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

Abstract

Provided is an n-type material for thermoelectric conversion, which is obtained by doping a p-type material for thermoelectric conversion with a dopant, wherein the p-type material for thermoelectric conversion contains carbon nanotubes and a conductive resin. The dopant contains: a complex ion containing divalent iron ion, an alkali metal cation, a cation scavenger, and a reducing agent.

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 having 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] The object of the present invention is to provide a novel dopant that can efficiently convert a p-type material for thermoelectric conversion into an n-type material for thermoelectric conversion. Another object of the present invention is to provide an n-type material for thermoelectric conversion obtained by doping the p-type material for thermoelectric conversion with the dopant. Furthermore, the object of the present invention is to provide a method for manufacturing the n-type material for thermoelectric conversion and a thermoelectric conversion element including the n-type material for thermoelectric conversion.

Means for Solving the Problems

[0008] The present invention relates to, for example, the following [1] to

[11] . [1] 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 a complex ion containing divalent iron ions, an alkali metal cation, a cation scavenger, and a reducing agent. [2] The n-type material for thermoelectric conversion according to [1], wherein the cation scavenger is a crown ether-based compound. [3] The n-type material for thermoelectric conversion according to [2], wherein the cation scavenger is a crown ether-based compound having a benzene ring in the molecule. [4] The n-type material for thermoelectric conversion according to any one of [1] to [3], wherein the conductive resin is composed of poly(3,4-ethylenedioxythiophene) and an electron acceptor. [5] The n-type material for thermoelectric conversion according to any one of [1] to [4], wherein the reducing agent contains at least one selected from the group consisting of ascorbic acid and its salts, reducing sugars, oxalic acid and its salts, formic acid, alkali metal iodides, and tin(II) chloride. [6] 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 material, A dopant containing an anion which is a complex ion, an alkali metal cation, a cation scavenger, and a reducing agent. [7] A process for doping a p-type material for thermoelectric conversion containing carbon nanotubes and a conductive resin with a dopant, The manufacturing method of an n-type material for thermoelectric conversion, wherein the dopant contains an anion which is a complex ion, an alkali metal cation, a cation scavenger, and a reducing agent. [8] The process is 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 manufacturing method of the n-type material for thermoelectric conversion according to [7], including these. [9] The process is 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 manufacturing method of the n-type material for thermoelectric conversion according to [7], including these.

[10] A thermoelectric conversion element including the n-type material for thermoelectric conversion according to any one of [1] to [5].

[11] The thermoelectric conversion element according to

[10] , further including the p-type material for thermoelectric conversion.

Advantages of the Invention

[0009] According to the present invention, a novel dopant capable of efficiently converting a p-type material for thermoelectric conversion into an n-type material for thermoelectric conversion is provided. Further, according to the present invention, an n-type material for thermoelectric conversion obtained by doping the p-type material for thermoelectric conversion with the dopant is provided. Furthermore, according to the present invention, a manufacturing method of the n-type material for thermoelectric conversion and a thermoelectric conversion element including the n-type material for thermoelectric conversion are provided.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, preferred embodiments of the present invention will be described in detail.

[0011] <n-type material for thermoelectric conversion> The n-type material for thermoelectric conversion in this embodiment is obtained by doping a dopant into a p-type material for thermoelectric conversion.

[0012] (p-type material for thermoelectric conversion) The p-type material for thermoelectric conversion contains carbon nanotubes and a conductive resin.

[0013] The carbon nanotubes may be any of single-layer, bilayer, and multi-layer. From the viewpoint of further improving the electrical conductivity of the thermoelectric conversion material (p-type material for thermoelectric conversion and n-type material for thermoelectric conversion described later), a single layer is preferred.

[0014] 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.

[0015] 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. The diameter of the single-walled carbon nanotubes has no particular lower limit, and 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.

[0016] 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.

[0017] 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 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 it 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.

[0018] The content of carbon nanotubes may be, for example, 20% by mass or more, preferably 30% by mass or more, and more preferably 40% by mass or more, based on the total amount of the solid content of the p-type material for thermoelectric conversion.

[0019] Also, the content of carbon nanotubes may be, for example, 99% by mass or less, preferably 95% by mass or less, and more preferably 90% by mass or less, based on the total amount of the solid content of the p-type material for thermoelectric conversion. That is, the content of carbon nanotubes may be, for example, 20 to 99% by mass, 20 to 95% by mass, 20 to 90% by mass, 30 to 99% by mass, 30 to 95% by mass, 30 to 90% by mass, 40 to 99% by mass, 40 to 95% by mass, or 40 to 90% by mass, based on the total amount of the solid content of the p-type material for thermoelectric conversion.

[0020] 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).

[0021] 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.

[0022] 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, polystyrene sulfonic acid (hereinafter sometimes referred to as PSS) is preferable as the electron acceptor.

[0023] (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.

[0024] 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.

[0025] The dopant of this embodiment contains a complex ion containing divalent iron ions (hereinafter, also simply referred to as "anion"), an alkali metal cation (hereinafter, also simply referred to as "cation"), a cation scavenger (hereinafter, also simply referred to as "scavenger"), and a reducing agent. By doping the thermoelectric conversion p-type material with the dopant of this embodiment, the Seebeck coefficient of the material can be changed to obtain a thermoelectric conversion n-type material. Further, according to the dopant of this embodiment, a thermoelectric conversion n-type material excellent in durability under a high-temperature and high-humidity environment (for example, 85°C / 85RH%) can be obtained.

[0026] The reason for the above effect is not particularly limited, but it is considered that the scavenger contained in the dopant captures the cation, dissociates the anion (complex ion), and the anion changes the carrier of the carbon nanotube from a hole to an electron. At this time, in this embodiment, since the anion is a complex ion having a metal atom at the center, it is considered that the metal atom and the carbon nanotube interact to significantly n-type. Further, since the complex ion has a large ion size, it is also considered that the good dissociability with the cation captured by the scavenger is also a factor in the above effect.

[0027] Further, in this embodiment, since the dopant contains a reducing agent, even if the anion (complex ion) and the cation scavenger in the dopant are in small amounts, the thermoelectric conversion p-type material can be efficiently converted into a thermoelectric conversion n-type material. That is, in this embodiment, it is also possible to efficiently convert the thermoelectric conversion p-type material into the thermoelectric conversion n-type material while reducing the usage amount of expensive anions and cation scavengers.

[0028] The reason for the above effect is not particularly limited, but it is considered that the iron ions oxidized when changing the carrier of the carbon nanotube from a hole to an electron are reduced by the reducing agent, so that it is possible to change the carrier of the carbon nanotube from a hole to an electron again.

[0029] In addition, in the present embodiment, when the amounts of the anion (complex ion) and the reducing agent doped into the p-type material for thermoelectric conversion are large, a n-type material for thermoelectric conversion with more excellent durability in a high-temperature environment (for example, 85°C / 85RH%) tends to be easily obtained. That is, when higher durability in a high-temperature environment is required, the amounts of the anion (complex ion) and the reducing agent doped into the p-type material for thermoelectric conversion may be increased. When it is desired to obtain a n-type material for thermoelectric conversion at a lower cost, the amount of the anion (complex ion) doped into the p-type material for thermoelectric conversion may be decreased.

[0030] The anion may be, for example, an anion selected from the group consisting of ferrocyanide ions and tetrachloroferrate (II) ions. From the viewpoint of easily obtaining a n-type material for thermoelectric conversion having better characteristics, the anion is preferably ferrocyanide ions.

[0031] The anion may be an anion generated by dissociation of a complex salt in a dopant solution. Examples of the complex salt include potassium ferrocyanide, sodium ferrocyanide, potassium tetrachloroferrate (II), sodium tetrachloroferrate (II), and the like.

[0032] Examples of the alkali metal cation include sodium ions, potassium ions, lithium ions, and the like.

[0033] The cation scavenger is not particularly limited as long as it is a substance having the ability to take in cations. Examples thereof include crown ether compounds, cyclodextrin, calixarene, ethylenediaminetetraacetic acid, porphyrin, phthalocyanine, and derivatives thereof. In an organic solvent, it is preferable to use a crown ether compound.

[0034] Examples of crown ether compounds 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 have its ring size selected according to the size of the metal ion to be incorporated. For example, when the metal ion is a potassium ion, an 18-membered ring crown ether is preferred; when the metal ion is a sodium ion, a 15-membered ring crown ether is preferred; and when the metal ion is a lithium ion, a 12-membered ring crown ether is preferred.

[0035] 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.

[0036] 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 or more, preferably 0.3 or more, and more preferably 0.5 or more. Also, the molar ratio (C2 / C1) of the content C2 of the scavenger to the content C1 of the cation may be, for example, 5 or less, preferably 3 or less, and more preferably 2 or less. Thereby, the above effects are more significantly exhibited. That is, 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, 0.1 to 3, 0.1 to 2, 0.3 to 5, 0.3 to 3, 0.3 to 2, 0.5 to 5, 0.5 to 3, or 0.5 to 2.

[0037] The reducing agent is not particularly limited as long as it is a substance capable of reducing trivalent iron ions. Examples of the reducing agent include ascorbic acid, ascorbate (e.g., sodium ascorbate, etc.), reducing sugar (e.g., glucose, fructose, glyceraldehyde, etc.), oxalic acid, oxalate (e.g., sodium oxalate, etc.), formic acid, alkali metal iodide (e.g., potassium iodide, etc.), and tin(II) chloride. At least one selected from the group consisting of these is mentioned.

[0038] The molar ratio (C4 / C3) of the content C4 of the reducing agent to the content C3 of the anion may be, for example, 0.1 or more, preferably 0.2 or more, more preferably 0.5 or more. Also, the molar ratio (C4 / C3) of the content C4 of the reducing agent to the content C3 of the anion may be, for example, 30 or less, preferably 20 or less, more preferably 10 or less. Thereby, the above effects are more significantly exhibited. That is, the molar ratio (C4 / C3) of the content C4 of the reducing agent to the content C3 of the anion may be, for example, 0.1 to 30, 0.1 to 20, 0.1 to 10, 0.2 to 30, 0.2 to 20, 0.2 to 10, 0.5 to 30, 0.5 to 20, or 0.5 to 10.

[0039] The dopant of this embodiment may contain, if necessary, substances other than the above-described anion, cation, scavenger, and reducing agent. 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.

[0040] The dopant of this embodiment may contain a plurality of types of anion, cation, scavenger, and reducing agent, respectively.

[0041] By doping the dopant of this embodiment into the p-type material for thermoelectric conversion, an n-type material for thermoelectric conversion can be obtained. The amount of the dopant doped into the p-type material for thermoelectric conversion is not particularly limited, and may be, for example, an amount that satisfies the preferable range of the amount of the anion (complex ion) doped into the p-type material for thermoelectric conversion described later.

[0042] The amount of anions (complex ions) doped into the p-type material for thermoelectric conversion may be, for example, 0.1 part by mass or more, preferably 1.0 part by mass or more, more preferably 10 parts by mass or more, with respect to 100 parts by mass of carbon nanotubes in the p-type material for thermoelectric conversion. Also, the amount of anions (complex ions) doped into the p-type material for thermoelectric conversion may be, for example, 300 parts by mass or less, preferably 200 parts by mass or less, more preferably 150 parts by mass or less, with respect to 100 parts by mass of carbon nanotubes in the p-type material for thermoelectric conversion. That is, the amount of anions (complex ions) doped into the p-type material for thermoelectric conversion may be, for example, 0.1 to 300, 1.0 to 300, 10 to 300, 0.1 to 200, 1.0 to 200, 10 to 200, 0.1 to 150, 1.0 to 150, or 10 to 150 with respect to 100 parts by mass of carbon nanotubes in the p-type material for thermoelectric conversion.

[0043] The method for manufacturing the n-type material for thermoelectric conversion of the present embodiment is not particularly limited, and for example, it can be manufactured by the following method.

[0044] <Method for manufacturing n-type material for thermoelectric conversion> The manufacturing method of the present 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.

[0045] The method of doping a dopant into the p-type material for thermoelectric conversion in the n-type conversion step is not particularly limited, and for example, a method of bringing a dopant solution containing a dopant into contact with the p-type material for thermoelectric conversion can be mentioned.

[0046] In a preferred aspect, 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 the dopant solution impregnation.

[0047] The boiling point of the solvent is preferably 70° C. or higher, more preferably 90° C. or higher, even more preferably 110° C. or higher, and may be 150° C. or higher. When a heat treatment is performed in the solvent removal step described below, a high boiling point of the solvent makes it difficult to remove the solvent during the heat treatment, and the effect of the heat treatment is more efficiently exerted. That is, by using a solvent having the above-mentioned suitable boiling point range, the effect of the heat treatment is more significantly exerted.

[0048] 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.

[0049] 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.

[0050] The method for impregnating the p-type material for thermoelectric conversion with the dopant solution is not particularly limited, and examples thereof include a method of immersing the p-type material for thermoelectric conversion in the dopant solution, and a method of applying the dopant solution to the p-type material for thermoelectric conversion.

[0051] The dopant of this embodiment has excellent doping efficiency, so that 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.

[0052] Here, in the present embodiment, the p-type material for thermoelectric conversion contains a conductive resin. However, when such a p-type material for thermoelectric conversion is used, there is a concern that the conductive resin may prevent the dopant from contacting the carbon nanotubes. In addition, with conventional dopants, it may be necessary to perform laborious processes such as doping the p-type material for thermoelectric conversion for a long time or shear-dispersing the p-type material for thermoelectric conversion in a dopant treatment solution. The dopant of the present embodiment eliminates such labor and can provide an n-type material having excellent thermoelectric conversion performance with an impregnation time as short as about 10 minutes.

[0053] In the impregnation step, a material impregnated with a dopant solution is obtained, and this material is subjected to a solvent removal step. Note that, 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.

[0054] In the solvent removal step, at least a part of the solvent is removed from the material after impregnation with the above-described dopant solution. In the solvent removal step, it is not necessarily required to remove all of the solvent, and the solvent may remain as long as it sufficiently functions as the n-type material for thermoelectric conversion.

[0055] 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.

[0056] 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 with improved compatibility with the conductive resin by heating causes the conductive resin in the material to flow, filling the gaps between the carbon nanotubes and forming a denser structure. Therefore, in this embodiment, the thermoelectric conversion characteristics tend to be more significantly improved.

[0057] 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. Further, 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, while considering the balance of the numerical values of the Seebeck coefficient and the electrical conductivity.

[0058] 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.

[0059] Note that the heat treatment in this embodiment does not necessarily need to be for the purpose of removing the solvent, and the solvent removal step according to this embodiment may be a step of further performing a treatment for removing the solvent after the heat treatment.

[0060] In this embodiment, among the p-type materials for thermoelectric conversion, the portion doped with the dopant becomes an 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 an 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.

[0061] In a preferred embodiment, the impregnation step may be a step of impregnating a part of a resin layer containing a 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 a p-type material for thermoelectric conversion and an n-type material for thermoelectric conversion. According to such an embodiment, a thermoelectric conversion layer containing a p-type material and an 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.

[0062] 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 in which a p-type material for thermoelectric conversion is formed into a film on a support to obtain an n-type material for thermoelectric conversion as a film supported by the support.

[0063] 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 preferably selected from the group consisting of polyimide, polyethylene terephthalate, and polyethylene naphthalate because the obtained thermoelectric conversion material exhibits good flexibility.

[0064] 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 even more preferably 300 nm to 600 μm.

[0065] The n-type material for thermoelectric conversion of the present embodiment can be suitably used as an n-type material for a thermoelectric conversion element. Further, the n-type material for thermoelectric conversion of the present embodiment can also be suitably used for applications such as Peltier elements and temperature sensors.

[0066] <Thermoelectric conversion element> The thermoelectric conversion element of this embodiment includes the above-described n-type material for thermoelectric conversion. The thermoelectric conversion element of this embodiment may further include the above-described p-type material for thermoelectric conversion.

[0067] The thermoelectric conversion element of this embodiment may, for example, include two conductive substrates and a thermoelectric conversion layer disposed between the conductive substrates and containing the above-described n-type material for thermoelectric conversion. Further, the thermoelectric conversion layer may further include the above-described p-type material for thermoelectric conversion.

[0068] The two conductive substrates may also be referred to as a first electrode and a second electrode, respectively.

[0069] The thermoelectric conversion element of this embodiment may be manufactured, for example, by a manufacturing method including a lamination step of disposing a thermoelectric conversion layer containing an n-type material for thermoelectric conversion and a p-type material for thermoelectric conversion on a conductive substrate.

[0070] The thermoelectric conversion element of this embodiment may be manufactured, for example, by a manufacturing method including a first lamination step of disposing a resin layer containing a p-type material for thermoelectric conversion on one of the conductive substrates, an impregnation step of impregnating a part of the resin layer 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 a p-type material for thermoelectric conversion and an n-type material for thermoelectric conversion, and a second lamination step of laminating the other conductive substrate on the thermoelectric conversion layer.

[0071] The thermoelectric conversion element may further include a configuration other than the above. For example, the thermoelectric conversion element may further include a sealing material for sealing the thermoelectric conversion layer, wiring for electrically connecting the thermoelectric conversion elements to each other or taking out electric power to an external circuit, a heat insulating material or a heat conductive material for controlling the heat conductivity of the thermoelectric conversion element, and the like.

[0072] 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

[0073] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. Unless otherwise specified, the following was carried out at 23°C.

[0074] (Example 1) <Preparation of mixed solution> 0.28 g of "Clevious PH1000" (PEDOT / PSS aqueous dispersion, solid content concentration: 1.2 mass%) manufactured by Heraeus and 5 g of "EC-DH" (single-walled carbon nanotube aqueous dispersion, single-walled CNT concentration 0.2 mass%, diameter of single-walled CNTs 0.9 to 1.7 nm, G / D ratio: 41) manufactured by Meijo Nano Carbon 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 CNTs was 75 mass% with respect to the total amount of PEDOT / PSS and single-walled CNTs. Note that "PEDOT / PSS" refers to a conductive polymer composed of PEDOT and PSS.

[0075] <Fabrication of composite film> The mixed solution was dropped onto a polyimide film (thickness 100 μm) washed with acetone, coated using a doctor blade with a gap of 2.5 mm, and placed in a hot air dryer set at 60°C and dried for 2 hours. Thereby, a composite film with a thickness of 25 μm was formed on the polyimide film. For the measurement of the film thickness, a high-precision digital micrometer ("MDH-25MB" manufactured by Mitutoyo Corporation) was used to measure the film thickness at the location where the composite film was formed and the film thickness at the location of only the polyimide film, respectively, and the difference between the two was calculated as the film thickness of the composite film.

[0076] <Solvent treatment and solvent removal> The above composite film was immersed in dimethyl sulfoxide (DMSO, boiling point 189°C) at room temperature for 5 minutes. Thereafter, it was placed on a hot plate set at 60°C for 120 minutes. Thereby, a layer (thickness 5 μm) of a p-type material for thermoelectric conversion was fabricated. The Seebeck coefficient of the obtained p-type thermoelectric conversion material (referred to as "Seebeck coefficient before doping treatment" in the following table) was 22.8 μV / K.

[0077] <Fabrication of n-type material for thermoelectric conversion> Dissolve 0.063 g of potassium ferricyanide trihydrate, 0.188 g of benzo-18-crown-6-ether, and 0.018 g of L-ascorbic acid in 5 mL of ultrapure water (the molar concentration of potassium ferricyanide is 0.03 M, the molar concentration of benzo-18-crown-6-ether is 0.12 M, and the molar concentration of L-ascorbic acid is 0.02 M) to obtain a dopant solution. Cut out the above p-type material for thermoelectric conversion together with the polyimide film into pieces of 10 mm × 10 mm, and drop 40 μL of the dopant solution onto it. Then, dry it at 60 °C for 30 minutes, and then put it into a hot air dryer set at 100 °C and perform a heat treatment for 60 minutes. Thereby, an n-type material for thermoelectric conversion was obtained. The Seebeck coefficient of the obtained n-type material for thermoelectric conversion (referred to as "Seebeck coefficient after doping treatment" in the following table) was -20.9 μV / K. Incidentally, potassium ferricyanide trihydrate contains divalent iron ions.

[0078] Incidentally, the Seebeck coefficients of the p-type material for thermoelectric conversion and the n-type material for thermoelectric conversion were measured by the following method. Cut out the thermoelectric conversion material (p-type material for thermoelectric conversion or n-type material for thermoelectric conversion) arranged on the polyimide film into pieces of 20 mm × 10 mm to prepare test pieces. Cool one end of the long side of the test piece (the initial temperature of the test piece - 5 °C = 18 °C), heat the other end of the long side of the test piece (the initial temperature of the test piece + 5 °C = 28 °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 the voltage.

[0079] (Example 2) An n-type material for thermoelectric conversion was obtained in the same manner as in Example 1, except that 0.018 g of D-(+)-glucose was used instead of L-ascorbic acid. Incidentally, the molar concentration of D-(+)-glucose in the dopant solution was 0.02 M. In Example 2, the Seebeck coefficient of the p-type material for thermoelectric conversion before the doping treatment was 23.3 μV / K, and the Seebeck coefficient of the n-type material for thermoelectric conversion after the doping treatment was -19.2 μV / K.

[0080] (Example 3) As a dopant solution, except that 0.021 g of potassium ferrocyanide trihydrate, 0.063 g of benzo-18-crown-6-ether, and 0.035 g of D-(+)-glucose were dissolved in 5 mL of ultrapure water, an n-type material for thermoelectric conversion was obtained in the same manner as in Example 1. In the dopant solution, the molar concentration of potassium ferrocyanide was 0.01 M, the molar concentration of benzo-18-crown-6-ether was 0.04 M, and the molar concentration of D-(+)-glucose was 0.04 M. In Example 3, the Seebeck coefficient of the p-type material for thermoelectric conversion before the doping treatment was 22.5 μV / K, and the Seebeck coefficient of the n-type material for thermoelectric conversion after the doping treatment was -16.4 μV / K.

[0081] (Example 4) An n-type material for thermoelectric conversion was obtained in the same manner as in Example 1, except that 0.009 g of oxalic acid was used instead of L-ascorbic acid. The molar concentration of oxalic acid in the dopant solution was 0.02 M. In Example 4, the Seebeck coefficient of the p-type material for thermoelectric conversion before the doping treatment was 21.4 μV / K, and the Seebeck coefficient of the n-type material for thermoelectric conversion after the doping treatment was -21.5 μV / K.

[0082] (Comparative Example 1) An n-type material for thermoelectric conversion was obtained in the same manner as in Example 1, except that L-ascorbic acid was not used. In Comparative Example 1, the Seebeck coefficient of the p-type material for thermoelectric conversion before the doping treatment was 23.1 μV / K, and the Seebeck coefficient of the n-type material for thermoelectric conversion after the doping treatment was -15.3 μV / K.

[0083] (Comparative Example 2) An n-type material for thermoelectric conversion was obtained in the same manner as in Example 3, except that D-(+)-glucose was not used. In Comparative Example 2, the Seebeck coefficient of the p-type material for thermoelectric conversion before the doping treatment was 23.4 μV / K, and the Seebeck coefficient of the n-type material for thermoelectric conversion after the doping treatment was -7.8 μV / K.

[0084] (Comparative Example 3) A dopant was doped into the p-type thermoelectric conversion material in the same manner as in Example 1, except that potassium ferrocyanide trihydrate was not used. In Comparative Example 3, the Seebeck coefficient before the doping treatment was 25.66 μV / K, and the Seebeck coefficient after the doping treatment was 25.54 μV / K.

[0085] The results of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Tables 1 and 2. In the tables, the concentration of the complex ion, the concentration of the cation scavenger, and the concentration of the reducing agent indicate the concentrations of the respective components in the doping solution. Also, in the tables, Reducing Agent 1 indicates L-ascorbic acid, Reducing Agent 2 indicates D-(+)-glucose, and Reducing Agent 3 indicates oxalic acid.

[0086] [Table 1]

[0087] [Table 2]

[0088] As shown in Table 1, in Examples 1 to 4, n-type conversion proceeded efficiently with a small amount of complex ion and cation scavenger, and an n-type material with a large absolute value of the Seebeck coefficient was obtained. In contrast, in Comparative Examples 1 and 2, the absolute value of the Seebeck coefficient of the obtained n-type material was smaller than that in Examples 1 and 3. Also, in Comparative Example 3, an n-type material could not be obtained.

[0089] (Example 5) <Fabrication of p-Type Material for Thermoelectric Conversion> A p-type material for thermoelectric conversion was fabricated in the same manner as in Example 1. The Seebeck coefficient of the obtained p-type thermoelectric conversion material (referred to as "Seebeck coefficient before doping treatment" in the table below) was 22.5 μV / K.

[0090] <Fabrication of n-Type Material for Thermoelectric Conversion> A dopant solution was prepared in the same manner as in Example 1, except that the molar concentration of potassium ferrocyanide in the dopant solution was changed to 0.05 M, the molar concentration of benzo-18-crown-6-ether was changed to 0.2 M, and the molar concentration of L-ascorbic acid was changed to 0.05 M. An n-type material for thermoelectric conversion was produced in the same manner as in Example 1, except that the obtained p-type material for thermoelectric conversion and the dopant solution were used. The Seebeck coefficient of the obtained n-type material for thermoelectric conversion (referred to as "Seebeck coefficient after doping treatment" in the following table) was -19.4 μV / K.

[0091] (Example 6) An n-type material for thermoelectric conversion was obtained in the same manner as in Example 5, except that the molar concentration of L-ascorbic acid in the dopant solution was changed to 0.12 M. In Example 6, the Seebeck coefficient of the p-type material for thermoelectric conversion before the doping treatment was 24.4 μV / K, and the Seebeck coefficient of the n-type material for thermoelectric conversion after the doping treatment was -21.0 μV / K.

[0092] (Example 7) An n-type material for thermoelectric conversion was obtained in the same manner as in Example 5, except that the molar concentration of L-ascorbic acid in the dopant solution was changed to 0.23 M. In Example 6, the Seebeck coefficient of the p-type material for thermoelectric conversion before the doping treatment was 23.8 μV / K, and the Seebeck coefficient of the n-type material for thermoelectric conversion after the doping treatment was -20.6 μV / K.

[0093] (Comparative Example 4) An n-type material for thermoelectric conversion was obtained in the same manner as in Example 5, except that L-ascorbic acid was not added to the dopant solution. In Comparative Example 4, the Seebeck coefficient of the p-type material for thermoelectric conversion before the doping treatment was 21.78 μV / K, and the Seebeck coefficient of the n-type material for thermoelectric conversion after the doping treatment was -23.0 μV / K.

[0094] The results of Examples 5 to 7 and Comparative Example 4 are shown in Table 3. In the table, the concentration of the complex ion, the concentration of the cation scavenger, and the concentration of the reducing agent indicate the concentrations of the respective components in the doping solution. Also, in the table, Reducing agent 1 indicates L-ascorbic acid.

[0095] (Durability test under high temperature and high humidity conditions) The n-type materials for thermoelectric conversion obtained in Examples 5 to 7 and Comparative Example 4 were allowed to stand in an environment of 85°C and 85% humidity, and were taken out after a predetermined time (500 hours, 1000 hours, 2000 hours, 3000 hours) had elapsed, and the Seebeck coefficient was measured. The measurement results at each time are shown in Table 3.

[0096]

Table 3

[0097] As shown in Table 3, in Examples 5 to 7, n-type conversion proceeded efficiently, and n-type materials with a large absolute value of the Seebeck coefficient were obtained. Also, in Examples 5 to 7, even under high temperature and high humidity conditions, the Seebeck coefficient was maintained at a value close to the initial value, and it was confirmed that the durability under high temperature and high humidity conditions was excellent. On the other hand, in Comparative Example 4, although n-type conversion proceeded by doping with the complex ion and the cation scavenger, the value of the Seebeck coefficient fluctuated greatly under high temperature and high humidity conditions, and after 1000 hours, the Seebeck coefficient became a positive value, making it difficult to use as an n-type material.

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, wherein the dopant contains ferrocyanide ions, an alkali metal cation, a cation scavenger that captures the alkali metal cation and dissociates the ferrocyanide ions, and a reducing agent that reduces trivalent iron ions, and the reducing agent contains at least one selected from the group consisting of ascorbic acid, ascorbate, reducing sugar, oxalic acid, and oxalate, an n-type material for thermoelectric conversion.

2. The n-type material for thermoelectric conversion according to claim 1, wherein the cation scavenger is a crown ether compound.

3. The n-type material for thermoelectric conversion according to claim 2, wherein the cation scavenger is a crown ether compound having a benzene ring in the molecule.

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

5. 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, wherein the dopant contains ferrocyanide ions, an alkali metal cation, a cation scavenger that captures the alkali metal cation and dissociates the ferrocyanide ions, and a reducing agent that reduces trivalent iron ions, and the reducing agent contains at least one selected from the group consisting of ascorbic acid, ascorbate, reducing sugar, oxalic acid, and oxalate, a dopant.

6. A method for producing an n-type material for thermoelectric conversion, comprising 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 ferrocyanide ions, an alkali metal cation, a cation scavenger that captures the alkali metal cation and dissociates the ferrocyanide ions, and a reducing agent that reduces trivalent iron ions, and the reducing agent contains at least one selected from the group consisting of ascorbic acid, ascorbate, reducing sugar, oxalic acid, and oxalate.

7. The step is, 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, and the method for producing an n-type material for thermoelectric conversion according to claim 6.

8. The process includes an impregnation step of impregnating a part of the 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 6, comprising the above steps.

9. A thermoelectric conversion element including the n-type material for thermoelectric conversion according to any one of claims 1 to 4.

10. The thermoelectric conversion element according to claim 9, further including the p-type material for thermoelectric conversion.

Images