Method for Directly Growing Metal Single-Atom Catalysts Supported on Metal-Catalyzed Nanocarbon

Abstract

The present invention discloses a method for directly growing metal single-atom catalysts supported on nano-carbon by metal catalysis, which comprises the following steps: mixing substance A and substance B evenly to obtain a powder; putting the powder into a sealed heating environment and heating it to 600-1000 °C in an atmosphere of a mixed gas of Ar / H2; then continuously introducing a mixed gas of Ar / H2 carrying a carbon source into the sealed heating environment, and carrying the carbon source to the powder through the mixed gas of Ar / H2 to carry out the direct growth of nano-carbon by metal catalysis; after the growth is completed, naturally cooling to room temperature; then stopping introducing the mixed gas of Ar / H2 to obtain a metal single-atom catalyst supported on nano-carbon. The present invention is based on a metal-catalyzed cracking strategy, uses metal salts dispersed in a high-melting-point substrate as a catalyst, and realizes the loading of metal single atoms while directly growing nano-carbon materials by metal-catalyzed cracking of the carbon source.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of metal single-atom catalysts supported on nano-carbon-based materials, and specifically relates to a method for directly growing metal single-atom catalysts supported on nano-carbon by metal catalysis. Background Art

[0002] The extensive use of fossil fuels has led to a continuous increase in the concentration of carbon dioxide (CO2) in the atmosphere, resulting in serious damage to the ecological environment and an increasingly serious energy shortage problem. Electrochemical CO2 reduction is to convert carbon dioxide into desired high-value energy fuels and chemical products under mild conditions by using electrical energy generated from clean energy sources (such as wind energy, water energy, solar energy, etc.), reduce the content of CO2 in the air, and realize the circular utilization of global carbon resources. It has broad application prospects and is of great significance for building a low-carbon society.

[0003] Among many CO2 electroreduction catalysts, metal single-atom catalysts have a clear active center structure, with fully exposed active sites, low-coordinated active centers, and novel electronic structures. The electronic structure of the central metal depends on the interaction between adjacent coordinated atoms, and can exhibit properties similar to those of homogeneous catalysts, promising to achieve efficient activation and directional conversion of CO2 molecules, and becoming a research hotspot in the fields of chemistry, materials, and energy catalysis in recent years. Therefore, single-atom catalysts show great potential in CO2 electrochemical reduction. However, single-atom catalysts have a high surface energy and are prone to migration and aggregation. Therefore, how to stabilize metal single atoms is the core problem in their preparation. At present, common methods for preparing single-atom catalysts mainly include wet chemical methods, electrochemical deposition, and chemical vapor deposition, etc., but they have disadvantages such as low yield and cumbersome preparation methods. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a method for directly growing metal single-atom catalysts supported on nano-carbon by metal catalysis.

[0005] The technical solution for the present invention to solve the above technical problem is to provide a method for directly growing metal single-atom catalysts supported on nano-carbon by metal catalysis, which is characterized in that the method comprises the following steps:

[0006] (1) Mix substance A and substance B evenly to obtain a uniformly mixed powder;

[0007] (2) Put the powder into a sealed heating environment and heat it to 600 - 1000 °C in an atmosphere of a mixed gas of Ar / H₂; then continuously introduce a mixed gas of Ar / H₂ carrying a carbon source into the sealed heating environment, and carry the carbon source to the powder through the mixed gas of Ar / H₂ to carry out the direct growth of metal-catalyzed nanocarbon; after the growth is completed, naturally cool to room temperature; then stop introducing the mixed gas of Ar / H₂ to obtain a metal single-atom catalyst supported on nanocarbon.

[0008] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0009] (1) Based on the metal-catalyzed cracking strategy, the present invention uses metal salts dispersed in a high-melting-point substrate as a catalyst, and realizes the direct growth of nanocarbon materials while being able to load metal single atoms by metal-catalyzed cracking of a carbon source.

[0010] (2) The present invention can efficiently and massively prepare a metal single-atom catalyst supported on nanocarbon. By regulating the growth conditions, the types of precursors, and the structure of the growth template, the composition of metal single-atom active centers and the geometric morphology of carbon nanotubes can be regulated to prepare different metal single atoms and carbon nanomaterials with different morphologies.

[0011] (3) The metal single-atom catalyst supported on nanocarbon prepared by the present invention can maintain a stable structure and performance, and realize stable and highly active electrocatalytic performance. Description of the Drawings

[0012] Figure 1 XRD pattern of the metal single-atom catalyst supported on nanocarbon loaded with Ni prepared in Example 1 of the present invention;

[0013] Figure 2 Raman pattern of the metal single-atom catalyst supported on nanocarbon loaded with Ni prepared in Example 1 of the present invention;

[0014] Figure 3 SEM image of the metal single-atom catalyst supported on nanocarbon loaded with Ni prepared in Example 1 of the present invention;

[0015] Figure 4 Low-magnification TEM image of the metal single-atom catalyst supported on nanocarbon loaded with Ni prepared in Example 1 of the present invention;

[0016] Figure 5 High-magnification TEM image of the metal single-atom catalyst supported on nanocarbon loaded with Ni prepared in Example 1 of the present invention;

[0017] Figure 6 Faraday efficiency diagram of the electrocatalytic reduction of CO₂ to CO by the metal single-atom catalyst supported on nanocarbon loaded with Ni prepared in Example 1 of the present invention;

[0018] Figure 7Stability diagram of current density and Faraday efficiency for the electrocatalytic reduction of CO2 to CO by the nano-carbon supported Ni single-atom catalyst prepared in Example 1 of the present invention. Detailed implementation mode

[0019] The following are specific examples of the present invention. The specific examples are only used to further illustrate the present invention in detail and do not limit the protection scope of the claims of this application.

[0020] The present invention provides a method for directly growing a metal-catalyzed nano-carbon supported metal single-atom catalyst (hereinafter referred to as the method), which is characterized in that the method includes the following steps:

[0021] (1) Mix substance A and substance B evenly by mixing methods such as dissolution or ball milling to obtain a uniformly mixed powder.

[0022] Preferably, in step (1), substance A is a transition metal salt, specifically a sulfate, nitrate or chloride of iron, ruthenium, cobalt, nickel, copper, manganese, platinum, rhodium, iridium, zinc or palladium, preferably nickel chloride, nickel nitrate, nickel sulfate, cobalt chloride or cobalt sulfate. Substance B is an inorganic salt with a high melting point (melting point > 600 °C).

[0023] Preferably, in step (1), the used substance A and substance B are commercially available products with uniform sizes.

[0024] Preferably, in step (1), the mass ratio of substance A to substance B is 1:1 to 10 (preferably 1:2).

[0025] (2) Place the powder in a closed heating environment (preferably at the thermal center of the closed heating environment), heat it to 600 - 1000 °C in an Ar / H2 mixed gas atmosphere; then change the gas path, continuously introduce an Ar / H2 mixed gas carrying a carbon source into the closed heating environment, carry the carbon source to the powder through the Ar / H2 mixed gas, and directly grow nano-carbon through metal catalysis; after the growth is completed, naturally cool to room temperature, and then stop introducing the Ar / H2 mixed gas; then wash to remove substance B, and after drying, obtain a black nano-carbon supported metal single-atom catalyst.

[0026] Preferably, in step (2), the closed heating environment uses a tubular furnace.

[0027] Preferably, in step (2), the metal-catalyzed direct growth time is 0.5 - 5 h.

[0028] Preferably, in step (2), the carbon source is an organic small molecule compound, specifically acetonitrile, pyridine, ethanol, ethylene or methane.

[0029] Preferably, in step (2), the flow rate of the Ar / H2 mixed gas is 200 - 1000 sccm, and the gas flow ratio is Ar:H2 = 5 - 20:1.

[0030] Example 1

[0031] (1) Dissolve 10 mg of nickel chloride and 20 mg of sodium chloride in 100 mL of water to form a salt solution, dry it to obtain a powder sample, and then ball-mill the powder sample for 2 h to make it uniformly mixed, obtaining a uniformly mixed powder.

[0032] (2) Put the powder obtained in step (1) into a closed heating environment, heat it to 720 °C under the atmosphere of an Ar / H2 mixed gas, with the argon flow rate being 450 sccm and the hydrogen flow rate being 50 sccm; then continuously introduce an Ar / H2 mixed gas carrying acetonitrile into the closed heating environment, carry the acetonitrile to the powder through the Ar / H2 mixed gas, and directly grow nano-carbon by metal-catalyzed cracking for 2 h; after naturally cooling to room temperature, stop introducing the Ar / H2 mixed gas; then wash away the sodium chloride in the sample, and dry it at 60 °C to obtain a nano-carbon supported Ni single-atom catalyst.

[0033] It can be seen that Figure 1 the main diffraction peaks of the obtained product can well correspond to the PDF#26 - 1079 card of graphite carbon.

[0034] It can be seen that Figure 2 the D peak and G peak in the figure are the main characteristic peaks of graphite.

[0035] It can be seen that Figure 3 the obtained product is mainly in the morphology of one-dimensional nano-carbon, with a diameter of 100 - 200 nm and a length of 2 - 5 μm.

[0036] It can be seen that Figure 4 the one-dimensional nano-carbon is mainly stacked by carbon nanosheets.

[0037] It can be seen that Figure 5 the bright spots on the nano-carbon are the supported metal Ni single atoms.

[0038] Use the nano-carbon supported Ni single-atom catalyst prepared in Example 1 for electrocatalytic CO2 reduction, and the specific steps are as follows:

[0039] (1) Disperse the nano-carbon supported metal Ni single-atom catalyst in absolute ethanol, add a small amount of nafion solution, ultrasonically disperse it evenly, and then drop-coat it on a hydrophobic carbon paper for drying, with a loading amount of 1 mg·cm -2 , which is used as the cathode; a platinum sheet is used as the anode, and a saturated calomel electrode is used as the reference electrode;

[0040] (2) During the electrochemical test, 0.2 mol / L potassium bicarbonate was used as the electrolyte. During the test, CO2 gas was continuously introduced to form a saturated solution, and electrochemical reduction of CO2 was carried out at a voltage of -0.6 to -1.1 V to produce CO; during the test, an on-line gas chromatograph was used to detect the gas products.

[0041] (3) After the reaction, the electrolyte was collected and the liquid-phase products were detected using 1H NMR.

[0042] It can be seen from Figure 6 that the Faradaic efficiency of CO reached up to 84%, and no liquid-phase products were formed, indicating that the prepared metal Ni single-atom catalyst supported on nano-carbon has excellent selectivity for CO synthesis.

[0043] It can be seen from Figure 7 that in the electrochemical (time-current) test of electrocatalytic CO2 reduction, the metal Ni single-atom catalyst supported on nano-carbon can stably operate at a current density of about 30 mA·cm -2 for 20 h, indicating that the prepared metal Ni single-atom catalyst supported on nano-carbon has good electrocatalytic stability.

[0044] Example 2

[0045] (1) 10 mg of nickel chloride and 20 mg of sodium chloride were dissolved in 100 mL of water to form a salt solution, which was dried to obtain a powder sample. Then the powder sample was ball-milled for 2 h to make it uniformly mixed, and a uniformly mixed powder was obtained.

[0046] (2) The powder obtained in step (1) was placed in a sealed heating environment and heated to 680 °C in an Ar / H2 mixed gas atmosphere, with the flow rate of argon being 450 sccm and the flow rate of hydrogen being 50 sccm; then a mixed gas of Ar / H2 carrying pyridine was continuously introduced into the sealed heating environment, and pyridine was carried to the powder by the Ar / H2 mixed gas to directly grow nano-carbon by metal-catalyzed cracking for 2 h; after natural cooling to room temperature, the introduction of the Ar / H2 mixed gas was stopped; then the sodium chloride in the sample was washed away, and after drying at 60 °C, a metal Ni single-atom catalyst supported on nano-carbon was obtained.

[0047] The metal Ni single-atom catalyst supported on nano-carbon prepared in Example 2 was used for electrocatalytic CO2 reduction, and the specific steps were as follows:

[0048] (1) The metal Ni single-atom catalyst supported on nano-carbon was dispersed in absolute ethanol, a small amount of nafion solution was added, and after ultrasonic dispersion, it was drop-coated on a hydrophobic carbon paper and dried, with a loading amount of 1 mg·cm -2, used as the cathode; a platinum sheet is used as the anode, and a saturated calomel electrode is used as the reference electrode;

[0049] (2) During the electrochemical test, 0.2 mol / L potassium bicarbonate is used as the electrolyte. During the test, CO2 gas is continuously introduced to form a saturated solution, and electrochemical reduction of CO2 is carried out at a voltage of -0.6 to -1.1 V to prepare CO; during the test, an on-line gas chromatograph is used to detect the gas products;

[0050] (3) After the reaction is completed, the electrolyte is collected and the liquid-phase products are detected by 1H NMR.

[0051] After testing, after the electrocatalytic reduction of CO2, the Faraday efficiency of CO reaches up to 82%, and no liquid-phase products are generated, indicating that the prepared metal Ni single-atom catalyst supported on nano-carbon has excellent selectivity for CO synthesis.

[0052] What is not described in the present invention applies to the prior art.

Claims

1. A method for directly growing a metal single-atom catalyst supported on nano-carbon by metal catalysis, characterized in that, The method comprises the following steps: (1) Mix substance A and substance B evenly to obtain a uniformly mixed powder; Substance A is a transition metal salt; substance B is an inorganic salt with a melting point > 600 °C; (2) Place the powder in a closed heating environment and heat it to 600 - 1000 °C in an atmosphere of a mixed gas of Ar / H2; then continuously introduce a mixed gas of Ar / H2 carrying a carbon source into the closed heating environment, carry the carbon source to the powder through the mixed gas of Ar / H2, and conduct direct metal-catalyzed growth of nano-carbon; after the growth is completed, naturally cool to room temperature; then stop introducing the mixed gas of Ar / H2 to obtain a nano-carbon supported metal single-atom catalyst; The carbon source is an organic small molecule compound.

2. The method for directly growing a metal single-atom catalyst supported on nanocarbon by metal catalysis according to claim 1, characterized in that In step (1), substance A is a sulfate, nitrate or chloride of iron, ruthenium, cobalt, nickel, copper, manganese, platinum, rhodium, iridium, zinc or palladium.

3. The method for directly growing a metal single-atom catalyst supported on nano-carbon by metal catalysis according to claim 1, characterized in that In step (1), the mass ratio of substance A to substance B is 1:1 - 10.

4. The method for directly growing a metal-catalyzed single-atom metal catalyst supported on nanocarbon according to claim 1, characterized in that, In step (2), the closed heating environment uses a tubular furnace.

5. The method for directly growing a metal single-atom catalyst supported on nanocarbon by metal catalysis according to claim 1, wherein In step (2), the time for direct metal-catalyzed growth is 0.5 - 5 h.

6. The method for directly growing a metal-catalyzed single-atom metal catalyst supported on nanocarbon according to claim 1, characterized in that, In step (2), the carbon source is acetonitrile, pyridine, ethanol, ethylene or methane.

7. The method for directly growing a metal single-atom catalyst supported on nano-carbon by metal catalysis according to claim 1, characterized in that, In step (2), the flow rate of the mixed gas of Ar / H2 is 200 - 1000 sccm, and the gas flow ratio is Ar:H2 = 5 - 20:1.

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