JP2024053489A - Porous oxide semiconductor particles - Google Patents

Abstract

To provide porous oxide semiconductor particles having a beaded structure and exhibiting relatively high conductivity.SOLUTION: Porous oxide semiconductor particles include a beaded structure in which porous primary particles are connected, consisting of an aggregate of crystallites made of tin oxide doped with pentavalent antimony, the doping amount of pentavalent antimony is 2.5 at% or more. Here, "doping amount of pentavalent antimony" is a value obtained from XAFS measurement and ICP analysis, is also the ratio of the number of atoms of pentavalent antimony to the total number of atoms of tin and antimony contained in the porous oxide semiconductor particles.SELECTED DRAWING: Figure 7

Description

The present invention relates to porous oxide semiconductor particles, and more specifically to porous oxide semiconductor particles having a beaded structure and a relatively high specific surface area.

A polymer electrolyte fuel cell (PEFC) has a membrane electrode assembly (MEA) in which catalyst layers are bonded to both sides of an electrolyte membrane. A gas diffusion layer is usually placed on the outside of the catalyst layer. Furthermore, a current collector (separator) with a gas flow path is placed on the outside of the gas diffusion layer. A PEFC usually has a structure (fuel cell stack) in which multiple single cells each consisting of such an MEA, gas diffusion layer, and current collector are stacked.

In PEFCs, the catalyst layer generally consists of a mixture of an electrode catalyst in which catalytic metal particles such as platinum are supported on the surface of the support, and a catalyst layer ionomer. Traditionally, carbon materials such as carbon black and acetylene black have been used primarily as catalyst supports. In particular, carbon supports with mesopores have been attracting attention in recent years (Non-Patent Document 1). It has been found that the use of porous carbon particles with appropriately controlled particle size and pore size as a support can reduce catalyst poisoning caused by the sulfonic acid groups of the ionomer and reduce the Knudsen diffusion resistance in the support pores, thereby achieving cell performance that is compatible with both low-load and high-load performance (Patent Document 1).

However, it is known that carbon supports oxidize and corrode when exposed to high potentials, causing the catalytic metal particles supported on the support to fall off, which in turn reduces electrode performance. In order to achieve both initial cell performance and durability, it is necessary to create a porous support using a material that is stable at high potentials instead of carbon. For this reason, it has been proposed to use conductive metal oxides, which are stable at high potentials, as support materials to replace carbon.

For example, non-patent document 2 suggests that porous tin oxide particles (M-SnO ₂ ) doped with a foreign element (M = Nb, Sb, Ta, W, etc.) may be a promising support material in terms of high potential stability.

Patent Document 2 discloses porous oxide semiconductor particles having a beaded structure in which porous primary particles, each of which is an aggregate of crystallites made of an oxide semiconductor, are linked together, and which have a specific surface area of 60 m ² /g or more.
The document describes that when such a porous oxide semiconductor is used as a catalyst support for a solid polymer fuel cell, the detachment of catalytic metal particles due to oxidative corrosion of the support is suppressed, mass transfer within the catalyst layer is promoted, and a decrease in activity due to catalyst poisoning is suppressed.

Patent Document 2 describes that the highest electrical conductivity is obtained when Sb is doped into beaded porous tin oxide particles, with the maximum value being 2.1×10 ⁻² S/cm. However, this value is lower than the electrical conductivity of conventional carbon supports by two or more orders of magnitude. In order to use Sb-doped beaded porous tin oxide as a catalyst support for fuel cells, further improvement in electrical conductivity is desired.

JP 2021-084852 A JP 2022-077821 A

S. Ott et al., Nature Mater., 2019, 19, 77 T. Arai et al., SAE Int. J. Alt. Power., 2017, 6, 145

An object of the present invention is to provide porous semiconductor oxide particles which have a bead-like structure and exhibit relatively high electrical conductivity.
Another problem to be solved by the present invention is to provide porous oxide semiconductor particles that have a suitable specific surface area, pore size, average primary particle size, pore volume, average crystallite size, and/or tap density in addition to the bead-like structure and electrical conductivity.
A further object of the present invention is to provide porous semiconductor oxide particles suitable as a catalyst support for a polymer electrolyte fuel cell.

In order to solve the above problems, the porous oxide semiconductor particles according to the present invention are
The porous primary particles are composed of an aggregate of crystallites of tin oxide doped with pentavalent antimony, and have a bead-linked structure.
The doping amount of the pentavalent antimony is 2.5 at % or more.
Here, the "doping amount of pentavalent antimony" is a value obtained by XAFS measurement and ICP analysis, and refers to the ratio of the number of pentavalent antimony atoms to the total number of tin and antimony atoms contained in the porous oxide semiconductor particles.

Sb doped in _SnO2 exists in a trivalent state and in a pentavalent state. Of these, pentavalent Sb contributes to improving the electrical conductivity of _SnO2 . Therefore, by optimizing the doping amount of pentavalent Sb, high electrical conductivity can be obtained. Specifically, when the doping amount of pentavalent Sb is 2.5 at% or more, the electrical conductivity is 1.0 x ^10-3 S/cm or more. Furthermore, when the doping amount of pentavalent Sb is more than 4.5 at%, the electrical conductivity is more than 2.1 x ^10-2 .

FIG. 2 is a schematic diagram of a method for producing bead-like mesoporous Sb—SnO ₂ particles. FIG. 2 shows the Sb K-edge absorption XANES spectrum of the bead-like mesoporous Sb—SnO ₂ particles obtained in Example 1 and waveform separation by fitting. FIG. 1 shows the Sb K-edge absorption XANES spectrum of the bead-like mesoporous Sb—SnO ₂ particles obtained in Example 2 and waveform separation by fitting. FIG. 1 shows the Sb K-edge absorption XANES spectrum of the bead-like mesoporous Sb—SnO ₂ particles obtained in Example 3 and waveform separation by fitting.

FIG. 1 shows the Sb K-edge absorption XANES spectrum of the bead-like mesoporous Sb—SnO ₂ particles obtained in Example 4 and waveform separation by fitting. FIG. 1 shows the Sb K-edge absorption XANES spectrum of the bead-like mesoporous Sb—SnO ₂ particles obtained in Example 5 and waveform separation by fitting. FIG. 1 is a graph showing the relationship between the concentration of pentavalent Sb in bead-like mesoporous Sb—SnO ₂ particles and electrical conductivity.

An embodiment of the present invention will be described in detail below.
[1. Porous oxide semiconductor]
The porous oxide semiconductor particles according to the present invention have the following configuration.

[Configuration 1]
The porous primary particles are composed of an aggregate of crystallites of tin oxide doped with pentavalent antimony, and have a bead-linked structure.
The porous oxide semiconductor particles are doped with pentavalent antimony in an amount of 2.5 at % or more.
Here, the "doping amount of pentavalent antimony" is a value obtained by XAFS measurement and ICP analysis, and refers to the ratio of the number of pentavalent antimony atoms to the total number of tin and antimony atoms contained in the porous oxide semiconductor particles.

[Configuration 2]
2. The porous semiconductor oxide particles according to claim 1, having a specific surface area of 60 m ² /g or more.

[Configuration 3]
3. The porous oxide semiconductor particle according to claim 1, wherein the pentavalent antimony is doped in an amount of more than 4.5 at %.

[Configuration 4]
4. The porous oxide semiconductor particles according to any one of claims 1 to 3, wherein the pore size is 1 nm or more and 20 nm or less.

[Configuration 5]
5. The porous oxide semiconductor particles according to any one of claims 1 to 4, wherein the electrical conductivity of the powder compact is 1.0 x 10 ^-3 S/cm or more.

[Configuration 6]
6. The porous oxide semiconductor particles according to any one of claims 1 to 5, wherein the average primary particle size is 0.05 μm or more and 2 μm or less.

[Configuration 7]
7. The porous oxide semiconductor particles according to any one of claims 1 to 6, having a pore volume of 0.1 mL/g or more.

[Configuration 8]
8. The porous oxide semiconductor particles according to any one of claims 1 to 7, wherein the average crystallite size is 2 nm or more and 40 nm or less.

[Configuration 9]
9. The porous oxide semiconductor particles according to any one of claims 1 to 8, having a tap density of 0.005 g/cm ³ or more and 1.0 g/cm ³ or less.

[Configuration 10]
10. The porous oxide semiconductor particles according to any one of claims 1 to 9, which are used as a catalyst support for a polymer electrolyte fuel cell.

[1.1. Primary particles]
The porous oxide semiconductor particles according to the present invention have a bead-like structure in which primary particles are linked together.
In the present invention, the term "primary particles" refers to porous particles consisting of an aggregate of crystallites made of tin oxide doped with pentavalent antimony.
The term "porous" refers to the presence of mesopores between the crystallites.

[1.1.1. Sb-doped tin oxide]
The crystallites constituting the primary particles are made of Sb-doped tin oxide (hereinafter also referred to as "Sb--SnO ₂ ") doped with pentavalent antimony.
Sb-- _SnO2 is suitable as an oxide semiconductor for forming crystallites because of its high durability in a fuel cell environment. In addition, Sb-- _SnO2 exhibits higher electrical conductivity than _SnO2 without a dopant and _SnO2 containing a dopant other than Sb.

[1.1.2. Doping amount of pentavalent antimony]
The "doping amount of pentavalent antimony" is a value obtained by XAFS measurement and ICP analysis, and refers to the ratio of the number of pentavalent antimony atoms to the total number of tin and antimony atoms contained in the porous oxide semiconductor particles.

In general, the higher the doping amount of pentavalent antimony, the higher the electrical conductivity. To obtain high electrical conductivity, the doping amount of pentavalent antimony must be 2.5 at% or more. The doping amount is more preferably more than 4.5 at%, 5.0 at% or more, or 5.5 at% or more.
On the other hand, even if the doping amount of pentavalent antimony is increased more than necessary, there is no difference in the effect and there is no practical benefit. Therefore, the doping amount of pentavalent antimony is preferably 15.0 at% or less. The doping amount is more preferably 12.5 at% or less, or 10.0 at% or less.

[1.1.3. Average primary particle size]
The term "average primary particle size" refers to the average value of the maximum dimension (= diameter) of the primary particles.
The average primary particle size can be measured by observation with a scanning electron microscope (SEM).

Generally, if the average primary particle size is too small, it becomes difficult to support catalyst particles. Therefore, the average primary particle size is preferably 0.05 μm or more. The average primary particle size is preferably 0.06 μm or more, and more preferably 0.07 μm or more.
On the other hand, if the average primary particle size is too large, the thickness of the catalyst layer becomes large, and the ionic resistance and electronic resistance in the catalyst layer become large. Therefore, the average primary particle size is preferably 2 μm or less. The average primary particle size is preferably 1 μm or less, and more preferably 0.5 μm or less.

[1.1.4. Average crystallite size]
The term "average crystallite size" refers to the average value of the maximum dimension (=diameter) of the crystallites.
The average crystallite size can be determined from the line width of the X-ray diffraction peak and Scherrer's formula.

If the average crystallite diameter is too small, the pore size will be too small. Therefore, the average crystallite diameter is preferably 2 nm or more. The average crystallite diameter is preferably 3 nm or more, and more preferably 4 nm or more.
On the other hand, if the average crystallite size is too large, the pore size will be too large. Therefore, the average crystallite size is preferably 40 nm or less. The average crystallite size is preferably 20 nm or less, and more preferably 10 nm or less.

[1.1.5. Primary particle shape]
In the present invention, the shape of the primary particles is not particularly limited. When porous oxide semiconductor particles are produced using the method described below, the primary particles are usually not perfectly spherical but have an irregular shape with an aspect ratio of about 1.1 to 3.

[1.2. Secondary particles]
The secondary particles have a bead-like structure.
Here, the term "beaded structure" refers to a structure in which primary particles are connected in a beaded shape. In secondary particles having a beaded structure, the primary particles are loosely connected to each other, so there are no gaps between the primary particles. In addition, since the primary particles are made up of an aggregate of minute crystallites, there are relatively small voids (mesopores) inside the primary particles.

As described below, the porous oxide semiconductor particles according to the present invention are produced using mesoporous carbon as a template. Also, mesoporous carbon is produced using mesoporous silica as a template. Mesoporous silica is usually synthesized by condensation polymerization of a silica source in a reaction solution containing a silica source, a surfactant, and a catalyst.

In this case, by limiting the concentration of the surfactant and the concentration of the silica source in the reaction solution to specific ranges, respectively, it is possible to obtain mesoporous silica having a bead-and-loop structure and having specific ranges for the average primary particle size, pore size, pore volume, tap density, etc.
When such mesoporous silica having a bead-and-loop structure is used as a first template, mesoporous carbon having a bead-and-loop structure can be obtained.Furthermore, when mesoporous carbon having a bead-and-loop structure is used as a second template, porous semiconductor oxide particles having a bead-and-loop structure can be obtained.

[1.3. Characteristic]
[1.3.1. Specific surface area]
When the porous oxide semiconductor particles according to the present invention are used as a catalyst support for PEFCs, if the specific surface area of the porous oxide semiconductor particles is too small, the active species of the catalyst cannot be supported in a fine and highly dispersed state, and the catalyst Therefore, the larger the specific surface area of the porous oxide semiconductor particles, the better.

The porous oxide semiconductor particles according to the present invention have a bead-like structure and mesopores in the primary particles, and therefore have a larger specific surface area than conventional materials. When the manufacturing conditions are optimized, the specific surface area becomes 60 ^m2 /g or more. When the manufacturing conditions are further optimized, the specific surface area becomes 80 ^m2 /g or more, 100 ^m2 /g or more, or 150 ^m2 /g or more.
By using the method described below, it is possible to synthesize porous semiconductor oxide particles even with a specific surface area of about 200 m ² /g.

[1.3.2. Pore diameter]
The "pore size" refers to the average diameter of the mesopores contained in the primary particles, and does not include the size of the voids between the primary particles.
The pore diameter is determined by analyzing the adsorption side data of the nitrogen adsorption isotherm of the porous oxide semiconductor particles by the BJH method, and determining the pore diameter at which the pore volume is maximum (the most frequent peak value or the mode pore diameter). This is obtained by:
In addition, the term "mesopores" generally refers to pores with a diameter of 2 to 50 nm, but in the present invention, the term "mesopores" also includes pores with a diameter of less than 2 nm (so-called "micropores"). included.

The primary particles are an aggregate of fine crystallites, and therefore have mesopores therein. When the porous oxide semiconductor particles according to the present invention are used as a catalyst support for PEFC, by supporting catalyst particles in the mesopores, poisoning by the catalyst layer ionomer can be suppressed. In general, if the pore size of the primary particles is too small, it becomes difficult to supply reaction gas or protons to the catalyst supported in the pores, or it becomes difficult to discharge water generated by the reaction. Therefore, the pore size is preferably 1 nm or more. The pore size is preferably 2 nm or more, more preferably 3 nm or more.
On the other hand, if the pore diameter is too large, the catalyst layer ionomer easily penetrates into the pores, which easily causes catalyst poisoning. Therefore, the pore diameter is preferably 20 nm or less. The pore diameter is preferably 10 nm or less, and more preferably 5 nm or less.

1.3.3. Pore volume
"Pore volume" refers to the volume of the mesopores contained in the primary particles, and does not include the volume of the voids between the primary particles.
The pore volume can be obtained by analyzing the adsorption data of the nitrogen adsorption isotherm of the porous oxide semiconductor by the BJH method and calculating the value of P/P ₀ =0.03 to 0.99.

When the porous oxide semiconductor particles according to the present invention are used as a catalyst support for PEFC, if the pore volume is too small, the ratio of catalyst particles supported in the pores will be small. Therefore, the pore volume is preferably 0.1 mL/g or more. The pore volume is preferably 0.15 mL/g or more, and more preferably 0.2 mL/g or more.
On the other hand, if the pore volume is too large, the ratio of the pore walls made of oxide semiconductor becomes small, and the electronic conductivity becomes low. Also, the amount of ionomer penetration increases, and the activity may decrease due to catalyst poisoning. Therefore, the pore volume is preferably 1 mL/g or less. The pore volume is preferably 0.7 mL/g or less, and more preferably 0.5 mL/g or less.

1.3.4. Electrical conductivity of powder compact
"Conductivity of green compact" means
(a) forming porous semiconductor oxide particles using two stainless steel disks and a plastic jig with a cylindrical hole;
(b) This refers to the value obtained by measuring the voltage while applying a constant current to the obtained green compact under a pressure of 2.4 MPa.
The electrical conductivity of the compact (i.e., the porous oxide semiconductor particles) depends mainly on the type of oxide semiconductor and the type and amount of dopant. When the composition of the oxide semiconductor is optimized, the electrical conductivity of the compact is 1.0×10 ⁻³ S/cm or more. When the manufacturing conditions are further optimized, the electrical conductivity is 1.0×10 ⁻² S/cm or more, or 4.0×10 ⁻² S/cm or more.
By using the method described below, it is possible to synthesize porous semiconductor particles even when the powder compact has an electrical conductivity of about 10 S/cm.

[1.3.5. Tap density]
The "tap density" refers to a value measured in accordance with JIS Z 2512.
When the porous oxide semiconductor particles according to the present invention are used in a catalyst layer of a PEFC, if the tap density of the porous oxide semiconductor particles is too small, the thickness of the resulting catalyst layer becomes too large, and the proton conductivity decreases. Therefore, the tap density is preferably 0.005 g/cm ³ or more. The tap density is preferably 0.01 g/cm ³ or more, and more preferably 0.05 g/cm ³ or more.
On the other hand, if the tap density is too high, when a catalyst layer is produced using this, it becomes difficult to ensure voids in the catalyst layer that can suppress flooding. Therefore, the tap density is preferably 1.0 g/ ^cm3 or less. The tap density is preferably 0.75 g/ ^cm3 or less.

[1.4. Applications
The porous semiconductor particles according to the present invention can be used as a catalyst support for a PEFC, a catalyst support for a polymer electrolyte electrolysis cell (PEEC), etc. The porous semiconductor particles according to the present invention have mesopores. Since it has a large specific surface area, high electrical conductivity, and is resistant to oxidation and corrosion, it is particularly suitable as a catalyst support for PEFCs.

[2. Method for producing mesoporous silica (first mold)]
In order to produce the porous semiconductor particles according to the present invention, it is first necessary to produce mesoporous silica (first template) having a bead-and-loop structure. Such mesoporous silica can be prepared by:
(a) preparing precursor particles by condensation polymerization of the silica source in a reaction solution containing a silica source, a surfactant, and a catalyst;
(b) separating the precursor particles from the reaction solution and drying;
(c) optionally subjecting the dried precursor particles to a diameter enlarging treatment;
(d) The precursor particles are calcined to obtain the porous material.

[2.1. Polycondensation process]
First, in a reaction solution containing a silica source, a surfactant, and a catalyst, the silica source is condensation-polymerized to obtain precursor particles (condensation polymerization step).

2.1.1. Silica Source
In the present invention, the type of silica source is not particularly limited. Examples of the silica source include
(a) tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, dimethoxydiethoxysilane, and tetraethyleneglycoxysilane;
(b) trialkoxysilanes such as 3-mercaptopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and 3-(2-aminoethyl)aminopropyltrimethoxysilane;
As the silica source, any one of these may be used alone or two or more of them may be used in combination.

[2.1.2. Surfactants]
When a silica source is polycondensed in a reaction solution, the surfactant forms micelles in the reaction solution. Hydrophilic groups are gathered around the micelles, so the silica source is adsorbed to the surface of the micelles. Furthermore, the micelles to which the silica source is adsorbed self-organize in the reaction solution, and the silica source is polycondensed. As a result, mesopores due to the micelles are formed inside the primary particles. The size of the mesopores can be controlled (up to 1 to 50 nm) mainly by the molecular length of the surfactant.

In the present invention, an alkyl quaternary ammonium salt is used as the surfactant. The alkyl quaternary ammonium salt refers to a compound represented by the following formula (a).
_CH3- ( _CH2 ) _n -N ⁺ ( _R1 )( _R2 )( _R3 )X ^-... (a)

In formula (a), R ₁ , R ₂ , and R ₃ each represent an alkyl group having 1 to 3 carbon atoms. R ₁ , R ₂ , and R ₃ may be the same as or different from each other. In order to facilitate aggregation (micelle formation) of alkyl quaternary ammonium salts, it is preferable that R ₁ , R ₂ , and R ₃ are all the same. Furthermore, it is preferable that at least one of R ₁ , R ₂ , and R ₃ is a methyl group, and it is preferable that all of them are methyl groups.
In formula (a), X represents a halogen atom. The type of the halogen atom is not particularly limited, but X is preferably Cl or Br in view of availability.

In formula (a), n represents an integer of 7 to 21. In general, the smaller n is, the smaller the central pore diameter of the mesopores is, resulting in a spherical mesoporous body. On the other hand, the larger n is, the larger the central pore diameter is, but if n is too large, the hydrophobic interaction of the alkyl quaternary ammonium salt becomes excessive. As a result, a layered compound is formed, and a mesoporous body cannot be obtained. n is preferably 9 to 17, and more preferably 13 to 17.

Among those represented by formula (a), alkyl trimethyl ammonium halides are preferred. Examples of alkyl trimethyl ammonium halides include hexadecyl trimethyl ammonium halides, octadecyl trimethyl ammonium halides, nonyl trimethyl ammonium halides, decyl trimethyl ammonium halides, undecyl trimethyl ammonium halides, and dodecyl trimethyl ammonium halides.
Among these, alkyltrimethylammonium bromide or alkyltrimethylammonium chloride is particularly preferred.

When synthesizing mesoporous silica, one type of alkyl quaternary ammonium salt may be used, or two or more types may be used. However, since the alkyl quaternary ammonium salt serves as a template for forming mesopores within the primary particles, the type of alkyl quaternary ammonium salt has a significant effect on the shape of the mesopores. In order to synthesize silica particles with more uniform mesopores, it is preferable to use one type of alkyl quaternary ammonium salt.

2.1.3. Catalyst
When the silica source is polycondensed, a catalyst is usually added to the reaction solution. When synthesizing particulate mesoporous silica, the catalyst may be an alkali such as sodium hydroxide or aqueous ammonia, or an acid such as hydrochloric acid.

2.1.4. Solvent
The solvent used may be water, an organic solvent such as alcohol, or a mixed solvent of water and an organic solvent.
Alcohol is
(1) Monohydric alcohols such as methanol, ethanol, and propanol,
(2) Dihydric alcohols such as ethylene glycol,
(3) Trihydric alcohols such as glycerin,
Either is fine.
When a mixed solvent of water and an organic solvent is used, the content of the organic solvent in the mixed solvent can be selected arbitrarily depending on the purpose. In general, adding an appropriate amount of an organic solvent to the solvent makes it easier to control the particle size and particle size distribution.

[2.1.5. Composition of reaction solution]
The composition of the reaction solution affects the external shape and pore structure of the synthesized mesoporous silica. In particular, the concentrations of the surfactant and silica source in the reaction solution have a large effect on the average primary particle size, pore size, pore volume, and tap density of the mesoporous silica particles.

A. Surfactant Concentration
If the concentration of the surfactant is too low, the particle precipitation speed will be slow, and a structure in which the primary particles are linked will not be obtained. Therefore, the concentration of the surfactant must be 0.03 mol/L or more. The concentration of the surfactant is preferably 0.035 mol/L or more, more preferably 0.04 mol/L or more.

On the other hand, if the surfactant concentration is too high, the particle precipitation rate becomes too fast and the primary particle size easily exceeds 300 nm. Therefore, the surfactant concentration must be 1.0 mol/L or less. The surfactant concentration is preferably 0.95 mol/L or less, and more preferably 0.90 mol/L or less.

B. Concentration of Silica Source
If the concentration of the silica source is too low, the particle precipitation rate will be slow, and a structure in which primary particles are connected will not be obtained. Alternatively, the surfactant will be excessive, and uniform mesopores may not be obtained. Therefore, the concentration of the silica source must be 0.05 mol/L or more. The concentration of the silica source is preferably 0.06 mol/L or more, and more preferably 0.07 mol/L or more.

On the other hand, if the concentration of the silica source is too high, the particle precipitation rate becomes too fast, and the primary particle size easily exceeds 300 nm. Alternatively, sheet-like particles may be obtained instead of spherical particles. Therefore, the concentration of the silica source must be 1.0 mol/L or less. The concentration of the silica source is preferably 0.95 mol/L or less, and more preferably 0.9 mol/L or less.

C. Catalyst Concentration
In the present invention, the catalyst concentration is not particularly limited. In general, if the catalyst concentration is too low, the particle precipitation speed becomes slow. On the other hand, if the catalyst concentration is too high, the particle precipitation speed becomes fast. It is preferable to select the optimum catalyst concentration according to the type of silica source, the type of surfactant, the target physical property value, etc.

2.1.6 Reaction conditions
A silica source is added to a solvent containing a predetermined amount of a surfactant, and hydrolysis and polycondensation are carried out, whereby precursor particles containing silica and the surfactant are obtained with the surfactant acting as a template.
The optimum reaction conditions are selected depending on the type of silica source, the particle size of the precursor particles, etc. In general, the reaction temperature is preferably −20 to 100° C. The reaction temperature is more preferably 0 to 90° C., and even more preferably 10 to 80° C.

[2.2. Drying process]
Next, the precursor particles are separated from the reaction solution and dried (drying step).
Drying is carried out in order to remove the solvent remaining in the precursor particles. The drying conditions are not particularly limited as long as the solvent can be removed.

[2.3. Diameter expansion process]
Next, if necessary, the dried precursor particles may be subjected to a diameter expansion treatment (diameter expansion step). The "diameter expansion treatment" refers to a treatment for expanding the diameter of mesopores in the primary particles.
Specifically, the diameter-enlarging treatment is carried out by subjecting the synthesized precursor particles (from which the surfactant has not been removed) to a hydrothermal treatment in a solution containing a diameter-enlarging agent, which can enlarge the pore size of the precursor particles.

Examples of the diameter expanding agent include:
(a) Hydrocarbons such as trimethylbenzene, triethylbenzene, benzene, cyclohexane, triisopropylbenzene, naphthalene, hexane, heptane, octane, nonane, decane, undecane, and dodecane;
(b) acids such as hydrochloric acid, sulfuric acid, and nitric acid;
and so on.

The reason why the pore size increases by hydrothermal treatment in the presence of a hydrocarbon is believed to be that rearrangement of silica occurs when the diameter-expanding agent is introduced from the solvent into the pores of the more hydrophobic precursor particles.
In addition, the pore size increases when the silica is hydrothermally treated in the presence of an acid such as hydrochloric acid. This is believed to be due to the dissolution and reprecipitation of silica inside the primary particles. When the manufacturing conditions are optimized, radial pores are formed inside the silica. When the silica is hydrothermally treated in the presence of an acid, the silica dissolves and reprecipitation occurs, and the radial pores are converted into interconnected pores.

There are no particular limitations on the conditions for the diameter expansion treatment, so long as the desired pore diameter is obtained. Usually, it is preferable to add about 0.05 mol/L to 10 mol/L of a diameter expansion agent to the reaction solution and perform hydrothermal treatment at 60 to 150°C.

[2.4. Firing process]
Next, after carrying out a diameter expansion treatment as necessary, the precursor particles are calcined (calcination step), thereby obtaining mesoporous silica particles having a bead-and-loop structure.
The calcination is carried out in order to dehydrate and crystallize the precursor particles with residual OH groups and to thermally decompose the surfactant remaining in the mesopores. The calcination conditions are not particularly limited as long as the dehydration, crystallization, and thermal decomposition of the surfactant are possible. The calcination is usually carried out by heating in the air at 400°C to 700°C for 1 hour to 10 hours.

[3. Manufacturing method of mesoporous carbon (second mold)]
Next, the mesoporous silica having a bead-like structure is used as a template to produce mesoporous carbon having a bead-like structure (second template). Such mesoporous carbon is
(a) preparing mesoporous silica to serve as a first template;
(b) depositing carbon in the mesopores of the mesoporous silica to produce a silica/carbon composite;
(c) By removing silica from the composite.
In order to promote graphitization of the obtained mesoporous carbon, the mesoporous carbon may be heat-treated at a temperature higher than 1500° C. after removing the silica.

[3.1. First mold preparation step]
First, mesoporous silica that will become the first template is prepared (first template preparation step). Details of the method for producing mesoporous silica are as described above, and therefore will not be described here.

[3.2. Carbon Deposition Process]
Next, carbon is precipitated in the mesopores of the mesoporous silica to prepare a silica/carbon composite (carbon precipitation step).
Specifically, the deposition of carbon in mesopores is as follows:
(a) introducing a carbon precursor into the mesopores;
(b) By polymerizing and carbonizing a carbon precursor within the mesopores.

[3.2.1. Introduction of carbon precursor]
The term "carbon precursor" refers to a material capable of producing carbon by pyrolysis. Specific examples of such carbon precursors include:
(1) A polymer precursor that is liquid at room temperature and is thermally polymerizable (e.g., furfuryl alcohol, aniline, etc.);
(2) A mixture of an aqueous solution of carbohydrates and an acid (e.g., a mixture of monosaccharides such as sucrose, xylose, glucose, etc., or a mixture of disaccharides or polysaccharides and an acid such as sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid),
(3) A mixture of two-component curing polymer precursors (e.g., phenol and formalin, etc.);
and so on.
Among these, polymer precursors can be impregnated into the mesopores without diluting them with a solvent, so that a relatively large amount of carbon can be produced in the mesopores with a relatively small number of impregnations. In addition, they have the advantage that they do not require a polymerization initiator and are easy to handle.

When a liquid or solution carbon precursor is used, the amount of liquid or solution adsorbed per one time is preferably as large as possible, and is preferably such an amount that the entire mesopores are filled with the liquid or solution.
When a mixture of an aqueous solution of a carbohydrate and an acid is used as the carbon precursor, the amount of acid is preferably the minimum amount capable of polymerizing the organic matter.
Furthermore, when a mixture of two-liquid curing type polymer precursors is used as the carbon precursor, the optimum ratio is selected depending on the type of polymer precursor.

[3.2.2. Polymerization and carbonization of carbon precursors]
The polymerized carbon precursor is then carbonized within the mesopores.
The carbon precursor is carbonized by heating the mesoporous silica containing the carbon precursor to a predetermined temperature in a non-oxidizing atmosphere (e.g., in an inert atmosphere, in a vacuum, etc.). Specifically, the heating temperature is preferably 500°C or higher and 1200°C or lower. If the heating temperature is lower than 500°C, the carbon precursor is not sufficiently carbonized. On the other hand, if the heating temperature exceeds 1200°C, silica and carbon react with each other, which is not preferable. The optimal heating time is selected depending on the heating temperature.

The amount of carbon generated in the mesopores should be equal to or greater than the amount that allows the carbon particles to maintain their shape when the mesoporous silica is removed. Therefore, when the amount of carbon generated in one filling, polymerization, and carbonization is relatively small, it is preferable to repeat these steps multiple times. In this case, the conditions for each repeated step may be the same or different.
Furthermore, when each of the steps of filling, polymerization, and carbonization is repeated multiple times, each carbonization step may be performed at a relatively low temperature, and after the final carbonization step is completed, another carbonization step may be performed at a higher temperature. If the final carbonization step is performed at a higher temperature than the previous carbonization steps, the carbon introduced into the pores in multiple steps is more likely to be integrated.

[3.3. First mold removal step]
Next, the mesoporous silica serving as the first template is removed from the composite (first template removal step), thereby obtaining mesoporous carbon (second template) having a bead-and-loop structure.
Specific examples of methods for removing mesoporous silica include:
(1) A method of heating the complex in an alkaline aqueous solution such as sodium hydroxide,
(2) Etching the composite with an aqueous solution of hydrofluoric acid;
and so on.

[3.4. Graphitization treatment process]
Next, if necessary, the mesoporous carbon is heat-treated at a temperature higher than 1500°C (graphitization step). When carbonizing a carbon source in the mesopores of mesoporous silica, the heat treatment temperature must be low in order to suppress the reaction between silica and carbon. Therefore, the degree of graphitization of the carbon after carbonization is low. In order to obtain a high degree of graphitization, it is preferable to heat-treat the mesoporous carbon at a high temperature after removing the first template.

If the heat treatment temperature is too low, graphitization becomes insufficient. Therefore, the heat treatment temperature is preferably higher than 1500° C. The heat treatment temperature is preferably 1700° C. or higher, and more preferably 1800° C. or higher.
On the other hand, if the heat treatment temperature is made higher than necessary, there is no difference in the effect and no practical benefit. Therefore, the heat treatment temperature is preferably 2300° C. or less. The heat treatment temperature is preferably 2200° C. or less.

[4. Method for producing porous semiconductor particles]
The method for producing porous semiconductor particles according to the present invention comprises the steps of:
A first step of preparing mesoporous carbon having a bead-and-loop structure;
a second step of precipitating an oxide semiconductor in the mesopores of the mesoporous carbon to obtain an oxide/carbon composite;
and a third step of removing the carbon from the oxide/carbon composite.

[4.1. First step]
First, mesoporous carbon having a bead-like structure is prepared (first step). Details of the method for producing mesoporous carbon are as described above, and therefore will not be described here.

[4.2. Second step]
Next, an oxide semiconductor is precipitated in the mesopores of the mesoporous carbon (second step), thereby obtaining an oxide/carbon composite.
Specifically, deposition of an oxide semiconductor in the mesopores is carried out by introducing a precursor of the oxide semiconductor into the mesopores and converting the precursor into the oxide semiconductor.

4.2.1. Precursors
Specific examples of precursors for forming an oxide semiconductor in the mesopores include:
(1) A compound that contains a metal element constituting an oxide semiconductor, is soluble in a solvent, and can be oxidized by dissolved oxygen in the solvent to be precipitated;
(2) A compound that contains a metal element constituting an oxide semiconductor and is capable of forming a metal oxide by thermal decomposition or hydrolysis;
and so on.

Compounds that can be oxidized by dissolved oxygen to precipitate _SnO2 include salts containing divalent Sn, such as _SnCl2 .
Compounds capable of forming _SnO2 by thermal decomposition or hydrolysis include:
(a) Chlorides such as _SnCl4 and _SnCl2 ;
(b) Alkoxides such as Sn( _OC2H5 ) _{2 and} Sn(OC( _CH3 ) ₃ ) ₄ ;
(c) acetylacetonate salts such as tin _{acetylacetonate} (Sn( _CH3COCHCOCH3 ) ₂ );
(d) Acetates such as Sn(CH ₃ COO) ₂ .

When preparing an oxide semiconductor containing a dopant, a precursor containing the dopant is used in addition to the precursor for forming the oxide semiconductor. When the dopant is Sb, the precursor containing Sb can be various salts (sulfates, carboxylates, chlorides, nitrates, acetylacetonates) or alkoxides, as in the precursor for forming the oxide semiconductor.

[4.2.2. Introduction of precursors into pores]
When the precursor is a liquid, it may be adsorbed directly into the mesopores of the mesoporous carbon. Alternatively, the precursor may be dissolved in an appropriate solvent, and the solution may be adsorbed into the mesopores of the mesoporous carbon. When the precursor is dissolved in a solvent, the type of solvent and the concentration of the precursor are not particularly limited, and an optimum solvent and precursor concentration may be selected depending on the purpose.

4.2.3. Conversion of precursors to oxides
After the precursor is adsorbed, the precursor is converted into an oxide by any method, and an optimal method is selected depending on the type of precursor.
For example, when a chloride is used as a precursor, mesoporous carbon is dispersed in a solution containing dissolved chloride and stirred in air. With continued stirring, the chloride is eventually adsorbed into the mesopores of the mesoporous carbon, and the chloride in the mesopores is gradually converted into an oxide by the dissolved oxygen.

For example, when an alkoxide is used as a precursor, the alkoxide or a solution in which it is dissolved is added to mesoporous carbon to impregnate the mesopores with the alkoxide or its solution. When this is heated to a predetermined temperature, polycondensation of the alkoxide occurs, producing an oxide in the mesopores.
When a sufficient amount of oxide semiconductor cannot be formed in the mesopores by one cycle of adsorption of the precursor and conversion to the oxide, the adsorption and conversion may be repeated several times.

[4.3. Third step]
Next, the carbon is removed from the oxide/carbon composite (third step), thereby obtaining the porous oxide semiconductor particles according to the present invention.
The method for removing carbon is not particularly limited, and various methods can be used. Examples of the carbon removal method include:
(1) A method of heating an oxide/carbon composite in an oxidizing atmosphere;
(2) subjecting the composite to oxygen plasma etching;
and so on.

The removal conditions, such as the heating temperature and heating time, may be any conditions that at least completely remove carbon without causing the crystallites of the oxide semiconductor to become coarse.
In the case of Sb- _SnO2 , the amount of pentavalent Sb depends mainly on the ratio of the amount of Sb source to the amount of Sn source in the raw material and the firing temperature (treatment temperature during carbon removal). Therefore, it is preferable to select the optimal removal conditions taking these points into consideration.

[5. Action]
A porous carbon material having mesopores is used as a template, an oxide semiconductor is precipitated in the mesopores of the template, and the template is then removed to obtain porous oxide semiconductor particles having mesopores. By using a carbon porous body having mesopores and a beaded structure as the porous material and optimizing the raw materials and manufacturing conditions, a porous tin oxide having mesopores and a beaded structure and doped with pentavalent antimony can be obtained. Oxide semiconductor particles can be obtained.

The obtained porous oxide semiconductor particles have low packing properties, so when a catalyst layer is prepared using them, appropriate voids can be formed in the catalyst layer. In addition, because of the high specific surface area, catalytic metal particles can be supported on the surface in a highly dispersed manner. In addition, by supporting catalytic metal particles in the mesopores, catalyst poisoning by the catalytic layer ionomer can be suppressed.
Therefore, when such a porous oxide semiconductor is used as a catalyst support for a solid polymer electrolyte fuel cell, the detachment of catalytic metal particles due to oxidative corrosion of the support is suppressed, mass transfer within the catalyst layer is promoted, and a decrease in activity due to catalyst poisoning is suppressed.

Sb- _SnO2 shows higher electrical conductivity than _SnO2 without dopant and _SnO2 with dopant other than Sb. The electrical conductivity of Sb- _SnO2 changed depending on the firing temperature and the total Sb doping amount (doping amount regardless of Sb valence). However, no clear correlation was found between the electrical conductivity of Sb- _SnO2 and the firing temperature or the total Sb doping amount.

In response to this, the inventors of the present application
(a) Sb doped in SnO ₂ exists in a trivalent state and in a pentavalent state; and
(b) Of these, it was found that pentavalent Sb contributes to improving the electrical conductivity of _SnO2 .
Therefore, by optimizing the doping amount of pentavalent Sb, high electrical conductivity can be obtained. Specifically, when the doping amount of pentavalent Sb is 2.5 at% or more, the electrical conductivity becomes 1.0×10 ⁻³ S/cm or more. Furthermore, when the doping amount of pentavalent Sb is more than 4.5 at%, the electrical conductivity becomes more than 2.1×10 ⁻² .

(Examples 1 to 5)
1. Preparation of Samples
A schematic diagram of the method for producing beaded mesoporous Sb- _SnO2 particles is shown in Figure 1. Beaded mesoporous Sb- _SnO2 particles were produced according to the procedure shown in Figure 1.

[1.1. Preparation of beaded starburst silica]
56.3 g of 30 mass% aqueous cetyltrimethylammonium chloride solution was added to a mixed solvent of 4.6 g of methanol (MeOH) and 4.6 g of ethylene glycol (EG), and the mixture was stirred at room temperature. 8.8 g of 1 M NaOH was added thereto, and the mixture was heated to 50° C. Hereinafter, this is referred to as the “first solution.”
Next, 12.3 g of tetraethoxysilane (TEOS) was dissolved in a mixed solvent of 6.5 g of MeOH and 6.5 g of EG. This solution is hereinafter referred to as a "second solution."

The second solution was added to the first solution heated to 50°C. After the mixture became cloudy, heating was stopped and the mixture was stirred for an additional 4 hours or more. Filtration and redispersion in purified water were repeated twice, and then the mixture was dried at 45°C. The dried powder was then calcined in air at 550°C for 6 hours to obtain connected starburst mesoporous silica with radial pores (hereinafter, also referred to as "connected starburst silica (CSS)").

[1.2. Preparation of bead-like starburst carbon]
0.5 g of CSS was placed in a PFA container, and furfuryl alcohol (FA) was added in an amount equal to the pore volume of the CSS, allowing it to penetrate into the pores of the CSS. This was heat-treated at 150°C for 24 hours to polymerize the FA. This was then heat-treated in a nitrogen atmosphere at 500°C for 6 hours to promote carbonization of the FA. This was repeated twice, and then further heat-treated in a nitrogen atmosphere at 900°C for 6 hours to obtain a CSS/carbon composite.

This composite was immersed in a 12% HF solution for 4 hours to dissolve the silica component. After dissolution, it was repeatedly filtered and washed, and then dried at 45°C to obtain a connected starburst carbon with radial pores (hereinafter, this is also referred to as "connected starburst carbon (CSC)"). The obtained porous body had a BET specific surface area of 2122 ^m2 /g, a pore volume of 1.3 mL/g, and a pore diameter of 2.2 nm.

[1.3. Preparation of bead-like mesoporous Sb- _SnO2 ]
[1.3.1. Example 1]
0.03 g of SbCl ₃ was dissolved in 4 mL of concentrated hydrochloric acid (35 mass%), and 36 mL of purified water was added to dilute the solution. 5.0 g of SnCl ₂ was further added and dissolved. 0.1 g of CSC was added to this solution and dispersed. This dispersion was stirred in air at room temperature for 2 hours. Then, 200 mL of purified water was added, and the mixture was further stirred in air at room temperature for 4 hours. Filtration and redispersion in purified water were repeated twice, and the mixture was dried at 45°C to obtain a beaded Sb-SnO ₂ /carbon composite.
This beaded Sb--SnO ₂ /carbon composite was treated in an air atmosphere at 300° C. for 24 hours to obtain beaded mesoporous Sb--SnO ₂ .

1.3.2. Example 2
0.12 g of SbCl ₃ was dissolved in 4 mL of concentrated hydrochloric acid (35 mass%), and 36 mL of purified water was added to dilute the solution. 5.0 g of SnCl ₂ was further added and dissolved. 0.1 g of CSC was added to this solution and dispersed. This dispersion was stirred in air at room temperature for 2 hours. Then, 200 mL of purified water was added, and the mixture was further stirred in air at room temperature for 4 hours. Filtration and redispersion in purified water were repeated twice, and the mixture was dried at 45°C to obtain a beaded Sb-SnO ₂ /carbon composite.
This beaded Sb--SnO ₂ /carbon composite was treated in an air atmosphere at 320° C. for 24 hours to obtain beaded mesoporous Sb--SnO ₂ .

Example 3
0.12 g of SbCl ₃ was dissolved in 4 mL of concentrated hydrochloric acid (35 mass%), and 36 mL of purified water was added to dilute the solution. 5.0 g of SnCl ₂ was further added and dissolved. 0.1 g of CSC was added to this solution and dispersed. This dispersion was stirred in air at room temperature for 2 hours. Then, 200 mL of purified water was added, and the mixture was further stirred in air at room temperature for 4 hours. Filtration and redispersion in purified water were repeated twice, and the mixture was dried at 45°C to obtain a beaded Sb-SnO ₂ /carbon composite.
This beaded Sb--SnO ₂ /carbon composite was treated in an air atmosphere at 320° C. for 24 hours, and further treated in an air atmosphere at 500° C. for 3 hours to obtain beaded mesoporous Sb--SnO ₂ .

1.3.4. Example 4
0.18 g of SbCl ₃ was dissolved in 4 mL of concentrated hydrochloric acid (35 mass%), and 36 mL of purified water was added to dilute the solution. 5.0 g of SnCl ₂ was further added and dissolved. 0.1 g of CSC was added to this solution and dispersed. This dispersion was stirred in air at room temperature for 2 hours. Then, 200 mL of purified water was added, and the mixture was stirred in air at room temperature for another 4 hours. Filtration and redispersion in purified water were repeated twice, and the mixture was dried at 45°C to obtain a beaded Sb-SnO ₂ /carbon composite.
This beaded Sb--SnO ₂ /carbon composite was treated in an air atmosphere at 320° C. for 24 hours, and further treated in an air atmosphere at 500° C. for 3 hours to obtain beaded mesoporous Sb--SnO ₂ .

1.3.5. Example 5
0.18 g of SbCl ₃ was dissolved in 4 mL of concentrated hydrochloric acid (35 mass%), and 36 mL of purified water was added to dilute the solution. 5.0 g of SnCl ₂ was further added and dissolved. 0.1 g of CSC was added to this solution and dispersed. This dispersion was stirred in air at room temperature for 2 hours. Then, 200 mL of purified water was added, and the mixture was stirred in air at room temperature for another 4 hours. Filtration and redispersion in purified water were repeated twice, and the mixture was dried at 45°C to obtain a beaded Sb-SnO ₂ /carbon composite.
This beaded Sb--SnO ₂ /carbon composite was treated in an air atmosphere at 320° C. for 24 hours, and further treated in an air atmosphere at 700° C. for 3 hours to obtain beaded mesoporous Sb--SnO ₂ .

2. Test Method
[2.1. XAFS Measurement]
XAFS measurement of the beaded mesoporous Sb- _SnO2 was carried out. For the XAFS measurement, the sample powder was diluted with boron nitride powder and pelletized. The K-edge XANES spectrum of Sb obtained by the measurement was subjected to waveform separation to determine the ratio of pentavalent Sb to the sum of trivalent Sb and pentavalent Sb contained in the beaded mesoporous Sb- _SnO2 .
The amount (concentration) of pentavalent antimony contained in the beaded mesoporous Sb—SnO ₂ was calculated by multiplying this ratio by the total amount of antimony contained in the beaded mesoporous Sb—SnO ₂ determined by ICP analysis.
For the waveform analysis, standard spectra of Sb ₂ O ₅ and Sb ₂ O ₃ in the publicly available data of the SPring-8 BENTEN database were used.

[2.2. _N2 adsorption measurement]
The nitrogen adsorption isotherm of the obtained particles was measured. From the obtained nitrogen adsorption isotherm, the pore size distribution was obtained by the BJH method, and the mode pore size (the most frequent value of the pore size) was taken as the pore size of the sample. In addition, the pore volume and BET specific surface area were determined from the adsorption isotherm.

[2.3. conductivity]
A compact of the sample powder was prepared, and a constant current was passed through it while applying a pressure of 2.4 MPa, and the voltage at that time was measured to obtain the electrical conductivity.

[2.4. ICP analysis
The beaded mesoporous Sb- _SnO2 was dissolved in an alkali, and the amount of antimony contained in the beaded mesoporous Sb- _SnO2 was quantified using an inductively coupled plasma optical emission spectrometer (ICP-OES).

[3. result]
[3.1. XAFS Measurement]
2 to 6 show the Sb K-edge XANES spectra of the bead-like mesoporous Sb- _SnO2 particles obtained in Examples 1 to 5, respectively, and waveform separation by fitting. The results of spectrum waveform separation by fitting are also shown. In Example 1, only pentavalent Sb (Sb2O5) was present. On the other hand, in Examples 2 to 5, It was found that trivalent Sb (Sb2O3) and pentavalent Sb were present. Table 1 shows the ratio of trivalent Sb to pentavalent Sb determined from the results of waveform separation.

[3.2. _N2 adsorption measurement, conductivity, ICP analysis]
Table 2 shows the Sb concentration (obtained by ICP analysis) of the bead-like mesoporous Sb- _SnO2 , the pentavalent Sb concentration (obtained by XAFS measurement and ICP analysis), the electrical conductivity, the BET specific surface area, and the fineness. The pore size and pore volume are shown in Fig. 7. The relationship between the pentavalent Sb concentration and the electrical conductivity of the beaded mesoporous Sb- _SnO2 particles is shown in Fig. 7.

A clear correlation was observed between the concentration of pentavalent Sb and the electrical conductivity. From FIG. 7, it can be seen that the higher the concentration of pentavalent Sb, the higher the electrical conductivity. From this, it can be seen that the concentration of pentavalent Sb obtained by ICP analysis and XAFS measurement is a good indicator of the electrical conductivity of the bead-like mesoporous Sb-SnO _2. In addition, it was found that when the concentration of pentavalent Sb was 6.7 at% (Example 5), the electrical conductivity was improved by about three times compared to when the concentration of pentavalent Sb was 4.5 at% (Example 3).

Although the embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the gist of the present invention.

The porous oxide semiconductor particles according to the present invention can be used as a catalyst support for the air electrode catalyst layer of a polymer electrolyte fuel cell, or as a catalyst support for the fuel electrode catalyst layer.

Claims (10)

The porous primary particles are composed of an aggregate of crystallites of tin oxide doped with pentavalent antimony, and have a bead-linked structure.
The porous oxide semiconductor particles are doped with pentavalent antimony in an amount of 2.5 at % or more.
Here, the "doping amount of pentavalent antimony" is a value obtained by XAFS measurement and ICP analysis, and refers to the ratio of the number of pentavalent antimony atoms to the total number of tin and antimony atoms contained in the porous oxide semiconductor particles. 2. The porous semiconductor oxide particles according to claim 1, which have a specific surface area of 60 m ² /g or more. The porous oxide semiconductor particles according to claim 1, in which the doping amount of the pentavalent antimony is greater than 4.5 at%. The porous oxide semiconductor particles according to claim 1, wherein the pore diameter is 1 nm or more and 20 nm or less. 2. The porous semiconductor oxide particles according to claim 1, wherein the electrical conductivity of the green compact is 1.0×10 ⁻³ S/cm or more. The porous oxide semiconductor particles according to claim 1, having an average primary particle diameter of 0.05 μm or more and 2 μm or less. The porous oxide semiconductor particles according to claim 1, having a pore volume of 0.1 mL/g or more. The porous oxide semiconductor particles according to claim 1, having an average crystallite size of 2 nm or more and 40 nm or less. 2. The porous semiconductor oxide particle according to claim 1, having a tap density of 0.005 g/cm ^<3> or more and 1.0 g/cm ^<3> or less. The porous oxide semiconductor particles according to claim 1, which are used as a catalyst support for a polymer electrolyte fuel cell.

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