Surface-coated porous ceramic composite material and method for producing surface-coated porous ceramic composite material

Abstract

A purpose of the present invention is to provide: a surface-coated porous ceramic composite material that exhibits catalytic activity higher than that of conventional carriers; and an electrode catalyst using the composite material. Another purpose of the present invention is to provide methods for manufacturing the same. Specifically, provided is a surface-coated porous ceramic composite material containing a ceramic material and a carbon material. The surface-coated porous ceramic composite material is characterized in that the ceramic material is at least one selected from the group consisting of silicon carbonates, silicon carbides, and silicon oxynitrides. The surface-coated porous ceramic composite material is characterized by having a coating layer comprising a resin including, in the molecular structure, a benzene ring and an atom that has an unpaired electron.

Description

Surface-coated porous ceramic composite material, and method for manufacturing the surface-coated porous ceramic composite material.

[0001] This invention relates to a surface-coated porous ceramic composite material and a method for producing the surface-coated porous ceramic composite material.

[0002] Fuel cells are devices that generate electricity and heat through a chemical reaction that produces water from hydrogen and oxygen. 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). Of these, polymer electrolyte fuel cells (PEFCs) have a structure in which a catalyst layer is provided on one side of a solid polymer electrolyte membrane, forming an anode (fuel electrode) and on the other side a cathode (air electrode), and a gas diffusion layer is attached to the outside of each catalyst layer. The catalyst layer is composed of a catalyst-supported carrier in which particulate catalyst containing noble metals is highly dispersed and supported on the surface of nano-level carrier particles.

[0003] Currently, carbon-based materials with high specific surface area and high conductivity are used as catalyst supports. However, conventional carbon-based materials have the problem of degrading the catalyst layer by causing the ionomer, a proton-conducting material, to leach out due to moisture generated by the electromotive force.

[0004] In response to this, it has been disclosed that the above problem can be solved by developing a catalyst layer structure (Patent Document 1) in which catalyst particles are supported on a carbon support via a support layer composed of two upper and lower layers, and the upper layer of the support layer is made of a polymer having proton conductivity, and the lower layer is made of a polymer having affinity for both the proton conductivity polymer and the carbon support, and a carbon-based support (Patent Document 2) in which a single layer of support made of a specific polymer modified with proton-conducting groups is formed on a carbon support.

[0005] Japanese Patent Publication No. 2013-179030 Japanese Patent Publication No. 2022-74425

[0006] However, in Patent Document 1, the catalyst's active sites are completely covered with a polymer having proton conductivity, which presented a significant challenge in terms of oxygen supply. Furthermore, the catalyst described in Patent Document 2 had room for improvement in area-specific activity and also presented challenges in terms of durability.

[0007] The object of the present invention is to provide porous ceramic composite materials surface-coated with a specific resin and methods for producing the same.

[0008] In other words, the present invention provides the following configuration: [1] A porous ceramic composite material comprising a ceramic material and a carbon material, wherein the ceramic material is at least one selected from the group consisting of silicon oxides, carbides, and nitrides, and the surface-coated porous ceramic composite material is characterized by having a coating layer made of a resin in which a benzene ring and an atom having unpaired electrons are contained in the molecular structure.

[0009] [2] The surface-coated porous ceramic composite material according to [1], wherein the ceramic material is silicon carbide or silicon oxycarbide.

[0010] [3] The surface-coated porous ceramic composite material according to [1] or [2] above, wherein the atom having unpaired electrons is at least one selected from the group consisting of nitrogen, oxygen, and sulfur.

[0011] [4] The surface-coated porous ceramic composite material according to any one of [1] to [3] above, wherein the resin is a polyazole compound or a polyimide compound.

[0012] [5] The surface-coated porous ceramic composite material according to [4] above, wherein the elemental ratio of nitrogen (N) to silicon (Si) (N / Si) measured by XPS is 0.12 or higher.

[0013] [6] The surface-coated porous ceramic composite material according to [4] above, wherein the elemental ratio of nitrogen (N) to carbon (C) (N / C) measured by XPS is 0.03 or higher.

[0014] [7] The surface-coated porous ceramic composite material according to any one of [1] to [6] above, wherein the coating layer is present on a ceramic material and / or a carbon material.

[0015] [8] The hydrophilic ratio (BET specific surface area [H ２ O] / BET specific surface area [N ２ ]) is 0.07 or more, and the surface-coated porous ceramic composite material according to any one of [1] to [7] above.

[0016] [9] The surface-coated porous ceramic composite material according to any one of [1] to [8] above, wherein the surface zeta potential is greater than -20 mV.

[0017]

[10] An electrode catalyst comprising the surface-coated porous ceramic composite material according to any one of [1] to [9] above, and particles containing a noble metal supported on the porous ceramic composite material.

[0018]

[11] The electrode catalyst according to [9] above, wherein the particles containing a noble metal are composed of one or more selected from the group consisting of platinum (Pt), platinum-cobalt alloy (PtCo), and platinum-nickel alloy (PtNi).

[0019]

[12] A membrane electrode assembly having a layer containing the electrode catalyst according to

[10] or

[11] above.

[0020]

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

[12] above.

[0021]

[14] A method for producing a surface-coated porous ceramic composite material, comprising: (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 to form a gel containing the carbon material or the organic polymer by a sol-gel reaction of the organic alkoxysilane; (B) washing the gel with alcohol; (C) drying the washed gel to form a porous ceramic precursor; (D) firing the porous ceramic precursor to obtain a porous ceramic composite material containing a ceramic material and a carbon material; (E) mixing the porous ceramic composite material with a solution in which a resin containing a benzene ring and an atom having unpaired electrons in its molecular structure is dissolved, thereby coating the composite material with the resin; and (F) washing and drying the porous ceramic composite material coated with the resin.

[0022]

[15] A method for producing a surface-coated porous ceramic composite material according to

[13] , wherein the resin is a polyazole compound or a polyimide compound.

[0023] According to the present invention, it is possible to provide a porous ceramic composite material coated with a specific resin, thereby improving catalytic activity and maintaining higher durability compared to conventional catalysts.

[0024] <Structure of Surface-Coated Porous Ceramic Composite Material> The surface-coated porous ceramic composite material according to this embodiment is a porous ceramic composite material comprising a ceramic material and a carbon material, and has a coating layer made of a resin in which a benzene ring and an atom having unpaired electrons are contained in the molecular structure.

[0025] The surface-coated porous ceramic composite material has a hydrophilicity ratio (BET specific surface area [H ２ O] / BET specific surface area [N ２ The hydrophilicity ratio (BET specific surface area [H)) is preferably 0.07 or higher, more preferably 0.10 or higher, and particularly preferably 0.15 or higher. ２ O] / BET specific surface area [N ２When [ ] is 0.07 or more, the ionomer described below tends to adsorb thinly and uniformly on the composite material, and high proton conductivity can be exhibited with a small amount of ionomer used when the surface-coated porous ceramic composite material is used as an electrode catalyst.

[0026] The BET specific surface area [H ２ O] is measured with a specific surface area meter (for example, BELSORP-mini manufactured by MicrotracBEL Corporation), and the surface area per 1 g of the sample measured from the adsorption amount of water vapor by the BET method (Brunauer-Emmett-Teller method) is defined as the specific surface area (m ２ / g). The BET specific surface area [N ２ ] is measured with a specific surface area meter (for example, BELSORP-mini manufactured by MicrotracBEL Corporation), and the surface area per 1 g of the sample measured from the adsorption amount of nitrogen by the BET method (Brunauer-Emmett-Teller method), is defined as the specific surface area (m ２ / g). Since nitrogen is inert to many surfaces, generally, the BET specific surface area [N ２ ] corresponds to the specific surface area of the solid structure.

[0027] The surface-coated porous ceramic composite material has a BET specific surface area [N ２ ] of preferably 10 m ２ / g or more, more preferably 20 m ２ / g or more, and particularly preferably 50 m ２ / g or more. Also, the BET specific surface area may be 300 m ２ / >g or less. When the BET specific surface area is 10 m ２ / g or more, a sufficient amount of catalyst particles can be supported on the carrier surface, and desired characteristics such as output and efficiency can be obtained when the porous silicon carbide composite material is used for the fuel cell electrode. Also, when the BET specific surface area is 300 m ２ / g or less, the ratio of mesopores suitable for catalyst loading is high, so the utilization rate of catalyst particles can be further improved.

[0028] The ratio of nitrogen to silicon on the surface of a surface-coated porous ceramic composite material can be measured by XPS (X-ray photoelectron spectroscopy) surface analysis. The elemental ratio of nitrogen (N) to silicon (Si) (N / Si), determined by XPS surface analysis of the surface-coated porous ceramic composite material, is preferably 0.10 or higher, more preferably 0.20 or higher, and particularly preferably 0.50 or higher. There is no particular upper limit, but it is preferably 10 or lower. By having the elemental ratio (N / Si) within the above range, the amount of resin coating on the ceramic material in the porous ceramic composite material can be adjusted to a desired range, resulting in high catalytic activity. The lower and upper limits may be combined in any way.

[0029] For the above XPS analysis, a scanning X-ray photoelectron spectroscopy analyzer (for example, QUANTERA SXM manufactured by ULVAC-PHI) can be used.

[0030] Herein, in this specification, "surface layer" refers to the area within 10 nm from the surface of the surface-coated porous ceramic composite material of the embodiment. This distance corresponds to the detection depth of the XPS used for measurement in the example.

[0031] Furthermore, if the ceramic material is a nitride, a resin containing a benzene ring and an atom with unpaired electrons in its molecular structure is considered sulfur-based, and the elemental ratio of sulfur (S) to silicon (Si) (S / Si) can be calculated using the same method as described above and kept within the above range. In addition, when using a nitrogen-based resin, the coating amount can be indirectly evaluated by combining XRF analysis with the XPS analysis. For example, evaluation can be performed by calculating the ratio of the elemental ratio (N / Si) obtained by XRF analysis to the elemental ratio (N / Si) obtained by XPS analysis.

[0032] The ratio of nitrogen to carbon in the surface layer of a surface-coated porous ceramic composite material can be measured by XPS (X-ray photoelectron spectroscopy) surface analysis. The elemental ratio of nitrogen (N) to carbon (C) (N / C), determined by XPS surface analysis of the surface-coated porous ceramic composite material, is preferably 0.02 or higher, more preferably 0.03 or higher, and particularly preferably 0.04 or higher. There is no particular upper limit, but it is preferably 10 or lower. When the elemental ratio (N / C) is within the above range, the amount of resin coating on the carbon material in the porous ceramic composite material is optimized, and high catalytic activity can be achieved. The lower and upper limits may be combined in any way.

[0033] The surface zeta potential value of the surface-coated porous ceramic composite material is preferably greater than -20 mV, more preferably greater than -10 mV, and particularly preferably greater than 0 mV. The upper limit is not particularly limited, but is preferably less than +40 mV, and more preferably less than +30 mV. Having the surface zeta potential value within the above range is preferable because it facilitates the adsorption of negatively potential ionomers. Note that the porous ceramic composite material before surface coating has a large negative potential for both the ceramic material and the carbon material, and by bringing the surface potential closer to positive or to a positive potential through surface coating, the adsorption with ionomers is improved. The lower and upper limits may be combined in any way.

[0034] The above surface zeta potential value can be measured as the absolute value (mV) of the zeta potential by electrophoresis using a zeta potential measuring device (Malvern Corporation, device name "Zetasizer Nano ZS").

[0035] The total pore volume of the surface-coated porous ceramic composite material is 0.1 cm³. ３ Preferably, it is 0.2 cm or more per gram. ３ It is more preferable that the amount is 0.1 / g or more. The total pore volume of the surface-coated porous ceramic composite material is 0.1 cm³. ３ When the concentration is above / g, the flow of reaction gases and electrolytes within the catalyst layer becomes easier, improving catalytic efficiency.

[0036] The pore size of the surface-coated porous ceramic composite material is preferably 1 nm to 1000 nm, and more preferably 2 nm to 500 nm. When the pore size of the porous ceramic composite material is 1 nm to 1000 nm, the flow of reaction gas and generated water within the catalyst layer becomes easier, and catalytic efficiency can be improved. In particular, when the pore size of the porous ceramic composite material is 1 nm or more, the supply of reaction gas to the supported catalyst particles and the discharge of generated water become stable, and a decrease in the utilization rate of catalyst particles can be suppressed.

[0037] [Porous Ceramic Composite Material] The form of the porous ceramic composite material is not particularly limited, but for example it may be in the form of powder, particulate, fibrous or needle-like, of which powder or particulate is preferred. When the porous ceramic composite material is in the form of powder or particulate, the particle size of the porous ceramic composite material is not particularly limited, but the particle size D of 50% of the cumulative particle size distribution based on volume is preferred. ５０ For example, it is preferably 0.05 μm or more and 50 μm or less, more preferably 0.1 μm or more and 10 μm or less, and even more preferably 0.1 μm or more and 2 μm or less.

[0038] Particle size D of porous ceramic composite material ５０ This refers to a value measured in accordance with JIS Z8825-1:2013, for example, the particle size D measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD-7000). ５０ This shall mean...

[0039] The total pore volume of the porous ceramic composite material is 0.3 cm³. ３ Preferably, it is 0.5 cm or more per gram. ３ It is more preferable that it be 0.6 cm or more per gram. ３ It is particularly preferable that the amount is 0.3 cm³ or more. ３ When the concentration is above / g, the flow of reaction gases and generated water within the catalyst layer becomes easier, improving catalytic efficiency.

[0040] The pore size of the porous ceramic composite material is preferably 10 nm to 1000 nm, more preferably 20 nm to 500 nm, and particularly preferably 50 nm to 300 nm. When the pore size of the porous ceramic composite material is 10 nm to 1000 nm, the flow of reaction gas and generated water within the catalyst layer becomes easier, and catalytic efficiency can be improved. In particular, when the pore size of the porous ceramic composite material is 10 nm or more, the supply of reaction gas to the supported catalyst particles and the discharge of generated water become stable, and a decrease in the utilization rate of catalyst particles can be suppressed.

[0041] The BET specific surface area, total pore volume, and pore diameter of porous ceramic composite materials can be calculated as measured values ​​by the gas adsorption method. For example, these values ​​are calculated from the amount of adsorption and condensation of non-corrosive gases such as nitrogen and argon when adsorbed using the constant volume method while changing the relative pressure at the adsorption isotherm.

[0042] In porous ceramics that make up porous ceramic composite materials, multiple micropores are provided individually by a three-dimensional skeletal structure, or some or all of the multiple micropores are connected to one another.

[0043] When silicon carbide, silicon oxycarbide, silicon nitrooxycarbide, or silicon nitride is used as the support material, this porous ceramic composite material contains carbon that constitutes the three-dimensional skeletal structure of the porous ceramic, and carbon material other than the carbon that constitutes the three-dimensional skeletal structure, which is supported on the porous ceramic.

[0044] In this specification, porous ceramics refer to spaces composed of a three-dimensional network structure formed by the interconnection of ceramic materials.

[0045] The porous silicon carbide composite material of this embodiment has an electrical conductivity of 0.1 S / cm or more, preferably 1 S / cm or more, more preferably 5 S / cm or more, and even more preferably 10 S / cm or more. Furthermore, the electrical conductivity may be 100 S / cm or less, 70 S / cm or less, or 50 S / cm or less. While a higher electrical conductivity of the porous silicon carbide provides a better fuel cell porous silicon carbide composite material, if the amount of carbon material retained, which contributes to improved conductivity, is increased too much, oxidation and corrosion of the carbon component may progress during the catalytic cycle, leading to a decrease in durability.

[0046] [Ceramic Material] The ceramic material constituting the porous ceramic composite material is at least one selected from the group consisting of silicon oxides, carbides, and nitrides. Examples of the material include silicon oxycarbide, silicon carbide, silicon nitride, silicon nitrooxycarbide, silicon nitride, and silicon nitride. Silicon oxycarbide and silicon carbide are more preferable, and silicon carbide is particularly preferable from the viewpoint of exhibiting crystallinity and consequently semiconducting properties.

[0047] The average diameter of the primary particles of the ceramic material in the porous ceramic composite material is preferably 20 nm to 800 nm, more preferably 30 nm to 500 nm, and even more preferably 40 nm to 300 nm. An average diameter of 20 nm to 800 nm of the primary particles of the ceramic material is preferable because it allows for good voids to be obtained when used as an electrode.

[0048] The particle size of ceramic materials in porous ceramic composite materials can be measured, for example, by observation using a transmission electron microscope or scanning electron microscope. Furthermore, the average diameter of primary particles can be determined, for example, from microscope images using image analysis-based particle size distribution measurement software.

[0049] [Carbon Material] The carbon material supported on the three-dimensional skeletal structure of the porous ceramic is not particularly limited, but can consist of one or more selected from, for example, carbon black, carbon nanofibers, carbon nanotubes, and amorphous carbon materials. Of these, carbon black is preferred as the carbon material because it can achieve high conductivity and is easy to manufacture.

[0050] When the carbon material is composed of carbon black, the average diameter of the primary particles of the carbon material is preferably 10 nm to 200 nm, more preferably 20 nm to 100 nm, and even more preferably 30 nm to 50 nm. When the average diameter of the primary particles of the carbon material is 10 nm to 200 nm, good conductivity can be achieved.

[0051] When the carbon material is composed of carbon nanofibers or carbon nanotubes, the average diameter of the carbon material is preferably 10 nm to 200 nm, and the length of the carbon material is preferably 1 μm to 20 μm.

[0052] The morphology and size of carbon materials held within porous ceramic composite materials can be measured, for example, by observation using a transmission electron microscope or scanning electron microscope. Furthermore, the average diameter of primary particles can be determined, for example, from microscope images using image analysis-based particle size distribution measurement software.

[0053] The carbon material content 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 ceramic composite material is 5% by mass or more and 50% by mass or less, high conductivity can be achieved while suppressing carbon corrosion and improving the durability of the catalyst cycle.

[0054] The mass ratio of silicon (Si) to carbon (C) contained in the porous ceramic composite material ([Si] / [C]) is preferably 0.4 / 1.0 or more and 2.0 / 1.0 or less, more preferably 0.5 / 1.0 or more and 1.8 / 1.0 or less, and even more preferably 0.7 / 1.0 or more and 1.7 / 1.0 or less. When the mass ratio of silicon (Si) to carbon (C) ([Si] / [C]) is 0.4 / 1.0 or more and 2.0 / 1.0 or less, high conductivity can be achieved while suppressing carbon corrosion and improving the durability of the catalyst cycle. In the above mass ratio, carbon (C) refers to the total of the carbon constituting the three-dimensional skeletal structure of the porous ceramic and the carbon in the carbon material supported on the porous ceramic.

[0055] The carbon (C) content in porous ceramic composite materials refers to a value measured by, for example, determining the ratio of elements through elemental analysis and combining this with thermogravimetric differential thermal analysis (TG-DTA) in air.

[0056] The silicon (Si) content in porous ceramic composite materials can be determined, for example, by identifying the ratio of elements by elemental analysis, and ２９ This refers to values ​​measured by combining Si-NMR spectra.

[0057] In porous ceramic composite materials, domains made of silicon oxide may be formed in part of the composite material. Examples of silicon oxide include silicon monoxide (SiO) and silicon dioxide (SiO ２ Examples include the following. The morphology of the domains is not particularly limited, but for example, they may be individual crystals or aggregates thereof. The domains made of silicon oxide are dispersed on the surface of the porous ceramic composite material. Furthermore, it is preferable that the domains made of silicon oxide are formed on the surface of the ceramic material in the porous ceramic composite material. This can suppress oxidation of the surface of the ceramic material.

[0058] In porous ceramic composite materials, the mass ratio of silicon (Si) to oxygen (O) ([Si] / [O]) is preferably 1 / 0.1 or more and 1 / 0.001 or less, more preferably 1 / 0.1 or more and 1 / 0.005 or less, and even more preferably 1 / 0.01 or more and 1 / 0.005 or less. When the mass ratio of silicon (Si) ([Si] / [O]) is 1 / 0.1 or more and 1 / 0.001 or less, the parts of the ceramic material that are prone to deterioration are oxidized in advance, thereby improving the stability of the porous ceramic composite material.

[0059] [Coating Layer] The coating layer is made of a resin in which a benzene ring and an atom having unpaired electrons are contained in its molecular structure. The coating layer may exist in any state, but it is preferably present on a ceramic material and / or a carbon material, and more preferably on at least a ceramic material. In general, the coating layer refers to complete coating of the entire material, but in this specification, it also includes cases where the coating is not complete. More preferably, the coating layer completely covers the entire semilac material and / or carbon material.

[0060] Examples of resins containing a benzene ring and an atom with unpaired electrons in their molecular structure include polyazole compounds and polyimide compounds. More specifically, polyazole compounds include polymers of compounds whose constituent elements are heterogeneous five-membered rings containing one or more nitrogen atoms, such as polyimidazole compounds, polybenzimidazole compounds, polybenzobisimidazole compounds, polybenzoxazole compounds, polyoxazole compounds, polythiazole compounds, and polybenzothiazole compounds. The heterogeneous five-membered ring may also contain oxygen atoms, sulfur atoms, etc., in addition to nitrogen atoms.

[0061] Furthermore, the molecular weight of the polyazole compound is preferably 300 to 500,000 (polystyrene equivalent) as the weight-average molecular weight when measured by GPC.

[0062] As a compound comprising the above-mentioned heterogeneous five-membered ring, it is preferable to use a compound in which a divalent aromatic group, such as a p-phenylene group, m-phenylene group, naphthalene group, diphenylene ether group, diphenylene sulfone group, biphenylene group, terphenyl group, or 2,2-bis(4-carboxyphenylene)hexafluoropropane group, is bonded to the heterogeneous five-membered ring. This is preferable from the viewpoint of increasing affinity with the ionomer and suppressing the reduction in durability due to oxidative corrosion of the carbon component. Specifically, polybenzimidazole is particularly preferred.

[0063] Furthermore, the polyazole compound may be a modified polyazole compound in which an ion exchange group has been introduced using the following general modification method. Examples of such modified polyazole compounds include those in which one or more groups selected from the group consisting of amino groups, quaternary ammonium groups, carboxyl groups, sulfonic acid groups, and phosphonic acid groups have been introduced to the polyazole compound. It is preferable that an anionic ion exchange group be introduced to the polyazole compound to increase the ion exchange capacity, thereby obtaining a high output during fuel cell operation. The ion exchange capacity of the above modified polyazole compound is preferably 0.1 to 3.5 milliequivalents / g.

[0064] The method for modifying polyazole compounds is not particularly limited, but examples include introducing ion exchange groups to polyazole compounds using fuming sulfuric acid, concentrated sulfuric acid, anhydrous sulfuric acid and its complexes, sultones such as propanesultone, α-bromottoluenesulfonic acid, chloroalkylsulfonic acid, etc., or polymerizing polyazole compounds by incorporating ion exchange groups during monomer synthesis.

[0065] Polyimide compounds can also be used in the same manner. The molecular weight of the polyimide compound is preferably 300 to 500,000 (polystyrene equivalent) as the weight-average molecular weight when the precursor polyamic acid compound is measured by GPC.

[0066] BET specific surface area [N] of porous ceramic composite material ２The amount of resin coating per unit area, which contains benzene rings and atoms with unpaired electrons in its molecular structure, is preferably 60 μg or more, more preferably 100 μg or more, and particularly preferably 130 μg or more. When the coating amount is within the above range, the entire porous ceramic composite material can be coated, which is preferable because it exhibits high catalytic activity.

[0067] The amount of coating is calculated by determining the amount of free resin from the amount of resin used in the coating process, based on the UV-Vis absorbance of the filtrate obtained by mixing a porous ceramic composite material used for surface coating treatment, a resin containing benzene rings and atoms with unpaired electrons in its molecular structure, and a solvent in the manufacturing process described later, subjecting it to ultrasonic treatment, and then filtering it, and then determining the amount of free resin from the amount of resin used in the coating treatment, based on the BET specific surface area [N] of the coated porous ceramic composite material. ２ The amount of coverage per unit area was calculated.

[0068] <Electrode Catalyst> The electrode catalyst of this embodiment comprises a surface-coated porous ceramic composite material and particles containing a noble metal supported on the surface-coated porous ceramic composite material.

[0069] [Particles containing precious metals] The amount of particles containing precious metals supported, when the total mass of the electrode catalyst is 100% by mass, is preferably 10% by mass or more and 60% by mass or less, preferably 15% by mass or more and 60% by mass or less, and more preferably 30% by mass or more and 60% by mass or less. When the amount of particles containing precious metals supported is 10% by mass or more and 60% by mass or less, the catalytic function is expressed and the durability is good, and silicon oxide can be sufficiently formed on the porous ceramic composite material. The amount of particles containing precious metals supported can be calculated, for example, by alkali fusion of the electrode catalyst, dissolving it in aqua regia, diluting it with ultrapure water, and then performing high-frequency induction heating emission spectroscopy (ICP).

[0070] The particles containing precious metals are preferably composed of one selected from the group consisting of, for example, platinum (Pt), gold (Au), ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), platinum-cobalt alloy (PtCo), platinum-nickel alloy (PtNi), and platinum-ruthenium alloy (PtRu). Among these, from the viewpoint of high durability at high temperatures and high catalytic function, it is more preferable to be composed of one or more selected from the group consisting of platinum (Pt), platinum-cobalt alloy (PtCo), and platinum-nickel alloy (PtNi), and even more preferable to be composed of platinum (Pt) or platinum-cobalt alloy (PtCo).

[0071] The particles containing the precious metal are preferably nanoparticles containing the precious metal. The average particle size of the primary particles of the particles containing the precious metal is preferably 2 nm to 10 nm, more preferably 2.5 nm to 7 nm, and even more preferably 3 nm to 5 nm. When the average particle size of the primary particles of the particles containing the precious metal is 2 nm to 10 nm, good catalytic performance can be achieved even with a small amount of precious metal.

[0072] <Method for Manufacturing Surface-Coated Porous Ceramic Composite Material> The method for manufacturing the porous ceramic composite material according to this embodiment includes a gel formation step (step (A)), a washing step (step (B)), a porous ceramic precursor formation step (step (C)), a firing step (step (D)), a coating step (step (E)), and a drying step (step (F)). It should be noted that, assuming that the surface-porous ceramic composite material according to this embodiment is obtained, other steps not listed above may be provided before or after each step.

[0073] [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 a carbon material or organic polymer is further added to form a gel containing the carbon material or organic polymer by a sol-gel reaction of the organic alkoxysilane. For example, a hydrolyzable organic alkoxysilane is hydrolyzed to produce a hydrolysate, and then the pH of the reaction system is further increased to carry out a polycondensation reaction of the organic alkoxysilane to obtain 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 25°C to 80°C, more preferably at 30°C to 70°C, and even more preferably at 40°C to 60°C. This allows polysilsesquioxane to be obtained as a wet gel containing water as a solvent inside. Furthermore, by gradually increasing the pH with a pH adjusting agent while the polysilsesquioxane condensation polymerization reaction proceeds, the carbon material or organic polymer can be more densely dispersed in the porous structure of the precursor gel. As a result, the dispersibility of the carbon material in the three-dimensional structural framework of the porous ceramic composite material can be further improved.

[0074] The content of the above 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.

[0075] There are no particular restrictions on the surfactant, but examples include nonionic surfactants and / or cationic surfactants. By appropriately selecting and using either or both nonionic surfactants and cationic surfactants, the desired BET specific surface area and pore size can be obtained. Examples of nonionic surfactants include polyethylene glycol type (ether type, ester-ether type) and polyhydric alcohol type. An example of a polyethylene glycol type nonionic surfactant is the Pluronic® type. Examples of cationic surfactants include amine salt type and quaternary ammonium salt type. By setting the surfactant content in the acidic aqueous solution to 0.1% by mass or more and 50% by mass or less, a porous polysilcesoxane gel with a large BET specific surface area and well-developed macropores from mesopores can be formed.

[0076] The content of the above pH adjusting agent 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 adjusting agent in the acidic aqueous solution to 5% by mass or more and 50% by mass or less, a porous polysilsesquioxane gel having high skeletal strength and flexibility can be formed.

[0077] There are no particular restrictions on the pH adjusting agent, but examples include substances selected from urea, ammonia, and sodium hydroxide.

[0078] There are no particular restrictions on the above-mentioned acidic aqueous solution, but examples include aqueous solutions of hydrochloric acid, nitric acid, and acetic acid.

[0079] The above organic alkoxysilane is preferably represented by the following formula (1) or formula (2). By using the organic alkoxysilane represented by the following formula (1) or formula (2), porous ceramics having a desired three-dimensional skeletal structure can be easily formed. １ -SiR ２ ｘ (OR ３ ) ３－ｘ ... (1) (However, R in the formula１ R is a group selected from a methyl group, an ethyl group, a vinyl group, and a phenyl group. ２ is a methyl group, R ３ represents a methyl group or an ethyl group. In the formula, the integer x is either 0 or 1. ) R ４ - (SiR ５ ｙ (OR ６ ) ３－ｙ ) ２ ... (2) (However, R in the formula ４ R comprises any group selected from methylene, ethylene, hexylene, vinylene, phenylene, and biphenylene groups, ５ is a methyl group, R ６ (where 'x' represents a methyl group or an ethyl group; the integer y in the formula is either 0 or 1.)

[0080] Specific examples of the organic alkoxysilane represented by formula (1) above include methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, methylethyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, methylvinyldimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, and methylphenyldimethoxysilane. Furthermore, specific examples of the organic alkoxysilane represented by formula (2) above include bis(trimethoxysilyl)methane, bis(triethoxysilyl)methane, bis(methyldimethoxysilyl)methane, bis(methyldiethoxysilyl)methane, 1,2-bis(trimethoxysilyl)ethane, 1,2-bis(triethoxysilyl)ethane, 1,2-bis(methyldimethoxysilyl)ethane, 1,2-bis(methyldiethoxysilyl)ethane, 1,6-bis(trimethoxysilyl)hexane, 1,6-bis(triethoxysilyl)hexane, 1,6-bis(methyldimethoxysilyl)hexane, 1,6-bis(methyldiethoxysilyl)hexane, Examples include 1,2-bis(trimethoxysilyl)ethene, 1,2-bis(triethoxysilyl)ethene, 1,2-bis(methyldimethoxysilyl)ethene, 1,2-bis(methyldiethoxysilyl)ethene, 1,4-bis(trimethoxysilyl)benzene, 1,4-bis(triethoxysilyl)benzene, 1,4-bis(methyldimethoxysilyl)benzene, 1,4-bis(methyldiethoxysilyl)benzene, 4,4'-bis(trimethoxysilyl)biphenyl, 4,4'-bis(triethoxysilyl)biphenyl, 4,4'-bis(methyldimethoxysilyl)biphenyl, and 4,4'-bis(methyldiethoxysilyl)biphenyl. The above ethene derivatives have cis / trans geometric isomers, and either isomer can be used. The organic alkoxysilane used may be one type or multiple types.

[0081] In step (A), a carbon material or organic polymer is further added to the above 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 the alkoxysilane, the carbon material can be arranged at the nanoscale within the porous three-dimensional structural framework after the precursor formed in step (C) is calcined in step (D), thereby imparting excellent conductivity to the porous ceramic, which is originally an insulator or semiconductor. The organic polymer undergoes thermal decomposition by calcination in step (D), and is retained in the porous ceramic as amorphous carbon, thus imparting conductivity.

[0082] In step (A) above, it is preferable to add the carbon material or organic polymer to the acidic aqueous solution such that the mass ratio of the carbon material or organic polymer to the organic alkoxysilane is 2.5 to 50:97.5 to 50. More preferably, the mass ratio of the carbon material or organic polymer to the organic alkoxysilane is 3 to 30:70 to 97, and even more preferably 5 to 20:80 to 95. By setting the mass ratio of the carbon material or organic polymer to the organic alkoxysilane within the above range, it is possible to achieve both a larger BET specific surface area and higher conductivity. If the amount of carbon material or organic polymer added is less than or equal to the amount of organic alkoxysilane added, separation from the sol-gel reaction system can be suppressed and gel formation consisting of polysilsesquioxane can be promoted.

[0083] The carbon material is not particularly limited, but can consist of one or more selected from, for example, carbon black, carbon nanofibers, carbon nanotubes, and amorphous carbon. Of these, carbon black is preferred as the carbon material from the viewpoint of achieving high conductivity and manufacturability.

[0084] The organic polymer is not particularly limited, but can consist of one or more selected from, for example, phenolic resins, polystyrene, and polydivinylbenzene.

[0085] [Step (B)] In step (B), the gel obtained in step (A) is washed with alcohol. The alcohol used for washing is not particularly limited, but examples include methanol, ethanol, 1-propanol, and 2-propanol. This removes unwanted surfactants from the acidic aqueous solution and replaces the water in the acidic aqueous solution with alcohol. Alternatively, after washing with alcohol, the water may be further replaced with a hydrocarbon solvent such as hexane or heptane. In this step (B), water, which is a high surface tension solvent, is replaced with alcohol or a hydrocarbon solvent, which are low surface tension solvents, thereby suppressing network shrinkage in the drying step at room temperature and atmospheric pressure described in step (C) below, and facilitating the formation of a porous gel structure.

[0086] [Step (C)] In step (C), the washed gel is dried to form a porous ceramic precursor. In this step (C), methods include supercritical drying with 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 manufacture and, when polysilsesquioxane with high skeletal strength and flexibility is formed, a high-density porous silicon carbide precursor with well-developed mesopores can be obtained.

[0087] [Process (D)] Process (D) yields a porous ceramic composite material, which more specifically includes the following steps.

[0088] [Process (D-1)] In process (D-1), a porous ceramic precursor containing the above-mentioned carbon material or organic polymer is fired to obtain a composite material containing the ceramic material and the carbon material. In this process, carbon atoms are supplied from the organic groups of polysilsesquioxane by firing, and a ceramic skeleton is formed via a carbonothermal reduction reaction. On the other hand, carbon atoms are also supplied to the skeleton from the carbon material or organic polymer dispersed at the nanoscale in the gel. The organic polymer undergoes thermal decomposition by firing and is retained in the porous ceramic as amorphous carbon.

[0089] Firing can be carried out by known and conventional methods, and there are no particular restrictions. For example, firing can be performed by raising the temperature at 2.5°C per minute under an inert gas atmosphere or a reactive gas atmosphere and maintaining the highest temperature reached for a certain period of time. The maximum temperature for firing is preferably 1300°C to 3000°C, more preferably 1350°C to 2500°C, and particularly preferably 1400°C to 2000°C. The duration for maintaining the maximum temperature can be appropriately determined based on an effective time for obtaining a porous ceramic composite material. For example, 5 minutes to 16 hours is preferred, 10 minutes to 10 hours is more preferred, and 30 minutes to 3 hours is particularly preferred. Firing may be carried out in two or more stages. That is, in the first stage, firing can be performed at a temperature lower than the highest temperature reached for a certain period of time, and then the temperature can be raised again for firing. Firing may be performed under atmospheric pressure. Examples of inert gases include helium and argon, and examples of reactive gases include nitrogen. Furthermore, these gases may contain reducing gases such as hydrogen gas. The calcination can be carried out in a fixed-bed or fluidized-bed carbonization furnace, and the heating method and type of the carbonization furnace are not particularly limited, as long as the furnace has the function of raising the temperature to a predetermined temperature. Examples of carbonization furnaces include reed hammer furnaces, tunnel furnaces, and single furnaces.

[0090] The type of inert and reactive gas used, as well as the firing temperature, can be appropriately set depending on the target ceramic material. For example, when obtaining silicon carbide or silicon oxycarbide, firing should be carried out in an inert gas atmosphere such as helium or argon. When obtaining silicon nitrooxycarbide or silicon nitride, firing should be carried out in a nitrogen atmosphere. In the former case, firing should be carried out at 1100°C or higher but less than 1500°C, and in the latter case, at 1500°C or higher but less than 2000°C.

[0091] In this step (D-1), a carbon material or an organic polymer may be further mixed with the porous ceramic precursor, and the mixture may be fired. When an organic polymer is mixed with the porous ceramic precursor in step (D-1), thermal decomposition proceeds during firing, similar to when it is mixed in step (A), and it is retained in the porous ceramic as amorphous carbon.

[0092] [Step (D-2)] The process may also include step (D-2). In step (D-2), a carbon material is further added to the porous ceramic composite material obtained in step (D-1). The carbon material to be added is not particularly limited, but can consist of one or more selected from, for example, carbon black, carbon nanofibers, carbon nanotubes, and amorphous carbon. Of these, carbon black is preferred as the carbon material from the viewpoint of achieving high conductivity and manufacturability. The carbon material used in step (A) may be the same as or different from the carbon material used in step (A), but it is preferable to use the same material from the viewpoint of manufacturing cost.

[0093] The compounding method can be any conventionally known method, including simple mixing of powders, mechanical mixing using a pulverizer or mixer, or mixing using a mortar and pestle. The resulting mixture may be in a dry or wet state, but from a cost perspective, a dry state is preferable.

[0094] The amount of each compound is not particularly limited, but it is preferable to compound the electrode catalyst so that the ratio of [Si] / [C] after calcination is 0.15 / 1.0 to 2.0 / 1.0.

[0095] [Step (E)] In step (E), the composite material is coated with a resin that contains benzene rings and atoms with unpaired electrons in its molecular structure. For example, the resin can be coated by dissolving a resin containing benzene rings and atoms with unpaired electrons in its molecular structure in a solvent, mixing it with a porous ceramic composite material, and then performing ultrasonic treatment.

[0096] The solvent is not particularly limited as long as it can dissolve the resin, and examples include N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone, with N,N-dimethylacetamide being more preferable. The resin can be a polyamic acid compound, which is a precursor of the polyazole compound or polyimide compound mentioned above.

[0097] It is preferable to add the porous ceramic composite material to the resin solution such that the mass ratio of the porous ceramic composite material to the resin is 8:1 or higher. More preferably, the mass ratio of the porous ceramic composite material to the resin is 4:1 to 1:2, and even more preferably 4:1 to 1:1. By setting the mass ratio of the porous ceramic composite material to the resin within the above range, improved catalytic activity can be achieved.

[0098] [Step (F)] In step (F), the composite material obtained in the previous step (E) is dried to obtain a surface-coated porous ceramic composite material. Specifically, the mixed solution after ultrasonic treatment in the previous step (E) is filtered by suction and the residue is collected. The obtained residue is added to a solvent, ultrasonic treatment and stirring are performed, and suction filtration is performed again. By vacuum heating and drying the obtained residue, a coated porous ceramic composite material can be obtained. By performing the above operations, excess resin that was not used for coating is removed, and the material can exhibit the desired effect when used as an electrode catalyst. The time for ultrasonic treatment and stirring is not particularly limited as long as excess resin that was not used for coating is removed, but it is preferable that each be 30 minutes or more. The drying temperature is preferably 60°C, and more preferably 60°C or higher. The drying time is preferably 9 hours or more, and more preferably 24 hours or more.

[0099] <Method for Manufacturing Electrode Catalyst> [Step (G-1)] In step (G-1), a dispersion containing a noble metal and a polar solvent is mixed with the surface-coated porous ceramic composite material to obtain an electrode catalyst containing particles containing the noble metal. The dispersion containing the noble metal and a polar solvent is obtained by dispersing a compound containing the noble metal, described later, in a mixed solvent of a polar solvent and water.

[0100] The mixing ratio of the dispersion containing the noble metal and polar solvent to the surface-coated porous ceramic composite material is preferably such that, for example, the mass of the noble metal after support 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.

[0101] The precious metal is preferably composed of one or more metal compounds selected from the group consisting of, for example, platinum (Pt), gold (Au), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), and iridium (Ir). Among these, it is more preferable to be composed of one or more selected from the group consisting of platinum (Pt), platinum-cobalt alloy (PtCo), and platinum-nickel alloy (PtNi), and even more preferable to be composed of platinum (Pt) or platinum-cobalt alloy (PtCo).

[0102] Examples of the polar solvent include ethylene glycol and ethanol, and ethylene glycol is preferred from the viewpoint of reducing and supporting noble metals at high boiling points.

[0103] In this step (G-1), when the mixture of a dispersion containing a noble metal and a polar solvent and a surface-coated porous ceramic composite material is stirred, the noble metal is supported on the surface-coated porous ceramic composite material, and an electrode catalyst containing particles of the noble metal can be obtained. After being left for a predetermined time, the solid phase and liquid phase separate. From the viewpoint of promoting solid-liquid separation, the mixture may be cooled. Furthermore, the washing of the solid components can be carried out by known and conventional methods and conditions. The washing solution used during washing is not particularly limited, but for example, water is used, and ultrapure water is preferred. This removes ions such as chloride ions from the solid components.

[0104] [Step (G-2)] The process may also include step (G-2). In step (G-2), a carbon material is further added to the electrode catalyst containing the noble metal particles obtained in step (G-1). The carbon material to be added is not particularly limited, but can consist of one or more selected from, for example, carbon black, carbon nanofibers, carbon nanotubes, and low-crystallinity nanocarbon. Of these, carbon black is preferred as the carbon material from the viewpoint of achieving high conductivity and manufacturability. The carbon material used in step (A) may be the same as or different from the carbon material used in step (A), but it is preferable to use the same material from the viewpoint of manufacturing cost.

[0105] The compounding method can be any conventionally known method, including simple mixing of powders, mechanical mixing using a pulverizer or mixer, or mixing using a mortar and pestle. The resulting mixture may be in a dry or wet state, but from a cost perspective, a dry state is preferable.

[0106] The amount of each compound is not particularly limited, but it is preferable to compound the electrode catalyst so that the ratio of [Si] / [C] after calcination is 0.15 / 1.0 to 2.0 / 1.0.

[0107] The above steps (D-2) and (G-2) may preferably include only one of them, and it is particularly preferable to include step (G-2) from the viewpoint of the performance of the resulting electrode catalyst. Including either step (D-2) or (G-2) is preferable because it is possible to improve the conductivity while maintaining the durability of the resulting electrode catalyst.

[0108] [Fuel Cell Electrode and Membrane Electrode Assembly] The fuel cell electrode according to this embodiment has a catalyst layer containing the electrode catalyst described above. Typically, the fuel cell electrode has the electrode catalyst layer and a gas diffusion layer. The fuel cell electrode may be a fuel cell anode or a fuel cell cathode. When the fuel cell electrode is a fuel cell anode, the fuel cell anode 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 cathode, the fuel cell cathode has a cathode catalyst layer to which an oxygen-containing gas such as air is supplied, and a second gas diffusion layer.

[0109] Furthermore, the membrane electrode assembly according to this embodiment includes the above-mentioned fuel cell electrode. The membrane electrode assembly comprises a fuel cell electrode and an electrolyte layer. Typically, a fuel cell comprises a fuel cell anode, a fuel cell cathode, an electrolyte layer disposed between them, a first separator disposed on the opposite side of the fuel cell anode from the electrolyte layer, and a second separator disposed on the opposite side of the fuel cell cathode from 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. Multiple of the membrane electrode assemblies are stacked to form a fuel cell.

[0110] The following describes embodiments of the present invention. The present invention is not limited to the embodiments shown below. Unless otherwise specified, the values ​​in the table mean "parts by weight".

[0111] (Example 1) [Synthesis of Porous Silicon Carbide Composite Material] 6 g of 5 mM aqueous acetic acid (manufactured by Kanto Chemical Co., Ltd.), 0.8 g of Pluronic® F-127 (manufactured by BASF), 0.5 g of urea (manufactured by Kanto Chemical Co., Ltd.), and 0.24 g of Ketjenbrak (manufactured by Lion Specialty Chemicals, product name "ECP-600JD") were placed in a vial and stirred at room temperature for 10 minutes. 5 g of methyltrimethoxysilane (manufactured by Kanto Chemical Co., Ltd.) was added and stirred at room temperature for 30 minutes. The reaction was then carried out at 60°C for 4 days to obtain a wet gel. The obtained wet gel was washed with methanol (manufactured by Kanto Chemical Co., Ltd.), dried at room temperature and atmospheric pressure for 3 days, and then further dried at 80°C and atmospheric pressure for 6 hours to obtain 3.5 g of porous silicon carbide precursor. After mixing 1 g of this porous silicon carbide precursor with 0.4 g of Ketjenbrak (ECP), the mixture was placed in a tubular furnace and fired under an argon atmosphere at a heating rate of 2.5 °C / min to 1500 °C, holding the temperature for 2 hours to obtain a porous silicon carbide composite material.

[0112] 0.1 g of polybenzimidazole (manufactured by Sato Light Co., Ltd.) was added to 200 mL of dimethylacetamide (manufactured by Kanto Chemical Co., Ltd.) and dissolved by sonication. Then, 0.2 g of the porous silicon carbide composite material was added and sonication was performed for 30 minutes. After that, the residue obtained by suction filtration was added to 30 mL of dimethylacetamide and sonicated for 30 minutes, followed by stirring for 30 minutes. The resulting stirred liquid was suction filtered, and the residue was vacuum-heat-dried at 60°C for 9 hours. After drying, it was pulverized in a mortar to obtain surface-coated porous silicon carbide.

[0113] (Example 2) A porous silicon carbide precursor and Ketjenblack (ECP) were mixed at a ratio of 0.25 (Ketjenblack / precursor) and calcined at 1500°C under an argon atmosphere. The other steps were the same as in Example 1.

[0114] (Example 3) A porous silicon carbide precursor and Ketjenblack (ECP) were mixed at a ratio of 1.8 (Ketjenblack / precursor) and calcined at 1500°C under an argon atmosphere. The other steps were the same as in Example 1.

[0115] (Comparative Example 1) Commercially available Ketjenblack (ECP) was calcined at 1500°C under an argon atmosphere. The other steps were the same as in Example 1 to obtain a surface-coated carbon black support.

[0116] Measurements for Examples 1 to 3 and Comparative Example 1 described above were performed using the following method.

[0117] [Measurement of carbon content] The carbon content was calculated from the weight loss in the temperature range of 600°C to 800°C using thermogravimetric differential thermal analysis (TG-DTA) under atmospheric conditions.

[0118] [Elemental Analysis of Porous Silicon Carbide Composite Materials] Carbon (C) Analysis: Analysis was performed by high-frequency combustion-infrared absorption method. Equipment: LECO CS844. Oxygen (O) Analysis: Analysis was performed by inert gas fusion-infrared absorption method. Equipment: LECO TCH600. Silicon (Si) Analysis: After melting and decomposing the sample with sodium hydroxide and sodium peroxide, the molten material was dissolved in hydrochloric acid and diluted to a fixed volume with ultrapure water to prepare the test solution, and ICP detection was performed. Equipment: Shimadzu ICPE-9820. From the Si, C, and O content, the mass ratios of [Si] / [C] and [Si] / [O] were calculated.

[0119] [Elemental Ratio (N / Si), Elemental Ratio (N / C)] Surface elemental analysis of the sample powder was performed using X-ray photoelectron spectroscopy (XPS) with K-Alpha (manufactured by FE-I Japan). Area measurements were performed in a 1000 μm square area, and the average value of n=2 measurements was obtained as atom% for each element. • X-ray source: Monochrome Al-Kα, beam diameter 400 μmφ, output 72W • Measurement: Area measurement (1000 μm square), n=2 • Charge correction: None • X-ray extraction angle: 90°

[0120] [BET specific surface area [H ２ O], BET specific surface area [N ２ 0.015 g of the sample was weighed and placed in a sample tube, and pre-treated by vacuum drying at 100°C for 5 hours. After pre-treatment, water vapor was adsorbed onto the sample at -196°C while varying the relative pressure using a specific surface area / pore distribution spectrometer (Microtrac-Bell, spectrometer name "BELSORP-miniII"). Nitrogen was adsorbed in the same manner. The hydrophilicity ratio was calculated using the following formula: Hydrophilicity ratio = BET specific surface area [H ２ O] / BET specific surface area [N ２ ]

[0121] [Surface Zeta Potential] The surface zeta potential was measured using an electrophoretic method with a zeta potential measuring device (Malvern, device name "Zetasizer Nano ZS") to obtain the absolute value (mV) of the zeta potential. 0.001 g of the sample was weighed and placed in 20 mL of 50 wt% ethanol aqueous solution, and measured at 25°C.

[0122] [Coverage Amount] A dispersion was prepared by mixing 0.2 g of porous silicon carbide composite material, 0.1 g of polybenzimidazole, and 188 g of dimethylacetamide, and subjecting the mixture to sonication. The mixture was then filtered, and the resulting filtrate was measured by ultraviolet-visible absorbance. The amount of polybenzimidazole contained in the filtrate was estimated using a calibration curve, thereby determining the BET specific surface area [N] of the porous silicon carbide composite material. ２ The amount of polybenzimidazole coating per unit area was calculated.

[0123]

[0124] [Synthesis of Electrode Catalysts] (Examples 4-6) A platinum compound dispersion was prepared by dispersing 0.0818 g of hexahydrate chlorplatinic acid in 200 mL of 60 wt% aqueous ethylene glycol. Separately, a dispersion was prepared by dispersing 0.1 g of the surface-coated porous silicon carbide composite material obtained in Examples 1-3 in 400 mL of 60 wt% aqueous ethylene glycol. This dispersion was added to the platinum compound dispersion and subjected to sonication and stirring. After confirming sufficient dispersion visually, reflux was carried out at 140°C for 6 hours. Subsequently, after cooling to room temperature, solid-liquid separation was performed, and the obtained powder was thoroughly washed with ultrapure water to remove chloride ions. Then, it was dried in air at 80°C for 12 hours to obtain an electrode catalyst in which platinum was supported on the surface of the surface-coated porous silicon carbide composite material.

[0125] (Comparative Example 2) An electrode catalyst was prepared in the same manner as in Example 4, except that a surface-coated carbon support from Comparative Example 1 was used instead of the surface-coated porous silicon carbide.

[0126] [Measurement of Conductivity] The electrode catalyst or catalyst powder was introduced into a powder resistance measurement system (Mitsubishi Chemical Analytec Co., Ltd., device name "MCP-PD51"), and the sample was pressurized using the attached hydraulic pump until it reached 12 kN. Then the resistivity was measured using a resistivity meter (Mitsubishi Chemical Analytec Co., Ltd., device name "Rolestar GX"), and the conductivity was calculated from the resistivity using the following formula. In Example 1, the resistivity was 6.6 × 10⁻⁶. －２The resistance was 15 S / cm in Ω·cm. These measurement results are shown in Table 1. Conductivity (S / cm) = (Resistivity (Ω·cm)) - 1

[0127] [Measurement of Pt Loading Amount] The electrode catalyst was dissolved in anhydrous sodium carbonate and sodium peroxide using alkali fusion, then dissolved in aqua regia, diluted to a specified concentration with ultrapure water, and calculated using radiofrequency induction heating emission spectroscopy (ICP; Shimadzu Corporation ICPE-9820).

[0128] [Catalyst Performance Evaluation Using Rotating Electrodes] (Electrode Preparation) A 5 mm diameter glassy carbon (GC) electrode was polished with alumina paste, and then ultrasonically cleaned with ultrapure water. The electrode catalyst was added to a 99 vol% ethanol aqueous solution and dispersed using an ultrasonic homogenizer. This was dropped onto a GC disk and dried at room temperature for 12 hours. After drying, a 5% Nafion® solution was dropped onto the electrode catalyst on the GC disk to a dry film thickness of 50 nm, and dried at room temperature for 12 hours.

[0129] (CV Measurement) Electrode evaluation was performed using an electrochemical measurement system (Hokuto Denko Co., Ltd., HZ-5000). After purging a 0.1 M perchloric acid aqueous solution with nitrogen gas for 30 minutes, a reversible hydrogen electrode (RHE) was used as the reference electrode, and cleaning was performed 50 times with a potential range of 0.05 to 1.2 V and a sweep rate of 150 mV / s. Subsequently, cyclic voltammetry (CV) measurements were performed with a potential range of 0.05 to 1.0 V and a sweep rate of 100 mV / s. Electrochemical active surface area (ECSA) analysis was performed using hydrogen adsorption waves observed below 0.4 V.

[0130] (Oxygen Reduction Activity Evaluation) After purging the electrolyte with oxygen gas for more than one hour, linear sweep voltammetry (LSV) was performed. Data was obtained for a total of eight conditions, with a temperature of 25°C, a potential range of 0.25 to 1.00 V, a sweep speed of 5 mV / s, and the rotation speed increased from 1000 rpm to 2750 rpm in 250 rpm increments. The obtained results were analyzed using a Koutecky-Levich plot, and the mass activity (A / m) at 0.85 V was calculated. ２ The value of ) was obtained. Also, according to the definition of area specific activity, dividing the mass activity by ECSA gives the area specific activity.

[0131] (Durability Test: Load Fluctuation Test) After purging the electrolyte with nitrogen gas for 30 minutes, the potential was alternately switched between 0.6V and 1.0V for 3 seconds each, for a total of 20,000 cycles. During this process, CV measurements were taken in the potential range of 0.05V to 1.0V after a predetermined number of cycles. The ECSA at cycle 0 and cycle 20,000 were compared to calculate the ECSA maintenance rate, which is one of the indicators of durability.

[0132]

[0133] Compared to Comparative Example 2, Examples 4-6 showed a decrease in the initial ECSA value, but exhibited an improvement in area-specific activity, and also showed improved durability in load fluctuation tests.

Claims

1. A porous ceramic composite material comprising a ceramic material and a carbon material, wherein the ceramic material is at least one selected from the group consisting of silicon oxides, carbides, and nitrides, and the surface-coated porous ceramic composite material is characterized by having a coating layer made of a resin in which a benzene ring and an atom having unpaired electrons are contained in the molecular structure.

2. The surface-coated porous ceramic composite material according to claim 1, wherein the ceramic material is silicon carbide or silicon oxycarbide.

3. The surface-coated porous ceramic composite material according to claim 1 or 2, wherein the atom having unpaired electrons is at least one selected from the group consisting of nitrogen, oxygen, and sulfur.

4. The surface-coated porous ceramic composite material according to any one of claims 1 to 3, wherein the resin is a polyazole compound or a polyimide compound.

5. The surface-coated porous ceramic composite material according to claim 4, wherein the elemental ratio of nitrogen (N) to silicon (Si) (N / Si) measured by XPS is 0.12 or greater.

6. The surface-coated porous ceramic composite material according to claim 4, wherein the elemental ratio of nitrogen (N) to carbon (C) measured by XPS (N / C) is 0.03 or greater.

7. The surface-coated porous ceramic composite material according to any one of claims 1 to 6, wherein the coating layer is present on a ceramic material and / or a carbon material.

8. Hydrophilicity ratio (BET specific surface area [H ２ O] / BET specific surface area [N ２ A surface-coated porous ceramic composite material according to any one of claims 1 to 7, wherein the coefficient of ) is 0.07 or greater.

9. A surface-coated porous ceramic composite material according to any one of claims 1 to 8, wherein the surface zeta potential is greater than -20 mV.

10. An electrode catalyst comprising a surface-coated porous ceramic composite material according to any one of claims 1 to 9, and particles containing a noble metal supported on the porous ceramic composite material.

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

12. A film electrode assembly having a layer containing the electrode catalyst according to claim 10 or 11.

13. A fuel cell comprising the membrane electrode assembly according to claim 12.

14. A method for producing a surface-coated porous ceramic composite material, comprising: (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 to form a gel containing the carbon material or the organic polymer by a sol-gel reaction of the organic alkoxysilane; (B) washing the gel with alcohol; (C) drying the washed gel to form a porous ceramic precursor; (D) firing the porous ceramic precursor to obtain a porous ceramic composite material containing a ceramic material and a carbon material; (E) mixing the porous ceramic composite material with a solution in which a resin containing a benzene ring and an atom having unpaired electrons in its molecular structure is dissolved, thereby coating the composite material with the resin; and (F) washing and drying the porous ceramic composite material coated with the resin.

15. The method for producing a surface-coated porous ceramic composite material according to claim 14, wherein the resin is a polyazole compound or a polyimide compound.

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