Graphene quantum dot-supported CuO catalyst for electrocatalytic production of ethylene from carbon dioxide with high current and its preparation method and application

Abstract

The present invention discloses a graphene quantum dot-supported CuO catalyst for electrocatalytic production of ethylene from high-current carbon dioxide, and its preparation method and application. In the present invention, two high-purity graphite carbon rods are inserted into a potassium bicarbonate solution, electrode clips are clamped, and electricity is passed to electrolytically strip the carbon material on the surface of the graphite rods to obtain graphene quantum dots. The supernatant is taken by centrifugal filtration, filled into a dialysis bag and dialyzed to remove potassium bicarbonate salt to obtain an aqueous solution of graphene quantum dots; the aqueous solution of graphene quantum dots is mixed with solid powder of CuO nanosheets, ethanol is added, stirred, the precipitate is taken by centrifugal filtration, and dried to obtain a graphene quantum dot-supported CuO catalyst. The graphene quantum dot-supported CuO catalyst prepared by the present invention effectively solves the problem of too rapid evolution of the catalyst structure due to electroreduction during the reaction process, and has a high yield and is easy to produce on a large scale, and shows good activity and stability in the electrochemical conversion of carbon dioxide to ethylene.

Description

Technical Field

[0001] The present invention belongs to the fields of nanotechnology and electrocatalysis, and particularly relates to a graphene quantum dot-supported CuO catalyst for electrocatalytic production of ethylene from carbon dioxide at high current, and a preparation method and application thereof. Background Art

[0002] For hundreds of years, the development of human society has relied on fossil fuels (such as coal and oil) as the main energy source. In recent years, the rapid development of various clean energy technologies (such as solar and wind farms) has provided an opportunity to replace traditional fossil fuels with renewable electricity. Although the growth rate of renewable energy is increasing, the percentage of these renewable energies in the total current energy consumption is still very low (<5%). In addition, most of these renewable resources are geographical, oceanic and intermittent. In addition to the development of renewable energy and related technologies, methods of carbon capture and carbon sequestration have also been used to prevent large amounts of CO2 from being released into the air. Among them, electrochemical CO2 fixation is becoming one of the most promising strategies for converting CO2 into value-added chemicals and effectively utilizing CO2.

[0003] In the field of electrochemical CO2 fixation technology, functional catalysts with high activity and high selectivity are crucial for the economy and environmental friendliness of the entire process. The development of high-performance catalysts has become an important research focus and development direction in catalytic science. Copper-based catalysts have received extensive attention in the field of CO2 electroreduction due to their high catalytic activity and high selectivity for producing high-value-added multi-carbon hydrocarbons. However, electrochemical CO2 catalysis still faces relatively large challenges. One is the problem of diverse product selectivity. In particular, ethylene, as the basic chemical raw material for synthetic fibers, rubber, plastics, and ethanol (alcohol), is also an important indicator for evaluating the development level of the petrochemical industry and an important chemical intermediate for synthesizing fine chemical products with high industrial added value. At present, the selectivity and activity of electrochemically catalyzing carbon dioxide to produce ethylene are relatively low, and the synthesis method is relatively complex, increasing the cost of the catalyst. Improving the selectivity of ethylene products still faces great challenges. Another problem is the low current density and low catalyst stability (Rabiee H, Ge L, Zhang X, et al. Gas diffusion electrodes (GDEs) for electrochemical reduction of carbon dioxide, carbon monoxide, and dinitrogen to value-added products: a review[J]. Energy & Environmental Science, 2021, 14, 1959–2008). Therefore, based on the above discussion, exploring a copper-based composite catalyst that can be prepared in large quantities and has high selectivity, high catalytic activity, and can stably exist at high current density will be one of the main goals to promote the realization of carbon dioxide resource utilization. Summary of the Invention

[0004] The object of the present invention is to address the problems existing in the prior art, such as complex preparation methods and small production yields, and to propose a graphene quantum dot-loaded CuO catalyst for electrocatalytic production of ethylene from carbon dioxide at high current, its preparation method, and its application. The graphene quantum dot-loaded CuO catalyst provided by the present invention can be used as a catalyst for electrochemical reduction reactions, and the catalyst has high catalytic activity and good stability. On the premise of ensuring operation at a high current density (>500 mA / cm 2 ), a high Faraday efficiency of the electrocatalytic CO2 reduction reaction can be obtained.

[0005] First, two graphite rods are placed in a sodium bicarbonate solution, and graphene quantum dots are prepared by an electro-stripping method. The graphene quantum dots are loaded on the surface of a CuO catalyst to obtain a copper oxide-carbon composite catalyst. The copper oxide-carbon composite catalyst is dispersed in ethanol, a small amount of Nafion solution is added, and after ultrasonic homogenization, it is sprayed on the surface of carbon paper with a spray gun to obtain a gas diffusion electrode, which can be installed in a flow cell for electrocatalytic reduction of carbon dioxide. The copper oxide-carbon composite catalyst prepared by the present invention effectively solves the problem of too rapid evolution of the catalyst structure due to electroreduction during the reaction process, and has a high yield and is easy to produce on a large scale. It exhibits good activity and stability in the electrochemical conversion of carbon dioxide to ethylene, has high selectivity for carbon dioxide and a high Faraday efficiency, and can operate stably at a current density of -500 mA / cm 2 and its Faraday efficiency exceeds 60%.

[0006] The preparation method of a graphene quantum dot-loaded CuO catalyst for electrocatalytic production of ethylene from carbon dioxide at high current proposed by the present invention is a simple and effective preparation technique. The core lies in that the prepared copper-based catalyst can be used for the stable conversion of carbon dioxide to ethylene products at high current.

[0007] The object of the present invention is achieved by at least one of the following technical solutions.

[0008] A preparation method of a graphene quantum dot-loaded CuO catalyst for electrocatalytic production of ethylene from carbon dioxide at high current, comprising the following steps:

[0009] (1) Using the electro-chemical stripping method, two high-purity graphite carbon rods are inserted into a potassium bicarbonate solution, electrode clips are clamped, and electricity is passed (the electrochemical workstation is used as the output power source) to electrolytically strip the carbon material on the surface of the graphite rods to obtain graphene quantum dots. The supernatant is taken by centrifugal filtration and filled into a dialysis bag to dialyze and remove the potassium bicarbonate salt to obtain an aqueous solution of graphene quantum dots;

[0010] (2) Mix the aqueous solution of graphene quantum dots described in step (1) with solid powder of CuO nanosheets, add ethanol, stir, take the precipitate by centrifugal filtration, and dry to obtain the graphene quantum dot-loaded CuO catalyst for electrocatalytic production of ethylene from carbon dioxide at high current.

[0011] Preferably, the concentration of the potassium bicarbonate solution in step (1) is 0.1 - 0.5 mol / L; the volume is 100 - 500 mL.

[0012] More preferably, the concentration of the potassium bicarbonate solution in step (1) is 0.1 mol / L and the volume is 150 mL.

[0013] Preferably, the electrolysis step in step (1) is constant current electrolysis; the current density of the constant current is -10 to -20 mA / cm 2 ; the electrolysis time is 10 to 24 hours.

[0014] More preferably, the current in step (1) is constant current; the current density of the constant current is -10 mA / cm 2 , and the electrolysis time is 20 hours.

[0015] Preferably, the rotation speed of the centrifugal filtration in step (1) is 4000 to 6000 revolutions per minute, and the time is 5 to 10 minutes;

[0016] More preferably, the rotation speed of the centrifugation process in step (1) is 4000 revolutions per minute, and the time is 10 minutes.

[0017] Preferably, the dialysis time in step (1) is 3 to 10 days.

[0018] Preferably, the concentration of the graphene quantum dot aqueous solution in step (2) is 0.5 to 1 mg / mL, and the mass ratio of the graphene quantum dots to the CuO nanosheet solid powder is 1% to 20%. The concentration of the graphene quantum dot aqueous solution is obtained by quantification. The quantification steps include: taking 20 mL of the graphene quantum dot aqueous solution in a plastic beaker, freezing it with liquid nitrogen and then putting it into a freeze dryer for freeze drying, and dividing the weighed mass by 20 to obtain the concentration of the graphene quantum dot aqueous solution.

[0019] More preferably, the concentration of the graphene quantum dot aqueous solution in step (2) is 0.6 mg / mL, and the mass ratio of the graphene quantum dots to the CuO nanosheet solid powder is 12%.

[0020] Preferably, the volume ratio of ethanol to the graphene quantum dot aqueous solution in step (2) is 5:1 to 20:1; the stirring time is 8 to 16 hours.

[0021] Preferably, the rotation speed of the centrifugal filtration in step (2) is 10000 to 12000 revolutions per minute, and the time is 5 to 10 minutes;

[0022] More preferably, the rotation speed of the centrifugation process in step (2) is 10000 revolutions per minute, and the time is 10 minutes.

[0023] Preferably, the CuO nanosheet solid powder in step (2) is any one of CuO synthesized with any size and any synthesis method.

[0024] More preferably, the CuO nanosheet solid powder in step (2) is prepared by a hydrothermal method.

[0025] The graphene quantum dot supported CuO catalyst for electrocatalytic ethylene production from carbon dioxide prepared by the above preparation method.

[0026] The application of the above-mentioned graphene quantum dot supported CuO catalyst for electrocatalytic ethylene production from carbon dioxide as an electrocatalyst in an electrochemical reduction reaction.

[0027] Preferably, the graphene quantum dot supported CuO catalyst is used for preparing a gas diffusion electrode for an electrochemical reduction reaction.

[0028] Preferably, the electrochemical reduction reaction is electrocatalytic ethylene production from carbon dioxide; the electrocatalytic ethylene production from carbon dioxide is carried out by assembling a gas diffusion electrode in a flow cell, and the current density is -100~-600 mA / cm 2 , and the electrolyte is 0.5~1.5 M potassium hydroxide solution.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] (1) The preparation method of the graphene quantum dot supported CuO catalyst provided by the present invention is realized through the electrostatic adsorption of nanomaterials, which has the characteristics of simple operation, low cost, large-scale synthesis, etc. The obtained product has a uniform morphology and good repeatability.

[0031] (2) The graphene quantum dot supported CuO catalyst provided by the present invention has high electrocatalytic performance. Taking the reversible hydrogen electrode as the standard, the graphene quantum dot supported CuO suspension is sprayed on a carbon paper with an area of 1 square centimeter by a spray gun. The prepared gas diffusion electrode material has a Faraday efficiency of up to 77.4% for carbon dioxide reduction to C 2 at a current density of -500 mA / cm 2+ , and the Faraday efficiency of ethylene exceeds 60%, showing a high C 2+ selectivity of the graphene quantum dot supported CuO catalyst in carbon dioxide reduction.

[0032] (3) The graphene quantum dot supported CuO catalyst provided by the present invention has a stable structure and morphology. After an electrocatalytic reaction at -500 mA / cm 2 , it can still maintain the initial sheet-like morphology and structure, indicating its excellent stability and the ability to achieve long-term large-current electrocatalytic CO2 reduction. Description of the Drawings

[0033] Figure 1 SEM image of the CuO nanosheets prepared in Example 1;

[0034] Figure 2TEM image of the graphene quantum dots prepared in Example 1;

[0035] Figure 3 HRTEM image of the graphene quantum dots prepared in Example 1;

[0036] Figure 4 SEM image of the CuO catalyst supported by the graphene quantum dots prepared in Example 1;

[0037] Figure 5 XRD pattern of the CuO catalyst supported by the graphene quantum dots prepared in Example 1;

[0038] Figure 6 SEM image of the CuO catalyst supported by graphene prepared in Example 4;

[0039] Figure 7 SEM image of the CuO catalyst supported by carbon nanotubes prepared in Example 5;

[0040] Figure 8 SEM image of the cross-section of the working electrode prepared in Example 6;

[0041] Figure 9 Faraday efficiency diagram of the CuO catalyst supported by graphene quantum dots prepared in Example 7 for the electrochemical reduction of carbon dioxide to different products in a flow cell;

[0042] Figure 10 Faraday efficiency diagram of the CuO catalyst prepared in Example 8 for the electrochemical reduction of carbon dioxide to different products in a flow cell;

[0043] Figure 11 Voltage-time curve of the graphene-supported CuO working electrode prepared in Example 8 for the electrochemical reduction of carbon dioxide at different current densities in a flow cell;

[0044] Figure 12 Voltage-time curve of the carbon nanotube-supported CuO working electrode prepared in Example 8 for the electrochemical reduction of carbon dioxide at different current densities in a flow cell;

[0045] Figure 13 Stability test diagram of the CuO catalyst supported by graphene quantum dots prepared in Example 9 for the electrochemical reduction of carbon dioxide to C2H4 in a flow cell. Detailed implementation mode

[0046] The following further illustrates the specific implementation of the present invention in conjunction with examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that for the processes not specifically described in detail below, those skilled in the art can implement or understand them with reference to the prior art. Reagents or instruments without indicating the manufacturer are regarded as conventional products that can be obtained through commercial purchase.

[0047] Example 1

[0048] A preparation method of a graphene quantum dot-loaded CuO catalyst for electrocatalytic production of ethylene from carbon dioxide with high current includes the following steps:

[0049] (1) Add 0.05 mol of CuCl2 . ·2H2O and 3 mol of NaOH to 80 mL of deionized water, mix evenly to form a blue suspension, transfer it to a 100 mL reaction kettle, keep it warm at 100 °C for 12 h, wash it by centrifugation with ethanol and water alternately for multiple times, and then place the centrifuged precipitate in an oven at 60 °C for drying for 12 hours to obtain CuO nanosheet powder.

[0050] (2) Place 100 mL of KHCO3 (0.1 mol / L) in a beaker, insert two graphite carbon rods as the positive and negative electrodes respectively, electrolyze under a constant current condition with a current density of -10 mA / cm 2 for 20 h, the transparent solution becomes a black suspension, centrifuge at 4000 rmp / min for 10 min and take the supernatant. Put the solution into a dialysis bag and dialyze for one week to remove the KHCO3 salt in the solution to obtain an aqueous solution of graphene quantum dots.

[0051] (3) Take 25 mg of the CuO nanosheet powder in the above (1), add 1 mL (1 mg / mL) of the above aqueous solution of graphene quantum dots, and add 9 mL of absolute ethanol, stir for 12 hours at a stirring speed of 600 rmp / min, then centrifuge at 10000 rmp / min for 10 min to take the precipitate, wash it by centrifugation with ethanol and water alternately for multiple times, and then place the centrifuged precipitate in an oven at 60 °C for drying for 12 hours to obtain graphene quantum dot-loaded CuO catalyst powder.

[0052] The SEM pattern of the CuO nanosheets prepared in Example 1 is as Figure 1 shown. The CuO synthesized by the hydrothermal method is CuO nanosheets with a smooth surface and regular morphology. The TEM and HRTEM patterns of the graphene quantum dots prepared in Example 1 are respectively as Figure 2 , Figure 3As shown, it can be seen from the figure that the graphene quantum dots prepared by the electrolytic exfoliation method are uniformly dispersed in water, and the size is 2 - 6 nm. The HRTEM pattern shows lattice fringes with a spacing of 0.21 nm, corresponding to the (100) plane of graphite. The XRD and SEM patterns of the graphene quantum dot-supported CuO catalyst prepared in Example 1 are respectively as Figure 4 , Figure 5 shown. It can be seen from Figure 4 that the graphene quantum dots are uniformly coated on the surface of CuO, and it can be seen from Figure 5 that the XRD peaks of the prepared graphene quantum dot-supported CuO catalyst completely correspond to the standard PDF card of CuO, indicating that the introduction of graphene quantum dots does not change the crystal form of CuO.

[0053] Example 2

[0054] A preparation method of a graphene quantum dot-supported CuO catalyst for electrocatalytic production of ethylene from carbon dioxide with high current includes the following steps:

[0055] (1) Add 0.05 mol of CuCl2 . ·2H2O and 3 mol of NaOH to 80 mL of deionized water, mix evenly to form a blue suspension, transfer it to a 100 mL reaction kettle, keep it at 100 °C for 12 h, wash it by centrifugation with ethanol and water alternately for several times, and then place the centrifuged precipitate in an oven at 60 °C for drying for 12 hours to obtain a solid powder of CuO nanosheets.

[0056] (2) Place 150 mL of KHCO3 (0.1 mol / L) in a beaker, insert two graphite carbon rods as the positive and negative electrodes respectively, electrolyze for 20 h under a constant current condition with a current density of -15 mA / cm 2 . The transparent solution becomes a black suspension. Centrifuge at 4000 rmp / min for 10 min and take the supernatant. Put the solution into a dialysis bag and dialyze for one week to remove the KHCO3 salt in the solution to obtain an aqueous solution of graphene quantum dots.

[0057] (3) Take 25 mg of the CuO nanosheet solid powder in the above (1), add 0.5 mL (1 mg / mL) of the above aqueous solution of graphene quantum dots, and add 9 mL of absolute ethanol, stir for 12 hours at a stirring speed of 600 rmp / min, then centrifuge at 10000 rmp / min for 10 min to take the precipitate, wash it by centrifugation with ethanol and water alternately for several times, and then place the centrifuged precipitate in an oven at 60 °C for drying for 12 hours to obtain a solid powder of the graphene quantum dot-supported CuO catalyst.

[0058] Example 3

[0059] A preparation method of a graphene quantum dot-loaded CuO catalyst for electrocatalytic production of ethylene from carbon dioxide with high current, comprising the following steps:

[0060] (1) Add 0.05 mol of CuCl2 . ·2H2O and 3 mol of NaOH to 80 mL of deionized water, mix evenly to form a blue suspension, transfer it to a 100 mL reaction kettle, keep it warm at 100 °C for 12 h, after centrifugally washing with ethanol and water alternately for multiple times, place the centrifuged precipitate in an oven and dry it at 60 °C for 12 hours to obtain a solid powder of CuO nanosheets.

[0061] (2) Place 200 mL of KHCO3 (0.2 mol / L) in a beaker, insert two graphite carbon rods as the positive electrode and the negative electrode respectively, and electrolyze for 20 h under a constant current condition with a current density of -20 mA / cm 2 . The transparent solution becomes a black suspension. Centrifuge at 4000 rmp / min for 10 min and take the supernatant. Put the solution into a dialysis bag and dialyze for one week to remove the KHCO3 salt in the solution to obtain an aqueous solution of graphene quantum dots.

[0062] (3) Take 250 mg of the CuO nanosheet solid powder in the above (1), add 10 mL (1 mg / mL) of the above aqueous solution of graphene quantum dots, and add 90 mL of absolute ethanol, stir for 12 hours at a stirring speed of 600 rmp / min, then centrifuge at 10000 rmp / min for 10 min to take the precipitate, after centrifugally washing with ethanol and water alternately for multiple times, place the centrifuged precipitate in an oven and dry it at 60 °C for 12 hours to obtain a solid powder of the graphene quantum dot-loaded CuO catalyst.

[0063] Example 4

[0064] A preparation method of a graphene oxide-loaded CuO catalyst for electrocatalytic production of ethylene from carbon dioxide with high current, comprising the following steps:

[0065] (1) Add 0.05 mol of CuCl2 . ·2H2O and 3 mol of NaOH to 80 mL of deionized water, mix evenly to form a blue suspension, transfer it to a 100 mL reaction kettle, keep it warm at 100 °C for 12 h, after centrifugally washing with ethanol and water alternately for multiple times, place the centrifuged precipitate in an oven and dry it at 60 °C for 12 hours to obtain a solid powder of CuO nanosheets.

[0066] (2) Take 25 mg of the CuO nanosheet solid powder obtained in (1) above, add 1.5 mL of the purchased 1 mg / mL graphene oxide aqueous solution (Macklin), and add 9 mL of absolute ethanol. Stir for 12 hours at a stirring speed of 600 rmp / min. Subsequently, centrifuge at 10000 rmp / min for 10 min to obtain the precipitate. After washing the precipitate alternately with ethanol and water by centrifugation for multiple times, place the centrifuged precipitate in an oven and dry it at 60 °C for 12 hours to obtain the solid powder of the graphene sheet-supported CuO catalyst.

[0067] The SEM image of the graphene oxide-supported CuO catalyst prepared in Example 4 is as Figure 6 shown. It can be seen from Figure 6 that most of the graphene oxide and CuO are phase-separated, and the CuO agglomerates seriously and fragmentation is observed, which may be caused by the collision between the relatively large-sized graphene oxide and CuO during the stirring process.

[0068] Example 5

[0069] A preparation method of a carbon nanotube-supported CuO catalyst for large-current electrocatalytic production of ethylene from carbon dioxide includes the following steps:

[0070] (1) Uniformly add 0.05 mol of CuCl2 . 2H2O and 3 mol of NaOH to 80 mL of deionized water to form a blue suspension, and transfer it to a 100 mL reaction kettle. Keep it at 100 °C for 12 h. After washing the precipitate alternately with ethanol and water by centrifugation for multiple times, place the centrifuged precipitate in an oven and dry it at 60 °C for 12 hours to obtain the solid powder of CuO nanosheets.

[0071] (2) Prepare a 1 mg / mL aqueous dispersion of carbon nanotubes (Macklin), and ultrasonicate it for two hours to make it uniformly dispersed. Take 25 mg of the CuO nanosheet solid powder obtained in (1) above, add 1.5 mL of the prepared carbon nanotube dispersion, and add 9 mL of absolute ethanol. Stir for 12 hours at a stirring speed of 600 rmp / min. Subsequently, centrifuge at 10000 rmp / min for 10 min to obtain the precipitate. After washing the precipitate alternately with ethanol and water by centrifugation for multiple times, place the centrifuged precipitate in an oven and dry it at 60 °C for 12 hours to obtain the solid powder of the graphene sheet-supported CuO catalyst.

[0072] The SEM image of the graphene oxide-supported CuO catalyst prepared in Example 5 is as Figure 7 shown. It can be seen from Figure 8 that most of the carbon nanotubes and CuO are phase-separated, and the CuO agglomerates seriously and fragmentation is observed, which may be caused by the collision between the relatively large-sized carbon nanotubes and CuO during the stirring process.

[0073] Example 6

[0074] To explore the electrocatalytic performance of the prepared graphene quantum dot-supported CuO catalyst, the graphene quantum dot-supported CuO catalyst prepared in the examples was subjected to an electrocatalytic carbon dioxide reduction experiment as follows. In Example 6, the graphene sheet-supported CuO catalyst prepared in Example 1 was selected for the electrocatalytic carbon dioxide reduction experiment.

[0075] The preparation of the working electrode and the assembly process of the flow-through electrolytic cell include:

[0076] (1) Preparation of the working electrode: 10 mg of the graphene quantum dot-supported CuO catalyst prepared in Example 1, 1.92 mL of absolute ethanol, and 80 μL of 5 wt% nafion solution were mixed and ultrasonically dispersed evenly for 0.5 h to obtain a dispersion. An appropriate amount of the dispersion was added to a spray gun, and the catalyst was evenly sprayed onto the carbon paper with a microporous layer through the spray gun to obtain a working electrode with a gas diffusion layer. On the working electrode, the loading amount of the graphene quantum dot-supported CuO catalyst prepared in Example 1 was ~1 mg / cm 2 ;

[0077] (2) A commercial flow-through electrolytic cell system made of Peek material was used as the electrochemical reduction CO2 reaction device, where the electrolyte solution was potassium hydroxide solution with a concentration of 1 mol / L. The working electrode was the working electrode prepared in step (1) with an effective area of 0.5 × 2 cm 2 , the counter electrode was a platinum sheet electrode, and the reference electrode was a mercury / mercuric oxide electrode;

[0078] Figure 8 Fig. is the SEM image of the cross-section of the working electrode prepared in Example 6. It can be seen from the figure that the thickness of the catalyst sprayed on the surface of the carbon paper microporous layer is about 3 μm;

[0079] (3) The three-electrode flow-through electrolytic cell system described in step (2) was assembled. Rubber gaskets were used to isolate each component. At the same time, a commercial anion exchange membrane was used as the electrolyte diaphragm, and the assembled entire test system was fixed with a clamp to ensure good airtightness.

[0080] After each test, the three-electrode flow-through electrolytic cell system was thoroughly cleaned with distilled water and reassembled in the same process after drying.

[0081] As a comparison, pure CuO catalyst, the graphene-supported CuO catalyst of Example 4, and the carbon nanotube-supported CuO catalyst of Example 5 were prepared into working electrodes in the same manner for testing.

[0082] Example 7

[0083] The three - electrode flow - type electrolytic cell system assembled in Example 6 above was used for the electrochemical reduction of CO₂ reaction experiment. The reaction conditions were as follows: Before connecting the power supply, high - purity CO₂ gas was introduced into the cathode chamber at a flow rate of 30 mL / min to exclude the air in the whole system. Subsequently, the power supply was connected at normal temperature and pressure for the Faraday efficiency and current density tests. The constant - current electrochemical technique was used to measure the Faraday efficiency of various products of the graphene quantum dot - loaded CuO working electrode at different current densities. The current densities were set to - 100 mA / cm 2 、 - 200 mA / cm 2 、 - 300 mA / cm 2 、 - 400 mA / cm 2 、 - 500 mA / cm 2 and - 600 mA / cm 2 , and each current condition was tested for 0.5 h.

[0084] Figure 9 Figure of the Faraday efficiency when different products were obtained by the electrochemical reduction of carbon dioxide of the graphene quantum dot - loaded CuO working electrode described in Example 7 in potassium hydroxide solution. As can be seen from Figure 9 it, the Faraday efficiency of ethylene of the prepared graphene quantum dot - loaded CuO catalyst was as high as 59.6% at a current density of - 500 mA / cm 2 , and the total Faraday efficiency of multi - carbon (C 2+ ) products exceeded 77%, indicating that the graphene quantum dot - loaded CuO catalyst provided by the present invention has a high C 2+ product selectivity in the electrocatalytic reduction of CO₂, can operate at industrial - level high currents, and has the potential for practical applications.

[0085] Example 8

[0086] The three - electrode flow - type electrolytic cell system assembled in Example 6 above was used for the electrochemical reduction of CO₂ reaction experiment. The reaction conditions were as follows: Before connecting the power supply, high - purity CO₂ gas was introduced into the cathode chamber at a flow rate of 30 mL / min to exclude the air in the whole system. Subsequently, the power supply was connected at normal temperature and pressure for the Faraday efficiency and current density tests. The constant - current electrochemical technique was used to measure the Faraday efficiency of various products of the CuO working electrode, the graphene - loaded CuO working electrode of Example 4, and the carbon nanotube - loaded CuO working electrode of Example 5 at different current densities. The current densities were set to - 100 mA / cm 2 、 - 200 mA / cm 2 、 - 300 mA / cm 2 、 - 400 mA / cm2 and -500 mA / cm 2 The test was carried out for 0.5 h under each current condition.

[0087] Figure 10 It is the Faraday efficiency diagram when the CuO working electrode described in Example 8 electrochemically reduces carbon dioxide in potassium hydroxide solution to obtain different products. It can be seen from Figure 10 that the prepared CuO working electrode has the highest Faraday efficiency of ethylene of 43.2% at a current density of -400 mA / cm 2 , which is much lower than that of the graphene quantum dot loaded CuO working electrode. Figure 11 and Figure 12 are the voltage-time curves of the prepared graphene loaded CuO working electrode and carbon nanotube loaded CuO working electrode during the electrochemical reduction of carbon dioxide at different current densities in a flow cell. It can be seen from the figure that the voltage-time curves of the graphene loaded CuO working electrode and carbon nanotube loaded CuO working electrode fluctuate particularly severely at -200 mA / cm 2 and -300 mA / cm 2 respectively. The highest Faraday efficiency of ethylene is only 28% and 21% respectively, and most of the energy is used for HER, resulting in poor catalyst stability. Due to the activity problem of the catalyst itself, the graphene loaded CuO working electrode and carbon nanotube loaded CuO working electrode cannot maintain the test at high current densities. Therefore, only the test data at lower currents are shown in Figure 11 and Figure 12 .

[0088] Example 9

[0089] The three-electrode flow-type electrolytic cell system assembled in Example 6 above was used for the electrochemical reduction of CO2 reaction experiment. The reaction conditions are as follows: Before connecting the power supply, high-purity CO2 gas was introduced into the cathode chamber at a flow rate of 30 mL / min to remove the air in the whole system. Subsequently, the power supply was connected at normal temperature and pressure for the Faraday efficiency and current density test. The Faraday efficiencies of ethylene products and hydrogen by-products of the graphene quantum dot loaded CuO working electrode were measured at a current density of -500 mA / cm 2 for 12 h.

[0090] Figure 13 It is the stability test diagram of the graphene quantum dot loaded CuO working electrode described in Example 9 for electrochemically reducing carbon dioxide to C2H4 in potassium hydroxide solution. It can be seen from Figure 13 that the prepared graphene quantum dot loaded CuO working electrode at -500 mA / cm 2It can maintain high activity and stability under a current density of

[0091] The above embodiments are only the preferred embodiments of the present invention, which are only used to explain the present invention rather than limit the present invention. Any changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit and essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A preparation method of a graphene quantum dot-supported CuO catalyst for electrocatalytic production of ethylene from carbon dioxide with high current, characterized in that, It includes the following steps: (1) Insert two high-purity graphite carbon rods into a potassium bicarbonate solution, clamp the electrode clips, and electrolyze and strip the carbon material on the surface of the graphite rods to obtain graphene quantum dots. Centrifuge and filter to take the supernatant, and put it into a dialysis bag to dialyze to remove potassium bicarbonate salt to obtain an aqueous solution of graphene quantum dots; (2) Mix the aqueous solution of graphene quantum dots described in step (1) with solid powder of CuO nanosheets, add ethanol, stir, centrifuge and filter to take the precipitate, and dry to obtain the graphene quantum dot-supported CuO catalyst for electrocatalytic production of ethylene from carbon dioxide under high current.

2. The preparation method of the graphene quantum dot-loaded CuO catalyst for electrocatalytic production of ethylene from carbon dioxide with high current as claimed in claim 1, wherein, The concentration of the potassium bicarbonate solution described in step (1) is 0.1 to 0.5 mol / L.

3. The preparation method of the graphene quantum dot-supported CuO catalyst for electrocatalytic production of ethylene from carbon dioxide with high current, as claimed in claim 1, is characterized in that, The electrolysis in step (1) is constant current electrolysis; the current density of the constant current is -10 to -20 mA / cm 2 ; the electrolysis time is 10 to 24 hours.

4. The preparation method of the graphene quantum dot-supported CuO catalyst for electrocatalytic production of ethylene from carbon dioxide with high current, characterized in that, The rotation speed of the centrifugal filtration described in step (1) is 4000 to 6000 revolutions per minute, and the time is 5 to 10 minutes; The dialysis time described in step (1) is 3 to 10 days.

5. The preparation method of the graphene quantum dot-loaded CuO catalyst for electrocatalytic production of ethylene from carbon dioxide with high current, characterized in that, The concentration of the aqueous solution of graphene quantum dots described in step (2) is 0.5 to 1 mg / mL, and the mass ratio of the graphene quantum dots to the solid powder of CuO nanosheets is 1% to 20%.

6. The preparation method of the graphene quantum dot-supported CuO catalyst for electrocatalytic production of ethylene from high-current carbon dioxide according to claim 1, characterized in that, The volume ratio of ethanol to the aqueous solution of graphene quantum dots described in step (2) is 5:1 to 20:1; the stirring time is 8 to 16 hours.

7. The preparation method of the graphene quantum dot-supported CuO catalyst for electrocatalytic production of ethylene from carbon dioxide with high current, characterized in that, The rotation speed of the centrifugal filtration described in step (2) is 10000 to 12000 revolutions per minute, and the time is 5 to 10 minutes; The solid powder of CuO nanosheets described in step (2) is prepared by a hydrothermal method.

8. A graphene quantum dot-supported CuO catalyst for electrocatalytic production of ethylene from carbon dioxide under high current, prepared by the preparation method according to any one of claims 1-7.

9. Application of the graphene quantum dot-supported CuO catalyst for electrocatalytic production of ethylene from carbon dioxide under high current according to claim 8 as an electrocatalyst in an electrochemical reduction reaction.

10. The application according to claim 9, wherein The electrochemical reduction reaction is the electrocatalytic production of ethylene from carbon dioxide; the electrocatalytic production of ethylene from carbon dioxide is carried out by assembling a gas diffusion electrode in a flow cell, and the current density is -100 to -600 mA / cm 2 , and the electrolyte is a potassium hydroxide solution with a concentration of 0.5 to 1.5 M.

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