KR20070031133A - Electrode catalyst with improved oxygen reduction activity and fuel cell using the same - Google Patents

Abstract

The present invention (a) metal or metal-containing alloy particles having catalytic activity; And (b) an electrode catalyst comprising a substance for storing or moving oxygen in contact with a part or all of the particles, a method for manufacturing the same, an electrode membrane assembly (MEA) including the electrode catalyst, and the electrode membrane assembly Provide a fuel cell.

The electrode catalyst according to the present invention uses a material that stores or moves oxygen as a constituent of the catalyst, thereby temporarily storing a large amount of oxygen that has been added to the oxygen electrode but failed to react with the catalyst metal, and subsequently has a metal having catalytic activity. By supplying to the oxygen electrode activity can be increased, it is possible to improve the performance of the fuel cell comprising the same.

Oxygen, storage, transfer, catalytic activity, oxygen electrode, electrode catalyst, fuel cell

Description

ELECTRODE CATALYST WITH IMPROVED OXYGEN REDUCTION ACTIVITY AND FUEL CELL USING THE SAME

1 is a schematic diagram of an electrode catalyst in which a metal or metal-containing alloy particle having catalytic activity and a material for storing or transferring oxygen form an alloying structure according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of an electrode catalyst in which a metal or metal-containing alloy particle having catalytic activity and a material for storing or transporting oxygen form a core-shell structure as a modification of the present invention.

3 is a schematic diagram of an electrode catalyst in which a substance for storing or moving oxygen exists in a band surrounding a surface of a metal or a metal-containing alloy particle having catalytic activity.

The present invention relates to an electrode catalyst for increasing the oxygen reduction reaction activity in a fuel cell oxygen electrode, a manufacturing method thereof, and a fuel cell including the electrode catalyst.

Fuel cells are pollution-free and clean energy sources that can replace existing energy sources. The basic concept of a fuel cell can be explained by the use of electrons generated by the reaction of hydrogen and oxygen. A fuel cell is defined as a battery having a capability of directly producing a direct current by directly converting the chemical reaction energy of an oxidant including hydrogen and a fuel gas including hydrogen and the like into electrical energy. And supply air to produce electricity continuously. Fuel cells can be classified into phosphate fuel cells, alkaline fuel cells, hydrogen ion exchange membrane fuel cells, molten carbonate fuel cells, direct methanol fuel cells and solid electrolyte fuel cells according to operating conditions. Sometimes classified as low temperature.

Oxygen reduction reaction of oxygen electrode in low temperature fuel cell is 10 ⁶ times higher than hydrogen oxidation of hydrogen electrode Since it occurs slowly, the oxygen reduction activity of the oxygen electrode is not only a major factor in determining the overall reaction rate, but also causes a decrease in fuel cell performance. There are largely two methods performed in order to increase the oxygen reduction reaction activity of the conventional oxygen electrode. The first is to increase the active area that can react with oxygen by reducing the size of platinum particles. Reducing the size of platinum particles is inversely related to the life of the fuel cell. The second method is to increase the amount of platinum particles supported, which is not appropriate because increasing the amount of platinum supported is counter to the economics of fuel cells.

In view of the above-described problems, the present inventors provide a material capable of temporarily storing a large amount of oxygen that has not reacted with the catalyst metal and subsequently supplying it to a metal having catalytic activity, or a metal having conventional catalytic activity known in the art. When contacted with the metal-containing alloy particles and used as an electrode catalyst, it was found that not only can the oxygen reduction reaction activity of the oxygen electrode be increased, but also the reaction rate and performance of the fuel cell can be improved.

Accordingly, an object of the present invention is to provide an electrode catalyst and its catalyst having increased oxygen cathode activity in a fuel cell.

Another object of the present invention is to provide a membrane electrode assembly (MEA) including the electrode catalyst and a fuel cell including the membrane electrode assembly.

Furthermore, another object of the present invention is to provide a method for increasing the oxygen activity of a fuel cell by contacting a material for storing or moving oxygen with a catalytically active metal as described above.

The present invention (a) metal or metal-containing alloy particles having catalytic activity; And (b) an electrode catalyst comprising a substance for storing or moving oxygen in contact with a part or all of the particles, a method for manufacturing the same, an electrode membrane assembly (MEA) including the electrode catalyst, and the electrode membrane assembly Provide a fuel cell.

The present invention also provides metal or metal-containing alloy particles having catalytic activity; And it provides a method for increasing the oxygen reduction reaction activity of the fuel cell oxygen electrode using an electrode catalyst comprising an electrode catalyst containing a substance for storing or moving oxygen in contact with some or all of the particles as the oxygen electrode catalyst.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention is to temporarily store a large amount of oxygen that did not react with the catalyst metal in order to activate the oxygen cathode oxygen reduction reaction to determine the overall reaction rate of the fuel cell, which can be subsequently supplied to the metal having catalytic activity, In other words, the electrode catalyst is constituted by forming a material for storing or moving oxygen in contact with each other, that is, alloying or coating the metal or metal-containing alloy particles having catalytic activity.

According to such a feature, the effects obtainable in the present invention are as follows.

1) In order to increase the oxygen cathode oxygen reduction activity of a conventional fuel cell, the size of a catalytically active metal, such as platinum particles, has been adjusted to a range of several nanometers, but these catalytically active component particles undergo electrochemical reactions. This leads to instability, which leads to coarsening, which inevitably leads to reduction of the surface of catalyst particles and deterioration of the fuel cell. In addition, a method of increasing the amount of the catalytically active component also caused side effects.

However, in the present invention, by forming an electrode catalyst by alloying or coating a material capable of storing or moving oxygen with the catalytically active ingredient particles, not only can the oxygen reduction reaction activity be improved at the oxygen electrode, but the overall performance of the fuel cell can be improved. Can be. That is, a large amount of oxygen introduced into the conventional oxygen electrode but not reacted with the catalyst metal is present in the form of accumulated around the catalyst metal, which is the main cause of the continuous retardation of the reduction reaction between the catalyst metal and oxygen. It became. However, in the present invention, since a large amount of oxygen is temporarily stored in the material, and then, when the reaction between the catalytically active particles and the stored oxygen can proceed, it is supplied to the catalytically active particles to improve the oxygen reduction reaction at the oxygen electrode. The reaction speed and overall performance of the fuel cell can be improved.

2) In addition, since the process of preparing the electrode catalyst is simple, not only can be easily applied to the existing process, but also cost reduction effect can be obtained.

One of the main components constituting the electrode catalyst according to the present invention is a material capable of storing or transporting the above-described oxygen, and can be applied regardless of the form or type just by performing such a function. As the material for storing or moving the oxygen, a material having an oxygen defect in a lattice structure is preferable. The oxygen (O ₂ ) injected into the oxygen electrode through the oxygen defect is temporarily stored, and the oxygen is catalytically active. It can be transferred to a metal or metal-containing alloy particles having.

Non-limiting examples of the material for storing or transporting oxygen include a metal in the form of lanthanide, actinium, nickel or a combination thereof and a metal oxide including the metal, and specific examples thereof include cerium oxide (CeO ₂ ), Rhenium oxide (ReO ₂ ) or nickel (Ni). In order to improve the oxygen storage capacity, a metal or a metal oxide may be alloyed with the metal oxide.

The content of the substance for storing or transporting oxygen is not particularly limited, but is preferably in the range of 10 to 90 parts by weight per 100 parts by weight of the total catalyst. When the content of the substance is less than 10 parts by weight and more than 90 parts by weight, the effect of increasing oxygen reduction activity in the oxygen electrode may be minimal.

The main catalytically active component constituting the electrode catalyst according to the invention can be used without limitation, conventional metals or metal-containing alloys well known in the art, capable of reducing oxygen, in particular precious metals such as platinum (Pt) alone or platinum Preferred alloy forms are preferred. At this time, non-limiting examples of the metal constituting the alloy with ruthenium (Ru), rhodium (Rh), palladium (Pd), gold (Au), silver (Au), iridium (Ir), osmium (Os) or these And 2 or more types of mixed forms.

The size (particle diameter) of the metal catalyst particles is not particularly limited, but is preferably in the range of 1.0 to 15 nm. In addition, the content of the metal catalyst is not particularly limited, but is preferably in the range of 10 to 90 parts by weight per 100 parts by weight of the total catalyst. When the content of the substance is less than 10 parts by weight and more than 90 parts by weight, the effect of increasing oxygen reduction activity in the oxygen electrode may be minimal.

The electrode catalyst of the present invention is not particularly limited as long as the metal having catalytic activity and a substance for storing or moving oxygen exist in contact with each other to supply oxygen to the catalyst metal. Three types of this embodiment are possible, and these are shown in FIGS. First, the alloy forms a alloy with a metal or metal-containing alloy particle having a catalytic activity and a substance that stores or moves oxygen (see FIG. 1). Second, a substance that stores or transfers oxygen is a catalytic activity. And a core-shell structure with the metal or metal-containing alloy particles having a core (see FIG. 2), and the third surface of the metal or metal-containing alloy particles having a catalytic activity of the material for storing or transporting oxygen. It is present in the form of a band surrounding (see FIG. 3).

In the core-shell structure, the core and the shell may include metal or metal-containing alloy particles each having catalytic activity, as shown in FIG. 2; Or a substance that stores or migrates oxygen, where the core and the shell are not composed of the same components.

The electrode catalyst of the present invention may be in a form supported on a conventional catalyst carrier known in the art.

The carrier is used to disperse the noble metal catalyst widely by using a large surface area and to improve physical properties such as thermal and mechanical stability that are difficult to obtain only by the metal catalyst. For example, the carrier may be coated on a support of conventional fine particles in the art. Other methods can be applied. Usable carriers include porous carbon, conductive polymers or metal oxides.

Activated carbon, carbon fibers, graphite fibers or carbon nanotubes may be used as the porous carbon, and the conductive polymer may be polyvinylcarbazole, polyanilin, polypyrrole or derivatives thereof. In addition, the metal oxide may be used at least one metal oxide selected from the group consisting of tungsten, titanium, nickel, ruthenium, tantalum or cobalt oxide.

The size of the carrier is not particularly limited, but 0.01 to 10 ㎛ is preferred. In addition, the specific surface area of the carrier is also not particularly limited, but is preferably in the range of 20 to 2000 m ² / g.

 The electrode catalyst of the present invention may be prepared according to conventional methods in the art, and for example, (a) alloys metal or metal-containing alloy particles having catalytic activity with a substance for storing or transporting oxygen. ); Or coating metal or metal containing alloy particles having catalytic activity with a material that stores or migrates oxygen or vice versa; And (b) drying the resultant obtained in step (a).

First, there is no particular limitation on the method of alloying metal or metal-containing alloy particles having catalytic activity with a substance for storing or transporting oxygen, and conventional methods known in the art, such as wet and / or dry methods, may be used. . Likewise, coating the catalytically active metal or metal containing alloy particles with a material that stores or migrates oxygen or vice versa is also common coating methods known in the art, such as brush methods, sprays ( Spray method, spin coating method or a mixture thereof can be used without limitation.

At this time, it is possible to add a catalyst carrier conventional in the art or to use a carrier carrying metal or metal-containing alloy particles having catalytic activity in this step, in which case an electrode catalyst supported on the catalyst carrier can be obtained. have.

2) The electrode catalyst according to the present invention can be obtained by drying the resultant prepared as described above. At this time, the drying method is also not particularly limited, it is preferable to dry for several hours at 90 ℃ or less.

The present invention provides an electrode for a fuel cell comprising the electrode catalyst prepared as described above.

The fuel cell electrode may be formed of, for example, a gas diffusion layer and a catalyst layer, and may be composed of only a catalyst layer, and a combination of a catalyst layer formed on the gas diffusion layer may be used.

The electrode for a fuel cell of the present invention may be prepared according to a conventional method known in the art, and for example, the electrode catalyst may include a catalyst including a polymer material having high hydrogen ion conductivity and a mixed solvent for enhancing catalyst dispersion. The slurry may be prepared by mixing with ink, and then coated and dried on a carbon paper by printing, spraying, rolling, or brushing.

In addition, the present invention (a) a first electrode having a first catalyst layer; (b) a second electrode having a second catalyst layer; And (c) an electrode membrane assembly for a fuel cell comprising an electrolyte membrane interposed between a first electrode and a second electrode, wherein the first catalyst layer, the second catalyst layer, or the first catalyst layer and the second catalyst layer use the electrode catalyst of the present invention. It provides a fuel electrode electrode membrane assembly (MEA) comprising a.

At this time, one of the first electrode and the second electrode is an anode, the other is a cathode. In particular, a positive electrode (oxygen electrode) to which an oxygen reduction reaction proceeds is preferable.

The electrode membrane assembly (MEA) refers to a conjugate of an electrode in which an electrochemical catalytic reaction between fuel and air occurs and a polymer membrane in which hydrogen ions are transferred, and is a single unitary unit to which a catalyst electrode and an electrolyte membrane are bonded.

The electrode membrane assembly for a fuel cell is a type in which the catalyst layer of the cathode and the catalyst layer of the anode are in contact with the electrolyte membrane, and may be manufactured according to conventional methods known in the art. For example, it may be prepared by placing an electrolyte membrane between the cathode and the anode, and then placing the electrolyte membrane between two hot plates that are hydraulically operated while maintaining a temperature of about 140 ° C., and then applying pressure under pressure.

As the electrolyte membrane, any material having hydrogen ion conductivity, mechanical strength enough to form a film, and high electrochemical stability can be used without particular limitation, and non-limiting examples thereof include tetrafluoroethylene and fluorine. There is a copolymer of rhovinyl ether, and the fluorovinyl ether moiety has a function of conducting hydrogen ions.

In addition, the present invention provides a fuel cell including the electrode membrane assembly (MEA).

In this case, all materials constituting the fuel cell may be any material used in the conventional fuel cell field known in the art, except for the electrode catalyst prepared in the present invention. In addition, the manufacturing method of the fuel cell is not particularly limited, and may be manufactured by configuring an electrode membrane assembly (MEA) and a bipolar plate manufactured according to conventional methods known in the art.

The fuel cell is applicable to any cell that adopts a reduction reaction of oxygen, and is not particularly limited thereto.

In addition, the present invention provides metal or metal-containing alloy particles having catalytic activity; And it provides a method for increasing the oxygen reduction reaction activity of the fuel cell oxygen electrode using an electrode catalyst comprising an electrode catalyst containing a substance for storing or moving oxygen in contact with some or all of the particles as the oxygen electrode catalyst.

The method is a novel method that is differentiated from the conventional techniques, such as a) increasing the specific surface area of the catalyst and b) increasing the loading amount of the catalyst, which are widely used to increase the oxygen reduction activity at the oxygen electrode. In addition, there are advantages such as simplifying the manufacturing process and securing economic feasibility.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

Example 1

1-1. Preparation of platinum supported carbon catalyst coated with metal oxide

Ammonium cerium nitride (Ce (NH ₄ ) ₂ (NO ₃ ) ₆ ) was added to a predetermined amount of distilled water, and the mixture was sufficiently stirred to dissolve, followed by slowly adding ammonia water to precipitate the cerium salt. After heating for 6 hours, the solution was filtered, washed with distilled water and dried, 0.2 g of this powder was added to 0.4 g of carbon black (KB600JD) having a surface area of 1200 m ² / g and 30 ml of distilled water. , Agitated to obtain a colloidal solution, which was heated to a temperature of 90 ° C. 1M sodium carbonate solution was added to the colloidal solution to adjust the pH in the range of 8 to 9, and the desired platinum loading after the pH was stabilized. 4 ml of an aqueous solution containing 1.01 g of chloroplatinic acid (H ₂ PtCl ₆ .xH ₂ O) corresponding to 40% by weight was added to the colloidal solution. The pH value was adjusted to a range of 8 to 9 by addition of sodium solution, and formaldehyde solution was added to the solution to reduce platinum in the liquid phase.The solution was filtered and the powder obtained was washed and then vacuum dried at 80 ° C Finally, a platinum / carbon powder was obtained.

1-2. Electrode manufacturing

A catalyst slurry was prepared by dispersing the ceria-coated platinum supported catalyst prepared in Example 1-1 by adding Nafion solution to a solution diluted 1: 100 by weight ratio of isopropyl alcohol using mechanical stirring. The required amount of catalyst in the prepared catalyst slurry was calculated and sprayed on a gas diffusion layer (GDL) to prepare an electrode.

1-3. Manufacture of Electrode Film Assembly (MEA)

An electrode membrane assembly was prepared by thermally and mechanically bonding a Nafion electrolyte membrane between the positive electrodes prepared in Examples 1-2, thereby preparing a hydrogen ion exchange membrane fuel cell.

In the present invention, by alloying or coating a material capable of supplying or storing oxygen to the catalyst material particles on the electrode catalyst material particles, it is possible to provide an increase in the oxygen reduction activity at the oxygen electrode and an improvement in the performance of the fuel cell.

Claims (19)

(a) metal or metal containing alloy particles having catalytic activity; And (b) a substance that stores or migrates oxygen in contact with some or all of the particles Electrode catalyst comprising a. The electrode catalyst of claim 1, wherein the material that stores or moves oxygen is a material having oxygen defects in a lattice structure. The electrode catalyst according to claim 1, wherein the material for storing or moving oxygen temporarily stores oxygen (O ₂ ) injected into the oxygen electrode and moves the oxygen to metal or metal-containing alloy particles having catalytic activity. . The electrode catalyst of claim 1, wherein the material for storing or moving oxygen is at least one metal selected from the group consisting of lanthanides, actinides, and nickel or a metal oxide including the metal. The electrode catalyst of claim 4, wherein the metal oxide is cerium oxide (CeO ₂ ), rhenium oxide (ReO ₂ ), or nickel (Ni). The method of claim 1, wherein the material for storing or moving oxygen is (i) alloying metal or metal containing alloy particles with catalytic activity; (ii) form a core-shell structure with metal or metal containing alloy particles having catalytic activity; or (iii) an electrode catalyst, characterized by being in the form of a band surrounding the surface of the metal or metal containing alloy particles having catalytic activity. 7. The core and shell structure of claim 6, wherein the core and the shell are made of metal or metal-containing alloy particles or a substance for storing or moving oxygen, each having catalytic activity, and the core and the shell are each other. An electrode catalyst characterized by not being composed of identical components. The method of claim 1, wherein the metal in the catalytically active metal or metal-containing alloy particles are platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), gold (Au), silver (Au), At least one electrode catalyst selected from the group consisting of iridium (Ir) and osmium (Os). The electrode catalyst of claim 1, wherein the particle size of the metal or metal-containing alloy particles having catalytic activity ranges from 1.0 to 15 nm. The amount of the metal or the metal-containing alloy having catalytic activity is in the range of 10 to 90 parts by weight per 100 parts by weight of the total catalyst, and the content of the substance for storing or transferring oxygen is 10 per 100 parts by weight of the total catalyst. Electrode catalyst in the range from to 90 parts by weight. The electrode catalyst of claim 1, wherein the catalyst is supported on at least one catalyst carrier selected from the group consisting of porous carbon, conductive polymers, and metal oxides. The electrode catalyst according to claim 11, wherein the specific surface area of the carrier is in the range of 20 to 2000 m ² / g. The electrode catalyst according to claim 1, wherein the catalyst is an anode (oxygen) catalyst. An electrode comprising the electrode catalyst of claim 1. (a) a first electrode having a first catalyst layer; (b) a second electrode having a second catalyst layer; And (c) an electrolyte membrane interposed between the first electrode and the second electrode An electrode membrane assembly for a fuel cell comprising: an electrode membrane assembly wherein the first catalyst layer, the second catalyst layer, or the first catalyst layer and the second catalyst layer comprise the catalyst of any one of claims 1 to 13. electrode assembly: MEA). A fuel cell comprising the electrode membrane assembly of claim 15. (a) alloying metal or metal containing alloy particles having catalytic activity with a substance that stores or migrates oxygen; Or coating metal or metal containing alloy particles having catalytic activity with a material that stores or migrates oxygen or vice versa; And (b) drying the resultant obtained in step (a) The method for producing an electrode catalyst of any one of claims 1 to 13 comprising a. 18. The method according to claim 17, wherein the production method includes adding a catalyst carrier in step (a) or using a carrier on which metal or metal-containing alloy particles having catalytic activity are supported. A method for increasing the oxygen reduction activity of a fuel cell oxygen electrode using the electrode catalyst of any one of claims 1 to 13 as an oxygen electrode catalyst.

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