KR102684620B1 - Activated Carbon Including Hierarchical Pore Structure And Method For Manufacturing The Same - Google Patents

Abstract

The present invention includes a hierarchical pore structure of micropores and mesopores, and the area of the mesopores is 100 m ² /g or more, and the specific surface area of the mesopores compared to the specific surface area of the micropores (A1) It relates to activated carbon and a method for producing the same, wherein the ratio (A2/A1) of (A2) is 0.1 or more.

Description

Activated Carbon Including Hierarchical Pore Structure And Method For Manufacturing The Same}

The present invention relates to activated carbon containing a hierarchical pore structure of micropores and mesopores and having a high mesopore specific surface area, and a method for manufacturing the same.

Supercapacitor, also known as Electric Double Layer Capacitor (EDLC) or Ultracapacitor, is a pair of charges with different signs at the interface of an electrode, a conductor, and an electrolyte solution impregnated with it. It is a device that uses a layer (electrical double layer) created, and does not require maintenance because the deterioration due to repeated charging/discharging operations is very small. Accordingly, supercapacitors are mainly used as IC (Integrated Circuit) backup for various electrical and electronic devices, and their use has recently expanded to include toys, solar energy storage, and HEV (Hybrid Electric Vehicle) power sources. there is.

The performance of a supercapacitor is determined by the electrode active material and electrolyte, and in particular, major performances such as storage capacity are largely determined by the electrode active material. Activated carbon, which has a high specific surface area, is mainly used as such electrode active material.

As the application field of supercapacitors expands, higher specific capacitance and energy density are required, and the development of electrode active materials that exhibit higher capacitance is required. To this end, there is a particular need for the development of activated carbon as an electrode active material with pores of an appropriate size so that electrolyte ions can easily move into the internal pores of activated carbon.

Japanese Patent Publication 2006-151784

One object of the present invention is to provide activated carbon that not only has a large specific surface area but also has a well-developed hierarchical pore structure including micropores and mesopores, and a method for manufacturing the same.

Another object of the present invention is to provide activated carbon with excellent electrochemical properties by providing activated carbon with a well-developed hierarchical pore structure including micropores and mesopores and specifically with a high proportion of mesopores.

Another object of the present invention is a method of producing activated carbon with a simple manufacturing process by impregnating wood in an aqueous solution containing salt and an activator and then proceeding with the carbonization process, thereby performing the conventional process consisting of two stages of carbonization and activation into a single process. is to provide.

In order to achieve the above purpose,

One embodiment of the present invention includes a hierarchical pore structure of micropores and mesopores, the area of the mesopores is 100 m ² /g or more, and the specific surface area (A1) of the mesopores is 100 m 2 /g or more. Provided is activated carbon, wherein the ratio (A2/A1) of the specific surface area (A2) of the pores is 0.1 or more.

Additionally, an embodiment of the present invention provides an adsorbent containing the above-described activated carbon.

Additionally, an embodiment of the present invention provides a supercapacitor including the above-described activated carbon as an electrode active material.

In addition, an embodiment of the present invention includes a first step of impregnating wood in an aqueous solution containing a water-soluble salt and an activator; A second step of drying the wood impregnated in the aqueous solution at 50°C to 100°C; and a third step of carbonizing the dried wood at 400°C to 1,200°C under an inert gas atmosphere; It provides a method for producing activated carbon comprising.

Activated carbon according to an embodiment of the present invention not only has a large specific surface area, but also has a well-developed hierarchical pore structure including micropores and mesopores and has a high proportion of mesopores, so it has the advantage of excellent electrochemical properties. There is. Accordingly, activated carbon according to an embodiment of the present invention is used as an electrode material for secondary batteries, fuel cells, supercapacitors, and solar steam power generation that generates steam by absorbing sunlight, water treatment systems such as capacitive desalination, dyes, and carbon dioxide. It can be used in various fields such as gas adsorbents such as methane and methane.

In addition, by impregnating wood in an aqueous solution containing salt and an activator and then proceeding with the carbonization process, the conventional process consisting of two steps of carbonization and activation can be performed in a single process, providing a method for producing activated carbon with a simple manufacturing process. .

Figure 1 shows the adsorption isotherm of activated carbon prepared according to Example 1 and Comparative Example 1.
Figure 2 is a graph analyzing activated carbon prepared according to Example 1 and Comparative Example 1 through XRD (X-ray Diffraction).
Figures 3 and 4 show the results of measuring the pore size distribution (PSD) of activated carbon prepared according to Example 1 and Comparative Example 1, respectively, using the Barrett-Joyner-Halenda (BJH) method.
Figures 5 and 6 are graphs showing the electrochemical performance of a supercapacitor manufactured using activated carbon prepared according to Example 1.

Embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Additionally, embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the relevant technical field. Additionally, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to also include the plural forms, unless the context clearly dictates otherwise. Furthermore, “including” a certain element throughout the specification means that other elements may be further included rather than excluding other elements unless otherwise stated.

In the present invention, “Micropore” refers to the average diameter of internal pores being less than 2 ㎚, “Mesopore” refers to the average diameter of internal pores being 2 ㎚ to 50 ㎚, and “Macropore” refers to the average diameter of internal pores being less than 2 ㎚. (Macropore)” means that the average diameter of the internal pores is greater than 50 nm.

Existing activated carbon is a two-step process in which tar is obtained by carbonizing vegetable raw materials such as sawdust, wood, and coconut shells, or mineral raw materials such as pitch, and then activating it using steam, CO ₂ , KOH, etc. Not only does it consume a lot of time and energy, but activated carbon produced through this process has more micropores than mesopores and macropores, making it unsuitable for application to energy storage devices such as supercapacitors.

As a result of repeated research on activated carbon with a more developed pore structure, the inventors of the present invention found that not only does it have a large specific surface area, but it also has a well-developed hierarchical pore structure including micropores and mesopores, and the proportion of mesopores is high. The present invention was completed by discovering that activated carbon suitable for implementing a supercapacitor with improved electrical properties such as specific capacitance can be provided.

Hereinafter, the present invention will be described in detail.

Activated carbon according to the present invention,

It includes a hierarchical pore structure of micropores and mesopores,

The area of the mesopores is 100 m ² /g or more, specifically 200 m ² /g or more, more specifically 300 m ² /g or more or 350 m ² /g or more, compared to the specific surface area of micropores (A1) The ratio (A2/A1) of the specific surface area (A2) of the mesopores is characterized in that it is 0.1 or more.

Activated carbon according to one embodiment has a well-developed hierarchical pore structure including micropores and mesopores and a high proportion of mesopores, thereby providing excellent electrochemical properties. Accordingly, activated carbon according to an embodiment of the present invention is an electrode material for secondary batteries, fuel cells, supercapacitors, and solar steam power generation that absorbs sunlight to generate steam, water treatment systems such as capacitive desalination, dyes, etc. It can be used in various fields such as gas adsorbents such as carbon dioxide and methane.

In one embodiment, the hierarchical pore structure of the micropores and mesopores is a hierarchical pore structure in which micropores with an average diameter of less than 2 nm are formed inside mesopores with an average diameter of 2 nm to 50 nm and are interconnected. You can.

Activated carbon according to one embodiment may further include macropores, and mesopores are formed inside the macropores with an average diameter of more than 50 nm, and micropores are formed inside the mesopores to form interconnected hierarchical structures. It may have a pore structure.

The average pore size in activated carbon according to one embodiment may be 1 nm to 20 nm, specifically 2 nm to 15 nm, and more specifically 2 nm to 10 nm.

In one embodiment, the area of the mesopores is 100 m ² /g or more, specifically 200 m ² /g or more, more specifically 250 m ² /g or more, 300 m ² /g or more, or 350 m ² It may be more than /g, and the upper limit is not limited thereto, but may be, for example, 1,000 m ² /g, 800 m ² /g, or 500 m ² /g. The area of the mesopores in the above-mentioned range is larger than that of the conventional activated carbon, and the activated carbon according to one embodiment has the advantage of excellent electrochemical properties by having the area of the mesopores in the above-mentioned range. have

In another embodiment, the ratio (A2/A1) of the specific surface area of mesopores (A2) to the specific surface area of micropores (A1) is 0.1 or more, specifically 0.2 or more, more specifically 0.25 or more, 0.3. It may be more than or equal to 0.32, and the upper limit is not limited thereto, but may be, for example, 1.0 or 0.8. Activated carbon according to one embodiment has an A2/A1 value in the above-mentioned range, and has excellent electrochemical properties, making it suitable for implementing not only a gas adsorbent such as carbon dioxide and methane, but also a supercapacitor with improved electrical characteristics such as specific capacitance. There is an advantage to this.

In one embodiment, the total pore volume of the activated carbon may be 0.50 cm ³ /g or more, specifically 0.75 cm ³ /g or more, more specifically 0.85 cm ³ /g or more, and even more specifically It may be 0.95 cm ³ /g or more, and the upper limit of the total pore volume is not limited thereto, but may be, for example, 2.5 cm ³ /g or 1.5 cm ³ /g.

In one embodiment, the specific surface area of the activated carbon may be 800 m ² /g or more, specifically 1,000 m ² /g or more, more specifically 1,200 m ² /g or more, and even more specifically 1,400 m 2 /g or more. It may be more than m ² /g, and the upper limit of the specific surface area is not limited thereto, but may be, for example, 3,500 m ² /g or 2,500 m ² /g.

In one embodiment, the activated carbon may be manufactured by carbonizing wood, but is not necessarily limited thereto. The wood may specifically be a wood by-product, and non-limiting examples may include waste wood, firewood, wood chips, sawdust, etc.

In one embodiment, the wood may be a water-soluble salt and an activator applied to the wood, and the water-soluble salt and an activator may be applied to the pore surface of the wood by molecularly penetrating into the pores of the wood in a solution phase. there is.

By applying the water-soluble salt and activator to the pore surface of wood, the activated carbon not only has a larger specific surface area than before, but also contains a high proportion of mesopores, so electrical properties such as remarkable ionic conductivity can be improved. .

In one embodiment, the water-soluble salt may preferably be an alkali metal salt, and the water-soluble salt may be lithium acetate, lithium carbonate, lithium bicarbonate, lithium chloride, sodium oxalate, sodium hydrogen phthalate, sodium acetate, sodium carbonate. , sodium bicarbonate, sodium chloride, potassium oxalate, potassium hydrogen phthalate, potassium acetate, potassium carbonate, potassium bicarbonate, and potassium chloride. It may be one or a combination of two or more selected from the group consisting of sodium chloride and It may be one or a combination of two or more selected from the group consisting of potassium chloride.

In one embodiment, the activator may be an alkali metal hydroxide, specifically NaOH or KOH, but is not limited thereto.

The water-soluble salt is one or a combination of two or more selected from the group consisting of sodium chloride (NaCl) and potassium chloride (KCl), and the activator is one or a combination of two or more selected from the group consisting of NaOH and KOH. It is preferred in that it is possible to obtain activated carbon with mesopores and a hierarchical pore structure including micropores and mesopores.

The present invention provides an adsorbent containing activated carbon as described above, and the adsorbent may be used to adsorb gases such as carbon dioxide and methane. The adsorbent according to the present invention has a high specific surface area and contains a high proportion of mesopores, so the diffusion resistance for gas is very low, so it can quickly adsorb and desorb the desired gas and can adsorb a high capacity of gas. .

Additionally, the present invention provides a supercapacitor containing activated carbon as described above. Specifically, the activated carbon according to an embodiment of the present invention not only has a large specific surface area, but also has a well-developed hierarchical pore structure including micropores and mesopores and has a high proportion of mesopores, so it has a high specific capacitance, etc. It is suitable for implementing a supercapacitor with improved electrical characteristics.

In one embodiment, the supercapacitor may have a reserve capacity of 150 F/g or more when the current density is 1 A/g, specifically 200 F/g or 250 F/g or more, and more specifically, is over 270 F/g. More specifically, it may be 300 F/g or more, and the upper limit is not limited thereto, but may be, for example, 700 F/g or 500 F/g.

A supercapacitor that satisfies the specific capacitance in the above range can exhibit significantly superior energy storage and output performance. This is because the activated carbon has the above-described pore characteristics, enabling rapid ion diffusion even at high current densities, giving excellent performance. It can be done. In addition, the supercapacitor containing the activated carbon has excellent ion conductivity and can achieve excellent electrochemical properties such as maintaining high efficiency, excellent ion storage, and high energy density.

In one embodiment, the activated carbon is not limited as long as it satisfies the pore characteristics described above, but may be manufactured by a manufacturing method described later.

The method for producing activated carbon according to one embodiment is,

A first step of impregnating wood in an aqueous solution containing a water-soluble salt and an activator;

A second step of drying the wood impregnated in the aqueous solution at 50°C to 100°C; and

A third step of carbonizing the dried wood at 400°C to 1,200°C under an inert gas atmosphere; may include.

Activated carbon produced by the above manufacturing method includes a hierarchical pore structure of micropores and mesopores, and the mesopore area is 100 m ² /g or more or 200 m ² /g or more, The ratio (A2/A1) of the specific surface area of mesopores (A2) to the specific surface area of micropores (A1) is 0.1 or more or 0.2 or more, so the electrochemical properties are excellent and can be used in secondary batteries, fuel cells, supercapacitors and It can be used in a variety of fields, such as electrode materials for solar steam power generation that absorbs sunlight to generate steam, water treatment systems such as capacitive desalination, dyes, and gas adsorbents such as carbon dioxide and methane.

In addition, the method for producing activated carbon involves impregnating wood in an aqueous solution containing salt and an activator and then proceeding with the carbonization process, thereby converting the conventional two-step process of carbonization and activation into a single process to produce activated carbon with a simple manufacturing process. A method can be provided.

The first step is to impregnate wood in an aqueous solution containing a water-soluble salt and an activator. The water-soluble salt may be an alkali metal salt and the activator may be an alkali metal hydroxide. More preferably, the water-soluble salt may be sodium. It is one or a combination of two or more selected from the group consisting of chloride (NaCl) and potassium chloride (KCl), and the activator may be one or a combination of two or more selected from the group consisting of NaOH and KOH.

In one embodiment, the concentration of water-soluble salt in the aqueous solution is 0.1 M to 3.0 M. Or it may be 0.5 M to 2.0 M.

In one embodiment, the concentration of the activator in the aqueous solution may be 0.1 M to 4.0 M, 0.5 M to 3.0 M, or 1.0 M to 3.0 M.

In one embodiment, the molar ratio of the water-soluble salt and the activator may be 1:0.5 to 5, and more preferably 1:0.7 to 3.

In one embodiment, the weight ratio of the water-soluble salt and the activator may be 1:0.1 to 5, more preferably 1:0.5 to 2, non-limiting examples of which are 1:0.5, 1: It may be 1 or 1:2, but is not necessarily limited thereto.

The second step is a step of drying the wood impregnated in the aqueous solution at 50 ℃ to 100 ℃, specifically, it can be dried at 70 ℃ to 90 ℃, and the drying time is not necessarily limited thereto, but is 10 hours. It may be from 12 hours to 15 hours, specifically 12 hours to 15 hours.

The third step is a step of carbonizing the dried wood at 400 ℃ to 1,200 ℃ in an inert gas atmosphere, specifically, it can be carbonized at 500 ℃ to 1,200 ℃, 700 ℃ to 1,200 ℃ or 800 ℃ to 1,000 ℃, , the inert gas may be at least one selected from nitrogen, helium, neon, argon, and krypton, and preferably nitrogen. Additionally, the carbonization time is not necessarily limited thereto, but may be 10 minutes to 5 hours or 10 minutes to 2 hours.

In one embodiment, after the third step, a step of washing the activated carbon with an acidic solution may be further included. Non-limiting examples of the acidic solution may be hydrochloric acid, sulfuric acid, or nitric acid.

In one embodiment, the wood may be a wood by-product, non-limiting examples of which may include waste wood, firewood, wood chips, sawdust, etc.

Hereinafter, examples and experimental examples of the present invention will be described in detail below. However, the examples and experimental examples described below only illustrate a part of the present invention, and the present invention is not limited thereto.

<Example 1>

12 g of NaCl and 24 g of NaOH were added to 200 ml of distilled water and mixed to prepare an aqueous salt/activator (NaCl/NaOH) solution.

6 g of wood by-products were impregnated in the salt/activator (NaCl/NaOH) aqueous solution prepared above for 12 hours, then dried in an oven at 80°C for 12 hours without washing, and then reached 800°C at a temperature increase rate of 5°C per minute. Afterwards, carbide was produced by carbonization in a tubular carbonization furnace in a nitrogen atmosphere for 1 hour. Afterwards, the prepared carbide was washed with 1 M HCl and distilled water to prepare activated carbon.

<Example 2>

Activated carbon was prepared in the same manner as Example 1, except that 18 g of NaCl and NaOH were used in Example 1.

<Example 3>

Activated carbon was prepared in the same manner as Example 1, except that 24 g and 12 g of NaCl and NaOH were used, respectively.

<Example 4>

Activated carbon was prepared in the same manner as Example 1, except that KCl and KOH were used instead of NaCl and NaOH.

<Comparative Example 1>

Activated carbon was prepared in the same manner as Example 1, except that wood by-products were not impregnated in the salt/activator (NaCl/NaOH) aqueous solution.

<Comparative Example 2>

Activated carbon was prepared in the same manner as in Example 1, except that an aqueous NaCl solution (36 g of NaCl and 200 ml of distilled water) was used instead of the aqueous salt/activator (NaCl/NaOH) solution.

<Comparative Example 3>

Activated carbon was prepared in the same manner as in Example 1, except that an aqueous NaOH solution (36 g of NaOH and 200 ml of distilled water) was used instead of the aqueous salt/activator (NaCl/NaOH) solution.

<Experimental Example 1> Evaluation of pore characteristics of activated carbon

The activated carbon prepared according to Example 1 and Comparative Examples 1 to 3 was degassed at 423 K to 20 μTorr for 12 hours, and then nitrogen was purified using a Nano POROSITY-XQ adsorption analyzer (Mirae SI) at 77 K. (N ₂ ) adsorption-desorption test was performed. At this time, the specific surface area and pore characteristics of the activated carbon prepared according to Example 1 and Comparative Examples 1 to 3 were measured using the volume of adsorbed nitrogen gas molecules and the Brunauer-Emmett-Teller (BET) equation, and the results were It is shown in Table 1 below and Figures 1 to 4.

Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Specific surface area (㎡/g) 1406.51 4.04 1100.7 914.36 Total volume (㎤/g) 0.97 0.05 0.34 0.6 Mesopore volume (㎤/g) 0.43 0.05 0.13 0.37 Micropore volume (㎤/g) 0.54 0 0.21 0.23 Mesopore area (A2)
(㎡/g) 353.60 36.32 180.87 317.83 Micropore area (A1)
(㎡/g) 1089.45 1.60 903.68 694.48 A2/A1 0.325 22.7 0.2 0.457 BJH pore size (㎚) 3.874 3.494 3.287 3.683

<Experimental Example 2> Electrochemical property evaluation

Activated carbon, carbon black, and PTFE (polytetrafluoro ethylene) prepared according to Example 1 were mixed with DMF solvent at a ratio of 8:1:1 to prepare a slurry, and then coated on nickel foam and placed in an oven at 70°C for 12 hours. After drying for a while, a working electrode was manufactured. Pt electrode and Hg/HgO electrode were used as counter electrode and reference electrode, respectively. At this time, KOH aqueous solution (6.0 M) was used as the electrolyte, and electrochemical properties were measured at a current density of 1 A/g to 50 A/g through galvanostatic charge/discharge test using ZIVE MP2A electrochemical workstation (Wonatec Co., Ltd.). Electrochemical properties were evaluated in the same manner using activated carbon prepared according to Comparative Examples 1 to 3, and the results are shown in Table 2, Figure 5, and Figure 6 below.

Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Reserve capacity (F/g) 310 30 243 287

As can be seen in Figure 4 and Table 2, when the activated carbon according to an embodiment of the present invention is used as a supercapacitor material, it exhibits excellent specific capacitance, and the activated carbon has a high specific surface area and hierarchical structure, resulting in excellent electrochemical properties. It was confirmed that it can be implemented.

As a result of using the activated carbon prepared in Example 1 as an active material for a supercapacitor electrode, it had a high specific capacitance of 310 F/g (@1 A/g), 65% at 10 A/g and 30% at 50 A/g. It was confirmed that it had excellent rate. Therefore, it can be confirmed that activated carbon according to an embodiment of the present invention is suitable for use as an electrode active material for energy storage devices such as supercapacitors and lithium secondary batteries. In addition, it can be used for various energy and environmental purposes such as adsorption and separation of gases such as carbon dioxide and methane. It can be used in many fields.

As described above, the present invention has been described with specific details and limited examples, but these are provided only to facilitate a more general understanding of the present invention, and the present invention is not limited to the above-mentioned embodiments. Those skilled in the art can make various modifications and variations from this description.

Accordingly, the spirit of the present invention should not be limited to the described embodiments, and the scope of the patent claims described below as well as all things that are equivalent or equivalent to the scope of this patent claim shall fall within the scope of the spirit of the present invention. .

Claims (15)

It includes a hierarchical pore structure of micropores and mesopores,
The area of the mesopores is more than 100 m ² /g, and the ratio of the specific surface area of the mesopores (A2) to the specific surface area of the micropores (A1) (A2/A1) is more than 0.1;
The activated carbon is manufactured by carbonizing wood to which a water-soluble salt and an activator have been applied;
Activated carbon is one in which the water-soluble salt and the activator molecularly penetrate into the pores of the wood in a solution phase and are applied to the pore surface of the wood. According to clause 1,
Activated carbon, wherein the total pore volume of the activated carbon is 0.50 cm ³ /g or more. According to clause 1,
Activated carbon has a specific surface area of 800 m ² /g or more. delete delete delete An adsorbent comprising activated carbon according to any one of claims 1 to 3. A supercapacitor comprising the activated carbon according to any one of claims 1 to 3 as an electrode active material. According to clause 8,
A supercapacitor with a specific capacitance of 150 F/g or more when the current density is 1 A/g. A first step of impregnating wood in an aqueous solution containing a water-soluble salt and an activator;
A second step of drying the wood impregnated in the aqueous solution at 50°C to 100°C; and
A third step of carbonizing the dried wood at 400°C to 1,200°C under an inert gas atmosphere;
Method for producing activated carbon comprising. According to clause 10,
A method for producing activated carbon, wherein the water-soluble salt is an alkali metal salt and the activator is an alkali metal hydroxide. According to clause 10,
A method for producing activated carbon, wherein the concentration of water-soluble salt in the aqueous solution is 0.1 M to 3.0 M. According to clause 10,
A method for producing activated carbon, wherein the concentration of the activator in the aqueous solution is 0.1 M to 4.0 M. According to clause 10,
After the third step above,
A method for producing activated carbon, further comprising washing the activated carbon with an acidic solution. According to clause 10,
A method of producing activated carbon, wherein the wood is a wood by-product.