CN110534754B - Carbon nanotube coated with Fe3C nanocrystalline and preparation method and application thereof - Google Patents

Carbon nanotube coated with Fe3C nanocrystalline and preparation method and application thereof Download PDF

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CN110534754B
CN110534754B CN201910827117.XA CN201910827117A CN110534754B CN 110534754 B CN110534754 B CN 110534754B CN 201910827117 A CN201910827117 A CN 201910827117A CN 110534754 B CN110534754 B CN 110534754B
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melamine
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carbon
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CN110534754A (en
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崔丽莉
张巧玲
何兴权
窦志宇
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Changchun University of Science and Technology
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8825—Methods for deposition of the catalytic active composition
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/9075—Catalytic material supported on carriers, e.g. powder carriers
    • H01M4/9083—Catalytic material supported on carriers, e.g. powder carriers on carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M2004/8678—Inert electrodes with catalytic activity, e.g. for fuel cells characterised by the polarity
    • H01M2004/8689—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Abstract

The invention provides a method for wrapping Fe3A carbon nano tube of C nano crystal, a preparation method and application thereof, belonging to the technical field of composite materials. Mixing an iron source, melamine, 1,3, 5-benzene tricarboxylic acid and a solvent, carrying out solvothermal reaction to obtain a metal organic framework material encapsulated with the melamine, and then sequentially carrying out pyrolysis and acid etching to obtain a coated Fe3Carbon nanotubes of C nanocrystals. Wherein, melamine is taken as object molecule, 1,3, 5-benzene tricarboxylic acid is taken as organic ligand, iron is taken as metal, the metal organic framework material which encapsulates the melamine can be formed by one-step self-assembly in the solvothermal reaction, the carbon nanotube structure is formed after the pyrolysis, and Fe is added3And C, forming a carbon nano tube packaging layer on the outer layer. The preparation method is simple, and the obtained carbon nano tube has high specific surface area, high activity and good stability, can catalyze oxygen reduction under alkaline and acidic conditions, and has good catalytic effect when used as a fuel cell cathode catalyst.

Description

Wrapped Fe3Carbon nano tube of C nano crystal and preparation method and application thereof
Technical Field
The invention relates to the technical field of composite materials, in particular to a Fe-coated composite material3A carbon nano tube of C nano crystal and a preparation method and application thereof.
Background
As the energy crisis and environmental damage have increased, fuel cells have been recognized as a new alternative to fossil fuels, and metal-air battery technology has been recognized as an efficient energy conversion technology. Efficient Oxygen Reduction Reaction (ORR) catalysts play an important role in renewable energy technology. Currently, noble metals platinum and alloys thereof exhibit excellent catalytic performance in these reactions. However, the high cost and resource shortage of these noble metal catalysts have been major factors impeding the large-scale application of these energy technologies. Therefore, it is urgent to develop a non-noble metal-based catalyst with low cost and high activity to replace a noble metal catalyst.
In recent years, some transition metal compounds such as nitrides, phosphides, oxides, and carbides, etc. have been widely studied. However, how to improve the catalytic performance of these materials remains a challenging issue in this field. The catalytic performance of the catalyst is mainly influenced by the following factors: (1) composition of the catalyst; (2) specific surface area of the catalyst; (3) pore structure of the catalyst; (4) the electrical conductivity of the material. Therefore, in order to obtain a high-performance catalyst, a material having high active sites and high specific surface area is required. The carbon nanotube of the hollow structure material has high catalytic activity and stability in the field of electrocatalysis, and becomes a research hotspot. However, carbon nanotube materials are usually formed by CVD or in H2The method is prepared by a pyrolysis method under the atmosphere, and the method has complex operation and harsh reaction conditions and is not beneficial to large-scale preparation.
Disclosure of Invention
In view of the above, the present invention aims to provide a method for wrapping Fe3The preparation method of the carbon nano tube of the C nano crystal is simple to operate, and the obtained carbon nano tube has high specific surface area and conductivity, high activity and good catalytic stability.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a method for wrapping Fe3The preparation method of the carbon nano tube of the C nano crystal comprises the following steps:
(1) mixing an iron source, melamine, 1,3, 5-benzene tricarboxylic acid and a solvent, and carrying out a solvothermal reaction to obtain a metal organic framework material packaged with the melamine;
(2) sequentially carrying out pyrolysis and acid etching on the metal organic framework material encapsulated with the melamine to obtain coated Fe3Carbon nanotubes of C nanocrystals.
Preferably, the iron source in the step (1) is a mixture of ferric chloride and ferric nitrate, and the mass ratio of the ferric chloride to the ferric nitrate in the mixture of the ferric chloride and the ferric nitrate is 1: 4-2: 1; the solvent is ethanol and/or methanol.
Preferably, the mass ratio of the iron source, the melamine and the 1,3, 5-benzene tricarboxylic acid in the step (1) is 0.01-1.36: 0.34-1.02: 0.52-1.04.
Preferably, the solvothermal reaction in the step (1) is carried out for 50-65 ℃ for 6-12 h.
Preferably, the pyrolysis temperature in the step (2) is 700-900 ℃, and the time is 1-2 h.
Preferably, the etchant for acid etching in the step (2) is an HCl solution, and the acid etching time is 12-24 hours.
Preferably, after the acid etching, the method further comprises performing post-treatment on the acid etching product, wherein the post-treatment comprises the following steps:
sequentially centrifuging, washing and drying the acid etching product to obtain the coated Fe3Carbon nanotube solids of C nanocrystals.
Preferably, the drying temperature is 40-50 ℃, and the drying time is 12-18 h.
The invention provides the coated Fe prepared by the preparation method3Carbon nanotube of C nanocrystal, the coated Fe3The specific surface area of the carbon nano tube of the C nano crystal is 295.78-465.30 m2A pore volume of 0.94 to 1.16 cm/g3The pore diameter is 3.88 to 3.94 nm.
The invention also provides the coated Fe3The carbon nanotube of C nanocrystal is applied to the cathode catalyst of the fuel cell.
The invention provides a method for wrapping Fe3The invention discloses a preparation method of a carbon nano tube of C nanocrystalline, which comprises the steps of mixing an iron source, melamine, 1,3, 5-benzenetricarboxylic acid and a solvent, carrying out solvothermal reaction to obtain a metal organic framework material encapsulated with the melamine, and then sequentially carrying out pyrolysis and acid etching on the metal organic framework material encapsulated with the melamine to obtain a coating Fe3Carbon nanotubes of C nanocrystals. In the invention, melamine is used as a guest molecule, 1,3, 5-benzene tricarboxylic acid is used as an organic ligand, iron is used as a metal, the melamine encapsulated metal organic framework material can be formed by one-step self-assembly in a solvothermal reaction, the carbon nanotube structure is formed after the organic framework material is pyrolyzed, and Fe is added3And C, forming a carbon nano tube packaging layer on the outer layer. The invention providesThe preparation method is simple, and the obtained carbon nano tube has high specific surface area and conductivity, high activity and good stability, has excellent performance of catalyzing oxygen reduction reaction under alkaline and acidic conditions, and has good catalytic effect when used as a cathode catalyst of a fuel cell.
Drawings
FIG. 1 shows Fe obtained in example 13C @ N-CNTs/800 as SEM picture;
FIG. 2 shows Fe obtained in example 13C @ N-CNTs/800 TEM picture;
FIG. 3 shows Fe obtained in example 13An XRD spectrum of C @ N-CNTs/800;
FIG. 4 shows Fe obtained in example 23SEM picture of C @ N-CNTs/700;
FIG. 5 shows Fe obtained in example 33SEM picture of C @ N-CNTs/900;
FIG. 6 is an SEM photograph of FeNC-Cl/800 obtained in comparative example 1;
FIG. 7 shows FeNC-NO obtained in comparative example 23SEM picture of/800;
FIG. 8 is a nitrogen adsorption-desorption curve of the products obtained in examples 1 to 3 and comparative examples 1 to 2;
FIG. 9 is different coating Fe3LSV curves of oxygen reduction of the carbon nanotube of the C nanocrystal and the glassy carbon electrode modified by the comparative sample in 0.1 MKOH;
FIG. 10 is Fe3LSV curves of oxygen reduction of the glassy carbon electrode modified by C @ N-CNTs/800 and the glassy carbon electrode modified by Pt/C in 0.1 MKOH;
FIG. 11 is Fe3The glassy carbon electrode modified by C @ N-CNTs/800 and the glassy carbon electrode modified by Pt/C are 0.5M H2SO4LSV curve of oxygen reduction in (d);
FIG. 12 is Fe3The i-t curves of the glassy carbon electrode modified by C @ N-CNTs/800 and the glassy carbon electrode modified by Pt/C in 0.1 MKOH;
FIG. 13 is Fe3The glassy carbon electrode modified by C @ N-CNTs/800 and the glassy carbon electrode modified by Pt/C are 0.5M H2SO4I-t curve in (1).
Detailed Description
The invention providesProvide a package of Fe3The preparation method of the carbon nano tube of the C nano crystal comprises the following steps:
(1) mixing an iron source, melamine, 1,3, 5-benzene tricarboxylic acid and a solvent, and carrying out a solvothermal reaction to obtain a metal organic framework material packaged with the melamine;
(2) sequentially carrying out pyrolysis and acid etching on the metal organic framework material encapsulated with the melamine to obtain coated Fe3Carbon nanotubes of C nanocrystals.
The preparation method comprises the steps of mixing an iron source, melamine, 1,3, 5-benzenetricarboxylic acid and a solvent, and carrying out solvothermal reaction to obtain the metal organic framework material packaged with the melamine. In the invention, the iron source is preferably a mixture of ferric chloride and ferric nitrate, and the mass ratio of the ferric chloride to the ferric nitrate in the mixture of the ferric chloride and the ferric nitrate is preferably 1: 4-2: 1; the solvent is preferably ethanol and/or methanol. In the invention, the mass ratio of the iron source, the melamine and the 1,3, 5-benzenetricarboxylic acid in the step (1) is preferably 0.01-1.36: 0.34-1.02: 0.52-1.04, and more preferably 0.5-1.0: 0.6-0.8: 0.7-0.9. In the invention, the ratio of the mass of the iron source to the volume of the solvent is preferably 0.01-1.36 g:20 mL.
In the invention, the mixing mode is preferably ultrasonic mixing, the power of the ultrasonic is preferably 80-100W, the time is preferably 0.5-1 h, and more preferably 0.6-0.8 h; dissolving an iron source, melamine and 1,3, 5-benzene tricarboxylic acid in a solvent, and then carrying out ultrasonic treatment; the invention mixes the above components more uniformly by ultrasound. According to the invention, the solvent thermal reaction is preferably carried out in a polytetrafluoroethylene reaction kettle, the temperature of the solvent thermal reaction is preferably 50-65 ℃, more preferably 55-60 ℃, and the time is preferably 6-12 h, more preferably 8-10 h. In the invention, melamine is taken as a guest molecule, 1,3, 5-benzene tricarboxylic acid is taken as an organic ligand, iron is taken as a metal, and the metal-organic framework material encapsulating the guest molecule melamine can be formed by one-step self-assembly in a solvothermal reaction. Wherein, melamine is taken as a guest molecule to be adsorbed in the pore channel of MOF formed by 1,3, 5-benzene tricarboxylic acid and metal Fe.
To obtainAfter the metal organic framework material encapsulated with the melamine is packaged, the metal organic framework material encapsulated with the melamine is subjected to pyrolysis and acid etching in sequence to obtain the wrapped Fe3Carbon nanotubes of C nanocrystals. The pyrolysis is preferably carried out in a vacuum tube furnace, preferably under argon protection. In the invention, the pyrolysis temperature is preferably 700-900 ℃, and more preferably 800 ℃; the heating rate for heating to the pyrolysis temperature is preferably 5 ℃/min; according to the invention, the pyrolysis time is calculated from the temperature reaching the pyrolysis temperature, and the pyrolysis time is preferably 1-2 h. In the invention, iron ions in the metal organic framework material encapsulated with melamine are reduced to generate metal Fe under the pyrolysis condition, and the metal Fe can be used as the encapsulated Fe in the carbon nano tube3C nano-crystalline catalyst.
In the invention, the etching solution used for acid etching is preferably an HCl solution, and the mass concentration of the HCl solution is preferably 1M; according to the invention, the acid etching is preferably carried out at normal temperature, and the time of the acid etching is preferably 12-24 h, and more preferably 16-20 h. The invention can remove unstable iron substances in the pyrolysis product by acid etching.
After the acid etching is completed, the present invention preferably further comprises post-processing the acid etched product, wherein the post-processing preferably comprises the following steps:
sequentially centrifuging, washing and drying the acid etching product to obtain the coated Fe3Carbon nanotube solids of C nanocrystals.
In the invention, the rotation speed of the centrifugation is preferably 8000-10000 r/min, and the time is preferably 10-15 min. In the invention, the washing detergent is preferably deionized water and ethanol, the washing mode is preferably that deionized water and ethanol are washed alternately, and the number of times of alternate washing is preferably 3. In the invention, the drying is preferably vacuum drying, the drying temperature is preferably 40-50 ℃, more preferably 45 ℃, and the drying time is preferably 12-18 h, more preferably 14-16 h.
The invention provides the coated Fe prepared by the preparation method3Carbon nanotube of C nanocrystal, the coated Fe3The carbon nanotube of C nanocrystal comprises Fe3A C nanocrystalline core layer and a plurality of layers of carbon nanotubes wrapped outside the core layer. In the present invention, the coating Fe3The carbon nano tube of the C nano crystal has high specific surface area and conductivity, high activity and good catalytic stability, and the specific surface area is 295.78-465.30 m2A pore volume of 0.94 to 1.16 cm/g3The pore diameter is 3.88 to 3.94 nm.
The invention provides the coated Fe3The carbon nano tube of the C nano crystal is applied to a fuel cell cathode catalyst. The invention provides a coated Fe3When the carbon nano tube of the C nano crystal is used as a cathode catalyst of a fuel cell, the carbon nano tube has better catalytic activity, stability and methanol resistance under alkaline and acidic conditions. In the invention, the application method specifically comprises the following steps:
will wrap Fe3Mixing the carbon nano tube of the C nano crystal with a solvent to obtain a carbon nano tube dispersion liquid;
dripping the dispersion liquid on the surface of a glassy carbon electrode, dripping an ethanol solution of perfluorosulfonic acid after the solvent is volatilized to obtain Fe3A glassy carbon electrode modified by a carbon nano tube of C nano crystal.
In the invention, the solvent is preferably ethanol, and the mass concentration of the carbon nanotubes in the carbon nanotube dispersion liquid is preferably 1-2 mg/mL, and more preferably 1.5 mg/mL. The invention does not require any particular mixing means, as known to the person skilled in the art, such as ultrasonic mixing.
In the invention, the glassy carbon electrode is preferably a rotating disc glassy carbon electrode, and the surface area of the glassy carbon electrode is preferably 0.19625cm2(ii) a The surface of the glassy carbon electrode is preferably polished before dispensing, and the polishing mode is not particularly required by the invention and can be polished by using a polishing mode well known to those skilled in the art. In the invention, the dropping amount of the carbon nanotube dispersion liquid on the surface of the glassy carbon electrode is preferably 25.5-65.0 μ L, and more preferably 45-55 μ L. In the present invention, the mass concentration of the ethanol solution of the perfluorosulfonic acid is preferably 0.5 wt%, and the ethanol solution of the perfluorosulfonic acid is preferably ethyl acetateThe amount of the alcohol solution to be dropped on the surface of the glassy carbon electrode is preferably 0.8 to 2.5. mu.L, and more preferably 1.0 to 1.5. mu.L. In the present invention, the ethanol solution of perfluorosulfonic acid functions to prevent the catalyst from falling off.
In the present invention, the Fe3The glassy carbon electrode modified by the carbon nano tube of the C nano crystal can be directly used as a cathode material of a fuel cell; said Fe3The carbon nano tube of the C nano crystal is used as a cathode catalyst of the fuel cell, and can improve the speed of oxygen reduction reaction, thereby improving the working performance of the fuel cell.
The following examples are given to encapsulate Fe provided by the present invention3The carbon nanotubes of C nanocrystals and the preparation method and application thereof will be described in detail, but they should not be construed as limiting the scope of the present invention.
Example 1
Dispersing 0.34g of ferric chloride hexahydrate, 1.02g of ferric nitrate nonahydrate, 0.68g of melamine and 0.52g of 1,3, 5-benzenetricarboxylic acid in 20mL of absolute ethyl alcohol, ultrasonically treating the mixed solution for 0.5h, transferring the mixed solution to a 50mL polytetrafluoroethylene reaction kettle, and heating at 65 ℃ for 12h to obtain a metal organic framework material (Fe-MOF-1) encapsulating melamine;
putting a crucible containing 100mgFe-MOF-1 into a vacuum tube furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under the protection of argon, then preserving heat for 2h, then etching a pyrolysis product in 1M HCl aqueous solution for 24h, removing unstable iron substances, centrifugally separating the product, washing with deionized water and ethanol for 3 times respectively, and drying in vacuum to obtain coated Fe3Carbon nanotube of C nanocrystal, and marking the obtained product as Fe3C@N-CNTs/800。
For the obtained Fe3C @ N-CNTs/800 having a specific surface area of 465.30m by BET analysis2G, pore volume 1.14cm3The pore diameter is 3.94 nm.
For the obtained Fe3C @ N-CNTs/800 is subjected to SEM scanning electron microscope analysis, and an obtained SEM picture is shown in figure 1; for the obtained Fe3C @ N-CNTs/800 are subjected to TEM transmission electron microscopy analysis, and an obtained TEM picture is shown in FIG. 2. As can be seen from FIG. 1, Fe3C@N-CNTs/800 the generated carbon nano tube has uniform appearance and the diameter of about 200-250 nm. As can be seen from FIG. 2, Fe3And metal iron nanoparticles are encapsulated in the carbon nanotubes in the C @ N-CNTs/800 material.
For the obtained Fe3C @ N-CNTs/800 was subjected to X-ray diffraction analysis, and the XRD spectrum obtained is shown in FIG. 3. As can be seen from FIG. 3, the material has a diffraction peak at 2 θ ≈ 26.5 degrees, which is consistent with the (002) crystal face of graphitized carbon, indicating that the graphitized carbon structure is formed in the catalyst, which is consistent with the structure of the multi-wall carbon nanotube. The diffraction peak appearing at 2 theta ≈ 43.1 DEG is Fe3The characteristic peak of the C (211) plane indicates the formation of Fe3And C, nano particles.
Example 2
Dispersing 0.34g of ferric chloride hexahydrate, 1.02g of ferric nitrate nonahydrate, 0.68g of melamine and 0.52g of 1,3, 5-benzenetricarboxylic acid in 20mL of absolute ethyl alcohol, ultrasonically treating the mixed solution for 0.5h, transferring the mixed solution to a 50mL polytetrafluoroethylene reaction kettle, and heating at 65 ℃ for 12h to obtain a metal organic framework material (Fe-MOF-1) encapsulating melamine;
putting a crucible containing 100mgFe-MOF-1 into a vacuum tube furnace, heating to 700 ℃ at a heating rate of 5 ℃/min under the protection of argon, preserving the temperature for 2h, then etching a pyrolysis product in 1M HCl aqueous solution for 24h, removing unstable iron substances, centrifugally separating the product, washing with deionized water and ethanol for 3 times respectively, and drying in vacuum to obtain coated Fe3Carbon nanotube of C nanocrystal, and marking the obtained product as Fe3C@N-CNTs/700。
For the obtained Fe3C @ N-CNTs/700 having a specific surface area of 326.45m by BET analysis2Per g, pore volume 0.94cm3(ii)/g, pore diameter is 3.90 nm.
For the obtained Fe3C @ N-CNTs/700 was subjected to SEM analysis, and the SEM picture obtained is shown in FIG. 4. As can be seen from FIG. 4, Fe3C @ N-CNTs/700 form carbon nanotubes, which have a more regular morphology.
Example 3
Dispersing 0.34g of ferric chloride hexahydrate, 1.02g of ferric nitrate nonahydrate, 0.68g of melamine and 0.52g of 1,3, 5-benzenetricarboxylic acid in 20mL of absolute ethyl alcohol, ultrasonically treating the mixed solution for 0.5h, transferring the mixed solution to a 50mL polytetrafluoroethylene reaction kettle, and heating at 65 ℃ for 12h to obtain a metal organic framework material (Fe-MOF-1) encapsulating melamine;
putting a crucible containing 100mgFe-MOF-1 into a vacuum tube furnace, heating to 900 ℃ at a heating rate of 5 ℃/min under the protection of argon, preserving the temperature for 2h, then etching a pyrolysis product in 1M HCl aqueous solution for 24h, removing unstable iron substances, centrifugally separating the product, washing with deionized water and ethanol for 3 times respectively, and drying in vacuum to obtain coated Fe3Carbon nanotube of C nanocrystal, and marking the obtained product as Fe3C@N-CNTs/900。
For the obtained Fe3C @ N-CNTs/900 having a specific surface area of 295.78m by BET analysis2G, pore volume 1.16cm3(ii)/g, pore diameter is 3.88 nm.
For the obtained Fe3C @ N-CNTs/900 was subjected to SEM analysis, and the SEM picture obtained is shown in FIG. 5. As can be seen from FIG. 5, Fe3C @ N-CNTs/900 form carbon nano tubes which have a relatively regular shape.
Comparative example 1
Dispersing 1.36g of ferric chloride hexahydrate, 0.68g of melamine and 0.52g of 1,3, 5-benzenetricarboxylic acid in 20mL of absolute ethyl alcohol, carrying out ultrasonic treatment on the mixed solution for 0.5h, transferring the mixed solution into a 50mL polytetrafluoroethylene reaction kettle, and heating at 65 ℃ for 12h to obtain a metal-organic framework material (Fe-Cl-MOF);
putting a crucible filled with 100mg of Fe-Cl-MOF into a vacuum tube furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under the protection of argon, then preserving the temperature for 2h, then etching a pyrolysis product in 1M HCl aqueous solution for 24h, removing unstable iron substances, centrifugally separating the product, washing with deionized water and ethanol for 3 times respectively, and drying in vacuum to obtain a product FeNC-Cl/800.
The BET analysis of the FeNC-Cl/800 thus obtained gave a specific surface area of 322.16m2Per g, pore volume 0.53cm3(ii)/g, pore diameter is 3.62 nm.
SEM scanning electron microscope analysis was performed on the obtained FeNC-Cl/800, and the obtained SEM picture is shown in FIG. 6. As can be seen from FIG. 6, FeNC-Cl/800 has no generation of carbon nanotube morphology, and the material has an irregular morphology.
Comparative example 2
Dispersing 1.36g of ferric nitrate nonahydrate, 0.68g of melamine and 0.52g of 1,3, 5-benzenetricarboxylic acid in 20mL of absolute ethyl alcohol, carrying out ultrasonic treatment on the mixed solution for 0.5h, transferring the mixed solution into a 50mL polytetrafluoroethylene reaction kettle, and heating at 65 ℃ for 12h to obtain the metal-organic framework material (Fe-NO)3-MOF)；
Will contain 100mg Fe-NO3Putting a crucible of MOF into a vacuum tube furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under the protection of argon, then preserving heat for 2h, then etching the pyrolysis product in 1M HCl aqueous solution for 24h, removing unstable iron substances, centrifugally separating the product, washing with deionized water and ethanol for 3 times respectively, and obtaining a product FeNC-NO after vacuum drying3/800。
For the obtained FeNC-NO 3800 BET analysis with a specific surface area of 315.39m2Per g, pore volume 1.06cm3(ii)/g, pore diameter is 3.60 nm.
For the obtained FeNC-NO3SEM analysis was performed at 800, and the SEM picture is shown in FIG. 7. As can be seen from FIG. 7, FeNC-NO3The/800 has no generation of carbon nano tube appearance, and the material has irregular appearance.
The products obtained in examples 1 to 3 and comparative examples 1 to 2 were subjected to nitrogen adsorption-desorption testing by taking about 40mg of a test sample, placing the test sample in a test sample tube, degassing for 6 hours, and then testing under a condition of 0K, and the results are shown in fig. 8. As can be seen from FIG. 8, the curve types of the five catalysts are IV curves and have obvious hysteresis loops, which indicates that the products obtained in examples 1-3 and comparative examples 1-2 are rich in mesoporous structures.
Example 4
Dispersing 0.34g of ferric chloride hexahydrate, 1.02g of ferric nitrate nonahydrate, 1.02g of melamine and 0.52g of 1,3, 5-benzenetricarboxylic acid in 20mL of absolute ethyl alcohol, ultrasonically treating the mixed solution for 1h, transferring the mixed solution into a 50mL polytetrafluoroethylene reaction kettle, and heating at 65 ℃ for 12h to obtain a metal organic framework material (Fe-MOF-2) encapsulating melamine;
putting a crucible containing 100mgFe-MOF-2 into a vacuum tube furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under the protection of argon, then preserving heat for 2h, then etching a pyrolysis product in 1M HCl aqueous solution for 24h, removing unstable iron substances, centrifugally separating the product, washing with deionized water and ethanol for 3 times respectively, and drying in vacuum to obtain coated Fe3C carbon nanotube, and labeling the obtained product as Fe3C@N-CNTs/800-2。
For the obtained Fe3C @ N-CNTs/800-2 were subjected to SEM analysis and TEM analysis, and the results were similar to those of example 1.
Example 5
Dispersing 0.17g of ferric chloride hexahydrate, 0.51g of ferric nitrate nonahydrate, 0.34g of melamine and 0.52g of 1,3, 5-benzenetricarboxylic acid in 10mL of absolute ethyl alcohol, ultrasonically treating the mixed solution for 0.5h, transferring the mixed solution to a 50mL polytetrafluoroethylene reaction kettle, and heating at 65 ℃ for 12h to obtain a metal organic framework material (Fe-MOF-3) encapsulating melamine;
putting a crucible containing 100mgFe-MOF-3 into a vacuum tube furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under the protection of argon, then preserving heat for 2h, then etching a pyrolysis product in 1M HCl aqueous solution for 24h, removing unstable iron substances, centrifugally separating the product, washing with deionized water and ethanol for 3 times respectively, and drying in vacuum to obtain coated Fe3C carbon nanotube, and labeling the obtained product as Fe3C@N-CNTs/800-3。
For the obtained Fe3C @ N-CNTs/800-3 was subjected to SEM analysis and TEM analysis, and the results were similar to those of example 1.
Example 6
The products obtained in examples 1 to 3 and comparative examples 1 to 2 were dispersed in ethanol, respectively, to obtain a catalyst dispersion of 1 mg/mL. 55 μ L of the above dispersion was added dropwise to the polished glassy carbon electrode surface, followed by 1.2 μ L of perfluorosulfonic acid (Nafion,0.5 wt%) ethyl acetateAlcohol solution, obtaining different wrapping Fe after ethanol is completely volatilized at room temperature3A carbon nanotube of C nanocrystal and a glassy carbon electrode modified by a comparative sample.
Preparation of 1M KOH and 0.5M H2SO4Putting the glassy carbon electrode modified by the carbon nano tube prepared in the previous step into 1M KOH or 0.5M H which is filled with saturated oxygen2SO4In the electrolyte, a Linear Sweep Voltammetry (LSV) test is carried out within the range of 0.2-1.1V or 0-1.0V, and the specific test method comprises the following steps: the glassy carbon electrode coated with the catalyst in a dripping mode is used as a working electrode, the saturated calomel electrode is used as a reference electrode, and the graphite rod is used as a counter electrode. Before testing, oxygen is firstly introduced into the tested electrolyte for 30min, and in the testing process, oxygen is introduced above the electrolyte to keep oxygen saturation. The obtained different coated Fe3The LSV curves of the carbon nanotubes of the C nanocrystals and the glassy carbon electrode modified by the comparative sample for oxygen reduction in 0.1M KOH are shown in fig. 9. As can be seen from FIG. 9, Fe obtained in example 13The C @ N-CNT/800 catalyst had the most positive initial potential and half-wave potential, 0.98 and 0.85V vs. rhe, respectively, indicating that it had the best catalytic performance.
Comparative example 3
Wrapping the coated Fe in example 63Replacing the carbon nano tube catalyst of the C nano crystal with a commercially available Pt/C catalyst, and keeping the rest operations unchanged to obtain the Pt/C modified glassy carbon electrode. The obtained Pt/C catalyst modified glassy carbon electrode was subjected to a Linear Sweep Voltammetry (LSV) test in the same manner as in example 6.
Fe3The glassy carbon electrode modified by C @ N-CNTs/800 and the glassy carbon electrode modified by Pt/C are between 0.1M KOH and 0.5M H2SO4LSV curves for oxygen reduction in (c) are shown in fig. 10, 11. As is clear from FIGS. 10 and 11, the catalyst Fe was obtained under alkaline conditions3The catalytic activity of C @ N-CNT/800 is superior to that of Pt/C catalyst. Under acidic conditions, the catalyst Fe3The catalytic activity of C @ N-CNT/800 is lower than that of Pt/C.
Respectively adding Fe3The timing current i-t test is carried out on the glassy carbon electrode modified by the C @ N-CNTs/800 and the glassy carbon electrode modified by the Pt/C catalyst, and the test method comprises the following steps: a glassy carbon electrode coated with a catalyst by dropping is used as workThe electrode, the saturated calomel electrode are reference electrodes and the graphite rod is a three-electrode testing system of a counter electrode. Before testing, oxygen is firstly introduced into the tested electrolyte for 30min, and in the testing process, oxygen is introduced above the electrolyte to keep oxygen saturation. Its i-t curve in 0.1M KOH is shown in FIG. 12, at 0.5M H2SO4The i-t curve in (1) is shown in FIG. 13, and it can be seen from FIGS. 12 and 13 that the catalyst Fe3The catalytic stability of C @ N-CNT/800 is superior to that of Pt/C.
From the above examples, it can be seen that the preparation method provided by the present invention is simple and easy to operate, and the obtained coated Fe is3The carbon nano tube of the C nano crystal has higher specific surface area, has excellent performance of catalyzing oxygen reduction reaction under alkaline and acidic conditions, and has good catalytic activity when used as a cathode catalyst of a fuel cell.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (9)

1. Wrapped Fe3The preparation method of the carbon nano tube of the C nano crystal is characterized by comprising the following steps:
(1) mixing an iron source, melamine, 1,3, 5-benzene tricarboxylic acid and a solvent, and carrying out a solvothermal reaction to obtain a metal organic framework material packaged with the melamine;
the iron source is a mixture of ferric chloride and ferric nitrate;
the temperature of the solvothermal reaction is 50-65 ℃, and the time is 6-12 h;
(2) sequentially carrying out pyrolysis and acid etching on the metal organic framework material encapsulated with the melamine to obtain coated Fe3Carbon nanotubes of C nanocrystals.
2. The preparation method according to claim 1, wherein the mass ratio of ferric chloride to ferric nitrate in the mixture of ferric chloride and ferric nitrate in the step (1) is 1: 4-2: 1; the solvent is ethanol and/or methanol.
3. The preparation method according to claim 1, wherein the mass ratio of the iron source, the melamine and the 1,3, 5-benzenetricarboxylic acid in the step (1) is 0.01-1.36: 0.34-1.02: 0.52-1.04.
4. The preparation method according to claim 1, wherein the pyrolysis in the step (2) is carried out at 700-900 ℃ for 1-2 h.
5. The preparation method according to claim 1, wherein the etching agent for acid etching in the step (2) is HCl solution, and the time for acid etching is 12-24 h.
6. The method according to claim 1, wherein after the acid etching, the method further comprises performing post-treatment on the acid etched product, wherein the post-treatment comprises the following steps:
sequentially centrifuging, washing and drying the acid etching product to obtain the coated Fe3Carbon nanotube solids of C nanocrystals.
7. The method according to claim 6, wherein the drying is carried out at a temperature of 40 to 50 ℃ for 12 to 18 hours.
8. Coated Fe prepared by the method of any one of claims 1 to 73C nanocrystalline carbon nanotube, characterized in that the coating Fe3The specific surface area of the carbon nano tube of the C nano crystal is 295.78-465.30 m2A pore volume of 0.94 to 1.16 cm/g3The pore diameter is 3.88 to 3.94 nm.
9. Coated Fe according to claim 83The carbon nanotube of C nanocrystal is applied to the cathode catalyst of the fuel cell.
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