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  Membrane-electrode assembly for fuel cell and fuel cell system comprising sameUSPTO Application #: 20060105225Title: Membrane-electrode assembly for fuel cell and fuel cell system comprising same Abstract: A membrane-electrode assembly for a fuel cell of the present invention includes an anode and a cathode facing each other, and a polymer electrolyte membrane interposed therebetween. At least one of the anode and the cathode includes a catalyst layer and an electrode substrate. The catalyst layer includes a catalyst and a porous ionomer. The polymer electrolyte membrane contacts one side of the catalyst layer and the electrode substrate contacts the other side of the catalyst layer. (end of abstract)
Agent: Robert E. Bushnell Suite 300 - Washington, DC, US Inventors: Hee-Tak Kim, Hae-Kwon Yoon, Young-Mi Park USPTO Applicaton #: 20060105225 - Class: 429040000 (USPTO) Related Patent Categories: Chemistry: Electrical Current Producing Apparatus, Product, And Process, Fuel Cell, Subcombination Thereof Or Methods Of Operating, Catalytic Electrode Structure Or Composition The Patent Description & Claims data below is from USPTO Patent Application 20060105225. Brief Patent Description - Full Patent Description - Patent Application Claims
CLAIM OF PRIORITY [0001] This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. .sctn.119 from an application for MEMBRANE-ELECTRODE ASSEMBLY FOR FUEL CELL AND FUEL CELL SYSTEM COMPRISING SAME earlier filed in the Korean Intellectual Property Office on 16 Nov. 2004 and there duly assigned Ser. No. 10-2004-0093428. FIELD OF THE INVENTION [0002] The present invention relates to a membrane-electrode assembly for a fuel cell and a fuel cell system comprising the same. More particularly, the present invention relates to a membrane-electrode assembly with high power and to a fuel cell system comprising the same. BACKGROUND OF THE INVENTION [0003] A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant and a fuel such as hydrogen or a hydrocarbon-based material such as methanol, ethanol, or natural gas. [0004] A fuel cell can be classified into a phosphoric acid type, a molten carbonate type, a solid oxide type, a polymer electrolyte type, or an alkaline type depending upon the kind of electrolyte used. Although each of these different types of fuel cells operates in accordance with the same basic principles, they may differ from one another in the kind of fuel, the operating temperature, the catalyst, and the electrolyte used. [0005] Recently, a polymer electrolyte membrane fuel cell (PEMFC) has been developed. The PEMFC has power characteristics that are superior to conventional fuel cells, as well as a lower operating temperature and faster start and response characteristics. Because of this, the PEMFC can be applied to a wide array of fields such as for transportable electrical sources for automobiles, distributed power sources such as for houses and public buildings, and small electrical sources for electronic devices. [0006] A PEMFC is essentially composed of a stack, a reformer, a fuel tank, and a fuel pump. The stack forms a body of the PEMFC, and the fuel pump provides fuel stored in the fuel tank to the reformer. The reformer reforms the fuel to generate hydrogen gas and supplies the hydrogen gas to the stack. Fuel stored in the fuel tank is pumped to the reformer using power which can be provided by the PEMFC. Then, the reformer reforms the fuel to generate the hydrogen gas, and the hydrogen gas is electrochemically oxidized and the oxidant is electrochemically reduced in the stack to generate the electrical energy. [0007] Alternatively, a fuel cell may include a direct oxidation fuel cell (DOFC) in which a liquid fuel is directly introduced to the stack. Unlike a PEMFC, a DOFC does not require a reformer. [0008] In the above-mentioned fuel cell system, the stack for generating the electricity has a structure in which several unit cells, each having a membrane electrode assembly (MEA) and a separator (also referred to as a "bipolar plate"), are stacked adjacent to one another. The MEA is composed of an anode (also referred to as a "fuel electrode" or "oxidation electrode") and a cathode (also referred to as an "air electrode" or "reduction electrode") that are separated by a polymer electrolyte membrane. [0009] The polymer electrolyte membrane can be fabricated using a perfluorosulfonic acid ionomer membrane such as Nafion.RTM. (by DuPont), Flemion.RTM. (by Asahi Glass), Asiplex.RTM. (by Asahi Chemical), and Dow XUS.RTM. (by Dow Chemical). The electrodes including the catalysts supported on the carbon can be fabricated by binding electrode substrates such as porous carbon paper or carbon cloth with a carbon powder carrying pulverized catalyst particles such as platinum (Pt) or ruthenium (Ru) using a water-repellent binder. [0010] What is needed is a high power membrane electrode assembly and a fuel cell system where the transferring rate of the reactant is fast and a high concentration of reactants can be present on the surface of a catalyst. SUMMARY OF THE INVENTION [0011] An exemplary embodiment of the present invention provides a membrane-electrode assembly for a fuel cell, wherein a catalyst layer has pores and can maintain a concentration of hydrogen and an oxidant on a surface of a catalyst and realize a high-power fuel cell. [0012] Another embodiment of the present invention provides a fuel cell system including the membrane-electrode assembly. [0013] According to one embodiment, a membrane-electrode assembly for a fuel cell includes an anode and a cathode facing each other, and a polymer electrolyte membrane interposed therebetween. At least one of the anode and the cathode includes a catalyst layer and an electrode substrate (a reactant diffusion layer). The catalyst layer includes a catalyst and a porous ionomer. The polymer electrolyte membrane contacts one side of the catalyst layer and the electrode substrate contacts the other side of the catalyst layer. [0014] According to another embodiment, a fuel cell system includes at least one electricity generating element for generating electricity through oxidation of fuel and reduction of an oxidant, a fuel supplier for providing fuel to the electricity generating element, and an oxidant supplier for supplying the oxidant to the electricity generating element. The electricity generating element includes the above membrane-electrode assembly and separators positioned at both sides of the membrane-electrode assembly. [0015] The porous ionomer layer has a porosity ranging from about 40 volume % to about 80 volume %. [0016] The porous ionomer layer has a pore size ranging from about 10 nm to about 1,000 nm. [0017] The porous ionomer layer is present on a surface of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS [0018] A more complete appreciation of the present invention, and many of the above and other features and advantages of the present invention, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawing in which like reference symbols indicate the same or similar components, wherein [0019] FIG. 1 is a schematic diagram showing processes of forming a porous ionomer layer included in the catalyst layer of the present invention; Continue reading... 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