Integrated preparation method and application of nitrogen-doped carbon nanotube loaded transition metal catalyst based on plasma

Abstract

The invention provides an integrated preparation method and application of a nitrogen-doped carbon nanotube loaded transition metal catalyst based on plasma, and the integrated preparation method comprises the following steps: dissolving an excessive nitrogen-containing organic compound in a 50% ethanol aqueous solution to a saturated state to obtain a solution A; mixing the solution A, carbon nanotubes and transition metal salt, and then performing vacuum drying treatment to obtain a powdery precursor B; uniformly mixing the powdery precursor B with deionized water until the mixture is in a semi-fluid state; pressing the semi-fluid state mixture into a cylindrical solid as a negative electrode, generating direct-current arc plasma between the negative electrode and a positive electrode to form carbon nanotube dispersion mist, and realizing nitrogen-doped modification of the carbon nanotubes and uniform loading of transition metal on the surfaces of the carbon nanotubes at the same time; the problems that in the prior art, high-melting-point metal is difficult to vaporize, condense and load, and active sites are insufficient and particles are difficult to load uniformly due to strong chemical inertness of the surface of the carbon nano tube are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst material preparation, and particularly relates to an integrated preparation method and application of a transition metal catalyst supported on nitrogen-doped carbon nanotubes based on plasma. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance some understanding of the overall background of the present disclosure, and does not necessarily constitute an admission or imply in any form that this information forms the prior art already known to those of ordinary skill in the art.

[0003] Heteroatom-doped carbon materials supported transition metal catalysts have become good substitutes for noble metal catalysts and received extensive attention due to their advantages such as good stability, low cost, and high activity. Among many carbon materials, carbon nanotubes (CNT) have a large aspect ratio and specific surface area, strong thermal stability, and specific catalytic properties due to their radial conduction effect, making them widely studied in fuel cell catalysts. However, CNT has strong surface chemical inertness and is prone to agglomeration, resulting in poor electrochemical activity when directly used as a fuel cell catalyst. Therefore, chemical modification of the CNT surface is an important means to enhance its electrochemical performance and promote its large-scale application.

[0004] Currently, the preparation methods for heteroatom-doped carbon nanotube supported transition metal catalysts usually adopt in-situ growth strategies. There is a technique that heats waste plastic powder and an iron-based catalyst in an inert atmosphere to pyrolyze the waste plastic and deposit carbon nanotubes on the surface of the iron-based catalyst. After purification, it is mixed and ground with a nitrogen-containing compound and thermally decomposed in a secondary inert atmosphere to obtain an Fe-N-CNT catalyst. Although this method is beneficial for the treatment of waste plastics, it has high requirements for the selection of pyrolysis catalysts and the control of conditions during the pyrolysis process. Whether it is applicable to the preparation of other transition metal catalysts supported on nitrogen-doped carbon nanotubes remains to be considered. There is a technique that induces the assembly of hemin on a template through olefin oxidation polymerization and π-π stacking effect, and prepares an Fe-N-CNT catalyst after carbonization. Similar to most in-situ growth methods, this method has high requirements for the preparation process and is not conducive to large-scale preparation.

[0005] Publication No. CN 113809304 B prepared a tin dioxide / carbon nanotube composite material by post-treating carbon nanotubes. However, this technology used low-melting-point metal tin powder as the raw material, and the preparation principle and process were the vaporization, condensation, and loading of low-melting-point metal tin powder under heating, but high-melting-point metals were not considered. At the same time, this technology could not achieve the surface modification of carbon nanotubes and could not solve the problems of insufficient active sites caused by the strong surface chemical inertness of carbon nanotubes and the difficulty of uniform particle loading, which limited this technology in the preparation of transition metal catalysts supported on nitrogen-doped carbon nanotubes.

[0006] In view of this, the present application is specifically proposed. Summary of the Invention

[0007] The object of the present invention is to provide an integrated preparation method and application of a transition metal catalyst supported on nitrogen-doped carbon nanotubes based on plasma, which solves the problems of difficult vaporization, condensation, and loading of high-melting-point metals and insufficient active sites and difficult uniform particle loading caused by the strong surface chemical inertness of carbon nanotubes in the background technology. Moreover, the present invention can integrally achieve the surface nitrogen doping modification of carbon nanotubes and the uniform loading of transition metal catalysts on their surfaces.

[0008] The integrated preparation method of a transition metal catalyst supported on nitrogen-doped carbon nanotubes based on plasma provided by the present invention can utilize the thermal effect of plasma to slightly damage the surface structure of carbon nanotubes and pyrolyze transition metal salts and nitrogen-containing compounds, so as to achieve the purpose of surface nitrogen doping modification of carbon nanotubes and nanoparticle loading. The surface nitrogen doping modification of carbon nanotubes not only increases the active sites but also is conducive to the uniform loading of transition metals on their surfaces. The whole process involves the chemical change process of materials, avoids the difficult vaporization of high-melting-point metals, covers a variety of methods to increase the active sites on the surface of carbon nanotubes, and achieves the purpose of loading transition metal catalysts while realizing the nitrogen doping modification of carbon nanotubes.

[0009] To solve the above problems, the technical solution adopted by the present invention is:

[0010] An integrated preparation method of a transition metal catalyst supported on nitrogen-doped carbon nanotubes based on plasma, comprising the following steps:

[0011] S1: Dissolve an excessive amount of nitrogen-containing organic compounds in a 50% ethanol aqueous solution until saturated to obtain solution A;

[0012] S2: Uniformly mix solution A, carbon nanotubes, and transition metal salts in a certain proportion, and then perform vacuum drying treatment to obtain a powdery precursor B;

[0013] S3: Uniformly mix the powdery precursor B with deionized water until it reaches a semi-fluid state; press the semi-fluid state mixture into a cylindrical solid;

[0014] S4: Use the cylindrical solid material prepared in step S3 as the negative electrode, and use a refractory conductive material as the positive electrode. Connect the negative electrode and the positive electrode to the power supply respectively; place the negative electrode and the positive electrode in a closed box, introduce gas and maintain it to the preset pressure;

[0015] S5: Turn on the power supply, a DC arc plasma is generated between the negative electrode and the positive electrode, forming a carbon nanotube dispersion mist. And the carbon nanotube structure is pretreated, while the nitrogen-containing organic compound and the transition metal salt are pyrolytically reduced; realizing the nitrogen doping modification of the carbon nanotubes and the uniform loading of the transition metal on the surface of the carbon nanotubes at the same time, forming a nitrogen-doped carbon nanotube-supported transition metal dispersion mist;

[0016] S6: Collect the nitrogen-doped carbon nanotube-supported transition metal dispersion mist prepared in step S5, and obtain a nitrogen-doped carbon nanotube-supported transition metal catalyst after drying.

[0017] Preferably, the nitrogen-containing organic compound is one of melamine and urea.

[0018] Preferably, the transition metal salt is one of cobalt acetylacetonate, iron acetylacetonate, nickel acetylacetonate, cobalt chloride, iron chloride, and nickel chloride.

[0019] Preferably, in step S6, collecting the nitrogen-doped carbon nanotube-supported transition metal dispersion mist prepared in step S5 specifically means using a negative pressure fan to collect the dispersion mist obtained in S5.

[0020] Preferably, solution A, carbon nanotubes, and transition metal salt are in a ratio of 8:1:1 to 2.

[0021] Preferably, the distance between the refractory conductive material of the positive electrode and the cylindrical solid material of the negative electrode is 0.5 - 2 mm.

[0022] Preferably, the gas is one of nitrogen and argon, and the pressure is one atmosphere.

[0023] Preferably, the refractory conductive material is one of tungsten wire, graphite, copper, and iron.

[0024] Preferably, the mixing ratio of the powdery precursor B to deionized water is 1:4 to 5.

[0025] An application of a plasma-based nitrogen-doped carbon nanotube-supported transition metal catalyst, the application of the plasma-based nitrogen-doped carbon nanotube-supported transition metal catalyst in the oxygen reduction reaction of the fuel cell negative electrode.

[0026] The beneficial effects of the present invention are:

[0027] 1. An integrated preparation method of a transition metal catalyst supported on nitrogen-doped carbon nanotubes based on plasma according to the present invention does not require strong acid treatment or secondary heat treatment, and has the advantages of simple, fast, and macroscale preparation processes. It can achieve uniform and stable loading of transition metal catalytic particles on the surface of carbon nanotubes while nitrogen-doping and dispersing the carbon nanotubes. The transition metal-N-CNT catalyst can be used for the oxygen reduction reaction at the cathode of a fuel cell, and its electrocatalytic activity can be comparable to that of commercial platinum-carbon catalysts, showing broad potential.

[0028] 2. By means of the thermal effect of plasma, the present invention realizes slight damage to the surface structure of carbon nanotubes, pyrolysis of transition metal salts and nitrogen-containing compounds, achieving the purpose of nitrogen-doping modification of the carbon nanotube surface and uniform loading of transition metals on the carbon nanotube surface, solving the problem of loading high-melting-point metals on the carbon nanotube surface and being unable to simultaneously achieve nitrogen-doping modification of the carbon nanotube surface. The whole process is mainly a chemical loading process of transition metals on the carbon nanotube surface, rather than just a physical loading. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Scanning electron microscope image (SEM) of Co / N-CNT-P prepared according to the present invention;

[0030] Figure 2 Transmission electron microscope image (TEM) of Co / N-CNT-P prepared according to the present invention;

[0031] Figure 3 Particle size distribution diagram of metal nanoparticles in Co / N-CNT-P prepared according to the present invention; Separated from the figure

[0032] Figure 4 X-ray diffraction (XRD) of Co / N-CNT-P prepared according to the present invention;

[0033] Figure 5 X-ray photoelectron spectroscopy (XPS) of Co / N-CNT-P prepared according to the present invention;

[0034] Wherein: (a) is the full XPS spectrum of the Co / N-CNT-P catalyst; (b) is the high-resolution C1s spectrum of the Co / N-CNT-P catalyst; (c) is the high-resolution Co 2p spectrum of the Co / N-CNT-P catalyst; (d) is the high-resolution N1s spectrum of the Co / N-CNT-P catalyst;

[0035] Figure 6 Oxygen reduction performance test of Co / N-CNT-P prepared according to the present invention and commercial platinum-carbon catalyst (JM-Pt / C);

[0036] Among them: (e) are the CV curves of Co / N-CNT-P and JM-Pt / C catalysts; (f) are the LSV curves of Co / N-CNT-P and JM-Pt / C catalysts; (g) are the initial potential and half-wave potential of Co / N-CNT-P and JM-Pt / C catalysts; (h) are the Tafel slopes of Co / N-CNT-P and JM-Pt / C catalysts obtained from the LSV curves. Detailed implementation manners

[0037] To clearly illustrate the technical features of this solution, the following will elaborate on this solution through specific implementation manners and in combination with its accompanying drawings.

[0038] It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanations for the present disclosure. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present disclosure belongs.

[0039] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0040] Example

[0041] I. Preparation of transition metal catalysts supported on nitrogen-doped carbon nanotubes

[0042] An integrated preparation method of a transition metal catalyst supported on nitrogen-doped carbon nanotubes based on plasma includes the following steps:

[0043] S1: Dissolve an excessive amount of nitrogen-containing organic compound in 50% ethanol aqueous solution until saturated to obtain solution A;

[0044] S2: Uniformly mix solution A, carbon nanotubes, and transition metal salt in a mass ratio of 8:1:1, and then perform vacuum drying treatment to obtain a powdery precursor B; In the embodiments of the present application, the transition metal salt is cobalt acetylacetonate.

[0045] S3: Uniformly mix the powdery precursor B and deionized water in a mass ratio of 1:5 until it becomes a semi-fluid state; Press the semi-fluid state mixture into a cylindrical solid;

[0046] S4: Use the cylindrical solid material prepared in step S3 as the negative electrode, and use a refractory conductive material as the positive electrode. Connect the negative electrode and the positive electrode to the power supply correspondingly; place the negative electrode and the positive electrode in a closed box, introduce a gas and maintain it at a preset pressure; the distance between the refractory conductive material of the positive electrode and the cylindrical solid material of the negative electrode is 0.5 - 2 mm.

[0047] Specifically, the gas can be nitrogen or argon, etc., non-explosive and non-flammable gases, and the pressure is one atmosphere.

[0048] Specifically, the positive electrode of the power supply uses a tungsten wire, and materials such as graphite, copper, and iron can also be used.

[0049] S5: Turn on the power supply, a direct current arc plasma is generated between the negative electrode and the positive electrode, forming a carbon nanotube dispersion mist, and the carbon nanotube structure is damaged to a certain extent for pretreatment. At the same time, the nitrogen-containing organic compound and the transition metal salt are pyrolyzed and reduced; realizing the nitrogen doping modification of the carbon nanotubes and the uniform loading of the transition metal on the surface of the carbon nanotubes simultaneously, forming a nitrogen-doped carbon nanotube supported transition metal dispersion mist;

[0050] S6: Use a negative pressure fan to collect the nitrogen-doped carbon nanotube supported transition metal dispersion mist prepared in step S5, and obtain a nitrogen-doped carbon nanotube supported transition metal catalyst after drying.

[0051] II. Application of the preparation of the nitrogen-doped carbon nanotube supported transition metal catalyst

[0052] Based on the application of the preparation of the nitrogen-doped carbon nanotube supported transition metal catalyst by plasma, apply the nitrogen-doped carbon nanotube supported transition metal catalyst based on plasma of the present invention to the oxygen reduction reaction of the fuel cell cathode.

[0053] Electrochemical performance test

[0054] The electrochemical performance is carried out under the following conditions: Weigh 2.5 mg of the nitrogen-doped carbon nanotube supported transition metal cobalt catalyst prepared in the example, disperse it into 470 μL and 30 μL of 5 wt% Nafion solution, and ultrasonically disperse for 2 h. Then take 5 μL of the above ultrasonically dispersed uniform catalyst suspension and coat it on the surface of the alumina polished glassy carbon electrode, and dry it naturally at room temperature. After the solution is completely volatilized, it is used as the working electrode. Then use a platinum wire and a saturated calomel electrode as the counter electrode and the reference electrode respectively, and measure its oxygen reduction activity in 0.1 mol / L KOH solution by linear sweep voltammetry.

[0055] Figures 1 to 3Morphology characterization diagram of the Co / N-CNT-P catalyst prepared according to the present invention. It can be seen from the SEM diagram that the surface of the carbon nanotubes shows a rough surface structure, indicating that the structure of the carbon nanotubes is damaged to a certain extent under the action of plasma; it can be clearly seen from the TEM diagram that Co metal nanoparticles are uniformly loaded on the surface of the carbon nanotubes, Figure 3 showing that the Co metal nanoparticles exhibit a uniform particle size distribution.

[0056] Figure 4 XRD pattern of the Co / N-CNT-P catalyst prepared according to the present invention. Its diffraction peaks can all correspond to the standard cards, indicating that cobalt acetylacetonate is successfully pyrolyzed under the action of plasma to form metal nanoparticles loaded on the surface of carbon nanotubes.

[0057] Figure 5 XPS spectrum of the Co / N-CNT-P catalyst prepared according to the present invention. It can be seen from Figure (a) that 4 obvious main peaks appear at 284.8, 400, 532 eV and 782 eV respectively, corresponding to the characteristic peaks of C1s, O 1s, N 1s and Co 2p respectively, indicating that nitrogen elements are successfully incorporated into the carbon nanotubes and indicating the presence of metallic Co. Figure (b) is the high-resolution C1s spectrum, which is decomposed into 4 peaks, corresponding to C-C (284.8 eV), C=N (285.9 eV), C-N (287.4 eV) and O=C-O (291.2 eV) respectively. Figure (c) is the high-resolution N1s spectrum, which is decomposed into 4 peaks, corresponding to pyridinic-N (398.8 eV), Co-N (400.2 eV), graphitic-N (401.9 eV) and oxidated N (404.3 eV) respectively. Figure (d) is the high-resolution Co 2p spectrum, which is decomposed into metallic Co (778.5 eV and 793.8 eV) and Co-N x of 2p 3 / 2 and 2p 1 / 2 (781.6 eV and 796.7 eV). The results in the figure confirm the existence of Co-N chemical bonds, which are generally considered to be the active sites for the oxygen reduction of the catalyst.

[0058] Figure 6Electrochemical performance test results of the Co / N-CNT-P catalyst and JM-Pt / C catalyst prepared for this invention. As can be seen from the CV curve in Figure (e), an oxygen reduction peak appears at about 0.81V for the catalyst, indicating catalytic activity for the oxygen reduction reaction. The LSV curve in Figure (f) shows that the oxygen reduction polarization curve of the Co / N-CNT-P catalyst is nearly coincident with that of the JM-Pt / C catalyst, demonstrating comparable electrocatalytic oxygen reduction activity to the JM-Pt / C catalyst. Figure (g) quantifies the onset potential (E onset ) and half-wave potential (E 1 / 2 ) of the Co / N-CNT-P catalyst and JM-Pt / C catalyst. It can be seen that the onset potential of both the Co / N-CNT-P catalyst and JM-Pt / C catalyst is 1.01V, and the half-wave potentials are 0.836V and 0.841V respectively, indicating that the Co / N-CNT-P catalyst has electrocatalytic oxygen reduction properties comparable to those of the JM-Pt / C catalyst. Figure (h) shows the Tafel slopes of the Co / N-CNT-P catalyst and JM-Pt / C catalyst, which are 83.6 mV dec -1 and 84.3 mV dec -1 respectively, indicating that the Co / N-CNT-P catalyst has an equally strong kinetic process during the oxygen reduction process compared to the JM-Pt / C catalyst.

[0059] In summary, for the preparation method of the transition metal catalyst supported by nitrogen-doped carbon nanotubes in this invention, with the help of the thermal effect of the plasma, slight damage to the surface structure of the carbon nanotubes, pyrolysis of the transition metal salt and nitrogen-containing compound are realized, achieving the purpose of nitrogen doping modification on the surface of the carbon nanotubes and uniform loading of the transition metal on the surface of the carbon nanotubes, solving the problem in the prior art that it is only limited to the loading of low-melting-point metals on the surface of the carbon nanotubes and the inability to simultaneously achieve nitrogen doping modification on the surface of the carbon nanotubes. The whole process involves the chemical loading process of the transition metal on the surface of the carbon nanotubes, rather than the simple physical loading in the prior art. This invention prepares a high-performance nitrogen-doped carbon nanotube-supported transition metal cobalt catalyst. This nitrogen-doped carbon nanotube-supported transition metal cobalt catalyst can be used for the oxygen reduction reaction at the cathode of a fuel cell, has a relatively high onset potential and half-wave potential, and its electrocatalytic activity can be comparable to that of commercial platinum carbon, with broad potential.

[0060] The above embodiments are the preferred embodiments of the present disclosure, but the embodiments of the present disclosure are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present disclosure shall be equivalent replacement methods and are all included in the protection scope of the present disclosure.

Claims

1. An integrated preparation method of a transition metal catalyst supported on nitrogen-doped carbon nanotubes based on plasma, characterized in that, It includes the following steps: S1: Dissolve an excessive amount of nitrogen-containing organic compound in 50% ethanol aqueous solution until it reaches a saturated state to obtain solution A; S2: Uniformly mix solution A, carbon nanotubes, and transition metal salt in a certain proportion, and then perform vacuum drying treatment to obtain powdery precursor B; S3: Uniformly mix the powdery precursor B with deionized water to a semi-fluid state; Press the semi-fluid state mixture into a cylindrical solid; S4: Use the cylindrical solid material prepared in step S3 as the negative electrode, and use a refractory conductive material as the positive electrode. Connect the negative electrode and the positive electrode to the power supply correspondingly; Place the negative electrode and the positive electrode in a closed box, introduce gas and maintain it to a preset pressure; S5: Turn on the power supply, generate a DC arc plasma between the negative electrode and the positive electrode to form a carbon nanotube dispersion mist, and the carbon nanotube structure is pretreated. At the same time, the nitrogen-containing organic compound and the transition metal salt are pyrolytically reduced; Realize the nitrogen doping modification of carbon nanotubes and the uniform loading of transition metals on the surface of carbon nanotubes simultaneously, forming a nitrogen-doped carbon nanotube-supported transition metal dispersion mist; S6: Collect the nitrogen-doped carbon nanotube-supported transition metal dispersion mist prepared in step S5, and obtain a nitrogen-doped carbon nanotube-supported transition metal catalyst after drying.

2. The integrated preparation method of the plasma-based transition metal catalyst supported on nitrogen-doped carbon nanotubes according to claim 1, characterized in that, The nitrogen-containing organic compound is one of melamine and urea.

3. The integrated preparation method of the plasma-based transition metal catalyst supported on nitrogen-doped carbon nanotubes according to claim 1, characterized in that, The transition metal salt is one of cobalt acetylacetonate, iron acetylacetonate, nickel acetylacetonate, cobalt chloride, iron chloride, and nickel chloride.

4. The integrated preparation method of the plasma-based transition metal catalyst supported on nitrogen-doped carbon nanotubes according to claim 1, characterized in that, In step S6, collecting the nitrogen-doped carbon nanotube-supported transition metal dispersion mist prepared in step S5 specifically means using a negative pressure fan to collect the dispersion mist obtained in S5.

5. The integrated preparation method of the plasma-based transition metal catalyst supported on nitrogen-doped carbon nanotubes according to claim 1, characterized in that, Solution A, carbon nanotubes, and transition metal salt are in a ratio of 8:1:1 - 2.

6. The integrated preparation method of the plasma-based transition metal catalyst supported on nitrogen-doped carbon nanotubes according to claim 1, characterized in that, The distance between the refractory conductive material of the positive electrode and the cylindrical solid material of the negative electrode is 0.5 - 2 mm.

7. The integrated preparation method of the plasma-based transition metal catalyst supported on nitrogen-doped carbon nanotubes according to claim 1, characterized in that, The gas is one of nitrogen and argon, and the pressure is one atmosphere.

8. The integrated preparation method of the plasma-based transition metal catalyst supported on nitrogen-doped carbon nanotubes according to claim 1, characterized in that, The refractory conductive material is one of tungsten wire, graphite, copper, and iron.

9. The integrated preparation method of the plasma-based transition metal catalyst supported on nitrogen-doped carbon nanotubes according to claim 1, characterized in that, The mixing ratio of the powdery precursor B and deionized water is 1:4 - 5.

10. Application of a transition metal catalyst supported on nitrogen-doped carbon nanotubes based on plasma, characterized in that, Application of a plasma-based nitrogen-doped carbon nanotube-supported transition metal catalyst in the oxygen reduction reaction of the fuel cell negative electrode.

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