KR101304489B1 - Method for preparing carbon paper by controling specific charge density and viscosity in solution, the carbon paper prepared using the method and fuel cell comprising the carbon paper - Google Patents

Abstract

PURPOSE: A manufacturing method of carbon paper provides carbon paper with excellent electric conductivity and air permeability by uniformly dispersing carbon fibers in an anisotropic arrangement. CONSTITUTION: A manufacturing method of carbon paper by a wet process includes a step of controlling the charge density of a dispersion solution in which carbon fiber is dispersed to 2-50 meq/L and the viscosity of the dispersion to 110-507 cP. The charge density and the viscosity of the dispersion liquid are controlled by adding a thickening agent and the anionic material into the dispersion. The thickening agent is selected from carboxymethyl cellulose, polyethylene oxide, polyethylene glycol, hydroxyethyl, cellulose, acrylic tackier and a mixture thereof.

Description

Method for preparing carbon paper by controling specific charge density and viscosity in solution, the carbon paper prepared using the method and fuel cell comprising the carbon paper}

The present invention relates to a method for producing carbon paper with improved dispersibility of carbon fibers, a carbon paper produced accordingly, and a fuel cell including the same.

A fuel cell is composed of a power generation unit, a reformer, a fuel tank, and a fuel pump, in which electricity is generated. The power generation portion forms the main body of the fuel cell, and the fuel pump supplies the fuel in the fuel tank to the reformer. Hydrogen gas is generated through the reformer and fuel is supplied to the power generation unit by the pump to generate electric energy by electrochemical reaction. The power generation unit may include a membrane electrode assembly (MEA) composed of an anode, a cathode, and a polymer electrolyte membrane.

The anode and the cathode each include a fuel cell electrode and a catalyst layer. When fuel or oxygen in each of the anode or the cathode moves to the catalyst layer through the fuel cell electrode, a catalytic reaction occurs in the catalyst layer, and the result of the catalytic reaction reacts with each other to generate electricity and water. For example, in a direct methanol fuel cell, methanol is supplied to the anode, and the supplied methanol is decomposed into hydrogen ions, electrons, and carbon dioxide by the oxidation reaction of the catalyst layer, and hydrogen ions move to the cathode through the polymer electrolyte membrane, And moves to the cathode through an external circuit. In the cathode, oxygen introduced in the air, electrons moved through the external circuit, and hydrogen ions moved through the membrane react in the catalyst layer to produce water.

On the other hand, the performance of such a fuel cell is determined according to the efficiency of the electrode reaction, the efficiency of the electrode reaction is determined by the mass transfer capacity of the fuel and the oxidant and the discharge capacity of the water generated by the electrode reaction. In fields where a high current density is required, such as an automobile, the fuel cell operates in a high current density region, thereby increasing the amount of water generated per unit area. Therefore, under these conditions, it is important to continuously supply a large amount of fuel and oxidant, and to continuously discharge a large amount of water, and the discharging ability of the generated water greatly depends on the hydrophobicity of the gas diffusion layer for a fuel cell.

In general, water-repellent carbon paper having excellent gas permeability and electron conductivity has been used as a gas diffusion layer for fuel cells. In the conventional carbon paper manufacturing method, when carbon paper is produced by a wet-laid process, the carbon fiber is first dispersed in an aqueous solution or the like, subjected to a dehydration and papermaking process through a wet paper forming apparatus, and then dried. A carbon fiber web is produced. The produced carbon fiber web is impregnated with a thermosetting resin or the like and then cured by applying heat and pressure. When a carbon sheet is formed through such a curing process, if the thermosetting resin in the finally formed sheet is produced by degreasing and high- Is completed.

However, the carbon paper produced by such a wet process exhibits the property that the carbon fibers constituting the carbon paper are not uniformly dispersed to each other, resulting in a decrease in electrical conductivity and gas permeability of the carbon paper produced.

In this regard, Korean Patent Laid-Open Publication No. 2007-79423 discloses a carbon slurry composition for preparing a gas diffusion layer for a fuel cell, and more specifically, a carbon slurry composition including a carbon powder, a dispersant, an aqueous polymer resin, and a fluoro resin. As an example, there is disclosed a carbon slurry composition for producing a gas diffusion layer in which no cracks appear in the microporous layer and the pores are uniformly distributed. However, the composition is a composition for forming a microporous layer by coating a slurry containing carbon particle powder on a separate carbon substrate such as carbon paper, carbon fiber, carbon felt, carbon sheet, or the like, prepared in advance, It does not provide a technique for producing the carbon substrate itself, such as.

Accordingly, in order to solve the problems of the prior art, it is an object of the present invention to adjust the dispersibility of carbon fibers, which are constituent materials of carbon paper, so that carbon fibers are dispersed evenly in an anisotropic arrangement in the produced carbon paper, To thereby improve the electrical conductivity and gas permeability of the resultant carbon paper, and to provide a carbon paper and a fuel cell including the carbon paper.

The present invention to solve the first problem,

In the method for producing carbon paper by a wet process, the carbon paper is characterized in that the charge density of the dispersion in which the carbon fiber is dispersed to 2 meq / L to 50 meq / L, the viscosity of the dispersion is adjusted to 110 cP to 507 cP It provides a manufacturing method.

According to one embodiment of the invention, the charge density and viscosity of the dispersion can be adjusted by adding a thickener and an anionic material to the dispersion.

According to another embodiment of the invention, the thickener is Carboxymethyl cellulose (CMC), polyethylene oxide (PEO), polyethylene glycol (PEG), hydroxyethyl cellulose (Hydroxyethyl cellulose: HEC) , Acrylic thickeners and mixtures thereof.

According to another embodiment of the present invention, the anionic material is polyacrylic acid (PAA), sodium dodecylsulfate (SDS), deoxyribonucleic acid (DNA), sodium dodecylbenzenesulfo Sodium (sodium dodecylbenzenesulfonate: NaDDBS), poly [p- {2,5-bis (3-propoxysulfonic acid sodium salt)} phenylene] ethylene (poly [p- {2,5-bis (3-propoxysulfonic acid sodium salt )} phenylene] ethynylene: PPES), derivatives thereof and mixtures thereof.

According to another embodiment of the present invention, the carbon fiber may have a length of 3.0mm to 8.0mm.

According to another embodiment of the present invention, the carbon fibers in the dispersion may be dispersed in an amount of 0.02 wt% to 0.5 wt%.

According to another embodiment of the present invention,

Preparing a carbon fiber web by dewatering, papermaking and drying the dispersion through a wet paper forming apparatus;

Impregnating the carbon fiber web with a thermosetting resin, and then applying heat and pressure to cure the carbon fiber web; And

The step of carbonizing the thermosetting resin

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According to another embodiment of the present invention, the step of applying heat during the curing step may be performed for 0.1 hours to 2 hours at a temperature of 120 ℃ to 300 ℃.

According to another embodiment of the present invention, the step of applying pressure during the curing step may be carried out under a pressure of 0.2 bar to 5 bar.

According to another embodiment of the present invention, the carbonization step may be performed for 0.2 hours to 10 hours at a temperature of 800 ℃ to 2100 ℃.

According to another embodiment of the present invention, the thermosetting resin may be selected from the group consisting of a phenol resin, a polyurethane resin, a melamine resin, an epoxy resin, and a mixture thereof.

According to another aspect of the present invention,

A carbon paper produced by the above method is provided.

Finally, in order to solve the third problem,

A fuel cell comprising carbon paper produced by the above method as a gas diffusion layer is provided.

According to the present invention, since carbon fibers have an anisotropic arrangement and are evenly dispersed, carbon paper having excellent electrical conductivity and gas permeability can be provided.

1 is a photograph of observing the degree of dispersion of carbon fiber according to the concentration of CMC immediately after adding CMC to the dispersion in the carbon fiber dispersion for producing carbon paper according to the present invention.
FIG. 2 is a photograph of the dispersions of FIG. 1 observed after 30 minutes. FIG.
3 is a graph measuring the charge density according to the CMC concentration in the dispersion.
4 is a graph measuring absolute viscosity according to the concentration of CMC in the dispersion.
Figure 5 is a carbon fiber dispersion for producing carbon paper according to the present invention, CMC is a photograph showing a change in the degree of dispersion observed after the addition of 0.1% by weight of PAA to the dispersion, each added in different amounts; .
FIG. 6 is a graph showing charge densities measured after adding 0.1 wt% PAA to dispersions in which CMCs are added in different contents.
Figure 7 is a graph measuring the thickness of the carbon paper prepared according to the pressure applied in the production of carbon paper using the carbon fiber dispersion according to the present invention.
Figure 8 is a graph measuring the in-plane gas permeability of the carbon paper prepared according to the pressure applied in the production of carbon paper using the carbon fiber dispersion according to the present invention.
Figure 9 is a graph measuring the in-plane resistance value of the carbon paper prepared according to the pressure applied in the production of carbon paper using the carbon fiber dispersion according to the present invention.

Hereinafter, the present invention will be described in more detail with reference to the drawings and examples.

The present invention relates to a process for producing carbon paper by controlling the dispersibility of carbon fibers constituting the carbon paper, thereby allowing the carbon fibers to be dispersed evenly in an anisotropic arrangement in the carbon paper thus produced, and thereby obtaining electrical conductivity and gas permeability . Specifically, the method for producing carbon paper according to the present invention, in the method for producing carbon paper by the wet process, the charge density of the dispersion in which the carbon fiber is dispersed to 2 meq / L to 50 meq / L, the viscosity of the dispersion It is characterized in that to adjust to 110 cP to 507 cP.

The specific charge density means the amount of charge (eq / L or meq / L) of particles per unit volume in the dispersion solution. Charge density is an important factor in the particle dispersion mechanism and electrostatic dispersion control. In general, when the charge density is large, it can be understood that the repulsive force between the particles is large, on the contrary, when the charge density is small, it can be understood that the cohesion between the particles is large.

The present invention comprises the steps of preparing a dispersion in which carbon fibers constituting the carbon paper is dispersed; Preparing a carbon fiber web using the dispersion; Curing the carbon fiber web; And in the conventional wet carbon paper manufacturing method consisting of a carbonization step, when adjusting the charge density and viscosity of the carbon fiber dispersion to a predetermined range, it is possible to produce a carbon fiber dispersion having excellent dispersibility, which is the resulting carbon The present invention has been completed based on the fact that the carbon fibers in the paper can be arranged with anisotropic properties to improve the electrical conductivity and gas permeability of the carbon paper.

Specifically, as can be seen from the results of the following examples, the excellent density when the charge density of the dispersion in which the carbon fiber is dispersed is 2 meq / L to 50 meq / L, and the viscosity of the dispersion is 110 cP to 507 cP. Acidity is achieved. In general, the higher the charge density, the greater the repulsive force between the particles, so it is preferable to have a larger charge density. However, if the charge density exceeds 50 meq / L, the production cost increases due to the added material without affecting the dispersion. It is not preferable because there is a problem, and similarly, when viscosity is high, it is excellent in dispersibility, but since there is a problem that dehydration is not carried out at viscosity 507 cP or more.

As a specific method of controlling the charge density and the viscosity, it can be controlled by adding a thickener for viscosity control and an anionic material for charge density control to the carbon fiber dispersion. The thickener may be selected from the group consisting of acrylic thickeners such as CMC, PEO, PEG, HEC, HISOL and mixtures thereof, and the anionic material from PAA, SDS, DNA, NaDDBS, PPES, derivatives thereof and mixtures thereof. Although not limited thereto, various materials for controlling viscosity and charge density may be used in addition to the above materials.

Carbon fibers having a length of 3.0 mm to 8.0 mm may be used as the carbon fibers in the dispersion. When the length of the carbon fibers is less than 3.0 mm, the dispersibility is improved, but there is a problem of poor porosity and electrical conductivity, and 8.0 mm If it exceeds, it is not preferable because it does not disperse well in the dispersion, it is not possible to produce a uniform carbon paper. In addition, such carbon fibers may be dispersed in an amount of 0.02 wt% to 0.5 wt%. When the carbon fiber content in the dispersion is less than 0.02% by weight, it is difficult to form a carbon fiber web in a subsequent step. When the carbon fiber content exceeds 0.5% by weight, the dispersibility of the carbon fiber is deteriorated. There is a problem that it is difficult to form carbon paper having anisotropy, which is not preferable.

Meanwhile, in order to produce carbon paper according to the method of the present invention, the carbon fiber dispersion is formed into a paper form using a wet paper forming apparatus, followed by dewatering, papermaking and drying to prepare a carbon fiber web , The carbon fiber web is impregnated with a thermosetting resin and cured by applying heat and pressure. Lastly, the carbon paper according to the present invention can be produced by carbonizing the thermosetting resin by an appropriate carbonization process.

The curing step may be carried out by treating the carbon fiber web impregnated with the thermosetting resin at a temperature of 120 ° C to 300 ° C and a pressure of 0.2 bar to 5 bar for 0.1 hour to 2 hours, , There is a problem that sufficient curing may not be performed, and if it exceeds the above range, the thermosetting resin and the carbon fiber may be damaged. As the thermosetting resin, various thermosetting resins selected from the group consisting of a phenol resin, a polyurethane resin, a melamine resin, an epoxy resin, and a mixture thereof may be used, though not limited thereto.

The carbon paper produced according to the method of the present invention described above has superior electrical conductivity and gas permeability compared to the carbon paper produced by the conventional method because carbon fibers have an anisotropic arrangement and are uniformly dispersed. Accordingly, the present invention also provides a fuel cell employing the carbon paper produced as described above as a gas diffusion layer in a fuel cell.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are intended to assist the understanding of the present invention and should not be construed as limiting the scope of the present invention.

Example 1 Dispersibility of Carbon Fiber with Changes in CMC Concentration

1.0 mg (0.01 wt.%) Of polyvinyl alcohol was added and 10 mg (0.05 wt.%) Of carbon fiber was increased in an aqueous solution in which 10 mg (0.05 wt.%) Carbon fiber (4.5 mm length) was dispersed, increasing the amount of CMC from 0.1 wt% to 0.6 wt%. Dispersibility was observed. In FIG. 1, immediately after adding CMC to the dispersion, a photograph of visual observation of the degree of dispersion of carbon fibers as the concentration of CMC is increased is shown, and FIG. 2 is a photograph of the dispersion after 30 minutes. 1 and 2, the dispersion having excellent dispersibility of carbon fiber (dispersion containing 0.5% by weight and 0.6% by weight of CMC) was observed to uniformly sink in the dispersion after 30 minutes after adding CMC. can do.

Meanwhile, FIGS. 3 and 4 show graphs of measuring charge density and absolute viscosity according to CMC concentration in the dispersion. Referring to FIGS. 3 and 4, as the concentration of CMC increases, the charge density and absolute viscosity increase. Able to know. For example, the dispersion containing 0.5 wt% CMC showed a charge density of 19.5 meq / L and a viscosity of 119 cP. After checking the dispersion after shaking for 30 minutes, the dispersion was confirmed. High dispersibility was observed.

Example 2: Dispersibility of Carbon Fiber with Changes in CMC Concentration of Dispersion Added 0.1 wt% Polyacrylic Acid (PAA)

1.0 mg (0.01 wt%) polyvinyl alcohol was added, 0.1 wt% PAA was added to an aqueous solution in which 10 mg (0.05 wt%) carbon fiber (4.5 mm length) was dispersed, and then the amount of CMC was 0.1 wt% Dispersibility of the carbon fiber was observed while increasing to 0.6 wt%.

5 is a photograph showing the change in the degree of dispersion observed after adding 0.1% by weight of PAA to the dispersion of 0.1% by weight, 0.3% by weight and 0.5% by weight of CMC, respectively. Referring to FIG. It can be seen that even in the CMC concentration, when PAA is added, the dispersion degree is more excellent. For example, when dispersibility was tested by adding only CMC to an aqueous solution (Example 1), carbon fibers began to disperse at a CMC concentration of 0.5 wt% or more (viscosity: 119 cP), but 0.1 wt% of PAA was added. In this case, it can be seen that dispersion is observed even at 0.3 wt% CMC concentration (viscosity: 50 cP). In addition, when 0.1% by weight of PAA is added at a CMC concentration of 0.5% by weight, it can be seen that the dispersibility is better.

In addition, FIG. 6 shows a graph in which charge density was measured after adding 0.1 wt% of PAA to a dispersion in which CMC was added in an amount of 0.1 wt% to 0.6 wt%. Referring to FIG. 6, it can be seen that the charge density is increased in the case of the dispersion in which PAA is additionally added as compared with the dispersion in which only the same concentration of CMC is added. For example, in the case of a dispersion in which only 0.3% by weight of CMC is added, the charge density is 11.9 meq / L, and when 0.1% by weight of PAA is added, the charge density is increased to about 13.1 meq / L. That is, it can be seen that the amount of charge per unit volume of the dispersion solution increases, which allows easy dispersion of the carbon fibers.

Example 3: Fabrication of Carbon Paper by Wet-laid Process and Measurement of Its Properties

1.5 g (0.075 wt%) of carbon fibers, 10 g (0.5 wt%) of CMC and 0.2 g (0.01 wt%) of polyvinyl alcohol were dispersed by stirring in a 2 L aqueous solution, and dewatered and papermaking in a wet paper molding machine. It was. Subsequently, a carbon fiber web was produced by drying in a drum dryer having a surface temperature of 75 ° C. The carbon fiber web was impregnated with a phenolic resin, and then cured at 105 to 250 ° C. for 1 hour, and carbonized at 1000 ° C. for 2 hours in a nitrogen atmosphere to prepare a carbon paper according to the present invention. The thickness of the carbon paper produced by the above method was 238 µm.

7 shows a graph measuring the thickness of the carbon paper produced according to the pressure applied in the production of carbon paper, referring to FIG. 7, for example, when compressing the carbon paper by applying a pressure of 16 bar 173 Carbon paper having a thickness of μm can be prepared.

On the other hand, Figure 8 is a graph measuring the in-plane gas permeability of the carbon paper prepared according to the pressure applied, Figure 9 in-plane (in-) of the carbon paper prepared according to the pressure applied plane) resistance graph, Figure 10 is a graph measuring the through-plane (through-plane) gas permeability according to the flow rate, referring to, for example, in-plane gas permeability at 16 bar Is 1.6 × 10 ⁻¹¹ m ² (see FIG. 8) and the in-plane resistance is 21 mΩ / cm ² (see FIG. 9). In addition, through-plane gas permeability was calculated by measuring the differential pressure in the flow range of 0 to 250 cc / s. Through-plane gas permeability was 1.6 × 10 ^-12 m ² , which shows excellent electrical conductivity and gas permeability. Since the carbon paper according to the present invention has excellent physical properties to be used as a gas diffusion layer for a fuel cell.

Claims (13)

In the method for producing carbon paper by a wet process, the carbon paper is characterized in that the charge density of the dispersion in which the carbon fiber is dispersed to 2 meq / L to 50 meq / L, the viscosity of the dispersion is adjusted to 110 cP to 507 cP Manufacturing method. The method of claim 1, wherein the charge density and viscosity of the dispersion is controlled by adding a thickener and an anionic substance to the dispersion. The method of claim 2, wherein the thickener is selected from the group consisting of carboxymethyl cellulose, polyethylene oxide, polyethylene glycol, hydroxyethyl cellulose, acrylic thickener and mixtures thereof. 3. The method of claim 2, wherein the anionic material is polyacrylic acid, sodium dodecyl sulfate, deoxyribonucleic acid, sodium dodecylbenzenesulfonate, poly [p- {2,5-bis (3-propoxysulfonic acid sodium) Salt)} phenylene] ethylene, its derivatives and mixtures thereof. The method of claim 1, wherein the carbon fiber has a length of 3.0 mm to 8.0 mm. The method of claim 1, wherein the carbon fiber in the dispersion is carbon paper manufacturing method, characterized in that dispersed in the content of 0.02% by weight to 0.5% by weight. The method of claim 1, wherein the wet process,
Preparing a carbon fiber web by dewatering, papermaking, and drying the dispersion through a wet paper forming apparatus;
Impregnating the carbon fiber web with a thermosetting resin, and then applying heat and pressure to cure the carbon fiber web; And
The step of carbonizing the thermosetting resin
Carbon paper production method, characterized in that carried out by. The method of claim 7, wherein the applying of heat during the curing step is performed at a temperature of 120 ° C. to 300 ° C. for 0.1 hour to 2 hours. The method of claim 7, wherein the applying of the pressure during the curing step is performed under a pressure of 0.2 bar to 5 bar. According to claim 7, wherein the carbonizing step is carbon paper manufacturing method, characterized in that carried out for 0.2 hours to 10 hours at a temperature of 800 ℃ to 2100 ℃. The method of claim 7, wherein the thermosetting resin is selected from the group consisting of phenol resins, polyurethane resins, melamine resins, epoxy resins and mixtures thereof. Carbon paper produced by the method according to any one of claims 1 to 11. A fuel cell comprising the carbon paper according to claim 12 as a gas diffusion layer.

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