Conductive metal oxide particle and catalyst particle for electrochemical reaction

Abstract

According to the present invention, a carrier for an electrode catalyst is conductive metal oxide particles having a specific surface area of 35 m2 / g or more and a pore volume of a pore having a pore diameter of 20-100 nm of 0.25 mL / g or more, and the electrode catalyst is catalyst particles for electrochemical reaction in which catalyst noble metal particles are carried on the conductive metal oxide particles.

Description

Conductive metal oxide particles and catalyst particles for electrochemical reactions

[0001] The present invention relates to conductive metal oxide particles and catalyst particles for electrochemical reactions using the same.

[0002] Research and development of fuel cells is underway to address the needs for preventing air pollution, reducing greenhouse gas emissions, and providing alternative energy sources to petroleum. Fuel cells have the advantages of being clean, having a high energy density, and not requiring charging.

[0003] A fuel cell has a structure in which an anode and a cathode are arranged opposite each other with an ion exchange membrane interposed between them. When a fuel (e.g., hydrogen) is supplied to the anode side and an oxidant (e.g., air) is supplied to the cathode side, a predetermined electrochemical reaction occurs at each of the electrodes, generating electricity.

[0004] Fuel cells use, for example, an electrode catalyst having a structure in which catalytic noble metal particles are supported on the surface of a conductive support. Carbon black, which has excellent conductivity, is often used as the conductive support, and platinum (Pt), which has excellent catalytic activity, is often used as the catalytic noble metal particles.

[0005] However, when a fuel cell using an electrode catalyst containing a carbon black support is used for a long period of time, the supported catalytic precious metal particles can fall off or aggregate due to oxidation degradation of the carbon black, resulting in a decrease in power generation performance. In an attempt to solve this problem, several attempts have been made in the prior art.

[0006] For example, Patent Document 1 discloses a method for producing a tin oxide (SnO) doped with niobium (Nb). ２ ) as an electrode catalyst support. Patent Document 2 discloses an electrode catalyst support in which primary particles of metal oxide having a size of 5 to 100 nm are fused and bonded to form a chain-like or cluster-like structure. Patent Document 3 discloses the use, as an electrode catalyst support, of an aggregate of metal oxide fine particles having voids and chain-like portions in which crystallites having a size of 10 to 30 nm are fused and bonded to form a chain.

[0007] International Publication No. WO 2015 / 146454 International Publication No. WO 2015 / 146454 International Publication No. WO 2020 / 080400

[0008] According to the techniques disclosed in Patent Documents 1 to 3, oxidation degradation of the electrode catalyst carrier that occurs with long-term use of the fuel cell can be suppressed, but there is a problem in that the output of the fuel cell is insufficient.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrode catalyst support that is inhibited from oxidative degradation due to long-term use and that provides a high-output fuel cell, and an electrode catalyst using the same.

[0010] The outline of the present invention is as follows.

[0011] <<Aspect 1>> Specific surface area is 35 m ２ / g or more, and the pore volume of pores with a pore size of 20 nm or more and 100 nm or less is 0.25 mL / g or more. <Aspect 2> Conductive metal oxide particles according to Aspect 1, having a primary particle size of 10 nm or more and 30 nm or less. <Aspect 3> Conductive metal oxide particles according to Aspect 1, having a crystallite size of 10.0 nm or more and 15.0 nm or less. <Aspect 4> Conductive metal oxide particles according to Aspect 1, having a macropore mode diameter of 15 nm or more as measured by a mercury porosimeter. <Aspect 5> Conductive metal oxide particles according to Aspect 1, having a secondary particle size of 0.05 μm or more and 5.0 μm or less. <Aspect 6> Conductive metal oxide particles according to Aspect 1, which are tin oxide particles doped with one or more elements selected from niobium, tantalum, tungsten, antimony, and bismuth. <Aspect 7> Conductive metal oxide particles according to Aspect 6, wherein the conductive metal oxide particles are tin oxide particles doped with niobium. <Aspect 8> Catalyst particles for electrochemical reactions, comprising catalytic noble metal particles supported on the conductive metal oxide particles according to any one of Aspects 1 to 7. <Aspect 9> Catalyst particles for electrochemical reactions according to Aspect 8, wherein the catalytic noble metal particles are platinum particles. <Aspect 10> Catalyst particles for electrochemical reactions according to Aspect 8, which are electrode catalysts for fuel cells. <Aspect 11> Catalyst particles for electrochemical reactions according to Aspect 10, which are electrode catalysts for cathodes. <Aspect 12> Fuel cells, comprising catalyst particles for electrochemical reactions according to Aspect 10. <Aspect 13> A method for producing conductive metal oxide particles according to any one of Aspects 1 to 7, comprising the steps of: (A) forming a conductive metal oxide particle having a specific surface area of ​​35 m; (B) forming a conductive metal oxide particle having a specific surface area of ​​35 m; (C) forming a conductive metal oxide particle having a specific surface area of ​​35 m; (D) forming a conductive metal oxide particle having a specific surface area of ​​35 m; (E) forming a conductive metal oxide particle having a specific surface area of ​​35 m; (F) forming a conductive metal oxide particle having a specific surface area of ​​35 m; (G) forming a conductive metal oxide particle having a specific surface area of ​​35 m; (H) forming a conductive metal oxide particle having a specific surface area of ​​35 m; (I ... ２A method for producing conductive metal oxide particles, comprising: (a) atomizing an aqueous dispersion containing a conductive metal oxide particle precursor having a pore volume of 1000 sq m / g or more and a pore volume of less than 0.25 mL / g for pores having a pore size of 20 nm or more and 100 nm or less, and a pore-forming material, and (b) drying the atomized aqueous dispersion by a diffusion flame to obtain aggregates of the conductive metal oxide particle precursor and the pore-forming material, and (c) heating the aggregates to combust the pore-forming material. Aspect 14: The method for producing conductive metal oxide particles according to Aspect 13, wherein the pore-forming material is one or more selected from the group consisting of an organic polymer, calcium carbonate, and zinc oxide. Aspect 15: The method for producing conductive metal oxide particles according to Aspect 13, further comprising, before step (A), (C) spraying and combusting a solution of a metal atom-containing organic compound dissolved in an organic solvent to obtain the conductive metal oxide particle precursor.

[0012] According to the present invention, there are provided conductive metal oxide particles suitable as supports for electrode catalysts, which are inhibited from oxidative degradation due to long-term use and which provide high-output fuel cells, and catalyst particles for electrochemical reactions suitable as electrode catalysts.

[0013] Fig. 1 is an SEM image of the Pt / NTO particles obtained in Comparative Example 1. Fig. 2(a) and (b) are SEM images of the Pt / porous NTO particles obtained in Example 2, respectively.

[0014] <Conductive Metal Oxide Particles> The conductive metal oxide particles of the present invention have a specific surface area of ​​35 m ２ / g or more, and the pore volume of pores with a pore diameter of 20 nm or more and 100 nm or less is 0.25 mL / g or more.

[0015] The metal oxide constituting the conductive metal oxide particles may be selected from conductive or semiconductive metal oxides, or metal oxides doped with specific impurity elements.

[0016] Examples of conductive or semiconductive metal oxides include TiO, VO, and Ti. ２ O ３ , V ２ O ３ , V.O. ２ , NbO ２, CrO ２ , MoO ２ , W.O. ２ , ReO ２ , RuO ２ , OsO ２ , RhO ２ , IrO ２ , SnO ２ , ReO ２ , LaTiO ３ , SrMoO ３ , SrRuO ３ , LaRhO ３ and the like.

[0017] The doping impurity element may be one or more selected from, for example, lithium (Li), niobium (Nb), tantalum (Ta), tungsten (W), antimony (Sb), bismuth (Bi), etc., and may be appropriately selected and used depending on the type of conductive or semiconductive metal oxide. The doping amount of the impurity element may be 0.5 atomic % or more, 1.0 atomic % or more, 2.0 atomic % or more, or 3.0 atomic % or more, or 10.0 atomic % or less, 8.0 atomic % or less, 6.0 atomic % or less, or 5.0 atomic % or less, when the total number of atoms of the metal element and the impurity element in the metal oxide is taken as 100 atomic %.

[0018] The conductive metal oxide particles of the present invention include tin oxide (SnO) doped with one or more elements selected from Nb, Ta, W, Sb, and Bi. ２ ) particles, in particular Nb-doped SnO ２ The particles may be of the formula:

[0019] The conductive metal oxide particles of the present invention are thought to be in the form of porous secondary particles with a high specific surface area, in which primary particles are aggregated to form pores (macropores) with a pore diameter of 20 nm to 100 nm between the particles.

[0020] The specific surface area of ​​the conductive metal oxide particles is 35 m ２ / g or more. When this requirement is satisfied, when catalytic noble metal particles are supported on the conductive metal oxide particles of the present invention, the catalytic noble metal particles can be firmly fixed to the surfaces of the conductive metal oxide particles. When such supported particles are used as catalyst particles for electrochemical reactions, it is believed that a decrease in activity due to migration and aggregation of the catalytic noble metal particles can be suppressed.

[0021] The specific surface area of ​​the conductive metal oxide particles is 35 m ２ / g or more, and 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, and 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.

[0022] The specific surface area of ​​the conductive metal oxide particles is measured by the BET method using nitrogen as an adsorbate.

[0023] The conductive metal oxide particles of the present invention have a pore volume of 0.25 mL / g or more for pores (macropores) with a pore diameter of 20 nm or more and 100 nm or less. If this requirement is satisfied, when catalytic precious metal particles are supported on the conductive metal oxide particles of the present invention and used as catalyst particles for electrochemical reactions, for example, reactants can easily flow through the particles and come into contact with the catalytic precious metal particles, thereby efficiently exerting catalytic action.

[0024] The pore volume of the macropores of the conductive metal oxide particles is 0.25 mL / g or more, and may be 0.27 mL / g or more, 0.30 mL / g or more, 0.32 mL / g or more, and may be 0.50 mL / g or less, 0.45 mL / g or less, 0.40 mL / g or less, 0.38 mL / g or less, 0.35 mL / g or less, 0.33 mL / g or less, or 0.30 mL / g or less.

[0025] The pore volume of the macropores of the conductive metal oxide particles is measured as the cumulative pore volume of pores with diameters in the range of 20 to 100 nm in the pore distribution determined by mercury intrusion porosimetry using a mercury porosimeter. The pore diameter is calculated using the Washburn equation. In this calculation, the surface tension of mercury may be set to 480 dynes / cm, and the contact angle between mercury and the sample may be set to 140 degrees (°). The sample may be subjected to pretreatment, such as constant temperature drying at 120°C for 4 hours, before being subjected to measurement.

[0026] The conductive metal oxide particles of the present invention may have pores (macropores) with a pore size of 20 nm to 100 nm both inclusive, with a mode diameter of 15 nm or more. If the mode diameter of the macropores is 15 nm or more, when catalytic noble metal particles are supported on the conductive metal oxide particles of the present invention and used, for example, as catalyst particles for electrochemical reactions, reactants can easily flow through the particles and come into contact with the catalytic noble metal particles, thereby efficiently exerting catalytic action.

[0027] The mode diameter of the macropores of the conductive metal oxide particles of the present invention may be 15 nm or more, 17 nm or more, 20 nm or more, 22 nm or more, or 25 nm or more, and may be 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, or 25 nm or less.

[0028] The mode diameter of the macropores of the conductive metal oxide particles is measured as the pore diameter corresponding to the peak top in the pore distribution in the pore diameter range of 20 to 100 nm in a pore distribution determined by mercury intrusion porosimetry using a mercury porosimeter.

[0029] The secondary particle diameter of the conductive metal oxide particles of the present invention may be appropriately set depending on the intended use. However, in order to ensure an appropriate macropore volume, it is preferable that the secondary particle diameter of the conductive metal oxide particles is not excessively small. On the other hand, in consideration of handling during the formation of the catalyst layer, etc., it is preferable that the secondary particle diameter of the conductive metal oxide particles is not excessively large. From these viewpoints, the secondary particle diameter of the conductive metal oxide particles may 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 may 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.

[0030] The secondary particle diameter of the conductive metal oxide particles is measured as a number average value by observation under an electron microscope.

[0031] The primary particle diameter of the conductive metal oxide particles of the present invention may be 10 nm or more, 12 nm or more, 15 nm or more, 17 nm or more, or 20 nm or more, and may be 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, in order to form the above-mentioned macropores between the particles when they become secondary particles.

[0032] The primary particle size of the conductive metal oxide particles is measured as a number average value by observation under an electron microscope.

[0033] In order to form the primary particles as described above, the crystallite diameter of the conductive metal oxide particles of the present invention may be 10.0 nm or more, 11.0 nm or more, 12.0 nm or more, or 13.0 nm or more, and may be 20 nm or less, 18 nm or less, 15 nm or less, 13 nm or less, or 12.0 nm or less.

[0034] The crystallite size of the conductive metal oxide particles is calculated from the results of XRD analysis of the conductive metal oxide particles using Scherrer's formula.

[0035] The conductive metal oxide particles of the present invention may have a structure in which secondary particles are connected to each other in a cluster or chain shape. "Cluster shape" refers to a shape similar to, for example, a cluster of grapes. "Chain shape" refers to a shape in which secondary particles are connected to each other to form, for example, a chain, ladder, net, or the like.

[0036] The conductive metal oxide particles of the present invention do not need to have a "sheet of dried sardines"-like form in which the fine particles are spread out and connected in two dimensions, or a clump-like form in which the fine particles are connected in a disordered manner in three dimensions.

[0037] <<Method for Producing Conductive Metal Oxide Particles>> The conductive metal oxide particles of the present invention may be produced by any method as long as the above requirements are met.

[0038] The conductive metal oxide particles of the present invention may have, for example, the following (A) and (B): (A) a specific surface area of ​​35 m ２ / g or more and having a pore volume of less than 0.25 mL / g for pores having a pore size of 20 nm or more and 100 nm or less, and a pore-forming material, to obtain an aggregate of the conductive metal oxide particle precursor and the pore-forming material (flame-assisted spray drying step); and (B) heating the aggregate to combust the pore-forming material (heating step).

[0039] The method for producing conductive metal oxide particles of the present invention may further include, before the flame-assisted spray drying step (A), (C) spraying and burning a solution obtained by dissolving a metal atom-containing organic compound in an organic solvent to obtain the conductive metal oxide particle precursor (spray flame combustion step).

[0040] Each step of the method for producing conductive metal oxide particles will be described below in order.

[0041] <(A) Flame-assisted spray drying process> In the (A) flame-assisted spray drying process, 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 composed of the conductive metal oxide particle precursor and the pore-forming material.

[0042] (Conductive Metal Oxide Particle Precursor) The conductive metal oxide particle precursor has a specific surface area of ​​35 m ２ / g or more, and the pore volume of pores (macropores) having a pore diameter of 20 nm or more and 100 nm or less is less than 0.25 mL / g.

[0043] The specific surface area of ​​the conductive metal oxide particle precursor may be the same as the specific surface area of ​​the desired conductive metal oxide particles. Thus, the specific surface area of ​​the conductive metal oxide particle precursor is 35 m 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, and 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.

[0044] According to the method for producing conductive metal oxide particles of the present invention, pores (macropores) with a pore diameter of 20 nm to 100 nm are formed in the conductive metal oxide particles by combustion of the pore-forming material, and the pore volume is 0.25 mL / g or more. Therefore, the pore volume of the macropores in the conductive metal oxide particle precursor may be smaller than the pore volume of the desired conductive metal oxide particles. Therefore, the pore volume of the macropores in the conductive metal oxide particle precursor may be less than 0.25 mL / g, 0.24 mL / g or less, 0.20 mL / g or less, 0.15 mL / g or less, 0.10 mL / g or less, or 0.05 mL / g or less, or the conductive metal oxide particle precursor may not have macropores.

[0045] As described above, according to the method for producing conductive metal oxide particles of the present invention, macropores are formed in the conductive metal oxide particles by combustion of the pore-forming material. Therefore, when the conductive metal oxide particle precursor has macropores, the mode diameter of the macropores may be any suitable value, regardless 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 may be 1.0 nm or more and 20.0 nm or less.

[0046] According to the method for producing 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 may be equal to or slightly smaller than the primary particle size of the desired conductive metal oxide particles. The primary particle size of the conductive metal oxide particle precursor may be 5 nm or more, 8 nm or more, 10 nm or more, 13 nm or more, or 15 nm or more, and may 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.

[0047] According to the method for producing 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 that of the conductive metal oxide particle precursor. Therefore, the crystallite diameter of the conductive metal oxide particle precursor may be equal to or slightly smaller than that of the desired conductive metal oxide particles. The crystallite diameter of the conductive metal oxide particle precursor may be 8.0 nm or more, 10.0 nm or more, or 12.0 nm or more, and may be 18 nm or less, 15 nm or less, 13 nm or less, 12.0 nm or less, or 10.0 nm or less.

[0048] The conductive metal oxide particle precursor may be in the form of secondary particles formed by aggregation of primary particles having the above-mentioned primary particle size, in which case the secondary particle size of the conductive metal oxide particle precursor may be the same as the secondary particle size of the desired conductive metal oxide particles.

[0049] Such a conductive metal oxide particle precursor can be produced, for example, by the spray flame combustion step (C) described below. Alternatively, a commercially available product that satisfies the above requirements may be used as the conductive metal oxide particle precursor.

[0050] (Pore-forming material) The pore-forming material may be one or more selected from organic polymers, calcium carbonate, zinc oxide, and the like.

[0051] Examples of organic polymers constituting the pore-forming material include acrylic polymers, aromatic polymers, and acrylic-aromatic polymers, and one or more selected from these may be used.

[0052] Examples of acrylic polymers include polymethyl methacrylate (PMMA); examples of aromatic polymers include polystyrene; and examples of acrylic-aromatic polymers include styrene-acrylic copolymers.

[0053] The pore-forming organic polymer may be crosslinked or non-crosslinked.

[0054] The pore-forming material may be in particulate form. The particle size of the particulate pore-forming material may be 50 nm or more, 100 nm or more, 150 nm or more, 200 nm or more, or 300 nm or more, and may be 1,000 nm or less, 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 producing conductive metal oxide particles of the present invention, when a pore-forming material with a particle size within the above range is used, conductive metal oxide particles having a macropore volume of 0.25 mL / g or more can be obtained.

[0055] (Aqueous Dispersion) (A) The aqueous dispersion used in the flame-assisted spray drying process comprises the conductive metal oxide particle precursor and a pore-forming material described above.

[0056] The solvent for the aqueous dispersion may be water or a mixed solvent of water and a water-soluble organic solvent, and typically may be water.

[0057] The amount of the conductive metal oxide particle precursor in the aqueous dispersion may be 0.1% by mass or more, 0.2% by mass or more, or 0.5% by mass or more, and may be 10.0% by mass or less, 8.0% by mass or less, 5.0% by mass or less, 3.0% by mass or less, 2.0% by mass or less, 1.5% by mass or less, or 1.0% by mass or less, relative to the total amount of the aqueous dispersion.

[0058] The amount of the pore-forming material in the aqueous dispersion may be 50 parts by mass or more, 100 parts by mass or more, 150 parts by mass or more, 200 parts by mass or more, 250 parts by mass or more, or 300 parts by mass or more, relative to 100 parts by mass of the conductive metal oxide particle precursor, and may be 1,000 parts by mass or less, 800 parts by mass or less, 600 parts by mass or less, 500 parts by mass or less, 400 parts by mass or less, or 300 parts by mass or less.

[0059] (Flame-assisted spray drying) In the flame-assisted spray drying step, the above-mentioned aqueous dispersion is dried in an atomized state by a diffusion flame to obtain aggregates composed of the conductive metal oxide particle precursor and the pore-forming material.

[0060] The particle size of the water droplets constituting the mist of the aqueous dispersion may be about 1 nm or more and 6 nm or less, and the concentration of the mist of the aqueous dispersion may be about 1 mL / min or more and 10 mL / min or less in terms of the volume of water droplets per unit time.

[0061] A commercially available ultrasonic atomizer, heating atomizer, or the like may be used to atomize the aqueous dispersion.

[0062] The mist of the aqueous dispersion is carried into the diffusion flame by a suitable carrier gas. The carrier gas may be an inert gas. By using an inert gas as the carrier gas, the drying of the aqueous dispersion by the heat of the diffusion flame proceeds mildly, and the self-assembly of the conductive metal oxide particle precursor and the pore-forming material is promoted. From this viewpoint, the carrier gas may be, for example, nitrogen (N ２ ), argon (Ar), etc. The flow rate of the carrier gas may be determined appropriately by those skilled in the art depending on the scale of production.

[0063] A diffusion flame is a flame that exists at the interface between a combustible gas and an oxidizing gas that exist separately, and the combustible gas and oxidizing gas that are consumed by combustion are continuously supplied toward the flame by diffusion, thereby maintaining combustion.

[0064] The combustible gas constituting the diffusion flame may be, for example, methane, ethane, propane, etc. The oxidizing gas may be, for example, oxygen, air, etc. The supply amounts of the combustible gas and the oxidizing gas and the ratio between them may be determined appropriately by those skilled in the art depending on the types of the combustible gas and the oxidizing gas and the scale of production.

[0065] The atomized aqueous dispersion is dried with a diffusion flame in a "flame-assisted spray drying" process to obtain aggregates of the conductive metal oxide particle precursor and the pore-forming material. The aggregates obtained may be collected, for example, using a suitable bag filter, and then subjected to the subsequent heating step (B).

[0066] <(B) Heating Step> In the (B) heating step, the aggregate of the metal oxide particle precursor and the pore-forming material obtained in the (A) flame-assisted spray drying step is heated, whereby the pore-forming material is burned and eliminated, and conductive metal oxide particles having predetermined macropores are formed.

[0067] The heating temperature in the (B) heating step may be a temperature at which the pore-forming material burns if it is an organic polymer, thermally decomposes if it is calcium carbonate, or volatilizes if it is zinc oxide, and may be, for example, 400°C or higher, 450°C or higher, or 500°C or higher. On the other hand, if the heating temperature is excessively high, there is a concern that sintering of particles will occur and the formed macropores will be "collapsed." From this perspective, the heating temperature may be 1,000°C or lower, 900°C or lower, 800°C or lower, 700°C or lower, 600°C or lower, or 550°C or lower. When an organic polymer is used as the pore-forming material, the heating temperature in the (B) heating step may be, for example, 400°C or higher and 800°C or lower.

[0068] The heating time may be 10 minutes or more, 20 minutes or more, 30 minutes or more, 40 minutes or more, 45 minutes or more, or 1 hour or more, and may be 6 hours or less, 4 hours or less, 3 hours or less, 2 hours or less, 1.5 hours or less, or 1 hour or less.

[0069] The ambient atmosphere during the heating step (B) may be an inert atmosphere or an oxidizing atmosphere, and in practice air is sufficient.

[0070] The conductive metal oxide particles of the present invention are obtained in this manner. The obtained conductive metal oxide particles may be used as they are, or after being crushed and classified as necessary.

[0071] <(C) Spray Flame Combustion Step> The (C) spray flame combustion step is an optional step for producing a conductive metal oxide particle precursor to be used in the (A) flame-assisted spray drying step. Therefore, the (C) spray flame combustion step may be performed before the (A) flame-assisted spray drying step.

[0072] (C) In the spray flame combustion step, a conductive metal oxide particle precursor is obtained by a method including: dissolving a metal atom-containing organic compound in an organic solvent to obtain a solution containing the metal atom-containing organic compound; and spraying and burning the solution containing the metal atom-containing organic compound.

[0073] (Metal atom-containing organic compound-containing solution) The term "metal atom-containing organic compound" refers to a compound, salt, or complex compound that contains a metal atom, a carbon atom, and a hydrogen atom, and may optionally further contain one or more atoms selected from an oxygen atom, a nitrogen atom, and a sulfur atom. The metal atom-containing organic compound in the present invention does not necessarily contain a halogen atom or a silicon atom.

[0074] The number of metal atoms in one metal atom-containing organic compound may be one or more, but a typical metal atom-containing organic compound in the present invention may contain one metal atom.

[0075] The metal atom-containing organic compound may be a metal atom-containing organic compound that is liquid at room temperature (25° C.) and atmospheric pressure (1 atm). By using a metal atom-containing organic compound that is liquid at room temperature and atmospheric pressure, decomposition of the metal atom-containing organic compound is promoted and precipitation (solidification) of the metal atom-containing organic compound is suppressed, resulting in the production of uniform nano-sized particles of a conductive metal oxide particle precursor.

[0076] The metal atom-containing organic compound that is liquid at room temperature and pressure may be, for example, one or more compounds selected from metal alkoxides, metal organic acid salts, metal complex compounds, and the like.

[0077] When the metal atom-containing organic compound contains two or more types of metals, a metal atom-containing organic compound containing two or more types of metals in one molecule may be used, or two or more types of metal atom-containing organic compounds containing one type of metal in one molecule may be used.

[0078] The metal contained in the metal atom-containing organic compound may be the same as the metal in the desired conductive metal oxide particles. The conductive metal oxide particles of the present invention are preferably tin oxide (SnO) doped with one or more elements selected from Nb, Ta, W, Sb, and Bi. ２ ) particles, in particular Nb-doped SnO ２ Therefore, the metal contained in the metal atom-containing organic compound in the spray flame combustion step (C) may include one or more metals selected from Nb, Ta, W, Sb, and Bi, and Sn.

[0079] Tin oxide (SnO ２ The metal atom-containing organic compound that is a precursor of the above-mentioned compound may particularly be a tin carboxylate. In the tin carboxylate, the tin may be divalent or tetravalent. The number of carbon atoms in the alkylcarbonyloxy group in the tin carboxylate, including the carbonyl carbon, may be 2 or more, 4 or more, 6 or more, or 8 or more, and may be 20 or less, 18 or less, 16 or less, 14 or less, 12 or less, or 10 or less. When the number of carbon atoms in the alkylcarbonyloxy group is 4 or more, the alkylcarbonyloxy group may be linear or branched.

[0080] The metal atom-containing organic compound, which is a precursor of the doping element, may be, for example, an alkoxide of a predetermined metal. When the predetermined metal can have multiple stable oxidation numbers, the oxidation number of the metal in this metal alkoxide may be any of the stable oxidation numbers. Furthermore, the number of carbon atoms in the alkoxide of the alkoxyl group may be 1 or more, 2 or more, 3 or more, or 4 or more, and may 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 alkoxyl group is 3 or more, the alkoxyl group may be linear or branched.

[0081] The conductive oxide particles of the present invention may be, in particular, niobium-doped tin oxide particles. In this case, the metal atom-containing organic compound that is a precursor of the doping element may be, for example, a niobium alkoxide or a tin carboxylate, in particular, niobium(V) ethoxide or tin(II) 2-ethylhexanoate.

[0082] The mixing ratio of the precursor of the tin oxide particles to the precursor of the doping element in the metal atom-containing organic compound-containing solution may be the same as the ratio of tin to the doping element in the desired conductive oxide particles. The molar ratio of the doping element to the total molar ratio of tin and the doping element may 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 may be 10 mol% or less, 8 mol% or less, 6 mol% or less, or 5 mol% or less.

[0083] The solvent of the metal atom-containing organic compound-containing solution is an organic solvent that can dissolve the metal atom-containing organic compound.

[0084] Specific examples of organic solvents include aromatic compounds, aliphatic hydrocarbons, alcohols, polar organic solvents, etc., and one or more selected from these may be used. Examples of aromatic compounds include benzene, toluene, ethylbenzene, xylene, cumene, durene, etc.; examples of aliphatic hydrocarbons include pentane, cyclopentane, hexane, cyclohexane, etc.; examples of alcohols include methanol, ethanol, 2-propanol, n-butanol, benzyl alcohol, etc.; and examples of polar organic solvents include tetrahydrofuran, acetonitrile, diethylhexanoic acid, etc.

[0085] The organic solvent may include one having a high combustion enthalpy, which is desirable because the conductive oxide particle precursor and the catalytic noble metal particle precursor are instantly converted into the target products during spray combustion of the precursor solution, thereby suppressing problems such as precipitation and aggregation of the precursors.

[0086] From this viewpoint, the organic solvent may contain a high combustion enthalpy solvent having a combustion enthalpy of 3,000 kJ / mol or more. The organic solvent used in the method of the present invention may contain the high combustion enthalpy solvent in an amount of 30 mass % or more, 50 mass % or more, 70 mass % or more, 80 mass % or more, 90 mass % or more, or 95 mass % or more based on the total amount of the organic solvent. Alternatively, all of the organic solvent may be high combustion enthalpy solvents.

[0087] The combustion enthalpy of the high combustion enthalpy solvent may be 3,500 kJ / mol or more, 4,000 kJ / mol or more, or 4,500 kJ / mol or more, and may be 6,000 kJ / mol or less, 5,500 kJ / mol or less, or 5,000 kJ / mol or less. Examples of high combustion enthalpy solvents having such combustion enthalpies include aromatic compounds and aliphatic hydrocarbons.

[0088] The organic solvent of the metal atom-containing organic compound-containing solution may be an aromatic compound, particularly toluene, ethylbenzene, xylene, and the like.

[0089] In this specification, the combustion enthalpy refers to the combustion enthalpy of a liquid at 25°C.

[0090] The amount of organic solvent used in the metal atom-containing organic compound-containing solution may be an amount such that the concentration of the metal atom-containing organic compound in the metal atom-containing organic compound-containing solution is 0.05 mol / L or more and 0.5 mol / L or less.

[0091] (Spray Flame Combustion Step) Next, the solution containing the metal atom-containing organic compound as described above is sprayed and burned to obtain a predetermined conductive metal oxide particle precursor.

[0092] (C) Combustion in the spray flame combustion step may be carried out by a flame spray method (FSP (Flame Spray Pyrolysis) method). In the flame spray method, a metal atom-containing organic compound-containing solution atomized by a dispersion gas flow is ignited by a pilot flame to form a flame. The flame formed at this time is a spray flame in which the metal atom-containing organic compound-containing solution sprayed in atomized form is burning. This spray combustion method using a spray flame is different from a particle synthesis method using a diffusion flame, in which droplets of raw material are supplied to an already formed flame and burned.

[0093] The dispersion gas may be an oxidizing gas, such as air, oxygen, etc. The pilot flame is not particularly limited as long as it can ignite the atomized metal atom-containing organic compound-containing solution, and may be formed, for example, from methane and air or oxygen.

[0094] The conductive metal oxide particle precursor is obtained by the spray flame combustion step (C) as described above. The obtained conductive metal oxide particle precursor may be collected, for example, using an appropriate bag filter or the like, and then subjected to the flame-assisted spray drying step (A) as is, or after being crushed and classified as necessary.

[0095] <<Catalyst Particles for Electrochemical Reactions>> According to another aspect of the present invention, catalyst particles for electrochemical reactions are provided.

[0096] The electrochemical reaction catalyst particles of the present invention have a configuration in which catalytic noble metal particles are supported on the conductive metal oxide particles of the present invention.

[0097] The catalytic noble metal particles may be, for example, particles of a platinum group metal, in particular, platinum particles or particles of an alloy of platinum with another metal, such as nickel (Ni), cobalt (Co), ruthenium (Ru), manganese (Mn), titanium (Ti), tin (Sn), or yttrium (Y).

[0098] The catalytic noble metal particles are particulate, and their particle size may be smaller than the particle size of the conductive metal oxide particles, and may be 1 nm or more, 2 nm or more, 3 nm or more, 4 nm or more, or 5 nm or more, and may be 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.

[0099] The amount of catalytic noble metal particles carried in the electrochemical reaction catalyst particles may be 5 mass % or more, 10 mass % or more, 12 mass % or more, 15 mass % or more, 17 mass % or more, or 20 mass % or more, as the mass ratio of the catalytic noble metal particles to the total mass of the electrochemical reaction catalyst particles, and may be 30 mass % or less, 28 mass % or less, 25 mass % or less, 23 mass % or less, or 20 mass % or less.

[0100] The catalyst particles for electrochemical reactions of the present invention are suitable as an electrode catalyst for fuel cells, and are particularly suitable as an electrode catalyst for the cathode (air electrode) of a fuel cell.

[0101] <<Method for Producing Catalyst Particles for Electrochemical Reactions>> The catalyst particles for electrochemical reactions of the present invention may be produced by any method as long as they have the above-described configuration.

[0102] The catalyst particles for electrochemical reactions of the present invention may be produced, for example, by a method comprising: bringing the conductive metal oxide particles of the present invention into contact with a catalytic metal precursor; and reducing the catalytic metal precursor to support the catalytic metal particles on the conductive metal oxide particles, thereby obtaining catalyst particles for electrochemical reactions.

[0103] The catalytic metal precursor may be appropriately selected from halides, sulfides, cyanides, complexes, etc. of the metal constituting the desired catalytic metal particles. When the catalytic metal particles are platinum particles, the catalytic metal precursor may be, for example, PtCl ２ , PtCl ４ , PtBr ２ , PtS, Pt(CN) ２ , PtCl ２ (NH ３ ) ２ (dinitrodiammine platinum), hexahydroxoplatinum, etc.

[0104] The contact between the conductive metal oxide particles and the catalytic metal precursor may be carried out, for example, in a suitable solvent. The solvent may be selected from those capable of dissolving the catalytic metal precursor. For example, when the catalytic metal particles are platinum particles and the catalytic metal precursor is PtCl ２ Hydrochloric acid may be used when PtBr ２ Aqueous hydrobromic acid may be used when PtCl ２ (NH ３ ) ２ Aqueous nitric acid solution may be used when PtCl ４ , PtS, or Pt(CN) ２ When it is hexahydroxoplatinum, water may be used, and when it is hexahydroxoplatinum, an amine-containing solvent may be used.

[0105] The reduction of the catalytic metal precursor may be carried out using a suitable reducing agent. The reducing agent may be, for example, ethanol, formic acid, acetic acid, acetaldehyde, sodium borohydride, hydrazine, etc. The reduction may be carried out at a temperature of 10°C or higher and 100°C or lower for a time of 0.5 hours or higher and 8 hours or lower. When sodium borohydride is used as the reducing agent, the reduction temperature is preferably 10°C or higher and 50°C or lower, and when ethanol, formic acid, acetic acid, acetaldehyde, or hydrazine is used as the reducing agent, the reduction temperature is preferably 60°C or higher and 100°C or lower.

[0106] In this way, catalyst particles for electrochemical reactions in which catalytic metal particles are supported on conductive metal oxide particles are obtained. The obtained catalyst particles for electrochemical reactions may be washed and dried as necessary, and further crushed and classified as necessary before being used.

[0107] <<Fuel Cell>> According to yet another aspect of the present invention, there is provided a fuel cell, which has electrodes containing the catalyst particles for electrochemical reactions of the present invention.

[0108] The electrode containing the catalyst particles for electrochemical reactions of the present invention may be a cathode (air electrode). This cathode may have a suitable substrate layer and a catalyst layer (cathode-side catalyst layer) on the substrate layer, and the cathode-side catalyst layer contains the catalyst particles for electrochemical reactions of the present invention.

[0109] The substrate layer may be appropriately selected from those having chemical and mechanical stability that can withstand the electrochemical reaction catalyst particles and solvent, as well as the heat treatment, pressure treatment, etc. that are preferably performed during electrode formation. Specifically, for example, a sheet of polyimide, polyethylene, polypropylene, polysulfone, polytetrafluoroethylene, etc. may be used.

[0110] The cathode catalyst layer contains the catalyst particles for electrochemical reactions of the present invention, and may further contain an ionomer and other optional components such as a binder. The ionomer may be, for example, Nafion (registered trademark, a sulfonated tetrafluoroethylene (co)polymer).

[0111] The cathode as described above is configured in the form of a fuel cell electrode assembly in which a solid polymer electrolyte membrane and an anode (hydrogen electrode) are laminated in this order on the cathode. The solid polymer electrolyte membrane and anode in this fuel cell electrode assembly may be known solid polymer electrolyte membranes and anodes, respectively. This fuel cell electrode assembly may be produced by a known method except that an electrode containing the electrochemical reaction catalyst particles of the present invention is used as the cathode.

[0112] The fuel cell of the present invention includes the above-mentioned fuel cell electrode assembly, and may additionally have, for example, 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 may be produced by a known method except for using an electrode containing the catalyst particles for electrochemical reactions of the present invention as the cathode.

[0113] Comparative Example 1 (1) Preparation of NTO particles Tin(II) 2-ethylhexanoate (Sn(C)) was dissolved in xylene so that the total concentration of Sn and Nb was 0.1 mol / L and the atomic ratio of Sn to Nb was 96:4. ８ H １５ O ２ ) ２ ) and niobium ethoxide (Nb(OC ２ H ５ ) ５ ) was dissolved to prepare a precursor solution of NTO particles.

[0114] Using a syringe pump, the resulting precursor solution was supplied at a flow rate of 3 mL / min to a two-fluid nozzle "AM6 type nozzle" manufactured by Atmax Co., Ltd. The precursor solution was atomized using an oxygen flow rate of 1.5 L / min and ignited using a methane / air mixture pilot flame of 1 L / min of methane and 10 L / min of air to form a spray flame of the precursor solution, synthesizing Nb-doped tin oxide (NTO) particles of Comparative Example 1.

[0115] The produced NTO particles were collected using a bag filter manufactured by Hokos Corporation.

[0116] (2) Pt Loading (Preparation of Pt / NTO Particles) 3.2 g of the NTO particles obtained above as carrier particles was added to 90 mL of pure water and stirred at 250 rpm for 30 minutes using a stirring blade to obtain a suspension. While stirring the suspension after stirring, an amine solution of hexahydroxoplatinic acid containing 0.8 g of platinum equivalent to metal was slowly added dropwise, and stirring was continued for 30 minutes after the completion of the dropwise addition. Next, while continuing stirring, the liquid was heated, and the liquid temperature was raised to 95 ° C. and maintained at this temperature. 40 mL of a formic acid solution with a concentration of 1 mol / L was slowly added dropwise thereto, and the liquid temperature was maintained at 95 ° C. for another 5 minutes, thereby reducing the platinum and loading it on the NTO particles.

[0117] The particles were collected from the reaction mixture by filtration, washed with pure water, and then dried at 80°C for 12 hours to obtain Pt / NTO particles of Comparative Example 1. Figure 1 shows an SEM image of the Pt / porous NTO particles of Comparative Example 1. Referring to Figure 1, it can be seen that the Pt / NTO particles of Comparative Example 1 do not have clear macropores and do not form a clear particle shape, but are connected and spread out in a "folded sardine" shape.

[0118] Comparative Example 2 Pt / NTO particles of Comparative Example 2 were obtained by supporting Pt in the same manner as in Comparative Example 1, except that NTO particles obtained in the same manner as in Comparative Example 1 were calcined in air at 1,200°C for 1 hour and used as support particles.

[0119] Comparative Example 3 (1) Preparation of NTO particles Tin (II) chloride (SnCl) was dissolved in ethanol so that the total concentration of Sn and Nb was 0.1 mol / L and the atomic ratio of Sn:Nb was 96:4. ２ ) and niobium chloride (NbCl ５ ) was dissolved to prepare a precursor solution of NTO particles.

[0120] The obtained precursor solution was converted into droplets by an ultrasonic nebulizer. ２ The NTO particles of Comparative Example 3 were synthesized by transporting them in a carrier gas and then burning and pyrolyzing them in a methane / oxygen diffusion flame.

[0121] (2) Pt Loading (Preparation of Pt / NTO Particles) Pt / NTO particles of Comparative Example 3 were obtained by loading Pt in the same manner as in Comparative Example 1, except that the NTO particles obtained above were used as support particles.

[0122] Example 1 (1) Preparation of porous NTO particles An aqueous dispersion for producing porous NTO particles was prepared by dispersing NTO particles (conductive oxide particle precursor) prepared in the same manner as in Comparative Example 1 and spherical particles of polymethyl methacrylate (PMMA) with a particle size of 100 nm in ultrapure water. In this aqueous dispersion, the concentration of the NTO particles was 1 mass % relative to the total amount of the aqueous dispersion, and the amount of PMMA spherical particles added was equivalent to three times the mass of the NTO particles.

[0123] The aqueous dispersion was introduced into an ultrasonic atomizer and atomized, and N ２ The carrier gas was supplied to the burner. A methane / oxygen diffusion flame with a flow rate of 0.5 L / min of methane and 1.3 L / min of oxygen was formed in the burner, and the atomized aqueous dispersion was dried by this diffusion flame, and some of the PMMA particles were further combusted to form aggregates (flame-assisted spray drying method). The resulting aggregates were collected in a bag filter and heated in air at 500°C for 1 hour to completely combust the PMMA particles, thereby obtaining the porous NTO particles (conductive metal oxide particles) of Example 1.

[0124] (2) Pt Loading (Preparation of Pt / Perforated NTO Particles) Pt loading was carried out in the same manner as in Comparative Example 1, except that the porous NTO particles obtained above were used as support particles, thereby obtaining Pt / perforated NTO particles of Example 1.

[0125] Example 2 Pt / porous NTO particles of Example 2 were obtained in the same manner as in Example 1, except that the particle size of the PMMA spherical particles was set to 300 nm and the amount added was set to twice the mass of the NTO particles.

[0126] Figure 2 shows an SEM image of the Pt / porous NTO particles of Example 2. Referring to Figure 2, it can be seen that the Pt / porous NTO particles of Example 1 have secondary particles with distinct macropores that are connected like a bunch of grapes.

[0127] Example 3 Pt / porous NTO particles of Example 3 were obtained in the same manner as in Example 2, except that the dried agglomerates were calcined in air at 1,000° C. for 1 hour.

[0128] <<Analysis>> The particles (NTO particles and Pt / NTO particles) obtained in each of the Examples and Comparative Examples were analyzed by the following methods.

[0129] <Pt Particle Diameter> The particle diameter of the supported Pt particles in the Pt / NTO particles was calculated from the XRD of the Pt / NTO particles using Scherrer's equation.

[0130] <Pt particle loading amount> The loading amount of Pt particles in the Pt / NTO particles was calculated from the amounts of raw materials charged. When the supernatant of the reaction mixture obtained in the Pt loading step was subjected to high-frequency inductively coupled plasma (ICP) analysis, no Pt ions were detected in the liquid in any of the examples and comparative examples.

[0131] <Specific Surface Area of ​​Particles> The specific surface area of ​​the NTO particles was determined by the BET method using nitrogen as an adsorbate.

[0132] <Primary Particle Diameter of NTO Particles> The primary particle diameter of the NTO particles was determined as an average value from a transmission electron microscope image.

[0133] <Crystallite diameter of NTO particles> The crystallite diameter of NTO particles was calculated from XRD using Scherrer's equation.

[0134] <Analysis of Macropores of NTO Particles> Analysis of macropores of NTO particles was carried out by mercury intrusion porosimetry using a pore distribution measuring device "AutoPore V (model 9620)" manufactured by Micrometrics Instruments.

[0135] The NTO particle sample was dried at a constant temperature of 120°C for 4 hours, and then the pore size distribution was determined by mercury intrusion porosimetry using the above-mentioned pore size distribution measurement device. The pore size was calculated using the Washburn equation. From the obtained pore size distribution, the cumulative pore volume in the pore size range of 20 to 100 nm was calculated and used as the macropore volume. Here, the surface tension of mercury was set to 480 dyne / cm, and the contact angle between mercury and the sample was set to 140°.

[0136] The pore diameter corresponding to the peak top in the pore distribution obtained above in the pore diameter range of 20 to 100 nm was taken as the mode diameter of the macropores.

[0137] Electrochemical Measurements (Maximum Current Density and Efficiency Point Voltage) Membrane electrode assemblies (MEAs) were fabricated using the Pt / NTO particles obtained in each Example and Comparative Example, and subjected to electrochemical measurements. Each Pt / NTO particle was pulverized in a mortar and then used to fabricate an MEA.

[0138] (1) Preparation of MEA (Membrane Electrode Assembly) 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 absolute ethanol, and a Nafion (registered trademark) dispersion (10% by mass) was added to obtain a mixture. The amount of Nafion (registered trademark) dispersion added was 0.175 times the mass of the NTO particles. The resulting mixture was ultrasonically dispersed in a water bath for 10 hours.

[0139] The ultrasonically dispersed mixture was applied to a Teflon sheet, and the solvent was evaporated to form a catalyst layer (cathode-side catalyst layer) containing Pt / NTO particles on the sheet. The Pt density per unit area of ​​this catalyst layer was 0.1 mg / cm. ２ It was decided.

[0140] A hydrogen electrode-side catalyst layer was formed on a sheet in the same manner as above, except that a catalyst powder of 20 mass % Pt supported on Ketzen Black was used instead of Pt / NTO particles. The Pt density per unit area of ​​this catalyst layer was 0.1 mg / cm, the same as that of the cathode-side catalyst layer. ２ It was decided.

[0141] Teflon sheets bearing the cathode and anode catalyst layers obtained above were laminated on both sides of the polymer electrolyte membrane, with the catalyst layer-forming surfaces facing each other, and the laminate was transferred by hot pressing. The Teflon sheets were then peeled off, and a diffusion layer was placed on the surface of each catalyst layer to obtain an MEA in which the air diffusion layer, cathode catalyst layer, polymer electrolyte membrane, anode catalyst layer, and hydrogen diffusion layer were laminated in this order.

[0142] (2) Electrochemical Measurement The MEA obtained above was then set in a single cell for electrochemical measurement and connected to a commercially available fuel cell evaluation device. Under conditions of a cell temperature of 80°C and a relative humidity of 100%, 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. The voltage was swept from 1.0 V to 0 V in a negative direction at a sweep rate of 10 mV / sec, to obtain an IV curve.

[0143] The maximum current value in the obtained IV curve was taken as the maximum current density, and the maximum current density was 0.5 A / cm ２ The voltage at this time was defined as the efficiency point voltage. Note that the MEA produced using the Pt / NTO particles of Comparative Example 3 had such low catalytic performance that the efficiency point voltage value could not be measured.

[0144] The above results are summarized in Tables 1 and 2.

[0145]

[0146]

[0147] With reference to Tables 1 and 2, the following can be understood.

[0148] When Pt / NTO particles were used as an electrode catalyst on the cathode side of a fuel cell, both the maximum current density and the efficiency point voltage were insufficient for the Pt / NTO particles of Comparative Examples 1 and 3, in which the macropore volume of the NTO particle support was small. Furthermore, the Pt / NTO particles of Comparative Example 2, in which the macropore volume of the NTO particle support was large but the specific surface area was small, showed a high maximum current density, but the efficiency point voltage was insufficient.

[0149] In contrast to these, when the Pt / NTO particles of Examples 1 to 3, in which the NTO particle support had a large macropore volume and a large specific surface area within the specified range of the present invention, were used, both the maximum current density and the efficiency point voltage showed high values.

[0150] This is thought to be due to the large macropore volume and large specific surface area of ​​the NTO particle support. In other words, the large macropore volume of the NTO particle support allows the H generated by power generation in the fuel cell to flow more easily. ２ O can be easily discharged from the catalyst layer. Therefore, it is believed that the diffusibility of gases in the catalyst layer is maintained high, resulting in a high maximum current density. In addition, the large specific surface area of ​​the NTO particle support suppresses the aggregation of the supported Pt particles. Therefore, it is believed that the ECSA (electrochemical surface area) of the catalytic precious metal particles is maintained large, resulting in a high efficiency point voltage.

[0151] It is believed that the electrocatalyst of the present invention exhibits efficient electrocatalytic action due to the combination of these two properties.

Claims

1. Specific surface area is 35m ２ / g or more, and the pore volume of pores having a pore diameter of 20 nm or more and 100 nm or less is 0.25 mL / g or more.

2. The conductive metal oxide particles according to claim 1, having a primary particle diameter of 10 nm or more and 30 nm or less.

3. The conductive metal oxide particles according to claim 1, having a crystallite size of 10.0 nm or more and 15.0 nm or less.

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

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

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

7. The conductive metal oxide particles of claim 6, wherein said conductive metal oxide particles are particles of niobium doped tin oxide.

8. A catalyst particle for electrochemical reactions, comprising catalytic precious metal particles supported on the conductive metal oxide particles according to any one of claims 1 to 7.

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

10. The catalyst particle for electrochemical reactions according to claim 8, which is an electrode catalyst for a fuel cell.

11. The catalyst particle for electrochemical reactions according to claim 10, which is an electrode catalyst for a cathode.

12. A fuel cell comprising the electrochemical reaction catalyst particles according to claim 10.

13. A method for producing conductive metal oxide particles according to any one of claims 1 to 7, comprising the steps of: (A) and (B) below: (A) a specific surface area of ​​35 m ２ 1. A method for producing conductive metal oxide particles, comprising: (a) atomizing an aqueous dispersion containing a conductive metal oxide particle precursor having a pore volume of less than 0.25 mL / g and a pore volume of less than 0.25 mL / g for pores having a pore size of 20 nm or more and 100 nm or less, and a pore-forming material, and (b) drying the aqueous dispersion using a diffusion flame to obtain an aggregate of the conductive metal oxide particle precursor and the pore-forming material; and (c) heating the aggregate to combust the pore-forming material.

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

15. The method for producing conductive metal oxide particles according to claim 13, further comprising, prior to step (A), (C) spraying and combusting a solution in which a metal atom-containing organic compound is dissolved in an organic solvent to obtain the conductive metal oxide particle precursor.

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