KR20170143195A - Method of manufacturing carbon paper used in gas diffusion layer of fuel cell - Google Patents

Abstract

According to the present invention, a method of manufacturing a carbon paper for a gas dispersing layer for a fuel cell includes: a process (i) of manufacturing a dispersing solution including cellulose carbon filaments; a process (ii) of applying the dispersing solution to a mesh, and then, removing a solvent from the dispersing solution to manufacture a sheet; and a process (iii) of compressing and drying the manufactured sheet. According to the present invention, carbonization (thermal treatment) at a high temperature leads to excellent electrical conductivity while the modulus of elasticity, which is not more than 100 Gpa, makes a soft texture, and also, a cellulose carbon filament, of which density is 1.4~1.5 g/cm^2, is used to manufacture a carbon paper for a gas dispersing layer, and thus, the carbon paper of the present invention has excellent electric conductivity, causes subtle damage due to the soft texture, and is light enough to be useful for a gas dispersing layer.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a carbon paper for a gas diffusion layer for a fuel cell,

The present invention relates to a method for producing carbon paper for a gas diffusion layer for a fuel cell, and more particularly, to a method for producing carbon paper for a gas diffusion layer for a fuel cell which is soft, .

As a conventional method for producing a carbon paper for a gas diffusion layer for a fuel cell, a polyacrylonitrile-based carbon fiber or a pitch-based carbon fiber, a surfactant, a defoaming agent, a binder which is a polyvinyl alcohol short fiber, There has been widely used a method of producing a carbon paper for a gas diffusion layer for a fuel cell by a wet papermaking method using the above dispersion.

However, since the conventional method uses polyacrylonitrile-based carbon fibers or pitch-based carbon fibers having a high modulus of elasticity of 200 to 600 Gpa as well as electric conductivity, the polyacrylonitrile-based carbon fibers Fiber or pitch-based carbon fibers are easily broken, the surface of the grass paper to be produced is uneven or the surface of the grass paper to be wound is damaged. As a result, the final product, carbon paper for gas diffusion layer for fuel cells, And the surface damage was increased.

In addition, since the density of the polyacrylonitrile-based carbon fiber or the pitch-based carbon fiber is as high as 1.7 g / cm 3 or more, there is a limit to the weight reduction of the carbon paper for a gas diffusion layer for a fuel cell.

The reason why the modulus of elasticity of the polyacrylonitrile-based carbon fiber or the pitch-based carbon fiber is increased to 200 to 600 Gpa is because the heat treatment (carbonization) is performed at a high temperature of 2,000 DEG C or more to improve the electrical conductivity. In other words, the higher the heat treatment (carbonization) temperature, the higher the electrical conductivity and the modulus of elasticity of the polyacrylonitrile-based carbon fiber or the pitch-based carbon fiber. If the temperature of the heat treatment (carbonization) And the electric conductivity is lowered at the same time, it is not suitable as a carbon paper material.

Another conventional technique for producing carbon paper for gas diffusion layers for fuel cells is polyacrylonitrile-based carbon fiber or pitch-based carbon fiber which is manufactured by a method of heat treatment (carbonization) at a temperature of less than 2,000 DEG C and has low elastic modulus and electrical conductivity. A fiber is used to prepare a dispersion as in the conventional method described above and then a carbon paper is produced by a wet pasting method using the dispersion and then a conductive material such as carbon black or carbon nanotubes is added to the surface of the carbon paper A method of manufacturing a carbon paper for a gas diffusion layer for a fuel cell by coating a fluororesin has been used. However, in order to supplement the electric conductivity, a process of coating a fluororesin added with a conductive material must be additionally performed, There is a problem in that it becomes complicated.

Another conventional technique for producing a carbon paper for a gas diffusion layer for a fuel cell is disclosed in Korean Patent No. 10-1392232, which comprises preparing a dispersion liquid containing carbon fibers whose surface has been oxidized by ozone treatment, However, in the conventional method, the dispersibility of the carbon fiber in the dispersion can be improved. However, when the electrical conductivity of the carbon fiber is high, the elasticity ratio also increases, so that the surface of the carbon paper The problem of damages could not be effectively solved.

The object of the present invention is to provide a carbon paper which is excellent in electric conductivity, soft, has less surface damage and is lightweight, and is particularly useful for a fuel cell gas diffusion layer.

In order to achieve the above object, in the present invention, when carbon paper for a gas diffusion layer for a fuel cell is produced by a wet laid paper method or the like using a dispersion containing carbon fibers, the carbon fiber is excellent in electrical conductivity and low in elastic modulus and density Cellulosic carbon short fibers are used.

At this time, the dispersion is prepared by dispersing 0.01 to 0.5 parts by weight of cellulose-based carbon short fibers per 100 parts by weight of the solvent, and adjusting the content of the sizing agent in the cellulose-based carbon short fibers to 0.3% by weight or less .

According to the present invention, a cellulose short carbon fiber having a low softness and a low density of 1.4 to 1.5 g / cm 2 is used as a gas diffusion layer for a fuel cell, which is carbonized (heat-treated) at a high temperature and has excellent electrical conductivity, Since the carbon paper is produced, the carbon paper produced by the present invention is excellent in electric conductivity, soft, less in surface damage, and light in weight, which is particularly useful for a fuel cell gas diffusion layer.

Hereinafter, the present invention will be described in detail.

Specifically, the present invention relates to a process for producing a cellulose-based carbon fiber, comprising the steps of: (i) preparing a dispersion comprising a cellulose-based carbon short fiber; (Ii) applying the dispersion to a mesh net and removing the solvent in the dispersion to produce a sheet; And (iii) pressing and drying the sheet produced as described above.

As an embodiment, the present invention first manufactures a dispersion by dispersing cellulose short carbon fibers, a surfactant, a defoamer, a binder and a tackifier in a solvent.

The cellulose-based carbon short staple fiber is prepared by heat-treating a cellulose short staple fiber precursor for producing carbon fibers at 2,000 to 2,600 ° C. The cellulose based carbon short staple fiber has a density of 1.4 to 1.5 g / cm 3 and an elastic modulus of 10 100 GPa, a strength of 0.5 to 1.2 GPa, a length of 3 to 56 mm, a diameter of 6 to 10 占 퐉, and a specific resistance of 10 to 70? / M.

Preferably, the cellulose-based carbon short fibers have a length of 3 to 12 mm and an elastic modulus of 40 to 70 GPa to prevent surface damage of the final product.

The content of the sizing agent in the cellulosic carbon short staple fiber is preferably 0 to 0.3 wt% to improve the dispersibility of the cellulose short carbon fibers in the dispersion.

In addition, it is preferable that 0.01 to 0.5 parts by weight of the cellulose-based carbon short fibers per 100 parts by weight of the solvent is dispersed in a solvent to prepare the dispersion.

In addition, it is preferable that 1 to 10 parts by weight of a surfactant, 1 to 10 parts by weight of a defoaming agent, 1 to 10 parts by weight of a binder and 1 to 10 parts by weight of a tackifier are dispersed in a solvent to prepare the dispersion Do.

When the cellulose-based carbon short staple fibers of less than 0.01 part by weight based on 100 parts by weight of the solvent are dispersed in the solvent, the content of the subordinate material is increased and the carbon paper is advantageous in forming the carbon paper. However, the electrical conductivity of the carbon paper is lowered and 0.5 parts by weight The dispersibility of the cellulose-based carbon short fibers in the dispersion becomes poor when the cellulose short carbon fibers are dispersed in the solvent.

As an embodiment of the present invention, water is used as the solvent, and a water-soluble binder or a thermoplastic binder having one form selected from a fiber form, a powder form and a solution form is used as the binder, and a cationic surfactant , An anionic surfactant and a nonionic surfactant are used.

As the water-soluble binder, polyvinyl alcohol or the like is used.

Next, the dispersion is applied to a mesh net, the solvent in the dispersion is removed to prepare a sheet, and the sheet thus prepared is compressed and dried to produce a carbon paper for a gas diffusion layer for a fuel cell according to the present invention .

At this time, it is preferable to control the weight of the carbon paper for a gas diffusion layer for a fuel cell to 10 to 60 g / m 2.

When the weight is less than 10 g / m 2, the porosity of the carbon paper becomes too large to be bonded to the carbon paper for gas diffusion for fuel cells. When the weight exceeds 60 g / m 2, the carbon paper becomes too thick, .

According to the present invention, a cellulose short carbon fiber having a low softness and a low density of 1.4 to 1.5 g / cm 2 is used as a gas diffusion layer for a fuel cell, which is carbonized (heat-treated) at a high temperature and has excellent electrical conductivity, Since the carbon paper is produced, the carbon paper produced by the present invention is excellent in electric conductivity, soft, less in surface damage, and light in weight, which is particularly useful for a fuel cell gas diffusion layer.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the scope of protection of the present invention should not be construed as being limited only by the following examples.

Example  One

A cellulosic carbon short staple fiber having a modulus of elasticity of 55 GPa, a density of 1.45 g / cm 3, a specific resistance of 10 Ω / m, a content of calligraphy of 0.1% by weight and a length of 7 mm, a cationic surfactant, a defoamer, The alcohol (binder) and the viscous agent were dispersed in water (solvent) to prepare a dispersion.

At this time, 0.1 part by weight of cellulose short carbon fibers, 3 parts by weight of a cationic surfactant, 2 parts by weight of a defoaming agent, 5 parts by weight of fibrous polyvinyl alcohol (binder) and 3 parts by weight of a tackifier were dispersed in a solvent.

Next, the dispersion was applied to a mesh net, and the solvent in the dispersion was removed to prepare a sheet, which was then compressed and dried to produce carbon paper for a fuel cell gas diffusion layer.

Table 1 shows the results of evaluating the weight, electrical conductivity and surface damage of the carbon paper for the fuel cell gas diffusion layer manufactured.

Comparative Example  One

A polyacrylonitrile-based (PAN-based) carbon short staple having a modulus of elasticity of 200 GPa, a density of 1.8 g / cm 3, a resistivity of 10 Ω / m, an acetygous content of 0.5 wt% and a length of 10 mm, The dispersant was prepared by dispersing the active agent, antifoaming agent, fibrous polyvinyl alcohol (binder) and tackifier in water (solvent).

At this time, 0.7 part by weight of polyacrylonitrile (PAN) carbon short staple fiber, 3 parts by weight of cationic surfactant, 2 parts by weight of defoaming agent, 5 parts by weight of fibrous polyvinyl alcohol (binder) and 3 parts by weight of The gum was dispersed in the solvent.

Next, the dispersion was applied to a mesh net, and the solvent in the dispersion was removed to prepare a sheet, which was then compressed and dried to produce carbon paper for a fuel cell gas diffusion layer.

Table 1 shows the results of evaluating the weight, electrical conductivity and surface damage of the carbon paper for the fuel cell gas diffusion layer manufactured.

Comparative Example  2

Based carbon short fibers having a modulus of elasticity of 600 GPa, a density of 1.7 g / cm 3, a resistivity of 10 Ω / m, an arc-like content of 0.4 wt% and a length of 10 mm, a cationic surfactant, The fibrous polyvinyl alcohol (binder) and the viscous agent were dispersed in water (solvent) to prepare a dispersion.

At this time, 0.1 part by weight of pitch short carbon fibers, 3 parts by weight of cationic surfactant, 2 parts by weight of defoamer, 5 parts by weight of fibrous polyvinyl alcohol (binder) and 3 parts by weight of tackifier were added to a solvent Lt; / RTI >

Next, the dispersion was applied to a mesh net, and the solvent in the dispersion was removed to prepare a sheet, which was then compressed and dried to produce carbon paper for a fuel cell gas diffusion layer.

Thickness, thickness, density, and electrical characteristics of the carbon paper for the fuel cell gas diffusion layer were evaluated. The results are shown in Table 1.

division Basis weight (g / ㎡) Thickness (㎛) Density (g / cm3) Electrical resistance (mΩ ㎠) Example 1 30 230 0.35 8 Comparative Example 1 30 245 0.42 10 Comparative Example 2 30 270 0.52 11

The electrical resistance was measured by a 4-point-probe method (ASTM C 611) using an electrical resistance meter.

Claims (12)

(I) a step of producing a dispersion liquid containing cellulose-based carbon short fibers;
(Ii) applying the dispersion to a mesh net and removing the solvent in the dispersion to produce a sheet; And
(Iii) compressing and drying the sheet produced as described above. ≪ Desc / Clms Page number 19 > The method for producing carbon paper for a fuel cell gas diffusion layer according to claim 1, wherein the cellulose-based carbon short staple fiber is produced by heat-treating a cellulose short fiber precursor for producing carbon fiber at 2,000 to 2,600 ° C. The fiber according to claim 1, wherein the cellulose-based carbon short staple fiber has a density of 1.4 to 1.5 g / cm 3, a modulus of elasticity of 10 to 100 GPa, a strength of 0.5 to 1.2 GPa, a length of 3 to 56 mm, Mu m and a specific resistance of 10 to 70? / M. The method for producing a carbon paper for a fuel cell gas diffusion layer according to claim 1, wherein the cellulosic carbon short staple fiber has a sizing agent content of 0 to 0.3 wt%. The method of claim 1, wherein the weight of the carbon paper is adjusted to 10 to 60 g / m 2. The carbon paper for a fuel cell gas diffusion layer according to claim 1, wherein the cellulose-based carbon short staple fiber, the surfactant, the defoaming agent, the binder and the tackifier are dispersed in a solvent to prepare a dispersion containing the cellulose- Way. The method for producing carbon paper for a fuel cell gas diffusion layer according to claim 6, wherein 0.01 to 0.5 parts by weight of the cellulose-based carbon short fibers per 100 parts by weight of the solvent is dispersed in a solvent to prepare the dispersion. [7] The method according to claim 6, wherein 1 to 10 parts by weight of a surfactant, 1 to 10 parts by weight of a defoamer, 1 to 10 parts by weight of a binder and 1 to 10 parts by weight of a viscous agent are dispersed in a solvent, Wherein the carbon paper for the fuel cell gas diffusion layer is produced by the following method. The method for producing carbon paper for a fuel cell gas diffusion layer according to claim 6, wherein water is used as the solvent. The carbon paper for a fuel cell gas diffusion layer according to claim 6, wherein one kind of binder selected from the group consisting of a water-soluble binder and a thermoplastic binder having one form selected from a fiber form, a powder form and a solution form is used as the binder Gt; The method for producing a carbon paper for a fuel cell gas diffusion layer according to claim 6, wherein one or two or more selected from the group consisting of a cationic surfactant, an anionic surfactant and a nonionic surfactant is used as a surfactant. 12. The method according to claim 11, wherein the water-soluble binder is polyvinyl alcohol.