Nanocarbon material

Abstract

This nanocarbon material comprises: a nanocarbon filament or band having a P-type conductive region doped with a P-type dopant and / or an N-type conductive region doped with an N-type dopant; and at least one adsorption compound selected from the group consisting of an aliphatic hydrocarbon compound having 20 or more carbon atoms and an aromatic hydrocarbon compound, the adsorption compound being adsorbed to the P-type conductive region and the N-type conductive region of the nanocarbon filament or band.

Description

Nanocarbon materials

[0001] This disclosure relates to nanocarbon materials.

[0002] In recent years, thermoelectric power generation elements have become known as solid-state devices that convert thermal energy into electrical energy. Thermoelectric power generation elements are being applied to applications such as space power supplies and thermoelectric conversion modules that operate using body heat (watches, wearable devices, etc.). Furthermore, nanocarbon materials such as carbon nanotube yarn and carbon nanotube ribbon are sometimes used in thermoelectric conversion elements, and various studies are being conducted on nanocarbon materials.

[0003] For example, Patent Document 1 discloses "a functional element in which spun yarn made of a conductive fibrous material is sewn into a sheet-like or strip-like insulating substrate, characterized in that the spun yarn is sewn so as to alternately penetrate the front and back surfaces of the insulating substrate, thereby forming a series cell structure of a π-type thermoelectric conversion element." Patent Document 2 also discloses that "the spun yarn is made of a composite material of one or more conductive nanofibers selected from the group consisting of carbon nanotubes (CNTs), carbon nanofibers (CNFs), graphene, graphene nanoribbons, fullerene nanowhiskers, and inorganic semiconductor whiskers, and an insulating or conductive flexible polymer."

[0004] International Publication No. 2016 / 151634, Patent No. 6529097

[0005] Conventionally, including in Patent Document 1, to impart N-type and P-type conductive regions to nanocarbon materials, conductive dopants are used to dope the nanocarbon material. However, since nanocarbon materials inherently possess P-type conductivity, doping with P-type dopants is sometimes used to enhance P-type conductivity. However, when oxygen from the atmosphere is adsorbed onto the N-type and P-type conductive regions of the doped dopants, the semiconductivity-imparting ability deteriorates. As a result, the carrier performance of the N-type or P-type conductive region decreases over time.

[0006] Therefore, the objective of this disclosure is to provide a nanocarbon material in which the deterioration of carrier performance over time is suppressed.

[0007] Means for solving the problem include the following embodiments: <1> A nanocarbon material comprising: a filamentous or strip-shaped nanocarbon having at least one of a P-type conductive region doped with a P-type dopant and an N-type conductive region doped with an N-type dopant; and at least one adsorbed compound selected from the group consisting of aliphatic hydrocarbon compounds having 20 or more carbon atoms and aromatic hydrocarbon compounds, adsorbed on the P-type conductive region and the N-type conductive region of the filamentous or strip-shaped nanocarbon; <2> The nanocarbon material according to <1>, wherein the aliphatic hydrocarbon compound is liquid paraffin; <3> The nanocarbon material according to <1> or <2>, wherein the aromatic hydrocarbon compound is polystyrene; <4> The nanocarbon material according to any one of <1> to <3>, wherein the P-type dopant and the N-type dopant are dopants having at least one of an aliphatic hydrocarbon group and an aromatic group.

[0008] According to this disclosure, it is possible to provide a nanocarbon material in which the deterioration of carrier performance over time is suppressed.

[0009] The following describes embodiments that are examples of this disclosure. These descriptions and examples are illustrative and do not limit the scope of the invention. In numerical ranges described stepwise in this specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Also, in numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with the value shown in the examples. Each component in the composition may contain multiple types of the corresponding substance. When referring to the amount of each component in the composition, if there are multiple types of the substance corresponding to each component in the composition, unless otherwise specified, it means the total amount of the multiple types of substances present in the composition.

[0010] <Nanocarbon Material> The nanocarbon material of this disclosure comprises a filamentous or strip-shaped nanocarbon having at least one of a P-type conductive region doped with a P-type dopant and an N-type conductive region doped with an N-type dopant, and at least one adsorbed compound selected from the group consisting of aliphatic hydrocarbon compounds having 20 or more carbon atoms and aromatic hydrocarbon compounds, adsorbed on the P-type conductive region and the N-type conductive region of the filamentous or strip-shaped nanocarbon.

[0011] The nanocarbon material of this disclosure has the above-mentioned specific adsorbent compound adsorbed onto each conductive region of the nanocarbon filament or strip, where each conductive dopant is doped. This makes it difficult for the dopant to come into contact with oxygen adsorbed on each conductive region. In addition, the adsorption of oxygen onto each conductive region is suppressed itself. Therefore, the deterioration of the semiconductivity is suppressed.

[0012] From the above, the nanocarbon material of this disclosure suppresses the deterioration of carrier performance over time. Here, as a technique to prevent contact between the dopant and oxygen, a technique is also conceivable in which a coating layer is provided on the nanocarbon filamentous or strip-shaped material, thereby inhibiting oxidative adsorption itself with the coating layer. However, with this technique, if damage or peeling of the coating layer occurs, the oxygen inhibition ability decreases, making it difficult to suppress the deterioration of carrier performance over time. In contrast, the nanocarbon material of this disclosure adsorbs the above-mentioned specific adsorbent compound that prevents contact between the dopant and oxygen onto the nanocarbon filamentous or strip-shaped material, so the adsorbed compound is less likely to detach over time. Therefore, compared to the technique of providing a coating layer, the nanocarbon material of this disclosure has a higher ability to suppress the deterioration of carrier performance over time.

[0013] The following provides a detailed explanation of nanocarbon materials.

[0014] (Nanocarbon filamentous or strip-like material) The nanocarbon filamentous or strip-like material has at least one of a P-type conductive region doped with a P-type dopant and an N-type conductive region doped with an N-type dopant.

[0015] -Nanocarbon- As the nanocarbon constituting the filamentous or strip-like nanocarbon, carbon nanotubes (CNTs) are preferred. In other words, the filamentous or strip-like nanocarbon is preferably a filamentous or strip-like carbon nanotube. The carbon nanotube may be a single-walled carbon nanotube (SWCNT) in which a single carbon film (graphene sheet) is wound into a cylindrical shape. The carbon nanotube may also be a multi-walled carbon nanotube (MWCNT), such as a double-walled carbon nanotube, triple-walled carbon nanotube, or quadruple-walled carbon nanotube, in which two graphene sheets are wound concentrically. Considering the thermoelectric properties, the carbon nanotube is preferably 10 layers or less. Single-walled carbon nanotubes are preferred because they easily provide high thermoelectric properties. Multi-walled carbon nanotubes are preferred because they are inexpensive and have excellent mass-producibility. Single-walled carbon nanotubes and multi-walled carbon nanotubes can also be used in mixture form. Furthermore, the carbon nanotube may be a metallic type, a semiconductor type, or a mixture of both. The method for producing carbon nanotubes is not particularly limited. Carbon nanotubes can be produced by methods such as arc discharge, chemical vapor deposition (CVD), and laser ablation. Commercially available carbon nanotubes may also be used.

[0016] Nanocarbon may also be graphene. By inserting carriers between two layers of graphene, graphene can be used as a semiconductor material.

[0017] Other examples of nanocarbons include carbon nanorods, carbon nanowires, graphene, and fullerenes.

[0018] - Dopant - One method for doping nanocarbon filaments or strips with a dopant is to immerse the heated nanocarbon filaments or strips in a dopant solution. This method allows for simple and low-cost doping. After doping, washing is performed. However, dopant doping may also be performed by methods such as coating or brushing.

[0019] --P-type dopant-- A P-type dopant refers to a dopant in which the Seebeck coefficient in the filamentous or strip-like region of the doped nanocarbon is a positive value, and examples include nonionic compounds or ionic compounds. In particular, when the solvent of the P-type dopant solution is water, a nonionic compound is preferred as the P-type dopant. On the other hand, when the solvent of the P-type dopant solution is an organic solvent, an ionic compound is preferred as the P-type dopant.

[0020] Examples of nonionic compounds that are P-type dopants include tetracyanoquinodimethane (TCNQ) derivatives (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, 2,5-dimethyl-7,7,8,8-tetracyanoquinodimethane, 2-fluoro-7,7,8,8-tetracyanoquinodimethane, 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane, etc.), benzoquinone derivatives (2,3-dichloro-5,6-dicyano-p-benzoquinone, tetrafluoro-1,4-benzoquinone, etc.), quinoxaline derivatives (5,8H-5,8-bis(dicyanomethylene)quinoxaline, dipyradino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitride, etc.), Examples include 9H-carbazole, 9H-carbazole-4-ol, and pyrazine.

[0021] Examples of ionic compounds that are P-type dopants include perchlorate ions (ClO2). ４－ ), permanganate ion (MnO ４－ ), iodate ion (IO ３－ ), thiocyanate ion (SCN － ), hexafluorophosphate ion (PF ６－), tetrafluoroborate ion (BF ４－ ), trifluoromethanesulfonate anion (TfO － ), bis(trifluoromethanesulfonyl)amine anion (TFSI － ), iodide ion (I － ), bromide ion (Br － ), chloride ion (Cl － ), nitrate ion (NO ３－ ), or metal salts and hydroacids of tosylate ion (Tos － ). Examples of the metal salts include silver salts and copper salts.

[0022] - - N-type dopant - - An N-type dopant means a dopant for which the Seebeck coefficient in the region of the filamentous or带状 region of the doped nanocarbon is a negative value, and examples include nonionic compounds or ionic compounds. In particular, when the solvent of the N-type dopant solution is water, nonionic compounds are preferred as the N-type dopant. On the other hand, when the solvent of the N-type dopant solution is an organic solvent, ionic compounds are preferred as the N-type dopant.

[0023] As the nonionic compound that is an N-type dopant, polyalkyleneimine is preferred. As the polyalkyleneimine, polyalkyleneimine having a structural unit with an alkylene group having 1 to 6 carbon atoms (preferably 1 to 4 carbon atoms, more preferably 1 to 2 carbon atoms) is preferred, and polyethyleneimine is more preferred.

[0024] Examples of the ionic compound that is an N-type dopant include alkali metal salts (such as salts of lithium, sodium, potassium, or cesium), and alkylammonium salts (such as salts of tetraethylammonium ion or tetrabutylammonium ion). Among these, as the ionic compound, alkylammonium halide salts are preferred, and the following compounds are exemplified.

[0025]

[0026] Examples of N-type dopants include complexes of alkali metal salts and cyclic ethylene oxides. Ions contained in alkali metal salts include hydroxyl ions (OH). － ), alkoxy ions (CH ３ O － ,CH ３ CH ２ O － i-Pro － and t-BuO － (etc.), thioions (SH － and alkylthioions (CH ３ S － and C ２ H ５ S － (etc.), cyanuryl ions (CN － ), carboxyl ion (CH ３ COO － Examples include the alkali metals contained in alkali metal salts, such as lithium, sodium, and potassium. Examples of cyclic ethylene oxides include crown ethers.

[0027] Examples of N-type dopants include phosphine compounds such as triphenylphosphine, trioctylphosphine, and 1,3-bis(diphenylphosphine)propane.

[0028] --Suitable Dopants-- If the P-type dopant and N-type dopant have a structure similar to that of the aliphatic hydrocarbon compound or aromatic hydrocarbon compound used as the adsorbent, the deterioration of carrier performance over time is more easily suppressed. For this reason, it is preferable that the P-type dopant and N-type dopant are dopants (polyalkyleneimines, triphenylphosphines, etc.) having at least one of an aliphatic hydrocarbon group (such as an alkylene group) and an aromatic group (such as a phenyl group).

[0029] --Dopant Solution-- The solvent of the dopant solution preferably contains water as a main component from the perspective of reducing environmental impact. The solvent containing water as a main component may contain water-soluble organic solvents such as alcohol (methanol, ethanol, propanol, etc.). Note that water being the main component means, for example, that the proportion of water is 50% by mass (preferably 70% by mass or 90% by mass) or more based on the total solvent. However, the solvent of the dopant solution may have an organic solvent as the main component. Examples of the organic solvent include alcohol (ethanol, propanol, etc.), acetone, methyl ethyl ketone, butyl acetate, etc. An organic solvent being the main component means, for example, that the proportion of the organic solvent is 50% by mass (preferably 70% by mass or 90% by mass) or more based on the total solvent.

[0030] (Adsorption Compound) The adsorption compound is at least one selected from the group consisting of aliphatic hydrocarbon compounds having 20 or more carbon atoms and aromatic hydrocarbon compounds. The adsorption compound is preferably selected from non-polar compounds that have no polar groups and do not react with the dopant and have no influence on the semi-conductive property imparting ability of the dopant. Note that examples of the polar group include acidic polar groups (carboxy group, carboxylate group, sulfo group, sulfonate group, phosphate group, phosphate salt group, formyl group, phenol group (phenolic hydroxyl group), etc.), neutral polar groups (hydroxy group, amide group, cyano group, etc.), basic polar groups (amino group, imino group, quaternary ammonium group, etc.).

[0031] -Aliphatic Hydrocarbon Compound- Examples of the aliphatic hydrocarbon compound include saturated or unsaturated hydrocarbon compounds such as liquid paraffin, isoparaffin, α-olefin oligomer, and polybutene.

[0032] -Aromatic Hydrocarbon Compound- Examples of the aromatic hydrocarbon compound include benzene, polycyclic aromatic compounds, polynuclear aromatic hydrocarbon compounds, etc.

[0033] Polycyclic aromatic compounds are compounds in which two or more aromatic rings are fused together. Specific examples of polycyclic aromatic compounds include naphthalene, fluorene, phenanthrene, anthracene, triphenylene, tetraphenylene, pyrene, chrysene, and tetracene. Polycyclic aromatic compounds may also be derivatives of these compounds in which halogen groups or aliphatic hydrocarbon groups (such as alkyl groups having 1 to 10 carbon atoms) are substituted.

[0034] Polynuclear aromatic hydrocarbon compounds are compounds that contain two or more aromatic rings, which are linked to each other by carbon-carbon bonds or by linking groups such as methylene, ethylene, vinylene, and ethynylene groups. Specific examples of polynuclear aromatic compounds include biphenyl and terphenyl. Polynuclear aromatic compounds may also be derivatives of these compounds in which halogen groups or aliphatic hydrocarbon groups (such as alkyl groups having 1 to 10 carbon atoms) are substituted.

[0035] Aromatic hydrocarbon compounds may be compounds in which two or more of the above-mentioned benzene, polycyclic aromatic compounds, and polynuclear aromatic hydrocarbon compounds are linked by carbon-carbon bonds, or linked via linking groups such as methylene groups, ethylene groups, vinylene groups, and ethynylene groups.

[0036] Aromatic hydrocarbon compounds also include aromatic hydrocarbon polymers such as polystyrene.

[0037] Among these, from the viewpoint of suppressing the deterioration of carrier performance over time, preferred adsorbent compounds include aliphatic hydrocarbon oils that are liquid at 25°C, such as liquid paraffin (paraffin with the highest purity from which impurities such as aromatic hydrocarbons and sulfur compounds have been removed); aromatic hydrocarbon monomers with 3 to 6 aromatic rings, such as anthracene and benzopyrene; and aromatic hydrocarbon polymers, such as polystyrene, with liquid paraffin and polystyrene being more preferred. The adsorbent compound may be used alone or in combination of two or more.

[0038] The confirmation that adsorbed compounds are present on the nanocarbon filamentous or strip-like material is as follows: For example, the presence or absence of the target adsorbed compound can be confirmed by detecting it using secondary ion mass spectrometry (SIMS).

[0039] - Method for adsorbing adsorbed compounds - A preferred method for adsorbing adsorbed compounds onto nanocarbon filamentous or strip-shaped bodies (conductive regions of each type) is, for example, immersion in a coating solution in which the adsorbed compound is dispersed or dissolved in a solvent (water or organic solvent, etc.), a liquid of the adsorbed compound that is liquid at room temperature (25°C), or a liquid in which the adsorbed compound is liquefied by heating (for example, heating up to 150°C). This is because the adsorption treatment of the adsorbed compound can be carried out simply and at low cost. After the adsorption treatment, washing may or may not be performed. In addition, the adsorption treatment of the adsorbed compound may be carried out by methods other than immersion, such as coating or brush application.

[0040] (Applications) The nanocarbon materials disclosed herein can be applied to a variety of applications. For example, the carbon materials disclosed herein can be suitably applied as carbon materials for connecting thermoelectric elements in thermoelectric conversion modules. In addition, the carbon materials disclosed herein can be suitably applied to semiconductor applications.

[0041] Examples are described below, but this disclosure is not limited to these examples. In the following description, unless otherwise specified, "parts" and "%" all refer to mass.

[0042] <Example 1> Carbon nanotube filaments (hereinafter referred to as "CNT filaments") were doped with polyethyleneimine. After doping, the N-type CNT filaments were immersed in liquid paraffin as an adsorbent compound for 24 hours, and then washed and dried with n-hexane. The Seebeck coefficient of the liquid paraffin-treated N-type CNT filaments obtained immediately after the procedure was measured, and the initial Seebeck coefficient was -65.1 (μV / K). On the other hand, the obtained liquid paraffin-treated N-type CNT filaments were left in the air at room temperature (25°C), and the change in the Seebeck coefficient over time was observed. As a result, the Seebeck coefficient after 4 months was -71.5 (μV / K), maintaining the N-type performance.

[0043] <Comparative Example 1> When the Seebeck coefficient of the N-type CNT yarn obtained in Example 1 was measured without immersion in liquid paraffin, the initial Seebeck coefficient was -65.1 (μV / K). On the other hand, when the change in the Seebeck coefficient over time was checked for the obtained N-type CNT yarn in the same manner as in Example 1, the Seebeck coefficient decreased by 60-30% after about one month (from -65 (μV / K) to -40 to -10 (μV / K)). After four months, the Seebeck coefficient became +2 (μV / K), resulting in a conversion to P-type.

[0044] <Example 2> Water-soluble oil-treated N-type CNT yarn was obtained in the same manner as in Example 1, except that a water-soluble oil (a compound whose main skeleton is an aliphatic hydrocarbon having hydroxyl groups and some ether groups at the terminal groups) was used as the adsorbent compound. The Seebeck coefficient of the water-soluble oil-treated N-type CNT yarn was then investigated at the initial and temporal stages.

[0045] <Example 3> Carbon nanotube filaments (hereinafter referred to as "CNT filaments") were doped with triphenylphosphine. After doping, the N-type CNT filaments were immersed in an acetone solution of polystyrene as an adsorbent compound for 24 hours, and then washed and dried with acetone. The Seebeck coefficient of the polystyrene-treated N-type CNT filaments obtained immediately afterward was measured, and the initial Seebeck coefficient was -40 (μV / K). On the other hand, the obtained polystyrene-treated N-type CNT filaments were left in the air at room temperature (25°C), and the change in the Seebeck coefficient over time was confirmed. As a result, the Seebeck coefficient after 3 weeks was -17 (μV / K), maintaining the N-type performance.

[0046] <Comparative Example 2> When the Seebeck coefficient of the N-type CNT yarn obtained in Example 1 was measured without immersion in an acetone solution of polystyrene, the initial Seebeck coefficient was -40 (μV / K). On the other hand, when the change in the Seebeck coefficient over time was checked for the obtained N-type CNT yarn in the same manner as in Example 3, the Seebeck coefficient became +30 to +20 (μV / K) after one week, indicating a shift to P-type.

[0047] <Example 4> Doped N-type CNT yarn was immersed in a water-soluble oil (the same water-soluble oil as in Example 2) as an adsorbent compound for 24 hours, and then washed / dried with n-hexane to obtain water-soluble oil-treated N-type CNT yarn in the same manner as in Example 2. The Seebeck coefficient of the water-soluble oil-treated N-type CNT yarn was then investigated at the initial and time-dependent stages.

[0048] The Seebeck coefficient was measured as follows: One end of a CNT yarn was heated to create a temperature difference between the two ends of the sample. The resulting thermoelectric voltage was then measured using a thermoelectric property measuring device, and the Seebeck coefficient was calculated.

[0049]

[0050] From the above results, it can be seen that the carbon material of this embodiment shows less variation in the Seebeck coefficient between the initial stage and over time compared to the carbon material of the comparative example. This indicates that the carbon material of this embodiment suppresses the deterioration of carrier performance over time.

[0051] Furthermore, the disclosure of Japanese Patent Application No. 2025-004409 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted as being incorporated by reference.

Claims

1. A nanocarbon material comprising: a filamentous or strip-shaped nanocarbon having at least one of a P-type conductive region doped with a P-type dopant and an N-type conductive region doped with an N-type dopant; and at least one adsorbed compound selected from the group consisting of aliphatic hydrocarbon compounds having 20 or more carbon atoms and aromatic hydrocarbon compounds, adsorbed on the P-type conductive region and the N-type conductive region of the nanocarbon filamentous or strip-shaped nanocarbon.

2. The nanocarbon material according to claim 1, wherein the aliphatic hydrocarbon compound is liquid paraffin.

3. The nanocarbon material according to claim 1, wherein the aromatic hydrocarbon compound is polystyrene.

4. The nanocarbon material according to claim 1, wherein the P-type dopant and the N-type dopant are dopants having at least one of an aliphatic hydrocarbon group and an aromatic group.

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