CN116926616A - Preparation method and application of flaky Cu-ZIF-8 material - Google Patents

Preparation method and application of flaky Cu-ZIF-8 material Download PDF

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CN116926616A
CN116926616A CN202311195045.4A CN202311195045A CN116926616A CN 116926616 A CN116926616 A CN 116926616A CN 202311195045 A CN202311195045 A CN 202311195045A CN 116926616 A CN116926616 A CN 116926616A
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zif
solution
flaky
particles
electrolyte solution
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CN116926616B (en
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王琪
李秀萍
冯齐云
刘霞
董雅鑫
李熠豪
魏玉玉
凌奇
魏强
李阳
黄汇林
刘建路
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Shandong Haihua Group Co Ltd
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    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
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    • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
    • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
    • C25B11/095—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds at least one of the compounds being organic
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    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
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    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
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Abstract

The invention discloses a preparation method and application of a flaky Cu-ZIF-8 material, which realize the efficient recycling of carbon dioxide and belong to the technical field of preparation of electrocatalytic carbon dioxide reduction catalysts. The invention takes ZIF-8 as a precursor, prepares the flaky Cu-ZIF-8 material by a two-step method, basically maintains the pore canal and structure of the ZIF-8, improves the surface roughness, the porosity and the conductivity, and has the pore diameter ranging from 0.4 nm to 50nm. The flaky Cu-ZIF-8 material has a unique flaky and mesoporous structure, improves the adsorption capacity to carbon dioxide, shows excellent activity in the field of carbon dioxide electroreduction, and is not limited to C 1 When 0.5MKHCO at-1.4 to-1.0V 3 When the electrolyte solution is used, the integral Faraday efficiency is up to 98.2 percent, which is higher than the level of a general non-noble metal catalyst,the catalyst level of noble metal is reached, and the catalyst has wide application prospect.

Description

Preparation method and application of flaky Cu-ZIF-8 material
Technical Field
The invention relates to a preparation method and application of a flaky Cu-ZIF-8 material, and belongs to the technical field of preparation of electrocatalytic carbon dioxide reduction catalysts.
Background
With the development of technology and the dramatic increase of population, the demand of people for energy is increasing. In addition, the use of energy sources is still based on burning fossil fuels, producing large amounts of carbon dioxide (CO 2 ) The gas is discharged into the air, which aggravates the energy crisis and the greenhouse effect. How to remove excessive CO in the atmosphere 2 Conversion to C 1 (CO, HCOOH, etc.) and C 2 （C 2 H 4 Etc.), etc., are becoming a hot spot for research.
Over the past several decades, a variety of technologies have been developed for electrocatalytic carbon dioxide reduction (CO 2 RR), such as metals, metal oxides, metal alloys, and carbon materials. Among the metal-based catalysts, copper-based catalysts are the only one that can form a two-carbon product. However, copper-based catalysts suffer from a number of problems including poor stability, high overpotential and low selectivity, limiting commercial applications. Noble metals, e.g.Ag and Au can effectively convert CO at a lower potential 2 Conversion to CO, but the high cost limits their widespread use. Therefore, it is urgent to find a non-noble metal catalyst having higher activity and selectivity.
Among the numerous metal organic framework materials, the Zeolitic Imidazolate Frameworks (ZIFs) are considered ideal precursors for the production of carbonized catalysts because of their controlled porosity, large surface area and uniform heteroatom decoration. In addition, ZIF-8 material has higher CO 2 Adsorption performance, which is CO 2 An important step of electrochemical reduction.
The Chinese patent document with publication number CN107447228A discloses a method for electrocatalytically reducing carbon dioxide, which comprises calcining ZIF-8 material at high temperature under argon atmosphere to obtain modified ZIF-8 material, and applying the modified ZIF-8 material in different electrolyte solutions for electrocatalytically reducing CO 2 . Because the ZIF-8 structure of some modified ZIF-8 materials is destroyed by high temperature, and the products of the modified ZIF-8 materials are only CO and H 2 And faraday efficiencies of no more than 65%, single product and low faraday efficiencies limit industrial applications.
Chinese patent document publication No. CN109999875A discloses a catalyst for electrocatalytic CO 2 The reduced Cu and N doped carbon-based catalyst and the preparation method thereof are characterized in that Cu-ZIF-8 is synthesized by a one-step method, and the Cu-ZIF-8 is calcined at high temperature to remove Zn, so that the Cu and N doped carbon-based catalyst is obtained. The method destroys the ZIF-8 structure, and does not utilize the self performance of ZIF-8 (CO adsorption) 2 ) Product singleness (CO and H 2 ) Further limiting the industrial applications.
Disclosure of Invention
Aiming at the problems of single product, low Faraday efficiency and poor conductivity of ZIF-8 serving as a catalyst in electrocatalytic carbon dioxide reduction, the invention provides a preparation method of a flaky Cu-ZIF-8 material, which is characterized in that the CuX-ZIF-8 is obtained by synthesizing and modifying the ZIF-8 by a solution containing copper salt, and then the CuX-ZIF-8 is calcined at a high temperature in a nitrogen-containing atmosphere to obtain the flaky Cu-ZIF-8 material, wherein the flaky Cu-ZIF-8 material shows excellent catalytic performance in electrocatalytic carbon dioxide reduction.
In order to solve the problems, the invention provides a preparation method of a flaky Cu-ZIF-8 material, which comprises the following steps:
(1) Respectively dissolving zinc salt, polyvinylpyrrolidone and 2-methylimidazole in a solvent to prepare a zinc salt solution, a polyvinylpyrrolidone solution and a 2-methylimidazole solution, uniformly mixing the zinc salt solution and the polyvinylpyrrolidone solution, adding the 2-methylimidazole solution, stirring for 10-50s, and reacting at 20-40 ℃ for 20-30h to obtain a ZIF-8-containing solution;
(2) Centrifuging the solution containing ZIF-8 to obtain a first solid, washing the first solid by methanol or ethanol, and drying at 60-120 ℃ for 1-12h to obtain ZIF-8 particles;
(3) Adding ZIF-8 particles into an alcohol organic solvent containing a strong acid copper salt, uniformly mixing, reacting at 50-85 ℃ for 1-8 hours, centrifuging after the reaction is finished to obtain a second solid, washing the second solid by methanol or ethanol, and drying at 60-120 ℃ for 1-12 hours to obtain flaky CuX-ZIF-8;
(4) Heating the flaky CuX-ZIF-8 to carbonization temperature in a nitrogen-containing atmosphere to obtain a flaky Cu-ZIF-8 material;
in the step (1), the zinc salt is one of zinc nitrate, zinc acetate and zinc chloride; the solvent is one or more than two of water, methanol and ethanol in any proportion;
In the step (3), X is a strong acid ion, cl - 、SO 4 2- 、NO 3 - One of them.
In the step (1), the ratio of the use amount of zinc salt, 2-methylimidazole and polyvinylpyrrolidone to the total volume of the zinc salt solution, the polyvinylpyrrolidone solution and the 2-methylimidazole solution is 0.75mmol:3-6mmol:0.075-1.92mmol:20-40ml.
In the step (3), the ratio relationship of the strong acid copper salt, the ZIF-8 and the alcohol organic solvent is 1-10mmol:1mmol:25-100ml.
In the step (3), the strong acid copper salt is one of copper nitrate, copper chloride and copper sulfate; the alcohol organic solvent is methanol or ethanol.
In the step (4), the atmosphere containing nitrogen is N 2 、NH 3 、N 2 Is mixed with NH 3 Is a mixed gas of the above components.
In the step (4), the gas flow rate under the atmosphere containing nitrogen is 50-200mL/min, the heating rate is 3-10 ℃/min, the carbonization temperature is 200-500 ℃, and the carbonization time is 1-6h.
The flaky Cu-ZIF-8 material prepared by the preparation method is used as an electrochemical reduction carbon dioxide catalyst, and the specific application steps are as follows:
(1) Activating the flaky Cu-ZIF-8 material for 12-24 hours under vacuum condition and at the temperature of 100-150 ℃, dispersing the activated flaky Cu-ZIF-8 material in ethanol or methanol solution of Nafion reagent containing carbon powder, and uniformly dispersing by ultrasonic to obtain a mixed solution A;
(2) Electrochemical measurement is carried out on an electrochemical workstation (CHI 760E), in a typical three-electrode H-type system electrolytic cell, an anion exchange membrane is used for separation, a mixed solution A is dripped on carbon cloth to be used as a working electrode, an Ag/AgCl electrode is used as a reference electrode, and a Pt electrode is used as a comparison electrode;
(3) CO is processed by 2 Introducing the mixture into an H-type system electrolytic cell containing 0.1-0.5M electrolyte solution, and foaming for at least 30min; in CO 2 In RR process, CO is continuously injected into electrolyte solution at a speed of 20-30ml/min 2 The method comprises the steps of carrying out a first treatment on the surface of the Gas Chromatograph (GC) is adopted to analyze gas products on line, nuclear magnetism is adopted to detect liquid products, and Faraday Efficiency (FE) is adopted to evaluate catalytic effect.
The electrolyte solution is KHCO 3 、NaHCO 3 、NaClO 4 One of NaCl; the total dosage of the flaky Cu-ZIF-8 material and the carbon powder is 10-30mg/ml calculated by the volume of methanol or ethanol solution of the Nafion reagent, wherein the dosage of the carbon powder is 50-80% of the total weight of the flaky Cu-ZIF-8 material and the carbon powder, and the dosage of the Nafion reagent is 10-30 mu L/ml calculated by the volume of the methanol or ethanol solution of the Nafion reagent; the dripping amount of the mixed solution A is 1-3mg/cm based on the mass area of the flaky Cu-ZIF-8 material distributed on the carbon cloth in the mixture A 2 。
After the technical scheme is adopted, compared with the prior art, the invention has the following beneficial effects:
(1) The electrocatalytic carbon dioxide reduction catalyst prepared by adopting a two-step method is prepared by firstly synthesizing a copper ion solution, then modifying and adjusting the morphology of ZIF-8 to obtain flaky CuX-ZIF-8, and then calcining the flaky CuX-ZIF-8 at a high temperature in a nitrogen-containing atmosphere to finally obtain the flaky Cu-ZIF-8 material, wherein the method is simple, easy to operate and strong in repeatability.
(2) Compared with ZIF-8, the flaky CuX-ZIF-8 and flaky Cu-ZIF-8 material (Cu-ZIF-8-n) basically maintains the pore canal and structure of the ZIF-8 although the original appearance of the ZIF-8 is changed, the roughness and the porosity of the surface of the ZIF-8 are improved, the flaky and high-roughness are beneficial to the catalytic reaction rate, and the high-porosity is increased by CO 2 Is helpful for improving the adsorption capacity of CO 2 Catalytic efficiency of RR.
(3) Calcining the flaky CuX-ZIF-8 in the atmosphere of high Wen Handan to obtain the flaky Cu-ZIF-8 material (Cu-ZIF-8-N) with the C/N doped layer, wherein the flaky Cu-ZIF-8 material with the C/N doped layer can provide good electron supply capacity and limiting effect, and can greatly improve the conductivity and C 2 Selectivity of the product.
(4) The flaky Cu-ZIF-8 material provided by the invention is applied as an electrocatalytic carbon dioxide reduction catalyst and is used for CO 2 The RR field shows excellent activity, the Faraday efficiency is more than 70 percent, and the products are not only CO and H 2 And also C 2 H 4 And HCOOH, changes ZIF-8 as CO 2 RR catalyst products are CO and H only 2 And poor catalytic performance, and has wide application prospect.
Drawings
FIG. 1 is a Scanning Electron Microscope (SEM) image of ZIF-8 particles obtained in step (2) of example 1;
FIG. 2 shows the sheet-like Cu (NO) obtained in the step (3) of example 1 3 ) 2 -SEM image of ZIF-8;
FIG. 3 is an SEM image of a sheet-like Cu-ZIF-8 material (Cu-ZIF-8-1) obtained in step (4) of example 1;
FIG. 4 is an X-ray diffraction pattern (XRD) of the ZIF-8 particles obtained in step (2) and the flaky CuX-ZIF-8 obtained in step (3) of examples 1 to 6 and the flaky Cu-ZIF-8 material (Cu-ZIF-8-n) obtained in step (4);
FIG. 5 shows the NLDFT model full pore size distribution of the ZIF-8 particles obtained in step (2) and the flaky CuX-ZIF-8 material obtained in step (3) of examples 1 to 6 and Cu-ZIF-8-N obtained in step (4), the NLDFT model full pore size distribution being measured by nitrogen full adsorption test (N at 77K 2 -BET) test results; and (3) injection: FIG. 5 (a) shows the distribution of the pore diameters of the whole pores of the ZIF-8 particles obtained in the step (2) and the NLDFT model of the flaky CuX-ZIF-8 obtained in the step (3), and FIG. 5 (b) shows the distribution of the pore diameters of the whole pores of the ZIF-8 particles obtained in the step (2) and the NLDFT model of the flaky Cu-ZIF-8 material obtained in the step (4);
FIG. 6 is a graph showing the total absorption of carbon dioxide (CO) of ZIF-8 particles obtained in step (2) and flaky CuX-ZIF-8 obtained in step (3) of examples 1 to 6 and flaky Cu-ZIF-8 material obtained in step (4) 2 -BET); and (3) injection: FIG. 6 (a) shows ZIF-8 particles obtained in step (2) and CO of flaky CuX-ZIF-8 obtained in step (3) 2 BET plot, FIG. 6 (b) is a CO of the ZIF-8 particles obtained in step (2) and the platelet-shaped Cu-ZIF-8 material obtained in step (4) 2 -BET map;
FIG. 7 is a schematic illustration of the use of Cu-ZIF-8-1 obtained in step (4) of example 1 in an electrocatalytic carbon dioxide reduction test (CO 2 RR) catalytic performance results plot;
FIG. 8 is an SEM image of ZIF-8 particles of step (2) of example 2;
FIG. 9 shows the sheet-like Cu (NO) obtained in the step (3) of example 2 3 ) 2 -SEM image of ZIF-8;
FIG. 10 is an SEM image of a sheet-like Cu-ZIF-8 material (Cu-ZIF-8-2) obtained in step (4) of example 2;
FIG. 11 is a schematic diagram showing the use of Cu-ZIF-8-2 obtained in step (4) of example 2 for CO in different electrolyte solutions 2 A catalytic performance result graph of RR test;
FIG. 12 is an SEM image of ZIF-8 particles of step (2) of example 3;
FIG. 13 shows the sheet-like Cu (NO) obtained in step (3) of example 3 3 ) 2 -SEM image of ZIF-8;
FIG. 14 is an SEM image of a sheet-like Cu-ZIF-8 material (Cu-ZIF-8-3) obtained in step (4) of example 3;
FIG. 15 is a schematic diagram showing the use of Cu-ZIF-8-3 obtained in step (4) of example 3 for CO in different electrolyte solutions 2 A catalytic performance result graph of RR test;
FIG. 16 is an SEM image of ZIF-8 particles of step (2) of example 4;
FIG. 17 shows a flaky CuCl obtained in the step (3) of example 4 2 -SEM image of ZIF-8;
FIG. 18 is an SEM image of a sheet-like Cu-ZIF-8 material (Cu-ZIF-8-4) obtained in step (4) of example 4;
FIG. 19 is a graph showing the use of Cu-ZIF-8-4 obtained in step (4) of example 4 for CO in different electrolyte solutions 2 A catalytic performance result graph of RR test;
FIG. 20 is an SEM image of ZIF-8 particles of step (2) of example 5;
FIG. 21 is a sheet-like CuSO obtained in step (3) of example 5 4 -SEM image of ZIF-8;
FIG. 22 is an SEM image of a sheet-like Cu-ZIF-8 material (Cu-ZIF-8-5) obtained in step (4) of example 5;
FIG. 23 is a graph showing the use of Cu-ZIF-8-5 obtained in step (4) of example 5 for CO in different electrolyte solutions 2 A catalytic performance result graph of RR test;
FIG. 24 is an SEM image of ZIF-8 particles of step (2) of example 6;
FIG. 25 shows the sheet-like Cu (NO) obtained in step (3) of example 6 3 ) 2 -SEM image of ZIF-8;
FIG. 26 is an SEM image of a sheet-like Cu-ZIF-8 material (Cu-ZIF-8-6) obtained in step (4) of example 6;
FIG. 27 is a schematic illustration of the use of Cu-ZIF-8-6 obtained in step (4) of example 6 for CO in different electrolyte solutions 2 A catalytic performance result graph of RR test;
FIG. 28 is a schematic representation of ZIF-8 particles of comparative example 1 for use in CO in different electrolyte solutions 2 A catalytic performance result graph of RR test;
FIG. 29 is Cu (NO) of comparative example 2 3 ) 2 Use of ZIF-8 for CO in different electrolyte solutions 2 A catalytic performance result graph of RR test;
FIG. 30 is a graph of calcined sheet-like Cu-ZIF-8 material without nitrogen atmosphere of comparative example 3 for CO in different electrolyte solutions 2 A catalytic performance result graph of RR test;
FIG. 31 is an SEM image of one-step synthesized Cu/ZIF-8 of comparative example 4;
FIG. 32 is a schematic representation of comparative example 4 where nitrogen-containing atmosphere calcined Cu/ZIF-8 was used for CO in different electrolyte solutions 2 A catalytic performance result graph of RR test;
FIG. 33 is an SEM image of the post-synthesis modification of ZIF-8 particles of comparative example 6 without polyvinylpyrrolidone addition with a copper nitrate solution;
FIG. 34 is a XRD comparison of the modified ZIF-8 particles of comparative example 6 without polyvinylpyrrolidone addition after synthesis with a copper nitrate solution and the ZIF-8 particles of example 1.
Detailed Description
The present invention will be further described with reference to examples and drawings, but the scope of the present invention is not limited thereto.
Example 1
(1) 0.75mmol of zinc nitrate hexahydrate, 3mmol of 2-methylimidazole and 0.3mmol of polyvinylpyrrolidone are respectively dissolved in 10ml of methanol to prepare a zinc nitrate solution, a 2-methylimidazole solution and a polyvinylpyrrolidone solution; and (3) uniformly stirring and mixing the zinc nitrate solution and the polyvinylpyrrolidone solution, then adding the 2-methylimidazole solution, stirring for 40s, and reacting at 28 ℃ for 24 hours to obtain a solution containing ZIF-8.
(2) And (3) centrifuging the solution containing ZIF-8 to obtain a first solid, washing the first solid with methanol for three times, and drying the washed solution at 80 ℃ for 12 hours to obtain ZIF-8 particles.
(3) Preparing copper nitrate solution from 0.3mmol copper nitrate trihydrate with 7ml methanol, adding 0.1mmol ZIF-8 particles, mixing well by ultrasonic treatment for 3min, reacting at 65deg.C for 3h to obtain sheet Cu (NO) 3 ) 2 -ZIF-8 material mother liquor, centrifuging to obtain a second mother liquorWashing the second solid with methanol three times, and drying at 80deg.C for 5 hr to obtain sheet Cu (NO) 3 ) 2 -ZIF-8。
(4) Cu (NO) in flake form 3 ) 2 -ZIF-8 at NH 3 And N 2 Under the atmosphere of the mixed gas (NH) 3 And N 2 The mass ratio of (2) is 0.2:0.8 The mixed gas is controlled to be 100ml/min through a flowmeter, and is heated to 300 ℃ at 3 ℃/min to be calcined for 5 hours, so that the flaky Cu-ZIF-8 material, namely Cu-ZIF-8-1, is obtained.
The ZIF-8 particles, flaky Cu (NO) and the preparation method of the composition of the invention in example 1 3 ) 2 Scanning Electron Microscope (SEM) morphology, X-ray diffraction (XRD) structure, nitrogen total adsorption (N) of ZIF-8 and flaky Cu-ZIF-8 material (Cu-ZIF-8-1) 2 Pore size distribution of BET), total adsorption of carbon dioxide (CO 2 -BET) characterization test. FIG. 1 is an SEM image of ZIF-8 particles; FIG. 2 is a sheet Cu (NO) 3 ) 2 -SEM image of ZIF-8; FIG. 3 is an SEM image of Cu-ZIF-8-1; FIG. 4 is an XRD pattern of the ZIF-8 particles and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6; FIG. 5 is a NLDFT model full pore size distribution plot of ZIF-8 particles and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6, wherein the NLDFT model full pore size distribution plot is defined by N 2 -BET results; FIG. 6 is a CO of the ZIF-8 granules and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6 2 -BET plot.
As can be seen from comparison of FIG. 1, FIG. 2 and FIG. 3, the ZIF-8 particles have a size of 2 μm, and the ZIF-8 particles are synthesized by copper nitrate solution to modify ion exchange reaction, the morphology is changed from dodecahedron to flaky, and flaky Cu (NO 3 ) 2 ZIF-8 has a coarser surface and flaky Cu (NO 3 ) 2 The surface of the sheet-shaped Cu-ZIF-8 material (Cu-ZIF-8-1) obtained by calcining the-ZIF-8 is higher than that of the sheet-shaped Cu (NO) 3 ) 2 The surface of the ZIF-8 is rougher, but the morphology is still kept in a sheet shape; as can be seen from FIG. 4, ZIF-8 particles were synthesized with modified Cu (NO 3 ) 2 -ZIF-8 and calcined Cu-ZIF-8-1 substantially maintain the structure of ZIF-8 particles, indicating that this is a gentle preparation method; as can be seen from FIG. 5, ZIF-8 particles were post-synthesized modifiedIs of sheet Cu (NO) 3 ) 2 The mesoporous increase of the surface of the ZIF-8, the pore diameter range is changed from 0.4-2nm to 0.4-15nm, and the flaky Cu (NO) 3 ) 2 The mesoporous Cu-ZIF-8-1 after the ZIF-8 is calcined is further increased, the porosity is greatly increased, and the pore diameter range is changed to 0.4-50nm; as can be seen from FIG. 6, the ZIF-8 particles have an increased CO content after post-synthesis modification and calcination 2 Is helpful to promote the catalytic effect of the catalyst.
The Cu-ZIF-8-1 obtained in the step (4) is used for electrocatalytic carbon dioxide reduction (CO 2 RR), comprising the following application steps:
1) Activating Cu-ZIF-8-1 in a vacuum oven at 120 ℃ for 12 hours, adding 10mgCu-ZIF-8-1 and 15mg carbon powder into 1ml ethanol solution containing 20 mu L of Nafion reagent, and performing ultrasonic treatment for 5 minutes to form a mixed solution A;
2) 50. Mu.L of the above mixed solution A was sucked up by a 100. Mu.L pipette each time, and the front and back sides of a 2cm X1 cm piece of carbon paper were coated 2 times, respectively, with the coated area controlled to be 1cm 2 The total loading of the flaky Cu-ZIF-8 material (Cu-ZIF-8-1) is 2.0mg, and the flaky Cu-ZIF-8 material is dried at room temperature and used as a working electrode;
3) The electrolytic cell was rinsed with ultrapure water before the test, 25mL of electrolyte solution was added to each of the two chambers of the H-type electrolytic cell, and 0.5M electrolyte solution was used as the H-type electrolytic cell, CO 2 The H-type system was charged with electrolysis Chi Qipao min and tested on a CHI 760E electrochemical workstation, during which time CO was continuously injected into the electrolyte solution at a rate of 30ml/min 2 The gas product was analyzed on-line by Gas Chromatograph (GC), the liquid product was detected by nuclear magnetism, and the catalytic effect was evaluated by Faraday Efficiency (FE).
Cu-ZIF-8-1 was applied to 0.5M KHCO, respectively 3 、NaHCO 3 、NaClO 4 CO in NaCl electrolyte solution 2 RR reaction, CO 2 The RR catalytic effect is shown in fig. 7.
As can be seen from FIG. 7, cu-ZIF-8-1 is in KHCO 3 The electrolyte solution has the best catalytic effect, the Faraday efficiency reaches 98.2 percent at-1.4 to-1.0V, and C 2 H 4 The Faraday rate is kept above 18.0%, and the CO Faraday efficiency is kept at 35.0% or more, H 2 The Faraday efficiency is 10-12%, and the catalyst level of noble metal is reached; cu-ZIF-8-1 in NaHCO 3 Catalytic effect in electrolyte solution is second, and KHCO 3 The catalytic effect (Faraday efficiency) of the electrolyte solution is close; cu-ZIF-8-1 in NaClO 4 The catalysis effect with NaCl electrolyte solution is far lower than KHCO 3 And NaHCO 3 But NaClO 4 The total Faraday efficiency with NaCl electrolyte solution is above 81.0%, which is higher than the level of non-noble metal catalyst (the non-noble metal catalyst is generally used in CO 2 RR Faraday efficiency of 70.0% or more is considered to be good, naClO 4 H with NaCl electrolyte solution 2 Faradaic efficiency is far higher than KHCO 3 And NaHCO 3 Electrolyte solution of NaClO) 4 With NaCl electrolyte solution to assist hydrogen evolution reaction, thus NaClO 4 With NaCl electrolyte solution to cause C 2 Poor selectivity, C 2 H 4 Faraday efficiency is not high (less than 10%). From this, it was found that the sheet-like Cu-ZIF-8 material was suitable for CO of the above electrolyte solution 2 RR application.
Example 2
(1) 2ml of deionized water and 18ml of absolute ethyl alcohol are prepared into 20ml of 90% ethyl alcohol, and then 0.75mmol of absolute zinc chloride is dissolved in 10ml of 90% ethyl alcohol to prepare zinc chloride solution; 0.075mol of polyvinylpyrrolidone is dissolved in 5ml of 90% ethanol to prepare polyvinylpyrrolidone solution; 3mmol of 2-methylimidazole is dissolved in 5ml of methanol to prepare a 2-methylimidazole solution; firstly, uniformly stirring and mixing a zinc chloride solution and a polyvinylpyrrolidone solution, then adding a 2-methylimidazole solution, stirring for 50s, and reacting for 30h at 20 ℃ to obtain a ZIF-8-containing solution.
(2) And (3) centrifuging the solution containing ZIF-8 to obtain a first solid, washing the first solid with ethanol for three times, and drying at 60 ℃ for 1h after washing to obtain ZIF-8 particles.
(3) Preparing 0.1mmol of copper nitrate trihydrate into a copper nitrate solution by using 2.5ml of methanol, adding 0.1mmol of ZIF-8 particles into the copper nitrate solution, uniformly mixing the copper nitrate solution by ultrasonic for 3min, and reacting the copper nitrate solution at 50 ℃ for 5h to obtain platy Cu (NO) 3 ) 2 Centrifuging ZIF-8 mother liquor to obtain a second solid, washing the second solid with ethanol for three times, and drying at 60deg.C for 1 hr to obtain sheet Cu (NO) 3 ) 2 -ZIF-8。
(4) Cu (NO) in flake form 3 ) 2 -ZIF-8 at NH 3 Under the atmosphere, NH 3 And (3) controlling the flow meter to be 50ml/min, heating to 200 ℃ at 10 ℃/min, and calcining for 6 hours to obtain the flaky Cu-ZIF-8 material, namely Cu-ZIF-8-2.
The ZIF-8 particles, flaky Cu (NO) and the preparation method of the composition of the invention in example 2 3 ) 2 SEM morphology, XRD structure and N of the ZIF-8 and flaky Cu-ZIF-8 material (Cu-ZIF-8-2) 2 Pore size distribution of BET, CO 2 -BET characterization test. FIG. 8 is an SEM image of ZIF-8 particles of example 2; FIG. 9 shows the sheet Cu (NO) of example 2 3 ) 2 -SEM image of ZIF-8; FIG. 10 is an SEM image of Cu-ZIF-8-2; FIG. 4 is an XRD pattern of the ZIF-8 particles and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6; FIG. 5 is a NLDFT model full pore size distribution plot of ZIF-8 particles and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6, wherein the NLDFT model full pore size distribution plot is defined by N 2 -BET results; FIG. 6 is a CO of the ZIF-8 granules and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6 2 -BET plot.
As can be seen from a comparison of FIGS. 1 and 8, the ZIF-8 particles of example 1 had a size of about 2 μm and the ZIF-8 particles of example 2 had a size of about 1 μm, and the addition of polyvinylpyrrolidone helped to adjust the size of the ZIF-8 particles; as can be seen from comparison of FIG. 8, FIG. 9 and FIG. 10, ZIF-8 particles are synthesized by copper nitrate solution and then modified, the morphology is changed from dodecahedron to sheet-shaped Cu (NO 3 ) 2 ZIF-8 has a coarser surface and flaky Cu (NO 3 ) 2 The surface of the Cu-ZIF-8-2 obtained by calcining the-ZIF-8 is more flaky Cu (NO) 3 ) 2 The surface of the ZIF-8 is rougher, but the morphology is still kept in a sheet shape; as can be seen from FIG. 4, the ZIF-8 particles were modified to form Cu (NO 3 ) 2 -ZIF-8 and calcined Cu-ZIF-8-2 substantially maintain the structure of ZIF-8 particles, indicating a gentle preparation method; as can be seen from FIG. 5, ZIFlaky Cu (NO) obtained by F-8 particle synthesis modification 3 ) 2 The mesoporous on the surface of the ZIF-8 is increased, the pore diameter range is changed from 0.4-2nm to 0.4-10nm, the calcined Cu-ZIF-8-2 mesoporous is further enhanced, the porosity is greatly increased, and the pore diameter range is changed to 0.40-40nm; as can be seen from FIG. 6, ZIF-8 particles have been post-synthesized and post-calcined to increase the CO pair 2 Helps to promote the catalytic application of the catalyst.
The Cu-ZIF-8-2 obtained in the step (4) is used for CO 2 Application of RR comprising the following application steps:
1) Activating Cu-ZIF-8-2 in a vacuum oven at 100deg.C for 24 hr, adding 5mgCu-ZIF-8-2 and 5mg carbon powder into 1ml methanol solution containing 10 μl Nafion reagent, and performing ultrasonic treatment for 5min to obtain mixed solution A;
2) 50. Mu.L of the above mixed solution A was sucked up by a 100. Mu.L pipette each time, and the front and back sides of a 2cm X1 cm piece of carbon paper were coated 2 times, respectively, with the coated area controlled to be 1cm 2 The total loading was 1.0mg, dried at room temperature, and used as a working electrode;
3) The electrolytic cell was rinsed with ultrapure water before the test, 25mL of electrolyte solution was added to each of the two chambers of the H-type electrolytic cell, and 0.1M electrolyte solution was used as the H-type electrolytic cell, CO 2 The H-type system was charged with electrolysis Chi Qipao min and tested on a CHI 760E electrochemical workstation, during which time CO was continuously injected into the electrolyte solution at a rate of 20ml/min 2 On-line analysis of gaseous products by GC, detection of liquid products by nuclear magnetism, and evaluation of CO by FE 2 RR catalytic effect.
Cu-ZIF-8-2 is applied to 0.1M KHCO respectively 3 、NaHCO 3 、NaClO 4 CO in NaCl electrolyte solution 2 RR reaction, CO 2 The RR catalytic effect is shown in fig. 11.
As can be seen from FIG. 11, cu-ZIF-8-2 is in KHCO 3 The catalytic effect in the electrolyte solution is optimal, the Faraday efficiency reaches 77.5% at-1.4 to-1.0V, C 2 H 4 The Faraday rate is kept above 10.0%, the CO Faraday efficiency is kept above 28.0%, and H 2 The Faraday efficiency is 10-12% and is higher than the level of a general non-noble metal catalyst; cu-ZIF-8-2 in NaHCO 3 Catalytic Effect in electrolyte solution second, naClO 4 Again, the NaCl electrolyte solution was worst; naClO 4 H with NaCl electrolyte solution 2 Faradaic efficiency is far higher than KHCO 3 And NaHCO 3 Thus, naClO 4 With NaCl electrolyte solution to cause C 1 And C 2 Poor selectivity, C 2 H 4 The Faraday efficiency is stabilized below 6% and C 1 (HCOOH) faraday efficiency stabilizes around 10%; the total Faraday efficiency of the Cu-ZIF-8-2 in all the electrolyte solutions was stabilized at 70% or more, and thus it was found that the sheet-like Cu-ZIF-8 material was suitable for CO of all the electrolyte solutions 2 RR application.
From the catalytic results of FIGS. 7 and 11, it can be seen that the concentration of the electrolyte solution affects CO 2 The catalytic effect of RR, the type of electrolyte solution and the addition amount of the flaky Cu-ZIF-8 material also influence CO 2 Catalytic effect of RR; in the same electrolyte solution, the structure (pore canal and roughness) of the flaky Cu-ZIF-8 material and the concentration of the electrolyte solution are key to influencing the catalytic performance; in the case of different electrolyte solutions, different ions can affect C 2 And C 1 Is selected from the group consisting of (1).
Example 3
(1) 0.75mmol of zinc nitrate hexahydrate is dissolved in 10ml of water to prepare zinc nitrate solution; 6mmol of 2-methylimidazole and 1.92mmol of polyvinylpyrrolidone are respectively dissolved in 5ml of water to prepare a 2-methylimidazole solution and a polyvinylpyrrolidone solution; firstly, uniformly stirring and mixing a zinc nitrate solution and a polyvinylpyrrolidone solution, then adding a 2-methylimidazole solution, stirring for 10s, and reacting at 40 ℃ for 20h to obtain a ZIF-8-containing solution.
(2) And (3) centrifuging the solution containing ZIF-8 to obtain a first solid, washing the first solid with methanol for three times, and drying the washed solution at 120 ℃ for 12 hours to obtain ZIF-8 particles.
(3) 1mmol of copper nitrate trihydrate is prepared into a copper nitrate solution by using 10ml of ethanol, then 0.1mmol of ZIF-8 particles are added into the copper nitrate solution, the mixture is evenly mixed by ultrasonic treatment for 3min, and the mixture is reacted for 1h at 85 ℃ to obtain platy Cu (NO) 3 ) 2 Centrifuging ZIF-8 mother liquor to obtain a second solid, washing the second solid with methanol for three times, and drying at 120deg.C for 12 hr to obtain sheet Cu (NO) 3 ) 2 -ZIF-8。
(4) Cu (NO) in flake form 3 ) 2 ZIF-8 at N 2 Under the atmosphere, N 2 And (3) controlling the flow meter to be 200ml/min, and heating to 500 ℃ at 5 ℃/min to calcine for 1h to obtain the flaky Cu-ZIF-8 material, namely Cu-ZIF-8-3.
The ZIF-8 particles, flaky Cu (NO) and the preparation method of the composition of the invention in example 3 3 ) 2 SEM morphology, XRD structure and N of the ZIF-8 and flaky Cu-ZIF-8 material (Cu-ZIF-8-3) 2 Pore size distribution of BET, CO 2 -BET characterization test. FIG. 12 is an SEM image of ZIF-8 particles of example 3; FIG. 13 shows the sheet Cu (NO) of example 3 3 ) 2 -SEM image of ZIF-8; FIG. 14 is an SEM image of Cu-ZIF-8-3; FIG. 4 is an XRD pattern of the ZIF-8 particles and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6; FIG. 5 is a NLDFT model full pore size distribution plot of ZIF-8 particles and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6, wherein the NLDFT model full pore size distribution plot is defined by N 2 -BET results; FIG. 6 is a CO of the ZIF-8 granules and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6 2 -BET plot.
As can be seen from the comparison of FIGS. 1, 8 and 12, the ZIF-8 particles of example 1 had a size of about 2. Mu.m, the ZIF-8 particles of example 2 had a size of about 1. Mu.m, the ZIF-8 particles of example 3 had a size of about 5. Mu.m, the concentration of polyvinylpyrrolidone and the concentration of 2-methylimidazole ligand affected the size of the ZIF-8 particles, and the polyvinylpyrrolidone exhibited a major size-controlling effect; as can be seen from comparison of FIG. 12, FIG. 13 and FIG. 14, ZIF-8 particles are synthesized by copper nitrate solution and then modified, the morphology is changed from dodecahedron to sheet-shaped, sheet-shaped Cu (NO 3 ) 2 ZIF-8 has a coarser surface and flaky Cu (NO 3 ) 2 The surface of the Cu-ZIF-8-3 obtained by calcining the-ZIF-8 is more flaky Cu (NO) 3 ) 2 The surface of the ZIF-8 is rougher, but the morphology is still kept in a sheet shape; as can be seen from FIG. 4, the ZIF-8 particles were modified after synthesis to give tabletsCu (NO) 3 ) 2 -ZIF-8 and calcined Cu-ZIF-8-3 substantially maintain the structure of ZIF-8 particles, indicating a gentle preparation method; as shown in FIG. 5, the modification after ZIF-8 particle synthesis leads to the increase of surface mesopores, the pore diameter range is changed from 0.4-2nm to 0.4-10nm, the (Cu-ZIF-8-3) mesopores are further reinforced after calcination, the porosity is greatly increased, and the pore diameter range is changed to 0.40-40nm; as can be seen from FIG. 6, the ZIF-8 particles have an increased CO content after post-synthesis modification and calcination 2 Is helpful for the next catalytic application.
The Cu-ZIF-8-3 obtained in the step (4) is used for CO 2 Application of RR comprising the following application steps:
1) Activating Cu-ZIF-8-3 in a vacuum oven at 110 ℃ for 18 hours, adding 6mgCu-ZIF-8-3 and 24mg carbon powder into 1ml ethanol solution containing 30 mu L of Nafion reagent, and performing ultrasonic treatment for 5 minutes to form a mixed solution A;
2) The mixed solution A was sucked up by a 250. Mu.L pipette at a time, and coated 1 time on the front and back surfaces of a 2cm X1 cm carbon paper, respectively, with the coated area controlled to be 1cm 2 The total loading was 3.0mg, dried at room temperature, and used as a working electrode;
3) The electrolytic cell was rinsed with ultrapure water before testing, 25mL of electrolyte solution was added to each of the two chambers of the H-type electrolytic cell, and 0.3M electrolyte solution was used as the H-type electrolytic cell, CO 2 The H-type system was charged with electrolysis Chi Qipao min and tested on a CHI 760E electrochemical workstation, during which time CO was continuously injected into the electrolyte solution at a rate of 25ml/min 2 Gas products were analyzed on-line by GC and liquid products were detected by nuclear magnetism.
Cu-ZIF-8-3 is applied to 0.3M KHCO respectively 3 、NaHCO 3 、NaClO 4 CO in NaCl electrolyte solution 2 RR reaction, CO 2 The RR catalytic effect is shown in fig. 15.
As can be seen from FIG. 15, cu-ZIF-8-3 is in KHCO 3 The electrolyte solution has the best catalytic effect, and the Faraday efficiency reaches 90.0% at-1.4 to-1.0V, C 2 H 4 The Faraday rate is kept above 13.0%, the CO Faraday efficiency is kept above 38.0%, and H 2 Faraday systemThe efficiency is 10-12% which is higher than the level of the general non-noble metal catalyst; cu-ZIF-8-3 in NaHCO 3 Catalytic Effect in electrolyte solution second, naClO 4 Again, the NaCl electrolyte solution was worst; naClO 4 H with NaCl electrolyte solution 2 Faradaic efficiency is far higher than KHCO 3 And NaHCO 3 Thus, naClO 4 With NaCl electrolyte solution to cause C 1 And C 2 Poor selectivity, C 2 H 4 The Faraday efficiency is stabilized below 8% and C 1 (HCOOH) faraday efficiency stabilizes below 13%; the total Faraday efficiency of Cu-ZIF-8-3 in all the electrolyte solutions was stabilized at 70% or more, and thus it was found that the sheet-like Cu-ZIF-8 material was suitable for CO of all the electrolyte solutions 2 RR application.
From the catalytic results of FIGS. 7 and 11 and FIG. 15, it can be seen that the concentration of the electrolyte solution affects CO 2 The catalytic effect of RR, the type of electrolyte solution and the addition amount of the flaky Cu-ZIF-8 material also influence CO 2 Catalytic effect of RR; in the same electrolyte solution, the structure (pore canal and roughness) of the flaky Cu-ZIF-8 material and the concentration of the electrolyte solution are key to influencing the catalytic performance; in the case of different electrolyte solutions, different ions can affect C 2 And C 1 Is selected from the group consisting of (1).
Example 4
0.75mmol of zinc nitrate hexahydrate is dissolved in 5ml of ethanol to prepare zinc nitrate solution; dissolving 4mmol of 2-methylimidazole and 0.3mmol of polyvinylpyrrolidone in 10ml of ethanol to prepare a 2-methylimidazole solution and a polyvinylpyrrolidone solution; and (3) uniformly stirring and mixing the zinc nitrate solution and the polyvinylpyrrolidone solution, then adding the 2-methylimidazole solution, stirring for 30s, and reacting at 30 ℃ for 24 hours to obtain a solution containing ZIF-8.
(2) And (3) centrifuging the solution containing ZIF-8 to obtain a first solid, washing the first solid with methanol for three times, and drying the washed solution at 100 ℃ for 3 hours to obtain ZIF-8 particles.
(3) A solution of 0.2mmol of copper chloride dihydrate in 9ml of methanol was prepared, and then 0.1mmol of ZIF-8 particles, ultrasonic mixing for 3min, reacting for 4h at 70 ℃ to obtain flaky CuCl 2 Centrifuging the mother liquor to obtain a second solid, washing the second solid with methanol for three times, and drying at 110deg.C for 3 hr to obtain sheet CuCl 2 -ZIF-8。
(4) Flake CuCl 2 ZIF-8 at N 2 And Ar is a group 2 Under the atmosphere of the mixed gas (N) 2 And Ar is a group 2 The mass ratio of (2) is 4: 1) N, N 2 And Ar is a group 2 The mixed gas is controlled to be 80ml/min through a flowmeter, and is heated to 250 ℃ at 4 ℃/min to be calcined for 2 hours, so that the flaky Cu-ZIF-8 material, namely Cu-ZIF-8-4, is obtained.
The ZIF-8 particles and flaky CuCl of example 4 were respectively treated 2 SEM morphology, XRD structure and N of the ZIF-8 and flaky Cu-ZIF-8 material (Cu-ZIF-8-4) 2 Pore size distribution of BET, CO 2 -BET characterization test. FIG. 16 is an SEM image of ZIF-8 particles of example 4; FIG. 17 is a sheet-like CuCl of example 4 2 -SEM image of ZIF-8; FIG. 18 is an SEM image of Cu-ZIF-8-4; FIG. 4 is an XRD pattern of the ZIF-8 particles and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6; FIG. 5 is a NLDFT model full pore size distribution plot of ZIF-8 particles and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6, wherein the NLDFT model full pore size distribution plot is defined by N 2 -BET results; FIG. 6 is a CO of the ZIF-8 granules and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6 2 -BET plot.
As can be seen from a comparison of FIGS. 1 and 16, the ZIF-8 particles of example 1 had a size of about 2. Mu.m, and the ZIF-8 particles of example 4 had a size of about 1.8. Mu.m, so that the change in the concentration of only a single organic ligand without introducing other organic ligand had a limited effect on the size of the ZIF-8 particles when the concentrations of polyvinylpyrrolidone were the same; likewise, changes in solvent have less effect on the size adjustment of ZIF-8 particles; as can be seen from FIGS. 16, 17 and 18, ZIF-8 particles are synthesized by copper chloride solution and then modified, the morphology of the particles is changed from dodecahedron to flake-shaped and flake-shaped CuCl 2 ZIF-8 has a coarser surface than ZIF-8 particles, and is flaky CuCl 2 The surface of the Cu-ZIF-8-4 obtained by calcining the-ZIF-8 is more flaky than that of CuCl 2 -ZIF8, the surface of the product is rougher, but the appearance of the product is still kept to be flaky; as can be seen from FIG. 4, the ZIF-8 particles were modified to give flaky CuCl 2 -ZIF-8 and calcined Cu-ZIF-8-4 substantially maintain the structure of ZIF-8 particles, indicating a gentle preparation method; as shown in FIG. 5, the modification after ZIF-8 particle synthesis leads to the increase of surface mesopores, the pore diameter range is changed from 0.4-2nm to 0.4-10nm, the (Cu-ZIF-8-4) mesopores are further reinforced after calcination, the porosity is greatly increased, and the pore diameter range is changed to 0.40-40nm; as can be seen from FIG. 6, the ZIF-8 particles have an increased CO content after post-synthesis modification and calcination 2 Is helpful for the next catalytic application.
The Cu-ZIF-8-4 obtained in the step (4) is used for CO 2 Application of RR comprising the following application steps:
1) Activating Cu-ZIF-8-4 in a vacuum oven at 150 ℃ for 13 hours, adding 7.5mgCu-ZIF-8-4 and 7.5mg carbon powder into 1ml ethanol solution containing 20 mu L of Nafion reagent, and performing ultrasonic treatment for 5 minutes to form a mixed solution A;
2) 50. Mu.L of the above mixed solution A was sucked up by a 100. Mu.L pipette each time, and the front and back sides of a 2cm X1 cm piece of carbon paper were coated 2 times, respectively, with the coated area controlled to be 1cm 2 The total loading was 1.5mg, dried at room temperature, and used as a working electrode;
3) The electrolytic cell was rinsed with ultrapure water before the test, 25mL of electrolyte solution was added to each of the two chambers of the H-type electrolytic cell, and 0.5M electrolyte solution was used as the H-type electrolytic cell, CO 2 The H-type system was charged with electrolysis Chi Qipao min and tested on a CHI 760E electrochemical workstation, during which time CO was continuously injected into the electrolyte solution at a rate of 30ml/min 2 Gas products were analyzed on-line by GC and liquid products were detected by nuclear magnetism.
Cu-ZIF-8-4 was applied to 0.5M KHCO, respectively 3 、NaHCO 3 、NaClO 4 CO in NaCl electrolyte solution 2 RR reaction, CO 2 The RR catalytic effect is shown in fig. 19.
As can be seen from FIG. 19, cu-ZIF-8-4 is in KHCO 3 The catalytic effect in the electrolyte solution is optimal, the Faraday efficiency reaches 85.8% at-1.4 to-1.0V, C 2 H 4 The Faraday rate is kept above 13.0%, the CO Faraday efficiency is kept above 38.8%, and H 2 The Faraday efficiency is 10-12% and is higher than the level of a general non-noble metal catalyst; cu-ZIF-8-4 in NaHCO 3 Catalytic Effect in electrolyte solution second, naClO 4 Again, the NaCl electrolyte solution was worst; naClO 4 H with NaCl electrolyte solution 2 Faradaic efficiency is far higher than KHCO 3 And NaHCO 3 Electrolyte solution NaClO of (C) 4 With NaCl electrolyte solution to assist hydrogen evolution reaction, thus NaClO 4 With NaCl electrolyte solution to cause C 1 And C 2 Poor selectivity, C 2 H 4 The Faraday efficiency is stabilized below 7% and C 1 (HCOOH) faraday efficiency stabilizes below 12%; the total Faraday efficiency of the Cu-ZIF-8-4 in all the electrolyte solutions was stabilized at 70% or more, and thus it was found that the sheet-like Cu-ZIF-8 material was suitable for CO of all the electrolyte solutions 2 RR application.
As can be seen from the catalytic results of fig. 7, 11, 15 and 19, the concentration of the electrolyte solution affects CO 2 The catalytic effect of RR, the type of electrolyte solution and the addition amount of the flaky Cu-ZIF-8 material also influence CO 2 Catalytic effect of RR; in the same electrolyte solution, the structure (pore canal and roughness) of the flaky Cu-ZIF-8 material and the concentration of the electrolyte solution are key to influencing the catalytic performance; in the case of different electrolyte solutions, different ions can affect C 2 And C 1 Is selected from the group consisting of (1).
Example 5
(1) Preparing an ethanol solution from 3ml of pure water and 27ml of absolute ethanol; dissolving 0.75mmol of anhydrous zinc chloride, 3.5mmol of 2-methylimidazole and 0.5mmol of polyvinylpyrrolidone in 8ml of ethanol solution respectively to prepare a zinc chloride solution, a polyvinylpyrrolidone solution and a 2-methylimidazole solution; firstly, uniformly stirring and mixing a zinc chloride solution and a polyvinylpyrrolidone solution, then adding a 2-methylimidazole solution, stirring for 40s, and reacting at 30 ℃ for 28h to obtain a ZIF-8-containing solution.
(2) Centrifuging the solution containing ZIF-8 to obtain a first solid, washing the first solid with ethanol for three times, and drying at 110deg.C for 10h to obtain ZIF-8 granule.
(3) Preparing 0.8mmol of anhydrous copper sulfate into a copper sulfate solution by using 3ml of ethanol, adding 0.1mmol of ZIF-8 particles into the solution, uniformly mixing the solution by ultrasonic treatment for 3min, and reacting the solution at 80 ℃ for 5h to obtain flaky CuSO 4 Centrifuging the mother liquor to obtain a second solid, washing the second solid with methanol for three times, and drying at 110deg.C for 10 hr to obtain sheet CuSO 4 -ZIF-8。
(4) Sheet CuSO 4 -ZIF-8 at NH 3 And N 2 Under the atmosphere of the mixed gas (NH) 3 And N 2 The mass ratio of (2) is 0.2:0.8 -NH) 3 And N 2 The mixed gas is controlled to be 150ml/min through a flowmeter, and is heated to 450 ℃ at 10 ℃/min to be calcined for 2 hours, so that the flaky Cu-ZIF-8 material, namely Cu-ZIF-8-5, is obtained.
The ZIF-8 particles and flaky CuSO of example 5 were respectively treated with 4 SEM morphology, XRD structure and N of the ZIF-8 and flaky Cu-ZIF-8 material (Cu-ZIF-8-5) 2 Pore size distribution of BET, CO 2 -BET characterization test. FIG. 20 is an SEM image of ZIF-8 particles of example 5; FIG. 21 is a sheet-like CuSO of example 5 4 -SEM image of ZIF-8; FIG. 22 is an SEM image of Cu-ZIF-8-5; FIG. 4 is an XRD pattern of the ZIF-8 particles and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6; FIG. 5 is a NLDFT model full pore size distribution plot of ZIF-8 particles and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6, wherein the NLDFT model full pore size distribution plot is defined by N 2 -BET results; FIG. 6 is a CO of the ZIF-8 granules and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6 2 -BET plot.
As can be seen from the comparison of FIGS. 1, 8, 12, 16 and 20, the ZIF-8 particles of example 1 had a size of about 2. Mu.m, the ZIF-8 particles of example 2 had a size of 1. Mu.m, the ZIF-8 particles of example 3 had a size of 3. Mu.m, the ZIF-8 particles of example 4 had a size of 1.8. Mu.m, and the ZIF-8 particles of example 5 had a size of 2 to 3. Mu.m, and the ZIF-8 particles could be adjusted by controlling the concentrations of polyvinylpyrrolidone and 2-methylimidazole; as can be seen from comparison of FIG. 20, FIG. 21 and FIG. 22, ZIF-8 particles were modified by copper sulfate solution synthesis The morphology of the CuSO is changed from dodecahedron to flake 4 ZIF-8 has a coarser surface than ZIF-8 particles, and is in the form of a platelet CuSO 4 The surface of the Cu-ZIF-8-5 obtained by calcining the ZIF-8 is coarser, but the morphology is still kept to be flaky; as can be seen from FIG. 4, the ZIF-8 particles were modified to give flaky CuSO 4 -ZIF-8 and calcined Cu-ZIF-8-5 substantially maintain the structure of ZIF-8 particles, indicating a gentle preparation method; as shown in FIG. 5, the modification after ZIF-8 particle synthesis leads to the increase of surface mesopores, the pore diameter range is changed from 0.4-2nm to 0.4-12nm, the (Cu-ZIF-8-5) mesopores are further reinforced after calcination, the porosity is greatly increased, and the pore diameter range is changed to 0.40-40nm; as can be seen from FIG. 6, the ZIF-8 particles have an increased CO content after post-synthesis modification and calcination 2 Is helpful for the next catalytic application.
The Cu-ZIF-8-5 obtained in the step (4) is used for CO 2 Application of RR comprising the following application steps:
1) Activating Cu-ZIF-8-5 in a vacuum oven at 120 ℃ for 20 hours, adding 6mgCu-ZIF-8-5 and 24mg carbon powder into 1ml ethanol solution containing 15 mu L of Nafion reagent, and performing ultrasonic treatment for 5 minutes to form a mixed solution A;
2) 100. Mu.L of the above mixed solution A was sucked up by a 100. Mu.L pipette each time, and the front and back sides of a 2cm X1 cm piece of carbon paper were coated 2 times, respectively, with the coated area controlled to be 1cm 2 The total loading was 2.4mg, dried at room temperature, and used as a working electrode;
3) The electrolytic cell was rinsed with ultrapure water before the test, 25mL of electrolyte solution was added to each of the two chambers of the H-type electrolytic cell, and 0.5M electrolyte solution was used as the H-type electrolytic cell, CO 2 The H-type system was charged with electrolysis Chi Qipao min and tested on a CHI 760E electrochemical workstation, during which time CO was continuously injected into the electrolyte solution at a rate of 30ml/min 2 Gas products were analyzed on-line by GC and liquid products were detected by nuclear magnetism.
Cu-ZIF-8-5 was applied to 0.5M KHCO, respectively 3 、NaHCO 3 、NaClO 4 CO in NaCl electrolyte solution 2 RR reaction, CO 2 The RR catalytic effect is shown in fig. 23.
From the graph23, cu-ZIF-8-5 was found in KHCO 3 The catalytic effect in the electrolyte solution is optimal, the Faraday efficiency reaches 92.3% at-1.4 to-1.0V, C 2 H 4 The Faraday rate is kept above 16.5%, the CO Faraday efficiency is kept above 37.0%, and H 2 The Faraday efficiency is 12-13.5%, and the catalyst level of noble metal is reached; cu-ZIF-8-5 in NaHCO 3 Catalytic effect in electrolyte solution is second, and KHCO 3 The catalytic effect (Faraday efficiency) of the electrolyte solution is close; cu-ZIF-8-5 in NaClO 4 The catalysis effect with NaCl electrolyte solution is far lower than KHCO 3 And NaHCO 3 But NaClO 4 The total Faraday efficiency with NaCl electrolyte solution is above 77.7%, which is higher than the level of non-noble metal catalyst (the non-noble metal catalyst is generally used in CO 2 RR Faraday efficiency of 70.0% or more is considered to be good, naClO 4 H with NaCl electrolyte solution 2 Faradaic efficiency is far higher than KHCO 3 And NaHCO 3 Electrolyte solution of NaClO) 4 With NaCl electrolyte solution to assist hydrogen evolution reaction, naClO 4 With NaCl electrolyte solution to cause C 1 And C 2 The selectivity is poor. However, the sheet-like Cu-ZIF-8 material is suitable for CO of the above electrolyte solution 2 RR application.
As can be seen from the catalytic results of fig. 7, 11, 15, 19 and 23, the concentration of the electrolyte solution affects CO 2 The catalytic effect of RR, the type of electrolyte solution and the addition amount of the flaky Cu-ZIF-8 material also influence CO 2 Catalytic effect of RR; in the same electrolyte solution, the structure (pore canal and roughness) of the flaky Cu-ZIF-8 material and the concentration of the electrolyte solution are key to influencing the catalytic performance; in the case of different electrolyte solutions, different ions can affect C 2 And C 1 Is selected from the group consisting of (1).
Example 6
(1) Taking 4ml of pure water and 36ml of methanol to prepare a methanol solution; 0.75mmol of zinc acetate, 5.5mmol of 2-methylimidazole and 1.5mmol of polyvinylpyrrolidone are respectively dissolved in 10ml of methanol solution to prepare a zinc acetate solution, a polyvinylpyrrolidone solution and a 2-methylimidazole solution; firstly, uniformly stirring and mixing a zinc acetate solution and a polyvinylpyrrolidone solution, then adding a 2-methylimidazole solution, stirring for 20s, and reacting at 25 ℃ for 22h to obtain a ZIF-8-containing solution.
(2) And (3) centrifuging the solution containing ZIF-8 to obtain a first solid, washing the first solid with methanol for three times, and drying at 80 ℃ for 5 hours after washing to obtain ZIF-8 particles.
(3) Preparing 0.5mmol of copper nitrate trihydrate into a copper nitrate solution by using 5ml of ethanol, adding 0.1mmol of ZIF-8 particles into the copper nitrate solution, uniformly mixing the copper nitrate solution by ultrasonic treatment for 3min, and reacting the copper nitrate solution at 65 ℃ for 8h to obtain platy Cu (NO) 3 ) 2 Centrifuging ZIF-8 mother liquor to obtain a second solid, washing the second solid with methanol for three times, and drying at 100deg.C for 2 hr to obtain sheet Cu (NO) 3 ) 2 -ZIF-8。
(4) Cu (NO) in flake form 3 ) 2 -ZIF-8 at NH 3 And N 2 Under the atmosphere of the mixed gas (NH) 3 And N 2 The mass ratio of (2) is 0.2:0.8 -NH) 3 And N 2 The mixed gas is controlled to be 100ml/min through a flowmeter, and is heated to 210 ℃ at 3 ℃/min to be calcined for 5 hours, so that the flaky Cu-ZIF-8 material, namely Cu-ZIF-8-6, is obtained.
The ZIF-8 particles, flaky Cu (NO) and the preparation method of the composition of the invention in example 6 3 ) 2 SEM morphology, XRD structure and N of the ZIF-8 and flaky Cu-ZIF-8 material (Cu-ZIF-8-6) 2 Pore size distribution of BET, CO 2 -BET characterization test. FIG. 24 is an SEM image of ZIF-8 particles of example 6; FIG. 25 shows the sheet Cu (NO) of example 6 3 ) 2 -SEM image of ZIF-8; FIG. 26 is an SEM image of Cu-ZIF-8-6; FIG. 4 is an XRD pattern of the ZIF-8 particles and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6; FIG. 5 is a NLDFT model full pore size distribution plot of ZIF-8 particles and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6, wherein the NLDFT model full pore size distribution plot is defined by N 2 -BET results; FIG. 6 is a CO of the ZIF-8 granules and platelet CuX-ZIF-8 and platelet Cu-ZIF-8 materials of examples 1-6 2 -BET plot.
As can be seen from a comparison of FIGS. 24 and 25 and FIG. 26, the size of ZIF-8 particles was about 3-4 μm, ZIF-8 particlesThe particles are synthesized by copper nitrate solution and then modified, the morphology is changed from dodecahedron to flaky, flaky Cu (NO) 3 ) 2 ZIF-8 has a coarser surface and flaky Cu (NO 3 ) 2 The surface of the Cu-ZIF-8-6 obtained by calcining the-ZIF-8 is more flaky Cu (NO) 3 ) 2 The surface of the ZIF-8 is rougher, but the morphology is still kept in a sheet shape; as can be seen from FIG. 4, the ZIF-8 particles were modified to form Cu (NO 3 ) 2 -ZIF-8 and calcined Cu-ZIF-8-6 substantially maintain the structure of ZIF-8 particles, indicating a gentle preparation method; as can be seen from FIG. 5, ZIF-8 particles were synthesized and modified to form Cu (NO) 3 ) 2 The mesoporous on the surface of the ZIF-8 is increased, the pore diameter range is changed from 0.4-2nm to 0.4-13nm, the Cu-ZIF-8-1 mesoporous obtained after calcination is further enhanced, the porosity is greatly increased, and the pore diameter range is changed to 0.4-40nm; as can be seen from FIG. 6, the ZIF-8 particles have an increased CO content after post-synthesis modification and calcination 2 Helps to promote the catalytic application of the catalyst.
The Cu-ZIF-8-6 obtained in the step (4) is used for CO 2 Application of RR comprising the following application steps:
1) Activating Cu-ZIF-8-6 in a vacuum oven at 120 ℃ for 12 hours, adding 10mgCu-ZIF-8-6 and 15mg carbon powder into 1ml ethanol solution containing 20 mu L of Nafion reagent, and performing ultrasonic treatment for 5 minutes to form a mixed solution A;
2) The mixture A was sucked up 75. Mu.L by a 100. Mu.L pipette, and the front and back sides of a 2cm X1 cm piece of carbon paper were coated 2 times, respectively, with a 1cm coating area 2 The total loading was 3.0mg, dried at room temperature, and used as a working electrode;
3) The electrolytic cell was rinsed with ultrapure water before the test, 25mL of electrolyte solution was added to each of the two chambers of the H-type electrolytic cell, and 0.5M electrolyte solution was used as the H-type electrolytic cell, CO 2 The H-type system was charged with electrolysis Chi Qipao min and tested on a CHI 760E electrochemical workstation, during which time CO was continuously injected into the electrolyte solution at a rate of 30ml/min 2 Gas products are analyzed on line by adopting GC, liquid products are detected by nuclear magnetism, and the catalytic effect is evaluated by adopting FE.
Cu-ZIF-8-6 was applied to 0.5M KHCO, respectively 3 、NaHCO 3 、NaClO 4 CO in NaCl electrolyte solution 2 RR reaction, CO 2 The RR catalytic effect is shown in fig. 27.
As can be seen from FIG. 27, cu-ZIF-8-6 is in KHCO 3 The electrolyte solution has the best catalytic effect, the Faraday efficiency reaches 94.7% at-1.4 to-1.0V, and C 2 H 4 The Faraday rate is kept above 15.0%, the CO Faraday efficiency is kept above 38.5%, and H 2 The Faraday efficiency is 12-13%, and the catalyst level of noble metal is reached; cu-ZIF-8-6 in NaHCO 3 Catalytic effect in electrolyte solution is second, and KHCO 3 The catalytic effect (Faraday efficiency) of the electrolyte solution is close; cu-ZIF-8-6 in NaClO 4 The catalysis effect with NaCl electrolyte solution is far lower than KHCO 3 And NaHCO 3 But NaClO 4 The total Faraday efficiency with NaCl electrolyte solution is above 76.0%, which is higher than the level of non-noble metal catalyst (the non-noble metal catalyst is generally used in CO 2 RR Faraday efficiency of 70.0% or more is considered to be good, naClO 4 H with NaCl electrolyte solution 2 Faradaic efficiency is far higher than KHCO 3 And NaHCO 3 Electrolyte solution of NaClO) 4 With NaCl electrolyte solution to assist hydrogen evolution reaction, thus, the difference of electrolyte solution leads to C 2 Poor selectivity, C 2 H 4 Faraday efficiency is not high (less than 8%). From this, it was found that the sheet-like Cu-ZIF-8 material was suitable for CO of the above electrolyte solution 2 RR application.
As can be seen from the catalytic results of fig. 7, 11, 15, 19, 23 and 27, the concentration of the electrolyte solution affects CO 2 The catalytic effect of RR, the type of electrolyte solution and the addition amount of the flaky Cu-ZIF-8 material also influence CO 2 Catalytic effect of RR; in the same electrolyte solution, the structure (pore canal and roughness) of the flaky Cu-ZIF-8 material and the concentration of the electrolyte solution are key to influencing the catalytic performance; in the case of different electrolyte solutions, different ions can affect C 2 And C 1 Is selected from the group consisting of (1).
Comparative example 1
The procedure of comparative example 1 was the same as that of example 1, steps (1) and (2), without synthetic modification of the copper nitrate solution and the step of calcining ZIF-8 particles at high temperature. Application of ZIF-8 particles to CO 2 RR，CO 2 The RR catalytic procedure is as in example 1.CO 2 The RR catalytic effect is shown in fig. 28.
As can be seen from FIG. 28, ZIF-8 particles are in CO 2 RR has a voltage in the range of-1.9 to-1.5V, CO 2 RR products with H only 2 And CO, in KHCO 3 The highest faradaic efficiency in the electrolyte solution was only 56.3%, and the other electrolyte solutions performed poorly.
Comparative example 2
The procedure of comparative example 2 was the same as that of example 1, step (1), step (2) and step (3), and there was NO alignment of Cu (NO) 3 ) 2 -a step of high temperature calcination of ZIF-8. Cu (NO) in flake form 3 ) 2 Direct application of ZIF-8 to CO 2 RR，CO 2 The RR catalytic procedure is as in example 1.CO 2 The RR catalytic effect is shown in fig. 29.
As can be seen from fig. 29, the sheet Cu (NO 3 ) 2 -ZIF-8 at CO 2 RR has a voltage in the range of-1.7 to-1.3V, CO 2 RR products have C 1 And C 2 ，C 2 The Faraday efficiency of the product is not more than 10%, in KHCO 3 The maximum faradaic efficiency in the electrolyte solution is only 64.9%, and the other electrolyte solutions perform poorly.
Comparative example 3
The procedure of comparative example 3 was substantially the same as that of example 1, except that Cu (NO 3 ) 2 High temperature calcination of-ZIF-8 in Ar 2 The process is carried out under an atmosphere. CO 2 The RR catalytic effect is shown in fig. 30.
As can be seen from fig. 30, sheet Cu (NO 3 ) 2 -ZIF-8 is passed through Ar 2 Calcining at high temperature under atmosphere to obtain carbon-doped flaky Cu-ZIF-8 material which is prepared by CO 2 RR has a voltage in the range of-1.4 to-1.0V, CO 2 RR products have C 1 And C 2 ，C 2 The Faraday efficiency of the product is not more than 10%, in KHCO 3 ElectrolysisThe maximum Faraday efficiency in the mass solution is only 77.9%, in NaHCO 3 The maximum faradaic efficiency in the electrolyte solution is only 75.0%, and the other electrolyte solutions perform poorly.
Comparative example 4
The difference from example 1 is the order of addition of copper nitrate (no post-synthesis modification is required). Adopts a one-step method to synthesize Cu doped ZIF-8 (Cu/ZIF-8), and adopts a high-temperature calcination step and CO 2 The RR catalytic procedure is as in example 1. SEM test of Cu/ZIF-8, see FIG. 31, CO 2 RR catalytic effect is shown in figure 32.
The preparation method of the Cu/ZIF-8 comprises the following steps:
(1) 0.375mmol of zinc nitrate hexahydrate and 0.375mmol of copper nitrate were prepared into a zinc nitrate and copper nitrate mixed solution using 10ml of methanol; 3mmol of 2-methylimidazole and 0.3mmol of polyvinylpyrrolidone are respectively dissolved in 10ml of methanol to prepare a 2-methylimidazole solution and a polyvinylpyrrolidone solution; firstly, uniformly stirring and mixing a zinc nitrate and copper nitrate mixed solution and a polyvinylpyrrolidone solution, then adding a 2-methylimidazole solution, stirring for 40s, and reacting at 28 ℃ for 24h to obtain a Cu/ZIF-8 solution.
(2) And (3) centrifuging the Cu/ZIF-8 solution to obtain a solid, washing the solid with methanol for three times, and drying the washed solid at 80 ℃ for 12 hours to obtain Cu/ZIF-8 particles.
CO 2 The RR catalyst application procedure was as in example 1.
As can be seen from FIG. 31, the sheet structure could not be synthesized by the one-step synthesis method, which destroyed the original morphology (dodecahedron) of ZIF-8; as can be seen from fig. 32, CO 2 RR has a voltage in the range of-1.4 to-1.0V, CO 2 RR products have C 1 And C 2 ，C 2 The Faraday efficiency of the product is not more than 10%, in KHCO 3 The maximum Faraday efficiency in electrolyte solution is only 78.4%, and the electrolyte solution is prepared by the method of the method 3 The maximum faradaic efficiency in the electrolyte solution is only 76.6%, which is poor in other electrolyte solutions.
Comparative example 5
Is different from example 1 in that CO 2 No CO in RR catalytic step 2 Introducing CO 2 Is changed into Ar 2 。CO 2 No C in RR catalytic results 1 And C 2 And (3) generating.
Comparative example 6
The procedure of comparative example 6 was essentially the same as that of example 1, except that no polyvinylpyrrolidone was added to the ZIF-8 pellet synthesis of step (1), and the other steps were unchanged; and (3) carrying out SEM and XRD tests on a product obtained by carrying out post-synthesis modification on ZIF-8 particles by using a copper nitrate solution, wherein the test results are shown in figures 33 and 34 respectively.
As can be seen from fig. 33, the ZIF-8 particles without polyvinylpyrrolidone addition were post-synthesized with a copper nitrate solution, and the exchanged test results showed that the morphology was mostly needle-shaped and not plate-shaped; as can be seen from FIG. 34, the ZIF-8 particles were modified after synthesis with a copper nitrate solution, and the structure of ZIF-8 was found to be destroyed, so that the addition of polyvinylpyrrolidone ensured that the structure of ZIF-8 particles was not destroyed during the post-synthesis modification of ZIF-8 particles.
As can be seen from a comparison of comparative examples 1-6 with example 1, ZIF-8 particles are present in CO 2 Higher voltages (ZIF-8 particles with poor conductivity) are required for RR reduction and the products are only CO and H 2 Thus, ZIF-8 particles are treated in CO without any modification 2 Poor catalytic performance in RR; post-synthesis modification of ZIF-8 particles with copper nitrate solution to give Cu (NO) 3 ) 2 -ZIF-8，Cu(NO 3 ) 2 The ZIF-8 not only changes the original shape of the ZIF-8 (the dodecahedron is changed into a sheet shape), but also changes the pore size distribution and the roughness, so that the conductivity of the ZIF-8 and the diversity of catalytic products are improved, and therefore, the sheet structure, the roughness and the pore size distribution can influence the catalytic performance; cu (NO) 3 ) 2 -ZIF-8 is passed through Ar 2 High temperature calcination of CO from ZIF-8 particles (comparative example 1) 2 The RR catalytic performance is improved, but the catalytic performance is poorer than that of the flaky Cu-ZIF-8 material (Cu-ZIF-8-1) of the example 1, and calcination in a nitrogen-containing atmosphere is one of factors influencing the catalytic performance; sheet structure, calcination under nitrogen-containing atmosphere, electrolyte solution type, continuous CO introduction 2 Are all CO 2 Key factors in RR affecting catalytic performanceThe plain, lamellar structure has larger roughness and defects and wider mesoporous pore size distribution, which is beneficial to CO 2 RR is carried out, calcination in nitrogen-containing atmosphere can further improve mesoporous distribution and surface roughness, the type of electrolyte solution can also influence the selectivity of catalytic products, and no CO exists 2 Is introduced into CO 2 RR will not be able to proceed; the addition of polyvinylpyrrolidone has a critical effect on maintaining the structure and lamellar morphology of ZIF-8.
The above-described embodiments are provided to illustrate the gist of the present invention, but are not intended to limit the scope of the present invention. It will be understood by those skilled in the art that various modifications and equivalent substitutions may be made to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention.

Claims (8)

1. The preparation method of the flaky Cu-ZIF-8 material is characterized by comprising the following steps of:
(1) Respectively dissolving zinc salt, polyvinylpyrrolidone and 2-methylimidazole in a solvent to prepare a zinc salt solution, a polyvinylpyrrolidone solution and a 2-methylimidazole solution, uniformly mixing the zinc salt solution and the polyvinylpyrrolidone solution, adding the 2-methylimidazole solution, stirring for 10-50s, and reacting at 20-40 ℃ for 20-30h to obtain a ZIF-8-containing solution;
(2) Centrifuging the solution containing ZIF-8 to obtain a first solid, washing the first solid by methanol or ethanol, and drying at 60-120 ℃ for 1-12h to obtain ZIF-8 particles;
(3) Adding ZIF-8 particles into an alcohol organic solvent containing a strong acid copper salt, uniformly mixing, reacting at 50-85 ℃ for 1-8 hours, centrifuging after the reaction is finished to obtain a second solid, washing the second solid by methanol or ethanol, and drying at 60-120 ℃ for 1-12 hours to obtain flaky CuX-ZIF-8;
(4) Heating the flaky CuX-ZIF-8 to carbonization temperature in a nitrogen-containing atmosphere to obtain a flaky Cu-ZIF-8 material;
in the step (1), the zinc salt is one of zinc nitrate, zinc acetate and zinc chloride; the solvent is one or more than two of water, methanol and ethanol in any proportion;
in the step (3), X is a strong acid ion, cl - 、SO 4 2- 、NO 3 - One of them.
2. The method for preparing a flaky Cu-ZIF-8 material according to claim 1, wherein in the step (1), the ratio of the amount of zinc salt, 2-methylimidazole and polyvinylpyrrolidone to the total volume of the zinc salt solution, polyvinylpyrrolidone solution and 2-methylimidazole solution is 0.75mmol:3-6mmol:0.075-1.92mmol:20-40ml.
3. The method for preparing the flaky Cu-ZIF-8 material according to claim 1, wherein in the step (3), the ratio of the strong acid copper salt, the ZIF-8 and the alcohol organic solvent is 1-10mmol:1mmol:25-100ml.
4. The method for preparing a flaky Cu-ZIF-8 material according to claim 1, wherein in the step (3), the strong acid copper salt is one of copper nitrate, copper chloride and copper sulfate; the alcohol organic solvent is methanol or ethanol.
5. The method for producing a sheet-like Cu-ZIF-8 material according to claim 1, wherein in said step (4), the atmosphere containing nitrogen is N 2 、NH 3 、N 2 Is mixed with NH 3 Is a mixed gas of the above components.
6. The method for preparing a flaky Cu-ZIF-8 material according to claim 1, wherein in the step (4), the gas flow rate under the atmosphere containing nitrogen is 50-200mL/min, the heating rate is 3-10 ℃/min, the carbonization temperature is 200-500 ℃, and the carbonization time is 1-6 hours.
7. Use of the sheet-like Cu-ZIF-8 material prepared by the method according to any one of claims 1-6 as a catalyst for electrochemical reduction of carbon dioxide, comprising the following specific application steps:
(1) Activating the flaky Cu-ZIF-8 material for 12-24 hours under vacuum condition and at the temperature of 100-150 ℃, dispersing the activated flaky Cu-ZIF-8 material in ethanol or methanol solution of Nafion reagent containing carbon powder, and uniformly dispersing by ultrasonic to obtain a mixed solution A;
(2) Electrochemical measurement is carried out on an electrochemical workstation, in a typical three-electrode H-type system electrolytic cell, an anion exchange membrane is used for separation, a mixed solution A is taken and dripped on carbon cloth to be used as a working electrode, an Ag/AgCl electrode is used as a reference electrode, and a Pt electrode is used as a comparison electrode;
(3) CO is processed by 2 Introducing the mixture into an H-type system electrolytic cell containing 0.1-0.5M electrolyte solution, and foaming for at least 30min; in CO 2 In RR process, CO is continuously injected into electrolyte solution at a speed of 20-30ml/min 2 The method comprises the steps of carrying out a first treatment on the surface of the And (3) analyzing the gas product on line by adopting a gas chromatograph, detecting the liquid product by adopting nuclear magnetism, and evaluating the catalytic effect by adopting Faraday efficiency.
8. The use of a platelet-shaped Cu-ZIF-8 material as in claim 7, wherein: the electrolyte solution is KHCO 3 、NaHCO 3 、NaClO 4 One of NaCl; the total dosage of the flaky Cu-ZIF-8 material and the carbon powder is 10-30mg/ml calculated by the volume of methanol or ethanol solution of the Nafion reagent, wherein the dosage of the carbon powder is 50-80% of the total weight of the flaky Cu-ZIF-8 material and the carbon powder, and the dosage of the Nafion reagent is 10-30 mu L/ml calculated by the volume of the methanol or ethanol solution of the Nafion reagent; the dripping amount of the mixed solution A is 1-3mg/cm based on the mass area of the flaky Cu-ZIF-8 material distributed on the carbon cloth in the mixture A 2 。
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