KR101468866B1 - Method for preparing carbon paper for fuel cell, the carbon paper prepared using the method and fuel cell comprising the carbon paper - Google Patents

Abstract

The present invention relates to a method for producing carbon paper for fuel cells, carbon paper produced thereby, and a fuel cell comprising the same. According to the production method of the present invention, it is possible to provide a carbon paper having low electrical resistance and excellent electrical conductivity and excellent gas diffusion ability when the carbon paper for a fuel cell is manufactured. As a result, the fuel cell including the carbon paper according to the present invention can provide a fuel cell having excellent water discharge capability, which is one of the factors that determine the performance of the fuel cell.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon paper for a fuel cell, a carbon paper produced thereby, and a fuel cell including the carbon paper,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing carbon paper for fuel cells, a carbon paper produced thereby, and a fuel cell including the carbon paper. More particularly, the present invention relates to a method for producing carbon paper having excellent electrical conductivity and excellent gas permeability , A carbon paper produced thereby, and a fuel cell including the carbon paper.

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 an electrode for a fuel cell and a catalyst layer. When the fuel or oxygen in each of the anode or the cathode moves to the catalyst layer through the electrode for the fuel cell, a catalytic reaction occurs in the catalyst layer, and the resultant products of the catalytic reaction react 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 the fuel cell is determined according to the efficiency of the electrode reaction, and the efficiency of the electrode reaction is determined according to the mass transfer capability of the fuel and the oxidant and the discharge capability of the water produced by the electrode reaction. In a field where a high current density such as an automobile is required, the fuel cell operates in a region where current density is high, so that the amount of water generated per unit area also increases. Therefore, under such conditions, it is important to continuously supply a large amount of fuel and oxidant, and continuously discharge a large amount of water. The discharge capability of the generated water is affected by the hydrophobicity of the gas diffusion layer (GDL) It depends heavily.

Conventionally, water repellent carbon paper excellent in gas permeability and electron conductivity has been used as a gas diffusion layer for a fuel cell. 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, dehydrated and ground through a wet paper forming apparatus, Carbon fiber web. 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, in the case of producing carbon paper by such a wet process, if the hardening or carbonization is not properly performed, the electrical resistance is increased due to the impregnated thermosetting resin, and the gas permeability is lowered, There is a problem in that the hydrogen gas can not smoothly contact with the catalyst layer and eventually the fuel cell is deteriorated in water discharge ability which is an important factor that determines the performance of the fuel cell.

Disclosure of the Invention The present invention has been conceived to solve the above problems, and an object of the present invention is to provide a method for producing carbon paper for fuel cells having low electrical resistance and excellent electrical conductivity and excellent gas permeability, And a fuel cell.

According to an aspect of the present invention, there is provided a method for manufacturing a carbon paper for a fuel cell by a wet process, comprising the steps of: 1) dewatering, papermaking and drying a dispersion through a wet paper- 2) a step of impregnating the carbon fiber web with a thermosetting resin, followed by curing by applying heat and pressure, and 3) carbonizing the thermosetting resin, and 3) the carbonization step Lt; RTI ID = 0.0 > 1200 C < / RTI >

The 2) curing step is characterized in that the temperature is raised to 170 to 300 ° C at a rate of 5 to 15 ° C per minute.

And 2) the curing step is maintained for 0.5 to 1 hour after the temperature rise.

And 3) in the carbonization step, the temperature is raised at a rate of 3 to 5 ° C per minute.

And 3) the carbonization step is carried out after the temperature is raised for 1 to 3 hours.

Further, the curing is characterized by being oxidized.

Further, the temperature of the carbonization step is elevated to a temperature of 900 to 1100 ° C.

Also, the carbon fiber in the dispersion is dispersed in an amount of 0.02 wt% to 0.5 wt%.

The thermosetting resin is characterized in that it is selected from the group consisting of a phenol resin, a polyurethane resin, a melamine resin, an epoxy resin, and a mixture thereof.

And the step of applying pressure during the curing step is performed under a pressure of 0.2 bar to 5 bar.

The carbon paper for a fuel cell according to another aspect of the present invention is produced by the above-described manufacturing method.

A fuel cell according to another aspect of the present invention is a fuel cell including the carbon paper for a fuel cell as a gas diffusion layer.

According to the production method of the present invention, it is possible to provide a carbon paper having low electrical resistance and excellent electrical conductivity and excellent gas diffusion ability when the carbon paper for a fuel cell is manufactured. As a result, the fuel cell including the carbon paper according to the present invention is a fuel cell that achieves an excellent effect of water discharge, which is the most important factor that determines the performance of the fuel cell.

1 is a cross-sectional view of a fuel cell according to a preferred embodiment of the present invention.
2 is a scanning electron microscope (SEM) photograph of the carbon fiber surface used in Example 1 of the present invention.
3 is a scanning electron microscope (SEM) photograph of the carbon fiber web in the carbonization step in Example 1 of the present invention.
4 is a photograph of the surface of the carbon fiber web in the carbonization step in Example 1 of the present invention.
Fig. 5 is a photograph of the carbon paper surface after carbonization in Example 1 of the present invention. Fig.
6 is a scanning electron microscope (SEM) observation image of carbon paper surface after carbonization in Example 1 of the present invention.

Accordingly, the present inventors have made extensive efforts to develop carbon paper for fuel cells having excellent electrical conductivity and excellent gas permeability, and as a result, they have found that the method for producing carbon paper for fuel cells according to the present invention, the carbon paper thus produced, and the fuel The battery was confirmed and the present invention was completed.

Specifically, the method for producing carbon paper for a fuel cell according to the present invention includes all known methods for producing carbon paper for a fuel cell by a wet process and is not particularly limited, but preferably 1) And 2) curing the carbon fiber web by impregnating the carbon fiber web with a thermosetting resin and then applying heat and pressure to the carbon fiber web, and 3) carbonizing the thermosetting resin. .

In the method for producing a carbon paper for a fuel cell by the wet process, the curing and carbonization should be carried out at an appropriate temperature and time to prevent the electrical resistance from being increased due to the thermosetting resin, to prevent the decrease of gas permeability, The gas smoothly contacts with the catalyst layer and consequently improves the water discharging ability of the fuel cell.

On the other hand, the length of the carbon fibers in the dispersion is not particularly limited, but preferably 3.0 mm to 8.0 mm carbon fibers can be used. When the length of the carbon fiber is less than 3.0 mm, the dispersibility is improved. However, since the carbon fiber has a poor porosity and electrical conductivity, the carbon fiber is not preferable. When the length is more than 8.0 mm, It is not preferable.

The carbon fibers may be dispersed in an amount of 0.02 wt% to 0.5 wt%. When the content of carbon fibers 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 is more than 0.5% by weight, I do not.

In the method for producing a carbon paper for a fuel cell according to the present invention, the heating rate of the curing step 2) is preferably performed at a rate of 5 to 15 ° C per minute, more preferably 8 to 12 ° C per minute . If the temperature raising rate is less than 5 캜, it takes too much time to raise the temperature to a high temperature, and if it exceeds 15 캜, the temperature raising rate becomes too high and it is difficult to provide a sufficient time required for curing .

The curing is preferably carried out at a temperature ranging from 170 to 300 ° C, and more preferably from 200 to 250 ° C. When the temperature of the curing is less than 170 ° C, it is not preferable because a sufficient temperature required for curing is not given. When the temperature exceeds 300 ° C, it takes too much time to raise the temperature, It is not preferable because there is a fear that the state can not be achieved.

Further, the time for the curing is preferably raised to the above-mentioned temperature and then maintained for 0.5 to 1 hour. If the time is less than 0.5 hours, it is not preferable because a sufficient time for curing after heating is not given. If the time exceeds 1 hour, a sufficient time is required for curing, but additional time and cost are unnecessary .

Also, the pressure applied in the curing step is not particularly limited as long as it can achieve an appropriate curing effect, but it is preferable to apply a pressure in the range of 0.2 bar to 5 bar. If the pressure is less than 0.2 bar, it is difficult to attain an appropriate curing effect. If the pressure exceeds 5 bar, excessive external force may damage the state of the carbon fiber web and the thermosetting resin in the curing process. I do not.

In addition, although the gas phase is not particularly limited in performing the curing step, it is preferable to carry out the curing step in a state in which oxidation is possible by injecting oxygen.

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, although it is not particularly limited as long as it is a substance that achieves the effect of curing on the carbon fiber web .

On the other hand, it is preferable that the heating rate of 3) the carbonization step is performed at a rate of 3 to 5 ° C per minute. When the temperature raising rate exceeds 5 캜, sufficient time for carbonization can not be given, and it is difficult to sufficiently attain the effect of carbonization due to a rapid temperature rise. Further, when the temperature raising rate is less than 3 캜, it takes too much time, which is not preferable. The temperature of the carbonization is preferably raised to 800 to 1200 ° C, and more preferably to 900 to 1100 ° C. When the temperature is lower than 800 ° C, a sufficient temperature for carbonization is not given, so that sufficient electrical conductivity and gas permeability are hardly imparted to the carbon paper. If the temperature exceeds 1200 ° C, the carbon paper is damaged There is a problem in that the manufacturing cost is increased to generate unnecessary heat and the like.

It is preferable that the time of carbonization is maintained for 1 to 3 hours after the temperature is raised to the above temperature. If the carbonization time is less than 1 hour, sufficient time and heat required for carbonization after heating can not be supplied and it is difficult to impart sufficient electrical conductivity and gas permeability to the carbon paper. If the carbonization time exceeds 3 hours, there is a possibility of damaging the carbon paper In addition, since a high-temperature state must be maintained for an unnecessarily long time, the manufacturing cost is too high, which is not preferable.

In carrying out the carbonization step, it is preferable to perform carbonization in a state where nitrogen is injected. By injecting nitrogen, the electrical conductivity and gas permeability of carbon paper can be more excellent.

The carbon paper for a fuel cell manufactured according to the method of the present invention described above is prepared by performing curing and carbonization under optimum conditions, and it is possible to prevent deterioration of electrical conductivity and deterioration of gas permeability due to a thermosetting resin and to improve electrical conductivity and gas permeability Is excellent. Thus, when the carbon paper for a fuel cell manufactured according to the manufacturing method of the present invention is used as a gas diffusion layer, it is possible to provide a fuel cell having significantly improved water discharge capability, which is the most important factor that affects the performance of the fuel cell.

Another carbon paper for a fuel cell of the present invention may comprise carbon paper for a fuel cell manufactured by the above method.

Further, the fuel cell according to another aspect of the present invention may include the carbon paper, and the method of manufacturing the fuel cell may include all the fuel cells manufactured by the manufacturing method of the fuel cell, have.

1 is a cross-sectional view of a fuel cell manufactured according to an embodiment of the fuel cell.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example

Example  One

The carbon fiber used was Toray T-700, and the average fiber diameter was about 7 탆. Carbon fibers having a length of 4.5 mm were used. These carbon fibers were mixed in CHCl ₂ organic solvent. The viscosity of the mixture was maintained at 60 cp or higher by mixing the binder fiber and the acrylic thickener for viscosity control, and the zeta potential was maintained at -90 균 to uniformly disperse the carbon fiber in the aqueous solution. The addition amount of the carbon fibers in the mixed solution was 0.05 wt% based on the total aqueous solution, and the binder fiber was added in an amount of 0.01 wt%. The aqueous solution was stirred at 1000 rpm for 2 hours. Thereafter, an aqueous solution was poured into a paper machine reactor 25 cm long and 25 cm long and laid under a 160 mesh stainless steel wire screen. Then, after the flow of the aqueous solution was stopped, dehydration was performed. Secondly, dehydration was performed using an absorbent paper, and the resultant was passed through a drum dryer having a surface temperature of 75 ° C to complete a carbon fiber web. The thickness of the carbon fiber web thus produced was about 180 micrometers on average when compressed at 2 atmospheres. FIG. 2 is a photograph of a surface of a carbon fiber used in the present invention taken by a scanning electron microscope (SEM), and FIG. 3 is a photograph of a surface of a carbon fiber web produced in this example by a scanning electron microscope (SEM). 4 is a photograph of the surface of such a carbon fiber web.

100 ml of phenol resin was mixed and dissolved in 300 ml of acetone solution with a thermosetting resin and then coated on a carbon fiber web cut to a predetermined size as a carbon fiber web prepared according to this example. Thereafter, the mixture was charged into an electric furnace, and the temperature was raised to 10 ° C per minute in an oxygen atmosphere. The temperature was raised to 200 ° C to induce oxidation, and the mixture was allowed to stand for 1 hour to cure the phenolic resin. Then, the temperature was raised again at a rate of 3 ° C. per minute in a nitrogen atmosphere, and the temperature was raised to 1000 ° C., followed by maintaining the carbonization for 2 hours. Thereafter, the temperature of the electric furnace was lowered naturally to prepare a carbon paper for a fuel cell. FIG. 5 is a photograph of the surface of carbonized paper after carbonization, and FIG. 6 is a scanning electron microscope (SEM) photograph of the surface of carbonized paper after carbonization.

Example  2

Carbon paper was prepared in the same manner as in Example 1, except that the carbonization temperature was elevated to 900 ° C.

Example  3

Carbon paper was prepared in the same manner as in Example 1, except that the carbonization temperature was elevated to 800 ° C.

Comparative Example

Carbon paper was prepared in the same manner as in Example 1, except that the cut carbon fiber web was coated with a phenol resin mixture and dried at room temperature.

Experimental Example : Of carbon paper  Electrical resistance and gas permeability measurement

Experiments were carried out to measure the thickness, electrical resistance and gas permeability of the carbon paper prepared in each of Examples 1, 2, 3 and Comparative Examples. This experiment was carried out by measuring the gas diffusion layer physical property evaluation apparatus (CPRT 10L) and measuring the pressure at a normal pressure up to 16 bar. The results are shown in Table 1 below.

In Table 1, the lower the resistance, the better the resistance and the higher the gas permeability, the better the carbon paper. In the case of the carbon paper prepared as in Table 1 and in Example 1, the through-plane resistance, which is the electrical resistance value acting in the thickness direction of the carbon paper, And the through-plane gas permeability, which means the gas permeability through the carbon paper in the thickness direction, are all excellent. In particular, in the case of Example 1, as the pressure was increased, the through-plane resistance value was remarkably lowered significantly as compared with the other cases, and it was confirmed that the carbon paper having excellent electrical conductivity there was. In addition, in the case of Example 1, it was confirmed that the thickness thereof was remarkably thinned with an increase in pressure, and it was confirmed that the carbon paper was much easier to apply in the fuel cell and thinning of the product. It was also confirmed that the measurement results of Examples 1, 2 and 3 are superior to those of Comparative Example in all cases.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. It is natural.

Claims (12)

A method for producing carbon paper for a fuel cell by a wet process,
1) preparing a carbon fiber web by dewatering, papermaking and drying the dispersion through a wet paper forming apparatus;
2) impregnating the carbon fiber web with a thermosetting resin and then curing by applying heat and pressure; And
3) carbonizing the thermosetting resin;
/ RTI >
The 2) curing step is characterized in that the temperature is raised to 170 to 300 ° C at a rate of 5 to 15 ° C per minute,
Also, the 2) curing step may be performed after the temperature is raised for 0.5 to 1 hour,
Further, the carbonization step 3) is characterized in that nitrogen is injected and the temperature is raised to 900 to 1,100 ° C.,
And 3) in the carbonization step, the temperature is raised at a rate of 3 to 5 ° C per minute,
And 3) the carbonization step is carried out after the temperature is raised for 1 to 3 hours.
delete delete delete delete The method according to claim 1,
Wherein the curing is performed by oxidation.
delete The method according to claim 1,
Wherein the carbon fibers in the dispersion are dispersed in an amount of 0.02 wt% to 0.5 wt%.
The method according to claim 1,
Wherein the thermosetting resin is selected from the group consisting of a phenol resin, a polyurethane resin, a melamine resin, an epoxy resin, and a mixture thereof.
The method according to claim 1,
Wherein the step of applying pressure during the curing step is performed under a pressure of 0.2 bar to 5 bar.
A carbon paper for a fuel cell produced by the manufacturing method according to claim 1.
11. A fuel cell comprising the carbon paper for a fuel cell according to claim 11 as a gas diffusion layer.

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