CN112053855B - Electrode material based on multi-walled carbon nanotube-carbonized wood mixed support, preparation method and supercapacitor - Google Patents
Electrode material based on multi-walled carbon nanotube-carbonized wood mixed support, preparation method and supercapacitor Download PDFInfo
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Abstract
An electrode material based on a multi-walled carbon nanotube-carbonized wood mixed scaffold comprises carbonized wood chips; the carbonized wood chip is formed by carbonizing and activating a fir chip, a tracheid structure is formed on the carbonized wood chip, multi-walled carbon nano tubes are grown on the inner wall of the tracheid structure in situ by chemical vapor deposition, so that MWCNT-CW scaffolds are formed on the carbonized wood chip, and Co (OH) is deposited by electrochemical deposition2And the nano sheets are wrapped on the multi-walled carbon nano tube to obtain the electrode material based on the multi-walled carbon nano tube-carbonized wood mixed support. The super capacitor prepared from the electrode material has high energy storage performance, including 3.31Fcm‑2Surface capacitance of (1), 0.9mWhcm‑2Energy density of 70mWcm‑2Power density of and at 60mAcm‑2The capacity retention after 11,000 charges at a current density of (3) was 97.8%.
Description
Technical Field
The invention relates to an electrode material of a super capacitor, in particular to an electrode material based on a multiwalled carbon nanotube-carbonized wood mixed support, a preparation method and a super capacitor.
Background
Due to the abundance of biomass-derived materials, their wide use, inherent porosity and low cost, they have attracted considerable interest to researchers in the construction of energy storage devices. Wood has a large number of tracheid structures, with chamber sizes of tens of microns, which can be carbonized to impart electrical conductivity. The resulting carbonized wood scaffold inherits the original porous structure, which allows for internal loading of active substances and rapid transport of electrons along the channels of the tracheid structure. Thus, carbonized wood is a suitable support for energy storage devices (e.g., supercapacitors). Electrochemically active materials such as cobalt hydroxide, manganese dioxide, polypyrrole, and polyaniline can be further introduced into the macropores to increase the specific capacitance. However, these active materials generally have poor integration with conductive scaffolds, which results in rapid decay of capacitance during periodic charge and discharge cycles, and also a large drop in capacitance at high currents. The combination of the active material with the conductive scaffold to achieve efficient electrical interaction is critical to promote redox chemistry at the interface and thus achieve high capacitance when storing charge. The inherent porosity makes carbonized wood less amenable to structural modification than synthetic electrodes, and thus changing the local morphology and surface chemistry inside each tracheid structure remains tricky.
Patent 2019110011575, polyaniline-carbon nanotube electrode material based on core-shell structure, preparation method and super capacitor; in this patent, carbon nanotubes are grown on the inner wall of the cell structure of fir chips, and a layer of polyaniline is deposited on the surface of the carbon nanotubes, thereby forming a core-shell structure. The addition of the polyaniline ensures that the electrode has good conductivity; meanwhile, the CNT effectively increases the bonding sites of PANI, so that more PANI can be loaded on the electrode, and the capacitance of the electrode is further increased. The core-shell structure formed by the CNT and the PANI promotes the rapid transmission of electrons. However, in this patent we use a theoretical specific volume higher (3460F g)-1) The cobalt hydroxide as an active material has the advantages of low cost and abundant reserves on the earth, and is one of the most promising candidate electrode materials of the super capacitor.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide an electrode material based on a multiwalled carbon nanotube-carbonized wood mixed support with higher energy storage capacity, a preparation method and a supercapacitor.
In order to solve the technical problems, the technical scheme provided by the invention is as follows: an electrode material based on a multi-walled carbon nanotube-carbonized wood mixed scaffold comprises carbonized wood chips; the carbonized wood chip is formed by carbonizing and activating a fir chip, a tracheid structure is formed on the carbonized wood chip, multi-walled carbon nano tubes are in-situ anchored and grown on the inner wall of the tracheid structure through chemical vapor deposition, so that MWCNT-CW scaffolds are formed on the carbonized wood chip, and Co (OH) is deposited through electrochemical deposition2And the nano sheets are wrapped on the multi-walled carbon nano tube to obtain the electrode material based on the multi-walled carbon nano tube-carbonized wood mixed support.
The above electrode material based on the multi-walled carbon nanotube-carbonized wood mixed scaffold is preferably carbonized by drying in a forced air drying oven at 250 ℃ for 3-9 hours to perform pre-carbonization, and then placing the wood chips in a tube furnace to heat to 1000 ℃ for 3-9 hours under the protection of Ar gas.
Preferably, the activation is carried out by using CO at 750 ℃ in the electrode material based on the multi-walled carbon nanotube-carbonized wood mixed scaffold2And activating for 8-12 hours in a gas flowing atmosphere, wherein the flowing speed of the CO2 is 60-100 sccm.
Preferably, the step of growing the multiwall carbon nanotube by chemical vapor deposition in-situ anchoring on the tracheid structure is as follows: the activated carbonized wood chips are treated at the temperature of 80-100 ℃ with 0.25mol/L of Ni (NO)3)2Soaking in water solution for 15min, and removing water; with H2Performing chemical vapor deposition in a tubular furnace by using reduction gas, ethylene as a carbon source and Ar as protective gas to obtain the flake fir wood chips subjected to chemical vapor deposition, and enabling the multi-walled carbon nanotubes to grow on the tube cell structures of the carbonized wood chips in an anchoring mode through chemical vapor deposition in situ.
Preferably, the flow rate of the H2 gas flow is 20-40sccm, the flow rate of the Ar gas flow is 300-500sccm, and the flow rate of the ethylene gas flow is 80-100 sccm; the time of chemical vapor deposition is 3-10 min.
Preferably, the electrode material based on the multiwalled carbon nanotube-carbonized wood mixed scaffold comprises the following electrochemical deposition: in the presence of 0.1mol/L Co (NO)3)2·6H2O solution, at-0.9V vs. saturated calomel electrode, Co (OH)2Electrodeposition into MWCNT-CW scaffolds; electrochemical deposition was carried out in a three-electrode system using carbonized wood chips containing MWCNT-CW scaffolds as the working electrode, a platinum electrode as the counter electrode, and a saturated calomel electrode as the reference electrode.
A preparation method of an electrode material based on a multi-walled carbon nanotube-carbonized wood mixed scaffold comprises the following steps: 1) naturally air-drying the fir wood chips, and cutting the fir wood chips into preset sizes;
2) carbonizing, namely placing the fir wood chips obtained in the step 1) in a hot air drying box for carbonizing for 4-8h, and carbonizing for 4-8h at 800-1200 ℃ under the protection of Ar gas to obtain OWC sheets;
3)CO2and (3) activation: slicing OWC in CO2Activating for 8-12h in Ar mixed gas flow, and cutting or grinding to a preset size to form an AWC electrode; the activation temperature is 650-850 ℃; ar gas flow rate of CO 23 times of the flow of CO2The flow rate is 60-80 sccm;
4) removing impurities;
5) preparation of MWCNT-CW scaffolds the AWC electrode treated in step 4) was placed in Ni (NO)3)2Soaking in water solution for 10-20min, and drying in drying oven to obtain water solution H2Performing chemical vapor deposition in a tubular furnace by using reducing gas, ethylene as a carbon source and Ar as protective gas to obtain the MWCNT-CW support; said H2The flow rate of the gas flow is 20-40sccm, the flow rate of the Ar gas flow is 300-500sccm, and the flow rate of the ethylene gas flow is 80-100 sccm; the chemical vapor deposition time is 3-10 min;
6) subjecting the MWCNT-CW scaffold of step 5) to a hydrophilic treatment;
7)Co(OH)2preparation of/MWCNT-CW composite electrode, the MWCNT-CW scaffold of step 6) was immersed in a solution containing 0.1mol/L Co (NO)3)26H2O, performing electrochemical deposition by using MWCNT-CW support as working electrode, platinum electrode as counter electrode, and saturated calomel electrode as reference electrode, wherein the electrochemical deposition time is 1-9 hours; drying after electrochemical deposition.
In the above method for preparing an electrode material based on a multiwalled carbon nanotube-carbonized wood mixed scaffold, preferably, the step 5) of preparing the MWCNT-CW scaffold comprises the steps of: the obtained carbonized wood chips have 0.25mol/L of Ni (NO) at 90 DEG C3)2Soaking in the solution for 15min, and then drying in air;
secondly, the slices are transferred into a tube furnace, the tube furnace is firstly blown by Ar gas flow for more than 30 minutes to discharge air, and then the temperature is 10 ℃ for min-1Heating rate of (3) to increase the temperature to 740 ℃ and introducing C2H4And H2Air flow and hold for 5 minutes.
In the above preparation method of the electrode material based on the multiwalled carbon nanotube-carbonized wood mixed scaffold, preferably, in the step 4), the electrode material obtained in the step 3) is washed with 6% HCl for more than 15 minutes, then washed with deionized water for more than 3 times until the cleaning solution becomes clear, and then dried in a blast drying oven at 60-100 ℃.
In the above method for preparing an electrode material based on a multiwalled carbon nanotube-carbonized wood mixed scaffold, preferably, in the step 6), the MWCNT-CW scaffold obtained in the step 5) is placed in 20 wt% of HNO3And 20% wt H2SO4The mixed solution of (2) is added for 5min to make it hydrophilic; then washing with deionized water to neutrality, and drying.
A super capacitor comprises the China fir carbon sheet electrode material based on the carbon nano tube and the manganese dioxide.
Compared with the prior art, the invention has the advantages that: this problem is addressed in the present invention by constructing a hierarchical structure within the fir tracheids to enhance the interaction between the active material and the wood-derived conductive scaffold. We proceed by the in situ methodMulti-walled carbon nanotubes (MWCNTs) were synthesized from the surface of the carbonized tracheid structure chamber. Carbon nanotubes have characteristics of high surface area and high electrical conductivity, and have been widely used in energy storage devices. MWCNTs can be synthesized by a Chemical Vapor Deposition (CVD) process, in which CH4Or C2H4As a carbon source, Fe or Ni is used as a catalyst. One of the drawbacks of MWCNTs is their tendency to entangle or aggregate with each other due to their large aspect ratio and strong interaction with each other, which makes their uniform dispersion in a functional matrix challenging. Our in situ synthesis route avoids such difficulties by depositing metal catalysts within the tracheid-cell structure scaffold and growing MWCNT arrays from the inner surface. The resulting MWCNT-carbonized wood hybrid scaffold provides sufficient surface area for the active material to reach and allows for rapid redox chemistry, resulting in high capacitance.
We use cedar waste as raw material as they are off-the-shelf wood chips discarded by the manufacturer. Compared with other woods, the fir wood has a more uniform and more suitable tracheid structure size. The wood chips are first sliced, pre-carbonized and carbonized at 1000 ℃, and then subjected to an activation procedure to create more micropores to increase their specific surface area.
The carbon nanotubes are first grown and anchored in situ on the inner wall of the carbonized wood cell structure by chemical vapor deposition. Then, Co (OH) is deposited by electrochemical deposition2The nanosheets being wrapped around each carbon nanotube to yield Co (OH)2an/MWCNT-CW composite electrode at 5mAcm-2Has a current density of 29.6F cm-2Large area specific capacitance. To increase the voltage window of the Supercapacitor (SC), Co (OH) was successfully used2the/MWCNT-CW electrode was used as the cathode and the MWCNT-CW electrode was used as the anode to successfully assemble the asymmetric supercapacitor. SC at 5mAcm-2Has a current density of 3.31F cm-2High area specific capacitance of 60mAcm-2After 11,000 charge-discharge cycles, the initial specific capacitance remained 97.8%. Meanwhile, it can provide 0.9mW h cm-2High energy density and 70mW cm-2High power density. The improved performance of the SC is mainly due to anchoring in the tracheid nodeMWCNT conductive network on the framework, which adds Co (OH)2The number of nanosheets and the increased conductive surface area make the electrical interaction between the scaffold and the active material more efficient. Therefore, the asymmetric super capacitor has higher energy storage capacity than other super capacitors.
Drawings
FIG. 1 shows Co (OH)2A flow chart for preparing the/MWCNT-CW electrode.
Fig. 2 is a top view of a slice of a CW electrode.
Fig. 3 is a side view of a slice of a CW electrode.
Figure 4 is an SEM image of a top view of a MWCNT-CW electrode slice.
FIG. 5 is an SEM image of a side view of a slice of a MWCNT-CW electrode.
Fig. 6 is an enlarged schematic view of fig. 5.
FIG. 7 shows Co (OH)2SEM image of top view of/MWCNT-CW electrode slice.
Fig. 8 is an enlarged schematic view of fig. 7.
FIG. 9 shows Co (OH)2SEM image of side view of/MWCNT-CW electrode slice.
FIG. 10 shows Co (OH)2SEM image of side view of/CW electrode slice.
FIG. 11 shows Co (OH)2TEM images of/MWCNT-CW electrode sections.
FIG. 12 shows Co (OH)2Elemental mapping plots of C/O/Co for the/MWCNT-CW electrode slices.
FIG. 13 shows Co (OH)2HRTEM image of/MWCNT-CW electrode section.
FIG. 14 shows Co (OH)2HRTEM image of/MWCNT-CW electrode section.
FIG. 15 shows Co (OH)2HRTEM image of/MWCNT-CW electrode section.
FIG. 16 shows Co (OH)2Selected area electron diffraction patterns of/MWCNT-CW electrode slices.
FIG. 17 shows Co (OH)2FTIR plots of/MWCNT-CW electrode slices.
FIG. 18 shows Co (OH)2the/MWCNT-CW electrode measures the scanning XPS spectrum.
FIG. 19 shows Co (OH)2High resolution C1s spectrogram of/MWCNT-CW electrode.
FIG. 20 shows Co (OH)2High resolution O1s spectrogram of/MWCNT-CW electrode.
FIG. 21 shows Co (OH)2High resolution Co2p spectrograms for the/MWCNT-CW electrode.
FIG. 22 shows electrodeposition of Co (OH) at different times2Rear, Co (OH)2Multiplying power performance diagram of the/MWCNT-CW electrode.
FIG. 23 shows electrodeposition for 6 hours Co (OH)2Co (OH)2the/MWCNT-CW electrode is at 1-10mV s under a window of-0.2V to 0.5V-1CV curve at sweep speed.
FIG. 24 shows Co (OH) electrodeposited for 6 hours2Co (OH)2the/MWCNT-CW electrode is 5-60mAcm under a window of-0.2V to 0.4V-2GCD curve at current density.
FIG. 25 shows electrodeposition of Co (OH) at different times2Rear, Co (OH)2Rate performance plot of/CW electrode.
FIG. 26 shows electrodeposition for 9 hours Co (OH)2Co (OH)2the/CW electrode is at 1-10mVs under a window of-0.2V to 0.5V-1CV curve at sweep speed.
FIG. 27 shows electrodeposition for 9 hours Co (OH)2Co (OH)2GCD curves at 5-60mA cm-2 current densities at windows of-0.2V to 0.4V for a/CW electrode.
FIG. 28 is Co (OH)2MWCNT-CW and Co (OH)2A CW electrode at 80mAcm-2Long-term contrast plot at current density.
FIG. 29 shows Co (OH)2MWCNT-CW and Co (OH)2Nyquist plot for/CW electrodes.
Fig. 30 is an enlarged view of fig. 29.
FIG. 31 shows CNT/CW | | Co (OH)2the/MWCNT-CW asymmetric super capacitor is 3-40mVs under a window of 0-1.5V-1Cyclic voltammogram at the sweep rate of (a).
FIG. 32 shows CNT/CW | | Co (OH)2the/MWCNT-CW asymmetric super capacitor is 5-100mAcm under the window of 0-1.4V-2Constant current charge and discharge curve diagram under the current density.
FIG. 33 shows CNT/CW | | Co (OH)2The area specific capacitance and the mass specific capacitance of the/MWCNT-CW asymmetric supercapacitor under different current densities.
FIG. 34 is a graph showing a curve at 60mAcm-2The current density of (a), the cycle performance of the asymmetric supercapacitor.
Fig. 35 is a nyquist plot for the asymmetric supercapacitor.
Fig. 36 is a schematic diagram of two series-connected asymmetric supercapacitors lighting a 2V small bulb.
Detailed Description
In order to facilitate an understanding of the present invention, the present invention will be described more fully and in detail with reference to the preferred embodiments, but the scope of the present invention is not limited to the specific embodiments described below.
It should be particularly noted that when an element is referred to as being "fixed to, connected to or communicated with" another element, it can be directly fixed to, connected to or communicated with the other element or indirectly fixed to, connected to or communicated with the other element through other intermediate connecting components.
Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.
Example 1
In this embodiment, the preparation method of the electrode material based on the multiwalled carbon nanotube-carbonized wood mixed scaffold comprises the following steps: 1) preparation of MWCNT-CW scaffolds
The fir wood chips were purchased from shoudon county of Hunan province, China. Drying in a forced air drying oven at 250 deg.C for 6 hr for pre-carbonization, placing the wood chips in a tube furnace, heating to 1000 deg.C under protection of Ar gas for carbonization for 6 hr, and carbonizing at 750 deg.C with CO2(80sccm) gas activation for 10 h. The activated carbonized wood was flaked into 0.5mm pieces with 2000 mesh sandpaper, washed with 6% HCl for 20 minutes, then several times with deionized water until the wash became clear, and then washed at 80 ℃ in a drumAnd (5) drying in an air drying box. Subjecting the obtained carbonized wood chips to Ni (NO) at 90 deg.C3)2The solution (0.25mol/L) was soaked for 15 minutes and then dried in air. The sections were then transferred to Ar (400sccm), H2(30sccm) and C2H4(99.9%, 90sccm) of a mixed gas. Purging the quartz tube with Ar gas flow for 30 minutes to remove air, then raising the temperature to 740 ℃ at a heating rate of 10 ℃ min-1, and introducing C2H4Gas and hold for 5 minutes. Immersing the resulting MWCNT-CW scaffold slice in HNO3(20 wt.%) and H2SO4(20 wt%) for 4 minutes to increase hydrophilicity, and then repeatedly washed with water until the pH is 7. Finally, MWCNT-CW sections were dried in air and cut into sections of 15mm × 5mm × 0.5mm before use.
2)Co(OH)2Preparation of/MWCNT-CW composite electrode
In the presence of 0.1mol/L Co (NO)3)2·6H2O solution of Co (OH) at-0.9V vs SCE2Electrodeposited into MWCNT-CW scaffolds. Electrochemical deposition was performed in a three-electrode system using MWCNT-CW scaffolds as working electrodes, platinum electrodes as counter electrodes, and saturated calomel electrodes as reference electrodes. Co (OH) can be controlled by varying the electrodeposition time (1 hour, 2 hours, 3 hours, 6 hours and 9 hours)2The amount of the supported catalyst. Followed by the reaction of Co (OH)2the/MWCNT-CW mixed electrode was dried in air at 80 ℃. The mass of the active substance is quantified by weighing.
The asymmetric super capacitor is made of Co (OH)2the/MWCNT-CW electrode (4 mm. times.5 mm. times.0.5 mm) was assembled as a cathode, and the MWCNT-CW electrode was assembled as an anode (4 mm. times.5 mm. times.0.5 mm). Polyvinyl alcohol (PVA) gel electrolyte was prepared by dissolving PVA (1.2g) in water (10g) at 90 ℃ for 3h, then adding KOH solution (2mL, 0.6g KOH) and stirring at 60 ℃ for 30 min. And finally, assembling the electrode and the non-woven fabric membrane into the super capacitor by using PVA-KOH gel electrolyte.
FIG. 1 is a flow chart of the preparation of the electrode in this example. We use waste fir as raw material. Pre-carbonizing Chinese fir wood slices, and processingCarbonizing at 1000 deg.C, and then adding CO at 750 deg.C2Activating to obtain carbonized wood. The carbon nano tube is synthesized on the inner surface of the carbonized wood tube cell by a chemical vapor deposition method, and provides a rich conductive surface for an active material. In a three-electrode electrochemical cell, Co (OH)2The nanoplatelets are electrodeposited on MWCNTs and tracheid scaffolds. Platinum and saturated calomel electrodes were used as counter and reference electrodes, respectively. Co (NO) electrodeposited at constant potential of 0.1mol/L3)2·6H2In O electrolyte at-0.9V. During electrochemical deposition, the following reactions occur at the surface of the CNT carbonized scaffold electrode:
NO3 -+7H2O+8e-→NH4 ++10OH- (1)
Co2++2OH→Co(OH)2 (2)
scanning Electron Microscope (SEM) images of top and cross-sectional views of Carbonized Wood (CW) sections are shown in fig. 2, 3. The tracheids of fir are arranged in order and uniformly, have an average size of 20 μm to 30 μm, are suitable for electrodeposition, and are loaded with active substances on the inner wall thereof to construct an energy storage device. Fig. 4, 5, 6 show that the length of MWCNTs is between 1 μm and 2 μm, and the MWCNTs are uniformly distributed on the inner wall of the carbonized wood tracheid structure. FIG. 7 and FIG. 8 illustrate Co (OH)2The nanoplatelets are grown by electrodeposition on the surface of the carbon nanotubes and the inner wall of the carbonaceous scaffold without blocking the macropores derived from the tracheid structure. FIG. 9 shows MWCNT coated with Co (OH)2Encapsulate and form a conductive network, then spread on Co (OH)2In the nanosheets. Increased surface roughness of the inner wall of the wooden tube cell, Co (OH)2The nano sheets are uniformly arranged and connected with each other to form a staggered net structure, which is beneficial to the contact between an electrode material and an electrolyte and the acceleration of electron transmission and electrochemical reaction. The high conductivity and chemical stability of the carbon nanotubes can effectively solve the problem of Co (OH)2And the electrochemical performance of the hybrid electrode is improved by the synergistic effect of the two materials. FIG. 10 shows a reaction product of Co (OH)2Direct electrodeposition on the inner surface of a carbonized tube cell without MWCNT，Co(OH)2The nanoplatelets are also vertically and uniformly attached to the scaffold. FIG. 11 and FIG. 12 are Co (OH), respectively2Transmission Electron Microscope (TEM) and energy dispersive X-ray spectrograms of/MWCNT-CW electrodes, showing Co (OH)2And Co (OH)2Are uniformly coated on the surface of the individual MWCNTs, making intimate contact with the conductive scaffold. FIGS. 13, 14, 15 are TEM high resolution images of samples showing typical interplanar spacings of 0.34nm, 0.24nm and 0.46nm, corresponding to the (002) lattice and Co (OH) of MWCNT, respectively2The (102), (002) crystal lattices of (1), (002). FIG. 16 is an electron diffraction pattern of selected regions showing Co (OH)2The nanoplatelets are polycrystalline.
FIG. 17 shows Co (OH)2Infrared spectrum of the/MWCNT-CW composite electrode. 3566cm-1The broad peak at (A) is attributed to Co (OH)2Stretching and vibrating the hydroxyl groups in the nanosheets. 1384cm-1The peak of (C) is derived from Co (OH)2H-O deformation vibration of the medium hydroxyl group. In addition, at 518cm-1And 634cm-1The peak at (a) is caused by tensile vibration and bending vibration of the Co — OH bond. FIG. 18, FIG. 19, FIG. 20 and FIG. 21 show Co (OH)2X-ray photoelectron Spectroscopy (XPS) of/MWCNT-CW composite electrodes. Fig. 18 shows that the complete XPS spectrum shows the presence of C1s, O1s and Co2p elemental peaks, which are consistent with the energy dispersive X-ray spectral and elemental mapping images. Fig. 19 shows that the C1s peak can be deconvoluted into five peaks with binding energies of 283.9, 284.8, 285.7, 286.9 and 288.8eV, respectively. Among them, peaks at 283.9eV and 284.8eV are assigned to CC (sp2) and CC (sp3) bonds, respectively. The binding energies at 285.7, 286.9 and 288.8eV indicate the presence of C-O, C-OH and C ═ O bonds, respectively. Fig. 20 shows that the high resolution O1s spectrum shows three peaks centered at 530.7, 531.6 and 533.0eV, assigned to Co-O, Co-OH and C ═ O bonds, respectively. FIG. 21 shows the deconvoluted Co2p spectrum showing two major peaks for Co2p 3/2 and Co2p 1/2 at 781.5 and 797.3eV, respectively, with a 15.8eV spin-orbit split. The satellite peaks are at 786.0 and 803.1eV, corresponding to a difference in binding energy of 4.5 and 5.8eV, respectively. The band gap of nearly 6.0eV is associated with Co2+, while the band gap of 9-10eV is associated with Co3+It is related. This indicates the divalent state of Co in the mixed electrode.
Next we compared Co (OH)2MWCNT-CW composite electrode and Co (OH)2Electrochemical performance of the/CW composite electrode. To optimize the electrodeposition time, Co (OH) with different deposition times was tested at different currents2And the corresponding calculated areal specific capacitance is shown in figure 22. Initially, the capacitance increases with deposition time, but the capacitance decreases with longer electrodeposition time. This may be due to Co (OH)2And their poor connectivity to the conductive scaffold. At the same time, excess Co (OH)2The nanosheets may block the pores of the cell structure scaffold, thereby making it difficult for the electrode surface and active material to enter the electrolyte. FIG. 22 shows that the mixed electrode with electrodeposition time of 6h shows the best chemical performance, corresponding to 0.42gcm-3Co (OH)2And (4) loading. At 5mAcm-2The area specific capacitance of the electrode was 29.6F cm at a current density of (2)-2. Even at 60mAcm-2The electrode remained 20.2Fcm-2Area to capacitance. The scanning rate of the Cyclic Voltammogram (CV) was 1mV s-1The redox peak of (A) is derived from Co of pseudocapacitance characteristics2 +/Co3 +Redox transformation of (a). Fig. 23 shows the CV curve of the electrode at different scan rates in the potential window of-0.2 to 0.5V and slightly deformed as the scan rate increases due to the effect of the electrode resistance. According to 1mVs-1The surface capacitance calculated from the CV curve of (d) was 23.8Fcm-2This is consistent with the capacitance resulting from a constant current discharge. FIG. 24 is a constant current charge and discharge curve showing charge and discharge at 5, 10, 20, 40 and 60mAcm-2The area capacitance of the electrode is 29.6, 27.3, 24.9, 22.3 and 20.2Fcm respectively at the current density of (A)-2. When calculated based on the mass of the active material, the corresponding mass specific capacitances are 1406.7, 1298.3, 1185.7, 1063.6 and 961.9Fg, respectively-1. The mass specific capacitances based on total mass were 826.3, 762.7, 696.5, 624.8 and 565.0Fg, respectively-1。
FIG. 25, FIG. 26, FIG. 27 show Co (OH)2A CW electrode at 5mAcm-2Shows the highest capacitance of 19.9Fcm when placed under electrodeposition for 9h-2. And areAnd the area capacitance at various current densities is less than that of Co (OH)2The area capacitance of the/MWCNT-CW electrode, which indicates the role of the MWCNT in the mixed electrode.
FIG. 28 shows the difference in the height of 80mAcm-2Current density of (3) after 7500 cycles of charging and discharging, Co (OH)2MWCNT-CW and Co (OH)2The CW electrode retains 84.7% and 67.0% of its initial capacitance, respectively. Co (OH)2The better cycling stability of the/MWCNT-CW composite electrode can be attributed to anchoring the Co (OH) while maintaining good electrical connectivity2Nanosheets of CNTs, thereby achieving better redox chemistry kinetics. FIG. 29 and FIG. 30 show Co (OH)2The advantages of MWCNT can be further demonstrated by Electrochemical Impedance Spectroscopy (EIS) of the/MWCNT-CW composite electrode, which shows Co (OH)2The equivalent series resistance (5.9 Ω) and the charge transfer resistance (0.5 Ω) of the/MWCNT-CW hybrid electrode are small. In the high frequency part, the intersection between the impedance curve and the real axis represents the sum of the electrode resistance and the electrolyte resistance (Rs), and the diameter of the semicircle is used to measure the charge transfer resistance (Rct). The larger the slope of the line in the low frequency part, the smaller the diffusion resistance of the electrode. Co (OH)2The equivalent series resistance (5.9 Ω) and charge transfer resistance (0.5 Ω) of the/MWCNT-CW electrode are small, indicating that the MWCNT can improve the conductivity of the material and promote rapid diffusion and transfer of ions. By comparison, Co (OH)2The electrochemical performance of the/MWCNT-CW electrode is better, which is mainly because the MWCNT promotes the electron transfer between the matrix and the active material, and the low conductivity of the cobalt hydroxide is effectively improved. At the same time, MWCNT anchored on substrate makes Co (OH)2Is more stable in position and structure. Co (OH)2Is not easy to fall off, and the cycle performance of the electrode material is obviously improved. Mixing Co (OH)2/MWCNT-CW composite electrode (electrodeposition Co (OH)2And 6 hours) is taken as a cathode, the MWCNT-CW electrode is taken as an anode to assemble an asymmetric supercapacitor, and non-woven fabric is taken as a diaphragm to assemble. PVA-KOH is used as electrolyte. The MWCNT-CW electrode has a voltage window of-1V to 0V and an area specific capacitance of 3.1F cm-2 measured in a three-electrode system using KOH solution (1M) as the electrolyte. After being assembled into an Asymmetric Super Capacitor (ASC), the CV scanning curve and the charge of the ASC are carried out under the potential window of 0 to 1.5VThe discharge curves are fig. 31 and fig. 32, which show that similar quasi-rectangular shapes are shown at various scanning rates, and the charge and discharge curves are kept symmetrical when the current density rises, both indicating that the asymmetric supercapacitor has better capacitance characteristics and high-rate performance. FIG. 33 shows that the area capacitance of the supercapacitor is 3.31Fcm at a current density of 5mAcm-2-2Mass specific capacitance of 65.6Fg-1. FIG. 34 shows the difference in the concentration at 60mAcm-2After 11,000 charge-discharge cycles, the asymmetric supercapacitor retained 97.8% of its initial capacitance. FIG. 35 shows Co (OH)2Nyquist plot for/MWCNT-CW// MWCNT-CW supercapacitors. The Rs and Rct of the asymmetric supercapacitor are 9.7 omega and 6.1 omega respectively. In addition, the super capacitor is at 5mAcm-2The lower surface energy density and the power density were 0.90mWhcm-2And 3.50mWcm-2. At 100mAcm-2The energy density and the power density were 0.18mWhcm-2And 70.00mWcm-2. Fig. 36 to show the practical application of asymmetric supercapacitors, two asymmetric SCs in series successfully lit a green light emitting diode (2V).
In this embodiment, a carbon nanotube is synthesized in carbonized wood by an in-situ synthesis method to serve as a conductive support to fix an electrochemical active material of the asymmetric supercapacitor. The presence of MWCNT increases Co (OH)2A conductive surface in contact with the substrate, thereby improving physical bonding and electrical connectivity. By mixing Co (OH)2the/MWCNT-CW loading electrode is coupled to the MWCNT-CW electrode to make an asymmetric supercapacitor. The super capacitor has high energy storage performance, including 3.31Fcm-2Surface capacitance of (1), 0.9mWhcm-2Energy density of 70mWcm-2Power density of and at 60mAcm-2The capacity retention after 11,000 charges at a current density of (3) was 97.8%.
Claims (9)
1. An electrode material based on a multiwalled carbon nanotube-carbonized wood mixed support is characterized in that: comprises carbonized wood chips; the carbonized wood chips are formed by carbonizing and activating Chinese fir chips, and the carbonized wood chips are formed by carbonizing and activating Chinese fir chipsA woodchip is formed with a tracheid structure, the inner wall of the tracheid structure is in-situ anchored with multi-walled carbon nanotubes grown by chemical vapor deposition, so that MWCNT-CW scaffolds are formed on the carbonized woodchip, and Co (OH) is deposited by electrochemical deposition2The nano-sheets are wrapped on the multi-walled carbon nano-tubes to obtain the electrode material based on the multi-walled carbon nano-tube-carbonized wood mixed support;
the electrochemical deposition is as follows: in the presence of 0.1mol/L Co (NO)3)2•6H2O solution, at-0.9V vs. saturated calomel electrode, Co (OH)2Electrodeposition into MWCNT-CW scaffolds; electrochemical deposition was carried out in a three-electrode system using carbonized wood chips containing MWCNT-CW scaffolds as the working electrode, a platinum electrode as the counter electrode, and a saturated calomel electrode as the reference electrode.
2. The multiwalled carbon nanotube-carbonized wood hybrid scaffold-based electrode material of claim 1, wherein: carbonization is carried out by drying for 3-9 hours in a blowing dry box at 250 ℃ for pre-carbonization, and then placing the wood chips in a tube furnace and heating to 1000 ℃ for carbonization for 3-9 hours under the protection of Ar gas.
3. The multiwalled carbon nanotube-carbonized wood hybrid scaffold-based electrode material of claim 1, wherein: the activation is with CO at 750 ℃2And activating for 8-12 hours in a gas flowing atmosphere, wherein the flowing speed of the CO2 is 60-100 sccm.
4. The multiwalled carbon nanotube-carbonized wood hybrid scaffold-based electrode material of claim 1, wherein: the chemical vapor deposition in-situ anchoring growth of the multi-walled carbon nanotube on the tracheid structure comprises the following steps: the activated carbonized wood chips are treated at the temperature of 80-100 ℃ with 0.25mol/L of Ni (NO)3）2Soaking in water solution for 15min, and removing water; with H2Performing chemical vapor deposition in a tubular furnace by using reducing gas, ethylene as a carbon source and Ar as a protective gas to obtain the chemical vapor deposited flaky fir wood chips, so that the wood chips are carbonizedThe multi-walled carbon nano-tube grows on the tracheid structure by chemical vapor deposition in-situ anchoring.
5. The multiwalled carbon nanotube-carbonized wood hybrid scaffold-based electrode material of claim 4, wherein: the flow rate of the H2 gas flow is 20-40sccm, the flow rate of the Ar gas flow is 300-500sccm, and the flow rate of the ethylene gas flow is 80-100 sccm; the time of chemical vapor deposition is 3-10 min.
6. A preparation method of an electrode material based on a multiwalled carbon nanotube-carbonized wood mixed support is characterized by comprising the following steps: the method comprises the following steps: 1) naturally air-drying the fir wood chips, and cutting the fir wood chips into preset sizes;
2) carbonizing, namely placing the fir wood chips obtained in the step 1) in a hot air drying box for carbonizing for 4-8h, and carbonizing for 4-8h at 800-1200 ℃ under the protection of Ar gas to obtain OWC sheets;
3）CO2and (3) activation: slicing OWC in CO2Activating for 8-12h in Ar mixed gas flow, and cutting or grinding to a preset size to form an AWC electrode; the activation temperature is 650-850 ℃; ar gas flow rate of CO23 times of the flow of CO2The flow rate is 60-80 sccm;
4) removing impurities;
5) preparation of MWCNT-CW scaffolds the AWC electrode treated in step 4) was placed in Ni (NO)3）2Soaking in water solution for 10-20min, and drying in drying oven to obtain water solution H2Performing chemical vapor deposition in a tubular furnace by using reducing gas, ethylene as a carbon source and Ar as protective gas to obtain the MWCNT-CW support; said H2The flow rate of the gas flow is 20-40sccm, the flow rate of the Ar gas flow is 300-500sccm, and the flow rate of the ethylene gas flow is 80-100 sccm; the chemical vapor deposition time is 3-10 min;
6) subjecting the MWCNT-CW scaffold of step 5) to a hydrophilic treatment;
7）Co(OH)2preparation of/MWCNT-CW composite electrode, the MWCNT-CW scaffold of step 6) was immersed in a solution containing 0.1mol/L Co (NO)3)26H2O in solutionThe MWCNT-CW stent is used as a working electrode, a platinum electrode is used as a counter electrode, and a saturated calomel electrode is used as a reference electrode for electrochemical deposition, wherein the electrochemical deposition time is 1-9 hours; drying after electrochemical deposition.
7. The method for preparing an electrode material based on a multiwalled carbon nanotube-carbonized wood hybrid scaffold according to claim 6, wherein the method comprises the following steps: the step 5) of preparing the MWCNT-CW scaffold comprises the steps of:
the obtained carbonized wood chips have 0.25mol/L of Ni (NO) at 90 DEG C3)2Soaking in the solution for 15min, and then drying in air;
8. The method for preparing an electrode material based on a multiwalled carbon nanotube-carbonized wood hybrid scaffold according to claim 6, wherein the method comprises the following steps: and the step 4) is to wash the step 3) with 6% HCl for more than 15 minutes, wash the solution with deionized water for more than 3 times until the cleaning solution becomes clear, and then dry the solution in a blast drying oven at 60-100 ℃.
9. A supercapacitor, characterized by: a fir wood carbon sheet electrode material based on carbon nanotubes and manganese dioxide comprising any one of claims 1 to 5.
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