JP2021150249A - Electrode catalyst, gas diffusion electrode formation composition, gas diffusion electrode, membrane-electrode assembly, and fuel cell stack - Google Patents

Abstract

To provide an electrode catalyst having an excellent catalytic activity which can be contributed to a low cost of a PEFC.SOLUTION: An electrode catalyst contains: a hollow carbon carrier having a meso hole of which a pore size is 2 to 50nm; and a plurality of catalyst particles carried on the carrier. The catalyst particles are held on both of an inner part and an outer part of the meso hole of the carrier, and contain a PtNi alloy. When executing an analysis of a particle diameter distribution of each catalyst particle using a three-dimentional reconstruction image obtained by an electron beam tomography measurement using a STEM, a rate of the catalyst particles carried in the inner part of the meso hole is 50% or larger.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electrode catalyst having a core-shell structure. More specifically, the present invention relates to an electrode catalyst preferably used for a gas diffusion electrode, and the present invention relates to an electrode catalyst preferably 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 containing the catalyst particles for electrodes.

Polymer electrolyte fuel cells (hereinafter, referred to as "PEFC" as necessary) are being researched and developed as power sources for fuel cell vehicles and household cogeneration systems.
As the catalyst used for the gas diffusion electrode of PEFC, 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" which is a powder of catalyst particles in which Pt fine particles are supported on a conductive carbon powder (hereinafter, referred to as "Pt / C catalyst" if necessary). It has been known.
Precious metal catalysts such as Pt account for a large proportion of the production cost of PEFC, which has become an issue for reducing the cost of PEFC and popularizing PEFC.
In these researches and developments, in order to reduce the amount of platinum used, catalyst particles having a core-shell structure formed from a core part made of non-platinum element and a shell part made of Pt (hereinafter, if necessary, "core shell" Powders of (referred to as "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 describes a particle composite material (corresponding to a core shell catalyst particle) having a structure in which palladium (Pd) or a Pd alloy (corresponding to a core portion) is coated with an atomic thin layer of Pt atoms (corresponding to a shell portion). (Equivalent) is disclosed. Further, Patent Document 1 describes, as an example, core-shell catalyst particles having a layer structure in which the core portion is Pd particles and the shell portion is Pt.
On the other hand, carriers for electrode catalysts include hollow carbon having many internal pores and solid carbon having fewer internal pores than the hollow carbon, and for improving performance by utilizing the characteristics of each. It is being considered.

For example, Patent Document 2 discloses an example of study in which hollow carbon is used as a carrier. Further, Patent Document 3 discloses an example of study in which solid carbon is used as a carrier.
For example, in Patent Document 2, as shown in FIG. 10, pores (primary pores, mesopores) P220 of a porous carrier (hollow carbon) 220 having an average particle diameter of 20 to 100 nm and a pore diameter of 4 to 20 nm. The configuration of the catalyst 200 for an electrode in which the pore volume and the mode diameter of the pore distribution are controlled within a predetermined range and the catalyst particles 230 are supported in the primary pores (mesopores) P220 of the carrier 220 is disclosed. There is.
In Patent Document 2, this prevents adsorption of the polymer electrolyte on the surface of the catalyst particles 230 existing in the primary pores (mesopores) P220, and prevents a decrease in the effective reaction surface area of the catalyst while gas transportability. It is mentioned that it is possible to secure a sufficient amount of gas. Further, as a result, it is mentioned that a catalyst layer for a fuel cell showing excellent power generation performance can be provided even when the activity per catalyst weight is improved and the amount of catalyst is reduced.

Further, for example, Patent Document 3 discloses an electrode catalyst (PtCo / C catalyst) for a fuel cell having a solid carbon carrier and catalyst particles containing an alloy of platinum and cobalt supported on the carrier. Has been done. This electrode catalyst has a molar ratio of platinum to cobalt in the alloy of 4 to 11: 1, and is acid-treated at 70 to 90 ° C.
In Patent Document 3, when a PtCo alloy is supported on a hollow carbon carrier, a part of the PtCo alloy is included inside the hollow carbon carrier, and even if an acid treatment for suppressing the elution of Co is performed, the carrier It is difficult to sufficiently treat the PtCo alloy existing inside, and as a result, it is considered a problem that Co is easily eluted from the PtCo alloy existing inside the carrier.
Therefore, Patent Document 3 mentions that by using a solid carbon carrier instead of the hollow carbon carrier, it is possible to avoid inclusion of the PtCo alloy inside the carrier. Furthermore. It is disclosed that this makes it possible to sufficiently acid-treat the PtCo alloy and suppress the elution of Co. As a result, it is mentioned that it is possible to achieve both the initial performance and the durability performance of the fuel cell.

Here, in Patent Document 3, solid carbon is defined as follows.
That is, in Patent Document 3, the solid carbon is a carbon having fewer voids inside the carbon than the hollow carbon, and specifically, the BET surface area and t-Pot (from the particle size) obtained by N2 adsorption. It is mentioned that the carbon has a ratio (t-Pot surface area / BET surface area) of 40% or more with the external surface area (calculated the surface area outside the particles).
The "t-Pot surface area" described in Patent Document 3 is, for example, the technical report "micro-fine by the t-plot method" published on the Internet by "MC Evatech" on February 1, 2019. It is understood to indicate the "t-plot surface area" described in "Analysis of pore surface area". The analysis of the surface area of micropores by the t-plot method is one of the methods of analysis from the adsorption isotherm of nitrogen (adsorption temperature: 77K). This method is a method of comparing and converting the adsorption isotherm data with the standard isotherm to graph the relationship between the thickness t of the adsorption layer and the adsorption amount. In addition to being able to separate the specific surface area into the inside and outside of the pores and quantify them, the tendency of the pores can be known from the shape of the graph.
Further, as an example of the solid carbon, for example, the carbon described in Japanese Patent No. 4362116 can be mentioned, and specifically, Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd. can be mentioned. Is disclosed.

Further, Patent Document 4 discloses an electrode catalyst (core-shell catalyst) in which catalyst particles are supported both inside and outside the mesopores of a hollow carbon carrier. This electrode catalyst can be used inside the mesopores when the particle size distribution of the catalyst particles is analyzed using a three-dimensional reconstructed image obtained by electron beam tomography measurement using a STEM (scanning transmission electron microscope). It has a structure in which the ratio of the catalyst particles supported on the is 50% or more.
In Non-Patent Document 1 and Non-Patent Document 2 below, regarding the catalyst particles supported on the hollow carbon carrier, the ratio of the catalyst particles supported on the inside of the pores and the catalyst particles supported on the outside of the pores are described. An example in which the ratio is analyzed by a method different from that of Patent Document 4 described above is disclosed.
More specifically, in Non-Patent Document 1, Strasser et al., A group of Berlin Institute of Technology, have a commercially available hollow carbon (trade name: "ketjenblack EC-300J", manufactured by Akzo Nobel, specific surface area: about 839 m ² g ^-1. ), The SEM (Scanning Electron Microscopy) image and the TSEM (Transmission SEM) image of the specific Pt / C catalyst particles of interest were simultaneously photographed in the same measurement area for the Pt / C catalyst in which Pt particles were highly dispersed. I am reporting. For example, see Table 1, FIG. 2 and the right column of P.79 of Non-Patent Document 1.

In their method, the SEM image provides information on the Pt particles present only on the observed portion (the outer surface on one side) of the outer surface of the hollow carbon carrier particles. That is, information on the number of particles of the catalyst particles supported on the outside of the hollow carbon carrier particles can be obtained. On the other hand, from the TSEM image (transmission image), information on all the catalyst particles (Pt particles) supported on the outside and inside of the hollow carbon carrier particles in the observed Pt / C catalyst particles can be obtained. Then, from the information from the TSE image and the information from the SEM image, among the Pt particles supported on the hollow carbon carrier particles, the Pt particles supported on the outer surface and the Pt particles supported on the inside are separated from each other. We are trying to distinguish them.
Here, they have not performed measurements on the "opposite back surface" of the SEM image with respect to the observed portion of the outer surface of the hollow carbon carrier particles ("one outer surface"). They assume that the state of the "outer surface on one side" and the state of the "back surface on the other side" are the same. That is, it is assumed that the number of particles of the catalyst particles supported on the "outer surface on one side" and the number of particles of the catalyst particles supported on the "back surface on the opposite side" are the same.

Next, in Non-Patent Document 2, Mr. Uchida and his group at Yamanashi University used a commercially available hollow STEM (Scanning Transmission Electron Microscope) device capable of photographing SEM images and TEM (transmission electron microscopy) images of Pt / C catalyst particles. We have reported the results of photographing a Pt / C catalyst in which Pt particles are highly dispersed in carbon (trade name: "Ketjenblack", manufactured by Ketjen Black International, specific surface area: about 875 m2 g-1). For example, see FIG. 1, Table 2 and the lower right column of P.181 of Non-Patent Document 2.
First, they obtain information on the number of particles of all Pt particles supported on the hollow carbon carrier particles from the TEM image of the specific Pt / C catalyst particles of interest. Next, they obtain information on the number of Pt particles present only on the back surface of the hollow carbon carrier particles from the measurement of the SEM image of the same Pt / C catalyst particles as those taken by the TEM image. .. Next, they used a special 3D sample holder to rotate the specific Pt / C catalyst particles (measurement sample) of interest by exactly 180 ° C, resulting in an SEM image of only the back surface of the same Pt / C catalyst particles. Is being measured. Using this information, we are trying to distinguish between the Pt particles supported on the outer surface and the Pt particles supported on the inside among the Pt particles supported on the hollow carbon carrier particles.
Regarding "internal carrying ratio" = "100 x (number of Pt particles carried inside) / (total number of Pt particles)" measured by this method, they have a commercially available 30wt% Pt / C catalyst (trade name: """TEC10E30E", manufactured by Tanaka Metal Industry Co., Ltd., 62% in the specification (denoted as "c-Pt / CB,"), commercially available 46wt% Pt / C catalyst (trade name: "TEC10E50E", manufactured by Tanaka Metal Industry Co., Ltd.) , In the specification, it is described as "Pt / CB"), and it is reported that it was 50% or more.

As described above, the present inventors recognize that the analysis methods of Non-Patent Document 1 and Non-Patent Document 2 are different from the analysis methods of Patent Document 4 in the following points. That is, the analysis method by electron tomography measurement in Patent Document 4 is a three-dimensional reconstruction method using an electron microscope, and an electron microscope image in which the same field of view of a measurement sample is projected from various directions is tertiary in a computer. This is a method of reconstructing an original image and creating a tomographic image (tomography) using a computer.
On the other hand, the analysis method of Non-Patent Document 1 performs analysis using two-dimensional images such as an SEM image and a TSEM image of a measurement sample taken from a specific one direction. Further, the analysis method of Non-Patent Document 2 includes an SEM image obtained by taking a measurement sample from two specific directions (two directions obtained by rotating the sample holder at 180 ° C.) and a TSEM obtained by taking the measurement sample from a specific one direction. Analysis is performed using a two-dimensional image such as an image. In these analysis methods of Non-Patent Document 1 and Non-Patent Document 2, for example, when the measurement sample (catalyst particles for electrodes) has irregularities, the supporting position is inside the hollow carbon carrier in the catalyst particles. There is a high possibility that there is something that cannot be sufficiently determined whether it is present or external.
Since the analysis method of Patent Document 4 uses a three-dimensional tomogram (tomogram) of the measurement sample and can be observed from various reports, the catalyst particles contained in the catalyst particles for electrodes of the measurement sample are supported on the carrier. It is possible to grasp the position more accurately while visually confirming the position.
The patent applicant presents the following publications as publications in which the above-mentioned inventions known in the literature are described.

U.S. Patent Application Publication No. 2007/31722 Japanese Unexamined Patent Publication No. 2013-109856 WO2016 / 063668 WO2019 / 221168

Nature Materials Vol 19 (January 2020) 77-85 Journal of Power Sources 315 (2016) 179-191

With the spread of PEFC, the electrode catalyst is required to further improve the catalytic activity in order to reduce the amount of Pt used and the material cost.
The present inventors use a three-dimensional reconstructed image obtained by electron beam tomography measurement using a STEM (scanning transmission electron microscope) for a PtNi / C catalyst in which PtNi alloy particles are supported on a carbon carrier. When analyzing the particle size distribution of particles, there has never been a report that an improved product having a structure in which more catalyst particles are supported inside than outside the mesopores of hollow carbon could be actually synthesized, and it has not been improved yet. The present inventors have found that there is room for this.
The present invention has been made in view of such technical circumstances, and an object of the present invention is to provide an electrode catalyst (PtNi / C catalyst) having excellent catalytic activity that can contribute to cost reduction of PEFC.
Another object of the present invention is to provide a composition for forming a gas diffusion electrode, a gas diffusion electrode, a membrane / electrode assembly (MEA), and a fuel cell stack, which include the above-mentioned electrode catalyst.

The inventors of the present invention have diligently studied the structure of the electrode catalyst in which a large number of catalyst particles of the PtNi / C catalyst are supported in the mesopores of hollow carbon, and the structure for further improving the catalytic activity.
As a result, they have found that it is effective for improving the catalytic activity that the catalyst particles are supported on the carrier so as to satisfy the following conditions, and have completed the present invention.
More specifically, the present invention comprises the following technical matters.

That is, the present invention
It contains a hollow carbon carrier having mesopores having a pore diameter of 2 to 50 nm, and a plurality of catalyst particles supported on the carrier.
The catalyst particles contain a PtNi alloy and
The catalyst particles are supported both inside the mesopores and outside the mesopores of the carrier.
When the particle size distribution of the catalyst particles was analyzed using a three-dimensional reconstructed image obtained by electron beam tomography measurement using a STEM (scanning transmission electron microscope), the particles were supported inside the mesopores. The proportion of the catalyst particles is 50% or more.
A catalyst for an electrode is provided.

By supporting the catalyst particles of the PtNi / C catalyst on the hollow carbon carrier so as to satisfy the condition that the ratio of the catalyst particles supported inside the mesopores is 50% or more as described above, the catalyst particles of the present invention can be used. The catalyst can exhibit excellent catalytic activity that can contribute to cost reduction of PEFC.
The detailed reason why the electrode catalyst of the present invention has excellent catalytic activity has not been fully elucidated.
However, the present inventors think as follows. That is, in the PtNi / C catalyst in which the proportion of the catalyst particles supported inside the mesopores is 50% or more, the catalyst particles having high activity inside the mesopores of the carrier are compared with the conventional catalyst for electrodes. There will be many with a small particle size.
The catalyst particles supported inside the mesopores of such a carrier are supported on the carrier in a state in which it is difficult to come into direct contact with the polymer electrolyte existing in the catalyst layer. Therefore, the electrode catalyst of the present invention can reduce the decrease in catalytic activity due to poisoning of the Pt component, and can exhibit excellent catalytic activity when electrodeposited as compared with the conventional electrode catalyst. Further, the electrode catalyst of the present invention also reduces the dissolution of the Pt component and the Ni component.
Further, in the electrode catalyst of the present invention, from the viewpoint of obtaining the effect of the present invention more reliably, the three-dimensional reconstructed image obtained by electron beam tomography measurement using a STEM (scanning transmission electron microscope) is used. When the particle size distribution of the catalyst particles is analyzed, the proportion of the catalyst particles supported inside the mesopores is preferably 60% or more.

Further, in the electrode catalyst of the present invention, from the viewpoint of obtaining the effect of the present invention more reliably, the three-dimensional reconstructed image obtained by electron beam tomography measurement using a STEM (scanning transmission electron microscope) is used. When the particle size distribution of the catalyst particles is analyzed, it is preferable that the conditions of the following formulas (1) and (2) are satisfied at the same time.
D1 <D2 ... (1)
(N1 / N2)> 1.0 ... (2)
Here, in the formula (1) and the formula (2), D1 indicates the sphere-equivalent diameter of the particles showing the maximum frequency among the catalyst particles supported inside the mesopores of the carrier. In the formula (1) and the formula (2), D2 indicates a particle sphere equivalent diameter indicating the maximum frequency among the catalyst particles supported on the outside of the mesopores of the carrier.
Further, in the formula (1) and the formula (2), N1 indicates the frequency of the catalyst particles supported inside the mesopores of the carrier, which indicates the maximum frequency. In the formula (1) and the formula (2), N2 indicates the frequency of the catalyst particles supported on the outside of the mesopores of the carrier, which indicates the maximum frequency.

By supporting the catalyst particles of the core-shell catalyst on the hollow carbon carrier so as to simultaneously satisfy the conditions of the above formulas (1) and (2), the catalyst for electrodes of the present invention is excellent in that it can contribute to cost reduction of PEFC. The catalytic activity can be exhibited more reliably.
Here, in the present invention, the "hollow carbon" is carbon having more voids inside the carbon than the solid carbon described above, and is a mesopore having a pore diameter of 2 to 50 nm as defined by IUPAC. Shows conductive carbon having.

Further, in the electrode catalyst of the present invention, at least a part of the surface of the catalyst particles may be coated with a Pt oxide film as long as the catalyst particles can exhibit excellent catalytic activity.
Further, in the electrode catalyst of the present invention, at least a part of the surface of the catalyst particles may be covered with a Ni oxide film as long as the catalyst particles can exhibit excellent catalytic activity.
Further, the electrode catalyst of the present invention may contain a second catalyst particle made of Pt (zero valence) as long as the effect of the present invention can be obtained.
Further, the electrode catalyst of the present invention may contain a third catalyst particle made of Ni (zero valence) as long as the effect of the present invention can be obtained.
Further, from the viewpoint of more reliably obtaining the effect of the present invention, it is preferable that the hollow carbon carrier is Ketjen Black EC300J in the catalyst for electrodes of the present invention.
Further, in the present invention, in this case, the BET specific surface area (nitrogen adsorption specific surface area) of the hollow carbon carrier (Ketjen Black EC300J) ^{is preferably 750 to 850 m 2} / g.

The present invention also provides a powder of the electrode catalyst containing 10 wt% or more of the above-mentioned electrode catalyst of the present invention.
In the powder of the electrode catalyst, the "containing component other than the electrode catalyst of the present invention described above" is "the electrode catalyst other than the electrode catalyst of the present invention described above". That is, the powder of the electrode catalyst of the present invention does not include the powder that does not function as the electrode catalyst.
Since the powder of the electrode catalyst of the present invention contains the above-mentioned electrode catalyst of the present invention, it is possible to exhibit excellent catalytic activity that can contribute to cost reduction of PEFC.
Here, from the viewpoint of more reliably obtaining the effect of the present invention, the content ratio of the above-mentioned electrode catalyst of the present invention in the powder of the electrode catalyst of the present invention is preferably 30 wt% or more, preferably 50 wt% or more. It is more preferably 70 wt% or more, and most preferably 90 wt% or more.
The powder of the electrode catalyst of the present invention may contain an electrode catalyst having the following configuration (for convenience, referred to as “electrode catalyst P”) in addition to the above-mentioned electrode catalyst of the present invention.

That is, the catalyst P for an electrode contains a hollow carbon carrier having mesopores having a pore diameter of 2 to 50 nm, and a plurality of catalyst particles supported on the carrier.
The catalyst particles contain a PtNi alloy and
The catalyst particles are supported both inside the mesopores and outside the mesopores of the carrier.
When the particle size distribution of the catalyst particles was analyzed using a three-dimensional reconstructed image obtained by electron beam tomography measurement using a STEM (scanning transmission electron microscope), the particles were supported inside the mesopores. It has a structure in which the ratio of the catalyst particles is "less than 50%".
The powder of the electrode catalyst of the present invention may consist of the above-mentioned electrode catalyst of the present invention and the electrode catalyst P.
Also in this case, from the viewpoint of more reliably obtaining the effect of the present invention, the content ratio of the above-mentioned electrode catalyst of the present invention in the powder of the electrode catalyst of the present invention is preferably 30 wt% or more, preferably 50 wt%. % Or more is more preferable, 70 wt% or more is further preferable, and 90 wt% or more is most preferable.

Furthermore, the present invention provides a composition for forming a gas diffusion electrode, which contains the above-mentioned catalyst for electrodes of the present invention.
Since the composition for forming a gas diffusion electrode of the present invention contains the catalyst for an electrode of the present invention, PEF
A gas diffusion electrode having excellent catalytic activity (polarization characteristics) that can contribute to cost reduction of C can be easily manufactured.

The present invention also provides a gas diffusion electrode containing the above-mentioned catalyst for the electrode of the present invention.
The gas diffusion electrode of the present invention is configured to include the electrode catalyst of the present invention. Therefore, P
It becomes easy to configure the structure having excellent catalytic activity (polarization characteristics) that can contribute to the cost reduction of EFC.

Furthermore, the present invention comprises a membrane-electrode assembly (ME) comprising the gas diffusion electrode of the present invention described above.
A) is provided.
Since the membrane-electrode assembly (MEA) of the present invention contains the gas diffusion electrode of the present invention, PE
It becomes easy to configure the configuration with battery characteristics that can contribute to the cost reduction of FC.

The present invention also provides a fuel cell stack comprising the membrane-electrode assembly (MEA) of the present invention described above.
According to the fuel cell stack of the present invention, since the membrane-electrode assembly (MEA) of the present invention is included, it becomes easy to configure the structure having battery characteristics that can contribute to cost reduction of PEFC.

According to the present invention, there is provided an electrode catalyst having excellent catalytic activity that can contribute to cost reduction of PEFC.
Further, according to the present invention, a composition for forming a gas diffusion electrode, a gas diffusion electrode, a membrane / electrode assembly (MEA), and a fuel cell stack containing such a catalyst for the electrode are provided.

It is a schematic cross-sectional view which shows one preferable form of MEA of this invention. It is a schematic cross-sectional view which shows a preferable form of the electrode catalyst of this invention contained in at least one of the cathode catalyst layer and the anode catalyst layer of MEA shown in FIG. It is an enlarged schematic cross-sectional view which shows the schematic structure of the catalyst for an electrode shown in FIG. It is a schematic cross-sectional view which shows another suitable form of MEA of this invention. It is a schematic cross-sectional view which shows one preferable form of the CCM of this invention. It is a schematic cross-sectional view which shows another suitable form of the CCM of this invention. It is a schematic cross-sectional view which shows one preferable form of GDE of this invention. FIG. 5 is a schematic cross-sectional view showing another preferred embodiment of the GDE of the present invention. It is a schematic diagram which shows one preferable embodiment of the fuel cell stack of this invention. It is a schematic cross-sectional view which shows the conventional catalyst for an electrode. 6 is a STEM image showing 3D-electron beam tomography measurement conditions (volume size) using the STEM of the electrode catalyst of Example 1. 3D-STEM image (three-dimensional reconstruction image) of the catalyst of Example 1. It is a graph which shows the particle size distribution of the internal particle among the catalyst particles obtained by the image analysis of the 3D-STEM image of the catalyst of Example 1 shown in FIG. It is a graph which shows the particle size distribution of the outer particle among the catalyst particles obtained by the image analysis of the 3D-STEM image of the catalyst of Example 1 shown in FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

<Membrane / Electrode Assembly (MEA)>
FIG. 1 is a schematic cross-sectional view showing a preferred embodiment of the MEA of the present invention.
The MEA10 shown in FIG. 1 has two flat plate-shaped gas diffusion electrodes (cathode 1 and anode 2) arranged so as to face each other, and a polymer electrolyte membrane (Polymer) arranged between the cathode 1 and the anode 2. It has a configuration including Electrolyte Membrane (hereinafter, referred to as “PEM” if necessary) 3.
In the case of this MEA10, at least one of the cathode 1 and the anode 2 has a configuration in which a core-shell catalyst described later is contained.
The MEA10 can be manufactured by laminating the cathode 1, the anode 2, and the PEM3 as shown in FIG. 1 and then crimping them.

<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 1 m of a water-repellent layer (Micro Porous Layer, hereinafter referred to as “MPL” if necessary) arranged between the gas diffusion layer 1 gd and the catalyst layer 1c.
Similarly to the cathode 1, the gas diffusion electrode 2 is also between the gas diffusion layer 2gd, the catalyst layer 2c formed on the surface of the gas diffusion layer 2gd on the PEM3 side, and the gas diffusion layer 2gd and the catalyst layer 2c. It has a configuration with an arranged MPL 2 m.

(Catalyst layer (CL))
In the cathode 1, the catalyst layer 1c is a layer in which the reaction of producing water from the air (oxygen gas) sent from the gas diffusion layer 1gd and the hydrogen ions moving in the PEM 3 from the anode 2 proceeds.
Further, in the anode 2, the catalyst layer 2c is a layer in which the reaction of 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 according to the catalyst for electrodes of the present invention.

(A preferred form of the electrode catalyst of the present invention)
Hereinafter, a preferred embodiment of the electrode catalyst of the present invention will be described with reference to FIG.
FIG. 2 is a schematic cross-sectional view showing a preferred form of an electrode catalyst (PtNi / C catalyst) contained in at least one of the cathode catalyst layer 1c and the anode catalyst layer 2c of MEA10 shown in FIG. Further, FIG. 3 is an enlarged schematic cross-sectional view showing a schematic configuration of the electrode catalyst 20 shown in FIG.
As shown in FIGS. 2 and 3, the electrode catalyst 20 includes a carrier 22 which is a hollow carbon carrier and catalyst particles 23 containing a PtNi alloy supported on the carrier 22.

Further, the electrode catalyst 20 shown in FIGS. 2 to 3 preferably satisfies the following conditions from the viewpoint of more reliably obtaining the effect of the present invention.
Here, the catalyst particles 23 contain a PtNi alloy, preferably made of a PtNi alloy. However, a Pt oxide layer and a Ni oxide layer may be formed on the surface of the catalyst particles as long as the effects of the present invention can be obtained.
The electrode catalyst 20 preferably has an average crystallite size of 3 to 16.0 nm measured by powder X-ray diffraction (XRD).
The electrode catalyst 20 has a Pt carrying ratio of preferably 10.0 to 40.0 wt%, and a Ni carrying ratio of preferably 1.0 to 25.0 wt%.

The carrier 22 has mesopores (mesopores defined by IUPAC) having a pore diameter of 2 to 50 nm, and can support a complex composed of a core portion 24 and a shell portion 26 (or shell portion 26a). Moreover, the hollow carbon carrier having a relatively large surface area is not particularly limited.
Further, the carrier 22 is preferably a hollow carbon carrier having good dispersibility and excellent conductivity in the composition for forming a gas diffusion electrode containing the core-shell catalyst 20 (or 20A).

Examples of the hollow carbon carrier include Ketjen Black EC300J and Ketjen Black EC600JD. For example, as these commercially available products, trade names such as "carbon EPC" and "carbon EPC600JD" (manufactured by Lion Chemical Corporation, etc.) can be exemplified. For details on Ketjen Black EC300J and Ketjen Black EC600JD, see, for example, the literature published on the Internet by the "Functional Carbon Filler Study Group" [Characteristics and application development of conductive carbon black "Ketchen Black EC"]. Features are described.

Other hollow carbon carriers include the product name "MCND (Mesoporous Carbon Nano-Dendrite)" (manufactured by Nippon Steel & Sumitomo Metal Corporation), the product name "CNovel" (manufactured by Toyo Carbon Co., Ltd.), and the product name "Black pearls 2000". (Manufactured by Cabot) can be exemplified.
Here, from the viewpoint of more reliably obtaining the effects of the present invention, the hollow carbon carrier is preferably one of Ketjen Black EC300J, Ketjen Black EC600JD and Knovel. In the case of Ketjen Black EC300J, the BET specific surface area (nitrogen adsorption specific surface area) measured using nitrogen of the hollow carbon carrier ^{is preferably 750 to 850 m 2} / g from the same viewpoint. In the case of CNovel, the BET specific surface area (nitrogen adsorption specific surface area) measured using nitrogen of the hollow carbon carrier ^{is preferably 750 to 1300 m 2} / g from the same viewpoint.

Here, as shown in FIG. 2, the catalyst particles 23 are supported both inside the mesopores P22 of the carrier 22 and outside the mesopores P22.
Then, the electrode catalyst 20 simultaneously satisfies the conditions of the following formulas (1) and (2) when the electron tomography measurement by 3D-STEM is carried out.
Electrode catalyst.
D1 <D2 ... (1)
(N1 / N2)> 1.0 ... (2)

Here, in the formulas (1) and (2), D1 determines the sphere-equivalent diameter (nm) of the particles showing the maximum frequency among the catalyst particles 23 (or 23a) supported inside the mesopores P22 of the carrier 22. show.
Further, in the formulas (1) and (2), D2 indicates the particle sphere equivalent diameter showing the maximum frequency among the catalyst particles 23 (or 23a) supported on the outside of the mesopores P22 of the carrier 22.
Further, in the formulas (1) and (2), N1 indicates the frequency (number of particles) of the catalyst particles 23 (or 23a) supported inside the mesopores P22 of the carrier 22, which indicates the maximum frequency.
Further, in the formulas (1) and (2), N2 indicates the frequency frequency (number of particles) of the particles showing the maximum frequency among the catalyst particles 23 (or 23a) supported on the outside of the mesopores P22 of the carrier 22. ..

In the electrode catalyst 20 that simultaneously satisfies the conditions of the formulas (1) and (2), the highly active catalyst particles 23 are relatively small particles inside the mesopores P22 of the carrier 22 as compared with the conventional electrode catalysts. There will be many in diameter. The catalyst particles 23 (or 23a) having a core-shell structure supported inside the mesopores P22 of the carrier 22 exhibit excellent catalytic activity when electrodeposited as compared with a conventional catalyst for electrodes. .. Further, the carrier 22 is supported on the carrier 22 in a state where it is difficult to come into direct contact with a polymer electrolyte such as Nafion contained in the catalyst, and the dissolution of the Pt component and the Ni component is also reduced.

Examples of the method for producing the electrode catalyst 20 include a "Pt salt solution preparation step", a "carrier addition step", and a "Ni salt solution dropping step" for satisfying the conditions of the formulas (1) and (2). It is not particularly limited except that it includes a "cleaning step", a "drying step" and a "reducing step", and can be produced by a known method.

In the "Pt salt solution preparation step", an aqueous solution prepared by dissolving a water-soluble Pt salt in ultrapure water is prepared at room temperature.
The "ultrapure water" used in the preparation of the above-mentioned aqueous solution in this Pt salt solution preparation step is measured by the resistivity R (JIS standard test method (JIS K0552)) represented by the following formula (3). The reciprocal of the electrical conductivity of water is 3.0 MΩ · cm or more. Further, it is preferable that the "ultrapure water" has a water quality equivalent to or higher than that of "A3" specified in JIS K0557 "Water used for irrigation / drainage test".

The ultrapure water is not particularly limited as long as it is water having an electric conductivity satisfying the relationship represented by the following formula (3). For example, examples of the above ultrapure water include ultrapure water produced using the ultrapure water production equipment "Milli-Q series" (manufactured by Merck Group) and "Elix UV series" (manufactured by Nippon Millipore Co., Ltd.). be able to.
R = 1 / ρ ・ ・ ・ (3)
In the above formula (3), R represents the specific resistance, and ρ represents the electrical conductivity measured by the JIS standard test method (JIS K0552).

The next step of the "Pt salt solution preparation step" is the "carrier addition step". In this "carrier addition step", the carrier 22 is added to the Pt salt solution obtained through the "Pt salt solution preparation step" at room temperature. Then, the temperature is maintained at 80 to 99 ° C., preferably 90 to 99 ° C. for a predetermined time (however, the state of not boiling is maintained) while stirring the dispersion liquid in which the carrier is dispersed, and then the temperature is lowered to room temperature. Next, a pH adjuster is added to the obtained dispersion to prepare a dispersion whose pH is adjusted to 9 to 13. Further, the dispersion liquid is kept at a predetermined temperature of 40 ° C. or higher for a predetermined time while stirring (however, the state of not boiling is maintained). Then, the temperature of the dispersion is lowered to room temperature.
As a result, the gas inside the mesopore P22 of the carrier 22 is removed, and the Pt salt aqueous solution can sufficiently penetrate into the mesopore P22. Then, a large number of precursors of catalyst particles are supported in the mesopores P22 of the carrier 22.

The next step of the "carrier addition step" is a "Ni salt solution dropping step". In the "Ni salt solution dropping step", an aqueous solution prepared by dissolving a water-soluble Ni salt in ultrapure water is added to the dispersion obtained through the "carrier addition step" at room temperature. Next, a pH adjuster is added to the obtained dispersion to prepare a dispersion whose pH is adjusted to 9 to 13. Further, the dispersion liquid is kept at a predetermined temperature of 40 ° C. or higher for a predetermined time while stirring (however, the state of not boiling is maintained). Then, the temperature of the dispersion is lowered to room temperature.

The next step of the "Ni salt solution dropping step" is the "cleaning step". In this "cleaning step", the solid component and the liquid component in the liquid obtained through the "Ni salt solution dropping step" are separated, and the solid content (a mixture of the precursor of the PtNi / C catalyst and other impurities)). To wash. For example, the solid component in the liquid obtained through the "Ni salt solution dropping step" may be separated from the liquid component using a filtering means such as filter paper or filter cloth. Cleaning of solids is performed by the above-mentioned ultrapure water, pure water (the specific resistance R represented by the above formula (3) is 0.1 MΩ · cm or more and less than 3.0 MΩ · cm), and pure hot water (the temperature of pure water). 40 to 80 ° C.) may be used. For example, when pure warm water is used, the filtrate is washed repeatedly until the electrical conductivity of the filtrate after washing becomes less than 20 μS / cm.
The next step after the "cleaning step" is the "drying step". In this "drying step", water is separated from the solid component (a mixture of the precursor of the PtNi / C catalyst and water) obtained through the "washing step". First, the solid component is air-dried, and then dried in a dryer at a predetermined temperature for a predetermined time.
The next step after the "drying step" is the "reduction step". In this "crushing step", the solid component (precursor of PtNi / C catalyst) obtained by obtaining the "drying step" is reduced.
As a reduction treatment method, a reduction furnace is used, and the solid component (precursor of PtNi / C catalyst) is reduced using hydrogen gas at a predetermined temperature of 800 ° C. or higher.

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 known ones can be used. For example, as the polymer electrolyte, a perfluorocarbon resin having a known sulfonic acid group or carboxylic acid group can be exemplified. As easily available polymer electrolytes with hydrogen ion conductivity, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) are used. It can be preferably exemplified.
Then, 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 has a mass ratio N / C of the mass C of the carrier 22 and the mass N of the polymer electrolyte of 0.5. It is set to ~ 1.2, and more preferably the mass ratio N / C is set to 0.7 to 1.0.

(Gas Diffusion Layer (GDL))
The gas diffusion layer 1gd provided on the cathode 1 shown in FIG. 1 is a layer provided for supplying an oxidizing agent 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 layer (1 gd) shown in FIG. 1 has a function and a structure of allowing hydrogen gas or air (oxygen gas) to pass through well to reach the catalyst layer. Therefore, the gas diffusion layer preferably 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 (1 gd) is not particularly limited, and a known member can be used. For example, carbon paper or carbon paper as a main raw material, and an auxiliary raw material composed of carbon powder, ion-exchanged water as an optional component, and polyethylene terephthalate dispersion as a binder is preferably applied to the carbon paper.

(Water repellent layer (MPL))
As shown in FIG. 1, a water repellent layer (MPL) 1 m is arranged between the gas diffusion layer 1 gd and the catalyst layer 1 c on the cathode 1. The water-repellent layer 1 m has electron conductivity, water repellency, and gas diffusivity, and is provided to promote the diffusion of the oxidant gas into the catalyst layer 1 gd and the discharge of the reaction-generated water generated in the catalyst layer 1 gd. It is something that is. The structure of the water-repellent layer 1 m is not particularly limited, and a known structure can be adopted.

(Polyelectrolyte 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 known ones conventionally used for PEFC can be adopted. For example, it may be a membrane containing what is exemplified as the polymer electrolyte contained in the catalyst layer 1c and the catalyst layer 2c described above as a constituent component.

<Modification of MEA>
Although 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, 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 structure of MEA 11 shown in FIG.
FIG. 4 is a schematic cross-sectional view showing another preferred embodiment of the MEA of the present invention. The MEA 11 shown in FIG. 4 has a configuration in which a gas diffusion electrode (GDE) 1A having the same configuration as the cathode 1 in the MEA 10 shown in FIG. 1 is arranged on only one side of the polymer electrolyte membrane (PEM) 3. However, the catalyst layer 1c of the gas diffusion electrode (GDE) 1A has the structure of the catalyst layer of the present invention. That is, the catalyst layer 1c of GDE1A has a mass ratio N / C of the mass C of the carrier of the core-shell catalyst and the mass N of the polyelectrolyte of 0.5 to 1.2, more preferably 0.7 to 1.0. ing.

<Membrane / Electrode Assembly (CCM)>
Next, a preferred embodiment of the membrane-electrode assembly (CCM) of the present invention will be described.
FIG. 5 is a schematic cross-sectional view showing a preferred embodiment of the CCM of the present invention. The CCM 12 shown in FIG. 5 has a configuration in which the polymer electrolyte membrane (PEM) 3 is arranged between the cathode catalyst layer 1c and the anode catalyst layer 2c. Then, at least one of the cathode catalyst layer 1c and the anode catalyst layer 2c has the structure 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 of the mass C of the carrier of the electrode catalyst and the mass N of the polymer electrolyte of 0.5 to 1.2. It is preferably 0.7 to 1.0.

<Deformation mode of membrane-electrode assembly (CCM)>
Although the preferred embodiment of the CCM of the present invention has been described above, 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. 7 is a schematic cross-sectional view showing another preferred embodiment of the CCM of the present invention. The CCM 13 shown in FIG. 6 has a configuration in which a catalyst layer 1c having the same configuration as the cathode 1 in the CCM 12 shown in FIG. 5 is arranged on only one side of the polymer electrolyte membrane (PEM) 3. However, the catalyst layer 1c of the gas diffusion electrode (GDE) 1A has the structure of the catalyst layer of the present invention. That is, the catalyst layer 1c of CCM13 has a mass ratio N / C of the mass C of the carrier of the electrode catalyst and the mass N of the polyelectrolyte of 0.5 to 1.2, more preferably 0.7 to 1.0. Has been done.

<Gas diffusion electrode (GDE)>
Next, a preferred embodiment of the gas diffusion electrode (GDE) of the present invention will be described.
FIG. 8 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. 7 has the same configuration as the cathode 1 mounted on the MEA10 shown in FIG. However, the catalyst layer 1c of the gas diffusion electrode (GDE) 1B has the structure of the catalyst layer of the present invention. That is, the catalyst layer 1c of the gas diffusion electrode (GDE) 1B has a mass ratio N / C of the mass C of the carrier of the electrode catalyst and the mass N of the polyelectrolyte of 0.5 to 1.2, more preferably 0. It is said to be 7 to 1.0.

<Deformation mode 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 GDE1C shown in FIG.
FIG. 9 is a schematic cross-sectional view showing another preferred embodiment of the GDE of the present invention. Compared with GDE1B shown in FIG. 8, GDE1C shown in FIG. 8 has a configuration in which a water-repellent layer (MPL) is not arranged between the catalyst layer 1c and the gas diffusion layer 1gd.

<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 contains an electrode catalyst, a polyelectrolyte, and a main component, and has a mass ratio N / of the mass C of the carrier of the electrode catalyst and the mass N of the polyelectrolyte. C 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-mentioned polymer electrolyte having hydrogen ion conductivity, water, and alcohol.

The composition ratio of the electrode catalyst, the polyelectrolyte, and other components (water, alcohol, etc.) contained in the catalyst layer forming composition is such that the dispersed state of the electrode catalyst in the obtained catalyst layer is good, and the catalyst layer is concerned. It is appropriately set so that the power generation performance of the MEA including the above can be improved.
The composition for forming a catalyst layer can be prepared by mixing and stirring a liquid containing a catalyst for electrodes and a polymer electrolyte. From the viewpoint of adjusting the coatability, a polyhydric alcohol such as glycerin and / or water may be contained. When mixing a liquid containing an electrode catalyst and a polymer electrolyte, a pulverizer / 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 by using a suitable embodiment of the catalyst layer forming composition of the present invention.

(Manufacturing method of gas diffusion electrode)
Next, an example of the method for manufacturing the gas diffusion electrode of the present invention will be described. The gas diffusion electrode may be formed so as to include the catalyst layer of the present invention, and a known method can be adopted as the manufacturing method thereof. If the composition for forming a catalyst layer of the present invention is used, it can be produced more reliably.
For example, the composition for forming a catalyst layer may be produced by applying it on a gas diffusion layer (or the water-repellent layer of a laminate having a water-repellent layer formed on the gas diffusion layer) and drying it.

<Fuel cell stack>
FIG. 9 is a schematic view showing a preferred embodiment of the fuel cell stack of the present invention.
The fuel cell stack 30 shown in FIG. 9 has a structure in which the MEA 10 shown in FIG. 1 is a single unit cell and a plurality of the single unit cells are stacked. Further, the fuel cell stack 30 has a configuration in which the MEA 10 is arranged 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 in more detail with reference to Examples, but the present invention is not limited to the following Examples.

(I) Preparation of electrode catalyst to be used for the catalyst layer of the cathode of MEA

(1) Production of PtNi / C catalyst used for cathode of MEA of Example 1 [Powder of PtNi alloy particle-supported carbon catalyst "PtNi / C catalyst"]
PtNi / C catalyst powder in which catalyst particles containing PtNi alloy are supported on carbon black powder {Pt support rate 28.0 wt%, Ni support rate 8.0 wt% Trade name "SA30ABKN8", manufactured by NE CHEMCAT )} Was prepared.
The powder of this PtNi / C catalyst was prepared by the following procedure.

(First step (Pt salt solution preparation step))
An aqueous solution prepared by dissolving a water-soluble Pt salt in ultrapure water was prepared at room temperature.
The "ultrapure water" used in this first step (Pt salt solution preparation step) is the electrical resistivity measured by the specific resistance R (JIS standard test method (JIS K0552)) represented by the following formula (3). Water having a resistivity (reciprocal of conductivity) of 3.0 MΩ · cm or more was used. Further, this "ultrapure water" has a water quality equivalent to or higher than that of "A3" specified in JIS K0557 "Water used for irrigation / drainage test".
This ultrapure water was produced using the ultrapure water production equipment "Milli-Q series" (manufactured by Merck Group) and "Elix UV series" (manufactured by Nippon Millipore Co., Ltd.).
R = 1 / ρ (3)
In the above general formula (3), R represents the specific resistance, and ρ represents the electrical conductivity measured by the JIS standard test method (JIS K0552).

(Second step (carrier addition step))
The carrier 22 was added to the Pt salt solution obtained through the "Pt salt solution preparation step" at room temperature. As the carrier 22, a commercially available hollow carbon carrier {manufactured by Lion Corporation, trade name "Carbon ECP" (registered trademark) (Ketjen Black EC300J), specific surface area of 750 to 800 m ² / g} was used.
Then, the temperature was maintained at 80 to 99 ° C., preferably 90 to 99 ° C. for a predetermined time (however, the state of not boiling was maintained) while stirring the dispersion liquid in which the carrier was dispersed, and then the temperature was lowered to room temperature. Next, a pH adjuster was added to the obtained dispersion to prepare a dispersion whose pH was adjusted to 9 to 13. Further, the dispersion was kept at a predetermined temperature of 40 ° C. or higher for a predetermined time while stirring (however, the state of not boiling was maintained). Then, the dispersion was cooled to room temperature.

(Third step (Ni salt solution dropping step))
An aqueous solution prepared by dissolving a water-soluble Ni salt in ultrapure water was added to the dispersion obtained through the second step (carrier addition step) at room temperature. Next, a pH adjuster was added to the obtained dispersion to prepare a dispersion whose pH was adjusted to 9 to 13. Further, the dispersion was kept at a predetermined temperature of 40 ° C. or higher for a predetermined time while stirring (however, the state of not boiling was maintained). Then, the dispersion was cooled to room temperature.

(4th step (cleaning step))
The solid component and the liquid component in the liquid obtained through the third step (Ni salt solution dropping step) were separated, and the solid content (a mixture of the precursor of the PtNi / C catalyst and other impurities) was washed. The solid component in the liquid obtained through the "Ni salt solution dropping step" using filter paper was separated from the liquid component. Cleaning of solids is performed by the above-mentioned ultrapure water, pure water (the specific resistance R represented by the above formula (3) is 0.1 MΩ · cm or more and less than 3.0 MΩ · cm), and pure hot water (the temperature of pure water). Was 40 to 80 ° C.). Pure warm water was used, and the filtrate was washed repeatedly until the electrical conductivity of the filtrate after washing became less than 20 μS / cm.

(Fifth step (drying step))
Next, the solid component (a mixture of the precursor of the PtNi / C catalyst and water) on the filter paper was air-dried in the air in this state. After this air drying, the solid component on the filter paper was transferred to a magnetic dish and dried in an electric dryer at a predetermined temperature of 60 ° C. or higher for a predetermined time. The dried solid component was pulverized using a mixer to obtain a powder of a precursor of the PtNi / C catalyst.

(6th step (reduction step))
The solid component (precursor of PtNi / C catalyst) obtained by obtaining the "drying step" was reduced.
The solid component (precursor of PtNi / C catalyst) was placed in a baking dish and placed in a reduction furnace. Next, nitrogen gas was passed through the reduction furnace at a predetermined flow rate to purge the residual oxygen. Next, hydrogen gas was introduced into the reduction furnace, and the reduction treatment was performed at a predetermined temperature of 800 ° C. or higher and a predetermined time. Then, the temperature in the reduction furnace was lowered, and the solid component after the reduction treatment was slowly oxidized. As a result, a PtNi / C catalyst was obtained.

<Measurement of loading rate (ICP analysis)>
For this core-shell catalyst A, the Pt carrying ratio (wt%) and the Ni carrying ratio (wt%) were measured by the following methods.
The PtNi / C catalyst was immersed in aqua regia to dissolve the metal. Next, carbon, an insoluble component, was removed from aqua regia. Next, the aqua regia excluding carbon was subjected to ICP analysis.
As a result of ICP analysis, the Pt carrying ratio of this PtNi / C catalyst was 28.0 wt% and the Ni carrying ratio was 8.0 wt%.

<Surface observation / structure observation of electrode catalyst>
In order to observe the three-dimensional structure of this PtNi / C catalyst, electronic warfare tomography measurement by STEM was carried out under the following conditions.
・ STEM equipment: JEM-ARM200F atomic resolution analysis electron microscope manufactured by JEOL Ltd. ・ Data analysis software: 3D reconstruction software Composer, 3D data visualization software Visualizer-kai, image analysis software Colorist manufactured by System Infrontia
・ Measurement conditions Acceleration voltage: 60 kV
Observation magnification 800,000 to 1,000,000 times Tilt angle of measured sample: -80 ° to + 80 °
Tilt step angle of measurement sample 2 °
Number of pixels 512 x 512 pixels 512 x 512 pixels
Pixel size: 0.350 nm / pixel ~ 0.500 nm / pixel
Volume size: Shown in FIG.

PtNi / C present inside the carbon carrier by image analysis of a three-dimensional reconstruction image (3D-STEM image) obtained by electron beam tomography measurement using STEM (scanning transmission electron microscope) for the PtNi / C catalyst. The catalyst particles (hereinafter, internal particles) and the PtNi / C catalyst particles (hereinafter, external particles) existing on the surface of the carbon carrier were separated, and the particle size distribution of the PtNi / C catalyst particles in each region was calculated.
A three-dimensional reconstruction image (3D-STEM image) of the core-shell catalyst A is shown in FIG.
The particle size analysis results of the internal particles and the external particles obtained by image analysis are shown in FIGS. 13 and 14.
The 3D-STEM image was obtained by reconstructing a plurality of two-dimensional STEM images obtained by inclining the sample stage stepwise under the above measurement conditions.

The image analysis (particle size analysis) of the three-dimensional reconstructed image (3D-STEM image) was performed by the following procedure. First, the region of the catalyst particles was selected from the three-dimensional reconstruction image, and each catalyst particle was labeled (not shown). Next, the equivalent sphere diameter was calculated from the volume of the labeled Pt particles, and the particle size distribution (FIGS. 13 and 14) was obtained.
Here, the equivalent diameter of the sphere was calculated by rounding off the values after the decimal point (values less than 1 nm) with the unit being nm.
For the PtNi / C catalyst, the proportion of the catalyst particles supported inside the mesopores of the carrier and the proportion of the catalyst particles supported outside the mesopores of the carrier were determined. The values of D1, D2, N1 and N2 were also obtained. The results are shown in Tables 1 and 2.
Furthermore, the average particle size of the catalyst particles of the PtNi / C catalyst measured from the STEM image is 5.5.
It was nm.

(2) Preparation of Pt / C Catalyst Powder Used for Cathode of MEA of Comparative Example 1 As a Pt / C catalyst, a Pt / C catalyst manufactured by NECHEMCAT with a Pt carrying ratio of 50 wt% (trade name: "" SA50BK ") was prepared. As the carrier of this Pt / C catalyst, a commercially available hollow carbon carrier {manufactured by Lion Co., Ltd., trade name "Carbon ECP" (registered trademark) (Ketjen Black EC300J), specific surface area of 750 to 800 m ² / g} is used. used.
XRD analysis was performed on this Pt / C catalyst. As a result, the average value of the crystallite size was 2.6 nm.

(II) Preparation of P / C catalyst used for the anode of MEA of Example 1 and Comparative Example 1 The same Pt / C catalyst as Pt / C catalyst B used for the cathode of MEA of Comparative Example 1 was used in Example 1, It was used as a P / C catalyst used for the anode of MEA of Comparative Example 1.

<Example 1>
An MEA having the same configuration as the MEA 10 shown in FIG. 1 was created by the following procedure.

(1) Preparation of cathode GDL of cathode
Carbon paper (trade name "TGP-H-60" manufactured by Toray Industries, Inc.) was prepared as GDL.
Ink for forming MPL of cathode In a ball mill container made of Teflon (registered trademark) containing balls made of Teflon (registered trademark), 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 Co., Ltd.) 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. As a result, an ink for forming MPL of the cathode was prepared.
Cathode MPL
A cathode MPL forming ink was applied to one side of the GDL using a bar coder to form a coating film. Then, the coating film was sufficiently dried in a dryer and further heat-bonded to prepare a laminate in which MPL was formed on GDL.
Ink for forming catalyst layer of cathode In a Teflon (registered trademark) ball mill container containing Teflon (registered trademark) balls, the above-mentioned PtNi / C catalyst, ion-exchanged water, and 10 wt% Nafion aqueous dispersion (Dupont) The product name “DE1021CS”) and glycerin were added and mixed to prepare an ink for forming a catalyst layer for the cathode. For this ink, N / C = 0.7. Further, the carbon: ion-exchanged water: glycerin = 1:10: 0.8 (mass ratio) in the core-shell catalyst A was set.
Cathode catalyst layer (CL)
The above-mentioned ink for forming a catalyst layer of a cathode was applied to the surface of the MPL of a laminate in which MPL was formed on the above-mentioned GDL by the bar coating method to form a coating film. The coating film was dried at room temperature for 30 minutes and then dried at 60 ° C. for 1.0 hour to form a catalyst layer. In this way, the cathode, which is a gas diffusion electrode, was created. The amount of Pt supported by the catalyst layer of the cathode was set to the numerical value shown in Table 1.

(2) Creation of anode GDL of anode
As GDL, the same carbon paper as the cathode was prepared.
Ink for forming MPL of anode In a ball mill container made of Teflon (registered trademark) containing balls made of Teflon (registered trademark), 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 Fluorochemicals Co., Ltd.) was placed in a ball mill container and mixed. As a result, an MPL forming ink for the anode was prepared.
Anode MPL
An anode MPL forming ink was applied to one side of the GDL using a bar coder to form a coating film. Then, the coating film was sufficiently dried in a dryer and further heat-bonded to prepare a laminate in which MPL was formed on GDL.
Ink for forming catalyst layer of anode In a Teflon (registered trademark) ball mill container containing Teflon (registered trademark) balls, SA50BK (Pt carrying ratio 50 wt%), ion-exchanged water, and 5 wt% Nafion alcohol dispersion (5 wt% Nafion alcohol dispersion) SIGMA-ALDRICH product name "Nafion 5 wt.% Dispersion", product number "274704") and glycerin were mixed and mixed to prepare an ink for forming a catalyst layer of an anode. For this ink, N / C = 1.2. Further, the carbon: ion-exchanged water: glycerin = 1: 6: 4 (mass ratio) in SA50BK was set.
Anode catalyst layer (CL)
The above-mentioned ink for forming a catalyst layer of the anode was applied to the surface of the MPL of the laminate in which the MPL was formed on the above-mentioned GDL by the bar coating method to form a coating film. The coating film was dried at room temperature for 30 minutes and then dried at 60 ° C. for 1.0 hour to form a catalyst layer. In this way, the anode, which is a gas diffusion electrode, was prepared. The amount of Pt supported by the catalyst layer of the anode was 0.3 mg / cm ² .

(3) Preparation of MEA A polymer electrolyte membrane (trade name “Nafion NR212” manufactured by DuPont) was prepared. A laminate in which this polymer electrolyte membrane was arranged between the cathode and the anode was prepared, and heat-pressed with a hot press to prepare MEA. The conditions for heat crimping were as follows: pressing at 140 ° C. and 5 KN for 5 minutes, and further pressing at 140 ° C. and 25 KN for 3 minutes.

<Comparative example 1>
For the catalyst layer of the cathode, each MEA was prepared under the same conditions and procedures as in Example 1 except that the following conditions were changed.
That is, in the preparation of the ink for forming the catalyst layer of the cathode,
-Instead of the PtNi / C catalyst, the P / C catalyst described above (trade name: "SA-50BK")
It was used.
-A 5 wt% Nafion alcohol dispersion (trade name "DE520CS" manufactured by DuPont; containing 48 wt% 1-propanol) was used instead of the 10 wt% Nafion aqueous dispersion.
-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 and the N / C were the values shown in Table 1.
-Carbon: ion-exchanged water: glycerin = 1:10: 1 (mass ratio) in the P / C catalyst (trade name: "SA50BH").

<Battery performance evaluation>
The battery performance of MEA of Example 1 and Comparative Example 1 was carried out by the following battery performance evaluation method.
The MEAs of Example 1 and Comparative Example 1 were installed in a fuel cell single cell evaluation device.
Next, the power generation reaction in the MEA was allowed to proceed under the following conditions.
The single cell (MEA) temperature was set to 80 ° C. Pure hydrogen at 1.0 atm humidified with saturated steam was supplied to the anode by adjusting the flow rate so that the utilization rate was 70%. Further, pure oxygen at 1.0 atm humidified with saturated steam at 80 ° C. was supplied to the cathode by adjusting the flow rate so that the utilization rate was 50%.
The single cell (MEA) is evaluated by controlling the current with the electronic load device attached to the fuel cell single cell evaluation device, ^{and scanning the current value from 0 to 1.0 A / cm 2} to obtain a current-voltage curve. Obtained as data.
From the above current-voltage curve data, a graph plotted with the X-axis (current density) as a logarithmic scale was created (not shown), and the 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 weight of platinum per unit area of the cathode, it is calculated as the activity per unit weight (Mass.Act.) Of platinum contained in the cathode and contained in the cathode. It was used as an index of the oxygen reducing ability of the catalyst to be produced. The results are shown in Table 1.
In Table 1, the Mass. Act. Mass. Obtained in other Examples and Comparative Examples as a relative value (relative ratio) with reference to (1.0). Act. The result of comparison is shown.

From the results shown in Table 1, it was clarified that the MEA of Example 1 had a higher Pt mass activity as compared with the MEA of Comparative Example 1.

The electrode catalyst of the present invention exhibits excellent catalytic activity. Further, the GDE, CCM, MEA, and the fuel cell stack including the catalyst layer of the present invention exhibit excellent battery characteristics that can contribute to 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 mobile mobiles, but also to the energy industry, cogeneration systems, and the like, and contributes to the development of the energy industry and environmental technology.

1 ... Cathode,
1A, 1B, 1C ... Gas diffusion electrode (GDE)
1c ... catalyst layer (CL),
1m ・ ・ ・ Water repellent layer (MPL),
1gd ... Gas diffusion layer (GDL),
2 ... Anode,
2c ... catalyst layer (CL),
2m ・ ・ ・ Water repellent layer (MPL),
2gd ... Gas diffusion layer (GDL),
3 ... Polyelectrolyte membrane (PEM),
4, 5 ... Separator 10, 11 ... Membrane electrode assembly (MEA),
12, 13 ... Membrane-catalyst layer junction (CCM)
20 ... PtNi / C catalyst,
22 ... Carrier,
23 ... catalyst particles,
30 ... Fuel cell stack,
P22: Mesopores of carrier

Claims (14)

It contains a hollow carbon carrier having mesopores having a pore diameter of 2 to 50 nm, and a plurality of catalyst particles supported on the carrier.
The catalyst particles contain a PtNi alloy and
The catalyst particles are supported both inside the mesopores and outside the mesopores of the carrier.
When the particle size distribution of the catalyst particles was analyzed using a three-dimensional reconstructed image obtained by electron beam tomography measurement using a STEM (scanning transmission electron microscope), the particles were supported inside the mesopores. The proportion of the catalyst particles is 50% or more.
Electrode catalyst. When the particle size distribution of the catalyst particles was analyzed using a three-dimensional reconstructed image obtained by electron beam tomography measurement using a STEM (scanning transmission electron microscope), the particles were supported inside the mesopores. The proportion of the catalyst particles is 60% or more.
The electrode catalyst according to claim 1. When the particle size distribution of the catalyst particles is analyzed using the three-dimensional reconstructed image obtained by electron beam tomography measurement using STEM (scanning transmission electron microscope), the following equations (1) and (2) The electrode catalyst according to claim 1 or 2, which simultaneously satisfies the conditions of.
D1 <D2 ... (1)
(N1 / N2)> 1.0 ... (2)
[In the formula (1) and the formula (2),
D1 indicates the sphere-equivalent diameter of the particles showing the maximum frequency among the catalyst particles supported inside the mesopores of the carrier.
D2 indicates a particle sphere equivalent diameter indicating the maximum frequency among the catalyst particles supported on the outside of the mesopores of the carrier.
N1 indicates the frequency of the catalyst particles supported inside the mesopores of the carrier, which indicates the maximum frequency of the catalyst particles.
N2 indicates the frequency of the particles showing the maximum frequency among the catalyst particles supported on the outside of the mesopores of the carrier. ] At least a part of the surface of the catalyst particles is coated with a Pt oxide film.
The electrode catalyst according to any one of claims 1 to 3. At least a part of the surface of the catalyst particles is coated with a Ni oxide film.
The electrode catalyst according to any one of claims 1 to 4. Further, a second catalyst particle composed of Pt (zero valence) is contained.
The electrode catalyst according to any one of claims 1 to 5. Further, a third catalyst particle made of Ni (zero valence) is contained.
The electrode catalyst according to any one of claims 1 to 5. The hollow carbon carrier is Ketjen Black EC300J.
The electrode catalyst according to any one of claims 1 to 7. The BET specific surface area (nitrogen adsorption specific surface area) of the hollow carbon carrier is 750 to 850 m ² / g.
The catalyst for electrodes according to claim 8. The electrode catalyst according to any one of claims 1 to 6 is contained in an amount of 10 wt% or more.
Electrode catalyst powder The electrode catalyst according to any one of claims 1 to 9 is contained.
Composition for forming a gas diffusion electrode. A gas diffusion electrode containing the electrode catalyst according to any one of claims 1 to 9. A membrane-electrode assembly (MEA) comprising the gas diffusion electrode according to claim 11. A fuel cell stack comprising the membrane-electrode assembly (MEA) of claim 12.

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