CN113795332A - Cathode electrode for fuel cell, method for producing same, and solid polymer fuel cell provided with cathode electrode for fuel cell - Google Patents

Cathode electrode for fuel cell, method for producing same, and solid polymer fuel cell provided with cathode electrode for fuel cell Download PDF

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CN113795332A
CN113795332A CN202080028626.7A CN202080028626A CN113795332A CN 113795332 A CN113795332 A CN 113795332A CN 202080028626 A CN202080028626 A CN 202080028626A CN 113795332 A CN113795332 A CN 113795332A
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catalyst
fuel cell
cathode electrode
metal oxide
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CN113795332B (en
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北村武昭
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ACR Co Ltd
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/84—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/16—Reducing
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
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Abstract

In the cathode electrode of the polymer solid electrolyte fuel cell, a reaction site called a three-phase interface catalyst, an ionomer and oxygen association is provided on more catalyst metal particles during catalysis, thereby improving the effective utilization rate of platinum. Further, even if the overvoltage is generated in accordance with the driving load fluctuation cycle and the start/stop cycle of the automobile, the reaction sites of the three-phase interface can be continuously maintained. The cathode electrode for a fuel cell has a catalyst layer containing a catalyst-supporting conductor and a polymer electrolyte, the surface of the catalyst-supporting conductor is covered with a conductive composite metal oxide having protrusions, and catalyst metal particles are supported on the conductive composite metal oxide.

Description

Cathode electrode for fuel cell, method for producing same, and solid polymer fuel cell provided with cathode electrode for fuel cell
Technical Field
The present invention relates to a cathode electrode for a fuel cell, a method for producing the same, and a polymer electrolyte fuel cell including the cathode electrode for a fuel cell.
Background
In recent years, among fuel cells, a solid polymer fuel cell having a proton conductive polymer electrolyte membrane has been expected to be widely used as a power source for automobiles and the like as a final measure for global warming because of its low operating temperature, high output density, and easy miniaturization and weight reduction. However, Pt is required to be 5 to 10 times the amount of Pt used in a conventional internal combustion engine, and Pt elution and deterioration of the polymer electrolyte due to overvoltage during load running cycles and start/stop cycles are problematic.
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 to form a three-phase interface as water molecules, thereby causing a chain reaction. Therefore, in a polymer electrolyte fuel cell, conventionally, a three-phase interface is formed by increasing the specific surface area of a catalyst-supporting conductor to increase the number of catalytically active sites and covering a catalyst layer with a fluorine-containing ion exchange resin (hereinafter, sometimes referred to as an "ionomer").
As the ionomer covering the catalyst, a perfluorocarbon polymer having a strongly acidic sulfonic acid group in a side chain is used in order to improve proton conductivity.
However, it is known that when a potential for power generation is generated in the catalyst layer of the conventional cathode electrode, the gap between the catalyst and the ionomer is enlarged, and water molecules exist therein, thereby reducing proton conduction (fig. 3). As described in (1) to (6) of fig. 3, in the conventional cathode electrode, when platinum on the surface layer is oxidized by the generated hydrogen peroxide and overvoltage at the time of power generation overload, the ionomer is separated from the platinum. The generated water is accumulated therein, and oxygen is dissolved in the generated water. Further, dissociation from the ionomer due to corrosion of sulfonic acid groups progresses, oxidation of platinum progresses, and platinum is eluted into the product water to reduce the platinum on the surface layer. It becomes impossible to maintain the three-phase interface as the reaction site. It is also known that the permeability to oxygen is reduced, the permeability to oxygen in the catalyst layer becomes insufficient, the overvoltage of the oxygen reduction reaction in the cathode electrode becomes large, oxidation and elution of platinum are caused by decomposition of hydrogen peroxide, and sulfonic acid is dissociated from the perfluorocarbon containing sulfonic acid groups in the polymer solid electrolyte.
In contrast, patent documents 1, 2, and 3 below propose a polymer electrolyte fuel cell and an electrode layer treated with a fluororesin or a fluorine-based silane coupling agent covered with a catalyst.
However, in the coating treatment using the fluorine-based resin and the fluorine-based silane, peeling of the fluorine resin and hydrolysis of the siloxane bond occur during a running load variation and a start/stop of the automobile, and are insufficient from the viewpoint of durability.
On the other hand, regarding the oxygen permeability of the cathode electrode layer, patent document 4 below discloses that pyrochlore-structured Ce is separately supported on the surface of the catalyst-supporting conductor so as not to overlap with each other, and oxygen is adsorbed and desorbed2Zr2O oxide method.
However, in the polymer electrolyte fuel cell described in patent document 4, Ce2Zr2The electron conductivity of the O oxide is insufficient, a three-phase interface cannot be formed, and the internal resistance of the cathode electrode increases. IntoIn one step, the Ce desorbed from the catalyst by adsorption with oxygen2Zr2Since the O oxide does not overlap, oxygen hardly reaches the surface of the catalyst metal particle, and the formation of a three-phase interface is insufficient.
Documents of the prior art
Patent document
Patent document 1: korean patent laid-open No. 20090118262
Patent document 2: japanese patent laid-open publication No. 20015-056298
Patent document 3: japanese laid-open patent publication No. H05-05182672
Patent document 4: japanese patent laid-open No. 2008-091264
Disclosure of Invention
Problems to be solved by the invention
In the present invention, in the cathode electrode of the polymer solid electrolyte fuel cell, in the catalytic action, more catalyst metal particles have reaction sites on which a catalyst called a three-phase interface, an ionomer, and oxygen (in other words, hydrogen ions, oxygen, and electrons are associated on the surface of the catalyst metal particles), thereby improving the effective utilization rate of platinum. Further, even if the overvoltage is generated in accordance with the driving load fluctuation cycle and the start/stop cycle of the automobile, the reaction sites of the three-phase interface can be continuously maintained.
As in patent documents 1, 2, and 3, when a fluororesin or a fluorine-based silane is coated on a catalyst-supporting carbon to impart hydrophobicity, peeling of the fluororesin and hydrolysis of siloxane bonds occur due to a variation in the running load of an automobile and a start-up stop, and a gap is formed at the interface between a catalyst and an ionomer, thereby reducing hydrogen ion conduction. Further, water is accumulated in the gap, oxygen is dissolved in the water, and the supply of oxygen is reduced. 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, pyrochlore-type Ce is contained2Zr2O7The oxygen adsorbing-desorbing material(s) is present in the catalyst-supported conductor without being in direct contact with the catalyst metal particlesIn the case of the surface, oxygen is easily dissolved in the produced water, and the supply to the reaction sites of the three-phase interface on the surface of the catalyst metal particle is reduced. Further, containing the above pyrochlore type Ce2Zr2O7The oxygen adsorption/desorption body of (2) has low electron conductivity, and therefore the internal resistance of the cathode electrode increases, and the overvoltage of the running load fluctuation cycle and the start/stop cycle of the automobile becomes high, resulting in oxidation and elution of platinum, decomposition of sulfonic acid groups of the ionomer, and corrosion of the catalyst-supporting conductor (conductive carbon).
Means for solving the problems
The present inventors have found that the above problems are solved by allowing a metal oxide having a protrusion shape to directly contact between catalyst metal particles and a catalyst-supporting conductor to have hydrophobicity, electron conductivity, and oxygen adsorption/desorption properties in order to realize hydrogen ion conduction, electron conduction, and association of oxygen to the surface of the catalyst metal particles and thereby continuously form sites of a three-phase interface, and have completed the present invention.
In order to solve the above problems, a cathode electrode for a fuel cell according to the present invention includes a catalyst layer containing a catalyst-supporting conductor and a polymer electrolyte, wherein the surface of the catalyst-supporting conductor is covered with a conductive composite metal oxide having protrusions, 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 5nm to 15 nm.
The conductive composite metal oxide may have hydrophobicity with a contact angle with water of 140 degrees or more.
The catalyst-supporting conductor may have a resistivity of 0.2 Ω · cm or less.
The conductive composite metal oxide may be an oxygen adsorption/desorption body.
The conductive composite metal oxide may be a p-type semiconductor.
The conductive composite metal oxide may have a structure containing Sn2M2O7(M ═ Ta and/orNb) pyrochlore structure.
The conductive composite metal oxide may include Ta-doped SnO2(Ta is more than or equal to 0.01 and less than or equal to 1.0 mass percent).
The catalyst metal particles may have a core-shell structure having a shell layer containing Pt.
The core layer of the core-shell structure may contain an alloy of Pd and at least one selected from Pt, Ru, and Co.
The catalyst-supporting conductor may contain at least one selected from conductive carbon, graphite, graphene, and a carbon alloy.
In order to solve the above problems, a method for manufacturing a cathode electrode for a fuel cell according to the present invention is a method for manufacturing a cathode electrode for a fuel cell according to the present invention, including: adding tin (II) chloride and tantalum (V) chloride to the suspension of the catalyst-supported conductor, and controlling the pH to 1.5-2.0 to obtain the conductive composite metal oxide.
The method may further include the following first reduction step: and a first reduction step of heating a material obtained by adding a metal salt that forms a nucleation layer to a suspension of the catalyst-supporting conductor that is coated with the conductive composite metal oxide to 40 to 80 ℃ to reduce the material, and forming a core layer of the catalyst metal particles on the surface of the protruding conductive composite metal oxide that coats the surface of the catalyst-supporting conductor.
The method may further include the following second reduction step: and a second reduction step of reducing the surface of the conductive composite metal oxide in the form of protrusions by adding a Pt salt solution and a reducing agent to a suspension of the catalyst-supporting conductor having the core layer of the catalyst metal particles, thereby forming Pt shell layers of the catalyst metal particles.
In order to solve the above problems, a polymer electrolyte fuel cell according to the present invention includes an anode electrode, a cathode electrode according to the present invention, and a polymer electrolyte membrane disposed between the anode electrode and the cathode electrode.
The conductive composite metal oxide may have a structure containing Sn2M2O7Pyrochlore structure of (M ═ Ta and/or Nb).
The conductive composite metal oxide may include Ta-doped SnO2(Ta is more than or equal to 0.01 and less than or equal to 1.0 mass percent).
Effects of the invention
According to the present invention, the cathode electrode for a fuel cell contains pyrochlore-type Sn having a protrusion shape2Ta2O7And/or Sn2Nb2O7The crystalline composite metal oxide of (3) has a persistent hydrophobicity, and further is doped with SnO by Ta due to electron conductivity and oxygen adsorption/desorption properties or not being an oxygen adsorption/desorption body2And the oxygen reduction reaction of the reaction sites of the three-phase interface is highly realized on the surface of the catalyst metal particles, so that higher power generation performance can be obtained.
Drawings
Fig. 1 is a conceptual view showing the structure of a catalyst carrier conductor, a composite oxide, catalyst metal particles, and an ionomer in a cathode electrode according to the present invention.
Fig. 2 is a conceptual diagram of reaction sites of a three-phase interface based on movement of hydrogen ions, electrons, and oxygen molecules to the surface of the catalyst metal particles.
Fig. 3 is a conceptual diagram illustrating a deterioration behavior during power generation in a conventional cathode electrode.
FIG. 4 is a conceptual diagram showing the structure of the core-shell catalyst of the present invention.
Detailed Description
Hereinafter, preferred embodiments of the cathode electrode and the polymer electrolyte fuel cell including the cathode electrode according to the present invention will be described in detail.
In the present invention, in order to secure the reaction sites of the three-phase interface, it is preferable to establish the following three elements (1) to (3).
(1) The present invention forms a composite metal oxide having a protrusion shape of 5nm to 15nm on the surface of a catalyst-supporting conductor, and thus has good wettability with an ionomer, a high platinum efficiency, and the ability to discharge water and maintain continuous hydrophobicity that enables the catalyst to be in close contact with the ionomer during operation of the catalyst.
(2) In the present invention, the complex metal oxide contains pyrochlore-type Sn2Ta2O7And/or Sn2Nb2O7The catalyst metal particles of (2) have an oxygen adsorption/desorption property, and the catalyst metal particles are in contact with the surface of the metal oxide, so that oxygen is not dissolved in the produced moisture, and can be efficiently supplied to the catalyst metal particles.
(3) In the present invention, the solder paste will contain pyrochlore type Sn2Ta2O7And/or Sn2Nb2O7The complex metal oxide having an oxygen adsorption/desorption property of the crystal structure of (1) is provided so as to be in contact with the catalyst-supporting conductor and the catalytic metal particles to have electron conductivity, whereby electrons can be supplied to the reaction sites of the three-phase interface on the surface of the catalytic metal particles. At the same time, the metal oxide can prevent corrosion of the catalyst-supporting conductor.
That is, the first aspect of the present invention is the invention of a fuel cell cathode electrode having a catalyst layer containing a catalyst-supporting conductor and an ionomer, wherein preferably, the surface of the catalyst-supporting conductor is formed with a projected pyrochlore-type Sn2Ta2O7、Sn2Nb2O7And/or Ta doped SnO2The conductive composite metal oxide of crystal structure (2) further comprises catalytic metal particles supported on the surface of the conductive composite metal oxide.
The cathode electrode of the present invention further comprises fine pyrochlore-type Sn in a protrudent form supported on the surface of the catalyst-supporting conductor2Ta2O7、Sn2Nb2O7And/or Ta doped SnO2In the case of the conductive composite metal oxide having a crystal structure of (3), since the protrusions are formed to have continuous hydrophobicity, and the catalyst metal particles are supported on the surface of the conductive composite metal oxide, electrons are conducted to the catalyst metal particles by oxygen defects of the conductive composite metal oxide, and thenSuccessively, by the above pyrochlore type Sn2Ta2O7、Sn2Nb2O7And/or Ta doped SnO2The oxygen carrier ensures a diffusion path of oxygen molecules directly to the catalyst metal particles.
As a result, due to the continuous hydrophobicity, hydrogen ion conduction, and pyrochlore-type Sn2Ta2O7、Sn2Nb2O7And/or Ta doped SnO2The electron conductivity and oxygen carrier property of the crystal structure of (a) can ensure that electrons and oxygen molecules are associated on the surface of the catalyst metal particles, and the exchange current density in the electrode reaction can be increased, and overvoltage can be reduced. That is, high electrode characteristics can be obtained. In particular, if the polymer electrolyte fuel cell is used as a cathode electrode of a polymer electrolyte fuel cell, overvoltage of an oxygen reduction reaction of the cathode electrode can be effectively reduced, and thus electrode characteristics of the cathode electrode can be improved. In particular, although oxygen deficiency occurs during fuel cell operation, the present invention can maintain high electrode characteristics even during long-term operation.
The present invention is capable of maintaining hydrophobicity which is durable against overvoltage and corrosion caused by hydrogen peroxide by forming protrusions having a height and a spacing of 5nm to 15nm, which are composed of a conductive composite metal oxide, on the surface of a catalyst carrier conductor composed of a particle diameter of 20nm to 50 nm.
The conductive composite metal oxide of the present invention has pyrochlore type Sn2Ta2O7And/or Sn2Nb2O7In the case of the crystal structure of (3), holes are generated due to oxygen defects, and the crystal has P-type semiconductor characteristics, and can realize electron conductivity.
Further, pyrochlore type Sn usable in the present invention2Ta2O7And/or Sn2Nb2O7The crystal of (a) is one of the oxygen carrier materials having the following functions: the adsorption and desorption of oxygen can be reversibly repeated by the oxygen defects of the crystal according to the change of the oxygen concentration in the vicinity. Namely, it isCan be at O2At a relatively high concentration, oxygen is adsorbed at O2Oxygen is desorbed under the atmosphere with lower concentration.
In the present invention, pyrochlore-type Sn is supported on the surface2Ta2O7And/or Sn2Nb2O7The catalyst-supporting conductor of (3) is preferably porous carbon powder, graphite powder or graphene powder.
Secondly, in the invention of the solid polymer fuel cell, it is preferable that the cathode electrode has a catalyst layer containing a catalyst supporting conductor and an ionomer, and a catalyst layer containing pyrochlore-containing Sn is further supported on a surface of the catalyst supporting conductor2Ta2O7And/or Sn2Nb2O7Or Ta-doped SnO which is not an oxygen adsorption/desorption body2And catalyst metal particles on the surface thereof.
As described above, the cathode electrode of the present invention having excellent electrode characteristics for oxygen reduction reaction as described above can constitute a polymer electrolyte fuel cell having high cell output. As described above, the cathode electrode of the present invention can prevent oxidation and elution of platinum, decomposition of sulfonic acid groups of an ionomer, and corrosion of a catalyst-supporting conductor (conductive carbon) due to an increase in overvoltage during a running load fluctuation cycle and a start-stop cycle of an automobile, and has excellent durability, and therefore, the solid polymer fuel cell of the present invention including the cathode electrode can stably obtain a high cell output for a long period of time.
As shown in fig. 1, the surface of the catalyst carrier conductor is covered with a composite metal oxide having a fine protrusion shape. Catalyst metal particles are supported on the surface of the composite metal oxide. In such composite particles, the protrusions act as spacers, and the ionomer covers to the apexes of the protrusions with a uniform thickness.
As shown in fig. 2, first, hydrogen ions are conducted in the ionomer to move to the surface of the catalyst metal particles. Then, electrons pass from the catalyst carrier conductor through the composite metal oxide having conductivity and move to the surface of the catalyst metal particle. Further, among the oxygen molecules, oxygen stored in the above-described composite oxide moves to the surface of the catalyst metal particle. In this way, the cathode electrode of the present invention establishes reaction sites at the three-phase interface on the surface of the catalyst metal particles, and performs an oxygen reduction reaction. This oxygen reduction reaction is shown in formula 1.
[ solution 1]
O2+4H++4e-→2H2O
The present invention is to support a pyrochlore-type Sn having a projection on the surface of a catalyst-supporting conductor2Ta2O7And/or Sn2Nb2O7The conductive composite metal oxide of (3). Since the fine protrusions have continuous hydrophobicity, the catalyst and the ionomer can be kept in close contact with each other even at high output, and a large amount of hydrogen ions can reach the catalyst metal particles.
As for oxygen, at the time of low output of the fuel cell, the amount of oxygen consumed in the catalyst is small, and the oxygen concentration in the vicinity of the oxygen adsorption/desorption body is high, so that the remaining oxygen is adsorbed by the oxygen adsorption/desorption body. On the other hand, since the amount of oxygen consumed in the catalyst is large and the oxygen concentration in the vicinity of the oxygen adsorption/desorption body is low, oxygen directly moves from the composite metal oxide to the catalyst metal particles, and therefore, oxygen is not affected by gas diffusion in the catalyst layer, and oxygen is dissolved in the produced water, and oxygen is reduced on the catalyst, thereby further improving the fuel cell performance.
The electrode reaction proceeds at sites where the reactant gases, catalyst, and electrolyte associate, referred to as three-phase interfaces. The supply of oxygen to the three-phase interface is an important topic. When the output of the battery is increased, a large amount of oxygen is required for the reaction, and if there is no oxygen in the vicinity of the catalyst, the power generation characteristics are drastically reduced. In the conventional technique, oxygen is supplied at a high concentration, but as shown in fig. 1, the actual reaction proceeds at a three-phase interface (near the catalyst), and therefore, if oxygen is not supplied thereto, the capacity cannot be sufficiently exhibited. In particular, in the case of increasing the output, the amount of oxygen consumed on the catalyst surface increases, but the diffusion rate of oxygen from the outside to the catalyst surface hardly changes. Therefore, when the consumption rate of oxygen on the catalyst surface exceeds the supply rate of oxygen to the catalyst surface at a certain rate or more, the power generation characteristics are degraded due to oxygen shortage in the vicinity of the catalyst. In contrast, as shown in fig. 2, in the present invention, the rate of supply of oxygen to the surface of the catalyst is increased, thereby preventing a decrease in power generation characteristics due to oxygen deficiency in the vicinity of the catalyst.
The cathode electrode of the polymer electrolyte fuel cell of the present invention includes a catalyst layer, but preferably includes a catalyst layer and a gas diffusion layer disposed adjacent to the catalyst layer. As a constituent material of the gas diffusion layer, for example, a porous body having electron conductivity (for example, carbon cloth or carbon paper) is used.
The catalyst layer of the cathode electrode contains pyrochlore-type Sn having water repellency, conductivity and oxygen adsorption/desorption properties due to the presence of the protrusions2Ta2O7And/or Sn2Nb2O7The electrode reaction speed of the cathode electrode is improved by reducing the overvoltage for the oxygen reduction reaction in the cathode electrode. On the other hand, Ta-doped SnO having no oxygen adsorption/desorption properties2In the composite metal oxide, the electrode reaction rate of the cathode electrode can be increased by reducing the overvoltage for the oxygen reduction reaction in the cathode electrode.
Furthermore, pyrochlore-type Sn contained in the catalyst layer2Ta2O7And/or Sn2Nb2O7The content of the composite metal oxide is preferably 0.01 to 30% by mass, and more preferably 0.01 to 20% by mass, based on the total amount of the catalyst-supported conductor, the polymer electrolyte, and the catalyst metal particles. Here, pyrochlore type Sn2Ta2O7And/or Sn2Nb2O7When the content of (3) is less than 0.01% by mass, the hydrophobicity, electron conductivity and oxygen adsorption/desorption properties are lowered, and separation of the ionomer from the catalyst metal particles, dissolution of oxygen into the produced water, oxidation and elution of the catalyst metal, decomposition of the sulfonic acid group of the ionomer, and catalyst-supporting conductivity are causedCorrosion of the electrode body does not allow sufficient oxygen reduction reaction, and continuous power generation tends to be difficult. On the other hand, pyrochlore type Sn2Ta2O7And/or Sn2Nb2O7When the content of the composite metal oxide exceeds 30 mass%, the content of the ionomer contained in the catalyst layer is relatively decreased, and as a result, the number of reaction sites that effectively function in the catalyst layer is decreased, and it is therefore difficult to obtain high electrode characteristics.
On the other hand, Ta-doped SnO contained in the catalyst layer2The content of the composite metal oxide is preferably 0.01 to 30% by mass, and more preferably 0.01 to 20% by mass, based on the total amount of the catalyst-supported conductor, the polymer electrolyte, and the catalyst metal particles. If Ta is doped with SnO2When the content of (2) is less than 0.01% by mass, the hydrophobicity, electron conductivity and oxygen adsorption/desorption properties are lowered, and separation of the ionomer from the catalyst metal particles, dissolution of oxygen into the produced water, oxidation and elution of the catalyst metal, decomposition of the sulfonic acid group of the ionomer and corrosion of the catalyst-supporting conductor occur, so that a sufficient oxygen reduction reaction cannot be performed, and a tendency to make continuous power generation difficult increases. In addition, if Ta is doped with SnO2When the content of the composite metal oxide exceeds 30 mass%, the content of the ionomer contained in the catalyst layer is relatively decreased, and as a result, the number of reaction sites that effectively function in the catalyst layer is decreased, and it is therefore difficult to obtain high electrode characteristics.
Doping Ta as described above with SnO2In SnO2The content of medium Ta is preferably 0.1 to 10 mass%, more preferably 0.5 to 5.0 mass%. If the content of Ta is less than 0.1 mass%, the association of electrons to the three-phase interface of the catalyst metal is reduced, and the power generation capacity is reduced.
The catalyst contained in the catalyst-supporting conductor of the cathode electrode of the present invention is not particularly limited, but is preferably platinum, a platinum alloy, or a core-shell type (for example, the shell layer 6 surrounding the core layer 5 shown in fig. 4 is platinum, and the core layer 5 is an alloy selected from Pd, Pt, Ru, and/or Co). Further, the catalyst-supporting conductor is not particularly limited, but is preferably a catalyst-supporting conductorHas a specific surface area of 200m2Carbon material per g or more. For example, carbon black, graphite, graphene, or the like is preferably used.
The ionomer contained in the catalyst layer of the present invention is preferably a fluorine-containing ion exchange resin, and particularly preferably a sulfonic acid type perfluorocarbon polymer. The sulfonic acid type perfluorocarbon polymer is chemically stable for a long period of time and rapidly conducts hydrogen ions in the cathode electrode.
The thickness of the catalyst layer of the cathode electrode of the present invention is preferably 1 to 50 μm, and more preferably 5 to 20 μm, as long as it is equivalent to that of a conventional polymer solid electrolyte interposed between an anode electrode and a cathode electrode.
In a polymer electrolyte fuel cell, generally, the overvoltage of the oxygen reduction reaction at the cathode electrode is very large compared to the overvoltage of the hydrogen oxidation reaction at the anode electrode, so that decomposition of sulfonic acid groups of the ionomer, oxidation and elution of the catalyst metal, and corrosion of the catalyst carrier conductor due to the generated hydrogen peroxide are likely to occur. In addition, the hydrophobic effect prevents dissolution of oxygen into the product water, and the oxygen adsorption/desorption effect increases the oxygen concentration at the reaction sites in the catalyst layer, thereby suppressing overvoltage, improving the electrode characteristics of the cathode electrode which continues, and stabilizing the output characteristics of the battery.
On the other hand, the structure of the anode electrode is not particularly limited, and may have a known structure of a gas diffusion electrode, for example.
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 in a wet state. 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 preferable. 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.
The catalyst layer of the cathode electrode of the present invention can be prepared by using a coating solution in which a substance having a catalyst carrier conductor surface covered with a composite metal oxide having a protrusion shape and carrying catalyst metal particles on the surface thereof and an ionomer are dissolved or dispersed in a solvent or a dispersion medium. Examples of the solvent or dispersion medium used herein include alcohols, fluorinated alcohols, and fluorinated ethers. Then, the catalyst layer is formed by applying the coating liquid to a carbon cloth or the like serving as an ion-exchange membrane or a gas diffusion layer. Further, the catalyst layer can also be formed on the polymer solid electrolyte membrane by applying the coating liquid described above on a separately prepared substrate to form a coating layer and transferring the coating layer onto the polymer solid electrolyte membrane.
Here, when the catalyst layer is formed on the gas diffusion layer, the catalyst layer and the polymer solid electrolyte membrane are preferably joined by an adhesive method, a hot press method, or the like. In the case where the catalyst layer is formed on the polymer solid electrolyte membrane, the cathode electrode may be formed of only the catalyst layer, or a gas diffusion layer may be disposed adjacent to the catalyst layer as the cathode electrode.
A separator having a flow path for a normal gas formed therein is disposed outside the cathode electrode, and a gas containing hydrogen is supplied to the anode electrode and a gas containing oxygen is supplied to the cathode electrode in the flow path, thereby constituting a polymer electrolyte fuel cell.
(measurement of particle size distribution)
The particle size distribution of the catalyst metal was measured by 100 points using a transmission electron microscope (Titan cube G260-300, manufactured by FEI) and the arithmetic mean was used as the average particle size.
(measurement of shape of Complex Metal oxide)
The shape (height and spacing) of the composite metal oxide having a protrusion shape of the present invention was measured by 100 points using a transmission electron microscope (Titan cube G260-300, manufactured by FEI) in the same manner as the particle size distribution of the catalyst metal, and the arithmetic mean was taken as the height and spacing.
(measurement of conductivity)
Regarding the electrical characteristics of the composite metal oxide having a protrusion shape of the present invention, a sample in which a metal electrode is deposited on four corners of a round pellet obtained by molding the final catalyst powder is prepared, and the resistivity is measured using a hall effect measuring apparatus (manufactured by Resitest8310, TOYOTech).
(measurement of degree of hydrophobicity)
With respect to the degree of hydrophobicity of the composite metal oxide having the protrusions in the following examples 1 to 3, a sample obtained by molding the final catalyst powder into round pellets was prepared and measured by a liquid drop method (automatic minimum contact angle meter MCA-3, manufactured by synechia scientific co. Also in reference example 1 and comparative examples 1 to 3, samples in which the final catalyst powder was molded into round pellets were prepared and measured in the same manner.
Examples
The cathode electrode and the polymer electrolyte fuel cell of the present invention will be described in detail below with reference to examples and comparative examples.
(example 1)
Pt (5 mass%)/pyrochlore type Sn was prepared according to the following procedure2Ta2O7(20%)/carbon black (75% by mass) were mixed to prepare an MEA, and the MEA was assembled in a cell to evaluate the performance.
(1) Tin (II) chloride and tantalum (V) chloride were dissolved in a predetermined amount in pure water, and stirred for 2 hours.
(2) Carbon black (Ketjen black EC300J, BET specific surface area 800 g/m)2Manufactured by Lion Specialty Chemicals) was adjusted to a powder form, and a predetermined amount of the powder was added to pure water and stirred to prepare a suspension.
(3) The solution of (1) was slowly added to the suspension with stirring, and the pH was adjusted to 1.5 with dilute hydrochloric acid to maintain the stateFor 3 hours. Then, the filtration and the washing were repeated three times to obtain carbon black particles coated with Sn2Ta2O7The carbon black powder of (1).
(4) Then, the coating obtained in (3) is coated with Sn2Ta2O7The carbon black powder of (2) was dispersed in pure water with stirring, and a predetermined amount of chloroplatinic acid (IV) solution (1 mass% in terms of platinum) was added. A small amount of ethanol was slowly added thereto, heated to 40 ℃ and held for 3 hours. Platinum on Sn2Ta2O7The surface of the composite metal oxide of (3) is reduced.
(5) Thereafter, the mixture was repeatedly filtered and washed three times, dried at 80 ℃ for 12 hours, pulverized in a mortar, and fired at 500 ℃ for 2 hours in an atmospheric firing furnace. And crushing by using the mortar again.
(6) The Pt/pyrochlore type Sn thus obtained was subjected to a transmission electron microscope2Ta2O7Carbon Black powder the average particle diameter of the platinum catalyst metal particles was 3nm, and the pyrochlore type Sn2Ta2O7The average height was 10nm and the average interval (pitch) was 10 nm. Then, the obtained powder was formed into pellets of 20mm in diameter by 5mm in thickness by using a press, and the degree of hydrophobicity was measured by a liquid drop method at a contact angle with water. The contact angle is 150 degrees. When the resistivity was measured using the pellets, the resistivity was 0.1 Ω · cm.
(7) Then, the above Pt/pyrochlore type Sn is added2Ta2O7Carbon black was mixed in a predetermined amount with ion-exchanged water, an ionomer electrolyte solution (Nafion D520), ethanol, and polyethylene glycol to prepare (Nafion/Carbon ═ 1.0 mass%, Pt (5 mass%)/pyrochlore Sn ═2Ta2O7(20%)/carbon black (75% by mass).
(8) The catalyst ink (6 mil in thickness) was cast on a Teflon (registered trademark) resin film, dried, and cut out to 25 (cm)2) As an electrode film.
(9) When the electrode film was completely dissolved and subjected to ICP analysis, Pt was 0.3mg/cm2，Sn2Ta2O7Is 1.2mg/cm2。
(10) The obtained cathode electrode film and an electrode film composed of the commercially available catalyst described in comparative example 1 as an anode electrode were thermally pressure bonded (150 ℃) to a polymer solid electrolyte membrane (nafion nr211, t ═ 25 μm) to prepare an MEA.
(11) The MEA was assembled in a cell, and performance evaluation was performed.
(example 2)
A catalyst metal using a core-shell type catalyst metal (5 mass%)/pyrochlore type Sn was prepared in the same manner as in example 1, except that the catalyst metal was replaced with a core-shell type catalyst metal (shell layer Pt/core layer Pd · Ru · Co alloy) from a Pt single metal in example 22Ta2O7(20%)/carbon black (75% by mass) MEA, performance evaluation was performed as a single cell unit.
The core-shell catalyst metal was prepared as follows.
(1) The coating obtained in (3) of example 1 was covered with Sn2Ta2O7The carbon black powder of (1) was dispersed in pure water with stirring, and predetermined amounts of each of a palladium chloride solution (1 mass% in terms of Pd), a ruthenium chloride solution (1 mass% in terms of Ru), and a cobalt chloride solution (1 mass% in terms of Co) were added.
(2) A small amount of ethanol was slowly added thereto, heated to 40 ℃ and held for 3 hours. Pd, Ru and Co in Sn2Ta2O7The surface reduction of the composite metal oxide of (3). Thereafter, the mixture was repeatedly filtered and washed three times, dried at 80 ℃ for 12 hours, pulverized in a mortar, and fired at 500 ℃ for 2 hours in an atmospheric firing furnace. And crushing by using the mortar again.
(3) Subsequently, Sn of the catalyst having a core part supported thereon obtained in (2)2Ta2O7The coated carbon black powder was dispersed in pure water with stirring, and a predetermined amount of chloroplatinic acid (IV) solution was added. A small amount of ethanol was slowly added thereto, heated to 40 ℃ and held for 3 hours.
(4) Thereafter, the mixture was repeatedly filtered and washed three times, dried at 80 ℃ for 12 hours, pulverized in a mortar, and fired at 500 ℃ for 2 hours in an atmospheric firing furnace. And crushing by using the mortar again.
(5) The obtained core-shell type catalyst (Pt/Pd. Ru. Co alloy)/pyrochlore type Sn was subjected to transmission electron microscopy2Ta2O7Carbon Black powder the average particle diameter of the core-shell catalyst (Pt/Pd Ru/Co alloy) particles was 3nm, and the pyrochlore type Sn2Ta2O7The average height was 10nm and the average interval (pitch) was 10 nm. Then, the obtained powder was formed into pellets of 20mm in diameter by 5mm in thickness by using a press, and the degree of hydrophobicity was measured by a liquid drop method at a contact angle with water. The contact angle is 150 degrees. When the resistivity was measured using the pellets, the resistivity was 0.1 Ω · cm.
(6) Next, the core-shell catalyst (Pt/Pd. Ru. Co alloy)/pyrochlore type Sn was added2Ta2O7Carbon black was mixed in a predetermined amount with ion exchange water, an ionomer electrolyte solution (Nafion D520), ethanol, and polyethylene glycol to prepare a mixture (Nafion/Carbon ═ 1.0 mass%, core-shell catalyst (Pt/Pd · Ru · Co alloy) (5 mass%)/pyrochlore type Sn2Ta2O7(20%)/carbon black (75% by mass).
(7) The catalyst ink (6 mil in thickness) was cast on a Teflon (registered trademark) resin film, dried, and cut out to 25 (cm)2) As an electrode film.
(8) When the electrode film was completely dissolved and subjected to ICP analysis, Pt was 0.05mg/cm2Pd of 0.03mg/cm2Ru is 0.10mg/cm2Co of 0.11mg/cm2，Sn2Ta2O7Is 1.2mg/cm2。
(9) The obtained cathode electrode film and an electrode film composed of the commercially available catalyst described in comparative example 1 as an anode electrode were thermally pressure bonded (150 ℃) to a polymer solid electrolyte membrane (nafion nr211, t ═ 25 μm) to prepare an MEA.
(10) The MEA was assembled in a cell, and performance evaluation was performed.
(example 3)
In example 3, pyrochlore type Sn was used2Ta2O7SnO doped by Ta2Except for this, SnO doped with core-shell type catalytic metal (5 mass%)/Ta was prepared in the same manner as in example 22(20%)/carbon black (75% by mass) MEA, performance evaluation was performed as a single cell unit.
The Ta-doped SnO was prepared by the following procedure2The composite metal oxide of (3).
(1) Tin (II) chloride was dissolved in a predetermined amount in pure water and stirred for 2 hours.
(2) Carbon black (Ketjen black EC300J, BET specific surface area 800 g/m)2Manufactured by Lion Specialty Chemicals) was adjusted to a powder form, and a predetermined amount of the powder was added to pure water and stirred to prepare a suspension.
(3) The solution of (1) was slowly added to the suspension with stirring, and the pH was adjusted to 1.5 with dilute hydrochloric acid, and the mixture was kept for 3 hours.
(4) Tantalum (V) chloride was dissolved in a predetermined amount in pure water and stirred for 2 hours.
(5) Subsequently, while stirring the suspension of (3), a predetermined amount of the above tantalum (V) chloride solution was gradually added, and the mixture was heated to 30 ℃ and held for 3 hours.
(6) Then, filtering and washing are carried out repeatedly for three times to obtain Ta-doped SnO2The carbon black powder of (1).
(7) Taking a small amount of the above-mentioned Ta-doped SnO2The carbon black powder of (3) was dried at 80 ℃ for 12 hours, pulverized in a mortar, and fired at 500 ℃ for 2 hours in an atmospheric firing furnace.
(8) Coating the obtained coating with Ta-doped SnO2When the carbon black powder of (1) is completely dissolved and subjected to ICP analysis, it is in SnO2In which 2.1 mass% of Ta is contained.
(9) The obtained core-shell catalyst (Pt/Pd. Ru. Co alloy)/Ta was doped with SnO by transmission electron microscope2Carbon Black powder the core-shell catalyst (Pt/Pd Ru Co alloy) particles had an average particle diameter of 3nm, doping SnO with respect to Ta2The average height was 10nm and the average interval (pitch) was 10 nm. Then, the obtained powder was formed into pellets of 20mm in diameter by 5mm in thickness by using a press, and the degree of hydrophobicity was measured by a liquid drop method at a contact angle with water. The contact angle was 145 degrees. When the resistivity was measured using the pellets, the resistivity was 0.2 Ω · cm.
(10) Next, the core-shell catalyst (Pt/Pd. Ru. Co alloy)/Ta was doped with SnO2Carbon black was mixed in a predetermined amount with ion exchange water, an ionomer electrolyte solution (Nafion D520), ethanol, and polyethylene glycol to prepare a mixture (Nafion/Carbon ═ 1.0 mass%, core-shell catalyst (Pt/Pd · Ru · Co alloy) (5 mass%)/pyrochlore type Sn2Ta2O7(20%)/carbon black (75% by mass).
(11) The catalyst ink (6 mil in thickness) was cast on a Teflon (registered trademark) resin film, dried, and cut out to 25 (cm)2) As an electrode film.
(12) When the electrode film was completely dissolved and subjected to ICP analysis, Pt was 0.05mg/cm2Pd of 0.03mg/cm2Ru is 0.10mg/cm2Co of 0.11mg/cm2Ta doped SnO2Is 1.2mg/cm2。
(13) The obtained cathode electrode film and an electrode film composed of the commercially available catalyst described in comparative example 1 as an anode electrode were thermally pressure bonded (150 ℃) to a polymer solid electrolyte membrane (nafion nr211, t ═ 25 μm) to prepare an MEA.
(14) The MEA was assembled in a cell, and performance evaluation was performed.
(reference example 1)
Reference example 1 except that pyrochlore type Sn was removed2Ta2O7Except that, in the same manner as in example 2, an MEA using core-shell type catalytic metal (5 mass%)/carbon black (75 mass%) was prepared, and performance evaluation was performed on a single unit cell.
(1) When the obtained powder of the core-shell catalyst (Pt/Pd · Ru · Co alloy)/carbon black was observed by a transmission electron microscope, the average particle diameter of the core-shell catalyst (Pt/Pd · Ru · Co alloy) particles was 3 nm. Then, the obtained powder was formed into pellets of 20mm in diameter by 5mm in thickness by using a press, and the degree of hydrophobicity was measured by a liquid drop method at a contact angle with water. The contact angle is 90 degrees. When the resistivity was measured using the pellets, the resistivity was 0.5 Ω · cm.
(2) Next, the core-shell catalyst (Pt/Pd · Ru · Co alloy)/Carbon black described above was mixed in a predetermined amount into ion-exchanged water, an ionomer electrolyte solution (Nafion D520), ethanol, and polyethylene glycol to prepare a catalyst ink (Nafion/Carbon ═ 1.0 mass%, core-shell catalyst (Pt/Pd · Ru · Co alloy) (5 mass%)/Carbon black (95 mass%).
(3) The catalyst ink (6 mil in thickness) was cast on a Teflon (registered trademark) resin film, dried, and cut out to 25 (cm)2) As an electrode film.
(4) When the electrode film was completely dissolved and subjected to ICP analysis, Pt was 0.05mg/cm2Pd of 0.03mg/cm2Ru is 0.10mg/cm2Co of 0.11mg/cm2。
(5) The obtained cathode electrode film and an electrode film composed of the commercially available catalyst described in comparative example 1 as an anode electrode were thermally pressure bonded (150 ℃) to a polymer solid electrolyte membrane (nafion nr211, t ═ 25 μm) to prepare an MEA.
(6) The MEA was assembled in a cell, and performance evaluation was performed.
Comparative example 1
In comparative example 1, an MEA was prepared using TEC10E50E (50 mass% Pt, manufactured by the field precious metal industry) in which platinum was supported on commercially available carbon black, and the MEA was incorporated into a cell to evaluate the performance.
(1) When the catalyst powder of TEC10E50E, which is commercially available, was observed by a transmission electron microscope, the average particle diameter of the platinum catalyst metal particles was 4 nm. Then, the obtained powder was formed into pellets of 20mm in diameter by 5mm in thickness by using a press, and the degree of hydrophobicity was measured by a liquid drop method at a contact angle with water. The contact angle is 90 degrees. When the resistivity was measured using the pellets, the resistivity was 0.01 Ω · cm.
(2) Next, the above commercially available catalyst powder of TEC10E50E was mixed in a predetermined amount into ion-exchanged water, an ionomer electrolyte solution (Nafion D520), ethanol, and polyethylene glycol to prepare a catalyst ink (Nafion/Carbon ═ 1.0 mass%, Pt (5 mass%)/Carbon black (95 mass%).
(3) The catalyst ink (6 mil in thickness) was cast on a Teflon (registered trademark) resin film, dried, and cut out to 25 (cm)2) As an electrode film.
(4) When the electrode film was completely dissolved and subjected to ICP analysis, Pt was 0.3mg/cm2。
(5) The obtained electrode films were used for both the cathode and anode electrodes, and were thermocompression bonded (150 ℃) to a polymer solid electrolyte membrane (nafion nr211, t ═ 25 μm) to prepare an MEA.
(6) The MEA was assembled in a cell, and performance evaluation was performed.
Comparative example 2
In comparative example 2, instead of pyrochlore type Sn2Ta2O7Using pyrochlore type Ce2Zr2O7As the complex metal oxide, in pyrochlore type Ce2Zr2O7An MEA was produced in the same manner as in example 1, and the MEA was incorporated into a cell to evaluate the performance, except that the composite metal oxide and the catalytic metal particles were each separately supported on carbon black without supporting the catalytic metal particles thereon.
(1) Predetermined amounts of diammonium cerium nitrate and zirconyl nitrate were dissolved in pure water and stirred for 2 hours.
(2) After evaporation of water at 120 ℃ vacuum drying was carried out. Thereafter, firing was carried out in an atmospheric firing furnace at 350 ℃ for 5 hours.
(3) In a reducing gas (H)22%) at 900 ℃ for 2 hours, and then switched to inert gas (N)2) And (5) slowly cooling.
(4) The obtained powder was pulverized in a mortar, immersed in an aqueous dinitrodiamine platinum solution and stirred, evaporated at 120 ℃ and dried. Platinum was 5 mass% based on the powder.
(5) Further, after pulverization in a mortar, firing was carried out in an atmospheric firing furnace at 500 ℃ for 2 hours. And crushing by using the mortar again.
(6) The obtained Pt/pyrochlore type Ce was subjected to a transmission electron microscope2Zr2O7Carbon black powder the average particle diameter of the platinum catalyst metal particles was 3 nm. Then, the obtained powder was formed into pellets of 20mm in diameter by 5mm in thickness by using a press, and the degree of hydrophobicity was measured by a liquid drop method at a contact angle with water. The contact angle is 75 degrees. When the resistivity was measured using the pellets, the resistivity was 1.5. omega. cm.
(7) The Pt/pyrochlore type Ce thus obtained2Zr2O7Carbon black was mixed in a predetermined amount with ion-exchanged water, an ionomer electrolyte solution (Nafion D520), ethanol, and polyethylene glycol to prepare (Nafion/Carbon ═ 1.0 mass%, Pt (5 mass%)/pyrochlore-type Ce2Zr2O (20 mass%)/carbon black (95 mass%) of a catalyst ink.
(8) The catalyst ink (6 mil in thickness) was cast on a Teflon (registered trademark) resin film, dried, and cut out to 25 (cm)2) As an electrode film.
(9) When the electrode film was completely dissolved and subjected to ICP analysis, Pt was 0.3mg/cm2Pyrochlore type Ce2Zr2O is 1.2mg/cm2。
(10) The obtained cathode electrode film and an electrode film composed of the commercially available catalyst described in comparative example 1 as an anode electrode were thermally pressure bonded (150 ℃) to a polymer solid electrolyte membrane (nafion nr211, t ═ 25 μm) to prepare an MEA.
(11) The MEA was assembled in a cell, and performance evaluation was performed.
Comparative example 3
Comparative example 3 an MEA was prepared in the same manner as in comparative example 1 except that fluorosilane treatment (0.1 mass%)/Pt (5 mass%)/carbon black (94.9 mass%) was used, and the MEA was incorporated in a cell to evaluate the performance.
(1) First, a predetermined amount of tridecafluorooctyltriethoxysilane (Dynasylan F8261, manufactured by EVONIK) was added to ethanol with stirring, and the mixture was kept in this state for 0.5 hour. Subsequently, a predetermined amount of the Pt/carbon black powder obtained in comparative example 1 was added, and the state was maintained for 2 hours. Thereafter, the filtration and the washing were repeated three times, and the mixture was dried at 80 ℃ for 5 hours.
(2) When the obtained fluorosilane-treated/Pt/carbon black powder was observed by a transmission electron microscope, the average particle diameter of the platinum catalyst metal particles was 4 nm. Then, the obtained powder was formed into pellets of 20mm in diameter by 5mm in thickness by using a press, and the degree of hydrophobicity was measured by a liquid drop method at a contact angle with water. The contact angle is 150 degrees. When the resistivity was measured using the pellets, the resistivity was 0.8 Ω · cm.
(3) The thus obtained fluorosilane-treated/Pt/Carbon black was mixed in a predetermined amount into ion-exchanged water, an ionomer electrolyte solution (Nafion D520), ethanol, and polyethylene glycol to prepare a catalyst ink (Nafion/Carbon ═ 1.0 mass%, fluorosilane-treated (0.1 mass%)/Pt (5 mass%)/Carbon black (94.9 mass%).
(4) The catalyst ink (6 mil in thickness) was cast on a Teflon (registered trademark) resin film, dried, and cut out to 25 (cm)2) As an electrode film.
(5) When the electrode film was completely dissolved and subjected to ICP analysis, Pt was 0.3mg/cm2。
(6) The obtained cathode electrode film and an electrode film composed of the commercially available catalyst described in comparative example 1 as an anode electrode were thermally pressure bonded (150 ℃) to a polymer solid electrolyte membrane (nafion nr211, t ═ 25 μm) to prepare an MEA.
(7) The MEA was assembled in a cell, and performance evaluation was performed.
[ evaluation test of Power Generation Performance ]
In the area of the electrode of 25cm2The following power generation performance evaluation test was performed on the unit cell of (1) (JARI standard cell, japan automobile research institute). The results are shown in Table 1"power generation performance".
Anode "gas flow rate": h2 500NmL/min
Cathode: 1000NmL/min of air
"humidification temperature" anode dew point (relative humidity): 77 deg.C (RH 88%)
Cathode dew point (relative humidity): 60 deg.C (RH 42%)
Pressure setting normal pressure
The temperature of the battery monomer is 80 DEG C
[ electrochemically effective surface area (ECA) test ]
Anode "gas flow rate": h2 200NmL/min
Cathode: n is a radical of2200 → 0NmL/min (N before measurement)2Nitrogen block)
"humidification temperature" anode dew point (relative humidity): 80 deg.C (RH 100%)
Cathode dew point (relative humidity): 80 deg.C (RH 100%)
Pressure setting normal pressure
The temperature of the battery monomer is 80 DEG C
"assay conditions" five scans at 50 mV/sec were performed between 0.05V and 0.9V after nitrogen blocking.
[ evaluation of durability (potential cycling test) ]
In order to confirm the half-life of the catalyst activity in the electrochemical effective surface area (ECA) test, durability evaluation was performed under the following conditions.
Anode "gas flow rate": h2 200NmL/min
Cathode: n is a radical of2 800NmL/min
The temperature of the battery monomer is 80 DEG C
"potential cycling" potentials
Figure BDA0003302021080000181
Cycle interval 2 seconds/cycle
The half-life of ECA cycle number is shown in "durability performance" of table 1 based on the results of electrochemical effective surface area (ECA) test and durability evaluation.
Figure BDA0003302021080000191
As is clear from the results in table 1, in the fuel cell using the electrode in which the conductive composite metal oxide having a protrusion shape is supported on the surface of the catalyst-supporting conductor of the present invention, the electrical generation performance and the durability performance are excellent in the electrical conductivity, the hydrophobicity, and/or the oxygen adsorption/desorption body as compared with comparative examples 2 and 3 using the electrode formed by the ordinary oxygen adsorption/desorption body or the fluorine-based treatment. Further, it is found that the amount of platinum used can be reduced by using the core-shell of the present invention in combination.
Description of the reference numerals
1: a catalyst metal support;
2: a conductive composite metal oxide having a protrusion shape;
3: catalyst metal particles;
4: ionomers (polymeric solid electrolytes);
5: a core layer;
6: and (4) shell layer.

Claims (17)

1. A cathode electrode for a fuel cell, wherein,
the cathode electrode for a fuel cell has a catalyst layer containing a catalyst-supporting conductor and a polymer electrolyte,
the surface of the catalyst-supporting conductor is covered with a conductive composite metal oxide having protrusions,
catalyst metal particles are supported on the conductive composite metal oxide.
2. The cathode electrode for a fuel cell according to claim 1,
the height of the protrusions of the conductive composite metal oxide is 5nm to 15 nm.
3. The cathode electrode for a fuel cell according to claim 1 or 2, wherein,
the conductive composite metal oxide has hydrophobicity with a contact angle with water of 140 degrees or more.
4. The cathode electrode for a fuel cell according to any one of claims 1 to 3,
the catalyst-supporting conductor covered with the conductive composite metal oxide has a resistivity of 0.2 Ω · cm or less.
5. The cathode electrode for a fuel cell according to any one of claims 1 to 4,
the conductive composite metal oxide is an oxygen adsorption/desorption body.
6. The cathode electrode for a fuel cell according to any one of claims 1 to 5,
the conductive composite metal oxide is a p-type semiconductor.
7. The cathode electrode for a fuel cell according to any one of claims 1 to 6,
the conductive composite metal oxide contains Sn2M2O7Pyrochlore structure of (M ═ Ta and/or Nb).
8. The cathode electrode for a fuel cell according to any one of claims 1 to 4,
the conductive composite metal oxide comprises Ta-doped SnO2(Ta is more than or equal to 0.01 and less than or equal to 1.0 mass percent).
9. The cathode electrode for a fuel cell according to any one of claims 1 to 8,
the catalyst metal particles have a core-shell structure with a shell layer containing Pt.
10. The cathode electrode for a fuel cell according to claim 9,
the core layer of the core-shell structure contains an alloy of Pd and at least one selected from Pt, Ru, and Co.
11. The cathode electrode for a fuel cell according to any one of claims 1 to 10,
the catalyst-supporting conductor contains at least one selected from the group consisting of conductive carbon, graphite, graphene, and a carbon alloy.
12. A method for producing a cathode electrode for a fuel cell according to any one of claims 1 to 11, wherein,
the manufacturing method comprises the following steps: adding tin (II) chloride and tantalum (V) chloride to the suspension of the catalyst-supported conductor, and controlling the pH to 1.5-2.0 to obtain the conductive composite metal oxide.
13. The method for manufacturing a cathode electrode for a fuel cell according to claim 12,
the manufacturing method comprises a first reduction step of: heating a suspension of the catalyst-supporting conductor covered with the conductive composite metal oxide to a temperature of 40 to 80 ℃ and adding a metal salt of the catalyst constituting the nucleation layer to the suspension to reduce the resultant mixture to a catalyst metal,
in the first reduction step, a core layer of the catalytic metal particles is formed on the surface of the conductive composite metal oxide in a protruding state covering the surface of the catalyst-supporting conductor.
14. The method for manufacturing a cathode electrode for a fuel cell according to claim 13,
the manufacturing method includes a second reduction step of: adding a Pt salt solution and a reducing agent to a suspension of the catalyst-supporting conductor having the core layer of the catalyst metal particles on the surface of the protruding conductive composite metal oxide to reduce Pt,
forming a Pt shell layer of the catalyst metal particles by the second reduction process.
15. A solid polymer fuel cell comprising an anode electrode, a cathode electrode according to any one of claims 1 to 11, and a polymer electrolyte membrane disposed between the anode electrode and the cathode electrode.
16. The solid polymer fuel cell according to claim 15,
the conductive composite metal oxide contains Sn2M2O7Pyrochlore structure of (M ═ Ta and/or Nb).
17. The solid polymer fuel cell according to claim 15,
the conductive composite metal oxide comprises Ta-doped SnO2(Ta is more than or equal to 0.01 and less than or equal to 1.0 mass percent).
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