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

Abstract

A platinum catalyst comprising a porous silicon carbide composite material and platinum nanostructures supported on the porous silicon carbide composite material, wherein the porous silicon carbide composite material comprises silicon carbide material containing SiC as the main component and carbon material, wherein the loading of the platinum nanostructures is 30-60% by mass when the total mass of the platinum catalyst is set to 100% by mass, and the intensity ratio of Pt(111) / Pt(200) determined by X-ray diffraction (XRD) is 2.5-3.0.

Description

Technical Field

[0001] This invention relates to a platinum catalyst containing a porous silicon carbide composite material, a catalyst electrode, a fuel cell, and a method for manufacturing the platinum catalyst.

[0002] This application claims priority based on Japanese Patent Application No. 2023-210051 filed on December 13, 2023, the contents of which are incorporated herein by reference. Background Technology

[0003] Fuel cells are devices that generate electricity and heat through the chemical reaction of hydrogen and oxygen to produce water. There are various types of fuel cells, including phosphoric acid fuel cells (PAFCs), molten carbonate fuel cells (MCFCs), solid oxide fuel cells (SOFCs), and polymeric electrolyte fuel cells (PEFCs). Among them, the polymeric electrolyte fuel cell (PEFC) has the following structure: a catalyst layer forming the anode (fuel electrode) is disposed on one side of a solid polymer electrolyte membrane, and a catalyst layer forming the cathode (air electrode) is disposed on the other side. A gas diffusion layer is bonded to the outside of each catalyst layer. The catalyst layer is composed of a catalyst support, in which particulate catalyst containing noble metals is highly dispersed and loaded onto the surface of nanoscale support particles.

[0004] Currently, carbon-based materials with high specific surface area and high conductivity are used as supports for catalysts. However, in the cathode, corrosion of the carbon support leads to a decrease in catalytic performance and durability, which becomes a major problem. In addition, fuel cells for commercial vehicles, which are expected to be used for multiple purposes, require higher catalyst activity than before. Therefore, the development of high-durability supports and high-activity catalysts to replace carbon is an urgent task. For example, as a catalyst using a support to replace carbon, Patent Document 1 discloses an electrode catalyst comprising: (A) group-13 doped SiC doped with group 13 (group 3B) elements, (B) conductive carbon particles, and (C) a noble metal supported on the surface of the group-13 doped SiC mentioned above (A). The group 13 element doped in SiC is, for example, Al (aluminum). The doping amount of the group 13 element in the SiC doped with group 13 in (A) is 1 to 5 mol%. The ratio of the group 13 doped SiC in (A) to the conductive carbon particles in (B) [(A):(B)] is 1:9 to 5:5 by weight.

[0005] In addition, as a catalyst exhibiting high activity, Non-Patent Document 1 discloses a catalyst in which platinum nanowires are supported on a carbon support.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2010-149008

[0009] Non-patent literature

[0010] Non-patent literature 1: X. Duan et al., Science, 2016, 354, 1414-1419. Summary of the Invention

[0011] The problem the invention aims to solve

[0012] Patent document 1 proposed an electrode catalyst comprising noble metal particles and conductive carbon particles loaded on a group 13-doped silicon carbide surface, which imparts conductivity to the originally non-conductive silicon carbide, thereby reducing its resistance. However, durability is not mentioned, leaving room for further research. Furthermore, there is no description of the shape of platinum; from a conventional perspective, it is unlikely that platinum-loaded nanoparticles would exhibit higher activity than previously thought.

[0013] Non-Patent Document 1 described above as having a one-dimensional arrangement of platinum supported on a carrier, but due to the use of a carbon support, it lacks durability. In addition, methods for pre-synthesizing platinum nanowires and the like and then supporting them on a carrier are complex and costly.

[0014] The purpose of this invention is to provide a platinum catalyst with excellent activity and durability, a catalyst electrode and a fuel cell, as well as a simple and low-cost method for producing the platinum catalyst.

[0015] Solution for solving the problem

[0016] To achieve the above objectives, this invention discovers that during the sol-gel reaction of an aqueous solution of an organoalkoxysilane in the presence of a surfactant, while ensuring that the formation of a porous gel is not hindered, a precursor gel is prepared by coexisting a carbon material or organic polymer as a carbon source and then sintering it. This produces a porous silicon carbide composite material with a well-developed pore structure from mesopores to macropores, and carbon materials are arranged at the nanoscale within a porous three-dimensional framework structure. Furthermore, it has been found that mixing the porous silicon carbide composite material, hydrogen peroxide water, and a dispersion containing platinum nanoparticles yields a mixture of platinum oxide colloids loaded onto the porous silicon carbide composite material. Moreover, heat-treating this mixture under nitrogen and hydrogen atmospheres forms platinum nanostructures with a specific increased crystal facet ratio, thereby enhancing catalyst activity.

[0017] That is, the present invention provides the following structure.

[0018] [1] A platinum catalyst comprising a porous silicon carbide composite material and platinum nanostructures supported on the porous silicon carbide composite material, wherein the porous silicon carbide composite material comprises silicon carbide material containing SiC as the main component and carbon material.

[0019] When the total mass of the platinum catalyst is set to 100% by mass, the loading of the platinum nanostructure is 30-60% by mass, and the intensity ratio of Pt(111) / Pt(200) obtained by X-ray diffraction (XRD) is 2.5-3.0.

[0020] [2] According to the platinum catalyst of [1], wherein the platinum nanostructure has a connection structure in which a plurality of adjacent platinum nanoparticles are partially connected.

[0021] [3] According to the platinum catalyst described in [2], the long side dimension of the platinum nanostructure is 4 nm or more and 20 nm or less, and the short side dimension of the platinum nanostructure is 2 nm or more and 5 nm or less.

[0022] [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-crystallinity nanocarbon.

[0023] [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 more than 20 nm and less than 800 nm.

[0024] [6] A catalyst electrode having a layer comprising any one of the platinum catalysts described in [1] to [5].

[0025] [7] A fuel cell having the catalyst electrode described in [6].

[0026] [8] A method for manufacturing a platinum catalyst, comprising:

[0027] Step (A) involves adding an organoalkoxysilane to an acidic aqueous solution containing a surfactant and a pH adjuster, and further adding a carbon material or an organic polymer, thereby forming a gel containing the carbon material or the organic polymer through a sol-gel reaction of the organoalkoxysilane.

[0028] Step (B): Wash the gel with alcohol;

[0029] Step (C) involves drying the cleaned gel to form a porous silicon carbide precursor.

[0030] Step (D) involves sintering the porous silicon carbide precursor to obtain a porous silicon carbide composite material containing silicon carbide material with SiC as the main component and carbon material.

[0031] Step (E) involves mixing a dispersion containing platinum nanoparticles and hydrogen peroxide with the porous silicon carbide composite material to obtain a mixture; and

[0032] Step (F) involves heat-treating the mixture under a nitrogen and hydrogen atmosphere to obtain a platinum catalyst containing platinum nanoparticles.

[0033] [9] The method for manufacturing a platinum catalyst according to [8], wherein, in step (F), the mixture is heat-treated at a temperature above 25°C and below 800°C.

[0034]

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

[0035]

[11] According to the method for manufacturing the platinum catalyst described in

[10] , in step (G), the mixture is heat-treated at a temperature above 100°C and below 800°C.

[0036]

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

[11] , wherein the organoalkoxysilane is represented by the following formula (1) or formula (2).

[0037] R 1 -SiR 2 x (OR) 3 ) 3-x …(1)

[0038] (where R) 1 R is any group selected from methyl, ethyl, vinyl, and phenyl. 2 R represents methyl. 3 This represents methyl or ethyl. The integer x in the formula is 0 or 1.

[0039] R 4 -(SiR) 5 y (OR) 6 ) 3-y )twenty two)

[0040] (where R) 4 Contains any group selected from methylene, ethylene, hexylene, vinylene, phenylene, and biphenylene, R 5 R represents methyl.6 This represents methyl or ethyl. The integer y in the formula is 0 or 1.

[0041]

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

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

[0042] The effects of the invention

[0043] According to the present invention, a platinum catalyst with excellent activity and durability, a catalyst electrode and a fuel cell, and a method for manufacturing the platinum catalyst in a simple and low-cost manner can be provided. Attached Figure Description

[0044] Figure 1 This is a schematic diagram illustrating an example of the composition of the platinum catalyst according to an embodiment of the present invention.

[0045] Figure 2 It means Figure 1 An enlarged view of an example of the composition of platinum nanostructures supported on a porous silicon carbide composite material with a platinum catalyst.

[0046] Figure 3 This is a flowchart illustrating an example of a method for manufacturing a platinum catalyst according to an embodiment of the present invention.

[0047] Figure 4 (A) ~ Figure 4 (D) are transmission electron microscope images of the platinum catalysts illustrated in Example 1, Example 2, Comparative Example 2 and Comparative Example 3, respectively.

[0048] Figure 5 (A) is a diagram showing a secondary electron image of the platinum catalyst illustrated in Example 1, obtained through scanning transmission electron microscopy. Figure 5 (B) is a diagram representing a transmission electron image.

[0049] Figure 6 This is a graph showing the cyclic voltammetry (CV) results of the platinum catalyst when the loading of platinum nanostructures is varied in the evaluation of a single fuel cell.

[0050] Figure 7 This is a graph showing the change in electrochemically active surface area (ECSA) relative to the loading of platinum particles or platinum nanostructures in fuel cell single-cell evaluation. Detailed Implementation

[0051] <Composition of Platinum Catalysts>

[0052] Figure 1This is a schematic diagram illustrating an example of the structure of the platinum catalyst according to an embodiment of the present invention. Figure 1 As shown, the platinum catalyst 1 comprises a porous silicon carbide composite material 10 and a platinum nanostructure 20 supported on the porous silicon carbide composite material 10. The porous silicon carbide composite material 10 comprises a silicon carbide material 11 containing SiC as the main component and a carbon material 12.

[0053] The form of the platinum catalyst is not particularly limited, such as powder, granules, fibers or needles, with powder or granules being preferred.

[0054] When the platinum catalyst is in powder or granular form, there is no particular limitation on the particle size, except that the particle size D represents the 50% cumulative particle size in the volume-based cumulative particle size distribution. 50 The preferred size is 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.

[0055] Particle size D of platinum catalyst 50 This refers to the value measured according to JIS Z8825-1:2013, such as the particle size D measured using a laser diffraction particle size distribution measuring device (Shimadzu SALD-7000). 50 .

[0056] The BET specific surface area of ​​the platinum catalyst in this embodiment is not particularly limited; for example, it is preferably 10 m². 2 / g or more, preferably 50m 2 / g or more, further preferably 100m 2 / g or more. Additionally, the specific surface area of ​​BET can be 300m². 2 / g or less. If the specific surface area of ​​BET is 10m² 2 With a particle loading of 1 g or higher, the catalyst particle loading on the support surface can be sufficiently ensured, enabling the application of platinum catalysts in fuel cell electrodes to achieve the desired power, efficiency, and other characteristics. Furthermore, with a BET specific surface area of ​​300 m² / g... 2 When the ratio is below / g, the proportion of mesoporous particles suitable for catalyst loading becomes higher, thus further improving the utilization rate of catalyst particles.

[0057] The total pore volume of the platinum catalyst is not particularly limited, but is preferably 0.3 cm³. 3 / g or more, preferably 0.5cm 3 / g or more, with a particularly preferred value of 0.6cm 3 / g or more. If the total pore volume of the platinum catalyst is 0.3 cm³. 3When the concentration of reactive gases and electrolytes in the catalyst layer is above a certain level (e.g.), the flow of reactive gases and electrolytes within the catalyst layer becomes easier, thereby improving catalytic efficiency.

[0058] The pore size of the platinum catalyst is not particularly limited, but is preferably 10 nm or more and 1000 nm or less, more preferably 20 nm or more and 500 nm or less, and particularly preferably 50 nm or more and 300 nm or less. When the pore size of the platinum catalyst is 10 nm or more and 1000 nm or less, the flow of reactant gases and electrolytes within the catalyst layer becomes easier, thereby improving catalytic efficiency. In particular, if the pore size of the porous silicon carbide composite material is 10 nm or more, the supply of reactant gases and electrolytes to the supported catalyst particles is stable, and the reduction in catalyst particle utilization can be suppressed.

[0059] The BET specific surface area, total pore volume, and pore size of platinum catalysts can be calculated as measured values ​​using gas adsorption methods. For example, these values ​​are calculated based on the adsorption amount and condensation of non-corrosive gases such as nitrogen and argon when the relative pressure in the adsorption isotherm is changed using a constant volume method.

[0060] [Porous silicon carbide composite material]

[0061] In the porous silicon carbide constituting the platinum catalyst, multiple micropores are individually arranged through a three-dimensional framework structure, or multiple micropores are arranged in a state where some or all of them are interconnected. The BET specific surface area, total pore volume, and pore size of the porous silicon carbide composite material are the same as those of the platinum catalyst.

[0062] The platinum catalyst of this embodiment contains: carbon constituting the three-dimensional framework structure of porous silicon carbide (SiC) as a support, and carbon materials other than the carbon constituting the three-dimensional framework structure that remain in the porous silicon carbide.

[0063] Furthermore, in this specification, porous silicon carbide refers to the spatial composition of a three-dimensional network structure formed by interconnected silicon carbide.

[0064] [Carbon Materials]

[0065] There are no particular limitations on the carbon material; for example, it can be composed of one or more selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystallinity nanocarbon. Among these, carbon black is preferred from the viewpoints of achieving high conductivity and manufacturability.

[0066] When the carbon material is composed of 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.

[0067] 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.

[0068] The carbon content in the porous silicon carbide composite material is preferably 5% by mass or more and 50% by mass or less, more preferably 8% by mass or more and 45% by mass or less, and even more preferably 10% by mass or more and 40% by mass or less. When the carbon content in the porous silicon carbide composite material is 5% by mass or more and 50% by mass or less, high electrical conductivity can be achieved, and the durability of the catalyst cycle can be improved by suppressing carbon corrosion, etc.

[0069] The morphology and size of the carbon material retained in the porous silicon carbide composite material can be measured, for example, by observation using a transmission electron microscope or a scanning electron microscope. Furthermore, the average diameter of the primary particles can be determined, for example, using image-resolved particle size distribution measurement software based on microscope images.

[0070] Silicon carbide materials

[0071] The porous silicon carbide composite material contains SiC as the main component, as described above. In this embodiment, "main component" refers to SiC containing 50% by mass or more when the total mass of the silicon carbide material is set to 100% by mass.

[0072] Silicon carbide materials may contain SiC as the main component and also contain oxygen (O). In this embodiment, "containing oxygen (O)" means that the silicon carbide material contains silicon oxides such as SiO2.

[0073] The content of silicon oxide is only required to be less than 50% by mass when the silicon carbide in the porous silicon carbide composite material is set to 100% by mass. If it is within the above range, the durability of the support and the activity of the catalyst are excellent, and it is preferred.

[0074] In addition, there is no particular limitation on the mass ratio of silicon (Si) to oxygen (O) in porous silicon carbide composite materials ([Si] / [O]), for example, it can be set to 1 / 0.1 to 1 / 0.001.

[0075] [SiC (Silicon Carbide)]

[0076] The average diameter of the primary silicon carbide particles in the porous silicon carbide composite material is preferably 20 nm or more and 800 nm or less, more preferably 30 nm or more and 500 nm or less, and even more preferably 40 nm or more and 300 nm or less. If the average diameter of the primary silicon carbide particles is 20 nm or more and 800 nm or less, good porosity can be obtained when forming the electrode, which is therefore preferred.

[0077] The particle size of silicon carbide in porous silicon carbide composites can be measured, for example, by observation using transmission electron microscopy or scanning electron microscopy. Furthermore, the average diameter of primary particles can be determined, for example, using image-resolved particle size distribution measurement software based on microscope images.

[0078] [Platinum Nanostructures]

[0079] In the platinum catalyst of this embodiment, the loading of platinum nanostructures when the total mass of the platinum catalyst is set to 100% by mass is 30% by mass or more and 60% by mass or less. When the loading of platinum nanostructures is 30% by mass or more and 60% by mass or less, the activity and durability are excellent. The loading of platinum nanostructures when the total mass of the platinum catalyst is set to 100% by mass 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.

[0080] The loading of platinum nanostructures can be calculated, for example, by dissolving the platinum catalyst in aqua regia after alkaline melting, diluting it with ultrapure water, and then using high-frequency induction heating luminescence spectrophotometry (ICP).

[0081] Furthermore, in this embodiment, the intensity ratio of Pt(111) / Pt(200) determined by X-ray diffraction (XRD) is 2.5 to 3.0. If the intensity ratio of Pt(111) / Pt(200) is 2.5 to 3.0, the proportion of highly active (111) faces in the platinum nanostructure is high, and the highly active platinum nanostructure is supported on the porous silicon carbide composite material, thereby resulting in excellent activity and durability of the platinum catalyst. The intensity ratio of Pt(111) / Pt(200) 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 intensity ratio of Pt(111) / Pt(200) obtained by X-ray diffraction (XRD) is the ratio of the height of the peak of the (111) plane of the crystal structure belonging to the platinum nanostructure to the height of the peak of the (200) plane belonging to the crystal structure.

[0082] The platinum nanostructure is composed of platinum-containing particles, and platinum nanoparticles are particularly preferred. The average diameter of the primary particles of the aforementioned platinum-containing particles is not particularly limited, but is preferably 2 nm or more and 10 nm or less, more preferably 2.5 nm or more and 7 nm or less, and even more preferably 3 nm or more and 5 nm or less. Within the above ranges, good catalytic performance can be achieved using a small amount of platinum.

[0083] Figure 2 It means Figure 1 An enlarged view of an example of the composition of platinum nanostructures 20 supported on a porous silicon carbide composite material 10 of platinum catalyst 1. Figure 1 As shown, the platinum nanostructure 20 has a connecting structure formed by partially connecting multiple adjacent platinum nanoparticles 21, 21, ... More specifically, the platinum nanostructure 20, having a connecting structure formed by one-dimensionally connecting multiple platinum nanoparticles 21, 21, ..., is loaded as a unit onto the porous silicon carbide composite material 10. Thus, the configuration of the present invention differs from the configuration where platinum nanoparticles 21 are loaded as a unit onto the porous silicon carbide composite material. Figure 1 In this embodiment, the platinum nanostructure 20 has a connection structure formed by one-dimensionally connecting multiple adjacent platinum nanoparticles 21, 21, ..., but is not limited to this; it may also have a connection structure formed by connecting multiple adjacent platinum nanoparticles 21, 21, ... and branching in multiple directions. It should be noted that the above-mentioned platinum nanostructure is a structure supported on silicon carbide or carbon material in a porous silicon carbide composite material. From the viewpoint of good catalytic performance, it is more preferable to support it on silicon carbide material.

[0084] Platinum nanostructures are typically elongated particles with long and short sides. The long side dimension of the platinum nanostructure is, for example, 4 nm or more and 20 nm or less, and the short side dimension is, for example, 2 nm or more and 5 nm or less. If the long side dimension of the platinum nanostructure is 4 nm or more and 20 nm or less, and the short side dimension is 2 nm or more and 5 nm or less, it helps to increase the proportion of the highly active (111) facets in the platinum nanostructure, improving the activity of the platinum catalyst. Furthermore, the platinum nanostructure acts as a bridge between silicon carbide and carbon, thereby further improving durability. The long side dimension of the platinum nanostructure can be 4 nm or more and 20 nm or less, 10 nm or more and 20 nm or less, or 15 nm or more and 20 nm or less. Additionally, the short side dimension of the platinum nanostructure can be 2 nm or more and 4 nm or less, or 2 nm or more and 3 nm or less.

[0085] In addition, the ratio of the long side dimension to the short side dimension of the platinum nanostructure can be 1.5~10, 3~10, or 5~10.

[0086] The dimensions of the platinum nanostructures along the long and short sides can be calculated from transmission electron microscope images.

[0087] There is no particular limitation on the number of platinum nanoparticles constituting the platinum nanostructure, as long as the intensity ratio of Pt(111) / Pt(200) is within the desired range. Preferably, there are two or more, and more preferably three or more.

[0088] <Methods for manufacturing platinum catalysts>

[0089] like Figure 3 As shown, the method for manufacturing the porous silicon carbide composite material of this embodiment includes: a gel formation step (step (A)), a cleaning step (step (B)), a porous silicon carbide precursor formation step (step (C)), a calcination step (step (D)), a mixing step (step (E)), and a heat treatment step (step (F)). It should be noted that, provided that the platinum catalyst of this embodiment is obtained, other steps besides those described above may be added before or after each step.

[0090] [Process (A)]

[0091] In step (A), for example, an organoalkoxysilane is added to an acidic aqueous solution containing a surfactant and a pH adjuster, and a gel is formed through a sol-gel reaction of the organoalkoxysilane. For example, a hydrolysate is generated from the hydrolysis of a hydrolyzable organoalkoxysilane, and the pH of the reaction system is further increased to carry out a polycondensation reaction of the organoalkoxysilane, thereby obtaining a polysilsesquioxane. The suitable pH for the polycondensation reaction varies depending on the isoelectric point of the organoalkoxysilane used, but if the pH is too high, the reaction efficiency may decrease, and gel formation may become difficult. This sol-gel reaction is preferably carried out at a temperature of 25°C or higher and 80°C or lower, more preferably at 30°C or higher and 70°C or lower, and even more preferably at 40°C or higher and 60°C or lower. Thus, a polysilsesquioxane can be obtained in the form of a wetted gel containing water as a solvent within its interior.

[0092] The content of the surfactant relative to 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.

[0093] There are no particular limitations on the surfactant used; examples include nonionic and / or cationic surfactants. By appropriately selecting and using either or both of nonionic and cationic surfactants as the surfactant, the desired BET specific surface area and pore size can be obtained. Examples of nonionic surfactants include polyethylene glycol type (ether type, ester / ether type), polyol type, etc. Examples of polyethylene glycol type nonionic surfactants include Pluronic (registered trademark) type. Examples of cationic surfactants include amine salt type, quaternary ammonium salt type, etc. By making the surfactant content relative to the acidic aqueous solution 0.1% by mass or more and 50% by mass or less, a porous polysilsesquioxane gel with well-developed mesopores and a large BET specific surface area can be formed.

[0094] The content of the pH adjuster relative to 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 relative to the acidic aqueous solution to 5% by mass or more and 50% by mass or less, a porous polysilsesquioxane gel with high skeletal strength and flexibility can be formed.

[0095] There are no particular limitations on its use as a pH adjuster; for example, any substance selected from urea, ammonia, and sodium hydroxide can be included.

[0096] There are no particular limitations on the above-mentioned acidic aqueous solutions; examples include aqueous solutions of hydrochloric acid, nitric acid, acetic acid, etc.

[0097] The aforementioned organoalkoxysilanes are preferably represented by the following formula (1) or formula (2). By using the organoalkoxysilanes shown in the following formula (1) or formula (2), porous silicon carbide with the desired three-dimensional framework structure can be readily formed.

[0098] R 1 -SiR 2 x (OR) 3 ) 3-x …(1)

[0099] (where R) 1 R is any group selected from methyl, ethyl, vinyl, and phenyl. 2 R represents methyl. 3 This represents methyl or ethyl. The integer x in the formula is 0 or 1.

[0100] R 4 -(SiR) 5 y (OR) 6 )3-y )twenty two)

[0101] (where R) 4 Contains any group selected from methylene, ethylene, hexylene, vinylene, phenylene, and biphenylene, R 5 R represents methyl. 6 This represents methyl or ethyl. The integer y in the formula is 0 or 1.

[0102] Specific examples of the organoalkoxysilanes represented by formula (1) above include methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, methylethyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, methylvinyldimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, and methylphenyldimethoxysilane. In addition, as specific examples of the organoalkoxysilanes shown in formula (2) above, 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, 1,6-bis(methyldiethoxysilyl)methane, 1,6-bis(methyldiethoxysilyl)hexane ... The following are ethylene derivatives: silyl hexane, 1,2-bis(trimethoxysilyl)ethylene, 1,2-bis(triethoxysilyl)ethylene, 1,2-bis(methyldimethoxysilyl)ethylene, 1,2-bis(methyldiethoxysilyl)ethylene, 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, 4,4'-bis(methyldiethoxysilyl)biphenyl. Cis / trans geometric isomers exist among the above ethylene derivatives, but any isomer can be used.

[0103] In step (A), carbon materials or organic polymers are further added to the aforementioned acidic aqueous solution to form a gel containing carbon materials or organic polymers. By adding carbon materials or organic polymers to the sol-gel reaction of alkoxysilanes, the precursor formed in step (C) can be sintered in step (D) to allow carbon materials to be arranged at the nanoscale within a porous three-dimensional framework structure, thus imparting excellent conductivity to porous silicon carbide, which is originally an insulator or semiconductor. The organic polymer undergoes thermal decomposition during sintering in step (D), remaining in the porous silicon carbide in the form of low-crystallinity nano-carbon, thereby imparting conductivity.

[0104] In step (A) above, it is preferable to add the carbon material or organic polymer to the acidic aqueous solution in a mass ratio of carbon material or organic polymer to organoalkoxysilane of 2.5 to 50: 97.5 to 50. More preferably, the mass ratio of carbon material or organic polymer to organoalkoxysilane is 3 to 30: 97 to 70, and even more preferably 5 to 20: 95 to 80. By setting the mass ratio of carbon material or organic polymer to organoalkoxysilane within the above range, a larger BET specific surface area and higher conductivity can be achieved. When the amount of carbon material or organic polymer added is less than or equal to the amount of organoalkoxysilane added, separation from the sol-gel reaction system can be suppressed, promoting gel formation containing polysilsesquioxane.

[0105] There are no particular limitations on the carbon material; for example, it can be composed of one or more selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystallinity nanocarbon. Among these, carbon black is preferred from the viewpoints of achieving high conductivity and manufacturability.

[0106] There are no particular limitations on the organic polymer; for example, it can be composed of one or more selected from phenolic resins, polystyrene, and polyvinylbenzene.

[0107] [Process (B)]

[0108] In step (B), the gel obtained in step (A) is washed with alcohol. There are no particular limitations on the alcohol used for washing; examples include methanol, ethanol, 1-propanol, and 2-propanol. This removes unwanted surfactants from the acidic aqueous solution and replaces the water in the solution with alcohol. Furthermore, after washing with alcohol, it can be further replaced with hydrocarbon solvents such as hexane or heptane. In this step (B), water, a high surface tension solvent, is replaced with alcohol or hydrocarbon solvents, which are low surface tension solvents. This process suppresses network shrinkage during the drying process at room temperature and pressure in step (C) described later, facilitating the formation of a porous gel structure.

[0109] [Process (C)]

[0110] In step (C), the cleaned 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 temperatures above 20°C and below 80°C. Considering the advantages of low manufacturing cost and obtaining a high-density, mesoporous porous silicon carbide precursor with high skeletal strength and flexibility, the method of drying at room temperature and atmospheric pressure is preferred.

[0111] [Process (D)]

[0112] In step (D), the porous silicon carbide precursor containing the aforementioned carbon material or organic polymer is sintered to obtain a porous silicon carbide composite material. In this step, carbon atoms are supplied by the organic groups of polysilsesquioxane through sintering, forming a silicon carbide framework via a carbothermic reduction reaction. Simultaneously, carbon atoms are supplied to the framework by carbon materials or organic polymers dispersed at the nanoscale in the gel. The organic polymer undergoes thermal decomposition during sintering, remaining in the porous silicon carbide as low-crystallinity nanocarbon.

[0113] Firing can be carried out using known and conventional methods without particular limitations. For example, firing can be performed by increasing the temperature at 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 or higher and 3000°C or lower, more preferably 1350°C or higher and 2500°C or lower, and particularly preferably 1400°C or higher and 2000°C or lower. The duration of maintaining the maximum temperature can be appropriately determined based on the effective time for obtaining the porous silicon carbide composite material. As an example, it is preferably 5 minutes to 16 hours, more preferably 10 minutes to 10 hours, and particularly preferably 30 minutes to 3 hours. Firing can be performed in two or more stages. That is, in the first stage, firing can be carried out at a temperature lower than the maximum reached temperature for a certain period of time, followed by a second heating for firing. Firing can be performed at atmospheric pressure.

[0114] Examples of inert gases include nitrogen, helium, and argon. It should be noted that these inert gases may include reducing gases such as hydrogen.

[0115] Firing can be carried out in a carbonization furnace with a fixed bed or fluidized bed configuration. As long as the furnace has the function of heating to a specified temperature, there are no particular limitations on the heating method and type of carbonization furnace. Examples of carbonization furnaces include: Riedhammer furnace, tunnel furnace, and stand-alone furnace.

[0116] In this step (D), carbon materials or organic polymers may be further mixed into the porous silicon carbide precursor, and the mixture may be calcined. In the case of mixing organic polymers into the porous silicon carbide precursor in step (D), the process is the same as in step (A), where thermal decomposition occurs through calcination, and the polymer is retained in the porous silicon carbide in the form of low-crystallinity nano-carbon.

[0117] [Process (E)]

[0118] In step (E), a mixture is obtained by mixing a dispersion containing a platinum nanoparticle colloid and hydrogen peroxide water with the porous silicon carbide composite material. The platinum nanoparticle colloid is a colloid in which platinum nanoparticles are dispersed in a liquid, and the dispersion containing the platinum nanoparticle colloid is a solution containing the aforementioned platinum nanoparticle colloid and hydrogen peroxide water. Both the platinum nanoparticle colloid and the dispersion containing the platinum nanoparticle colloid and hydrogen peroxide water can be prepared by conventionally known methods.

[0119] Regarding the mixing ratio of the dispersion containing platinum nanoparticles and the porous silicon carbide composite material, it is preferred, for example, that the mass of the loaded platinum nanoparticles relative to the total mass of the platinum catalyst is 10% or more and 60% or less by mass, more preferably 20% or more and 55% or less by mass, and even more preferably 30% or more and 50% or less by mass.

[0120] In this step (E), if the mixture of a colloid containing platinum nanoparticles and a dispersion of hydrogen peroxide water with a porous silicon carbide composite material is stirred, the colloid containing platinum nanoparticles is loaded onto the porous silicon carbide composite material, resulting in a platinum catalyst containing platinum nanoparticles. If left for a predetermined time, the solid and liquid phases separate. From the viewpoint of promoting solid-liquid separation, the mixture can be cooled. Furthermore, the solid components can be cleaned using known and conventional methods and conditions. There are no particular limitations on the cleaning solution used; for example, water is preferred, but ultrapure water is preferred. This removes chloride ions and other ions from the solid components.

[0121] [Process (F)]

[0122] 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, multiple platinum nanoparticles supported on the porous silicon carbide composite material are interconnected in a one-dimensional manner, and the highly active Pt(111) facet increases, resulting in a platinum catalyst with a high Pt(111) / Pt(200) strength ratio. The concentration of hydrogen in the nitrogen / hydrogen mixture used to form the nitrogen and hydrogen atmosphere is preferably set to, for example, 0.5 vol% to 4 vol%, more preferably 1 vol% to 4 vol%.

[0123] 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. If the mixture is heat-treated at a temperature of 25°C or higher and 800°C or lower in an atmosphere of nitrogen and hydrogen, the platinum nanoparticles are more easily bonded together, and the strength ratio of Pt(111) / Pt(200) can be further improved. Other conditions for heat treatment include heating at a rate of 1°C / min to 20°C / min and maintaining the highest temperature reached for a certain period of time. The maintenance time for this heat treatment temperature can be set, for example, to 0 to 3 hours.

[0124] [Process (G)]

[0125] After step (E) and before step (F), there may be a step (G) in which the mixture is heat-treated in a nitrogen atmosphere. As the first stage of heat treatment, the mixture is heat-treated in a nitrogen atmosphere, and then as the second stage of heat treatment, it is heat-treated in a nitrogen and hydrogen atmosphere, thereby further increasing the highly active Pt (111) surface and further improving the Pt (111) / Pt (200) strength ratio.

[0126] 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. If the mixture is heat-treated at a temperature of 100°C or higher and 800°C or lower under a nitrogen atmosphere, the platinum nanoparticles are more easily linked together, and the strength ratio of Pt(111) / Pt(200) can be further improved. Other heat treatment conditions include heating at a rate of 1°C / min to 20°C / min and maintaining the highest temperature reached for a certain period of time. The maintenance time of this heat treatment temperature can be set, for example, from 0 minutes to 3 hours.

[0127] [Catalyst Electrode and Fuel Cell]

[0128] The catalyst electrode of this embodiment has a catalyst layer comprising the aforementioned platinum catalyst. The application of the catalyst electrode is not limited; for example, it can be used as an electrode for a fuel cell. The catalyst electrode typically has the aforementioned platinum catalyst layer and a gas diffusion layer. The catalyst electrode can be a negative electrode (anode) or a positive electrode (cathode) for a fuel cell. When the catalyst electrode is a negative electrode for a fuel cell, it has, for example, an anode catalyst layer supplied with fuel such as hydrogen and a first gas diffusion layer. When the catalyst electrode is a positive electrode for a fuel cell, it has, for example, a cathode catalyst layer supplied with oxygen-containing gas such as air and a second gas diffusion layer.

[0129] Furthermore, the fuel cell of this embodiment includes the aforementioned catalyst electrode. The fuel cell includes a catalyst electrode and an electrolyte layer. Typically, the fuel cell includes: a negative electrode (anode) for a fuel cell, a positive electrode (cathode) for a fuel cell, an electrolyte layer disposed therebetween, a first separator disposed on the side of the negative electrode opposite to the electrolyte layer, and a second separator disposed on the side of the positive electrode opposite to the electrolyte layer. In this case, the anode catalyst layer is disposed between the electrolyte layer and the first gas diffusion layer, and the cathode catalyst layer is disposed between the electrolyte layer and the second gas diffusion layer.

[0130] Based on the aforementioned catalyst electrode and fuel cell, since it has a catalyst layer containing the aforementioned platinum catalyst, the platinum nanostructure of the porous silicon carbide composite material supported on the platinum catalyst can achieve high activity and high durability. Furthermore, by configuring carbon materials at the nanoscale within the porous three-dimensional framework structure of silicon carbide, the possibility of oxidative degradation of the carbon materials under high temperature / high humidity environments, a previous problem, can be reduced, thus achieving excellent durability as both a catalyst electrode and a fuel cell.

[0131] Example

[0132] The embodiments of the present invention will be described below. The present invention is not limited to the embodiments shown below.

[0133] (Example 1)

[0134] Synthesis of porous silicon carbide composite materials

[0135] 6 g of 5 mM acetic acid aqueous solution (manufactured by Kanto Chemical Co., Ltd.), 0.8 g of Pluronic F-127 (manufactured by BASF), 0.5 g of urea (manufactured by Kanto Chemical Co., Ltd.), and 0.24 g of Ketjen Black (manufactured by Lion Specialty Chemicals, product name "ECP-600JD") were placed in a vial and stirred at room temperature for 10 minutes. Then, 5 g of methyltrimethoxysilane (manufactured by Kanto Chemical Co., Ltd.) was added, and the mixture was stirred at room temperature for 30 minutes. The mixture was then reacted at 60°C for 4 days to obtain a wetted gel. The wetted gel was washed with methanol (manufactured by Kanto Chemical Co., Ltd.), 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. The porous silicon carbide precursor (1g) and Ketjen Black (ECP) (0.4g) were mixed and placed in a tubular furnace. The mixture was then sintered under an argon atmosphere at a heating rate of 2.5℃ / min to 1500℃ and held for 2 hours to obtain the porous silicon carbide composite material.

[0136] Synthesis of platinum catalysts containing platinum nanoparticles

[0137] 0.43 g of chloroplatinic acid hexahydrate was dissolved in 60 mL of ultrapure water. After reduction by adding 3.1 g of sodium bisulfite, 280 mL of ultrapure water was added for dilution. Next, a 5% sodium hydroxide aqueous solution was added, and while adjusting the pH to approximately 5, 24 mL of 35% hydrogen peroxide was added dropwise to obtain a dispersion containing platinum colloids. The colloidal dispersion was then separated such that the amount of loaded platinum (Pt) relative to the total amount of platinum catalyst including the support was 45% by mass. 0.4 g of porous silicon carbide composite material was added as a support, and the mixture was stirred at 90 °C for 3 hours. After cooling, solid-liquid separation was performed. To remove chloride ions from the resulting powder (solid component), it was thoroughly washed with ultrapure water and then dried at 80 °C for 12 hours under atmospheric conditions to obtain a platinum catalyst precursor with platinum oxide supported on the surface of a porous silicon carbide composite material.

[0138] The platinum catalyst precursor obtained above was placed in an alumina boat and heated at 10 °C / min under a nitrogen gas flow, held at 300 °C for 2 hours, and then cooled to room temperature. Then, under a nitrogen and hydrogen gas flow (hydrogen concentration in the mixed gas: 1 vol%), the temperature was increased at 10 °C / min and held at 100 °C for 2 hours, and then cooled to room temperature to obtain platinum catalyst A.

[0139] (Example 2)

[0140] After synthesizing the platinum catalyst precursor, without heat treatment under a nitrogen gas flow, the temperature was increased at 10°C / min under a nitrogen and hydrogen gas flow (hydrogen concentration in the mixed gas: 1% by volume) and held at 100°C for 2 hours. Otherwise, the same process as in Example 1 was followed to synthesize platinum catalyst B.

[0141] (Example 3)

[0142] Platinum catalyst C was prepared in the same manner as in Example 1, except that the amount of supported platinum (Pt) was 30% by mass relative to the total amount of platinum catalyst containing the support.

[0143] (Comparative Example 1)

[0144] After synthesizing the platinum catalyst precursor, heat treatment was performed only as follows: heating was carried out under a nitrogen gas flow at 10°C / min and held at 300°C for 2 hours, without heat treatment under a nitrogen and hydrogen gas flow. Otherwise, the process was carried out in the same manner as in Example 1 to obtain platinum catalyst D.

[0145] (Comparative Example 2)

[0146] Platinum catalyst E was prepared in the same manner as in Example 1, except that the amount of supported platinum (Pt) was 17% by mass relative to the total amount of platinum catalyst containing the support.

[0147] (Comparative Example 3)

[0148] The carrier was changed to Ketjen Black (manufactured by Lion Specialty Chemicals, product name "CarbonECP"), and Pt was loaded and heat-treated in the same manner as in Example 1.

[0149] (Comparative Example 4)

[0150] As a catalyst, carbon black (Pt / CB) supported on platinum (Pt) was obtained (TEC10E50E, manufactured by Tanaka Precious Metals Industry).

[0151] The above Examples 1-3 and Comparative Examples 1-4 were measured using the following methods.

[0152] [Determination of Pt Loading]

[0153] The platinum catalyst was alkali-fused using anhydrous sodium carbonate and sodium peroxide, dissolved in aqua regia, diluted to a specified concentration with ultrapure water, and then calculated using high-frequency induction heating luminescence spectrophotometry (ICP; Shimadzu ICPE-9820 model).

[0154] [Evaluation of Catalytic Performance Using Rotating Electrodes]

[0155] (Electrode fabrication)

[0156] A glassy carbon (GC) electrode with a diameter of 5 mm was ground using an alumina paste, followed by ultrasonic cleaning with ultrapure water. Platinum catalyst A was added to a 99% (v / v) aqueous ethanol solution and dispersed using an ultrasonic homogenizer. This was then dropped onto a GC plate and dried at room temperature for 12 hours. After drying, a 5% Nafion (registered trademark) solution was added dropwise to the platinum catalyst on the GC plate to achieve a dry film thickness of 50 nm, and the film was dried at room temperature for another 12 hours.

[0157] (CV measurement)

[0158] Electrode evaluation was performed using an electrochemical measurement system (HZ-5000, manufactured by Beidou Electric Co., Ltd.). After purging with nitrogen gas for 30 minutes using 0.1M perchloric acid aqueous solution, a reversible hydrogen electrode (RHE) was used as the reference electrode, and 50 cleaning cycles were performed at a potential range of 0.05–1.2 V and a scan rate of 150 mV / s. Cyclic voltammetry (CV) was then performed at a potential range of 0.05–1.0 V and a scan rate of 100 mV / s. Analysis of the electrochemically active surface area (ECSA) was performed using hydrogen adsorption waves appearing below 0.4 V.

[0159] (Oxygen Reduction Activity Evaluation)

[0160] After purging the electrolyte with oxygen for more than 1 hour, linear sweep voltammetry (LSV) was performed. At a temperature of 25°C, a potential range of 0.25–1.00 V, and a scan rate of 5 mV / s, the rotational speed was increased from 1000 rpm to 2750 rpm in 250 rpm increments, and data were obtained under a total of 8 conditions. The results were analyzed using Koutecky-Levich plots to obtain the mass activity (A / g-Pt) value at 0.85 V.

[0161] (Start-up / Stop Durability Evaluation)

[0162] After purging the electrolyte with nitrogen for 30 minutes, the electrolyte was scanned 500 times within a potential range of 1.0–1.5 V, and the CV was measured within a potential range of 0.05–1.0 V. This measurement procedure was used as one group, and the experiment was performed for 56,000 cycles. The results are shown in Table 1.

[0163] [Table 1]

[0164]

[0165] Transmission electron microscope images of platinum catalyst A obtained in Example 1 are shown below. Figure 4 (A) A transmission electron microscope image of platinum catalyst B obtained in Example 2 is shown in (A). Figure 4(B) A transmission electron microscope image of the platinum catalyst E obtained in Comparative Example 2 is shown in (B). Figure 4 (C) A transmission electron microscope image of the platinum catalyst F obtained in Comparative Example 3 is shown in (C). Figure 4 (D). Additionally, secondary electron images of platinum catalyst A obtained in Example 1, obtained through scanning transmission electron microscopy, are shown in [the image / image / etc.]. Figure 5 (A) shows the transmission electron image. Figure 5 (B) In Examples 1 and 2, it was confirmed that elongated platinum nanostructures were loaded onto porous silicon carbide composite materials. Furthermore, it was confirmed that the elongated platinum nanostructures had a connecting structure formed by multiple platinum nanoparticles. On the other hand, in Comparative Example 2, it was confirmed that platinum nanoparticles were loaded onto porous silicon carbide composite materials. Additionally, in Comparative Example 3, it was confirmed that aggregates of platinum nanoparticles were loaded onto carbon black along with the platinum nanoparticles.

[0166] Furthermore, as shown in Table 1, in Examples 1-3, the loading of platinum nanostructures in platinum catalysts A-C was 30-45% by mass, the intensity ratio of Pt(111) / Pt(200) was 2.5-2.8, the mass activity was above 600 (A / g-Pt), the current per unit mass of platinum (Pt) was high, and the area ratio activity was 9.8 μA / cm². 2 The above demonstrates high oxygen reduction activity. Furthermore, it can be seen that the ECSA retention rate in Examples 1-3 is 83-87%, exhibiting excellent durability.

[0167] On the other hand, in Comparative Example 1, the Pt(111) / Pt(200) intensity ratio in platinum catalyst D was not detected, the mass activity was 330 (A / g-Pt), and the area ratio activity was 6.6 μA / cm². 2 The ECSA retention rate was 79%, indicating poor activity and durability.

[0168] In Comparative Example 2, the platinum catalyst E had a platinum loading of 17% by mass, a Pt(111) / Pt(200) strength ratio of 2.3, a mass activity of 450 (A / g-Pt), and an area specificity activity of 6.4 μA / cm². 2 The ECSA retention rate was 76%, indicating poor activity and durability.

[0169] In Comparative Example 3, the platinum catalyst F had a platinum loading of 51% by mass, a Pt(111) / Pt(200) strength ratio of 2.4, a mass activity of 550 (A / g-Pt), and an area specificity activity of 8.0 μA / cm². 2 The ECSA retention rate was 56%, indicating poor activity and durability.

[0170] In Comparative Example 4, the platinum loading in Pt / CB was 46% by mass, and the intensity ratio of Pt(111) / Pt(200) was 2.1, with a mass activity of 420 (A / g-Pt) and an area specificity activity of 5.9 μA / cm². 2 The ECSA retention rate was 55%, indicating poor activity and durability.

[0171] (Example 4)

[0172] [Fabrication of a single fuel cell]

[0173] (Preparation of anode catalyst ink)

[0174] Carbon black (Pt / CB, Tanaka Precious Metals, TEC10E50E, 46wt% Pt loading) loaded with 0.45g platinum (Pt) and a polymer electrolyte (DuPont, Nafion DE521) were mixed at a volume ratio of 1.0. This mixture, along with 2.5g ethanol, 2g water, and zirconia balls (5mm in diameter), was placed in a zirconia jar and mixed for 60 minutes using a planetary ball mill (Fritsch P-6). The mixture obtained from this ball milling process will be referred to as the anode catalyst ink.

[0175] (Fabrication of cathode catalyst ink)

[0176] Platinum catalyst A was mixed with a polymeric electrolyte (DuPont, Nafion DE521) at a volume ratio of 0.7. This mixture was then placed in a zirconia jar with 2.5 g of ethanol, 2 g of water, and zirconia balls (5 mm in diameter). The mixture was then mixed for 60 minutes using a planetary ball mill (Fritsch P-6).

[0177] (Fabrication of membrane electrode assembly (MEA))

[0178] Regarding the anode and cathode catalyst layers, a spray coating apparatus (manufactured by Energy Technology Co., Ltd.) was used on a polymer electrolyte membrane (manufactured by DuPont, Nafion NR212) with a platinum unit area weight of 0.5 mg / cm² at the anode. 2 The platinum content per unit area of ​​the cathode is 0.3 mg / cm². 2 The anode catalyst ink and cathode catalyst ink are coated separately in different ways.

[0179] The fuel cell electrode membrane (CCM), which consists of an anode catalyst layer or a cathode catalyst layer and a polymer electrolyte membrane, is hot-pressed for 3 minutes (140°C, 2.86kN) using a hot press (TCMD-2.5 manufactured by Toho Kogyo Co., Ltd.).

[0180] In the above CCM, a gas diffusion layer (GDL, SGL, 22BB) is overlapped on both sides of each catalyst layer to obtain a membrane electrode assembly (MEA) in which the cathode catalyst layer and the anode catalyst layer are stacked opposite each other on the polymer electrolyte membrane.

[0181] The above-mentioned MEA was used to assemble a single cell, which was then installed on a power generation evaluation device (manufactured by Panasonic Production Technology).

[0182] (Comparative Example 5)

[0183] The cathode catalyst was changed to platinum catalyst E, and the fuel cell was fabricated in the same manner as in Example 4.

[0184] For Example 4 and Comparative Example 5 above, the measurements were performed using the following methods.

[0185] [Evaluation of a Single Fuel Cell]

[0186] (CV measurement)

[0187] Hydrogen gas was supplied to the anode side of the single cell obtained in Example 4, and the gas was blocked at the cathode side. CV measurements were performed within a potential range of 0.05–1.0 V, and the results are presented below. Figure 6 Furthermore, the platinum catalysts were prepared with the amount of supported platinum (Pt) relative to the total amount of the supported platinum catalyst being 17%, 25%, 37%, 41%, and 51% by mass. Otherwise, they were synthesized in the same manner as in Example 1, and the CV measurement results of each obtained platinum catalyst are shown in the same figure. The results confirmed that when the Pt loading was 30% by mass or more, the ratio of the peak intensity of Pt(100) to the peak intensity of Pt(110) (the intensity ratio of Pt(100) / Pt(110)) decreased. Additionally, the change in electrochemically active surface area (ECSA) relative to the platinum loading is shown in... Figure 7 It can be seen that the ECSA tends to decrease with a Pt loading of around 30% by mass. From the above, it can be seen that when the Pt loading is above 30% by mass, the Pt (100) planes are connected to each other to form Pt nanostructures.

[0188] (Measurement of IV characteristics and battery resistance)

[0189] Hydrogen was supplied to the anode side of the single cell obtained in Example 4, and oxygen was supplied to the cathode side. The flow rates were set to achieve a hydrogen utilization rate of 70% and an oxygen utilization rate of 40%. The anode and cathode gases were humidified using external humidifiers 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 to a relative humidity of 80% RH. Power generation was conducted within an applied current range where the voltage of the single cell was not lower than 0.4V, and the power generation performance was evaluated. A Tafel plot was constructed from the obtained data, and 1.0 A / cm² was calculated. 2 The activation overvoltage was determined. The results are shown in Table 2.

[0190] [Table 2]

[0191]

[0192] As shown in Table 2, in Example 4, when platinum catalyst A is used as the cathode electrode, the activation overvoltage is 0.38V, the energy loss is small, and it shows better battery performance as a single cell of fuel cell.

[0193] On the other hand, in Comparative Example 5, when platinum catalyst E was used as the cathode electrode, the activation overvoltage was 0.41V, resulting in large energy loss and poor cell performance as a single cell in a fuel cell.

[0194] Industrial availability

[0195] The platinum catalyst of this embodiment exhibits excellent activity and durability, making it suitable as an electrode material for use in the catalyst layer of a catalyst electrode. In particular, it is extremely useful as a fuel cell for commercial vehicles where multi-purpose applications are expected, as it can withstand a wide operating temperature range from conventional temperatures (around 70°C) to high temperatures (above 120°C) while maintaining both power generation performance and durability.

[0196] Explanation of reference numerals in the attached figures

[0197] 1. Platinum catalyst

[0198] 10 Porous silicon carbide composite materials

[0199] 11 Silicon Carbide Materials

[0200] 12 Carbon materials

[0201] 20 Platinum Nanostructures

[0202] 21 Platinum nanoparticles

Claims

1. A platinum catalyst comprising a porous silicon carbide composite material and platinum nanostructures supported on the porous silicon carbide composite material, wherein the porous silicon carbide composite material comprises silicon carbide material containing SiC as the main component and carbon material. When the total mass of the platinum catalyst is set to 100% by mass, the loading of the platinum nanostructure is 30-60% by mass. The intensity ratio of Pt(111) / Pt(200) obtained by X-ray diffraction (XRD) is 2.5~3.

0.

2. The platinum catalyst according to claim 1, wherein, The platinum nanostructure has a connection structure formed by the partial connection of multiple adjacent platinum nanoparticles.

3. The platinum catalyst according to claim 2, wherein, The platinum nanostructure has a long side dimension of 4 nm or more and 20 nm or less, and a short side dimension of 2 nm or more and 5 nm or less.

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

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

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

7. A fuel cell comprising the catalyst electrode of claim 6.

8. A method for manufacturing a platinum catalyst, comprising: Step (A) involves adding an organoalkoxysilane to an acidic aqueous solution containing a surfactant and a pH adjuster, and further adding a carbon material or an organic polymer, thereby forming a gel containing the carbon material or the organic polymer through a sol-gel reaction of the organoalkoxysilane. Step (B): Wash the gel with alcohol; Step (C) involves drying the cleaned gel to form a porous silicon carbide precursor. Step (D) involves sintering the porous silicon carbide precursor to obtain a porous silicon carbide composite material, wherein the porous silicon carbide composite material comprises silicon carbide material containing SiC as the main component and carbon material. Step (E) involves mixing a dispersion containing platinum nanoparticles and hydrogen peroxide with the porous silicon carbide composite material to obtain a mixture; and Step (F) involves heat-treating the mixture under a nitrogen and hydrogen atmosphere to obtain a platinum catalyst containing platinum nanoparticles.

9. The method for manufacturing the platinum catalyst according to claim 8, wherein, In the process (F), the mixture is heat-treated at a temperature above 25°C and below 800°C.

10. The method for manufacturing the platinum catalyst according to claim 8, wherein, After step (E) and before step (F), there is a step (G) in which the mixture is heat-treated in a nitrogen atmosphere.

11. The method for manufacturing the platinum catalyst according to claim 10, wherein, In the process (G), the mixture is heat-treated at a temperature above 100°C and below 800°C.

12. The method for manufacturing the platinum catalyst according to claim 8, wherein, The organoalkoxysilane is represented by the following formula (1) or formula (2), R 1 -SiR 2 x (OR 3 ) 3-x …(1) In equation (1), R 1 R is any group selected from methyl, ethyl, vinyl, and phenyl. 2 R represents methyl. 3 To represent methyl or ethyl, the integer x in the formula is 0 or 1. R 4 -(SiR 5 y (OR 6 ) 3-y )2 …(2) In equation (2), R 4 Contains any group selected from methylene, ethylene, hexylene, vinylene, phenylene, and biphenylene, R 5 R represents methyl. 6 This indicates methyl or ethyl, where the integer y is 0 or 1.

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

Images