WO2018159524A1 - Electrode catalyst, composition for forming gas diffusion electrode, gas diffusion electrode, membrane electrode assembly, and fuel cell stack - Google Patents

Abstract

Provided is an electrode catalyst which has high durability compared with conventional Pt/C catalysts and which contributes to cost reduction. The electrode catalyst of the present invention comprises a carrier and catalyst particles carried on the carrier. The catalyst particles comprise a core portion, a first shell portion formed on the core portion, and a second shell portion formed on the first shell portion. The core portion includes WC and a W carbide including WC_1-x(0 < x < 1). The first shell portion includes Pd (0 valence). The second shell portion includes Pt (0 valence). Core particles as a precursor of the core portion satisfy the condition of an expression (1): 0.03 ≤ {I2/(I1 + I2)} ≤ 0.75, where I1 and I2 are respectively the intensity of a peak attributed to WC and the intensity of a peak attributed to WC_1-x(0 < x < 1), as determined by XRD measurement of the core particles.

Description

Electrode catalyst, gas diffusion electrode forming composition, gas diffusion electrode, membrane / electrode assembly, fuel cell stack

The present invention relates to an electrode catalyst. More specifically, the present invention relates to an electrode catalyst suitably used for a gas diffusion electrode, and relates to an electrode catalyst suitably used for a gas diffusion electrode of a fuel cell.
The present invention also relates to a composition for forming a gas diffusion electrode, a membrane / electrode assembly, and a fuel cell stack comprising the electrode catalyst particles.

The polymer electrolyte fuel cell (hereinafter referred to as “PEFC” as required) is being researched and developed as a power source for fuel cell vehicles and household cogeneration systems.

As a catalyst used for a PEFC gas diffusion electrode, a noble metal catalyst composed of noble metal particles of a platinum group element such as platinum (Pt) is used.
For example, as a typical conventional catalyst, a “Pt-supported carbon catalyst” in which Pt fine particles are supported on conductive carbon powder (hereinafter referred to as “Pt / C catalyst” if necessary) is known (for example, Pt / C catalyst having a Pt loading of 50 wt% manufactured by NE CHEMCAT, trade name: “NE-F50”, etc.).
The ratio of the cost occupied by the noble metal catalyst such as Pt is large in the manufacturing cost of PEFC, which is a problem for reducing the cost of PEFC and popularizing PEFC.
In order to solve this problem, research and development of a low noble metalization technology or a de noble metalization technology of a catalyst has been advanced.

In these research and development, in order to reduce the amount of platinum used, conventionally, catalyst particles having a core-shell structure formed of a core portion made of a non-platinum element and a shell portion made of Pt (hereinafter referred to as “core-shell” "Catalyst particles" are being studied, and many reports have been made.
For example, Patent Document 1 discloses a particle composite material (core-shell catalyst particle) having a configuration in which palladium (Pd) or a Pd alloy (corresponding to a core part) is covered with an atomic thin layer of Pt atoms (corresponding to a shell part). Is disclosed. Furthermore, this patent document 1 describes, as an example, core-shell catalyst particles in which the core part is a layer made of Pd particles and the shell part is made of Pt.
Further, a configuration including a metal element other than the core Pt group as a constituent element has been studied. On the contrary, a configuration in which a metal element other than the Pt group is included in the shell portion as a constituent element has been proposed.
For example, as a configuration including tungsten (W) as a constituent element of the core portion, a configuration having a core portion made of W alone, a W alloy, and a W oxide has been proposed (for example, Patent Documents 2 to 9).
Further, as a configuration including W as a constituent element of the shell portion, a configuration having a shell portion made of W alone, a W alloy, and a W oxide has been proposed (for example, Patent Document 10).

More specifically, Patent Documents 2 to 5 disclose configurations having a core portion containing W oxide.
In Patent Document 2, particles that are an alloy of a reduction product (WO _2-y , 0 <y ≦ 2) having a core part of WO ₂ and a shell part of WO ₂ and Pd are supported on a carbon support. A synthesis example of the catalyst having the structure is disclosed (Patent Document 2, Example 8).
Patent Document 3 discloses platinum-metal oxide composite particles having W oxide (such as sodium tungsten oxide) as a core portion and Pt as a shell portion.
In Patent Document 4, metal oxide particles composed of two or more solid solutions selected from a single element of W or a group of metal elements containing W are used as base particles (core part), and a group of Pt (zero-valent) or Pt is included. Catalyst particles having a structure in which two or more solid solutions selected from metal elements are used as a metal coating layer (shell portion) have been proposed.
Patent Document 5 proposes a catalyst particle having a structure in which W oxide is used as a base particle (core part) and one or more metals such as Pt (shell part) covering at least a part of the surface of the base particle. Yes.

Patent Documents 6 to 9 disclose a structure having a core portion containing W alone or a W alloy (W solid solution).
Patent Document 6 discloses catalyst particles having W alone, an alloy of W and a metal selected from another group of metals, a mixture thereof as an inner core (core part), and Pt or Pt alloy as an outer shell part. Has been.
In Patent Document 7, a core particle (core part) made of a metal atom other than Pt or an alloy of a metal atom other than Pt (core part), and a metal particle having a shell layer (shell part) made of Pt on the surface of the core particle are electrically conductive carriers. A Pt-containing catalyst having a structure supported on the catalyst is disclosed. W is disclosed as a constituent material of both the core part and the shell part (Patent Document 7, paragraph number 0020, paragraph number 0021).
Patent Document 8 discloses a core particle (core part) having a face-centered cubic crystal structure made of W alone or a W alloy as a material, and a shell layer (shell) having a face-centered cubic crystal structure made of a metal such as Pt. Part) is disclosed.
Patent Document 9 discloses core-shell type fine particles having a core particle (core part) made of W alone or a W alloy as a material and a shell layer (shell part) made of a metal such as Pt.

Further, although it is unclear as to whether the catalyst particles have a core-shell structure, a catalyst in which Pt or a Pt alloy is supported on W carbide particles has been proposed as an electrode catalyst for a fuel cell (Patent Document 11). To 12, Non-Patent Document 1).
In Patent Document 11, W carbide particles (particles of a mixture of WC and W ₂ C or particles composed of WC) are generated on the conductive carbon to modify the surface of the conductive carbon. A catalyst having Pt particles supported on the particles is disclosed.
Patent Document 12 discloses a catalyst in which Pt particles are supported on particles mainly composed of WC. However, a configuration in which catalyst particles are supported on a conductive carbon support has not been studied.
Non-Patent Document 1 discloses a catalyst in which Pt particles are supported on particles mainly composed of W ₂ C. However, a configuration in which catalyst particles are supported on a conductive carbon support has not been studied.
Further, in a catalyst particle having a core-shell structure formed of a core part made of a non-Pt element and a shell part made of Pt, a structure intended to improve the catalytic activity as well as the amount of Pt has been proposed (for example, Patent Documents). 13).
For example, Patent Document 13 discloses a center particle (core part) containing a Pd alloy, an outermost layer (shell part) containing Pt, and an intermediate layer made of only Pd (zero valence) between the center particle and the outermost layer. There have been proposed electrode catalyst fine particles for a fuel cell having a child core-shell structure provided with.

In addition, this patent applicant presents the following publications as publications in which the above-mentioned literature known invention is described.

US Patent Application Publication No. 2007/31722 JP 2012-143753 A Special table 2008-545604 JP 2005-125282 A Japanese Patent Laid-Open No. 2003-080077 Special table 2010-501345 JP 2011-072981 A JP 2012-041581 A JP 2013-163137 A JP 2012-216292 A Special table 2013-518710 gazette JP 2008-021610 A WO2010 / 011170 Publication

Angew. Chem. Int. Ed. 2005, 44, 6557-6560

However, the present invention relates to an electrode catalyst for a fuel cell comprising a conductive carrier and catalyst particles having a core-shell structure supported on the carrier, and for an electrode having a core portion containing a W compound (particularly W carbide) as a main constituent. When focusing on the catalyst and looking at the above-mentioned conventional technology, in addition to reducing the amount of Pt used, the study of the structure for obtaining superior durability compared with the conventional Pt / C catalyst, and the embodiment The present inventors have found that sufficient demonstration has not been made and there is still room for improvement.
That is, in Patent Document 2 in which a structure having a core portion containing W oxide is disclosed, a reduction product (WO _2-y , 0) having a core portion of WO ₂ and a shell portion of WO ₂ on a carbon support. There is a description of an example of a catalyst having a structure in which particles that are an alloy of <y ≦ 2) and Pd are supported (Patent Document 2, Example 8), and the catalytic activity of this example is Pd on a carbon support. It is shown that the improvement is made with respect to the comparative example (Patent Document 2, Comparative Example 2) in which particles are supported (Patent Document 2, FIG. 11). However, it is unclear whether the configuration of this example is an effective configuration in terms of obtaining excellent durability as compared with the conventional Pt / C catalyst.

In addition, Patent Documents 3 to 5, which disclose other configurations having a core portion containing W oxide, do not describe examples corresponding to catalysts having a core portion containing W oxide, and are durable. Sex has not been demonstrated.
That is, Patent Document 3 does not describe an example. Further, Patent Document 4 and Patent Document 5 do not describe examples of catalysts having a structure using conductive carbon as a carrier. Further, when the configuration of the example is expressed by “shell part / core part”, the example is “Pt / CeO ₂ ”, “reduction-precipitated Pt (zero valence) and Ru simple substance / CeO ₂ ”, “reduction precipitation”. Pt (zero valence) and Ru simple substance / CeO ₂ .ZrO ₂ solid solution ”, which is only a result of a toxic substance purification performance evaluation test.

Further, Patent Documents 6 to 9 which disclose a structure having a core portion containing W alone or a W alloy (W solid solution) have a core portion containing W alone or a W alloy (W solid solution). There is no description of examples corresponding to the catalyst, and durability has not been demonstrated.
About patent document 6, what is described as an Example and performance evaluation is expressed as "Pt / Ag" (Patent Document 6, Example 1, Example 4), "Shell part / core part", " This is only the configuration of “Pt / Au” (Patent Document 6, Example 2, and Example 3). Regarding performance evaluation, it is only described that “a high specific activity can be obtained in an electrochemical test using an RDE (rotating ring disk electrode)”, and the details of how much durability is improved are unknown.
With respect to Patent Document 7, the performance evaluation is described as an example, and only the configuration of “Pt / Ru” (Patent Document 7, Example 1) is expressed by “shell part / core part”.
In Patent Document 8 and Patent Document 9, an example of synthesizing “W core fine particles (fine particles of W simple substance)” is described, but there is no description of an example in which a shell portion is formed and used as a catalyst. What is described as an example and evaluated for performance is only the configuration of “Pt / Ru” and “Pt / Ni” when expressed as “shell part / core part” (paragraph [0111] of Patent Document 8, Example 1 and Example 2 of Patent Document 9).

Further, in Patent Document 11 in which a catalyst in which Pt or a Pt alloy is supported on W carbide particles is proposed, W carbide particles are generated on the conductive carbon by surface modification of the conductive carbon. A catalyst in which Pt particles are supported on the particles is disclosed (Patent Document 11, Example 1, Example 2).
Specifically, if the configuration of the examples (“Example 1” and “Example 2” in Patent Document 11) is expressed as “shell part / core part”, Pt / (mixture of WC and W ₂ C), Pt / (particles made of WC).
The durability of the catalyst (the degree of deterioration of the initial performance) is estimated by an accelerated deterioration test. Specifically, for the catalytic activity related to the oxygen reduction reaction of the cathode, a 150 potential cycle between 0.5 and 1.3 V was carried out at a rate of 50 mV / s in an oxygen saturated electrolyte, and the decrease in performance was measured. , It is disclosed that performance degradation is improved compared to conventional Pt / C catalysts.
However, it is unclear whether the catalyst particles of Examples disclosed in Patent Document 11 have a core-shell structure.

Further, in Patent Document 12 in which a catalyst in which Pt or a Pt alloy is supported on W carbide particles is proposed, an example of a configuration in which catalyst particles are supported on a conductive carbon carrier is not described. The catalyst having Pt particles supported on WC synthesized via a specific precursor compound such as W ₂ N and WS ₂ (Patent Document 12, Examples 1 to 6) improves CO poisoning resistance and anode catalyst It is shown that the activity is improved. However, it is unclear whether the configuration of this example is an effective configuration in terms of obtaining excellent durability as compared with the conventional Pt / C catalyst.
Further, in Non-Patent Document 1, in which a catalyst in which Pt or a Pt alloy is supported on W carbide particles is proposed, an example of a configuration in which catalyst particles are supported on a conductive carbon support is not described. An example of a catalyst having a structure in which Pt particles are supported on W ₂ C is disclosed. Furthermore, this example discloses that catalytic activity such as ECSA is improved as compared with a catalyst having a structure in which alloy particles of Pt and Ru are supported on a carbon support. However, it is unclear whether the configuration of this example is an effective configuration in terms of obtaining excellent durability as compared with the conventional Pt / C catalyst.

The present invention has been made in view of such technical circumstances, and provides an electrode catalyst that has superior durability compared to conventional Pt / C catalysts and can contribute to cost reduction. For the purpose.
Another object of the present invention is to provide a gas diffusion electrode forming composition, a gas diffusion electrode, a membrane / electrode assembly (MEA), and a fuel cell stack, each including the electrode catalyst.

The present inventors have a configuration capable of obtaining excellent durability as compared with a conventional Pt / C catalyst in the case of adopting a W-based material as a constituent material of the core portion with the intention of reducing the amount of Pt used. We conducted an intensive study.
As a result, the inventors of the present invention are effective in a configuration including a core portion including at least W carbide and a two-layer shell portion. More specifically, the Pd is provided between the core portion and the shell portion including Pt (zero valence). The inventors have found that it is effective to provide a shell portion including (zero valence) (a configuration that is neither disclosed nor suggested in the prior art) and have completed the present invention.
More specifically, the present invention includes the following technical matters.

That is, the present invention
A conductive carrier;
Catalyst particles supported on the carrier;
Contains
The catalyst particles have a core part formed on the carrier, a first shell part formed on the core part, and a second shell part formed on the first shell part. And
The core portion includes WC and W carbide including WC _1-x (0 <x <1),
The first shell portion includes Pd (zero valence),
The second shell portion contains Pt (zero valence),
The core particles serving as the precursor of the core part satisfy the condition of the following formula (1).
An electrode catalyst is provided.
0.03 ≦ {I2 / (I1 + I2)} ≦ 0.75 (1)
Here, in formula (1), “I1” indicates the peak intensity of a peak attributed to WC obtained by X-ray diffraction measurement of the core particle, and “I2” is obtained by X-ray diffraction measurement of the core particle. The peak intensity of the peak attributed to WC _1-x (0 <x <1) is shown.

Although the detailed mechanism has not been sufficiently elucidated, the electrode catalyst of the present invention has superior durability and low cost compared to the conventional Pt / C catalyst by adopting the above-described configuration. Can contribute to

Here, in the present invention, the “W carbide” indicates a form in which a tungsten (W) atom and a carbon (C) atom exist as a compound having a bond.

Further, in the electrode catalyst of the present invention, W ₂ C may further be included in the core part within a range where the effects of the present invention are obtained.

Furthermore, in the electrode catalyst of the present invention, when W ₂ C is further contained in the core part, it is preferable that the core particles serving as the precursor of the core part further satisfy the condition of the following formula (2).
0.02 ≦ {I3 / (I1 + I2 + I3)} ≦ 0.30 (1)
[In formula (2), I1 represents the same peak intensity as I1 in the formula (1), I2 represents the same peak intensity as I2 in the formula (1), and I3 represents X of the core particle. The peak intensity of the peak attributed to W ₂ C obtained by line diffraction measurement is shown.

In the present invention, the W carbide includes WC, WC _1-x (0 <x <1), and may further include W ₂ C. Here, WC, WC _1-x (0 <x <1), and W ₂ C are “Binary Alloy Phase Diagrams, Second Edition (author / editor H. Okamoto et al, publisher / publisher ASM International)”. This corresponds to the δ phase (WC), γ phase (WC _1-x ), and β phase (W ₂ C) described on page 896, “WC Phase Diagram”. WC, WC _1-x (0 <x <1), and W ₂ C are also described in, for example, the following papers. M. Gubisch, Y. Liu et al., “Tribological characteristics of WC _1-x , W ₂ C and WC tungsten carbide films”. Elsevier, Tribology and Interface Engineering Serie, Life cycle Tribology, volume 48, 2005, 409-417 .

In the present invention, the W carbide contained in the core particle that is a precursor of the core part of the electrode catalyst is confirmed by X-ray diffraction measurement (hereinafter referred to as “XRD measurement” if necessary). be able to.

That is, in the present invention, X-ray diffraction spectrum is measured by irradiating X-ray (Cu—Kα ray) to the core particle powder which is a precursor of the electrode catalyst core part, and WC, WC _1-x (0 <x <1), W ₂ C and the like can be confirmed by the presence or absence by observing characteristic peaks attributed to each W carbide.

For example, as a peak attributed to WC, as a peak at a diffraction angle 2θ (± 0.3 °) of X-ray diffraction, for example, 31.513 °, 35.639 °, 48.300 °, 64.016 °. , A characteristic peak observed in the vicinity of 65.790 °.

For example, the peak attributed to WC _1-x is a peak at a diffraction angle 2θ (± 0.3 °) of X-ray diffraction, for example, 36.977 °, 42.887 °, 62.027 °, 74 The characteristic peaks observed in the vicinity of 198 ° and 78.227 ° are listed.

For example, as a peak attributed to W ₂ C, a peak at a diffraction angle 2θ (± 0.3 °) of X-ray diffraction is 34.535 °, 38.066 °, 39.592 °, 52.332 °. The characteristic peak observed in the vicinity of 61.879 ° is raised.

Here, in the present invention, “I1” means a diffraction angle 2θ (± 0.3 °) of X-ray diffraction = 48.200 among peaks attributed to WC obtained by X-ray diffraction measurement of core particles. The peak intensity of the peak near ° is shown.
“I2” means a diffraction angle 2θ (± 0.3 °) of X-ray diffraction among peaks attributed to WC _1-x (0 <x <1) obtained by X-ray diffraction measurement of core particles. ) = Peak intensity of a peak near 42.700 °.
In addition, “I3” means a diffraction angle 2θ (± 0.3 °) of the vicinity of 39.300 ° among peaks attributed to W ₂ C obtained by X-ray diffraction measurement of the core particles. The peak intensity of the peak is shown.

In the present specification, when describing the configuration of the electrode catalyst, if necessary, “the configuration of the catalyst particles supported on the support (main constituent material) / the configuration of the conductive support (main It is written " More specifically, it is expressed as “shell configuration / core configuration / support configuration”. More specifically, it is expressed as “configuration of second shell portion / configuration of first shell portion / configuration of core portion / configuration of carrier”. For example, the structure of the electrode catalyst is “a second shell portion made of Pt (zero valence), a first shell portion made of Pd (zero valence), a core portion mainly composed of W carbide, and a carrier made of conductive carbon. ”Is expressed as“ Pt / Pd / WC / C ”.

In addition, in the electrode catalyst of the present invention, the core portion may further contain W oxide as long as the effects of the present invention are obtained.

Furthermore, in the electrode catalyst of the present invention, W (zero valence) may further be included in the core portion within a range where the effects of the present invention are obtained.

Furthermore, this invention provides the composition for gas diffusion electrode formation containing the electrode catalyst of any one of the above-mentioned this invention.
Since the composition for forming a gas diffusion electrode of the present invention contains the electrode catalyst of the present invention, it has superior durability compared to conventional Pt / C catalysts and can contribute to cost reduction. A gas diffusion electrode can be easily manufactured.

Moreover, this invention provides the gas diffusion electrode containing the catalyst for electrodes of the above-mentioned this invention.
The gas diffusion electrode of the present invention includes the electrode catalyst of the present invention. Therefore, it becomes easy to set it as the structure which has the outstanding durability compared with the conventional Pt / C catalyst, and can contribute to cost reduction.

Furthermore, this invention provides the membrane electrode assembly (MEA) containing the gas diffusion electrode of the above-mentioned this invention.
Since the membrane-electrode assembly (MEA) of the present invention includes the gas diffusion electrode of the present invention, it has superior durability compared to conventional Pt / C catalysts and contributes to cost reduction. It becomes easy to set it as the structure which can be performed.

The present invention also provides a fuel cell stack including the above-described membrane-electrode assembly (MEA) of the present invention.
According to the fuel cell stack of the present invention, since it includes the membrane-electrode assembly (MEA) of the present invention, the fuel cell stack has excellent durability compared with the conventional Pt / C catalyst, and is low in cost. It becomes easy to make it the structure which can contribute to.

ADVANTAGE OF THE INVENTION According to this invention, it has the durability outstanding compared with the conventional Pt / C catalyst, and the catalyst for electrodes which can contribute to cost reduction is provided.
The present invention also provides a gas diffusion electrode forming composition, a gas diffusion electrode, a membrane / electrode assembly (MEA), and a fuel cell stack comprising such an electrode catalyst.

It is a schematic cross section which shows one suitable form of the catalyst for electrodes (core-shell catalyst) of this invention. It is a schematic cross section which shows another suitable one form of the catalyst for electrodes (core-shell catalyst) of this invention. It is a schematic diagram which shows suitable one Embodiment of the fuel cell stack of this invention. It is a schematic diagram which shows schematic structure of the rotating disk electrode measuring apparatus provided with the rotating disk electrode used in the Example. 7 is a graph illustrating a “rectangular wave potential sweep mode” in which the potential (vsRHE) of the rotating disk electrode WE is swept with respect to the reference electrode RE in the embodiment.

Hereinafter, preferred embodiments of the present invention will be described in detail with appropriate reference to the drawings.
<Catalyst for electrode>
FIG. 1 is a schematic cross-sectional view showing a preferred embodiment of the electrode catalyst (core-shell catalyst) of the present invention. FIG. 2 is a schematic cross-sectional view showing another preferred embodiment of the electrode catalyst (core-shell catalyst) of the present invention.
As shown in FIG. 1, the electrode catalyst 10 of the present invention includes a carrier 2 and catalyst particles 3 having a so-called “core-shell structure” formed on the carrier 2.
Further, the catalyst particle 3 includes a so-called “core shell” including a core portion 4 formed on the carrier 2 and a shell portion 7 (first shell portion 5 and second shell portion 6) formed on the core portion 4. Structure ".
That is, the electrode catalyst 10 has a structure in which the core part 4 is a core (core) on the carrier 2 and the surface of the core part 4 is covered with the first shell part 5 and the second shell part 6 being the shell part 7. have.
In addition, the constituent elements (chemical composition) of the core portion, the constituent elements (chemical composition) of the first shell portion 5 and the second shell portion 6 are different.

In the present invention, the electrode catalyst only needs to have a shell portion formed on at least a part of the surface of the core portion.
For example, from the viewpoint of obtaining the effect of the present invention more reliably, as shown in FIG. 1, the electrode catalyst 10 is preferably in a state in which substantially the entire surface of the core portion 4 is covered by the shell portion 7. .
In addition, as shown in FIG. 2, the electrode catalyst 1 is covered with a part of the surface of the core part 4 and the surface of the core part 4 is partially exposed within the range in which the effect of the present invention can be obtained ( For example, a state in which a part 4s of the surface of the core portion 4 shown in FIG. In other words, the shell part 7a and the shell part 7b may be partially formed on part of the surface of the core part 4 as in the electrode catalyst 10A shown in FIG.
Furthermore, in this case, as shown in FIG. 2, it is preferable that the second shell portion 6a covers a substantially entire surface of the first shell portion 5a.
In addition, as shown in FIG. 2, in a range where the effect of the present invention can be obtained, a part of the surface of the first shell portion 5b is covered and the surface of the first shell portion 5b is partially exposed (for example, 2 may be a state in which a part 5s of the surface of the first shell portion 5b shown in FIG. 2 is exposed.
Furthermore, the electrode catalyst of the present invention may be in a state where the electrode catalyst 10 shown in FIG. 1 and the electrode catalyst 10A shown in FIG.

Furthermore, in the present invention, as long as the effect of the present invention can be obtained, the shell portion 7a and the shell portion 7b may be mixed with respect to the same core portion 4 as shown in FIG. . Further, in the present invention, as long as the effects of the present invention can be obtained, only the shell portion 7 a may be formed on the same core portion 4, and only the shell portion 7 b is formed on the same core portion 4. May be in a state where any of the states is formed (not shown).
In addition, within the range in which the effects of the present invention can be obtained, the electrode catalyst 1 includes, on the carrier 2, in addition to at least one of the electrode catalyst 10 and the electrode catalyst 10A described above, A state in which “particles of only the core portion 4 not covered” are supported may be included (not shown).
Furthermore, within the range in which the effect of the present invention can be obtained, the electrode catalyst 1 includes “particles consisting only of constituent elements of the shell portion 7 in addition to at least one of the electrode catalyst 10 and the electrode catalyst 10A described above. "May be included in a state where it is not in contact with the core portion 4 (not shown).
In addition, within the range where the effects of the present invention can be obtained, the electrode catalyst 1 includes, in addition to at least one of the above-described electrode catalyst 10 and electrode catalyst 10A, “a core portion not covered with the shell portion 7. A state in which “only four particles” and “particles composed only of the constituent elements of the shell portion 7” are independently supported may be included.

About the thickness of the 1st shell part 5 and the 2nd shell part 6, a preferable range is suitably set by the design concept of the catalyst for electrodes.
For example, when it is intended to minimize the use amount of Pt constituting the second shell portion 6, it is preferably a layer composed of one atom (one atomic layer). The thickness of the second shell portion 6 is equivalent to twice the diameter of one atom of the metal element (when approximating a sphere) when the metal element constituting the second shell portion 6 is one kind. It is preferable that the thickness be
When there are two or more types of metal elements constituting the second shell portion 6, a layer composed of one atom (one atom formed by juxtaposing two or more types of atoms on the surface of the core portion 4. The thickness corresponding to the layer) is preferable.
For example, when the durability is improved by increasing the thickness of the second shell portion 6, the thickness is preferably 1 to 5 nm, and more preferably 2 to 10 nm.
In the present invention, the “average particle diameter” refers to an average value of the diameters of particles composed of an arbitrary number of particle groups, as observed with an electron micrograph.
The thickness of the first shell portion 5 is preferably equal to or less than the thickness of the second shell portion 6. This is preferable because the amount of Pd used can be reduced and the amount of Pd eluted when used as an electrode catalyst can be reduced.

The carrier 2 is not particularly limited as long as it can carry a composite composed of the core part 4, the first shell part 5, and the second shell part 6 and has a large surface area.
Furthermore, it is preferable that the support | carrier 2 has a favorable dispersibility in the composition for gas diffusion electrode formation containing the electrode catalyst 1, and has the outstanding electroconductivity.

Carrier 2 is glassy carbon (GC), fine carbon, carbon black, graphite, carbon fiber, activated carbon, pulverized product of activated carbon, carbon nanofiber, carbon nanotube, etc., or glass or ceramics material such as oxide. It can be adopted as appropriate.
Among these, a carbon-based material is preferable from the viewpoint of the adsorptivity with the core portion 4 and the BET specific surface area of the carrier 2.
Furthermore, as the carbon-based material, conductive carbon is preferable, and as the conductive carbon, conductive carbon black is particularly preferable.
Examples of the conductive carbon black include trade names “Ketjen Black EC300J”, “Ketjen Black EC600”, “Carbon EPC” and the like (manufactured by Lion Chemical Co., Ltd.).

The core portion 4 has a configuration including WC and W carbide including WC _1-x (0 <x <1). Further, the core portion 4 may further include W ₂ C. Further, the core portion 4 may further contain W oxide as the W compound as another component of the W carbide. Further, when a component other than the W compound is included, the component is preferably W (zero valent).
Furthermore, the core part 4 has the core particle | grains used as the precursor of a core part satisfy | fills the conditions of following formula (1) from a viewpoint of obtaining sufficient durability.
0.03 ≦ {I2 / (I1 + I2)} ≦ 0.75 (1)

Further, when the core portion 4 W _{2 C} is further contained, from the viewpoint of obtaining a sufficient durability, the core particles as the precursor of the core is further satisfies the condition of formula (2) It is preferable.
0.02 ≦ {I2 / (I1 + I2 + I3)} ≦ 0.30 (2)

Here, in formula (1), “I1” indicates the peak intensity of a peak attributed to WC obtained by X-ray diffraction measurement of the core particle, and “I2” indicates WC obtained by X-ray diffraction measurement of the core particle. The peak intensity of the peak attributed to _1-x (0 <x <1) is shown.
More specifically, “I1” refers to a diffraction angle 2θ (± 0.3 °) = 48.200 ° of X-ray diffraction among peaks attributed to WC obtained by X-ray diffraction measurement of core particles. The peak intensity of nearby peaks is shown.
“I2” means a diffraction angle 2θ (± 0.3 °) of X-ray diffraction among peaks attributed to WC _1-x (0 <x <1) obtained by X-ray diffraction measurement of core particles. ) = Peak intensity of a peak near 42.700 °.

Here, in Formula (2), “I1” indicates the same peak intensity as I1 in Formula (1), “I2” indicates the same peak intensity as I2 in Formula (1), and “I3” Indicates the peak intensity of the peak attributed to W ₂ C obtained by X-ray diffraction measurement of the core particles.
In the formula (2), “I3” means a diffraction angle 2θ (± 0.3 °) of X-ray diffraction among peaks attributed to W ₂ C obtained by X-ray diffraction measurement of core particles = The peak intensity of a peak near 39.300 ° is shown.

The first shell portion 5 includes Pd (zero valence). From the viewpoints of obtaining the effects of the present invention more reliably and manufacturing easiness, the first shell portion 5 is preferably composed of Pd (zero valence) as a main component (50 wt% or more). More preferably, it is composed of 0 valence).

The second shell portion 6 contains Pt (zero valence). From the viewpoints of obtaining the effects of the present invention more reliably and manufacturing easiness, the second shell portion 6 is preferably composed of Pt (zero valence) as a main component (50 wt% or more), Pt ( More preferably, it is composed of 0 valence).

Although the detailed mechanism has not been fully elucidated, the cores of the electrode catalyst 10 and the electrode catalyst 10A so that the value of {I2 / (I1 + I2)} in the above formula (1) is 0.03 to 0.75. The present inventors have found that the effects of the present invention can be obtained by constituting the core particles that are the precursors of the parts.

Here, when the value of {I2 / (I1 + I2)} in the above formula (1) is 0.03 or more, the present inventors have WC _1-x (0 <x <1) with respect to WC in the core particle. ) Is relatively increased and durability is expected to improve. On the other hand, when the value of {I2 / (I1 + I2)} is 0.75 or less, the present inventors set the content of WC _1-x (0 <x <1) relative to WC to an amount necessary for improving durability. It is speculated that sufficient conductivity of the core particles can be ensured while ensuring the same.

Further, although the detailed mechanism has not been sufficiently elucidated, when W ₂ C is further included in the core portion 4, the value of {I2 / (I1 + I2 + I3)} in the above formula (2) is 0.02 to 0 The present inventors have found that the effects of the present invention can be obtained more easily by configuring the core particles serving as the precursor of the core portion of the electrode catalyst 10 and the electrode catalyst 10A so as to be .30. .

Here, when the value of {I2 / (I1 + I2 + I3)} is 0.02 or more, the inventors of the present invention have WC _1-x (0 <x <1) with respect to WC and W ₂ C in the core particle. It is speculated that the proportion will increase relatively and durability will improve. On the other hand, when the value of {I2 / (I1 + I2 + I3)} is 0.30 or less, the inventors improved the content of WC _1-x (0 <x <1) with respect to WC and W ₂ C. It is presumed that sufficient conductivity of the core particles can be easily secured while easily securing the amount necessary for the above.

<Method for producing electrode catalyst>
The method for producing electrode catalyst 10 (10A) includes a “core particle forming step” in which core particles containing W carbide and W oxide are formed on a support, and the surface of the core particles obtained through the core particle forming step. The first shell part 5 (5a, 5b) is formed on at least a part of the first shell part forming step, and the second shell part is formed on at least a part of the surface of the particles obtained through the first shell part forming step. 6 (6a, 6b) and the “second shell part forming step”.

The electrode catalyst 10 (10A) includes catalyst particles 3 (3a) that are catalyst components of the electrode catalyst, that is, the core portion 4, the first shell portion 5 (5a, 5b), and the second shell portion 6 (6a, 6b). ) Are sequentially supported on the carrier 2.
The method for producing the electrode catalyst 10 (10A) is not particularly limited as long as the catalyst particles 3 (3a) as the catalyst component can be supported on the carrier 2.
For example, an impregnation method in which a solution containing a catalyst component is brought into contact with the support 2 and the support component 2 is impregnated with the catalyst component, a liquid phase reduction method in which a reducing agent is added to the solution containing the catalyst component, underpotential deposition (UPD ) And other electrochemical deposition methods, chemical reduction methods, reduction deposition methods using adsorbed hydrogen, alloy catalyst surface leaching methods, displacement plating methods, sputtering methods, vacuum deposition methods and the like can be exemplified. .
However, in the “core particle forming step”, the above-mentioned known methods are combined so as to satisfy the condition of the formula (1) described above, preferably the condition of the formula (2) described above, etc. It is preferable to adjust the raw materials, the mixing ratio of the raw materials, the reaction conditions for the synthesis reaction, and the like.

Further, for the core particles obtained through the “core particle forming step”, before forming the first shell portion in the “first shell portion forming step”, a treatment for reducing the W oxide present on the surface of the core particles is performed. You may give it. For example, a reduction treatment of the surface of the core particle or a W oxide removal treatment with an acid may be performed.
In addition, as a method of configuring the core particles of the electrode catalyst 10 and the electrode catalyst 10A so as to satisfy preferable conditions such as the condition represented by the above-described formula (1) and the condition represented by the formula (2), for example, Analyze the chemical composition and structure of the product (catalyst) using various known analytical methods, feed back the analysis results obtained to the manufacturing process, select the raw material to be selected, the blending ratio of the raw material, the selected synthesis reaction, Examples thereof include a method for preparing / changing the reaction conditions of the synthesis reaction.

<Structure of fuel cell>
FIG. 3 shows a gas diffusion electrode forming composition containing the electrode catalyst of the present invention, a gas diffusion electrode produced using this gas diffusion electrode forming composition, and a membrane / electrode assembly comprising this gas diffusion electrode ( FIG. 2 is a schematic diagram showing a preferred embodiment of a fuel cell stack including a MEMBRANE ELECTRODE ASSEMBLY (hereinafter abbreviated as “MEA” as necessary).
The fuel cell stack 40 shown in FIG. 3 has a configuration in which the MEA 42 is a unit cell and a plurality of the unit cells are stacked.

Further, the fuel cell stack 40 includes an anode 43 (negative electrode) that is a gas diffusion electrode, a cathode 44 (positive electrode) that is a gas diffusion electrode, and an electrolyte membrane 45 disposed between these electrodes. have.
The fuel cell stack 40 has a configuration in which the MEA 42 is sandwiched between a separator 46 and a separator 48.

Hereinafter, the gas diffusion electrode forming composition, the anode 43 and the cathode 44, and the MEA 42, which are members of the fuel cell stack 40 including the electrode catalyst of the present invention, will be described.

<Composition for forming gas diffusion electrode>
The electrode catalyst of the present invention can be used as a so-called catalyst ink component to form the gas diffusion electrode forming composition of the present invention.
The gas diffusion electrode forming composition of the present invention is characterized by containing the electrode catalyst of the present invention.
The composition for forming a gas diffusion electrode contains the electrode catalyst and an ionomer solution as main components. The composition of the ionomer solution is not particularly limited. For example, the ionomer solution may contain a polymer electrolyte having hydrogen ion conductivity, water, and alcohol.

The polymer electrolyte contained in the ionomer solution is not particularly limited. For example, the polymer electrolyte can be exemplified by a perfluorocarbon resin having a known sulfonic acid group or carboxylic acid group. As readily available polymer electrolytes having hydrogen ion conductivity, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) It can be illustrated.

The composition for forming a gas diffusion electrode can be prepared by mixing, crushing, and stirring an electrode catalyst and an ionomer solution.
The composition for forming a gas diffusion electrode can be prepared using a pulverizing mixer such as a ball mill or an ultrasonic disperser. The pulverization conditions and the stirring conditions when operating the pulverization mixer can be appropriately set according to the mode of the gas diffusion electrode forming composition.
Each composition of the electrode catalyst, water, alcohol, and polymer electrolyte having hydrogen ion conductivity contained in the gas diffusion electrode forming composition has a good dispersion state of the electrode catalyst, and the electrode catalyst is gas diffused. It is appropriately set so that the entire catalyst layer of the electrode can be widely spread and the power generation performance of the fuel cell can be improved.

<Gas diffusion electrode>
The anode 43, which is a gas diffusion electrode, has a configuration including a gas diffusion layer 43a and a catalyst layer 43b formed on the surface of the gas diffusion layer 43a on the electrolyte membrane 45 side.
Similarly to the anode 43, the cathode 44 has a gas diffusion layer (not shown) and a catalyst layer (not shown) formed on the surface of the gas diffusion layer on the electrolyte membrane 45 side.
The electrode catalyst of the present invention may be contained in at least one of the anode 43 and the cathode 44.
In addition, the gas diffusion electrode of this invention can be used as an anode and can also be used as a cathode.

(Catalyst layer for electrodes)
The catalyst layer 43b is a layer in the anode 43 where a chemical reaction is performed in which the hydrogen gas sent from the gas diffusion layer 43a is dissociated into hydrogen ions by the action of the electrode catalyst 10 contained in the catalyst layer 43b. Further, the catalyst layer 43b is formed of the electrode catalyst 10 in which, in the cathode 44, the catalyst layer 43b contains air (oxygen gas) sent from the gas diffusion layer 43a and hydrogen ions that have moved through the electrolyte membrane from the anode. It is a layer in which a chemical reaction that binds by action takes place.

The catalyst layer 43b is formed using the gas diffusion electrode forming composition. The catalyst layer 43b preferably has a large surface area so that the reaction between the electrode catalyst 10 and the hydrogen gas or air (oxygen gas) sent from the gas diffusion layer 43a can be sufficiently performed. The catalyst layer 43b is preferably formed so as to have a uniform thickness throughout. The thickness of the catalyst layer 43b may be appropriately adjusted and is not limited, but is preferably 2 to 200 μm.

(Gas diffusion layer)
The gas diffusion layer provided in the anode 43 serving as the gas diffusion electrode and the cathode 44 serving as the gas diffusion electrode is introduced into the gas flow path formed between the separator 46 and the anode 43 from the outside of the fuel cell stack 40. This is a layer provided for diffusing the hydrogen gas and the air (oxygen gas) introduced into the gas flow path formed between the separator 48 and the cathode 44 into each catalyst layer.
The gas diffusion layer has a role of supporting the catalyst layer and immobilizing it on the surface of the gas diffusion electrode.

The gas diffusion layer has a function / structure that allows hydrogen gas or air (oxygen gas) to pass through well and reach the catalyst layer. For this reason, it is preferable that the gas diffusion layer has water repellency. For example, the gas diffusion layer has a water repellent component such as polyethylene terephthalate (PTFE).

The member which can be used for the gas diffusion layer is not particularly limited, and a known member used for the gas diffusion layer of the fuel cell electrode can be used. For example, carbon paper, carbon paper as a main raw material, and carbon powder, ion-exchanged water as optional components, and a secondary material made of polyethylene terephthalate dispersion as a binder are applied to carbon paper.
The anode 43 that is a gas diffusion electrode and the cathode 44 that is a gas diffusion electrode may include an intermediate layer (not shown) between the gas diffusion layer and the catalyst layer.

(Manufacturing method of gas diffusion electrode)
A method for manufacturing the gas diffusion electrode will be described. The gas diffusion electrode of this invention should just be manufactured so that the electrode catalyst of this invention may become a structural component of a catalyst layer, and a manufacturing method is not specifically limited, A well-known manufacturing method is employable.
For example, the gas diffusion electrode is formed by applying a gas diffusion electrode forming composition containing an electrode catalyst, a polymer electrolyte having hydrogen ion conductivity, and an ionomer to the gas diffusion layer, and You may manufacture through the process of drying the gas diffusion layer with which the composition was apply | coated, and forming a catalyst layer.

<Membrane / electrode assembly (MEA)>
An MEA 42 that is a preferred embodiment of the MEA of the present invention shown in FIG. 3 has a configuration including an anode 43, a cathode 44, and an electrolyte membrane 45. The MEA 42 has a configuration in which at least one of an anode and a cathode includes a gas diffusion electrode containing the electrode catalyst of the present invention.
The MEA 42 can be manufactured by laminating the anode 43, the electrolyte 300, and the cathode 44 in this order, and then press-bonding them.

<Fuel cell stack>
A fuel cell stack 40 that is a preferred embodiment of the fuel cell stack of the present invention shown in FIG. 3 has a configuration in which a separator 46 is disposed outside the anode 43 of the MEA 42 and a separator 48 is disposed outside the cathode 44. One unit cell (single cell) is used, and this unit cell (single cell) has a single configuration or a configuration in which two or more units are integrated (not shown).
The fuel cell system is completed by attaching and assembling peripheral devices to the fuel cell stack 40.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

(I) Preparation of electrode catalysts of Examples and Comparative Examples

Example 1
<Manufacture of electrode catalyst>

[“Pt / Pd / W / C” powder in which a second shell portion made of Pt is formed on Pd / W / C]
“Pt / Pd / W / C” powder {trade name “NE-F12W10-AAA”, N.P., on which a second shell portion made of Pt is formed on Pd of the particles of the following “Pd / W / C” powder. E. CHEMCAT)} was produced as the electrode catalyst of Example 1.
This Pt / Pd / W / C powder is prepared by preparing a mixed solution of the following Pd / W / C powder, potassium chloroplatinate, and water, and adding a reducing agent to the Pt / Pd / W / C powder. It was obtained by reducing the ions.

[“Pd / W / C” powder in which a first shell portion made of Pd is formed on W / C]
“Pd / W / C” powder in which a first shell portion made of Pd is formed on W of the following “W / C” powder particles {trade name “NE-F02W00-AA”, NE CHEMCAT Made)}.
This Pd / W / C powder was prepared by preparing a mixed solution of the following W / C powder, sodium tetrachloropalladium (II) and water, and adding a reducing agent to the palladium in the liquid obtained. It can be obtained by reducing ions.

[Core particle-supported carbon “W / C” powder (core particle serving as a precursor of the core of the electrode catalyst)]
A W / C powder {trade name “NE-F00W00-A”, manufactured by NE CHEMCAT)} in which core particles composed of W carbide and W oxide were supported on carbon black powder was prepared.
The W / C powder was measured by the following XRD measurement, and the peak intensity ratio {I2 / (I1 + I2)} in which WC, W ₂ C, and WC _1-x (0 <x <1) are shown in Table 1 was obtained. , {I2 / (I1 + I2 + I3)}, respectively.
This W / C powder is a powder containing a commercially available carbon black powder (specific surface area 750 to 850 m ² / g), a commercially available tungstate, and a commercially available water-soluble polymer (carbon source) in a reducing atmosphere. It was prepared by heat treatment.

<X-ray diffraction measurement>
In this example, XRD measurement was performed with the following apparatus and measurement conditions. As the apparatus, the apparatus name “X′PertPRO” manufactured by Panallytical was used. The measurement conditions were tube current: 40 mA, tube voltage: 45 kV, target: Cu, step size (step width): 0.017 ° = 2θ.

Under this measurement condition, X-ray diffraction measurement of the core particle was performed, and among the peaks attributed to WC, the peak at the diffraction angle 2θ (± 0.3 °) = 48.200 ° of X-ray diffraction The peak intensity was set to “I1”. Of the peaks attributed to WC _1-x (0 <x <1) obtained by X-ray diffraction measurement of the core particles, the diffraction angle 2θ (± 0.3 °) of X-ray diffraction = 42.700 °. The peak intensity of the nearby peak was defined as “I2”. Further, among the peaks attributed to W ₂ C obtained by X-ray diffraction measurement of the core particles, the peak intensity of the peak near the diffraction angle 2θ (± 0.3 °) = 39.300 ° of X-ray diffraction is expressed as “ I3 ".

<Measurement of loading rate (ICP analysis)>
For the electrode catalyst of Example 1, the Pt loading rate L _Pt (wt%), the Pd loading rate L _Pd (wt%), and the W loading rate L _W (wt%) were measured by the following methods.
The electrode catalyst of Example 1 was immersed in aqua regia to dissolve the metal. Next, insoluble component carbon was removed from the aqua regia. Next, aqua regia without carbon was analyzed by ICP.
The results of ICP analysis are shown in Table 1.

<Surface observation and structure observation of electrode catalyst>
As a result of confirming the STEM-HAADF image and the EDS elementary mapping image of the electrode catalyst of Example 1, the first shell made of Pd was formed on at least a part of the surface of the core part particles made of W carbide and W oxide. And a catalyst particle having a core-shell structure in which a second shell portion layer made of Pt is formed on at least a part of the first shell portion layer is supported on a conductive carbon carrier. (See FIG. 1 and FIG. 2).

(Example 2)
<Manufacture of electrode catalyst>

[“Pt / Pd / W / C” powder in which a second shell portion made of Pt is formed on Pd / W / C]
“Pt / Pd / W / C” powder in which a second shell portion made of Pt is formed on Pd of the following “Pd / W / C” powder particles {trade name “NE-G12W10-AAA”, N. E. CHEMCAT)) was produced as the electrode catalyst of Example 2.
This Pt / Pd / W / C powder is prepared by preparing a mixed solution of the following Pd / W / C powder, potassium chloroplatinate, and water, and adding a reducing agent to the Pt / Pd / W / C powder. It was obtained by reducing the ions.

[“Pd / W / C” powder in which a first shell portion made of Pd is formed on W / C]
“Pd / W / C” powder in which a first shell portion made of Pd is formed on W of the following “W / C” powder particles {trade name “NE-G02W00-AA”, NE CHEMCAT Made)}.
This Pd / W / C powder was prepared by preparing a mixed solution of the following W / C powder, sodium tetrachloropalladium (II) and water, and adding a reducing agent to the palladium in the liquid obtained. It can be obtained by reducing ions.

[Core particle-supported carbon “W / C” powder (core particle serving as a precursor of the core of the electrode catalyst)]
W / C powder {trade name “NE-G00W00-A”, manufactured by NE CHEMCAT)} in which core particles composed of W carbide and W oxide were supported on carbon black powder was prepared.
The W / C powder was measured by the following XRD measurement, and the peak intensity ratio {I2 / (I1 + I2)} in which WC, W ₂ C, and WC _1-x (0 <x <1) are shown in Table 1 was obtained. , {I2 / (I1 + I2 + I3)}, respectively.
This W / C powder is a powder containing a commercially available carbon black powder (specific surface area 200 to 300 m ² / g), a commercially available tungstate, and a commercially available water-soluble polymer (carbon source) in a reducing atmosphere. It was prepared by heat treatment.
The electrode catalyst of Example 2 was subjected to ICP analysis of the electrode catalyst under the same conditions as the electrode catalyst of Example 1. The results of each analysis are shown in Table 1.
Next, also for the electrode catalyst of Example 2, as a result of confirming the STEM-HAADF image and the EDS elementary mapping image, at least part of the surface of the particle of the core portion composed of W carbide and W oxide was formed from Pd. The catalyst particles having the core-shell structure in which the first shell layer is formed and the second shell portion layer made of Pt is formed on at least a part of the first shell layer are supported on the conductive carbon carrier. It was confirmed that it has the configuration (see FIGS. 1 and 2).

(Example 3 to Example 6)
XRD measurement results {I2 / (I1 + I2)} and {I2 / (I1 + I2 + I3)} of core particles that are precursors of the core part of the electrode catalyst shown in Table 1, ICP analysis results (L Example 3 to Example 3 were carried out using the same preparation conditions and the same raw materials as in Example 2 except that the amount of raw materials charged, reaction conditions, etc. were finely adjusted to have _Pt , L _Pd , L _W ). The electrode catalyst of Example 6 was produced.
ICP analysis was performed under the same conditions as in Example 1.
Further, with respect to the electrode catalysts of Examples 3 to 6, as a result of confirming the STEM-HAADF image and the EDS elementary mapping image, it was found that at least a part of the surface of the core particle composed of W carbide and W oxide was present. The catalyst particles having the core-shell structure in which the first shell layer made of Pd is formed and the second shell layer made of Pt is formed on at least a part of the first shell layer are conductive carbon. It was confirmed that the structure supported on the carrier (see FIGS. 1 and 2) was provided.

(Examples 7 to 10)
XRD measurement results {I2 / (I1 + I2)} and {I2 / (I1 + I2 + I3)} of core particles that are precursors of the core part of the electrode catalyst shown in Table 1, ICP analysis results (L _{Pt 1} , L _Pd , L _W ), Examples 7 to 5 were carried out using the same raw materials and preparation conditions as in Example 1 except that the amount of raw materials charged and reaction conditions were finely adjusted. The electrode catalyst of Example 10 was prepared.
XPS analysis and ICP analysis were also performed under the same conditions as in Example 1.
Further, with respect to the electrode catalysts of Examples 7 to 10, as a result of confirming the STEM-HAADF image and the EDS elementary mapping image, it was found that at least a part of the surface of the core particle composed of W carbide and W oxide was present. The catalyst particles having the core-shell structure in which the first shell layer made of Pd is formed and the second shell layer made of Pt is formed on at least a part of the first shell layer are conductive carbon. It was confirmed that the structure supported on the carrier (see FIGS. 1 and 2) was provided.

(Comparative Example 1)
As a Pt / C catalyst, a Pt / C catalyst (trade name: “SA50BH”) manufactured by NE CHEMCAT with a Pt loading rate of 50 wt% was prepared. This catalyst uses the same carrier as the electrode catalyst of Example 1 as a raw material.
The electrode catalyst of Comparative Example 1 was subjected to XRD analysis and ICP analysis under the same conditions as those of the electrode catalyst of Example 1. The results are shown in Table 1.

(Comparative Example 2)
<Manufacture of electrode catalyst>

[“Pt / Pd / W / C” powder in which a second shell portion made of Pt is formed on Pd / W / C]
“Pt / Pd / W / C” powder in which a second shell portion made of Pt is formed on Pd of the following “Pd / W / C” powder particles {trade name “NE-G12W09-ADB”; E. CHEMCAT)} was prepared as an electrode catalyst for Comparative Example 2.
This Pt / Pd / W / C powder is prepared by preparing a mixed solution of the following Pd / W / C powder, potassium chloroplatinate, and water, and adding a reducing agent to the Pt / Pd / W / C powder. It was obtained by reducing the ions.

[“Pd / W / C” powder in which a first shell portion made of Pd is formed on W / C]
“Pd / W / C” powder in which a first shell portion made of Pd is formed on W of the following “W / C” powder particles {trade name “NE-G02W00-DB”, NE CHEMCAT Made)}.
This Pd / W / C powder was prepared by preparing a mixed solution of the following W / C powder, sodium tetrachloropalladium (II) and water, and adding a reducing agent to the palladium in the liquid obtained. It can be obtained by reducing ions.

[Core particle-supported carbon “W / C” powder (core particle serving as a precursor of the core of the electrode catalyst)]
W / C powder {trade name “NE-G00W00-B”, manufactured by NE CHEMCAT)} in which core particles composed of W carbide and W oxide were supported on carbon black powder was prepared.
As a result of XRD measurement, it was confirmed that this W / C powder consists of WC only.
This W / C powder is obtained by heat-treating a powder containing a commercially available carbon black powder (specific surface area 200 to 300 m ² / g) and a commercially available tungstate salt in a reducing atmosphere containing a hydrocarbon gas (carbon source). Adjusted.
The electrode catalyst of Comparative Example 2 was also subjected to ICP analysis of the electrode catalyst under the same conditions as those of the electrode catalyst of Example 1. The results are shown in Table 1.
In addition, as a result of confirming the STEM-HAADF image and the EDS elementary mapping image, the electrode catalyst of Comparative Example 2 was confirmed to have a configuration (see FIGS. 1 and 2).

(Comparative Examples 3 to 4)
XRD measurement results {I2 / (I1 + I2)} and {I2 / (I1 + I2 + I3)} of core particles that are precursors of the core part of the electrode catalyst shown in Table 1, ICP analysis results (L _For the electrodes of Comparative Examples 3 to 4, using the same preparation conditions and the same raw materials except that the amount of raw materials charged, reaction conditions, etc. were finely adjusted so as to have _Pt , L _Pd , L _W ) A catalyst was prepared.
ICP analysis was also performed under the same conditions as in Example 1.
As for the W / C powder of Comparative Example 3 and the W / C powder of Comparative Example 4, as in the case of the W / C powder of Comparative Example 2, as a result of XRD measurement, it was confirmed that the W carbide was composed only of WC. .
Further, with respect to the electrode catalysts of Comparative Examples 3 to 4, as a result of confirming the STEM-HAADF image and the EDS elementary mapping image, it was found that at least a part of the surface of the core particle composed of W carbide and W oxide was present. The catalyst particles having the core-shell structure in which the first shell layer made of Pd is formed and the second shell layer made of Pt is formed on at least a part of the first shell layer are conductive carbon. It was confirmed that the structure supported on the carrier (see FIGS. 1 and 2) was provided.

(II) Production of Gas Diffusion Electrode Composition Composition About 8.0 mg of electrode catalyst powders of Examples 1 to 10 and Comparative Examples 1 to 4 were weighed and sample bottles together with 2.5 mL of ultrapure water. The mixture was mixed while being irradiated with ultrasonic waves to prepare a slurry (suspension) of the electrode catalyst.
Next, 10.0 mL of ultrapure water and 20 μL of a 10 wt% Nafion (registered trademark) aqueous dispersion (trade name “DE1020CS” manufactured by Wako Chemical Co., Ltd.) are mixed in another container to prepare a Nafion-ultrapure aqueous solution. did.
Put 2.5 mL of this Nafion-ultra-pure aqueous solution into a sample bottle containing a slurry (suspension) of electrode catalyst, irradiate with ultrasonic waves at room temperature for 15 minutes, stir well, and gas diffusion electrode A forming composition was obtained.

(III) Formation of catalyst layer on electrode for evaluation test As preparation for an electrode catalyst evaluation test by the rotating disk electrode method (RDE method) described later, it was carried out on the electrode surface of the rotating disk electrode WE (see FIG. 4). The catalyst layer CL containing the electrode catalyst powder of Example 1 (see FIG. 4), the catalyst layer CL containing the electrode catalyst powder of Example 2 (see FIG. 4), and the electrode catalyst powder of Comparative Example 1 A catalyst layer CL (see FIG. 4) and a catalyst layer CL (see FIG. 4) containing the electrode catalyst powder of Comparative Example 2 were formed by the following procedure.
That is, 10 μL of the gas diffusion electrode forming composition was taken and dropped onto the clean surface of the rotating disk electrode WE. Thereafter, the composition was applied to the entire electrode surface of the rotating disk electrode WE to form a coating film. The coating film made of this gas diffusion electrode forming composition was dried at a temperature of 23 ° C. and a humidity of 50% RH for 2.5 hours to form a catalyst layer CL on the surface of the rotating disk electrode WE.

(IV) Evaluation Test of Catalyst Activity of Electrode Catalyst Next, the rotating disk electrode WE on which the catalyst layer CL containing the electrode catalyst of Example 1 to Example 10 was formed, and the electrode catalyst of Comparative Example 1 to Comparative Example 4 And a rotating disk electrode WE on which a catalyst layer CL containing a carbon black was formed, and a durability evaluation test was performed according to the following procedure.

[Configuration of rotating disk electrode measuring device]
FIG. 4 is a schematic diagram showing a schematic configuration of a rotating disk electrode measuring apparatus 50 used in the rotating disk electrode method (RDE method).
As shown in FIG. 4, the rotating disk electrode measuring device 50 mainly includes a measurement cell 51, a reference electrode RE, a counter electrode CE, and a rotating disk electrode WE. Furthermore, when evaluating a catalyst, electrolyte solution ES is put into the measurement cell 51.
The measurement cell 51 has a substantially cylindrical shape having an opening on the upper surface, and a fixing member 52 for the rotating disk electrode WE that also serves as a lid capable of gas sealing is disposed in the opening. A gas sealable opening for fixing the electrode main body portion of the rotating disk electrode WE while being inserted into the measurement cell 51 is provided at the center of the fixing member 52.
Next to the measurement cell 51, a substantially L-shaped Lugin tube 53 is arranged. Further, one end portion of the Luggin tube 53 has a Luggin capillary structure, and is inserted into the measurement cell 51, so that the electrolyte ES of the measurement cell 51 also enters the Luggin tube 53. . The other end of the Lugin tube 53 has an opening, and the reference electrode RE is inserted into the Lugin tube 53 through the opening.
As the rotating disk electrode measuring device 50, “Model HSV110” manufactured by Hokuto Denko Co., Ltd. was used. Further, an Ag / AgCl saturated electrode was used as the reference electrode RE, a Pt mesh with Pt black was used as the counter electrode CE, and an electrode having a diameter of 5.0 mmφ and an area of 19.6 mm ² was used as the rotating disk electrode WE. . Furthermore, using the HCl0 ₄ of 0.1M as the electrolyte ES.

(V) Durability Evaluation Test of Electrode Catalyst A catalyst layer CL containing the electrode catalyst of Examples 1 to 10 different from that used in the initial electrochemical surface area (ECSA) evaluation test was formed. A rotating disk electrode WE and a rotating disk electrode WE on which a catalyst layer CL containing the electrode catalysts of Comparative Examples 1 to 4 was prepared, respectively, were subjected to ECSA measurement by the RDE method according to the following procedure, and were durable. Sexuality was evaluated.

[Cleaning of rotating disk electrode WE]
[Cleaning of rotating disk electrode WE]
As shown in FIG. 4, in the rotating disk electrode measuring device 50, after the rotating disk electrode WE is immersed in the HClO ₄ electrolyte ES, argon gas is supplied from the gas introduction pipe 54 connected to the side surface of the measuring cell 51. By introducing it into the measurement cell 51, the oxygen in the electrolyte ES was purged with argon gas for 30 minutes or more.
Thereafter, the potential (vsRHE) of the rotating disk electrode WE with respect to the reference electrode RE was swept for 20 cycles in a so-called “triangular wave potential sweep mode” in which +85 mV to +1085 mV and a scanning speed of 50 mV / sec.

(V-1) [Initial ECSA measurement]
(I) Potential sweep process The potential (vsRHE) of the rotating disk electrode WE with respect to the reference electrode RE was swept in a so-called "rectangular wave potential sweep mode" shown in FIG.
More specifically, a potential sweep was performed for 6 cycles with the operation shown in (A) to (D) below as one cycle.
(A) Potential at start of sweep: +600 mV, (B) Sweep from +600 mV to +1000 mV, (C) Hold potential at +1000 mV for 3 seconds, (D) Sweep from +1000 mV to +600 mV, (E) Hold potential at +600 mV 3 seconds.
(Ii) CV measurement Next, CV measurement is performed for 2 cycles in the “triangular wave potential sweep mode” in which the potential (vsRHE) of the rotating disk electrode WE is set to the measurement start potential +119 mV, +50 mV to 1200 mV, and the scanning speed is 50 mV / sec. Went. The rotational speed of the rotating disk electrode WE was 1600 rpm.
From the CV measurement result at the second cycle, the initial ECSA value based on the hydrogen desorption wave was calculated. The results are shown in Table 1.

(V-2) [Measurement of ECSA after 12420 cycles of potential sweep]
Subsequent to the initial ECSA measurement, the above “(i) potential sweep process” was performed under the same conditions except that the number of potential sweeps was 12 cycles. Next, the above “(ii) CV measurement” was performed under the same conditions.
In this way, “(i) potential sweep process” was performed by sequentially changing the number of potential sweeps, and “(ii) CV measurement” described above was performed under the same conditions each time. The number of potential sweeps was sequentially changed to 22, 40, 80, 160, 300, 600, 800, 1000, 1000, and 8400 cycles.
Thus, the ECSA value obtained in the last “(ii) CV measurement” (the ECSA value after the potential sweep process in which the total number of potential sweeps is 12420 cycles) was obtained.
In addition, by dividing the ECSA value based on the hydrogen desorption wave obtained in the last “(ii) CV measurement” by the “initial ECSA value”, the retention rate of ESCA (% ) Was calculated.
Next, the ESCA retention rate (%) after 12420 cycles of potential sweep obtained for the electrode catalyst of Comparative Example 1 and the electrode catalysts of Examples 1 to 10 and Comparative Examples 2 to 4 In order to compare the obtained ESCA maintenance rate (%) after the number of potential sweeps 12420 cycles, the ESCA maintenance rate (%) after the number of potential sweeps 12420 cycles obtained for the electrode catalyst of Comparative Example 1 was calculated. The relative value of the retention rate (%) of ESCA after 12420 cycles of potential sweeps of other catalysts when 1.00 was set was calculated.
The relative value results obtained for Examples 1 to 10 and Comparative Examples 1 to 4 are shown in Table 1.

From the results of “Relative value of ESCA retention rate” shown in Table 1, the electrode catalysts of Examples 1 to 10 have superior durability compared to the electrode catalysts of Comparative Examples 1 to 4. It became clear to have. From the above results, it has been clarified that the electrode catalyst of this example has superior durability compared to the conventional Pt / C catalyst. Furthermore, since the electrode catalyst of this example uses a tungsten compound as the core material, it has been clarified that the amount of platinum used can be reduced and the cost can be reduced.

The electrode catalyst of the present invention has excellent durability compared to conventional Pt / C catalysts and can contribute to cost reduction.
Accordingly, the present invention is an electrode catalyst that can be applied not only to the electric equipment industry such as fuel cells, fuel cell vehicles, and portable mobiles, but also to energy farms, cogeneration systems, etc. Contribute to development.

2 ... carrier
3 ... catalyst particles,
4 ... Core part,
5 ... 1st shell part,
6 ... 2nd shell part,
7 ... Shell part,
10, 10A ... electrode catalyst,
40: Fuel cell stack 40,
42 ... MEA,
43 ... anode,
43a ... Gas diffusion layer,
43b ... catalyst layer,
44... Cathode
45 ... electrolyte membrane,
46 ... Separator,
48 ... separator,
50... Rotating disk electrode measuring device,
51 ... Measurement cell,
52... Fixing member,
53 ... Lugin tube,
CE ... Counter electrode,
CL: catalyst layer,
ES ... electrolyte,
RE: Reference electrode,
WE: rotating disk electrode.

Claims (9)

A conductive carrier;
Catalyst particles supported on the carrier;
Contains
The catalyst particles have a core part formed on the carrier, a first shell part formed on the core part, and a second shell part formed on the first shell part. And
The core portion includes WC and W carbide including WC _1-x (0 <x <1),
The first shell portion includes Pd (zero valence),
The second shell portion contains Pt (zero valence),
The core particles serving as the precursor of the core part satisfy the condition of the following formula (1).
Electrode catalyst.
0.03 ≦ {I2 / (I1 + I2)} ≦ 0.75 (1)
[In the formula (1), I1 represents the peak intensity of a peak attributed to WC obtained by X-ray diffraction measurement of the core particle, and I2 represents WC _1-x (which is obtained by X-ray diffraction measurement of the core particle. The peak intensity of the peak attributed to 0 <x <1) is shown. ] The electrode catalyst according to claim 1, wherein the core portion further contains W ₂ C. The core particles that are the precursor of the core part further satisfy the condition of the following formula (2),
The electrode catalyst according to claim 2.
0.02 ≦ {I3 / (I1 + I2 + I3)} ≦ 0.30 (1)
[In formula (2), I1 represents the same peak intensity as I1 in the formula (1), I2 represents the same peak intensity as I2 in the formula (1), and I3 represents X of the core particle. The peak intensity of the peak attributed to W ₂ C obtained by line diffraction measurement is shown. ] The electrode catalyst according to any one of claims 1 to 3, wherein the core portion further contains W oxide. The electrode catalyst according to any one of claims 1 to 4, wherein the core portion further contains W (zero valence). The electrode catalyst according to any one of claims 1 to 5 is included.
A composition for forming a gas diffusion electrode. The electrode catalyst according to any one of claims 1 to 6 is included,
Gas diffusion electrode. A membrane / electrode assembly (MEA) comprising the gas diffusion electrode according to claim 7. A fuel cell stack comprising the membrane-electrode assembly (MEA) according to claim 8.

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