CN114956077A - Green preparation of hierarchical pore carbon microtube with ultra-large specific surface area and application of supercapacitor of hierarchical pore carbon microtube - Google Patents
Green preparation of hierarchical pore carbon microtube with ultra-large specific surface area and application of supercapacitor of hierarchical pore carbon microtube Download PDFInfo
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- C01B32/00—Carbon; Compounds thereof
- C01B32/30—Active carbon
- C01B32/312—Preparation
- C01B32/318—Preparation characterised by the starting materials
- C01B32/324—Preparation characterised by the starting materials from waste materials, e.g. tyres or spent sulfite pulp liquor
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
- H01G11/22—Electrodes
- H01G11/24—Electrodes characterised by structural features of the materials making up or comprised in the electrodes, e.g. form, surface area or porosity; characterised by the structural features of powders or particles used therefor
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
- H01G11/22—Electrodes
- H01G11/30—Electrodes characterised by their material
- H01G11/32—Carbon-based
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The invention discloses green preparation of a hierarchical pore carbon microtube with an ultra-large specific surface area and application of the hierarchical pore carbon microtube in a super capacitor, and relates to the field of green preparation of novel carbon materials and energy storage application of the novel carbon materials. The technology comprises the following steps of S1, obtaining dry phoenix tree batting; s2, heating and self-activating the phoenix tree seed sealed in a self-made high-temperature-resistant crucible under an inert protective atmosphere, wherein the self-activating temperature is 900-1300 ℃, the self-activating time is 2-8h, and then cooling to obtain the multi-hole carbon microtube with the super-large specific surface area; the obtained carbon microtube is directly used as a supercapacitor material without cleaning and drying, and the assembled supercapacitor is high in specific capacitance, energy density and power density. The method for preparing the multi-stage porous carbon microtube has the advantages that raw materials are biomass waste, the biomass waste is changed into valuable, a pore-forming agent is not required to be added, the preparation process is simple, the one-step method is completed, the process is green and environment-friendly, and the prepared porous carbon microtube as an electrode material has excellent electrochemical performance.
Description
Technical Field
The invention relates to the field of green preparation of novel carbon materials and energy storage application thereof, in particular to green preparation of a hierarchical pore carbon microtube with an ultra-large specific surface area and application of a supercapacitor of the hierarchical pore carbon microtube.
Background
The super capacitor is an electric energy storage device with great potential at present, and the electrode material is one of important factors influencing the performance of the super capacitor, so that the super capacitor is also a focus of attention of researchers, and the research of the research has been motivated to continuously try to synthesize novel electrode materials.
The porosity and the conductivity of the electrode material are key factors influencing the electrochemical performance of the supercapacitor, and the porosity and the conductivity respectively have important influences on the charge storage capacity and the electrochemical impedance of the material. Carbon materials are low in cost, and have good electrical conductivity, environmental friendliness, and chemical stability, compared to metal oxides and conductive polymers, and thus carbon materials are considered as the most promising electrode materials for supercapacitors, mainly including activated carbon, graphene, and carbon nanotubes. Among these carbon electrode materials, graphene and carbon nanotubes require relatively complicated and costly preparation processes, and are not suitable for mass production. The biomass-based activated carbon material has gradually become the most potential electrode material due to the advantages of low cost, strong renewability and good economy.
The preparation method of the biomass-based activated carbon material mainly adopts a chemical activation method, and chemical substances such as ZnCl are introduced to be used as pore-forming agents 2 KOH, in order to remove pore-forming agents for activation, often introduces new hazardous chemical waste (HCl, etc.), and thus, hazardous waste is accompanied in the activation process, environmental damage and complicated steps. Therefore, a technical scheme for preparing the biomass-based activated carbon material by a simpler and more environment-friendly method is urgently needed to be developed.
Disclosure of Invention
In view of the above, the green preparation method of the hierarchical porous carbon microtube with the ultra-large specific surface area and the application of the supercapacitor thereof are provided, a pore-forming agent is not required to be added, the preparation process is simple and environment-friendly, and the prepared porous carbon microtube as an electrode material has excellent electrochemical performance.
In order to achieve the technical purpose, the following technical scheme is adopted in the application:
in a first aspect, the application provides a preparation method of a hierarchical porous carbon microtube with an ultra-large specific surface area, which comprises the following steps:
s1, obtaining dry phoenix tree batting;
s2, heating the phoenix tree batting in a closed high-temperature-resistant crucible under an inert atmosphere for self-activation at the temperature of 900-1300 ℃ for 2-8h, and then cooling to obtain the multi-level pore carbon microtube with a large specific surface area.
As used herein, the "temperature-raising self-activation" process refers to a process in which the phoenix tree batting is placed in a high-temperature sealed molybdenum crucible, and then the whole is placed in a sealed tube furnace in an inert atmosphere, such as nitrogen, argon, etc., and is heated to a target temperature, and pyrolysis is performed for a certain period of time.
Suitable but non-limiting temperatures for self-activation are as herein defined, from 900 ℃ to 1300 ℃, e.g. 900 ℃, 1000 ℃, 1100 ℃, 1200 ℃, 1300 ℃; the suitable but non-limiting self-activating time is as shown in the text, and is 2-8h, such as 2h, 3h, 4h, 5h, 6h, 7h, 8h, under the activation process parameters, the phoenix tree seed can complete self-activating pore-forming, and then the room temperature is reduced by natural cooling, so that the hierarchical porous carbon microtube with the super-large specific surface area can be formed.
According to the technical scheme, the phoenix tree batting is used as a precursor, self-activation pore-forming is carried out to prepare the hierarchical pore carbon microtubule with the ultra-large specific surface area, the characteristic that the phoenix tree batting has higher content of H, O element compared with other biomasses is utilized, and sufficient amount of H is pyrolyzed under the conditions that the self-activation temperature is 900-1300 ℃ and the self-activation time is 2-8H 2 ，CO 2 ，CO，CH 4 ，H 2 O and the like, and the phoenix tree wadding also contains more than 5.64 wt.% of ash content K element, so that the surface structure of the carbon material can be etched at high temperature, and further conditions are provided for self-activating pore-forming.
The scheme solves the problem of pollution and also solves another technical problem, in the prior art, the pore-forming agent and the precursor are not uniformly mixed, so that the problems of insufficient and nonuniform activation degree are caused, and the electrochemical performance of the obtained electrode material is poor.
Preferably, the high-temperature-resistant crucible can resist 1500 ℃.
Preferably, the self-activation temperature is 1000-1100 ℃, such as 1000 ℃, 1010 ℃, 1020 ℃, 1030 ℃, 1040 ℃, 1050 ℃, 1060 ℃, 1070 ℃, 1080 ℃, 1090 ℃ and 1100 ℃, and more preferably, the self-activation temperature is 1100 ℃, under the temperature condition, the self-activation is more highly caused, the specific surface area of the prepared super-large specific surface area hierarchical pore carbon microtubule is larger, and the total pore volume is higher.
Preferably, the self-activation time is 6-8h, such as 6h, 6.5h, 7h, 7.5h and 8h, more preferably, the self-activation time is 6h, and within the time range, the self-activation pore-forming degree is higher, the specific surface area of the prepared super-large specific surface area hierarchical pore carbon microtube is larger, and the total pore volume is higher.
Preferably, the temperature rising rate is 5-10 ℃/min, for example, 5 ℃/min, 6 ℃/min and 7 ℃/min, more preferably, the temperature rising rate is 5 ℃/min, and at the temperature rising rate, the phoenix tree wadding can complete the self-activation pore-forming process mildly, and the influence on the structure of the porous carbon microtube is small.
Preferably, the drying mode in the step S1 is air blast drying, and because the phoenix tree seed has a relatively low specific gravity, the drying mode can be used for quickly and uniformly drying the phoenix tree seed without affecting the original pipeline structure of the phoenix tree seed, thereby providing a relatively complete raw material basis for the subsequent preparation of the porous carbon microtube.
Preferably, the temperature of the forced air drying is 65-70 deg.C, such as 65 deg.C, 68 deg.C, 70 deg.C, and the time is 12-14h, such as 12h, 13h, 14 h.
Preferably, step S1 is preceded by the following steps: soaking/rinsing Phoenix Tree seed with ultrapure water, specifically, soaking Phoenix Tree seed with ultrapure water for 2 hr, or 1-3cm 3 Washing with ultra-pure water at a flow rate of/min for 20min to remove impurities adsorbed on the surface of the phoenix tree seed.
In a second aspect, the application provides a hierarchical porous carbon microtube with an ultra-large specific surface area, which is prepared by the above preparation method, wherein the specific surface area of the hierarchical porous carbon microtube with the ultra-large specific surface area is 856- 2 Per g, total pore volume of 0.43-1.98cm 3 /g。
Preferably, the mesoporous volume is 0.14-1.36cm 3 The proportion of mesopores is 30-70 percent per gram.
In a third aspect, the application provides an application of the hierarchical porous carbon microtube with the ultra-large specific surface area, the hierarchical porous carbon microtube is directly used as an electrode material of a super capacitor, and the assembled capacitor is high in specific capacitance, energy density and power density.
The beneficial effect of this application is as follows:
1. the phoenix tree seed is used as a precursor, under a limited process condition, the multistage porous carbon microtube with the ultra-large specific surface area can be obtained without adding a pore-forming agent, the process is simple and environment-friendly, no subsequent pollution is caused, and the environment protection is facilitated;
2. in the application, the activation degree of the phoenix tree wadding is high and uniform, and the prepared hierarchical porous carbon micro-tube with the super-large specific surface area has the advantages of ordered structure, concentrated pore diameter, large specific surface area, high total pore volume and good electrochemical performance when used as an electrode material;
3. the application provides a direction for the treatment of the phoenix tree wadding waste, and realizes the high added value utilization of the phoenix tree wadding;
4. the obtained carbon microtube is directly used as a supercapacitor material without being cleaned and dried, and the assembled supercapacitor is high in specific capacitance, energy density and power density; the method for preparing the multi-stage porous carbon microtube has the advantages that raw materials are biomass waste, the biomass waste is changed into valuable, a pore-forming agent is not required to be added, the preparation process is simple, the one-step method is completed, the process is green and environment-friendly, and the prepared porous carbon microtube as an electrode material has excellent electrochemical performance.
Drawings
FIG. 1 is a flow chart of the preparation of the present invention.
FIG. 2 is a scanning electron micrograph of a sample according to an embodiment of the present invention.
FIG. 3 is a graph of TG-MS of phoenix tree batting.
FIG. 4 is a plot of cyclic voltammetry for porous carbon microtubes prepared in examples 2-6 of the present invention.
Fig. 5 is a cyclic voltammogram of the porous carbon microtubes prepared in examples 4 and 7-10 of the present invention.
Fig. 6 is a graph showing the relationship between the capacity retention rate, the coulombic efficiency and the number of charge and discharge cycles of the sample in example 4 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
It is generally recognized that pyrolysis of biomass produces H 2 ，CO 2 ，CO，CH 4 ，H 2 O, and the like. Wherein, CO 2 And H 2 O has been used as an activator for producing activated carbon. Thus, CO produced by thermal decomposition of biomass 2 And H 2 O can be used as a pore former during activation when the biomass can uniformly decompose sufficient amounts of CO 2 And H 2 And when O is used, no additional gas is needed to be input, so that an idea is provided for solving the environmental problem caused by activation of the carbon material.
The pore-forming agent is still used by the prior art when preparing the electrode material of the supercapacitor based on the biomass-based activated carbon because the content of O, H element in the same biomass is constant, and CO which can be decomposed by the biomass in the prior art 2 And H 2 The use of pore-forming agents cannot be completely abandoned because of insufficient O content, and biomass with a high content of O, H elements can be simply selected as the pore-forming agentThe electrochemical properties of the raw materials for preparing the electrode material and the structure of the obtained material are also affected by the structural limitations of the selected biomass and the activation process.
The applicant unexpectedly finds that the phoenix tree batting as a biomass waste has H, O, K elements (see table 1) which are more abundant than carbon materials derived from other biomass wastes, and the phoenix tree batting has a special microtubule structure, so that when the phoenix tree batting is used as a precursor to prepare the carbon microtubule under a specific activation process, a pore-forming agent is not required to be added, and the prepared carbon microtubule has excellent electrochemical performance.
Specifically, in the self-activation process, a sufficient amount of gas can be pyrolyzed from H, O element with high content in the phoenix tree seed, the content of heteroatom K element is more than that in other biomasses, K element can etch the surface structure of the carbon material at high temperature, the pore-forming of the biomass-based carbon material is facilitated without an additional pore-forming agent, and the thermogravimetric analysis is performed on the phoenix tree seed in the activation pyrolysis process by combining the element content characteristic of the phoenix tree seed, and the pore-forming mechanism can be clarified by observing the amount of gas generated in the phoenix tree seed pyrolysis process: as shown in FIG. 3, the weight loss initially occurred during pyrolysis of phoenix tree seed between 250 ℃ and 400 ℃ with the concomitant H 2 O、CO、CO 2 、NO 2 The four gases content rises, which is the main reaction in the pyrolysis of phoenix tree batts, with increasing temperature, after which H 2 The content of CO slowly increases with the temperature, mainly because H 2 C + H is etched on the surface structure of the carbon material while CO is generated by the reaction of O and the surface carbon material 2 O→CO+H 2 Other gases also have a pore-forming effect, CO 2 With NO 2 The similar trend of rising before falling also appears, and the principle is 2C +2NO 2 →2CO 2 +N 2 With C + CO 2 → 2CO also activates the surface of the carbon microtubule in the self-activation process, and meanwhile, the phoenix tree wadding contains more than 5.64 wt.% of ash K element which can etch the surface structure of the carbon material at high temperature, and the reaction formula is K 2 O + C → K + CO; on the other hand, the phoenix tree wadding has a special microtubule structure and is also self-aliveThe difficulty is reduced by chemical pore-forming, after self-activation pore-forming is carried out under a specific activation process, no additional pore-forming agent is required to be added, and the formed electrode material has a multi-level pore structure comprising macropores, mesopores and micropores, so that the specific surface area is high, the total pore volume is high, and the electrochemical performance is good.
Therefore, the invention is created.
TABLE 1 surface element content and ash element content of Biomass
As shown in fig. 1, an embodiment of the present application provides a method for preparing a hierarchical porous carbon microtube with an ultra-large specific surface area, which includes the following steps:
s1, obtaining dry phoenix tree batting;
s2, placing the phoenix tree seed in a high-temperature sealed molybdenum crucible under an inert atmosphere, then placing the whole in a sealed tube furnace under the inert atmosphere such as nitrogen, argon and the like, heating up and self-activating, wherein the self-activating temperature is 900-1300 ℃, the self-activating time is 2-8h, and then naturally cooling to room temperature to obtain the super-large specific surface area multi-level hole carbon microtube.
In some embodiments, step S1 is preceded by: s0. soaking or washing the collected Firmiana simplex seed with ultrapure water, specifically soaking Firmiana simplex seed with ultrapure water for 2 hr or 1-3cm for 2 hr 3 Washing with ultrapure water at a flow rate of/min for 20 min;
in some embodiments, the drying mode of the phoenix tree seed is air blast drying, the temperature of the air blast drying is 65-70 ℃, and the time is 12-14 h;
in some embodiments, the ramp rate of ramp self-activation is 5-7 ℃/min.
The embodiment of the application also provides the hierarchical porous carbon micro-tube with the ultra-large specific surface area, wherein the specific surface area of the hierarchical porous carbon micro-tube with the ultra-large specific surface area is 856-2805m 2 Per g, total pore volume of 0.43-1.98cm 3 /g。
The embodiment of the application also provides an application of the hierarchical pore carbon microtube with the ultra-large specific surface area as an electrode material of a supercapacitor.
Example 1
A preparation method of a hierarchical porous carbon microtube with an ultra-large specific surface area comprises the following steps: drying the naturally collected phoenix tree seed floss for 14 hours at 70 ℃ by using a blast dryer to obtain pure and dry phoenix tree seed floss, then putting 0.5g of the dried phoenix tree seed floss into a 50ml high-temperature sealed molybdenum crucible, then putting the whole into a sealed tubular furnace in a nitrogen atmosphere, activating for 6 hours at 900 ℃, naturally cooling to room temperature, and obtaining the ultra-large specific surface area multi-stage porous carbon microtubule.
Example 2
A preparation method of a hierarchical porous carbon microtube with an ultra-large specific surface area comprises the following steps: soaking the naturally collected phoenix tree seed in ultrapure water to remove impurities adsorbed on the surface, and then drying at 65 ℃ for 12 hours to obtain pure and dried phoenix tree seed; putting 0.5g of dried phoenix tree batting into a 50ml high-temperature sealed molybdenum crucible, then putting the whole into a sealed tube furnace in a nitrogen atmosphere, activating for 6h at 900 ℃, naturally cooling to room temperature to obtain the super-large specific surface area hierarchical pore carbon microtube, wherein a scanning electron microscope picture is shown as a picture in fig. 2(A), as can be seen from the picture, a porous carbon sample has a hollow microtube structure with the diameter of 3-8 mu m and the wall thickness of 1-2 mu m, and the tubular structure is not damaged in the activation process, thereby proving that the sample in the invention is really a carbon microtube.
Example 3
A preparation method of a hierarchical porous carbon microtube with an ultra-large specific surface area comprises the following steps: soaking the naturally collected phoenix tree seed in ultrapure water to remove impurities adsorbed on the surface, and then drying at 65 ℃ for 12 hours to obtain pure and dried phoenix tree seed; putting 0.5g of dried phoenix tree batting into a 50ml high-temperature sealed molybdenum crucible, then putting the whole into a sealed tube furnace in a nitrogen atmosphere, activating for 6h at 1000 ℃, naturally cooling to room temperature to obtain the super-large specific surface area hierarchical pore carbon microtube, wherein a scanning electron microscope picture is shown as a picture in figure 2(B), as can be seen from the picture, a porous carbon sample has a hollow microtube structure with the diameter of 3-8 mu m and the wall thickness of 1-2 mu m, and the tubular structure is not damaged in the activation process, thereby proving that the sample in the invention is really a carbon microtube.
Example 4
The other steps are the same as example 3, except that the activation temperature of the phoenix tree seed is 1100 ℃, the scanning electron micrograph is shown in fig. 2(C), and it can be seen from the figure that the porous carbon sample has a hollow microtube structure with a diameter of 3-8 μm and a wall thickness of 1-2 μm, and the tubular structure is not destroyed in the activation process, which proves that the sample in the present invention is actually a carbon microtube.
Example 5
The other steps are the same as example 3, except that the activation temperature of the phoenix tree seed is 1200 ℃, the scanning electron micrograph is shown in fig. 2(D), and it can be seen from the figure that the porous carbon sample has a hollow microtube structure with the diameter of 3-8 μm and the wall thickness of 1-2 μm, and the tubular structure is not destroyed in the activation process, which proves that the sample in the invention is actually a carbon microtube.
Example 6
The other steps are the same as example 3, except that the activation temperature of the phoenix tree seed is 1300 ℃, the scanning electron micrograph is shown in fig. 2(E), and it can be seen from the figure that the porous carbon sample has a hollow microtube structure with the diameter of 3-8 μm and the wall thickness of 1-2 μm, and the tubular structure is not destroyed in the activation process, which proves that the sample in the invention is actually a carbon microtube.
Example 7
The other steps are the same as example 4, except that the activation time of the phoenix tree seed is 2h, the scanning electron microscope image is shown as figure 2(F), it can be seen from the figure that the porous carbon sample has a hollow microtube structure with the diameter of 3-8 μm and the wall thickness of 1-2 μm, and the tubular structure is not destroyed in the activation process, which proves that the sample in the invention is actually the carbon microtube.
Example 8
The other steps are the same as example 4, except that the activation time of the phoenix tree seed is 3h, the scanning electron microscope image is shown as figure 2(G), it can be seen from the figure that the porous carbon sample has a hollow microtube structure with the diameter of 3-8 μm and the wall thickness of 1-2 μm, and the tubular structure is not destroyed in the activation process, which proves that the sample in the invention is actually the carbon microtube.
Example 9
The other steps are the same as example 4, except that the activation time of the phoenix tree seed is 4H, the scanning electron microscope image is shown as figure 2(H), it can be seen from the figure that the porous carbon sample has a hollow microtube structure with the diameter of 3-8 μm and the wall thickness of 1-2 μm, and the tubular structure is not destroyed in the activation process, which proves that the sample in the invention is actually the carbon microtube.
Example 10
The other steps are the same as example 4, except that the activation time of the phoenix tree seed is 8h, the scanning electron microscope image is shown as figure 2(I), it can be seen from the figure that the porous carbon sample has a hollow microtube structure with the diameter of 3-8 μm and the wall thickness of 1-2 μm, and the tubular structure is not destroyed in the activation process, which proves that the sample in the invention is actually the carbon microtube.
Comparative example 1
A preparation method of a hierarchical porous carbon microtube with an ultra-large specific surface area comprises the following steps: soaking the naturally collected phoenix tree seed in ultrapure water to remove impurities adsorbed on the surface, and then drying at 65 ℃ for 12 hours to obtain pure and dried phoenix tree seed; and (3) putting 0.5g of dried phoenix tree batting into a 50ml high-temperature sealed molybdenum crucible, then putting the whole into a sealed tube furnace in a nitrogen atmosphere, activating at 800 ℃ for 6h, naturally cooling to room temperature to obtain an electrode material, and scanning by an electron microscope to find no target carbon microtubule.
Comparative example 2
The other steps were the same as in comparative example 1, except that the activation temperature of the phoenix tree seed was 1400 ℃, and the target carbon microtubule was not found in the product by scanning electron microscope.
Comparative example 3
The other steps were the same as in comparative example 1, except that corncob was replaced with phoenix tree seed, and the product was scanned by electron microscope, and the target carbon microtubule was not found.
Comparative example 4
The other steps were the same as in comparative example 1, except that the phoenix tree batting was replaced with straw, and the target carbon microtubule was not found by scanning the product with an electron microscope.
Evaluation test
Specific surface area and total pore volume test: the specific surface area and the porous structure of the super large specific surface area hierarchical porous carbon microtubes prepared in examples 2 to 6 were calculated by using a full-automatic specific surface area and porosity analyzer (ASAP2020), and the results are shown in table 2, and the specific surface area and the porous structure of the super large specific surface area hierarchical porous carbon microtubes prepared in examples 4 and 7 to 10 were calculated by using a full-automatic specific surface area and porosity analyzer (ASAP2020), and the results are shown in table 2.
Evaluation of electrochemical properties: the electrochemical test is carried out on an electrochemical workstation (Shanghai Hua 760E), all tests adopt a three-electrode system, and the preparation flow of a working electrode is as follows: dispersing the prepared carbon microtube, acetylene black and polytetrafluoroethylene emulsion (solid content is 60 wt%) in absolute ethyl alcohol according to the mass ratio of 8:1:1, fully grinding, coating the ethanol on 1cm x 1cm of foamed nickel after the ethanol is completely volatilized, tabletting to obtain a working electrode, wherein a platinum sheet electrode is adopted as a counter electrode, and a mercury/mercury oxide electrode is adopted as a reference electrode. The electrolyte is 6mol/LKOH solution.
The cyclic voltammetry curve test is completed at a scanning speed of 10-100mv/s under a voltage window of-1-0 v, the cyclic voltammetry curves of the hierarchical pore carbon microtubes with the ultra-large specific surface areas prepared in examples 2-6 are shown in figure 4, and the cyclic voltammetry curves of the hierarchical pore carbon microtubes with the ultra-large specific surface areas prepared in examples 4 and 7-10 are shown in figure 5.
The constant current charging and discharging curve test is completed under a voltage window of-1-0 v and at a current density of 0.2-10A/g, the capacitance calculation is measured by the constant current charging and discharging curve, the specific capacitance and the capacitance retention rate of the ultra-large specific surface area multi-hole carbon micro-tube prepared in the embodiment 2-6 are shown in the table 2, and the specific capacitance and the capacitance retention rate of the ultra-large specific surface area multi-hole carbon micro-tube prepared in the embodiment 4 and the embodiment 7-10 are shown in the table 3.
TABLE 2 comparison table of properties of porous carbon microtubes prepared by activating for 6h at different temperatures
TABLE 31100 deg.C porous carbon microtube Performance comparison Table with different activation times
Evaluation of cycle stability: the super large specific surface area hierarchical pore carbon micro tube prepared in example 4 was used as an electrode for long-term cycling stability under the conditions of current density of 1A/g and 10A/g, potential window of-1.0 to 0V and reference electrode of Hg/HgO, and the results are shown in FIG. 6.
Evaluation results
As can be seen from Table 2, the BET surface area and the total pore volume increase from 856m of the 900 ℃ sample during the activation temperature increase 2 G and 0.44cm 3 Increase to 2805m for the 1100 ℃ sample 2 G and 1.98cm 3 The temperature of the sample drops below 1100 ℃ and the temperature of the sample at 1300 ℃ is only 897m 2 G and 0.43cm 3 The mesoporous proportion has the same rule, although self-activation pore-forming can be completed at 900-1300 ℃, the optimal reaction temperature is 1100 ℃, and the pore structure of the phoenix tree seed can be damaged due to excessive pyrolysis on the surface of the phoenix tree seed at an excessive temperature.
In table 2, the specific capacitance of the electrode material was calculated by a constant current charge/discharge method. At the activation time of 6h, the specific capacitance of the porous carbon microtube is increased from 112.5F/g to 208.4F/g as the activation temperature is increased from 900 ℃ to 1100 ℃ at a current density of 0.2A/g. However, when the activation temperature was increased to 1300 ℃, the capacitance dropped to 141.7F/g. Meanwhile, the specific capacitance of the 1100 ℃ sample is still the highest at 10A/g, can reach 148.5F/g, the retention rate of the capacitance is 71%, and the sample shows good electrochemical performance.
As shown in Table 2, BET surface area and Total porosity with extended activation timeVolume 1213m from 2h 2 G and 0.68cm 3 The/g is remarkably increased to 2805m of 6h 2 G and 1.98cm 3 (ii) in terms of/g. However, the proportion of mesopores is increased from 35% to 59% and decreased to 55% of 8h, and although the activation for 2-8h can complete self-activation pore-forming, a part of over-pyrolysis may occur within 8h of activation time.
The specific capacitance of the electrode material was calculated using the constant current discharge curve, and the results are shown in table 2. When the current density is 0.2A/g, the specific capacitance of the porous carbon microtube is increased from 121.7F/g to 208.4F/g as the activation time at 1100 ℃ is increased from 2h to 6 h. When the activation time was extended to 8h, the capacitance dropped to 171.3F/g. Under the high current density of 10A/g, the specific capacitance of the 6h sample is also the largest, the capacitance retention rate is 71%, and the optimal electrochemical performance is shown.
Fig. 4 and 5 are graphs of Cyclic Voltammetry (CV) measurements of samples in examples of the present invention, which are used to evaluate the electrochemical capacitance performance of porous carbon microtubes as supercapacitor electrode materials. The CV curves of the porous carbon microtubes are quasi-rectangular at a scan rate of 10 mV/s. In contrast, the rectangular shape of the sample electrode of example 4 is best, with the largest area of the CV curve enclosure. Generally, the larger the pseudo-rectangular area of the electrode CV curve, the larger the electrochemical capacitance. Thus, the electrochemical capacitance value of the sample electrode of example 4 was the largest under the same measurement conditions, which is consistent with the capacitance value calculated from the electrostatic current charge-discharge (GCD) curve. As shown in table 2 and table 3, the samples of example 4 have the highest mesoporous rate, which is probably the reason for the best electrochemical performance.
Fig. 6 is a graph showing the capacity retention and coulombic efficiency as a function of cycle number, with a small change in specific capacity as a function of cycle number. After the circulation is carried out for more than 3000 weeks at 1A/g, the specific capacitance performance keeps about 79% of the initial specific capacitance at 3000 weeks, and the coulomb efficiency keeps nearly 100%, which indicates that the porous carbon microtube electrode material prepared in example 4 has good circulation stability.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are also included in the scope of the present invention.
Claims (6)
1. A preparation method of a hierarchical porous carbon microtube with an ultra-large specific surface area is characterized by comprising the following steps:
s1, obtaining dry phoenix tree batting;
s2, heating the phoenix tree batting in a closed high-temperature-resistant crucible under an inert atmosphere for self-activation at the temperature of 900-1300 ℃ for 2-8h, and then cooling to obtain the multi-level-hole carbon microtube with a large specific surface area;
s3, the multi-level porous carbon micro-tube obtained in the step S2 is directly used as an electrode material of the super capacitor, and the assembled capacitor is high in specific capacitance, energy density and power density.
2. The method for preparing the ultra-large specific surface area hierarchical pore carbon microtube as claimed in claim 1, wherein the high temperature resistant crucible is a crucible capable of withstanding 1500 ℃.
3. The method for preparing the hierarchical porous carbon microtube with the ultra-large specific surface area as claimed in claim 1, wherein the temperature rise rate is 5-10 ℃/min.
4. The preparation method of any one of claims 1 to 3, wherein the specific surface area of the multi-stage porous carbon microtube is 856-2805m 2 Per g, total pore volume of 0.43-1.98cm 3 /g。
5. The ultra-large specific surface area hierarchical pore carbon microtube of claim 4, wherein the mesoporous volume is 0.14-1.36cm 3 The proportion of mesopores is 30-70 percent per gram.
6. The use of the hierarchical porous carbon microtube with extra large specific surface area according to any one of claims 4 to 5, wherein the hierarchical porous carbon microtube is directly used as an electrode material of a supercapacitor.
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| CN102557026A (en) * | 2011-11-09 | 2012-07-11 | 南京邮电大学 | Method for preparing porous carbon micron tube from catkin, poplar seed or phoenix tree seed as raw material |
| CN111785535A (en) * | 2020-08-04 | 2020-10-16 | 山东理工大学 | Preparation method of self-activated high-specific-capacitance carbon nanotube electrode |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102557026A (en) * | 2011-11-09 | 2012-07-11 | 南京邮电大学 | Method for preparing porous carbon micron tube from catkin, poplar seed or phoenix tree seed as raw material |
| CN111785535A (en) * | 2020-08-04 | 2020-10-16 | 山东理工大学 | Preparation method of self-activated high-specific-capacitance carbon nanotube electrode |
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