WO2023116261A1

WO2023116261A1 - Method for preparing nitrogen-doped porous carbon material

Info

Publication number: WO2023116261A1
Application number: PCT/CN2022/131953
Authority: WO
Inventors: 卢颖莉; 荆葛; 王恒; 冯冬梅; 乔志军; 刘丛刚
Original assignee: 宁波中车新能源科技有限公司
Priority date: 2021-12-24
Filing date: 2022-11-15
Publication date: 2023-06-29
Also published as: CN114516635B; CN114516635A

Abstract

The present application relates to the technical field of porous carbon materials, and provides a method for preparing a nitrogen-doped porous carbon material and an application of the nitrogen-doped porous carbon material in a supercapacitor. The nitrogen-doped porous carbon material is prepared by using humic acid in weathered coal as a carbon material precursor, using urea as a nitrogen source, using a potassium metal compound as an activating agent, and performing a high-temperature reaction. When the nitrogen-doped porous carbon material is used as the electrode material of a supercapacitor, the supercapacitor exhibits excellent electrochemical performance. The initial raw materials are humic acid and urea, are widely present in nature, and are cheap in price and abundant in source; moreover, the method only relates to a small number of processes such as activation and cleaning, and large-scale industrial production is facilitated.

Description

A kind of preparation method of nitrogen-doped porous carbon material

Technical field:

The invention belongs to the technical field of porous carbon materials, and in particular relates to a preparation method of nitrogen-doped porous carbon materials and its application in supercapacitors.

Background technique:

Supercapacitors, also known as electrochemical capacitors, are efficient and stable energy storage devices that combine the high-power discharge of traditional capacitors with the high energy density of batteries. Because of its advantages such as good electrochemical stability, high energy density, fast charge and discharge speed, and long cycle life, it is expected to become the main force for power supplementation of electronic equipment in the fields of wearable devices, electric vehicles, and aerospace. Electrode materials play a central role in supercapacitors and are the key points to improve the electrochemical performance of supercapacitors.

Common electrode materials include metal oxides, conductive polymers, carbon materials, and their composite materials. Among them, electric double layer capacitors with carbon materials as key energy storage materials have low manufacturing costs, excellent high and low temperature performance, long life, and low cost. It has outstanding advantages such as non-toxicity and has become the most extensive supercapacitor in the industrialization process at this stage. Although the energy storage device has been widely used in many fields, its insufficient energy density (usually less than or equal to 10Wh/kg) has limited the large-scale commercial application of the device, and because of this, Improving the energy density has become the main research direction of electric double layer capacitors.

Porous carbon materials with high-quality pore size distribution can increase the effective contact area between electrode materials and electrolyte, increase the active sites of electrochemical reactions, and thereby improve the energy storage capacity of carbon materials. Therefore, researchers mainly improve the contact between carbon materials and electrolytes. Area, the preparation of high mesopority carbon materials and other aspects to improve the electrochemical performance of this type of supercapacitor. At the same time, the pseudocapacitance provided by heteroatoms can also improve its electrochemical performance. The structure of nitrogen atoms is similar to that of carbon atoms, and it is easier to dope into carbon atoms, thereby improving the electrical conductivity of carbon materials.

According to E=0.5CV ² , it can be seen that increasing the intrinsic capacity of the porous carbon material while improving its withstand voltage characteristics can also effectively increase the energy density of the electric double layer capacitor. Patent CN110963477A uses melamine as a nitrogen source to prepare a porous carbon material with a high specific surface area of 1600-1800m ² /g. Patent CN109534341A uses melamine as a nitrogen source and discarded fruit peels as a carbon source to prepare a nitrogen-doped peel-based porous carbon material with a specific surface area of 2796m ² /g. Patent CN106629724B uses natural waste product peanut shell as raw material (melamine as nitrogen source), and after ball milling, screening, high-temperature activation and washing, nitrogen-doped porous carbon with a specific surface area of 1000-1200m ² /g is prepared. However, the above-mentioned patented technologies all have problems such as long stabilization time, unreasonable pore size distribution, and complicated manufacturing process.

Invention content:

The purpose of the present invention is to propose a simple method for preparing nitrogen-doped porous carbon materials, so as to solve the defects of complex preparation process, high production cost and non-adjustable pore diameter of nitrogen-doped porous carbon materials.

A method for preparing a nitrogen-doped porous carbon material, comprising the steps of:

(1) adding weathered coal humic acid into the mixed aqueous solution of potassium metal compound and urea, drying after stirring;

(2) Put the sample obtained by drying in step (1) into a reaction furnace for high-temperature calcination;

(3) After the high-temperature calcination, the samples were naturally cooled to room temperature, washed with water, and dried to obtain a nitrogen-doped porous carbon material.

As a precursor of carbon materials, weathered coal humic acid has abundant oxygen-containing functional groups, and is easily soluble in potassium metal compound solution, realizing the contact between the active agent and the precursor at the molecular level, which helps the activation process to proceed uniformly.

In the present invention, a potassium metal compound is added in the preparation process of the nitrogen-doped porous carbon material, and the potassium metal compound is used to react with carbon at high temperature, so that the carbon is released in the form of oxide to form pores. This process is accompanied by the generation of metal potassium, which will be embedded in the graphite crystallite plane, and then etch the carbon not exposed on the surface, resulting in a large number of microporous structures. Potassium metal compound itself can be uniformly mixed with other components at the molecular level, and at the same time, after pyrolysis of the material, there are no other impurity elements except K, which can effectively ensure the activation efficiency and the purity of the activated carbon material.

As a nitrogen source, urea has a high nitrogen content and is easily decomposed into various nitrogen-containing substances during the heating process, including ammonia, biuret, triuret, and cyanuric acid. At higher temperatures, NH and CN radicals, these radicals will react with edge carbon atoms and oxygen-containing functional groups in weathered coal humic acid to achieve nitrogen doping.

Further, the potassium metal compound in step (1) is one or more of potassium carbonate, potassium bicarbonate, and potassium oxide, preferably potassium carbonate.

Further, in step (1), the mass ratio of humic acid from weathered coal to the mixed aqueous solution of potassium metal compound and urea is 5-10:100.

Further, the mass ratio of urea to weathered coal humic acid in step (1) is 1-2:1.

Further, in step (1), the mass ratio of potassium metal compound to weathered coal humic acid is 1.5-2.5:1.

Further, in step (1), the stirring time is 2-3 hours, the drying temperature is 80-90° C., and the drying time is 20-24 hours.

Further, in step (2), the activation furnace is raised to 750-850° C. at 1-4° C./min, and kept warm for 2-4 hours.

Further, in step (3), wash with deionized water for 3 to 5 times, the drying temperature is 80 to 90° C., and the drying time is 20 to 24 hours.

Described weathered coal humic acid is weathered coal humic acid after purification treatment, and the method for purification treatment comprises the following steps:

A1, add weathered coal humic acid into aqueous sodium hydroxide solution and stir to remove lower alkali-insoluble matter;

A2. Add hydrochloric acid to the upper layer solution, obtain the lower layer sediment after standing at room temperature, wash with water and dry.

The present invention uses weathered coal humic acid after purification as the carbon material precursor, and the purification process can produce more oxygen-containing defect sites, providing active sites for nitrogen doping, so that more C-N bonds and potassium Metal compound reaction, low ash content and high carbon content at the same time, can effectively improve the carbonization yield, and is conducive to the formation of a stable carbonaceous porous structure to achieve the purpose of adjusting the pore size, thereby improving the electrochemical performance of the material.

Further, in step A1, the pH value of the aqueous sodium hydroxide solution is 10-12, and the stirring time is 2-3 hours.

Further, in step A2, hydrochloric acid is added to adjust the pH value to 2-3, the standing time at room temperature is 10-12 hours, the deionized water is washed 3-5 times, the drying temperature is 80-90° C., and the drying time is 20-24 hours.

Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

1. Weathered coal humic acid, as a precursor of carbon materials, has abundant oxygen-containing functional groups and is easily soluble in potassium metal compound solutions, realizing the contact between the active agent and the precursor at the molecular level, which helps the activation process to be uniform conduct;

2. As a nitrogen source, urea has a high nitrogen content and is easily decomposed into various nitrogen-containing substances during the heating process. At higher temperatures, NH and CN free radicals will be generated, which will interact with the edge carbon atoms in the humic acid of weathered coal and Oxygen-containing functional groups react to realize nitrogen doping;

3. Potassium metal compound, as an activator, reacts with carbon at high temperature, causing carbon to be released in the form of oxides to form pores, accompanied by the generation of metal potassium, which will be embedded in the graphite crystallite plane. The carbon not exposed on the surface is etched to produce a large number of microporous structures. At the same time, there are no other impurity elements except K after pyrolysis, which can effectively ensure the activation efficiency and the purity of the activated carbon material;

4. The weathered coal humic acid used in the present invention is purified to produce more oxygen-containing defect sites, providing active sites for nitrogen doping, allowing more C-N bonds to react with potassium metal compounds, and the ash content Low, high carbon content, can effectively increase the carbonization yield, and is conducive to the formation of a stable carbonaceous porous structure, in order to achieve the purpose of adjusting the pore size, thereby improving the electrochemical performance of the material;

5. The initial raw materials used in this method are humic acid and urea, which widely exist in nature, and are cheap, rich in sources, and easy to realize large-scale industrial production;

6. The preparation process of the present invention is simple, only involves a small number of processes such as activation and cleaning, and is easy to realize large-scale production.

Description of drawings

Fig. 1 is the SEM picture of the nitrogen-doped porous carbon material obtained in embodiment 1;

Fig. 2 is the TEM figure of the obtained nitrogen-doped porous carbon material of embodiment 1;

Fig. 3 is the nitrogen adsorption-desorption curve figure of the nitrogen-doped porous carbon material obtained in Example 1;

Fig. 4 is that embodiment 1 gained is the XPS spectrogram of nitrogen-doped porous carbon material;

Fig. 5 is the CV curve diagram of the nitrogen-doped porous carbon material obtained in Example 1;

Fig. 6 is the charge-discharge curve diagram of the rate of nitrogen-doped porous carbon material obtained in Example 1;

FIG. 7 is a cycle test life diagram of the nitrogen-doped porous carbon material obtained in Example 1. FIG.

Detailed ways

The technical solutions of the present invention will be further described below through specific embodiments and drawings. It should be understood that the specific embodiments described here are only used to help understand the present invention, and are not intended to specifically limit the present invention. And the drawings used herein are only for better illustrating the disclosed content of the present invention, and do not limit the scope of protection. Unless otherwise specified, the raw materials used in the examples of the present invention are commonly used raw materials in the art, and the methods used in the examples are conventional methods in the art.

The weathered coal humic acid used in the following examples is the weathered coal humic acid after the purification treatment, and the method for the purification treatment comprises the following steps:

A1. Mix weathered coal humic acid and aqueous sodium hydroxide solution with a pH value of 10 at a mass ratio of 1:25 and stir for 2 hours to remove alkali-insoluble matter in the lower layer;

A2. Add hydrochloric acid to the upper layer solution to adjust the pH value to 2. After standing at room temperature for 10 hours, obtain the lower layer sediment, wash it with deionized water 3 times until neutral, and dry it at 80°C for 24 hours in a blast drying oven.

The weathered coal humic acid raw material used above was purchased from Tianjin Kemiou Chemical Reagent Co., Ltd., and the content of humic acid was ≥80%.

Example 1

The preparation method of nitrogen-doped porous carbon material in this embodiment includes the following steps:

(1) Dissolve 100g of urea and 125g of potassium carbonate in 725g of water to form a mixed aqueous solution, then add 50g of purified weathered coal humic acid, stir for 2 hours, and put it into a blast drying oven for drying at 80°C;

(2) Put the sample dried in step (1) into an activation furnace, and raise it to 800°C at a rate of 2°C/min for 4 hours;

(3) Cool naturally after high-temperature calcination, take out the sample, wash 5 times with deionized water, and dry in a blast drying oven at 90° C. for 24 hours to obtain a nitrogen-doped porous carbon material.

Example 2

(1) Dissolve 75g of urea and 100g of potassium carbonate in 725g of water to form a mixed aqueous solution, then add 45g of purified weathered coal humic acid, stir for 2.5 hours, and put it into a blast drying oven for drying at 85°C;

(2) Put the sample dried in step (1) into an activation furnace, and raise it to 850°C at a rate of 3°C/min for 3 hours;

(3) Cool naturally after high-temperature calcination, take out the sample, wash with deionized water 4 times, and dry in a blast drying oven at 85° C. for 22 hours to obtain a nitrogen-doped porous carbon material.

Example 3

(1) Dissolve 50g of urea and 75g of potassium carbonate in 675g of water to form a mixed aqueous solution, then add 40g of purified weathered coal humic acid, stir for 3 hours, and put it into a blast drying oven at 90°C for drying;

(2) Put the sample dried in step (1) into an activation furnace, and raise it to 850°C at a rate of 4°C/min for 4 hours;

(3) Cool naturally after high-temperature calcination, take out the sample, wash with deionized water for 3 times, and dry at 80° C. for 20 h in a blast drying oven to obtain a nitrogen-doped porous carbon material.

Comparative example 1

The difference between Comparative Example 1 and Example 1 is that step (1) does not add potassium metal compound.

Comparative example 2

The only difference between Comparative Example 2 and Example 1 is that step (1) does not add urea.

Comparative example 3

The difference between Comparative Example 3 and Example 1 is that step (1) uses unpurified weathered coal humic acid.

The materials prepared in the above examples and comparative examples are used as electrode materials for supercapacitors. The specific preparation process is as follows: After fully mixing the active material, conductive agent and binder in the dispersant at a mass ratio of 8:1:1, they are coated with Lay on aluminum foil to dry. EMIM TFSI ionic liquid is selected as the electrolyte, and the working voltage range is 0-3.5V.

Accompanying drawing is the performance characterization figure of embodiment 1, it can be clearly seen that the surface of nitrogen-doped porous carbon material has abundant macroporous structure in Fig. 1, and it can be seen in Fig. 2 that nitrogen-doped porous carbon material has interconnected pore structure , Figure 3 shows that the material has a typical type IV adsorption-desorption curve, indicating the existence of medium and large pores, and its specific surface area can reach 2420m ² /g. Figure 4 shows that nitrogen has been successfully doped into the carbon material, and Figure 5 It can be seen that the material can still maintain a good rectangular-like CV curve at a high scan rate of 300mV/s, indicating its fast current response characteristics, corresponding to its interconnected pore structure. It can be seen from Figure 6 that the current When the density increases from 1A/g to 20A/g, the lateral flow charge-discharge curve of the material always maintains good symmetry, further indicating its good capacitance characteristics. At a current density of 1A/g, the specific capacity of the material can reach 175F/g. When the current density increases to 20A/g, the specific capacity can still reach 148F/g. Figure 7 shows that the material has good rate characteristics, and the current When the density is 0.05A/g, the specific capacity is 210F/g. When the current density increases to 20A/g, the specific capacity is 148F/g, and the capacity retention rate is as high as 70%. After 10,000 cycles at 1A/g, the capacity remains The rate can reach more than 90%.

Each embodiment of table 1 and comparative example electrochemical performance

It can be seen from Table 1 that the cycle performance and rate performance of each comparative example are worse than those of the examples, fully reflecting the excellent performance of the nitrogen-doped porous carbon material in the present invention. In the method of the present invention, the activator potassium metal compound reacts with carbon at high temperature, so that the carbon is released in the form of oxides to form pores, and the generated metal potassium will be embedded in the graphite crystallite plane, and the carbon that is not exposed on the surface is processed. Etching produces a large number of microporous structures, increases the effective contact area between the electrode material and the electrolyte, and increases the active sites for electrochemical reactions, thereby improving the energy storage capacity of the carbon material. As a nitrogen source, urea has a high nitrogen content and is easily decomposed into various nitrogen-containing substances during the heating process. At higher temperatures, NH and CN free radicals will be generated, which will interact with the edge carbon atoms and oxygen-containing substances in weathered coal humic acid. The functional group reacts to achieve nitrogen doping. As a precursor of carbon materials, weathered coal humic acid has abundant oxygen-containing functional groups, and is easily soluble in potassium metal compound solution, realizing the contact between the active agent and the precursor at the molecular level, which helps the activation process to proceed uniformly. The purified weathered coal humic acid has more oxygen-containing defect sites to provide active sites for nitrogen doping, so that more C-N bonds can react with potassium metal compounds, while the ash content is low and the carbon content is high. It can effectively improve the carbonization yield and is conducive to the formation of a stable carbonaceous porous structure to achieve the purpose of adjusting the pore size, thereby improving the electrochemical performance of the material.

Finally, it should be noted that the specific embodiments described herein are only for illustrating the spirit of the present invention, rather than limiting the implementation of the present invention. Those skilled in the technical field to which the present invention pertains may make various modifications or supplements to the described specific embodiments, or replace them in similar ways, and it is not necessary and impossible to give a full example of all the implementation modes here. However, the obvious changes or variations derived from the essential spirit of the present invention still belong to the protection scope of the present invention, and interpreting them as any additional limitation is contrary to the spirit of the present invention.

Claims

A method for preparing a nitrogen-doped porous carbon material, comprising the steps of:

(1) adding weathered coal humic acid into the mixed aqueous solution of potassium metal compound and urea, drying after stirring;

(2) Put the sample obtained by drying in step (1) into a reaction furnace for high-temperature calcination;

(3) After the high-temperature calcination, the samples were naturally cooled to room temperature, washed with water, and dried to obtain a nitrogen-doped porous carbon material.
A method for preparing a nitrogen-doped porous carbon material according to claim 1, wherein the potassium metal compound in step (1) is one or more of potassium carbonate, potassium bicarbonate, and potassium oxide.
A method for preparing a nitrogen-doped porous carbon material according to claim 1, characterized in that the mass ratio of humic acid from weathered coal to the mixed aqueous solution of potassium metal compound and urea is 5-10:100.
The method for preparing a nitrogen-doped porous carbon material according to claim 1, characterized in that the mass ratio of urea to weathered coal humic acid in step (1) is 1-2:1.
A method for preparing a nitrogen-doped porous carbon material according to claim 1, characterized in that the mass ratio of potassium metal compound to weathered coal humic acid in step (1) is 1.5-2.5:1.
The preparation method of nitrogen-doped porous carbon material according to claim 1, characterized in that the stirring time in step (1) is 2-3 hours, the drying temperature is 80-90°C, and the drying time is 20-24 hours.
A method for preparing a nitrogen-doped porous carbon material according to claim 1, characterized in that the high-temperature calcination in step (2) is: heating at 1-4°C/min to 750-850°C for 2-4 hours.
A method for preparing a nitrogen-doped porous carbon material according to claim 1, wherein the weathered coal humic acid is purified, and the purified process comprises the following steps:

A1, add weathered coal humic acid into aqueous sodium hydroxide solution and stir to remove lower alkali-insoluble matter;

A2. Add hydrochloric acid to the upper layer solution, obtain the lower layer sediment after standing at room temperature, wash with water and dry.
A method for preparing nitrogen-doped porous carbon material according to claim 8, characterized in that in step A1, the pH value of the aqueous sodium hydroxide solution is 10-12, and the stirring time is 2-3 hours.
A method for preparing a nitrogen-doped porous carbon material according to claim 8, characterized in that in step A2, hydrochloric acid is added to adjust the pH value to 2-3, the standing time at room temperature is 10-12 hours, and the water is washed 3-5 times , The drying temperature is 80~90℃, and the drying time is 20~24h.