KR20200031845A - Method of manufacturing carbon fiber paper used in gas diffusion layer of fuel cell - Google Patents

Abstract

The present invention includes: a process (i) of producing a carbon fiber web by a wet papermaking method of dispersing carbon fibers in the form of short fibers in water or aqueous solution and then, lifting the carbon fibers with a screen to dehydrate the carbon fibers; a process (ii) of impregnating thermoplastic resin in the carbon fiber web; a process (iii) of crosslinking and stabilizing the carbon fiber web with the thermoplastic resin impregnated therein in sulfuric acid; and a process (iv) of carbonizing the crosslinked and stabilized carbon fiber web to produce carbon fiber paper. The present invention greatly improves the electrical conductivity of produced carbon fiber paper while effectively preventing problems of the greatly reduced mechanical properties of carbon fiber paper as thermosetting resin impregnated in a carbon fiber web is carbonized. The carbon fiber paper produced by the present invention has excellent mechanical properties and electrical conductivity at the same time and thus, is particularly useful as a material for producing a gas diffusion layer of a fuel cell.

Description

Method of manufacturing carbon fiber paper used in gas diffusion layer of fuel cell}

The present invention relates to a method of manufacturing a carbon fiber paper for a gas diffusion layer for a fuel cell, specifically for manufacturing a gas diffusion layer (hereinafter referred to as "GDL") of a polymer electrolyte fuel cell having excellent electrical conductivity and mechanical properties at the same time. It relates to a method for producing carbon fiber paper useful as a material.

Hereinafter, in the present invention, the "carbon fiber paper" is a carbon in the form of a short fiber as a paper form that is impregnated with a resin in a carbon fiber web manufactured through a wet papermaking process, dried and pressurized, and carbonized at high temperature. It is used as a term to mean a material composed of fibers.

The polymer electrolyte fuel cell (Proton exchange membrane fuel cell) has a small volume and light weight, and is used as a power source for portable devices such as mobile phones and laptops, and automobiles, and currently accounts for 90% of fuel cell research and development.

The principle of the polymer electrolyte fuel cell is a technology that generates electricity by an electrochemical reaction by hydrogen as fuel and oxygen in air, and is an eco-friendly technology in which electricity, water, and heat are generated while hydrogen and oxygen are combined. The power generation efficiency of such a fuel cell is more than 40%, and when the thermal efficiency is included, an energy efficiency of about 80% can be obtained, which has an effect of improving fuel efficiency of up to 50% compared to thermal power generation.

The polymer electrolyte fuel cell is composed of a separator, an electrode, and a polymer electrolyte membrane, and the electrode of the polymer electrolyte membrane is further composed of a catalyst layer, a polymer electrolyte, and a gas diffusion layer. The gas diffusion layer serves as a passage for gas diffusion in a membrane electrode assembly in a fuel cell stack, and is a material that serves as a membrane electrode assembly support, an electrophoretic passage, and a discharge passage of water generated during reaction. Therefore, since the material used at this time should be a material having hydrophobicity, excellent electrical conductivity and gas permeability, and sufficient mechanical strength, porous and highly conductive carbon fiber paper and carbon fiber fabric are mainly used as materials for the gas diffusion layer.

As a prior art for manufacturing carbon fiber paper for gas diffusion layer of a fuel cell, it is manufactured by wet papermaking for the purpose of improving the electrical conductivity of carbon fiber paper. After impregnating, drying and pressing it, carbonization at a high temperature to produce a carbon fiber paper for gas diffusion is widely used, but the prior art can improve the electrical conductivity of the produced carbon fiber paper, but is manufactured. There was a problem in that the mechanical properties of the carbon fiber paper were significantly reduced.

As another prior art, Japanese Patent Laid-Open No. 2014-100106 discloses a method for preparing carbon fiber paper by impregnating a carbon fiber web with a thermosetting resin and then carbonizing it at a high temperature. Also, the electrical conductivity of the carbon fiber paper before manufacturing was improved, but there was a problem in that mechanical properties were significantly reduced.

As another prior art, in Korean Patent Publication No. 10-2018-31529, carbon fiber paper having good electrical conductivity and mechanical strength is impregnated by impregnating a carbon fiber web with a binder pitch (coal / petroleum additive) and carbonizing it. Although a method of manufacturing is published, the prior art has a problem in that it is difficult to commercialize due to high manufacturing cost.

On the other hand, Korean Patent Registration No. 10-1683006 discloses a method of manufacturing activated carbon inexpensively by crosslinking with polyolefin sulfuric acid and then carbonizing at high temperature and then activating it with water vapor, but the conventional method is used for the production of carbon fiber paper for gas diffusion layers. It is not a related technology, and its purpose is also significantly different from simultaneously improving the electrical conductivity and mechanical properties of the carbon fiber paper for the gas diffusion layer.

On the other hand, Korean Patent Publication No. 10-2017-0033708 discloses a method for preparing carbon fibers by carbonizing at high temperature after crosslinking by supporting polyolefin fibers in sulfuric acid, but the prior art method replaces the conventional acrylonitrile-based precursors. As a method of manufacturing carbon fibers using polyolefin fibers, it is not a technique for manufacturing carbon fiber paper for a gas diffusion layer, and its purpose is also significantly different from simultaneously improving electrical conductivity and mechanical properties of the carbon fiber paper for a gas diffusion layer.

An object of the present invention is to provide a carbon fiber paper for a gas diffusion layer of a fuel cell having a relatively superior electrical conductivity and mechanical properties than a carbon fiber paper for a gas diffusion layer prepared by impregnating a carbon fiber web with a thermosetting resin and then carbonizing it. It is to provide a manufacturing method.

In order to solve the above problems, in the present invention, a thermoplastic resin is impregnated into a carbon fiber web made of carbon fibers in the form of short fibers and produced by a wet papermaking method, and then treated with sulfuric acid to crosslink and stabilize. And then carbonized at high temperature to produce carbon fiber paper.

The carbon fiber paper produced by the present invention has a high carbonization yield and an increased C = C bond content, thereby exhibiting excellent electrical conductivity.

Therefore, the fuel cell including the gas diffusion layer of the fuel cell made of the carbon fiber paper is greatly improved fuel cell efficiency.

In addition, the carbon fiber paper produced by the present invention has excellent mechanical properties, and thus it is easy to manufacture a roll type carbon fiber paper or to manufacture a gas diffusion layer, and also improves durability in a fuel cell stack. .

Hereinafter, the present invention will be described in detail.

The present invention (i) a process for producing a carbon fiber web (Web) by a wet papermaking method of carbon fiber in the form of short fibers; (Ii) a process of impregnating the carbon fiber web with a thermoplastic resin; (Iii) a process of crosslinking and stabilizing a carbon fiber web impregnated with a thermoplastic resin by supporting it in sulfuric acid; And (iii) carbonizing the crosslinked and stabilized carbon fiber web to produce carbon fiber paper.

As an example of implementation of the present invention, after dispersing the carbon fibers in the form of a short fiber in water or an aqueous solution, the carbon fibers are webted by a wet papermaking method in which the carbon fibers are lifted with a screen and then dehydrated. The thermoplastic resin is impregnated into the fiber web.

At this time, it is preferable to use a polyolefin-based resin as the thermoplastic resin.

As the polyolefin-based resin, polypropylene resin or low density polyethylene (LDPE) resin or a mixture thereof is used.

The first implementation example of impregnating a thermoplastic resin in a carbon fiber web is a method of dipping a carbon fiber web in a thermoplastic resin solution (impregnation solution) prepared by dissolving a thermoplastic resin in a solvent. Can be used.

As an example of the implementation of the thermoplastic resin solution, a solution in which a polypropylene resin or a low density polyethylene resin is dissolved in an ortho-dichlorobenzene solvent is used, wherein the viscosity of the solution is 10 centipoise or less. , And the concentration of the resin solid content in the solution is preferably 5 to 10%.

In addition, in order to maintain the amorphous state of the solution in which polypropylene or low density polyethylene is dissolved in the solvent, the solution is poured into liquid nitrogen and quenched to prepare a gel, and then stabilized for a certain temperature and time. By re-stirring, an impregnation liquid for dipping the carbon fiber web can be prepared.

At this time, the temperature during the stabilization is preferably in the range of -16 to -8 ℃. If it is lower than -16 ℃, there is a problem that the solution is completely frozen because the freezing point of the solvent 1,2-dichlorobenzene (ortho-dichlorobenzene) is -17 ℃, and if the temperature exceeds -8 ℃, it is not a gel, but a liquid. It can become a state. That is, it is preferable to stabilize within the above range because it is difficult to maintain the amorphous form outside the above range. In addition, the stabilization time is preferably 20 to 30 hours because the sample rapidly cooled to amorphous form in liquid nitrogen slowly melts to obtain a gel while maintaining the amorphous form. This may occur and is undesirable. In addition, after stabilization is complete, re-stirring for 1 to 4 hours at about 40 to 60 ° C is preferable because the viscosity of the impregnation liquid can be appropriately lowered to 10 centipoises or less.

It is preferable to dip the carbon fiber web into a thermoplastic resin solution (impregnation solution) for about 1 minute to 3 minutes.

As a second implementation example of impregnating a thermoplastic resin in a carbon fiber web, the thermoplastic film is laminated to both sides of a carbon fiber web, and then hot-pressed with a hot press to heat the laminated thermoplastic film. A method of melting and impregnating the carbon fiber web inside may be used.

Next, the carbon fiber web impregnated with the thermoplastic resin is supported on sulfuric acid to crosslink and stabilize.

Since the thermoplastic polymer has a property of softening at a glass transition temperature (Tg) or higher, it is necessary to improve heat resistance to prevent this during a high temperature carbonization process. The dehydrogenation reaction that occurs when sulfuric acid treatment of low density polyethylene is as shown in the following reaction formula, wherein C = C double bond increases and the pi bond of the terminal double bond opens and cross-links with the double bonds of neighboring molecular chains.

In the crosslinking process, cyclization of the low-density polyethylene chain structure occurs, and when the molecular chains are connected to each other, mechanical properties are improved by forming a polygonal structure. In addition, since the polyolefin does not have O and N structurally, when carbonized, less oxide is generated, so that the carbonization yield is relatively higher than that of the thermosetting resin, thereby improving electrical conductivity.

At this time, it is preferable to support the carbon fiber web impregnated with the thermoplastic resin at 150 to 180 ° C. for 10 to 60 minutes, preferably 10 to 30 minutes in sulfuric acid.

When the loading temperature is less than 150 ° C, a crosslinking reaction does not occur and the carbonization yield is reduced, and when the carbon fiber web is impregnated with a thermoplastic resin solution, the carbon fiber web is impregnated with the thermoplastic resin. When it exceeds 180 ° C, the solvent in the thermoplastic resin solution (impregnation solution) is vaporized, which is not preferable.

Next, carbon fiber paper is prepared by carbonizing a crosslinked and stabilized carbon fiber web.

At this time, the primary carbonization of the carbon fiber web impregnated with the thermoplastic resin at 800 to 1,000 ° C for 20 to 40 minutes, followed by secondary carbonization at 2,000 to 2,400 ° C for 7 to 15 minutes increases the carbonization yield. desirable.

Meanwhile, in the present invention, sulfuric acid remaining on the carbon fiber web may be washed and neutralized before carbonization of the crosslinked and stabilized carbon fiber web is selectively performed. At this time, washing may be performed until the pH of the carbon fiber web is 7 and heat-treated at a temperature of 180 ° C. or higher to remove even the solvent contained in the thermoplastic resin solution (impregnation solution).

Hereinafter, the present invention will be described in more detail through Examples and Comparative Examples.

However, the protection scope of the present invention should not be construed as being limited to the following examples.

Example 1

After dispersing the carbon fiber having an average length of 10 mm in water, the carbon fiber was raised by a screen to prepare a carbon fiber web.

Next, the carbon fiber web was added to a polypropylene resin solution (impregnation solution) having a viscosity of 7 centipoise (impregnation solution) by dissolving a polypropylene resin in an ortho-dichlorobenzene solvent at a concentration of 7% solids. Dipping was performed for 1 minute to impregnate the carbon fiber web with a polypropylene resin.

Next, the carbon fiber web impregnated with the polypropylene resin was supported in sulfuric acid at 160 ° C for 25 minutes to crosslink and stabilize.

Next, after washing and neutralizing the crosslinked and stabilized carbon fiber web, the first carbonization was performed at 900 ° C for 30 minutes, followed by secondary carbonization at 2,400 ° C for 10 minutes to prepare carbon fiber paper.

Table 1 shows the results of measuring the surface resistance (electric conductivity) and bending stiffness of the manufactured carbon fiber paper.

Example 2

After dispersing the carbon fiber having an average length of 10 mm in water, the carbon fiber was raised by a screen to prepare a carbon fiber web.

Next, the carbon fiber web is placed in a low density polyethylene resin solution (impregnation solution) having a viscosity of 7 centipoise (impregnation solution) by dissolving a low density polyethylene resin in an ortho-dichlorobenzene solvent at a concentration of 7% solids. Dipping was performed for 1 minute to impregnate the carbon fiber web with a low density polyethylene resin.

Next, the carbon fiber web impregnated with the low-density polyethylene resin was supported in sulfuric acid at 160 ° C for 25 minutes to crosslink and stabilize.

Next, after washing and neutralizing the crosslinked and stabilized carbon fiber web, the first carbonization was performed at 900 ° C for 30 minutes, followed by secondary carbonization at 2,400 ° C for 10 minutes to prepare carbon fiber paper.

Table 1 shows the results of measuring the surface resistance (electric conductivity) and bending stiffness of the manufactured carbon fiber paper.

Example 3

After dispersing the carbon fiber having an average length of 10 mm in water, the carbon fiber was raised by a screen to prepare a carbon fiber web.

Next, two pieces of low-density polyethylene films were prepared, overlapped on both sides of the carbon fiber web, and pressurized at 700KGS at 150 ° C for 5 minutes with a hot press to impregnate the carbon fiber web with low-density polyethylene resin.

Next, the carbon fiber web impregnated with the low-density polyethylene resin was supported in sulfuric acid at 160 ° C for 25 minutes to crosslink and stabilize.

Next, after washing and neutralizing the crosslinked and stabilized carbon fiber web, the first carbonization was performed at 900 ° C for 30 minutes, followed by secondary carbonization at 2,400 ° C for 10 minutes to prepare carbon fiber paper.

Table 1 shows the results of measuring the surface resistance (electric conductivity) and bending stiffness of the manufactured carbon fiber paper.

Comparative Example 1

After dispersing the carbon fiber having an average length of 10 mm in water, the carbon fiber was raised by a screen to prepare a carbon fiber web.

Next, the phenol resin, a thermosetting resin, is dissolved in a solvent at a concentration of 7% solids, and the carbon fiber web is dipping for 1 minute in a phenol resin solution (impregnation solution) having a viscosity of 7 centipoise. The carbon fiber web was impregnated with phenol resin.

In order to remove the solvent of the phenol resin remaining on the carbon fiber web, it was dried in an oven at 150 ° C. for 5 minutes, and pressed and cured for 5 minutes in a hot press at 150 ° C. for curing of the phenol resin.

Next, the carbon fiber paper impregnated with phenol resin was secondary carbonized at 2,400 ° C. for 10 minutes to prepare carbon fiber paper.

Table 1 shows the results of measuring the surface resistance (electric conductivity) and bending stiffness of the manufactured carbon fiber paper.

Comparative Example 2

After dispersing the carbon fiber having an average length of 10 mm in water, the carbon fiber was raised by a screen to prepare a carbon fiber web.

Next, carbon fiber paper was prepared by carbonizing the carbon fiber web manufactured as described above at 2,400 ° C.

Table 1 shows the results of measuring the surface resistance (electric conductivity) and bending stiffness of the manufactured carbon fiber paper.

division Surface resistance (Ω / sq) Banding stiffness (g · ㎝) Example 1 0.43 ± 0.04 5.02 Example 2 0.48 ± 0.06 6.04 Example 3 0.45 ± 0.04 5.58 Comparative Example 1 0.76 ± 0.22 3.53 Comparative Example 2 3.65 ± 0.27 1.06

The surface resistance and bending stiffness of Table 1 were measured by the following method.

Surface resistance

Nine points (Pint) of 10 × 10 cm samples were measured using a 4-probe measuring instrument.

Banding stiffness

Using a Taber stiffness tester (model 150E), the load value when bending a 1.5 × 2.75 inch sample at an angle of 15 ° was measured.

Claims (9)

(Iii) a process of manufacturing a carbon fiber web in a wet papermaking method using carbon fiber in the form of a short fiber;
(Ii) a process of impregnating the carbon fiber web with a thermoplastic resin;
(Iii) a process of crosslinking and stabilizing a carbon fiber web impregnated with a thermoplastic resin by supporting it in sulfuric acid; And
(I) carbonizing the crosslinked and stabilized carbon fiber web to produce carbon fiber paper; a method for producing a carbon paper for a fuel cell gas diffusion layer, comprising: The method of claim 1, wherein the thermoplastic resin is a polyolefin-based resin. [3] The fuel cell gas diffusion layer according to claim 2, wherein the polyolefin-based resin is a resin selected from polypropylene resin, low density polyethylene (LDPE) resin, and a mixture of polypropylene resin and low density polyethylene resin. Method of manufacturing carbon paper. The method of claim 1, wherein the carbon fiber web (Web) of the carbon paper for the fuel cell gas diffusion layer, characterized in that by impregnating the thermoplastic resin to the carbon fiber web (Web) by dipping (Dipping) in a thermoplastic resin solution Manufacturing method. The method of claim 4, wherein the thermoplastic resin solution has a viscosity of 10 centipoise or less. The method of claim 4, wherein the thermoplastic resin solution has a thermoplastic resin solids concentration of 5 to 10%. The method of claim 1, wherein after laminating the thermoplastic resin film on both sides of the carbon fiber web, the laminated thermoplastic resin film is melted and heated and pressed at a high temperature to be impregnated into the interior of the carbon fiber web. Manufacturing method of carbon paper for fuel cell gas diffusion layer. The carbon fiber paper according to claim 1, wherein the carbon fiber paper impregnated with the thermoplastic resin is first carbonized at 800 to 1,000 ° C for 20 to 40 minutes and then continuously carbonized at 2,000 to 2,400 ° C for 7 to 15 minutes. Method for producing a carbon paper for a fuel cell gas diffusion layer, characterized in that to manufacture. The carbon paper for a fuel cell gas diffusion layer according to claim 1, wherein the sulfuric acid remaining on the carbon fiber web is washed and neutralized before carbonization of the crosslinked and stabilized carbon fiber web. Manufacturing method.