n-Type Material for Thermoelectric Conversion, Method for Producing the Same, Dopant, and Thermoelectric Conversion Element

Abstract

An n-type material for thermoelectric conversion, which is obtained by doping a p-type material for thermoelectric conversion with a dopant, said p-type material containing carbon nanotubes and a conductive resin. With respect to this n-type material for thermoelectric conversion, the dopant contains: an anion that is a complex ion; an alkali metal cation; and a cation scavenger.

Description

Technical Field

[0001] The present invention relates to an n-type material for thermoelectric conversion, a method for manufacturing the same, a dopant, and a thermoelectric conversion element.

Background Art

[0002] Thermoelectric conversion is a technology that directly converts heat into electricity using the Seebeck effect, and is attracting attention as an energy recovery technology that converts waste heat generated when using fossil fuels into electricity.

[0003] The thermoelectric conversion element used in the above field is preferably a bipolar element including both a material exhibiting p-type conductivity and a material exhibiting n-type conductivity. However, many of the nanomaterials exhibit p-type conductivity. Therefore, a technology for converting a nanomaterial exhibiting p-type conductivity into a nanomaterial exhibiting n-type conductivity is required.

[0004] For example, Patent Document 1 discloses an n-type dopant that converts a nanomaterial exhibiting p-type conductivity into a nanomaterial exhibiting n-type conductivity.

[0005] Whether a nanomaterial exhibits p-type conductivity or n-type conductivity can be determined by the sign of the Seebeck coefficient (when the Seebeck coefficient is positive, the nanomaterial exhibits p-type conductivity, and when the Seebeck coefficient is negative, the nanomaterial exhibits n-type conductivity).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a thermoelectric conversion element having excellent thermoelectric conversion performance and an n-type material for thermoelectric conversion capable of realizing the same. Another object of the present invention is to provide a novel dopant capable of forming the above-described n-type material for thermoelectric conversion and a method for producing the above-described n-type material for thermoelectric conversion.

Means for Solving the Problems

[0008] One aspect of the present invention is an n-type material for thermoelectric conversion obtained by doping a dopant into a p-type material for thermoelectric conversion containing carbon nanotubes and a conductive resin, wherein the dopant contains an anion which is a complex ion, an alkali metal cation, and a cation scavenger.

[0009] In one embodiment, the anion may be selected from the group consisting of ferrocyanide ion, ferricyanide ion, tetrachloroferrate(III) ion, and tetrachloroferrate(II) ion.

[0010] In one embodiment, the anion may contain an iron atom, and the content of the iron atom in the n-type material for thermoelectric conversion may be 0.001 mass% to 15 mass%.

[0011] In one embodiment, the cation scavenger may be a crown ether compound.

[0012] In one embodiment, the cation scavenger may be a crown ether compound having a benzene ring in the molecule.

[0013] In one embodiment, the conductive resin may be composed of poly(3,4-ethylenedioxythiophene) and an electron acceptor.

[0014] Another aspect of the present invention relates to a dopant which is doped into a p-type material for thermoelectric conversion containing carbon nanotubes and a conductive resin and converts the p-type material for thermoelectric conversion into an n-type material, wherein the dopant contains an anion which is a complex ion, an alkali metal cation, and a cation scavenger.

[0015] Still another aspect of the present invention relates to a method for manufacturing an n-type material for thermoelectric conversion, which includes a step of doping a p-type material for thermoelectric conversion containing carbon nanotubes and a conductive resin with a dopant, wherein the dopant contains an anion that is a complex ion, an alkali metal cation, and a cation scavenger.

[0016] In one aspect, the step may include an impregnation step of impregnating at least a part of the p-type material for thermoelectric conversion with a dopant solution containing the dopant and a solvent, and a solvent removal step of removing the solvent.

[0017] In one aspect, the step of doping the p-type material for thermoelectric conversion with a dopant may include an impregnation step of impregnating a part of a resin layer containing the p-type material for thermoelectric conversion with a dopant solution containing the dopant and a solvent, and a solvent removal step of removing the solvent to obtain a thermoelectric conversion layer containing the p-type material for thermoelectric conversion and an n-type material for thermoelectric conversion.

[0018] Still another aspect of the present invention relates to a thermoelectric conversion element including the n-type material for thermoelectric conversion.

[0019] In one aspect, the thermoelectric conversion element may further include the p-type material for thermoelectric conversion.

Advantages of the Invention

[0020] According to the present invention, it is possible to provide a thermoelectric conversion element having excellent thermoelectric conversion performance and an n-type material for thermoelectric conversion capable of realizing the same. Further, according to the present invention, it is possible to provide a novel dopant capable of forming the n-type material for thermoelectric conversion and a method for manufacturing the n-type material for thermoelectric conversion.

Embodiments for Carrying Out the Invention

[0021] Hereinafter, preferred embodiments of the present invention will be described in detail.

[0022] <n-type material for thermoelectric conversion> The n-type material for thermoelectric conversion of this embodiment is obtained by doping a dopant into the p-type material for thermoelectric conversion.

[0023] (p-type material for thermoelectric conversion) The p-type material for thermoelectric conversion contains carbon nanotubes and a conductive resin.

[0024] The carbon nanotubes may be any of single-layer, double-layer, and multi-layer. From the viewpoint of further improving the electrical conductivity of the thermoelectric conversion material, a single layer is preferred.

[0025] The carbon nanotubes preferably include single-walled carbon nanotubes. The content ratio of single-walled carbon nanotubes to the total amount of carbon nanotubes is preferably, for example, 25% by mass or more, more preferably 50% by mass or more, and may be 100% by mass. That is, the content ratio of single-walled carbon nanotubes to the total amount of carbon nanotubes may be, for example, 25 to 100% by mass or 50 to 100% by mass.

[0026] The diameter of the single-walled carbon nanotubes is not particularly limited, and may be, for example, 20 nm or less, preferably 10 nm or less, and more preferably 3 nm or less. There is no particular limitation on the lower limit of the diameter of the single-walled carbon nanotubes, and it may be, for example, 0.4 nm or more, or 0.5 nm or more. That is, the diameter of the single-walled carbon nanotubes may be, for example, 0.4 to 20 nm, 0.4 to 10 nm, 0.4 to 3 nm, 0.5 to 20 nm, 0.5 to 10 nm, or 0.5 to 3 nm.

[0027] In this specification, the diameter of the single-walled carbon nanotubes can be obtained from the wave number (ω (cm -1 )) of the peak appearing at 100 to 300 cm -1 by the formula diameter (nm) = 248 / ω.

[0028] As an evaluation method for single-walled carbon nanotubes, the G / D ratio in laser Raman spectroscopy is known. In the present embodiment, the single-walled carbon nanotubes preferably have a G / D ratio of 10 or more, more preferably 20 or more, in laser Raman spectroscopy with a laser wavelength of 532 nm. By using such single-walled carbon nanotubes, a thermoelectric conversion material with even better electrical conductivity tends to be obtained. Note that the upper limit of the G / D ratio is not particularly limited, and may be, for example, 500 or less, or may be 300 or less. That is, the G / D ratio may be, for example, 10 to 500, 10 to 300, 20 to 500, or 20 to 300.

[0029] The content of the carbon nanotubes may be, for example, 20 parts by mass or more, preferably 30 parts by mass or more, and more preferably 40 parts by mass or more, based on 100 parts by mass of the p-type material for thermoelectric conversion.

[0030] Also, the content of the carbon nanotubes may be, for example, 99 parts by mass or less, preferably 95 parts by mass or less, and more preferably 90 parts by mass or less, based on 100 parts by mass of the p-type material for thermoelectric conversion. That is, the content of the carbon nanotubes may be, for example, 20 to 99 parts by mass, 20 to 95 parts by mass, 20 to 90 parts by mass, 30 to 99 parts by mass, 30 to 95 parts by mass, 30 to 90 parts by mass, 40 to 99 parts by mass, 40 to 95 parts by mass, or 40 to 90 parts by mass, based on 100 parts by mass of the p-type material for thermoelectric conversion.

[0031] The conductive resin of the present embodiment is not particularly limited, and known conductive resins used for p-type materials for thermoelectric conversion can be used without particular limitation. Examples of the conductive resin include those containing polyaniline-based conductive polymers, polythiophene-based conductive polymers, polypyrrole-based conductive polymers, polyacetylene-based conductive polymers, polyphenylene-based conductive polymers, polyphenylene vinylene-based conductive polymers, and the like. Examples of the polythiophene-based conductive polymer include poly(3,4-ethylenedioxythiophene).

[0032] As the conductive resin of the present embodiment, a conductive resin composed of poly(3,4-ethylenedioxythiophene) (hereinafter sometimes referred to as PEDOT) and an electron acceptor is preferable. With such a conductive resin, the electrical conductivity of the thermoelectric conversion material tends to be higher.

[0033] Examples of the electron acceptor include polystyrene sulfonic acid, polyvinyl sulfonic acid, poly(meth)acrylic acid, polyvinyl sulfonic acid, toluene sulfonic acid, dodecylbenzene sulfonic acid, camphor sulfonic acid, bis(2-ethylhexyl) sulfosuccinate, chlorine, bromine, iodine, phosphorus pentafluoride, arsenic pentafluoride, boron trifluoride, hydrogen chloride, sulfuric acid, nitric acid, tetrafluoroboric acid, perchloric acid, iron(III) chloride, tetracyanoquinodimethane, and the like. From the viewpoint of further improving the electrical conductivity of the thermoelectric conversion material, as the electron acceptor, polystyrene sulfonic acid (hereinafter sometimes referred to as PSS) is preferable.

[0034] (Dopant) In this specification, the dopant is intended to be a substance that changes the Seebeck coefficient of the material to be doped with the dopant.

[0035] In this specification, "changing the Seebeck coefficient" is intended to mean decreasing the value of the Seebeck coefficient or changing the value of the Seebeck coefficient from a positive value to a negative value. A thermoelectric conversion material having a positive Seebeck coefficient has p-type conductivity, and a thermoelectric conversion material having a negative Seebeck coefficient has n-type conductivity. The Seebeck coefficient can be measured, for example, by the measurement method in the examples described later, and the polarity of the thermoelectric conversion material can be determined from the positive or negative of the measured value.

[0036] The dopant of this embodiment contains an anion which is a complex ion (hereinafter also simply referred to as "anion"), an alkali metal cation (hereinafter also simply referred to as "cation"), and a cation scavenger (hereinafter also simply referred to as "scavenger"). By doping the above dopant into carbon nanotubes exhibiting p-type conductivity, the Seebeck coefficient of the carbon nanotubes can be changed to obtain carbon nanotubes exhibiting n-type conductivity.

[0037] The reason for the above effect is not particularly limited, but it is considered that the scavenger contained in the dopant captures the cation to dissociate the anion, and this anion changes the carrier of the carbon nanotubes from holes to electrons. At this time, in this embodiment, since the anion is a complex ion having a metal atom at the center, it is considered that it is significantly n-type due to the interaction between the metal atom and the carbon nanotubes. Also, since the complex ion has a large ionic size, it is considered that the good dissociability with the cation captured by the scavenger is also a factor contributing to the above effect.

[0038] In addition, since the anion of the dopant of this embodiment is a complex ion, metal atoms derived from the complex ion remain in the n-type material for thermoelectric conversion. Therefore, in this embodiment, the metal atoms remaining in the n-type material for thermoelectric conversion function as an antioxidant, suppressing the physical property change over time and improving the storage stability.

[0039] Examples of the anion that is a complex ion include anions selected from the group consisting of ferrocyanide ion, ferricyanide ion, tetrachloroferrate(III) ion, tetrachloroferrate(II) ion, tetracyanonickelate(II) ion, tetrachloronickelate(II) ion, tetracyanocobalt(II) ion, tetrachlorocobaltate(II) ion, tetracyanocopper(I) ion, tetrachlorocuprate(II) ion, hexacyanochromium(III) ion, tetrahydroxozincate(II) ion, and tetrahydroxoaluminate(III) ion. Among these, ferrocyanide ion is preferred. When the anion is ferrocyanide ion, an n-type material for thermoelectric conversion having better properties can be obtained. Also, when the anion is ferrocyanide ion, the iron atoms remaining in the n-type material for thermoelectric conversion preferably function as an antioxidant, physical property changes over time are more suppressed, and the storage stability tends to be more improved.

[0040] The anion that is a complex ion may contain iron atoms, and is preferably selected from the group consisting of, for example, ferrocyanide ion, ferricyanide ion, tetrachloroferrate(III) ion, and tetrachloroferrate(II) ion. Since an n-type material for thermoelectric conversion having better properties can be obtained, the anion containing iron atoms is preferably ferrocyanide ion. Also, from the viewpoint of the antioxidant effect, the content of the iron atoms in the n-type material for thermoelectric conversion is preferably 0.001 mass% to 15 mass%, more preferably 0.005 mass% to 12 mass%, and still more preferably 0.01 mass% to 10 mass%. The content of the iron atoms in the n-type material for thermoelectric conversion may be, for example, 0.001 to 12 mass%, 0.001 to 10 mass%, 0.005 to 15 mass%, 0.005 to 10 mass%, 0.01 to 15 mass%, or 0.01 to 12 mass%. In this specification, the content of the iron atoms indicates a value measured by scanning electron microscope (SEM)-energy dispersive X-ray spectroscopy (EDS).

[0041] The anion may be an anion generated by dissociation of the complex salt in the dopant solution. Examples of the complex salt include potassium ferrocyanide, sodium ferrocyanide, potassium ferricyanide, sodium ferricyanide, potassium tetrachloroferrate(III), sodium tetrachloroferrate(III), potassium tetrachloroferrate(II), sodium tetrachloroferrate(II), and the like. The complex salt may be a hydrate.

[0042] Examples of the alkali metal cation include sodium ion, potassium ion, lithium ion, and the like.

[0043] The cation scavenger is not particularly limited as long as it is a substance having the ability to capture cations. For example, crown ether compounds, cyclodextrins, calixarenes, ethylenediaminetetraacetic acid, porphyrins, phthalocyanines, and their derivatives can be mentioned. In an organic solvent, it is preferable to use a crown ether compound.

[0044] Examples of the crown ether compound include 15-crown-5-ether, 18-crown-6-ether, 12-crown-4-ether, benzo-18-crown-6-ether, benzo-15-crown-5-ether, benzo-12-crown-4-ether, and the like. The crown ether used as the scavenger may be selected according to the size of the metal ion to be captured. For example, when the metal ion is a potassium ion, an 18-membered crown ether is preferable; when the metal ion is a sodium ion, a 15-membered crown ether is preferable; when the metal ion is a lithium ion, a 12-membered crown ether is preferable.

[0045] The crown ether compound preferably has a benzene ring in the molecule. By using such a crown ether compound, p-type formation due to oxidation is suppressed, and the storage stability tends to be further improved. Examples of the crown ether compound having a benzene ring include benzo-18-crown-6-ether, benzo-15-crown-5-ether, benzo-12-crown-4-ether, and the like.

[0046] The molar ratio (C2 / C1) of the content C2 of the scavenger to the content C1 of the cation may be, for example, 0.1 to 5, preferably 0.3 to 3, and more preferably 0.5 to 2. The above molar ratio (C2 / C1) may be, for example, 0.1 to 3, 0.1 to 2, 0.3 to 5, 0.3 to 2, 0.5 to 5, or 0.5 to 3.

[0047] The dopant of this embodiment may contain, if necessary, substances other than the above-described anions, cations, and scavengers. Such substances are not particularly limited as long as they do not inhibit the function of the dopant, and examples include water, organic solvents, and the like.

[0048] The dopant of this embodiment may contain a plurality of types of anions, cations, and scavengers, respectively.

[0049] The method for producing the thermoelectric conversion material of this embodiment is not particularly limited, and for example, it can be produced by the following method.

[0050] <Method for Producing n-Type Material for Thermoelectric Conversion> The production method of this embodiment includes a step of doping a dopant into a p-type material for thermoelectric conversion containing carbon nanotubes and a conductive resin. The above step is also referred to as an n-type conversion step.

[0051] The method for doping a dopant into a p-type material for thermoelectric conversion in the n-type conversion step is not particularly limited, and examples include a method of bringing a dopant solution containing the dopant into contact with the p-type material for thermoelectric conversion.

[0052] In a preferred embodiment, the n-type conversion step may include an impregnation step of impregnating at least a part of the p-type material for thermoelectric conversion with a dopant solution containing a dopant and a solvent, and a solvent removal step of removing the solvent from the material after being impregnated with the dopant solution.

[0053] The boiling point of the solvent is preferably 70°C or higher, more preferably 90°C or higher, further preferably 110°C or higher, and may be 150°C or higher. When heat treatment is performed in the solvent removal step described below, if the boiling point of the solvent is low, most of the solvent is removed at the initial stage of the heat treatment, and the effect of the heat treatment may not be fully exerted. By using a solvent having the above-mentioned suitable boiling point range, the effect of the heat treatment is more remarkable. The upper limit of the boiling point of the solvent is not particularly limited. The boiling point of the solvent may be, for example, 300°C or lower, or 250°C or lower. That is, the boiling point of the solvent may be, for example, 70 to 300°C, 70 to 250°C, 90 to 300°C, 90 to 250°C, 110 to 300°C, 110 to 250°C, 150 to 300°C, or 150 to 250°C.

[0054] Examples of the solvent include water, acetonitrile, ethanol, ethylene glycol, dimethylsulfoxide (DMSO), N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, etc. The solvent may be used alone or in combination of two or more.

[0055] The dopant solution of the present embodiment may contain other components in addition to the dopant and the solvent, as long as the effects of the present invention are not impaired. Examples of the other components include a binder resin, an antioxidant, a thickener, and a surfactant.

[0056] The method of impregnating the p-type material for thermoelectric conversion with the dopant solution is not particularly limited. For example, methods such as immersing the p-type material for thermoelectric conversion in the dopant solution and applying the dopant solution to the p-type material for thermoelectric conversion can be mentioned. Among these, from the viewpoint of being able to easily expose the p-type material for thermoelectric conversion to the dopant solution while maintaining its shape, the method of immersing the p-type material for thermoelectric conversion in the dopant solution is preferable.

[0057] Since the dopant of the present embodiment is excellent in doping efficiency, doping can be completed in a short time. The time for impregnating the p-type material for thermoelectric conversion with the dopant solution may be, for example, 10 minutes to 72 hours, or may be 30 minutes to 24 hours. When the time for impregnating the dopant solution is within the above range, the productivity of the n-type material for thermoelectric conversion is excellent.

[0058] Here, in the present embodiment, although the conductive resin is included to obtain an excellent p-type material for thermoelectric conversion, on the other hand, there has been a concern that the conductive resin may prevent the dopant from contacting the carbon nanotubes. In addition, accordingly, procedures such as subjecting the p-type material for thermoelectric conversion to a long-time doping treatment or shear-dispersing the p-type material for thermoelectric conversion in the dopant treatment solution have been necessary. The dopant of the present invention eliminates such procedures and can provide an n-type material having excellent thermoelectric conversion performance with a short impregnation time of about 10 minutes.

[0059] In the impregnation step, a material impregnated with the dopant solution is obtained, and this material is subjected to the solvent removal step. Among the solvents used in the impregnation step, those other than those impregnated or adhered to the material may be removed at the end of the impregnation step. For example, when the p-type material for thermoelectric conversion is immersed in the dopant solution in the impregnation step, the material may be taken out of the dopant solution and subjected to the solvent removal step.

[0060] In the solvent removal step, at least a part of the solvent is removed from the material after impregnation with the above-mentioned dopant solution. In the solvent removal step, it is not necessarily required to remove all of the solvent, and the solvent may remain within a range where it functions sufficiently as the n-type material for thermoelectric conversion.

[0061] The solvent removal step may be, for example, a step of removing the solvent by natural drying, or may be a step of removing the solvent by performing heat treatment, reduced pressure treatment, or the like.

[0062] In a preferred embodiment, the solvent removal step may include a step of heat-treating the thermoelectric conversion material impregnated with the solvent. In this embodiment, it is considered that the solvent whose compatibility with the conductive resin is improved by heating flows the conductive resin in the material, filling the gaps between the carbon nanotubes to form a denser structure. Therefore, in this embodiment, the thermoelectric conversion characteristics tend to be more significantly improved.

[0063] In this embodiment, the temperature of the heat treatment is not particularly limited and may be, for example, 40°C or higher, preferably 50°C or higher, and more preferably 60°C or higher. By increasing the temperature of the heat treatment, the Seebeck coefficient of the thermoelectric conversion material tends to improve. Also, the temperature of the heat treatment may be, for example, 250°C or lower, preferably 225°C or lower, and more preferably 200°C or lower. By decreasing the temperature of the heat treatment, the electrical conductivity of the thermoelectric conversion material tends to improve. In this embodiment, the Seebeck coefficient and the electrical conductivity tend to vary depending on the temperature of the heat treatment. Therefore, the temperature of the heat treatment may be appropriately selected, for example, within the above-mentioned range, by looking at the balance of the numerical values of the Seebeck coefficient and the electrical conductivity. The temperature of the heat treatment may be, for example, 40 - 250°C, 40 - 220°C, 40 - 200°C, 50 - 250°C, 50 - 220°C, 50 - 200°C, 60 - 250°C, 60 - 220°C, or 60 - 200°C.

[0064] In this embodiment, the time of the heat treatment is not particularly limited. The time of the heat treatment may be, for example, 1 minute or longer, preferably 10 minutes or longer, and may be 12 hours or shorter, preferably 6 hours or shorter. That is, the time of the heat treatment may be, for example, 1 minute - 12 hours, 1 minute - 6 hours, 10 minutes - 12 hours, or 10 minutes - 6 hours.

[0065] Note that the heat treatment in this embodiment does not necessarily aim to remove the solvent, and the solvent removal step according to this embodiment may be a step of further performing a treatment to remove the solvent after the heat treatment.

[0066] In this embodiment, among the p-type materials for thermoelectric conversion, the portion doped with the dopant becomes the n-type material for thermoelectric conversion. In this embodiment, all of the p-type materials for thermoelectric conversion may be doped with the dopant to form the n-type material for thermoelectric conversion, or a part of the p-type materials for thermoelectric conversion may be doped with the dopant to form a composite of the p-type material for thermoelectric conversion and the n-type material for thermoelectric conversion.

[0067] In a preferred embodiment, the impregnation step may be a step of impregnating a part of the resin layer containing the p-type material for thermoelectric conversion with a dopant solution containing a dopant and a solvent, and the solvent removal step may be a step of removing the solvent from the resin layer after the dopant solution impregnation to obtain a thermoelectric conversion layer containing the p-type material for thermoelectric conversion and the n-type material for thermoelectric conversion. According to such an embodiment, a thermoelectric conversion layer containing the p-type material and the n-type material can be easily obtained. Further, in such an embodiment, a thermoelectric conversion layer having a desired p / n configuration can be easily obtained by appropriately setting the range in which the dopant solution is impregnated in the impregnation step.

[0068] The shape of the n-type material for thermoelectric conversion is not particularly limited. For example, a doping treatment may be performed on a composite material obtained by forming a film of the p-type material for thermoelectric conversion on a support to obtain the n-type material for thermoelectric conversion as a film supported by the support.

[0069] Examples of the support include polyimide, polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, polybutylene terephthalate, polycarbonate, polyether ether ketone, polyphenyl sulfide, polysulfone, glass, copper, silver, gold, aluminum, etc. Among these, it is preferable to be selected from the group consisting of polyimide, polyethylene terephthalate, and polyethylene naphthalate because the obtained thermoelectric conversion material exhibits good flexibility.

[0070] From the viewpoint of obtaining appropriate electrical resistance and excellent flexibility, the film thickness of the n-type material for thermoelectric conversion is preferably 100 nm to 1 mm, more preferably 200 nm to 800 μm, and still more preferably 300 nm to 600 μm. That is, the film thickness of the n-type material for thermoelectric conversion may be, for example, 100 nm to 1 mm, 100 nm to 800 μm, 100 nm to 600 μm, 200 nm to 1 mm, 200 nm to 800 μm, 200 nm to 600 μm, 300 nm to 1 mm, 300 nm to 800 μm, or 300 nm to 600 μm.

[0071] The thermoelectric conversion material according to the present embodiment can be suitably used as a thermoelectric conversion material for a thermoelectric conversion element. Further, the thermoelectric conversion material according to the present embodiment can also be suitably used for applications such as a Peltier element and a temperature sensor.

[0072] <Thermoelectric conversion element> The thermoelectric conversion element according to the present embodiment includes two conductive substrates and a thermoelectric conversion layer disposed between the conductive substrates and containing the thermoelectric conversion material. Since such a thermoelectric conversion element uses the thermoelectric conversion material obtained by the above-described manufacturing method, it has excellent thermoelectric conversion characteristics.

[0073] The two conductive substrates can also be referred to as a first electrode and a second electrode, respectively.

[0074] The thermoelectric conversion element according to the present embodiment may be manufactured, for example, by a manufacturing method including a lamination step of disposing a thermoelectric conversion material between two conductive substrates.

[0075] The lamination step may be carried out, for example, by forming a layer (thermoelectric conversion layer) of a thermoelectric conversion material on one of the conductive substrates and laminating the other conductive substrate on the formed thermoelectric conversion layer. Further, the lamination step may be carried out, for example, by preparing a film-like thermoelectric conversion material and attaching two conductive substrates to both sides thereof.

[0076] The thermoelectric conversion element may further include configurations other than those described above. For example, the thermoelectric conversion element may further include a sealing material for sealing the thermoelectric conversion material, wiring for electrically connecting the thermoelectric conversion elements to each other or extracting electric power to an external circuit, a heat insulating material or a heat conductive material for controlling the thermal conductivity of the thermoelectric conversion element, and the like.

[0077] As described above, the preferred embodiments of the present invention have been described, but the present invention is not limited to the above embodiments.

Example

[0078] Example 1 (Preparation of mixed solution) Unless otherwise specified, the following operations were carried out at 27°C. 0.28 g of "Clevious PH1000" (PEDOT / PSS aqueous dispersion, solid content concentration: 1.2% by mass) manufactured by Heraeus and 5 g of "EC-DH" (single-walled carbon nanotube aqueous dispersion, single-walled CNT concentration 0.2% by mass, diameter of single-walled CNT 1.4 nm, G / D ratio 100) manufactured by Meijo Nanocarbon were stirred and mixed with a planetary mixer ("Avatori Rintaro ARE-310" manufactured by Shinki Co., Ltd.) to prepare a mixed solution in which the content of single-walled CNT was 75% by mass based on the total amount of PEDOT / PSS and single-walled CNT. "PEDOT / PSS" refers to a conductive polymer composed of PEDOT and PSS.

[0079] (Preparation of composite material) About 1.5 mL of the mixed solution was dropped onto a polyimide film (thickness 100 μm) washed with acetone, coated using a doctor blade with a gap of 2 mm, and dried at 60°C for 3 hours to prepare a composite material with a thickness of 25 μm.

[0080] (Solvent treatment and solvent removal) The above composite was immersed in dimethyl sulfoxide (DMSO, boiling point 189°C) at room temperature for 5 minutes. Then, it was heat-treated at 60°C for 30 minutes to prepare a p-type material for thermoelectric conversion with a thickness of 5 μm. The Seebeck coefficient of the obtained p-type material for thermoelectric conversion was 24.8 μV / K.

[0081] (Fabrication of n-Type Material for Thermoelectric Conversion) Dissolve 0.032 g of potassium ferrocyanide trihydrate and 0.094 g of benzo-18-crown-6-ether in 3 mL of ultrapure water (the concentrations of potassium ions and benzo-18-crown-6-ether are 0.1 M and C2 / C1 = 1 respectively) to obtain a dopant solution. Cut the obtained thermoelectric conversion material into 15 mm × 15 mm pieces and immerse them in the dopant solution at room temperature for 10 minutes. Then, pull the thermoelectric conversion material out of the dopant solution and heat-treat it at 60 °C for 30 minutes to fabricate a doped thermoelectric conversion material.

[0082] The Seebeck coefficient of the obtained doped thermoelectric conversion material was -17.4 μV / K.

[0083] (Calculation of Seebeck Coefficient) Cut the polyimide plate coated with the doped thermoelectric conversion material into 20 mm × 10 mm pieces. Cool one end of the long side of the test piece (5 °C), heat the other end of the long side of the test piece (5 °C), measure the temperature difference and voltage generated at both ends with an Alumel-Chromel thermocouple, and calculate the Seebeck coefficient from the slopes of the temperature difference and voltage. The Seebeck coefficient of the polyimide plate coated with the thermoelectric conversion material before doping treatment was also calculated in the same way.

[0084] Example 2 An n-type material for thermoelectric conversion was obtained in the same manner as in Example 1, except that sodium ferrocyanide trihydrate was used instead of potassium ferrocyanide trihydrate and benzo-15-crown-5-ether was used instead of benzo-18-crown-6-ether.

[0085] Comparative Example 1 A dopant was doped into the p-type material for thermoelectric conversion in the same manner as in Example 1, except that potassium carbonate was used instead of potassium ferrocyanide trihydrate.

[0086] Comparative Example 2 A dopant was doped into the p-type material for thermoelectric conversion in the same manner as in Example 2, except that sodium hydrogen carbonate was used instead of sodium ferrocyanide trihydrate.

[0087] Comparative Example 3 A dopant was doped into the p-type material for thermoelectric conversion in the same manner as in Example 2, except that sodium carbonate was used instead of sodium ferrocyanide trihydrate.

[0088] Table 1 shows the Seebeck coefficient values before and after the doping treatment. Examples 1 and 2 show a negative Seebeck coefficient after the doping treatment, indicating the performance as an n-type material for thermoelectric conversion. Comparative Examples 1 to 3 show a positive Seebeck coefficient after the doping treatment and do not show the performance as an n-type material for thermoelectric conversion.

[0089]

Table 1

Claims

1. An n-type material for thermoelectric conversion obtained by doping a p-type material for thermoelectric conversion containing carbon nanotubes and a conductive resin with a dopant, The dopant contains an anion that is a complex ion containing iron atoms, an alkali metal cation, and a cation scavenger, and is an n-type material for thermoelectric conversion.

2. The n-type material for thermoelectric conversion according to claim 1, wherein the anion is selected from the group consisting of ferrocyanide ions, ferricyanide ions, tetrachloroferrate(III) ions, and tetrachloroferrate(II) ions.

3. The n-type material for thermoelectric conversion according to claim 1 or 2, wherein the content of the iron atoms in the n-type material for thermoelectric conversion is 0.001% by mass to 15% by mass.

4. The n-type material for thermoelectric conversion according to any one of claims 1 to 3, wherein the cation scavenger is a crown ether-based compound.

5. The n-type material for thermoelectric conversion according to any one of claims 1 to 4, wherein the cation scavenger is a crown ether-based compound having a benzene ring in the molecule.

6. The n-type material for thermoelectric conversion according to any one of claims 1 to 5, wherein the conductive resin is composed of poly(3,4-ethylenedioxythiophene) and an electron acceptor.

7. A dopant that is doped into a p-type material for thermoelectric conversion containing carbon nanotubes and a conductive resin to convert the p-type material for thermoelectric conversion into an n-type, The dopant contains an anion that is a complex ion containing iron atoms, an alkali metal cation, and a cation scavenger.

8. A method for producing an n-type material for thermoelectric conversion, including a step of doping a p-type material for thermoelectric conversion containing carbon nanotubes and a conductive resin with a dopant, The dopant contains an anion that is a complex ion containing iron atoms, an alkali metal cation, and a cation scavenger.

9. The process comprises: An impregnation step of impregnating at least a part of the p-type material for thermoelectric conversion with a dopant solution containing the dopant and a solvent; A solvent removal step of removing the solvent; The method for manufacturing an n-type material for thermoelectric conversion according to claim 8, comprising the above steps.

10. The process comprises: An impregnation step of impregnating a part of a resin layer containing the p-type material for thermoelectric conversion with a dopant solution containing the dopant and a solvent; A solvent removal step of removing the solvent to obtain a thermoelectric conversion layer containing the p-type material for thermoelectric conversion and an n-type material for thermoelectric conversion; The method for manufacturing an n-type material for thermoelectric conversion according to claim 8, comprising the above steps.

11. A thermoelectric conversion element comprising the n-type material for thermoelectric conversion according to any one of claims 1 to 6.

12. The thermoelectric conversion element according to claim 11, further comprising the p-type material for thermoelectric conversion.

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