CN107010624A - Nitrogen and boron doped porous carbon for supercapacitor electrode and preparation method thereof - Google Patents

Abstract

The invention discloses a nitrogen- and boron-doped porous carbon for supercapacitor electrodes and a preparation method thereof, belonging to the technical field of energy materials and applications. The invention uses natural reed stalks as carbon source, nitrogen fertilizer and boron fertilizer as nitrogen source and boron source respectively, and is prepared through carbonization and activation process. The nitrogen- and boron-doped porous carbon prepared by the present invention has a hierarchical three-dimensional pore structure of both micropores and mesopores, the pore diameter is mainly distributed in the range of 1 to 5 nanometers, the specific surface area is 1400 to 1700 square meters per gram, and the nitrogen-doped atomic ratio 6-8%, boron-doped atomic ratio is 2-4%. When used as a supercapacitor electrode material, it has a specific capacitance of 225-250 Faradays/gram at a current density of 1 A/gram. After 5000 cycles of charge and discharge, the capacitance retention is higher than 95%, and the power density is 500 W/kg. It has an energy density of 30-35 Wh/kg.

Description

A kind of nitrogen, boron doped porous carbon for supercapacitor electrode and preparation method thereof

technical field

The invention belongs to the technical field of energy materials and applications, and in particular relates to a nitrogen- and boron-doped porous carbon used for supercapacitor electrodes and a preparation method thereof.

Background technique

Porous carbon has become the preferred electrode material for supercapacitors due to its advantages such as large specific surface area, adjustable pore structure, good chemical stability and low cost. Porous carbon electrodes in supercapacitors mainly form an electric double layer at the electrode/electrolyte interface to store energy. Therefore, activated carbon materials for efficient energy storage should have a large specific surface area that is conducive to charge accumulation and facilitate electrolyte wetting and rapid ion migration. the pore structure. The study found that the heteroatom-doped porous carbon has better electrochemical performance than the traditional porous carbon.

The raw materials used to prepare porous carbon are various, and small organic molecules, polymers, petroleum coke, natural products, etc. can be used as carbon sources.

For example, the patent application No. 201310297709.8 discloses a method for preparing porous carbon for supercapacitors using complex salicylate. The prepared porous carbon has a specific surface area of up to 2000 square meters per gram and good capacitance performance, but the raw material cost It is expensive, the preparation process is cumbersome, the structure is not easy to control, and it is difficult to obtain large-scale application.

For example, the patent application No. 201410508582.4 discloses a method for preparing porous carbon materials, which specifically relates to a method for preparing porous carbon electrode materials by using scraps of high-temperature-resistant polymer films that are difficult to recycle and regenerate. Although cheap polymer film scraps are used as Carbon source, the prepared porous carbon has a specific surface area of 1000-2000 square meters per gram, but the electrical conductivity is not good, and the specific capacitance is only 160-180 Faradays per gram, which is not conducive to commercial application.

For example, the patent application number 201410506124.7 discloses a preparation method of porous carbon for supercapacitors, using petroleum coke, acrylic resin, etc. as raw materials, and then making porous carbon after high-temperature activation, and its specific surface area is 1700-1900 square meters per gram , but the specific capacitance is 120-190 Faradays/g, which is still at a low level, which limits the wide application of porous carbon.

For example, Chen H, Xiong Y, Yu T, et al. Boron and nitrogen co-doped porous carbon with a high concentration of boron and its superior capacitive behavior [J]. Carbon, 2017, 113: 266-273. reported a Phenol and formaldehyde are used as raw materials, melamine and boric acid are used as nitrogen source and boron source, and then silica is used as a template. After a multi-step treatment process, nitrogen and boron co-doped porous carbon with hierarchical structure has been prepared. Although it has 189~ The specific capacitance is 304 Faradays/gram, but its specific surface area is only 648 square meters/gram, and the toxic chemical reagents such as phenol and formaldehyde used are easy to pollute the environment and do not conform to the development trend of clean energy.

Among the many raw materials that can be used to prepare porous carbons, natural products have been widely promoted because of their wide distribution, low cost and easy availability.

For example, the patent application number 201510611801.6 discloses a method for preparing a super porous carbon material with persimmon peel, using persimmon peel as a raw material, carbonized and activated to make porous carbon, the specific surface area is 1186 square meters per gram, but the electric capacity of the material The chemical activity is low, so it is not suitable as an electrode material for supercapacitors.

Contents of the invention

The object of the present invention is to provide a nitrogen- and boron-doped porous carbon with light texture, large specific surface area, pore classification and high electrochemical activity, which can be applied to supercapacitor electrode materials and a preparation method thereof.

The present invention provides a nitrogen- and boron-doped porous carbon for supercapacitor electrodes, which is made from natural reed stalks, nitrogen fertilizer and boron fertilizer as nitrogen source and boron source respectively, and is obtained through a carbonization activation process. The porous carbon material has a hierarchical three-dimensional pore structure of both micropores and mesopores, the specific surface area is 1400-1700 square meters per gram, the atomic ratio of nitrogen doping is 6-8%, and the atomic ratio of boron doping is 2-4%. It has a hierarchical pore structure, and the pore diameter is mainly distributed in the range of 1 to 5 nanometers. When used as a supercapacitor electrode material, it has a specific capacitance of 225-250 Faradays/gram at a current density of 1 A/gram. After 5000 cycles of charge and discharge, the capacitance retention is higher than 95%, and the power density is 500 W/kg. It has an energy density of 30-35 Wh/kg.

The present invention provides a kind of preparation method of above-mentioned nitrogen, boron doped porous carbon for supercapacitor electrode, it comprises the following steps:

(1) take natural reed stalk as raw material, obtain pretreated reed stalk powder after peeling, drying, pre-crushing, ball milling, centrifugation, washing, and drying;

(2) Weigh reed stalk powder, nitrogen fertilizer, and boron fertilizer in deionized water according to a mass ratio of 1:1 to 3:1 to 3, and obtain a pre-carbonized product after a high-temperature hydrothermal treatment at 120 to 160 degrees Celsius for 12 to 24 hours;

(3) Weigh the pre-carbonized product and potassium hydroxide at a mass ratio of 1:1 to 4, pass through argon or nitrogen, raise the temperature to 700-800 degrees Celsius at a heating rate of 1-5 degrees Celsius/minute and keep it warm for 1-2 hours ;

(4) Alternately washing three times with 3-8% by mass hydrochloric acid solution, ethanol and deionized water to remove residual reagents, drying at 40-60 degrees Celsius to obtain nitrogen- and boron-doped porous carbon.

In the above-mentioned preparation method of nitrogen and boron doped porous carbon used for supercapacitor electrodes, preferably, in step (1), a tissue smasher is used for pre-crushing, and a planetary ball mill is used for ball milling, and the ball milling speed is 400 ～500 rpm, the ball milling time is 12～24 hours, the slurry after ball milling is then centrifuged at a speed of 3000～5000 rpm, the sediment is repeatedly washed alternately with deionized water and absolute ethanol for 3 times, and the Dry at 60 degrees centigrade to obtain pretreated reed stalk powder.

The present invention provides the second preparation method of the above-mentioned nitrogen and boron doped porous carbon for supercapacitor electrodes, which comprises the following steps:

(1) Using natural reed stalks as raw materials, obtain pretreated reed stalk powder after peeling, drying, pre-crushing, ball milling, centrifugation, washing, and drying;

(2) Weigh the reed stalk powder, nitrogen fertilizer, boron fertilizer, and potassium hydroxide according to the mass ratio of 1:1～3:1～3:1～4, mix them evenly, add an appropriate amount of deionized water to the system, and continue stirring Uniform to paste, dried at 40-60 degrees Celsius;

(3) Transfer to a tube furnace, pass argon or nitrogen, first raise the temperature to 300-400 degrees Celsius at a rate of 1-5 degrees Celsius/min and keep it warm for 1-2 hours, then raise the temperature to 700-800 degrees Celsius and keep it warm for 1 ~2 hours;

(4) Alternately washing three times with 3-8% by mass hydrochloric acid solution, ethanol and deionized water to remove residual reagents, drying at 40-60 degrees Celsius to obtain nitrogen- and boron-doped porous carbon.

In the above-mentioned preparation method of nitrogen and boron doped porous carbon used for supercapacitor electrodes, preferably, in step (1), a tissue smasher is used for pre-crushing, and a planetary ball mill is used for ball milling, and the ball milling speed is 400 ～500 rpm, the ball milling time is 12～24 hours, the slurry after ball milling is then centrifuged at a speed of 3000～5000 rpm, the sediment is repeatedly washed alternately with deionized water and absolute ethanol for 3 times, and the Dry at 60 degrees centigrade to obtain pretreated reed stalk powder.

The present invention provides the third preparation method of the above-mentioned nitrogen and boron doped porous carbon for supercapacitor electrodes, comprising the following steps:

(1) planing the fresh and alive reeds containing roots, and cultivating them for 7 to 30 days in the mixed solution of nitrogen fertilizer containing 2 to 5% mass ratio and 2 to 5% mass ratio of boron fertilizer;

(2) intercepting the reed stalks cultivated in step (1), peeling, drying, pre-crushing, ball milling, centrifuging, washing, and drying to obtain reed stalk powder doped with nitrogen and boron;

(3) Weigh nitrogen-doped, boron-doped reed stalk powder and potassium hydroxide at a mass ratio of 1:1 to 4, mix and dry them; The heating rate of Celsius/min is to first raise the temperature to 300-400 degrees Celsius and keep it warm for 1-2 hours, then raise the temperature to 700-800 degrees Celsius and keep it warm for 1-2 hours;

(4) Alternately washing three times with 3-8% by mass hydrochloric acid solution, ethanol and deionized water to remove residual reagents, drying at 40-60 degrees Celsius to obtain nitrogen- and boron-doped porous carbon.

In the above-mentioned preparation method of nitrogen and boron doped porous carbon used for supercapacitor electrodes, preferably, in step (2), a tissue smasher is used for pre-crushing, and a planetary ball mill is used for ball milling, and the ball milling speed is 400 ～500 rpm, the ball milling time is 12～24 hours, the slurry after ball milling is then centrifuged at a speed of 3000～5000 rpm, the sediment is repeatedly washed alternately with deionized water and absolute ethanol for 3 times, and the Reed stalk powder doped with nitrogen and boron is obtained by drying at 60 degrees Celsius.

The nitrogen- and boron-doped porous carbon of the invention can be used as an electrode material for a supercapacitor.

The natural reed stalks of the present invention are taken from natural aquatic reeds, and are mainly rich in crude fiber, crude protein, polysaccharide and the like.

For step (4) of the present invention, adopt the hydrochloric acid solution washing of 5% mass ratio to remove inorganic salt impurities such as residual potassium hydroxide, potassium (hydrogen) carbonate and potassium oxide, adopt ethanol washing to remove residual organic small molecules Impurities.

The present invention uses natural reed stalks as the carbon source, nitrogen fertilizer and boron fertilizer as the nitrogen source and boron source respectively, and nitrogen and boron doped porous carbon is prepared through a high-temperature carbonization activation process, which has the following advantages when used as a supercapacitor electrode material:

(1) The nitrogen- and boron-doped porous carbon prepared in the present invention has a hierarchical three-dimensional porous structure with micropores of less than 2 nanometers and mesopores of 2-5 nanometers, and a specific surface area of 1400-1700 square meters per gram.

(2) The nitrogen and boron doped porous carbon prepared by the present invention has a nitrogen doping atomic ratio of 6 to 8%, a boron doping atomic ratio of 2 to 4%, and a higher heteroatom doping amount. The synergistic effect of the two heteroatoms of boron and boron can not only improve the conductivity of the porous carbon material and improve the wettability of the electrolyte on the surface of the porous carbon, but also significantly improve the pseudocapacitive properties of the porous carbon, so that it is more efficient than that without heteroatoms. Doped porous carbon has higher specific capacitance.

(3) When nitrogen and boron doped porous carbon obtained by the present invention are used as supercapacitor electrode materials, they have a specific capacitance of 225 to 250 Faradays/gram at a current density of 1 ampere/gram, and after 5000 cycles of charging and discharging, The capacity retention is higher than 95%, and the energy density is 30-35 Wh/kg under the power density of 500 W/kg, so it has a very broad market application prospect.

As a cheap and easy-to-obtain natural product, the reed in the present invention is distributed in ditches, embankments and swamps all over the world, and is easy to cultivate and collect. As an important part of reed, reed stalk mainly contains crude fiber, crude protein and polysaccharide, and is an ideal porous carbon raw material. Using common commercially available nitrogen fertilizers and boron fertilizers as nitrogen and boron sources has low production costs and is easier to industrialize the technology of the present invention.

The nitrogen and boron doped porous carbon used for supercapacitor electrodes prepared by the present invention, in addition to having a large specific surface area and a hierarchical three-dimensional porous structure, can improve the pore utilization rate to obtain higher electric double layer capacitance characteristics. It also has a higher nitrogen and boron doping content, which can provide more pore surface polarization sites, surface wettability and surface nitrogen and boron functional groups, thereby simultaneously improving the electric double layer capacitance and pseudo capacitive properties. The nitrogen- and boron-doped porous carbon of the patent invention has high specific capacitance and energy density when applied to supercapacitor electrodes.

Description of drawings

Fig. 1 is a field emission scanning electron microscope image of the nitrogen and boron doped porous carbon of the present invention.

Fig. 2 is the nitrogen adsorption/desorption isotherm curve of the nitrogen and boron doped porous carbon of the present invention.

Fig. 3 is the X-ray photoelectron spectrum of the nitrogen- and boron-doped porous carbon of the present invention, and the inserted table shows the content of each element.

Fig. 4 is the cyclic voltammetry curve of nitrogen and boron doped porous carbon prepared in the present invention.

Fig. 5 is the galvanostatic charge and discharge curves of the nitrogen- and boron-doped porous carbon prepared in the present invention under the two-electrode system, and the current densities are 1, 2, 5 and 10 A/g respectively.

Fig. 6 is the charge-discharge cycle stability curve of the nitrogen- and boron-doped porous carbon prepared in the present invention.

detailed description

The following examples are a further description of the content of the present invention as an explanation of the technical content of the present invention, but the essential content of the present invention is not limited to the following examples, those of ordinary skill in the art can and should know any Simple changes or replacements of the essential spirit of the invention shall fall within the scope of protection required by the present invention.

Example 1

(1) intercept the reed stalk, peel it, dry it, adopt a tissue masher to pre-crumble it, use deionized water as a dispersant, and adopt a planetary ball mill to further ball-mill the pre-broken reed stalk, and the rotating speed is 500 rpm Minutes, ball milling time is 24 hours.

(2) The slurry after ball milling was centrifuged at a speed of 5000 rpm, and the sediment was alternately washed three times with deionized water and absolute ethanol, and dried at 50 degrees Celsius to obtain pretreated reed stalk powder.

(3) Weigh reed stalk powder, urea ammonium nitrogen fertilizer (nitrogen ≥ 30%, China Salt Anhui Hongsifang Co., Ltd.), boron fertilizer (sodium borate ≥ 99%, boron-containing ≥15%, Anhui Nongwang Agricultural Science and Technology Development Co., Ltd.) was dispersed in deionized water, heated at 160 degrees Celsius for 12 hours in a hydrothermal reaction kettle, and the precipitate was repeatedly washed alternately with deionized water and absolute ethanol for 3 times. The pre-carbonized product can be obtained after drying at 50°C.

(4) Weigh the pre-carbonized product and potassium hydroxide according to the mass ratio of 1:3, mix them evenly, add an appropriate amount of deionized water to the system, continue to stir until it becomes a paste, dry it at 50 degrees Celsius, and transfer it to a tube furnace , the temperature was raised to 700°C at a rate of 2°C/min and kept at a temperature of 1 hour with an argon atmosphere.

(5) After cooling to room temperature, alternately wash 3 times with 5% hydrochloric acid solution, ethanol and deionized water, and dry at 50 degrees Celsius to obtain nitrogen- and boron-doped porous carbon.

As shown in FIG. 1 , it is a field emission scanning electron microscope image of the nitrogen- and boron-doped porous carbon prepared in the present invention, which has a remarkable three-dimensional porous structure.

As shown in Figure 2, it is the nitrogen adsorption/desorption isotherm curve of nitrogen and boron doped porous carbon prepared by the present invention, and its specific surface area is as high as 1650 square meters per gram.

As shown in Fig. 3, it is the X-ray photoelectron spectrum of the nitrogen and boron doped porous carbon prepared in the present invention, wherein the doping amount of nitrogen is 7.22%, and the doping amount of boron is 3.23%.

As shown in Figure 4, it is the cyclic voltammetry curve of nitrogen and boron doped porous carbon prepared by the present invention, wherein nitrogen, boron doped porous carbon has higher specific capacitance than undoped porous carbon, nitrogen, boron The prominent oxidation peaks of doped porous carbon indicate its good pseudocapacitive properties.

As shown in Fig. 5, it is the galvanostatic charge-discharge curve of the nitrogen- and boron-doped porous carbon prepared in the present invention under the two-electrode system. According to the formula C _s =I×Δt/(m×ΔV), the mass specific capacitance C _s (Faraday/gram) can be calculated, where I (ampere) is the discharge current, Δt (second) is the discharge time, and m (gram) is The total mass of the active material on the two electrodes, ΔV (volt) is the discharge potential window. It can be calculated that when the current density is 1 ampere/gram, the mass specific capacitance of the nitrogen- and boron-doped porous carbon prepared by the present invention is 242 Faradays/gram. In addition, even at a high current density of 10 A/g, the nitrogen- and boron-doped porous carbon prepared by the present invention still has a specific capacitance as high as 235 Faradays/g, and thus has excellent rate charge and discharge capabilities. In addition, energy density E _m (Wh/kg) and power density P _m (W/kg) can be calculated according to the formula E _m =0.5×C _s ×(ΔV) ² and P _m =E _m / _Δt , (Faraday/gram) is the mass specific capacitance, ΔV (volt) is the discharge potential window, and Δt (second) is the discharge time. When the power density is 500 W/kg, the energy density can reach 33.6 Wh/kg, so it has a very broad market application prospect.

As shown in FIG. 6 , it is the charge-discharge cycle stability curve of the nitrogen- and boron-doped porous carbon prepared in the present invention. At a current density of 10 A/g, after 5,000 cycles of constant current charge and discharge tests, the capacitor still retains about 96% of its initial capacitance, and the Coulombic efficiency is basically stable above 99% after 150 cycles, showing excellent performance. The cycle stability provides a solid foundation for its commercial application.

Example 2

(1) intercept the reed stalk, peel it, dry it, adopt a tissue masher to pre-crumble it, use deionized water as a dispersant, and adopt a planetary ball mill to further ball-mill the pre-broken reed stalk, and the rotating speed is 500 rpm Minutes, ball milling time is 24 hours.

(2) The slurry after ball milling was centrifuged at a speed of 5000 rpm, and the sediment was alternately washed three times with deionized water and absolute ethanol, and dried at 50 degrees Celsius to obtain pretreated reed stalk powder.

(3) Take reed stalk powder, nitrogen fertilizer, boron fertilizer, and potassium hydroxide according to the mass ratio of 1:2:2:3, add an appropriate amount of deionized water to the system after mixing, continue to stir until it becomes a paste, and after 50 Dry at °C, transfer to a tube furnace, pass an argon atmosphere, first raise the temperature to 300 °C at a rate of 2 °C/min and keep it warm for 1 hour, then raise the temperature to 700 °C and keep it warm for 1 hour.

(4) After cooling to room temperature, alternately wash 3 times with 5% hydrochloric acid solution, ethanol and deionized water, and dry at 50 degrees Celsius to obtain nitrogen- and boron-doped porous carbon.

The prepared nitrogen and boron doped porous carbon has a three-dimensional porous structure, its specific surface area is as high as 1500 square meters per gram, the nitrogen doping amount is 6.72%, and the boron doping amount is 3.15%. Hybrid capacitive properties of capacitors. At a current density of 1 ampere/gram, the mass specific capacitance of the nitrogen and boron doped porous carbon is 225 Faradays/gram, and the energy density is 31.3 Wh/kg. After the nitrogen and boron doped porous carbon is charged and discharged 5,000 times, the capacitance retention is still higher than 97%, which has a good market application prospect.

Example 3

(1) Plane the fresh and alive reed that contains root hair, cultivate after 15 days in the nitrogenous fertilizer that contains 5% mass ratio and the boron fertilizer mixed solution of 5% mass ratio, intercept reed stalk, peel, adopt tissue masher to its For pre-crushing, deionized water is used as a dispersant, and the pre-broken reed stalks are further ball-milled with a planetary ball mill at a speed of 500 rpm, and the ball-milling time is 24 hours.

(2) The slurry after ball milling was centrifuged at a speed of 5000 rpm, and the sediment was alternately washed three times with deionized water and absolute ethanol, and dried at 50 degrees Celsius to obtain pretreated reed stalk powder.

(3) Weigh the reed stalk powder and potassium hydroxide according to the mass ratio of 1:3, mix them evenly, add an appropriate amount of deionized water to the system, continue to stir until it becomes a paste, dry it at 50 degrees Celsius, and transfer it to a tube furnace In the process, the argon atmosphere was passed, and the temperature was first raised to 300 degrees Celsius at a heating rate of 2 degrees Celsius/minute and kept for 1 hour, and then the temperature was raised to 700 degrees Celsius and kept for 1 hour.

(4) After cooling to room temperature, alternately wash 3 times with 5% hydrochloric acid solution, ethanol and deionized water, and dry at 50 degrees Celsius to obtain nitrogen- and boron-doped porous carbon.

The obtained nitrogen- and boron-doped porous carbon also has a hierarchical porous structure, the pore size is mainly distributed in the range of 1 to 5 nanometers, the nitrogen doping amount is 5.78%, and the boron doping amount is 1.92%. and pseudocapacitive hybrid capacitive properties. At a current density of 1 ampere/gram, the mass specific capacitance of the nitrogen and boron doped porous carbon is 231 Faradays/gram, and the energy density is 32 Wh/kg. The nitrogen and boron doped porous carbon has a capacitance retention higher than 95% after being charged and discharged 5000 times, has relatively excellent capacitance performance, and can be better applied to the market.

Claims (7)

1. A nitrogen- and boron-doped porous carbon for supercapacitor electrodes is characterized in that it is made from natural reed stalks as a nitrogen source and a boron source with nitrogen fertilizer and boron fertilizer respectively through carbonization activation process , the porous carbon material has a hierarchical three-dimensional pore structure of both micropores and mesopores, the pore size distribution is 1-5 nanometers, the specific surface area is 1400-1700 square meters per gram, the atomic ratio of nitrogen doping is 6-8%, and the atomic ratio of boron doping The ratio is 2 to 4%. 2. claim 1 is used for the preparation method of the nitrogen of supercapacitor electrode, boron doped porous carbon, is characterized in that, comprises the steps: (1) take natural reed stalk as raw material, obtain pretreated reed stalk powder after peeling, drying, pre-crushing, ball milling, centrifugation, washing, and drying; (2) Weigh reed stalk powder, nitrogen fertilizer, and boron fertilizer in deionized water according to a mass ratio of 1:1 to 3:1 to 3, and obtain a pre-carbonized product after a high-temperature hydrothermal treatment at 120 to 160 degrees Celsius for 12 to 24 hours; (3) Weigh the pre-carbonized product and potassium hydroxide at a mass ratio of 1:1 to 4, pass through argon or nitrogen, raise the temperature to 700-800 degrees Celsius at a heating rate of 1-5 degrees Celsius/minute and keep it warm for 1-2 hours ; (4) Alternately washing three times with 3-8% by mass hydrochloric acid solution, ethanol and deionized water to remove residual reagents, drying at 40-60 degrees Celsius to obtain nitrogen- and boron-doped porous carbon. 3. as claimed in claim 2 for the preparation method of the nitrogen of supercapacitor electrode, boron-doped porous carbon, it is characterized in that, in step (1), adopt tissue pounder to carry out pre-crushing, planetary ball mill carries out ball milling process , the ball milling speed is 400-500 rpm, the ball milling time is 12-24 hours, the slurry after ball milling is centrifuged at a speed of 3000-5000 rpm, and the sediment is repeatedly washed alternately with deionized water and absolute ethanol for 3 The second time, dry the pretreated reed stalk powder at 40-60 degrees Celsius. 4. claim 1 is used for the preparation method of the nitrogen of supercapacitor electrode, boron doped porous carbon, is characterized in that, comprises the steps: (1) take natural reed stalk as raw material, obtain pretreated reed stalk powder after peeling, drying, pre-crushing, ball milling, centrifugation, washing, and drying; (2) Weigh the reed stalk powder, nitrogen fertilizer, boron fertilizer, and potassium hydroxide according to the mass ratio of 1:1～3:1～3:1～4, mix them evenly, add an appropriate amount of deionized water to the system, and continue stirring Uniform to paste, dried at 40-60 degrees Celsius; (3) Transfer to a tube furnace, pass argon or nitrogen, first raise the temperature to 300-400 degrees Celsius at a rate of 1-5 degrees Celsius/min and keep it warm for 1-2 hours, then raise the temperature to 700-800 degrees Celsius and keep it warm for 1 ~2 hours; (4) Alternately washing three times with 3-8% by mass hydrochloric acid solution, ethanol and deionized water to remove residual reagents, drying at 40-60 degrees Celsius to obtain nitrogen- and boron-doped porous carbon. 5. as claimed in claim 4 for the preparation method of the nitrogen of supercapacitor electrode, boron doped porous carbon, it is characterized in that, in step (1), adopt tissue pounder to carry out pre-crushing, planetary ball mill carries out ball milling process , the ball milling speed is 400-500 rpm, the ball milling time is 12-24 hours, the slurry after ball milling is centrifuged at a speed of 3000-5000 rpm, and the sediment is repeatedly washed alternately with deionized water and absolute ethanol for 3 The second time, dry the pretreated reed stalk powder at 40-60 degrees Celsius. 6. claim 1 is used for the preparation method of the nitrogen of supercapacitor electrode, boron doped porous carbon, is characterized in that, comprises the steps: (1) planing the fresh and alive reeds containing roots, and cultivating them for 7 to 30 days in the mixed solution of nitrogen fertilizer containing 2 to 5% mass ratio and 2 to 5% mass ratio of boron fertilizer; (2) intercepting the reed stalks cultivated in step (1), peeling, drying, pre-crushing, ball milling, centrifuging, washing, and drying to obtain reed stalk powder doped with nitrogen and boron; (3) Weigh nitrogen-doped, boron-doped reed stalk powder and potassium hydroxide at a mass ratio of 1:1 to 4, mix and dry them; The heating rate of Celsius/minute is to first raise the temperature to 300-400 degrees Celsius and keep it warm for 1-2 hours, then raise the temperature to 700-800 degrees Celsius and keep it warm for 1-2 hours; (4) Alternately washing three times with 3-8% by mass hydrochloric acid solution, ethanol and deionized water to remove residual reagents, drying at 40-60 degrees Celsius to obtain nitrogen- and boron-doped porous carbon. 7. The application of claim 1 or the nitrogen and boron doped porous carbon obtained by the preparation method described in any one of claims 2 to 6 as supercapacitor electrode materials.