WO2010010990A1 - Electrode for a fuel cell comprising a catalyst layer and a gas diffusion layer integrated with one nanofiber web and method of preparing the same and fuel cell using the same - Google Patents

Electrode for a fuel cell comprising a catalyst layer and a gas diffusion layer integrated with one nanofiber web and method of preparing the same and fuel cell using the same Download PDF

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Publication number
WO2010010990A1
WO2010010990A1 PCT/KR2008/005773 KR2008005773W WO2010010990A1 WO 2010010990 A1 WO2010010990 A1 WO 2010010990A1 KR 2008005773 W KR2008005773 W KR 2008005773W WO 2010010990 A1 WO2010010990 A1 WO 2010010990A1
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Prior art keywords
platinum
fuel cell
electrode
nanofiber web
oxides
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PCT/KR2008/005773
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French (fr)
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Chan Kim
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Amomedi Co., Ltd.
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Publication of WO2010010990A1 publication Critical patent/WO2010010990A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/94—Non-porous diffusion electrodes, e.g. palladium membranes, ion exchange membranes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/023—Porous and characterised by the material
    • H01M8/0241—Composites
    • H01M8/0245—Composites in the form of layered or coated products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/8605—Porous electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8803—Supports for the deposition of the catalytic active composition
    • H01M4/8807—Gas diffusion layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8817—Treatment of supports before application of the catalytic active composition
    • H01M4/8821—Wet proofing
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8825—Methods for deposition of the catalytic active composition
    • H01M4/8828—Coating with slurry or ink
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8825—Methods for deposition of the catalytic active composition
    • H01M4/8846—Impregnation
    • H01M4/885—Impregnation followed by reduction of the catalyst salt precursor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8825—Methods for deposition of the catalytic active composition
    • H01M4/8867—Vapour deposition
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/92—Metals of platinum group
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/92—Metals of platinum group
    • H01M4/923—Compounds thereof with non-metallic elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/023—Porous and characterised by the material
    • H01M8/0234—Carbonaceous material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/023—Porous and characterised by the material
    • H01M8/0239—Organic resins; Organic polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M2008/1095—Fuel cells with polymeric electrolytes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/92—Metals of platinum group
    • H01M4/921—Alloys or mixtures with metallic elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1009—Fuel cells with solid electrolytes with one of the reactants being liquid, solid or liquid-charged
    • H01M8/1011—Direct alcohol fuel cells [DAFC], e.g. direct methanol fuel cells [DMFC]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a solid polymer electrolyte-type electrode for a fuel cell, which comprises a gas diffusion layer and a catalyst layer integrated with one nanofiber web, a method for producing the same, and a fuel cell using the same.
  • a solid polymer electrolyte fuel cell (the fuel cell includes a direct methanol fuel cell, and hereinafter, referred to as "fuel cell", FIG. 1, 100) is produced by adding a gasket to both sides of the Membrane Electrode Assembly (MEA), attaching a separator 110 thereto, and layering the resulting assemblies.
  • MEA Membrane Electrode Assembly
  • a catalyst layer 130 in which platinum (Pt) or a platinum alloy (Pt alloy) is provided to both sides of a hydrogen ion conductive electrolyte membrane is provided, and a gas diffusion layer (diffusion layer: carbon paper, carbon clothe, carbon fabrics and the like) 120 that diffuse hydrogen and the reactive gas of oxygen used for the electrode reaction and generated electrons and moisture comes into contact with the catalyst layer, and a separator 110 having a channel for a reactant, which is prepared with graphite, metal or the like, comes into contact with the outside of the gas diffusion layer.
  • FIG. 1 is a schematic view that illustrates a known electrode for a fuel cell.
  • fuel such as hydrogen or air passes through a channel 150 of the collecting gas separating membrane (bipolar plate) 110 and supplied through an opening of the gas diffusion layer 120, the hydrogen fuel is decomposed into a hydrogen ion and an electron at a fuel electrode of the catalyst layer 130 that comes into contact with the electrolyte, the hydrogen ion passes through the polymer ion exchange membrane (polymer electrolyte) 140, the electron is transported via a conductive carbon black that is the catalyst carrier, a carbon material, a conductive porous gas diffusion layer 120, and the assembly gas separation membrane (bipolar plate) 110 through the outer circuit into the air electrode (cathode), and oxygen, electrons, and a hydrogen ion are reacted with each other at the air electrode to generate water.
  • the generated water passes through the assembly gas separation membrane (bipolar plate) 110 and discharged into the outside.
  • Most commercialized gas diffusion layer 120 is manufactured with weaves, felt, non- woven fabrics, or papers which are prepared with the fiber having tens ⁇ hundreds ⁇ m in diameter, wherein the fiber is prepared by melt spinning and carbonizing or graphitiztng. Therefore, in case that uses such the gas diffusion layer 120, it is difficult to bring the provided reaction gas into uniform contact with the surface of a catalyst that is dispersed on a catalyst carrier and the amount of noneffective catalyst that does not contact with the reaction gas is increased, thus resulting in reducing the efficiency of the whole system.
  • an electric resistance between the layers is low and uniform, the production cost of the fuel cell is reduced, it is compacted, and the efficiency in generating power is improved.
  • the present invention provides an electrode for a fuel cell 300 which comprises a carbonized or graphitized nanofiber web 310, which is subjected to water-repellent treatment on one side, both sides or as a whole, being used as a gas diffusion layer; and a catalyst layer 230 that is formed by directly fixing a platinum-based catalyst 320 to, in the case of when only one side of the nanofiber web is subjected to the water- repellent treatment, the other side thereof, or to, in the case of when both sides or the whole of the nanofiber web are subjected to the water-repellent treatment, any one side thereof.
  • nanofiber web 310 are integrated to the nanofiber web 310.
  • the present invention provides a method for producing an electrode for a fuel cell comprising the steps of (a) producing a nanofiber web 310 that has the fiber diameter of less than 1 ⁇ m by electrically spinning a spinning solution that comprises a carbon fiber precursor; (b) oxidizing and stabilizing the nanofiber web that is produced in step a in atmosphere; (c) carbonizing the oxidized and stabilized nanofiber web that is produced in step b in an inert gas or in a vacuum; (d) performing water-repellent treatment on one side, both sides or as a whole of the carbonized nanofiber web 310 that is produced in step c; and (e) forming a catalyst layer 230 by directly fixing a platinum-based catalyst 320 to, in the case of when only one side of the nanofiber web is subjected to the water-repellent treatment in the step d, the other side thereof, or to, in the case of when both sides or the whole of the nanofiber web are subjected to the water-repellent treatment
  • the gas diffusion layer 220 and the catalyst layer 230 are integrated to the nanofiber web 310.
  • the method for producing an electrode for a fuel cell according to the present invention may further comprises, between steps c and d, the step of graphitiztng the carbonized nanofiber web that is produced in step c in an inert gas or in a vacuum.
  • the present invention provides a membrane-electrode assembly and a fuel cell 200 that include an electrode for a fuel cell that comprises the gas diffusion layer 220 and the catalyst layer 230 integrated with the nanofiber web 310.
  • a electrode for a fuel cell uses a carbonized or a graphitized nanofiber web as substrate for a gas diffusion layer and a catalyst layer
  • the gas diffusion layer comprised in the electrode for a fuel cell has minimized thickness, excellent mechanical properties and electric properties, uniform pores, ability of smooth supply of fuel and air, and ability of uniform moisture control
  • the catalyst layer comprised in the electrode for a fuel cell has high activity, the excellent electronic conductive channel, the excellent moving channel of the reactant and the product.
  • FIG. 1 is a schematic view that illustrates a known solid electrolyte-type electrode for a fuel cell
  • FIG. 2 is a schematic view of a fuel cell using a electrode for a fuel cell according to the present invention [(a) a view of the electrode, and (b) a sectional view of the catalyst layer and the gas diffusion layer integrated with one thin nanofiber web] ;
  • FIG. 6 is a scanning electron microscopic (SEM) picture of a surface of (a) a flu- orinated carbon nanofiber that is produced according to the present invention, and a scanning electron microscopic (SEM) picture of (b) a commercialized carbon fiber for a gas diffusion layer (magnification x 100); and
  • FIG. 7 is a scanning electron microscopic (SEM) picture of a cross-sectional surface of a gas diffusion layer and a catalyst layer integrated with a carbon nanofiber according to the present invention. Best Mode for Carrying Out the Invention
  • the present invention relates to an electrode for a fuel cell that comprises a carbonized or graphitized nanofiber web 310, which is subjected to water-repellent treatment on one side, both sides or as a whole, being used as a gas diffusion layerweb; and a catalyst layer 230 that is formed by directly fixing a platinum-based catalyst 320 to, in the case of when only one side of the nanofiber web is subjected to the water- repellent treatment, the other side thereof, or to, in the case of when both sides or the whole of the nanofiber web are subjected to the water-repellent treatment, any one side thereof.
  • nanofiber web 310 are integrated to the nanofiber web 310.
  • the water-repellent treatment may be performed by a water- repellent treatment agent, such as a fluorine-based resin, that is known in the art.
  • a water- repellent treatment agent such as a fluorine-based resin
  • the fkorine-based resin one or more from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, fluorinated ethylene propylene, polychlorotrifluoro- ethylene, a fluoroethylene polymer, and so on can be selected.
  • the platinum-based catalyst may be selected from the group consisting of platinum oxides; complex oxides of the platinum oxides and oxides of the metal element other than platinum; platinum that is obtained by the reduction treatment of the platinum oxides or the complex oxides; multi-metal that includes platinum; a mixture of platinum and the oxides of the metal element other than platinum; and a mixture of the multi-metal that includes platinum and the oxides of the metal element other than platinum.
  • the metal element other than platinum may be one or more metals that are selected from the group consisting of Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, Ta, W, Os, Ir, Au, La, Ce and Nd.
  • the carbonized or graphitized nanofiber web may comprises one or more nanomaterials that are selected from the group consisting of a single walled carbon nanotube (SWCNT), a multi- walled carbon nanotube (MWCNT), a nano hone, a cup stacked carbon nanotube, a vapor grown carbon fiber (VGCF), a graphite nanopartile, and a carbon black.
  • SWCNT single walled carbon nanotube
  • MWCNT multi- walled carbon nanotube
  • VGCF vapor grown carbon fiber
  • graphite nanopartile a carbon black
  • the nanomaterial is added to improve the electric conductivity and the strength of the carbonized or graphitized nanofiber web, while increasing effect throughout the surface area.
  • the content of the nanomaterial is preferably in the range of 0.5 ⁇ 15 parts by weight on the basis of 100 parts by weight of the carbon fiber precursor solid portion that is included in the production of the carbonized or graphitized nanofiber web, and more preferably in the range of 0.5 ⁇ 5 parts by weight.
  • the effect that is obtained by ading the nano- material is low, and if it is included in the content of more than 15 parts by weight, the nanomaterial protrudes from the outside of the fiber, and passes through the ion conductive membrane or tears the ion conductive membrane while the MEA is produced.
  • the thickness of the carbonized or graphitized nanofiber web that is subjected to the water-repellent treatment may be in the range of 100 ⁇ m ⁇ 5,000 ⁇ m, and preferably in the range of 300 ⁇ m ⁇ 1,000 ⁇ m. If the thickness of the nanofiber web is too high, it becomes difficult to compact the fuel cell, and if the thickness of the nanofiber web is too low, there are problems in views of strength and handling of the web while the MEA is produced.
  • the carbonized or graphitized nanofiber web 310 may be produced by using the same method as following.
  • the present invention relates to a method for producing an electrode for a fuel cell 300 comprising the steps of (a) producing a nanofiber web that has the fiber diameter of less than 1 ⁇ m by electrically spinning a spinning solution that includes a carbon fiber precursor; (b) oxidizing and stabilizing the nanofiber web that is produced in step a in atmosphere; (c) carbonizing the oxidized and stabilized nanofiber web that is produced in step b in an inert gas or in a vacuum; (d) performing water-repellent treatment on one side, both sides or as a whole of the carbonized nanofiber web 310 that is produced in step c; and (e) forming a catalyst layer 230 by directly fixing a platinum-based catalyst 320 to, in the case of when only one side of the nanofiber web is subjected to the water-repellent treatment in the step d, the other side thereof, or to, in the case of when both sides or the whole of the nanofiber web are subjected to the water-repellent treatment
  • the gas diffusion layer 220 and the catalyst layer 230 are integrated to the nanofiber web 310.
  • the production method according to the present invention may further comprises, between steps c and d, the step of graphitiztng the carbonized nanofiber web that is produced in step c in an inert gas or in a vacuum.
  • the carbon fiber precursor for example, one or more that are selected from the group consisting of polyacrylo nitrile (PAN), polyben- zyleimidazole (PBI), cellulose, phenol, pitch, and polyimide (PI) that are the polymer may be used.
  • PAN polyacrylo nitrile
  • PBI polyben- zyleimidazole
  • PI polyimide
  • the spinning solution may further comprise the nanomaterial.
  • the nan- omaterial one or more that are selected from the group consisting of a single walled carbon nanotube (SWCNT), a multi-walled carbon nanotube (MWCNT), a nano hone, a cup stacked carbon nanotube, a vapor grown carbon fiber (VGCF), a graphite nan- opartile, a carbon black and the like may be used, The amount of use is the same as the above amount.
  • the electric spinning is performed by supplying the produced spinning solution to an electric spinning nozzle using a supply device and forming a high electric field (10 kV ⁇ 100 kV) between the nozzle and the assembly by using a high voltage generation device.
  • the size of the electric field relates to the distance between the nozzle and the assembly, and the distance may be controlled in order to easily electrically spin.
  • a general electric spinning device may be used, and an electro-brown method or a centrifuge electric spinning method may be used.
  • the fiber diameter of the nanofiber that is produced by using the above method is mostly less than 1 ⁇ m, and the nanofiber has a nonwoven fiber form.
  • the oxidization and stabilization, the carbonization, and the graphitization of the electrically spun nanofiber may be performed by applying a method that is known in the art. Specific examples of the oxidization and stabilization, the carbonization, and the graphitization of the electrically spun nanofiber are described below.
  • the oxidization and stabilization are to obtain the nanofiber web that is not dissolved by putting the produced nanofiber web in an electric furnace which is capable of controlling temperature and flow rate of air and increasing the temperature of the electric furnace from normal temperature to 35O 0 C at a rate of 0.5 ⁇ 5 0 C per min.
  • the carbonization is to obtain the carbonized nanofiber web by treating the oxidized and stabilized fiber under an inert gas atmosphere or a vacuum state at a temperature in the range of 500 ⁇ 1500 0 C.
  • the fiber diameter of the nanofiber that forms the obtained carbonized nanofiber web is mostly in the range of 100 nm ⁇ 1000 nm.
  • the electric conductivity of the carbonized nanofiber web is not less than 2 S/cm and the porosity is not less than 20%.
  • the graphitization is to obtain the graphitized nanofiber web by treating the carbonized nanofiber web by using a graphitizing furnace at a temperature of not more than 3000 0 C.
  • the water-repellent treatment may be performed by using a water-repellent treatment agent, such as a fluorine-based resin, that is known in the art.
  • a water-repellent treatment agent such as a fluorine-based resin
  • the fluorine-based resin one or more selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, fluorinated ethylene propylene, poly- chlorotrifluoroethylene, and a fluoroethylene polymer may be used.
  • the electric conductivity of the graphitized nanofiber web which is subjected to the water-repellent treatment is not more than 11.5 m ⁇ cnf.
  • the platinum-based catalyst 320 may be selected from the group consisting of platinum oxides; complex oxides of the platinum oxides and oxides of the metal element other than platinum; platinum that is obtained by the reduction treatment of the platinum oxides or the complex oxides; multi-metal that includes platinum; a mixture of platinum and the oxides of the metal element other than platinum; and a mixture of the multi-metal that includes platinum and the oxides of the metal element other than platinum.
  • the metal element other than platinum may be one or more metals that are selected from the group consisting of Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, Ta, W, Os, Ir, Au, La, Ce and Nd.
  • the catalyst layer 230 may be formed by using a method that is known in the art.
  • the platinum-based catalyst 320 may be fixed by a reactive vacuum deposition method, a metal ion reduction method, or a spray coating method to the nanofiber web 310.
  • the reactive vacuum deposition method includes reactive sputtering, reactive electronic beam deposition, reactive ion plating and the like.
  • the present invention provides a membrane-electrode assembly and a fuel cell 200 that comprise an electrode for a fuel cell that comprises the gas diffusion layer 220 and the catalyst layer 230 integrated with one nanofiber web 310.
  • the membrane-electrode assembly and the fuel cell are excellent in views of production cost, compacting, and the efficiency in generating power.
  • Example 1 On the basis of 100 parts by weight of PAN and the PAN solid portion, 0 parts by weight of (Example 1), 1 parts by weight of (Example 2), 3 parts by weight of (Example 3), 5 parts by weight of (Example 4), 10 parts by weight of (Example 5), 15 parts by weight of (Example 6) the MWCNT (multiwalled carbon nanotubes) were uniformly mixed.
  • the mixture was dissolved in DMF in the amount of 10 ⁇ 30 parts by weight based on 100 parts by weight of the spinning solution and electrically spun at 25 KV to obtain the nanofiber web that has the fiber diameter of less than 1 ⁇ m.
  • the oxidized and stabilized nanofiber web was obtained by putting the nanofiber web into an electric furnace that is capable of controlling temperature and a flow rate of air, and increasing the temperature of the electric furnace from a normal temperature to 35O 0 C at a rate of 0.5 ⁇ 5 0 C per min.
  • the carbonized nanofiber 310 web was obtained by treating the oxidized and stabilized nanofiber web under an inert gas atmosphere or a vacuum state at a temperature in the range of 500 ⁇ 1500 0 C.
  • the graphitized nanofiber web 310 was obtained by treating the carbonized nanofiber web in the graphitization furnace at a temperature of not more than 3000 0 C.
  • FIG. 3 A scanning electron microscopic (SEM) picture of a nanocomplex fiber that is electrically spun in Examples 1 to 4 according to the content of MWCNT is shown in FIG. 3.
  • SEM scanning electron microscopic
  • FIGS. 4 and 5 a scanning electron microscopic (SEM) picture of a nanocomplex fiber that is carbonized at 1000 0 C and graphitized at 3000 0 C is shown.
  • SEM scanning electron microscopic
  • Example 7 Production of the electrode for a fuel cell that comprises the gas diffusion layer and the catalyst layer integrated with one nanofiber web
  • the carbonized nanofiber web that was produced in Examples 1 to 6 was dipped in 10 - 50% Teflon to perform the water-repellent treatment, and it was vacuum dried at a temperature of not more than 15O 0 C.
  • the platinumoxide catalyst layer was formed on one side of the carbonized nanofiber web that was subjected to the water-repellent treatment as a whole by using the reactive sputtering in a thickness of 10 ⁇ 1,000 nm.
  • the scanning electron microscopic (SEM) picture (FIG. 6A) in respects to the surface of the carbonized nanofiber web that subjected to the water-repellent treatment in the above and the scanning electron microscopic (SEM) picture (FIG. 6B) of the commercialized carbon fiber web that was produced by the melt spinning were compared to each other at the same magnification and shown.
  • the carbon nanofiber according to the present invention has the fiber diameter which is about 100 times as small as that of the commercialized carbon fiber, and the size of fine pores which is 10 ⁇ 100 times as small as that of the commercialized carbon fiber.
  • the uniform distribution of the reactive gas is obtained, and the number of noneffective catalysts is largely reduced. Accordingly, it is expected that the efficiency in generating power is improved.

Abstract

The present invention relates to an electrode for a fuel cell which comprises a carbonized or graphitized nanofiber web, which is subjected to water-repellent treatment on one side, both sides or as a whole, being used as a gas diffusion layer; and a catalyst layer that is formed by directly fixing a platinum-based catalyst to, in the case of when only one side of the nanofiber web is subjected to the water-repellent treatment, the other side thereof, or to, in the case of when both sides or the whole of the nanofiber web are subjected to the water-repellent treatment, any one side thereof. In the electrode for a fuel cell 300, the gas diffusion layer 220 and the catalyst layer 230 are integrated to the nanofiber web 310. The present invention provides a electrode for a fuel cell which is effective in reducing the production cost of the fuel cell, compacting the fuel cell, and improving the efficiency in generating power, and a method for producing the same.

Description

Description
ELECTRODE FOR A FUEL CELL COMPRISING A CATALYST LAYER AND A GAS DIFFUSION LAYER INTEGRATED WITH ONE NANOFIBER WEB AND METHOD OF PREPARING THE
SAME AND FUEL CELL USING THE SAME Technical Field
[1] The present invention relates to a solid polymer electrolyte-type electrode for a fuel cell, which comprises a gas diffusion layer and a catalyst layer integrated with one nanofiber web, a method for producing the same, and a fuel cell using the same. Background Art
[2] A solid polymer electrolyte fuel cell (the fuel cell includes a direct methanol fuel cell, and hereinafter, referred to as "fuel cell", FIG. 1, 100) is produced by adding a gasket to both sides of the Membrane Electrode Assembly (MEA), attaching a separator 110 thereto, and layering the resulting assemblies. In the MEA, a catalyst layer 130 in which platinum (Pt) or a platinum alloy (Pt alloy) is provided to both sides of a hydrogen ion conductive electrolyte membrane is provided, and a gas diffusion layer (diffusion layer: carbon paper, carbon clothe, carbon fabrics and the like) 120 that diffuse hydrogen and the reactive gas of oxygen used for the electrode reaction and generated electrons and moisture comes into contact with the catalyst layer, and a separator 110 having a channel for a reactant, which is prepared with graphite, metal or the like, comes into contact with the outside of the gas diffusion layer. FIG. 1 is a schematic view that illustrates a known electrode for a fuel cell. In the drawing, fuel such as hydrogen or air passes through a channel 150 of the collecting gas separating membrane (bipolar plate) 110 and supplied through an opening of the gas diffusion layer 120, the hydrogen fuel is decomposed into a hydrogen ion and an electron at a fuel electrode of the catalyst layer 130 that comes into contact with the electrolyte, the hydrogen ion passes through the polymer ion exchange membrane (polymer electrolyte) 140, the electron is transported via a conductive carbon black that is the catalyst carrier, a carbon material, a conductive porous gas diffusion layer 120, and the assembly gas separation membrane (bipolar plate) 110 through the outer circuit into the air electrode (cathode), and oxygen, electrons, and a hydrogen ion are reacted with each other at the air electrode to generate water. By the above reaction, the generated water passes through the assembly gas separation membrane (bipolar plate) 110 and discharged into the outside.
[3] Most commercialized gas diffusion layer 120 is manufactured with weaves, felt, non- woven fabrics, or papers which are prepared with the fiber having tens ~ hundreds μm in diameter, wherein the fiber is prepared by melt spinning and carbonizing or graphitiztng. Therefore, in case that uses such the gas diffusion layer 120, it is difficult to bring the provided reaction gas into uniform contact with the surface of a catalyst that is dispersed on a catalyst carrier and the amount of noneffective catalyst that does not contact with the reaction gas is increased, thus resulting in reducing the efficiency of the whole system.
[4] In the fuel cell field, reducing the production cost, and increasing the efficiency in generating power as well as making it compact are studied. However, the gas diffusion layer or the catalyst layer that forms the membrane-electrode assembly (MEA) is separately studied and a technology for providing a synergy effect by an integrated study thereof can be hardly found. Accordingly, technologies for showing excellent effects in respects to the gas diffusion layer or the catalyst layer that forms the membrane-electrode assembly (MEA) are separately disclosed, but a technology that provides how to reduce the production cost, compact the size, and increase the efficiency in generating power thereof by the integrated study is hardly found. In this situation, the gas diffusion layer or the catalyst layer is produced by separate processes. However, it is extensively known that in the electrode that comprises the gas diffusion layer and the catalyst layer produced by separate processes, there is a high possibility of an increase in electric resistance between the layers and non- uniformity. In addition to the above, it provides the factor of an increase in production cost and size of the fuel cell. Disclosure of Invention Technical Problem
[5] It is an object of the present invention to provide an electrode for a fuel cell, which comprises a gas diffusion layer 220 and a catalyst layer 230 integrated with one nanofiber web 310 and a method for producing the same. In the electrode, an electric resistance between the layers is low and uniform, the production cost of the fuel cell is reduced, it is compacted, and the efficiency in generating power is improved. Technical Solution
[6] The present invention provides an electrode for a fuel cell 300 which comprises a carbonized or graphitized nanofiber web 310, which is subjected to water-repellent treatment on one side, both sides or as a whole, being used as a gas diffusion layer; and a catalyst layer 230 that is formed by directly fixing a platinum-based catalyst 320 to, in the case of when only one side of the nanofiber web is subjected to the water- repellent treatment, the other side thereof, or to, in the case of when both sides or the whole of the nanofiber web are subjected to the water-repellent treatment, any one side thereof.
[7] In the electrode for a fuel cell 300, the gas diffusion layer 220 and the catalyst layer
230 are integrated to the nanofiber web 310.
[8] In aάϊtion, the present invention provides a method for producing an electrode for a fuel cell comprising the steps of (a) producing a nanofiber web 310 that has the fiber diameter of less than 1 μm by electrically spinning a spinning solution that comprises a carbon fiber precursor; (b) oxidizing and stabilizing the nanofiber web that is produced in step a in atmosphere; (c) carbonizing the oxidized and stabilized nanofiber web that is produced in step b in an inert gas or in a vacuum; (d) performing water-repellent treatment on one side, both sides or as a whole of the carbonized nanofiber web 310 that is produced in step c; and (e) forming a catalyst layer 230 by directly fixing a platinum-based catalyst 320 to, in the case of when only one side of the nanofiber web is subjected to the water-repellent treatment in the step d, the other side thereof, or to, in the case of when both sides or the whole of the nanofiber web are subjected to the water-repellent treatment in the step d, any one side thereof.
[9] According to the method for producing an electrode for a fuel cell 300, the gas diffusion layer 220 and the catalyst layer 230 are integrated to the nanofiber web 310.
[10] The method for producing an electrode for a fuel cell according to the present invention may further comprises, between steps c and d, the step of graphitiztng the carbonized nanofiber web that is produced in step c in an inert gas or in a vacuum.
[11] In aάϊtion, the present invention provides a membrane-electrode assembly and a fuel cell 200 that include an electrode for a fuel cell that comprises the gas diffusion layer 220 and the catalyst layer 230 integrated with the nanofiber web 310.
Advantageous Effects
[12] Since a electrode for a fuel cell according to the present invention uses a carbonized or a graphitized nanofiber web as substrate for a gas diffusion layer and a catalyst layer, the gas diffusion layer comprised in the electrode for a fuel cell has minimized thickness, excellent mechanical properties and electric properties, uniform pores, ability of smooth supply of fuel and air, and ability of uniform moisture control; and the catalyst layer comprised in the electrode for a fuel cell has high activity, the excellent electronic conductive channel, the excellent moving channel of the reactant and the product.
[13] Also, since the gas diffusion layer and the catalyst layer are integrated with one thin nanofiber web, an electric resistance between the layers is very low and uniform, the production cost of the fuel cell is reduced, the fuel cell is compacted, and the efficiency in generating power is improved. Brief Description of the Drawings
[14] FIG. 1 is a schematic view that illustrates a known solid electrolyte-type electrode for a fuel cell;
[15] FIG. 2 is a schematic view of a fuel cell using a electrode for a fuel cell according to the present invention [(a) a view of the electrode, and (b) a sectional view of the catalyst layer and the gas diffusion layer integrated with one thin nanofiber web] ;
[16] FIG. 3 is a scanning electron microscopic (SEM) picture of a nanofiber web that is electrically spun in Examples 1 to 4 according to the present invention [(a) the weight ratio of PAN/MWCNT = 100/0, (b) the weight ratio of PAN/MWCNT = 99/1, (c) the weight ratio of PAN/MWCNT = 97/3, and (d) the weight ratio of PAN/MWCNT = 95/5];
[17] FIG. 4 is a scanning electron microscopic (SEM) picture of a carbonized nanofiber web (heat treatment of 10000C) that is produced in Examples 1 to 4 according to the present invention [(a) the weight ratio of PAN/MWCNT = 100/0, (b) the weight ratio of PAN/MWCNT = 99/1, (c) the weight ratio of PAN/MWCNT = 97/3, and (d) the weight ratio of PAN/MWCNT = 95/5];
[18] FIG. 5 is a scanning electron microscopic (SEM) picture of a graphitized nanofiber web (heat treatment of 30000C) that is produced in Examples 1 to 4 according to the present invention [(a) the weight ratio of PAN/MWCNT = 100/0, (b) the weight ratio of PAN/MWCNT = 99/1, (c) the weight ratio of PAN/MWCNT = 97/3, and (d) the weight ratio of PAN/MWCNT = 95/5];
[19] FIG. 6 is a scanning electron microscopic (SEM) picture of a surface of (a) a flu- orinated carbon nanofiber that is produced according to the present invention, and a scanning electron microscopic (SEM) picture of (b) a commercialized carbon fiber for a gas diffusion layer (magnification x 100); and
[20] FIG. 7 is a scanning electron microscopic (SEM) picture of a cross-sectional surface of a gas diffusion layer and a catalyst layer integrated with a carbon nanofiber according to the present invention. Best Mode for Carrying Out the Invention
[21] The present invention relates to an electrode for a fuel cell that comprises a carbonized or graphitized nanofiber web 310, which is subjected to water-repellent treatment on one side, both sides or as a whole, being used as a gas diffusion layerweb; and a catalyst layer 230 that is formed by directly fixing a platinum-based catalyst 320 to, in the case of when only one side of the nanofiber web is subjected to the water- repellent treatment, the other side thereof, or to, in the case of when both sides or the whole of the nanofiber web are subjected to the water-repellent treatment, any one side thereof.
[22] In the electrode for a fuel cell 300, the gas diffusion layer 220 and the catalyst layer
230 are integrated to the nanofiber web 310.
[23] In the present invention, the water-repellent treatment may be performed by a water- repellent treatment agent, such as a fluorine-based resin, that is known in the art. As the fkorine-based resin, one or more from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, fluorinated ethylene propylene, polychlorotrifluoro- ethylene, a fluoroethylene polymer, and so on can be selected.
[24] In the present invention, the platinum-based catalyst may be selected from the group consisting of platinum oxides; complex oxides of the platinum oxides and oxides of the metal element other than platinum; platinum that is obtained by the reduction treatment of the platinum oxides or the complex oxides; multi-metal that includes platinum; a mixture of platinum and the oxides of the metal element other than platinum; and a mixture of the multi-metal that includes platinum and the oxides of the metal element other than platinum.
[25] In the above description, the metal element other than platinum may be one or more metals that are selected from the group consisting of Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, Ta, W, Os, Ir, Au, La, Ce and Nd.
[26] In the present invention, the carbonized or graphitized nanofiber web may comprises one or more nanomaterials that are selected from the group consisting of a single walled carbon nanotube (SWCNT), a multi- walled carbon nanotube (MWCNT), a nano hone, a cup stacked carbon nanotube, a vapor grown carbon fiber (VGCF), a graphite nanopartile, and a carbon black.
[27] The nanomaterial is added to improve the electric conductivity and the strength of the carbonized or graphitized nanofiber web, while increasing effect throughout the surface area. The content of the nanomaterial is preferably in the range of 0.5 ~ 15 parts by weight on the basis of 100 parts by weight of the carbon fiber precursor solid portion that is included in the production of the carbonized or graphitized nanofiber web, and more preferably in the range of 0.5 ~ 5 parts by weight. If it is included in the content of less than 0.5 parts by weight, the effect that is obtained by ading the nano- material is low, and if it is included in the content of more than 15 parts by weight, the nanomaterial protrudes from the outside of the fiber, and passes through the ion conductive membrane or tears the ion conductive membrane while the MEA is produced.
[28] In the present invention, the thickness of the carbonized or graphitized nanofiber web that is subjected to the water-repellent treatment may be in the range of 100 μm ~ 5,000 μm, and preferably in the range of 300 μm ~ 1,000 μm. If the thickness of the nanofiber web is too high, it becomes difficult to compact the fuel cell, and if the thickness of the nanofiber web is too low, there are problems in views of strength and handling of the web while the MEA is produced.
[29] In the present invention, the carbonized or graphitized nanofiber web 310 may be produced by using the same method as following.
[30] In adition, the present invention relates to a method for producing an electrode for a fuel cell 300 comprising the steps of (a) producing a nanofiber web that has the fiber diameter of less than 1 μm by electrically spinning a spinning solution that includes a carbon fiber precursor; (b) oxidizing and stabilizing the nanofiber web that is produced in step a in atmosphere; (c) carbonizing the oxidized and stabilized nanofiber web that is produced in step b in an inert gas or in a vacuum; (d) performing water-repellent treatment on one side, both sides or as a whole of the carbonized nanofiber web 310 that is produced in step c; and (e) forming a catalyst layer 230 by directly fixing a platinum-based catalyst 320 to, in the case of when only one side of the nanofiber web is subjected to the water-repellent treatment in the step d, the other side thereof, or to, in the case of when both sides or the whole of the nanofiber web are subjected to the water-repellent treatment in the step d, any one side thereof.
[31] According to the method for producing an electrode for a fuel cell 300, the gas diffusion layer 220 and the catalyst layer 230 are integrated to the nanofiber web 310.
[32] The production method according to the present invention may further comprises, between steps c and d, the step of graphitiztng the carbonized nanofiber web that is produced in step c in an inert gas or in a vacuum.
[33] In the present invention, as the carbon fiber precursor, for example, one or more that are selected from the group consisting of polyacrylo nitrile (PAN), polyben- zyleimidazole (PBI), cellulose, phenol, pitch, and polyimide (PI) that are the polymer may be used.
[34] In aάϊtion, the spinning solution may further comprise the nanomaterial. As the nan- omaterial, one or more that are selected from the group consisting of a single walled carbon nanotube (SWCNT), a multi-walled carbon nanotube (MWCNT), a nano hone, a cup stacked carbon nanotube, a vapor grown carbon fiber (VGCF), a graphite nan- opartile, a carbon black and the like may be used, The amount of use is the same as the above amount.
[35] In the present invention, the electric spinning is performed by supplying the produced spinning solution to an electric spinning nozzle using a supply device and forming a high electric field (10 kV ~ 100 kV) between the nozzle and the assembly by using a high voltage generation device. The size of the electric field relates to the distance between the nozzle and the assembly, and the distance may be controlled in order to easily electrically spin. At this time, a general electric spinning device may be used, and an electro-brown method or a centrifuge electric spinning method may be used. The fiber diameter of the nanofiber that is produced by using the above method is mostly less than 1 μm, and the nanofiber has a nonwoven fiber form.
[36] In the present invention, the oxidization and stabilization, the carbonization, and the graphitization of the electrically spun nanofiber may be performed by applying a method that is known in the art. Specific examples of the oxidization and stabilization, the carbonization, and the graphitization of the electrically spun nanofiber are described below.
[37] The oxidization and stabilization are to obtain the nanofiber web that is not dissolved by putting the produced nanofiber web in an electric furnace which is capable of controlling temperature and flow rate of air and increasing the temperature of the electric furnace from normal temperature to 35O0C at a rate of 0.5 ~ 50C per min.
[38] The carbonization is to obtain the carbonized nanofiber web by treating the oxidized and stabilized fiber under an inert gas atmosphere or a vacuum state at a temperature in the range of 500 ~ 15000C. The fiber diameter of the nanofiber that forms the obtained carbonized nanofiber web is mostly in the range of 100 nm ~ 1000 nm. In the present invention, it is preferable that the electric conductivity of the carbonized nanofiber web is not less than 2 S/cm and the porosity is not less than 20%.
[39] The graphitization is to obtain the graphitized nanofiber web by treating the carbonized nanofiber web by using a graphitizing furnace at a temperature of not more than 30000C.
[40] In the present invention, the water-repellent treatment may be performed by using a water-repellent treatment agent, such as a fluorine-based resin, that is known in the art. As the fluorine-based resin, one or more selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, fluorinated ethylene propylene, poly- chlorotrifluoroethylene, and a fluoroethylene polymer may be used.
[41] In the present invention, it is preferable that the electric conductivity of the graphitized nanofiber web which is subjected to the water-repellent treatment is not more than 11.5 mΩcnf.
[42] In the present invention, the platinum-based catalyst 320 may be selected from the group consisting of platinum oxides; complex oxides of the platinum oxides and oxides of the metal element other than platinum; platinum that is obtained by the reduction treatment of the platinum oxides or the complex oxides; multi-metal that includes platinum; a mixture of platinum and the oxides of the metal element other than platinum; and a mixture of the multi-metal that includes platinum and the oxides of the metal element other than platinum.
[43] In the above description, the metal element other than platinum may be one or more metals that are selected from the group consisting of Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, Ta, W, Os, Ir, Au, La, Ce and Nd.
[44] In the present invention, in step e, the catalyst layer 230 may be formed by using a method that is known in the art. For example, the platinum-based catalyst 320 may be fixed by a reactive vacuum deposition method, a metal ion reduction method, or a spray coating method to the nanofiber web 310. The reactive vacuum deposition method includes reactive sputtering, reactive electronic beam deposition, reactive ion plating and the like.
[45] In aάϊtion, the present invention provides a membrane-electrode assembly and a fuel cell 200 that comprise an electrode for a fuel cell that comprises the gas diffusion layer 220 and the catalyst layer 230 integrated with one nanofiber web 310. The membrane-electrode assembly and the fuel cell are excellent in views of production cost, compacting, and the efficiency in generating power. Mode for the Invention
[46] Hereinafter, the present invention will be described in more detail by using the
Examples. However, the following Examples are set to illustrate, but are not to be construed to limit the present invention.
[47] Examples 1 to 6: Production of the nanofiber web
[48] On the basis of 100 parts by weight of PAN and the PAN solid portion, 0 parts by weight of (Example 1), 1 parts by weight of (Example 2), 3 parts by weight of (Example 3), 5 parts by weight of (Example 4), 10 parts by weight of (Example 5), 15 parts by weight of (Example 6) the MWCNT (multiwalled carbon nanotubes) were uniformly mixed. The mixture was dissolved in DMF in the amount of 10 ~ 30 parts by weight based on 100 parts by weight of the spinning solution and electrically spun at 25 KV to obtain the nanofiber web that has the fiber diameter of less than 1 μm.
[49] The oxidized and stabilized nanofiber web was obtained by putting the nanofiber web into an electric furnace that is capable of controlling temperature and a flow rate of air, and increasing the temperature of the electric furnace from a normal temperature to 35O0C at a rate of 0.5 ~ 50C per min. The carbonized nanofiber 310 web was obtained by treating the oxidized and stabilized nanofiber web under an inert gas atmosphere or a vacuum state at a temperature in the range of 500 ~ 15000C. The graphitized nanofiber web 310 was obtained by treating the carbonized nanofiber web in the graphitization furnace at a temperature of not more than 30000C.
[50] A scanning electron microscopic (SEM) picture of a nanocomplex fiber that is electrically spun in Examples 1 to 4 according to the content of MWCNT is shown in FIG. 3. In FIG. 3, (a) the weight ratio of PAN/MWCNT = 100/0, (b) the weight ratio of PAN/MWCNT = 99/1, (c) the weight ratio of PAN/MWCNT = 97/3, and (d) the weight ratio of PAN/MWCNT = 95/5.
[51] In aάϊtion, in FIGS. 4 and 5, a scanning electron microscopic (SEM) picture of a nanocomplex fiber that is carbonized at 10000C and graphitized at 30000C is shown. In FIGS. 4 and 5, (a) the weight ratio of PAN/MWCNT = 100/0, (b) the weight ratio of PAN/MWCNT = 99/1, (c) the weight ratio of PAN/MWCNT = 97/3, and (d) the weight ratio of PAN/MWCNT = 95/5.
[52] The change in physical properties and the fiber diameter of the carbonized nanofiber web (heat treatment of 10000C) that was obtained in Examples 2 ~ 4 is described in the following Table 1. In the following Table 1, the electric conductivity was obtained by measuring the bulk electric conductivity using the four terminal method, and the porosity (%) was measured by using the Mercury porosimetry method. In the case of the porosity, it may vary according to the spinning condition. That is, the porosity can be controlled according to the layering thickness of the fiber. The results of Table 1 were measured by controlling the thickness of the carbonized nanofiber web in the range of 300 μm ~ 500 μm.
[53] Table 1 [Table 1] [Table ]
Figure imgf000011_0001
[54] [55] Example 7: Production of the electrode for a fuel cell that comprises the gas diffusion layer and the catalyst layer integrated with one nanofiber web
[56] The carbonized nanofiber web that was produced in Examples 1 to 6 was dipped in 10 - 50% Teflon to perform the water-repellent treatment, and it was vacuum dried at a temperature of not more than 15O0C. The platinumoxide catalyst layer was formed on one side of the carbonized nanofiber web that was subjected to the water-repellent treatment as a whole by using the reactive sputtering in a thickness of 10 ~ 1,000 nm.
[57] The scanning electron microscopic (SEM) picture (FIG. 6A) in respects to the surface of the carbonized nanofiber web that subjected to the water-repellent treatment in the above and the scanning electron microscopic (SEM) picture (FIG. 6B) of the commercialized carbon fiber web that was produced by the melt spinning were compared to each other at the same magnification and shown. As shown in the drawings, as compared to the commercialized carbon fiber, the carbon nanofiber according to the present invention has the fiber diameter which is about 100 times as small as that of the commercialized carbon fiber, and the size of fine pores which is 10 ~ 100 times as small as that of the commercialized carbon fiber. Thus, the uniform distribution of the reactive gas is obtained, and the number of noneffective catalysts is largely reduced. Accordingly, it is expected that the efficiency in generating power is improved.

Claims

Claims
[1] An electrode for a fuel cell comprising: a carbonized or graphitized nanofiber web, which is subjected to water-repellent treatment on one side, both sides or as a whole, being used as a gas diffusion layer; and a catalyst layer that is formed by directly fixing a platinum-based catalyst to, in the case of when only one side of the nanofiber web is subjected to the water- repellent treatment, the other side thereof, or to, in the case of when both sides or the whole of the nanofiber web are subjected to the water-repellent treatment, any one side thereof.
[2] The electrode for a fuel cell as set forth in claim 1, wherein the water-repellent treatment is performed by a fluorine-based resin.
[3] The electrode for a fuel cell as set forth in claim 1, wherein the platinum-based catalyst is selected from the group consisting of platinum oxides; complex oxides of the platinum oxides and oxides of the metal element other than platinum; platinum that is obtained by the reduction treatment of the platinum oxides or the complex oxides; multi-metal that includes platinum; a mixture of platinum and the oxides of the metal element other than platinum; and a mixture of the multi- metal that includes platinum and the oxides of the metal element other than platinum.
[4] The electrode for a fuel cell as set forth in claim 1, wherein the fixing of the platinum-based catalyst is performed by a vacuum deposition method, a metal ion reduction method, or a spray coating method.
[5] The electrode for a fuel cell as set forth in claim 1, wherein the carbonized or graphitized nanofiber web includes one or more nanomaterials that are selected from the group consisting of a single walled carbon nanotube (SWCNT), a multi- walled carbon nanotube (MWCNT), a nano hone, a cup stacked carbon nanotube, a vapor grown carbon fiber (VGCF), a graphite nanopartile, and a carbon black.
[6] A method for producing an electrode for a fuel cell comprising the steps of:
(a) producing a nanofiber web that has the fiber diameter of less than 1 μm by electrically spinning a spinning solution that includes a carbon fiber precursor;
(b) oxidizing and stabilizing the nanofiber web that is produced in step a in atmosphere; (c) carbonizing the oxidized and stabilized nanofiber web that is produced in step b in an inert gas or in a vacuum;
(d) performing water-repellent treatment on one side, both sides or as a whole of the carbonized nanofiber web that is produced in step c; and
(e) forming a catalyst layer by directly fixing a platinum-based catalyst to, in the case of when only one side of the nanofiber web is subjected to the water- repellent treatment in the step d, the other side thereof, or to, in the case of when both sides or the whole of the nanofiber web are subjected to the water-repellent treatment in the step d, any one side thereof.
[7] The method for producing an electrode for a fuel cell as set forth in claim 6, further comprising: between steps c and d, the step of graphitiztng the carbonized nanofiber web that is produced in step c in an inert gas or in a vacuum.
[8] The method for producing an electrode for a fuel cell as set forth in claim 6 or 7, wherein the carbon fiber precursor of the step a is one or more that are selected from the group consisting of polyacrylo nitrile (PAN), polybenzyleimida2)le (PBI), cellulose, phenol, pitch, and polyimide (PI).
[9] The method for producing an electrode for a fuel cell as set forth in claim 6 or 7, wherein the spinning solution of the step a further comprises one or more nano- materials that are selected from the group consisting of a single walled carbon nanotube (SWCNT), a multi- walled carbon nanotube (MWCNT), a nano hone, a cup stacked carbon nanotube, a vapor grown carbon fiber (VGCF), a graphite nanopartile, and a carbon black.
[10] The method for producing an electrode for a fuel cell as set forth in claim 6 or 7, wherein in the step d, the water-repellent treatment is performed by a fluorine- based resin.
[11] The method for producing an electrode for a fuel cell as set forth in claim 6 or 7, wherein the platinum-based catalyst in the step e is selected from the group consisting of platinum oxides; complex oxides of the platinum oxides and oxides of the metal element other than platinum; platinum that is obtained by the reduction treatment of the platinum oxides or the complex oxides; multi-metal that includes platinum; a mixture of platinum and the oxides of the metal element other than platinum; and a mixture of the multi-metal that includes platinum and the oxides of the metal element other than platinum.
[12] The method for producing an electrode for a fuel cell as set forth in claim 6 or 7, wherein in the step e, the catalyst layer is formed by fixing the platinum-based catalyst to the nanofiber web according to a reactive vacuum deposition method, a metal ion reduction method, or a spray coating method. [13] A membrane-electrode assembly comprising the electrode for fuel cell according to any one of claims 1 to 5. [14] A fuel cell comprising the electrode for fuel cell according to any one of claims 1 to 5.
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