WO2018123790A1 - Catalyst layer, gas diffusion electrode, membrane-catalyst layer assembly, membrane-electrode assembly, fuel cell stack, and composition for forming catalyst layer - Google Patents

Abstract

Provided is a catalyst layer which contains a core shell catalyst and exhibits excellent performance. The present invention relates to a catalyst layer of a gas diffusion electrode that is provided in a solid polymer fuel cell, and the present invention comprises: a core shell catalyst which contains a first carrier that is formed from a conductive carbon material and catalyst particles that are supported by the first carrier and have a core shell structure; a polymer electrolyte; and a second carrier that is formed from a conductive carbon material and does not support the catalyst particles. In addition, this catalyst layer is configured such that the conductive carbon material of the first carrier and the conductive carbon material of the second carrier are the same as each other.

Description

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

The present invention relates to a catalyst layer of a gas diffusion electrode provided in a polymer electrolyte fuel cell.
The present invention also relates to a gas diffusion electrode, a membrane / catalyst layer assembly, a membrane / electrode assembly, a fuel cell stack, and a composition for forming a catalyst layer on which the catalyst layer is mounted.

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, “Pt-supported carbon catalyst” which is a powder of catalyst particles in which Pt fine particles are supported on conductive carbon powder (hereinafter referred to as “Pt / C catalyst” if necessary). It has been known.
For example, as a Pt / C catalyst, a Pt / C catalyst having a Pt loading rate of 50 wt% manufactured by NE CHEMCAT, trade name: “SA50BK” is known.
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, development for reducing the Pt of the PEFC catalyst layer has been underway. For example, Non-Patent Document 1 describes an outline of development so far.

In these research and development, in order to reduce the amount of platinum used, conventionally, catalyst particles having a core-shell structure formed from a core portion made of a non-platinum element and a shell portion made of Pt (hereinafter referred to as “core shell if necessary”). Catalyst particles ”(hereinafter referred to as“ core-shell catalysts ”as necessary) have been studied and many reports have been made.
For example, Patent Document 1 discloses a particle composite material (a core-shell catalyst particle having a structure in which palladium (Pd) or a Pd alloy (corresponding to a core part) is covered with an atomic thin layer (corresponding to a shell part) of Pt atoms. Equivalent). Furthermore, this patent document 1 describes, as an example, core-shell catalyst particles having a layer structure in which the core portion is made of Pd particles and the shell portion is made of Pt.

Further, for example, in Patent Document 2, flooding can be reliably prevented even when a large current (for example, a current density exceeding 2000 mA / cm ² ) is passed, and the amount of expensive catalytic metal components such as platinum is reduced. In order to provide a PEFC electrocatalyst useful for manufacturing a polymer electrolyte fuel cell capable of reducing the cost, a catalytic metal component is supported on a support carbon material made of a porous carbon material. A catalyst obtained by mixing a catalytic metal-supporting carbon material and a non-catalytic metal-supporting carbon material made of a dendritic graphitic carbon material that does not support a catalytic metal component has been proposed.
In Patent Document 2, the carrier carbon material of the catalyst-supporting carbon material has a mesopore specific surface area (S _{4-10 nm} ) of 100 nm ² / g or more with a pore diameter of 4 nm or more and less than 10 nm measured by nitrogen adsorption measurement. . Further, the dendritic graphitic carbon material not supporting the catalytic metal component has a BET specific surface area (S _BET ) of 80 m ² / g or more and 220 m ² / g or less, and a DBP oil absorption (O _DBP ) of 80 mL / 100 g. The above is 170 mL / 100 g or less, and the crystallite size (Lc) by X-ray diffraction is 5 nm or more and 10 nm or less. Specifically, a platinum-supported carbon material (platinum catalyst) is disclosed as the catalyst-supported carbon material (see, for example, Patent Document 2, paragraphs 0045 to 0063).

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 2016-1000026 A

When adopting a core-shell catalyst for the spread of PEFC, the catalyst layer produced using the catalyst and the gas diffusion electrode (GDE), membrane / catalyst layer membrane assembly (Catalyst Coated Membrane) Hereinafter, it is important that the membrane / electrode assembly (hereinafter referred to as “MEA” if necessary) has a configuration suitable for the core-shell catalyst.
However, there is still room for improvement in the configuration of the catalyst layer having excellent performance including the core-shell catalyst.

This invention is made | formed in view of this technical situation, Comprising: It aims at providing the catalyst layer which has the outstanding performance containing a core-shell catalyst.
Another object of the present invention is to provide a gas diffusion electrode, a membrane / catalyst layer membrane assembly, a membrane / electrode assembly, and a fuel cell stack on which the catalyst layer is mounted.
Furthermore, this invention aims at providing the composition for catalyst layer formation containing the core-shell catalyst which can manufacture the above-mentioned catalyst layer of this invention more easily.

As a result of studying a catalyst layer including a core-shell catalyst, the present inventors have determined that a core-shell catalyst (a catalyst having a configuration including a support made of a conductive carbon material and catalyst particles having a core-shell structure supported on the support). ) And a conductive carbon material in which catalyst particles having a core-shell structure are not supported, and the core-shell catalyst support and the conductive carbon material in which no catalyst particles are supported are the same. The present inventors have found that the construction of a material is effective in improving the catalytic activity and have completed the present invention.
More specifically, the present invention includes the following technical matters.

That is, the present invention
A catalyst layer of a gas diffusion electrode provided in a polymer electrolyte fuel cell,
A core-shell catalyst comprising: a first support made of a conductive carbon material; and catalyst particles having a core-shell structure supported on the first support;
A polymer electrolyte;
A second support made of a conductive carbon material on which the catalyst particles are not supported;
Contains
The conductive carbon material of the first carrier and the conductive carbon material of the second carrier are the same;
A catalyst layer is provided.

Here, the “core-shell catalyst including catalyst particles having a core-shell structure” is a catalyst (powder) having a configuration having catalyst particles formed on a carrier, and the catalyst particles are placed on the carrier. The catalyst which has the structure which has the core part formed and the shell part formed so that at least one part of the surface of this core part may be covered is shown. A more detailed configuration will be described later with reference to FIGS.
The catalyst layer of the present invention can be used as a catalyst layer for the PEFC anode and can also be used as a cathode catalyst layer.
By adopting this configuration, the conventional catalyst layer including the Pt / C catalyst and the conventional catalyst layer including the core-shell catalyst (the catalyst layer not including the conductive carbon material other than the core-shell catalyst support) have excellent performance. The catalyst layer can be easily configured.
In particular, the catalyst layer of the present invention is substantially equivalent to the above two conventional catalyst layers even if the amount of catalyst supported (mass of precious metal per unit area / mg · cm ⁻² ) is reduced. Excellent performance can be demonstrated.
From the above viewpoint, the catalyst loading amount in the catalyst layer of the present invention may be 50% or less of the catalyst loading amount of the conventional catalyst layer containing the Pt / C catalyst. In the catalyst layer of the present invention, when Pt (zero-valent metal state Pt) is contained in the shell portion of the core-shell catalyst, the catalyst loading amount (Pt loading amount) in the catalyst layer of the present invention is: It may be 0.05 mg · cm ⁻² or less.

In the catalyst layer of the present invention, the average value of the crystallite size measured by powder X-ray diffraction (XRD) of the core-shell catalyst is preferably 3 to 16.0 nm.
If the average value of the crystallite size of the catalyst particles of the core-shell catalyst is less than 3 nm, it becomes extremely difficult to form particles that become the core portion on the support, and thus it is extremely difficult to form the catalyst particles on the support. become.
Further, when the average value of the crystallite size of the catalyst particles of the core-shell catalyst exceeds 16.0 nm, it becomes extremely difficult to form the particles serving as the core portion on the support in a highly dispersed state, and sufficient catalytic activity is obtained. It becomes extremely difficult.
In the present invention, when the surreal part made of Pt of the catalyst particles has one or two Pt atomic layers, the peak of the Pt (111) plane cannot be seen by XRD. The average value calculated from the peak of the surface is the average value of the crystallite size of the catalyst particles.

In the catalyst layer of the present invention,
The catalyst particles of the core-shell catalyst have a core part formed on the carrier and a shell part formed so as to cover at least a part of the surface of the core part;
The core part includes Pd (zero-valent metal state Pd), and the shell part includes Pt (zero-valent metal state Pt),
The Pt loading of the core-shell catalyst is 0.6-33.0 wt%,
The core shell catalyst has a Pd loading of 4.7 to 47.0 wt%;
It is preferable that the loading ratio of the noble metal combined with Pt and Pd of the core-shell catalyst is 5.6 to 66.5 Wt%.

When the Pt loading is less than 0.6 wt%, the tendency that sufficient catalytic activity cannot be obtained increases. In addition, the average thickness of the shell portion becomes excessively thin, and the surface of the core portion is not sufficiently covered with the shell portion, so that the constituent material of the core portion is eluted and the tendency to maintain the core-shell structure is increased.
Furthermore, when the Pt loading exceeds 33.0 wt%, it tends to be extremely difficult to form catalyst particles having a core-shell structure in a highly dispersed state on the support. Further, in this case, the average thickness of the shell portion becomes excessively thick, making it difficult to exhibit a so-called base effect (ligand effect) of the core portion, and it is difficult to obtain a catalytic activity exceeding that of a conventional Pt / C catalyst. The tendency to become becomes large.

In addition, when the Pd loading is less than 4.7 wt%, the number of particles forming the core portion on the support is reduced, and the shell portion formed on the core portion is also reduced, so that sufficient catalytic activity is obtained. The tendency to disappear increases.
When the Pd loading rate exceeds 47.0 wt%, it becomes extremely difficult to carry the particles that will become the core portion on the carrier in a highly dispersed state. As a result, the tendency that it becomes extremely difficult to form catalyst particles having a core-shell structure in a highly dispersed state increases.

Furthermore, when the supporting rate of the noble metal combined with Pt and Pd of the catalyst particles is less than 5.6 Wt%, there is a tendency that sufficient catalytic activity cannot be obtained.
If the loading ratio of the noble metal combined with Pt and Pd exceeds 66.5 Wt%, it tends to be extremely difficult to form catalyst particles having a core-shell structure in a highly dispersed state.
In addition, the value measured by ICP emission analysis using the electrode catalyst is adopted for the Pt loading rate and the Pd loading rate.

Further, in the present specification, when describing the configuration of the electrode catalyst, if necessary, “configuration of catalyst particles supported on the support (main constituent material) / configuration of conductive support (main It is written " More specifically, it is expressed as “shell configuration / core configuration / support configuration”.
For example, when the configuration of the electrode catalyst includes “a shell portion made of Pt, a core portion made of Pd, and a carrier made of conductive carbon”, it is expressed as “Pt / Pd / C”.

Furthermore, in the catalyst layer of the present invention, it is preferable that the core portion of the core-shell catalyst is made of Pd from the viewpoint of more reliably obtaining excellent catalytic activity. In this case, Pd oxide may be included in the core part as long as the catalyst particles can exhibit excellent catalytic activity.
Further, in the catalyst layer of the present invention, from the viewpoint of more reliably obtaining excellent catalytic activity,
It is preferable that the shell part of the core-shell catalyst is made of Pt. In this case, Pt oxide may be contained in the shell portion as long as the catalyst particles can exhibit excellent catalytic activity.
Furthermore, in the catalyst layer of the present invention, from the viewpoint of more reliably obtaining excellent catalytic activity,
It is preferable that the core part of the core-shell catalyst is made of Pd and the shell part is made of Pt.

Furthermore, the present invention provides:
A gas diffusion electrode provided in a polymer electrolyte fuel cell,
A gas diffusion layer;
A catalyst layer disposed on the gas diffusion layer;
Have
The catalyst layer is the catalyst layer of the present invention described above,
A gas diffusion electrode is provided.

The gas diffusion electrode of the present invention includes the catalyst layer of the present invention. Therefore, it becomes easy to set it as the structure which has the outstanding catalyst activity (polarization characteristic) which can contribute to the cost reduction of PEFC.
In addition, the gas diffusion electrode of this invention can be used as an anode and can also be used as a cathode.

Furthermore, the present invention provides:
A membrane-catalyst layer assembly (CCM) provided in a polymer electrolyte fuel cell,
A solid polymer electrolyte membrane;
A catalyst layer disposed on at least one surface of the solid polymer electrolyte membrane;
Have
The catalyst layer is the catalyst layer of the present invention described above,
A membrane-catalyst layer assembly (CCM) is provided.
Since the membrane / catalyst layer assembly (CCM) of the present invention includes the catalyst layer of the present invention for anode and / or cathode, it has excellent catalytic activity (cell characteristics) that can contribute to cost reduction of PEFC. It becomes easy to set it as having a structure.

Furthermore, the present invention provides:
A membrane-electrode assembly (MEA) provided in a polymer electrolyte fuel cell,
A solid polymer electrolyte membrane;
A gas diffusion electrode disposed on at least one surface of the solid polymer electrolyte membrane;
Have
The gas diffusion electrode is the gas diffusion electrode of the present invention described above,
A membrane-electrode assembly (MEA) is provided.
Since the membrane / electrode assembly (MEA) of the present invention includes the catalyst layer of the present invention and the gas diffusion electrode of the present invention, the membrane / electrode assembly (MEA) has an excellent battery characteristic that can contribute to the cost reduction of PEFC. It becomes easy.

The present invention also provides:
Provided is a fuel cell stack including the membrane-electrode assembly (MEA) of the present invention described above.
Since the fuel cell stack of the present invention includes the catalyst layer of the present invention and the membrane-electrode assembly (MEA) of the present invention, the fuel cell stack has excellent battery characteristics that can contribute to the cost reduction of PEFC. It becomes easy.

Furthermore, the present invention provides
A composition for forming a catalyst layer for forming a catalyst layer of a gas diffusion electrode provided in a polymer electrolyte fuel cell,
A core-shell catalyst comprising: a first support made of a conductive carbon material; and catalyst particles having a core-shell structure supported on the first support;
A polymer electrolyte;
A second support made of a conductive carbon material on which the catalyst particles are not supported;
Contains
The conductive carbon material of the first carrier and the conductive carbon material of the second carrier are the same;
A composition for forming a catalyst layer is provided.
According to the composition for forming a gas diffusion electrode of the present invention, a conventional catalyst layer containing a Pt / C catalyst, a conventional catalyst layer containing a core-shell catalyst (a catalyst layer containing no conductive carbon material other than the core-shell catalyst support) Thus, a catalyst layer having excellent performance can be easily and reliably produced.

ADVANTAGE OF THE INVENTION According to this invention, the catalyst layer which has the outstanding performance containing a core-shell catalyst can be provided.
Further, according to the present invention, there are provided GDL, CCM, MEA, and fuel cell stack having such excellent catalytic activity that can contribute to the cost reduction of PEFC, including such a catalyst layer.
Furthermore, according to this invention, the composition for catalyst layer formation which can manufacture the catalyst layer of this invention easily and reliably is provided.

It is a schematic cross section which shows one suitable form of MEA of this invention. FIG. 2 is a schematic cross-sectional view showing a preferred embodiment of a core-shell catalyst included in at least one of the cathode catalyst layer and the anode catalyst layer of the MEA shown in FIG. 1. FIG. 2 is a schematic cross-sectional view showing another preferred embodiment of the core-shell catalyst included in at least one of the cathode catalyst layer and the anode catalyst layer of the MEA shown in FIG. 1. FIG. 6 is a schematic cross-sectional view showing still another preferred embodiment of the core-shell catalyst included in at least one of the cathode catalyst layer and the anode catalyst layer of the MEA shown in FIG. 1. FIG. 6 is a schematic cross-sectional view showing still another preferred embodiment of the core-shell catalyst included in at least one of the cathode catalyst layer and the anode catalyst layer of the MEA shown in FIG. 1. It is a schematic cross section which shows another suitable one form of MEA of this invention. It is a schematic cross section which shows one suitable form of CCM of this invention. It is a schematic cross section which shows another suitable one form of CCM of this invention. It is a schematic cross section which shows one suitable form of GDE of this invention. It is a schematic cross section which shows another suitable one form of GDE of this invention. It is a schematic diagram which shows suitable one Embodiment of the fuel cell stack of this invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with appropriate reference to the drawings.
<Membrane / electrode assembly (MEA)>
FIG. 1 is a schematic cross-sectional view showing a preferred embodiment of the MEA of the present invention.
The MEA 10 shown in FIG. 1 includes two plate-like gas diffusion electrodes (cathode 1 and anode 2) arranged in a state of facing each other, and a polymer electrolyte membrane (Polymer) arranged between the cathode 1 and the anode 2. Electrolyte Membrane, hereinafter referred to as “PEM” 3 as required).
The MEA 10 has a configuration in which at least one of the cathode 1 and the anode 2 contains a core-shell catalyst described later.
The MEA 10 can be manufactured by laminating the cathode 1, the anode 2 and the PEM 3 as shown in FIG.

<Gas diffusion electrode (GDE)>
The cathode 1 which is a gas diffusion electrode has a configuration including a gas diffusion layer 1gd and a catalyst layer 1c formed on the surface of the gas diffusion layer 1gd on the PEM3 side. Further, the cathode 1 has a water-repellent layer (Micro Porous Layer, hereinafter referred to as “MPL” if necessary) 1 m disposed between the gas diffusion layer 1 gd and the catalyst layer 1 c.
Similarly to the cathode 1, the anode 2 that is a gas diffusion electrode also has a gas diffusion layer 2 gd, a catalyst layer 2 c formed on the surface of the gas diffusion layer 2 gd on the PEM 3 side, and between the gas diffusion layer 2 gd and the catalyst layer 2 c. It has a configuration with an MPL2m arranged.

(Catalyst layer (CL))
In the cathode 1, the catalyst layer 1c is a layer in which a reaction in which water is generated from air (oxygen gas) sent from the gas diffusion layer 1gd and hydrogen ions moving from the anode 2 through the PEM 3 proceeds.
In the anode 2, the catalyst layer 2c is a layer in which a reaction for generating hydrogen ions and electrons from the hydrogen gas sent from the gas diffusion layer 2gd proceeds.
At least one of the catalyst layer 1c of the cathode 1 and the catalyst layer 2c of the anode 2 contains a core-shell catalyst.

(Core shell catalyst)
Hereinafter, the core-shell catalyst will be described with reference to FIGS.
FIG. 2 is a schematic cross-sectional view showing a preferred embodiment 20 of the core-shell catalyst included in at least one of the cathode catalyst layer 1c and the anode catalyst layer 2c of the MEA 10 shown in FIG.
As shown in FIG. 2, the core-shell catalyst 20 includes a first carrier 22 and catalyst particles 23 having a so-called “core-shell structure” supported on the first carrier 22.
Further, the catalyst particle 23 has a core part 24 and a shell part 26 formed so as to cover at least a part of the surface of the core part 24.
That is, the core-shell catalyst 20 has catalyst particles 23 supported on the first carrier 22, and the catalyst particles 23 have the core portion 24 as a core and the shell portion 26 as a shell. It has a structure (core shell structure) covering at least a part of the surface of 24.

In addition, the constituent element (chemical composition) of the core portion and the constituent element (chemical composition) of the shell portion are different.
The configuration of the core-shell catalyst 20 is not particularly limited as long as the shell portion 26 is formed on at least a part of the surface of the core portion 24 of the catalyst particle 23.
For example, from the viewpoint of more surely obtaining excellent catalytic activity and durability, as shown in FIG. 2, the core-shell catalyst 20 is in a state where substantially the entire surface of the core portion 24 is covered by the shell portion 26. It is preferable.

FIG. 3 is a schematic cross-sectional view showing another preferred embodiment 20A of the core-shell catalyst included in at least one of the cathode catalyst layer 1c and the anode catalyst layer 2c of the MEA 10 shown in FIG.
The core-shell catalyst 20A illustrated in FIG. 3 includes a core portion 24 and catalyst particles 23a configured from a shell portion 26 that covers a part of the surface of the core portion 24.
Thus, in the range in which the effect of the present invention can be obtained, the core-shell catalyst 20A is partially covered by the shell portion 26, and a part of the surface of the core portion 24 (core portion exposed surface 24s). May be exposed.
That is, as long as the effects of the present invention can be obtained, the core-shell catalyst 20A only needs to have the shell part 26a or 26b formed on at least a part of the surface of the core part 24.

FIG. 4 is a schematic cross-sectional view showing still another preferred embodiment 20B of the core-shell catalyst included in at least one of the cathode catalyst layer 1c and the anode catalyst layer 2c of the MEA 10 shown in FIG.
The core-shell catalyst 20B shown in FIG. 4 has a core part 24 and catalyst particles 23b having a shell part 26b that covers substantially the entire surface of the core part 24.
Furthermore, the shell portion 26 b has a configuration including a first shell portion 25 that covers substantially the entire surface of the core portion 24 and a second shell portion 27 that covers substantially the entire outer surface of the first shell portion 25.
The constituent element (chemical composition) of the core portion 24, the constituent element (chemical composition) of the first shell portion 25, and the constituent element (chemical composition) of the second shell portion 27 are different from each other. .

Further, the shell part 26 b in the core-shell catalyst 20 </ b> B may have a configuration in which another shell part is arranged inside the second shell part 27 in addition to the first shell part 25 and the second shell part 27. Good.
From the viewpoint of more reliably obtaining the effects of the present invention, as shown in FIG. 4, the core-shell catalyst 20B is preferably in a state where substantially the entire surface of the core portion 24 is covered by the shell portion 26b.

FIG. 5 is a schematic cross-sectional view showing yet another preferred embodiment 20C of the core-shell catalyst included in at least one of the cathode catalyst layer and the anode catalyst layer of the MEA 10 shown in FIG.
The core-shell catalyst 20 </ b> C illustrated in FIG. 5 includes catalyst particles 23 c having a core portion 24 and a shell portion 26 c that covers a part of the surface of the core portion 24.
Furthermore, the shell part 26 c shown in FIG. 5 has a two-layer structure including a first shell part 25 and a second shell part 27.
In the shell portion 26c constituting the catalyst particle 23c shown in FIG. 5, there is a first shell portion 25 that is not covered by the second shell portion 27. A part of the outer surface of the first shell portion 25 not covered by the second shell portion 27 becomes the first shell portion exposed surface 25s.
Here, regarding the shell portion 26 c of the catalyst particle 23 c, it is preferable that substantially the entire area of the first shell portion 25 is covered with the second shell portion 27. However, as long as the effects of the present invention can be obtained, the surface of the first shell portion 25 of the shell portion 26c is partially exposed (for example, a portion 25s of the surface of the first shell portion 25 shown in FIG. 5). May be exposed).

In addition, in the range where the effect of the present invention can be obtained, the core-shell catalyst is a composite of the core part and the shell part in a state where substantially the entire surface of the core part is covered with the shell part on the first support, A state where “a composite of a core part and a shell part in which a part of the surface of the core part is covered with the shell part” may be mixed.
For example, the core-shell catalysts 20B and 20C shown in FIGS. 4 and 5 may be mixed. Furthermore, the core-shell catalyst of the present invention is in a state where at least two of the core-shell catalysts 20, 20A, 20B and 20C shown in FIGS. May be.

In addition, the core-shell catalysts 20, 20A, 20B, and 20C shown in FIGS. 2 to 5 are provided on the first support 22 within the range in which the effects of the present invention can be obtained, and the catalysts shown in FIGS. In addition to at least one of the particles 23, 23a, 23b, and 23c, a state in which “particles including only a core portion in which the core portion is not covered by the shell portion” is supported may be included (FIG. Not shown).
Furthermore, within the range in which the effects of the present invention can be obtained, the core-shell catalysts 20, 20A, 20B, and 20C shown in FIGS. 2 to 5 include the catalyst shown in FIGS. In addition to at least one of the particles 23, 23 a, 23 b, and 23 c, a state in which “particles composed only of constituent elements of the shell portion” are supported on the first carrier without contacting the core portion is included. It is good (not shown).

In addition, the core-shell catalysts 20, 20A, 20B, and 20C shown in FIGS. 2 to 5 are provided on the first support 22 within the range in which the effects of the present invention can be obtained, and the catalysts shown in FIGS. In addition to at least one of the particles 23, 23 a, 23 b, and 23 c, “particles of only the core portion not covered with the shell portion” and “particles composed only of the constituent elements of the shell portion” are independent of each other. The state carried by the first carrier 22 may be included (not shown).
In addition, the core-shell catalysts 20, 20A, 20B, and 20C shown in FIGS. 2 to 5 preferably satisfy the following conditions from the viewpoint of obtaining the effects of the present invention more reliably.
That is, as described above, the core-shell catalysts 20, 20A, 20B, and 20C shown in FIGS. 2 to 5 preferably have an average crystallite size measured by powder X-ray diffraction (XRD). 3 to 16.0 nm.

In the core-shell catalysts 20 and 20A shown in FIGS. 2 and 3, the core portion 24 preferably contains Pd. In addition, from the viewpoints of obtaining the effects of the present invention more reliably and ease of manufacture, the core portion 24 is composed of Pd (zero-valent metal state Pd) as a main component (50 wt% or more). It is more preferable that it is composed of Pd (Pd in a zero-valent metal state).
In the core-shell catalysts 20 and 20A shown in FIGS. 2 and 3, the shell portions 26 and 26a preferably contain Pt. In addition, from the viewpoints of obtaining the effects of the present invention more reliably and manufacturability, the shell portions 26 and 26a are composed mainly of Pt (zero-valent metal state Pt) (50 wt% or more). It is preferable that it is made of Pt (zero-valent metal state Pt).

In the core-shell catalysts 20B and 20C shown in FIGS. 4 and 5, the first shell portion 25 preferably contains Pd. Further, from the viewpoints of obtaining the effects of the present invention more reliably and ease of manufacture, the first shell portion 25 is configured with Pd (zero-valent metal state Pd) as a main component (50 wt% or more). It is preferable that it is made of Pd (zero-valent metal state Pd).
In the core-shell catalysts 20B and 20C shown in FIGS. 4 and 5, the second shell portion 27 preferably contains Pt. Further, from the viewpoints of obtaining the effects of the present invention more reliably and ease of manufacture, the second shell portion 27 is composed of Pt (zero-valent metal state Pt) as a main component (50 wt% or more). It is preferable that it is made of Pt (zero-valent metal state Pt).
In the core-shell catalysts 20B and 20C shown in FIGS. 4 and 5, a third shell portion (not shown) may be further formed at least partly between the core portion 24 and the first shell portion 25. Good. The third shell portion has a chemical composition different from that of the core portion 24, the first shell portion 25, and the second shell portion 26, and this configuration is not particularly limited as long as it has electronic conductivity.

As described above, the core-shell catalysts 20, 20A, 20B, and 20C shown in FIGS. 2 to 5 have a Pt loading rate of preferably 0.6 to 33.0 wt%. The loading rate is preferably 4.7 to 47.0 wt%.
Further, as described above, the core-shell catalysts 20, 20A, 20B, and 20C shown in FIGS. 2 to 5 preferably have a precious metal loading ratio of Pt and Pd of preferably 5.6 to 66. 5 wt%.
The core-shell catalysts 20, 20A, 20B, and 20C shown in FIGS. 2 to 5 and the catalyst particles 23, 23a, 23b, and 23c shown in FIGS. 2 to 5 exhibit excellent catalytic activity. The outermost shell portions 26, 26 a and the second shell portion 27 have sufficiently thin thicknesses that can exhibit the so-called base effect (ligand effect) of the core portion 24.

That is, the average thickness of the shell portions (shell portions 26, 26a, second shell portion 27) of the core-shell catalysts 20, 20A, 20B, and 20C shown in FIGS. 2 to 5 is 0.2 to 1.0 nm. It is preferably 0.2 to 0.9 nm, more preferably 0.2 to 0.7 nm, and still more preferably 0.2 to 0.5 nm.
For example, when the shell part (shell part 26, 26a, second shell part 27) is a layer made of Pt, the Pt atomic layer has a thickness of 4 layers or less, preferably 3 layers within the above average thickness range. Hereinafter, the thickness can be made more preferably two layers or less. The reason is that since the metal bond radius of Pt is 0.139 nm, the average thickness of one Pt atom layer is about 0.21 nm to 0.23 nm. Or, when the lattice constant (K) of Pt is K = 0.39231 nm, the plane spacing (d111) of platinum is 0.2265 nm (= k / √3).

When the average thickness of the shell parts (shell parts 26, 26a, second shell part 27) is less than 0.2 nm, the surface of the core part 24 is more adequate for the shell parts (shell parts 26, 26a, second shell part 27). It is difficult to maintain the core-shell structure because the constituent material of the core portion 24 is eluted without being coated. Therefore, the tendency that sufficient catalytic activity as a core-shell catalyst cannot be obtained increases. Moreover, the tendency for durability and reliability to become insufficient increases.
In addition, when the average thickness of the shell portions (shell portions 26 and 26a, second shell portion 27) exceeds 1.0 nm, the tendency to be unable to contribute to the cost reduction (low platinumization) of PEFC increases. Further, in this case, the tendency to make it difficult to exhibit the so-called base effect (ligand effect) of the core portion 24 is increased, and the tendency to obtain a catalytic activity exceeding the conventional Pt / C catalyst is increased. .

Furthermore, the average thickness of the shell parts (shell parts 26, 26a, second shell part 27) is, for example, an SEM image (Scanning Electron Microscopy image) or an average particle diameter of the catalyst particles and an average particle diameter of the core part, respectively. It can be determined by evaluating a TEM image (Transmission Electron Microscopy image). That is, it can be determined by the difference between the average particle diameter of the catalyst particles (23, 23a, 23b, 23c) and the average particle diameter of the core portion 24.
The average thickness of the shell portions (shell portions 26, 26a, second shell portion 27) is, for example, TEM-EDX (Transmission Electron Microscopy-Energy Dispersive X-ray Spectroscopy: transmission electron) in the particle size direction of the catalyst particles. The catalyst particles (23, 23a) are analyzed by line analysis using a microscope energy dispersive X-ray analysis) or TEM-EDX (Transmission Electron Microscopy-Energy Dispersive X-ray Spectroscopy). , 23b, 23c) and the average particle diameter of the core portion 24 can be obtained.

The first carrier 22 is not particularly limited as long as the first carrier 22 can carry a composite composed of the core portion 24 and the shell portion 26 (or the shell portions 26a, 26b, and 26c) and has a relatively large surface area.
Further, the first carrier 22 has good dispersibility in the gas diffusion electrode forming composition containing the core-shell catalyst 20 (or 20A, 20B, and 20C), and has excellent conductivity. Preferably there is.

The first carrier 22 is made of glassy carbon (GC), fine carbon, carbon black, graphite, carbon fiber, activated carbon, activated carbon, a carbon-based material such as carbon nanofiber or carbon nanotube, or a glass-based or ceramic such as oxide. It can be appropriately selected from a system material.
Among these, a carbon-based material is preferable from the viewpoint of the adsorptivity with the core portion 24 and the BET specific surface area of the first support 22.
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 production method of the core-shell catalysts 20, 20A, 20B, and 20C is not particularly limited and can be produced by a known method. For example, the core particle containing Pd forms a Pd / C particle (powder) supported on a first carrier containing a conductive carbon material as a constituent component, and a core part forming process. The manufacturing method which has a structure including the "shell part formation process" which forms the shell part containing Pt so that at least one part of the surface of the said core particle of the obtained said Pd / C particle | grain (powder) may be covered is mentioned. It is done.
The core-shell catalysts 20 and 20A can be manufactured by sequentially supporting the core part 24 and the shell parts 26 and 26a constituting the catalyst particles 23 and 23a on the first carrier 22.
For example, an impregnation method in which a solution containing a catalyst component is brought into contact with the first support 22 and the first support 22 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, Examples include electrochemical deposition methods such as potential deposition (UPD), chemical reduction, reduction deposition with adsorbed hydrogen, surface leaching of alloy catalysts, displacement plating, sputtering, and vacuum deposition. can do.

The polymer electrolyte contained in the catalyst layer 1c and the catalyst layer 2c is not particularly limited as long as it has hydrogen ion conductivity, and a known one can be used. 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 preferably.

The catalyst includes at least one of the catalyst layer 1c of the cathode 1 and the catalyst layer 2c of the anode 2 shown in FIG. 1 and includes a core-shell contact (any one of the core-shell catalysts 20, 20A, 20B, and 20C). The layer includes a second carrier made of a conductive carbon material on which catalyst particles (catalyst particles 23, 23a, 23b, and 23c) are not supported.
Here, the conductive carbon material of the second carrier is the same as the conductive carbon material of the first carrier.

(Gas diffusion layer (GDL))
The gas diffusion layer 1gd provided in the cathode 1 shown in FIG. 1 is a layer provided for supplying an oxidant gas (for example, oxygen gas, air) to the catalyst layer 1c. Further, the gas diffusion layer 1gd has a role of supporting the catalyst layer 1c.
The gas diffusion layer 2gd provided in the anode 2 is a layer provided for supplying a reducing agent gas (for example, hydrogen gas) to the catalyst layer 2c. Further, the gas diffusion layer 2gd has a role of supporting the catalyst layer 2c.

The gas diffusion layers (1c, 2c) shown in FIG. 1 have 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 that can be used for the gas diffusion layer (1c, 2c) is not particularly limited, and a known member can be used. For example, carbon paper, carbon paper as a main raw material, and carbon powder, ion-exchanged water as an optional component, and an auxiliary material made of polyethylene terephthalate dispersion as a binder are preferably applied to carbon paper.

(Water repellent layer (MPL))
As shown in FIG. 1, in the cathode 1, a water repellent layer (MPL) 1m is disposed between the gas diffusion layer 1gd and the catalyst layer 1c. The water repellent layer 1m has electronic conductivity, water repellency, and gas diffusibility, and is provided to promote the diffusion of the oxidizing gas into the catalyst layer 1gd and the discharge of the reaction product water generated in the catalyst layer 1gd. It is what. The configuration of the water repellent layer 1m is not particularly limited, and a known configuration can be adopted.

(Polymer electrolyte membrane (PEM))
The polymer electrolyte membrane (PEM) 3 shown in FIG. 1 is not particularly limited as long as it has hydrogen ion conductivity, and a known one conventionally used for PEFC can be adopted. For example, it may be a film containing the constituents exemplified as the polymer electrolyte contained in the catalyst layer 1c and the catalyst layer 2c described above.

<Deformation mode of MEA>
The preferred embodiments of the MEA of the present invention (and the catalyst layer of the present invention and the gas diffusion electrode of the present invention) have been described above, but the MEA of the present invention is not limited to the configuration of the MEA 10 shown in FIG.
For example, the MEA of the present invention may have the configuration of the MEA 11 shown in FIG.
FIG. 6 is a schematic cross-sectional view showing another preferred embodiment of the MEA of the present invention. The MEA 11 shown in FIG. 6 has a configuration in which a gas diffusion electrode (GDE) 1A having the same configuration as that of the cathode 1 in the MEA 10 shown in FIG. 1 is disposed only on one surface of the polymer electrolyte membrane (PEM) 3. However, the catalyst layer 1c of the gas diffusion electrode (GDE) 1A has the configuration of the catalyst layer of the present invention. That is, in the catalyst layer 1c of GDE1A, the mass ratio N / C between the mass C of the support of the core-shell catalyst and the mass N of the polymer electrolyte is 0.5 to 1.2, more preferably 0.7 to 1.0. ing.

<Membrane / catalyst layer assembly (CCM)>
Next, a preferred embodiment of the membrane / catalyst layer assembly (CCM) of the present invention will be described.
FIG. 7 is a schematic cross-sectional view showing a preferred embodiment of the CCM of the present invention. The CCM 12 shown in FIG. 7 has a configuration in which a polymer electrolyte membrane (PEM) 3 is disposed between the cathode catalyst layer 1c and the anode catalyst layer 2c. At least one of the cathode catalyst layer 1c and the anode catalyst layer 2c has the configuration of the catalyst layer of the present invention. That is, at least one of the cathode catalyst layer 1c and the anode catalyst layer 2c has a mass ratio N / C between the mass C of the core-shell catalyst support and the mass N of the polymer electrolyte of 0.5 to 1.2, more preferably. Is set to 0.7 to 1.0.

<Deformation of membrane / catalyst layer assembly (CCM)>
The preferred embodiment of the CCM of the present invention has been described above, but the CCM of the present invention is not limited to the configuration of the CCM 12 shown in FIG.
For example, the CCM of the present invention may have the configuration of the CCM 13 shown in FIG.
FIG. 8 is a schematic cross-sectional view showing another preferred embodiment of the CCM of the present invention. The CCM 13 shown in FIG. 8 has a configuration in which a catalyst layer 1c having the same configuration as that of the cathode 1 in the CCM 12 shown in FIG. 7 is disposed only on one surface of the polymer electrolyte membrane (PEM) 3. However, the catalyst layer 1c of the gas diffusion electrode (GDE) 1A has the configuration of the catalyst layer of the present invention. That is, in the catalyst layer 1c of the CCM 13, the mass ratio N / C between the mass C of the support of the core-shell catalyst and the mass N of the polymer electrolyte is 0.5 to 1.2, more preferably 0.7 to 1.0. ing.

<Gas diffusion electrode (GDE)>
Next, a preferred embodiment of the gas diffusion electrode (GDE) of the present invention will be described.
FIG. 9 is a schematic cross-sectional view showing a preferred embodiment of the GDE of the present invention. The gas diffusion electrode (GDE) 1B shown in FIG. 9 has the same configuration as the cathode 1 mounted on the MEA 10 shown in FIG. However, the catalyst layer 1c of the gas diffusion electrode (GDE) 1B has the configuration of the catalyst layer of the present invention. That is, in the catalyst layer 1c of the gas diffusion electrode (GDE) 1B, the mass ratio N / C between the mass C of the support of the core-shell catalyst and the mass N of the polymer electrolyte is 0.5 to 1.2, more preferably 0.7. To 1.0.

<Modification of Gas Diffusion Electrode (GDE)>
Although the preferred embodiment of the GDE of the present invention has been described above, the GDE of the present invention is not limited to the configuration of the GDE 1B shown in FIG.
For example, the GDE of the present invention may have the configuration of GDE 1C shown in FIG.
FIG. 10 is a schematic cross-sectional view showing another preferred embodiment of the GDE of the present invention. The GDE 1C illustrated in FIG. 10 has a configuration in which a water repellent layer (MPL) is not disposed between the catalyst layer 1c and the gas diffusion layer 1gd as compared with the GDE 1B illustrated in FIG.

<Composition for forming catalyst layer>
Next, a preferred embodiment of the composition for forming a catalyst layer of the present invention will be described.
The composition for forming a catalyst layer of the present embodiment includes a core-shell catalyst, a polymer electrolyte, and main components, and a mass ratio N / C between the mass C of the core-shell catalyst carrier and the mass N of the polymer electrolyte is 0.5 to 1.2, more preferably 0.7 to 1.0.
Here, the composition of the liquid containing the polymer electrolyte is not particularly limited. For example, the liquid containing the polymer electrolyte may contain the above-described polymer electrolyte having hydrogen ion conductivity, water, and alcohol.

The composition ratio of the core-shell catalyst, polymer electrolyte, and other components (water, alcohol, etc.) contained in the catalyst layer-forming composition is such that the core-shell catalyst is well dispersed in the resulting catalyst layer and includes the catalyst layer. It is set as appropriate so that the power generation performance of the MEA can be improved.
The composition for forming a catalyst layer can be prepared by mixing and stirring a liquid containing a core-shell catalyst and a polymer electrolyte. You may contain polyhydric alcohols, such as glycerol, and / or water from a viewpoint of adjusting applicability | paintability. When mixing the liquid containing the core-shell catalyst and the polymer electrolyte, a pulverizing mixer such as a ball mill or an ultrasonic disperser may be used.
At least one of the catalyst layer 1c of the cathode 1 and the catalyst layer 2c of the anode 2 shown in FIG. 1 can be formed using a preferred embodiment of the composition for forming a catalyst layer of the present invention.

(Manufacturing method of gas diffusion electrode)
Next, an example of the manufacturing method of the gas diffusion electrode of this invention is demonstrated. The gas diffusion electrode should just be formed so that the catalyst layer of this invention may be included, and the manufacturing method can employ | adopt a well-known method. If the composition for forming a catalyst layer of the present invention is used, it can be more reliably produced.
For example, you may manufacture by apply | coating the composition for catalyst layer formation on a gas diffusion layer (or the said water-repellent layer of the laminated body which formed the water-repellent layer on the gas diffusion layer), and making it dry.

<Fuel cell stack>
FIG. 11 is a schematic diagram showing a preferred embodiment of the fuel cell stack of the present invention.
The fuel cell stack 30 shown in FIG. 11 has a configuration in which the MEA 10 shown in FIG. 1 is a unit cell and a plurality of the unit cells are stacked. The fuel cell stack 30 has a configuration in which the MEA 10 is disposed between the separator 4 and the separator 5. A gas flow path is formed in each of the separator 4 and the separator 5.

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 Electrocatalyst Used for MEA Cathode Catalyst Layer (1) Production of Core-Shell Catalyst Used for MEA Cathodes of Examples 1, 2, 2, and 8 [on Pd / C] "Pt / Pd / C" powder in which a shell portion made of Pt is formed on]
“Pt / Pd / C” powder in which a shell portion made of Pt is formed on Pd of the following “Pd / C” powder particles {Pt loading 16.8 wt% (ICP analysis result), trade name “NE- F10217-BD "(manufactured by NE CHEMCAT)} was prepared as a core-shell catalyst (hereinafter referred to as" core-shell catalyst A ").
As this Pt / Pd / C powder, the following Pd / C powder is used, and a coating film made of Cu is formed on the surface of the core particles made of Pd / C Pd by a general Cu-UPD method. It was prepared by allowing galvanic substitution reaction of Cu and Pt to proceed using potassium platinate.
[Core particle supported carbon “Pd / C” powder]
Pd / C powder {Pd loading 30 wt%, trade name “NE-F00230-D”, manufactured by NE CHEMCAT)} in which core particles made of Pd were supported on carbon black powder was prepared.
For this Pd / C powder, a mixture of commercially available carbon black powder (specific surface area 750 to 800 m ² / g), sodium tetrachloropalladium (II) and water is prepared, and a reducing agent is added thereto. Prepared by reducing palladium ions in the liquid obtained.

<Measurement of loading rate (ICP analysis)>
With respect to this core-shell catalyst A, the Pt loading rate (wt%) and the Pd loading rate (wt%) were measured by the following methods.
The core-shell catalyst A 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.
As a result of ICP analysis, this core-shell catalyst had a Pt loading rate of 16.8 wt% and a Pd loading rate of 25.0 wt%.

<Measurement of average value of crystallite size (XRD analysis)>
With respect to the core-shell catalyst A, the average value of crystallite sizes (average value calculated from the peak of the Pd (111) plane of the core part) measured by powder X-ray diffraction (XRD) was measured. As a result, the average value of the crystallite size of the core-shell catalyst A was 4.4 nm.

<Surface observation and structure observation of electrode catalyst>
For this core-shell catalyst A, a STEM-HAADF image and an EDS elementary mapping image were confirmed. As a result, catalyst particles having a core-shell structure in which a shell layer layer made of Pt is formed on at least a part of the surface of the core particle particles made of Pd are supported on a conductive carbon carrier. It was confirmed that

(2) Manufacture of core-shell catalyst used for MEA cathode of Comparative Example 1 [Pt / Pd / C powder with Pt / C formed shell part]
“Pt / Pd / C” powder in which a shell portion made of Pt is formed on Pd of the following “Pd / C” powder particles {Pt loading 16.4 wt% (ICP analysis result), trade name “NE- F10216-BD "(manufactured by NE CHEMCAT)} was prepared as a core-shell catalyst (hereinafter referred to as" core-shell catalyst B ").
As this Pt / Pd / C powder, the following Pd / C powder is used, and a coating film made of Cu is formed on the surface of the core particles made of Pd / C Pd by a general Cu-UPD method. It was prepared by allowing galvanic substitution reaction of Cu and Pt to proceed using potassium platinate.
[Core particle supported carbon “Pd / C” powder]
Pd / C powder {Pd loading 30 wt%, trade name “NE-F00230-D”, manufactured by NE CHEMCAT)} in which core particles made of Pd were supported on carbon black powder was prepared.
For this Pd / C powder, a mixture of commercially available carbon black powder (specific surface area 750 to 800 m ² / g), sodium tetrachloropalladium (II) and water is prepared, and a reducing agent is added thereto. Prepared by reducing palladium ions in the liquid obtained.

<Measurement of loading rate (ICP analysis)>
With respect to this core-shell catalyst A, the Pt loading rate (wt%) and the Pd loading rate (wt%) were measured by the following methods.
The core-shell catalyst A 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.
As a result of ICP analysis, this core-shell catalyst had a Pt loading rate of 16.4 wt% and a Pd loading rate of 25.1 wt%.

<Measurement of average value of crystallite size (XRD analysis)>
With respect to the core-shell catalyst A, the average value of crystallite sizes (average value calculated from the peak of the Pd (111) plane of the core part) measured by powder X-ray diffraction (XRD) was measured. As a result, the average value of the crystallite size of the core-shell catalyst A was 4.5 nm.

<Surface observation and structure observation of electrode catalyst>
For this core-shell catalyst A, a STEM-HAADF image and an EDS elementary mapping image were confirmed. As a result, catalyst particles having a core-shell structure in which a shell layer layer made of Pt is formed on at least a part of the surface of the core particle particles made of Pd are supported on a conductive carbon carrier. It was confirmed that

(3) Manufacture of core-shell catalyst used for MEA cathodes of Comparative Examples 2 to 4 [“Pt / Pd / C” powder with Pt / C formed shell part]
“Pt / Pd / C” powder in which a shell portion made of Pt is formed on Pd of the following “Pd / C” powder particles {Pt loading 24.3 wt% (ICP analysis result), trade name “NE- F10224-BC "(manufactured by NE CHEMCAT)} was prepared as a core-shell catalyst (hereinafter referred to as" core-shell catalyst C ").
As this Pt / Pd / C powder, the following Pd / C powder is used, and a coating film made of Cu is formed on the surface of the core particles made of Pd / C Pd by a general Cu-UPD method. It was prepared by allowing galvanic substitution reaction of Cu and Pt to proceed using potassium platinate.
[Core particle supported carbon “Pd / C” powder]
Pd / C powder {Pd loading 30 wt%, trade name “NE-F00230-C”, manufactured by NE CHEMCAT)} in which core particles made of Pd were supported on carbon black powder was prepared.
For this Pd / C powder, a mixture of commercially available carbon black powder (specific surface area 750 to 800 m ² / g), sodium tetrachloropalladium (II) and water is prepared, and a reducing agent is added thereto. Prepared by reducing palladium ions in the liquid obtained.

<Measurement of loading rate (ICP analysis)>
With respect to this core-shell catalyst A, the Pt loading rate (wt%) and the Pd loading rate (wt%) were measured by the following methods.
The core-shell catalyst A 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.
As a result of ICP analysis, this core-shell catalyst had a Pt loading rate of 24.3 (wt%) and a Pd loading rate of 21.1 wt%.

<Measurement of average value of crystallite size (XRD analysis)>
With respect to the core-shell catalyst A, the average value of crystallite sizes (average value calculated from the peak of the Pd (111) plane of the core part) measured by powder X-ray diffraction (XRD) was measured. As a result, the average value of the crystallite size of the core-shell catalyst A was 4.9 nm.

<Surface observation and structure observation of electrode catalyst>
For this core-shell catalyst A, a STEM-HAADF image and an EDS elementary mapping image were confirmed. As a result, catalyst particles having a core-shell structure in which a shell layer layer made of Pt is formed on at least a part of the surface of the core particle particles made of Pd are supported on a conductive carbon carrier. It was confirmed that

(4) Preparation of Pt / C catalyst used for cathode of MEA of Comparative Example 5 and Comparative Example 6 As Pt / C catalyst, Pt / C catalyst with a Pt loading rate of 50 wt% manufactured by NE CHEMCAT (trade name) : “SA50BK”).
The Pt / C catalyst was subjected to XRD analysis with the above core-shell catalyst. As a result, the average value of the crystallite size was 2.6 nm.
(1) Production of core-shell catalyst used for MEA cathode of Example 3 [Pt / Pd / C powder with Pt / C formed shell part]
“Pt / Pd / C” powder in which a shell portion made of Pt is formed on Pd of the following “Pd / C” powder particles {Pt loading rate 18.2 wt% (ICP analysis result), trade name “NE- F10218-BF "(manufactured by NE CHEMCAT)} was prepared as a core-shell catalyst (hereinafter referred to as" core-shell catalyst D ").
As this Pt / Pd / C powder, the following Pd / C powder is used, and a coating film made of Cu is formed on the surface of the core particles made of Pd / C Pd by a general Cu-UPD method. It was prepared by allowing galvanic substitution reaction of Cu and Pt to proceed using potassium platinate.
[Core particle supported carbon “Pd / C” powder]
Pd / C powder {Pd loading 25.3 wt%, trade name “NE-F00225-F”, manufactured by NE CHEMCAT)} having core particles made of Pd supported on carbon black powder was prepared.
For this Pd / C powder, a mixture of commercially available carbon black powder (specific surface area 750 to 800 m ² / g), sodium tetrachloropalladium (II) and water is prepared, and a reducing agent is added thereto. Prepared by reducing palladium ions in the liquid obtained.

<Measurement of loading rate (ICP analysis)>
With respect to this core-shell catalyst A, the Pt loading rate (wt%) and the Pd loading rate (wt%) were measured by the following methods.
The core-shell catalyst A 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.
As a result of ICP analysis, this core-shell catalyst had a Pt loading rate of 18.2 wt% and a Pd loading rate of 25.3 wt%.

<Measurement of average value of crystallite size (XRD analysis)>
With respect to the core-shell catalyst A, the average value of crystallite sizes (average value calculated from the peak of the Pd (111) plane of the core part) measured by powder X-ray diffraction (XRD) was measured. As a result, the average value of the crystallite size of the core-shell catalyst A was 4.7 nm.

<Surface observation and structure observation of electrode catalyst>
For this core-shell catalyst A, a STEM-HAADF image and an EDS elementary mapping image were confirmed. As a result, catalyst particles having a core-shell structure in which a shell layer layer made of Pt is formed on at least a part of the surface of the core particle particles made of Pd are supported on a conductive carbon carrier. It was confirmed that

(II) Preparation of P / C catalyst used for anode of MEA in Examples 1 to 3 and Comparative Examples 1 to 8 Pt / C having a Pt loading rate of 50 wt% manufactured by NE CHEMCAT as Pt / C catalyst A catalyst (trade name: “SA50BK”) was prepared.
The Pt / C catalyst was subjected to XRD analysis with the above core-shell catalyst. As a result, the average value of the crystallite size was 2.6 nm.

<Example 1>
The MEA having the same configuration as the MEA 10 shown in FIG.
(1) Creation of cathode GDL of cathode
Carbon paper (trade name “TGP-H-60” manufactured by Toray Industries, Inc.) was prepared as GDL.
Cathode MPL forming ink In a Teflon (registered trademark) ball mill container containing Teflon (registered trademark) balls, 1.5 g of carbon powder (trade name “DENKA BLACK” manufactured by Denki Kagaku Kogyo Co., Ltd.) and ion exchange 1.1 g of water and 6.0 g of a surfactant (trade name “Triton” (35 wt% aqueous solution) manufactured by Dow Chemical Company) were added and mixed.
Next, 1.75 g of polytetrafluoroethylene (PTFE) dispersion (trade name “31-JR” manufactured by Mitsui DuPont Fluorochemical Co., Ltd.) was placed in a ball mill container and mixed. This produced a cathode MPL forming ink.
Cathode MPL
A cathode MPL forming ink was applied to one side of the GDL using a bar coater to form a coating film. Thereafter, the coating film was sufficiently dried in a drier, and further subjected to thermocompression bonding (360 ° C., 3.5 bar) to prepare a laminate in which MPL was formed on GDL.
Cathode catalyst layer forming ink In a Teflon (registered trademark) ball mill container containing Teflon (registered trademark) balls, the core-shell catalyst A, ion-exchanged water, 10 wt% Nafion aqueous dispersion (manufactured by DuPont) A product name “DE1021CS”) and glycerin were added and mixed to prepare an ink for forming a cathode catalyst layer. For this ink, N / C = 0.7. Moreover, it was set as the core-shell catalyst A: ion-exchange water: glycerol = 10: 78: 5 (mass ratio). Further, the ratio of the core-shell catalyst A to the second support (the same material as the first support in the core-shell catalyst A) was set to 5: 1 (mass ratio).
Cathode catalyst layer (CL)
The cathode catalyst layer forming ink was applied to the surface of the MPL of the laminate in which the MPL was formed on the GDL described above by a bar coating method to form a coating film. This coating film was dried at room temperature for 30 minutes, and then dried at 60 ° C. for 1.0 hour to obtain a catalyst layer. In this way, a cathode as a gas diffusion electrode was produced. The amount of Pt supported on the cathode catalyst layer was set to the values shown in Table 1.

(2) Creation of anode GDL of anode
The same carbon paper as the cathode was prepared as GDL.
Anode MPL forming ink In a Teflon (registered trademark) ball mill container containing Teflon (registered trademark) balls, 1.5 g of carbon powder (trade name “Denka Black” manufactured by Denki Kagaku Kogyo Co., Ltd.) and ion exchange 1.0 g of water and 6.0 g of a surfactant (trade name “Triton” (35 wt% aqueous solution) manufactured by Dow Chemical Co., Ltd.) were added and mixed.
Next, 2.5 g of polytetrafluoroethylene (PTFE) dispersion (trade name “31-JR” manufactured by Mitsui DuPont Fluorochemical Co., Ltd.) was placed in a ball mill container and mixed. This produced the MPL forming ink for anodes.
Anode MPL
An anode MPL forming ink was applied to one side of the GDL using a bar coder to form a coating film. Thereafter, the coated film was sufficiently dried in a drier, and further subjected to thermocompression treatment (360 ° C., 13.8 bar) to prepare a laminate in which MPL was formed on GDL.
Ink for forming anode catalyst layer In a Teflon (registered trademark) ball mill container containing Teflon (registered trademark) balls, SA50BK (Pt loading 50 wt%), ion-exchanged water, 5 wt% Nafion alcohol dispersion ( SIGMA-ALDRICH's product name “Nafion 5 wt.% Dispersion”, product number “274704”) and glycerin were mixed and mixed to form an anode catalyst layer forming ink. For this ink, N / C = 1.2. Moreover, it was set as carbon: ion-exchange water: glycerin = 1: 6: 4 (mass ratio) in SA50BK.
Anode catalyst layer (CL)
The anode catalyst layer forming ink described above was applied to the surface of the MPL of the laminate in which MPL was formed on the GDL described above by the bar coating method to form a coating film. This coating film was dried at room temperature for 30 minutes, and then dried at 60 ° C. for 1.0 hour to obtain a catalyst layer. In this way, an anode as a gas diffusion electrode was produced. The amount of Pt supported on the anode catalyst layer was 0.30 mg / cm ² .

(3) Creation of MEA A polymer electrolyte membrane (trade name “Nafion NR212” manufactured by DuPont) was prepared. A laminate in which this polymer electrolyte membrane was disposed between the cathode and the anode was prepared and heat-pressed by a hot press machine to prepare an MEA. The thermocompression bonding was performed by pressing at 140 ° C. and 18.5 bar for 5 minutes, and further at 140 ° C. and 88.8 bar for 3 minutes.

<Example 2>
For the cathode catalyst layer, the same conditions as in Example 1 except that the composition of the cathode catalyst layer forming ink and the coating conditions of the ink were adjusted so that the Pt loading was the value shown in Table 1. Each MEA was made according to the procedure.

<Example 3>
For the cathode catalyst layer, instead of the core-shell catalyst A, the above-described core-shell catalyst D was used, and the composition of the cathode catalyst layer-forming ink was adjusted so that the amount of Pt supported was the value shown in Table 1. Each MEA was prepared under the same conditions and procedures as in Example 1 except that the coating conditions were adjusted.

<Comparative Example 1>
Each MEA was prepared under the same conditions and procedures as in Example 1 except that the following conditions were changed for the catalyst layer of the cathode.
That is, in creating the cathode catalyst layer forming ink,
-Instead of the core-shell catalyst A, the core-shell catalyst B described above was used.
A cathode catalyst-forming ink was prepared using only the core-shell catalyst B without using the second carrier on which the catalyst particles were not supported.
The composition of the cathode catalyst layer forming ink and the coating conditions of the ink were adjusted so that the amount of Pt supported was the value shown in Table 1.

<Comparative Example 2> to <Comparative Example 4>
Each MEA was prepared under the same conditions and procedures as in Comparative Example 1 except that the following conditions were changed for the cathode catalyst layer.
That is, in creating the cathode catalyst layer forming ink,
-Instead of the core-shell catalyst B, the core-shell catalyst C described above was used.
The composition of the cathode catalyst layer forming ink and the coating conditions of the ink were adjusted so that the amount of Pt supported was the value shown in Table 1.

<Comparative Example 5> to <Comparative Example 6>
Each MEA was prepared under the same conditions and procedures as in Example 1 except that the following conditions were changed for the catalyst layer of the cathode.
That is, in creating the cathode catalyst layer forming ink,
-Instead of the core-shell catalyst A, the P / C catalyst (trade name: “SA50BK”) described above was used.
-Instead of 10 wt% Nafion aqueous dispersion, 5 wt% Nafion alcohol dispersion (DuPont brand name "DE520CS"; 1-propanol 48wt% containing) was used.
The composition of the cathode catalyst layer forming ink and the coating conditions of the ink were adjusted so that the amount of Pt supported was the value shown in Table 1 and N / C = 0.5.
-Carbon in a P / C catalyst (trade name: “SA50BK”): ion-exchanged water: glycerin = 1: 10: 1 (mass ratio).

<Comparative Example 7> to <Comparative Example 8>
Each MEA was prepared under the same conditions and procedures as in Example 1 except that the core-shell catalyst A was used for the catalyst layer of the cathode and the following conditions were changed.
A cathode catalyst-forming ink was prepared using only the core-shell catalyst A without using the second carrier on which the catalyst particles were not supported.
The composition of the cathode catalyst layer forming ink and the coating conditions of the ink were adjusted so that the amount of Pt supported was the value shown in Table 1.

<Battery performance evaluation>
The battery performances of the MEAs in Examples 1 and 2 and Comparative Examples 1 to 6 were carried out by the following battery performance evaluation method.
The MEAs produced in Examples 1 and 2 and Comparative Examples 1 to 6 were installed in a fuel cell single cell evaluation apparatus (manufactured by Chino Corporation). Next, the power generation reaction in the MEA was advanced under the following conditions.
That is, the single cell (MEA) temperature was 80 ° C. To the anode, 1.0 atm of pure hydrogen humidified with saturated steam was supplied with the flow rate adjusted to 70%. Further, 1.0 atm of pure oxygen humidified with saturated steam at 80 ° C. was supplied to the cathode at a flow rate adjusted to 50%.
The single cell (MEA) is evaluated by controlling the current with an electronic load device attached to the fuel cell single cell evaluation device, and a current-voltage curve obtained by scanning the current value from 0 to 1.0 A / cm ² is obtained. Obtained as data.
A graph plotting the X-axis (current density) as a logarithmic scale was created from the current-voltage curve data (not shown), and a current density value (current value per unit area of the electrode) at a voltage of 850 mV was obtained. .
By dividing the current density value thus obtained by the platinum weight per unit area of the cathode, the activity per unit weight (Mass. Act.) Of platinum contained in the cathode was calculated and contained in the cathode. It was used as an index of oxygen reduction ability of the catalyst. The results are shown in Table 1. Table 1 shows Mass. Obtained in Comparative Example 4. Act. As a relative value (relative ratio) with reference (1.0) as a reference, Mass. Obtained in other examples and comparative examples. Act. The result of having compared is shown.

From the results shown in Table 1, it was clarified that the MEAs of Examples 1 to 3 have higher Pt mass activity than the MEAs of Comparative Examples 1 to 7.
For example, compared with the MEAs of Comparative Examples 1 to 3 and Comparative Example 7, the MEAs of Examples 1 to 3 have substantially the same or better performance even when the catalyst loading is reduced to about 50%. It was revealed that
From the above results, it became clear that the MEA (catalyst layer, GDE, CCM) of this example has excellent catalytic activity and can contribute to the cost reduction of PEFC.

The catalyst layer of the present invention includes a core-shell catalyst and exhibits excellent catalytic activity. In addition, the GDL, CCM, MEA, and fuel cell stack including the catalyst layer of the present invention exhibit excellent battery characteristics that can contribute to the cost reduction of PEFC.
Therefore, the present invention can be applied not only to the electrical equipment industry such as fuel cells, fuel cell vehicles, and portable mobiles but also to energy farms, cogeneration systems, etc., and contributes to development related to the energy industry and environmental technology.

1 ... cathode,
1A, 1B, 1C ... Gas diffusion electrode (GDE)
1c: catalyst layer (CL),
1 m ... water repellent layer (MPL),
1 gd: gas diffusion layer (GDL),
2 ... anode,
2c ... catalyst layer (CL),
2 m ... water repellent layer (MPL),
2 gd ... gas diffusion layer (GDL),
3 ... Polymer electrolyte membrane (PEM),
4, 5 ... Separator 10, 11 ... Membrane / electrode assembly (MEA),
12, 13 ... Membrane / catalyst layer assembly (CCM)
20, 20A, 20B, 20C ... core-shell catalyst,
22 ... carrier,
23, 23a, 23b, 23c ... catalyst particles,
24 ... Core part,
24 s ... exposed surface of the core part,
25 ... 1st shell part,
25s ... exposed surface of the first shell,
26, 26a, 26b, 26c ... shell part,
27 ... second shell part,
30 ... Fuel cell stack,

Claims (10)

1. A catalyst layer of a gas diffusion electrode provided in a polymer electrolyte fuel cell,
   A core-shell catalyst comprising: a first support made of a conductive carbon material; and catalyst particles having a core-shell structure supported on the first support;
   A polymer electrolyte;
   A second support made of a conductive carbon material on which the catalyst particles are not supported;
   Contains
   The conductive carbon material of the first carrier and the conductive carbon material of the second carrier are the same;
   Catalyst layer.
2. The average crystallite size measured by powder X-ray diffraction (XRD) of the core-shell catalyst is 3 to 16.0 nm.
   The catalyst layer according to claim 1.
3. The catalyst particles of the core-shell catalyst have a core part formed on the carrier and a shell part formed so as to cover at least a part of the surface of the core part;
   The core portion includes Pd, the shell portion includes Pt,
   The Pt loading of the core-shell catalyst is 0.6-33.0 wt%,
   The core shell catalyst has a Pd loading of 4.7 to 47.0 wt%;
   The precious metal supporting ratio of Pt and Pd of the core-shell catalyst is 5.6 to 66.5 wt%.
   The catalyst layer according to claim 1 or 2.
4. The catalyst layer according to any one of claims 1 to 3, wherein the core portion of the core-shell catalyst is made of Pd.
5. The catalyst layer according to any one of claims 1 to 4, wherein the shell portion of the core-shell catalyst is made of Pt.
6. A gas diffusion electrode provided in a polymer electrolyte fuel cell,
   A gas diffusion layer;
   A catalyst layer disposed on the gas diffusion layer;
   Have
   The catalyst layer is the catalyst layer according to any one of claims 1 to 5,
   Gas diffusion electrode.
7. A membrane-catalyst layer assembly (CCM) provided in a polymer electrolyte fuel cell,
   A solid polymer electrolyte membrane;
   A catalyst layer disposed on at least one surface of the solid polymer electrolyte membrane;
   Have
   The catalyst layer is the catalyst layer according to any one of claims 1 to 5,
   Membrane / catalyst layer assembly (CCM).
8. A membrane-electrode assembly (MEA) provided in a polymer electrolyte fuel cell,
   A solid polymer electrolyte membrane;
   A gas diffusion electrode disposed on at least one surface of the solid polymer electrolyte membrane;
   Have
   The gas diffusion electrode is the gas diffusion electrode according to claim 6,
   Membrane / electrode assembly (MEA).
9. A fuel cell stack including the membrane-electrode assembly (MEA) according to claim 8.
10. A composition for forming a catalyst layer for forming a catalyst layer of a gas diffusion electrode provided in a polymer electrolyte fuel cell,
    A core-shell catalyst comprising: a first support made of a conductive carbon material; and catalyst particles having a core-shell structure supported on the first support;
    A polymer electrolyte;
    A second support made of a conductive carbon material on which the catalyst particles are not supported;
    Contains
    The conductive carbon material of the first carrier and the conductive carbon material of the second carrier are the same;
    A composition for forming a catalyst layer.
    
    

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