KR100814844B1 - Membrane-electrode assembly for fuel cell, method of preparing same and fuel cell system comprising same - Google Patents

Abstract

A membrane-electrode assembly for a fuel cell is provided to improve the output density of a fuel cell by increasing the active surface area of a catalyst layer and by fixing a catalyst to the surface of a polymer electrolyte membrane. A membrane-electrode assembly(112) for a fuel cell comprises: an anode(30) and a cathode(30') facing to each other; and a polymer electrolyte membrane(20) interposed between the anode and the cathode, wherein at least one of the anode and the cathode comprises an electrode substrate(70,70') and a catalyst layer(60,60') formed on the electrode substrate. The catalyst layer comprises a first catalyst layer(40,40') comprising a first metal catalyst grown in the form of nodules on the polymer electrolyte membrane along the direction of the electrode substrate, and a second catalyst layer(50,50') comprising a second metal catalyst formed on an inclined surface having the same orientation as the nano-nodules of the first metal catalyst.

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 OF PREPARING 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 process diagram showing a method of manufacturing a membrane-electrode assembly according to another embodiment of the present invention.

Figure 3 is a schematic diagram showing the structure of the catalyst layer produced by the production method of the present invention briefly.

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

 [Industrial use]

The present invention relates to a membrane-electrode assembly for a fuel cell, a method for manufacturing the same, and a fuel cell system including the same. More specifically, the interaction between the polymer electrolyte membrane and the catalyst layer is increased, and the polymer adhesive force including pores in the catalyst layer is increased. Membrane-electrode assembly for fuel cell, which can facilitate mass transfer to electrolyte membrane, and can increase the output density of fuel cell with increased active surface area, its manufacturing method and fuel cell comprising the same It's about the system.

 [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 is called an anode electrode (also called a “fuel electrode” or an “oxide electrode”) and a cathode electrode (one side “air electrode” or “reduction electrode”) with a polymer electrolyte membrane including 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 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.

 It is an object of the present invention to provide a membrane-electrode assembly for a fuel cell, in which the interaction between the polymer electrolyte membrane and the catalyst layer is increased and also includes pores in the catalyst layer, thereby facilitating mass transfer to the polymer electrolyte membrane.

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

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

In order to achieve the above object, the present invention provides a membrane-electrode assembly comprising 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 includes an electrode substrate and a catalyst layer positioned on the electrode substrate, wherein the catalyst layer comprises a first metal catalyst grown in the form of nano nodules on the polymer electrolyte membrane in the direction of the electrode substrate. And a second catalyst layer including a first catalyst layer and a second metal catalyst formed on the inclined surfaces of the first metal catalyst nano nodules in the same orientation.

The present invention also provides a polymer electrolyte membrane, depositing a first metal catalyst on the polymer electrolyte membrane to form a first catalyst layer, and depositing a second metal catalyst on the first catalyst layer by using a shadowing method. It provides a method for producing a fuel cell membrane-electrode assembly comprising the step of forming a catalyst layer, and bonding the polymer electrolyte membrane on which the second catalyst layer is formed with an electrode substrate.

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 a fuel cell, the membrane-electrode assembly is composed of a polymer electrolyte membrane and anode and cathode electrodes positioned on both sides of the polymer electrolyte membrane. In this membrane-electrode assembly, electricity is generated by oxidation and reduction reactions by fuel and oxidant. Let's do it. In order to facilitate the reaction in the membrane-electrode assembly, the interaction between the polymer electrolyte membrane and the catalyst layer should be large. In other words, the interface adhesion between the polymer electrolyte membrane and the electrode catalyst layer and the contact area of the electrode at the interface should be high.

In addition, the larger the catalytically active surface area in the catalyst layer, the higher the catalytic activity is desirable.

On the other hand, in the present invention, by forming the first catalyst layer and the second catalyst layer by different deposition methods, the catalyst layer is formed in a form including micropores, thereby increasing the catalytically active surface area and immobilizing the catalyst on the surface of the polymer electrolyte membrane. The battery performance of the fuel cell can be improved.

That is, the catalyst layer in the fuel cell membrane-electrode assembly according to an embodiment of the present invention includes a first catalyst layer including a first metal catalyst grown on the polymer electrolyte membrane in the form of a nodule, and the first metal catalyst nano nodule. A second catalyst layer comprising a second metal catalyst formed on the inclined surface of the same orientation.

 1 is a cross-sectional view schematically showing a membrane-electrode assembly for a fuel cell of the present invention. In the structure shown in FIG. 1, the catalyst layer having a two-layer structure is formed on both sides of the anode electrode and the cathode electrode, but the membrane-electrode assembly of the present invention is not limited to this structure, and the catalyst layer of the two-layer structure is the anode electrode. Of course, it may be formed only in any one of the cathode electrode.

 Referring to FIG. 1, the membrane-electrode assembly 112 according to an embodiment of the present invention includes the polymer electrolyte membrane 20 and the fuel cell electrodes 30 and 30 disposed on both surfaces of the polymer electrolyte membrane 20, respectively. Include '). The electrodes 30 and 30 'include an electrode substrate 70 and 70' and a catalyst layer 60 and 60 'positioned on the electrode substrate.

In the membrane-electrode assembly 112, the electrode 30 disposed on one surface of the polymer electrolyte membrane 20 is called an anode electrode (or a cathode electrode), and the electrode 30 ′ disposed on the other surface is called a cathode electrode ( Or anode electrode). The anode electrode 30 causes an oxidation reaction to generate hydrogen ions and electrons from the fuel delivered to the catalyst layer 60 through the electrode base 70, and the polymer electrolyte membrane 20 is hydrogen generated from the anode electrode 30 Ions are moved to the cathode electrode 30 ', and the cathode electrode 30' is transferred to the catalyst layer 60 'through the hydrogen ions supplied through the polymer electrolyte membrane 20 and the electrode base 70'. It causes a reduction reaction to produce water from the oxidant.

The catalyst layers 60 and 60 'catalyze the related reaction (oxidation of fuel and reduction of oxidant), and include a first catalyst layer 40 and 40' and a second catalyst layer 50 and 50 '. .

The first catalyst layers 40 and 40 'include a first metal catalyst grown in the form of a nodule toward the electrode substrates 70 and 70' on the polymer electrolyte membrane 20.

In detail, the first catalyst layer may be prepared by growing the first metal catalyst toward the electrode substrate in the polymer electrolyte membrane by vapor deposition or chemical adsorption. By the above method, the first metal catalyst is directly grown in the form of a nodule in the polymer electrolyte membrane by the interaction between the electrostatic force and the metal particles, thereby increasing the bonding force between the polymer electrolyte membrane and the catalyst layer. Mass transfer to the polymer electrolyte membrane can be facilitated.

The first metal catalyst grown in the form of a nodule in the polymer electrolyte membrane has a height of nano size to micro size, and preferably may have an average height of 50 nm to 5 μm, more preferably an average of 200 nm to 2 μm. May have a height. If the average height of the first metal catalyst exceeds 5 μm, the area in contact with the second metal catalyst is relatively small, and the effect obtained is insignificant. If the average height of the first metal catalyst is less than 50 nm, the density of the first metal catalysts on the surface of the polymer electrolyte membrane is high, resulting in dense It is not preferred to have a flat catalyst layer.

The growth position or spacing of the first metal catalyst may be controlled by the pattern or roughness of the surface of the polymer electrolyte membrane during deposition. Preferably, the interval between the first metal catalysts is preferably 1 nm to 1 mm, more preferably 10 to 500 nm. When the spacing of the first metal catalyst is less than 1 nm, the second metal catalyst does not enter between the nodules of the already grown first metal catalyst or the space between the grown first metal catalysts is left as an empty space so that the film resistance There is a possibility that this increases, and if it exceeds 1 mm, the surface area of the second metal catalyst in contact with the first metal catalyst is relatively small, which is not preferable because the obtained effect is insignificant.

In addition, as the first metal catalyst grows in the form of a nodule, micropores may be formed in the catalyst layer. As such, the micropores formed in the catalyst layer facilitate mass transfer to the polymer electrolyte membrane, and also increase the catalytically active surface area to maximize the catalytic activity.

As the first metal catalyst, platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy and 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. Representative 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 / One or more selected from the group consisting of Ru / 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, carbon such as acetylene black, denka black, activated carbon, ketjen black, graphite may be used, or inorganic fine particles such as alumina, silica, titania, zirconia may be used, but carbon is generally used.

The first catalyst layer including the first metal catalyst may first attach a support having high ionic conductivity to the polymer electrolyte membrane in order to increase the adhesion rate of the first metal catalyst in the polymer electrolyte membrane and grow to a certain shape when forming the catalyst layer. have. Accordingly, the first catalyst layer may further include a support having a high ion conductivity together with the first metal catalyst. Examples of such a support include metals such as Ce, Ni, Mn, Fe, Co, and Zr; Zirconia; Polyoxometalate (POM) such as polytungstate and polymolybdate; Heteropolyacid (heteropolyacid) etc. can be used, More preferably, Ce can be used.

The second catalyst layers 50 and 50 'including the second metal catalyst are formed on the inclined surfaces having the same orientation of the nodule of the first catalyst layers 40 and 40'.

The second catalyst layer is formed by a shadowing method in which deposition is performed by tilting the deposition gun at a predetermined angle. In this manner, the second metal catalyst is obliquely stacked on the inclined surface of the nodule of the first catalyst metal. As a result, the deposited second metal catalyst becomes porous, thereby increasing the catalytically active surface area, and also hydroxy group can be easily supplied to the first metal catalyst, thereby maximizing the catalytic activity.

If the inclination is not given, the second metal catalysts deposited and grown may aggregate together to form a dense film on the surface, thereby preventing the transfer of fuel or charge, but when inclined, the formation of a relatively dense film on the surface Can be effectively reduced.

 The second metal catalyst may be selected from the group consisting of Pt, Ru, Au, W, Pd, Fe, and alloys thereof, and more preferably in the group consisting of Pt, W, Au, and alloys thereof. You can use what is selected. In particular, when the W and Au alloy catalyst of PtRu as the first metal catalyst, the hydroxy group is more smoothly supplied to Ru in the bifunctional mechanism of the PtRu catalytic reaction, thereby easily removing carbon monoxide bound to Pt. It is most preferable because it can raise a catalytic effect.

In the catalyst layer including the first catalyst layer and the second catalyst layer according to the present invention, the second metal catalyst has a weight that is too small to be measured by weight so that the second metal catalyst may be in an error range from the first metal catalyst to the second metal catalyst. It may be included in the catalyst layer in a weight ratio of about 98: 2. When converting it into a thickness ratio, the catalyst layer preferably includes a first catalyst layer and a second catalyst layer in a thickness ratio of 25: 1 to 2500: 1, and more preferably includes a thickness ratio of 65: 1 to 650: 1. When the ratio of the thickness of the first catalyst layer and the second catalyst layer is within the above range, the contact surface area of the first metal catalyst and the second metal catalyst may increase to increase the catalytic activity. It is not preferable because the growth of the metal oxide is small or difficult to grow in a certain form, and the first metal catalyst may be excessively concentrated to cover the surface of the polymer electrolyte membrane in the form of a membrane rather than growing in a certain form.

The catalyst layers 60 and 60 'having the above configuration may be included in any one of the anode electrode and the cathode electrode, and in particular, the second metal catalyst serves to increase the number of hydroxyl groups in a bifunctional mechanism. It is more preferable to be included in the anode electrode because

The electrode substrates 70 and 70 'play a role of supporting the electrode and diffuse fuel and oxidant to the catalyst layer so that the fuel and oxidant can easily access the catalyst layer.

A conductive substrate may be used as the electrode base material, and representative examples thereof include a carbon film, a carbon cloth, a carbon felt, or a metal cloth (porous film composed of a metal cloth in a fibrous state). Or a metal film formed on a surface of a cloth formed of polymer fiber (referred to as metalized polymer fiber), but is not limited thereto. In addition, the electrode substrate is water-repellent treated with a fluorine resin such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated ethylene propylene, polychlorotrifluoroethylene, fluoroethylene polymer, and the like. It is more preferable because the gas diffusion efficiency can be prevented from being lowered by water generated when the fuel cell is driven.

In addition, the anode electrode or the cathode electrode may further include a microporous layer on the electrode substrate in order to further enhance the gas diffusion effect between the electrode substrate and the catalyst layer. The microporous layer is formed by applying a composition comprising a conductive powder material, a binder, and an ionomer as necessary. Examples of the conductive powder include carbon powder, carbon black, acetylene black, activated carbon, or carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nano-horns, or carbon nano rings. Nano carbon and the like can be used.

The membrane-electrode assembly according to an embodiment of the present invention also includes a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode.

The polymer electrolyte membrane functions as an ion exchange to transfer hydrogen ions generated in the catalyst layer of the anode electrode to the catalyst layer of the cathode electrode, and it is preferable to use a polymer having excellent hydrogen ion conductivity. Representative examples thereof may be any polymer resin having a cation exchange group selected from the group consisting of sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, phosphonic acid groups and derivatives thereof in the side chain. 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 ion selected from poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole), poly (2,5-benzimidazole) or copolymers thereof Conductive mound You can use anything that contains a ruler.

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

In addition, the polymer electrolyte membrane may have high surface power by increasing the contact area with the catalyst layer of the electrode and may have surface roughness on one or both surfaces thereof to facilitate the growth of the metal catalyst in a certain form, and more preferably. Preferably, it is desirable to have surface roughness on both sides of the polymer electrolyte membrane.

The membrane-electrode assembly having such a configuration can be manufactured by the following manufacturing method.

2 is a process chart showing a method of manufacturing a membrane-electrode assembly according to another embodiment of the present invention. Referring to Figure 2 describes a method of manufacturing a membrane-electrode assembly of the present invention, the manufacturing method comprises the steps of preparing a polymer electrolyte membrane (S1); Depositing a first metal catalyst on the polymer electrolyte membrane to form a first catalyst layer (S2); Depositing a second metal catalyst on the first catalyst layer by using a shadowing method to form a second catalyst layer (S3); And bonding the polymer electrolyte membrane on which the second catalyst layer is formed with an electrode base (S4).

More specifically, first, a high molecular electrolyte membrane is prepared from a cation exchange resin having hydrogen ion conductivity (S1).

The manufacturing method of the polymer electrolyte membrane is not particularly limited, and may be manufactured in a thin film form by a conventional manufacturing method using a cation exchange resin having hydrogen ion conductivity. The cation exchange resin having the hydrogen ion conductivity is the same as described above.

One or both surfaces of the prepared polymer electrolyte membrane are subjected to plasma treatment, etching treatment with acid, anodizing, corona treatment, rubbing method, pressing method using a plastic substrate having a predetermined pattern, sand paper or The surface treatment may be further carried out by surface treatment by a sand blasting method or the like to further increase the surface roughness.

In addition, in order to increase the adhesion rate of the first metal catalyst to the polymer electrolyte membrane prior to growing the first metal catalyst on the polymer electrolyte membrane, a step of attaching a support having a high ion conductivity may be optionally further performed.

In this case, the support is the same as described above, and the attachment process of the support is sputtering, physical vapor deposition (PVD), plasma enhanced chemical vapor deposition (PECVD), thermochemical vapor phase. Thermal Chemical Vapor Deposition, Ion Beam Evaporation, Vaccum Thermal Evaporation, Laser Ablation, Thermal Evaporation, Electron Beam Evaporation The method selected from the group consisting of evaporation can be used, and more preferably, sputtering can be used.

It is preferable to perform the said support body attachment process within the temperature range of 0-25 degreeC. Within this temperature range, the adhesion rate of the support is high, thereby facilitating the subsequent growth of the first metal catalyst into a certain form.

Next, the first metal catalyst is grown toward the electrode substrate on the prepared polymer electrolyte membrane or on the support attached to the polymer electrolyte membrane to form a first catalyst layer (S2).

The first metal catalyst is the same as described above, and the process of growing the first metal catalyst is spraying, sputtering, physical vapor deposition (PVD), plasma enhanced chemical vapor deposition (Plasma Enhanced Chemical Vapor Deposition). vapor deposition (PECVD), Thermal Chemical Vapor Deposition, ion beam evaporation, vacuum thermal evaporation, laser ablation, thermal evaporation , And e-beam evaporation may be used.

It is preferable to perform the said process in the temperature range of 0-25 degreeC. Within this temperature range, the growth process in a certain form is easy.

By the manufacturing process as described above, the first metal catalyst grows toward the electrode substrate on the polymer electrolyte membrane or the support attached thereon, and has a form of nodule.

Subsequently, a second catalyst layer including a second metal catalyst is formed on the first catalyst layer (S3).

The second metal catalyst is the same as described above, and the second catalyst layer forming process including the second metal catalyst may be formed by using a shadowing method.

The shadow method is a method of depositing at a predetermined angle, and is less energy than deposition by sputtering, so that the metal particles can be easily deposited on the rough surface with porousity. Conventional depositions such as physical vapor deposition (PVD), plasma enhanced chemical vapor deposition (PECVD), thermal chemical vapor deposition, and ion beam evaporation Method can be used.

More specifically, the second catalyst metal is cut to 3 to 5 mg of the tungsten filament and placed at 15 cm with a slope of about 15 degrees with the first catalyst layer in a vacuum of 0.1 torr or less. While the vacuum is maintained, the tungsten filament instantly rises to the thousands of degrees and the gold is vaporized by vapor deposition when the current adjustment knob (nob) is raised immediately.

In addition, the deposition of the second metal catalyst is preferably carried out after positioning to have an inclination angle of 5 to 50 degrees with respect to the first catalyst layer, and more preferably to be carried out after positioning to have an inclination angle of 10 to 20 degrees. If the position of the second metal catalyst relative to the first catalyst layer is out of the inclination angle range, the second catalyst layer formed may be too dense, which is not preferable.

In this case, the current size may vary depending on the size of the vacuum chamber, etc., and the deposition rate may vary according to the tungsten temperature rising rate. In order to obtain a porous structure, it is desirable to raise the temperature as soon as possible and lower it immediately.

As described above, the second catalyst layer is formed on the inclined surface of the nodule having the same orientation in the first catalyst layer.

3 is a schematic diagram schematically showing the structure of the catalyst layer produced by the above production method. After the second catalyst layer forming step (S3), a first catalyst layer 40 having a nodule shape is formed on the surface of the polymer electrolyte membrane 20, and the second catalyst layer 50 is disposed on the inclined surface of the nodule having the same orientation in the first catalyst layer. ) Is formed.

The polymer electrolyte membrane on which the second catalyst layer is formed is bonded to an electrode substrate (S4) to prepare a membrane-electrode assembly (S5).

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

The method of manufacturing the membrane-electrode assembly as described above is excellent in the interaction between the polymer electrolyte membrane and the catalyst layer by immobilizing a metal catalyst on the surface of the polymer electrolyte membrane by forming a catalyst layer directly on the polymer electrolyte membrane using a deposition method. It is easy to control the density of the catalyst layer can be formed having a sufficient porosity. In addition, when the first catalyst layer and the second catalyst layer are formed, the first catalyst layer and the second catalyst layer may be formed to have a specific form by using different deposition methods, thereby maximizing catalyst activity. Accordingly, the membrane-electrode assembly of the present invention manufactured by the manufacturing method may increase the output density of the fuel cell when applied to the fuel cell.

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. 4, which will be described in more detail with reference to the following. Although the structure shown in FIG. 4 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 115 for generating electrical energy through an oxidation reaction of a fuel and a reduction reaction of an oxidant, a fuel supply unit 120 for supplying the fuel, And an oxidant supply unit 130 for supplying an oxidant to the electricity generating unit 115.

In addition, the fuel supply unit 120 for supplying the fuel may include a fuel tank 122 storing fuel and a fuel pump 124 connected to the fuel tank 122. The fuel pump 124 serves to discharge the fuel stored in the fuel tank 122 by a predetermined pumping force.

The oxidant supply unit 130 supplying the oxidant to the electricity generating unit 115 includes at least one oxidant pump 132 that sucks the oxidant with a predetermined pumping force.

The electricity generator 115 includes a membrane-electrode assembly 112 for oxidizing and reducing a fuel and an oxidant, and a separator 114 and 114 'for supplying fuel and an oxidant to both sides of the membrane-electrode assembly. At least one electricity generating unit 115 gathers to form a stack 110.

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

 Example 1

A commercial NAFION 115 membrane (125 μm) was treated with 3% hydrogen peroxide and 1 M sulfuric acid solution at 90 ° C. for 2 hours, and then washed in deionized water at 100 ° C. for 1 hour to prepare an H + type Nafion 115 membrane.

After sputtering Ce at 20 ° C. with respect to one surface of the polymer electrolyte membrane, PtRu was grown on Ce as a first metal catalyst by ion sputtering to form a first catalyst layer. Thereafter, a gold wire having a purity of 99.99% was cut to 3 mg to 5 mg of tungsten filament and placed at 15 cm with an inclination of 15 degrees with the first catalyst layer in a vacuum of 0.1 torr or less. The second catalyst layer was formed by instantaneously raising the current adjusting knob so that the temperature of the tungsten filament rose to several thousand degrees while maintaining the vacuum, and immediately lowering the vaporization by vaporizing gold. The same was true for the other side of the polymer electrolyte membrane to form the catalyst layers of the cathode and the anode on both sides of the polymer electrolyte membrane.

Thereafter, a commercial electrode substrate (SGL Carbon 31BC) is physically bonded to both surfaces of the polymer electrolyte membrane in which the catalyst layer is formed, and inserted between two gaskets, and then inserted into two separators having a predetermined gas flow channel and cooling channel. And pressed between the copper end (end) plate to prepare a single cell.

Example 2

A single cell was manufactured in the same manner as in Example 1, except that the catalyst layer was formed only on the anode electrode side.

Example 3

Except that PtRu supported on graphite is used as the first metal catalyst, W is used as the second metal catalyst, and a catalyst layer including the first metal catalyst and the second metal catalyst is formed only on the anode electrode side. And was carried out in the same manner as in Example 1 to prepare a single cell.

Comparative Example 1

A commercial NAFION 115 membrane (125 μm) was treated for 2 hours in 90% 3% hydrogen peroxide and 1M aqueous sulfuric acid solution, and then washed in deionized water at 100 ° C. for 1 hour to prepare a H + type Nafion 115 membrane.

3.0 g of Pt black (Hispec ^® 1000, manufactured by Johnson Matthey) and Pt / Ru black (Hispec ^® 6000, manufactured by Johnson Matthey) were added dropwise to 4.5 g of 10 wt% Nafion (NAFION ^® Dupont) aqueous dispersion and mechanically stirred. To prepare a composition for forming a catalyst layer.

The catalyst layer forming composition was directly coated on one surface of the polymer electrolyte membrane by screen printing. At this time, the catalyst layer forming area is 5 X 5 cm ^{2 And the} catalyst loading amount is 3 mg / cm ² respectively. The same was true for the other side of the polymer electrolyte membrane to form the catalyst layers of the cathode and the anode on both sides of the polymer electrolyte membrane.

Thereafter, a commercial electrode substrate (SGL Carbon 31BC) was physically bonded to both surfaces of the polymer electrolyte membrane in which the catalyst layer was formed, and inserted into two gaskets, and then a certain shape of a gas flow channel and a cooling channel were formed. A single cell was prepared by inserting into two separators and pressing between copper end plates.

In the unit cells prepared according to Examples 1 to 3 and Comparative Example 1, the output of the unit cell according to the battery temperature and the methanol concentration in the state in which methanol was introduced into the cathode electrode layer and ambient air was introduced into the anode electrode side Was measured. The measurement results are shown in Table 1 below.

Power density at 70 ℃ (mW / cm ² at 0.4 V) Example 1 120 Example 2 135 Example 3 145 Comparative Example 1 110

As shown in Table 1, the fuel cells of Examples 1 to 3 showed an excellent power density compared to Comparative Example 1. This is because the fuel cell of Examples 1 to 3 includes a first catalyst layer of the nodule grown on the polymer electrolyte membrane and a second catalyst layer formed on the inclined surface of the first catalyst layer to assist the catalytic activity of the first metal catalyst, thereby increasing the catalytic activity. In addition, it is considered that the micropores in the catalyst layer are formed to facilitate the transfer of substances and ions to the polymer electrolyte membrane.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications and changes can be made within the scope of the claims and the detailed description of the invention and the accompanying drawings. Naturally, it belongs to the scope of the invention.

In the membrane-electrode assembly according to the present invention, the catalyst layer is formed in a form including micropores, thereby increasing the catalytically active surface area, and also improving the output density of the fuel cell by immobilizing the catalyst on the surface of the polymer electrolyte membrane.

Claims (17)

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 includes an electrode substrate, and a catalyst layer located on the electrode substrate,  The catalyst layer includes a first catalyst layer including a first metal catalyst grown in the form of a nodule in the direction of an electrode substrate on the polymer electrolyte membrane, and a second metal catalyst formed on an inclined surface of the same orientation of the first metal catalyst nano nodule. Membrane electrode assembly for a fuel cell comprising a second catalyst layer.  The method of claim 1, The first metal catalyst is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-M alloy, platinum-ruthenium-M alloy (M = Ga, Ti, V, Cr, Mn , Fe, Co, Ni, Cu, Zn, Sn, Mo, W, Rh, and a metal selected from the group consisting of a combination thereof) and a mixture thereof.  The method of claim 1, The second metal catalyst is at least one member selected from the group consisting of Pt, Ru, Au, W, Pd, Fe and alloys thereof.  The method of claim 1, Wherein the first metal catalyst is PtRu and the second metal catalyst is W or Au.  The method of claim 1, The catalyst layer is a fuel cell membrane-electrode assembly further comprising a support selected from the group consisting of Ce, Ni, Mn, Fe, Co, Zr, zirconia, polyoxometallate, heteropoly acid.  The method of claim 1, The catalyst layer is a fuel cell membrane-electrode assembly that is included in the anode electrode.  The method of claim 1, Any one of the anode electrode and the cathode electrode comprises a microporous layer between the electrode substrate and the catalyst layer.  The method of claim 1, The polymer electrolyte membrane comprises a polymer resin having a cation exchange group selected from the group consisting of sulfonic acid group, carboxylic acid group, phosphoric acid group, and phosphonic acid group in the side chain. Preparing a polymer electrolyte membrane; Depositing a first metal catalyst on the polymer electrolyte membrane to form a first catalyst layer; Depositing a second metal catalyst on the first catalyst layer by using a shadowing method to form a second catalyst layer; And Bonding the polymer electrolyte membrane on which the second catalyst layer is formed to an electrode substrate; Method of manufacturing a membrane-electrode assembly for a fuel cell comprising a.  The method of claim 9, The method of forming the first metal layer includes a spray method, sputtering, physical vapor deposition, plasma enhanced chemical vapor deposition, thermochemical vapor deposition, ion beam evaporation, vacuum thermal evaporation, laser ablation, thermal evaporation, and electron beam evaporation. Method of manufacturing a membrane-electrode assembly for a fuel cell that is carried out by the method selected from. The method of claim 9, The first metal catalyst is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-M alloy, platinum-ruthenium-M alloy (M = Ga, Ti, V, Cr, Mn , Fe, Co, Ni, Cu, Zn, Sn, Mo, W, Rh and combinations thereof) and a mixture thereof, the preparation of a membrane-electrode assembly for a fuel cell Way. The method of claim 9, Wherein the second metal catalyst is at least one selected from the group consisting of Pt, Ru, Au, W, Pd, Fe, and alloys thereof. The method of claim 9, Wherein the second metal layer is formed by depositing at an inclination angle of 5 to 50 degrees with respect to the first metal layer. The method of claim 9, After the production of the polymer electrolyte membrane, a method of manufacturing a fuel cell membrane-electrode assembly further comprising the step of attaching a support having a large ion conductivity to the polymer electrolyte membrane. The method of claim 14, Wherein the support is Ce, Ni, Mn, Fe, Co, Zr, zirconia, polyoxometallate, heteropoly acid is a method for producing a membrane-electrode assembly for a fuel cell.  The method of claim 14, The attachment process of the support is selected from the group consisting of sputtering, physical vapor deposition, plasma enhanced chemical vapor deposition, thermochemical vapor deposition, ion beam evaporation, vacuum thermal evaporation, laser ablation, thermal evaporation, and electron beam evaporation. Method of manufacturing a membrane-electrode assembly for a fuel cell that is carried out by.  At least one electricity generating unit comprising a membrane-electrode assembly according to any one of claims 1 to 8, and a separator, for generating electricity through the electrochemical reaction of the fuel and the oxidant; A fuel supply unit supplying fuel to the electricity generation unit; And Oxidant supply unit for supplying an oxidant to the electricity generating unit  Fuel cell system comprising a.

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