WO2025234332A1 - Electrode catalyst containing porous silicon nitrooxy carbide composite material, electrode for fuel cell, fuel cell, and method for manufacturing electrode catalyst - Google Patents

Abstract

The purpose of the present invention is to provide an electrode catalyst containing a porous silicon nitrooxy carbide composite material having both a high BET specific surface area and high conductivity, an electrode for a fuel cell, and a fuel cell, and a method for manufacturing the electrode catalyst containing a porous silicon nitrooxy carbide composite material capable of controlling the pore diameter by using an organic alkoxysilane of a type widely distributed as an industrial raw material. The electrode catalyst according to the present invention comprises: a porous silicon nitrooxy carbide composite material that contains silicon nitrooxy carbide (SiCNO) and a carbon material; and particles that are supported on the porous silicon nitrooxy carbide composite material and contain a noble metal. The porous silicon nitrooxy carbide composite material has a BET specific surface area of 100 m²/g-400 m²/g, and a conductivity of 1.0-25 S/cm.

Description

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

The present invention relates to an electrode catalyst containing a porous silicon nitroxycarbide composite material, an electrode for a fuel cell, a fuel cell, and a method for producing the electrode catalyst.
This application claims priority based on Japanese Patent Application No. 2024-077520, filed on May 10, 2024, the contents of which are incorporated herein by reference.

A fuel cell is a device that generates 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) 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 silicon carbide particles carrying a precious metal, which have a silicon oxide layer carrying precious metal particles on the surface of silicon carbide particles having an average primary particle size of 0.005 μm to 5 μm. The specific surface area of the silicon carbide particles is said to be 1.0 m ² /g to 400 m ² /g.

JP 2010-149008 A JP 2011-093756 A

Fuel cell electrodes that achieve high efficiency and high output require a support that combines a large specific surface area with high conductivity. However, while Patent Document 1 describes an electrode catalyst that contains silicon carbide particles with a noble metal supported on the surface and conductive carbon particles to impart conductivity, there is no mention of durability, leaving room for improvement. In particular, there is a need for an electrode catalyst that can demonstrate high durability even during start-stop cycles, which are the most susceptible to deterioration under the power generation conditions of a fuel cell.

Patent Document 2, cited above, describes precious metal-loaded silicon carbide particles having a silicon oxide layer on the surface of silicon carbide loaded with precious metal particles, but makes no mention of the silicon carbide particles being porous, nor of their electrical conductivity.

The present invention was made in consideration of the above circumstances, and aims to provide an electrode catalyst, a fuel cell electrode, and a fuel cell containing a porous silicon nitroxycarbide composite material that has both a high BET specific surface area and high electrical conductivity, as well as a method for producing an electrode catalyst containing a porous silicon nitroxycarbide composite material whose pore size can be controlled.

The inventors discovered that by preparing 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 the precursor gel under a nitrogen atmosphere, a porous silicon nitroxycarbide composite material was produced in which a mesoscopic pore structure (mesopores) developed into a macroscopic pore structure (macropores), and in which the carbon material was arranged at the nano-level within a porous three-dimensional framework. Furthermore, by gradually advancing the polysilsesquioxane condensation polymerization reaction while adjusting the pH to form a precursor gel with a porous structure, the carbon material could be densely dispersed within the porous three-dimensional framework, resulting in a porous silicon nitroxycarbide composite material with higher conductivity. They then discovered that mixing the resulting porous silicon nitroxycarbide composite material with a dispersion in which a precious metal-containing colloid was dispersed produced an electrocatalyst containing precious metal particles.

That is, the present invention provides the following configurations.
[1] A porous silicon nitroxycarbide composite material containing silicon nitroxycarbide (SiCNO) and a carbon material;
particles supported on the porous silicon nitroxycarbide composite material and containing a precious metal;
Equipped with
An electrode catalyst, wherein the porous silicon nitroxycarbide composite material has a BET specific surface area of 100 m ² /g or more and 400 m ² /g or less, and the porous silicon nitroxycarbide composite material has a conductivity of 1.0 S/cm or more and 25 S/cm or less.
[2] The electrode catalyst according to [1], wherein the amount of the particles containing the noble metal supported is 10% by mass or more and 60% by mass or less when the total mass of the electrode catalyst is taken as 100% by mass.
[3] The electrode catalyst according to [1] or [2], wherein the content of the carbon material is 5% by mass or more and 50% by mass or less.
[4] The electrode catalyst according to any one of [1] to [3], wherein the carbon material is composed of one or more selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons.
[5] The electrode catalyst according to any one of [1] to [4], wherein the particles containing the noble metal are composed of one or more kinds selected from the group consisting of platinum (Pt), platinum-cobalt alloy (PtCo), and platinum-nickel alloy (PtNi).
[6] The electrode catalyst according to any one of [1] to [5], wherein the total pore volume of the porous silicon nitroxycarbide composite material is 1.3 cm ³ /g or more and 2.5 cm ³ /g or less.
[7] The electrode catalyst according to any one of [1] to [6], wherein the pore size of the porous silicon nitroxycarbide composite material is 10 nm or more and 500 nm or less.
[8] The electrode catalyst according to any one of [1] to [7], 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.
[9] The electrode catalyst according to any one of [1] to [8], 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.
[10] The electrode catalyst according to any one of [1] to [9], 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.
[11] A fuel cell electrode having a layer containing the electrode catalyst according to any one of [1] to [10].
[12] A fuel cell comprising the fuel cell electrode according to [11].
[13] 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, 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;
Step (C) of 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 porous silicon nitroxycarbide composite material containing silicon nitroxycarbide (SiCNO) and a carbon material;
a step (E) of mixing the porous silicon nitroxycarbide composite material with a dispersion containing a colloid containing a noble metal and hydrogen peroxide solution to obtain an electrode catalyst containing particles containing a noble metal;
The method for producing an electrode catalyst comprising the steps of:
[14] The method for producing an electrode catalyst according to [13], wherein in the step (D), the porous silicon nitroxycarbide precursor is calcined at 1100°C or higher and lower than 1450°C.
[15] The method for producing an electrode catalyst according to either [13] or [14], wherein the organic alkoxysilane is represented by the following formula (1) or formula (2):
R ¹ -SiR ² _x (OR ³ ) _3-x ...(1)
(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.)
[16] The method for producing an electrode catalyst according to any one of [13] to [15], wherein the carbon material is composed of one or more types selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons.
[17] The method for producing an electrode catalyst according to any one of [13] to [16], wherein the colloid containing a noble metal is composed of one or more colloids selected from the group consisting of platinum (Pt) colloid, platinum-cobalt alloy (PtCo) colloid, and platinum-nickel alloy (PtNi) colloid.
[18] The method for producing an electrode catalyst according to any one of [13] to [17], 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.
[19] The method for producing an electrode catalyst according to any one of [13] to [18], wherein the organic polymer is composed of one or more selected from a phenolic resin, polystyrene, and polydivinylbenzene.

The present invention can provide an electrode catalyst, a fuel cell electrode, and a fuel cell containing a porous silicon nitroxycarbide composite material that has both a high BET specific surface area and high electrical conductivity. It can also provide a method for producing an electrode catalyst containing a porous silicon nitroxycarbide composite material whose pore size can be controlled using organic alkoxysilanes of the type widely available as industrial raw materials.

FIG. 1 is a flowchart illustrating an example of a method for producing an electrode catalyst according to an embodiment of the present invention. 1 is a scanning electron microscope image of a porous silicon nitroxycarbide composite material (Synthesis Example 2, SC2). 1 is an X-ray diffraction pattern of a porous silicon nitroxycarbide composite material (Synthesis Example 2, SC2). 1 shows the results of Si-NMR measurement of a porous silicon nitroxycarbide composite material (Synthesis Example 2, SC2). 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. FIG. 10 is a transmission electron microscope image of electrode catalyst B. FIG. 10 is a diagram showing the results of cyclic voltammetry (CV) measurement of electrode catalyst B. FIG. 10 is a graph showing the change in electrochemically active surface area (ECSA) of electrode catalyst B with respect to the CV measurement cycle.

The following describes a porous silicon nitroxycarbide composite material, a fuel cell electrode, and a method for producing the porous silicon nitroxycarbide composite material according to one embodiment of the present invention, with reference to the drawings. 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 portions to make the features of the present invention easier to understand, and the dimensional proportions of the various components may not necessarily be the same as in reality.

<Configuration of electrode catalyst>
The electrode catalyst according to this embodiment comprises a porous silicon nitroxycarbide composite material containing silicon nitroxycarbide (SiCNO) and a carbon material, and particles containing a noble metal supported on the porous silicon nitroxycarbide composite material.

The form of the electrode catalyst is not particularly limited, but may be, for example, powder, particulate, fibrous or needle-like, with powder or particulate being preferred.
When the electrode catalyst is in a powder or particulate form, the particle size of the electrode catalyst is not particularly limited. For example, the particle size _D50 , which is the 50% particle size in the cumulative particle size distribution based on volume, is preferably 0.1 μm or more and 50 μm or less, more preferably 0.1 μm or more and 10 μm or less, and even more preferably 0.1 μm or more and 2 μm or less.

The particle diameter _D50 of the electrode catalyst means a value measured in accordance with JIS Z8825-1:2013, and means, for example, a particle diameter _D50 measured using a laser diffraction particle size distribution measuring device (SALD-7000, manufactured by Shimadzu Corporation).

The electrode catalyst 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. The BET specific surface area may be 400 m ² /g or less. When the BET specific surface area is 100 m ² /g or more, a sufficient amount of catalyst particles is supported on the support surface, and when the electrode catalyst is used in a fuel cell electrode, desired characteristics such as output and efficiency can be obtained. When 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 electrode catalyst is preferably 1.3 ^cm /g or more, more preferably 1.5 ^cm /g or more, and particularly preferably 2.0 ^cm /g or more. When the total pore volume of the electrode catalyst is 1.3 ^cm /g or more, the flow of reaction gases and electrolytes in the catalyst layer becomes easy, and the catalytic efficiency can be improved.

The pore diameter of the electrode catalyst 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 electrode catalyst is 10 nm or more and 1000 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 an electrode catalyst can be calculated as measured values using the gas adsorption method. For example, these values refer to values calculated from the amount of adsorption and condensation of non-corrosive gas when non-corrosive gases such as nitrogen or argon are adsorbed using the constant volume method while changing the relative pressure in the adsorption isotherm.

<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 of 100 ^m /g to 400 ^m /g and a conductivity of 1.0 S/cm to 25 S/cm.

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 analyzer (SALD-7000, manufactured by Shimadzu Corporation).

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 the gas adsorption method. For example, these values refer to values calculated from the amount of adsorption and condensation of non-corrosive gas when non-corrosive gases such as nitrogen or argon are adsorbed using the 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 the 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 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.
[Silicon nitroxycarbide]

The average diameter of the primary particles of silicon nitroxycarbide in the porous silicon nitroxycarbide composite material is preferably 20 nm or more and 200 nm or less, more preferably 30 nm or more and 150 nm or less, and even more preferably 40 nm or more and 100 nm or less. An average diameter of the primary particles of silicon nitroxycarbide of 20 nm or more and 200 nm or less is preferable because it allows for good voids to be obtained when the material is made into 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.

<Method for producing porous silicon nitroxycarbide composite material>
FIG. 5 is a flow chart showing the steps of a method for manufacturing 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 3-30:97-70, and even more preferably 5-20:95-80.

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.

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

[Particles containing noble metals]
When the total mass of the electrode catalyst is taken as 100 mass%, the amount of the particles containing the noble metal supported is preferably 10 mass% to 60 mass%, more preferably 15 mass% to 60 mass%, and more preferably 30 mass% to 60 mass%. When the amount of the particles containing the noble metal supported is 10 mass% to 60 mass%, the catalytic function and durability are good.
The amount of particles containing a noble metal carried can be calculated, for example, by subjecting the electrode catalyst to alkali melting, dissolving it in aqua regia, diluting it with ultrapure water, and then subjecting it to high-frequency induction heating optical emission spectroscopy (ICP).

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

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

The mass ratio of carbon (C) to silicon (Si) contained in the electrode catalyst ([C]/[Si]) is preferably 3.0/1.0 to 8.0/1.0, more preferably 3.0/1.0 to 7.5/1.0, and even more preferably 3.0/1.0 to 7.0/1.0 or less. A mass ratio of carbon (C) to silicon (Si) ([C]/[Si]) of 3.0/1.0 to 8.0/1.0 achieves high conductivity while suppressing carbon corrosion and other problems, improving the durability of the catalytic cycle. Note that carbon (C) in the above mass ratio refers to the sum of the carbon that constitutes the three-dimensional framework structure of the porous silicon nitroxycarbide and the carbon in the carbon material supported on the porous silicon nitroxycarbide.

The silicon (Si) content in the electrode catalyst can be calculated, for example, by inductively coupled plasma emission spectroscopy (ICP). The carbon (C) content can be calculated by high-frequency combustion-infrared absorption spectroscopy.

[Electrode catalyst characteristics]
The electrode catalyst of this embodiment has a conductivity of 0.1 S/cm or more, preferably 1 S/cm or more, more preferably 5 S/cm or more, and even more preferably 10 S/cm or more. The conductivity may be 100 S/cm or less, 70 S/cm or less, or 50 S/cm or less. The higher the conductivity of the porous silicon nitroxycarbide, the better the fuel cell electrode catalyst that can be provided. However, if the amount of carbon material that contributes to improving conductivity is too high, corrosion of the carbon component may progress during the catalytic cycle, resulting in reduced durability.

<Method of manufacturing electrode catalyst>
The method for producing an electrode catalyst according to this embodiment includes a gel formation step (step (A)), a washing step (step (B)), a porous silicon nitroxycarbide precursor formation step (step (C)), a firing step (step (D)), and a mixing step (step (E)), as shown in Figure 1. Note that, on the premise that an electrode catalyst according to this embodiment is obtained, steps other than those described above may be provided before or after each step.
In the method for producing an electrode catalyst according to this embodiment, the gel-forming step (step (A)), the washing step (step (B)), the porous silicon nitroxycarbide precursor-forming step (step (C)), and the firing step (step (D)) may be, for example, steps (A), (B), (C), and (D), respectively, of the method for producing a porous silicon nitroxycarbide composite material described above.
That is, the method for producing an electrode catalyst according to this embodiment may include the method for producing a porous silicon nitroxycarbide composite material according to this embodiment, and the following mixing step (step (E)) using the produced porous silicon nitroxycarbide composite material.

[Step (E)]
In step (E), a dispersion containing a noble metal-containing colloid and aqueous hydrogen peroxide is mixed with the porous silicon nitroxycarbide composite material to obtain an electrode catalyst containing noble metal-containing particles. The noble metal-containing colloid is a dispersion of noble metal-containing particles in a liquid, and the dispersion containing a noble metal-containing colloid is a solution containing the noble metal-containing colloid and aqueous hydrogen peroxide. The noble metal-containing colloid and the dispersion containing the noble metal-containing colloid and aqueous hydrogen peroxide can be prepared by known, conventional methods.

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

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

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

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

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

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

The above-mentioned fuel cell electrode and fuel cell have a catalyst layer containing the above-mentioned electrode catalyst, which allows for high conductivity while maintaining a large BET specific surface area. In addition, by disposing the carbon material at the nano-level within silicon nitroxycarbide, which has a porous three-dimensional structural framework, it is possible to reduce the possibility of oxidative degradation of the carbon material in high-temperature, high-humidity environments, a problem that has existed in the past, thereby achieving excellent durability for the fuel cell electrode and fuel cell.

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.

The following describes examples of the present invention. The present invention is not limited to the examples shown below. "Example*" represents an embodiment of the present invention, and "Comparative Example*" represents an embodiment of the prior art. Values in the table represent "parts by weight" unless otherwise specified.

(Synthesis 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 reacted 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 0.5 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 1400°C at a rate of 2.5°C/min and holding for two hours to yield porous silicon nitroxycarbide composite material SC1.

(Synthesis Example 2)
A porous silicon nitroxycarbide composite material SC2 was obtained in the same manner as in Synthesis Example 1, except that 0.4 g of Ketjen black was added during firing.

(Synthesis Example 3)
A porous silicon nitroxycarbide composite material SC3 was obtained in the same manner as in Synthesis Example 1, except that 0.2 g of Ketjen black was added during firing.

Comparative Synthesis Example 1
A porous silicon nitroxycarbide composite material cSC1 was obtained in the same manner as in Synthesis Example 1, except that 0.1 g of Ketjen black was added during firing.

Example 1
[Synthesis of electrocatalysts containing platinum nanoparticles]
0.43 g of chloroplatinic acid hexahydrate was dissolved in 60 mL of ultrapure water, and 3.1 g of sodium bisulfite was added to the solution to allow the reduction reaction to proceed. The solution was then diluted with 280 mL of ultrapure water. Next, 24 mL of 35% hydrogen peroxide was added dropwise while adding a 5% aqueous sodium hydroxide solution to adjust the pH to approximately 5, yielding a dispersion containing platinum colloid. Subsequently, the colloidal dispersion was separated so that the amount of platinum (Pt) after loading was 45 mass% relative to the total amount of the electrode catalyst including the carrier. 0.4 g of the porous silicon nitroxycarbide composite material SC1 obtained in Synthesis Example 1 was added as a carrier and mixed at 90 ° C for 3 hours. After cooling, the mixture was subjected to solid-liquid separation. The resulting powder (solids) was thoroughly washed with ultrapure water to remove chloride ions, and then dried at 80 ° C for 12 hours to obtain an electrode catalyst A in which platinum was supported on the surface of the porous silicon nitroxycarbide composite material SC1.

Example 2
An electrode catalyst B was obtained in the same manner as in Example 1, except that the porous silicon nitroxycarbide composite material SC2 obtained in Synthesis Example 2 was used.
A transmission electron microscope image of electrode catalyst B is shown in Figure 6. It was confirmed that platinum nanoparticles with a particle size of about 3 nm were supported on the porous silicon nitroxycarbide composite material.

Example 3
An electrode catalyst C was obtained in the same manner as in Example 1, except that the porous silicon nitroxycarbide composite material SC3 obtained in Synthesis Example 3 was used.

Example 4
An electrode catalyst D was obtained in the same manner as in Example 2, except that the colloidal dispersion was dispensed so that the amount of platinum (Pt) after loading was 30 mass % based on the total amount of the electrode catalyst including the carrier.

Example 5
An electrode catalyst E was obtained in the same manner as in Example 2, except that the colloidal dispersion was dispensed so that the amount of platinum (Pt) after loading was 60 mass % based on the total amount of the electrode catalyst including the carrier.

(Comparative Example 1)
An electrode catalyst F was obtained in the same manner as in Example 1, except that the porous silicon nitroxycarbide composite material cSC1 obtained in Comparative Synthesis Example 1 was used.

(Comparative Example 2)
As the cathode catalyst, Pt/CB (Tanaka Kikinzoku K.K., TEC10E50E, Pt loading 46 wt %) was used.

The following measurements were carried out for the porous silicon nitroxycarbide composite materials SC1-SC3 and cSC1, which are the samples of Synthesis Examples 1-3 and Comparative Synthesis Example 1, as well as the electrode catalysts A-F, which are the samples of Examples 1-5 and Comparative Example 1, and the Pt/CB of Comparative Example 2. The results are shown in Table 1.

[Element composition ratio]
[Composition analysis of porous silicon nitroxycarbide composite material]
The porous silicon nitroxycarbide composite materials SC1 to SC3 and cSC1 were fixed to carbon tape, and the elemental ratios of [C]/[Si], [O]/[Si], and [N]/[Si] were calculated from the elemental contents of Si, C, O, and N obtained by SEM-EDS (Energy Dispersive X-ray Spectroscopy).

[Measurement of BET specific surface area, pore volume and pore diameter]
0.04 g of powder of porous silicon nitroxycarbide composite materials SC1 to SC3 and cSC1 was weighed out and placed in a sample tube, and pretreated by vacuum drying for 6 hours at 100°C. After pretreatment, nitrogen was adsorbed onto the sample at -196°C while changing the relative pressure using a specific surface area/pore size distribution device (Microtrac BEL Corporation: device name "BELSORP-mini II").

[Conductivity Measurement]
The porous silicon nitroxycarbide composite materials SC1 to SC3 and cSC1 were introduced into a powder resistivity measurement system (manufactured by Mitsubishi Chemical Analytech Co., Ltd.: apparatus name "MCP-PD51"), and the samples were 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.: apparatus name "Loresta GX"), and the conductivity was calculated from the resistivity using the following equation (1).
Conductivity (S/cm) = (Resistivity (Ω cm)) ^-1 ...(1)

[Measurement of particle diameter _D50 ]
The particle diameters _D50 of the porous silicon nitroxycarbide composite materials SC1 to SC3 and cSC1 were measured using a laser diffraction particle size distribution analyzer (Horiba, Partica LA-960V2) in accordance with JIS Z8825-1:2013.

[Measurement of Pt Loading Rate]
Examples 1 to 5, 50DA to F of Comparative Example 1, and Pt/CB of Comparative Example 2 were alkali-fused using anhydrous sodium carbonate and sodium peroxide. Then, they were dissolved in aqua regia and diluted with ultrapure water to a specified concentration, and the concentration was measured using high-frequency induction heating optical emission spectroscopy (ICP; Shimadzu Corporation, Model ICPE-9820).

[Evaluation of catalytic performance using a rotating electrode]
(Preparation of electrodes)
A 5 mm diameter glassy carbon (GC) electrode was polished using alumina paste and then ultrasonically cleaned using ultrapure water. The electrode catalysts A to F of Examples 1 to 5 and Comparative Example 1, and the Pt/CB of Comparative Example 2 were added to a 99% by volume aqueous ethanol solution and dispersed using an ultrasonic homogenizer. This was dropped onto a GC disk and dried at room temperature for 12 hours. After drying, a 5% Nafion (registered trademark) solution was dropped onto the electrode catalyst on the GC disk to a dry film thickness of 50 nm, and the electrode catalyst was dried at room temperature for 12 hours.

(CV measurement)
Electrode evaluation was performed using an electrochemical measurement system (HZ-5000, manufactured by Hokuto Denko Corporation). After purging a 0.1 M aqueous solution of perchloric acid with nitrogen gas for 30 minutes, cleaning was performed 50 times using a reversible hydrogen electrode (RHE) as the reference electrode at a potential range of 0.05 to 1.2 V and a sweep rate of 150 mV/s. Cyclic voltammetry (CV) measurements were then performed at a potential range of 0.05 to 1.0 V and a sweep rate of 100 mV/s. The CV measurement results for electrode catalyst B are shown in Figure 7. Analysis of the electrochemically active surface area (ECSA) was performed using the hydrogen adsorption wave observed below 0.4 V.
The electrochemically active surface area (ECSA) is analyzed using the method described in Non-Patent Document A below.
[Non-Patent Document A] FC-Cubic Technology Research Association: Electrode Catalyst RDE Evaluation Method, 2023/7/21, ver. 1.2.1.

(Oxygen reduction activity evaluation)
After purging the electrolyte with oxygen gas for at least 1 hour, linear sweep voltammetry (LSV) was performed. Data were acquired under eight conditions: temperature 25°C, potential range 0.25 to 1.00 V, sweep rate 5 mV/s, and rotation speed 1000 rpm to 2750 rpm, increasing in 250 rpm increments. The results were analyzed using a Koutecky-Levich plot to obtain the mass activity (A/g-Pt) at 0.85 V.
The mass activity analysis method is based on the method described in Non-Patent Document A above.

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

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

(Preparation of cathode catalyst ink)
Electrode catalyst B or Pt/CB and a polymer electrolyte (Nafion® DE521, manufactured by Du Pont) were mixed at a volume ratio of 0.7. This mixture, 2.5 g of ethanol, 2 g of water, and zirconia balls (diameter 5 mm) were placed in a zirconia pot and mixed for 60 minutes in a planetary ball mill (P-6, manufactured by Fritsch).

(Fabrication of Membrane Electrode Assembly (MEA))
The anode catalyst layer and cathode catalyst layer were formed by applying the anode catalyst ink and cathode catalyst ink to a polymer electrolyte membrane (Nafion NR212, manufactured by Du Pont) using a spray coating device (manufactured by Acing Technologies) so that the platinum coverage for the anode was 0.5 mg/ ^cm2 and the platinum coverage for the cathode was 0.3 mg/ ^cm2 .
A fuel cell electrode membrane (CCM) composed of an anode catalyst layer or a cathode catalyst layer and a polymer electrolyte membrane was hot pressed (140°C, pressure 2.86 kN) for 3 minutes in a hot press machine (TCMD-2.5, manufactured by Toho Kogyo Co., Ltd.).

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

[Fuel cell single cell evaluation (80°C)]
(IV characteristics)
Hydrogen gas was supplied to the anode side of a single cell obtained using electrode catalyst B or Pt/CB as the cathode catalyst, and oxygen gas was supplied to the cathode side. The flow rates were set so that the hydrogen gas utilization rate was 70% and the oxygen gas utilization rate was 40%. The anode and cathode gases were each humidified using an external humidifier before being supplied to the single cell. The temperature of the single cell was adjusted to 80°C, and the humidity of the supplied gas was adjusted to a relative humidity of 80% RH. Power generation was performed within an applied current range in which the voltage of this single cell did not fall below 0.4 V, and the IV characteristics were evaluated.

(Measurement of start/stop durability)
Hydrogen gas was introduced into the anode side of the single cell, and nitrogen gas was introduced into the cathode side. A start/stop durability test of 5,000 cycles was performed at a temperature of 80°C, a relative humidity of 80% RH, and a potential range of 1.0 V to 1.5 V, and the rate of change in electrochemically effective surface area (ECSA) was measured. ECSA was measured using cyclic voltammetry (CV) by sweeping six times at a temperature of 80°C, a relative humidity of 80% RH, and a sweep potential of 0.05 V to 1.0 V, and calculating the amount of hydrogen adsorbed electricity in the sixth sweep. The rate of change in ECSA for electrode catalyst B is shown in Figure 8.

(Consideration)
As shown in Table 1, in Examples 1 to 5, the porous silicon nitroxycarbide composite material used as the support had a BET specific surface area of 150 m ² /g or more and a conductivity of 1.0 S/cm or more, demonstrating high conductivity while maintaining a large BET specific surface area. Furthermore, catalyst performance evaluation using a rotating electrode revealed that Examples 1 to 5 had a mass activity of 451 (A/g-Pt) or more, indicating a high current per unit mass of platinum (Pt) and high oxygen reduction activity. Furthermore, the ECSA retention rate after durability testing was 75% or more, demonstrating excellent durability.
When electrode catalyst B was used as the cathode catalyst for a single fuel cell, excellent power generation performance of 0.66 V at 1.0 A/ ^cm2 was demonstrated. Furthermore, the durability test results showed that the ECSA maintenance rate was 70%, demonstrating excellent durability as a single fuel cell.

In Comparative Example 1, the conductivity of the porous silicon nitroxycarbide composite material was as low as 0.9 S/cm, and as a result, the ECSA was very low in the catalytic performance evaluation using a rotating electrode, making it impossible to calculate the mass activity. In Comparative Example 2, the mass activity was 450 (A/g-Pt), but the ECSA retention rate after the durability test was low at 55%, making it inferior to the Examples.
When Pt/CB was used as the cathode catalyst for the single fuel cell, excellent power generation performance of 0.66 V at 1.0 A/ ^cm2 was observed. However, the durability test results showed that the ECSA maintenance rate was 55%, indicating that the durability as a single fuel cell was inferior to that of the Examples.

The electrode catalyst, fuel cell electrode, fuel cell, 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 in the catalyst layer of a fuel cell electrode, this can produce a fuel cell with high power generation efficiency. Therefore, it has industrial applicability.

Claims (19)

a porous silicon nitroxycarbide composite material comprising silicon nitroxycarbide (SiCNO) and a carbon material;
particles supported on the porous silicon nitroxycarbide composite material and containing a precious metal;
Equipped with
An electrode catalyst, wherein the porous silicon nitroxycarbide composite material has a BET specific surface area of 100 m ² /g or more and 400 m ² /g or less, and the porous silicon nitroxycarbide composite material has a conductivity of 1.0 S/cm or more and 25 S/cm or less. The electrode catalyst according to claim 1, wherein the amount of particles containing the precious metal supported is 10% by mass or more and 60% by mass or less, when the total mass of the electrode catalyst is taken as 100% by mass. The electrode catalyst according to claim 1 or 2, wherein the carbon material content is 5% by mass or more and 50% by mass or less. The electrode catalyst described in claim 1 or 2, wherein the carbon material is composed of one or more selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons. The electrode catalyst described in claim 1 or 2, wherein the particles containing the precious metal are composed of one or more types selected from the group consisting of platinum (Pt), platinum-cobalt alloy (PtCo), and platinum-nickel alloy (PtNi). 3. The electrocatalyst according to claim 1 or 2, wherein the total pore volume of the porous silicon nitroxycarbide composite material is 1.3 cm ^<3> /g or more and 2.5 cm ^<3> /g or less. The electrode catalyst described in claim 1 or 2, wherein the pore diameter of the porous silicon nitroxycarbide composite material is 10 nm or more and 500 nm or less. The electrode catalyst according to claim 1 or 2, 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 electrode catalyst according to claim 1 or 2, 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 electrode catalyst according to claim 1 or 2, 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. A fuel cell electrode having a layer containing the electrode catalyst according to claim 1 or 2. A fuel cell comprising the fuel cell electrode according to claim 11. 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;
Step (C) of 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 porous silicon nitroxycarbide composite material containing silicon nitroxycarbide (SiCNO) and a carbon material;
a step (E) of mixing the porous silicon nitroxycarbide composite material with a dispersion containing a colloid containing a noble metal and hydrogen peroxide solution to obtain an electrode catalyst containing particles containing a noble metal;
The method for producing an electrode catalyst comprising the steps of: The method for producing an electrode catalyst described in claim 13, wherein in step (D), the porous silicon nitroxycarbide precursor is calcined at a temperature of 1100°C or higher and lower than 1450°C. The method for producing an electrode catalyst according to claim 13 or 14, wherein the organic alkoxysilane is represented by the following formula (1) or formula (2):
R ¹ -SiR ² _x (OR ³ ) _3-x ...(1)
(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 an electrode catalyst according to claim 13 or 14, wherein the carbon material is composed of one or more materials selected from carbon black, carbon nanofibers, carbon nanotubes, and low-crystalline nanocarbons. The method for producing an electrode catalyst according to claim 13 or 14, wherein the colloid containing a precious metal is composed of one or more colloids selected from the group consisting of platinum (Pt) colloid, platinum-cobalt alloy (PtCo) colloid, and platinum-nickel alloy (PtNi) colloid. The method for producing an electrode catalyst according to claim 13 or 14, 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 an electrocatalyst according to claim 13 or 14, wherein the organic polymer is composed of one or more selected from the group consisting of phenolic resin, polystyrene, and polydivinylbenzene.