocatalytic reduction of carbon dioxide to ethylene in a neutral medium of a flow electrolytic cell. The results show that the Faraday efficiency of the copper nanosheets obtained in Example 1 for electrocatalytic reduction of carbon dioxide to ethylene can be as high as 72%, and the partial current density can be as high as 360 mA / cm 2 . And its stability was tested, and the stability curve and ethylene Faraday efficiency diagram at a current density of 500 mA / cm 2 were obtained, as Figure 9 shown. Figure 9 This is the stability test diagram of the copper nanosheets of Example 1 and Comparative Example 1 of the present invention for electrocatalytic reduction of carbon dioxide to ethylene in a neutral medium of a flow electrolytic cell. The results show that at a high current density of 500 mA / cm 2 , the performance stable time exceeds 100 h.

[0100] The copper nanosheets obtained in steps 1-3) of Example 1 were tested for electrocatalytic reduction of carbon dioxide to ethylene in a membrane electrode assembly electrolytic cell device. The anolyte used in the test was 0.1 mol / L KHCO 3 solution, and there was no catholyte. The ethylene Faraday efficiency diagram and energy efficiency diagram at different currents were obtained, as Figure 10 and 11 shown. Figure 10 This is the Faraday efficiency of the copper nanosheets of Example 1 of the invention for electrocatalytic reduction of carbon dioxide to ethylene in a neutral medium of a membrane electrode assembly electrolytic cell. Figure 11 This is the energy conversion efficiency of the copper nanosheets of Example 1 of the invention for electrocatalytic reduction of carbon dioxide to ethylene in a neutral medium of a membrane electrode assembly electrolytic cell. The results show that in the membrane electrode assembly electrolytic cell device, the Faraday efficiency of the sheet copper for electrocatalytic reduction of carbon dioxide to ethylene is as high as 64%, and the energy conversion efficiency is as high as 24%. And its stability was tested, and the stability curve and ethylene Faraday efficiency diagram at a current of -800 mA were obtained, as Figure 12 shown. Figure 12Stability test chart of electrocatalytic reduction of carbon dioxide to ethylene by copper nanosheets in the neutral medium of a membrane electrode assembly electrolyzer in Invention Example 1. The results show that at a large current of -800 mA, the performance stable time exceeds 70 h.

[0101] Example 2

[0102] The difference from Example 1 is as follows:

[0103] In step 2), the plasma deposition time is 60 min.

[0104] The oxygen vacancy-rich flaky copper oxide obtained in Example 2 was analyzed using a transmission electron microscope, and its transmission electron microscope photograph was obtained, as Figure 13 shown Figure 13 is the TEM image of the oxygen vacancy-rich flaky copper oxide in Invention Example 2 of the present invention. The results show that the flaky copper oxide in Example 2 is an incomplete flaky structure with broken edges.

[0105] Example 3

[0106] The difference from Example 1 is as follows:

[0107] In step 2), the plasma deposition time is 90 min.

[0108] The oxygen vacancy-rich flaky copper oxide obtained in Example 3 was analyzed using a transmission electron microscope, and its transmission electron microscope photograph was obtained, as Figure 14 shown Figure 14 is the TEM image of the oxygen vacancy-rich flaky copper oxide in Invention Example 3 of the present invention. The results show that the flaky copper oxide in Example 3 maintains a flaky structure, and the degree of fragmentation increases.

[0109] Example 4

[0110] The difference from Example 1 is as follows:

[0111] In step 2), the plasma deposition power is 200 W.

[0112] The oxygen vacancy-rich flaky copper oxide obtained in Example 4 was analyzed using a transmission electron microscope, and its transmission electron microscope photograph was obtained, as Figure 15 shown Figure 15 is the TEM image of the oxygen vacancy-rich flaky copper oxide in Invention Example 4 of the present invention. The results show that the flaky copper oxide in Example 4 maintains a flaky structure, the thickness becomes uneven, and it is significantly thinner in some places.

[0113] Example 5

[0114] The difference from Example 1 is as follows:

[0115] In step 2), the power of plasma deposition is 300 W.

[0116] The flaky copper oxide rich in oxygen vacancies obtained in Example 5 was analyzed using a transmission electron microscope, and its transmission electron microscope photograph was obtained. As Figure 16 shown, Figure 16 This is the TEM image of the flaky copper oxide rich in oxygen vacancies of Example 5 of the present invention. The results show that the flaky copper oxide in Example 5 is a broken small flaky structure.

[0117] Comparative Example 1

[0118] D-1) First, 0.51 g of copper chloride dihydrate was dissolved in 30 mL of deionized water to obtain an aqueous copper chloride solution. Then, 30 mL of 3 mol / L sodium hydroxide solution was added dropwise to the aqueous copper chloride solution, and the mixture was stirred at room temperature for 30 min to obtain a homogeneous solution. Subsequently, it was placed in a 100 mL reaction kettle and reacted at 100 °C for 10 h. The obtained product was centrifuged, then washed 3 times with deionized water and 3 times with ethanol, and dried in vacuum to obtain flaky copper oxide;

[0119] D-2) Weigh 10 mg of the flaky copper oxide obtained in step D-1), add 2 mL of isopropanol, and then add 50 μL of a 5% Nafion solution by mass. Ultrasonic until the catalyst (flaky copper oxide rich in oxygen vacancies) is uniformly dispersed, and the dispersion is evenly sprayed on a 3×3 cm -2 gas diffusion carbon paper to prepare a copper oxide gas diffusion electrode (copper oxide electrode).

[0120] D-3) Use the copper oxide electrode as the working electrode, a titanium mesh coated with iridium oxide and potassium chloride as the counter electrode, and a saturated silver / silver chloride electrode (Ag / AgCl) as the reference electrode. Connect it to a multi-channel electrochemical workstation (IM6ex, ZAHNER elektrik, made in Germany) equipped with an amplifier.

[0121] Use 1 mol / L KCl solution as the cathode electrolyte and 1 mol / L KOH solution as the anode electrolyte. The flaky copper oxide was pre-reduced at a current density of 20 mA cm -2 for 10 min, and CO was continuously introduced into the cathode electrolyte during the pre-reduction process 2 to obtain flaky copper.

[0122] The flaky copper oxide obtained in Comparative Example 1 was analyzed using a transmission electron microscope, and its transmission electron microscope photograph was obtained. As Figure 17 shown, Figure 17 This is the TEM image of the flaky copper oxide of Comparative Example 1 of the present invention. The results show that the copper oxide in Comparative Example 1 is a flaky structure.

[0123] The flaky copper oxide obtained in Comparative Example 1 was analyzed by X-ray diffraction to obtain its X-ray crystal diffraction pattern, as Figure 2 shown. The results indicate that the phase in Comparative Example 1 is copper oxide, which corresponds well to the standard card.

[0124] The flaky copper oxide obtained in Comparative Example 1 was analyzed by an electron spin resonance spectrometer to obtain its electron spin resonance spectrum pattern, as Figure 4 shown. The results show that there are no oxygen vacancy defects in the flaky copper oxide in Comparative Example 1.

[0125] 10 mg of the flaky copper oxide in Comparative Example 1 was weighed, 2 mL of isopropanol was added, and then 50 μL of a 5% Nafion solution by mass was added. After ultrasonic treatment until the catalyst (flaky copper oxide) was uniformly dispersed, the dispersion was evenly sprayed on a 3×3 cm -2 gas diffusion carbon paper to prepare a copper oxide gas diffusion electrode. Iridium oxide and potassium chloride were coated on a titanium mesh as the counter electrode, and a saturated silver / silver chloride electrode (Ag / AgCl) was used as the reference electrode. It was connected to a multi-channel electrochemical workstation (IM6ex, ZAHNER elektrik, made in Germany) equipped with an amplifier for testing, and the results are as Figures 5 - 7 shown.

[0126] Figure 18 This is a high-angle annular dark-field scanning transmission electron microscope photograph of the flaky copper obtained in step D-2) of Comparative Example 1 of the present invention. The results show that the pre-reduced product in Comparative Example 1 is flaky and porous copper.

[0127] Electrochemical hydroxide adsorption tests were carried out in a rotating disk electrode device to analyze the exposed crystal planes of the flaky copper obtained in step D-2). Specifically, linear cyclic voltammetry tests were carried out on the flaky copper in a 1 mol / L KOH solution saturated with nitrogen. The linear voltammogram was obtained at a scanning rate of 20 mV / s in a voltage range of -0.4 to 0.7 V relative to the standard hydrogen electrode, and the data were collected after the scanning current was stable, as Figure 6 shown. The results show that the main exposed crystal plane of the flaky copper obtained in Comparative Example 1 is the Cu(111) crystal plane.

[0128] Tests for electrocatalytic reduction of carbon dioxide to ethylene were carried out in a flow electrolytic cell device. The cathode electrolyte used for the test was a 1 mol / L KCl solution; the anode electrolyte was a 1 mol / L KOH solution. The ethylene Faraday efficiency diagram and partial current density diagram at different current densities were obtained, as Figure 7 and 8 shown. The results show that the Faraday efficiency of the flaky copper obtained in Comparative Example 1 for electrocatalytic reduction of carbon dioxide to ethylene can be as high as 43%, and the partial current density can be as high as 190 mA / cm2 。

[0129] The description of the above embodiments is only used to help understand the method of the present invention and its core idea. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing copper nanosheets, comprising the following steps: A) Mix copper salt, sodium hydroxide and water, and react at 80 - 120 °C to obtain nanosheet-shaped copper oxide; B) Perform nitrogen plasma treatment on the nanosheet-shaped copper oxide to obtain nanosheet-shaped copper oxide rich in oxygen vacancies; C) Fabricate the nanosheet-shaped copper oxide rich in oxygen vacancies into a copper oxide electrode; D) Perform an electrochemical pre-reduction reaction on the copper oxide electrode to obtain copper nanosheets with specifically exposed (100) crystal planes.

2. The preparation method according to claim 1, wherein, in step A), the copper salt is copper chloride dihydrate; the molar ratio of the copper salt to sodium hydroxide is 0.5 - 1.5:55 - 125; the reaction time is 8 - 15 h.

3. The preparation method according to claim 1, wherein, in step B), in the nitrogen plasma treatment, nitrogen is used as the carrier gas, the power is 100 - 300 W, the time is 30 - 90 min, and the temperature is room temperature.

4. The preparation method according to claim 1, wherein, in step B), the thickness of the nanosheet-shaped copper oxide rich in oxygen vacancies is 5 - 7 nm.

5. The preparation method according to claim 1, wherein, In step D), the current density of the electrochemically pre-reduction reaction is preferably 10-100 mA cm -2 , and the time is 5-30 min.

6. The preparation method according to claim 1, wherein, in step D), during the electrochemical pre-reduction reaction, the cathode electrolyte used is 0.8 - 1.2 mol / L KCl solution, and the anode electrolyte is 0.8 - 1.2 mol / L KOH solution.

7. The preparation method according to claim 1, wherein, in step D), during the electrochemical pre-reduction reaction, carbon dioxide is introduced into the electrolyte as the reaction gas.

8. Copper nanosheets prepared by the preparation method according to any one of claims 1 - 7.

9. Application of the copper nanosheets according to claim 8 as a catalyst for electrocatalytic reduction of carbon dioxide to produce ethylene.

10. The application according to claim 9, wherein, the electrocatalytic reduction of carbon dioxide to produce ethylene is carried out in a flow electrolytic cell; or the electrocatalytic reduction of carbon dioxide to produce ethylene is carried out in a membrane electrode assembly electrolytic cell.

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