Metal atomic-scale dispersion catalyst for directional confinement growth in micropores and preparation method of metal atomic-scale dispersion catalyst

Abstract

The invention discloses a metal atomic-scale dispersion catalyst material for directional confinement growth in micropores and a preparation method of the metal atomic-scale dispersion catalyst material. According to the catalyst material, carbon nanofibers with a microporous / mesoporous graded pore channel structure are used as a carrier, and metal atoms exist in pore channels of the carbon carrier in an atom dispersion form. The structure is helpful for improving the catalytic efficiency and the stability. The method is simple in preparation flow, controllable in process, good in stability, capable of achieving batch production and suitable for macro preparation.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanocatalyst preparation, and relates to a single-atom catalyst and a preparation method and application thereof, and specifically to a metal atomic-level dispersed catalyst that directionally grows in a confined area in a micropore and a preparation method thereof. Background Art

[0002] As the consumption of traditional fossil energy and the emission of greenhouse gases (such as CO2, N2O, etc.) have caused serious environmental problems, the development and utilization of efficient clean energy (wind energy, solar energy) has become the commanding heights of the new generation of energy technology and a new field of economic development. In recent years, metal-air fuel cells and water electrolysis hydrogen production systems based on electrocatalytic reactions such as oxygen reduction reaction (ORR), oxygen oxidation reaction (OER), and hydrogen evolution reaction (HER) can be used as complementary energy storage for electrochemical energy storage power stations to achieve stable grid connection, and use clean energy water electrolysis to produce hydrogen for periodic storage for distributed power generation, which has attracted people's attention. Among them, the catalyst, as an "accelerator" of the catalytic reaction, can not only effectively reduce the activation energy of the reaction, making the reaction easier to proceed, but also greatly reduce the reaction energy consumption and improve the energy conversion efficiency.

[0003] At present, commercial catalysts are still highly dependent on the precious metal platinum (Pt). However, the scarcity of Pt not only leads to its high price and long-term dependence on imports, but also makes it account for as much as 36% of the cost of fuel cells (stacks), limiting the large-scale application of such battery stacks. In order to solve the problem of resource constraints and cost reduction and efficiency improvement, there is an urgent need to develop high-performance non-platinum catalysts. However, non-platinum catalysts often have low activity and poor stability under actual working conditions. Therefore, the development of highly active and stable non-platinum catalysts is a key point in research and practical applications.

[0004] Constructing atomically dispersed materials with fully exposed active metal atoms can not only achieve maximum atomic utilization efficiency, but also improve catalytic efficiency and selectivity. Low metal content will also effectively reduce costs and have high application value. However, due to the high surface energy of isolated atoms, atomically dispersed catalysts tend to agglomerate to form nanoparticles under pyrolysis and electrochemical action, resulting in poor stability. In addition, the preparation conditions of most atomically dispersed materials are harsh, and the coordination effect between the carrier and the metal needs to be fully considered.

[0005] After searching the existing patent literature, it was found that CN 117996096 A discloses using polyacrylonitrile-b-polymethyl methacrylate block copolymer as a polymer precursor, using electrospinning-chemical vapor deposition to synthesize a carrier with a mesoporous carbon fiber @ carbon nanolayer three-dimensional network structure, and using the carrier to load single-atom metals for fuel cell cathode oxygen reduction reaction and electrolytic carbon dioxide reduction reaction. The formation of its single-atom metal catalyst needs to rely on the strong interaction between nitrogen atoms and metal atoms in the carrier, and this interaction is called metal-carrier electronic interaction. Therefore, when preparing mesoporous carbon fibers, it is necessary to introduce a nitrogen source (dicyandiamide), and the nitrogen source is pyrolyzed to grow nitrogen-containing nanosheets in situ, so that nitrogen anchors iron metal atoms to form iron single-atom materials. That is, nitrogen and metal atoms are used to generate metal-carrier electronic interactions to anchor single atoms. However, this interaction may limit the selection of metal species and the performance optimization of the catalyst. In addition, the process of preparing mesoporous carbon fiber @ carbon nanolayer network-loaded single-atom iron catalyst involves multiple steps, including the mass ratio control of mesoporous PAN fibers adsorbing iron salts and dicyandiamide and heat treatment under N2 atmosphere. Such complicated preparation steps may result in lower yield and higher energy consumption.

[0006] Based on the above research, the present invention proposes for the first time a method for a metal atomic-level dispersed catalyst that amplifies the capillary adsorption process to allow confined growth in micropores and a preparation method thereof, which only relies on the capillary force between the carrier and the metal organic group for indiscriminate adsorption, directionally adsorbs the metal group into the micropores, and confines the synthesis of atomic-level dispersed materials, effectively solving the technical difficulties of the harsh preparation conditions of traditional atomic-level materials. In addition, due to its special highly directional confinement, the prepared atomic-level catalyst is not easy to agglomerate during heat treatment and electrochemical processes, and has ultra-high stability and activity. Summary of the invention

[0007] The purpose of the present invention is to provide a metal atomic-level dispersed catalyst material with directional confined growth in micropores and a preparation method thereof. The preparation method can achieve multi-dimensional control of single-atom, cluster, and particle catalyst materials with high activity and stability.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] The present invention relates to a metal atomic-level dispersed catalyst material with directional confined growth in micropores, wherein the carbon material is a carbon nanofiber with a micropore / mesopore hierarchical pore structure, and the metal atoms exist in the pores of the carbon carrier in the form of atomic dispersion. The atomic-level material prepared by the present invention is directional and confinedly grown in the micropores by capillary adsorption. The method of directional confined growth in micropores helps to achieve high dispersion of metal species and helps to improve catalytic efficiency and stability.

[0010] As an embodiment, the atomic dispersion includes single atom dispersion or dispersion in the form of atomic clusters; the particle size of the atomic clusters is 1 to 5 nm.

[0011] The present invention also relates to a method for preparing a metal atomic-level dispersed catalyst material with directional confined growth in micropores, the method comprising the following steps:

[0012] S1. Pretreatment: Mixing a polymer precursor with a pore-forming agent, adding a solvent to form a uniform solution, and forming polymer nanofibers under the action of an electric field by electrospinning technology; obtaining carbon nanofibers by high-temperature pyrolysis; washing the carbon nanofibers with a gradient of water and an organic solvent and vacuum drying to remove excess pore-forming agent and impurities, thereby obtaining carbon nanofibers with a dry microporous / mesoporous hierarchical pore structure;

[0013] S2, capillary adsorption process: vacuum mixing the carbon nanofibers obtained in step S1 and solutions with different surface tensions, and adding a metal organic group with a size smaller than the pore size of the carbon nanofiber as an adsorbent; fully stirring under a vacuum environment, the metal organic group is absorbed into the porous carbon fiber; and naturally drying to obtain a metal-carbon mixture;

[0014] S3, pyrolysis treatment process: the metal-carbon mixture material obtained in step S2 is placed in an inert atmosphere for pyrolysis treatment; the metal organic group is pyrolyzed and anchored on the carrier to form highly active and stable atomic-level dispersed materials such as single atoms and clusters.

[0015] The highly conductive and stable atomic-level dispersed catalyst material is prepared by a capillary adsorption-pyrolysis annealing process. The capillary adsorption process is to add the metal organic group and the carbon material of suitable size in proportion and mix them evenly, add solvents with different surface tensions, and mix them evenly in a vacuum environment; the pyrolysis annealing process is to use a tubular furnace to heat the mixture under an inert atmosphere, and the organic group is pyrolyzed and anchored at different positions of the carrier to obtain atomic-level dispersed materials such as single atoms and clusters.

[0016] As an embodiment, in step S1, the polymer precursor is preferably polyacrylonitrile. The pore-forming agent is one or more of potassium hydroxide, potassium carbonate, ammonium chloride, and sodium chloride, which have a small diameter and are easily decomposed.

[0017] As an embodiment, in step S1, the usage ratio of polymer precursor, pore former and solvent (DMF) is 2g:0.01-0.1g:20mL.

[0018] As an embodiment, in step S1, the high temperature pyrolysis temperature is 800°C and the time is 1 to 2 hours.

[0019] As an embodiment, in step S1, the vacuum drying temperature is 110° C. and the time is 24 to 36 hours.

[0020] As an embodiment, in step S1, the solvent includes N,N-dimethylformamide.

[0021] As an embodiment, in step S1, the organic solvent for gradient washing is an alcohol solvent, including methanol and ethanol.

[0022] As an embodiment, the carbon nanofiber material having dry pores obtained by gradient washing the carbon nanofiber material with water and an organic solvent and then vacuum drying needs to have a pore size controlled within a range of 0.5 to 5 nm.

[0023] As an embodiment, in step S2, the solutions with different surface tensions are one or more of water, methanol, ethanol, dimethylformamide, N-methyl-2-pyrrolidone, acetone, and cyclohexane.

[0024] As an embodiment, in step S2, the metal organic group is an organic chelate molecule group containing noble metals and non-noble metals, including an organic chelate molecule group containing ruthenium, iron, cobalt or nickel.

[0025] As an embodiment, in step S2, the usage ratio of carbon nanofibers, solutions with different surface tensions, and metal organic matter is 200 mg:10 mL:15-35 mg.

[0026] As an embodiment, in step S3, the pyrolysis temperature is 700-800°C, and the time is 0.5-2h.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) The present invention amplifies the capillary adsorption process and relies on the capillary force between the carrier and the metal organic group for indiscriminate adsorption, thereby simplifying the complex conditions in the traditional atomic-level material preparation process and reducing the difficulty of preparation; by directed adsorption of metal groups into micropores, confined synthesis of atomic-level dispersed materials is achieved, and this high degree of directionality helps to improve the uniformity and consistency of the material.

[0029] 2) The prepared atomic-level catalyst is not easy to agglomerate during the pyrolysis and electrochemical processes due to its special highly directional confinement, thus having ultra-high stability, which is crucial for the long-term and effective use of the catalyst.

[0030] 3) The simplified preparation process and reduced reliance on harsh conditions can reduce production costs, improve efficiency and yield, and make large-scale application of atomically dispersed catalysts possible.

[0031] 4) The present invention prepares carbon fibers through electrospinning of polymer and pore-forming agent solution → preparing polymer fibers → high temperature treatment to obtain carbon fibers with microporous / mesoporous channels → gradient washing to obtain dry carbon nanofibers with microporous / mesoporous hierarchical channel structures → achieving precursor adsorption in solvents with surface tension → pyrolysis to obtain atomic-level materials. This preparation process does not rely on nitrogen in the carrier to produce metal-carrier electronic interactions with metal atoms to anchor single atoms, but instead controls the difference in capillary adsorption forces of solvents with different surface tensions by constructing carbon materials with micropores / mesoporose, and amplifies capillary adsorption, so that the channels become "straws" to evenly disperse the precursor solution into the bulk phase; the channels provide a confining effect to prevent metal elements from aggregating during pyrolysis. This simple atomic dispersion strategy achieves differential distribution of metal organic molecular precursors during the adsorption process through differences in capillary adsorption forces, thereby synthesizing atomic-level materials such as single atoms and clusters, providing a wider range of metal choices and better performance regulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0033] Figure 1 It is a process flow chart of capillary adsorption-pyrolysis annealing;

[0034] Figure 2 is a SEM image of carbon nanofibers with hierarchical pore structure;

[0035] Figure 3 The pore size distribution diagram of carbon nanofibers under the action of different pore-forming agents;

[0036] Figure 4 is a spherical aberration AC-TEM image of the Ru single atom dispersed catalyst in Example 1;

[0037] Figure 5 is a SEM image of carbon nanofibers with hierarchical pore structure;

[0038] Figure 6 is the spherical aberration AC-TEM image of the Ru cluster dispersed catalyst in Example 2;

[0039] Figure 7 This is the spherical aberration AC-TEM image of the Ru cluster dispersed catalyst in Example 3;

[0040] Figure 8 is a SEM image of carbon nanofibers with hierarchical pore structure;

[0041] Fig. 9 This is the spherical aberration AC-TEM image of the Fe single atom dispersed catalyst in Example 4;

[0042] Fig.10 This is the spherical aberration diagram of the Fe cluster dispersed catalyst in Example 5.

[0043] Fig.11 The spherical aberration AC-TEM and TEM images of the Ru particle material in Comparative Example 1;

[0044] Fig.12 The UV spectra of the changes in phenanthroline content in the solution before and after adsorption in water and propanol environments;

[0045] Fig.13 This is the spherical aberration AC-TEM image of the Ru particle material in Comparative Example 2;

[0046] Fig.14 These are the spherical aberration AC-TEM and HRTEM images of the Ru particle material in Comparative Example 3. DETAILED DESCRIPTION

[0047] The present invention is described in detail below in conjunction with embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, some adjustments and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0048] Example 1

[0049] Metal ruthenium single-atom catalyst material with directional confined growth in micropores; its preparation process is as follows Figure 1 As shown, including:

[0050] (1) Pretreatment: 2g of polyacrylonitrile was mixed with 0.07g of pore-forming agent potassium hydroxide (KOH), and 20mL of N,N-dimethylformamide (DMF) was added. The mixture was stirred at 50°C for 12h to form a uniform solution. The polymer solution was loaded into a syringe, and a voltage of 25kV was applied at a flow rate of 0.8mL / h. As the strength of the external electric field increased, the charged droplets were gradually elongated due to the action of electrostatic force, and finally formed polymer nanofibers on the collection device. After pyrolysis at 800°C in an inert atmosphere for 1h, the obtained polymer nanofibers were carbonized and their graphitization degree increased. At the same time, since KOH can react with carbon rings at high temperatures, a large number of microporous / mesoporous hierarchical pore structures are formed in the fibers. The prepared carbon nanofibers were washed with 5mL of water, methanol, and ethanol in a gradient manner to remove excess pore-forming agents and impurities, and then vacuum dried at 110°C for 36h to obtain carbon nanofibers with dry microporous / mesoporous hierarchical pore structures, such as Figure 2 As shown. The pore size distribution of the obtained carbon nanofibers is 0.8 to 2.2 nm. Figure 3 shown.

[0051] (2) Capillary adsorption process: 200 mg of porous carbon nanofibers and 10 mL of water were added to a vacuum mixer. At the same time, 15 mg of tri-(1,10-phenanthroline) ruthenium chloride was added as the adsorbent (the maximum diameter of this molecule is about ~1.2 nm). After addition, the adsorbent will dissolve in water to form a mixed aqueous solution. Under a vacuum environment, the material was fully stirred for 12 hours, and the metal organic group was absorbed into the porous carbon fiber. After natural drying for 3 days, a metal-carbon mixture was obtained.

[0052] (3) Pyrolysis process: The obtained metal-carbon mixture material is placed in an inert atmosphere and pyrolyzed at 700°C for 2 hours with a heating rate of 5°C / min. The metal organic groups are pyrolyzed and anchored on the support to form a highly active and stable Ru single-atom catalyst with directional confined growth in micropores. Figure 4 This is the spherical aberration diagram of the Ru atomic-level dispersed catalyst in Example 1. The Ru metal is dispersed on the carrier in the form of single atoms. At this time, the Ru content is 1.52 wt%.

[0053] Example 2

[0054] Metal ruthenium cluster catalyst material with directional confined growth in micropores

[0055] (1) Pretreatment: 2g of polyacrylonitrile was mixed with 0.02g of pore-forming agent ammonium chloride (NH4Cl), and 20mL of N,N-dimethylformamide (DMF) was added. The mixture was stirred at 50°C for 12h to form a uniform solution. The polymer solution was loaded into a syringe, and a voltage of 25kV was applied at a flow rate of 0.8mL / h. As the strength of the external electric field increased, the charged droplets were gradually elongated due to the action of electrostatic force, and finally formed polymer nanofibers on the collection device. After pyrolysis at 800°C in an inert atmosphere for 1.5h, the obtained polymer nanofibers were carbonized and their graphitization degree increased. At the same time, since NH4Cl would melt and become a molten state, it would penetrate into the carbon source and generate a large number of microporous / mesoporous hierarchical channels in the carbon fibers. The prepared carbon nanofibers were washed with 10mL of water, methanol, and ethanol in a gradient manner to remove excess pore-forming agents and impurities, and then dried at 110°C in a vacuum oven for 24h to obtain carbon nanofibers with a dry microporous / mesoporous hierarchical channel structure, such as Figure 5 As shown. The pore size distribution of the obtained carbon nanofibers is 0.4 to 2.5 nm. Figure 3 shown.

[0056] (2) Capillary adsorption process: 200 mg of porous carbon nanofibers and 10 mL of water were added to a vacuum mixer. At the same time, 15 mg of tri-(1,10-phenanthroline) ruthenium chloride (C 36 H 24Cl2N6Ru) is used as the adsorbent. After addition, the adsorbent will dissolve in water to form a mixed aqueous solution. Under vacuum, the material is fully stirred for 12 hours, and the metal organic group is absorbed into the porous carbon fiber. Natural drying for 3 days, a metal-carbon mixture is obtained.

[0057] (3) Pyrolysis process: The obtained metal-carbon mixture material is placed in an inert atmosphere and pyrolyzed at 700°C for 2 hours with a heating rate of 5°C / min. The metal organic groups are pyrolyzed and anchored on the support to form Ru cluster catalysts with high activity and stability and directional confined growth in micropores. Figure 6 This is a spherical aberration diagram of the Ru cluster dispersed catalyst in Example 2. The Ru metal is dispersed on the carrier in the form of small clusters. At this time, the Ru content is 1.53 wt%.

[0058] Example 3

[0059] Metal ruthenium cluster catalyst material with directional confined growth in micropores

[0060] (1) Pretreatment: 2g polyacrylonitrile was mixed with 0.07g pore-forming agent potassium hydroxide (KOH), and 20mL N,N-dimethylformamide (DMF) was added. The mixture was stirred at 50°C for 12h to form a uniform solution. The polymer solution was loaded into a syringe, and a voltage of 25kV was applied at a flow rate of 0.8mL / h. As the strength of the applied electric field increased, the charged droplets were gradually elongated due to the electrostatic force, and finally polymer nanofibers were formed on the collection device. After pyrolysis at 800°C in an inert atmosphere for 1h, the prepared carbon nanofibers were washed with 5mL of water, methanol, and ethanol in a gradient manner to remove excess pore-forming agents and impurities, and then vacuum dried at 110°C for 36h to obtain carbon nanofibers with a dry microporous / mesoporous hierarchical pore structure. The pore size distribution of the obtained carbon nanofibers was 0.8-2.2nm.

[0061] (2) Capillary adsorption process: 200 mg of porous carbon nanofibers and 10 mL of ethanol were added to a vacuum mixer. At the same time, 15 mg of tri-(1,10-phenanthroline) ruthenium chloride was added as the adsorbent. After addition, the adsorbent will dissolve in the ethanol to form a mixed ethanol solution. Under a vacuum environment, the material was fully stirred for 12 hours, and the metal organic groups were absorbed into the porous carbon fibers. After natural drying for 3 days, a metal-carbon mixture was obtained.

[0062] (3) Pyrolysis process: The obtained metal-carbon mixture material is placed in an inert atmosphere and pyrolyzed at 700°C for 2 hours with a heating rate of 5°C / min. The metal organic groups are pyrolyzed and anchored on the support to form Ru cluster catalysts with high activity and stability and directional confined growth in micropores. Figure 7This is a spherical aberration diagram of the Ru cluster dispersed catalyst in Example 3. The Ru metal is dispersed on the carrier in the form of small clusters. At this time, the Ru content is 1.53 wt%.

[0063] Example 4

[0064] Directed confined growth of metallic iron single atom catalyst materials in micropores

[0065] (1) Pretreatment: 2g of polyacrylonitrile was mixed with 0.04g of pore-forming agent potassium carbonate (K2CO3), and 20mL of N,N-dimethylformamide (DMF) was added. The mixture was stirred at 50°C for 12h to form a uniform solution. The polymer solution was loaded into a syringe, and a voltage of 25kV was applied at a flow rate of 0.8mL / h. As the strength of the external electric field increased, the charged droplets were gradually elongated due to the action of electrostatic force, and finally polymer nanofibers were formed on the collection device. After pyrolysis at 800°C in an inert atmosphere for 2h, the obtained polymer nanofibers were carbonized and their graphitization degree increased. At the same time, since potassium carbonate decomposes at high temperature to generate KOH and K2O, the carbon material is etched to form a developed pore structure. The prepared carbon nanofibers were washed with 10mL of water, methanol, and ethanol in a gradient manner to remove excess pore-forming agents and impurities, and then vacuum dried at 110°C for 36h to obtain carbon nanofibers with a dry microporous / mesoporous hierarchical pore structure, such as Figure 8 As shown. The pore size distribution of the carbon nanofibers obtained at this time is 2 to 4 nm, as shown Figure 3 shown.

[0066] (2) Capillary adsorption process: 200 mg of porous carbon nanofibers and 10 mL of water were added to a vacuum mixer. At the same time, 35 mg of o-phenanthroline ferrous complex (the maximum diameter of this molecule is about ~1.2 nm) was added as the adsorbent. After addition, the adsorbent will dissolve in water to form a mixed aqueous solution. Under a vacuum environment, the material was fully stirred for 12 hours, and the metal organic group was absorbed into the porous carbon fiber. Natural drying for 3 days gave a metal-carbon mixture.

[0067] (3) Pyrolysis process: The obtained metal-carbon mixture material is placed in an inert atmosphere and pyrolyzed at 800°C for 1 hour with a heating rate of 5°C / min. The Fe-containing metal organic groups are pyrolyzed and anchored on the support to form a Fe single atom catalyst with directional confined growth in the micropores. Fig. 9 This is the spherical aberration diagram of the Fe single-atom dispersed catalyst in Example 4. The Fe metal is dispersed on the carrier in the form of single atoms. At this time, the Fe content is 4.92wt%.

[0068] Example 5

[0069] Metallic iron cluster catalyst materials

[0070] (1) Pretreatment: 2g polyacrylonitrile was mixed with 0.04g pore-forming agent potassium carbonate (K2CO3), 20mL N,N-dimethylformamide (DMF) was added, and stirred at 50°C for 12h to form a uniform solution. The polymer solution was loaded into a syringe, and a voltage of 25kV was applied at a flow rate of 0.8mL / h. Under the action of the electric field, polymer nanofibers were finally formed on the collection device. After pyrolysis at 800°C in an inert atmosphere for 2h, carbon fibers with a developed pore structure were obtained. The prepared carbon nanofibers were washed with 10mL of water, methanol, and ethanol in a gradient manner to remove excess pore-forming agents and impurities, and vacuum dried at 110°C to obtain carbon nanofibers with a dry microporous / mesoporous hierarchical pore structure. The pore size distribution of the carbon nanofibers obtained at this time was 2 to 4nm.

[0071] (2) Capillary adsorption process: 200 mg of porous carbon nanofibers and 10 mL of acetone were added to a vacuum mixer. At the same time, 35 mg of o-phenanthroline ferrous complex was added as the adsorbent. After addition, the adsorbent will dissolve in acetone to form a mixed acetone solution. The surface tension and dielectric constant of acetone are much smaller than those of water, and the capillary adsorption force is relatively low. The material was fully stirred for 12 hours under vacuum. After natural drying for 3 days, a metal-carbon mixture was obtained.

[0072] (3) Pyrolysis process: The obtained metal-carbon mixture material is placed in an inert atmosphere and pyrolyzed at 800°C for 1 hour with a heating rate of 5°C / min. The Fe-containing metal organic group is pyrolyzed to form a Fe cluster catalyst with directional confined growth in the micropores. Fig.10 This is the spherical aberration diagram of the Fe cluster dispersed catalyst in Example 5. The Fe metal is anchored on the carbon support in the form of clusters. At this time, the Fe content is 4.95wt%.

[0073] Comparative Example 1

[0074] Ruthenium metal particle catalyst material

[0075] (1) Pretreatment: Add 2g of polyacrylonitrile to 20mL of N,N-dimethylformamide (DMF), stir at 50°C for 12h, and dissolve to form a solution. Load the polymer solution into a syringe, apply a voltage of 25kV, and the flow rate is 0.8mL / h. Under the action of the electric field, polymer nanofibers are finally formed on the collection device. After pyrolysis at 800°C in an inert atmosphere for 1h, the obtained polymer nanofibers are carbonized. The prepared carbon nanofibers are washed with 5mL of water, methanol, and ethanol in a gradient manner, and then vacuum dried at 110°C for 36h to obtain carbon nanofibers without micropores / mesopores, and their pore size distribution is as follows: Figure 3 shown.

[0076] (2) Capillary adsorption process: 200 mg of carbon nanofibers and 10 mL of water were added to a vacuum mixer. At the same time, 15 mg of tri-(1,10-phenanthroline) ruthenium chloride was added as the adsorbent. After addition, the adsorbent will dissolve in water to form a mixed aqueous solution. Under vacuum conditions, the material was fully stirred for 12 hours and naturally dried for 3 days. The metal organic groups were simply attached to the surface of the carbon fibers to obtain a metal-carbon mixture.

[0077] (3) Pyrolysis process: The obtained metal-carbon mixture material is placed in an inert atmosphere and pyrolyzed at 700°C for 2 hours with a heating rate of 5°C / min. The metal organic group is pyrolyzed to form a catalyst having Ru particles. Fig.11 The spherical aberration and TEM image of the Ru particle material in Comparative Example 1 show that the Ru metal migrates and aggregates severely during the pyrolysis process to form Ru particles, and the Ru content is 1.50 wt%.

[0078] Comparative Example 2

[0079] Ruthenium metal particle catalyst material

[0080] (1) Pretreatment: 2g of polyacrylonitrile was mixed with 0.07g of pore-forming agent potassium hydroxide (KOH), 20mL of N,N-dimethylformamide (DMF) was added, and stirred at 50°C for 12h to form a uniform solution. The polymer solution was loaded into a syringe, and a voltage of 25kV was applied at a flow rate of 0.8mL / h. After the electric field was applied, polymer nanofibers were finally formed on the collection device. After pyrolysis at 800°C in an inert atmosphere, a large number of carbon nanofibers with microporous / mesoporous hierarchical pore structures were obtained. The prepared carbon nanofibers were washed with 5mL of water, methanol, and ethanol in a gradient manner to remove excess pore-forming agents and impurities, and vacuum dried at 110°C for 36h to obtain carbon nanofibers with dry microporous / mesoporous hierarchical pore structures. The pore size distribution of the obtained carbon nanofibers was 0.8-2.2nm.

[0081] (2) Capillary adsorption process: 200 mg of porous carbon nanofibers and 10 mL of propanol were added to a vacuum mixer. At the same time, 15 mg of tri-(1,10-phenanthroline) ruthenium chloride was added as the adsorbent. After addition, the adsorbent will dissolve in the propanol to form a mixed propanol solution. Under a vacuum environment, the material is fully stirred for 12 hours. The surface tension and dielectric constant of propanol are much smaller than those of water, and the capillary adsorption force is relatively low. Therefore, the metal organic group will not be absorbed into the pores of the porous carbon fiber, but will be attached to the fiber surface through Π-Π adsorption. Natural drying for 3 days will give a metal-carbon mixture. The change in the phenanthroline content in the solution before and after adsorption is shown in Figure 2. Fig.12 As shown in the figure, in the water mixed solution, the phenanthroline content in the solution completely disappears after the capillary adsorption process, while in the propanol mixed solution, the phenanthroline in the solution still exists in large quantities after the capillary adsorption process.

[0082] (3) Pyrolysis process: The obtained metal-carbon mixture material is placed in an inert atmosphere and pyrolyzed at 700°C for 2 hours with a heating rate of 5°C / min. The metal organic group is pyrolyzed to form a catalyst with Ru particles. Fig.13 This is the spherical aberration diagram of the Ru particle material in Comparative Example 2. The Ru metal migrates and aggregates severely during the pyrolysis process to form Ru particles. At this time, the Ru content is 1.52 wt%.

[0083] Comparative Example 3

[0084] Ruthenium metal particle catalyst material

[0085] (1) Pretreatment: Commercial carbon nanotubes were selected as the carbon source, washed with 5 mL of water, methanol, and ethanol in a gradient manner, and dried at 110° C. in a vacuum oven for 24 h to obtain dry carbon nanotubes with a diameter distribution of 8 to 10 nm.

[0086] (2) Capillary adsorption process: 200 mg of carbon nanotubes and 10 mL of water were added to a vacuum mixer. At the same time, 15 mg of tris-(1,10-phenanthroline) ruthenium chloride was added as the adsorbent. After addition, the adsorbent was dissolved in water to form a mixed aqueous solution. The material was fully stirred for 12 hours under vacuum and then dried naturally for 3 days.

[0087] (3) Pyrolysis process: The obtained metal-carbon mixture material is placed in an inert atmosphere and pyrolyzed at 700°C for 2 hours with a heating rate of 5°C / min. The metal organic group is pyrolyzed to form a catalyst with Ru particles. Fig.14 The spherical aberration and HRTEM image of the Ru particle material in Comparative Example 3 show that the Ru metal migrates and aggregates severely during the pyrolysis process to form Ru particles, and the Ru content is 1.53 wt%.

[0088] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A metal atomic-level dispersed catalyst material with directional confined growth in micropores, characterized in that: The carbon material is a carbon nanofiber with a microporous / mesoporous hierarchical pore structure, and metal atoms exist in the pores of the carbon carrier in the form of atomic dispersion.

2. The metal atomic-level dispersed catalyst material with directional confined growth in micropores according to claim 1, characterized in that: The atomic dispersion includes single atom dispersion or dispersion in the form of atomic clusters; the particle size of the atomic clusters is 1 to 5 nm.

3. A method for preparing a metal atomic-level dispersed catalyst material with directional confined growth in micropores according to claim 1 or 2, characterized in that: The method comprises the following steps: S1. Pretreatment: Mix the polymer precursor and the pore-forming agent, add a solvent to dissolve and stir to form a uniform solution, and form polymer nanofibers under the action of an electric field by electrospinning technology; obtain carbon nanofibers by high-temperature pyrolysis; wash the carbon nanofibers with a gradient of water and an organic solvent and vacuum dry them to remove excess pore-forming agent and impurities, and obtain carbon nanofibers with a dry microporous / mesoporous hierarchical pore structure; S2, capillary adsorption process: vacuum mixing the carbon nanofibers obtained in step S1 and solutions with different surface tensions, and adding a metal organic group with a size smaller than the pore size of the carbon nanofiber as an adsorbent; fully stirring under a vacuum environment, the metal organic group is absorbed into the porous carbon fiber; and naturally drying to obtain a metal-carbon mixture; S3, pyrolysis treatment process: the metal-carbon mixture material obtained in S2 is placed in an inert atmosphere for pyrolysis treatment; the metal organic group is pyrolyzed and anchored on the carrier to form atomic-level dispersed materials such as single atoms and clusters.

4. The method for preparing a metal atomic-level dispersed catalyst material with directional confined growth in micropores according to claim 3, characterized in that: The polymer precursor is polyacrylonitrile; the pore-forming agent is one or more of potassium hydroxide, potassium carbonate, ammonium chloride and sodium chloride.

5. The method for preparing a metal atomic-level dispersed catalyst material with directional confined growth in micropores according to claim 3, characterized in that: In step S1, the usage ratio of polymer precursor, pore former and solvent is 2 g: 0.01-0.1 g: 20 mL.

6. The method for preparing a metal atomic-level dispersed catalyst material with directional confined growth in micropores according to claim 3, characterized in that: In step S1, the temperature of the high temperature pyrolysis is 800°C, and the time is 1 to 2 hours; the temperature of the vacuum drying is 110°C, and the time is 24 to 36 hours; the solvent includes N,N-dimethylformamide; and the organic solvent is an alcohol solvent, including methanol and ethanol.

7. The method for preparing a metal atomic-level dispersed catalyst material with directional confined growth in micropores according to claim 3, characterized in that: The pore size of the carbon nanofibers prepared in step S1 is controlled to be 0.5-5 nm.

8. The method for preparing a metal atomic-level dispersed catalyst material with directional confined growth in micropores according to claim 3, characterized in that: The solutions with different surface tensions are one or more of water, methanol, ethanol, acetone, dimethylformamide, N-methyl-2-pyrrolidone, and cyclohexane; the metal organic group is an organic chelate molecular group containing precious metals and non-precious metals, including an organic chelate molecular group containing ruthenium, iron, cobalt or nickel.

9. The method for preparing a metal atomic-level dispersed catalyst material with directional confined growth in micropores according to claim 3, characterized in that: In step S2, the usage ratio of carbon nanofiber, solution with different surface tensions, and metal organic matter is 200 mg:10 mL:15-35 mg.

10. The method for preparing a metal atomic-level dispersed catalyst material with directional confined growth in micropores according to claim 3, characterized in that: The temperature of the pyrolysis treatment is 700-800° C., and the time is 0.5-2 hours.

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