KR20070049809A - Separator for fuel cell, method of producing same and fuel cell system comprising same - Google Patents

Abstract

The present invention relates to a fuel cell separator, a method for manufacturing the same, and a fuel cell system including the same, wherein the separator includes a carbon-based additive and a polymer matrix.

The separator of the present invention has a very low gas permeability, high conductivity, and can be formed in a thin thickness, thereby providing a fuel cell having excellent physical properties.

Separator, Fuel Cell, Carbon Additive, Polymer Matrix

Description

A separator for a fuel cell, a method for manufacturing the same, and a fuel cell system including the same TECHNICAL FIELD

1 is a view schematically showing an example of a fuel cell separator of the present invention.

2 schematically shows another example of a fuel cell separator of the present invention.

3 is a view schematically showing another example of a fuel cell separator of the present invention.

4 is a schematic diagram schematically showing a configuration of a fuel cell system of the present invention.

[Industrial use]

The present invention relates to a fuel cell separator, a manufacturing method thereof, and a fuel cell system including the same, and more particularly, to a fuel cell separator having excellent strength, a manufacturing method thereof, and a fuel cell system 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. This fuel cell is a clean energy source that can replace fossil energy, and has the advantage of generating a wide range of outputs by stacking unit cells, and having an energy density of 4-10 times that of a small lithium battery. It is attracting attention as a compact and mobile portable power source.

Representative examples of the fuel cell include a polymer electrolyte fuel cell (PEMFC) and a direct oxidation fuel cell (Direct Oxidation Fuel Cell). When methanol is used as a fuel in the direct oxidation fuel cell, it is called a direct methanol fuel cell (DMFC).

The polymer electrolyte fuel cell is a clean energy source that can replace fossil energy, and has a high power density and energy conversion efficiency, can be operated at room temperature, and can be miniaturized and encapsulated. It can be widely used in fields such as portable power supply and military equipment.

The polymer electrolyte fuel cell has an advantage of having a high energy density and a high output, but requires attention to handling hydrogen gas and reforms fuel for reforming methane, methanol, natural gas, etc. to produce hydrogen as fuel gas. There is a problem that requires additional equipment such as a device.

On the other hand, the direct oxidation fuel cell has a lower energy density than the polymer electrolyte fuel cell, but it is easy to handle fuel and has a low operating temperature, and thus can be operated at room temperature, and in particular, there is no need for a fuel reforming device.

In such fuel cell systems, the stack that substantially generates electricity may comprise several to tens of unit cells consisting of a membrane / electrode assembly (MEA) and a separator (or bipolar plate). It has a laminated structure. The membrane / electrode assembly is called an anode electrode (also called "fuel electrode" or "oxide electrode") and a cathode electrode (also called "air electrode" or "reduction electrode") with a polymer electrolyte membrane containing a hydrogen ion conductive polymer therebetween. Has a bonded structure.

An object of the present invention is to provide a fuel cell separator having excellent strength.

Another object of the present invention is to provide a fuel cell separator in which gas permeation is suppressed.

Another object of the present invention is to provide a method for producing the separator.

Still another object of the present invention is to provide a fuel cell system including the separator.

In order to achieve the above object, the present invention is a carbon-based additive; And it provides a fuel cell separator comprising a polymer matrix.

The invention also mixes a polymer with a carbonaceous additive; Injecting the mixture into a molding and heat-treating; It provides a method for producing a separator for fuel cells comprising the step of curing the heat treatment product.

The invention also provides an anode electrode and a cathode electrode located opposite each other; And a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode; And at least one electricity generating unit including the separator and generating electricity through an electrochemical reaction between a fuel and an oxidant. A fuel supply unit supplying fuel to the electricity generation unit; And an oxidant supply unit supplying an oxidant to the electricity generation unit.

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

The present invention is in close contact with both sides of a membrane electrode assembly (MEA) in a fuel cell, separates each membrane electrode assembly, and the fuel and oxidant required for the reaction of the fuel cell anode electrode of the membrane electrode assembly And a separator (also known as a bipolar plate) that serves as a passage for supplying to the cathode electrode and a conductor that connects the anode electrode and the cathode electrode in series in each membrane-electrode assembly.

Such a separator should have strong corrosion resistance and no gas permeability. Conventional separators are manufactured by machining metal or by forming or pressing graphite, but metal separators are not preferable due to deterioration of battery characteristics due to corrosion due to oxygen generated in fuel cells and shortened lifetime. The graphite separator is not economical as the processing cost for forming the flow channel is expensive, and also fragile and porous, there is a problem in that the gas permeability when broken or less than a certain thickness during machining.

In order to solve this problem, there have been attempts to use a carbon-carbon composite form, but this method has also been difficult to solve the above-mentioned problems.

The separator of the present invention includes a polymer matrix and a carbon-based additive, and may be manufactured by the following process.

A mixture is prepared by mixing a polymer resin and a carbon-based additive. At this time, the mixing ratio of the polymer resin and the carbon-based additive can be appropriately adjusted within the range for obtaining the effect of the present invention.

The mixing process may be carried out by any method of a general mixing method such as ball milling, kneading or mixing.

Thermosetting or thermoplastic resins may be used as the polymer resin, and representative examples thereof include phenol resins, epoxy resins, polyanilines, and polyolefins. Polyolefin, polypropylene, etc. can be used as a polyolefin.

As the carbon-based additive, one or a mixture of two or more graphites such as carbon nanotubes, carbon nanofibers, carbon black or flaky graphite, mesocarbon microbeads (MCMB), mesocarbon fibers (MCF), and the like may be used. These carbon-based additives serve as a reinforcing material for maintaining the mechanical strength of the separator to be prepared and a conductive material to help the electron conducting role.

In this case, the carbon-based additive may be used as it is, or may be used after first performing a pretreatment for introducing the reactor. The reactor introduction pretreatment step is performed by introducing a reactor and subjecting it to an oxidation treatment. The reactor introduction process may be performed by a silane treatment method, and the oxidation treatment process may be performed by an acid washing and a heat treatment process. The acid washing process is a process of washing the carbon-based additive subjected to the reactor introduction process with an acid such as sulfuric acid, and the heat treatment process is a process of heat-treating the washed carbon-based additive in the air at a temperature of about 500 ° C. or less. To be carried out.

According to the reactor introduction pretreatment process, a carbon-based additive having a reactor such as oxygen introduced on the surface thereof is obtained. When the carbon-based additive introduced into the surface of the reactor is mixed with the polymer as described above, the additive and the polymer matrix are very strongly chemically bonded, which is preferable because the gas permeation phenomenon that may occur at the interface can be further suppressed.

After inject | pouring the said mixture into the mold of a desired shape, it heat-processes and hardens and manufactures the separator of this invention. The heat treatment step can be carried out at an appropriate temperature according to the type of polymer resin and carbon-based additive used.

 The separator of the present invention prepared as described above includes a polymer matrix and a carbon-based additive, and a schematic structure thereof is shown in FIGS. 1 to 3. As shown in Figures 1 to 3, the separator of the present invention is one or two or more carbon-based additives in the polymer matrix 10, nanofiber 30, a single particle form or agglomeration form thereof (50) And carbon-based particles 70.

Since the separator of the present invention is not porous, the gas permeability is very low, the conductivity of the carbon-based additive is very high, and the strength is excellent, and thus the thin film can be formed.

The fuel cell system of the present invention including the separator of the present invention includes at least one electricity generating section, a fuel supply section and an oxidant supply section.

The electricity generation unit includes a polymer electrolyte membrane, cathode and anode electrodes and separators present on both sides of the polymer electrolyte membrane, and serves to generate electricity through an electrochemical reaction between a fuel and an oxidant.

The fuel supply unit serves to supply fuel containing hydrogen to the electricity generator, and the oxidant supply unit serves to supply an oxidant such as oxygen or air to the electricity generator.

A schematic structure of the fuel cell system of the present invention is shown in FIG. 4, which will be described in more detail with reference to the following. The fuel cell system 100 of the present invention includes a stack 7 having at least one electricity generating unit 19 for generating electrical energy through an electrochemical reaction between fuel and an oxidant, and a fuel supply source for supplying the fuel. (1) and the oxidant supply source 5 which supplies an oxidant to the electricity generation part 19, and is comprised.

In addition, the fuel supply source 1 for supplying the fuel has a fuel tank 9 for storing fuel and a fuel pump 11 connected to the fuel tank 9. The fuel pump 11 serves to discharge fuel stored in the fuel tank 9 by a predetermined pumping force.

The oxidant source 5 for supplying the oxidant to the electricity generating unit 19 of the stack 7 has at least one air pump 13 which sucks air with a predetermined pumping force.

The electricity generating unit 19 is a membrane-electrode assembly 21 for oxidizing and reducing an oxidant in fuel and air, and a separator 23 for supplying air containing fuel and an oxidant to both sides of the membrane-electrode assembly. 25).

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

(Example 1)

The mixture was prepared by ball milling graphite with a phenolic resin, and the mixture was injected into a mold in which a flow path was designed. Then, it was heat treated and cured to prepare a separator.

(Comparative Example 1)

Graphite having flow channel formed therein was used as a separator.

(Comparative Example 2)

A carbon / carbon composite having a flow channel formed therein was used as the separator.

As a result of comparing the gas permeability and conductivity of the separators of Example 1 and Comparative Examples 1 to 2, the gas permeability of Example 1 was low and the conductivity was excellent.

As described above, the separator of the present invention has a very low gas permeability, high conductivity, and can be formed in a thin thickness, thereby providing a fuel cell having excellent physical properties.

Claims (14)

Carbon-based additives; And Polymer matrix Separator for a fuel cell comprising a. The method of claim 1, The polymer is a thermosetting or thermoplastic resin separator for fuel cells. The method of claim 2, The polymer is a fuel cell separator that is selected from the group consisting of phenol resin, epoxy resin, polyaniline and polyolefin. The method of claim 1, The carbon-based additive is selected from the group consisting of carbon nanotubes, carbon nanofibers, graphite and carbon black separator for fuel cells. The method of claim 1, The fuel cell bipolar plate further comprises a reactor on the surface of the fuel cell separator. Mixing the polymer and the carbonaceous additive; Injecting the mixture into a mold for heat treatment; Curing the heat treatment product The manufacturing method of the separator for fuel cells containing a process. The method of claim 6, The carbon-based additive is selected from the group consisting of carbon nanotubes, carbon nanofibers, graphite, and carbon black. The method of claim 6, The carbon-based additive is a method for producing a separator for fuel cells that is subjected to a reactor pretreatment step. The method of claim 8, The reactor introduction pretreatment step includes a reactor introduction step and an oxidation treatment step. An anode electrode and a cathode electrode located opposite each other; And a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode; And a separator including a carbon-based additive and a polymer matrix, wherein the separator includes at least one electricity generator configured to generate electricity through an electrochemical reaction between a fuel and an oxidant; A fuel supply unit supplying fuel to the electricity generation unit; And Oxidant supply unit for supplying an oxidant to the electricity generating unit Fuel cell system comprising a. The method of claim 10, The polymer is a thermoset or thermoplastic resin. The method of claim 11, Wherein said polymer is selected from the group consisting of phenol resins, epoxy resins, polyaniline and polyethylene. The method of claim 10, The carbon-based additive is selected from the group consisting of carbon nanotubes, carbon nanofibers, graphite and carbon black. The method of claim 10, The fuel cell bipolar plate further comprises a reactor on the surface.

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