Porous silicon carbide composite material, fuel cell electrode, and method for producing porous silicon carbide composite material

Abstract

To provide a porous silicon carbide composite material that has both a high BET specific surface area and high electrical conductivity, and a method for producing the porous silicon carbide composite material in which the pore size can be controlled using an organic alkoxysilane of the type widely available as an industrial raw material.SOLUTION: A porous silicon carbide composite material is a porous silicon carbide composite material containing silicon carbide (SiC) and a carbon material, and has a BET specific surface area of 10 m2 / g or more and an electrical conductivity of 0.1 S / cm or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a porous silicon carbide composite material, an electrode for a fuel cell, and a method for producing the porous silicon carbide composite material. This application claims priority based on Japanese Patent Application No. 2023-041000, filed on March 15, 2023, the contents of which are incorporated herein by reference. Regarding. [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 electrical conductivity are used as catalyst supports. However, deterioration of catalytic performance due to corrosion of the carbon support has become a major problem in the cathode and anode. Therefore, there is an urgent need to develop a material with high specific surface area, high electrical conductivity, and excellent durability to replace carbon.

[0004] For example, Patent Document 1 discloses an electrode catalyst comprising (A) Group 13-doped SiC, in which SiC is doped with a Group 13 (Group 3B) element, (B) conductive carbon particles, and (C) a noble metal supported on the surface of the (A) Group 13-doped SiC. The Group 13 element doped into SiC is, for example, 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 2 discloses a method for producing conductive silicon carbide porous bodies with different resistivities, which includes an oxidation treatment step in which a sintered body of conductive porous silicon carbide ceramics is heated in an oxidizing atmosphere at a predetermined heating temperature for a predetermined heating time to form a silicon dioxide layer on the surface of the silicon carbide particles, and the heating temperature and / or heating time in the oxidation treatment step is changed.

[0006] Patent Document 3 also discloses a method for producing an ordered mesoporous silicon carbide nanocomposite material, which comprises forming a precursor mixture containing a carbon precursor, a silica precursor, a surfactant, and an oil, drying the precursor mixture, crosslinking the carbon precursor and the silica precursor to form a surfactant-based self-assembled template and a mesostructured phase of the carbon precursor and silica precursor that is ordered by the template, and heat-treating the precursor to form an ordered mesoporous silicon carbide nanocomposite material. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-149008 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-051748 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-155372 Summary of the Invention [Problem to be solved by the invention]

[0008] Fuel cell electrodes that achieve high efficiency and high output require supports that have both a large specific surface area and high electrical conductivity. Although Patent Document 1 describes a silicon carbide composite material that contains silicon carbide particles with a noble metal supported on the surface and conductive carbon particles to impart electrical conductivity, it does not mention the specific surface area or specific electrical conductivity of the porous silicon carbide, leaving room for improvement.

[0009] Patent Document 2 describes a conductive silicon carbide porous body having a resistivity of 3.4 to 21.7 Ω·cm (0.046 to 0.29 S / cm), but the conductivity is insufficient, and there is no mention of the specific surface area of ​​the porous silicon carbide composite material. Patent Document 2 also describes a porous silicon carbide composite material obtained by adding a binder, a lubricant, and water to a raw material mixture of silicon carbide, silicon nitride, and graphite, kneading the mixture, extruding, and firing the mixture in a non-oxidizing atmosphere. However, this manufacturing method does not allow for control of pore size, making it impossible to produce a variety of porous silicon carbide composite materials with different pore sizes and specific surface areas.

[0010] Furthermore, Patent Document 3 discloses that the desorption cumulative surface area (DCSA) of porous silicon carbide is 354.7 to 950.9 m 2 / g (N2 or Ar), cumulative adsorption surface area (ACSA) is 311.4 to 862.7 m 2 / g (N2 or Ar), but makes no mention of electrical conductivity. Furthermore, in Patent Document 3, a ceramic precursor is synthesized by mixing an alkoxysilane, a carbon-containing compound, and a surfactant, and then fired in an inert atmosphere to obtain a porous silicon carbide composite material, but this manufacturing method, like Patent Document 2, is unable to produce a variety of porous silicon carbide composite materials with different pore sizes and specific surface areas.

[0011] The object of the present invention is to provide a porous silicon carbide composite material and a fuel cell electrode that have both a high BET specific surface area and high electrical conductivity, and to provide a method for producing a porous silicon carbide composite material in which the pore size can be controlled using an organoalkoxysilane of the type that is widely available as an industrial raw material. [Means for solving the problem]

[0012] To achieve the above objective, the present invention has 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 aqueous 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 a porous three-dimensional framework. Specifically, it has been found that adjusting the porous structure during the preparation of the precursor gel and then preparing the porous silicon carbide composite material allows for control of the pore size and specific surface area of ​​the porous silicon carbide composite material. Furthermore, it has been discovered that gradually progressing the condensation polymerization reaction of polysilsesquioxane while adjusting the pH to form a precursor gel with a porous structure allows for a densely dispersed arrangement of the carbon material within the porous three-dimensional framework, resulting in a porous silicon carbide composite material with higher electrical conductivity. They also found that by subjecting a porous silicon carbide composite material to a heat treatment in an oxygen atmosphere, silicon oxide can be formed on the surface of the silicon carbide, thereby stabilizing the areas that are prone to deterioration by pre-oxidizing them, and that it is possible to provide a porous silicon carbide composite material that can exhibit high electrical conductivity while maintaining a large BET specific surface area.

[0013] That is, the present invention provides the following configurations. [1] A porous silicon carbide composite material comprising silicon carbide (SiC) and a carbon material, BET specific surface area is 10m 2 / g or more and a conductivity of 0.1 S / cm or more.

[0014] [2] A porous silicon carbide composite material containing silicon carbide (SiC) and a carbon material (A), A carbon material (B), BET specific surface area is 10m 2 / g or more and a conductivity of 0.1 S / cm or more.

[0015] [3] The total pore volume is 0.3 cm 3 / g or more.

[0016] [4] The porous silicon carbide composite material according to [1] or [2] above, wherein the pore diameter is 10 nm or more and 1000 nm or less.

[0017] [5] The porous silicon carbide composite material according to any one of [1] to [3] above, wherein the mass ratio of silicon (Si) to carbon (C) contained in the porous silicon carbide composite material ([Si] / [C]) is 0.4 / 1.0 to 2.0 / 1.0.

[0018] [6] The porous silicon carbide composite material according to [2] above, wherein the mass ratio of silicon (Si) to carbon (C) contained in the porous silicon carbide composite material ([Si] / [C]) is 0.15 / 1.0 to 2.0 / 1.0.

[0019] [7] The porous silicon carbide composite material 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.

[0020] [8] The porous silicon carbide composite material according to [2] above, wherein the total content of the carbon materials (A) and (B) is 5% by mass or more and 50% by mass or less.

[0021] [9] The porous silicon carbide composite material according to any one of [1] to [5] above, wherein the carbon material (A) and / or (B) is one or more selected from carbon black, carbon nanofiber, carbon nanotube, and low-crystalline nanocarbon.

[0022]

[10] The porous silicon carbide composite material according to any one of [1] to [9] above, 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.

[0023]

[11] The porous silicon carbide composite material according to any one of [1] to

[10] above, wherein a domain made of silicon oxide formed by oxidation of the silicon carbide (SiC) is formed in a part of the composite material.

[0024]

[12] The porous silicon carbide composite material according to

[11] above, wherein the domains made of silicon oxide are formed on the surface of silicon carbide (SiC) in the porous silicon carbide composite material.

[0025]

[13] The porous silicon carbide composite material according to any one of the above [1] to

[12] , wherein the mass ratio of silicon (Si) to oxygen (O) contained in the porous silicon carbide composite material ([Si] / [O]) is 1 / 0.1 to 1 / 0.001.

[0026]

[14] An electrode for a fuel cell, having a layer containing the porous silicon carbide composite material according to any one of [1] to

[13] above.

[0027]

[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; A step (C-1) of drying the washed gel to form a porous silicon carbide precursor; and a step (D-1) of calcining the porous silicon carbide precursor to obtain a porous silicon carbide composite material containing silicon carbide (SiC) and a carbon material (A). 1. A method for producing a porous silicon carbide composite material comprising:

[0028]

[16] 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; A step (C-1) of drying the washed gel to form a porous silicon carbide precursor; and a step (D-1) of firing the porous silicon carbide precursor to obtain a composite material containing silicon carbide (SiC) and a carbon material (A). and A method for producing a porous silicon carbide composite material further comprising any one of the following steps (1) to (2): (1) A step (C-2) of further blending a carbon material (B) with the porous silicon carbide precursor obtained in the step (C-1). (2) A step (D-2) of further blending a carbon material (B) with the porous silicon carbide composite material obtained in the step (D-1).

[0029]

[17] A method for producing a porous silicon carbide composite material according to

[15] or

[16] above, comprising, after step (D-1) or (D-2), step (E-1) of heat-treating the composite material in the presence of oxygen to form a domain made of silicon oxide in a part of the composite material.

[0030]

[18] The method for producing a porous silicon carbide composite material according to

[15] or

[16] above, wherein in the step (D-1), the porous silicon carbide precursor is fired at 1300°C or higher and 3000°C or lower.

[0031]

[19] The method for producing a porous silicon carbide composite material according to any one of the above

[15] to

[18] , 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.

[0032]

[20] The method for producing a porous silicon carbide composite material according to any one of the above

[15] to

[19] , wherein the mass ratio of the carbon material (A) or the organic polymer to the organic alkoxysilane is 2.5-50:97.5-50.

[0033]

[21] The method for producing a porous silicon carbide composite material according to any one of

[15] to

[20] above, wherein the carbon material (A) and / or (B) is one or more selected from carbon black, carbon nanofiber, carbon nanotube, and low-crystalline nanocarbon.

[0034]

[22] The method for producing a porous silicon carbide composite material according to any one of

[15] to

[21] above, wherein the organic polymer is one or more selected from the group consisting of phenolic resin, polystyrene, and polydivinylbenzene. [Effects of the Invention]

[0035] The present invention provides a porous silicon carbide composite material and a fuel cell electrode that have both a high BET specific surface area and high electrical conductivity, and a method for producing a porous silicon carbide composite material in which the pore size can be controlled using an organoalkoxysilane of the type widely used as an industrial raw material. [Brief explanation of the drawings]

[0036] [Figure 1] FIG. 1 is a flow chart illustrating an example of a method for producing a porous silicon carbide composite material according to an embodiment of the present invention. [Figure 2] FIG. 2 shows a transmission electron microscope image of the porous silicon carbide composite material exemplified in Example 1. [Figure 3] FIG. 3 shows the X-ray diffraction pattern of the porous silicon carbide composite material exemplified in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0037] <Structure of porous silicon carbide composite material> The porous silicon carbide composite material according to this embodiment is composed of either the following porous silicon carbide composite material (I) or porous silicon carbide composite material (II). The porous silicon carbide composite material (I) is a porous silicon carbide composite material containing silicon carbide (SiC) and a carbon material (A), and has a BET specific surface area of ​​10 m 2 / g or more, and the electrical conductivity is 0.1 S / cm or more.

[0038] The porous silicon carbide composite material (II) is a porous silicon carbide composite material containing silicon carbide (SiC) and a carbon material (A), A carbon material (B), BET specific surface area is 10m 2 / g or more, and the electrical conductivity is 0.1 S / cm or more.

[0039] The form of the porous silicon carbide composite materials (I) and (II) is not particularly limited, but may be, for example, powder, particulate, fibrous or acicular, with powder or particulate being preferred. When the porous silicon carbide composite materials (I) and (II) are in the form of powder or particles, the particle size of the porous silicon carbide composite materials (I) and (II) is not particularly limited, but the particle size D of the 50% cumulative particle size in the volume-based cumulative particle size distribution is 50 For example, the thickness is preferably 0.05 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.

[0040] Particle size D of porous silicon carbide composite materials (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:

[0041] The porous silicon carbide composite materials (I) and (II) of this embodiment have a BET specific surface area of ​​10 m 2 / g or more, and 20m 2 / g or more, and 2 / g or more. 2 / g or less. The BET specific surface area is 10 m 2 When the BET specific surface area is 300 m or more, the amount of catalyst particles supported on the support surface is sufficiently secured, and when the porous silicon carbide composite materials (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.

[0042] The total pore volume of the porous silicon carbide composites (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 porous silicon carbide composite materials (I) and (II) 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.

[0043] The pore diameter of the porous silicon carbide composite materials (I) and (II) 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 diameter of the porous silicon carbide composite materials (I) and (II) is 10 nm or more and 1000 nm or less, the flow of the reaction gas and electrolyte within the catalyst layer is facilitated, thereby improving the catalytic efficiency. In particular, when the pore diameter of the porous silicon carbide composite materials (I) and (II) is 10 nm or more, the supply of the reaction gas and electrolyte to the supported catalyst particles is stabilized, preventing a decrease in the catalyst particle utilization rate.

[0044] The BET specific surface area, total pore volume, and pore diameter of the porous silicon carbide composite materials (I) and (II) can be calculated as measured values ​​by a gas adsorption method, and refer to values ​​calculated from the amount of adsorption and condensation of 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.

[0045] In the porous silicon carbide constituting the porous silicon carbide composite materials (I) and (II), a plurality of micropores are provided independently by a three-dimensional framework structure, or a plurality of micropores are provided in a state in which some or all of the micropores are interconnected.

[0046] The porous silicon carbide composite materials (I) and (II) contain carbon that constitutes the three-dimensional skeletal structure of porous silicon carbide (SiC) as a carrier, and a carbon material (A) that is other than the carbon that constitutes the three-dimensional skeletal structure and is supported on the porous silicon carbide (I) and (II).

[0047] 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.

[0048] [Carbon material (A)] The carbon material (A) is contained in both the electrode catalysts (I) and (II). The carbon material (A) supported on the three-dimensional skeleton structure of the porous silicon carbide 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.

[0049] 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 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 (A) is 10 nm or more and 200 nm or less, good electrical conductivity can be achieved.

[0050] 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.

[0051] The shape and size of the carbon material (A) held in the porous silicon carbide composite material (I) 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.

[0052] In the porous silicon carbide (I), the content of the carbon material (A) 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 (I) 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.

[0053] [Carbon material (B)] The carbon material (B) is contained in the porous silicon carbide composite material (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, carbon material (B) is preferably carbon black from the viewpoint of realizing high conductivity and manufacturability. Alternatively, carbon material (B) may be the same as carbon material (A).

[0054] 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.

[0055] 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.

[0056] The content of the carbon material (B) in the porous silicon carbide composite material (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 (B) 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.

[0057] The shape and size of the carbon material (B) held in the porous silicon carbide composite material (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 microscope images using image analysis particle size distribution measurement software.

[0058] The total content of the carbon materials (A) and (B) in the porous silicon carbide composite material (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. [Silicon carbide]

[0059] The average diameter of the primary particles of silicon carbide in the porous silicon carbide composite materials (I) and (II) 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, which is preferable.

[0060] The particle size of silicon carbide in the porous silicon carbide composite materials (I) and (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 microscope images using image analysis particle size distribution measurement software.

[0061] 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. Within this range, the mass transport of the resulting electrode layer containing the porous silicon carbide composite material can be improved.

[0062] The ratio of the average diameter of the primary particles of silicon carbide to the average diameter of the carbon material (B) (SiC:carbon material (B)) 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. Within this range, the mass transport of the resulting electrode layer containing the porous silicon carbide composite material can be improved.

[0063] [Silicon oxide] In the porous silicon carbide composite materials (I) and (II) of this embodiment, a domain made of silicon oxide formed by oxidation of silicon carbide (SiC) may be formed in a portion of the composite material. Examples of silicon oxide include silicon monoxide (SiO) and silicon dioxide (SiO2). The form of the domain is not particularly limited, but may be, for example, a single crystal or an aggregate thereof. The silicon oxide domain is dispersed and arranged on the surface of the porous silicon carbide composite materials (I) and (II). Furthermore, it is preferable that the silicon oxide domain is formed on the surface of silicon carbide (SiC) in the porous silicon carbide composite materials (I) and (II). This can suppress oxidation of the silicon carbide surface.

[0064] In the case of the porous silicon carbide composite material (I), the mass ratio of silicon (Si) to carbon (C) ([Si] / [C]) contained in the porous silicon carbide composite material is preferably 0.4 / 1.0 or more and 2.0 / 1.0 or less, more preferably 0.5 / 1.0 or more and 1.8 / 1.0 or less, and even more preferably 0.7 / 1.0 or more and 1.7 / 1.0 or less.

[0065] In the case of the porous silicon carbide composite material (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 or more and 2.0 / 1.0 or less, or 0.15 / 1.0 to 2.0 / 1.0, high conductivity is achieved while suppressing corrosion of the carbon, thereby improving the durability of the catalytic cycle. Note that the carbon (C) in the above mass ratio refers to the total of the carbon that constitutes the three-dimensional framework structure of the porous silicon carbide and the carbon materials (A) and (B) contained in the porous silicon carbide composite material.

[0066] The mass ratio of silicon (Si) to oxygen (O) ([Si] / [O]) in the porous silicon carbide composite materials (I) and (II) is preferably 1 / 0.1 or more and 1 / 0.001 or less, more preferably 1 / 0.1 or more and 1 / 0.005 or less, and even more preferably 1 / 0.01 or more and 1 / 0.005 or less. When the mass ratio of silicon (Si) ([Si] / [O]) is 1 / 0.1 or more and 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.

[0067] The carbon (C) content in the porous silicon carbide composite materials (I) and (II) refers to a value measured by, for example, combining the determination of the ratio of contained elements by elemental analysis and thermogravimetric-differential thermal analysis (TG-DTA) under atmospheric conditions.

[0068] The content of silicon (Si) in the porous silicon carbide composite materials (I) and (II) means a value determined by, for example, elemental analysis to identify the ratio of contained elements.

[0069] [Characteristics of porous silicon carbide composites] The porous silicon carbide composite materials (I) and (II) of this embodiment have an electrical 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 electrical conductivity may be 100 S / cm or less, 70 S / cm or less, or even 50 S / cm or less. The higher the electrical conductivity of the porous silicon carbide, the better the porous silicon carbide composite material for fuel cells. However, if the amount of carbon material that contributes to improving electrical conductivity is too high, oxidation corrosion of the carbon component may occur during the catalytic cycle, reducing durability.

[0070] <Method for manufacturing porous silicon carbide composite material> As shown in FIG. 1, the method for producing the porous silicon carbide composite material (I) according to this embodiment includes a gel formation step (step (A)), a cleaning step (step (B)), a porous silicon carbide precursor formation step (step (C-1)), and a firing step (step (D-1)).

[0071] The method for producing the porous silicon carbide composite material (II) according to this embodiment includes a gel-forming step (step (A)), a cleaning step (step (B)), a porous silicon carbide precursor-forming step (step (C-1)), and a firing step (step (D-1)), and further includes any one of the following steps (1) to (2): (1) A step (C-2) of further blending a carbon material with the porous silicon carbide precursor obtained in the step (C-1). (2) A step (D-2) of further blending a carbon material with the porous silicon carbide composite material obtained in the step (D-1). It should be noted that other steps may be performed before or after each step, provided that the porous silicon carbide composite material according to this embodiment is obtained. The manufacturing method described below makes it possible to obtain a porous silicon carbide composite material having a desired mass ratio ([Si] / [C]) by a single firing.

[0072] [Process (A)] In step (A), for example, an organic alkoxysilane is added to an acidic aqueous solution containing a surfactant and a pH adjuster, followed by the addition of a carbon material (A) or an organic polymer, and a gel containing the carbon material (A) or the organic polymer 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. Furthermore, by gradually increasing the pH with a pH adjuster while allowing the condensation polymerization reaction of polysilsesquioxane to proceed, the carbon material or organic polymer can be more densely dispersed in the porous structure of the precursor gel, thereby further improving the dispersibility of the carbon material in the three-dimensional structural framework of the porous silicon carbide composite material.

[0073] 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.

[0074] 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 the nonionic surfactant and 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 a large BET specific surface area and developed mesopores to macropores can be formed.

[0075] 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.

[0076] The pH adjuster is not particularly limited, but examples thereof include substances containing any one selected from urea, ammonia, and sodium hydroxide.

[0077] The acidic aqueous solution is not particularly limited, but examples thereof include aqueous solutions of hydrochloric acid, nitric acid, acetic acid, and the like.

[0078] The organic alkoxysilane is preferably represented by the following formula (1) or (2): By using an organic alkoxysilane represented by the following formula (1) or (2), porous silicon carbide having a desired three-dimensional framework structure can be easily formed. 1 -SiR 2 x (OR3 ) 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.

[0079] Specific examples of the organic alkoxysilane represented by the above formula (1) include methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, methylethyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, methylvinyldimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, and methylphenyldimethoxysilane. Specific examples of the organic alkoxysilane represented by the formula (2) include bis(trimethoxysilyl)methane, bis(triethoxysilyl)methane, bis(methyldimethoxysilyl)methane, bis(methyldiethoxysilyl)methane, 1,2-bis(trimethoxysilyl)ethane, 1,2-bis(triethoxysilyl)ethane, 1,2-bis(methyldimethoxysilyl)ethane, 1,2-bis(methyldiethoxysilyl)ethane, 1,6-bis(trimethoxysilyl)hexane, 1,6-bis(triethoxysilyl)hexane, 1,6-bis(methyldimethoxysilyl)hexane, 1,6-bis(methyldiethoxysilyl)hexane, Examples of suitable organic alkoxysilanes include 1,2-bis(trimethoxysilyl)ethene, 1,2-bis(triethoxysilyl)ethene, 1,2-bis(methyldimethoxysilyl)ethene, 1,2-bis(methyldiethoxysilyl)ethene, 1,4-bis(trimethoxysilyl)benzene, 1,4-bis(triethoxysilyl)benzene, 1,4-bis(methyldimethoxysilyl)benzene, 1,4-bis(methyldiethoxysilyl)benzene, 4,4'-bis(trimethoxysilyl)biphenyl, 4,4'-bis(triethoxysilyl)biphenyl, 4,4'-bis(methyldimethoxysilyl)biphenyl, and 4,4'-bis(methyldiethoxysilyl)biphenyl. The above ethene derivatives include cis / trans geometric isomers, and either isomer can be used. The organic alkoxysilanes used may be of one type or multiple types.

[0080] 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.

[0081] 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 3-30:70-97, and even more preferably 5-20:80-95. By maintaining the mass ratio of the carbon material (A) or the organic polymer to the organic alkoxysilane within the above range, both a larger BET specific surface area and higher electrical conductivity can be achieved. 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.

[0082] 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.

[0083] The organic polymer is not particularly limited, but may be composed of one or more selected from, for example, phenolic resin, polystyrene, and polydivinylbenzene.

[0084] [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.

[0085] [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.

[0086] [Process (C-2)] The method for producing the porous silicon carbide composite material (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. Of these, from the viewpoints of achieving high conductivity and manufacturability, carbon material (B) is preferably 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.

[0087] 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.

[0088] The amount of the carbon material (B) to be blended is not particularly limited, but it is preferable to blend it so that the [Si] / [C] ratio in the porous silicon carbide composite material (II) after firing is 0.4 / 1.0 to 2.0 / 1.0.

[0089] [Process (D-1)] In step (D-1), the porous silicon carbide precursor containing the carbon material (A) or organic polymer is calcined to obtain a composite material containing silicon carbide (SiC) and a carbon 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 through 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.

[0090] 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.

[0091] 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.

[0092] [Process (D-2)] The method for producing the porous silicon carbide composite material (II) may further include step (D-2). In step (D-2), a carbon material (B) is blended with the porous silicon carbide composite material obtained in 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. Of these, from the viewpoints of achieving high conductivity and manufacturability, 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.

[0093] 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.

[0094] The amount of the carbon material (B) to be blended is not particularly limited, but it is preferable to blend it so that the [Si] / [C] ratio in the porous silicon carbide composite material (II) after firing is 0.15 / 1.0 to 2.0 / 1.0.

[0095] While it is sufficient to include either one of the steps (C-2) and (D-2), it is preferable to include the step (D-2) from the viewpoint of the performance of the resulting porous silicon carbide composite material (II). By including the step (D-2), it is possible to improve the electrical conductivity while maintaining the durability of the resulting porous silicon carbide composite material (II), which is preferable.

[0096] [Process (E-1)] The method for producing the porous silicon carbide composite material (I) or (II) may further include a step (E-1). In step (E-1), the composite material is heat-treated in an oxygen atmosphere to form a silicon oxide domain in a portion of the composite material. The heat treatment in this step can be performed by a known, conventional method under any conditions, as long as the heat treatment is performed in an oxygen atmosphere. For example, the temperature is increased at a rate of 10°C per minute in air, and the maximum temperature reached is maintained for a certain period of time. The heat treatment temperature is preferably 500°C to 800°C, more preferably 550°C to 750°C, and even more preferably 600°C to 700°C. The heat treatment temperature maintenance time can be determined appropriately based on the time effective for forming a silicon oxide domain in a portion of the porous silicon carbide composite material. For example, 15 minutes to 4 hours is preferred, 20 minutes to 3 hours is more preferred, and 30 minutes to 2 hours is even more preferred. In this process, a portion of the silicon in the porous silicon carbide composite material is oxidized to silicon oxide, and domains consisting of this silicon oxide are formed on the surface of the silicon carbide in the porous silicon carbide composite material. Examples of silicon oxide include silicon monoxide (SiO) and silicon dioxide (SiO2). The morphology of the domains is not particularly limited, but may be, for example, amorphous. The effect of this process is to further increase the specific surface area of ​​the porous silicon carbide composite material while maintaining a certain degree of electrical conductivity compared to porous silicon carbide composite materials that are not heat-treated in an oxygen atmosphere. In addition, the stability of the porous silicon carbide composite material can be improved by pre-oxidizing the areas of silicon carbide that are prone to deterioration.

[0097] [Process (E-2)] The method for producing the porous silicon carbide composite material (I) or (II) may further include step (E-2). In step (E-2), a carbon material (B) is blended with the mixture 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. Of these, from the viewpoints of achieving high conductivity and manufacturability, 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 electrode catalyst after firing is 0.15 / 1.0 to 2.0 / 1.0.

[0100] When the step (E-2) is included, the steps (C-2) and (D-2) can be omitted. [Example]

[0101] Examples of the present invention will be described below. The present invention is not limited to the examples shown below. Values ​​in the tables mean "parts by weight" unless otherwise specified.

[0102] 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), and then placed in a tubular furnace. The mixture was heated to 1500°C at a rate of 2.5°C / min in an argon atmosphere and held at this temperature for 2 hours to obtain porous silicon carbide composite material 1.

[0103] Example 2 Porous silicon carbide composite material 2 was obtained in the same manner as in Example 1, except that the amount of Ketjen black (ECP) mixed with 1 g of the obtained porous silicon carbide precursor was changed to 0.6 g.

[0104] Example 3 The porous silicon carbide composite material 1 obtained in Example 1 was heat-treated in the atmosphere at 600° C. for 2 hours while blocking the air flow, to obtain a porous silicon carbide composite material 3.

[0105] Example 4 Porous silicon carbide composite material 4 was obtained in the same manner as in Example 1, except that the porous silicon carbide precursor was synthesized using 2.5 g of methyltrimethoxysilane (manufactured by Kanto Chemical Co., Ltd.) and 2.5 g of phenyltrimethoxysilane (manufactured by Kanto Chemical Co., Ltd.).

[0106] Example 5 Porous silicon carbide composite material 5 was obtained in the same manner as in Example 1, except that the porous silicon carbide precursor was synthesized using 2.5 g of methyltrimethoxysilane (manufactured by Kanto Chemical Co., Ltd.) and 2.5 g of vinyltrimethoxysilane (manufactured by Kanto Chemical Co., Ltd.).

[0107] Example 6 Porous silicon carbide composite material 6 was obtained in the same manner as in Example 1, except that the raw material Ketjen black (ECP-600JD) and the Ketjen black (ECP) mixed with the porous silicon carbide precursor were changed to carbon nanotubes (manufactured by Osaka Soda Co., Ltd.).

[0108] Example 7 Porous silicon carbide composite material 7 was obtained in the same manner as in Example 1, except that the raw material Ketjen black (ECP-600JD) and the Ketjen black (ECP) mixed with the porous silicon carbide precursor were changed to graphene (manufactured by Nishina Materials Co., Ltd.).

[0109] Example 8 Porous silicon carbide composite material 8 was obtained in the same manner as in Example 4, except that the porous silicon carbide precursor was fired at 1400°C.

[0110] Example 9 Porous silicon carbide composite material 9 was obtained in the same manner as in Example 8, except that 0.4 g of Ketjen black (ECP) was used in synthesizing the porous silicon carbide precursor and 0.4 g of Ketjen black (ECP) was not mixed into the porous silicon carbide precursor before calcination.

[0111] (Comparative Example 1) A porous silicon carbide composite material 10 was obtained in the same manner as in Example 1, except that urea was not used.

[0112] (Comparative Example 2) Porous silicon carbide composite material 11 was obtained in the same manner as in Example 1, except that the raw material Ketjen black (ECP-600JD) was not used when producing the porous silicon carbide precursor, and the amount of Ketjen black (ECP) mixed with 1 g of the obtained porous silicon carbide precursor was changed to 0.3 g.

[0113] (Comparative Example 3) Porous silicon carbide composite material 12 was obtained in the same manner as in Example 4, except that the porous silicon carbide precursor was fired at 1600° C. The raw materials and conditions for each step are shown in Table 1.

[0114] [Table 1]

[0115] The above-mentioned Examples 1 to 9 and Comparative Examples 1 to 3 were measured by the following methods.

[0116] [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.

[0117] [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.

[0118] [Measurement of BET specific surface area, pore volume and pore diameter] 0.04 g of electrode catalyst or catalyst 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 changing the relative pressure using a specific surface area / pore size distribution apparatus (Microtrack-Bell, device name "BELSORP-miniII").

[0119] [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 2. Conductivity (S / cm) = (Resistivity (Ω cm)) -1

[0120] [Table 2]

[0121] As shown in Table 2, in Examples 1 to 9, the porous silicon carbide composite material contained silicon carbide (SiC) and a carbon material, and had a BET specific surface area of ​​10 m 2 / g or more and electrical conductivity of 0.1 S / cm or more, and it was found that a porous silicon carbide composite material having both a high BET specific surface area and high electrical conductivity could be obtained.

[0122] As an example, a scanning electron microscope image of the porous silicon carbide composite material 1 illustrated in Example 1 is shown in Figure 2. Porous silicon carbide composite particles were confirmed in which silicon carbide particles with a diameter of approximately 200 nm and carbon material particles with a diameter of approximately 40 nm were developed into a three-dimensional structure.

[0123] 3 shows the X-ray diffraction pattern of the porous silicon carbide composite material exemplified in Example 1. In the crystal structure analysis by X-ray diffraction (XRD), a peak attributable to the (111) plane of the 3C-SiC crystal structure was observed near 2θ = 36°, and a peak attributable to the (220) plane of the 3C-SiC crystal structure was observed near 2θ = 60°, indicating that a porous silicon carbide composite material having the same crystal structure as cubic silicon carbide (3C-SiC) was obtained.

[0124] On the other hand, in Comparative Example 1, the BET specific surface area was 10 m 2 Although the conductivity was high, the specific surface area was small and poor.

[0125] In Comparative Example 2, the BET specific surface area was 15 m 2 / g, but the conductivity is 4.4 × 10 -7 S / cm, which was very poor in conductivity.

[0126] In Comparative Example 3, the BET specific surface area was 16 m 2 / g and electrical conductivity was 17.1 S / cm, indicating high electrical conductivity values. However, the particle size ratio of the average diameter of silicon carbide to that of the carbon material was as large as 13, and no clear pores were formed within the measurement range. [Industrial Applicability]

[0127] The porous silicon carbide composite material of this embodiment has both a larger BET specific surface area and high electrical conductivity, and is therefore suitable as an electrode material used in the catalyst layer of a fuel cell electrode.

Claims

1. A porous silicon carbide composite material comprising silicon carbide (SiC) and a carbon material, BET specific surface area is 10m ２ / g or more and a conductivity of 0.1 S / cm or more.

2. a porous silicon carbide composite material comprising silicon carbide (SiC) and a carbon material (A); A carbon material (B), BET specific surface area is 10m ２ / g or more and a conductivity of 0.1 S / cm or more.

3. The total pore volume is 0.3 cm ３ 3. The porous silicon carbide composite material according to claim 1, wherein the surface roughness of the porous silicon carbide composite is 0.1 / g or more.

4. 3. The porous silicon carbide composite material according to claim 1, wherein the pore diameter is 10 nm or more and 1000 nm or less.

5. the mass ratio ([Si] / [C]) of silicon (Si) to carbon (C) contained in the porous silicon carbide composite material is 0.4 / 1.0 to 2.0 / 1.0; 2. The porous silicon carbide composite material of claim 1, wherein:

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

0.

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

8. 3. The porous silicon carbide composite material 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 porous silicon carbide composite material 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 nanofiber, carbon nanotube, and low-crystalline nanocarbon.

10. 3. The porous silicon carbide composite material according to claim 1, wherein a particle size ratio of an average diameter of primary particles of said silicon carbide (SiC) to an average diameter of said carbon material is 10:1 to 1:

5.

11. 3. The porous silicon carbide composite material according to claim 1, wherein a domain made of silicon oxide formed by oxidation of the silicon carbide (SiC) is formed in a part of the composite material.

12. 12. The porous silicon carbide composite of claim 11, wherein the domains of silicon oxide are formed on the surface of silicon carbide (SiC) in the porous silicon carbide composite.

13. 13. The porous silicon carbide composite material according to claim 11, wherein the mass ratio of silicon (Si) to oxygen (O) contained in the porous silicon carbide composite material ([Si] / [O]) is 1 / 0.1 to 1 / 0.

001.

14. 3. An electrode for a fuel cell, comprising a layer comprising the porous silicon carbide composite material of claim 1 or 2.

15. 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; (D-1) a step of calcining the porous silicon carbide precursor to obtain a composite material containing silicon carbide (SiC) and a carbon material (A); 1. A method for producing a porous silicon carbide composite material comprising:

16. 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; a step (C-1) of drying the washed gel to form a porous silicon carbide precursor; and a step (D-1) of firing the porous silicon carbide precursor to obtain a composite material containing silicon carbide (SiC) and a carbon material (A). and A method for producing a porous silicon carbide composite material, further comprising any one of the following steps (1) to (2): (1) A step (C-2) of further blending a carbon material (B) with the porous silicon carbide precursor obtained in the step (C-1). (2) A step (D-2) of further blending a carbon material (B) with the porous silicon carbide composite material obtained in the step (D-1).

17. 17. The method for producing a porous silicon carbide composite material according to claim 15 or 16, further comprising, after step (D-1) or (D-2), a step (E-1) of heat-treating the composite material in the presence of oxygen to form a domain made of silicon oxide in a part of the composite material.

18. 17. The method for producing a porous silicon carbide composite material according to claim 15, wherein in the step (D-1), the porous silicon carbide precursor is fired at 1300°C or higher and 3000°C or lower.

19. 17. The method for producing a porous silicon carbide composite material according to claim 15 or 16, 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.

20. 17. The method for producing a porous silicon carbide composite material according to claim 15 or 16, wherein a mass ratio of the carbon material (A) or the organic polymer to the organic alkoxysilane is 2.5-50:97.5-50.

21. 17. The method for producing a porous silicon carbide composite material according to claim 15 or 16, wherein the carbon material (A) and / or (B) is one or more selected from the group consisting of carbon black, carbon nanofiber, carbon nanotube, and low-crystalline nanocarbon.

22. 21. The method of claim 20, wherein the organic polymer comprises one or more selected from phenolic resin, polystyrene, and polydivinylbenzene.

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