JP7613757B2 - Electrode material, and electrode, membrane electrode assembly, and solid polymer electrolyte fuel cell using the same - Google Patents

Description

The present invention relates to an electrode material suitable for use in electrodes of polymer electrolyte fuel cells, and to electrodes, membrane electrode assemblies, and polymer electrolyte fuel cells that use the electrode material.

Fuel cell vehicles (FCVs) that use polymer electrolyte fuel cells (PEFCs) as their power source are already commercially available, and their use is expected to expand and become more widespread in trucks, buses, ships, and other vehicles in the future. PEFCs generally have a structure in which a membrane electrode assembly (MEA), in which a pair of electrodes are arranged on both sides of a solid polymer electrolyte membrane, is sandwiched between separators with gas flow paths. Fuel cell electrodes (particularly PEFC electrodes) generally consist of an electrode catalyst layer made of an electrode material with electrocatalytic activity and a polymer electrolyte, and a gas diffusion layer that combines gas permeability and electronic conductivity.

Currently, the most widely used electrode material for PEFCs is one in which electrode catalyst particles (typically Pt or Pt alloy particles) are dispersed and supported on a carbon-based support. In recent years, electrode materials that use mesoporous carbon as the catalyst support skeleton and support Pt particles in the pores (mesopores) of the mesoporous carbon have attracted attention (e.g., Patent Documents 1 and 2). Mesoporous carbon has excellent electrical conductivity, is easy to diffuse gases, and has a large surface area, so when it is used as a support for the electrode catalyst of a polymer electrolyte fuel cell, an electrode with excellent power generation performance can be obtained.

Patent No. 6969996 Patent No. 6931808

Incidentally, since the electrolyte membrane of a PEFC is acidic (pH=0-3), the electrode material of the PEFC is used in an acidic atmosphere. In addition, the cell voltage during normal operation is 0.4-1.0 V, but it is known that the cell voltage rises to 1.5 V during start-up and shutdown. The state of the cathode and anode under such PEFC operating conditions is a region in which the carbon-based material, which is the carrier, decomposes into carbon dioxide (CO ₂ ) in the cathode. Therefore, in the cathode, a reaction occurs in which the carbon-based carrier is electrochemically oxidized and decomposed into CO ₂ , resulting in corrosion of the carbon-based carrier (carbon corrosion), which causes aggregation and detachment of Pt particles, which are catalytically active components, and causes a decrease in the performance of the fuel cell. In addition, if the fuel gas is insufficient not only in the cathode but also in the anode at the beginning of operation, a voltage drop or concentration polarization occurs in that part, resulting in a localized potential opposite to normal, and an electrochemical oxidation and decomposition reaction of carbon may occur.

The electrode materials disclosed in Patent Documents 1 and 2, which support Pt fine particles within the pores (mesopores) of mesoporous carbon, are said to be less prone to aggregation of the Pt fine particles. However, because the Pt fine particles are supported in direct contact with the pore walls of the mesoporous carbon, carbon corrosion cannot be avoided, and there is a problem that when generating electricity for a long period of time, it is impossible to prevent the aggregation and falling off of Pt particles caused by carbon corrosion.

In this situation, the object of the present invention is to provide an electrode material that provides a fuel cell electrode with excellent electrode performance and durability, as well as an electrode, a membrane electrode assembly, and a solid polymer electrolyte fuel cell that use the same.

The inventors conducted extensive research to solve the above problems and discovered that the following invention meets the above objectives, leading to the present invention.

That is, the present invention relates to the following inventions.
<1> An electrode material which is either the following electrode material (A) or electrode material (B).
Electrode material (A): A porous composite support comprising a support skeleton made of mesoporous carbon and a support metal fixed to at least the inner pore surface of the inner pore surface and the outer pore surface of the mesoporous carbon, and electrode catalyst particles supported on the porous composite support;
An electrode material in which a part or all of the electrode catalyst particles are supported within the pores of the mesoporous carbon via the support metal.
Electrode material (B): A support skeleton made of mesoporous carbon and an electrode catalyst composite fixed to at least the inner pore surface of the mesoporous carbon, among the inner pore surface and the outer pore surface,
The electrode catalyst composite is an electrode material that includes electrode catalyst particles and a support metal, the support metal being present so as to fill the spaces between the electrode catalyst particles.
<2> The electrode material according to <1>, wherein the support metal is any one of metals selected from tantalum (Ta), tungsten (W), niobium (Nb) and tin (Sn), and an alloy containing any one of these metals as a main component.
<3> The electrode material according to <1> or <2>, wherein the support metal is tantalum (Ta) or a tantalum alloy.
<4> The electrode material according to any one of <1> to <3>, wherein the mesoporous carbon has interconnected pores in which some or all of the pores in the mesopore regions are interconnected with the pores in the adjacent mesopore regions.
<5> The electrode material according to any one of <1> to <4>, wherein the mesoporous carbon has a pore diameter of 3 nm or more and 40 nm or less.
<6> The electrode material according to any one of <1> to <5>, wherein the electrode catalyst particles are particles made of Pt or an alloy containing Pt.
<7> An electrode comprising the electrode material according to any one of <1> to <6> and a proton-conductive electrolyte material.
<8> A membrane electrode assembly having a solid polymer electrolyte membrane, a cathode bonded to one side of the solid polymer electrolyte membrane, and an anode bonded to the other side of the solid polymer electrolyte membrane, wherein either or both of the anode and the cathode are the electrodes according to <7>.
<9> A polymer electrolyte fuel cell comprising the membrane electrode assembly according to <8>.

The present invention provides an electrode material that provides a fuel cell electrode with excellent electrode performance and durability, as well as an electrode, a membrane electrode assembly, and a solid polymer electrolyte fuel cell that use the electrode material.

1A is a conceptual schematic diagram of an example of an electrode material of the present invention, FIG. 1B is an enlarged schematic diagram of the vicinity of the pores (support metal is dispersed and fixed), and FIG. 1C is an enlarged schematic diagram of the vicinity of the pores (support metal is continuously fixed (coated)). FIG. 2A is a conceptual schematic diagram of another example of the electrode material of the present invention, and FIG. 2B is an enlarged schematic diagram of the vicinity of a pore. 1 is a schematic cross-sectional view of a membrane electrode assembly of the present invention. FIG. 1 is a conceptual diagram showing a typical configuration of a polymer electrolyte fuel cell according to the present invention. 1 is a flowchart of a procedure for producing an electrode material (Ta/MC, no electrode catalyst supported) in an experimental example. 1 is a flowchart of a procedure for producing an electrode material (Pt/Ta/MC) in an experimental example. 1 shows an FESEM image and an STEM image of the electrode material of Example 1 (electrode catalyst not supported, reduction treatment at 300° C. for 4 hours). 1 shows an FESEM image and an STEM image of the electrode material of Example 2 (electrode catalyst not supported, reduction treatment at 500° C. for 2 h). 1 is an STEM image of the electrode material of Example 3 (electrode catalyst not supported, reduction treatment at 600° C. for 2 h). 1 shows cyclic voltammograms (CV) of the electrode material (Pt/Ta/MC) of Example 2 and the electrode material (Pt/MC) of the comparative example. FIG. 1 is a diagram showing the electrochemically effective surface area (ECSA) of the electrode material (Pt/Ta/MC) of Example 2 and the electrode material (Pt/MC) of the comparative example. 1 shows linear sweep voltammograms (LSV, 1600 rpm) of the electrode material (Pt/Ta/MC) of Example 2 and the electrode material (Pt/MC) of the comparative example. FIG. 13 is a graph showing the mass activity (0.9 V _RHE ) of the electrode material (Pt/Ta/MC) of Example 2 and the electrode material (Pt/MC) of the comparative example. FIG. 13 is a diagram showing conditions of a start-stop cycle test. FIG. 1 is a diagram showing the relationship between the number of start-stop cycle tests and the electrochemically effective surface area (ECSA) for the electrode material of Example 2 (Pt/Ta/MC) and the electrode material of the comparative example (Pt/MC) (Example 2: Pt/Ta/MC, Comparative example: Pt/MC). FIG. 13 is a diagram showing conditions of a load change cycle test. FIG. 1 is a diagram showing the relationship between the number of load change cycle tests and the electrochemically effective surface area (ECSA) for the electrode material (Pt/Ta/MC) of Example 2. 1 shows the LSV (1600 rpm) of the electrode material (Pt/Ta/MC) of Example 2 before and after the load change cycle test.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to the examples below and can be modified as desired without departing from the spirit of the present invention. In this specification, the word "~" is used as an expression that includes the numerical values or physical quantities before and after it.

In this specification, the term "pore" includes, for example, pores with a diameter of 150 nm or less (particularly pores with a diameter of 100 nm or less). "Mesopore region pores" refer to pores with a diameter of 2 nm to 50 nm. In addition, in this specification, "micropore region pores" refer to pores with a diameter of less than 2 nm, and "macropore region pores" refer to pores with a diameter of more than 50 nm and less than 150 nm.

1. Electrode materials
The present invention relates to the following electrode material (A) and electrode material (B).
The electrode material (A) may be referred to as the electrode material of the present invention (first embodiment), and the electrode material (B) may be referred to as the electrode material of the present invention (second embodiment). These may also be collectively referred to as the "electrode material of the present invention."

Electrode material (A):
A porous composite support comprising a support skeleton made of mesoporous carbon and a support metal fixed to at least the inner pore surface of the inner pore surfaces and the outer pore surfaces of the mesoporous carbon, and electrode catalyst particles supported on the porous composite support,
An electrode material in which a part or all of the electrode catalyst particles are supported within the pores of the mesoporous carbon via the support metal.

Electrode material (B):
The support includes a support skeleton made of mesoporous carbon and an electrode catalyst composite fixed to at least the inner pore surface of the mesoporous carbon,
The electrode catalyst composite is an electrode material that includes electrode catalyst particles and a support metal, the support metal being present so as to fill the spaces between the electrode catalyst particles.

In this specification, "fixed" means that the carrier metal (in the case of electrode catalyst (A)) or the electrode catalyst composite (in the case of electrode catalyst (B)) is fixed to the inner and outer pore surfaces of the mesoporous carbon, which is the carrier skeleton, to such an extent that it does not easily detach (peel off).

In the electrode material (A), the support metal is fixed so as to cover a part or the whole of the inner surface of the pores in the mesopore region of the mesoporous carbon, and the electrode catalyst particles are supported on the support metal. That is, the electrode catalyst particles are supported in the pores in the mesopore region of the mesoporous carbon via the support metal. Note that in the electrode material (A), the electrode catalyst particles may be supported not only inside the pores in the mesopore region, but also on the pores other than the pores in the mesopore region and on the outer surface via the support metal.
The form of the fixed carrier metal may be any of particulate, island, thin film, etc., as long as it does not impair the object of the present invention. "Island" means a state in which several particulate carrier metals are aggregated and separated from each other, and "film" means a state in which the carrier metals are continuously connected to form a thin film.

In the electrode material (B), an electrode catalyst composite consisting of electrode catalyst particles and a carrier metal is fixed so as to cover a part or the whole of the inner surface of the pores in the mesopore region of the mesoporous carbon. Note that in the electrode material (B), the electrode catalyst composite may be fixed not only to the inside of the pores in the mesopore region, but also to pores other than the pores in the mesopore region and to the outer surface.
The form of the fixed electrode catalyst composite may be any of particulate, island, thin film, etc., as long as it does not impair the object of the present invention. "Island" refers to a state in which several particulate support metals are aggregated and separated from each other, and "film" refers to a state in which the support metals are continuously connected to form a thin film.

The first embodiment (electrode material (A)) and the second embodiment (electrode material (B)) of the electrode material of the present invention have a common feature in that "mesoporous carbon is used as a support skeleton, and electrode catalyst particles and a support metal are present in the pores of the mesoporous carbon."
Electrode material (A) has a different characteristic in that "a part or all of the electrode catalyst particles are supported in the pores of the mesoporous carbon via a carrier metal", whereas electrode material (B) has a different characteristic in that "a part or all of the electrode catalyst particles are fixed in the pores of the mesoporous carbon as an electrode catalyst composite".

The electrode material of the present invention is suitable as an electrode material for use in electrodes for polymer electrolyte fuel cells, but can also be used for other purposes (e.g., electrodes for polymer electrolyte water electrolysis).

Below, a preferred embodiment of the present invention will be described in detail with reference to the drawings. Note that the following description will be given assuming that the electrode material of the present invention is used as an electrode for a polymer electrolyte fuel cell (PEFC).

<Electrode Material (A)>
Hereinafter, the electrode material (A), which is a first embodiment of the electrode material of the present invention, will be described.
FIG. 1(a) is a schematic diagram showing a typical structure of an electrode material (A) of the present invention, and FIG. 1(b) and FIG. 1(c) are enlarged schematic diagrams of the vicinity of a pore.

As shown in FIG. 1(a), the electrode material 1A according to the present invention is composed of a porous composite carrier consisting of mesoporous carbon 2, which is the carrier skeleton, and particulate carrier metal 3a fixed to the mesoporous carbon 2 (pore inner surface 2a and outer surface 2b), and electrode catalyst particles 3b supported on the carrier metal 3a.

The electrode material 1A shown in FIG. 1(a) has the carrier metal 3a and the electrode catalyst particles 3b dispersed and supported on the outer surface 2b, but the carrier metal 3a and the electrode catalyst particles 3b may be present only on the inner pore surface 2a.

Mesoporous carbon 2, which is the support skeleton of electrode material 1A (hereinafter, sometimes referred to as "mesoporous carbon according to the present invention"), is a porous carbon having many pores in the mesopore region.

Mesoporous carbon 2 can be porous carbon with pores in the mesopore region (2 to 50 nm), but the pore diameter is preferably 3 nm to 40 nm. If the pore diameter is within this range, the diffusion of materials into the pores is not significantly hindered and proceeds smoothly even when a carrier metal or an electrode catalyst is fixed (supported) on the inner walls of the pores.

As described below, when preparing a fuel cell electrode, the electrode material of the present invention is mixed with a proton-conductive electrolyte material (ionomer). Since the proton-conductive electrolyte material (ionomer) is several tens of nanometers in size, it cannot penetrate into the mesopores with small pore diameters. This makes it possible to suppress poisoning of the electrode catalyst particles supported in the pores of the mesoporous carbon via the carrier metal caused by the ionomer.

The mesoporous carbon according to the present invention may contain regions (micropore region, macropores) other than the mesopore region (2 nm to 50 nm), but it is preferable that the proportion of pores in the mesopore region is high.

The pore structure (pore size, shape, etc.) of mesoporous carbon can be confirmed by observation with an electron microscope. Examples of electron microscopes include a field emission scanning electron microscope (FESEM) and a scanning transmission electron microscope (STEM).

The pores in the mesopore region of the mesoporous carbon 2 preferably have a three-dimensional network structure, with some or all of the pores in the mesopore region interconnected with the pores in adjacent mesopore regions, as well as individual pores that are independent of other pores. The presence of the interconnected pores promotes the diffusion of substances inside the pores of the mesoporous carbon.

The size and shape of the electrode material 1A depend on the size and shape of the mesoporous carbon that is its framework material. The size and shape of the mesoporous carbon are determined so that the electrode material can be in continuous contact when the fuel cell electrode is formed, and a space can be formed that allows smooth diffusion of gases such as hydrogen and oxygen and smooth discharge of water (steam) within the fuel cell electrode.

The mesoporous carbon used in the electrode material of the present invention may be appropriately synthesized or a commercially available product may be used. An example of a commercially available product is the CNovel series (designed mesopore size: 5 to 150 nm) manufactured by Toyo Tanso Co., Ltd., which is mesoporous carbon using MgO as a template.

(Carrier Metal)
1, in the fuel cell electrode material 1A of this embodiment, the support metal 3a is fixed to the inner surface 2a of the pores in the mesopore region of the mesoporous carbon 2. In the fuel cell electrode material 1 of this embodiment, the support metal 3a is also fixed to the outer surface of the mesoporous carbon 2, but the support metal on the outer surface is not necessarily required.

The optimal amount of the carrier metal to be adhered varies depending on the particle size (film thickness in the case of a thin film) and surface area, as well as the physical properties of the carrier metal, and the method of manufacturing the carrier metal, so it is determined appropriately within the range in which a sufficient amount of electrode catalyst particles can be supported.

The size of the carrier metal in the pores is determined so as not to block the pores of the mesoporous carbon 2 and not to inhibit the transfer of substances such as gas. Although it depends on the pore size of the mesoporous carbon 2, the size of the carrier metal adhered to the inner surface of the pores is preferably a particle size of 0.5 nm or more and 3 nm or less.

The carrier metal 3a on the outer surface does not substantially contribute to blocking the mesopores and may be larger than the carrier metal inside the pores, but in order to reduce electrical resistance, it is preferable that the particle size be small within the range in which the electrode catalyst particles 3b can be dispersed and supported. If there is a carrier metal on the outer surface, its size is preferably 0.5 nm or more and 10 nm or less.

The "average particle size of the particulate carrier metal" can be obtained by averaging the particle sizes of any particulate carrier metal (20 particles) examined using an electron microscope image.

In Fig. 1(a) and (b), the carrier metal 3a is a particulate carrier metal dispersed and fixed to the mesoporous carbon 2, but this is not limited thereto, and the carrier metal 3a may be fixed to the mesoporous carbon 2. For example, as shown in Fig. 1(c), the particulate carrier metal 3a may not be dispersed, but may be continuously fixed to the surface of the mesoporous carbon 2 (particularly the inner surface of the pores) so as to coat the surface in a thin film.

The carrier metal constituting the carrier metal 3a may be any metal that has sufficient durability and electronic conductivity under at least one of the anode conditions and cathode conditions of the PEFC.
The cathode conditions of a PEFC refer to the conditions at the cathode during normal operation of the PEFC, where the temperature is from room temperature to about 150°C and an oxygen-containing gas such as air is supplied (oxidizing atmosphere), whereas the anode conditions refer to the conditions at the anode during normal operation of the PEFC, where the temperature is from room temperature to about 150°C and an oxygen-containing fuel gas such as air is supplied (reducing atmosphere).

Materials used as carrier metals include metals such as tantalum (Ta), tungsten (W), niobium (Nb) and tin (Sn), as well as alloys containing these metals as the main components. When these metals are attached to the electrode material, the outermost surface of the metal may be oxidized to form an oxide layer, but in the present invention, the metals that have an oxide layer on the outermost surface are also considered to be carrier metals.

In the case of the carrier metal, "an alloy containing the main component metal species" means "an alloy consisting of the main component metal species and other metals, containing 50 mass% or more of the main component metal species." In the case of the carrier metal, the "other metals" to be alloyed with the main component metal species are not particularly limited, but suitable examples include Co, Ni, Ti, W, Ta, Nb, and Sn (however, these are elements different from the main component metal species). One or more of these may be used. Also, an alloy containing the main component metal species and other metals in a phase-separated state may be used.

Preferred examples of the carrier metal are any metal selected from tantalum (Ta), tungsten (W) and niobium (Nb), and alloys containing these metals as the main component, with tantalum (Ta) or a tantalum alloy being particularly preferred.

The amount of the support metal is appropriately determined taking into consideration the type of metal used, the physical properties of the mesoporous carbon (pore distribution, specific surface area, etc.), etc. If the amount of the support metal is too small, the amount of the electrode catalyst supported on it will be small, resulting in insufficient electrode performance, whereas if the amount is too large, a large amount of the support metal will adhere to the outside of the pores of the mesoporous carbon and agglomerate, which may result in reduced performance.
The amount of adhered support metal can be examined by, for example, inductively coupled plasma emission spectrometry (ICP).

(Electrode catalyst particles)
The electrode catalyst particles 3b are dispersed and supported on the carrier metal 3a. The ratio of the electrode catalyst particles supported on the carrier metal can be evaluated by selecting any electrode catalyst particles (100 or more) observed under an electron microscope from the fuel cell electrode material to be evaluated, and counting the number of particles supported on the carrier metal and the number of particles supported on the mesoporous carbon.

The electrode catalyst particles 3b may be either a precious metal catalyst or a non-precious metal catalyst as long as they have electrochemical catalytic activity for the reduction of oxygen (and the oxidation of hydrogen), but are preferably selected from precious metals such as Pt, Ru, Ir, Pd, Rh, Os, Au, and Ag, and alloys containing these precious metals. The term "alloy containing a precious metal" includes "alloys consisting only of the above-mentioned precious metals" and "alloys consisting of the above-mentioned precious metals and other metals and containing 10 mass% or more of the above-mentioned precious metals". The "other metals" to be alloyed with the precious metal are not particularly limited, but suitable examples include Co and Ni, and one or more of these may be used. Two or more of the above-mentioned precious metals and alloys containing the precious metals in a phase-separated state may also be used. In this specification, the above-mentioned precious metals and alloys containing these precious metals may be referred to as "electrode catalyst metals" hereinafter.

Among the electrode catalyst metals, Pt and alloys containing Pt (Pt alloys) are particularly suitable for use because they have high electrochemical catalytic activity for the reduction of oxygen (and the oxidation of hydrogen) in the temperature range around 80° C., which is the operating temperature of solid polymer electrolyte fuel cells.
The metal species other than Pt in the Pt alloy is not particularly limited as long as it is capable of forming an alloy, but is preferably cobalt (Co).

The shape of the electrode catalyst particles 3b is not particularly limited, and any shape similar to that of known electrode catalyst particles can be used. Specific shapes include a sphere, an ellipse, a polyhedron, and a core-shell structure. In addition, the structure of the electrode catalyst particles 3b is not limited to a crystal, and may be amorphous or a mixture of crystal and amorphous.

The smaller the size of the electrode catalyst particles 3b, the greater the effective surface area for the electrochemical reaction to proceed, and therefore the higher the electrochemical catalytic activity tends to be. However, if the size is too small, the electrochemical reaction activity decreases. Therefore, it is preferable that the size of the electrode catalyst particles 3b be 0.5 to 4 nm as the average particle size.

In addition, the "average particle size of electrode catalyst particles" in the present invention can be obtained by averaging the particle sizes of electrode catalyst particles (20 particles) examined from electron microscope images. When calculating the average particle size from electron microscope images, if the shape of the fine particles is other than spherical, the length in the direction showing the maximum length of the particle is taken as the particle size.

The amount of electrode catalyst particles supported is determined appropriately taking into consideration the type of catalyst, the size (thickness) of the carrier metal, and other conditions. If the amount of catalyst supported is too small, the electrode performance will be insufficient, and if it is too large, the electrode catalyst particles may aggregate and performance may decrease. The amount of electrode catalyst particles supported can be examined, for example, by inductively coupled plasma emission spectrometry (ICP).

The method for producing the above-mentioned electrode material (A) is not particularly limited, and a suitable method may be selected depending on the types of mesoporous carbon, carrier metal, and electrode catalyst particles constituting the electrode material (A). Usually, a method is employed in which the carrier metal is supported on the mesoporous carbon, and then the electrode catalyst particles are supported on the carrier metal.
It should be noted that the method employed in the examples described below makes it possible to fix a support metal of sub-nano order inside the pores of the mesoporous carbon that constitutes the support skeleton.

In addition, known metal loading methods can be used to load the electrode catalyst precursor or electrode catalyst particles onto the carrier metal. One suitable example is the method of using a noble metal acetylacetonate as the electrode catalyst precursor (noble metal acetylacetonate method) used in the examples. In the acetylacetonate method, mesoporous carbon loaded with a carrier metal is dispersed in a solution in which a noble metal acetylacetonate is dissolved in a suitable solvent such as dichloromethane, and the solution is stirred and the solvent is removed, whereby electrode catalyst particles with a uniform nano-sized particle size distribution can be loaded with good dispersibility onto the carrier metal.

<Electrode Material (B)>
Hereinafter, the electrode material (B) which is the second embodiment of the electrode material of the present invention will be described. In the following description, the contents overlapping with those of the electrode material (A) will be omitted as appropriate.

FIG. 2(a) is a conceptual schematic diagram showing a representative structure of electrode material (B) (second embodiment) of the present invention, and FIG. 2(b) is an enlarged schematic diagram of the vicinity of a pore.
The electrode material (second embodiment) of the present invention is characterized in that the electrode catalyst particles fixed to the mesoporous carbon form an electrode catalyst structure together with the carrier metal.

As shown in FIG. 2(a), the electrode material 1B (second embodiment) according to the present invention is composed of mesoporous carbon 2, which is a support skeleton, and an electrode catalyst complex 3 fixed to the mesoporous carbon (pore inner surface 2a and pore inner and outer surfaces 2b). Note that the electrode material 1B shown in FIG. 2(a) also has an electrode catalyst complex 3 on the outer surface 2b, but the electrode catalyst complex 3 may be present only on the pore inner surface 2a.

That is, in electrode material 1B, the electrode catalyst composite 3 is supported on part or all of the inner pore surface of the mesopore region in the mesoporous carbon 2.

In the electrode material 1B, the electrode catalyst composite 3 may be supported not only inside the pores in the mesopore region, but also in pores other than the pores in the mesopore region and on the outer surface.

In electrode material (B), mesoporous carbon 2 functions as a support for adhering (supporting) the electrode catalyst composite, improves electronic conductivity when the electrode is formed, and also serves as the skeleton of the electrode. The same mesoporous carbon as in electrode material (A) can be used for the mesoporous carbon, so a detailed explanation is omitted.

In the electrode material (B), the electrode catalyst composite 3 includes a carrier metal 3a and electrode catalyst particles 3b, and is characterized in that the carrier metal 3a is present so as to fill the gaps between the electrode catalyst particles 3b. The electrode catalyst composite 3 can suppress the electrode catalyst particles 3b from agglomerating and becoming enlarged because the carrier metal 3a is present so as to fill the gaps between the electrode catalyst particles 3b. In addition, the electrode catalyst composite 3 is also fixed to the mesoporous carbon surface (particularly the inner pore surface), so that the electrode catalyst composite itself can be suppressed from agglomerating.

In FIG. 2, the carrier metal between the electrode catalyst particles is in the form of particles, but the form of the carrier metal is not limited to particles as long as it is between the electrode catalyst particles, and may be indefinite. The carrier metal may be crystalline or amorphous, but it is preferable that it is partially crystalline (i.e., a mixture of crystalline and amorphous), and it is more preferable that it is entirely crystalline.

In the electrode material (B), mesoporous carbon serves as the skeleton of the electrode, allowing the particle size of the electrode catalyst composite 3 to be reduced.

The "size of the electrode catalyst composite" can be obtained by averaging the sizes of any electrode catalyst composites (20 pieces) examined from electron microscope images. If the shape of the electrode catalyst composite is not spherical, the length in the direction showing the maximum length is regarded as the size of the electrode catalyst composite.

In the electrode material (B), a part or all of the electrode catalyst complex may be present in the pores of the mesoporous carbon. In this case, the size of the electrode catalyst complex must be smaller than the diameter of the pores of the mesoporous carbon, and is 2 to 30 nm, which corresponds to the pore diameter of the mesoporous carbon (e.g., 3 to 40 nm).

The proportion of the electrode catalyst composites within the pores of the mesoporous carbon is preferably 50% or more, more preferably 80% or more, and even more preferably 90% or more (including 100%), when the total number of electrode catalyst composites (the sum of the electrode catalyst composites outside and inside the pores) is taken as 100%.
The number of electrocatalyst composites within the pores of the mesoporous carbon can be confirmed using high angle dark field scanning transmission electron microscopy (HAADF-STEM).

The size of the electrode catalyst composite in the pores is determined so as not to block the pores of the mesoporous carbon or inhibit the transfer of substances such as gas. Although it depends on the pore size of the mesoporous carbon, the size of the electrode catalyst composite attached to the inner surface of the pores is preferably a particle size of 0.5 nm or more and 15 nm or less.

The electrode catalyst composite on the outer surface does not substantially contribute to blocking the mesopores, so it may be larger than the electrode catalyst composite inside the pores, but preferably has an average particle size of typically 10 to 500 nm. The "average particle size of the electrode catalyst composite" can be obtained by averaging the particle sizes of any electrode catalyst composite (20 pieces) examined from an electron microscope image.

The amount of the electrode catalyst composite supported is appropriately determined within a range that contains a sufficient amount of electrode catalyst metal as an electrode. The activity of the electrode catalyst metal depends on the type, crystallinity, particle size, etc. of the electrode catalyst metal and the type, crystallinity, particle size, etc. of the carrier metal to be composited, so the amount of the electrode catalyst composite supported is determined taking this into consideration.

The support metal and electrode catalyst metal that constitute the electrode catalyst composite of electrode material (B) are described in detail below.

The carrier metal that constitutes the electrode catalyst composite is the same as the carrier metal described in the electrode material (A) above, so a detailed explanation is omitted and a brief explanation is given below.

The support metal constituting the electrode catalyst composite has both sufficient durability and electronic conductivity under PEFC cathode conditions and/or PEFC anode conditions.
The form of the support metal is arbitrary as long as it does not impair the object of the present invention, and examples of the form include particulate, island, film, etc. Furthermore, the support metal is not limited to being crystalline, and may be amorphous or a mixture of crystalline and amorphous, but in order to enhance better electronic conductivity, the support metal is preferably crystalline.

Materials used as carrier metals include metals such as tantalum (Ta), tungsten (W), niobium (Nb) and tin (Sn), as well as alloys containing these metals as the main components. When these metals are attached to the electrode material, the outermost surface of the metal may be oxidized to form an oxide layer, but in the present invention, the metals that have an oxide layer on the outermost surface are also considered to be carrier metals.

Preferred examples of the carrier metal are any metal selected from tantalum (Ta), tungsten (W) and niobium (Nb), and alloys containing these metals as the main component, with tantalum (Ta) or a tantalum alloy being particularly preferred.

As described above, in the electrode catalyst composite of the present invention, the support metal is present so as to fill the spaces between the electrode catalyst particles, thereby inhibiting the aggregation of the electrode catalyst particles, and the support metal may be contained in a form that can achieve this purpose.
The proportion of the support metal in the electrode catalyst composite is appropriately determined depending on the type, size and crystallinity of the support metal, as well as the type, amount and size of the electrode catalyst metal to be composited.

In the electrode material of the present invention, the carrier metal fills the gaps between the electrode catalyst particles in the electrode catalyst composite, and the carrier metal can be made small, so the electrical resistance caused by this can be reduced. Therefore, the carrier metal may not only be crystalline, but may also be amorphous. However, in order to further reduce the electrical resistance, it is preferable that at least a portion of the carrier metal is crystalline, and it is preferable that the entire carrier metal is crystalline.

The amount of carrier metal is determined appropriately taking into consideration the type of carrier metal, the type and size of the electrode catalyst particles that make up the electrode catalyst composite, the physical properties of the mesoporous carbon (pore distribution, specific surface area, etc.), etc. If there is too little carrier metal, it will not be possible to suppress the aggregation of the electrode catalyst in the electrode catalyst composite, and if there is too much, too much will adhere to the outside of the pores of the mesoporous carbon, which may result in aggregation and reduced performance. The amount of adhered carrier metal can be investigated, for example, by inductively coupled plasma optical emission spectrometry (ICP).

The electrode catalyst particles that make up the electrode catalyst composite are the same as those described in the electrode material (A) above, so a detailed description is omitted and a brief description is given below.

The electrode catalyst particles may be any that have electrochemical catalytic activity for the reduction of oxygen (and the oxidation of hydrogen), but are preferably electrode catalyst metals selected from precious metals such as Pt, Ru, Ir, Pd, Rh, Os, Au, and Ag, and alloys containing these precious metals.

Among the electrode catalyst metals, Pt and alloys containing Pt (Pt alloys) are particularly suitable for use because they have high electrochemical catalytic activity for the reduction of oxygen (and the oxidation of hydrogen) in the temperature range around 80° C., which is the operating temperature of solid polymer electrolyte fuel cells.
The metal species other than Pt in the Pt alloy is not particularly limited as long as it is capable of forming an alloy, but is preferably cobalt (Co).

In addition, the electrode catalyst metal is preferably crystalline, but may be a mixture of crystalline and amorphous.

That is, one of the preferred embodiments of the electrode catalyst metal in the electrode catalyst (B) is that the electrode catalyst metal is made of particles of a precious metal (preferably Pt or an alloy containing Pt) having an average particle size of 1 to 10 nm.

The amount of electrocatalyst metal is determined taking into consideration the desired electrocatalytic activity and the type and amount of carrier metal to be composited. The amount of electrocatalyst metal supported can be determined, for example, by inductively coupled plasma emission spectrometry (ICP).

From the viewpoint of electrode catalytic activity, a loading of 0.1 to 60 mass% and more preferably 0.5 to 30 mass% relative to the total weight of the electrode material provides excellent catalytic activity per unit mass and allows for the desired electrode reaction activity according to the loading amount.

The method for producing the electrode material (B) is not particularly limited, and a suitable method may be selected depending on the types of mesoporous carbon, carrier metal, and electrode catalyst metal that constitute the electrode material.
An example of a method for producing the electrode material (B) includes a production method including the steps of: step (1) of dissolving an acetylacetonate compound of an electrode catalyst metal precursor and an acetylacetonate compound of a support metal precursor in a dispersion liquid obtained by dispersing mesoporous carbon in an aqueous organic solvent, stirring the mixture, and distilling off the solvent to obtain a support skeleton carrying the electrode catalyst metal precursor and the support metal precursor; and step (2) of heat-treating, in an inert gas atmosphere, the support skeleton carrying the electrode catalyst metal precursor and the support metal precursor obtained in step (1), to form an electrode catalyst composite.

2. Electrodes
The electrode of the present invention includes the above-mentioned electrode material of the present invention and a proton-conductive electrolyte material. In the electrode of the present invention, the electrode materials of the present invention are in contact with each other to form a conductive path.

The following describes a fuel cell electrode formed using the electrode material of the present invention. Specifically, we will explain the case where the above-mentioned electrode material is used as an electrode in a PEFC.

The fuel cell electrode may be composed only of the above-mentioned electrode materials, but typically contains a proton-conductive electrolyte material used in the electrolyte of the fuel cell (hereinafter, sometimes referred to as "proton-conductive electrolyte material" or simply "electrolyte material"). The electrolyte material contained in the fuel cell electrode together with the electrode material may be the same as the electrolyte material used in the fuel cell electrolyte membrane, or may be different. From the viewpoint of improving the adhesion between the fuel cell electrode and the electrolyte membrane, it is preferable to use the same material.

The electrolyte materials used in the electrodes and electrolyte membranes of PEFCs include proton-conductive electrolyte materials. These proton-conductive electrolyte materials are broadly divided into fluorine-based electrolyte materials that contain fluorine atoms in all or part of the polymer backbone, and hydrocarbon-based electrolyte materials that do not contain fluorine atoms in the polymer backbone, and both of these can be used as electrolyte materials.

Specific examples of suitable fluorine-based electrolyte materials include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.).

Specific examples of suitable hydrocarbon electrolyte materials include polymers such as polysulfonic acid, polystyrene sulfonic acid, polyaryl ether ketone sulfonic acid, polyphenyl sulfonic acid, polybenzimidazole sulfonic acid, polybenzimidazole phosphonic acid, and polyimide sulfonic acid, as well as polymers having side chains such as alkyl groups.

The mass ratio of the electrode material to the electrolyte material mixed with the electrode material may be appropriately determined so as to provide good proton conductivity in the electrode formed using these materials and to smoothly diffuse gas and discharge water vapor in the electrode. However, if the amount of electrolyte material mixed with the electrode material is too large, the proton conductivity will be good but the gas diffusibility will be low. Conversely, if the amount of electrolyte material mixed is too small, the gas diffusibility will be good but the proton conductivity will be low. Therefore, the mass ratio of the electrolyte material to the electrode material is preferably in the range of 10 to 50 mass%. If this mass ratio is less than 10 mass%, the continuity of the proton-conductive material will be poor, and sufficient proton conductivity cannot be secured as an electrode for a fuel cell. Conversely, if it is more than 50 mass%, the continuity of the electrode material will be poor, and it may not be possible to have sufficient electronic conductivity as an electrode for a fuel cell. Furthermore, the diffusibility of gases (oxygen, hydrogen, water vapor) inside the electrode may be reduced.

The fuel cell electrode of the present invention may contain components other than the above-mentioned electrode material and proton conductive material, provided that the object of the present invention is not impaired.
For example, the electrode material may contain a conductive material other than the mesoporous carbon (hereinafter, referred to as "another conductive material") contained in the electrode material. By containing the other conductive material, the number of conductive paths connecting the electrode materials increases, and the conductivity of the electrode as a whole may be improved.

As the other conductive material, known conductive materials used in fuel cell electrodes can be used. Typical conductive materials are carbon-based, and examples include particulate carbon such as carbon black and activated carbon (including chain-linked carbon particles), and fibrous carbon such as carbon fiber and carbon nanotubes (CNT). Unsupported mesoporous carbon can also be used as the other conductive material.

Although the electrode for a PEFC has been described as an electrode for a fuel cell including the electrode material of the present invention, the electrode material can be used as an electrode for various fuel cells other than PEFC, such as alkaline fuel cells, phosphoric acid fuel cells, etc. The electrode material can also be suitably used as an electrode for a water electrolysis device using a polymer electrolyte membrane similar to that of a PEFC.
The electrode for a fuel cell containing the electrode material of the present invention has excellent electrochemical catalytic activity for oxygen reduction and hydrogen oxidation, and can be used as a cathode and an anode. In particular, the electrode has excellent electrochemical catalytic activity for oxygen reduction, and electrochemical oxidative decomposition of the conductive material, which is the carrier, does not occur under the operating conditions of the fuel cell, and therefore can be suitably used as a cathode.

The fuel cell electrode of the present invention can be used as an electrode in various fuel cells other than PEFC, such as alkaline fuel cells and phosphoric acid fuel cells. It can also be suitably used as an electrode for water electrolysis devices that use a solid polymer electrolyte membrane similar to that of PEFC.

<3. Membrane electrode assembly (MEA)>
The membrane electrode assembly of the present invention comprises a solid polymer electrolyte membrane, a cathode bonded to one side of the solid polymer electrolyte membrane, and an anode bonded to the other side of the solid polymer electrolyte membrane. The membrane electrode assembly is characterized in that either or both of the cathode and the anode are the electrodes of the present invention.

As a preferred embodiment of the present invention, a membrane electrode assembly using a fuel cell electrode containing the electrode material of the present invention as a cathode will be described.
3 is a schematic diagram showing a cross-sectional structure of a membrane electrode assembly according to an embodiment of the present invention. As shown in FIG. 3, a membrane electrode assembly 10 has a structure in which a cathode 4 and an anode 5 are disposed facing a solid polymer electrolyte membrane 6.

The cathode 4 is composed of an electrode catalyst layer 4a and a gas diffusion layer 4b.

A conventionally known gas diffusion layer can be used as the gas diffusion layer 4b. For example, a conductive carbon-based sheet-like member having a pore size distribution of about 100 nm to 90 μm, which has been conventionally used as a gas diffusion layer in PEFCs, can be used. Carbon paper, carbon cloth, carbon nonwoven fabric, etc. that have been subjected to a water-repellent treatment can be preferably used. Sheet-like members other than carbon-based materials such as stainless steel can also be used. There is no particular limit to the thickness of such a gas diffusion layer 4b, but it is usually about 50 μm to 1 mm. In addition, the gas diffusion layer 4b may have a microporous layer on one side thereof, which is made of an aggregate of carbon fine particles with an average particle size of about 10 to 100 nm and a water-repellent material.

The anode 5 is composed of an electrode catalyst layer 5a and a gas diffusion layer 5b. As the anode 5, in addition to the fuel cell electrode of the present invention, other known anodes can be used in the same manner. For example, an electrode in which an electrode catalyst layer 5a is formed on a gas diffusion layer 5b by applying and drying a dispersion of an electrode material carrying precious metal particles as a catalyst and an electrolyte material of the fuel cell on the surface of a conductive support made of a carbon-based material such as graphite, carbon black, activated carbon, carbon nanotubes, or glassy carbon. The gas diffusion layer 5b of the anode 5 can be the same as the gas diffusion layer 4b described for the cathode 4.

As the solid polymer electrolyte membrane 6, any known electrolyte membrane for PEFCs may be used as long as it has proton conductivity and is chemically and thermally stable. Note that although the thickness is emphasized in FIG. 3, the thickness of the solid polymer electrolyte membrane 6 is usually about 0.007 to 0.05 mm in order to reduce electrical resistance.

The electrolyte material constituting the solid polymer electrolyte membrane 6 may be a fluorine-based electrolyte material or a hydrocarbon-based electrolyte material. In particular, an electrolyte membrane formed from a fluorine-based electrolyte material is preferred because of its excellent heat resistance and chemical stability. Specifically, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) are suitable examples.

The above describes embodiments of the MEA of the present invention with reference to the drawings, but these are merely examples of the present invention, and various configurations other than those described above can also be adopted.

<4. Polymer electrolyte fuel cell>
The polymer electrolyte fuel cell (single cell) of the present invention comprises the membrane electrode assembly of the present invention, and generally has a structure in which the membrane electrode assembly is sandwiched between separators having gas flow paths formed therein.

Fig. 4 is a conceptual diagram showing a typical configuration of a polymer electrolyte fuel cell of the present invention. As shown in Fig. 4, in a polymer electrolyte fuel cell 20, hydrogen is supplied to the anode 5, and protons (H ⁺ ) generated by (reaction 1) 2H ₂ → 4H ⁺ + 4e ^- are supplied to the cathode 4 via the solid polymer electrolyte membrane 6, and the generated electrons are supplied to the cathode via an external circuit 21, and react with oxygen by (reaction 2) O ₂ + 4H ⁺ + 4e ^- → 2H ₂ O to generate water.
A potential difference is generated between the two electrodes by the electrochemical reaction between the anode and the cathode. In the polymer electrolyte fuel cell of the present invention, the components other than the membrane electrode assembly of the present invention are similar to those of known polymer electrolyte fuel cells, and therefore detailed description thereof will be omitted.
In practice, a fuel cell stack is formed by stacking the solid polymer electrolyte fuel cells (single cells) of the present invention in a number appropriate for the power generation performance, and the fuel cell stack is used by assembling other associated devices such as a gas supply device and a cooling device.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these.

1. Preparation of Electrode Materials Electrode materials of the following examples and comparative examples were produced.

The porous carbon, the noble metal precursor compound, and the electronically conductive oxide used are as follows.
<Porous carbon>
As the porous carbon, the following mesoporous carbon (MC) (manufactured by Toyo Tanso Co., Ltd., "Porous Carbon CNovel MJ(4)010 (grade name)") was used.
Design pore diameter: 10nm
Specific surface area: 1100m ² /g
Total pore volume: 2.0 mL/g
Micropore volume: 0.4 mL/g
Particle size: 100 mesh pass (used after crushing)
<Ta raw material compound>
Tantalum ethoxide (Ta(OC ₂ H ₅ ) ₄ , Kojundo Chemical Laboratory Co., Ltd.) was used as the Ta raw material compound.
<Precious metal precursor compound>
As a precious metal precursor compound, Pt acetylacetonate (Pt( _{C5H7O2 ) 2} , Platinum(II) acetylacetonate, 97%, Sigma Aldrich) was used. Hereinafter, Pt acetylacetonate may be referred to as Pt precursor (Pt( _acac ) ₂ ).

<Examples 1 to 3>
As shown in the flow chart of FIG. 5, an electrode material of the example (without supporting an electrode catalyst) was produced by a steam hydrolysis method.
First, 50 mg of the above mesoporous carbon (MC) as the support skeleton was pulverized in a ball mill to a particle size of about 1 μm, and then dispersed in an organic solvent (a mixture of acetylacetone and toluene in a volume ratio of 2:1) to obtain a dispersion containing MC. Next, a tantalum ethoxide reagent was dissolved in an organic solvent (ethanol) to prepare a metal ethoxide solution containing 35 wt % Ta. This metal ethoxide solution was added to the dispersion containing MC, and the total amount of solvent was adjusted to 50 mL. The pressure was reduced while ultrasonic stirring was performed, and the organic solvent was evaporated to obtain a dry powder in which the metal ethoxide reagent was uniformly adsorbed on the MC surface (the inner and outer surfaces of the pores).
The obtained dried powder was pulverized and then held for 1 hour in a water vapor nitrogen atmosphere (3% humidified _N2 atmosphere) at 30°C to allow steam hydrolysis of the metal ethoxide reagent to proceed, and then heated to 400°C in a nitrogen atmosphere and held for 2 hours, and further heated to 800°C in a nitrogen atmosphere and held for 30 minutes. After that, the electrode materials (Ta/MC, no electrode catalyst supported) of Examples 1 to 3 were produced by holding the material at a predetermined temperature for a predetermined time in a hydrogen atmosphere for reduction treatment.
Table 1 shows the conditions in the hydrogen atmosphere during the preparation of the electrode materials (Ta/MC) of Examples 1 to 3.

Next, as shown in the flow chart of Fig. 6, Pt catalyst particles, which are electrode catalyst particles, were supported on the electrode material (not supporting an electrode catalyst) of Example 2 by a platinum acetylacetonate method. The amount of Pt precursor (Pt(acac) ₂ ) was adjusted so that Pt was 32 wt%.
The electrode material of Example 2 (electrode catalyst not supported) consisting of tantalum-supported MC and Pt precursor were added to the eggplant flask, and acetone was further added to dissolve. Next, while cooling the eggplant flask on ice, the mixture was stirred with an ultrasonic stirrer until all the solvent was evaporated to obtain a dry powder. Next, the obtained dry powder was subjected to reduction treatment in a _N2 atmosphere at 210°C for 3 hours and at 240°C for 3 hours to obtain the electrode material of Example 2 (Pt/Ta/MC).

Comparative Example
As a comparative example, a comparative electrode material (Pt/MC) was obtained in the same manner as in Example 1, except that the metal ethoxide solution was not used.

<Reference Example>
As a reference example, a commercially available platinum-supported carbon black catalyst (Pt/C, (Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E) was used.

2. Physical property evaluation (microstructure observation)
(1) Electrode material (without electrode catalyst)
Fig. 7 shows an FESEM image and an STEM image of the electrode material (electrode catalyst not supported) of Example 1, Fig. 8 shows an FESEM image and an STEM image of the electrode material (electrode catalyst not supported) of Example 2, and Fig. 9 shows an STEM image of the electrode material (electrode catalyst not supported) of Example 3. Note that the residual oxygen values below are values measured by energy dispersive X-ray spectroscopy (EDS).
As shown in Figures 7 to 9, it was confirmed that Ta particles were uniformly supported in all of the electrode materials (electrode catalyst not supported) of Examples 1 to 3. In addition, the residual oxygen was 8 to 10% in Example 1 (under hydrogen atmosphere at 300°C for 4 hours), and the residual oxygen was 4 to 5% in Example 2 (under hydrogen atmosphere at 500°C for 2 hours) and Example 3 (under hydrogen atmosphere at 600°C for 2 hours). Therefore, it was determined that the reduction of the Ta precursor to Ta was more advanced by heat treatment at 500°C or higher under a hydrogen atmosphere. In addition, it was determined from Figure 9 that Example 3 (under hydrogen atmosphere at 600°C for 2 hours) had a Ta monoatomic portion and a portion of about 10 atomic layers in the pores.

3. Electrochemical evaluation (half cell)
3-1. Evaluation by cyclic voltammetry (CV) The electrode materials of Example 2 (Pt/Ta/MC) and Reference Example (Pt/C) were evaluated by cyclic voltammetry (CV). The electrochemical surface area (ECSA) was calculated from the amount of hydrogen adsorption determined by CV. The ECSA corresponds to the effective surface area of Pt contained in the electrode material.

The fuel cell electrodes for evaluation were prepared in the following manner.
First, a mixed solution of 19 mL of ultrapure water and 6 mL of 2-propanol was added to a sample bottle containing an electrode material powder, followed by adding 100 μL of 5% Nafion dispersion, and then ultrasonic stirring was performed for 30 minutes while the sample bottle was immersed in ice water to obtain an electrode material dispersion. The amount of electrode material powder was such that when 10 μL of the electrode material dispersion was dropped onto the electrode, the Pt mass per unit area on the electrode was 17.3 μg _-Pt / cm ^2. 10 μL of the prepared electrode material dispersion was dropped onto an Au disk electrode using a micropipette, and the electrode material was dried in a thermostatic chamber at 60 ° C. for about 15 minutes to form a Nafion film and fix the electrode material on the Au electrode, thereby obtaining a fuel cell electrode (working electrode) for evaluation.

The CV measurement conditions are as follows: If it is assumed that one atom of H is adsorbed per one atom of Pt, the electrical charge is 210 μC/cm ² .

Measurement: Three-electrode cell (working electrode: fuel cell electrode for evaluation, counter electrode: Pt, reference electrode: Ag/AgCl)
Electrolyte: 0.1M HClO ₄ (pH: approx. 1)
Measurement potential range: 0.05 to 1.2 V (based on reversible hydrogen electrode)
Scanning speed: 50 mV/s
Hydrogen adsorption amount: Calculated from the peak area showing hydrogen adsorption at 0.05 to 0.4 V Electrochemical surface area (ECSA): Calculated from the following formula

ECSA = (hydrogen adsorption amount) [μC] / 210 [μC/cm ² ]

Fig. 10 shows cyclic voltammograms of the electrode materials of Example 2 and Reference Example. As shown in Fig. 10, in the electrode using the electrode material of Example 2 (Pt/Ta/MC), a peak (0.05 to 0.4 V) due to the adsorption and desorption of hydrogen originating from Pt was observed, and it was confirmed that the electrode functions as an electrode for a fuel cell.
Furthermore, the electrode material of Example 2 (Pt/Ta/MC) was comparable to the electrode material of the reference example (Pt/C, TEC10E50E), and as shown in Figure 11, it was confirmed that the electrochemical surface areas (ECSA) were equivalent (ECSA Example 2: 78.5 ^m2 /g, Reference Example: 73.8 ^m2 /g).

3-2. Evaluation of ORR Activity The ORR activity of the electrode materials of Example 2 and Reference Example was evaluated.
The ORR activity was measured by linear sweep voltammetry (LSV) using the rotating disk electrode method (RDE method), and the mass activity (activity per unit Pt weight) calculated based on the activation current ( _ik ) obtained was used as an index.

Mass activity = i _k / Pt mass on electrode

The activation current (i _k ) was determined from the intercept by extrapolating the straight line obtained by plotting the current-potential curve obtained by rotating electrode measurement at i ^-1 and ω ^-1/2 at an arbitrary potential to create a Koutecky-Levich plot.
Specifically, _O2 was bubbled at 50 mL/min for 30 minutes, and then the potential was scanned from 0.2 V _RHE to 1.20 V _RHE at 10 mV/s in the noble direction and the measurement was performed. Note that _O2 was constantly purged at 50 mL/min during the measurement. Note that V _RHE is the potential based on the reversible hydrogen electrode (RHE).

Figure 12 shows linear sweep voltammograms (1600 rpm) of the electrode materials of Example 2 and Reference Example, and Figure 13 shows the mass activity of the electrode material of Example 2 at 0.9 V _RHE obtained by ORR measurement, which was 179.2 A/ _{g_Pt} , and showed a relatively high initial activity, although it was not as high as that of the Reference Example. It was determined that the conductive path was secured by the conductivity of the metal Ta, resulting in high activity.

3-3. Start-stop cycle test A start-stop cycle test was conducted for the electrode materials of Example 2 and Comparative Example by the method recommended by the Fuel Cell Commercialization Council of Japan (FCCJ) (Proposal of goals, research and development issues and evaluation methods for polymer electrolyte fuel cells, published in January 2011). The start-stop cycle test is a cycle test that promotes carbon corrosion, and specifically, a rectangular wave of 1.0 to 1.5 V _RHE shown in Figure 14 is repeatedly applied for 2 seconds per cycle, and the deterioration behavior of the electrode catalyst after the cycle test is evaluated as an ECSA change.

FIG. 15 shows the change in ECSA of the electrodes using the electrode materials of Example 2 and the comparative example during a start-stop cycle test (up to 20,000 cycles).
As shown in FIG. 15, the ECSA of Example 2 (Pt/Ta/MC) was slightly smaller than that of the Comparative Example (Pt/MC) up to 5000 cycles, but after 5000 cycles, the relationship was reversed and Example 2 became larger than the Comparative Example.

3-4. Load change cycle test A load change cycle durability test was conducted on the electrode materials of Example 2 and Comparative Example. The load change cycle test was conducted by applying a potential cycle simulating a load change according to the method recommended by the Fuel Cell Commercialization Promotion Council of Japan (FCCJ) (Proposal of the Goals, Research and Development Issues and Evaluation Methods of Polymer Electrolyte Fuel Cells, published in January 2011). The load change cycle shown in FIG. 16 is a cycle that promotes deterioration accompanied by dissolution and reprecipitation of the catalyst itself, and an experiment was conducted by applying a rectangular wave of 0.6 to 1.0 V _RHE for 6 seconds, 3 seconds per cycle, and measuring the ECSA change and LSV change before and after the load change cycle test.

The ECSA retention rate after the load change cycle test (400,000 cycles) is shown in Fig. 17. The ECSA retention rate after the load change cycle test (400,000 cycles) was 43% for the electrode material of Example 2 (Pt/Ta/MC).
The LSV change of the electrode material of Example 2 before and after the load change cycle test (400,000 cycles) is shown in Figure 18. It can be seen that the negative shift of the LSV curve is suppressed to some extent, and activity is maintained even after 400,000 cycles.

The electrode material of the present invention can provide a fuel cell electrode with excellent electrocatalytic activity, electronic conductivity, gas diffusion, and excellent durability, and is promising as an electrode component of solid polymer fuel cells used in the automobile, electric power, gas, and home appliance industries. It is particularly expected to be used for fuel cell vehicles (passenger cars and commercial vehicles) that are subject to large load fluctuations.

1A, 1B Electrode material 2 Mesoporous carbon 2a Pore inner surface 2b Outer surface 3 Electrode catalyst composite 3a Support metal 3b Electrode catalyst particle 4 Fuel cell electrode (cathode)
4a Electrode catalyst layer (cathode)
4b Gas diffusion layer 5 Fuel cell electrode (anode)
5a Electrode catalyst layer (anode)
5b Gas diffusion layer 6 Solid polymer electrolyte membrane 10 Membrane electrode assembly (MEA)
20 Solid polymer fuel cell 21 External circuit P Pore (mesopore)

Claims (10)

An electrode material which is the following electrode material (A).
Electrode material (A):
The present invention comprises a porous composite support comprising a support skeleton made of mesoporous carbon and a support metal fixed to at least the inner pore surface of the inner pore surface and the outer pore surface of the mesoporous carbon, and electrode catalyst particles supported on the support metal ,
An electrode material, characterized in that a part or all of the electrode catalyst particles are supported within the pores of the mesoporous carbon via the support metal. An electrode material which is the following electrode material (B).
Electrode material (B):
The support includes a support skeleton made of mesoporous carbon and an electrode catalyst composite fixed to at least the inner pore surface of the mesoporous carbon,
The electrode material, wherein the electrode catalyst composite comprises electrode catalyst particles and a support metal, the support metal being present so as to fill spaces between the electrode catalyst particles. 3. The electrode material according to claim 1, wherein the support metal is any metal selected from the group consisting of tantalum (Ta), tungsten (W), niobium (Nb) and tin (Sn), or an alloy containing any of these metals as a main component. 4. The electrode material according to claim 3 , wherein the support metal is tantalum (Ta) or a tantalum alloy. 3. The electrode material according to claim 1, wherein the mesoporous carbon has interconnected pores in which some or all of the pores in a mesopore region are interconnected with the pores in an adjacent mesopore region. 3. The electrode material according to claim 1, wherein the mesoporous carbon has a pore size of 3 nm or more and 40 nm or less. 3. The electrode material according to claim 1, wherein the electrode catalyst particles are particles made of Pt or an alloy containing Pt. An electrode comprising the electrode material according to claim 1 or 2 and a proton-conducting electrolyte material. 9. A membrane electrode assembly comprising a solid polymer electrolyte membrane, a cathode bonded to one side of the solid polymer electrolyte membrane, and an anode bonded to the other side of the solid polymer electrolyte membrane, wherein either or both of the anode and the cathode are the electrodes according to claim 8 . A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 9 .