High-stability metal atom catalyst as well as preparation method and application thereof

Abstract

The invention discloses a high-stability metal atom catalyst as well as a preparation method and application thereof. On the basis of commercially available multiwalled carbon nanotubes, metal impurities contained in the multiwalled carbon nanotubes are utilized, and the multiwalled carbon nanotubes are prepared through heat treatment. The high-stability metal atom catalyst is obtained by a simple process, can efficiently, quickly and stably catalyze electrochemical reaction, and is beneficial to industrial large-scale production and application.

Description

Technical Field

[0001] The invention belongs to the field of electrochemical catalysis, and specifically relates to a high-stability metal atom catalyst and a preparation method and application thereof. Background Art

[0002] In the electrochemical catalytic process, the performance of the electrocatalyst determines the catalytic effect. In recent years, metal atom catalysts supported on carbon substrates have attracted much attention due to their advantages such as atom economy, high activity, and high conductivity. At present, there are two main types of carbon substrates: porous carbon / carbon substrates obtained by heat-treating carbon precursors and advanced carbon substrates represented by graphene, carbon nanotubes, and carbon quantum dots. Among them, carbon nanotubes have high mechanical strength and high chemical stability, which are more conducive to the stable dispersion of metal atoms. There are two main methods for synthesizing metal atom catalysts based on carbon nanotubes: one is a one-step method, in which carbon source, metal source and heteroatom source are mixed to synthesize carbon nanotubes containing metal atoms in one step. The crystallinity of carbon nanotubes obtained by this method is usually poor, resulting in a loss of catalyst structure and performance stability; the other is a two-step method, in which carbon nanotubes are first synthesized, and then small molecules containing metal single atoms such as metal sources and heteroatom sources or metal porphyrins are mixed to synthesize carbon nanotubes containing metal atoms in two steps. The metal atoms obtained by this method are usually only distributed on the surface of carbon nanotubes. They are prone to poisoning, detachment from the carbon nanotube substrate or agglomeration during the electrocatalytic process, resulting in degradation of catalyst performance, which is not conducive to large-scale promotion and application.

[0003] CN111769298A discloses a method for preparing a metal single-atom single-walled carbon nanotube electrocatalyst based on residual metal. The method is a floating catalyst vapor deposition method, in which a carbon nanotube film containing transition metal residues is reacted with xenon fluoride and ammonia in sequence to finally obtain a single-walled carbon nanotube electrocatalytic film containing iron single atoms. The reagents used to synthesize the catalyst are expensive, and the operation is complicated and requires high requirements, which is not conducive to large-scale promotion and application. The iron single atoms on the electrocatalytic film finally obtained are exposed on the surface of the single-walled carbon nanotubes, which are prone to poisoning, separation from the carbon nanotube substrate or agglomeration during the electrocatalytic process, resulting in catalyst performance degradation.

[0004] Compared with single-walled carbon nanotubes, multi-walled carbon nanotubes have a multi-layer carbon wall structure, which can retain more metals, and have lower manufacturing costs and larger single-time production volumes, with metal loading and cost advantages. The multi-layer carbon wall structure can effectively protect the residual metal in the inner layer after forming metal single atoms, stably play a role, prevent poisoning, shedding and agglomeration, and has performance advantages. However, there are no related reports yet. Summary of the invention

[0005] The purpose of the present invention is to provide a highly stable metal atom catalyst and its preparation method and application. The commercially available multi-walled carbon nanotubes are innovatively selected as the carbon substrate, and a highly active and highly stable metal atom catalyst is obtained through a simple synthesis process, which is more conducive to actual production and application.

[0006] According to the first aspect of the present invention, a high-stability metal atom catalyst material is provided, characterized in that the multi-walled carbon nanotubes have carbon defects, and the metal exists in an atomically dispersed form in the carbon layer on the subsurface and inside the multi-walled carbon nanotubes.

[0007] According to a second aspect of the present invention, the present invention provides a method for preparing a high-stability metal atom catalyst, comprising the following steps: Step 1: reflux the multi-walled carbon nanotubes in a hot acid solution under air conditions, and wash the separated precipitate with water until it is neutral and dry; Step 2: fully mixing the multi-walled carbon nanotubes obtained in step 1 with a nitrogen source and a fluorine source; Step 3: heat treating the mixture obtained in step 2 under a protective atmosphere; Step 4: The material obtained in step 3 is washed with acid, then washed with water until neutral, and dried to obtain a highly stable metal atom catalyst.

[0008] The multi-walled carbon nanotubes have a purity of not less than 80%, a diameter of not less than 5 nm, a metal type of one or a combination of Fe, Co, Ni, Cu, Zn, Mn, La, and a metal content of 0.1wt% to 3wt%.

[0009] The nitrogen source is one or a combination of urea, melamine, dicyandiamide, thiourea, polyethyleneimine, cyanuric chloride, polypyrrole, terpyridine, glycine, o-aminoazotoluene, bipyridine, o-phenanthroline, L-alanine, polyaniline, glutamic acid, tris(hydroxymethyl)aminomethane, and the fluorine source is polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorinated ethylene propylene copolymer (FEP), polyvinyl fluoride (PVF), polychlorotrifluoroethylene (PCTFE), 4-fluorophenol, 4-fluorosalicylic acid, 2,4-difluorobenzoic acid, 3-fluoroacetic acid, 4-fluorophenylacetic acid, tetrafluoroterephthalonitrile, tetrafluoro Terephthalaldehyde, polytetrafluoroethylene-ethylene copolymer (ETFE), vinylidene fluoride-trifluorochloroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene terpolymer, vinylidene fluoride-tetrafluoroethylene-perfluoromethyl vinyl ether-vulcanization point monomer quaternary copolymer, tetrafluoroethylene and hydrocarbon propylene copolymer, polyvinylidene fluoride-hexafluoropropylene copolymer, ammonium fluorosilicate, perfluorosulfonic acid monomer, perfluoroalkoxy resin, ammonium fluoride, ammonium hydrogen fluoride, zinc fluoride, sodium fluoride, potassium fluoride, barium fluoride, calcium fluoride, lithium fluoride, rubidium fluoride, silver fluoride, nickel fluoride, cobalt fluoride, ammonium fluorotitanate, or a combination of several thereof.

[0010] The mixing is one or a combination of grinding mixing, ball milling mixing, stirring mixing, and ultrasonic mixing.

[0011] The protective atmosphere is one or a combination of helium, argon, nitrogen and ammonia.

[0012] The heat treatment temperature is 600-1300°C, and the heating rate is 2-10°C·min -1 , constant temperature time is 0.5-10 h.

[0013] The hot acid and the leaching acid are one or a combination of sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid, and the concentration is 0.5-8 mol·L -1 , the pickling time is 0.5~48 h.

[0014] The high-stability metal atom catalyst prepared by the preparation method has metals in the multi-walled carbon nanotubes in the form of atomic-level dispersion in the sub-surface and internal carbon layers.

[0015] The application of the high-stability metal atom catalyst in electrochemical catalysis.

[0016] The applications are carbon dioxide reduction, hydrogen production, and oxygen reduction.

[0017] According to the third aspect of the present invention, the present invention provides an application of a high-stability metal atom catalyst in electrochemical catalysis.

[0018] The beneficial effects of the present invention are embodied in: (1) The multi-walled carbon nanotubes used are low-cost and conducive to large-scale production. Compared with advanced carbon substrates such as single-walled carbon nanotubes, graphene, and carbon quantum dots, multi-walled carbon nanotubes have low synthesis environment requirements, simple processes, and great potential for large-scale production, and have performance and cost advantages. Compared with the two-step method that requires additional addition of metal sources, directly using the metals remaining in the production process of multi-walled carbon nanotubes as metal single-atom precursors has cost advantages. Therefore, it is conducive to promotion and application.

[0019] (2) Based on the characteristics of multi-walled carbon nanotubes, as a carbon substrate, metal atom catalysts with high activity and high stability can be obtained. Compared with porous carbon / carbon substrates made from carbon sources such as glucose and biomass, multi-walled carbon nanotubes have higher mechanical stability and chemical stability, better conductivity, and have activity and stability advantages as a carbon substrate; compared with advanced carbon substrates such as single-walled carbon nanotubes, graphene, and carbon quantum dots, multi-walled carbon nanotubes have a stable multi-layer tube structure, which can effectively protect the inner metal atoms to stabilize their function and prevent metal atoms from being poisoned, falling off, and agglomerating, and have stability advantages. Therefore, it is conducive to promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a scanning electron microscope image of the high-stability metal atom catalyst prepared in Example 1.

[0021] Figure 2 This is a scanning transmission electron microscope image of the high-stability metal atom catalyst prepared in Example 1.

[0022] Figure 3 The Faraday efficiency and current density of the products of the high-stability metal atom catalyst prepared in Example 1 after 108 h of electrocatalytic carbon dioxide reduction.

[0023] Figure 4 This is the CO partial current density diagram of the high stability metal atom catalyst prepared in Example 2-3. DETAILED DESCRIPTION

[0024] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings. The following content is only an example and explanation of the concept of the present invention. The technicians in the field may make various modifications or supplements to the specific implementation cases described, or replace them with similar methods, as long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention. Example 1

[0025] A preparation method of a high-stability metal atom catalyst comprises the following steps: Step 1: Multi-walled carbon nanotubes with a purity of 90% and a Ni metal residue of 1 wt% were heated to 9 mol·L -1 refluxed in nitric acid at 80°C for 3 h, and the separated precipitate was washed with water and ethanol until neutral and dried; Step 2: Weigh 1 g of the precipitate obtained in step 1, 10 g of urea and 5 g of polytetrafluoroethylene and grind them thoroughly to obtain a mixed powder; Step 3: Heat-treat the mixed powder obtained in step 2 at 800°C in an argon atmosphere at a heating rate of 5°C min -1 , constant temperature time is 1 h; Step 4: The material obtained in step 3 was treated with 3 mol·L -1 The mixture was soaked in HCl for 1 h, and the separated precipitate was washed with water and ethanol until neutral, and dried to obtain a highly stable metal atom catalyst.

[0026] The scanning electron microscope photo of the high stability metal atom catalyst obtained in this example is as follows: Figure 1 Scanning transmission electron microscopy images are shown in Figure 2 The catalyst is a multi-layer nested tubular structure with a large amount of atomic-level metals distributed in the inner layer.

[0027] Application of this highly stable metal atom catalyst in electrochemical carbon dioxide reduction: The catalyst in this embodiment was used as a cathode catalyst and loaded on a gas diffusion layer substrate to obtain a cathode; a platinum sheet was used as an anode, a silver / silver chloride electrode (the electrolyte was saturated potassium chloride) was used as a reference electrode, and a 0.5 M KHCO3 aqueous solution containing saturated carbon dioxide was used as an electrolyte, and electrochemical carbon dioxide reduction was carried out in a double-chamber electrolytic cell separated by a Nafion membrane. Figure 3 This is the Faraday efficiency and current density test result of the electrocatalytic carbon dioxide reduction for 108 h. As can be seen from the figure, the high-stability metal atom catalyst can efficiently catalyze carbon dioxide reduction and has high long-term stability, which is conducive to practical promotion and application. Example 2

[0028] A preparation method of a high-stability metal atom catalyst comprises the following steps: Step 1: Multi-walled carbon nanotubes with a purity of 85% and a Ni metal residue of 0.5 wt% were heated to 6 mol·L -1 refluxed in nitric acid at 80°C for 4 h, and the separated precipitate was washed with water and ethanol until neutral and dried; Step 2: Weigh 0.5 g of the precipitate obtained in step 1, 10 g of dicyandiamide and 6 g of polyvinyl fluoride, and mix them thoroughly using a ball mill to obtain a mixed powder; Step 3: Heat-treat the mixed powder obtained in step 2 at 900°C in a nitrogen atmosphere at a heating rate of 7°C min -1 , constant temperature time is 2.5 h; Step 4: The material obtained in step 3 is soaked in 10% hydrofluoric acid solution for 12 h, the separated precipitate is washed with water and ethanol until neutral, and dried to obtain a highly stable metal atom catalyst.

[0029] Application of this highly stable metal atom catalyst in electrochemical carbon dioxide reduction: The catalyst in this embodiment was used as a cathode catalyst and loaded on a gas diffusion layer substrate to obtain a cathode; a platinum sheet was used as an anode, a silver / silver chloride electrode (the electrolyte was saturated potassium chloride) was used as a reference electrode, and a 0.5 M KHCO3 aqueous solution containing saturated carbon dioxide was used as an electrolyte, and electrochemical carbon dioxide reduction was carried out in a double-chamber electrolytic cell separated by a Nafion membrane. Figure 4 This is the CO partial current density test result of the prepared high-stability metal atom catalyst. As can be seen from the figure, the high-stability metal atom catalyst can efficiently catalyze the reduction of carbon dioxide, and the partial current density of the product can reach 145 mA cm at a potential of -1.7 V. -2 , which is conducive to practical promotion and application. Example 3

[0030] A preparation method of a high-stability metal atom catalyst comprises the following steps: Step 1: Multi-walled carbon nanotubes with a purity of 95% and a Ni metal residue of 2 wt% were heated to 8 mol·L -1 The mixture was refluxed in sulfuric acid at 70°C for 5 h, and the separated precipitate was washed with water and ethanol until neutral and dried; Step 2: Weigh 1 g of the precipitate obtained in step 1, 8 g of dicyandiamide and 6 g of polyvinylidene fluoride, and stir and mix them thoroughly to obtain a mixed powder; Step 3: Heat-treat the mixed powder obtained in step 2 at 750°C in a helium atmosphere at a heating rate of 6°C min -1 , calcination time is 3 h; Step 4: The material obtained in step 3 was treated with 4 mol·L -1 The mixture was washed with sulfuric acid for 0.5 h, and the separated precipitate was washed with water until it became neutral and dried to obtain a highly stable metal atom catalyst.

[0031] Application of this highly stable metal atom catalyst in electrochemical carbon dioxide reduction: The catalyst in this embodiment was used as a cathode catalyst and loaded on a gas diffusion layer substrate to obtain a cathode; a platinum sheet was used as an anode, a silver / silver chloride electrode (the electrolyte was saturated potassium chloride) was used as a reference electrode, and a 0.5 M KHCO3 aqueous solution containing saturated carbon dioxide was used as an electrolyte, and electrochemical carbon dioxide reduction was carried out in a double-chamber electrolytic cell separated by a Nafion membrane. Figure 4 This is the CO partial current density test result of the prepared high-stability metal atom catalyst. As can be seen from the figure, the high-stability metal atom catalyst can efficiently catalyze the reduction of carbon dioxide, and the partial current density of the product can reach 147 mA cm at a potential of -1.7 V. -2 , which is conducive to practical promotion and application. Example 4

[0032] A preparation method of a high-stability metal atom catalyst comprises the following steps: Step 1: Multi-walled carbon nanotubes with a purity of 90% and a Ni metal residue of 1 wt% were heated to 8 mol·L -1 refluxed in nitric acid at 85°C for 2 h, and the separated precipitate was washed with water and ethanol until neutral and dried; Step 2: Weigh 0.5 g of the precipitate obtained in step 1, 5 g of melamine and 3 g of ammonium fluoride, and grind and mix them thoroughly; Step 3: Heat-treat the mixed powder obtained in step 2 at 700°C in an argon atmosphere at a heating rate of 3°C min -1 , calcination time is 5 h; Step 4: The material obtained in step 3 was treated with 2 mol·L -1 After HCl soaking for 2 h, the separated precipitate was washed with water and ethanol until neutral, and dried to obtain a highly stable metal atom catalyst. Example 5

[0033] A preparation method of a high-stability metal atom catalyst comprises the following steps: Step 1: Multi-walled carbon nanotubes with a purity of 90% and a residual Fe content of 1 wt% were heated to 8 mol·L -1 refluxed in nitric acid at 85°C for 2.5 h, and the separated precipitate was washed with water and ethanol until neutral and dried; Step 2: Weigh 1 g of the precipitate obtained in step 1, 12 g of melamine and 5 g of PTFE, and mix them thoroughly using a ball mill to obtain a mixed powder; Step 3: Heat the mixed powder obtained in step 2 at 800°C under argon atmosphere at a heating rate of 5°C min -1 , constant temperature time is 1 h; Step 4: The material obtained in step 3 was treated with 5 mol·L -1After immersion for 8 h, the separated precipitate was washed with water and ethanol until neutral, and dried to obtain a highly stable metal atom catalyst.

Claims

1. A highly stable metal atom catalyst, characterized in that: There are carbon defects on the multi-walled carbon nanotubes, and the metal exists in the carbon layer on the subsurface and inside the multi-walled carbon nanotubes in an atomically dispersed form.

2. A method for preparing a high-stability metal atom catalyst as claimed in claim 1, characterized in that: The steps include: Step 1: reflux the multi-walled carbon nanotubes in a hot acid solution under air conditions, and wash the separated precipitate with water until it is neutral and dry; Step 2: fully mixing the multi-walled carbon nanotubes obtained in step 1 with a nitrogen source and a fluorine source; Step 3: heat treating the mixture obtained in step 2 under a protective atmosphere; Step 4: The material obtained in step 3 is washed with acid, then washed with water until neutral, and dried to obtain a highly stable metal atom catalyst.

3. The method for preparing a highly stable metal atom catalyst according to claim 2, characterized in that: The multi-walled carbon nanotubes have a purity of not less than 80%, a diameter of not less than 5 nm, a metal type of one or a combination of Fe, Co, Ni, Cu, Zn, Mn, La, and a metal content of 0.1wt% to 3wt%.

4. The method for preparing a highly stable metal atom catalyst according to claim 2, characterized in that: The nitrogen source is one or a combination of urea, melamine, dicyandiamide, thiourea, polyethyleneimine, cyanuric chloride, polypyrrole, terpyridine, glycine, o-aminoazotoluene, bipyridine, o-phenanthroline, L-alanine, polyaniline, glutamic acid, tris(hydroxymethyl)aminomethane; the fluorine source is polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorinated ethylene propylene copolymer (FEP), polyvinyl fluoride (PVF), polychlorotrifluoroethylene (PCTFE), 4-fluorophenol, 4-fluorosalicylic acid, 2,4-difluorobenzoic acid, 3-fluoroacetic acid, 4-fluorophenylacetic acid, tetrafluoroterephthalonitrile, tetrafluoro Terephthalaldehyde, polytetrafluoroethylene-ethylene copolymer (ETFE), vinylidene fluoride-trifluorochloroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene terpolymer, vinylidene fluoride-tetrafluoroethylene-perfluoromethyl vinyl ether-vulcanization point monomer quaternary copolymer, tetrafluoroethylene and hydrocarbon propylene copolymer, polyvinylidene fluoride-hexafluoropropylene copolymer, ammonium fluorosilicate, perfluorosulfonic acid monomer, perfluoroalkoxy resin, ammonium fluoride, ammonium hydrogen fluoride, zinc fluoride, sodium fluoride, potassium fluoride, barium fluoride, calcium fluoride, lithium fluoride, rubidium fluoride, silver fluoride, nickel fluoride, cobalt fluoride, ammonium fluorotitanate, or a combination of several thereof.

5. The method for preparing a highly stable metal atom catalyst according to claim 2, characterized in that: The mixing is one or a combination of grinding mixing, ball milling mixing, stirring mixing, and ultrasonic mixing.

6. The method for preparing a highly stable metal atom catalyst according to claim 2, characterized in that: The protective atmosphere is one or a combination of helium, argon, nitrogen and ammonia.

7. The method for preparing a highly stable metal atom catalyst according to claim 2, characterized in that: The heat treatment temperature is 600-1300°C, and the heating rate is 2-10°C·min -1 , constant temperature time is 0.5-10 h.

8. The method for preparing a highly stable metal atom catalyst according to claim 2, characterized in that: The hot acid and the leaching acid are one or a combination of sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid, and the concentration is 0.5-8 mol·L -1 , the pickling time is 0.5~48 h.

9. A high-stability metal atom catalyst prepared by the preparation method according to any one of claims 1 to 8, characterized in that: In multi-walled carbon nanotubes, metals are dispersed at the atomic level in the subsurface and internal multi-layer carbon walls.

10. Use of the high-stability metal atom catalyst as claimed in claim 9 in electrochemical catalysis.

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