KR20080013101A - Electrode for fuel cell, membrane-electrode assembly for fuel cell and fuel cell system comprising same - Google Patents

Abstract

An electrode for a fuel cell is provided to obtain a membrane-electrode assembly for a fuel cell having excellent water absorptivity even at high temperature, and thus allow a fuel cell to be driven at high temperature. An electrode for a fuel cell comprises: an electrode substrate; and a catalyst layer formed on the electrode substrate, and comprising a water-absorbing material to which a metal and inorganic ion conductor are bound, a binder and a catalyst. The inorganic conductor includes phosphorus tungstate. The metal includes a monovalent metal element such as Cs, Na or K. The water-absorbing material is used in an amount of 10-90 parts by weight based on 100 parts by weight of the binder.

Description

Electrode for fuel cell, membrane-electrode assembly including the same, and system for fuel cell comprising the same {ELECTRODE FOR FUEL CELL, MEMBRANE-ELECTRODE ASSEMBLY FOR FUEL CELL AND FUEL CELL SYSTEM COMPRISING SAME}

1 is a view schematically showing the structure of a fuel cell system of the present invention.

[Industrial use]

The present invention relates to a fuel cell electrode, a fuel cell membrane-electrode assembly including the same, and a fuel cell system including the same. More particularly, a fuel cell electrode capable of providing a battery that can be used at a high temperature, and a fuel cell comprising the same Membrane-electrode assembly and a fuel cell system comprising the same.

[Prior art]

A fuel cell is a power generation system that directly converts the chemical reaction energy of hydrogen and oxygen contained in hydrocarbon-based materials such as methanol, ethanol and natural gas into electrical energy.

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

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

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

In contrast, the direct oxidation fuel cell has a lower energy density than the polymer electrolyte fuel cell, but is easy to handle in a liquid state and has a low operating temperature, and thus can be operated at room temperature. As a result, it is recognized as a system suitable as a compact and general-purpose mobile power supply. In addition, the stack configuration by stacking unit cells has the advantage that can produce a wide range of output, it is attracting attention as a new portable power source because it shows an energy density of 4-10 times compared to a small lithium battery.

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

It is an object of the present invention to provide an electrode for a fuel cell which has good moisture absorption and can operate at high temperatures.

Another object of the present invention is to provide a method for manufacturing a membrane-electrode assembly for a fuel cell, which can easily manufacture the membrane-electrode assembly.

It is another object of the present invention to provide a fuel cell system comprising the membrane-electrode assembly.

In order to achieve the above object, the present invention provides an electrode for a fuel cell comprising an electrode substrate and a catalyst layer formed on the electrode substrate and comprising an inorganic ion conductor salt, a binder, and a catalyst to which a metal is bound.

The invention also includes an anode electrode and a cathode electrode positioned opposite each other and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, wherein at least one of the anode electrode and the cathode electrode is an electrode having the above configuration. Provide an electrode assembly.

The invention also provides a fuel cell system comprising at least one electricity generator, a fuel supply and an oxidant supply. The electricity generation unit serves to generate electricity through the oxidation reaction of the fuel and the reduction reaction of the oxidant. The electricity generation unit includes at least one membrane-electrode assembly and a separator including an anode electrode and a cathode electrode disposed to face each other, and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, wherein the anode electrode and the cathode electrode At least one of the electrodes has the above configuration. The fuel supply unit serves to supply fuel to the electricity generation unit, and the oxidant supply unit serves to supply an oxidant to the electricity generation unit.

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

The present invention relates to an electrode for fuel cells having excellent water retention.

The electrode for fuel cells of this invention contains an electrode base material and the catalyst layer formed in this electrode base material. The catalyst layer includes a water absorbent binder and a catalyst in which a metal and an inorganic ion conductor are combined. Since the moisture absorbing material has excellent moisture holding power, the moisture absorbing material can maintain moisture well even at a high temperature, thereby enabling operation of the fuel cell even at a high temperature. In general, the fuel cell is difficult to operate when the temperature rises to dry because the polymer electrolyte membrane used is operated under humidification conditions, but the electrode of the present invention has excellent moisture retention so that the polymer electrolyte membrane in contact with the electrode continues to be humidified. Will be able to maintain.

In the present invention, the inorganic ion conductor coupled to the metal in the water absorbing material is phosphotungstic acid, silicon tungsten acid, zirconium hydrogen phosphate, α-Zr (O _a1 PCH _a2 OH) a (O _b1 PC _b2 H _b4 SO _b5 H) _b nH ₂ O (where a1, a2, a, b1, b2, b4, b5 and b are the same or independently of each other an integer from 0 to 14, n Is an integer from 0 to 50), γ-Zr (PO _a1 ) (H _a2 PO _a3 ) _a (HO _b1 PC _b2 H _b3 SO _b4 H) _b nH ₂ O (where a1, a2, a3, a, b1, b2, b3, b4 and b are the same or independently of each other an integer from 0 to 14, n is an integer from 0 to 50), Zr (O _a1 PC _a2 H _a3 ) _a Y _b (where a1, a2 , a3, a and b are the same or independently from each other an integer from 0 to 14, Zr (O _a1 PCH _a2 OH) _a Y _b nH ₂ O (where a1, a2, a and b are the same or independent of each other) a is an integer from 0 to 14, n is an integer of 0 to 50), α-Zr (O a1 PC a2 H a3 SO a4 H) a · nH 2 O (where a1, a2, a3, a4 and a are the same or independently from each other an integer from 0 to 14, n is an integer from 0 to 50), α-Zr (O _a1 POH) .H ₂ O (here Where a1 is an integer from 0 to 14, (P ₂ O ₅ ) _a (ZrO ₂ ) _b , where a and b are the same or independently of each other an integer from 0 to 14, glass and P ₂ O Preference is given to one or more mixtures selected from the group consisting of ₅ -ZrO ₂ -SiO ₂ glass.

As the metal, a monovalent metal may be used, and representative examples thereof may include Cs, Na, or K.

That is, the water absorbing material of the present invention is a proton ion is substituted with metal ions in the inorganic ion conductor. That is, the H ⁺ -inorganic ion conductor is converted to a metal ⁺ -inorganic ion conductor salt.

The most preferred water absorbing material in the present invention is the Cs-linked phosphotungstic acid salt.

In the electrode of the present invention, the content of the moisture absorbing material is preferably 3 to 50 parts by weight based on 100 parts by weight of the binder. When the content of the moisture absorbing material is less than 3 parts by weight, no difference in performance is observed, and when it exceeds 50 parts by weight, it is not preferable because it impedes the transfer of hydrogen ions.

As the catalyst, any one that can be used as a catalyst may participate in the reaction of the fuel cell, and as a representative example, a platinum-based catalyst may be used. The platinum-based catalyst may be platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy or platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, Co, Ni, At least one catalyst selected from the group consisting of Cu, Zn, Sn, Mo, W, Rh and Ru). Specific examples include Pt, Pt / Ru, Pt / W, Pt / Ni, Pt / Sn, Pt / Mo, Pt / Pd, Pt / Fe, Pt / Cr, Pt / Co, Pt / Ru / W, Pt / Ru One or more selected from the group consisting of / Mo, Pt / Ru / V, Pt / Fe / Co, Pt / Ru / Rh / Ni, and Pt / Ru / Sn / W can be used.

In addition, the platinum-based catalyst may be used in a black form which is supported or not supported on a carrier. Carbon-based materials such as graphite, denka black, ketjen black, acetylene black, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanoballs or activated carbon may be used, or inorganic materials such as alumina, silica, zirconia, titania, etc. Although fine particles may be used, carbon-based materials are generally used. In the case of using the noble metal supported on the carrier as a catalyst, a commercially available commercially available product may be used, or the 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 descriptions thereof will be readily understood by those skilled in the art even if the detailed description is omitted.

The binder may be a fluoro-based polymer such as perfluorosulfonate, a polyamide-based polymer, a polyether-based polymer, a benzimidazole-based polymer, a polyimide-based polymer, a polyetherimide-based polymer, or a polyphenylene sulfide-based polymer. At least one hydrogen ion conductive polymer such as a polymer, a polysulfone polymer, a polyether sulfone polymer, a polyether ketone polymer, a polyether ether ketone crab polymer or a polyphenylquinoxaline polymer may be used. The hydrogen ion conductive polymer may replace H with Na, K, Li, Cs or tetrabutylammonium in an ion exchange group at the side chain end. In case of replacing H with Na in the side chain terminal ion exchanger, NaOH is substituted for the preparation of the catalyst composition, and tetrabutylammonium hydroxide is substituted for tetrabutylammonium, and K, Li or Cs may be substituted with appropriate compounds. It can be substituted using. Since this substitution method is well known in the art, detailed description thereof will be omitted.

The binder may be used in the form of a single substance or a mixture, and may also be optionally used with a nonconductive polymer for the purpose of further improving adhesion to the polymer electrolyte membrane. It is preferable to adjust the usage-amount so that it may be suitable for a purpose of use.

The non-conductive polymer may be polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer ethylene / tetrafluoroethylene, chloro At least one selected from the group consisting of a trifluoroethylene-ethylene copolymer, polyvinylidene fluoride, and a copolymer of polyvinylidene fluoride-hexafluoropropylene can be used.

In addition, the electrode substrate plays a role of supporting the electrode and diffuses the fuel and the oxidant into the catalyst layer to play the role of fuel and oxidant easily accessible to the catalyst layer. The electrode substrate is a conductive substrate, and representative examples thereof include carbon paper, carbon cloth, carbon felt, or metal cloth (porous film or polymer fiber composed of metal cloth in a fibrous state). The metal film is formed on the surface of the cloth formed with)) may be used, but is not limited thereto.

In addition, it is preferable to use a water-repellent treatment with a fluorine-based resin as the electrode base material because it can prevent the reactant diffusion efficiency from being lowered by water generated when the fuel cell is driven. As the fluorine-based resin, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated ethylene propylene, polychlorotrifluoroethylene, fluoroethylene polymer, or the like may be used.

In addition, a microporous layer may be further included to enhance the reactant diffusion effect in the electrode substrate. These microporous layers are generally conductive powders having a small particle diameter, such as carbon powder, carbon black, acetylene black, activated carbon, carbon fiber, fullerene, carbon nanotubes, carbon nanowires, and carbon nanohorns. -horn or carbon nano ring.

The microporous layer is prepared by coating a composition comprising a conductive powder, a binder resin and a solvent on the electrode substrate. As the binder resin, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, cellulose acetate, and the like may be preferably used. The solvent may be ethanol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, or the like. Alcohol, water, dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone and the like can be preferably used. The coating process may be screen printing, spray coating, or coating using a doctor blade according to the viscosity of the composition, but is not limited thereto.

The membrane-electrode assembly of the present invention having the above configuration is used in an electricity generating unit, and the fuel cell system of the present invention including the same includes at least one electricity generating unit, a fuel supply unit, and an oxidant supply unit.

The electricity generator includes the membrane-electrode assembly of the present invention and also includes a separator (also called a bipolar plate). The electricity generation unit serves to generate electricity through the oxidation reaction of the fuel and the reduction reaction of the oxidant.

The fuel supply unit serves to supply fuel to the electricity generation unit, and the oxidant supply unit serves to supply an oxidant such as oxygen or air to the electricity generation unit. In the present invention, the fuel refers to a hydrocarbon fuel such as methanol, ethanol, propanol, butanol, and natural gas in a gas or liquid state. Of course, hydrogen can also be used.

A schematic structure of the fuel cell system of the present invention is shown in FIG. 1, which will be described in more detail with reference to the following. Although the structure shown in FIG. 1 shows a system for supplying fuel and oxidant to an electric generator using a pump, the fuel cell system of the present invention is not limited to such a structure, and a fuel cell using a diffusion method without using a pump is shown. Of course, it can also be used for system architecture.

The fuel cell system 1 of the present invention includes at least one electricity generation unit 3 for generating electrical energy through an oxidation reaction of a fuel and a reduction reaction of an oxidant, a fuel supply unit 5 for supplying the fuel, And an oxidant supply unit 7 for supplying an oxidant to the electricity generation unit 3.

In addition, the fuel supply unit 5 for supplying the fuel may include a fuel tank 9 storing fuel and a fuel pump 11 connected to the fuel tank 9. The fuel pump 11 serves to discharge the fuel stored in the fuel tank 9 by a predetermined pumping force.

The oxidant supply unit 7 for supplying the oxidant to the electricity generating unit 3 includes at least one oxidant pump 13 for sucking the oxidant with a predetermined pumping force.

The electricity generator 3 is composed of a membrane-electrode assembly 17 for oxidizing and reducing a fuel and an oxidant, and a separator 19 and 19 'for supplying fuel and an oxidant to both sides of the membrane-electrode assembly. At least one of these electricity generating units 17 constitutes a stack 15.

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

(Example 1)

5.0 g of Pt-Ru black (Johnson Matthey, HiSpec 6000) anode catalyst, 10.0 g of 10 wt.% Nafion / H ₂ O / 2-propanol (Solution Technology Inc.) binder and 0.1 g of Cs ⁺ -phosphotungstic acid To prepare a catalyst composition for the anode electrode.

5.0 g of Pt black (Johnson Matthey, HiSpec 100) cathode catalyst, 10.0 g of 10 wt.% Nafion / H ₂ O / 2-propanol (Solution Technology Inc.) binder and 0.1 g of Cs ⁺ -phosphotungstic acid To prepare a catalyst composition for the cathode electrode.

The anode electrode catalyst composition and the cathode electrode catalyst composition were coated on carbon paper to prepare an anode electrode and a cathode electrode, respectively.

A membrane-electrode assembly was prepared using the prepared anode and cathode electrodes and a commercial Nafion 115 (perfluorosulfonic acid) polymer electrolyte membrane.

(Comparative Example 1)

A unit cell was prepared in the same manner as in Example 1, except that Cs ⁺ -phosphotungstic acid was not added to the catalyst composition for the anode electrode and the catalyst composition for the cathode electrode.

As a result of measuring moisture absorption at high temperatures of the membrane-electrode assembly prepared according to Example 1 and Comparative Example 1, Example 1 was much better than Comparative Example 1, and therefore, the battery of Example 1 was not operated at high temperature. It was possible to find out.

As described above, the membrane-electrode assembly for a fuel cell of the present invention is excellent in water absorption even at high temperatures, and thus it is possible to provide a fuel cell that can operate even at high temperatures.

Claims (17)

Electrode substrates; And A catalyst layer formed on the electrode substrate and containing a moisture absorbing material, a binder, and a catalyst, to which a metal and an inorganic ion conductor are combined. Electrode for a fuel cell comprising a. The method of claim 1, The inorganic ion conductor is Phosphotungstic acid, silicon tungstic acid, zirconium hydrogen phosphate, α-Zr (O _a1 PCH _a2 OH) _a (O _b1 PC _b2 H _b4 SO _b5 H) _b nH ₂ O (here In, a1, a2, a, b1, b2, b4, b5 and b are the same or independently of each other an integer from 0 to 14, n is an integer from 0 to 50), γ-Zr (PO _a1 ) (H _a2 PO _a3 ) _a (HO _b1 PC _b2 H _b3 SO _b4 H) _b nH ₂ O (where a1, a2, a3, a, b1, b2, b3, b4 and b are the same or independently of each other 0 to 14 An integer, n is an integer from 0 to 50), Zr (O _a1 PC _a2 H _a3 ) _a Y _b , where a1, a2, a3, a and b are the same or independently of each other an integer from 0 to 14, Zr (O _a1 PCH _a2 OH) _a Y _b nH ₂ O (where a1, a2, a and b are the same or independently of each other an integer from 0 to 14, n is an integer from 0 to 50), α- Zr (O _a1 PC _a2 H _a3 SO _a4 H) _a nH ₂ O (where a1, a2, a3, a4 and a are the same or independently of each other an integer from 0 to 14 , n is an integer from 0 to 50, α-Zr (O _a1 POH) .H ₂ O (where a1 is an integer from 0 to 14), (P ₂ O ₅ ) _a (ZrO ₂ ) _b (here a and b are the same or independently of each other an integer from 0 to 14) a fuel that is a salt of an inorganic ion conductor, one or more mixtures selected from the group consisting of glass and P ₂ O ₅ -ZrO ₂ -SiO ₂ glass Battery electrode. The method of claim 2, The inorganic ion conductor is a tungsten acid electrode for a fuel cell. The method of claim 1, The metal is a monovalent metal electrode for a fuel cell. The method of claim 4, wherein The metal is a fuel cell electrode is selected from the group consisting of Cs, Na and K. The method of claim 1, The water absorbing material is a fuel cell electrode of the phosphorus tungstic acid salt combined with Cs. The method of claim 1, The content of the moisture absorbing material is a fuel cell electrode of 10 to 90 parts by weight based on 100 parts by weight of the binder. The method of claim 1, The catalyst is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy or platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn , Sn, Mo, W, Rh and Ru, at least one transition metal selected from the group consisting of; and a fuel cell electrode comprising at least one catalyst selected from. The method of claim 1, The binder may be a fluoropolymer, a polyamide polymer, a polyether polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, or a polyether sulfonate. An electrode for a fuel cell, which is at least one hydrogen ion conductive polymer selected from the group consisting of a phone polymer, a polyether ketone polymer, a polyether ether ketone crab polymer, and a polyphenylquinoxaline polymer. The method of claim 9, The binder is a fuel cell electrode that further comprises a non-conductive polymer. The method of claim 10, The non-conductive polymer is polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer ethylene / tetrafluoroethylene, chlorotri An electrode for a fuel cell, which is at least one selected from the group consisting of a fluoroethylene-ethylene copolymer, a polyvinylidene fluoride, and a copolymer of polyvinylidene fluoride-hexafluoropropylene. An anode electrode and a cathode electrode located opposite each other; And A polymer electrolyte membrane positioned between the anode electrode and the cathode electrode Including; 12. A membrane-electrode assembly for a fuel cell, wherein at least one of the anode electrode and the cathode electrode is the electrode of any one of claims 1-11. The method of claim 12, The polymer electrolyte membrane is a fuel cell membrane-electrode assembly which is a polymer resin having a cation exchange group selected from the group consisting of sulfonic acid group, carboxylic acid group, phosphoric acid group, phosphonic acid group and derivatives thereof in the side chain. The method of claim 13, The polymer resin may be a fluoropolymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, a polyether sulfone polymer, a polyether ketone polymer, The membrane-electrode assembly for a fuel cell, which is selected from the group consisting of a polyether-etherketone crab polymer and a polyphenylquinoxaline-based polymer. The method of claim 13, The polymer electrolyte membrane is a fuel cell membrane-electrode assembly in which the H of the cation exchanger is substituted with one selected from the group consisting of Na, K, Li, Cs and tetrabutylammonium. At least one membrane-electrode assembly and a separator including an anode electrode and a cathode electrode positioned opposite to each other, and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, and including an oxidation reaction of a fuel and a reduction reaction of an oxidant. At least one electricity generating unit generating electricity; A fuel supply unit supplying fuel to the electricity generation unit; And An oxidant supply unit for supplying an oxidant to the electricity generation unit, At least one of the anode electrode and the cathode electrode The electrode according to any one of claims 1 to 11 Fuel cell system. The method of claim 16, The fuel cell system is a direct oxidation fuel cell system.

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