JP5599095B2 - Method for producing organic-inorganic hybrid thermoelectric material - Google Patents

Description

The present invention, organic - process for producing inorganic hybrid thermoelectric material. More particularly, and thermoelectric power generation using the Seebeck effect, organic Ru is used in so-called thermoelectric conversion such as electronic cooling by Peltier effect - a process for producing inorganic hybrid thermoelectric material.

  In recent years, interest in global environmental issues and effective use of energy resources has increased. In addition, a part of the energy supplied to the current society is discharged into the environment as heat without being used in the process of transportation, storage, conversion and use, and the amount is about 2/3 of the total primary supply energy. It is said to extend. In addition, fossil fuels account for 90% of the energy consumption, and the problem that fossil fuel resources will be depleted in the 21st century has also occurred.

  One of solutions for overcoming such environmental problems and energy problems is thermoelectric conversion technology. If this technology is used, there is a possibility that it can be used as “energy recycling” that can directly upgrade unused thermal energy to electrical energy that is easy to use. With thermoelectric conversion technology, when a temperature difference is given to two different types of metals or thermoelectric conversion materials such as p-type semiconductors and n-type semiconductors, thermal energy is directly generated using the Seebeck effect that generates thermoelectromotive force at both ends. This technology converts power into electric power, has no moving parts such as motors and turbines, and has an excellent feature that no waste is generated.

Thermoelectric materials (also called thermoelectric conversion materials) used in thermoelectric conversion technology are materials that can mutually convert heat energy and electrical energy, and are used as thermoelectric cooling elements and thermoelectric power generation elements. It is a material that constitutes. And in evaluating the characteristic in a thermoelectric material, the physical internal factor (TPF) and thermoelectric figure of merit (ZT) which are represented by the following formulas (I) and (II) are used. Here, S represents the Seebeck coefficient, σ represents electrical conductivity (conductivity), κ represents thermal conductivity, and T represents absolute temperature. Further, S ² σ in the formulas (I) and (II) is also called a power factor.

  From formula (I) and formula (II), it can be seen that in order to increase the thermoelectric conversion performance of the thermoelectric material, the Seebeck coefficient and electrical conductivity should be increased and the thermal conductivity should be decreased. On the other hand, these physical quantities cannot be improved individually in one material, but when one characteristic is improved, one of the other characteristics is reduced. For example, the electrical conductivity and Seebeck constant are increased. If so, the thermal conductivity often increases accordingly.

  In general, an inorganic material (inorganic thermoelectric material) has a problem that the Seebeck coefficient and electrical conductivity are high and the thermal conductivity is high. On the other hand, an organic material (organic thermoelectric material) has an advantage of low thermal conductivity. By hybridizing such an inorganic material and an organic material, two types of properties of the organic material and the inorganic material can be developed at the same time. The thermoelectric conversion has a low thermal conductivity and a high Seebeck coefficient and electrical conductivity. It is considered possible to synthesize a thermoelectric material having a function. And development of the organic-inorganic hybrid thermoelectric material which hybridized the inorganic material and the organic material is advanced (for example, refer patent document 1).

Japanese Patent No. 4296236

  However, conventional thermoelectric materials have a high Seebeck coefficient and electrical conductivity as well as low thermal conductivity when hybridized, and it has been difficult to exhibit stable thermoelectric properties.

The present invention has been made in view of the above problems, low with heat conductivity, high Seebeck has a coefficient and electric conductivity, good thermal conductive properties and stable organic that can be exerted - The object is to provide a method for producing an inorganic hybrid thermoelectric material.

The method for producing an organic-inorganic hybrid thermoelectric material according to the present invention has an average particle diameter of 1 to 100 nm, Bi— (Te, Se), Si—Ge, Pb—Te, GeTe—AgSbTe, Co, Ir, Ru) -Sb-based and (Ca, Sr, Bi) Co ₂ O _5- based inorganic particles that are substantially free of a protective agent and correspond to the inorganic particles. After mixing the precursor, the protective agent, and the solvent, heated above the decomposition temperature of the protective agent to prepare a dispersion solution of the inorganic particles, the inorganic particles obtained by purifying and dispersing the dispersion solution, Polyaniline or derivative thereof, polypyrrole or derivative thereof, polythiophene or derivative thereof, polyphenylene vinylene derivative, polyparaphenylene derivative, polyacene or derivative thereof Body, and characterized by mixing at least one organic thermoelectric material selected from these copolymers.

  The method for producing an organic-inorganic hybrid thermoelectric material according to the present invention is the above-described present invention, wherein the organic thermoelectric material is polyaniline, the polyaniline, the inorganic particles, camphorsulfonic acid, naphthalenesulfonic acid, toluenesulfonic acid. And m-cresol is mixed with at least one selected from phosphoric acid.

In the method for producing an organic-inorganic hybrid thermoelectric material according to the present invention, the inorganic particles are bismuth telluride (Bi ₂ Te ₃ ) in the present invention described above, and the precursor corresponding to the inorganic particles is tellurium tetrachloride or Tetraethoxytellurium and bismuth chloride, the protective agent is polyvinylpyrrolidone (PVP), the solvent is tetraethylene glycol, and the decomposition temperature of the protective agent is 230 ° C.

  The method for producing an organic-inorganic hybrid thermoelectric material according to the present invention is characterized in that it is formed into a film shape in the above-described present invention.

The organic-inorganic hybrid thermoelectric material obtained in the present invention uses inorganic particles having an average particle diameter of 1 to 100 nm and substantially no protective agent as the inorganic thermoelectric material. It is able to efficiently enter and disperse into the gaps between materials, stably maintain excellent thermoelectric properties, and have high Seebeck coefficient, electrical conductivity, and low thermal conductivity, so that it is a physical internal factor (TPF) And a thermoelectric material having an excellent thermoelectric figure of merit (ZT). In addition, since an organic thermoelectric material, which is an organic polymer material, is used as a constituent material, it becomes a thermoelectric material with good workability, for example, a thin film can be easily formed, and a thermoelectric conversion having good thermoelectric properties. Elements and thermoelectric conversion modules can be easily manufactured, and in addition, they can be applied to various products using thermoelectric conversion technology such as thermal sensors and thermoelectric cooling devices.

In addition , since the thermoelectric conversion element uses the organic-inorganic hybrid thermoelectric material obtained in the above-described present invention, the thermoelectric conversion element enjoys the effect of such a thermoelectric material, stably maintains excellent thermoelectric characteristics, and has high Seebeck. By having a coefficient, electrical conductivity, and low thermal conductivity, a thermoelectric conversion element having excellent physical internal factor (TPF) and thermoelectric figure of merit (ZT) is obtained.

  In the method for producing an organic-inorganic hybrid thermoelectric material according to the present invention, the average particle diameter is 1 to 100 nm, and inorganic particles substantially free of a protective agent are mixed with a specific organic thermoelectric material. Inorganic particles with a small average particle diameter are dispersed in the matrix of organic thermoelectric material, and the inorganic particles are coordinated to the constituent elements of the organic thermoelectric material, and have a high Seebeck coefficient, electrical conductivity, and low thermal conductivity. Thus, a thermoelectric material having excellent physical internal factor (TPF) and thermoelectric figure of merit (ZT) can be provided efficiently and simply.

FIG. 3 is a diagram showing the Seebeck coefficient of the organic-inorganic hybrid thermoelectric material obtained in Example 1. FIG. 3 is a diagram showing the electrical conductivity of the organic-inorganic hybrid thermoelectric material obtained in Example 1. FIG. 3 is a diagram showing a thermoelectric figure of merit (ZT) of the organic-inorganic hybrid thermoelectric material obtained in Example 1. FIG. 3 is a diagram showing the power factor of the organic-inorganic hybrid thermoelectric material obtained in Example 1. It is the figure which showed the Seebeck coefficient of the organic-inorganic hybrid thermoelectric material obtained by the comparative example 1. FIG. 3 is a diagram showing the electrical conductivity of the organic-inorganic hybrid thermoelectric material obtained in Comparative Example 1. It is the figure which showed the thermoelectric figure of merit (ZT) of the organic-inorganic hybrid thermoelectric material obtained in Comparative Example 1. FIG. 4 is a diagram showing the power factor of the organic-inorganic hybrid thermoelectric material obtained in Comparative Example 1. 6 is a graph showing the electrical conductivity of the organic-inorganic hybrid thermoelectric material obtained in Example 4. FIG. It is the figure which showed the Seebeck coefficient of the organic-inorganic hybrid thermoelectric material obtained in Example 5. 6 is a graph showing the electrical conductivity of the organic-inorganic hybrid thermoelectric material obtained in Example 5. FIG. 6 is a graph showing a thermoelectric figure of merit (ZT) of an organic-inorganic hybrid thermoelectric material obtained in Example 5. FIG. 6 is a diagram showing the power factor of the organic-inorganic hybrid thermoelectric material obtained in Example 5. FIG.

  Hereinafter, one embodiment of the present invention will be described. The organic-inorganic hybrid thermoelectric material of the present invention has an average particle diameter of 1 to 100 nm, and is basically composed of inorganic particles substantially free of a protective agent and an organic thermoelectric material.

The inorganic particles that can be used in the organic-inorganic hybrid thermoelectric material (hereinafter sometimes simply referred to as “thermoelectric material”) according to the present invention are an inorganic thermoelectric material having a high Seebeck coefficient and a high electrical conductivity. Bi- (Te, Se) system, Si-Ge system, Pb-Te system, GeTe-AgSbTe system, (Co, Ir, Ru) -Sb system, (Ca, Sr, Bi) Co ₂ O ₅ system, etc. Tellurization which is excellent in these characteristics, can be an n-type or p-type thermoelectric material, and can be well hybridized with an organic thermoelectric material to be a p-type thermoelectric material Bismuth (Bi ₂ Te ₃ ) is preferably used.

  The inorganic particles used in the organic-inorganic hybrid thermoelectric material according to the present invention have an average particle size of 1 to 100 nm, and the average particle size is in such a range (a relatively small particle size range in the nano-order). As a result, the density of states (DOS) increases, the thermoelectromotive force increases, and the thermoelectric figure of merit (ZT) represented by the formula (II) significantly increases compared to the bulk, thereby improving the thermoelectric characteristics. be able to. In addition, dispersibility in organic thermoelectric materials, which are polymers, has improved, stable thermoelectric properties, and even when hybridized, the characteristic advantages of inorganic thermoelectric materials (high Seebeck coefficient and electrical conductivity) Rate). On the other hand, if the average particle diameter exceeds 100 nm, an increase in the density of states (DOS) cannot be expected, the dispersibility is poor, and the thermoelectric characteristics become unstable. The average particle diameter is more preferably 1 to 50 nm, further preferably 1 to 20 nm, and particularly preferably 1 to 10 nm. The “average particle size” in the present invention may be an average value of the particle sizes of an appropriate number (for example, 100 particles) of primary particles observed by TEM, SEM or the like. Here, the index for evaluating the characteristics of the thermoelectric material is the physical internal factor (TPF) or the thermoelectric figure of merit (ZT) calculated by the formulas (I) and (II) as described above. In the hybrid thermoelectric material of the present invention, a high Seebeck coefficient and electrical conductivity indicate that at least one of the Seebeck coefficient and electrical conductivity is increased. Therefore, both the Seebeck coefficient and the electrical conductivity may be high in some cases, but one value becomes high, and as a result, the physical internal factor calculated by the formula (I) and the formula (II). (TPF) and thermoelectric figure of merit (ZT) become high and may show excellent thermoelectric characteristics.

  Further, such inorganic particles are substantially free of a protective agent. When applying chemically synthesized inorganic particles to thermoelectric conversion materials, it becomes difficult to deliver carriers due to the protective agent present on the surface of the inorganic particles, which adversely affects thermoelectric properties. Ensure that the particles are substantially free of protective agents. Thereby, it is possible to improve the thermoelectric characteristics in combination with good carrier delivery and an average particle diameter of 1 to 100 nm. The term “protective agent” as used herein means a protective agent generally used in the synthesis of inorganic particles, such as polyvinylpyrrolidone (PVP), polyethyleneimine (PEI), polyacrylic acid, polyvinylamine, polyvinyl alcohol, so-called wedges. (Wedge) type coordination polymer and the like.

  In the present invention, “substantially free” excludes the act of intentionally adding a trace amount of a protective agent that does not affect the effect of the invention so that it does not fall within the technical scope of the present invention. However, even when such a small amount of protective agent is intentionally added, the purpose is to make it belong to the technical scope of the present invention. For example, the content of the protective agent is 0.1 mass of the whole thermoelectric material. %, Preferably the content of the protective agent is 0.01% by mass or less, and more preferably, it contains no protective agent at all (the content is 0% by mass).

  In many cases, a protective agent is required in the synthesis of the inorganic particles. However, when used in the thermoelectric material according to the present invention, the decomposition temperature of the protective agent (for example, about about polyvinylpyrrolidone is used in the synthesis stage). 230 ° C.) or higher to remove the protective agent so that it does not substantially exist.

  For the synthesis of inorganic particles, for example, a precursor corresponding to the inorganic particles, a protective agent and a solvent are mixed, and then heated above the decomposition temperature of the protective agent (preferably heated reflux) to prepare a dispersion solution of inorganic particles, It can be obtained by purifying the dispersion solution into powder. Here, in order to suitably control the average particle diameter of the inorganic particles in the range of 1 to 100 nm, it is necessary to suppress aggregation and appropriately remove the decomposition products, for example, the number of moles of the precursor The molar ratio r to the number of moles of the monomer constituting the protective agent relative to the sum is the sum of the number of moles of the monomer constituting the protective agent / the number of moles of the precursor = 1 or more (preferably 2 to 10) (the average particle size is In the case of 1 to 10 nm, r = 4 or more), heating or heating reflux is performed in a short time (approximately 30 to 90 minutes), and forced cooling such as water cooling is not performed after completion of heating or heating reflux, Natural cooling by air cooling or the like is preferable.

  For purification, the solvent is replaced with an alcohol such as ethanol by centrifugation and the decomposition product of the protective agent is removed. Thereafter, the solvent alcohol may be removed and dried.

Here, for example, when synthesizing bismuth telluride (Bi ₂ Te ₃ ), precursors corresponding to inorganic particles (bismuth telluride) are made of tellurium tetrachloride or tetraethoxytellurium (or both), and bismuth chloride. These are mixed with polyvinylpyrrolidone (PVP) which is a protective agent and tetraethylene glycol (TEG) as a solvent, and heated at 230 ° C. or higher which is a decomposition temperature of polyvinylpyrrolidone (PVP) under a nitrogen stream (preferably By heating and refluxing and purifying, bismuth telluride having an average particle diameter of 1 to 100 nm can be suitably produced. In the purification, the solvent is substituted from tetraethylene glycol (TEG) to an alcohol such as ethanol during centrifugation under argon, and the decomposed polyvinyl pyrrolidone (PVP) is removed. And the thermoelectric material of a desired average particle diameter can be obtained by drying, such as reduced pressure drying. The molar ratio r (number of moles of monomers constituting the protective agent / sum of moles of precursors) is preferably 4 or more.

  Organic thermoelectric materials that can be used in the organic-inorganic hybrid thermoelectric material according to the present invention include, for example, polyaniline or a derivative thereof, polypyrrole or a derivative thereof, polythiophene or a derivative thereof, a polyphenylene vinylene derivative, a polyparaphenylene derivative, a polyacene or a derivative thereof Derivatives and copolymers of these materials can be mentioned, and in particular, polyaniline and polypyrrole, which are conductive polymers and excellent in thermoelectric properties, are preferably used, and the thermoelectric power of inorganic particles is infinite. N-type polyacene, which can be extracted into the following, may be used. In addition, the synthesis | combination of this organic thermoelectric material should just implement a conventionally well-known polymerization method, and is not restrict | limited in particular.

  The molar ratio R between the inorganic particles and the organic thermoelectric material R (R is the molar ratio of the organic thermoelectric material to the inorganic particles, R = organic thermoelectric material / inorganic particles) is not particularly limited, and depends on the required characteristics and the like. What is necessary is just to adjust suitably, but it is preferable to set it as R = 0.001-1000, and it is especially set as R = 1-500 in order to make the workability of the organic-inorganic hybrid thermoelectric material obtained excellent. preferable.

  The organic-inorganic hybrid thermoelectric material according to the present invention can be obtained by mixing the above-described inorganic particles and the organic thermoelectric material. By mixing the inorganic particles and the organic thermoelectric material, the inorganic particles having an average particle diameter of 1 to 100 nm are dispersed in the matrix of the organic thermoelectric material, and the inorganic particles are coordinated to the constituent elements of the organic thermoelectric material. Here, in the present invention, since the average particle diameter is thus small, the inorganic particles can efficiently enter the gaps between the organic thermoelectric materials, and aggregation is unlikely to occur. Therefore, it has a high Seebeck coefficient, electrical conductivity, and low thermal conductivity, and becomes a thermoelectric material having excellent physical internal factor (TPF) and thermoelectric figure of merit (ZT). For example, when the organic thermoelectric material is polyaniline, inorganic particles are coordinated with nitrogen (N) in the polyaniline.

  The mixing of the inorganic particles and the organic thermoelectric material is preferably performed by mixing in a solvent in which the organic thermoelectric material can be dissolved or dispersed. If the organic thermoelectric material is dissolved or dispersed in a solvent and mixed with inorganic particles, and the solvent is removed after mixing to obtain the thermoelectric material, the inorganic particles can be uniformly dispersed in the organic thermoelectric material. .

  In addition, the selection of the solvent is not limited to the fact that the organic thermoelectric material can be dissolved, but it does not adversely affect the coordination of the inorganic particles to the organic thermoelectric material (a solvent that does not cause strong interaction with the inorganic particles). Is preferably used. In the case of the above-described organic thermoelectric material, at least one of 1,4-dioxane, tetrahydrofuran (THF) and the like can be used in the case of polyaniline or a derivative thereof, and 1,4 in the case of polypyrrole or a derivative thereof. -At least 1 sort (s), such as a dioxane, tetrahydrofuran (THF), n-butanol, and ethyl acetate, can be used.

  Of the organic thermoelectric materials listed above, polythiophene, polyphenylene vinylene, polyparaphenylene, and polyacene are very difficult to dissolve in a solvent, so alkyl groups, carboxylic acid groups, sulfonic acid groups, or esters thereof have been introduced. Derivatives are preferably used. In addition, since polyacene cannot be dissolved in a solvent, it is preferable that after mixing with inorganic particles in the state of a precursor (resole resin), heat treatment is performed so that the resole resin is polyacene.

  As the organic thermoelectric material, a material doped with a dopant such as camphorsulfonic acid, naphthalenesulfonic acid, toluenesulfonic acid, phosphoric acid or the like may be used as necessary. These may be used individually by 1 type and may be used in combination of 2 or more type. In particular, when polyaniline is used as the organic thermoelectric material, when mixed with inorganic particles, camphorsulfonic acid, naphthalenesulfonic acid, toluenesulfonic acid, phosphoric acid (preferably camphorsulfonic acid) and m- By mixing cresols together (direct coordination method), inorganic particles can be coordinated efficiently without being adversely affected by solvents and protective agents, and filming such as casting can be easily performed. Can do.

  The organic-inorganic hybrid thermoelectric material obtained by the direct coordination method is free of impurities (1,4-dioxane, tetrahydrofuran (THF) in the solution coordination method described later, and water-soluble polyaniline in the water-soluble polyaniline method). In addition, since the dispersibility of the inorganic particles is high, stable thermoelectric characteristics can be obtained.

When polyaniline is used as the organic thermoelectric material, after mixing polyaniline and inorganic particles previously dissolved in a solvent such as 1,4-dioxane and tetrahydrofuran (THF), the above-described dopant such as camphorsulfonic acid and the like An organic-inorganic hybrid thermoelectric material may be obtained by mixing m-cresol (solution coordination method) and replacing the solvent with m-cresol.

  When polyaniline is used as the organic thermoelectric material, a water-soluble polyaniline having a weight average molecular weight of 10,000 or less (preferably 5000 to 500) is used as a protective agent used in the production of inorganic particles. As inorganic particles coated with polyaniline, in mixing this with inorganic particles, the above-mentioned dopant (preferably camphorsulfonic acid) and m-cresol are mixed together (bismuth telluride coated by the water-soluble polyaniline method). Method used: water-soluble polyaniline method), an organic-inorganic hybrid thermoelectric material may be obtained.

  Polyaniline having a weight average molecular weight of 10,000 or less is very soluble and soluble in alcohols such as ethanol. Even when water is used as a solvent, hydrochloric acid or the like is added to protons in the solvent. When present, the amine in the polyaniline is protonated and becomes hydrophilic, which is a phenomenon peculiar to low molecular weight polyaniline.

  As the form of the organic-inorganic hybrid thermoelectric material to be manufactured, the thickness is approximately 3 μm to 0.5 mm (preferably 5 μm to 50 μm), taking advantage of the high workability material made of the organic thermoelectric material. It is preferable to form into a film shape (thin film shape). Here, examples of the application means for forming the organic-inorganic hybrid thermoelectric material into a film (thin film) include casting, spin coating, dipping, and ink jet.

  In addition, after coating by such a method, a film-like (thin film-like) organic-inorganic hybrid thermoelectric material can be obtained by removing the organic solvent and the like by drying. You may make it implement. Such heat treatment may be performed at 50 ° C. to 1200 ° C., for example, and is preferably performed at 50 ° C. to 500 ° C. Such heat treatment densifies the thermoelectric material and improves thermoelectric properties.

  The organic-inorganic hybrid thermoelectric material according to the present invention described above uses inorganic particles having an average particle diameter of 1 to 100 nm and having substantially no protective agent as the inorganic particles. It is able to efficiently enter and disperse into the gaps between materials, stably maintain excellent thermoelectric properties, and have high Seebeck coefficient, electrical conductivity, and low thermal conductivity, so that it is a physical internal factor (TPF) And a thermoelectric material having an excellent thermoelectric figure of merit (ZT). Moreover, since the organic thermoelectric material which is an organic polymer material is used as a constituent material, it becomes a thermoelectric material with favorable workability, and for example, it can be easily reduced in thickness.

  Further, the organic-inorganic hybrid thermoelectric material according to the present invention can be used for direct conversion between thermal energy and electric energy, so-called thermoelectric conversion, and the workability is also good by using the organic thermoelectric material as a constituent material. Therefore, it becomes possible to easily manufacture thermoelectric conversion elements and thermoelectric conversion modules having good thermoelectric characteristics. In addition, it can be applied to various devices using thermoelectric conversion technology such as a thermal sensor and a thermoelectric cooling device.

  When the organic-inorganic hybrid thermoelectric material of the present invention is used as a thermoelectric conversion element, for example, a semiconductor thermoelectric conversion material such as bismuth selenium, aluminum-doped zinc oxide, or a metal such as platinum or palladium is electrically and physically used. It is preferable that the joined element is a basic unit. As a joining method, for example, adhesion using a conductive paste or a method of coating by vapor deposition or sputtering can be used. Further, in order to obtain a desired output, a plurality of basic units connected in series can be used as a thermoelectric conversion element. When a temperature difference is applied between the junction points, a thermoelectromotive force is generated to become a thermoelectric power generation element. On the other hand, when a current is passed through this element, heat transfer occurs between the junction points to become a Peltier cooling element. .

  The aspect described above shows one aspect of the present invention, and the present invention is not limited to the above-described embodiment, and has the configuration of the present invention and can achieve the objects and effects. It goes without saying that modifications and improvements within the scope are included in the content of the present invention. Further, the specific structure, shape, and the like in carrying out the present invention are not problematic as other structures, shapes, and the like as long as the objects and effects of the present invention can be achieved. The present invention is not limited to the above-described embodiments, and modifications and improvements within the scope that can achieve the object of the present invention are included in the present invention.

For example, in the thermoelectric conversion element of the present invention, the minimum condition is that the organic-inorganic hybrid thermoelectric material of the present invention is used, and other configurations are not limited. Although the thermoelectric conversion material used for a thermoelectric conversion element may use what was processed into the film form, the shape is not limited. Various modifications are possible. Moreover, a composite with other materials, such as laminating a protective material or a sealing material on the surface of the thermoelectric conversion material, is also possible.
In addition, the specific structure, shape, and the like in the implementation of the present invention may be other structures as long as the object of the present invention can be achieved.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to this Example at all.

[Synthesis Example 1]
Synthesis of bismuth telluride (Bi ₂ Te ₃ ) nanoparticles:
In a 500 mL four-necked flask, 250 mL of dehydrated and degassed TEG (tetraethylene glycol), 1.8 mmol of bismuth chloride (BiCl ₃ ), 2.7 mmol of tellurium chloride (TeCl ₄ ), and PVP (polyvinylpyrrolidone) 18 mmol (r = 4) was added and stirred at 324 rpm for 30 minutes to obtain a mixture.

Next, using a mantle heater to which a slidac was connected, the obtained mixture was heated and refluxed under a nitrogen stream for 1 hour at an applied voltage of 70 V (relationship between elapsed time and temperature is shown below). After the heating was completed, the temperature was slowly lowered by air cooling, and when the temperature dropped to a level where it could be touched, centrifugation was performed at 3000 rpm for 40 minutes, and the solvent was replaced from TEG (tetraethylene glycol) to ethanol. After solvent replacement, ethanol washing was performed 4 times. The solvent (ethanol) was removed using an evaporator with argon substitution. The powder was collected and dried in a vacuum dryer for 12 hours to obtain inorganic particles of bismuth telluride (Bi ₂ Te ₃ ) as powder.

(Relationship between elapsed time and temperature in heated reflux)
Elapsed time Temperature 10 minutes: 106 ° C
20 minutes: 167 ° C
30 minutes: 226 ° C
40 minutes: 269 ° C
50 minutes: 298 ° C
60 minutes: 307 ° C

(Analysis by X-ray diffraction (XRD))
As a result of XRD analysis of the obtained bismuth telluride (Bi ₂ Te ₃ ), no oxide peak was confirmed, and only the bismuth telluride peak was confirmed.

(Cross-section observation with a transmission cross-sectional microscope (TEM))
As a result of observation by TEM, it was confirmed that many nanoparticles with small polydispersion and small particle diameter were obtained. The average particle size was about 10 nm (the majority was in the range of 5-15 nm).

(Analysis by Fourier transform infrared spectroscopy (FT-IR))
As a result of confirming whether or not an organic substance (protective agent: PVP) is present in the obtained bismuth telluride by FT-IR analysis, it was confirmed that no organic substance (protective agent) was present.

[Synthesis Example 2]
Synthesis of polyaniline:
After adding 0.778 mol of lithium chloride (LiCl) to a 1 L eggplant-shaped flask, 117 mmol of 1 mol / L hydrochloric acid aqueous solution was slowly added. Furthermore, 0.054 mol of aniline was added to make a mixed solution, and after taking heat in a refrigerator, it was cooled with an acetone refrigerant at −30 ° C. for 1 hour. To the mixed solution after cooling, a mixed solution of ammonium peroxodisulfate 0.11 mol, ion-exchanged water 100 mL, and lithium chloride 0.67 mol was added dropwise over 50 hours. After completion of the dropwise addition, the reaction was stirred for 1 hour as a post reaction, and slowly returned to room temperature to obtain an intermediate product.

  Next, the obtained intermediate product was subjected to suction filtration (0.2 μm) with ion-exchanged water, and then washed until the filtrate became neutral. After washing, the filtrate was further washed with acetone until the filtrate became colorless and transparent. It dried under reduced pressure at 40 degreeC for 12 hours, and obtained the powdery polyaniline. To the obtained polyaniline, 100 mL of 1 mol / L aqueous ammonia was added and stirred for 1 hour for dedoping. The polyaniline after undoping was suction filtered with ion-exchanged water, washed until the filtrate became neutral, and then filtered with acetone until the filtrate became colorless and transparent. The obtained product was dried under reduced pressure at 50 ° C. for 12 hours to obtain emeraldine-structured polyaniline (PANi) as an organic thermoelectric material as a powder.

(Identification by ultraviolet visible near infrared spectroscopy (UV-Vis))
The polyaniline obtained in Synthesis Example 2 was taken in a sample tube, dissolved in NMP (1-methylpyrrolidone), transferred to a quartz cell, and measured. Generally, polyaniline has a benzenoid structure peak at 329 nm and a quinoid structure peak at 639 nm as a literature value, and an absorbance ratio of 1.1 to 1.7. A similar peak was observed in the polyaniline obtained in Synthesis Example 2, and the obtained product could be identified as a polyaniline having an emeraldine structure.

(Analysis by Fourier transform infrared spectroscopy (FT-IR) measurement)
The polyaniline obtained in Synthesis Example 2 was subjected to FT-IR measurement by the KBr method. In general, polyaniline has a quinoid structure at 1589 cm ⁻¹ , a benzenoid structure at 1492 cm ^−1, and 1-4 bending vibration at 827 cm ⁻¹ in the literature values, and the same peak as the polyaniline obtained in Synthesis Example 2 is observed. It was confirmed that the polyaniline had an emeraldine structure.

(Measurement of molecular weight by gel permeation chromatography)
The molecular weight of the polyaniline obtained in Synthesis Example 2 was determined using gel permeation chromatography (GPC). For GPC measurement, polyvinyl pyridine was used as a standard sample, and a calibration curve was prepared to determine the weight average molecular weight and the like. The mobile phase used was N-methyl-2-pyrrolidone (NMP). The weight average molecular weight (M _w ) = 92000, the number average molecular weight (M _n ) = 81000, and the weight average molecular weight (M _w ) / number average molecular weight (M _n ) = 1.1.

[Examples 1 to 3]
Production of organic-inorganic hybrid thermoelectric materials:
Using the bismuth telluride (Bi ₂ Te ₃ ) nanoparticles that are the inorganic particles obtained in Synthesis Example 1 and the polyaniline that is the organic thermoelectric material obtained in Synthesis Example 2, the following “direct coordination method”, “ It is an organic-inorganic hybrid thermoelectric material by three kinds of manufacturing methods, “solution coordination method” and “method using bismuth telluride coated with water-soluble polyaniline method” (hereinafter referred to as “water-soluble polyaniline method”). A polyaniline-bismuth telluride hybrid thermoelectric material was produced.

[Example 1]
Production of hybrid thermoelectric materials (1) (Production by direct coordination method):
Table 1 shows the bismuth telluride obtained in Synthesis Example 1 (applied voltage: 70 V), the polyaniline, camphorsulfonic acid and m-cresol obtained in Synthesis Example 2 in a 4 mL sample tube in a glove box. As a configuration, a stir bar was inserted and sealed. After irradiation with ultrasonic waves for 1 hour, the mixture was stirred for 24 hours with stirring. This was cast on a glass plate and dried to obtain a film-like hybrid thermoelectric material.

(Composition: Direct coordination method)

[Example 2]
Production of hybrid thermoelectric material (2) (Production by solution coordination method):
In a 1 L eggplant-shaped flask, 300 mg of polyaniline and 600 mL of dehydrated and degassed 1,4-dioxane were added, and stirred with a stirrer for 48 hours to completely dissolve polyaniline in 1,4-dioxane (referred to as polyaniline solution). .) Next, a bismuth telluride nanoparticle (applied voltage: 70 V) and a polyaniline solution were placed in a 100 mL eggplant type flask in the glove box as shown in Table 2 below, and sealed with a stirrer. This was stirred for 48 hours with stirring.

(Configuration: Solution coordination method)

  Furthermore, in the configuration shown in Table 3 below, camphorsulfonic acid and m-cresol equivalent to those in the direct coordination method were added, stirring was performed in a glove box for 72 hours, and pressure was reduced using a rotary pump at the same time. This solution was cast on a glass plate and dried to obtain a film-like hybrid thermoelectric material.

(Configuration: Solution coordination method)

[Synthesis Example 3]
Synthesis of water-soluble polyaniline:
0.05 mol (4.657 g) of aniline was placed in a 300 mL eggplant-shaped flask, and 1 mol / L hydrochloric acid aqueous solution (10 mL) was added. The oil bath was heated to 80 ° C., and 0.0625 mol (14.260 g) of ammonium persulfate was added as a powder. Polymerization occurred vigorously within a few seconds after the addition, and water contained in the hydrochloric acid aqueous solution was instantly vaporized and removed from the system by the heat generated at that time, thereby producing polyaniline. The polyaniline remaining in the eggplant-shaped flask is recovered, filtered and washed with acetone and water in the same manner as in Synthesis Example 2, and dedoped using aqueous ammonia to obtain water-soluble polyaniline having a weight average molecular weight of about 10,000 as a powder. Obtained.

[Synthesis Example 4]
Synthesis of bismuth telluride protected with water-soluble polyaniline:
In Synthesis Example 1, the same amount (R = 4) (18 mmol, 419.09 mg) of the water-soluble polyaniline obtained in Synthesis Example 3 was used instead of polyvinylpyrrolidone (PVP) as a protective agent, and the applied voltage was 70V. Except for the synthesis, bismuth telluride protected with water-soluble polyaniline (average particle size: about 10 nm) was obtained using the same method as shown in Synthesis Example 1.

[Example 3]
Production of hybrid thermoelectric material (3) (Production by water-soluble polyaniline method):
Table 4 below shows the bismuth telluride protected with the water-soluble polyaniline obtained in Synthesis Example 3, polyaniline, camphorsulfonic acid, and m-cresol obtained in Synthesis Example 2 in a 4 mL sample tube in a glove box. As a configuration, a stir bar was inserted and sealed. After irradiation with ultrasonic waves for 1 hour, the mixture was stirred for 24 hours with stirring. This was cast on a glass plate and dried to obtain a film-like hybrid thermoelectric material. Since it was considered that polyaniline was decomposed by heating, polyaniline obtained in Synthesis Example 2 that was not decomposed was used.

(Composition: Water-soluble polyaniline method)

  The hybrid thermoelectric material obtained in Examples 1 to 3 was evaluated by performing XRD measurement, FT-IR measurement, and SEM measurement.

(XRD measurement)
For any of the hybrid thermoelectric materials of Examples 1 to 3, since a broad peak derived from polyaniline and a sharp peak derived from bismuth telluride were confirmed, the obtained film-like hybrid thermoelectric material includes polyaniline and It was confirmed that bismuth telluride was present.

(FT-IR measurement)
The obtained film-like hybrid thermoelectric material was pulverized as much as possible in an agate mortar, and FT-IR measurement was measured by the KBr method. When the oxide is present, two peaks are observed. It is considered that two peaks of ether (oxygen enters the crystal structure) and ketone (structure that can be formed on the surface of bismuth telluride) are confirmed. In any of the measurement results of Examples 1 to 3, However, such a peak did not exist. Therefore, it was confirmed that these hybrid thermoelectric materials were not oxidized beyond the measurement limit because bismuth telluride was firmly contained in the film.

(SEM measurement)
As a result of observation by SEM, it was confirmed that the hybrid thermoelectric materials obtained in Example 1 (direct coordination method) and Example 3 (water-soluble polyaniline method) had a smooth surface. In the hybrid thermoelectric material obtained by the solution coordination method, an agglomerated part was observed although it was slightly.

(Measurement of thermoelectric conversion efficiency)
About the hybrid thermoelectric material obtained in Example 1, the thermoelectric conversion efficiency was measured using the thermoelectric characteristic measuring apparatus. From the temperature difference, thermoelectromotive force, and potential difference obtained by this measurement, the Seebeck coefficient S and the electrical conductivity σ were calculated. The calculation formula used for the calculation is shown below.

  In addition, the measurement was implemented about Example 1 (direct coordination method). The form factor is shown below. Moreover, the measurement was performed twice for confirmation of reproducibility. Polyaniline was also measured as a reference (blank), but polyaniline is a conductive polymer and the Seebeck coefficient is not stable, so the number of plots is increased. Based on this result, the physical intrinsic factor (TPF) and the thermoelectric figure of merit (ZT) were calculated from the formulas (I) and (II). The results are shown in FIG. 1 (Seebeck coefficient), FIG. 2 (electric conductivity), FIG. 3 (thermoelectric figure of merit (ZT)) and FIG. 4 (power factor), respectively. The thermal conductivity was almost the same as that of polyaniline, which is an organic thermoelectric material, and was a low thermal conductivity possessed by the organic thermoelectric material. Therefore, in the calculation of the thermoelectric figure of merit (ZT) and power factor, the thermal conductivity of polyaniline was used.

(Form factor: Polyaniline)
Sample thickness (film thickness): 12.73 μm
Sample width: 0.31 cm
Distance between electrodes: 0.65cm

(Form factor: R = 1)
Sample thickness (film thickness): 14.01 μm
Sample width: 0.3 cm
Distance between electrodes: 0.65cm

(Form factor: R = 5)
Sample thickness (film thickness): 8.36 μm
Sample width: 0.32 cm
Distance between electrodes: 0.26 cm

(Form factor: R = 10)
Sample thickness (film thickness): 13.95 μm
Sample width: 0.32 cm
Distance between electrodes: 0.7cm

  In general, the Seebeck coefficient is considered to increase when the R value is low, but at the same time, the dispersibility also decreases and the potential difference cannot be uniformly applied. Therefore, as shown in FIG. 1, the Seebeck coefficient is low at R = 1 and high at R = 5. Further, when R = 10, the bismuth telluride nanoparticles are uniformly dispersed, so that the properties of bismuth telluride itself are exhibited, and, like bismuth telluride, can have a peak top around 300K. And at the intermediate R value, the dispersibility is high, the current can be sufficiently blocked by the bismuth telluride nanoparticles, and the Seebeck coefficient is considered to increase greatly in the high temperature range (350-400K). Moreover, the electrical conductivity was a result that the electrical conductivity was not greatly reduced as shown in FIG. 2 because the direct coordination method has only bismuth telluride as the substance that lowers the insulating property.

  In the direct coordination method, the reason why the electric conductivity does not decrease although the Seebeck coefficient is high is that the current flows normally in a portion where the resistance is low. It is considered that both the Seebeck coefficient and the electrical conductivity can be achieved by the bismuth telluride nanoparticle carrying the work of imparting a potential difference. On the other hand, in order to cause such a phenomenon, since the substance that gives the potential difference is sufficiently small and the dispersibility is a necessary condition, in the direct coordination method, the substance that gives the potential difference is sufficiently small, It is considered that the hybrid material is manufactured with high dispersibility. The hybrid thermoelectric material of Example 1 has a high Seebeck coefficient in this way, but the electrical conductivity does not decrease so much, so that the thermoelectric figure of merit (ZT) and power factor are also good as shown in FIGS. It was a result.

  Also, instead of the bismuth telluride obtained in Synthesis Example 1, micrometer-order bismuth telluride (average particle size: 3 to 5 μm) obtained by pulverizing a commercial bulk bismuth telluride was used, and the others Was prepared as Comparative Example 1 (R = 5) as a film-like hybrid thermoelectric material produced by the same method as in Example 1. The hybrid thermoelectric material of Comparative Example 1 was measured for thermoelectric conversion efficiency in the same manner as in Example 1. The results are shown in FIG. 5 (Seebeck coefficient), FIG. 6 (electrical conductivity), FIG. 7 (thermoelectric figure of merit (ZT)) and FIG. 8 (power factor), respectively. In addition, like the evaluation of Example 1, polyaniline was also measured as a reference (blank).

(Form factor: Polyaniline)
Sample thickness (film thickness): 7.54 μm
Sample width: 0.96 cm
Distance between electrodes: 0.692 cm

(Form factor: Comparative Example 1)
Sample thickness (film thickness): 18.9 μm
Sample width: 1.12 cm
Distance between electrodes: 0.527cm

  As shown in FIGS. 5 and 6, the hybrid thermoelectric material of Comparative Example 1 has a lower electrical conductivity than the result of Example 1 as compared with the polyaniline. The Seebeck coefficient was as low as that of polyaniline. As described above, since the hybrid thermoelectric material of Example 1 exhibits a higher Seebeck coefficient than polyaniline, the average particle of bismuth telluride that is an inorganic particle (inorganic thermoelectric material) as in Comparative Example 1 is used. It was confirmed that the hybrid thermoelectric material having a diameter of 3 to 5 μm that does not satisfy the requirements of the present invention is inferior to the hybrid thermoelectric material of Example 1 with respect to the Seebeck coefficient.

  Further, since the Seebeck coefficient and the like were such results, the thermoelectric performance index (ZT) and the power factor of the hybrid thermoelectric material of Comparative Example 1 were larger than those of polyaniline as shown in FIGS. It was inferior. This also confirmed that the hybrid thermoelectric material that does not satisfy the requirements of the present invention for the average particle size of the inorganic particles (inorganic thermoelectric material) is inferior to the hybrid thermoelectric material of Example 1 in terms of thermoelectric properties.

[Synthesis Example 5]
Formalin aqueous solution 1.06 mol (31.83 g) and sodium hydroxide 49.5 mmol (1.98 g) were added to phenol 0.528 mol (49.69 g). A resol resin aqueous solution was obtained by heating and refluxing at 80 ° C. for 2 hours. On the other hand, since impurities still exist in this state, the resol resin was obtained by adjusting the pH from 11 to 4 using an ion exchange resin and removing the inorganic salt. An excess amount of 1-butanol from which the inorganic salt had been removed was added, and the solvent was removed with an evaporator. This was repeated 5 times, water remaining in the solution was removed, and a resole resin in which solvent was substituted from water to 1-butanol was obtained.

[Example 4]
Production of hybrid thermoelectric material (4):
The resole resin obtained by subjecting 1-butanol obtained in Synthesis Example 5 to solvent substitution and the bismuth telluride nanoparticles obtained in Synthesis Example 1 were added in the configuration shown in Table 5 below, followed by stirring for 24 hours. Then, it was placed on a hot plate at 120 ° C. in a decompressed glove box, and the solvent was removed until it became a castable viscosity. The glass plate was cast on a hot plate at 120 ° C., and the degree of vacuum was gradually lowered so as not to foam, and dried under reduced pressure at 120 ° C. for 24 hours. Thereafter, heat treatment was performed at 500 ° C. for 30 minutes and at 850 ° C. for 1 hour using a tubular electric furnace to obtain a polyacene-telluride bismuth hybrid thermoelectric material which is an organic-inorganic hybrid thermoelectric material using polyacene as the resole resin. .

(Configuration: Example 4)

(Measurement of thermoelectric conversion efficiency)
The polyacene-bismuth telluride hybrid thermoelectric material obtained in Example 4 was measured for thermoelectric conversion efficiency using the same method as in Example 1. The measurement was performed for R = 500. The measurement result of electric conductivity is shown in FIG.

(Form factor: Polyacene)
Sample thickness (film thickness): 0.1 cm
Sample width: 0.27 cm
Distance between electrodes: 0.55cm

(Form factor: R = 500)
Sample thickness (film thickness): 0.05 cm
Sample width: 0.23 cm
Distance between electrodes: 0.1 cm

  As shown in FIG. 9, the electrical conductivity of the polyacene-bismuth telluride hybrid thermoelectric material of Example 4 was higher than that of polyacene. This is considered to be due to the effect of the dopant for extracting electrons from the polyacene when the bismuth telluride nanoparticles having an average particle diameter of about 10 nm emit holes to the polyacene, which is a conductive polymer.

[Synthesis Example 6]
Synthesis of bismuth telluride (Bi ₂ Te ₃ ) nanoparticles (2):
A mixture was prepared using the same method as in Synthesis Example 1. The obtained mixture was heated with a mantle heater, heated to 280 ° C. in 20 minutes, and heated to reflux. Heating was continued at an applied voltage of 60 to 70 V, and refluxing was continued at 280 ° C. for 60 minutes. After the heating was completed, the power was turned off and the system was cooled for about 2 hours under a nitrogen stream. 50 mL of this solution-like mixture was placed in 450 mL of ethanol and stirred, and then allowed to stand for 6 days. The precipitate obtained after standing was separated by decantation and dried under reduced pressure to obtain inorganic particles of bismuth telluride (Bi ₂ Te ₃ ) nanoparticles as a powder.

(Analysis by X-ray diffraction (XRD))
As a result of XRD analysis of the obtained bismuth telluride (Bi ₂ Te ₃ ), no oxide peak was confirmed, and only the bismuth telluride peak was confirmed.

(Cross-section observation with a transmission cross-sectional microscope (TEM))
As a result of observation by TEM, the particle size distribution was broader than that of Synthesis Example 1, and the average particle size was about 35 nm (the majority was in the range of 20 to 50 nm).

(Analysis by Fourier transform infrared spectroscopy (FT-IR))
As a result of confirming whether or not an organic substance (protective agent: PVP) is present in the obtained bismuth telluride by FT-IR analysis, it was confirmed that no organic substance (protective agent) was present.

[Example 5]
Production of organic-inorganic hybrid thermoelectric materials:
Using the bismuth telluride (Bi ₂ Te ₃ ) nanoparticles, which are inorganic particles obtained in Synthesis Example 6, and the polyaniline obtained in Synthesis Example 2, the method (direct coordination method) shown in Example 1 By the same method, a film-like hybrid thermoelectric material was prepared with R = 5.

(Measurement of thermoelectric conversion efficiency)
For the hybrid thermoelectric material obtained in Example 5, the thermoelectric conversion efficiency was measured in the same manner as in Example 1. The results are shown in FIG. 10 (Seebeck coefficient), FIG. 11 (electric conductivity), FIG. 12 (thermoelectric figure of merit (ZT)) and FIG. 13 (power factor), respectively. In addition, like the evaluation of Example 1, polyaniline was also measured as a reference (blank).

(Form factor: Polyaniline)
Sample thickness (film thickness): 7.54 μm
Sample width: 0.96 cm
Distance between electrodes: 0.692 cm

(Form factor: Example 5)
Sample thickness (film thickness): 3.57 μm
Sample width: 1.21 cm
Distance between electrodes: 0.658cm

  As shown in FIGS. 10 and 11, the hybrid thermoelectric material of Example 5 had higher electrical conductivity than polyaniline. And as shown in FIG.12 and FIG.13, a thermoelectric figure of merit (ZT) and a power factor were also higher than polyaniline, and it was a favorable result.

  The thermoelectric material of the present invention is applied to thermoelectric conversion technology, and can be advantageously used as a means capable of realizing “energy recycling” that clears environmental problems and energy problems.

Claims (4)

The average particle diameter is 1 to 100 nm, Bi— (Te, Se), Si—Ge, Pb—Te, GeTe—AgSbTe, (Co, Ir, Ru) —Sb, and (Ca, Sr, Bi) Inorganic particles which are at least one selected from the Co ₂ O ₅ system and are substantially free of a protective agent, and after mixing a precursor, a protective agent and a solvent corresponding to the inorganic particles, Prepare a dispersion solution of the inorganic particles by heating at a decomposition temperature or higher, purify the dispersion solution and pulverize, and polyaniline or a derivative thereof, polypyrrole or a derivative thereof, polythiophene or a derivative thereof, At least one kind selected from polyphenylene vinylene derivatives, polyparaphenylene derivatives, polyacene or derivatives thereof, and copolymers thereof. Organic characterized by mixing the thermoelectric material - method for producing inorganic hybrid thermoelectric material. The organic thermoelectric material is polyaniline;
And said polyaniline, and the inorganic particles, camphorsulfonic acid, organic according to claim 1, naphthalene sulfonic acid, and at least one selected from toluene sulfonic acid and phosphoric acid, characterized by mixing m- cresol -Manufacturing method of inorganic hybrid thermoelectric material. The inorganic particles are bismuth telluride (Bi ₂ Te ₃ ),
The precursor corresponding to the inorganic particles is tellurium tetrachloride or tetraethoxytellurium, and bismuth chloride,
The protective agent is polyvinylpyrrolidone (PVP);
The solvent is tetraethylene glycol;
The method for producing an organic-inorganic hybrid thermoelectric material according to claim 1 or 2 , wherein a decomposition temperature of the protective agent is 230 ° C. Method for producing inorganic hybrid thermoelectric materials - organic according to any one of claims 1 to 3, characterized in that molding into a film form.

Images