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

Abstract

Provided is an electrode catalyst having excellent catalyst activity, which contributes to the low cost of a PEFC. The electrode catalyst includes a hollow carrier having nanopores with a pore diameter of 1 to 20 nm and micropores with a pore diameter of less than 1 nm, and a plurality of catalyst particles supported on the carrier. The catalyst particles are supported inside and outside the mesopores of the carrier, contain Pt (0 valence), and satisfy the condition of formula (S1) {100 x (N10 / N20) ≤ 8.0} in the case where analysis of the particle size distribution of the catalyst particles is performed using a three-dimensional reconstruction image obtained by electron tomography using a STEM. N10 is the number of noble metal particles not in contact with the micropores with a pore diameter of 1 nm or more, and N20 is the number of catalyst particles supported inside the nanopores of the carrier.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrode catalyst using hollow carbon as a carrier. More specifically, it relates to an electrode catalyst suitable for a gas diffusion electrode, and to an electrode catalyst more suitable for a gas diffusion electrode of a fuel cell.

[0002] Further, the present application relates to a gas diffusion electrode forming composition containing the above electrode catalyst particles, a membrane-electrode assembly, and a fuel cell stack. BACKGROUND

[0003] A solid polymer fuel cell (hereinafter, referred to as "PEFC" as needed) is being developed as a power source for a fuel cell vehicle, a domestic cogeneration system.

[0004] Among catalysts used in a gas diffusion electrode of a PEFC, a noble metal catalyst composed of noble metal particles of a platinum group element such as platinum (Pt) is used.

[0005] For example, as a typical catalyst in the prior art, a "Pt-supporting carbon catalyst" (hereinafter, referred to as "Pt / C catalyst" as needed) of a powder of catalyst particles in which Pt fine particles are supported on a conductive carbon powder is known.

[0006] In the manufacturing cost of a PEFC, the cost proportion of a noble metal catalyst such as Pt is large, and becomes a technical problem toward the cost reduction of a PEFC and the popularization of a PEFC.

[0007] Among these research and development, in order to reduce the amount of use of platinum, a powder (hereinafter, referred to as "core-shell catalyst" as needed) of catalyst particles (hereinafter, referred to as "core-shell catalyst particles" as needed) having a core-shell structure of a core portion composed of a non-platinum element and a shell portion composed of Pt is discussed in the prior art, and there are a large number of reports.

[0008] For example, in Patent Literature 1, a particle composite (with respect to the core-shell catalyst particles) having a structure in which palladium (Pd) or a Pd alloy (corresponding to the core portion) is coated with a thin layer of atoms of Pt atoms (with respect to the shell portion) is disclosed. Further, in this Patent Literature 1, as an example, a core-shell catalyst particle having a structure in which the core portion is a Pd particle and the shell portion is a layer composed of Pt is described.

[0009] On the other hand, as a carrier of an electrode catalyst, there are hollow carbon having a large number of pores in the inside of primary particles, and solid carbon having fewer pores in the inside of primary particles than the hollow carbon, and each of them is discussed to exert its own characteristics to achieve performance improvement.

[0010] For example, in Patent Literature 2, a study example in which hollow carbon is employed as a carrier is disclosed. Further, in Patent Literature 3, a study example in which mesocarbon is employed as a carrier is disclosed.

[0011] For example, in Patent Literature 2, as shown in Figure 10 Fig. 2, a structure of an electrode catalyst 200 for a fuel cell in which a porous carrier (hollow carbon) 220 having an average particle diameter of 20 to 100 nm is employed, a pore volume of pores P220 having a pore diameter of 4 to 20 nm is controlled to a prescribed range, and a catalyst particle 230 is supported within the pores P220 of the carrier 220 is disclosed.

[0012] In Patent Literature 2, it is mentioned that, by this, adsorption of a polymer electrolyte onto the surface of the catalyst particle 230 present within the primary pores P220 can be prevented, and gas transportability can be sufficiently ensured while preventing a decrease in the effective reaction surface area of the catalyst. It is further mentioned that, as a result thereof, the activity per catalyst weight is increased, and a catalyst layer for a fuel cell that exhibits excellent power generation performance can be provided even when the catalyst amount is reduced.

[0013] Further, for example, in Patent Literature 3, an electrode catalyst for a fuel cell (PtCo / C catalyst) having a catalyst particle including a mesocarbon carrier, platinum, and an alloy of cobalt supported on the carrier is disclosed. In the alloy of the electrode catalyst, the molar ratio of platinum to cobalt is 4 to 11: 1, and acid treatment is performed at 70 to 90°C.

[0014] In Patent Literature 3, when the PtCo alloy is supported on a hollow carbon carrier, a part of the PtCo alloy is contained within the hollow carbon carrier, and even when acid treatment for suppressing the elution of Co is performed, it is difficult to sufficiently treat the PtCo alloy present within the carrier, as a result of which there is a phenomenon in which Co is easily eluted from the PtCo alloy present within the carrier, and this is considered to be a technical problem.

[0015] For this reason, in Patent Literature 3, it is mentioned that, by using a mesocarbon carrier instead of a hollow carbon carrier, it is possible to avoid the case in which the PtCo alloy is contained within the carrier. It is further disclosed that, by this, it is possible to perform sufficient acid treatment of the PtCo alloy, and to suppress the elution of Co. As a result thereof, it is described that it is possible to balance the initial performance and the durability performance of the fuel cell.

[0016] Here, in Patent Literature 3, the mesocarbon is defined as follows.

[0017] That is, in Patent Literature 3, it is described that the medium-dense carbon means carbon in which the voids inside the carbon are less than in hollow carbon, and specifically means carbon in which the ratio of the BET surface area obtained by the N2 adsorption method to the outer surface area obtained by t-Pot (the surface area outside the particles calculated from the particle size) (t-Pot surface area / BET surface area) is 40% or more.

[0018] In addition, the "t-Pot surface area" described in Patent Literature 3 should be understood as a value represented by, for example, the "t-plot surface area" described in the technical report "Fine Pore Surface Area Analysis by t-plot Method" publicly disclosed on the network by MC Evolve Technologies, Inc. on February 1, 2019. The analysis of the fine pore surface area by the t-plot method is one of the methods of analyzing based on the adsorption isotherm of nitrogen (adsorption temperature: 77 K). This method is a method of comparing and transforming the data of the adsorption isotherm with the standard isotherm, thereby plotting the relationship between the thickness t of the adsorption layer and the adsorption amount. It not only can distinguish and numerically express the inside and outside of the fine pores, but also can know the tendency of the fine pores from the shape of the graph.

[0019] In addition, as an example of the medium-dense carbon, for example, the carbon described in Japanese Patent No. 4362116 can be cited, and specifically, it is disclosed that DENKA BLACK (registered trademark) manufactured by Denki Kagaku Kogyo Kabushiki Kaisha, etc. can be cited.

[0020] In addition, in Patent Literature 4, an electrode catalyst (core-shell catalyst) in which catalyst particles are supported inside and outside of the mesopores {more specifically, the nanopores formed in the primary particles of the hollow carbon carrier} of a hollow carbon carrier is disclosed. The electrode catalyst has the following configuration: when the analysis of the particle size distribution of the catalyst particles is performed using the three-dimensional reconstruction image obtained by electron beam tomography measurement using STEM (scanning transmission electron microscope), the proportion of the catalyst particles supported inside the mesopores {more specifically, the nanopores formed in the primary particles of the hollow carbon carrier} is 50% or more.

[0021] In the present specification, the "nanopore (Nanopore)" of the hollow carbon carrier means a fine pore having a pore diameter of 1 to 20 nm as described later.

[0022] In addition, in Non-Patent Literature 1 and Non-Patent Literature 2 described below, examples are disclosed in which the proportion of catalyst particles supported inside the pores {nanopores described above} and the proportion of catalyst particles supported outside the pores {nanopores described above} are analyzed for catalyst particles supported in a hollow carbon support, in a method different from that of Patent Literature 4 described above.

[0023] More specifically, in Non-Patent Literature 1, it is reported that a research group of Strasser et al. of the Technical University of Berlin analyzed the results obtained by simultaneously taking SEM (Scanning Electron Microscopy) images and TSEM (Transmission SEM) images of specific Pt / C catalyst particles of interest for a Pt / C catalyst in which Pt catalyst particles are highly dispersed in a commercially available hollow carbon (trade name: "ketjenblack EC-300J", manufactured by Akzo Nobel, specific surface area: about 839 m 2 g -1 ) in the same measurement area. For example, refer to Table 1, Figure 2 and P. 79 right column of Non-Patent Literature 1.

[0024] In their method, information on Pt catalyst particles present only in the observed portion (one-side outer surface) of the outer surface of the hollow carbon support particles is obtained from the SEM images. That is, information on the number of particles of catalyst particles supported outside the nanopores of the hollow carbon support particles is obtained. On the other hand, information on all of the catalyst particles supported outside and inside the hollow carbon support particles (primary particles described above) in the observed Pt catalyst particles is obtained from the TSEM images (transmission images). Then, they attempted to distinguish between Pt catalyst particles supported on the outer surface (outside the nanopores) and Pt catalyst particles supported inside in the Pt catalyst particles supported in the hollow carbon support particles, based on the information from the TSEM images and the information from the SEM images.

[0025] Here, in Non-Patent Literature 1, they did not perform measurement of the "opposite-side back surface" opposite the observed portion ("one-side outer surface") in the outer surface (outside the nanopores) of the hollow carbon support particles for the SEM images. They assumed that the state of the "one-side outer surface" and the state of the "opposite-side back surface" are the same state. That is, it was assumed that the number of particles of catalyst particles supported on the "one-side outer surface" and the number of particles of catalyst particles supported on the "opposite-side back surface" are the same.

[0026] After that, in Non-Patent Literature 2, the research group of Uchida et al. of the University of Yamanashi reported the results obtained by photographing a Pt / C catalyst obtained by highly dispersing Pt catalyst particles in a commercially available hollow carbon (trade name: "Ketjenblack" manufactured by Ketjen Black International, specific surface area: about 875 m2 / g) using a STEM (Scanning Transmission Electron Microscope) device capable of photographing SEM images and TEM (transmission electron microscopy) images of Pt catalyst particles. For example, refer to Table 2 and the right lower column of P. 181 of Non-Patent Literature 2. 2 g -1 ) using a STEM (Scanning Transmission Electron Microscope) device capable of photographing SEM images and TEM (transmission electron microscopy) images of Pt catalyst particles. For example, refer to Table 2 and the right lower column of P. 181 of Non-Patent Literature 2. Figure 1

[0027] They first acquired the particle number information of all the Pt catalyst particles supported on the hollow carbon support particles from the TEM image of the specific Pt / C catalyst particles of interest. Then they acquired the particle number information of the Pt catalyst particles present only on the inner side surface of the hollow carbon support particles from the SEM image of the same Pt / C catalyst particles photographed with the TEM image. Next, they used a special 3D sample holder to accurately rotate the specific Pt / C catalyst particles of interest (measurement sample) by 180 degrees, thereby measuring the SEM image of only the back surface of the same Pt / C catalyst particles. Using this information, they implemented an attempt to distinguish between the Pt catalyst particles supported on the outer surface and the Pt catalyst particles supported on the inside among the Pt catalyst particles supported on the hollow carbon support particles.

[0028] Regarding the "internal support rate" = "100 x (number of Pt catalyst particles supported on the inside) / (total number of Pt catalyst particles)" measured by this method, they reported that it was 62% in a commercially available 30 wt% Pt / C catalyst (trade name: "TEC10E30E" manufactured by Tanaka Kikinzoku Kogyo, referred to as "c-Pt / CB" in this specification) and 50% or more in a commercially available 46 wt% Pt / C catalyst (trade name: "TEC10E50E" manufactured by Tanaka Kikinzoku Kogyo, referred to as "Pt / CB" in this specification).

[0029] As described above, the present inventors recognized that the analysis methods of Non-Patent Literature 1 and Non-Patent Literature 2 are different from the analysis method of Patent Literature 4 in the following aspects.

[0030] ​That is, the analysis method of Patent Literature 4 using electron beam tomography measurement is a three-dimensional reconstruction method using an electron microscope, and is a method in which electron microscope images of the same field of view of a measurement sample (a block of a measurement target sample having a size in which the long diameter or the short diameter is in the range of about 100 to 300 nm, which will be described later Figure 11 , Figure 16 and Figure 21 ) projected from a plurality of directions are reconstructed into a three-dimensional image in a computer, and a tomographic image (a tomogram) is created using a computer.

[0031] On the other hand, the analysis method of Non-Patent Literature 1 is a method in which two-dimensional images of an SEM image and a TSEM image of a measurement sample taken from a specific one direction are analyzed. In addition, the analysis method of Non-Patent Literature 2 is a method in which an SEM image of a measurement sample taken from a specific two directions (directions of two axes orthogonal to each other obtained by rotating a sample holder by 180 degrees) and a TSEM image of a measurement sample taken from a specific one direction are analyzed. The present inventors consider that, in these analysis methods of Non-Patent Literature 1 and Non-Patent Literature 2, for example, in the case where the measurement sample (a catalyst particle for an electrode) has a concave-convex shape, there is a high possibility that the position of the catalyst particle cannot be sufficiently determined as being inside or outside of a hollow carbon support.

[0032] In the analysis method of Patent Literature 4, a three-dimensional tomographic image (a tomogram) of a measurement sample is used, and it is possible to observe it according to various reports, and therefore, the present inventors consider that it is possible to visually confirm and more accurately grasp the position of a catalyst particle contained in a catalyst for an electrode on a support. Figure 11 , Figure 16 and Figure 21 of a measurement sample (a block of a measurement target sample having a size in which the long diameter or the short diameter is in the range of about 100 to 300 nm, which will be described later

[0033] In addition, as a publication in which the above-described known inventions of the literatures are described, the applicant of the present patent suggests the following publications.

[0034] Prior Art Literature

[0035] Patent Literature

[0036] Patent Literature 1: U.S. Patent Application Publication No. 2007 / 31722

[0037] Patent Literature 2: Japanese Patent Application Laid-Open No. 2013-109856

[0038] Patent Literature 3: International Publication WO 2016 / 063968

[0039] Patent Literature 4: International Publication WO2019 / 221168

[0040] Non-Patent Literature

[0041] Non-Patent Literature 1: Nature Materials, Vol 19 (January 2020) 77-85

[0042] Non-Patent Literature 2: Journal of Power Sources, 315 (2016) 179-191 SUMMARY

[0043] Technical problem to be solved by the invention

[0044] In order to popularize PEFC, for an electrode catalyst, for reduction of Pt usage amount and reduction of material cost, further improvement of catalyst activity is required.

[0045] The present inventors found that, in the case where analysis of particle size distribution of catalyst particles is performed on a three-dimensional reconstruction image obtained by electron tomography measurement using STEM (scanning transmission electron microscope) for an electrode catalyst such as Pt / C catalyst, there is no report that a modified product having a structure in which catalyst particles are supported in the interior of a Nanopore of a hollow carbon support more than in the exterior has been actually successfully synthesized, and thus there is room for improvement.

[0046] The present invention was made in view of this technical problem, and aims to provide an electrode catalyst having excellent catalyst activity, which can contribute to cost reduction of PEFC.

[0047] In addition, the present invention also aims to provide a gas diffusion electrode-forming composition, a gas diffusion electrode, a membrane-electrode assembly (MEA), and a fuel cell stack, each of which contains the above electrode catalyst.

[0048] Technical solution for solving the technical problem

[0049] The present inventors and the like have intensively studied an electrode catalyst in which catalyst particles of a Pt / C catalyst or the like are supported in a Nanopore of a hollow carbon primary particle, with respect to a structure that achieves further improvement of catalyst activity.

[0050] As a result, it was found that catalyst particles can be effectively supported on a support in a manner satisfying the following conditions, and the present invention was completed.

[0051] More specifically, the present invention is constituted by the following technical solutions.

[0052] That is, the present application provides an electrode catalyst containing: a hollow carbon support having a nanopore with a pore diameter of 1 to 20 nm, and a plurality of catalyst particles supported on the support,

[0053] A region composed of Pt (0 valence) is formed on at least a part of the surface of the catalyst particle,

[0054] The catalyst particle is supported inside the nanopore of the support and outside the nanopore,

[0055] In the case where the particle size distribution analysis of the catalyst particle is performed using a three-dimensional reconstruction image obtained by electron tomography using a STEM (scanning transmission electron microscope), the following formula (S1) is satisfied,

[0056] 100 x (N10 / N20) ≤ 8.0 …… (S1).

[0057] In the formula (S1), N10 represents the number of non-contact particles (n101 + n102) obtained by adding the number of noble metal particles (n101) not in contact with a fine pore with a fine pore diameter of 1 nm or more, which can be confirmed by the electron tomography measurement, and the number of noble metal particles (n102) existing outside the hollow carbon support itself, which is not in contact with the hollow carbon support itself.

[0058] N20 represents the number of catalyst particles supported inside the nanopore of the support.

[0059] In addition, in the present application, with respect to the non-contact particles and the number of non-contact particles N10 (= n101 + n102), in the case where the presence of the noble metal particles of (II) cannot be confirmed by the electron tomography measurement, that is, the number of noble metal particles n102 of (II) = 0 (or in the case where n102 can be considered to be approximately 0), the present inventors consider that the non-contact particles can be identified as follows. That is, in this case, the "non-contact particles" are "noble metal particles (catalyst particles) that can be confirmed by the electron tomography measurement and are not in contact with a fine pore with a fine pore diameter of 1 nm or more", in other words, in this case, the "non-contact particles" are "catalyst particles that are in contact with a fine pore with a fine pore diameter of less than 1 nm that cannot be confirmed by the electron tomography measurement". In fact, in the electrode catalyst of the present application prepared by the present inventors, the presence of the noble metal particles of (I) was not confirmed.

[0060] Note that in the present specification, in order to distinguish from nanopores, "pores having a pore diameter of less than 1 nm" are referred to as "micropores", and "pores having a pore diameter of more than 20 nm" are referred to as "macropores".

[0061] The present inventors believe that in this case, the non-contact particles (catalyst particles that do not contact micropores having a pore diameter of less than 1 nm that cannot be confirmed by the above-mentioned electron beam tomography measurement) are highly likely to be buried in the micropores and not to effectively contribute to the progress of the electrode reaction. Figure 2 and Figure 10 As shown in FIG. 1, in the case where micropores exist in the hollow carbon support used, the non-contact particles (catalyst particles) buried in the micropores are believed to exist in both the existing electrode catalyst 200 and the electrode catalyst 20 of the present application (refer to FIG. 1). Figure 2 the non-contact particles 25 of FIG. 1, Figure 10 the non-contact particles 250 of FIG. 2).

[0062] In the present application, by supporting the catalyst particles of the electrode catalyst such as Pt / C catalyst in the hollow carbon support in a manner satisfying the condition of the above-mentioned formula (S1), the electrode catalyst of the present application can exhibit excellent catalyst activity that contributes to the cost reduction of PEFC.

[0063] The detailed reason why the electrode catalyst of the present application has excellent catalyst activity is not sufficiently clear.

[0064] However, the present inventors believe as follows. That is, in the electrode catalyst of Pt / C catalyst and the like in which the catalyst particles supported in the inside of the nanopores satisfy the condition of formula (S1), compared with the existing electrode catalyst, the non-contact particles (catalyst particles) buried in the micropores of the support are less, and more highly active catalyst particles exist in the inside of the nanopores of the support.

[0065] Such catalyst particles supported in the inside of the nanopores of the support are supported in the support in a state not easily coming into direct contact with the polymer electrolyte existing in the catalyst layer. Therefore, the electrode catalyst of the present application reduces the decrease in catalyst activity due to the poisoning of Pt components, and can exhibit excellent catalyst activity when polarized compared with the existing electrode catalyst. In addition, in the electrode catalyst of the present application, the dissolution of Pt components from the catalyst particles is also reduced.

[0066] Further, from the viewpoint of more reliably obtaining the effect of the present application, the value of [100 x (N10 / N20)] of formula (S1) is preferably 6.5 or less, and more preferably 1.0 or less.

[0067] Herein, in the present application, "Nanopore" of the hollow carbon support means a fine pore having a fine pore diameter of 1 to 20 nm, and "Micropore" means a fine pore having a fine pore diameter of less than 1 nm. Further, in the present application, "Fine pore diameter of Nanopore" means "size of the entrance of Nanopore". "Fine pore diameter of Micropore" means "size of the entrance of Micropore".

[0068] In the present application, "Fine pore diameter of Nanopore (size of the entrance of Nanopore)" means "size of the entrance of Nanopore" obtained by a three-dimensional reconstruction image in the case where the electrode catalyst is analyzed by electron beam tomography measurement using a general STEM (scanning transmission electron microscope).

[0069] More preferably, in the present application, "Fine pore diameter of Nanopore (size of the entrance of Nanopore)" means "size of the entrance of Nanopore" obtained by the above-mentioned "USAL-KM3D analysis method".

[0070] More specifically, "size of the entrance of Nanopore" means diameter (equivalent circle diameter) of a circle having the same area as the area of the entrance of Nanopore obtained from the image of the entrance of Nanopore obtained by the "USAL-KM3D analysis method".

[0071] Further, herein, in the present application, "the above-mentioned analysis method of particle size distribution of catalyst particles using a three-dimensional reconstruction image obtained by electron beam tomography measurement using a STEM (scanning transmission electron microscope)" means an analysis method using a STEM (scanning transmission electron microscope) of UBE Scientific Analysis Center, Inc., and means an analysis method (analysis method name: "USAL-KM3D analysis method") in which electron beam tomography measurement is performed, and image analysis is performed on the obtained measurement data using image analysis software (FEI Company's "Avizo").

[0072] In the USAL-KM3D analysis method, a measurement sample to be a measurement object is produced by the following procedure and conditions.

[0073] <Measurement sample production method, conditions>

[0074] First, in order to be able to perform optimal measurement of the structure of the measurement sample, on the "Cu grid with carbon support film" for TEM observation, production is performed by a general electron microscope sample production method, i.e., a dispersion method, in a manner satisfying the following conditions.

[0075] (A) The powder pieces (pieces having a length or a short diameter in the range of about 60 to 300 nm, which will be described later) of the sample to be measured (catalyst for electrode) are measured at a moderate frequency {the number of particles (the number of catalyst particles that can be observed is 100 or more, preferably 200 or more, more preferably 300 or more, and further preferably 400 or more)} at which the pieces can be measured (can be observed) on the above-mentioned grid. Figure 11 、 Figure 16 and Figure 21 ) are present on the above-mentioned grid.

[0076] (B) When the above-mentioned grid is rotated by a rotation angle of ±80° around its rotation axis, the photographed image of the powder pieces of the sample to be measured does not overlap with the photographed image of other micro powder pieces. If the photographed image of the powder pieces of the sample to be measured overlaps with the photographed image of other micro powder pieces, three-dimensional analysis cannot be performed.

[0077] (C) With respect to the powder pieces of the sample to be measured, a plurality of powder pieces that can be seen within the measurement region are arranged separately from each other to the extent that three-dimensional tomographic observation can be performed.

[0078] <Measurement Conditions>

[0079] With respect to the nano-pores of 1 nm or more among the fine pores contained in the powder pieces of the sample to be measured (catalyst for electrode), three-dimensional tomographic observation is performed under conditions (for example, adjustment of the acceleration voltage of an electron beam, etc.) at which the powder pieces of the sample to be measured (catalyst for electrode) can be observed and distinguished three-dimensionally without being damaged.

[0080] Thereafter, with respect to the powder pieces of the sample to be measured (catalyst for electrode), the measurement data that can be obtained even in the case of measuring "the distance from the entrance of the nano-pore to the supported position of the catalyst particle (the shortest path)" described later are subjected to image analysis using image analysis software (FEI Corporation "Avizo") to obtain.

[0081] In addition, in the catalyst for electrode of the present application, from the viewpoint of more reliably obtaining the effects of the present application, it is preferable that:

[0082] In the above-mentioned three-dimensional reconstructed image of the above-mentioned STEM, attention is paid to the catalyst piece composed of the above-mentioned catalyst particle and the above-mentioned carrier that can be accommodated in a cuboid having one side in the range of 60 to 300 nm, and the case where the six square cross sections of the cubic image having one side in the range of 20 to 50 nm extracted from the internal region of the catalyst piece are observed, and at least one of the above-mentioned nano-pores is formed in at least one of the cross sections,

[0083] Preferably, the nanopore formed in at least one of the six square cross sections has a shape in which at least one opening is in contact with a first side of four sides of the square cross section, and at least one opening is in contact with a second side of the square cross section that is parallel to the first side, and a communication hole extends from the opening of the first side to the opening of the second side without obstruction.

[0084] In the electrode catalyst of the present application, when the microstructure is observed using a STEM three-dimensional reconstruction image, by satisfying the condition of (a) the aforementioned formula (S1) and the condition of (β) the nanopore is formed in the shape of the aforementioned communication hole, the excellent catalyst activity that contributes to the low cost of the PEFC can be more reliably exhibited.

[0085] The detailed reason why the electrode catalyst of the present application has more reliably excellent catalyst activity by satisfying the aforementioned condition of (β) is not sufficiently clear.

[0086] However, the present inventors believe as follows. That is, the present inventors believe that, in the case of observing the microstructure using a STEM three-dimensional reconstruction image, the electrode catalyst in which the nanopore is formed in the shape of the aforementioned communication hole has excellent diffusivity of water and protons or reaction gas (hydrogen, oxygen, or air) contained therein in the case of being used for the catalyst layer of the gas diffusion electrode of the PEFC, and the catalyst particles supported inside the nanopore are easily utilized for the reaction.

[0087] Next, the method using a STEM three-dimensional reconstruction image for confirming the condition of (β) in the present application in which the nanopore is formed in the shape of the aforementioned communication hole will be described.

[0088] The confirmation of the condition of (β) can be performed by a three-dimensional reconstruction image obtained by analysis of the electrode catalyst measured by electron beam tomography using a general STEM (scanning transmission electron microscope). However, from the viewpoint of reliably confirming the condition of (β), it is preferable to perform using the STEM three-dimensional reconstruction image obtained in the process of performing the aforementioned USAL-KM3D analysis method.

[0089] The procedure for confirming the condition of (β) will be described below.

[0090] (D) First, a STEM three-dimensional reconstruction image is obtained with respect to the catalyst to be measured. From among the catalyst block (a block composed of catalyst particles and hollow carbon supports) reflected in this three-dimensional reconstruction image, a catalyst block having a size in which a space (region of interest) of a cuboid having one side of 60 to 300 nm is accommodated is selected. This procedure can be easily understood by referring to the cubic images extracted from the 3D-STEM images (three-dimensional reconstruction images) of the catalyst blocks of the catalysts of Example 1, Example 2, and Comparative Example 2 described later (refer to the cubic images of (a), (f), and (k) described later). Figure 27 (a), Figure 27 (f) and Figure 27 (k)).

[0091] (E) Subsequently, a cubic image (one side of 20 to 50 nm) is extracted from the internal region of the catalyst block selected in the step of (D). This procedure can be easily understood by referring to the cubic images obtained from the 3D-STEM images (three-dimensional reconstruction images) of the catalyst blocks of the catalysts of Example 1, Example 2, and Comparative Example 2 described later (refer to the cubic images of (b), (g), and (1) described later). Figure 27 (b), Figure 27 (g) and Figure 27 (l)).

[0092] (F) Subsequently, the cubic image (three-dimensional reconstruction image) of the interior of the catalyst block obtained in the step of (E) is observed, and the void portion (portion of fine pores such as nanopores) and the hollow carbon support portion are divided using the difference in brightness.

[0093] More specifically, the cubic image (three-dimensional reconstruction image) is composed in a state in which the pixels (voxels) divided into smaller cubic images are accommodated. Subsequently, brightness (unitless) is accommodated in each pixel (voxel). Subsequently, the analyst clearly divides (binarizes) the void portion (portion of fine pores such as nanopores) and the hollow carbon support portion of the cubic image (three-dimensional reconstruction image) by setting an appropriate threshold value with respect to the brightness. With respect to a certain pixel (voxel), it is automatically determined to be a carbon portion as long as the brightness is above the threshold value. In addition, with respect to a certain pixel (voxel), it is automatically determined to be a void portion as long as the brightness is below the threshold value. This division can be performed by setting the same threshold value of brightness with respect to all of the pixels (voxels) contained in the same cubic image (three-dimensional reconstruction image). With respect to different cubic images (three-dimensional reconstruction images), the analyst can set different threshold values of brightness (threshold values suitable for division).

[0094] From the viewpoint of more accurately performing the division, it is preferable that the size of the pixel (voxel) be a cubic image having one side of 1 nm or less.

[0095] Further, in the present application, in the case where the porosity of the stereoscopic image (three-dimensional reconstruction image by STEM) of the catalyst block described later is measured, the division is performed, and the catalyst particles are regarded as voids.

[0096] The same is true for the step of (F). For example, it can be easily understood by referring to the stereoscopic images extracted from the 3D-STEM images (three-dimensional reconstruction images) of the catalyst blocks of the catalysts for electrodes of Example 1, Example 2, and Comparative Example 2 described later (see the stereoscopic images of (a), (b), (c), (d), (e), (f), (g), (h), (i), (j), (k), (1), (m), (n), and (o) described later). Figure 27 (b), Figure 27 (g) and Figure 27 (l)). Further, it can be easily understood by referring to the 3 cross sections (3 cross sections after division) of the stereoscopic images (three-dimensional reconstruction images by STEM) obtained from the catalyst blocks of Example 1, Example 2, and Comparative Example 2 (see the stereoscopic images of (a), (b), (c), (d), (e), (f), (g), (h), (i), (j), (k), (1), (m), (n), and (o) described later). Figure 27 (c), Figure 27 (d), Figure 27 (e), Figure 27 (h), Figure 27 (i), Figure 27 (j), Figure 27 (m), Figure 27 (n), and Figure 28 (o)).

[0097] After (G), in the case where the 6 square cross sections of the stereoscopic image (three-dimensional reconstruction image by STEM) after the division in the step of (F) are observed, it is confirmed whether at least one nano-pore (communicating hole) having at least one of the following shapes is formed in at least one cross section.

[0098] That is, it is confirmed whether the nano-pore (communicating hole) seen in the cross section of the square of interest has at least one opening in contact with a first side and at least one opening in contact with a second side parallel to the first side among the 4 sides of the cross section. Further, it is confirmed whether the nano-pore has the shape of a communicating hole that continuously extends without obstruction from the opening of the first side to the opening of the second side.

[0099] For example, as described in the example of Example 1 described later, as shown in FIG. 1, the nano-pore P1 seen in the cross section of interest (x-y plane of the square) has two openings (opening A11 and opening A12) in contact with a first side L1. Further, the nano-pore P1 has two openings (opening A21 and opening A22) in contact with a second side L2 parallel to the first side L1. Further, the nano-pore P1 has the shape of a communicating hole that continuously extends without obstruction from the openings (opening A11 and opening A12) of the first side L1 to the openings (opening A21 and opening A22) of the second side L2. Figure 28

[0100] ​Further, from the viewpoint of more reliably obtaining the effects of the present application, in the electrode catalyst of the present application, the nanopore (communicating pore) seen in the square cross section of the cubic image of interest preferably has a shape with two or more openings on the first side (see Figure 28 ). In the case where the catalyst particles carried inside such nanopores are used for the catalyst layer of the gas diffusion electrode of a PEFC, it is easy to be carried on the carrier in a state where it is more difficult to come into contact with the polymer electrolyte present inside the catalyst layer. Further, the diffusivity of water and the protons or reaction gas (hydrogen, oxygen or air) contained therein of such nanopores is excellent. Therefore, in the case where the electrode catalyst having such nanopores is used for the catalyst layer of the gas diffusion electrode of a PEFC, the catalyst particles carried inside the nanopores are easily utilized for the electrode reaction of the PEFC.

[0101] Further, from the viewpoint of more reliably obtaining the effects of the present application, based on the same reason as the above, in the electrode catalyst of the present application, the nanopore (communicating pore) seen in the square cross section of the cubic image of interest preferably has two or more openings on the first side (see Figure 28 ).

[0102] Further, from the viewpoint of more reliably obtaining the effects of the present application, based on the same reason as the above, in the electrode catalyst of the present application, the nanopore (communicating pore) seen in the square cross section of the cubic image of interest preferably has two or more openings on the second side (see Figure 28 ).

[0103] Further, from the viewpoint of more reliably obtaining the effects of the present application, based on the same reason as the above, in the electrode catalyst of the present application, the nanopore (communicating pore) seen in the square cross section of the cubic image of interest preferably has at least one opening on the third side perpendicular to the first side.

[0104] For example, referring to the example of the following Example 1, as shown in Figure 28 , the nanopore P1 seen in the cross section of interest (x-y plane of square) has one opening (opening A31) on the third side L3 perpendicular to the first side L1.

[0105] Further, from the viewpoint of more reliably obtaining the effects of the present application, based on the same reason as the above, in the electrode catalyst of the present application, the nanopore (communicating pore) seen in the square cross section of the cubic image of interest preferably has at least one opening on the fourth side perpendicular to the first side.

[0106] For example, referring to the example of the following Example 1, as shown in Figure 2As shown, the nanopore P1 seen from the cross section of interest (x-y plane of the square) has two openings (opening A41 and opening A42) also in the fourth side L4 perpendicular to the first side L1.

[0107] Further, from the viewpoint of more reliably obtaining the effects of the present application, in the electrode catalyst of the present application, the porosity measured using the three-dimensional reconstruction image (cubic image of interest) of STEM is preferably 35% or more, further preferably 40% or more, more preferably 45% or more, even more preferably 50% or more, still more preferably 55% or more, yet more preferably 60% or more, and further more preferably 65% or more. On the other hand, from the viewpoint of durability, in the electrode catalyst of the present application, the porosity measured using the three-dimensional reconstruction image (cubic image of interest) of STEM is preferably 80% or less, more preferably 75% or less.

[0108] In addition, in the electrode catalyst of the present application, the hollow carbon support preferably contains a large number of nanopores having a pore diameter (size of the entrance of the pore) of 1 to 10 nm in the nanopores. It has been reported that the micelle diameter of the polymer electrolyte of the catalyst layer of the anode and the cathode of the MEA is about 10 nm (for example, Y. S. Kim, et al, DOE Hydrogen Program Merit Review and Peer Meeting FC16, (2009)). Therefore, by using a hollow carbon support containing a large number of fine pores having a pore diameter (size of the entrance of the pore) of 1 to 10 nm, it is difficult for the polymer electrolyte to intrude into the nanopores, and it is possible to more reliably prevent the contact of the catalyst particles supported in the inside of the nanopores with the polymer electrolyte.

[0109] Further, in the electrode catalyst of the present application, the hollow carbon support can further have micropores having a pore diameter of less than 1 nm, within a range in which the effects of the present application can be obtained.

[0110] Further, from the viewpoint of more reliably obtaining the effects of the present application, the hollow carbon support is preferably "CNovel (manufactured by Toyo Carbon Co., Ltd., product name, registered trademark)" (for example, the porous carbon described in Japanese Patent No. 5636171, Japanese Patent No. 5695147, Japanese Patent No. 5860600, Japanese Patent No. 5860601, and Japanese Patent No. 5860602) among which the conditions of (α) and (β) described above can be satisfied when the electrode catalyst is produced.

[0111] CNovel is a porous carbon having at least a nano-pore (pore diameter of 1 to 20 nm) and a carbonaceous wall constituting the periphery of the nano-pore, and the carbonaceous wall has a portion that becomes a layered structure, and the carbonaceous wall forms a three-dimensional network structure, the nano-pore is an open pore, and the nano-pore has a continuous shape (shape of a connected pore. Refer to "a plurality of nano-pores P22 connected to a connected pore PI" described later Figure 1

[0112] In addition, in the electrode catalyst of the present application, the catalyst particle can be composed of Pt (0 valence).

[0113] Further, in the electrode catalyst of the present application, the catalyst particle can be composed of a Pt alloy. The kind of metal that becomes an alloy element other than Pt is not particularly limited. From the viewpoint of obtaining excellent catalyst activity, the kind of metal that becomes an alloy element other than Pt is preferably at least one metal among Co and Ni.

[0114] In addition, in the electrode catalyst of the present application, the above catalyst particle can be a core-shell catalyst particle. In this case, from the viewpoint of obtaining excellent catalyst activity, the core-shell catalyst particle is preferably a core particle, and a Pt shell layer (a region composed of Pt (0 valence)) formed on at least a portion of the surface of the core particle. The kind of metal that constitutes the core particle is not particularly limited, but from the viewpoint of obtaining excellent catalyst activity, it is preferably at least one of Pd, Ni, and Co. In addition, the core particle can also be an alloy of at least one of Pd, Ni, and Co and another metal. From the viewpoint of reducing the amount of use of noble metal, the core particle can also contain, in its interior, at least one of a base metal other than a noble metal, and an oxide of the base metal, a nitride of the base metal, and a carbide of the base metal.

[0115] In addition, in the electrode catalyst of the present application, from the viewpoint of more reliably obtaining the effects of the present application, in the case where the analysis of the particle size distribution of the above catalyst particle is performed using a three-dimensional reconstruction image obtained by electron tomography using a STEM (scanning transmission electron microscope), it is preferable to satisfy the following condition of formula (S2).

[0116] 100 x {N10 / (N20 + N30)} ≤ 5.0... (S2)

[0117] Here, in formula (S2), N10 has the same meaning as N10 in formula (S1).

[0118] In addition, in formula (S2), N20 has the same meaning as N10 in the above formula (S1).

[0119] ​Further, in formula (S2), N30 represents the number of particles of the catalyst particles that are carried on the outside of the nanopores of the above-mentioned carrier.

[0120] By carrying the catalyst particles on the hollow carbon carrier in such a manner that the above-mentioned conditions of formula (S2) are satisfied, in the electrode catalyst of the present application, as compared with the conventional electrode catalyst, the non-contact particles (catalyst particles) that are buried in the micropores of the carrier are less, and the catalyst particles having high activity exist more in the inside of the nanopores of the carrier. Then, the electrode catalyst of the present application can more reliably exhibit the excellent catalyst activity that contributes to the cost reduction of the PEFC.

[0121] Further, from the viewpoint of more reliably obtaining the effects of the present application, the value of [100 x {N10 / (N20+N30)}] of formula (S2) is preferably 3.0 or less, more preferably 1.0 or less.

[0122] Further, in the case where the analysis of the particle size distribution of the above-mentioned catalyst particles is performed using the three-dimensional reconstruction image obtained by electron beam tomography using a STEM (scanning transmission electron microscope), the average distance from the inlet of the above-mentioned nanopore to the position at which the above-mentioned catalyst particles are carried in the inside of the above-mentioned nanopore of the above-mentioned carrier is preferably 5.0 nm or more. The present inventors believe that the catalyst particles satisfying this condition are carried in the inside of the nanopore of the carrier, and can sufficiently prevent contact with the polymer electrolyte. In addition, the present application believes that the catalyst particles satisfying this condition are carried in the inside of the nanopore of the carrier, but exist at a moderate depth from the inlet of the nanopore, and can more easily obtain the supply of protons, oxygen, and hydrogen.

[0123] Here, the "distance from the inlet of the nanopore to the position at which the catalyst particles are carried" means the length of the shortest line drawn from the inlet of the nanopore to the position at which the catalyst particles are carried along the non-flat shape of the inner wall of the nanopore (there are irregularities or curved surfaces) using the three-dimensional image that maps the three-dimensional structure of the inside of the carrier containing the nanopore obtained by electron beam tomography. Further, in the case where there are a plurality of inlets of the nanopore with respect to the catalyst particles of interest in the inside of the nanopore, the distance from the inlet of each nanopore to the position at which the catalyst particles are carried (the shortest path) is obtained, and the shortest distance is selected among these. In addition, the "average distance from the inlet of the nanopore to the position at which the catalyst particles are carried" means the arithmetic mean of all of the "distances from the inlet of the nanopore to the position at which the catalyst particles are carried" in the powder block of the measurement target sample (the electrode catalyst) of interest.

[0124] From the viewpoint of more reliably obtaining the effects of the present application, the average distance from the entrance of the nanopore to the supported position of the catalyst particle is preferably 5.0 to 8.5 nm, and further preferably 5.0 to 5.5 nm, with respect to the catalyst particle supported inside the nanopore of the carrier. In this way, by setting the supported position of the catalyst particle in the range of preferably 8.5 nm or less, and further preferably 5.5 nm or less, the tendency of the catalyst particle to be supplied with protons into the interior of the nanopore is increased even in the case where the MEA is required to generate electricity under conditions of higher than usual temperature and lower than usual humidification.

[0125] Further, in the electrode catalyst of the present application, from the viewpoint of more reliably obtaining the effects of the present application, in the case where the particle size distribution analysis of the catalyst particle is performed using a three-dimensional reconstruction image obtained by electron beam tomography measurement using a STEM (scanning transmission electron microscope), the catalyst particle supported inside the nanopore of the carrier is preferably present in the range of a distance of 0 to 27 nm from the entrance of the nanopore to the supported position of the catalyst particle.

[0126] The present inventors believe that the catalyst particle satisfying this condition, although supported inside the nanopore of the carrier, is present at a moderate depth from the entrance of the nanopore, and can more reliably obtain the effects of avoiding contact with the aforementioned polymer electrolyte while supplying sufficient reaction gas and protons.

[0127] From the same viewpoint as described above, the catalyst particle supported inside the nanopore is more preferably present in the range of a distance of 0 to 18 nm from the entrance of the nanopore to the supported position of the catalyst particle.

[0128] Further, in the electrode catalyst of the present application, from the viewpoint of more reliably obtaining the effects of the present application, in the case where the particle size distribution analysis of the catalyst particle is performed using a three-dimensional reconstruction image obtained by electron beam tomography measurement using a STEM (scanning transmission electron microscope), the catalyst particle supported inside the nanopore of the carrier is preferably present in the range of a distance of 0 to 27 nm from the entrance of the nanopore to the supported position of the catalyst particle.

[0129] The present inventors believe that the catalyst particle satisfying this condition, although supported inside the nanopore of the carrier, is present at a moderate depth from the entrance of the nanopore, and can more reliably obtain the effects of avoiding contact with the aforementioned polymer electrolyte while supplying sufficient reaction gas and protons.

[0130] Further, in the electrode catalyst of the present application, from the viewpoint of more reliably obtaining the effects of the present application, the BET specific surface area (nitrogen adsorption specific surface area) of the hollow carbon support is preferably 200 to 1500 m2 / g, more preferably 300 to 1400 m2 / g, further preferably 400 to 1300 m2 / g, and particularly preferably 500 to 1200 m2 / g.

[0131] By supporting the catalyst particles of the Pt / C catalyst in the nanoholes of the hollow carbon support in such a manner, a larger number of catalyst particles having a relatively small particle diameter and high activity exist in the inside of the nanoholes of the support compared to the conventional electrode catalyst.

[0132] Such catalyst particles supported in the inside of the nanoholes of the support are supported in the state of not directly contacting the polymer electrolyte present in the catalyst layer. Therefore, the electrode catalyst of the present application reduces the decrease in catalyst activity due to poisoning of the Pt component and can exhibit excellent catalyst activity after being polarized compared to the conventional electrode catalyst. Further, the electrode catalyst of the present application also reduces the elution of the Pt component from the catalyst particles.

[0133] Further, in the electrode catalyst of the present application, at least a part of the region of the surface of the catalyst particle composed of Pt (0 valence) can also be coated with the Pt oxide coating film within the range in which the catalyst particle can exhibit excellent catalyst activity.

[0134] Further, in the electrode catalyst of the present application, from the viewpoint of more reliably obtaining the effects of the present application, the BET specific surface area (nitrogen adsorption specific surface area) of the hollow carbon support is preferably 200 to 1500 m 2 / g.

[0135] Further, in the case where the electrode catalyst is used for the cathode, from the viewpoint of more reliably obtaining the effects of the present application, the BET specific surface area (nitrogen adsorption specific surface area) of the hollow carbon support is preferably 700 to 1500 m 2 / g, further preferably 750 to 1400 m 2 Further, in the case where the electrode catalyst is used for the cathode, from the viewpoint of preferably maintaining the durability prescribed according to the working environment (temperature variation range, potential variation range) of the cathode, the BET specific surface area (nitrogen adsorption specific surface area) of the hollow carbon support is preferably 750 to 900 m 2 / g.

[0136] Further, the present application also provides a powder of the electrode catalyst containing 10 wt% or more of the above-mentioned electrode catalyst of the present application.

[0137] Furthermore, in the powder of the electrode catalyst, "components other than the electrode catalyst of the present invention" refers to "electrode catalysts 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 contain powders that do not function as electrode catalysts.

[0138] Since the electrode catalyst powder of the present invention contains the electrode catalyst of the present invention described above, it can exhibit excellent catalytic activity that contributes to the cost reduction of PEFC.

[0139] From the viewpoint of more reliably obtaining the effects of the present invention, the content 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, more preferably 50 wt% or more, more preferably 70 wt% or more, and most preferably 90 wt% or more.

[0140] In addition to the electrode catalyst of the present invention described above, the powder of the electrode catalyst of the present invention may also contain an electrode catalyst with the following composition (for convenience, referred to as "electrode catalyst P").

[0141] That is, the electrode catalyst P contains: a hollow carbon support with nanopores having a fine pore size of 1-20 nm and multiple catalyst particles supported on the support.

[0142] The catalyst particles are composed of Pt (0 valence).

[0143] The catalyst particles are supported inside the nanopores and outside the micropores of the aforementioned support.

[0144] When the particle size distribution of the catalyst particles is analyzed using the “USAL-KM3D analysis method” described above, the proportion of the catalyst particles supported inside the nanopores is “less than 50%”.

[0145] The powder of the electrode catalyst of the present invention can be composed of the electrode catalyst of the present invention and electrode catalyst P described above.

[0146] In this case, from the viewpoint of more reliably obtaining the effects of the present invention, the content 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, more preferably 50 wt% or more, more preferably 70 wt% or more, and most preferably 90 wt% or more.

[0147] Further, in the powder of the electrode catalyst of the present application, one or more kinds of electrically conductive carbon supports other than the hollow carbon support involved in the electrode catalyst of the present application can be contained within a range where the effects of the present application can be obtained. For example, at least one of Ketjen black and acetylene black can be contained. For example, the electrically conductive carbon supports other than the hollow carbon support involved in the electrode catalyst of the present application can be contained at 10 to 100% by weight relative to the weight of the hollow carbon support involved in the electrode catalyst of the present application.

[0148] Further, the present application provides a gas diffusion electrode forming composition containing the electrode catalyst of the present application or the powder of the electrode catalyst of the present application described above.

[0149] The gas diffusion electrode forming composition of the present application contains the electrode catalyst of the present application or the powder of the electrode catalyst of the present application, and thus a gas diffusion electrode having excellent catalyst activity (polarization characteristics) that can contribute to the cost reduction of a PEFC can be easily produced.

[0150] Further, the present application provides a gas diffusion electrode containing the electrode catalyst of the present application or the powder of the electrode catalyst of the present application described above.

[0151] The gas diffusion electrode of the present application is composed of the electrode catalyst of the present application. Thus, a composition having excellent catalyst activity (polarization characteristics) that can contribute to the cost reduction of a PEFC can be easily obtained.

[0152] Further, the present application provides a membrane-electrode assembly (MEA) containing the gas diffusion electrode of the present application described above.

[0153] The membrane-electrode assembly (MEA) of the present application contains the gas diffusion electrode of the present application, and thus a composition having cell characteristics that can contribute to the cost reduction of a PEFC can be easily obtained.

[0154] Further, the present application can provide a fuel cell stack characterized by containing the membrane-electrode assembly (MEA) of the present application described above.

[0155] The fuel cell stack according to the present application contains the membrane-electrode assembly (MEA) of the present application, and thus a composition having cell characteristics that can contribute to the cost reduction of a PEFC can be easily obtained.

[0156] Effects of the Invention

[0157] According to the present application, an electrode catalyst having excellent catalyst activity that can contribute to the cost reduction of a PEFC can be provided.

[0158] Furthermore, according to the present invention, a gas diffusion electrode forming composition containing the above-mentioned electrode catalyst, a gas diffusion electrode, a membrane-electrode assembly (MEA), and a fuel cell stack can be provided. Attached Figure Description

[0159] Figure 2 This is a schematic cross-sectional view illustrating a preferred embodiment of the MEA of the present invention.

[0160] Figure 1 It means Figure 3 A schematic cross-sectional view of a preferred embodiment of the electrode catalyst of the present invention contained in at least one of the cathode catalyst layer and the anode catalyst layer of the MEA shown.

[0161] Figure 2 It means Figure 4 The diagram shows an enlarged schematic cross-sectional view of the general structure of the catalyst used in the electrode.

[0162] Figure 5 This is a schematic cross-sectional view illustrating another preferred embodiment of the MEA of the present invention.

[0163] Figure 6 This is a schematic cross-sectional view illustrating a preferred embodiment of the CCM of the present invention.

[0164] Figure 7 This is a schematic cross-sectional view illustrating another preferred embodiment of the CCM of the present invention.

[0165] Figure 8 This is a schematic cross-sectional view illustrating a preferred embodiment of the GDE of the present invention.

[0166] Figure 9 This is a schematic cross-sectional view illustrating another preferred embodiment of the GDE of the present invention.

[0167] Figure 10 This is a schematic diagram illustrating a preferred embodiment of the fuel cell stack of the present invention.

[0168] Figure 11 This is a schematic cross-sectional view of existing electrode catalysts.

[0169] Figure 12 This is a STEM image showing the 3D electron beam tomography measurement conditions (volume size) of the electrode catalyst of Example 1 using STEM.

[0170] Figure 13 This is a 3D-STEM image (three-dimensional reconstructed image) of the electrode catalyst of Example 1.

[0171] Figure 12 It means through Figure 14A chart showing the distribution state of Pt catalyst particles in the depth direction of the fine pores, inside and outside the nanopores of the carbon support, obtained by image analysis of the 3D-STEM image of the electrode catalyst of Example 1.

[0172] Figure 12 is a chart showing the distribution state of Pt catalyst particles in the depth direction of the fine pores, inside the nanopores of the carbon support, obtained by image analysis of the 3D-STEM image of the electrode catalyst of Example 1. Figure 15 A chart showing the distribution state of Pt catalyst particles in the depth direction of the fine pores, inside the nanopores of the carbon support, obtained by image analysis of the 3D-STEM image of the electrode catalyst of Example 1.

[0173] Figure 12 is a chart showing the distribution state of Pt catalyst particles in the depth direction of the fine pores, inside the nanopores of the carbon support, obtained by image analysis of the 3D-STEM image of the electrode catalyst of Example 1. Figure 16 A chart showing the distribution state of Pt catalyst particles in the depth direction of the fine pores, inside the nanopores of the carbon support, obtained by image analysis of the 3D-STEM image of the electrode catalyst of Example 1.

[0174] Figure 17 is a STEM image of the electrode catalyst of Example 2, measured under the 3D-electron beam tomography measurement conditions (volume size) using STEM.

[0175] Figure 18 is a 3D-STEM image (three-dimensional reconstructed image) of the electrode catalyst of Example 2.

[0176] Figure 17 is a chart showing the distribution state of Pt catalyst particles in the depth direction of the fine pores, inside and outside the nanopores of the carbon support, obtained by image analysis of the 3D-STEM image of the electrode catalyst of Example 2. Figure 19 A chart showing the distribution state of Pt catalyst particles in the depth direction of the fine pores, inside the nanopores of the carbon support, obtained by image analysis of the 3D-STEM image of the electrode catalyst of Example 2.

[0177] Figure 17 is a chart showing the distribution state of Pt catalyst particles in the depth direction of the fine pores, inside the nanopores of the carbon support, obtained by image analysis of the 3D-STEM image of the electrode catalyst of Example 2. Figure 20 A chart showing the distribution state of Pt catalyst particles in the depth direction of the fine pores, inside the nanopores of the carbon support, obtained by image analysis of the 3D-STEM image of the electrode catalyst of Example 2.

[0178] Figure 17 is a chart showing the distribution state of Pt catalyst particles in the depth direction of the fine pores, inside the nanopores of the carbon support, obtained by image analysis of the 3D-STEM image of the electrode catalyst of Example 2. Figure 21 A chart showing the distribution state of Pt catalyst particles in the depth direction of the fine pores, inside the nanopores of the carbon support, obtained by image analysis of the 3D-STEM image of the electrode catalyst of Example 2.

[0179] Figure 22is a STEM image of the electrode catalyst of Comparative Example 1 measured under the 3D- electron beam tomography measurement conditions (volume size) using STEM.

[0180] Figure 23 is a 3D-STEM image (three-dimensional reconstruction image) of the electrode catalyst of Comparative Example 1.

[0181] Figure 22 is a graph showing the distribution state of the Pt catalyst particles in the depth direction of the fine pores outside and inside the nanopores (Nanopore) of the carbon carrier of the electrode catalyst of Comparative Example 1, obtained by image analysis of the 3D-STEM image shown in Figure 24

[0182] Figure 22 is another graph showing the distribution state of the Pt catalyst particles in the depth direction of the fine pores inside the nanopores (Nanopore) of the carbon carrier of the electrode catalyst of Comparative Example 1, obtained by image analysis of the 3D-STEM image shown in Figure 25

[0183] Figure 22 is another graph showing the distribution state of the Pt catalyst particles in the depth direction of the fine pores inside the nanopores (Nanopore) of the carbon carrier of the electrode catalyst of Comparative Example 1, obtained by image analysis of the 3D-STEM image shown in Figure 26

[0184] is a STEM image of the electrode catalyst of Comparative Example 1 measured under the 3D- electron beam tomography measurement conditions (volume size) using STEM. Figure 27

[0185] is a table showing a plurality of 3D-STEM images (three-dimensional reconstruction images) of the electrode catalyst of Comparative Example 2, obtained by electron beam tomography measurement using STEM. Figure 28

[0186] is an enlarged view of the cross section (x-y plane) of the cubic image extracted from the 3D-STEM image (three-dimensional reconstruction image) of the catalyst block of the electrode catalyst of Example 1 shown in Figure 27 Figure 1 Symbol explanation:

[0187] 1 …… Cathode

[0188] 1A, 1B, 1C …… Gas diffusion electrode (GDE)

[0189] 1A, 1B, 1C …… Gas diffusion electrode (GDE) ​​​

[0190] 1c... catalyst layer (CL);

[0191] 1m... water-repellent layer (MPL);

[0192] 1gd... gas diffusion layer (GDL);

[0193] 2... anode;

[0194] 2c... catalyst layer (CL);

[0195] 2m... water-repellent layer (MPL);

[0196] 2gd... gas diffusion layer (GDL);

[0197] 3... polymer electrolyte membrane (PEM);

[0198] 4, 5... separator;

[0199] 10, 11... membrane-electrode assembly (MEA);

[0200] 12, 13... membrane-catalyst layer assembly (CCM);

[0201] 20... catalyst for electrode (Pt / C catalyst);

[0202] 22... hollow carbon support (CNovel);

[0203] 23... catalyst particle;

[0204] 25... non-contact particle;

[0205] 30... fuel cell stack;

[0206] P1... communication hole connected to a plurality of nano-pores P22

[0207] P22... nano-pore of support;

[0208] P24... micro-pore of support. DETAILED DESCRIPTION

[0209] Hereinafter, preferred embodiments of the present application will be described in detail with appropriate reference to the accompanying drawings.

[0210] <Membrane-electrode assembly (MEA)>

[0211] Figure 1 is a schematic cross-sectional view showing a preferred one of MEAs of the present application.

[0212] Figure 1The illustrated MEA 10 has a structure that includes two gas diffusion electrodes (cathode 1 and anode 2) each having a flat plate shape, and a polymer electrolyte membrane (hereinafter, referred to as "PEM" as needed) 3 disposed between the cathode 1 and the anode 2, in a state of facing each other.

[0213] In the case of the MEA 10, at least one of the cathode 1 and the anode 2 has a structure that contains an electrode catalyst 20 (Pt catalyst 20) described later.

[0214] The MEA 10 can be manufactured by laminating the cathode 1, the anode 2, and the PEM 3 in the manner illustrated, and then performing press bonding. Figure 2

[0215] <Gas Diffusion Electrode (GDE)>

[0216] The cathode 1 as a gas diffusion electrode has a structure that includes a gas diffusion layer 1gd, and a catalyst layer 1c formed on a surface of the PEM 3 side of the gas diffusion layer 1gd. Further, the cathode 1 has a micro porous layer (hereinafter, referred to as "MPL" as needed) 1m disposed between the gas diffusion layer 1gd and the catalyst layer 1c.

[0217] The anode 2 as a gas diffusion electrode also has a structure that includes a gas diffusion layer 2gd, a catalyst layer 2c formed on a surface of the PEM 3 side of the gas diffusion layer 2gd, and an MPL 2m disposed between the gas diffusion layer 2gd and the catalyst layer 2c, similarly to the cathode 1.

[0218] (Catalyst Layer (CL))

[0219] In the cathode 1, the catalyst layer 1c is a layer that performs a reaction of generating water from air (oxygen) sent from the gas diffusion layer 1gd and hydrogen ions moved from the anode 2 through the PEM 3.

[0220] In addition, in the anode 2, the catalyst layer 2c is a layer that performs a reaction of generating hydrogen ions and electrons from hydrogen gas sent from the gas diffusion layer 2gd.

[0221] At least one of the catalyst layer 1c of the cathode 1 and the catalyst layer 2c of the anode 2 contains the electrode catalyst 20 of the present application.

[0222] (Prefe rred One Mode of the Electrode Catalyst of the Present Invention)

[0223] Hereinafter, the electrode catalyst 20 of the present application will be described using Figure 3 , Figure 27 , Figure 28 , and Figure 2 ​A preferred one of the electrode catalysts of the present application will be described.

[0224] Figure 1 is a schematic cross-sectional view showing a preferred one of the electrode catalysts contained in at least one of the cathode catalyst layer 1c and the anode catalyst layer 2c of the MEA 10. Figure 3

[0225] In addition, Figure 2 is a schematic cross-sectional view showing a preferred one of the electrode catalysts contained in at least one of the cathode catalyst layer 1c and the anode catalyst layer 2c of the MEA 10. Figure 2 As

[0226] Figure 3 and Figure 27 As shown in FIG. 2, the electrode catalyst 20 contains a carrier 22 as a hollow carbon carrier and a catalyst particle 23 supported on the carrier 22.

[0227] Figure 28 is a table showing a plurality of 3D-STEM images (three-dimensional reconstruction images) of the electrode catalysts of Example 1, Example 2 (embodiments of the electrode catalyst 20 of the present application) and Comparative Example 2, each of which was measured by electron tomography using STEM.

[0228] Figure 27 is an enlarged view showing a cross section (x-y plane) of a cubic image extracted from the 3D-STEM image (three-dimensional reconstruction image) of the catalyst block of the electrode catalyst of Example 1 (embodiment of the electrode catalyst 20 of the present application). Figure 2-3

[0229] In addition, from the viewpoint of more reliably obtaining the effects of the present application, Figure 27 The electrode catalyst 20 shown in FIG. 2 preferably satisfies the following conditions.

[0230] That is, as described above, the electrode catalyst 20 has a constitution satisfying the condition of formula (S1) of (a) and the condition of (β) that the nano-pores are formed in the shape of the above-described communication holes, in the case of observing the fine structure from the information of the STEM three-dimensional reconstruction image.

[0231] The condition of (a) will be described in detail. In the case of observing the fine structure from the information of the STEM three-dimensional reconstruction image obtained by the procedures of (A) to (C) described above, the value of [100 x (N10 / N20)] of formula (S1) is 8.0 or less for the electrode catalyst 20.

[0232] ​​​Furthermore, from the viewpoint of obtaining the effects of the present invention more reliably, in the electrode catalyst 20, the value of [100×(N10 / N20)] of formula (S1) is preferably 6.5 or less, and more preferably 1.0 or less.

[0233] The conditions for (β) are described in detail. When the electrode catalyst 20 is observed using information from the STEM three-dimensional reconstructed image obtained through the aforementioned procedure from (D) to (G), it has the following structure.

[0234] More specifically, the electrode catalyst 20 has the following structure: when a "cube image (with one side of 20 to 50 nm)" is further extracted from the "catalyst block constituting the electrode catalyst 20 (a catalyst block consisting of catalyst particles 23 and a support 22 that can be housed in a cuboid space with one side of 60 to 300 nm)" that can be seen in a 3D-STEM image (three-dimensional reconstructed image) and the cross-sections of the "cube image" of the six squares are observed, at least one "connecting pore P1 of multiple nanopores P22" with the following shape is formed in at least one cross-section.

[0235] That is, in the electrode catalyst 20, when the microstructure is observed using a 3D-STEM image (three-dimensional reconstruction image), the nanopore P22 formed on at least one face of a cross-section of six squares cut from the interior of the catalyst block has at least one opening connected to a first side of the four sides of the square cross-section, and at least one opening connected to a second side of the square cross-section parallel to the first side. Furthermore, the nanopore P22 has a shape that forms a continuous, unobstructed connecting hole P1 extending from the opening on the first side to the opening on the second side.

[0236] The following uses Figure 28 and Figure 27 The example of the catalyst used in the electrode of Example 1 is illustrated in more detail.

[0237] (D) First, a three-dimensional reconstruction image of the electrode catalyst of Example 1, the object to be measured, was obtained by STEM. From the catalyst blocks reflected in this three-dimensional reconstruction image, a catalyst block of a size accommodating a cuboid space (region of interest) with a side length of 60–300 nm was selected. Figure 27 (a)).

[0238] (E) Subsequently, a cubic image (20-50 nm on each side) is extracted from the internal region of the catalyst block of the electrode catalyst of Example 1 selected in step (D). Figure 27 (b)).

[0239] (F) Following this, observe the internal stereoscopic image (STEM three-dimensional reconstruction image) of the catalyst block for the electrode of Example 1 obtained from step (E), and use the difference in brightness to distinguish between the porous portion (the portion with fine pores such as nanopores) and the hollow carbon support portion (…). Figure 28 (b)).

[0240] (G) Following this, when observing the six square cross-sections of the interior of the catalyst block for the electrode of Example 1 after the division performed in step (F), as... Figure 28 As shown, the nanopore P1 visible in the cross-section of interest (the xy-plane of a square) has two openings (opening A11 and opening A12) connected to the first side L1. Additionally, the nanopore P1 has two openings (opening A21 and opening A22) connected to the second side L2, which is parallel to the first side L1. Furthermore, the nanopore P1 has the shape of a continuous, unobstructed connecting hole P1 extending from the openings (opening A11 and opening A12) on the first side L1 to the openings (opening A21 and opening A22) on the second side L2.

[0241] From the viewpoint of obtaining the effects of the present invention more reliably, such as Figure 28 As shown in Example 1, the nanopores P1 of the electrode catalyst 20 preferably have a multi-branched shape.

[0242] Furthermore, from the viewpoint of more reliably obtaining the effects of the present invention, such as Figure 28 As shown in Example 1, the nanopores P1 of the electrode catalyst 20 preferably have two or more openings on the first side.

[0243] Furthermore, from the viewpoint of more reliably obtaining the effects of the present invention, such as Figure 28 As shown in Example 1, the nanopores P1 of the electrode catalyst 20 preferably have two or more openings on the second side.

[0244] Furthermore, from the viewpoint of more reliably obtaining the effects of the present invention, such as Figure 28 As shown in Example 1, the nanopore P1 of the electrode catalyst 20 preferably has at least one opening on the third side perpendicular to the first side. If the example of Example 1 is used for illustration, as... Figure 28 As shown, the nanopore P1 seen in the cross section of interest (the xy plane of the square) also has an opening (opening A31) on the third side L3, which is perpendicular to the first side L1.

[0245] Furthermore, from the viewpoint of more reliably obtaining the effects of the present invention, such as Figure 28As shown in the example of Embodiment 1, the nanopores P1 of the electrode catalyst 20 preferably have at least one opening in the fourth side perpendicular to the first side. For example, as explained with reference to the example of Embodiment 1, as shown in Figure 2 the nanopores P1 seen in the cross section (x-y plane of the square) of interest have two openings (opening A41 and opening A42) in the fourth side L4 perpendicular to the first side L1.

[0246] Further, from the viewpoint of more reliably obtaining the effects of the present application, in the electrode catalyst 20, the porosity measured using the STEM three-dimensional reconstruction image (cubic image of interest) is preferably 35% or more, further preferably 40% or more, more preferably 45% or more, even more preferably 50% or more, still more preferably 55% or more, yet more preferably 60% or more, and further more preferably 65% or more. On the other hand, from the viewpoint of durability, in the electrode catalyst 20, the porosity measured using the STEM three-dimensional reconstruction image (cubic image of interest) is preferably 80% or less, more preferably 75% or less.

[0247] Here, the catalyst particle 23 has a region composed of Pt (0 valence) formed on at least a portion of the surface thereof, but a layer of Pt oxide can be formed on the region composed of Pt (0 valence) on the surface of the catalyst particle 23 within a range in which the effects of the present application can be obtained.

[0248] As a more specific structure of the catalyst particle 23, the catalyst particle 23 is not particularly limited in the case where the catalyst particle 23 is composed of Pt (0 valence), but in the case where the catalyst particle 23 is composed of a Pt alloy, the catalyst particle 23 is preferably selected as a core-shell catalyst particle.

[0249] In the case where the catalyst particle 23 is composed of a Pt alloy, the type of metal that becomes an alloy element other than Pt is not particularly limited. From the viewpoint of obtaining excellent catalyst activity, the type of metal that becomes an alloy element other than Pt is preferably at least one metal among Co and Ni.

[0250] When the catalyst particle 23 is a core-shell catalyst particle, from the viewpoint of obtaining excellent catalyst activity, the core-shell catalyst particle is preferably composed of a core particle and a Pt shell (a region composed of Pt (0 valence)) formed on at least a portion of the surface of the core particle. The type of metal constituting the core particle is not particularly limited, but from the viewpoint of obtaining excellent catalyst activity, at least one of Pd, Ni, and Co is preferred. Alternatively, the core particle may be an alloy of at least one of Pd, Ni, and Co with other metals. From the viewpoint of reducing the amount of noble metal used, the core particle may contain at least one of a base metal other than a noble metal, an oxide of a base metal, a nitride of a base metal, and a carbide of a base metal.

[0251] In the electrode catalyst 20, the average value of the unit cell size, as determined by powder X-ray diffraction (XRD), is preferably 3 to 16.0 nm.

[0252] In addition, the Pt loading of the electrode catalyst 20 is preferably 5.6 to 66.5 wt%.

[0253] When the support 22 is manufactured into an electrode catalyst, it is preferably a support that can satisfy the conditions (α) and (β) described above. From this point of view, the support 22 is preferably one of the CNovel (manufactured by Toyo Carbon Co., Ltd., product name, registered trademark) that can satisfy the conditions (α) and (β) described above when manufacturing an electrode catalyst.

[0254] like Figure 2 As shown, in this embodiment, the support 22 is a porous carbon having nanopores P22 (pore size 1-20 nm, preferably 1-10 nm), micropores P24 (pore size less than 1 nm), and carbonaceous walls forming the periphery of the nanopores P22. The carbonaceous walls contain a layered structure, and further, a three-dimensional mesh structure is formed within the carbonaceous walls. The layered structure portion of the carbonaceous walls has well-developed crystalline material.

[0255] Typically, this layered structure can be formed by heating carbon materials at a temperature above a certain level. However, carbon materials generally shrink during heat treatment, causing pores to collapse and resulting in a tendency for the specific surface area to decrease. Consequently, when the crystal structure is well-developed, it is difficult to obtain porous carbon with a high specific surface area.

[0256] In contrast, the carrier 22, having nanopores P22 and carbonaceous walls surrounding the nanopores P22, is able to withstand shrinkage during heat treatment, thus enabling the formation of a layered structure within the carbonaceous walls and ensuring sufficient specific surface area.

[0257] Furthermore, because the carbonaceous walls of support 22 form a three-dimensional mesh structure, it can achieve highly dispersed support of small catalyst particles at the nanometer scale, making it suitable as a support for the catalyst layer of a fuel cell. Additionally, support 22 does not need to have all the carbonaceous walls in a layered structure; it can also contain amorphous portions.

[0258] In addition, the carrier 22 preferably has a specific surface area of ​​200 m². 2 / g~1500m 2 / g. Specific surface area is 200m². 2 At a specific surface area of ​​1500 m² / g or higher, a three-dimensional mesh structure can be formed more reliably. This allows for the formation of sufficient pores, resulting in adequate gas adsorption capacity. Furthermore, the specific surface area is 1500 m² / g. 2 At g / g or below, carbonaceous walls are formed more readily and reliably. This facilitates the formation of nanopores (P22).

[0259] Here, as Figure 2 As shown, in the support 22, the nanopores P22 are open pores, and the nanopores P22 are continuously connected to form connecting pores P1. This structure allows for smooth flow of the reactant gas in the catalyst layer (catalyst layer 1c or catalyst layer 2c).

[0260] From the viewpoint that the carrier 22 has sufficient conductivity, a resistivity of 10.0 × 10⁻⁶ is preferred. 2 Below Ω·cm, more preferably 5.0 × 10⁻⁶. 2 Ω·cm, more preferably 1.0×10 2 Below Ω·cm.

[0261] In addition, the carrier 22 may also contain pores with a diameter of less than 1 nm (smaller pores among those classified as so-called micropores) and pores with a diameter of more than 20 nm and less than 50 nm (larger pores among those classified as so-called mesopores), within the range that can achieve the effects of the present invention.

[0262] Furthermore, the support 22 is preferably a hollow carbon support that has good dispersibility in the gas diffusion electrode forming composition containing the electrode catalyst 20 and has excellent conductivity.

[0263] Here, as Figure 10 As shown, catalyst particles 23 are supported inside and outside the nanopores P22 of the support 22.

[0264] Furthermore, when performing electron beam tomography using 3D-STEM, the electrode catalyst 20 satisfies the conditions of the following formula (S1).

[0265] 100×(N10 / N20)≤8.0……(S1)

[0266] Here, in formula (S1), N10 represents the number of non-contact particles 25 obtained by adding (I) the number of noble metal particles that do not contact the pores with a diameter of 1 nm or more that can be confirmed by electron beam tomography (n101) and (II) the number of noble metal particles that do not contact the hollow carbon support 22 itself but exist on its exterior (n102).

[0267] N20 represents the number of catalyst particles 23 supported inside the nanopores P22 of the support 22.

[0268] Electrode catalyst 20 that satisfies the conditions of formula (S1) and existing electrode catalyst 200 (refer to...) Figure 1 In contrast, there are fewer non-contact particles 25 (catalyst particles that are difficult to contribute to the electrode reaction) buried in the micropores P24 of the support 22, while there are more highly active catalyst particles 23 inside the nanopores P22 of the support 22.

[0269] Such catalyst particles 23 supported inside the nanopores P22 of the support 22 are difficult to interact with those present in the catalyst layer ( Figure 1 The polymeric electrolyte within catalyst layer 2c or catalyst layer 1c is supported on the support 22 in a state of direct contact. Therefore, the electrode catalyst 20 of this embodiment can reduce the decrease in catalyst activity caused by Pt poisoning, and compared with the conventional electrode catalyst 200, it can exhibit superior catalyst activity after being electrodeized. In addition, the electrode catalyst 20 of this embodiment also reduces the dissolution of Pt from the catalyst particles 23.

[0270] From the viewpoint of more reliably obtaining the effects of the present invention, the value of [100×(N10 / N20)] in formula (S1) is preferably 6.5 or less, and more preferably 1.0 or less.

[0271] In the electrode catalyst 20, when performing electron beam tomography using 3D-STEM, it is preferable to further satisfy the following formula (S2).

[0272] 100×{N10 / (N20+N30)}≤5.0……(S2)

[0273] In this equation (S2), N10 has the same meaning as N10 in equation (S1).

[0274] In addition, in equation (S2), N20 has the same meaning as N10 in equation (S1) above.

[0275] Further, in formula (S2), N30 represents the number of particles of the catalyst particles 23 that are carried outside the nanopores P22 of the carrier 22.

[0276] By carrying the catalyst particles in the carrier 22 in such a manner that the above-described conditions of formula (S2) are satisfied, the electrode catalyst 20 has less non-contact particles 25 (catalyst particles) buried in the micropores P24 of the carrier 22, and has more catalyst particles 23 with high activity inside the nanopores P22 of the carrier 22, as compared with the conventional electrode catalyst 200. Thus, the electrode catalyst 20 can more reliably exhibit excellent catalyst activity that contributes to the cost reduction of the PEFC.

[0277] Here, from the viewpoint of more reliably obtaining the effects of the present application, the value of [100 x {N10 / (N20+N30)}] of formula (S2) is preferably 3.0 or less, and further preferably 1.0 or less.

[0278] Further, in the case where the analysis of the particle size distribution of the catalyst particles 23 is performed using a three-dimensional reconstruction image obtained by electron tomography using a STEM (scanning transmission electron microscope), in the electrode catalyst 20, with respect to the catalyst particles 23 carried inside the nanopores P22 of the carrier 22, the average distance from the entrance of the nanopore P22 to the position at which the catalyst particle 23 is carried is preferably 5.0 nm or more.

[0279] The present inventors believe that the catalyst particles 23 that satisfy this condition are carried inside the nanopores P22 of the carrier 22, and can sufficiently prevent contact with the polymer electrolyte. In addition, it is believed that the catalyst particles 23 that satisfy this condition, although carried inside the nanopores P22 of the carrier 22, exist at a moderate depth from the entrance of the nanopore, and are relatively easily supplied with protons, oxygen, and hydrogen.

[0280] From the viewpoint of more reliably obtaining the effects of the present application, with respect to the catalyst particles 23 carried inside the nanopores P22 of the carrier 22, the average distance from the entrance of the nanopore P22 to the position at which the catalyst particle 23 is carried is preferably 5.0 to 8.5 nm, and more preferably 5.0 to 5.5 nm. In this way, by making the position at which the catalyst particle 23 is carried preferably 8.5 nm or less, and further preferably in the range of 5.5 nm or less, even in the case where the MEA 10 is required to generate power under conditions of higher temperature than usual or lower humidification than usual, the tendency of the catalyst particles 23 inside the nanopores P22 to be easily supplied with protons is easily maintained.

[0281] Further, in a case where the analysis of the particle size distribution of the catalyst particles 23 is performed using a three-dimensional reconstruction image measured by electron beam tomography using a STEM (scanning transmission electron microscope), the catalyst particles 23 supported inside the nanopores P22 of the support 22 in the electrode catalyst 20 are more preferably present in a range of 0 to 27 nm from the entrance of the nanopores P22 to the supporting position of the catalyst particles 23.

[0282] It is considered that the catalyst particles 23 satisfying this condition, although supported inside the nanopores P22 of the support 22, are present at a moderate depth from the entrance of the nanopores P22, and the effects of avoiding contact with the aforementioned polymer electrolyte and supplying sufficient reaction gas and protons can be more reliably obtained.

[0283] From the same viewpoint as described above, the catalyst particles 23 supported inside the nanopores P22 of the support 22 are more preferably present in a range of 0 to 18 nm from the entrance of the nanopores P22 to the supporting position of the catalyst particles 23.

[0284] Further, in a case where the analysis of the particle size distribution of the catalyst particles 23 is performed using a three-dimensional reconstruction image measured by electron beam tomography using a STEM (scanning transmission electron microscope), the particle size of the catalyst particles 23 supported inside the nanopores P22 of the support 22 in the electrode catalyst 20 is preferably more than 0 nm and 7 nm or less.

[0285] It is considered that the catalyst particles 23 satisfying this condition have a sufficient reaction surface area because of having a moderate particle size, and the electrode reaction can be sufficiently promoted even if supported inside the nanopores P22 of the support 22.

[0286] Further, in a case where the analysis of the particle size distribution of the catalyst particles 23 is performed using a three-dimensional reconstruction image measured by electron beam tomography using a STEM (scanning transmission electron microscope), the proportion of the catalyst particles 23 supported inside the nanopores P22 in the electrode catalyst 20 is preferably 50% or more, and further preferably 70% or more.

[0287] By supporting the catalyst particles 23 in the support 22 in such a manner as to satisfy the above conditions, the catalyst particles 23 having a relatively small particle size and high activity are present more inside the nanopores P22 of the support 22 than in the conventional electrode catalyst.

[0288] Such catalyst particles 23 supported inside the nanopores P22 of the support 22 are supported in the state of being hardly in direct contact with the high molecular electrolyte present in the catalyst layer (catalyst layer 1c or catalyst layer 2c) in the support. Therefore, the electrode catalyst 20 can reduce the decrease in catalyst activity caused by Pt component poisoning, and can exhibit excellent catalyst activity after being polarized, compared with the conventional electrode catalyst 200. In addition, in the electrode catalyst 20, the elution of the Pt component from the catalyst particles 23 is also reduced.

[0289] As the manufacturing method of the electrode catalyst 20, a "support pretreatment step", a "Pt addition step", and a "reduction step" for satisfying the formula (1), formula (2), and the above other conditions are included, and other than this, it can be manufactured without particular limitation by a publicly known method.

[0290] In the support pretreatment step, the support 22 is put into ultrapure water, and a pH adjuster is further added, and a dispersion liquid in which the pH is adjusted to 2 to 5 is prepared. Further, while stirring the dispersion liquid, the temperature is maintained at 80 to 99°C, preferably 90 to 99°C for a prescribed time (but in a state of not boiling). After that, the dispersion liquid is cooled to room temperature.

[0291] By this, the gas inside the nanopores P22 of the support 22 is removed, and the ultrapure water can sufficiently infiltrate inside the nanopores P22. Then, in the "Pt addition step" thereafter, the Pt raw material can be sufficiently held inside the nanopores P22 of the support 22. By this, the precursor of the Pt catalyst particle is supported in the inside of the nanopores P22 of the support 22.

[0292] Note that, in this support pretreatment step, the "ultrapure water" used for the preparation of the above aqueous solution is water in which the specific resistance R (reciprocal of the conductivity measured by the JIS standard test method (JIS K0552)) represented by the following formula (4) is 3.0 MΩ·cm or more. In addition, the "ultrapure water" preferably has a water quality corresponding to "A3" prescribed in JIS K0557 "Water used in tests of water, wastewater" or a cleaner water quality than this.

[0293] This ultrapure water is not particularly limited as long as it is water having a conductivity satisfying the relationship represented by the following formula (4). For example, as the above ultrapure water, the ultrapure water manufactured using an ultrapure water manufacturing device "Milli-Q series" (manufactured by MERCK Corporation), "Elix UV series" (manufactured by Japan MILLIPORE Corporation) can be cited.

[0294] R = 1 / p …… (4)

[0295] In the above formula (4), R represents specific resistance, and p represents conductivity measured by JIS standard test method (JIS K0552).

[0296] The process after the "support pretreatment process" is a "Pt addition process". In the "Pt addition process", an aqueous solution obtained by dissolving a water-soluble Pt salt (N.E. CHEMCAT Co., trade name "A-salt" (Fe component concentration: 8 ppm or less)) in ultrapure water is added to the dispersion liquid of the support 22 obtained by the "support pretreatment process" at room temperature.

[0297] The process after the "Pt addition process" is a "reduction process". In the "reduction process", the temperature of the solution obtained by the "Pt addition process" is increased to 50°C or higher, and then an aqueous solution in which a water-soluble reducing agent (preferably an acidic water-soluble reducing agent) is dissolved is added. After the addition of the reducing agent, the liquid temperature is maintained at 50°C or higher for a prescribed time, and after the reduction reaction, the temperature of the solution is decreased to room temperature.

[0298] The process after the "reduction process" is a "washing process". In the "washing process", the solid component and the liquid component in the solution obtained by the "reduction process" are separated, and the solid component (a mixture of a Pt / C catalyst and impurities other than the Pt / C catalyst) is washed. For example, the solid component and the liquid component in the solution obtained by the "reduction process" can be separated using a filter paper, a filter cloth, or the like as a filtration means. The washing of the solid component can be performed using the above-described ultrapure water, pure water (the specific resistance R represented by the above formula (4) is 0.1 MΩ-cm or more and less than 3.0 MΩ-cm), or pure hot water (water obtained by setting the temperature of the pure water to 40 to 80°C). For example, in the case of using the pure hot water, the washing is repeated until the conductivity of the filtrate after the washing reaches less than 10 μS / cm.

[0299] The process after the "washing process" is a "drying process". In the "drying process", moisture is separated from the solid component (a mixture of a Pt / C catalyst and water) obtained by the "washing process". First, the solid component is air-dried, and then dried in a drier at a prescribed temperature for a prescribed time.

[0300] The process after the "drying process" is a "pulverization process". In the "pulverization process", the solid component (a Pt / C catalyst) obtained by the "drying process" is made into a powder of the catalyst by using a mixer or the like as a pulverization means.

[0301] The polymer electrolyte contained in the catalyst layer 1c, the catalyst layer 2c is not particularly limited as long as it has hydrogen ion conductivity, and a publicly known polymer electrolyte can be used. For example, the polymer electrolyte can exemplify a publicly known perfluoroalkane resin having a sulfonic acid group, a carboxylic acid group. As a polymer electrolyte having hydrogen ion conductivity that can be easily obtained, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), FLEMION (registered trademark, manufactured by Asahi Glass Company Limited) can be exemplified.

[0302] After that, Figure 1 The mass ratio N / C of the mass C of the carrier 22 to the mass N of the polymer electrolyte in at least one of the catalyst layer 1c of the cathode 1 and the catalyst layer 2c of the anode 2 is 0.5 to 1.2, and the mass ratio N / C is more preferably 0.7 to 1.0.

[0303] (Gas diffusion layer (GDL))

[0304] Figure 1 The gas diffusion layer 1gd provided in the cathode 1 is a layer provided to supply an oxidizing gas (for example, oxygen, air) to the catalyst layer 1c. In addition, the gas diffusion layer 1gd has a function of supporting the catalyst layer 1c.

[0305] In addition, the gas diffusion layer 2gd provided in the anode 2 is a layer provided to supply a reducing gas (for example, hydrogen) to the catalyst layer 2c. In addition, the gas diffusion layer 2gd has a function of supporting the catalyst layer 2c.

[0306] Figure 1 The gas diffusion layer (1gd) has a function and a structure that hydrogen or air (oxygen) passes 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).

[0307] The material that can be used for the gas diffusion layer (1gd) is not particularly limited, and a publicly known material can be used. For example, carbon paper, a material obtained by using carbon paper as a main raw material and coating a secondary raw material composed of carbon powder, ion-exchange water, and polyethylene terephthalate dispersion liquid as a binder as an arbitrary component on the carbon paper can be preferably selected.

[0308] (Moisture-repellent layer (MPL))

[0309] As Figure 1As shown, in 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-repellent properties, and gas diffusion properties, and is a layer disposed to promote the diffusion of oxidant gas to the catalyst layer 1gd and the discharge of water generated in the reaction in the catalyst layer 1gd. The structure of the water-repellent layer 1m is not particularly limited and can adopt a known configuration.

[0310] (Polymer electrolyte membrane (PEM))

[0311] Figure 1 The polymeric electrolyte membrane (PEM) 3 shown is not particularly limited as long as it has hydrogen ion conductivity, and can be any known polymeric electrolyte membrane that has been used in PEFCs. For example, it can be a membrane containing the polymeric electrolyte exemplified above as contained in catalyst layer 1c and catalyst layer 2c.

[0312] <MeA's Transformation Methods>

[0313] The preferred embodiments of the MEA (and the catalyst layer and gas diffusion electrode of the present invention) of the present invention have been described above, but the MEA of the present invention is not limited to these embodiments. Figure 4 The structure of MEA10 is shown.

[0314] For example, the MEA of the present invention may also have Figure 4 The structure of MEA11 is shown.

[0315] Figure 4 This is a schematic cross-sectional view illustrating another preferred embodiment of the MEA of the present invention. Figure 1 The MEA11 shown has a layer with the same properties as the polymer electrolyte membrane (PEM) 3 on only one side. Figure 5 The MEA10 shown has a gas diffusion electrode (GDE) 1A with the same structure as the cathode 1. The catalyst layer 1c of the gas diffusion electrode (GDE) 1A has the structure of the catalyst layer of the present invention. That is, in the catalyst layer 1c of GDE1A, the mass ratio N / C of the support 22 for the electrode catalyst 20 to the mass N of the polymer electrolyte is 0.5 to 1.2, more preferably 0.7 to 1.0.

[0316] <Chemical membrane-catalyst layer bonding assembly (CCM)>

[0317] Hereinafter, a preferred embodiment of the film-catalyst layer bonding body (CCM) of the present invention will be described.

[0318] Figure 5This is a schematic cross-sectional view illustrating a preferred embodiment of the CCM of the present invention. Figure 5 The CCM12 shown has a structure in which a polymer electrolyte membrane (PEM) 3 is disposed between a cathode catalyst layer 1c and an anode catalyst layer 2c. Furthermore, at least one of the cathode catalyst layer 1c and the anode catalyst layer 2c has the composition of the catalyst layer of the present invention. That is, the mass ratio N / C of the carrier of the electrode catalyst 20 of at least one of the cathode catalyst layer 1c and the anode catalyst layer 2c to the mass N of the polymer electrolyte is 0.5 to 1.2, more preferably 0.7 to 1.0.

[0319] <Deformation Modes of Membrane-Catalyst Layer Bonds (CCMs)>

[0320] The preferred embodiments of the CCM of the present invention have been described above, but the CCM of the present invention is not limited to those described above. Figure 6 The structure of CCM12 is shown.

[0321] For example, the CCM of the present invention may also have Figure 7 The structure of CCM13 is shown.

[0322] Figure 6 This is a schematic cross-sectional view illustrating another preferred embodiment of the CCM of the present invention. Figure 5 The CCM13 shown is configured with a coating on only one side of the polymer electrolyte membrane (PEM) 3, having a coating similar to... Figure 8 The catalyst layer 1c in the cathode 1 of the CCM12 shown has the same structure. The catalyst layer 1c of the gas diffusion electrode (GDE) 1A has the composition of the catalyst layer of the present invention. Specifically, in the catalyst layer 1c of the CCM13, the mass ratio N / C of the mass C of the electrode catalyst 20 support to the mass N of the polymer electrolyte is set to 0.5 to 1.2, more preferably 0.7 to 1.0.

[0323] <Gas Diffusion Electrode (GDE)>

[0324] Next, a preferred embodiment of the gas diffusion electrode (GDE) of the present invention will be described.

[0325] Figure 7 This is a schematic cross-sectional view illustrating a preferred embodiment of the GDE of the present invention. Figure 1 The gas diffusion electrode (GDE) 1B shown has the same characteristics as that mounted on Figure 7The cathode 1 of the MEA 10 shown is the same constitution. Among them, the catalyst layer 1c of the gas diffusion electrode (GDE) IB has the constitution of the catalyst layer of the present application. That is, in the catalyst layer 1c of the gas diffusion electrode (GDE) IB, the mass ratio N / C of the mass C of the carrier 22 of the electrode catalyst 20 to the mass N of the polymer electrolyte is set to 0.5 to 1.2, and further preferably to 0.7 to 1.0.

[0326] <MODIFICATION OF THE GDE>

[0327] The above describes the preferred embodiment of the GDE of the present application, but the GDE of the present application is not limited to Figure 8 The constitution of the GDE IB shown.

[0328] For example, the GDE of the present application can also have Figure 9 The constitution of the GDE IC shown.

[0329] Figure 8 is a schematic cross-sectional view showing another preferred embodiment of the GDE of the present application. Figure 8 The GDE IC shown becomes the constitution without disposing the water-repellent layer (MPL) between the catalyst layer 1c and the gas diffusion layer 1gd, compared to the GDE IB shown. Figure 1

[0330] <COMPOSITION FOR FORMING THE CATALYST LAYER>

[0331] The preferred embodiment of the composition for forming the catalyst layer of the present application is described below.

[0332] The composition for forming the catalyst layer of the present application contains the electrode catalyst 20, the polymer electrolyte, and the main component, and the mass ratio N / C of the mass C of the carrier 22 of the electrode catalyst 20 to the mass N of the polymer electrolyte is 0.5 to 1.2, and further preferably 0.7 to 1.0.

[0333] Here, the composition of the solution containing the polymer electrolyte is not particularly limited. For example, the solution containing the polymer electrolyte can contain the aforementioned polymer electrolyte having hydrogen ion conductivity, water, and alcohol.

[0334] The composition ratio of the electrode catalyst 20, the polymer electrolyte, and the other components (water, alcohol, etc.) contained in the composition for forming the catalyst layer is appropriately set so that the dispersion state of the electrode catalyst 20 in the obtained catalyst layer becomes good, and the power generation performance of the MEA 10 containing the catalyst layer can be improved.

[0335] ​The catalyst layer-forming composition can be prepared by mixing and stirring the electrode catalyst 20 and the solution containing the polymer electrolyte. From the viewpoint of adjusting the coatability, a polyhydric alcohol such as glycerol and / or water can also be contained. In the case of mixing the electrode catalyst 20 and the solution containing the polymer electrolyte, a pulverizing mixer such as a ball mill, an ultrasonic disperser, or the like can be used.

[0336] Figure 9 At least one of the catalyst layer 1c of the cathode 1 and the catalyst layer 2c of the anode 2 of the illustrated MEA 10 can be formed using the preferred embodiment of the catalyst layer-forming composition suitable for the present application.

[0337] (Method for manufacturing gas diffusion electrode)

[0338] Next, an example of the method for manufacturing the gas diffusion electrode of the present application will be described. The gas diffusion electrode can be formed in a manner containing the catalyst layer of the present application, and the manufacturing method thereof can employ a publicly known method. By using the catalyst layer-forming composition of the present application, the manufacturing can be performed more reliably.

[0339] For example, the catalyst layer-forming composition is applied to the gas diffusion layer (or the water-repellent layer of the laminate in which the water-repellent layer is formed on the gas diffusion layer) and dried to manufacture.

[0340] <fuel cell stack>

[0341] Figure 9 is a schematic view showing a preferred one embodiment of the fuel cell stack of the present application.

[0342] Figure 1 The illustrated fuel cell stack 30 has a structure in which Figure 11 The illustrated MEA 10 is one cell unit, and the single cell unit is laminated multiple times. In addition, the fuel cell stack 30 has a structure in which the MEA 10 is disposed between the separators 4 and 5. The gas flow paths are formed in the separators 4 and 5, respectively.

[0343] Example

[0344] Hereinafter, the present application will be described more specifically by examples, but the present application is not limited to the following examples.

[0345] (I) Preparation of electrode catalyst used in the catalyst layer of the cathode of the MEA

[0346] (1) Manufacture of Pt / C catalyst used in the cathode of the MEA of Example 1

[0347] [Carbon catalyst on which Pt catalyst particles are supported, "Pt / C catalyst"]

[0348] A powder of a Pt / C catalyst in which catalyst particles composed of Pt were supported on a carrier prepared as follows {Pt supporting rate: 48.0 wt%, trade name "SA50BM-A207", manufactured by N. E. CHEMCAT Co., Ltd.} was prepared.

[0349] The powder of the Pt / C catalyst (hereinafter, referred to as "Pt / C catalyst A" as necessary) can be prepared by the following procedure.

[0350] (First step (carrier pretreatment step))

[0351] A trial sample product manufactured by Toyo Carbon Co., Ltd. with the product name "C Novel A" (BET specific surface area: 1200 m 2 The dispersion liquid was prepared by dispersing the hollow carbon carrier in an aqueous solution adjusted to pH = 2 to 5 (prepared by adding a pH adjuster to ultrapure water) while stirring and maintaining at a temperature of 90 to 99°C for about 0.5 hours (however, maintained in a state without boiling).

[0352] Note that the "ultrapure water" used in the first step (carrier pretreatment step) used water having a specific resistance R (reciprocal of conductivity measured based on JIS Standard Test Method (JIS K0552)) of 3.0 MΩ-cm or more represented by the following formula (4). In addition, the "ultrapure water" has a water quality corresponding to "A3" of the standards in JIS K0557 "Water used in tests of water and wastewater" or a cleaner water quality than that.

[0353] The ultrapure water was manufactured using an ultrapure water manufacturing device "Milli-Q series" (manufactured by MERCK Co., Ltd.), "Elix UV series" (manufactured by Japan MILLIPORE Co., Ltd.).

[0354] R = 1 / p... (4)

[0355] In the above general formula (4), R represents the specific resistance, and p represents the conductivity measured by JIS Standard Test Method (JIS K0552).

[0356] (Second step (Pt addition step))

[0357] To the dispersion liquid obtained in the first step, an aqueous solution obtained by dissolving a water-soluble Pt salt (N. E. CHEMCAT Co., Ltd., product name "A-salt" (Fe component concentration: 8 ppm or less)) in ultrapure water was added, thereby preparing a mixed liquid, the pH was adjusted to 7 to 12, and the mixed liquid was maintained at a prescribed temperature of 50°C or more and stirred for a prescribed time.

[0358] (Third step (reduction step))

[0359] To the liquid obtained by the second process, an aqueous solution in which an acidic water-soluble reducing agent is dissolved is added, and the Pt ions in the mixture are reduced, thereby obtaining a Pt catalyst particle-carried carbon "Pt / C" powder.

[0360] (Fourth process (cleaning process))

[0361] The solid component in the liquid obtained by the "third process" is separated from the liquid component using filter paper. Thereafter, the solid component (a mixture of the Pt / C catalyst and impurities other than the same) remaining on the filter paper is cleaned using the pure water and the pure hot water described above. The cleaning is first performed using the pure water. The cleaning is repeated until the conductivity of the filtrate after the cleaning is lower than 20 μS / cm. Then, the cleaning is performed using the pure hot water. The cleaning is repeated until the conductivity of the filtrate after the cleaning is lower than 10 μS / cm.

[0362] (Fifth process (drying process))

[0363] The solid component (a mixture of the Pt / C catalyst and water) on the filter paper obtained by the "fourth process" is directly air-dried in this state. After the air-drying, the solid component on the filter paper is transferred to a magnetic dish, and dried in an electric drier at a prescribed temperature of 60°C or higher for a prescribed time.

[0364] (Sixth process (pulverization process))

[0365] The solid component (the Pt / C catalyst) obtained by the "fifth process" is pulverized using a mixer, and a powder of the Pt / C catalyst A is obtained.

[0366] Measurement of the loading rate (ICP analysis)

[0367] The Pt loading rate (wt%) of the Pt / C catalyst A was measured by the following method.

[0368] The Pt / C catalyst A was immersed in aqua regia, and the metal was dissolved. Thereafter, the carbon of the insoluble component was removed from the aqua regia. Then, the aqua regia from which the carbon was removed was subjected to ICP analysis.

[0369] As a result of the ICP analysis, it was found that the Pt loading rate of the Pt / C catalyst A was 48.0 wt%.

[0370] Surface observation and structure observation of the catalyst for electrodes

[0371] For the Pt / C catalyst A of Example 1, in order to observe the three-dimensional structure thereof, measurement of electron beam tomography using a STEM (scanning transmission electron microscope) of the UBE Scientific Analysis Center Co., Ltd. was performed using the "USAL-KM3D analysis method".

[0372] The measurement of electron beam tomography using STEM (scanning transmission electron microscope) was carried out in accordance with the aforementioned sample preparation method, conditions, and (A) to (C) and (D) to (G) of the analysis procedure, conditions of the sample. The following describes the more detailed information.

[0373] • STEM device: JEM-ARM200F atomic resolution analytical electron microscope manufactured by JEOL Ltd.

[0374] • Data analysis software: 3D reconstruction software Composer, 3D data visualization software Visualizer-kai, and image analysis software Colorist manufactured by SYSTEM IN FRONTIER

[0375] • Measurement conditions

[0376] Acceleration voltage: 60 kV

[0377] Observation magnification: 800,000 to 1,000,000 times

[0378] Tilt angle of the sample for measurement: -80° to +80°

[0379] Tilt step angle of the sample for measurement: 2°

[0380] Number of pixels: 512 x 512 pixels 512 x 512 pixels

[0381] Pixel size: 0.350 nm / pixel to 0.500 nm / pixel

[0382] Volume size: Figure 12 as shown.

[0383] For the Pt / C catalyst A, the image analysis of the three-dimensional reconstruction image (3D-STEM image) obtained by the measurement of electron beam tomography using STEM (scanning transmission electron microscope) separates the Pt catalyst particles present inside the carbon carrier (hereinafter referred to as "internal particles") and the Pt catalyst particles present on the surface portion of the carbon carrier (hereinafter referred to as "external particles"), and calculates the particle size distribution of the Pt catalyst particles in each region.

[0384] The three-dimensional reconstruction image (3D-STEM image) of the Pt / C catalyst A is shown in Figure 12 .

[0385] The graph showing the distribution state of the Pt catalyst particles in the nanometer pores (Nanopore) of the carbon carrier in the fine pore depth direction obtained by the image analysis of the 3D-STEM image of the electrode catalyst of Example 1 shown in Figure 13 is shown in Figure 12 .

[0386] In addition, a graph showing the distribution state of Pt catalyst particles inside the nanopores of the carbon support in the pore depth direction obtained by image analysis of the 3D-STEM image of the electrode catalyst of Example 1 is shown in FIG. 2. Figure 14 Figure 12 .

[0387] Further, a graph showing the distribution state of Pt catalyst particles inside the nanopores of the carbon support in the pore depth direction obtained by image analysis of the 3D-STEM image of the electrode catalyst of Example 1 is shown in FIG. 2. Figure 15 Figure 13 .

[0388] The 3D-STEM image is obtained by reconstructing a plurality of two-dimensional STEM images obtained by tilting the sample stage stage by stage under the above measurement conditions.

[0389] In addition, the image analysis (particle size analysis) of the three-dimensional reconstructed image (3D-STEM image) is performed by the following procedure. First, an observation area of the catalyst particles is selected from the three-dimensional reconstructed image, and each catalyst particle is labeled (not shown). Thereafter, the volume of the labeled Pt catalyst particles is obtained, the diameter of a sphere having the same volume as the volume (equivalent sphere diameter) is calculated, and the particle size distribution (diameter distribution) is obtained. Figure 14 、 Figure 15 、 Figure 16 .

[0390] Here, the equivalent sphere diameter is calculated by setting the unit as nm and rounding off the numerical value below the decimal point (a numerical value below 1 nm).

[0391] For this Pt / C catalyst A, the proportion of the catalyst particles supported inside the nanopores of the support and the proportion of the catalyst particles supported outside the nanopores of the support were obtained. In addition, the values of N10, N20, and N30 were obtained. The results are shown in Tables 1 and 2.

[0392] In addition, in the electron tomography measurement of the electrode catalyst of this Example 1, the presence of the aforementioned (II) noble metal particles was not confirmed. That is, there were no noble metal particles present outside the hollow carbon support that were not in contact with the hollow carbon support itself (n102 = 0).

[0393] Further, the average value of the particle size of the catalyst particles of the Pt / C catalyst A determined from the STEM image was 3.1 nm (average value of the particle size of the catalyst particles inside the nanopores: 3.1 nm; average value of the particle size of the catalyst particles outside the nanopores: 3.2 nm). ​​

[0394] (2) Preparation of Pt / C catalyst used in the cathode of MEA in Example 2

[0395] [Pt catalyst particles supporting carbon catalyst "Pt / C catalyst" powder]

[0396] In addition to using it as a hollow carbon carrier, a prototype product manufactured by Toyo Carbon Co., Ltd., named "CNovelB" (BET specific surface area: 800 m²), was also used. 2 Except for / g), the Pt / C catalyst used in the cathode of the MEA of Example 2 (hereinafter referred to as "Pt / C catalyst B" as needed) was prepared under the same conditions and operations as the Pt / C catalyst A used in the cathode of the MEA of Example 1.

[0397] <Surface and structural observations of catalysts used in electrodes>

[0398] For the Pt / C catalyst B of Example 2, in order to observe its three-dimensional structure, the same operation and conditions as the Pt / C catalyst of Example 1 were used, and the electron beam tomography measurement was carried out using the "USAL-KM3D analysis method" with STEM (scanning transmission electron microscope) of UBE Scientific Analysis Center Co., Ltd.

[0399] exist Figure 17 STEM images of the electrode catalyst of Example 2 are shown under 3D electron beam tomography measurement conditions (volume size).

[0400] exist Figure 18 A 3D-STEM image (three-dimensional reconstructed image) of the electrode catalyst of Example 2 is shown.

[0401] exist Figure 17 Show Figure 19 The graph shown in Example 2 illustrates the distribution of Pt catalyst particles located outside and inside the nanopores of the carbon support along the pore depth direction, obtained through image analysis of 3D-STEM images.

[0402] exist Figure 17 Show Figure 20 The graph shown is a diagram of the distribution of Pt catalyst particles inside the nanopores of the carbon support in the pore depth direction, obtained by image analysis of 3D-STEM images of the electrode catalyst of Example 2.

[0403] exist Figure 17 ShowFigure 21 Other charts showing the distribution of Pt catalyst particles inside the nanopores of the carbon support in the pore depth direction, obtained by image analysis of 3D-STEM images of the electrode catalyst of Example 2.

[0404] For the electrode catalyst (Pt / C catalyst B), the proportions of catalyst particles supported inside the nanopores of the support and the proportions of catalyst particles supported outside the nanopores of the support were determined. The values ​​of N10, N20, and N30 were also determined. The results are shown in Tables 1 and 2.

[0405] It should be noted that the presence of the noble metal particles mentioned in (II) was not confirmed in the electron beam tomography measurement of the electrode catalyst in Example 2. That is, there were no noble metal particles (n102 = 0) that were not in contact with the hollow carbon support itself and existed on its exterior.

[0406] Furthermore, the average particle size of the catalyst particles for the electrode (Pt / C catalyst B), as determined from STEM images, is 3.3 nm (average particle size of catalyst particles inside the nanopores: 3.2 nm; average particle size of catalyst particles outside the nanopores: 3.7 nm).

[0407] (3) Preparation of Pt / C catalyst powder used in the cathode of Comparative Example 1 MEA

[0408] As a Pt / C catalyst, a Pt / C catalyst (trade name: "SA50BK") with a Pt loading of 50 wt% manufactured by NECHEMCAT was prepared. It should be noted that the support used for this Pt / C catalyst was a commercially available hollow carbon support manufactured by LION Corporation, trade name "Carbon ECP" (registered trademark) (Ketjen Black EC300J), with a specific surface area of ​​750–800 m². 2 / g}.

[0409] <Surface and structural observations of catalysts used in electrodes>

[0410] In order to observe its three-dimensional structure, the Pt / C catalyst of Comparative Example 1 was subjected to electron tomography using STEM (scanning transmission electron microscope) at UBE Scientific Analysis Center, Inc., under the same operation and conditions as the Pt / C catalyst of Example 1.

[0411] exist Figure 22 STEM images of the Pt / C catalyst of Comparative Example 1 under 3D electron beam tomography measurement conditions (volume size) using STEM are shown.

[0412] exist Figure 22 A 3D-STEM image (three-dimensional reconstructed image) of the Pt / C catalyst of Comparative Example 1 is shown.

[0413] It will show as passed Figure 23 The distribution of Pt catalyst particles in the nanopores of the carbon support along the pore depth direction, obtained from image analysis of the 3D-STEM image of the catalyst used in Comparative Example 1, is shown in the figure. Figure 22 .

[0414] Additionally, it will display via Figure 24 The distribution of Pt catalyst particles within the nanopores of the carbon support along the pore depth direction, obtained from image analysis of a 3D-STEM image of the catalyst used in Comparative Example 1, is shown in the figure. Figure 22 .

[0415] Furthermore, it will be displayed via Figure 25 Other images showing the distribution of Pt catalyst particles within the nanopores of the carbon support along the pore depth direction, obtained from image analysis of the 3D-STEM image of the catalyst used in Comparative Example 1, are presented in [the image description]. Figure 26 .

[0416] For this Pt / C catalyst, the proportions of catalyst particles supported inside the nanopores of the support and the proportions of catalyst particles supported outside the nanopores of the support were determined. The values ​​of N10, N20, and N30 were also determined. The results are shown in Tables 1 and 2.

[0417] It should be noted that the presence of the noble metal particles mentioned in (II) was not confirmed in the electron beam tomography measurement of the electrode catalyst in Comparative Example 1. That is, there were no noble metal particles (n102 = 0) that were not in contact with the hollow carbon support itself and existed on the outside.

[0418] Furthermore, the average particle size of the Pt / C catalyst, as determined from STEM images, is 3.1 nm (average particle size of catalyst particles inside the nanopores: 3.1 nm, average particle size of catalyst particles outside the nanopores: 3.2 nm).

[0419] (4) Preparation of the Pt / C catalyst used in the cathode of the MEA of Comparative Example 2

[0420] [Pt catalyst particles supporting carbon catalyst "Pt / C catalyst" powder]

[0421] The powder of the Pt / C catalyst (hereinafter, referred to as "Pt / C catalyst C" as occasion demands) used in the cathode of the MEA of Example 2 was prepared under the same conditions and operations as those of the Pt / C catalyst A used in the cathode of the MEA of Example 1 except that a trial sample product manufactured by Toyo Carbon Co., Ltd., "C Novel C" (BET specific surface area: 800 m 2 The powder of the Pt / C catalyst (hereinafter, referred to as "Pt / C catalyst C" as occasion demands) used in the cathode of the MEA of Example 2 was prepared under the same conditions and operations as those of the Pt / C catalyst A used in the cathode of the MEA of Example 1 except that a trial sample product manufactured by Toyo Carbon Co., Ltd., "C Novel C" (BET specific surface area: 800 m

[0422] < Surface observation and structure observation of the catalyst for electrode >

[0423] For the Pt / C catalyst C of this Comparative Example 2, in order to observe its three-dimensional structure, the measurement of electron beam tomography using a STEM (scanning transmission electron microscope) of UBE Scientific Analysis Center Co., Ltd. was also carried out under the same operations and conditions as those of the Pt / C catalyst of Example 1 using the "USAL-KM3D analysis method".

[0424] For the electrode catalyst (Pt / C catalyst C) of this Comparative Example 2, the measurement of electron beam tomography using a STEM (scanning transmission electron microscope) was also carried out similarly to Example 1, Example 2 and Comparative Example 1, and information equivalent to the analysis results thereof was obtained, but the illustration thereof was omitted.

[0425] Figure 27 The STEM image of the 3D-electron beam tomography measurement conditions (volume size) of the Pt / C catalyst of Comparative Example 2 using a STEM is shown in the middle.

[0426] For the electrode catalyst (Pt / C catalyst C) of this Comparative Example 2, the proportion of the catalyst particles supported inside the nanopores of the carrier and the proportion of the catalyst particles supported outside the nanopores of the carrier were obtained. In addition, the values of D10, D20, D1, D2, N1, N2 were also obtained. The results are shown in Tables 2 and 3.

[0427] Further, the average value of the particle diameters of the catalyst particles of the electrode catalyst (Pt / C catalyst C) measured from the STEM image was 3.2 nm (average value of the particle diameters of the catalyst particles inside the nanopores: 2.9 nm; average value of the particle diameters of the catalyst particles outside the nanopores: 3.5 nm).

[0428] (5) Confirmation of the fine structure of the electrode catalyst of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 using the three-dimensional reconstructed image of a STEM

[0429] For the electrode catalysts of Example 1, Example 2, and Comparative Example 2, in order to confirm the aforementioned condition (β) "whether or not a nanopore is formed in the shape of the communication hole of the present application", an investigation was performed using the three-dimensional reconstructed image of the STEM. In addition, the void fraction of each catalyst was separately obtained using the three-dimensional reconstructed image of the STEM.

[0430] The results thereof are shown in Figure 28 and Figure 27 .

[0431] As shown in Figure 28 (c) and Figure 27 , the nanopore PI seen in the cross section (x-y plane of the square) of interest among the six square cross sections of the stereoscopic image of the interior of the catalyst block of the electrode catalyst of Example 1 has two openings (opening Al l and opening A12) that border the first side LI. In addition, the nanopore PI has two openings (opening A21 and opening A22) that border the second side L2 that is parallel to the first side LI. Furthermore, the nanopore PI has the shape of a communication hole PI that continuously extends without obstruction from the openings (opening Al l and opening A12) of the first side LI to the openings (opening A21 and opening A22) of the second side L2.

[0432] Further, as shown in Figure 28 (c) and Figure 27 , the nanopore PI of the interior of the electrode catalyst of Example 1 has the shape of a plurality of branches.

[0433] Further, as shown in Figure 28 (c) and Figure 27 , the nanopore PI of the interior of the electrode catalyst of Example 1 has two or more openings (opening Al l and opening A12) on the first side LI.

[0434] In addition, as shown in Figure 28 (c) and Figure 27 , the nanopore PI of the interior of the electrode catalyst of Example 1 has two or more openings (opening A21 and opening A22) on the second side L2.

[0435] Further, as shown in Figure 28 (c) and Figure 27 , the nanopore PI of the interior of the electrode catalyst of Example 1 also has one opening (opening A31) on the third side L3 that is perpendicular to the first side LI.

[0436] In addition, as shown in Figure 27 (c) and Figure 27 , the nanopore PI of the interior of the electrode catalyst of Example 1 also has two openings (opening A41 and opening A42) on the fourth side L4 that is perpendicular to the first side LI.

[0437] As Figure 27 (d) and Figure 27 (e) show, the nano-pores P1 having the same shape as described above were also confirmed on the other two faces (y-z plane, z-x plane) of the stereogram of the inside of the catalyst block of the electrode catalyst of Example 1.

[0438] Further, as Figure 27 (h), Figure 27 (i), and Figure 1 (j) show, for the electrode catalyst of Example 2, too, the nano-pores P22 having the shape of the communication hole P1 according to the present application were confirmed to be formed similarly to the electrode catalyst of Example 1.

[0439] On the other hand, as ​ (m), ​ (n), and ​ (o) show, for the electrode catalyst of Comparative Example 1, the nano-pores P22 having the shape of the communication hole P1 according to the present application were confirmed not to be formed. The nano-pores P1 seen in the cross sections (x-y plane, y-z plane, z-x plane) of the stereogram of the inside of the catalyst block of the electrode catalyst of Comparative Example 1 had one opening in contact with the first side and an opening in contact with the second side parallel to the first side, but the shape of the communication hole P1 continuously extending without obstruction from the opening of the first side to the opening of the second side was not confirmed.

[0440] (II) Preparation of P / C catalyst used in the anode of the MEA of Example 1, Example 2, Comparative Example 1, Comparative Example 2

[0441] The same Pt / C catalyst as used in the cathode of the MEA of Comparative Example 1 was used as the P / C catalyst used in the anode of the MEA of Example 1, Example 2, Comparative Example 1, Comparative Example 2.

[0442] <Example 1>

[0443] An MEA having the same structure as the MEA 10 shown in ​ was produced according to the following procedure.

[0444] (1) Production of cathode

[0445] GDL of cathode

[0446] As the GDL, a carbon paper (manufactured by Toray Industries, Inc., trade name "TGP-H-60") was prepared.

[0447] Ink for MPL formation of cathode

[0448] Into a TEFLON (registered trademark) -made ball mill container equipped with TEFLON (registered trademark) -made balls, 1.5 g of carbon powder (manufactured by Denki Kagaku Kogyo K.K., trade name "DENKA BLACK"), 1.1 g of ion exchange water, and 6.0 g of a surfactant (manufactured by Dow Chemical Company, trade name "TRITON" (35 wt% aqueous solution)) were put, and mixed.

[0449] Subsequently, 1.75 g of a polytetrafluoroethylene (PTFE) dispersion (manufactured by Mitsui Dupont Fluorochemical Co., Ltd., trade name "31-JR") was added to the ball mill container, and mixed. Thus, an MPL formation ink for a cathode was prepared.

[0450] MPL of cathode

[0451] The MPL formation ink for a cathode was applied to one face of the GDL using a bar coater to form an applied film. Subsequently, the applied film was sufficiently dried in a drier, and further subjected to a heat press bonding treatment, thereby preparing a laminate in which an MPL was formed on the GDL.

[0452] Catalyst layer formation ink for cathode

[0453] Into a TEFLON (registered trademark) -made ball mill container equipped with TEFLON (registered trademark) -made balls, the above-mentioned Pt / C catalyst A, ion exchange water, 10 wt% Nafion aqueous dispersion (manufactured by DuPont Company, trade name "DE1021CS"), and glycerin were put, and mixed, thereby preparing a catalyst layer formation ink for a cathode. Note that the ink was set to N / C = 0.7. In addition, in the electrode catalyst A, carbon: ion exchange water: glycerin = 1: 10: 0.8 (mass ratio) was set.

[0454] Catalyst layer (CL) of cathode

[0455] The surface of the MPL of the MPL-formed laminate on the above-mentioned GDL was applied with the above-mentioned catalyst layer formation ink for a cathode by a bar coating method to form an applied film. The applied film was dried at room temperature for 30 minutes, and then dried at 60°C for 1.0 hour, thereby preparing a catalyst layer. Thus, a cathode was prepared as a gas diffusion electrode. Note that the Pt loading amount of the catalyst layer of the cathode was set to the values shown in Table 1.

[0456] (2) Preparation of anode

[0457] GDL of anode

[0458] As the GDL, the same carbon paper as the cathode was prepared.

[0459] MPL formation ink for anode

[0460] Into a TEFLON (registered trademark) -made ball mill container equipped with TEFLON (registered trademark) -made balls, 1.5 g of carbon powder (manufactured by Denki Kagaku Kogyo K.K., trade name "DENKA BLACK"), 1.0 g of ion exchange water, and 6.0 g of a surfactant (manufactured by Dow Chemical, trade name "TRITON" (35 wt% aqueous solution)) were put and mixed.

[0461] After that, 2.5 g of a polytetrafluoroethylene (PTFE) dispersion (manufactured by Mitsui Dupont Fluorochemical Co., Ltd., trade name "31-JR") was added to the ball mill container and mixed. Thus, an MPL formation ink for an anode was prepared.

[0462] MPL of anode

[0463] The MPL formation ink for anode was applied to one face of the GDL using a bar coater and a coated film was formed. After that, the coated film was sufficiently dried in a drier and further subjected to a heat press bonding treatment, and a laminate in which an MPL was formed on the GDL was prepared.

[0464] Catalyst layer formation ink for anode

[0465] Into a TEFLON (registered trademark) -made ball mill container equipped with TEFLON (registered trademark) -made balls, SA50BK (Pt loading rate 50 wt%), ion exchange water, 5 wt% Nafion alcohol dispersion (manufactured by SIGMA-ALDRICH Co., trade name "Nafion 5 wt.% dispersion", product number "274704"), and glycerin were put and mixed, and a catalyst layer formation ink for anode was prepared. Note that the N / C in the ink was set to 1.2. Also, in the SA50BK, carbon:ion exchange water:glycerin = 1:6:4 (mass ratio) was set.

[0466] Catalyst layer (CL) of anode

[0467] The MPL of the laminate in which the MPL was formed on the MPL on the GDL described above was coated with the catalyst layer formation ink for anode described above by a bar coating method, and a coated film was formed. After the coated film was dried at room temperature for 30 minutes and at 60°C for 1.0 hour, a catalyst layer was prepared. Thus, an anode as a gas diffusion electrode was prepared. Note that the Pt loading amount of the catalyst layer of the anode was set to 0.3 mg / cm 2 .

[0468] (3) Preparation of MEA

[0469] A polymer electrolyte membrane (manufactured by DuPont, trade name "Nafion NR212") was prepared. A laminate having the polymer electrolyte membrane disposed between the cathode and the anode was prepared, and a hot press was used to perform heat press bonding, thereby producing an MEA. The conditions for heat press bonding were set to 140°C, 5 KN for 5 minutes, and 140°C, 25 KN for 3 minutes.

[0470] Example 2

[0471] Each MEA was produced under the same conditions and procedures as in Example 1, except that the following changes were made to the cathode catalyst layer.

[0472] That is, in the production of the ink for forming the catalyst layer of the cathode,

[0473] • The aforementioned Pt / C catalyst B was used instead of the Pt / C catalyst A.

[0474] Comparative Example 1

[0475] Each MEA was produced under the same conditions and procedures as in Example 1, except that the following changes were made to the cathode catalyst layer.

[0476] That is, in the production of the ink for forming the catalyst layer of the cathode,

[0477] • The aforementioned P / C catalyst (trade name: "SA-50BK") was used instead of the Pt / C catalyst A.

[0478] • A 5 wt% Nafion alcohol dispersion (manufactured by DuPont, trade name "DE520CS"; containing 48 wt% 1-propanol) was used instead of the 10 wt% Nafion water dispersion.

[0479] • The composition of the ink for forming the catalyst layer of the cathode and the coating conditions of the ink were adjusted so that the Pt loading and the N / C became the values shown in Table 1.

[0480] • The carbon: ion exchange water: glycerin in the P / C catalyst (trade name: "SA50BH") was set to 1:10:1 (mass ratio).

[0481] Comparative Example 2

[0482] Each MEA was produced under the same conditions and procedures as in Example 1, except that the following changes were made to the cathode catalyst layer.

[0483] That is, in the production of the ink for forming the catalyst layer of the cathode,

[0484] • The aforementioned Pt / C catalyst C was used instead of the Pt / C catalyst A.

[0485] <Battery Performance Evaluation>

[0486] The battery performance of the MEAs of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 was evaluated by the following battery performance evaluation method.

[0487] The MEAs of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were set in a fuel cell single cell evaluation device.

[0488] After that, power generation reaction in the MEA was performed under the following conditions.

[0489] The single cell (MEA) temperature was set to 80°C. Pure hydrogen at 1.0 atm humidified with saturated water vapor was supplied to the anode, and the flow rate was adjusted so that the utilization became 70%. In addition, pure oxygen at 1.0 atm humidified with saturated water vapor at 80°C was supplied to the cathode, and the flow rate was adjusted so that the utilization became 50%.

[0490] The evaluation of the single cell (MEA) was performed using an electronic load device attached to the fuel cell single cell evaluation device to control the current so that the current value was scanned in the range of 0 to 1.0 A / cm 2 , and the obtained current-voltage curve was taken as data.

[0491] From the data of the current-voltage curve described above, a graph (not shown) was prepared in which the X axis (current density) was plotted on a logarithmic scale, and the current density value at a voltage of 850 mV (current value per unit area of the electrode) was obtained.

[0492] The current density value thus obtained was divided by the platinum weight per unit area of the cathode, and thus the activity per unit weight of platinum contained in the cathode (Mass. Act.) was calculated, which was taken as an index of the oxygen reduction ability of the catalyst contained in the cathode. The results are shown in Table 1.

[0493] In addition, in Table 1, the results obtained in the other examples are shown as relative values (relative ratio) with respect to the Mass. Act. obtained in Comparative Example 1 (1.0).

[0494]

[0495] As is clear from the results shown in Tables 1 to 2, the MEAs of Example 1 and Example 2 had higher Pt mass activity than the MEAs of Comparative Example 1 and Comparative Example 2.

[0496] In the above embodiments and comparative examples, we explored embodiments in which the catalyst particles are composed of the purest form of Pt. However, the electrode catalyst of the present invention is characterized by having a three-dimensional structure that, when the microstructure is observed using STEM three-dimensional reconstruction images, satisfies the conditions of (α) formula (S1) (conditions regarding the supporting position of the catalyst particles constituting the electrode catalyst and the number of catalyst particles at that supporting position) and (β) the condition that the nanopores are formed in the shape of the aforementioned interconnected pores (conditions regarding the microstructure of the nanopores constituting the support of the electrode catalyst). Therefore, it is clear that even if the chemical composition of the catalyst particles is changed, the same result can be obtained. That is, it is obvious that as long as the three-dimensional structure of the present invention is present, regardless of whether the catalyst particles are Pt alloy particles containing Pt, which are the same as those composed of Pt particles, or core-shell particles with a Pt shell, they can exhibit the same excellent Pt mass activity as in the above embodiments.

[0497] Industrial availability

[0498] The electrode catalyst of the present invention exhibits excellent catalytic activity. Furthermore, GDEs, CCMs, MEAs, and fuel cell stacks containing the catalyst layer of the present invention demonstrate excellent battery performance that contributes to the cost reduction of PEFCs.

[0499] Therefore, this invention is applicable not only to the electrical equipment industry such as dye-coated batteries, fuel cell vehicles, and portable mobile devices, but also to ENE-FARM (home fuel cell cogeneration system), cogeneration system, etc., which is conducive to the development of the energy industry and related environmental protection technology industries.

Claims

1. A catalyst for an electrode, wherein, It contains: a conductive hollow carbon support with nanopores having a fine pore size of 1-20 nm, and multiple catalyst particles supported on the support. At least a portion of the surface of the catalyst particles has a region composed of Pt with zero valence. The catalyst particles are supported both inside and outside the nanopores of the support. When analyzing the particle size distribution of the catalyst particles using three-dimensional reconstructed images obtained by scanning transmission electron microscopy (STEM) with electron beam tomography, the following condition (S1) must be satisfied. 100×(N10 / N20)≤8.0……(S1) In the formula (S1), N10 represents the number of non-contact particles obtained by adding the number of noble metal particles n101 (which can be confirmed by electron beam tomography as not being in contact with pores larger than 1 nm) and the number of noble metal particles n102 (which are not in contact with the hollow carbon support itself but exist on its exterior), i.e., N10 = n101 + n102. N20 represents the number of catalyst particles supported inside the nanopores of the carrier.

2. The electrode catalyst according to claim 1, wherein, In the three-dimensional reconstructed image of the STEM, focusing on a catalyst block composed of catalyst particles and a support, which can be housed in a space of a cuboid with one side of 60–300 nm, and observing six square cross-sections of a cubic image with one side of 20–50 nm extracted from the internal region of the catalyst block, at least one nanopore is formed in at least one cross-section. The nanopore formed in at least one of the cross sections of the six squares has at least one opening connected to a first side of the four sides of the cross section of the square, and at least one opening connected to a second side of the cross section of the square parallel to the first side, and has the shape of a connecting hole that extends continuously and unobstructedly from the opening on the first side to the opening on the second side.

3. The electrode catalyst according to claim 2, wherein, The connecting hole has a multi-branched shape.

4. The electrode catalyst according to claim 3, wherein, The connecting hole has two or more openings on the first side.

5. The electrode catalyst as described in claim 4, wherein, The connecting hole has two or more openings on the second side.

6. The electrode catalyst as described in claim 3 or 4, wherein, The connecting hole has at least one opening on the third side perpendicular to the first side.

7. The electrode catalyst according to claim 6, wherein, The connecting hole has at least one opening on the fourth side perpendicular to the first side.

8. The electrode catalyst according to at least one of claims 1 to 5, wherein, The porosity measured using the three-dimensional reconstructed image obtained using the STEM is greater than 35%.

9. The electrode catalyst according to at least one of claims 1 to 5, wherein, The nanopores have a diameter of 1–10 nm.

10. The electrode catalyst according to at least one of claims 1 to 5, wherein, The hollow carbon support also has micropores with a pore size of less than 1 nm.

11. The electrode catalyst according to at least one of claims 1 to 5, wherein, The catalyst particles are composed of Pt with a zero valence.

12. The electrode catalyst according to at least one of claims 1 to 5, wherein, The catalyst particles are composed of Pt alloy.

13. The electrode catalyst according to at least one of claims 1 to 5, wherein, The catalyst particles are core-shell catalyst particles, which have a core particle and a Pt shell layer on at least a portion of the surface of the core particle, which is a region composed of the zero-valent Pt.

14. The electrode catalyst according to at least one of claims 1 to 5, wherein, When analyzing the particle size distribution of the catalyst particles using the three-dimensional reconstructed images from the STEM, the following condition (S1) must be satisfied: 100×{N10 / (N20+N30)}≤5.0……(S2) In the formula (S2), N10 is the same as N10 in the above formula (S1); N20 is the same as N10 in the above formula (S1); N30 represents the number of catalyst particles supported on the outside of the nanopores of the carrier.

15. The electrode catalyst according to at least one of claims 1 to 5, wherein, When performing particle size distribution analysis of the catalyst particles using the three-dimensional reconstructed images from the STEM, Regarding the catalyst particles supported inside the nanopores of the carrier, the average distance from the inlet of the nanopore to the support position of the catalyst particles is 5.0 nm or more.

16. The electrode catalyst according to at least one of claims 1 to 5, wherein, When performing particle size distribution analysis of the catalyst particles using the three-dimensional reconstructed images from the STEM, The catalyst particles supported inside the nanopores of the carrier exist in a range of 0 to 27 nm from the inlet of the nanopore to the location where the catalyst particles are supported.

17. The electrode catalyst according to at least one of claims 1 to 5, wherein, In the case of analyzing the particle size distribution of the catalyst particles using the STEM three-dimensional reconstructed images, The catalyst particles supported inside the nanopores of the carrier have a particle size greater than 0 nm and less than 7 nm.

18. The electrode catalyst according to at least one of claims 1 to 5, wherein, When the particle size distribution of the catalyst particles is analyzed using the STEM three-dimensional reconstruction image, the proportion of the catalyst particles loaded inside the nanopores is more than 50%.

19. The electrode catalyst as claimed in claim 18, wherein, When the particle size distribution of the catalyst particles is analyzed using the STEM three-dimensional reconstruction image, the proportion of the catalyst particles loaded inside the nanopores is more than 70%.

20. The electrode catalyst according to at least one of claims 1 to 5, wherein, At least a portion of the region on the surface of the catalyst particle composed of zero-valent Pt is coated with a Pt oxide film.

21. The electrode catalyst according to at least one of claims 1 to 5, wherein, The hollow carbon support has a BET specific surface area of ​​200–1500 m². 2 / g, where the BET specific surface area is the nitrogen adsorption specific surface area.

22. A powder of a catalyst for electrodes, wherein, An electrode catalyst containing 10 wt% or more of any one of claims 1 to 21.

23. A composition for forming a gas diffusion electrode, wherein, Powder containing any one of the electrode catalysts according to claims 1 to 21 or the electrode catalyst according to claim 22.

24. A gas diffusion electrode, wherein, Powder containing any one of the electrode catalysts according to claims 1 to 21 or the electrode catalyst according to claim 22.

25. A membrane-electrode junction, in, It contains the gas diffusion electrode as described in claim 24.

26. A fuel cell stack, wherein, It contains the membrane-electrode junction as described in claim 25.

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