Carbon support, fuel cell catalyst, fuel cell catalyst layer, and method for manufacturing carbon support

Abstract

To provide a carbon carrier for a fuel cell catalyst, a fuel cell catalyst, a fuel cell catalyst layer, and a method for manufacturing the carbon carrier that can improve the power generation performance of a fuel cell.SOLUTION: In a carbon carrier with pores, the thickness of a carbon wall of the carbon carrier, which is derived from a three-dimensional pore structure of a silica mold obtained by measuring the pore volume of the silica mold using a nitrogen adsorption analysis method, is 3.3 nm or more and 11.2 nm or less, and a carbon wall content is more than 60.3 ml / g and less than 190.8 ml / g.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a carbon support, a catalyst for a fuel cell, a catalyst layer for a fuel cell, and a method for manufacturing a carbon support. [Background technology]

[0002] Various research projects are being conducted on fuel cells. For example, Patent Document 1 discloses a mesoporous carbon that is low in packing and low in cost, a method for producing the same, and a polymer electrolyte fuel cell using the same.

[0003] Patent Document 2 discloses a monodispersed spherical carbon porous body having a diameter, pore size, and specific surface area within a specific range and suitable as a catalyst support for the air electrode side catalyst layer of a polymer electrolyte fuel cell, and a polymer electrolyte fuel cell using the same.

[0004] Patent Document 3 discloses spherical mesoporous carbon with a central pore diameter of more than 2 nm and a method for producing the same.

[0005] Patent Document 4 discloses a catalyst layer that has high water retention and can provide high cell performance even in a low humidity environment, and a polymer electrolyte fuel cell using the same. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-084852 [Patent Document 2] Japanese Patent Application Publication No. 2019-169317 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-265125 [Patent Document 4] Japanese Patent Application Laid-Open No. 2007-220414 Summary of the Invention [Problem to be solved by the invention]

[0007] To achieve high power generation performance (efficiency point performance) in the low current density region, the carbon support must have a three-dimensional pore structure. Conventional technologies specify the average primary particle size, average pore size, and pore volume of carbon, but do not specify the carbon wall content determined by nitrogen adsorption, the carbon support ratio determined by 3D-TEM, or the average diameter of the constricted portions within the pores. As a result, conventional technologies may result in insufficient power generation performance in fuel cells.

[0008] The present disclosure has been made in consideration of the above-described circumstances, and has as its main object to provide a carbon support for a fuel cell catalyst, a fuel cell catalyst, a fuel cell catalyst layer, and a method for manufacturing a carbon support, which can improve the power generation performance of a fuel cell. [Means for solving the problem]

[0009] The carbon support of the present disclosure is a carbon support having pores, The carbon support for fuel cell catalysts has a carbon wall thickness of 3.3 nm or more and 11.2 nm or less, as derived from the three-dimensional pore structure of a silica template obtained by measuring the pore volume of the silica template using nitrogen adsorption analysis, and a carbon wall content of more than 60.3 ml / g and less than 190.8 ml / g.

[0010] In the carbon support of the present disclosure, the carbon support ratio calculated by 3D-TEM observation may be more than 36% and less than 67%.

[0011] In the carbon support of the present disclosure, the carbon support has at least one constricted portion in the pore, The average diameter of the narrowed portions of the pores calculated by 3D-TEM observation may be 1.9 nm or more and less than 2.5 nm.

[0012] In the carbon support of the present disclosure, the carbon wall content is 61.5 ml / g or more and 168.4 ml / g or less, The carbon support ratio is 46% or more and 57% or less, The average diameter of the narrowed portion of the pores may be 1.9 nm or more and 2.0 nm or less.

[0013] The fuel cell catalyst of the present disclosure is a fuel cell catalyst including a carbon support supporting a metal catalyst, The carbon support is the carbon support described above.

[0014] The fuel cell catalyst layer of the present disclosure includes the fuel cell catalyst described above.

[0015] The method for producing a carbon support according to the present disclosure is the above-described method for producing a carbon support, in which porous silica is used as a template. [Effects of the Invention]

[0016] According to the present disclosure, the power generation performance of a fuel cell can be improved. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 shows (1) a planar TEM image and (2) a three-dimensional reconstructed image of the carbon support of Example 1. [Figure 2] FIG. 2 shows (1) a planar TEM image and (2) a three-dimensional reconstructed image of the carbon support of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present disclosure will be described. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of a carbon support or the like that do not characterize the present disclosure) can be understood as design matters for a person skilled in the art based on prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field. Furthermore, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect the actual dimensional relationships. In this specification, the use of "to" to indicate a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. Any combination of upper and lower limits in the numerical range can be adopted.

[0019] 1. Carbon support The carbon support of the present disclosure is a carbon support having pores, The carbon support for fuel cell catalysts has a carbon wall thickness of 3.3 nm or more and 11.2 nm or less, as derived from the three-dimensional pore structure of a silica template obtained by measuring the pore volume of the silica template using nitrogen adsorption analysis, and a carbon wall content of more than 60.3 ml / g and less than 190.8 ml / g.

[0020] According to the present disclosure, by using silica having a three-dimensional pore structure as a template, a carbon support with a controlled carbon wall thickness and carbon wall content can be obtained. The carbon support of the present disclosure has carbon walls of a predetermined thickness range and a three-dimensional pore structure containing a predetermined amount of carbon walls, which enables a metal catalyst to be uniformly supported within the pores of the carbon support. By using a carbon support on which a metal catalyst is uniformly supported as a fuel cell catalyst, the power generation performance of the fuel cell can be improved, and in particular, the efficiency point performance (power generation performance in a low current density region) can be improved.

[0021] The carbon support of the present disclosure may have pores and be a porous body. The pores may be mesopores. The carbon support may be mesoporous carbon. The average pore diameter of the mesopores may be 2 nm to 50 nm. The average pore diameter is obtained by measuring the pore diameters of a plurality of randomly selected pores and calculating the average value. The average pore diameter can be measured using a 3D-TEM (transmission electron microscope) or the like.

[0022] In the carbon support of the present disclosure, the carbon wall thickness of the carbon support derived from the three-dimensional pore structure of the silica template obtained by measuring the pore volume of the silica template using nitrogen adsorption analysis is 3.3 nm or more and 11.2 nm or less, and the carbon wall content is more than 60.3 ml / g and less than 190.8 ml / g. From the viewpoint of further improving the power generation performance of the fuel cell, the carbon wall content may be 61.5 ml / g or more and 168.4 ml / g or less. The carbon support of the present disclosure is obtained by using silica having a three-dimensional pore structure as a template, introducing a carbon source into the pores of the silica to obtain a silica-carbon composite, carbonizing the carbon source in the silica-carbon composite, and removing the silica from the silica-carbon composite. Therefore, the structure of the silica is transferred to the carbon support of the present disclosure. Therefore, the thickness of the carbon wall of the carbon support can be determined by measuring the pore diameter of the three-dimensional pore structure of the silica template, which is obtained by measuring the pore volume of the silica template using nitrogen adsorption analysis. The thickness of the carbon wall can be determined by measuring the pore diameters of multiple randomly selected pores in the three-dimensional pore structure of the silica template and calculating the average value. In the present disclosure, the carbon wall is synonymous with the so-called pore wall and means a carbon pore wall. The carbon wall content can be determined by measuring the pore volume of the three-dimensional pore structure of the silica template, which is obtained by measuring the pore volume of the silica template using nitrogen adsorption analysis. The pore volume of the three-dimensional pore structure of the silica template may be calculated, for example, from the difference between the amount of nitrogen adsorbed into the silica pores when the relative nitrogen adsorption pressure is 0.8 and the amount of nitrogen adsorbed when the relative nitrogen adsorption pressure is 0.4. In the present disclosure, the carbon wall content is the volume of carbon walls per 1 g of carbon support (unit: ml / g).

[0023] In the carbon support of the present disclosure, the carbon support ratio calculated by 3D-TEM observation may be more than 36% and less than 67%, and from the viewpoint of further improving the power generation performance of the fuel cell, it may be 46% or more and 57% or less. In the present disclosure, the carbon support ratio means the ratio of the area occupied by carbon when the area occupied by the entire carbon support is taken as 100%, and the area other than the area occupied by carbon is occupied by voids. The porosity of the carbon support may be, for example, 33% to 64%.

[0024] The carbon support may have at least one constricted portion within the pores. The diameter of the constriction is smaller than the pore size. In the carbon support of the present disclosure, the average diameter of the constricted portions of the pores calculated by 3D-TEM observation may be 1.9 nm or more but less than 2.5 nm, or from the viewpoint of further improving the power generation performance of the fuel cell, may be 1.9 nm or more but 2.0 nm or less. The average diameter of the constricted portions is the average value obtained by measuring the diameters of a plurality of randomly selected constricted portions.

[0025] The carbon support may be carbon support particles that are particulate in shape. The particle size of the carbon support particles is not particularly limited as long as it is larger than the pore size, and may be, for example, 4 nm or more and 100 nm or less. The particle size of the carbon support particles can be measured by 3D-TEM or the like.

[0026] 2. Carbon support manufacturing method In the method for producing a carbon support according to the present disclosure, silica having fine holes is used as a template. The method for producing a carbon support according to the present disclosure may include: (1) preparing silica having pores as a template; (2) precipitating carbon in the pores of the silica to obtain a silica-carbon composite; and (3) removing silica from the silica-carbon composite to obtain a carbon support.

[0027] (1) Preparation of silica The silica to be prepared has pores and a three-dimensional pore structure. The silica may be porous or may be mesoporous silica. The three-dimensional pore structure may be a bead-and-loop structure (random structure) described later. The silica to be used may be commercially available or synthesized. A method for producing silica typically includes a polymerization step in which a silica source is condensed and polymerized in a reaction solution containing a silica source, a surfactant, and a catalyst to obtain precursor particles; a drying step in which the precursor particles are separated from the reaction solution and dried; and a calcination step in which the precursor particles are calcined to obtain pore-containing silica particles. When the concentrations of the surfactant and the silica source in the reaction solution are each limited to a specific range during silica production, mesoporous silica having a bead-and-loop structure and pore diameters and volumes within specific ranges can be obtained. Furthermore, when mesoporous silica having such a bead-and-loop structure is used as a template, mesoporous carbon having a bead-and-loop structure can be obtained. Here, the term "bead-and-loop structure" refers to a structure in which primary particles are connected in a string-like pattern. The primary particles constituting the bead-and-loop structure have pores within them. In the bead-and-loop structure, the primary particles are connected to each other, and therefore, interconnected pores may be formed, in which the pores of the primary particles are interconnected. The shape of the primary particles is usually not perfectly spherical, but has an irregular shape with an aspect ratio of about 1.1 to 3, and in the bead-and-loop structure, one or more constricted portions having a diameter smaller than the pore diameter may be formed within the interconnected pores.

[0028] (1-1) Polymerization process First, precursor particles are obtained by polycondensing the silica source in a reaction solution containing the silica source, a surfactant, and a catalyst.

[0029] 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; etc. As the silica source, any one of these may be used alone, or two or more of them may be used in combination. If the concentration of the silica source is too low, the deposition rate of the precursor particles will be slow and a structure in which the primary particles are linked together will not be obtained. Therefore, the concentration of the silica source may be 0.05 mol / L or more. On the other hand, if the concentration of the silica source is too high, the precipitation rate of the precursor particles becomes too fast, and the primary particle size easily exceeds 300 nm. Therefore, the concentration of the silica source may be 1.0 mol / L or less.

[0030] 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, pores resulting from the micelles are formed inside the primary particles. The size of the pores can be controlled, for example, to 1 to 50 nm, mainly by the molecular length of the surfactant. Examples of surfactants include hexadecyltrimethylammonium halide, octadecyltrimethylammonium halide, nonyltrimethylammonium halide, decyltrimethylammonium halide, undecyltrimethylammonium halide, and dodecyltrimethylammonium halide. When synthesizing silica having pores, one type of surfactant may be used, or two or more types may be used. However, since the surfactant serves as a template for forming pores in the primary particles, the type of surfactant has a significant effect on the shape of the pores. From the viewpoint of synthesizing silica particles having more uniform pores, one type of surfactant may be used. If the surfactant concentration is too low, the deposition rate of the precursor particles will be slow and a structure in which the primary particles are linked together will not be obtained. Therefore, the surfactant concentration may be 0.03 mol / L or more. On the other hand, if the surfactant concentration is too high, the precipitation rate of the precursor particles becomes too fast, and the primary particle size easily exceeds 300 nm. Therefore, the surfactant concentration may be 1.0 mol / L or less.

[0031] When polycondensing the silica source, a catalyst is usually added to the reaction solution, and examples of the catalyst include alkalis such as sodium hydroxide and aqueous ammonia. The catalyst concentration is not particularly limited. Generally, if the catalyst concentration is too low, the precipitation rate of the precursor particles will be slow. On the other hand, if the catalyst concentration is too high, the precipitation rate of the precursor particles will be fast. The optimal catalyst concentration may be selected depending on the type of silica source, the type of surfactant, the target physical property values, etc.

[0032] The solvent used may be water, an organic solvent, or a mixed solvent of water and an organic solvent. Examples of the organic solvent include monohydric alcohols such as methanol, ethanol, and propanol, dihydric alcohols such as ethylene glycol, and trihydric alcohols such as glycerin. 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 of the silica particles.

[0033] 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. Generally, the reaction temperature may be -20°C to 100°C.

[0034] (1-2) Drying process Next, the precursor particles are separated from the reaction solution and dried. 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.

[0035] (1-3) Diameter expansion process Next, if necessary, the dried precursor particles may be subjected to a diameter expansion treatment, which refers to a treatment for expanding the diameter of the pores 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. Examples of diameter-enlarging agents include (a) hydrocarbons such as trimethylbenzene, triethylbenzene, benzene, cyclohexane, triisopropylbenzene, naphthalene, hexane, heptane, octane, nonane, decane, undecane, and dodecane; and (b) acids such as hydrochloric acid, sulfuric acid, and nitric acid. 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. Furthermore, 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 within the primary particles. Optimizing the manufacturing conditions results in the formation of radial pores within the silica. When this is subjected to hydrothermal treatment in the presence of an acid, the silica dissolves and reprecipitation occurs, converting the radial pores into interconnected pores. The conditions for the diameter-enlarging treatment are not particularly limited as long as the desired pore diameter is obtained. Typically, 0.05 mol / L to 10 mol / L of a diameter-enlarging agent is added to the reaction solution, and the mixture is subjected to hydrothermal treatment at 60°C to 150°C. The pore diameter obtained may be controlled by controlling the hydrothermal temperature.

[0036] (1-4) Firing process Next, after optionally carrying out a diameter expansion treatment, the precursor particles are calcined, thereby obtaining silica particles having pores. The calcination is carried out to dehydrate and crystallize the precursor particles with residual OH groups and to thermally decompose the surfactant remaining in the pores. The calcination conditions are not particularly limited as long as they allow for dehydration, crystallization, and thermal decomposition of the surfactant. The calcination is usually carried out by heating in the atmosphere at 400°C to 700°C for 1 hour to 10 hours.

[0037] (2) A process for obtaining a silica-carbon composite The method for depositing carbon in the pores of silica to obtain a silica-carbon composite is not particularly limited, and any conventionally known method can be appropriately employed. Specifically, carbon is deposited in the pores by introducing a carbon precursor into the pores and polymerizing and carbonizing the carbon precursor in the pores. The term "carbon precursor" refers to a substance capable of producing carbon by thermal decomposition. Specific examples of such carbon precursors include polymer precursors that are liquid at room temperature and are thermally polymerizable (e.g., furfuryl alcohol and aniline), mixtures of aqueous carbohydrate solutions and acids (e.g., mixtures of carbohydrates such as monosaccharides, disaccharides, and polysaccharides, such as sucrose, xylose, and glucose, with acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid), and mixtures of two-component curing polymer precursors (e.g., phenol and formalin). When a liquid or solution carbon precursor is used, the amount of liquid or solution adsorbed per one time is preferably as large as possible, and may be such an amount that the entire pores 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 may be 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.

[0038] The polymerized carbon precursor is then carbonized within the pores. Carbonization of the carbon precursor is carried out by heating silica containing the carbon precursor to a predetermined temperature in a non-oxidizing atmosphere (e.g., in an inert atmosphere, a vacuum, etc.). The heating temperature may be 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, the silica and carbon will react. The optimal heating time is selected depending on the heating temperature.

[0039] (3) Silica removal process Next, the silica template is removed from the silica-carbon composite, yielding a carbon support with fine pores. The method for removing silica from a silica-carbon composite is not particularly limited, and any conventionally known method can be appropriately employed. Examples of methods for removing silica from a silica-carbon composite include a method in which the silica-carbon composite is heated in an aqueous alkali solution such as sodium hydroxide to dissolve and remove the silica, and a method in which the silica in the silica-carbon composite is etched with an aqueous hydrofluoric acid solution.

[0040] (4) Graphitization process Next, if necessary, the carbon support is heat-treated at a temperature higher than 1500°C. When carbonizing a carbon source in the pores of silica, the heat treatment temperature must be low in order to suppress the reaction between silica and carbon. Therefore, the degree of graphitization of the carbon support after carbonization is low. In order to obtain a high degree of graphitization, it is preferable to heat-treat the carbon support at a high temperature after removing the template. If the heat treatment temperature is too low, graphitization will be insufficient. Therefore, the heat treatment temperature may be higher than 1500°C. On the other hand, if the heat treatment temperature is made higher than necessary, there will be no difference in the effect and there will be no practical benefit. Therefore, the heat treatment temperature may be 2300°C or lower.

[0041] 3.Catalyst for fuel cells The fuel cell catalyst of the present disclosure is a catalyst for a fuel cell that includes a carbon support supporting a metal catalyst, and the carbon support is the carbon support described above.

[0042] The metal catalyst is supported on the carbon support of the present disclosure. Examples of the metal catalyst include platinum and platinum alloys. The platinum alloy may be an alloy containing platinum and one or more metals selected from the group consisting of cobalt, nickel, iron, manganese, copper, titanium, tungsten, tin, gallium, zirconium, chromium, gadolinium, terbium, ytterbium, hafnium, and osmium. Among these, platinum, platinum-cobalt alloys, and platinum-nickel alloys may be used, and particularly platinum-cobalt alloys may be used. The metal catalyst may be metal catalyst particles that are particulate in shape. The particle size of the metal catalyst particles is not particularly limited, but may be 1 nm or more and 10 nm or less. The particle size of the metal catalyst particles can be measured by 3D-TEM or the like. When the particle diameter of the metal catalyst particles is equal to or larger than the pore diameter of the carbon support, the metal catalyst particles may be supported on the outer peripheral surface of the carbon support. When the particle diameter of the metal catalyst particles is equal to or larger than the average diameter of the constricted portions in the pores of the carbon support and smaller than the pore size of the carbon support, the metal catalyst particles may be supported in a region on the front side of the constricted portions in the pores of the carbon support. When the particle diameter of the metal catalyst particles is less than the average diameter of the constricted portions in the pores of the carbon support, the metal catalyst particles may be supported in a region deeper than the constricted portions in the pores of the carbon support.

[0043] 4.Catalyst layer for fuel cells The fuel cell catalyst layer of the present disclosure contains the above-described fuel cell catalyst and usually further contains an electrolyte. The electrolyte may be a proton-conductive material, such as a fluorine-based resin, etc. As the fluorine-based resin, for example, a perfluorosulfonic acid-based resin such as Nafion (registered trademark) may be used.

[0044] The catalyst layer of the present disclosure is for use in a fuel cell. The fuel cell of the present disclosure comprises the catalyst layer of the present disclosure. The fuel cell may have only one unit cell, or may be a fuel cell stack, which is a stack of a plurality of unit cells. The number of stacked unit cells is not particularly limited, and may be, for example, from 2 to several hundred.

[0045] A single cell of the fuel cell comprises at least a membrane electrode gas diffusion layer assembly. The membrane electrode gas diffusion layer assembly has, in this order, an anode gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode gas diffusion layer.

[0046] The cathode (oxidant electrode) includes a cathode catalyst layer, and optionally a cathode-side gas diffusion layer. The anode (fuel electrode) includes an anode catalyst layer, and optionally an anode-side gas diffusion layer. The fuel cell catalyst layer of the present disclosure may be used as a cathode catalyst layer, an anode catalyst layer, or both a cathode catalyst layer and an anode catalyst layer. The cathode catalyst layer and the anode catalyst layer are collectively referred to as catalyst layers.

[0047] The cathode side gas diffusion layer and the anode side gas diffusion layer are collectively referred to as gas diffusion layers. The gas diffusion layer may be a gas-permeable conductive material or the like. Examples of the conductive member include porous carbon materials such as carbon cloth and carbon paper, and porous metal materials such as metal mesh and foam metal.

[0048] The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of the solid polymer electrolyte membrane include a fluorine-based electrolyte membrane such as a thin film of perfluorosulfonic acid containing water, and a hydrocarbon-based electrolyte membrane. The electrolyte membrane may be, for example, a Nafion membrane (manufactured by DuPont).

[0049] The single cell may optionally include two separators sandwiching both sides of the membrane electrode gas diffusion layer assembly. One of the two separators is an anode-side separator, and the other is a cathode-side separator. In the present disclosure, the anode-side separator and the cathode-side separator are collectively referred to as separators. The separator may have supply holes and discharge holes for allowing the reaction gas, coolant, etc. to flow in the stacking direction of the unit cells. As the coolant, for example, a mixed solution of ethylene glycol and water can be used to prevent freezing at low temperatures. In this disclosure, the fuel gas and the oxidant gas are collectively referred to as reactant gases. The reactant gas supplied to the anode is the fuel gas, and the reactant gas supplied to the cathode is the oxidant gas. The fuel gas is a gas that mainly contains hydrogen and may be hydrogen. The oxidant gas may be oxygen, air, dry air, or the like. The separator may have a reactant gas flow path on the surface in contact with the gas diffusion layer, and may have a coolant flow path on the surface opposite to the surface in contact with the gas diffusion layer to maintain a constant temperature of the fuel cell. The separator may be a gas-impermeable conductive material. Examples of the conductive material include dense carbon made by compressing carbon to make it gas-impermeable, and press-formed metal (e.g., iron, aluminum, stainless steel, etc.) plates. The separator may also have a current collecting function. [Example]

[0050] Hereinafter, the present disclosure will be described in more detail using examples and comparative examples, but the technical scope of the present disclosure is not limited thereto. Note that examples and comparative examples are not distinguished by whether they are included in the scope of the claims. Embodiments that obtained particularly good results are designated as examples, and other embodiments are designated as comparative examples.

[0051] Example 1 Mesoporous silica was prepared, and a carbon support was produced using the mesoporous silica as a template. The mesoporous silica used as the template was one that would result in a carbon support with a carbon wall thickness of 3.3 nm to 11.2 nm and a carbon wall content of 168.4 ml / g. The pore volume of the three-dimensional pore structure of the silica was calculated from the difference between the adsorption amounts when the nitrogen adsorption relative pressure of the silica pores was 0.8 and when it was 0.4, and the carbon wall content of the carbon support was derived from this pore volume.

[0052] Example 2 The carbon support of Example 2 was obtained in the same manner as in Example 1, except that mesoporous silica was used as the template so that the carbon wall thickness of the resulting carbon support was in the range of 3.3 nm to 11.2 nm and the carbon wall content was 166.6 ml / g.

[0053] Example 3 The carbon support of Example 3 was obtained in the same manner as in Example 1, except that mesoporous silica was used as the template so that the carbon wall thickness of the resulting carbon support was in the range of 3.3 nm to 11.2 nm and the carbon wall content was 61.5 ml / g.

[0054] (Comparative Example 1) The carbon support of Comparative Example 1 was obtained in the same manner as in Example 1, except that mesoporous silica was used as the template so that the carbon wall thickness of the resulting carbon support was in the range of 3.3 nm to 11.2 nm and the carbon wall content was 42.5 ml / g.

[0055] (Comparative Example 2) The carbon support of Comparative Example 2 was obtained in the same manner as in Example 1, except that mesoporous silica was used as the template so that the carbon wall thickness of the resulting carbon support was in the range of 3.3 nm to 11.2 nm and the carbon wall content was 40.6 ml / g.

[0056] (Comparative Example 3) The carbon support of Comparative Example 3 was obtained in the same manner as in Example 1, except that mesoporous silica was used as the template so that the carbon wall thickness of the resulting carbon support was in the range of 3.3 nm to 11.2 nm and the carbon wall content was 190.8 ml / g.

[0057] Comparative Example 4 The carbon support of Comparative Example 4 was obtained in the same manner as in Example 1, except that mesoporous silica was used as the template so that the carbon wall thickness of the resulting carbon support was in the range of 3.3 nm to 11.2 nm and the carbon wall content was 60.3 ml / g.

[0058] [3D-TEM observation] The obtained carbon supports of Examples 1 to 3 and Comparative Examples 1 to 4 were observed by 3D-TEM to measure the carbon support ratio (%) and the average diameter (nm) of the constricted portions in the pores of the carbon support. The measurement results are shown in Table 1. FIG. 1 shows (1) a planar TEM image and (2) a three-dimensional reconstructed image of the carbon support of Example 1. FIG. 2 shows (1) a planar TEM image and (2) a three-dimensional reconstructed image of the carbon support of Comparative Example 1. As shown in FIG. 1 and Table 1, the carbon support of Example 1 has an appropriate carbon wall content, an appropriate carbon support ratio, and an appropriate average diameter of the constricted portions in the pores of the carbon support. As shown in FIG. 2 and Table 1, the carbon support of Comparative Example 1 has a low carbon wall content, a low carbon support ratio, and an excessively large average diameter of the constricted portions in the pores of the carbon support.

[0059] [Creating catalysts for fuel cells] A platinum-cobalt alloy was supported as a metal catalyst on each of the carbon supports obtained in Examples 1 to 3 and Comparative Examples 1 to 4, to obtain a platinum-cobalt alloy-supported carbon support as a catalyst for a fuel cell.

[0060] [Mass activity of fuel cell catalysts] For each of the fuel cell catalysts of Examples 1 to 3 and Comparative Examples 1 to 4, the mass activity per gram of platinum (A / g-Pt) was evaluated by the rotating disk electrode (RDE) method. Specifically, a catalyst ink was prepared by dispersing a fuel cell catalyst in a mixed solvent containing ultrapure water, alcohol, and Nafion®. This catalyst ink was applied to a glassy carbon (GC) electrode and dried to obtain an electrode for evaluation. The RDE cell was a three-electrode type, and a 0.1 M aqueous solution of perchloric acid was used as the electrolyte. A reversible hydrogen electrode (RHE) was used as the reference electrode, and a black Pt mesh was used as the counter electrode. The mass activity (MA) of the oxygen reduction reaction (ORR) was determined from linear sweep voltammogram (LSV) measurements. The measurement results are shown in Table 1.

[0061] <Manufacturing of single cells> Each of the fuel cell catalysts of Examples 1 to 3 and Comparative Examples 1 to 4 was dispersed in an organic solvent. The resulting dispersion was applied to a Teflon (registered trademark) sheet to form an electrode. Two electrodes were formed, and the electrolyte membrane was sandwiched between the two electrodes and bonded together by hot pressing to obtain a membrane electrode assembly. The membrane electrode assembly was sandwiched between two diffusion layers to obtain a single cell.

[0062] <Evaluation of efficiency point performance> The temperature of each single cell in Examples 1 to 3 and Comparative Examples 1 to 4 was set to 80°C, the relative humidity of the two electrodes of each single cell was set to 85%, and the IV of each single cell was measured using a small single cell evaluation device system (manufactured by Toyo Corporation). For IV measurements, 0.01A / cm 2 ~4.0A / cm 2 The current was controlled arbitrarily within the range of 0.2 A / cm 2 The voltage value at this point was defined as the efficiency point voltage and was measured. The measurement results are shown in Table 1.

[0063] [Table 1]

[0064] The fuel cell catalysts using the carbon supports of Examples 1 to 3 have higher mass activity than the fuel cell catalysts using the carbon supports of Comparative Examples 1 to 4. The single cells using the fuel cell catalysts using the carbon supports of Examples 1 to 3 have higher efficiency point voltages than the single cells using the fuel cell catalysts using the carbon supports of Comparative Examples 1 to 4. This is because the use of the carbon supports of Examples 1 to 3 allows the metal catalyst to be uniformly supported, thereby improving the power generation performance, especially the efficiency performance.

Claims

1. A carbon support having fine pores, A carbon support for a fuel cell catalyst, wherein the carbon wall thickness of the carbon support derived from the three-dimensional pore structure of a silica template obtained by measuring the pore volume of the silica template using nitrogen adsorption analysis is 3.3 nm or more and 11.2 nm or less, and the carbon wall content is more than 60.3 ml / g and less than 190.8 ml / g.

2. The carbon support according to claim 1, wherein the carbon support ratio calculated by 3D-TEM observation is more than 36% and less than 67%.

3. the carbon support has at least one constricted portion within the pore, 3. The carbon support according to claim 2, wherein the average diameter of the constricted portions of the pores calculated by 3D-TEM observation is 1.9 nm or more and less than 2.5 nm.

4. The carbon wall content is 61.5 ml / g or more and 168.4 ml / g or less, The carbon support ratio is 46% or more and 57% or less, The carbon support according to claim 3 , wherein the average diameter of the narrowed portions of the pores is 1.9 nm or more and 2.0 nm or less.

5. A catalyst for a fuel cell comprising a carbon support carrying a metal catalyst, A catalyst for a fuel cell, wherein the carbon support is the carbon support according to any one of claims 1 to 4.

6. A catalyst layer for a fuel cell comprising the catalyst for a fuel cell according to claim 5 .

7. The method for producing a carbon support according to any one of claims 1 to 4, wherein the carbon support is produced using porous silica as a template.

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