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 carbon carrier having nanopores with a pore diameter of 1 to 20 nm, and a plurality of catalyst particles supported on the carrier. The catalyst particles contain Pt (0 valence), are supported inside and outside the nanopores of the carrier, and in a 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 STEM, the proportion of the catalyst particles supported inside the nanopores is 50% or more, and at least one nanopore having the shape of a continuous communication hole is formed in a cubic image having one side of 20 to 50 nm obtained from the three-dimensional reconstruction image of the catalyst block.

Description

Technical Field

[0001] This invention relates to electrode catalysts using hollow carbon as a support. More specifically, it relates to an electrode catalyst suitable for a gas diffusion electrode, and further to an electrode catalyst more suitable for a gas diffusion electrode in a fuel cell.

[0002] In addition, the present invention relates to a composition for forming a gas diffusion electrode containing the above-mentioned electrode catalyst particles, a membrane-electrode assembly, and a fuel cell stack. Background Technology

[0003] Solid polymer fuel cells (PEFCs) are being developed for use as power sources in fuel cell vehicles and residential cogeneration systems.

[0004] The catalyst used in the gas diffusion electrode of PEFC is a noble metal catalyst composed of noble metal particles of platinum group elements such as platinum (Pt).

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

[0006] In the manufacturing cost of PEFC, precious metal catalysts such as Pt account for a large proportion of the cost, which has become a technical problem for reducing the cost of PEFC and popularizing PEFC.

[0007] In these research and development efforts, in order to reduce the amount of platinum used, existing technologies have explored powders (hereinafter referred to as "core-shell catalysts") having a core-shell structure of catalyst particles (hereinafter referred to as "core-shell catalyst particles") with a core composed of non-platinum elements and a shell composed of Pt, and there are numerous reports on this.

[0008] For example, Patent Document 1 discloses a particulate composite material (relative to core-shell catalyst particles) having a structure in which a thin layer (relative to the shell) of palladium (Pd) or Pd alloy (corresponding to the core) is covered by Pt atoms. Furthermore, Patent Document 1 describes, as an example, core-shell catalyst particles having a structure in which the core is a Pd particle and the shell is a layer made of Pt.

[0009] On the other hand, as a support for the catalyst for the electrode, there are hollow carbon with more pores inside the primary particles and solid carbon with fewer pores inside the primary particles compared to hollow carbon, and the performance improvement can be achieved by leveraging their respective characteristics.

[0010] For example, in Patent Literature 2, a case where hollow carbon is employed as a carrier is disclosed. Further, in Patent Literature 3, a case where mesocarbon is employed as a carrier is disclosed. For example, in Patent Literature 2, as shown in FIG. 2, a structure of an electrode catalyst 200 for a fuel cell is disclosed, 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 mode diameter of a pore distribution is controlled to a prescribed range, and catalyst particles 230 are supported in the pores P220 of the carrier 220. Figure 10

[0011] In Patent Literature 2, it is mentioned that, by this, it is possible to prevent the catalyst particles 230 present in the primary pores P220 from adsorbing a high-molecular electrolyte on the surface thereof, and it is possible to sufficiently ensure the gas transportability 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 it is possible to provide a catalyst layer for a fuel cell that exhibits excellent power generation performance even when the amount of catalyst is reduced.

[0012] Further, for example, in Patent Literature 3, an electrode catalyst for a fuel cell (PtCo / C catalyst) having catalyst particles containing 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 the acid treatment is performed at 70 to 90°C.

[0013] In Patent Literature 3, when the PtCo alloy is supported on the hollow carbon carrier, a part of the PtCo alloy is contained in the inside of the hollow carbon carrier, and even when the acid treatment for suppressing the elution of Co is performed, it is difficult to sufficiently treat the PtCo alloy present in the inside of the carrier, and as a result thereof, there is a phenomenon in which Co is easily eluted from the PtCo alloy present in the inside of the carrier, and this is considered to be a technical problem.

[0014] 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 where the PtCo alloy is contained in the inside of the carrier. It is further disclosed that, by this, it is possible to perform sufficient acid treatment of the PtCo alloy, and it is possible 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 of the fuel cell.

[0015] Here, in Patent Literature 3, the mesocarbon is defined as follows.

[0016] ​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.

[0017] 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, and 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] After that, in Non-Patent Literature 2, the research group of Uchida et al. of the University of Shizuoka 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

[0026] 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.

[0027] 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, 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, referred to as "Pt / CB" in this specification).

[0028] 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.

[0029] ​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 15 and Figure 19 ) 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.

[0030] 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 taken from a specific one direction of a measurement sample are analyzed. In addition, the analysis method of Non-Patent Literature 2 is a method in which two-dimensional images of an SEM image 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 taken from a specific one direction of a measurement sample 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, which is the subject of analysis, cannot be sufficiently determined as being inside or outside of a hollow carbon support.

[0031] 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 the same in accordance with various reports, and thus 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 15 and Figure 19 ) which is the subject of analysis (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

[0032] In addition, as a publication in which the above-described known inventions are described, the applicant of the present patent suggests the following publications.

[0033] Prior Art Literature

[0034] Patent Literature

[0035] Patent Literature 1: U.S. Patent Application Publication No. 2007 / 31722

[0036] Patent Literature 2: Japanese Patent Application Laid-Open No. 2013-109856

[0037] Patent Literature 3: International Publication WO 2016 / 063968

[0038] Patent Literature 4: International Publication WO 2019 / 221168

[0039] Non-Patent Literature

[0040] Non-Patent Literature 1: Nature Materials, Vol 19 (January 2020) 77-85

[0041] Non-Patent Literature 2: Journal of Power Sources, 315 (2016) 179-191 SUMMARY

[0042] Technical problem to be solved by the invention

[0043] In order to popularize PEFC, for an electrode catalyst, in order to reduce the amount of Pt used and reduce the material cost, further improvement of catalyst activity is required.

[0044] The present inventors found that, in the case of performing analysis of the particle size distribution of catalyst particles in a three-dimensional reconstruction image obtained by electron tomography measurement using STEM (scanning transmission electron microscope) for an electrode catalyst such as a Pt / C catalyst, there has been 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 primary particle more than in the exterior has been actually successfully synthesized, and thus there is room for improvement.

[0045] The present invention is an invention made in view of this technical problem, and aims to provide an electrode catalyst having excellent catalyst activity that can contribute to the cost reduction of PEFC.

[0046] 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 containing the above electrode catalyst.

[0047] Technical solution for solving the technical problem

[0048] The present inventors and the like have intensively investigated an electrode catalyst in which catalyst particles of a Pt / C catalyst or the like are supported in the interior of a Nanopore of a hollow carbon primary particle, with respect to a structure that achieves further improvement of catalyst activity.

[0049] 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.

[0050] More specifically, the present invention is constituted by the following technical solutions.

[0051] That is, the present application provides an electrode catalyst containing: a hollow carbon carrier having a nanopore with a pore diameter of 1 to 20 nm, and a plurality of catalyst particles supported on the carrier,

[0052] A region composed of Pt (0 valence) is formed on at least a part of the surface of the catalyst particle,

[0053] The catalyst particle is supported inside the nanopore and outside the nanopore of the carrier,

[0054] In a 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 proportion of the catalyst particle supported inside the nanopore is 50% or more,

[0055] In the three-dimensional reconstruction image of the STEM, a catalyst block composed of the catalyst particle and the carrier that can be accommodated in a space of a cuboid with one side of 60 to 300 nm is focused on, and in a case where 6 square cross sections of a cubic image with one side of 20 to 50 nm extracted from the internal region of the catalyst block are observed, at least one nanopore is formed in at least one cross section,

[0056] The nanopore formed in at least one of the 6 square cross sections has at least one opening in contact with a first side among four sides of the square cross section, and at least one opening in contact with a second side of the square cross section parallel to the first side, and has a shape of a communication hole continuously extending without obstruction from the opening of the first side to the opening of the second side.

[0057] In the electrode catalyst of the present application, in a case where the fine structure is observed using a STEM three-dimensional reconstruction image, by satisfying the condition that the proportion of the catalyst particle supported inside the nanopore is 50% or more (α), and the condition that the nanopore is formed in the above-described shape of the communication hole (β), an excellent catalyst activity that contributes to the cost reduction of a PEFC can be exhibited.

[0058] The reason why the electrode catalyst of the present application has excellent catalyst activity is not sufficiently clear.

[0059] However, the present inventors believe as follows.

[0060] That is, in the case of observing the microstructure using the STEM three-dimensional reconstruction image, (α) the electrode catalyst of the present application in which the proportion of the catalyst particles supported inside the nanopores is 50% or more has a larger number of catalyst particles with a smaller particle diameter and higher activity inside the nanopores of the support, compared with the conventional electrode catalyst.

[0061] Such catalyst particles supported inside the nanopores of the support are supported in a state in which it is difficult to directly contact the polymer electrolyte present inside the catalyst layer, in the case of being used for the catalyst layer of the gas diffusion electrode of the PEFC. Therefore, the electrode catalyst of the present application reduces the decrease in catalyst activity caused by poisoning of the Pt component, and can exhibit superior catalyst activity after being polarized, compared with the conventional electrode catalyst. In addition, the electrode catalyst of the present application also reduces the elution of the Pt component from the catalyst particles.

[0062] 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 of performing the particle size distribution analysis of the above catalyst particles using the three-dimensional reconstruction image obtained by electron beam tomography measurement using STEM (scanning transmission electron microscope), the proportion of the above catalyst particles supported inside the above nanopores is preferably 70% or more.

[0063] In addition, in the case of observing the microstructure using the STEM three-dimensional reconstruction image, (β) the electrode catalyst of the present application in which the nanopores are formed in the shape of the above communication holes has superior diffusivity of water and protons and reaction gases (hydrogen, oxygen, or air) contained therein, and the catalyst particles supported inside the nanopores are easily utilized for the reaction, in the case of being used for the catalyst layer of the gas diffusion electrode of the PEFC. Therefore, from this viewpoint, the electrode catalyst of the present application can also exhibit superior catalyst activity.

[0064] Here, in the present application, the "analysis method of the particle size distribution of the above catalyst particles using the three-dimensional reconstruction image obtained by electron beam tomography measurement using STEM (scanning transmission electron microscope)" refers to an analysis method using the analysis method of the STEM (scanning transmission electron microscope) of UBE Scientific Analysis Center, Ltd., and indicates an analysis method in which electron beam tomography measurement is performed, and image analysis is performed on the obtained measurement data using image analysis software ("Avizo" manufactured by FEI Company) (analysis method name: "USAL-KM3D analysis method").

[0065] In the USAL-KM3D analysis method, the measurement sample to be the measurement object is produced by the following procedure and conditions.

[0066] <Measurement sample preparation method, conditions>

[0067] First, in order to be able to optimally measure the structure of a measurement sample, on a "Cu grid with carbon support film" for TEM observation, using a general electron microscope sample preparation method, i.e., a dispersion method, preparation is performed in a manner satisfying the following conditions.

[0068] (A) The powder pieces of the measurement target sample (electrode catalyst) having a length or a short diameter in the range of about 60 to 300 nm (refer to the powder pieces of the measurement target sample (electrode catalyst) described later) are present on the above grid at a moderate frequency {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)} that enables measurement (observation). Figure 11 , Figure 15 and Figure 19

[0069] (B) When the above grid is rotated around its rotation axis by a rotation angle of ±80°, the photographed image of the powder pieces of the measurement sample does not overlap with the photographed image of other fine powder pieces. If the photographed image of the powder pieces of the measurement sample overlaps with the photographed image of other fine powder pieces, three-dimensional analysis cannot be performed.

[0070] (C) With respect to the powder pieces of the measurement sample, a plurality of powder pieces that can be seen within the measurement region are arranged separately from each other to a degree that enables 3D tomographic observation.

[0071] <Measurement Conditions>

[0072] With respect to the nano-pores of 1 nm or more among the fine pores contained in the powder pieces of the measurement target sample (electrode catalyst), 3D tomographic observation is performed under conditions (for example, adjustment of the acceleration voltage of an electron beam, etc.) that enable three-dimensional observation and discrimination of the powder pieces of the measurement target sample (electrode catalyst) without causing damage thereto.

[0073] The "nanopore" of a hollow carbon support refers to a fine pore having a fine pore diameter of 1 to 20 nm, and the "micropore" refers to a fine pore having a fine pore diameter of less than 1 nm. In addition, in the present application, the "fine pore diameter of a nanopore" refers to the "size of the entrance of a nanopore". The "fine pore diameter of a micropore" refers to the "size of the entrance of a micropore".

[0074] In the present application, the "fine pore diameter (size of the entrance of a pore)" of a nanopore refers to the "size of the entrance of a nanopore" obtained by three-dimensional reconstruction images in the case where an electrode catalyst is analyzed using electron beam tomography measurement using a general STEM (scanning transmission electron microscope).

[0075] ​More preferably, in the present application, the "pore diameter (size of the entrance of the pore)" of the nanopore means the size of the entrance of the nanometer-sized pore obtained by the above-described "USAL-KM3D analysis method".

[0076] More specifically, the "size of the entrance of the nanometer-sized pore" means the diameter of a circle (equivalent circle diameter) having the same area as the area of the entrance of the nanometer-sized pore obtained from the image of the entrance of the nanometer-sized pore obtained by the "USAL-KM3D analysis method".

[0077] Next, the method using the STEM three-dimensional reconstruction image for confirming the condition (β) in the present application in which the catalyst is formed into the above-described shape of the communication hole will be described.

[0078] The confirmation of the condition (β) can be performed by using the three-dimensional reconstruction image obtained by the analysis of the electrode catalyst by electron beam tomography measurement using a general STEM (scanning transmission electron microscope). However, from the viewpoint of reliably confirming the condition (β), it is preferable to perform using the STEM three-dimensional reconstruction image obtained in the process of performing the above-described USAL-KM3D analysis method.

[0079] The procedure for confirming the condition (β) will be described below.

[0080] (D) First, the STEM three-dimensional reconstruction image is obtained with respect to the catalyst to be measured. From among the catalyst blocks (blocks composed of catalyst particles and hollow carbon supports) reflected in the three-dimensional reconstruction image, a catalyst block housed in a space (region of interest) having one side of 60 to 300 nm is selected. This procedure can be easily understood, for example, by referring to the cubic image extracted from the 3D-STEM image (three-dimensional reconstruction image) of the catalyst block of the catalyst of Example 1, Example 2, and Comparative Example 2 described below (see Figs. 1, 2, and 3, respectively). Figure 24 (a), Figure 24 (f) and Figure 24 (k) ).

[0081] (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, for example, by referring to the cubic image obtained from the 3D-STEM image (three-dimensional reconstruction image) of the catalyst block of the catalyst of Example 1, Example 2, and Comparative Example 2 described below (see Figs. 4, 5, and 6, respectively). Figure 24 (b), Figure 24 (g) and Figure 24 (1) ).

[0082] After (F), a stereoscopic image (a 3D-STEM image) of the inside of the catalyst block obtained in the step of (E) is observed, and the void portion (the portion of fine pores such as nano-pores) and the hollow carbon support portion are divided using the difference in brightness.

[0083] More specifically, the stereoscopic image (the 3D-STEM image) is constituted in a state of being divided into smaller cubes of pixels (voxels). Then, brightness (unitless) is held in each pixel (voxel). Then, the analyst divides (binarizes) the void portion (the portion of fine pores such as nano-pores) and the hollow carbon support portion of the stereoscopic image (the 3D-STEM image) by setting an appropriate threshold value for the brightness. For a certain pixel (voxel), it is automatically determined as the carbon portion as long as its brightness is above the threshold value. In addition, for a certain pixel (voxel), it is automatically determined as the void portion as long as its brightness is below the threshold value. This division can be performed by setting the same threshold value of brightness for all the pixels (voxels) contained in the same stereoscopic image (the 3D-STEM image). For different stereoscopic images (the 3D-STEM images), the analyst can set different threshold values of brightness (threshold values suitable for division).

[0084] From the viewpoint of more accurately performing the division, it is preferable that the size of the pixel (voxel) be a cube of which one side is 1 nm or less.

[0085] In addition, in the present application, in the case where the porosity of the stereoscopic image (the 3D-STEM image) of the catalyst block described later is measured, the catalyst particles are regarded as voids at the time of the division.

[0086] For the step of (F) as well, it can be easily understood, for example, by referring to the stereoscopic images extracted from the 3D-STEM images (the 3D-STEM images) of the catalyst blocks of the catalysts for electrodes of Example 1, Example 2, and Comparative Example 2 described later (refer to the stereoscopic images of (a), (b), (c), (d), (e), (f), (g), (h), (i), (j), (k), (1), (m), (n), and (o) described later). Figure 24 (b), Figure 24 (g) and Figure 24 (1)). Further, it can be easily understood by referring to the 3 cross sections (3 cross sections after division) of the stereoscopic images (the 3D-STEM images) obtained from the catalyst blocks of Example 1, Example 2, and Comparative Example 2 (refer to the 3 cross sections of (a), (b), (c), (d), (e), (f), (g), (h), (i), (j), (k), (1), (m), (n), and (o) described later). Figure 24 (c), Figure 24 (d), Figure 24 (e), Figure 24 (h), Figure 24 (i), Figure 24 (j), Figure 24 (m), Figure 24 (n) and Figure 24 (o)).

[0087] (G) After that, in a case where the six square cross sections of the stereoscopic image (three-dimensional reconstruction image of STEM) after the division in the step of (F) are observed, it is confirmed whether at least one nano-pore (communicating pore) having at least one of the following shapes is formed in at least one cross section.

[0088] That is, it is confirmed whether the nano-pore (communicating pore) seen in the cross section of the square of interest has at least one opening which is contiguous to a first side and at least one opening which is contiguous to a second side parallel to the first side, among the four sides of the cross section. Further, it is confirmed whether the nano-pore has a shape of a communicating pore which continuously extends without obstruction from the opening of the first side to the opening of the second side.

[0089] For example, when explained with reference to the example of Embodiment 1 described later, as shown in FIG. 1, the nano-pore P1 seen in the cross section of the square of interest (x-y plane) has two openings (opening A11 and opening A12) which are contiguous to a first side L1. In addition, the nano-pore P1 has two openings (opening A21 and opening A22) which are contiguous to a second side L2 parallel to the first side L1. Further, the nano-pore P1 has a shape of a communicating pore which 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 25

[0090] In addition, from the viewpoint of more reliably obtaining the effects of the present application, in the electrode catalyst of the present application, the nano-pore (communicating pore) seen in the cross section of the square of the stereoscopic image of interest preferably has a shape with multiple branches (see FIG. 1). Figure 25 In a case where the catalyst particles supported inside such a nano-pore are used for the catalyst layer of the gas diffusion electrode of a PEFC, it is easy to be supported in the state where it is more difficult to come into contact with the polymer electrolyte present inside the catalyst layer. In addition, the diffusivity of water and the protons or the reaction gas (hydrogen, oxygen or air) contained therein of such a nano-pore is excellent. Therefore, in a case where the electrode catalyst having such a nano-pore is used for the catalyst layer of the gas diffusion electrode of a PEFC, the catalyst particles supported inside the nano-pore are easily utilized for the electrode reaction of the PEFC.

[0091] Further, from the viewpoint of more reliably obtaining the effects of the present application, based on the same reason as described above, in the electrode catalyst of the present application, the nano-pore (communicating pore) seen in the cross section of the square of the stereoscopic image of interest preferably has two or more openings on the first side (see FIG. 1). Figure 25

[0092] ​​Further, from the viewpoint of more reliably obtaining the effects of the present application, based on the same reason as described above, in the electrode catalyst of the present application, the nanopores (communication holes) seen in the square cross section of the cubic image of interest preferably have two or more openings on the second side (see FIG. 2). Figure 25 ).

[0093] Further, from the viewpoint of more reliably obtaining the effects of the present application, based on the same reason as described above, in the electrode catalyst of the present application, the nanopores (communication holes) seen in the square cross section of the cubic image of interest preferably have at least one opening on the third side perpendicular to the first side.

[0094] For example, referring to the example of Example 1 described later, as shown in FIG. 6, 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. Figure 25

[0095] Further, from the viewpoint of more reliably obtaining the effects of the present application, based on the same reason as described above, in the electrode catalyst of the present application, the nanopores (communication holes) seen in the square cross section of the cubic image of interest preferably have at least one opening on the fourth side perpendicular to the first side.

[0096] For example, referring to the example of Example 1 described later, as shown in FIG. 6, 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. Figure 2

[0097] Further, from the viewpoint of more reliably obtaining the effects of the present application, in the electrode catalyst of the present application, the porosity determined 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 determined using the three-dimensional reconstruction image (cubic image of interest) of STEM is preferably 80% or less, more preferably 75% or less.

[0098] ​​In addition, in the electrode catalyst of the present application, the hollow carbon support preferably has a large number of nano-pores having a pore size (size of the entrance of the pore) of 1 to 10 nm. It has been reported that the diameter of the micelle 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 having a large number of fine pores having a pore size (size of the entrance of the pore) of 1 to 10 nm, the polymer electrolyte is difficult to intrude into the nano-pores, and the contact of the catalyst particles supported in the inside of the nano-pores with the polymer electrolyte can be more reliably prevented.

[0099] Further, in the electrode catalyst of the present application, the hollow carbon support can further have micropores having a pore size of less than 1 nm, within a range in which the effects of the present application can be obtained.

[0100] Further, from the viewpoint of more reliably obtaining the effects of the present application, the hollow carbon support is preferably a "CNovel" (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 the hollow carbon supports that satisfy the conditions (α) and (β) described above when the electrode catalyst is produced.

[0101] The CNovel is a porous carbon having at least nano-pores having a pore size of 1 to 20 nm and a carbon wall constituting the periphery of the nano-pores, and the carbon wall has a portion that becomes a layered structure, and the carbon wall forms a three-dimensional network structure, the nano-pores are open pores, and the nano-pores have a continuous shape (shape of the communication hole. Refer to "a plurality of nano-pores P22 connected communication hole PI" described later Figure 1 ), and when the catalyst is produced, has a structure that easily satisfies the condition (β) described above.

[0102] In addition, in the electrode catalyst of the present application, the catalyst particles can be composed of Pt (0 valence).

[0103] Further, in the electrode catalyst of the present application, the catalyst particles can be composed of a Pt alloy. The kind of metal that becomes an element of the alloy other than Pt is not particularly limited. From the viewpoint of obtaining excellent catalyst activity, the kind of metal that becomes an element of the alloy other than Pt is preferably at least one metal among Co and Ni.

[0104] In addition, in the electrode catalyst of the present application, the above-mentioned catalyst particles can be core-shell catalyst particles. In this case, from the viewpoint of obtaining excellent catalyst activity, the core-shell catalyst particles are preferably those having a core particle, and a Pt shell layer (a region composed of Pt (0 valence)) formed on at least a part of the surface of the core particle. The kind 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 preferable. 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 noble metal, an oxide of the base metal, a nitride of the base metal, and a carbide of the base metal.

[0105] 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-mentioned catalyst particles is performed using a three-dimensional reconstruction image obtained by electron beam tomography measurement using a STEM (scanning transmission electron microscope), it is preferable to satisfy the following condition of formula (1).

[0106] (D10 / D20) ≥ 0.80... (1)

[0107] In the above-mentioned formula (1) of the above-mentioned formula, D10 represents the arithmetic mean of the equivalent spherical diameters of the above-mentioned catalyst particles carried in the interior of the above-mentioned nanopores of the above-mentioned support, and D20 represents the arithmetic mean of the equivalent spherical diameters of the above-mentioned catalyst particles carried in the exterior of the above-mentioned nanopores of the above-mentioned support.

[0108] By carrying the catalyst particles in the hollow carbon support in such a manner that the above-mentioned condition of formula (1) is satisfied, the electrode catalyst of the present application can more reliably exhibit excellent catalyst activity that contributes to the cost reduction of a PEFC.

[0109] Here, from the viewpoint of more reliably obtaining the effects of the present application, the value of (D10 / D20) of the above-mentioned formula (1) is preferably 0.85 or greater, and further preferably 0.90 or greater.

[0110] 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 analysis of the particle size distribution of the above-mentioned catalyst particles is performed using a three-dimensional reconstruction image obtained by electron beam tomography measurement using a STEM (scanning transmission electron microscope), it is more preferable to further satisfy the following conditions of formulas (2) and (3) simultaneously.

[0111] D1 ≤ D2... (2)

[0112] (N1 / N2) > 1.0 (3)

[0113] In the above formula (2) and the above formula (3), D1 represents an equivalent spherical diameter of a particle showing the maximum frequency (the maximum number of particles) among the above catalyst particles loaded inside the above nanopores of the above carrier. In the above formula (2) and the above formula (3), D2 represents an equivalent spherical diameter of a particle showing the maximum frequency (the maximum number of particles) among the above catalyst particles loaded outside the above nanopores of the above carrier.

[0114] In the above formula (2) and the above formula (3), N1 represents the frequency (the number of particles) of a particle showing the maximum frequency (the maximum number of particles) among the above catalyst particles loaded inside the above nanopores of the above carrier. In the above formula (1) and the above formula (2), N2 represents the frequency (the number of particles) of a particle showing the maximum frequency (the maximum number of particles) among the above catalyst particles loaded outside the above nanopores of the above carrier.

[0115] By loading the catalyst particles to the hollow carbon carrier in a manner that the above formula (2) and formula (3) are satisfied at the same time, the electrode catalyst of the present application can more reliably exhibit the excellent catalyst activity that can contribute to the cost reduction of the PEFC.

[0116] Further, in the electrode catalyst of the present application, at least a part of the region of the surface of the catalyst particles composed of Pt (0 valence) can also be coated with the Pt oxide coating film, within a range in which the catalyst particles can exhibit the excellent catalyst activity.

[0117] Further, from the viewpoint of more reliably obtaining the effects of the present application, in the electrode catalyst of the present application, the BET specific surface area (nitrogen adsorption specific surface area) of the above hollow carbon carrier is preferably 200 to 1500 m 2 / g.

[0118] 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 carrier is preferably 700 to 1500 m 2 / g, and further preferably 750 to 1400 m 2 / g. Further, in the case where the electrode catalyst is used for the cathode, from the viewpoint of preferably maintaining the prescribed durability 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 carrier is preferably 750 to 900 m 2 / g.

[0119] Further, the present application also provides a powder of an electrode catalyst containing 10 wt% or more of the above-mentioned electrode catalyst of the present application.

[0120] Further, in the powder of an electrode catalyst, the "content other than the above-mentioned electrode catalyst of the present application" means "an electrode catalyst other than the above-mentioned electrode catalyst of the present application". That is, the powder of an electrode catalyst of the present application does not contain a powder that does not function as an electrode catalyst.

[0121] In the powder of an electrode catalyst of the present application, since the above-mentioned electrode catalyst of the present application is contained, excellent catalyst activity that contributes to the cost reduction of a PEFC can be exhibited.

[0122] Here, from the viewpoint of more reliably obtaining the effects of the present application, the content ratio of the above-mentioned electrode catalyst of the present application in the powder of an electrode catalyst of the present application is preferably 30 wt% or more, further preferably 50 wt% or more, more preferably 70 wt% or more, and most preferably 90 wt% or more.

[0123] In the powder of an electrode catalyst of the present application, in addition to the above-mentioned electrode catalyst of the present application, an electrode catalyst (for convenience, referred to as "electrode catalyst P") composed of the following can also be contained.

[0124] That is, the electrode catalyst P contains: a hollow carbon carrier having a nano-pore with a pore diameter of 1 to 20 nm and a plurality of catalyst particles supported on the carrier,

[0125] The catalyst particles are composed of Pt (0 valence),

[0126] The catalyst particles are supported inside the above-mentioned nano-pore of the above-mentioned carrier and outside the above-mentioned fine pores,

[0127] In the case where the analysis of the particle size distribution of the above-mentioned catalyst particles is performed using the above-mentioned "USAL-KM3D analysis method", the proportion of the above-mentioned catalyst particles supported inside the above-mentioned nano-pore has the feature of being "less than 50%".

[0128] The powder of an electrode catalyst of the present application can be composed of the above-mentioned electrode catalyst of the present application and the electrode catalyst P.

[0129] In this case as well, from the viewpoint of more reliably obtaining the effects of the present application, the content ratio of the above-mentioned electrode catalyst of the present application in the powder of an electrode catalyst of the present application is preferably 30 wt% or more, further preferably 50 wt% or more, more preferably 70 wt% or more, and most preferably 90 wt% or more.

[0130] 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.

[0131] 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.

[0132] The gas diffusion electrode forming composition of the present application can easily produce a gas diffusion electrode having excellent catalyst activity (polarization characteristics) that can contribute to the cost reduction of a PEFC, because it contains the electrode catalyst of the present application or the powder of the electrode catalyst of the present application.

[0133] 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.

[0134] The gas diffusion electrode of the present application is constituted by containing the electrode catalyst of the present application. Therefore, it is easily constituted to have excellent catalyst activity (polarization characteristics) that can contribute to the cost reduction of a PEFC.

[0135] Further, the present application provides a membrane-electrode assembly (MEA) containing the gas diffusion electrode of the present application described above.

[0136] The membrane-electrode assembly (MEA) of the present application is easily constituted to have cell characteristics that can contribute to the cost reduction of a PEFC, because it contains the gas diffusion electrode of the present application.

[0137] Further, the present application can provide a fuel cell stack characterized by containing the membrane-electrode assembly (MEA) of the present application described above.

[0138] The fuel cell stack according to the present application is easily constituted to have cell characteristics that can contribute to the cost reduction of a PEFC, because it contains the membrane-electrode assembly (MEA) of the present application.

[0139] Effects of the Invention

[0140] 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.

[0141] Further, according to the present application, it is possible to provide a gas diffusion electrode forming composition containing the above-described electrode catalyst, a gas diffusion electrode, a membrane-electrode assembly (MEA), and a fuel cell stack. BRIEF DESCRIPTION OF DRAWINGS

[0142] Figure 2 is a schematic cross-sectional view showing a preferred one of MEAs of the present application.

[0143] Figure 1 is a schematic cross-sectional view showing Figure 3 is a schematic cross-sectional view showing a preferred one of electrode catalysts of the present application contained in at least one of the cathode catalyst layer and the anode catalyst layer of the MEA shown in

[0144] Figure 2 is a schematic cross-sectional view showing Figure 4 is an enlarged schematic cross-sectional view showing the general structure of the electrode catalyst shown in

[0145] Figure 5 is a schematic cross-sectional view showing another preferred one of MEAs of the present application.

[0146] Figure 6 is a schematic cross-sectional view showing a preferred one of CCMs of the present application.

[0147] Figure 7 is a schematic cross-sectional view showing another preferred one of CCMs of the present application.

[0148] Figure 8 is a schematic cross-sectional view showing a preferred one of GDEs of the present application.

[0149] Figure 9 is a schematic cross-sectional view showing another preferred one of GDEs of the present application.

[0150] Figure 10 is a schematic view showing a preferred one of fuel cell stacks of the present application.

[0151] Figure 11 is a schematic cross-sectional view showing a conventional electrode catalyst.

[0152] Figure 12 is a STEM image of the electrode catalyst of Example 1 using the 3D- electron beam tomography measurement conditions (volume size) of STEM.

[0153] Figure 13 is a 3D-STEM image (three-dimensional reconstruction image) of the electrode catalyst of Example 1.

[0154] Figure 12 is a schematic cross-sectional view showing Figure 14A graph showing the particle size distribution (particle size distribution in terms of equivalent spherical diameter) of the catalyst particles supported inside the nanoholes of the support in the catalyst particles in the catalyst for electrodes of Example 1 obtained by image analysis of the 3D-STEM image of the catalyst for electrodes of Example 1.

[0155] Figure 12 is a STEM image showing the 3D-STEM measurement conditions (volume size) of the catalyst for electrodes of Example 2 using STEM. Figure 15 A graph showing the particle size distribution (particle size distribution in terms of equivalent spherical diameter) of the catalyst particles supported inside the nanoholes of the support in the catalyst particles in the catalyst for electrodes of Example 1 obtained by image analysis of the 3D-STEM image of the catalyst for electrodes of Example 1.

[0156] Figure 16 is a STEM image showing the 3D-STEM measurement conditions (volume size) of the catalyst for electrodes of Example 2 using STEM.

[0157] Figure 17 is a 3D-STEM image (three-dimensional reconstructed image) of the catalyst for electrodes of Example 2.

[0158] Figure 16 is a STEM image showing the 3D-STEM measurement conditions (volume size) of the catalyst for electrodes of Example 2 using STEM. Figure 18 A graph showing the particle size distribution (particle size distribution in terms of equivalent spherical diameter) of the catalyst particles supported inside the nanoholes of the support in the catalyst particles in the catalyst for electrodes of Example 2 obtained by image analysis of the 3D-STEM image of the catalyst for electrodes of Example 2.

[0159] Figure 16 is a STEM image showing the 3D-STEM measurement conditions (volume size) of the catalyst for electrodes of Example 2 using STEM. Figure 19 A graph showing the particle size distribution (particle size distribution in terms of equivalent spherical diameter) of the catalyst particles supported inside the nanoholes of the support in the catalyst particles in the catalyst for electrodes of Example 2 obtained by image analysis of the 3D-STEM image of the catalyst for electrodes of Example 2.

[0160] Figure 20 is a STEM image showing the 3D-STEM measurement conditions (volume size) of the catalyst for electrodes of Example 2 using STEM.

[0161] Figure 21 is a 3D-STEM image (three-dimensional reconstructed image) of the catalyst for electrodes of Example 2.

[0162] Figure 20 is a STEM image showing the 3D-STEM measurement conditions (volume size) of the catalyst for electrodes of Example 2 using STEM. Figure 22A graph of the particle size distribution (particle size distribution in terms of equivalent spherical diameter) of the catalyst particles supported in the inside of the nano-pores of the support in the catalyst particles obtained by image analysis of the 3D-STEM image of the electrode catalyst of Comparative Example 1 shown below.

[0163] Figure 20 is a graph showing Figure 23 A graph of the particle size distribution (particle size distribution in terms of equivalent spherical diameter) of the catalyst particles supported in the outside of the nano-pores of the support in the catalyst particles obtained by image analysis of the 3D-STEM image of the electrode catalyst of Comparative Example 1 shown below.

[0164] Figure 24 is a STEM image showing the 3D-electron beam tomography measurement conditions (volume size) of STEM using the electrode catalyst of Comparative Example 1.

[0165] Figure 25 is a table showing the merging of the recording of a plurality of 3D-STEM images (three-dimensional reconstructed images) obtained by electron beam tomography measurement using STEM for each of the electrode catalysts of Example 1, Example 2, and Comparative Example 2, respectively.

[0166] Figure 24 is a table showing Figure 1 is an enlarged view of the cross section (x-y plane) of the cubic image extracted from the 3D-STEM image (three-dimensional reconstructed image) of the catalyst block of the electrode catalyst of Example 1 shown below.

[0167] Explanation of symbols:

[0168] 1 …… Cathode

[0169] 1A, 1B, 1C …… Gas diffusion electrode (GDE)

[0170] 1c …… Catalyst layer (CL)

[0171] 1m …… Water repellent layer (MPL)

[0172] 1gd …… Gas diffusion layer (GDL)

[0173] 2 …… Anode

[0174] 2c …… Catalyst layer (CL)

[0175] 2m …… Water repellent layer (MPL)

[0176] 2gd …… Gas diffusion layer (GDL)

[0177] 3 Polymer Electrolyte Membrane (PEM)

[0178] 4, 5 Separator

[0179] 10, 11 Membrane-Electrode Assembly (MEA)

[0180] 12, 13 Membrane-Catalyst Layer Assembly (CCM)

[0181] 20 Catalyst for Electrode (Pt / C catalyst)

[0182] 22 Hollow Carbon Support

[0183] 23 Catalyst Particle

[0184] 25 Non-Contact Particle

[0185] 30 Fuel Cell Stack

[0186] P1 Multiple communication holes P22 connected

[0187] P22 Nanopore of Support

[0188] P24 Micropore of Support DETAILED DESCRIPTION

[0189] Hereinafter, preferred embodiments of the present application will be described in detail with appropriate reference to the accompanying drawings.

[0190] <Membrane-Electrode Assembly (MEA)>

[0191] Figure 1 is a schematic cross-sectional view showing a preferred one of MEAs of the present application.

[0192] Figure 1 The MEA 10 shown has a configuration in which two gas diffusion electrodes (cathode 1 and anode 2) in the form of flat plates are arranged in a state of facing each other, and a polymer electrolyte membrane (hereinafter, referred to as "PEM" as needed) 3 is arranged between the cathode 1 and the anode 2.

[0193] In the case of this MEA 10, there is a structure in which at least one of the cathode 1 and the anode 2 contains a catalyst for electrode 20 (Pt catalyst 20) described later.

[0194] The MEA 10 can be manufactured by laminating the cathode 1, the anode 2, and the PEM 3 in the manner shown in Figure 2 and then performing press bonding.

[0195] <Gas Diffusion Electrode (GDE)>

[0196] The cathode 1 as a gas diffusion electrode has a structure provided with a gas diffusion layer 1gd, and a catalyst layer 1c formed on the surface of the gas diffusion layer 1gd on the PEM 3 side. Further, the cathode 1 has a water-repellent layer (Micro Porous Layer, hereinafter, referred to as "MPL" as necessary) 1m disposed between the gas diffusion layer 1gd and the catalyst layer 1c.

[0197] The anode 2 as a gas diffusion electrode also has a structure provided with a gas diffusion layer 2gd, a catalyst layer 2c formed on the surface of the gas diffusion layer 2gd on the PEM 3 side, and an MPL 2m disposed between the gas diffusion layer 2gd and the catalyst layer 2c, similarly to the cathode 1.

[0198] (Catalyst layer (CL))

[0199] 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.

[0200] 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.

[0201] 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.

[0202] (PREFERRED EMBODIMENT OF THE ELECTRODE CATALYST OF THE PRESENT INVENTION)

[0203] Hereinafter, a preferred embodiment of the electrode catalyst of the present application will be described using Figure 3 , Figure 24 , Figure 25 and Figure 2 .

[0204] Figure 1 is a schematic cross-sectional view showing a preferred embodiment of the electrode catalyst contained in at least one of the cathode catalyst layer 1c and the anode catalyst layer 2c of the MEA 10 shown in Figure 3 . In addition, Figure 2 is an enlarged schematic cross-sectional view showing the general constitution of the electrode catalyst 20 shown in Figure 2 .

[0205] As shown in Figure 3 and Figure 24 , the electrode catalyst 20 contains a carrier 22 as a hollow carbon carrier and a catalyst particle 23 supported on the carrier 22.

[0206] Figure 25is a table showing a plurality of 3D-STEM images (three-dimensional reconstruction images) of each of the electrode catalysts for Examples 1 and 2 (the electrode catalyst 20 of the present embodiment) and Comparative Example 2, respectively, measured by electron beam tomography using STEM.

[0207] Figure 24 is a cross-sectional (x-y plane) enlarged view of a cubic image extracted from the 3D-STEM image (three-dimensional reconstruction image) of the catalyst block of the electrode catalyst for Example 1 (the electrode catalyst 20 of the present embodiment) shown in Figure 2-3

[0208] Further, from the viewpoint of more reliably obtaining the effects of the present application, Figure 24 The electrode catalyst 20 shown in

[0209] That is, as described above, the electrode catalyst 20 has a constitution satisfying the conditions of (a) the proportion of catalyst particles supported inside the nanopores is 50% or more, and (b) the nanopores are formed in the above-described shape, in the case of observing the fine structure using the STEM three-dimensional reconstruction image.

[0210] The condition of (a) is described in detail. In the case of observing the fine structure using the information of the STEM three-dimensional reconstruction image obtained by the procedures of (A) to (C) described above, the proportion of catalyst particles 23 supported inside the nanopores P22 is 50% or more in the electrode catalyst 20.

[0211] Further, from the viewpoint of more reliably obtaining the effects of the present application, in the case of performing analysis of the particle size distribution of the catalyst particles 23 using the three-dimensional reconstruction image described above, the proportion of catalyst particles 23 supported inside the nanopores P22 is preferably 55% or more, further preferably 60% or more, and more preferably 70% or more in the electrode catalyst 20.

[0212] The condition of (b) is described in detail. The electrode catalyst 20 has the following structure when observed using the information of the STEM three-dimensional reconstruction image obtained by the procedures of (D) to (G) described above.

[0213] ​More specifically, the electrode catalyst 20 has the following configuration: from the "catalyst block (a catalyst block composed of catalyst particles 23 and the carrier 22 that can be accommodated in a space of a cuboid with one side of 60 to 300 nm) constituting the electrode catalyst 20" that can be seen in the 3D-STEM image (three-dimensional reconstruction image), a "cubic image (one side of 20 to 50 nm)" is further extracted from the six square cross sections of the cubic image, and the six square cross sections are observed, and in at least one cross section, at least one "plurality of nano-pores P22-connected communication holes P1" having the following shape are formed.

[0214] That is, in the electrode catalyst 20, in the case where the microstructure is observed using the 3D-STEM image (three-dimensional reconstruction image), the nano-pore P22 formed on at least one face of the six square cross sections of the cubic image cut from the inside of the catalyst block has at least: at least one opening in contact with a first side among the four sides of the square cross section, and at least one opening in contact with a second side of the square cross section parallel to the first side. Also, the nano-pore P22 has a shape that becomes a communication hole P1 that continuously extends without obstruction from the opening of the first side to the opening of the second side.

[0215] Hereinafter, a more specific description will be given using the example of the electrode catalyst of Example 1 shown in Figure 25 and Figure 24 .

[0216] (D) First, a three-dimensional reconstruction image of STEM is obtained for the electrode catalyst of Example 1 that is the measurement target. From among the catalyst blocks reflected in the three-dimensional reconstruction image, a catalyst block that is accommodated in a space of a cuboid with one side of 60 to 300 nm (a region of interest) is selected as a catalyst block that is the measurement target ( Figure 24 (a)).

[0217] (E) Thereafter, a cubic image (one side of 20 to 50 nm) is extracted from the internal region of the catalyst block of the electrode catalyst of Example 1 selected in the step of (D) Figure 24 (b).

[0218] (F) Thereafter, the cubic image (three-dimensional reconstruction image of STEM) of the inside of the catalyst block of the electrode catalyst of Example 1 obtained in the step of (E) is observed, and the void portion (the portion of the fine pore such as the nano-pore) and the hollow carbon carrier portion are divided using the difference in brightness Figure 25 (b).

[0219] (G) Thereafter, in the case where the six square cross sections of the cubic image of the inside of the catalyst block of the electrode catalyst of Example 1 on which the division is performed in the step of (F) are observed, as Figure 25As 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.

[0220] From the viewpoint of obtaining the effects of the present invention more reliably, such as Figure 25 As shown in Example 1, the nanopores P1 of the electrode catalyst 20 preferably have a multi-branched shape.

[0221] Furthermore, from the viewpoint of more reliably obtaining the effects of the present invention, such as Figure 25 As shown in Example 1, the nanopores P1 of the electrode catalyst 20 preferably have two or more openings on the first side.

[0222] Furthermore, from the viewpoint of more reliably obtaining the effects of the present invention, such as Figure 25 As shown in Example 1, the nanopores P1 of the electrode catalyst 20 preferably have two or more openings on the second side.

[0223] Furthermore, from the viewpoint of more reliably obtaining the effects of the present invention, such as Figure 25 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 25 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.

[0224] Furthermore, from the viewpoint of more reliably obtaining the effects of the present invention, such as Figure 25 As shown in Example 1, the nanopore P1 of the electrode catalyst 20 preferably has at least one opening on the fourth side perpendicular to the first side. For example, referring to the example of Example 1, as... Figure 2 As shown, the nanopore P1 seen in the cross section of interest (the xy plane of the square) also has two openings (opening A41 and opening A42) on the fourth side L4, which is perpendicular to the first side L1.

[0225] Further, from the viewpoint of more reliably obtaining the effects of the present application, in the electrode catalyst 20, the porosity measured using a STEM three-dimensional reconstruction image (a cubic image of interest) is preferably 35% or greater, further preferably 40% or greater, more preferably 45% or greater, even more preferably 50% or greater, still more preferably 55% or greater, yet more preferably 60% or greater, and further more preferably 65% or greater. On the other hand, from the viewpoint of durability, in the electrode catalyst 20, the porosity measured using a STEM three-dimensional reconstruction image (a cubic image of interest) is preferably 80% or less, more preferably 75% or less.

[0226] Here, the catalyst particle 23 has a region composed of Pt (0 valence) formed on at least a part 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.

[0227] 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.

[0228] In the case where the catalyst particle 23 is 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.

[0229] In the case where 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 a core particle, and a Pt shell layer (a region composed of Pt (0 valence)) formed on at least a part 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 metals, it is also possible to contain at least one of a base metal other than a noble metal, an oxide of the base metal, a nitride of the base metal, and a carbide of the base metal in the inside of the core particle.

[0230] In addition, in the electrode catalyst 20, the average value of the unit cell size measured by powder X-ray diffraction (XRD) is preferably 3 to 16.0 nm.

[0231] In addition, the Pt support ratio of the electrode catalyst 20 is preferably 5.6 to 66.5 wt%.

[0232] The carrier 22 is preferably a carrier that satisfies the conditions (α) and (β) described above when made into a catalyst for an electrode. From this viewpoint, as the carrier 22, a carrier that satisfies the conditions (α) and (β) described above when made into a catalyst for an electrode is preferably used among CNovel (manufactured by Toyo Carbon Co., Ltd., product name, registered trademark).

[0233] As shown in FIG. 1, in the present embodiment, the carrier 22 is a porous carbon having nano-pores P22 (fine pore diameter of 1 to 20 nm, preferably fine pore diameter of 1 to 10 nm), micro-pores P24 (fine pore diameter of less than 1 nm), and carbonaceous walls that constitute the periphery of the nano-pores P22. In the carbonaceous walls, there are portions that become a layered structure, and further, a three-dimensional mesh structure is formed in the carbonaceous walls. The crystalline portions of the carbonaceous walls that become a layered structure are developed. Figure 2

[0234] Generally, by performing heat treatment of a carbon material at a temperature or higher, the layered structure can be formed. However, generally, the carbon material shrinks in the heat treatment, and thus the pores collapse, and there is a tendency that the specific surface area becomes small, and when the crystalline portions are developed, it is difficult to obtain a porous carbon having a high specific surface area.

[0235] In contrast to this, the carrier 22 has the nano-pores P22 and the carbonaceous walls that constitute the periphery of the nano-pores P22, and thus can tolerate the shrinkage in the heat treatment, and can sufficiently form the layered structure in the carbonaceous walls and sufficiently secure the specific surface area.

[0236] In addition, the carrier 22 has the carbonaceous walls that become a three-dimensional mesh structure, and thus can realize the high dispersion of the small catalyst particles of the order of several nanometers, and is suitable as a carrier for a catalyst layer of a fuel cell. In addition, the carrier 22 does not need to have the entire carbonaceous walls as a layered structure, and can have amorphous portions in a part thereof.

[0237] In addition, the carrier 22 preferably has a specific surface area of 200 m 2 / g to 1500 m 2 / g. When the specific surface area is 200 m 2 / g or more, it is easy to more reliably form a three-dimensional mesh structure. Thus, it is easy to sufficiently form pores, and it is easy to have sufficient gas adsorption capacity. On the other hand, when the specific surface area is 1500 m 2 / g or less, it is easy to more reliably form carbonaceous walls. Thus, it is easy to form nano-pores P22.

[0238] Here, as shown in FIG. 2, the carrier 22 has a three-dimensional mesh structure in which the nano-pores P22 and the micro-pores P24 are connected to each other by the carbonaceous walls. Figure 2 ​As shown, in the carrier 22, the nanopores P22 are open pores, and have a structure in which the nanopores P22 are continuously linked to form a linked pore Pl. By having this structure, it is possible to make the flow of the reaction gas in the catalyst layer (catalyst layer 1c or catalyst layer 2c) smooth.

[0239] From the viewpoint of the carrier 22 having sufficient electrical conductivity, the specific resistance is preferably 10.0 x 10 2 Ω·cm or less, further preferably 5.0 x 10 2 Ω·cm, and more preferably 1.0 x 10 2 Ω·cm or less.

[0240] In addition, the carrier 22 can also contain pores having a pore diameter of less than 1 nm (pores that are relatively small among pores classified as so-called micropores) and pores having a pore diameter of more than 20 nm and 50 nm or less (pores that are relatively large among pores classified as so-called mesopores) within a range in which the effects of the present application can be obtained.

[0241] Further, the carrier 22 is preferably a hollow carbon carrier that has good dispersibility in a gas diffusion electrode-forming composition containing the electrode catalyst 20, and has excellent electrical conductivity.

[0242] Here, as shown in FIG. 1, the catalyst particles 23 are supported inside the nanopores P22 of the carrier 22 and outside the nanopores P22. Figure 1

[0243] Further, in a case where the electrode catalyst 20 satisfies the conditions of the following formulas (1) to (3) simultaneously in a measurement in which electron tomography by 3D-STEM is performed.

[0244] (D10 / D20) ≥ 0.80 …… (1)

[0245] D1 ≤ D2 …… (2)

[0246] (N1 / N2) > 1.0 …… (3)

[0247] Here, in formulas (1) to (3), D10 represents the arithmetic average of the equivalent spherical diameters of the catalyst particles 23 supported inside the nanopores P22 of the carrier 22.

[0248] In addition, D20 represents the arithmetic average of the equivalent spherical diameters of the catalyst particles 23 supported outside the nanopores P22 of the carrier 22.

[0249] Further, D1 represents the equivalent spherical diameter (nm) of the particle showing the maximum frequency (the maximum number of particles) among the catalyst particles 23 supported inside the nanopores P22 of the carrier 22. ​

[0250] Further, D2 represents an equivalent spherical diameter of a particle showing the maximum frequency (the maximum number of particles) among the catalyst particles 23 supported outside the nanopores P22 of the carrier 22.

[0251] Further, N1 represents the frequency (the number of particles) of a particle showing the maximum frequency (the maximum number of particles) among the catalyst particles 23 supported inside the nanopores P22 of the carrier 22.

[0252] Further, N2 represents the frequency (the number of particles) of a particle showing the maximum frequency (the maximum number of particles) among the catalyst particles 23 supported outside the nanopores P22 of the carrier 22.

[0253] The electrode catalyst 20 satisfying the conditions of the formulae (1) to (3) has, in comparison with the existing electrode catalyst 200, a larger number of catalyst particles 23 of a smaller particle diameter and high activity inside the nanopores P22 of the carrier 22. Such catalyst particles 23 supported inside the nanopores P22 of the carrier 22 exhibit superior catalyst activity after being polarized in comparison with the existing electrode catalyst 200. Further, the catalyst particles 23 are supported in the carrier 22 in a state of not being in direct contact with a high-molecular electrolyte such as Nafion contained in the catalyst layer (catalyst layer 1c or catalyst layer 2c), and the dissolution of Pt components can be reduced.

[0254] Here, from the viewpoint of more reliably obtaining the effects of the present application, the value of (D10 / D20) of the above formula (1) is preferably 0.85 or greater, and further preferably 0.90 or greater.

[0255] As a method of manufacturing the electrode catalyst 20, a "carrier pretreatment step", a "Pt addition step", and a "reduction step" for satisfying the conditions of the formulae (1) to (3) are included, and otherwise, the manufacturing can be performed without particular limitation by a publicly known method.

[0256] In the carrier pretreatment step, the carrier 22 is put into ultrapure water, and a pH adjuster is further added to prepare a dispersion liquid in which the pH is adjusted to 2 to 5. Further, while the dispersion liquid is stirred, the temperature is maintained at 80 to 99°C, and preferably 90 to 99°C for a prescribed time (while maintaining a state of not boiling). After that, the dispersion liquid is cooled to room temperature.

[0257] By this, the gas inside the nanopores P22 of the carrier 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 carrier 22. By this, the precursor of the Pt catalyst particles is supported in a larger number inside the nanopores P22 of the carrier 22.

[0258] Note that, in the carrier pretreatment step, the "ultrapure water" used for the preparation of the above aqueous solution is water having a specific resistance R (reciprocal of conductivity measured by JIS standard test method (JIS K0552)) of 3.0 MΩ-cm or more represented by the following formula (4). In addition, the "ultrapure water" preferably has a water quality corresponding to "A3" prescribed in JIS K0557 "Water used in tests of water and wastewater" or a cleaner water quality.

[0259] The ultrapure water is not particularly limited as long as it has a conductivity satisfying the following formula (4) representing relationship. For example, as the above ultrapure water, there can be mentioned ultrapure water manufactured using an ultrapure water manufacturing device "Milli-Q series" (manufactured by MERCK Corporation) or "Elix UV series" (manufactured by Japan MILLIPORE Corporation).

[0260] R = 1 / p... (4)

[0261] In the above formula (4), R represents specific resistance, and p represents conductivity measured by JIS standard test method (JIS K0552).

[0262] The process after the "carrier pretreatment step" is a "Pt addition step". In the "Pt addition step", an aqueous solution obtained by dissolving a water-soluble Pt salt (N.E. CHEMCAT Corporation, trade name "A-salt" (Fe component concentration: 8 ppm or less)) in ultrapure water is added to the dispersion liquid of the carrier 22 obtained by the "carrier pretreatment step" at room temperature.

[0263] The process after the "Pt addition step" is a "reduction step". In the "reduction step", the temperature of the solution obtained by the "Pt addition step" 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.

[0264] The process after the "reduction process" is a "cleaning process". In the "cleaning process", the solid component in the solution obtained by the "reduction process" is separated from the liquid component, and the solid component (a mixture of the Pt / C catalyst and impurities other than the same) is cleaned. For example, the solid component in the solution obtained by the "reduction process" can be separated from the liquid component using a filter paper, a filter cloth, or the like as a filtration means. The cleaning of the solid component can use the above-described ultrapure water, pure water (specific resistance R represented by the above-described 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 cleaning is repeated until the conductivity of the filtrate after the cleaning reaches less than 10 μS / cm.

[0265] The process after the "cleaning process" is a "drying process". In the "drying process", moisture is separated from the solid component (a mixture of the Pt / C catalyst and water) obtained by the "cleaning process". First, the solid component is air-dried, and then dried in a drier at a predetermined temperature for a predetermined time.

[0266] The process after the "drying process" is a "pulverization process". In the "pulverization process", the solid component (the 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.

[0267] The high-molecular electrolyte contained in the catalyst layer 1c and the catalyst layer 2c of the cathode 1 and the anode 2 is not particularly limited as long as it has hydrogen ion conductivity, and a publicly known high-molecular electrolyte can be used. For example, the high-molecular electrolyte can exemplify a publicly known perfluoroalkane resin having a sulfonic acid group, a carboxylic acid group. As a high-molecular 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.

[0268] After that, Figure 1 In at least one of the catalyst layer 1c of the cathode 1 and the catalyst layer 2c of the anode 2 illustrated in the drawing, the mass ratio N / C of the mass C of the carrier 22 to the mass N of the high-molecular electrolyte is 0.5 to 1.2, and the mass ratio N / C is more preferably 0.7 to 1.0.

[0269] (Gas Diffusion Layer (GDL))

[0270] Figure 1 The gas diffusion layer 1gd provided in the cathode 1 illustrated in the drawing is a layer provided to supply an oxidizing agent 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.

[0271] Furthermore, the gas diffusion layer 2gd of the anode 2 is provided for supplying a reducing agent gas (e.g., hydrogen) to the catalyst layer 2c. Additionally, the gas diffusion layer 2gd also serves to support the catalyst layer 2c.

[0272] Figure 1 The gas diffusion layer (1gd) shown has the function and structure to allow hydrogen or air (oxygen) to pass through effectively to the catalyst layer. Therefore, the gas diffusion layer preferably has water-repellent properties. For example, the gas diffusion layer contains water-repellent components such as polyethylene terephthalate (PTFE).

[0273] There are no particular limitations on the materials that can be used for the gas diffusion layer (1gd), and known materials can be used. For example, carbon paper, or a material obtained by coating the carbon paper with carbon paper as the main raw material and by coating the carbon paper with a by-product consisting of carbon powder as any component, ion-exchanged water, and a polyethylene terephthalate dispersion as a binder.

[0274] (Water-repellent layer (MPL))

[0275] like Figure 1 As 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.

[0276] (Polymer electrolyte membrane (PEM))

[0277] 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.

[0278] <MeA's Transformation Methods>

[0279] 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.

[0280] For example, the MEA of the present invention may also have Figure 4 The structure of MEA11 is shown.

[0281] Figure 4is a schematic cross-sectional view showing another preferred embodiment of the MEA of the present application. Figure 1 The MEA 11 shown is provided with a gas diffusion electrode (GDE) 1A having the same structure as the cathode 1 on only one side of a polymer electrolyte membrane (PEM) 3. Figure 5 The configuration of the gas diffusion electrode (GDE) 1A having the same structure as the cathode 1 in the MEA 10 shown. Among them, the catalyst layer 1c of the gas diffusion electrode (GDE) 1A has the structure of the catalyst layer of the present application. That is, in the catalyst layer 1c of the GDE 1A, the mass ratio N / C of the mass C of the support 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.

[0282] <Membrane-catalyst layer assembly (CCM)>

[0283] Hereinafter, a preferred embodiment of the membrane-catalyst layer assembly (CCM: Catalyst Coated Membrane) of the present application will be described.

[0284] Figure 5 is a schematic cross-sectional view showing another preferred embodiment of the CCM of the present application. Figure 5 The CCM 12 shown has a structure in which a polymer electrolyte membrane (PEM) 3 is provided between a cathode catalyst layer 1c and an anode catalyst layer 2c. Then, at least one of the cathode catalyst layer 1c and the anode catalyst layer 2c has the configuration of the catalyst layer of the present application. That is, in at least one of the cathode catalyst layer 1c and the anode catalyst layer 2c, the mass ratio N / C of the mass C of the support 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.

[0285] <Membrane-catalyst layer assembly (CCM) of a modified embodiment>

[0286] The above describes a preferred embodiment of the CCM of the present application, but the CCM of the present application is not limited to Figure 6 The structure of the CCM 12 shown.

[0287] For example, the CCM of the present application can also have Figure 7 The structure of the CCM 13 shown.

[0288] Figure 6 is a schematic cross-sectional view showing another preferred embodiment of the CCM of the present application. Figure 5 The CCM 13 shown is provided with a gas diffusion electrode (GDE) 1A having the same structure as the cathode 1 on only one side of a polymer electrolyte membrane (PEM) 3. Figure 8The cathode 1 in the CCM 12 shown has the same structure as the structure of the catalyst layer 1c of the GDE IB shown. Among them, the catalyst layer 1c of the GDE IB has the configuration of the catalyst layer of the present application. That is, in the catalyst layer 1c of the CCM 13, the mass ratio N / C of the mass C of the carrier 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.

[0289] <Gas Diffusion Electrode (GDE)>

[0290] Next, a preferred embodiment of the gas diffusion electrode (GDE) of the present application will be described.

[0291] Figure 7 is a schematic cross-sectional view showing a preferred one of the GDEs of the present application. Figure 1 The gas diffusion electrode (GDE) IB shown has the same configuration as the GDE IB shown in Figure 7 The cathode 1 of the MEA 10 shown has the same configuration as the cathode 1 of the CCM 12 shown. Among them, the catalyst layer 1c of the GDE IB has the configuration of the catalyst layer of the present application. That is, in the catalyst layer 1c of the 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.

[0292] <Modified Mode of the Gas Diffusion Electrode (GDE)>

[0293] The above describes a preferred embodiment of the GDE of the present application, but the GDE of the present application is not limited to Figure 8 The structure of the GDE IB shown.

[0294] For example, the GDE of the present application can also have Figure 9 The configuration of the GDE IC shown.

[0295] Figure 8 is a schematic cross-sectional view showing another preferred one of the GDEs of the present application. Figure 8 The GDE IC shown becomes the configuration in which Figure 1 The GDE IC shown does not have the configuration in which the water-repellent layer (MPL) is disposed between the catalyst layer 1c and the gas diffusion layer 1gd, compared to the GDE IB shown.

[0296] <Catalyst Layer Forming Composition>

[0297] Next, a preferred embodiment of the catalyst layer forming composition of the present application will be described.

[0298] The catalyst layer-forming composition of the present embodiment contains the electrode catalyst 20, the polymer electrolyte, and the main component, and the mass ratio N / C of the mass C of the support 22 of the electrode catalyst 20 to the mass N of the polymer electrolyte is 0.5 to 1.2, and is further preferably set to 0.7 to 1.0.

[0299] 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.

[0300] The composition ratio of the electrode catalyst 20, the polymer electrolyte, and other components (water, alcohol, and the like) contained in the catalyst layer-forming composition 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.

[0301] 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 polyol 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.

[0302] Figure 9 At least one of the catalyst layer 1c of the cathode 1 and the catalyst layer 2c of the anode 2 can be formed using the preferred embodiment of the catalyst layer-forming composition suitable for the present application.

[0303] (Method for manufacturing gas diffusion electrode)

[0304] 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.

[0305] 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.

[0306] < Fuel cell stack >

[0307] Figure 9 is a schematic view showing a preferred one embodiment of the fuel cell stack of the present application.

[0308] Figure 1 The fuel cell stack 30 shown has a configuration in which Figure 11The MEA 10 shown is a structure as a single cell and stacking a plurality of the single cell. 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.

[0309] Embodiment

[0310] Hereinafter, the present application will be described more specifically by way of examples, but the present application is not limited to the following examples.

[0311] (I) Preparation of an electrode catalyst used in a catalyst layer of a cathode of an MEA

[0312] (1) Production of a Pt / C catalyst used in a cathode of an MEA of Example 1

[0313] [Pt catalyst particle-supported carbon catalyst "Pt / C catalyst" powder]

[0314] A powder of a Pt / C catalyst in which catalyst particles composed of Pt were supported on a carrier described below was prepared (Pt support rate: 48.0 wt%, trade name "SA50BM-A207", manufactured by N. CHEMCAT Co., Ltd.).

[0315] The powder of the Pt / C catalyst (hereinafter, referred to as "Pt / C catalyst A" as needed) can be prepared by the following procedure.

[0316] (First process (carrier pretreatment process))

[0317] A trial sample product name "C Novel A" (BET specific surface area: 1200 m 2 / g) manufactured by Toyo Carbon Co., Ltd. as a hollow carbon carrier was dispersed in an aqueous solution adjusted to pH = 2 to 5 (prepared by adding a pH adjuster to ultrapure water) while stirring and maintained at a temperature of 90 to 99°C for about 0.5 hours (however, maintained in a state without boiling).

[0318] Note that the "ultrapure water" used in the first process (carrier pretreatment process) 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.

[0319] The ultrapure water was produced using an ultrapure water production device "Milli-Q series" (manufactured by MERCK Corporation) and "Elix UV series" (manufactured by MILLIPORE Corporation, Japan).

[0320] R = 1 / p... (4)

[0321] In the above formula (4), R represents specific resistance, and p represents conductivity measured by a JIS standard test method (JIS K0552).

[0322] (Second Step (Pt Addition Step))

[0323] To the dispersion liquid obtained in the first step, an aqueous solution obtained by dissolving a water-soluble Pt salt (N.E. CHEMCAT Corporation, product name "A-salt" (Fe component concentration: 8 ppm or less)) in ultrapure water was added, and a mixed liquid was prepared, the pH of which was adjusted to 7 to 12, and which was maintained at a prescribed temperature of 50°C or more and stirred for a prescribed time.

[0324] (Third Step (Reduction Step))

[0325] To the liquid obtained in the second step, an aqueous solution in which an acidic water-soluble reducing agent was dissolved was added, and Pt ions in the mixed liquid were reduced, thereby obtaining a Pt catalyst particle-supported carbon "Pt / C" powder.

[0326] (Fourth Step (Cleaning Step))

[0327] The solid component in the liquid obtained in the "third step" was 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 was cleaned using the pure water and the pure hot water described above. The cleaning was performed first using the pure water. This cleaning was repeated until the conductivity of the filtrate after the cleaning was 20 μS / cm or less. Then, the cleaning was performed using the pure hot water. This cleaning was repeated until the conductivity of the filtrate after the cleaning was 10 μS / cm or less.

[0328] (Fifth Step (Drying Step))

[0329] The solid component (a mixture of the Pt / C catalyst and water) on the filter paper obtained in the "fourth step" was directly air-dried in this state. After this air-drying, the solid component on the filter paper was transferred to a magnetic dish, and dried in an electric drier at a prescribed temperature of 60°C or more for a prescribed time.

[0330] (Sixth Step (Pulverization Step))

[0331] The solid component (the Pt / C catalyst) obtained in the "fifth step" was pulverized using a mixer, and a powder of the Pt / C catalyst A was obtained.

[0332] Measurement of the loading rate (ICP analysis)

[0333] For this Pt / C catalyst A, the Pt loading rate (wt%) was measured by the following method.

[0334] The Pt / C catalyst A was immersed in aqua regia, and the metal was dissolved. After that, 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.

[0335] The result of the ICP analysis found that the Pt loading rate for this Pt / C catalyst A was 48.0 wt%.

[0336] Surface observation and structure observation of the catalyst for electrode

[0337] For this Pt / C catalyst A of Example 1, in order to observe its three-dimensional structure, measurement of electron beam tomography using STEM (scanning transmission electron microscope) of UBE Scientific Analysis Center Co., Ltd. was performed using "USAL-KM3D analysis method".

[0338] Measurement of electron beam tomography using STEM (scanning transmission electron microscope) was performed in accordance with the aforementioned (A) to (C) and (D) to (G) of the preparation method of the measurement sample, the conditions and the analysis program, and the conditions. The more detailed information is described below.

[0339] • STEM device: JEM-ARM200F atomic resolution analysis electron microscope manufactured by JEOL Ltd.

[0340] • Data analysis software: 3D reconstruction software Composer, 3D data visualization software Visualizer-kai, and image analysis software Colorist manufactured by SYSTEM IN FRONTIER

[0341] • Measurement conditions

[0342] Acceleration voltage: 60 kV

[0343] Observation magnification: 800,000 to 1,000,000 times

[0344] Tilt angle of the measurement sample: -80° to +80°

[0345] Tilt step angle of the measurement sample: 2°

[0346] Number of pixels: 512 x 512 pixels 512 x 512 pixels

[0347] Pixel size: 0.350 nm / pixel to 0.500 nm / pixel

[0348] Volume size: Figure 12 as shown.

[0349] For the Pt / C catalyst A, the image analysis of the three-dimensional reconstruction image (3D-STEM image) obtained by the electron beam tomography measurement using STEM (scanning transmission electron microscope) separates the Pt catalyst particles existing inside the carbon support (hereinafter referred to as "internal particles") and the Pt catalyst particles existing in the surface portion of the carbon support (hereinafter referred to as "external particles") and calculates the particle size distribution of the Pt catalyst particles in each region.

[0350] The three-dimensional reconstruction image (3D-STEM image) of the Pt / C catalyst A is shown in Figure 13 .

[0351] The results of the particle size analysis (particle size distribution expressed in equivalent spherical diameter) of the catalyst particles inside the nano-pores of the support and the catalyst particles outside the nano-pores obtained by the image analysis are shown in Figure 14 , Figure 13 .

[0352] 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.

[0353] In addition, the image analysis (particle size analysis) of the three-dimensional reconstruction image (3D-STEM image) is performed by the following procedure. First, the observation regions of the catalyst particles are selected from the three-dimensional reconstruction image, and the respective catalyst particles are labeled (not shown). Then, the volume of the labeled Pt catalyst particles is obtained, the diameter of a sphere having the same volume as the volume (equivalent spherical diameter) is calculated, and the particle size distribution is obtained. Figure 14 , Figure 15 .

[0354] Here, the equivalent spherical diameter is calculated by setting the unit to nm and rounding off the numerical value below the decimal point (numerical value below 1 nm).

[0355] For this Pt / C catalyst A, the proportion of the catalyst particles inside the nano-pores of the support and the proportion of the catalyst particles outside the nano-pores of the support 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.

[0356] Further, the average value of the particle size of the catalyst particles of the Pt / C catalyst A measured from the STEM image was 3.1 nm (average value of the particle size of the catalyst particles inside the nano-pores: 3.1 nm; average value of the particle size of the catalyst particles outside the nano-pores: 3.2 nm).

[0357] (2) Preparation of Pt / C catalyst used in the cathode of MEA in Example 2

[0358] [Pt catalyst particles supporting carbon catalyst "Pt / C catalyst" powder]

[0359] 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.

[0360] <Surface and structural observations of catalysts used in electrodes>

[0361] 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.

[0362] Figure 16 The image shows a 3D electron beam tomography measurement under the volumetric conditions of the STEM of the electrode catalyst (Pt / C catalyst B) of Example 2.

[0363] Figure 17 A 3D-STEM image (three-dimensional reconstructed image) of the electrode catalyst (Pt / C catalyst B) of Example 2 is shown.

[0364] Figure 16 Showing through Figure 18 The graph shows the particle size distribution (expressed as equivalent sphere diameter) of the catalyst particles inside the nanopores of the support within the catalyst particles, obtained from image analysis of the 3D-STEM image of the electrode catalyst (Pt / C catalyst B) of Example 2.

[0365] Figure 16 Showing through Figure 19The chart of the particle size distribution of the catalyst particles (particle size distribution in terms of equivalent spherical diameter) of the catalyst particles supported outside the nanopores of the support obtained from the image analysis of the 3D-STEM image of the electrode catalyst (Pt / C catalyst B) of Example 2.

[0366] For this electrode catalyst (Pt / C catalyst B), 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 determined. In addition, the values of D10, D20, D1, D2, N1, N2 were determined. The results are shown in Tables 2 and 3.

[0367] Further, the average value of the particle size of the catalyst particles of the electrode catalyst (Pt / C catalyst B) determined from the STEM image was 3.3 nm (average value of the particle size of the catalyst particles inside the nanopores: 3.2 nm; average value of the particle size of the catalyst particles outside the nanopores: 3.7 nm).

[0368] (3) Preparation of the powder of the Pt / C catalyst used for the cathode of the MEA of Comparative Example 1

[0369] As the Pt / C catalyst, a Pt / C catalyst (trade name: "SA50BK") manufactured by N.E. CHEMCAT Co., Ltd. having a Pt support ratio of 50 wt% was prepared. Note that the support of this Pt / C catalyst used a commercially available hollow carbon support {manufactured by LION Corporation, trade name "Carbon ECP" (registered trademark) (Ketjenblack EC300J), specific surface area 750 to 800 m 2 / g}.

[0370] < Surface observation and structure observation of the electrode catalyst >

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

[0372] Figure 20 STEM image showing the 3D-electron beam tomography measurement conditions (volume size) of the Pt / C catalyst of Comparative Example 1 using a STEM.

[0373] Figure 21 3D-STEM image (three-dimensional reconstruction image) of the Pt / C catalyst of Comparative Example 1.

[0374] Figure 20 Figure 2 shows a graph of the particle size distribution of the catalyst particles supported inside the nano-pores of the support in the catalyst particles in the 3D-STEM image of the Pt / C catalyst of Comparative Example 1, obtained by image analysis of the 3D-STEM image. Figure 22

[0375] Figure 20 Figure 11-14 Figure 2 shows a graph of the particle size distribution of the catalyst particles supported inside the nano-pores of the support in the catalyst particles in the 3D-STEM image of the Pt / C catalyst of Comparative Example 1, obtained by image analysis of the 3D-STEM image.

[0376] For this Pt / C catalyst, the proportion of the catalyst particles supported inside the nano-pores of the support and the proportion of the catalyst particles supported outside the nano-pores of the support 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.

[0377] Further, the average value of the particle size of the catalyst particles of the Pt / C catalyst determined from the STEM image was 3.1 nm (average value of the particle size of the catalyst particles inside the nano-pores: 3.1 nm, average value of the particle size of the catalyst particles outside the nano-pores: 3.2 nm).

[0378] (4) Production of the Pt / C catalyst used in the cathode of the MEA of Comparative Example 2

[0379] [Powder of the Pt catalyst particle-supported carbon catalyst "Pt / C catalyst"]

[0380] Except for using a trial sample product name: "C Novel C" (BET specific surface area: 800 m 2 / g) manufactured by Toyo Carbon Co., Ltd. as the hollow carbon support, the powder of the Pt / C catalyst used in the cathode of the MEA of Example 2 (hereinafter, referred to as "Pt / C catalyst C" as necessary) was produced under the same conditions and operations as the Pt / C catalyst A used in the cathode of the MEA of Example 1 {Pt-supporting rate: 48.0 wt%, product name: "SA50BM-C207", manufactured by N.E. CHEMCAT Co., Ltd.).

[0381] < Surface observation and structure observation of the catalyst for electrode >

[0382] ​​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 STEM (scanning transmission electron microscope) of UBE Scientific Analysis Center, Ltd. was also carried out in the same operation and conditions as the Pt / C catalyst of Example 1 using the "USAL-KM3D analysis method".

[0383] For the electrode catalyst of this Comparative Example 2 (Pt / C catalyst C), the measurement of electron beam tomography using STEM (scanning transmission electron microscope) shown in the above-mentioned (b) and (c) was also carried out, and information equivalent to the analysis results thereof was obtained, but the illustrations thereof were omitted. Figure 15-17 、 Figure 20-22 、 Figure 23

[0384] Figure 24 The STEM image showing the measurement conditions of 3D-electron beam tomography using STEM of the Pt / C catalyst of Comparative Example 2 (volume size) is shown.

[0385] For the electrode catalyst of this Comparative Example 2 (Pt / C catalyst C), 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.

[0386] 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).

[0387] (5) Confirmation of the fine structure of the electrode catalysts of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 using the three-dimensional reconstructed images of STEM

[0388] For the electrode catalysts of Example 1, Example 2, and Comparative Example 2, in order to confirm the aforementioned (b) condition "whether the nanopores are formed in the shape of the communication holes of the present application", the three-dimensional reconstructed images using STEM were used for the investigation. In addition, the void fractions of the respective catalysts were obtained using the three-dimensional reconstructed images of STEM.

[0389] The results thereof are shown in Figure 25 and Figure 24 .

[0390] As shown in Figure 25 (c) and Figure 24 ​As shown in (c) and (d), the nanohole P1 in the inside of the catalyst block of the electrode catalyst of Example 1 has two openings (opening Al l and opening A12) on the first side LI.

[0391] Further, as shown in Figure 25 (c) and Figure 24 , the nanohole P1 in the inside of the catalyst block of the electrode catalyst of Example 1 has a shape of a plurality of branches.

[0392] Further, as shown in Figure 25 (c) and Figure 24 , the nanohole P1 in the inside of the catalyst block of the electrode catalyst of Example 1 has two or more openings (opening Al l and opening A12) on the first side LI.

[0393] Further, as shown in Figure 25 (c) and Figure 24 , the nanohole P1 in the inside of the catalyst block of the electrode catalyst of Example 1 has two or more openings (opening Al l and opening A12) on the first side LI.

[0394] Further, as shown in Figure 25 (c) and Figure 24 , the nanohole P1 in the inside of the catalyst block of the electrode catalyst of Example 1 has one opening (opening A31) on the third side L3 which is perpendicular to the first side LI.

[0395] Further, as shown in Figure 25 (c) and Figure 24 , the nanohole P1 in the inside of the catalyst block of the electrode catalyst of Example 1 has two openings (opening Al l and opening A12) on the first side LI.

[0396] As shown in Figure 24 (d) and Figure 24 (e), the nanohole P1 in the inside of the catalyst block of the electrode catalyst of Example 1 was also confirmed to have the same shape as described above on the other two faces (y-z plane, z-x plane) of the stereoscopic image of the catalyst block.

[0397] Further, as shown in Figure 24 (h), Figure 24 (i) and Figure 24(j) As shown, for the electrode catalyst of Example 2, it was also confirmed that the nanopores P22 having the shape of the communication hole P1 related to the present application were formed as with the electrode catalyst of Example 1.

[0398] On the other hand, as shown in Figure 24 (m), Figure 24 (n) and Figure 1 (o) As shown, for the electrode catalyst of Comparative Example 1, it was confirmed that the nanopores P22 having the shape of the communication hole P1 related to the present application were not formed. The nanopores P1 seen in the stereoscopic images of the cross sections (x-y plane, y-z plane, z-x plane) of the interior of the catalyst block of the electrode catalyst of Comparative Example 1 had one opening in contact with the first edge and an opening in contact with the second edge parallel to the first edge, but it was confirmed that there were no communication holes P1 having the shape of a continuous extension without obstruction from the opening of the first edge to the opening of the second edge.

[0399] (II) Preparation of P / C catalyst used in the anode of the MEA of Example 1, Example 2, Comparative Example 1, Comparative Example 2

[0400] The same Pt / C catalyst as that 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.

[0401] <Example 1>

[0402] An MEA having the same structure as the MEA 10 shown in ​ was produced in accordance with the following procedure.

[0403] (1) Production of the cathode

[0404] GDL of the cathode

[0405] As the GDL, a carbon paper (manufactured by Toray Industries, Inc., trade name "TGP-H-60") was prepared.

[0406] Ink for MPL formation of the cathode

[0407] 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, trade name "DENKA BLACK"), 1.1 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.

[0408] After that, 1.75 g of 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 the cathode was prepared.

[0409] MPL of the cathode

[0410] The MPL formation ink for the cathode was applied to one face of the GDL using a bar coater to form an applied film. After that, the applied film was sufficiently dried in a drier, and further subjected to a heat press treatment, thereby producing a laminate in which the MPL was formed on the GDL.

[0411] Catalyst layer formation ink for the cathode

[0412] A ball mill container made of TEFLON (registered trademark) was charged with the Pt / C catalyst A, ion-exchanged water, 10 wt% Nafion aqueous dispersion (manufactured by DuPont Co., trade name "DE1021CS"), and glycerin, and mixed, thereby preparing a catalyst layer formation ink for the cathode. Note that the ink was set so that N / C = 0.7. In addition, in the electrode catalyst A, carbon: ion-exchanged water: glycerin = 1:10:0.8 (mass ratio) was set.

[0413] Catalyst layer (CL) of the cathode

[0414] The MPL of the laminate in which the MPL was formed on the MPL of the GDL described above was coated with the catalyst layer formation ink for the cathode described above 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 producing a catalyst layer. Thus, a cathode was produced 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.

[0415] (2) Production of the anode

[0416] GDL of the anode

[0417] As the GDL, the same carbon paper as the cathode was prepared.

[0418] MPL formation ink for the anode

[0419] A ball mill container made of TEFLON (registered trademark) was charged with 1.5 g of carbon powder (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name "DENKA BLACK"), 1.0 g of ion-exchanged water, and 6.0 g of a surfactant (manufactured by Dow Chemical Co., trade name "TRITON" (35 wt% aqueous solution)), and mixed.

[0420] Next, 2.5 g of polytetrafluoroethylene (PTFE) dispersion (manufactured by Mitsui-DuPont Fluorochemicals, trade name "31-JR") was added to the ball mill container and mixed. This produced an ink for forming MPL for the anode.

[0421] MPL of the anode

[0422] Using a bar coater, anodized MPL forming ink is applied to one side of the GDL to form a coating film. The coating film is then thoroughly dried in a dryer and further subjected to heat-pressing to create a laminate with MPL formed on the GDL.

[0423] Ink for forming catalyst layer of anode

[0424] An ink for forming the catalyst layer of the anode was prepared by adding SA50BK (50wt% Pt loading), ion-exchanged water, 5wt% Nafion alcohol dispersion (manufactured by SIGMA-ALDRICH, trade name "Nafion 5wt.% dispersion", product number "274704") and glycerol to a ball mill container containing TEFLON (registered trademark) balls. It should be noted that the N / C ratio in this ink was set to 1.2. Furthermore, in SA50BK, the carbon:ion-exchanged water:glycerol ratio was set to 1:6:4 (mass ratio).

[0425] Catalyst layer (CL) of the anode

[0426] On the surface of the MPL, on which the MPL laminate is formed on the GDL, an ink for forming the catalyst layer of the anode is applied by a rod coating method to form a coating film. This coating film is dried at room temperature for 30 minutes, then dried at 60°C for 1 hour, thereby forming the catalyst layer. Thus, an anode serving as a gas diffusion electrode is fabricated. The Pt loading of the catalyst layer of the anode is set to 0.3 mg / cm³. 2 .

[0427] (3) MEA creation

[0428] A polymeric electrolyte membrane (manufactured by DuPont, trade name "Nafion NR212") was prepared. A laminate with the polymeric electrolyte membrane disposed between the cathode and anode was fabricated, and then heated and pressed together using a hot press to produce the MEA. The heating and pressing conditions were set as follows: pressing at 140°C and 5 kN for 5 minutes, followed by pressing at 140°C and 25 kN for 3 minutes.

[0429] <Example 2>

[0430] Each MEA was produced under the same conditions and procedures as in Example 1 except that the following condition change was made for the catalyst layer of the cathode.

[0431] That is, in the production of the ink for forming the catalyst layer of the cathode,

[0432] • The aforementioned Pt / C catalyst B was used instead of the Pt / C catalyst A.

[0433] <Comparative Example 1>

[0434] Each MEA was produced under the same conditions and procedures as in Example 1 except that the following condition change was made for the catalyst layer of the cathode.

[0435] That is, in the production of the ink for forming the catalyst layer of the cathode,

[0436] • The aforementioned P / C catalyst (trade name: "SA-50BK") was used instead of the Pt / C catalyst A.

[0437] • 5 wt% Nafion alcohol dispersion (manufactured by DuPont, trade name "DE520CS"; containing 48 wt% of 1-propanol) was used instead of the 10 wt% Nafion water dispersion.

[0438] • 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 N / C would be the values shown in Table 1.

[0439] • The carbon: ion-exchanged water: glycerin in the P / C catalyst (trade name: "SA50BH") was set to 1:10:1 (mass ratio).

[0440] <Comparative Example 2>

[0441] Each MEA was produced under the same conditions and procedures as in Example 1 except that the following condition change was made for the catalyst layer of the cathode.

[0442] That is, in the production of the ink for forming the catalyst layer of the cathode,

[0443] • The aforementioned Pt / C catalyst C was used instead of the Pt / C catalyst A.

[0444] <Battery Performance Evaluation>

[0445] 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.

[0446] The MEAs of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were set in a fuel cell single cell evaluation device.

[0447] After that, power generation reaction in the MEA was performed under the following conditions.

[0448] The temperature of the single cell (MEA) 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%.

[0449] 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 acquired as data.

[0450] From the data of the current-voltage curve, 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.

[0451] 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 used as an index of the oxygen reduction ability of the catalyst contained in the cathode. The results are shown in Table 1.

[0452] 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) as a reference.

[0453]

[0454]

[0455] As is clear from the results shown in Tables 1 to 3, the MEA of Example 1 and Example 2 had higher Pt mass activity than the MEA of Comparative Example 1 and Comparative Example 2.

[0456] In the above embodiments and comparative examples, we explored embodiments where the catalyst particles were 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 aforementioned conditions (α) the proportion of catalyst particles supported inside the nanopores is 50% or more (conditions regarding the support position of the catalyst particles constituting the electrode catalyst) and (β) the nanopores are formed in the aforementioned interconnected pore shape (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.

[0457] Industrial availability

[0458] 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 exhibit excellent battery characteristics that contribute to the cost reduction of PEFCs.

[0459] Therefore, this invention is applicable not only to the electrical equipment industry such as fuel cells, 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 pore size of 1–20 nm and micropores having a pore size of less than 1 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 through electron beam tomography (STEM), it was found that the proportion of catalyst particles loaded inside the nanopores was more than 50%. 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.

2. The electrode catalyst according to claim 1, wherein, The connecting hole has a multi-branched shape.

3. The electrode catalyst according to claim 2, wherein, The connecting hole has two or more openings on the first side.

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

5. 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.

6. The electrode catalyst as described in claim 5, wherein, The connecting hole has at least one opening on the fourth side perpendicular to the first side.

7. The electrode catalyst according to any one of claims 1 to 4, wherein, The porosity measured using the three-dimensional reconstructed image obtained using the STEM is greater than 35%.

8. The electrode catalyst according to any one of claims 1 to 4, wherein, The nanopores have a diameter of 1–10 nm.

9. The electrode catalyst according to any one of claims 1 to 4, wherein, The hollow carbon support also has micropores with a pore size of less than 1 nm.

10. The electrode catalyst according to any one of claims 1 to 4, wherein, The catalyst particles are composed of Pt with a zero valence.

11. The electrode catalyst according to any one of claims 1 to 4, wherein, The catalyst particles are composed of Pt alloy.

12. The electrode catalyst according to any one of claims 1 to 4, wherein, The catalyst particles are core-shell catalyst particles. The core-shell catalyst particle has a core particle and a Pt shell layer consisting of at least a region of the zero-valent Pt formed on the surface of the core particle.

13. The electrode catalyst according to any one of claims 1 to 4, wherein, When analyzing the particle size distribution of the catalyst particles using the three-dimensional reconstructed images from the STEM, the following condition (1) must be met: (D10 / D20)≥0.80……(1) In the above formula (1), D10 represents the arithmetic mean of the equivalent sphere diameters of the catalyst particles supported within the nanopores of the carrier. D20 represents the arithmetic mean of the equivalent sphere diameters of the catalyst particles located outside the nanopores of the carrier.

14. The electrode catalyst according to any one of claims 1 to 4, wherein, When analyzing the particle size distribution of the catalyst particles using the three-dimensional reconstructed images from the STEM, in addition to satisfying the condition of equation (1), the following conditions (2) and (3) are also satisfied simultaneously. D1≤D2……(2) (N1 / N2)>1.0……(3) In equations (2) and (3), D1 represents the equivalent sphere diameter of the catalyst particles exhibiting the highest frequency within the nanopores of the support. D2 represents the equivalent sphere diameter of the catalyst particles exhibiting the highest frequency in the catalyst particles located outside the nanopores of the support. N1 represents the frequency of the particle exhibiting the highest frequency among the catalyst particles located inside the nanopores of the support. N2 represents the frequency of the particles exhibiting the highest frequency in the catalyst particles located outside the nanopores of the carrier.

15. The electrode catalyst according to any one of claims 1 to 4, 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.

16. The electrode catalyst according to any one of claims 1 to 4, 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.

17. A powder of a catalyst for electrodes, wherein, An electrode catalyst containing 10 wt% or more of any one of claims 1 to 16.

18. A composition for forming a gas diffusion electrode, wherein, Powder containing any one of the electrode catalysts according to claims 1 to 16 or the electrode catalyst according to claim 17.

19. A gas diffusion electrode, wherein, Powder containing any one of the electrode catalysts according to claims 1 to 16 or the electrode catalyst according to claim 17.

20. A membrane-electrode junction, in, It contains the gas diffusion electrode as described in claim 19.

21. A fuel cell stack, wherein, It contains the membrane-electrode junction as described in claim 20.

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