N, S co-doped hierarchical porous carbon electrode material and preparation method thereof

Abstract

The invention discloses an N and S co-doped graded porous carbon electrode material and a preparation method, and belongs to the technical field of carbon-based functional materials.The preparation method comprises the steps that bran, potassium bicarbonate, thiourea and water are evenly mixed at the room temperature and dried; carbonizing the dried object under the protection of nitrogen by a one-step pyrolysis method to obtain a black product; and grinding the black product, mixing with dilute acid, washing to be neutral, and drying to obtain the N, S co-doped graded porous carbon electrode material. Potassium bicarbonate is adopted as a chemical activator, operation is easy and convenient, environment friendliness is achieved, compared with high corrosivity of potassium hydroxide, potassium bicarbonate is relatively mild, and the specific surface area of the material is increased; meanwhile, thiourea serves as a heteroatom source, the heteroatom doping amount and active sites are increased, the electronic structure of the material is optimized, and when the N and S co-doped hierarchical porous carbon electrode material is applied to supercapacitor electrode material testing, the N and S co-doped hierarchical porous carbon electrode material shows high pseudocapacitance performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon-based functional materials, and in particular relates to a N, S co-doped graded porous carbon electrode material and a preparation method thereof. Background Art

[0002] Supercapacitors, as an efficient energy storage device, have attracted widespread attention due to their fast charging and discharging capabilities, long cycle life and high power density. Carbon-based materials have become the preferred electrode materials for supercapacitors due to their excellent chemical stability, high specific surface area and good conductivity. Traditional carbon-based electrode materials such as activated carbon and carbon nanotubes, despite their high specific surface area, still have room for improvement in pseudocapacitance performance.

[0003] Pseudocapacitance significantly improves the energy density of supercapacitors through redox reactions on the surface of electrode materials. Therefore, the development of carbon-based electrode materials with high pseudocapacitance performance has become a research hotspot. Improving the electronic structure of carbon materials and increasing active sites by heteroatom doping is an effective means to improve pseudocapacitance performance.

[0004] However, the existing doping methods are often complicated to operate, with low doping amounts, and the resulting carbon materials have low specific surface area and poor specific capacitance. Therefore, it is urgent to develop a carbon electrode material that is simple in process, environmentally friendly, low in cost, and has a high specific surface area and multi-level pore structure. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a N, S co-doped hierarchical porous carbon electrode material and a preparation method thereof. The N, S co-doped hierarchical porous carbon electrode material of the present invention has high specific surface area and multi-level pore structure characteristics, and the preparation process is simple, environmentally friendly and low cost.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention:

[0008] A method for preparing a N, S co-doped graded porous carbon electrode material comprises the following steps: potassium bicarbonate activation and heteroatom doping to prepare the N, S co-doped graded porous carbon electrode material, wherein the heteroatom is sulfur and nitrogen.

[0009] Furthermore, the method for preparing the N, S co-doped graded porous carbon electrode material comprises the following steps:

[0010] The bran, potassium bicarbonate and thiourea are mixed, stirred evenly, water is added, stirred evenly again, allowed to stand and then dried, the calcined product is soaked in an acid solution, washed with water until neutral and then dried to obtain the N, S co-doped graded porous carbon electrode material.

[0011] Bran is light and is often used as feed. Bran-derived carbon materials have a relatively low specific surface area, which is unfavorable for supercapacitor electrode materials because the size of the specific surface area directly affects the electrochemical properties (including capacitance properties) of the electrode materials. The pore size distribution of bran-derived carbon materials may not be suitable as electrode materials because ideal supercapacitor electrode materials should have a progressive pore structure and pores of different sizes should be interconnected to facilitate ion transport and improve capacitance performance. When bran-derived carbon materials are used as supercapacitor electrode materials, there may be problems with low charging and discharging efficiency and severe self-discharge, which limits their performance in practical applications. Bran-derived carbon materials may be prone to agglomeration, which will affect the effective contact surface area of ​​the electrode material and thus affect the efficiency of the supercapacitor. At the same time, bran has a high ash content and is not suitable for the preparation of carbon electrode materials. However, the present application uses potassium bicarbonate as an activator, and the gas expansion effect produced by high-temperature decomposition is used to manufacture macropores. On the other hand, the decomposition product reacts with the carbon in the bran to etch, thereby obtaining micropores and mesopores. Therefore, the bran biochar prepared with potassium bicarbonate as an activator has a hierarchical porous structure of macropores, mesopores and micropores. These types are rich and the pore structure with complex spatial distribution greatly improves the specific surface area of ​​the bran biochar. Moreover, potassium bicarbonate has weak alkalinity and a relatively mild reaction. It can slow down the rate of etching during the activation process, increase the proportion of micropores and mesopores and the uniformity of pore size, which also provides favorable conditions for improving the specific surface area of ​​the bran biochar. In addition, potassium bicarbonate activation can also enrich the types of surface functional groups of bran biochar, and these functional groups can provide favorable conditions for improving the pseudocapacitance performance of carbon materials. Thiourea is used as a heteroatom source to increase the heteroatom doping amount and active sites, optimize the electronic structure of the material, and when applied to supercapacitor electrode material testing, N, S co-doped hierarchical porous carbon materials show higher pseudocapacitance performance.

[0012] The mass ratio of the bran, potassium bicarbonate and thiourea is 2:1:1.

[0013] Before the bran, potassium bicarbonate and thiourea are mixed, the method further includes a pretreatment step of washing and drying the bran.

[0014] The pretreatment steps of washing and drying the bran are as follows: after washing the bran with deionized water, transferring it to an ultrasonic cleaning machine for ultrasonic cleaning, and then placing it in an oven for drying at a drying temperature of 80° C. for a drying time of 12 hours.

[0015] The ultrasonic cleaning machine includes a cleaning tank, an ultrasonic generator is arranged below the cleaning tank, a transducer is arranged next to the ultrasonic generator, a drainage hole is arranged at the bottom of the cleaning tank, a first cleaning basket is arranged in the cleaning tank, and the height in the vertical direction is less than the depth of the cleaning tank in the vertical direction, a grip rod is arranged above the two opposite side edges of the top of the first cleaning basket and parallel to the corresponding side edges, and the grip rod is arranged outside the cleaning tank, and movable and detachable sliding rods parallel to the corresponding side edges are arranged on the opposite sides of the grip rod, and a detachable second cleaning basket is arranged on the movable and detachable sliding rod, the height of the second cleaning basket in the vertical direction is less than the depth of the first cleaning basket in the vertical direction, and the mesh size of the second cleaning basket is much smaller than the mesh size of the first cleaning basket, and the second cleaning basket includes two layers, the first layer is a cleaning layer with fine mesh, and a detachable solid collecting basket (i.e., the second layer) is arranged below the cleaning layer.

[0016] After the bran, potassium bicarbonate and thiourea are mixed, the stirring time is 30 minutes; and / or

[0017] After adding water, the stirring time is 1 hour; and / or

[0018] The standing time is 12 hours.

[0019] The calcination is first calcined at a low temperature and then calcined at a high temperature;

[0020] The temperature of the low temperature is 400° C., and the insulation time is 1 hour; the temperature of the high temperature is 800° C., and the insulation time is 2 hours.

[0021] The concentration of the acid solution is 1.0 mol / L. Soaking in the acid solution can effectively remove ash and inorganic impurities in the carbon material, improve the purity and surface state of the porous carbon electrode material, improve the structural characteristics of the carbon electrode material, and thus improve its performance.

[0022] Exemplarily, the preparation method of the N, S co-doped hierarchical porous carbon electrode material is:

[0023] (1) After the bran is rinsed with deionized water, it is transferred to the second cleaning basket of an ultrasonic cleaning machine for ultrasonic cleaning, and then placed in an oven for drying at a drying temperature of 80° C. for a drying time of 12 h;

[0024] (2) Weigh 6 g of bran, 3 g of potassium bicarbonate and 3 g of thiourea after the above treatment, and stir them evenly for 30 min;

[0025] (3) Add 100 mL of deionized water and stir thoroughly at room temperature for 1 h;

[0026] (4) The stirred mixture was allowed to stand at room temperature for 12 h and then dried in an oven at 80° C. for 12 h.

[0027] (5) The dried material was placed in an alumina porcelain boat, and the alumina porcelain boat was placed in a high-temperature tube furnace. Nitrogen was introduced as a protective gas at a nitrogen flow rate of 120 sccm. The heating rate was 5°C / min, and the temperature was maintained at a low temperature (400°C) for 1 hour. Then, the temperature was increased to a high temperature (800°C) at the same rate and maintained for 2 hours to obtain a black block solid product.

[0028] (6) The black block solid product was ground into powder in a mortar, passed through a 100-mesh sieve, and stirred in a hydrochloric acid solution with a concentration of 1.0 mol / L. The product was washed with deionized water until neutral, and dried in an oven at a drying temperature of 80°C for 14 h to obtain a N, S co-doped graded porous carbon electrode material.

[0029] The second technical solution of the present invention:

[0030] The present invention also provides a N, S co-doped graded porous carbon electrode material prepared according to the above method.

[0031] The N, S co-doped hierarchical porous carbon electrode material prepared by the present invention has a multi-level pore structure distribution. The micropores contribute to the ultra-high capacity by providing a rich electrode / electrolyte interface; the mesopores provide a rich ion transport channel, improve the accessibility of the micropores, and shorten the transport path; the macropores optimize the interface wettability and serve as an electrolyte reservoir to effectively reduce the ion transport resistance. The three work together to optimize the transmission and storage efficiency of ions. Therefore, the N, S co-doped hierarchical porous carbon electrode material prepared by the present invention has high pseudocapacitance.

[0032] The third technical solution of the present invention:

[0033] The present invention also provides the use of the N, S co-doped graded porous carbon electrode material in the preparation of a supercapacitor.

[0034] The fourth technical solution of the present invention:

[0035] The present invention also provides a supercapacitor, which contains the above-mentioned N, S co-doped graded porous carbon electrode material.

[0036] Compared with the prior art, the present invention has the following advantages and technical effects:

[0037] (1) The raw bran used in the present invention has a wide range of sources, low price, simple preparation process, low cost, green and environmental protection, and meets the requirements of sustainable development. In addition, a device for washing bran is provided for the raw material. The device can be used for washing bran, which has a light density, small mass, small particle size, and is easy to precipitate and thus block the drainage hole.

[0038] (2) In the present invention, the ratio of bran, potassium bicarbonate and thiourea is 6:3:3, which helps to achieve N, S co-doping, increase the heteroatom doping amount and active sites, and optimize the electronic structure of the material. When applied to supercapacitor electrode material testing, the N, S co-doped hierarchical porous carbon material exhibits higher pseudocapacitive performance.

[0039] (3) The present invention adopts a method of first calcining at low temperature and then calcining at high temperature. The low temperature calcination helps to maintain the initial pore structure of the material, while the high temperature calcination helps to further open and expand the pore size, forming a hierarchical porous structure that is more conducive to ion transmission. On this basis, a one-step pyrolysis method is adopted to combine the activation pore-forming and heteroatom doping steps into one, which has simple steps, efficient methods, and can save a lot of preparation time.

[0040] (4) The present invention uses potassium bicarbonate as an activator and utilizes the gas expansion effect generated by high-temperature decomposition to produce macropores. At the same time, the decomposition products react with the carbon in the bran to etch, thereby obtaining micropores and mesopores, thereby forming a hierarchical porous structure of macropores, mesopores and micropores. This structure greatly increases the specific surface area of ​​the bran biochar and has better electrochemical performance than the prior art.

[0041] (5) The N, S co-doped graded porous carbon electrode material with high pseudocapacitance prepared by the present invention has a high specific capacitance of up to 307.3 F / g at a current density of 0.5 A / g, and still has a specific capacitance of 216 F / g at a current density of 15 A / g, and has excellent rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0043] Figure 1 It is a schematic diagram of the structure of the ultrasonic cleaning machine, wherein 1-grip rod, 2-first cleaning basket, 3-slide rod, 4-second cleaning basket, 5-drain hole, 6-function control panel;

[0044] Figure 2 This is a scanning electron microscope image of the N, S co-doped hierarchical porous carbon electrode material prepared in Example 1;

[0045] Figure 3 This is an element scanning diagram of the N, S co-doped hierarchical porous carbon electrode material prepared in Example 1;

[0046] Figure 4 This is a nitrogen adsorption-desorption curve of the N, S co-doped graded porous carbon electrode material prepared in Example 1;

[0047] Figure 5 This is a pore size distribution spectrum of the N, S co-doped graded porous carbon electrode material prepared in Example 1;

[0048] Figure 6 The constant current charge-discharge curve of the N, S co-doped graded porous carbon electrode material prepared in Example 1 in a three-electrode system;

[0049] Figure 7 The cyclic voltammetry curve of the N, S co-doped hierarchical porous carbon electrode material prepared in Example 1 in a three-electrode system;

[0050] Figure 8 This is the electrochemical impedance spectrum of the N, S co-doped graded porous carbon electrode material prepared in Example 1 in a three-electrode system. DETAILED DESCRIPTION

[0051] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0052] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0053] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0054] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0055] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0056] Unless otherwise specified, the room temperature in the present invention is 25±2°C.

[0057] All raw materials used in the examples and comparative examples of the present invention are purchased from commercial sources.

[0058] In the embodiment of the present invention, the structural schematic diagram of the ultrasonic cleaning machine used is as follows Figure 1 As shown (wherein 1-grip rod, 2-first cleaning basket, 3-slide rod, 4-second cleaning basket, 5-drain hole, 6-function control panel), including a cleaning tank, an ultrasonic generator is arranged below the cleaning tank, a transducer is arranged next to the ultrasonic generator, a drainage hole 5 is arranged at the bottom of the cleaning tank, a first cleaning basket 2 is arranged in the cleaning tank, and the height of the first cleaning basket 2 in the vertical direction is less than the depth of the cleaning tank in the vertical direction, a grip rod 1 is arranged above the opposite side edges of the top of the first cleaning basket 2 and parallel to the corresponding side edges, and the grip rod 1 is arranged outside the cleaning tank, two movable and detachable slide rods 3 are arranged in parallel between the grip rods 1 on both sides, and a detachable second The cleaning basket 4, the height of the second cleaning basket 4 in the vertical direction is smaller than the depth of the first cleaning basket 2 in the vertical direction, and the mesh size of the second cleaning basket 4 is much smaller than the mesh size of the first cleaning basket 2 (for example, the mesh size of the second cleaning basket 4 is 100 mesh, and the mesh size of the first cleaning basket 2 is 1cm×1cm grid), the second cleaning basket 4 includes two layers, the first layer is a cleaning layer with fine mesh (100 mesh), and a detachable solid collection basket (i.e., the second layer) is arranged below the cleaning layer. For cleaning bran, which has light density, small mass, small particle size, and is easy to precipitate, thereby clogging the drainage hole, the second cleaning basket 4 (the mesh size of the second cleaning basket 4 is 100 mesh) of the ultrasonic cleaning machine can be used.

[0059] In some embodiments of the present invention, a method for preparing a N, S co-doped graded porous carbon electrode material is provided:

[0060] The bran, potassium bicarbonate and thiourea are mixed, stirred evenly, water is added, stirred evenly again, allowed to stand and then dried, the calcined product is soaked in an acid solution, washed with water until neutral and then dried to obtain a N, S co-doped graded porous carbon electrode material.

[0061] The present invention uniformly mixes bran, potassium bicarbonate, thiourea and water at room temperature and dries; carbonizes the dried object under nitrogen protection by a one-step pyrolysis method to obtain a black product; the black product is ground and mixed with dilute acid, then washed with water to neutrality, and dried to obtain a N, S co-doped hierarchical porous carbon electrode material. The present invention uses potassium bicarbonate as a chemical activator, which is easy to operate and environmentally friendly. Compared with the strong corrosiveness of potassium hydroxide, potassium bicarbonate is relatively mild and increases the specific surface area of ​​the material; at the same time, thiourea is used as a heteroatom source to increase the heteroatom doping amount and active sites, optimize the electronic structure of the material, and when applied to supercapacitor electrode material testing, the N, S co-doped hierarchical porous carbon electrode material exhibits higher pseudocapacitance performance.

[0062] In some embodiments of the present invention, the mass ratio of bran, potassium bicarbonate and thiourea is 2:1:1.

[0063] In some embodiments of the present invention, before mixing the bran, potassium bicarbonate and thiourea, a pretreatment step of washing and drying the bran is also included.

[0064] In some embodiments of the present invention, the pretreatment steps for cleaning and drying the bran are: after rinsing the bran with deionized water, transfer it to the second cleaning basket 4 of the ultrasonic cleaning machine for ultrasonic cleaning, and then place it in an oven for drying at a drying temperature of 80°C and a drying time of 12 hours.

[0065] In some embodiments of the present invention, after the bran, potassium bicarbonate and thiourea are mixed, the stirring time is 30 minutes; and / or

[0066] After adding water, the stirring time is 1 hour; and / or

[0067] The standing time is 12h.

[0068] In some embodiments of the present invention, the drying temperature after standing is 80° C. and the drying time is 12 h.

[0069] In some embodiments of the present invention, the drying temperature after washing to neutrality is 80° C. and the drying time is 12 to 16 hours.

[0070] In some embodiments of the present invention, the calcination is first calcined at a low temperature and then calcined at a high temperature;

[0071] The low temperature is 400℃, and the holding time is 1h; the high temperature is 800℃, and the holding time is 2h. The heating rate is 5℃ / min, and nitrogen is used as the protective gas during calcination. Low-temperature calcination helps to remove moisture from the material and preliminary heat treatment, while high-temperature calcination is more conducive to the crystallization and phase change of the material. Low-temperature calcination may result in smaller particle size, which is conducive to the formation of uniform morphology. High-temperature calcination may cause particle fusion and agglomeration, affecting the specific surface area and pore structure of the material.

[0072] In some embodiments of the present invention, the nitrogen flow rate is 120-150 sccm.

[0073] In some embodiments of the present invention, the concentration of the acid solution is 1.0 mol / L. The present invention does not limit the type of acid, and in the following embodiments of the present invention, a hydrochloric acid solution with a concentration of 1.0 mol / L is used for illustration.

[0074] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in the art and are not the focus of the present invention.

[0075] The technical solution of the present invention is further illustrated by the following embodiments.

[0076] Example 1

[0077] A method for preparing N, S co-doped graded porous carbon electrode material:

[0078] (1) After the bran is rinsed with deionized water, it is transferred to the second cleaning basket 4 of the ultrasonic cleaning machine for ultrasonic cleaning, and then placed in an oven for drying at a drying temperature of 80° C. for a drying time of 12 h;

[0079] (2) Weigh 6 g of bran, 3 g of potassium bicarbonate and 3 g of thiourea after the above treatment, and stir them evenly for 30 min;

[0080] (3) Add 100 mL of deionized water and stir thoroughly at room temperature for 1 h;

[0081] (4) The stirred mixture was allowed to stand at room temperature for 12 h and then dried in an oven at 80° C. for 12 h.

[0082] (5) The dried material was placed in an alumina porcelain boat, and the alumina porcelain boat was placed in a high-temperature tube furnace. Nitrogen was introduced as a protective gas at a nitrogen flow rate of 120 sccm. The heating rate was 5°C / min, and the temperature was maintained at a low temperature (400°C) for 1 hour. Then, the temperature was increased to a high temperature (800°C) at the same rate and maintained for 2 hours to obtain a black block solid product.

[0083] (6) The black block solid product was ground into powder in a mortar, passed through a 100-mesh sieve, and stirred in a hydrochloric acid solution with a concentration of 1.0 mol / L. The product was washed with deionized water until neutral, and dried in an oven at a drying temperature of 80°C for 14 h to obtain a N, S co-doped graded porous carbon electrode material.

[0084] The morphology and performance of the N, S co-doped graded porous carbon electrode material prepared in this example were tested.

[0085] The scanning electron microscope image of the N, S co-doped hierarchical porous carbon electrode material prepared in this example is shown in FIG. Figure 2 It can be seen that the obtained N, S co-doped graded porous carbon electrode material has a multi-level pore structure distribution. The micropores contribute to the ultra-high capacity by providing a rich electrode / electrolyte interface; the mesopores provide abundant ion transport channels, improve the accessibility of the micropores, and shorten the transport path; the macropores optimize the interface wettability and serve as an electrolyte reservoir to effectively reduce the ion transport resistance. The three work together to optimize the ion transmission and storage efficiency.

[0086] Figure 3 This is an element scanning diagram of the N, S co-doped graded porous carbon electrode material prepared in this embodiment. It can be seen that the obtained N, S co-doped graded porous carbon electrode material contains three elements of C, N, and S at the same time, indicating that nitrogen and sulfur elements are successfully doped in the carbon material.

[0087] Figure 4 : is the nitrogen adsorption-desorption curve of the N, S co-doped graded porous carbon electrode material prepared in this embodiment. It can be seen that the adsorption curve of the obtained N, S co-doped graded porous carbon electrode material is a typical I / IV type adsorption curve, and its specific surface area is 1209.14m 2 / g.

[0088] The pore size distribution spectrum calculated by the DJH method, the pore size distribution spectrum of N, S co-doped graded porous carbon electrode material is shown in Figure 5 As shown, it can be seen that the pore size distribution of the obtained N, S co-doped graded porous carbon electrode material is clear and uniform, which makes the N, S co-doped graded porous carbon electrode material have good electrochemical performance.

[0089] Figure 6This is the constant current charge and discharge curve of the N, S co-doped graded porous carbon electrode material prepared in this embodiment in a three-electrode system (Hg / HgO salt bridge as the reference electrode, platinum sheet electrode as the counter electrode, and the electrode sheet made of the carbon material prepared in this embodiment as the working electrode). Using 6M KOH as the electrolyte, it is measured that the specific capacitance is as high as 307.3F / g at a current density of 0.5A / g, and still has a specific capacitance of 216F / g at a current density of 15A / g, with excellent rate performance.

[0090] Figure 7 The cyclic voltammetry curve of the N, S co-doped graded porous carbon electrode material prepared in this example in a three-electrode system shows that the curves at different scanning speeds are close to a rectangular shape, which has the characteristics of a typical double-layer capacity.

[0091] Figure 8 The electrochemical impedance spectrum of the N, S co-doped hierarchical porous carbon electrode material prepared in this example in a three-electrode system. The results show that when the open circuit voltage is -0.05 V and the frequency is 0.01 to 10 5 At Hz, through fitting, the charge transfer impedance (Rct) of the obtained N,S co-doped graded porous carbon electrode material was 1.23Ω, and the ohmic impedance (Rs) was 0.25Ω, indicating that the material has excellent conductivity and small interface resistance.

[0092] Comparative Example 1

[0093] A method for preparing N, S co-doped graded porous carbon electrode material:

[0094] (1) After the bran is rinsed with deionized water, it is transferred to the second cleaning basket 4 of an ultrasonic cleaning machine for ultrasonic cleaning, and then placed in an oven for drying at a drying temperature of 80° C. for a drying time of 12 h;

[0095] (2) Weigh 6 g of bran, 6 g of potassium bicarbonate and 3 g of thiourea after the above treatment, stir evenly for 30 min;

[0096] (3) Add 100 mL of deionized water and stir thoroughly at room temperature for 1 h;

[0097] (4) The stirred mixture was allowed to stand at room temperature for 12 h and then dried in an oven at 80° C. for 12 h.

[0098] (5) The dried material was placed in an alumina porcelain boat, and the alumina porcelain boat was placed in a high-temperature tube furnace. Nitrogen was introduced as a protective gas at a nitrogen flow rate of 120 sccm. The heating rate was 5°C / min. The temperature was kept at a low temperature (400°C) for 1 hour, and then the temperature was raised to a high temperature (800°C) at the same rate and kept for 2 hours to obtain a black block solid product.

[0099] (6) The black block solid product was ground into powder in a mortar, passed through a 100-mesh sieve, and stirred in a hydrochloric acid solution with a concentration of 1.0 mol / L. The product was washed with deionized water until neutral, and dried in an oven at a drying temperature of 80°C for 14 h to obtain a N, S co-doped graded porous carbon electrode material.

[0100] The N, S co-doped graded porous carbon electrode material prepared in this comparative example has a specific capacitance of up to 204.35 F / g at a current density of 0.5 A / g in a three-electrode system using 6 M KOH as an electrolyte.

[0101] This comparative example is compared with Example 1 by changing the amount of activator. The test results show that the specific capacitance of this comparative example at a current density of 0.5A / g is significantly lower than that of Example 1. This may be due to excessive activators, which may lead to over-activation, thereby destroying the partial structure of the carbon material, affecting its specific surface area and pore structure, and thus affecting the electrochemical performance. And in the embodiment, through specific doping and activator ratios, a more favorable pore structure may be formed, such as a reasonable distribution of micropores and mesopores, which helps to improve the specific capacitance. In this comparative example, the increase in the activator ratio may cause changes in the pore structure, which is not conducive to the adsorption and transmission of electrolyte ions, thereby affecting the capacitance performance.

[0102] Comparative Example 2

[0103] A method for preparing N, S co-doped graded porous carbon electrode material:

[0104] (1) After the bran is rinsed with deionized water, it is transferred to the second cleaning basket 4 of an ultrasonic cleaning machine for ultrasonic cleaning, and then placed in an oven for drying at a drying temperature of 80° C. for a drying time of 12 h;

[0105] (2) Weigh 6 g of bran, 6 g of potassium bicarbonate and 6 g of thiourea after the above treatment, stir evenly for 30 min;

[0106] (3) Add 100 mL of deionized water and stir thoroughly at room temperature for 1 h;

[0107] (4) The stirred mixture was allowed to stand at room temperature for 12 h and then dried in an oven at 80° C. for 12 h.

[0108] (5) The dried material was placed in an alumina porcelain boat, and the alumina porcelain boat was placed in a high-temperature tube furnace. Nitrogen was introduced as a protective gas at a nitrogen flow rate of 120 sccm. The heating rate was 5°C / min, and the temperature was maintained at a low temperature (400°C) for 1 hour. Then, the temperature was increased to a high temperature (800°C) at the same rate and maintained for 2 hours to obtain a black block solid product.

[0109] (6) The black block solid product was ground into powder in a mortar, passed through a 100-mesh sieve, and stirred in a hydrochloric acid solution with a concentration of 1.0 mol / L. The product was washed with deionized water until neutral, and dried in an oven at a drying temperature of 80°C for 14 h to obtain a N, S co-doped graded porous carbon electrode material.

[0110] The N, S co-doped graded porous carbon electrode material prepared in this comparative example has a specific capacitance of 171.25 F / g at a current density of 0.5 A / g in a three-electrode system using 6 M KOH as an electrolyte.

[0111] The test results show that the specific capacitance of this comparative example at a current density of 0.5A / g is significantly lower than that of Example 1. Appropriate doping can increase active sites and improve pseudocapacitive performance, but improper proportions may reduce material performance. The increase in the amount of potassium bicarbonate and thiourea may affect the uniformity of doping and the pore structure of the material, and excessive sulfur content may aggravate the distortion and destruction of the graphitized structure of the carbon material, resulting in reduced conductivity. The specific raw material ratio in the embodiment may help to form a more uniform N, S co-doped structure, and the increase in the ratio of potassium bicarbonate and thiourea in this comparative example may affect the uniformity of doping, thereby affecting the electrochemical performance.

[0112] Comparative Example 3

[0113] A method for preparing N, S co-doped graded porous carbon electrode material:

[0114] (1) After the bran is rinsed with deionized water, it is transferred to the second cleaning basket 4 of an ultrasonic cleaning machine for ultrasonic cleaning, and then placed in an oven for drying at a drying temperature of 80° C. for a drying time of 12 h;

[0115] (2) Weigh 6 g of bran, 3 g of potassium bicarbonate and 3 g of thiourea after the above treatment, and stir them evenly for 30 min;

[0116] (3) Add 100 mL of deionized water and stir thoroughly at room temperature for 1 h;

[0117] (4) The stirred mixture was allowed to stand at room temperature for 12 h and then dried in an oven at 80° C. for 12 h.

[0118] (5) The dried material was placed in an alumina porcelain boat, and the alumina porcelain boat was placed in a high-temperature tube furnace. Nitrogen was introduced as a protective gas at a nitrogen flow rate of 120 sccm and a heating rate of 5°C / min. The temperature was raised to a high temperature (800°C) and maintained for 2 h to obtain a black block solid product.

[0119] (6) The black block solid product was ground into powder in a mortar, passed through a 100-mesh sieve, and stirred in a hydrochloric acid solution with a concentration of 1.0 mol / L. The product was washed with deionized water until neutral, and dried in an oven at a drying temperature of 80°C for 14 h to obtain a N, S co-doped graded porous carbon electrode material.

[0120] The N, S co-doped graded porous carbon electrode material prepared in this comparative example was placed in a three-electrode system with 6M KOH as the electrolyte, and had a specific capacitance of 227.7F / g at a current density of 0.5A / g. The test results show that the specific capacitance of this comparative example at a current density of 0.5A / g is significantly lower than that of Example 1. This may be due to the lack of a step of calcining at low temperature (400°C) for 1 hour in Comparative Example 3, which directly heats up to high temperature (800°C) and maintains for 2 hours. Low-temperature calcination helps to preliminarily remove volatiles and some impurities in the raw materials, while avoiding excessive sintering that may occur at high temperatures and maintaining the pore structure of the material. The lack of this step may result in the pore structure of the material not being fully optimized, affecting its electrochemical properties. And low-temperature calcination helps to maintain the initial pore structure of the material, while high-temperature calcination further promotes the graphitization of the material, improving its conductivity and structural stability. The lack of a low-temperature calcination step may result in the pore structure and specific surface area not being fully developed, thereby affecting the adsorption and transmission of electrolyte ions.

[0121] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing a N, S co-doped hierarchical porous carbon electrode material, characterized in that: N, S co-doped hierarchical porous carbon electrode materials were prepared by potassium bicarbonate activation and heteroatom doping, wherein the heteroatoms were sulfur and nitrogen.

2. The method for preparing the N, S co-doped hierarchical porous carbon electrode material according to claim 1, characterized in that: The following steps are involved: The bran, potassium bicarbonate and thiourea are mixed, stirred evenly, water is added, stirred evenly again, allowed to stand and then dried, the calcined product is soaked in an acid solution, washed with water until neutral and then dried to obtain the N, S co-doped graded porous carbon electrode material.

3. The method for preparing the N, S co-doped hierarchical porous carbon electrode material according to claim 2, characterized in that: The mass ratio of the bran, potassium bicarbonate and thiourea is 2:1:

1.

4. The method for preparing the N, S co-doped hierarchical porous carbon electrode material according to claim 2, characterized in that: Before the bran, potassium bicarbonate and thiourea are mixed, the method further includes a pretreatment step of washing and drying the bran.

5. The method for preparing the N, S co-doped hierarchical porous carbon electrode material according to claim 2, characterized in that: After the bran, potassium bicarbonate and thiourea are mixed, the stirring time is 30 minutes; and / or After adding water, the stirring time is 1 hour; and / or The standing time is 12 hours.

6. The method for preparing the N, S co-doped hierarchical porous carbon electrode material according to claim 2, characterized in that: The calcination is first calcined at a low temperature and then calcined at a high temperature; The temperature of the low temperature is 400° C., and the insulation time is 1 hour; the temperature of the high temperature is 800° C., and the insulation time is 2 hours.

7. The method for preparing the N, S co-doped hierarchical porous carbon electrode material according to claim 2, characterized in that: The concentration of the acid solution is 1.0 mol / L.

8. A N, S co-doped hierarchical porous carbon electrode material, characterized in that: Prepared according to the method according to any one of claims 1 to 7.

9. Use of the N, S co-doped graded porous carbon electrode material according to claim 8 in the preparation of supercapacitors.

10. A supercapacitor, characterized in that: Contains the N, S co-doped graded porous carbon electrode material as described in claim 8.

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