Porous tin oxide particles

Abstract

To provide a porous tin oxide particle which includes Nb-doped SnO2 and has a relatively high electric conductivity.SOLUTION: A porous tin oxide particle has a beaded structure of porous primary particles connected with each other, the porous primary particles each composed of an aggregate of crystallites composed of Nb-doped SnO2, and has an electric conductivity ratio of less than 68.4, where the electric conductivity ratio means a ratio (=σbulk / σtotal) of an electric conductivity of an inside of the porous tin oxide particle (σbulk) to an electric conductivity of the whole porous tin oxide particle (σtotal). The porous tin oxide particle preferably has a Nb concentration ratio of less than 2.6, where the Nb concentration ratio means a ratio (=CXPS / CICP) of a Nb concentration of a porous tin oxide surface determined by XPS (CXPS) to an average Nb concentration of the porous tin oxide particle determined by ICP (CICP).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to porous tin oxide particles, and more particularly to porous tin oxide particles comprising Nb-doped tin oxide and having relatively high electrical conductivity. [Background technology]

[0002] A polymer electrolyte fuel cell (PEFC) comprises a membrane electrode assembly (MEA) in which catalyst layers are bonded to both sides of an electrolyte membrane. Typically, a gas diffusion layer is located outside the catalyst layer. Furthermore, a current collector (separator) with a gas channel is located outside the gas diffusion layer. A PEFC typically 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.

[0003] In PEFCs, the catalyst layer generally consists of a mixture of an electrode catalyst, in which catalyst metal nanoparticles such as platinum are supported on the surface of a support, and a catalyst layer ionomer. Conventionally, carbon materials such as carbon black and acetylene black have been mainly used as catalyst supports. In particular, carbon supports with mesopores have attracted attention in recent years (Non-Patent Document 1). It has been found that by using porous carbon particles with appropriately controlled particle size and pore diameter as a support, it is possible to achieve both a reduction in catalyst poisoning by sulfonic acid groups of the ionomer and a reduction in Knudsen diffusion resistance within the support pores, thereby obtaining cell performance that does not conflict with low-load performance and high-load performance (Patent Document 1).

[0004] However, it is known that carbon supports undergo oxidative corrosion when exposed to high potentials, causing catalyst metal nanoparticles supported on the support to detach and resulting in a decrease in electrode performance. To achieve both initial performance and durability of the cell, it is necessary to fabricate porous supports using a high-potential stable material as an alternative to carbon. Therefore, it has been proposed to use high-potential stable conductive metal oxides as support materials as an alternative to carbon.

[0005] For example, Patent Document 2 describes a porous structure in which primary particles made up of aggregates of crystallites of an oxide semiconductor are linked together, with a specific surface area of ​​60 m². 2 Porous oxide semiconductor particles with a weight of 1 / g or more are disclosed. The document states that when such porous oxide semiconductor particles are used as catalyst supports in polymer electrolyte fuel cells, the detachment of catalyst metal nanoparticles due to oxidative corrosion of the support is suppressed, mass transfer within the catalyst layer is promoted, and the reduction in activity due to catalyst poisoning is suppressed.

[0006] Non-patent document 2 discloses an oxygen reduction catalyst in which Pt is supported on a support made of Sb-doped SnO2(ATO). The same document states that when such an oxygen reduction catalyst is exposed to a potential of 0.3V or less, Sb elutes from ATO.

[0007] Non-patent document 3 discloses a catalyst support for polymer electrolyte fuel cells consisting of Nb-doped SnO2 aerogel or Sb-doped SnO2 aerogel. Furthermore, the same document describes the conductivity of the entire aerogel σ based on DC resistance and electrochemical impedance measurements of the aerogel. global And the conductivity of the bulk portion σ, excluding the resistance at the particle interface. bulk They are looking for that.

[0008] The document states: (A) Sb-doped SnO2 aerogel is σ global and σ bulk The fact that they are almost equivalent (i.e., there is almost no resistance at the particle interface), and (B) Nb-doped SnO2 aerogel is σ global ga σ bulk Points that are one or two orders of magnitude lower than (i.e., where resistance exists at the particle interface). It is stated.

[0009] Non-patent document 4 discloses a catalyst for a polymer electrolyte fuel cell in which Pt is supported on a carrier made of Nb-doped SnO2. The same document discusses the origin of resistance at particle interfaces, Oxygen and water are reduced by electrons supplied from the surfaces of SnO₂ particles, oxygen species (O 2- , O - , O₂ - ) and hydroxides (OH - ) are chemically adsorbed on the surfaces of SnO₂ particles, and an electron depletion layer is formed near the interface of the SnO₂ particles in this process , as explained in the related art.

[0010] Sb-doped SnO₂ exhibits higher electrical conductivity than Nb-doped SnO₂. However, when Sb-doped SnO₂ is used under exposure to low potential, the doped Sb may be eluted. Elution of Sb may reduce the electrical conductivity of Sb-doped SnO₂. It is also a concern that eluted Sb may be adsorbed on the Pt surface or substitute with protons of sulfonic acid groups in the electrolyte membrane, thereby adversely affecting cell performance.

[0011] On the other hand, Nb-doped SnO₂ has high stability in a low-potential environment of 0.3 V or lower. However, conventional Nb-doped SnO₂ has the problem of lower electrical conductivity compared to Sb-doped SnO₂. PRIOR ART DOCUMENT PATENT DOCUMENT

[0012] PATENT DOCUMENT 1 Japanese Patent Laid-Open No.2021-084852 PATENT DOCUMENT 2 Japanese Patent Laid-Open No.2022-077821 NON-PATENT DOCUMENT

[0013] NON-PATENT DOCUMENT 1 S. Ott et al., Nature Mater., 2019, 19, 77 NON-PATENT DOCUMENT 2 D. Jalalpoor et al., J. Electrochem. Soc., 2021, 168, 024502 [Non-Patent Document 3] G. Ozouf et al., J. Mater. Sci., 2016, 51, 5305 [Non-Patent Document 4] K. Kakinuma et al., ACS Appl. Mater. Interfaces, 2019, 11, 34957 [Overview of the Initiative] [Problems that the invention aims to solve]

[0014] The problem that this invention aims to solve is to provide porous tin oxide particles made of Nb-doped SnO2 and having relatively high conductivity. [Means for solving the problem]

[0015] To solve the above problems, the porous tin oxide particles according to the present invention are It has a beaded structure in which porous primary particles, which are made up of aggregates of crystallites composed of Nb-doped SnO2, are linked together. The conductivity ratio is less than 68.4. However, the "conductivity ratio" refers to the overall conductivity of the porous tin oxide particles (σ total The conductivity (σ) inside the porous tin oxide particles relative to ) bulk ) ratio (=σ bulk / σ total ) refers to. [Effects of the Invention]

[0016] When porous tin oxide particles are produced by filling the pores of mesoporous carbon with a solution containing dissolved Sn and Nb sources (filling method), porous tin oxide particles with a low conductivity ratio can be obtained. This is thought to be because, when using the filling method, the Sn and Nb sources are uniformly filled into the pores, making it difficult for an unevenly distributed layer of Nb (high-resistance layer) to form on the particle surface. As a result, the electronic resistance at the particle interface of the porous tin oxide particles is reduced, and the overall conductivity of the particles is reduced σ total The conductivity σ inside the particle bulk It is thought that it will get closer to that. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic diagram of a method for producing beaded mesoporous Nb-SnO2 particles. [Figure 2] These are the σbulk and σtotal values ​​of the beaded mesoporous Nb-SnO2 particles obtained in Examples 1-3 and Comparative Example 1. [Figure 3] These are the CXPS and CICP of the beaded mesoporous Nb-SnO2 particles obtained in Examples 1-3 and Comparative Example 1. [Modes for carrying out the invention]

[0018] An embodiment of the present invention will be described in detail below. [1. Porous tin oxide particles] The porous tin oxide particles according to the present invention have the following configuration.

[0019] [Configuration 1] It has a beaded structure in which porous primary particles, which are made up of aggregates of crystallites composed of Nb-doped SnO2, are linked together. The conductivity ratio is less than 68.4. Porous tin oxide particles. However, the "conductivity ratio" refers to the overall conductivity of the porous tin oxide particles (σ total The conductivity (σ) inside the porous tin oxide particles relative to ) bulk ) ratio (=σ bulk / σ total) refers to.

[0020] [Configuration 2] Porous tin oxide particles according to configuration 1, wherein the concentration ratio of Nb is less than 2.6. However, the "Nb concentration ratio" refers to the average Nb concentration (C) of the porous tin oxide particles determined by ICP. ICP The Nb concentration on the surface of the porous tin oxide (C) determined by XPS for ) XPS ) ratio (=C XPS / C ICP ) refers to.

[0021] [Configuration 3] The average Nb concentration (C) of the porous tin oxide particles determined by IPC ICP Porous tin oxide particles according to composition 1 or 2, wherein the content of ) is 0.1 at% or more.

[0022] [Structure 4] The aforementioned σ total 5 x 10 -5 Porous tin oxide particles as described in any one of the three configurations 1 to 3, having a density of S / cm or higher.

[0023] [Composition 5] Specific surface area is 50 m 2 Porous tin oxide particles as described in any one of the compositions 1 to 4, having a value of / g or more.

[0024] [Composition 6] Porous tin oxide particles as described in any one of configurations 1 to 5, wherein the pore size is between 2 nm and 20 nm.

[0025] [Composition 7] Porous tin oxide particles as described in any one of configurations 1 to 6, wherein the average primary particle diameter is 0.05 μm or more and 2.0 μm or less.

[0026] [Structure 8] Porous tin oxide particles as described in any one of configurations 1 to 7, wherein the pore volume is 0.1 mL / g or more.

[0027] [Composition 9] Porous tin oxide particles as described in any one of configurations 1 to 8, wherein the average crystallite diameter is 2 nm or more and 40 nm or less.

[0028] [1.1. Primary particles] The porous tin oxide particles according to the present invention have a beaded structure in which porous primary particles, which are made up of aggregates of crystallites composed of Nb-doped SnO2, are linked together. In the present invention, "primary particles" refers to porous particles consisting of aggregates of crystallites made of pentavalent niobium-doped tin oxide (hereinafter also referred to as "Nb-SnO2"). "Porous" refers to the presence of mesopores in the spaces between crystallites. Generally, "mesopores" refer to pores with a diameter of 2 to 50 nm, but in this invention, "mesopores" also include pores with a diameter of less than 2 nm (so-called "micropores").

[0029] [1.1.1. Nb-SnO2] The crystallites constituting the primary particles are made of Nb-SnO2. Nb-SnO2 is suitable as an oxide semiconductor for constituting crystallites because it has high durability in fuel cell environments (especially in low-potential environments).

[0030] [1.1.2. Average Nb concentration] "Average Nb concentration (C ICP "Nb concentration" refers to the average Nb concentration of the entire particle, as measured by inductively coupled plasma (ICP) emission spectroscopy (hereinafter also simply referred to as "ICP").

[0031] Generally, C ICP The higher the value, the higher the conductivity of the porous tin oxide particles. To obtain high conductivity, C ICP It is preferable that the concentration be 0.1 at% or higher. ICP More preferably, this is 0.5 at% or more, 1.0 at% or more, or 1.5 at% or more. On the other hand, C ICP If the value becomes too high, carrier mobility decreases, and conductivity may decrease. Therefore, C ICPIt is preferable that the concentration be 15.0 at% or less. ICP More preferably, it is 12.5 at% or less, or 10.0 at% or less.

[0032] [1.1.3. Nb concentration ratio] "Nb concentration ratio" refers to the average Nb concentration (C) of porous tin oxide particles. ICP The Nb concentration (C) on the surface of porous tin oxide relative to ) XPS ) ratio (=C XPS / C ICP ) refers to. "Surface Nb concentrations (C XPS "Nb concentration" refers to the Nb concentration on the particle surface, measured by X-ray photoelectron spectroscopy (hereinafter also simply referred to as "XPS").

[0033] When porous tin oxide particles made of Nb-SnO2 are produced using porous carbon as a template, if the production conditions are inappropriate, Nb tends to become unevenly distributed on the particle surface. As a result, the concentration ratio of Nb increases. When Nb is unevenly distributed on the particle surface, some of the unevenly distributed Nb does not replace Sn in the SnO2 crystal lattice, and NbO2 is produced. x These exist as such. Such unevenly distributed layers of Nb cause a decrease in the conductivity of porous tin oxide particles. In contrast, the method described later can be used to suppress the uneven distribution of Nb on the particle surface. By optimizing the manufacturing conditions, the Nb concentration ratio becomes less than 2.6. By further optimizing the manufacturing conditions, the Nb concentration ratio becomes 2.4 or less, or even 2.0 or less.

[0034] [1.1.4. Average primary particle size] "Average primary particle diameter" refers to the average value of the maximum dimensions (= diameter) of primary particles. The average primary particle size can be measured by scanning electron microscopy (SEM) observation.

[0035] Generally, if the average primary particle diameter becomes too small, it becomes difficult to support the catalyst particles. Therefore, an average primary particle diameter of 0.05 μm or more is preferable. More preferably, the average primary particle diameter is 0.06 μm or more, or 0.07 μm or more. On the other hand, when using porous tin oxide particles according to the present invention as a catalyst support to manufacture a catalyst layer for a fuel cell, if the average primary particle diameter becomes too large, the thickness of the catalyst layer may increase, and the ionic resistance and electronic resistance in the catalyst layer may increase. Therefore, an average primary particle diameter of 2.0 μm or less is preferable. More preferably, the average primary particle diameter is 1.0 μm or less, or 0.5 μm or less.

[0036] [1.1.5. Average crystallite size] "Average crystallite diameter" refers to the average value of the maximum dimensions (=diameter) of crystallites. The average crystallite size can be determined from the linewidth of the X-ray diffraction peak and Scherrer's formula.

[0037] If the average crystallite size becomes too small, the pore size becomes too small. Therefore, an average crystallite size of 2 nm or more is preferable. More preferably, the average crystallite size is 3 nm or more, or 4 nm or more. On the other hand, if the average crystallite diameter becomes too large, the pore diameter becomes too large. Therefore, an average crystallite diameter of 40 nm or less is preferable. More preferably, the average crystallite diameter is 20 nm or less, or 10 nm or less.

[0038] [1.1.6. Shape of primary particles] In the present invention, the shape of the primary particles is not particularly limited. When porous tin oxide particles are produced using the method described later, the primary particles are usually not perfectly spherical, but have an irregular shape with an aspect ratio of about 1.1 to 3.

[0039] [1.2. Secondary particles] The porous tin oxide particles according to the present invention are secondary particles having a beaded structure. Here, "beaded structure" refers to a structure in which primary particles are linked together in a bead-like fashion. In secondary particles with a beaded structure, the primary particles are loosely connected to each other, resulting in relatively large voids between the primary particles. Furthermore, since primary particles consist of aggregates of fine crystallites, there are relatively fine voids (mesopores) within the primary particles.

[0040] As described later, the porous tin oxide particles according to the present invention are manufactured using mesoporous carbon as a template. Mesoporous carbon is manufactured 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.

[0041] At this time, by limiting the concentrations of the surfactant and the silica source in the reaction solution to a specific range, mesoporous silica is obtained that has a beaded structure and whose average primary particle diameter, pore diameter, pore capacity, tap density, etc., are within a specific range. When mesoporous silica with such a beaded structure is used as the first mold, mesoporous carbon with a beaded structure is obtained. Furthermore, when mesoporous carbon with a beaded structure is used as the second mold, porous tin oxide particles with a beaded structure are obtained.

[0042] [1.3. Characteristics] [1.3.1. Conductivity ratio] "Conductivity ratio" refers to the overall conductivity (σ) of porous tin oxide particles. total The conductivity (σ) inside porous tin oxide particles relative to ) bulk ) ratio (=σ bulk / σ total ) refers to.

[0043] "Overall conductivity (σ total )” means, (a) Using two stainless steel discs and a plastic jig with a cylindrical hole, porous tin oxide particles are formed. (b) While applying a pressure of 2.4 MPa to the obtained compacted powder, measure the voltage while passing a constant current through it. This refers to the conductivity obtained by doing so.

[0044] "Internal conductivity (σ bulk )” means, (a) Using two stainless steel discs and a plastic jig with a cylindrical hole, porous tin oxide particles are formed. (b) With the obtained compacted powder under a pressure of 2.4 MPa, electrochemical impedance measurements (holding voltage: 0.2 V, amplitude: 0.1 V, frequency: 10 Hz to 5 MHz) were performed. (c) Determine the value of the intercept between the high-frequency side and the real axis of the obtained Nyquist plot. This refers to the conductivity obtained by doing so.

[0045] When porous tin oxide particles are manufactured using porous carbon as a mold, if the manufacturing conditions are inappropriate, Nb tends to become unevenly distributed on the particle surface. Since the unevenly distributed Nb layer is a high-resistance layer, the unevenly distributed Nb layer present on the particle surface is σ total This can cause a decrease in [something]. On the other hand, Nb is not unevenly distributed inside the particle, and SnO2 is doped with an appropriate amount of Nb, so σ bulk It remains relatively small. Therefore, when manufacturing conditions are inappropriate, the conductivity ratio increases.

[0046] In contrast, optimizing the manufacturing conditions can suppress the uneven distribution of Nb on the particle surface. As a result, the conductivity ratio of porous tin oxide particles becomes relatively smaller. When the manufacturing conditions are optimized, the conductivity ratio becomes less than 68.4. Further optimization of the manufacturing conditions results in conductivity ratios of 60.0 or less, 50.0 or less, 40.0 or less, 30.0 or less, 20.0 or less, or 10.0 or less.

[0047] [1.3.2. Overall conductivity] Overall conductivity (σ total ) depends on the amount of Nb doping and the degree of Nb segregation on the particle surface. Optimizing the manufacturing conditions, σ total is 5 x 10 -5The result will be S / cm or higher. Further optimization of the manufacturing conditions will result in σ total 7.5 × 10 -5 S / cm or more, or 1.0 × 10 -4 The result will be S / cm or higher.

[0048] [1.3.3. Specific surface area] When using porous tin oxide particles according to the present invention as a catalyst support for PEFCs, if the specific surface area of ​​the porous tin oxide particles becomes too small, the active species of the catalyst cannot be supported in a fine, highly dispersed manner, and the effective area of ​​the catalyst becomes smaller. Therefore, the larger the specific surface area of ​​the porous tin oxide particles, the better.

[0049] The porous tin oxide particles according to the present invention have a beaded structure and mesopores within the primary particles, resulting in a larger specific surface area compared to conventional materials. When the manufacturing conditions are optimized, the specific surface area becomes 50 m². 2 The result is 60 m² or more. Further optimization of the manufacturing conditions will increase the specific surface area to 60 m². 2 / g or more, 70m 2 / g or more, or 80m 2 The result will be / g or more. Using the method described later, the specific surface area is 200 m². 2 Even porous tin oxide particles in the form of approximately / g can be synthesized.

[0050] [1.3.4. Pore diameter] "Pore diameter" refers to the average diameter of mesopores contained in primary particles, and does not include the size of voids between primary particles. The pore size is obtained by analyzing the adsorption-side data of the nitrogen adsorption isotherm of porous tin oxide particles using the BJH method, and determining the pore size (most frequent peak value, or mode pore size) when the pore volume is maximum.

[0051] Since primary particles are aggregates of fine crystallites, they have mesopores inside. When the porous tin oxide particles according to the present invention are used as a catalyst support for PEFCs, supporting the catalyst particles in the mesopores can suppress poisoning by the catalyst layer ionomer. In general, if the pore diameter of the primary particles becomes too small, it becomes difficult to supply reaction gases and protons to the catalyst supported in the pores, or it becomes difficult to discharge water produced by the reaction. Therefore, a pore diameter of 2 nm or more is preferable. More preferably, the pore diameter is 3 nm or more, or 4 nm or more. On the other hand, if the pore size becomes too large, the catalyst ionomer layer can easily penetrate into the pores, making catalyst poisoning more likely. Therefore, a pore size of 20 nm or less is preferable. More preferably, the pore size is 10 nm or less, or 7 nm or less.

[0052] [1.3.5. Pore Capacity] "Pore volume" refers to the volume of mesopores contained in primary particles, and does not include the volume of voids between primary particles. Pore ​​capacity is obtained by analyzing the adsorption data of nitrogen adsorption isotherms of porous tin oxide particles using the BJH method, and calculating it as a value of P / P0 = 0.03 to 0.99.

[0053] When the porous tin oxide particles according to the present invention are used as a catalyst support for PEFCs, if the pore volume becomes too small, the proportion of catalyst particles supported within the pores decreases. Therefore, a pore volume of 0.1 mL / g or more is preferred. More preferably, the pore volume is 0.15 mL / g or more, or 0.2 mL / g or more. On the other hand, if the pore volume becomes too large, the proportion of pore walls made of Nb-SnO2 decreases, which may reduce electronic conductivity. Also, the amount of ionomers entering the pores increases, which may reduce activity due to catalyst poisoning. Therefore, a pore volume of 1.0 mL / g or less is preferable. More preferably, the pore volume is 0.7 mL / g or less, or 0.5 mL / g or less.

[0054] [1.3.6. Tap Density] "Tap density" refers to a value measured in accordance with JIS Z 2512. When the porous tin oxide particles according to the present invention are used in the catalyst layer of a PEFC, if the tap density of the porous tin oxide particles becomes too low, the thickness of the resulting catalyst layer becomes too thick, and the proton conductivity decreases. Therefore, the tap density should be 0.005 g / cm³. 3 The above is preferable. The tap density is more preferably 0.01 g / cm³. 3 Above, or 0.05 g / cm³ 3 That's all. On the other hand, if the tap density becomes too high, it becomes difficult to secure sufficient voids within the catalyst layer to suppress flooding when the catalyst layer is fabricated using this density. Therefore, the tap density should be 1.0 g / cm³. 3 The following is preferable. The tap density is more preferably 0.75 g / cm³. 3 The following applies:

[0055] [1.4. Purpose] The porous tin oxide particles according to the present invention can be used as catalyst supports for PEFCs, catalyst supports for polymer electrolyte water electrolysis cells (PEECs), and the like. The porous tin oxide particles according to the present invention have mesopores, a large specific surface area, high conductivity, and are resistant to oxidative corrosion, making them particularly suitable as catalyst supports for PEFCs.

[0056] [2. Method for producing mesoporous silica (first mold)] In order to produce the porous tin oxide particles according to the present invention, it is first necessary to produce mesoporous silica (first mold) having a beaded structure. Such mesoporous silica is (a) Precursor particles are produced by condensation polymerization of the silica source in a reaction solution containing a silica source, a surfactant and a catalyst. (b) Separate the precursor particles from the reaction solution and dry them. (c) If necessary, the dried precursor particles are subjected to a diameter-expanding treatment. (d) Calcining the precursor particles It is obtained by doing so.

[0057] [2.1. Polycondensation process] First, the silica source is subjected to condensation polymerization in a reaction solution containing a silica source, a surfactant, and a catalyst to obtain precursor particles (condensation polymerization step).

[0058] [2.1.1. Silica Sources] In the present invention, the type of silica source is not particularly limited. Examples of silica sources 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, These are some examples. Any one of these can be used as the silica source, or a combination of two or more can be used.

[0059] [2.1.2. Surfactants] When a silica source is subjected to condensation polymerization in a reaction solution, the addition of a surfactant to the reaction solution causes the surfactant to form micelles. Because hydrophilic groups are aggregated around the micelles, the silica source is adsorbed onto the surface of the micelles. Furthermore, the micelles with the adsorbed silica source self-assemble in the reaction solution, causing the silica source to undergo condensation polymerization. As a result, mesopores are formed inside the primary particles due to the micelles. The size of the mesopores can be controlled primarily by the molecular length of the surfactant (from 1 to 50 nm).

[0060] In this invention, an alkyl quaternary ammonium salt is used as the surfactant. An alkyl quaternary ammonium salt is a compound represented by the following formula (a). CH3-(CH2) n -N + (R1)(R2)(R3)X - ...(a)

[0061] (a) In formula (a), R1, R2, and R3 each represent an alkyl group having 1 to 3 carbon atoms. R1, R2, and R3 may be the same as or different from each other. To facilitate aggregation (micelle formation) of alkyl quaternary ammonium salts, it is preferable that R1, R2, and R3 are all the same. Furthermore, it is preferable that at least one of R1, R2, and R3 is a methyl group, and it is preferable that all of them are methyl groups. (a) In formula X, X represents a halogen atom. The type of halogen atom is not particularly limited, but due to their availability, X is preferably Cl or Br.

[0062] (a) In formula n, n represents an integer from 7 to 21. Generally, the smaller n is, the smaller the central pore diameter of the mesopores, resulting in a spherical mesoporous material. On the other hand, the larger n is, the larger the central pore diameter, 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 material cannot be obtained. n is preferably 9 to 17, and more preferably 13 to 17.

[0063] Among those represented by formula (a), alkyltrimethylammonium halides are preferred. Examples of alkyltrimethylammonium halides include hexadecyltrimethylammonium halide, octadecyltrimethylammonium halide, nonyltrimethylammonium halide, decyltrimethylammonium halide, undecyltrimethylammonium halide, and dodecyltrimethylammonium halide. Among these, alkyltrimethylammonium bromide or alkyltrimethylammonium chloride is particularly preferred.

[0064] 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 acts as a template for forming mesopores within the primary particles, its type greatly affects the shape of the mesopores. To synthesize silica particles with more uniform mesopores, it is preferable to use one type of alkyl quaternary ammonium salt.

[0065] [2.1.3. Catalyst] When condensing a silica source, a catalyst is usually added to the reaction solution. When synthesizing particulate mesoporous silica, an alkali such as sodium hydroxide or aqueous ammonia may be used as the catalyst, or an acid such as hydrochloric acid may be used.

[0066] [2.1.4. Solvents] The solvent used can be water, organic solvents such as alcohol, or a mixture of water and an organic solvent. Alcohol is (1) Monohydric alcohols such as methanol, ethanol, and propanol, (2) Divalent alcohols such as ethylene glycol, (3) Trivalent alcohols such as glycerin, Either one is fine. When using a mixed solvent of water and an organic solvent, the amount of organic solvent in the mixed solvent can be arbitrarily selected depending on the purpose. Generally, adding an appropriate amount of organic solvent to the solvent makes it easier to control particle size and particle size distribution.

[0067] [2.1.5. Composition of the 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 the silica source in the reaction solution have a significant impact on the average primary particle size, pore size, pore volume, and tap density of the mesoporous silica particles.

[0068] [A. Concentration of surfactant] If the surfactant concentration is too low, the particle precipitation rate will be slow, and a structure in which primary particles are linked together will not be obtained. Therefore, the surfactant concentration must be 0.03 mol / L or higher. Preferably, the surfactant concentration is 0.035 mol / L or higher, and more preferably 0.04 mol / L or higher.

[0069] 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 needs to be 1.0 mol / L or less. Preferably, the surfactant concentration is 0.95 mol / L or less, and more preferably 0.90 mol / L or less.

[0070] [B. Concentration of silica source] If the silica source concentration is too low, the particle precipitation rate will be slow, and a structure in which primary particles are linked together will not be obtained. Alternatively, there may be an excess of surfactant, and uniform mesopores may not be obtained. Therefore, the silica source concentration needs to be 0.05 mol / L or higher. Preferably, the silica source concentration is 0.06 mol / L or higher, and more preferably 0.07 mol / L or higher.

[0071] On the other hand, if the silica source concentration is too high, the particle precipitation rate may become too fast, resulting in an excessively large primary particle size. Alternatively, sheet-like particles may be obtained instead of spherical particles. Therefore, the silica source concentration must be 1.0 mol / L or less. Preferably, the silica source concentration is 0.95 mol / L or less, and more preferably 0.9 mol / L or less.

[0072] [C. Catalyst concentration] In this invention, the catalyst concentration is not particularly limited. Generally, if the catalyst concentration is too low, the particle deposition rate will be slow. On the other hand, if the catalyst concentration is too high, the particle deposition rate will be fast. It is preferable to select the optimal catalyst concentration according to the type of silica source, the type of surfactant, the target physical properties, etc.

[0073] [2.1.6 Reaction Conditions] A silica source is added to a solvent containing a predetermined amount of surfactant, and hydrolysis and polycondensation are carried out. This allows the surfactant to function as a template, yielding precursor particles containing silica and the surfactant. The reaction conditions are selected according to the type of silica source, the particle size of the precursor particles, and other factors to ensure optimal conditions. Generally, the reaction temperature is preferably -20 to 100°C. More preferably, the reaction temperature is 0 to 90°C, and even more preferably, 10 to 80°C.

[0074] [2.2. Drying process] Next, the precursor particles are separated from the reaction solution and dried (drying step). Drying is performed to remove any residual solvent within the precursor particles. The drying conditions are not particularly limited, as long as the solvent can be removed.

[0075] [2.3. Diameter expansion process] Next, if necessary, the dried precursor particles may be subjected to a diameter-expanding process (diameter-expanding step). "Diameter-expanding process" refers to a process that enlarges the diameter of the mesopores within the primary particles. Specifically, the pore size expansion process is carried out by hydrothermally treating the synthesized precursor particles (with the surfactant still intact) in a solution containing a pore size expanding agent. This process can enlarge the pore size of the precursor particles.

[0076] Examples of diameter-expanding agents 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, These are some examples.

[0077] The reason why hydrothermal treatment in the presence of hydrocarbons expands the pore size is thought to be because silica rearrangement occurs when the pore-expanding agent is introduced from the solvent into the pores of the more hydrophobic precursor particles. Furthermore, the expansion of pore size due to hydrothermal treatment in the presence of an acid such as hydrochloric acid is thought to be due to the dissolution and reprecipitation of silica within the primary particles. Optimizing the manufacturing conditions forms radial pores within the silica. When this is subjected to hydrothermal treatment in the presence of an acid, dissolution and reprecipitation of silica occurs, and the radial pores are converted into interconnected pores.

[0078] The conditions for the pore expansion treatment are not particularly limited, as long as the desired pore size can be obtained. Typically, it is preferable to add a pore-expanding agent in a concentration of about 0.05 mol / L to 10 mol / L to the reaction solution and perform hydrothermal treatment at 60 to 150°C.

[0079] [2.4. Firing Process] Next, after performing a diameter-expanding process as necessary, the precursor particles are calcined (calcination step). This yields mesoporous silica particles with a beaded structure. Calcination is performed to dehydrate and crystallize precursor particles containing residual OH groups, and to thermally decompose surfactants remaining in the mesopores. The calcination conditions are not particularly limited, as long as dehydration, crystallization, and thermal decomposition of surfactants are possible. Calcination is usually carried out by heating in air at 400°C to 700°C for 1 to 10 hours.

[0080] [3. Method for producing mesoporous carbon (second mold)] Next, mesoporous silica with a beaded structure is used as a mold to produce mesoporous carbon (second mold) with a beaded structure. Such mesoporous carbon is (a) Prepare a mesoporous silica to serve as the first mold, (b) A silica / carbon composite is prepared by precipitating carbon in the mesopores of the mesoporous silica, (c) Remove silica from the composite It is obtained by doing so. Furthermore, in order to promote the graphitization of the obtained mesoporous carbon, the mesoporous carbon may be heat-treated at a temperature higher than 1500°C after the silica has been removed.

[0081] [3.1. First mold preparation process] First, a mesoporous silica, which will serve as the first mold, is prepared (first mold preparation step). The details of the manufacturing method for mesoporous silica are as described above, so the explanation will be omitted.

[0082] [3.2. Carbon Deposition Process] Next, carbon is deposited within the mesopores of mesoporous silica to create a silica / carbon composite (carbon deposition step). The deposition of carbon into mesopores is, specifically, (a) A carbon precursor is introduced into the mesopore, (b) Polymerize and carbonize the carbon precursor within the mesopore. This is done by [means].

[0083] [3.2.1. Introduction of carbon precursors] A "carbon precursor" refers to a substance that can produce carbon through thermal decomposition. Specifically, such carbon precursors include: (1) A polymer precursor that is liquid at room temperature and is thermopolymerizable (e.g., furfuryl alcohol, aniline, etc.), (2) A mixture of an aqueous solution of carbohydrates and an acid (for example, a mixture of monosaccharides such as sucrose, xylose, and glucose, or disaccharides, polysaccharides, and acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid), (3) A mixture of two-component curable polymer precursors (e.g., phenol and formalin), These are some examples. Among these, polymer precursors can be impregnated into mesopores without dilution with a solvent, allowing for the generation of a relatively large amount of carbon within the mesopores with a relatively small number of impregnation steps. Furthermore, they have the advantages of not requiring polymerization initiators and being easy to handle.

[0084] When using a liquid or solution carbon precursor, the amount of liquid or solution adsorbed per step is preferable to be large, and it is desirable that the entire mesopore is filled with the liquid or solution. Furthermore, when using a mixture of an aqueous solution of carbohydrates and an acid as a carbon precursor, it is preferable to use the minimum amount of acid necessary to polymerize the organic material. Furthermore, when using a mixture of two-component curable polymer precursors as the carbon precursor, the optimal ratio should be selected depending on the type of polymer precursor.

[0085] [3.2.2. Polymerization and carbonization of carbon precursors] Next, the polymerized carbon precursor is carbonized within the mesopore. Carbonization of the carbon precursor is carried out by heating 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.). The heating temperature is preferably between 500°C and 1200°C. If the heating temperature is below 500°C, the carbonization of the carbon precursor will be insufficient. On the other hand, if the heating temperature exceeds 1200°C, the silica and carbon will react, which is undesirable. The heating time should be selected to be optimal according to the heating temperature.

[0086] The amount of carbon generated within the mesopores should be greater than or equal to the amount that allows the carbon particles to maintain their shape after the mesoporous silica is removed. Therefore, if the amount of carbon generated in a single filling, polymerization, and carbonization cycle 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 the filling, polymerization, and carbonization processes are repeated multiple times, each carbonization step may be performed at a relatively low temperature, and after the final carbonization is completed, another carbonization may be performed at a higher temperature. Performing the final carbonization at a higher temperature than the previous carbonization steps makes it easier for the carbon introduced into the pores in multiple stages to integrate.

[0087] [3.3. First Mold Removal Process] Next, the first template, mesoporous silica, is removed from the composite (first template removal step). This yields mesoporous carbon with a beaded structure (second template). Specifically, the methods for removing mesoporous silica include: (1) A method of heating the composite in an alkaline aqueous solution such as sodium hydroxide, (2) A method of etching the composite with hydrofluoric acid aqueous solution, These are some examples.

[0088] [3.4. Graphitization Process] Next, if necessary, the mesoporous carbon is heat-treated at a temperature higher than 1500°C (graphitization process). When carbonizing a carbon source within the mesopores of mesoporous silica, the heat treatment temperature must be kept low in order to suppress the reaction between silica and carbon. Therefore, the degree of graphitization of the carbon after carbonization is low. To obtain a high degree of graphitization, it is preferable to heat-treat the mesoporous carbon at a high temperature after removing the first mold.

[0089] If the heat treatment temperature is too low, graphitization will be insufficient. Therefore, a heat treatment temperature of over 1500°C is preferable. Preferably, the heat treatment temperature is 1700°C or higher, and more preferably, 1800°C or higher. On the other hand, raising the heat treatment temperature unnecessarily does not make a difference in effect and is not beneficial. Therefore, the heat treatment temperature is preferably 2300°C or lower. Preferably, the heat treatment temperature is 2200°C or lower.

[0090] [4. Method for producing porous tin oxide particles] The method for producing porous tin oxide particles according to the present invention is: The first step is to prepare mesoporous carbon with a beaded structure, The second step involves precipitating Nb-SnO2 in the mesopores of mesoporous carbon to obtain an Nb-SnO2 / carbon composite, The third step involves removing carbon from the Nb-SnO2 / carbon composite. It is equipped with.

[0091] [4.1. 1st step] First, a mesoporous carbon with a beaded structure is prepared (Step 1). The details of the manufacturing method for mesoporous carbon are as described above, so the explanation will be omitted.

[0092] [4.2. 2nd step] Next, Nb-SnO2 is precipitated in the mesopores of the mesoporous carbon (second step). This yields an Nb-SnO2 / carbon composite. Specifically, the precipitation of Nb-SnO2 into the mesopore is carried out by introducing a Sn source and an Nb source (hereinafter collectively referred to as "precursors") into the mesopore and converting the precursors into Nb-SnO2.

[0093] [4.2.1. Method for introducing the precursor into the pores] Methods for introducing the precursor into the pores include: (a) A method of dispersing mesoporous carbon in a large aqueous solution containing a Sn source and a Nb source, and precipitating the Sn source and Nb source in the pores (precipitation method), (b) A method of filling the pores of mesoporous carbon with a solution containing an Sn source and an Nb source equal to the pore volume (filling method). These are some examples.

[0094] In this invention, a packing method is used to introduce the precursor into the pores. Porous tin oxide particles produced using the packing method have a lower conductivity ratio compared to those produced using the precipitation method. This is thought to be because, when using the precipitation method, the Nb source preferentially precipitates into the pores, forming an unevenly distributed layer of Nb (high-resistance layer) on the particle surface, whereas when using the packing method, such an unevenly distributed layer of Nb is less likely to form.

[0095] [4.2.2. Precursors] The precursor for producing Nb-SnO2 is (a) containing Sn or Nb, (b) It is a liquid at room temperature or soluble in a solvent at room temperature, (c) It is possible to form oxides by thermal decomposition or hydrolysis. Compounds are preferred.

[0096] For example, as an Sn source, (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(CH3COO)2 These are some examples.

[0097] For example, Nb sources include: (a) Chlorides such as NbCl5, (b) Alkoxides such as Nb(OC2H5)5 and Nb(OC4H9)5, (c) Acetylacetonate salts such as niobium acetylacetonate (Nb(CH3COCHCOCH3)5), (d) Acetates such as Nb(CH3COO)3 These are some examples.

[0098] The solvent used to dissolve the precursor is not particularly limited, as long as it can dissolve the precursor and allow the solution to fill the pores of the mesoporous carbon. Examples of solvents include ethanol, methanol, 1-propanol, 2-propanol, acetonitrile, acetone, N,N-dimethylformamide, and dimethyl sulfoxide. The concentration of the Sn or Nb source in the solution is not particularly limited, as long as it allows the solution to be packed into the pores of the mesoporous carbon. To precipitate the required amount of Nb-SnO2 in the pores with fewer packing cycles, a higher concentration of the Sn or Nb source in the solution is preferable.

[0099] [4.2.3. Conversion of Precursors to Oxides] After filling the pores of mesoporous carbon with a solution containing a precursor, heating the mesoporous carbon to a predetermined temperature causes thermal decomposition or hydrolysis of the precursor, generating Nb-SnO2 within the pores. The heating conditions are not particularly limited, as long as they are sufficient to form Nb-SnO2 within the pores.

[0100] Generally, the higher the heating temperature, the easier it is for Nb-SnO2 to form. On the other hand, if the heating temperature is too high, the crystallite size and pore size increase, making it difficult to obtain Nb-SnO2 with mesopores. Therefore, a heating temperature of 300°C to 800°C is preferable. If a sufficient amount of Nb-SnO2 cannot be formed in the pores by a single precursor packing and conversion to oxide, the packing process may be repeated multiple times, or the packing and conversion process may be repeated multiple times.

[0101] [4.3. Third step] Next, carbon is removed from the Nb-SnO2 / carbon composite (third step). This yields porous tin oxide particles according to the present invention. The method for removing carbon is not particularly limited, and various methods can be used. For example, the method for removing carbon is: (1) A method of heating Nb-SnO2 / carbon composite under an oxidizing atmosphere. (2) A method for etching the composite with oxygen plasma, These are some examples.

[0102] The removal conditions, such as heating temperature and heating time, should at least be such that the carbon is completely removed without coarsening the crystallites of Nb-SnO2.

[0103] [5. Effect] Porous tin oxide particles can be produced by introducing a Sn source and an Nb source into the pores of mesoporous carbon, generating Nb-doped SnO2 within the pores, and then removing the mesoporous carbon.

[0104] In this case, a method for introducing the Sn source and Nb source into the pores is: (a) A method of dispersing mesoporous carbon in a large aqueous solution containing a Sn source and a Nb source, and precipitating the Sn source and Nb source in the pores (precipitation method), (b) A method of filling the pores of mesoporous carbon with a solution containing an Sn source and an Nb source equal to the pore volume (filling method). These are some examples.

[0105] However, when the precipitation method is used to produce porous tin oxide particles, the conductivity ratio of the porous tin oxide particles increases. This is thought to be because, when the precipitation method is used, Nb sources preferentially precipitate into the pores. Some of the Nb that is unevenly distributed on the particle surface does not replace Sn in the SnO2 crystal lattice, and NbO x It is thought to exist as a high-resistance layer, which hinders the electron conduction of porous tin oxide particles.

[0106] In contrast, when a packing method is used to manufacture porous tin oxide particles, porous tin oxide particles with a low conductivity ratio are obtained. This is thought to be because, when using the packing method, the Sn source and Nb source are uniformly packed into the pores, making it difficult for an unevenly distributed layer of Nb (high-resistance layer) to form on the particle surface. As a result, the electronic resistance at the particle interface of the porous tin oxide particles is reduced, and the overall conductivity of the particles σ total The conductivity σ inside the particle bulk It is thought that it will get closer to that. [Examples]

[0107] (Examples 1-3, Comparative Example 1) [1. Sample Preparation] Figure 1 shows a schematic diagram of the method for producing beaded mesoporous Nb-SnO2 particles. Beaded mesoporous Nb-SnO2 particles were prepared according to the procedure shown in Figure 1.

[0108] [1.1. Fabrication of beaded starburst silica] A mixed solvent of methanol (MeOH): 4.6 g and ethylene glycol (EG): 4.6 g was mixed with 56.3 g of 30 mass% cetyltrimethylammonium chloride aqueous solution and stirred at room temperature. 8.8 g of 1 M NaOH was then added and the mixture was heated to 50°C. This solution is hereafter referred to as "Solution 1". 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 will be referred to as "solution 2" below.

[0109] The second solution was added to the first solution, which had been heated to 50°C. After the mixture became cloudy, heating was stopped and the mixture was stirred for more than 4 hours. After filtration and redispersion in purified water were repeated twice, the mixture was dried at 45°C. Furthermore, the dried powder was calcined in the air at 550°C for 6 hours to obtain beaded mesoporous silica with radial pores (hereinafter also referred to as "Connected Starburst Silica (CSS)").

[0110] [1.2. Fabrication of beaded starburst carbon] 0.5g 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 permeate the pores of the CSS. This was then heat-treated at 150°C for 24 hours to polymerize the FA. Furthermore, this was heat-treated at 500°C for 6 hours in a nitrogen atmosphere to promote the carbonization of the FA. After repeating this process twice, the CSS / carbon composite was obtained by further heat-treating at 900°C for 6 hours in a nitrogen atmosphere.

[0111] This composite was immersed in a 12% HF solution for 4 hours to dissolve the silica component. After dissolution, filtration and washing were repeated, and then it was dried at 45°C to obtain beaded mesoporous carbon with radial pores (hereinafter also referred to as "Connected Starburst Carbon (CSC)"). The resulting porous material had a BET specific surface area of ​​2122 m². 2 The values ​​were: 1.3 mL / g, pore volume, and pore diameter: 2.2 nm.

[0112] [1.3. Fabrication of beaded mesoporous Nb-SnO2 particles] [1.3.1. Example 1 (Filling Method)] NbCl5: 19.7 mg and SnCl2·2H2O: 0.8 g were dissolved in ethanol: 0.3 mL to obtain a precursor solution. 0.2 mL of this precursor solution was added to 219 mg of CSC and shaken. The CSC filled with the precursor solution was vacuum dried at 80°C for 4 hours, and then another 0.08 mL of the precursor solution was added to the CSC and shaken. This was treated in an air atmosphere at 700°C for 3 hours to obtain beaded mesoporous Nb-SnO2 particles.

[0113] [1.3.2. Example 2 (Filling Method)] 40.0 mg of NbCl5 and 0.8 g of SnCl2·2H2O were dissolved in 0.3 mL of ethanol to obtain a precursor solution. Beaded mesoporous Nb-SnO2 particles were then obtained in the same manner as in Example 1.

[0114] [1.3.3. Example 3 (Filling Method)] 83.7 mg of NbCl5 and 0.8 g of SnCl2·2H2O were dissolved in 0.3 mL of ethanol to obtain a precursor solution. Beaded mesoporous Nb-SnO2 particles were then obtained in the same manner as in Example 1.

[0115] [1.3.4. Comparative Example 1 (Precipitation Method)] A mixture was obtained by mixing 250 mL of purified water, 4 mL of concentrated hydrochloric acid (35 mass%), 5.0 g of SnCl2, and 0.074 g of NbCl5. 0.1 g of CSC was added to this mixture and dispersed. This dispersion was stirred in air at room temperature for 4 hours, and then filtered and redispersed in purified water twice. After that, it was dried at 45°C to obtain a beaded Nb-SnO2 / carbon composite. This beaded Nb-SnO2 / carbon composite was treated at 320°C for 24 hours in an air atmosphere, and then further treated at 700°C for 3 hours in an air atmosphere to obtain beaded mesoporous Nb-SnO2 particles.

[0116] [2. Test Method] [2.1. N2 adsorption measurement] The N2 adsorption isotherms of the obtained beaded mesoporous Nb-SnO2 particles were measured. From the obtained N2 adsorption isotherms, the pore size distribution was determined by the BJH method, and the mode pore size (most frequent value of pore size) was defined as the pore size of the sample. In addition, the pore volume and BET specific surface area were determined from the N2 adsorption isotherms.

[0117] [2.2. Conductivity] A compacted powder of beaded mesoporous Nb-SnO2 particles was prepared. A DC current was passed through it while applying a pressure of 2.4 MPa, and the voltage value at that time was measured to determine the overall conductivity σ of the particles. total They sought it. Furthermore, electrochemical impedance measurements (holding voltage: 0.2V, amplitude: 0.1V, frequency: 10Hz~5MHz) were performed on the same compacted powder while applying a pressure of 2.4MPa. From the intercept value of the high-frequency side of the obtained Nyquist plot with respect to the real axis, the conductivity inside the particle (conductivity excluding the resistance at the particle interface) σ was determined. bulk They sought it.

[0118] [2.3. Nb concentration] Beaded mesoporous Nb-SnO2 particles were dissolved in a solution by alkaline fusion. Using this solution as a test solution, the Nb concentration (C) contained in the beaded mesoporous Nb-SnO2 particles was determined by ICP emission spectroscopy (ICP-OES). ICP ) was quantified. Furthermore, XPS measurements revealed the Nb concentration (C) near the surface of beaded mesoporous Nb-SnO2 particles. XPS ) was quantified. Note that "Nb concentration (at%)" refers to the ratio of the number of Nb atoms to the total number of Nb and Sn atoms (=Nb × 100 / (Nb + Sn)).

[0119] [3. Results] [3.1. BET specific surface area, pore diameter, pore volume] Table 1 shows the BET specific surface area, pore diameter, and pore volume of pearl-chain-like mesoporous Nb-SnO₂ particles produced by the filling method and the precipitation method. It was found that regardless of the production method used, these physical property values are roughly the same, and if the firing temperature is the same, particles with similar structures can be obtained regardless of the production method.

[0120]

Table 1

[0121] [3.2. Electrical Conductivity] Fig. 2 shows σ of the pearl-chain-like mesoporous Nb-SnO₂ particles obtained in Examples 1 to 3 and Comparative Example 1 bulk and σ total . σ of Comparative Example 1 (particles produced by the precipitation method) total was 1.9×10 -5 S / cm. In contrast, σ of Examples 1 to 3 (particles produced by the filling method) total was 1.8×10 -4 to 2.8×10 -4 S / cm, which was about one order of magnitude higher than that of Comparative Example 1.

[0122] On the other hand, σ of Comparative Example 1 bulk is 1.3×10 -3 S / cm, while σ of Examples 1 to 3 bulk is 7.7×10 -4 to 1.2×10 -3 S / cm, and no clear difference was observed. These results indicate that particles produced by the filling method have lower resistance at the particle interface portion than those produced by the precipitation method.

[0123] [3.3. Nb Concentration] Fig. 3 shows C of the pearl-chain-like mesoporous Nb-SnO₂ particles obtained in Examples 1 to 3 and Comparative Example 1 XPS and C ICP . Since XPS measurement provides information from the particle surface to a depth of several nanometers, C XPSrepresents the Nb concentration on the surface of the particles. Meanwhile, in ICP analysis, since the entire particles are dissolved and analyzed, C ICP represents the average Nb concentration of the entire particles.

[0124] In the case of Comparative Example 1 (rosary-shaped mesoporous Nb-SnO₂ particles obtained by the precipitation method), C XPS is C ICP 2.6 times that of . Meanwhile, in the case of Examples 1 to 3 (rosary-shaped mesoporous Nb-SnO₂ particles obtained by the filling method), C XPS is C ICP 1.2 to 1.8 times that of . Furthermore, C of Comparative Example 1 XPS is 24.7 at%, whereas C of Examples 1 to 3 XPS was 3.3 to 13.0 at%.

[0125] From this, it was found that the rosary-shaped mesoporous Nb-SnO₂ particles produced by the filling method have suppressed uneven distribution of Nb on the particle surface compared to those produced by the precipitation method. As a result, the rosary-shaped mesoporous Nb-SnO₂ particles produced by the filling method have lower electronic resistance at the particle interface than those produced by the precipitation method, and the overall electrical conductivity σ of the particles total is considered to have improved by approximately one order of magnitude.

[0126] Heretofore, the embodiments of the present invention have been described in detail, but the present invention is not limited to the above embodiments in any way, and various modifications can be made without departing from the scope of the gist of the present invention. [Industrial Applicability]

[0127] The porous tin oxide particles according to the present invention can be used as a catalyst support for an air electrode catalyst layer of a polymer electrolyte fuel cell, or as a catalyst support for a fuel electrode catalyst layer thereof.

Claims

1. Nb-doped SnO 2 It has a beaded structure in which porous primary particles, which are made up of aggregates of crystallites, are linked together, The conductivity ratio is 10.0 or less. The total σ is 1.0 × 10⁻⁴ S / cm or greater. Porous tin oxide particles. however, The aforementioned "σ total" refers to the total conductivity of the porous tin oxide particles. The aforementioned "conductivity ratio" refers to the overall conductivity (σ) of the porous tin oxide particles. total The conductivity (σ) inside the porous tin oxide particles relative to ) bulk ) ratio (=σ bulk / σ total ) refers to.

2. The porous tin oxide particles according to claim 1, wherein the concentration ratio of Nb is less than 2.

6. Provided that the "Nb concentration ratio" refers to the average Nb concentration (C ICP ) of the porous tin oxide particles determined by ICP, the Nb concentration (C XPS ) on the surface of the porous tin oxide determined by XPS is the ratio (=C XPS / C ICP ).

3. The average Nb concentration (C) of the porous tin oxide particles determined by ICP ICP The porous tin oxide particles according to claim 1, wherein the content of ) is 0.1 at% or more.

4. Specific surface area is 50 m² 2 Porous tin oxide particles according to claim 1, wherein the amount is 1 / g or more.

5. Porous tin oxide particles according to claim 1, wherein the pore diameter is 2 nm or more and 20 nm or less.

6. The porous tin oxide particles according to claim 1, wherein the average primary particle diameter is 0.05 μm or more and 2.0 μm or less.

7. Porous tin oxide particles according to claim 1, wherein the pore volume is 0.1 mL / g or more.

8. Porous tin oxide particles according to claim 1, wherein the average crystallite size is 2 nm or more and 40 nm or less.

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