CN117819533A - N/O co-doped carbon nanotube and preparation method and application thereof - Google Patents
N/O co-doped carbon nanotube and preparation method and application thereof Download PDFInfo
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 89
- 239000002041 carbon nanotube Substances 0.000 title claims abstract description 80
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- 238000002360 preparation method Methods 0.000 title claims abstract description 21
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- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical compound [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 description 1
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- 239000013154 zeolitic imidazolate framework-8 Substances 0.000 description 1
- MFLKDEMTKSVIBK-UHFFFAOYSA-N zinc;2-methylimidazol-3-ide Chemical compound [Zn+2].CC1=NC=C[N-]1.CC1=NC=C[N-]1 MFLKDEMTKSVIBK-UHFFFAOYSA-N 0.000 description 1
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- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/15—Nano-sized carbon materials
- C01B32/158—Carbon nanotubes
- C01B32/16—Preparation
- C01B32/162—Preparation characterised by catalysts
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
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- H—ELECTRICITY
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- H01M10/00—Secondary cells; Manufacture thereof
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- H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
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- 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
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- 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
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Abstract
The invention discloses an N/O co-doped carbon nano tube and a preparation method and application thereof, wherein the preparation method comprises the following steps: s1, placing MOF powder into a container, covering a liquid gallium layer above the MOF powder, and vacuumizing; s2, covering a liquid gallium layer in the container again, vacuumizing, performing pyrolysis reaction, and taking out a lower-layer product Co@NCNTFs; s3, pickling the lower-layer product Co@NCNTFs obtained in the S2, and drying to obtain the N/O co-doped carbon nanotube. The present invention discloses a novel, simple and high yield pyrolysis strategy based on liquid gallium-assisted pyrolysis of ZIF-67 to yield CNTs, producing high yields (77.8 wt%) of N (7.7 at%) rich CNTs. A large amount of O element (34.31 at%) is introduced into the carbon nano tube through proper oxidation treatment, and the obtained N/O-enriched NOCNTF-15 shows excellent sodium storage performance.
Description
Technical Field
The invention relates to the technical field of nano materials, in particular to an N/O co-doped carbon nano tube and a preparation method and application thereof.
Background
In order to achieve the goal of sustainable development, a wide variety of renewable clean energy sources are continually rising, resulting in rapid development of electrochemical energy storage technologies. As a one-dimensional nanomaterial, carbon Nanotubes (CNTs) have the characteristics of large specific surface area, excellent conductivity, good chemical stability, excellent flexibility and the like, and are a promising energy storage material. There are many methods for preparing CNTs, mainly arc discharge, chemical vapor deposition, laser ablation, etc., but these methods have high temperature requirements and may generate impurities (Science, 2009,323,760-764.Chem. Rev.,1999,99,1787-1800.). For economic and safety reasons, there is an increasing interest in sodium-ion batteries and the use of CNTs in sodium-ion batteries, but their sodium storage properties are severely limited due to the small interlayer spacing (d=0.34 nm) of CNTs. Many studies have shown that by expanding the interlayer spacing and introducing heteroatoms, the properties of sodium storage active sites can be effectively improved, and the electron distribution of the carbon matrix can be adjusted, thereby alleviating the severe volume expansion phenomenon and slow kinetics occurring during the charging and discharging processes of Sodium Ion Batteries (SIBs).
Metal Organic Frameworks (MOFs) are a porous material formed by self-assembly of organic ligands and metal ions or clusters through coordination bonds, which contain a large number of C and N atoms, and a high content of metal ions, are good precursors for the preparation of CNTs. CNTs can be produced by pyrolysis of MOFs, but their pyrolysis process also has a critical impact on the production of CNTs. Lou et al obtained a nitrogen doped carbon nanotube framework by pyrolysis of ZIF-67 at Ar/H 2 The Co nanoparticles formed rapidly in the pyrolysis atmosphere and resulted in a hollow structure carbon nanotube framework (nat. Energy,2016,1,15006.). Li et al obtained hollow polyhedrons with Co nanoparticles embedded in N-doped carbon nanotubes by pyrolysis of ZIF-8@ZIF-67 (J.Am.chem.Soc., 2018,140,2610)-2618). Although prior art pyrolysis ZIF-67 can obtain CNTs, small molecules formed by ligand decomposition during pyrolysis diffuse out, resulting in CNTs growing only on the surface of the framework and lower yields. Currently, MOFs-derived carbon-based materials are attracting interest in energy applications, however, the limitations of pyrolysis methods limit further development. Thus, developing a simple and efficient process for preparing CNTs based on pyrolysis and successfully applying it to sodium storage remains a formidable challenge.
Disclosure of Invention
In order to solve the technical problems, the primary purpose of the invention is to provide a preparation method of N/O co-doped carbon nanotubes, which is simple to operate and easy to implement by liquid gallium-assisted pyrolysis of MOF and subsequent strong acid treatment.
It is a further object of the present invention to provide an N/O co-doped carbon nanotube prepared by the above method.
The third object of the present invention is to provide an application of the above-mentioned N/O co-doped carbon nanotube in preparing sodium ion battery.
A fourth object of the present invention is to provide a sodium ion battery.
The above object of the present invention is achieved by the following technical solutions:
the first aspect of the present invention provides a method for preparing an N/O co-doped carbon nanotube, comprising the steps of:
s1, placing MOF powder into a container, covering a liquid gallium layer above the MOF powder, and vacuumizing;
s2, covering a liquid gallium layer in the container again, vacuumizing, performing pyrolysis reaction, and taking out a lower-layer product Co@NCNTFs;
s3, pickling the lower-layer product Co@NCNTFs obtained in the S2, and drying to obtain the N/O co-doped carbon nanotube (NOCNTF).
According to the invention, the liquid gallium is adopted to assist in pyrolysis of MOF, so that a carbon source and a nitrogen source decomposed by a ligand in the pyrolysis process can be effectively limited in a reaction frame, and the obtained product has high yield and high nitrogen content and has a non-hollow structure formed by interweaving carbon nano tubes. And acid washing is adopted to treat the carbon nanotube frame, and Co nano particles at the end of the carbon nanotube are etched to form an open carbon nanotube. Meanwhile, a large number of C=O groups are introduced on the surface of the carbon nanotube, and finally, a non-hollow three-dimensional framework material (NOCNTF) consisting of the open high-content N/O co-doped carbon nanotube is obtained.
Specifically, x can be used to represent the total thickness of the liquid gallium layer covered twice, the unit is mm, then the lower layer product prepared in the step S2 can be expressed as Co@NCNTFs-x, and the N/O co-doped carbon nanotube prepared in the step S3 can be expressed as NOCNTF-x.
In a specific embodiment, in step S1, MOF powder is placed at the bottom of a container and compacted, a liquid gallium layer is covered above the MOF powder, and vacuum is applied by using a vacuum drying oven.
Further, in step S1, the thickness of the liquid gallium layer is 2-8 mm.
The effect of liquid gallium layer is to prevent the carbon source escape, limits the carbon source and the nitrogen source that the ligand decomposed in the pyrolysis process in reaction frame to can improve productivity and nitrogen content, but when the liquid gallium layer of first time cover is too thick, can't take out the oxygen in MOF powder and the liquid gallium layer contact interface, can influence the formation of carbon nanotube on the contrary.
Preferably, in step S1, the thickness of the liquid gallium layer is 5-6 mm.
Further, in step S1, the MOF is ZIF-67, ZTF-8@ZIF-67 or ZIF-67@ZIF-8.
Further, in step S1, the time of the vacuum pumping is 1-4 hours.
Further, in step S1, the temperature of the vacuum drying oven is 40 to 80 ℃.
In a specific embodiment, in step S2, a liquid gallium layer is covered in the container again, vacuum is applied to the container, a muffle furnace is used for pyrolysis reaction, upper liquid gallium is recovered after cooling, and a lower product co@ncntfs-x is taken out.
Further, in step S2, the time of the vacuum pumping is 1-4 hours.
Further, in step S2, the temperature of the vacuum drying oven is 40 to 80 ℃.
Further, in step S2, the thickness of the liquid gallium layer is 0-30 mm.
Further, the pressure difference between the contact surface of the liquid gallium layer and the MOF powder is 115 Pa to 2200Pa.
The invention can change the diameter of CNTs and the crystallinity of CNTs by changing the thickness of liquid gallium in the pyrolysis process.
Further, in the step S2, the temperature of the pyrolysis reaction is 400-1000 ℃.
Further, in the step S2, the temperature rising rate from the room temperature to the pyrolysis reaction temperature is 2-5 ℃/min before the pyrolysis reaction.
Further, in the step S2, the pyrolysis reaction time is 2-10 hours.
In a specific embodiment, in the step S3, co@NCNTFs-x is placed in a strong acid solution for ultrasonic dispersion, heating and stirring are carried out under the condition of condensation and reflux, products are centrifugally collected, deionized water and ethanol are used for washing 3-4 times, and the N/O co-doped carbon nano tube NOCNTF-x is obtained after drying.
Further, in step S3, acid washing is performed with a strong acid, preferably nitric acid.
Further, in step S3, the concentration of the nitric acid is 2 to 10M.
Further, in the step S3, the temperature of heating and stirring is 40-90 ℃ and the time is 1-4 days.
Further, in step S3, the time of the ultrasonic dispersion is 10 to 30 minutes.
Further, in step S3, a vacuum drying oven with the temperature of 40-80 ℃ is adopted for drying.
The second aspect of the invention provides the N/O co-doped carbon nanotube prepared by the method of the first aspect.
The third aspect of the invention provides an application of the N/O co-doped carbon nano tube in the second aspect in preparing a sodium ion battery.
According to a fourth aspect of the present invention, there is provided a sodium ion battery comprising the N/O co-doped carbon nanotubes of the second aspect as a negative electrode material.
According to the invention, the N/O co-doped carbon nano tube NOCNTF-x is used for preparing the negative electrode material of the sodium ion battery, and the NOCNTF-x shows excellent rate capability, excellent long-cycle stability and high specific discharge capacity.
The invention takes the NOCNTF-x electrode after the pre-sodium treatment as the negative electrode and Na 3 V 2 (PO 4 ) 2 O 2 F (NVPOF) positive electrodes are paired and assembled into a sodium ion full battery, and the full battery is marked as NOCNTF-x-NVPOF. The NOCNTF-x NVPOF full battery shows excellent rate performance and long-cycle stability in a voltage window of 1.25-4.3V.
The invention has the beneficial effects that:
1. according to the invention, the liquid gallium is adopted to assist in pyrolysis ZIF-67, so that a carbon source and a nitrogen source decomposed by a ligand in the pyrolysis process can be effectively limited in a reaction frame, the obtained product has high yield (77.8 wt%) and high nitrogen content (7.7 at%) and has a non-hollow structure formed by interweaving carbon nano tubes, and the diameter of CNTs and the crystallinity of CNTs can be changed by changing the thickness of the liquid gallium in the pyrolysis process.
2. The invention adopts acid washing to treat the carbon nanotube frame, and Co nano particles at the end of the carbon nanotube are etched to form an open carbon nanotube. Simultaneously, a large number of C=O groups are introduced on the surface of the carbon nano tube, and finally the non-hollow three-dimensional framework material NOCNTF-x formed by the open high-content N/O co-doped carbon nano tube is obtained.
3. The N/O co-doped carbon nano tube NOCNTF-15 prepared by the invention has excellent rate capability as a negative electrode material of a sodium ion battery, and is 0.1, 0.2, 0.5, 1, 2, 5 and 10 A.g -1 Specific discharge capacities of 371.4, 348.9, 337.2, 322.4, 304, 278.5 and 252.7 mAh.g -1 Exhibits excellent rate performance even at high current density when the current density is restored to 0.1 A.g -1 When the capacity of the NOCNTF-15 electrode is quickly restored to 338.9 mAh.g -1 And remain stable during subsequent cycles. In addition, NOCNTF-15 also exhibits excellent long-cycle stability and high specific discharge capacity. At 1 A.g -1 The reversible capacity still keeps 286.8 mAh.g after 400 times of circulation -1 Has a high capacity retention of 86.5% and an average attenuation capacity per turn of only 0.11 mAh.g -1 . In addition, NOCNTF-15 electrode was shown to be 10 A.g -1 182.4 mAh.g can be provided after 20000 cycles of current density -1 And the coulombic efficiency is close to 100%.
4. The invention takes the NOCNTF-15 electrode after the pre-sodium treatment as the negative electrode and Na 3 V 2 (PO 4 ) 2 O 2 F (NVPOF) positive electrodes are paired and assembled into a sodium ion full battery, and the sodium ion full battery is recorded as NOCNTF-15 NVPOF. The NOCNTF-15 NVPOF full battery shows excellent rate performance and long-cycle stability in a voltage window of 1.25-4.3V. At 0.1, 0.2, 0.5, 1, 2, 5 and 10A.g -1 Specific discharge capacities at current densities of 547, 439, 393, 372, 308, 202 and 124 mAh.g, respectively -1 When the current density is restored to 0.1 A.g -1 When the capacity of NOCNTF-15 NVPOF is quickly recovered to 381 mAh.g -1 And remain stable during subsequent cycles. NOCNTF-15 NVPOF full battery is 10 A.g -1 After 15400 circles, the product still keeps 38 mAh.g -1 Is a specific discharge capacity of (a). In addition, the highest energy density of NOCNTF-15 NVPOF can reach 233 Wh.kg -1 (based on the total active mass of the two electrodes).
Drawings
FIG. 1 is a Scanning Electron Microscope (SEM) image and a Transmission Electron Microscope (TEM) image of Co@NCNTF-15 obtained in the preparation process of example 2; wherein, (a-c) are SEM images and (d-f) are TEM images.
FIG. 2 is an SEM image and a TEM image of Co@NCNTF-5 obtained in the preparation process of example 1; wherein, (a-c) are SEM images and (d-f) are TEM images.
FIG. 3 is an SEM image and a TEM image of Co@NCNTF-25 obtained in the preparation process of example 3; wherein, (a-c) are SEM images and (d-f) are TEM images.
FIG. 4 is an SEM image and a TEM image of NOCNTF-5 prepared in example 1; wherein, (a-b) are SEM images and (c-d) are TEM images.
FIG. 5 is an SEM image and a TEM image of NOCNTF-15 prepared in example 2; wherein, (a-c) are SEM images and (d-f) are TEM images.
FIG. 6 is an SEM image and a TEM image of NOCNTF-25 prepared in example 3; wherein, (a-b) are SEM images and (c-d) are TEM images.
FIG. 7 is an X-ray powder diffraction (XRD) pattern and Raman spectrum of the NOCNTF-5, NOCNTF-15 and NOCNTF-25 prepared in examples 1 to 3; wherein, (a) is XRD pattern, and (b) is Raman spectrum pattern.
FIG. 8 is an X-ray photoelectron spectrum (XPS) of NOCNTF-15 prepared in example 2.
FIG. 9 is an XPS spectrum of N1s and O1s of NOCNTF-15 prepared in example 2; wherein, (a) is an N1s XPS spectrum, and (b) is an O1s XPS spectrum.
FIG. 10 is an SEM image and a TEM image of Co@NPCF obtained during the preparation of comparative example 1; wherein, (a-b) are SEM images and (c-d) are TEM images.
FIG. 11 is an SEM image of NOPCF prepared in comparative example 1.
FIG. 12 is an XRD spectrum for NOPCF prepared in comparative example 1.
FIG. 13 is an SEM image and a TEM image of ETCNTs prepared in comparative example 2; wherein, (a-b) are SEM images and (c-d) are TEM images.
FIG. 14 is a graph showing the rate performance of NOCNTF-5, NOCNTF-15 and NOCNTF-25 at different current densities, NOCNTF-15 at 1 A.g -1 And 10 A.g -1 Long cycle performance at current density; wherein (a) is a rate performance graph and (b) is 1 A.g -1 A long-cycle performance at current density of (c) 10 A.g -1 Long cycle performance at current density.
Fig. 15 is a plot of the rate performance of the nocf at different current densities.
FIG. 16 is a graph of the rate performance of NOCNTF-15 NVPOF at 0.1Ag at different current densities -1 Charge-discharge curve graph at current density and at 10Ag -1 Long cycle performance at current density; wherein, (a) is a rate performance graph; (b) Is 0.1Ag -1 A charge-discharge curve graph at a current density of (c) 10Ag -1 Long cycle performance at current density.
Detailed Description
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.
The present invention will be further described with reference to the accompanying drawings and specific examples, which are not intended to be limiting, so that those skilled in the art will better understand the invention and practice it.
The experimental methods used in the following examples are conventional methods unless otherwise specified, and materials, reagents, etc. used, unless otherwise specified, are commercially available.
Example 1
A preparation method of N/O co-doped carbon nano tube (NOCNTF-5) comprises the following steps:
s1, placing 42mg of ZIF-67 at the bottom of a quartz bottle with the radius of 5mm, covering liquid gallium with the thickness of 5mm above the ZIF-67, and then placing the quartz bottle into a vacuum drying oven with the temperature of 60 ℃ for 2h.
S2, placing the quartz bottle in a muffle furnace, heating to 600 ℃ at a heating rate of 2 ℃/min, pyrolyzing for 4 hours, cooling to room temperature, recovering liquid gallium on the upper layer to obtain black powder at the bottom of the quartz bottle, marking the black powder as Co@NCNTF-5, and recording the yield; the pressure difference ΔP between the liquid gallium layer and the ZIF-67 powder interface was 289.296Pa (approximately 0.0029 atmospheres).
S3, placing Co@NCNTs-5 into HNO with the concentration of 9M 3 In the solution, ultrasound is carried out for 30min, then the solution is condensed, refluxed and stirred for 4 days at 70 ℃, the product is collected by centrifugation, and is centrifugally washed for 4 times by deionized water and absolute ethyl alcohol, and finally the product is placed in a vacuum drying oven at 80 ℃ for drying, thus obtaining NOCNTF-5.
Example 2
A preparation method of N/O co-doped carbon nano tube (NOCNTF-15) comprises the following steps:
s1, placing 42mg of ZIF-67 at the bottom of a quartz bottle with the radius of 5mm, covering liquid gallium with the thickness of 5mm above the ZIF-67, and then placing the quartz bottle into a vacuum drying oven with the temperature of 60 ℃ for 2h.
S2, adding 10mm of liquid gallium into the quartz bottle, and placing the quartz bottle into a vacuum drying oven for vacuumizing for 2 hours. Placing the quartz bottle in a muffle furnace, heating to 600 ℃ at a heating rate of 2 ℃/min, pyrolyzing for 4 hours, cooling to room temperature, recovering the upper liquid gallium to obtain black powder at the bottom of the quartz bottle, marking as Co@NCNTF-15, and recording the yield; the pressure difference delta P between the liquid gallium layer and the ZIF-67 powder contact surface is 867.888Pa (delta P= 5.904 ×103 kg/m) 3 ×9.8N/kg×15×10 -3 m＝867.888N/m 2 I.e., 867.888Pa, about 0.0086 atmospheres gauge).
S3, placing Co@NCNTs-15 into HNO with the concentration of 9M 3 In the solution, ultrasound is carried out for 30min, then the solution is condensed, refluxed and stirred for 4 days at 70 ℃, the product is collected by centrifugation, and is centrifugally washed for 4 times by deionized water and absolute ethyl alcohol, and finally the product is placed in a vacuum drying oven at 80 ℃ for drying, thus obtaining NOCNTF-15.
Example 3
A preparation method of N/O co-doped carbon nanotubes comprises the following steps:
s1, placing 42mg of ZIF-67 at the bottom of a quartz bottle with the radius of 5mm, covering liquid gallium with the thickness of 5mm above the ZIF-67, and then placing the quartz bottle into a vacuum drying oven with the temperature of 60 ℃ for 2h.
S2, adding 20mm of liquid gallium into the quartz bottle, and placing the quartz bottle into a vacuum drying oven for vacuumizing for 2 hours. Placing the quartz bottle in a muffle furnace, heating to 600 ℃ at a heating rate of 2 ℃/min, pyrolyzing for 4 hours, cooling to room temperature, recovering the upper liquid gallium to obtain black powder at the bottom of the quartz bottle, marking as Co@NCNTF-25, and recording the yield; the pressure difference ΔP between the liquid gallium layer and the ZIF-67 powder interface was 1446.78Pa (approximately 0.0143 atmospheres).
S3, placing Co@NCNTs-25 into HNO with the concentration of 9M 3 Ultrasonic processing for 30min, condensing, refluxing and stirring at 70deg.C for 4 days, and centrifugingAnd centrifugally washing the product for 4 times by using deionized water and absolute ethyl alcohol, and finally drying the product in a vacuum drying oven at 80 ℃ to obtain the NOCNTF-25.
FIG. 1 is a Scanning Electron Microscope (SEM) image and a Transmission Electron Microscope (TEM) image of Co@NCNTF-15 obtained in the preparation process of example 2, and it can be seen from FIG. 1 that Co@NCNTF-15 retains the original skeleton morphology of ZIF-67 after pyrolysis, and a large number of CNTs are distributed on the surface thereof. Unlike the previously reported hollow structure, it can be seen from TEM pictures that Co@NCNTF-15 has a non-hollow structure. In addition, the tips of CNTs are filled with Co nanoparticles, consistent with the description of the tip growth mechanism.
Fig. 2 is a scanning electron microscope image and a transmission electron microscope image of co@ncntf-5 obtained during the preparation of example 1, and fig. 3 is a scanning electron microscope image and a transmission electron microscope image of co@ncntf-25 obtained during the preparation of example 3, from which it can be seen that changing the thickness of the liquid gallium layer significantly affects the outer diameter of the generated CNTs, and that an increase in the thickness of the liquid gallium layer results in an increase in the outer diameter of the CNTs from about 8nm possessed by co@ncntf-5 to about 27nm possessed by co@ncntf-25.
FIGS. 4 to 6 are a scanning electron microscope image and a transmission electron microscope image of NOCNTF-5, NOCNTF-15 and NOCNTF-25 prepared in examples 1 to 3, respectively, using concentrated HNO at 70 ℃C 3 (9M) after Co@NCNTF-5, co@NCNTs-15 and Co@NCNTs-25 were treated, the morphology of the products NOCNTF-5, NOCNTF-15 and NOCNTF-25 was not changed much, and it was seen from the damaged frames during the acid treatment that CNTs were densely grown inside the frames. In addition, TEM results show that Co nanoparticles coated on the ends of CNTs in Co@NCNTF-5, co@NCNTs-15 and Co@NCNTs-25 are etched to form an open CNTs.
FIG. 7 is an X-ray powder diffraction pattern and Raman spectrum of the NOCNTF-5, NOCNTF-15, and NOCNTF-25 prepared in examples 1 to 3, and the crystallinity of the carbon material was confirmed by X-ray powder diffraction (XRD) (FIG. 7 a), having a sharp peak at 26.1℃corresponding to the (002) crystal plane of the medium graphite, further confirming that the NOCNTF-5, NOCNTF-15, and NOCNTF-25 were composed of CNTs having high crystallinity. No characteristic peak of the metal Co is found in the XRD pattern, which indicates that the metal Co is coated with HNO 3 Etching with TEM junctionThe fruits are consistent. Raman spectra (fig. 7 b) shows the I of the product when the thickness of the liquid gallium layer is increased from 5mm to 25mm D /I G The decrease in value from 0.96 to 0.73 indicates that an increase in the thickness of the liquid gallium layer results in an increase in the graphitization degree of the CNTs.
FIG. 8 is an X-ray photoelectron Spectrometry (XPS) chart of NOCNTF-15 prepared in example 2, showing that XPS full spectrum (FIG. 8) shows HNO subjected to high concentration 3 In the treatment, a large amount of O (34.31 at%) and N (7.7 at%) elements were introduced into NOCNTF-15.
FIG. 9 is an N1s and O1s XPS spectrum of NOCNTF-15 prepared in example 2, where high resolution N1s XPS spectrum reveals the presence of two types of nitrogen: pyridine N at-397.88 eV and pyrrole N at-399.43 eV (FIG. 9 a). The O1s spectra showed two peaks at-531.47 eV and-532.96 eV, respectively attributed to c=o and C-OH (fig. 9 b).
Comparative example 1
A method for preparing porous carbon, comprising the steps of:
42mg of ZIF-67 was placed in an Ar atmosphere, heated to 600℃at a heating rate of 2℃per minute and pyrolysed for 4 hours, cooled to give a black powder (Co@NPCF), and the yield of the product was recorded. Co@NPCF was placed in 2M dilute HNO 3 In the solution, ultrasound is carried out for 30min, then the solution is condensed, refluxed and stirred for 4 days at 45 ℃, the product is collected by centrifugation, and is centrifugally washed for 4 times by deionized water and absolute ethyl alcohol, and finally the product is placed in a vacuum drying oven at 80 ℃ for drying, thus obtaining NOPCF.
The yields of pyrolysis ZIF-67 for examples 1-3 and comparative example 1 are shown in Table 1:
TABLE 1
Fig. 10 is an SEM image and a TEM image of co@npcf obtained during the preparation of comparative example 1, and it can be seen from fig. 10 that co@npcf obtained by pyrolysis under Ar atmosphere substantially retains the original skeleton of ZIF-67 without a liquid gallium layer, and ZIF-67 particles sharply shrink inward to form a hollow structure due to outward diffusion of gas generated by rapid decomposition of 2-methylimidazole. In this case, CNTs are not observed in the framework, which may be due to the rapid escape of carbon sources generated by ligand decomposition during pyrolysis, which may not provide sufficient material for CNTs growth. This was further confirmed by the far lower yield of co@npcf (43.2 wt%) than that of co@ncntf-x (x=5, 15 and 25) (77.8 wt%) in table 1, compared to experiments performed under liquid gallium.
FIG. 11 is an SEM image of NOPCF prepared in comparative example 1, as can be seen from FIG. 11, using dilute HNO at 45 ℃C 3 After (2M) treatment of Co@NPCF, the original morphology of the product NOPCF can be maintained.
FIG. 12 is an XRD spectrum of NOPCF prepared in comparative example 1, FIG. 12 shows that the inclusion peak at 26℃corresponds to the (002) crystal face of graphitic carbon, and furthermore, no characteristic peak of metallic Co is found in the XRD spectrum, indicating that metallic Co is hnO 3 Etching.
Comparative example 2
A preparation method of carbon nanotubes comprises the following steps:
uniformly mixing 42mg of ZIF-67 powder with 10mL of absolute ethyl alcohol, placing in Ar atmosphere, heating to 600 ℃ at a heating rate of 2 ℃/min, pyrolyzing for 4 hours, and cooling to obtain black powder ETCNTs.
Fig. 13 is (a-b) SEM images and (c-d) TEM images of ETCNTs prepared in comparative example 2, and it can be seen from fig. 13 that CNTs can be grown by introducing additional carbon source (absolute ethyl alcohol) into the reaction system in the same pyrolysis environment, thereby confirming the role of the liquid gallium layer in preventing the escape of the carbon source.
Test example 1
Sodium storage performance of NOCNTF-5, NOCNTF-15, NOCNTF-25 prepared in examples 1 to 3 and NOPCF prepared in comparative example 1 was tested by the following method: the active material (NOCNTF-5, NOCNTF-15, NOCNTF-25 or NOPCF), conductive carbon black and sodium carboxymethylcellulose (CMC) were mixed at 7:2:1, and the deionized water is used as a solvent to prepare the working electrode by stirring and mixing. The mixed slurry was coated on Cu foil and dried under vacuum at 60 ℃ for 12h. The active material has a mass loading of about 0.5 to 1.0mg. 1M sodium hexafluorophosphate (NaPF) 6 ) Dissolved in ethylene glycol dimethyl ether as an electrolyte, glass fiber purchased from Whatman (Whatman) as a separator, sodium sheet having a diameter of 12mm as a counter electrode in a glove box (O 2 <0.01ppm，H 2 O<0.01 ppm) was assembled into a CR 2023 coin cell. Uses Land CT 2001A instrument at 0.01-3.00V (vs Na + Charge and discharge tests were performed between the voltage windows of/Na).
FIG. 14a shows the rate capability of NOCNTF-5, NOCNTF-15 and NOCNTF-25 electrodes at different current densities, where NOCNTF-15 exhibits the most excellent performance at 0.1, 0.2, 0.5, 1, 2, 5 and 10A.g -1 Specific discharge capacities of 371.4, 348.9, 337.2, 322.4, 304, 278.5 and 252.7 mAh.g -1 Excellent rate performance is exhibited even at high current densities. In addition, when the current density is restored to 0.1 A.g -1 When the capacity of the NOCNTF-15 electrode is quickly restored to 338.9 mAh.g -1 And remain stable during subsequent cycles. As shown in FIG. 14b, NOCNTF-15 electrode was shown in 1 A.g -1 The reversible capacity is still kept at about 286.8 mAh.g after 400 cycles -1 Has a high capacity retention of 86.5% and an average attenuation capacity per turn of only 0.11 mAh.g -1 . As shown in FIG. 14c, to evaluate the long-cycle stability of the NOCNTF-15 electrode at high current density, the NOCNTF-15 electrode was measured at 10A.g -1 20000 cycles of charge and discharge tests were performed. Impressively, the NOCNTF-15 electrode still provided 182.4 mAh.g -1 And the coulombic efficiency remains close to 100% during cycling. In summary, the excellent sodium storage properties of NOCNTF-15 electrodes may be attributed to the specific structure of NOCNTF-15. The three-dimensional framework formed by the cross-linking of open CNTs from inside to outside provides a fast transport path for electrons, avoiding electrical contact loss, and thus producing excellent rate performance, especially at high current densities. In addition, high levels of N/O co-doping, especially c=o at the carbon nanotube surface, not only promote rapid charge transfer at the electrode/electrolyte interface, but also facilitate enhanced Na + Adsorption/desorption at the surface of CNTs and surface oxidation-reduction reaction, thereby exhibiting high sodium storage capacity.
As shown in FIG. 15, NOPCF electrodes were at 0.1, 0.2, 0.5, 1, 2, 5 and 10A.g -1 Specific discharge capacities of 264.1, 235.1, 212.2, 191.3, 169.6, 141.7 and 116.1 mAh.g respectively -1 . In addition, when the current density is restored to 0.1 A.g -1 When the capacity of the NOCNTF-15 electrode is restored to 248.5 mAh.g -1 And remain stable during subsequent cycles.
Test example 2
The NOCNTF-15||NVPOF sodium ion full battery performance test is carried out on the NOCNTF-15 prepared in the embodiment 2, and the test method is as follows: na is mixed with 3 V 2 (PO 4 ) 2 O 2 F. Conductive carbon black and polyvinylidene fluoride (PVDF) at 7:2:1, and N-methyl-2-pyrrolidone is used as a solvent to prepare the anode slurry by stirring and mixing. Then it was coated on an Al foil and dried in vacuo at 60 ℃ for 12h. The mass-to-load ratio of the active materials of the positive electrode and the negative electrode is (4.5-5): 1 to ensure that the full cell produced has optimal performance. By mixing the sodium half-cell with 0.1 A.g before assembling the full cell -1 The NOCNTF-15 electrode was pre-sodified by three charging and discharging cycles. Subsequently, the half cells were disassembled in a glove box to obtain pre-sodified cathodes. Adopts Na 3 V 2 (PO 4 ) 2 O 2 F as positive electrode and pre-sodified NOCNTF-15 electrode as negative electrode, the full cell was assembled using the same electrolyte and separator. The constant current charge/discharge test of the full cell was performed between voltage windows of 1.25-4.3V (based on the active material mass of the negative electrode).
As shown in FIG. 16a, the values of 0.1, 0.2, 0.5, 1, 2, 5, 10A.g -1 The specific discharge capacities of NOCNTF-15 NVPOF under the current density are 547, 439, 393, 372, 308, 202 and 124 mAh.g respectively -1 When the current density is restored to 0.1 A.g -1 When the capacity of NOCNTF-15 NVPOF is quickly recovered to 381 mAh.g -1 And remain stable during subsequent cycles. Fig. 16b shows that NOCNTF-15||nvpof has a high operating voltage of 4.0V. More importantly, as shown in FIG. 16c, the NOCNTF-15 NVPOF full cell is at 10A.g -1 After 15400 circles, the product still keeps 38 mAh.g -1 Is to be placed in (a)Specific electrical capacity. In addition, the highest energy density of NOCNTF-15 NVPOF can reach 233 Wh.kg -1 (based on the total active mass of the two electrodes).
The present invention discloses a novel, simple and high yield pyrolysis strategy based on liquid gallium-assisted pyrolysis ZIF-67 to yield CNTs, wherein the strategy provides air isolation to facilitate heat transfer by limiting H generated by thermal decomposition of 2-imidazole 2 To promote the reduction of cobalt ions to form catalytically active Co nanoparticles that catalyze the formation of CNTs. In addition, liquid gallium is advantageous in retaining carbon and nitrogen atoms in ZIF-67, resulting in high yields (77.8 wt%) of N (7.7 at%) rich CNTs synthesis. A large amount of O element (34.31 at%) is introduced into the carbon nano tube through proper oxidation treatment, and the obtained N/O-enriched NOCNTF-15 shows excellent sodium storage performance. The pyrolysis strategy of the invention provides a brand-new way for preparing CNTs and MOFs derived carbon materials with low cost by pyrolysis by taking MOFs as precursors and applying the CNTs and the MOFs derived carbon materials to the negative electrode material of the sodium ion battery.
It is to be understood that the above examples of the present invention are provided by way of illustration only and are not intended to limit the scope of the invention. It will be appreciated by persons skilled in the art that other variations or modifications may be made in the various forms based on the description above. It is not necessary here nor is it exhaustive of all embodiments. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the invention are desired to be protected by the following claims.
Claims (10)
1. The preparation method of the N/O co-doped carbon nano tube is characterized by comprising the following steps of:
s1, placing MOF powder into a container, covering a liquid gallium layer above the MOF powder, and vacuumizing;
s2, covering a liquid gallium layer in the container again, vacuumizing, performing pyrolysis reaction, and taking out a lower-layer product Co@NCNTFs;
s3, pickling the lower-layer product Co@NCNTFs obtained in the S2, and drying to obtain the N/O co-doped carbon nanotube.
2. The method according to claim 1, wherein in step S1, the thickness of the liquid gallium layer is 2 to 8mm.
3. The method according to claim 1, wherein in step S1, the MOF is ZIF-67, ZTF-8@zif-67 or ZIF-67@zif-8.
4. The method according to claim 1, wherein in step S2, the thickness of the liquid gallium layer is 0 to 30mm.
5. The method according to claim 1, wherein the pressure difference between the contact surface of the liquid gallium layer and the MOF powder is 115 Pa to 2200Pa.
6. The method according to claim 1, wherein the pyrolysis reaction temperature in step S2 is 400 to 1000 ℃.
7. The method according to claim 1, wherein in step S3, acid washing is performed with a strong acid.
8. The N/O co-doped carbon nanotubes prepared by the method of any one of claims 1 to 7.
9. The use of the N/O co-doped carbon nanotube of claim 8 for the preparation of a sodium ion battery.
10. A sodium ion battery comprising the N/O co-doped carbon nanotube of claim 8 as a negative electrode material.
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