KR20100027701A - Preparing method of gas diffusion layer for fuel cell - Google Patents

Abstract

PURPOSE: A method for preparing a gas diffusion layer for a fuel cell is provided to prepare a gas diffusion layer with improved electrical and mechanical properties compared with conventional porous carbon materials using carbon nanotube with excellent electrical and mechanical properties. CONSTITUTION: A method for preparing a gas diffusion layer for a fuel cell comprises the steps of: forming a mixture by mixing carbon nanotubes and polyvinylalcohol aqueous solution; forming a drafting paper material by drying the mixture; impregnating the drafting paper material in a phenol resin solution and compressing the drafting paper material to form a precursor; and plasticizing the precursor at 500~1600 °C.

Description

Manufacturing method of gas diffusion layer for fuel cell {Preparing method of gas diffusion layer for fuel cell}

The present invention relates to a gas diffusion layer for a fuel cell manufactured in paper form using carbon nanotubes in yarn form as a base material, and in detail, mechanical and electrical properties are improved by using carbon nanotubes having excellent physical properties as a base material. The present invention relates to a method for producing a gas diffusion layer for fuel cells, which is greatly improved.

The fuel cell relates to a device for converting chemical energy contained in fuel and oxygen into electrical energy by an electrochemical reaction. The fuel cell is an environmentally friendly power generation device with excellent power generation efficiency and low emission and noise of pollutants.

Fuel cells are classified into polymer electrolyte membrane fuel cells, phosphate fuel cells, molten carbonate fuel cells, and solid oxide fuel cells, depending on the type of electrolyte used. These fuel cell types have their own characteristics and various conditions. And their applications are different.

Among these fuel cells, polymer electrolyte membrane fuel cells have the characteristics that they have a higher current density than other types of fuel cells, can be used at low temperatures, and can be used as a power source for automobiles because they can use methanol and natural gas as fuel. have.

The polymer electrolyte membrane fuel cell is composed of a polymer electrolyte membrane, an electrode and a separator, the electrode is composed of a gas diffusion layer and a catalyst layer consisting of a catalyst for diffusing a gas, which is fuel, the gas diffusion layer is a carbon substrate and a microporous layer It consists of. The gas diffusion layer included in the electrode of the polymer electrolyte membrane fuel cell supplies fuel and air to the electrode, collects electricity generated by the electrochemical reaction, and discharges water and carbon dioxide generated by the electrochemical reaction. do.

Conventionally, a porous carbon material having a thickness of 100 to 300 µm is used as a substrate, and a gas diffusion layer is prepared by treating the porous carbon material with a waterproof material such as polytetrafluoroethylene (PTFE) for moisture management, but improves fuel efficiency. In order to achieve this, there is an urgent need for a gas diffusion layer manufactured using a material having excellent mechanical and electrical properties as a substrate as a conventional porous carbon material.

Accordingly, it is an object of the present invention to provide a method for producing a gas diffusion layer for a fuel cell using carbon nanotubes having excellent mechanical and electrical properties as a base material, in which mechanical and electrical properties are significantly improved compared to conventional porous carbon materials.

In order to achieve the above object, the present invention is to form a mixture by mixing a carbon nanotube and a polyvinyl alcohol aqueous solution: forming a papermaking body by drying the mixture; Impregnating the papermaking body with a phenol resin solution and heating and pressing to form a precursor; And it provides a method for producing a gas diffusion layer for a fuel cell comprising the step of firing the precursor at 500 ~ 1600 ℃.

The gas diffusion layer for a fuel cell manufactured according to the present invention has a significant improvement in mechanical and electrical properties using carbon nanotubes as a base material, and has an effect of greatly increasing fuel efficiency of a fuel cell manufactured using such a gas diffusion layer.

The present invention is characterized by providing a gas diffusion layer for a fuel cell, which is composed of carbon nanotubes excellent in mechanical and electrical properties as compared to conventional porous carbon materials.

US Patent Publication No. 2008-022129, US Patent Publication No. 2007-016631, Japanese Patent Application Publication No. 2006-54020 disclose carbon nanotubes in the form of yarns, and a number of recently published research papers Various mechanical and electrical properties of carbon nanotubes are disclosed in detail. In the present invention, a gas diffusion layer for a fuel cell is prepared using the carbon nanotubes disclosed as the above.

The manufacturing method of the gas diffusion layer for fuel cells by this invention is demonstrated in detail with reference to an Example.

First, the method of manufacturing a gas diffusion layer for a fuel cell of the present invention includes a step of mixing a carbon nanotube and a polyvinyl alcohol aqueous solution to form a mixture.

A carbon nanotube, which is a substrate of the gas diffusion layer for a fuel cell, and an aqueous polyvinyl alcohol solution that imparts a bonding force required for papermaking of the carbon nanotube are mixed and uniformly dispersed to form a mixture for producing a papermaking body.

That is, the carbon nanotubes and the polyvinyl alcohol aqueous solution are mixed, and the carbon nanotubes contained in the mixture are dispersed by applying ultrasonic waves under a constant temperature so that the carbon nanotubes and the polyvinyl alcohol aqueous solution are mixed and dispersed uniformly. To form a mixture.

If the thickness of the carbon nanotubes included in the mixture for preparing the papermaking body is less than 5 μm, the price of the carbon nanotubes increases, which leads to an increase in the manufacturing cost of the gas diffusion layer, and the thickness of the carbon nanotubes included in the mixture is 20 If the thickness is larger than that, it is difficult to construct a papermaking body due to the excessive thickness of the carbon nanotubes. In addition, when the length of the carbon nanotubes contained in the mixture for producing a papermaking body is less than 1 mm, the mixture containing the carbon nanotubes is not properly papered, and the length of the carbon nanotubes included in the mixture exceeds 6 mm. If it is difficult to control the thickness of the papermaking body made from the mixture containing the carbon nanotubes, it is preferable to form the mixture using carbon nanotubes having a thickness of 5 to 20 µm and a length of 1 to 6 mm.

And, if the concentration of the polyvinyl alcohol aqueous solution contained in the mixture for producing a papermaking body is less than 10 Vol.%, It is difficult to maintain the form of the papermaking body made from the mixture containing the polyvinyl alcohol aqueous solution, and the polyvinyl alcohol aqueous solution. If the concentration exceeds 50 Vol.%, It is difficult to form a paper body due to the viscosity of the mixture containing the aqueous solution of polyvinyl alcohol. Therefore, using a polyvinyl alcohol solution having a concentration of 10 to 50 vol.% It is preferable to form a mixture.

In a state where the carbon nanotubes having a thickness of 5 to 20 µm and a length of 1 to 6 mm and a polyvinyl alcohol aqueous solution having a concentration of 10 to 50 Vol.% Are mixed, ultrasonic waves are applied at 30 to 40 ° C. for 1 to 3 hours. By dispersing the carbon nanotubes, it is preferable to form a mixture in which the carbon nanotubes and the polyvinyl alcohol aqueous solution are uniformly mixed and dispersed.

When the temperature condition when applying ultrasonic waves to disperse the carbon nanotubes in the polyvinyl alcohol aqueous solution in a state in which the carbon nanotubes and the polyvinyl alcohol aqueous solution is mixed, the carbon nanotubes are not properly dispersed, and the polyvinyl vinyl When the temperature condition when applying ultrasonic waves to disperse the carbon nanotubes in an aqueous alcohol solution exceeds 40 ℃, the effect of the ultrasonic waves to disperse the carbon nanotubes may be reduced. In addition, the carbon nanotubes are not properly dispersed when the time of applying ultrasonic waves to disperse the carbon or the tube in the polyvinyl alcohol aqueous solution in the state of mixing the carbon nanotubes and the polyvinyl alcohol aqueous solution, the polyvinyl alcohol When the time for applying ultrasonic waves to disperse the carbon nanotubes in the aqueous solution exceeds 3 hours, the carbon nanotubes are no longer dispersed.

By mixing the carbon nanotubes and the polyvinyl alcohol aqueous solution as described above and applying a ultrasonic wave under a constant temperature to form a paper-like papermaking body by forming a mixture.

In addition, the manufacturing method of the gas diffusion layer for a fuel cell of the present invention includes the step of forming a papermaking body by drying the mixture.

Specifically, a carbon nanotube and a polyvinyl alcohol aqueous solution are mixed with a uniformly dispersed state to form a web having a thickness of 200 to 300 µm, and dried sufficiently under high temperature so that liquid components do not remain on the surface of the web to be fueled. The papermaking body which is a carbon base material of the gas diffusion layer of the electrode of a battery is formed.

When the thickness of the web made of carbon nanotubes and polyvinyl alcohol aqueous solution is less than 200 μm, the gas diffusion layer formed from the web is reduced in the electricity collection function generated by the electrochemical reaction, and the carbon nanotube and polyvinyl alcohol aqueous solution When the thickness of the web made of the paper sheet exceeds 300 µm, the gas diffusion layer formed from the web has a function of diffusing the gas, which is a fuel, and the discharge function of water and carbon dioxide generated by an electrochemical reaction.

As described above, the paper rolled to a thickness of 200 to 300 µm is sufficiently dried at high temperature to form a paper stock, and the paper dried sheet is used to form a precursor which is a previous step of the gas diffusion layer for a fuel cell of the present invention.

In addition, the method of manufacturing a gas diffusion layer for a fuel cell of the present invention includes the step of impregnating the paper body in a phenol resin solution and heat-pressed to form a precursor.

The gas diffusion layer of the electrode of the fuel cell is composed of a carbon substrate and a microporous layer.

Therefore, in order to provide a microporous layer in the gas diffusion layer for a fuel cell of the present invention, the papermaking body formed in the step of forming the papermaking body is impregnated with the phenolic resin solution, and the papermaking body impregnated with the phenolic resin solution is 150 to 300 ° C. , By hot pressing at 50-100 kgf / cm 2, the phenolic resin layer for forming the microporous layer on the surface of the papermaking body constitutes the doped precursor.

In order to doping the phenolic resin layer on the surface of the papermaking body, when the temperature of the papermaking body impregnated with the phenolic resin solution is lower than 150 ° C., the phenolic resin layer may not be properly doped on the surface of the papermaking body. When the temperature for hot pressing the impregnated paper stock exceeds 300 ° C., the phenol resin layer doped on the surface of the paper stock may be modified. In addition, when the pressure for heating and pressing the paper body impregnated in the phenolic resin solution to doping the phenolic resin layer on the surface of the paper body is less than 50 kgf / cm 2, the phenol resin layer doped on the surface of the paper body may be detached. When the pressure for heating and pressing the paper body impregnated in the phenolic resin solution exceeds 100 kgf / cm 2, the porosity of the paper body and the phenolic resin layer is lowered, which results in the diffusion function of the gas in the gas diffusion layer and the electrochemical reaction. Water generated by this leads to a decrease in the emission function of this carbon oxide.

As described above, the precursor is impregnated with the phenol resin solution and heated and pressed to form a gas diffusion layer.

In addition, the manufacturing method of the gas diffusion layer for a fuel cell of the present invention includes the step of firing the precursor at 500 ~ 1600 ℃.

In order to achieve the object of the present invention to provide a gas diffusion layer for fuel cells with improved mechanical and electrical properties, the precursor is calcined at a high temperature to increase the electrical properties such as mechanical properties such as strength, porosity, resistance, and the like. It is essential to pore the phenolic resin layer doped on the surface.

To this end, the precursor formed in the step of forming the precursor is calcined at 500 to 1600 ° C, wherein the precursor is gradually calcined at a temperature rising rate of 100 ° C / min from 500 ° C to 1600 ° C in the calcining process. It is preferable in view of preventing damage to the precursor, shrinkage or deterioration due to instantaneous high heat exposure.

When the temperature for firing the precursor is less than 500 ° C. to prepare a gas diffusion layer for a fuel cell, the precursor is not calcined properly. When the temperature for firing the precursor exceeds 1600 ° C., the precursor is no longer calcined. However, the phenolic resin layer doped on the surface of the precursor is deteriorated, so that no microporous layer is formed.

As described above, the gas diffusion layer in which the precursor is calcined is cooled at room temperature to prepare a gas diffusion layer for a fuel cell of the present invention.

The manufacturing method of the gas diffusion layer for fuel cells of this invention is demonstrated in detail with reference to a specific Example. However, the embodiments described below are merely for illustrating the present invention in detail, and do not limit the present invention.

<Example 1>

1. A mixture was formed by mixing 100 parts by weight of carbon nanotubes having an average thickness of 10 μm and an average length of 3 mm, and 10 parts by weight of an aqueous polyvinyl alcohol solution having a concentration of 10 Vol.%.

2. The mixture was papermaking to form a web having a thickness of 1 mm, and the web was dried at 200 ° C. for 10 minutes to form a papermaking body.

3. The papermaking body was impregnated with a phenolic resin solution and heated and pressed at 150 캜 and 50 kgf / cm 2 to form a precursor.

4. The precursor was heated at a temperature increase rate of 100 ° C./min from 500 ° C. to 1600 ° C. under a nitrogen atmosphere, and calcined at 1600 ° C. for 10 minutes to prepare a gas diffusion layer.

<Example 2>

The same procedure as in Example 1 was carried out except that 100 parts by weight of carbon nanotubes having an average thickness of 10 µm and an average length of 3 mm and 50 parts by weight of a polyvinyl alcohol aqueous solution having a concentration of 10 Vol.% Were mixed to form a mixture.

<Example 3>

The paper body was impregnated with a phenol resin solution and heated and pressed at 300 캜 and 100 kgf / cm 2 to form a precursor, which was the same as in Example 1.

<Comparative Example 1>

In Example 1 was the same as in Example 1 except that the carbon fiber (TGP-H-060, manufactured by Toray Industries, Inc.) was used.

<Comparative Example 2>

In Example 3, it was the same as in Example 3 except that the carbon fiber (TGP-H-060, manufactured by Toray Industries, Inc.) was used.

Process conditions and physical properties of the gas diffusion layers prepared according to Examples 1 to 3 and Comparative Examples 1 and 2 are shown in Table 1 below.

<Table 1> Process condition and physical property comparison of gas diffusion layer

division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Process conditions Tube: PVA weight ratio 1: 0.1 1: 0.5 1: 0.1 1: 0.1 1: 0.1 Hot pressing temperature (℃) 150 150 300 150 300 Hot pressing pressure (㎏f / ㎠) 50 50 100 50 100 Properties Resistance value (mΩ) 75 80 68 135 122 Bending strength (kgf / ㎠) 208 227 203 151 133 Porosity (%) 80 78 82 76 81

Table 1 shows that the gas diffusion layer according to the embodiment of the present invention is superior to the gas diffusion layer according to the comparative example in terms of mechanical and electrical properties, and is suitable for use as an electrode material of a fuel cell.

The present invention is not limited to the above-described specific preferred embodiments, and various modifications can be made by those skilled in the art without departing from the gist of the present invention as claimed in the claims. Of course, such changes will fall within the scope of the claims.

Claims (4)

Mixing carbon nanotubes and polyvinyl alcohol (PVA) aqueous solution to form a mixture: Papermaking to dry the mixture to form a papermaking body; Impregnating the papermaking body with a phenol resin solution and heating and pressing to form a precursor; And Process for producing a gas diffusion layer for a fuel cell comprising the step of firing the precursor at 500 ~ 1600 ℃. The method of claim 1, wherein the forming of the mixture comprises mixing a carbon nanotube and a polyvinyl alcohol aqueous solution and dispersing for 1 to 3 hours with ultrasonic waves at 30 to 40 ℃ of the gas diffusion layer of the fuel cell Manufacturing method. The method of claim 1, wherein the step of forming the precursor is manufactured of a gas diffusion layer for a fuel cell, characterized in that configured to heat-press the paper body impregnated in the phenolic resin solution at 150 ~ 300 ℃, 50 ~ 100 kgf / ㎠ Way. The method of claim 1, wherein the firing step is configured to raise the precursor at a temperature increase rate of 100 ° C / min from 500 ° C to 1600 ° C.