JP7203422B2 - Cathode electrode for fuel cell, manufacturing method thereof, polymer electrolyte fuel cell provided with cathode electrode for fuel cell - Google Patents

Description

TECHNICAL FIELD The present invention relates to a fuel cell cathode electrode, a manufacturing method thereof, and a polymer electrolyte fuel cell provided with a fuel cell cathode electrode.

In recent years, among fuel cells, polymer electrolyte fuel cells, which have a polymer electrolyte membrane that conducts protons, have a low operating temperature, a high output density, and are easy to reduce in size and weight. As a countermeasure, it is expected to spread as a power source for automobiles and the like. However, compared to the amount of Pt used in conventional internal combustion engines, the amount of Pt required is 5 to 10 times, and there are problems with Pt elution and deterioration of the polymer electrolyte due to overvoltage during load driving cycles and start-stop cycles. It's becoming

In a polymer solid electrolyte fuel cell, oxygen is reduced on the catalyst surface of the cathode electrode, and the cathode electrode receives electrons from the catalyst-supporting conductor of the anode electrode, forming a three-phase interface that becomes water molecules, forming a chain reaction. happens. Therefore, in polymer electrolyte fuel cells, it has been conventionally practiced to increase the specific surface area of the catalyst-carrying conductor to increase the number of catalytic active sites, and to form the catalyst layer with a fluorine-containing ion-exchange resin (hereinafter referred to as "ionomer"). ) to form an electrode and form a three-phase interface.

As the ionomer for coating the above catalyst, a perfluorocarbon polymer having a strongly acidic sulfonic acid group in the side chain is used in order to increase the proton conductivity.

However, it is known that in the catalyst layer of the conventional cathode electrode, when an electric potential is generated due to power generation, the gap between the catalyst and the ionomer widens, and water molecules intervene there, reducing proton conduction ( Figure 3). As shown in (1) to (6) in FIG. 3, in the conventional cathode electrode, when the platinum on the surface layer is oxidized by the generated hydrogen peroxide and the overvoltage during power generation overload, the ionomer is converted into platinum. deviate. The generated water is accumulated there, and oxygen is dissolved in the generated water. Further, sulfonic acid groups are detached from the ionomer due to corrosion, and oxidation of platinum progresses, eluting into the generated water and reducing platinum on the surface layer. The three-phase interface as a reaction site cannot be maintained. In addition, the oxygen permeability decreases, the oxygen permeability in the catalyst layer becomes insufficient, the overvoltage of the oxygen reduction reaction at the cathode electrode increases, the oxidation and elution of platinum due to the decomposition of hydrogen peroxide, and the solid polymer electrolyte. It is known that sulfonic acid dissociates from sulfonic acid group-containing perfluorocarbons.

On the other hand, Patent Literatures 1, 2, and 3 below propose polymer electrolyte fuel cells and electrode layers treated with a fluororesin or a fluorine-based silane coupling agent for coating a catalyst.

However, the coating treatment with a fluororesin and a fluorosilane was insufficient in terms of durability because the fluororesin peeled off and the siloxane bond hydrolyzed when the running load of the automobile fluctuated and the start and stop of the automobile occurred.

On the other hand, regarding the oxygen permeability of the cathode electrode layer, there is a method in which Ce ₂ Zr ₂ O oxides having a pyrochlore structure that absorbs and releases oxygen are separately supported on the surface of the catalyst-supporting conductor without overlapping. , which is disclosed in Patent Document 4 below.

However, even in the polymer electrolyte fuel cell described in Patent Document 4, the Ce ₂ Zr ₂ O oxide has insufficient electronic conductivity, a three-phase interface cannot be generated, and the internal resistance of the cathode electrode increases. do. Furthermore, since the catalyst and the Ce ₂ Zr ₂ O oxide that absorbs and releases oxygen do not overlap each other, less oxygen reaches the surface of the catalyst metal particles, resulting in insufficient formation of the three-phase interface.

Korean Patent Publication No. 20090118262 JP 20015-056298 A Japanese Patent Application Laid-Open No. 05-05182672 JP 2008-091264 A

In the present invention, the catalyst, ionomer, and oxygen (in other words, hydrogen ions, oxygen, and electrons on the surface of the catalyst metal particles) associate at the cathode electrode of a polymer solid electrolyte fuel cell during catalysis, which is called a three-phase interface. To improve the effective utilization of platinum by having a larger number of catalytic metal particles having reaction sites for reaction. Another object of the present invention is to make it possible to maintain the reaction site of the three-phase interface continuously even with the overvoltage of the running load fluctuation cycle and the start-stop cycle of the automobile.

As in Patent Documents 1, 2 and 3, when the catalyst-carrying carbon is coated with a fluororesin or a fluorosilane to impart water repellency, the fluororesin peels off and the siloxane bond is formed due to fluctuations in the running load and starting and stopping of the automobile. Hydrolysis occurs, creating gaps at the interface between the catalyst and the ionomer and reducing hydrogen ion conduction. Furthermore, water accumulates in the gaps, and oxygen dissolves in the water, reducing the supply of oxygen. Therefore, there is a problem that the association of hydrogen ions and oxygen to the reaction sites of the three-phase interface is reduced, and the power generation performance is lowered.

On the other hand, as in Patent Document 4, when the oxygen absorbing/releasing material composed of pyrochlore-type Ce ₂ Zr ₂ O ₇ exists separately on the surface of the catalyst-carrying conductor without being in direct contact with the catalyst metal particles, Oxygen tends to be dissolved in the generated water, and the supply to the reaction site of the three-phase interface on the surface of the catalyst metal particles is reduced. Furthermore, since the oxygen absorbing/releasing material comprising the pyrochlore-type Ce ₂ Zr ₂ O ₇ has low electronic conductivity, the internal resistance of the cathode electrode increases, and the overvoltage during the running load fluctuation cycle and the start-stop cycle of the automobile increases. , oxidation and leaching of platinum, decomposition of ionomer sulfonic acid groups and corrosion of catalyst-supporting conductors (conductive carbon).

The inventors of the present invention have found that the metal oxide having projections is formed so that hydrogen ion conduction, electron conduction, and oxygen can associate with the surface of the catalyst metal particle, and three-phase interface sites can be continuously formed. The present inventors have found that the above problems can be solved by having the particles directly contact between the particles and the catalyst-carrying conductor and having water repellency, electronic conductivity, and oxygen absorbing/releasing properties, thus leading to the present invention.

In order to solve the above-mentioned problems, the cathode electrode for a fuel cell of the present invention has a catalyst layer comprising a catalyst-carrying conductor and a polymer electrolyte, and the surface of the catalyst-carrying conductor is conductive with projections. It is covered with a composite metal oxide, and catalyst metal particles are supported on the conductive composite metal oxide.

The height of the protrusions of the conductive composite metal oxide may be 5 nm to 15 nm.

The conductive composite metal oxide may have water repellency with a contact angle with water of 140 degrees or more.

The catalyst-carrying conductor may have a specific resistance of 0.2 Ω·cm or less.

The conductive composite metal oxide may be an oxygen absorbing/releasing material.

The conductive composite metal oxide may be a p-type semiconductor.

The conductive composite metal oxide may have a pyrochlore structure consisting of Sn ₂ M ₂ O ₇ (M=Ta and/or Nb).

The conductive composite metal oxide may contain Ta-doped SnO ₂ (0.01% by mass≦Ta≦1.0% by mass).

The catalytic metal particles may have a core-shell structure consisting of a Pt shell layer.

The core layer of the core-shell structure may be made of an alloy selected from Pd and at least one of Pt, Ru and Co.

The catalyst-carrying conductor may be made of at least one selected from conductive carbon, graphite, graphene and carbon alloy.

Further, in order to solve the above problems, a method for producing a cathode electrode for a fuel cell of the present invention is the method for producing a cathode electrode for a fuel cell according to the above-described present invention, comprising: , tin (II) chloride and tantalum (V) chloride are added to control the pH to 1.5 to 2.0 to obtain the conductive composite metal oxide.

A first reduction in which a metal salt constituting a core layer is added to a suspension of the catalyst-supporting conductor coated with the conductive composite metal oxide, and the resulting mixture is heated to 40° C. to 80° C. for reduction. A core layer of the catalyst metal particles may be formed on the surface of the conductive composite metal oxide projecting to cover the surface of the catalyst-carrying conductor by the first reduction step.

A second reduction in which a Pt salt solution and a reducing agent are added to the suspension of the catalyst-carrying conductor having the core layer of the catalyst metal particles on the surfaces of the projecting conductive composite metal oxides. A Pt shell layer of the catalyst metal particles may be formed by the second reduction step.

Further, in order to solve the above problems, a polymer electrolyte fuel cell of the present invention comprises an anode electrode, the above-described cathode electrode of the present invention, and a polymer disposed between the anode electrode and the cathode electrode. and an electrolyte membrane.

The conductive composite metal oxide may have a pyrochlore structure consisting of Sn ₂ M ₂ O ₇ (M=Ta and/or Nb).

The conductive composite metal oxide may contain Ta-doped SnO ₂ (0.01% by mass≦Ta≦1.0% by mass).

According to the present invention, in the cathode electrode for a fuel cell, a composite metal oxide composed of pyrochlore-type Sn ₂ Ta ₂ O ₇ and/or Sn ₂ Nb ₂ O ₇ crystals having a projecting shape has long-lasting water repellency. Furthermore, from electron conductivity and oxygen storage/release, or Ta-doped SnO ₂ which is not an oxygen storage/release material, the reaction site of the three-phase interface is highly realized on the surface of the catalyst metal particle. A high power generation performance was obtained.

FIG. 1 shows a conceptual diagram of the catalyst-supporting conductor, composite oxide, catalytic metal particles, and ionomer in the cathode electrode of the present invention. FIG. 2 shows a conceptual diagram of the reaction sites at the three-phase interface due to the migration of hydrogen ions, electrons, and oxygen molecules to the surface of the catalyst metal particles. FIG. 3 shows a conceptual diagram of deterioration behavior during power generation in a conventional cathode electrode. FIG. 4 shows a structural conceptual diagram of the core-shell type catalyst of the present invention.

Preferred embodiments of the cathode electrode of the present invention and a polymer electrolyte fuel cell having the same will be described in detail below.

In the present invention, it is preferable that the following three elements (1) to (3) are satisfied in order to secure the reaction site of the three-phase interface.

(1) In the present invention, by forming a composite metal oxide having protrusions of 5 nm to 15 nm on the surface of a catalyst-carrying conductor, it has good wettability with ionomers, a high platinum efficiency, and can discharge moisture. Furthermore, the catalyst and the ionomer can be brought into close contact with each other when the catalyst is activated, so that a sustained water repellency can be maintained.
(2) In the present invention, the composite metal oxide has a pyrochlore-type Sn ₂ Ta ₂ O ₇ and/or Sn ₂ Nb ₂ O ₇ crystal structure. The catalyst metal particles are in contact with the surface of the metal oxide, and oxygen is not dissolved in the moisture generated, and can be supplied to the catalyst metal particles with high efficiency. be.
(3) In the present invention, the composite metal oxide having an oxygen absorbing/releasing property consisting of a pyrochlore-type Sn ₂ Ta ₂ O ₇ and/or Sn ₂ Nb ₂ O ₇ crystal structure comprises a catalyst-carrying conductor and a catalyst metal. It is provided in contact with the particles and has electron conductivity, thereby making it possible to supply electrons to the reaction site of the three-phase interface on the surface of the catalyst metal particles. At the same time, the metal oxide can prevent corrosion of the catalyst-carrying conductor.

That is, firstly, the present invention is an invention of a fuel cell cathode electrode having a catalyst layer comprising a catalyst-supporting conductor and an ionomer, wherein projecting pyrochlore-type Sn ₂ A conductive composite metal oxide having a crystal structure of Ta ₂ O ₇ , Sn ₂ Nb ₂ O ₇ and/or Ta-doped SnO ₂ is formed, and catalyst metal particles are supported on the surface of the conductive composite metal oxide. is preferred.

The cathode electrode of the present invention is a conductive composite metal having a crystal structure of fine projections of pyrochlore-type Sn ₂ Ta ₂ O ₇ , Sn ₂ Nb ₂ O ₇ and/or Ta-doped SnO ₂ on the surface of a catalyst-carrying conductor. When the oxide is further supported, the formation of the projections provides a long-lasting water repellency, and since the catalyst metal particles are supported on the surface of the conductive composite metal oxide, the catalyst metal particles are electrically conductive. electrons are conducted by oxygen defects in the complex metal oxide, and oxygen carriers are generated by oxygen defects in the crystal structure of the pyrochlore-type Sn ₂ Ta ₂ O ₇ , Sn ₂ Nb ₂ O ₇ and/or Ta-doped SnO ₂ . A diffusion path for oxygen molecules is ensured directly to the catalyst metal particles.

As a result, the electron conductivity and oxygen carrier properties of the crystal structure of the pyrochlore-type Sn ₂ Ta ₂ O ₇ , Sn ₂ Nb ₂ O ₇ and/or Ta-doped SnO ₂ lead to hydrogen ion conduction with persistent water repellency. And oxygen molecules can be secured to the surface of the catalyst metal particles to increase the exchange current density in the electrode reaction and reduce the overvoltage. That is, high electrode characteristics can be obtained. In particular, if it is used as a cathode electrode of a polymer electrolyte fuel cell, the overvoltage of the oxygen reduction reaction of the cathode electrode can be effectively reduced, so that the electrode characteristics of the cathode electrode can be improved. Oxygen gas shortage occurs especially during operation of the fuel cell, but the present invention enables the maintenance of high electrode properties even during long-term operation.

The present invention forms projections having a height and spacing of 5 nm to 15 nm made of a conductive composite metal oxide on the surface of a catalyst carrier conductor having a particle diameter of 20 nm to 50 nm, and is resistant to overvoltage and corrosion by hydrogen peroxide. It made it possible to maintain durable water repellency.

When the conductive composite metal oxide of the present invention has a pyrochlore-type Sn ₂ Ta ₂ O ₇ and/or Sn ₂ Nb ₂ O ₇ crystal structure, oxygen defects generate holes, forming a P-type semiconductor It has properties and enables electronic conductivity.

Furthermore, pyrochlore-type Sn ₂ Ta ₂ O ₇ and/or Sn ₂ Nb ₂ O ₇ crystals that can be used in the present invention absorb and release oxygen due to oxygen defects in the crystal due to fluctuations in the oxygen concentration in the vicinity. It is a kind of oxygen carrier material that has the function of being able to reversibly repeat the That is, it can absorb oxygen when the O ₂ concentration is relatively high, and can release oxygen in an atmosphere with a low O ₂ concentration.

In the present invention, a porous carbon powder, graphite powder or graphene powder is preferably used as the catalyst-carrying conductor having pyrochlore-type Sn ₂ Ta ₂ O ₇ and/or Sn ₂ Nb ₂ O ₇ supported on its surface. .

Secondly, in the invention of a solid polymer fuel cell, the cathode electrode has a catalyst-supporting conductor and a catalyst layer made of an ionomer, and the surface of the catalyst-supporting conductor has pyrochlore-type Sn ₂ Ta ₂ O ₇ and/or Sn ₂ Nb ₂ O ₇ or Ta-doped SnO ₂ which is not an oxygen storage/release material, and catalytic metal particles are further supported on the surface thereof. .

As described above, by providing the cathode electrode of the present invention having the excellent electrode characteristics for the oxygen reduction reaction described above, it is possible to construct a polymer electrolyte fuel cell having a high cell output. In addition, as described above, the cathode electrode of the present invention exhibits high overvoltage during vehicle running load fluctuation cycles and start-stop cycles, leading to oxidation and elution of platinum, decomposition of sulfonic acid groups of ionomers, and catalyst-supported conductivity. It can prevent corrosion of the body (conductive carbon) and has excellent durability, so the polymer electrolyte fuel cell of the present invention equipped with this can stably obtain high battery output over a long period of time. becomes.

As shown in FIG. 1, the surface of the catalyst carrier conductor is coated with a composite metal oxide having fine protrusions. Catalytic metal particles are carried on the surface of the composite metal oxide. In the thus-composited particles, the protrusions serve as spacers, and the ionomer covers the apexes of the protrusions with a uniform thickness.

As shown in FIG. 2, first, hydrogen ions conduct through the ionomer and move to the surface of the catalyst metal particles. Next, the electrons move from the catalyst carrier conductor through the conductive composite metal oxide to the surface of the catalyst metal particles. Furthermore, the oxygen molecules stored in the composite oxide move to the surface of the catalyst metal particles. In this way, in the cathode electrode of the present invention, the reaction site of the three-phase interface is established on the surface of the catalytic metal particles, and the oxygen reduction reaction proceeds. This oxygen reduction reaction is shown in [Chem. 1].

[Chemical 1]
O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O

In the present invention, a conductive complex metal oxide of pyrochlore-type Sn ₂ Ta ₂ O ₇ and/or Sn ₂ Nb ₂ O ₇ having protrusions is supported on the surface of a catalyst-supporting conductor. Since the fine protrusions have persistent water repellency, the catalyst and the ionomer can maintain close contact even at high output, and many hydrogen ions can reach the catalyst metal particles.

When the output of the fuel cell is low, the amount of oxygen consumed by the catalyst is small and the oxygen concentration in the vicinity of the oxygen absorbing/releasing member is high, so excess oxygen is stored in the oxygen absorbing/releasing member. On the other hand, since the oxygen consumption in the catalyst is high and the oxygen concentration in the vicinity of the oxygen absorbing/releasing material is low, the oxygen is directly transferred from the composite metal oxide to the catalyst metal particles, so the effect of gas diffusion in the catalyst layer is Oxygen is dissolved in the generated water without being subjected to oxygen, and oxygen is reduced on the catalyst without being consumed, thereby further improving fuel cell performance.

An electrode reaction proceeds at a site called a three-phase interface, where a reaction gas, a catalyst, and an electrolyte meet. One important topic is the supply of oxygen to the three-phase interface. When the output of the battery is increased, a large amount of oxygen is required for the reaction. In the conventional technology, high-concentration oxygen is supplied, but as shown in Fig. 1, the actual reaction takes place at the three-phase interface (near the catalyst). I can't make full use of my abilities. In particular, when the output is increased, the oxygen consumption on the catalyst surface increases, but the diffusion rate of oxygen from the outside to the catalyst surface hardly changes. Therefore, when the rate of oxygen consumption on the catalyst surface above a certain level exceeds the rate of oxygen supply to the catalyst surface, the power generation characteristics are degraded due to the lack of oxygen in the vicinity of the catalyst. In contrast, as shown in FIG. 2, in the present invention, the rate of oxygen supply to the catalyst surface is increased to prevent deterioration of power generation characteristics due to lack of oxygen in the vicinity of the catalyst.

The cathode electrode of the polymer electrolyte fuel cell of the present invention comprises a catalyst layer, and preferably comprises a catalyst layer and a gas diffusion layer arranged adjacent to the catalyst layer. As a constituent material of the gas diffusion layer, for example, an electronically conductive porous body (for example, carbon cloth or carbon paper) is used.

The catalyst layer of the cathode electrode contains pyrochlore-type Sn ₂ Ta ₂ O ₇ and/or Sn ₂ Nb ₂ O ₇ having water repellency, conductivity, and oxygen storage/release properties due to projections. The electrode reaction rate of the cathode electrode can be improved by reducing the overvoltage for the oxygen reduction reaction in . On the other hand, even in a Ta-doped SnO ₂ composite metal oxide that does not have oxygen storage/release properties, the electrode reaction rate of the cathode electrode can be improved by reducing the overvoltage for the oxygen reduction reaction in the cathode electrode.

In addition, the content of the pyrochlore-type Sn ₂ Ta ₂ O ₇ and/or Sn ₂ Nb ₂ O ₇ composite metal oxide contained in the catalyst layer is the total of the catalyst-supporting conductor, the polymer electrolyte, and the catalyst metal particles. It is preferably 0.01 to 30% by mass, more preferably 0.01 to 20% by mass, based on the amount. Here, when the content of pyrochlore-type Sn ₂ Ta ₂ O ₇ and/or Sn ₂ Nb ₂ O ₇ is less than 0.01% by mass, the water repellency, electron conductivity and oxygen absorption/release properties are lowered, Separation between the ionomer and the catalyst metal particles, dissolution of oxygen in the generated water, oxidation and elution of the catalyst metal, decomposition of the sulfonic acid groups of the ionomer, and corrosion of the catalyst-carrying conductor can cause insufficient oxygen reduction reaction, resulting in continuous The tendency for it to become difficult to generate power increases. On the other hand, when the content of pyrochlore-type Sn ₂ Ta ₂ O ₇ and/or Sn ₂ Nb ₂ O ₇ mixed metal oxide exceeds 30% by mass, the content of ionomer contained in the catalyst layer relatively decreases. As a result, the number of reaction sites that function effectively in the catalyst layer decreases, making it difficult to obtain high electrode properties.

On the other hand, the content of the Ta-doped SnO ₂ composite metal oxide contained in the catalyst layer is 0.01 to 30% by mass with respect to the total amount of the catalyst-supporting conductor, the polymer electrolyte, and the catalyst metal particles. is preferred, and 0.01 to 20% by mass is more preferred. If the content of Ta _- doped SnO2 is less than 0.01% by mass, the water repellency, electronic conductivity, and oxygen storage/release properties are lowered, leading to separation between the ionomer and the catalyst metal particles, dissolution of oxygen in the generated water, and deterioration of the catalyst metal. Oxidation and elution of the ionomer, decomposition of the sulfonic acid group of the ionomer, and corrosion of the catalyst-carrying conductor occur, making it impossible to carry out a sufficient oxygen reduction reaction and making it difficult to generate power continuously. In addition, when the content of the Ta _- doped SnO2 composite metal oxide exceeds 30% by mass, the content of the ionomer contained in the catalyst layer is relatively decreased, resulting in a reaction that functions effectively in the catalyst layer. Since the number of sites decreases, it becomes difficult to obtain high electrode properties.

The Ta-doped SnO ₂ preferably has a Ta content in SnO ₂ of 0.1 to 10% by mass, more preferably 0.5 to 5.0% by mass. If the Ta content is less than 0.1% by mass, the association of electrons with the catalyst metal at the three-phase interface is reduced, resulting in a decrease in power generation.

The catalyst contained in the catalyst-carrying conductor of the cathode electrode of the present invention is not particularly limited, but may be platinum, a platinum alloy, or a core-shell type (for example, the shell layer 6 surrounding the core layer 5 shown in FIG. An alloy in which layer 5 is selected from Pd, Pt, Ru and/or Co) is preferred. Furthermore, the catalyst-carrying conductor is not particularly limited, but a carbon material having a specific surface area of 200 m ² /g or more is preferable. For example, carbon black, graphite or graphene are preferably used.

As the ionomer contained in the catalyst layer of the present invention, a fluorine-containing ion exchange resin is preferable, and a sulfonic acid type perfluorocarbon polymer is particularly preferable. The sulfonic acid-type perfluorocarbon polymer enables long-term chemically stable and rapid hydrogen ion conduction within the cathode electrode.

In addition, the layer thickness of the catalyst layer of the cathode electrode of the present invention may be equivalent to that of a polymer solid electrolyte sandwiched between an ordinary anode electrode and a cathode electrode, preferably 1 to 50 μm, more preferably 5 to 20 μm. is more preferable.

In polymer electrolyte fuel cells, the overvoltage of the oxygen reduction reaction at the cathode electrode is usually much higher than the overvoltage of the hydrogen oxidation reaction at the anode electrode, so that the generated hydrogen peroxide decomposes the sulfonic acid groups of the ionomer. , oxidation and elution of the catalyst metal and corrosion of the catalyst carrier conductor are likely to occur. can be prevented by doing In addition, the water repellent effect of mosquitoes prevents dissolution of oxygen in the generated water, and the oxygen absorption/release effect increases the oxygen concentration at the reaction site in the catalyst layer, suppressing overvoltage. Improving the electrode characteristics of the electrode is effective in stabilizing the output characteristics of the battery.

On the other hand, the configuration of the anode electrode is not particularly limited, and may have, for example, the configuration of a known gas diffusion electrode.

Moreover, the polymer electrolyte membrane sandwiched between the anode electrode and the cathode electrode used in the polymer electrolyte fuel cell of the present invention is not particularly limited as long as it is an ion exchange membrane that exhibits good ion conductivity under wet conditions. As the solid polymer material constituting the polymer electrolyte membrane, for example, a perfluorocarbon polymer having a sulfonic acid group, a polysulfone resin, a perfluorocarbon polymer having a phosphonic acid group or a carboxylic acid group, or the like can be used. Among them, sulfonic acid-type perfluorocarbon polymers are preferred. The polymer electrolyte membrane may be made of the same resin as the ionomer contained in the catalyst layer, or may be made of a different resin.

In the catalyst layer of the cathode electrode of the present invention, the surface of the catalyst-supporting conductor is previously covered with a composite metal oxide having projections, and catalyst metal particles are supported on the surface of the composite metal oxide. It can be prepared using a coating liquid dissolved or dispersed in a medium. Examples of the solvent or dispersion medium used here include alcohols, fluorine-containing alcohols, and fluorine-containing ethers. Then, a catalyst layer is formed by applying the coating liquid to an ion-exchange membrane or a carbon cloth or the like serving as a gas diffusion layer. Alternatively, the catalyst layer can be formed on the solid polymer electrolyte membrane by applying the above coating solution to a separately prepared base material to form a coating layer, and transferring this onto the solid polymer electrolyte membrane. .

Here, when the catalyst layer is formed on the gas diffusion layer, it is preferable to bond the catalyst layer and the solid polymer electrolyte membrane together by an adhesion method, a hot press method, or the like. Further, when the catalyst layer is formed on the polymer solid electrolyte membrane, the cathode electrode may be constituted only by the catalyst layer. good.

A separator in which a gas flow path is formed is disposed outside the cathode electrode, and a hydrogen-containing gas is supplied to the anode electrode and an oxygen-containing gas is supplied to the cathode electrode to the flow path to form a solid polymer type separator. A fuel cell is constructed.

(Measurement of particle size distribution)
The particle size distribution of the catalyst metal was obtained by measuring 100 points using a transmission electron microscope (Titan Cubed G2 60-300, manufactured by FEI) and taking the arithmetic average as the average particle size.

(Measurement of composite metal oxide shape)
The shape (height, spacing) of the composite metal oxide having protrusions of the present invention was determined using a transmission electron microscope (Titan Cubed G2 60-300, manufactured by FEI) in the same manner as the particle size distribution of the catalyst metal. 100 points of measurement were measured using the tape, and the arithmetic average was taken as the height and the interval.

(Measurement of conductivity)
The electrical properties of the composite metal oxide having projections of the present invention were evaluated by molding the final catalyst powder into circular pellets, preparing a sample in which metal electrodes were vapor-deposited on the four corners of the pellet, and using a Hall effect measuring device (Resitest). 8310, manufactured by Toyo Technica) was used to measure the specific resistance.

(Measurement of water repellency)
In the following Examples 1 to 3, the water repellency of the composite metal oxide having projections was measured by preparing a sample obtained by molding the final catalyst powder into a circular pellet, and measuring the droplet method (automatic minimal contact angle meter MCA-3 , manufactured by Kyowa Interface Science Co., Ltd.). Also for Reference Example 1 and Comparative Examples 1 to 3, samples were prepared by molding the final catalyst powder into circular pellets, and measurements were made in the same manner.

EXAMPLES The cathode electrode and polymer electrolyte fuel cell of the present invention will be described in detail below with reference to examples and comparative examples.

(Example 1)
A mixture of Pt (5% by mass)/pyrochlore-type Sn ₂ Ta ₂ O ₇ (20%)/carbon black (75% by mass) was prepared by the following procedure, an MEA was prepared, the MEA was assembled into a cell, and performance was evaluated. bottom.

(1) Predetermined amounts of tin (II) chloride and tantalum (V) chloride were dissolved in pure water and stirred for 2 hours.
(2) Carbon black (Ketjenblack EC300J, BET specific surface area 800 g/m2, manufactured by Lion Specialty Chemicals Co., Ltd.) was powdered, and a predetermined amount was added to pure water and stirred to prepare a suspension. .
(3) The solution of (1) was slowly added to the suspension while stirring, adjusted to pH 1.5 using dilute hydrochloric acid, and maintained in that state for 3 hours. Thereafter, filtration and washing with water were repeated three times to obtain carbon black powder in which carbon black particles were coated with Sn ₂ Ta ₂ O ₇ .
(4) Next, the carbon black powder coated with Sn ₂ Ta ₂ O ₇ obtained in (3) is dispersed in pure water with stirring, and a predetermined amount of chloroplatinic acid (IV) solution (as platinum 1% by mass) was added. A small amount of ethanol was slowly added thereto, and the mixture was heated to 40° C. and held for 3 hours. Platinum was reduced to the surface of the Sn ₂ Ta ₂ O ₇ composite metal oxide.
(5) Thereafter, filtration and washing with water were repeated three times, dried at 80°C for 12 hours, pulverized in a mortar, and fired in an atmospheric firing furnace at 500°C for 2 hours. It was ground again in a mortar.
(6) When the Pt/pyrochlore-type Sn ₂ Ta ₂ O ₇ /carbon black powder thus obtained was observed with a transmission electron microscope, the average particle size of the platinum catalyst metal particles was 3 nm, and the pyrochlore-type Sn ₂ The shape of Ta ₂ O ₇ had an average height of 10 nm and an average interval (pitch) of 10 nm. Next, the obtained powder was pressed into pellets of 20 mm in diameter and 5 mm in thickness, and the degree of water repellency was measured by the contact angle with water by the droplet method. This contact angle was 150 degrees. Moreover, when the specific resistance was measured using the pellet, it was 0.1 Ω·cm.
(7) Next, a predetermined amount of Pt/pyrochlore-type Sn ₂ Ta ₂ O ₇ /carbon black was mixed with ion-exchanged water, ionomer electrolyte solution (Nafion D520), ethanol, and polyethylene glycol (Nafion/Carbon=1 0% by mass, Pt (5% by mass)/pyrochlore-type Sn ₂ Ta ₂ O ₇ (20%)/carbon black (75% by mass) catalyst ink was prepared.
(8) Cast the above catalyst ink on a Teflon (registered trademark) resin film (thickness 6 mil), dry it, cut it into 25 (cm ² ),
It was used as an electrode film.
(9) When the electrode film was completely dissolved and subjected to ICP analysis, Pt was 0.3 mg/cm ² and Sn ₂ Ta ₂ O ₇ was 1.2 mg/cm ² .
(10) Using the obtained cathode electrode film and the anode electrode film made of the commercially available catalyst described in Comparative Example 1, thermocompression bonding (150 °C) to prepare an MEA.
(11) The MEA was assembled into a cell and performance was evaluated.

(Example 2)
In Example 2, core-shell type catalyst metal was prepared in the same manner as in Example 1, except that the catalyst metal was changed from Pt single metal to core-shell type catalyst metal (shell layer Pt/core layer Pd·Ru·Co alloy). (5% by mass)/pyrochlore-type Sn ₂ Ta ₂ O ₇ (20%)/carbon black (75% by mass) was used to fabricate an MEA, and the performance was evaluated in a single cell.

The core-shell catalyst metal was produced by the following procedure.
(1) The carbon black powder coated with Sn ₂ Ta ₂ O ₇ obtained in (3) of Example 1 was dispersed in pure water with stirring, and a palladium chloride solution (1% by mass as Pd) and Predetermined amounts of a ruthenium chloride solution (1% by mass as Ru) and a cobalt chloride solution (1% by mass as Co) were added.
(2) A small amount of ethanol was slowly added thereto, heated to 40° C. and held for 3 hours. Pd, Ru and Co were reduced to the surface of the Sn ₂ Ta ₂ O ₇ composite metal oxide. Thereafter, filtration and washing with water were repeated three times, drying at 80° C. for 12 hours, pulverizing in a mortar, and firing in an air firing furnace at 500° C. for 2 hours. It was ground again in a mortar.
(3) Next, the Sn ₂ Ta ₂ O ₇ -coated carbon black powder supporting the catalyst in the core obtained in (2) was dispersed in pure water with stirring, and a chloroplatinic acid (IV) solution was added. A specified amount was added. A small amount of ethanol was slowly added thereto, and the mixture was heated to 40° C. and held for 3 hours.
(4) Thereafter, filtration and washing with water were repeated three times, dried at 80°C for 12 hours, pulverized in a mortar, and fired in an air firing furnace at 500°C for 2 hours. It was ground again in a mortar.
(5) When the obtained core-shell catalyst (Pt/Pd.Ru.Co alloy)/pyrochlore-type Sn ₂ Ta ₂ O ₇ /carbon black powder was observed with a transmission electron microscope, the core-shell catalyst (Pt /Pd.Ru.Co alloy) particles had an average particle diameter of 3 nm, and the pyrochlore-type Sn ₂ Ta ₂ O ₇ particles had an average height of 10 nm and an average interval (pitch) of 10 nm. Next, the obtained powder was pressed into pellets of 20 mm in diameter and 5 mm in thickness, and the degree of water repellency was measured by the contact angle with water by the droplet method. This contact angle was 150 degrees. Moreover, when the specific resistance was measured using the pellet, it was 0.1 Ω·cm.
(6) Next, the core-shell type catalyst (Pt/Pd·Ru·Co alloy)/pyrochlore type Sn ₂ Ta ₂ O ₇ /carbon black was mixed with ion-exchanged water, ionomer electrolyte solution (Nafion D520), ethanol, and polyethylene glycol. (Nafion/Carbon=1.0% by mass, core-shell type catalyst (Pt/Pd-Ru-Co alloy) (5% by mass)/pyrochlore-type Sn ₂ Ta ₂ O ₇ (20%)/carbon A black (75 mass %) catalyst ink was prepared.
(7) The catalyst ink was cast on a Teflon (registered trademark) resin film (thickness: 6 mil), dried, and cut into 25 (cm ² ) pieces to obtain electrode films.
(8) When the electrode film was completely dissolved and subjected to ICP analysis, Pt was 0.05 mg/cm ² , Pd was 0.03 mg/cm ² , Ru was 0.10 mg/cm ² , and Co was 0.11 mg/cm 2 . cm ² and 1.2 mg/cm ² as Sn ₂ Ta ₂ O ₇ .
(9) Using the obtained cathode electrode film and the anode electrode film made of the commercially available catalyst described in Comparative Example 1, thermocompression bonding (150 °C) to prepare an MEA.
(10) The MEA was assembled into a cell and performance was evaluated.

(Example 3)
_In Example 3, core-shell catalyst metal ( ₅ % by mass)/Ta _- doped SnO ₂ ( ₂₀ % )/carbon black (75% by mass) was prepared, and the performance was evaluated in a single cell.

The composite metal oxide of Ta _- doped SnO2 was prepared by the following procedure.
(1) A predetermined amount of tin (II) chloride was dissolved in pure water and stirred for 2 hours.
(2) Carbon black (Ketjenblack EC300J, BET specific surface area 800 g/m ² , manufactured by Lion Specialty Chemicals Co., Ltd.) is adjusted to powder, and a predetermined amount is added to pure water and stirred to prepare a suspension. bottom.
(3) The solution of (1) was slowly added to the suspension while stirring, adjusted to pH 1.5 using dilute hydrochloric acid, and maintained in that state for 3 hours.
(4) A predetermined amount of tantalum (V) chloride was dissolved in pure water and stirred for 2 hours.
(5) Next, while stirring the suspension in (3), a predetermined amount of the tantalum (V) chloride solution was slowly added, heated to 30°C, and held for 3 hours.
(6) Thereafter, filtration and washing with water were repeated three times to obtain carbon black powder coated with Ta-doped SnO ₂ .
(7) A small amount of the Ta-doped SnO ₂ -coated carbon black powder was sampled, dried at 80°C for 12 hours, pulverized in a mortar, and fired in an air firing furnace at 500°C for 2 hours.
(8) When the obtained carbon black powder coated with Ta-doped SnO ₂ was completely dissolved and subjected to ICP analysis, it was found that 2.1% by mass of Ta was contained in SnO ₂ .
(9) When the obtained core-shell type catalyst (Pt/Pd·Ru·Co alloy)/Ta-doped SnO ₂ /carbon black powder was observed with a transmission electron microscope, the core-shell type catalyst (Pt/Pd·Ru Co alloy) particles had an average particle size of 3 nm, and the shape of the Ta-doped SnO ₂ had an average height of 10 nm and an average interval (pitch) of 10 nm. Next, the obtained powder was pressed into pellets of 20 mm in diameter and 5 mm in thickness, and the degree of water repellency was measured by the contact angle with water by the droplet method. This contact angle was 145 degrees. Moreover, when the specific resistance was measured using the pellet, it was 0.2 Ω·cm.
(10) Next, a predetermined amount of the core-shell type catalyst (Pt/Pd·Ru·Co alloy)/Ta-doped SnO ₂ /carbon black is mixed with ion-exchanged water, ionomer electrolyte solution (Nafion D520), ethanol, and polyethylene glycol. (Nafion/Carbon=1.0% by mass, core-shell type catalyst (Pt/Pd.Ru.Co alloy) (5% by mass)/pyrochlore type Sn ₂ Ta ₂ O ₇ (20%)/carbon black (75% by mass %) catalyst ink was prepared.
(11) The above catalyst ink was cast on a Teflon (registered trademark) resin film (thickness: 6 mil), dried, and cut into 25 (cm ² ) pieces to obtain electrode films.
(12) When the electrode film was completely dissolved and subjected to ICP analysis, Pt was 0.05 mg/cm ² , Pd was 0.03 mg/cm ² , Ru was 0.10 mg/cm ² , and Co was 0.11 mg/cm 2 . cm ² and 1.2 mg/cm ² as Ta-doped SnO ₂ .
(13) Using the obtained cathode electrode film and the anode electrode film made of the commercially available catalyst described in Comparative Example 1, thermocompression bonding (150 °C) to prepare an MEA.
(14) The MEA was assembled into a cell and performance was evaluated.

(Reference example 1)
In Reference Example 1, an MEA using a core-shell catalyst metal (5% by mass)/carbon black (75% by mass) was prepared in the same manner as in Example 2, except that pyrochlore-type Sn ₂ Ta ₂ O ₇ was omitted. , the performance was evaluated with a single cell.

(1) When the obtained core-shell type catalyst (Pt/Pd·Ru·Co alloy)/carbon black powder was observed with a transmission electron microscope, the core-shell type catalyst (Pt/Pd·Ru·Co alloy) particles had an average particle size of 3 nm. Next, the obtained powder was pressed into pellets of 20 mm in diameter and 5 mm in thickness, and the degree of water repellency was measured by the contact angle with water by the droplet method. This contact angle was 90 degrees. Moreover, when the specific resistance was measured using the pellet, it was 0.5 Ω·cm.
(2) Next, a predetermined amount of the core-shell type catalyst (Pt/Pd.Ru.Co alloy)/carbon black is mixed with ion-exchanged water, ionomer electrolyte solution (Nafion D520), ethanol, and polyethylene glycol (Nafion/ Carbon = 1.0% by mass, a catalyst ink of core-shell type catalyst (Pt/Pd-Ru-Co alloy) (5% by mass)/carbon black (95% by mass) was prepared.
(3) Cast the above catalyst ink on a Teflon (registered trademark) resin film (thickness 6 mil), dry it, cut it into 25 (cm ² ),
It was used as an electrode film.
(4) When the electrode film was completely dissolved and subjected to ICP analysis, Pt was 0.05 mg/cm ² , Pd was 0.03 mg/cm ² , Ru was 0.10 mg/cm ² , and Co was 0.11 mg/cm 2 . ^cm2 .
(5) Using the obtained cathode electrode film and the anode electrode film made of the commercially available catalyst described in Comparative Example 1, thermocompression bonding (150 °C) to prepare an MEA.
(6) The MEA was assembled into a cell and performance was evaluated.

(Comparative example 1)
In Comparative Example 1, an MEA was prepared using TEC10E50E (50% by mass as Pt, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) in which platinum is supported on commercially available carbon black as a catalyst, and the MEA was assembled into a cell and performance was evaluated.

(1) Observation of commercially available catalyst powder of TEC10E50E with a transmission electron microscope revealed that the average particle size of platinum catalyst metal particles was 4 nm. Next, the obtained powder was pressed into pellets of 20 mm in diameter and 5 mm in thickness, and the degree of water repellency was measured by the contact angle with water by the droplet method. This contact angle was 90 degrees. Moreover, when the specific resistance was measured using the pellet, it was 0.01 Ω·cm.
(2) Next, a predetermined amount of the commercially available TEC10E50E catalyst powder was mixed with ion-exchanged water, ionomer electrolyte solution (Nafion D520), ethanol, and polyethylene glycol (Nafion/Carbon = 1.0% by mass, Pt ( 5% by mass)/carbon black (95% by mass) catalyst ink was prepared.
(3) Cast the above catalyst ink on a Teflon (registered trademark) resin film (thickness 6 mil), dry it, cut it into 25 (cm ² ),
It was used as an electrode film.
(4) When the electrode film was completely dissolved and subjected to ICP analysis, it was found to be 0.3 mg/cm ² as Pt.
(5) Using both the cathode electrode and the anode electrode, the obtained electrode film was thermocompression bonded (150° C.) to a solid polymer electrolyte membrane (Nafion NR211, t=25 μm) to prepare an MEA.
(6) The MEA was assembled into a cell and performance was evaluated.

(Comparative example 2)
In Comparative Example 2, instead of pyrochlore-type Sn ₂ Ta ₂ O ₇ , pyrochlore-type Ce ₂ Zr ₂ O ₇ was used as a composite metal oxide, and catalyst metal particles were not supported on pyrochlore-type Ce ₂ Zr ₂ O ₇ . A MEA was prepared in the same manner as in Example 1, except that the composite metal oxide and the catalyst metal particles were separately supported on the carbon black, and the MEA was assembled in a cell and evaluated for performance.

(1) Predetermined amounts of diammonium cerium nitrate and zirconium oxynitrate were dissolved in pure water and stirred for 2 hours.
(2) After evaporating water at 120° C., vacuum drying was performed. After that, it was fired at 350° C. for 5 hours in an atmospheric firing furnace.
(3) Hold at 900° C. for 2 hours in reducing gas (H ₂ , 2%) atmosphere, then switch to inert gas (N ₂ ) and slowly cool.
(4) After pulverizing the obtained powder in a mortar, the powder was immersed in an aqueous solution of dinitrodiamine platinum, stirred, and evaporated to dryness at 120°C. Platinum was 5 mass % with respect to powder.
(5) Further, after pulverizing in a mortar, it was fired in an atmospheric firing furnace at 500° C. for 2 hours. It was ground again in a mortar.
(6) When the obtained Pt/pyrochlore-type Ce ₂ Zr ₂ O ₇ /carbon black powder was observed with a transmission electron microscope, the average particle size of platinum catalyst metal particles was 3 nm. Next, the obtained powder was pressed into pellets of 20 mm in diameter and 5 mm in thickness, and the degree of water repellency was measured by the contact angle with water by the droplet method. This contact angle was 75 degrees. Moreover, when the specific resistance was measured using the pellet, it was 1.5 Ω·cm.
(7) A predetermined amount of Pt/pyrochlore-type Ce ₂ Zr ₂ O ₇ /carbon black thus obtained was mixed with ion-exchanged water, ionomer electrolyte solution (Nafion D520), ethanol, and polyethylene glycol (Nafion/Carbon=1 0% by mass, Pt (5% by mass)/pyrochlore-type Ce ₂ Zr ₂ O (20% by mass)/carbon black (95% by mass) catalyst ink was prepared.
(8) Cast the above catalyst ink on a Teflon (registered trademark) resin film (thickness 6 mil), dry it, cut it into 25 (cm ² ),
It was used as an electrode film.
(9) When the electrode film was completely dissolved and subjected to ICP analysis, Pt was 0.3 mg/cm ² and pyrochlore-type Ce ₂ Zr ₂ O was 1.2 mg/cm ² .
(10) Using the obtained cathode electrode film and the anode electrode film made of the commercially available catalyst described in Comparative Example 1, thermocompression bonding (150 °C) to prepare an MEA.
(11) The MEA was assembled into a cell and performance was evaluated.

(Comparative Example 3)
In Comparative Example 3, an MEA was prepared in the same manner as in Comparative Example 1 except that fluorine silane treatment (0.1% by mass)/Pt (5% by mass)/carbon black (94.9% by mass) was used. was assembled into a cell and evaluated for performance.

(1) First, a predetermined amount of tridecafluorooctyltriethoxysilane (Dynasylan F8261, manufactured by EVONIK) was added to ethanol while stirring, and the mixture was kept for 0.5 hours. Next, a predetermined amount of the Pt/carbon black powder obtained in Comparative Example 1 was added, and the mixture was kept as it was for 2 hours. Thereafter, filtration and washing with water were repeated three times, and drying was performed at 80° C. for 5 hours.
(2) Observation of the obtained fluorosilane-treated/Pt/carbon black powder with a transmission electron microscope revealed that the average particle diameter of platinum catalyst metal particles was 4 nm. Next, the obtained powder was pressed into pellets of 20 mm in diameter and 5 mm in thickness, and the degree of water repellency was measured by the contact angle with water by the droplet method. This contact angle was 150 degrees. Moreover, when the specific resistance was measured using the pellet, it was 0.8 Ω·cm.
(3) A predetermined amount of the fluorine silane treatment/Pt/carbon black thus obtained is mixed with ion-exchanged water, ionomer electrolyte solution (Nafion D520), ethanol, and polyethylene glycol (Nafion/Carbon=1.0% by mass, A catalyst ink of fluorine silane treatment (0.1% by mass)/Pt (5% by mass)/carbon black (94.9% by mass) was prepared.
(4) Cast the above catalyst ink on a Teflon (registered trademark) resin film (thickness 6 mil), dry it, cut it into 25 (cm ² ),
It was used as an electrode film.
(5) When the electrode film was completely dissolved and subjected to ICP analysis, it was found to be 0.3 mg/cm ² as Pt.
(6) Using the obtained cathode electrode film and the anode electrode film made of the commercially available catalyst described in Comparative Example 1, thermocompression bonding (150 °C) to prepare an MEA.
(7) The MEA was assembled into a cell and performance was evaluated.

[Power generation performance evaluation test]
A single cell (JARI standard cell, Japan Automobile Research Institute) with an electrode area of 25 cm ² was subjected to the following power generation performance evaluation test. The results are shown in Table 1, "power generation performance."
"Gas flow rate" anode: H2 500 _NmL /min
Cathode: Air 1000NmL/min
"Humidification temperature" anode dew point (relative humidity): 77 ° C (RH 88%)
Cathode dew point (relative humidity): 60°C (RH42%)
"Preset pressure" Normal pressure "Cell temperature" 80°C

[Electrochemical effective surface area (ECA) test]
"Gas flow rate" anode: H2 ₂₀₀ NmL/min
Cathode: N ₂ 200 → 0 NmL/min (N ₂ nitrogen shut off before measurement)
"Humidification temperature" anode dew point (relative humidity): 80 ° C (RH 100%)
Cathode dew point (relative humidity): 80°C (RH100%)
"Preset pressure" Normal pressure "Cell temperature" 80°C
"Measurement conditions" Scan between 0.05 V and 0.9 V at 50 mV/sec five times after shutting off nitrogen.

[Durability evaluation (potential cycle test)]
In order to confirm the half-life of catalytic activity in an electrochemical effective surface area (ECA) test, durability was evaluated under the following conditions.
"Gas flow rate" anode: H2 ₂₀₀ NmL/min
Cathode: _N2 800NmL/min
"Cell temperature" 80℃
"Potential cycle" potential 1.0V ⇔ 1.5V
Cycle interval: 2 seconds/cycle Based on the results of the electrochemical effective surface area (ECA) test and durability evaluation, the half-life of the number of ECA cycles is shown in Table 1, "Durability performance."

From the results in Table 1, the fuel cell using the electrode in which the conductive composite metal oxide having projections is supported on the surface of the catalyst-supporting conductor of the present invention has conductivity, water repellency, and/or oxygen storage and release. It can be seen that the body is superior in power generation performance and durability performance even when compared with Comparative Examples 2 and 3 using electrodes made of ordinary oxygen absorbing/releasing material or fluorine-based treatment. Furthermore, it can be seen that the amount of platinum used can be reduced by also using the core-shell type of the present invention.

1: Catalyst metal carrier 2: Conductive composite metal oxide having protrusions 3: Catalyst metal particles 4: Ionomer (solid polymer electrolyte)
5: core layer 6: shell layer

Claims (17)

Having a catalyst layer composed of a catalyst-carrying conductor and a polymer electrolyte,
the surface of the catalyst-carrying conductor is covered with a conductive composite metal oxide having projections;
A cathode electrode for a fuel cell, wherein catalyst metal particles are supported on the conductive composite metal oxide. 2. The fuel cell cathode electrode according to claim 1, wherein the height of said projections of said conductive composite metal oxide is 5 nm to 15 nm. 3. The fuel cell cathode electrode according to claim 1, wherein said conductive composite metal oxide has water repellency with a contact angle with water of 140 degrees or more. 4. The fuel cell cathode electrode according to claim 1, wherein said catalyst-carrying conductor covered with said conductive composite metal oxide has a specific resistance of 0.2 Ω·cm or less. 5. The fuel cell cathode electrode according to claim 1, wherein said conductive composite metal oxide is an oxygen absorbing/releasing material. 6. The fuel cell cathode electrode according to claim 1, wherein said conductive composite metal oxide is a p-type semiconductor. 7. The fuel cell cathode electrode according to claim 1, wherein said conductive mixed metal oxide has a pyrochlore structure consisting of Sn ₂ M ₂ O ₇ (M=Ta and/or Nb). 5. The fuel cell cathode electrode according to claim 1, wherein said conductive mixed metal oxide contains Ta-doped SnO ₂ (0.01% by mass≦Ta≦1.0% by mass). 9. The fuel cell cathode electrode according to claim 1, wherein said catalytic metal particles have a core-shell structure consisting of a Pt shell layer. 10. The fuel cell cathode electrode according to claim 9, wherein the core layer of the core-shell structure is made of an alloy selected from Pd and at least one of Pt, Ru and Co. 11. The fuel cell cathode electrode according to any one of claims 1 to 10, wherein said catalyst-carrying conductor comprises at least one selected from conductive carbon, graphite, graphene and carbon alloy. A method for manufacturing a cathode electrode for a fuel cell according to any one of claims 1 to 11,
A fuel comprising the step of adding tin (II) chloride and tantalum (V) chloride to the suspension of the catalyst-supporting conductor and controlling the pH to 1.5 to 2.0 to obtain the conductive composite metal oxide. A method for manufacturing a cathode electrode for a battery. A metal salt of the catalyst constituting the core layer is added to the suspension of the catalyst-supporting conductor coated with the conductive composite metal oxide, and the mixture is heated to 40° C. to 80° C. to obtain the catalyst metal. including a first reduction step of reducing,
13. The fuel according to claim 12, wherein in the first reduction step, a core layer of the catalyst metal particles is formed on the surface of the projecting conductive composite metal oxide covering the surface of the catalyst-carrying conductor. A method for manufacturing a cathode electrode for a battery. A Pt salt solution and a reducing agent are added to the suspension of the catalyst-supporting conductor having the core layer of the catalyst metal particles on the surface of the projecting conductive composite metal oxide to reduce Pt. 2 including a reduction step,
14. The method of manufacturing a cathode electrode for a fuel cell according to claim 13, wherein the second reduction step forms a Pt shell layer of the catalyst metal particles. an anode electrode;
a cathode electrode according to any one of claims 1 to 11;
a polymer electrolyte membrane disposed between the anode electrode and the cathode electrode;
A polymer electrolyte fuel cell having 16. The polymer electrolyte fuel cell according to claim 15, wherein said conductive composite metal oxide has a pyrochlore structure consisting of _{Sn2M2O7 (} M ₌ Ta and/or Nb). 16. The polymer electrolyte fuel cell according to claim 15, wherein said conductive composite metal oxide contains Ta-doped SnO2 ₍ 0.01% by mass≤Ta≤1.0% by mass).

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