KR20080008605A - Membrane electrode assembly for fuel cell, preparing method for same, and fuel cell system comprising same - Google Patents

Abstract

A membrane electrode assembly for a fuel cell, a method for preparing the membrane electrode assembly, and a fuel cell system containing the membrane electrode assembly are provided to allow materials to be transported and discharged easily and smoothly through pores, thereby improving the performance of a fuel cell. A membrane electrode assembly comprises an anode(20') and a cathode(20) which are located so as to face each other; and a polymer electrolyte membrane(10) which is located between the anode and the cathode, wherein at least one of the anode and the cathode has an electrode substrate(40,40') and a catalyst layer(30,30') formed on the surface of the electrode substrate, and the catalyst layer has a nanosized micropore(32) and a macropore(34) having an average pore size of 5-25 micrometers.

Description

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

1 is a schematic view showing a structure of a membrane-electrode assembly according to an embodiment of the present invention.

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

Figure 3 is a graph measuring the pore distribution in the catalyst layer prepared according to Example 1 and Comparative Example 1 of the present invention.

[Industrial use]

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 facilitate material movement and discharge through pores in a catalyst layer, thereby improving performance of a fuel cell. 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.

[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.

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). The use of methanol as fuel in the direct oxidation fuel cell 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 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 includes 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 structure in which

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. Reaching the cathode 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 generating water.

An object of the present invention is to provide a membrane-electrode assembly for a fuel cell that can facilitate the movement and discharge of material through the pores in the catalyst layer to improve the performance of the fuel cell.

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

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

In order to achieve the above object, the present invention includes an anode electrode and a cathode electrode positioned opposite to each other, 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 a catalyst layer formed on the electrode substrate, the catalyst layer is micropores having a pore diameter of nano size, and macropores having an average pore diameter of 5 to 25㎛ It includes.

The present invention also provides a catalyst layer forming composition comprising a catalyst and a pore forming agent, applying the catalyst layer forming composition to an electrode substrate to form a catalyst layer, and acid treating the electrode substrate on which the catalyst layer is formed to form pores in the catalyst layer. It provides a method of manufacturing a membrane-electrode assembly comprising the step of preparing an electrode, and forming a polymer electrolyte membrane on the catalyst layer of the electrode.

The present invention also includes the membrane-electrode assembly and the separator, and includes at least one electricity generating unit for generating electricity through an electrochemical reaction between a fuel and an oxidant, a fuel supply unit supplying fuel to the electricity generating unit, and an oxidant. It provides a fuel cell system including an oxidant supply unit for supplying to the electricity generating unit.

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 bed serve to enhance the activity of the electrode catalyst by supplying fuel or oxidant and draining 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. Therefore, in order to improve the performance of the fuel cell, it is important to minimize the resistance to mass movement by maintaining the pores contained in the catalyst layer in an optimal state.

A pore former such as (NH ₄ ) ₂ CO ₃ , NH ₄ HCO ₃ , or (NH ₄ ) ₂ C ₂ O ₄ was used to form pores in the catalyst layer. These pore formers are used in admixture with the catalyst in the composition for forming the catalyst layer and then removed by a heat treatment at 50 to 170 ° C. to form pores in the resulting catalyst layer.

However, in order to control the pore size in the catalyst layer of the membrane-electrode assembly, the pore-forming agent is pulverized by using a milling apparatus such as a ball mill. The control of size was not easy. Accordingly, the pore forming method in the catalyst layer using the pore-forming agent has a problem that size control is difficult for the fine pores in the catalyst layer. In addition, the heat treatment process is performed to remove the used pore formers. At this time, the pore former removal efficiency by the heat treatment is low, and as a result, when the pore formers remain in the catalyst layer, there is a problem that the electron conductivity is lowered. In addition, when the temperature is too high during heat treatment, there is a problem of deteriorating the catalyst activity.

In the present invention, by using a novel pore-forming agent that can easily control the pore size in the catalyst layer, the pores in the catalyst layer are separated and formed for supplying the reactants and for discharging the reaction product, thereby improving resistance to mass transfer in the catalyst layer. It can minimize and facilitate the movement and release of material through the pores in the resulting catalyst bed can improve the performance of the fuel cell.

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

Referring to FIG. 1, the membrane-electrode assembly 151 of the present invention includes a cathode electrode 20 and an anode electrode 20 ′ facing each other, and the cathode electrode 20 and the anode electrode ( 20 ') between the polymer electrolyte membrane 10.

The cathode electrode 20 and the anode electrode 20 'include a catalyst layer 30, 30' and an electrode substrate 40, 40 'for supporting the catalyst layer, respectively.

The catalyst layers 30, 30 'according to the present invention are two or more different, such as micropores 32 for the movement of the oxidant and macropores 34 for the discharge of the reaction product, in order to minimize resistance to mass transfer. Pores having a pore diameter.

Preferably, the catalyst layers 30 and 30 'may include micropores 32 having nanopore diameters and macropores 34 having an average pore diameter of 5 μm or more. More preferably, the catalyst layer may include micropores 32 having an average pore diameter of 100 nm or less and macropores 34 having an average pore diameter of 5 to 25 μm, even more preferably 30 to 60 nm. It may include a fine pore 32 having an average pore diameter of and a large pore 34 having an average pore diameter of 5 to 20㎛. In addition, the macropores 34 may include a first macropores having an average pore diameter of 5 to 7 μm, a second macropores having an average pore diameter of 10 to 12 μm, and an average pore diameter of 18 to 20 μm. It may also contain 3 macropores.

When the average pore diameters of the micropores and the macropores included in the catalyst layers 30 and 30 'are within the above ranges, the reaction products in the gas phase are discharged through the micropores, and the liquid reaction products are discharged through the macropores, thereby reacting and reacting. Easy delivery and discharge of product However, when the average pore diameter of the micropores and the macropores is out of the above range, the reaction products of the gaseous phase and the liquid phase are separated and not transferred and discharged.

The catalyst layers 30 and 30 'may include micropores and macropores uniformly mixed in the catalyst layer, and vary the distribution amount or pore size of the micropores and the macropores according to positions in the catalyst layers 30 and 30'. It may be included.

When the distribution of macropores is greater than that of micropores at the junction interface between the catalyst layers 30 and 30 'and the polymer electrolyte membrane 10, the reaction product water tends to be liquefied in the macropores. It is unpreferable because there is a risk of blocking and supply of the oxidizing agent as a reactant. Accordingly, the catalyst layers 30 and 30 ′ preferably have a concentration gradient in which the pore size decreases from the first interface where the catalyst layer and the electrode substrate are bonded to the second interface where the catalyst layer and the polymer electrolyte membrane contact each other. Specifically, the pore size decreases from the first interface where the catalyst layer and the electrode substrate are bonded to the second interface where the catalyst layer and the polymer electrolyte membrane contact each other, and the micropores and the macropores in the first interface are 0 to 2:10, Preferably it is present in a volume ratio of 1: 9 to 2: 8, and in the second interface it is preferably present in a volume ratio of 10: 0 to 2, preferably 9: 1 to 8: 2. Most preferably, the micropores and the macropores in the first interface are present in a volume ratio of 2: 8 and in the second interface in a volume ratio of 8: 2. In the case of containing micropores and macropores in the ratio, it is possible to separate and deliver the reaction products or reactants in gaseous and liquid phases to facilitate mass transfer.

The catalyst layers 30 and 30 'may be applied to any of the anode catalyst layer and the cathode catalyst layer of the membrane-electrode assembly, but when the production of the reaction product is applied to many cathode catalyst layers, a better material transfer effect may be obtained.

In addition, the catalyst layers 30 and 30 'catalyze related reactions (oxidation of fuel and reduction of oxidant) and include a catalyst.

In the catalyst layer, any catalyst that can be used as a catalyst may be used as a catalyst in the reaction of the fuel cell, and a representative 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, At least one catalyst selected from the group consisting of Cu, Zn, Sn, Mo, W, and Rh). 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 catalyst layers 30 and 30 'may further include a binder resin to improve adhesion of the catalyst layer and transfer of 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 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, polyphenylquinoxaline polymers or copolymers thereof, more preferably poly (perfluorosulfonic acid), poly (perfluoro Carboxylic acid), copolymers of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid groups, defluorinated sulfide polyether ketones, aryl ketones, poly (2,2'-m-phenylene) -5,5 ' At least one hydrogen selected from poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole), poly (2,5-benzimidazole), or copolymers thereof Ionic conductivity It can be used to contain characters.

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 the cation exchanger at the side chain terminal, when Na is replaced with Na, tetrabutylammonium hydroxide is used when tetrabutylammonium is used, and K, Li or Cs may be substituted with an appropriate compound. Can be. 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 material 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 material may be polytetrafluoroethylene (PTFE), tetra fluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer (PFA), ethylene / tetrafluoro Ethylene / tetrafluoroethylene (ETFE), ethylenechlorotrifluoro-ethylene copolymer (ECTFE), polyvinylidene fluoride, copolymer of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), dode At least one selected from the group consisting of silbenzenesulfonic acid and sorbitol is more preferred.

In addition, the catalyst layers 30 and 30 'are used to form fine pores in the catalyst layer, and may include some pore formers which are not eluted during acid treatment during the manufacturing process.

An alkali metal-containing carbonate may be used as the pore forming agent. Specifically, it is selected from the group consisting of LiCO ₃ , K ₂ CO ₃ , Na (CO ₃ ) ₂ , and mixtures thereof, and more preferably LiCO ₃ may be used.

The catalyst layers 30 and 30 'having the above configuration are supported by the electrode substrates 40 and 40'.

The electrode substrates 40 and 40 'serve to support the electrode and diffuse fuel and oxidant to the catalyst layers 30 and 30', thereby easily accessing the fuel and oxidant to the catalyst layer.

A conductive substrate may be used as the electrode substrates 40 and 40 ', and representative examples thereof include carbon paper, carbon cloth, carbon felt, or metal cloth (fibrous metal cloth). The metal film is formed on the surface of the cloth formed of a porous film or polymer fibers) may be used, but is not limited thereto.

In addition, using the water-repellent treatment with a fluorine-based resin as the electrode substrates 40 and 40 'can prevent the reactant diffusion efficiency from being lowered by the electrochemically generated water in the catalyst layer of the cathode when the fuel cell is driven. It is preferable. 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, copolymers thereof or mixtures thereof may be used.

In addition, the membrane-electrode assembly 10 according to the present invention may further be formed with a microporous layer (not shown) to enhance the diffusion effect of the reactants in the electrode substrate (40, 40 '). 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, and the like.

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 polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride, alkoxy vinyl ether, polyvinyl alcohol, cellulose acetate , Copolymers thereof or mixtures thereof may 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 membrane-electrode assembly 151 including the electrodes 20 and 20 'having the above structure includes the polymer electrolyte membrane 10 positioned between the anode and the cathode electrode.

The polymer electrolyte membrane 10 functions as an ion exchange to move the hydrogen ions generated in the catalyst layer 30 'of the anode electrode 20' to the catalyst layer 30 of the cathode electrode 20. Therefore, it is preferable to use a polymer having excellent hydrogen ion conductivity as the polymer electrolyte membrane 10.

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.

Specifically, 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 selected from the group consisting of ether ketone polymers, polyphenylquinoxaline polymers, copolymers thereof and mixtures thereof, more preferably poly (perfluorosulfonic acid) (generally marketed as Nafion) ), Poly (perfluorocarboxylic acid), copolymer of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid group, defluorinated sulfide polyether ketone, aryl ketone, poly (2,2'-m -Phenylene) -5,5'-bibenzimidazole (poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole), poly (2,5-benzimidazole), their air Consisting of coalescing and mixtures thereof It is selected from may be used.

It is also possible to substitute H with Na, K, Li, Cs or tetrabutylammonium in the cation exchanger of such a hydrogen ion conductive polymer. In the cation exchanger at the side chain terminal, when Na is replaced with Na, tetrabutylammonium hydroxide is used when tetrabutylammonium is used, and K, Li or Cs may be substituted with an appropriate compound. Can be. Since this substitution method is well known in the art, detailed description thereof will be omitted.

The membrane-electrode assembly having the structure as described above may include catalyst layers having different pore diameters, thereby minimizing resistance to mass transfer, thereby improving battery characteristics of the fuel cell.

The membrane-electrode assembly comprises the steps of preparing a catalyst layer forming composition comprising a catalyst and a pore former; Applying the catalyst layer forming composition to an electrode substrate to form a catalyst layer; Acid-treating the electrode substrate on which the catalyst layer is formed to form pores in the catalyst layer to manufacture an electrode; It can be prepared by a manufacturing method comprising the step of forming a polymer electrolyte membrane on the catalyst layer of the electrode.

Hereinafter, a method of manufacturing the membrane-electrode assembly of the present invention will be described in detail. First, a composition for forming a catalyst layer including a catalyst and a pore-forming agent is prepared.

The catalyst layer forming composition may be prepared by mixing a catalyst and a pore former in a solvent.

It is preferable to use the solvent which shows polarity as said solvent. Specifically water; Alcohol solvents such as methanol, ethanol and isopropyl alcohol; Amide solvents such as N, N-dimethylacetamide (DMAC), N-methyl pyrrolidone (NMP) and dimethylformamide (DMF); And sulfoxide solvents such as dimethyl sulfoxide and the like.

The catalyst is the same as described above.

The pore former may be an alkali metal-containing carbonate. Specifically, it is selected from the group consisting of LiCO ₃ , K ₂ CO ₃ , Na (CO ₃ ) ₂ , and a combination thereof, and more preferably LiCO ₃ may be used.

The pore formers are then dissolved and removed by acid in an acid treatment process during the manufacture of the membrane-electrode assembly, and the pore formers removed by the acid become pores. Therefore, the particle diameter of the pore former may be adjusted and used according to the diameter of the pores to be formed in the catalyst layer.

The pore formers can easily control the particle diameter by the grinding process. As a result, pores having a desired size can be easily formed in the catalyst layer, and pores having various sizes can be uniformly formed.

Accordingly, the pore former may be a fine pore former having a nano-sized particle diameter, and a macroscopic pore having an average particle diameter of 5 μm or larger so that the fine pores and the macropores having the pore diameter as described above can be formed. It is preferable to include an agent. More preferably, the pore forming agent may include a fine pore forming agent having an average particle diameter of 100 nm or less, and a macroporous forming agent having an average particle diameter of 5 to 25 μm, even more preferably 30 to Micropore formers having an average particle diameter of 60 nm and macroporous formers having an average particle diameter of 5 to 20 μm. The macropore formers are also first macropore formers having an average particle diameter of 5-7 μm, second macropore formers having an average particle diameter of 10-12 μm, and average particles of 18-20 μm. It may also comprise a third macropore former having a diameter.

The prepared catalyst layer forming composition is applied to an electrode substrate and dried to form a catalyst layer.

The electrode substrate is the same as described above.

The coating process of the composition for forming the catalyst layer may be screen printing, spray coating, doctor blade coating, gravure coating, dip coating, silk screening, painting, and slot die depending on the viscosity of the composition. The method may be performed by a method selected from the group consisting of, but is not limited thereto. More preferably, the doctor blade method can be used.

In addition, when forming a catalyst layer, a single catalyst layer forming composition comprising a mixture of the fine pore forming agent and the macropore forming agent is coated on the electrode substrate so that the micropores and the macropores in the catalyst layer are uniformly mixed in the catalyst layer. It is also possible to form, or to prepare a plurality of composition for forming a catalyst layer comprising a micropore forming agent and a macropore forming agent in various mixing ratios so that the distribution of micropores and macropores can vary depending on the position in the catalyst layer on the electrode substrate It may be formed by coating in sequence.

In this case, the catalyst layer forming composition is sequentially applied on the electrode substrate such that a concentration gradient is formed in which the pore size decreases from the first interface where the catalyst layer and the electrode substrate are bonded to the second interface where the catalyst layer and the polymer electrolyte membrane contact each other. You may. Specifically, the pore size decreases from the first interface where the catalyst layer and the electrode substrate are bonded to the second interface where the catalyst layer and the polymer electrolyte membrane contact each other, and the micropores and the macropores in the first interface are preferably 0 to 2:10. Preferably it is present in a volume ratio of 1: 9 to 2: 8, it is preferable to apply a composition for forming a catalyst layer to exist in a volume ratio of 10: 0 to 2, preferably 9: 1 to 8: 2 in the second interface. . Most preferably, the micropore and the macropore in the first interface are present in a volume ratio of 2: 8, and in the second interface, the composition for forming a catalyst layer is preferably applied.

Thereafter, the electrode substrate on which the catalyst layer is formed is acid treated to elute the pore-forming agent in the catalyst layer to form pores in the catalyst layer to prepare an electrode. In this case, the manufactured electrode is called a first electrode.

The acid treatment process also serves to activate the catalyst in addition to the elution of the pore former.

The acid treatment step can be formed by impregnating an electrode substrate having the catalyst layer in an acid solution selected from the group consisting of sulfuric acid, phosphoric acid, hydrofluoric acid, and mixtures thereof.

The acid solution is preferably used at a concentration of 0.2 to 5M, more preferably at a concentration of 1 to 2M. If the concentration of the acid solution is less than 0.2M, the pore-forming agent is not sufficiently eluted and the pore-forming effect is insignificant. If the concentration of the acid solution is more than 5M, it is not easy to work and may cause deformation of battery characteristics.

A polymer electrolyte membrane is formed on the catalyst layer of the prepared first electrode.

The polymer electrolyte membrane may be formed by directly applying a composition for forming a polymer electrolyte membrane on the catalyst layer of the first electrode and then drying, or may be bonded to the catalyst layer of the first electrode in the form of a film.

The polymer electrolyte membrane includes a hydrogen ion conductive polymer as described above. Since the method for producing a polymer electrolyte membrane using the hydrogen ion conductive polymer may be performed by a conventional polymer electrolyte membrane forming method, a detailed description thereof will be omitted.

Thereafter, a separate electrode including an electrode substrate and a catalyst layer formed on the electrode substrate is formed on the polymer electrolyte membrane to prepare a membrane-electrode assembly. In this case, the electrode is called a second electrode.

The second electrode may be manufactured by the same method as the first electrode.

Since the binding method between the electrode and the polymer electrolyte membrane is well known in the art, a detailed description thereof will be omitted.

The membrane-electrode assembly manufactured as described above includes a catalyst layer including pores having pores having diameters controlled in various sizes, and thus fuel can be easily used by minimizing resistance to mass movement during fuel cell operation. The output characteristics of the fuel cell of the battery can be improved. Such a membrane-electrode assembly may be applied to a conventional fuel cell system, and more preferably to a direct oxidation fuel cell system.

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

The fuel cell system includes at least one electricity generating unit including the membrane-electrode assembly and the separator, and includes a fuel supply unit supplying fuel to the electricity generating unit and an oxidant supply unit supplying an oxidant to the electricity generating unit.

The electricity generating unit includes a membrane-electrode assembly, a separator (also called a bipolar plate), 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 100 of the present invention includes at least one electricity generation unit 150 for generating electrical energy through an electrochemical reaction between a fuel and an oxidant, a fuel supply unit 101 for supplying the fuel, and an oxidant. It is configured to include an oxidant supply unit 103 for supplying to the electricity generating unit 150.

In addition, the fuel supply unit 101 for supplying fuel includes a fuel tank 110 for storing fuel, and optionally, may further include a fuel pump 120 connected to the fuel tank 110. The fuel pump 120 serves to discharge fuel stored in the fuel tank 110 by a predetermined pumping force.

The oxidant supply unit 103 supplying the oxidant to the electricity generating unit 150 may include at least one oxidant pump 130 that sucks the oxidant with a predetermined pumping force.

The electricity generation unit 150 includes a membrane electrode assembly 151 for oxidizing and reducing a fuel and an oxidant, and separators 152 and 153 for supplying fuel and an oxidant to both sides of the membrane electrode assembly. At least one generation unit 150 constitutes a stack 105.

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

10 wt% Nafion (Nafion ^® , manufactured by Dupont) aqueous solution in 3.0 g of a mixed catalyst of Pt black (Hispec ^® 1000, manufactured by Johnson Matthey) and Pt / Ru black (Hispec ^® 6000, manufactured by Johnson Matthey) in 30 ml of isopropyl alcohol 10 g of the dispersion was added dropwise, and then 4.5 g of a mixture in which Li ₂ CO ₃ having an average particle diameter of 40 nm and 10 μm was mixed in a weight ratio of 1: 1 was added, followed by mechanical stirring to prepare a composition for forming a catalyst layer.

The catalyst layer-forming composition was coated on a 25 μm thick carbon paper by screen printing and then dried to form a catalyst layer. Subsequently, the carbon paper on which the catalyst layer was formed was impregnated in a 2 M sulfuric acid aqueous solution to elute Li ₂ CO ₃ in the catalyst layer to form pores to prepare a first electrode.

Commercial Nafion 115 membrane (molecular weight: 50 to 80 million, thickness: 125㎛) to the respective washing and then for 2 hours at 3% hydrogen peroxide, 0.5M sulfuric acid aqueous solution of 90 ℃ treatment, for 1 hour in deionized water of 100 ℃ H ⁺ A type Nafion 115 membrane was bonded onto the prepared first electrode using a polymer electrolyte membrane.

In the same manner as for the other side of the polymer electrolyte membrane, a first electrode and a second electrode were formed as anode and cathode electrodes on both sides of the polymer electrolyte membrane to prepare a membrane-electrode assembly.

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

Example 2

Except for using Pt / C (20% by weight, manufactured by E-tek) instead of a mixed catalyst of Pt black (Hispec ^® 1000, manufactured by Johnson Matthey) and Pt / Ru black (Hispec ^® 6000, manufactured by Johnson Matthey) In the same manner as in Example 1, a single cell was manufactured.

Example 3

First, second, and first mixtures of Li ₂ CO ₃ having an average particle diameter of 60 nm, 5 μm, and 15 μm as 1: 1: 8, 1: 8: 1, and 8: 1: 1 as pore-forming agents Three mixtures were used to prepare compositions for forming the first, second, and third catalyst layers, which were then coated on 25 μm thick carbon paper in order of the composition for forming the first, second, and third catalyst layers to form a catalyst layer. A single cell was manufactured by the same method as Example 1 except for preparing.

Example 4

Except for using Pt / C (20% by weight, manufactured by E-tek) instead of a mixed catalyst of Pt black (Hispec ^® 1000, manufactured by Johnson Matthey) and Pt / Ru black (Hispec ^® 6000, manufactured by Johnson Matthey) In the same manner as in Example 3, a single cell was manufactured.

Comparative Example 1

Aqueous dispersion of 10 wt% Nafion (Nafion ^® , manufactured by Dupont) to 3.0 g of catalyst of Pt black (Hispec ^® 1000, manufactured by Johnson Matthey) and Pt / Ru black (Hispec ^® 6000, manufactured by Johnson Matthey) in 3 ml of isopropyl alcohol 4.5 g was added dropwise, and then 4.5 g of (NH ₄ ) ₂ CO ₃ having a particle diameter of 40 nm to 200 μm was added, followed by mechanical stirring to prepare a composition for forming a catalyst layer.

The catalyst layer-forming composition was coated on a 25 μm thick carbon paper by screen printing and then dried to form a catalyst layer. Subsequently, the carbon paper on which the catalyst layer was formed was heat-treated at 120 ° C. to evaporate the (NH ₄ ) ₂ CO ₃ pore former to form pores in the catalyst layer to prepare a first electrode.

Commercial Nafion 115 membrane (molecular weight: 50 to 80 million, thickness: 125㎛) to the respective washing and then for 2 hours at 3% hydrogen peroxide, 0.5M sulfuric acid aqueous solution of 90 ℃ treatment, for 1 hour in deionized water of 100 ℃ H ⁺ A type Nafion 115 membrane was bonded onto the prepared first electrode using a polymer electrolyte membrane.

In the same manner with respect to the other surface of the polymer electrolyte membrane, a first electrode and a second electrode were formed as anode and cathode electrodes on both sides of the polymer electrolyte membrane to prepare a membrane-electrode assembly.

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

Comparative Example 2

Except for using Pt / C (20% by weight, manufactured by E-tek) instead of a mixed catalyst of Pt black (Hispec ^® 1000, manufactured by Johnson Matthey) and Pt / Ru black (Hispec ^® 6000, manufactured by Johnson Matthey) In the same manner as in Example 1, a single cell was manufactured.

In the unit cells manufactured according to Example 1 and Comparative Example 1, pore distributions formed in the catalyst layer were observed. The results are shown in FIG.

As shown in FIG. 3, it can be seen that pores corresponding to the particle size of the pore former used are formed in the case of the catalyst layer in the unit cell of Example 1 formed using the pore former of the present invention. On the other hand, in the case of the catalyst layer in the unit cell of Comparative Example 1 formed using a conventional pore-forming agent, it was difficult to control the particle size of the pore-forming agent, so that a large pore having a very large pore size was formed. From this, it can be seen that the pore-forming agent of Example 1 of the present invention is easier to control the particle size than the pore-forming agent of Comparative Example 1, and as a result, it is more advantageous to control the pore size when forming pores in the catalyst layer.

For the cells prepared in Examples 1, 3 and Comparative Example 1, the current density was measured under the conditions of the direct oxidation fuel cell (hydrogen / air and 3M methanol / air). The results are shown in Table 1 below.

Evaluation item Example 1 Example 3 Comparative Example 1 Current density at 50 ° C, 0.4V (mA / cm ² ) 280mA / cm ² 300 mA / cm ² 220mA / cm ²

As shown in Table 1, the cells of Examples 1 and 3 including the catalyst layer according to the present invention showed a higher current density than the cells of Comparative Example 1 under the same operating conditions (3M methanol / air at 50 ℃) It was confirmed that it has excellent output characteristics.

In addition, the current densities of the unit cells of Examples 2, 4 and Comparative Example 2 were measured under the conditions of direct oxidation fuel cells (hydrogen / air and 3M methanol / air). The results are shown in Table 2 below.

Evaluation item Example 2 Example 4 Comparative Example 2 Current density at 60 ℃, 0.6V (mA / cm ² ) 1600mA / cm ² 1800mA / cm ² 1100mA / cm ²

As shown in Table 2, the unit cells of Examples 2 and 4 including the catalyst layer according to the present invention showed a higher current density than the unit cell of Comparative Example 2 under the same operating conditions (1M methanol / air at 60 ℃) It was confirmed that it has excellent output characteristics.

The membrane-electrode assembly for a fuel cell of the present invention includes pores having a controlled pore diameter to facilitate material movement and discharge through pores in the catalyst layer, thereby improving performance of the fuel cell.

Claims (23)

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 It includes a catalyst layer formed on the electrode substrate, The catalyst layer is to include micropores having a pore diameter of nano-size, and macropores having an average pore diameter of 5 to 25㎛ Membrane-electrode assembly for fuel cell. The method of claim 1, The micro-pores are fuel cell membrane-electrode assembly having an average pore diameter of less than 100nm. The method of claim 1, The micro-pores membrane-electrode assembly for a fuel cell having an average pore diameter of 30 to 60nm. The method of claim 1, The macropores are fuel cell membrane-electrode assembly having an average pore diameter of 5 to 20㎛. The method of claim 1, The macropores include first macropores having an average pore diameter of 5 to 7 μm, second macropores having an average pore diameter of 10 to 12 μm, and third macropores having an average pore diameter of 18 to 20 μm. Membrane electrode assembly for a fuel cell comprising a. The method of claim 1, The catalyst layer is a fuel cell membrane-electrode assembly having a concentration gradient in which the pore size decreases from the first interface where the catalyst layer and the electrode substrate are bonded to the second interface where the catalyst layer and the polymer electrolyte membrane contact each other. The method of claim 1, In the catalyst layer, the pore size decreases from the first interface where the catalyst layer and the electrode substrate are bonded to the second interface where the catalyst layer and the polymer electrolyte membrane contact each other. And, in the second interface, present in a volume ratio of 10: 0 to 2 in the fuel cell membrane-electrode assembly. The method of claim 1, The catalyst layer is a fuel cell membrane-electrode assembly comprising a platinum-based catalyst. The method of claim 1, The catalyst layer is a fuel cell membrane-electrode assembly further comprising one selected from the group consisting of binder resins, pore formers, and mixtures thereof. The method of claim 9, The binder resin is a polymer resin having a cation exchange group selected from the group consisting of sulfonic acid group, carboxylic acid group, phosphoric acid group, phosphonic acid group and derivatives thereof in the side chain. The method of claim 9, The pore former is a membrane-electrode assembly for a fuel cell is an alkali metal carbonate. The method of claim 1, The membrane-electrode assembly is a membrane-electrode assembly for a direct oxidation fuel cell membrane-electrode assembly. Preparing a composition for forming a catalyst layer comprising a catalyst and a pore former; Applying the catalyst layer forming composition to an electrode substrate to form a catalyst layer; Acid-treating the electrode substrate on which the catalyst layer is formed to form pores in the catalyst layer to manufacture an electrode; And Forming a polymer electrolyte membrane on the catalyst layer of the electrode Method of manufacturing a membrane-electrode assembly for a fuel cell comprising a. The method of claim 13, And the pore former is a carbonate of an alkali metal. The method of claim 13, The pore former is selected from the group consisting of LiCO ₃ , K ₂ CO ₃ , Na (CO ₃ ) ₂ , and mixtures thereof. The method of claim 13, The pore former is a method for producing a membrane-electrode assembly for a fuel cell comprising a micropore former having a nanoparticle size average particle diameter, and a macroporous former having an average particle diameter of 5 to 25㎛. The method of claim 16, Wherein the fine pore former has an average particle diameter of 100 nm or less. The method of claim 16, The macro pore former is a method for producing a membrane-electrode assembly for a fuel cell having an average particle diameter of 5 to 20㎛. The method of claim 16, The macropore-forming agent comprises a first macropore-forming agent having an average particle diameter of 5 to 7 μm, a second macroporous forming agent having an average particle diameter of 10 to 12 μm, and an average particle diameter of 18 to 20 μm. Method for producing a membrane-electrode assembly for a fuel cell comprising a third macropore forming agent having. The method of claim 13, Wherein the catalyst layer is formed to have a concentration gradient in which the pore size decreases from the first interface where the catalyst layer and the electrode substrate are bonded to the second interface where the catalyst layer and the polymer electrolyte membrane are in contact with each other. The method of claim 13, The acid treatment process is a method of manufacturing a membrane-electrode assembly for a fuel cell is performed by treating an acid selected from the group consisting of sulfuric acid, phosphoric acid, hydrofluoric acid, and mixtures thereof. 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 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 22, The fuel cell system is a direct oxidation fuel cell system.

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