Metal composite oxide, composite, oxygen generation catalyst, catalyst ink and electrode, and method for producing metal composite oxide and composite

Abstract

This metal composite oxide contains iridium, ruthenium, and molybdenum. The molybdenum oxide is a low crystalline oxide or an amorphous oxide.

Description

Metal composite oxides, composites, oxygen-evolving catalysts, catalytic inks and electrodes, and methods for producing metal composite oxides and composites.

[0001] The present invention relates to metal composite oxides, composites, oxygen-evolving catalysts, catalytic inks and electrodes, and methods for producing metal composite oxides and composites. This application claims priority under Japanese Patent Application No. 2024-164242, filed in Japan on September 20, 2024, the contents of which are incorporated herein by reference.

[0002] Water electrolysis technology is attracting attention as a technology that can produce hydrogen from water using renewable energy, aiming to solve environmental and energy resource problems. When hydrogen is produced from one electrode through water electrolysis, oxygen is produced from the other electrode.

[0003] Patent Document 1 describes a catalyst composition comprising tin oxide particles and an iridium-ruthenium oxide layer coating the tin oxide particles, as an efficient electrode catalyst for an oxygen generation reaction by water electrolysis.

[0004] Japanese Patent Publication No. 2022-169613

[0005] However, further improvement in catalytic activity is desired for catalyst materials containing iridium oxide and ruthenium oxide. The present invention aims to provide metal composite oxides, composites, oxygen-evolving catalysts, catalytic inks, and electrodes, as well as methods for producing metal composite oxides and composites, that can further improve catalytic activity.

[0006] The present invention encompasses the following embodiments: [1] A metal composite oxide comprising iridium, ruthenium, and molybdenum, wherein the composite oxide comprises iridium, ruthenium, and molybdenum, and the molybdenum oxide is a low-crystalline oxide or an amorphous oxide. [2] The metal composite oxide according to [1], further comprising a fourth metal (M). [3] The metal composite oxide according to [2], wherein the fourth metal (M) is one or more elements selected from the group consisting of B, Al, Sn, Cr, Mn, Fe, Co, Ni, Cu, and Nd. [4] The metal composite oxide according to any one of [1] to [3], wherein the iridium content is 50% by mass or less and the molybdenum content is 1% by mass or more and 10% by mass or less. [5] The metal composite oxide according to any one of [1] to [4], wherein the particle size of the primary particles is 100 nm or less. [6] Median diameter D determined by dynamic light scattering. ５０ However, the metal composite oxide described in any of [1] to [5] is 500 nm or less. [7] The specific surface area measured by the BET method is 10 m². ２ [1] to [6] or more, a metal composite oxide according to any one of [1] to [6]. [8] A metal composite oxide according to any one of [1] to [7], wherein the ratio of the total content of iridium and ruthenium to the total mass of the metal composite oxide, as determined by XRF analysis, is 50% by mass or more and 80% by mass or less. [9] A composite comprising a metal composite oxide according to any one of [1] to [8] and a carrier, wherein the metal composite oxide is supported on the carrier, and the carrier is an inorganic material.

[10] The carrier is tin oxide (SnO ２[9] A composite comprising at least one selected from the group consisting of ) and carbon.

[11] An oxygen-evolving catalyst comprising a metal composite oxide according to any one of [1] to [8].

[12] An oxygen-evolving catalyst according to

[11] , further comprising a conductive material.

[13] An oxygen-evolving catalyst comprising a composite comprising the composite according to [9] or

[10] .

[14] An oxygen-evolving catalyst according to

[13] , further comprising a conductive material.

[15] A catalyst ink comprising a metal composite oxide according to any one of [1] to [8] and a medium.

[16] A catalyst ink according to

[15] , further comprising a conductive material.

[17] A catalyst ink according to

[15] or

[16] , further comprising a polymer electrolyte.

[18] A catalyst ink comprising a composite comprising the composite according to [9] or

[10] and a medium.

[19] A catalyst ink according to

[18] , further comprising a conductive material.

[20] A catalyst ink according to

[18] or

[19] , further comprising a polymer electrolyte.

[21] An electrode having a metal composite oxide described in any of [1] to [8] on its surface.

[22] An electrode having a composite described in [9] or

[10] on its surface.

[23] A method for producing a metal composite oxide, comprising the steps of: preparing a first mixed solution containing an iridium compound, a ruthenium compound, and an aqueous medium; adding a molybdenum compound to the first mixed solution to prepare a second mixed solution; adjusting the pH of the second mixed solution obtained in the first step using ammonia water to generate a precipitate; isolating the precipitate from the aqueous medium; and calcining the precipitate obtained in the first step.

[24] A method for producing a metal composite oxide, comprising the steps of: preparing a first mixed solution containing an iridium compound, a ruthenium compound, a compound of a fourth metal (M), and an aqueous medium; preparing a second mixed solution by adding a molybdenum compound to the first mixed solution; adjusting the pH of the second mixed solution obtained in the first step using aqueous ammonia to generate a precipitate; isolating the precipitate from the aqueous medium; and calcining the precipitate obtained in the first step.

[25] A method for producing a composite, comprising the steps of: dispersing an inorganic material that serves as a carrier in an aqueous medium to prepare a first aqueous dispersion containing the inorganic material; mixing the first aqueous dispersion with a mixture containing an iridium compound and a ruthenium compound to prepare a second aqueous dispersion; blending a molybdenum compound into the second aqueous dispersion to prepare a third aqueous dispersion; adjusting the pH of the third aqueous dispersion using ammonia water to generate a precipitate; isolating the precipitate from the aqueous medium; and calcining the precipitate obtained in the above steps.

[0007] According to the present invention, it is possible to provide metal composite oxides, composites, oxygen-evolving catalysts, catalytic inks and electrodes that can further improve catalytic activity, as well as methods for producing metal composite oxides and composites.

[0008] This is the XRD spectrum of the particles obtained in Example 3. This is an image obtained by transmission electron microscopy (TEM) of the particles obtained in Example 2. This is an image obtained by transmission electron microscopy (TEM) of the particles obtained in Example 3. This figure shows the scanning electron microscope energy-dispersive X-ray spectroscopy (SEM-EDS) observation image of the particles obtained in Example 8. The upper left is the SEM image, the upper right is the ruthenium element mapping image, the lower left is the iron element mapping image, and the lower right is the cobalt element mapping image. This figure shows the scanning electron microscope energy-dispersive X-ray spectroscopy (SEM-EDS) observation image of the particles obtained in Example 8. The upper left is the tin element mapping image, the upper right is the molybdenum element mapping image, the lower left is the iridium element mapping image, and the lower right is the nickel element mapping image. This is the XRD spectrum of the particles obtained in Example 6.

[0009] (Metal Composite Oxide) The metal composite oxide of one embodiment of the present invention contains iridium, ruthenium, and molybdenum. The metal composite oxide of this embodiment contains a composite oxide of iridium, ruthenium, and molybdenum (hereinafter referred to as "Ir-Ru-Mo composite oxide") as an essential component. In the metal composite oxide of this embodiment, the molybdenum oxide is a low-crystallinity oxide or an amorphous oxide. The crystallinity of the molybdenum oxide can be evaluated, for example, using X-ray diffraction (powder X-ray diffraction, XRD).

[0010] In addition to containing Ir-Ru-Mo composite oxide as an essential component, the metal composite oxide of this embodiment may further contain iridium-ruthenium composite oxide (hereinafter referred to as "Ir-Ru composite oxide"), iridium oxide, ruthenium oxide, or molybdenum oxide. The metal elements of the metal composite oxide of this embodiment may further contain metal elements other than iridium, ruthenium, and molybdenum. "Metal elements other than iridium, ruthenium, and molybdenum" are referred to as the fourth metal (M). In that case, the metal composite oxide of this embodiment contains iridium, ruthenium, molybdenum, and the fourth metal (M) (hereinafter referred to as "Ir-Ru-Mo-M composite oxide") as an essential component. In this embodiment, if the metal element of the metal composite oxide further includes a fourth metal (M), the metal composite oxide of this embodiment may, in addition to containing Ir-Ru-Mo-M composite oxide as an essential component, further contain Ir-Ru composite oxide, iridium oxide, ruthenium oxide, molybdenum oxide, or an oxide of the fourth metal (M). The fourth metal (M) may be one or more elements selected from the group consisting of Group 2, Group 13, Group 14, and transition metals. The transition metals are a general term for elements that exist between Group 3 and Group 11 of the periodic table. Specific examples of the fourth metal (M) include, for example, one or more elements selected from the group consisting of B, Al, Sn, Cr, Mn, Fe, Co, Ni, Cu, and Nd.

[0011] [Composition Ratio of Metal Composite Oxide] In the metal composite oxide of this embodiment, the elemental composition ratio (mass ratio) of iridium (Ir), ruthenium (Ru), molybdenum (Mo), and oxygen (O) is preferably within the following ranges, based on a total of 100% by mass of iridium (Ir), ruthenium (Ru), molybdenum (Mo), and oxygen (O): Iridium (Ir): From the viewpoint of exhibiting excellent catalytic performance, 1% by mass or more is preferred, and 5% by mass or more is more preferred. From the viewpoint of cost reduction, 50% by mass or less is preferred, and 30% by mass or less is more preferred. Ruthenium (Ru): From the viewpoint of exhibiting excellent catalytic performance, 10% by mass or more is preferred, and 30% by mass or more is more preferred. From the viewpoint of cost reduction, 60% by mass or less is preferred, and 40% by mass or less is more preferred. Molybdenum (Mo): From the viewpoint of reducing precious metals (iridium, ruthenium), 1% by mass or more is preferred, and 3% by mass or more is more preferred. From the viewpoint of improving activity, 10% by mass or less is preferred, and 7% by mass or less is more preferred. Oxygen (O): From the viewpoint of constituting a metal oxide, 10% by mass or more is preferred, and 20% by mass or more is more preferred. From the viewpoint of improving performance, 50% by mass or less is preferred, and 40% by mass or less is more preferred.

[0012] The composition ratio of each metal component in the metal composite oxide of this embodiment can be measured, for example, by X-ray fluorescence analysis (XRF), inductively coupled plasma (ICP) emission spectroscopy, etc. Furthermore, if the metal composite oxide of this embodiment contains the fourth metal (M), the total content of the fourth metal (M) may be, for example, 0.1 parts by mass or more, 1 part by mass or more, or 10 parts by mass or less, or 5 parts by mass or less, based on 100 parts by mass of iridium (Ir), ruthenium (Ru), and molybdenum (Mo) combined.

[0013] The metal composite oxide of this embodiment can be represented, for example, by the following general formula (A): Mo ｘ Ru ｙ Ir ｚ O ｗ　　(A) In formula (A), x, y, z, and w are the atomic number ratios (molar ratios) of the respective elements in the metal composite oxide. For example, when x + y + z + w = 1, it is preferably within the following ranges. x: It may be 0.01 or more, and may be 0.02 or more. It may be 0.10 or less, and may be 0.07 or less. y: It may be 0.10 or more, and may be 0.13 or more. It may be 0.25 or less, and may be 0.20 or less. z: It may be 0.01 or more, and may be 0.02 or more. It may be 0.20 or less, and may be 0.13 or less. w: It may be 0.50 or more, and may be 0.60 or more. It may be 0.90 or less, and may be 0.85 or less. When the metal composite oxide of the present embodiment contains the fourth metal (M), for example, it can be represented by the following general formula (A1). Mo ｘ１ Ru ｙ１ Ir ｚ１ M ｔ１ O ｗ１　　 (A1) In formula (A1), x1, y1, z1, t1, and w1 are the atomic number ratios (molar ratios) of the respective elements in the metal composite oxide. For example, when x1 + y1 + z1 + t1 + w1 = 1, it is preferably within the following ranges. x1: It may be 0.01 or more, and may be 0.02 or more. It may be 0.10 or less, and may be 0.07 or less. y1: It may be 0.10 or more, and may be 0.13 or more. It may be 0.25 or less, and may be 0.20 or less. z1: It may be 0.01 or more, and may be 0.02 or more. It may be 0.20 or less, and may be 0.13 or less. t1: It may be 0.01 or more, and may be 0.02 or more. It may be 0.25 or less, and may be 0.20 or less. w1: It may be 0.50 or more, and may be 0.60 or more. It may be 0.90 or less, and may be 0.85 or less.

[0014] [Metal Composite Oxide Particles] The metal composite oxide in this embodiment may be a particulate structure (metal composite oxide particles). In the metal composite oxide of this embodiment, the particle diameter of the primary particles is preferably 150 nm or less, more preferably 130 nm or less, and even more preferably 110 nm or less. The lower limit is not particularly limited, but it is preferably 1 nm or more. The method for measuring the particle diameter of the primary particles will be described in detail below.

[0015] <Method for measuring the particle diameter of primary particles> The particle diameter of primary particles is the average particle diameter of primary particles. A powder of metal composite oxide is photographed using a scanning electron microscope (SEM) or transmission electron microscope (TEM), and the major axis (the Ferret diameter of the longest observed part) and minor axis (the shorter Ferret diameter perpendicular to the Ferret diameter of the longest part) of the smallest unit particle constituting the aggregate on the two-dimensional image (i.e., primary particles) are measured, and the average value of these is taken as the particle diameter of the primary particles. The average value was taken as the average of the particle diameters of 50 randomly selected primary particles.

[0016] In this embodiment, the metal composite oxide may be formed by the aggregation of multiple primary particles to create secondary particles. The median diameter D is determined by dynamic light scattering. ５０ Aggregates such as secondary particles are usually observed together. The median diameter D of the metal composite oxide determined by the dynamic light scattering method of this embodiment ５０ The median diameter D is preferably 800 nm or less, more preferably 500 nm or less, and even more preferably 300 nm or less. ５０ Metal composite oxides whose performance is below the above upper limit can exhibit more effective catalytic efficiency.

[0017] The median diameter D of the metal composite oxide of this embodiment, determined by dynamic light scattering. ５０ For example, it may be 50 nm or more, 100 nm or more, 150 nm or more, or 200 nm or more.

[0018] The median diameter D of the metal composite oxide of this embodiment, determined by dynamic light scattering. ５０Examples of the above numerical ranges include 50 nm to 800 nm, 50 nm to 500 nm, 100 nm to 500 nm, and 150 nm to 300 nm.

[0019] The median diameter D of the metal composite oxide of this embodiment, calculated by dynamic light scattering. ５０ This is determined by using a dynamic light scattering particle size distribution analyzer (e.g., Nanotrac Wave II, manufactured by Microtrac-Bell) to measure the particle size distribution wet using acetone as the medium, and defining the particle size at which the volume integrated percentage accounts for 50%.

[0020] The specific surface area (BET method) of the metal composite oxide in this embodiment is 10 m². ２ It is preferable that it be 20 m or more ２ It is more preferable that it be 30m or more per gram. ２ It is even more preferable that it be 50m or more per g. ２ It is particularly preferable that the specific surface area be greater than or equal to the lower limit. Metal composite oxides having a large specific surface area can more effectively improve catalytic efficiency because the number of catalytically active sites increases and mass transfer in the reaction system is facilitated.

[0021] The specific surface area (BET method) of the metal composite oxide in this embodiment is, for example, 200 m². ２ It may be less than / g, and 100m ２ It may be less than / g, and 90m ２ It may be less than / g, and 80m ２ It may be less than / g.

[0022] An example of the numerical range for the specific surface area (BET method) of the metal composite oxide in this embodiment is 10 m. ２ / g or more 200m ２ It may be less than / g, and 20m ２ / g or more 100m ２ It may be less than / g, and 30m ２ / g or more 100m ２ It may be less than / g, and 50m ２ / g or more 100m ２It may be less than / g, and 50m ２ / g or more 80m ２ It may be less than / g.

[0023] The specific surface area mentioned above is measured using a specific surface area meter (e.g., BELSORP-mini from Microtrac-Bel), and the surface area per gram of sample, measured from the amount of nitrogen gas adsorbed by the BRETA method (Brunauer-Emmett-Teller method), is defined as the specific surface area (m²). ２ It is calculated as ( / g).

[0024] [Structure of Metal Composite Oxide] In the metal composite oxide of this embodiment, which has Ir-Ru-Mo composite oxide as an essential component and also contains iridium, ruthenium, and molybdenum, the molybdenum oxide is a low-crystalline oxide or amorphous oxide. The metal composite oxide of this embodiment can be represented by, for example, the following general formula (1): IrO ２ / RuO ２ / MoO ３　　　 (1)

[0025] When the metal composite oxide of this embodiment contains a fourth metal (M), in the metal composite oxide containing Ir-Ru-Mo-M composite oxide as an essential component, the molybdenum oxide is a low-crystalline oxide or an amorphous oxide. The metal composite oxide of this embodiment can be represented, for example, by the following general formula (1-1): MoO ３ / IrO ２ / RuO ２ / MoO ３ / M ｓ O ｔ　　　 (1-1) (In equation (1-1), s and t are integers from 1 to 4, and [2 × t / s] is the valence of the quaternary metal (M). For example, if the quaternary metal (M) is B, Al, Sn, Cr, Mn, Fe, Co, Ni, Cu, Nd, then the quaternary metal oxide M ｓ O ｔ Each of them is B ２ O ３ Al ２ O ３ , SnO ２ , Cr ２ O ３ MnO ２ Fe ２ O３ , CoO, NiO, CuO, Nd ２ O ３ (That is the case.)

[0026] The metal composite oxide of this embodiment, for example, as shown in formula (1) above, contains an Ir-Ru-Mo composite oxide as an essential component, as well as MoO, which is a low-crystalline oxide or amorphous oxide. ３ It may also contain a mixed oxide (1) with an Ir-Ru composite oxide, and MoO is a low-crystalline oxide or amorphous oxide. ３ and IrO ２ Mixed oxides (part 2) and MoO, which is a low-crystalline oxide or amorphous oxide. ３ and RuO ２ It may contain a mixed oxide (part 3) with a mixed oxide. It may also contain a mixed oxide of mixed oxide (part 1), mixed oxide (part 2), and mixed oxide (part 3). Molybdenum oxide is MoO ３ It contains as an essential component. Molybdenum oxide is MoO ３ It may also contain other molybdenum oxides. When the metal element of the metal composite oxide of this embodiment includes a fourth metal (M), the metal composite oxide of this embodiment, as shown in formula (1-1) above, contains Ir-Ru-Mo-M composite oxide as an essential component, as well as the above mixed oxide (1), mixed oxide (2), above mixed oxide (3), low-crystallinity oxide or amorphous oxide MoO ３ and M ｓ O ｔ The mixed oxide (of the fourth) may also be included. ｓ O ｔ　 The s and t in the expression are the same as the s and t in formula (1-1) above. Molybdenum oxide is MoO ３ It contains as an essential component. Molybdenum oxide is MoO ３Other molybdenum oxides may be included. It is presumed that by including low-crystallinity molybdenum oxide or amorphous molybdenum oxide, the iridium and ruthenium elements in the metal composite oxide of this embodiment will be more uniformly dispersed, and even with low content, sufficiently high performance can be achieved. The metal composite oxide of this embodiment is not particularly limited in terms of the form in which molybdenum oxide and Ir-Ru composite oxide are included, other than containing Ir-Ru-Mo composite oxide as an essential component. Examples include random dispersion structures, uniform dispersion structures, core-shell structures, island-sea structures, or mixed structures thereof.

[0027] In the composite metal oxide, it is preferable that iridium, ruthenium, molybdenum, or, if necessary, the fourth metal (M) is uniformly distributed among the multi-element metals. Uniform distribution can be confirmed, for example, using energy-dispersive X-ray spectroscopy (EDS). In elemental mapping by EDS, if each metal constituting the composite metal oxide is uniformly distributed and not aggregated, it is determined that the multi-element metals are uniformly distributed.

[0028] [MoO ３ The molybdenum oxide contained in the metal composite oxide of this embodiment has a low crystallinity or amorphous structure. Crystallinity can be evaluated, for example, using X-ray diffraction (powder X-ray diffraction, XRD). For example, if no peaks originating from molybdenum oxide are observed in the XRD spectrum despite the presence of any molybdenum oxide in the metal composite oxide, the molybdenum oxide is judged to be an amorphous (non-crystalline) oxide. If the intensity of the peak is excessively small relative to the molybdenum oxide content, or if the peak width is wide, the molybdenum oxide is judged to be a low crystallinity oxide.

[0029] [Iro ２ / RuO ２ The metal composite oxide of this embodiment is an Ir-Ru composite oxide (IrO ２ / RuO ２If it contains ), Ir-Ru composite oxide (IrO ２ / RuO ２ In this embodiment, the oxidation state of iridium and / or ruthenium is preferably +IV. The Ir-Ru composite oxide may also contain iridium and / or ruthenium with an oxidation state of +III. The structure of the Ir-Ru composite oxide contained in the metal composite oxide of this embodiment is not particularly limited. In the profile obtained from XRD using Cu-Kα rays as the X-ray source, the Ir-Ru composite oxide has peaks around 2θ = 28°, 2θ = 35°, 2θ = 40°, 2θ = 57.9°, and 2θ = 59.4°.

[0030] [Method for producing metal composite oxides] The method for producing metal composite oxides according to this embodiment includes the following steps: (I) A step of preparing a first mixed solution containing an iridium compound, a ruthenium compound, a compound of the fourth metal (M) if necessary, and an aqueous medium. (II) A step of adding a molybdenum compound to the first mixed solution to prepare a second mixed solution. (III) A step of adjusting the pH of the second mixed solution obtained in the above step to 1 using ammonia water to produce a precipitate. (IV) A step of isolating the precipitate obtained in the above step from the aqueous medium. (V) A step of calcining the precipitate obtained in the above step. In step (III), it is preferable to adjust the pH of the second mixed solution to 11 or more and 13 or less.

[0031] According to the method for producing metal composite oxides of this embodiment, it is possible to suitably produce the metal composite oxides of this embodiment described above.

[0032] Examples of the iridium compound include iridium salts and iridium-containing acids. The oxidation state of iridium is +III or +IV. Examples of iridium salts include halogenated salts, chloro complexes, nitrates, or acetates. Examples of iridium-containing acids include H ２ IrCl ６ Examples of ruthenium compounds include ruthenium salts. The oxidation state of ruthenium is +III or +IV. Examples of ruthenium salts include halogenated salts, chloro complexes, nitrates, or acetates.

[0033] As the molybdenum compound, for example, molybdenum salts and molybdenum-containing acids or their salts can be mentioned. The oxidation state of molybdenum is +III or +IV. As the molybdenum salt, for example, halide salts, chloro complexes, nitrates, or acetates can be mentioned. As the molybdenum-containing acid, for example, molybdic acid (H ２ MoO ４ ), etc. can be mentioned. As the salt of the molybdenum-containing acid, for example, ammonium molybdate ((NH ４ ) ６ Mo ７ O ２４ ), etc. can be mentioned.

[0034] As the compound of the fourth metal (M), for example, salts of the fourth metal (M) can be mentioned. As the salt of the fourth metal (M), for example, halide salts, chloro complexes, nitrates, or acetates can be mentioned. When the fourth metal (M) is, for example, Fe, Co, Ni, B, Al, Sn, Cr, Mn, Cu, Nd, specific examples of their compounds are, for example, FeCl ３ , Co(CH ３ COO) ２ ·4H ２ O, Ni(CH ３ COO) ２ ·4H ２ O, BCl ３ , AlCl ３ ·6H ２ O, SnCl ４ ·5H ２ O, MnCl ２ ·4H ２ O, CuCl ２ ·2H ２ O, NdCl ３ ·6H ２ O, etc. can be mentioned.

[0035] The total concentration of the iridium compound, the ruthenium compound, and optionally the compound of the fourth metal (M) in the first mixed solution is preferably 1 mmol / L to 100 mmol / L, and more preferably 10 mmol / L to 30 mmol / L, relative to the aqueous medium. The metal-equivalent molar ratio (iridium compound:ruthenium compound:fourth metal (M)) of the amounts of the iridium compound, the ruthenium compound, and optionally the compound of the fourth metal (M) is preferably 1:1:0.1 to 1:10:10, and more preferably 1:2:0.2 to 1:10:5.5. The concentration of the molybdenum compound in the second mixed solution is preferably 1 mmol / L to 500 mmol / L, and more preferably 5 mmol / L to 300 mmol / L, relative to the aqueous medium. The metal-equivalent molar ratio (iridium compound:ruthenium compound:molybdenum compound:fourth metal (M)) of the amounts of the molybdenum compound, iridium compound, ruthenium compound, and optionally the compound of the fourth metal (M) is preferably 1:1:0.1:0.1 to 1:10:40:10, and more preferably 1:2:1:0.2 to 1:10:35:5.5.

[0036] The aqueous medium can be any medium capable of dissolving the iridium compound, ruthenium compound, molybdenum compound, and the compound of the fourth metal (M) used in combination as needed, and can be water, an aqueous medium containing an organic medium, etc. Examples of organic media include alcohols such as methanol, benzene, dichloromethane, acetone, chloroform, etc.

[0037] The temperature of the second mixed solution should be such that it is possible to dissolve the iridium compound, ruthenium compound, molybdenum compound, and the compound of the fourth metal (M) which may be used in combination as needed. For example, it may be 10 to 100°C or 20 to 80°C. It may also be stirred as needed. In this step, the processing time may be, for example, 5 minutes or more or 10 minutes or more in order to sufficiently dissolve the metal compound.

[0038] Regarding the pH of the second mixed solution, it is preferable that the pH be between 11 and 13 from the viewpoint of obtaining the Ir-Ru-Mo composite oxide in the composite oxide. Furthermore, the reason for adjusting the pH of the second mixed solution with ammonia water is to prevent the inclusion of unwanted metal species (such as Na and K).

[0039] After a precipitate is formed from the above mixture, the metal composite oxide of this embodiment can be easily obtained by isolating the precipitate by washing, centrifugal separation, drying, and calcination as needed. In the calcination step of the precipitate obtained in the above step, the calcination temperature is preferably 300°C or higher, more preferably 330°C or higher, and even more preferably 360°C or higher. The calcination atmosphere may be air or atmospheric pressure. When the calcination temperature is 300°C or higher in the manufacturing method of this embodiment, the metal composite oxide of this embodiment can be formed more easily. Furthermore, when the calcination temperature is 800°C or lower, the crystallization of the molybdenum compound in the metal composite oxide can be suppressed. The calcination time may be 2 hours or more, or 10 hours or less.

[0040] (Composite) The composite of one embodiment of the present invention comprises the above-mentioned metal composite oxide and a carrier. The metal composite oxide is supported on the carrier. The carrier is an inorganic material. The inorganic material is tin oxide (SnO ２ Examples include ), transition metal oxides, carbon, etc. The proportion of the support in the composite of this embodiment is preferably 10% to 90% by mass.

[0041] [Tin oxide (SnO ２Examples of the tin oxide include undoped tin oxide particles and tin oxide particles doped with metal dopant. The undoped tin oxide particles and tin oxide particles doped with metal dopant can be, for example, the undoped tin oxide particles and tin oxide particles doped with metal dopant described in Patent Document 1. The tin oxide is preferably undoped tin oxide particles, more preferably titanium-doped tin oxide particles, and even more preferably niobium-doped tin oxide particles.

[0042] [Carbon] Examples of the carbon (carbon material) include graphite, carbon nanotubes, carbon fibers, carbon microbeads, or combinations thereof. Examples of the carbon shape include mesh, foam, porous, or combinations thereof. Carbon nanotubes are preferred as the carbon (carbon material), carbon microbeads are more preferred, and graphite is even more preferred.

[0043] [Transition metal oxides] Examples of the transition metal oxides include titanium oxide (e.g., TiO ２ ), zirconium oxide (for example, ZrO ２ ), niobium oxide (e.g., Nb ２ O ５ ), tantalum oxide (for example, Ta ２ O ５ ) or cerium oxide (e.g., CeO ２ Examples include the following. The transition metal oxide can be in powder or particulate form. The transition metal oxide may be doped with a suitable element. The transition metal oxide is preferably tantalum oxide, more preferably niobium oxide, and even more preferably titanium oxide.

[0044] (Method for producing the composite) The method for producing the composite according to this embodiment includes, for example, the following steps: (I) A step of dispersing the inorganic material as the carrier in an aqueous medium to prepare a dispersion (first aqueous dispersion). (II) A step of mixing the obtained dispersion with the following mixed liquid to prepare a mixed dispersion (second aqueous dispersion). The mixed liquid is a mixture containing an iridium compound, a ruthenium compound, and, if necessary, a compound of the fourth metal (M). (III) A step of blending a molybdenum compound into the mixed dispersion (second aqueous dispersion) to prepare a mixed dispersion (third aqueous dispersion). (IV) A step of adjusting the pH of the mixed dispersion (third aqueous dispersion) obtained in the above step using ammonia water to generate a precipitate. (V) A step of isolating the precipitate from the aqueous medium. (VI) A step of calcining the precipitate obtained in the above step. In step (IV), it is preferable to adjust the pH of the mixed dispersion (third aqueous dispersion) to 11 or more and 13 or less. Furthermore, the pH of the mixed dispersion is adjusted with ammonia water to prevent the inclusion of unwanted metal species (Na, K, etc.). In the step of calcining the precipitate obtained in the above step, the calcination temperature is preferably 300°C or higher, more preferably 330°C or higher, and even more preferably 360°C or higher. The calcination atmosphere may be air or atmospheric pressure. In the manufacturing method of this embodiment, if the calcination temperature is 300°C or higher, the composite supporting the metal composite oxide can be formed more easily. Also, if the calcination temperature is 800°C or lower, the crystallization of the molybdenum compound in the supported metal composite oxide can be suppressed. The calcination time may be 2 hours or more, or 10 hours or less.

[0045] In the step of preparing the mixed dispersion (second aqueous dispersion), it is preferable to adjust the proportion of the carrier in the resulting precipitate to be in the range of 10% to 90% by mass. Furthermore, it is preferable that the total concentration of the iridium compound, the ruthenium compound, the molybdenum compound, and optionally the compound of the fourth metal (M) be in the mixed dispersion (third aqueous dispersion) to be in the range of 1 mol / L to 30 mmol / L, and particularly preferably 5 mmol / L to 20 mmol / L. When other metal elements are used in combination, it is also preferable to adjust their total concentration to be within the above range.

[0046] The order in which the dispersion (first aqueous dispersion) and the mixture are mixed is not particularly limited. A preferred procedure is to add the mixture to the dispersion, as this makes it easy to control the mixing speed and adjust the temperature.

[0047] In the method for producing the composite of this embodiment, the iridium compound, the ruthenium compound, the molybdenum compound, the compound of the fourth metal (M), the aqueous medium, and other matters are the same as when obtaining the metal composite oxide.

[0048] (Oxygen Evolution Catalyst of the First Embodiment) The metal composite oxide of this embodiment can be suitably used as a catalyst (sometimes referred to as "oxygen evolution catalyst" in this specification) in the oxygen evolution reaction (OER). Furthermore, the metal composite oxide of this embodiment can also be used as an oxygen evolution catalyst when used in combination with a conductive material. By using the metal composite oxide of this embodiment in combination with a conductive material, the catalytic activity of the oxygen evolution catalyst in the oxygen evolution reaction (OER) is further increased. The oxygen evolution catalyst of this embodiment further contains a conductive material, but other than that, the components are the same as those of the metal composite oxide described above.

[0049] [Conductive material] The conductive material may be a known material. Examples of the conductive material include highly conductive carbon and metals. The oxygen generation catalyst may contain only one type of conductive material or two or more types.

[0050] Examples of the conductive material include acetylene black, carbon black such as Cabot carbon black and Ketjen black, graphite, carbon fiber, and metal powder.

[0051] Examples of the conductive metal include gold, silver, copper, aluminum, rhodium, molybdenum, tungsten, iron, nickel, cobalt, and iridium. Unlike iridium, ruthenium, and the fourth metal (M) in the metal composite oxide of this embodiment, the conductive metal in the oxygen evolution catalyst is simply mixed with the metal composite oxide of this embodiment.

[0052] The metal used as a conductive material in the oxygen-evolving catalyst of the first embodiment may be one type or two or more types.

[0053] The oxygen-evolving catalyst of the first embodiment may, for example, contain carbon but no metal as a conductive material, contain metal but no carbon, or contain both metal and carbon.

[0054] In the oxygen generation catalyst of the first embodiment, the content of the conductive material is preferably 0.1 to 100 parts by mass, and more preferably 0.5 to 50 parts by mass, based on the content of 100 parts by mass of the metal composite oxide of this embodiment.

[0055] In the oxygen evolution catalyst of the first embodiment, the total content ratio of the metal composite oxide of this embodiment and the conductive material to the total mass (100 mass%) of the oxygen evolution catalyst is preferably 80 mass% or more, more preferably 90 mass% or more, and even more preferably 95 mass% or more. For example, it may be 97 mass% or more, 99 mass% or more, or 100 mass%. When the ratio is above the lower limit, the catalytic activity of the oxygen evolution catalyst in the oxygen evolution reaction (OER) is increased. The ratio may be 100 mass% or less.

[0056] (Oxygen Evolution Catalyst of the Second Embodiment) The composite of this embodiment can be suitably used as a catalyst (sometimes referred to as "oxygen evolution catalyst" in this specification) in the oxygen evolution reaction (OER). Furthermore, the composite of this embodiment can also be used as an oxygen evolution catalyst when used in combination with a conductive material. When the composite of this embodiment is used in combination with a conductive material, the catalytic activity of the oxygen evolution catalyst in the oxygen evolution reaction (OER) is further increased. The oxygen evolution catalyst of the second embodiment is the same as the composite of this embodiment in terms of other components, except that it further contains a conductive material.

[0057] The conductive material may be the same as the conductive material of the oxygen generation catalyst in the first embodiment described above.

[0058] In the oxygen generation catalyst of the second embodiment, the content of the conductive material is preferably 0.1 to 100 parts by mass, and more preferably 0.5 to 50 parts by mass, based on 100 parts by mass of the composite content of this embodiment.

[0059] In the oxygen evolution catalyst, the total content ratio of the composite of this embodiment and the conductive material relative to the total mass (100% by mass) of the oxygen evolution catalyst is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. For example, it may be 97% by mass or more, 99% by mass or more, or 100% by mass. When the ratio is above the lower limit, the catalytic activity of the oxygen evolution catalyst in the oxygen evolution reaction (OER) is increased. The ratio may be 100% by mass or less.

[0060] (Catalyst Ink) The catalyst ink of one embodiment contains the metal composite oxide or composite of the embodiment described above, and a medium. The catalyst ink of the embodiment may contain the metal composite oxide or composite of the embodiment described above, a polymer electrolyte, and a medium.

[0061] The catalyst ink of this embodiment may further contain a conductive material. Examples of the type and content of the conductive material are those exemplified above.

[0062] The catalyst ink can be applied to, for example, a substrate for a working electrode to form a catalyst layer.

[0063] As the aforementioned polymer electrolyte, those commonly used in the formation of catalyst layers can be used. Specifically, examples include perfluorocarbon polymers having sulfonic acid groups (e.g., Nafion®), oxygen-carbide polymer compounds having sulfonic acid groups, polymer compounds doped with inorganic acids such as phosphoric acid, organic / inorganic hybrid polymers in which a portion is substituted with proton-conducting functional groups, and proton conductors in which a polymer matrix is ​​impregnated with a phosphoric acid solution or sulfuric acid solution.

[0064] The medium can be any medium capable of dispersing the metal composite oxide of this embodiment or the composite of this embodiment, and capable of being applied to a substrate for a working electrode or the like to form a catalyst layer. Preferably, the medium contains alcohols such as 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 1-hexanol, 2-hexanol, 1-heptanol, and 2-heptanol.

[0065] (Electrode) An electrode according to one embodiment of the present invention is provided with the metal composite oxide or composite on its surface. For example, an electrode provided with the metal composite oxide or composite on its surface can be produced by applying the catalyst ink in the dispersion state obtained above to the electrode surface, allowing it to air dry, then transferring it to a vacuum dryer and drying it at 30 to 90°C for 2 hours or more. The oxygen evolution activity of the produced electrode can be evaluated using a three-electrode method. The evaluation conditions are, for example, the LSV method, with a scan voltage range from -0.3V to 0V and a scan speed of 5mV / s.

[0066] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0067] (Evaluation) [Measurement of composition ratio by XRF] [XRF analysis] Using a Primus IV X-ray fluorescence analyzer (manufactured by Rigaku Corporation), approximately 20-30 mg of the sample was placed on filter paper, covered with a PP film, and subjected to compositional analysis. The amounts of iridium, ruthenium, molybdenum, cobalt, iron, nickel, tin, and oxygen, which were determined from the XRF analysis results, were calculated as the content of each element relative to 100% by mass of the sample particles.

[0068] [Measurement of Primary Particle Size] The particle size of the primary particles in the sample powder was measured using the <Method for Measuring Primary Particle Size> described above. In this example and comparative example, the primary particle size was measured using a transmission electron microscope. A JEM-1400 transmission electron microscope manufactured by JEOL Ltd. was used.

[0069] [EDS Mapping Measurement] To evaluate the compositional distribution of the sample powders obtained in the examples, EDS (energy-dispersive X-ray spectroscopy) mapping measurements were performed. Equipment used: Desktop scanning electron microscope with EDS function, JEOL Ltd., JCM-7000

[0070] [Median diameter D] ５０ [Measurement] 0.1 g of sample powder was added to 20 mL of acetone, and sonicated in an ice bath for 4 hours. Then, the concentration was adjusted with acetone to a level within the measurable range of a dynamic light scattering particle size distribution analyzer (Microtrac Bell, Nanotrac Wave II) to obtain a measurement sample. Using this measurement sample, the particle size distribution in the range of 0.0001 μm to 10 μm was measured using a dynamic light scattering particle size distribution analyzer, and the median diameter D was determined as the particle size at which the volume integrated percentage was 50%. ５０ The median diameter D was calculated. ５０ For particles larger than 10 μm (Comparative Example 2), the solution was prepared similarly, and the particle size distribution in the range of 0.015 μm to 500 μm was measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD-7000), and the median diameter D ５０ The result was calculated.

[0071] [Measurement of BET specific surface area] The specific surface area was measured using a specific surface area meter (Microtrac-Bel, BELSORP-mini), and the surface area per gram of sample, measured from the amount of nitrogen gas adsorbed by the BET method, was calculated as the specific surface area.

[0072] [Measurement of Overpotential (Evaluation of Oxygen Evolution Activity)] The overpotential of the fabricated electrodes was measured using a three-electrode system. The measurement conditions were LSV method, with a scan voltage range from -0.3V to 0V and a scan speed of 5mV / s. Current density: 10mA / cm² ２ The overvoltage (mV) was measured at [location].

[0073] [Crystal structure analysis of metal composite oxides: XRD method] Samples of metal composite oxides obtained in each example were packed into a 0.5 mm deep sample holder, and then set in an X-ray diffraction (XRD) apparatus (Ultima IV manufactured by Rigaku Corporation, using a parallel beam method + scintillation counter detector and rotating stage). Measurements were performed under the following conditions: Cu / Kα rays, 40 kV / 40 mA, scan speed (2θ) 2° / min, step (2θ) 0.02°, and scan range (2θ) 10° to 130°.

[0074] (Example 1) SnO ２ (Kanto Chemical Co., Ltd. reagent) 24 mg was dispersed in 12 ml of pure water using ultrasound for 30 minutes. IrCl ３ 3H ２ O (Kanto Chemical Co., Ltd. reagent) 72 mg and RuCl ３ 3H ２ Dissolve 160 mg of O (Kanto Chemical Co., Ltd. reagent) in 1 ml of pure water, and prepare the above SnO ２ It was added to the dispersion. The mixed dispersion was heated at 80°C for 10 minutes, then cooled to room temperature (25°C). While stirring, (NH ４ ) ６ Mo ７ O ２４ 6H ２ 36 mg of O (Kanto Chemical Co., Ltd. reagent) was added to the above mixed dispersion. Subsequently, ammonia water (Kanto Chemical Co., Ltd., NH ３ ・H ２The pH of the above mixed dispersion was adjusted to 12, and it was allowed to stand for 1 hour. The precipitate was collected by centrifugation. The precipitate was washed three times with pure water and then dried under vacuum at 80°C. The obtained product was further calcined at 400°C for 1 hour to obtain a powder. The obtained powder was a metal composite oxide containing Ir, Ru, and Mo, with SnO as the support. ２ It was a composite supported on. Hereinafter, the powder obtained in this embodiment and the particles constituting the powder will be referred to as "SnO ２ / / IrO ２ / RuO ２ / Ir-Ru-Mo-O ｘ It is sometimes written as "complex."

[0075] The composition of the obtained powder and the percentage of each element were measured by the above-mentioned X-ray fluorescence analysis (XRF). The results are shown in Table 2. The particle size and median diameter D of the primary particles of the obtained powder are shown below. ５０ The surface area and specific surface area were measured using the above measurement method, and the results are shown in Table 2.

[0076] A catalyst ink was prepared by adding 4 mg of the obtained powder, 2 mg of Ketjenbrak EC300J (Lion Specialty Chemicals Co., Ltd.), and 40 μL of 5% Nafion dispersion (Fujifilm Wako Pure Chemical Industries, Ltd. Nafion dispersion solution) to 1 mL of ethanol and treating it in an ultrasonic disperser for 1 hour. 20 μL of the obtained catalyst ink was applied to the electrode surface, the liquid on the surface was allowed to dry naturally, and then it was transferred to a vacuum dryer and dried at 60°C for 6 hours to obtain an electrode with a composite on its surface. The current density of the fabricated electrode was 10 mA / cm². ２ The overvoltage (mV) at this location was measured to be 231 mV. The results are shown in Table 2.

[0077] (Example 2) As shown in Table 1, (NH ４ ) ６ Mo ７ O ２４ 6H ２ Except for changing the amount of O added to 252 mg, the same procedure as in Example 1 was followed to obtain SnO ２ / / IrO ２ / RuO ２ / Ir-Ru-Mo-Oｘ A composite was obtained. The composition was calculated in the same manner as in Example 1, and the particle size and median diameter D of the primary particles were also determined. ５０ The specific surface area was evaluated, and the results are shown in Table 2. Figure 2 shows images obtained using a transmission electron microscope (TEM, JEOL Ltd., JEM-1400) of the particles obtained in this example. Then, in the same manner as in Example 1, except that the obtained powder was used, the catalyst ink was prepared and electrodes were fabricated, and the oxygen evolution activity (overpotential) of the electrodes was evaluated. The results are shown in Table 2.

[0078] (Example 3) As shown in Table 1, (NH ４ ) ６ Mo ７ O ２４ 6H ２ Except for changing the amount of O added to 504 mg, the same procedure as in Example 1 was followed to obtain SnO ２ / / IrO ２ / RuO ２ / Ir-Ru-Mo-O ｘ A composite was obtained. The composition was calculated in the same manner as in Example 1, and the particle size and median diameter D of the primary particles were also determined. ５０ The specific surface area was evaluated, and the results are shown in Table 2. Figure 3 shows images obtained using a transmission electron microscope (TEM, JEOL Ltd., JEM-1400) of the particles obtained in this example. Then, the catalyst ink was prepared and electrodes were fabricated in the same manner as in Example 1, except that the obtained powder was used, and the oxygen evolution activity (overpotential) of the electrodes was evaluated. The results are shown in Table 2.

[0079] (Example 4) As shown in Table 1, (NH ４ ) ６ Mo ７ O ２４ 6H ２ Except for changing the amount of O added to 1009 mg, the same procedure as in Example 1 was followed to obtain SnO ２ / / IrO ２ / RuO ２ / Ir-Ru-Mo-O ｘ A composite was obtained. The composition was calculated in the same manner as in Example 1, and the particle size and median diameter D of the primary particles were also determined. ５０The specific surface area was evaluated, and the results are shown in Table 2. Then, the catalyst ink was prepared and the electrode fabricated in the same manner as in Example 1, except that the obtained powder was used, and the oxygen evolution activity (overpotential) of the electrode was evaluated. The results are shown in Table 2.

[0080] (Example 5) As shown in Table 1, (NH ４ ) ６ Mo ７ O ２４ 6H ２ Except for changing the amount of O added to 1261 mg, the same procedure as in Example 1 was followed to obtain SnO ２ / / IrO ２ / RuO ２ / Ir-Ru-Mo-O ｘ A composite was obtained. The composition was calculated in the same manner as in Example 1, and the particle size and median diameter D of the primary particles were also determined. ５０ The specific surface area was evaluated, and the results are shown in Tables 1 and 2. Then, the catalyst ink was prepared and the electrode was fabricated in the same manner as in Example 1, except that the obtained powder was used, and the oxygen evolution activity (overpotential) of the electrode was evaluated. The results are shown in Table 2.

[0081] (Comparative Example 1) As shown in Table 1, (NH ４ ) ６ Mo ７ O ２４ 6H ２ Except for not adding any oxygen, the process was the same as in Example 1, but with respect to SnO ２ / / RuO ２ / IrO ２ A composite was obtained. Then, the catalyst ink was prepared and an electrode was fabricated in the same manner as in Example 1, except that the obtained powder was used, and the oxygen evolution activity of the electrode was evaluated. The results are shown in Table 2.

[0082] (Comparative Example 2) "Commercial IrO ｘ "IrO purchased from Tanaka Precious Metals Co., Ltd." ｘ (With an Ir content of 76% by mass) was used as the powder for this comparative example. Then, except for the use of this powder, the catalyst ink was prepared and the electrode was fabricated in the same manner as in Example 1, and the oxygen evolution activity of the electrode was evaluated. The results are shown in Table 2.

[0083] (Example 6) As shown in Table 3, (NH ４ ) ６ Mo ７ O ２４ 6H ２ The amount of O added was changed to 36.05 mg, and Co(CH) ３ COO) ２ 4H ２ Except for adding 50.86 mg of O (Kanto Chemical Co., Ltd. reagent) to the mixed dispersion, the procedure was the same as in Example 1, and SnO was prepared. ２ / / Ir-Ru-Mo-Co-O ｘ A composite was obtained. The composition was calculated in the same manner as in Example 1, and the particle size and median diameter D of the primary particles were also determined. ５０ The specific surface area was evaluated, and the results are shown in Table 4. Then, the catalyst ink was prepared and the electrode was fabricated in the same manner as in Example 1, except that the obtained powder was used, and the oxygen evolution activity (overpotential) of the electrode was evaluated. The results are shown in Table 4.

[0084] (Example 7) As shown in Table 3, (NH ４ ) ６ Mo ７ O ２４ 6H ２ The amount of O added was changed to 36.05 mg, and Co(CH) ３ COO) ２ 4H ２ 50.86 mg of O and FeCl ３ 6H ２ Except for adding 55.2 mg of O (Kanto Chemical Co., Ltd. reagent) to the mixed dispersion, the same procedure as in Example 1 was followed to prepare SnO ２ / / Ir-Ru-Mo-Co-Fe-O ｘ A composite was obtained. The composition was calculated in the same manner as in Example 1, and the particle size and median diameter D of the primary particles were also determined. ５０ The specific surface area was evaluated, and the results are shown in Table 4. Then, the catalyst ink was prepared and the electrode was fabricated in the same manner as in Example 1, except that the obtained powder was used, and the oxygen evolution activity (overpotential) of the electrode was evaluated. The results are shown in Table 4.

[0085] (Example 8) As shown in Table 3, (NH ４ ) ６ Mo７ O ２４ 6H ２ The amount of O added was changed to 36.05 mg, and Co(CH) ３ COO) ２ 4H ２ O 25.4 mg and FeCl ３ 6H ２ O 27.6 mg and Ni (CH ３ COO) ２ 4H ２ Except for adding 25.4 mg of O (Kanto Chemical Co., Ltd. reagent) to the mixed dispersion, the same procedure as in Example 1 was followed to prepare SnO ２ / / Ir-Ru-Mo-Co-Fe-Ni-O ｘ A composite was obtained. The composition was calculated in the same manner as in Example 1, and the particle size and median diameter D of the primary particles were also determined. ５０ The specific surface area was evaluated, and the results are shown in Table 4. Then, the catalyst ink was prepared and the electrode was fabricated in the same manner as in Example 1, except that the obtained powder was used, and the oxygen evolution activity (overpotential) of the electrode was evaluated. The results are shown in Table 4.

[0086]

[0087]

[0088]

[0089]

[0090] Figure 1 shows the XRD spectrum of the particles obtained in Example 3. In Figure 1, SnO ２ The peak of origin, RuO ２ The origin of the peak and IrO ２ A peak indicating the origin was observed. RuO ２ The origin of the peak and IrO ２ The originating peak was observed as a synthesis peak. However, no peak originating from molybdenum oxide was observed. Furthermore, in the XRD spectra of the particles obtained in Examples 1-2 and 5, similar to Example 3, SnO ２ The peak of origin, RuO ２ The origin of the peak and IrO ２Peaks originating from the substance were observed, but peaks originating from molybdenum oxide were not.

[0091] Figure 6 shows the XRD spectrum of the particles obtained in Example 6. In Figure 6, SnO ２ A peak was observed in the origin of RuO ２ The origin of the peak and IrO ２ No peaks originating from the substance were observed, nor were any peaks originating from molybdenum oxide or cobalt oxide. Furthermore, in the XRD spectra of the particles obtained in Examples 7-8, similar to Example 6, SnO ２ Peaks originating from the respective metal oxides were observed, but peaks originating from Ru, Ir, Mo, Co, Fe, and Ni were not observed.

[0092] Figures 2 and 3 show observation images of the particles from Example 2 and Example 3, respectively, obtained using a transmission electron microscope (TEM, JEOL Ltd., JEM-1400). From Figures 2 and 3, composites with particle sizes of several nanometers were observed. Furthermore, TEM observation images of the particles obtained in Examples 1, 4-8 also confirmed that they had similar particle sizes.

[0093] Figures 4 and 5 show images obtained by elemental mapping using scanning electron microscope energy-dispersive X-ray spectroscopy (SEM-EDS, JEOL Ltd., JSM-7900F) on the particles obtained in Example 8. Ir, Ru, Mo, Fe, Co, Ni, and Sn were mapped. From Figures 4 and 5, it was confirmed that these metals are uniformly distributed in the particles obtained in Example 8, as they are uniformly scattered and not aggregated. Similarly, in Examples 1 to 7, the images obtained by elemental mapping also showed that the various metals are uniformly distributed, as they are uniformly scattered and not aggregated.

[0094] From Table 2, the particles of Example 1 are the same as the commercially available IrO of Comparative Example 2. ｘIn comparison, it was found that despite having about 1 / 4 the iridium content, the overpotential was similar and the catalytic performance was similar. Furthermore, the particles of Example 1 had a lower overpotential than the particles of Comparative Example 1, despite having a lower total iridium and ruthenium content. And the particles of Example 5 were similar to the commercially available IrO2 of Comparative Example 2. ｘ In comparison, despite having an iridium content of 1 / 7.6, it was found to exhibit significantly lower overpotential and remarkably superior catalytic performance.

[0095] From Table 4, the particles of Examples 6-8 are the same as the commercially available IrO of Comparative Example 2. ｘ In comparison, it was found that the overpotential was low despite the iridium content being about 1 / 5 to 1 / 3.5. Furthermore, the particles of Examples 6 to 8 showed low overpotential despite having lower iridium and ruthenium content compared to the particles of Comparative Example 1. These results indicate that the present invention contributes to the reduction of iridium and ruthenium. It is also presumed that the catalytic performance can be maintained over the long term by using the metal composite oxide in the present invention.

Claims

1. A metal composite oxide containing iridium, ruthenium, and molybdenum, wherein the composite oxide of iridium, ruthenium, and molybdenum is a low-crystalline oxide or amorphous oxide.

2. The metal composite oxide according to claim 1, further comprising a quaternary metal (M), and comprising a composite oxide of iridium, ruthenium, molybdenum, and the quaternary metal (M).

3. The metal composite oxide according to claim 2, wherein the fourth metal (M) is one or more elements selected from the group consisting of B, Al, Sn, Cr, Mn, Fe, Co, Ni, Cu, and Nd.

4. The metal composite oxide according to claim 1 or 2, wherein the iridium content is 50% by mass or less and the molybdenum content is 1% by mass or more and 10% by mass or less.

5. The metal composite oxide according to claim 1 or 2, wherein the particle size of the primary particles is 100 nm or less.

6. Median diameter D determined by dynamic light scattering method ５０ However, the metal composite oxide according to claim 1 or 2, wherein the wavelength is 500 nm or less.

7. The specific surface area measured by the BET method is 10 m². ２ The metal composite oxide according to claim 1 or 2, wherein the amount is 1 / g or more.

8. The metal composite oxide according to claim 1 or 2, wherein the ratio of the total content of iridium and ruthenium to the total mass of the metal composite oxide, as determined by XRF analysis, is 50% by mass or more and 80% by mass or less.

9. A composite comprising a metal composite oxide according to claim 1 or 2 and a carrier, wherein the metal composite oxide is supported on the carrier, and the carrier is an inorganic material.

10. The carrier is tin oxide (SnO ２ The composite according to claim 9, wherein the composite is at least one selected from the group consisting of ) and carbon.

11. An oxygen-evolving catalyst comprising a metal composite oxide as described in claim 1 or 2.

12. The oxygen-evolving catalyst according to claim 11, further comprising a conductive material.

13. An oxygen-evolving catalyst comprising the complex described in claim 9.

14. The oxygen-evolving catalyst according to claim 13, further containing a conductive material.

15. A catalyst ink comprising a metal composite oxide according to claim 1 or 2 and a medium.

16. The catalyst ink according to claim 15, further comprising a conductive material.

17. The catalyst ink according to claim 15, further comprising a polymer electrolyte.

18. A catalyst ink comprising the composite according to claim 9 and a medium.

19. The catalyst ink according to claim 18, further comprising a conductive material.

20. The catalyst ink according to claim 18, further comprising a polymer electrolyte.

21. An electrode having a metal composite oxide as described in claim 1 or 2 on its surface.

22. An electrode having the composite material described in claim 9 on its surface.

23. A method for producing a metal composite oxide, comprising the steps of: preparing a first mixed solution containing an iridium compound, a ruthenium compound, and an aqueous medium; preparing a second mixed solution by adding a molybdenum compound to the first mixed solution; adjusting the pH of the second mixed solution obtained in the first step using aqueous ammonia to generate a precipitate; isolating the precipitate from the aqueous medium; and calcining the precipitate obtained in the first step.

24. A method for producing a metal composite oxide, comprising the steps of: preparing a first mixed solution containing an iridium compound, a ruthenium compound, a compound of a fourth metal (M), and an aqueous medium; preparing a second mixed solution by adding a molybdenum compound to the first mixed solution; adjusting the pH of the second mixed solution obtained in the first step using aqueous ammonia to generate a precipitate; isolating the precipitate from the aqueous medium; and calcining the precipitate obtained in the first step.

25. A method for producing a composite, comprising the steps of: dispersing an inorganic material that serves as a carrier in an aqueous medium to prepare a first aqueous dispersion containing the inorganic material; mixing the first aqueous dispersion with a mixture containing an iridium compound and a ruthenium compound to prepare a second aqueous dispersion; blending a molybdenum compound into the second aqueous dispersion to prepare a third aqueous dispersion; adjusting the pH of the third aqueous dispersion using ammonia water to generate a precipitate; isolating the precipitate from the aqueous medium; and calcining the precipitate obtained in the above steps.

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