KR100599711B1 - Bipolar plate for fuel cell, method of preparing same and fuel cell comprising same - Google Patents

Abstract

The present invention relates to a bipolar plate for a fuel cell, a method for manufacturing the same, and a fuel cell including the same, wherein the bipolar plate has a surface roughness (Ra) of 0.1 to 50 μm, and a metal, a metal, a graphite, and carbon on which a coating layer is deposited. It is formed of a material selected from the group consisting of composites, the flow channel is formed.

The bipolar plate for a fuel cell of the present invention has a controlled surface roughness, so that the cell reaction of the fuel cell can occur smoothly.

Fuel Cell, Bipolar Plate, Hydrophobic Coating

Description

Bipolar plate for fuel cell, manufacturing method thereof, and fuel cell comprising same TECHNICAL FIELD

1 shows schematically an operating state of a fuel cell comprising a bipolar plate of the invention.

Figure 2 schematically shows the structure used when measuring the contact resistance of the bipolar plate of the present invention.

Figure 3 is a graph showing the measurement of the contact resistance of the bipolar plates of Examples 1 to 3.

[Industrial use]

The present invention relates to a bipolar plate for a fuel cell, a method for manufacturing the same, and a fuel cell including the same, and more particularly, to a bipolar plate for a fuel cell that can easily discharge water, a method for manufacturing the same, and a fuel cell including the same.

[Prior art]

A fuel cell is a power generation system that directly converts the chemical reaction energy of hydrogen and oxygen contained in hydrocarbon-based materials such as methanol, ethanol and natural gas into electrical energy.

Fuel cells are classified into phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, polymer electrolyte or alkaline fuel cells, etc., depending on the type of electrolyte used. Each of these fuel cells operates on essentially the same principle, but differs in the type of fuel used, operating temperature, catalyst, electrolyte, and the like.

Among these, the polymer electrolyte fuel cell (PEMFC), which is being developed recently, has superior output characteristics compared to other fuel cells, has a low operating temperature, fast start-up and response characteristics, and is a mobile power source such as an automobile. Of course, it has a wide range of applications, such as distributed power supply for homes, public buildings and small power supply for electronic devices.

Such a PEMFC basically includes a stack, a reformer, a fuel tank, a fuel pump, and the like to constitute a system. The stack forms the body of the fuel cell, and the fuel pump supplies the fuel in the fuel tank to the reformer. The reformer reforms the fuel to generate hydrogen gas and supplies the hydrogen gas to the stack. Accordingly, the PEMFC supplies fuel in the fuel tank to the reformer by operation of a fuel pump, reforming the fuel in the reformer to generate hydrogen gas, and electrochemically reacting the hydrogen gas and oxygen in a stack to generate electrical energy. Let's do it.

In such a fuel cell system, a stack that substantially generates electricity is stacked in units of several to several tens of unit cells including a membrane electrode assembly (MEA) and a bipolar plate that adheres to both surfaces thereof. Has a structure. The membrane / electrode assembly has a structure in which an anode electrode and a cathode electrode are attached with a polymer electrolyte membrane interposed therebetween. The bipolar plate separates each membrane / electrode assembly and serves as a passage for supplying hydrogen gas and oxygen necessary for the reaction of the fuel cell to the anode electrode and the cathode electrode of the membrane / electrode assembly, and the anode of each membrane / electrode assembly. Simultaneously serves as a conductor that connects the electrode and the cathode electrode in series. Thus, hydrogen gas is supplied to the anode electrode through the bipolar plate, while oxygen is supplied to the cathode electrode. In this process, an oxidation reaction of hydrogen gas occurs at an anode electrode, and a reduction reaction of oxygen occurs at a cathode electrode, thereby generating electricity due to the movement of electrons generated, and additionally generating heat and moisture.

SUMMARY OF THE INVENTION An object of the present invention is to provide a bipolar plate for a fuel cell which is easy to discharge water which may be generated during operation of the fuel cell.

Another object of the present invention is to provide a fuel cell comprising the bipolar plate.

In order to achieve the above object, the present invention has a surface roughness (Ra) of 0.1 to 50㎛, is formed of a material selected from the group consisting of metal, metal, graphite and carbon composite on which the coating layer is deposited, Provided is a bipolar plate for a fuel cell.

The invention also includes at least one membrane / electrode assembly comprising an anode and a cathode electrode positioned opposite each other, and a polymer electrolyte membrane positioned between the anode and the cathode electrode; And a bipolar plate having a flow channel for contacting any one of an anode and a cathode of the membrane / electrode assembly and supplying gas, wherein the bipolar plate has a surface roughness Ra of 0.1 to 50 μm, a metal, Provided is a fuel cell in which a coating layer is formed of a material selected from the group consisting of metal, graphite, and carbon composites on which a coating layer is deposited, and a flow channel is formed.

Hereinafter, the present invention will be described in more detail.

The present invention separates a plurality of membrane / electrode assemblies from a fuel cell, and serves as a passage for supplying hydrogen gas and oxygen required for the reaction of the fuel cell to the anode electrode and the cathode electrode of the membrane / electrode assembly. The present invention relates to a bipolar plate that serves as a conductor connecting an anode electrode and a cathode electrode in series.

Such bipolar plates should have strong corrosion resistance and no gas permeability. In addition, it should be possible to drain the water formed at the cathode during fuel cell operation.

In the present invention, the surface roughness (Ra) of the bipolar plate is adjusted to improve these characteristics. In this specification, surface roughness and Ra means the arithmetic mean value of each peak (peak according to the height of the surface of a bipolar plate).

0.1-50 micrometers is preferable and, as for surface roughness Ra of the bipolar plate of this invention, 1-10 micrometers is more preferable. Lowering the surface roughness value to less than 0.1 [mu] m is very difficult and expensive in the process, and if it is larger than 50 [mu] m, the number of point contact becomes very low and the contact resistance becomes large, thus requiring a larger clamping pressure. However, the excessive clamping pressure is not preferable because the pore structure of the membrane / electrode assembly collapses, resulting in degradation of the membrane / electrode assembly, and the strength of the bipolar plate must also be increased.

The bipolar plate of the present invention is composed of a metal, a metal, graphite or carbon composite having a coating layer deposited on the surface. As the metal, Al, Cu, Ti, or stainless steel may be used, and the coating layer may include Au, Pt, nitrides thereof, borides, oxides or conductive polymers such as polypyrrole, polyaniline, and the like. It is not limited.

The bipolar plate of the present invention can be usefully used in a fuel cell, and the operating state of the fuel cell including the anode (3), the cathode (5), the polymer electrolyte membrane (7) and the bipolar plate (9) in FIG. As shown. The anode 3 and the cathode 5 comprise a catalyst layer in which a metal catalyst participating in an electrochemical reaction is supported on carbon. In the fuel cell, hydrogen or fuel is supplied to the anode 3 and oxygen is supplied to the cathode 5 to generate electricity by the electrochemical reaction of the anode and the cathode. That is, an oxidation reaction of the organic fuel occurs at the anode 3 and a reduction reaction of oxygen occurs at the cathode 5 to generate a voltage difference between the two electrodes.

The polymer electrolyte membrane is made of a proton-conducting polymer material, i.e., an ionomer, and is generally a tetrafluoroethylene and fluorovinyl ether copolymer containing sulfonic acid groups, defluorinated sulfided polyether ketones, aryl ketones or Polybenzimidazole and the like may be used, but the present invention is not limited thereto. In general, the polymer electrolyte membrane has a thickness of 10 to 200㎛.

After stacking the structure shown in FIG. 1 to produce a stack, the fuel cell may be manufactured by inserting the stack between two end plates. Fuel cells can be readily manufactured by conventional techniques in the art.

Hereinafter, examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

(Example 1)

A flow channel having a surface roughness Ra of 1 μm was formed, and a bipolar plate made of stainless steel metal was manufactured.

(Example 2)

A flow channel having a surface roughness Ra of 5 μm was formed, and a bipolar plate made of graphite was manufactured.

(Example 3)

A flow channel having a surface roughness Ra of 10 μm was formed, and a bipolar plate made of a carbon composite material was manufactured.

The contact resistance of the bipolar plates of Examples 1 to 3 was measured. The contact resistance (unit mOhm X cm ² ) flows a current of 1A as shown in FIG. 2, and the measured voltage is measured by multiplying the measured resistance value by the area of the entire specimen. At this time, the compressive stress was measured while changing to 50, 100, 200N / cm ² . In Figure 2, R _{c / Cu} represents the resistance between the carbon paper and the copper plate, R _{c / ss} represents the resistance of the carbon paper and stainless steel.

The measured contact resistance is shown in FIG. 3, and as shown in FIG. 3, it can be seen that the contact resistance increases as the surface roughness of the bipolar plate is changed. That is, when the surface roughness is increased, the contact resistance is increased because the number of actual point contacts is not reduced between the bipolar plate and the gas diffusion layer layer, and the contact resistance is increased, so that the conductivity is lowered and the performance of the overall fuel cell is not preferable.

As described above, the bipolar plate for a fuel cell of the present invention has a controlled surface roughness so that the cell reaction of the fuel cell can occur smoothly.

Claims (6)

 It is formed of a material selected from the group consisting of a metal, a metal on which the coating layer is deposited, graphite and carbon composite, a reactant flow channel is formed, Surface roughness (Ra) of the surface on which the reactant flow channel is formed is 0.1 to 50㎛ Bipolar plate for fuel cell. The bipolar plate of claim 1, wherein the surface roughness Ra is 1 to 10 μm. The bipolar plate according to claim 1, wherein the metal and the metal on which the coating layer is deposited are selected from the group consisting of Al, Ti, Cu, Fe, Ni, and stainless steel. At least one membrane / electrode assembly comprising an anode and a cathode electrode positioned opposite each other, and a polymer electrolyte membrane positioned between the anode and the cathode electrode; And a bipolar plate having a flow channel for supplying a gas by contacting any one of an anode and a cathode of the membrane / electrode assembly. The bipolar plate is formed of a material selected from the group consisting of a metal, a metal on which a coating layer is deposited, graphite and a carbon composite, a reactant flow channel is formed, and the surface roughness Ra of the surface on which the reactant flow channel is formed is The fuel cell is 0.1 to 50㎛. The fuel cell of claim 4, wherein the surface roughness Ra is 1 to 10 μm. The fuel cell of claim 4, wherein the metal and the metal on which the coating layer is deposited are selected from the group consisting of Al, Ti, Cu, Fe, Ni, and stainless steel.

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