KR20100094907A - Separator for fuel cell and method of manufacturing the separator - Google Patents

Abstract

PURPOSE: A separator for a fuel cell is provided to secure corrosion resistance and electrical conductivity by forming a surface layer into a polymer composite in which a conductive additive is dispersed and to reinforce adhesive force of a carbon paper layer by forming a conductive adhesive layer in advance. CONSTITUTION: A separator for a fuel cell comprises: a conductive substrate(110); a conductive adhesive layer(120) which is formed on the surface of the conductive substrate; a carbon paper layer(130) which is formed on the conductive adhesive layer; and a surface layer(140) which is formed on the carbon paper layer and is comprised of a polymer composite in which a conductive additive is dispersed.

Description

Separator for fuel cell and its manufacturing method {SEPARATOR FOR FUEL CELL AND METHOD OF MANUFACTURING THE SEPARATOR}

The present invention relates to a separator for a fuel cell and a method of manufacturing the same. More particularly, after coating a conductive composite having excellent adhesion to a surface of a conductive substrate to improve conductivity and corrosion resistance, conductive carbon paper (Carbon Paper) And a surface layer made of a composite in which a conductive additive is dispersed in a polymer, thereby improving contact resistance and corrosion resistance, and having a processability suitable for mass production, and a method for manufacturing the same.

A fuel cell is a cell that directly converts chemical energy generated by the oxidation of fuel into electrical energy. In order to overcome the problems of depletion of fossil fuel, greenhouse effect due to carbon dioxide generation and global warming, etc. A lot of research is being done together.

Since a unit cell of a fuel cell has low voltage and low practicality, generally, several to hundreds of unit cells are stacked and used. In the stacking of unit cells, a separator is used to make an electrical connection between each unit cell and to separate a reaction gas, and a stack is connected to a plurality of separators.

Conventional fuel cell separators were manufactured by milling graphite in accordance with a flow path shape. In this case, the graphite separator took up 50% of the stack and 80% of the weight. Therefore, the graphite separator has problems such as high cost and large volume.

In order to overcome the problems of the graphite separator plate, a metal separator plate has been developed, the metal separator plate has a number of advantages, such as easy to process, lowering the manufacturing cost. The metal separator is developed around stainless steel, and has excellent competitiveness in terms of workability, contact resistance, and price.

On the other hand, the separation plate of the metal material must be electrically connected to each unit cell, it should be provided with sufficient conductivity. In addition, since the environment inside the fuel cell is high in the concentration of hydrogen ions and easily corroded at a high temperature, the surface of the metal separator should have sufficient corrosion resistance.

To this end, studies of coating gold, platinum, tungsten, etc., which are highly resistant to corrosion on the surface of the metal separator plate have been conducted. However, since the coating materials also correspond to expensive metals, it is expensive to manufacture the separator plate. This problem still remained.

In order to solve the problem of the metal separator, recently, a separator in the form of coating a composite material such as a polymer in which conductive filler is dispersed on a metal plate or covering a metal plate with carbon nanotubes has been studied. Such fuel cell separators are excellent in conductivity, and have advantages in that they are inexpensive materials compared to expensive metal coating materials such as gold and platinum, but are prone to breakage.

An object of the present invention is to improve the adhesion between the substrate and the carbon paper (Carbon Paper) layer using a conductive composite material with excellent adhesion, and to form the surface of the separator plate as a composite in which a conductive additive is dispersed in a polymer, the contact resistance and corrosion resistance An improved fuel cell separator is provided.

Another object of the present invention is to provide a method of manufacturing a separator for a fuel cell, which has a fairness suitable for mass production, and has a property of not increasing contact resistance when forming a surface layer with a composite in which a conductive additive is dispersed in a polymer.

Separation plate for a fuel cell according to the present invention for achieving the above object is a conductive substrate; A conductive adhesive layer formed on a surface of the conductive substrate; A carbon paper layer formed on the conductive adhesive layer; And a surface layer formed on the carbon paper layer and comprising a composite in which a conductive additive is dispersed in a polymer.

Separating method for manufacturing a fuel cell according to the present invention for achieving the above another object comprises the steps of: (a) coating a conductive adhesive layer on the conductive substrate; (b) adhering a carbon paper layer on the conductive adhesive layer; And (c) forming a surface layer on the carbon paper layer as a composite having conductive additives dispersed in a polymer.

In this case, the surface layer is formed by compressing and molding the plate made of the composite using a compression / molding apparatus, a screen printing method, a dipping method, a tape casting method, and a painting process. It can be formed by coating the coating liquid composition containing the composite by any one of the method) and doctor blade (doctor blade) method.

The separator for a fuel cell according to the present invention has the effect of simultaneously securing corrosion resistance and electrical conductivity by forming a surface layer of a composite in which a conductive additive is dispersed in a polymer, and also requires a lower cost than the method through growth of carbon nanotubes. There is an advantage that the adhesive strength of the carbon paper layer can be enhanced by forming a conductive adhesive layer having excellent adhesion in advance while using the carbon paper.

In addition, the method of manufacturing a separator for a fuel cell according to the present invention uses a compression molding method, a screen printing method, a dipping method, a tape casting method, a painting method, a doctor blade method, and the like when forming a surface layer with a composite in which a conductive additive is dispersed in a polymer. The surface layer can be easily formed, and the mass production is possible as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, and only the embodiments make the disclosure of the present invention complete, and those skilled in the art to which the present invention pertains. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

Hereinafter, a separator for a fuel cell and a method of manufacturing the same according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Separator for Fuel Cell

1 schematically shows a separator for a fuel cell according to an embodiment of the present invention.

Referring to FIG. 1, a separator for a fuel cell according to the present invention includes a conductive substrate 110, a conductive adhesive layer 120, a carbon paper layer 130, and a surface layer 140.

Conductive substrate

The conductive substrate 110 may be stainless steel, aluminum, copper, or the like, and may have a thickness of about 0.1 to 3 mm. When the back surface of the substrate is not patterned as shown in FIG. 1, the thickness of the substrate may be relatively thinner, and when the back surface of the substrate is patterned as shown in FIG. 2, the thickness of the substrate may be relatively thick.

Conductive Adhesive Layer

The conductive adhesive layer 120 is formed on the surface of the conductive substrate 110 and is formed of a material having excellent adhesion.

The conductive adhesive layer 120 may be formed of a composite material in which a conductive additive is dispersed in a polymer. The polymer may be a thermoplastic resin such as polyethylene, polypropylene, polyamide imide, or a thermosetting resin such as polyethylene.

Meanwhile, the conductive additive dispersed in the polymer may impart conductivity of the conductive adhesive layer 120, and may be carbon black, graphite, carbon fiber, conductive carbon such as carbon nanotubes, silver coated copper, or the like having excellent electrical conductivity. .

The amount of such conductive additives is preferably added at 35 to 65% by weight of the total weight of the conductive adhesive layer, more preferably can present 60% by weight. When the amount of the conductive additive is less than 35% by weight, sufficient conductivity cannot be imparted to the conductive adhesive layer, and when the amount of the conductive additive exceeds 65% by weight, the conductivity is excellent because the contact resistance is lowered, but the adhesive strength is lowered. There is this.

The conductive adhesive layer 120 may be formed to a thickness of 0.01 ~ 200㎛, the thinner the thickness of the conductive adhesive layer 120, the better the conductivity is preferably formed as thin as possible.

Carbon Paper Layer

The carbon paper layer 130 is formed on the conductive adhesive layer 120 in the form of a thin sheet made of graphite, which is a nonmetal and has excellent electrical conductivity.

In the present invention, the carbon paper layer 130 serves to supplement the contact resistance of the separator plate for fuel cells and to suppress corrosion of the conductive substrate. In the related art, there is no layer that can replace the carbon paper layer 130. Although not present, it is more expensive than carbon paper and manufactured by a carbon nanotube growth method in which adhesion to a conductive substrate is weak.

However, in the present invention, in order to replace the carbon nanotubes by using relatively inexpensive carbon paper and to improve the adhesion to the conductive substrate 110, the conductive adhesive layer having excellent adhesion in advance before the carbon paper layer 130 is formed ( Forming 120 can solve the problems of conventional cost and adhesion.

The carbon paper layer 130 may be formed to a thickness of approximately 0.01 μm to 1 mm. If the thickness of the carbon paper layer is less than 0.01㎛, the contact resistance properties are reduced, if the thickness of the carbon paper layer exceeds 1mm, the contact resistance properties can be improved, but there is a problem that the flow path is difficult to form.

Surface layer

The surface layer 140 is formed on the carbon paper layer 130 and is formed of a composite in which a conductive additive is dispersed in a polymer.

The surface layer 140 serves to protect the conductive substrate 110 and the carbon paper layer 130 to improve the corrosion resistance of the separator for fuel cell. In addition, the polymer included in the surface layer 140 is a more flexible material such as metal, graphite, etc. to increase the bending strength of the separator plate and to facilitate the formation of flow paths through which fuel and air flow on the surface of the separator plate for fuel cells. do.

In addition, the surface layer 140 is a conductive additive excellent in electrical conductivity is dispersed in the polymer. Accordingly, the conductive substrate 110 is electrically connected to the outside through the conductive additives of the carbon paper layer 130 and the surface layer 140, and electrically connects each unit cell constituting the fuel cell.

In order to play the role, the surface layer 140 is preferably added in an amount of 35 to 55% by weight of the polymer and 45 to 65% by weight of the conductive additive. If the conductive additive is added below 45% by weight, there is a concern that the contact resistivity may be increased. When the conductive additive exceeds 65% by weight, the content of the polymer may be relatively low, which may lower the bending strength of the separator.

Of the materials constituting the surface layer 140, the polymer preferably has heat resistance at a temperature of approximately 60 ~ 250 ℃ to sufficiently endure the temperature inside the fuel cell, such a polymer is a thermosetting polymer epoxy resin (Epoxy resins, phenolic resins, furan resins, vinyl esters, and the like, and are thermoplastic polymers such as polypropylene, polyamide imide, and polyvinylidene fluoride. (poly (binylidene fluoride)), polyethylene (Polyethylene), polyphenylene sulfide (Poly (phenylene sulfide)), poly (phenylene oxide) (Poly (phenylene oxide)) and the like. These polymers can be used individually or in mixture of 2 or more.

In addition, among the materials constituting the surface layer 140, the conductive additives dispersed in the polymer may be carbon black, graphite, carbon fiber, conductive carbon such as carbon nanotubes, silver coated copper, etc. having excellent electrical conductivity. These materials may be used alone or in combination of two or more thereof.

The separator for fuel cells according to the present invention may have a low contact resistivity of about 10 to 100 mPa · cm ² by the conductive additive included in the carbon paper layer 130 and the surface layer 140.

In order to concentrate the flow of current between the conductive substrate 110 and the outside and increase the surface area to increase the efficiency of dissipating heat inside the fuel cell, the surface layer 140 may be patterned as shown in FIG. 1.

Figure 2 schematically shows a separator for a fuel cell according to another embodiment of the present invention.

The fuel cell separator shown in FIG. 2, like the fuel cell separator shown in FIG. 1, is formed on a conductive substrate 110, such as stainless steel, aluminum, copper, and the surface of the conductive substrate 110. Carbon in the form of a thin sheet formed of a conductive adhesive layer 120 formed of a composite material having excellent adhesion and the like, and a graphite formed on the conductive adhesive layer 120 and having a non-metal and excellent conductivity. It is formed on the paper layer 130 and the carbon paper layer 130, and comprises a surface layer 140 made of a composite in which a conductive additive is dispersed in a polymer.

In FIG. 2, the back surface of the conductive substrate 110 is patterned by etching or the like. This is for the same purpose as the patterning of the surface layer 140 described above, in order to concentrate the current flow between the substrate and the outside and to widen the surface area so as to easily release heat inside the fuel cell.

Method for manufacturing separator for fuel cell

3 is a flowchart schematically illustrating a method of manufacturing a separator for a fuel cell according to an embodiment of the present invention.

Referring to FIG. 3, the method of manufacturing a separator for a fuel cell according to the present invention includes a conductive adhesive layer forming step S310, a carbon paper layer forming step S320, and a surface layer forming step S330.

In the conductive adhesive layer forming step (S310), a conductive composite having excellent adhesiveness is coated on the conductive substrate to form a conductive adhesive layer. The conductive adhesive layer serves to increase the adhesion of the carbon paper layer while maintaining conductivity.

In the forming of the carbon paper layer (S320), in order to compensate for the contact resistance of the separator plate for fuel cell, carbon paper having a thin sheet shape of graphite is adhered on the conductive adhesive layer.

In the surface layer forming step (S330), a surface layer is formed on the carbon paper layer as a composite in which a conductive additive is dispersed in a thermoplastic or thermosetting polymer having heat resistance at 60 to 250 ° C.

The method of forming the surface layer may be made by using a compression / molding apparatus after preparing a composite in which a conductive additive is dispersed in a polymer into a plate shape. In addition, the method for forming the surface layer is prepared by the coating liquid composition comprising the composite, screen printing (dipping), tape casting (tape casting), painting (painting) method and doctor blade coating by a (doctor blade) method or the like can be used.

When the compression / molding apparatus is used among the surface layer forming methods, there is an advantage suitable for mass production, but the physical force is applied to the composite during the compression and molding process, so that the contact resistance of the surface layer may be increased after the separation plate is formed. Therefore, it is more preferable to use the coating method without such a concern.

After the surface layer is formed, the surface layer may be patterned by etching or the like to concentrate the flow of current between the conductive substrate 110 and the outside, and the surface area may be increased to facilitate heat dissipation.

Contact Resistance Characteristics of Fuel Cell Separator

4 is a graph showing the contact resistance characteristics of the separator plate for a fuel cell according to the present invention.

According to the present invention, a carbon paper was attached to stainless steel, and a fuel cell separator plate (Coating with attached carbon paper) coated with polyamide imide to which 40 wt% carbon black was added as a surface layer was prepared.

On the other hand, as a comparison group for comparing the contact resistance characteristics, a coating plate coated with a polyamide imide containing carbon black added to 40% by weight of a separator plate made of stainless steel (304 steel), stainless steel without a carbon paper layer A separator plate (Only PAI / carbon coating) and a separator plate in which carbon nanotubes were grown on stainless steel were used.

Referring to FIG. 4, in the case of a fuel cell separating plate, in which a carbon paper is attached to a stainless steel substrate and a surface layer in which a conductive additive is added to the polymer according to the present invention, a contact specific resistance is approximately 20 mΩ. It can be confirmed that it is about cm ² .

This corresponds to a value having a contact resistivity similar to that of a coating plate made with carbon nanotubes grown on a stainless steel substrate.

As described above, in the case of carbon nanotube growth, carbon nanotubes are grown mainly by chemical vapor deposition, and thus, manufacturing costs are higher than those of carbon paper. There is a problem falling.

In addition, when aluminum is selected as the conductive substrate, aluminum has a low melting point, making it difficult to grow carbon nanotubes. That is, in the case of carbon nanotube growth, the material of the conductive substrate is affected. However, carbon paper is not affected by the material of the conductive substrate.

Therefore, in order to bond the carbon paper on the conductive substrate, but first to form a conductive adhesive layer made of a composite material having excellent adhesion and to bond the carbon paper in order to supplement the problem of adhesion, excellent contact resistance characteristics and excellent conductive substrate even at low cost There is an advantage that can show the adhesion to.

On the other hand, in the case of the stainless steel separator plate (304 steel) and the separator plate (only PAl / carbon coating) in which only the surface layer with the conductive additive is added to the polymer without the carbon paper layer, the contact resistance is relatively high because of the relatively high contact resistivity. You can see it falling.

5 is a graph showing contact resistance characteristics of the separator plate bonded with carbon paper according to the present invention.

For the measurement, according to the present invention, a carbon paper (Carbon paper) was attached to an aluminum substrate as a conductive substrate, and a separation plate was manufactured by molding by hot pressing using polypropylene to which carbon black was added at 60% by weight. On the other hand, in the comparative group, a car separator plate coated with a polyamide imide in which 40% by weight of carbon black was added to the aluminum substrate without a carbon paper layer was prepared.

Referring to FIG. 5, when the carbon paper was attached to the aluminum substrate as in the present invention, the contact specific resistance was about 30 mΩ · cm ^2. However, when carbon black was spray coated on the aluminum substrate, 70 mΩ The contact resistivity value was more than two times higher than that of carbon paper attached to about cm ² .

Although the above has been described with reference to one embodiment of the present invention, various changes and modifications can be made at the level of those skilled in the art. Such changes and modifications may belong to the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention will be determined by the claims described below.

1 schematically shows a separator for a fuel cell according to an embodiment of the present invention.

Figure 2 schematically shows a separator for a fuel cell according to another embodiment of the present invention.

3 is a flowchart schematically illustrating a method of manufacturing a separator for a fuel cell according to an embodiment of the present invention.

4 is a graph showing the contact resistance characteristics of the separator plate for a fuel cell according to the present invention.

5 is a graph showing contact resistance characteristics of the separator plate bonded with carbon paper according to the present invention.

Claims (20)

Conductive substrates; A conductive adhesive layer formed on a surface of the conductive substrate; A carbon paper layer formed on the conductive adhesive layer; And A separator for a fuel cell formed on the carbon paper layer and including a surface layer made of a composite in which a conductive additive is dispersed in a polymer. The method of claim 1, The substrate is a separator for a fuel cell, characterized in that selected from stainless steel, aluminum and copper. The method of claim 1, The conductive substrate is a separator for a fuel cell, characterized in that the back surface is patterned (patterning). The method of claim 1, The conductive substrate is made of a thickness of 0.1 ~ 3mm, The conductive adhesive layer is formed to a thickness of 0.01 ~ 200㎛, The carbon paper layer is a separator for a fuel cell, characterized in that formed in a thickness of 0.01㎛ ~ 1mm. The method of claim 1, The polymer is composed of at least one of an epoxy resin, a phenol resin, a furan resin, a vinyl ester, polypropylene, polyamide imide, polyvinylidene fluoride, polyethylene, polyphenylene sulfide, and polyphenylene oxide. Separator for fuel cell. The method of claim 1, The conductive additive is a fuel cell separator, characterized in that made of at least one material of carbon black, graphite, carbon fiber, carbon nanotubes and silver coated copper. The method of claim 1, The composite forming the surface layer is a separator for a fuel cell, characterized in that consisting of 35 to 55% by weight of a polymer and 45 to 65% by weight of a conductive additive. The method of claim 1, The conductive adhesive layer is a separator for a fuel cell, characterized in that made of a composite material in which a conductive additive is dispersed in a polymer. The method of claim 8, The polymer is made of at least one material of polyethylene, polypropylene, polyamide imide and polyethylene, The conductive additive is a fuel cell separator, characterized in that made of at least one material of carbon black, graphite, carbon fiber, carbon nanotubes and silver coated copper. The method of claim 8, The conductive adhesive layer is a fuel cell separator, characterized in that consisting of 35 to 70% by weight of the polymer and 30 to 65% by weight of the conductive additive. The method of claim 1, The surface layer is a separator for a fuel cell, characterized in that the patterned. A fuel cell comprising the separator of any one of claims 1 to 11. The method of claim 12, The separator is a fuel cell, characterized in that it has a contact resistivity of 10 ~ 100 mPa · cm ² . (a) coating a conductive adhesive layer on the conductive substrate; (b) adhering a carbon paper layer on the conductive adhesive layer; And (c) forming a surface layer on the carbon paper layer as a composite in which conductive additives are dispersed in a polymer. The method of claim 14, (D) a method for producing a separator for a fuel cell, characterized in that it further comprises the step of patterning the surface layer. The method of claim 14, In the step (c), the plate made of the composite is compressed and molded to form the surface layer of the fuel cell. The method of claim 14, In step (c), the composite may be formed by any one of a screen printing method, a dipping method, a tape casting method, a painting method, and a doctor blade method. Method of manufacturing a separator for a fuel cell, characterized in that to form a surface layer by coating a coating liquid composition comprising. The method of claim 14, The substrate is made of a thickness of 0.1 ~ 3mm, The conductive adhesive layer is formed to a thickness of 0.01 ~ 200㎛, The carbon paper layer is a fuel cell separation plate manufacturing method, characterized in that formed in a thickness of 0.01㎛ ~ 1mm. The method of claim 14, Composite for forming the surface layer is a fuel cell separator manufacturing method, characterized in that consisting of 35 to 55% by weight of the polymer and 45 to 65% by weight of the conductive additive. The method of claim 14, The conductive adhesive layer is a fuel cell separation plate manufacturing method, characterized in that consisting of 35 to 70% by weight of a polymer and 30 to 65% by weight of a conductive additive.

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