NITROGEN-DOPED POROUS CARBON MATERIAL AND PREPARATION METHOD AND APPLICATION THEREOF

Abstract

A nitrogen-doped porous carbon material and a preparation method and an application thereof; wherein the nitrogen-doped porous carbon material has a specific surface area of 1600-3500 m.sup.2.Math.g.sup.−1, mesopores with a pore size of 2-50 nm account for 20-40% of all pores, an average pore size is 2-20 nm, and a mass fraction of nitrogen atoms in the porous carbon material is 13.6-19.3 wt %. When being used as a supercapacitor material, the porous carbon material has a larger specific capacitance and a better capacitance retention rate. At a current density of 0.1 A.Math.g.sup.−1, the porous carbon material has a specific capacitance of about 847 F.Math.g.sup.−1. After 5000 cycles of charging and discharging, the capacitance retention rate is about 99.7%. Moreover, the porous carbon material features an excellent pore structure distribution, thus providing good CO.sub.2 adsorption performance.

Claims

1. A nitrogen-doped porous carbon material, having a specific surface area of 1600-3500 m.sup.2.Math.g.sup.−1, wherein mesopores with a pore size of 2-50 nm account for 20-40% of all pores, an average pore size is 2-20 nm, and a mass fraction of nitrogen atoms in the porous carbon material is 13.6-19.3 wt %.

2. A method for preparing a nitrogen-doped porous carbon material, comprising the following steps: washing, drying and pulverizing a carbonaceous precursor to obtain biomass powder; carbonizing the biomass powder at high temperature in an inert gas or ammonia gas atmosphere, to obtain a carbonized product, wherein the temperature of carbonization is 600-800° C.; ultrasonically mixing and impregnating the carbonized product, a saturated chemical activator solution, and a nitrogen source material, wherein the nitrogen source material is melamine, polyaniline or pyridine; and heating the impregnated product in an inert atmosphere to obtain biomass nitrogen-doped porous carbon.

3. The method for preparing a nitrogen-doped porous carbon material according to claim 2, wherein the carbonaceous precursor comprises but is not limited to garlic stalk, sargassum, wood sawdust, fruit shell and straw; the carbonaceous precursor is passed through an 80 mesh sieve after being pulverized; the time of the carbonization is 1.5-2.5 h; the saturated chemical activator solution is a KOH saturated solution; and a mass ratio of the carbonized product, the saturated chemical activator solution and the nitrogen source material is 1-3:1-5:0.1-2.

4. The method for preparing a nitrogen-doped porous carbon material according to claim 2, wherein the frequency of the ultrasonic treatment is 10-50 kHz, power of the ultrasonic treatment is 80-150 W, and the time of the ultrasonic treatment is 4-8 min.

5. The method for preparing a nitrogen-doped porous carbon material according to claim 2, wherein the temperature of the heating is 750-800° C., and the time of the heating is 2-2.5 h; the preparation method further comprises a step of washing and drying the obtained biomass nitrogen-doped porous carbon; and the obtained biomass nitrogen-doped porous carbon is pickled with 10-20 wt % hydrochloric acid, and then is washed to neutrality with deionized water.

6. A nitrogen-doped porous carbon prepared by the preparation method according to claim 2.

7. A method comprising applying the nitrogen-doped porous carbon according to claim 6 in preparation of a supercapacitor material.

8. An activated carbon electrode, wherein components of the activated carbon electrode comprise the nitrogen-doped porous carbon according to claim 6; and further, the components of the activated carbon electrode further comprise a conductive agent and a binder, the conductive agent is carbon black, acetylene black, graphite or other conductive additives or is a carbon nanotube additive, and the binder is polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose sodium, polyolefin, rubber or polyurethane.

9. A method for preparing the activated carbon electrode according to claim 8, comprising the following steps: adding a solvent to a mixture of the nitrogen-doped porous carbon, the binder and the conductive agent to prepare a slurry; and evenly coating a current collector with the slurry and drying to obtain the activated carbon electrode; or hot-pressing the slurry to obtain the activated carbon electrode.

10. An application of the nitrogen-doped porous carbon according to claim 6 in a CO.sub.2 adsorbent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The accompanying drawings that constitute a part of this application are used to provide a further understanding of this application. Exemplary embodiments of this application and descriptions of the embodiments are used for describing this application, and do not constitute any inappropriate limitation to this application.

[0052] FIG. 1 is a graph showing a nitrogen adsorption-desorption curve according to Embodiment 1 of the present invention;

[0053] FIG. 2 is a graph showing the distribution of pore sizes according to Embodiment 1 of the present invention;

[0054] FIG. 3 is a graph showing the cycle performance according to Embodiment 1 of the present invention;

[0055] FIG. 4 shows a cyclic voltammetric curve obtained by testing an electrode material prepared in Embodiment 2 of the present invention at a scan rate of 200 mV.Math.s.sup.−1;

[0056] FIG. 5 shows a constant-current charging and discharging curve obtained by testing the electrode material prepared in Embodiment 2 of the present invention at a current density of 5 A.Math.g.sup.−1;

[0057] FIG. 6 is a graph showing the rate capability of an electrode material prepared in Embodiment 2 of the present invention; and

[0058] FIG. 7 is a scanning electron microscope (SEM) image of a nitrogen-doped porous carbon material prepared in Embodiment 3 of the present invention.

DETAILED DESCRIPTION

[0059] It is to be noted that the following detailed descriptions are all exemplary and are intended to provide a further understanding of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this application belongs.

[0060] It should be noted that terms used herein are only for describing specific implementations and are not intended to limit exemplary implementations according to this application. As used herein, the singular form is also intended to include the plural form unless the context clearly dictates otherwise. In addition, it should be further understood that, terms “comprise” and/or “include” used in this specification indicate that there are features, steps, operations, devices, components, and/or combinations thereof.

Embodiment 1

[0061] This embodiment relates to a method for preparing nitrogen-doped porous carbon, including the following steps:

[0062] Step 1: Garlic stalk as the raw material was washed, placed in a blow drying oven and dried at 120° C. for 48 h, pulverized, and passed through an 80 mesh sieve.

[0063] Step 2: The product obtained in the step 1 was placed in a tube furnace for carbonization at 600° C. for 2 h. Nitrogen gas was used as an inert gas.

[0064] Step 3: The product obtained in the step 2 was washed and dried.

[0065] Step 4: The product obtained in the step 3, a KOH saturated solution and melamine were mixed at a mass ratio of 1:4:0.2, and the mixture was ultrasonically treated for 6 min, wherein the ultrasonic frequency was 40 kHz, and the power was 120 W.

[0066] Step 5: The product obtained in the step 4 was placed in a muffle furnace for treatment at 800° C. for 2 h. Nitrogen gas was used as an inert gas.

[0067] Step 6: The product obtained in the step 5 was first pickled with hydrochloric acid, and then washed to neutrality with deionized water, and dried to obtain a nitrogen-doped biomass-based porous carbon material.

[0068] Implementation effect: The mass ratio of nitrogen atoms of the product is as high as 19.3 wt %. The specific surface area calculated by the BET method is 2642 m.sup.2/g, the pore volume is 1.41 cm.sup.3/g, and the average pore size is 2.14 nm. The product is a carbon material having a high specific surface area. A constant-current charging and discharging test was performed on a supercapacitor electrode material prepared by mixing the carbon material, a conductive agent and a binder at a mass ratio of 8:1:1, using 6 mol/L KOH as an electrolyte. At a current density of 0.1 A/g, specific capacitance reaches 847 F/g. As shown in FIG. 6, at a current density of 10 A/g, the specific capacitance can still reach 649 F/g.

[0069] It may be learned from FIG. 1 that an isothermal adsorption-desorption curve of the material shows an obvious hysteresis loop, indicating that the material has a typical three-dimensional hierarchical pore structure. It may be learned from FIG. 2 that the material after being doped still has a large number of hierarchical structures. It may be learned from FIG. 3 that after 5000 cycles, the material can still maintain relatively high capacitance.

Embodiment 2

[0070] This embodiment relates to a method for preparing nitrogen-doped porous carbon, including the following steps:

[0071] Step 1: Sargassum as the raw material was washed, placed in a blow drying oven and dried at 120° C. for 48 h, pulverized, and passed through an 80 mesh sieve.

[0072] Step 2: The product obtained in the step 1 was placed in a tube furnace, heated to 800° C., and held at this temperature for 1.5 h. Argon gas was used as an inert gas.

[0073] Step 3: The product obtained in the step 2 was washed and dried.

[0074] Step 4: The product obtained in the step 3, a KOH saturated solution and polyaniline were mixed at a mass ratio of 1:5:0.3, and the mixture was ultrasonically treated for 10 min, wherein the ultrasonic frequency was 50 kHz, and the power was 100 W.

[0075] Step 5: The product obtained in the step 4 was placed in a muffle furnace for treatment at 750° C. for 2.5 h. Nitrogen gas was used as an inert gas.

[0076] Step 6: The product obtained in the step 5 was first pickled with 15 wt % hydrochloric acid, and then washed to neutrality with deionized water, and dried to obtain a nitrogen-doped biomass-based porous carbon material.

[0077] Implementation effect: The mass ratio of nitrogen atoms of the product is up to 15.4 wt %. The specific surface area calculated by the BET method is 2543 m.sup.2/g, the pore volume is 1.52 cm.sup.3/g, and the average pore size is 2.39 nm. The product is a carbon material having a high specific surface area. A constant-current charging and discharging test was performed on a supercapacitor electrode material prepared by mixing the carbon material, a conductive agent and a binder at a mass ratio of 8:1:1, using 6 mol/L KOH as an electrolyte. At a current density of 0.1 A/g, specific capacitance reaches 594 F/g. At a current density of 10 A/g, the specific capacitance can still reach 463 F/g.

[0078] It may be learned from the shapes in FIG. 4 and FIG. 5 that the cyclic voltammetric curve of the material is approximately rectangular, and the constant-current charging and discharging curve of the material exhibits the characteristics of an isosceles triangle, indicating that the material is mainly double-layer capacitance, and nitrogen doping introduces more structural nitrogen instead of nitrogen-containing functional groups. It may be learned from FIG. 6 that the capacitance value of the material can still remain stable at a large current density, and the material has a good rate capability.

Embodiment 3

[0079] This embodiment relates to a method for preparing nitrogen-doped porous carbon, including the following steps:

[0080] Step 1: Wood sawdust as the raw material was washed, placed in a blow drying oven and dried at 105° C. for 72 h, pulverized, and passed through a 120 mesh sieve.

[0081] Step 2: The product obtained in the step 1 was placed in a tube furnace and held at 600° C. for 2 h. Helium gas was used as an inert gas.

[0082] Step 3: The product obtained in the step 2 was washed and dried.

[0083] Step 4: The product obtained in the step 3 was mixed with a KOH saturated solution at a mass ratio of 3:1 (carbon:activator) and with pyridine at a mass ratio of 1:7 (carbon:nitrogen source), and the mixture was ultrasonically treated for 4 min, wherein the ultrasonic frequency was 30 kHz, and the power was 140 W.

[0084] Step 5: The product obtained in the step 4 was placed in a muffle furnace and held at 750° C. for 2.5 h. Ammonia gas was used as an inert gas.

[0085] Step 6: The product obtained in the step 5 was washed and dried to obtain a nitrogen-doped biomass-based porous carbon material.

[0086] Implementation effect: The mass ratio of nitrogen atoms of the product is up to 13.6 wt %. The specific surface area calculated by the BET method is 2098 m.sup.2/g, the pore volume is 1.40 cm.sup.3/g, and the average pore size is 2.14 nm. The product is a carbon material having a high specific surface area. A constant-current charging and discharging test was performed on a supercapacitor electrode material prepared by mixing the carbon material, a conductive agent and a binder at a mass ratio of 8:1:1, using 6 mol/L KOH as an electrolyte. At a current density of 0.1 A/g, specific capacitance reaches 330 F/g. At a current density of 10 A/g, the specific capacitance can still reach 260 F/g.

[0087] FIG. 7 is an SEM image of a nitrogen-doped porous carbon material prepared in Embodiment 3. It may be learned from the image that the material has abundant pore structures.

Embodiment 4

[0088] This embodiment relates to a method for preparing biomass-based nitrogen-doped porous carbon, including the following steps:

[0089] Step 1: Garlic stalk as the raw material was washed, placed in a blow drying oven and dried at 120° C. for 48 h, pulverized, and passed through an 80 mesh sieve.

[0090] Step 2: The product obtained in the step 1 was placed in a tube furnace for carbonization at 600° C. for 2 h. Nitrogen gas was used as an inert gas.

[0091] Step 3: The product obtained in the step 2 was washed and dried.

[0092] Step 4: The product obtained in the step 3, KOH and melamine were mixed at a mass ratio of 1:3:0.2, and the mixture was ultrasonically treated for 8 min, wherein the ultrasonic frequency was 10 kHz, and the power was 80 W.

[0093] Step 5: The product obtained in the step 4 was placed in a muffle furnace for treatment at 800° C. for 2 h. Nitrogen gas was used as an inert gas.

[0094] Step 6: The product obtained in the step 5 was first pickled with hydrochloric acid, and then washed to neutrality with deionized water, and dried to obtain a nitrogen-doped biomass-based porous carbon material.

[0095] Implementation effect: A CO.sub.2 adsorption test on the product under atmospheric conditions indicates that the adsorption amounts at 25° C. and 0° C. are respectively as high as 3.59 mmol/g and 6.11 mmol/g, which are quite high among the adsorption amounts of porous carbon materials.

Embodiment 5

[0096] This embodiment relates to a method for preparing biomass-based nitrogen-doped porous carbon, including the following steps:

[0097] Step 1: Wood sawdust as the raw material was washed, placed in a blow drying oven and dried at 105° C. for 72 h, pulverized, and passed through a 120 mesh sieve.

[0098] Step 2: The product obtained in the step 1 was placed in a tube furnace and held at 600° C. for 2 h. Helium gas was used as an inert gas.

[0099] Step 3: The product obtained in the step 2 was washed and dried.

[0100] Step 4: The product obtained in the step 3 was mixed with a KOH saturated solution at a mass ratio of 3:1 (carbon:activator) and with pyridine at a mass ratio of 1:7 (carbon:nitrogen source), and the mixture was ultrasonically treated for 5 min, wherein the ultrasonic frequency was 50 kHz, and the power was 150 W.

[0101] Step 5: The product obtained in the step 4 was placed in a muffle furnace and held at 750° C. for 2.5 h. Ammonia gas was used as an inert gas.

[0102] Step 6: The product obtained in the step 5 was washed and dried to obtain a nitrogen-doped biomass-based porous carbon material.

[0103] Implementation effect: A CO.sub.2 adsorption test on the product under atmospheric conditions indicates that the adsorption amounts at 25° C. and 0° C. are respectively as high as 3.86 mmol/g and 6.17 mmol/g, which are quite high among the adsorption amounts of porous carbon materials.

TABLE-US-00001 TABLE 1 Statistics on carbon sources, nitrogen sources, methods and nitrogen doping effects in nitrogen doping patents Carbon Nitrogen Nitrogen Patent number source source Method content CN Water Melamine Premixing, low-temperature 5-9 wt % 107055531 A chestnut carbonization, activation CN Reed rod Nitrogen Hydrothermal carbonization, 6-8 at. % 107010624 A fertilizer activation CN Soybean Soybean meal KOH activation 5.63 at. % 106517183 A meal CN Peanut shell Melamine Ball milling, 8-10 at. % 106629724 A low-temperature pre-carbonization, KOH activation CN Soy fiber Soy fiber Template method, potassium 4.56 at. % 108940191 A oxalate activation CN Biomass Biomass One-step “foaming method” 3.6 at. % 106006636 A CN Cottonseed Urea NaOH one-step activation 1.84-7.35 at. % 108455597 A husk The present Carbon-rich Melamine, High-temperature 13.6-19.3 wt % invention precursor polyaniline, carbonization, pyrrole, high-temperature KOH pyridine activation, hybridization

[0104] Table 1 shows relevant information about carbon sources, nitrogen sources, doping methods and doping efficiency in nitrogen doping carbon material patents in recent years collected by the inventor. It is found through statistics that the existing nitrogen doping processes still have the problems of complex process and low doping efficiency.

[0105] The foregoing descriptions are merely preferred embodiments of this application, but are not intended to limit this application. Those skilled in the art may make various modifications and changes to this application. Any modification, equivalent replacement, or improvement made without departing from the spirit and principle of this application shall fall within the protection scope of this application.