Catalysts for fuel cells

Abstract

To provide a catalyst for a fuel battery, of which the performance is enhanced further than conventional one.SOLUTION: A catalyst for a fuel battery according to an embodiment hereof comprises: a catalyst metal; and a carrier that supports the catalyst metal. Of the carrier, the ratio of inside and outside superficial areas (an outside superficial area of the carrier / an inside superficial area of the carrier) is 0.56-0.69. A percentage of the catalyst metal supported on the outer surface of the carrier is 23-35%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to catalysts for fuel cells. [Background technology]

[0002] Fuel cells convert chemical energy directly into electrical energy by supplying fuel gas (hydrogen gas) and oxidizing gas (oxygen gas) to two electrically connected electrodes, causing electrochemical oxidation of the fuel. These fuel cells are typically constructed by stacking multiple single cells, each having a membrane electrode assembly as its basic structure, in which an electrolyte membrane is sandwiched between a pair of electrodes (catalyst layers). Among these, solid polymer electrolyte fuel cells, which use a solid polymer electrolyte membrane as the electrolyte membrane, are attracting particular attention as power sources for portable and mobile devices due to their advantages such as ease of miniaturization and operation at low temperatures.

[0003] In a solid polymer electrolyte fuel cell, the reaction shown in equation (1) below proceeds at the anode (fuel electrode) to which hydrogen is supplied. H2 → 2H + + 2e - ...(1)

[0004] The electrons (e) produced in the above equation (1) - The protons (H) generated in equation (1) above travel through an external circuit, perform work on an external load, and then reach the cathode (air electrode / oxidant electrode). + ) moves from the anode side to the cathode side within the solid polymer electrolyte membrane by electroosmosis while hydrated with water.

[0005] Meanwhile, the reaction shown in equation (2) below proceeds at the cathode. 2H + + 1 / 2O2 + 2e - → H2O ···(2)

[0006] Therefore, the chemical reaction shown in equation (3) below proceeds throughout the battery, generating an electromotive force that performs electrical work on an external load. H2 + 1 / 2O2 → H2O ... (3)

[0007] The catalyst layer usually contains a catalyst in which a catalyst metal such as platinum or a platinum alloy for promoting the electrode reaction is supported on a carrier having fine pores such as carbon, and an ionomer for ensuring proton conductivity.

[0008] In the field of fuel cells having such a configuration, attempts have conventionally been made to improve the performance of fuel cells by focusing on the catalyst layer. For example, in Patent Document 1, a carrier made of mesoporous carbon is heat-treated at 2300°C or higher and 2500°C or lower, a catalyst metal is supported on the heat-treated carrier, and the carrier supporting the catalyst metal is immersed in an acidic solution at 80°C or higher and 95°C or lower and having a concentration of 0.5 mol / L or higher for oxidation treatment, and a method for producing a catalyst for a fuel cell is disclosed.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present inventors have conducted studies on whether it is possible to improve the performance of a catalyst for a fuel cell from a different perspective than the conventional one in order to further improve the power generation performance of the fuel cell.

[0011] An object of the present disclosure is to provide a catalyst for a fuel cell having improved performance compared to the conventional one.

Means for Solving the Problems

[0012] The present inventors conducted intensive research to solve the above problems and discovered that by setting the ratio of the inner and outer surface areas of the support constituting the fuel cell catalyst and the proportion of the catalyst metal supported on the outer surface of the support to a specific range, a fuel cell catalyst with improved performance compared to conventional fuel cell catalysts can be obtained, leading to this disclosure.

[0013] Examples of embodiments of this embodiment are described below.

[0014] (1) A catalyst for a fuel cell comprising a catalytic metal and a carrier supporting the catalytic metal, The ratio of the inner surface area of ​​the carrier to the outer surface area of ​​the carrier (outer surface area of ​​the carrier / inner surface area of ​​the carrier) is 0.56 to 0.69. A fuel cell catalyst wherein the proportion of the catalyst metal supported on the outer surface of the carrier is 23-35%. (2) The fuel cell catalyst according to (1), wherein the support is mesoporous carbon. (3) The fuel cell catalyst according to (1) or (2), wherein the catalyst metal is platinum or a platinum alloy. [Effects of the Invention]

[0015] This disclosure makes it possible to provide a fuel cell catalyst with improved performance compared to conventional fuel cell catalysts. [Brief explanation of the drawing]

[0016] [Figure 1] This is an illustrative diagram showing the state in which the catalyst metal is supported on a carrier in a fuel cell catalyst. [Modes for carrying out the invention]

[0017] This embodiment is a fuel cell catalyst comprising a catalytic metal and a carrier supporting the catalytic metal, wherein the ratio of the inner surface area of ​​the carrier (outer surface area of ​​the carrier / inner surface area of ​​the carrier) is 0.56 to 0.69, and the proportion of the catalytic metal supported on the outer surface of the carrier is 23 to 35%. The fuel cell catalyst of this embodiment is suitably used as a catalyst for the cathode (air electrode) of a fuel cell. This embodiment will be described in detail below.

[0018] (Catalytic metal) The fuel cell catalyst of this embodiment includes a catalyst metal. The catalyst metal is not particularly limited, and for example, precious metal elements such as platinum, ruthenium, palladium, iridium, and rhodium, or alloys thereof, can be used, but platinum or a platinum alloy is preferred. Examples of platinum alloys include alloys containing platinum and at least one metal selected from cobalt, nickel, iron, manganese, copper, titanium, tungsten, tin, gallium, zirconium, chromium, gadolinium, terbium, ytterbium, hafnium, and osnium. As platinum alloys, platinum-cobalt alloys and platinum-nickel alloys are preferred. The average particle size of the catalyst metal is not particularly limited, but for example, 2 nm or more is preferred, and 2.5 nm or more is more preferred. Furthermore, the average particle size of the catalyst metal is, for example, 10 nm or less, and 5 nm or less is more preferred.

[0019] When the catalyst metal is platinum or a platinum alloy, the platinum loading density of the fuel cell catalyst is typically 1 to 99 wt%, preferably 10 to 90 wt%, and more preferably 30 to 70 wt%, from the viewpoint of excellent catalytic performance. The platinum loading density can be calculated by the formula: platinum weight / (fuel cell catalyst weight) × 100 (wt%).

[0020] (carrier) The fuel cell catalyst of this embodiment includes a carrier on which the catalyst metal is supported. There are no particular restrictions on the carrier, but a carbon material, preferably mesoporous carbon, can usually be used.

[0021] The carrier has an external-to-internal surface area ratio (external surface area of the carrier / internal surface area of the carrier) of 0.56 to 0.69. Note that the external surface area of the carrier is the area of the external surface of the carrier, and the internal surface area of the carrier is the area of the internal surface of the carrier. In the present embodiment, the surface of the carrier is a concept that includes not only the surface in contact with the outside of the carrier but also the surfaces of the internal structures (walls, pores) of the particles such as the pores of the carrier. In the present embodiment, the external surface of the carrier means the surface in contact with the outside of the carrier, and the internal surface of the carrier means the surface of the internal structure of the particle. The internal surface (internal surface area) and external surface (external surface area) of the carrier can be determined by analyzing the catalyst by 3D-TEM. Specifically, it can be determined by the method described in the examples.

[0022] The carrier preferably has an external surface area of 0.03 to 0.2 μm 2 / piece. Further, the carrier preferably has an internal surface area of 0.05 to 0.35 μm 2 / piece. Furthermore, the carrier preferably has a surface area (external surface area + internal surface area) of 0.08 to 0.5 μm 2 / piece.

[0023] The carrier supports the above-described catalytic metal, and the catalytic metal is supported on the internal and external surfaces of the carrier. The fuel cell catalyst will be described using an image diagram (Figure 1) showing the state in which the catalytic metal is supported on the carrier in the fuel cell catalyst.

[0024] The carrier has an external surface 1 and an internal surface 3 which is a surface of an internal structure such as pores. In the fuel cell catalyst of the present embodiment, the catalytic metal is supported on the external surface 1 and the internal surface 3. The catalytic metal supported on the external surface 1 is also referred to as external particles 5, and the catalytic metal supported on the internal surface 3 is also referred to as internal particles 7.

[0025] In the fuel cell catalyst of the present embodiment, the ratio of the catalytic metal supported on the external surface of the carrier is 23 to 35%. This ratio can be calculated from the following formula by analyzing the three-dimensional structure of the fuel cell catalyst by 3D-TEM, counting the number of external particles and the number of internal particles, for example, by the method described in the examples. The percentage of catalyst metal supported on the outer surface of the carrier (%) = Number of external particles / (Number of external particles + Number of internal particles) × 100

[0026] When the support is mesoporous carbon, it is preferable that the mesoporous carbon is carbon particles having mesopores (also written as mesopores) inside, with the pore volume in the 2-10 nm pore size distribution being 80% or more, based on the total pore volume in the 1-100 nm pore size distribution.

[0027] The average primary particle diameter (average circular equivalent diameter) of mesoporous carbon is not particularly limited, but is preferably between 30 nm and 300 nm. The average primary particle diameter of mesoporous carbon is preferably 270 nm or less, and more preferably 250 nm or less. Furthermore, the average primary particle diameter of mesoporous carbon is preferably 50 nm or more, and more preferably 70 nm or more.

[0028] The pore size and primary particle size of mesoporous carbon are values ​​measured by methods common in the field. For example, the pore size can be obtained by analyzing the adsorption data of nitrogen adsorption isotherms using the BJH method and calculating it with a P / PO = 0.03 to 0.99 value. The primary particle size can be determined, for example, by calculating the diameter (area circle equivalent diameter) of a single particle when considered as a circle in a transmission electron microscope (TEM) or scanning electron microscope (SEM) image at an appropriate magnification (e.g., 50,000 to 1,000,000x), and then performing this particle size calculation using TEM or SEM observation for 100 particles of the same type, and taking the number average of these particles as the average primary particle size.

[0029] (Method of manufacturing a carrier) The method for manufacturing the support will be explained below, using the case where the support is mesoporous carbon as an example. Mesoporous carbon is manufactured using mesoporous silica as a mold.

[0030] [Methoporous silica (mold) manufacturing method] The following methods are suggested for producing mesoporous silica used as a mold in the production of mesoporous carbon. Preferably, the method for producing mesoporous silica (mold) comprises a polymerization step (step 1-1) in which the silica source is polymerized in a reaction solution containing a silica source, a surfactant, and a catalyst to obtain precursor particles; a drying step (step 1-2) in which the precursor particles are separated from the reaction solution and dried; and a calcination step (step 1-3) in which the precursor particles are calcined to obtain mesoporous silica. A method for producing mesoporous silica may further include a diameter-expanding step in which dried precursor particles are subjected to a diameter-expanding treatment.

[0031] (Step 1-1: Polymerization step) First, the silica source is polymerized in a reaction solution containing a silica source, a surfactant, and a catalyst to obtain precursor particles (polymerization step). The polymerization step is usually carried out in a solvent.

[0032] (Silica source) In the present invention, the type of silica source is not particularly limited. Examples of silica sources 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) These include silicates such as sodium silicate and kanemite (NaHSi2O5·3H2O). Any one of these silica sources may be used, or a combination of two or more may be used.

[0033] (Surfactants) When a silica source is subjected to condensation polymerization in a reaction solution, the addition of a surfactant to the reaction solution causes the surfactant to form micelles. Because hydrophilic groups are aggregated around the micelles, the silica source is adsorbed onto the surface of the micelles. Furthermore, the micelles with the adsorbed silica source self-assemble in the reaction solution, and the silica source undergoes condensation polymerization. As a result, mesopores (including micropores with a diameter of 2 nm or less; the same applies hereinafter) are formed inside the primary particles due to the micelles. The size of the mesopores can be controlled mainly by the molecular length of the surfactant (from 1 to 50 nm).

[0034] 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. As the alkyl quaternary ammonium salt, a compound represented by the following formula (a) is preferred. CH3-(CH2) n -N + (R 1 )(R 2 )(R 3 )X - ...(a)

[0035] (a) In the formula, R 1 , R 2 , R 3 Each of these represents an alkyl group with 1 to 3 carbon atoms. 1 , R 2 , and R 3 These may be identical or different. In order to facilitate aggregation (micelle formation) of alkyl quaternary ammonium salts, R 1 , R 2 , and R 3 It is preferable that all of them are identical. Furthermore, R 1 , R 2 , and R 3 Preferably, at least one of them is a methyl group, and more preferably, all of them are methyl groups. (a) In formula X, X represents a halogen atom. The type of halogen atom is not particularly limited, but due to their availability, X is preferably Cl or Br.

[0036] (a) In formula n, n represents an integer from 7 to 21. Generally, the smaller n is, the smaller the central pore diameter of the mesopores, resulting in a spherical mesoporous material. On the other hand, the larger n is, the larger the central pore diameter, but if n is too large, the hydrophobic interaction of the alkyl quaternary ammonium salt becomes excessive. As a result, a layered compound is formed, and a spherical mesoporous material cannot be obtained. n is preferably 9 to 17, and more preferably 13 to 17.

[0037] Among those represented by formula (a), alkyltrimethylammonium halides are preferred. Examples of alkyltrimethylammonium halides include hexadecyltrimethylammonium halide, octadecyltrimethylammonium halide, nonyltrimethylammonium halide, decyltrimethylammonium halide, undecyltrimethylammonium halide, dodecyltrimethylammonium halide, tridecyltrimethylammonium halide, tetradecyltrimethylammonium halide, pentadecyltrimethylammonium halide, and hexadecyltrimethylammonium halide. Among these, alkyltrimethylammonium bromide or alkyltrimethylammonium chloride is particularly preferred.

[0038] When producing mesoporous silica, one type of alkyl quaternary ammonium salt may be used as the surfactant, or two or more types may be used. However, since the alkyl quaternary ammonium salt acts as a template for forming mesopores within the primary particles, its type greatly affects the shape of the mesopores. To synthesize silica particles with more uniform mesopores (mesoporous silica), it is preferable to use one type of alkyl quaternary ammonium salt.

[0039] (catalyst) When a silica source is subjected to condensation polymerization, a catalyst is usually added to the reaction solution. When synthesizing particulate mesoporous silica, an alkali such as sodium hydroxide or aqueous ammonia may be used as the catalyst, or an acid such as hydrochloric acid may be used.

[0040] (solvent) It is preferable to use water, organic solvents such as alcohol, or a mixed solvent of water and an organic solvent as the solvent.

[0041] The alcohol may be any of the following: (1) a monohydric alcohol such as methanol, ethanol, or propanol; (2) a dihydric alcohol such as ethylene glycol; or (3) a trihydric alcohol such as glycerin.

[0042] When using a mixed solvent of water and an organic solvent, the content of the organic solvent in the mixed solvent can be arbitrarily selected 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 using a mixed solvent of water and an organic solvent, if the organic solvent content is 5% by mass or less (i.e., the water content is 95% by mass or more), mesoporous silica for producing mesoporous carbon with excellent flooding resistance can be manufactured at low cost.

[0043] (Composition of the 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 the silica source in the reaction solution have a significant impact on the average diameter of the primary particles, pore size, pore volume, and linearity of the mesoporous silica particles.

[0044] (Concentration of surfactant) If the surfactant concentration is too low, the particle precipitation rate will be slow, and a structure in which primary particles are linked together will not be obtained. Therefore, the surfactant concentration is usually 0.03 mol / L or higher. Preferably, the surfactant concentration is 0.035 mol / L or higher, and more preferably 0.04 mol / L or higher.

[0045] On the other hand, if the surfactant concentration is too high, the particle precipitation rate becomes too fast, and the primary particle size easily exceeds 300 nm. Therefore, the surfactant concentration usually needs to be 1.0 mol / L or less. Preferably, the surfactant concentration is 0.95 mol / L or less, and more preferably 0.90 mol / L or less.

[0046] (Concentration of silica source) If the silica source concentration is too low, the particle precipitation rate will be slow, and a structure in which primary particles are linked may not be obtained. Alternatively, an excess of surfactant may result, preventing the acquisition of uniform mesopores. Therefore, the silica source concentration is usually 0.05 mol / L or higher. Preferably, the silica source concentration is 0.06 mol / L or higher, and more preferably 0.07 mol / L or higher.

[0047] On the other hand, if the silica source concentration is too high, the particle precipitation rate becomes too fast, and the primary particle diameter may easily exceed 300 nm, or sheet-like particles may be obtained instead of spherical particles. Therefore, the silica source concentration should normally be 1.0 mol / L or less. Preferably, the silica source concentration is 0.95 mol / L or less, and more preferably 0.90 mol / L or less.

[0048] (Catalyst concentration) The concentration of the catalyst used in the production of mesoporous silica is not particularly limited. Generally, if the catalyst concentration is too low, the particle deposition rate will be slow. On the other hand, if the catalyst concentration is too high, the particle deposition rate will be fast. It is preferable to select the optimal catalyst concentration according to the type of silica source, the type of surfactant, the target physical properties, etc.

[0049] For example, when using an acid 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. Preferably, the pH of the reaction solution is 8.5 or less, and more preferably less than 5. On the other hand, when using an alkali as a catalyst, it is preferable to adjust the concentration of the catalyst so that the pH of the reaction solution is greater than 7.

[0050] (Reaction conditions) A silica source is added to a solvent containing a predetermined amount of surfactant, and hydrolysis and polycondensation are carried out. This allows the surfactant to function as a template, yielding precursor particles containing silica and the surfactant. The reaction conditions are selected according to the type of silica source, the particle size of the precursor particles, etc. Generally, the reaction temperature is preferably -20 to 100°C. More preferably, the reaction temperature is 0 to 100°C, even more preferably 0 to 90°C, particularly preferably 10 to 80°C, and most preferably 35 to 80°C.

[0051] (Step 1-2: Drying process) Next, the precursor particles are separated from the reaction solution and dried (drying step). Drying is performed to remove any residual solvent within the precursor particles. The drying conditions are not particularly limited, as long as the solvent can be removed.

[0052] (Diameter expansion process) Next, if necessary, the dried precursor particles may be subjected to a diameter-expanding process (diameter-expanding step). "Diameter-expanding process" refers to a process that enlarges the diameter of the mesopores within the primary particles. Specifically, the pore size expansion process is carried out by hydrothermally treating the synthesized precursor particles (with the surfactant still intact) in a solution containing a pore size expanding agent. This process can enlarge the pore size of the precursor particles.

[0053] Examples of diameter-expanding 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.

[0054] The reason why hydrothermal treatment in the presence of hydrocarbons expands the pore size is thought to be because silica rearrangement occurs when the pore-expanding agent is introduced from the solvent into the pores of the more hydrophobic precursor particles.

[0055] Furthermore, the expansion of pore size due to hydrothermal treatment in the presence of an acid such as hydrochloric acid is thought to be due to the dissolution and reprecipitation of silica within the primary particles. Optimizing the manufacturing conditions forms radial pores within the silica. When this is subjected to hydrothermal treatment in the presence of an acid, dissolution and reprecipitation of silica occurs, and the radial pores are converted into interconnected pores.

[0056] The conditions for the pore expansion treatment are not particularly limited, as long as the desired pore diameter can be obtained. Typically, it is preferable to add a pore-expanding agent at a concentration of about 0.05 mo¹ / L to 10 mo¹ / L to the reaction solution and perform hydrothermal treatment at 60 to 150°C.

[0057] (Steps 1-3: Firing process) Next, after performing a diameter-expanding process as necessary, the precursor particles are calcined (calcination step). This yields mesoporous silica. Calcination is performed to dehydrate and polymerize precursor particles containing residual OH groups, and to thermally decompose surfactants remaining in the mesopores. The calcination conditions are not particularly limited, as long as dehydration, polymerization, and thermal decomposition of surfactants are possible. Calcination is usually carried out by heating in air at 400°C to 700°C for 1 to 10 hours.

[0058] [Methopore Carbon Manufacturing Method] A method for producing mesoporous carbon comprises a first step of preparing mesoporous silica to serve as a mold, a second step of precipitating carbon in the mesopores of the mesoporous silica to produce a mesoporous silica / carbon composite, and a third step of removing the mesoporous silica from the composite. The method for producing mesoporous carbon may further include a fourth step after the third step of heat-treating the mesoporous carbon at a temperature higher than 1500°C.

[0059] (Step 1: Manufacturing of the mold (mesoporous silica)) First, a mesoporous silica template is prepared (Step 1). Details of the mesoporous silica manufacturing method are described above under [Methoporous Silica Manufacturing Method (Template)], so the explanation will be omitted here.

[0060] (Step 2: Carbon deposition into mesopores) Next, carbon is deposited within the mesopores of the mesoporous silica to create a mesoporous silica / carbon composite (second step). Specifically, the deposition of carbon into the mesopores is carried out by (a) introducing a carbon precursor into the mesopore, and (b) polymerizing and carbonizing the carbon precursor within the mesopore.

[0061] (a) Introduction of carbon precursor A "carbon precursor" refers to a substance that can produce carbon through thermal decomposition. Specific examples of such carbon precursors include: (1) polymer precursors that are liquid at room temperature and are thermopolymerizable (e.g., furfuryl alcohol, aniline, etc.); (2) mixtures of aqueous carbohydrate solutions and acids (e.g., monosaccharides such as sucrose, xylose, glucose, etc., or mixtures of disaccharides, polysaccharides, etc., with acids such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, etc.); and (3) mixtures of two-component curing polymer precursors (e.g., phenol and formalin, etc.).

[0062] Among these, polymer precursors can be impregnated into mesopores without dilution with a solvent, allowing for the generation of a relatively large amount of carbon within the mesopores with a relatively small number of impregnation steps. Furthermore, they have the advantages of not requiring polymerization initiators and being easy to handle.

[0063] When using a liquid or solution carbon precursor, the amount of liquid or solution adsorbed per application should be as large as possible, preferably enough to fill the entire mesopore. Furthermore, when using a mixture of an aqueous carbohydrate solution and an acid as the carbon precursor, the amount of acid should be the minimum amount necessary to polymerize the organic material. Additionally, when using a mixture of two-component curable polymer precursors as the carbon precursor, the optimal ratio should be selected according to the type of polymer precursor.

[0064] (b) Polymerization and carbonization of carbon precursors The carbon precursor introduced into the mesopore can be polymerized by known methods such as heating, depending on the type of carbon precursor, and then the polymerized carbon precursor is carbonized within the mesopore. 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, in a vacuum, etc.). The heating temperature is preferably between 500°C and 1200°C. If the heating temperature is below 500°C, the carbonization of the carbon precursor will be insufficient. On the other hand, if the heating temperature exceeds 1200°C, the silica and carbon will react, which is undesirable. The heating time should be selected to be optimal according to the heating temperature.

[0065] The amount of carbon generated within the mesopores should be greater than or equal to the amount that allows the carbon particles to maintain their shape after the mesoporous silica is removed. Therefore, if the amount of carbon generated in a single filling, polymerization, and carbonization is relatively small, it is preferable to repeat these steps multiple times. In this case, the conditions for each repeated step may be the same or different.

[0066] Furthermore, when the filling, polymerization, and carbonization processes are repeated multiple times, each carbonization step may be performed at a relatively low temperature, and after the final carbonization is completed, another carbonization may be performed at a higher temperature. Performing the final carbonization at a higher temperature than the previous carbonization steps makes it easier for the carbon introduced into the pores in multiple stages to integrate.

[0067] (Step 3: Removal of Mesoporous Silica) Next, the mesoporous silica template is removed from the composite (third step). This yields mesoporous carbon. Specific methods for removing mesoporous silica include (1) heating the composite in an alkaline aqueous solution such as sodium hydroxide, and (2) etching the composite with an aqueous hydrofluoric acid solution.

[0068] (Fourth step (heat treatment)) Next, if necessary, the mesoporous carbon is heat-treated at a temperature higher than 1500°C (fourth step). When carbonizing a carbon source within the mesopores of mesoporous silica, the heat treatment temperature must be kept low in order to suppress the reaction between silica and carbon. Therefore, the degree of graphitization of the carbon obtained by carbonization treatment in the second step tends to be low. To obtain mesoporous carbon with a high degree of graphitization, it is preferable to remove the mesoporous silica, which is the mold, and then heat-treat the mesoporous carbon at a high temperature (graphitization treatment).

[0069] When heat treatment is performed in the fourth step, it is preferable that the heat treatment temperature exceeds 1500°C from the viewpoint of ensuring sufficient graphitization. Preferably, the heat treatment temperature is 1700°C or higher, and more preferably 1800°C or higher. On the other hand, since raising the heat treatment temperature unnecessarily does not make a difference in effect and is not practical, the heat treatment temperature is preferably 2300°C or lower, and more preferably 2200°C or lower.

[0070] The graphitization treatment can be carried out under an inert atmosphere such as an argon atmosphere. Graphitization (heat treatment) is preferable because it promotes graphitization of mesoporous carbon, resulting in mesoporous carbon with a high degree of graphitization and improved electronic conductivity.

[0071] (Method for manufacturing fuel cell catalysts) The fuel cell catalyst of this embodiment can be manufactured by supporting a catalyst metal on a support such as mesoporous carbon obtained by the method described above.

[0072] The method for supporting a catalyst metal on a mesoporous carbon support is not particularly limited, and known methods can be used. Examples of such methods include (1) contacting the support with a solution containing ions of the elements constituting the catalyst metal particles to adsorb these ions onto the support, and then holding the support with the adsorbed ions under a reducing atmosphere to reduce the ions adsorbed on the support back to metal to form catalyst metal particles; (2) immersing the support in a solution containing ions of the elements constituting the catalyst metal particles and reducing the ions in this solution to directly support the catalyst metal particles on the support; and (3) physically supporting the metal elements constituting the catalyst metal particles directly onto the support. Furthermore, if the catalyst metal is an alloy, a method for supporting the catalyst metal on the support may include, for example, supporting each metal constituting the alloy on the support and then alloying it by heating.

[0073] The fuel cell catalyst of this embodiment can be suitably used as a catalyst for the cathode (air electrode) of a fuel cell, and together with an ionomer, it can form an air electrode (air electrode catalyst layer). The air electrode can be manufactured, for example, by mixing the fuel cell catalyst of this embodiment with an ionomer, coating the fuel cell catalyst with the ionomer, and then forming a catalyst layer using the ionomer-coated fuel cell catalyst to produce the fuel cell electrode.

[0074] (Ionomer coating process) The ionomer coating process involves mixing a fuel cell catalyst with an ionomer and coating the fuel cell catalyst with the ionomer.

[0075] The ionomer is not particularly limited, but for example, perfluorocarbon sulfonic acid polymers, highly oxygen-permeable ionomers, etc., can be used. One type of ionomer may be used alone, or two or more types may be used together.

[0076] Examples of perfluorocarbon sulfonic acid polymers include fluoride-containing ion exchange resins that contain repeating units based on sulfonyl vinyl ether monomers. Examples of perfluorocarbon sulfonic acid polymers include Nafion®, Flemion®, Aquivion®, and Aciplex®.

[0077] A high-oxygen-permeable ionomer is a polymer compound that contains acidic groups and cyclic structures within its molecular structure. Because high-oxygen-permeable ionsomers contain cyclic structures within their molecular structure, they have a high oxygen permeability coefficient. Therefore, when a high-oxygen-permeable ionomer is used as an ionomer, the oxygen transport resistance at the interface with the catalyst becomes relatively small. In other words, a highly oxygen-permeable ionomer is an ionomer whose oxygen permeability coefficient is higher than that of perfluorocarbon sulfonic acid polymers such as Nafion (registered trademark).

[0078] Examples of highly oxygen-permeable ionomers include (a) an electrolyte polymer comprising a perfluorocarbon unit having an aliphatic ring structure and an acid group unit having perfluorosulfonic acid as a side chain, (b) an electrolyte polymer comprising a perfluorocarbon unit having an aliphatic ring structure and an acid group unit having perfluoroimide as a side chain, and (c) an electrolyte polymer comprising a unit in which perfluorosulfonic acid is directly bonded to a perfluorocarbon having an aliphatic ring structure (see, for example, Japanese Patent Publication No. 2003-036856, International Publication No. 2012 / 088166, Japanese Patent Publication No. 2013-216811, and Japanese Patent Publication No. 2006-152249).

[0079] The ionomer content in the catalyst layer may be appropriately set according to the amount of support, and the I / C ratio (ionomer mass / carbon (support) mass) may be, for example, 0.3 to 1.3, preferably 0.4 to 1.1, and more preferably 0.5 to 1.0.

[0080] In this coating step, a dispersion medium may be added to coat the carrier with the ionomer. The dispersion medium is not particularly limited and can be appropriately selected depending on the ionomer used. For example, alcohols such as methanol, ethanol, propanol, and propylene glycol, or N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, or mixtures thereof or mixtures with water may be used.

[0081] The coating method is not particularly limited, but examples include homogenizers, ball mills, shear mixers, and roll mills.

[0082] (Catalyst layer formation process) After this coating process, a catalyst layer is formed. The method for forming the catalyst layer is not particularly limited. For example, after the coating process, a dispersion medium may be added as needed to prepare a catalyst ink, which may then be applied to the surface of a substrate such as carbon paper or a solid electrolyte membrane, and dried. The thickness of this fuel cell catalyst layer is not particularly limited, but may be 20 μm or less, 10 μm or less, or 3 μm or more. There are no particular restrictions on the amount of catalyst metal contained in the catalyst layer, but the basis weight of the catalyst metal should be 0.10 to 0.40 mg / cm³. 2 It may be 0.15-0.30 mg / cm³. 2 That's fine.

[0083] The fuel cell catalyst of this embodiment can be suitably used as a catalyst for the cathode (air electrode) of a fuel cell, particularly a solid polymer electrolyte fuel cell, and there are no particular restrictions on other components of the fuel cell. A fuel cell using the fuel cell catalyst of this embodiment exhibits improved performance compared to a fuel cell using a conventional fuel cell catalyst. It is particularly preferable because, as described in the later examples, the efficiency point voltage increases under over-humidification conditions. [Examples]

[0084] The embodiments will be described below with reference to examples, but this disclosure is not limited to these examples.

[0085] [Example 1] (Manufacturing of Mesoporous Silica-1) The surfactant n-hexadecyltrimethylammonium chloride [C 16 H 33 N(CH3)3C1 and 1 N sodium hydroxide were added to a mixed solvent containing water, methanol, and ethylene glycol (EG) to obtain the first solution. Separately, tetraethoxysilane (TEOS) was added to a mixed solvent containing methanol and EG to obtain the second solution. The amounts of each raw material used are shown in Table 1 below.

[0086] [Table 1]

[0087] When the second solution was added to the first solution, the solution became cloudy after a while, confirming that particles had been synthesized. After stirring at room temperature for 8 hours, the mixture was filtered, and the residue was redispersed in water. After filtering again, the residue was dried in an oven at 45°C to obtain the sample. The obtained sample was dispersed in 2 N sulfuric acid and heated in an autoclave at 120°C for 3 days. After filtering and washing the autoclaved sample, the organic components were removed by calcining at 550°C for 6 hours to obtain mesoporous silica-1. The peak diameter of the silica mesopores, determined by the BJH method of nitrogen adsorption measurement, was 5-10 nm. The peak diameter of the silica macropores, determined by the mercury intrusion method, was 0.14 μm.

[0088] (Manufacturing of Mesoporous Carbon-1) Mesoporous silica-1 was placed in a PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) container, and FA (furfuryl alcohol) equivalent to the pore volume of mesoporous silica-1 was added and allowed to permeate into the silica pores.

[0089] The FA polymerized by heat-treating mesoporous silica-1 impregnated with FA at 150°C for 18 hours. Furthermore, the FA was further carbonized by heat-treating this in a nitrogen atmosphere at 500°C for 6 hours.

[0090] To the obtained mesoporous silica-1 / FA carbide, FA equivalent to the pore volume of the mesoporous silica-1 / FA carbide was added and allowed to permeate into the pores. The mesoporous silica-1 / FA carbide permeated with FA was heat-treated at 150°C for 18 hours to polymerize the FA, and then heat-treated in a nitrogen atmosphere at 900°C for 6 hours to obtain a mesoporous silica / carbon composite.

[0091] This composite was immersed in a 12% HF solution for 12 hours to dissolve the silica component. After dissolution, filtration and washing were repeated, and then it was dried at 45°C to obtain mesoporous carbon-1. Mesoporous carbon-1 was heat-treated (graphitized) by holding it in an argon stream at 1800°C for 1 hour to obtain heat-treated mesoporous carbon-1 (support).

[0092] (Supporting process) 1 g of heat-treated mesoporous carbon-1 was dispersed in 41.6 mL of pure water. An aqueous solution of dinitrodiamine platinum salt containing 0.72 g of platinum (Patent No. 4315857: manufactured by Cataler Co., Ltd.) was added to this solution, and then 3.2 g of ethanol was added. The solution was heated to reduce the platinum. This caused platinum particles, which are catalytic metal particles, to be supported on a support made of mesoporous carbon-1, thereby obtaining a platinum-supported catalyst. Next, cobalt was supported on the platinum catalyst to obtain a platinum-cobalt-supported catalyst. The amount of cobalt supported was such that the platinum:cobalt ratio in the final fuel cell catalyst was 7:1 (molar ratio).

[0093] (Alloying process) The obtained platinum-cobalt supported catalyst was heated at 800°C under an argon atmosphere to alloy the platinum and cobalt, thereby obtaining a powdered fuel cell catalyst. The platinum loading density of the fuel cell catalyst was 42 wt%.

[0094] The platinum loading density was calculated using the formula: platinum weight / (electrode catalyst weight) × 100 (wt%). The platinum weight is the weight of platinum loaded onto the fuel cell catalyst, determined by ICP spectroscopy.

[0095] (Measurement of surface area and external surface area, and calculation of internal surface area and internal / external surface area ratio) For fuel cell catalysts, TEM observations were performed using a JEOL JEM-ARM200F (Cs-STEM) with an acceleration voltage of 60kV or less and a tilt angle of ±75° to 80°, obtaining continuous tilt images.

[0096] The obtained continuous tilt images were analyzed as follows using Composer and Visualizer-evo from System Infrontia. (1) Using Composer, 3D reconstruction was performed based on the continuous tilt images acquired by TEM. (2) Z-slice images were created using Visualizer-evo. (3) The Z-slice images obtained above were input into JSOL Simpleware. (4) Select Threshold, check Enable, and apply. (5) The carbon areas (gray areas) were visually identified. A threshold (40-70) was determined and applied so that the carbon areas were completely filled in. (6) A Gaucian (smoothing) value of 0.9 was applied once. (7) Island removal was performed to remove voxels of 500 or less, and the carbon portion was extracted. (8) Press the "Meausments [X2]" (surface area measurement) button to measure the surface area of ​​the carrier (internal surface area + external surface area). (9) Close (fill the hole) was performed using cavity fill to seal the hole. (10) Press the Measurings [X2] button to measure the outer surface area of ​​the carrier. The internal surface area of ​​the carrier was calculated by subtracting the external surface area of ​​the carrier obtained in (10) from the surface area of ​​the carrier obtained in (8) (11). (12) The ratio of the inner surface area to the outer surface area of ​​the carrier was calculated by dividing the outer surface area by the inner surface area.

[0097] (Calculation of the proportion of platinum-cobalt alloy particles supported on the outer surface of the carrier) For fuel cell catalysts, TEM observations were performed using a JEOL JEM-ARM200F (Cs-STEM) with an acceleration voltage of 60kV or less and a tilt angle of ±75° to 80°, obtaining continuous tilt images.

[0098] The obtained continuous tilt images were analyzed as follows using Composer and Visualizer-evo from System Infrontia. (1) The outer surface and inner surface of the carrier were defined by the method described above (measurement of surface area and outer surface area, and calculation of inner surface area and inner and outer surface area). (2) All platinum-cobalt alloy particles that have a portion exposed from the outer surface of the carrier were counted as platinum-cobalt alloy particles supported on the outer surface of the carrier, i.e., external particles. (4) Platinum-cobalt alloy particles that are not exposed from the outer surface of the carrier were counted as platinum-cobalt alloy particles supported on the inner surface of the carrier, i.e., internal particles. (5) The total number of external and internal particles was set to 100%, and the proportion of external particles (the proportion of platinum-cobalt alloy particles supported on the outer surface of the carrier) (%) was calculated.

[0099] (Average particle size of platinum-cobalt alloy particles) For fuel cell catalysts, the average particle size of platinum-cobalt alloy particles was calculated using the Schuller equation from the linewidth of the diffraction peak of the (220) plane of the platinum-cobalt alloy particles in powder XRD.

[0100] (Equivalent diameter of the carrier's mean circle) The average equivalent circle diameter of heat-treated mesoporous carbon-1 (support) was determined by the following method. Using an electro-emission scanning electron microscope (FE-SEM) (manufactured by Hitachi High-Tech), SEM images of heat-treated mesoporous carbon-1 were obtained. For each individual particle, the diameter (equivalent area circle diameter) was calculated, assuming the particle was circular. Similarly, the equivalent area circle diameter was calculated for a total of 100 particles. The number average of the equivalent area circle diameters of the 100 particles was calculated as the average equivalent circle diameter of the carrier.

[0101] (Preparation of catalytic ink) To 1 g of the fuel cell catalyst powder, 8 g of ultrapure water and 6 g of ethanol were added and stirred, and then 0.52 g of ionomer was added. Next, the mixture was dispersed in an ultrasonic disperser for 30 minutes, and then dispersed for 15 minutes at 30 m / s using a thin-film swirling mixer (Filmix) manufactured by Primix Corporation to obtain a catalyst ink as a uniform slurry.

[0102] (Fabrication of air electrode catalyst layer sheet) The catalyst ink was coated onto a polytetrafluoroethylene sheet using an ink coating machine, and after coating, it was dried for 5 minutes in a forced-air dryer at 80°C to obtain an air electrode catalyst layer sheet in which an air electrode catalyst layer was formed on the polytetrafluoroethylene sheet. The air electrode catalyst layer has a platinum basis weight of 0.2 mg / cm³. 2 The I / C ratio (ionomer mass / carbon (carrier) mass) was 0.95.

[0103] (Fabrication of fuel electrode catalyst layer sheet) To 1 g of the platinum-supported carbon black powder (ketjen), 8 g of ultrapure water and 6 g of ethanol were added and stirred, and then 0.26 g of ionomer (Nafion) was added. Next, the mixture was dispersed in an ultrasonic disperser for 30 minutes, and then dispersed for 15 minutes at 30 m / s using a thin-film swirling mixer (Filmix) manufactured by Primix Corporation to obtain a catalyst ink as a uniform slurry.

[0104] The catalyst ink was applied onto a polytetrafluoroethylene sheet using an ink coating machine, and after coating, it was dried for 5 minutes in a forced-air dryer at 80°C to obtain a fuel electrode catalyst layer sheet in which a fuel electrode catalyst layer was formed on the polytetrafluoroethylene sheet. The fuel electrode catalyst layer has a platinum content of 0.2 mg / cm³. 2 The I / C ratio (ionomer mass / carbon black (carrier) mass) was 0.5.

[0105] (Fuel cell fabrication) A Teflon® sheet, which is an electrolyte membrane, was sandwiched between an air electrode catalyst layer sheet and a fuel electrode catalyst layer sheet, and the catalyst layers (air electrode catalyst layer and fuel electrode catalyst layer) were transferred to the Teflon by heating and pressing. Then, the polytetrafluoroethylene sheet was peeled off to obtain a membrane electrode assembly (MEA). MEA 1cm 2 The fuel cell was assembled into a rectangular cell. Next, a diffusion layer and current collectors were placed on both sides of the MEA to obtain a fuel cell. Carbon paper (with a microporous layer) was used for the diffusion layer. A gold-plated copper plate with an integrated flow channel (flow channel: straight flow channel with a pitch of 0.4 mm) was used for the current collector.

[0106] (Fuel cell performance evaluation) Regarding the fuel cell, after heating the cell temperature to 60°C, under super-humidified conditions of 80%RH, it was subjected to 0.2 A / cm². 2 The voltage value (mV) (efficiency point voltage) at this point was evaluated. The power generation conditions were: H2 flow rate of 500 cc / min, air flow rate of 1000 cc / min, and back pressure of 1 kg / cm². 2 That's what I decided. As the measurement device, we used the As-510-340 fuel cell power generation characteristics evaluation system manufactured by NF Circuit Design Block Co., Ltd.

[0107] [Example 2] The procedure was carried out in the same manner as in Example 1, except that heat-treated mesoporous carbon-1 was replaced with heat-treated mesoporous carbon-2 produced by the method described below.

[0108] (Manufacturing of Mesoporous Silica-2) The surfactant n-hexadecyltrimethylammonium chloride [C 16 H 33 20g of N(CH3)3Cl and 14g of ethanol were added to 700g of 1.5wt% hydrochloric acid to obtain a hydrochloric acid solution. While heating and stirring this hydrochloric acid solution at 70°C, 65g of sodium silicate No. 1 (33wt% as SiO2, SiO2 / Na2O=2.00) was added and held for 3 hours to carry out the condensation polymerization reaction.

[0109] The obtained solid product was filtered off, and then dispersed in 1000 g of deionized water and stirred. This filtration, dispersion, and stirring process was repeated five times to wash the solid product, and the washed solid product was dried at 70°C for 24 hours. Next, the dried solid product was dispersed in 2 N hydrochloric acid and heated in a sealed container at 80°C for 3 days. After the heat treatment, the solid product was filtered, washed, and dried, and then calcined at 550°C for 6 hours in the presence of air to obtain mesoporous silica-2. The peak diameter of the silica mesopores, determined by the BJH method of nitrogen adsorption measurement, was 6.9 nm. The peak diameter of the silica macropores, determined by the mercury intrusion method, was 0.25 μm.

[0110] (Manufacturing of Mesoporous Carbon-2) Except for changing mesoporous silica-1 to mesoporous silica-2, the procedure was carried out in the same manner as in Example 1 to obtain heat-treated mesoporous carbon-2 (support).

[0111] [Example 3] The procedure was the same as in Example 1, except that heat-treated mesoporous carbon-1 was replaced with heat-treated mesoporous carbon-3 produced by the method described below.

[0112] (Manufacturing of Mesoporous Silica-3) The surfactant n-hexadecyltrimethylammonium chloride [C 16 H 3320g of N(CH3)3Cl and 14g of ethanol were added to 550g of 2wt% hydrochloric acid to obtain a hydrochloric acid solution. While heating and stirring this hydrochloric acid solution at 70°C, 65g of sodium silicate No. 1 (33wt% as SiO2, SiO2 / Na2O=2.00) was added and held for 3 hours to carry out the condensation polymerization reaction.

[0113] The obtained solid product was filtered off, and then dispersed in 1000 g of deionized water and stirred. This filtration, dispersion, and stirring process was repeated five times to wash the solid product, and the washed solid product was dried at 70°C for 24 hours. Next, the dried solid product was dispersed in 2 N hydrochloric acid and heated in a sealed container at 80°C for 3 days. After the heat treatment, the solid product was filtered, washed, and dried, and then calcined in the presence of air at 550°C for 6 hours to obtain mesoporous silica-3. The peak diameter of the silica mesopores, determined by the BJH method of nitrogen adsorption measurement, was 8.1 nm. The peak diameter of the silica macropores, determined by the mercury intrusion method, was 0.27 μm.

[0114] (Manufacturing of Mesoporous Carbon-3) Except for replacing mesoporous silica-1 with mesoporous silica-3, the procedure was carried out in the same manner as in Example 1 to obtain heat-treated mesoporous carbon-3 (support).

[0115] [Example 4] The procedure was the same as in Example 1, except that heat-treated mesoporous carbon-1 was replaced with heat-treated mesoporous carbon-4 produced by the method described below.

[0116] (Manufacturing of Mesoporous Silica-4) The surfactant n-hexadecyltrimethylammonium chloride [C 16 H 33 18g of N(CH3)3Cl and 13g of ethanol were added to 550g of 1.5wt% hydrochloric acid to obtain a hydrochloric acid solution. While heating and stirring this hydrochloric acid solution at 40°C, 65g of sodium silicate No. 1 (33wt% as SiO2, SiO2 / Na2O=2.00) was added and held for 3 hours to carry out the condensation polymerization reaction.

[0117] The obtained solid product was filtered off, and then dispersed in 1000 g of deionized water and stirred. This filtration, dispersion, and stirring process was repeated five times to wash the solid product, and the washed solid product was dried at 70°C for 24 hours. Next, the dried solid product was dispersed in 2 N hydrochloric acid and heated in a sealed container at 80°C for 3 days. After the heat treatment, the solid product was filtered, washed, and dried, and then calcined at 550°C for 6 hours in the presence of air to obtain mesoporous silica-4. 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 the mercury intrusion method, was 0.26 μm.

[0118] (Manufacturing of Mesoporous Carbon-4) Except for replacing mesoporous silica-1 with mesoporous silica-4, the procedure was carried out in the same manner as in Example 1 to obtain heat-treated mesoporous carbon-4 (support).

[0119] [Example 5] The procedure was the same as in Example 1, except that the heat-treated mesoporous carbon-1 was replaced with heat-treated mesoporous carbon-5 produced by the method described below.

[0120] (Manufacturing of Mesoporous Carbon-5) Except for replacing mesoporous silica-1 with mesoporous silica-4 described in Example 4, and changing the heat treatment (graphitization treatment) from holding at 1800°C for 1 hour to holding at 2200°C for 1 hour, the procedure was carried out in the same manner as in Example 1 to obtain heat-treated mesoporous carbon-5 (support). The peak diameter of the silica mesopores, determined by the BJH method for nitrogen adsorption measurement, was 9.2 nm. The peak diameter of the silica macropores, determined by the mercury intrusion method, was 0.28 μm.

[0121] [Comparative Example 1] The procedure was the same as in Example 1, except that the heat-treated mesoporous carbon-1 was replaced with commercially available mesoporous carbon that had undergone heat treatment (graphitization treatment) by holding it at 1980°C for 1 hour.

[0122] [Comparative Example 2] The procedure was the same as in Example 1, except that the heat-treated mesoporous carbon-1 was replaced with commercially available carbon black.

[0123] [Comparative Example 3] The procedure was carried out in the same manner as in Example 1, except that the heat-treated mesoporous carbon-1 was replaced with a commercially available mesoporous carbon different from that used in Comparative Example 1.

[0124] [Comparative Example 4] The procedure was the same as in Example 1, except that heat-treated mesoporous carbon-1 was replaced with heat-treated mesoporous carbon-c4 produced by the method described below.

[0125] (Manufacturing of Mesoporous Silica-C4) The surfactant n-hexadecyltrimethylammonium chloride [C 16 H 33 18g of N(CH3)3Cl and 12g of ethanol were added to 600g of 1.5wt% hydrochloric acid to obtain a hydrochloric acid solution. While heating and stirring this hydrochloric acid solution at 70°C, 60g of sodium silicate No. 1 (30wt% as SiO2, SiO2 / Na2O=2.00) was added and held for 3 hours to carry out the condensation polymerization reaction.

[0126] The obtained solid product was filtered off, and then dispersed in 1000 g of deionized water and stirred. This filtration, dispersion, and stirring process was repeated five times to wash the solid product, and the washed solid product was dried at 70°C for 24 hours. Next, the dried solid product was dispersed in 2 N hydrochloric acid and heated in a sealed container at 130°C for 3 days. After the heat treatment, the solid product was filtered, washed, and dried, and then calcined in the presence of air at 550°C for 6 hours to obtain mesoporous silica-C4.

[0127] (Manufacturing of Mesoporous Carbon-C4) Except for replacing mesoporous silica-1 with mesoporous silica-c4, the procedure was carried out in the same manner as in Example 1 to obtain heat-treated mesoporous carbon-c4 (support).

[0128] [Comparative Example 5] The procedure was the same as in Example 1, except that the heat-treated mesoporous carbon-1 was replaced with mesoporous carbon from Comparative Example 1 that had been heat-treated (graphitized) by holding it at 2100°C for 1 hour.

[0129] [Comparative Example 6] The procedure was the same as in Example 1, except that the heat-treated mesoporous carbon-1 was replaced with mesoporous carbon from Comparative Example 1 that had been heat-treated (graphitized) by holding it at 1400°C for 1 hour.

[0130] Tables 2 and 3 show the surface area, outer surface area, inner surface area, inner-outer surface area ratio, proportion of platinum-cobalt alloy particles supported on the outer surface of the carrier, and the results of the fuel cell performance evaluation for the fuel cell catalysts (catalysts used to form the air electrode catalyst layer) of the examples and comparative examples. In Tables 2 and 3 below, platinum-cobalt alloy particles will be referred to as platinum alloy particles.

[0131] [Table 2]

[0132] [Table 3]

[0133] The fuel cell using the fuel cell catalyst of the example had a higher efficiency point voltage and superior performance as a fuel cell catalyst compared to the fuel cell using the fuel cell catalyst of the comparative example.

[0134] The upper and / or lower limits of the numerical ranges described herein can be arbitrarily combined to define a preferred range. For example, the upper and lower limits of the numerical ranges can be arbitrarily combined to define a preferred range, the upper limits of the numerical ranges can be arbitrarily combined to define a preferred range, and the lower limits of the numerical ranges can be arbitrarily combined to define a preferred range.

[0135] Although this embodiment has been described in detail above, the specific configuration is not limited to this embodiment, and any design changes that do not depart from the gist of this disclosure are also included in this disclosure. [Explanation of Symbols]

[0136] 1 Outer surface 3 Inner surface 5. External particles 7 Internal particles

Claims

1. A fuel cell catalyst comprising a catalytic metal and a carrier supporting the catalytic metal, The ratio of the inner surface area of ​​the carrier to the outer surface area of ​​the carrier (outer surface area of ​​the carrier / inner surface area of ​​the carrier) is 0.56 to 0.

69. The proportion of the catalyst metal supported on the outer surface of the carrier is 23-35%. The aforementioned carrier is mesoporous carbon, A fuel cell catalyst wherein the catalyst metal is platinum or a platinum alloy.

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