KR20090032772A - Membrane electrode assembly for fuel cell, method for preparing same, and fuel cell system including same - Google Patents

Abstract

A membrane electrode assembly for a fuel cell is provided to ensure excellent battery capacity by comprising a catalyst layer having a structure that has low content of a binder at the part adjacent to a solid polymer electrolyte membrane and high density and a structure that has high content of a binder at the part adjacent to an electrode substrate and proper porosity. A membrane electrode assembly for a fuel cell comprises an anode electrode and a cathode electrode which are faced with each other, and a polymeric electrolyte membrane positioned between the anode electrode and cathode electrode. At least one of the anode electrode and cathode electrode comprises an electrode base material and at least two catalyst layers including a catalyst and binder, which are positioned on the electrode substrate. The first catalyst layer contacting with the polymeric electrolyte membrane comprises the binder of less amount than the second catalyst layer contacting with the electrode substrate. The content ratio of the first catalyst layer and the second catalyst layer is 1 : 1.3 to 1 : 4.

Description

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

The present invention relates to a membrane-electrode assembly for a fuel cell, a method for manufacturing the same, and a fuel cell system including the same, and more particularly to a membrane-electrode assembly for a fuel cell, a method for manufacturing the same, and the like, which can exhibit improved cell performance. It relates to a fuel cell system.

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. This fuel cell is a clean energy source that can replace fossil energy, and has the advantage of generating a wide range of outputs by stacking unit cells, and having an energy density of 4-10 times that of a small lithium battery. It is attracting attention as a compact and mobile 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 the 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 a fuel reformer for reforming methane, methanol, natural gas, etc. in order to produce hydrogen, which is a fuel gas, requires attention to handling hydrogen gas. There is a problem that requires additional equipment such as.

On the other hand, the direct oxidation fuel cell has a lower energy density than the polymer electrolyte fuel cell, but it is easy to handle fuel and has a low operating temperature, so that it can be operated at room temperature, in particular, it does not require a fuel reformer.

In such fuel cell systems, the stack that substantially generates electricity comprises several unit cells consisting of a membrane-electrode assembly (MEA) and a separator (also called a bipolar plate). It has a structure laminated to several tens. The membrane-electrode assembly is called an anode electrode (also called "fuel electrode" or "oxidation electrode") and a cathode electrode (also called "air electrode" or "reduction electrode") with a polymer electrolyte membrane containing a hydrogen ion conductive polymer therebetween. ) Is located.

The principle of generating electricity in a fuel cell is that fuel is supplied to an anode electrode, which is a fuel electrode, adsorbed by a catalyst of the anode electrode, and then oxidized to generate hydrogen ions and electrons. The generated electrons are anode electrodes according to an external circuit. Is reached, the 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.

The present invention provides a membrane-electrode assembly that exhibits improved cell performance.

The present invention also provides a method of manufacturing the fuel cell membrane-electrode assembly.

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

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, 2. A fuel cell comprising a substrate and two catalyst layers positioned on the electrode substrate and comprising a catalyst and a binder, wherein the first catalyst layer in contact with the polymer electrolyte membrane comprises a smaller amount of binder than the second catalyst layer in contact with the electrode substrate. Provided is a membrane-electrode assembly.

In addition, the content ratio of the binder included in the first catalyst layer and the second catalyst layer is preferably 1: 1.3 to 1: 4.

In addition, it is preferable that at least one third catalyst layer exists between the first catalyst layer and the second catalyst layer.

In addition, the first catalyst layer preferably has a thickness of 10 to 40㎛.

In addition, the second catalyst layer preferably has a thickness of 20 to 50㎛.

In addition, the first catalyst layer preferably has a porosity of 30 to 70% by volume.

In addition, the second catalyst layer preferably has a porosity of 40 to 80% by volume.

In another aspect, the present invention, by applying a composition for forming the first catalyst layer on one surface of the release film, forming a first catalyst layer, transferring the first catalyst layer formed on the release film to a polymer electrolyte membrane, to the polymer electrolyte membrane Directly fixing the composition for forming the second catalyst layer on the transferred first catalyst layer to form a second catalyst layer, and placing and then binding the polymer electrolyte membrane having the first catalyst layer and the second catalyst layer formed thereon between electrode substrates. Provided is a method of manufacturing a membrane-electrode assembly for a fuel cell.

The composition for forming the first catalyst layer may include the first catalyst and the first binder in a weight ratio of 1: 0.05 to 1: 0.15, and the composition for forming the second catalyst layer may include the first catalyst and the second binder from 1: 0.1 to 0.1. It is preferable to include in the weight ratio of 1: 0.2.

The present invention also includes a separator located on both sides of the membrane-electrode assembly and the membrane-electrode assembly, the at least one electricity generating unit for generating electricity through an electrochemical reaction between a fuel and an 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.

The membrane-electrode assembly for a fuel cell of the present invention has an optimized structure having a low binder content and a dense structure at a portion adjacent to the polymer electrolyte membrane, and a high binder content at an adjacent portion with the electrode substrate and an appropriate porosity. Including a catalyst layer, excellent battery performance can be exhibited.

In general, a catalyst layer capable of easily penetrating and reacting with a hydrocarbon fuel is preferred as a catalyst layer of the membrane-electrode assembly. However, in this case, a large amount of fuel contacts at the interface between the anode electrode and the polymer electrolyte membrane, and the fuel is polymer. There is a problem in that crossover occurs that moves to the cathode electrode through the electrolyte membrane. In addition, the catalyst layer is usually formed through a direct coating, when the fuel cell is driven for a long time there is a problem that the polymer electrolyte membrane is expanded, so that desorption between the polymer electrolyte membrane and the catalyst layer occurs.

On the other hand, when the catalyst layer and the polymer electrolyte membrane are bonded by hot rolling, a catalyst layer having a dense structure can be formed to prevent a fuel crossover problem. In addition, the catalyst layer in a portion adjacent to the polymer electrolyte membrane has an advantage that the catalyst particles are inserted into the polymer electrolyte membrane in a portion, thereby improving adhesion and hydrogen ion conductivity between the catalyst layer and the polymer electrolyte membrane even with a small amount of binder.

However, in the case of forming the catalyst layer by hot rolling, the porosity of the catalyst layer as a whole is low, and it is difficult to easily discharge products such as CO ₂ and water generated at the anode electrode toward the electrode substrate.

Therefore, in the present invention, the structure adjacent to the polymer electrolyte membrane has a dense structure, and the portion adjacent to the electrode substrate has an optimized structure having an appropriate porosity, and even with a small amount of binder, adhesion with the polymer electrolyte membrane and excellent hydrogen ions Provided is a catalyst layer for fuel cells having conductivity.

The membrane electrode assembly according to an embodiment of the present invention,

An anode electrode and a cathode electrode which are located 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 includes an electrode substrate and two catalyst layers positioned on the electrode substrate.

The catalyst layer includes a catalyst and a binder, and the first catalyst layer in contact with the polymer electrolyte membrane has a structure including a smaller amount of binder than the second catalyst layer in contact with the electrode substrate. The content ratio of the binder included in the first catalyst layer and the second catalyst layer is preferably 1: 1.3 to 1 : 4, and more preferably 1: 2 to 1: 2.5. In the above range, the three-phase interface of the electrode is well formed, it is preferable because there is an advantage not affected by the mass transfer resistance. However, when out of the above range, problems may occur in electrical conductivity and mass transfer resistance, or ion conductivity may be deteriorated, and three-phase interface of catalyst, binder, and water may not be well formed in the catalyst layer, thereby degrading battery performance. , Not preferred.

The first catalyst layer preferably includes a first catalyst and a first binder in a weight ratio of 1: 0.05 to 1: 0.15, and more preferably includes a weight ratio of 1: 0.07 to 1: 0.1. In the above range, even a small amount of binder may exhibit excellent adhesion between the catalyst layer and the polymer electrolyte membrane, and the three-phase interface is well formed in the catalyst layer, thereby improving battery performance.

The second catalyst layer preferably includes the second catalyst and the second binder in a weight ratio of 1: 0.1 to 1: 0.2, and more preferably in a weight ratio of 1: 0.12 to 1: 0.16. In the above range, it is possible to increase the hydrogen ion conductivity of the catalyst layer, thereby exhibiting improved battery performance, and the three-phase interface is well formed in the catalyst layer without affecting the mass transfer resistance and the electron conductivity, which is preferable.

In addition, a third catalyst layer may be present between the first catalyst layer and the second catalyst layer, wherein the third catalyst layer has a content ratio of the first catalyst and the first binder of the first catalyst layer, the second catalyst and the second catalyst of the second catalyst layer. It may be one containing a catalyst and a binder in the middle of the content ratio of the binder.

The first catalyst layer preferably has a porosity of 30 to 70% by volume, more preferably a porosity of 30 to 55% by volume, and even more preferably has a porosity of 45 to 55% by volume. In the above range, the first catalyst layer may have a dense structure, thereby preventing a problem of crossover in which fuel flows through the polymer electrolyte membrane.

In addition, the second catalyst layer preferably has a porosity of 40 to 80% by volume, more preferably 50 to 80% by volume, even more preferably 55 to 80% by volume. It is even more preferable to have a porosity of 60 to 70% by volume. Within this range, products such as CO ₂ and water generated at the anode electrode can be easily discharged toward the electrode substrate.

It is preferable that the said 1st catalyst layer has a thickness of 10-40 micrometers, It is more preferable that it has a thickness of 10-30 micrometers, It is further more preferable that it has a thickness of 15-25 micrometers. In the above range, there is an advantage that the transfer is well achieved when transferring to the polymer electrolyte membrane through hot rolling. In addition, the second catalyst layer preferably has a thickness of 20 to 50 μm, more preferably 25 to 35 μm. Within this range, the delivery distance between the reactants and the product can be reduced, which is preferable.

The first catalyst and the second catalyst may be the same or different from each other, and the first catalyst and the second catalyst may participate in the reaction of the fuel cell, and any one that can be used as a catalyst may be used. System catalysts can 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, Transition metals selected from the group consisting of Cu, Zn, Sn, Mo, W, Rh, Ru, 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 / Mo, Pt / Ru / V, Pt / Fe / Co, Pt / Ru / Rh / Ni, Pt / Ru / Sn / W, and combinations thereof may 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. 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 first binder and the second binder may be the same or different from each other, and as the first binder and the second binder, it is preferable to use a polymer resin having hydrogen ion conductivity, and more preferably a sulfonic acid group, Any polymer resin having a cation exchange group selected from the group consisting of a carboxylic acid group, a phosphoric acid group, a phosphonine acid group and derivatives thereof can be used. Preferably, a fluorine polymer, 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 and fluorovinyl ethers containing sulfonic acid groups, defluorinated sulfided polyether ketones, aryl ketones, poly [2,2 '-(m-phenylene) -5,5'-bibenziimi Containing one or more hydrogen ion conducting polymers selected from dazole] (poly [2,2 '-(m-phenylene) -5,5'-bibenzimida zole]) or poly (2,5-benzimidazole) Available All.

The hydrogen ion conductive polymer may replace H with Na, K, Li, Cs or tetrabutylammonium in a cation exchanger at the side chain terminal. 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 first binder resin and the second binder resin 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 use the amount adjusted so that it is suitable for the purpose of use.

The non-conductive polymer may be polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoro alkylvinyl ether copolymer (PFA), ethylene / tetrafluoroethylene ( ethylene / tetrafluoroethylene (ETFE)), ethylenechlorotrifluoro-ethylene copolymer (ECTFE), polyvinylidene fluoride, copolymers of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), dodecylbenzenesulfonic acid And sorbitol (Sorbitol) is one or more selected from the group consisting of.

The electrode substrate plays a role of supporting the electrode and diffuses the fuel and the oxidant to the catalyst layer, thereby serving to easily access the fuel and the oxidant 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 in a fibrous state). The metal film is formed on the surface of the formed cloth) 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 due to water generated when the fuel cell is driven. Examples of the fluorine-based resin include polytetrafluoroethylene, polyvinylidene fluoride, polypolyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride alkoxy vinyl ether, and fluorinated ethylene propylene ( Fluorinated ethylene propylene), polychlorotrifluoroethylene or copolymers thereof can 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 of the microporous layer, polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride, alkoxy vinyl ether, polyvinyl Alcohols, cellulose acetates or copolymers thereof can be preferably used. In addition, the solvent of the microporous layer is preferably alcohol, such as ethanol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, water, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, etc. Can be 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 polymer electrolyte membrane is positioned between the anode electrode and the cathode electrode including the catalyst layer having the structure.

The polymer electrolyte membrane may be made of any polymer resin having hydrogen ion conductivity. 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 one selected from poly (2,5-benzimidazole) The above is mentioned.

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.

Method of manufacturing a membrane-electrode assembly for a fuel cell according to an embodiment of the present invention, the step of forming a first catalyst layer by applying a composition for forming a first catalyst layer on one surface of a release film (S1), formed on the release film Transferring the first catalyst layer to the polymer electrolyte membrane (S2), directly fixing the composition for forming the second catalyst layer on the first catalyst layer transferred to the polymer electrolyte membrane to form a second catalyst layer (S3), and And placing the polymer electrolyte membrane in which the first catalyst layer and the second catalyst layer are formed between the electrode substrates and then binding the polymer electrolyte membrane (S4).

First, a step of forming a first catalyst layer by applying a composition for forming a first catalyst layer on one surface of a release film (S1).

The first catalyst layer-forming composition is prepared by mixing the first catalyst and the first binder in a solvent such as methanol, and the kind of the first catalyst and the first binder is the same as described above.

The first catalyst layer-forming composition preferably includes the first catalyst and the first binder in a weight ratio of 1: 0.05 to 1: 0.15, and more preferably in a weight ratio of 1: 0.07 to 1: 0.1. In the above range, even a small amount of binder can exhibit excellent adhesion between the catalyst layer and the polymer electrolyte membrane, the three-phase interface of the catalyst layer can be formed well, it is preferable to improve the battery performance.

Examples of the release film include polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoro alkylvinyl ether copolymer, ethylene / tetrafluoroethylene and polyvinylidene fluoride. Polyethylene, polypropylene, polyethylene terephthalate, polyimide, silicone (silicone) and combinations thereof may be used.

The method of applying the composition for forming the first catalyst layer to the release film may include a screen printing method, a spray coating method, a coating method using a doctor blade, a gravure coating method, a dip coating method, a silk screen method, a painting method, and a slot die method. It may be carried out by a method selected from the group consisting of, but is not limited thereto. Also, more preferably, the silk screen method may be used, and in addition, all conventional methods may be used.

Next, the step of transferring the first catalyst layer formed on the release film to the polymer electrolyte membrane (S2).

It is preferable that it is 80-180 degreeC, and, as for the temperature of the said transfer step, it is more preferable that it is 120-135 degreeC. Within the above range, the glass transition temperature of the binder and the polymer electrolyte membrane is near 100 ° C., so that the binder is well bonded during hot rolling, and if it is out of the above range, the polymer electrolyte membrane and the electrode are not bound and the sulfon is high. The problem of decomposition of the group may occur, which is undesirable.

The pressure of the transfer step that is 20 to 70kgf / cm ^2, and more preferably of 45 to 55kgf / cm ^2. In the above range, a large amount of catalyst particles can form a dense structure in which the polymer electrolyte membrane is adhered to the polymer electrolyte membrane, and it is preferable to prevent desorption from the catalyst layer due to expansion of the polymer electrolyte membrane even when the fuel cell is driven for a long time. . If it is out of the above range, the first catalyst layer is not easily transferred to the polymer electrolyte membrane, or if the transfer pressure is high, the transferred first catalyst layer may be too dense, which may cause a problem in that mass transfer resistance and reaction discharge are not easy. Can not do it.

By hot rolling, the first catalyst layer transferred to the polymer electrolyte membrane has a dense structure to prevent the problem of crossover in which fuel moves through the polymer electrolyte membrane, and the catalyst particles of the first catalyst layer are partially deposited on the polymer electrolyte membrane. It can be inserted, so that even a small amount of binder can maintain excellent adhesion between the catalyst layer and the polymer electrolyte membrane.

Subsequently, the second catalyst layer is formed by directly coating the composition for forming a second catalyst layer on the polymer electrolyte membrane in which the first catalyst layer is formed (S3).

The composition for forming the second catalyst layer may be prepared by mixing the second catalyst and the second binder in a solvent such as methanol, and the second catalyst and the second binder are the same as described above.

The composition for forming the second catalyst layer preferably includes the second catalyst and the second binder in a weight ratio of 1: 0.1 to 1: 0.2, and more preferably in a weight ratio of 1: 0.12 to 1: 0.16. Within this range, the hydrogen ion conductivity of the catalyst layer can be increased, which can result in improved battery output, and the three-phase interface of the catalyst layer can be well formed.

Direct coating of the second catalyst layer on the first catalyst layer may be performed by a method selected from the group consisting of spray coating method, coating method using a doctor blade, gravure coating method, dip coating method, painting method and slot die method. However, the present invention is not limited thereto, and all direct coating methods that are commonly practiced may be used.

As such, since the second catalyst layer formed on the first catalyst layer is formed by direct coating, the second catalyst layer has an increased porosity than the first catalyst layer, so that products such as CO ₂ and water generated at the anode electrode are easily directed toward the electrode substrate. Can be discharged.

Next, the polymer electrolyte membrane in which the first catalyst layer and the second catalyst layer are formed is positioned between the electrode substrates and then bound (S4).

The polymer electrolyte membrane and the electrode substrate are the same as described above, the binding of the electrode substrate to the polymer electrolyte membrane can be carried out in a conventional manner bar detailed description thereof will be omitted.

As described above, according to the method of manufacturing the membrane-electrode assembly according to the embodiment of the present invention, the membrane-electrode assembly having an optimized structure can be manufactured by manufacturing the catalyst layer by the transfer step and the direct coating step.

According to another embodiment of the present invention, there is provided a fuel cell system including the membrane-electrode assembly having the above configuration.

The fuel cell system includes at least one electricity generating unit including separators on both sides of the membrane-electrode assembly and the membrane-electrode assembly, and generates a fuel supply unit and an oxidant to supply fuel to the electricity generating unit. And an oxidant supply unit for supplying to the unit.

The electricity generating unit includes a membrane-electrode assembly, includes a separator, and serves to generate electricity through an oxidation reaction of a fuel and a reduction reaction of an 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. Fuels in the present invention include hydrogen or hydrocarbon fuels 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 using a diffusion method without using a pump is shown. Of course, it can also be used in the battery system structure.

The fuel cell system 1 of the present invention includes at least one electricity generating unit 3 for generating electrical energy through an electrochemical reaction between a fuel and an oxidant, a fuel supply unit 5 for supplying the fuel, and an oxidant. It comprises a oxidant supply unit 7 for supplying to the electricity generating 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 3 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)

Pt black, a cathode catalyst, and Pt / Ru black, an anode catalyst, were mixed in 50 ml of isopropyl alcohol solution at a weight ratio of Nafion and 92: 8, respectively, to form a composition for forming a first catalyst layer for cathode and a first catalyst layer for anode The composition was prepared.

The cathode and anode first catalyst layer-forming compositions were coated on a Teflon film with a thickness of 50 μm, respectively, to form a cathode and an anode first catalyst layer, respectively. The Teflon film coated with the first catalyst layer was dried in an 80 ° C. drying furnace under a nitrogen atmosphere for 6 hours to evaporate the solvent.

After aligning the release film on which the first catalyst layer for the cathode is formed and the release film on which the first catalyst layer for the anode is formed on both sides of the polymer electrolyte membrane of Nafion, a temperature of 135 ° C. and a pressure of 55 kgf / cm ² are applied thereto. The first catalyst layer for the cathode and the first catalyst layer for the anode were transferred to both sides of the polymer electrolyte membrane, respectively.

Subsequently, Pt black as a cathode catalyst and Pt / Ru black as an anode catalyst are mixed with Nafion at a weight ratio of 85: 15, respectively, in 50 ml of isopropyl alcohol solution to form a composition for forming a second catalyst layer for the cathode and a second catalyst layer for the anode. A composition for formation was prepared. This was directly coated on both surfaces of the polymer electrolyte membrane to which the first catalyst layer was transferred, thereby preparing a polymer electrolyte membrane in which the first catalyst layer and the second catalyst layer were formed.

Subsequently, the membrane-electrode assembly was inserted between two gaskets, and then inserted into two separators having a predetermined gas flow channel and a cooling channel, and pressed between copper end plates to prepare a unit cell. .

In the manufactured single cell, the content ratio of the binder included in the first catalyst layer and the second catalyst layer was 1: 1.88. In addition, the porosity of the first catalyst layer was 45% by volume, the thickness was 15 μm, the porosity of the second catalyst layer was 70% by volume, and the thickness was 35 μm.

(Example 2)

Pt black and Pt / Ru black were mixed in 50 ml of isopropyl alcohol solution at a weight ratio of Nafion and 89: 11, respectively, to prepare a composition for forming the first catalyst layer, and Pt black and Pt / Ru black were respectively mixed with Nafion and Nafion. A single cell was prepared in the same manner as in Example 1 except that the composition for forming the second catalyst layer was prepared by mixing in 50 ml of isopropyl alcohol at a weight ratio of 85:15, and using the same to form the first catalyst layer and the second catalyst layer. Prepared. In the manufactured single cell, the content ratio of the binder included in the first catalyst layer and the second catalyst layer was 1: 1.36. In addition, the porosity of the first catalyst layer was 40% by volume, the thickness was 15 μm, the porosity of the second catalyst layer was 70% by volume, and the thickness was 35 μm.

(Comparative Example 1)

Pt black (Hispec ^® 1000, manufactured by Johnson Matthey) as the cathode catalyst and Pt / Ru black (Hispec ^® 6000 manufactured by Johnson Matthey) as the anode catalyst were respectively used in a weight ratio of 1: 0.15 and Nafion (manufactured by Nafion ^® Dupont). It was mixed in 50 ml of propyl alcohol solution to prepare a composition for forming a catalyst layer for the cathode and a composition for forming a catalyst layer for the anode.

The cathode and anode catalyst layer-forming compositions were directly coated on the electrolyte membrane with a thickness of 50 μm, respectively, to form a catalyst layer for the cathode and the anode, respectively.

A single cell was prepared in the same manner as in Example 1, except that the polymer electrolyte membrane in which the catalyst layer was formed was used.

(Comparative Example 2)

Pt black, a cathode catalyst, and Pt / Ru black, an anode catalyst, were mixed in 50 ml of isopropyl alcohol at a weight ratio of 85: 15 with Nafion, respectively, and sufficiently stirred to prepare a catalyst catalyst composition and a catalyst catalyst composition for anode. Prepared.

The cathode and anode catalyst part formation compositions were coated on a Teflon film with a thickness of 50 μm, respectively, to form a catalyst layer for the cathode and the anode. The catalyst layer coated Teflon film was dried in an 80 ° C. drying furnace under a nitrogen atmosphere for 6 hours to evaporate the solvent.

After aligning the release film having the cathode catalyst layer and the release film having the anode catalyst layer formed on both sides of the polymer electrolyte membrane of Nafion, and then applying a temperature of 135 ° C. and a pressure of 55 kgf / cm ² , the cathode and anode The catalyst layer for transfer was transferred to both sides of the polymer electrolyte membrane.

A single cell was prepared in the same manner as in Example 1 except that the catalyst layer was transferred to a polymer electrolyte membrane.

Power density measurement

The porosities of the first catalyst layer in contact with the polymer electrolyte membrane and the second catalyst layer in contact with the electrode substrate were measured for the unit cells of Examples 1 to 2, and the unit cells of Examples 1 to 2 and the unit cells of Comparative Example 1 were measured. By measuring the porosity of the electrode, it is shown in Table 1 below.

In addition, while maintaining the unit cells prepared in Examples 1 and 2 and Comparative Examples 1 and 2 at 70 ° C., 1M methanol and ambient air were stoichiometry (the amount of methanol supplied to the anode / the amount of air supplied to the cathode, the electricity Theoretical value for the chemical reaction) = 3.0 / 3.0 and the power density was measured at the operating voltage of 0.4 V.

TABLE 1

Porosity of the first catalyst layer (% by volume) Porosity of Volume 2 (Volume%) Porosity of the electrode (% by volume) Power density (mW / Cm ² ) Example 1 45 70 65 115 Example 2 40 70 60 106 Comparative Example 1 - - 65 100 Comparative Example 2 - - 40 95

Referring to Table 1, Examples 1 to 2 form the first catalyst layer by the transfer process, form the second catalyst layer by the direct coating process, and vary the content of the binder of the second catalyst layer of the first catalyst layer. As a result, it was confirmed that the porosities of the first catalyst layer and the second catalyst layer were different. In addition, it was confirmed that the unit cells of Examples 1 to 2 including two catalyst layers having different porosities and binder contents showed better output densities than those of Comparative Examples 1 to 2.

All simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

1 is a flowchart illustrating a method of manufacturing a membrane-electrode assembly according to an embodiment of the present invention.

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

Claims (19)

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, An electrode substrate, and at least two catalyst layers positioned on the electrode substrate and comprising a catalyst and a binder, The membrane-electrode assembly of a fuel cell, wherein the first catalyst layer in contact with the polymer electrolyte membrane comprises a smaller amount of binder than the second catalyst layer in contact with the electrode substrate. The method of claim 1, The content ratio of the binder contained in the first catalyst layer and the second catalyst layer is 1: 1.3 to 1: 4 for the fuel cell membrane electrode assembly. The method of claim 1, At least one third catalyst layer is present between the first catalyst layer and the second catalyst layer, the fuel cell membrane electrode assembly. The method of claim 1, The first catalyst layer is a fuel cell membrane-electrode assembly having a thickness of 10 to 40 ㎛. The method of claim 1, The second catalyst layer is a membrane-electrode assembly for a fuel cell having a thickness of 20 to 50 ㎛. The method of claim 1, The first catalyst layer is a fuel cell membrane-electrode assembly having a porosity of 30 to 70% by volume. The method of claim 1, The second catalyst layer is a fuel cell membrane-electrode assembly having a porosity of 40 to 80% by volume. The method of claim 1, The catalyst is a membrane-electrode assembly for a fuel cell that is a platinum-based catalyst. The method of claim 1, The binder is a membrane-electrode assembly for a fuel cell is a polymer resin having a hydrogen ion conductivity. The method of claim 9, The binder has a cation exchange resin 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. The method of claim 1, The electrode substrate may include a carbon film, a carbon cloth, a carbon felt, or a metal cloth (a porous film composed of a metal in a fibrous state or a metal film formed on a surface of a cloth formed of polymer fibers). Membrane electrode assembly for a fuel cell. The method of claim 1, Wherein the polymer electrolyte membrane is a polymer resin having a hydrogen ion conductivity membrane-electrode assembly for a fuel cell. Forming a first catalyst layer by coating a composition for forming a first catalyst layer on one surface of the release film; Transferring the first catalyst layer formed on the release film to a polymer electrolyte membrane; Forming a second catalyst layer by directly coating a composition for forming a second catalyst layer on the first catalyst layer transferred to the polymer electrolyte membrane; And And placing the polymer electrolyte membrane having the first catalyst layer and the second catalyst layer formed between the electrode substrates and then binding the polymer electrolyte membrane. The method of claim 13, The first catalyst layer-forming composition comprises a first catalyst and the first binder in a weight ratio of 1: 0.05 to 1: 0.15 of the manufacturing method of the fuel cell membrane-electrode assembly. The method of claim 13, The composition for forming the second catalyst layer comprises a second catalyst and the second binder in a weight ratio of 1: 0.1 to 1: 0.2. The method of claim 13, The release film is a polytetrafluoroethylene, tetrafluoroethylene-nucleus fluoropropylene copolymer, tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer, ethylene / tetrafluoroethylene, polyvinylidene fluoride. A method for producing a membrane-electrode assembly for a fuel cell, which is selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, and combinations thereof. The method of claim 13, The transfer step is a method of manufacturing a membrane-electrode assembly for a fuel cell that is carried out at a temperature of 80 to 180 ℃. The method of claim 13, The transfer step is a method of manufacturing a membrane-electrode assembly for a fuel cell that is carried out under a pressure of 20 to 70 kgf / cm ² . 13. A membrane-electrode assembly according to any one of claims 1 to 12, and a separator located on both sides of the membrane-electrode assembly, at least one of generating electricity through an electrochemical reaction of a fuel and an oxidant. Electricity generating unit; 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.

Images