Platinum catalyst containing porous silicon carbide composite material, catalytic electrode, fuel cell, and method for producing said platinum catalyst

Abstract

This platinum catalyst includes: a porous silicon carbide composite material comprising a silicon carbide material containing SiC as a main component and a carbon material; and a platinum nanostructure supported on the porous silicon carbide composite material. The supported amount of the platinum nanostructure when the total mass of the platinum catalyst is 100 mass% is 30-60 mass% and the intensity ratio of Pt (111) / Pt (200) obtained from X-ray diffraction (XRD) is 2.5-3.0.

Description

Platinum catalyst containing porous silicon carbide composite material, catalytic electrode, fuel cell, and method for producing said platinum catalyst

[0001] The present invention relates to a platinum catalyst containing a porous silicon carbide composite material, a catalyst electrode, a fuel cell, and a method for producing the platinum catalyst. This application claims priority from Japanese Patent Application No. 2023-210051, filed on December 13, 2023, the contents of which are incorporated herein by reference.

[0002] Fuel cells are devices that generate electricity and heat through a chemical reaction that converts hydrogen and oxygen into water. There are several types of fuel cells, including phosphoric acid fuel cells (PAFCs), molten carbonate fuel cells (MCFCs), solid oxide fuel cells (SOFCs), and polymer electrolyte fuel cells (PEFCs). Among these, polymer electrolyte fuel cells (PEFCs) have a structure in which a catalyst layer constituting an anode (fuel electrode) is provided on one side of a solid polymer electrolyte membrane and a cathode (air electrode) is provided on the other side, with a gas diffusion layer bonded to the outside of each catalyst layer. The catalyst layer is composed of a catalyst-supported carrier in which particulate catalysts containing precious metals are highly dispersed and supported on the surface of nano-level support particles.

[0003] Currently, carbon-based materials with high specific surface area and high conductivity are used as catalyst carriers. However, deterioration of catalytic performance and durability due to corrosion of the carbon carrier are major issues in cathodes. Furthermore, fuel cells for commercial vehicles, which are expected to be used in a wide range of applications, require higher catalytic activity than conventional fuel cells. Therefore, the development of highly durable carriers and highly active catalysts that can replace carbon is urgently needed. For example, Patent Document 1 discloses an electrode catalyst using a carrier that replaces carbon, which includes (A) Group 13-doped SiC, in which SiC is doped with a Group 13 (Group 3B) element, (B) conductive carbon particles, and (C) a noble metal supported on the surface of the (A) Group 13-doped SiC. The Group 13 element doped into SiC is, for example, Al (aluminum), and the amount of the Group 13 element doped in the (A) Group 13-doped SiC is 1 to 5 mol %, and the ratio of the (A) Group 13-doped SiC to the (B) conductive carbon particles [(A):(B)] is 1:9 to 5:5 by weight.

[0004] Furthermore, Non-Patent Document 1 discloses a catalyst in which platinum nanowires are supported on a carbon support as a catalyst that exhibits high activity.

[0005] JP 2010-149008 A

[0006] X. Duan te al. , Science, 2016, 354, 1414-1419.

[0007] The above-mentioned Patent Document 1 proposes an electrode catalyst containing particles of Group 13-doped silicon carbide with a noble metal supported on its surface and conductive carbon particles, which imparts conductivity to silicon carbide, which is inherently poorly conductive, thereby reducing resistance. However, there is no mention of durability, leaving room for further study. Furthermore, there is no description of the shape of the platinum, and from a general perspective, it is thought that platinum nanoparticles are supported, making it difficult to demonstrate higher activity than conventional catalysts.

[0008] Although Non-Patent Document 1 describes that platinum supported on a support is arranged in a one-dimensional manner, the use of a carbon support results in poor durability. Furthermore, the method of synthesizing platinum nanowires or the like in advance and supporting them on a support is both complicated and expensive.

[0009] An object of the present invention is to provide a platinum catalyst, a catalyst electrode and a fuel cell which are excellent in activity and durability, and a method for producing the platinum catalyst simply and at low cost.

[0010] To achieve the above object, the present invention has discovered that a precursor gel is produced by coexisting a carbon material or organic polymer as a carbon source during a sol-gel reaction of an organic alkoxysilane aqueous solution in the presence of a surfactant, while taking care not to interfere with the formation of a porous gel, and then calcining the precursor gel to produce a porous silicon carbide composite material in which a mesoscopic pore structure (mesopores) develops into a macroscopic pore structure (macropores), and the carbon material is arranged at the nano-level within the porous three-dimensional framework. It has also been discovered that mixing the porous silicon carbide composite material with aqueous hydrogen peroxide and a dispersion of platinum nanoparticle-containing colloids produces a mixture in which platinum oxide colloids are supported on the porous silicon carbide composite material, and that heat-treating the mixture in a nitrogen and hydrogen environment results in the formation of platinum nanostructures with an increased proportion of specific crystal faces, thereby improving catalytic activity.

[0011] That is, the present invention provides the following: [1] A platinum catalyst comprising: a porous silicon carbide composite material containing a silicon carbide material containing SiC as a main component and a carbon material; and a platinum nanostructure supported on the porous silicon carbide composite material, wherein the amount of the platinum nanostructure supported is 30 to 60 mass% when the total mass of the platinum catalyst is taken as 100 mass%, and the intensity ratio of Pt(111) / Pt(200) determined by X-ray diffraction (XRD) is 2.5 to 3.0.

[0012] [2] The platinum catalyst described in [1], wherein the platinum nanostructure has a connected structure in which adjacent platinum nanoparticles are partially connected.

[0013] [3] The platinum catalyst described in [2], wherein the longitudinal dimension of the platinum nanostructure is 4 nm or more and 20 nm or less, and the lateral dimension of the platinum nanostructure is 2 nm or more and 5 nm or less.

[0014] [4] The platinum catalyst according to any one of [1] to [3], wherein the carbon material is composed of one or more selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons.

[0015] [5] The platinum catalyst according to any one of [1] to [4], wherein the average diameter of the primary particles of the silicon carbide material is 20 nm or more and 800 nm or less.

[0016] [6] A catalytic electrode having a layer containing the platinum catalyst according to any one of [1] to [5].

[0017] [7] A fuel cell comprising the catalytic electrode according to [6].

[0018] [8] A method for producing a platinum catalyst, comprising: (A) a step of adding an organic alkoxysilane to an acidic aqueous solution containing a surfactant and a pH adjuster, and further adding a carbon material or an organic polymer, to form a gel containing the carbon material or the organic polymer through a sol-gel reaction of the organic alkoxysilane; (B) a step of washing the gel with alcohol; (C) a step of drying the washed gel to form a porous silicon carbide precursor; (D) a step of calcining the porous silicon carbide precursor to obtain a porous silicon carbide composite material containing a silicon carbide material containing SiC as a main component and a carbon material; (E) a step of mixing the porous silicon carbide composite material with a dispersion containing a colloid containing platinum nanoparticles and aqueous hydrogen peroxide to obtain a mixture; and (F) a step of heat-treating the mixture under an atmosphere of nitrogen and hydrogen to obtain a platinum catalyst containing platinum nanoparticles.

[0019] [9] The method for producing a platinum catalyst according to [8], wherein in the step (F), the mixture is heat-treated at a temperature of 25°C or higher and 800°C or lower.

[0020]

[10] The method for producing a platinum catalyst according to [8] or [9], further comprising a step (G) of heat-treating the mixture under a nitrogen atmosphere after the step (E) and before the step (F).

[0021]

[11] The method for producing a platinum catalyst according to

[10] , wherein in the step (G), the mixture is heat-treated at 100°C or higher and 800°C or lower.

[0022]

[12] The method for producing a platinum catalyst according to any one of [8] to

[11] , wherein the organic alkoxysilane is represented by the following formula (1) or formula (2): R １ -SiR ２ ｘ (OR ３ ) ３－ｘ ...(1) (in the formula R １ is any group selected from a methyl group, an ethyl group, a vinyl group, and a phenyl group, and R ２ is a methyl group, R ３ represents a methyl group or an ethyl group. In the formula, the integer x is 0 or 1. ４ -(SiR ５ ｙ (OR ６ ) ３－ｙ ) ２ ...(2) (in the formula R ４ contains any group selected from a methylene group, an ethylene group, a hexylene group, a vinylene group, a phenylene group, and a biphenylene group, and R ５ is a methyl group, R ６ represents a methyl group or an ethyl group. In the formula, the integer y is 0 or 1.

[0023]

[13] The method for producing a platinum catalyst according to any one of [8] to

[12] , wherein the carbon material is composed of one or more types selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons.

[0024] According to the present invention, it is possible to provide a platinum catalyst, a catalyst electrode and a fuel cell which are excellent in activity and durability, as well as a method for producing the platinum catalyst simply and at low cost.

[0025] FIG. 1 is a schematic diagram illustrating an example of the configuration of a platinum catalyst according to an embodiment of the present invention. FIG. 2 is an enlarged view illustrating an example of the configuration of platinum nanostructures supported on a porous silicon carbide composite material of the platinum catalyst of FIG. 1. FIG. 3 is a flowchart illustrating an example of a method for manufacturing a platinum catalyst according to an embodiment of the present invention. FIGS. 4(A) to 4(D) are transmission electron microscope images of the platinum catalysts exemplified in Example 1, Example 2, Comparative Example 2, and Comparative Example 3, respectively. FIG. 5(A) is a secondary electron image of the platinum catalyst exemplified in Example 1 observed by a scanning transmission electron microscope, and FIG. 5(B) is a transmission electron image. FIG. 6 is a graph showing the results of cyclic voltammetry (CV) measurements of platinum catalysts when the amount of platinum nanostructures supported was changed in a single fuel cell evaluation. FIG. 7 is a graph showing the change in electrochemically active surface area (ECSA) versus the amount of platinum particles or platinum nanostructures supported in a single fuel cell evaluation.

[0026] <Configuration of Platinum Catalyst> Figure 1 is a schematic diagram illustrating an example of the configuration of a platinum catalyst according to an embodiment of the present invention. As shown in Figure 1, platinum catalyst 1 includes porous silicon carbide composite material 10 including silicon carbide material 11 containing SiC as a main component and carbon material 12, and platinum nanostructure 20 supported on porous silicon carbide composite material 10.

[0027] The form of the platinum catalyst is not particularly limited, but may be, for example, powder, particulate, fibrous, or needle-like, and among these, powder or particulate is preferred. When the platinum catalyst is powder or particulate, the particle size of the platinum catalyst is not particularly limited, but may be 50% of the particle size D in the volume-based cumulative particle size distribution. ５０ For example, the thickness is preferably 0.1 μm or more and 50 μm or less, more preferably 0.1 μm or more and 10 μm or less, and even more preferably 0.1 μm or more and 2 μm or less.

[0028] Platinum catalyst particle diameter D ５０ means a value measured in accordance with JIS Z8825-1:2013, and is, for example, a particle diameter D measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD-7000). ５０This means:

[0029] The BET specific surface area of ​​the platinum catalyst of this embodiment is not particularly limited, but is, for example, 10 m ２ / g or more, and ２ / g or more is more preferable, and 100m ２ / g or more. ２ / g or less. ２ When the BET specific surface area is 300 m / g or more, the amount of catalyst particles carried on the surface of the carrier is sufficiently secured, and when the platinum catalyst is used in a fuel cell electrode, desired characteristics such as output and efficiency can be obtained. ２ / g or less, the proportion of mesopores suitable for supporting the catalyst increases, and the catalyst particle utilization rate can be further improved.

[0030] The total pore volume of the platinum catalyst is not particularly limited, but is preferably 0.3 cm ３ / g or more, and ３ / g or more, and more preferably 0.6 cm ３ It is particularly preferred that the total pore volume of the platinum catalyst is 0.3 cm ３ When the SiO 2 content is 1 / g or more, the reaction gas and electrolyte can easily flow through the catalyst layer, and the catalytic efficiency can be improved.

[0031] The pore size of the platinum catalyst is not particularly limited, but is preferably 10 nm to 1000 nm, more preferably 20 nm to 500 nm, and particularly preferably 50 nm to 300 nm. When the pore size of the platinum catalyst is 10 nm to 1000 nm, the flow of the reaction gas and electrolyte within the catalyst layer is facilitated, thereby improving the catalytic efficiency. In particular, when the pore size of the porous silicon carbide composite material is 10 nm or more, the supply of the reaction gas and electrolyte to the supported catalyst particles is stabilized, preventing a decrease in the catalyst particle utilization rate.

[0032] The BET specific surface area, total pore volume, and pore diameter of the platinum catalyst can be calculated as measured values ​​by a gas adsorption method, and refer to values ​​calculated from the amount of adsorption and condensation of the non-corrosive gas when a non-corrosive gas such as nitrogen or argon is adsorbed while changing the relative pressure in the adsorption isotherm using a constant volume method, for example.

[0033] [Porous silicon carbide composite material] The porous silicon carbide constituting the platinum catalyst has a three-dimensional framework structure in which multiple micropores are provided independently, or in which some or all of the multiple micropores are interconnected. The BET specific surface area, total pore volume, and pore diameter of the porous silicon carbide composite material are the same as those of the platinum catalyst.

[0034] The platinum catalyst of this embodiment contains carbon that constitutes the three-dimensional skeletal structure of porous silicon carbide (SiC) as a support, and a carbon material other than the carbon that constitutes the three-dimensional skeletal structure, which is supported by the porous silicon carbide.

[0035] In this specification, porous silicon carbide refers to a material that is composed of spaces in a three-dimensional network structure in which silicon carbide is connected.

[0036] [Carbon materials]

[0037] The carbon material is not particularly limited, and may be composed of one or more materials selected from, for example, carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons. Among these, carbon black is preferred as the carbon material from the viewpoint of achieving high conductivity and manufacturability.

[0038] When the carbon material is carbon black, the average diameter of the primary particles of the carbon material is preferably 10 nm or more and 200 nm or less, more preferably 20 nm or more and 100 nm or less, and even more preferably 30 nm or more and 50 nm or less. When the average diameter of the primary particles of the carbon material is 10 nm or more and 200 nm or less, good electrical conductivity can be achieved.

[0039] When the carbon material is composed of carbon nanofibers or carbon nanotubes, the average diameter of the carbon material is preferably 10 nm or more and 200 nm or less, and the length of the carbon material is preferably 1 μm or more and 20 μm or less.

[0040] The content of the carbon material in the porous silicon carbide composite material is preferably 5% by mass to 50% by mass, more preferably 8% by mass to 45% by mass, and even more preferably 10% by mass to 40% by mass. When the content of the carbon material in the porous silicon carbide composite material is 5% by mass to 50% by mass, high electrical conductivity is achieved, and corrosion of the carbon is suppressed, thereby improving the durability of the catalytic cycle.

[0041] The morphology and size of the carbon material retained in the porous silicon carbide composite can be measured, for example, by observation using a transmission electron microscope or a scanning electron microscope. The average diameter of the primary particles can be determined, for example, from microscope images using image analysis particle size distribution measurement software.

[0042] [Silicon Carbide Material] The silicon carbide material in the porous silicon carbide composite material contains SiC as a main component, as described above. In this embodiment, "main component" means that SiC is contained in an amount of 50 mass% or more when the total mass of the silicon carbide material is taken as 100 mass%. The silicon carbide material may contain SiC as a main component and may also contain oxygen (O). In this embodiment, "containing oxygen (O)" means that the silicon carbide material contains SiO ２ This means that the porous silicon carbide composite material contains silicon oxides such as silicon carbide (SiO 2 ) and silicon carbide (SiO 3 ). The silicon oxide content may be less than 50% by mass, assuming that the silicon carbide content in the porous silicon carbide composite material is 100% by mass. A content within this range is preferred, as it results in excellent carrier durability and catalytic activity. Furthermore, the mass ratio of silicon (Si) to oxygen (O) ([Si] / [O]) in the porous silicon carbide composite material is not particularly limited, but can be, for example, 1 / 0.1 to 1 / 0.001.

[0043] [SiC (Silicon Carbide)] The average diameter of the primary particles of silicon carbide in the porous silicon carbide composite material is preferably 20 nm to 800 nm, more preferably 30 nm to 500 nm, and even more preferably 40 nm to 300 nm. When the average diameter of the primary particles of silicon carbide is 20 nm to 800 nm, it is possible to obtain good voids when the material is used as an electrode, which is preferable.

[0044] The particle size of silicon carbide in a porous silicon carbide composite material can be measured, for example, by observation using a transmission electron microscope or a scanning electron microscope, and the average diameter of primary particles can be determined, for example, from microscope images using image analysis particle size distribution measurement software.

[0045] [Platinum Nanostructure] In the platinum catalyst of this embodiment, the amount of the platinum nanostructure supported is 30% by mass or more and 60% by mass or less when the total mass of the platinum catalyst is 100% by mass. When the amount of the platinum nanostructure supported is 30% by mass or more and 60% by mass or less, excellent activity and durability are achieved. When the total mass of the platinum catalyst is 100% by mass, the amount of the platinum nanostructure supported is preferably 30% by mass or more and 50% by mass or less, more preferably 30% by mass or more and 45% by mass or less, and even more preferably 30% by mass or more and 40% by mass or less. The amount of the platinum nanostructure supported can be calculated, for example, by alkali-melting the platinum catalyst, dissolving it in aqua regia, diluting it with ultrapure water, and then performing high-frequency induction heating optical emission spectroscopy (ICP).

[0046] In this embodiment, the Pt(111) / Pt(200) intensity ratio determined by X-ray diffraction (XRD) is 2.5 to 3.0. When the Pt(111) / Pt(200) intensity ratio is 2.5 to 3.0, the proportion of the highly active (111) plane in the platinum nanostructure is high, and the highly active platinum nanostructure is supported on the porous silicon carbide composite, resulting in excellent platinum catalyst activity and durability. The Pt(111) / Pt(200) intensity ratio determined by X-ray diffraction (XRD) is preferably 2.55 to 3.0, more preferably 2.6 to 2.9, and even more preferably 2.7 to 2.9. The Pt(111) / Pt(200) intensity ratio determined from X-ray diffraction (XRD) is a value determined from the ratio of the height of the peak attributable to the (111) plane of the crystal structure in the platinum nanostructure to the height of the peak attributable to the (200) plane of the crystal structure.

[0047] The platinum nanostructure is composed of platinum-containing particles, and is particularly preferably platinum nanoparticles. The average diameter of the primary particles of the platinum-containing particles is not particularly limited, but is preferably 2 nm to 10 nm, more preferably 2.5 nm to 7 nm, and even more preferably 3 nm to 5 nm. Within this range, good catalytic performance can be achieved with a small amount of platinum.

[0048] FIG. 2 is an enlarged view showing an example of the configuration of a platinum nanostructure 20 supported on the porous silicon carbide composite material 10 of the platinum catalyst 1 of FIG. 1 . As shown in FIG. 1 , the platinum nanostructure 20 has a connected structure in which adjacent platinum nanoparticles 21, 21, ... are partially connected. More specifically, a platinum nanostructure 20 having a connected structure in which multiple platinum nanoparticles 21, 21, ... are connected one-dimensionally is supported on the porous silicon carbide composite material 10 as a single unit. As such, the configuration of the present invention differs from a configuration in which platinum nanoparticles 21 are supported on the porous silicon carbide composite material as a single unit. In FIG. 1 , the platinum nanostructure 20 has a connected structure in which adjacent platinum nanoparticles 21, 21, ... are connected one-dimensionally. However, the present invention is not limited to this, and the platinum nanostructure 20 may have a connected structure in which adjacent platinum nanoparticles 21, 21, ... are connected and branched in multiple directions. The platinum nanostructure is supported on a silicon carbide material or a carbon material in the porous silicon carbide composite material, and is more preferably supported on a silicon carbide material from the viewpoint of good catalytic performance.

[0049] Platinum nanostructures are typically elongated particles having longitudinal and transverse dimensions. The longitudinal dimension of the platinum nanostructure is, for example, 4 nm to 20 nm, and the transverse dimension of the platinum nanostructure is, for example, 2 nm to 5 nm. When the longitudinal dimension of the platinum nanostructure is 4 nm to 20 nm and the transverse dimension of the platinum nanostructure is 2 nm to 5 nm, this contributes to increasing the proportion of the highly active (111) plane in the platinum nanostructure, enhancing the activity of the platinum catalyst, and the platinum nanostructure acts as a bridge between silicon carbide and carbon, thereby further improving durability. The longitudinal dimension of the platinum nanostructure may be 4 nm to 20 nm, 10 nm to 20 nm, or 15 nm to 20 nm. The transverse dimension of the platinum nanostructure may also be 2 nm to 4 nm, or 2 nm to 3 nm. The ratio of the longitudinal dimension to the lateral dimension of the platinum nanostructure may be 1.5-10, 3-10, or 5-10.

[0050] The above-mentioned longitudinal and lateral dimensions of the platinum nanostructure can be calculated from a transmission electron microscope image.

[0051] The number of platinum nanoparticles constituting the platinum nanostructure is not particularly limited as long as the intensity ratio of Pt(111) / Pt(200) is within the desired range, but is preferably two or more, and more preferably three or more.

[0052] <Method for producing platinum catalyst> The method for producing a porous silicon carbide composite material according to this embodiment includes a gel-forming step (step (A)), a washing step (step (B)), a porous silicon carbide precursor-forming step (step (C)), a firing step (step (D)), a mixing step (step (E)), and a heat-treating step (step (F)), as shown in Figure 3. Note that, on the premise that the platinum catalyst according to this embodiment is obtained, steps other than those described above may be provided before or after each of these steps.

[0053] [Step (A)] In step (A), for example, an organic alkoxysilane is added to an acidic aqueous solution containing a surfactant and a pH adjuster, and a gel is formed by a sol-gel reaction of the organic alkoxysilane. For example, a hydrolyzable organic alkoxysilane is hydrolyzed to produce a hydrolyzate, and the pH of the reaction system is then increased to carry out a polycondensation reaction of the organic alkoxysilane, thereby obtaining a polysilsesquioxane. The pH suitable for the polycondensation reaction varies depending on the isoelectric point of the organic alkoxysilane used, but if the pH is too high, the reaction efficiency decreases and gel formation may become difficult. This sol-gel reaction is preferably carried out at a temperature of 25°C to 80°C, more preferably 30°C to 70°C, and even more preferably 40°C to 60°C. This allows the polysilsesquioxane to be obtained as a wet gel containing water as a solvent therein.

[0054] The content of the surfactant in the acidic aqueous solution is preferably 0.1% by mass or more and 50% by mass or less, more preferably 0.5% by mass or more and 35% by mass or less, and even more preferably 2% by mass or more and 15% by mass or less.

[0055] The surfactant is not particularly limited, and examples thereof include nonionic surfactants and / or cationic surfactants. By appropriately selecting and using either or both of a nonionic surfactant and a cationic surfactant as the surfactant, the desired BET specific surface area and pore size can be obtained. Examples of nonionic surfactants include polyethylene glycol types (ether types, ester-ether types), polyhydric alcohol types, etc. Examples of polyethylene glycol-type nonionic surfactants include Pluronic (registered trademark) types. Examples of cationic surfactants include amine salt types, quaternary ammonium salt types, etc. By setting the surfactant content to 0.1% by mass or more and 50% by mass or less in the acidic aqueous solution, a porous polysilsesquioxane gel having developed mesopores and a large BET specific surface area can be formed.

[0056] The content of the pH adjuster in the acidic aqueous solution is preferably 5% by mass or more and 50% by mass or less, more preferably 5.5% by mass or more and 35% by mass or less, and even more preferably 6% by mass or more and 23% by mass or less. By setting the content of the pH adjuster in the acidic aqueous solution to 5% by mass or more and 50% by mass or less, a porous polysilsesquioxane gel having high skeletal strength and flexibility can be formed.

[0057] The pH adjuster is not particularly limited, but examples thereof include substances containing any one selected from urea, ammonia, and sodium hydroxide.

[0058] The acidic aqueous solution is not particularly limited, but examples thereof include aqueous solutions of hydrochloric acid, nitric acid, acetic acid, and the like.

[0059] The organic alkoxysilane is preferably represented by the following formula (1) or formula (2). By using an organic alkoxysilane represented by the following formula (1) or formula (2), porous silicon carbide having a desired three-dimensional framework structure can be easily formed. R １ -SiR ２ ｘ (OR ３ ) ３－ｘ ...(1) (in the formula R１ is any group selected from a methyl group, an ethyl group, a vinyl group, and a phenyl group, and R ２ is a methyl group, R ３ represents a methyl group or an ethyl group. In the formula, the integer x is 0 or 1. ４ -(SiR ５ ｙ (OR ６ ) ３－ｙ ) ２ ...(2) (in the formula R ４ contains any group selected from a methylene group, an ethylene group, a hexylene group, a vinylene group, a phenylene group, and a biphenylene group, and R ５ is a methyl group, R ６ represents a methyl group or an ethyl group. In the formula, the integer y is 0 or 1.

[0060] Specific examples of the organic alkoxysilane represented by the above formula (1) include methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, methylethyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, methylvinyldimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, and methylphenyldimethoxysilane. Specific examples of the organic alkoxysilane represented by the formula (2) include bis(trimethoxysilyl)methane, bis(triethoxysilyl)methane, bis(methyldimethoxysilyl)methane, bis(methyldiethoxysilyl)methane, 1,2-bis(trimethoxysilyl)ethane, 1,2-bis(triethoxysilyl)ethane, 1,2-bis(methyldimethoxysilyl)ethane, 1,2-bis(methyldiethoxysilyl)ethane, 1,6-bis(trimethoxysilyl)hexane, 1,6-bis(triethoxysilyl)hexane, 1,6-bis(methyldimethoxysilyl)hexane, 1,6-bis(methyldiethoxysilyl)hexane, Examples of suitable ethene derivatives include 1,2-bis(trimethoxysilyl)ethene, 1,2-bis(triethoxysilyl)ethene, 1,2-bis(methyldimethoxysilyl)ethene, 1,2-bis(methyldiethoxysilyl)ethene, 1,4-bis(trimethoxysilyl)benzene, 1,4-bis(triethoxysilyl)benzene, 1,4-bis(methyldimethoxysilyl)benzene, 1,4-bis(methyldiethoxysilyl)benzene, 4,4'-bis(trimethoxysilyl)biphenyl, 4,4'-bis(triethoxysilyl)biphenyl, 4,4'-bis(methyldimethoxysilyl)biphenyl, and 4,4'-bis(methyldiethoxysilyl)biphenyl. The above ethene derivatives include cis / trans geometric isomers, and either isomer can be used.

[0061] In this step (A), a carbon material or an organic polymer is further added to the acidic aqueous solution to form a gel containing the carbon material or the organic polymer. By adding the carbon material or the organic polymer during the sol-gel reaction of the alkoxysilane, the precursor formed in step (C) can be calcined in step (D) to arrange the carbon material at the nano level in a porous three-dimensional skeleton structure, thereby imparting excellent conductivity to the porous silicon carbide, which is originally an insulator or semiconductor. By calcining in step (D), the organic polymer undergoes thermal decomposition and is retained in the porous silicon carbide as low-crystalline nanocarbon, making it possible to impart conductivity.

[0062] In the above step (A), it is preferable to add the carbon material or organic polymer to the acidic aqueous solution so that the mass ratio of the carbon material or organic polymer to the organic alkoxysilane is 2.5 to 50:97.5 to 50. Furthermore, the mass ratio of the carbon material or organic polymer to the organic alkoxysilane is more preferably 3 to 30:97 to 70, and even more preferably 5 to 20:95 to 80. By setting the mass ratio of the carbon material or organic polymer to the organic alkoxysilane to a value within the above range, it is possible to achieve both a larger BET specific surface area and higher electrical conductivity. When the amount of the carbon material or organic polymer added is equal to or less than the amount of the organic alkoxysilane added, separation from the sol-gel reaction system is suppressed, and the formation of a gel composed of polysilsesquioxane can be promoted.

[0063] The carbon material is not particularly limited, and may be composed of one or more selected from, for example, carbon black, carbon nanofiber, carbon nanotube, and low-crystalline nanocarbon. Among these, from the viewpoints of realizing high conductivity and manufacturability, the carbon material is preferably carbon black.

[0064] The organic polymer is not particularly limited, but may be composed of one or more selected from, for example, phenolic resin, polystyrene, and polydivinylbenzene.

[0065] [Step (B)] In step (B), the gel obtained in step (A) is washed with alcohol. The alcohol used in washing is not particularly limited, but examples include methanol, ethanol, 1-propanol, and 2-propanol. This allows unnecessary surfactants to be removed from the acidic aqueous solution, and the water in the acidic aqueous solution to be replaced with alcohol. After washing with alcohol, the solution may be further replaced with a hydrocarbon solvent such as hexane or heptane. In step (B), water, which is a high surface tension solvent, is replaced with alcohol or a hydrocarbon solvent, which is a low surface tension solvent. This prevents network shrinkage during the drying step at room temperature and normal pressure in step (C), which will be described later, and facilitates the formation of a porous gel structure.

[0066] [Step (C)] In step (C), the washed gel is dried to form a porous silicon carbide precursor. Examples of methods for this step (C) include supercritical drying using carbon dioxide at 80°C and 14 MPa, drying at room temperature and atmospheric pressure, and vacuum drying at 20°C to 80°C. Among these, drying at room temperature and atmospheric pressure is preferred, as it is inexpensive to produce and, when a polysilsesquioxane having high skeletal strength and flexibility is formed, it can produce a high-density porous silicon carbide precursor with developed mesopores.

[0067] [Step (D)] In step (D), the porous silicon carbide precursor containing the carbon material or organic polymer is calcined to obtain a porous silicon carbide composite material. In this step, carbon atoms are supplied from the organic groups of the polysilsesquioxane by the calcination, and a silicon carbide skeleton is formed via a carbothermal reduction reaction. At the same time, carbon atoms are also supplied to the skeleton from the carbon material or organic polymer dispersed at the nano level in the gel. The organic polymer undergoes thermal decomposition by the calcination, and is retained in the porous silicon carbide as low-crystalline nanocarbon.

[0068] The firing can be carried out by a known, conventional method without any particular limitations. For example, firing can be carried out by raising the temperature at a rate of 2.5°C per minute in an inert gas atmosphere and maintaining the reached maximum temperature for a certain period of time. The maximum firing temperature is preferably 1300°C to 3000°C, more preferably 1350°C to 2500°C, and particularly preferably 1400°C to 2000°C. The maximum temperature can be maintained for an appropriate period of time based on the effective time required to obtain a porous silicon carbide composite material. For example, 5 minutes to 16 hours is preferred, 10 minutes to 10 hours is more preferred, and 30 minutes to 3 hours is particularly preferred. The firing can be carried out in two or more stages. That is, in the first stage, firing can be carried out for a certain period of time at a temperature lower than the maximum temperature, and then the temperature can be raised again for firing. The firing can be carried out at atmospheric pressure. Examples of inert gases include nitrogen, helium, and argon. The inert gas may contain a reducing gas such as hydrogen gas. The calcination can be carried out in a fixed-bed or fluidized-bed carbonization furnace, and the heating method and type of the carbonization furnace are not particularly limited as long as the furnace has the function of raising the temperature to a predetermined temperature. Examples of the carbonization furnace include a lead hammer furnace, a tunnel furnace, and a single furnace.

[0069] In step (D), a carbon material or an organic polymer may be further mixed with the porous silicon carbide precursor and the mixture may be calcined. When an organic polymer is mixed with the porous silicon carbide precursor in step (D), similar to the case of mixing in step (A), pyrolysis proceeds by calcination, and the organic polymer is retained in the porous silicon carbide as low-crystalline nanocarbon.

[0070] [Step (E)] In step (E), a dispersion containing a colloid containing platinum nanoparticles and aqueous hydrogen peroxide is mixed with the porous silicon carbide composite material to obtain a mixed liquid. The colloid containing platinum nanoparticles is a dispersion of particles containing platinum nanoparticles in a liquid, and the dispersion containing a colloid containing platinum nanoparticles is a solution containing the colloid containing platinum nanoparticles and aqueous hydrogen peroxide. The colloid containing platinum nanoparticles and the dispersion containing the colloid containing platinum nanoparticles and aqueous hydrogen peroxide can be prepared by known, conventional methods.

[0071] The mixing ratio of the dispersion containing a colloid containing platinum nanoparticles and the porous silicon carbide composite material is, for example, preferably such that the mass of the platinum nanoparticles after loading is 10% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 55% by mass or less, and even more preferably 30% by mass or more and 50% by mass or less, relative to the total mass of the platinum catalyst.

[0072] In step (E), when a mixture of a colloid containing platinum nanoparticles, a dispersion containing hydrogen peroxide, and a porous silicon carbide composite material is stirred, the colloid containing platinum nanoparticles is supported on the porous silicon carbide composite material, yielding a platinum catalyst containing particles containing platinum nanoparticles. After leaving the mixture for a predetermined period of time, the solid and liquid phases are separated. To promote solid-liquid separation, the mixture may be cooled. Furthermore, the solid content can be washed using known, conventional methods and conditions. The washing liquid used for washing is not particularly limited, but may be, for example, water, preferably ultrapure water. This removes ions such as chloride ions from the solid content.

[0073] [Step (F)] In step (F), the mixture obtained in step (E) is heat-treated under a nitrogen and hydrogen atmosphere to obtain a platinum catalyst containing platinum nanoparticles. By heat-treating the mixture under a nitrogen and hydrogen atmosphere, the platinum nanoparticles supported on the porous silicon carbide composite material are one-dimensionally connected to each other, the highly active Pt(111) plane is increased, and a platinum catalyst with a high Pt(111) / Pt(200) intensity ratio is obtained. The concentration of hydrogen gas in the nitrogen / hydrogen mixed gas to create the nitrogen and hydrogen atmosphere is preferably, for example, 0.5% to 4% by volume, and more preferably 1% to 4% by volume.

[0074] In step (F), the temperature at which the mixture is heat-treated is preferably 25°C or higher and 800°C or lower, more preferably 50°C or higher and 600°C or lower, and even more preferably 100°C or higher and 400°C or lower. When the temperature at which the mixture is heat-treated in a nitrogen and hydrogen atmosphere is 25°C or higher and 800°C or lower, the platinum nanoparticles are more easily linked together and the Pt(111) / Pt(200) intensity ratio can be further increased. Other conditions for the heat treatment include, for example, heating at a temperature rise rate of 1°C / min to 20°C / min, and maintaining the maximum temperature reached for a certain period of time. The temperature maintenance time for this heat treatment can be, for example, 0 to 3 hours.

[0075] [Step (G)] The method may further include a step (G) of heat-treating the mixture in a nitrogen atmosphere after step (E) and before step (F). By heat-treating the mixture in a nitrogen atmosphere as the first step of the heat treatment and then heat-treating it in a nitrogen and hydrogen atmosphere as the second step of the heat treatment, the highly active Pt(111) plane can be further increased, and the intensity ratio of Pt(111) / Pt(200) can be further increased.

[0076] In step (G), the temperature at which the mixture is heat-treated is preferably 100°C or higher and 800°C or lower, more preferably 150°C or higher and 600°C or lower, and even more preferably 200°C or higher and 400°C or lower. When the temperature at which the mixture is heat-treated in a nitrogen atmosphere is 100°C or higher and 800°C or lower, the platinum nanoparticles are more easily linked together and the Pt(111) / Pt(200) intensity ratio can be further increased. Other conditions for the heat treatment include, for example, heating at a temperature rise rate of 1°C / min to 20°C / min, and maintaining the maximum temperature reached for a certain period of time. The temperature maintenance time for this heat treatment can be, for example, 0 minutes to 3 hours.

[0077] [Catalyst Electrode and Fuel Cell] The catalyst electrode according to this embodiment has a catalyst layer containing the platinum catalyst. The application of the catalyst electrode is not limited, and it can be used, for example, as an electrode for a fuel cell. The catalyst electrode typically has the platinum catalyst layer and a gas diffusion layer. The catalyst electrode may be a negative electrode (anode) for a fuel cell, or a positive electrode (cathode) for a fuel cell. When the catalyst electrode is a negative electrode for a fuel cell, the negative electrode for a fuel cell has an anode catalyst layer to which a fuel such as hydrogen is supplied, and a first gas diffusion layer. When the catalyst electrode is a positive electrode for a fuel cell, the positive electrode for a fuel cell has a cathode catalyst layer to which an oxygen-containing gas such as air is supplied, and a second gas diffusion layer.

[0078] The fuel cell according to this embodiment includes the catalytic electrode. The fuel cell includes the catalytic electrode and an electrolyte layer. Typically, the fuel cell includes a fuel cell negative electrode (anode), a fuel cell positive electrode (cathode), an electrolyte layer disposed therebetween, a first separator disposed on the fuel cell negative electrode opposite the electrolyte layer, and a second separator disposed on the fuel cell positive electrode opposite the electrolyte layer. In this case, the anode catalytic layer is disposed between the electrolyte layer and the first gas diffusion layer, and the cathode catalytic layer is disposed between the electrolyte layer and the second gas diffusion layer.

[0079] The catalyst electrode and fuel cell described above have a catalyst layer containing the platinum catalyst, and therefore can achieve high activity and durability due to the platinum nanostructure supported on the porous silicon carbide composite material in the platinum catalyst. In addition, the nano-level arrangement of carbon material in silicon carbide with a porous three-dimensional framework structure reduces the possibility of oxidative degradation of the carbon material, which has been a problem in the past, for example, in high-temperature and high-humidity environments, thereby achieving excellent durability as a catalyst electrode and fuel cell.

[0080] Examples of the present invention will be described below, but the present invention is not limited to the examples shown below.

[0081] Example 1 Synthesis of Porous Silicon Carbide Composite Material 6 g of a 5 mM aqueous acetic acid solution (Kanto Chemical), 0.8 g of Pluronic® F-127 (BASF), 0.5 g of urea (Kanto Chemical), and 0.24 g of Ketjen Black (Lion Specialty Chemicals, product name "ECP-600JD") were placed in a vial and stirred at room temperature for 10 minutes. 5 g of methyltrimethoxysilane (Kanto Chemical) was added thereto and stirred at room temperature for 30 minutes. The mixture was then allowed to react at 60°C for 4 days to obtain a wet gel. The obtained wet gel was washed with methanol (Kanto Chemical), dried at room temperature and atmospheric pressure for 3 days, and then further dried at 80°C and atmospheric pressure for 6 hours to obtain 3.5 g of porous silicon carbide precursor. 1 g of this porous silicon carbide precursor was mixed with 0.4 g of ketjen black (ECP), and then the mixture was placed in a tubular furnace and fired in an argon atmosphere under conditions where the temperature was raised to 1500°C at a rate of 2.5°C / min and maintained at that temperature for 2 hours, yielding a porous silicon carbide composite material.

[0082] [Synthesis of platinum catalyst containing platinum nanoparticles] 0.43 g of chloroplatinic acid hexahydrate was dissolved in 60 mL of ultrapure water, and 3.1 g of sodium hydrogen sulfite was added to the solution to allow the reduction reaction to proceed. Then, 280 mL of ultrapure water was added for dilution. Next, 5% aqueous sodium hydroxide solution was added, and 24 mL of 35% hydrogen peroxide was added dropwise while adjusting the pH to approximately 5, to obtain a dispersion containing platinum colloid. Subsequently, the colloidal dispersion was separated so that the amount of platinum (Pt) after support was 45 mass% relative to the total amount of platinum catalyst including the support, and 0.4 g of porous silicon carbide composite material was added as a support and mixed at 90 ° C for 3 hours. After cooling, the mixture was subjected to solid-liquid separation. The resulting powder (solid content) was thoroughly washed with ultrapure water to remove chloride ions, and then dried at 80 ° C for 12 hours in air to obtain a platinum catalyst precursor in which platinum oxide was supported on the surface of the porous silicon carbide composite material. The platinum catalyst precursor obtained above was placed in an alumina boat, heated at 10°C / min under a nitrogen stream, held at 300°C for 2 hours, and cooled to room temperature. Thereafter, the boat was heated at 10°C / min under a nitrogen and hydrogen stream (hydrogen gas concentration in the mixed gas: 1% by volume), held at 100°C for 2 hours, and cooled to room temperature to obtain platinum catalyst A.

[0083] (Example 2) Platinum catalyst B was obtained by the same synthesis as in Example 1, except that after the platinum catalyst precursor was synthesized, the temperature was increased at a rate of 10°C / min in a nitrogen and hydrogen stream (hydrogen gas concentration in the mixed gas: 1% by volume) without heat treatment in a nitrogen stream, and the mixture was maintained at 100°C for 2 hours.

[0084] Example 3 Platinum catalyst C was obtained in the same manner as in Example 1, except that the amount of platinum (Pt) after support was adjusted to 30 mass % based on the total amount of the platinum catalyst including the support.

[0085] (Comparative Example 1) Platinum catalyst D was obtained in the same manner as in Example 1, except that after synthesizing a platinum catalyst precursor, heat treatment was performed by raising the temperature at a rate of 10°C / min under a nitrogen stream and holding it at 300°C for 2 hours, and no heat treatment under a nitrogen or hydrogen stream was performed.

[0086] Comparative Example 2 Platinum catalyst E was obtained in the same manner as in Example 1, except that the amount of platinum (Pt) after support was adjusted to 17 mass % based on the total amount of the platinum catalyst including the support.

[0087] Comparative Example 3 Pt was supported and heat treatment was carried out in the same manner as in Example 1, except that the support was changed to Ketjen Black (manufactured by Lion Specialty Chemicals, product name "Carbon ECP").

[0088] Comparative Example 4 Platinum (Pt)-supported carbon black (Pt / CB) (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Kogyo) was obtained as a catalyst.

[0089] The above-mentioned Examples 1 to 3 and Comparative Examples 1 to 4 were measured by the following methods.

[0090] [Measurement of Pt Loading Amount] The platinum catalyst was alkali-fused using anhydrous sodium carbonate and sodium peroxide, then dissolved in aqua regia, and diluted to a specified concentration with ultrapure water, and the Pt loading amount was calculated using high-frequency induction heating optical emission spectroscopy (ICP; Model ICPE-9820, manufactured by Shimadzu Corporation).

[0091] [Evaluation of catalytic performance using a rotating electrode] (Electrode preparation) A glassy carbon (GC) electrode with a diameter of 5 mm was polished using alumina paste and then ultrasonically cleaned using ultrapure water. Platinum catalyst A was added to a 99% by volume aqueous ethanol solution and dispersed using an ultrasonic homogenizer. This was dropped onto a GC disk and dried at room temperature for 12 hours. After drying, a 5% Nafion (registered trademark) solution was dropped onto the platinum catalyst on the GC disk to a dry film thickness of 50 nm and then dried at room temperature for 12 hours.

[0092] (CV Measurement) Electrode evaluation was performed using an electrochemical measurement system (HZ-5000, manufactured by Hokuto Denko Corporation). After purging a 0.1 M aqueous solution of perchloric acid with nitrogen gas for 30 minutes, cleaning was performed 50 times using a reversible hydrogen electrode (RHE) as the reference electrode at a potential range of 0.05 to 1.2 V and a sweep rate of 150 mV / s. Subsequently, cyclic voltammetry (CV) measurements were performed at a potential range of 0.05 to 1.0 V and a sweep rate of 100 mV / s. Electrochemically active surface area (ECSA) analysis was performed using the hydrogen adsorption wave observed below 0.4 V.

[0093] (Evaluation of oxygen reduction activity) After purging the electrolyte with oxygen gas for at least one hour, linear sweep voltammetry (LSV) was performed. Data was acquired under eight conditions: temperature 25°C, potential range 0.25 to 1.00 V, sweep rate 5 mV / s, and rotation speed 1000 rpm to 2750 rpm, increasing in 250 rpm increments. The results were analyzed using a Koutecky-Levich plot to obtain the mass activity (A / g-Pt) at 0.85 V.

[0094] (Start / Stop Durability Evaluation) After purging the above electrolyte with nitrogen gas for 30 minutes, the potential range of 1.0 to 1.5 V was swept 500 times, and CV measurement was performed in the potential range of 0.05 to 1.0 V. This measurement procedure constituted one set, and a test was performed for 56,000 cycles. The results are shown in Table 1.

[0095]

[0096] FIG. 4(A) shows a transmission electron microscope image of platinum catalyst A obtained in Example 1, FIG. 4(B) shows a transmission electron microscope image of platinum catalyst B obtained in Example 2, FIG. 4(C) shows a transmission electron microscope image of platinum catalyst E obtained in Comparative Example 2, and FIG. 4(D) shows a transmission electron microscope image of platinum catalyst F obtained in Comparative Example 3. Also, FIG. 5(A) shows a secondary electron image of platinum catalyst A obtained in Example 1 observed by a scanning transmission electron microscope, and FIG. 5(B) shows a transmission electron image, respectively. In Examples 1 and 2, it was confirmed that long platinum nanostructures were supported on the porous silicon carbide composite material. It was also confirmed that the long platinum nanostructures had a connected structure in which multiple platinum nanoparticles were linked. On the other hand, in Comparative Example 2, it was confirmed that platinum nanoparticles were supported on the porous silicon carbide composite material. It was also confirmed that in Comparative Example 3, platinum nanoparticles and platinum nanoparticle aggregates were supported on the carbon black.

[0097] Furthermore, as shown in Table 1, in Examples 1 to 3, the amount of platinum nanostructure supported in platinum catalysts A to C was 30 to 45 mass%, the intensity ratio of Pt(111) / Pt(200) was 2.5 to 2.8, the mass activity was 600 (A / g-Pt) or more, the current per unit mass of platinum (Pt) was high, and the area specific activity was 9.8 μA / cm ２ Furthermore, in Examples 1 to 3, the ECSA retention rate was 83 to 87%, demonstrating excellent durability.

[0098] On the other hand, in Comparative Example 1, the intensity ratio of Pt(111) / Pt(200) in platinum catalyst D was not detected, and the mass activity was 330 (A / g-Pt) and the area specific activity was 6.6 μA / cm ２ The ECSA retention rate was 79%, and the activity and durability were poor.

[0099] In Comparative Example 2, the platinum loading in platinum catalyst E was 17 mass%, the Pt(111) / Pt(200) intensity ratio was 2.3, the mass activity was 450 (A / g-Pt), and the area specific activity was 6.4 μA / cm ２ The ECSA retention rate was 76%, and the activity and durability were poor.

[0100] In Comparative Example 3, the platinum loading in platinum catalyst F was 51 mass%, the Pt(111) / Pt(200) intensity ratio was 2.4, the mass activity was 550 (A / g-Pt), and the area specific activity was 8.0 μA / cm ２ The ECSA retention rate was 56%, and the activity and durability were poor.

[0101] In Comparative Example 4, the amount of platinum supported on Pt / CB was 46 mass%, the intensity ratio of Pt(111) / Pt(200) was 2.1, the mass activity was 420 (A / g-Pt), and the area specific activity was 5.9 μA / cm ２ The ECSA retention rate was 55%, and the activity and durability were poor.

[0102] Example 4 [Preparation of Single Fuel Cell] (Preparation of Anode Catalyst Ink) Carbon black carrying 0.45 g of platinum (Pt) (Pt / CB, Tanaka Kikinzoku Co., Ltd., TEC10E50E, Pt loading 46 wt%) and a polymer electrolyte (Du Pont, Nafion (registered trademark) DE521) were mixed at a volume ratio of 1.0, and this mixture, 2.5 g of ethanol, 2 g of water, and zirconia balls (diameter 5 mm) were placed in a zirconia pot and mixed for 60 minutes in a planetary ball mill (Fritsch, P-6). The mixture obtained by mixing in this ball mill is hereinafter referred to as the anode catalyst ink.

[0103] (Preparation of Cathode Catalyst Ink) Platinum catalyst A and a polymer electrolyte (Nafion (registered trademark) DE521, manufactured by Du Pont) were mixed at a volume ratio of 0.7, and this mixture, 2.5 g of ethanol, 2 g of water, and zirconia balls (diameter 5 mm) were placed in a zirconia pot and mixed for 60 minutes in a planetary ball mill (P-6, manufactured by Fritsch).

[0104] (Fabrication of Membrane Electrode Assembly (MEA)) The anode catalyst layer and the cathode catalyst layer were formed by spray coating a polymer electrolyte membrane (Nafion NR212, manufactured by Du Pont) with a platinum coating weight of 0.5 mg / cm2. ２ , the platinum content of the cathode is 0.3 mg / cm ２The anode catalyst ink and the cathode catalyst ink were applied so that the anode catalyst layer and the cathode catalyst layer were coated on the cathode catalyst ink ...

[0105] In the above CCM, gas diffusion layers (GDL, manufactured by SGL, 22BB) were overlaid on both sides of each catalyst layer, and a cathode catalyst layer and an anode catalyst layer were laminated on the polymer electrolyte membrane so as to face each other, to obtain a membrane electrode assembly (MEA). A single cell was assembled using the above MEA and placed in a power generation evaluation device (manufactured by Panasonic Production Technology).

[0106] Comparative Example 5 A single fuel cell was fabricated in the same manner as in Example 4, except that the cathode catalyst was changed to platinum catalyst E.

[0107] For the above Example 4 and Comparative Example 5, measurements were carried out by the following methods.

[0108] [Evaluation of Single Fuel Cell] (CV Measurement) Hydrogen gas was supplied to the anode side of the single cell obtained in Example 4, and gas was shut off on the cathode side. CV measurement was performed over a potential range of 0.05 to 1.0 V. The results are shown in Figure 6. The platinum catalysts were synthesized in the same manner as in Example 1, except that the amount of platinum (Pt) after loading was adjusted to 17 mass%, 25 mass%, 37 mass%, 41 mass%, or 51 mass% relative to the total amount of platinum catalyst including the support. CV measurement results for the resulting platinum catalysts are also shown in the same figure. As a result, it was confirmed that the ratio of the Pt(100) peak intensity to the Pt(110) peak intensity (Pt(100) / Pt(110) intensity ratio) decreased when the Pt loading was 30 mass% or more. The change in electrochemically active surface area (ECSA) versus platinum loading is also shown in Figure 7. It was found that the tendency for ECSA to decrease with increasing Pt loading changes around 30 mass%. From the above, it was suggested that when the Pt loading amount was 30 mass % or more, the Pt (100) planes were connected to each other to form Pt nanostructures.

[0109] (Measurement of I-V characteristics and cell resistance) Hydrogen gas was supplied to the anode side of the single cell obtained in Example 4, and oxygen gas was supplied to the cathode side. The flow rates were set so that the utilization rate of hydrogen gas was 70% and the utilization rate of oxygen gas was 40%. The anode and cathode gases were each humidified using an external humidifier before being supplied to the single cell. The temperature of the single cell was adjusted to 80°C, and the humidity of the supplied gas was adjusted so that the relative humidity was 80% RH. Power generation was performed within an applied current range in which the voltage of this single cell did not fall below 0.4 V, and the power generation performance was evaluated. A Tafel plot was created from the obtained data, and the 1.0 A / cm ２ The activation overpotential at 1000 kJ / cm2 was calculated, and the results are shown in Table 2.

[0110]

[0111] As shown in Table 2, in Example 4, when platinum catalyst A was used for the cathode electrode, the activation overvoltage was 0.38 V, the energy loss was small, and it was found that the cell performance as a single fuel cell was superior. On the other hand, in Comparative Example 5, when platinum catalyst E was used for the cathode electrode, the activation overvoltage was 0.41 V, the energy loss was large, and the cell performance as a single fuel cell was inferior.

[0112] The platinum catalyst of this embodiment has excellent activity and durability, making it suitable as an electrode material used in the catalytic layer of a catalytic electrode. In particular, it can operate over a wide temperature range, from conventional temperatures (approximately 70°C) to high temperatures (120°C or higher), and can achieve both high power generation performance and durability in a fuel cell, making it extremely useful as a fuel cell for commercial vehicles, which are expected to be used in a wide variety of applications.

[0113] 1 Platinum catalyst 10 Porous silicon carbide composite material 11 Silicon carbide material 12 Carbon material 20 Platinum nanostructure 21 Platinum nanoparticles

Claims

1. A platinum catalyst comprising: a porous silicon carbide composite material containing a silicon carbide material containing SiC as a main component and a carbon material; and a platinum nanostructure supported on the porous silicon carbide composite material, wherein the amount of the platinum nanostructure supported is 30 to 60 mass% when the total mass of the platinum catalyst is taken as 100 mass%, and the intensity ratio of Pt(111) / Pt(200) determined by X-ray diffraction (XRD) is 2.5 to 3.

0.

2. The platinum catalyst according to claim 1, wherein the platinum nanostructure has a connected structure in which adjacent platinum nanoparticles are partially connected.

3. The platinum catalyst according to claim 2, wherein the platinum nanostructure has a longitudinal dimension of 4 nm or more and 20 nm or less, and a lateral dimension of the platinum nanostructure is 2 nm or more and 5 nm or less.

4. The platinum catalyst according to claim 1, wherein the carbon material is one or more selected from the group consisting of carbon black, carbon nanofibers, carbon nanotubes and low-crystalline nanocarbon.

5. The platinum catalyst according to claim 1, wherein the average diameter of the primary particles of the silicon carbide material is 20 nm or more and 800 nm or less.

6. A catalytic electrode having a layer containing the platinum catalyst according to any one of claims 1 to 5.

7. A fuel cell comprising the catalytic electrode according to claim 6.

8. A method for producing a platinum catalyst comprising: a step (A) of adding an organic alkoxysilane to an acidic aqueous solution containing a surfactant and a pH adjuster, and further adding a carbon material or an organic polymer to form a gel containing the carbon material or the organic polymer through a sol-gel reaction of the organic alkoxysilane; a step (B) of washing the gel with alcohol; a step (C) of drying the washed gel to form a porous silicon carbide precursor; a step (D) of calcining the porous silicon carbide precursor to obtain a porous silicon carbide composite material containing a silicon carbide material containing SiC as a main component and a carbon material; a step (E) of mixing a dispersion containing a colloid containing platinum nanoparticles and hydrogen peroxide water with the porous silicon carbide composite material to obtain a mixture; and a step (F) of heat-treating the mixture under an atmosphere of nitrogen and hydrogen to obtain a platinum catalyst containing platinum nanoparticles.

9. The method for producing a platinum catalyst according to claim 8, wherein in step (F), the mixture is heat-treated at a temperature of 25°C or higher and 800°C or lower.

10. The method for producing a platinum catalyst according to claim 8, further comprising a step (G) of heat treating the mixture under a nitrogen atmosphere after step (E) and before step (F).

11. The method for producing a platinum catalyst according to claim 10, wherein in the step (G), the mixture is heat-treated at 100°C or higher and 800°C or lower.

12. The method for producing a platinum catalyst according to claim 8, wherein the organic alkoxysilane is represented by the following formula (1) or formula (2). １ -SiR ２ ｘ (OR ３ ) ３－ｘ ...(1) (in the formula R １ is any group selected from a methyl group, an ethyl group, a vinyl group, and a phenyl group; R ２ is a methyl group, R ３ represents a methyl group or an ethyl group. In the formula, the integer x is 0 or 1. ４ -(SiR ５ ｙ (OR ６ ) ３－ｙ ) ２ ...(2) (in the formula R ４ R includes any group selected from a methylene group, an ethylene group, a hexylene group, a vinylene group, a phenylene group, and a biphenylene group; ５ is a methyl group, R ６ represents a methyl group or an ethyl group. In the formula, the integer y is 0 or 1.

13. The method for producing a platinum catalyst according to claim 8, wherein the carbon material is one or more selected from carbon black, carbon nanofibers, carbon nanotubes and low-crystalline nanocarbon.

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