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

Abstract

This electrode catalyst comprises: a porous silicon carbide composite material that contains silicon carbide (SiC) and a carbon material; particles that are supported by the porous silicon carbide composite material and contain a noble metal; and a domain that is formed in a portion of the porous silicon carbide composite material and comprises a silicon oxide, wherein the BET specific surface area is 10 m 2 / g or more, and the conductivity is 0.1 S / cm or more.

Description

[Technical Field]

[0001] The present invention relates to an electrode catalyst containing a porous silicon carbide composite material, an electrode for the electrode catalyst, a fuel cell, and a method for producing the electrode catalyst. This application claims priority based on Japanese Patent Application No. 2023-041007, filed on March 15, 2023, the contents of which are incorporated herein by reference. [Background technology]

[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 that forms the anode (fuel electrode) on one side of a solid polymer electrolyte membrane and the cathode (air electrode) on the other side is provided, with a gas diffusion layer bonded to the outside of each catalyst layer. The catalyst layer is made 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. For example, Patent Document 1 describes C / SiC composite particles in which SiC particles are distributed on the inner wall surfaces of the pores of porous carbon particles, which are said to suppress electrolyte degradation. However, the catalyst activity retention rate (durability) is evaluated under low-load conditions, and durability under high-load conditions has not been fully studied. Therefore, deterioration of catalytic performance due to corrosion of the carbon support remains a major problem in the cathode and anode. Therefore, there is an urgent need to develop a material that has a high specific surface area, high conductivity, and excellent durability to replace carbon.

[0004] For example, Patent Document 2 discloses an electrode catalyst comprising (A) Group 13-doped SiC, which is SiC 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, aluminum (Al), and the doping amount of the Group 13 element 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.

[0005] Patent Document 3 discloses noble metal-supported silicon carbide particles having a silicon oxide layer on the surface of silicon carbide particles having an average primary particle diameter of 0.005 μm to 5 μm, on which noble metal particles are supported. The specific surface area of ​​the silicon carbide particles is 1.0 m 2 / g~400m 2 It is said to be / g. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2023-9699 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-149008 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-093756 Summary of the Invention [Problem to be solved by the invention]

[0007] Fuel cell electrodes that achieve high efficiency and high output require durable electrode catalysts that simultaneously satisfy the requirements of a large specific surface area and high electrical conductivity. However, while Patent Document 2 describes an electrode catalyst that contains silicon carbide particles with a noble metal supported on the surface and conductive carbon particles to impart electrical conductivity, it makes no mention of durability, leaving room for improvement. In particular, there is a need for electrode catalysts that can exhibit high durability even during start-stop cycles, which are the most susceptible to deterioration under the power generation conditions of fuel cells.

[0008] The above-mentioned Patent Document 3 describes precious metal-supported silicon carbide particles having a silicon oxide layer on the surface of silicon carbide supporting precious metal particles, but does not mention that the silicon carbide particles are porous, nor does it mention their electrical conductivity.

[0009] The object of the present invention is to provide an electrode catalyst that achieves high conductivity while maintaining a large BET specific surface area and also has excellent durability, and to provide a method for producing an electrode catalyst using an organic alkoxysilane of the type that is widely distributed as an industrial raw material. [Means for solving the problem]

[0010] To achieve the above objective, the present inventors discovered that a precursor gel is produced by coexisting a carbon material or organic polymer as a carbon source during the sol-gel reaction of an organic alkoxysilane solution in the presence of a surfactant, while taking care not to interfere with the formation of the porous gel. The precursor gel is then calcined 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 nanometer level within the porous three-dimensional framework. Furthermore, they discovered that mixing a porous silicon carbide composite with a dispersion containing a noble metal colloid results in the formation of silicon oxide domains within the porous silicon carbide composite, while also producing an electrocatalyst containing noble metal particles. Furthermore, they discovered that drying the solid content of the mixture under an oxygen atmosphere to form silicon oxide within the porous silicon carbide composite stabilizes the porous silicon carbide by pre-oxidizing vulnerable sites. Furthermore, the sacrificial effect of trace amounts of carbon (C) allows for the production of an electrocatalyst with high conductivity while maintaining a large BET specific surface area, as well as excellent durability.

[0011] That is, the present invention provides the following configurations. [1] A porous silicon carbide composite material containing silicon carbide (SiC) and a carbon material (A), particles supported on the porous silicon carbide composite material and containing a precious metal; a domain formed in a portion of the porous silicon carbide composite material and made of silicon oxide; Equipped with BET specific surface area is 10m 2 / g or more and a conductivity of 0.1 S / cm or more.

[0012] [2] A porous silicon carbide composite material containing silicon carbide (SiC) and a carbon material (A), a carbon material (B); Particles containing a precious metal supported on the porous silicon carbide composite material and / or the carbon material (B); a domain formed in a portion of the porous silicon carbide composite material and made of silicon oxide; Equipped with BET specific surface area is 10m 2 / g or more and a conductivity of 0.1 S / cm or more.

[0013] [3] The electrode catalyst according to the above [1] or [2], wherein the amount of the particles containing the noble metal supported is 10% by mass or more and 60% by mass or less when the total mass of the electrode catalyst is 100% by mass.

[0014] [4] The electrocatalyst according to any one of the above [1] to [3], wherein the mass ratio of silicon (Si) to oxygen (O) contained in the electrocatalyst ([Si] / [O]) is 1 / 0.1 to 1 / 0.001.

[0015] [5] The electrocatalyst according to any one of the above [1] to [4], wherein the mass ratio ([Si] / [C]) of silicon (Si) to carbon (C) contained in the electrocatalyst is 0.4 / 1.0 to 2.0 / 1.0.

[0016] [6] The electrocatalyst according to any one of the above [2] to [4], wherein the mass ratio ([Si] / [C]) of silicon (Si) to carbon (C) contained in the electrocatalyst is 0.15 / 1.0 to 2.0 / 1.0.

[0017] [7] The electrode catalyst according to any one of the above [1] to [6], wherein the content of the carbon material (A) is 5% by mass or more and 50% by mass or less.

[0018] [8] The electrode catalyst according to any one of the above [2] to [6], wherein the total content of the carbon materials (A) and (B) is 5% by mass or more and 50% by mass or less.

[0019] [9] The electrode catalyst according to any one of the above [1] to [8], wherein the carbon material (A) and / or (B) is composed of one or more selected from carbon black, carbon nanofiber, carbon nanotube, and low-crystalline nanocarbon.

[0020]

[10] The electrode catalyst according to any one of the above [1] to [9], wherein the particle size ratio of the average diameter of the primary particles of the silicon carbide (SiC) to the average diameter of the carbon material is 10:1 to 1:5.

[0021]

[11] The electrode catalyst according to any one of the above [1] to

[10] , wherein the particles containing a noble metal are composed of one or more kinds selected from the group consisting of platinum (Pt), platinum-cobalt alloy (PtCo), and platinum-nickel alloy (PtNi).

[0022]

[12] A fuel cell electrode having a layer containing the electrode catalyst according to any one of the above [1] to

[11] .

[0023]

[13] A fuel cell comprising the fuel cell electrode according to

[12] above.

[0024]

[14] A step (A) of adding an organic alkoxysilane to an acidic aqueous solution containing a surfactant and a pH adjuster, and then adding a carbon material (A) or an organic polymer to the aqueous solution, thereby forming a gel containing the carbon material (A) or the organic polymer through a sol-gel reaction of the organic alkoxysilane; (B) washing the gel with alcohol; (C-1) a step of drying the washed gel to form a porous silicon carbide precursor; (D-1) a step of calcining the porous silicon carbide precursor to obtain a porous silicon carbide composite material containing silicon carbide (SiC) and the carbon material (A); a step (E-1) of mixing the porous silicon carbide composite material with a dispersion containing a colloid containing a noble metal and aqueous hydrogen peroxide to obtain a mixture, and forming a domain of silicon oxide in a part of the porous silicon carbide composite material to obtain an electrode catalyst containing particles containing a noble metal; The method for producing an electrode catalyst comprising the steps of:

[0025]

[15] A step (A) of adding an organic alkoxysilane to an acidic aqueous solution containing a surfactant and a pH adjuster, and then adding a carbon material (A) or an organic polymer to the aqueous solution, thereby forming a gel containing the carbon material (A) or the organic polymer through a sol-gel reaction of the organic alkoxysilane; (B) washing the gel with alcohol; (C-1) a step of drying the washed gel to form a porous silicon carbide precursor; (D-1) a step of calcining the porous silicon carbide precursor to obtain a porous silicon carbide composite material containing silicon carbide (SiC) and the carbon material (A); a step (E-1) of mixing the porous silicon carbide composite material with a dispersion containing a colloid containing a noble metal and aqueous hydrogen peroxide to obtain a mixture, and forming a domain of silicon oxide in a part of the porous silicon carbide composite material to obtain an electrode catalyst containing particles containing a noble metal; and A method for producing an electrode catalyst further comprising any one of the following steps (1) to (4): (1) A step (C-2) of blending a carbon material (B) with the porous silicon carbide precursor obtained in the step (C-1). (2) A step (D-2) of blending a carbon material (B) with the porous silicon carbide composite material obtained in the step (D-1). (3) A step (E-2) of blending a carbon material (B) with the electrode catalyst containing the noble metal-containing particles obtained in the step (E-1). (4) After the step (E-1), a step (F-1) is performed in which the solid content of the mixture is heat-treated in an oxygen atmosphere to further grow the domains of silicon oxide formed in part of the porous silicon carbide, and a step (F-2) is performed in which a carbon material (B) is blended with the mixture obtained in the step (F-1).

[0026]

[16] The method for producing an electrode catalyst according to

[14] or

[15] above, further comprising, after the step (E-1) or (E-2), a step (F-1) of heat-treating the solid content of the mixture in an oxygen atmosphere to further grow the domains made of silicon oxide formed on the surface of the silicon carbide.

[0027]

[17] The method for producing an electrode catalyst according to

[16] above, wherein in the step (F-1), the solid content of the mixture is heat-treated at 100°C or higher and 800°C or lower.

[0028]

[18] The method for producing an electrocatalyst according to any one of the above

[14] to

[17] , wherein the organic alkoxysilane is represented by the following formula (1) or formula (2): R 1 -SiR 2 x (OR 3 ) 3-x ···(1) (However, 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, and the integer x is 0 or 1. R 4 -(SiR 5 y (OR 6 ) 3-y )2···(2) (However, in the formula, R 4 R contains 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, and the integer y is 0 or 1.

[0029]

[19] The method for producing an electrode catalyst according to any one of the above

[14] to

[18] , wherein the carbon material (A) and / or (B) is composed of one or more materials selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons.

[0030]

[20] The method for producing an electrode catalyst according to any one of the above

[14] to

[19] , wherein the colloid containing a precious metal is composed of one or more colloids selected from the group consisting of platinum (Pt) colloid, platinum-cobalt (PtCo) colloid, and platinum-nickel (PtNi) colloid. [Effects of the Invention]

[0031] The present invention provides an electrocatalyst that achieves high conductivity while maintaining a large BET specific surface area and also has excellent durability. It also provides a method for producing an electrocatalyst using an organoalkoxysilane of the type that is widely available as an industrial raw material. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 is a flowchart illustrating an example of a method for producing an electrode catalyst according to an embodiment of the present invention. [Figure 2] 2(A) and 2(B) are transmission electron microscope images of the electrode catalyst A exemplified in Example 1. FIG. [Figure 3] FIG. 3 is a diagram showing the results of cyclic voltammetry (CV) measurements of the electrode catalyst A exemplified in Example 1. [Figure 4] FIG. 4 is a graph showing the change in the electrochemically active surface area (ECSA) of the electrode catalyst A exemplified in Example 1 with respect to the CV measurement cycle. DETAILED DESCRIPTION OF THE INVENTION

[0033] <Electrode catalyst composition> The electrode catalyst according to this embodiment is composed of either the following electrode catalyst (I) or electrode catalyst (II). The electrode catalyst (I) comprises a porous silicon carbide composite material containing silicon carbide (SiC) and a carbon material (A), particles containing a noble metal supported on the porous silicon carbide composite material, and domains made of silicon oxide formed in part of the porous silicon carbide composite material.

[0034] The electrode catalyst (II) comprises a porous silicon carbide composite material containing silicon carbide (SiC) and a carbon material (A), a carbon material (B), particles containing a noble metal supported on the porous silicon carbide composite material and / or the carbon material (B), and a domain made of silicon oxide formed in a part of the porous silicon carbide composite material.

[0035] The form of the electrode catalysts (I) and (II) is not particularly limited, but may be, for example, powder, particulate, fibrous or needle-like, with powder or particulate being preferred. When the electrode catalysts (I) and (II) are in the form of powder or particles, the particle size of the electrode catalyst is not particularly limited, but it is preferable that the particle size be 50% of the cumulative particle size in the volume-based cumulative particle size distribution D 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.

[0036] Particle diameter D of electrode catalysts (I) and (II) 50 means a value measured in accordance with JIS Z8825-1:2013, for example, the particle diameter D measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD-7000) 50 This means:

[0037] The electrode catalysts (I) and (II) of this embodiment have a BET specific surface area of ​​10 m 2 / g or more, and 50m 2 / g or more, and2 / g or more. 2 / g or less. The BET specific surface area is 10 m 2 / g or more, the amount of catalyst particles supported on the support surface is sufficiently ensured, and when the electrode catalysts (I) and (II) are 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.

[0038] The total pore volume of the electrode catalysts (I) and (II) is 0.3 cm 3 / g or more, and 3 / g or more is more preferable, and 0.6 cm 3 It is particularly preferred that the total pore volume of the electrode catalyst is 0.3 cm3 / g or more. 3 When the SiO2 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.

[0039] The pore diameters of the electrode catalysts (I) and (II) are 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 diameters of the electrode catalysts (I) and (II) are 10 nm or more and 1000 nm or less, the flow of reactant gases and electrolytes within the catalyst layer is facilitated, thereby improving catalytic efficiency. In particular, when the pore diameter 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 stabilized, preventing a decrease in catalyst particle utilization rate.

[0040] The BET specific surface area, total pore volume, and pore diameter of the electrode catalysts (I) and (II) can be calculated as measured values ​​by a gas adsorption method, and mean values ​​calculated from the amount of adsorption and condensation of the noncorrosive gas when a noncorrosive gas such as nitrogen or argon is adsorbed while changing the relative pressure in the adsorption isotherm using a constant volume method, for example.

[0041] [Porous silicon carbide composite material] The porous silicon carbide constituting the electrode catalysts (I) and (II) has a three-dimensional framework structure that provides multiple individual micropores, or multiple micropores that are interconnected in part or in whole. 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 electrode catalysts (I) and (II).

[0042] The electrode catalysts (I) and (II) of this embodiment contain carbon that constitutes the three-dimensional skeletal structure of porous silicon carbide (SiC) as a support, and a carbon material (A) other than the carbon that constitutes the three-dimensional skeletal structure, which is supported on the porous silicon carbide.

[0043] 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.

[0044] [Carbon material (A)] The carbon material (A) is contained in both the electrode catalysts (I) and (II). The carbon material (A) is not particularly limited, and may be composed of, for example, one or more selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons. Among these, from the viewpoints of realizing high conductivity and manufacturability, the carbon material (A) is preferably carbon black.

[0045] When the carbon material (A) is composed of carbon black, the average diameter of the primary particles of the carbon material (A) is preferably 10 nm to 200 nm, more preferably 20 nm to 100 nm, and even more preferably 30 nm to 50 nm. When the average diameter of the primary particles of the carbon material is 10 nm to 200 nm, good electrical conductivity can be achieved.

[0046] When the carbon material (A) is composed of carbon nanofibers or carbon nanotubes, the average diameter of the carbon material (A) is preferably 10 nm or more and 200 nm or less, and the length of the carbon material (A) is preferably 1 μm or more and 20 μm or less.

[0047] In the electrode catalyst (I), the content of the carbon material (A) in the porous silicon carbide composite material is preferably 5 to 50% by mass, more preferably 8 to 45% by mass, and even more preferably 10 to 40% by mass. When the content of the carbon material (A) in the porous silicon carbide composite material is 5 to 50% by mass, high electrical conductivity is achieved, and corrosion of the carbon is suppressed, thereby improving the durability of the catalytic cycle.

[0048] In the electrode catalyst (II), the content of the carbon material (A) in the porous silicon carbide composite material is preferably 1% by mass to 40% by mass, more preferably 2% by mass to 35% by mass, and even more preferably 4% by mass to 30% by mass. When the content of the carbon material (A) in the porous silicon carbide composite material is 1% by mass to 40% by mass, high electrical conductivity can be achieved while suppressing corrosion of the carbon, thereby improving the durability of the catalytic cycle.

[0049] The shape and size of the carbon material (A) held in the porous silicon carbide composite material 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.

[0050] [Carbon material (B)] The carbon material (B) is contained in the electrode catalyst (II). The carbon material (B) is not particularly limited, and may be composed of one or more selected from, for example, carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons. Among these, from the viewpoint of realizing high conductivity and manufacturability, the carbon material (B) is preferably carbon black. Furthermore, the carbon material (B) may be the same as the carbon material (A).

[0051] When the carbon material (B) is composed of carbon black, the average diameter of the primary particles of the carbon material (B) is preferably 10 nm to 200 nm, more preferably 20 nm to 100 nm, and even more preferably 30 nm to 50 nm. When the average diameter of the primary particles of the carbon material is 10 nm to 200 nm, good conductivity can be achieved.

[0052] When the carbon material (B) is composed of carbon nanofibers or carbon nanotubes, the average diameter of the carbon material (B) is preferably 10 nm or more and 200 nm or less, and the length of the carbon material (B) is preferably 1 μm or more and 20 μm or less.

[0053] The content of the carbon material (B) in the electrode catalyst (II) is preferably 1% by mass to 20% by mass, more preferably 3% by mass to 15% by mass, and even more preferably 4% by mass to 10% by mass. When the content of the carbon material (A) in the porous silicon carbide composite material is 1% by mass to 20% by mass, high electrical conductivity can be achieved while suppressing corrosion of the carbon, thereby improving the durability of the catalytic cycle.

[0054] The shape and size of the carbon material (B) held in the electrode catalyst (II) 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 a microscope image using image analysis particle size distribution measurement software.

[0055] The total content of the carbon materials (A) and (B) in the electrode catalyst (II) 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 total content of the carbon materials (A) and (B) in the electrode catalyst (II) is 5% by mass or more and 50% by mass or less, high electrical conductivity can be achieved while suppressing corrosion of the carbon, thereby improving the durability of the catalytic cycle.

[0056] [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, good voids can be obtained when the material is used as an electrode.

[0057] 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.

[0058] The ratio of the average diameter of the primary particles of silicon carbide to the average diameter of the carbon material (A) (SiC:carbon material (A)) is not particularly limited, but is preferably 10:1 to 1:5, more preferably 5:1 to 1:3, and particularly preferably 2:1 to 1:2. If the ratio is within the above range, the mass transport of the catalyst layer made of the obtained electrode catalyst can be improved.

[0059] [Particles containing precious metals] When the total mass of the electrode catalysts (I) and (II) is taken as 100 mass%, the amount of the particles containing the noble metal is preferably 10 mass% to 60 mass%, more preferably 15 mass% to 60 mass%, and even more preferably 30 mass% to 60 mass%. When the amount of the particles containing the noble metal is 10 mass% to 60 mass%, the catalytic function and durability are excellent, and silicon oxide can be sufficiently formed in the porous silicon carbide composite material. The amount of the particles containing the precious metals supported can be calculated, for example, by subjecting the electrode catalysts (I) and (II) to an alkali melting, dissolving them in aqua regia, diluting them with ultrapure water, and then subjecting them to high-frequency induction heating optical emission spectroscopy (ICP).

[0060] The particles containing a noble metal are preferably composed of one selected from the group consisting of platinum (Pt), gold (Au), ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), platinum-cobalt alloy (PtCo), platinum-nickel alloy (PtNi), and platinum-ruthenium alloy (PtRu). Among these, from the viewpoint of high durability at high temperatures and high catalytic function, it is more preferable to be composed of one or more selected from the group consisting of platinum (Pt), platinum-cobalt alloy (PtCo), and platinum-nickel alloy (PtNi), and it is even more preferable to be composed of platinum (Pt) or platinum-cobalt alloy (PtCo).

[0061] The particles containing a noble metal are preferably nanoparticles containing a noble metal. The average particle size of the primary particles of the particles containing a noble metal is preferably 2 nm to 10 nm, more preferably 2.5 nm to 7 nm, and even more preferably 3 nm to 5 nm. When the average particle size of the primary particles of the particles containing a noble metal is 2 nm to 10 nm, good catalytic performance can be achieved even with a small amount of noble metal.

[0062] [Silicon oxide] In the electrode catalysts (I) and (II) of this embodiment, domains made of silicon oxide are formed in a portion of the porous silicon carbide composite material by oxidation of silicon carbide (SiC). Examples of silicon oxide include silicon monoxide (SiO) and silicon dioxide (SiO2). The form of the domains is not particularly limited, but may be amorphous, for example. The silicon oxide domains are dispersed and arranged on the surface of the porous silicon carbide composite material. It is also preferable that the silicon oxide domains are formed on the surface of silicon carbide (SiC) in the porous silicon carbide composite material. This can suppress oxidation of the silicon carbide surface.

[0063] The mass ratio ([Si] / [C]) of silicon (Si) to carbon (C) contained in the electrode catalysts (I) and (II) may be set to a range appropriate for each embodiment of the electrode catalysts (I) and (II). In the case of the electrode catalyst (I), the [Si] / [C] ratio is preferably 0.4 / 1.0 to 2.0 / 1.0, more preferably 0.5 / 1.0 to 1.8 / 1.0, and even more preferably 0.7 / 1.0 to 1.7 / 1.0.

[0064] In the case of the electrocatalyst (II), the [Si] / [C] ratio is preferably 0.15 / 1.0 to 2.0 / 1.0, more preferably 0.2 / 1.0 to 1.8 / 1.0, and even more preferably 0.3 / 1.0 to 1.6 / 1.0. When the mass ratio of silicon (Si) to carbon (C) ([Si] / [C]) is 0.4 / 1.0 to 2.0 / 1.0 or 0.15 / 1.0 to 2.0 / 1.0, high conductivity is achieved while suppressing carbon corrosion and other problems, thereby improving the durability of the catalytic cycle. In particular, in the electrode catalyst (II), when the [Si] / [C] is within the range of 0.15 / 1.0 to 2.0 / 1.0, pores that are excellent for material transport can be formed when the electrode is used as an electrode catalyst, which is preferable. Note that carbon (C) in the above mass ratios refers to the total carbon that constitutes the three-dimensional framework of the porous silicon carbide and the carbon in the carbon material supported on the porous silicon carbide.

[0065] The mass ratio of silicon (Si) to oxygen (O) ([Si] / [O]) in the electrode catalysts (I) and (II) is preferably 1 / 0.1 to 1 / 0.001, more preferably 1 / 0.1 to 1 / 0.005, and even more preferably 1 / 0.01 to 1 / 0.005. When the mass ratio of silicon (Si) ([Si] / [O]) is 1 / 0.1 to 1 / 0.001 or less, the sites of silicon carbide that are prone to deterioration are oxidized in advance, thereby improving the stability of the porous silicon carbide composite material.

[0066] The silicon (Si) content in the electrode catalysts (I) and (II) can be calculated by, for example, inductively coupled plasma emission spectroscopy (ICP), the carbon (C) content can be calculated by high-frequency combustion-infrared absorption spectroscopy, and the oxygen (O) content can be calculated by inert gas fusion-infrared absorption spectroscopy.

[0067] [Electrocatalytic properties] The electrode catalysts (I) and (II) of this embodiment have a conductivity of 0.1 S / cm or more, preferably 1 S / cm or more, more preferably 5 S / cm or more, and even more preferably 10 S / cm or more. The conductivity may be 100 S / cm or less, 70 S / cm or less, or 50 S / cm or less. The higher the conductivity of the porous silicon carbide, the better the fuel cell electrode catalyst can be. However, if the amount of carbon material that contributes to improving conductivity is too high, corrosion of the carbon component may occur during the catalytic cycle, resulting in reduced durability.

[0068] <Electrode catalyst manufacturing method> As shown in FIG. 1, the method for producing the electrode catalyst (I) 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-1)), a firing step (step (D-1)), and a mixing step (step (E-1)).

[0069] The method for producing the electrode catalyst (II) 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-1)), a firing step (step (D-1)), and a mixing step (step (E-1)), and further includes any one of the following steps (1) to (4): (1) Step (C-2) of blending the porous silicon carbide precursor obtained in step (C-1) with a carbon material (B). (2) A step (D-2) of blending a carbon material (B) with the porous silicon carbide composite material obtained in the step (D-1). (3) A step (E-2) of blending a carbon material (B) with the electrode catalyst containing the noble metal-containing particles obtained in the step (E-1). (4) After the step (E-1), a step (F-1) is performed in which the solid content of the mixture is heat-treated in an oxygen atmosphere to further grow the domains of silicon oxide formed in part of the porous silicon carbide, and a step (F-2) is performed in which a carbon material (B) is blended with the mixture obtained in the step (F-1). Incidentally, on the premise that the electrode catalyst according to this embodiment is obtained, other steps than those described above may be carried out before or after each step.

[0070] [Process (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 inside.

[0071] The content of the surfactant in the acidic aqueous solution is preferably 0.1% by mass to 50% by mass, more preferably 0.5% by mass to 35% by mass, and even more preferably 2% by mass to 15% by mass.

[0072] 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) and polyhydric alcohol types. Examples of polyethylene glycol-type nonionic surfactants include Pluronic® types. Examples of cationic surfactants include amine salt types and quaternary ammonium salt types. By adjusting 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 with developed mesopores and a large BET specific surface area can be formed.

[0073] The content of the pH adjuster in the acidic aqueous solution is preferably 5% by mass to 50% by mass, more preferably 5.5% by mass to 35% by mass, and even more preferably 6% by mass to 23% by mass. By setting the content of the pH adjuster in the acidic aqueous solution to 5% by mass to 50% by mass, a porous polysilsesquioxane gel having high skeletal strength and flexibility can be formed.

[0074] The pH adjuster is not particularly limited, but examples thereof include substances containing any one selected from urea, ammonia, and sodium hydroxide.

[0075] The acidic aqueous solution is not particularly limited, but examples thereof include aqueous solutions of hydrochloric acid, nitric acid, acetic acid, and the like.

[0076] The organic alkoxysilane is preferably represented by the following formula (1) or (2): By using the organic alkoxysilane represented by the following formula (1) or (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) (However, 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, and the integer x is 0 or 1. R 4 -(SiR 5 y (OR 6 ) 3-y )2···(2) (However, in the formula, R 4 R contains 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, and the integer y is 0 or 1.

[0077] 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 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 have cis / trans geometric isomers, and either isomer can be used.

[0078] In this step (A), a carbon material (A) or an organic polymer is further added to the acidic aqueous solution to form a gel containing the carbon material (A) or the organic polymer. By adding the carbon material (A) 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 (A) at the nano level in a porous three-dimensional structural framework, thereby imparting excellent electrical conductivity to porous silicon carbide, which is inherently an insulator or semiconductor. The organic polymer undergoes thermal decomposition by calcination in step (D), and is retained in the porous silicon carbide as low-crystalline nanocarbon, thereby imparting electrical conductivity.

[0079] In the above step (A), the carbon material (A) or the organic polymer is preferably added to the acidic aqueous solution so that the mass ratio of the carbon material (A) or the organic polymer to the organic alkoxysilane is 2.5-50:97.5-50. Furthermore, the mass ratio of the carbon material (A) or the organic polymer to the organic alkoxysilane is more preferably 3-30:97-70, and even more preferably 5-20:95-80. By setting the mass ratio of the carbon material (A) or the 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 (A) or the 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.

[0080] The carbon material (A) is not particularly limited, and may be composed of, for example, one or more selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons. Among these, from the viewpoints of realizing high electrical conductivity and manufacturability, the carbon material (A) is preferably carbon black.

[0081] The organic polymer is not particularly limited, but may be composed of one or more selected from, for example, phenolic resin, polystyrene, and polydivinylbenzene.

[0082] [Process (B)] In step (B), the gel obtained in step (A) is washed with alcohol. The alcohol used for 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 process at room temperature and normal pressure in step (C), which will be described later, and facilitates the formation of a porous gel structure.

[0083] [Process (C-1)] In step (C-1), the washed gel is dried to form a porous silicon carbide precursor. Methods for this step (C-1) 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 because it is inexpensive to produce and, when a polysilsesquioxane with high skeletal strength and flexibility is formed, it can produce a high-density porous silicon carbide precursor with developed mesopores.

[0084] [Process (C-2)] The method for producing the electrode catalyst (II) may further include step (C-2). In step (C-2), a carbon material (B) is blended with the porous silicon carbide precursor obtained in step (C-1). The carbon material (B) to be blended is not particularly limited, and may be, for example, one or more selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons. Among these, from the viewpoints of realizing high conductivity and manufacturability, it is preferable that the carbon material (A) is carbon black. The carbon material (B) used in step (C-2) may be the same as or different from the carbon material (A) used in step (A), but it is preferable that they are the same from the viewpoint of production costs.

[0085] The carbon material (A) may be blended by a conventionally known method, and examples thereof include simple mixing of powders, mechanical mixing using a grinder or mixer, and mixing using a mortar, etc. In this case, the resulting mixture may be in either a dry state or a wet state, but a dry state is preferred from the viewpoint of cost.

[0086] The amount of the carbon material (B) to be blended is not particularly limited, but it is preferably blended so that the [Si] / [C] ratio in the calcined electrode catalyst (II) is 0.4 / 1.0 to 2.0 / 1.0.

[0087] [Process (D-1)] In step (D-1), a porous silicon carbide precursor containing the carbon material (A) 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 (A) 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.

[0088] 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 maintenance time for the maximum temperature can be determined appropriately based on the time effective for obtaining a porous silicon carbide composite material. For example, 5 minutes to 16 hours is preferable, 10 minutes to 10 hours is more preferable, and 30 minutes to 3 hours is particularly preferable. 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 and firing can be carried out. The firing can be carried out at atmospheric pressure. Examples of inert gases include nitrogen, helium, argon, etc. 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.

[0089] In step (D-1), the porous silicon carbide precursor may be further mixed with a carbon material (A) or an organic polymer, and the mixture may then be fired. When an organic polymer is mixed with the porous silicon carbide precursor in step (D-1), pyrolysis proceeds during firing, as in the case of mixing in step (A), and the organic polymer is retained in the porous silicon carbide as low-crystalline nanocarbon.

[0090] [Process (D-2)] The method for producing the electrode catalyst (II) may further include a step (D-2). In the step (D-2), a carbon material (B) is blended with the porous silicon carbide composite material obtained in the above step (D-1). The carbon material (B) to be blended is not particularly limited, and may be, for example, one or more selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons. Among these, from the viewpoints of realizing high conductivity and manufacturability, the carbon material (B) is preferably carbon black. The carbon material (B) used in step (D-2) may be the same as or different from the carbon material (A) used in step (A), but it is preferable that they are the same from the viewpoint of production costs.

[0091] The carbon material (B) may be blended by a conventionally known method, and examples thereof include simple mixing of powders, mechanical mixing using a grinder or mixer, mixing using a mortar, etc. In this case, the resulting mixture may be in either a dry state or a wet state, but a dry state is preferred from the viewpoint of cost.

[0092] The amount of the carbon material (B) to be blended is not particularly limited, but it is preferably blended so that the [Si] / [C] ratio in the calcined electrode catalyst (II) is 0.15 / 1.0 to 2.0 / 1.0.

[0093] [Process (E-1)] In step (E-1), a dispersion containing a noble metal-containing colloid and aqueous hydrogen peroxide is mixed with the porous silicon carbide composite material to obtain a mixed liquid, and an electrode catalyst containing noble metal-containing particles is obtained while forming silicon oxide domains in part of the porous silicon carbide composite material. The noble metal-containing colloid is a dispersion of noble metal-containing particles in a liquid, and the dispersion containing the noble metal-containing colloid is a solution containing the noble metal-containing colloid and aqueous hydrogen peroxide. The noble metal-containing colloid and the dispersion containing the noble metal-containing colloid and aqueous hydrogen peroxide can be prepared by known, commonly used methods.

[0094] The mixing ratio of the dispersion containing the colloid containing the precious metal and the porous silicon carbide composite material is, for example, preferably such that the mass of the supported precious metal is 10 mass % or more and 60 mass % or less, more preferably 20 mass % or more and 55 mass % or less, and even more preferably 30 mass % or more and 50 mass % or less, relative to the total mass of the electrode catalyst.

[0095] The colloid containing a noble metal is preferably composed of colloids of one or more metals selected from the group consisting of platinum (Pt), gold (Au), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), and iridium (Ir). Among these, it is more preferable to be composed of one or more metals selected from the group consisting of platinum (Pt) colloid, platinum-cobalt alloy (PtCo) colloid, and platinum-nickel alloy (PtNi) colloid, and it is even more preferable to be composed of platinum (Pt) colloid or platinum-cobalt alloy (PtCo) colloid.

[0096] In step (E-1), stirring the mixture of the porous silicon carbide composite material with the noble metal-containing colloid and the hydrogen peroxide solution forms domains of silicon oxide on the silicon carbide surface, thereby obtaining an electrode catalyst containing noble metal-containing particles. The mixture may be cooled to promote solid-liquid separation. The solids can be washed using 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 solids.

[0097] [Process (E-2)] The method for producing the electrode catalyst (II) may further include step (E-2). In step (E-2), a carbon material (B) is blended with the electrode catalyst containing the noble metal-containing particles obtained in step (E-1). The carbon material (B) to be blended is not particularly limited, and may be, for example, one or more selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons. Among these, from the viewpoints of realizing high conductivity and manufacturability, the carbon material (B) is preferably carbon black. The carbon material (B) used in step (E-2) may be the same as or different from the carbon material (A) used in step (A), but it is preferable that they are the same from the viewpoint of production costs.

[0098] The carbon material (B) may be blended by a conventionally known method, and examples thereof include simple mixing of powders, mechanical mixing using a grinder or mixer, mixing using a mortar, etc. In this case, the resulting mixture may be in either a dry state or a wet state, but a dry state is preferred from the viewpoint of cost.

[0099] The amount of the carbon material (B) to be blended is not particularly limited, but it is preferably blended so that the [Si] / [C] ratio in the calcined electrode catalyst (II) is 0.15 / 1.0 to 2.0 / 1.0.

[0100] The method for producing the electrode catalyst (II) may include any one of the steps (C-2), (D-2), and (E-2), but from the viewpoint of improving the performance of the resulting electrode catalyst, it is preferable to include step (D-2) or (E-2), and it is particularly preferable to include step (E-2). By including step (D-2) or (E-2), it is possible to improve the electrical conductivity of the resulting electrode catalyst while maintaining its durability, which is preferable.

[0101] [Process (F-1)] In the method for producing the electrode catalyst (I) or (II), after step (E-1) or (E-2), if necessary, the solid content of the mixture can be heat-treated in an oxygen atmosphere to further grow the silicon oxide domains formed in part of the porous silicon carbide composite material (step (F-1)). Typically, by heat-treating the solid content of the mixture in an oxygen atmosphere, the solid content of the mixture is dried and the silicon oxide domains formed on the surface of the silicon carbide are further grown, thereby obtaining an electrode catalyst containing particles containing a noble metal.

[0102] [Process (F-2)] The method for producing the electrode catalyst (II) may further include step (F-2). In step (F-2), a carbon material (B) is blended with the mixture obtained in step (F-1). The carbon material (B) to be blended is not particularly limited, and may be, for example, one or more selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons. Among these, from the viewpoints of realizing high conductivity and manufacturability, the carbon material is preferably carbon black. The carbon material (B) used in step (F-2) may be the same as or different from the carbon material (A) used in step (A), but it is preferable that they are the same from the viewpoint of production costs.

[0103] The carbon material (B) may be blended by a conventionally known method, and examples thereof include simple mixing of powders, mechanical mixing using a grinder or mixer, mixing using a mortar, etc. In this case, the resulting mixture may be in either a dry state or a wet state, but a dry state is preferred from the viewpoint of cost.

[0104] The amount of the carbon material (B) to be blended is not particularly limited, but it is preferably blended so that the [Si] / [C] ratio in the electrode catalyst after firing is 0.15 / 1.0 to 2.0 / 1.0.

[0105] When the step (F-2) is included, the steps (C-2), (D-2), and (E-2) can be omitted.

[0106] The heat treatment of the solid content can be performed in an oxygen atmosphere using a known, commonly used method and under conditions that are not particularly limited. For example, in air, the temperature is increased at a rate of 10°C per minute, and the maximum temperature reached is maintained for a certain period of time. The heat treatment temperature is preferably 100°C or higher and 800°C or lower, more preferably 200°C or higher and 750°C or lower, and even more preferably 300°C or higher and 700°C or lower. The time for which the heat treatment temperature is maintained may be determined appropriately based on the time effective for obtaining an electrode catalyst. For example, 30 minutes to 4 hours is preferred, 40 minutes to 3 hours is more preferred, and 1 to 2 hours is even more preferred.

[0107] In the above step (E-1), particles containing a noble metal are dispersed and supported on the porous silicon carbide composite material. The particles containing a noble metal are preferably composed of one or more elements selected from the group consisting of platinum (Pt), gold (Au), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), and iridium (Ir). Among these, from the viewpoint of high durability at high temperatures and high catalytic function, particles containing one or more elements selected from the group consisting of platinum (Pt), platinum-cobalt alloy (PtCo), and platinum-nickel alloy (PtNi) are more preferred, and platinum (Pt) or platinum-cobalt alloy (PtCo) are even more preferred. Furthermore, it is preferable that nanoparticles containing a noble metal are supported on the porous silicon carbide composite material.

[0108] In the above steps (E-1) or (E-2), a portion of the silicon in the porous silicon carbide composite material is oxidized to silicon oxide, and domains consisting of the silicon oxide are formed on the surface and / or inside of the porous silicon carbide. Examples of silicon oxide include silicon monoxide (SiO) and silicon dioxide (SiO2). The morphology of the domain is not particularly limited, and may be, for example, amorphous.

[0109] [Fuel cell electrodes and fuel cells] The fuel cell electrode according to this embodiment has a catalyst layer containing the electrode catalyst. The fuel cell electrode typically has the electrode catalyst layer and a gas diffusion layer. The fuel cell electrode may be a fuel cell negative electrode (anode) or a fuel cell positive electrode (cathode). When the fuel cell electrode is a fuel cell negative electrode, the fuel cell negative electrode has an anode catalyst layer to which a fuel such as hydrogen is supplied, and a first gas diffusion layer. When the fuel cell electrode is a fuel cell positive electrode, the fuel cell positive electrode has a cathode catalyst layer to which an oxygen-containing gas such as air is supplied, and a second gas diffusion layer.

[0110] The fuel cell according to this embodiment includes the above-described fuel cell electrode. The fuel cell includes a fuel cell 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 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.

[0111] The above-mentioned fuel cell electrode and fuel cell have a catalyst layer containing the above-mentioned electrode catalyst, which allows for high conductivity while maintaining a large BET specific surface area. In addition, the nano-level arrangement of carbon material within silicon carbide having a porous three-dimensional structure skeleton reduces the possibility of oxidative degradation of the carbon material, which has been a conventional problem, for example, in high-temperature and high-humidity environments, thereby achieving excellent durability as a fuel cell electrode and fuel cell. [Example]

[0112] Examples of the present invention will be described below, but the present invention is not limited to the examples shown below.

[0113] Example 1 [Synthesis of porous silicon carbide composite materials] 6 g of 5 mM 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 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 resulting 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), then placed in a tubular furnace and fired in an argon atmosphere at a heating rate of 2.5°C / min up to 1500°C, and held at this temperature for 2 hours to obtain a porous silicon carbide composite material.

[0114] [Synthesis of electrocatalysts containing platinum nanoparticles] 0.43 g of chloroplatinic acid hexahydrate was dissolved in 60 mL of ultrapure water, and 3.1 g of sodium bisulfite was added to the solution to initiate a reduction reaction. The solution was then diluted with 280 mL of ultrapure water. Next, 24 mL of 35% hydrogen peroxide was added dropwise while adding 5% aqueous sodium hydroxide to adjust the pH to approximately 5, yielding a platinum colloid dispersion. Next, 0.4 g of porous silicon carbide composite was added as a support to a sample of the colloidal dispersion so that the amount of platinum (Pt) after loading was 40 mass% of the total weight of the electrode catalyst, including the support. The mixture was then mixed at 90°C for 3 hours. After cooling, the mixture was subjected to solid-liquid separation. The resulting powder (solids) was thoroughly washed with ultrapure water to remove chloride ions, and then dried at 80°C for 12 hours in air to obtain electrode catalyst A, in which platinum was supported on the surface of the porous silicon carbide composite. Transmission electron microscope images of electrode catalyst A are shown in Figures 2(A) and 2(B). It was confirmed that platinum nanoparticles with a particle size of approximately 3 nm were supported on the porous silicon carbide composite material, and that domains consisting of silicon oxide were formed on the surface of silicon carbide (SiC) in the porous silicon carbide composite material.

[0115] Example 2 An electrode catalyst B was obtained in the same manner as in Example 1, except that the colloidal dispersion was dispensed so that the amount of platinum (Pt) after loading was 37 mass % relative to the total amount of the electrode catalyst including the carrier.

[0116] Example 3 An electrode catalyst C was obtained in the same manner as in Example 1, except that the colloidal dispersion was dispensed so that the amount of platinum (Pt) after loading was 30 mass % relative to the total amount of the electrode catalyst including the carrier.

[0117] Example 4 An electrode catalyst D was obtained in the same manner as in Example 1, except that the colloidal dispersion was dispensed so that the amount of platinum (Pt) after loading was 20 mass % relative to the total amount of the electrode catalyst including the carrier.

[0118] Example 5 An electrode catalyst E was obtained in the same manner as in Example 4, except that the obtained powder (solid content) was calcined in an air stream at 600° C. for 2 hours during synthesis of the electrode catalyst.

[0119] Example 6 Catalyst F was obtained in the same manner as in Example 4, except that the amount of Ketjen black (ECP) mixed with 1 g of porous silicon carbide precursor was changed to 0.25 g during the synthesis of the porous silicon carbide composite material.

[0120] Example 7 Catalyst G was obtained in the same manner as in Example 4, except that the amount of Ketjen black (ECP) mixed with 1 g of porous silicon carbide precursor was changed to 0.7 g during the synthesis of the porous silicon carbide composite material.

[0121] Example 8 Catalyst H was obtained in the same manner as in Example 1, except that 2.5 g of methyltrimethoxysilane (manufactured by Kanto Chemical Co., Ltd.) and 2.5 g of phenyltrimethoxysilane (manufactured by Kanto Chemical Co., Ltd.) were used in synthesizing the porous silicon carbide precursor, and that the porous silicon carbide composite material was calcined at 1400°C.

[0122] (Comparative Example 1) Electrode catalyst I was obtained in the same manner as in Example 4, except that 1 g of porous silicon carbide precursor was calcined without using Ketjen black (ECP) mixed with the porous silicon carbide precursor during synthesis of the porous silicon carbide composite material.

[0123] (Comparative Example 2) Catalyst J was obtained in the same manner as in Example 8, except that the porous silicon carbide composite material was calcined at 1600°C during synthesis, and the colloidal dispersion was separated during synthesis of the electrode catalyst so that the amount of platinum (Pt) after support was 35 mass% based on the total amount of the electrode catalyst including the support.

[0124] The above-mentioned Examples 1 to 8 and Comparative Examples 1 and 2 were measured by the following methods.

[0125] [Measurement of carbon material content] The weight loss was calculated from the weight loss in the temperature range from 600 to 800°C by thermogravimetric differential thermal analysis (TG-DTA) in air.

[0126] [Elemental analysis of porous silicon carbide composite material] Carbon (C) analysis: Analysis was carried out by high-frequency combustion-infrared absorption method. Equipment: LECO, CS844 type Oxygen (O) analysis: Analysis was carried out by inert gas fusion-infrared absorption spectroscopy. Equipment: LECO TCH600 Silicon (Si) analysis: After the sample was melted and decomposed with sodium hydroxide and sodium peroxide, the melt was dissolved in hydrochloric acid and the volume was adjusted with ultrapure water to obtain the test solution, which was then subjected to ICP detection. Equipment: Shimadzu Corporation, ICPE-9820 From the contents of Si, C, and O, the mass ratios of [Si] / [C] and [Si] / [O] were calculated.

[0127] [Measurement of the average diameter of primary particles] The powder of the porous silicon carbide composite material was fixed to carbon tape, and the primary particle diameters of the silicon carbide and carbon material were measured from images obtained by scanning electron microscopy. The average value of 50 particles was taken as the average diameter of the primary particles. The average diameter ratio of the primary particles of silicon carbide and the carbon material was calculated from the obtained average diameters of the primary particles.

[0128] [Measurement of BET specific surface area, pore volume and pore diameter] 0.04 g of porous silicon carbide composite powder was weighed and placed in a sample tube, and pretreated by vacuum drying at 100°C for 6 hours. After pretreatment, nitrogen was adsorbed onto the sample at -196°C while varying the relative pressure using a specific surface area / pore size distribution apparatus (Microtrack-Bell, model name "BELSORP-miniII").

[0129] [Conductivity measurement] The electrode catalyst or catalyst powder was introduced into a powder resistivity measurement system (manufactured by Mitsubishi Chemical Analytech Co., Ltd., device name "MCP-PD51"), and the sample was pressurized using the attached hydraulic pump. After the pressure reached 12 kN, the resistivity was measured using a resistivity meter (manufactured by Mitsubishi Chemical Analytech Co., Ltd., device name "Loresta GX"), and the conductivity was calculated from the resistivity using the following formula. In Example 1, the resistivity was 6.6 × 10 -2 The measured values ​​were Ω·cm and the conductivity was 15 S / cm. The results are shown in Table 1. Conductivity (S / cm) = (Resistivity (Ω cm)) -1

[0130] [Measurement of Pt loading amount] The electrode catalyst was alkali-fused using anhydrous sodium carbonate and sodium peroxide, then dissolved in aqua regia, diluted to a specified concentration with ultrapure water, and measured using high-frequency induction heating optical emission spectroscopy (ICP; Shimadzu Corporation, ICPE-9820).

[0131] [Evaluation of catalytic performance using a rotating electrode] (Electrode preparation) A 5 mm diameter glassy carbon (GC) electrode was polished with alumina paste and then ultrasonically cleaned with ultrapure water. Electrocatalyst 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® solution was dropped onto the electrode catalyst on the GC disk to a dry film thickness of 50 nm, and the electrode catalyst was dried at room temperature for 12 hours.

[0132] (CV measurement) Electrode evaluation was performed using an electrochemical measurement system (Hokuto Denko, HZ-5000). 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. Cyclic voltammetry (CV) measurements were then 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.

[0133] (Oxygen reduction activity evaluation) After purging the electrolyte with oxygen gas for over an hour, linear sweep voltammetry (LSV) was performed. Data were collected under eight conditions: temperature 25°C, potential range 0.25–1.00 V, sweep rate 5 mV / s, and rotation speed 1000–2750 rpm, increasing in 250 rpm increments. The results were analyzed using the Koutecky-Levich plot to obtain the mass activity (A / g-Pt) at 0.85 V.

[0134] (Start / Stop durability evaluation) After purging the electrolyte with nitrogen gas for 30 minutes, the potential range from 1.0 to 1.5 V was swept 500 times, and CV measurements were performed in the potential range from 0.05 to 1.0 V. This measurement procedure constituted one set, and 56,000 cycles of testing were performed. The results are shown in Table 1.

[0135] [Table 1]

[0136] As shown in Table 1, in Examples 1 to 8, the BET specific surface area of ​​the electrode catalysts A to H was 10 m 2 / g or more and electrical conductivity of 0.1 S / cm or more, showing high electrical conductivity while maintaining a large BET specific surface area. Furthermore, in Examples 1 to 7, the ECSA retention rate was 75% or more, showing excellent durability. Furthermore, the mass activity was 400 (A / g-Pt) or more, showing a high current per unit mass of platinum (Pt), showing high oxygen reduction activity.

[0137] As an example, the CV measurement results for electrode catalyst A in Example 1 are shown in Figure 3. The current value was constant in each measurement cycle. The change in ECSA for electrode catalyst A in Example 1 versus the measurement cycle is shown in Figure 4. Evaluation up to 8,000 cycles revealed that the decrease in ECSA was limited to approximately 20% of the initial value, confirming that electrode catalyst A showed little deterioration and had high potential stability.

[0138] On the other hand, in Comparative Example 1, the BET specific surface area was 15 m 2 / g, and the ECSA retention rate is 85%, but the conductivity is 4.0 × 10 -7 In Comparative Example 2, the average primary particle size ratio of silicon carbide to the carbon material was as large as 13, and the BET specific surface area was 120 m 2 / g and electrical conductivity was 19 S / cm, but the ECSA retention rate and mass activity were significantly inferior.

[0139] Example 9 [Fabrication of a single fuel cell] (Preparation of anode catalyst ink) Carbon black (Pt / CB, Tanaka Kikinzoku Co., Ltd., TEC10E50E, Pt loading 46 wt%) loaded with 0.45 g of platinum (Pt) was mixed with a polymer electrolyte (Du Pont, Nafion® DE521) at a volume ratio of 1.0. This mixture, 2.5 g of ethanol, 2 g of water, and zirconia balls (5 mm diameter) 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 hereafter referred to as the anode catalyst ink.

[0140] (Preparation of cathode catalyst ink) Electrode 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 (manufactured by Fritsch, P-6).

[0141] (Fabrication of membrane electrode assembly (MEA)) The anode catalyst layer and cathode catalyst layer were formed using a spray coating device (manufactured by Acing Technologies) by applying platinum to a polymer electrolyte membrane (manufactured by DuPont, Nafion NR212) with a platinum content of 0.5 mg / cm2. 2 , the platinum content of the cathode is 0.3 mg / cm 2 The anode catalyst ink and the cathode catalyst ink were applied so that the ... A fuel cell electrode membrane (CCM) composed of an anode catalyst layer or a cathode catalyst layer and a polymer electrolyte membrane was hot pressed (140°C, pressure 2.86 kN) for 3 minutes using a hot press machine (Toho Kogyo Co., Ltd., TCMD-2.5).

[0142] In the above CCM, gas diffusion layers (GDL, manufactured by SGL, 22BB) were stacked on both sides of each catalyst layer, and a membrane electrode assembly (MEA) was obtained in which the cathode catalyst layer and the anode catalyst layer were stacked on the polymer electrolyte membrane so that they faced each other. A single cell was assembled using the above MEA and placed in a power generation evaluation device (manufactured by Panasonic Production Technology Co., Ltd.).

[0143] Example 10 A membrane electrode assembly (MEA) and a single cell were obtained in the same manner as in Example 8, except that electrode catalyst C was used as the cathode catalyst.

[0144] Example 11

[0145] A membrane electrode assembly (MEA) and a single cell were obtained in the same manner as in Example 8, except that electrode catalyst D was used as the cathode catalyst.

[0146] Example 12 A membrane electrode assembly (MEA) and a single cell were obtained in the same manner as in Example 9, except that electrode catalyst K, which was obtained by mixing electrode catalyst A with 5 mass % of Ketjen Black (ECP-600JD), was used as the cathode catalyst.

[0147] (Comparative Example 3) A membrane electrode assembly (MEA) and a single cell were obtained in the same manner as in Example 8, except that Pt / CB (Tanaka Kikinzoku Co., Ltd., TEC10E50E, Pt loading 46 wt %) was used as the cathode catalyst.

[0148] For the above Examples 9 to 12 and Comparative Example 3, measurements were carried out by the following methods.

[0149] [Fuel cell single cell evaluation (80℃)] (Measurement of IV characteristics and cell resistance) Hydrogen gas was supplied to the anode side of the single cells obtained in the examples and comparative examples, and oxygen gas was supplied to the cathode side. The flow rates were set so that the hydrogen gas utilization rate was 70% and the oxygen gas utilization rate 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 to a relative humidity of 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 initial performance before the start-stop durability test was evaluated.

[0150] (Start / Stop durability measurement) Hydrogen gas was introduced into the anode side of the single cell, and nitrogen gas into the cathode side. A start / stop durability test was conducted at a temperature of 80°C, a relative humidity of 80% RH, and a potential range of 1.0 V to 1.5 V, and the rate of change in electrochemically effective surface area (ECSA) was measured. ECSA was calculated using cyclic voltammetry (CV) by sweeping six times at a temperature of 80°C, a relative humidity of 80% RH, and a potential range of 0.05 V to 1.0 V, using the hydrogen adsorption charge for the sixth sweep. After 5,000 cycles, the IV characteristics and cell resistance were measured in the same manner as above. The results are shown in Table 2.

[0151] [Table 2]

[0152] As shown in Table 2, in Examples 9 to 12, when electrode catalysts A, C, and D were used as cathode catalysts for the single fuel cell, the ECSA maintenance rate was 75% or more, demonstrating excellent durability as a single fuel cell. In particular, in Examples 9, 10, and 12, 2 The initial cell voltages (IV characteristics) at these times were 0.69 V, 0.69 V, and 0.71 V, respectively, and the cell resistances were 78 mΩ cm 2 , 80mΩ·cm 2 , 80mΩ·cm 2After 5,000 cycles, the cell voltage (IV characteristics) was 0.66 V, 0.66 V, and 0.67 V, respectively, and the cell resistance was 81 mΩ cm 2 , 83 mΩ·cm 2 , 82 mΩ·cm 2 The changes in the IV characteristics and cell voltage before and after the start-stop durability test were very small, demonstrating superior durability as a single fuel cell. The Pt particles themselves are conductive, and the Pt particles on the silicon carbide composite material (support) tend to migrate and gradually aggregate during potential cycling tests. However, in Examples 9, 10, and 12, the Pt loading amount (Pt loading density) of electrode catalysts A, C, and electrode catalyst K was greater than in Example 11, suppressing migration and aggregation of Pt and increasing the proportion of Pt densely packed on the support. As a result, the cell resistance was lower than in Example 11, and the IV characteristics were better.

[0153] On the other hand, in Comparative Example 1, when a Pt / CB catalyst was used as the cathode catalyst of the single fuel cell, the ECSA maintenance rate was 55%, and the durability of the single fuel cell was poor. 2 The initial cell voltage (IV characteristics) was 0.68 V and the cell resistance was 85 mΩ cm 2 After 5,000 cycles, the current was 0.8A / cm 2 The cell voltage (IV characteristics) was 0.53V and the cell resistance was 114mΩ cm 2 The changes in IV characteristics and cell voltage before and after the start / stop durability test were very large, and the durability as a single fuel cell was inferior to that of Examples 8 and 9.

[0154] [Fuel cell single cell evaluation (120℃)] (Measurement of IV characteristics and cell resistance) Hydrogen gas was supplied to the anode side of the single cell obtained in Example 10, 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 that 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 120°C, the humidity of the supplied gas was adjusted to a relative humidity of 80% RH, and the back pressure was set to 200 kPa. Power generation was performed within an applied current range in which the voltage of this single cell did not fall below 0.4 V, resulting in a power output of 0.8 A / cm. 2 The cell voltage (IV characteristics) at this time was 0.68 V and the cell resistance was 76 mΩ cm 2 It was found that the material exhibited excellent power generation performance even at a high temperature of 120°C.

[0155] [Fuel cell single cell evaluation (80℃)] (IV characteristics in the high load range) Hydrogen gas was supplied to the anode side of the single cells obtained in Examples 9 and 12 and Comparative Example 2, and air was supplied to the cathode side. The flow rates were set so that the utilization rate of the hydrogen gas was 50% and the utilization rate of the air was 50%. 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 to a relative humidity of 80% RH. The current density at 0.6 V was evaluated, and the result was 0.7 A / cm for Comparative Example 2. 2 In contrast, Example 9 had a value of 0.8 A / cm 2 and Example 12 is 1.0 A / cm 2 It was found that the excellent material transport properties resulted in excellent performance in the high load range. [Industrial Applicability]

[0156] The electrode catalyst of this embodiment achieves high conductivity while maintaining a large BET specific surface area, and also has excellent durability, making it suitable as an electrode material used in the catalyst layer of a fuel cell electrode. In particular, since 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 the power generation performance and durability of a fuel cell, it is expected to make a significant contribution to the practical application of fuel cells for commercial vehicles, which are expected to be used in a wide variety of applications.

Claims

1. A porous silicon carbide composite material containing silicon carbide (SiC) and a carbon material (A); particles supported on the porous silicon carbide composite material and containing a precious metal; a domain formed in a portion of the porous silicon carbide composite material and made of silicon oxide; Equipped with BET specific surface area is 10m ２ / g or more and electrical conductivity is 0.1 S / cm or more, The electrode catalyst has a particle size ratio of an average diameter of primary particles of the silicon carbide (SiC) to an average diameter of the carbon material of 10:1 to 1:

5.

2. A porous silicon carbide composite material containing silicon carbide (SiC) and a carbon material (A); A carbon material (B), Particles containing a noble metal supported on the porous silicon carbide composite material and / or the carbon material (B); a domain formed in a portion of the porous silicon carbide composite material and made of silicon oxide; Equipped with BET specific surface area is 10m ２ / g or more and electrical conductivity is 0.1 S / cm or more, The electrode catalyst has a particle size ratio of an average diameter of primary particles of the silicon carbide (SiC) to an average diameter of the carbon material of 10:1 to 1:

5.

3. 3. The electrode catalyst according to claim 1, wherein the amount of the particles containing the noble metal carried is 10% by mass or more and 60% by mass or less when the total mass of the electrode catalyst is taken as 100% by mass.

4. 3. The electrode catalyst according to claim 1, wherein the mass ratio of silicon (Si) to oxygen (O) contained in the electrode catalyst ([Si] / [O]) is 1 / 0.1 to 1 / 0.

001.

5. 2. The electrode catalyst according to claim 1, wherein the mass ratio ([Si] / [C]) of silicon (Si) to carbon (C) contained in the electrode catalyst is 0.4 / 1.0 to 2.0 / 1.

0.

6. 3. The electrode catalyst according to claim 2, wherein the mass ratio ([Si] / [C]) of silicon (Si) to carbon (C) contained in the electrode catalyst is 0.15 / 1.0 to 2.0 / 1.

0.

7. 2. The electrode catalyst according to claim 1, wherein the content of the carbon material (A) is 5% by mass or more and 50% by mass or less.

8. 3. The electrode catalyst according to claim 2, wherein the total content of the carbon materials (A) and (B) is 5% by mass or more and 50% by mass or less.

9. 3. The electrode catalyst according to claim 1, wherein the carbon material (A) and / or (B) is one or more selected from the group consisting of carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons.

10. 3. The electrode catalyst according to claim 1, wherein the particles containing a noble metal are composed of one or more types selected from the group consisting of platinum (Pt), a platinum-cobalt alloy (PtCo), and a platinum-nickel alloy (PtNi).

11. 3. An electrode for a fuel cell, comprising a layer containing the electrode catalyst according to claim 1.

12. A fuel cell comprising the fuel cell electrode according to claim 11.

13. A method for producing the electrode catalyst of claim 1, 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 (A) or an organic polymer to the acidic aqueous solution, thereby forming a gel containing the carbon material (A) or the organic polymer through a sol-gel reaction of the organic alkoxysilane; (B) washing the gel with alcohol; (C-1) a step of drying the washed gel to form a porous silicon carbide precursor; A step (D-1) of calcining the porous silicon carbide precursor to obtain a porous silicon carbide composite material containing silicon carbide (SiC) and the carbon material (A); a step (E-1) of mixing the porous silicon carbide composite material with a dispersion containing a colloid containing a noble metal and aqueous hydrogen peroxide to obtain a mixture, and forming a domain of silicon oxide in a part of the porous silicon carbide composite material to obtain an electrode catalyst containing particles containing a noble metal; The method for producing an electrode catalyst comprising the steps of:

14. A method for producing the electrode catalyst according to claim 2, 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 (A) or an organic polymer to the acidic aqueous solution, thereby forming a gel containing the carbon material (A) or the organic polymer through a sol-gel reaction of the organic alkoxysilane; (B) washing the gel with alcohol; (C-1) a step of drying the washed gel to form a porous silicon carbide precursor; A step (D-1) of calcining the porous silicon carbide precursor to obtain a porous silicon carbide composite material containing silicon carbide (SiC) and the carbon material (A); a step (E-1) of mixing the porous silicon carbide composite material with a dispersion containing a colloid containing a noble metal and aqueous hydrogen peroxide to obtain a mixture, and forming a domain of silicon oxide in a part of the porous silicon carbide composite material to obtain an electrode catalyst containing particles containing a noble metal; and The method for producing an electrode catalyst further comprises any one of the following steps (1) to (4): (1) Step (C-2) of blending the porous silicon carbide precursor obtained in step (C-1) with a carbon material (B). (2) A step (D-2) of blending a carbon material (B) with the porous silicon carbide composite material obtained in the step (D-1). (3) A step (E-2) of blending a carbon material (B) with the electrode catalyst containing the noble metal-containing particles obtained in the step (E-1). (4) After the step (E-1), a step (F-1) is performed in which the solid content of the mixture is heat-treated in an oxygen atmosphere to further grow the silicon oxide domain formed in part of the porous silicon carbide composite material, and a step (F-2) is performed in which a carbon material (B) is blended with the mixture obtained in the step (F-1).

15. 15. The method for producing an electrode catalyst according to claim 13 or 14, further comprising, after step (E-1) or (E-2), step (F-1) of heat-treating the solid content of the mixture in an oxygen atmosphere to further grow the domains made of silicon oxide formed in part of the porous silicon carbide composite material.

16. The method for producing an electrode catalyst according to claim 15, wherein in the step (F-1), the solid content of the mixture is heat-treated at 100° C. or higher and 800° C. or lower.

17. The method for producing an electrode catalyst according to claim 13 or 14, wherein the organic alkoxysilane is represented by the following formula (1) or formula (2): R １ -SiR ２ ｘ (OR ３ ) ３－ｘ ・・・(1) (wherein 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. R ４ -(SiR ５ ｙ (OR ６ ) ３－ｙ ) ２ ・・・(2) (wherein 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.

18. 15. The method for producing an electrode catalyst according to claim 13 or 14, wherein the carbon material (A) and / or (B) is composed of one or more materials selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons.

19. 15. The method for producing an electrode catalyst according to claim 13 or 14, wherein the colloid containing a noble metal is composed of one or more colloids selected from the group consisting of platinum (Pt) colloid, platinum-cobalt (PtCo) colloid, and platinum-nickel (PtNi) colloid.

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