KR20070082697A - Membrane-electrode assembly for fuel cell and fuel cell system comprising same - Google Patents

Abstract

A membrane-electrode assembly for a fuel cell is provided to realize excellent ion conductivity, to prevent a fuel crossover phenomenon, and to impart high output and high efficiency to a fuel cell. A membrane-electrode assembly(200) for a fuel cell comprises: an anode(140) and a cathode(130) disposed opposite to each other; and a polymer electrolyte membrane(120) interposed between the anode and the cathode, wherein the polymer electrolyte membrane has a metal coating layer(122) on at least one surface thereof. The metal coating layer comprises a metal selected from the group consisting of Ay, Ag, Ir, and a combination thereof.

Description

Membrane-electrode assembly for fuel cell and fuel cell system comprising same {MEMBRANE-ELECTRODE ASSEMBLY FOR FUEL CELL AND FUEL CELL SYSTEM COMPRISING SAME}

1 is a schematic representation of a membrane-electrode assembly for a fuel cell of the present invention.

2 schematically illustrates the structure of a fuel cell system of the present invention;

[Industrial use]

The present invention relates to a fuel cell membrane-electrode assembly and a fuel cell system including the same, and more particularly, to a fuel cell membrane-electrode assembly and a fuel cell system including the same capable of providing a high power and high efficiency cell.

[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. Such a fuel cell is a clean energy source that can replace fossil energy, and has a merit that it can produce a wide range of outputs in a stack configuration by stacking unit cells, and 4-10 times more energy than a small lithium battery. It is drawing attention as a small and portable portable power source.

Representative examples of the fuel cell 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 has an advantage of having a high energy density and a high output, but requires attention to handling hydrogen gas and reforms fuel for reforming methane, methanol, natural gas, etc. to produce hydrogen as fuel gas. There is a problem that requires additional equipment such as a device.

On the other hand, the direct oxidation fuel cell has a slower reaction rate and has a lower energy density, a lower output, and a larger amount of electrode catalyst than the polymer electrolyte fuel cell. However, the liquid fuel is easy to handle and the operating temperature is high. Has the advantage of being low and in particular not requiring a fuel reformer.

An object of the present invention is to provide a membrane-electrode assembly for a fuel cell which is excellent in ion conductivity and can prevent crossover of fuel.

Another object of the present invention is to provide a fuel cell system that can exhibit high power and high efficiency including the membrane-electrode assembly.

In order to achieve the above object, the present invention includes an anode electrode and a cathode electrode positioned opposite each other, and comprises a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, at least one surface of the polymer electrolyte membrane Provided is a membrane-electrode assembly for which a coating layer is formed.

The present invention also includes the membrane-electrode assembly, and includes an electricity generator for generating electricity through an oxidation reaction of a fuel and a reduction reaction of an oxidant, a fuel supply unit for supplying fuel to the electricity generator, and an oxidant for supplying the electricity generator to the electricity generator. It provides a fuel cell system comprising an oxidant supply.

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

According to the recent research results of the membrane-electrode assembly of a direct oxidation fuel cell, there has been a study showing that the output of gold particles is coated on the polymer electrolyte membrane by chemical vapor deposition (CVD) and plasma vapor deposition (PVD). This is because the coated gold particles have affinity with S of the polyperfluorosulfonic acid constituting the polymer electrolyte membrane, so that the gold can be adsorbed to maintain the surface of the polymer electrolyte membrane in the hydrophilic state, thereby improving the ion conductivity of the polymer electrolyte membrane. Can be. However, since gold vapor deposition, chemical vapor deposition or plasma vapor deposition is performed in an ultra-high vacuum state, excessive stress is applied to the polymer electrolyte membrane, and thus the physical properties of the polymer electrolyte membrane are remarkably degraded.

The present invention provides a fuel cell membrane-electrode assembly comprising a polymer electrolyte membrane having improved conductivity without deteriorating the swelling characteristics of the polymer electrolyte membrane.

The membrane-electrode assembly for a fuel cell of the present invention includes an anode electrode and a cathode electrode positioned to face each other, and includes a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode. On at least one surface of the polymer electrolyte membrane, a metal coating layer is formed. 1 illustrates a structure in which a metal coating layer is formed on one surface of an anode electrode in the membrane-electrode assembly of the present invention having such a configuration. That is, the membrane-electrode assembly 200 of the present invention includes a polymer electrolyte membrane 120 having a metal coating layer 122 formed on one surface thereof, and includes a cathode electrode 130 and an anode electrode 140 positioned on both sides of the polymer electrolyte membrane. ).

As said metal, Au, Ag, Rh, Ir, and mixtures thereof are preferable, and Au is more preferable. Along with the metal (called the first metal), a second metal, which is W, Mo, and a mixture thereof, may also be used. In the case of further using the second metal, the amount thereof is preferably 1 to 10 parts by weight based on 100 parts by weight of the first metal. If the second metal is used in an amount less than 1 part by weight, the effect of additional use of the second metal is inadequate. If it is more than 10 parts by weight, the resistance is increased and the reactant is poor, and thus the output is lowered.

The membrane-electrode assembly for a fuel cell of the present invention is preferred because it can accelerate the CO oxidation reaction to improve the oxidation reaction of fuels, especially hydrocarbon fuels, and therefore, it is preferable to apply the fuel cell membrane electrode assembly directly.

The metal coating layer is preferably formed in an area corresponding to 1 to 99% of the total area of the surface of the polymer electrolyte membrane, more preferably in an area corresponding to 10 to 50%. When the width of the metal coating layer is less than 1% of the total area of the surface of the polymer electrolyte membrane, the effect of forming a metal coating layer is inadequate, and when the width of the metal coating layer exceeds 99%, the output is reduced due to too many metal particles. It is not desirable that the polymer electrolyte membrane is detached.

In addition, the thickness of the metal coating layer formed is preferably 10nm to 10㎛, more preferably 100nm to 5㎛. If the thickness of the metal coating layer is thinner than 10nm, the effect of forming the metal coating layer is insignificant, and if the thickness of the metal coating layer is thicker than 10㎛, the coating layer is too thick, the output is reduced, the catalyst layer and the polymer electrolyte membrane is detached is not preferable.

In the present invention, the metal coating layer is preferably formed of metal nanoparticles having an average particle size of nanometers. As such, since the metal coating layer is formed using fine metal nanoparticles having an average particle size of nanometers, there is no problem that the metal nanoparticles are not uniformly coated in the spraying process.

The average particle size of the metal nanoparticles is preferably 1 to 200 nm, more preferably 10 to 100 nm. If the average particle size of the metal nanoparticles is smaller than 1 nm, the dispersibility is not good, it is easily aggregated, and if it exceeds 200 nm, the catalytic properties are not low, which is not preferable.

The polymer electrolyte membrane is generally used as a polymer electrolyte membrane in a fuel cell, and any one made of a polymer resin having hydrogen ion conductivity may be used. Representative examples thereof include a polymer resin having a cation exchange group selected from the group consisting of sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, phosphonic acid groups and derivatives thereof in the side chain.

Representative examples of the polymer resin include a fluorine polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, a polyether sulfone polymer and a polyether ketone It may include one or more selected from polymers, polyether-etherketone-based polymers or polyphenylquinoxaline-based polymers, more preferably poly (perfluorosulfonic acid) (generally marketed as Nafion), poly (Perfluorocarboxylic acid), copolymers of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid groups, defluorinated sulfide polyether ketones, aryl ketones, poly (2,2'-m-phenylene)- 5,5'-bibenzimidazole (poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole) or poly (2,5-benzimidazole) may be mentioned. In addition, such hydrogen H may be substituted with Na, K, Li, Cs or tetrabutylammonium in the hydrogen-conducting group of the on-conductive polymer, and in the case of replacing the H with Na in an ion exchanger at the side chain end, In the case of using butylammonium, tetrabutylammonium hydroxide may be substituted, and K, Li, or Cs may also be substituted using an appropriate compound. The description will be omitted.

In the method of manufacturing a polymer electrolyte membrane having at least one metal layer of the present invention, first, metal nanoparticles are dispersed in a solvent to prepare a metal nanoparticle liquid. In this case, isopropyl alcohol, methanol, ethanol or propanol may be used as the solvent. In addition, the addition amount of the metal nanoparticles is preferably 0.0001 to 1% by weight. If the added amount of the metal nanoparticles is less than 0.0001% by weight, the effect of using the metal nanoparticles is insignificant. If the amount of the metal nanoparticles exceeds 1% by weight, the metal particles grow to become large particles, which is not preferable.

In this case, a hydrogen ion conductive binder may be further added to the solvent. Examples of the hydrogen ion conductive binder include fluoro polymers such as perfluorosulfonate, polyamide polymers, polyether polymers, benzimidazole polymers, polyimide polymers, polyetherimide polymers, and polyphenylene sulfides. 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 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 by Na in the ion-exchange group of the side chain terminal, NaOH is substituted in the preparation of the catalyst composition, and tetrabutylammonium hydroxide is used in the case of using tetrabutylammonium, and K, Li or Cs is also 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 metal nanoparticle liquid is sprayed on at least one surface of the polymer electrolyte membrane and then dried to form a metal coating layer on the surface of the polymer electrolyte membrane.

The injection process may be carried out at room temperature and atmospheric pressure conditions. In addition, the drying process may be carried out at room temperature to 60 ℃. If the spraying process and the drying process are performed at too high a temperature, the size of the metal nanoparticles is increased, which is not preferable.

The membrane-electrode assembly of the present invention includes an anode electrode and a cathode electrode which face each other with the polymer electrolyte membrane interposed therebetween. The anode electrode and the cathode electrode include an electrode substrate and a catalyst layer formed on the electrode substrate.

The catalysts include platinum, ruthenium, osmium, platinum-ruthenium alloys, platinum-osmium alloys, platinum-palladium alloys and platinum-M alloys (M is Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Preference is given to one or more catalysts selected from the group consisting of one or more transition metals selected from the group consisting of Zn. 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 Or at least one selected from the group consisting of / Mo, Pt / Ru / V, Pt / Fe / Co, Pt / Ru / Rh / Ni, and Pt / Ru / Sn / W.

In addition, such a metal catalyst may be used as the metal catalyst (black) itself, or may be supported on a carrier. As the carrier, carbon such as acetylene black, denka black, activated carbon, ketjen black, graphite may be used, or inorganic fine particles such as alumina, silica, titania, zirconia may be used, but carbon is generally used.

The substrate may be 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 of the (metalized polymer fiber)) 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 a coating method using a doctor blade according to the viscosity of the composition, but is not limited thereto.

In the electrode of the present invention having the above-described configuration, the metal nanoparticles and the catalyst are first mixed to maximize the effect of enhancing the interaction between the metal nanoparticles and the catalyst, and then the binder is mixed with the mixture to prepare a catalyst composition, and the catalyst It can be prepared by the process of applying the composition to the electrode substrate.

The binder may be a fluoropolymer such as perfluorosulfonate, a polyamide polymer, a polyether polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, At least one hydrogen ion conductive polymer such as polysulfone polymer, polyether sulfone polymer, polyether ketone polymer, polyether ether ketone crab polymer or 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 by Na in the ion-exchange group of the side chain terminal, NaOH is substituted in the preparation of the catalyst composition, and tetrabutylammonium hydroxide is used in the case of using tetrabutylammonium, and K, Li or Cs is also 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 the fuel cell system including the membrane-electrode assembly of the present invention, the electricity generation unit serves to generate electricity through an oxidation reaction of a fuel and a reduction reaction of an oxidant, and includes an anode electrode and a cathode electrode located opposite to each other, And a membrane-electrode assembly comprising a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode.

The fuel supply unit serves to supply fuel to the electricity generator. In the present invention, the fuel may include hydrogen or hydrocarbon fuel in gas or liquid state. Representative examples of the hydrocarbon fuel include methanol, ethanol, propanol, butanol or natural gas.

A schematic structure of the fuel cell system of the present invention is shown in FIG. 2, which will be described in more detail with reference to the following. Although the structure shown in FIG. 2 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 generating unit 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)

Gold nanoparticle dispersions were prepared by dispersing 0.01% by weight of the gold nanoparticles with an average particle size of 5-10 nm in an isopropyl alcohol solvent. The gold nanoparticle dispersion was sprayed on a Nafion 115 (perfluorosulfonic acid) polymer membrane at room temperature and atmospheric pressure and dried at 60 ° C. to prepare a polymer electrolyte membrane having a gold coating layer having a thickness of 100 nm.

88% by weight of Pt-Ru black catalyst and Pt black catalyst and 12% by weight of Nafion / H ₂ O / 2-propanol (Solution Technology Inc.) at a concentration of 5% by weight for the anode and cathode electrodes A catalyst composition was prepared, respectively, and the catalyst composition was coated on carbon paper to prepare an anode electrode and a cathode electrode.

A unit cell was manufactured using the anode electrode, the cathode electrode, and the polymer electrolyte membrane.

(Comparative Example 1)

The same procedure as in Example 1 was carried out except that a Nafion 115 (perfluorosulfonic acid) polymer electrolyte membrane without a gold coating layer was used.

The output densities at 0.45V, 0.4V and 0.35V of the batteries prepared according to Example 1 and Comparative Example 1 were measured at 50 ° C., 60 ° C. and 70 ° C., respectively, and the results are shown in Table 1 below.

Comparative Example 1 (mW / cm ² ) Example 1 (mW / cm ² ) 0.45V 0.4 V 0.35V 0.45V 0.4 V 0.35V 50 ℃ 40 65 80 43 71 86 60 ℃ 63 90 118 69 100 138 70 ℃ 90 110 139 99 133 158

As shown in Table 1, it can be seen that the output density of the fuel cell of Example 1 using the polymer electrolyte membrane having the metal coating layer is superior to that of Comparative Example 1.

As described above, the membrane-electrode assembly for a fuel cell of the present invention has excellent ion conductivity as the metal coating layer is formed, and can prevent fuel crossover, thereby implementing a high power and high efficiency fuel cell system.

Claims (15)

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, At least one surface of the polymer electrolyte membrane is a metal coating layer is formed for the fuel cell membrane electrode assembly. The method of claim 1, And said metal is selected from the group consisting of Au, Ag, Ir and mixtures thereof. The method of claim 2, And said metal is Au. The method of claim 1, The metal is a first metal selected from the group consisting of Au, Ag, Rh and Ir and mixtures thereof A membrane-electrode assembly for a fuel cell comprising a second metal selected from the group consisting of W, Mo and mixtures thereof. The method of claim 1, Wherein the metal coating layer is a fuel cell membrane-electrode assembly formed of metal nanoparticles having an average particle size of 1 to 200nm. The method of claim 5, Wherein the metal coating layer is formed of metal nanoparticles having an average particle size of 10 to 100 nm. The method of claim 1, Wherein the metal coating layer is a fuel cell membrane-electrode assembly formed of an area corresponding to 1 to 99% of the total surface area of the polymer electrolyte membrane. The method of claim 7, wherein Wherein the metal coating layer is a fuel cell membrane-electrode assembly that is formed in an area corresponding to 10 to 50% of the total surface area of the polymer electrolyte membrane. The method of claim 1, The metal coating layer is a fuel cell membrane electrode assembly having a thickness of 10nm to 10㎛. The method of claim 9, The metal coating layer is a fuel cell membrane-electrode assembly having a thickness of 100nm to 5㎛. The method of claim 1, The polymer electrolyte membrane in which the metal coating layer is formed Dispersion of the metal nanoparticles in a solvent to prepare a dispersion Membrane electrode assembly for a fuel cell prepared by the step of spraying the dispersion to a polymer membrane. The method of claim 11, Membrane electrode assembly for a fuel cell further comprising a hydrogen ion conductive binder to the dispersion. The method of claim 1, The membrane electrode assembly is a fuel cell membrane electrode assembly for direct oxidation fuel cells. An electric generator comprising the membrane-electrode assembly according to any one of claims 1 to 13 and generating electricity through an oxidation reaction of a fuel and a reduction reaction of an oxidant; A fuel supply unit supplying fuel to the electricity generation unit; And Oxidant supply unit for supplying an oxidant to the electricity generating unit Fuel cell system comprising a. The method of claim 14, And the fuel is a hydrocarbon fuel.

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