WO2015118922A1

WO2015118922A1 - Electrode catalyst and method for producing same

Info

Publication number: WO2015118922A1
Application number: PCT/JP2015/050968
Authority: WO
Inventors: 允宣内村; 伊藤　仁; 京谷　隆; 洋知西原; 弘行糸井
Original assignee: 日産自動車株式会社; 国立大学法人東北大学
Priority date: 2014-02-07
Filing date: 2015-01-15
Publication date: 2015-08-13
Also published as: JP2017060901A

Abstract

[Problem] The purpose of the present invention is to provide an electrode catalyst which has desired catalytic activity. [Solution] An electrode catalyst according to the present invention is obtained by having a carbon material loaded with a noble metal, and is characterized in that the noble metal has an average particle diameter of 1 nm or less and the loading density of the noble metal is 5-60% by mass relative to the mass of the electrode catalyst.

Description

Electrode catalyst and method for producing the same

The present invention relates to an electrode catalyst and a method for producing the same. More specifically, the present invention relates to a technique for improving the catalytic activity of an electrode catalyst used in a fuel cell.

A solid polymer fuel cell using a proton conductive solid polymer membrane operates at a lower temperature than other types of fuel cells such as a solid oxide fuel cell and a molten carbonate fuel cell. For this reason, the polymer electrolyte fuel cell is expected as a stationary power source or a power source for a moving body such as an automobile, and its practical use has been started.

In such a polymer electrolyte fuel cell, generally, an expensive noble metal catalyst represented by Pt (platinum) or a Pt alloy is used, which is a high cost factor of such a fuel cell. . For this reason, development of a technique capable of reducing the cost of fuel cells by reducing the amount of noble metal catalyst used is required.

In Patent Document 1, an electrode catalyst for a fuel cell, which is obtained by heat-treating a carbon support in an ammonia gas atmosphere, contacting the carbon support with a platinum salt solution, and heat-treating the obtained carbon support in an inert gas atmosphere. A manufacturing method is disclosed. According to this document, a functional group capable of adsorbing a platinum salt on the surface of a carbon carrier is introduced by heat treatment in an ammonia gas atmosphere, and platinum is uniformly dispersed and distributed on the surface of the carrier. Thereby, the reduction | decrease of the specific surface area of the platinum particle by aggregation and sintering is suppressed, and the electrode catalyst with which the fine platinum particle was carry | supported is obtained. As a result, in the fuel cell, high power generation efficiency can be obtained while reducing the amount of platinum used.

International Publication No. 2010/14311

However, according to the method described in Patent Document 1, the particle size of the noble metal in the electrode catalyst can be reduced, but a sufficient amount of the noble metal cannot be supported on the carbon material and has a desired catalytic activity. There was a problem that an electrode catalyst could not be obtained.

Accordingly, an object of the present invention is to provide a fuel cell electrode catalyst having a desired catalytic activity.

In order to solve the above problems, the electrode catalyst of the present invention is an electrode catalyst in which a noble metal is supported on a carbon material, the average particle diameter of the noble metal is 1 nm or less, and the noble metal loading density is an electrode catalyst. It is characterized by being 5 to 60% by mass with respect to the mass of.

It is a schematic sectional drawing which shows the basic composition of the polymer electrolyte fuel cell which concerns on one Embodiment of this invention. It is a graph showing the X-ray-diffraction (XRD) pattern about the catalyst 1, blank (only ketjen black), and a commercially available platinum carrying | support carbon catalyst (the Tanaka Kikinzoku Kogyo make, TEC10E50E). It is a graph showing the cyclic voltammogram at the time of performing electrochemical evaluation about the

catalysts

1 and 2 and the comparative catalyst 1. FIG. 3 is a graph showing the results of CO stripping for

Catalysts

1 and 2 and Comparative Catalyst 1. 3 is a graph showing the relationship between the specific surface area of platinum particles and the particle diameter for

Catalysts

1 and 2 and Comparative Catalyst 1. 2 is a high angle scattering dark field scanning transmission electron microscope (HAADF-STEM) photograph of Comparative Catalyst 1. FIG. 2 is a high angle scattering dark field scanning transmission electron microscope (HAADF-STEM) photograph of Comparative Catalyst 1. FIG. 2 is a high angle scattering dark field scanning transmission electron microscope (HAADF-STEM) photograph of Comparative Catalyst 1. FIG. 2 is a high angle scattering dark field scanning transmission electron microscope (HAADF-STEM) photograph of Comparative Catalyst 1. FIG.

<Electrocatalyst>
The electrode catalyst according to an embodiment of the present invention is formed by supporting a noble metal on a carbon material. The average particle diameter of the noble metal is 1 nm or less, and the loading density of the noble metal is 5 to 60% by mass with respect to the mass of the electrode catalyst. In the electrode catalyst of this embodiment, compared with the conventional electrode catalyst, fine noble metal particles are supported on the carbon material at a high support density, so that the surface area of the noble metal involved in the reaction is larger than that of the conventional electrode catalyst. Therefore, the electrode catalyst of this embodiment can exhibit excellent catalytic activity. Hereinafter, the electrode catalyst of this embodiment will be described. In the present specification, the “electrode catalyst” is also simply referred to as “catalyst”.

[Carbon material]
In the electrode catalyst of this embodiment, the carbon material has a role as a carrier for supporting a noble metal and a role of conducting generated electric energy to an external circuit. Such a carbon material is not particularly limited, and is not particularly limited as long as it has a specific surface area sufficient to support a noble metal in a dispersed state and sufficient conductivity. Specifically, natural graphite, artificial graphite, coke, carbon fiber, glassy carbon, activated carbon, activated carbon fiber, carbon black (Ketjen Black (registered trademark), gas furnace black (for example, Vulcan), oil furnace black, channel Black, lamp black, thermal black, acetylene black, etc.), reduced graphite oxide, reduced graphene oxide, carbon gel, manufactured by the method described in JP 2010-208887 A, International Publication No. 2009/75264, etc. Zeolite-templated carbon (ZTC) having a structure in which nano-sized band-shaped graphene is regularly connected in a three-dimensional manner is exemplified. Of these, Ketjen Black (registered trademark) and zeolite template carbon (ZTC) having a large specific surface area are preferable from the viewpoint of supporting a noble metal at a high support density. In addition, these carbon materials may be used individually by 1 type, and may be used in combination of 2 or more type.

The BET specific surface area of the carbon material is not particularly limited, but is preferably 900 m ² / g or more, more preferably 1000 to 3000 m ² / g, and further preferably 1100 to 1800 m ² / g. With the specific surface area as described above, a sufficient amount of noble metal can be supported and good gas transportability in the catalyst layer can be achieved. In addition, the BET specific surface area (m ² / g) of the catalyst can be obtained by a nitrogen adsorption method described in Examples described later.

The particle size (average primary particle size) of the carbon material is not particularly limited, but is preferably 10 to 100 nm. Alternatively, from the viewpoint of ease of loading, catalyst utilization, etc., the particle diameter (average primary particle diameter) of the carbon material is preferably 15 to 80 nm, more preferably 20 to 60 nm. Within such a range, the mechanical strength of the carbon material can be maintained, and the later-described catalyst layer can be controlled within an appropriate range. As the value of “particle diameter of carbon material”, the average particle diameter of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). A value calculated as a value is adopted. The “particle diameter” means the maximum distance among the distances between any two points passing through the center of the particle and on the particle outline.

In addition, the carbon material in this form does not necessarily need to have a porous particulate form as described above, and is not a non-porous carbon material, carbon fiber, a nonwoven fabric made of carbon fiber, carbon paper, carbon A cloth or the like may be used.

[Precious metal]
In this embodiment, the noble metal functions as a catalyst such as an electrochemical reaction. In the fuel cell, the noble metal used for the anode catalyst layer functions as a catalyst for hydrogen oxidation reaction, and the noble metal used for the cathode catalyst layer functions as a catalyst for oxygen reduction reaction. Specific examples of noble metals include platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), osmium (Os), gold (Au), silver (Ag), and these. An alloy containing at least one of these elements can be used.

Among these, platinum or a platinum-containing alloy is preferably used as the noble metal from the viewpoint of excellent catalytic activity, poisoning resistance to carbon monoxide, heat resistance, and high catalytic activity. In the case of the platinum-containing alloy, the composition of the alloy depends on the type of metal to be alloyed, but the platinum content is 30 to 90 atomic%, and the metal content to be alloyed with platinum is 10 to 70 atoms. % Is good. In general, an alloy is a generic term for a metal element having one or more metal elements or non-metal elements added and having metallic properties. The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There are things that are forming. In the present embodiment, any of them may be used.

In the electrode catalyst of the present embodiment, the noble metal has an average particle diameter of 1 nm or less. The lower limit of the average particle diameter is not particularly limited and may be 2.6 mm or more, but is usually 0.5 nm or more, preferably 0.7 nm or more, more preferably 0.8 nm or more, and further preferably Is 0.85 nm or more, most preferably 0.9 nm or more. By reducing the particle size of the noble metal in this way, the specific surface area of the noble metal is increased, so that higher catalytic activity can be exhibited. If the average particle diameter of the noble metal is as small as 1 nm or less, it is difficult to directly measure the average particle diameter. Therefore, in this specification, the specific surface area of the noble metal is measured by an electrochemical evaluation method by CO stripping described in Examples described later, and the average particle diameter is calculated from the specific surface area. In particular, when the specific surface area is 280 m ² / g or more, it is considered that the average particle diameter of the noble metal is 1 nm or less.

In the electrode catalyst of this embodiment, the loading density of the noble metal is 5 to 60% by mass, preferably 8 to 50% by mass, more preferably 10 to 30% by mass with respect to the mass of the electrode catalyst. By setting the loading density in the above range, an electrode catalyst having sufficient catalytic activity can be obtained while suppressing the cost of the catalyst. In the present specification, the mass of the noble metal in the electrode catalyst when calculating the loading density of the noble metal is determined by the method described in Examples described later. More specifically, after the fully dried electrode catalyst is alkali-melted to form a solution, an inductively coupled plasma (ICP) emission spectroscopic analyzer (SPS-manufactured by SII Nano Technology Co., Ltd.) is added to the noble metal contained in the solution. 3500 type), and this is defined as the mass of the noble metal in the electrode catalyst.

<Method for producing electrode catalyst>
Although the manufacturing method of the electrode catalyst which concerns on the above-mentioned this invention is not restrict | limited in particular, The novel manufacturing method using an organic noble metal complex as the following noble metal source is mentioned as an example. That is, the method for producing an electrode catalyst according to another aspect of the present invention includes a step of bringing a carbon material and a gaseous organic noble metal complex into contact with each other and supporting the organic noble metal complex on the carbon material (hereinafter simply referred to as “supporting step”). And a step of reducing the organic noble metal complex supported on the carbon material (hereinafter also simply referred to as “reduction step”). According to this novel manufacturing method, fine noble metal particles can be supported on the carbon material at a high supporting density, which is suitable as a method for manufacturing the above-described electrode catalyst of the present embodiment. Hereinafter, the manufacturing method of the electrode catalyst of this form is demonstrated.

[Supporting process]
In the supporting step, the carbon material and the gaseous organic noble metal complex are brought into contact with each other to support the organic noble metal complex on the carbon material.

Since the carbon material used in this embodiment is the same as the carbon material in the above-described electrode catalyst, detailed description is omitted here.

The organic noble metal complex serves as a raw material (noble metal source) for the above-mentioned electrode catalyst. An organic noble metal complex generally has a lower melting point than the noble metal itself, and can therefore become a gas at a relatively low temperature under reduced pressure conditions. The organic noble metal complex is not particularly limited, and specifically, 1,5-cyclooctadiene dimethyl platinum complex, ethylene bis (triphenylphosphine) platinum (0), tetrakis (triphenylphosphine) platinum (0), Bis (tri-tert-butylphosphine) platinum (0), (trimethyl) cyclopentadienylplatinum (IV), platinum (II) cyanide, (trimethyl) methylcyclopentadienylplatinum (IV), (trimethyl) penta And methylcyclopentadienylplatinum (IV). These organic noble metal complexes may be used alone or in combination of two or more.

The amount used (preparation amount) of the organic noble metal complex is not particularly limited, but is preferably 30 to 150% by mass, more preferably 40 to 80% by mass with respect to the mass of the carbon material. With such an amount, a sufficient organic noble metal complex can be supported on the carbon material.

In the production method of the present embodiment, it is preferable to dry the carbon material under reduced pressure conditions before bringing the carbon material into contact with the gaseous organic noble metal complex. The decompression conditions are not particularly limited and can be appropriately set by those skilled in the art, but are preferably 1.0 × 10 ⁻⁷ to 1.0 × 10 ⁻² Pa, more preferably 1.0 × 10 6. ^-7 to 1.0 × 10 ⁻⁴ Pa. In addition, the temperature at the time of drying is not particularly limited, and can be appropriately set by those skilled in the art. Drying may be performed under heating conditions as long as the carbon material is not adversely affected.

The temperature at which the carbon material and the gaseous organic noble metal complex are brought into contact with each other is not particularly limited, but is preferably 40 to 200 ° C, more preferably 60 to 150 ° C. By setting it as the said range, an organic noble metal complex can fully be vaporized, suppressing the thermal decomposition etc. of an organic noble metal complex.

The time for contacting the carbon material and the gaseous organic noble metal complex is not particularly limited, but is preferably 1 to 72 hours, more preferably 6 to 48 hours. By setting it as the above range, the particle diameter of the organic noble metal complex after being supported on the carbon material does not become too large, and a sufficient amount of the organic noble metal complex can be supported.

The supporting step in this embodiment is not particularly limited as long as the carbon material and the gaseous organic noble metal complex can be brought into contact with each other, as long as the other conditions, the apparatus to be used, and the operation method are used. As an example, a glass tube A containing an organic noble metal complex and a carbon material are placed in a glass tube B, sealed under reduced pressure, and the glass tube B is heated as in the examples described later. Thereby, the organic noble metal complex in the glass tube A becomes a gas and fills the glass tube B, and the organic noble metal complex is supported on the carbon material by contacting with the carbon material.

[Reduction process]
In the production method of this embodiment, after the supporting step, the organic noble metal complex supported on the carbon material is reduced to obtain an electrode catalyst in which the noble metal is supported on the carbon material.

In this step, the method for reducing the organic noble metal complex supported on the carbon material is not particularly limited, and a known method can be appropriately employed. As an example, a method of reducing an organic noble metal complex by heat-treating a carbon material carrying the organic noble metal complex under reduced pressure conditions (hereinafter also simply referred to as “thermal reduction method”) as in the examples described later. Is mentioned. However, this method is not limited only to the reduced pressure condition, and heat treatment may be performed in an inert atmosphere or a hydrogen atmosphere. The heat treatment conditions in the thermal reduction method are not particularly limited, but preferable conditions are as follows. The temperature during the heat treatment is preferably 150 to 400 ° C, more preferably 200 to 300 ° C. The atmospheric pressure during the heat treatment is preferably 1.0 × 10 ⁻² Pa or less, more preferably 1.0 × 10 ⁻⁷ to 1.0 × 10 ⁻⁴ Pa. The heat treatment time is preferably 0.5 to 48 hours, more preferably 1 to 12 hours. Within the above range, the organic noble metal complex supported on the carbon material can be sufficiently reduced.

In addition to the thermal reduction method described above, a method of reducing the organic noble metal complex by treating the carbon material carrying the organic noble metal complex with hydrogen (hereinafter also simply referred to as “hydrogen reduction method”) may be used. The conditions in the hydrogen reduction method are also not particularly limited, but are preferably brought into contact with a carbon material carrying an organic noble metal complex under a temperature condition of 25 to 100 ° C., preferably for 30 minutes or more. Thereby, similarly to the case of the thermal reduction method, the organic noble metal complex supported on the carbon material can be sufficiently reduced.

<Fuel cell>
In the electrode catalyst according to the present invention described above, since the fine noble metal particles are supported on the carbon material at a higher support density than the conventional electrode catalyst, the specific surface area of the noble metal involved in the reaction is higher than that of the conventional one. As a result, excellent catalytic activity can be exhibited. Therefore, the power generation performance of the fuel cell can be improved by using the electrode catalyst in the catalyst layer of the fuel cell. Therefore, according to another aspect of the present invention, there is provided a fuel cell including an electrode catalyst layer having the electrode catalyst. Hereinafter, the fuel cell of this embodiment will be described.

A fuel cell generally includes a pair of separators comprising a membrane electrode assembly (MEA), an anode separator having a fuel gas passage through which fuel gas flows, and a cathode separator having an oxidant gas passage through which oxidant gas flows. It consists of.

FIG. 1 is a schematic diagram showing a basic configuration of a polymer electrolyte fuel cell (PEFC) 1 according to an embodiment of the present invention. The PEFC 1 first includes a solid polymer electrolyte membrane 2 and a pair of catalyst layers (an anode catalyst layer 3a and a cathode catalyst layer 3c) that sandwich the membrane. The laminate of the solid polymer electrolyte membrane 2 and the catalyst layers (3a, 3c) is further sandwiched between a pair of gas diffusion layers (GDL) (anode gas diffusion layer 4a and cathode gas diffusion layer 4c). Thus, the polymer electrolyte membrane 2, the pair of catalyst layers (3a, 3c), and the pair of gas diffusion layers (4a, 4c) constitute a membrane electrode assembly (MEA) 10 in a stacked state.

In PEFC1, the MEA 10 is further sandwiched between a pair of separators (anode separator 5a and cathode separator 5c). In FIG. 1, the separators (5 a, 5 c) are illustrated so as to be positioned at both ends of the illustrated MEA 10. However, in a fuel cell stack in which a plurality of MEAs are stacked, the separator is generally used as a separator for an adjacent PEFC (not shown). In other words, in the fuel cell stack, the MEAs are sequentially stacked via the separator to form a stack. In an actual fuel cell stack, a gas seal portion is disposed between the separator (5a, 5c) and the solid polymer electrolyte membrane 2, or between the PEFC 1 and another adjacent PEFC. These descriptions are omitted in FIG.

The separators (5a, 5c) are obtained, for example, by forming a concavo-convex shape as shown in FIG. 1 by subjecting a thin plate having a thickness of 0.5 mm or less to a press treatment. The convex part seen from the MEA side of the separator (5a, 5c) is in contact with the MEA 10. Thereby, the electrical connection with MEA10 is ensured. Further, a recess (space between the separator and the MEA generated due to the concavo-convex shape of the separator) viewed from the MEA side of the separator (5a, 5c) is a gas for circulating gas during operation of the PEFC 1 Functions as a flow path. Specifically, a fuel gas (for example, hydrogen) is circulated through the gas flow path 6a of the anode separator 5a, and an oxidant gas (for example, air) is circulated through the gas flow path 6c of the cathode separator 5c.

On the other hand, the recess viewed from the side opposite to the MEA side of the separator (5a, 5c) serves as a refrigerant flow path 7 for circulating a refrigerant (for example, water) for cooling the PEFC during operation of the PEFC 1. . Further, the separator is usually provided with a manifold (not shown). This manifold functions as a connection means for connecting cells when a stack is formed. With such a configuration, the mechanical strength of the fuel cell stack can be ensured.

In the embodiment shown in FIG. 1, the separators (5a, 5c) are formed in an uneven shape. However, the separator is not limited to such a concavo-convex shape, and may be any form such as a flat plate shape and a partially concavo-convex shape as long as the functions of the gas flow path and the refrigerant flow path can be exhibited. Also good.

The fuel cell having the MEA of the present invention as described above exhibits excellent power generation performance. Here, the type of the fuel cell is not particularly limited. In the above description, the solid polymer fuel cell has been described as an example. However, in addition to the above, an alkaline fuel cell and a direct methanol fuel cell are used. And a micro fuel cell. Among them, a polymer electrolyte fuel cell (PEFC) is preferable because it is small and can achieve high density and high output. The fuel cell is useful as a stationary power source in addition to a power source for a moving body such as a vehicle in which a mounting space is limited. Among them, it is particularly preferable to use as a power source for a mobile body such as an automobile that requires a high output voltage after a relatively long time of operation stop.

The fuel used when operating the fuel cell is not particularly limited. For example, hydrogen, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, secondary butanol, tertiary butanol, dimethyl ether, diethyl ether, ethylene glycol, diethylene glycol and the like can be used. Of these, hydrogen and methanol are preferably used in that high output is possible.

Further, the application application of the fuel cell is not particularly limited, but it is preferably applied to a vehicle. The electrolyte membrane-electrode assembly of the present invention is excellent in power generation performance and durability, and can be downsized. For this reason, the fuel cell of this invention is especially advantageous when this fuel cell is applied to a vehicle from the point of in-vehicle property.

Hereinafter, although the members constituting the fuel cell of the present embodiment will be briefly described, the technical scope of the present invention is not limited only to the following embodiments.

[Catalyst layer]
The catalyst layer includes the above-described electrode catalyst and electrolyte according to the present invention. In the fuel cell of the present embodiment, the above-described electrode catalyst according to the present invention may be present in either the cathode catalyst layer or the anode catalyst layer, or may be present in both. From the viewpoint of oxygen reduction activity, the above-described electrode catalyst according to the present invention is preferably present in the anode catalyst layer.

The electrolyte is not particularly limited, but is preferably an ion conductive polymer electrolyte. Since the polymer electrolyte plays a role of transmitting protons generated around the catalyst active material on the fuel electrode side, it is also called a proton conductive polymer.

The polymer electrolyte is not particularly limited, and conventionally known knowledge can be appropriately referred to. Polymer electrolytes are roughly classified into fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes depending on the type of ion exchange resin that is a constituent material.

Examples of ion exchange resins constituting the fluorine-based polymer electrolyte include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride-per Examples thereof include fluorocarbon sulfonic acid polymers. From the viewpoint of excellent heat resistance, chemical stability, durability, and mechanical strength, these fluorine-based polymer electrolytes are preferably used, and particularly preferably fluorine-based polymer electrolytes composed of perfluorocarbon sulfonic acid polymers. Is used.

Specific examples of the hydrocarbon electrolyte include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, sulfonated poly Examples include ether ether ketone (S-PEEK) and sulfonated polyphenylene (S-PPP). These hydrocarbon polymer electrolytes are preferably used from the viewpoint of production such that the raw material is inexpensive, the production process is simple, and the selectivity of the material is high. In addition, as for the ion exchange resin mentioned above, only 1 type may be used independently and 2 or more types may be used together. Moreover, it is not restricted only to the material mentioned above, Other materials may be used.

Proton conductivity is important in polymer electrolytes responsible for proton transmission. Here, when the EW of the polymer electrolyte is too large, the ionic conductivity in the entire catalyst layer is lowered. Therefore, it is preferable that the catalyst layer of this embodiment contains a polymer electrolyte having a small EW. Specifically, the catalyst layer of this embodiment preferably has an EW of 1500 g / eq. The following polymer electrolyte is contained, More preferably, it is 1200 g / eq. The following polymer electrolyte is included, and particularly preferably 1000 g / eq. The following polymer electrolytes are included.

On the other hand, if the EW is too small, the hydrophilicity is too high and it becomes difficult to smoothly move water. From such a viewpoint, the EW of the polymer electrolyte is preferably 600 or more. Note that EW (Equivalent Weight) represents an equivalent weight of an exchange group having proton conductivity. The equivalent weight is the dry weight of the ion exchange membrane per equivalent of ion exchange group, and is expressed in units of “g / eq”.

Further, the catalyst layer includes two or more types of polymer electrolytes having different EWs in the power generation surface. At this time, the polymer electrolyte having the lowest EW among the polymer electrolytes has a relative humidity of 90% or less of the gas in the flow path. It is preferable to use in the region. By adopting such a material arrangement, the resistance value becomes small regardless of the current density region, and the battery performance can be improved. The EW of the polymer electrolyte used in the region where the relative humidity of the gas in the flow channel is 90% or less, that is, the polymer electrolyte having the lowest EW is 900 g / eq. The following is desirable. Thereby, the above-mentioned effect becomes more reliable and remarkable.

Furthermore, it is desirable to use a polymer electrolyte with the lowest EW in a region higher than the average temperature of the cooling water inlet and outlet. As a result, the resistance value is reduced regardless of the current density region, and the battery performance can be further improved.

Furthermore, from the viewpoint of reducing the resistance value of the fuel cell system, the polymer electrolyte having the lowest EW is within 3/5 from the gas supply port of at least one of the fuel gas and the oxidant gas with respect to the channel length. It is desirable to use it in the range area.

The catalyst layer of this embodiment may include a liquid proton conductive material that can connect the catalyst and the polymer electrolyte (solid proton conductive material) in a proton conductive state between the catalyst and the polymer electrolyte. By introducing a liquid proton conductive material, a proton transport path through the liquid proton conductive material is secured between the catalyst and the polymer electrolyte, and protons necessary for power generation are efficiently transported to the catalyst surface. Is possible. Thereby, since the utilization efficiency of a catalyst improves, it becomes possible to reduce the usage-amount of a catalyst, maintaining electric power generation performance. The liquid proton conductive material only needs to be interposed between the catalyst and the polymer electrolyte, and the pores (secondary pores) between the porous carriers in the catalyst layer and the pores (micropores) in the porous carrier. Or mesopores: primary vacancies).

The liquid proton conductive material is not particularly limited as long as it has ion conductivity and can exhibit a function of forming a proton transport path between the catalyst and the polymer electrolyte. Specific examples include water, protic ionic liquid, aqueous perchloric acid solution, aqueous nitric acid solution, aqueous formic acid solution, and aqueous acetic acid solution.

When water is used as the liquid proton conductive material, water as the liquid proton conductive material is introduced into the catalyst layer by moistening the catalyst layer with a small amount of liquid water or humidified gas before starting power generation. Can do. Moreover, the water produced by the electrochemical reaction during the operation of the fuel cell can be used as the liquid proton conductive material. Therefore, it is not always necessary to hold the liquid proton conductive material when the fuel cell is in operation. For example, the surface distance between the catalyst and the electrolyte is preferably 0.28 nm or more, which is the diameter of oxygen ions constituting water molecules. By maintaining such a distance, water (liquid proton conductive material) is interposed between the catalyst and the polymer electrolyte (liquid conductive material holding part) while maintaining a non-contact state between the catalyst and the polymer electrolyte. Therefore, a proton transport route by water between them can be secured.

When a material other than water, such as an ionic liquid, is used as the liquid proton conducting material, it is desirable to disperse the ionic liquid, the polymer electrolyte, and the catalyst in the solution when preparing the catalyst ink. An ionic liquid may be added when applying to the layer substrate.

For the catalyst layer, a water repellent such as polytetrafluoroethylene, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, a dispersing agent such as a surfactant, glycerin, ethylene glycol (EG), as necessary. ), A thickener such as polyvinyl alcohol (PVA) and propylene glycol (PG), and an additive such as a pore-forming agent may be contained.

The thickness (dry film thickness) of the catalyst layer is preferably 0.05 to 30 μm, more preferably 1 to 20 μm, still more preferably 2 to 15 μm. In addition, the said thickness is applied to both a cathode catalyst layer and an anode catalyst layer. However, the thickness of the cathode catalyst layer and the anode catalyst layer may be the same or different.

[Electrolyte membrane]
The electrolyte membrane is composed of a solid polymer electrolyte membrane 2 as shown in FIG. The solid polymer electrolyte membrane 2 has a function of selectively permeating protons generated in the anode catalyst layer 3a during operation of the PEFC 1 to the cathode catalyst layer 3c along the film thickness direction. The solid polymer electrolyte membrane 2 also has a function as a partition wall for preventing the fuel gas supplied to the anode side and the oxidant gas supplied to the cathode side from being mixed.

The electrolyte material constituting the solid polymer electrolyte membrane 2 is not particularly limited, and conventionally known knowledge can be appropriately referred to. For example, the fluorine-based polymer electrolyte or hydrocarbon-based polymer electrolyte described above as the polymer electrolyte can be used. At this time, it is not always necessary to use the same polymer electrolyte used for the catalyst layer.

The thickness of the electrolyte layer may be appropriately determined in consideration of the characteristics of the obtained fuel cell, and is not particularly limited. The thickness of the electrolyte layer is usually about 5 to 300 μm. When the thickness of the electrolyte layer is within such a range, the balance of strength during film formation, durability during use, and output characteristics during use can be appropriately controlled.

[Gas diffusion layer]
The gas diffusion layers (anode gas diffusion layer 4a, cathode gas diffusion layer 4c) are catalyst layers (3a, 3c) of gas (fuel gas or oxidant gas) supplied via the gas flow paths (6a, 6c) of the separator. ) And a function as an electron conduction path.

The material which comprises the base material of a gas diffusion layer (4a, 4c) is not specifically limited, A conventionally well-known knowledge can be referred suitably. For example, a sheet-like material having conductivity and porosity such as a carbon woven fabric, a paper-like paper body, a felt, and a non-woven fabric can be used. The thickness of the substrate may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. If the thickness of the substrate is within such a range, the balance between mechanical strength and diffusibility such as gas and water can be appropriately controlled.

The gas diffusion layer preferably contains a water repellent for the purpose of further improving water repellency and preventing flooding. The water repellent is not particularly limited, but fluorine-based high repellents such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Examples thereof include molecular materials, polypropylene, and polyethylene.

In order to further improve the water repellency, the gas diffusion layer has a carbon particle layer (microporous layer; MPL, not shown) made of an aggregate of carbon particles containing a water repellent agent on the catalyst layer side of the substrate. You may have.

The carbon particles contained in the carbon particle layer are not particularly limited, and conventionally known materials such as carbon black, graphite, and expanded graphite can be appropriately employed. Among them, carbon black such as oil furnace black, channel black, lamp black, thermal black, acetylene black and the like can be preferably used because of excellent electron conductivity and a large specific surface area. The average particle size of the carbon particles is preferably about 10 to 100 nm. Thereby, while being able to obtain the high drainage property by capillary force, it becomes possible to improve contact property with a catalyst layer.

Examples of the water repellent used for the carbon particle layer include the same water repellents as described above. Among these, fluorine-based polymer materials can be preferably used because of excellent water repellency, corrosion resistance during electrode reaction, and the like.

The mixing ratio of the carbon particles to the water repellent in the carbon particle layer is about 90:10 to 40:60 (carbon particles: water repellent) by weight in consideration of the balance between water repellency and electronic conductivity. It is good. In addition, there is no restriction | limiting in particular also about the thickness of a carbon particle layer, What is necessary is just to determine suitably in consideration of the water repellency of the gas diffusion layer obtained.

[Separator]
The separator has a function of electrically connecting each cell in series when a plurality of single cells of a fuel cell such as a polymer electrolyte fuel cell are connected in series to form a fuel cell stack. The separator also functions as a partition that separates the fuel gas, the oxidant gas, and the coolant from each other. In order to secure these flow paths, as described above, each of the separators is preferably provided with a gas flow path and a cooling flow path. As a material constituting the separator, conventionally known materials such as dense carbon graphite, carbon such as a carbon plate, and metal such as stainless steel can be appropriately employed without limitation. The thickness and size of the separator and the shape and size of each flow path provided are not particularly limited, and can be appropriately determined in consideration of the desired output characteristics of the obtained fuel cell.

The manufacturing method of the fuel cell is not particularly limited, and conventionally known knowledge can be appropriately referred to in the field of the fuel cell.

Furthermore, a fuel cell stack having a structure in which a plurality of membrane electrode assemblies are stacked and connected in series via a separator may be formed so that the fuel cell can exhibit a desired voltage. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

The PEFC and membrane electrode assembly of the present embodiment described above can exhibit excellent power generation performance because the electrode catalyst layer according to the present invention is used for the catalyst layer. Therefore, the PEFC of this embodiment and the fuel cell stack using the PEFC can be mounted on a vehicle as a driving power source, for example.

The present invention will be described in further detail using the following examples. However, the technical scope of the present invention is not limited only to the following examples. In the following, room temperature means (25 ° C.).

<Manufacture of electrode catalyst>
[Example 1]
80 mg of 1,5-cyclooctadiene dimethylplatinum complex was placed in a glass tube A, and quartz wool was filled in the mouth of the glass tube. The glass tube A is put into a glass tube B containing 200 mg of a carbon material (Ketjen Black (registered trademark) ECP600JP, manufactured by Ketjen Black International), and the inside of the glass tube B is reduced in pressure using an oil pump (1 0.0 × 10 ⁻² Pa), only the carbon carrier contained in the glass tube B is vacuum-heated and dried, and the glass tube A is removed from the glass tube B so that the complex contained in the glass tube A does not decompose during that time. It was put on the part of the handle which was not heated. After drying the carbon support under vacuum heating, the carbon support was allowed to cool, the glass tube A was moved to the side of the glass tube B containing the carbon support, and the glass tube B was sealed with a gas burner. Next, the said glass tube B which enclosed the glass tube A was hold | maintained for 28 hours at 100 degreeC in the oil bath. As a result, the 1,5-cyclooctadiene dimethyl platinum complex sublimated and contacted the carbon material. Thereafter, the glass tube B was naturally allowed to cool to room temperature, and the carbon material adsorbed with the 1,5-cyclooctadiene dimethyl platinum complex was taken out of the glass tube B.

The carbon material adsorbed with the 1,5-cyclooctadiene dimethylplatinum complex obtained above is put into a glass tube C, and the inside of the glass tube C is reduced under pressure (1.0 × 10 ⁻⁴ Pa) using a turbomolecular pump. The glass tube C was heated from room temperature to 300 ° C. at a rate of 5 ° C./min, and then kept at 300 ° C. for 1 hour. Thereafter, the glass tube C was naturally cooled to room temperature, and the catalyst 1 was taken out from the glass tube C.

[Example 2]
160 mg of 1,5-cyclooctadiene dimethylplatinum complex was placed in a glass tube A, and quartz wool was filled in the mouth of the glass tube. The glass tube A is put into a glass tube B containing 200 mg of a carbon material (Ketjen Black (registered trademark) ECP600JP, manufactured by Ketjen Black International), and the inside of the glass tube B is reduced in pressure using an oil pump (1 0.0 × 10−2 Pa), only the carbon support contained in the glass tube B is vacuum-heated and dried, and during this time, the glass tube A is heated to the glass tube B so that the complex contained in the glass tube A is not decomposed. It was put on the part of the handle that was not done. After drying the carbon support under vacuum heating, the carbon support was allowed to cool, the glass tube A was moved to the side of the glass tube B containing the carbon support, and the glass tube B was sealed with a gas burner. Next, the said glass tube B which enclosed the glass tube A was hold | maintained for 24 hours at 150 degreeC in the oil bath. As a result, the 1,5-cyclooctadiene dimethyl platinum complex sublimated and contacted the carbon material. Thereafter, the glass tube B was naturally allowed to cool to room temperature, and the carbon material adsorbed with the 1,5-cyclooctadiene dimethyl platinum complex was taken out of the glass tube B.

The carbon material adsorbed with the 1,5-cyclooctadiene dimethylplatinum complex obtained above is placed in a glass tube C, and the inside of the glass tube C is reduced under reduced pressure (1.0 × 10 −4 Pa) using a turbomolecular pump. The glass tube C was heated from room temperature to 300 ° C. at a rate of 5 ° C./min, and then kept at 300 ° C. for 1 hour. Thereafter, the glass tube C was naturally cooled to room temperature, and the catalyst 2 was taken out from the glass tube C.

[Comparative Example 1]
0.5014 g of carbon material (Ketjen Black (registered trademark) ECP600JP, manufactured by Ketjen Black International Co., Ltd.) was placed in a 100 ml two-necked eggplant type flask together with a magnetic stirrer bar. And after performing vacuum heating drying at 150 degreeC for 6 hours, it stood to cool naturally. Subsequently, 25 ml of acetonitrile in which 255 mg of 1,5-cyclooctadienedimethylplatinum complex was dissolved was vacuum impregnated into the flask containing the carbon material using a syringe, and then stirred at room temperature for 10 minutes. After refluxing for 6 hours (the temperature of the oil bath during reflux was 110 ° C.), the mixture was allowed to cool, 25 ml of acetonitrile was added, and the solution was filtered through a membrane filter. Further, the sample was washed with 50 ml of acetonitrile, and dried under vacuum heating at 100 ° C. for 6 hours to obtain a comparative catalyst 1 (yield: 0.5357 g).

<Measurement of platinum loading density>
The platinum loading density in each catalyst obtained above was measured by the following method. First, in order to remove the water adsorbed on the catalyst, vacuum heat drying treatment was performed at 100 ° C. for 6 hours. Thereafter, about 5 mg of the catalyst is weighed in a glove box, and this is converted into a solution, and platinum contained in the obtained solution is converted into an inductively coupled plasma (ICP) emission spectroscopic analyzer (manufactured by SII Nano Technology, SPS-3500 type) ). And based on the following formula 1, the carrying density of platinum in the catalyst was calculated. The results are shown in Table 1.

From the results of Table 1, it was shown that the

catalysts

1 and 2 according to the present invention have a higher platinum loading density than the comparative catalyst 1 obtained by the conventional liquid phase loading method.

<X-ray diffraction (XRD) measurement>
X-ray diffraction measurement was performed on the catalyst 1, the blank (only Ketjen Black) obtained above, and a commercially available platinum-supported carbon catalyst (manufactured by Tanaka Kikinzoku Kogyo, TEC10E50E). X-ray diffraction measurement was performed using an XRD-6100 manufactured by Shimadzu Corporation, and the radiation source was Cu-Kα, a voltage of 30 kV, and a current of 20 mA. The results are shown in FIG.

2. From FIG. 2, in the XRD pattern of the commercially available TEC10E50E, a peak derived from platinum was observed around 40 °. However, in the XRD pattern of the catalyst 1, no peak was observed in the vicinity of 40 °, and the same pattern as the blank was shown. From this result, it was suggested that the platinum particles supported on the catalyst 1 are very fine compared to the commercially available platinum particles of TEC10E50E.

<Electrochemical evaluation>
The

catalysts

1 and 2 and the comparative catalyst 1 obtained above were subjected to electrochemical evaluation by the following method.

Catalysts

1 and 2 and Comparative Catalyst 1 were weighed 11.4 mg, 12.8 mg, and 10.4 mg, respectively, and dispersed in a mixed solution of 19 mL of water and 6 mL of isopropanol, and Nafion solution (DE521CS, 5 wt%, manufactured by Aldrich) ) 100 μL was added to prepare a catalyst ink. Thereafter, ultrasonic dispersion was performed for 1 hour or longer. 10 μL of the prepared catalyst ink was applied to a polished glassy carbon electrode (φ5.0 mm, manufactured by Hokuto Denko), and dried in a dryer at 60 ° C. for 10 minutes. The surface coating state of the electrode was confirmed by microscopic observation, and the electrode without any uncoated catalyst layer and protruding was used for evaluation.

Electrochemical measurement was performed with a normal three-chamber cell (Mick Lab). As the electrolyte solution, 0.1 M perchloric acid (Ultrapur, manufactured by Kanto Chemical Co., Inc.) was used. The counter electrode was a Pt line, and the reference electrode was a reversible hydrogen electrode (RHE). Potential control was performed using HZ-5000 (manufactured by Hokuto Denko). HR-301 (manufactured by Hokuto Denko) was used as the rotating electrode (RDE) device. The cell temperature was controlled to 25 ° C. (± 1 ° C.) using an external circulation thermostat (CHL300, manufactured by YAMATO). For the measurement of CO stripping, 1% CO Ar balance gas (manufactured by Taiyo Nippon Sanso) was used. All measurements were performed in the draft.

As a pretreatment of the electrodes, a range of 0 to 1.2 V was scanned for 20 cycles at 100 mV / s, and then measurements such as cyclic voltammetry (results are shown in FIG. 3) and convective voltammetry were performed. In the measurement of CO stripping, the electrode was held at 0.05 V for 30 minutes in an electrolyte solution saturated with 1% CO gas while rotating the electrode at 400 rpm. It was confirmed that the CO adsorption amount reached saturation under these conditions. After the CO gas in the solution was completely replaced with nitrogen, CV measurement was performed for 3 cycles from 0.05 V to 1.2 V at 20 mV / s. The CVs in the second and third cycles were observed with a clear overlap. The amount of electricity at the CO stripping peak is calculated from the difference between the response currents after the first cycle and the second cycle, and the maximum Pt coverage by CO is assumed to be 0.68, and the conversion factor is 285.6 μC · cmPt ⁻² Was applied to calculate the electrochemically active surface area. The electrochemical area (ECA) was calculated by assigning this by the amount of platinum (the result is shown in FIG. 4A).

As shown in the cyclic voltammogram of FIG. 3, the current due to the generation and oxidation of hydrogen derived from the presence of platinum was observed in any catalyst. Furthermore, it was confirmed that the amount of electricity due to adsorption / desorption of hydrogen on the platinum surface and oxidation / reduction of platinum increases as the platinum loading density increases.

From the value calculated based on the results of the CO stripping Figure 4A, the specific surface area of the platinum particles is 290 m ² / g in catalyst 1 299m ² / g, the catalyst 2 337m ² / g, with comparative catalyst 1 I understood. This value means that when the platinum particles are assumed to be spheres, the average particle diameter is 1 nm or less (see FIG. 4B).

<High-angle scattering dark field scanning transmission electron microscope (HAADF-STEM) observation>
The comparative catalyst 1 was observed with a high angle scattering dark field scanning transmission electron microscope (HAADF-STEM) in order to observe how platinum was supported. Specifically, the observation was performed using an HD-2700 scanning transmission electron microscope (STEM) manufactured by Hitachi High-Technologies Corporation at an acceleration voltage of 200 kV. The results are shown in FIGS. 5A-5D.

From the results shown in FIGS. 5A to 5D, it was confirmed that most of the platinum particles supported on the comparative catalyst 1 were 1 nm or less and the average particle diameter was 1 nm or less. Considering the result of the specific surface area of the platinum particles calculated based on the result of the above-mentioned CO stripping, the average particle diameter of the platinum particles is 1 nm or less even in the

catalysts

1 and 2 having a larger specific surface area of the platinum particles than the comparative catalyst 1 It was shown that

<Measurement of nitrogen adsorption / desorption>
Nitrogen adsorption / desorption measurements were performed on the

catalysts

1 and 2 and the blank (carbon material only) obtained above. Nitrogen adsorption / desorption measurement was performed using BELSORP mini manufactured by Nippon Bell Co., Ltd., and a multipoint method was performed at a temperature of −196 ° C. The BET specific surface area (S _BET ) was determined from the adsorption isotherm in the range of 0.01 <P / P ₀ <0.05. The _total pore volume (V _total ) was determined from the volume of adsorbed N ₂ at a relative pressure of 0.96. The micropore volume (V _micro ) was calculated by the Dubinin-Radushkevich (DR) equation using the respective nitrogen adsorption isotherm data. The mesopore volume (V _meso ) was determined by subtracting the micropore volume (V _micro ) from the total pore volume. The results when each value in the blank is set to 1.00 are shown in Table 2 below.

As shown in Table 2, it was found that in the

catalysts

1 and 2 of the present invention, the micropores were relatively smaller than the mesopores compared to the blank. From these results, it was suggested that in

Catalysts

1 and 2, a large amount of platinum was supported in the micropores.

This application is based on Japanese Patent Application No. 2014-022809 filed on February 7, 2014, the disclosure of which is incorporated by reference in its entirety.

1 Polymer electrolyte fuel cell (PEFC),
2 solid polymer electrolyte membrane,
3 catalyst layer,
3a anode catalyst layer,
3c cathode catalyst layer,
4a Anode gas diffusion layer,
4c cathode gas diffusion layer,
5 separator,
5a anode separator,
5c cathode separator,
6a Anode gas flow path,
6c cathode gas flow path,
7 Refrigerant flow path,
10 Membrane electrode assembly (MEA).

Claims

An electrode catalyst in which a noble metal is supported on a carbon material,
The noble metal has an average particle size of 1 nm or less,
The noble metal loading density is 5 to 60% by mass with respect to the mass of the electrode catalyst.
Contacting the carbon material with a gaseous organic noble metal complex to support the organic noble metal complex on the carbon material;
Reducing the organic noble metal complex supported on the carbon material;
A method for producing an electrode catalyst, comprising:
The organic noble metal complex includes 1,5-cyclooctadiene dimethylplatinum complex, ethylenebis (triphenylphosphine) platinum (0), tetrakis (triphenylphosphine) platinum (0), bis (tri-tert-butylphosphine) platinum (0), (trimethyl) cyclopentadienylplatinum (IV), platinum (II) cyanide, (trimethyl) methylcyclopentadienylplatinum (IV), and (trimethyl) pentamethylcyclopentadienylplatinum (IV) The method for producing an electrocatalyst according to claim 2, comprising at least one selected from the group consisting of: