Preparation method and application of cadmium-modified copper-based electrocatalyst

Abstract

The invention relates to the field of electrochemical acetylene reduction, in particular to a preparation method and application of a cadmium-modified copper-based electrocatalyst. The catalyst comprises a zirconium hydroxide carrier; the copper-cadmium heterostructure is loaded on the zirconium hydroxide carrier and is formed by a cadmium-modified copper simple substance. The electrocatalyst is applied to electrochemical acetylene reduction to generate ethylene, not only has high activity on acetylene hydrogenation to ethylene, but also has an excellent effect of inhibiting acetylene carbon-carbon coupling, inhibits the Faraday efficiency of a C4 product to 0.06% under a relative reversible hydrogen electrode-0.5 V in acetylene gas flow with a volume fraction of 5%, and has a good application prospect. The Faraday efficiency of the main product ethylene reaches 98.38%, and 99.99% of ethylene selectivity is realized in ethylene-rich gas flow containing trace acetylene. Compared with other copper-based electrochemical acetylene reduction catalysts, the copper-based electrochemical acetylene reduction catalyst has a maximum inhibition effect on a carbon-carbon coupling side reaction, realizes high Faraday efficiency and selectivity of ethylene, and can inhibit generation of ethane and hydrogen at the same time.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical acetylene reduction. Specifically, it relates to a preparation method and application of a cadmium-modified copper-based electrocatalyst. Background Art

[0002] As an important basic chemical raw material, ethylene is an important monomer for synthesizing polymers, especially polyethylene. Currently, ethylene mainly comes from the high-temperature cracking of naphtha or saturated C2-C6 hydrocarbons. Inevitably, a small amount of acetylene is produced as a by-product in this process. The residual acetylene impurity in ethylene gas is very harmful to the polymerization of ethylene. It not only irreversibly reduces the performance of Ziegler-Natta catalysts but also affects the quality of polymer products. Therefore, removing acetylene impurities is crucial for the downstream ethylene industry. Among various methods, the selective hydrogenation of acetylene to ethylene is the most ideal method for purifying ethylene, and the thermal catalytic method is widely used industrially. However, due to the use of high temperature, high pressure, and hydrogen, this method has relatively large safety hazards. In recent years, the electrochemical reduction of acetylene to ethylene has attracted much attention from researchers due to its room-temperature and atmospheric-pressure reaction and the use of water as a proton source. The design of acetylene electroreduction catalysts is the core of acetylene electroreduction technology. Excellent acetylene electroreduction catalysts not only need to have high reaction activity and ethylene selectivity but also need to suppress carbon-carbon coupling reactions, hydrogen evolution reactions, and over-hydrogenation reactions.

[0003] Currently, non-precious metal copper-based materials show good performance in the electrochemical reduction of acetylene to ethylene. However, due to the inherent endowment of carbon-carbon coupling in the electrocatalytic small molecule reaction process of copper-based materials, carbon-carbon coupling reactions of acetylene will also be induced during the acetylene electroreduction process, resulting in the formation of C4 or C 4+ products, reducing the selectivity of ethylene. Therefore, designing an electrocatalyst with high selectivity for ethylene, strong inhibition of carbon-carbon coupling side reactions, and minimizing hydrogen evolution reactions and over-hydrogenation reactions during the acetylene electroreduction process is one of the main difficulties in this technology. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a cadmium-modified copper-based electrocatalyst, its preparation method, and application. The cadmium-modified copper-based electrocatalyst of the present invention is an electrocatalyst that highly selectively generates ethylene and efficiently inhibits carbon-carbon coupling reactions during the electrochemical reduction of acetylene.

[0005] In the first aspect, the cadmium-modified copper-based electrocatalyst provided by the present invention comprises a zirconium hydroxide support; and a copper-cadmium heterostructure formed by a cadmium-modified copper element supported on the zirconium hydroxide support. The cadmium-modified copper-based electrocatalyst provided by the present invention is applied to the electrochemical reduction of acetylene to generate ethylene, and not only has high activity for the hydrogenation of acetylene to ethylene, but also has an excellent effect of inhibiting acetylene carbon-carbon coupling, which can suppress the Faraday efficiency of carbon four products to 0.06% at a relative reversible hydrogen electrode voltage of -0.5V in a 5% volume fraction of acetylene gas flow, and the Faraday efficiency of the main product ethylene reaches 98.38%, and 99.99% ethylene selectivity is achieved in an ethylene-rich gas flow containing trace amounts of acetylene. Compared with other copper-based electrochemical acetylene reduction catalysts, this catalyst has the greatest degree of inhibition of carbon-carbon coupling side reactions, thereby achieving high Faraday efficiency and selectivity of ethylene, while inhibiting the generation of ethane and hydrogen.

[0006] It should be noted that in the electrocatalyst, the metallic copper in the copper-cadmium heterostructure formed by the cadmium-modified copper element is the active center for the semi-hydrogenation of acetylene to generate ethylene. During the electroreduction of acetylene, adsorption activation of acetylene molecules and adsorption activation of water molecules occur on metallic copper. The metallic cadmium forms a heterostructure with metallic copper, thereby greatly optimizing the electronic structure of metallic copper, making it easier to crack water molecules on metallic copper, thereby generating more active hydrogen species to participate in the hydrogenation of acetylene molecules adsorbed on metallic copper to generate ethylene, so that more acetylene is generated to generate ethylene instead of acetylene due to lack of active hydrogen. Carbon-carbon coupling reaction. At the same time, the regulation of the electronic structure of metallic copper by metallic cadmium makes it more conducive to the cracking of water molecules on metallic copper, but not conducive to the occurrence of hydrogen evolution reaction. In addition, the intrinsic properties of metallic copper enable the heterostructure catalyst to still inhibit the occurrence of perhydrogenation reaction. The zirconium hydroxide carrier can evenly load the copper-cadmium heterostructure, and will not dissolve and react under alkaline electrolysis conditions, thereby maintaining the stability of the electrocatalyst in the electrolysis system.

[0007] In the present invention, the cadmium-modified copper-based electrocatalyst is specifically a copper-cadmium heterostructure electrocatalyst used to inhibit carbon-carbon coupling reaction during electrochemical acetylene reduction to ethylene.

[0008] Preferably, in the copper-cadmium heterostructure electrocatalyst formed by the above-mentioned cadmium-modified copper element, the heterostructure is formed by elemental copper and elemental cadmium; and / or, in the copper-cadmium heterostructure electrocatalyst formed by the cadmium-modified copper element, the content of metallic copper is 6-6.3wt.%, and the content of metallic cadmium is 6.8-7.2wt.%; preferably, the content of metallic copper is 6.15wt.%, and the content of metallic cadmium is 6.98wt.%.

[0009] Further preferably, in the above electrocatalyst, the zirconium hydroxide carrier is amorphous zirconium hydroxide; and / or, the zirconium hydroxide carrier is in the form of fragments.

[0010] In a second aspect, the present invention provides a method for preparing the above cadmium-modified copper-based electrocatalyst, comprising the following steps:

[0011] 1) Dissolve copper salt, cadmium salt, and zirconium salt in deionized water, add a precipitant, and preferably age at a temperature of 50-70 °C to obtain a crude product;

[0012] 2) Wash the crude product obtained in step 1) to obtain a precursor metal hydroxide material;

[0013] 3) Prepare the precursor metal hydroxide material obtained in step 2) into a slurry with a concentration of 0.3-0.8 mg / mL -1 and coat it on carbon paper. The coating amount is preferably 0.68-0.79 mg / cm 2 to obtain a precursor coated on the working electrode;

[0014] 4) Electrochemically in-situ reduce the precursor coated on the working electrode obtained in step 3) in an acetylene atmosphere to obtain a copper-cadmium heterostructure catalyst formed by cadmium-modified copper single crystals supported on zirconium hydroxide.

[0015] Preferably, in step 1), age in a 60 °C oil bath for 0.5 h.

[0016] Preferably, in step 1), the concentration of the copper salt dissolved in deionized water is 0.04-0.045 mol / L -1 and preferably 0.043 mol / L -1 ; the concentration of the cadmium salt dissolved in deionized water is 0.04-0.045 mol / L -1 and preferably 0.043 mol / L -1 ; the concentration of the zirconium salt dissolved in deionized water is 0.4-0.45 mol / L -1 and preferably 0.43 mol / L -1 .

[0017] Preferably, the molar ratio of the copper salt, the cadmium salt, and the zirconium salt is 1-2:1-2:10-15, and preferably 1:1:10; preferably, the copper salt is copper nitrate trihydrate, copper chloride, or copper sulfate; the cadmium salt is cadmium nitrate tetrahydrate, cadmium chloride, or cadmium sulfate; the zirconium salt is zirconyl nitrate, zirconium nitrate pentahydrate, zirconium oxychloride, or zirconium sulfate.

[0018] Preferably, the precipitating agent is sodium hydroxide, and the molar amount of the precipitating agent added is 3.5 to 3.8 times, preferably 3.67 times, the total molar amount of the copper salt, cadmium salt and zirconium salt.

[0019] Preferably, in step 2), the washing is carried out 8 to 10 times with deionized water until neutral, and preferably without drying.

[0020] In the present invention, the precursor metal hydroxide material obtained in step 2) is named CuCdZr(OH) x .

[0021] Preferably, in step 3), the precursor metal hydroxide material slurry is prepared with water: ethylene glycol: n-propanol in a volume ratio of 1:0.5 to 1:1; more preferably, water: ethylene glycol: n-propanol in a volume ratio of 1:1:1 or 1:0.5:1.

[0022] Preferably, in step 3), the precursor metal hydroxide material is prepared into a slurry of 0.3 to 0.8 mg mL -1 , preferably 0.5 mg mL -1 .

[0023] Preferably, in step 4), electrochemical in-situ reduction is carried out in an acetylene atmosphere with a volume fraction of 0.5% to 5%; preferably an acetylene atmosphere with a volume fraction of 5%, and the other components therein are argon; the reduction potential is -0.4 to -0.7 V relative to the reversible hydrogen electrode, preferably -0.5 V.

[0024] Preferably, in step 4), the electrochemical reduction of the precursor uses a three-phase flow electrolytic cell device, and the electrolyte is 1 to 10 mol L -1 KOH, preferably 1 mol L -1 KOH, 3 mol L -1 KOH, 5 mol L -1 KOH or 10 mol L -1 KOH, and the gas flow rate is 5 to 50 mL min -1 .

[0025] More preferably, in the above step 4), the reduction process of the precursor coated on the working electrode is as follows: first, place the working electrode at the interface between the gas chamber and the electrolyte chamber, and then blow the gas flow chamber with the reactant gas at a flow rate of 40 mL min -1 for 4 min. Then, fill the electrolyte chamber of the flow cell with KOH solution. Subsequently, connect the three electrodes to an electrochemical workstation for reduction.

[0026] In the present invention, the copper-cadmium heterostructure catalyst formed by cadmium-modified copper supported on zirconium hydroxide obtained in step 4) is named Cu-Cd / Zr(OH)4.

[0027] In a third aspect, the present invention provides the use of the above-mentioned cadmium-modified copper-based electrocatalyst or the copper-cadmium heterostructure electrocatalyst formed by cadmium-modified copper obtained by the preparation method of the above-mentioned cadmium-modified copper-based electrocatalyst in the electrochemical acetylene reduction reaction.

[0028] Preferably, the above application includes passing the reactant gas into the gas flow chamber at a certain flow rate for electrochemical reaction; preferably, the flow rate of the reactant gas is 5-50 mL min -1 ; and / or using a three-phase electrochemical flow cell for electrochemical reaction, the electrode area of the three-phase electrochemical flow cell is 0.4-3.2 cm 2 .

[0029] As a preference, in the embodiments of the present invention, a three-phase electrochemical flow cell is used for electrochemical reaction, and the reactant gas is passed into the gas flow chamber at a certain flow rate for reaction; data acquisition is carried out using a CHI660E electrochemical workstation (Shanghai Chenhua), and a platinum wire electrode and a silver / silver chloride (saturated KCl) electrode are used as the counter electrode and the reference electrode respectively; the resistance of the system is tested before each electrochemical test, and no ohmic resistance correction is carried out; gas samples are collected from the outlet flow by a syringe and quantified by a gas chromatograph.

[0030] Further preferably, the electrode area of the three-phase electrochemical flow cell is 0.4-3.2 cm 2 ; preferably, a three-phase electrochemical flow cell with an electrode area of 0.44 cm 2 or a three-phase electrochemical flow cell with an electrode area of 3.14 cm 2 is used.

[0031] It should be noted that, unless otherwise specified, any range described in the present invention includes the end values and any numerical value between the end values and any sub-range formed by any numerical value between the end values or the end values. In the present invention, the preparation methods are all conventional methods unless otherwise specified, and the raw materials used can be obtained from public commercial channels or prepared according to the existing technology unless otherwise specified.

[0032] The beneficial effects of the present invention are at least as follows: The electrocatalyst provided by the present invention has the advantages of low cost, simple preparation, simple process, and good stability. When this electrocatalyst is applied to the reaction of electrochemically reducing acetylene to ethylene, it can exhibit excellent activity for hydrogenating acetylene to ethylene, as well as a strong inhibitory effect on the side reaction of carbon-carbon coupling, while maintaining the inhibitory effect on the side reactions of hydrogen evolution and over-hydrogenation. Compared with the copper-based catalyst without cadmium, the introduction of cadmium in the cadmium-modified copper-based catalyst not only enhances the reaction activity of hydrogenating acetylene to ethylene, but also greatly inhibits the side reaction of carbon-carbon coupling. The inhibitory effect of this electrocatalyst on the carbon-carbon coupling reaction during the electroreduction of acetylene exceeds that of the previous catalysts, and the target product ethylene has a high selectivity, showing promise for industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0034] Figure 1 X-ray powder diffraction patterns of the CuCdZr(OH) x , CuZr(OH) x , CuInZr(OH) x and CuSnZr(OH) x precursors prepared in Example 1 of the present invention and Zr(OH)4.

[0035] Figure 2 Transmission electron microscope images of the CuCdZr(OH) x precursor prepared in Example 1 of the present invention; where a is a low-magnification transmission electron microscope image, b is a high-resolution transmission electron microscope image, c is an aberration-corrected high-angle annular dark-field scanning transmission electron microscope image, and d-g are elemental mapping images.

[0036] Figure 3 X-ray powder diffraction pattern of Cu-Cd / Zr(OH)4 prepared in Example 1 of the present invention.

[0037] Figure 4 X-ray photoelectron spectroscopy spectra of Cu-Cd / Zr(OH)4 prepared in Example 1 of the present invention; where a is the X-ray photoelectron spectroscopy spectrum of Cu, b is the X-ray photoelectron spectroscopy spectrum of Cd, c is the X-ray photoelectron spectroscopy spectrum of Zr, and d is the Auger spectrum of Cu.

[0038] Figure 5Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image of Cu-Cd / Zr(OH)4 prepared in Example 1 of the present invention; a is the aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image, b is the enlarged view of the selected area A in Figure a, c is the pseudo-color image of Figure b, d is the inverse fast Fourier transform image of the selected area A in Figure b, e is the inverse fast Fourier transform image of the selected area B in Figure b, and f is the elemental mapping image of Figure a.

[0039] Figure 6 CuZr(OH) prepared in Comparative Example 1 of the present invention x Transmission electron microscopy image of the precursor; a is the low-magnification transmission electron microscopy image, b is the aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image, and c-e are the elemental mapping images.

[0040] Figure 7 X-ray powder diffraction pattern and X-ray photoelectron spectroscopy spectrum of Cu / Zr(OH)4 prepared in Comparative Example 1 of the present invention; a is the X-ray powder diffraction pattern of Cu / Zr(OH)4, b is the X-ray photoelectron spectroscopy spectrum of Cu, c is the X-ray photoelectron spectroscopy spectrum of Zr, and d is the Auger spectrum of Cu.

[0041] Figure 8 Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image of Cu / Zr(OH)4 prepared in Comparative Example 1 of the present invention; a is the aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image, and b-d are the elemental mapping images of Figure a.

[0042] Figure 9 CuInZr(OH) prepared in Comparative Example 2 of the present invention x High-resolution transmission electron microscopy image of the precursor; a is the high-resolution transmission electron microscopy image, and the upper right inset is the selected area electron diffraction pattern, and b-e are the elemental mapping images.

[0043] Figure 10 CuSnZr(OH) prepared in Comparative Example 3 of the present invention x High-resolution transmission electron microscopy image of the precursor; a is the high-resolution transmission electron microscopy image, and the upper right inset is the selected area electron diffraction pattern, and b-e are the elemental mapping images.

[0044] Figure 11 Faraday efficiency distribution of each product of Cu-Cd / Zr(OH)4 and Cu / Zr(OH)4 obtained in Experimental Example 1 of the present invention at different voltages in the voltage range of -0.4V to -0.7V.

[0045] Figure 12 Reduced CuInZr(OH) obtained in Experimental Example 2 of the present invention x and CuSnZr(OH)x Faraday efficiency distribution of each product at -0.5 V voltage.

[0046] Figure 13 Faraday efficiency distribution of each product of cadmium-modified copper catalysts with different copper:cadmium molar ratios obtained in Experimental Example 3 of the present invention at -0.5 V voltage.

[0047] Figure 14 Faraday efficiency of each product and ethylene partial current density of Cu-Cd / Zr(OH)4 obtained in Experimental Example 4 of the present invention at -0.5 V voltage in different KOH electrolyte concentrations.

[0048] Figure 15 For Cu-Cd / Zr(OH)4 obtained in Experimental Example 5 of the present invention at -0.5 V voltage, 5 mol L -1 Faraday efficiency of each product at different gas flow rates in KOH electrolyte.

[0049] Figure 16 For Cu-Cd / Zr(OH)4 obtained in Experimental Example 6 of the present invention at -0.5 V voltage, 5 mol L -1 KOH electrolyte, 15 ml min -1 Long-term stability test results at gas flow rate.

[0050] Figure 17 Picture of an electrolytic cell with a large electrode area used in Experimental Example 7 of the present invention.

[0051] Figure 18 Long-term stability test results of Cu-Cd / Zr(OH)4 obtained in Experimental Example 7 of the present invention in an ethylene-rich mixed gas. Detailed implementation manners

[0052] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the protection scope of the present invention.

[0053] For those not specifying specific technologies or conditions in the embodiments of the present invention, they shall be in accordance with the technologies or conditions described in the literature in the field or in accordance with the product specifications. For those devices, instruments, reagents, etc. not specifying the manufacturer, they are all conventional products that can be obtained through regular channels. The raw materials used in the present invention can be conveniently purchased in the domestic product market.

[0054] In the embodiment of the present invention, the reduction process of the precursor coated on the working electrode is as follows: first, the working electrode is placed at the interface between the gas chamber and the electrolyte chamber, and then the reactant gas is used at a rate of 40 mL min -1 The gas flow chamber was purged at a flow rate of 100 μg / min for 4 min. Then, the electrolyte chamber of the flow cell was filled with KOH solution. Subsequently, the three electrodes were connected to the electrochemical workstation for reduction.

[0055] In the following examples of the present invention, a three-phase electrochemical flow cell is used for electrochemical testing, and the reactant gases are introduced into the gas flow chamber at different flow rates for reaction. Data acquisition uses a CHI660E electrochemical workstation (Shanghai Chenhua), and a platinum wire electrode and a silver / silver chloride (saturated KCl) electrode are used as the counter electrode and the reference electrode, respectively. Before each electrochemical test, the resistance of the system is tested first, and no ohmic resistance correction is performed. The gas sample is collected from the outlet flow by a syringe and quantified by a gas chromatograph. In the above steps, the three-phase electrochemical flow cell has two sizes, one of which has an electrode area of ​​0.44cm 2 , the other is 3.14cm 2 The flow rate of the reactant gas is 5-50 mL min -1 .

[0056] Example 1

[0057] This embodiment provides a method for preparing a copper-cadmium heterostructure electrocatalyst formed by cadmium-modified copper element to inhibit carbon-carbon coupling reaction during electrochemical acetylene reduction to ethylene, the steps of which are as follows:

[0058] Dissolve 5.28g NaOH in 60mL deionized water (referred to as solution A), and dissolve 0.7248g Cu(NO3)2·3H2O, 0.9254g Cd(NO3)2·4H2O, and 6.9369g ZrO(NO3)2 in 70mL deionized water (referred to as solution B). Then add solutions A and B simultaneously to a stirred flask containing 50mL deionized water. After the addition is completed, a blue suspension is obtained, which is then aged at 60°C for 0.5h. The product is collected by centrifugation and washed with deionized water 8 to 10 times to a pH of about 7. This precursor is named CuCdZr(OH) x , and then the prepared CuCdZr(OH) x Redisperse in deionized water and store in a refrigerator at 2°C for later use. CuCdZr(OH) x The concentration of the precursor is generally between 6 and 12.0 mg mL -1 Next, the precursor was dispersed in a water-ethylene glycol-n-propanol mixture with a volume ratio of 1:1:1 to prepare 0.5 mg mL -1The slurry was then sonicated for 20 min to make it uniform. Then, 100 μL of the slurry was drop-coated on a carbon-based gas diffusion layer (GDL, H14C9, Freudenberg Group, Germany) and dried under an infrared lamp. Then, this process was repeated 5 times. The obtained coated precursor was electrochemically reduced in 1 molL -1 KOH at -0.5 V for 3 minutes (in an acetylene atmosphere with a volume fraction of 5%), and the Cu-Cd / Zr(OH)4 catalyst could be obtained. Then, further electrochemical tests were carried out.

[0059] The copper-cadmium heterostructure electrocatalyst formed by cadmium-modified copper metal in the process of electrochemically reducing acetylene to ethylene provided in this example is Cu-Cd / Zr(OH)4. The above cadmium-modified copper-based electrocatalyst uses zirconium hydroxide as the carrier; the heterostructure formed by metallic copper and metallic cadmium is loaded on this zirconium hydroxide carrier. The zirconium hydroxide carrier is amorphous zirconium hydroxide and is in the form of fragments. In the above electrocatalyst, both copper and cadmium exist in the form of simple substances, the content of metallic copper is 6.15 wt.%, and the content of metallic cadmium is 6.98 wt.%. The above cadmium-modified copper-based electrocatalyst was characterized. The results showed that Figure 1 including CuCdZr(OH) x The X-ray powder diffraction pattern of the precursor, where the peak signals belong to amorphous Zr(OH)4. Figure 2 is CuCdZr(OH) x The transmission electron microscope image of the precursor shows that it is in the form of fragments. Figure 3 is the X-ray powder diffraction pattern of Cu-Cd / Zr(OH)4, where the peak signals belong to copper metal. Figure 4 is the X-ray photoelectron spectroscopy spectrum of Cu-Cd / Zr(OH)4, showing that copper belongs to zero valence, cadmium belongs to zero valence, and zirconium belongs to tetravalence. Figure 5 is the aberration-corrected high-angle annular dark-field scanning transmission electron microscope image of Cu-Cd / Zr(OH)4, showing that copper and cadmium exist in the form of a heterostructure, and Zr(OH)4 serves as the carrier.

[0060] Example 2

[0061] Preparation of the working electrode for the electrochemical acetylene reduction process with a large electrode area, the steps are as follows:

[0062] Disperse the CuCdZr(OH) x precursor prepared in Example 1 in a water-ethylene glycol-n-propanol mixture with a volume ratio of 1:0.5:1 to prepare a 0.5 mg mL -1The slurry was then ultrasonicated for 20 min to make it uniform. Next, 450 μL of the slurry was drop-coated on a carbon-based gas diffusion layer (GDL, H14C9, Freudenberg Group, Germany) and dried under an infrared lamp. Then, this process was repeated 11 times. The coated precursor was electrochemically reduced in a KOH electrolyte at a voltage of -0.5 V for 3 minutes (acetylene atmosphere), and then immediately subjected to the next electrochemical test.

[0063] Comparative Example 1

[0064] A method for preparing a copper catalyst for electrochemical acetylene reduction to ethylene reaction, comprising the following steps:

[0065] The precursor of the cadmium-free zirconium hydroxide-supported copper catalyst was named CuZr(OH) x The preparation steps of the precursor are the same as those in Example 1, except that 0.24 g of NaOH is reduced and 0.9254 g of Cd(NO3)2·4H2O is omitted, and other conditions remain unchanged. Prepared CuZr(OH) x Redisperse in deionized water and store in a refrigerator at 2°C for later use. CuZr(OH) x The concentration of the precursor is generally between 6 and 12.0 mg mL -1 Next, the precursor was dispersed in a water-ethylene glycol-n-propanol mixture with a volume ratio of 1:1:1 to prepare 0.5 mg mL -1 The slurry was then ultrasonicated for 20 min to make it uniform. Next, 100 μL of the slurry was drop-coated on a carbon-based gas diffusion layer (GDL, H14C9, Freudenberg Group, Germany) and dried under an infrared lamp. This process was then repeated 5 times. The resulting coated precursor was heated to 1 mol L -1 The Cu / Zr(OH)4 catalyst was obtained by reduction in KOH for 3 min, and then further electrochemical tests were performed.

[0066] Figure 1 Including CuZr(OH) x X-ray powder diffraction pattern of the precursor, in which the peak signal is attributed to amorphous Zr(OH)4. Figure 6 CuZr(OH) x Transmission electron microscopy image of the precursor, showing that it is fragmented. Figure 7 It is the X-ray powder diffraction spectrum and X-ray photoelectron spectrum of Cu / Zr(OH)4, wherein the peak signal of the X-ray powder diffraction spectrum belongs to the copper element; the X-ray photoelectron spectrum shows that copper is zero-valent and zirconium is tetravalent. Figure 8This is an aberration-corrected high-angle annular dark field scanning transmission image of Cu / Zr(OH)4, showing that copper exists in the form of nanoparticles and Zr(OH)4 acts as a carrier.

[0067] Comparative Example 2

[0068] A method for preparing an indium-modified copper catalyst for electrochemical acetylene reduction to ethylene reaction, comprising the following steps:

[0069] The indium-modified copper catalyst precursor was named CuInZr(OH) x The preparation steps of the precursor are the same as those in Example 1, except that 0.9254 g of Cd(NO3)2·4H2O is replaced by 0.9565 g of In(NO3)3·H2O and 5.40 g of NaOH is used, and other conditions remain unchanged. Prepared CuInZr(OH) x Redisperse in deionized water and store in a refrigerator at 2°C for later use. CuInZr(OH) x The concentration of the precursor is generally between 6 and 12.0 mg mL -1 Next, the precursor was dispersed in a water-ethylene glycol-n-propanol mixture with a volume ratio of 1:1:1 to prepare 0.5 mg mL -1 The slurry was then ultrasonicated for 20 min to make it uniform. Next, 100 μL of the slurry was drop-coated on a carbon-based gas diffusion layer (GDL, H14C9, Freudenberg Group, Germany) and dried under an infrared lamp. This process was then repeated 5 times. The resulting coated precursor was heated to 1 mol L -1 The reduced catalyst was obtained by reduction in KOH for 3 minutes, and then further electrochemical tests were performed.

[0070] Figure 1 Including CuInZr(OH) x X-ray powder diffraction pattern of the precursor, in which the peak signal is attributed to amorphous Zr(OH)4. Figure 9 CuInZr(OH) x Transmission electron microscope image of the precursor, showing that it is fragmented.

[0071] Comparative Example 3

[0072] A method for preparing a tin-modified copper catalyst for electrochemical acetylene reduction to ethylene reaction, comprising the following steps:

[0073] The tin-modified copper catalyst precursor was named CuSnZr(OH) x。The preparation steps of the precursor are the same as those in Example 1, except that 0.9254 g of Cd(NO3)2·4H2O is replaced with 0.6442 g of SnSO4, and other conditions remain unchanged. The prepared CuSnZr(OH) x is redispersed in deionized water and stored in a refrigerator at 2 °C for later use. CuSnZr(OH) x The concentration of the precursor is generally in the range of 6 - 12.0 mg mL -1 Next, the precursor is dispersed in a water-ethylene glycol-n-propanol mixture with a volume ratio of 1:1:1 to prepare a slurry of 0.5 mg mL -1 . Then it is ultrasonicated for 20 min to make it uniform. Next, 100 μL of the slurry is drop-coated on a carbon-based gas diffusion layer (GDL, H14C9, Freudenberg Group, Germany) and dried under an infrared lamp. Then, this process is repeated 5 times. The coated precursor is reduced in 1 mol L -1 KOH at -0.5 V voltage in an acetylene atmosphere for 3 minutes to obtain the reduced catalyst, and then further electrochemical tests are carried out.

[0074] Figure 1 including CuSnZr(OH) x X-ray powder diffraction pattern of the precursor, where the peak signals are attributed to amorphous Zr(OH)4. Figure 10 is the transmission electron microscope image of CuSnZr(OH) x precursor, showing that it presents a fragmented shape.

[0075] Comparative Example 4

[0076] Preparation method of a copper-based catalyst modified with different contents of cadmium in the electrochemical acetylene reduction to ethylene reaction, the steps are as follows:

[0077] The preparation steps of the precursors of cadmium-modified copper-based catalysts with different copper:cadmium molar ratios are the same as those in Example 1, except for the feeding amounts. 1) For copper:cadmium = 1:0.2, 3 mmol of Cu(NO3)2·3H2O, 0.6 mmol of Cd(NO3)2·4H2O, 30 mmol of ZrO(NO3)2 and 127.2 mmol of NaOH are used; 2) For copper:cadmium = 1:0.3, 3 mmol of Cu(NO3)2·3H2O, 1 mmol of Cd(NO3)2·4H2O, 30 mmol of ZrO(NO3)2 and 128 mmol of NaOH are used; 3) For copper:cadmium = 1:3, 3 mmol of Cu(NO3)2·3H2O, 9 mmol of Cd(NO3)2·4H2O, 30 mmol of ZrO(NO3)2 and 144 mmol of NaOH are used; 4) For copper:cadmium = 1:5, 3 mmol of Cu(NO3)2·3H2O, 15 mmol of Cd(NO3)2·4H2O, 30 mmol of ZrO(NO3)2 and 156 mmol of NaOH are used; 5) For copper:cadmium = 0:1, 0 mmol of Cu(NO3)2·3H2O, 3 mmol of Cd(NO3)2·4H2O, 30 mmol of ZrO(NO3)2 and 126 mmol of NaOH are used. Other conditions remain unchanged. The prepared precursors are redispersed in deionized water and stored in a refrigerator at 2 °C for later use. The concentration of the precursors can generally be 6 - 12.0 mg mL -1 . Next, the precursors are dispersed in a water-ethylene glycol-n-propanol mixture with a volume ratio of 1:1:1 to prepare a slurry of 0.5 mg mL -1 , and then ultrasonicated for 20 min to make it uniform. Then, 100 μL of the slurry is drop-coated on a carbon-based gas diffusion layer (GDL, H14C9, Freudenberg Group, Germany) and dried under an infrared lamp. Then, this process is repeated 5 times. The coated precursors obtained are reduced in 1 mol L -1 KOH at -0.5 V voltage in an acetylene atmosphere for 3 minutes to obtain the reduced catalyst, and then further electrochemical tests are carried out.

[0078] The following tests are carried out on the electrocatalysts prepared in Example 1 and Example 2 above (Experiment Example 7 is for Example 2) and Comparative Examples 1 - 4:

[0079] Experiment Example 1

[0080] The catalysts Cu-Cd / Zr(OH)4 and Cu / Zr(OH)4 are respectively applied to the electrochemical acetylene reduction reaction, and the test method includes the following steps:

[0081] Electrochemical acetylene reduction reaction at an electrode area of ​​0.44 cm 2 The three-phase flow electrolysis cell was used. -1 In KOH electrolyte, 15 ml min -1 5% acetylene gas was introduced into the gas flow chamber at a flow rate of 1.5 % acetylene gas. Constant voltage electrolysis tests were performed on Cu-Cd / Zr(OH)4 and Cu / Zr(OH)4 in the voltage range of -0.4 V to -0.7 V. The sampling time for each electrochemical test was 25 minutes. The product gas was collected from the outlet flow by a syringe and quantified by a gas chromatograph (see the electrochemical test results for details). Figure 11 ).

[0082] Test results: At a voltage of -0.5V, the Cu-Cd / Zr(OH)4 catalyst achieved an ethylene Faraday efficiency of 98.38%, a C4H6 Faraday efficiency of 0.06%, a hydrogen Faraday efficiency of 0.15%, and almost no C2H6 and C4H8. In the voltage range of -0.5V to -0.7V, the Faraday efficiency of ethylene exceeded 96.22%, and the Faraday efficiency of C4H6 was less than 0.08%, showing a strong inhibitory effect on the carbon-carbon coupling reaction. At a voltage of -0.5V, Cu / Zr(OH)4 achieved an ethylene Faraday efficiency of 93.67%, a C4H6 Faraday efficiency of 3.20%, a hydrogen Faraday efficiency of 0.18%, a C2H6 Faraday efficiency of 0.12%, and a C4H8 Faraday efficiency of 0.12%. As the voltage shifts negatively to -0.7 V, the ethylene Faraday efficiency of Cu / Zr(OH)4 drops to 84.17%, the hydrogen Faraday efficiency increases to 2.86%, the C4H6 Faraday efficiency is 1.35%, the C2H6 Faraday efficiency is 0.54%, and the C4H8 Faraday efficiency is 0.17%. The above results show that the addition of metallic cadmium has a strong inhibitory effect on the carbon-carbon coupling side reaction of the copper catalyst during the acetylene electroreduction process, enabling it to maintain a high ethylene Faraday efficiency and highly efficient inhibition of side reactions over a wide voltage range.

[0083] Experimental Example 2

[0084] The reduced CuInZr(OH) x and CuSnZr(OH) x They were applied to the electrochemical acetylene reduction reaction. The test steps were the same as those in Experimental Example 1, except that only the test was performed at a voltage of -0.5 V (see the test results in Figure 12 ).

[0085] like Figure 12 As shown, the reduced CuInZr(OH) x It has a certain degree of inhibitory effect on the carbon-carbon coupling side reaction in the electrochemical acetylene reduction reaction, and the reduced CuSnZr(OH) xThere is no obvious inhibitory effect on the carbon-carbon coupling reaction.

[0086] The above results show that only the addition of metallic cadmium can enable copper-based catalysts to effectively inhibit carbon-carbon coupling reactions during acetylene electroreduction.

[0087] Experimental Example 3

[0088] The cadmium-modified copper catalysts with different copper:cadmium molar ratios were respectively applied to the electrochemical acetylene reduction reaction. The test steps were the same as those in Experimental Example 1, except that only the test was performed at a voltage of -0.5 V (see the test results in Figure 13 ).

[0089] like Figure 13 As shown in Figure 2, with the increase of cadmium content, the Faraday efficiency of C4 products gradually decreased from 3.20% in the absence of cadmium to 0.06% when the theoretical copper: cadmium molar ratio was 1:1. At the same time, the Faraday efficiency of ethylene increased from 93.67% to 98.38%. Further increasing the cadmium content, although the Faraday efficiency of C4 products remained below 0.10%, the Faraday efficiency of hydrogen gradually increased from 0.15% when copper: cadmium = 1:1 to 3.14% when copper: cadmium = 1:5, resulting in the Faraday efficiency of ethylene falling to 93.70%. In the absence of copper (copper: cadmium = 0:1), the hydrogen evolution reaction became serious, and the Faraday efficiency of ethylene was significantly reduced to 28.17%, indicating that metal cadmium is not an active site for acetylene electroreduction.

[0090] The above results indicate that the cadmium-modified copper catalyst with a theoretical copper:cadmium molar ratio of 1:1 is the optimal ratio, which enables the copper-based catalyst to efficiently suppress the carbon-carbon coupling reaction and achieve a high ethylene Faradaic efficiency during the acetylene electroreduction process.

[0091] Experimental Example 4

[0092] The test target is Cu-Cd / Zr(OH)4. The test steps are the same as those in Experiment 1, except that the electrolysis experiment is only carried out at a voltage of -0.5V, and the concentration of KOH electrolyte is changed. -1 KOH, 3 mol L -1 KOH, 5 mol L -1 KOH and 10 mol L -1 Distribution of each product in KOH electrolyte (test results see Figure 14 ).

[0093] like Figure 14 As shown: At -0.5V, whether in 1mol L -1 In KOH electrolyte, or at up to 10 molL -1In KOH electrolyte, Cu-Cd / Zr(OH)4 catalysts can maintain high ethylene Faraday efficiency and highly inhibit side reactions such as carbon-carbon coupling. -1 In KOH electrolyte, the Faradaic efficiency and current density of the main product ethylene are the highest, which are 99.62% and 22.83 mA cm 2 .

[0094] Experimental Example 5

[0095] The test target is Cu-Cd / Zr(OH)4. The test steps are the same as those in Experiment 1. The difference is that 5 mol L -1 KOH was used as electrolyte, and the gas flow rate was changed. The tests were performed at 5 ml min -1 , 15ml min -1 , 30ml min -1 , 50ml min -1 The electrolysis results of the catalyst at a voltage of -0.5V at a flow rate (test results see Figure 15 ).

[0096] like Figure 15 As shown: At -0.5V, 5mol L -1 In KOH electrolyte, changes in gas flow rate do not bring about changes in product distribution, and this catalyst can still maintain high reaction activity and effectively inhibit side reactions such as carbon-carbon coupling.

[0097] Experimental Example 6

[0098] The test target is Cu-Cd / Zr(OH)4. The test steps are the same as those in Experiment 1. The difference is that 5 mol L -1 KOH was used as the electrolyte and the catalyst was tested for long-term stability at a voltage of -0.5 V. The test results are shown in Figure 16 .

[0099] like Figure 16 As shown: At 5 mol L -1 In KOH electrolyte, electrolysis was performed at a voltage of -0.5 V. During the nearly 12-hour electrochemical test, the catalyst maintained an ethylene Faradaic efficiency of 98.20% ± 0.27%, and the Faradaic efficiency of C4H6 was always below 0.05%.

[0100] Experimental Example 7

[0101] The test target is Cu-Cd / Zr(OH)4 of Example 2, and the test method includes the following steps:

[0102] Using the prepared working electrode with a large electrode area, the electrode area was 3.14 cm 2The three-phase flow electrolysis cell is operated, and the reactor is as Figure 17 As shown. At 5 mol L -1 In KOH electrolyte, 10 ml min -1 A mixed gas of 0.5% acetylene + 20% ethylene + 79.5% argon was introduced into the gas flow chamber at a flow rate of 1.5 % to 1.5 % and a constant current electrolysis (chronopotentiometry) of Cu-Cd / Zr(OH)4 was performed at a current of -7.0 mA for a long time. The sampling time interval was not fixed each time. The product gas was collected from the outlet flow by a syringe and quantified by a gas chromatograph (test results are shown in Figure 18 ).

[0103] like Figure 18 As shown: 5 mol L in ethylene-rich gas -1 During long-term electrolysis in KOH electrolyte, the catalyst achieved a maximum acetylene conversion rate of 99.45% and maintained 99.99% ethylene selectivity during 12 hours of electrolysis, demonstrating the catalyst's strong stability and excellent performance in inhibiting carbon-carbon coupling side reactions.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cadmium-modified copper-based electrocatalyst, characterized in that, The cadmium-modified copper-based electrocatalyst comprises a zirconium hydroxide carrier; and a copper-cadmium heterostructure formed by a cadmium-modified copper element supported on the zirconium hydroxide carrier.

2. The cadmium-modified copper-based electrocatalyst according to claim 1, wherein In the copper-cadmium heterostructure electrocatalyst formed by the cadmium-modified copper element, the heterostructure is formed by elemental copper and elemental cadmium; and / or, in the copper-cadmium heterostructure electrocatalyst formed by the cadmium-modified copper element, the content of metallic copper is 6-6.3wt.%, and the content of metallic cadmium is 6.8-7.2wt.%.

3. The cadmium-modified copper-based electrocatalyst according to claim 1 or 2, wherein In the electrocatalyst, the zirconium hydroxide support is amorphous zirconium hydroxide; and / or, the zirconium hydroxide support is in the form of fragments.

4. The preparation method of the cadmium-modified copper-based electrocatalyst according to any one of claims 1 to 3, characterized in that, The following steps are involved: 1) dissolving copper salt, cadmium salt and zirconium salt in deionized water, adding a precipitant, and aging to obtain a crude product; 2) washing the crude product obtained in step 1) to obtain a precursor metal hydroxide material; 3) preparing the precursor metal hydroxide material obtained in step 2) into a slurry, and applying it on carbon paper to obtain a precursor coated on a working electrode; 4) The precursor coated on the working electrode obtained in step 3) is subjected to electrochemical in-situ reduction in an acetylene atmosphere to obtain a copper-cadmium heterostructure catalyst formed by zirconium hydroxide-supported cadmium-modified copper element.

5. The preparation method of the cadmium-modified copper-based electrocatalyst according to claim 4, wherein, In step 1), the concentration of the copper salt dissolved in deionized water is 0.04 - 0.045 mol / L -1 , preferably 0.043 mol / L -1 ; the concentration of the cadmium salt dissolved in deionized water is 0.04 - 0.045 mol / L -1 , preferably 0.043 mol / L -1 ; the concentration of the zirconium salt dissolved in deionized water is 0.4 - 0.45 mol / L -1 , preferably 0.43 mol / L -1 ; the molar ratio of the copper salt, the cadmium salt and the zirconium salt is 1 - 2:1 - 2:10 - 15, preferably 1:1:10; preferably, the copper salt is copper nitrate trihydrate, copper chloride or copper sulfate; the cadmium salt is cadmium nitrate tetrahydrate, cadmium chloride or cadmium sulfate; the zirconium salt is zirconyl nitrate, zirconium nitrate pentahydrate, zirconium oxychloride or zirconium sulfate; the precipitant is sodium hydroxide, and the added molar amount of the precipitant is 3.5 - 3.8 times the total molar amount of the copper salt, the cadmium salt and the zirconium salt, preferably 3.67 times.

6. The preparation method of the cadmium-modified copper-based electrocatalyst according to claim 4, characterized in that, In step 2), the washing is performed by washing with deionized water for 8 to 10 times until the mixture becomes neutral.

7. The preparation method of the cadmium-modified copper-based electrocatalyst according to any one of claims 4-6, characterized in that, In step 3), the precursor metal hydroxide material slurry is prepared with water: ethylene glycol: n-propanol at a volume ratio of 1:0.5 to 1:1; the precursor metal hydroxide material is formulated into a slurry of 0.3 to 0.8 mg mL -1 and preferably 0.5 mg mL -1 .

8. The preparation method of the cadmium-modified copper-based electrocatalyst according to any one of claims 4-7, characterized in that, In step 4), electrochemical in-situ reduction is carried out in an acetylene atmosphere with a volume fraction of 0.5% to 5%; preferably, an acetylene atmosphere with a volume fraction of 5% is used, and the other component therein is argon; the reduction potential is -0.4 to -0.7 V relative to the reversible hydrogen electrode, preferably -0.5 V; the electrochemical reduction of the precursor uses a three-phase flow electrolytic cell device, and the electrolyte is 1 to 10 molL -1 KOH, and the gas flow rate is 5 to 50 mL min -1 .

9. Use of the copper-cadmium heterostructure electrocatalyst obtained by the cadmium-modified copper-based electrocatalyst according to any one of claims 1 to 3 or the preparation method of the cadmium-modified copper-based electrocatalyst according to any one of claims 4 to 8 in an electrochemical acetylene reduction reaction.

10. Use of the cadmium-modified copper-based electrocatalyst according to claim 9 in an electrochemical acetylene reduction reaction, characterized in that, The method comprises passing reactant gas into a gas flow chamber at a certain flow rate to perform an electrochemical reaction; Preferably, the flow rate of the reactant gas is 5 to 50 mL / min -1 ; and / or, an electrochemical flow cell of the three-phase type is used for the electrochemical reaction, and the electrode area of the three-phase electrochemical flow cell is preferably 0.4 to 3.2 cm 2 .

Images