KR20060001741A - A electrode for fuel cell and a fuel cell comprising the same - Google Patents

Abstract

The present invention relates to a fuel cell electrode and a fuel cell comprising the same, the fuel cell electrode comprising a catalyst layer; 20 μm to 80 μm A microporous layer having a thickness; And a gas diffusion layer made of a conductive substrate. The fuel cell includes at least one membrane / electrode assembly including an anode and a cathode electrode facing each other, and a polymer electrolyte membrane located between the anode and the cathode electrode; And a bipolar plate formed on both sides of the membrane / electrode assembly in contact with the anode and the cathode electrode and having a flow channel for supplying gas, wherein at least one of the anode and the cathode electrode comprises: a catalyst layer; 20 μm to 80 μm A microporous layer having a thickness; And a gas diffusion layer made of a conductive substrate.

Fuel cell, microporous layer, gas diffusion layer, membrane / electrode assembly

Description

A fuel cell electrode and a fuel cell including the same {A ELECTRODE FOR FUEL CELL AND A FUEL CELL COMPRISING THE SAME}

1 is a view schematically showing an operating state of a fuel cell including a polymer electrolyte membrane.

<Description of the symbols for the main parts of the drawings>

1: fuel cell 3: anode

5: cathode 7: polyelectrolyte membrane

[Industrial use]

The present invention relates to a fuel cell electrode and a fuel cell including the same, and more particularly, to a fuel cell electrode and a fuel cell including the microporous layer having a predetermined range of thickness to improve gas dispersion efficiency. It is about.

[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 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. Thus, the PEMFC supplies fuel in the fuel tank to the reformer by operation of the fuel pump, reforming the fuel in the reformer to generate hydrogen gas, and electrochemically reacting the hydrogen gas and oxygen in the stack to generate electrical energy. Let's do it.

In such a fuel cell system, a stack that substantially generates electricity is stacked with several to several tens of unit cells including a membrane electrode assembly (MEA) and a bipolar plate that adheres to both sides thereof. Has a structure. The membrane / electrode assembly has a structure in which an anode electrode and a cathode electrode are coupled with an electrolyte membrane interposed therebetween. The bipolar plate separates the respective membrane / electrode assemblies 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, and for each membrane / electrode assembly. It simultaneously serves as a conductor that connects the anode and cathode electrodes in series. 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.

An object of the present invention is to provide a fuel cell electrode and a fuel cell including the same that can improve the gas dispersion efficiency by including a microporous layer having a range of thickness.

In order to achieve the above object, a catalyst layer; 20 μm to 80 μm A microporous layer having a thickness; And it provides a fuel cell electrode comprising a gas diffusion layer made of a conductive substrate.

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 formed on both surfaces of the membrane / electrode assembly in contact with the anode and the cathode and having a flow channel for supplying gas.

At least one of the anode and the cathode electrode is a catalyst layer; 20 μm to 80 μm A microporous layer having a thickness; And it provides a fuel cell comprising a gas diffusion layer made of a conductive substrate.

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

The electrode of a fuel cell is generally composed of a catalyst layer and a gas diffusion layer (GDL), and in order to enhance the gas diffusion effect of the gas diffusion layer, a microporous layer having a predetermined thickness range between the catalyst layer and the gas diffusion layer. It includes.

The catalyst layer includes a so-called metal catalyst that catalyzes related reactions (oxidation of hydrogen and reduction of oxygen), and platinum, ruthenium, osmium, platinum-transition metal alloy, and the like may be preferably used. Preferred examples of the platinum-transition metal alloy include platinum-ruthenium, platinum-cobalt, platinum-nickel, platinum-osmium and the like. Oxides of the above metals or alloys may also be used as catalysts. These metal catalysts are preferably supported by a carrier and used. As the carrier, carbon such as acetylene black, graphite, or the like may be used, or inorganic fine particles such as alumina or silica may be used. In the case of using the noble metal supported on the carrier as a catalyst, a commercially available one may be used, or a noble metal supported on the carrier may be prepared and used. Since the process of supporting the precious metal on the carrier is well known in the art, detailed description thereof will be omitted.

The microporous layer is used to enhance the gas diffusion effect, and serves to uniformly supply gas to the catalyst layer and transfer electrons formed in the catalyst layer to the gas diffusion layer. In general, conductive particles having a small particle diameter, such as carbon powder, carbon black, acetylene black, activated carbon, ketjen black, graphite particles, graphite fibers, carbon nanotubes, carbon nanofibers, nanocarbons such as carbon nanowires, carbon nano Horn (carbon nano-horn) and the like. In the present invention, the thickness of the microporous layer may be adjusted to a range of 20 μm to 80 μm, preferably 30 μm to 60 μm, more preferably 40 μm to 50 μm, thereby improving gas dispersion efficiency. The efficiency of the battery can be improved. When the thickness of the microporous layer is less than 20 μm, the gas dispersion efficiency cannot be improved, and when the thickness of the microporous layer is more than 80 μm, the thickness of the electrode becomes thick, which is not preferable.

The microporous layer is prepared by coating a conductive substrate with a composition comprising a conductive powder, a fluorine-based binder resin, and a solvent. The fluorine-based binder resin may be polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), copolymer of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), polyvinyl alcohol, cellulose acetate , Styrene-butadiene rubber (SBR) and the like can be preferably used. The solvent may be an alcohol such as isopropyl alcohol, ethyl alcohol, n-propyl alcohol, butyl alcohol, acetone, water, dimethylacetamide (DMAc), dimethylformamide, dimethyl sulfoxide (DMSO), N-methylpyrrolidone , Tetrahydrofuran and the like can be preferably used. According to the viscosity of the composition, the screen printing method, the spray coating method, the coating method using a doctor blade, the slit die coating method (Slit die), roll coating, etc. may be used, but is not limited thereto. In the present invention, the coating composition preferably has a viscosity of 800 to 15000 cps and more preferably has a viscosity of 4000 to 7000 cps. It is easy to control the thickness of the microporous layer to 20 to 80㎛ only to have a viscosity in the above range.

The gas diffusion layer plays a role of supporting the fuel cell electrode while diffusing the reaction gas into the catalyst layer to easily access the reaction gas to the catalyst layer. The gas diffusion layer is generally composed of a conductive substrate. The carbon paper, carbon cloth, carbon felt, or the like may be used. It is preferable that the thickness of the said gas diffusion layer exists in the range of 200-300 micrometers. The thickness ratio of the fine pore layer and the gas diffusion layer is preferably 1: 4 to 1: 8, more preferably in the range of 1: 5 to 1: 7. When it is in this range, gas dispersion efficiency can be improved. The conductive substrate may be used by water repellent treatment with polytetrafluoroethylene (PTFE).

In the fuel cell, the cathode and the anode electrode are not distinguished by materials but in their role, and the fuel cell electrode is divided into an anode for hydrogen oxidation and a cathode for reducing oxygen. Therefore, the fuel cell electrode of the present invention can be used for both the cathode and the anode electrode. That is, in a fuel cell, hydrogen or fuel is supplied to the anode and oxygen is supplied to the cathode to generate electricity by an electrochemical reaction between the anode and the cathode. An oxidation reaction of hydrogen or organic fuel occurs at the anode and a reduction reaction of oxygen occurs at the cathode to generate a voltage difference between the two electrodes.

FIG. 1 is a view schematically showing an operating state of a fuel cell 1 including an anode 3, a cathode 5, and a polymer electrolyte membrane 7. The electrode of the present invention may be used as the anode 3 and the cathode 5 electrodes. The polymer electrolyte membrane 7 is made of a hydrogen ion-conductive polymer material, i.e., an ionomer, and is generally a tetrafluoroethylene and fluorovinyl ether copolymer containing a sulfonic acid group, and a defluorinated sulfide polyether ketone. , Aryl ketone or polybenzimidazole and the like can be used, but is not limited thereto. In general, the polymer membrane has a thickness of 10 to 200㎛.

The fuel cell inserts a membrane / electrode assembly between a gas flow channel and a bipolar plate on which a cooling channel is formed to fabricate a unit cell, stacks it, and manufactures a stack, and then inserts it between two end plates. Can be prepared. Fuel cells can be readily manufactured by conventional techniques in the art.

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.

(Examples and Comparative Examples: Production of Electrode and Unit Battery)

Platinum-supported carbon powder (Pt / C), polytetrafluoroethylene polymer, and isopropyl alcohol were mixed with a solvent to prepare a coating composition for catalyst layer formation. In addition, isopropyl alcohol was mixed with a carbon powder, a polytetrafluoroethylene polymer, and a solvent to prepare a coating composition for forming a microporous layer. The coating composition for forming the microporous layer was coated on carbon paper to form a microporous layer with a thickness as shown in Table 1 below, and then coated with a coating composition for forming a catalyst layer to prepare an electrode.

The electrode was used as an anode and a cathode, and a Nafion (manufactured by DuPont) polymer membrane was placed therebetween, fired at 130 degrees for about 3 minutes, and hot rolled to prepare a membrane / electrode assembly (MEA).

The prepared membrane / electrode assembly is inserted between two gaskets, and then inserted into two bipolar plates in which a gas flow channel and a cooling channel of a predetermined shape are formed, and then compressed between copper end plates. The battery was prepared. The voltage and current density of the unit cell were measured at 60 ° C. and atmospheric pressure. The current density measurement results at 0.6 V are shown in Table 1 below.

TABLE 1

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Thickness of microporous layer 40 μm 50 μm - 15 μm Current density at 0.6 V (mA / cm ² ) 370 520 200 280

As shown in Table 1, it can be seen that the current density of Examples 1 and 2 according to the present invention is superior to Comparative Examples 1 and 2.

The electrode for a fuel cell of the present invention includes a microporous layer having a predetermined range of thickness between the catalyst layer and the gas diffusion layer to improve gas dispersion efficiency and ultimately improve the efficiency of the battery.

Claims (12)

Catalyst layer; 20 μm to 80 μm A microporous layer having a thickness; And A fuel cell electrode comprising a gas diffusion layer made of a conductive substrate. The electrode of claim 1, wherein the catalyst layer comprises at least one catalyst selected from the group consisting of platinum, ruthenium, osmium, platinum-transition metal alloy, and platinum-transition metal oxide. The fuel cell electrode of claim 1, wherein the microporous layer has a thickness of 40 μm to 50 μm. The electrode of claim 1, wherein a thickness ratio of the microporous layer and the gas diffusion layer is in a range of 1: 4 to 1: 8. The method of claim 1, wherein the microporous layer is selected from the group consisting of carbon powder, carbon black, acetylene black, activated carbon, ketjen black, graphite particles, graphite fiber, nanocarbon, and carbon nano-horn. An electrode for a fuel cell comprising a conductive powder to be. The fuel of claim 1, wherein the microporous layer is formed by a method selected from the group consisting of a screen printing method, a spray coating method, a coating method using a doctor blade, a slit die coating method, and a roll coating method. Battery electrode. 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 formed on both surfaces of the membrane / electrode assembly in contact with the anode and the cathode and having a flow channel for supplying gas. At least one of the anode and the cathode electrode is a catalyst layer; A microporous layer having a thickness of 20 μm to 80 μm; And a gas diffusion layer made of a conductive substrate. The fuel cell of claim 7, wherein the catalyst layer comprises at least one catalyst selected from the group consisting of platinum, ruthenium, osmium, platinum-transition metal alloy, and platinum-transition metal oxide. The fuel cell of claim 7, wherein the microporous layer has a thickness in the range of 40 μm to 50 μm. The fuel cell electrode of claim 7, wherein the thickness ratio of the microporous layer and the gas diffusion layer is in a range of 1: 4 to 1: 8. The method of claim 7, wherein the microporous layer is selected from the group consisting of carbon powder, carbon black, acetylene black, activated carbon, Ketjen black, graphite particles, graphite fiber, nanocarbon, and carbon nano-horn. A fuel cell comprising the conductive powder to be. The fuel of claim 7, wherein the microporous layer is formed by a method selected from the group consisting of a screen printing method, a spray coating method, a coating method using a doctor blade, a slit die coating method, and a roll coating method. battery.

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