KR100728186B1 - Cathod catalyst for fuel cell, and cathod electrode for fuel cell, membrane-electrode assembly for fuel cell, and fuel cell system comprising same - Google Patents

Abstract

Provided are a cathode catalyst for a fuel cell, which is superior in catalytic activity for the reduction of an oxidant, and a cathode electrode for a fuel cell comprising the same, which has excellent catalytic activity. The cathode catalyst for a fuel cell comprises a metal oxide represented by a formula 1 of Co_xM_yO_z, wherein M is a rare earth element, x is 40-60, y is 25-30, and z is 10-35. The cathode electrode(5) for a fuel cell includes an electrode substrate(31) and a catalytic layer(33) formed on the electrode substrate(31), wherein the catalytic layer(33) comprises the cathode catalyst including metal oxide represented by the formula 1.

Description

Cathode catalyst for fuel cell, cathode electrode for fuel cell comprising same, membrane-electrode assembly for fuel cell and fuel cell system TECHNICAL CELL, AND CATHOD ELECTRODE FOR FUEL CELL, MEMBRANE-ELECTRODE ASSEMBLY FOR FUEL CELL SAME}

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

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

[Industrial use]

The present invention relates to a fuel cell cathode catalyst, a fuel cell cathode electrode comprising the same, a fuel cell membrane-electrode assembly, and a fuel cell system, and more particularly, to a fuel cell cathode catalyst having excellent catalytic activity against a reduction reaction of an oxidant. And a cathode electrode for a fuel cell, a membrane-electrode assembly for a fuel cell, and a fuel cell system including the same.

[Prior art]

A fuel cell is a power generation system that converts chemical reaction energy of hydrogen and oxidant contained in hydrogen or hydrocarbon-based material directly into electrical energy.

Representative examples of the fuel cell include a polymer electrolyte fuel cell (PEMFC) and a direct oxidation fuel cell (Direct Oxidation Fuel Cell). When methanol is used as a fuel in the direct oxidation fuel cell, it is called a direct methanol fuel cell (DMFC).

Generally, polymer electrolyte fuel cells have the advantages of high energy density and high output, but they require attention to handling hydrogen gas and fuels for reforming methane, methanol, and natural gas to produce hydrogen, which is fuel gas. There is a problem that requires additional equipment such as a reforming device.

On the other hand, the direct oxidation fuel cell has a lower reaction speed than the polymer electrolyte type due to the slow reaction rate, and requires a large amount of electrode catalyst, but it is easy to handle the liquid fuel and the operating temperature is low. In particular, it has the advantage of not requiring a fuel reformer.

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

The principle of generating electricity in a fuel cell is that fuel is supplied to an anode electrode, which is a fuel electrode, adsorbed to a catalyst of the anode electrode, and the fuel is oxidized to generate hydrogen ions and electrons. 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 producing water.

An object of the present invention is to provide a cathode catalyst for a fuel cell having excellent catalytic activity against the reduction reaction of an oxidant.

Another object of the present invention is to provide a cathode electrode for a fuel cell having excellent catalytic activity.

Yet another object of the present invention is to provide a membrane-electrode assembly for a fuel cell comprising the cathode catalyst.

It is another object of the present invention to provide a fuel cell system comprising the cathode catalyst.

In order to achieve the above object, the present invention provides a cathode catalyst for a fuel cell containing a metal oxide of the formula (1).

[Formula 1]

Co _x M _y O _z

(Wherein M is a rare earth element, x is 40 to 60, y is 25 to 30, and z is 10 to 35)

The present invention also provides an electrode substrate, and a catalyst layer formed on the electrode substrate, wherein the catalyst layer provides a cathode electrode for a fuel cell comprising a cathode catalyst comprising the metal oxide of the formula (1). In this case, the catalyst layer may further include an electrically conductive polymer.

The present invention also includes an anode electrode and a cathode electrode located opposite to each other, and an electrolyte located between the anode electrode and the cathode electrode, wherein the cathode electrode comprises a cathode catalyst comprising a metal oxide of the formula (1) A membrane-electrode assembly for phosphorus fuel cells is provided.

The invention also relates to at least one electricity generating unit comprising an anode electrode and a cathode electrode positioned opposite each other, and at least one membrane-electrode assembly including an electrolyte located between the anode electrode and the cathode electrode, and a separator; It provides a fuel cell system comprising a fuel supply unit for supplying fuel to the electricity generation unit and an oxidant supply unit for supplying an oxidant to the electricity generation unit, wherein the cathode electrode comprises a cathode catalyst comprising a metal oxide of the formula (1). do.

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

The present invention relates to a cathode catalyst of a fuel cell. In particular, the present invention relates to a cathode catalyst of an alkaline electrolyte fuel cell (AlFC) using an alkaline solution as an electrolyte. These alkaline electrolyte fuel cells have a high power density, low operating temperature, and rapid driving, and thus, are being researched for special purposes such as spacecraft or submarine power supplies. It operates at low temperatures, making it a popular power source in extreme regions.

In the alkaline electrolyte fuel cell, H ₂ fuel and OH ⁻ present in the electrolyte react at the anode to generate water and electrons, and the generated water and electrons move to the cathode electrode and then oxygen and oxygen supplied into the cathode electrode. It is a battery that reacts to form OH ^- ions and generates electricity.

An oxide of AB ₂ O ₄ (A is Co, Ni or Cu, B is Co, Fe, or Mn) has a spinel structure, and the more unstable spinel structure of the oxide shows excellent catalytic activity against oxidant reduction reactions. It is reported. Accordingly, various studies have been made to use the oxide having the spinel structure as a catalyst for the cathode electrode. In this regard, it has been reported that composite films containing CoFe ₂ O ₄ particles and polypyrrole (PPy) have excellent catalytic activity against oxygen reduction reactions (RNSingh et al., Electrochimica Acta 49 (2004) 4605). -4612).

On the other hand, the present invention provides a cathode catalyst for a fuel cell comprising a metal oxide of the formula (1) comprising a rare earth element in place of Fe in the conventional CoFe ₂ O ₄ .

[Formula 1]

Co _x M _y O _z

Wherein M is a rare earth element, x is from 40 to 60, y is from 25 to 30, and z is from 10 to 35, more preferably x is from 45 to 55, y is from 26 to 28, and z is from 20 To 30)

In the above formula, x, y and z represent mol% of each element.

If the content of Co in the metal oxide x is less than 40 mol%, the catalyst stability is not preferable, and if x is more than 60 mol%, the particle size may be increased and the catalytic activity may be lowered, which is not preferable.

Moreover, when y which is content of M is less than 25 mol%, there exists a possibility that a catalyst activity may fall, and when y exceeds 30 mol%, there exists a possibility that catalyst stability may fall and it is unpreferable.

If the z content of O is less than 10 mol%, the selectivity to the oxidant reduction reaction may be lowered, which is not preferable. If z exceeds 35 mol%, the catalytic activity may be lowered, which is not preferable.

In addition, M is a rare earth element and has various oxidation numbers, and can easily form a spinel structure. Accordingly, the cathode catalyst of the present invention not only exhibits excellent catalytic activity against the reduction reaction of the oxidant due to the spinel structure of the metal oxide, but is also very stable under alkaline conditions. More preferably, M is La, Yb or a combination thereof.

It is preferable that the cathode catalyst having the above configuration has an average particle diameter of 3 to 15 nm, and more preferably, an average particle diameter of 4 to 10 nm. If the average particle diameter of the metal oxide is less than 3 nm, the stability may be deteriorated, and if it is more than 15 nm, the catalytic activity may be deteriorated due to the decrease of the reaction specific surface area due to the increase in the particle size.

In addition, the cathode catalyst may be used as the catalyst itself (black), or may be used 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 cathode catalyst having the composition as described above is prepared by a manufacturing method comprising mixing a Co source and a rare earth element source in a solvent to prepare a mixture, drying the mixture to obtain a powder, and heat treating the obtained powder. Can be.

As the Co source, a water-soluble salt of Co such as Co (NO ₃ ) ₂ may be used, and as a rare earth element source, a water-soluble salt containing a rare earth element may be used, and representative examples thereof include La (NO ₃ ) _3. 6H ₂ O, etc. may be mentioned.

The addition amount of the Co source and the rare earth element source may be appropriately adjusted in consideration of the content ratio of each element in the finally obtained metal oxide.

The solvent includes water; Alcohols such as methanol and ethanol; Or a mixed solvent thereof.

The drying process is preferably carried out at 60 to 130 ℃, more preferably may be carried out at 80 to 100 ℃. If the drying temperature is less than 60 ° C, drying takes a long time, and if it is over 130 ° C, the size of the catalyst particles may increase due to the aggregation of particles, which is not preferable.

The heat treatment process for the powder obtained after drying is preferably carried out at a temperature of 450 to 800 ℃, more preferably may be carried out at a temperature of 650 to 800 ℃. If the heat treatment temperature is less than 450 ° C., the source of each element used as a raw material may not be sufficiently decomposed, and it is not preferable. If the heat treatment temperature is higher than 800 ° C., the size of the catalyst particles may increase due to the aggregation of particles, which is not preferable.

The cathode catalyst of the present invention prepared by the above method includes a metal oxide having a spinel structure, thereby exhibiting high catalytic activity for the reduction reaction of the oxidant. Accordingly, the cathode catalyst of the present invention can be used in an alkaline electrolyte fuel cell, a direct oxidation fuel cell or a mixed fuel cell, and the like. Can be used. In addition, among the alkaline electrolyte fuel cells, the activity in the direct oxidation fuel cell using a hydrocarbon fuel is more excellent, and the catalytic activity in the direct ethanol fuel cell using ethanol as the fuel is very excellent. It is most useful in battery.

The present invention also provides a cathode electrode for a fuel cell comprising the cathode catalyst.

That is, the cathode electrode according to the embodiment of the present invention includes an electrode substrate and a catalyst layer formed on the electrode substrate, and the catalyst layer includes a cathode catalyst including the metal oxide of Chemical Formula 1.

The catalyst layer may comprise an electrically conductive polymer together with the catalyst.

The electrically conductive polymer has electron conductivity and may also serve as a binder in the catalyst layer. In addition, when the metal oxide catalyst and the electrically conductive polymer are used together in the catalyst layer, the conductive bond between the metal oxide of the spinel structure and the electrically conductive polymer may be increased to further increase the catalytic activity.

As the electrically conductive polymer, a polymer having an intramolecular double bond or containing an atom of N, O, or S may be used. Specifically, those selected from the group consisting of polyaniline, polypyrrole, polyacetylene, polyacene, polythiophene, and copolymers thereof may be used. have. More preferably, polypyrrole can be used.

When the electrically conductive polymer is included, the catalyst layer preferably includes a catalyst and the electrically conductive polymer in a weight ratio of 5:95 to 75:25, and more preferably 10:90 to 60:40. Can be. Within the content ratio range, excellent electrical conductivity and catalytic activity can be obtained. However, when the content of the electrically conductive polymer to the catalyst is out of the content ratio range is too high, the catalyst center is covered by the electrically conductive polymer and thus the catalytic activity is reduced or the amount of the catalyst is relatively small so that the catalytic activity may be reduced. Not.

In addition, the catalyst layer may further include a binder resin in order to improve the transfer capacity 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 or polyphenylquinoxaline polymers, more preferably poly (perfluorosulfonic acid), poly (perfluorocarboxylic acid), Copolymers of tetrafluoroethylene and fluorovinyl ethers containing sulfonic acid groups, defluorinated sulfide polyether ketones, aryl ketones, poly (2,2'-m-phenylene) -5,5'-bibenziimi One containing at least one hydrogen ion conductive polymer selected from poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole) or poly (2,5-benzimidazole) may be used. .

The hydrogen ion conductive polymer may replace H with Na, K, Li, Cs or tetrabutylammonium in an ion exchange group at the side chain end. In case of replacing H by Na in the ion-exchange group of the side chain terminal, NaOH is substituted in the preparation of the catalyst composition, and tetrabutylammonium hydroxide is used in the case of using tetrabutylammonium, and K, Li or Cs is also substituted with appropriate compounds. It can be substituted using. Since this substitution method is well known in the art, detailed description thereof will be omitted.

The binder resin may be used in the form of a single substance or a mixture, and may also be optionally used with a non-hydrogen ion conductive compound for the purpose of further improving adhesion to the polymer electrolyte membrane. It is preferable to adjust the usage-amount so that it may be suitable for a purpose of use.

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

The catalyst layer having such a configuration is preferably formed to a thickness of 5nm to 15㎛, more preferably may have a thickness of 100nm to 12㎛. If the thickness of the catalyst layer is less than 5 nm, the stability is lowered, which is not preferable.

This catalyst layer is supported by the electrode substrate.

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. A conductive substrate is used as the electrode substrate, and representative examples thereof include carbon paper, carbon cloth, carbon felt, or metal cloth (porous film or polymer composed of metal cloth in a fibrous state). It means that the metal film is formed on the surface of the cloth formed of fibers) 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, since it is possible to prevent the reactant diffusion efficiency from being lowered by water generated when the fuel cell is driven. Examples of the fluorine-based resin include polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride alkoxy vinyl ether, and fluorinated ethylene propylene ( Fluorinated ethylene propylene), polychlorotrifluoroethylene or copolymers thereof 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. The binder resin may be polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride, alkoxy vinyl ether, polyvinyl alcohol, cellulose acetate Or copolymers thereof and the like can be preferably used. As the solvent, alcohols such as ethanol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, water, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, etc. may be preferably used. The coating process may be screen printing, spray coating, or coating using a doctor blade according to the viscosity of the composition, but is not limited thereto.

Such a cathode electrode for a fuel cell of the present invention may be formed by coating a composition for forming a catalyst layer comprising the metal oxide on an electrode substrate and then drying.

In addition, when the catalyst layer of the cathode electrode includes a cell conductive polymer, the catalyst may be mixed with the electrically conductive polymer and then coated on the electrode substrate using a conventional coating method, or the catalyst may be mixed with the electrically conductive polymer. After preparing the electrolyte, the catalyst layer may be formed by dipping the electrode substrate in the electrolyte and performing an electrodeposition process.

When the electrically conductive polymer is used together, the catalyst and the electrically conductive polymer are preferably mixed in a weight ratio of 5:95 to 75:25, and more preferably in a weight ratio of 10:90 to 60:40. have. If the content of the electrically conductive polymer to the catalyst is out of the content ratio range is too high, the center of the catalyst is covered by the electrically conductive polymer, the catalytic activity is reduced or the amount of the catalyst is relatively small, so the catalytic activity may be reduced. not.

In addition, when the catalyst layer is formed by the electrodeposition process, when the electrode substrate is immersed in the prepared electrolyte solution and subjected to the electrodeposition process, an electrically conductive polymer is deposited on the electrode substrate, and a catalyst is present between the electrically conductive polymers.

The electro-deposit process is preferably performed under a current density condition of 0.1 to 25 mAcm ^{- 2} , more preferably under a current density condition of 2 to 20 mAcm ^{- 2} . If the current density is less than 0.1 mAcm ^-2, electrodeposition may not occur sufficiently, and if the current density exceeds 25 mAcm ^-2, the material may be oxidized in the electrolyte, which is not preferable.

The catalyst included in the cathode electrode of the present invention prepared as described above exhibits high catalytic activity for the reduction reaction of the oxidant. Accordingly, as described above, the cathode electrode including the cathode catalyst may be more effectively employed in an alkaline electrolyte fuel cell, especially a direct oxidation fuel cell using a hydrocarbon fuel.

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

The membrane-electrode assembly of the present invention includes an anode electrode and a cathode electrode located opposite each other, and an electrolyte located between the anode and the cathode electrode. The cathode electrode is the same as described above, the anode electrode includes an electrode substrate and a catalyst layer formed on the electrode substrate.

1 is a view schematically showing a cross section of the membrane-electrode assembly 131 according to an embodiment of the present invention. Hereinafter, the membrane-electrode assembly 131 of the present invention will be described with reference to the drawings.

The membrane-electrode assembly 131 generates electricity through oxidation of a fuel and reduction of an oxidant, and one or several are stacked and mounted in a stack.

As described above, the cathode electrode 5 may include a metal oxide exhibiting excellent activity and selectivity for the reduction reaction of the oxidant, thereby improving performance of the membrane-electrode assembly 131 including the same. In addition, as described above, the catalyst layer may further include an electrically conductive polymer.

The anode electrode 3 includes a catalyst layer 33 and an electrode base 31, and the catalyst layer includes a metal catalyst, and may further include a binder resin.

In the catalyst layer 33 of the anode electrode, an oxidation reaction of the fuel occurs, and includes a catalyst capable of promoting this, and includes an anode catalyst of Pt or Ni-based alloy. As the Ni-based alloy, any one commonly used as an anode electrode in an alkaline fuel cell such as Co-Ni or Fe-Ni 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.

The catalyst layer 33 of the anode electrode may also further include a binder resin to improve adhesion of the catalyst layer and transfer of hydrogen ions as in the cathode electrode. The binder resin is as described above.

The electrode substrate 31 of the anode electrode serves to support the electrode and diffuses the fuel into the catalyst layer to play the fuel easily accessible to the catalyst layer. The electrode substrate 31 is also the same as described above.

Further, in order to enhance the reactant diffusion effect, a microporous layer (not shown) may be further included on the electrode substrate. This microporous layer may generally comprise a conductive powder having a small particle diameter, such as carbon powder, carbon black, acetylene black, ketjen black, activated carbon, carbon fiber, fullerene or carbon nanotubes.

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 Or copolymers thereof and the like can be preferably used. As the solvent, alcohols such as ethanol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, water, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, etc. may be preferably used. The coating process may be screen printing, spray coating, or coating using a doctor blade according to the viscosity of the composition, but is not limited thereto.

The electrolyte 1 is positioned between the anode electrode and the cathode electrode having the above structure.

The electrolyte 1 is OH ^- ions as a material which serves to selectively transmit, an aqueous alkali solution, or -OH groups brought OH ^- is also possible to use a solid electrolyte capable of carrying ions film. The alkaline aqueous solution include KOH, NaOH or LiOH to may be used alone or a mixture one or more of, the OH ^- group the solid electrolyte membrane as the commercially available polymer film (for example, Tokuyama Co. solid polymer film) having Can be used. The concentration of the aqueous alkali solution may be appropriately adjusted according to the content of the constituent elements in the catalyst.

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

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

The electricity generating portion includes a membrane-electrode assembly and a separator (also called bipolar plate). The membrane-electrode assembly includes an anode electrode and a cathode electrode, and an electrolyte located between the anode electrode and the cathode electrode. The electricity generation unit serves to generate electricity through the oxidation reaction of the fuel and the reduction reaction of the oxidant.

The fuel supply unit serves to supply fuel to the electricity generation unit, and the oxidant supply unit serves to supply an oxidant such as oxygen or air to the electricity generation unit.

In the present invention, the fuel may include hydrogen or hydrocarbon fuel in gas or liquid state. Representative examples of the hydrocarbon fuel include methanol, ethanol, propanol, butanol or natural gas.

The fuel cell system of the present invention can be employed without limitation, for example, an alkaline electrolyte fuel cell, an alkaline electrolyte direct oxidation fuel cell, or a mixed injection fuel cell.

A schematic structure of a fuel cell system 100 according to an embodiment of the present invention is shown in FIG. 2, which will be described in more detail with reference to the following. 2 illustrates a system for supplying fuel and oxidant to the electricity generator 130 using pumps 151 and 171, but the membrane-electrode assembly 131 for fuel cells of the present invention is limited to such a structure. Of course, it is not used, it can also be used in a fuel cell system having a structure using a diffusion method without using a pump.

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

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

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

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

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

Example 1 Preparation of Cathode Catalyst

A mixture was prepared by adding 1.2 g of cobalt nitrate and 1.6 g of lanthanum nitrate in 20 ml of water and then mixing at room temperature for 24 hours. The mixture was treated at 100 ° C. for 4 hours to evaporate water to obtain a powder, and the powder was heat treated at 650 ° C. under air to prepare Co _x La _y O _z .

In Co _x La _y O _z , x was 43 mol%, y was 28 mol%, z was 29 mol%, and the particle size of the metal oxide was 4 nm.

In order to measure the catalytic activity of the Co _x La _y O _z (x = 43 mol, y = 28 mol% and z = 29 mol%) catalyst prepared in Example 1, oxygen gas was added to a 0.5 M sulfuric acid solution. Bubbling (bubbling) for 2 hours to prepare an oxygen-saturated KOH solution, the catalyst of Example 1 was loaded by 3.78x10 ^-3 mg onto glassy carbon, respectively, as a working electrode, platinum mesh Was added to the sulfuric acid solution as a counter electrode and the current density was measured while changing the voltage.

The measurement result showed a current density of 1.18 mA / cm ² . From this, it was confirmed that the catalyst of Example 1 exhibited excellent catalytic activity.

Example 2 Fabrication of Cathode Electrode

10 parts by weight of Co _x La _y O _z (x = 43 mol, y = 28 mol% and z = 29 mol%) obtained in Example 1 was added to a solvent in which water and isopropyl alcohol were mixed at a weight ratio of 10:80. It was. Then, it puts more in the solvent of 10 wt% Nafion (Nafion ^® Dupont Co.) aqueous dispersion of 40 parts by weight, and mixed, to thereby prepare a catalyst layer-forming composition was uniformly stirred by applying ultrasound. The cathode electrode was prepared by spray coating the composition for forming a catalyst layer on the Teflon-treated carbon paper substrate (manufactured by SGL carbon group).

Example 3 Fabrication of Cathode Electrode

Carbon paper substrate in an electrolyte prepared by adding 0.5 g of Co _x La _y O _z (x = 43 mol, y = 28 mol% and z = 29 mol%) obtained in Example 1 to a 0.1 M polypyrrole mixture in 100 ml of water After the addition of the electrodeposition process was carried out at j = 2mA / cm ² to form a catalyst layer having a thickness of 12㎛ on the carbon paper. Thereafter, the carbon paper substrate on which the catalyst layer was formed was washed with distilled water and dried at 90 ° C. to prepare an electrode.

(Comparative Example 1)

0.7 g of Pt black was added to a 0.2 M polypyrrole mixture in 100 ml of water, and the carbon paper substrate was placed in an electrolyte. Then, an electrodeposition process was performed at j = 7 mA / cm ² to form a catalyst layer having a thickness of 12 μm on the carbon paper. Thereafter, the carbon paper substrate on which the catalyst layer was formed was washed with distilled water and dried at 90 ° C. to prepare an electrode.

(Comparative Example 2)

8.33 g of CoFe ₂ O ₄ was added to a 0.1 M polypyrrole mixture in 100 ml of water, and the carbon paper substrate was placed in an electrolyte, followed by electrodeposition at j = 2 mA / cm ² to form a catalyst layer having a thickness of 12 μm on the carbon paper. Formed. Thereafter, the carbon paper substrate on which the catalyst layer was formed was washed with distilled water and dried at 90 ° C. to prepare an electrode.

(Manufacture of Test Cells)

Test cells were prepared in the following manner using the cathode electrodes prepared in Example 3 and Comparative Examples 1 and 2.

The cathode electrodes prepared in Example 3 or Comparative Examples 1 and 2 were used.

10 parts by weight of Pt / Ru black catalyst was added to a solvent in which water and isopropyl alcohol were mixed in a weight ratio of 10:80. Then, the further into the solvent of 10 wt% Nafion (Nafion ^® Dupont Co.) aqueous dispersion of 40 parts by weight, mixed and uniformly stirred by applying ultrasound to prepare an anode catalyst layer forming composition.

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

Next, a polymer electrolyte membrane (Nafion 115 Membrane, manufactured by DuPont) for commercial fuel cells was laminated on both sides to prepare a membrane-electrode assembly. After inserting the prepared membrane / electrode assembly between the gasket (gasket), and inserted into the two separator gas channel channel and the cooling channel formed of a predetermined shape, and then compressed between the copper end (end) plate to manufacture a unit cell It was.

For the unit cells including the electrodes prepared in Example 3 and Comparative Examples 1 and 2, 1M methanol and dry air were supplied and operated at a temperature of 70 ° C. for 10 hours to measure voltage and evaluate current density. . The results are shown in Table 1 below.

Current density (mA / cm ² , at 0.7 V) Example 3 1.42 Comparative Example 1 0.91 Comparative Example 2 0.48

As shown in Table 1, the electrode of Comparative Example 1 comprising a platinum-based metal catalyst and an electrically conductive polymer is a unit cell including the electrode of Example 3 including the catalyst of Example 1 and the electrically conductive polymer, and CoFe _It was confirmed that the current density was better than that of the unit cell of Comparative Example 2 containing a metal oxide of ₂ O ₄ and an electrically conductive polymer.

The electrode of Example 2 was also fabricated in the same manner as above to prepare a single cell and to measure the current density thereof.

As a result, it was confirmed that the unit cell including the electrode of Example 2 also exhibited the same current density as the unit cell including the electrode of Example 3.

The cathode electrode of the present invention is very excellent in catalytic activity for the reduction reaction of the oxidant can improve the performance of the fuel cell membrane-electrode assembly and fuel cell system comprising the same.

Claims (20)

Cathode catalyst for a fuel cell comprising a metal oxide of the formula (1). [Formula 1] Co _x M _y O _z (Wherein M is a rare earth element, x is 40 to 60, y is 25 to 30, and z is 10 to 35) The method of claim 1, M is selected from the group consisting of La, Yb, and combinations thereof. The method of claim 1, X is 45 to 55, y is 26 to 28, and z is 20 to 30 cathode catalyst for fuel cells. The method of claim 1, The metal oxide is a cathode catalyst for a fuel cell having an average particle diameter of 3 to 15nm. The method of claim 1, The fuel cell cathode catalyst is a cathode catalyst for fuel cell, which is an alkali electrolyte type cathode catalyst. The method of claim 1, The fuel cell cathode catalyst is a cathode catalyst for fuel cell which is an alkali electrolyte type direct oxidation fuel cell cathode catalyst. Electrode substrates; And It includes a catalyst layer formed on the electrode substrate, The catalyst layer is a fuel cell cathode electrode comprising a cathode catalyst comprising a metal oxide of the formula (1). [Formula 1] Co _x M _y O _z (Wherein M is a rare earth element, x is 40 to 60, y is 25 to 30, and z is 10 to 35) The method of claim 7, wherein The cathode catalyst is a fuel cell cathode electrode having an average particle diameter of 10 to 15nm. The method of claim 7, wherein The catalyst layer is a cathode for a fuel cell that further comprises an electrically conductive polymer. The method of claim 9, The catalyst layer is a cathode electrode for a fuel cell comprising a cathode catalyst and an electrically conductive polymer in a weight ratio of 5:95 to 75:25. The method of claim 9, The electrically conductive polymer is selected from the group consisting of polyaniline, polypyrrole, polyacetylene, polyacene, polythiophene, and copolymers thereof. The method of claim 7, wherein The catalyst layer is a cathode electrode for a fuel cell further comprises a binder resin. The method of claim 7, wherein The binder resin is a cathode electrode for a fuel cell 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. An anode electrode and a cathode electrode positioned opposite each other; And An electrolyte located between the anode electrode and the cathode electrode, 14. The membrane-electrode assembly of a fuel cell, wherein said cathode is the cathode of any one of claims 7-13. The method of claim 14, The electrolyte is a membrane-electrode assembly for a fuel cell which is a solid electrolyte membrane having an aqueous alkali solution or -OH group. The method of claim 14, The fuel cell membrane electrode assembly is a fuel cell membrane electrode assembly for an alkaline electrolyte fuel cell. The method of claim 14, The fuel cell anode catalyst is an anode catalyst for an alkaline electrolyte type direct oxidation fuel cell membrane-electrode assembly for a fuel cell. At least one electricity generating unit including an anode electrode and a cathode electrode positioned opposite to each other, and at least one membrane-electrode assembly including an electrolyte positioned between the anode electrode and the cathode electrode, and a separator; A fuel supply unit supplying fuel to the electricity generation unit; And An oxidant supply unit for supplying an oxidant to the electricity generating unit, 14. The fuel cell system of claim 7, wherein the cathode electrode is a cathode electrode according to claim 7. The method of claim 18, And the fuel cell system is an alkaline electrolyte fuel cell system. The method of claim 18, The fuel cell system is an alkali electrolyte type direct oxidation type fuel cell system.

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