Composite, hydrogen generation catalyst, catalytic ink, electrode, and method for producing composite

Abstract

This composite comprises a molybdenum compound and a noble metal. The molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide and molybdenum carbides, and the noble metal is at least one metal selected from the group consisting of platinum and palladium.

Description

Composite, hydrogen generation catalyst, catalytic ink, electrode, and method for producing the composite

[0001] The present invention relates to a composite, a hydrogen generation catalyst, a catalytic ink, an electrode, and a method for manufacturing the composite. This application claims priority based on Japanese Patent Application No. 2024-014259, filed February 1, 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 electricity, with the aim of solving environmental and energy resource problems. ２ Layered transition metal chalcogen compounds, such as , are expected to be inexpensive, abundant, and highly catalytically active materials.

[0003] Patent Document 1 discloses a method for producing molybdenum disulfide doped with metal ions, and cites that the metal cations of the doped metal are uniformly dispersed between the layers of molybdenum disulfide, and that the material maintains the two-dimensional sheet structure of molybdenum disulfide in its crystalline structure.

[0004] Chinese Patent Application Publication No. 106608652

[0005] However, there is still room for further study on providing a novel catalytic material containing a molybdenum compound such as molybdenum disulfide. An object of the present invention is to provide a composite, a hydrogen generation catalyst, a catalytic ink, an electrode, and a method for producing the composite, which can be used as a catalyst.

[0006] The present invention encompasses the following aspects: [1] A composite containing a molybdenum compound and a noble metal, wherein the molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide and molybdenum carbide, and the noble metal is at least one metal selected from the group consisting of platinum and palladium. [2] The composite according to [1], wherein the noble metal is platinum and palladium. [3] The molybdenum sulfide is MoS having a 3R structure. ２ [4] The composite according to [1] or [2], wherein the molybdenum carbide is Mo ２The composite according to [1] or [2], wherein the molybdenum carbide has a C crystal structure and a carbon content of 6% or more relative to the total mass (100% by mass) of the molybdenum carbide. [5] The composite according to any one of [1] to [4], wherein the molybdenum carbide has a carbon-derived graphite band G and a disorder band D measured by Raman spectroscopy. [6] The composite according to [5], wherein the molybdenum carbide has a ratio (G / D) of the carbon-derived graphite band G to the disorder band D of 0.75 or more. [7] The composite has a median diameter D of 0.75 or more measured by dynamic light scattering. ５０ [8] The composite according to any one of [1] to [6], wherein the specific surface area of ​​the composite measured by the BET method is 10 m ２ / g or more. [9] The composite according to any one of [1] to [8], wherein the ratio of the content of the precious metal to the total mass of the composite, as determined by XRF analysis, is 0.1 mass% or more.

[10] The composite according to any one of [1] to [9], wherein the precious metal is a precious metal particle having an average particle size of 20 nm or less.

[11] The composite according to any one of [1] to

[10] , wherein the palladium particles comprise aggregates of palladium atoms not having a crystalline structure.

[12] A hydrogen generating catalyst comprising the composite according to any one of [1] to

[11] .

[13] The hydrogen generating catalyst according to

[12] , further containing a conductive material.

[14] A catalyst ink comprising the composite according to any one of [1] to

[11] and a solvent.

[15] The catalyst ink according to

[14] , further containing a conductive material.

[16] The catalyst ink according to

[14] or

[15] , further containing a polymer electrolyte.

[17] An electrode coated with the catalyst ink according to any one of

[14] to

[16] .

[18] A method for producing a composite, comprising the steps of: mixing a molybdenum compound with a precious metal solution, wherein the content of the precious metal relative to the total mass (100 mass%) of the molybdenum compound is 50 mass% or less, the molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide and molybdenum carbide, and the precious metal is at least one metal selected from the group consisting of platinum and palladium.

[19] A method for producing a composite, comprising the steps of: mixing a molybdenum compound with a solvent to obtain a molybdenum compound dispersion, and mixing an alkali metal hydroxide and a precious metal compound with the molybdenum compound dispersion, wherein the molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide and molybdenum carbide, and the precious metal in the precious metal compound is at least one metal selected from the group consisting of platinum and palladium.

[20] The method for producing a composite according to

[18] or

[19] , wherein the molybdenum compound comprises molybdenum carbide, and the molybdenum carbide is obtained by calcining molybdenum trioxide containing α-crystals and carbon in the presence of at least one inorganic compound selected from the group consisting of inorganic salts and inorganic hydroxides.

[21] The method for producing a composite according to

[20] , wherein the average crystallite size of α crystals of the molybdenum trioxide is 50 nm or less.

[0007] According to the present invention, it is possible to provide a composite, a hydrogen generating catalyst, a catalytic ink, an electrode, and a method for producing the composite, which can be used as a catalyst.

[0008] Fig. 1 is a schematic diagram showing an example of an apparatus used for producing molybdenum trioxide particles. Fig. 2 is a transmission electron microscope (TEM, manufactured by JEOL Ltd., JEM-1400) image of each particle obtained in Example 1. Fig. 3 is a transmission electron microscope (TEM, manufactured by JEOL Ltd., JEM-1400) image of each particle obtained in Example 10. Fig. 4 is a transmission electron microscope (TEM, manufactured by JEOL Ltd., JEM-1400) image of each particle obtained in Example 17.

[0009] <<Composite>> A composite according to one embodiment of the present invention includes a molybdenum compound and a noble metal. The molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide and molybdenum carbide. The noble metal is at least one metal selected from the group consisting of platinum and palladium. The molybdenum compound may be molybdenum compound particles, and the noble metal may be noble metal particles.

[0010] The composite of this embodiment has a structure in which the molybdenum compound and the noble metal are combined.

[0011] In this specification, the "composite" may refer to a state in which a molybdenum compound and a precious metal are integrated through any interaction. The interaction is not particularly limited, but examples include physical interactions between the surface of the molybdenum compound particles (for example, if the molybdenum compound particles are in the form of a sheet or ribbon (described below), this would be assumed to be depressions or wrinkles on the surface) and the surface of the precious metal particles, as well as chemical bonds such as coordinate bonds, ionic bonds, and intermolecular forces. Examples of chemical bonds include S-Pd, S-Pt, C-Pd, and C-Pt bonds, depending on the type of molybdenum compound and precious metal.

[0012] The composite of this embodiment may be a particulate structure (composite particle).

[0013] The median diameter D of the complex of this embodiment determined by dynamic light scattering ５０ The median diameter D is preferably 1000 nm or less, more preferably 600 nm or less, and even more preferably 500 nm or less. ５０ A composite having a t value equal to or less than the upper limit can more effectively exhibit catalytic efficiency.

[0014] The median diameter D of the complex of this embodiment determined by dynamic light scattering ５０ For example, the thickness may be 20 nm or more, 40 nm or more, 100 nm or more, or 300 nm or more.

[0015] The median diameter D of the complex of this embodiment determined by dynamic light scattering ５０ An example of the range of the above numerical value may be 20 nm or more and 1000 nm or less, 40 nm or more and 600 nm or less, 100 nm or more and 500 nm or less, or 300 nm or more and 500 nm or less.

[0016] The median diameter D of the complex of this embodiment calculated by dynamic light scattering ５０ can be determined as the particle size at which the volume cumulative percentage is 50% in a particle size distribution measured in a wet state using a dynamic light scattering particle size distribution analyzer (e.g., Nanotrac Wave II, manufactured by Microtrac-Bell) and ethanol as a medium.

[0017] The specific surface area of ​​the composite of this embodiment measured by the BET method is 10 m ２ / g or more, and ２ / g or more is more preferable, and 40m ２ A composite having a specific surface area equal to or greater than the above lower limit has a large specific surface area, which increases catalytically active sites and facilitates material transfer in the reaction system, thereby enabling the catalytic efficiency to be improved more effectively.

[0018] The specific surface area of ​​the composite of this embodiment measured by the BET method is, for example, 1000 m ２ / g or less, and ２ / g or less, and ２ / g or less, and ２ / g or less.

[0019] An example of the range of the specific surface area of ​​the composite of this embodiment measured by the BET method is 10 m ２ / g or more 1000m ２ / g or less, and ２ / g or more 500m ２ / g or less, and ２ / g or more 300m ２ / g or less, and ２ / g or more 200m ２ / g or less.

[0020] The specific surface area is measured using a specific surface area meter (for example, BELSORP-mini manufactured by Microtrac-Bell Co., Ltd.), and the surface area per 1 g of sample measured from the amount of nitrogen gas adsorbed by the BET method (Brunauer-Emmett-Teller method) is defined as the specific surface area (m ２ / g).

[0021] The ratio of the content of the noble metal in the composite of this embodiment to the total mass (100 mass%) of the composite, as determined by X-ray fluorescence (XRF) analysis, is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, and even more preferably 1 mass% or more. A composite having a noble metal content equal to or greater than the lower limit can more effectively exhibit catalytic efficiency derived from the noble metal.

[0022] The ratio of the content of the precious metal to the total mass (100% by mass) of the composite of this embodiment, as determined by XRF analysis, may be, for example, 50% by mass or less, 20% by mass or less, or 10% by mass or less.

[0023] An example of the range of the ratio of the content of the precious metal to the total mass (100% by mass) of the composite of this embodiment, as determined by XRF analysis, is 0.1% by mass or more and 50% by mass or less, 0.5% by mass or more and 20% by mass or less, or 1% by mass or more and 10% by mass or less.

[0024] The ratio of the molybdenum content of the composite of the present embodiment to the total mass (100 mass%) of the composite, as determined by X-ray fluorescence (XRF) analysis, may be 30 mass% or more, 40 mass% or more, or 50 mass% or more.

[0025] The molybdenum content of the composite of this embodiment relative to the total mass (100 mass%) of the composite, as determined by XRF analysis, may be, for example, 80 mass% or less, 75 mass% or less, or 70 mass% or less.

[0026] For the composite of this embodiment, the ratio of the molybdenum content relative to the total mass (100 mass%) of the composite, as determined by XRF analysis, may be, for example, 30 mass% or more and 80 mass% or less, 40 mass% or more and 75 mass% or less, or 50 mass% or more and 70 mass% or less.

[0027] The ratio of the sulfur content of the composite of the present embodiment to the total mass (100 mass%) of the composite, as determined by X-ray fluorescence (XRF) analysis, may be 15 mass% or more, 20 mass% or more, or 25 mass% or more.

[0028] The ratio of the sulfur content of the composite of this embodiment relative to the total mass (100% by mass) of the composite, as determined by XRF analysis, may be, for example, 50% by mass or less, 45% by mass or less, or 40% by mass or less.

[0029] For the composite of this embodiment, the ratio of the sulfur content relative to the total mass (100 mass%) of the composite, as determined by XRF analysis, may be, for example, 15 mass% or more and 50 mass% or less, 20 mass% or more and 45 mass% or less, or 25 mass% or more and 40 mass% or less.

[0030] The molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide and molybdenum carbide. The molybdenum sulfide is preferably molybdenum disulfide. The noble metal is at least one metal selected from the group consisting of platinum and palladium. The noble metal is preferably platinum, and more preferably platinum and palladium. When the noble metals are platinum and palladium, the mass ratio of platinum to palladium (Pd:Pt) is preferably 10:1 to 1:10, preferably 5:1 to 1:5, and more preferably 2:1 to 1:2, from the viewpoint of catalytic activity. Details of molybdenum disulfide, molybdenum carbide, palladium (Pd), and platinum (Pt) are described below.

[0031] <Molybdenum disulfide> The molybdenum compound contained in the composite of the present embodiment may be molybdenum disulfide. The molybdenum disulfide may be MoS containing a 3R structure. ２ The molybdenum disulfide is preferably combined with the noble metal to form a composite.

[0032] The molybdenum disulfide in the composite of this embodiment is preferably molybdenum disulfide particles. The shape of the primary particles of the molybdenum disulfide particle portion in a two-dimensional image obtained by photographing the molybdenum disulfide particles with a transmission electron microscope (TEM) may be any shape, but is preferably particulate, spherical, plate-like, needle-like, string-like, ribbon-like, or sheet-like, and more preferably string-like, ribbon-like, or sheet-like. The molybdenum disulfide particles may include a combination of these shapes. Here, "ribbon-like" or "sheet-like" refers to a thin layer shape, and "ribbon-like" refers to a long thin layer shape.

[0033] When the shape of the primary particles of the molybdenum disulfide particle portion is string-like, ribbon-like, or sheet-like, the average thickness measured for 50 primary particles of the molybdenum disulfide particle portion is preferably 100 nm or less, more preferably 50 nm or less, even more preferably 30 nm or less, and particularly preferably 15 nm or less.

[0034] As an example of the numerical range of the thickness, when the shape of the primary particles of the molybdenum disulfide particle portion is string-like, ribbon-like, or sheet-like, the average thickness measured for 50 primary particles of the molybdenum disulfide particle portion may be 1 to 100 nm, 3 to 50 nm, 5 to 30 nm, or 5 to 15 nm.

[0035] The molybdenum disulfide particle portion preferably has a string-like, ribbon-like, or sheet-like shape, and the average shape of 50 primary particles of the molybdenum disulfide particle portion preferably has a size in the range of length (vertical) × width (horizontal) × thickness (height) = 50-1000 nm × 50-1000 nm × 3-100 nm, more preferably 100-500 nm × 100-500 nm × 5-50 nm, and particularly preferably 50-200 nm × 50-200 nm × 5-20 nm. The string-like, ribbon-like, or sheet-like shape allows the specific surface area of ​​the molybdenum disulfide particle portion to be increased. The aspect ratio of the primary particles of the molybdenum disulfide particle portion, i.e., the value of (length (length and width)) / thickness (height)), is preferably 1.2 to 1200, more preferably 2 to 800, even more preferably 5 to 400, and particularly preferably 10 to 200, on average for 50 particles.

[0036] The length, width, and thickness of the molybdenum disulfide particle portions can be measured with an atomic force microscope (AFM).

[0037] When the shape of the primary particles of the molybdenum disulfide particles is not simple spheres but string-like, ribbon-like, or sheet-like with a large aspect ratio, the specific surface area is increased, and the catalytic efficiency can be effectively improved.

[0038] The molybdenum disulfide particles are molybdenum disulfide (MoS ２ The composite of the present embodiment contains molybdenum disulfide (MoS) relative to the total mass (100 mass%) of the composite. ２ The composite preferably contains 50 mass % or more, more preferably 80 mass % or more, and even more preferably 85 mass % or more of molybdenum disulfide. A composite having a molybdenum disulfide content of at least the above lower limit can more effectively exhibit catalytic efficiency derived from molybdenum disulfide.

[0039] Molybdenum disulfide (MoS) relative to the total mass of the composite (100% by mass) ２ The upper limit of the content of ) may be a value that does not exceed the total mass (100 mass%) of the composite of this embodiment, and may be, for example, 99.9 mass% or less, 99.5 mass% or less, or 99.0 mass% or less.

[0040] In addition, the above molybdenum disulfide (MoS ２ The content of molybdenum and sulfur may be a value determined by XRF analysis, and can be calculated as the sum of the molybdenum content and the sulfur content determined by XRF analysis of the composite of the present embodiment exemplified above.

[0041] In this embodiment, the content ratio of the precious metal contained in the composite with respect to the total mass (100 mass%) of the composite determined by XRF analysis is 0.1 mass% or more and 20 mass% or less, and molybdenum disulfide (MoS ２ ) content ratio of 80 mass % or more and 99.9 mass % or less, and the content ratio of the noble metal is 0.5 mass % or more and 15 mass % or less, and molybdenum disulfide (MoS ２ ) content ratio of 85 mass % or more and 99.5 mass % or less, and the content ratio of the noble metal is 1 mass % or more and 12 mass % or less, and molybdenum disulfide (MoS ２ An example of the composite is one in which the content of the component (II) is 88% by mass or more and 99% by mass or less.

[0042] The composite of this embodiment can be provided as an aggregate of composite particles (for example, powder), and molybdenum disulfide (MoS) can be contained in the aggregate.２ ), MoS ｘ The molybdenum sulfide particles may contain one or more molybdenum sulfides represented by (X=1 to 3).

[0043] Also, the above D ５０ The values ​​relating to the specific surface area and XRF analysis can be values ​​measured using an aggregate of composite particles (for example, powder) as a sample.

[0044] Molybdenum disulfide may include a 3R crystal structure, or may include a 2H crystal structure and a 3R crystal structure. Such molybdenum disulfide particles including a 2H crystal structure and a 3R crystal structure are uniquely developed by the present applicant, and have not only a 2H crystal structure but also a rare 3R (rhombohedral) crystal structure. Since a 3R structure tends to have a distorted crystal structure and has more catalytically active sites, the inclusion of a 3R crystal structure in molybdenum disulfide contributes to improving catalytic performance.

[0045] The molybdenum disulfide particles containing the 3R crystal structure can be produced, for example, by the <Method for producing molybdenum disulfide particles> described below. This makes it possible to synthesize molybdenum disulfide containing the 3R structure, which is advantageous for achieving a large surface area on the nm scale, and which is difficult to achieve by crushing mine products or synthesis from general-purpose molybdenum trioxide.

[0046] The abundance ratio of the 3R crystal structure in the crystal phase of molybdenum disulfide may be 5% or more and 90% or less, 10% or more and 80% or less, 20% or more and 70% or less, or 20% or more and 50% or less.

[0047] The fact that molybdenum disulfide particles have a 2H crystal structure and a 3R crystal structure can be confirmed, for example, by using an extended Rietveld analysis software (manufactured by Malvern Panalytical, High Score Plus) that can take into account crystallite size. In this Rietveld analysis software, the entire XRD diffraction profile is simulated using a crystal structure model including the crystallite size, and compared with the XRD diffraction profile obtained experimentally. The residual between the diffraction profile obtained experimentally and the diffraction profile obtained by calculation is minimized by the least squares method, and the crystal lattice constants of the crystal structure model, crystal structure factors such as atomic coordinates, weight fraction (abundance ratio), etc. are optimized, and each phase of the 2H crystal structure and the 3R crystal structure is identified and quantified with high precision, and in addition to the crystal structure type and its ratio calculated by normal Rietveld analysis, the crystallite size can be calculated. Hereinafter, in this specification, the analysis method using the above-mentioned High Score Plus will be referred to as "extended Rietveld analysis".

[0048] Furthermore, in the molybdenum disulfide particles, the crystallite size of the 3R crystal structure obtained by extended Rietveld analysis using the profile obtained from the XRD may be 1 nm or more and 150 nm or less, and preferably consists of a crystalline phase composed of crystallites of 5 nm or more and 50 nm or less, and more preferably the crystallite size is 10 nm or more and 40 nm or less.

[0049] Furthermore, in the molybdenum disulfide particles of this embodiment, the crystallite size of the 2H crystal structure obtained by extended Rietveld analysis using the profile obtained from the XRD is preferably 1 nm or more and 150 nm or less, and the crystalline phase is preferably composed of crystallites having sizes of 1 nm or more and 150 nm or less, and more preferably the crystallite size is 5 nm or more and 150 nm or less.

[0050] The 2H crystal structure obtained by the extended Rietveld analysis preferably consists of a single crystalline phase composed of crystallites having a predetermined crystallite size, more preferably 1 nm to 20 nm, and even more preferably 5 nm to 15 nm.

[0051] The crystallite size of the 2H crystal structure and the crystallite size of the 3R crystal structure can also be calculated using, for example, the peak half width of an XRD diffraction profile.

[0052] The abundance ratio (2H:3R) of the 2H crystal structure and the 3R crystal structure in the crystal phase obtained by extended Rietveld analysis using the profile obtained from the XRD is preferably 10:90 to 90:10.

[0053] From the viewpoint of the above-mentioned effects, the abundance ratio (2H:3R) of the 2H crystal structure and the 3R crystal structure in the crystal phase obtained by extended Rietveld analysis using the profile obtained from the above-mentioned XRD is more preferably 10:90 to 80:20, and even more preferably 40:60 to 80:20.

[0054] The 2H crystal structure obtained by the extended Rietveld analysis may also consist of a first crystal phase composed of crystallites having a predetermined crystallite size and a second crystal phase having a smaller crystallite size than the first crystal phase. The crystallite size of the first crystal phase of the 2H crystal structure is, for example, greater than 20 nm and less than 150 nm, and may be 50 nm to 150 nm, or 100 nm to 150 nm. However, it is preferable that the first crystal phase is absent or present in a small proportion in the 2H crystal structure. The crystallite size of the second crystal phase of the 2H crystal structure is preferably 1 nm to 20 nm, and may be 1 nm to 10 nm, or 5 nm to 15 nm.

[0055] The crystallite size of the first crystalline phase of the 2H crystalline structure, the crystallite size of the 3R crystalline structure, and the crystallite size of the second crystalline phase of the 2H crystalline structure can also be calculated using, for example, the peak half-width of the XRD diffraction profile, as described above.

[0056] The abundance ratio of the first crystalline phase of the 2H crystalline structure, the 3R crystalline structure, and the second crystalline phase of the 2H crystalline structure in the crystalline phase (2H (first crystalline phase):3R:2H (second crystalline phase)) obtained by extended Rietveld analysis using the profile obtained from the XRD is preferably 30 to 0:10 to 70:80 to 15, more preferably 25 to 0:20 to 60:75 to 20.

[0057] In a profile obtained by powder X-ray diffraction (XRD) of the molybdenum disulfide particles using Cu-Kα radiation as an X-ray source, the peaks near 2θ = 39.5° and 49.5° are derived from a 2H crystal structure, and the peaks near 2θ = 32.5°, 39.5°, and 49.5° are derived from a 3R crystal structure, and the half-widths of the peaks near 2θ = 39.5° and 49.5° are preferably 1° or more. Furthermore, the molybdenum disulfide particles may contain a crystal structure other than the 2H crystal structure and 3R crystal structure of molybdenum disulfide, such as a 1H crystal structure.

[0058] The fact that the molybdenum disulfide particles contain a metastable 3R crystal structure can be distinguished by the fact that in a profile obtained by powder X-ray diffraction (XRD) using Cu-Kα rays as an X-ray source, a peak near 2θ = 39.5° and a peak near 2θ = 49.5° are both composed of composite peaks of the 2H crystal structure and the 3R crystal structure.

[0059] In practice, the abundance ratio of 2H crystal structure is determined by the peak around 2θ=39.5 ° and the broad peak around 49.5 ° using the profile obtained from the powder X-ray diffraction (XRD).In addition, the difference between the peak around 2θ=39.5 ° and the broad peak around 49.5 ° is optimized by two peaks around 2θ=32.5 ° and two peaks around 39.5 °, thereby determining the abundance ratio of 3R crystal structure.That is, both the peak around 2θ=39.5 ° and the peak around 49.5 ° are composite waves derived from 2H crystal structure and 3R crystal structure, and these composite waves can be used to calculate the abundance ratio of 2H crystal structure and 3R crystal structure in molybdenum disulfide particles.

[0060] The molybdenum disulfide particles may also contain an amorphous phase. The ratio of the amorphous phase in the molybdenum disulfide particles, expressed as 100(%) - (crystallinity(%)), is preferably 5% or more, more preferably 15% or more, and even more preferably 20% or more.

[0061] Whether the crystal structure of molybdenum disulfide is a 2H crystal structure or a 3R crystal structure, the distance between Mo and S is approximately the same due to covalent bonding, and therefore the intensity of the peak due to Mo—S is the same in the extended X-ray absorption fine structure (EXAFS) profile at the K absorption edge of molybdenum. On the other hand, because the 2H crystal structure of molybdenum disulfide is hexagonal, the same hexagon is located 90° directly below the hexagon of Mo atoms, thereby shortening the distance between Mo-Mo atoms and increasing the peak intensity II due to Mo-Mo. Conversely, because the 3R crystal structure of molybdenum disulfide is rhombohedral, the hexagon is located halfway down from the hexagon rather than directly below it, thereby increasing the distance between Mo-Mo atoms and decreasing the peak intensity II due to Mo-Mo. In the pure 2H crystal structure of molybdenum disulfide, the ratio (I / II) is small, but as the 3R crystal structure is included, the ratio (I / II) becomes larger.

[0062] <Molybdenum Carbide> The molybdenum compound contained in the composite of the present embodiment may be molybdenum carbide. Molybdenum carbide has a crystal structure of Mo ２ It is preferable that the molybdenum carbide has a C crystal structure and that the carbon content relative to the total mass (100 mass%) of the molybdenum carbide is 6% or more.

[0063] In this embodiment, Mo ２ The presence of the C crystal structure can be detected from a diffraction profile obtained by XRD analysis of a molybdenum carbide sample. ２ The C crystal structure may be either an α crystal or a β crystal, but is preferably an α crystal.

[0064] In the molybdenum carbide according to this embodiment, the carbon content relative to the total mass (100 mass%) of the molybdenum carbide is preferably 6% or more, more preferably 8% or more, more preferably 10% or more, and even more preferably 15% or more. If the carbon content is equal to or greater than the lower limit of the above range, the specific surface area of ​​the molybdenum carbide tends to increase.

[0065] In the molybdenum carbide according to the present embodiment, the upper limit of the carbon content relative to the total mass (100 mass%) of the molybdenum carbide is not particularly limited, but is preferably 90% or less, more preferably 80% or less, and even more preferably 60% or less. When the carbon content is equal to or less than the upper limit of the above range, the electrical conductivity and catalytic performance of the molybdenum carbide are likely to be improved.

[0066] The molybdenum carbide according to the present embodiment preferably has a carbon-derived graphite band G and a disorder band D measured by Raman spectroscopy. Specifically, the molybdenum carbide according to the present embodiment has a crystalline Mo ２ A hybrid structure of C and carbon is preferred. ２ The state of C and carbon is not particularly limited. For example, Mo ２ The state where carbon exists on the surface of C, Mo ２ For example, carbon domains are scattered in a C matrix.

[0067] In the present embodiment, the molybdenum carbide preferably has a ratio (G / D) of the graphite bands G to the disorder bands D of 0.75 or more, more preferably 0.78 or more, and even more preferably 0.80 or more. When G / D is equal to or more than the lower limit of the above range, defects resulting from the disorder bands D are reduced, and the electrical conductivity and catalytic performance of the molybdenum carbide are likely to be improved.

[0068] In this embodiment, the upper limit of the G / D ratio is not particularly limited, but is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.0 or less. When the G / D ratio is equal to or less than the upper limit of the above range, a synergistic effect with molybdenum carbide is easily exhibited, and catalytic performance is easily improved. Measurement by Raman spectroscopy is performed according to the following procedure.

[0069] [Analysis by Raman spectroscopy] A powder sample is placed on a glass slide and measured using a laser Raman spectrophotometer (NRS-5500, manufactured by JASCO Corporation) under the following measurement conditions: excitation laser 532 nm, laser intensity 0.6 mW, exposure time 30 sec, and point measurement with an objective lens of 100x magnification. After measurement, the baseline-corrected XPS spectrum is analyzed using the analysis software Spectra Manager.

[0070] In this embodiment, the molybdenum carbide has a specific surface area measured by the BET method of 10 to 2000 m ２ / g, and 20 to 1500m ２ / g, and more preferably 50 to 1500m ２ When the specific surface area measured by the BET method is within the above-mentioned preferred range, for example, when molybdenum carbide is used as a catalyst, the number of catalytically active sites can be increased and mass transfer in the reaction system can be facilitated, thereby enabling the catalytic efficiency to be improved more effectively.

[0071] The specific surface area is measured using a specific surface area meter (for example, BELSORP-mini manufactured by Microtrac-Bell), and the surface area per 1 g of sample measured from the amount of nitrogen gas adsorbed by the BET method (Brunauer-Emmett-Teller method) is defined as the specific surface area (m ２ / g).

[0072] In this embodiment, the molybdenum carbide has a median diameter D calculated by dynamic light scattering. ５０ is preferably 1500 nm or less, more preferably 1000 nm or less, and even more preferably 500 nm or less. ５０When is equal to or less than the upper limit of the above-mentioned preferred range, for example, when molybdenum carbide is used as the catalyst, the catalytic efficiency is likely to be more effectively exhibited.

[0073] The median diameter D of the molybdenum carbide of this embodiment determined by dynamic light scattering ５０ For example, the thickness may be 20 nm or more, or 40 nm or more.

[0074] The median diameter D of the molybdenum carbide of this embodiment determined by dynamic light scattering ５０ An example of the range of the above numerical value may be 20 nm or more and 1500 nm or less, 40 nm or more and 1000 nm or less, or 40 nm or more and 500 nm or less.

[0075] The median diameter D of the molybdenum carbide of this embodiment calculated by dynamic light scattering ５０ can be determined as the particle size at which the volume cumulative percentage is 50% in a particle size distribution measured in a wet state using a dynamic light scattering particle size distribution analyzer (for example, Nanotrac Wave II manufactured by Microtrac Bell).

[0076] In this embodiment, the molybdenum carbide preferably has an average crystallite size of 50 nm or less, more preferably 45 nm or less, and even more preferably 40 nm or less, determined from the peak at 2θ = 39.4 ± 0.5° in the profile obtained by X-ray diffraction measurement. The average crystallite size is considered to reflect the particle size and shape of the molybdenum carbide particles, and is preferred because a smaller crystallite size tends to increase catalytically active sites such as interfaces and defects. The lower limit of the average crystallite size may be, for example, 1 nm or more, 3 nm or more, 4 nm or more, or 5 nm or more.

[0077] [Measurement of crystallite size] An X-ray diffractometer (e.g., Rigaku Corporation, SmartLab 9kW) is used, a scintillation counter is used as a detector, and PDXL2 is used as analysis software. The measurement method is the 2θ / θ method, and the average crystallite size is calculated using the Scherrer equation from the half-width of the peak appearing at 2θ = 39.4 ± 0.5 °. The measurement conditions are a scan speed (2θ) of 2.0 ° / min, a scan range (2θ) of 10 to 70 °, a step (2θ) of 0.02 °, and no standard width for the device.

[0078] <Palladium> The palladium contained in the composite of this embodiment is preferably a palladium particle. The palladium particle is a granular structure containing palladium. The palladium contained in the composite of this embodiment is composited with the molybdenum compound contained in the composite of this embodiment to form a composite. Furthermore, when the composite of this embodiment also contains palladium and platinum described below, the palladium contained in the composite of this embodiment may be composited with the platinum, and the composited precious metal may be composited with the molybdenum compound to form a composite. Furthermore, the palladium contained in the composite of this embodiment may be composited with the molybdenum compound independently of the platinum to form a composite. The precious metal composite of the palladium and the platinum is preferably in the form of a particle. The precious metal composite of the palladium and the platinum may be an alloy of palladium and platinum, may be a composite particle having a core-shell structure, or may be a hetero particle comprising palladium primary particles containing palladium and platinum primary particles containing platinum particles. A composite particle having a core-shell structure is a particle having a core made of one material and a layer of another material on the surface of the core. For example, a precious metal composite of palladium and platinum having a core-shell structure is, for example, a composite particle having a platinum layer on the surface of a palladium-containing core, or a composite particle having a palladium layer on the surface of a platinum-containing core.

[0079] The shape of the palladium particles is not particularly limited, and examples thereof include a spherical shape, a hemispherical shape, a wire shape connecting a plurality of palladium particles together, and a shape formed by assembling these shapes.

[0080] The form in which the palladium particles are contained in the composite of the present embodiment is not particularly limited, but the palladium particles may be present on the surface of the molybdenum compound particles, or may be attached to or bonded to the surface of the molybdenum compound particles.

[0081] The number of palladium particles present per 100 nm × 100 nm surface area on the surface of the molybdenum compound particle, as confirmed on a two-dimensional image obtained by photographing the composite with a transmission electron microscope (TEM), may be, for example, 5 to 5,000 particles, or 10 to 1,000 particles.

[0082] The average particle size of the palladium particles may be 20 nm or less, 15 nm or less, or 13 nm or less.

[0083] The lower limit of the average particle size of the palladium particles may be, for example, 0.5 nm or more, 0.7 nm or more, or 1 nm or more.

[0084] An example of the range of the average particle size of the palladium particles is 0.5 nm or more and 20 nm or less, 0.7 nm or more and 15 nm or less, or 1 nm or more and 13 nm or less.

[0085] The average particle size of the palladium particles is determined by photographing the composite with a transmission electron microscope (TEM) and measuring the maximum distance between two points on the outline of 50 randomly selected palladium particles (however, aggregates of multiple palladium particles are not selected) from the palladium particles observed in the two-dimensional image, and the average value is used.

[0086] The palladium particles contain palladium. The form of the palladium contained in the composite of the present embodiment is not particularly limited, and for example, the palladium may be contained in the palladium particles as a palladium compound.

[0087] However, the results obtained include that the palladium particles do not exhibit the crystal structure of palladium metal crystals, that at least a portion of the palladium constitutes palladium particles, and that the palladium particles are observed to be attached to or bonded to the surfaces of the particles of the molybdenum compound contained in the composite of this embodiment, that no change in the layer spacing constituting the molybdenum compound is observed, and that the valence of palladium is zero.

[0088] For these reasons, the palladium particles may contain palladium that does not have a crystalline structure. The palladium particles may contain palladium that does not have the crystalline structure of palladium metal crystals. The palladium particles may contain palladium that is not in a form in which a portion of the molybdenum in the crystalline structure of the molybdenum compound contained in the composite of this embodiment is substituted. The palladium particles may contain zero-valent palladium.

[0089] With respect to the content ratio of palladium in the above-mentioned form, the palladium particles may contain 50% or more, on a molar basis, of palladium not having a crystalline structure relative to the palladium contained in the palladium particles. The palladium particles may contain 50% or more, on a molar basis, of palladium not having a crystalline structure of palladium metal crystals relative to the palladium contained in the palladium particles. The palladium particles may contain 50% or more, on a molar basis, of palladium not in a form in which a portion of the molybdenum in the crystalline structure of a molybdenum compound is substituted relative to the palladium contained in the palladium particles. The palladium particles may contain 50% or more, on a molar basis, of zero-valent palladium relative to the palladium contained in the palladium particles.

[0090] The palladium particles may include aggregates of palladium atoms, or may include aggregates of palladium atoms not having a crystal structure. The palladium particles may include aggregates of palladium atoms not having the crystal structure of a palladium metal crystal. The palladium particles may include aggregates of palladium atoms not in a form substituted with a portion of the molybdenum in the crystal structure of a molybdenum compound. The palladium particles may include aggregates of zero-valent palladium atoms.

[0091] The palladium contained in the palladium particles preferably does not have a crystalline structure, and more preferably does not have the crystalline structure of palladium metal crystals.

[0092] Similarly, the composite of this embodiment may contain palladium that does not have a crystal structure. The composite of this embodiment may contain palladium that does not have the crystal structure of a palladium metal crystal. The composite of this embodiment may contain palladium that is not in a form in which a portion of the molybdenum in the crystal structure of a molybdenum compound is substituted. The composite of this embodiment may contain palladium whose valence is zero.

[0093] With respect to the content ratio of palladium in the above-described form, the composite of this embodiment may contain, on a molar basis, 50% or more of palladium not having a crystalline structure relative to the palladium contained in the composite. The composite of this embodiment may contain, on a molar basis, 50% or more of palladium not having a crystalline structure of palladium metal crystal relative to the palladium contained in the composite. The composite of this embodiment may contain, on a molar basis, 50% or more of palladium not in a form in which a portion of the molybdenum in the crystalline structure of a molybdenum compound is substituted, relative to the palladium contained in the composite. The composite of this embodiment may contain, on a molar basis, 50% or more of palladium with a valence of zero relative to the palladium contained in the composite.

[0094] Similarly, the complex of this embodiment may include an aggregate of palladium atoms that does not have a crystal structure. The complex of this embodiment may include an aggregate of palladium atoms that does not have the crystal structure of a palladium metal crystal. The complex of this embodiment may include an aggregate of palladium atoms that is not in a form where it is substituted for a portion of the molybdenum in the crystal structure of a molybdenum compound. The complex of this embodiment may include an aggregate of palladium atoms whose valence is zero.

[0095] The palladium contained in the composite of the present embodiment preferably does not have a crystalline structure, and more preferably does not have the crystalline structure of palladium metal crystals.

[0096] In another aspect, the composite of the present embodiment includes molybdenum compound particles and palladium particles, and the molybdenum compound contained in the molybdenum compound particles has an average crystallite size of 150 nm or less, as determined from a peak at 2θ=14.4°±0.5° obtained by X-ray diffraction measurement (excluding composites in which the palladium contained in the composite has a crystal structure of palladium metal crystals).

[0097] The palladium in the composite of this embodiment may form palladium clusters. Also, the palladium in the palladium particles may form palladium clusters.

[0098] The presence of a palladium-containing crystal structure can be detected based on a diffraction profile obtained by X-ray diffraction analysis of the composite of this embodiment as a sample. It can also be detected based on analysis of the crystal structure by electron beam diffraction.

[0099] According to the composite of the present embodiment described above, the molybdenum compound particles having a fine crystallite size, such as an average crystallite size of 150 nm or less, and the palladium particles are composited together, and therefore, excellent catalytic performance can be exhibited.

[0100] Furthermore, it is believed that the palladium in the palladium particles does not constitute the crystal structure of palladium metal crystals, but is present in the particles of the molybdenum compound contained in the composite of this embodiment, preferably as an aggregate of palladium atoms, thereby enabling the composite to exhibit even better catalytic performance.

[0101] The composite of this embodiment can be suitably used as a constituent material of a catalyst ink capable of forming a catalyst layer, and also as an electrode material used as a constituent material of an electrode catalyst layer.

[0102] <Platinum> The platinum contained in the composite of this embodiment is preferably platinum particles. The platinum particles are granular structures containing platinum. The platinum contained in the composite of this embodiment is composited with the molybdenum compound contained in the composite of this embodiment to form a composite. Furthermore, when the composite of this embodiment also contains the above-mentioned palladium, the platinum contained in the composite of this embodiment may be composited with the above-mentioned palladium, and the composited precious metal may be composited with the molybdenum compound to form a composite. Furthermore, the platinum contained in the composite of this embodiment may be composited with the molybdenum compound independently of the palladium to form a composite.

[0103] The shape of the platinum particles is not particularly limited, and examples thereof include a spherical shape, a hemispherical shape, a wire shape connecting a plurality of platinum particles together, and a shape formed by assembling these shapes.

[0104] The form in which the platinum particles are contained in the composite of this embodiment is not particularly limited, but the platinum particles may be present on the surface of the molybdenum compound particles, or may be attached to or bonded to the surface of the molybdenum compound particles.

[0105] The number of platinum particles present per 100 nm × 100 nm surface area on the surface of the molybdenum compound particle, as confirmed on a two-dimensional image obtained by photographing the composite with a transmission electron microscope (TEM), may be, for example, 5 to 5,000, or 10 to 1,000.

[0106] The average particle size of the platinum particles may be 20 nm or less, 15 nm or less, or 13 nm or less.

[0107] The lower limit of the average particle size of the platinum particles may be, for example, 0.5 nm or more, 0.7 nm or more, or 1 nm or more.

[0108] An example of the range of the average particle size of the platinum particles may be 0.5 nm or more and 20 nm or less, 0.7 nm or more and 15 nm or less, or 1 nm or more and 13 nm or less.

[0109] The average particle size of the platinum particles is determined by photographing the composite with a transmission electron microscope (TEM) and measuring the maximum distance between two points on the outline of 50 randomly selected platinum particles (however, aggregates of multiple platinum particles are not selected) from the platinum particles observed in the two-dimensional image, and the average value is used.

[0110] The platinum particles contain platinum. The form of the platinum contained in the composite of the present embodiment is not particularly limited, and for example, the platinum particles may be contained as a platinum compound.

[0111] However, the following results may be obtained: the platinum particles do not exhibit the crystal structure of platinum metal crystals; at least a portion of the platinum constitutes platinum particles, and the platinum particles are observed to be attached or bonded to the surfaces of the particles of the molybdenum compound contained in the composite of this embodiment; no change in the layer spacing constituting the molybdenum compound is observed; and the valence of platinum is zero.

[0112] For these reasons, the platinum particles may contain platinum that does not have a crystalline structure. The platinum particles may contain platinum that does not have the crystalline structure of platinum metal crystals. The platinum particles may contain platinum that is not in a form in which a portion of the molybdenum in the crystalline structure of the molybdenum compound contained in the composite of this embodiment is substituted. The platinum particles may contain zero-valent platinum.

[0113] Regarding the content ratio of platinum in the above-mentioned form, the platinum particles may contain, on a molar basis, 50% or more of platinum not having a crystalline structure relative to the platinum contained in the platinum particles. The platinum particles may contain, on a molar basis, 50% or more of platinum not having a crystalline structure of platinum metal crystal relative to the platinum contained in the platinum particles. The platinum particles may contain, on a molar basis, 50% or more of platinum not in a form in which a portion of the molybdenum in the crystalline structure of a molybdenum compound is substituted, relative to the platinum contained in the platinum particles. The platinum particles may contain, on a molar basis, 50% or more of zero-valent platinum relative to the platinum contained in the platinum particles.

[0114] The platinum particles may include an aggregate of platinum atoms, or may include an aggregate of platinum atoms that does not have a crystal structure. The platinum particles may include an aggregate of platinum atoms that does not have the crystal structure of a platinum metal crystal. The platinum particles may include an aggregate of platinum atoms that is not in a form where it is substituted with a portion of the molybdenum in the crystal structure of a molybdenum compound. The platinum particles may include an aggregate of zero-valent platinum atoms.

[0115] The platinum contained in the platinum particles preferably does not have a crystalline structure, and more preferably does not have the crystalline structure of platinum metal crystals.

[0116] Similarly, the composite of this embodiment may contain platinum that does not have a crystal structure. The composite of this embodiment may contain platinum that does not have the crystal structure of a platinum metal crystal. The composite of this embodiment may contain platinum that is not in a form that substitutes for a portion of the molybdenum in the crystal structure of a molybdenum compound. The composite of this embodiment may contain platinum that has a valence of zero.

[0117] Regarding the content ratio of platinum in the above-described form, the composite of this embodiment may contain, on a molar basis, 50% or more of platinum not having a crystalline structure relative to the platinum contained in the composite. The composite of this embodiment may contain, on a molar basis, 50% or more of platinum not having a crystalline structure of platinum metal crystal relative to the platinum contained in the composite. The composite of this embodiment may contain, on a molar basis, 50% or more of platinum not in a form in which a portion of the molybdenum in the crystalline structure of a molybdenum compound is substituted relative to the platinum contained in the composite. The composite of this embodiment may contain, on a molar basis, 50% or more of platinum having a valence of zero relative to the platinum contained in the composite.

[0118] Similarly, the composite of this embodiment may include an aggregate of platinum atoms that does not have a crystal structure. The composite of this embodiment may include an aggregate of platinum atoms that does not have the crystal structure of a platinum metal crystal. The composite of this embodiment may include an aggregate of platinum atoms that is not in a form where it is substituted for a portion of the molybdenum in the crystal structure of a molybdenum compound. The composite of this embodiment may include an aggregate of platinum atoms whose valence is zero.

[0119] The platinum contained in the composite of this embodiment preferably does not have a crystalline structure, and more preferably does not have the crystalline structure of platinum metal crystals.

[0120] In another aspect, the composite of the present embodiment includes molybdenum compound particles and platinum particles, and when the molybdenum compound contained in the molybdenum compound particles is molybdenum disulfide, the average crystallite size determined from the peak at 2θ = 14.4° ± 0.5° obtained by X-ray diffraction measurement is 150 nm or less (excluding those in which the platinum contained in the composite has a crystal structure of platinum metal crystal).

[0121] The platinum in the composite of this embodiment may form platinum clusters. Also, the platinum in the platinum particles may form platinum clusters.

[0122] The presence of a crystalline structure containing platinum can be detected based on a diffraction profile obtained by X-ray diffraction analysis of the composite of this embodiment as a sample. It can also be detected based on analysis of the crystalline structure by electron diffraction.

[0123] According to the composite of the present embodiment described above, the molybdenum compound particles having a minute crystallite size, such as an average crystallite size of 150 nm or less, and the platinum particles are composited together, and therefore, excellent catalytic performance can be exhibited.

[0124] Furthermore, it is believed that the platinum in the platinum particles does not constitute the crystal structure of platinum metal crystals, but is present in the molybdenum compound particles contained in the composite of this embodiment, preferably as an aggregate of platinum atoms, thereby enabling the composite to exhibit even better catalytic performance.

[0125] The composite of this embodiment can be suitably used as a constituent material of a catalyst ink capable of forming a catalyst layer, and also as an electrode material used as a constituent material of an electrode catalyst layer.

[0126] <<Method for Producing a Composite>> A method for producing a composite according to a first aspect of the present invention includes a step of mixing a molybdenum compound with a precious metal solution. The content of the precious metal relative to the total mass (100 mass%) of the molybdenum compound is 50% or less. The molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide and molybdenum carbide. The precious metal is at least one metal selected from the group consisting of platinum and palladium.

[0127] A method for producing a composite according to a second aspect of the present invention includes the steps of mixing a molybdenum compound with a solvent to obtain a molybdenum compound dispersion, and mixing an alkali metal hydroxide and a noble metal compound with the molybdenum compound dispersion, wherein the molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide and molybdenum carbide, and the noble metal in the noble metal compound is at least one metal selected from the group consisting of platinum and palladium.

[0128] According to the method for producing a composite of the present embodiment, the composite of the present embodiment described above can be produced. Hereinafter, the method for producing a composite according to each aspect will be described.

[0129] <Method for producing a composite according to the first aspect> The method for producing a composite according to the first aspect of the present invention includes a step of mixing a molybdenum compound with a precious metal solution. The content of the precious metal relative to the total mass (100 mass%) of the molybdenum compound is 50% or less. The molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide and molybdenum carbide. The precious metal is at least one metal selected from the group consisting of platinum and palladium.

[0130] The molybdenum sulfide, molybdenum carbide, platinum, and palladium have the same meanings as those described for the composite of this embodiment. The molybdenum compound may be molybdenum compound particles, and the noble metal may be noble metal particles.

[0131] The noble metal solution (noble metal compound solution) can be obtained by dissolving any of the noble metal sources (noble metal compounds) in a solvent.

[0132] When the noble metal is palladium, the palladium source (palladium compound) may be any source that can produce a palladium solution (a solution of a palladium compound), and examples thereof include palladium compounds such as palladium acetate, palladium nitrate, palladium nitrite, palladium sulfate, palladium carbonate, palladium chloride, palladium hydroxide, palladium oxide, and sodium palladium (II) chloride.

[0133] When the noble metal is platinum, the platinum source (platinum compound) may be any source that can produce a platinum solution (a solution of a platinum compound), and examples of platinum compounds include hexachloroplatinic (IV) acid hexahydrate, potassium hexachloroplatinate, ammonium hexachloroplatinate, sodium hexachloroplatinate, ammonium tetrachloroplatinate, and potassium tetrachloroplatinate.

[0134] The solvent may be any solvent capable of dissolving the noble metal source, and examples thereof include alcohols such as methanol and ethanol, benzene, dichloromethane, acetone, and chloroform.

[0135] The method of mixing is not particularly limited, but it is preferable to mix the noble metal solution with the dispersion of the molybdenum compound particles.

[0136] When the noble metals include platinum and palladium, the platinum solution and the palladium solution may be prepared and then mixed to prepare a noble metal solution containing platinum and palladium. Alternatively, the platinum source and the palladium source may be dissolved in the solvent to prepare a noble metal solution containing platinum and palladium. The method for mixing the noble metal solutions is not particularly limited, but it is preferable to mix the noble metal solution with a dispersion of the molybdenum compound particles.

[0137] In preparing the noble metal solution, it is preferable to add a compound (dispersant) that promotes dispersion in the solvent in order to enhance dispersibility. Examples of dispersants include polyvinylpyrrolidone (PVP), sodium citrate, and polyacrylic acid. The amount of dispersant used in the solvent after addition of the dispersant may be such that the molar ratio of dispersant to noble metal is 1:1 or more and 100:1 or less.

[0138] The dispersion of molybdenum compound particles can be obtained by mixing the molybdenum compound particles with the solvent exemplified above for the noble metal solution.

[0139] A composite of the molybdenum compound particles and the noble metal particles can be formed by mixing a noble metal solution with molybdenum compound particles to obtain a mixture and then contacting the molybdenum compound particles with the noble metal solution.

[0140] In order to prevent aggregation of the molybdenum compound particles, it is preferable to stir the mixture of the noble metal solution and the molybdenum compound particles, for example, at a speed of 50 to 1000 rpm.

[0141] The concentration of the noble metal in the noble metal solution may be, for example, 0.00001 to 0.1 mol / L, or may be 0.0001 to 0.01 mol / L.

[0142] The temperature of the mixture of the molybdenum compound particles and the noble metal solution may be any temperature that allows the formation of a composite, and may be, for example, 10 to 100°C, or 20 to 80°C.

[0143] The time for which the mixture of molybdenum compound particles and precious metal solution is kept may be long enough to form a composite, and may be, for example, from 10 minutes to 48 hours, or from 30 minutes to 12 hours.

[0144] In the method for producing a composite according to the first aspect of the present invention, the mixture of molybdenum compound particles and a precious metal solution may be irradiated with light to promote photoreduction of the precious metal. The light irradiation can be carried out by appropriately selecting the light intensity and wavelength to an extent that photoreduction of the precious metal occurs. The light irradiation may be carried out by installing a light source to control the light intensity, or by irradiating with light in a normal indoor environment (such as fluorescent lamps or LEDs) or natural light.

[0145] In the composite manufacturing method of the first aspect of the present invention, the composite can be manufactured without heat treatment. For example, the obtained composite or the mixture of the noble metal solution and the molybdenum compound particles is preferably not heated to 200°C or higher, more preferably not heated to above 100°C, and even more preferably not heated to above 80°C.

[0146] After the complex is formed from the mixture, the complex can be separated by centrifugal separation, drying, or the like, and the complex of this embodiment can be easily recovered.

[0147] The method for producing a composite according to the first aspect of the present invention may further comprise a step of producing the molybdenum compound particles.

[0148] Hereinafter, an example of a method for producing molybdenum disulfide particles when the molybdenum compound is molybdenum disulfide will be described.

[0149] <Method for Producing Molybdenum Disulfide Particles> The molybdenum disulfide particles can be produced, for example, by a molybdenum disulfide particle production step that includes heating molybdenum trioxide particles having an average primary particle size of 2 nm to 1000 nm in the presence of a sulfur source at a temperature of 200 to 1000°C.

[0150] In another aspect, the molybdenum disulfide particles can be produced, for example, by a molybdenum disulfide particle production process comprising heating molybdenum trioxide particles obtained by a molybdenum trioxide particle production process described below at a temperature of 200 to 1000°C in the presence of a sulfur source.

[0151] In this specification, the average particle size of the primary particles of molybdenum trioxide particles refers to the average value of primary particle diameters of 50 randomly selected primary particles when the molybdenum trioxide particles are photographed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), the major axis (the Feret diameter of the longest observed part) and minor axis (the shorter Feret diameter in the direction perpendicular to the Feret diameter of the longest part) of the smallest unit particle (i.e., primary particle) constituting the aggregate in the two-dimensional image are measured, and the average value is defined as the primary particle diameter.

[0152] In the method for producing molybdenum disulfide particles, the molybdenum trioxide particles preferably have an average primary particle size of 1 μm or less. From the viewpoint of reactivity with sulfur, the average primary particle size is more preferably 600 nm or less, even more preferably 400 nm or less, and particularly preferably 200 nm or less. The average primary particle size of the molybdenum trioxide particles may be 2 nm or more, 5 nm or more, or 10 nm or more.

[0153] The molybdenum trioxide particles used in the production of the molybdenum disulfide particles are preferably composed of an aggregate of primary particles containing the β crystal structure of molybdenum trioxide. The molybdenum trioxide particles have a better reactivity with sulfur than conventional molybdenum trioxide particles that are composed only of α crystals, and because they contain the β crystal structure of molybdenum trioxide, they react with a sulfur source to form MoS ２ Conversion rate R Ｃ can be made larger.

[0154] In this specification, the β crystal structure of molybdenum trioxide is defined as MoO in a profile obtained by powder X-ray diffraction (XRD) using Cu-Kα radiation as an X-ray source. ３ The α-crystal structure of molybdenum trioxide can be confirmed by the presence of a peak (2θ: around 23.01°, No. 86426 (Inorganic Crystal Structure Database (ICSD))) which is assigned to the (011) plane of the β-crystal of MoO. ３ This can be confirmed by the presence of a peak on the (021) plane of the α-crystal (2θ: around 27.32°, No. 166363 (Inorganic Crystal Structure Database (ICSD))).

[0155] The molybdenum trioxide particles have a profile obtained by powder X-ray diffraction (XRD) using Cu-Kα radiation as an X-ray source, which profile is MoO ３ The peak intensity attributed to the (011) plane of the β crystal of MoO ３ It is preferable that the ratio (β(011) / α(021)) of the peak intensity of the α-crystal (2θ: around 27.32°_No. 166363 (Inorganic Crystal Structure Database (ICSD))) assigned to the (021) plane of the α-crystal is 0.1 or more.

[0156] MoO ３ The peak intensity attributed to the (011) plane of the β crystal of MoO ３ For the peak intensities attributable to the (021) plane of the α crystal, the maximum intensity of each peak is read, and the ratio (β(011) / α(021)) is calculated.

[0157] In the molybdenum trioxide particles, the ratio (β(011) / α(021)) is preferably 0.1 to 10.0, more preferably 0.2 to 10.0, and particularly preferably 0.4 to 10.0.

[0158] The β crystal structure of molybdenum trioxide is determined by Raman spectroscopy at wave numbers of 773 and 848 cm －１ and 905 cm －１ The α-crystalline structure of molybdenum trioxide can also be confirmed by the presence of peaks at wavenumbers 663 and 816 cm. －１ and 991 cm －１ This can be confirmed by the presence of a peak at

[0159] The molybdenum trioxide particles may have an average primary particle size of 5 nm or more and 2000 nm or less.

[0160] Examples of sulfur sources include sulfur and hydrogen sulfide, which may be used alone or in combination.

[0161] The method for producing molybdenum disulfide particles may include heating molybdenum trioxide particles comprising an aggregate of primary particles having a β crystal structure of molybdenum trioxide at a temperature of 100 to 800°C in the absence of a sulfur source, and then heating at a temperature of 200 to 1000°C in the presence of a sulfur source.

[0162] The heating time in the presence of the sulfur source may be any time that allows the sulfurization reaction to proceed sufficiently, and may be 1 to 20 hours, 2 to 15 hours, or 3 to 10 hours.

[0163] In the method for producing the molybdenum disulfide particles, the molybdenum trioxide particles are ３ The ratio of the amount of S in the sulfur source to the amount of MoO of the molybdenum trioxide particles is preferably set to a value that satisfies the condition for the sulfurization reaction to proceed sufficiently. ３ The amount of S in the sulfur source is preferably 450 mol% or more, more preferably 600 mol% or more, and even more preferably 700 mol% or more, relative to 100 mol% of the amount of MoO in the molybdenum trioxide particles. ３ The amount of S in the sulfur source may be 3000 mol % or less, 2000 mol % or less, or 1500 mol % or less, relative to 100 mol % of the amount of S.

[0164] In the method for producing molybdenum disulfide particles, the heating temperature in the presence of the sulfur source may be any temperature at which the sulfurization reaction proceeds sufficiently, and is preferably 320° C. or higher, more preferably 340° C. or higher, and even more preferably 360° C. or higher. The heating temperature may be 320 to 1000° C., 340 to 1000° C., or 360 to 500° C. By lowering the heating temperature, the crystallinity of the molybdenum disulfide particles decreases, and the proportion of amorphous phases present can be increased.

[0165] In the method for producing molybdenum disulfide particles, the obtained molybdenum disulfide particles may be cooled and then heated as a post-treatment, if necessary. In this heat treatment, it is preferable to calcinate the molybdenum disulfide particles, for example, in an inert atmosphere. Heating and calcining the obtained molybdenum disulfide particles promotes crystallization of the amorphous phase, improving the crystallinity. Furthermore, as the crystallinity improves, new 2H crystal structures and 3R crystal structures are generated, changing the abundance ratio of the 2H crystal structure and the 3R crystal structure. In this way, reheating as a post-treatment can improve the abundance ratio of the 3R crystal structure. Furthermore, by changing the temperature at which the obtained molybdenum disulfide particles are heated, the abundance ratio of the 2H crystal structure and the 3R crystal structure can be adjusted.

[0166] When the obtained molybdenum disulfide particles are heated and fired at a predetermined temperature or higher to change the amorphous phase to a 2H crystalline structure, a second crystalline phase composed of crystallites with a crystallite size of 20 nm or less, preferably 10 nm or less, is newly generated. In this case, if crystallites with a crystallite size of 10 nm or less existed in the 2H crystalline structure before heating the molybdenum disulfide particles, these crystallites will grow to a crystallite size of 100 nm or more after heating the molybdenum disulfide particles, and a first crystalline phase composed of these grown crystallites will be generated.

[0167] From the viewpoint of increasing the abundance ratio of the crystalline phase of the 3R crystalline structure while decreasing the abundance ratio of the first crystalline phase of the 2H crystalline structure as much as possible, the heating temperature of the molybdenum disulfide particles in the post-treatment is preferably 500 to 900°C, and more preferably 500 to 800°C.

[0168] The heating rate of the molybdenum disulfide particles in the post-treatment is preferably 1° C. / min or more and 50° C. / min or less, and more preferably 2° C. / min or more and 10° C. / min or less.

[0169] In the method for producing molybdenum disulfide particles, the molybdenum trioxide particles are MoO measured by X-ray fluorescence (XRF). ３ It is preferable that the content of MoS is 99.5% or more. ２ Conversion rate RＣ Therefore, it is possible to obtain high-purity molybdenum disulfide that is free from the risk of producing disulfides derived from impurities and has good storage stability.

[0170] The molybdenum trioxide particles have a specific surface area of ​​10 m as measured by the BET method. ２ / g to 100m ２ / g.

[0171] The specific surface area of ​​the molybdenum trioxide particles is 10 m because it improves reactivity with sulfur. ２ / g or more, and ２ / g or more is more preferable, and 30m ２ In the molybdenum trioxide particles, it is more preferable that the particle size is 100 m / g or more because it is easy to produce them. ２ / g or less, and ２ / g or less is more preferable, and ２ It is more preferable that the SiO2 content is 1 / g or less.

[0172] The molybdenum trioxide particles have a peak intensity I due to Mo—O in a radial distribution function obtained from an extended X-ray absorption fine structure (EXAFS) profile at the K absorption edge of molybdenum. Ｏ and peak intensity II due to Mo-Mo Ｏ The ratio of (I Ｏ / II Ｏ ) is preferably greater than 1.1.

[0173] Intensity I of the peak due to Mo—O Ｏ , and peak intensity II due to Mo-Mo Ｏ The maximum intensity of the peak is read, and the ratio (I Ｏ / II Ｏ ) is calculated. Ｏ / II Ｏ ) in the molybdenum trioxide particles, MoO ３ It is considered that the above ratio (I Ｏ / II Ｏ ) is larger, the reactivity with sulfur is better.

[0174] In the molybdenum trioxide particles, the ratio (I Ｏ / II Ｏ ) is preferably 1.1 to 5.0, may be 1.2 to 4.0, or may be 1.2 to 3.0.

[0175] (Method for producing molybdenum trioxide particles used in the method for producing molybdenum disulfide particles) In the method for producing molybdenum disulfide particles, the molybdenum trioxide particles used as a raw material can be produced by a molybdenum trioxide production step including vaporizing a molybdenum oxide precursor compound to form molybdenum trioxide vapor and cooling the molybdenum trioxide vapor.

[0176] The method for producing molybdenum trioxide particles includes calcining a raw material mixture containing a molybdenum oxide precursor compound and a metal compound other than the molybdenum oxide precursor compound, and vaporizing the molybdenum oxide precursor compound to form molybdenum trioxide vapor, and it is preferable that the proportion of the metal compound relative to 100 mass% of the raw material mixture is 70 mass% or less in terms of oxide.

[0177] The method for producing the molybdenum trioxide particles can be suitably carried out using a production apparatus 1 shown in FIG.

[0178] Fig. 1 is a schematic diagram showing an example of an apparatus used for producing molybdenum trioxide particles. As shown in Fig. 1, the production apparatus 1 includes a calcination furnace 2 that calcines a molybdenum trioxide precursor compound or the raw material mixture and vaporizes the molybdenum trioxide precursor compound, a cross-shaped cooling pipe 3 connected to the calcination furnace 2 and that pulverizes the molybdenum trioxide vapor vaporized by the calcination, and a recovery machine 4 serving as recovery means for recovering the molybdenum trioxide particles pulverized by the cooling pipe 3. The calcination furnace 2 and the cooling pipe 3 are connected via an exhaust port 5. The cooling pipe 3 is also provided with an opening adjustment damper 6 for an outside air intake (not shown) at its left end and an observation window 7 at its upper end. An exhaust device 8 serving as a first air blowing means is connected to the recovery machine 4. When the exhaust device 8 exhausts air, the gas inside the recovery machine 4 and the cooling pipe 3 is sucked in, and outside air is blown into the cooling pipe 3 through the opening adjustment damper 6 of the cooling pipe 3. In other words, the exhaust device 8 performs a suction function, thereby passively blowing air into the cooling pipe 3. The manufacturing apparatus 1 may also have an external cooling device 9, which makes it possible to arbitrarily control the cooling conditions for the molybdenum trioxide vapor generated from the calcination furnace 2.

[0179] By opening the opening adjustment damper 6, air is taken in from the outside air intake port, and the molybdenum trioxide vapor evaporated in the baking furnace 2 is cooled in the air atmosphere and converted into molybdenum trioxide particles, thereby achieving the ratio (I Ｏ / II Ｏ ) can be greater than 1.1, and in the molybdenum trioxide particles, MoO ３ When molybdenum trioxide vapor is cooled using liquid nitrogen or the like in a nitrogen atmosphere with a low oxygen concentration, the oxygen vacancy density increases, and the ratio (I Ｏ / II Ｏ ) is likely to decrease.

[0180] The molybdenum oxide precursor compound is not particularly limited as long as it can form molybdenum trioxide vapor by firing it. Examples of the molybdenum oxide precursor compound include metallic molybdenum, molybdenum trioxide, molybdenum dioxide, molybdenum sulfide, ammonium molybdate, and phosphomolybdic acid (H ３ PMo １２ O ４０ ), silicomolybdic acid (H ４ SiMo １２ O ４０ ), aluminum molybdate, silicon molybdate, magnesium molybdate (MgMo ｎ O ３ｎ＋１ (n=1 to 3)), sodium molybdate (Na ２ Mo ｎ O ３ｎ＋１ (n=1 to 3)), titanium molybdate, iron molybdate, potassium molybdate (K ２ Mo ｎ O ３ｎ＋１ (n=1 to 3)), zinc molybdate, boron molybdate, lithium molybdate (Li ２ Mo ｎ O ３ｎ＋１ Examples of the molybdenum oxide precursor compound include molybdenum oxide precursors such as cobalt molybdate, nickel molybdate, manganese molybdate, chromium molybdate, cesium molybdate, barium molybdate, strontium molybdate, yttrium molybdate, zirconium molybdate, and copper molybdate. These molybdenum oxide precursor compounds may be used alone or in combination of two or more. The form of the molybdenum oxide precursor compound is not particularly limited, and may be, for example, a powder such as molybdenum trioxide or a liquid such as an aqueous solution of ammonium molybdate. However, a powder form that is easy to handle and energy efficient is preferred.

[0181] It is particularly preferable to use commercially available α-crystalline molybdenum trioxide as the molybdenum trioxide precursor compound. When ammonium molybdate is used as the molybdenum oxide precursor compound, it is converted into thermodynamically stable molybdenum trioxide by calcination, and the vaporized molybdenum oxide precursor compound becomes the molybdenum trioxide.

[0182] Molybdenum trioxide vapor can also be produced by firing a raw material mixture containing a molybdenum oxide precursor compound and a metal compound other than the molybdenum oxide precursor compound.

[0183] Of these, the molybdenum oxide precursor compound preferably contains molybdenum trioxide, in terms of ease of controlling the purity, average particle size of the primary particles, and crystal structure of the resulting molybdenum trioxide particles.

[0184] There are cases where an intermediate is generated between a molybdenum oxide precursor compound and a metal compound other than the molybdenum oxide precursor compound. Even in this case, the intermediate is decomposed by calcination, and molybdenum trioxide can be vaporized in a thermodynamically stable form.

[0185] Among these, it is preferable to use an aluminum compound as the metal compound other than the molybdenum oxide precursor compound in order to prevent damage to the firing furnace, and it is also possible not to use any metal compound other than the molybdenum oxide precursor compound in order to improve the purity of the molybdenum trioxide particles.

[0186] The metal compound other than the molybdenum oxide precursor compound is not particularly limited and examples thereof include aluminum compounds, silicon compounds, titanium compounds, magnesium compounds, sodium compounds, potassium compounds, zirconium compounds, yttrium compounds, zinc compounds, copper compounds, iron compounds, etc. Among these, it is preferable to use the aluminum compounds, silicon compounds, titanium compounds, or magnesium compounds as the metal compound.

[0187] There are cases where an intermediate is generated between a molybdenum oxide precursor compound and a metal compound other than the molybdenum oxide precursor compound. Even in this case, the intermediate is decomposed by calcination, and molybdenum trioxide can be vaporized in a thermodynamically stable form.

[0188] It is preferable to use an aluminum compound as the metal compound other than the molybdenum oxide precursor compound in order to prevent damage to the firing furnace. In the production method, it is not necessary to use a metal compound other than the molybdenum oxide precursor compound in order to improve the purity of the molybdenum trioxide particles.

[0189] Examples of the aluminum compound include aluminum chloride, aluminum sulfate, basic aluminum acetate, aluminum hydroxide, boehmite, pseudo-boehmite, transition aluminum oxides (such as γ-aluminum oxide, δ-aluminum oxide, and θ-aluminum oxide), α-aluminum oxide, and mixed aluminum oxides having two or more crystal phases.

[0190] When a raw material mixture containing a molybdenum oxide precursor compound and a metal compound other than the molybdenum oxide precursor compound is fired, the content of the molybdenum oxide precursor compound relative to 100 mass% of the raw material mixture is preferably 40 mass% or more and 100 mass% or less, may be 45 mass% or more and 100 mass% or less, or may be 50 mass% or more and 100 mass% or less.

[0191] The firing temperature varies depending on the molybdenum oxide precursor compound and metal compound used, the desired molybdenum trioxide particles, etc., but is usually preferably a temperature at which the intermediate can be decomposed. For example, when a molybdenum compound is used as the molybdenum oxide precursor compound and an aluminum compound is used as the metal compound, aluminum molybdate may be formed as an intermediate, and therefore the firing temperature is preferably 500 to 1500°C, more preferably 600 to 1550°C, and even more preferably 700 to 1600°C.

[0192] The firing time is not particularly limited, but may be, for example, 1 minute to 30 hours, 10 minutes to 25 hours, or 100 minutes to 20 hours.

[0193] The temperature rise rate varies depending on the molybdenum oxide precursor compound used, the metal compound, and the desired properties of the molybdenum trioxide particles, but from the viewpoint of production efficiency, it is preferably 0.1°C / min to 100°C / min, more preferably 1°C / min to 50°C / min, and even more preferably 2°C / min to 10°C / min.

[0194] The internal pressure within the calcination furnace is not particularly limited and may be either positive pressure or reduced pressure. However, from the viewpoint of suitably discharging the molybdenum oxide precursor compound from the calcination furnace into a cooling pipe, the calcination is preferably carried out under reduced pressure. Specifically, the degree of reduced pressure is preferably −5000 Pa to −10 Pa, more preferably −2000 Pa to −20 Pa, and even more preferably −1000 Pa to −50 Pa. A degree of reduced pressure of −5000 Pa or more is preferred because it does not require excessively high airtightness or mechanical strength from the calcination furnace, thereby reducing production costs. On the other hand, a degree of reduced pressure of −10 Pa or less is preferred because it prevents clogging of the exhaust port of the calcination furnace with the molybdenum oxide precursor compound.

[0195] When gas is blown into the firing furnace during firing, the temperature of the gas blown is preferably 5 to 500°C, and more preferably 10 to 100°C.

[0196] The gas blowing speed is preferably 1 L / min to 500 L / min, more preferably 10 L / min to 200 L / min, relative to an effective volume of 100 L of the firing furnace.

[0197] The temperature of the vaporized molybdenum trioxide vapor varies depending on the type of molybdenum oxide precursor compound used, but is preferably 200 to 2000° C., and more preferably 400 to 1500° C. When the temperature of the vaporized molybdenum trioxide vapor is 2000° C. or lower, it usually tends to be easily granulated in a cooling pipe by blowing outside air (0 to 100° C.).

[0198] The discharge rate of molybdenum trioxide vapor from the calcination furnace can be controlled by the amount of the molybdenum oxide precursor compound and the amount of the metal compound used, the temperature of the calcination furnace, the amount of gas blown into the calcination furnace, and the diameter of the calcination furnace exhaust port. Although it varies depending on the cooling capacity of the cooling piping, the discharge rate of molybdenum trioxide vapor from the calcination furnace to the cooling piping is preferably 0.001 g / min or more and 100 g / min or less, and more preferably 0.1 g / min or more and 50 g / min or less.

[0199] The content of molybdenum trioxide vapor contained in the gas discharged from the calciner is preferably 0.01 mg / L or more and 1000 mg / L or less, and more preferably 1 mg / L or more and 500 mg / L or less.

[0200] Next, the molybdenum trioxide vapor is cooled and granulated. The molybdenum trioxide vapor is cooled by lowering the temperature of the cooling pipe. In this case, cooling means may include, as described above, cooling by blowing gas into the cooling pipe, cooling by a cooling mechanism of the cooling pipe, or cooling by an external cooling device.

[0201] The molybdenum trioxide vapor is preferably cooled in an air atmosphere. By cooling the molybdenum trioxide vapor in an air atmosphere to form molybdenum trioxide particles, the ratio (I Ｏ / II Ｏ ) can be greater than 1.1, and in the molybdenum trioxide particles, MoO ３ The β crystal structure is easily obtained.

[0202] The cooling temperature (temperature of the cooling pipe) is not particularly limited, but is preferably from -100 to 600°C, and more preferably from -50 to 400°C.

[0203] The cooling rate of the molybdenum trioxide vapor is not particularly limited, but is preferably 100° C. / s or more and 100,000° C. / s or less, and more preferably 1,000° C. / s or more and 50,000° C. / s or less. Note that as the cooling rate of the molybdenum trioxide vapor increases, molybdenum trioxide particles having a smaller particle size and a larger specific surface area tend to be obtained.

[0204] When the cooling means is a method of cooling by blowing gas into a cooling pipe, the temperature of the blown gas is preferably -100 to 300°C, more preferably -50 to 100°C.

[0205] The gas flow rate is 0.1 m ３ / min or more 20m ３ / min or less, and ３ / min or more 10m ３ It is more preferable that the gas blowing speed is 0.1 m / min or less. ３ When the gas blowing speed is 20 m / min or more, a high cooling rate can be achieved and clogging of the cooling pipe can be prevented, which is preferable. ３ / min or less is preferable because it eliminates the need for an expensive first blowing means (exhaust fan, etc.), thereby reducing manufacturing costs.

[0206] The molybdenum trioxide vapor is cooled and the resulting particles are transported to a collector for recovery.

[0207] In the method for producing molybdenum trioxide particles, the particles obtained by cooling the molybdenum trioxide vapor may be calcined again at a temperature of 100 to 320°C.

[0208] That is, the molybdenum trioxide particles obtained by the method for producing molybdenum trioxide particles may be calcined again at a temperature of 100 to 320°C. The calcination temperature for the second calcination may be 120 to 280°C, or 140 to 240°C. The calcination time for the second calcination may be, for example, 1 minute to 4 hours, 10 minutes to 5 hours, or 100 minutes to 6 hours. However, the second calcination will result in a partial disappearance of the β crystal structure of molybdenum trioxide. When the molybdenum trioxide particles are calcined for 4 hours at a temperature of 350°C or higher, the β crystal structure in the molybdenum trioxide particles disappears, the ratio (β(011) / α(021)) becomes 0, and reactivity with sulfur is impaired. The method for producing molybdenum trioxide particles described above can produce molybdenum trioxide particles suitable for producing the molybdenum disulfide particles.

[0209] In the method for producing a composite according to the first aspect of the present invention, when the molybdenum compound is molybdenum carbide, an example of a method for producing molybdenum carbide particles will be described below.

[0210] <Method for Producing Molybdenum Carbide> The method for producing molybdenum carbide comprises calcining molybdenum trioxide and carbon in the presence of at least one inorganic compound selected from the group consisting of inorganic salts and inorganic hydroxides.

[0211] In the method for producing molybdenum carbide, the molybdenum trioxide used as a raw material is not particularly limited, but it is preferable to use molybdenum trioxide containing α-crystals, which tends to have better reactivity with carbon.

[0212] In the method for producing molybdenum carbide, the average crystallite size of α-crystals contained in the crystal structure of molybdenum trioxide is preferably 50 nm or less, more preferably 5 nm or more and 50 nm or less, even more preferably 5 nm or more and 45 nm or less, still more preferably 10 nm or more and 40 nm or less, and particularly preferably 10 nm or more and 35 nm or less. When the average crystallite size of α-crystals is within the above range, the reactivity of the molybdenum trioxide particles with carbon tends to be better.

[0213] In the method for producing molybdenum carbide, the crystal structure of molybdenum trioxide may further include β crystals having an average crystallite size of 50 nm or less. When the crystal structure of molybdenum trioxide includes α crystals and β crystals, the reactivity of the molybdenum trioxide particles with carbon tends to be improved.

[0214] In the method for producing molybdenum carbide, the average crystallite size of β crystals contained in the crystal structure of molybdenum trioxide is preferably 5 nm or more and 50 nm or less, more preferably 5 nm or more and 45 nm or less, even more preferably 10 nm or more and 40 nm or less, and particularly preferably 10 nm or more and 30 nm or less. When the average crystallite size of β crystals is within the above preferred range, the reactivity of the molybdenum trioxide particles with carbon tends to be better.

[0215] In the method for producing molybdenum carbide, the α-crystalline structure of molybdenum trioxide is determined to be MoO in a profile obtained by powder X-ray diffraction (XRD) using Cu-Kα radiation as an X-ray source. ３ The β-crystal structure can be confirmed by the presence of a peak on the (021) plane of the α-crystal (2θ: around 27.32°, No. 166363 (Inorganic Crystal Structure Database, ICSD)). ... ３ This can be confirmed by the presence of a peak (2θ: around 23.01°, No. 86426 (Inorganic Crystal Structure Database, ICSD)) which is assigned to the (011) plane of the β crystal of the compound.

[0216] In the method for producing molybdenum carbide, the molybdenum trioxide particles have a profile obtained by powder X-ray diffraction (XRD) using Cu-Kα rays as an X-ray source, which profile is MoO ３ The peak intensity attributed to the (011) plane of the β crystal of MoO ３ The ratio (β(011) / α(021)) of the peak intensity of the molybdenum trioxide particles to the peak intensity attributable to the (021) plane of the α crystal is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.4 or more. In the method for producing molybdenum carbide, the ratio (β(011) / α(021)) of the molybdenum trioxide particles is preferably 10.0 or less.

[0217] MoO ３ The peak intensity attributed to the (011) plane of the β crystal of MoO ３ For the peak intensities attributable to the (021) plane of the α crystal, the maximum intensity of each peak is read, and the ratio (β(011) / α(021)) is calculated.

[0218] In the method for producing molybdenum carbide, the ratio (β(011) / α(021)) of the molybdenum trioxide particles is preferably 0.1 to 10.0, more preferably 0.2 to 10.0, and particularly preferably 0.4 to 10.0.

[0219] In the method for producing molybdenum carbide, the α-crystal content of the molybdenum trioxide particles is not particularly limited, but may be 20% or more, 50% or more, 70% or more, 80% or more, or 100%.

[0220] MoO ３ In a mixture of α and β crystals of MoO ３ The content of α crystals in MoO can be determined from the obtained profile data by the RIR (reference intensity ratio) method. ３ The RIR value K of the α crystal Ａ and MoO ３ Integrated intensity I of the (021) plane of the α-crystal (2θ: around 27.32°_No. 166363 (Inorganic Crystal Structure Database, ICSD)) Ａ , and MoO ３ The RIR value K of the β crystal Ｂ and MoO ３ The integrated intensity I of (2θ: around 23.01°, No. 86426 (Inorganic Crystal Structure Database, ICSD)) belongs to the (011) plane of the β crystal of Ｂ Using the following formula (2), MoO ３ The content (%) of α crystals in MoO can be calculated. ３ α crystal content (%) = (I Ａ / K Ａ ) / ((I Ａ / K Ａ ) + (I Ｂ / K Ｂ )) × 100 (2) Here, the RIR values ​​can be those listed in the ICSD database, and the analysis can be performed using integrated powder X-ray analysis software (PDXL2, manufactured by Rigaku Corporation).

[0221] In the method for producing the molybdenum carbide, the molybdenum trioxide particles have a median diameter D of the primary particles determined by a dynamic light scattering method. ５０ is preferably 10 nm or more and 2000 nm or less, more preferably 10 nm or more and 500 nm or less, and even more preferably 10 nm or more and 200 nm or less. ５０When the median diameter D of the primary particles of the molybdenum trioxide particles is within the above preferred range, the reactivity of the molybdenum trioxide particles with carbon tends to be improved. ５０ is calculated from the volume-based cumulative particle size distribution measured using, for example, a dynamic light scattering particle size distribution measuring device.

[0222] In the method for producing molybdenum carbide, the ratio of MoO measured by X-ray fluorescence (XRF) to the total mass of molybdenum trioxide particles is ３ The content of MoO is preferably 99.5% by mass or more, more preferably 99.7% by mass or more, and even more preferably 99.9% by mass or more, based on the total detected peak intensity. ３ When the content ratio of is within the above preferred range, it is easy to obtain a highly pure molybdenum carbide having good storage stability and no risk of producing carbides derived from impurities by subjecting the molybdenum trioxide particles to a carbonization reaction.

[0223] In the method for producing molybdenum carbide, the specific surface area of ​​the molybdenum trioxide particles is preferably 10 m or less because this improves reactivity with carbon. ２ / g or more, and ２ / g or more is more preferable, and 30m ２ / g or more is more preferable. ２ / g or less, and ２ / g or less, ２ / g or less.

[0224] (Method for Producing Molybdenum Trioxide Particles Used in the Method for Producing Molybdenum Carbide) In the method for producing molybdenum carbide, the molybdenum trioxide particles used as a raw material may be manufactured or may be a commercially available product. However, the median diameter D of the primary particles ５０From the viewpoint of controlling the particle size and crystal structure and improving the reactivity, it is preferable to use the molybdenum trioxide particles produced by the method described in the above section (Production method of molybdenum trioxide particles used in the production method of molybdenum disulfide particles). ５０ , the MoO ３ The molybdenum trioxide particles having the content ratio and the specific surface area falling within the above ranges can be obtained by the method described in the above section (Method for producing molybdenum trioxide particles used in the method for producing molybdenum disulfide particles).

[0225] The at least one inorganic compound is preferably an alkali metal compound, more preferably at least one selected from the group consisting of sodium compounds and potassium compounds, and particularly preferably KCl, NaCl, Na ２ CO ３ and KOH are more preferred.

[0226] The amount of the at least one inorganic compound is not particularly limited, but is preferably 5% to 1000%, more preferably 10% to 500%, and even more preferably 20% to 200%, based on the mass of molybdenum trioxide and carbon. When the amount of the at least one inorganic compound is within the above-mentioned preferred range, it is easy to form a molybdenum carbide having high electrical conductivity and catalytic activity.

[0227] In the method for producing molybdenum carbide according to this embodiment, the at least one inorganic compound functions as a flux, accelerating the reaction between molybdenum trioxide and carbon. The flux method is characterized by its ability to synthesize inorganic compounds or control their crystal structure and composition at temperatures relatively lower than those of ordinary firing.

[0228] In the method for producing molybdenum carbide according to this embodiment, the firing temperature is not particularly limited, but is preferably 400 to 1500° C., more preferably 500 to 1000° C., and even more preferably 750 to 880° C. When the firing temperature is within the above preferred range, molybdenum carbide with high electrical conductivity and catalytic activity is easily formed.

[0229] In the method for producing molybdenum carbide, the heating time is not particularly limited, but may be a time period during which the reaction proceeds sufficiently, and may be 1 to 48 hours, 2 to 24 hours, or 4 to 12 hours.

[0230] The method for producing molybdenum carbide may include a step of calcining molybdenum trioxide and carbon, and then washing the calcined product with water to remove the at least one inorganic compound.

[0231] In the method for producing molybdenum carbide, the carbon is not particularly limited, and commercially available carbon particles such as carbon black, carbon nanotubes, and activated carbon can be used.

[0232] <Method for producing a composite according to a second aspect> The method for producing a composite according to a second aspect of the present invention includes a step of adding a molybdenum compound to a solvent to obtain a molybdenum compound dispersion (step 1), and a step of mixing a noble metal compound and an alkali metal hydroxide with the molybdenum compound dispersion (step 2). The molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide and molybdenum carbide, and the noble metal in the noble metal compound is at least one metal selected from the group consisting of platinum and palladium.

[0233] (Step 1) Step 1 is a step of obtaining a molybdenum compound dispersion by adding a molybdenum compound to a solvent, wherein the molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide and molybdenum carbide.

[0234] The molybdenum sulfide and the molybdenum carbide have the same meanings as the molybdenum sulfide and the molybdenum carbide described above in connection with the composite of this embodiment. The molybdenum compound may be molybdenum compound particles.

[0235] The solvent is not particularly limited, and specific examples thereof include water and organic solvents. These may be used alone or in combination of two or more. Examples of the organic solvent include benzene, toluene, xylene, methanol, ethanol, ethylene glycol, diethylene glycol, diethyl ether, dibutyl ether, and tetrahydrofuran.

[0236] The method for dispersing the molybdenum compound in the solvent is not particularly limited, and examples thereof include ultrasonic dispersion, stirring dispersion, and collision dispersion.

[0237] (Step 2) Step 2 is a step of mixing a noble metal compound and an alkali metal hydroxide with the molybdenum compound dispersion obtained in step 1. The noble metal in the noble metal compound is at least one metal selected from the group consisting of platinum and palladium. When adding the noble metal compound and the alkali metal hydroxide to the molybdenum compound dispersion, the noble metal compound and the alkali metal hydroxide may be added simultaneously, or the alkali metal hydroxide may be added first and then the noble metal compound, or the noble metal compound may be added first and then the alkali metal hydroxide. Alternatively, the alkali metal hydroxide may be dissolved in water and then added.

[0238] A composite containing a molybdenum compound and a precious metal can be formed by mixing a precious metal compound and a molybdenum compound in the presence of an alkali metal hydroxide. The rate of the reduction reaction can be adjusted by adding an alkali metal hydroxide in step 2. This eliminates the need to ensure dispersibility after adding the precious metal compound to the dispersion, and for example, substantially no dispersant need be added. Examples of the dispersant include those similar to those described in the method for producing a composite according to the first aspect. Note that "substantially no dispersant is added" means that no dispersant is added, or, if added, the amount added is 50 mol% or less relative to the amount of precious metal.

[0239] As the alkali metal hydroxide, from the viewpoint of hydration energy, it is preferable to use at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, and potassium hydroxide, it is more preferable to use at least one selected from the group consisting of sodium hydroxide and potassium hydroxide, and it is particularly preferable to use sodium hydroxide.

[0240] The amount of the alkali metal hydroxide added, in terms of molar ratio relative to the noble metal compound, is preferably within a range of 0.5 to 100, more preferably within a range of 1 to 50, and even more preferably within a range of 3 to 10. By setting the amount of the alkali metal hydroxide added within the above range, the catalytic activity of the resulting composite is improved.

[0241] The noble metal compound is composed of at least one metal selected from the group consisting of platinum and palladium. When the noble metal is palladium, examples of the noble metal compound include palladium acetate, palladium nitrate, palladium nitrite, palladium sulfate, palladium carbonate, palladium chloride, palladium hydroxide, palladium oxide, and sodium palladium (II) chloride. When the noble metal is platinum, examples of the noble metal compound that can be used include hexachloroplatinic (IV) acid hexahydrate, potassium hexachloroplatinate, ammonium hexachloroplatinate, sodium hexachloroplatinate, ammonium tetrachloroplatinate, and potassium tetrachloroplatinate.

[0242] The temperature of the mixture of the molybdenum compound particles and the noble metal solution may be any temperature that allows the formation of a composite, and may be, for example, 10 to 100°C, or 20 to 80°C.

[0243] The retention time after adding and mixing the noble metal compound and the alkali metal hydroxide to the molybdenum compound dispersion may be long enough to form a complex, and may be, for example, from 10 minutes to 48 hours, or from 30 minutes to 12 hours.

[0244] In the method for producing a composite according to the second aspect of the present invention, in order to promote photoreduction of the noble metal, the alkali metal hydroxide and the noble metal compound may be added to the molybdenum compound dispersion and the mixed solution may be irradiated with light. Examples of the light irradiation method include the same methods as those described in the method for producing a composite according to the first aspect of the present invention.

[0245] In the composite manufacturing method of the second aspect of the present invention, the composite can be manufactured without heat treatment. For example, the obtained composite or the mixture of the noble metal solution and the molybdenum compound particles is preferably not heated to 200°C or higher, more preferably not heated to above 100°C, and even more preferably not heated to above 80°C.

[0246] After the complex is formed from the mixture, the process may include a step of separating the complex by centrifugal separation, drying, etc. By such a step, the complex of the present embodiment can be easily recovered.

[0247] The method for producing the composite according to the second aspect of the present invention can further include a step of producing the molybdenum compound particles. Examples of the method for producing molybdenum disulfide particles when the molybdenum compound is molybdenum disulfide and the method for producing molybdenum carbide particles when the molybdenum compound is molybdenum carbide include the methods described above in the section <Method for producing the composite according to the first aspect>.

[0248] <Hydrogen generating catalyst> The composite of the embodiment can be suitably used as a catalyst in the hydrogen generating reaction (HER) (sometimes referred to as "hydrogen generating catalyst" in this specification). The composite of the embodiment can also be used as a hydrogen generating catalyst when used in combination with a conductive material. That is, preferred hydrogen generating catalysts include, for example, those containing the composite of the embodiment, and the hydrogen generating catalyst may further contain a conductive material in addition to the composite of the embodiment. The catalytic activity of a hydrogen generating catalyst containing the composite of the embodiment and a conductive material in the hydrogen generating reaction (HER) is further increased.

[0249] The conductive material may be a known material. Examples of the conductive material include carbon and metals, which have high conductivity. The hydrogen generation catalyst may contain only one type of conductive material, or two or more types of conductive materials.

[0250] Examples of the conductive material include carbon black such as acetylene black, Cabot carbon black, and Ketjen black, graphite, carbon fiber, metal powder, etc. Ketjen black has a high specific surface area and electrical conductivity, and is also excellent in that it can suppress the aggregation of molybdenum sulfide.

[0251] Examples of the metal that is the conductive material include gold, silver, copper, aluminum, rhodium, molybdenum, tungsten, iron, nickel, cobalt, indium, etc. Unlike palladium in the composite of the embodiment, the metal that is the conductive material is simply mixed with the composite of the embodiment in the hydrogen generation catalyst.

[0252] The hydrogen generation catalyst may contain only one type of metal as a conductive material, or two or more types of metals.

[0253] The hydrogen generation catalyst may contain, for example, no metal but carbon as the conductive material, may contain no carbon but metal, or may contain both metal and carbon.

[0254] In the hydrogen generation catalyst, the content of the conductive material is preferably 0.1 to 100 parts by mass, more preferably 0.5 to 50 parts by mass, relative to 100 parts by mass of the content of the composite of the embodiment.

[0255] In the hydrogen generation catalyst, the ratio of the total content of the composite of the embodiment and the conductive material to the total mass (100 mass%) of the hydrogen generation 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 either 97 mass% or more or 99 mass% or more, or it may be 100 mass%. When the ratio is equal to or more than the lower limit, the catalytic activity of the hydrogen generation catalyst in the hydrogen generation reaction (HER) becomes higher. The ratio may be 100 mass% or less.

[0256] <Catalyst Ink> A catalyst ink according to one embodiment of the present invention contains the composite according to the present embodiment and a solvent. The catalyst ink according to the embodiment may contain the composite according to the present embodiment, a polymer electrolyte, and a solvent.

[0257] The catalyst ink of this embodiment may further contain a conductive material. The type and content of the conductive material may be those exemplified above.

[0258] The catalyst ink can be applied to, for example, a substrate for a working electrode to form a catalyst layer.

[0259] The polymer electrolyte may be one generally used in forming a catalyst layer, such as a perfluorocarbon polymer having a sulfonic acid group (e.g., Nafion (registered trademark)), a hydrocarbon polymer compound having a sulfonic acid group, a polymer compound doped with an inorganic acid such as phosphoric acid, an organic / inorganic hybrid polymer partially substituted with a proton-conductive functional group, or a proton conductor obtained by impregnating a polymer matrix with a phosphoric acid solution or a sulfuric acid solution.

[0260] Examples of the solvent include a solvent in which the composite of the embodiment can be dispersed and which can be applied to a working electrode substrate or the like to form a catalyst layer. The solvent preferably contains an alcohol such as 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 1-hexanol, 2-hexanol, 1-heptanol, or 2-heptanol.

[0261] <Electrode> An electrode according to one embodiment of the present invention is obtained by applying the catalyst ink according to the present embodiment. For example, an electrode can be produced by applying a dispersion of the catalyst ink obtained above to the surface of an electrode, allowing the surface liquid to dry naturally, and then transferring the electrode to a vacuum dryer and drying it at 30 to 90°C for at least two hours. The hydrogen evolution activity of the produced electrode can be evaluated using a three-electrode method. The evaluation conditions were an LSV method with a scan voltage range of -0.3 V to 0 V and a scan speed of 5 mV / s.

[0262] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0263] Reference Example 1 "Production and Evaluation of Molybdenum Trioxide Particles" <Production of Molybdenum Trioxide Particles> Molybdenum trioxide was produced using an RHK simulator (manufactured by Noritake Co., Ltd.) as a firing furnace and a VF-5N dust collector (manufactured by Amano Corporation) as a dust collector. 1.5 kg of aluminum hydroxide (manufactured by Nippon Light Metal Co., Ltd.) and 1 kg of molybdenum trioxide (manufactured by Nippon Inorganic Co., Ltd.) were mixed and then charged into a sagger and fired at a temperature of 1100°C for 10 hours. During firing, outside air (air flow rate: 150 L / min, outside air temperature: 25°C) was introduced from the side and bottom of the firing furnace. Molybdenum trioxide evaporated in the furnace and then cooled near the dust collector, where it precipitated as particles. 900 g of molybdenum trioxide (1) was obtained using the dust collector.

[0264] Median diameter D of primary particles determined by dynamic light scattering ５０ The purity of molybdenum trioxide (1) was 87.8 nm (MoO ３ It was confirmed that the molybdenum trioxide (1) content (ratio of molybdenum trioxide and β-crystal molybdenum trioxide) was 99.9% by mass. Furthermore, when the crystal structure of molybdenum trioxide (1) was analyzed by X-ray diffraction (XRD), peaks attributable to α-crystal molybdenum trioxide and β-crystal molybdenum trioxide were observed, but no other peaks were observed. Next, the peak intensity ratios of the (011) plane of the β-crystal and the (021) plane of the α-crystal were compared, and it was found that β(011) / α(021) was 4. Furthermore, the integrated powder X-ray analysis software PDXL2 manufactured by Rigaku Corporation was used, and LaB was used as a standard substance.６ The XRD instrument constants were determined using NIST SRM660c LaB6 Standard Powder, and the crystallite size was evaluated using the Scherrer method. As a result, it was confirmed that molybdenum trioxide (1) had a crystalline structure containing α crystals with an average crystallite size of 15.7 nm and β crystals with an average crystallite size of 16.8 nm.

[0265] <Evaluation of Molybdenum Oxide Powder> [Method for Measuring the Average Particle Size of Primary Particles of Molybdenum Trioxide Particles] 0.1 g of molybdenum trioxide (1) obtained in Reference Example 1 was added to 10 ml of ethanol, and the mixture was subjected to ultrasonic treatment in an ice bath for 4 hours. The concentration was then adjusted appropriately with ethanol to a range measurable by a dynamic light scattering particle size distribution analyzer (MicrotracBEL Nanotrac Wave II) to obtain a measurement sample. Using this measurement sample, the particle size distribution in the particle size range of 0.0001 to 10 μm was measured using the dynamic light scattering particle size distribution analyzer (MicrotracBEL Nanotrac Wave II), and the median diameter D ５０ was calculated. However, the median diameter D ５０ For particles having a particle size of more than 10 μm, a solution is prepared in the same manner, and the particle size distribution in the particle size range of 0.015 to 500 μm is measured using a laser diffraction particle size distribution measuring device (SALD-7000 manufactured by Shimadzu Corporation). ５０ was calculated.

[0266] [Crystal Structure Analysis of Molybdenum Trioxide Particles: XRD Method] A sample of molybdenum trioxide (1) was filled into a measurement sample holder with a depth of 0.5 mm, and the holder was set in an X-ray diffraction (XRD) device (Ultima IV manufactured by Rigaku Corporation, an optical system using a parallel beam method + scintillation counter detector, and a rotary stage), and measurement was performed under the conditions of Cu / Kα radiation, 40 kV / 40 mA, a scan speed (2θ) of 2° / min, a step (2θ) of 0.02°, and a scan range (2θ) of 10° to 70°.

[0267] [Method for Measuring Crystallite Size of Molybdenum Trioxide Particles] Measurements were performed using a SmartLab 9kW (manufactured by Rigaku Corporation) as an X-ray diffractometer, a scintillation counter detector as a detector, and PDXL2 as analysis software. The measurement method was the 2θ / θ method, and the average crystallite size of molybdenum trioxide was calculated using the Scherrer equation from the half-width of the peak appearing at 2θ = 12.7° ± 0.5°. The measurement conditions were a scan speed (2θ) of 2.0° / min, a scan range (2θ) of 10 to 70°, a step (2θ) of 0.02°, and no standard width for the device.

[0268] [Measurement of Molybdenum Trioxide Purity: XRF Analysis] Using a Primus IV X-ray fluorescence analyzer (manufactured by Rigaku Corporation), approximately 20 to 30 mg of a sample of the recovered molybdenum trioxide particles was placed on filter paper and covered with a PP film for composition analysis. The amount of molybdenum determined from the results of the XRF analysis was calculated as molybdenum trioxide (mass %) relative to 100% by mass of the molybdenum trioxide particles.

[0269] (Synthesis Example 1) "Mo ２ Synthesis of Molybdenum C: 30.0 g of molybdenum trioxide (Sinopharm Group Chemical Reagent Co., Ltd., average particle size 5 μm), 15.0 g of activated carbon (Yantai Tongyi Environmental Production Technology Co., Ltd.), and 56.3 g of sodium carbonate (Sinopharm Group Chemical Reagent Co., Ltd.) were mixed, then placed in a crucible and fired at 850°C for 6 hours in a nitrogen atmosphere. After natural cooling, the fired product was washed with ion-exchanged water to remove salts. XRD analysis showed that the obtained molybdenum carbide (Mo ２It was confirmed that the molybdenum carbide exhibited the α-crystal structure of molybdenum carbide (C). Furthermore, the crystallite size measured by XRD was 47 nm. Furthermore, the carbon content relative to the total mass (100 mass%) of the molybdenum carbide was 48%. Furthermore, as a result of performing Raman spectroscopy on the molybdenum carbide, a carbon-derived graphite band G and a disorder band D were confirmed, and the ratio of the carbon-derived graphite band G to the disorder band D (G / D) was 0.84. Note that even when the molybdenum carbide is modified with a noble metal, the carbon content and the G / D do not usually change.

[0270] (Synthesis Example 2) “MoS ２ Synthesis of "40.0 g (277.9 mmol) of molybdenum trioxide (1) obtained in Reference Example 1 and 40.0 g (1250 mmol, 4.5 equivalents per Mo atom) of sulfur powder (manufactured by Kanto Chemical Co., Inc.) were added to an alumina crucible and mixed with a stirrer until the powder was uniform. After mixing, the alumina crucible was covered with a lid and placed in a high-temperature atmosphere firing furnace (manufactured by Motoyama Co., Ltd., SKM-2030P-OP). The furnace interior was evacuated and replaced with nitrogen, followed by firing. The firing conditions were as follows: the temperature was raised from room temperature of 25°C at a rate of 5°C / min, and after reaching 500°C, the temperature was maintained for 4 hours. Nitrogen gas was blown in at 0.5 L / min during the firing process. The furnace was then allowed to cool naturally, yielding 44.5 g of molybdenum disulfide particles. XRD analysis confirmed that the particles contained a 3R crystal structure.

[0271] (Synthesis Example 3) "MoO ３ / MoS ２ Synthesis of "500 mg of molybdenum trioxide (1) obtained in Reference Example 1 and 556 mg of sulfur (Kanto Chemical Co., Ltd. Reagent, S) were mixed to a uniform mixture. After mixing, a lid was placed on the crucible, and the mixture was placed in a nitrogen atmosphere furnace and fired. The firing conditions were as follows: the temperature was raised from room temperature of 25°C at a rate of 5°C / min, and after reaching 300°C, the temperature was maintained for 4 hours. During the firing process, nitrogen gas was blown at 0.2 ml / min. Thereafter, the temperature inside the furnace was allowed to cool naturally, and the product was washed three times with toluene and vacuum dried to obtain a composite of molybdenum trioxide and molybdenum sulfide.

[0272] (Example 1) "Catalyst A, PVP added" Mo obtained in Synthesis Example 1 ２ 95 mg of C was dissolved in 10 ml of ethanol (Kanto Chemical Co., Ltd., reagent, C ２ H ５ The mixture was ultrasonically dispersed in a first mixed solvent of 20 ml of NaOH and 20 ml of pure water for 30 minutes to obtain a dispersion. ２ PdCl ４ 4.9 mg, Kanto Chemical Co., Ltd. Reagent, H ２ PtCl ６ ・6H ２ 8.6 mg of PO, Kanto Chemical Co., Inc., and 18.4 mg of polyvinylpyrrolidinone (hereinafter, sometimes referred to as "PVP") (K=15) were dissolved by ultrasonic dispersion in a second mixed solvent of 10 ml ethanol and 20 ml pure water, and the resulting solution was added to the dispersion with stirring. The mixture was then stirred at room temperature for 0.5 hours. The dispersion was then heated at 80°C for 1 hour. The precipitate in the dispersion was recovered using a centrifuge, ultrasonically washed three times with water, and vacuum dried to obtain a molybdenum carbide powder (Catalyst A) modified with Pd and Pt. The resulting molybdenum carbide powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis, confirming that it contained aggregates of palladium atoms without a crystalline structure. More specifically, the presence of Pd was confirmed by XRF elemental analysis. Next, XRD analysis was performed, and no Pd peak was detected. Furthermore, HR-TEM (high resolution electron microscope (HR-TEM (JEOL Ltd., JEM-ARM300F)) analysis was performed, and no diffraction was confirmed, confirming that the sample had no crystallinity.

[0273] Example 2 "Catalyst B" A molybdenum carbide powder (catalyst B) modified with Pd and Pt was obtained in the same manner as in Example 1, except that a mixed solvent of 10 ml ethanol and 10 ml pure water was used as the first mixed solvent, a mixed solvent of 15 ml ethanol and 15 ml pure water was used as the second mixed solvent, and PVP was not added to the second mixed solvent. XRF elemental analysis, XRD analysis, and HR-TEM analysis were performed on the obtained molybdenum carbide powder in the same manner as in Example 1, and it was confirmed that it contained aggregates of palladium atoms without a crystalline structure.

[0274] (Example 3) "Catalyst C, PVP added" Na ２ PdCl ４ The amount of H added was changed to 9.8 mg. ２ PtCl ６ ・6H ２ A molybdenum carbide powder (catalyst C) modified with Pd and Pt was obtained in the same manner as in Example 1, except that the amount of O added was changed to 17.2 mg and the amount of PVP added was changed to 36.8 mg. The obtained molybdenum carbide powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis in the same manner as in Example 1, and it was confirmed that it contained aggregates of palladium atoms without a crystalline structure.

[0275] (Example 4) "Catalyst D" 25 ml of a single solvent consisting of ethanol was used instead of the first mixed solvent and the second mixed solvent. ２ The amount of C added was changed to 74 mg, and Na ２ PdCl ４ The amount of H added was changed to 25.4 mg. ２ PtCl ６ ・6H ２ A molybdenum carbide powder (catalyst D) modified with Pd and Pt was obtained in the same manner as in Example 2, except that the amount of O added was changed to 44.6 mg. The obtained molybdenum carbide powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis in the same manner as in Example 1, and it was confirmed that it contained aggregates of palladium atoms without a crystalline structure.

[0276] (Example 5) "Catalyst E" 25 ml of a single solvent consisting of methanol was used instead of the first mixed solvent and the second mixed solvent. ２ Instead of C, MoS obtained in Synthesis Example 2 ２ A molybdenum sulfide powder (Catalyst E) modified with Pd and Pt was obtained in the same manner as in Example 2, except that 90 mg of palladium sulfide was used. The obtained molybdenum sulfide powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis in the same manner as in Example 1, and it was confirmed that it contained aggregates of palladium atoms without a crystalline structure.

[0277] (Example 6) "Catalyst F, Pd:Pt=3:7" A mixed solvent of 10 ml ethanol and 10 ml pure water was used as the first mixed solvent, a mixed solvent of 15 ml ethanol and 15 ml pure water was used as the second mixed solvent, and Mo ２ The amount of C added was changed to 90 mg, and Na ２ PdCl ４ The amount of H was changed to 5.2 mg. ２ PtCl ６ ・6H ２ A molybdenum carbide powder (catalyst F) modified with Pd and Pt was obtained in the same manner as in Example 2, except that the amount of O added was changed to 21.5 mg. The obtained molybdenum carbide powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis in the same manner as in Example 1, and it was confirmed that it contained aggregates of palladium atoms without a crystalline structure.

[0278] (Example 7) "Catalyst G" Na ２ PdCl ４ The amount of H added was changed to 15.5 mg. ２ PtCl ６ ・6H ２ A molybdenum carbide powder (catalyst G) modified with Pd and Pt was obtained in the same manner as in Example 6, except that the amount of O added was changed to 11.7 mg. The obtained molybdenum carbide powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis in the same manner as in Example 1, and it was confirmed that it contained aggregates of palladium atoms without a crystalline structure.

[0279] (Example 8) "Catalyst H, PVP added" Mo ２ The amount of C added was changed to 97 mg, and Na ２ PdCl ４ The amount of H was changed to 2.9 mg. ２ PtCl ６ ・6H ２ A molybdenum carbide powder (Catalyst H) modified with Pd and Pt was obtained by the same procedure as in Example 1, except that the amount of O added was changed to 5.2 mg and 11.0 mg of polyvinylpyrrolidinone (K=15) manufactured by Kanto Chemical Co., Inc. was used as the PVP. The obtained molybdenum carbide powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis in the same manner as in Example 1, and it was confirmed that it contained aggregates of palladium atoms without a crystalline structure.

[0280] (Example 9) "Catalyst I" Mo ２ Instead of C, MoS obtained in Synthesis Example 2 ２ 90 mg of Na ２ PdCl ４ The point that no H was added ２ PtCl ６ ・6H ２ A Pt-modified molybdenum sulfide powder (catalyst I) was obtained in the same manner as in Example 4, except that the amount of O added was changed to 26.5 mg.

[0281] (Example 10) "Catalyst J" Mo obtained in Synthesis Example 1 ２ 95 mg of C was used, and instead of PVP, Kanto Chemical Co., Ltd. reagent, H ２ PtCl ６ ・6H ２ A molybdenum carbide powder (Catalyst J) modified with Pd and Pt was obtained by the same procedure as in Example 1, except that 8.6 mg of palladium dioxide (manufactured by Kanto Chemical Co., Inc.) and 4.9 mg of sodium citrate (K=15) were added to the second mixed solvent. The sodium citrate acted as a dispersant. XRF elemental analysis, XRD analysis, and HR-TEM analysis of the obtained molybdenum carbide powder were performed in the same manner as in Example 1, and the results confirmed that it contained aggregates of palladium atoms without a crystalline structure.

[0282] Example 11 "Catalyst K" A molybdenum carbide powder (catalyst K) modified with Pd and Pt was obtained in the same manner as in Example 10, except that 47.8 mg of polyacrylic acid (molecular weight 5000) manufactured by Kanto Chemical Co., Inc. was added to the second mixed solvent instead of sodium citrate as a dispersant. The obtained molybdenum carbide powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis in the same manner as in Example 1, and it was confirmed that it contained aggregates of palladium atoms without a crystalline structure.

[0283] (Example 12) "Catalyst L" Mo ２ The amount of C added was changed to 80 mg, and Na ２ PdCl ４ The amount of H added was changed to 55.3 mg. ２ PtCl ６ ・6H ２ A Pd-modified molybdenum carbide powder (catalyst L) was obtained in the same manner as in Example 6, except that no O was added. The obtained molybdenum carbide powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis in the same manner as in Example 1, and it was confirmed that it contained aggregates of palladium atoms without a crystalline structure.

[0284] (Example 13) "Catalyst M" Na ２ PdCl ４ The amount of H added was changed to 22.7 mg. ２ PtCl ６ ・6H ２ A Pd-modified molybdenum carbide powder (catalyst M) was obtained in the same manner as in Example 6, except that no O was added. The obtained molybdenum carbide powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis in the same manner as in Example 1, and it was confirmed that it contained aggregates of palladium atoms without a crystalline structure.

[0285] (Example 14) "Catalyst N" Na ２ PdCl ４ The point that no H was added ２ PtCl ６ ・6H ２A Pt-modified molybdenum carbide powder (catalyst N) was obtained in the same manner as in Example 6, except that the amount of O added was changed to 26.5 mg.

[0286] (Example 15) "Catalyst O" Na ２ PdCl ４ The amount of H added was changed to 27.7 mg. ２ PtCl ６ ・6H ２ A Pd-modified molybdenum sulfide powder (catalyst O) was obtained in the same manner as in Example 9, except that no O was added. The obtained molybdenum sulfide powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis in the same manner as in Example 1, and it was confirmed that it contained aggregates of palladium atoms without a crystalline structure.

[0287] (Example 16) "Catalyst P" MoS ２ Instead of MoO obtained in Synthesis Example 3 ３ / MoS ２ 96 mg of Na ２ PdCl ４ The amount of H added was changed to 11.1 mg. ２ PtCl ６ ・6H ２ A powder (catalyst P) in which a composite of molybdenum oxide and molybdenum sulfide was modified with Pd was obtained in the same manner as in Example 5, except that no O was added. The obtained powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis in the same manner as in Example 1, and it was confirmed that the powder contained aggregates of palladium atoms without a crystalline structure.

[0288] (Example 17) "Catalyst Q (NaOH added)" Mo obtained in Synthesis Example 1 ２ 95 mg of C was dissolved in 10 ml of ethanol (Kanto Chemical Co., Ltd., reagent, C ２ H ５ The mixture was ultrasonically dispersed in a mixed solvent of 20 ml of NaOH and 20 ml of pure water for 30 minutes to obtain a dispersion. 199 μL of 1 M NaOH solution (NaOH, manufactured by Kanto Chemical Co., Ltd., dissolved in pure water) was added to the obtained dispersion with stirring, and then the mixture was diluted with a reagent solution of Kanto Chemical Co., Ltd., NaOH, ２ PdCl ４4.9 mg, Kanto Chemical Co., Ltd. Reagent, H ２ PtCl ６ ・6H ２ To the mixture, 8.6 mg of 0 was added with stirring. Stirring was then continued at room temperature for 0.5 hours. The dispersion was then heated at 80°C for 1 hour. The precipitate in the dispersion was recovered using a centrifuge, ultrasonically washed three times with water, washed once with ethanol, and vacuum dried to obtain a molybdenum carbide powder (Catalyst Q) modified with Pd and Pt. The obtained molybdenum carbide powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis in the same manner as in Example 1, and was confirmed to contain aggregates of palladium atoms without a crystalline structure.

[0289] Example 18 "Catalyst R (NaOH added)" A molybdenum carbide powder (Catalyst R) modified with Pd and Pt was obtained in the same manner as in Example 17, except that the amount of NaOH aqueous solution added was changed so that the molar ratio of sodium hydroxide (NaOH) to the precious metals (total of Pd and Pt) in Example 17 was as shown in Table 1. The obtained molybdenum carbide powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis in the same manner as in Example 1, and it was confirmed that it contained aggregates of palladium atoms without a crystalline structure.

[0290] Example 19 "Catalyst S (NaOH added)" A molybdenum carbide powder (catalyst S) modified with Pd and Pt was obtained in the same manner as in Example 17, except that the amount of NaOH aqueous solution added was changed so that the molar ratio of sodium hydroxide (NaOH) to the precious metals (total of Pd and Pt) in Example 17 was as shown in Table 1. The obtained molybdenum carbide powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis in the same manner as in Example 1, and it was confirmed that it contained aggregates of palladium atoms without a crystalline structure.

[0291] (Example 20) "Catalyst T (KOH added)" Mo ２95 mg of C was dispersed in a mixed solvent of 10 ml of ethanol and 20 ml of pure water by ultrasonic waves for 30 minutes to obtain a dispersion. 398 μL of 0.5 M KOH solution (Kanto Chemical Co., Ltd., KOH dissolved in pure water) was added to the obtained dispersion with stirring, and then Na ２ PdCl ４ 4.9 mg, H ２ PtCl ６ ・6H ２ To the mixture, 8.6 mg of 0 was added with stirring. Stirring was then continued at room temperature for 0.5 hours. The dispersion was then heated at 80°C for 1 hour. The precipitate in the dispersion was recovered using a centrifuge, ultrasonically washed three times with water, washed once with ethanol, and vacuum dried to obtain a molybdenum carbide powder (Catalyst T) modified with Pd and Pt. The obtained molybdenum carbide powder was subjected to XRF elemental analysis, XRD analysis, and HR-TEM analysis in the same manner as in Example 1, and was confirmed to contain aggregates of palladium atoms without a crystalline structure.

[0292] (Comparative Example 1) "MoS ２ MoS obtained in Synthesis Example 2 ２ This was used as the powder of this comparative example.

[0293] Comparative Example 2 "Commercially Available 50% Pt / C" A platinum-carbon catalyst with a platinum content of 50% purchased from Tanaka Kikinzoku Co., Ltd. was used as the powder in this comparative example.

[0294] Comparative Example 3 "Commercially Available 20% Pt / C" A platinum-carbon catalyst with a platinum content of 20% purchased from Tanaka Kikinzoku Co., Ltd. was used as the powder in this comparative example.

[0295] The powders of Examples 1 to 20 and Comparative Examples 1 to 3 were used as samples and evaluated as follows.

[0296] <Evaluation> [XRF Analysis] Using a Primus IV X-ray fluorescence analyzer (manufactured by Rigaku Corporation), approximately 20 to 30 mg of sample was placed on filter paper and covered with PP film for composition analysis. The platinum amount, palladium amount, molybdenum amount, and sulfur amount obtained from the XRF analysis results were calculated as the content of palladium and platinum ("Pd-Pt content", mass %) and the mass ratio of palladium to platinum ("Pd:Pt") relative to 100% mass of sample particles. The results are shown in Table 1.

[0297] [Measurement of BET specific surface area] Measurement was performed using a specific surface area meter (Microtrac-Bell, BELSORP-mini), and the surface area per 1 g of sample measured from the amount of nitrogen gas adsorbed by the BET method was calculated as the specific surface area. The results are shown in Table 1.

[0298] [Median diameter D ５０ Measurement of particle size distribution in the range of 0.0001 μm to 10 μm using this measurement sample. 0.1 g of sample powder was added to 20 ml of acetone, and subjected to ultrasonic treatment in an ice bath for 4 hours. The concentration was then adjusted appropriately with acetone to a range measurable by a dynamic light scattering particle size distribution analyzer (Microtrac-Bell, Nanotrac Wave II) to obtain a measurement sample. The particle size distribution in the range of 0.0001 μm to 10 μm was measured using this measurement sample with the dynamic light scattering particle size distribution analyzer, and the median diameter D ５０ The median diameter D ５０ For those having a particle size of more than 10 μm (Comparative Example 2), a solution was prepared in the same manner, and the particle size distribution in the particle size range of 0.015 μm to 500 μm was measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD-7000). ５０ The results are shown in Table 1.

[0299] [Measurement of Average Particle Diameter of Precious Metal Particles] The composite was photographed with a transmission electron microscope (TEM), and the precious metal particles observed in the two-dimensional image were analyzed by measuring the maximum distance between two points on the outline of 50 randomly selected precious metal particles (however, aggregates of multiple precious metal particles were not selected), and the average value was used.

[0300] [Volume Resistivity Measurement] 0.5 g of sample powder was placed in a sample powder measuring jig, and the resistance was measured under a set pressure range of 4 to 20 kN using an automatic powder resistivity measurement system (MCP-PD600, manufactured by Nitto Seiko Air Analytec), and the volume resistivity was calculated from the volume of the powder. Table 1 shows the volume resistivity under a pressure of 64 MPa.

[0301] [Evaluation of Hydrogen Evolution Activity] An ink dispersion was prepared by ultrasonically dispersing 4 mg of sample powder, 2 mg of Ketjen Black EC300J (Lion Specialty Chemicals Co., Ltd.), and 40 μL of 5% Nafion dispersion (Fujifilm Wako Pure Chemical Industries, Ltd. Nafion dispersion solution) in 1 mL of ethanol for 1 hour. 20 μL of the resulting ink dispersion was applied to the electrode surface, and after allowing the surface liquid to dry naturally, the electrode was dried at 60°C in a vacuum dryer for 6 hours. The overvoltage of the dried electrode was measured using a three-electrode system to evaluate hydrogen evolution activity. This indicates catalytic performance. The measurement conditions were an LSV method with a scan voltage range of -0.3 V to 0 V and a scan speed of 5 mV / s. Table 1 shows the current density and current density of 10 mA / cm. ２ The overpotential (mV) at

[0302]

[0303] 2 to 4 show images of the particles of Examples 1, 10, and 17 obtained by a transmission electron microscope (TEM, manufactured by JEOL Ltd., JEM-1400). The magnifications are 50K and 250K. From FIGS. 2 to 4, it can be seen that Pt—Pd particles having a particle diameter of about several nanometers are formed on the Mo ２ It can be seen that the carbon nanotubes are uniformly distributed on the surface of C.

[0304] (Discussion) From the results of Table 1 and Figures 2 to 4, it is clear that the noble metal nanoparticles are Mo ２ C, MoS ２ , MoO ３ / MoS ２ By modifying it to ２ Furthermore, despite the extremely low noble metal modification of 3-10% compared to the commercially available 50% Pt / C and 20% Pt / C, it was possible to exhibit catalytic activity (overvoltage) at the same level as the commercially available 50% Pt / C and 20% Pt / C, thereby achieving a significant reduction in the cost of the catalyst. In particular, when comparing Example 5 with Comparative Example 1 and Comparative Example 2, in Comparative Example 1, the unmodified MoS ２In Example 5, the overvoltage was 400 mV, and in Comparative Example 2, the Pt content was 50 wt %, but the overvoltage was 12 mV. However, in Example 5, 10 wt % Pt-Pd particles, the noble metal content of which was reduced to 1 / 5 of that in Comparative Example 2, were used in a MoS ２ As a result of modifying the catalyst, the overvoltage was 11 mV. The catalytic activity was increased. ２ C, MoS ２ , MoO ３ / MoS ２ When Pt-Pd noble metal nanoparticles are modified on MoS, the unmodified MoS ２ The catalytic activity observed was unexpected from the catalytic activity of the carbon-supported precious metals and that of the platinum-supported precious metals. This is presumed to be due to the interaction between platinum and palladium, and / or the interaction between platinum-palladium and molybdenum compounds (synergistic effect).

[0305] REFERENCE SIGNS LIST 1 Manufacturing equipment 2 Sintering furnace 3 Cooling piping 4 Recovery machine 5 Exhaust port 6 Opening adjustment damper 7 Observation window 8 Exhaust device 9 External cooling device

Claims

1. A composite comprising a molybdenum compound and a noble metal, wherein the molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide and molybdenum carbide, and the noble metal is at least one metal selected from the group consisting of platinum and palladium.

2. The composite of claim 1, wherein said noble metals are platinum and palladium.

3. The molybdenum sulfide is MoS containing a 3R structure. ２ The complex according to claim 1 or 2, 4. The molybdenum carbide is Mo ２ 3. The composite according to claim 1, having a C crystal structure, and a carbon content relative to the total mass (100 mass%) of the molybdenum carbide is 6% or more.

5. The composite according to claim 1 or 2, wherein the molybdenum carbide has a carbon-derived graphite band G and a disorder band D as measured by Raman spectroscopy.

6. The composite according to claim 5, wherein the molybdenum carbide has a ratio (G / D) of the carbon-derived graphite band G to the disorder band D of 0.75 or more.

7. The median diameter D of the complex determined by dynamic light scattering ５０ The complex according to claim 1 or 2, wherein the average particle diameter is 1000 nm or less.

8. The specific surface area of the composite, as measured by the BET method, is 10 m ２ The composite according to claim 1 or 2, wherein the tensile strength is 1 / g or more.

9. The composite according to claim 1 or 2, wherein the ratio of the content of the precious metal to the total mass of the composite determined by XRF analysis is 0.1 mass% or more.

10. The composite according to claim 1 or 2, wherein the noble metal is in the form of noble metal particles having an average particle size of 20 nm or less.

11. The composite according to claim 1 or 2, wherein the palladium comprises an aggregate of palladium atoms that does not have a crystalline structure.

12. A hydrogen generation catalyst comprising the composite of claim 1 or 2.

13. The hydrogen generation catalyst according to claim 12, further comprising a conductive material.

14. A catalyst ink comprising the composite of claim 1 or 2 and a solvent.

15. The catalyst ink of claim 14, further comprising a conductive material.

16. The catalyst ink of claim 14, further comprising a polyelectrolyte.

17. An electrode coated with the catalytic ink of claim 14.

18. A method for producing a composite, comprising a step of mixing a molybdenum compound with a precious metal solution, wherein the content of the precious metal relative to the total mass (100 mass%) of the molybdenum compound is 50 mass% or less, the molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide and molybdenum carbide, and the precious metal is at least one metal selected from the group consisting of platinum and palladium.

19. A method for producing a composite, comprising: a step of mixing a molybdenum compound with a solvent to obtain a molybdenum compound dispersion; and a step of mixing an alkali metal hydroxide and a noble metal compound with the molybdenum compound dispersion, wherein the molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide and molybdenum carbide, and the noble metal in the noble metal compound is at least one metal selected from the group consisting of platinum and palladium.

20. The method for producing a composite according to claim 18 or 19, wherein the molybdenum compound comprises molybdenum carbide, and the molybdenum carbide is obtained by calcining molybdenum trioxide containing α crystals and carbon in the presence of at least one inorganic compound selected from the group consisting of inorganic salts and inorganic hydroxides.

21. The method for producing a composite according to claim 20, wherein the average crystallite size of the α crystals of the molybdenum trioxide is 50 nm or less.

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