Porous titanium suboxide, anode catalyst, method for producing porous titanium suboxide, and method for producing anode catalyst

Abstract

Provided is a porous titanium suboxide which has a ratio of the volume of mesopores having a diameter of more than 2 nm and less than 50 nm to the total pore volume, of 50 vol % or more.

Description

Porous titanium suboxide, anode catalyst, method for producing porous titanium suboxide, and method for producing anode catalyst

[0001] The present disclosure relates to a porous titanium suboxide, an anode catalyst, a method for producing the porous titanium suboxide, and a method for producing the anode catalyst.

[0002] In recent years, development of polymer electrolyte membrane (PEM) water electrolysis devices capable of generating hydrogen as a clean energy source has progressed. PEM water electrolysis devices include an anode catalyst, a solid polymer electrolyte membrane, and a cathode catalyst. In PEM water electrolysis devices, a water decomposition reaction progresses on the anode catalyst side, and protons generated by the water decomposition reaction migrate to the cathode catalyst side via the solid polymer electrolyte membrane. The protons are then reduced by the cathode catalyst to generate hydrogen.

[0003] In such a PEM-type water electrolysis device, the anode catalyst is known to include a platinum group element as an active metal and titanium suboxide as a support for supporting the active metal (see, for example, Patent Document 1). In Example 1 of Patent Document 1, a method for producing a titanium suboxide support used in the anode catalyst is described, in which titanium dioxide powder (TiO ２ The method involves calcining the powder at high temperature in a hydrogen atmosphere.

[0004] Japanese Patent Application Laid-Open No. 2021-188095

[0005] However, such titanium suboxide supports have the drawback of low active metal loading, and when used in anode catalysts, the titanium suboxide supports must be able to suppress a decrease in catalytic activity in the highly oxidizing atmosphere at high potentials that occurs during the water decomposition reaction.

[0006] An object of the present disclosure is to provide a porous titanium suboxide, an anode catalyst, a method for producing a porous titanium suboxide, and a method for producing an anode catalyst, which can improve the amount of active metal supported and further suppress a decrease in catalytic activity.

[0007] The present disclosure [1] includes a porous titanium suboxide in which the ratio of the volume of mesopores with a pore diameter of more than 2 nm and less than 50 nm to the total pore volume is 50 vol % or more.

[0008] The present disclosure [2] is a method for producing a cellulose ester having a specific surface area of ​​100 m ２ / g or less.

[0009] The present disclosure [3] includes the porous titanium suboxide according to the above [1] or [2], in which the ratio of the volume of micropores having a pore diameter of 2 nm or less to the total pore volume is 20 vol % or less.

[0010] The present disclosure [4] is directed to the porous titanium suboxide (TiO Ｘ The porous titanium suboxide according to any one of [1] to [3] above, wherein the average oxidation degree (X) of the porous titanium suboxide is greater than 1.70 and less than 1.85.

[0011] The present disclosure [5] includes the porous titanium suboxide according to any one of [1] to [4] above, which has a volume-based average particle size of 15 μm or less.

[0012] The present disclosure [6] includes the porous titanium suboxide according to any one of the above [1] to [5], in which the standard deviation in the volume-based particle size distribution is 20% or less.

[0013] This disclosure [7] describes the volume-based mode diameter (D ｍｏｄｅ ) for the volume-based median diameter (D50) and the mode diameter (D ｍｏｄｅ ) and the ratio of the absolute value of the difference (|D50 - D ｍｏｄｅ | / D ｍｏｄｅ The porous titanium suboxide according to any one of [1] to [6] above, wherein the ρ is 0.3 or less.

[0014] The present disclosure [8] provides an anode catalyst comprising the porous titanium suboxide according to any one of the above [1] to [7] and an active metal supported on the porous titanium suboxide, wherein the active metal comprises a platinum group metal and / or an oxide thereof.

[0015] The present disclosure [9] includes the anode catalyst according to the above [8], wherein the active metal includes iridium and / or iridium oxide.

[0016] The present disclosure

[10] includes the anode catalyst according to the above [8] or [9], wherein a ratio of the initial content of the active metal per 1 g of the anode catalyst to the theoretical content of the active metal per 1 g of the anode catalyst is 90.0% or more.

[0017] The present disclosure

[11] includes a method for producing the porous titanium suboxide according to any one of the above [1] to [7], comprising a preparation step of preparing a precursor in which titanium dioxide and a cationic surfactant are composited, and a reduction step of firing the precursor in a reducing atmosphere.

[0018] The present disclosure

[12] includes the method for producing porous titanium suboxide according to the above

[11] , wherein the preparation step includes a step of aging a mixed liquid containing a titania source for forming the titanium dioxide, the cationic surfactant, and a solvent.

[0019] The present disclosure

[13] includes the method for producing porous titanium suboxide according to the above

[12] , wherein the solvent contains water.

[0020] The present disclosure

[14] includes the method for producing porous titanium suboxide according to the above

[12] , wherein the solvent includes an alcohol.

[0021] The present disclosure

[15] includes the method for producing porous titanium suboxide according to any one of the above

[11] to

[14] , wherein the molar mass of the cationic surfactant is 400 g / mol or less.

[0022] The present disclosure

[16] includes a method for producing an anode catalyst, comprising a step of supporting an active metal on the porous titanium suboxide according to any one of the above [1] to [7].

[0023] In the porous titanium suboxide of the present disclosure, the ratio of the volume of mesopores with pore diameters of 2 to 50 nm to the total pore volume is 50% by volume or more. Therefore, when such porous titanium suboxide is used as a catalyst support, the amount of active metal supported can be increased. Furthermore, by suppressing the release of the supported active metal, a decrease in catalytic activity can be suppressed.

[0024] The anode catalyst of the present disclosure comprises the porous titanium suboxide and an active metal supported on the porous titanium suboxide, the active metal being a platinum group metal and / or an oxide thereof. This allows for an increased amount of the active metal to be supported. Furthermore, by preventing the supported active metal from being liberated, a decrease in catalytic activity can be prevented.

[0025] The method for producing porous titanium suboxide of the present disclosure comprises the steps of preparing a precursor in which titanium oxide and a cationic surfactant are composited, and calcining the precursor in a reducing atmosphere. This relatively simple process makes it possible to produce porous titanium suboxide with an improved ratio of mesopore volume to total pore volume. As a result, it is possible to easily produce porous titanium suboxide that can increase the amount of active metal supported and suppress a decrease in catalytic activity.

[0026] The method for producing an anode catalyst according to the present disclosure includes a step of supporting an active metal on the porous titanium suboxide, making it possible to produce an anode catalyst with an improved amount of supported active metal through a relatively simple process.

[0027] Figure 1 shows X-ray diffraction pattern spectra of the porous titanium suboxides of Examples 1, 3, and 6 and Comparative Example 3. Figure 2 shows graphs of nitrogen adsorption isotherms of the porous titanium suboxides of Example 1 and Comparative Example 3. Figure 3 shows graphs of pore size distributions of the porous titanium suboxides of Example 1 and Comparative Example 3. Figure 4 shows SEM (scanning electron microscope) images of anode catalysts (Catalyst Example 1 and Catalyst Comparative Example 3) using the porous titanium suboxides of Example 1 and Comparative Example 3. Figure 5 shows particle size distributions of the porous titanium suboxides of Example 1, Examples 6 to 10, and Comparative Example 1.

[0028] 1. Porous titanium suboxide Porous titanium suboxide (TiO Ｘ ) is used as a support for supporting active metals in the anode catalyst of a PEM-type water electrolysis device.

[0029] The porous titanium suboxide is porous. Specifically, the porous titanium suboxide has mesopores with a pore size of more than 2 nm and less than 50 nm. The porous titanium suboxide may further have micropores with a pore size of 2 nm or less and macropores with a pore size of 50 nm or more.

[0030] The total pore volume per 1 g of porous titanium suboxide is, for example, 0.050 cc / g or more, preferably 0.100 cc / g or more, more preferably 0.120 cc / g or more, and even more preferably 0.140 cc / g or more, and from the viewpoint of durability, for example, 1.00 cc / g or less.

[0031] The total pore volume is the total volume of the micropore volume, the mesopore volume, and the macropore volume.

[0032] A porous titanium suboxide having a total pore volume per gram of porous titanium suboxide equal to or greater than the above lower limit is defined as porous.

[0033] The mesopore volume per 1 g of porous titanium suboxide is, for example, 0.050 cc / g or more, preferably 0.070 cc / g or more, more preferably 0.090 cc / g or more, even more preferably 0.095 cc / g or more, particularly preferably 0.100 cc / g or more, and, for example, 1.00 cc / g or less.

[0034] The micropore volume per 1 g of porous titanium suboxide is, for example, 0.070 cc / g or less, preferably 0.050 cc / g or less, more preferably 0.030 cc / g or less, even more preferably 0.020 cc / g or less, and for example, 0.001 cc / g or more.

[0035] The macropore volume per gram of porous titanium suboxide is, for example, 0.070 cc / g or less, preferably 0.060 cc / g or less, more preferably 0.050 cc / g or less, and for example, 0.001 cc / g or more.

[0036] The total pore volume and the volume of each pore (micropores, mesopores, macropores) can be measured by the method described in Examples. Specifically, the total pore volume and the volume of each pore (micropores, mesopores, macropores) can be calculated by analyzing a nitrogen adsorption isotherm at 77 K by BET analysis using a specific surface area / pore size distribution measuring device.

[0037] The ratio of the mesopore volume to the total pore volume of the porous titanium suboxide is, for example, 50 vol% to 100 vol%, preferably 55 vol% to 100 vol%, more preferably 60 vol% to 98 vol%, even more preferably 65 vol% to 98 vol%, and particularly preferably 70 vol% to 95 vol%.

[0038] The ratio of the volume of mesopores to the total pore volume of the porous titanium suboxide is 50 vol% or more, preferably 55 vol% or more, more preferably 60 vol% or more, even more preferably 65 vol% or more, particularly preferably 70 vol% or more, and for example, less than 100 vol%, preferably 98 vol% or less, more preferably 95 vol% or less.

[0039] When the ratio of the mesopore volume to the total pore volume of porous titanium suboxide is equal to or greater than the above lower limit, the active metal can be accommodated in the mesopores when used as a catalyst support, thereby improving the amount of the active metal supported. Furthermore, by accommodating the active metal in the mesopores, liberation of the supported active metal can be suppressed, and as a result, a decrease in catalytic activity can be suppressed.

[0040] The phrase "improving the amount of active metal carried" means that the ratio of the initial (actual) active metal content per gram of anode catalyst to the theoretical active metal content per gram of anode catalyst is high during the production process. In other words, this means that there is less loss of active metal during production.

[0041] Furthermore, the "theoretical" active metal content per gram of anode catalyst is a value calculated from the amounts of porous titanium suboxide and active metal used in preparing the anode catalyst, and is simply the amount of active metal charged per gram of anode catalyst.

[0042] The ratio of the volume of micropores to the total pore volume of the porous titanium suboxide is, for example, 0 vol % to 50 vol %, preferably 0 vol % to 40 vol %, more preferably 1 vol % to 30 vol %, even more preferably 1 vol % to 20 vol %, particularly preferably 3 vol % to 15 vol %, and most preferably 3 vol % to 10 vol %.

[0043] The ratio of the volume of micropores to the total pore volume of the porous titanium suboxide is, for example, more than 0 vol%, preferably 1 vol% or more, more preferably 3 vol% or more, and for example, 50 vol% or less, preferably 40 vol% or less, more preferably 30 vol% or less, even more preferably 20 vol% or less, particularly preferably 15 vol% or less, and most preferably 10 vol% or less.

[0044] If the ratio of the micropore volume to the total pore volume of the porous titanium suboxide is excessively high, the active metal cannot be accommodated in the micropores, and the amount of active metal supported near the surface of the porous titanium suboxide increases, leading to loss of active metal during production and use. Therefore, if the ratio of the micropore volume to the total pore volume of the porous titanium suboxide is not more than the above-mentioned upper limit, the volume ratio of mesopores can be ensured. Consequently, the amount of active metal supported can be improved and a decrease in catalytic activity can be suppressed.

[0045] The ratio of the volume of macropores to the total pore volume of the porous titanium suboxide is, for example, 0 vol % to 30 vol %, preferably 0 vol % to 28 vol %, more preferably 1 vol % to 25 vol %, and even more preferably 2 vol % to 24 vol %.

[0046] The ratio of the volume of macropores to the total pore volume of the porous titanium suboxide is, for example, more than 0 vol%, preferably 1 vol% or more, more preferably 2 vol% or more, and for example, less than 30 vol%, preferably 28 vol% or less, more preferably 25 vol% or less, and even more preferably 24 vol% or less.

[0047] When the ratio of the macropore volume to the total pore volume of the porous titanium suboxide is within the above range, the volume ratio of mesopores can be ensured, which in turn can improve the amount of active metal supported and prevent a decrease in catalytic activity.

[0048] The ratio of the volume of micropores to the volume of mesopores of the porous titanium suboxide (micropore volume / mesopore volume) is, for example, less than 1.0, preferably 0.80 or less, more preferably 0.50 or less, even more preferably 0.30 or less, and particularly preferably 0.20 or less.

[0049] The ratio of the macropore volume to the mesopore volume of the porous titanium suboxide (macropore volume / mesopore volume) is, for example, less than 0.60, preferably 0.50 or less, more preferably 0.45 or less, even more preferably 0.40 or less, and particularly preferably 0.35 or less.

[0050] In addition, porous titanium suboxide (TiO Ｘ ) is titanium dioxide (TiO ２ ) contains titanium oxide with a lower oxidation number.

[0051] Specifically, the main component of the porous titanium suboxide is, for example, Ti ４ O ７ (oxidation number: 1.75). The main component is Ti in the total amount of porous titanium suboxide. ４ O ７ This indicates that the content of is 50 mass % or more.

[0052] Porous titanium suboxide is Ti ４ O ７ The titanium oxide (other component) may contain titanium oxide having an oxidation number other than TiO. ２ (oxidation number: 2), Ti ３ O ５ (oxidation number: 1.67), Ti ５ O ９ (oxidation number: 1.80), Ti ６ O １１ (oxidation number: 1.83), and Ti ８ O １５ (oxidation number: 1.86). From the viewpoint of electrical conductivity, Ti３ O ５ It is preferable that it does not contain fluorine-containing iodide (oxidation number: 1.67).

[0053] Ti in the total amount of porous titanium suboxide ４ O ７ The content is, for example, 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0054] The components contained in the porous titanium suboxide can be confirmed by powder X-ray diffraction. Specifically, if there are peaks in the diffraction pattern at around 2θ=22.8° and 2θ=26.4°, the components are Ti. ６ O １１ If peaks exist near 2θ=22.0° and 2θ=26.4°, it can be determined that the sample contains titanium suboxide. ５ O ９ If peaks exist around 2θ=20.8° and 2θ=26.4°, it can be determined that the sample contains titanium suboxide. ４ O ７ If peaks are present around 2θ=18.9° and 2θ=26.4°, it can be determined that the sample contains titanium suboxide. ３ O ５ If peaks exist near 2θ=27.5° and 2θ=36.1°, it can be determined that the sample contains titanium dioxide (TiO ２ ) can be determined to be included.

[0055] Porous titanium suboxide (TiO Ｘ The average oxidation degree (X) of the hydroxybenzoates is, for example, 1.65 or more, preferably 1.70 or more, more preferably more than 1.70, even more preferably 1.73 or more, particularly preferably 1.75 or more, and for example, less than 2.00, preferably 1.90 or less, more preferably 1.85 or less, even more preferably less than 1.85, particularly preferably 1.80 or less, and most preferably less than 1.80.

[0056] Porous titanium suboxide (TiO ＸWhen the average oxidation degree (X) of the porous titanium suboxide is within the above range, when the porous titanium suboxide is used as a catalyst support, the porous titanium suboxide has good electrical conductivity, improving the charge transfer efficiency and, as a result, improving the catalytic efficiency.

[0057] In addition, porous titanium suboxide (TiO Ｘ The average oxidation degree (X) of porous titanium suboxide (TiO) can be measured by the method described in the Examples. Ｘ The average oxidation degree (X) of the cellulose acetate solution can be calculated based on the carbon content measured using a total organic carbon analyzer and the weight change due to the heat treatment measured using a thermogravimetric analyzer.

[0058] The crystallite diameter of the porous titanium suboxide is, for example, 70 nm or less, preferably 60 nm or less, more preferably 55 nm or less, and even more preferably 50 nm or less, and for example, 10 nm or more.

[0059] The crystallite refers to the smallest unit of a crystal grain that can be regarded as a single crystal. The crystallite diameter of porous titanium suboxide can be calculated using the position of the diffraction peak in X-ray diffraction and the half-width of the peak according to the Scherrer formula below. In the examples described below, the crystallite diameter of the main component Ti ４ O ７ The crystallite size is calculated based on the peak information around 2θ=20.8°, which is a peak specific to the structure. Scherrer formula: D=Kλ / Bcosθ D: crystallite size (nm) K: Scherrer constant (0.90) λ: X-ray wavelength (nm) B: diffraction line width (rad) θ: Bragg angle (rad)

[0060] The carbon content in the porous titanium suboxide is, for example, 10% by mass or less, preferably 8.0% by mass or less, more preferably 6.0% by mass or less, even more preferably 5.0% by mass or less, particularly preferably 3.0% by mass or less, and most preferably 2.5% by mass or less, and for example, 0% by mass or more.

[0061] Porous titanium suboxide contains carbon due to the manufacturing method. As will be described in detail later, when a titanium suboxide precursor contains an organic substance, the carbon in the organic substance remains in the porous titanium suboxide manufactured by reducing the titanium suboxide precursor. Therefore, the porous titanium suboxide contains carbon.

[0062] If the carbon content in the porous titanium suboxide is excessively high, when the porous titanium suboxide is used as a catalyst support, depending on the environment in which the catalyst is used, the carbon in the porous titanium suboxide may be decomposed, causing the supported active metal to be liberated. Therefore, if the carbon content in the porous titanium suboxide is equal to or less than the above upper limit, the liberation of the active metal can be suppressed, and as a result, a decrease in catalytic activity can be suppressed.

[0063] The specific surface area of ​​the porous titanium suboxide is, for example, 10 m ２ / g or more, preferably 20m ２ / g, more preferably 25m ２ / g or more, more preferably 30m ２ / g or more, particularly preferably 40m ２ / g or more, for example, 200m ２ / g or less, preferably 150m ２ / g or less, more preferably 120m ２ / g or less, more preferably 100m ２ / g or less, particularly preferably 80m ２ / g or less.

[0064] If the specific surface area of ​​the porous titanium suboxide is equal to or greater than the lower limit, the amount of active metal supported can be increased. If the specific surface area of ​​the porous titanium suboxide is equal to or less than the upper limit, it is considered that the amount of residual carbon can be controlled, and a decrease in catalytic activity can be suppressed.

[0065] The specific surface area of ​​the porous titanium suboxide can be measured by the method described in the Examples. Specifically, the specific surface area of ​​the porous titanium suboxide can be calculated by analyzing the nitrogen adsorption isotherm at 77 K by BET analysis using a specific surface area / pore size distribution measuring device.

[0066] The average particle diameter (Dv) of the secondary particles of the porous titanium suboxide is, for example, 50 μm or less, preferably 30 μm or less, more preferably 25 μm or less, even more preferably 20 μm or less, and particularly preferably 15 μm or less. The lower limit of the average particle diameter (Dv) of the secondary particles of the porous titanium suboxide is not particularly limited, but is, for example, 0.1 μm or more.

[0067] The average particle size (Dv) of the secondary particles of porous titanium suboxide is expressed as the product of the particle size (μm) and the frequency (%) in the volume-based particle size distribution.

[0068] When the average particle size (Dv) of the secondary particles of the porous titanium suboxide is equal to or less than the upper limit, the dispersibility of the anode catalyst can be improved when the anode catalyst is used in a PEM water electrolysis system, and the coatability of the anode catalyst can be improved. In addition, steps such as pulverization and classification are not required, thereby improving manufacturability.

[0069] The standard deviation (σDv) of the volumetric particle size distribution of the porous titanium suboxide secondary particles is, for example, 50% or less, preferably 40% or less, more preferably 30% or less, even more preferably 20% or less, and particularly preferably 15% or less. The lower limit of the standard deviation (σDv) of the volumetric particle size distribution of the porous titanium suboxide secondary particles is not particularly limited, but is, for example, 0.01% or more.

[0070] The standard deviation (σDv) in the volume-based particle size distribution of the secondary particles of porous titanium suboxide indicates the degree of variation in the particle diameter of the secondary particles of porous titanium suboxide.

[0071] When the standard deviation (σDv) of the volume-based particle size distribution of the secondary particles of porous titanium suboxide is equal to or less than the upper limit, the particle size of the secondary particles of porous titanium suboxide can be made uniform, thereby suppressing variations in the amount of active metal supported on the porous titanium suboxide and improving the catalytic activity and durability of the anode catalyst.

[0072] The median diameter (D50) of the secondary particles of the porous titanium suboxide is, for example, 30 μm or less, preferably 20 μm or less, more preferably 15 μm or less, even more preferably 10 μm or less, and particularly preferably 8.0 μm or less. The lower limit of the median diameter (D50) of the secondary particles of the porous titanium suboxide is not particularly limited, but is, for example, 0.1 μm or more.

[0073] The median diameter (D50) of the secondary particles of porous titanium suboxide is the particle diameter at which the volume cumulative frequency reaches 50% from the small diameter side in the volume-based particle size distribution.

[0074] When the median diameter (D50) of the secondary particles of the porous titanium suboxide is equal to or less than the upper limit, the dispersibility of the anode catalyst can be improved when the anode catalyst is used in a PEM water electrolysis system, and the coatability of the anode catalyst can be improved. In addition, steps such as pulverization and classification are not required, thereby improving manufacturability.

[0075] The median diameter (D10) of the secondary particles of the porous titanium suboxide is, for example, 10 μm or less, preferably 5.0 μm or less. The lower limit of the median diameter (D10) of the secondary particles of the porous titanium suboxide is not particularly limited, but is, for example, 0.01 μm or more.

[0076] The median diameter (D10) of the secondary particles of porous titanium suboxide is the particle diameter at which the volume cumulative frequency reaches 10% from the small diameter side in the volume-based particle size distribution.

[0077] The median diameter (D90) of the secondary particles of the porous titanium suboxide is, for example, 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less. The lower limit of the median diameter (D90) of the secondary particles of the porous titanium suboxide is not particularly limited, but is, for example, 0.3 μm or more.

[0078] The median diameter (D90) of the secondary particles of porous titanium suboxide is the particle diameter at which the volume cumulative frequency reaches 90% from the small diameter side in the volume-based particle size distribution.

[0079] The mode diameter (D ｍоｄｅ) is, for example, 30 μm or less, preferably 20 μm or less, more preferably 15 μm or less, even more preferably 10 μm or less, and particularly preferably 8.0 μm or less. ｍоｄｅ The lower limit of the thickness is not particularly limited, but is, for example, 0.1 μm or more.

[0080] The mode diameter (D ｍоｄｅ ) is the most frequent particle size in the volume-based particle size distribution.

[0081] The mode diameter (D ｍоｄｅ ) is equal to or less than the upper limit, the dispersibility of the anode catalyst can be improved when the anode catalyst is used in a PEM water electrolysis device, and the coatability of the anode catalyst can be improved. In addition, steps such as pulverization and classification are not required, and productivity can be improved.

[0082] The particle size distribution of the secondary particles of porous titanium suboxide can be obtained by a laser diffraction / scattering method. That is, the average particle diameter (Dv), its standard deviation (σDv), median diameter (D50), median diameter (D10), median diameter (D90), and mode diameter (D ｍоｄｅ ) can be determined based on the particle size distribution obtained by a laser diffraction / scattering method. More specifically, it can be determined by the method described in the Examples.

[0083] The median diameter (D50) and mode diameter (D ｍоｄｅ ) and the absolute value of the difference (|D50 - D ｍｏｄｅ |) is, for example, 20 μm or less, preferably 10 μm or less, more preferably 5.0 μm or less, and even more preferably 3.0 μm or less, and is, for example, 0 μm or more.

[0084] The median diameter (D50) and mode diameter (D ｍоｄｅ ) and the absolute value of the difference (|D50 - D ｍｏｄｅWhen |) is equal to or less than the upper limit, the particle size distribution of the secondary particles of the porous titanium suboxide is sharp and the particle diameter of the secondary particles of the porous titanium suboxide is uniform. Therefore, variation in the amount of the active metal supported on the porous titanium suboxide can be suppressed, and the catalytic activity and durability of the anode catalyst can be improved.

[0085] In the secondary particles of porous titanium suboxide, the mode diameter (D ｍоｄｅ ) for the median diameter (D50) and mode diameter (D ｍоｄｅ ) and the ratio of the absolute value of the difference (|D50 - D ｍｏｄｅ | / D ｍоｄｅ ) is, for example, 0.5 or less, preferably 0.4 or less, more preferably 0.3 or less, more preferably 0.2 or less, and, for example, 0 or more.

[0086] In the secondary particles of porous titanium suboxide, the mode diameter (D ｍоｄｅ ) for the median diameter (D50) and mode diameter (D ｍоｄｅ ) and the ratio of the absolute value of the difference (|D50 - D ｍｏｄｅ | / D ｍоｄｅ ) is equal to or less than the upper limit, the particle size distribution of the secondary particles of the porous titanium suboxide is close to a normal distribution, and the particle diameter of the secondary particles of the porous titanium suboxide is uniform. Therefore, variation in the amount of the active metal supported on the porous titanium suboxide can be suppressed, and the catalytic activity and durability of the anode catalyst can be improved.

[0087] 2. Method for Producing Porous Titanium Suboxide A method for producing the porous titanium suboxide will now be described.

[0088] The method for producing porous titanium suboxide includes a step of preparing a precursor in which titanium dioxide and a cationic surfactant are combined (preparation step), and a step of firing the precursor in a reducing atmosphere (reduction step).

[0089] (Preparation Step) In the preparation step, a precursor in which titanium dioxide and a cationic surfactant are composited is prepared.

[0090] Specifically, a titania source is added to a solution in which a cationic surfactant is dissolved in a solvent to prepare a mixed solution. The resulting mixed solution (containing the titania source and the cationic surfactant) is aged to form a composite of titanium dioxide and the cationic surfactant. If necessary, the titania source may be mixed with a chelating agent in advance and then mixed with the solution in which the cationic surfactant is dissolved in a solvent.

[0091] The titania source is not particularly limited as long as it is a titanium compound that forms titanium dioxide upon hydrolysis. Examples of the titania source include organic titanium compounds and inorganic titanium compounds. The titania source is preferably water-soluble.

[0092] Examples of organic titanium compounds include titanium alkoxides. Examples of titanium alkoxides include titanium ethoxide, titanium propoxide, titanium isopropoxide, titanium butoxide, titanium tetrabutoxide, titanium tetrapropoxide, titanium tetraisopropoxide, titanium tetraisobutoxide, and titanium tetraisopropenyl oxide. Preferably, titanium tetraisopropoxide is used.

[0093] Inorganic titanium compounds include, for example, titanium tetrachloride, titanium tetranitrate, and titanyl sulfate.

[0094] Examples of cationic surfactants include surfactants having an amino group in the molecular structure and surfactants having a quaternary ammonium salt in the molecular structure.

[0095] Furthermore, from the viewpoint of reducing the carbon content remaining in the porous titanium suboxide, it is preferable that the carbon chain length of the cationic surfactant is not excessively long. The carbon chain length of the cationic surfactant is, for example, 20 or less, preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less, and for example, 4 or more, preferably 6 or more, more preferably 8 or more, and even more preferably 10 or more.

[0096] When the carbon chain length of the cationic surfactant is equal to or less than the upper limit, the carbon content of the porous titanium suboxide can be reduced, thereby suppressing a decrease in catalytic activity.When the carbon chain length of the cationic surfactant is equal to or greater than the lower limit, the titanium dioxide and the cationic surfactant are appropriately composited, and porous titanium suboxide can be obtained.

[0097] Examples of surfactants having an amino group in their molecular structure include monoamines such as hexadecylamine, tetradecylamine, dodecylamine, decylamine, and octaneamine, and diamines such as 1,12-dodecanediamine, 1,10-decanediamine, 1,8-octanediamine, and 1,6-hexanediamine. Preferred are 1,12-dodecanediamine, 1,10-decanediamine, and dodecylamine.

[0098] Examples of surfactants having a quaternary ammonium salt in their molecular structure include hexadecyltrimethylammonium salt, tetradecyltrimethylammonium salt, dodecyltrimethylammonium salt, decyltrimethylammonium salt, n-octyltrimethylammonium salt, and halides thereof, with dodecyltrimethylammonium bromide being preferred.

[0099] The molar mass of the cationic surfactant is, for example, 80 g / mol or more, preferably 100 g / mol or more, more preferably 120 g / mol or more, even more preferably 140 g / mol or more, particularly preferably 160 g / mol or more, and for example, 400 g / mol or less, preferably 350 g / mol or less, more preferably 320 g / mol or less.

[0100] When the molar mass of the cationic surfactant is equal to or less than the upper limit, the carbon content of the porous titanium suboxide can be reduced, thereby suppressing a decrease in catalytic activity.When the molar mass of the cationic surfactant is equal to or more than the lower limit, the titanium dioxide and the cationic surfactant are appropriately composited, and porous titanium suboxide can be obtained.

[0101] Examples of the solvent include water and organic solvents. The solvents may be used alone or in combination of two or more.

[0102] Examples of water include ion-exchanged water, distilled water, and ultrapure water.

[0103] The organic solvent is preferably a water-soluble organic solvent, such as an alcohol, a ketone, or a nitrogen-containing solvent.

[0104] Examples of alcohols include monohydric alcohols, polyhydric alcohols, and polyhydric alcohol alkyl ethers. Examples of monohydric alcohols include methanol, ethanol, 1-propanol, 2-propanol, tert-butanol, and diacetone alcohol. Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, propylene glycol (1,2-propanediol), 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, triethylene glycol, glycerin, polyethylene glycol, and polypropylene glycol. Examples of polyhydric alcohol alkyl ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, and dipropylene glycol monoethyl ether.

[0105] Examples of ketones include acetone and 4-hydroxy-4-methyl-2-pentanone. Examples of nitrogen-containing solvents include N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone.

[0106] The solvent may, for example, contain water. Preferably, the solvent consists of water or contains water and an organic solvent. When the solvent contains water and an organic solvent, it more preferably contains water and a water-soluble organic solvent. Even more preferably, it contains water and an alcohol. Especially preferably, it contains water and a monohydric alcohol. Most preferably, it contains water and 2-propanol.

[0107] By adjusting the composition of the solvent, it is possible to control the particle size distribution of the porous titanium suboxide, and the average particle diameter (Dv), its standard deviation (σDv), median diameter (D50), median diameter (D10), median diameter (D90), and mode diameter (D ｍоｄｅ In particular, if the solvent contains an organic solvent, the particle size distribution of the porous titanium suboxide can be controlled, and the average particle diameter (Dv), its standard deviation (σDv), median diameter (D50), median diameter (D10), median diameter (D90), and mode diameter (D ｍоｄｅ ) can be set to a desired range.

[0108] An aqueous alkaline solution may be added to the solvent to adjust the pH, such as aqueous ammonia and aqueous sodium hydroxide.

[0109] Examples of chelating agents include acetylacetone and triethanolamine. By premixing the titania source and the chelating agent, the rates of hydrolysis and polycondensation can be controlled, enabling uniform complexation with the surfactant.

[0110] The amount of the titania source mixed per 1 mol of the chelating agent is, for example, 0.1 mol or more, preferably 0.2 mol or more, more preferably 0.3 mol or more, and for example, 3 mol or less, preferably 1 mol or less, more preferably 0.8 mol or less.

[0111] In the preparation step, aging promotes the formation of a complex between titanium dioxide and the cationic surfactant. During aging, the mixed solution may be left to stand or may be stirred. The aging temperature is, for example, 20°C to 150°C, preferably 50°C to 100°C. The aging time is 1 hour to 120 hours.

[0112] After aging, the resulting gel-like solid is collected, and the washing and collection procedure is repeated. The collected sample is then dried to obtain a precursor in which titanium dioxide and a cationic surfactant are combined.

[0113] (Reduction Step) In the reduction step, the precursor is fired in a reducing atmosphere.

[0114] Specifically, a precursor in which titanium dioxide and a cationic surfactant are combined is fired in a state in which a reducing gas is passed through, thereby preparing porous titanium suboxide.

[0115] When a precursor composite of titanium dioxide and a cationic surfactant is calcined in a state where a reducing gas is passed through it, part of the cationic surfactant functions as a reducing agent while thermal decomposition proceeds, which causes a templating effect and enables the production of porous titanium suboxide with a high volume fraction of mesopores.

[0116] Examples of reducing gases include hydrogen gas and carbon monoxide gas. The flow rate of the reducing gas is, for example, 1 mL / min to 1000 mL / min per 1 g of precursor. An inert gas (e.g., argon gas) may be added to the reducing gas. This allows the average oxidation degree of the porous titanium suboxide to be adjusted.

[0117] The precursor can be fired using a heating device such as an electric furnace. The firing temperature is, for example, 800°C to 1200°C. The firing time is, for example, 0.5 hours to 10 hours. The firing time indicates the holding time in the examples.

[0118] In this manner, porous titanium suboxide can be obtained.

[0119] In this embodiment, the method for producing porous titanium suboxide includes a preparation step and a reduction step, but may also include other steps, such as a step of pulverizing the obtained porous titanium suboxide (pulverization step), a step of washing (washing step), and a step of classifying (classification step), as necessary. Preferably, the method does not include the pulverization step and the classification step.

[0120] 3. Anode Catalyst Anode catalysts promote oxidation reactions in polymer electrolyte membrane (PEM) water electrolysis devices. Specifically, the anode catalyst in a PEM water electrolysis device promotes the following water decomposition reaction: ２ O → O ２ +4H ＋ +4e －

[0121] The anode catalyst comprises the porous titanium suboxide and an active metal supported on the porous titanium suboxide. That is, in the anode catalyst, the porous titanium suboxide serves as a support for supporting the active metal.

[0122] [Support] The support in the anode catalyst includes porous titanium suboxide, and is preferably porous titanium suboxide.

[0123] If the support in the anode catalyst contains porous titanium suboxide, the active metal can be accommodated in the mesopores, thereby improving the amount of the active metal supported. Furthermore, by accommodating the active metal in the mesopores, the release of the supported active metal can be suppressed, and as a result, the decrease in catalytic activity can be suppressed.

[0124] The support in the anode catalyst may contain a support other than the porous titanium suboxide, but preferably does not contain any other support.

[0125] Examples of other carriers include silica, alumina, titania, and zeolite. Titania refers to titanium dioxide. The other carriers may be used alone or in combination of two or more.

[0126] [Active Metal] The active metal is supported on the catalyst support and promotes the water decomposition reaction, in other words, the active metal has activity in the water decomposition reaction.

[0127] The active metal is not particularly limited as long as it is a metal and / or metal oxide that promotes the water decomposition reaction. The active metal preferably includes a platinum group metal and / or an oxide thereof. The active metal may be used alone or in combination of two or more kinds.

[0128] Examples of platinum group metals include iridium, ruthenium, and palladium. Preferably, iridium is used. That is, the active metal preferably includes iridium and / or iridium oxide.

[0129] The active metal is, for example, a particle. The crystallite diameter of the active metal particles is, for example, 0.1 nm to 50 nm, preferably 0.5 nm to 45 nm, more preferably 1.0 nm to 40 nm. The crystallite diameter of the active metal particles is, for example, 0.1 nm or more, preferably 0.5 nm or more, more preferably 1.0 nm or more, and for example, less than 50 nm, preferably 45 nm or less, more preferably 40 nm or less.

[0130] The crystallite diameter of the active metal, like the crystallite diameter of porous titanium suboxide, can be calculated using the Scherrer equation from the position of the diffraction peak in X-ray diffraction and the half-width of the peak. The active metal typically exhibits a peak in the range of 2θ = 20° to 50°. Specifically, when the active metal is iridium, a peak appears near 2θ = 40.6°, and when the active metal is tetravalent iridium oxide, a peak appears near 2θ = 27.3°. If the active metal peak is not located at a fixed position, the diffraction peaks before and after the active metal is loaded on the porous titanium suboxide are compared, and the peak with the highest detected intensity among the peaks that newly appear after the active metal is loaded on the porous titanium suboxide is considered to be the active metal peak. The active metal particles are crystalline nanoparticles, and the crystallite diameter of the active metal can be approximated to the average primary particle diameter of the active metal.

[0131] The initial active metal content per 1 g of the anode catalyst is, for example, 0.01 g or more, preferably 0.10 g or more, more preferably 0.20 g or more, still more preferably 0.27 g or more, and particularly preferably 0.30 g or more.

[0132] The initial active metal content per gram of anode catalyst refers to the active metal content per gram of anode catalyst after production, before use as a catalyst.

[0133] From the viewpoint of improving catalytic function, the initial active metal content in the anode catalyst is, for example, 1 mass % or more, preferably 10 mass % or more, more preferably 20 mass % or more, even more preferably 27 mass % or more, and particularly preferably 30 mass % or more. From the viewpoint of cost reduction, the initial active metal content in the anode catalyst is, for example, 70 mass % or less, preferably 60 mass % or less, more preferably 50 mass % or less.

[0134] The ratio of the initial active metal content per gram of anode catalyst to the theoretical active metal content per gram of anode catalyst ((initial active metal content per gram of anode catalyst) / (theoretical active metal content per gram of anode catalyst)×100(%)) is, for example, 81.0% or more, preferably 83.0% or more, more preferably 85.0% or more, even more preferably 90.0% or more, particularly preferably 93.0% or more, and most preferably 95.0% or more.

[0135] When the ratio of the initial active metal content per gram of anode catalyst to the theoretical active metal content per gram of anode catalyst ((initial active metal content per gram of anode catalyst) / (theoretical active metal content per gram of anode catalyst)×100(%)) is equal to or greater than the lower limit, loss of active metal during production is small, and the active metal content can be improved. Furthermore, an increase in production costs due to loss of active metal can be suppressed.

[0136] The theoretical active metal content per gram of anode catalyst is calculated from the weight of the active metal raw material used in producing the anode catalyst and the amount (weight) of the anode catalyst used.

[0137] The ratio of the active metal content per gram of anode catalyst after evaluation to the initial active metal content per gram of anode catalyst ((active metal content per gram of anode catalyst after evaluation) / (initial active metal content per gram of anode catalyst)×100(%)) is, for example, 60.0% or more, preferably 70.0% or more, more preferably 80.0% or more, even more preferably 85.0% or more, particularly preferably 93.0% or more, and most preferably 95.0% or more.

[0138] When the ratio of the evaluated active metal content per gram of anode catalyst to the initial active metal content per gram of anode catalyst ((evaluated active metal content per gram of anode catalyst) / (initial active metal content per gram of anode catalyst)×100(%)) is equal to or greater than the lower limit, liberation of the active metal when used as an anode catalyst can be suppressed, thereby suppressing a decrease in catalytic activity. In addition, an increase in production costs due to loss of the active metal can be suppressed.

[0139] The content of active metals per gram of anode catalyst after evaluation refers to the content of active metals per gram of anode catalyst after production and use as a catalyst.

[0140] The initial active metal content per gram of the anode catalyst and the active metal content per gram of the anode catalyst after evaluation are specifically measured by the method described in the Examples.

[0141] [Additives] Additives may be added to the anode catalyst as needed.

[0142] The additives are not particularly limited as long as they are additives that are commonly used in anode catalysts, and examples thereof include diluents and binders.

[0143] The diluent component is a substance that is inert to the water splitting reaction, and adding the diluent component to the anode catalyst makes it easier to control the temperature and also increases the surface area of ​​the anode catalyst.

[0144] Examples of the diluent component include alumina (e.g., α-alumina, θ-alumina, γ-alumina, etc.) and titania (e.g., rutile-type titania, anatase-type titania, etc.). Titania refers to titanium dioxide. The diluent component may be used alone or in combination of two or more types.

[0145] The binder is, for example, a binding component for binding the anode catalyst together.

[0146] Examples of binders include silicates, titanates, aluminates, etc. The binders may be used alone or in combination of two or more.

[0147] The ratio of the diluent and binder to be added may be selected arbitrarily.

[0148] 4. Method for Producing Anode Catalyst Next, a method for producing the anode catalyst of the present disclosure will be described.

[0149] The method for producing an anode catalyst includes a step of supporting an active metal on the porous titanium suboxide.

[0150] The step of supporting an active metal on porous titanium suboxide is not particularly limited as long as it is a method commonly used in the production of anode catalysts.

[0151] Specifically, the method for producing an anode catalyst (a step of supporting an active metal on porous titanium suboxide) includes a step (first step) of mixing a slurry containing porous titanium suboxide with a solution containing an active metal to prepare a mixed slurry, and a step (second step) of supporting the active metal on the porous titanium suboxide and then drying the mixture to obtain an anode catalyst.

[0152] (First Step) In the first step, a slurry containing porous titanium suboxide and a solution containing an active metal are mixed to prepare a mixed slurry.

[0153] The slurry containing porous titanium suboxide can be prepared, for example, by dispersing porous titanium suboxide in a solvent.

[0154] The solvent is not particularly limited as long as it can disperse porous titanium suboxide, and examples thereof include water (e.g., ion-exchanged water and ultrapure water) and organic solvents. Examples of organic solvents include alcohol, acetone, dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, and dioxane. Examples of alcohols include monohydric water-soluble alcohols (e.g., methanol, ethanol, and propanol) and dihydric or higher water-soluble alcohols (e.g., ethylene glycol and glycerin). The solvent is preferably an organic solvent, more preferably an alcohol, and even more preferably ethylene glycol.

[0155] The slurry containing porous titanium suboxide may contain additives to improve dispersibility, such as a pH adjuster (e.g., sodium acetate), a chelating agent, and a dispersant.

[0156] The content (concentration) of porous titanium suboxide in the slurry containing porous titanium suboxide is, for example, 0.1 mass% or more, preferably 0.3 mass% or more, more preferably 0.5 mass% or more, and for example, 10 mass% or less, preferably 5 mass% or less, more preferably 3 mass% or less.

[0157] The solution containing the active metal can be prepared, for example, by mixing a salt of the active metal with a solvent.

[0158] Examples of salts of active metals include organic acid salts of active metals and inorganic salts of active metals. Examples of organic acid salts include acetates and oxalates. Examples of inorganic salts include sulfates, nitrates, chlorides, and phosphates. Examples of salts of active metals include preferably inorganic salts of active metals. More preferably, examples of salts of active metals include chlorides of active metals.

[0159] The active metal salt includes a salt of a platinum group metal, preferably an iridium salt, and more preferably iridium chloride. The active metal salt may also include a salt of an active metal other than a platinum group metal.

[0160] The solvent is not particularly limited as long as it is one that is normally used in preparing a solution containing an active metal, and examples thereof include the solvents used in preparing the above-mentioned slurry containing porous titanium suboxide. The solvent used in the solution containing an active metal is preferably water, and more preferably ion-exchanged water.

[0161] A mixed slurry can be prepared by mixing the above-mentioned slurry containing porous titanium suboxide with the above-mentioned solution containing active metal. In preparing the mixed slurry, ultrasonic treatment is preferably carried out in order to improve the dispersibility of the porous titanium suboxide.

[0162] The slurry containing the porous titanium suboxide and the solution containing the active metal are mixed so that the amount of active metal salt per 1 g of porous titanium suboxide is, for example, 0.01 g or more, preferably 0.1 g or more, more preferably 0.3 g or more, even more preferably 0.5 g or more, and for example, 5 g or less, preferably 3 g or less, more preferably 2 g or less, even more preferably 1 g or less.

[0163] In this way, a mixed slurry containing porous titanium suboxide and active metal is obtained.

[0164] (Second Step) In the second step, the active metal is supported on the porous titanium suboxide, and then the porous titanium suboxide is dried to obtain an anode catalyst.

[0165] Specifically, the mixed slurry is heated while being stirred, then cooled to room temperature, and the solid content is recovered by centrifugation, washed, and then dried.

[0166] The heating temperature of the mixed slurry is, for example, 80° C. to 200° C. The heating time of the mixed slurry is, for example, 1 hour to 15 hours.

[0167] Before heating, a reducing agent such as formic acid can be added to the mixed slurry. The reducing agent reduces the active metal ions in the mixed slurry and promotes particle formation.

[0168] The drying temperature is, for example, 80° C. to 150° C. The drying time is, for example, 1 hour to 24 hours.

[0169] In this manner, an anode catalyst can be produced in which an active metal is supported on the porous titanium suboxide.

[0170] In the present embodiment, the method for producing an anode catalyst includes the first step and the second step, but may also include other steps, such as a step of pulverizing the obtained anode catalyst (pulverizing step), a step of classifying the anode catalyst (classifying step), or a step of compression molding the anode catalyst (molding step), as necessary.

[0171] Examples of the shape of the anode catalyst include spherical, pellet, and tablet shapes. A spherical shape is preferred. When the anode catalyst has a spherical shape, the median diameter (D50) of the anode catalyst (the median diameter (D50) of the secondary particles of the anode catalyst) is, for example, 100 μm or less, preferably 80 μm or less, and more preferably 50 μm or less. The median diameter D50 of the anode catalyst is the particle diameter at which the volume cumulative frequency reaches 50% from the small diameter side in the volume-based particle size distribution. The median diameter (D50) of the anode catalyst is determined based on the particle size distribution obtained by laser diffraction / scattering.

[0172] 5. Effects and Benefits In the porous titanium suboxide of the present disclosure, the ratio of the volume of mesopores with pore diameters of 2 to 50 nm to the total pore volume is 50% by volume or more. Therefore, when such porous titanium suboxide is used as a catalyst support, the amount of active metal supported can be increased. Furthermore, by suppressing the release of the supported active metal, a decrease in catalytic activity can be suppressed.

[0173] The anode catalyst of the present disclosure comprises the porous titanium suboxide and an active metal supported on the porous titanium suboxide, the active metal being a platinum group metal and / or an oxide thereof. This allows for an increased amount of the active metal to be supported. Furthermore, by preventing the supported active metal from being liberated, a decrease in catalytic activity can be prevented.

[0174] The method for producing porous titanium suboxide of the present disclosure comprises the steps of preparing a precursor in which titanium oxide and a cationic surfactant are composited, and calcining the precursor in a reducing atmosphere. This relatively simple process makes it possible to produce porous titanium suboxide with an improved ratio of mesopore volume to total pore volume. As a result, it is possible to easily produce porous titanium suboxide that can increase the amount of active metal supported and suppress a decrease in catalytic activity.

[0175] The method for producing an anode catalyst according to the present disclosure includes a step of supporting an active metal on the porous titanium suboxide, making it possible to produce an anode catalyst with an improved amount of supported active metal through a relatively simple process.

[0176] The porous titanium suboxide of the present disclosure can be used as a support for various catalysts, and is particularly suitable as a support for the anode catalyst of a PEM-type water electrolysis device.

[0177] The present disclosure will be described in more detail below with reference to examples and comparative examples. It should be noted that the present disclosure is not limited to these examples and comparative examples. The specific numerical values ​​of the blending ratios (content ratios), physical property values, parameters, etc. used in the following description can be replaced with the upper limit (a numerical value defined as "equal to or less than") or lower limit (a numerical value defined as "equal to or more than") of the corresponding blending ratios (content ratios), physical property values, parameters, etc. described in the above-mentioned "Modes for Carrying Out the Invention."

[0178] Example 1 <Preparation of porous titanium suboxide> (Preparation step) 0.14 mol of triethanolamine was mixed with 0.07 mol of titanium tetraisopropoxide while being ice-cooled and stirred to prepare a solution A. In addition, 0.02 mol of 12-dodecanediamine (molecular formula: C) was added to 20.0 g of ion-exchanged water. １２ H ２８ N ２(a cationic surfactant having two amino groups in its molecular structure, a carbon chain length of 12, a molar mass of 200.37 g / mol) was mixed to prepare solution B. Next, solutions A and B were mixed and stirred at room temperature for 10 minutes. The resulting mixed solution was transferred to a sealable reaction vessel and allowed to stand in a thermostatic bath at 80°C (aging). After 24 hours, the gel-like solid content in the reaction vessel was removed. The gel-like solid content was washed with ion-exchanged water, and the washed solid content was recovered (centrifugation, 6000 rpm, 20 minutes). Note that the washing and recovery after washing were repeated approximately three times. The recovered sample was then dried at 110°C, yielding 9.58 g of a light yellowish-brown powder sample (titanium suboxide precursor).

[0179] (Reduction step) The titanium suboxide precursor was packed into a tubular furnace and reduced at 950° C. while flowing hydrogen gas at 0.5 L / min. The temperature was increased at a rate of 20° C. / min, the holding time was 3 hours, and the material was allowed to cool naturally.

[0180] In this way, the porous titanium suboxide of Example 1 was obtained. The obtained porous titanium suboxide was in the form of black particles and weighed 5.27 g.

[0181] Example 2 Instead of 1,12-dodecanediamine, 1,10-decanediamine (molecular formula C １０ H ２４ N ２ The porous titanium suboxide of Example 2 was obtained in the same manner as in Example 1, except that a cationic surfactant having a molecular structure of 1.50, a carbon chain length of 10, a molar mass of 172.32 g / mol, and two amino groups in its molecular structure was used. In Example 2, 9.22 g of titanium suboxide precursor was obtained, and the amount of the resulting porous titanium suboxide was 5.12 g.

[0182] Example 3 Instead of 1,12-dodecanediamine, 1,8-octanediamine (molecular formula C ８ H ２０ N ２The porous titanium suboxide of Example 3 was obtained in the same manner as in Example 1, except that a cationic surfactant having a molecular structure of 1.50 g, a carbon chain length of 8, a molar mass of 144.26 g / mol, and two amino groups in its molecular structure was used. In Example 3, 9.50 g of titanium suboxide precursor was obtained, and the amount of the resulting porous titanium suboxide was 5.02 g.

[0183] Example 4 Dodecylamine (molecular formula C) was used instead of 1,12-dodecanediamine. １２ H ２７ The porous titanium suboxide of Example 4 was obtained in the same manner as in Example 1, except that a cationic surfactant having one amino group in its molecular structure, carbon chain length 12, molar mass 185.36 g / mol, and one amino group in its molecular structure, was used. In Example 4, 9.34 g of titanium suboxide precursor was obtained, and the amount of the resulting porous titanium suboxide was 5.16 g.

[0184] Example 5 Instead of 1,12-dodecanediamine, dodecyltrimethylammonium bromide (molecular formula C １５ H ３４ Porous titanium suboxide of Example 5 was obtained in the same manner as in Example 1, except that a cationic surfactant (BrN, carbon chain length 12, molar mass 308.34 g / mol, and having one quaternary ammonium salt in its molecular structure) was used. In Example 5, 9.82 g of titanium suboxide precursor was obtained, and the amount of the resulting porous titanium suboxide was 4.96 g.

[0185] Example 6 Instead of 1,12-dodecanediamine, 1,6-hexanediamine (molecular formula C ６ H １６ N ２ The porous titanium suboxide of Example 6 was obtained in the same manner as in Example 1, except that a cationic surfactant having a molecular structure of 1.06 g, a carbon chain length of 6, a molar mass of 116.21 g / mol, and two amino groups in its molecular structure was used. In Example 6, 11.22 g of the titanium suboxide precursor was obtained, and the amount of the resulting porous titanium suboxide was 6.15 g.

[0186] Example 7 Porous titanium suboxide was prepared according to the following procedure.

[0187] (Preparation Step) 0.14 mol of triethanolamine was mixed with 0.07 mol of titanium tetraisopropoxide while being ice-cooled and stirred to prepare a solution A. 20.0 g of a 2-propanol aqueous solution (concentration: 20% by mass) was mixed with 0.02 mol of 12-dodecanediamine (molecular formula: C １２ H ２８ N ２ (a cationic surfactant having two amino groups in its molecular structure, a carbon chain length of 12, a molar mass of 200.37 g / mol) was mixed to prepare solution B. Next, solutions A and B were mixed and stirred at room temperature for 10 minutes, then allowed to stand at room temperature (aging). After 24 hours, the reaction vessel had separated into two layers (a water layer and a solid layer), and the settled solid was removed. The solid was washed with ion-exchanged water, and the washed solid was recovered (centrifugation, 6000 rpm, 20 minutes). Note that the washing and recovery after washing were repeated approximately three times. The recovered sample was then dried at 110°C, yielding 8.96 g of a light yellowish-brown powder sample (titanium suboxide precursor).

[0188] (Reduction Step) The reduction step was carried out under the same conditions as in Example 1.

[0189] In this way, porous titanium suboxide of Example 7 was obtained. The obtained porous titanium suboxide was in the form of black particles and weighed 5.27 g.

[0190] Example 8 Porous titanium suboxide of Example 8 was obtained in the same manner as in Example 7, except that an aqueous 2-propanol solution (concentration: 50% by mass) was used instead of the aqueous 2-propanol solution (concentration: 20% by mass). In Example 8, 7.45 g of titanium suboxide precursor was obtained, and the amount of the obtained porous titanium suboxide was 5.10 g.

[0191] Example 9 Porous titanium suboxide of Example 9 was obtained in the same manner as in Example 7, except that an aqueous 2-propanol solution (concentration 70% by mass) was used instead of the aqueous 2-propanol solution (concentration 20% by mass). In Example 9, 5.88 g of titanium suboxide precursor was obtained, and the amount of the obtained porous titanium suboxide was 5.05 g.

[0192] Example 10 Porous titanium suboxide of Example 10 was obtained in the same manner as in Example 7, except that an aqueous ethanol solution (concentration: 50% by mass) was used instead of the aqueous 2-propanol solution (concentration: 20% by mass). In Example 10, 7.45 g of titanium suboxide precursor was obtained, and the amount of the obtained porous titanium suboxide was 5.10 g.

[0193] Comparative Example 1 Commercially available titanium oxide nanoparticles (trade name: P25, TiO ２ 10.0 g of nanoparticles (manufactured by Evonic) were placed in a tubular furnace and subjected to reduction treatment at 950° C. while flowing hydrogen gas at 0.5 L / min. The heating rate was 20° C. / min, the holding time was 3 hours, and cooling was carried out naturally.

[0194] In this way, porous titanium suboxide of Comparative Example 1 was obtained. The obtained porous titanium suboxide was in the form of black particles and weighed 9.49 g.

[0195] Comparative Example 2 Sodium laurate (molecular formula C) was used instead of 1,12-dodecanediamine. １２ H ２３ NaO ２ The porous titanium suboxide of Comparative Example 2 was obtained in the same manner as in Example 1, except that an anionic surfactant having one laurate group in its molecular structure, carbon chain length 12, molar mass 222.30 g / mol, and one laurate group in its molecular structure was used. In Comparative Example 2, 10.87 g of titanium suboxide precursor was obtained, and the amount of the resulting porous titanium suboxide was 6.55 g.

[0196] Comparative Example 3 Instead of 1,12-dodecanediamine, polyethylene glycol 200 (molecular formula H(OCH ２ CH ２ ) ｎ The porous titanium suboxide of Comparative Example 3 was obtained in the same manner as in Example 1, except that a compound having a molecular structure containing a hydrophilic hydroxyl group and a hydrophobic polyethylene chain (HCOOH, molar mass of 180 g / mol to 220 g / mol, and a molecular structure containing a hydrophilic hydroxyl group and a hydrophobic polyethylene chain) was used. In Comparative Example 3, 12.52 g of titanium suboxide precursor was obtained, and the amount of the resulting porous titanium suboxide was 6.27 g.

[0197] <Evaluation> [Evaluation of X-ray diffraction pattern] For the porous titanium suboxide of each example and each comparative example, the powder X-ray diffraction pattern was measured using an X-ray diffractometer (product name: Ultima IV, manufactured by Rigaku Corporation). The conditions were as follows: {Measurement conditions} X-ray source: CuKα radiation Scanning range: 10° to 60° (2θ range) Scanning speed: 5.0° / min Voltage: 40 kV Current: 40 mA

[0198] In each of the porous titanium suboxides in the examples and comparative examples, Ti ４ O ７ The diffraction peaks due to Ti were clearly observed. ４ O ７ It was confirmed that Ti ４ O ７ The crystallite diameter calculated from the half-width of the diffraction peak derived from was 20 to 60 nm, and it was confirmed that they were aggregates of fine crystals. ４ O ７ It was confirmed that the substance contained titanium suboxide TiOx (x = 1.5 to 2.0) with different oxidation degrees, rather than the structure. ４ O ７ The crystallite diameters calculated based on the peak information around 2θ = 20.8°, which is a peak specific to the structure, are shown in Table 1. As an example of the analysis results, the X-ray diffraction patterns of the porous titanium suboxides prepared in Examples 1, 3, and 4 and Comparative Example 3 are shown in Figure 1.

[0199] [Carbon Content] The carbon content of the porous titanium suboxide samples of each Example and Comparative Example was measured using a total organic carbon meter (product name: SSM-5000A, manufactured by Shimadzu Corporation). Specifically, the carbon content was measured by oxidatively decomposing the organic matter contained in the sample to generate carbon dioxide, and converting the total amount of carbon dioxide generated into the carbon content. The amount of carbon dioxide generated was quantified using a highly sensitive non-dispersive infrared gas analyzer (ND Iridium). The results are shown in Table 1.

[0200] [Average oxidation degree] For the porous titanium suboxide of each example and comparative example, the weight change associated with heat treatment of the porous titanium suboxide was measured by thermogravimetric analysis (TG) using a thermogravimetric analyzer (product name: TG / DTA7200, manufactured by Seiko Instruments Inc.), and the average oxidation degree of the titanium suboxide particles was calculated by combining this result with the carbon content of the porous titanium suboxide.

[0201] Specifically, in thermogravimetric analysis (TG), 10 to 30 mg of porous titanium suboxide was placed in a measurement cell and heated from room temperature to 1000°C at a heating rate of 20°C / min in an air atmosphere, and the weight gain rate from 200°C to 800°C was determined. When porous titanium suboxide is heated in an air atmosphere, it oxidizes and changes to titanium dioxide, resulting in an increase in weight. Therefore, the average oxidation degree can be calculated by checking this weight gain rate. For example, Ti ４ O ７ The molar mass of titanium suboxide is 75.87 g / mol, and the molar mass of titanium dioxide is 79.87 g / mol, resulting in a 5.27% weight gain upon complete oxidation. In other words, the rate of weight gain due to oxidation corresponds to the average oxidation degree of the product, so the average oxidation degree of the product can be estimated from the weight gain rate. If the porous titanium suboxide contains carbon, the weight loss due to combustion requires a correction for the carbon content. The carbon content can be measured using the total organic carbon measurement method described above. The average oxidation degree of porous titanium suboxide can be calculated by adding the carbon content (wt%) to the weight change rate (wt%) and substituting the result into the following formula. The results are shown in Table 1. Average oxidation degree = 2.00 x EXP (-2.55 x Z') Z' = weight change rate (wt%) + carbon content (wt%)

[0202] [Specific Surface Area and Pore Volume] The specific surface area and pore volume of the porous titanium suboxide of each Example and Comparative Example were evaluated using a specific surface area and pore distribution measuring device (product name: BELSORP MAX, manufactured by Microtrac-Bell). Specifically, 100 to 200 mg of porous titanium suboxide was placed in a measurement cell, and the nitrogen adsorption isotherm at 77 K was analyzed to calculate the specific surface area and pore volume. The values ​​for the specific surface area and pore volume were calculated using BET analysis. The volume ratio of each pore (micropores, mesopores, macropores) to the total pore volume was also calculated.

[0203] Specifically, the specific surface area and pore size distribution analyzer measures the specific surface area of ​​a sample by exposing porous titanium suboxide to nitrogen gas and observing changes in the amount of nitrogen adsorption while varying the pressure or temperature. It also measures the pore size distribution based on the condensation of nitrogen gas molecules. When nitrogen gas is exposed to cooled porous titanium suboxide, nitrogen molecules first adsorb onto the pore surfaces. Even after the entire surface is covered with a monolayer of nitrogen molecules, further increasing the nitrogen gas pressure causes adsorption of nitrogen molecules, filling the pores. As a result of the adsorption of a large number of nitrogen molecules within the pores, condensation of the nitrogen molecules from gas to liquid occurs at a certain pressure. The pressure and adsorption amount at which condensation occurs can be used to evaluate the pore volume and pore size. In this study, the region where the relative pressure of nitrogen gas, p / P, at 77 K, is 0 to 0.20 or less was defined as the micropore region. The amount of nitrogen adsorption at p / P = 0.20 was converted to liquid density to calculate the micropore volume. The mesopore volume was calculated by subtracting the micropore volume from the pore volume calculated from the nitrogen adsorption amount at p / P0 = 0.96, which was defined as the mesopore region. Similarly, the macropore region was defined as the relative pressure p / P0 = 0.96 to 0.99, which was defined as the macropore region. The mesopore volume was calculated by subtracting the micropore volume and mesopore solution values ​​from the pore volume calculated from the nitrogen adsorption amount at p / P0 = 0.99. The results are shown in Table 1. Note that FIG. 2 shows a graph of the nitrogen adsorption isotherms for Example 1 and Comparative Example 3, and FIG. 3 shows a graph of the pore size distributions for Example 1 and Comparative Example 3.

[0204] [Particle size distribution] The particle size distribution of the porous titanium suboxides of Examples 1, 6 to 10 and Comparative Example 3 was measured using a laser diffraction / scattering particle size distribution analyzer (product name: MT300II, manufactured by Microtrac-Bell). Specifically, 0.1 g of porous titanium suboxide was added to 50 mL of ion-exchanged water, and ultrasonic waves were irradiated for 30 minutes to obtain a dispersion of porous titanium suboxide. The obtained dispersion of porous titanium suboxide was placed in the laser diffraction / scattering particle size distribution analyzer, and the particle size distribution was measured. The conditions were as follows, and the average value of three measurements was used as the particle size distribution. The obtained particle size distribution is shown in Figure 5. {Measurement conditions} Measurement mode: Absorption Particle refractive index: 1.81 Solvent refractive index: 1.333 Particle shape: Aspherical Measurement time: 30 seconds

[0205] The obtained particle size distribution was analyzed on a volume basis to determine the average particle diameter (Dv), standard deviation (σDv), median diameter (D50), median diameter (D10), median diameter (D90), and mode diameter (D ｍоｄｅ ) was calculated. Furthermore, the median diameter (D50) and the mode diameter (D ｍоｄｅ ) and the absolute value of the difference between the mode diameter (D ｍоｄｅ ) for the median diameter (D50) and mode diameter (D ｍоｄｅ The ratio of the absolute values ​​of the differences between the values ​​of the two groups was calculated. The results are shown in Table 3.

[0206] Catalyst Example 1 <Preparation of Anode Catalyst> An anode catalyst was prepared using the porous titanium suboxide of Example 1. Specifically, 85.0 g of ethylene glycol was placed in a beaker, 1.0 g of sodium acetate was mixed, and 0.75 g of the porous titanium suboxide of Example 1 was added. Next, an iridium solution was prepared by mixing 0.5 g of iridium chloride with 5.75 g of ion-exchanged water. This iridium solution was added to the beaker and subjected to ultrasonic treatment for 90 minutes. After ultrasonic treatment, 103.7 g of formic acid was added to the beaker, and the mixture was heated at 120°C for 5 hours while stirring. After heating, the reaction solution was cooled to room temperature, and the solid content was recovered using a centrifuge. Next, the solid content was washed with 30 g of deionized water and 30 g of ethanol and dried overnight in a dryer at 110°C. In this way, iridium oxide (IrO) was added to the porous titanium suboxide of Example 1. ２ The theoretical iridium oxide content per gram of the anode catalyst, calculated from the weight of iridium chloride and the amount of porous titanium suboxide used, was 0.334 g-IrO ２ / g-catalyst.

[0207] Catalyst Example 3 An anode catalyst of Catalyst Example 3 was obtained in the same manner as in Catalyst Example 1, except that the porous titanium suboxide of Example 3 was used.

[0208] Catalyst Example 6 An anode catalyst of Catalyst Example 6 was obtained in the same manner as in Catalyst Example 1, except that the porous titanium suboxide of Example 6 was used.

[0209] Catalyst Example 7 An anode catalyst of Catalyst Example 7 was obtained in the same manner as in Catalyst Example 1, except that the porous titanium suboxide of Example 7 was used.

[0210] Comparative Catalyst Example 1 An anode catalyst of Comparative Catalyst Example 1 was obtained in the same manner as in Catalyst Example 1, except that the porous titanium suboxide of Comparative Example 1 was used.

[0211] Comparative Catalyst Example 3 An anode catalyst of Comparative Catalyst Example 3 was obtained in the same manner as in Catalyst Example 1, except that the porous titanium suboxide of Comparative Example 3 was used.

[0212] <Evaluation> [Iridium Support State and Iridium Support Amount] The anode catalysts of each catalyst example and each catalyst comparison example were evaluated for their iridium support state and iridium support amount using a scanning electron microscope (product name: S5500, manufactured by Hitachi High-Technologies Corporation) and an energy dispersive X-ray spectroscopy elemental analyzer (product name: Quantax, manufactured by Bruker). Specifically, analysis was performed using the energy dispersive X-ray spectroscopy elemental analyzer at an acceleration voltage of 30 kV, and the iridium oxide content per gram of anode catalyst (g-IrO ２ / g-catalyst) was estimated. The results of the initial iridium oxide content per gram of anode catalyst are shown in Table 2, and SEM images of the anode catalysts of Catalyst Example 1 and Comparative Catalyst 3 are shown in FIG. 4. In addition, the ratio of the initial iridium oxide content per gram of anode catalyst to the theoretical iridium oxide content per gram of anode catalyst was calculated ((initial iridium oxide content per gram of anode catalyst) / (theoretical iridium oxide content per gram of anode catalyst)×100(%)). The results are shown in Table 2.

[0213] [Evaluation of catalytic performance] The catalytic performance of the anode catalysts of each catalyst example and each catalyst comparison example was evaluated by a half-cell measurement method using a rotating electrode. The half-cell measurement method is a method in which a catalyst ink consisting of an anode catalyst and an electrolyte is applied to an electrode and evaluated by electrochemical measurement.

[0214] Specifically, 4 to 10 mg of anode catalyst was placed in a beaker, and 0.8 g of ethanol and 3.0 g of pure water were added and mixed. Next, a 5 wt % Nafion solution was added so that the mass ratio of anode catalyst to Nafion was 10:1. The resulting anode catalyst-containing mixture was stirred at 700 rpm for 10 minutes, ultrasonicated for 30 minutes, then further stirred at 700 rpm for 10 minutes, ultrasonicated for 15 minutes, and stirred again at 700 rpm for 10 minutes to obtain a suspension. Using a micropipette, 20 to 30 μg iridium / cm was added. ２ The suspension was sucked up so that the thickness became 0.01 mm, dropped onto a rotating electrode (material: gold, electrode radius: 3.0 mm), and dried in a dryer set at 50° C. for 30 minutes.

[0215] Electrochemical measurements were performed using 0.1 M HClO, which was degassed with nitrogen before the measurements. ４ The experiments were carried out in aqueous solution. The electrode potential was controlled with a potentiostat. After the temperature of the electrolyte stabilized at 25°C, 100 cycles of CV (cyclic voltammetry) measurements were performed at 100 mV / s in the potential range of 0.05-1.2 V vs. RHE to determine the electrochemical stabilization of the catalyst. Next, five round trips of CV measurements were performed in the potential range of 1.0-1.55 V vs. RHE at 1 mV / s and 3600 rpm. The current values ​​obtained from these CV measurements were compensated, and the current value at 1.5 V vs. RHE divided by the weight of iridium (weight in terms of metallic iridium) in the anode catalyst coated on the electrode was used to determine the catalytic activity. The solution resistance between the reference electrode and working electrode was measured using EIS (electrochemical impedance spectroscopy) and used to compensate for the iR loss in the electrochemical measurements. For capacitance current compensation, a 1.3 V vs. RHE was used. The current value in RHE was used. The catalytic activity of the prepared anode catalyst was evaluated as the current value (mA / mg-Ir) required for water decomposition per iridium weight (weight in terms of metallic iridium). Five repeated measurements were performed, and the result of the first measurement was designated as the "initial catalytic activity," while the result of the fifth measurement was designated as the "steady-state catalytic activity." The rate of change in catalytic activity (steady-state catalytic activity / initial catalytic activity × 100(%)) was calculated. After all five catalytic activity evaluations were completed, the anode catalyst remaining on the electrode was recovered, and the iridium oxide content after evaluation was measured again. Furthermore, the ratio of the iridium oxide content after evaluation per gram of anode catalyst to the initial iridium oxide content per gram of anode catalyst ((iridium oxide content after evaluation per gram of anode catalyst) / (initial iridium oxide content per gram of anode catalyst) × 100(%)) was calculated. The results are shown in Table 2.

[0216]

[0217]

[0218]

[0219] <Discussion> As shown in Table 1 and Figures 2 and 3, the porous titanium suboxides of Examples 1 to 10 had mesopore volumes that accounted for 50% or more by volume relative to the total pore volume. In contrast, the porous titanium suboxides of Comparative Examples 1 to 3 had mesopore volumes that accounted for less than 50% by volume relative to the total pore volume. Referring to Table 2, Catalyst Examples 1, 3, 6, and 7, which used the porous titanium suboxides of Examples 1, 3, 6, and 7, had high initial iridium contents and suppressed a decrease in the iridium content after evaluation. In contrast, Catalyst Comparative Example 1, which used the porous titanium suboxide of Comparative Example 1, had a significantly low initial iridium content. Furthermore, Catalyst Comparative Example 3, which used the porous titanium suboxide of Comparative Example 3, had a relatively low initial iridium content and a significantly decreased iridium content after evaluation. This is thought to be because the porous titanium suboxides of Examples 1, 3, 6, and 7 had mesopore volumes that accounted for 50% or more by volume relative to the total pore volume, allowing iridium to be efficiently immobilized in the mesopores. In other words, it was suggested that the porous titanium suboxides of Examples 1 to 10, in which the ratio of mesopore volume to total pore volume was 50 vol.% or more, were able to increase the amount of iridium supported and suppress a decrease in the amount of iridium supported, compared to the porous titanium suboxides of Comparative Examples 1 to 3, in which the ratio of mesopore volume to total pore volume was less than 50 vol.%.

[0220] Furthermore, as shown in Figure 4, the surface of the anode catalyst in Catalyst Example 1 was smooth. This is presumably because iridium was loaded through the mesopores, resulting in an anode catalyst structure in which iridium was not excessively exposed on the support surface. On the other hand, the surface of the anode catalyst in Catalyst Comparative Example 3 was uneven. This is thought to be because the porous titanium suboxide in Comparative Example 3 had a low proportion of mesopores, causing iridium to cling randomly to the outer surface of the porous titanium suboxide.

[0221] 5, the porous titanium suboxides of Examples 6 to 10 had a sharper particle size distribution than the porous titanium suboxides of Example 1 and Comparative Example 3. In other words, the porous titanium suboxides of Examples 6 to 10 had smaller variations in particle size than the porous titanium suboxides of Example 1 and Comparative Example 3. Therefore, it is expected that the variations in the amount of active metal supported on the porous titanium suboxide can be suppressed, and the catalytic activity and durability of the anode catalyst can be improved.

[0222] The above invention is provided as an exemplary embodiment of the present disclosure, but this is merely an example and should not be interpreted as limiting. Modifications of the present disclosure that are obvious to those skilled in the art are intended to be included in the scope of the following claims.

[0223] The porous titanium suboxide can be used as a support for various catalysts, and is particularly suitable as a support for an anode catalyst in a PEM-type water electrolysis device.

Claims

1. Porous titanium suboxide in which the ratio of the volume of mesopores with a pore diameter of more than 2 nm and less than 50 nm to the total pore volume is 50 vol % or more.

2. The specific surface area is 100m ２ The porous titanium suboxide according to claim 1, wherein the molecular weight of the porous titanium suboxide is 1 / g or less.

3. The porous titanium suboxide according to claim 1, wherein the ratio of the volume of micropores having a pore diameter of 2 nm or less to the total pore volume is 20% by volume or less.

4. The porous titanium suboxide (TiO Ｘ 2. The porous titanium suboxide according to claim 1, wherein the average oxidation degree (X) of the porous titanium suboxide is greater than 1.70 and less than 1.

85.

5. The porous titanium suboxide according to claim 1, having a volume-based average particle size of 15 μm or less.

6. The porous titanium suboxide according to claim 1, wherein the standard deviation in the volumetric particle size distribution is 20% or less.

7. Volumetric mode diameter (D ｍｏｄｅ ) for the volume-based median diameter (D50) and the mode diameter (D ｍｏｄｅ ) and the ratio of the absolute value of the difference (|D50 - D ｍｏｄｅ | / D ｍｏｄｅ 2. The porous titanium suboxide according to claim 1, wherein the ρ is 0.3 or less.

8. An anode catalyst comprising: the porous titanium suboxide according to any one of claims 1 to 7; and an active metal supported on the porous titanium suboxide, wherein the active metal comprises a platinum group metal and / or an oxide thereof.

9. The anode catalyst according to claim 8, wherein the active metal comprises iridium and / or iridium oxide.

10. The anode catalyst according to claim 8, wherein the ratio of the initial content of the active metal per gram of the anode catalyst to the theoretical content of the active metal per gram of the anode catalyst is 90.0% or more.

11. A method for producing the porous titanium suboxide according to any one of claims 1 to 7, comprising: a preparation step of preparing a precursor in which titanium dioxide and a cationic surfactant are composited; and a reduction step of firing the precursor in a reducing atmosphere.

12. The method for producing porous titanium suboxide according to claim 11, wherein the preparation step includes a step of aging a mixture containing a titania source for forming the titanium dioxide, the cationic surfactant, and a solvent.

13. The method for producing porous titanium suboxide according to claim 12, wherein the solvent comprises water.

14. The method for producing porous titanium suboxide according to claim 12, wherein the solvent comprises an alcohol.

15. The method for producing porous titanium suboxide according to claim 11, wherein the molar mass of the cationic surfactant is 400 g / mol or less.

16. A method for producing an anode catalyst, comprising the step of supporting an active metal on the porous titanium suboxide according to any one of claims 1 to 7.

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