KR20070109233A - 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 facilitate supply of fuel and discharge of a reaction product, thereby improving an output characteristic of a fuel cell. A membrane electrode assembly(131) for a fuel cell includes: an anode electrode and a cathode electrode(20,20') which are located to face each other; and a polymeric electrolyte membrane(70) placed between the anode electrode and cathode electrode. At least one of the anode electrode and cathode electrode comprises an electrode substrate(60,60') and a catalytic layer(50,50') placed on the electrode substrate. The catalytic layer includes: a first catalytic layer(30,30') which is placed on the electrode substrate and comprises a hydrophobic polymer and a metal catalyst; and a second layer(40.40') which is placed on the first catalytic layer and comprises a metal catalyst.

Description

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

1 is a view schematically showing a membrane-electrode assembly for a fuel cell according to an embodiment of the present invention,

2 is a view schematically showing a fuel cell system according to another embodiment of the present invention.

[Industrial use]

The present invention relates to a membrane-electrode assembly for a fuel cell, and a fuel cell system including the same, and more particularly, to smoothly supply fuel and discharge a reaction product, thereby improving output characteristics of the fuel cell. A membrane-electrode assembly for a fuel cell, 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, ethyl alcohol, 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). In addition, the case of using methanol as fuel in the direct oxidation fuel cell 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 fuel, has a low operating temperature, and is particularly suitable as a compact and general purpose mobile power source due to the fact that no fuel reforming device is required. It is recognized as a system.

In such a fuel cell system, a substantially generating stack is a unit cell (hereinafter referred to as "electric generation") consisting of a membrane-electrode assembly (MEA) and a separator (or bipolar plate). Sub- ") are stacked to several tens. 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.

The principle of generating electricity in a fuel cell is that fuel is supplied to an anode electrode, which is a fuel electrode, adsorbed to a catalyst of the anode electrode, and the fuel is oxidized to generate hydrogen ions and electrons, and the generated electrons are an anode cathode according to an external circuit. Reaching the electrode, hydrogen ions pass through the polymer electrolyte membrane and are delivered to the cathode electrode. An oxidant is supplied to the cathode, and the oxidant, hydrogen ions, and electrons react on the catalyst of the cathode to generate electricity while producing water.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel cell membrane-electrode assembly capable of smoothly supplying fuel and discharging reaction products, thereby improving output characteristics of the fuel cell.

Another object of the present invention is to provide a fuel cell system comprising the membrane-electrode assembly for fuel cells.

The present invention, in order to achieve the above object, the present invention includes 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, at least one of the anode electrode and the cathode electrode Provides a membrane-electrode assembly for a fuel cell comprising an electrode substrate and a catalyst layer positioned on the electrode substrate. At this time, the catalyst layer is located on the electrode substrate, it is preferable to include a first catalyst layer containing a hydrophobic polymer and a metal catalyst, and a second catalyst layer located on the first catalyst layer and including a metal catalyst.

The invention also includes a membrane electrode assembly, and separators located on both sides of the membrane electrode assembly, at least one electricity generating unit for generating electricity through the electrochemical reaction of the fuel and the oxidant, the fuel to the electricity A fuel cell system includes a fuel supply unit for supplying a generator, and an oxidant supply unit for supplying an oxidant to the electricity generator.

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

In general, the catalyst layer of the membrane-electrode assembly is formed by applying a composition in which a metal catalyst and a binder are dispersed in a solvent to an electrode substrate or a polymer electrolyte membrane. The pores present in this catalyst layer serve to enhance the activity of the electrode catalyst, to supply fuel or oxidant and to discharge the reaction product.

However, when the discharge function of the reaction product in the catalyst layer is not smooth, it becomes difficult to supply the reactants such as fuel or oxidant, thereby reducing the output characteristics of the fuel cell.

In contrast, in the present invention, the hydrophobic first catalyst layer is in contact with the electrode substrate where the reactant supply and the reaction product are actively discharged, and the first catalyst layer is in contact with the polymer electrolyte membrane in which the catalytic reaction occurs more actively in the catalyst layer. By forming a second catalyst layer containing a metal catalyst in a higher content than that, it is possible to smooth the fuel supply and the discharge of the reaction product in the catalyst layer, increase the catalytic activity, and as a result, improve the output characteristics of the fuel cell.

1 is a schematic cross-sectional view of a membrane-electrode assembly for a fuel cell of the present invention. Although the structure shown in FIG. 1 has a two-layered catalyst layer formed on both sides of the anode electrode and the cathode electrode, the membrane-electrode assembly of the present invention is not limited to such a structure, and the catalyst layer of the two-layer structure includes an anode electrode and Of course, it may be formed only on any one of the cathode electrode.

Referring to FIG. 1, the membrane-electrode assembly 131 according to the exemplary embodiment of the present invention may include the polymer electrolyte membrane 70 and the fuel cell electrodes 20 and 20 disposed on both surfaces of the polymer electrolyte membrane 70, respectively. Include '). The electrodes 20 and 20 'include electrode substrates 60 and 60' and catalyst layers 50 and 50 'formed on the surface of the electrode substrate.

In the membrane-electrode assembly 131, an electrode 20 disposed on one surface of the polymer electrolyte membrane 70 is called an anode electrode (or a cathode electrode), and an electrode 20 ′ disposed on the other surface is called a cathode electrode ( Or anode electrode). The anode electrode 20 causes an oxidation reaction to generate hydrogen ions and electrons from the fuel delivered through the electrode substrate 60 to the catalyst layer 50, and the polymer electrolyte membrane 70 generates hydrogen generated at the anode electrode 20. Ions are moved to the cathode electrode 20 ', and the cathode electrode 20' is the hydrogen ions supplied through the polymer electrolyte membrane 70 and the oxidant transferred to the catalyst layer 50 'through the electrode substrate 60'. Causes a reduction reaction to produce water.

The catalyst layers 50 and 50 'catalyze the related reaction (oxidation of fuel and reduction of oxidant), and include a first catalyst layer 30 and 30' and a second catalyst layer 40 and 40 '. .

The first catalyst layers 30 and 30 'are formed on the electrode substrates 60 and 60' and include a hydrophobic polymer and a metal catalyst.

The hydrophobic polymer is included in the form of particles to form pores in the first catalyst layer, the pores formed by the hydrophobic polymer serves to facilitate the supply of fuel and the emission of gaseous carbon dioxide which is a reaction product generated in the first catalyst layer. do. Such hydrophobic polymers include polyvinylidene fluoride, polytetrafluoroethylene, fluorinated ethylene propylene, polychlorotrifluoroethylene, fluoroethylene polymer, polyhexafluoropropylene, Fluorine-based polymers such as polyperfluoroalkyl vinyl ether and polyperfluorosulfonyl fluoride alkoxy vinyl ether; Polyolefin-based polymers such as polyethylene, polypropylene, polyisoprene, polyethylenepropylene, and polybutadiene; Benzene group-containing polymers such as polystyrene and polyalphamethylstyrene; Or these copolymers etc. can be used.

The hydrophobic polymer is preferably included in the form of particles so as to form pores having an optimal size in the catalyst layer together with the metal catalyst. Specifically, the hydrophobic polymer particles preferably have an average particle diameter of 10 to 100 nm, more preferably may have an average particle diameter of 10 to 50 nm. If the average particle diameter of the hydrophobic polymer is less than 10 nm, it is not preferable to form hydrophobic pores, and if it exceeds 100 nm, the electron transfer resistance is large, which is not preferable.

In addition, the metal catalyst may participate in the reaction of a fuel cell as a catalyst, and any one that can be used as a catalyst may be used, and a platinum-based catalyst may be used as a representative example. 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, Transition metals selected from the group consisting of Cu, Zn, Sn, Mo, W, Rh, and combinations thereof). As described above, the anode electrode and the cathode electrode may use the same material, but in order to prevent the catalyst poisoning caused by CO generated during the anode electrode reaction in the direct oxidation fuel cell, a platinum-ruthenium alloy catalyst is used as the anode. It is more preferable as an electrode catalyst. 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, such a metal catalyst may be used as the metal catalyst (black) itself, or may be supported on a carrier. As the carrier, carbonaceous 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 alumina, silica, zirconia, Inorganic fine particles such as titania may be used, but carbon-based materials are generally used.

The first catalyst layers 30 and 30 'may include the hydrophobic polymer and the metal catalyst in a weight ratio of 10:90 to 60:40, and more preferably 20:80 to 50:50. have. The mixing weight ratio of the hydrophobic polymer and the metal catalyst is preferably within the above range because it is easy to form hydrophobic pores, and if it is out of the above range, the electron transfer resistance may increase, which is not preferable.

The first catalyst layer (30, 30 ') also improves the electrical conductivity by easily moving the electrons generated by the catalyst surface reaction by the formation of a conductive network in the first catalyst layer, to secure the pores in the catalyst layer to supply fuel and Carbonaceous materials may be further included to facilitate mass transfer such as discharge of reaction products.

The carbon-based material preferably has an aspect ratio of at least one, specifically, selected from the group consisting of carbon fiber, carbon nanotube, carbon nanonode, vapor grown carbon fiber (VGCF), and combinations thereof. It can be used, more preferably in terms of cost competitiveness compared to electronic conductivity can be used vapor-grown carbon fiber.

In addition, the first catalyst layers 30 and 30 ′ may further include a binder resin to improve adhesion of the catalyst layer and transfer hydrogen ions.

It is preferable to use a polymer resin having hydrogen ion conductivity as the binder resin, more preferably 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. Any polymer resin which has can be used. Preferably, 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, a polyether One or more hydrogen ion conductive polymers selected from ether ketone polymers or polyphenylquinoxaline polymers, more preferably poly (perfluorosulfonic acid), poly (perfluorocarboxylic acid), Copolymers of tetrafluoroethylene with fluorovinyl ethers containing sulfonic acid groups, defluorinated sulfided polyether ketones, aryl ketones, poly (2,2'-m-phenylene) -5,5'-bibenzimidazole One containing one or more hydrogen ion conductive polymers selected from (poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole) or poly (2,5-benzimidazole) 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 resin may be used in the form of a single substance or a mixture, and may also be optionally used with a nonconductive compound 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.

Examples of the non-conductive compound include tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer (PFA), and ethylene / tetrafluoroethylene (ETFE). )), Ethylenechlorotrifluoro-ethylene copolymer (ECTFE), polyvinylidene fluoride, copolymer of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), dodecylbenzenesulfonic acid and sorbitol (Sorbitol) At least one selected from the group consisting of more preferred.

The binder resin is preferably included in 10 to 30 parts by weight, more preferably 15 to 25 parts by weight with respect to 100 parts by weight of the metal catalyst. When the content of the metal catalyst is less than 10 parts by weight, it is not preferable because the ion transfer force is insufficient and cannot act as a binding of the catalyst, and when the content of the metal catalyst exceeds 30 parts by weight, the reaction area of the catalyst is reduced.

The second catalyst layers 40 and 40 'including the metal catalyst are formed on the first catalyst layers 30 and 30' having the above configuration. The second catalyst layers 40 and 40 'may exhibit relatively hydrophilicity as compared to the first catalyst layers 30 and 30' including hydrophobic polymers, and may further include hydrophilic polymers to show hydrophilicity.

The metal catalyst is the same as described above. However, the metal catalyst included in the second catalyst layers 40 and 40 ′ is preferably included in a larger amount than the first catalyst layer so that a higher catalytic reaction may occur.

Examples of the hydrophilic polymer include polyether polymers such as poly (ethylene oxide), polypropylene oxide, poly (methylene oxide), or copolymers thereof, polyvinyl alcohol, polyvinylacetate-polyvinyl alcohol copolymer, and poly (hydroxy Polymers having hydroxy groups such as methyl acrylate), poly (hydroxyethyl acrylate), poly (hydroxyethyl methacrylate), acrylamide-based polymers such as polyacrylamide, polymethacrylamide, cellulose, methylcellulose And cellulose polymers such as carboxylate methylene cellulose, polycarboxylic acid polymers such as polyacrylic acid and polymethacrylic acid, and polymers such as polysulfonic acid such as polystyrene sulfonic acid and polyacrylamidopropyl sulfonic acid.

The hydrophilic polymer may be included in an amount of 5 to 50% by weight, and more preferably 5 to 25% by weight, based on the total weight of the second catalyst layers 40 and 40 '. If the content of the hydrophilic polymer is less than 5% by weight, it is not preferable because the migration of hydrogen ions is not easy. If the content of the hydrophilic polymer exceeds 50% by weight, it is not preferable because it acts as a barrier to the surface of the catalyst and inhibits diffusion of the reactants.

The second catalyst layer may further include a binder resin to improve adhesion to the polymer electrolyte membrane and transfer hydrogen ions as in the first catalyst layer. The binder resin is the same as described above.

The first catalyst layers 30 and 30 'and the second catalyst layers 40 and 40' have a thickness ratio of 1: 1 to 3: 1, more preferably 3: 2 to 3: 1. It may have a thickness ratio. When the thickness ratio range of the first catalyst layer and the second catalyst layer is out of the range, the diffusion resistance of the reactant and the product is increased, which is not preferable because the diffusion resistance increases.

The catalyst layers 50 and 50 'are supported by the electrode substrates 60 and 60'.

The electrode substrate (60, 60 ') serves to support the electrode and to diffuse the fuel and oxidant to the catalyst layer to facilitate the fuel and oxidant easily accessible to the catalyst layer (50, 50'). A conductive substrate is used as the electrode substrate, and representative examples thereof include carbon paper, carbon cloth, carbon felt, or metal cloth (porous film or polymer composed of metal cloth in a fibrous state). The metal film formed on the surface of the fabric formed of fibers (referred to as metalized polymer fiber) may be used, but is not limited thereto.

The electrode substrates 60 and 60 'are preferably water-repellent treated with a fluorine-based resin because they can prevent the reactant diffusion efficiency from being lowered by water generated when the fuel cell is driven. Examples of the fluorine-based resin include polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride alkoxy vinyl ether, and fluorinated ethylene propylene (Fluorinated). ethylene propylene), polychlorotrifluoroethylene or copolymers thereof.

In addition, it may further include a microporous layer (not shown) to enhance the reactant diffusion effect in the electrode substrate (60, 60 '). 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. The binder resin may be polytetrafluoro ethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride, alkoxy vinyl ether, polyvinyl alcohol, cellulose acetate Or copolymers thereof and the like can be preferably used. As the solvent, alcohols such as ethanol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, water, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, etc. may 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 fuel cell electrode having the structure as described above may be used as at least one of the anode and the cathode electrode, the anode electrode when considering the ease of supply of fuel and carbon dioxide through the pores formed by the hydrophobic polymer in the first catalyst layer It is more preferable to use the same, and in consideration of the ease of supply of the oxidant through the pores formed by the hydrophobic polymer in the first catalyst layer, it is more preferable to use it as the cathode electrode. Even more preferably, an electrode having such a structure is used for both the anode electrode and the cathode electrode.

In addition, the membrane-electrode assembly 131 including the electrode includes the polymer electrolyte membrane 70 positioned between the anode and the cathode electrodes 20 and 20 '.

The polymer electrolyte membrane 70 functions as an ion exchange to transfer hydrogen ions generated in the catalyst layer of the anode electrode to the catalyst layer of the cathode electrode, and it is preferable to use a polymer having excellent hydrogen ion conductivity. Generally used as a polymer electrolyte membrane in a fuel cell, anything made of a polymer resin having hydrogen ion conductivity can be used. Representative examples thereof include 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.

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. have.

In the hydrogen ion conductive group of the hydrogen ion conductive polymer, H may be substituted with Na, K, Li, Cs or tetrabutylammonium. In the hydrogen ion conductive group of the hydrogen ion conductive polymer, NaOH is substituted when H is replaced with Na, and tetrabutylammonium hydroxide is used when the substituent is substituted with tetrabutylammonium. It can be substituted using. Since this substitution method is well known in the art, detailed description thereof will be omitted.

In addition, the polymer electrolyte membrane 70 is plasma-treated and acid-etched on at least one surface of the polymer electrolyte membrane in order to increase the interaction between the catalyst layers 50 and 50 'and the surface of the polymer electrolyte membrane 70 and increase the three-phase interface area. Having surface roughness by surface treatment by methods such as anodizing, corona treatment, rubbing, pressing using a plastic substrate having a certain pattern, sand papering or sand blasting desirable.

More preferably, both surfaces of the polymer electrolyte membrane 70 may have surface roughness.

The membrane-electrode assembly 131 having the structure as described above is coated with a composition for forming a first catalyst layer including a hydrophobic polymer and a metal catalyst on one surface of an electrode substrate to form a first catalyst layer; Forming a second catalyst layer by applying a composition for forming a second catalyst layer comprising a metal catalyst and a hydrogen ion conductive binder resin on the first catalyst layer, and bonding the electrode substrate on which the catalyst layer is formed to the polymer electrolyte membrane. It can be prepared by.

Hereinafter, a method of manufacturing the membrane-electrode assembly will be described in detail. First, a composition for forming a first catalyst layer is prepared by dispersing a hydrophobic polymer and a metal catalyst in a solvent.

The hydrophobic polymer and the metal catalyst are the same as described above, and the high hydrophobic polymer and the metal catalyst are included in the composition for forming the first catalyst layer in a 10:90 to 60:40 weight ratio, and more preferably 20:80 to 50: It may be included in 50 weight ratio.

As the solvent, an alcohol such as ethyl alcohol, isopropyl alcohol, ethyl alcohol, n-propyl alcohol, butyl alcohol, or water may be used, and more preferably, a mixture of water and 2-propyl alcohol may be used. The solvent may be included as a remainder in the composition for forming the catalyst layer, and preferably added in an appropriate amount so as to form the catalyst layer at an appropriate viscosity.

The composition for forming the catalyst layer may further include one selected from the group consisting of carbonaceous materials, binder resins, and combinations thereof.

The carbonaceous material and the binder resin are the same as described above.

Next, the prepared composition for forming the first catalyst layer is applied to one surface of the electrode substrate to form a first catalyst layer.

The coating process is spray coating method, immersion method, reverse roll method, direct roll method, gravure method, screen printing method, spray coating method, coating method using a doctor blade, gravure coating method, dip coating method, silk screen depending on the viscosity of the composition It may be carried out by a method selected from the group consisting of a method, a painting method, a slot die coating method and the like, but is not limited thereto. More preferably, a spray coating method can be used.

Subsequently, a second catalyst layer-forming composition prepared by dispersing a metal catalyst in a solvent is applied on the first catalyst layer and dried to form a second catalyst layer.

The coating method of the metal catalyst, the solvent, and the composition for forming the second catalyst layer including the same is the same as described above for the first catalyst layer.

In addition, the composition for forming the second catalyst layer may further include one selected from the group consisting of a hydrophilic polymer, a binder resin, and a combination thereof. The hydrophilic polymer and binder resin are the same as described above.

Thereafter, a membrane-electrode assembly may be manufactured by bonding a polymer electrolyte membrane to the electrode substrate on which the second catalyst layer is formed.

In the above method, the catalyst layer is formed on the electrode substrate, but the catalyst layer may be formed on the polymer electrolyte membrane first. In this case, the membrane-electrode assembly may be manufactured by forming a second catalyst layer on the polymer electrolyte membrane, and then forming a first catalyst layer and then bonding the electrode substrate.

The electrode substrate and the polymer electrolyte membrane are the same as described above, and the method of binding the polymer electrolyte membrane and the electrode substrate is well known in the art, and thus detailed description thereof will be omitted.

The membrane-electrode assembly manufactured by the above-described manufacturing method has a hydrophobic first catalyst layer on the electrode substrate side where the reactant supply and the reaction product are actively discharged, and a polymer electrolyte membrane side where the catalytic reaction occurs actively. By forming a hydrophilic second catalyst layer, it is possible to facilitate reactant supply and discharge of the reaction product without reducing the catalytic reaction. As a result, the output of the fuel cell can be improved. Accordingly, the membrane-electrode assembly has excellent effects when employed in a polymer electrolyte fuel cell (PEMFC), a direct oxidation fuel cell, and a mixed reactant fuel cell. It may be represented, and more preferably may be employed in a direct oxidation fuel cell.

The present invention also provides a fuel cell system comprising the membrane-electrode assembly.

The fuel cell system of the present invention includes at least one electricity generator, a fuel supply and an oxidant supply.

The electricity generating portion includes a membrane-electrode assembly and a separator (also called bipolar plate). The membrane-electrode assembly includes a polymer electrolyte membrane and cathode and anode electrodes existing on both sides of the polymer electrolyte membrane. 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 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.

The fuel cell system of the present invention can be employed without limitation in Polymer Electrolyte Membrane Fuel Cell (PEMFC), Direct Oxidation Fuel Cell, and Mixed Reactant Fuel Cell. Can be.

A schematic structure of a fuel cell system 100 according to an embodiment of the present invention is shown in FIG. 2, which will be described in more detail with reference to the following. 2 shows a system for supplying fuel and oxidant to the electricity generation unit 130 using pumps 151 and 171, but the membrane-electrode assembly 131 for fuel cells of the present invention is limited to such a structure. Of course, it can be used in a fuel cell system having a structure using a diffusion method without using a pump.

The fuel cell system 100 includes a stack 110 having at least one electricity generator 130 for generating electrical energy through an oxidation reaction of a fuel and a reduction reaction of an oxidant, and a fuel supply unit 150 for supplying the fuel. ) And an oxidant supply unit 170 for supplying an oxidant to the electricity generation unit 130.

The fuel supply unit 150 supplying the fuel includes a fuel tank 153 for storing fuel and a fuel pump 151 connected to the fuel tank 153. The fuel pump 151 serves to discharge the fuel stored in the fuel tank 153 by a predetermined pumping force.

The oxidant supply unit 170 for supplying an oxidant to the electricity generating unit 130 of the stack 110 includes at least one oxidant pump 171 that sucks the oxidant with a predetermined pumping force.

The electricity generating unit 130 is a membrane-electrode assembly 131 for oxidizing and reducing a fuel and an oxidant and a separator (bipolar plate) 133 and 135 for supplying fuel and an oxidant to both sides of the membrane-electrode assembly 131. ), The electricity generating unit 130 is at least one gather to constitute a stack (110).

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)

Pt black (Hispec ^® 1000, manufactured by Johnson Matthey) and Pt / Ru black (Hispec ^® 6000, manufactured by Johnson Matthey) were mixed at a weight ratio of 5: 5 in a solvent in which water and isopropyl alcohol were mixed at a weight ratio of 10:80. One mixed catalyst and polytetrafluoroethylene particles having an average particle size of 50 nm were added in a weight ratio of 50:50. Subsequently, in the solvent of 10 wt% Nafion (Nafion ^®, Dupont Co.) aqueous dispersion of 40 parts by weight, to prepare a composition for forming the further first catalyst layer and then uniformly stirred by applying an ultrasonic insert.

The Teflon-treated carbon paper substrate (manufactured by SGL carbon group) was spray coated with the composition for forming the first catalyst layer to form a first catalyst layer having a thickness of 20 μm.

Separately, 10 parts by weight of a mixed catalyst obtained by mixing Pt black (Hispec ^® 1000, manufactured by Johnson Matthey) and Pt / Ru black (Hispec ^® 6000, manufactured by Johnson Matthey) in a weight ratio of 5: 5 was added 10:80 parts of water and isopropyl alcohol. It was added to the mixed solvent in weight ratio. Subsequently, in the solvent of 10 wt% Nafion (Nafion ^®, Dupont Co.) aqueous dispersion and further mixed into 40 parts by weight, to prepare a composition for forming the catalyst layer 2 by uniformly stirred by applying ultrasound.

The composition for forming the second catalyst layer was spray-coated on an electrode substrate on which the first catalyst layer was formed, and then dried to form a second catalyst layer having a thickness of 10 μm, thereby preparing the cathode.

An anode electrode was prepared in the same manner as above except for using a Pt / Ru black catalyst instead of a mixed catalyst of Pt black and Pt / Ru black.

Next, the cathode electrode and the anode electrode were laminated on both sides of a commercial fuel cell polymer electrolyte membrane (Nafion 115 Membrane, manufactured by DuPont) to prepare a membrane-electrode assembly. After inserting the prepared membrane-electrode assembly between the gasket (gasket), and inserted into two separators having a channel shape and a cooling channel of a predetermined shape, it was pressed between the copper end plate to prepare a single cell. .

(Example 2)

To a solvent in which water and isopropyl alcohol were mixed at a weight ratio of 10:80, a mixed catalyst and polytetrafluoroethylene particles were mixed at a weight ratio of 50:50 with Pt black and Pt / Ru black at a weight ratio of 5: 5. It was. Subsequently, 5 parts by weight of VGCF and 40 parts by weight of 10% by weight of Nafion's aqueous dispersion were added to the solvent, and then the first catalyst layer forming composition was prepared by uniformly stirring by applying ultrasonic waves. In the same manner as in the production of a single cell.

(Example 3)

To a solvent in which water and isopropyl alcohol were mixed at a weight ratio of 10:80, a mixed catalyst and poly (ethylene oxide) in which Pt black and Pt / Ru black were mixed at a weight ratio of 5: 5 were added at a weight ratio of 50:50. . Subsequently, 40 parts by weight of 10% by weight of Nafion's aqueous dispersion was added to the solvent, followed by mixing, and the same method as in Example 1 except for using the second catalyst layer-forming composition prepared by uniformly stirring by applying ultrasonic waves. A single cell was prepared by the method.

(Example 4)

A single cell was manufactured in the same manner as in Example 1, except that a polymer electrolyte membrane (Nafion 115 Membrane, manufactured by DuPont) for fuel cells having increased surface roughness by sandpapering on both surfaces thereof was used.

(Comparative Example 1)

10 parts by weight of a mixed catalyst containing Pt black and Pt / Ru black in a weight ratio of 5: 5 was added to a solvent in which water and isopropyl alcohol were mixed in a weight ratio of 10:80, followed by 40 parts by weight of 10% by weight Nafion aqueous dispersion. Put the ultrasonic wave was applied and uniformly stirred to prepare a catalyst layer forming composition.

A cathode electrode was prepared by spray coating a composition for forming a catalyst layer on the Teflon treated carbon paper substrate (manufactured by SGL carbon group).

An anode electrode was prepared in the same manner as above except using a Pt / Ru black catalyst.

Next, the anode electrode and the cathode electrode were laminated on both surfaces of a commercial electrolyte polymer electrolyte membrane (Nafion 115 Membrane, manufactured by DuPont) to manufacture a membrane-electrode assembly. After inserting the prepared membrane-electrode assembly between the gasket (gasket), and inserted into two separators having a channel shape and a cooling channel of a predetermined shape, it was pressed between the copper end plate to prepare a single cell. .

(Comparative Example 2)

To a solvent in which water and isopropyl alcohol were mixed at a weight ratio of 10:80, a mixed catalyst in which Pt black and Pt / Ru black were mixed at a weight ratio of 5: 5 and polytetrafluoroethylene particles having an average particle size of 50 nm It was added at a weight ratio of 50:50. Subsequently, after adding 40 parts by weight of 10% by weight of Nafion's aqueous dispersion into the solvent, ultrasonic wave was applied and uniformly stirred to prepare a composition for forming a catalyst layer.

The cathode electrode was prepared by spray coating the composition for forming a catalyst layer on the Teflon-treated carbon paper substrate (manufactured by SGL carbon group).

An anode electrode was prepared in the same manner as above except using a Pt / Ru black catalyst.

Next, the anode electrode and the cathode electrode were laminated on both surfaces of a commercial electrolyte polymer electrolyte membrane (Nafion 115 Membrane, manufactured by DuPont) to prepare a membrane-electrode assembly. After inserting the prepared membrane-electrode assembly between the gasket (gasket), and inserted into two separators having a channel shape and a cooling channel of a predetermined shape, it was pressed between the copper end plate to prepare a single cell. .

For each of the unit cells prepared in Example 1 and Comparative Examples 1 and 2, 1M methanol and dry air were supplied and operated at a temperature of 70 ° C. for 10 hours to measure output. The results are shown in Table 1 below.

In Table 1 below, the output of the unit cells of Example 1 and Comparative Example 2 is shown as a relative value when the output of the unit cell of Comparative Example 1 is 100%.

Print Example 1 130% Comparative Example 1 100% Comparative Example 2 20%

As shown in Table 1, the fuel cell of Example 1 including a catalyst layer having a hydrophobic and hydrophilic two-layered structure was found to show an excellent output compared to Comparative Examples 1 and 2 under the same operating conditions. In Table 1, the unit cell of Comparative Example 2 exhibits a significantly lower output than the unit cell of Comparative Example 1 because the content of the catalyst metal is relatively small due to the addition of a hydrophobic polymer, thereby lowering the catalytic activity.

Also about the unit cells of the said Examples 2-4, it carried out by the same method as the above, and measured the output.

As a result, the output of the same level as the unit cell of Example 1, it was confirmed that the unit cells of Examples 2 to 4 also have excellent output characteristics.

The membrane-electrode assembly according to the present invention can facilitate the supply of fuel and the discharge of reaction products, and as a result, the output of the fuel cell can be improved.

Claims (18)

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, At least one of the anode electrode and the cathode electrode, the electrode substrate; And a catalyst layer positioned on the electrode substrate, The catalyst layer is A first catalyst layer disposed on the electrode substrate and including a hydrophobic polymer and a metal catalyst; And Located on the first catalyst layer and comprising a second catalyst layer comprising a metal catalyst Membrane-electrode assembly for fuel cell. The method of claim 1, The hydrophobic polymer is a fuel cell membrane-electrode assembly selected from the group consisting of fluorine-based polymer, polyolefin-based polymer, benzene group-containing polymer, and copolymers thereof. The method of claim 2, The hydrophobic polymer may be polyvinylidene fluoride, polytetrafluoroethylene, fluorinated ethylene propylene, polychlorotrifluoroethylene, fluoroethylene polymer, polyhexafluoropropylene, poly purple Fluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride alkoxy vinyl ether, polyethylene, polypropylene, polyisoprene, polyethylenepropylene, polybutadiene, polystyrene, polyalphamethylstyrene, and copolymers thereof Membrane electrode assembly for fuel cells. The method of claim 1, The hydrophobic polymer is a fuel cell membrane-electrode assembly that is included in the form of particles having an average particle diameter of 10 to 100nm. The method of claim 1, The metal catalyst is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, A transition metal selected from the group consisting of Zn, Sn, Mo, W, Rh, and a combination thereof), and a membrane-electrode assembly for a fuel cell. The method of claim 1, The first catalyst layer is a fuel cell membrane-electrode assembly comprising a hydrophobic polymer: metal catalyst in a weight ratio of 10:90 to 60:40. The method of claim 1, The first catalyst layer further comprises a carbon-based material for a fuel cell membrane electrode assembly. The method of claim 7, wherein The carbon-based material is selected from the group consisting of carbon fibers, carbon nanotubes, carbon nano nodes, vapor grown carbon fibers (VGCF), and combinations thereof. The method of claim 1, The second catalyst layer is a fuel cell membrane-electrode assembly further comprising a hydrophilic polymer. The method of claim 9, The hydrophilic polymer is poly (ethylene oxide), poly (propylene oxide), poly (methylene oxide), polyvinyl alcohol, polyvinylacetate-polyvinyl alcohol copolymer, poly (hydroxymethyl acrylate), poly (hydroxyethyl Acrylates), poly (hydroxyethyl methacrylate) polyacrylamide, polymethacrylamide, cellulose, methylcellulose, carboxylatemethylene cellulose, polyacrylic acid, polymethacrylic acid, polystyrenesulfonic acid, polyacrylamidopropylsulfonic acid Membrane electrode assembly for a fuel cell is selected from the group consisting of, and copolymers thereof. The method of claim 9, The hydrophilic polymer is a fuel cell membrane-electrode assembly that is contained in 5 to 50% by weight relative to the total weight of the second catalyst layer. The method of claim 1, Wherein the first catalyst layer and the second catalyst layer has a thickness ratio of 1: 1 to 3: 1 fuel cell membrane electrode assembly. The method of claim 1, Wherein the polymer electrolyte membrane comprises 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 1, The polymer electrolyte membrane has a surface roughness membrane-electrode assembly for a fuel cell. The method of claim 1, The polymer electrolyte membrane may be plasma treated, etching with acid, anodizing, corona treatment, rubbing, pressing using a plastic substrate having a predetermined pattern, sand papering, sand blasting, and A membrane-electrode assembly for a fuel cell, which is surface treated by a method selected from the group consisting of a combination of these. The method of claim 1, The fuel cell membrane electrode assembly is a fuel cell membrane electrode assembly for a direct oxidation fuel cell membrane. A membrane-electrode assembly according to any one of claims 1 to 16, and a separator located on both sides of the membrane-electrode assembly, at least one of the electricity to generate electricity through the electrochemical reaction of the fuel and the oxidant Generator; 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 17,  The fuel cell system is a direct oxidation fuel cell system.

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