KR100570768B1 - 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 including the same, the fuel cell electrode comprising a catalyst layer comprising a metal catalyst, an electrically conductive polymer and a hydrogen ion conductive polymer; And a gas diffusion layer made of a conductive substrate. In addition, the electrode for a fuel cell of the present invention is a catalyst layer; It includes a microporous layer comprising a conductive powder and an electrically conductive polymer 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 having a flow channel for supplying a gas in contact with one of the anode and the cathode of the membrane / electrode assembly, wherein at least one of the anode and the cathode is made of the electrode.

Fuel Cell, Porous Layer, Conductive Particles, Gas Diffusion Layer, Electroconductive Polymer

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 showing an operating state of a fuel cell including a polymer electrolyte membrane.

2 is a graph showing the voltage and current density characteristics of the fuel cells of Examples 1, 2 and Comparative Example 1 according to the present invention.

<Description of Symbols for Main Parts of 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 same that can improve the current conductivity of the electrode.

[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.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel cell electrode and a fuel cell including the same, which include an electrically conductive polymer in a catalyst layer or a microporous layer to improve current conductivity of an electrode and suppress water repellency.

In order to achieve the above object, a catalyst layer comprising a metal catalyst, an electrically conductive polymer and a hydrogen ion conductive polymer; And it provides a fuel cell electrode comprising a gas diffusion layer made of a conductive substrate.

The present invention also provides a catalyst layer; A microporous layer comprising a conductive powder and an electrically conductive polymer; 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 having a flow channel for supplying a gas in contact with one of an anode and a cathode of the membrane / electrode assembly.

At least one of the anode and the cathode electrode is a catalyst layer comprising a metal catalyst, an electrically conductive polymer and a hydrogen ion conductive polymer; And it provides a fuel cell 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 having a flow channel for supplying a gas in contact with one of an anode and a cathode of the membrane / electrode assembly.

At least one of the anode and the cathode electrode is a catalyst layer; It provides a fuel cell comprising a microporous layer comprising a conductive powder and an electrically conductive polymer and 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 includes a microporous layer for enhancing the gas diffusion effect of the gas diffusion layer.

In the present invention, an electrically conductive polymer is added to at least one of the catalyst layer and the microporous layer to increase the current conductivity of the electrode and to suppress water repellency.

First, when an electrically conductive polymer is added to the catalyst layer, the catalyst layer includes a metal catalyst, an electrically conductive polymer, and a hydrogen ion conductive polymer.

The metal catalyst serves to help catalytically related reactions (oxidation of hydrogen and reduction of oxygen), and platinum group metals of the periodic table of elements, that is, platinum, platinum-ruthenium, ruthenium, osmium, and the like may be preferably used. 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. The process of supporting the precious metal on the carrier is well known in the art, and thus detailed description thereof will be omitted.

Examples of the electrically conductive polymer include polythiophene, polyacetylene, polyphenylenevinylene, polyphenylene, polyaniline, polyacene, and mixtures thereof.

 The hydrogen ion conductive polymer may be used as long as it has hydrogen ion conductivity, and preferred examples thereof include tetrafluoroethylene and fluorovinyl ether including poly (perfluorosulfonic acid), polyimide, and sulfonic acid groups. Copolymers, defluorinated sulfide polyetherketones, aryl ketones or poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole) (poly (2,2'-(m-phenylene) ) -5,5'-bibenzimidazole)), poly (2,5-benzimidazole), and the like.

The electrically conductive polymer may be used in a weight ratio of 10 ⁻⁴ to 5: 1 based on the hydrogen ion conductive polymer, and more preferably used in a weight ratio of 0.1 to 0.8: 1. If the electrically conductive polymer is used in an amount less than 10 ^-4 : 1, it is not possible to contribute to the improvement of the current conductivity of the electrode, and when used in an amount greater than 5: 1 there is a problem that the performance of the battery falls, which is not preferable.

In the present invention, the catalyst layer is prepared by adding a supported metal catalyst, an electrically conductive polymer, and a hydrogen ion conductive polymer to a solvent to prepare a composition, and then coating it on a conductive substrate. As the solvent, an alcohol such as isopropyl alcohol, ethanol, butanol, water, dimethylformamide, tetrahydrofuran, methylpyrrolidone or a mixture thereof may be preferably used. The coating process may be a coating method using a doctor blade, a spin coating method, a spray coating method, a gravure coating method, a dip coating method, a silk screen method, a painting method, etc., depending on the viscosity of the composition, but is not limited thereto.

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. The conductive substrate may be used after water repellent treatment with the electrically conductive polymer.

The electrically conductive polymer may be added to the microporous layer. That is, in the present invention, the microporous layer includes a conductive powder and an electrically conductive polymer. Preferred examples of the conductive powder include carbon powder, carbon black, acetylene black, activated carbon, nanocarbon, carbon nanotube, and the like. The conductive powder and the electrically conductive polymer are preferably used in a weight ratio of 1: 0.01 to 0.8.

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. As the fluorine-based binder resin, polytetrafluoroethylene (PTFE), polyvinylidene fluoride, or the like may be preferably used. The solvent may be an alcohol such as isopropyl alcohol, butanol, ethanol, tetrahydrofuran, methylpyrroli, etc. Don, dimethylformamide and the like can be preferably used. The coating process may be screen printing, spray coating, or a coating method using a doctor blade according to the viscosity of the composition, but is not limited thereto.

By forming the microporous layer and then forming a catalyst layer, an electrode for a fuel cell may be manufactured. The catalyst layer may contain an electrically conductive polymer.

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. 2 is a schematic view 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 made of poly (perfluorosulfonic acid) and tetrafluoroethylene and fluorovinyl ether air containing sulfonic acid groups. Coalesced, defluorinated sulfided polyetherketones, aryl ketones, poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole) (poly (2,2'-(m-phenylene) -5,5'-bibenzimidazole)), poly (2,5-benzimidazole) 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.

Example 1 Fabrication of Electrode and Unit Cell

4 g of platinum powder (Pt / C) and 10 g of Nafion 5% solution were added to 50 ml of isopropyl alcohol and 50 ml of water. Then, 1 g of polyphenylenevinylene was added thereto and stirred to prepare a coating composition for forming a catalyst layer. The coating composition was coated on carbon paper to form 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 100 ° C. for 30 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.

(Example 2)

10 g of carbon black and 2 g of polytetrafluoroethylene polymer were added to 100 ml of isopropyl alcohol as a solvent, and then 1 g of polyphenylene vinylene was added thereto, followed by stirring to prepare a coating composition for forming a microporous layer. The coating composition was coated on carbon paper and then heat-treated to form a microporous layer. A catalyst layer was formed by coating a catalyst layer-forming composition prepared by adding 4 g of platinum-supported carbon powder (Pt / C) and 10 g of Nafion 5% solution to 50 ml of isopropyl alcohol and 50 ml of water on carbon paper having a microporous layer. An electrode was prepared. A fuel cell was manufactured in the same manner as in Example 1 using the electrode.

(Comparative Example 1)

A catalyst layer was formed by coating a catalyst layer on carbon paper by adding 4 g of platinum-supported carbon powder (Pt / C) and 10 g of Nafion 5% solution to 50 ml of isopropyl alcohol and 50 ml of water to form a catalyst layer. A fuel cell was manufactured in the same manner as in Example 1, except that.

Voltage and current densities of the fuel cells of Examples 1 and 2 and Comparative Example 1 were measured and described in FIG. 2. As shown in FIG. 2, the current densities of Examples 1 and 2 were superior to those of Comparative Example 1. It can be seen that the current conductivity of the electrode of Example 1 and Example 2 was improved.

The electrode for a fuel cell of the present invention includes an electrically conductive polymer in the catalyst layer or the microporous layer, thereby providing excellent current conductivity and suppressing water repellency.

Claims (12)

 A catalyst layer comprising a metal catalyst, an electrically conductive polymer, and a hydrogen ion conductive polymer; And A gas diffusion layer made of a conductive substrate, The electrically conductive polymer is used in a weight ratio of 10 ^-4 to 5: 1 relative to the hydrogen ion conductive polymer, the fuel cell electrode. The electrode of claim 1, wherein the metal catalyst comprises a metal catalyst selected from the group consisting of platinum, platinum-ruthenium, ruthenium, osmium, and mixtures thereof. The electrode of claim 1, wherein the electrically conductive polymer is selected from the group consisting of polythiophene, polyacetylene, polyphenylenevinylene, polyphenylene, polyaniline, polyacene, and mixtures thereof. The method of claim 1, wherein the hydrogen ion conductive polymer is a poly (perfluorosulfonic acid), polyimide, tetrafluoroethylene containing a sulfonic acid group and fluorovinyl ether copolymer, defluorinated sulfide polyether ketone, aryl Ketone or poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole) (poly (2,2'-(m-phenylene) -5,5'-bibenzimidazole)), poly An electrode for a fuel cell, which is at least one selected from the group consisting of (2,5-benzimidazole) and mixtures thereof. delete The electrode of claim 1, wherein the electrically conductive polymer is used in a weight ratio of 0.1 to 0.8: 1 based on the hydrogen ion conductive polymer. Catalyst layer; A microporous layer comprising a conductive powder and an electrically conductive polymer; And A fuel cell electrode comprising a gas diffusion layer made of a conductive substrate. The electrode of claim 7, wherein the metal catalyst comprises a metal catalyst selected from the group consisting of platinum, platinum-ruthenium, ruthenium, osmium, and mixtures thereof. The electrode of claim 7, wherein the conductive powder is selected from the group consisting of carbon powder, carbon black, acetylene black, activated carbon, nanocarbon, carbon nanotubes, and mixtures thereof. The electrode of claim 7, wherein the electrically conductive polymer is selected from the group consisting of polythiophene, polyacetylene, polyphenylenevinylene, polyphenylene, polyaniline, polyacene, and mixtures thereof. The electrode of claim 7, wherein the electrically conductive polymer is used in a weight ratio of 0.01 to 0.8: 1 based on the conductive powder. 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 in contact with one of an anode and a cathode of the membrane / electrode assembly. At least one of the anode and the cathode electrode is a fuel cell comprising the electrode according to any one of claims 1 to 4 and 6 to 11.

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