Preparation method of coal-based nitrogen-doped activated carbon

Abstract

The application discloses a preparation method of coal-based nitrogen-doped activated carbon, comprising the following steps: firstly, adding an aniline-hydrochloric acid solution into deashed coal, deashed coal rich in vitrinite or deashed coal rich in inertinite, mechanically stirring and swelling, then adding an ammonium persulfate aqueous solution dropwise, stirring and reacting, and finally treating to obtain coal-based polyaniline powder; secondly, fully grinding the coal-based polyaniline powder and KOH powder, washing after calcination to obtain black coal-based nitrogen-doped activated carbon powder. The raw material is easy to obtain, the process is simple, the yield is high, the prepared coal-based nitrogen-doped activated carbon has developed mesopores, coordinated pore structure, large specific surface area, adjustable nitrogen doping state and dosage. When the coal-based nitrogen-doped activated carbon is used as an electrode material of a super capacitor, the coal-based nitrogen-doped activated carbon shows good capacitive characteristics.

Description

TECHNICAL FIELD

[0001] The present application belongs to the cross technical field of coal chemical industry and energy storage material, and particularly relates to a preparation method of coal-based nitrogen-doped activated carbon. BACKGROUND

[0002] Activated carbon is a kind of carbon material with developed pore structure, rich surface chemical functional groups, large specific surface area, strong specific adsorption capacity, good chemical stability and high mechanical strength, which is widely used as adsorbent, catalyst and catalyst carrier. Activated carbon is composed of graphite crystallite, single plane net-like carbon and amorphous carbon, in which graphite crystallite is the main part of activated carbon, so activated carbon also has good electrical conductivity. Due to the developed pore, large specific surface area, rich surface chemical functional groups and good electrical conductivity, activated carbon is also developed as electrode material of energy storage device, and is currently a commercial supercapacitor electrode material. The raw materials for preparing activated carbon are widely available, mainly including coal, biomass and synthetic materials. Coal is abundant and low in price, and is one of the main raw materials for preparing activated carbon. The coal-based activated carbon prepared by physical activation method has low specific surface area and low capacitance performance, while the coal-based super activated carbon prepared by KOH chemical activation method has high specific surface area, developed pore and high specific capacitance. The activated carbon prepared from different metamorphic degree coals or different chemical structure macerals in the same metamorphic degree coal has great difference in structure and properties. Coal-based activated carbon generally has good affinity to organic matter and organic electrolyte, and poor affinity to aqueous electrolyte. Nitrogen doping can change the electronic structure and surface properties of carbon material, enhance the interaction between carbon material and polar electrolyte, and further improve the affinity between them, as well as the adsorption capacity, selectivity and electrochemical activity of carbon material. Polyaniline is a high polymer material rich in carbon and nitrogen, and is a good carbon and nitrogen source for preparing nitrogen-doped carbon material. However, the nitrogen-doped carbon material derived from polyaniline has large pores, and the pore structure is easy to collapse. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a preparation method of coal-based nitrogen-doped activated carbon in view of the above-mentioned deficiencies of the prior art. The method uses deashed anthracite or deashed bituminous coal with ash content less than 0.5% as raw material, and first separates the macerals to obtain vitrinite-rich and inertinite-rich fractions. Then, aniline monomer is introduced into the pores of deashed coal whole fraction, deashed coal vitrinite-rich fraction or deashed coal inertinite-rich fraction, and a series of coal-based polyaniline is prepared by in-situ polymerization. The prepared coal-based polyaniline is chemically activated by KOH, and finally coal-based nitrogen-doped activated carbon is prepared. The raw material of the present application is easy to obtain, and the process is simple. The coal-based nitrogen-doped activated carbon product prepared by the present application has high yield, developed mesopore, coordinated matching pore structure, large specific surface area, adjustable nitrogen doping state and dosage, high thermal stability and electrical conductivity. When used as supercapacitor electrode material, the coal-based nitrogen-doped activated carbon shows good capacitive characteristics, such as wide working current density range, high specific capacitance, rate performance and cycle stability.

[0004] To solve the above technical problems, the technical scheme adopted by the present application is: a preparation method of coal-based nitrogen-doped activated carbon, characterized in that it comprises the following steps:

[0005] Step one: aniline-hydrochloric acid solution is added to deashed coal, deashed coal vitrinite-rich group or deashed coal inertinite-rich group, mechanical stirring is carried out for 1h-3h, then ammonium persulfate aqueous solution is added dropwise while stirring, the dropwise adding time is controlled to be 20min-30min, after the dropwise adding is completed, stirring is continued for 4h-8h, then filtration is carried out, washing is carried out, vacuum drying is carried out, grinding is carried out, sieving is carried out, and coal-based polyaniline powder is obtained; the dropwise adding amount of the ammonium persulfate aqueous solution is such that the molar ratio of ammonium persulfate to aniline is (0.9-1.1):1, and the concentration of hydrochloric acid in the system after the dropwise adding is completed is 1.5mol / L-2.5mol / L;

[0006] Step two: KOH powder and the coal-based polyaniline powder in step one are fully ground according to a mass ratio of (3-5):1, then calcination is carried out in a nitrogen atmosphere furnace, then water washing and hydrochloric acid washing are carried out, and black coal-based nitrogen-doped activated carbon powder is obtained.

[0007] The preparation method of the coal-based nitrogen-doped activated carbon described above is characterized in that the deashed coal in step one is deashed anthracite or deashed bituminous coal, and the ash content is not more than 0.5%.

[0008] The preparation method of the coal-based nitrogen-doped activated carbon described above is characterized in that the preparation method of the deashed coal vitrinite-rich group and the deashed coal inertinite-rich group in step one comprises: ZnCl2 heavy liquid is added to the deashed coal, the height of the heavy liquid above the coal powder is 2cm-3cm, stirring is carried out first for 20min-30min, then centrifugation is carried out for 10min-20min; the material after the centrifugation is left to stand for 10min-120min, the upper layer of coal powder after the standing is taken out, washed with deionized water, filtered, and vacuum dried, and the deashed coal vitrinite-rich group is obtained; the lower layer of coal powder after the standing is taken out, washed with deionized water, filtered, and vacuum dried, and the deashed coal inertinite-rich group is obtained.

[0009] The preparation method of the coal-based nitrogen-doped activated carbon described above is characterized in that the density of the ZnCl2 heavy liquid is 1.36g·cm -3 -1.40g·cm -3 .

[0010] The preparation method of the coal-based nitrogen-doped activated carbon described above is characterized in that the speed of the centrifugation is 1000r·min -1 -3000r·min -1 .

[0011] The preparation method of the coal-based nitrogen-doped activated carbon has the characteristics that the preparation method of the aniline-hydrochloric acid solution in the step one comprises the following steps: preparing a concentrated hydrochloric acid solution of aniline, the volume of the concentrated hydrochloric acid is 2-4 times of the mass of the aniline, then deionized water is added for dilution to obtain the aniline-hydrochloric acid solution, and the volume of the deionized water is 8-12 times of the mass of the aniline; wherein the unit of the volume is mL, the unit of the mass is mg, and the mass percentage concentration of the concentrated hydrochloric acid is 37%.

[0012] The preparation method of the coal-based nitrogen-doped activated carbon has the characteristics that the mass ratio of the deashed coal, the vitrinite-rich component of the deashed coal or the inertinite-rich component of the deashed coal to the aniline in the aniline-hydrochloric acid solution in the step one is (1-4):1.

[0013] The preparation method of the coal-based nitrogen-doped activated carbon has the characteristics that the flow rate of the nitrogen atmosphere in the step two is 30 mL·min -1 -50 mL·min -1 , the heating rate of the atmosphere furnace is 1℃·min -1 -3℃·min -1 , and the temperature rising program is first rising to 550℃-650℃ and keeping for 1h-2h, and then rising to 750℃-850℃ and keeping for 1h-2h.

[0014] Compared with the prior art, the preparation method of the coal-based nitrogen-doped activated carbon has the following advantages:

[0015] 1. The coal-based polyaniline carbon source is obtained by in-situ polymerization of aniline in the pores and on the surface of coal by taking advantage of the abundant molecular sieve pore structure of coal and the strong adsorption and swelling characteristics of aniline. The high nitrogen content can make the coal-based nitrogen-doped activated carbon have better adsorption capacity and selectivity. Nitrogen doping is an effective strategy to improve the surface properties of carbon materials. By nitrogen doping, the electronic structure and chemical environment of adjacent carbon atoms can be significantly changed, and the carbon material is endowed with higher surface polarity and conductivity. Therefore, the coal-based polyaniline obtained by in-situ polymerization of aniline in the pores and on the surface of coal provides an excellent carbon source for the subsequent preparation of coal-based nitrogen-doped activated carbon with high specific surface area, developed pore structure and high nitrogen content.

[0016] 2. The deashed coal selected in the present application can be full component or two kinds of maceral components, i.e. vitrinite-rich component and inertinite-rich component. Especially, the vitrinite-rich component and the inertinite-rich component obtained by heavy liquid separation have more developed pore structure and more uniform chemical structure, so it is easier to obtain coal-based polyaniline with high composite degree and high uniformity, and then to prepare coal-based nitrogen-doped activated carbon with more uniform and controllable structure.

[0017] 3. The raw material of the present application is easy to obtain, the process is simple, and the yield is high. The coal-based nitrogen-doped activated carbon electrode material prepared by the present application shows good capacitive characteristics, has a wide working current density range, high specific capacitance, rate characteristics and cycle stability.

[0018] The technical solutions of the present application will be described in further detail below in combination with the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 SEM image of the coal-based nitrogen-doped activated carbon prepared in Example 1 of the present application, magnification 10000 times.

[0020] Figure 2 SEM image of the coal-based nitrogen-doped activated carbon prepared in Example 2 of the present application, magnification 17500 times.

[0021] Figure 3 SEM image of the coal-based nitrogen-doped activated carbon prepared in Example 3 of the present application, magnification 10000 times.

[0022] Figure 4 SEM image of the coal-based nitrogen-doped activated carbon prepared in Example 4 of the present application, magnification 10000 times

[0023] Figure 5 SEM image of the coal-based nitrogen-doped activated carbon prepared in Example 5 of the present application, magnification 10000 times.

[0024] Figure 6 SEM image of the coal-based activated carbon prepared in Comparative Example 1, magnification 10000 times.

[0025] Figure 7 XRD image of the coal-based nitrogen-doped activated carbon prepared in Example 1, Example 2, Example 3, Example 4 and Example 5 of the present application.

[0026] Figure 8 Raman spectrum of the coal-based nitrogen-doped activated carbon prepared in Example 1, Example 2, Example 3, Example 4 and Example 5 of the present application.

[0027] Figure 9 Nitrogen adsorption-desorption curve of the coal-based nitrogen-doped activated carbon prepared in Example 1, Example 3 and Comparative Example 1 of the present application.

[0028] Figure 10 Pore size distribution graph of the coal-based nitrogen-doped activated carbon prepared in Example 1, Example 3 and Comparative Example 1 of the present application.

[0029] Figure 11 XPS full spectrum of the coal-based nitrogen-doped activated carbon prepared in Example 1 of the present application.

[0030] Figure 12 N1s spectrum of the coal-based nitrogen-doped activated carbon prepared in Example 1 of the present application.

[0031] Figure 13Cyclic voltammetry curves of coal-based nitrogen-doped activated carbon prepared in Examples 1, 2, 3, 4, 5 and Comparative Example 1 of the present invention under a three-electrode system.

[0032] Figure 14 The constant current charge-discharge curves of the coal-based nitrogen-doped activated carbon prepared in Examples 1, 2, 3, 4, 5 and Comparative Example 1 of this invention are shown in the three-electrode system.

[0033] Figure 15 The AC impedance spectra of coal-based nitrogen-doped activated carbon prepared in Examples 1, 2, 3, 4, 5 and Comparative Example 1 of this invention are shown in a three-electrode system.

[0034] Figure 16 The rate performance curves of the coal-based nitrogen-doped activated carbon prepared in Examples 1, 2, 3, 4, 5 and Comparative Example 1 of this invention are shown in the three-electrode system.

[0035] Figure 17 The CV curves are for the supercapacitors assembled from the coal-based nitrogen-doped activated carbon prepared in Example 1 of this invention and the coal-based activated carbon prepared in Comparative Example 1.

[0036] Figure 18 Rate characteristic curves (GCD curves) of supercapacitors assembled from coal-based nitrogen-doped activated carbon prepared in Example 1 and coal-based activated carbon prepared in Comparative Example 1.

[0037] Figure 19 The Ragon curves are assembled from the coal-based nitrogen-doped activated carbon prepared in Example 1 of this invention and the coal-based activated carbon prepared in Comparative Example 1.

[0038] Figure 20 Cyclic stability curves of supercapacitors assembled from coal-based nitrogen-doped activated carbon prepared in Example 1 and coal-based activated carbon prepared in Comparative Example 1. Detailed Implementation

[0039] Example 1

[0040] The preparation method of coal-based nitrogen-doped activated carbon in this embodiment specifically includes the following steps:

[0041] Step 1: Add a 1.36 g·cm³ density compound to the deashed anthracite (ash content 0.29%). -3 Add ZnCl2 heavy liquid to a level 2 cm above the coal powder, then stir for 20 min, followed by centrifugation for 10 min at a speed of 2000 r·min. -1 ;

[0042] Step two, the centrifuged material is left for 10 min, the lower layer of coal powder after standing is taken out, repeatedly washed and suction filtered with deionized water for multiple times, and vacuum dried to obtain the rich inert group;

[0043] Step three, the aniline-hydrochloric acid solution is added to the rich inert group in step two, mechanically stirred for 2 h, then slowly drop the ammonium persulfate aqueous solution while stirring, the drop time is controlled within 30 min, after the drop is completed, continue to stir for 6 h, then suction filter, wash, vacuum dry, grind, and sieve through a 200 mesh sieve to obtain dark coal-based polyaniline powder; the molar ratio of ammonium persulfate to aniline is 1:1, the concentration of hydrochloric acid in the system after the drop is completed is 2 mol / L; the mass ratio of the rich inert group to aniline in the aniline-hydrochloric acid solution is 1.5:1;

[0044] The preparation method of the aniline-hydrochloric acid solution comprises: preparing a concentrated hydrochloric acid solution of aniline, the volume of the concentrated hydrochloric acid is 3 times the mass of the aniline, then deionized water is added for dilution to obtain an aniline-hydrochloric acid solution, the volume of the deionized water is 10 times the mass of the aniline; the unit of volume is mL, and the unit of mass is mg, and the mass percentage concentration of the concentrated hydrochloric acid is 37%;

[0045] Step four, the coal-based polyaniline powder in step three is fully ground with KOH powder at a mass ratio of 1:4, placed in a nitrogen atmosphere furnace for calcination, and then subjected to water washing-hydrochloric acid washing-water washing treatment to obtain black coal-based nitrogen-doped activated carbon powder; the nitrogen atmosphere flow rate during calcination is 40 mL·min -1 , the atmosphere furnace heating rate is 2 ℃·min -1 , and the temperature rising program is first rising to 600 ℃ and keeping for 1 h, then rising to 800 ℃ and keeping for 1 h.

[0046] Figure 1 The SEM graph of the coal-based nitrogen-doped activated carbon prepared in Example 1 shows that the coal-based nitrogen-doped activated carbon has a developed pore structure, and macropores, mesopores and micropores are very rich. Figure 7 The weak and wide C(002) and C(001) crystal face diffraction peaks in the XRD graph of Figure 8 The paired D peak and G peak in the Raman spectrum of Figure 9 The pore adsorption curve and pore size distribution of Figure 10 , and the pore structure data in Table 1, together show that the coal-based nitrogen-doped activated carbon prepared in Example 1 has a high specific surface area, a developed pore structure and is mainly mesoporous. Figure 11 The nitrogen content of the coal-based nitrogen-doped activated carbon prepared in Example 1 tested on an elemental analyzer is shown in Table 2, and the XPS full spectrum and N1s spectrum are shown in Figure 12It can be seen that nitrogen is successfully incorporated into the active carbon framework in the form of high electrochemically active pyrrole-type nitrogen and pyridine-type nitrogen, and the amount of nitrogen incorporated reaches 0.64wt%.

[0047] Example 2

[0048] The preparation method of the coal-based nitrogen-doped active carbon of the present embodiment specifically comprises the following steps:

[0049] Step one, add ZnCl2 heavy liquid with a density of 1.40 g·cm-3 to the de-ashed anthracite (ash content of 0.29%) to a height of 3 cm above the coal powder, then stir for 25 min, and then centrifuge for 15 min at a speed of 3000 r·min-1. -3 -1 ;

[0050] Step two, place the centrifuged material for 120 min, take out the upper layer of coal powder after standing, repeatedly wash and suction filter with deionized water for multiple times, and vacuum dry to obtain vitrinite-rich;

[0051] Step three, add aniline-hydrochloric acid solution to the vitrinite-rich obtained in step two, mechanically stir for swelling for 3 h, then slowly drop the ammonium persulfate aqueous solution while stirring, control the dropping time to be 25 min, continue to stir for 4 h after the dropping is completed, then suction filter, wash, vacuum dry, grind, and pass through a 200 mesh sieve to obtain dark coal-based polyaniline powder; the molar ratio of ammonium persulfate to aniline is 0.9:1, the concentration of hydrochloric acid in the system after the dropping is completed is 1.5 mol / L, and the mass ratio of the vitrinite-rich to aniline in the aniline-hydrochloric acid solution is 1:1;

[0052] The preparation method of the aniline-hydrochloric acid solution comprises: preparing a concentrated hydrochloric acid solution of aniline, the volume of the concentrated hydrochloric acid is 4 times the mass of the aniline, then add deionized water to dilute to obtain an aniline-hydrochloric acid solution, and the volume of the deionized water is 12 times the mass of the aniline; wherein the units of volume are mL, and the units of mass are mg, and the mass percentage concentration of the concentrated hydrochloric acid is 37%;

[0053] Step four, fully grind the coal-based polyaniline powder obtained in step three with KOH powder according to a mass ratio of 1:3, place in a nitrogen atmosphere furnace for calcination, and then perform water washing-hydrochloric acid washing-water washing treatment to obtain black coal-based nitrogen-doped active carbon powder; the nitrogen atmosphere flow rate during calcination is 30 mL·min-1, the atmosphere furnace heating rate is 1 ℃·min-1, and the temperature rising program is to first rise to 550 ℃ and keep for 2 h, and then rise to 750 ℃ and keep for 2 h. -1 -1

[0054] Figure 2 , Figure 7 , Figure 8 ​​​SEM, XRD, Raman of the coal-based nitrogen-doped activated carbon composite powder prepared in this example. Comparison found that it has similar micro-morphology, crystal structure and chemical structure with the coal-based nitrogen-doped activated carbon composite powder prepared in Example 1.

[0055] Example 3

[0056] The preparation method of the coal-based nitrogen-doped activated carbon in this example specifically includes the following steps:

[0057] Step one, first prepare aniline-hydrochloric acid solution, the volume of the concentrated hydrochloric acid is 3 times the mass of aniline; then dilute with deionized water to obtain aniline-hydrochloric acid dilute solution, the volume of deionized water in the dilute solution is 10 times the mass of aniline; wherein the unit of volume is mL, the unit of mass is mg, and the mass percentage concentration of concentrated hydrochloric acid is 37%.

[0058] Step two, add deashed anthracite (ash content is 0.29%) to the aniline-hydrochloric acid solution of step one and mechanically stir for 2h; wherein the mass ratio of deashed anthracite to aniline is 7 / 3;

[0059] Step three, slowly add ammonium persulfate aqueous solution to the mixed solution of step two while stirring, and the dropping time is 20min; wherein the molar ratio of ammonium persulfate to aniline in the system after dropping is 1:1, and the concentration of hydrochloric acid is 2mol / L;

[0060] Step four, continue to stir the system after dropping for 6h, then filter, wash, vacuum dry, grind and pass through a 200 mesh sieve to obtain dark coal-based polyaniline powder;

[0061] Step five, grind the coal-based polyaniline and KOH powder according to a mass ratio of 1:4, place them in a nitrogen atmosphere furnace for calcination, then perform water washing-hydrochloric acid washing-water washing treatment, and finally obtain black coal-based nitrogen-doped activated carbon powder. Wherein, the nitrogen flow rate is 40mL / min -1 , the heating rate of the atmosphere furnace is 2℃ / min -1 , and the temperature rising program is first rising to 600℃ and keeping for 1h, then rising to 800℃ and keeping for 1h.

[0062] Figure 3 , Figure 7 , Figure 8 SEM, XRD, Raman of the coal-based nitrogen-doped activated carbon composite powder prepared in this example. Comparison found that it has similar micro-morphology, crystal structure and chemical structure with the coal-based nitrogen-doped activated carbon composite powder prepared in Example 1, except that the skeleton structure is not firm.

[0063] Example 4

[0064] The preparation method of the coal-based nitrogen-doped activated carbon in this example specifically includes the following steps:

[0065] Step one, add ZnCl2 heavy liquid with density of 1.38 g·cm -3 to the deashed bituminous coal (ash content of 0.46%) to 2.5 cm above the coal powder, then stir for 30 min, and centrifuge for 20 min at a speed of 1000 r·min -1 ;

[0066] Step two, place the centrifuged material for 30 min, take out the lower layer of coal powder after standing, repeatedly wash and suction filter with deionized water for multiple times, and vacuum dry to obtain the rich inert group.

[0067] Step three, add aniline-hydrochloric acid solution to the rich inert group in step two, mechanically stir for 1 h, then slowly drop the ammonium persulfate aqueous solution while stirring, control the dropping time within 20 min, continue to stir for 8 h after dropping, suction filter, wash, vacuum dry, grind, and pass through a 200 mesh sieve to obtain dark coal-based polyaniline powder; the molar ratio of ammonium persulfate to aniline is 1.1:1, the concentration of hydrochloric acid in the system after dropping is 2.5 mol / L, and the mass ratio of the rich inert group to aniline in the aniline-hydrochloric acid solution is 4:1.

[0068] The preparation method of the aniline-hydrochloric acid solution comprises: preparing a concentrated hydrochloric acid solution of aniline, the volume of the concentrated hydrochloric acid is 2 times the mass of the aniline, then adding deionized water to dilute to obtain an aniline-hydrochloric acid solution, and the volume of the deionized water is 8 times the mass of the aniline; wherein the units of volume are mL, and the units of mass are mg, and the mass percentage concentration of the concentrated hydrochloric acid is 37%;

[0069] Step four, fully grind the coal-based polyaniline powder in step three with KOH powder according to a mass ratio of 1:5, place in a nitrogen atmosphere furnace for calcination, and then perform water washing-hydrochloric acid washing-water washing treatment to obtain black coal-based nitrogen-doped activated carbon powder; the nitrogen atmosphere flow rate during calcination is 50 mL·min -1 , the atmosphere furnace heating rate is 3℃·min -1 , and the temperature rising program is first rising to 650℃ and keeping for 1.5 h, and then rising to 850℃ and keeping for 1.5 h.

[0070] Figure 4 , Figure 7 , Figure 8 The SEM, XRD, and Raman of the coal-based nitrogen-doped activated carbon composite powder prepared in this embodiment are shown respectively. It is found that it has similar micro-morphology, crystal structure, and chemical structure to the coal-based nitrogen-doped activated carbon composite powder prepared in Example 1.

[0071] Example 5

[0072] The preparation method of the coal-based nitrogen-doped activated carbon in this embodiment specifically comprises the following steps:

[0073] Step one, add ZnCl2 heavy liquid with density of 1.38 g·cm -3 to the de-ashed bituminous coal (ash content of 0.46%) to 2 cm above the coal powder, then stir for 30 min, and centrifuge for 20 min at a speed of 2000 r·min -1 ;

[0074] Step two, let the centrifuged material stand for 30 min, take out the upper layer of coal powder after standing, repeatedly wash and suction filter with deionized water for multiple times, vacuum dry to obtain vitrinite-rich;

[0075] Step three, add aniline-hydrochloric acid solution to the vitrinite-rich in step two, mechanically stir for 2 h, then slowly drop the ammonium persulfate aqueous solution while stirring, the dropping time is controlled within 30 min, after dropping, continue to stir for 6 h, then suction filter, wash, vacuum dry, grind, and pass through a 200 mesh sieve to obtain dark coal-based polyaniline powder; the molar ratio of ammonium persulfate to aniline in the system after dropping is 1:1, the concentration of hydrochloric acid is 2 mol / L; the mass ratio of vitrinite-rich to aniline in the aniline-hydrochloric acid solution is 1.5:1;

[0076] The preparation method of the aniline-hydrochloric acid solution comprises: preparing aniline concentrated hydrochloric acid solution, the volume of the concentrated hydrochloric acid is 3 times the mass of aniline, then adding deionized water to dilute to obtain aniline-hydrochloric acid solution, the volume of the deionized water is 10 times the mass of aniline; wherein the unit of volume is mL, the unit of mass is mg, and the mass percentage concentration of the concentrated hydrochloric acid is 37%;

[0077] Step four, fully grind the coal-based polyaniline powder in step three with KOH powder according to a mass ratio of 1:4, place in a nitrogen atmosphere furnace for calcination, then perform water washing-hydrochloric acid washing-water washing treatment to obtain black coal-based nitrogen-doped activated carbon powder; the nitrogen atmosphere flow rate during calcination is 40 mL·min -1 , the atmosphere furnace heating rate is 2℃·min -1 , and the temperature rising program is first rising to 600℃ and keeping for 1 h, then rising to 800℃ and keeping for 1.5 h.

[0078] Figure 5 , Figure 7 , Figure 8 The SEM, XRD, and Raman of the coal-based nitrogen-doped activated carbon composite powder prepared in this example are shown respectively. It is found that it has similar micro-morphology, crystal structure and chemical structure to the coal-based nitrogen-doped activated carbon composite powder prepared in example 1, only the number of large pores is relatively more.

[0079] Comparative example 1

[0080] The preparation method of anthracite-based activated carbon is as follows: Deashed anthracite (ash content 0.29%) and KOH powder are thoroughly ground at a mass ratio of 1:4, calcined in a nitrogen atmosphere furnace, and then subjected to a water-washing-hydrochloric acid-washing-water-washing treatment to finally obtain black coal-based nitrogen-doped activated carbon powder. The nitrogen flow rate is 40 mL / min. -1 The heating rate of the atmosphere furnace is 2℃·min. -1 The heating program is as follows: first heat to 600℃, hold for 1 hour, then heat to 800℃ and hold for 1 hour.

[0081] Comparative Example 2

[0082] The preparation method of bituminous coal-based activated carbon is as follows: Deashed bituminous coal (ash content 0.46%) and KOH powder are thoroughly ground at a mass ratio of 1:4, calcined in a nitrogen atmosphere furnace, and then subjected to a water-washing-hydrochloric acid-washing-water-washing treatment to finally obtain black coal-based nitrogen-doped activated carbon powder. The nitrogen flow rate is 40 mL / min. -1 The heating rate of the atmosphere furnace is 2℃·min. -1 The heating program is as follows: first heat to 600℃, hold for 1 hour, then heat to 800℃ and hold for 1 hour.

[0083] Table 1. Pore structure parameters of activated carbon prepared in Examples 1, 3 and Comparative Example 1.

[0084]

[0085]

[0086] Table 2. Nitrogen content of coal-based nitrogen-doped activated carbon prepared in each example.

[0087]

[0088] and Figure 6 Compared to SEM images of anthracite-based activated carbon, Figures 1-5 The micropores of the coal-based nitrogen-doped activated carbon are significantly more abundant. Figure 9 , Figure 10 Table 1 shows the specific surface area and pore size analysis results of the coal-based nitrogen-doped activated carbon prepared in Examples 1 and 3, and the coal-based activated carbon prepared in Comparative Example 1. From... Figure 9 The isothermal adsorption curves of the three materials show a hysteresis loop within the relative pressure range of 0.4–1.0, indicating the presence of a mesoporous structure in the samples. Figure 10 As can be seen from Table 1, the main pore sizes of the three activated carbons are distributed in the range of 1 nm to 50 nm, exhibiting a rich micro-mesoporous structure. Furthermore, Table 1 shows that the pore structures of each activated carbon differ significantly. The activated carbon in Example 1 has the most developed pore structure, with the largest BET specific surface area, total pore volume, and average pore size, all at 3462 nm. 2·g -1 , 1.8830 cm 3 ·g -1 and 2.4 nm, and the mesopore rate is up to 66.4%. The large specific surface area and pore volume can increase the contact area of the electrode with electrolyte and the amount of charge storage, the large average pore diameter and high mesopore rate can promote the transmission and diffusion of ions, and improve the power density of the capacitor. Compared with Comparative Example 1, the coal-based nitrogen-doped activated carbon prepared in Example 1 and Example 3 has a larger specific surface area, pore volume and average pore diameter, which is mainly due to the superiority of the coal-based polyaniline as a carbon source, the swelling effect of aniline on coal and the penetration and adsorption of aniline in the molecular sieve pore of coal to achieve primary pore expansion of coal, and further aniline polymerization to produce secondary pore expansion of coal, and subsequent KOH activation to comprehensively permeate the pores of coal. These jointly create a high mesopore rate and a matching and coordinated pore structure, which is beneficial to the diffusion and storage of electrolyte ions therein, and thus can significantly improve the specific capacitance. These data fully reflect that the coal-based polyaniline precursor is an excellent carbon and nitrogen source for preparing nitrogen-doped activated carbon. In addition, the coal-based nitrogen-doped activated carbon prepared in Example 1 has a larger specific surface area, pore volume and average pore diameter than that prepared in Example 3, and has a higher mesopore rate, indicating that the separation of macerals of coal is very beneficial to optimizing the pore structure of activated carbon. Therefore, it is very effective and necessary to use separated macerals to prepare coal-based polyaniline precursors to prepare nitrogen-doped activated carbon with higher specific surface area and more abundant mesopores.

[0089] The coal-based nitrogen-doped activated carbon prepared in Example 1, Example 2, Example 3, Example 4 and Example 5, and the coal-based activated carbon prepared in Comparative Example 1 and Comparative Example 2 were used as active materials to prepare electrode materials, and the specific preparation method was as follows:

[0090] Step one, a certain amount of activated carbon powder, conductive carbon black and polyvinylidene fluoride were added to N,N-dimethylformamide in proportion, ultrasonic dispersion was carried out for 1 h to obtain a slurry mixture; the mass ratio of the composite powder, conductive carbon black and polyvinylidene fluoride was 8:1:1; the volume of N,N-dimethylformamide was 2 times the mass of the nitrogen-doped activated carbon, wherein the unit of volume was mL and the unit of mass was g;

[0091] Step two, the slurry mixture in step one was uniformly coated on a dry graphite paper with a size of 1 cm x 4 cm, and the coating area was 1 x 1 cm 2 . Then the electrode was dried in a vacuum drying box to a constant weight. The active electrode with a loading amount in the range of 0.65-1.2 mg·cm -2 was selected for subsequent testing. The temperature of the vacuum drying was 60°C;

[0092] Step three, in a three-electrode system, the prepared electrode material was used as the working electrode, Hg / HgO as the reference electrode, Pt sheet as the counter electrode, and 6M KOH aqueous solution as the electrolyte; in a two-electrode asymmetric system, the pre-prepared nitrogen-doped activated carbon was used as the positive electrode, and the activated carbon was used as the negative electrode, and the electrochemical performance test was carried out on a Shanghai Chenhua CHI660E electrochemical workstation;

[0093] Step four, the electrochemical performance was studied by cyclic voltammetry (CV), constant current charge and discharge method (GCD) and electrochemical impedance spectroscopy (EIS). The two-electrode system was tested by 10000 times of GCD cycle test by CT3001A battery system of Wuhan Lan electrical company, and the test results were analyzed, and the capacity retention rate and coulombic efficiency of the device were obtained.

[0094] The cyclic voltammetry and constant current charge and discharge test were carried out on a Shanghai Chenhua CHI660E electrochemical workstation. The related test results are shown in Tables 3 and 4.

[0095] Table 3 Specific capacitance data of activated carbon prepared in each example and comparative example in three-electrode system

[0096]

[0097]

[0098] It can be found from the comparison of the data in Tables 3 and 4 that the specific capacitance of all nitrogen-doped activated carbons is higher than that of the activated carbon without nitrogen doping, which is consistent with the performance of the cyclic voltammetry curve, indicating that the capacitance performance of the nitrogen-doped activated carbon is more excellent than that of the ordinary activated carbon. On the one hand, nitrogen doping improves the affinity and adsorption of carbon material to electrolyte, and on the other hand, the nitrogen doped in the activated carbon has electrochemical activity and can produce pseudo-capacitance in the process of charge and discharge, which is beneficial to improve the specific capacitance of the activated carbon and significantly improve the capacitance performance of the activated carbon.

[0099] Table 4 Specific capacitance data of nitrogen-doped activated carbon prepared in Example 1 in two-electrode system

[0100] Current density (A / g) 1 2 5 10 20 50 Specific capacitance (F / g) 195 168 140 125 101 80

[0101] From Figure 13 It can be seen that the CV curves of nitrogen-doped activated carbons prepared from different metamorphic degrees of coal, different macerals and different coal / aniline ratios all present a rectangular ring shape with good symmetry, indicating that their capacitance storage is mainly in the form of double-layer. The CV ring area of the five nitrogen-doped activated carbons is larger than that of the activated carbon without nitrogen doping, which indicates that the specific capacitance of the nitrogen-doped activated carbon has been significantly improved. From Figure 14It can be seen that the GCD curves of the five nitrogen-doped activated carbons all have good isosceles triangle shape, indicating that they still have good charge and discharge efficiency at high current density, which is consistent with the fast charge and discharge characteristics and good reversibility of double-layer supercapacitors. By calculation, the specific capacitance of all nitrogen-doped activated carbons is higher than that of the non-nitrogen-doped activated carbon, which is also consistent with the performance of the CV curve, indicating that doping nitrogen in activated carbon is beneficial to improve the specific capacitance of activated carbon, and the capacitive performance of activated carbon is significantly improved. From the AC impedance spectrum of Figure 15 , it can be seen that the five nitrogen-doped activated carbons all have small internal resistance and charge transfer resistance, which is a necessary condition for high-power capacitive materials. Figure 16 The rate curve shows that the specific capacitance of the five nitrogen-doped activated carbons at different current densities is higher than that of the activated carbon, especially the nitrogen-doped activated carbon prepared from the inert group, which has more excellent capacitive performance.

[0102] In order to further study the practicability of the prepared electrode material, the nitrogen-doped activated carbon prepared in Example 1 was used as the positive electrode, and the activated carbon prepared in Comparative Example 1 was used as the negative electrode, and an asymmetric supercapacitor was assembled using 6M KOH electrolyte. The electrochemical performance was studied. Figure 17 、 Figure 18 、 Figure 19 and Figure 20 are the electrochemical test data of this supercapacitor. It can be found that this supercapacitor has a wide voltage working window (1.2V), high specific capacitance and rate performance (at current densities of 1, 2, 5, 10, 20 and 50A·g -1 , the specific capacitances are 195, 168, 140, 125, 101 and 80F·g -1 , respectively), high energy density (when the power density is 550W·kg -1 , the energy density reaches 20Wh·kg -1 ), excellent cycle stability (after 10000 cycles of GCD at a current density of 5A·g -1 , the capacitance retention rate can reach 99%, and the coulombic efficiency can reach 98%). These data together show that the nitrogen-doped activated carbon prepared by the present application has excellent capacitive performance and great practical application potential.

[0103] The above is only a preferred embodiment of the present application, and does not limit the present application in any way. Any simple modification, change and equivalent structural change made according to the technical essence of the present application to the above embodiment are still within the protection scope of the technical solution of the present application.

Claims

1. A method for preparing a coal-based nitrogen-doped activated carbon, characterized by, It comprises the following steps: Step one, add aniline-hydrochloric acid solution to the vitrinite-rich group of deashed coal or the inert-matter-rich group of deashed coal, mechanically stir for 1-3 hours, then add ammonium persulfate aqueous solution dropwise while stirring, the dropwise adding time is controlled to 20-30 minutes, after the dropwise adding is completed, continue to stir for 4-8 hours, then filter, wash, vacuum dry, grind, sieve, and obtain coal-based polyaniline powder; the dropwise adding amount of the ammonium persulfate aqueous solution is such that the molar ratio of ammonium persulfate to aniline is (0.9-1.1):1, and the concentration of hydrochloric acid in the system after the dropwise adding is completed is 1.5-2.5 mol / L; Step two, fully grind KOH powder and the coal-based polyaniline powder in step one according to a mass ratio of (3-5):1, then place in a nitrogen atmosphere furnace for calcination, then wash with water, wash with hydrochloric acid, and wash with water, and obtain black coal-based nitrogen-doped activated carbon powder.

2. The preparation method of the coal-based nitrogen-doped activated carbon according to claim 1, characterized in that, The deashed coal in step one is deashed anthracite or deashed bituminous coal, and the ash content is not more than 0.5%.

3. The preparation method of the coal-based nitrogen-doped activated carbon according to claim 1, characterized in that, The preparation method of the vitrinite-rich group of deashed coal and the inert-matter-rich group of deashed coal in step one comprises the following steps: add ZnCl2 heavy liquid to deashed coal such that the heavy liquid is 2-3 cm higher than the coal powder, first stir for 20-30 minutes, then centrifuge for 10-20 minutes; take out the upper layer of coal powder after standing for 10-120 minutes, wash with deionized water, filter, and vacuum dry, and obtain the vitrinite-rich group of deashed coal; take out the lower layer of coal powder after standing, wash with deionized water, filter, and vacuum dry, and obtain the inert-matter-rich group of deashed coal.

4. The preparation method of the coal-based nitrogen-doped activated carbon according to claim 3, characterized in that, The density of the ZnCl2 heavy liquid is 1.36 g-cm -3 ~ 1.40 g-cm -3 .

5. The preparation method of the coal-based nitrogen-doped activated carbon according to claim 3, characterized in that, The speed of the centrifugation is 1000 r·min -1 ~ 3000 r·min -1 .

6. The method of claim 1, wherein the coal-based nitrogen-doped activated carbon is prepared by the steps of: mixing coal and a nitrogen source to form a mixture; and heating the mixture to form the coal-based nitrogen-doped activated carbon. The preparation method of the aniline-hydrochloric acid solution in step one comprises the following steps: prepare aniline concentrated hydrochloric acid solution, the volume of the concentrated hydrochloric acid is 2-4 times the mass of aniline, then add deionized water to dilute, and obtain aniline-hydrochloric acid solution, the volume of the deionized water is 8-12 times the mass of aniline; wherein the unit of volume is mL, and the unit of mass is mg, and the mass percentage concentration of the concentrated hydrochloric acid is 37%.

7. The method for preparing coal-based nitrogen-doped activated carbon according to claim 1, characterized in that, The mass ratio of the vitrinite-rich group of deashed coal or the inert-matter-rich group of deashed coal to aniline in the aniline-hydrochloric acid solution in step one is (1-4):

1.

8. The method according to claim 1, wherein, The flow rate of nitrogen atmosphere in step two is 30 mL / min -1 ~ 50 mL / min -1 The heating rate of the atmosphere furnace is 1 ℃ / min -1 ~ 3 ℃ / min -1 The heating program is first heated to 550 ℃ ~ 650 ℃, maintained for 1 h ~ 2 h, and then heated to 750 ℃ ~ 850 ℃, maintained for 1 h ~ 2 h.

Images