WO2025234346A1 - Porous silicon nitro-oxycarbide composite material, fuel cell electrode, and method for producing porous silicon nitro-oxycarbide composite material - Google Patents

Abstract

Provided is a porous silicon nitro-oxycarbide composite material comprising a silicon nitro-oxycarbide (SiCNO) and a carbon material, wherein the BET specific surface area is in the range of 100-400 m²/g, and the electrical conductivity is in the range of 1.0-25 S/cm.

Description

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

The present invention relates to a porous silicon nitroxycarbide composite material, an electrode for a fuel cell, and a method for producing the porous silicon nitroxycarbide composite material.
This application claims priority based on Japanese Patent Application No. 2024-077457, filed on May 10, 2024, the contents of which are incorporated herein by reference.

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: Phosphoric Acid Fuel Cells), molten carbonate fuel cells (MCFCs: Molten Carbonate Fuel Cells), solid oxide fuel cells (SOFCs: Solid Oxide Fuel Cells), and polymer electrolyte fuel cells (PEFCs: Polymer Electrolyte Fuel Cells).

Among these, polymer electrolyte fuel cells (PEFCs) generally have a structure in which a catalyst layer that constitutes the anode (fuel electrode) is provided on one side of a solid polymer electrolyte membrane and the cathode (air electrode) is provided on the other side, with a gas diffusion layer bonded to the outside of each catalyst layer. The catalyst layer is composed of a catalyst-supported carrier in which particulate catalyst containing, for example, precious metals is highly dispersed and supported on the surface of nano-level carrier particles.

Currently, carbon-based materials with high specific surface area and high conductivity are used as catalyst carriers. However, a major problem at the cathode and anode is the deterioration of catalytic performance due to corrosion of the carbon carrier. Therefore, there is an urgent need to develop a material that has high specific surface area, high conductivity, and excellent durability to replace carbon.

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 the SiC is, for example, Al (aluminum), 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.

Patent Document 2 discloses a method for producing conductive silicon carbide porous bodies with different resistivities by varying the heating temperature and/or heating time in 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.

JP 2010-149008 A JP 2012-051748 A

Fuel cell electrodes that achieve high efficiency and high output require a carrier that combines a large specific surface area with high electrical conductivity. However, while Patent Document 1 describes a silicon carbide composite material that contains conductive carbon particles and particles with noble metals supported on the surface of silicon carbide to impart electrical conductivity, there is no mention of the specific surface area or specific electrical conductivity of the porous silicon carbide, leaving room for improvement.

Patent Document 2 describes an electrically conductive silicon carbide porous body having a resistivity of 3.4 to 21.7 Ω cm (0.046 to 0.29 S/cm), but this range of resistivity is not sufficient for electrical conductivity. Furthermore, there is no mention of the specific surface area of the porous silicon carbide composite material, leaving room for improvement.
Furthermore, in Patent Document 2, a porous silicon carbide composite material is obtained by adding a binder, a lubricant, and water to a mixed raw material of silicon carbide, silicon nitride, and graphite, kneading the mixture, extruding the mixture, and firing it in a non-oxidizing atmosphere. However, this manufacturing method does not allow for control of the pore size, and therefore does not allow for the production of various porous silicon carbide composite materials with different pore sizes and specific surface areas.

The present invention was made in consideration of the above circumstances, and aims to provide a porous silicon nitroxycarbide composite material and a fuel cell electrode that have both a high BET specific surface area and high conductivity, as well as a method for producing a porous silicon nitroxycarbide composite material that allows for control of pore size.

The inventors discovered that by producing a precursor gel by adding a carbon material or organic polymer as a carbon source during the sol-gel reaction process 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, and then baking this precursor gel in a nitrogen atmosphere, a porous silicon nitroxycarbide composite material is produced in which a mesoscopic pore structure (mesopores) develops into a macroscopic pore structure (macropores), and the carbon material is arranged at the nano-level within a porous three-dimensional framework. Furthermore, by gradually advancing the condensation polymerization reaction of polysilsesquioxane while adjusting the pH to form a precursor gel with a porous structure, the carbon material can be densely dispersed within the porous three-dimensional framework, resulting in a porous silicon nitroxycarbide composite material with higher conductivity.

That is, the present invention provides the following configurations.
(1) Aspect 1 of the present invention is a porous silicon nitroxycarbide composite material comprising silicon nitroxycarbide (SiCNO) and a carbon material, the porous silicon nitroxycarbide composite material having a BET specific surface area of 100 m ² /g or more and 400 m ² /g or less and an electrical conductivity of 1.0 S/cm or more and 25 S/cm or less.

(2) Aspect 2 of the present invention is the porous silicon nitroxycarbide composite material of aspect 1, wherein the total pore volume is 1.3 cm ³ /g or more and 2.5 cm ³ /g or less.

(3) Aspect 3 of the present invention is a porous silicon nitroxycarbide composite material according to aspect 1 or 2, in which the pore diameter is 10 nm or more and 500 nm or less.

(4) Aspect 4 of the present invention relates to a porous silicon nitroxycarbide composite material according to any one of aspects 1 to 3, wherein the mass ratio of carbon (C) to silicon (Si) contained in the porous silicon nitroxycarbide composite material ([C]/[Si]) is 3.0 or more and 8.0 or less.

(5) Aspect 5 of the present invention is a porous silicon nitroxycarbide composite material according to any one of aspects 1 to 4, wherein the mass ratio of oxygen (O) to silicon (Si) contained in the porous silicon nitroxycarbide composite material ([O]/[Si]) is 0.2 or more and 1.5 or less.

(6) Aspect 6 of the present invention relates to the porous silicon nitroxycarbide composite material of any one of aspects 1 to 5, wherein the mass ratio of nitrogen (N) to silicon (Si) contained in the porous silicon nitroxycarbide composite material ([N]/[Si]) is 0.05 or more and 2.0 or less.

(7) Aspect 7 of the present invention is a porous silicon nitroxycarbide composite material according to any one of aspects 1 to 6, wherein the content of the carbon material is 5% by mass or more and 50% by mass or less.

(8) Aspect 8 of the present invention is a porous silicon nitroxycarbide composite material according to any one of aspects 1 to 7, wherein the carbon material is composed of one or more selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons.

(9) Aspect 9 of the present invention relates to the porous silicon nitroxycarbide composite material of any one of aspects 1 to 8, wherein the porous silicon nitroxycarbide composite material is an amorphous material.

(10) Aspect 10 of the present invention relates to an electrode for a fuel cell having a layer containing the porous silicon nitroxycarbide composite material of any one of aspects 1 to 9.

(11) Aspect 11 of the present invention is a method for producing a porous silicon nitroxycarbide composite material, comprising the steps of: (A) adding an organic alkoxysilane to an acidic aqueous solution containing a surfactant and a pH adjuster, and further adding a carbon material or an organic polymer, and forming a gel containing the carbon material or the organic polymer through a sol-gel reaction of the organic alkoxysilane; (B) washing the gel with alcohol; (C) drying the washed gel to form a porous silicon nitroxycarbide precursor; and (D) firing the porous silicon nitroxycarbide precursor in a nitrogen-containing atmosphere to obtain a composite material containing silicon nitroxycarbide (SiCNO) and a carbon material.

(12) Aspect 12 of the present invention relates to a method for producing a porous silicon nitroxycarbide composite material according to aspect 11, wherein in step (D), the porous silicon nitroxycarbide precursor is calcined at a temperature of 1100°C or higher but lower than 1450°C.

(13) A thirteenth aspect of the present invention is the method for producing a porous silicon nitroxycarbide composite material according to the eleventh or twelfth aspect, wherein the organic alkoxysilane is represented by the following formula (1) or formula (2):
R ¹ -SiR ² _x (OR ³ ) _3-X ...(1)
(In the formula, ^R1 represents a group selected from a methyl group, an ethyl group, a vinyl group, and a phenyl group, ^R2 represents a methyl group, and ^R3 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)
(In the formula, ^R4 includes any group selected from a methylene group, an ethylene group, a hexylene group, a vinylene group, a phenylene group, and a biphenylene group; ^R5 represents a methyl group; and ^R6 represents a methyl group or an ethyl group. In the formula, the integer y is 0 or 1.)

(14) Aspect 14 of the present invention relates to a method for producing a porous silicon nitroxycarbide composite material according to any one of aspects 11 to 13, wherein the mass ratio of the carbon material or the organic polymer to the organic alkoxysilane is 2.5 to 50:97.5 to 50.

(15) Aspect 15 of the present invention is a method for producing a porous silicon nitroxide carbide composite material according to any one of aspects 11 to 14, wherein the carbon material is one or more selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons.

(16) Aspect 16 of the present invention relates to a method for producing a porous silicon nitroxycarbide composite material according to aspect 14, wherein the organic polymer is composed of one or more selected from the group consisting of phenolic resin, polystyrene, and polydivinylbenzene.

The present invention provides a porous silicon nitroxycarbide composite material and a fuel cell electrode that combine a high BET specific surface area and high conductivity, and also provides a method for producing a porous silicon nitroxycarbide composite material in which the pore size can be controlled using organic alkoxysilanes of the type widely available as industrial raw materials.

1 is a flow chart showing a step-by-step method for manufacturing a porous silicon nitroxycarbide composite material according to one embodiment of the present invention. 1 is a transmission electron microscope image of a porous silicon nitroxycarbide composite material. 1 is an X-ray diffraction pattern of a porous silicon nitroxycarbide composite material. 1 shows the results of Si-NMR measurement of a porous silicon nitroxycarbide composite material.

Below, with reference to the drawings, a porous silicon nitroxycarbide composite material, a fuel cell electrode, and a method for producing a porous silicon nitroxycarbide composite material according to one embodiment of the present invention will be described. Note that the embodiment shown below is a specific description to provide a better understanding of the spirit of the invention, and does not limit the present invention unless otherwise specified. Furthermore, the drawings used in the following description may, for convenience, show enlarged essential parts to make the features of the present invention easier to understand, and the dimensional proportions of each component may not necessarily be the same as in reality.

<Configuration of porous silicon nitroxycarbide composite material>
The porous silicon nitroxycarbide composite material according to this embodiment is a porous nitroxycarbide composite material containing silicon nitroxycarbide (SiCNO) and a carbon material, and has a BET specific surface area in the range of 100 m ² /g or more and 400 m ² /g or less, and a conductivity in the range of 1.0 S/cm or more and 25 S/cm or less.

The form of the porous silicon nitroxycarbide composite material is not particularly limited, but may be, for example, powder, particulate, fibrous or needle-like, with powder or particulate being preferred.
When the porous silicon nitroxycarbide composite material is in the form of a powder or particles, the particle size of the porous silicon nitroxycarbide composite material is not particularly limited, but is preferably, for example, 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, in terms of the 50% particle size D50 of the cumulative particle size in the volume-based cumulative particle size distribution.

The particle diameter _D50 of the porous silicon nitroxycarbide composite material refers to a value measured in accordance with JIS Z8825-1:2013, and refers to the particle diameter _D50 measured using, for example, a laser diffraction particle size distribution measuring device (Partica LA-960V2, manufactured by Horiba, Ltd.).

The porous silicon nitroxycarbide composite material of this embodiment has a BET specific surface area of 100 m ² /g or more, preferably 150 m ² /g or more, and more preferably 200 m ² /g or more. If the BET specific surface area is 100 m ² /g or more, a sufficient amount of catalyst particles can be supported on the support surface, and when the porous silicon nitroxycarbide composite material is used in a fuel cell electrode, desired characteristics such as output and efficiency can be obtained. Furthermore, if the BET specific surface area is 400 m ² /g or less, the proportion of mesopores suitable for catalyst support increases, thereby further improving the catalyst particle utilization rate.

The total pore volume of the porous silicon nitroxycarbide composite material is preferably 1.3 ^cm3 /g or more and 2.5 ^cm3 /g or less, more preferably 1.5 ^cm3 /g or more and 2.5 ^cm3 /g or less, and particularly preferably 2.0 ^cm3 /g or more and 2.5 ^cm3 /g or less. When the total pore volume of the porous silicon nitroxycarbide composite material is 1.3 ^cm3 /g or more, the flow of reaction gases and electrolytes within the catalyst layer becomes easy, and the catalytic efficiency can be improved.

The pore diameter of the porous silicon nitroxycarbide composite material is preferably 10 nm or more and 500 nm or less, more preferably 20 nm or more and 400 nm or less, and particularly preferably 50 nm or more and 300 nm or less. When the pore diameter of the porous silicon nitroxycarbide composite material is 10 nm or more and 500 nm or less, the flow of reactant gases and electrolytes within the catalyst layer is facilitated, improving catalytic efficiency. In particular, when the pore diameter of the porous silicon nitroxycarbide 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.

The BET specific surface area, total pore volume, and pore diameter of the porous silicon nitroxycarbide composite material described above can be calculated as measured values using a gas adsorption method, and refer to values calculated from the amount of adsorption and condensation of non-corrosive gas when a non-corrosive gas such as nitrogen or argon is adsorbed using, for example, a constant volume method while changing the relative pressure in the adsorption isotherm.

In the porous silicon nitroxycarbide that makes up the porous silicon nitroxycarbide composite material, multiple micropores are provided individually by a three-dimensional skeletal structure, or multiple micropores are provided in a state where some or all of them are connected to each other.

This porous silicon nitroxycarbide composite material contains carbon that constitutes the three-dimensional skeletal structure of porous silicon nitroxycarbide (SiCNO) as a carrier, and a carbon material other than the carbon that constitutes the three-dimensional skeletal structure, which is supported on the porous silicon nitroxycarbide.

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

[Carbon materials]
The carbon material supported on the three-dimensional skeleton structure of porous silicon nitroxycarbide is not particularly limited, and may be composed of one or more selected from, for example, carbon black, carbon nanofiber, carbon nanotube, and low-crystalline nanocarbon. Of these, carbon black is preferred as the carbon material from the viewpoint of achieving high conductivity and manufacturability.

When the carbon material is composed of carbon black, the average diameter of the primary particles of the carbon material is preferably 10 nm or more and 200 nm or less, more preferably 20 nm or more and 100 nm or less, and even more preferably 30 nm or more and 50 nm or less. Good conductivity can be achieved when the average diameter of the primary particles of the carbon material is 10 nm or more and 200 nm or less.

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

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

The carbon material content relative to the porous silicon nitroxycarbide is preferably 5% by mass or more and 50% by mass or less, more preferably 8% by mass or more and 45% by mass or less, and even more preferably 10% by mass or more and 40% by mass or less. When the carbon material content in the porous silicon nitroxycarbide composite material is 5% by mass or more and 50% by mass or less, high conductivity is achieved while suppressing carbon corrosion and other problems, improving the durability of the catalytic cycle.

The mass ratio of carbon (C) to silicon (Si) ([C]/[Si]) contained in the porous silicon nitroxycarbide composite material is preferably 3.0 or more and 8.0 or less, more preferably 3.5 or more and 7.5 or less, and even more preferably 4.0 or more and 7.0 or less.
When the mass ratio of carbon (C) to silicon (Si) ([C]/[Si]) is 3.0 or more and 8.0 or less, high conductivity is achieved in the porous silicon nitroxycarbide composite material, while corrosion of carbon and the like are suppressed, thereby improving the durability of the catalytic cycle.

In the above mass ratio, carbon (C) means the sum of carbon constituting the three-dimensional framework structure of the porous silicon nitroxycarbide and carbon in the carbon material supported on this porous silicon nitroxycarbide.
The carbon (C) content in the porous silicon nitroxycarbide composite material refers to a value measured by, for example, determining the ratio of contained elements through elemental analysis or by SEM-EDS (Energy Dispersive X-ray Spectroscopy) analysis.
The silicon (Si) content in the porous silicon nitroxycarbide composite material refers to a value measured by, for example, determining the ratio of contained elements through elemental analysis or by SEM-EDS (Energy Dispersive X-ray Spectroscopy) analysis.

The mass ratio of oxygen (O) to silicon (Si) ([O]/[Si]) contained in the porous silicon nitroxycarbide composite material is preferably 0.2 or more and 1.5 or less, more preferably 0.3 or more and 1.4 or less, and even more preferably 0.4 or more and 1.3 or less.

The oxygen (O) content in porous silicon nitroxycarbide composite materials refers to values measured, for example, by determining the ratio of contained elements through elemental analysis or by SEM-EDS (Energy Dispersive X-ray Spectroscopy) analysis.

The mass ratio of nitrogen (N) to silicon (Si) ([N]/[Si]) contained in the porous silicon nitroxycarbide composite material is preferably in the range of 0.05 to 2.0, more preferably in the range of 0.1 to 1.8, and even more preferably in the range of 0.5 to 1.5.

The nitrogen (N) content in porous silicon nitroxycarbide composite materials refers to values measured, for example, by determining the ratio of contained elements through elemental analysis or by SEM-EDS (Energy Dispersive X-ray Spectroscopy) analysis.

[Silicon nitroxycarbide]
The average diameter of the primary particles of silicon nitroxycarbide in the porous silicon nitroxycarbide composite material is preferably 20 nm to 200 nm, more preferably 30 nm to 150 nm, and even more preferably 40 nm to 100 nm. When the average diameter of the primary particles of silicon nitroxycarbide is 20 nm to 200 nm, good voids can be obtained when the material is used as an electrode.

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

[Characteristics of porous silicon nitroxycarbide composite material]
The porous silicon nitroxycarbide composite material of this embodiment has an electrical conductivity of 1.0 S/cm to 25 S/cm, preferably 2.0 S/cm to 25 S/cm, more preferably 3.0 S/cm to 25 S/cm, and even more preferably 5.0 S/cm to 25 S/cm. The higher the electrical conductivity of the porous silicon nitroxycarbide, the better the porous silicon nitroxycarbide composite material for fuel cells can be provided. However, if the amount of carbon material that contributes to improving electrical conductivity is too high, oxidation corrosion of the carbon component may occur in the catalytic cycle, reducing durability.
In one aspect of this embodiment, the porous silicon nitroxycarbide composite material does not have a characteristic peak as determined by X-ray diffraction (XRD) analysis, and is therefore an amorphous material.

The intensity ratio of the G band to the D band (G/D ratio) of the porous silicon nitroxycarbide composite material as measured by Raman spectroscopy is preferably 0.8 or greater, and more preferably 0.9 or greater. When the G/D ratio is within the above-mentioned range, the conductivity of the resulting porous silicon nitroxycarbide composite material can be further improved when the same carbon material and the same loading amount are used.

The relationship between the G/D ratio and electrical conductivity has not been precisely clarified, but the following can be inferred. Generally, the G band is derived from the in-plane motion of carbon atoms, so a large G band means that there are fewer defects in the crystallites. In other words, the range in which π electrons can move freely increases, which is thought to result in improved electrical conductivity.

In this embodiment, the wavelength of the laser light used in Raman spectroscopy is 457.101 nm. The G band refers to a Raman peak located near 1580 cm ⁻¹ , and the D band refers to a Raman peak located near 1360 cm ⁻¹ .

<Method for producing porous silicon nitroxycarbide composite material>
FIG. 1 is a flow chart showing the steps of a method for producing a porous silicon nitroxycarbide composite material according to one embodiment of the present invention.
A method for producing a porous silicon nitroxycarbide composite material according to one embodiment of the present invention includes a gel-forming step (step (A)), a washing step (step (B)), a porous silicon nitroxycarbide precursor-forming step (step (C)), and a calcination step (step (D)).

Note that other steps may be performed before or after each step, provided that the porous silicon nitroxycarbide composite material according to this embodiment is obtained. According to the manufacturing method described below, it is possible to obtain a porous silicon nitroxycarbide composite material having the desired mass ratios ([C]/[Si]), ([O]/[Si]), and ([N]/[Si]) with a single firing.

[Step (A)]
In step (A), for example, an organic alkoxysilane is added to an acidic aqueous solution containing a surfactant and a pH adjuster, and then a carbon material or an organic polymer is added to form a gel containing the carbon material or the organic polymer through 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 between 25°C and 80°C, more preferably between 30°C and 70°C, and even more preferably between 40°C and 60°C. By carrying out the polycondensation reaction within this temperature range, polysilsesquioxane can be obtained as a wet gel containing water as a solvent inside.

Furthermore, by gradually increasing the pH using a pH adjuster while allowing the polysilsesquioxane condensation polymerization reaction 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 nitroxycarbide composite material.

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

The surfactant is not particularly limited, but examples 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 diameter can be obtained.

Nonionic surfactants include, for example, polyethylene glycol types (ether types, ester-ether types), polyhydric alcohol types, etc. Examples of polyethylene glycol nonionic surfactants include Pluronic (registered trademark) types. Examples of cationic surfactants include amine salt types and quaternary ammonium salt types. By setting the surfactant content in the acidic aqueous solution to 0.1% by mass or more and 50% by mass or less, it is possible to form a porous polysilsesquioxane gel with a large BET specific surface area and developed mesopores to macropores.

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

There are no particular limitations on the pH adjuster, but examples include substances containing any of the following: urea, ammonia, and sodium hydroxide.

The acidic aqueous solution is not particularly limited, but examples include aqueous solutions of hydrochloric acid, nitric acid, acetic acid, etc.

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 nitroxycarbide having a desired three-dimensional framework structure can be easily formed.
R ¹ -SiR ² _x (OR ³ ) _3-x ...(1)
(In the formula, ^R1 represents a group selected from a methyl group, an ethyl group, a vinyl group, and a phenyl group, ^R2 represents a methyl group, and ^R3 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)
(In the formula, ^R4 includes any group selected from a methylene group, an ethylene group, a hexylene group, a vinylene group, a phenylene group, and a biphenylene group; ^R5 represents a methyl group; and ^R6 represents a methyl group or an ethyl group. In the formula, the integer y is 0 or 1.)

Specific examples of organic alkoxysilanes 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 exist as cis/trans geometric isomers, and either isomer can be used. One or more types of organic alkoxysilanes may be used.

In this step (A), a carbon material or organic polymer is further added to the acidic aqueous solution to form a gel containing the carbon material or organic polymer. By adding the carbon material or organic polymer during the sol-gel reaction of alkoxysilane, the precursor formed in step (C) can be calcined in step (D) to arrange the carbon material at the nano-level in a porous three-dimensional structural framework, imparting excellent conductivity to porous silicon nitroxycarbide, 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 nitroxycarbide as low-crystalline nanocarbon, making it possible to impart conductivity.

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

By setting the mass ratio of carbon material or organic polymer to organic alkoxysilane within the above range, it is possible to achieve both a larger BET specific surface area and higher electrical conductivity. When the amount of carbon material or organic polymer added is equal to or less than the amount of organic alkoxysilane added, separation from the sol-gel reaction system is suppressed, and gel formation from polysilsesquioxane can be promoted.

The carbon material is not particularly limited, but can be composed of one or more selected from, for example, carbon black, carbon nanofiber, carbon nanotube, and low-crystalline nanocarbon. Of these, carbon black is preferred as the carbon material from the standpoint of achieving high conductivity and manufacturability.

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

[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 thereof include methanol, ethanol, 1-propanol, and 2-propanol. This allows unnecessary surfactants to be removed from the acidic aqueous solution, and also allows the water in the acidic aqueous solution to be replaced with alcohol.

Furthermore, after washing with alcohol, the solvent may be further replaced with a hydrocarbon solvent such as hexane or heptane. In this step (B), water, a high surface tension solvent, is replaced with alcohol or a hydrocarbon solvent, a low surface tension solvent. This can suppress network shrinkage during the drying step at room temperature and normal pressure in step (C) described below, making it easier to form a porous gel structure.

[Step (C)]
In step (C), the washed gel is dried to form a porous silicon nitroxycarbide precursor that will be converted into porous silicon nitroxycarbide in a subsequent step. Examples of methods for this step (C) include supercritical drying using carbon dioxide at 80°C and 14 MPa, drying at room temperature and atmospheric pressure, and vacuum drying at 20°C to 80°C. Among these, drying at room temperature and atmospheric pressure is preferred 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 nitroxycarbide precursor with developed mesopores.

[Step (D)]
In step (D), the porous silicon nitroxycarbide precursor containing the carbon material or organic polymer is calcined to obtain a composite material containing silicon nitroxycarbide (SiCNO) and a carbon material. In this step, carbon atoms are supplied from the organic groups of the polysilsesquioxane by the calcination, nitrogen atoms are supplied by supplying nitrogen gas to create a nitrogen atmosphere, and oxygen atoms are supplied from the precursor formed from the alkoxysilane, forming a silicon nitroxycarbide skeleton. At the same time, carbon atoms are also supplied to the skeleton from the carbon material or organic polymer dispersed at the nano level in the gel. The organic polymer undergoes thermal decomposition by the calcination, and is retained in the porous silicon nitroxycarbide as low-crystalline nanocarbon.

Firing can be carried out by any known, conventional method, and is not particularly limited. For example, firing can be carried out in a nitrogen gas atmosphere by raising the temperature at a rate of 2.5°C per minute and maintaining the maximum temperature reached for a certain period of time. The maximum firing temperature is preferably 1100°C or higher and lower than 1450°C, more preferably 1200°C or higher and 1425°C or lower, and particularly preferably 1300°C or higher and 1400°C or lower.

The time for which the maximum temperature is maintained during firing may be determined appropriately based on the time that is effective for obtaining a porous silicon nitroxycarbide 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 may be carried out in two or more stages. That is, in the first stage, firing may be carried out for a certain period of time at a temperature lower than the maximum temperature, and then the temperature may be raised again and firing may be carried out again. The firing may be carried out at atmospheric pressure. The nitrogen gas atmosphere may contain oxygen gas or an inert gas in addition to nitrogen gas.

The firing can be carried out in a fixed-bed or fluidized-bed carbonization furnace, and there are no particular restrictions on the heating method or type of carbonization furnace, as long as it has the function of raising the temperature to the specified temperature. Examples of carbonization furnaces include lead hammer furnaces, tunnel furnaces, and single furnaces.

In this step (D), a carbon material or an organic polymer can be further mixed with the porous silicon nitroxycarbide precursor, and the mixture can then be fired. When an organic polymer is mixed with the porous silicon nitroxycarbide precursor in step (D), as in the case of mixing in step (A), thermal decomposition occurs during firing, and the organic polymer is retained in the porous silicon nitroxycarbide as low-crystalline nanocarbon.

Although the above describes embodiments of the present invention, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be embodied in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included within the scope of the invention and its equivalents as set forth in the claims, as well as within the scope and spirit of the invention.

<Verification Example 1>
Verification Example 1 of the present invention will be described below. The present invention is not limited to the verification example shown below. "Example *" is an embodiment of the present invention, and "Comparative Example *" is an embodiment of the prior art. Values in the table mean "parts by weight" unless otherwise specified.

Example 1
[Synthesis of Porous Silicon Nitroxycarbide Composite]
6 g of a 5 mM aqueous acetic acid solution (Kanto Chemical Co., Inc.), 0.8 g of Pluronic (registered trademark) F-127 (BASF Corporation), 0.5 g of urea (Kanto Chemical Co., Inc.), and 0.24 g of Ketjen Black (Lion Specialty Chemicals Corporation, product name "EC-600") were placed in a vial and stirred at room temperature for 10 minutes. 5 g of methyltrimethoxysilane (Kanto Chemical Co., Inc.) was added thereto, and the mixture was stirred at room temperature for 30 minutes.

This was then allowed to react at 60°C for four days to yield a wet gel. The resulting wet gel was washed with methanol (Kanto Chemical Co., Ltd.) and dried at room temperature and atmospheric pressure for three days, and then further dried at 80°C and atmospheric pressure for six hours to yield 3.5 g of porous silicon nitroxycarbide precursor 1. 1 g of this porous silicon nitroxycarbide precursor was mixed with 0.4 g of Ketjen Black (Lion Specialty Chemicals Co., Ltd., product name "Carbon ECP"), then placed in a tubular furnace and calcined in a nitrogen atmosphere, heating the mixture to 1300°C at a rate of 2.5°C/min and holding for two hours to yield porous silicon nitroxycarbide composite material 1.

Example 2
Porous silicon nitroxycarbide composite material 2 was obtained in the same manner as in Example 1, except that the amount of Ketjen black (carbon ECP) mixed with precursor 1 was changed to 0.5 g and the firing temperature was changed to 1400°C.
Example 3
Porous silicon nitroxycarbide composite material 3 was obtained in the same manner as in Example 2, except that the amount of Ketjen black (carbon ECP) mixed with precursor 1 was changed to 0.4 g.
Example 4
Porous silicon nitroxycarbide composite material 4 was obtained in the same manner as in Example 2, except that the amount of Ketjen black (carbon ECP) mixed with precursor 1 was changed to 0.3 g.
Example 5
Porous silicon nitroxycarbide composite material 5 was obtained in the same manner as in Example 2, except that the amount of Ketjen black (carbon ECP) mixed with precursor 1 was changed to 0.2 g.
Example 6
A porous silicon nitroxycarbide composite material 6 was obtained in the same manner as in Example 3, except that precursor 2 was synthesized using 2.5 g of methyltrimethoxysilane (manufactured by Kanto Chemical Co., Inc.) and 2.5 g of phenyltrimethoxysilane (manufactured by Kanto Chemical Co., Inc.).
Example 7
Porous silicon nitroxycarbide composite material 7 was obtained in the same manner as in Example 3, except that precursor 3 was synthesized using 2.5 g of methyltrimethoxysilane (manufactured by Kanto Chemical Co., Inc.) and 2.5 g of vinyltrimethoxysilane (manufactured by Kanto Chemical Co., Inc.).
(Example 8)
Porous silicon nitroxycarbide composite material 8 was obtained in the same manner as in Example 3, except that the Ketjen black (carbon ECP) mixed with precursor 1 was changed to carbon nanotubes (manufactured by Osaka Soda Co., Ltd.).
Example 9
Porous silicon nitroxycarbide composite material 9 was obtained in the same manner as in Example 3, except that the Ketjen black (carbon ECP) mixed with precursor 1 was changed to graphene (manufactured by Nishina Materials Co., Ltd.).

(Comparative Example 1)
A porous silicon oxycarbide composite material 1 was obtained in the same manner as in Example 2, except that the firing temperature was changed to 1000°C.
(Comparative Example 2)
A porous silicon oxycarbide composite material 2 was obtained in the same manner as in Example 3, except that the firing temperature was changed to 1000°C.
(Comparative Example 3)
Porous silicon oxycarbide composite material 3 was obtained in the same manner as in Example 4, except that the firing temperature was changed to 1000°C.
(Comparative Example 4)
Porous silicon oxycarbide composite material 4 was obtained in the same manner as in Example 5, except that the firing temperature was changed to 1000°C.
The raw materials for each sample and the conditions for each step are summarized in Table 1.

For each of the samples of Examples 1 to 9 and Comparative Examples 1 to 4, the following measurement items were measured.
[Element composition ratio]
Carbon tape was applied to a metal plate, and the sample was placed on top of the tape, and the sample was observed using a SEM-EDS (JMC7000, manufactured by JEOL Corporation).

[Measurement of BET specific surface area, pore volume and pore diameter]
0.04 g of the electrode catalyst or catalyst powder was weighed and placed in a sample tube, and pre-treated by vacuum drying for 6 hours at 100° C. After pre-treatment, nitrogen was adsorbed onto the sample at −196° C. while changing the relative pressure using a specific surface area/pore size distribution device (manufactured by Microtrac BEL Corporation: device name "BELSORP-mini II").

[Conductivity Measurement]
The electrode catalyst or catalyst powder was introduced into a powder resistivity measurement system (manufactured by Mitsubishi Chemical Analytech Co., Ltd.: apparatus name "MCP-PD51"), and the sample was pressurized using an attached hydraulic pump until a pressure of 12 kN was reached. After that, the resistivity was measured using a resistivity meter (manufactured by Mitsubishi Chemical Analytech Co., Ltd.: apparatus name "Loresta GX"), and the conductivity was calculated from the resistivity using the following formula (1):
Electrical conductivity (S/cm) = (resistivity (Ω cm)) -1 ... (1)

[Raman spectroscopy measurement]
The Raman spectrum was measured using a microscopic Raman spectrometer (NRS-5500 manufactured by JASCO Corporation) under the following conditions and with the following spectral processing.
(Equipment conditions)
Light source: laser light source with wavelength 457.101 nm Wave number range 4000 to 100 cm ⁻¹ , exposure time 300 sec, number of integrations 2 Wave number calibration: calibrated to 520±1 cm ⁻¹ using a Si crystal (spectrum processing)
Using the software provided with the above-mentioned device, (i) the rise in the baseline due to fluorescence, etc. was corrected, (ii) the detected intensity was normalized using the peak of the carbon G band (1590 cm ⁻¹ ), and (iii) the detected intensity ratio (area ratio) of the G band (1590 cm ⁻¹ ) to the D band (1360 cm ⁻¹ ) was calculated as the G/D ratio.

[Measurement of particle diameter _D50 ]
The particle diameter D ₅₀ (μm) was calculated using a laser diffraction particle size distribution analyzer (Partica LA-960V2, manufactured by Horiba, Ltd.) in accordance with JIS Z8825-1:2013.

The results of each of the above measurement items are summarized in Table 2. Note that "-" in the table means that the item was not measured.

The results shown in Table 2 indicate that in Examples 1 to 9, the porous silicon nitroxycarbide composite materials had a BET specific surface area of 100 m ² /g or more and 400 m ² /g or less and a conductivity of 1.0 S/cm or more, and thus porous silicon nitroxycarbide composite materials having both a BET specific surface area within an appropriate range and high conductivity were obtained.

Furthermore, in Examples 1 to 9, the intensity ratio between the G band and the D band (G/D ratio), which is used as an indicator of the amount of defects, was 0.8 or higher in all cases, confirming that the materials had few defects.

On the other hand, in Comparative Examples 1 to 4, nitrogen was not fixed even when the precursor was calcined, and porous silicon oxycarbide without nitrogen in its structure was produced. For example, when Example 2 and Comparative Example 1 were compared, which used the same amount of raw carbon material, Comparative Example 1 had a high specific surface area but low conductivity. The G/D ratio was also less than 0.8, meaning the material had many defects.

<Verification Example 2>
In Verification Example 2 of the present invention, the porous silicon nitroxycarbide composite material 2 exemplified in Example 2 of Verification Example 1 was observed with a scanning electron microscope. An SEM photograph of the observation results is shown in Figure 2. Figure 2 confirms that the porous silicon nitroxycarbide composite material 2 forms a three-dimensionally developed network structure.

Furthermore, X-ray diffraction was performed using the 2θ/θ measurement method on the porous silicon nitroxycarbide composite material 2 illustrated in Example 2. The obtained X-ray pattern is shown in Figure 3. As Figure 3 shows, porous silicon nitroxycarbide composite material 2 does not exhibit, for example, a peak attributable to the (111) plane of the 3C-SiC crystal structure around 2θ = 36°, or a peak attributable to the (220) plane of the 3C-SiC crystal structure around 2θ = 60°, and since no diffraction due to the crystal structure was observed, it was confirmed to be amorphous.

Furthermore, Figure 4 shows the Si-NMR of porous silicon nitroxycarbide composite material 2 exemplified in Example 2. According to the results shown in Figure 4, broad peaks were observed near -45 ppm and -112 ppm, confirming that the material has a structure with Si-N-O-C bonds.

The porous silicon nitroxycarbide composite material, fuel cell electrode, and method for producing the porous silicon nitroxycarbide composite material of the present invention can produce a porous silicon nitroxycarbide composite material that has both a higher BET specific surface area and high electrical conductivity.When used as an electrode material for the catalyst layer of a fuel cell electrode, it can produce a fuel cell with high power generation efficiency.Therefore, it has industrial applicability.

Claims (16)

A porous silicon nitroxycarbide composite material comprising silicon nitroxycarbide (SiCNO) and a carbon material,
A porous silicon nitroxycarbide composite material having a BET specific surface area of 100 m ² /g or more and 400 m ² /g or less and an electrical conductivity of 1.0 S/cm or more and 25 S/cm or less. 2. The porous silicon nitroxycarbide composite material of claim 1, wherein the total pore volume is 1.3 cm ^<3> /g or more and 2.5 cm ^<3> /g or less. The porous silicon nitroxycarbide composite material according to claim 1 or 2, having a pore diameter of 10 nm or more and 500 nm or less. The porous silicon nitroxycarbide composite material according to claim 1, wherein the mass ratio of carbon (C) to silicon (Si) contained in the porous silicon nitroxycarbide composite material ([C]/[Si]) is 3.0 or more and 8.0 or less. The porous silicon nitroxycarbide composite material according to claim 1, wherein the mass ratio of oxygen (O) to silicon (Si) contained in the porous silicon nitroxycarbide composite material ([O]/[Si]) is 0.2 or more and 1.5 or less. The porous silicon nitroxycarbide composite material according to claim 1, wherein the mass ratio of nitrogen (N) to silicon (Si) contained in the porous silicon nitroxycarbide composite material ([N]/[Si]) is 0.05 or more and 2.0 or less. The porous silicon nitroxycarbide composite material according to claim 1, wherein the carbon material content is 5% by mass or more and 50% by mass or less. The porous silicon nitroxycarbide composite material of claim 1, wherein the carbon material is composed of one or more selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons. The porous silicon nitroxycarbide composite material of claim 1, wherein the porous silicon nitroxycarbide composite material is an amorphous material. An electrode for a fuel cell having a layer containing the porous silicon nitroxycarbide composite material described in claim 1 or 2. a step (A) of adding an organic alkoxysilane to an acidic aqueous solution containing a surfactant and a pH adjuster, and further adding a carbon material or an organic polymer to the aqueous solution, thereby forming a gel containing the carbon material or the organic polymer through a sol-gel reaction of the organic alkoxysilane;
(B) washing the gel with alcohol;
(C) drying the washed gel to form a porous silicon nitroxycarbide precursor;
(D) a step of calcining the porous silicon nitroxycarbide precursor in a nitrogen-containing atmosphere to obtain a composite material containing silicon nitroxycarbide (SiCNO) and a carbon material;
1. A method for producing a porous silicon nitroxycarbide composite material comprising: The method for producing a porous silicon nitroxycarbide composite material described in claim 11, wherein in step (D), the porous silicon nitroxycarbide precursor is calcined at a temperature of 1100°C or higher and lower than 1450°C. 13. The method for producing a porous silicon nitroxycarbide composite material according to claim 11 or 12, wherein the organic alkoxysilane is represented by the following formula (1) or formula (2):
R ¹ -SiR ² _x (OR ³ ) _3-X ...(1)
(In the formula, ^R1 represents a group selected from a methyl group, an ethyl group, a vinyl group, and a phenyl group, ^R2 represents a methyl group, and ^R3 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)
(In the formula, ^R4 includes any group selected from a methylene group, an ethylene group, a hexylene group, a vinylene group, a phenylene group, and a biphenylene group; ^R5 represents a methyl group; and ^R6 represents a methyl group or an ethyl group. In the formula, the integer y is 0 or 1.) The method for producing a porous silicon nitroxycarbide composite material according to claim 11 or 12, wherein the mass ratio of the carbon material or the organic polymer to the organic alkoxysilane is 2.5-50:97.5-50. The method for producing a porous silicon nitroxycarbide composite material according to claim 11 or 12, wherein the carbon material is composed of one or more selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons. The method for producing a porous silicon nitroxycarbide composite material described in claim 14, wherein the organic polymer is one or more selected from the group consisting of phenolic resin, polystyrene, and polydivinylbenzene.