CN111704133A - A kind of preparation method of self-supporting porous carbon electrode material - Google Patents

Abstract

The invention relates to a preparation method of a self-supporting porous carbon electrode material, and belongs to the technical field of electrode material preparation. The specific method comprises the following steps: dissolving acrylamide, N' -methylene bisacrylamide, sodium carboxymethyl cellulose, potassium tetraborate and a chemical activating agent in water to obtain a mixed solution, adding an initiator, carrying out free radical polymerization at 65-75 ℃ to obtain hydrogel, freeze-drying the hydrogel to obtain dry gel, and carbonizing, washing and drying the dry gel to obtain the self-supporting porous carbon electrode material. The self-supporting porous carbon material is obtained by the steps of free radical polymerization, freeze drying, carbonization and the like from an acrylamide micromolecule raw material, the structure and the performance of the prepared porous carbon can be conveniently regulated and controlled through reaction conditions, the preparation process is simple and convenient and easy to control, and the obtained porous carbon electrode material has large specific surface area and excellent capacitance performance.

Description

A kind of preparation method of self-supporting porous carbon electrode material

technical field

The invention relates to the technical field of electrode material preparation, in particular to a preparation method of a self-supporting porous carbon electrode material.

Background technique

Energy crisis and environmental pollution are two major challenges facing human beings, and the development and utilization of new energy is the golden key to solve these two major problems. However, new energy sources such as solar energy and wind energy generally have the characteristics of high volatility. Efficient energy storage and conversion devices are the key to the utilization of new energy sources. Supercapacitors are one of the most promising new energy storage devices with many advantages, such as high power density, rapid charge and discharge, and long cycle life. The study of electrode materials with excellent performance is of great significance for the development of supercapacitors.

Carbon materials have the advantages of good electrical conductivity and stable chemical properties, and are currently the most widely used electrode materials for supercapacitors. A variety of carbon-rich species are used in the preparation of carbon electrode materials, including carbon nanotubes, graphene, phenolic resins, biomass, etc. Although carbon nanotubes have excellent physical and chemical properties, their relatively small specific surface area limits their application as electrode materials for high-performance supercapacitors; graphene is prone to interlayer stacking due to its strong interlayer van der Waals forces, resulting in The actual specific capacitance is low, and the expensive price is also an important obstacle that limits its application; the preparation of carbon aerogels by phenolic resins has been intensively studied, however, the pore structure of carbon aerogels has an impact on the pH value of the reaction system during the synthesis of phenolic resins. It is very sensitive, and the synthesis of carbon aerogels with specific structures requires precise control of the pH value, which increases the difficulty of preparation. Moreover, the strong toxicity of phenolic resin synthetic raw materials is very unfavorable for environmental protection; the preparation of porous carbon electrode materials by biomass has attracted many However, the composition and structure of biomass are greatly affected by source and individual differences, making it difficult to guarantee the performance stability of the prepared porous carbon materials. Therefore, it has become an important topic of supercapacitor research to study the preparation of high-performance carbon-based electrode materials by a new carbon source and a facile and controllable method.

On the other hand, most of the currently prepared porous carbon materials with high specific surface area are powdered, and compared with powdered carbon materials, self-supporting carbon materials have significant advantages. The self-supporting porous carbon material has a certain mechanical strength, and can maintain a certain shape without any support. It is more convenient to make electrodes, and does not require the addition of binders and paste coating methods, which avoids the comparison caused by binders and other additives. Unfavorable factors such as large contact resistance and the reduction of the effective contact area between the active material and the electrolyte. In addition, the self-supporting porous carbon materials also provide favorable conditions for the loading of pseudocapacitive materials on their surfaces. There have been some introductions about self-supporting porous carbon materials in the prior art, for example: the Chinese invention patent with the application number of 201611192154.0 discloses a preparation method of self-supporting mesoporous carbon, using self-supporting sheet MFI molecular sieve as a hard template, Dissolve furfural and oxalic acid in ethanol, and obtain self-supporting mesoporous carbon material after drying, pre-carbonization and carbonization; the Chinese invention patent with the application number of 201710175633.X discloses a preparation method of a self-supporting flexible nitrogen-doped carbon sponge, It is prepared by one-step pyrolysis with commercial melamine sponge as raw material; the Chinese invention patent with application number 201910383857.9 discloses a preparation method of a self-supporting porous carbon electrode loaded with two-dimensional materials. Preparation of wood with natural pore structure. In the preparation process of these self-supporting porous carbons, a template agent is generally required, so the preparation and removal steps of the template agent are involved in the process, which is complicated, and because it is prepared by using commercial self-supporting polymer materials or direct carbonization of biomass Porous carbon, so it is difficult to control the structure and properties of porous carbon.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the above-mentioned deficiencies in the background technology, and to provide a preparation method of a self-supporting porous carbon electrode material. The preparation method of the present invention does not use a template agent, and does not require complicated steps of preparation and removal of the template agent, and also overcomes the disadvantage that it is difficult to control the structure and properties of porous carbon from commercial self-supporting polymer materials or direct carbonization of biomass.

Technical solutions

In the present invention, acrylamide is used as a raw material, and a gel is obtained by radical polymerization of acrylamide, and a chemical activator and potassium tetraborate are added to the reaction system before the polymerization, so that the chemical activator and potassium tetraborate are evenly embedded in the gel, The porous carbon is then obtained by carbonization at high temperature. Due to the addition of potassium tetraborate, the prepared porous carbon is self-supporting. The preparation method of the self-supporting porous carbon of the present invention realizes carbonization and activation in one step, the process is simple, the prepared porous carbon is self-supporting, has a large specific surface area, and has excellent capacitance performance. The specific plans are as follows:

A preparation method of a self-supporting porous carbon electrode material, comprising the following steps:

(1) Preparation of hydrogel: acrylamide, N,N'-methylenebisacrylamide, sodium carboxymethylcellulose, chemical activator, potassium tetraborate tetrahydrate and water are mixed uniformly to obtain a mixed solution, Passing nitrogen into the mixed solution to remove oxygen for half an hour, then adding an initiator, and reacting at 65-75° C. for 1-4 hours to obtain a hydrogel;

(2) Carbonization of the gel: the obtained hydrogel is freeze-dried to obtain a xerogel, which is then carbonized, washed with water and dried to obtain a self-supporting porous carbon electrode material.

In step (1), the mass ratio of acrylamide, N,N'-methylenebisacrylamide, sodium carboxymethylcellulose, chemical activator, potassium tetraborate tetrahydrate and water is 0.02-0.1:0.002-0.015 :0～0.03:0～0.1:0.01～0.15:1, preferably 0.03～0.06:0.002～0.008:0.008～0.012:0.03～0.06:0.03～0.06:1.

Further, in step (1), the chemical activator is selected from one or a combination of two or more of KOH, NaOH, K ₂ CO ₃ , Na ₂ CO ₃ or KHCO ₃ in any proportion.

Further, in step (1), the initiator is potassium persulfate or ammonium persulfate.

Further, in step (1), the amount of the initiator is 1% to 6% of the mass of acrylamide.

Further, in step (2), the carbonization is carried out under N ₂ atmosphere, the temperature is 700-1000°C, and the time is 1-3h.

The reaction principle of the present invention is as follows: the composite gel is prepared by free radical polymerization, using acrylamide as a monomer, N,N'-methylenebisacrylamide as a cross-linking agent, and sodium carboxymethyl cellulose as a modifier , before the polymerization, the chemical activator and potassium tetraborate are added to the reaction system. As the polymerization progresses, the hydrogel is gradually formed. At the same time, the chemical activator and potassium tetraborate are embedded in the gel matrix in situ. Freeze-drying to obtain a xerogel, and the xerogel is subjected to high temperature carbonization, water washing, drying and other steps to obtain porous carbon. Due to the chemical activator contained in the gel, the activation of the porous carbon is simultaneously realized during the high-temperature carbonization process. The potassium tetraborate added to the gel improves the skeleton strength of the porous carbon, and the prepared porous carbon is self-supporting.

The beneficial effects of the present invention are as follows:

(1) A new method for preparing porous carbon by radical polymerization gelation and high temperature carbonization was invented using acrylamide as a carbon source.

(2) The radical polymerization of acrylamide is basically not affected by alkaline chemical activators such as KOH, K ₂ CO ₃ , etc., so the chemical activator can be directly added to the polymerization reaction system and embedded in the formed gel, Therefore, the activation of porous carbon can be simultaneously completed during the high-temperature carbonization process.

(3) Potassium tetraborate is added to the gel, so that the prepared porous carbon is self-supporting, which is beneficial to the further modification and application of the porous carbon.

(4) The prepared porous carbon has a large specific surface area, up to 3500 m ² /g, and has a good specific capacitance, and the mass specific capacitance can reach 370 F/g when the current density is 0.5 A/g.

Description of drawings

1 is a photo of the self-supporting porous carbon electrode materials prepared in Example 1 and Comparative Example 1;

FIG. 2 is a scanning electron microscope image of the porous carbon electrode material prepared in Example 4. FIG.

Detailed ways

In order to make the objects and advantages of the present invention more clear, the present invention will be described in detail below with reference to the embodiments and the accompanying drawings. It should be understood that the following text is only used to describe one or more specific embodiments of the present invention, and does not strictly limit the protection scope of the specific claims of the present invention.

Example 1

A preparation method of a self-supporting porous carbon electrode material, comprising the following steps:

(1) Preparation of hydrogel: 0.36 g of acrylamide, 0.04 g of N,N'-methylenebisacrylamide, 0.01 g of sodium carboxymethylcellulose, 0.30 g of potassium tetraborate tetrahydrate and 9.0 g of water were stirred Mix well to form a uniform solution, deoxidize with nitrogen for half an hour, then add 10 mg of amine persulfate (dissolved in 1.0 g of water) successively, and react at 70° C. for 2 hours to obtain a hydrogel.

(2) Carbonization of the gel: The obtained hydrogel was freeze-dried to obtain a xerogel. The xerogel was carbonized at 800° C. under nitrogen for 2 h, washed with water and dried to obtain a porous carbon material.

The self-supporting porous carbon material prepared by the above method has a specific surface area of 486.2 m ² /g, and a specific capacitance of 210.1 F/g when the charge-discharge current density is 0.5 A/g.

Comparative Example 1

The preparation process is the same as that of Example 1, and the difference is only to change the addition amount of potassium tetraborate tetrahydrate. In this embodiment, the consumption of potassium tetraborate tetrahydrate is 0 g.

The prepared porous carbon electrode material has a specific surface area of 153.4 m ² /g, and a specific capacitance of 104.5 F/g when the charge-discharge current density is 0.5 A/g.

Example 2

The preparation process is the same as in Example 1, and the difference is only to change the addition amount of potassium tetraborate tetrahydrate. In this embodiment, the amount of potassium tetraborate tetrahydrate is 0.10 g.

The prepared porous carbon electrode material has a specific surface area of 325.8 m ² /g, and a specific capacitance of 180.6 F/g when the charge-discharge current density is 0.5 A/g.

Example 3

The preparation process is the same as in Example 1, and the difference is only to change the addition amount of potassium tetraborate tetrahydrate. In this embodiment, the amount of potassium tetraborate tetrahydrate is 0.50 g.

The prepared porous carbon electrode material has a specific surface area of 513.9 m ² /g, and a specific capacitance of 223.2 F/g when the charge-discharge current density is 0.5 A/g.

Figure 1 is a photo of the porous carbon electrode materials prepared in Example 1 and Example 1, wherein Figure 1a is the porous carbon electrode material prepared in Comparative Example 1, and Figure 1b is the porous carbon electrode material prepared in Example 1. Figure 1 and the test results of Comparative Example 1 and Examples 1-3 can be seen: the porous carbon prepared without adding potassium tetraborate tetrahydrate is in a collapsed shape, and the original polymer gel shape cannot be maintained, and potassium tetraborate tetrahydrate is added. The prepared porous carbon maintains the original shape of the polymer gel and is self-supporting, and the addition of potassium tetraborate tetrahydrate improves the capacitance performance of the prepared porous carbon.

Example 4

A preparation method of a self-supporting porous carbon electrode material, comprising the following steps:

(1) Preparation of hydrogel: 0.36g acrylamide, 0.04g N,N'-methylenebisacrylamide, 0.01g sodium carboxymethylcellulose, 0.30g potassium tetraborate tetrahydrate, 0.50g K ₂ CO ₃ and 9.0 g of water were stirred and mixed evenly to obtain a mixed solution, which was deoxygenated by nitrogen for half an hour, and then 10 mg of amine persulfate (dissolved in 1.0 g of water) was added, and reacted at 70°C for 2 hours to obtain a hydrogel.

(2) Carbonization of the gel: The obtained hydrogel was freeze-dried to obtain a xerogel. The xerogel was carbonized at 800 °C under nitrogen for 2 h, and then washed with water and dried to obtain a porous carbon electrode material.

FIG. 2 is a scanning electron microscope image of the porous carbon electrode material prepared in Example 4. It can be seen from FIG. 2 that the porous carbon is composed of interconnected carbon walls and has a rich pore structure.

The self-supporting porous carbon material prepared by the above method has a specific surface area of 3398.3 m ² /g, and a specific capacitance of 362.7 F/g when the charge-discharge current density is 0.5 A/g.

Example 5

The preparation process is the same as that in Example 4, except that the amount of K ₂ CO ₃ added is changed. In this example, the amount of K ₂ CO ₃ added is 0.1 g.

The prepared porous carbon electrode material has a specific surface area of 1223.9 m ² /g, and a specific capacitance of 256.6 F/g when the charge-discharge current density is 0.5 A/g.

Example 6

The preparation process is the same as that of Example 4, except that the amount of K ₂ CO ₃ added is changed. In this example, the amount of K ₂ CO ₃ added is 0.3 g.

The prepared porous carbon electrode material has a specific surface area of 2652.7 m ² /g, and a specific capacitance of 298.4 F/g when the charge-discharge current density is 0.5 A/g.

Example 7

The preparation process is the same as that of Example 4, except that the amount of K ₂ CO ₃ added is changed. In this example, the amount of K ₂ CO ₃ added is 0.7 g.

The prepared porous carbon electrode material has a specific surface area of 3501.9 m ² /g, and a specific capacitance of 372.4 F/g when the charge-discharge current density is 0.5 A/g.

It can be seen from the test results of Example 1 and Examples 4-7 that K ₂ CO ₃ has a good activation effect. With the increase of the amount of K ₂ CO ₃ added, the specific surface area of the prepared porous carbon increases and the capacitance performance improves .

In summary, the present invention provides a new method for preparing self-supporting porous carbon from acrylamide. Since the free radical polymerization of acrylamide is basically unaffected by the added alkaline activator, the activator and other modifiers can be mixed with monomers before polymerization to form a homogeneous solution, enabling chemical activators and other modifiers to It is uniformly embedded in polyacrylamide gel, so that the activation of porous carbon can be realized at the same time during high temperature carbonization, which simplifies the preparation process of porous carbon. At the same time, the potassium tetraborate added to the polyacrylamide gel keeps the three-dimensional skeleton of the gel stable during the carbonization process, and the prepared porous carbon is self-supporting, which provides convenience for the application and further modification of the porous carbon.

The embodiments of the present invention have been described in detail above in conjunction with the examples, but the present invention is not limited to the above-mentioned embodiments. For those of ordinary skill in the art, after learning the contents of the present invention, without departing from the principles of the present invention Under the premise of the present invention, several equivalent transformations and substitutions can also be made, and these equivalent transformations and substitutions should also be regarded as belonging to the protection scope of the present invention.

Claims (6)

1. a preparation method of self-supporting porous carbon electrode material, is characterized in that, comprises the following steps: (1) Preparation of hydrogel: acrylamide, N,N'-methylenebisacrylamide, sodium carboxymethylcellulose, chemical activator, potassium tetraborate tetrahydrate and water are mixed uniformly to obtain a mixed solution, The mixed solution is passed nitrogen to remove oxygen, then an initiator is added, and the reaction is carried out at 65 to 75 ° C for 1 to 4 hours to obtain a hydrogel; (2) Carbonization of the gel: freeze-dry the obtained hydrogel to obtain a xerogel, which is then carbonized, washed with water and dried to obtain a self-supporting porous carbon electrode material; In step (1), the mass ratio of acrylamide, N,N'-methylenebisacrylamide, sodium carboxymethylcellulose, chemical activator, potassium tetraborate tetrahydrate and water is 0.02-0.1:0.002-0.015 :0～0.03:0～0.1:0.01～0.15:1. 2. The method for preparing a self-supporting porous carbon electrode material according to claim 1, wherein in step (1), acrylamide, N,N'-methylenebisacrylamide, sodium carboxymethylcellulose, The mass ratio of the chemical activator, potassium tetraborate tetrahydrate and water is 0.03-0.06:0.002-0.008:0.008-0.012:0.03-0.06:0.03-0.06:1. 3. The method for preparing a self-supporting porous carbon electrode material according to claim 1, wherein in step (1), the chemical activator is selected from KOH, NaOH, K ₂ CO ₃ , Na ₂ CO ₃ or KHCO One or two or more of ₃ in any ratio. 4. The method for preparing a self-supporting porous carbon electrode material according to claim 1, wherein in step (1), the initiator is potassium persulfate or ammonium persulfate. 5 . The method for preparing a self-supporting porous carbon electrode material according to claim 1 , wherein, in step (1), the amount of the initiator is 1-6% of the mass of acrylamide. 6 . 6. The preparation method of the self-supporting porous carbon electrode material according to any one of claims 1 to 5, characterized in that, in step ( ₂ ), the carbonization is carried out in an N atmosphere at a temperature of 700-1000°C, The time is 1-3h.

Images