A nano copper-based catalyst, its preparation method, and its application in the electrocatalytic reduction of carbon dioxide and carbon monoxide

Abstract

The present invention discloses a nano copper-based catalyst, its preparation method, and its application in the electrocatalytic reduction of carbon dioxide and carbon monoxide. Copper chloride (or copper nitrate, copper acetate) is dissolved in ultrapure water, and a sodium borohydride solution is added dropwise. Stir at room temperature for 5-60 min, filter, and dry to obtain a nano copper catalyst. Further, through a displacement reaction, nano copper-palladium and copper-silver catalysts are obtained. The present invention is applied to the electrocatalytic reduction of carbon monoxide. In a membrane electrode assembly (MEA) electrolyzer, the Faraday efficiency of multi-carbon products (C2+) reaches up to 95%, the partial current density reaches up to 3 A cm-2, and the overall electrolyzer energy efficiency reaches up to 39%. It can stably electrolyze for 30 hours at 1 A cm-2. This nano copper catalyst is applied to the electrocatalytic reduction of carbon dioxide. In an MEA electrolyzer, the Faraday efficiency of C2+ reaches up to 66%, and the partial current density reaches up to 331 mA cm-2.

Description

Technical Field

[0001] The present invention belongs to the field of catalysis, and particularly relates to a nano copper-based catalyst for electrocatalytic reduction of carbon dioxide and carbon monoxide. Background Art

[0002] At present, with the depletion of fossil resources, the sustainable production of chemicals based on petrochemical and coal chemical industries has gradually become the focus of attention. The electrocatalytic reduction reaction of carbon dioxide (CO2RR) uses clean electric energy to convert CO2 and water into fuels and chemicals, which is an effective strategy to simultaneously achieve carbon cycle utilization and renewable energy storage. However, during the process of directly electro-reducing CO2 to multi-carbon (C 2+ ) products in alkaline electrolytes, a large amount of carbonate is generated. The formation of carbonate will lead to CO2 loss and high energy consumption (consuming up to 72% of the energy). The two-step electro-reduction of CO2 to multi-carbon (C 2+ ) products can effectively avoid such problems, that is, first convert CO2 to CO in a solid oxide electrolyzer (SOEC) (the first step), and then convert the CO obtained in the SOEC to C 2+ (the second step) in a membrane electrode assembly (MEA) electrolyzer, thereby eliminating the loss of CO2 conversion to carbonate, and the reduction of carbon monoxide has a lower overpotential and higher C 2+ product selectivity than the reduction of carbon dioxide, and then achieving high-activity, high-selectivity CO2-C 2+ conversion and high CO2 utilization efficiency.

[0003] The key to achieving efficient CO2-C 2+ conversion is to improve the carbon-carbon (C-C) coupling efficiency of CO to C 2+ conversion in the MEA and the long-term stability of the MEA electrolyzer. Therefore, the development of a highly active, inexpensive and stable copper catalyst for electrocatalytic reduction of carbon monoxide (CORR) is of great significance for the electrocatalytic reduction of carbon dioxide and carbon monoxide.

[0004] At present, the strategies for improving the activity of CORR catalysts mainly include the following: organic modification, doping, grain boundary and crystal plane engineering, etc. The literature (Joule 2021, 5, 706-719) designed a layered catalyst structure composed of metallic copper, N-tolyl-tetrahydropyridine and short side chain copolymer (SSC) ions, and realized the efficient conversion of CO to C2H4 in the MEA electrolyzer. The literature (Adv. Mater. 2020, 32, e2002382) reported a copper nitride (Cu3N) nanocrystal catalyst with a rich twin structure synthesized in ammonia solution. This catalyst has more than 90% of C 2+Faradaic efficiency. The literature (Energy Environ. Sci. 2020, 13, 2993 - 3006) reported a hybrid metal oxide Ag2Cu2O3 catalyst as a starting template material for the effective electroreduction of CO to produce C 2+ products. The CORR electrochemical test results showed that at 600 mA cm -2 , the Faradaic efficiency of the C 2+ products was close to 92%. The literature (Nat. Commun. 2020, 11, 3685) reported a Pd-doped Cu catalyst, which weakened the adsorption of hydrogen and contributed to the hydrogenation of C2 intermediates to promote the formation of alcohols. The Faradaic efficiency of alcohol formation on this catalyst was 40%, and the partial current density was 277 mA cm -2 . However, copper catalysts prepared using organic ligands, surfactants, etc. often require a relatively complex preparation process, have a high cost, and poor stability. Therefore, there is an urgent need to develop a simple, rapid, and high-yield preparation method for efficient copper catalysts. Summary of the Invention

[0005] The problem solved by the technical solution of the present invention: Overcoming the deficiencies of the prior art, a preparation method for a nano-copper-based catalyst for the electrocatalytic reduction of carbon dioxide and carbon monoxide has been developed. This method is simple, rapid, and has a high yield. The prepared copper-based catalyst has high electrocatalytic reduction activity, selectivity, and stability for CO.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A preparation method for a nano-copper-based catalyst, the steps are as follows:

[0008] Step 1: Dissolve copper salt in ultrapure water to obtain a copper salt solution, and the concentration of the copper salt solution is 0.01 - 0.2 mol L -1 ;

[0009] Step 2: Dropwise add sodium borohydride solution to the above copper salt solution, stir at room temperature for 5 - 60 min, filter, and dry to obtain a nano-copper catalyst; the molar ratio of sodium borohydride to copper salt is 1 - 20, and the concentration of the sodium borohydride solution is 0.1 - 1 mol L -1 .

[0010] A preparation method for a nano-copper-based binary catalyst, including the following steps:

[0011] Step 1: Dissolve copper salt in ultrapure water to obtain a copper salt solution, and the concentration of the copper salt solution is 0.01 - 0.2 mol L -1 ;

[0012] Step 2: Dropwise add a sodium borohydride solution into the above copper salt solution, stir at room temperature for 5 - 60 min, filter, and dry to obtain a nano copper catalyst; the molar ratio of sodium borohydride to copper salt is 1 - 20, and the concentration of the sodium borohydride solution is 0.1 - 1 mol / L -1 ;

[0013] Step 3: Ultrasonically disperse the above nano copper catalyst in ultrapure water, under nitrogen protection, add a second metal precursor, ultrasonically treat for 10 - 30 min, filter, and dry to obtain a nano copper-based binary catalyst. The second metal precursor is a soluble silver salt or a soluble palladium salt. The concentration of the second metal precursor is 0.01 - 0.2 mol / L -1 . The molar ratio of the second metal precursor to the copper salt is 0.01 - 0.2.

[0014] A suitable copper salt concentration can obtain copper nanoparticles with relatively uniform size. A suitable ratio of sodium borohydride to copper salt is beneficial to ensure complete reduction of the metal. A suitable sodium borohydride concentration is beneficial to control the reduction rate of the reaction and obtain copper nanoparticles with appropriate size.

[0015] Using ultrasound during the reaction is beneficial to accelerating the reaction rate. Using nitrogen protection during the reaction can avoid oxidation of the nano copper-based catalyst. A suitable concentration of the second metal precursor is beneficial to the uniform dispersion of the second metal.

[0016] Based on the above scheme, preferably, the copper salt can be copper nitrate, copper chloride, copper acetate, etc.

[0017] Based on the above scheme, preferably, the concentration of the copper salt solution is 0.01 - 0.1 mol / L -1 .

[0018] Based on the above scheme, preferably, the molar ratio of sodium borohydride to copper salt is 5 - 10.

[0019] Based on the above scheme, preferably, the soluble silver salt is silver nitrate, and the soluble palladium salt is palladium chloride.

[0020] Based on the above scheme, preferably, the concentration of the second metal precursor is 0.01 - 0.1 mol / L -1 ; the molar ratio of the second metal precursor to the copper salt is 0.1 - 0.2.

[0021] The catalyst prepared by the above method of the present invention has a nano-porous structure. The catalyst is composed of particles with a particle size of 10 - 20 nm connected together; it has a porous structure with a pore size of 50 - 100 nm; and it has a core-shell structure, with metallic copper inside and a layer of cuprous oxide about 3 - 5 nm thick wrapped outside.

[0022] The catalyst prepared as described above in the present invention can be used for the electrocatalytic reduction reaction of carbon dioxide and / or carbon monoxide. It is realized as follows: The nano-copper catalyst has a nano-porous structure with abundant defects and grain boundary structures. When applied to the electrocatalytic reduction of carbon monoxide, it exhibits high electrolysis performance. In the MEA electrolyzer, C 2+ The Faraday efficiency can reach up to 95%, and the current density can reach up to 3 A cm -2 , and the overall electrolyzer energy efficiency can reach up to 39%. It can stably electrolyze for 30 hours at 1 A cm -2 .

[0023] The advantages of the present invention over the prior art are as follows:

[0024] By means of the liquid-phase reduction method, a gram-scale nano-copper-based catalyst can be prepared in one step. The nano-copper catalyst has a nano-porous structure with abundant defects and grain boundary structures. And this catalyst has excellent performance in the CORR of C in the MEA electrolyzer 2+ , and C 2+ The Faraday efficiency can reach up to 95%, and the current density can reach up to 3 A cm -2 , and the overall electrolyzer energy efficiency can reach up to 39%. It can stably electrolyze for 30 hours at 1 A cm -2 . This invention provides an important research basis for promoting the industrial application of CO2RR. Description of the Drawings

[0025] Figure 1 (Left) and (right) are the scanning electron microscope and transmission electron microscope pictures of the nano-copper catalyst in Example 1 respectively.

[0026] Figure 2 is the X-ray diffraction pattern of the nano-copper catalyst in Example 1.

[0027] Figure 3 is the CORR reaction performance graph of the nano-copper catalyst in Example 1 in the MEA electrolyzer.

[0028] Figure 4 is the CO2RR reaction performance graph of the nano-copper catalyst in Example 1 in the MEA electrolyzer.

[0029] Figure 5 is the test result graph of the CORR reaction stability of the nano-copper catalyst in Example 1 in the MEA electrolyzer.

[0030] Figure 6 is the CORR reaction performance graph of the nano-copper-palladium catalyst in Example 2 in the MEA electrolyzer.

[0031] Figure 7 is the X-ray diffraction pattern of the OD-Cu-350 catalyst in Comparative Example 1.

[0032] Figure 8 It is the transmission electron microscope image of the OD-Cu-350 catalyst in Comparative Example 1.

[0033] Figure 9 It is the CORR reaction performance graph of the OD-Cu-350 catalyst in the MEA electrolyzer in Comparative Example 1.

[0034] Figure 10 It is the X-ray diffraction spectrum of the Cu-He-200, Cu-He-300, Cu-He-400, and Cu-He-500 catalysts in Comparative Example 2.

[0035] Figure 11 It is the X-ray diffraction spectrum of the Cu-H2-150, Cu-H2-250, and Cu-H2-350 catalysts in Comparative Example 3.

[0036] Figure 12 It is the transmission electron microscope picture of the nano copper catalyst. Detailed implementation manners

[0037] The following will make a detailed description of the whole process through the attached drawings and embodiments, but the claims of the present invention are not limited by these embodiments. At the same time, the embodiments only give some conditions for achieving this purpose, but it does not mean that these conditions must be met to achieve this purpose. The protection scope of the present invention should include all the contents of the claims.

[0038] Example 1

[0039] Weigh 1.7048 g of copper chloride and dissolve it in 300 mL of ultrapure water. Add 50 mL of 1 mol / L -1 sodium borohydride solution dropwise into the copper chloride solution. Stir at room temperature for 20 min, filter, and dry to obtain the nano copper catalyst. Figure 1 (Left) and (right) are the scanning and transmission electron microscope images of the nano copper catalyst respectively. It can be seen from the figure that the catalyst is composed of particles with a particle size of 10 - 20 nm connected together; it has a porous structure with a pore size of 50 - 100 nm; and it has a core-shell structure, with metallic copper in the middle and a layer of cuprous oxide about 3 - 5 nm thick wrapped outside. Figure 2 It is the X-ray diffraction spectrum of the nano copper catalyst. It can be seen from the figure that the catalyst is composed of two phases, metallic copper and cuprous oxide.

[0040] Coat the catalyst on the carbon paper to prepare a gas diffusion electrode, and the catalyst loading is 1.5 mg / cm -2. In the MEA electrolyzer, this gas diffusion electrode serves as the working electrode, the Ti foam coated with iridium oxide is the counter electrode, and a layer of N-methylpiperidine p-terphenyl copolymer (QAPPT) anion exchange membrane is sandwiched between the working electrode and the counter electrode. These three form a membrane electrode with a sandwich structure. The cathode plate is a graphite plate with a gas flow field. The anode plate is a platinum-coated titanium plate with a liquid flow field. During actual reaction testing, carbon monoxide or carbon dioxide gas is introduced into the cathode, and a KOH solution is introduced into the anode. The test is carried out in a constant current mode. The cathode gas is condensed and then analyzed online by chromatography. At the same time, the anode liquid is collected for liquid nuclear magnetic analysis.

[0041] Figure 3 、 4 The reaction results of and 5 show that when this nanocopper catalyst is applied to the electrocatalytic reduction of carbon monoxide, it exhibits high electrolysis performance. In the MEA electrolyzer, the 2+ Faradaic efficiency reaches up to 95%, and the current density reaches up to 3 A cm -2 . The overall cell energy efficiency reaches up to 39%, and it can stably electrolyze for 30 hours at 1 A cm -2 . When this catalyst is applied to the electrocatalytic reduction of carbon dioxide, in the MEA electrolyzer, the 2+ Faradaic efficiency reaches up to 66%, and the partial current density reaches up to 331 mA cm -2 .

[0042] Example 2

[0043] Take 50 mg of the nanocopper catalyst obtained in Example 1 and place it in deoxygenated ultrapure water. Ultrasonic for 30 min, add 1.39 mL of palladium chloride solution (1 g of palladium chloride dissolved in 100 mL of 0.1 M hydrochloric acid), ultrasonic for 30 min, filter, wash, and dry to obtain a nanocopper-palladium catalyst.

[0044] Under the same reaction conditions as in Example 1, it is used for the electrocatalytic reduction reaction of carbon monoxide. Figure 6 The reaction results show that when this nanocopper-palladium catalyst is applied to the electrocatalytic reduction of carbon monoxide, it exhibits relatively high electrolysis performance. And in the MEA electrolyzer, the 2+ Faradaic efficiency reaches up to 93%, and the partial current density reaches up to 1.3 A cm -2 . Figure 6 The data comparison with that in Example 1 Figure 3 shows that the introduction of palladium improves the selectivity of acetic acid. The Faradaic efficiency of acetic acid reaches up to 33%, and the partial current density is up to 572 mA cm -2 .

[0045] Example 3

[0046] Take 50 mg of the nano copper catalyst obtained in Example 1 and place it in deoxygenated ultrapure water. Ultrasonicate for 30 min, add 2 mL of 25 mM silver nitrate solution, ultrasonicate for 30 min, filter, wash, and dry to obtain a nano copper-silver catalyst. The introduction of the second component silver in this catalyst is beneficial to improving the selectivity of acetic acid. The Faraday efficiency of acetic acid is up to 42%, and the partial current density is at most 1012 mA cm -2 。

[0047] Comparative Example 1

[0048] Take 50 mg of the nano copper catalyst obtained in Example 1 and place it in a quartz boat. Put it into a muffle furnace and heat-treat at 350 °C for 2 h to obtain the OD-Cu-350 catalyst. Figure 7 is the X-ray diffraction pattern of the OD-Cu-350 catalyst. It can be seen from the figure that this catalyst only has a copper oxide phase. Figure 8 is the transmission electron microscope spectrum of the OD-Cu-350 catalyst. It can be seen from the figure that after heat treatment, the particle size of this catalyst becomes larger, there is no core-shell structure, the crystallinity becomes better, and the grain boundaries decrease.

[0049] Figure 9 The reaction results of show that the OD-Cu-350 catalyst is applied to the electrocatalytic reduction of carbon monoxide. In the MEA electrolyzer, C 2+ The Faraday efficiency is 92%, and the current density is 1.8 A cm -2 , compared with the reaction results of Example 1, it can be seen that the nano copper catalyst is not conducive to improving the catalytic performance after calcination in air. It is speculated that the reason is that after the nano copper catalyst is calcined in air, it completely becomes an oxidized state, loses the core-shell structure, and the grain boundaries decrease, which is not conducive to improving the catalytic performance.

[0050] Comparative Example 2

[0051] Take 50 mg of the nano copper catalyst obtained in Example 1 and place it in a quartz boat. Put it into a quartz tube and heat-treat at 200, 300, 400, and 500 °C for 2 h respectively under the protection of high-purity helium to obtain the Cu-He-200, Cu-He-300, Cu-He-400, and Cu-He-500 catalysts. Figure 10 is the X-ray diffraction pattern of the Cu-He-200, Cu-He-300, Cu-He-400, and Cu-He-500 catalysts. It can be seen from the figure that under an inert atmosphere, heat treatment at different temperatures can change the crystal phase of the catalyst. The higher the temperature, the more cuprous oxide phase, and the higher the temperature, the larger the grain size and the fewer the grain boundaries, which will all lead to the deterioration of the catalyst performance. When the Cu-He-300 catalyst is subjected to constant current electrolysis in CORR, under the same current density condition, the voltage is 0.1 V higher than that of the catalyst in Example 1, resulting in a decrease in energy efficiency.

[0052] Comparative Example 3

[0053] 50 mg of the nano copper catalyst obtained in Example 1 was placed in a quartz boat and put into a quartz tube. Under the protection of high-purity hydrogen, it was heat-treated at 150, 250, and 350 °C for 3 h to obtain Cu-H2-150, Cu-H2-250, and Cu-H2-350 catalysts. Figure 11 are the X-ray diffraction patterns of the Cu-H2-150, Cu-H2-250, and Cu-H2-350 catalysts. It can be seen from the figure that after hydrogen reduction, there is only the metallic copper phase and no cuprous oxide phase, indicating that the oxide layer has been removed. Moreover, the higher the temperature, the sharper the peak shape, indicating that the grain size is larger. All of the above lead to a significant deterioration in the CORR performance of this catalyst compared to the nano copper catalyst in Example 1. Under the same conditions, during CORR electrolysis with the Cu-H2-150 catalyst, C 2+ The highest Faraday efficiency of the product is only 78%, and the highest partial current density is only 946 mA cm- 2 . Under the same conditions, during CORR electrolysis with the Cu-H2-250 catalyst, C 2+ The highest Faraday efficiency of the product is only 88%, and the highest partial current density is only 159 mA cm- 2 .

[0054] Example 4

[0055] 2.4160 g of copper nitrate was dissolved in 300 mL of ultrapure water. 50 mL of 1 mol L -1 sodium borohydride solution was dropped into the copper chloride solution. At room temperature, it was stirred for 20 min, filtered, and dried to obtain a nano copper catalyst. Figure 12 is the transmission electron micrograph of the nano copper catalyst. It can be seen from the figure that this catalyst is composed of particles with a particle size of 10-20 nm connected together; it has a porous structure with a pore size of 50-100 nm; and it has a core-shell structure, with metallic copper in the middle and a layer of cuprous oxide about 3-5 nm thick wrapped outside.

[0056] It can be seen from the above examples that the nano copper catalyst in gram scale can be prepared in one step by the liquid-phase reduction method in the present invention. The nano copper catalyst has a nano-porous structure, rich defect and grain boundary structures, and shows high electrolysis performance when applied to the electrocatalytic reduction of carbon monoxide. In the MEA electrolyzer, C 2+ The highest Faraday efficiency reaches 95%, the highest current density reaches 3 A cm -2 , the highest overall cell energy efficiency reaches 39%, and it can stably electrolyze for 30 hours at 1 A cm -2 . When this catalyst is applied to the electrocatalytic reduction of carbon dioxide, in the MEA electrolyzer, C 2+The Faraday efficiency reaches up to 66%, and the partial current density reaches up to 331 mA cm -2 .

[0057] It should be noted that according to the above embodiments of the present invention, those skilled in the art can fully implement the entire scope of the independent claims and dependent claims of the present invention, and the implementation process and method are the same as those of the above embodiments; and the parts not elaborated in detail in the present invention belong to the well-known technology in the art.

[0058] As mentioned above, only some specific embodiments of the present invention are described, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those familiar with the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A preparation method of a nano copper-based two-component catalyst, characterized in that, It includes the following steps: Step 1: Dissolve the copper salt in ultrapure water to obtain a copper salt solution, and the concentration of the copper salt solution is 0.01 - 0.2 mol / L -1 ; Step 2: Dropwise add a sodium borohydride solution into the copper salt solution, stir at room temperature for 5 - 60 min, filter, and dry to obtain a nano copper catalyst; the molar ratio of sodium borohydride to copper salt is 1 - 20, and the concentration of the sodium borohydride solution is 0.1 - 1 mol / L -1 ; Step 3: Ultrasonically disperse the nano copper catalyst in ultrapure water. Under nitrogen protection, add the second metal precursor, and ultrasonically treat for 10 - 30 min, then filter and dry to obtain a nano copper-based binary catalyst; the second metal precursor is a soluble silver salt or a soluble palladium salt; the concentration of the second metal precursor is 0.01 - 0.2 mol / L -1 ; the molar ratio of the second metal precursor to the copper salt is 0.01 - 0.

2.

2. The preparation method according to claim 1, characterized in that: The copper salt is copper nitrate, copper chloride or copper acetate.

3. The preparation method according to claim 1, characterized in that: The concentration of the copper salt solution is 0.01 - 0.1 mol / L -1 .

4. The preparation method according to claim 1, characterized in that: The molar ratio of sodium borohydride to the copper salt is 5 - 10.

5. The preparation method according to claim 1, characterized in that: The soluble silver salt is silver nitrate, and the soluble palladium salt is palladium chloride.

6. The preparation method according to claim 1, characterized in that: The concentration of the second metal precursor is 0.01 - 0.1 mol / L -1 ; the molar ratio of the second metal precursor to the copper salt is 0.1 - 0.

2.

7. A catalyst prepared by the method according to claim 1, characterized in that, The catalyst has a nanoporous structure.

8. The catalyst according to claim 7, characterized in that: The catalyst is composed of particles with a particle size of 10 - 20 nm connected together; it has a porous structure with a pore size of 50 - 100 nm; and it has a core-shell structure, with metallic copper inside and a layer of cuprous oxide with a thickness of 3 - 5 nm wrapped outside.

9. Use of the catalyst according to claim 7 in the electrocatalytic reduction of carbon dioxide and / or carbon monoxide.

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