Mesoporous carbon, and electrode catalyst and catalyst layer for fuel cells

Abstract

To provide a mesoporous carbon that has excellent water retention under high temperature and low humidity conditions, and to provide an electrode catalyst and a catalyst layer for a fuel cell using such a mesoporous carbon as a catalyst carrier.SOLUTION: A mesoporous carbon has a connected structure in which carbon particles (primary particles) having primary pores are connected, and the primary pores have an average entrance diameter of 2.0 nm or more and 3.0 nm or less. The primary pores have an average constriction diameter of 1.6 nm or more and 2.4 nm or less. A fuel cell electrode catalyst includes such a mesoporous carbon and catalyst particles supported within the primary pores of the mesoporous carbon. Further, the catalyst layer includes such a fuel cell electrode catalyst and a catalyst layer ionomer.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to mesoporous carbon, and an electrode catalyst and catalyst layer for a fuel cell, and more particularly to mesoporous carbon having excellent water retention properties under high-temperature, low-humidity conditions, and an electrode catalyst and catalyst layer for a fuel cell that use the same as a catalyst support. [Background technology]

[0002] A polymer electrolyte fuel cell comprises a membrane electrode assembly (MEA) in which electrodes (catalyst layers) containing a catalyst are bonded to both sides of an electrolyte membrane. A gas diffusion layer is usually disposed on the outside of the catalyst layer. Furthermore, a current collector (separator) with a gas flow path is disposed on the outside of the gas diffusion layer. A polymer electrolyte fuel cell typically comprises a structure (fuel cell stack) in which a plurality of unit cells each consisting of such an MEA, gas diffusion layer, and current collector are stacked.

[0003] In a polymer electrolyte fuel cell, the catalyst layer generally consists of a mixture of an electrode catalyst, in which catalytic metal particles such as platinum are supported on the surface of a support, and a catalyst layer ionomer. Carbon materials such as carbon black and acetylene black are typically used for the catalyst support. Furthermore, it is known that the pore size, specific surface area, etc., of the carbon material used for the catalyst support affect the characteristics of the fuel cell. Therefore, various proposals have been made for carbon materials with controlled pore size, specific surface area, etc.

[0004] For example, Patent Document 1 states: (a) A mixture of gamma-alumina particles and polyvinyl alcohol is fired under an inert gas atmosphere to form an alumina-carbon composite; (b) Using sodium hydroxide, the alumina in the alumina-carbon composite is dissolved and removed to obtain a carbon material. (c) The obtained carbon material is pulverized and the pulverized carbon material is subjected to an activation treatment. A method for producing a support carbon material is disclosed.

[0005] The same document states: (A) The thus obtained carbon support material contains mesopores (catalyst-supporting pores) with a radius of 2 nm to 5 nm and mesopores (gas diffusion pores) with a radius of 5 nm to 25 nm that are connected to the catalyst-supporting pores. (B) When catalytic metal particles having a radius of 1 to 3 nm are supported on such a support carbon material, the catalytic metal particles are supported within the catalyst support pores. (C) When a carbon support material having catalytic metal particles supported in catalyst support pores is used as an air electrode catalyst for a fuel cell, water molecules generated on the catalytic metal particles diffuse from the catalyst support pores through the gas diffusion pores to the outside of the carbon support material; and (D) This makes it possible to suppress flooding that occurs inside the support carbon material. is stated.

[0006] To enable higher temperature operation of polymer electrolyte fuel cells, a carbon support material with a small voltage drop under high-temperature, low-humidity conditions and an electrode catalyst using the same are required. Hereinafter, power generation performance under high-temperature, low-humidity conditions (in other words, conditions under which a large thermal load is imposed on the polymer electrolyte fuel cell) is also referred to as "high-temperature, low-humidity performance." Conventional carbon supports do not have sufficient high-temperature, low-humidity performance.

[0007] For example, Patent Document 1 describes that flooding occurring inside the carbon support material can be suppressed by using a carbon support material having catalyst-supporting pores with a radius of 2 to 5 nm and gas diffusion pores with a radius of 5 to 25 nm. However, this document merely defines the ranges of pore diameter and pore volume assuming that the pore structure contained in the porous carbon material is uniform. Furthermore, the carrier carbon material described in this document does not have a pore structure that can retain water necessary for proton conduction within the pores under high-temperature, low-humidity conditions. Therefore, it is considered that the carrier carbon material described in this document does not have sufficient high-temperature, low-humidity performance. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2016 / 152447 Summary of the Invention [Problem to be solved by the invention]

[0009] The problem to be solved by the present invention is to provide a mesoporous carbon having excellent water retention properties under high temperature and low humidity conditions. Another problem to be solved by the present invention is to provide an electrode catalyst for a fuel cell that uses such mesoporous carbon as a catalyst support. Another object of the present invention is to provide a catalyst layer including such an electrode catalyst for a fuel cell. [Means for solving the problem]

[0010] In order to solve the above problems, the mesoporous carbon according to the present invention comprises: It has a connected structure in which carbon particles (primary particles) with primary pores are connected, The average entrance diameter of the primary pores is 2.0 nm or more and 3.0 nm or less, The average constriction diameter of the primary pores is 1.6 nm or more and 2.4 nm or less. The gist of this is as follows. however, The term "average entrance diameter" refers to the average value of the circle-equivalent diameters of the entrances of the primary pores that open to the surface of the carbon particles, as measured by three-dimensional transmission electron microscope image analysis; The term "average constriction diameter" refers to the average value of the circle-equivalent diameter of the constriction of the primary pores inside the carbon particles, measured by the three-dimensional transmission electron microscope image analysis.

[0011] The fuel cell electrode catalyst according to the present invention comprises: The mesoporous carbon according to the present invention; catalyst particles supported in the primary pores of the mesoporous carbon; It is equipped with:

[0012] Furthermore, the catalyst layer according to the present invention is an electrode catalyst for a fuel cell according to the present invention; Catalyst layer ionomer and It is equipped with: [Effects of the Invention]

[0013] When mesoporous carbon with a primary pore average entrance diameter and average constriction diameter within a predetermined range is used as a catalyst support for a fuel cell, it becomes possible to effectively retain generated water within the primary pores when generating electricity under high-temperature, low-humidity conditions. Furthermore, because the generated water retained within the primary pores transports protons to the catalyst particle surface, it becomes possible to effectively utilize the catalyst particles within the primary pores. As a result, the high-temperature, low-humidity performance of the fuel cell is improved. [Brief explanation of the drawings]

[0014] [Figure 1] 1 shows a three-dimensional image (bottom right) of the mesoporous carbon obtained in Example 1 and a schematic diagram of the pore structure (top left). [Figure 2] 1 shows a three-dimensional image (bottom right) of the mesoporous carbon obtained in Comparative Example 1 and a schematic diagram of the pore structure (top left).

[0015] [Figure 3] FIG. 10 is a diagram showing the relationship between the average inlet diameter and the high-temperature low humidification voltage. [Figure 4] FIG. 10 is a diagram showing the relationship between the average inlet diameter and the efficiency point voltage. [Figure 5] FIG. 10 is a diagram showing the relationship between the average constriction diameter and the high-temperature low-humidification voltage. [Figure 6] FIG. 10 is a diagram showing the relationship between the average constriction diameter and the efficiency point voltage. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the present invention will be described in detail below. [1. Mesoporous carbon] The mesoporous carbon according to the present invention is It has a connected structure in which carbon particles (primary particles) with primary pores are connected, The average entrance diameter of the primary pores is 2.0 nm or more and 3.0 nm or less, The average constriction diameter of the primary pores is 1.6 nm or more and 2.4 nm or less.

[0017] [1.1. Connection structure] As described below, the mesoporous carbon according to the present invention is produced using mesoporous silica as a template. Mesoporous silica is typically synthesized by condensation polymerization of a silica source in a reaction solution containing a silica source, a surfactant, and a catalyst. By optimizing the type of solvent, the surfactant concentration in the reaction solution, and / or the silica source concentration, mesoporous silica having a connected structure and pore sizes (average inlet size, average constriction size, average pore size) and pore volumes within specific ranges can be obtained. Furthermore, by using such mesoporous silica as a template, mesoporous carbon having a connected structure and pore sizes and pore volumes within specific ranges can be obtained.

[0018] Here, the term "connected structure" refers to a structure in which primary particles made of carbon particles are connected in a beaded pattern. Each primary particle constituting the connected structure has a primary pore inside. The primary pores within the primary particles are cavities that remain after removing the pore walls of the mesoporous silica used as the template. The shape of the primary particles is usually not perfectly spherical, but rather has an irregular shape with an aspect ratio of approximately 1.1 to 3. Furthermore, the size of the primary pores inside mesoporous carbon is usually not uniform, but varies depending on the location. In general, the size of the entrance to a primary pore is different from the size of the inside of the primary pore. Furthermore, the size of the inside of a primary pore is also not uniform, and usually has voids (constrictions) that are smaller than the adjacent voids.

[0019] [1.2. Primary particles] The primary particles are composed of carbon particles having primary pores. The mesoporous carbon according to the present invention is produced using the method described below, and therefore the primary particles constituting the mesoporous carbon have the following characteristics.

[0020] [1.2.1. Average inlet diameter] The "average inlet diameter" refers to the average value of the circle-equivalent diameters of the inlets of the primary pores that open to the surface of the carbon particles, as measured by three-dimensional transmission electron microscope image analysis. In order to reduce measurement errors, it is preferable to calculate the circle-equivalent diameters of inlets at 500 or more locations. Using a three-dimensional transmission electron microscope (3DTEM), two-dimensional projection images are continuously taken while tilting the sample at predetermined angular intervals, and by mathematically processing the obtained two-dimensional projection images, a three-dimensional image of the sample can be reconstructed. Furthermore, from the obtained three-dimensional image, the diameter of the entrance of each primary pore can be measured.

[0021] The average inlet diameter affects the high-temperature, low-humidification performance of electrode catalysts that use mesoporous carbon as a support. If the average inlet diameter is too small, it may be difficult to support catalyst particles in the primary pores. Therefore, the average inlet diameter must be 2.0 nm or larger.

[0022] On the other hand, if the average inlet diameter is too large, the high-temperature, low-humidification performance may be reduced. This is thought to be because if the average inlet diameter is too large, water remaining in the primary pores is more likely to be discharged to the outside under high-temperature, low-humidification conditions. Therefore, the average inlet diameter must be 3.0 nm or less. The average inlet diameter is preferably 2.8 nm or less.

[0023] [1.2.2. Average neck diameter] The "average constriction diameter" refers to the average value of the equivalent circle diameter of the constrictions of the primary pores inside the carbon particles, measured by three-dimensional transmission electron microscope image analysis. To reduce measurement error, it is preferable to calculate the equivalent circle diameters of 500 or more constrictions. As mentioned above, a three-dimensional transmission electron microscope can be used to obtain a three-dimensional image of the sample. Furthermore, the diameter of the constricted portion of each primary pore can be measured from the obtained three-dimensional image.

[0024] The average constriction diameter affects the high-temperature, low-humidity performance of electrode catalysts that use mesoporous carbon as a support. If the average constriction diameter is too small, it may be difficult to support catalyst particles within the primary pores. Therefore, the average constriction diameter must be 1.6 nm or more.

[0025] On the other hand, if the average constriction diameter is too large, the high-temperature, low-humidification performance may be reduced. This is thought to be because if the average constriction diameter is too large, water remaining in the primary pores is more likely to be discharged to the outside under high-temperature, low-humidification conditions. Therefore, the average constriction diameter must be 2.4 nm or less. The average constriction diameter is preferably 2.3 nm or less.

[0026] [1.2.3. Average pore size] "Average pore size" refers to the average diameter of the primary pores contained in the primary particles, and does not include the size of the voids (secondary pores) between the primary particles. The average pore diameter can be obtained by analyzing the adsorption side data of the nitrogen adsorption isotherm of mesoporous carbon using the BJH method and determining the pore diameter (most frequent peak value) when the pore volume is at its maximum.

[0027] Generally, if the average pore size is too small, it may be difficult to supply reactant gases or protons to the catalyst particles supported in the primary pores. Furthermore, when power generation is performed in a high current density range, it may be difficult to discharge water generated by the reaction. Therefore, the average pore size is preferably 2 nm or more. The average pore size is preferably 2.5 nm or more. On the other hand, if the average pore size is too large, the ionomer easily penetrates into the primary pores. As a result, the catalyst particles are poisoned by the ionomer, resulting in a decrease in activity. Therefore, the average pore size is preferably less than 20 nm. The average pore size is preferably 10 nm or less, more preferably 7 nm or less, and even more preferably 5 nm or less.

[0028] 1.2.4. Average Pore Wall Thickness The "average pore wall thickness" refers to the average value of the thickness of the pore walls of the primary pores contained in the primary particles. The average pore wall thickness can be obtained by measuring the thickness of pore walls at 100 or more randomly selected locations using a microscope and calculating the average value.

[0029] If the average thickness of the pore walls is too thin, the carbon may be easily oxidized, resulting in poor durability. Therefore, the average thickness of the pore walls is preferably 3 nm or more. The average thickness is preferably 3.5 nm or more, and more preferably 4 nm or more. On the other hand, if the average thickness of the pore walls is too thick, the pore volume of the primary particles will be small, making it difficult to support the catalyst particles. Therefore, the average thickness of the pore walls is preferably 15 nm or less. The average thickness is preferably 12 nm or less, more preferably 10 nm or less.

[0030] 1.2.5. Primary pore volume "Pore volume of primary pores" refers to the volume of primary pores contained in primary particles, and does not include the volume of voids (secondary pores) between primary particles. The pore volume of the primary pores can be obtained by analyzing the adsorption data of the nitrogen adsorption isotherm of the mesoporous carbon by the BJH method and calculating it with a value of P / P0 = 0.03 to 0.99.

[0031] Generally, if the pore volume of the primary pores is too small, it becomes difficult to support catalyst particles. Therefore, the pore volume of the primary pores is preferably 0.2 mL / g or more. The pore volume of the primary pores is preferably 0.5 mL / g or more, and more preferably 1.0 mL / g or more. On the other hand, if the pore volume of the primary pores is too large, the ratio of the pore wall volume to the primary particle volume will decrease, which may result in lower electronic conductivity. Furthermore, the amount of ionomer penetration will increase, which may result in catalyst poisoning and reduced activity. Therefore, the pore volume of the primary pores is preferably 3.0 mL / g or less. The pore volume of the primary pores is preferably 2.5 mL / g or less, and more preferably 2.0 mL / g or less.

[0032] [1.2.6. Average particle size of primary particles] The term "average particle size of primary particles" refers to the average length of the primary particles in the minor axis direction. The "length in the minor axis direction" refers to the length in the direction perpendicular to the longest direction (long axis direction) of the length of the primary particle. The average particle size of the primary particles can be obtained by measuring the length in the minor axis direction of 100 or more randomly selected primary particles using a microscope and calculating the average value.

[0033] Generally, if the average particle size of the primary particles is too small, it becomes difficult for the catalyst particles to be supported in the primary pores. Therefore, the average particle size of the primary particles is preferably 30 nm or more. The average particle size is preferably 40 nm or more, and more preferably 50 nm or more.

[0034] On the other hand, if the average particle size of the primary particles is too large, it may be difficult to supply reactant gases and protons to the catalyst particles supported in the primary pores. Furthermore, when power generation is performed in a high current density range, it may be difficult to discharge water produced by the reaction. Therefore, the average particle size is preferably 300 nm or less. The average particle size is preferably 250 nm or less, and more preferably 150 nm or less.

[0035] [1.3. High temperature and low humidification voltage] "High temperature low humidification voltage" means (a) The Pt loading of the electrode catalyst is 40 mass%, and the Pt coverage is 0.1 mg / cm 2 and a polymer electrolyte fuel cell having an air electrode catalyst layer with an ionomer / carbon ratio (I / C) of 1.0 was used. (b) Cell temperature: 105°C, relative humidity: 30%, current density: 3.2 A / cm 2 This refers to the voltage measured under the following conditions.

[0036] The mesoporous carbon of the present invention exhibits high water retention even under high-temperature, low-humidification conditions because the average inlet diameter and average constriction diameter are within the specified ranges. By optimizing the average inlet diameter and average constriction diameter, the high-temperature, low-humidification voltage becomes 570 mV or higher. By further optimizing the pore structure, the high-temperature, low-humidification voltage becomes 590 mV or higher.

[0037] [1.4. Degree of graphitization] Mesoporous carbon can be obtained by filling the mesopores of mesoporous silica with a carbon source and carbonizing the carbon source. However, to suppress the reaction between mesoporous silica and carbon, the carbonization temperature of the carbon source must be relatively low. Therefore, the mesoporous carbon obtained after carbonization of the carbon source tends to have a turbostratic structure. Mesoporous carbon with a turbostratic structure has lower electronic conductivity than mesoporous carbon with a graphite structure.

[0038] In contrast, when mesoporous carbon with a turbostratic structure is graphitized at temperatures above 1500°C, the turbostratic mesoporous carbon gradually changes to a graphite structure. Generally, the higher the graphitization temperature, the higher the degree of graphitization.

[0039] [2. Electrode catalyst for fuel cells] The fuel cell electrode catalyst according to the present invention comprises: The mesoporous carbon according to the present invention; Catalyst particles supported in the primary pores of mesoporous carbon It is equipped with:

[0040] [2.1. Mesoporous carbon] In the fuel cell electrode catalyst according to the present invention, the mesoporous carbon is a catalyst support for supporting catalyst particles. The catalyst particles are supported mainly in the primary pores of the primary particles that constitute the mesoporous carbon. Details of the mesoporous carbon are as described above, and therefore will not be described here.

[0041] 2.2. Catalyst particles In the present invention, the material of the catalyst particles is not particularly limited as long as it is a material that exhibits oxygen reduction reaction activity or hydrogen oxidation reaction activity. (a) Precious metals (Pt, Au, Ag, Pd, Rh, Ir, Ru, Os), (b) an alloy containing two or more precious metal elements; (c) Alloys containing one or more precious metal elements and one or more base metal elements (e.g., Fe, Co, Ni, Cr, V, Ti, etc.); (d) metal oxynitride; (e) Carbon alloy etc.

[0042] [3. Catalyst layer] The catalyst layer according to the present invention comprises: an electrode catalyst for a fuel cell according to the present invention; Catalyst layer ionomer and It is equipped with: The catalyst layer according to the present invention is particularly suitable as a catalyst layer on the air electrode side, but may also be used as a catalyst layer on the fuel electrode side.

[0043] [3.1. Electrode catalyst for fuel cells] The catalyst layer according to the present invention includes the fuel cell electrode catalyst according to the present invention. Details of the fuel cell electrode catalyst are as described above, and therefore further explanation will be omitted.

[0044] [3.2. Catalyst Layer Ionomer] In the catalyst layer according to the present invention, the material of the catalyst layer ionomer is not particularly limited. Examples of the catalyst layer ionomer include perfluorocarbon sulfonic acid polymers and high-oxygen-permeable ionomers. The ionomer may consist of any one of these, or may be a combination of two or more of them.

[0045] "Perfluorocarbon sulfonic acid polymer" refers to a fluorine-containing ion exchange resin containing repeating units based on a sulfonyl vinyl ether fluoride monomer. Examples of perfluorocarbon sulfonic acid polymers include Nafion (registered trademark), Flemion (registered trademark), Aquivion (registered trademark), and Aciplex (registered trademark).

[0046] A "highly oxygen-permeable ionomer" refers to a polymer compound that contains an acid group and a cyclic structure within its molecular structure. Highly oxygen-permeable ionomers have a high oxygen permeability coefficient due to the cyclic structure within their molecular structure. Therefore, when used as an ionomer, the oxygen transfer resistance at the interface with the catalyst becomes relatively small. In other words, the "highly oxygen-permeable ionomer" refers to an ionomer having an oxygen permeability coefficient higher than that of perfluorocarbon sulfonic acid polymers such as Nafion (registered trademark).

[0047] Examples of highly oxygen-permeable ionomers include: (a) an electrolyte polymer containing a perfluorocarbon unit having an aliphatic ring structure and an acid group unit having a perfluorosulfonic acid in a side chain; (b) an electrolyte polymer containing a perfluorocarbon unit having an aliphatic ring structure and an acid group unit having a perfluoroimide in the side chain; (c) an electrolyte polymer containing a unit in which perfluorosulfonic acid is directly bonded to a perfluorocarbon having an aliphatic ring structure; (See References 1-4). [Reference 1] Japanese Patent Application Laid-Open No. 2003-036856 [Reference 2] International Publication No. 2012 / 088166 [Reference 3] JP 2013-216811 A [Reference 4] JP 2006-152249 A

[0048] [4. Manufacturing method of mesoporous silica (template)] The mesoporous carbon according to the present invention is produced by using mesoporous silica as a template. a polymerization step of condensation-polymerizing the silica source in a reaction solution containing a silica source, a surfactant, and a catalyst to obtain precursor particles; a drying step of separating the precursor particles from the reaction solution and drying them; a calcination step of calcining the precursor particles to obtain mesoporous silica; It is equipped with: The method for producing mesoporous silica according to the present invention may further include a diameter expansion step of performing a diameter expansion treatment on the dried precursor particles.

[0049] [4.1. Polymerization process] First, in a reaction solution containing a silica source, a surfactant, and a catalyst, the silica source is polycondensed to obtain precursor particles (polymerization step).

[0050] 4.1.1. Silica Source In the present invention, the type of silica source is not particularly limited. Examples of the silica source include: (a) tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, dimethoxydiethoxysilane, and tetraethyleneglycoxysilane; (b) trialkoxysilanes such as 3-mercaptopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and 3-(2-aminoethyl)aminopropyltrimethoxysilane; (c) Silicates such as sodium silicate and kanemite As the silica source, any one of these may be used alone, or two or more of them may be used in combination.

[0051] 4.1.2. Surfactants When a silica source is polycondensed in a reaction solution, adding a surfactant to the reaction solution causes the surfactant to form micelles in the reaction solution. Because hydrophilic groups are clustered around the micelles, the silica source is adsorbed to the surface of the micelles. Furthermore, the micelles with the adsorbed silica source self-assemble in the reaction solution, causing the silica source to polycondense. As a result, mesopores (including micropores with a diameter of 2 nm or less; the same applies hereinafter) resulting from the micelles are formed inside the primary particles. The size of the mesopores can be controlled (1 to 50 nm) mainly by the molecular length of the surfactant.

[0052] In the present invention, the type of surfactant is not particularly limited, but it is preferable to use an alkyl quaternary ammonium salt as the surfactant. The alkyl quaternary ammonium salt refers to a compound represented by the following formula (a): CH3-(CH2) n -N + (R1)(R2)(R3)X - (a)

[0053] In formula (a), R1, R2, and R3 each represent an alkyl group having 1 to 3 carbon atoms. R1, R2, and R3 may be the same or different. To facilitate aggregation of alkyl quaternary ammonium salts (micelle formation), it is preferable that R1, R2, and R3 are all the same. Furthermore, it is preferable that at least one of R1, R2, and R3 is a methyl group, and it is preferable that all of them are methyl groups. In formula (a), X represents a halogen atom. The type of halogen atom is not particularly limited, but X is preferably Cl or Br in view of availability.

[0054] In formula (a), n represents an integer of 7 to 21. Generally, as n decreases, a spherical mesoporous material with a smaller central pore diameter is obtained. On the other hand, as n increases, the central pore diameter increases, but if n is too large, the hydrophobic interaction of the alkyl quaternary ammonium salt becomes excessive. As a result, a layered compound is produced, and a mesoporous material cannot be obtained. n is preferably 9 to 17, and more preferably 13 to 17.

[0055] Among those represented by formula (a), alkyltrimethylammonium halides are preferred, such as hexadecyltrimethylammonium halide, octadecyltrimethylammonium halide, nonyltrimethylammonium halide, decyltrimethylammonium halide, undecyltrimethylammonium halide, dodecyltrimethylammonium halide, and tetradecylammonium halide. Among these, alkyltrimethylammonium bromide or alkyltrimethylammonium chloride is particularly preferred.

[0056] When synthesizing mesoporous silica, one type of alkyl quaternary ammonium salt may be used, or two or more types may be used. However, since the alkyl quaternary ammonium salt serves as a template for forming mesopores within the primary particles, the type of alkyl quaternary ammonium salt significantly affects the shape of the mesopores. To synthesize silica particles with more uniform mesopores, it is preferable to use one type of alkyl quaternary ammonium salt.

[0057] 4.1.3. Catalyst When polycondensing a silica source, a catalyst is usually added to the reaction solution. When synthesizing particulate mesoporous silica, the catalyst may be an alkali such as sodium hydroxide or aqueous ammonia, or an acid such as hydrochloric acid.

[0058] 4.1.4. Solvents The solvent used may be water, an organic solvent such as alcohol, or a mixed solvent of water and an organic solvent. Alcohol is (1) Monohydric alcohols such as methanol, ethanol, and propanol, (2) Dihydric alcohols such as ethylene glycol, (3) Trihydric alcohols such as glycerin, Either is fine.

[0059] When a mixed solvent of water and an organic solvent is used, the content of the organic solvent in the mixed solvent can be selected arbitrarily depending on the purpose. Generally, adding an appropriate amount of organic solvent to the solvent makes it easier to control the particle size and particle size distribution. Furthermore, when a mixed solvent of water and an organic solvent is used, if the mixed solvent contains 5 mass% or less of the organic solvent, mesoporous silica for producing mesoporous carbon with excellent flooding resistance can be produced at low cost.

[0060] 4.1.5. Composition of reaction solution The composition of the reaction solution affects the external shape and pore structure of the synthesized mesoporous silica. In particular, the concentrations of the surfactant and silica source in the reaction solution have a significant effect on the average primary particle size, pore size, and pore volume of the mesoporous silica particles.

[0061] [A. Surfactant concentration] If the surfactant concentration is too low, the particle precipitation rate will be slow and a structure in which the primary particles are connected will not be obtained. Therefore, the surfactant concentration must be 0.03 mol / L or more. The surfactant concentration is preferably 0.035 mol / L or more, more preferably 0.04 mol / L or more.

[0062] On the other hand, if the surfactant concentration is too high, the particle precipitation rate becomes too fast, and the primary particle diameter easily exceeds 300 nm. Therefore, the surfactant concentration must be 1.0 mol / L or less. The surfactant concentration is preferably 0.95 mol / L or less, and more preferably 0.90 mol / L or less.

[0063] B. Silica Source Concentration If the concentration of the silica source is too low, the particle precipitation rate will be slow, and a structure in which primary particles are connected will not be obtained. Alternatively, the surfactant will be excessive, and uniform mesopores may not be obtained. Therefore, the concentration of the silica source must be 0.05 mol / L or higher. The concentration of the silica source is preferably 0.06 mol / L or higher, and more preferably 0.07 mol / L or higher.

[0064] On the other hand, if the silica source concentration is too high, the particle precipitation rate becomes too fast, and the primary particle diameter easily exceeds 300 nm. Alternatively, sheet-like particles may be obtained instead of spherical particles. Therefore, the silica source concentration must be 1.0 mol / L or less. The silica source concentration is preferably 0.95 mol / L or less, and more preferably 0.9 mol / L or less.

[0065] C. Catalyst Concentration In the present invention, the catalyst concentration is not particularly limited. Generally, if the catalyst concentration is too low, the particle precipitation rate will be slow. On the other hand, if the catalyst concentration is too high, the particle precipitation rate will be fast. It is preferable to select the optimum catalyst concentration depending on the type of silica source, the type of surfactant, the target physical property values, etc. For example, when an acid is used as a catalyst, it is preferable to adjust the concentration of the catalyst so that the pH of the reaction solution is 9 or less. The pH of the reaction solution is preferably 8.5 or less, and more preferably less than 5. On the other hand, when an alkali is used as the catalyst, it is preferable to adjust the concentration of the catalyst so that the pH of the reaction solution is greater than 7.

[0066] 4.1.6 Reaction conditions A silica source is added to a solvent containing a predetermined amount of surfactant, and hydrolysis and polycondensation are carried out, whereby precursor particles containing silica and surfactant are obtained, with the surfactant acting as a template. The optimum reaction conditions are selected depending on the type of silica source, the particle size of the precursor particles, etc. In general, the reaction temperature is preferably −20 to 100° C. The reaction temperature is preferably 0 to 100° C., more preferably 0 to 90° C., even more preferably 10 to 80° C., and still more preferably 35 to 80° C.

[0067] [4.2. Drying process] Next, the precursor particles are separated from the reaction solution and dried (drying step). Drying is carried out to remove the solvent remaining in the precursor particles. The drying conditions are not particularly limited as long as the solvent can be removed.

[0068] [4.3. Expansion Processing] Next, if necessary, the dried precursor particles may be subjected to a diameter expansion treatment (diameter expansion step). The "diameter expansion treatment" refers to a treatment for expanding the diameter of mesopores in the primary particles. Specifically, the diameter-enlarging treatment is carried out by subjecting the synthesized precursor particles (from which the surfactant has not been removed) to a hydrothermal treatment in a solution containing a diameter-enlarging agent, which can enlarge the pore size of the precursor particles.

[0069] Examples of the diameter expanding agent include: (a) Hydrocarbons such as trimethylbenzene, triethylbenzene, benzene, cyclohexane, triisopropylbenzene, naphthalene, hexane, heptane, octane, nonane, decane, undecane, and dodecane; (b) Acids such as hydrochloric acid, sulfuric acid, and nitric acid; etc.

[0070] The reason why the pore size increases upon hydrothermal treatment in the presence of hydrocarbons is thought to be that rearrangement of silica occurs when the diameter-expanding agent is introduced from the solvent into the pores of the more hydrophobic precursor particles. Additionally, the pore size increases when hydrothermal treatment is performed in the presence of an acid such as hydrochloric acid. This is thought to be due to the dissolution and reprecipitation of silica inside the primary particles. When the manufacturing conditions are optimized, radial pores are formed inside the silica. When this is subjected to hydrothermal treatment in the presence of an acid, silica dissolution and reprecipitation occurs, converting the radial pores into interconnected pores.

[0071] The conditions for the diameter-enlarging treatment are not particularly limited as long as the desired pore diameter is obtained. Usually, it is preferable to add about 0.05 mol / L to 10 mol / L of a diameter-enlarging agent to the reaction solution and perform hydrothermal treatment at 50 to 150°C.

[0072] [4.4. Firing process] Next, after carrying out a diameter expansion treatment as necessary, the precursor particles are calcined (calcination step), thereby obtaining the mesoporous silica according to the present invention. Calcination is carried out to dehydrate and polymerize the precursor particles with residual OH groups and to thermally decompose the surfactant remaining in the mesopores. The calcination conditions are not particularly limited as long as they allow for dehydration, crystallization, and thermal decomposition of the surfactant. Calcination is usually carried out by heating in air at 400°C to 800°C for 1 to 10 hours.

[0073] [5. Manufacturing method of mesoporous carbon] The method for producing mesoporous carbon according to the present invention includes the steps of: A first step of preparing mesoporous silica to serve as a template; a second step of depositing carbon in the mesopores of the mesoporous silica to prepare a mesoporous silica / carbon composite; a third step of removing the mesoporous silica from the composite; It is equipped with: The method for producing mesoporous carbon may further include a fourth step of heat treating the mesoporous carbon at a temperature higher than 1500°C after the third step.

[0074] [5.1. First step (making a mold)] First, mesoporous silica to be used as a template is prepared (Step 1). Details of the method for producing mesoporous silica are as described above, and therefore will not be described here.

[0075] [5.2. Second step (carbon deposition in mesopores)] Next, carbon is deposited in the mesopores of the mesoporous silica to produce a mesoporous silica / carbon composite (second step). Specifically, carbon deposition in mesopores is achieved by: (a) introducing a carbon precursor into the mesopores; (b) Polymerizing and carbonizing the carbon precursor within the mesopores This is done by:

[0076] 5.2.1. Introduction of carbon precursors The term "carbon precursor" refers to a material capable of producing carbon by thermal decomposition. Specific examples of such carbon precursors include: (1) A polymer precursor that is liquid at room temperature and thermally polymerizable (e.g., furfuryl alcohol, aniline, etc.), (2) A mixture of an aqueous solution of carbohydrates and an acid (for example, a mixture of monosaccharides such as sucrose, xylose, glucose, or a mixture of disaccharides or polysaccharides with an acid such as sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid), (3) A mixture of two-component curing polymer precursors (e.g., phenol and formalin), etc. Among these, polymer precursors can be impregnated into mesopores without dilution with a solvent, allowing a relatively large amount of carbon to be produced in the mesopores with a relatively small number of impregnation cycles. Furthermore, they have the advantage of not requiring a polymerization initiator and are easy to handle.

[0077] When a liquid or solution carbon precursor is used, the larger the amount of liquid or solution adsorbed per one time, the better, and it is preferable that the amount be such that the entire mesopores are filled with the liquid or solution. When a mixture of an aqueous solution of a carbohydrate and an acid is used as the carbon precursor, the amount of acid is preferably the minimum amount that can polymerize the organic material. Furthermore, when a mixture of two-component curing polymer precursors is used as the carbon precursor, the optimum ratio is selected depending on the type of polymer precursor.

[0078] 5.2.2. Polymerization and carbonization of carbon precursors The polymerized carbon precursor is then carbonized within the mesopores. Carbonization of the carbon precursor is carried out by heating mesoporous silica containing the carbon precursor to a predetermined temperature in a non-oxidizing atmosphere (e.g., in an inert atmosphere, vacuum, etc.). Specifically, the heating temperature is preferably 500°C or higher and 1200°C or lower. If the heating temperature is lower than 500°C, the carbon precursor will not be sufficiently carbonized. On the other hand, if the heating temperature exceeds 1200°C, silica and carbon will react, which is not preferable. The optimal heating time is selected depending on the heating temperature.

[0079] The amount of carbon generated in the mesopores should be at least the amount that allows the carbon particles to maintain their shape when the mesoporous silica is removed. Therefore, if the amount of carbon generated in one filling, polymerization, and carbonization process is relatively small, it is preferable to repeat these processes multiple times. In this case, the conditions for each repeated process may be the same or different. Furthermore, when each of the steps of filling, polymerization, and carbonization is repeated multiple times, each carbonization step may be performed at a relatively low temperature, and after the final carbonization step is completed, another carbonization step may be performed at a higher temperature. If the final carbonization step is performed at a higher temperature than the previous carbonization steps, the carbon introduced into the pores in multiple steps is more likely to be integrated.

[0080] [5.3. Third step (removal of the template)] Next, the mesoporous silica template is removed from the composite (third step), thereby obtaining mesoporous carbon. Specific methods for removing mesoporous silica include: (1) A method of heating the complex in an alkaline aqueous solution such as sodium hydroxide, (2) Etching the composite with an aqueous hydrofluoric acid solution; etc.

[0081] [5.4. Fourth step (graphitization)] Next, if necessary, the mesoporous carbon is heat-treated at a temperature higher than 1500°C (step 4). When carbonizing a carbon source within the mesopores of mesoporous silica, the heat-treatment temperature must be low to suppress the reaction between silica and carbon. As a result, the degree of graphitization of the carbon after carbonization is low. To achieve a high degree of graphitization, it is preferable to heat-treat the mesoporous carbon at a high temperature after removing the template.

[0082] If the heat treatment temperature is too low, graphitization will be insufficient. Therefore, the heat treatment temperature is preferably higher than 1500° C. The heat treatment temperature is preferably 1700° C. or higher, and more preferably 1800° C. or higher. On the other hand, if the heat treatment temperature is made higher than necessary, there is no difference in the effect and it is of no practical benefit. Therefore, the heat treatment temperature is preferably 2300°C or less. The heat treatment temperature is preferably 2200°C or less.

[0083] [6. Effect] The size of the primary pores inside mesoporous carbon is not usually uniform, but varies depending on the location. Generally, the size of the entrance to a primary pore is different from the size of the interior of the primary pore. The size of the interior of the primary pore is also not uniform, with some areas being constricted. Furthermore, both the average size of the entrance to the primary pores (average entrance diameter) and the average size of the constricted parts of the primary pores (average constriction diameter) affect the water retention capacity of mesoporous carbon under high-temperature, low-humidity conditions.

[0084] Therefore, when mesoporous carbon with a primary pore average entrance diameter and average constriction diameter within a predetermined range is used as a catalyst support for a fuel cell, it becomes possible to effectively retain generated water within the primary pores when generating electricity under high-temperature, low-humidity conditions. Furthermore, because the generated water retained within the primary pores transports protons to the catalyst particle surfaces, it becomes possible to effectively utilize the catalyst particles within the primary pores. As a result, the high-temperature, low-humidity performance of the fuel cell is improved. [Example]

[0085] (Examples 1 to 6, Comparative Example 1) 1. Sample Preparation 1.1. Preparation of mesoporous silica 1.1.1. Example 1 The surfactant n-hexadecyltrimethylammonium chloride [C 16 H 33 18 g of [N(CH3)3Cl] and 13 g of ethanol were added to 650 g of 1.5 mass% hydrochloric acid. This was heated and stirred at 70°C, and 70 g of No. 1 sodium silicate (27 mass% as SiO2, SiO2 / Na2O = 2.00) was added, and the mixture was maintained for 3 hours to carry out a polycondensation reaction. The resulting solid product was filtered, dispersed in 1000 g of ion-exchanged water, and stirred. This process of filtering, dispersing, and stirring was repeated five times for washing, and the washed solid product was then dried at 70°C for 24 hours. The dried sample was dispersed in 2N hydrochloric acid and heated in a sealed container at 100°C for 3 days. After filtering, washing, and drying the treated sample, the solid product was calcined in air at 550°C for 6 hours to obtain mesoporous silica. The peak diameter of the silica mesopores, determined by the BJH method of nitrogen adsorption measurement, was 6.5 nm. The peak diameter of the silica macropores, determined by mercury intrusion porosimetry, was 0.20 μm.

[0086] 1.1.2. Example 2 The surfactant n-hexadecyltrimethylammonium chloride [C 16 H 3318 g of [N(CH3)3Cl] and 13 g of ethanol were added to 650 g of 1.5 mass% hydrochloric acid. This was heated and stirred at 40°C, and 65 g of No. 1 sodium silicate (27 mass% as SiO2, SiO2 / Na2O = 2.00) was added, and the mixture was maintained for 3 hours to carry out a polycondensation reaction. The resulting solid product was filtered, dispersed in 1000 g of ion-exchanged water, and stirred. This process of filtering, dispersing, and stirring was repeated five times for washing, and the washed solid product was then dried at 70°C for 24 hours. The dried sample was dispersed in 2N hydrochloric acid and heated in a sealed container at 100°C for 3 days. After filtering, washing, and drying the treated sample, the solid product was calcined in air at 550°C for 6 hours to obtain mesoporous silica. The peak diameter of the silica mesopores, determined by the BJH method of nitrogen adsorption measurement, was 6.8 nm. The peak diameter of the silica macropores, determined by mercury intrusion porosimetry, was 0.25 μm.

[0087] 1.1.3. Example 3 The surfactant n-hexadecyltrimethylammonium chloride [C 16 H 33 18 g of N(CH3)3Cl and 13 g of ethanol were added to 470 g of 2 mass% hydrochloric acid. This was heated and stirred at 40°C, and 70 g of No. 1 sodium silicate (27 mass% as SiO2, SiO2 / Na2O = 2.00) was added, and the mixture was maintained for 3 hours to carry out a polycondensation reaction. The resulting solid product was filtered, dispersed in 1000 g of ion-exchanged water, and stirred. This process of filtering, dispersing, and stirring was repeated five times for washing, and the washed solid product was then dried at 70°C for 24 hours. The dried sample was dispersed in 2N hydrochloric acid and heated in a sealed container at 100°C for 3 days. After filtering, washing, and drying the treated sample, the solid product was calcined in air at 550°C for 6 hours to obtain mesoporous silica. The peak diameter of the silica mesopores, determined by the BJH method of nitrogen adsorption measurement, was 5.5 nm. The peak diameter of the silica macropores, determined by mercury intrusion porosimetry, was 0.23 μm.

[0088] 1.1.4. Example 4 The surfactant n-hexadecyltrimethylammonium chloride [C 16 H 33 17 g of [N(CH3)3Cl] and 12 g of ethanol were added to 650 g of 1.5 mass% hydrochloric acid. This was heated and stirred at 60°C, and 70 g of No. 1 sodium silicate (27 mass% as SiO2, SiO2 / Na2O = 2.00) was added, and the mixture was maintained for 3 hours to carry out a polycondensation reaction. The resulting solid product was filtered, dispersed in 1000 g of ion-exchanged water, and stirred. This process of filtering, dispersing, and stirring was repeated five times for washing, and the washed solid product was then dried at 70°C for 24 hours. The dried sample was dispersed in 2N hydrochloric acid and heated in a sealed container at 100°C for 3 days. After filtering, washing, and drying the treated sample, the solid product was calcined in air at 550°C for 6 hours to obtain mesoporous silica. The peak diameter of the silica mesopores, determined by the BJH method of nitrogen adsorption measurement, was 7.2 nm. The peak diameter of the silica macropores, determined by mercury intrusion porosimetry, was 0.26 μm.

[0089] 1.1.5. Example 5 The surfactant n-hexadecyltrimethylammonium chloride [C 16 H 33 18 g of N(CH3)3Cl and 13 g of ethanol were added to 470 g of 2 mass% hydrochloric acid. This mixture was heated and stirred at 60°C, and 70 g of No. 1 sodium silicate (27 mass% as SiO2, SiO2 / Na2O = 2.00) was added, and the mixture was maintained for 3 hours to carry out a polycondensation reaction. The resulting solid product was filtered, dispersed in 1000 g of ion-exchanged water, and stirred. This process of filtering, dispersing, and stirring was repeated five times for washing, and the washed solid product was then dried at 70°C for 24 hours. The dried sample was dispersed in 2N hydrochloric acid and heated in a sealed container at 100°C for 3 days. After filtering, washing, and drying the treated sample, the solid product was calcined in air at 550°C for 6 hours to obtain mesoporous silica. The peak diameter of the silica mesopores, determined by the BJH method of nitrogen adsorption measurement, was 7.8 nm. The peak diameter of the silica macropores, determined by mercury intrusion porosimetry, was 0.25 μm.

[0090] 1.1.6. Example 6 A predetermined amount of surfactant and 1N sodium hydroxide were added to a mixed solvent containing a predetermined amount of water, methanol, and ethylene glycol (EG) to obtain a first solution. Separately, a predetermined amount of tetraethoxysilane (TEOS) was added to a mixed solvent containing a predetermined amount of methanol and EG to obtain a second solution. Table 1 shows the amounts of the solutions used.

[0091] [Table 1]

[0092] When the second solution was added to the first solution, the solution turned cloudy after a while, confirming the synthesis of particles. After stirring for 8 hours at room temperature, the mixture was filtered and the residue was redispersed in water. After filtering again, the residue was dried in an oven at 45°C. The dried sample was dispersed in 2N sulfuric acid and heated in an autoclave at 120°C for 3 days. After autoclaving, the sample was filtered and washed, and then calcined at 550°C for 6 hours to remove organic components and obtain mesoporous silica. The peak diameter of the silica mesopores, determined by the BJH method of nitrogen adsorption measurement, was 5.2 nm. The peak diameter of the silica macropores, determined by mercury intrusion porosimetry, was 0.22 μm.

[0093] 1.2. Preparation of carbon support 1.2.1. Examples 1 to 6 Mesoporous silica was placed in a PFA container, and furfuryl alcohol (FA) was added in an amount equal to the pore volume, allowing it to penetrate into the silica pores. This was then heat-treated at 150°C for 18 hours to polymerize the FA. This was then heat-treated in a nitrogen atmosphere for 6 hours at 500°C to further carbonize the FA. This process was repeated twice, and then heat-treated in a nitrogen atmosphere for 6 hours at 900°C to obtain a mesoporous silica / carbon composite. This composite was immersed in a 12% HF solution for 12 hours to dissolve the silica component. After dissolution, it was filtered and washed repeatedly, and then dried at 45°C to obtain mesoporous carbon. The dried mesoporous carbon was then heated at 1800°C for 1 hour (graphitization treatment).

[0094] 1.2.2. Comparative Example 1 Commercially available hollow (mesoporous) carbon (Comparative Example 1) was used as is as the carbon support.

[0095] 1.3. Fuel Cell Construction Pt was loaded onto the carbon support obtained as described above. The Pt loading was 40 mass%. This was used to prepare an air electrode catalyst layer. The Pt loading on the air electrode side was 0.15 mg / cm. 2 The I / C of the air electrode catalyst layer was set to 1.0. In addition, a commercially available platinum-loaded carbon with a Pt loading of 30 mass% was used to fabricate an anode catalyst layer. The Pt loading on the anode side was 0.1 mg / cm. 2 The I / C of the anode catalyst layer was set to 0.75. Furthermore, a fluorine-based solid polymer electrolyte was used as the catalyst layer ionomer for both the air electrode catalyst layer and the anode catalyst layer.

[0096] The MEA was obtained by transferring an air electrode catalyst layer and a fuel electrode catalyst layer onto both sides of the electrolyte membrane. The electrolyte membrane was a fluorine-based solid polymer electrolyte membrane. 1cm of MEA 2The MEA was assembled into a rectangular cell for use. A diffusion layer and a current collector were placed on both sides of the MEA. Carbon paper (with a microporous layer) was used for the diffusion layer. A gold-plated copper plate with an integrated flow channel (flow channel: linear flow channel with a 0.4 mm pitch) was used for the current collector.

[0097] 2. Test Method [2.1. Three-dimensional transmission electron microscope observation] The carbon support was observed by three-dimensional transmission electron microscope (3DTEM). Furthermore, the average entrance diameter and average constriction diameter of the primary pores were calculated using the obtained 3DTEM images.

[0098] [2.2. Average pore size] The nitrogen adsorption isotherm of the carbon support was measured. The adsorption side data of the nitrogen adsorption isotherm was analyzed using the BJH method to determine the pore diameter (most frequent peak value) at which the pore volume was maximized.

[0099] [2.3. High temperature and low humidification voltage] The high-temperature, low-humidity voltage was determined according to the following procedure. Specifically, a power generation cell assembled with an MEA, diffusion layer, and flow path was heated and maintained at 105°C, and humidified air was passed through the air electrode and humidified hydrogen through the hydrogen electrode, and a power generation test was performed. The air electrode stoichiometry was 1.25, and the hydrogen electrode stoichiometry was 1.5. The relative humidity of the air electrode and hydrogen electrode was 30%.

[0100] [2.4. Efficiency point voltage] "Efficiency point voltage" is measured under the conditions of cell temperature: 80°C, relative humidity: 30%, current density: 0.2 A / cm 2 This refers to the voltage at The efficiency point voltage was determined according to the following procedure. Specifically, a power generation cell assembled with an MEA, diffusion layer, and flow path was maintained at 80°C, and humidified air was passed through the air electrode and humidified hydrogen through the hydrogen electrode, and a power generation test was performed. The air electrode stoichiometry was 1.25, and the hydrogen electrode stoichiometry was 1.5. The relative humidity of the air electrode and hydrogen electrode was 30%.

[0101] [3. Results] [3.1. Three-dimensional transmission electron microscope observation] Figure 1 shows a three-dimensional image (lower right) and a schematic diagram of the pore structure (upper left) of the mesoporous carbon obtained in Example 1. Figure 2 shows a three-dimensional image (lower right) and a schematic diagram of the pore structure (upper left) of the mesoporous carbon obtained in Comparative Example 1. 1 and 2, it can be seen that the pores inside the carbon support are not uniform in size, but have many constricted portions. It can also be seen that the size of the constricted portions is not uniform, but varies depending on the location.

[0102] 3.2. Pore size and power generation performance Table 2 shows the average inlet diameter, average constriction diameter, and average pore diameter of the carbon support, as well as the high-temperature, low-humidification voltage and efficiency point voltage of the polymer electrolyte fuel cell. Fig. 3 shows the relationship between the average inlet diameter and the high-temperature, low-humidification voltage. Fig. 4 shows the relationship between the average inlet diameter and the efficiency point voltage. Fig. 5 shows the relationship between the average constriction diameter and the high-temperature, low-humidification voltage. Fig. 6 shows the relationship between the average constriction diameter and the efficiency point voltage. The following can be seen from Table 2 and Figs. 3 to 6.

[0103] [Table 2]

[0104] (1) Comparative Example 1 is a material equivalent to the material described in Patent Document 1. Comparative Example 1 has a low high-temperature, low-humidification voltage. This is thought to be because the average inlet diameter exceeds 3.0 nm and the average constriction diameter exceeds 2.4 nm, making it difficult for generated water to remain in the primary pores under high-temperature, low-humidification conditions. (2) The high-temperature low-humidification voltage was high in all of Examples 1 to 6. This is thought to be because the average inlet diameter and the average constriction diameter were within appropriate ranges.

[0105] (3) The efficiency point voltage is low in Comparative Example 1. This is thought to be because the inlet diameter and the constricted diameter are large, making it difficult to retain the water produced during power generation. (4) The efficiency point voltage is high in all of Examples 1 to 6. This is thought to be because the small inlet diameter and the small constriction diameter make it easier for the water produced during power generation to be retained.

[0106] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are possible within the scope of the gist of the present invention. [Industrial Applicability]

[0107] The mesoporous carbon according to the present invention can be used as a catalyst support for the air electrode catalyst layer of a polymer electrolyte fuel cell, or as a catalyst support for the anode catalyst layer.

Claims

1. It has a connected structure in which carbon particles (primary particles) with primary pores are connected to each other, The average entrance diameter of the primary pores is 2.0 nm or more and 3.0 nm or less, The average neck diameter of the primary pores is 1.6 nm or more and 2.4 nm or less. Mesoporous carbon. however, The term "average entrance diameter" refers to the average value of the circle-equivalent diameters of the entrances of the primary pores that open to the surface of the carbon particles, as measured by three-dimensional transmission electron microscope image analysis; The term "average constriction diameter" refers to the average value of the equivalent circle diameter of the constriction of the primary pores inside the carbon particles, measured by the three-dimensional transmission electron microscope image analysis.

2. 2. The mesoporous carbon according to claim 1, which has a high-temperature low-humidification voltage of 570 mV or more.

3. 3. The mesoporous carbon according to claim 1, wherein the carbon particles have an average particle size of 30 nm or more and 300 nm or less.

4. The mesoporous carbon according to any one of claims 1 to 3, Catalyst particles supported in the primary pores of the mesoporous carbon; An electrode catalyst for a fuel cell comprising:

5. The fuel cell electrode catalyst according to claim 4; Catalyst layer ionomer and A catalyst layer comprising:

Images