Conductive metal oxide particles and catalyst particles for electrochemical reaction

Abstract

In the catalyst particles for electrochemical reaction, the carrier of the electrode catalyst is conductive metal oxide particles having a specific surface area of 35 m2 / g or more and a pore volume of pores having a pore diameter of 20-100 nm or less of 0.25 mL / g or more, and the electrode catalyst is obtained by supporting catalyst noble metal particles on the conductive metal oxide particles.

Description

Technical Field

[0001] This invention relates to conductive metal oxide particles and catalyst particles for electrochemical reactions using the conductive metal oxide particles. Background Technology

[0002] To meet the requirements of preventing air pollution, suppressing greenhouse gas emissions, and providing alternative energy sources to petroleum, research and development of fuel cells are underway. Fuel cells have advantages such as being clean, having high energy density, and requiring no recharging.

[0003] A fuel cell, for example, has a structure in which the anode and cathode are arranged opposite each other across an ion exchange membrane. If fuel (e.g., hydrogen) is supplied to the anode side and an oxidant (e.g., air) is supplied to the cathode side, predetermined electrochemical reactions occur at the two electrodes to generate electricity.

[0004] In fuel cells, electrode catalysts, for example, are used where noble metal catalyst particles are supported on the surface of a conductive support. Carbon black, with its excellent conductivity, is often used as the conductive support, and platinum (Pt), with its excellent catalytic activity, is often used as the noble metal catalyst particles.

[0005] However, if fuel cells using electrode catalysts supported by carbon black are used for extended periods, the precious metal particles in the supported catalyst may detach or agglomerate due to the oxidative degradation of the carbon black, leading to a decline in power generation performance. To address this issue, several attempts have been proposed in the prior art.

[0006] For example, Patent Document 1 discloses the use of niobium (Nb)-doped tin oxide (SnO2) nanoparticles as a support for an electrode catalyst. Patent Document 2 discloses an electrode catalyst support in which primary particles of metal oxide with a size of 5-100 nm are fused together, forming a chain-like or cluster-like structure. Patent Document 3 discloses the use of an aggregate of metal oxide particles as a support for an electrode catalyst, wherein the aggregate of metal oxide particles has chain-like portions and voids formed by the chain-like fusion bonding of microcrystals with a size of 10-30 nm.

[0007] Existing technical documents

[0008] Patent Document 1: International Publication No. 2015 / 146454

[0009] Patent Document 2: International Publication No. 2015 / 146454

[0010] Patent Document 3: International Publication No. 2020 / 080400 Summary of the Invention

[0011] According to the technology in Patent Documents 1-3, although the oxidation and degradation of the electrode catalyst support associated with long-term use of fuel cells can be suppressed, there is a problem of insufficient output power of the fuel cell.

[0012] The present invention was made in view of the above circumstances. The object of the present invention is to provide a support for an electrode catalyst and an electrode catalyst using the support, which can suppress oxidative degradation associated with long-term use and provide a fuel cell with high output power.

[0013] The general outline of this invention is as follows.

[0014] [Option 1]

[0015] A conductive metal oxide particle with a specific surface area of ​​35 m² 2 The pore volume is 0.25 mL / g or more, and the pore size is 20 nm or more and less than 100 nm.

[0016] [Scheme 2] The conductive metal oxide particles according to Scheme 1 have a primary particle size of 10 nm or more and 30 nm or less.

[0017] [Scheme 3] The conductive metal oxide particles according to Scheme 1 have a crystallite diameter of 10.0 nm or more and 15.0 nm or less.

[0018] [Scheme 4] The conductive metal oxide particles described in Scheme 1 have a macropore diameter of more than 15 nm as measured by a mercury porosimeter.

[0019] [Scheme 5] The conductive metal oxide particles according to Scheme 1 have a secondary particle size of 0.05 μm or more and 5.0 μm or less.

[0020] [Solution 6] The conductive metal oxide particles according to Solution 1 are tin oxide particles doped with one or more elements selected from niobium, tantalum, tungsten, antimony and bismuth.

[0021] [Solution 7] The conductive metal oxide particles according to Solution 6 are tin oxide particles doped with niobium.

[0022] [Scheme 8] A catalyst particle for electrochemical reaction, wherein a catalyst noble metal particle is supported on a conductive metal oxide particle as described in any one of Schemes 1 to 7.

[0023] [Scheme 9] The catalyst particles for electrochemical reaction according to Scheme 8, wherein the catalyst noble metal particles are platinum particles.

[0024] [Scheme 10] The catalyst particles for the electrochemical reaction described in Scheme 8 are electrode catalysts for fuel cells.

[0025] [Scheme 11] The catalyst particles for the electrochemical reaction described in Scheme 10 are electrode catalysts for the cathode.

[0026] [Solution 12] A fuel cell comprising the catalyst particles for electrochemical reaction described in Solution 10.

[0027] [Solution 13] A method for manufacturing conductive metal oxide particles, which is the method for manufacturing conductive metal oxide particles according to any one of Solutions 1 to 7, includes the following steps (A) and (B):

[0028] Step (A): An aqueous dispersion containing a conductive metal oxide particle precursor and a pore-forming material is dried in an atomized state using a diffusion flame to obtain an aggregate of the conductive metal oxide particle precursor and the pore-forming material. The specific surface area of ​​the conductive metal oxide particle precursor is 35 m². 2 The pore volume of the fine pores is less than 0.25 mL / g and the pore size is greater than 20 nm and less than 100 nm.

[0029] Step (B): Heating the condensate to burn the pore-forming material.

[0030] [Scheme 14] In the method for manufacturing conductive metal oxide particles according to Scheme 13, the pore-forming material is selected from one or more of organic polymers, calcium carbonate and zinc oxide.

[0031] [Solution 15] The method for manufacturing conductive metal oxide particles according to Solution 13 further includes a step (C) before step (A):

[0032] The solution obtained by dissolving an organic compound containing metal atoms in an organic solvent is sprayed and then burned to obtain the conductive metal oxide particle precursor.

[0033] According to the present invention, conductive metal oxide particles suitable as supports for electrode catalysts and fuel cells capable of suppressing oxidative degradation associated with long-term use and providing high output power can be provided, as well as catalyst particles suitable as electrode catalysts for electrochemical reactions. Attached Figure Description

[0034] Figure 1 The image shows the SEM image of the Pt / NTO particles obtained in Comparative Example 1.

[0035] Figure 2(a) and (b) are SEM images of Pt / porous NTO particles obtained in Example 2, respectively. Detailed Implementation

[0036] [Conductive metal oxide particles]

[0037] The conductive metal oxide particles of this invention have a specific surface area of ​​35 m². 2 Conductive metal oxide particles with a pore volume of 0.25 mL / g or more and a pore size of 20 nm or more and less than 100 nm.

[0038] The metal oxides constituting the conductive metal oxide particles can be selected from metal oxides that are conductive or semiconductor, or metal oxides that have been doped with specific impurity elements.

[0039] The metal oxides that are conductive or semiconductor can be one or more selected from TiO, VO, Ti2O3, V2O3, VO2, NbO2, CrO2, MoO2, WO2, ReO2, RuO2, OsO2, RhO2, IrO2, SnO2, ReO2, LaTiO3, SrMoO3, SrRuO3, LaRhO3, etc.

[0040] The doping impurity element can be one or more selected from lithium (Li), niobium (Nb), tantalum (Ta), tungsten (W), antimony (Sb), bismuth (Bi), etc., and can be appropriately selected according to the type of metal oxide with conductive or semiconducting properties. When the total atomic number of the metal element and impurity element in the metal oxide is 100 atomic%, the doping amount of the impurity element can be 0.5 atomic% or more, 1.0 atomic% or more, 2.0 atomic% or more, or 3.0 atomic% or more, or less than 10.0 atomic%, less than 8.0 atomic%, less than 6.0 atomic% or less, or less than 5.0 atomic%.

[0041] The conductive metal oxide particles of the present invention may be tin oxide (SnO2) particles doped with one or more elements selected from Nb, Ta, W, Sb and Bi, and in particular, may be SnO2 particles doped with Nb.

[0042] The conductive metal oxide particles of the present invention are considered to be primary particles aggregated in a manner that creates fine pores (macropores) with a diameter of 20 nm or more and less than 100 nm between the particles, thus forming a secondary particle morphology with a porous texture and a high specific surface area.

[0043] The specific surface area of ​​the conductive metal oxide particles is 35 m². 2 / g or more. If this condition is met, when catalyst noble metal particles are supported on the conductive metal oxide particles of the present invention, the catalyst noble metal particles can be firmly fixed on the surface of the conductive metal oxide particles. It is believed that if such supported particles are used, for example, as catalyst particles for electrochemical reactions, the decrease in activity caused by the migration and aggregation of catalyst noble metal particles can be suppressed.

[0044] The specific surface area of ​​the conductive metal oxide particles is 35 m². 2 / g or more, can be 40m 2 / g or more, 45m 2 / g or more, 50m 2 / g or more, 55m 2 / g or more, 60m 2 / g or more, 65m 2 / g or more or 70m 2 / g or more, can be 200m 2 / g or less, 180m 2 / g or less, 160m 2 / g or less, 140m 2 / g or less, 120m 2 / g or less, 100m 2 / g or less, 80m 2 / g or less or 70m 2 / g or less.

[0045] The specific surface area of ​​conductive metal oxide particles was determined by the BET method using nitrogen as the adsorbate.

[0046] The conductive metal oxide particles of the present invention have pores (macropores) with a diameter of 20 nm or more and 100 nm or less, and a pore volume of 0.25 mL / g or more. If this condition is met, when catalyst noble metal particles are supported on the conductive metal oxide particles of the present invention, for example, when applicable to catalyst particles for electrochemical reactions, the reactants can easily flow within the particles and come into contact with the catalyst noble metal particles, thus enabling highly efficient catalytic activity.

[0047] The macropore volume of the conductive metal oxide particles is greater than or equal to 0.25 mL / g, and can be greater than or equal to 0.27 mL / g, greater than or equal to 0.30 mL / g, or greater than or equal to 0.32 mL / g, or less than or equal to 0.50 mL / g, less than or equal to 0.45 mL / g, less than or equal to 0.40 mL / g, less than or equal to 0.38 mL / g, less than or equal to 0.35 mL / g, less than or equal to 0.33 mL / g, or less than or equal to 0.30 mL / g.

[0048] The pore volume of the macropores of conductive metal oxide particles was determined using mercury porosimetry, as the cumulative pore volume within the range of 20–100 nm pore diameters, based on the pore distribution obtained using a mercury porosimetry apparatus. The pore diameter was calculated using the Washburn equation. In this calculation, the surface tension of mercury was assumed to be 480 dynes / cm, and the contact angle between the mercury and the sample was assumed to be 140 degrees (°). As a pretreatment, the sample was dried at 120 °C for 4 hours before measurement.

[0049] The conductive metal oxide particles of the present invention have a pore size of 20 nm or more and 100 nm or less, and the mode diameter of the macropores can be 15 nm or more. If the mode diameter of the macropores is 15 nm or more, then when catalyst noble metal particles are supported on the conductive metal oxide particles of the present invention, for example, when applicable to catalyst particles for electrochemical reactions, the reactants flow within the particles and easily come into contact with the catalyst noble metal particles, thus enabling highly efficient catalytic activity.

[0050] The modal diameter of the macropores of the conductive metal oxide particles of the present invention can be 15nm or more, 17nm or more, 20nm or more, 22nm or more, or 25nm or more, or less than 50nm, 45nm or less, 40nm or less, 35nm or less, 30nm or less, or 25nm or less.

[0051] The mode diameter of the macropores of conductive metal oxide particles is determined using a mercury porosimeter by the mercury porosimeter method, and is used as the micropore diameter corresponding to the peak of the micropore distribution in the micropore diameter range of 20~100nm.

[0052] The secondary particle size of the conductive metal oxide particles of the present invention can be appropriately set according to the intended use. However, in order to ensure a suitable macropore volume, it is preferable that the secondary particle size of the conductive metal oxide particles is not too small. On the other hand, considering the operability during catalyst layer formation, it is preferable that the secondary particle size of the conductive metal oxide particles is not too large. From these viewpoints, the secondary particle size of the conductive metal oxide particles can be 0.05 μm or more, 0.07 μm or more, 0.1 μm or more, 0.2 μm or more, 0.3 μm or more, or 0.5 μm or more, and can be 5.0 μm or less, 4.0 μm or less, 3.0 μm or less, 2.0 μm or less, 1.5 μm or less, 1.0 μm or less, 0.8 μm or less, or 0.5 μm or less.

[0053] The secondary particle size of conductive metal oxide particles was determined as the numerical average value obtained by electron microscopy.

[0054] In order to form large pores between particles as described above when they become secondary particles, the primary particle size of the conductive metal oxide particles of the present invention can be 10 nm or more, 12 nm or more, 15 nm or more, 17 nm or more, or 20 nm or more, or 30 nm or less, 25 nm or less, 23 nm or less, 20 nm or less, 18 nm or less, or 15 nm or less.

[0055] The primary particle size of conductive metal oxide particles is determined as the numerical average value obtained by electron microscopy.

[0056] In order to form the primary particles as described above, the crystallite diameter of the conductive metal oxide particles of the present invention can be 10.0 nm or more, 11.0 nm or more, 12.0 nm or more, or 13.0 nm or more, or 20 nm or less, 18 nm or less, 15 nm or less, 13 nm or less, or 12.0 nm or less.

[0057] The crystallite diameter of conductive metal oxide particles is calculated using the Scherer formula based on the XRD analysis results of the conductive metal oxide particles.

[0058] The conductive metal oxide particles of the present invention can have a structure in which secondary particles are linked together in a cluster or chain. "Cluster" refers to a shape similar to a grape cluster. "Chain" refers to a shape in which secondary particles are linked together to form a chain, ladder, net, or similar shape.

[0059] The conductive metal oxide particles of the present invention can form a "sheet of dried sardines" shape with two-dimensional extended connections, or a block shape with three-dimensional disordered connections, etc.

[0060] [Method for manufacturing conductive metal oxide particles]

[0061] The conductive metal oxide particles of the present invention can be manufactured by various methods as long as the above conditions are met.

[0062] The conductive metal oxide particles of the present invention can be manufactured, for example, by a method comprising the following steps (A) and (B):

[0063] Step (A): An aqueous dispersion containing conductive metal oxide particle precursors and pore-forming materials is dried in an atomized state using a diffusion flame to obtain an aggregate of the conductive metal oxide particle precursors and the pore-forming materials (flame-assisted spray drying step). The specific surface area of ​​the conductive metal oxide particle precursors is 35 m². 2 The pore volume is less than 0.25 mL / g, and the pore size is 20 nm or more and less than 100 nm.

[0064] Step (B): Heating the condensate to burn the pore-forming material (heating step).

[0065] In the method for manufacturing conductive metal oxide particles of the present invention, before the flame-assisted spray drying step (A) described above, step (C) may be further included:

[0066] The solution obtained by dissolving an organic compound containing metal atoms in an organic solvent is sprayed and then combusted to obtain the conductive metal oxide particle precursor (spray flame combustion process).

[0067] The following describes each step of the manufacturing method for conductive metal oxide particles.

[0068] <(A) Flame-assisted spray drying process>

[0069] (A) In the flame-assisted spray drying process, an aqueous dispersion containing conductive metal oxide particle precursors and pore-forming materials is dried by a diffusion flame in an atomized state to obtain a condensate composed of conductive metal oxide particle precursors and pore-forming materials.

[0070] (Conductive metal oxide particle precursor)

[0071] Conductive metal oxide particle precursors can have a specific surface area of ​​35 m². 2 Particles with a pore size of 20 nm or more and less than 100 nm, and a pore volume of less than 0.25 mL / g.

[0072] The specific surface area of ​​the conductive metal oxide particle precursor can be the same as the specific surface area of ​​the desired conductive metal oxide particles. Therefore, the specific surface area of ​​the conductive metal oxide particle precursor can be 35 m². 2 / g or more, 40m 2 / g or more, 45m 2 / g or more, 50m 2 / g or more, 55m 2 / g or more, 60m 2 / g or more, 65m 2 / g or more or 70m 2 / g or more, can be 200m 2 / g or less, 180m 2 / g or less, 160m 2 / g or less, 140m 2 / g or less, 120m 2 / g or less, 100m 2 / g or less, 80m 2 / g or less or 70m 2 / g or less.

[0073] According to the method for manufacturing conductive metal oxide particles of the present invention, fine pores (macropores) with a pore size of 20 nm or more and 100 nm or less are formed in the conductive metal oxide particles by combustion of a pore-forming material, and the fine pore volume is 0.25 mL / g or more. Therefore, the fine pore volume of the macropores in the conductive metal oxide particle precursor can be smaller than the desired fine pore volume of the macropores in the conductive metal oxide particles. Therefore, the fine pore volume of the macropores in the conductive metal oxide particle precursor can be less than 0.25 mL / g, less than 0.24 mL / g, less than 0.20 mL / g, less than 0.15 mL / g, less than 0.10 mL / g, or less than 0.05 mL / g; alternatively, the conductive metal oxide particle precursor may not have macropores.

[0074] As described above, in the method for manufacturing conductive metal oxide particles according to the present invention, macropores are formed in the conductive metal oxide particles by combustion of a pore-forming material. Therefore, when the conductive metal oxide particle precursor has macropores, its mode diameter can be an appropriate value independent of the mode diameter of the macropores in the desired conductive metal oxide particles. The mode diameter of the macropores in the conductive metal oxide particle precursor can be 1.0 nm or more and 20.0 nm or less.

[0075] According to the method for manufacturing conductive metal oxide particles of the present invention, the primary particle size of the obtained conductive metal oxide particles is equal to or slightly larger than the primary particle size of the conductive metal oxide particle precursor. Therefore, the primary particle size of the conductive metal oxide particle precursor can be equal to or slightly smaller than the desired primary particle size of the conductive metal oxide particles. The primary particle size of the conductive metal oxide particle precursor can be 5 nm or more, 8 nm or more, 10 nm or more, 13 nm or more, or 15 nm or more, and can be 25 nm or less, 23 nm or less, 20 nm or less, 18 nm or less, 15 nm or less, or 10 nm or less.

[0076] According to the method for manufacturing conductive metal oxide particles of the present invention, the crystallite diameter of the obtained conductive metal oxide particles is equal to or slightly larger than the crystallite diameter of the conductive metal oxide particle precursor. Therefore, the crystallite diameter of the conductive metal oxide particle precursor can be equal to or slightly smaller than the desired crystallite diameter of the conductive metal oxide particles. The crystallite diameter of the conductive metal oxide particle precursor can be 8.0 nm or more, 10.0 nm or more, or 12.0 nm or more, or 18 nm or less, 15 nm or less, 13 nm or less, 12.0 nm or less, or 10.0 nm or less.

[0077] The conductive metal oxide particle precursor can be in the form of secondary particles formed by the aggregation of primary particles with the aforementioned primary particle size. In this case, the secondary particle size of the conductive metal oxide particle precursor can be the same as the secondary particle size of the desired conductive metal oxide particles.

[0078] Such conductive metal oxide particle precursors can be manufactured, for example, by the spray flame combustion process described later (C). Alternatively, commercially available products that meet the above conditions can also be used as conductive metal oxide particle precursors.

[0079] (Pore-forming materials)

[0080] The pore-forming material can be one or more selected from organic polymers, calcium carbonate, zinc oxide, etc.

[0081] Organic polymers that form pores can be, for example, acrylic polymers, aromatic polymers, acrylic-aromatic polymers, etc., and one or more of them can be used.

[0082] Examples of acrylic polymers include polymethyl methacrylate (PMMA).

[0083] As an aromatic polymer, examples include polystyrene;

[0084] Examples of acrylic-aromatic polymers include styrene-acrylic acid copolymers.

[0085] Organic polymers used as pore-forming materials can be cross-linked or not.

[0086] The pore-forming material can be in particulate form. The particle size of the particulate pore-forming material can be 50 nm or more, 100 nm or more, 150 nm or more, 200 nm or more, or 300 nm or more, and can be less than 1000 nm, 800 nm or less, 600 nm or less, 500 nm or less, 400 nm or less, 300 nm or less, or 200 nm or less. According to the method for manufacturing conductive metal oxide particles of the present invention, if a pore-forming material with a particle size within the above-mentioned range is used, conductive metal oxide particles with a macropore-to-micropore volume of 0.25 mL / g or more can be obtained.

[0087] (Aqueous dispersion)

[0088] The aqueous dispersion used in process (A) flame-assisted spray drying contains the aforementioned conductive metal oxide particle precursor and pore-forming material.

[0089] The solvent for aqueous dispersions can be water or a mixture of water and a water-soluble organic solvent, typically water.

[0090] Relative to the total amount of the aqueous dispersion, the amount of conductive metal oxide particle precursor in the aqueous dispersion can be more than 0.1% by mass, more than 0.2% by mass, or more than 0.5% by mass, and can be less than 10.0% by mass, less than 8.0% by mass, less than 5.0% by mass, less than 3.0% by mass, less than 2.0% by mass, less than 1.5% by mass, or less than 1.0% by mass.

[0091] The amount of pore-forming material in the aqueous dispersion can be more than 50 parts by mass, more than 100 parts by mass, more than 150 parts by mass, more than 200 parts by mass, more than 250 parts by mass, or more than 300 parts by mass, relative to 1000 parts by mass, less than 800 parts by mass, less than 600 parts by mass, less than 500 parts by mass, less than 400 parts by mass, or less than 300 parts by mass.

[0092] (Flame-assisted spray drying)

[0093] In the flame-assisted spray drying process, the above-mentioned aqueous dispersion is dried by a diffusion flame in an atomized state to obtain a condensate composed of conductive metal oxide particle precursors and pore-forming materials.

[0094] The droplet size of the mist constituting the aqueous dispersion can be greater than 1 nm and less than 6 nm. The concentration of the mist in the aqueous dispersion, as the volume of water droplets per unit time, can be greater than 1 mL / min and less than 10 mL / min.

[0095] Atomization of water-based dispersions can be achieved using commercially available ultrasonic atomizers, heated atomizers, etc.

[0096] The mist of the aqueous dispersion is delivered into the diffusion flame via a suitable carrier gas. The carrier gas can be an inert gas. By using an inert gas as the carrier gas, the drying of the aqueous dispersion caused by the heat of the diffusion flame proceeds gently, promoting the self-organization of conductive metal oxide particle precursors and pore-forming materials. From this perspective, the carrier gas can be, for example, nitrogen (N2), argon (Ar), etc. The flow rate of the carrier gas can be appropriately determined by those skilled in the art based on the scale of manufacturing.

[0097] A diffusion flame is a flame that exists at the interface between a combustible gas and an oxidizing gas. The combustible gas and the oxidizing gas consumed by combustion are continuously supplied to the flame through diffusion to maintain the flame during combustion.

[0098] The combustible gas constituting the diffusion flame can be, for example, methane, ethane, propane, etc. The oxidizing gas can be, for example, oxygen, air, etc. The supply amount of the combustible gas and the oxidizing gas, as well as their ratio, can be appropriately determined by those skilled in the art based on the types of combustible gas and the scale of production.

[0099] A condensate of conductive metal oxide particle precursors and pore-forming materials is obtained by "flame-assisted spray drying," which dries an atomized aqueous dispersion using a diffusion flame. The resulting condensate can be collected, for example, using a suitable bag filter, and then fed into the heating process (B) below.

[0100] <(B) Heating Process>

[0101] (B) In the heating process, the metal oxide particle precursor and the condensate of the pore-forming material obtained in the flame-assisted spray drying process (A) are heated. As a result, the pore-forming material is burned off, forming conductive metal oxide particles with predetermined macropores.

[0102] (B) The heating temperature in the heating process can be the combustion temperature when the pore-forming material is an organic polymer, the thermal decomposition temperature when it is calcium carbonate, or the volatilization temperature when it is zinc oxide, for example, above 400°C, above 450°C, or above 500°C. On the other hand, if the heating temperature is too high, sintering of the particles may occur, and the formed macropores will be "distorted". From this point of view, the heating temperature can be below 1000°C, below 900°C, below 800°C, below 700°C, below 600°C, or below 550°C. When using an organic polymer as the pore-forming material, the heating temperature in the heating process (B) can be, for example, above 400°C and below 800°C.

[0103] The heating time can be more than 10 minutes, more than 20 minutes, more than 30 minutes, more than 40 minutes, more than 45 minutes or more than 1 hour, or less than 6 hours, less than 4 hours, less than 3 hours, less than 2 hours, less than 1.5 hours or less than 1 hour.

[0104] The ambient atmosphere during the (B) heating process can be an inactive or oxidizing atmosphere; in fact, air is sufficient.

[0105] As described above, the conductive metal oxide particles of the present invention can be obtained. The obtained conductive metal oxide particles can be used directly, or they can be crushed and graded as needed before use.

[0106] <(C) Spray Flame Combustion Process>

[0107] (C) The spray flame combustion process is an optional process for manufacturing the conductive metal oxide particle precursor used in the (A) flame-assisted spray drying process. Therefore, the (C) spray flame combustion process can be performed before the (A) flame-assisted spray drying process.

[0108] (C) In the spray flame combustion process, a conductive metal oxide particle precursor is obtained by a method including the following steps:

[0109] Dissolve an organic compound containing metal atoms in an organic solvent to obtain a solution containing the organic compound containing metal atoms;

[0110] The solution containing the organic compound with metal atoms is sprayed and then burned.

[0111] (A solution containing organic compounds with metal atoms)

[0112] "Organic compounds containing metal atoms" refers to compounds, salts, or complexes that contain metal atoms, carbon atoms, and hydrogen atoms, and may optionally contain one or more atoms selected from oxygen atoms, nitrogen atoms, and sulfur atoms. The organic compounds containing metal atoms in this invention may not contain halogen atoms and silicon atoms.

[0113] An organic compound containing metal atoms can contain one or more metal atoms. However, a typical organic compound containing metal atoms in this invention can contain one metal atom.

[0114] Organic compounds containing metal atoms can be liquid at room temperature (25°C) and atmospheric pressure (1 atm). By using organic compounds containing metal atoms that are liquid at room temperature and atmospheric pressure, the decomposition of organic compounds containing metal atoms can be promoted, and the precipitation (solidification) of organic compounds containing metal atoms can be inhibited, thereby obtaining homogeneous and nano-sized conductive metal oxide particle precursor particles.

[0115] Organic compounds containing metal atoms that are liquid at room temperature and pressure can be, for example, one or more selected from metal alkoxides, metal organic acid salts, metal complexes, etc.

[0116] When an organic compound containing metal atoms contains two or more metals, it may be used to use organic compounds containing two or more metals per molecule, or it may be used to use two or more organic compounds containing one metal per molecule.

[0117] The metal contained in the organic compound containing metal atoms can be of the same kind as the metal in the desired conductive metal oxide particles. The conductive metal oxide particles of the present invention are preferably tin oxide (SnO2) particles doped with one or more elements selected from Nb, Ta, W, Sb, and Bi, particularly SnO2 particles doped with Nb. Therefore, the metal contained in the organic compound containing metal atoms in the (C) spray flame combustion process can include one or more elements selected from Nb, Ta, W, Sb, and Bi, as well as Sn.

[0118] Organic compounds containing metal atoms that serve as precursors to tin oxide (SnO2) can particularly be tin carboxylates. In tin carboxylates, tin can be divalent or tetravalent. The number of carbon atoms in the alkyl carbonyl group of the tin carboxylate, including the carbonyl carbon, can be 2 or more, 4 or more, 6 or more, or 8 or more, and can be less than 20, less than 18, less than 16, less than 14, less than 12, or less than 10. When the alkyl carbonyl group has 4 or more carbon atoms, it can be linear or branched.

[0119] The precursor of the dopant element, an organic compound containing metal atoms, can be, for example, an alkoxide of a predetermined metal. When the predetermined metal can have multiple stable oxidation states, the oxidation state of the metal in the metal alkoxide can be any one of these stable oxidation states. Furthermore, the number of carbon atoms in the alkoxy group of the alkoxide can be 1 or more, 2 or more, 3 or more, or 4 or more, or it can be 10 or less, 8 or less, 6 or less, 4 or less, or 3 or less. When the number of carbon atoms in the alkoxy group is 3 or more, the alkoxy group can be linear or branched.

[0120] The conductive oxide particles of the present invention can be niobium-doped tin oxide particles. In this case, the metal-containing organic compound that serves as the precursor of the dopant element can be, for example, an alkoxide of niobium and a carboxylate of tin, particularly niobium ethoxide (V) and tin 2-ethylhexanoate (II).

[0121] In a solution containing an organic compound with metal atoms, the mixing ratio of the tin oxide particle precursor and the dopant precursor can be the same as the tin:dopant ratio in the desired conductive oxide particles. The molar number of the dopant, relative to the total molar number of tin and the dopant, can be, for example, 0.5 mol% or more, 1 mol% or more, 2 mol% or more, 3 mol% or more, 4 mol% or more, or 5 mol% or more, and can be 10 mol% or less, 8 mol% or less, 6 mol% or less, or 5 mol% or less.

[0122] The solvent for the solution containing the organic compound with metal atoms is an organic solvent. This organic solvent can be an organic solvent capable of dissolving the aforementioned organic compound containing metal atoms.

[0123] As organic solvents, specifically, examples include aromatic compounds, aliphatic hydrocarbons, alcohols, and polar organic solvents, and one or more selected from these can be used. Examples of aromatic compounds include benzene, toluene, ethylbenzene, xylene, cumene, and mesitylene; examples of aliphatic hydrocarbons include pentane, cyclopentane, hexane, and cyclohexane; examples of alcohols include methanol, ethanol, 2-propanol, n-butanol, and benzyl alcohol; and examples of polar organic solvents include tetrahydrofuran, acetonitrile, and diethylhexanoic acid.

[0124] Organic solvents can include solvents with high combustion enthalpy. If the solvent has a high combustion enthalpy, then during the spray combustion of the precursor solution, the conductive oxide particle precursor and the catalyst noble metal particle precursor are instantly converted into the target material, which is preferred in terms of suppressing undesirable conditions such as precursor precipitation and agglomeration.

[0125] From this perspective, the organic solvent can include high enthalpy solvents with a combustion enthalpy of 3000 kJ / mol or higher. The organic solvent used in the method of this invention can contain high enthalpy solvents at a concentration of 30% by mass or higher, 50% by mass or higher, 70% by mass or higher, 80% by mass or higher, 90% by mass or higher, or 95% by mass or higher relative to the total amount of organic solvents; alternatively, all organic solvents can be high enthalpy solvents.

[0126] The enthalpy of combustion of solvents with high enthalpy of combustion can be above 3500 kJ / mol, above 4000 kJ / mol, or above 4500 kJ / mol, or below 6000 kJ / mol, below 5500 kJ / mol, or below 5000 kJ / mol. Examples of solvents with such high enthalpy of combustion include aromatic compounds and aliphatic hydrocarbons.

[0127] The organic solvent in a solution containing an organic compound with metal atoms can be an aromatic compound, particularly toluene, ethylbenzene, xylene, etc.

[0128] Furthermore, the enthalpy of combustion in this specification refers to the enthalpy of combustion of a liquid at 25°C.

[0129] The amount of organic solvent used in a solution containing an organic compound with metal atoms can be an amount in which the concentration of the organic compound with metal atoms in the solution is 0.05 mol / L or more and 0.5 mol / L or less.

[0130] (Spray flame combustion process)

[0131] Next, a predetermined conductive metal oxide particle precursor is obtained by spraying and burning a solution containing an organic compound with metal atoms as described above.

[0132] (C) Combustion in the spray flame combustion process can be carried out using the spray flame method (FSP). In the spray flame method, an ignition source is used to ignite a solution containing organic compounds with metal atoms, which is formed as a mist by a dispersed gas stream, thus creating a flame. The flame formed at this time is a spray flame in which the solution containing organic compounds with metal atoms, which is sprayed into a mist, is burning. The spray combustion method using this spray flame differs from the synthesis method using diffused flame particles, which involves supplying droplets of raw materials to an already formed flame and causing them to burn.

[0133] The dispersed gas can be an oxidizing gas, such as air or oxygen. The ignition source is not particularly limited as long as it can ignite the atomized solution containing an organic compound with metal atoms; for example, it can be formed from methane and air or oxygen.

[0134] Conductive metal oxide particle precursors are obtained through the spray flame combustion process described in (C) above. The obtained conductive metal oxide particle precursors can be collected, for example, using a suitable bag filter, and then directly or, as needed, crushed and graded before being supplied to the flame-assisted spray drying process in (A).

[0135] [Catalyst particles for electrochemical reactions]

[0136] According to another aspect of the present invention, a catalyst particle for electrochemical reactions is provided.

[0137] The catalyst particles for electrochemical reactions of the present invention have a structure in which a noble metal catalyst particle is supported on a conductive metal oxide particle of the present invention.

[0138] The catalyst noble metal particles can be, for example, platinum group metal particles, particularly platinum particles or alloys of platinum and other metals. Other metals used herein can be selected from, for example, nickel (Ni), cobalt (Co), ruthenium (Ru), manganese (Mn), titanium (Ti), tin (Sn), yttrium (Y), etc.

[0139] The catalyst noble metal particles are in particulate form, and their particle size can be smaller than that of the conductive metal oxide particles. They can be 1 nm or more, 2 nm or more, 3 nm or more, 4 nm or more, or 5 nm or less, or less than 20 nm or less, 15 nm or less, 10 nm or less, 8 nm or less, 7 nm or less, or 6 nm or less.

[0140] The loading of noble metal catalyst particles in the catalyst particles for electrochemical reactions, as a mass ratio of noble metal catalyst particles to the total mass of catalyst particles for electrochemical reactions, can be 5% or more by mass, 10% or more by mass, 12% or more by mass, 15% or more by mass, 17% or more by mass, or 20% or more by mass, or less than 30% by mass, less than 28% by mass, less than 25% by mass, less than 23% by mass, or less than 20% by mass.

[0141] The electrochemical reaction catalyst particles of the present invention are suitable as electrode catalysts for fuel cells, and particularly suitable as electrode catalysts for the cathode (air electrode) of fuel cells.

[0142] [Method for manufacturing catalyst particles for electrochemical reactions]

[0143] The catalyst particles for electrochemical reactions of the present invention can be manufactured by various methods as long as they have the above-described structure.

[0144] The catalyst particles for electrochemical reactions of the present invention can be manufactured, for example, by a method comprising the following steps:

[0145] This allows the conductive metal oxide particles of the present invention to come into contact with the catalyst metal precursor;

[0146] The catalyst metal precursor is reduced, and the catalyst metal particles are supported on conductive metal oxide particles to obtain catalyst particles for electrochemical reactions.

[0147] Catalyst metal precursors can be appropriately selected from halides, sulfides, cyanides, complexes, etc., of the metals constituting the desired catalyst metal particles. When the catalyst metal particles are platinum particles, the catalyst metal precursors can be, for example, PtCl2, PtCl4, PtBr2, PtS, Pt(CN)2, PtCl2(NH3)2 (dinitrodiammineplatinum), hexahydroxyplatinum, etc.

[0148] Contact between conductive metal oxide particles and the catalyst metal precursor can be carried out, for example, in a suitable solvent. The solvent can be selected from those capable of dissolving the catalyst metal precursor. For example, hydrochloric acid can be used when the catalyst metal particles are platinum particles and the catalyst metal precursor is PtCl2; an aqueous solution of hydrobromic acid can be used when it is PtBr2; an aqueous solution of nitric acid can be used when it is PtCl2(NH3)2; water can be used when it is PtCl4, PtS, or Pt(CN)2; and a solvent containing an amine can be used when it is hexahydroxyplatinum.

[0149] The reduction of the catalyst metal precursor can be carried out using a suitable reducing agent. Reducing agents can be, for example, ethanol, formic acid, acetic acid, acetaldehyde, sodium borohydride, hydrazine, etc. Reduction can be carried out at a temperature above 10°C and below 100°C for a time of 0.5 hours to 8 hours. When using sodium borohydride as a reducing agent, the reduction temperature is preferably above 10°C and below 50°C; when using ethanol, formic acid, acetic acid, acetaldehyde, or hydrazine as a reducing agent, the reduction temperature is preferably above 60°C and below 100°C.

[0150] In this way, catalyst particles for electrochemical reactions are obtained, in which catalyst metal particles are supported on conductive metal oxide particles. The obtained catalyst particles for electrochemical reactions can be washed and dried as needed, and then crushed and classified for use as required.

[0151] [Fuel Cell]

[0152] According to another aspect of the present invention, a fuel cell is provided. The fuel cell of the present invention has electrodes comprising catalyst particles for electrochemical reactions according to the present invention.

[0153] The electrode containing the catalyst particles for electrochemical reactions of the present invention can be a cathode (air electrode). The cathode may have a suitable substrate layer and a catalyst layer on the substrate layer (cathode-side catalyst layer), the cathode-side catalyst layer containing the catalyst particles for electrochemical reactions of the present invention.

[0154] The substrate layer can be appropriately selected from materials that possess chemical and mechanical stability capable of withstanding catalyst particles and solvents used in electrochemical reactions, as well as heat treatments and pressure treatments preferably performed during electrode formation. Specifically, sheets of materials such as polyimide, polyethylene, polypropylene, polysulfone, and polytetrafluoroethylene can be used, for example.

[0155] The cathode-side catalyst layer contains the catalyst particles for the electrochemical reaction of the present invention, and may also contain ionomers, such as binders or other optional components. For example, the ionomer may be Nafion (NAFION (registered trademark), a sulfonated tetrafluoroethylene (co)polymer).

[0156] The cathode described above is configured as a fuel cell electrode assembly formed by sequentially stacking a solid polymer electrolyte membrane and an anode (hydrogen electrode) on the cathode. The solid polymer electrolyte membrane and anode in this fuel cell electrode assembly can be known solid polymer electrolyte membranes and anodes, respectively. This fuel cell electrode assembly can be manufactured using known methods, except when using an electrode containing the catalyst particles for electrochemical reactions of the present invention as the cathode.

[0157] The fuel cell of the present invention includes the aforementioned fuel cell electrode assembly, and in addition, for example, may have an air channel or an oxygen channel on the cathode side, and a fuel channel on the anode side. The fuel cell of the present invention can be manufactured by known methods, except that it uses an electrode containing the catalyst particles of the present invention as the cathode.

[0158] Example

[0159] [Comparative Example 1]

[0160] (1) Modulation of NTO particles

[0161] With a combined Sn and Nb concentration of 0.1 mol / L and an atomic ratio of Sn:Nb = 96:4, tin(II) 2-ethylhexanoate (Sn(C8H) 15 O2)2) and niobium ethanol (Nb(OC2H5)5) were dissolved in xylene to prepare a precursor solution for NTO particles.

[0162] The obtained precursor solution was supplied to an AM6 type two-fluid nozzle manufactured by Atomax Co., Ltd. at a flow rate of 3 mL / min using a syringe pump. The precursor solution was atomized by an oxygen flow rate of 1.5 L / min and ignited by a methane / air mixture of 1 L / min and 10 L / min to form a spray flame of the precursor solution, thus synthesizing Nb-doped tin oxide (NTO) particles of Comparative Example 1.

[0163] The generated NTO particles are captured by a bag filter manufactured by HORKOS Co., Ltd.

[0164] (2) Pt loading (modulation of Pt / NTO particles)

[0165] 3.2 g of the NTO particles obtained above were added to 90 mL of pure water as carrier particles, and the solution was stirred at 250 rpm for 30 minutes using a stirrer to obtain a suspension. While stirring the suspension, an amine solution containing hexahydroxyplatinic acid equivalent to 0.8 g of platinum was slowly added dropwise. After the addition was completed, stirring was continued for another 30 minutes. Next, the solution was heated to 95°C while stirring was continued, and this temperature was maintained. 40 mL of a 1 mol / L formic acid aqueous solution was slowly added dropwise, and the solution temperature was maintained at 95°C for another 5 minutes, thereby reducing the platinum and loading it onto the NTO particles.

[0166] The particles were recovered from the reaction mixture by filtration, washed with pure water, and dried at 80°C for 12 hours to obtain the Pt / NTO particles of Comparative Example 1. Figure 1 SEM images of Pt / porous NTO particles from Comparative Example 1 are shown. (Refer to...) Figure 1It can be seen that the Pt / NTO particles in Comparative Example 1 do not have well-defined macropores and do not form a well-defined particle shape, but rather extend in a "dried sardine slice" manner.

[0167] [Comparative Example 2]

[0168] The NTO particles obtained in the same manner as in Comparative Example 1 were calcined in air at 1200°C for 1 hour and used as carrier particles. Otherwise, the Pt / NTO particles of Comparative Example 2 were obtained by loading Pt, just as in Comparative Example 1.

[0169] [Comparative Example 3]

[0170] (1) Modulation of NTO particles

[0171] A precursor solution for NTO particles was prepared by dissolving tin(II) chloride (SnCl2) and niobium chloride (NbCl5) in ethanol, with a total concentration of Sn and Nb of 0.1 mol / L and an atomic ratio of Sn:Nb = 96:4.

[0172] The obtained precursor solution was dropletized using an ultrasonic atomizer. The resulting droplets were transported by N2 carrier gas and subjected to combustion and thermal decomposition via a methane / oxygen diffusion flame to synthesize NTO particles of Comparative Example 3.

[0173] (2) Pt loading (modulation of Pt / NTO particles)

[0174] Using the NTO particles obtained above as carrier particles, Pt was loaded in the same manner as in Comparative Example 1, thereby obtaining the Pt / NTO particles of Comparative Example 3.

[0175] [Example 1]

[0176] (1) Modulation of porous NTO particles

[0177] NTO particles (conductive oxide particle precursor) and spherical polymethyl methacrylate (PMMA) particles with a particle size of 100 nm, prepared in the same manner as in Comparative Example 1, were dispersed in ultrapure water to prepare an aqueous dispersion for manufacturing porous NTO particles. In this aqueous dispersion, the concentration of NTO particles was 1% by mass relative to the total amount of the aqueous dispersion, and the amount of PMMA spherical particles added was three times the mass of the NTO particles.

[0178] The aqueous dispersion was atomized in an ultrasonic atomizer, and N2 carrier gas at a flow rate of 3 L / min was supplied to the burner. A methane / oxygen diffusion flame with 0.5 L / min of methane and 1.3 L / min of oxygen was formed in the burner. The atomized aqueous dispersion was dried by this diffusion flame, and some PMMA particles were burned, forming condensates (flame-assisted spray drying). The condensates obtained by bag filter were collected and heated in air at 500°C for 1 hour to completely burn the PMMA particles, thereby obtaining the porous NTO particles (conductive metal oxide particles) of Example 1.

[0179] (2) Pt loading (modulation of Pt / porous NTO particles)

[0180] Using the porous NTO particles obtained above as carrier particles, Pt was loaded in the same manner as in Comparative Example 1, thereby obtaining the Pt / porous NTO particles of Example 1.

[0181] [Example 2]

[0182] The PMMA spherical particles were made to have a particle size of 300 nm and were added in an amount equivalent to twice the mass of the NTO particles. Otherwise, the Pt / porous NTO particles of Example 2 were obtained in the same manner as in Example 1.

[0183] Figure 2 SEM images of Pt / porous NTO particles from Example 2 are shown. (Refer to...) Figure 2 It can be confirmed that in the Pt / porous NTO particles of Example 1, secondary particles with well-defined macropores are linked in a grape-like cluster.

[0184] [Example 3]

[0185] The firing conditions of the dried condensate were set to air, 1000°C and 1 hour, otherwise the Pt / porous NTO particles of Example 3 were obtained in the same manner as in Example 2.

[0186] [analyze]

[0187] The analysis of the particles (NTO particles and Pt / NTO particles) obtained in each embodiment and comparative example was performed by the following method.

[0188] <Pt particle size>

[0189] The particle size of the Pt-loaded Pt particles in the Pt / NTO particles is calculated using the Scherer formula based on the XRD of the Pt / NTO particles.

[0190] <Pt particle carrying capacity>

[0191] The loading amount of Pt particles in Pt / NTO particles was calculated based on the addition amount of raw materials. Furthermore, the supernatant of the reaction mixture obtained in the Pt loading process was analyzed by high-frequency inductively coupled plasma (ICP). As a result, in all examples and comparative examples, Pt ions were not detected in the liquid.

[0192] <Specific surface area of particles>

[0193] The specific surface area of NTO particles was determined by the BET method using nitrogen as the adsorbate.

[0194] <Primary particle size of NTO particles>

[0195] The primary particle size of NTO particles was determined as an average value based on transmission electron microscope images.

[0196] <Crystallite diameter of NTO particles>

[0197] The crystallite diameter of NTO particles was calculated by the Scherrer formula from XRD.

[0198] <Analysis of macropores in NTO particles>

[0199] The analysis of macropores in NTO particles was performed by mercury intrusion porosimetry using a pore size distribution measurement device "AutoPore V (model 9620)" manufactured by Micrometrics Instruments Corporation. <00004�2>After the NTO particle sample was dried at a constant temperature of 120 °C for 4 hours, the pore size distribution was determined by mercury intrusion porosimetry using the above-mentioned pore size distribution measurement device. The pore diameter was calculated using the Washburn equation. The cumulative pore volume in the range of 20 - 100 nm pore diameter was calculated from the obtained pore size distribution and used as the macropore volume. Here, the surface tension of mercury was 480 dyne / cm, and the contact angle between mercury and the sample was 140°.

[0201] In addition, the pore diameter corresponding to the peak in the pore size distribution in the range of 20 - 100 nm pore diameter obtained above was defined as the modal diameter of the macropores.

[0202] [Electrochemical measurement (maximum current density and efficiency point voltage)]

[0203] Membrane electrode assemblies (MEA) were fabricated using the Pt / NTO particles obtained in each example and comparative example and subjected to electrochemical measurement. Each Pt / NTO particle was pulverized in a mortar and used for the fabrication of MEA.

[0204] (1) Fabrication of MEA (Membrane Electrode Assembly) <00 00461>

[0205] 800 mg of Pt / NTO particles were dispersed in a mixed solvent consisting of 1.25 g of pure water and 1.0 g of anhydrous ethanol, and then Nafion (registered trademark) dispersion (10% by mass) was added to obtain a mixture. Here, the amount of Nafion (registered trademark) dispersion added was approximately 0.175 times the mass of the NTO particles. The resulting mixture was ultrasonically dispersed in a water bath for 10 hours.

[0206] An ultrasonically dispersed mixture is coated onto a Teflon (registered trademark) sheet, causing the solvent to evaporate and forming a catalyst layer (cathode-side catalyst layer) containing Pt / NTO particles. The Pt density per unit area of ​​this catalyst layer is 0.1 mg / cm³. 2 .

[0207] Instead of Pt / NTO particles, a catalyst powder with 20% by mass of Pt supported on Ketjen Black was used, and a hydrogen electrode-side catalyst layer was formed on the sheet in the same manner as described above. The Pt density per unit area of ​​this catalyst layer was the same as that of the cathode-side catalyst layer, which was 0.1 mg / cm³. 2 .

[0208] On both sides of the polymer electrolyte membrane, Teflon (registered trademark) sheets having the above-obtained cathode-side catalyst layer and anode-side catalyst layer are stacked with the catalyst layers facing each other, and transferred by hot pressing. Subsequently, the Teflon (registered trademark) sheets are peeled off, and a diffusion layer is formed on the surface of each catalyst layer, thereby obtaining an MEA with an air diffusion layer, a cathode-side catalyst layer, a polymer electrolyte membrane, an anode-side catalyst layer, and a hydrogen diffusion layer stacked sequentially.

[0209] (2) Electrochemical determination

[0210] Next, the MEA obtained above was placed on a single cell for electrochemical measurement and connected to a commercially available fuel cell evaluation device. Then, under conditions of 80°C and 100% relative humidity, air was supplied to the cathode side at 1.0 L / min and hydrogen was supplied to the anode side at 0.5 L / min, while the voltage was scanned from 1.0 V to 0 V and down at a scan rate of 10 mV / s to obtain the IV curve.

[0211] The maximum current value obtained from the IV curve is taken as the maximum current density, and the current density is set to 0.5 A / cm². 2 The voltage at which the efficiency point voltage is measured is used as the efficiency point voltage. Furthermore, the MEA prepared using the Pt / NTO particles from Comparative Example 3 exhibited such low catalytic performance that the efficiency point voltage could not be determined.

[0212] The results are summarized in Tables 1 and 2.

[0213] Table 1

[0214]

[0215] Table 2

[0216]

[0217] The following information can be understood by referring to Tables 1 and 2.

[0218] When Pt / NTO particles are used as electrode catalysts on the cathode side of fuel cells, the maximum current density and efficiency point voltage of the Pt / NTO particles in Comparative Examples 1 and 3, which have small macropore volumes on NTO particle supports, are insufficient. Furthermore, in Comparative Example 2, where the Pt / NTO particles have large macropore volumes but small specific surface areas on NTO particle supports, the maximum current density is high, but the efficiency point voltage is insufficient.

[0219] In contrast, if Pt / NTO particles from Examples 1 to 3, which are within the predetermined scope of the present invention and have large macropore volume and specific surface area as NTO particle carriers, are used, both the maximum current density and the efficiency point voltage exhibit high values.

[0220] This is attributed to the large macropore volume and specific surface area of ​​the NTO particle support. Specifically, the large macropore volume of the NTO particle support facilitates the removal of H2O generated during fuel cell power generation from the catalyst layer. Therefore, the gas diffusivity within the catalyst layer is considered to be high, resulting in a high maximum current density. Furthermore, the large specific surface area of ​​the NTO particle support suppresses the aggregation of the supported Pt particles. Therefore, the ECSA (electrochemical surface area) of the noble metal catalyst particles is considered to be large, resulting in a high efficiency point voltage.

[0221] It is believed that these two elements complement each other in the electrode catalyst of the present invention, exhibiting highly efficient electrode catalytic activity.

Claims

1. A conductive metal oxide particle with a specific surface area of ​​35 m² 2 The pore volume is 0.25 mL / g or more, and the pore size is 20 nm or more and less than 100 nm.

2. The conductive metal oxide particles according to claim 1, wherein the primary particle size is 10 nm or more and 30 nm or less.

3. The conductive metal oxide particles according to claim 1, wherein the crystallite diameter is 10.0 nm or more and 15.0 nm or less.

4. The conductive metal oxide particles according to claim 1, wherein the mode diameter of the macropores measured by mercury porosimetry is 15 nm or more.

5. The conductive metal oxide particles according to claim 1, wherein the secondary particle size is 0.05 μm or more and 5.0 μm or less.

6. The conductive metal oxide particles according to claim 1, wherein the conductive metal oxide particles are tin oxide particles doped with one or more elements selected from niobium, tantalum, tungsten, antimony and bismuth.

7. The conductive metal oxide particles according to claim 6, wherein the conductive metal oxide particles are tin oxide particles doped with niobium.

8. A catalyst particle for an electrochemical reaction, wherein a catalyst noble metal particle is supported on a conductive metal oxide particle according to any one of claims 1 to 7.

9. The catalyst particles for electrochemical reactions according to claim 8, wherein the noble metal catalyst particles are platinum particles.

10. The catalyst particles for electrochemical reactions according to claim 8 are electrode catalysts for fuel cells.

11. The catalyst particles for electrochemical reactions according to claim 10 are electrode catalysts for cathodes.

12. A fuel cell comprising the catalyst particles for electrochemical reaction as described in claim 10.

13. A method for manufacturing conductive metal oxide particles, as described in any one of claims 1 to 7, comprising the following steps (A) and (B): Step (A): An aqueous dispersion containing a conductive metal oxide particle precursor and a pore-forming material is dried in an atomized state using a diffusion flame to obtain an aggregate of the conductive metal oxide particle precursor and the pore-forming material. The specific surface area of ​​the conductive metal oxide particle precursor is 35 m². 2 The pore volume of the fine pores is less than 0.25 mL / g and the pore size is greater than 20 nm and less than 100 nm. Step (B): Heating the condensate to burn the pore-forming material.

14. The method for manufacturing conductive metal oxide particles according to claim 13, wherein the pore-forming material is selected from one or more of organic polymers, calcium carbonate, and zinc oxide.

15. The method for manufacturing conductive metal oxide particles according to claim 13, further comprising the following step (C) before step (A): The conductive metal oxide particle precursor is obtained by spraying and burning a solution obtained by dissolving an organic compound containing metal atoms in an organic solvent.

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