Supported metal catalyst and method for producing the same

Abstract

A supported metal catalyst is provided which has excellent utilization efficiency of active metal particles.　This supported metal catalyst is provided with a carrier, which is an aggregate of conductive particles, and active metal particles, which are supported dispersed on the conductive particles. The conductive particles include multiple pores; the pores have an average entrance pore size of 1-20nm, the standard deviation of the average entrance pore size is less than or equal to 50% of the average entrance pore size, and the fraction of the active metal particles supported on the surface layer region of the conductive particles is greater than or equal to 50%. The surface layer region is a region on the surface of the conductive particles, or the region in the pores with a depth no more than 15nm from the surface; the active metal particles have an average inter-particle distance of 5-20nm, and the standard deviation of tshe average inter-particle distance is less than or equal to 50% of the average inter-particle distance.

Description

[Technical Field] 【0001】 This invention relates to a supported metal catalyst and a method for producing the same. The supported metal catalyst of this invention is suitably used as an electrode catalyst (particularly a cathode catalyst) for fuel cells. [Background technology] 【0002】 Patent Document 1 discloses a supported metal catalyst obtained by supporting a catalytic component on MCND (mesoporous carbon nanodendrite). MCND has a well-developed pore structure, and by supporting the catalytic component within these pores, the utilization efficiency of the catalytic component is enhanced. [Prior art documents] [Patent Documents] 【0003】 [Patent Document 1] Japanese Patent Publication No. 2018-10806 [Overview of the Initiative] [Problems that the invention aims to solve] 【0004】 However, even with the configuration described in Patent Document 1, the utilization efficiency of the catalyst component is not sufficiently high, and further improvements in utilization efficiency are desired. 【0005】 This invention has been made in view of these circumstances, and provides a supported metal catalyst with excellent utilization efficiency of activated metal particles. [Means for solving the problem] 【0006】 According to the present invention, a supported metal catalyst is provided, comprising a carrier which is an aggregate of conductive particles, and active metal particles dispersed and supported on the conductive particles, wherein the conductive particles include a plurality of pores, the average entrance pore diameter of the pores is 1 to 20 nm, the standard deviation of the average entrance pore diameter is 50% or less of the average entrance pore diameter, the percentage of the active metal particles supported on the surface region of the conductive particles is 50% or more, the surface region is a region on the surface of the conductive particles, or a region within the pores within a depth of 15 nm from the surface, and the active metal particles have an average inter-particle distance of 5 to 20 nm, and the standard deviation of the average inter-particle distance is 50% or less of the average inter-particle distance. 【0007】 The inventors conducted diligent research and obtained the following findings. Since the MCND described in Patent Document 1 is formed by explosively reacting silver acetylide, the pore size of the MCND varies considerably. To increase the utilization efficiency of the catalyst component, it is necessary to support the catalyst component in shallow positions within the pores. However, because the pore size of MCND varies considerably, it is difficult to control the position of the catalyst component within the pores. As a result, the catalyst component ends up being supported in deeper positions within the pores. In these deeper positions, the catalytic reaction rate decreases due to the diffusion resistance of the reactants used in the catalytic reaction and the products generated, leading to low catalyst utilization efficiency. Therefore, the supported metal catalyst using the MCND described in Patent Document 1 did not exhibit sufficient utilization efficiency of the catalyst component. 【0008】 Based on this finding, we discovered that by reducing the variation in pore size of the pores in the carrier and supporting more than 50% of the active metal particles on the surface region of the conductive particles constituting the carrier, the utilization efficiency of the active metal particles can be increased. 【0009】 Furthermore, the supported metal catalyst of the present invention is characterized by an average interparticle distance of 5 to 20 nm for the active metal particles, and a standard deviation of the average interparticle distance of 50% or less. If the average interparticle distance is too small, the activity of each active metal particle tends to decrease, or adjacent active metal particles tend to fuse together, causing the particles to coarseen and degrade the catalyst. However, in the supported metal catalyst of the present invention, the average interparticle distance of the active metal particles and its standard deviation are appropriately set, resulting in excellent activity and durability. 【0010】 The present invention provides the following: (1) A supported metal catalyst comprising a carrier which is an aggregate of conductive particles, and active metal particles dispersed and supported on the conductive particles, wherein the conductive particles include a plurality of pores, the average entrance pore diameter of the pores is 1 to 20 nm, the standard deviation of the average entrance pore diameter is 50% or less of the average entrance pore diameter, the percentage of the active metal particles supported on the surface region of the conductive particles is 50% or more, the surface region is a region on the surface of the conductive particles, or a region within the pores within a depth of 15 nm from the surface, and the active metal particles have an average inter-particle distance of 5 to 20 nm, and the standard deviation of the average inter-particle distance is 50% or less of the average inter-particle distance. (2) A supported metal catalyst according to (1), wherein the proportion of the active metal particles in the supported metal catalyst is 16 to 50% by mass. (3) A supported metal catalyst according to (1) or (2), wherein the proportion of the active metal particles in the supported metal catalyst is 21 to 35% by mass. (4) A supported metal catalyst according to any one of (1) to (3), wherein the conductive particles are carbon particles. (5) A supported metal catalyst according to any one of (1) to (4), wherein the pores have an average interpore distance of 5 to 20 nm, and the standard deviation of the average interpore distance is 50% or less of the average interpore distance. (6) A supported metal catalyst according to any one of (1) to (5), wherein the conductive particles are linked structures in which an average of 5 or more primary particles are linked together. A supported metal catalyst according to (7)(6), wherein the average number of series connections of the linked structures is 3 or more. (8) A supported metal catalyst according to any one of (1) to (7), wherein the conductive particles have an average primary particle diameter of 20 to 100 nm. A supported metal catalyst according to any one of (9)(1) to (8), wherein the fraction of the active metal particles supported in the surface region that are supported in the pores is 40% or more. A supported metal catalyst according to any one of (10)(1) to (9), wherein the active metal particles are particles of platinum or a platinum alloy. A supported metal catalyst according to any one of (1)(1) to (10), wherein the average particle size of the active metal particles is 1 to 8 nm. A supported metal catalyst according to any one of (12)(1) to (11), wherein the value of [average particle diameter of the active metal particles / average inlet pore diameter] is 0.2 to 0.8. (13) A supported metal catalyst according to any one of (1) to (12), wherein the fraction of the active metal particles supported on the surface region of the conductive particles is 60% or more. (14) A fuel cell having a cathode-side catalyst layer, wherein the cathode-side catalyst layer contains a supported metal catalyst according to any one of (1) to (13). (15) A method for producing a supported metal catalyst, comprising an initial addition step, a simultaneous addition step, a supporting step, and an arrangement step, wherein in the initial addition step, an oxidizing agent is added to an active metal precursor solution containing an active metal precursor to oxidize the active metal precursor to form oxide particles of the active metal, thereby generating a colloid; in the simultaneous addition step, a neutralizing agent and the oxidizing agent are added simultaneously to the colloid until the amount of the oxidizing agent reaches a specified amount; in the supporting step, the oxide particles are supported on the conductive particles by mixing a carrier which is an aggregate of conductive particles with the colloid; and in the arrangement step, an arrangement treatment is performed to improve the regularity of the arrangement of the oxide particles or the active metal particles produced by their reduction, wherein the conductive particles include a plurality of pores, the average entrance pore diameter is 1 to 20 nm, and the standard deviation of the average entrance pore diameter is 50% or less of the average entrance pore diameter. A method according to (16)(15), wherein the oxidizing agent is hydrogen peroxide. A method according to (17), (15), or (16), wherein the pH immediately after the initial addition step is 1.0 to 2.5, and the pH immediately after the simultaneous addition step is 4.0 to 6.0. A method according to any one of (18), (15), to (17), wherein the time from the start of the initial addition step to the completion of the simultaneous addition step is 10 to 30 minutes. A method according to any one of (19), (15), to (18), wherein the sequencing treatment comprises at least one of a heat treatment and an electrochemical treatment. (20) A method for producing a supported metal catalyst, comprising a first step, a surfactant removal step, and a second step, wherein the first step comprises a first mixing step, a first reduction step, and a first supporting step, and the second step comprises a second mixing step, a second reduction step, and a second supporting step, wherein in the first mixing step, an active metal precursor solution containing an active metal precursor is mixed with a surfactant and an organic solvent to produce a first active metal precursor mixed solution, in the first reduction step, the active metal precursor in the first active metal precursor mixed solution is reduced to produce active metal particles, in the first supporting step, the active metal particles are dispersed and supported on the conductive particles by mixing a carrier which is an aggregate of conductive particles with the active metal particles, in the surfactant removal step, the surfactant adhering to the carrier is removed, and the second mixing step A method comprising: a mixing step in which an active metal precursor solution containing an active metal precursor is mixed with a surfactant and an organic solvent to produce a second active metal precursor mixed solution; a second reduction step in which the active metal precursor in the second active metal precursor mixed solution is reduced to produce active metal particles; and a second loading step in which the carrier after the surfactant removal step is mixed with the active metal particles obtained in the second reduction step to disperse and support the active metal particles obtained in the second reduction step on the conductive particles, wherein the conductive particles contain a plurality of pores, the average entrance pore diameter is 1 to 20 nm, the standard deviation of the average entrance pore diameter is 50% or less of the average entrance pore diameter, and the median number diameter measured by dynamic light scattering in the mixed solution is 0.5 to 2 times the average entrance pore diameter. A method according to (21)(20), wherein in the first reduction step, the reduction is carried out by mixing a reducing agent mixed solution containing a reducing agent, an organic solvent, water, and a surfactant with a first active metal precursor mixed solution, and in the second reduction step, the reduction is carried out by mixing a reducing agent mixed solution containing a reducing agent, an organic solvent, water, and a surfactant with a second active metal precursor mixed solution. A method according to (22), (20), or (21), wherein the removal of the surfactant is carried out by heat treatment of the carrier under a reducing gas atmosphere. A method according to any one of (23)(20) to (22), wherein the conductive particles are annealed in a vacuum at 800 to 2000°C before the first loading step. A method according to any one of (24), (20), to (23), wherein the conductive particles are annealed in a vacuum at 1100 to 2000°C prior to the first loading step. (25) A method for producing a supported metal catalyst, comprising a mixing step, a reduction step, and a supporting step, wherein in the mixing step, an active metal precursor solution containing an active metal precursor is mixed with a surfactant and an organic solvent to produce an active metal precursor mixed solution; in the reduction step, the active metal precursor in the active metal precursor mixed solution is reduced to produce active metal particles; in the supporting step, the active metal particles are dispersed and supported on the conductive particles by mixing the active metal particles with a carrier which is an aggregate of conductive particles, wherein the conductive particles contain a plurality of pores, the average entrance pore diameter is 1 to 20 nm, the standard deviation of the average entrance pore diameter is 50% or less of the average entrance pore diameter, the median number diameter measured by dynamic light scattering in the mixed solution is 0.5 to 2 times the average entrance pore diameter, and the conductive particles are annealed in a vacuum at 1100 to 2000°C before the supporting step. A method according to any one of (20) to (25), wherein the method comprises an arrangement step after a second loading step according to any one of (20) to (24), or after the loading step according to (25), wherein the arrangement step involves an arrangement treatment to enhance the regularity of the arrangement of the active metal particles. A method according to (27)(26), wherein the sequencing treatment comprises at least one of a heat treatment and an electrochemical treatment. A method according to any one of (28)(20) to (27), wherein the organic solvent is a hydrophobic organic solvent comprising at least one selected from cyclohexane, heptane, and toluene. A method according to any one of (29), (20), to (28), wherein the surfactant is a nonionic surfactant. A method according to any one of (20) to (29), wherein the active metal precursor contains a platinum precursor compound. A method according to any one of (15) to (30), wherein the conductive particles are carbon particles. A method according to any one of (15) to (31), wherein the pores have an average pore-to-pore distance of 5 to 20 nm and a standard deviation of the average pore-to-pore distance of 50% or less of the average pore-to-pore distance. A method according to any one of (15) to (32), wherein the conductive particles are a connected structure in which an average of 5 or more primary particles are connected. A method according to (33), wherein the average number of series connections of the connected structure is 3 or more. A method according to any one of (15) to (34), wherein the primary particles of the conductive particles have an average particle diameter of 20 to 100 nm. BRIEF DESCRIPTION OF THE DRAWINGS 【0011】 [Figure 1] It is a schematic diagram of the supported metal catalyst 1. [Figure 2] FIG. 2A is a schematic cross-sectional view of the supported metal catalyst 1, and FIG. 2B is an enlarged view of region B in FIG. 2A. [Figure 3] It is a schematic diagram of the conductive particle 2 composed of single particles. [Figure 4] It is a schematic diagram of the conductive particle 2 composed of the connected structure 2a. [Figure 5] It is a schematic diagram of the carbon source aggregate 8 in which the carbon source spheres 7 are aggregated. [Figure 6] It is a schematic diagram showing a state in which the carbon source aggregates 8 are connected to each other. [Figure 7] It is a schematic diagram of a fuel cell. [Figure 8] It is a secondary electron image of the carbon particles of Production Example 1. [Figure 9] It is a secondary electron image of the carbon particles of Production Example 2. [Figure 10]Image A on the left is a cross-sectional secondary electron image of the supported metal catalyst of Example 1, and image on the right is its Z-contrast image. [Figure 11] This graph shows the relationship between Rw and the median diameter in the inverse micelle method of Reference Example 1. [Figure 12] The image on the upper left is a secondary electron image of the supported metal catalyst of Example 2, the image on the upper right is its Z-contrast image, and the images on the lower left and right are other secondary electron images of the supported metal catalyst of Example 2. [Figure 13] This is a Z-contrast image of the supported metal catalyst in Example 2. [Figure 14] Figures 14A and 14B show the distance distribution between the centers of gravity of platinum particles in the supported metal catalyst of Example 2. Figure 14A shows the untreated state, and Figure 14B shows the state after hydrogen reduction treatment. [Figure 15] Figures 15A to 15C show the Z-contrast image or secondary electron image of the supported metal catalyst of Example 2, respectively. Figure 15A shows the Z-contrast image of the untreated state after the loading process, Figure 15B shows the secondary electron image of the state after hydrogen reduction treatment following the loading process, and Figure 15C shows the secondary electron image of the state after the oxygen reduction activity measurement described above following hydrogen reduction. [Figure 16] This graph shows the relationship between carrier oxygen concentration and Pt loading rate in Reference Example 2. [Figure 17] This graph shows the relationship between annealing temperature and oxygen concentration in Reference Example 3. [Figure 18] This is a secondary electron image of the supported metal catalyst in Example 3. [Figure 19] This is a secondary electron image of the supported metal catalyst in Example 4. [Figure 20] This graph shows the results of a quadrupole mass spectrometer analysis to investigate the effectiveness of hydrogen treatment in removing residual surfactants, as shown in Reference Example 4. [Figure 21] Graphs showing the time course of pH when the oxidizing agent and neutralizing agent were added dropwise in Example 5 and Comparative Example 1. [Figure 22]Figure 22A shows a secondary electron image of a supported metal catalyst prepared in the same manner as in Example 5, except that the platinum load was 50% by mass. Figures 22B and 22C show secondary electron images of the supported metal catalyst from Example 5. Figure 22A shows the untreated state after the loading process, Figure 22B shows the state after hydrogen reduction treatment following the loading process, and Figure 22C shows the state after oxygen reduction activity measurement in the same manner as in Example 2 following the hydrogen reduction treatment. [Figure 23] Figures 23A to 23C are secondary electron images of the supported metal catalyst of Example 6. Figures 23A to 23B show the state after hydrogen reduction treatment following the supporting process, and Figure 23C shows the state after oxygen reduction activity measurement, similar to Example 2, following the hydrogen reduction treatment. [Figure 24] Figure 24A is a secondary electron image of the supported metal catalyst of Example 6, and Figure 24B is its Z-contrast image. [Figure 25] The image on the left is a secondary electron image of the supported metal catalyst in Comparative Example 1, and the image on the right is its Z-contrast image. [Modes for carrying out the invention] 【0012】 Embodiments of the present invention will be described below with reference to the drawings. The various features shown in the embodiments below can be combined with each other. Furthermore, each feature constitutes an independent invention. 【0013】 1. Supported metal catalyst 1 As shown in Figures 1 to 4, the supported metal catalyst 1 of one embodiment of the present invention comprises a carrier 3 and active metal particles 4. Each component will be described in detail below. 【0014】 2. Structure of Carrier 3 The carrier 3 is an aggregate of conductive particles 2, and is preferably in powder form. Note that in Figures 1 to 4, only one conductive particle 2 is shown. 【0015】 Conductive particles 2 are conductive particles. The composition of conductive particles 2 is not particularly limited, but from the viewpoint of conductivity and ease of manufacture, conductive particles 2 are preferably carbon particles, more preferably mesoporous carbon particles, and even more preferably ordered mesoporous carbon (OMC) particles having small pore diameter and pore spacing deviations, and a periodic arrangement of pores. 【0016】 The shape of the conductive particles 2 is not particularly limited and may consist of single particles (preferably approximately spherical) as shown in Figure 3, or preferably a linked structure 2a in which multiple primary particles 2b (preferably approximately spherical) are linked together (preferably an average of 5 or more) as shown in Figure 4. In the following description, single particles will also be referred to as "primary particles" for convenience. The linked structure 2a is called an aggregate, and is preferred because it forms a channel 2e surrounded by primary particles 2b, which reduces the diffusion resistance of the substance and facilitates the catalytic reaction. The channel 2e can also be called a "primary pore". Furthermore, aggregates of aggregates formed by the aggregation of linked structures 2a are called secondary particles or agglomerates. Since agglomerates are secondary aggregates, they can be broken down relatively easily. The pores created by the gaps between these agglomerates can also be called "secondary pores". 【0017】 The average primary particle diameter of the conductive particles 2 is preferably 20 to 100 nm. If this value is too small, the entrance diameter of the pores 5 may become too small, and if this value is too large, the specific surface area of ​​the carrier 3 may become too small. Specifically, this average particle diameter may be, for example, 20, 30, 40, 50, 60, 70, 80, 90, or 100 nm, and may also be within the range of any two of the values ​​exemplified here. The pores 5 open to the primary particle surface of the conductive particles 2, are of nanoscale size, and can also be referred to as "nanopores". 【0018】 Here, we will explain an example of a method for measuring the average primary particle diameter of conductive particles 2, using the case where conductive particles 2 are linked carbon particle structures 2a as an example. First, a secondary electron image, as shown in Figure 8, is taken of the conductive particle 2 powder using a scanning transmission electron microscope (STEM, Hitachi High-Technologies Corporation, HD-2700) with aberration correction lenses. From the secondary electron image, it can be seen that the carbon particles are arranged in alternating thick and thin sections, forming a linked structure in which an average of 5 or more primary particles are linked together. The maximum diameter of the thick section is taken as the primary particle diameter, and measurements are taken at 100 or more locations, and the average value is calculated. Also, the minimum diameter of the thin section is taken as the diameter of the linkage between primary particles, and measurements are taken at 100 or more locations, and the average value is calculated. 【0019】 As shown in Figure 4, the connecting structure 2a has alternating thick and thin sections along its connecting direction, with the thick sections being primary particles 2b and the thin sections being connecting sections 2c between the primary particles 2b. If the average primary particle diameter of the connecting structure 2a is A and the average diameter of the connecting sections 2c is B, then B / A is preferably 0.1 to 0.9, and more preferably 0.2 to 0.8. If B / A is too small, the strength of the connecting structure 2a may be insufficient. Specifically, B / A may be, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9, and may also be within the range of any two of the values ​​exemplified here. 【0020】 The average particle diameter of the primary particle 2b is the average of the equivalent circular diameter of the conductive particle 2 if the conductive particle 2 is a single particle, and the average of the maximum width of the thickest part of the connected structure 2a if the conductive particle 2 is a connected structure 2a. In this specification, the average is preferably the average of 50 or more (preferably 100 or more) measured values. 【0021】 The average number of connections in the connected structure 2a (the average number of primary particles 2b included in the connected structure 2a) is preferably 5 or more, more preferably 10 or more, and even more preferably 100 or more. This average number of connections is, for example, 5 to 10000, specifically, for example 5, 10, 50, 100, 500, 1000, 5000, 10000, and may be within the range of any two of the values ​​exemplified here. The average number of series connections in the connected structure 2a (the average number of primary particles 2b connected in series) is preferably 3 or more, and even more preferably 5 or more. Series connection means being connected along a line (straight or curved). The number of series connections is counted starting from the primary particle where branching occurs. For example, in the branch of line L in Figure 4, the number of series connections is 4. The average number of series connections is the average number of series connections for 50 or more (preferably 100 or more) branches. This average number of series connections is, for example, 3 to 100, specifically, for example, 3, 5, 10, 50, 100, and may be within the range of any two of the values ​​exemplified here. When conductive particles 2 have such a structure, the diffusion resistance of the material becomes particularly low. 【0022】 As shown in Figures 1 to 3, the conductive particle 2 has a plurality of pores 5. Preferably, the plurality of pores 5 are regular in size, arrangement, shape, etc. The diameter of the pores 5 may be constant or vary along the depth direction. In Figure 2, the conductive particle 2 is shown as having a hollow center, but the conductive particle 2 and primary particles may be hollow or solid in the center. 【0023】 The average entrance pore diameter of pore 5 is 1 to 20 nm. The average entrance pore diameter is the average value of the circular equivalent diameter at the entrance of pore 5. If the average entrance pore diameter is too small, it may be difficult to support the active metal particles 4 within pore 5, and if the average entrance pore diameter is too large, the active metal particles 4 may be supported at a deep position within pore 5 and may not be utilized in the catalytic reaction. Specifically, the average entrance pore diameter can be, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nm, and may also be within the range of any two of the values ​​exemplified here. 【0024】 Here, we will explain an example of how to measure the average entrance pore diameter of pore 5, using the case where conductive particle 2 is a carbon particle as an example. Secondary electron imaging is performed at a magnification between 500,000x and 1,000,000x to measure the pore size. At that time, the brightness and density of the electron microscope image are adjusted so that the boundary between the outer surface of the primary carbon particle and the pore opening on the outer surface becomes clear. Using particle size measurement software (Nireco Corporation, Luzex AP), the equivalent circular diameter of each pore is measured for more than 100 times, and the average entrance pore diameter and its standard deviation are determined. 【0025】 Furthermore, the following three conditions will result in the pores not being counted: (1) Since the primary particles of carbon particles are spherical or spindle-shaped, the size of pores located near the sides cannot be accurately measured by electron microscopy. (2) Even after adjusting the brightness and density of the electron microscope image, the boundary between the outer surface of the carbon particles and the pores may not be sufficiently clear depending on the shape of the sample and the observation conditions. (3) If the sample is not within the range of the crescent focus, the pore size cannot be accurately determined. 【0026】 The standard deviation of the average entrance pore diameter of pore 5 is 50% or less of the average entrance pore diameter, preferably 30% or less. The smaller the standard deviation, the smaller the variation in the entrance diameter of pore 5, and the easier it is to control the position of the conductive particles 2. Specifically, this standard deviation may be, for example, 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50% of the average entrance pore diameter, and may also be within the range of any two of the values ​​exemplified here. 【0027】 The average interpore distance of pores 5 is preferably 5 to 20 nm. The average interpore distance is the average value of the interpore distances obtained from the distance between the centroid points of adjacent pores 5. If the average interpore distance is too small, the supply of reactants for the catalytic reaction may not keep up, and the reaction rate may decrease. If the average interpore distance is too large, the number of pores 5 may become too small, or active metal particles 4 may be more easily supported on the outer surface of the pores. 【0028】 Here, we will explain an example of a method for measuring the average interpore distance of pore 5, using the case where conductive particle 2 is a carbon particle as an example. Secondary electron imaging is performed at a magnification between 500,000x and 1,000,000x to measure the pore size. At that time, the brightness and density of the electron microscope image are adjusted so that the boundary between the outer surface of the primary carbon particle and the pore opening on the outer surface becomes clear. The equivalent circular diameter of each pore is measured 100 or more times using particle size measurement software (Luzex AP, manufactured by Nireco). 【0029】 Furthermore, the following three conditions will result in the pores not being counted: (1) Since the primary particles of carbon particles are spherical or spindle-shaped, the size of pores located near the sides cannot be accurately measured by electron microscopy. (2) Even after adjusting the brightness and density of the electron microscope image, the boundary between the outer surface of the carbon particles and the pores may not be sufficiently clear depending on the shape of the sample and the observation conditions. (3) If the sample is not within the range of the crescent focus, the pore size cannot be accurately determined. 【0030】 Next, when determining the equivalent diameter of the pores, the centroid coordinates of the pores approximated as circles are recorded, and the inter-pore distance is calculated at more than 100 locations from the distance between the centroid points of adjacent pores. The average inter-pore distance and its standard deviation are then calculated. 【0031】 The standard deviation of the average interpore distance of the pores 5 is preferably 50% or less of the average interpore distance, and more preferably 30% or less. The smaller the standard deviation, the easier it is for the conductive particles 2 to be uniformly supported. Specifically, this standard deviation may be, for example, 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50% of the average entrance pore diameter, and may also be within the range of any two of the values ​​exemplified here. 【0032】 3. Method for manufacturing the carrier 3 The carrier 3 can be manufactured by any method capable of forming the pores 5 with the above-described physical properties. Examples of methods for manufacturing the carrier 3 include the hard template method and the soft template method. 【0033】 The hard template method is a technique that uses solids such as microparticles or zeolites as templates. For example, if conductive particle 2 is a carbon particle, a template with regular pores, such as mesoporous silica, is prepared. A carbon source (e.g., sugars such as sucrose) is impregnated into the pores of this template, the carbon source is carbonized, and the template is removed to obtain carbon particles with regular pores. The template portion becomes the pore. 【0034】 The soft template method is a technique that uses the phase separation structure of soft matter such as micelles, emulsions, liposomes, polymer blends, and liquid crystals as templates. 【0035】 For example, if the conductive particles 2 are carbon particles, the conductive particles 2 can be manufactured by a method comprising an aggregate formation step, a bonding step, and a carbonization step. 【0036】 <Aggregate Formation Process> As shown in Figure 5, the aggregate formation process forms a carbon source aggregate 8 by accumulating carbon source spheres 7. The carbon source aggregate 8 becomes the primary particles of the conductive particles 2. 【0037】 Carbon source spheres 7 can be formed, in one example, by forming a film of carbon source on the surface of a micelle. Carbon source spheres 7 have reactive functional groups such as methylol groups and hydroxyl groups, and can be bonded together by, for example, a condensation reaction of the reactive functional groups. Since carbon source spheres 7 are spherical and cannot be stacked without gaps, gaps 8a surrounded by multiple carbon source spheres 7 are inevitably formed in the carbon source aggregate 8. These gaps 8a become the pores 5 of the conductive particles 2. Since the gaps 8a are formed regularly, the pores 5 are also formed regularly. 【0038】 The following are examples of how carbon source spheres 7 and carbon source aggregates 8 are manufactured. First, a mixed solution is prepared by mixing 0.6057 g of phenol (a carbon source), 2.1 mL of formaldehyde solution, and 15.1613 g of 0.1 M NaOH. Next, the mixed solution is stirred in a 70°C bath at 345 rpm for 0.5 hours. Next, 0.96 g of the template molecule Pluronic F-127 (BASF, a nonionic surfactant, a triblock copolymer in which a hydrophobic block is sandwiched between a pair of hydrophilic blocks, hereinafter referred to as "F-127") and 15.0033 g of ultrapure water are added, and the mixture is stirred in a 65°C bath at 345 rpm for 2 hours. Next, 50g of ultrapure water is added, followed by stirring in a 65°C bath at 345 rpm for 16-18 hours. After that, the mixture is allowed to stabilize at 25°C, and 17.7mL of the supernatant is collected. Through the above reaction, a carbon source sphere 7 is produced in which micelles composed of F-127 are coated with resol, and the carbon source sphere 7 self-assembles to form a carbon source aggregate 8. 【0039】 Micelles can be formed, for example, by dispersing a block copolymer having hydrophilic and hydrophobic blocks in a dispersion medium such as water. Preferably, the block copolymer is a triblock copolymer in which a hydrophobic block is sandwiched between a pair of hydrophilic blocks. For example, the block copolymer can be one in which the hydrophobic block is a polymer of propylene oxide and the hydrophilic block is a polymer of ethylene oxide. 【0040】 The coating is composed of, for example, resol. Resol is a phenolic resin having reactive functional groups. The resol coating can be formed by polymerizing phenol and formaldehyde in a dispersion medium containing micelles under conditions where formaldehyde is in excess. In one example, the carbon source sphere 7 is composed of micelles made of triblock copolymer coated with a resol coating. 【0041】 <Joining process> In the bonding step, a carbon source aggregate is formed by bonding the carbon source spheres 7 together in a dispersion containing the carbon source aggregate 8, either without stirring or with stirring. 【0042】 When bonding carbon source spheres 7 together, if the dispersion containing the carbon source aggregate 8 is bonded without stirring or with stirring to a Reynolds number of 1400 or less (hereinafter referred to as "low-speed stirring"), as shown in Figure 6, not only will carbon source spheres 7 contained within the same carbon source aggregate 8 bond together, but carbon source spheres 7 contained within different carbon source aggregates 8 will also bond together. In this case, a carbon source binder having a bonded structure in which an average of 5 or more carbon source aggregates 8 are linked together is obtained. By carbonizing such a carbon source binder, a bonded structure 2a in which an average of 5 or more primary particles 2b are linked together can be formed. The Reynolds number is preferably 1200 or less, and more preferably 1000 or less. The Reynolds number is, for example, between 0 and 1400, specifically, for example, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, and 1400, and may also be within the range of any two of the numbers exemplified here. 【0043】 The Reynolds number Re can be calculated based on the following formula. Re=d 2 ×n × ρ / μ (Here, d: blade diameter of the stirring bar [m], n: rotation speed [s]) -1 ], ρ: Liquid density [kg / m 3 ], μ: liquid viscosity [Pa·s]. 【0044】 In one example, d = 20 × 10 -3 m, n = 0.83s -1 (At 50 rpm), at 130°C and using pure water, ρ = 934.5 kg / m³ 3 When μ = 0.208 mPa·s, the Reynolds number Re = 1490. 【0045】 On the other hand, when the carbon source spheres 7 are bonded together while the dispersion is rapidly stirred, bonding between carbon source spheres 7 contained within the same carbon source aggregate 8 becomes dominant, and single-particle carbon source aggregates are obtained. By carbonizing such carbon source aggregates, conductive particles 2 with a single-particle structure in which primary particles 2b are not linked to each other are obtained. 【0046】 The dispersion medium is preferably water. Furthermore, the bonding of the carbon source spheres 7 is preferably carried out by heating the dispersion. The reaction temperature is, for example, 100 to 150°C, specifically, for example, 100, 110, 120, 130, 140, 150°C, and may be within the range of any two of the values ​​exemplified here. The reaction time is, for example, 5 to 48 hours, specifically, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45, 48 hours, and may be within the range of any two of the values ​​exemplified here. 【0047】 The structure of the carbon source aggregate obtained by the reaction can be altered by changing the reaction temperature, reaction time, and reaction solution concentration. By increasing the reaction temperature, extending the reaction time, or increasing the reaction solution concentration, the number of linked carbon source aggregates 8 and the primary particle size can be increased. 【0048】 <Carbonization Process> In the carbonization process, conductive particles 2 can be obtained by carbonizing the carbon source binder. 【0049】 By the way, if the carbon source conjugate obtained in the above bonding process is heated and carbonized as is, the primary particles 2b (primary particles 2b in a single particle state, or primary particles 2b that have become a linked structure 2a) tend to become three-dimensionally linked to each other, resulting in a structure in which the primary particles 2b are excessively aggregated. Therefore, it is preferable to redisperse the carbon source conjugate and then dry it before carbonization. This can alleviate the aggregation of the primary particles 2b. It is also preferable to spread the dispersion obtained by redispersing the carbon source conjugate thinly and then dry it. This can further alleviate the aggregation of the primary particles 2b. One method for spreading the dispersion thinly is to drop the dispersion onto a surface such as the surface of a glass plate. For example, by dropping the dispersion onto a glass plate heated on a hot plate, the dispersion can be dried in a thinly spread state. 【0050】 Furthermore, the carbon source conjugate may be redispersed, and the resulting dispersion may be spray-dried to mitigate the aggregation of the primary particles 2b. Freeze-drying is preferred for drying. 【0051】 Carbonization of the carbon source conjugate can be carried out by heating the carbon source conjugate under an inert gas (e.g., nitrogen gas) atmosphere. Carbonization of the carbon source conjugate can be carried out, for example, by heating the carbon source conjugate to 600-1000°C. Specifically, this temperature may be, for example, 600, 650, 700, 750, 800, 850, 900, 950, or 1000°C, and may be within the range of any two of the values ​​exemplified here. 【0052】 The carbonization process may include an annealing step in which the conductive particles 2 are annealed. The structure of the conductive particles 2 can be controlled by changing the temperature and time of the annealing process. The annealing process can be carried out, for example, by heating the conductive particles 2 in a vacuum. The temperature of the annealing process is, for example, 800 to 2000°C. Specifically, this temperature may be, for example, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, or 2000°C, and may be within the range of any two of the values ​​exemplified here. 【0053】 When supporting the active metal particles 4 by the reverse micelle method described later, it is preferable to perform an annealing step before the initial supporting step. This annealing step is preferably performed in a vacuum at 1100 to 2000°C. As shown in the examples described later, it is known that (1) in the reverse micelle method, the lower the oxygen content in the conductive particles 2, the higher the amount of active metal particles 4 that can be supported, and (2) the oxygen content in the conductive particles 2 is reduced by performing annealing in a vacuum at 1100 to 2000°C. Combining these findings, it can be seen that by performing annealing in a vacuum at 1100 to 2000°C, the oxygen content in the conductive particles 2 can be reduced, thereby increasing the amount of active metal particles 4 that can be supported. 【0054】 The annealing time is, for example, 0.5 hours or more, and preferably 0.5 to 20 hours. Specifically, this time is, for example, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20 hours, and may be within the range between any two of the numerical values exemplified here or any value above. 【0055】 In addition, in this specification, "vacuum" means a reduced pressure state to 10 -2 hPa or less (preferably 10 -3 hPa or less, 10 -4 hPa or less, or 10 -5 hPa or less). 【0056】 <Others> In addition to the above method, the connecting structure 2a may be generated by connecting the primary particles 2b to each other using a connecting agent. The primary particles 2b may be generated by bonding carbon source spheres 7 to each other while stirring the dispersion liquid at high speed, or may be generated by dividing coarse particles of the carbon source (carbon source coarse particles). Here, the carbon source coarse particles may be manufactured by the method described in Production Example 2 below, and are particles having a primary particle diameter larger than 100 nm. Examples of the connecting agent include compounds having a plurality of reactive functional groups. When each reactive functional group is connected to the primary particle 2b, the primary particles 2b are connected to each other via the connecting agent. As specific connecting agents, for example, saccharides such as sucrose and alcohols such as furfuryl alcohol can be used. 【0057】 4. Structure of the active metal particles 4 As shown in FIG. 1, the active metal particles 4 are dispersed and supported on the conductive particles 2. The active metal particles 4 are fine particles of a metal or alloy that can function as a catalyst. The active metal particles 4 are preferably particles of platinum or a platinum alloy. As the platinum alloy, an alloy of platinum and a transition metal is preferable. Examples of the transition metal include cobalt and nickel. 【0058】 As shown in Figures 1 and 2, the active metal particles 4 are supported in a region on the surface 2d of the conductive particle 2, or within the pores 5. Since the diffusion rate of the substance is low in the deeper parts of the pores 5, the active metal particles 4 supported in the deeper parts of the pores 5 contribute little to or no to the catalytic reaction. Therefore, if a large fraction of the active metal particles 4 are supported in the deeper parts of the pores 5, the utilization efficiency of the active metal particles 4 decreases accordingly. When the utilization efficiency of the active metal particles 4 decreases, it becomes necessary to support more active metal particles 4 to ensure the required reaction rate, which leads to an increase in the cost of the catalyst. 【0059】 Therefore, it is preferable that a high proportion of the active metal particles 4 are supported in the surface region of the conductive particles 2. The surface region refers to the region on the surface 2d of the conductive particles 2, or the region within the pores 5 within a depth X (=15 nm) from the surface 2d (i.e., the region outside the dashed line in Figure 2B). 【0060】 Specifically, it is preferable that the percentage of active metal particles 4 supported in the surface region (hereinafter referred to as "surface-supported particles") (number of active metal particles 4 supported in the surface region / total number of active metal particles 4) be 50% or more, and more preferably 60% or more. In this case, the utilization efficiency of the active metal particles 4 is excellent. Specifically, this percentage may be, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 99, or 100%, and may also be within the range of any two of the values ​​exemplified here. 【0061】 Here, we will explain an example of how to calculate the fractional percentage of surface-supported particles, using the case where the active metal particle 4 is a platinum particle and the conductive particle 2 is a carbon particle. 【0062】 First, a powder of carbon particles supported with platinum particles is placed on a silicon wafer substrate, and a protective layer is formed on the outer surface of the sample particles by gold deposition. Then, the sample particles are cut with a gallium ion beam using a focused ion beam (FIB) system (FB2200, Hitachi High-Technologies Corporation) to prepare sample sections for electron microscopy observation. Subsequently, when observing the cut surface with an electron microscope, the metal particles (Au particles and Pt particles) present on the sample are observed from the Z-contrast image (atomic number contrast image) shown in Figure 10, and at the same time, the composition of each metal particle is analyzed using an energy-dispersive X-ray spectrometer to distinguish between Pt particles and Au particles. The point of transition (boundary line) from the area where Au particles are present to the area where only Pt particles are present but Au particles are absent is defined as the boundary line between the outer surface of the carbon particles and the cross-section. On the electron microscope image, a line segment parallel to the outer surface boundary line is drawn 15 nm from the outer surface boundary line toward the center of the sample particles. The fraction of surface-supported particles is calculated from the ratio of the number of Pt particles between the outer surface boundary line and the line segment at 15 nm to the number of Pt particles located deeper toward the particle center than the line segment at 15 nm. 【0063】 Furthermore, X may be 5 nm or 10 nm, with 5 nm or less being more preferable. Additionally, X may be set as the average particle diameter of the primary particles 2b × Y. Y is, for example, 0.1, 0.2, 0.3, 0.4, or 0.5, with 0.3 being preferred. Furthermore, X may be set as the average entrance pore diameter of the pores 5 × Z. Z is, for example, 1, 2, 3, 4, or 5, with 1 being preferred. 【0064】 Furthermore, it is preferable that the percentage of the active metal particles 4 supported on the surface region of the conductive particles 2 that are supported within the pores 5 is 40% or more. The supported metal catalyst 1 may be thickly coated with an electrolyte material, in which case the activity of the active metal particles 4 coated with the electrolyte material may decrease. By increasing the percentage of the active metal particles 4 supported within the pores 5, the effect of the decrease in activity of the active metal particles 4 can be suppressed. Specifically, this percentage may be, for example, 40, 45, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 65, 70, 75, 80, 85, 90, 95, 99, or 100%, and may be within the range of any two of the values ​​exemplified here. 【0065】 In actual operation of fuel cell vehicles, during low-speed driving with a low current density on the electrode catalyst, the electrolyte material present on the support surface may adhere to the active metal particles present on the support surface, reducing their activity (speed reduction on the active metal particles on the surface). On the other hand, during high-speed driving with a high current density, the large amount of water generated on the cathode catalyst alleviates the adhesion of the electrolyte material to the active metal particles on the support surface, restoring their activity. However, because the reaction rate of the entire catalyst layer is high, the speed on the active metal deep within the pores may decrease due to diffusion resistance to the deep pores (speed reduction on the active metal particles deep within the pores). For these reasons, to cover all operating conditions of fuel cell vehicles, a better catalyst for fuel cell vehicles can be produced by placing the majority of the active metal particles inside the pores, while also placing active metal particles in the region from near the support surface to inside the pores (15 nm or less). From this viewpoint, it is considered even more effective to place active metal particles in a range of 10 nm or less, preferably 5 nm or less, from the surface. 【0066】 The active metal particles 4 have an average interparticle distance of 5 to 20 nm, and the standard deviation of the average interparticle distance is 50% or less of the average interparticle distance. 【0067】 The average interparticle distance of the active metal particles 4 is preferably 5 to 20 nm. The average interparticle distance is the average value of the interparticle distances obtained from the distance between the centroid points of adjacent active metal particles 4. If the average interparticle distance is too small, the supply of reactants for the catalytic reaction may not keep up, and the reaction rate may decrease. If the average interparticle distance is too large, the number of active metal particles 4 may become too small. 【0068】 Here, we will explain an example of a method for measuring the average interparticle distance of active metal particles 4, using the case where conductive particles 2 are carbon particles as an example. Secondary electron imaging is performed at a magnification between 500,000 and 1,000,000 times to measure the particle size. At that time, the brightness and density of the electron microscope image are adjusted so that the active metal particles 4 are clearly visible. The equivalent circular diameter of each particle is measured more than 100 times using particle size measurement software (Luzex AP, manufactured by Nireco). 【0069】 Furthermore, particles will not be counted in the following three cases: (1) Since the primary carbon particles are spherical or spindle-shaped, the size of particles located near the sides cannot be accurately measured by electron microscopy. (2) Even after adjusting the brightness and density of the electron microscope image, the active metal particles 4 may not be sufficiently clear depending on the shape of the sample and the observation conditions. (3) If the sample is not within the range of the crescent focus, the particle size cannot be accurately determined. 【0070】 Next, when determining the equivalent circular diameter of the particle, the centroid coordinates of the particle approximated as a circle are recorded, and the inter-particle distances are calculated at more than 100 locations from the distance between the centroid points of adjacent particles, and the average inter-particle distance and its standard deviation are calculated. 【0071】 The standard deviation of the average interparticle distance of the active metal particles 4 is preferably 50% or less of the average interparticle distance, and more preferably 30% or less. The smaller the standard deviation, the more easily the active metal particles 4 are supported uniformly. Specifically, this standard deviation may be, for example, 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50% of the average interparticle distance, and may also be within the range of any two of the values ​​exemplified here. 【0072】 The average particle size of the active metal particles 4 is preferably 1 to 8 nm. Specifically, this average particle size may be, for example, 1, 2, 3, 4, 5, 6, 7, or 8 nm, and may also be within the range of any two of the values ​​exemplified here. If the average particle size of the active metal particles 4 is less than 1 nm, they may dissolve as the electrode reaction progresses, and if it is larger than 8 nm, the electrochemically active surface area will be small, and the desired electrode performance may not be obtained. The average particle size of the active metal particles 4 is the average value of the equivalent circle diameter. 【0073】 Here, we will explain the method for calculating the average particle diameter, using the case where the active metal particle 4 is platinum particle as an example. First, the catalyst supported with platinum particles is placed on a grid with a carbon support film for electron microscopy, and the average particle diameter of the equivalent circle diameter of the platinum particles is calculated from the image obtained by observing it with an electron microscope. 【0074】 It is preferable that the value of [average particle diameter of active metal particles 4 / average entrance pore diameter of pores 5] is between 0.2 and 0.8. In this relationship, the active metal particles 4 are more easily supported in the surface region. Specifically, this value may be, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or 0.8, and may also be within the range of any two of the values ​​exemplified here. 【0075】 The proportion of active metal particles 4 in the supported metal catalyst 1 (hereinafter referred to as "supporting rate of active metal particles 4") is preferably 16 to 50 mass%, and more preferably 21 to 35 mass%. If this proportion is too small, the performance of the catalyst may not be fully exhibited. If this proportion is too large, the distance between adjacent active metal particles 4 becomes too small, which may lead to degradation due to aggregation and enlargement of the active metal particles 4. Specifically, the supporting rate of active metal particles 4 can be, for example, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 mass%, and may be within the range of any two of the values ​​exemplified here. 【0076】 The loading rate of the active metal particles 4 can be measured by thermogravimetric analysis. In thermogravimetric analysis, the supported metal catalyst 1 is burned in air, and the loading rate can be calculated using the residue as the active metal particles 4. 【0077】 5. Method for producing supported metal catalyst One possible method for supporting the active metal particles 4 is the conventional impregnation method. However, with the conventional impregnation method, it is not possible to selectively support the particles only near the entrance of the pores. In addition to adsorption inhibition by the electrolyte material and resistance to mass diffusion, the particle size distribution of the active metal particles 4 becomes broad. Therefore, when used as a cathode in a fuel cell, the particle growth of the active metal particles 4 progresses during operation, causing degradation. 【0078】 Therefore, a method is preferred in which the activated metal particles 4 are synthesized in the liquid phase beforehand and then supported. That is, activated metal particles 4 or their oxides of uniform size are synthesized in the liquid phase beforehand using methods such as the reverse micelle method or the colloid method, and then supported on a carrier having regular pores. Since the size of the pores 5 of the conductive particles 2 is uniform, the selectivity of the support position of the activated metal particles 4 can be increased, which leads to the suppression of degradation and the reduction of the amount of activated metal particles 4 used. 【0079】 Furthermore, by supporting the activated metal particles 4 using the method described below, a supported metal catalyst 1 can be obtained in which the average interparticle distance and its standard deviation of the activated metal particles 4 are of an appropriate value. 【0080】 5-1. Reverse micelle method In the reverse micelle method, the method for producing a supported metal catalyst comprises a mixing step, a reduction step, and a supporting step. Each step is described below. 【0081】 <Mixing process> In the mixing step, an active metal precursor solution containing an active metal precursor, a surfactant, and an organic solvent are mixed to produce a mixed solution (hereinafter referred to as the "active metal precursor mixed solution"). 【0082】 An active metal precursor is a compound that serves as a raw material for reduction to form an active metal, and examples include acids, salts, or complexes of the active metal. Examples of active metal precursors include chlorinated metal acids and their salts (e.g., potassium salts), as well as ammine complexes, ethylenediamine complexes, and acetylacetonate complexes of the active metal. When the active metal is platinum, platinum precursor compounds can be used, such as chlorplatinic acid (e.g., hexachloride platinumic acid, tetrachloride platinumic acid), acetylacetonate platinum [Pt(acac)2], chlorplatinate salts (e.g., potassium chlorplatinate [K2PtCl4]), and platinum ammine complexes. The active metal precursor solution is preferably an aqueous solution. Furthermore, the active metal precursor does not need to be of only one type, and second and third metal salts may be added. 【0083】 Any surfactant capable of forming reverse micelles can be used. Examples of surfactants include anionic surfactants (e.g., soap, sulfated oil, polyoxyethylene alkyl ether sulfate, alkyl sulfate ester, alkylbenzene sulfonate, alkane sulfonate, α-olefin sulfonate, N-acyl amino acid salt, dialkyl sulfosuccinate, alkylnaphthalene sulfonate), cationic surfactants (e.g., alkyltrimethylammonium salt, alkylpyridinium salt), nonionic surfactants (e.g., polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, polyhydric alcohol fatty acid ester), and amphoteric surfactants (e.g., betaine, sulfobetaine). Nonionic surfactants are preferred, those having a phenylene group are more preferred, polyoxyalkylene alkylphenyl ethers are even more preferred, polyoxyethylene alkylphenyl ethers are preferred, and polyoxyethylene nonylphenyl ethers are even more preferred. The average number of moles of polyoxyalkylene added is preferably 2 to 10, more preferably 3 to 7, and even more preferably 5. The average number of moles added is, specifically, for example, 2, 3, 4, 5, 6, 7, 8, 9, or 10, and may be within the range of any two of the values ​​exemplified here. 【0084】 The molar ratio Rw of water to surfactant is preferably 1 to 7, and more preferably 2 to 5. Furthermore, the concentration of the surfactant is preferably above the critical micelle concentration, and more preferably 40 to 160 mmol / L. 【0085】 As the organic solvent, a hydrophobic organic solvent is preferred, and one containing at least one selected from cyclohexane, heptane, and toluene is more preferred. 【0086】 <Restoration Process> In the reduction step, the active metal precursors in the active metal precursor mixed solution are reduced to produce active metal particles 4. The liquid temperature is preferably 20°C to 30°C. 【0087】 The active metal precursor can be reduced by adding a reducing agent to the mixed solution. Examples of reducing agents include MBR3H, MH (where M represents lithium, sodium, or potassium, and R represents a hydrogen atom or a hydrocarbon group, and the hydrocarbon group may be linear or branched, saturated or unsaturated), and hydrogen, with NaBH4 being preferred. 【0088】 The reduction is preferably carried out by mixing a reducing agent mixture solution containing a reducing agent, an organic solvent, water, and a surfactant with the activated metal precursor mixture solution. In this case, compared to directly adding a solid reducing agent to the activated metal precursor mixture solution, the reduction rate of the activated metal precursor is controlled, the monodispersity of the Pt particles is improved, and as a result, an increase in surface loading is expected. 【0089】 The surfactant in the reducing agent mixed solution can be selected from the group listed in the <mixing step> described above, and is preferably the same as the one mixed in the <mixing step>. 【0090】 The molar ratio Rw of water to surfactant in the reducing agent mixture solution is preferably 1 to 7, more preferably 2 to 5, and even more preferably the same concentration as the activated metal precursor mixture solution. 【0091】 The organic solvent in the reducing agent mixture is preferably a hydrophobic organic solvent, more preferably one selected from cyclohexane, heptane, and toluene, and even more preferably the same as the active metal precursor mixture. 【0092】 The activated metal particles 4 obtained in the reduction process are contained within inverse micelles, and the diameter of the inverse micelles is larger than the diameter of the activated metal particles 4 themselves. As a result, the accumulation of activated metal particles 4 in deep locations within the pores 5 is suppressed, and the proportion of activated metal particles 4 accumulated in the surface region is increased. 【0093】 The median particle size measured by dynamic light scattering in the mixed solution is the inverse micelle diameter. It is preferable that this inverse micelle diameter is 0.5 to 2 times the average entrance pore diameter of the pores 5. In this case, the fraction of active metal particles 4 supported in the surface region is particularly increased. Specifically, this fraction can be, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2 times, and may be within the range of any two of the values ​​exemplified here. 【0094】 In a solvent, inverse micelles consist of a surfactant layer surrounding a tiny water droplet containing active metal particles, and a solvent layer formed around it. If the inverse micelle diameter is sufficiently smaller than the pore inlet diameter (inverse micelle diameter is less than 0.5 times the pore inlet diameter of pore 5), the surfactant layer is isolated from the inner wall of the pore inlet by the solvent layer formed outside the surfactant layer. As a result, the interaction between the pore wall and the surfactant is weak, and the inverse micelle penetrates deep into the pore without collapsing. In contrast, if the inverse micelle diameter exceeds twice the pore inlet diameter of pore 5, the inverse micelle diameter is too large relative to the pore inlet diameter, preventing it from penetrating the pore. Consequently, the active metal particles are supported on the outer surface of the pore. On the other hand, when the reverse micelle diameter is in the range of 0.5 to 2 times the pore inlet diameter of pore 5, the diameter of the surfactant layer surrounded by the solvent layer and the pore inlet diameter are roughly the same. As a result, when the reverse micelle enters the pore inlet, strong adsorption occurs between the hydrophobic portion of the surfactant molecule and the support pore wall, causing the instability of the reverse micelle and the collapse of the micelle structure. At that time, since the active metal particles are adsorbed on the hydrophilic portion of the surfactant, the active metal particles are trapped near the pore inlet via the surfactant and become fixed at a short distance from the pore inlet. 【0095】 <Supporting process> In the loading process, the active metal particles 4 obtained in the reduction process are mixed with the carrier 3, which is an aggregate of conductive particles 2, to disperse and load the active metal particles 4 onto the conductive particles 2. 【0096】 The carrier 3 can be the one described in "2. Composition of Carrier 3". Mixing is preferably done by mixing the mixed solution after the reduction step with the carrier 3. By stirring the mixed solution obtained after mixing, the uniformity of the support can be improved. The stirring time is preferably 1 hour or more, and more preferably 6 hours or more. This time is, for example, 1 to 100 hours, specifically, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 100 hours, and may be within the range of any two of the values ​​exemplified here or greater than or equal to either of them. 【0097】 The supported metal catalyst 1 can be removed from the mixed solution by solid-liquid separation methods such as filtration after loading. 【0098】 <Surfactant removal process> The extracted supported metal catalyst 1 can be subjected to a treatment to remove any remaining surfactant. Surfactant removal can be carried out by washing with a solvent or by a reduction treatment. It is preferable to remove most of the surfactant by washing with a solvent, and then remove any trace amounts of surfactant remaining in the pores by a subsequent reduction treatment. Examples of solvents include water and compounds having hydrophilic and hydrophobic groups. Examples of compounds having hydrophilic and hydrophobic groups include alcohols. In this case, methanol or ethanol is preferable. It is preferable to dry the washed supported metal catalyst 1 by vacuum drying or the like. 【0099】 The reduction treatment can be carried out by heat-treating the supported metal catalyst 1, which has been removed from the mixed solution, under a reducing gas atmosphere. It is preferable that the supported metal catalyst 1 has been solvent-washed and dried under reduced pressure before the reduction treatment. The reducing gas is a gas that has a reducing effect, and examples include a mixed gas of hydrogen and an inert gas (e.g., nitrogen). The hydrogen concentration in the reducing gas is, for example, 1 to 100%, and preferably 1 to 10%. Specifically, this concentration may be, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 50, 100%, and may be within the range of any two of the values ​​exemplified here. The heat treatment temperature is, for example, 100 to 400°C, and preferably 150 to 250°C. Since the reducing gas also enters the pores 5 of the conductive particles 2, it is possible to hydrogenate and effectively remove the surfactant remaining in the pores 5. These temperatures are specifically, for example, 100, 150, 200, 250, 300, 350, and 400°C, and may also be within the range of any two of the values ​​exemplified here. 【0100】 <Arraying process> A sorting step may be included after the loading step. In the sorting step, a sorting treatment is performed to improve the regularity of the arrangement of the active metal particles 4. The sorting treatment can be carried out in the same way as in "<Sorting Step>" in "5-3. Colloidal Method". When active metal particles 4 are loaded by the reverse micelle method, many of the active metal particles 4 are loaded within the pores 5 and are already regularly arranged, but some are loaded at the edges of the pores 5 or outside of the pores 5. It is thought that by performing the sorting treatment, these active metal particles 4 loaded in unstable positions will move into the more stable pores 5, and by increasing the proportion of active metal particles 4 present in the pores 5, the active metal particles 4 will become more regularly arranged. In addition, it is thought that the dissolution and reprecipitation of the active metal particles 4 will proceed during the potential sweep in the electrolyte, reducing the variation in particle size of the active metal particles 4 and increasing the proportion of active metal particles 4 loaded within the pores 5. 【0101】 Furthermore, the reduction treatment in the surfactant removal step described above can also serve as an arrangement treatment. In other words, the reduction treatment removes the surfactant and promotes the arrangement of the active metal particles 4. The arrangement treatment may consist of only the reduction treatment, or another arrangement treatment may be performed before or after the reduction treatment. 【0102】 5-2. Reverse micelle method with multiple cycles In the reverse micelle method described above, it may be difficult to sufficiently increase the loading rate of the active metal particles 4 with only one cycle. In such cases, the loading rate can be increased by performing the reverse micelle method for multiple cycles. 【0103】 This method, in one example, comprises a first step, a surfactant removal step, and a second step. The first step comprises a first mixing step, a first reduction step, and a first loading step, while the second step comprises a second mixing step, a second reduction step, and a second loading step. 【0104】 The following describes each step. 【0105】 <First mixing process> In the first mixing step, the active metal precursor solution containing the active metal precursor, a surfactant, and an organic solvent are mixed to produce a first active metal precursor mixed solution. This step can be carried out in the same manner as the <mixing step> described above. 【0106】 <First Reduction Process> In the first reduction step, the active metal precursor in the first active metal precursor mixed solution is reduced to produce active metal particles 4. This step can be carried out in the same manner as the <reduction step> described above. 【0107】 <First loading process> In the first loading step, the active metal particles 4 obtained in the first reduction step are mixed with the carrier 3, which is an aggregate of conductive particles 2, to disperse and support the active metal particles 4 on the conductive particles 2. This step can be carried out in the same manner as the <loading step> described above. 【0108】 <Surfactant removal process> In the surfactant removal step, surfactants adhering to the carrier 3 are removed. Surfactant removal can be carried out by the method described in the <Surfactant Removal Step> above. This step is preferably carried out by a reduction treatment, and more preferably by solvent washing followed by a reduction treatment. In this case, surfactants in the pores 5 that do not support the active metal particles 4 can also be effectively removed, thereby promoting the support of active metal particles 4 in the pores 5 that do not support the active metal particles 4 in the next support step. 【0109】 <Second mixing process> In the second mixing step, the active metal precursor solution containing the active metal precursor, a surfactant, and an organic solvent are mixed to produce a second active metal precursor mixed solution. This step can be carried out in the same manner as the first mixing step. The active metal precursor solution, surfactant, and organic solvent may be different from those used in the first mixing step, but it is preferable that they be the same. 【0110】 <Second Reduction Process> In the second reduction step, the active metal precursor in the second active metal precursor mixed solution is reduced to produce active metal particles 4. This step can be carried out in the same manner as the <reduction step> described above. 【0111】 <Second loading process> In the second loading step, the carrier after the surfactant removal step is mixed with the activated metal particles 4 obtained in the second reduction step, thereby dispersing and supporting the activated metal particles 4 obtained in the second reduction step onto the conductive particles 2. This step can be carried out in the same manner as the <loading step> described above. 【0112】 <Surfactant removal process> A surfactant removal step may be performed after the second loading step. This step can be carried out in the same manner as the <surfactant removal step> in "5-1. Reverse micelle method". 【0113】 <Arraying process> A sequencing step may be included after the second loading step. This step can be carried out in the same way as the <sequencing step> in "5-1. Reverse Micelle Method". 【0114】 Through the above steps, a supported metal catalyst 1 with an increased load-bearing rate of active metal particles 4 can be obtained. If it is desired to further increase the load-bearing rate of active metal particles, a second surfactant removal step and a third step can be performed after the second step. The second surfactant removal step can be performed in the same manner as the <surfactant removal step> described above. The third step can be performed in the same manner as the second step. 【0115】 5-3. Colloid Method In the colloid method, the method for producing a supported metal catalyst comprises an initial addition step, a simultaneous addition step, a supporting step, and an arrangement step. 【0116】 <Initial addition process> In the initial addition step, an oxidizing agent is added to the active metal precursor solution containing the active metal precursor to oxidize the active metal precursor into oxide particles of the active metal, thereby generating a colloid. 【0117】 The explanation for the activated metal precursor solution is similar to that of the reverse micelle method. 【0118】 The oxidizing agent is, for example, hydrogen peroxide. The oxidizing agent oxidizes the active metal precursor to produce an oxide of the active metal. This oxide is in the form of fine particles and is dispersed in the mixed solution. 【0119】 For example, the pH decreases upon the addition of an oxidizing agent, and the pH immediately after the initial addition step is, for example, 1.0 to 2.5. Specifically, this pH can be, for example, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or 2.5, and may also be within the range of any two of the values ​​exemplified here. 【0120】 In the initial addition step, only the oxidizing agent may be added, or the oxidizing agent may be added along with the neutralizing agent. Alternatively, only the neutralizing agent may be added before the initial addition to bring the pH closer to the target value described later. 【0121】 <Simultaneous addition process> In the simultaneous addition step, the neutralizing agent and the oxidizing agent are added to the colloid simultaneously until the amount of the oxidizing agent reaches a specified amount. 【0122】 The neutralizing agent is, for example, an aqueous solution of a basic substance such as sodium hydroxide, and is added to raise the pH, which has decreased in the initial addition step, to approach the target value. The target pH is, for example, 4.0 to 6.0, preferably 4.5 to 5.5, and more preferably 4.9 to 5.1. If the pH is too low, the oxidation of the active metal precursor may not proceed smoothly, and if the pH is too high, the colloid may become unstable. Specifically, the target values ​​are, for example, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, and 6.0, and may also be within the range of any two of the values ​​exemplified here. 【0123】 In Comparative Example 1, described later, the specified amount of oxidizing agent was added by repeatedly performing a neutralizing agent addition step (adding only the neutralizing agent) and an oxidizing agent addition step (adding only the oxidizing agent) after the initial addition step. In this method, the pH rose immediately after adding the neutralizing agent and fell immediately after adding the oxidizing agent, making the colloid unstable and prone to aggregation of oxide particles in the colloid. Furthermore, in Comparative Example 1, it took time to add the specified amount of oxidizing agent and finally adjust to the target pH, which also made the oxide particles in the colloid prone to aggregation. 【0124】 In contrast, this method involves adding a neutralizing agent and an oxidizing agent simultaneously. More specifically, when adding a neutralizing agent to raise the pH that has decreased in the initial addition step, the oxidizing agent is also added at the same time. This method allows for the addition of a specified amount of oxidizing agent in a short time while suppressing pH fluctuations, and the pH immediately after the simultaneous addition step will be the target pH value mentioned above. According to this method, the aggregation of oxide particles in the colloid is suppressed due to colloid destabilization, resulting in a colloid in which fine and uniform oxide particles are suspended. 【0125】 While the neutralizing agent and oxidizing agent may be added manually, it is preferable to add them using an automatic titrator to more reliably suppress pH fluctuations. 【0126】 <Supporting process> In the support process, the oxide particles are supported on the conductive particles 2 by mixing the carrier 3, which is an aggregate of conductive particles 2, with a colloid. 【0127】 The carrier 3 can be the one described in "2. Composition of Carrier 3". By stirring the mixed solution obtained after mixing, the uniformity of the support can be improved. The stirring time is preferably 1 hour or more, and more preferably 6 hours or more. This time is, for example, 1 to 100 hours, specifically, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 100 hours, and may be within the range of any two of the values ​​exemplified here or greater than or equal to any two of them. The stirring temperature is, for example, 70 to 100°C, specifically, for example, 70, 75, 80, 85, 90, 95, 99, 100°C, and may be within the range of any two of the values ​​exemplified here. 【0128】 The supported metal catalyst 1 can be removed from the mixed solution by solid-liquid separation methods such as filtration after loading. 【0129】 <Arraying process> In the arrangement process, an arrangement treatment is applied to enhance the regularity of the arrangement of oxide particles, or active metal particles 4 generated by their reduction. 【0130】 The sequencing treatment preferably includes at least one of heat treatment and electrochemical treatment. 【0131】 Heat treatments include those using inert gases, reducing gases, oxidizing gases, or in a vacuum. More specifically, these include heating and reduction under hydrogen flow (e.g., 5% H2 / N2, 500 mL / min flow, 300°C, 1 hour holding), heating in an inert gas (e.g., N2, 500 mL / min flow, 300°C, 1 hour holding), and vacuum heating (e.g., 5 × 10⁻¹⁰ -5 Examples include heating under exhaust pressure to hPa, holding at 300°C for 1 hour, and heating oxidation under oxygen (or oxygen-containing gas) flow (for example, 5% O2 / N2, 500 mL / min flow, holding at 200°C for 1 hour). 【0132】 Electrochemical treatments include potential sweeps in an electrolyte solution (e.g., 0.1M perchloric acid aqueous solution, 0.1M sulfuric acid aqueous solution, etc.) (e.g., 100 cycles of sweeping from 0.05V to 1.15V at 500mV / s under N2 saturation), potential sweeps (e.g., 20 cycles of sweeping from 0.25V to 1.0V at 20mV / s under O2 saturation), and potential steps (e.g., 10,000 cycles of holding at 1.0V for 3 seconds, then at 0.6V for 3 seconds under N2 saturation). 【0133】 Immediately after the loading process, the oxide particles are attached in layers to the surface of the conductive particles 2 and are not supported in a regular arrangement. However, by performing the arrangement process, the regularity of the arrangement of the oxide particles, or the active metal particles 4 that are generated when they are reduced, can be increased. 【0134】 If the arrangement process involves the reduction of oxide particles, such as heat treatment with a reducing gas, the reduction of oxide particles and the arrangement of oxide particles or the active metal particles 4 generated by their reduction proceed simultaneously. On the other hand, if the arrangement process does not involve the reduction of oxide particles, it is preferable to perform the reduction treatment of oxide particles before or after the arrangement process. Active metal particles 4 are generated by the reduction treatment of oxide particles. 【0135】 For example, it is preferable to perform a reduction treatment (which also serves as an alignment treatment) on the oxide particles supported on the conductive particles 2 after the support process, and then perform another alignment treatment as needed. 【0136】 5-4. Protective Colloid Method In the protective colloid method, the method for producing a supported metal catalyst comprises a mixing step, a reduction step, and a supporting step. Each step is described below. 【0137】 <Mixing process> In the mixing step, a mixed solution is produced by mixing an active metal precursor solution containing an active metal precursor with a polymer protective agent and a reducing agent. 【0138】 The description of the activated metal precursor and its solution is the same as that of the reverse micelle method. 【0139】 The polymer protective agent is any substance capable of adhering to the active metal precursor and forming a hydrophilic protective colloid, and preferably contains at least one of polyvinylpyrrolidone, polyacrylic acid, and polyvinyl alcohol. 【0140】 Any reducing agent capable of reducing the active metal precursor can be used as the reducing agent. For example, the reducing agents mentioned in the description of the reverse micelle method and alcohols (ethylene glycol, ethanol, methanol, etc.) can be used, with alcohols being preferred. <Restoration Process> In the reduction step, the active metal precursor in the mixed solution is reduced to produce active metal particles 4. 【0141】 The reduction of the active metal precursor can be carried out using a reducing agent in a mixed solution, and when an alcohol is used as the reducing agent, it is preferable to reflux the mixed solution. 【0142】 The activated metal particles 4 obtained in the reduction process form a hydrophilic protective colloid, and the overall diameter of the hydrophilic protective colloid is larger than the diameter of the activated metal particles 4 themselves. As a result, the accumulation of activated metal particles 4 in deep locations within the pores 5 is suppressed, and the proportion of activated metal particles 4 accumulated in the surface region is increased. 【0143】 The median number diameter measured by dynamic light scattering in the mixed solution corresponds to the overall diameter of the hydrophilic protective colloid, and it is preferable that this median number diameter is 0.5 to 2 times the average entrance pore diameter of pore 5, similar to the reverse micelle method. Specifically, this ratio is, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2 times, and may be within the range of any two of the values ​​exemplified here. 【0144】 <Supporting process> The explanation of the loading process is the same as that for the reverse micelle method. 【0145】 6.Fuel cell 200 Figure 7 shows a schematic diagram of a fuel cell. In Figure 7, the fuel cell 200 is configured such that the catalyst layer 220A and gas diffusion layer 210A on the anode 201 side and the catalyst layer 220K and gas diffusion layer 210K on the cathode 202 side face each other with an electrolyte membrane 230 in between. The configuration is such that the anode-side gas diffusion layer 210A, anode-side catalyst layer 220A, electrolyte membrane 230, cathode-side catalyst layer 220K, and cathode-side gas diffusion layer 210K are arranged in this order. By connecting a load 203 between the anode 201 and cathode 202 of the fuel cell 200, power is output to the load 203. 【0146】 It is preferable that the cathode-side catalyst layer 220K contains the supported metal catalyst 1. If the cathode reaction occurs at a deep position in the pore 5, the water generated by the reaction is not properly discharged, which leads to a problem in which the activity of the active metal particles 4 decreases. However, in the supported metal catalyst 1 of the present invention, a high fraction of the active metal particles 4 are supported on the surface region of the conductive particles 2, so the above problem is mitigated by including the supported metal catalyst 1 in the cathode-side catalyst layer 220K. [Examples] 【0147】 1. Manufacturing of the carrier The carrier was manufactured using the method described below. 【0148】 1-1. Manufacturing Example 1 (Micelle template, no stirring, linked structure) In manufacturing example 1, a carrier, which is a powder of carbon particles, was manufactured using micelles as a template. 【0149】 <Aggregate Formation Process> First, a mixed solution was prepared by mixing 0.6057 g of phenol (a carbon source), 2.1 mL of formaldehyde solution, and 15.1613 g of 0.1 M NaOH. Next, the mixed solution was stirred in a 70°C bath at 345 rpm for 0.5 hours. Next, 0.96 g of the template molecule Pluronic F-127 (manufactured by BASF, a nonionic surfactant, a triblock copolymer in which a hydrophobic block is sandwiched between a pair of hydrophilic blocks, hereinafter referred to as "F-127") and 15.0033 g of ultrapure water were added, and the mixture was stirred in a 65°C bath at 345 rpm for 2 hours. Next, 50g of ultrapure water was added, followed by stirring in a 65°C bath at 345 rpm for 16-18 hours. After that, the mixture was allowed to stabilize at 25°C, and 17.7mL of the supernatant was collected. Through the above reaction, carbon source spheres 7, in which micelles composed of F-127 are coated with resol, were produced, and the carbon source spheres 7 self-assembled to form a carbon source aggregate 8. 【0150】 <Joining process> A dispersion obtained by mixing 17.7 mL of supernatant liquid with 56 g of ultrapure water was allowed to stand in an autoclave at 130°C for 24 hours without stirring, thereby bonding the carbon source spheres 7 together to form a carbon source aggregate. Next, the carbon source conjugate was extracted by filtration, washed with water, and then vacuum-heated and dried at 50°C. 【0151】 <Carbonization Process> Next, 0.3 g of the carbon source conjugate powder, after vacuum heating and drying, was treated in 40 mL of ultrapure water using an ultrasonic homogenizer for 5 minutes to prepare a dispersion. This dispersion was then sprayed into 750 mL of liquid nitrogen. The resulting frozen fine powder was freeze-dried in a freeze-drying apparatus for 16 hours to obtain a dried powder of the carbon source conjugate. 【0152】 Next, the dried powder obtained in the above process was carbonized by heating it in nitrogen at 700°C for 2 hours to obtain carbon particle powder. The resulting carbon particle powder had a very low degree of aggregation between particles. 【0153】 The obtained powder was subjected to a scanning transmission electron microscope (STEM, Hitachi High-Technologies Corporation, HD-2700) with aberration correction lenses to capture secondary electron images, as shown in Figure 8. As is clear from the secondary electron images, the carbon particles were found to consist of alternating thick and thin sections, forming a linked structure in which an average of 5 or more primary particles were linked together. The linked structure had an average of 10 or more primary particles linked together and an average of 4.3 primary particles linked in series. 【0154】 The maximum diameter of the thickest part was defined as the primary particle diameter, and measurements were taken at more than 100 locations. The average value was found to be 55.7 ± 5.4 nm. The minimum diameter of the thinnest part was defined as the diameter of the connection between primary particles, and measurements were taken at more than 100 locations. The average value was found to be 37.7 ± 5.4 nm. 【0155】 Next, secondary electron imaging was performed at magnifications between 500,000x and 1,000,000x to measure the pore size. The brightness and contrast of the electron microscope image were adjusted to clearly distinguish the boundary between the outer surface of the primary carbon particles and the pores opening to that surface. Using particle size measurement software (Nireco Corporation, Luzex AP), the equivalent circular diameter of over 100 pores was measured, and the average entrance pore diameter and its standard deviation were determined to be 5.2 ± 0.5 nm. The number after ± indicates the standard deviation. 【0156】 Furthermore, the following three conditions were met in order to not count the area as a pore: (1) Since the primary particles of carbon particles are spherical or spindle-shaped, the size of pores located near the sides cannot be accurately measured by electron microscopy. (2) Even after adjusting the brightness and density of the electron microscope image, the boundary between the outer surface of the carbon particles and the pores may not be sufficiently clear depending on the shape of the sample and the observation conditions. (3) If the sample is not within the range of the crescent focus, the pore size cannot be accurately determined. 【0157】 Next, in determining the equivalent circular diameter of the pores, the centroid coordinates of the pores approximated as circles were recorded. The interpore distance was then calculated at more than 100 locations using the distance between the centroid points of adjacent pores, and the average interpore distance and its standard deviation were calculated to be 12.6 ± 1.4 nm. 【0158】 1-2. Manufacturing Example 2 (Micelle Template, Coarse Particles) <Resol precursor gel formation process> First, a mixed solution was prepared by mixing 69.11g of ethanol, 4.48mL of ultrapure water, and 3.62g of F-127. Next, the mixed solution was stirred at room temperature for 0.5 hours. Next, 11.01 g of resorcinol, a carbon source, was added, and the mixture was stirred at room temperature for 0.5 hours. Next, 7.3048 g of 37% formalin was added, and the mixture was stirred at room temperature for 0.5 hours. Next, 5 mol / dm 3 After adding 1.182g of hydrochloric acid, the mixture was stirred at 30°C and 300rpm for 72 hours. Next, after static decomposition, 16.0226 g of the biphase-separated lower layer was taken out. 【0159】 <Resol precursor gel polymerization process> Next, the removed lower layer was left to stand at 90°C for 24 hours. 【0160】 <Carbonization Process> Next, carbonization was performed by heating in nitrogen at 800°C for 3 hours to obtain a carbon particle powder. 【0161】 A secondary electron image, as shown in Figure 9, was taken of the obtained carbon particle powder, in the same manner as in Production Example 1. As is clear from the secondary electron image, the carbon particles were coarse. 【0162】 The average inlet pore diameter and its standard deviation, as well as the average interpore distance and its standard deviation, were determined using the same method as in Manufacturing Example 1, and were found to be 4.6 ± 1.1 nm and 10.4 ± 1.1 nm, respectively. 【0163】 1-3. Manufacturing Example 3 (Annealing at 1000°C) A graphite crucible containing 200 mg of carbon particle powder obtained in Manufacturing Example 1 was placed in a high-vacuum induction heating furnace and pre-vacuumed for 12 hours. 5 × 10 -4 The carbon particles of Production Example 3 were obtained by raising the temperature from 25°C to 700°C in 30 minutes while evacuating the system to maintain a pressure below hPa, holding it at the same temperature for 5 minutes, then raising the temperature at 100°C / h to the target maximum temperature, holding it at the same temperature for 1 hour, and then cooling. For example, if the target temperature was 1000°C, the heating time from 700°C to 1000°C was 3 hours. 【0164】 1-4. Manufacturing Example 4 (Annealing at 1200°C) Except for setting the target temperature to 1200°C, the carbon particles of Production Example 4 were obtained using the same method as in Production Example 3. 【0165】 1-5. Manufacturing Example 5 (Annealing at 1400°C) Except for setting the target temperature to 1400°C, the carbon particles of Production Example 5 were obtained using the same method as in Production Example 3. 【0166】 2. Supporting of active metal particles The activated metal particles were supported on a carrier according to the following method. 【0167】 2-1. Example 1 (Reverse micelle method, Rw=3, coarse particles) <Mixing process> A 60 mmol / L surfactant (NP-5, polyoxyethylene nonylphenyl ether, average number of moles added = 5) / cyclohexane solution was prepared in a volumetric flask. After allowing the prepared solution to stand for one day, a 40 mmol / L (Pt: 7684 ppm) H2PtCl6 aqueous solution was added to produce an activated metal precursor mixed solution, where Rw is 3 (mol / mol). Here, Rw is the molar ratio of water to surfactant (water / surfactant). 【0168】 <Restoration Process> The resulting mixed solution of activated metal precursors was stirred at room temperature for 5 hours, during which 20 equivalents of NaBH4 were added relative to the Pt. During this process, H2PtCl6 was reduced by the NaBH4, causing a change in the solution's color and indicating that the platinum particles were encapsulated in inverse micelles. The median diameter of the inverse micelles, measured by dynamic scattering, was 5.9 nm. This was 1.28 times the average entrance pore diameter (4.6 nm) of the carbon particles obtained in Production Example 2. 【0169】 <Supporting process> The carbon particles obtained in Production Example 2 were added to the solution after the reduction process in a ratio that resulted in a Pt load of 20 wt%, and the mixture was stirred overnight at room temperature. Next, the obtained product was filtered through a membrane filter, washed with methanol (100 mL) on the membrane filter, and the surfactant was removed by vacuum drying. Through these steps, a supported metal catalyst was obtained in which platinum particles were supported on carbon particles. 【0170】 The average particle size of platinum particles supported on carbon particles was calculated using the following method. First, the Pt-supported catalyst was placed on a grid with a carbon support film for electron microscopy, and the average particle size of the platinum particles was calculated from the image obtained by electron microscopy using the elliptic approximation. As a result, the average particle size of the platinum particles was 2.9 nm. 【0171】 The fraction of platinum particles supported in the surface region (hereinafter referred to as "surface-supported particles") was calculated using the following method. First, a powder of carbon particles supported with platinum particles was placed on a silicon wafer substrate, and a protective layer was formed on the outer surface of the sample particles by gold deposition. Then, the sample particles were cut with a gallium ion beam using a focused ion beam (FIB) system (FB2200, Hitachi High-Technologies Corporation) to prepare sample sections for electron microscopy observation. Subsequently, when observing the cut surface with an electron microscope, the metal particles (Au particles and Pt particles) present on the sample were observed from the Z-contrast image (atomic number contrast image) shown on the right side of Figure 10, and at the same time, the composition of each metal particle was analyzed using an energy-dispersive X-ray spectrometer to distinguish between Pt particles and Au particles. The point of change (boundary line) from the region where Au particles are present to the region where only Pt particles are present and Au particles are absent was defined as the boundary line between the outer surface of the carbon particles and the cross-section. On the electron microscope image, a line segment B2 parallel to the outer surface boundary line B1 was drawn 15 nm in the direction toward the particle center of the sample. The percentage of surface-supported particles was calculated from the ratio of the number of Pt particles between the outer surface boundary line B1 and the line segment B2 at 15 nm to the number of Pt particles located deeper toward the particle center than the line segment at 15 nm. As a result, the percentage of surface-supported particles was 86%. 【0172】 Furthermore, the percentage of surface-supported particles that are supported within the pores (hereinafter referred to as "surface-pore-supported particles") was calculated using the following method. In STEM observation of platinum-supported carbon particles, the planar position of the pore entrance was identified from the secondary electron image, and then the planar position of all platinum supported on and inside the carbon particle within the observation field was identified from the Z-contrast image. Next, the percentage of platinum supported within the pores was calculated by comparing the obtained pore entrance positions with the platinum positions. In this case, platinum that was not observed in the secondary electron image but was observed in the Z-contrast image was judged to be supported inside the pores. Platinum present in the back hemisphere of the carbon particle was excluded based on the depth of focus when acquiring the Z-contrast image. As a result, the percentage of surface-pore-supported particles was 74.4%. 【0173】 The platinum particles were arranged in the same manner as in Example 2 described later, and the average interparticle distance and standard deviation of the platinum particles were also similar. 【0174】 2-2. Reference Example 1 (Inverse Micelle Method, Rw=2~6, Coarse Particles) Except for varying Rw between 2 and 6, the mixing and reduction steps were carried out in the same manner as in Example 1, and the median number diameter measured by dynamic light scattering in the mixed solution after the reduction step was measured. The results are shown in Figure 11. In Figure 11, the horizontal axis is Rw and the vertical axis is the median number diameter. 【0175】 The measurement conditions for the median diameter are as follows: Measuring device: Horiba, Ltd., Model: SZ-100V2 Measurements were taken in nanoanalysis mode with a gate time of 640 ns. Three or more measurements were performed, and the average value was used as the median diameter. 【0176】 As shown in Figure 11, the number median diameter value depends on the Rw value, and was approximately 6 nm when Rw = 3. 【0177】 2-3. Example 2 (Reverse micelle method, Rw=3, two-component mixing method) <Mixing process> A 100 mL solution of 60 mmol / L surfactant (NP-5, polyoxyethylene nonylphenyl ether, average number of moles added = 5) / cyclohexane was prepared in a volumetric flask. After allowing the prepared solution to stand for one day, a 40 mmol / L (Pt: 7684 ppm) aqueous H2PtCl6 solution was added to produce a mixed solution of activated metal precursors, with Rw being 3 (mol / mol). 【0178】 <Restoration Process> Similarly, a 60 mmol / L surfactant (NP-5, polyoxyethylene nonylphenyl ether, average number of moles added = 5) / cyclohexane solution was prepared in a volumetric flask. After allowing the prepared solution to stand for one day, an aqueous NaBH4 solution was added to produce a reducing agent mixture solution with a Rw of 3 (mol / mol). Here, the concentration of NaBH4 was added to 20 equivalents relative to Pt. Subsequently, the reducing agent mixture solution was added to the activated metal precursor mixture solution and mixed while stirring. 【0179】 In this process, H2PtCl6 was reduced by NaBH4, and the median diameter of the reverse micelles was 6.1 nm. This was 1.3 times the average entrance pore diameter (=4.6 nm) of the carbon particles obtained in Production Example 2. 【0180】 <Supporting process> A supported metal catalyst was obtained in which platinum particles were supported on carbon particles by performing the support process in the same manner as in Example 1, except that the carbon particles obtained in Manufacturing Example 3 were used in the support process. At this time, the carbon particles and the solution from the reduction process were mixed in a ratio such that the amount of supported Pt was 20 wt%. The ZC image (Z contrast image) and SE image (secondary electron image) of the surface of the obtained supported metal catalyst are shown in Figures 12 and 13. As shown in Figure 13, it can be seen that many of the supported platinum particles are arranged on the dotted line and are arranged regularly. Furthermore, when the centroidal distance distribution of the platinum particles was measured, the distribution shown in Figure 14A was obtained, with an average interparticle distance of 11 nm and a standard deviation of 3 nm. 【0181】 The average particle size of platinum particles, calculated using the same method as in Example 1, was 4.8 nm. The percentage of surface pore-supported particles, calculated using the same method as in Example 1, was 60% or more. Furthermore, the platinum support percentage, as measured by thermogravimetric analysis, was 16% by mass. 【0182】 <Oxygen reduction activity> The oxygen reduction activity of the prepared catalyst was measured by the rotating electrode method. A catalyst ink was prepared by ultrasonically dispersing the catalyst powder in an ethanol solution with a small amount of ultrapure water. The catalyst ink was dropped onto a 10 mm diameter graphite disc and dried in an ethanol vapor atmosphere, resulting in a Pt load of 11 μg / cm³. 2The ink was added and dried in several stages to achieve the (typical value). Next, a 5 wt% Nafion solution was added dropwise so that the Nafion film thickness after drying was 0.05 μm. After drying at room temperature, it was placed in an electric furnace maintained at 130°C and solidified for 3 hours. A graphite disc coated with a catalyst was fixed to a stainless steel rod and used as the working electrode. This was mounted on a rotating electrode device, and the working electrode was immersed in a Pyrex triode cell filled with 0.1 M perchloric acid electrolyte. After purging the electrolyte with nitrogen for 30 minutes, sweeping was repeated at a speed of 500 mV / s between 0.05 V and 1.0 V until the waveform stopped changing. Next, sweeping was performed at a speed of 50 mV / s between 0.05 V and 1.0 V, a cyclic voltammogram was obtained, and the electrochemical surface area (ECA) was determined from the area of ​​the hydrogen adsorption wave. Next, the electrolyte was purged with oxygen for 30 minutes, and a convection voltammogram was obtained by sweeping at 5 mV / s between 0.25 V and 1.0 V. Area specific activity and mass activity were calculated from Koutecky-Levich plots using the current values ​​at 0.70 V, 0.75 V, 0.85 V, and 0.90 V of the obtained convection voltammogram. 【0183】 The mass activity of the supported metal catalyst obtained in Example 5 was calculated using the same method. The results are shown in Table 1. As shown in Table 1, both the catalyst of Example 2, prepared by the reverse micelle method, and the catalyst of Example 5 (OMC catalyst), prepared by the colloid method using an automatic titrator, showed much higher mass activity than the commercially available catalyst (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., model TEC10E50E, 50wt%Pt / CB catalyst). 【0184】 [Table 1] 【0185】 <Platinum particle arrangement state> Figures 15A to 15C show the Z-contrast image or secondary electron image of the supported metal catalyst, respectively. Figure 15A shows the Z-contrast image of the untreated state after the loading process, Figure 15B shows the secondary electron image of the state after hydrogen reduction treatment following the loading process, and Figure 15C shows the secondary electron image of the state after the oxygen reduction activity measurement described above following the hydrogen reduction treatment. 【0186】 The hydrogen reduction treatment was carried out by transferring the sample to a quartz boat and heating it from room temperature to 200°C at a rate of 1.5°C / min in a tubular furnace equipped with a quartz reactor under a 5% hydrogen / 95% nitrogen atmosphere, and maintaining this temperature for 2 hours. 【0187】 From a comparison of these images, it can be seen that the supported metal catalyst produced by the method of this embodiment already has the platinum particles arranged in an untreated state, and this state does not change significantly even after hydrogen reduction and oxygen reduction activity measurements. This is thought to be because many of the platinum particles are supported within the pores of the carbon particles, and the regularity of the pore arrangement is reflected in the regularity of the platinum particle arrangement. When the distance distribution between the centroids of the platinum particles was measured for the supported metal catalyst after hydrogen reduction, the distribution shown in Figure 14B was obtained, with an average inter-particle distance of 12 nm and a standard deviation of 3 nm. Comparing the graphs in Figure 14A and Figure 14B, it can be seen that the distance distribution between the centroids of the platinum particles does not change significantly before and after hydrogen reduction. 【0188】 2-4. Reference Example 2 (Relationship between carrier oxygen concentration and Pt loading rate) Supported metal catalysts were prepared in the same manner as in Example 2, except that the support material was changed to the one shown in Figure 16. The oxygen content of each support material was measured by the EDS method. The platinum load was measured in the same manner as in Example 2. 【0189】 As shown in Figure 16, the higher the oxygen content, the lower the platinum load, suggesting that the platinum load can be increased by reducing the oxygen content. 【0190】 2-5. Reference Example 3 (Relationship between annealing temperature and oxygen concentration) The oxygen content of carbon particles produced in production examples 3-5 was measured by the EDS method. Figure 17 shows the relationship between annealing temperature and oxygen content. As shown in Figure 17, annealing at 1200°C drastically reduced the oxygen content of the carbon particles to approximately 0.5 wt%. Raising the annealing temperature to 1400°C only slightly reduced the oxygen content. Since an oxygen content of 0.5 wt% is equivalent to that of XC-72 in Figure 16, an increase in Pt loading is expected. 【0191】 2-6. Example 3 (Reverse micelle method, double loading, 1000°C annealing) In Example 3, the mixing, reduction, and loading steps were carried out in the same manner as in Example 2, except that carbon particles annealed at 1000°C as in Production Example 3 were used. 【0192】 Next, after performing a hydrogen reduction step (surfactant removal step), a second mixing step, reduction step, and support step were performed in the same manner, and then the hydrogen reduction step (surfactant removal step) was performed again to obtain the supported metal catalyst. 【0193】 The hydrogen reduction process involved transferring the sample to a quartz boat and using a tubular furnace equipped with a quartz reactor to raise the temperature from room temperature to 200°C at a rate of 1.5°C / min in a 5% hydrogen / 95% nitrogen atmosphere, and maintaining this temperature for 2 hours. 【0194】 The obtained supported metal catalyst had a platinum loading of approximately 20% by mass. The secondary electron image of this supported metal catalyst is shown in Figure 18. As shown in Figure 18, the platinum particles were linearly arranged according to the pore arrangement of the carbon particles. The average interparticle distance and standard deviation of the platinum particles were similar to those in Example 2. 【0195】 2-7. Example 4 (Reverse micelle method, double loading, 1400°C annealing) In Example 4, the supported metal catalyst was manufactured in the same manner as in Example 3, except that carbon particles annealed at 1400°C, as in Manufacturing Example 5, were used. 【0196】 The obtained supported metal catalyst had a platinum loading of approximately 30% by mass. The secondary electron image of this supported metal catalyst is shown in Figure 19. As shown in Figure 19, the platinum particles were arranged linearly according to the pore arrangement of the carbon particles. The average interparticle distance and standard deviation of the platinum particles were similar to those in Example 2. 【0197】 2-8. Reference Example 4 (Removal of residual surfactants by hydrogen treatment) Approximately 50 mg of Pt / KB (reverse micelle method, single loading, no hydrogen reduction) was heated from room temperature at 5°C / min in a 5% H2 / 95% Ar gas stream, and the resulting product was detected using a quadrupole mass spectrometer. The results are shown in Figure 20. 【0198】 As a result, H2O (m / z=17,18) and CO2 (m / z=44) were detected at around 184°C. This is thought to be because the oxygen atom in the surfactant (polyoxyethylene nonylphenyl ether) molecule was reduced by hydrogen to produce H2O, and the carbon skeleton was oxidized by intramolecular oxygen to produce CO2. 【0199】 Based on these results, it is estimated that any trace amounts of surfactant remaining on the catalyst after loading are removed by hydrogen reduction treatment at 200°C. 【0200】 2-9. Example 5 (Colloidal method, automatic titration, 20% by mass) <Supporting process> 55.6 mL of ultrapure water, 0.94 g of H2PtCl6 aqueous solution (equivalent to 200 g / L of platinum), and 2.94 g of sodium bisulfite were added to a flat-bottomed beaker and stirred with a magnetic stirrer. Next, 225 g of ultrapure water was added to this solution while stirring. 【0201】 Next, using an automatic titrator, 5% by weight sodium hydroxide and 30% hydrogen peroxide solution were added dropwise to adjust the final pH to 5.0. More specifically, as shown in the graph in Figure 21, first, only sodium hydroxide was added dropwise to adjust the pH to approximately 5.0, then only hydrogen peroxide solution was added dropwise to rapidly lower the pH to around 1.8, and finally, sodium hydroxide and hydrogen peroxide solution were added simultaneously. The time from the start to the completion of hydrogen peroxide solution addition was approximately 15 minutes. 【0202】 The amounts of sodium hydroxide solution and hydrogen peroxide solution added vary depending on external factors such as temperature. As an example, the amount of 5% sodium hydroxide solution added in this process was 17.4 mL, and the amount of 30% hydrogen peroxide solution added was 22.5 mL. The solution obtained in this operation is referred to as the platinum colloid solution. 【0203】 Next, 100 mL of ultrapure water was added to another flat-bottomed beaker and stirred with a magnetic stirrer. 17.1 mg of the carbon particle powder obtained in Production Example 1 was added and stirred until a homogeneous suspension was formed. Then, while stirring this carbon particle suspension, 10.2 mL of platinum colloid solution (equivalent to 20% by mass of platinum) was added dropwise over 1 minute. This mixture was heated on a hot stirrer at 90°C for 3 hours while stirring, then allowed to cool, filtered, washed with ultrapure water, and dried to obtain the powder. 【0204】 <Hydrogen Reduction Process> This powder was placed in a quartz boat and subjected to hydrogen reduction treatment at 300°C for 1 hour under a hydrogen gas stream. 【0205】 <Platinum particle arrangement state> Figure 22A shows a secondary electron image of a supported metal catalyst prepared in the same manner as in Example 5, except that the platinum load was 50% by mass. Figures 22B and 22C show secondary electron images of the supported metal catalyst from Example 5. Figure 22A shows the untreated state after the loading process, Figure 22B shows the state after hydrogen reduction treatment following the loading process, and Figure 22C shows the state after oxygen reduction activity measurement in the same manner as in Example 2 following the hydrogen reduction treatment. 【0206】 A comparison of these images reveals that in the untreated state, the supported metal catalyst produced by the method of this embodiment has platinum deposited in layers on the surface of the carbon particles, and is not supported in a regular arrangement. On the other hand, after hydrogen reduction treatment, the platinum is particulate and regularly arranged, and after oxygen reduction activity measurement, the platinum is even more regularly arranged. This result indicates that both hydrogen reduction treatment and oxygen reduction activity measurement contribute to the arrangement of platinum particles. 【0207】 The average interparticle distance and standard deviation of platinum particles after hydrogen reduction treatment were similar to those in Example 2. 【0208】 2-10. Example 6 (Colloidal method, automatic titration, 30% by mass) A supported metal catalyst was prepared in the same manner as in Example 5, except that the amount of platinum colloid solution added was changed to 15.3 mL (equivalent to 30% by mass of platinum). 【0209】 <Platinum particle arrangement state> Figures 23A and 23B are secondary electron images of the state after hydrogen reduction treatment following the loading process, and Figure 23C is a secondary electron image of the state after oxygen reduction activity measurement was performed in the same manner as in Example 2 after the hydrogen reduction treatment. 【0210】 From a comparison of these images, it was found that the supported metal catalyst produced by the method of this embodiment showed a regular arrangement of platinum particles both after hydrogen reduction treatment and after measurement of oxygen reduction activity. The average interparticle distance and standard deviation of the platinum particles after hydrogen reduction treatment were similar to those in Example 2. 【0211】 Furthermore, Figures 24A and 24B show secondary electron images and Z-contrast images, respectively, of the state after hydrogen reduction treatment following the supporting process. A comparison of these images reveals that in the supported metal catalyst obtained in this embodiment, almost all of the platinum particles are supported on the surface region of the carbon particles. 【0212】 2-11. Comparative Example 1 (Colloidal Method, Manual Titration) <Supporting process> In a flat-bottomed beaker, 37 mL of ultrapure water, 0.82 g of H2PtCl6 aqueous solution (equivalent to 20 g / L of platinum), and 1.96 g of sodium bisulfite were mixed. Next, 150 g of ultrapure water was added, and 5 wt% sodium hydroxide and 30% hydrogen peroxide solution were added to adjust the pH to 5.0. More specifically, as shown in the graph in Figure 21, first, only sodium hydroxide was added dropwise to adjust the pH to approximately 5.0, then only hydrogen peroxide solution was added dropwise to rapidly lower the pH to around 1.8, and then only sodium hydroxide was added dropwise until the pH exceeded the target value of 5.0. After that, hydrogen peroxide and sodium hydroxide were added manually alternately dropwise. The pH fluctuation during the alternating additions was approximately 1. The time from the start to the completion of hydrogen peroxide addition was approximately 50 minutes. 【0213】 The total amount of 30% hydrogen peroxide solution added during this process was 15 mL. Next, 500 mg of the carbon particles obtained in Production Example 1 were added and stirred. This mixture was heated to 90°C on a hot stirrer while stirring, then allowed to cool, filtered, washed with ultrapure water, and dried to obtain a powder. 【0214】 <Restoration Process> This powder was transferred to a quartz U-shaped tube and subjected to reduction treatment at 300°C for 2 hours (heating rate 10°C / min) under a hydrogen gas stream. 【0215】 Figure 25 shows the ZC (Z-contrast image) and SE (secondary electron image) of the surface of the obtained supported metal catalyst. The size of the platinum particles supported on the carbon particles was calculated using the same method as in Example 1. As a result, the average particle size of the platinum was 1.1 nm. A comparison of the secondary electron image and ZC image using STEM showed that the platinum particles were uniformly and non-selectively supported both on the surface and inside the support particles. 【0216】 Furthermore, in Comparative Example 1, there was no difference in the concentration of the active metal in the surface layer and the center, and the active metal was uniformly supported throughout the entire carrier. In contrast, in Example 6, as shown in Figure 24, almost all of the platinum particles were supported in the surface region of the carbon particles (surface layer > center). [Explanation of symbols] 【0217】 1: Supported metal catalyst, 2: Conductive particles, 2a: Linked structure, 2b: Primary particles, 2c: Linking part, 2d: Surface, 3: Carrier, 4: Activated metal particles, 5: Pore, 7: Carbon source sphere, 8: Carbon source aggregate, 8a: Gap, 200: Fuel cell, 201: Anode, 202: Cathode, 203: Load, 210A: Anode-side gas diffusion layer, 210K: Cathode-side gas diffusion layer, 220A: Anode-side catalyst layer, 220K: Cathode-side catalyst layer, 230: Electrolyte membrane

Claims

[Claim 1] The device comprises a carrier which is an aggregate of conductive particles, and active metal particles dispersed and supported on the conductive particles, The conductive particles include a plurality of pores, The aforementioned pores have an average entrance pore diameter of 1 to 20 nm. The standard deviation of the average entrance pore diameter is 50% or less of the average entrance pore diameter. Of the active metal particles, the proportion of those supported on the surface region of the conductive particles is 50% or more. The surface region is the region on the surface of the conductive particle, or the region within the pores within a depth of 15 nm from the surface. The active metal particles are a supported metal catalyst having an average interparticle distance of 5 to 20 nm and a standard deviation of the average interparticle distance of 50% or less of the average interparticle distance. [Claim 2] A supported metal catalyst according to claim 1, A supported metal catalyst wherein the proportion of the active metal particles in the supported metal catalyst is 16 to 50% by mass. [Claim 3] A supported metal catalyst according to claim 1, A supported metal catalyst wherein the proportion of the active metal particles in the supported metal catalyst is 21 to 35% by mass. [Claim 4] A supported metal catalyst according to claim 1, The conductive particles are carbon particles, which are a supported metal catalyst. [Claim 5] A supported metal catalyst according to claim 1, The aforementioned pores have an average interpore distance of 5 to 20 nm. A supported metal catalyst wherein the standard deviation of the average interpore distance is 50% or less of the average interpore distance. [Claim 6] A supported metal catalyst according to claim 1, The conductive particles are a supported metal catalyst, which is a linked structure in which an average of five or more primary particles are linked together. [Claim 7] A supported metal catalyst according to claim 6, A supported metal catalyst wherein the average number of series connections in the aforementioned connected structure is 3 or more. [Claim 8] A supported metal catalyst according to claim 1, The conductive particles are a supported metal catalyst having an average primary particle diameter of 20 to 100 nm. [Claim 9] A supported metal catalyst according to claim 1, A supported metal catalyst in which, of the active metal particles supported in the surface region, the proportion of those supported within the pores is 40% or more. [Claim 10] A supported metal catalyst according to claim 1, The supported metal catalyst is a supported metal catalyst in which the activated metal particles are particles of platinum or a platinum alloy. [Claim 11] A supported metal catalyst according to claim 1, A supported metal catalyst wherein the average particle size of the active metal particles is 1 to 8 nm. [Claim 12] A supported metal catalyst according to claim 1, A supported metal catalyst having a value of [average particle diameter of the active metal particles / average inlet pore diameter] of 0.2 to 0.

8. [Claim 13] A supported metal catalyst according to claim 1, A supported metal catalyst wherein the proportion of the active metal particles supported on the surface region of the conductive particles is 60% or more. [Claim 14] A fuel cell having a cathode-side catalyst layer, The cathode-side catalyst layer comprises a supported metal catalyst according to any one of claims 1 to 13, in a fuel cell. [Claim 15] A method for producing a supported metal catalyst, The process comprises an initial addition step, a simultaneous addition step, a loading step, and a sequencing step. In the initial addition step, an oxidizing agent is added to the active metal precursor solution containing the active metal precursor to oxidize the active metal precursor into oxide particles of the active metal, thereby generating a colloid. In the simultaneous addition step, the neutralizing agent and the oxidizing agent are added simultaneously to the colloid until the amount of the oxidizing agent reaches a specified amount. In the aforementioned supporting step, the oxide particles are supported on the conductive particles by mixing the carrier, which is an aggregate of conductive particles, with the colloid. In the aforementioned arrangement step, an arrangement treatment is performed to enhance the regularity of the arrangement of the oxide particles, or the active metal particles produced by their reduction. The conductive particles include a plurality of pores, The aforementioned pores have an average entrance pore diameter of 1 to 20 nm. A method wherein the standard deviation of the average entrance pore diameter is 50% or less of the average entrance pore diameter. [Claim 16] The method according to claim 15, The oxidizing agent is hydrogen peroxide, in this method. [Claim 17] The method according to claim 15, The pH immediately after the initial addition step is 1.0 to 2.

5. The method wherein the pH immediately after the simultaneous addition step is 4.0 to 6.

0. [Claim 18] The method according to claim 15, A method wherein the time from the start of the initial addition step to the completion of the simultaneous addition step is 10 to 30 minutes. [Claim 19] The method according to claim 15, The sequence treatment is a method comprising at least one of a heat treatment and an electrochemical treatment. [Claim 20] A method for producing a supported metal catalyst, The process comprises a first step, a surfactant removal step, and a second step. The first step comprises a first mixing step, a first reduction step, and a first loading step. The second process comprises a second mixing process, a second reduction process, and a second loading process. In the first mixing step, an active metal precursor solution containing an active metal precursor, a surfactant, and an organic solvent are mixed to produce a first active metal precursor mixed solution. In the first reduction step, the active metal precursor in the first active metal precursor mixed solution is reduced to generate active metal particles. In the first loading step, the active metal particles are dispersed and supported on the conductive particles by mixing the carrier, which is an aggregate of conductive particles, with the active metal particles. In the surfactant removal step, the surfactant adhering to the carrier is removed. In the second mixing step, the active metal precursor solution containing the active metal precursor, a surfactant, and an organic solvent are mixed to produce a second active metal precursor mixed solution. In the second reduction step, the active metal precursor in the second active metal precursor mixed solution is reduced to generate active metal particles. In the second loading step, the carrier after the surfactant removal step is mixed with the activated metal particles obtained in the second reduction step, thereby dispersing and supporting the activated metal particles obtained in the second reduction step on the conductive particles. The conductive particles include a plurality of pores, The aforementioned pores have an average entrance pore diameter of 1 to 20 nm. The standard deviation of the average entrance pore diameter is 50% or less of the average entrance pore diameter. A method wherein the number median diameter measured by dynamic light scattering in the mixed solution is 0.5 to 2 times the average entrance pore diameter. [Claim 21] The method according to claim 20, In the first reduction step, the reduction is carried out by mixing a reducing agent mixed solution containing a reducing agent, an organic solvent, water, and a surfactant with a first active metal precursor mixed solution. In the second reduction step, the reduction is carried out by mixing a reducing agent mixed solution containing a reducing agent, an organic solvent, water, and a surfactant with a second active metal precursor mixed solution. [Claim 22] The method according to claim 20, The removal of the surfactant is carried out by heat-treating the carrier under a reducing gas atmosphere. [Claim 23] The method according to claim 20, The conductive particles are annealed in a vacuum at 800 to 2000°C before the first loading step. [Claim 24] The method according to claim 20, The conductive particles are annealed in a vacuum at 1100 to 2000°C before the first loading step. [Claim 25] A method for producing a supported metal catalyst, The process comprises a mixing step, a reduction step, and a support step. In the mixing step, an active metal precursor solution containing an active metal precursor is mixed with a surfactant and an organic solvent to produce an active metal precursor mixed solution. In the reduction step, the active metal precursor in the active metal precursor mixed solution is reduced to produce active metal particles. In the aforementioned supporting step, the active metal particles are dispersed and supported on the conductive particles by mixing the carrier, which is an aggregate of conductive particles, with the active metal particles. The conductive particles include a plurality of pores, The aforementioned pores have an average entrance pore diameter of 1 to 20 nm. The standard deviation of the average entrance pore diameter is 50% or less of the average entrance pore diameter. The number median diameter measured by dynamic light scattering in the aforementioned mixed solution is 0.5 to 2 times the average entrance pore diameter. The method wherein the conductive particles are annealed in a vacuum at 1100 to 2000°C prior to the loading process. [Claim 26] A method according to any one of claims 20 to 25, The method comprises an arrangement step after the second loading step described in any one of claims 20 to 24, or after the loading step described in claim 25. The aforementioned arrangement step involves applying an arrangement treatment to enhance the regularity of the arrangement of active metal particles. [Claim 27] The method according to claim 26, The sequence treatment is a method comprising at least one of a heat treatment and an electrochemical treatment. [Claim 28] A method according to any one of claims 20 to 25, The method wherein the organic solvent is a hydrophobic organic solvent, comprising at least one selected from cyclohexane, heptane, and toluene. [Claim 29] A method according to any one of claims 20 to 25, The method wherein the surfactant is a nonionic surfactant. [Claim 30] A method according to any one of claims 20 to 25, The method wherein the activated metal precursor comprises a platinum precursor compound. [Claim 31] A method according to any one of claims 15 to 25, The method wherein the conductive particles are carbon particles. [Claim 32] A method according to any one of claims 15 to 25, The aforementioned pores have an average interpore distance of 5 to 20 nm. A method wherein the standard deviation of the average interpore distance is 50% or less of the average interpore distance. [Claim 33] A method according to any one of claims 15 to 25, The method wherein the conductive particles are linked structures in which an average of five or more primary particles are linked together. [Claim 34] The method according to claim 33, A method wherein the average number of series connections of the aforementioned connected structures is 3 or more. [Claim 35] A method according to any one of claims 15 to 25, The method wherein the primary particles of the conductive particles have an average particle diameter of 20 to 100 nm.

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