WO2021132189A1 - Composite material, composite material manufacturing method, and thermoelectric conversion material - Google Patents

Composite material, composite material manufacturing method, and thermoelectric conversion material Download PDF

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WO2021132189A1
WO2021132189A1 PCT/JP2020/047768 JP2020047768W WO2021132189A1 WO 2021132189 A1 WO2021132189 A1 WO 2021132189A1 JP 2020047768 W JP2020047768 W JP 2020047768W WO 2021132189 A1 WO2021132189 A1 WO 2021132189A1
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Prior art keywords
composite material
fibrous carbon
thermoelectric conversion
bite
nanoplate
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PCT/JP2020/047768
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French (fr)
Japanese (ja)
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内田　秀樹
雅之 高尻
隼人 矢吹
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日本ゼオン株式会社
学校法人東海大学
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Priority to JP2021567455A priority Critical patent/JPWO2021132189A1/ja
Publication of WO2021132189A1 publication Critical patent/WO2021132189A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B19/00—Selenium; Tellurium; Compounds thereof
    • C01B19/04—Binary compounds including binary selenium-tellurium compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/158—Carbon nanotubes
    • C01B32/168—After-treatment
    • C01B32/174—Derivatisation; Solubilisation; Dispersion in solvents
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H10N10/01—Manufacture or treatment
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H10N10/80—Constructional details
    • H10N10/85—Thermoelectric active materials
    • H10N10/851—Thermoelectric active materials comprising inorganic compositions
    • H10N10/852—Thermoelectric active materials comprising inorganic compositions comprising tellurium, selenium or sulfur
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H10N10/80—Constructional details
    • H10N10/85—Thermoelectric active materials
    • H10N10/851—Thermoelectric active materials comprising inorganic compositions
    • H10N10/855—Thermoelectric active materials comprising inorganic compositions comprising compounds containing boron, carbon, oxygen or nitrogen
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H10N10/80—Constructional details
    • H10N10/85—Thermoelectric active materials
    • H10N10/857—Thermoelectric active materials comprising compositions changing continuously or discontinuously inside the material

Definitions

  • the present invention relates to composite materials, methods for producing composite materials, and thermoelectric conversion materials.
  • thermoelectric conversion element is an element that utilizes the "Zebec effect" that a voltage is generated when a temperature difference is generated at both ends of a substance, and is usually an n (negative) type thermoelectric conversion material and a p (positive) type. It is constructed in combination with the thermoelectric conversion material of.
  • thermoelectric conversion materials that can be used for the thermoelectric conversion element
  • a bismuth tellurium (Bi 2 Te 3 ) nanoplate (hereinafter, also referred to as “BiTe nanoplate”) is known (non-).
  • Patent Document 1 BiTe nanoplates are attracting attention as n-type thermoelectric conversion materials having a large absolute value of Seebeck coefficient.
  • the BiTe nanoplate has a problem that the electric conductivity is low and the resistance of the thermoelectric conversion element increases when it is used as a thermoelectric conversion material.
  • thermoelectric conversion material a mixture of BiTe nanoplates and a conductive substance such as carbon nanotubes (hereinafter, also referred to as “CNT”) as a thermoelectric conversion material.
  • CNT carbon nanotubes
  • an object of the present invention is to provide a composite material having both thermoelectric conversion characteristics and conductivity at a high level. Another object of the present invention is to provide a method for producing a composite material, which can produce a composite material having both thermoelectric conversion characteristics and conductivity at a high level. Furthermore, an object of the present invention is to provide a thermoelectric conversion material containing a composite material having both thermoelectric conversion characteristics and conductivity at a high level.
  • the present inventors have conducted diligent studies to achieve the above object. As a result, if the BiTe nanoplates are synthesized by the sorbothermal method in the presence of fibrous carbon nanostructures such as CNTs, the BiTe nanoplates and the fibrous carbon nanostructures are integrated. We have found that a composite material having both thermoelectric conversion characteristics and conductivity at a high level can be obtained, and have completed the present invention.
  • the present invention advantageously solves the above problems, and the composite material of the present invention is characterized in that a bismuth tellurium nanoplate and a fibrous carbon nanostructure are integrated.
  • the composite material of the present invention can be suitably used as a thermoelectric conversion material.
  • the content of the fibrous carbon nanostructures is preferably 7% by mass or more and 15% by mass or less.
  • the thermoelectric conversion characteristics and the conductivity can be compatible at a higher level.
  • the content of the fibrous carbon nanostructures in the composite material can be measured by the method described in the examples of the present specification.
  • the fibrous carbon nanostructure is a carbon nanotube. If the fibrous carbon nanostructure is a carbon nanotube, thermoelectric conversion characteristics and conductivity can be compatible at a higher level.
  • the present invention aims to advantageously solve the above problems, and the method for producing a composite material of the present invention includes a bismuth source, a tellurium source, a fibrous carbon nanostructure, and a solvent.
  • the fibrous carbon nanostructure is a carbon nanotube. If the fibrous carbon nanostructure is a carbon nanotube, thermoelectric conversion characteristics and conductivity can be compatible at a higher level.
  • thermoelectric conversion material of the present invention aims to solve the above problems advantageously, and the thermoelectric conversion material of the present invention is characterized by containing any of the above composite materials. If any of the above composite materials is included in this way, the thermoelectric conversion characteristics and the conductivity of the thermoelectric conversion material can be compatible at a high level.
  • the thermoelectric conversion material of the present invention can be suitably used for manufacturing a thermoelectric conversion element.
  • thermoelectric conversion material having both thermoelectric conversion characteristics and conductivity at a high level. Further, according to the present invention, it is possible to provide a method for producing a composite material capable of producing a composite material having both thermoelectric conversion characteristics and conductivity at a high level. Further, according to the present invention, it is possible to provide a thermoelectric conversion material having both thermoelectric conversion characteristics and conductivity at a high level.
  • thermoelectric conversion material of the present invention is excellent in thermoelectric conversion characteristics and conductivity, it can be suitably used as a thermoelectric conversion material for a thermoelectric conversion element.
  • the method for producing a composite material of the present invention can be used for producing a composite material of the present invention.
  • thermoelectric conversion material of the present invention contains the composite material of the present invention, and can be suitably used for, for example, manufacturing a thermoelectric conversion element.
  • the composite material of the present invention is a composite material in which a BiTe nanoplate and a fibrous carbon nanostructure are integrated. Further, since the composite material of the present invention integrates the BiTe nanoplate and the fibrous carbon nanostructure, it is higher than the case where the BiTe nanoplate and the fibrous carbon nanostructure are simply mixed. It is possible to achieve both thermoelectric conversion characteristics and high conductivity. Here, “high thermoelectric conversion characteristics” means that the absolute value of the Seebeck coefficient is large.
  • the composite material of the present invention usually has a negative Seebeck coefficient and can be used as an n-type thermoelectric conversion material.
  • the composite material of the present invention can be produced by the method for producing a composite material of the present invention, which will be described later.
  • the composite material of the present invention is not particularly limited, but is preferably obtained as a sheet as described later from the viewpoint of handleability and the like. Since the composite material of the present invention has good properties, it is not necessary to perform a treatment such as high-temperature firing after the film formation.
  • BiTe nanoplates are thin plate-like nanostructures composed of bismuth tellurium crystals.
  • the composition of bismuth tellurium is tritellurium dibismuth (Bi 2 Te 3 ).
  • the planar shape of the BiTe nanoplate is typically hexagonal as shown in FIGS. 1 to 3, but is not limited thereto.
  • the average size (size of one side) of the BiTe nanoplate is not particularly limited, and is typically in the range of 500 nm or more and 2000 nm or less.
  • the average size of the BiTe nanoplates is determined by measuring the length of one side of 100 randomly selected BiTe nanoplates from a scanning electron microscope (SEM) photograph of the surface of the composite material and calculating the average value. Obtainable.
  • SEM scanning electron microscope
  • the size of the BiTe nanoplate can be controlled by adjusting various conditions of the solvothermal treatment described later.
  • the size (size of one side) of the BiTe nanoplate is not uniform and varies (Figs. 1 to 3).
  • the size of the BiTe nanoplate typically varies in the range of 500 nm or more and 2000 nm or less. The reason for such variation is not always clear, but in order to synthesize BiTe nanoplates in the presence of fibrous carbon nanostructures, BiTe nanoplates are formed with the fibrous carbon nanostructures as the core as described above. It is presumed that this is because it does.
  • the size of the BiTe nanoplate does not vary and is uniform (Fig. 4). ..
  • the average thickness of the BiTe nanoplate is not particularly limited, but is typically 50 nm or less, for example, about 30 nm.
  • the average thickness of BiTe nanoplates can be obtained by measuring the thickness of 100 randomly selected BiTe nanoplates from scanning electron microscope (SEM) photographs of the cross section of the composite and calculating the average value. it can.
  • the thickness of the BiTe nanoplate can be controlled by adjusting various conditions of the solvothermal treatment described later.
  • BiTe nanoplates are synthesized from bismuth source compounds and tellurium source compounds by the solvothermal method described later.
  • the BiTe nanoplate is an n-type thermoelectric conversion material and has a negative Seebeck coefficient (unit: ⁇ V ⁇ K -1 ).
  • the Seebeck coefficient is an index showing the thermoelectromotive force per 1K of absolute temperature, and the larger the absolute value, the larger the thermoelectromotive force.
  • the Seebeck coefficient can be measured by the method described in the examples.
  • the fibrous carbon nanostructure contained in the composite material of the present invention is not particularly limited as long as it is a conductive nano-sized carbon structure, and examples thereof include carbon nanotubes (CNTs), carbon nanohorns, and carbon nanofibers. Be done. From the viewpoint of achieving both thermoelectric conversion characteristics and conductivity at a higher level, the fibrous carbon nanostructure is preferably CNT.
  • the CNT may be a single-walled carbon nanotube or a multi-walled carbon nanotube, but the CNT preferably contains at least a single-walled CNT.
  • the conductivity of the obtained composite material can be enhanced and the Seebeck coefficient can be sufficiently secured, and the thermoelectric conversion characteristics and conductivity of the composite material can be compatible at a higher level.
  • the ratio of the single-walled CNTs in the CNTs is preferably 50% or more, more preferably 70% or more, and further preferably 90% or more.
  • the "ratio of single-walled CNTs in CNTs" can be determined by counting the number of single-walled CNTs in 100 CNTs randomly selected using a transmission electron microscope.
  • the average diameter of the fibrous carbon nanostructures can be 0.5 nm or more, 1 nm or more, and 2.5 nm or more.
  • the upper limit of the average diameter of the fibrous carbon nanostructure is not particularly limited, but is, for example, 15 nm or less, 10 nm or less, and 6 nm or less.
  • the average length of the fibrous carbon nanostructures is preferably 0.1 ⁇ m or more, preferably 1 cm or less, and more preferably 3 mm or less. If fibrous carbon nanostructures having an average length within the above range are used, the thermoelectric conversion characteristics and conductivity of the composite material can be compatible at a higher level.
  • the average length of the fibrous carbon nanostructures can be determined by measuring the length of 100 randomly selected fibrous carbon nanostructures using a transmission electron microscope.
  • the average diameter (Av) and the standard deviation ( ⁇ ) of the diameter satisfy the relational expression: 0.20 ⁇ (3 ⁇ / Av) ⁇ 0.80. If a fibrous carbon nanostructure satisfying the above relationship is used, the thermoelectric conversion characteristics and conductivity of the composite material can be compatible at a higher level.
  • "average diameter of fibrous carbon nanostructures (Av)” and “standard deviation of diameter of fibrous carbon nanostructures ( ⁇ : sample standard deviation)” are determined by a transmission electron microscope, respectively. The diameter (outer diameter) of 100 fibrous carbon nanostructures randomly selected using the nanostructures can be measured and determined.
  • the BET specific surface area of the fibrous carbon nanostructure is preferably 600 m 2 / g or more, and more preferably 800 m 2 / g or more.
  • the thermoelectric conversion characteristics and conductivity of the composite material can be compatible at a higher level.
  • the upper limit of the BET specific surface area of the fibrous carbon nanostructure is not particularly limited, but is, for example, 2600 m 2 / g or less.
  • the "BET specific surface area" of the fibrous carbon nanostructure can be determined by the BET method by measuring the nitrogen adsorption isotherm at 77K.
  • BELSORP registered trademark
  • -max manufactured by Nippon Bell Co., Ltd.
  • the method for producing the fibrous carbon nanostructure used in the present invention is not particularly limited, and is not particularly limited, a method by catalytic hydrogen reduction of carbon dioxide, an arc discharge method, a chemical vapor deposition method (CVD method), and a laser. Examples thereof include an evaporation method, a vapor phase growth method, a vapor phase flow method, and a HiPCO method.
  • the fibrous carbon nanostructure for example, when a raw material compound and a carrier gas are supplied on a substrate having a catalyst layer for producing carbon nanotubes on the surface and CNTs are synthesized by a CVD method, the CNTs are contained in the system.
  • the fibrous carbon nanostructure may have a functional group such as a carboxyl group introduced therein.
  • the functional group can be introduced by a known method such as an oxidation treatment method using hydrogen peroxide or nitric acid, or a contact treatment method with a supercritical fluid, a subcritical fluid or a high-temperature high-pressure fluid.
  • the content of the fibrous carbon nanostructures is preferably 2% by mass or more, more preferably 5% by mass or more, and further preferably 7% by mass or more.
  • the content of the fibrous carbon nanostructure is preferably 20% by mass or less, more preferably 17% by mass or less, and further preferably 15% by mass or less. If the fibrous carbon nanostructures are present in the composite material within the above abundance ratio, thermoelectric conversion characteristics and conductivity can be compatible at a higher level.
  • the content of the fibrous carbon nanostructure may be 2.7% by mass or more, 4.9% by mass or more, or 6.7% by mass or more. Further, it may be 14.4% by mass or less.
  • the fibrous carbon nanostructures in the composite material is increased, the fibrous carbon nanostructures may be densely packed in the composite material, and uneven density of the fibrous carbon nanostructures may occur. ..
  • a bismuth tellurium nanoplate (BiTe nanoplate) and a fibrous carbon nanostructure are integrated.
  • the bismuth tellurium nanoplate and the fibrous carbon nanostructure are integrated means that the bismuth tellurium nanoplate and the fibrous carbon nanostructure are bonded to the extent that they are not separated.
  • the nanoplate of bismuth tellurium and the fibrous carbon nanostructure are integrated means that one or more fibrous carbon nanostructures and one or more bismuth tellurium nanostructures are integrated.
  • a state in which the plates are entangled and bonded to each other a state in which one or more fibrous carbon nanostructures penetrate one or more bismuth tellurium nanoplates and are bonded to each other, and a combination thereof. It refers to the state. Therefore, in "the bismuth tellurium nanoplate and the fibrous carbon nanostructure are integrated", for example, both are simply mixed by simply mixing the bismuth tellurium nanoplate and the fibrous carbon nanostructure. It does not include the state where it overlaps with and is connected only by a weak bond such as van der Waals force.
  • FIGS. 1 to 4 the structure in which the BiTe nanoplate and the fibrous carbon nanostructure in the composite material of the present invention are integrated and the structure in which both are not integrated are concretely described.
  • FIGS. 1 to 3 are scanning electron microscope (SEM) photographs of the surface of a coating film (sheet) formed using the composite material of the present invention.
  • FIG. 4 is a scanning electron microscope (SEM) photograph of a sheet made from a mixture of BiTe nanoplates and CNTs as fissure carbon nanostructures.
  • SEM scanning electron microscope
  • thermoelectric conversion characteristics and the conductivity can be achieved at a high level by integrating the BiTe nanoplate and the fibrous carbon nanostructure.
  • the BiTe nanoplates and the fibrous carbon nanostructures are simply mixed, the BiTe nanoplates having low electrical conductivity enter between the individual fibrous carbon nanostructures, and the fibrous carbon nanostructures are interleaved with each other. It is presumed that the movement of electrons is hindered and the conductivity decreases.
  • the fibrous carbon nanostructures are inserted between the individual BiTe nanoplates and the BiTe nanoplates are separated from each other, so that the movement of carriers (electrons) is hindered and the thermoelectromotive force is reduced.
  • the BiTe nanoplate and the fibrous carbon nanostructure are integrated, the movement of electrons (carriers) is not hindered, so it is presumed that thermoelectric conversion characteristics and conductivity can be compatible at a high level. Will be done.
  • the composite material of the present invention it is preferable that all of the BiTe nanoplates and the fibrous carbon nanostructures are integrated, but to the extent that the effects of the present invention are not impaired, the unintegrated BiTe nanoplates and / or Fibrous carbon nanostructures may be included in the composite.
  • the composite material of the present invention can be dispersed in a solvent by a general dispersion method used when dispersing CNTs in a solvent, such as an ultrasonic method, an ultrasonic homogenizer method, a jet mill method, or a bead mill method. , It is preferable that the structure in which the BiTe nanoplate and the fibrous carbon nanostructure are integrated remains.
  • the method for producing a composite material of the present invention is a step of preparing a raw material composition containing a bismuth source, a tellurium source, a fibrous carbon nanostructure, and a solvent, and optionally further containing other components (hereinafter, """Preparationstep")and; A step of subjecting the raw material composition to a sorbothermal treatment to form a composite material in which BiTe nanoplates and fibrous carbon nanostructures are integrated (hereinafter referred to as "formation step"). And at least include.
  • the BiTe nanoplate and the fibrous carbon nanostructure are easily integrated to achieve both thermoelectric conversion characteristics and conductivity at a high level. It is possible to obtain a composite material that can be obtained.
  • the method for producing the composite material of the present invention may optionally include steps other than the preparation step and the forming step (hereinafter, referred to as "other steps"). Hereinafter, each step will be described.
  • the preparation step is a step of preparing a raw material composition containing a bismuth source, a tellurium source, a fibrous carbon nanostructure, and a solvent, and is not particularly limited as long as the raw material composition can be finally prepared.
  • the raw material composition may be purchased, or the above-mentioned components may be mixed to prepare a raw material composition.
  • a raw material composition can be prepared by subjecting a mixed solution containing a predetermined amount of a bismuth source, a tellurium source, a fibrous carbon nanostructure, a solvent, an arbitrary additive, and the like to an arbitrary dispersion treatment. it can.
  • Examples of such a dispersion treatment include the dispersion treatment for obtaining a cavitation effect or the dispersion treatment for obtaining a crushing effect described in International Publication No. 2016/103706.
  • a mixture (precursor solution) containing a predetermined amount of a bismuth source, a tellurium source, a solvent, and an arbitrary additive is prepared, and a fibrous carbon nanostructure dispersion having a predetermined concentration is added to the precursor solution.
  • a raw material composition (dispersion liquid) may be prepared by mixing a predetermined amount.
  • the fibrous carbon nanostructure dispersion liquid can be obtained by mixing the fibrous carbon nanostructures with a solvent so as to have a predetermined concentration and subjecting them to an arbitrary dispersion treatment.
  • the concentration of the fibrous carbon nanostructures in the fibrous carbon nanostructure dispersion is generally 0.02% by mass or more, preferably 0.1% by mass or more, and generally 1.0% by mass. Hereinafter, it is preferably 0.5% by mass or less. If it exceeds 2.0% by mass, the fibrous carbon nanostructures may aggregate and become difficult to integrate with the synthesized BiTe nanoplate.
  • the content of the fibrous carbon nanostructures in the raw material composition is preferably 0.03% by mass or more and 0.12% by mass or less, and 0.05% by mass or more, based on the solvent of the raw material composition. More preferably, it is 0.09% by mass or less. When the content of the fibrous carbon nanostructures with respect to the solvent is within the above range, the fibrous carbon nanostructures can be satisfactorily dispersed.
  • the compound of the bismuth source is not particularly limited as long as it can react with the compound of the tellurium source to synthesize a BiTe nanoplate, and bismuth oxide, bismuth chloride, bismuth fluoride, bismuth hydroxide, and bismuth nitrate. , Bismuth acetate, hydrates thereof and the like.
  • the concentration of the bismuth source compound in the precursor solution is not particularly limited, but is generally 0.005 mol / L or more, preferably 0.01 mol / L or more, and generally 0.1 mol / L or less. , Preferably 0.05 mol / L or less.
  • the tellurium source compound is not particularly limited as long as it can react with a bismuth source compound to synthesize a BiTe nanoplate, and tellurium oxide, tellurium chloride, tellurium fluoride, tellurium hydroxide, and tellurium nitrate are not particularly limited. , Tellurium acetate, hydrates thereof and the like.
  • the concentration of the tellurium source compound in the precursor solution is not particularly limited, but is generally 0.01 mol / L or more, preferably 0.05 mol / L or more, and generally 0.15 mol / L or less. It is preferably 0.09 mol / L or less.
  • Other ingredients include, but are not limited to, additives that help dissolve bismuth and tellurium sources in solvents and control crystal growth.
  • the additive is not particularly limited, but for example, polyvinylpyrrolidone can be added.
  • the concentration of the additive in the precursor solution is not particularly limited, but is generally 0.5% by mass or more, preferably 1.0% by mass or more, and generally 5.0% by mass or more with respect to the solvent. It is mass% or less, preferably 3.0 mass% or less.
  • the solvent contained in the raw material composition is not particularly limited, and either water or an organic solvent can be used.
  • the solvent one type may be used alone, or two or more types may be used in combination.
  • the organic solvent is not particularly limited, and alcohols such as methanol, ethanol and ethylene glycol; toluene, xylene, ethylbenzene, anisole, trimethylbenzene, p-fluorophenol, p-chlorophenol, o-chlorophenol, and purple olo.
  • alcohols such as methanol, ethanol and ethylene glycol; toluene, xylene, ethylbenzene, anisole, trimethylbenzene, p-fluorophenol, p-chlorophenol, o-chlorophenol, and purple olo.
  • Aromatic solvents such as phenol; tetrahydrofuran, dioxane, cyclopentyl monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate , And ethers such as 3-methoxybutyl acetate; ketones such as acetone, cyclohexanone, methylisobutylketone, methylethylketone, and diisobutylketone; N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethyl Formamide, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N, N, N, N-te
  • Nitrogen-containing polar organic solvents such as acid triamide; ethyl acetate, methyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, n-pentyl acetate, methyl lactate, ethyl lactate, n-butyl lactate, ⁇ -Ethers such as butyrolactone and ⁇ -valerolactone; dimethylsulfoxide can be mentioned.
  • polar organic solvents such as acid triamide
  • ethyl acetate, methyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, n-pentyl acetate, methyl lactate, ethyl lactate, n-butyl lactate, ⁇ -Ethers such as butyrolactone and ⁇ -valerolactone; dimethylsulfoxide can be mentioned.
  • water is preferable from the viewpoint of improving the dispersibility of the fibrous carbon nanostructures.
  • the forming step is a step of subjecting the raw material composition produced in the above preparatory step to a sorbothermal treatment to obtain a composite material in which the BiTe nanoplate and the fibrous carbon nanostructure are integrated.
  • the solvothermal treatment refers to a treatment in which a raw material is reacted in a solvent under high pressure at a temperature higher than the boiling point of the solvent to obtain crystals of the reaction product.
  • the means of the solvothermal treatment is not particularly limited, and any device used for the solvothermal reaction in the technical field such as an autoclave can be used.
  • the raw material composition (dispersion liquid) in which the fibrous carbon nanostructures are dispersed is sealed in a pressure-resistant container such as an autoclave, and stirred under a pressure that does not inhibit crystallization. This is done by heating to a predetermined temperature while or in a stationary state. Heating can be performed using any heating device such as a hot stirrer.
  • Solvothermal treatment is preferably performed in the presence of a base.
  • the base is not limited, but an inorganic compound such as potassium hydroxide or sodium hydroxide can be used.
  • the heating temperature during the solvothermal treatment needs to be higher than the boiling point of the solvent used, and is generally 160 ° C. or higher, preferably 180 ° C. or higher, and generally 240 ° C. or lower, preferably 220 ° C. It is as follows.
  • the heating time is generally 20 minutes or more, preferably 30 minutes or more, and generally 20 hours or less, preferably 8 hours or less.
  • the heating temperature may be constant during the reaction, or may be changed stepwise or continuously.
  • the pressure during the solvothermal treatment depends on the heating temperature and is determined by defining the heating temperature.
  • the other steps that the method for producing the composite material of the present invention can optionally include are not particularly limited.
  • the method for producing a composite material of the present invention can include, for example, a step of performing post-treatment after the above-mentioned forming step (post-treatment step).
  • a composite material (a structure in which a BiTe nanoplate and a fibrous carbon nanostructure are integrated) is obtained in a state of being dispersed in a solvent.
  • the composite material can be recovered from this dispersion (recovery step).
  • the recovery method include known recovery methods such as a centrifugation method.
  • the composite material can be dried after the formation step or recovery step described above (drying step). Examples of the drying method include known drying methods such as vacuum drying. Further, after the above-mentioned drying step, the obtained composite material powder can be used for thinning (sheeting) (thinning step).
  • a printing method (drop casting method) can be used.
  • the drop casting method is more cost effective and simpler than other film forming methods because it does not require its easy scalability, high deposition rate, and vacuum conditions.
  • the powder of the obtained composite material is mixed with a solvent such as ethanol at a predetermined concentration and dispersed by an ultrasonic cleaner or the like.
  • the obtained dispersion liquid is dropped onto the substrate by any dropping means such as a dropper to obtain a coating film.
  • the obtained coating film can be arbitrarily dried to obtain a sheet of composite material.
  • thermoelectric conversion material of the present invention includes the composite material of the present invention described above.
  • the thermoelectric conversion material of the present invention may consist only of the composite material of the present invention, but may include other thermoelectric conversion materials.
  • Other thermoelectric conversion materials are not particularly limited, but are selenium-based compounds; bismastellu-based compounds; antimony-based compounds; silicon-based compounds; metal oxide-based compounds; Whistler alloy-based compounds; polythiophene-based compounds, polyacetylene-based compounds, and polyaniline.
  • Conductive polymer compounds such as system compounds and polypyrrole compounds; fibrous carbon nanostructures such as carbon nanotubes; and composite materials thereof can be used.
  • thermoelectric conversion material of the present invention is excellent in thermoelectric conversion characteristics and conductivity, it can be suitably used as a material for a thermoelectric conversion element. Specifically, the thermoelectric conversion material of the present invention can be suitably used for forming an n-type thermoelectric conversion material layer of a thermoelectric conversion element.
  • thermoelectric conversion element The thermoelectric conversion element is characterized by containing the composite material of the present invention described above.
  • the structure of the thermoelectric conversion element is not particularly limited, but the thermoelectric conversion element can include the composite material of the present invention as an n-type thermoelectric conversion material layer. Further, the thermoelectric conversion element can include a p-type thermoelectric conversion material layer. The thickness of each thermoelectric conversion material layer may be appropriately determined. Examples of the thermoelectric conversion material of the p-type thermoelectric conversion material layer include selenium-based compounds; bismastellu-based compounds; antimony-based compounds; silicon-based compounds; metal oxide-based compounds; Whistler alloy-based compounds; polythiophene-based compounds and polyacetylene-based compounds.
  • thermoelectric conversion element can be manufactured, for example, by attaching two electrodes to the thermoelectric conversion material layer on the base material.
  • the electrode is not particularly limited, and for example, those described in JP-A-2014-199837 can be used. Further, the positional relationship between the thermoelectric conversion material layer and the two electrodes is not particularly limited. For example, electrodes may be arranged at both ends of the thermoelectric conversion material layer, or the thermoelectric conversion material layer may be sandwiched between two electrodes.
  • thermoelectric characteristic evaluation device having the same configuration as the thermoelectric characteristic evaluation device (manufactured by Advance Riko Co., Ltd., "ZEM-3") was manufactured, and the temperature was about 1 to 5 ° C in the atmosphere near room temperature (temperature of 20 ° C to 40 ° C).
  • the Seebeck coefficient S ( ⁇ V ⁇ K -1 ) and conductivity ⁇ (S ⁇ cm -1 ) of the composite material sheet when the temperature difference was added were measured.
  • the CNT ratio in the composite material was determined by AI qualitative analysis (point analysis) using an electron probe microanalyzer (EPMA) (EPMA-1610 manufactured by Shimadzu Corporation).
  • Example 1 ⁇ Preparation of CNT dispersion liquid> According to the description of International Publication No. 2006/011655, by the super growth method, CNT (SGCNT, single-walled CNT ratio: 90%, average diameter: 3.5 nm, average length: 350 ⁇ m, BET specific surface area: 1200 m 2 / g ) was prepared.
  • the obtained CNTs were dispersed in ethanol using an ultrasonic homogenizer (manufactured by Branson, "Model 250 DA”) at an output of 50% for 15 minutes to prepare a 0.2 mass% ethanol dispersion of CNTs.
  • an ultrasonic homogenizer manufactured by Branson, "Model 250 DA
  • the obtained raw material composition (dispersion liquid) was placed in a Teflon (registered trademark) container, which was placed in an autoclave container.
  • the dispersion was heated at 200 ° C. for 24 hours using a hot stirrer while stirring at 500 rpm with a stirrer.
  • the autoclave container was taken out, cooled, and the contents were transferred to a test tube. This was set in a centrifuge and centrifuged at 15,000 rpm to separate an aqueous solution and a precipitate. Next, only the precipitate was taken out into a saucer and dried at a temperature of 60 ° C. for 24 hours using a vacuum dryer (“Vacuum Oven ADP-21” manufactured by Yamato Scientific Co., Ltd.).
  • the obtained composite powder was mixed with ethanol at a concentration of 0.01 mol / L and dispersed by an ultrasonic cleaner. Next, the obtained dispersion liquid was applied onto a polyimide sheet as a substrate to form a film (drop casting method). Then, the obtained coating film was dried at 60 ° C. for 24 hours using a vacuum dryer (“Vacuum Oven ADP-21” manufactured by Yamato Scientific Co., Ltd.) to obtain a sheet of composite material. The obtained sheet of the composite material was observed with a scanning electron microscope, and it was confirmed that the BiTe nanoplate and the CNT were integrated. Moreover, the CNT ratio in the sheet of the composite material was measured by EPMA. In addition, the conductivity and Seebeck coefficient of the composite sheet were measured. The results are shown in Table 1.
  • Example 2 Sheet of composite material in the same manner as in Example 1 except that the amount of 0.2% by mass ethanol dispersion of CNT added was changed to 3.0 mL, 6.0 mL, 9.0 mL, 12.0 mL, and 15.0 mL, respectively.
  • Got The obtained composite material sheet was observed with a scanning electron microscope, and it was confirmed that the BiTe nanoplate and the CNT were integrated.
  • the CNT content in the composite material sheet was measured in the same manner as in Example 1.
  • the conductivity and Seebeck coefficient of the composite sheet were measured. The results are shown in Table 1.
  • the BiTe nanoplate was synthesized by subjecting only the precursor solution of the BiTe nanoplate to the above-mentioned solvothermal treatment without adding the 0.2% by mass ethanol dispersion of CNT. After the synthesis reaction, the autoclave container was taken out, cooled, and the contents were transferred to a test tube. This was set in a centrifuge and centrifuged at 15,000 rpm to separate an aqueous solution and a precipitate. Then, only the precipitate was taken out into a saucer and dried at 60 ° C. for 24 hours using a vacuum dryer (“Vacuum Oven ADP-21” manufactured by Yamato Scientific Co., Ltd.).
  • the obtained BiTe nanoplate powder was mixed with ethanol at a concentration of 0.01 mol / L and dispersed by an ultrasonic cleaner.
  • the obtained dispersion liquid was applied onto a polyimide sheet as a substrate to form a film (drop casting method).
  • the obtained coating film was dried at 60 ° C. for 24 hours using a vacuum dryer (“Vacuum Oven ADP-21” manufactured by Yamato Scientific Co., Ltd.) to obtain a sheet.
  • a vacuum dryer (“Vacuum Oven ADP-21” manufactured by Yamato Scientific Co., Ltd.) to obtain a sheet.
  • heat treatment was performed at 250 ° C. for 1 hour in an atmosphere containing 95% by volume of argon and 5% by volume of hydrogen.
  • the conductivity and Seebeck coefficient of the obtained sheet were measured. The results are shown in Table 1.
  • thermoelectric conversion characteristics and high conductivity have a good balance (Example).
  • Example 4 in which 9 mL of a 0.2 mass% ethanol dispersion of CNTs was added, a composite material having a CNT content of 7.0 mass% was obtained, and the thermoelectric conversion characteristics (Seebeck coefficient) and conductivity were the best. It can be seen that both were achieved at a high level.
  • Example 6 in which 15 mL of a 0.2 mass% ethanol dispersion of CNTs was added, the CNT content was reduced to 2.7 mass%, but this was due to the large amount of CNTs, which aggregated and the BiTe nanoplate. It is probable that it was not fully integrated with.
  • the sheet produced using only the BiTe nanoplate although the BiTe nanoplate has obtained high thermoelectric conversion characteristics, it can be seen that the conductivity is low due to the absence of CNT (Comparative Example 1). Further, in the sheet produced using only CNTs, high conductivity is obtained due to the presence of CNTs, but the Seebeck coefficient takes a positive value due to the absence of BiTe nanoplates and is not n-shaped.
  • thermoelectric conversion material having both thermoelectric conversion characteristics and conductivity at a high level. Further, according to the present invention, it is possible to provide a method for producing a composite material capable of producing a composite material having both thermoelectric conversion characteristics and conductivity at a high level. Further, according to the present invention, it is possible to provide a thermoelectric conversion material containing a composite material having both thermoelectric conversion characteristics and conductivity at a high level.

Abstract

The purpose of the present invention is to provide a composite material which achieves a high level of both thermoelectric conversion characteristics and conductivity. This composite material is characterized in that bismuth tellurium nanoplates and fibrous carbon nanostructures are integrated. This manufacturing method of the composite material is characterized by involving: a step for preparing a raw material composition containing a bismuth source, a tellurium source, fibrous carbon nanostructures and a solvent, and a step for subjecting the aforementioned raw material compositions to solvothermal treatment to form a composite material in which bismuth tellurium nanoplates and fibrous carbon nanostructures are integrated.

Description

複合材料、複合材料の製造方法、および熱電変換材料Composites, composite manufacturing methods, and thermoelectric conversion materials
　本発明は、複合材料、複合材料の製造方法、および熱電変換材料に関する。 The present invention relates to composite materials, methods for producing composite materials, and thermoelectric conversion materials.
　近年、ＩｏＴ（モノのインターネット）技術を支える持続的電源として、身の回りにあるエネルギーを活用するＥＨ（Ｅｎｅｒｇｙ　Ｈａｒｖｅｓｔｉｎｇ）技術を用いた電源が注目されている。このような電源に使用される発電素子の１つとして、熱電変換素子がある。熱電変換素子は、物質の両端に温度差を生じさせると電圧が生じるという「ゼーべック効果」を利用した素子であり、通常、ｎ（ネガティブ）型の熱電変換材料とｐ（ポジティブ）型の熱電変換材料とを組み合わせて構成する。 In recent years, as a sustainable power source that supports IoT (Internet of Things) technology, a power source that uses EH (Energy Harvesting) technology that utilizes the energy around us has been attracting attention. As one of the power generation elements used for such a power source, there is a thermoelectric conversion element. A thermoelectric conversion element is an element that utilizes the "Zebec effect" that a voltage is generated when a temperature difference is generated at both ends of a substance, and is usually an n (negative) type thermoelectric conversion material and a p (positive) type. It is constructed in combination with the thermoelectric conversion material of.
　ここで、熱電変換素子に使用され得るｎ型の熱電変換材料の１つとして、ビスマステルル（Ｂｉ２Ｔｅ３）のナノプレート（以下、「ＢｉＴｅナノプレート」ともいう）が知られている（非特許文献１）。ＢｉＴｅナノプレートは、ゼーベック係数の絶対値が大きいｎ型の熱電変換材料として注目されている。 Here, as one of the n-type thermoelectric conversion materials that can be used for the thermoelectric conversion element, a bismuth tellurium (Bi 2 Te 3 ) nanoplate (hereinafter, also referred to as “BiTe nanoplate”) is known (non-). Patent Document 1). BiTe nanoplates are attracting attention as n-type thermoelectric conversion materials having a large absolute value of Seebeck coefficient.
　しかし、ＢｉＴｅナノプレートには、電気伝導率が低く、熱電変換材料として用いた場合に熱電変換素子の抵抗が上昇してしまうという問題があった。 However, the BiTe nanoplate has a problem that the electric conductivity is low and the resistance of the thermoelectric conversion element increases when it is used as a thermoelectric conversion material.
　このような問題に対し、本発明者らは、ＢｉＴｅナノプレートと、カーボンナノチューブ（以下、「ＣＮＴ」ともいう）などの導電性物質との混合物を熱電変換材料として用いることに着想した。しかし、ＢｉＴｅナノプレートと、ＣＮＴなどの繊維状炭素ナノ構造体とを混合してなる熱電変換材料では、熱電変換特性（ゼーべック係数）と導電性とを高いレベルで両立させることができなかった。 In response to such problems, the present inventors have come up with the idea of using a mixture of BiTe nanoplates and a conductive substance such as carbon nanotubes (hereinafter, also referred to as “CNT”) as a thermoelectric conversion material. However, in a thermoelectric conversion material formed by mixing BiTe nanoplates and fibrous carbon nanostructures such as CNTs, thermoelectric conversion characteristics (Zebec coefficient) and conductivity can be compatible at a high level. There wasn't.
　そこで、本発明は、熱電変換特性と導電性とを高いレベルで両立させた複合材料を提供することを目的とする。
　また、本発明は、熱電変換特性と導電性とを高いレベルで両立させた複合材料を製造し得る、複合材料の製造方法を提供することを目的とする。
　さらに、本発明は、熱電変換特性と導電性とを高いレベルで両立させた複合材料を含む熱電変換材料を提供することを目的とする。 Therefore, an object of the present invention is to provide a composite material having both thermoelectric conversion characteristics and conductivity at a high level.
Another object of the present invention is to provide a method for producing a composite material, which can produce a composite material having both thermoelectric conversion characteristics and conductivity at a high level.
Furthermore, an object of the present invention is to provide a thermoelectric conversion material containing a composite material having both thermoelectric conversion characteristics and conductivity at a high level.
　本発明者らは、上記目的を達成するために鋭意検討を行った。その結果、本発明者らは、ＢｉＴｅナノプレートをＣＮＴなどの繊維状炭素ナノ構造体の存在下でソルボサーマル法により合成させれば、ＢｉＴｅナノプレートと繊維状炭素ナノ構造体とが一体化し、熱電変換特性と導電性とを高いレベルで両立させた複合材料が得られることを見出し、本発明の完成に至った。 The present inventors have conducted diligent studies to achieve the above object. As a result, if the BiTe nanoplates are synthesized by the sorbothermal method in the presence of fibrous carbon nanostructures such as CNTs, the BiTe nanoplates and the fibrous carbon nanostructures are integrated. We have found that a composite material having both thermoelectric conversion characteristics and conductivity at a high level can be obtained, and have completed the present invention.
　すなわち、本発明は、上記課題を有利に解決するものであり、本発明の複合材料は、ビスマステルルのナノプレートと繊維状炭素ナノ構造体とが一体化されてなることを特徴とする。このように、ビスマステルルのナノプレートと繊維状炭素ナノ構造体とを一体化させれば、両者を単純に混合する場合と比較し、熱電変換特性と導電性とを高いレベルで両立させることができる。
　なお、本発明の複合材料は熱電変換材料として好適に使用できる。 That is, the present invention advantageously solves the above problems, and the composite material of the present invention is characterized in that a bismuth tellurium nanoplate and a fibrous carbon nanostructure are integrated. In this way, if the bismuth tellurium nanoplate and the fibrous carbon nanostructure are integrated, it is possible to achieve both thermoelectric conversion characteristics and conductivity at a high level as compared with the case where both are simply mixed. it can.
The composite material of the present invention can be suitably used as a thermoelectric conversion material.
　また、本発明の複合材料においては、繊維状炭素ナノ構造体の含有量が７質量％以上１５質量％以下であることが好ましい。繊維状炭素ナノ構造体の含有量が上記範囲内であれば、熱電変換特性と導電性とをより高いレベルで両立させることができる。
　ここで、複合材料中の繊維状炭素ナノ構造体の含有量は本願明細書の実施例に記載の方法により測定することができる。 Further, in the composite material of the present invention, the content of the fibrous carbon nanostructures is preferably 7% by mass or more and 15% by mass or less. When the content of the fibrous carbon nanostructure is within the above range, the thermoelectric conversion characteristics and the conductivity can be compatible at a higher level.
Here, the content of the fibrous carbon nanostructures in the composite material can be measured by the method described in the examples of the present specification.
　また、本発明の複合材料においては、繊維状炭素ナノ構造体はカーボンナノチューブであることが好ましい。繊維状炭素ナノ構造体がカーボンナノチューブであれば、熱電変換特性と導電性とをより高いレベルで両立させることができる。 Further, in the composite material of the present invention, it is preferable that the fibrous carbon nanostructure is a carbon nanotube. If the fibrous carbon nanostructure is a carbon nanotube, thermoelectric conversion characteristics and conductivity can be compatible at a higher level.
　また、本発明は、上記課題を有利に解決することを目的とするものであり、本発明の複合材料の製造方法は、ビスマス源と、テルル源と、繊維状炭素ナノ構造体と、溶媒とを含む原料組成物を準備する工程と、前記原料組成物をソルボサーマル処理に供して、ビスマステルルのナノプレートと繊維状炭素ナノ構造体とが一体化されてなる複合材料を形成する工程と、を含むことを特徴とする。このように繊維状炭素ナノ構造体の存在下でビスマステルルのナノプレートを合成すれば、ビスマステルルのナノプレートと繊維状炭素ナノ構造体とを容易に一体化させ、熱電変換特性と導電性とを高いレベルで両立させた複合材料を得ることができる。 Further, the present invention aims to advantageously solve the above problems, and the method for producing a composite material of the present invention includes a bismuth source, a tellurium source, a fibrous carbon nanostructure, and a solvent. A step of preparing a raw material composition containing the above, a step of subjecting the raw material composition to a solvent thermal treatment, and a step of forming a composite material in which a bismasterul nanoplate and a fibrous carbon nanostructure are integrated. It is characterized by including. By synthesizing bismuth tellurium nanoplates in the presence of fibrous carbon nanostructures in this way, the bismuth tellurium nanoplates and fibrous carbon nanostructures can be easily integrated, resulting in thermoelectric conversion characteristics and conductivity. It is possible to obtain a composite material in which the above is compatible at a high level.
　また、本発明の複合材料の製造方法においては、繊維状炭素ナノ構造体はカーボンナノチューブであることが好ましい。繊維状炭素ナノ構造体がカーボンナノチューブであれば、熱電変換特性と導電性とをより高いレベルで両立させることができる。 Further, in the method for producing a composite material of the present invention, it is preferable that the fibrous carbon nanostructure is a carbon nanotube. If the fibrous carbon nanostructure is a carbon nanotube, thermoelectric conversion characteristics and conductivity can be compatible at a higher level.
　さらに、本発明は、上記課題を有利に解決することを目的とするものであり、本発明の熱電変換材料は、上記複合材料のいずれかを含むことを特徴とする。このように上記複合材料のいずれかが含まれていれば、熱電変換材料の熱電変換特性と導電性とを高いレベルで両立させることができる。
　なお、本発明の熱電変換材料は熱電変換素子の製造に好適に使用することができる。 Furthermore, the present invention aims to solve the above problems advantageously, and the thermoelectric conversion material of the present invention is characterized by containing any of the above composite materials. If any of the above composite materials is included in this way, the thermoelectric conversion characteristics and the conductivity of the thermoelectric conversion material can be compatible at a high level.
The thermoelectric conversion material of the present invention can be suitably used for manufacturing a thermoelectric conversion element.
　本発明によれば、熱電変換特性と導電性とを高いレベルで両立させた複合材料を提供することができる。
　また、本発明によれば、熱電変換特性と導電性とを高いレベルで両立させた複合材料を製造し得る、複合材料の製造方法を提供することができる。
　さらに、本発明によれば、熱電変換特性と導電性とを高いレベルで両立させた熱電変換材料を提供することができる。 According to the present invention, it is possible to provide a composite material having both thermoelectric conversion characteristics and conductivity at a high level.
Further, according to the present invention, it is possible to provide a method for producing a composite material capable of producing a composite material having both thermoelectric conversion characteristics and conductivity at a high level.
Further, according to the present invention, it is possible to provide a thermoelectric conversion material having both thermoelectric conversion characteristics and conductivity at a high level.
本発明の一実施形態に係る複合材料を用いて作製したシートの走査型電子顕微鏡（ＳＥＭ）写真である。It is a scanning electron microscope (SEM) photograph of a sheet made using the composite material which concerns on one Embodiment of this invention. 本発明の一実施形態に係る複合材料を用いて作製したシートの他の走査型電子顕微鏡（ＳＥＭ）写真である。It is another scanning electron microscope (SEM) photograph of the sheet made using the composite material which concerns on one Embodiment of this invention. 本発明の一実施形態に係る複合材料を用いて作製したシートの他の走査型電子顕微鏡（ＳＥＭ）写真である。It is another scanning electron microscope (SEM) photograph of the sheet made using the composite material which concerns on one Embodiment of this invention. ビスマステルルのナノプレートとカーボンナノチューブとの混合物を用いて作製したシートの走査型電子顕微鏡（ＳＥＭ）写真である。6 is a scanning electron microscope (SEM) photograph of a sheet prepared using a mixture of bismuth tellurium nanoplates and carbon nanotubes.
　以下、本発明の実施形態について詳細に説明する。
　本発明の複合材料は、熱電変換特性および導電性に優れるため、熱電変換素子用の熱電変換材料として好適に使用することができる。本発明の複合材料の製造方法は、本発明の複合材料の製造に使用することができる。また、本発明の熱電変換材料は本発明の複合材料を含み、例えば、熱電変換素子の製造に好適に使用することができる。 Hereinafter, embodiments of the present invention will be described in detail.
Since the composite material of the present invention is excellent in thermoelectric conversion characteristics and conductivity, it can be suitably used as a thermoelectric conversion material for a thermoelectric conversion element. The method for producing a composite material of the present invention can be used for producing a composite material of the present invention. Further, the thermoelectric conversion material of the present invention contains the composite material of the present invention, and can be suitably used for, for example, manufacturing a thermoelectric conversion element.
（複合材料）
　本発明の複合材料は、ＢｉＴｅナノプレートと繊維状炭素ナノ構造体とが一体化されてなる複合材料である。そして、本発明の複合材料は、ＢｉＴｅナノプレートと繊維状炭素ナノ構造体とが一体化されているため、ＢｉＴｅナノプレートと繊維状炭素ナノ構造体とを単に混合する場合などと比較し、高い熱電変換特性と、高い導電性とを両立させることができる。
　ここで、「高い熱電変換特性」とは、ゼーベック係数の絶対値が大きいことをいう。なお、本発明の複合材料は、通常、ゼーベック係数が負の値をとり、ｎ型の熱電変換材料として用いることができるものである。 (Composite material)
The composite material of the present invention is a composite material in which a BiTe nanoplate and a fibrous carbon nanostructure are integrated. Further, since the composite material of the present invention integrates the BiTe nanoplate and the fibrous carbon nanostructure, it is higher than the case where the BiTe nanoplate and the fibrous carbon nanostructure are simply mixed. It is possible to achieve both thermoelectric conversion characteristics and high conductivity.
Here, "high thermoelectric conversion characteristics" means that the absolute value of the Seebeck coefficient is large. The composite material of the present invention usually has a negative Seebeck coefficient and can be used as an n-type thermoelectric conversion material.
　本発明の複合材料は、後述する本発明の複合材料の製造方法により製造することができる。また、本発明の複合材料は、特に限定されないが、取り扱い性などの観点から、後述するようにシートとして得ることが好ましい。本発明の複合材料は材料自身が良好な特性を有しているため、成膜後に高温焼成などの処理を施す必要はない。  The composite material of the present invention can be produced by the method for producing a composite material of the present invention, which will be described later. The composite material of the present invention is not particularly limited, but is preferably obtained as a sheet as described later from the viewpoint of handleability and the like. Since the composite material of the present invention has good properties, it is not necessary to perform a treatment such as high-temperature firing after the film formation.
＜ＢｉＴｅナノプレート＞
　ＢｉＴｅナノプレートは、ビスマステルルの結晶で構成される、薄いプレート状のナノ構造体である。ビスマステルルの組成は三テルル化二ビスマス（Ｂｉ２Ｔｅ３）である。 <BiTe nanoplate>
BiTe nanoplates are thin plate-like nanostructures composed of bismuth tellurium crystals. The composition of bismuth tellurium is tritellurium dibismuth (Bi 2 Te 3 ).
　ＢｉＴｅナノプレートの平面形状は、図１～３に示すように典型的には六角形であるが、これに限定されない。
　また、ＢｉＴｅナノプレートの平均の大きさ（１辺の大きさ）は、特に限定されず、典型的には、５００ｎｍ以上２０００ｎｍ以下の範囲である。ＢｉＴｅナノプレートの平均の大きさは、複合材料の表面の走査型電子顕微鏡（ＳＥＭ）写真から無作為に選択したＢｉＴｅナノプレート１００個の一辺の長さを測定し、その平均値を求めることで得ることができる。なお、ＢｉＴｅナノプレートの大きさは、後述するソルボサーマル処理の諸条件を調整することで制御され得る。 The planar shape of the BiTe nanoplate is typically hexagonal as shown in FIGS. 1 to 3, but is not limited thereto.
The average size (size of one side) of the BiTe nanoplate is not particularly limited, and is typically in the range of 500 nm or more and 2000 nm or less. The average size of the BiTe nanoplates is determined by measuring the length of one side of 100 randomly selected BiTe nanoplates from a scanning electron microscope (SEM) photograph of the surface of the composite material and calculating the average value. Obtainable. The size of the BiTe nanoplate can be controlled by adjusting various conditions of the solvothermal treatment described later.
　本発明の複合材料において、ＢｉＴｅナノプレートの大きさ（１辺の大きさ）は均一ではなく、バラツキがある（図１～３）。ＢｉＴｅナノプレートの大きさは、典型的には、５００ｎｍ以上２０００ｎｍ以下の範囲でバラツキがある。このようなバラツキが生じる理由は必ずしも明確ではないが、繊維状炭素ナノ構造体の存在下でＢｉＴｅナノプレートを合成するため、前述したように繊維状炭素ナノ構造体を核としてＢｉＴｅナノプレートが形成するからであると推察される。これに対して、ＢｉＴｅナノプレートと繊維状炭素ナノ構造体としてのＣＮＴとを単純に混合してなる材料では、ＢｉＴｅナノプレートの大きさのバラツキはなく、均一な大きさである（図４）。 In the composite material of the present invention, the size (size of one side) of the BiTe nanoplate is not uniform and varies (Figs. 1 to 3). The size of the BiTe nanoplate typically varies in the range of 500 nm or more and 2000 nm or less. The reason for such variation is not always clear, but in order to synthesize BiTe nanoplates in the presence of fibrous carbon nanostructures, BiTe nanoplates are formed with the fibrous carbon nanostructures as the core as described above. It is presumed that this is because it does. On the other hand, in the material obtained by simply mixing the BiTe nanoplate and the CNT as the fibrous carbon nanostructure, the size of the BiTe nanoplate does not vary and is uniform (Fig. 4). ..
　ＢｉＴｅナノプレートの平均厚さは、特に限定されないが、典型的には５０ｎｍ以下であり、例えば、約３０ｎｍである。ＢｉＴｅナノプレートの平均厚さは、複合材料の断面の走査型電子顕微鏡（ＳＥＭ）写真から無作為に選択したＢｉＴｅナノプレート１００個の厚さを測定し、その平均値を求めることで得ることができる。なお、ＢｉＴｅナノプレートの厚さは、後述するソルボサーマル処理の諸条件を調整することで制御され得る。 The average thickness of the BiTe nanoplate is not particularly limited, but is typically 50 nm or less, for example, about 30 nm. The average thickness of BiTe nanoplates can be obtained by measuring the thickness of 100 randomly selected BiTe nanoplates from scanning electron microscope (SEM) photographs of the cross section of the composite and calculating the average value. it can. The thickness of the BiTe nanoplate can be controlled by adjusting various conditions of the solvothermal treatment described later.
　ＢｉＴｅナノプレートは、ビスマス源の化合物およびテルル源の化合物から、後述するソルボサーマル法により合成される。 BiTe nanoplates are synthesized from bismuth source compounds and tellurium source compounds by the solvothermal method described later.
　上述したように、ＢｉＴｅナノプレートはｎ型の熱電変換材料であり、負のゼーベック係数（単位：μＶ・Ｋ－１）を有する。ゼーベック係数は、絶対温度１Ｋあたりの熱起電力を示す指標であり、その絶対値が大きいほど熱起電力が大きいことを示す。ゼーベック係数は実施例に記載の方法で測定することができる。 As mentioned above, the BiTe nanoplate is an n-type thermoelectric conversion material and has a negative Seebeck coefficient (unit: μV · K -1 ). The Seebeck coefficient is an index showing the thermoelectromotive force per 1K of absolute temperature, and the larger the absolute value, the larger the thermoelectromotive force. The Seebeck coefficient can be measured by the method described in the examples.
＜繊維状炭素ナノ構造体＞
　本発明の複合材料に含まれる繊維状炭素ナノ構造体は、導電性を有するナノサイズの炭素構造体である限り特に限定されず、カーボンナノチューブ（ＣＮＴ）、カーボンナノホーン、およびカーボンナノファイバーなどが挙げられる。熱電変換特性と導電性とをより高いレベルで両立させる観点からは、繊維状炭素ナノ構造体はＣＮＴであることが好ましい。
　ＣＮＴは、単層カーボンナノチューブであっても、多層カーボンナノチューブであってもよいが、ＣＮＴは、少なくとも単層ＣＮＴを含むことが好ましい。ＣＮＴとして単層ＣＮＴを用いれば、得られる複合材料の導電性を高めると共にゼーベック係数を十分に確保することができ、複合材料の熱電変換特性と導電性とをより高いレベルで両立し得る。
　そして、ＣＮＴ中に占める単層ＣＮＴの割合は、５０％以上であることが好ましく、７０％以上であることがより好ましく、９０％以上であることが更に好ましい。
　なお、「ＣＮＴ中に占める単層ＣＮＴの割合」は、透過型電子顕微鏡を用いて無作為に選択したＣＮＴ１００本中の単層ＣＮＴの数を数えることで、求めることができる。 <Fibrous carbon nanostructures>
The fibrous carbon nanostructure contained in the composite material of the present invention is not particularly limited as long as it is a conductive nano-sized carbon structure, and examples thereof include carbon nanotubes (CNTs), carbon nanohorns, and carbon nanofibers. Be done. From the viewpoint of achieving both thermoelectric conversion characteristics and conductivity at a higher level, the fibrous carbon nanostructure is preferably CNT.
The CNT may be a single-walled carbon nanotube or a multi-walled carbon nanotube, but the CNT preferably contains at least a single-walled CNT. When single-walled CNTs are used as CNTs, the conductivity of the obtained composite material can be enhanced and the Seebeck coefficient can be sufficiently secured, and the thermoelectric conversion characteristics and conductivity of the composite material can be compatible at a higher level.
The ratio of the single-walled CNTs in the CNTs is preferably 50% or more, more preferably 70% or more, and further preferably 90% or more.
The "ratio of single-walled CNTs in CNTs" can be determined by counting the number of single-walled CNTs in 100 CNTs randomly selected using a transmission electron microscope.
　ここで、繊維状炭素ナノ構造体の平均直径は、０．５ｎｍ以上、１ｎｍ以上、２．５ｎｍ以上とすることができる。繊維状炭素ナノ構造体の平均直径が０．５ｎｍ以上であれば、繊維状炭素ナノ構造体の凝集を抑制して、複合材料の熱電変換特性と導電性とをより高いレベルで両立し得る。また、繊維状炭素ナノ構造体の平均直径の上限は、特に限定されないが、例えば１５ｎｍ以下、１０ｎｍ以下、６ｎｍ以下である。 Here, the average diameter of the fibrous carbon nanostructures can be 0.5 nm or more, 1 nm or more, and 2.5 nm or more. When the average diameter of the fibrous carbon nanostructures is 0.5 nm or more, aggregation of the fibrous carbon nanostructures can be suppressed, and the thermoelectric conversion characteristics and conductivity of the composite material can be compatible at a higher level. The upper limit of the average diameter of the fibrous carbon nanostructure is not particularly limited, but is, for example, 15 nm or less, 10 nm or less, and 6 nm or less.
　また、繊維状炭素ナノ構造体の平均長さは、０．１μｍ以上であることが好ましく、１ｃｍ以下であることが好ましく、３ｍｍ以下であることがより好ましい。平均長さが上述の範囲内である繊維状炭素ナノ構造体を用いれば、複合材料の熱電変換特性と導電性とをより高いレベルで両立し得る。
　なお、繊維状炭素ナノ構造体の平均長さは、透過型電子顕微鏡を用いて無作為に選択した繊維状炭素ナノ構造体１００本の長さを測定して求めることができる。 The average length of the fibrous carbon nanostructures is preferably 0.1 μm or more, preferably 1 cm or less, and more preferably 3 mm or less. If fibrous carbon nanostructures having an average length within the above range are used, the thermoelectric conversion characteristics and conductivity of the composite material can be compatible at a higher level.
The average length of the fibrous carbon nanostructures can be determined by measuring the length of 100 randomly selected fibrous carbon nanostructures using a transmission electron microscope.
　繊維状炭素ナノ構造体は、平均直径（Ａｖ）と直径の標準偏差（σ）とが、関係式：０．２０＜（３σ／Ａｖ）＜０．８０を満たすことが好ましい。上記関係を満たす繊維状炭素ナノ構造体を用いれば、複合材料の熱電変換特性と導電性とをより高いレベルで両立し得る。
　なお、本発明において、「繊維状炭素ナノ構造体の平均直径（Ａｖ）」および「繊維状炭素ナノ構造体の直径の標準偏差（σ：標本標準偏差）」は、それぞれ、透過型電子顕微鏡を用いて無作為に選択した繊維状炭素ナノ構造体１００本の直径（外径）を測定して求めることができる。 In the fibrous carbon nanostructure, it is preferable that the average diameter (Av) and the standard deviation (σ) of the diameter satisfy the relational expression: 0.20 <(3σ / Av) <0.80. If a fibrous carbon nanostructure satisfying the above relationship is used, the thermoelectric conversion characteristics and conductivity of the composite material can be compatible at a higher level.
In the present invention, "average diameter of fibrous carbon nanostructures (Av)" and "standard deviation of diameter of fibrous carbon nanostructures (σ: sample standard deviation)" are determined by a transmission electron microscope, respectively. The diameter (outer diameter) of 100 fibrous carbon nanostructures randomly selected using the nanostructures can be measured and determined.
　そして、繊維状炭素ナノ構造体のＢＥＴ比表面積は、６００ｍ2／ｇ以上であることが好ましく、８００ｍ2／ｇ以上であることがより好ましい。ＢＥＴ比表面積が６００ｍ2／ｇ以上である繊維状炭素ナノ構造体を用いれば、複合材料の熱電変換特性と導電性とをより高いレベルで両立し得る。ここで、繊維状炭素ナノ構造体のＢＥＴ比表面積の上限は、特に限定されないが、例えば２６００ｍ2／ｇ以下である。
　なお、繊維状炭素ナノ構造体の「ＢＥＴ比表面積」は、７７Ｋにおける窒素吸着等温線を測定し、ＢＥＴ法により求めることができる。ここで、ＢＥＴ比表面積の測定には、例えば、「ＢＥＬＳＯＲＰ（登録商標）－ｍａｘ」（日本ベル（株）製）を用いることができる。 The BET specific surface area of the fibrous carbon nanostructure is preferably 600 m 2 / g or more, and more preferably 800 m 2 / g or more. By using a fibrous carbon nanostructure having a BET specific surface area of 600 m 2 / g or more, the thermoelectric conversion characteristics and conductivity of the composite material can be compatible at a higher level. Here, the upper limit of the BET specific surface area of the fibrous carbon nanostructure is not particularly limited, but is, for example, 2600 m 2 / g or less.
The "BET specific surface area" of the fibrous carbon nanostructure can be determined by the BET method by measuring the nitrogen adsorption isotherm at 77K. Here, for the measurement of the BET specific surface area, for example, "BELSORP (registered trademark) -max" (manufactured by Nippon Bell Co., Ltd.) can be used.
　本発明で用いられる繊維状炭素ナノ構造体を製造する方法としては、特に限定されることなく、二酸化炭素の接触水素還元による方法、アーク放電法、化学的気相成長法（ＣＶＤ法）、レーザー蒸発法、気相成長法、気相流動法、および、ＨｉＰＣＯ法等が挙げられる。繊維状炭素ナノ構造体としては、例えば、カーボンナノチューブ製造用の触媒層を表面に有する基材上に、原料化合物およびキャリアガスを供給して、ＣＶＤ法によりＣＮＴを合成する際に、系内に微量の酸化剤（触媒賦活物質）を存在させることで、触媒層の触媒活性を飛躍的に向上させるという方法（スーパーグロース法；国際公開第２００６／０１１６５５号参照）により得られたものを用いることができる（なお、以下では、スーパーグロース法により得られるカーボンナノチューブを「ＳＧＣＮＴ」と称することがある）。また、繊維状炭素ナノ構造体としては、例えば、気相流動法の一種であるｅＤＩＰＳ法により得られたものも用いることができる（ｅＤＩＰＳ法により得られるカーボンナノチューブは「ｅＤＩＰＳ－ＣＮＴ」とも称される）。
　後述する原料組成物中で分散し易いため、ＣＮＴとしてはＳＧＣＮＴを使用することが好ましい。 The method for producing the fibrous carbon nanostructure used in the present invention is not particularly limited, and is not particularly limited, a method by catalytic hydrogen reduction of carbon dioxide, an arc discharge method, a chemical vapor deposition method (CVD method), and a laser. Examples thereof include an evaporation method, a vapor phase growth method, a vapor phase flow method, and a HiPCO method. As the fibrous carbon nanostructure, for example, when a raw material compound and a carrier gas are supplied on a substrate having a catalyst layer for producing carbon nanotubes on the surface and CNTs are synthesized by a CVD method, the CNTs are contained in the system. Use the one obtained by the method of dramatically improving the catalytic activity of the catalyst layer by the presence of a trace amount of oxidizing agent (catalyst activator) (super growth method; see International Publication No. 2006/011655). (In the following, carbon nanotubes obtained by the super growth method may be referred to as "SGCNT"). Further, as the fibrous carbon nanostructure, for example, those obtained by the eDIPS method, which is a kind of gas phase flow method, can also be used (the carbon nanotubes obtained by the eDIPS method are also referred to as "eDIPS-CNT". ).
It is preferable to use SGCNT as the CNT because it is easily dispersed in the raw material composition described later.
　また、繊維状炭素ナノ構造体は、カルボキシル基等の官能基が導入されたものであってもよい。官能基の導入は、例えば、過酸化水素や硝酸等を用いる酸化処理法や、超臨界流体、亜臨界流体又は高温高圧流体との接触処理法などの既知の方法により行うことができる。 Further, the fibrous carbon nanostructure may have a functional group such as a carboxyl group introduced therein. The functional group can be introduced by a known method such as an oxidation treatment method using hydrogen peroxide or nitric acid, or a contact treatment method with a supercritical fluid, a subcritical fluid or a high-temperature high-pressure fluid.
＜＜繊維状炭素ナノ構造体の含有量＞＞
　本発明の複合材料において、繊維状炭素ナノ構造体の含有量は、２質量％以上であることが好ましく、５質量％以上であることがより好ましく、７質量％以上であることが更に好ましい。また、繊維状炭素ナノ構造体の含有量は、２０質量％以下であることが好ましく、１７質量％以下であることがより好ましく、１５質量％以下であることが更に好ましい。繊維状炭素ナノ構造体が上記存在割合の範囲内で複合材料中に存在すれば、熱電変換特性および導電性をより高いレベルで両立させることができる。ここで、繊維状炭素ナノ構造体の含有量は、２．７質量％以上であってもよく、４．９質量％以上であってもよく、６．７質量％以上であってもよく、また、１４．４質量％以下であってもよい。
　なお、複合材料中の繊維状炭素ナノ構造体の含有量が多くなると、複合体中に繊維状炭素ナノ構造体の粗密が形成され、繊維状炭素ナノ構造体の密度ムラが発生することがある。 << Content of fibrous carbon nanostructures >>
In the composite material of the present invention, the content of the fibrous carbon nanostructures is preferably 2% by mass or more, more preferably 5% by mass or more, and further preferably 7% by mass or more. The content of the fibrous carbon nanostructure is preferably 20% by mass or less, more preferably 17% by mass or less, and further preferably 15% by mass or less. If the fibrous carbon nanostructures are present in the composite material within the above abundance ratio, thermoelectric conversion characteristics and conductivity can be compatible at a higher level. Here, the content of the fibrous carbon nanostructure may be 2.7% by mass or more, 4.9% by mass or more, or 6.7% by mass or more. Further, it may be 14.4% by mass or less.
When the content of the fibrous carbon nanostructures in the composite material is increased, the fibrous carbon nanostructures may be densely packed in the composite material, and uneven density of the fibrous carbon nanostructures may occur. ..
＜複合材料の構造＞
　上述したとおり、本発明の複合材料はビスマステルルのナノプレート（ＢｉＴｅナノプレート）と繊維状炭素ナノ構造体とが一体化されている。ここで、「ビスマステルルのナノプレートと繊維状炭素ナノ構造体とが一体化されている」とは、ビスマステルルのナノプレートと繊維状炭素ナノ構造体とが分離しない程度に結合している状態をいう。具体的には、例えば、「ビスマステルルのナノプレートと繊維状炭素ナノ構造体とが一体化されている」とは、１つ以上の繊維状炭素ナノ構造体と１つ以上のビスマステルルのナノプレートとが絡み合って両者が結合している状態、１つ以上の繊維状炭素ナノ構造体が１つ以上のビスマステルルのナノプレートを貫いて両者が結合している状態、および、それらを組み合わせた状態などをいう。そのため、「ビスマステルルのナノプレートと繊維状炭素ナノ構造体とが一体化されている」には、例えば、ビスマステルルのナノプレートと繊維状炭素ナノ構造体を単純に混ぜ合わせることにより両者が単純に重なり合い、ファンデルワールス力などの弱い結合だけで結合しているような状態は含まれない。 <Structure of composite material>
As described above, in the composite material of the present invention, a bismuth tellurium nanoplate (BiTe nanoplate) and a fibrous carbon nanostructure are integrated. Here, "the bismuth tellurium nanoplate and the fibrous carbon nanostructure are integrated" means that the bismuth tellurium nanoplate and the fibrous carbon nanostructure are bonded to the extent that they are not separated. Say. Specifically, for example, "the nanoplate of bismuth tellurium and the fibrous carbon nanostructure are integrated" means that one or more fibrous carbon nanostructures and one or more bismuth tellurium nanostructures are integrated. A state in which the plates are entangled and bonded to each other, a state in which one or more fibrous carbon nanostructures penetrate one or more bismuth tellurium nanoplates and are bonded to each other, and a combination thereof. It refers to the state. Therefore, in "the bismuth tellurium nanoplate and the fibrous carbon nanostructure are integrated", for example, both are simply mixed by simply mixing the bismuth tellurium nanoplate and the fibrous carbon nanostructure. It does not include the state where it overlaps with and is connected only by a weak bond such as van der Waals force.
　以下、図１～４を参照して、本発明の複合材料中のＢｉＴｅナノプレートと繊維状炭素ナノ構造体とが一体化されている構造と、両者が一体化されていない構造とについて具体的に説明する。図１～３は、本発明の複合材料を用いて形成した塗布膜（シート）の表面の走査型電子顕微鏡（ＳＥＭ）写真である。図４は、ＢｉＴｅナノプレートと維状炭素ナノ構造体としてのＣＮＴとの混合物から作製したシートの走査型電子顕微鏡（ＳＥＭ）写真である。
　本発明の複合材料では、図１～３に示すように、ＢｉＴｅナノプレートと繊維状炭素ナノ構造体としてのＣＮＴとが互いに絡み合った構造や、ＣＮＴがＢｉＴｅナノプレートを厚み方向に貫いたような構造が観察される。このように、本発明の複合材料ではＢｉＴｅナノプレートと繊維状炭素ナノ構造体とが一体化されている。これに対して、ＢｉＴｅナノプレートと繊維状炭素ナノ構造体とが一体化されていない構造では、図４に示すように、ＢｉＴｅナノプレートと繊維状炭素ナノ構造体が単に重なり合っているだけであり、ＢｉＴｅナノプレートと繊維状炭素ナノ構造体とが互いに絡み合った構造や、繊維状炭素ナノ構造体がＢｉＴｅナノプレートを厚み方向に貫いたような構造は有さない。 Hereinafter, with reference to FIGS. 1 to 4, the structure in which the BiTe nanoplate and the fibrous carbon nanostructure in the composite material of the present invention are integrated and the structure in which both are not integrated are concretely described. Explain to. 1 to 3 are scanning electron microscope (SEM) photographs of the surface of a coating film (sheet) formed using the composite material of the present invention. FIG. 4 is a scanning electron microscope (SEM) photograph of a sheet made from a mixture of BiTe nanoplates and CNTs as fissure carbon nanostructures.
In the composite material of the present invention, as shown in FIGS. 1 to 3, a structure in which the BiTe nanoplate and the CNT as a fibrous carbon nanostructure are entangled with each other, or the CNT penetrates the BiTe nanoplate in the thickness direction. The structure is observed. As described above, in the composite material of the present invention, the BiTe nanoplate and the fibrous carbon nanostructure are integrated. On the other hand, in the structure in which the BiTe nanoplate and the fibrous carbon nanostructure are not integrated, as shown in FIG. 4, the BiTe nanoplate and the fibrous carbon nanostructure simply overlap each other. , There is no structure in which the BiTe nanoplate and the fibrous carbon nanostructure are entangled with each other, or a structure in which the fibrous carbon nanostructure penetrates the BiTe nanoplate in the thickness direction.
　上述のようにＢｉＴｅナノプレートと繊維状炭素ナノ構造体とが一体化される理由は必ずしも明確ではないが、以下のとおりと推察される。すなわち、後述するように、ソルボサーマル処理によるＢｉＴｅナノプレートの合成時に繊維状炭素ナノ構造体が存在しているため、繊維状炭素ナノ構造体の外表面上にビスマステルルが析出し、繊維状炭素ナノ構造体を核としてＢｉＴｅナノプレートが形成されるからであると推察される。 The reason why the BiTe nanoplate and the fibrous carbon nanostructure are integrated as described above is not always clear, but it is presumed to be as follows. That is, as will be described later, since the fibrous carbon nanostructures are present during the synthesis of the BiTe nanoplates by the sorbothermal treatment, bismastellu is precipitated on the outer surface of the fibrous carbon nanostructures, and the fibrous carbon is formed. It is presumed that this is because the BiTe nanoplate is formed with the nanostructure as the core.
　また、ＢｉＴｅナノプレートと繊維状炭素ナノ構造体とが一体化されることにより熱電変換特性と導電性とを高いレベルで両立させることができる理由は必ずしも明確ではないが、以下のとおりであると推察される。すなわち、単純にＢｉＴｅナノプレートと繊維状炭素ナノ構造体を混合した場合、個々の繊維状炭素ナノ構造体の間に電気伝導率が低いＢｉＴｅナノプレートが入り込み、繊維状炭素ナノ構造体間での電子の移動が妨げられ、導電性が低下すると推察される。同様に、個々のＢｉＴｅナノプレートの間に繊維状炭素ナノ構造体が入り込み、ＢｉＴｅナノプレート同士が離間する結果、キャリア（電子）の移動が妨げられ、熱起電力が低下すると推察される。これに対して、ＢｉＴｅナノプレートと繊維状炭素ナノ構造体とが一体化している場合、電子（キャリア）の移動が妨げられないため、熱電変換特性と導電性とを高いレベルで両立できると推察される。 Further, the reason why the thermoelectric conversion characteristics and the conductivity can be achieved at a high level by integrating the BiTe nanoplate and the fibrous carbon nanostructure is not always clear, but it is as follows. Inferred. That is, when the BiTe nanoplates and the fibrous carbon nanostructures are simply mixed, the BiTe nanoplates having low electrical conductivity enter between the individual fibrous carbon nanostructures, and the fibrous carbon nanostructures are interleaved with each other. It is presumed that the movement of electrons is hindered and the conductivity decreases. Similarly, it is presumed that the fibrous carbon nanostructures are inserted between the individual BiTe nanoplates and the BiTe nanoplates are separated from each other, so that the movement of carriers (electrons) is hindered and the thermoelectromotive force is reduced. On the other hand, when the BiTe nanoplate and the fibrous carbon nanostructure are integrated, the movement of electrons (carriers) is not hindered, so it is presumed that thermoelectric conversion characteristics and conductivity can be compatible at a high level. Will be done.
　本発明の複合材料においては、ＢｉＴｅナノプレートおよび繊維状炭素ナノ構造体の全てが一体化していることが好ましいが、本発明の効果を損なわない範囲で、一体化していないＢｉＴｅナノプレートおよび／または繊維状炭素ナノ構造体が複合材料中に含まれていてもよい。
　そして、本発明の複合材料は、超音波法、超音波ホモジナイザー法、ジェットミル法、またはビーズミル法など、ＣＮＴを溶媒に分散する際に用いる一般的な分散方法で溶媒中に分散させた場合でも、ＢｉＴｅナノプレートと繊維状炭素ナノ構造体とが一体化した構造が残ることが好ましい。 In the composite material of the present invention, it is preferable that all of the BiTe nanoplates and the fibrous carbon nanostructures are integrated, but to the extent that the effects of the present invention are not impaired, the unintegrated BiTe nanoplates and / or Fibrous carbon nanostructures may be included in the composite.
The composite material of the present invention can be dispersed in a solvent by a general dispersion method used when dispersing CNTs in a solvent, such as an ultrasonic method, an ultrasonic homogenizer method, a jet mill method, or a bead mill method. , It is preferable that the structure in which the BiTe nanoplate and the fibrous carbon nanostructure are integrated remains.
（複合材料の製造方法）
　本発明の複合材料の製造方法は、ビスマス源と、テルル源と、繊維状炭素ナノ構造体と、溶媒とを含み、任意にその他の成分を更に含む原料組成物を準備する工程（以下、「準備工程」という）と；前記原料組成物をソルボサーマル処理に供して、ＢｉＴｅナノプレートと繊維状炭素ナノ構造体とが一体化してなる複合材料を形成する工程（以下、「形成工程」という）と、を少なくとも含む。上述の準備工程および形成工程を少なくとも含む本発明の製造方法によれば、ＢｉＴｅナノプレートと繊維状炭素ナノ構造体とを容易に一体化させ、熱電変換特性と導電性とを高いレベルで両立させることができる複合材料を得ることができる。なお、本発明の複合材料の製造方法は、準備工程および形成工程以外の工程（以下、「その他の工程」と称する）を任意に含んでもよい。以下、各工程について説明する。 (Manufacturing method of composite material)
The method for producing a composite material of the present invention is a step of preparing a raw material composition containing a bismuth source, a tellurium source, a fibrous carbon nanostructure, and a solvent, and optionally further containing other components (hereinafter, """Preparationstep")and; A step of subjecting the raw material composition to a sorbothermal treatment to form a composite material in which BiTe nanoplates and fibrous carbon nanostructures are integrated (hereinafter referred to as "formation step"). And at least include. According to the production method of the present invention including at least the above-mentioned preparation step and formation step, the BiTe nanoplate and the fibrous carbon nanostructure are easily integrated to achieve both thermoelectric conversion characteristics and conductivity at a high level. It is possible to obtain a composite material that can be obtained. The method for producing the composite material of the present invention may optionally include steps other than the preparation step and the forming step (hereinafter, referred to as "other steps"). Hereinafter, each step will be described.
＜準備工程＞
　準備工程は、ビスマス源と、テルル源と、繊維状炭素ナノ構造体と、溶媒とを含む原料組成物を準備する工程であり、原料組成物を最終的に準備できれば特に限定されず、調製済みの原料組成物を購入してきてもよいし、上述した成分を混合して原料組成物を調製してもよい。例えば、所定の量のビスマス源、テルル源、繊維状炭素ナノ構造体、溶媒、および任意の添加剤などを含む混合液に、任意の分散処理を施すことにより、原料組成物を準備することができる。このような分散処理としては、例えば、国際公開第２０１６／１０３７０６号に記載された、キャビテーション効果が得られる分散処理または解砕効果が得られる分散処理が挙げられる。
　あるいは、所定量のビスマス源、テルル源、溶媒、および任意の添加剤を含む混合液（前駆体溶液）を調製し、この前駆体溶液に、所定の濃度の繊維状炭素ナノ構造体分散液を所定量混合して、原料組成物（分散液）を準備してもよい。繊維状炭素ナノ構造体分散液は、所定の濃度になるように繊維状炭素ナノ構造体を溶媒に混合し、任意の分散処理を施すことで得ることができる。
　繊維状炭素ナノ構造体分散液中の繊維状炭素ナノ構造体の濃度は、一般的に、０．０２質量％以上、好ましくは０．１質量％以上であり、一般的に１．０質量％以下、好ましくは０．５質量％以下である。２．０質量％を超えると、繊維状炭素ナノ構造体が凝集し、合成されるＢｉＴｅナノプレートと一体化し難くなる虞がある。
　また、原料組成物中の繊維状炭素ナノ構造体の含有量は、原料組成物の溶媒に対して０．０３質量％以上０．１２質量％以下であることが好ましく、０．０５質量％以上０．０９質量％以下であることがより好ましい。繊維状炭素ナノ構造体の溶媒に対する含有量が上記範囲内であれば、繊維状炭素ナノ構造体を良好に分散させることができる。 <Preparation process>
The preparation step is a step of preparing a raw material composition containing a bismuth source, a tellurium source, a fibrous carbon nanostructure, and a solvent, and is not particularly limited as long as the raw material composition can be finally prepared. The raw material composition may be purchased, or the above-mentioned components may be mixed to prepare a raw material composition. For example, a raw material composition can be prepared by subjecting a mixed solution containing a predetermined amount of a bismuth source, a tellurium source, a fibrous carbon nanostructure, a solvent, an arbitrary additive, and the like to an arbitrary dispersion treatment. it can. Examples of such a dispersion treatment include the dispersion treatment for obtaining a cavitation effect or the dispersion treatment for obtaining a crushing effect described in International Publication No. 2016/103706.
Alternatively, a mixture (precursor solution) containing a predetermined amount of a bismuth source, a tellurium source, a solvent, and an arbitrary additive is prepared, and a fibrous carbon nanostructure dispersion having a predetermined concentration is added to the precursor solution. A raw material composition (dispersion liquid) may be prepared by mixing a predetermined amount. The fibrous carbon nanostructure dispersion liquid can be obtained by mixing the fibrous carbon nanostructures with a solvent so as to have a predetermined concentration and subjecting them to an arbitrary dispersion treatment.
The concentration of the fibrous carbon nanostructures in the fibrous carbon nanostructure dispersion is generally 0.02% by mass or more, preferably 0.1% by mass or more, and generally 1.0% by mass. Hereinafter, it is preferably 0.5% by mass or less. If it exceeds 2.0% by mass, the fibrous carbon nanostructures may aggregate and become difficult to integrate with the synthesized BiTe nanoplate.
The content of the fibrous carbon nanostructures in the raw material composition is preferably 0.03% by mass or more and 0.12% by mass or less, and 0.05% by mass or more, based on the solvent of the raw material composition. More preferably, it is 0.09% by mass or less. When the content of the fibrous carbon nanostructures with respect to the solvent is within the above range, the fibrous carbon nanostructures can be satisfactorily dispersed.
＜＜ビスマス源＞＞
　上記ビスマス源の化合物としては、テルル源の化合物と反応してＢｉＴｅナノプレートを合成することができるものであれば特に限定されず、酸化ビスマス、塩化ビスマス、フッ化ビスマス、水酸化ビスマス、硝酸ビスマス、酢酸ビスマス、これらの水和物などが挙げられる。
　前駆体溶液中のビスマス源の化合物の濃度は、特に限定されないが、一般的に０．００５ｍｏｌ／Ｌ以上、好ましくは０．０１ｍｏｌ／Ｌ以上であり、また、一般的に０．１ｍｏｌ／Ｌ以下、好ましくは０．０５ｍｏｌ／Ｌ以下である。 << Bismuth source >>
The compound of the bismuth source is not particularly limited as long as it can react with the compound of the tellurium source to synthesize a BiTe nanoplate, and bismuth oxide, bismuth chloride, bismuth fluoride, bismuth hydroxide, and bismuth nitrate. , Bismuth acetate, hydrates thereof and the like.
The concentration of the bismuth source compound in the precursor solution is not particularly limited, but is generally 0.005 mol / L or more, preferably 0.01 mol / L or more, and generally 0.1 mol / L or less. , Preferably 0.05 mol / L or less.
＜＜テルル源＞＞
　上記テルル源の化合物としては、ビスマス源の化合物と反応してＢｉＴｅナノプレートを合成することができるものであれば特に限定されず、酸化テルル、塩化テルル、フッ化テルル、水酸化テルル、硝酸テルル、酢酸テルル、これらの水和物などが挙げられる。
　前駆体溶液中のテルル源の化合物の濃度は、特に限定されないが、一般的に０．０１ｍｏｌ／Ｌ以上、好ましくは０．０５ｍｏｌ／Ｌ以上であり、また、一般的に０．１５ｍｏｌ／Ｌ以下、好ましくは０．０９ｍｏｌ／Ｌ以下である。 << Tellurium Source >>
The tellurium source compound is not particularly limited as long as it can react with a bismuth source compound to synthesize a BiTe nanoplate, and tellurium oxide, tellurium chloride, tellurium fluoride, tellurium hydroxide, and tellurium nitrate are not particularly limited. , Tellurium acetate, hydrates thereof and the like.
The concentration of the tellurium source compound in the precursor solution is not particularly limited, but is generally 0.01 mol / L or more, preferably 0.05 mol / L or more, and generally 0.15 mol / L or less. It is preferably 0.09 mol / L or less.
＜＜その他の成分＞＞
　その他の成分は、限定されないが、例えば、ビスマス源やテルル源の溶媒への溶解を助け、結晶成長を制御するための添加剤が挙げられる。添加剤としては、特に限定されないが、例えば、ポリビニルピロリドンを添加することができる。
　前駆体溶液中の添加剤の濃度は、特に限定されないが、溶媒に対して、一般的に０．５質量％以上、好ましくは１．０質量％以上であり、また、一般的に５．０質量％以下、好ましくは３．０質量％以下である。 << Other ingredients >>
Other components include, but are not limited to, additives that help dissolve bismuth and tellurium sources in solvents and control crystal growth. The additive is not particularly limited, but for example, polyvinylpyrrolidone can be added.
The concentration of the additive in the precursor solution is not particularly limited, but is generally 0.5% by mass or more, preferably 1.0% by mass or more, and generally 5.0% by mass or more with respect to the solvent. It is mass% or less, preferably 3.0 mass% or less.
＜＜溶媒＞＞
　原料組成物に含まれる溶媒は、特に限定されず、水および有機溶媒の何れも用いることができる。なお、溶媒は、１種を単独で使用してもよく、２種以上を組み合わせて使用してもよい。 << Solvent >>
The solvent contained in the raw material composition is not particularly limited, and either water or an organic solvent can be used. As the solvent, one type may be used alone, or two or more types may be used in combination.
　有機溶媒としては、特に限定されず、メタノール、エタノール、エチレングリコール等のアルコール類；トルエン、キシレン、エチルベンゼン、アニソール、トリメチルベンゼン、ｐ－フルオロフェノール、ｐ－クロロフェノール、ｏ－クロロフェノール、およびパープルオロフェノール等の芳香族溶媒；テトラヒドロフラン、ジオキサン、シクロペンチルモノメチルエーテル、エチレングリコールモノエチルエーテル、エチレングリコールモノメチルエーテルアセテート、エチレングリコールモノエチルエーテルアセテート、プロピレングリコールモノメチルエーテルアセテート、ジエチレングリコールモノブチルエーテルアセテート、ジエチレングリコールモノエチルエーテルアセテート、および酢酸－３－メトキシブチル等のエーテル類；アセトン、シクロヘキサノン、メチルイソブチルケトン、メチルエチルケトン、およびジイソブチルケトン等のケトン類；Ｎ，Ｎ－ジメチルホルムアミド、Ｎ，Ｎ－ジメチルアセトアミド、Ｎ，Ｎ－ジエチルホルムアミド、２－ピロリドン、Ｎ－メチル－２－ピロリドン、１,３－ジメチル－２－イミダゾリジノン、Ｎ，Ｎ，Ｎ，Ｎ－テトラメチル尿素、Ｎ－メチル－ε－カプロラクタム、およびヘキサメチルリン酸トリアミド等の含窒素極性有機溶媒；酢酸エチル、酢酸メチル、酢酸－ｎ－プロピル、酢酸イソプロピル、酢酸－ｎ－ブチル、酢酸－ｎ－ペンチル、乳酸メチル、乳酸エチル、乳酸－ｎ－ブチル、γ－ブチロラクトン、およびγ－バレロラクトン等のエステル類；ジメチルスルホキシドが挙げられる。 The organic solvent is not particularly limited, and alcohols such as methanol, ethanol and ethylene glycol; toluene, xylene, ethylbenzene, anisole, trimethylbenzene, p-fluorophenol, p-chlorophenol, o-chlorophenol, and purple olo. Aromatic solvents such as phenol; tetrahydrofuran, dioxane, cyclopentyl monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate , And ethers such as 3-methoxybutyl acetate; ketones such as acetone, cyclohexanone, methylisobutylketone, methylethylketone, and diisobutylketone; N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethyl Formamide, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N, N, N, N-tetramethylurea, N-methyl-ε-caprolactam, and hexamethylline. Nitrogen-containing polar organic solvents such as acid triamide; ethyl acetate, methyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, n-pentyl acetate, methyl lactate, ethyl lactate, n-butyl lactate, γ -Ethers such as butyrolactone and γ-valerolactone; dimethylsulfoxide can be mentioned.
　そして、溶媒としては、繊維状炭素ナノ構造体の分散性を向上させる観点からは、水が好ましい。 As the solvent, water is preferable from the viewpoint of improving the dispersibility of the fibrous carbon nanostructures.
＜形成工程＞
　形成工程は、上記準備工程で作製した原料組成物をソルボサーマル処理に供して、ＢｉＴｅナノプレートと繊維状炭素ナノ構造体とが一体化されてなる複合材料を得る工程である。
　ここで、ソルボサーマル処理とは、溶媒中、高圧下で原料材料を当該溶媒の沸点よりも高い温度で反応させて、反応生成物の結晶を得る処理をいう。ソルボサーマル処理により、上記原料組成物に含まれるビスマス源およびテルル源が反応して、ＢｉＴｅナノプレートが合成される。
　ソルボサーマル処理の手段は特に限定されず、オートクレーブなどの当該技術分野でソルボサーマル反応に使用されている任意の装置を使用することができる。具体的には、ソルボサーマル処理は、例えば、繊維状炭素ナノ構造体が分散した上記原料組成物（分散液）をオートクレーブなどの耐圧容器内に密封し、結晶化を阻害しない圧力下、攪拌しながらまたは静置させた状態で、所定温度に加熱することにより行われる。加熱はホットスターラーなどの任意の加熱装置を使用して行うことができる。 <Formation process>
The forming step is a step of subjecting the raw material composition produced in the above preparatory step to a sorbothermal treatment to obtain a composite material in which the BiTe nanoplate and the fibrous carbon nanostructure are integrated.
Here, the solvothermal treatment refers to a treatment in which a raw material is reacted in a solvent under high pressure at a temperature higher than the boiling point of the solvent to obtain crystals of the reaction product. By the solvothermal treatment, the bismuth source and the tellurium source contained in the raw material composition react with each other to synthesize a BiTe nanoplate.
The means of the solvothermal treatment is not particularly limited, and any device used for the solvothermal reaction in the technical field such as an autoclave can be used. Specifically, in the solvothermal treatment, for example, the raw material composition (dispersion liquid) in which the fibrous carbon nanostructures are dispersed is sealed in a pressure-resistant container such as an autoclave, and stirred under a pressure that does not inhibit crystallization. This is done by heating to a predetermined temperature while or in a stationary state. Heating can be performed using any heating device such as a hot stirrer.
　ソルボサーマル処理は塩基の存在下で行うことが好ましい。塩基としては、限定されないが、水酸化カリウム、水酸化ナトリウムなどの無機化合物を使用することができる。 Solvothermal treatment is preferably performed in the presence of a base. The base is not limited, but an inorganic compound such as potassium hydroxide or sodium hydroxide can be used.
　ソルボサーマル処理の際の加熱温度は、使用する溶媒の沸点よりも高い必要があり、一般的に１６０℃以上、好ましくは１８０℃以上であり、また、一般的に２４０℃以下、好ましくは２２０℃以下である。
　また、加熱時間は一般的に２０分間以上、好ましくは３０分間以上であり、また、一般的に２０時間以下、好ましくは８時間以下である。なお、加熱温度は反応中一定でもよいし、段階的又は連続的に変化させてもよい。
　なお、ソルボサーマル処理の際の圧力は、加熱温度に依存し、加熱温度を規定することにより決まる。 The heating temperature during the solvothermal treatment needs to be higher than the boiling point of the solvent used, and is generally 160 ° C. or higher, preferably 180 ° C. or higher, and generally 240 ° C. or lower, preferably 220 ° C. It is as follows.
The heating time is generally 20 minutes or more, preferably 30 minutes or more, and generally 20 hours or less, preferably 8 hours or less. The heating temperature may be constant during the reaction, or may be changed stepwise or continuously.
The pressure during the solvothermal treatment depends on the heating temperature and is determined by defining the heating temperature.
＜その他の工程＞
　本発明の複合材料の製造方法が任意に含み得るその他の工程としては、特に限定されない。本発明の複合材料の製造方法は、例えば、上記形成工程の後に後処理を行う工程（後処理工程）を含むことができる。 <Other processes>
The other steps that the method for producing the composite material of the present invention can optionally include are not particularly limited. The method for producing a composite material of the present invention can include, for example, a step of performing post-treatment after the above-mentioned forming step (post-treatment step).
＜＜後処理工程＞＞
　上述した形成工程において、複合材料（ＢｉＴｅナノプレートと繊維状炭素ナノ構造体とが一体化してなる構造体）が、溶媒中に分散した状態で得られる。この分散液から複合材料を回収することができる（回収工程）。回収方法としては、遠心分離法などの既知の回収方法が挙げられる。
　また、上述した形成工程または回収工程の後に、複合材料を乾燥することができる（乾燥工程）。乾燥方法としては、例えば、真空乾燥などの既知の乾燥方法が挙げられる。
　さらに、上述した乾燥工程後に、得られた複合材料の粉末を用いて薄膜化（シート化）することができる（薄膜化工程）。薄膜の作製は、例えば、印刷法（ドロップキャスト法）を使用することができる。ドロップキャスト法は、その容易なスケーラビリティ、高い堆積速度、および真空条件の必要がないため、他の成膜方法と比較してコスト効率と簡易さに優れた方法である。具体的には、まず、得られた複合材料の粉末を所定の濃度でエタノールなどの溶媒に混合し、超音波洗浄器などで分散させる。次いで、得られた分散液をスポイトなどの任意の滴下手段で基板上に滴下して、塗布膜を得る。そして、得られた塗布膜を任意に乾燥させ、複合材料のシートを得ることができる。 << Post-treatment process >>
In the above-mentioned forming step, a composite material (a structure in which a BiTe nanoplate and a fibrous carbon nanostructure are integrated) is obtained in a state of being dispersed in a solvent. The composite material can be recovered from this dispersion (recovery step). Examples of the recovery method include known recovery methods such as a centrifugation method.
In addition, the composite material can be dried after the formation step or recovery step described above (drying step). Examples of the drying method include known drying methods such as vacuum drying.
Further, after the above-mentioned drying step, the obtained composite material powder can be used for thinning (sheeting) (thinning step). For the production of the thin film, for example, a printing method (drop casting method) can be used. The drop casting method is more cost effective and simpler than other film forming methods because it does not require its easy scalability, high deposition rate, and vacuum conditions. Specifically, first, the powder of the obtained composite material is mixed with a solvent such as ethanol at a predetermined concentration and dispersed by an ultrasonic cleaner or the like. Next, the obtained dispersion liquid is dropped onto the substrate by any dropping means such as a dropper to obtain a coating film. Then, the obtained coating film can be arbitrarily dried to obtain a sheet of composite material.
（熱電変換材料）
　本発明の熱電変換材料は、上述した本発明の複合材料を含む。本発明の熱電変換材料は、本発明の複合材料のみからなってもよいが、他の熱電変換材料を含んでもよい。他の熱電変換材料としては、特に限定されないが、セレン系化合物；ビスマステルル系化合物；アンチモン系化合物；シリコン系化合物；金属酸化物系化合物；ホイスラー合金系化合物；ポリチオフェン系化合物、ポリアセチレン系化合物、ポリアニリン系化合物、ポリピロール系化合物等の導電性高分子化合物；カーボンナノチューブ等の繊維状炭素ナノ構造体；これらの複合材料等を用いることができる。
　本発明の熱電変換材料は、熱電変換特性と導電率に優れるため、熱電変換素子の材料として好適に使用することができる。具体的には、本発明の熱電変換材料は、熱電変換素子のｎ型の熱電変換材料層を形成するために好適に使用することができる。 (Thermoelectric conversion material)
The thermoelectric conversion material of the present invention includes the composite material of the present invention described above. The thermoelectric conversion material of the present invention may consist only of the composite material of the present invention, but may include other thermoelectric conversion materials. Other thermoelectric conversion materials are not particularly limited, but are selenium-based compounds; bismastellu-based compounds; antimony-based compounds; silicon-based compounds; metal oxide-based compounds; Whistler alloy-based compounds; polythiophene-based compounds, polyacetylene-based compounds, and polyaniline. Conductive polymer compounds such as system compounds and polypyrrole compounds; fibrous carbon nanostructures such as carbon nanotubes; and composite materials thereof can be used.
Since the thermoelectric conversion material of the present invention is excellent in thermoelectric conversion characteristics and conductivity, it can be suitably used as a material for a thermoelectric conversion element. Specifically, the thermoelectric conversion material of the present invention can be suitably used for forming an n-type thermoelectric conversion material layer of a thermoelectric conversion element.
（熱電変換素子）
　熱電変換素子は、上述した本発明の複合材料を含むことを特徴とする。熱電変換素子の構造は、特に限定されないが、熱電変換素子は、本発明の複合材料をｎ型の熱電変換材料層として備えることができる。また、熱電変換素子は、ｐ型の熱電変換材料層を備えることができる。各熱電変換材料層の厚さは適宜決定すればよい。
　ｐ型の熱電変換材料層の熱電変換材料としては、例えば、セレン系化合物；ビスマステルル系化合物；アンチモン系化合物；シリコン系化合物；金属酸化物系化合物；ホイスラー合金系化合物；ポリチオフェン系化合物、ポリアセチレン系化合物、ポリアニリン系化合物、ポリピロール系化合物等の導電性高分子化合物；カーボンナノチューブ等の繊維状炭素ナノ構造体；これらの複合材料等を用いることができる。
　熱電変換素子は、例えば、基材上の熱電変換材料層に二つの電極を取り付けることで作製することができる。電極は特に限定されず、例えば特開２０１４－１９９８３７号公報に記載のものを用いることができる。また、熱電変換材料層と二つの電極の位置関係は、特に限定されない。例えば、熱電変換材料層の両端に電極が配置されていてもよいし、熱電変換材料層が二つの電極で挟まれていてもよい。 (Thermoelectric conversion element)
The thermoelectric conversion element is characterized by containing the composite material of the present invention described above. The structure of the thermoelectric conversion element is not particularly limited, but the thermoelectric conversion element can include the composite material of the present invention as an n-type thermoelectric conversion material layer. Further, the thermoelectric conversion element can include a p-type thermoelectric conversion material layer. The thickness of each thermoelectric conversion material layer may be appropriately determined.
Examples of the thermoelectric conversion material of the p-type thermoelectric conversion material layer include selenium-based compounds; bismastellu-based compounds; antimony-based compounds; silicon-based compounds; metal oxide-based compounds; Whistler alloy-based compounds; polythiophene-based compounds and polyacetylene-based compounds. Conductive polymer compounds such as compounds, polyaniline compounds, and polypyrrole compounds; fibrous carbon nanostructures such as carbon nanotubes; and composite materials thereof can be used.
The thermoelectric conversion element can be manufactured, for example, by attaching two electrodes to the thermoelectric conversion material layer on the base material. The electrode is not particularly limited, and for example, those described in JP-A-2014-199837 can be used. Further, the positional relationship between the thermoelectric conversion material layer and the two electrodes is not particularly limited. For example, electrodes may be arranged at both ends of the thermoelectric conversion material layer, or the thermoelectric conversion material layer may be sandwiched between two electrodes.
　以下、本発明について実施例に基づき具体的に説明するが、本発明はこれら実施例に限定されるものではない。なお、評価および測定には以下の方法を採用した。
＜ゼーベック係数、および導電率＞
　熱電特性評価装置（アドバンス理工社製、「ＺＥＭ－３」）と同様の構成の熱電特性評価装置を作製し、大気中、室温付近（２０℃～４０℃の温度）で１～５℃程度の温度差をつけた時の、複合材料シートのゼーベック係数Ｓ（μＶ・Ｋ－１）および導電率σ（Ｓ・ｃｍ－１）を測定した。 Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. The following methods were adopted for evaluation and measurement.
<Seebeck coefficient and conductivity>
A thermoelectric characteristic evaluation device having the same configuration as the thermoelectric characteristic evaluation device (manufactured by Advance Riko Co., Ltd., "ZEM-3") was manufactured, and the temperature was about 1 to 5 ° C in the atmosphere near room temperature (temperature of 20 ° C to 40 ° C). The Seebeck coefficient S (μV · K -1 ) and conductivity σ (S · cm -1 ) of the composite material sheet when the temperature difference was added were measured.
＜ＣＮＴ比率の測定＞
　複合材料中のＣＮＴ比率は、電子プローブマイクロアナライザー（ＥＰＭＡ）（島津社製ＥＰＭＡ－１６１０）を用いて、ＡＩ定性分析（点分析）により求めた。 <Measurement of CNT ratio>
The CNT ratio in the composite material was determined by AI qualitative analysis (point analysis) using an electron probe microanalyzer (EPMA) (EPMA-1610 manufactured by Shimadzu Corporation).
（実施例１）
＜ＣＮＴ分散液の調製＞
　国際公開第２００６／０１１６５５号の記載に従い、スーパーグロース法により、ＣＮＴ（ＳＧＣＮＴ、単層ＣＮＴの割合：９０％、平均直径：３．５ｎｍ、平均長さ：３５０μｍ、ＢＥＴ比表面積：１２００ｍ２／ｇ）を調製した。得られたＣＮＴをエタノール中に超音波ホモジナイザー（ブランソン社製、「Ｍｏｄｅｌ　２５０　ＤＡ」）を用いて出力５０％で１５分間分散し、ＣＮＴの０．２質量％エタノール分散液を調製した。
＜前駆体溶液の調製＞
　添加剤としてのポリビニルピロリドン０．４ｇを１８ｍＬのエチレングリコールに溶解した。次いで、ビスマス源としてのＢｉ２Ｏ３、テルル源としてのＴｅＯ２、および２ｍＬの水酸化ナトリウム水溶液を、終濃度がそれぞれ０．２ｍｏｌ／Ｌ、０．７ｍｏｌ／Ｌ、および５．０ｍｏｌ／Ｌとなるように、得られた溶液に添加し、ＢｉＴｅナノプレートの前駆体溶液を調製した。
＜ソルボサーマル処理＞
　次に、上記前駆体溶液に上記ＣＮＴの０．２質量％エタノール分散液１．０ｍＬを加え、混合した。得られた原料組成物（分散液）をテフロン（登録商標）製容器に入れ、これをオートクレープ容器に入れた。該分散液を、撹拌子を用いて５００ｒｐｍで撹拌しながら、２００℃で２４時間ホットスターラーを用いて加熱した。合成反応後、オートクレーブ容器を取り出し、冷却後、中身を試験管に移した。これを遠心分離器にセットし、１５０００ｒｐｍで遠心させて、水溶液と沈殿物に分けた。次いで、沈殿物のみを受け皿に取り出し、真空乾燥機（ヤマト科学株式会社製、「Ｖａｃｕｕｍ Ｏｖｅｎ ＡＤＰ－２１」）を用いて温度６０℃で２４時間乾燥させた。
＜シートの作製＞
　得られた複合材料の粉末を０．０１ｍｏｌ／Ｌの濃度でエタノールに混合し、超音波洗浄機で分散させた。次いで、得られた分散液を基板としてのポリイミド製シート上に塗布して成膜した（ドロップキャスト法）。そして、得られた塗膜を、真空乾燥機（ヤマト科学社製、「Ｖａｃｕｕｍ　Ｏｖｅｎ　ＡＤＰ－２１」）を用い、６０℃で２４時間乾燥させて複合材料のシートを得た。
　得られた複合材料のシートを走査型電子顕微鏡で観察し、ＢｉＴｅナノプレートとＣＮＴとが一体化していることを確認した。また、複合材料のシートにおけるＣＮＴ比率をＥＰＭＡで測定した。さらに、複合材料のシートの導電率およびゼーベック係数を測定した。結果を表１に示す。 (Example 1)
<Preparation of CNT dispersion liquid>
According to the description of International Publication No. 2006/011655, by the super growth method, CNT (SGCNT, single-walled CNT ratio: 90%, average diameter: 3.5 nm, average length: 350 μm, BET specific surface area: 1200 m 2 / g ) Was prepared. The obtained CNTs were dispersed in ethanol using an ultrasonic homogenizer (manufactured by Branson, "Model 250 DA") at an output of 50% for 15 minutes to prepare a 0.2 mass% ethanol dispersion of CNTs.
<Preparation of precursor solution>
0.4 g of polyvinylpyrrolidone as an additive was dissolved in 18 mL of ethylene glycol. Next, Bi 2 O 3 as a bismuth source , TeO 2 as a tellurium source, and 2 mL of sodium hydroxide aqueous solution were added to the final concentrations of 0.2 mol / L, 0.7 mol / L, and 5.0 mol / L, respectively. So, it was added to the obtained solution to prepare a precursor solution of BiTe nanoplate.
<Solvothermal treatment>
Next, 1.0 mL of the 0.2 mass% ethanol dispersion of CNT was added to the precursor solution and mixed. The obtained raw material composition (dispersion liquid) was placed in a Teflon (registered trademark) container, which was placed in an autoclave container. The dispersion was heated at 200 ° C. for 24 hours using a hot stirrer while stirring at 500 rpm with a stirrer. After the synthesis reaction, the autoclave container was taken out, cooled, and the contents were transferred to a test tube. This was set in a centrifuge and centrifuged at 15,000 rpm to separate an aqueous solution and a precipitate. Next, only the precipitate was taken out into a saucer and dried at a temperature of 60 ° C. for 24 hours using a vacuum dryer (“Vacuum Oven ADP-21” manufactured by Yamato Scientific Co., Ltd.).
<Making a sheet>
The obtained composite powder was mixed with ethanol at a concentration of 0.01 mol / L and dispersed by an ultrasonic cleaner. Next, the obtained dispersion liquid was applied onto a polyimide sheet as a substrate to form a film (drop casting method). Then, the obtained coating film was dried at 60 ° C. for 24 hours using a vacuum dryer (“Vacuum Oven ADP-21” manufactured by Yamato Scientific Co., Ltd.) to obtain a sheet of composite material.
The obtained sheet of the composite material was observed with a scanning electron microscope, and it was confirmed that the BiTe nanoplate and the CNT were integrated. Moreover, the CNT ratio in the sheet of the composite material was measured by EPMA. In addition, the conductivity and Seebeck coefficient of the composite sheet were measured. The results are shown in Table 1.
（実施例２～６）
　ＣＮＴの０．２質量％エタノール分散液の添加量をそれぞれ３．０ｍＬ、６．０ｍＬ、９．０ｍＬ、１２．０ｍＬ、１５．０ｍＬに変更した以外は実施例１と同様にして複合材料のシートを得た。
　得られた複合材料シートを走査型電子顕微鏡で観察し、ＢｉＴｅナノプレートとＣＮＴとが一体化していることを確認した。また、複合材料シートにおけるＣＮＴ含有量を実施例１と同様にして測定した。さらに、複合材料シートの導電率およびゼーベック係数を測定した。結果を表１に示す。 (Examples 2 to 6)
Sheet of composite material in the same manner as in Example 1 except that the amount of 0.2% by mass ethanol dispersion of CNT added was changed to 3.0 mL, 6.0 mL, 9.0 mL, 12.0 mL, and 15.0 mL, respectively. Got
The obtained composite material sheet was observed with a scanning electron microscope, and it was confirmed that the BiTe nanoplate and the CNT were integrated. Moreover, the CNT content in the composite material sheet was measured in the same manner as in Example 1. In addition, the conductivity and Seebeck coefficient of the composite sheet were measured. The results are shown in Table 1.
（比較例１）
　ＣＮＴの０．２質量％エタノール分散液を添加せずに、ＢｉＴｅナノプレートの前駆体溶液のみを上述のソルボサーマル処理に供して、ＢｉＴｅナノプレートを合成した。合成反応後、オートクレーブ容器を取り出し、冷却後、中身を試験管に移した。これを遠心分離器にセットし、１５０００ｒｐｍで遠心させて、水溶液と沈殿物に分けた。次いで、沈殿物のみを受け皿に取り出し、真空乾燥機（ヤマト科学社製、「Ｖａｃｕｕｍ　Ｏｖｅｎ　ＡＤＰ－２１」）を用い、６０℃で２４時間乾燥させた。そして、得られたＢｉＴｅナノプレートの粉末を０．０１ｍｏｌ／Ｌの濃度でエタノールに混合し、超音波洗浄機で分散させた。次いで、得られた分散液を基板としてのポリイミド製シート上に塗布して成膜した（ドロップキャスト法）。次いで、得られた塗膜を真空乾燥機（ヤマト科学社製、「Ｖａｃｕｕｍ　Ｏｖｅｎ　ＡＤＰ－２１」）を用い、６０℃で２４時間乾燥させてシートを得た。次いで、電気炉を使用し、アルゴン９５体積％および水素５体積％を含む雰囲気中で、２５０℃で１時間熱処理を行った。得られたシートの導電率およびゼーベック係数を測定した。結果を表１に示す。 (Comparative Example 1)
The BiTe nanoplate was synthesized by subjecting only the precursor solution of the BiTe nanoplate to the above-mentioned solvothermal treatment without adding the 0.2% by mass ethanol dispersion of CNT. After the synthesis reaction, the autoclave container was taken out, cooled, and the contents were transferred to a test tube. This was set in a centrifuge and centrifuged at 15,000 rpm to separate an aqueous solution and a precipitate. Then, only the precipitate was taken out into a saucer and dried at 60 ° C. for 24 hours using a vacuum dryer (“Vacuum Oven ADP-21” manufactured by Yamato Scientific Co., Ltd.). Then, the obtained BiTe nanoplate powder was mixed with ethanol at a concentration of 0.01 mol / L and dispersed by an ultrasonic cleaner. Next, the obtained dispersion liquid was applied onto a polyimide sheet as a substrate to form a film (drop casting method). Next, the obtained coating film was dried at 60 ° C. for 24 hours using a vacuum dryer (“Vacuum Oven ADP-21” manufactured by Yamato Scientific Co., Ltd.) to obtain a sheet. Then, using an electric furnace, heat treatment was performed at 250 ° C. for 1 hour in an atmosphere containing 95% by volume of argon and 5% by volume of hydrogen. The conductivity and Seebeck coefficient of the obtained sheet were measured. The results are shown in Table 1.
（比較例２）
　ＣＮＴの０．２質量％エタノール分散液をドロップキャスト法により基板としてのポリイミド製シート上に塗布し、得られた塗布膜を真空乾燥機（ヤマト科学社製、「Ｖａｃｕｕｍ　Ｏｖｅｎ　ＡＤＰ－２１」）を用い、６０℃で２４時間乾燥して、ＣＮＴのシートを作製した。得られたシートの導電率およびゼーベック係数を測定した。結果を表１に示す。 (Comparative Example 2)
A 0.2 mass% ethanol dispersion of CNT was applied onto a polyimide sheet as a substrate by a drop casting method, and the obtained coating film was vacuum dried (manufactured by Yamato Scientific Co., Ltd., "Vacuum Ofen ADP-21"). It was dried at 60 ° C. for 24 hours to prepare a CNT sheet. The conductivity and Seebeck coefficient of the obtained sheet were measured. The results are shown in Table 1.
（比較例３～６）
　比較例１で合成したＢｉＴｅナノプレートと、実施例１で調製したＣＮＴの０．２質量％エタノール分散液とを６：１、５：１、４：１、３：１の混合比（ナノプレート：分散液、質量比）でそれぞれ混合して分散液を調製した。そして、上述と同様に成膜してシートを得た。得られたシートを走査型電子顕微鏡で観察したところ、ＢｉＴｅナノプレートとＣＮＴとは一体化していないことが確認された（図４を参照）。また、得られたシートの導電率およびゼーベック係数を測定した。結果を表１に示す。 (Comparative Examples 3 to 6)
The BiTe nanoplate synthesized in Comparative Example 1 and the 0.2% by mass ethanol dispersion of CNT prepared in Example 1 were mixed at a mixing ratio of 6: 1, 5: 1, 4: 1, 3: 1 (nanoplate). : Dispersion solution, mass ratio) were mixed to prepare a dispersion solution. Then, a film was formed in the same manner as described above to obtain a sheet. When the obtained sheet was observed with a scanning electron microscope, it was confirmed that the BiTe nanoplate and the CNT were not integrated (see FIG. 4). In addition, the conductivity and Seebeck coefficient of the obtained sheet were measured. The results are shown in Table 1.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１の結果から、ＣＮＴの存在下でＢｉＴｅナノプレートを合成して得られた、ＢｉＴｅナノプレートとＣＮＴとが一体化された複合材料のシートは、高い熱電変換特性と、高い導電率とをバランスよく兼ね備えていることがわかる（実施例）。特に、ＣＮＴの０．２質量％エタノール分散液を９ｍＬ添加した実施例４では、ＣＮＴ含有量が７．０質量％の複合材料が得られ、熱電変換特性（ゼーベック係数）と導電性とを最も高レベルで両立できたことがわかる。なお、ＣＮＴの０．２質量％エタノール分散液を１５ｍＬ添加した実施例６では、ＣＮＴ含有量が２．７質量％に低下しているが、これは、ＣＮＴが多いため凝集し、ＢｉＴｅナノプレートと十分に一体化しなかったためと考えられる。
　これに対して、ＢｉＴｅナノプレートのみを用いて作製したシートでは、ＢｉＴｅナノプレートにより高い熱電変換特性が得られているものの、ＣＮＴが存在しないため導電率が低いことがわかる（比較例１）。また、ＣＮＴのみを用いて作製したシートでは、ＣＮＴが存在するため高い導電率が得られているものの、ＢｉＴｅナノプレートが存在しないためゼーベック係数は正の値をとり、ｎ型化されていないことがわかる（比較例２）。さらに、ＢｉＴｅナノプレートとＣＮＴとを単純に混合して得られた材料を用いて作製したシートでは、両者の特性を引き出せず、熱電変換特性および導電率を高いレベルで両立できていないことがわかる（比較例３～６）。これは、ＢｉＴｅナノプレートとＣＮＴとが一体化されていないことに起因すると考えられる。 From the results in Table 1, a composite material sheet in which BiTe nanoplates and CNTs are integrated, which was obtained by synthesizing BiTe nanoplates in the presence of CNTs, has high thermoelectric conversion characteristics and high conductivity. It can be seen that they have a good balance (Example). In particular, in Example 4 in which 9 mL of a 0.2 mass% ethanol dispersion of CNTs was added, a composite material having a CNT content of 7.0 mass% was obtained, and the thermoelectric conversion characteristics (Seebeck coefficient) and conductivity were the best. It can be seen that both were achieved at a high level. In Example 6 in which 15 mL of a 0.2 mass% ethanol dispersion of CNTs was added, the CNT content was reduced to 2.7 mass%, but this was due to the large amount of CNTs, which aggregated and the BiTe nanoplate. It is probable that it was not fully integrated with.
On the other hand, in the sheet produced using only the BiTe nanoplate, although the BiTe nanoplate has obtained high thermoelectric conversion characteristics, it can be seen that the conductivity is low due to the absence of CNT (Comparative Example 1). Further, in the sheet produced using only CNTs, high conductivity is obtained due to the presence of CNTs, but the Seebeck coefficient takes a positive value due to the absence of BiTe nanoplates and is not n-shaped. Can be understood (Comparative Example 2). Furthermore, it can be seen that in the sheet prepared using the material obtained by simply mixing BiTe nanoplate and CNT, the characteristics of both cannot be brought out, and the thermoelectric conversion characteristics and the conductivity cannot be compatible at a high level. (Comparative Examples 3 to 6). It is considered that this is because the BiTe nanoplate and the CNT are not integrated.
　本発明によれば、熱電変換特性と導電性とを高いレベルで両立させた複合材料を提供することができる。
　また、本発明によれば、熱電変換特性と導電性とを高いレベルで両立させた複合材料を製造し得る、複合材料の製造方法を提供することができる。
　さらに、本発明によれば、熱電変換特性と導電性とを高いレベルで両立させた複合材料を含む熱電変換材料を提供することができる。 According to the present invention, it is possible to provide a composite material having both thermoelectric conversion characteristics and conductivity at a high level.
Further, according to the present invention, it is possible to provide a method for producing a composite material capable of producing a composite material having both thermoelectric conversion characteristics and conductivity at a high level.
Further, according to the present invention, it is possible to provide a thermoelectric conversion material containing a composite material having both thermoelectric conversion characteristics and conductivity at a high level.

Claims (6)

  1. 　ビスマステルルのナノプレートと繊維状炭素ナノ構造体とが一体化されてなる、複合材料。 A composite material in which bismuth tellurium nanoplates and fibrous carbon nanostructures are integrated.
  2. 　前記繊維状炭素ナノ構造体の含有量が７質量％以上１５質量％以下である、請求項１に記載の複合材料。 The composite material according to claim 1, wherein the content of the fibrous carbon nanostructure is 7% by mass or more and 15% by mass or less.
  3. 　前記繊維状炭素ナノ構造体が、カーボンナノチューブである、請求項１または２に記載の複合材料。 The composite material according to claim 1 or 2, wherein the fibrous carbon nanostructure is a carbon nanotube.
  4. 　ビスマス源と、テルル源と、繊維状炭素ナノ構造体と、溶媒とを含む原料組成物を準備する工程と、
    　前記原料組成物をソルボサーマル処理に供して、ビスマステルルのナノプレートと繊維状炭素ナノ構造体とが一体化されてなる複合材料を形成する工程と、を含む、複合材料の製造方法。     A step of preparing a raw material composition containing a bismuth source, a tellurium source, a fibrous carbon nanostructure, and a solvent.
    A method for producing a composite material, which comprises a step of subjecting the raw material composition to a sorbothermal treatment to form a composite material in which a bismuth tellurium nanoplate and a fibrous carbon nanostructure are integrated.
  5. 　前記繊維状炭素ナノ構造体が、カーボンナノチューブである、請求項４に記載の複合材料の製造方法。 The method for producing a composite material according to claim 4, wherein the fibrous carbon nanostructure is a carbon nanotube.
  6. 　請求項１～３のいずれか一項に記載の複合材料を含む、熱電変換材料。
          A thermoelectric conversion material comprising the composite material according to any one of claims 1 to 3.
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