CN110407581B

CN110407581B - Copper-sulfur-based thermoelectric compound and preparation method thereof

Info

Publication number: CN110407581B
Application number: CN201910575801.3A
Authority: CN
Inventors: 万春磊; 宗鹏安; 潘伟
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2019-06-28
Filing date: 2019-06-28
Publication date: 2020-10-13
Anticipated expiration: 2039-06-28
Also published as: CN110407581A

Abstract

The invention relates to a P-type thermoelectric compound material and a preparation method thereof, belonging to the technical field of thermoelectric materials. The structural formula of the thermoelectric compound is KCu_7‑xS₄Wherein x is more than or equal to 0.01 and less than or equal to 0.5. The thermoelectric powder material is obtained mainly through hydrothermal reaction, washing and drying. And grinding and sintering to obtain the thermoelectric block material. The thermoelectric material prepared by the method has the advantages of simple process, low cost and low toxicity. The material has low thermal conductivity, and the thermoelectric figure of merit is as high as 0.4 at 400 ℃. Therefore, the p-type thermoelectric compound material based on copper and sulfur prepared by the invention is a thermoelectric compound material with better application prospect.

Description

Copper-sulfur-based thermoelectric compound and preparation method thereof

Technical Field

The invention belongs to the technical field of thermoelectric energy conversion materials, and relates to a p-type semiconductor thermoelectric compound based on copper and sulfur and a preparation method thereof.

Background

The thermoelectric conversion material is a solid clean energy material. The material can utilize the seebeck effect and the Parcel effect to carry out direct interconversion of heat energy and electric energy. When two ends of different conductors are connected to form a closed loop and the two joints have temperature difference, the closed loop can generate thermoelectromotive force, thereby forming thermoelectromotive current. This phenomenon was the first thermoelectric effect discovered by Seebeck, a german scientist, in 1821. When no temperature gradient exists in the material, the internal carrier concentration is uniformly distributed. When temperature difference exists, the carrier energy at the high temperature end is higher and is diffused to the low temperature end, and after dynamic balance is achieved, the carrier concentration at the low temperature end is higher than that at the high temperature end, so that temperature difference potential is generated. By utilizing the seebeck effect, power generation can be performed. When two different conductors are connected and then energized, there is a heat absorption and release at the junction, which is known as peltier heat. This is the second thermoelectric effect discovered by french scientist peltier in 1834. When current is passed to two different conductors, due to the difference in fermi levels, when a carrier flows from a conductor with a low fermi level to a conductor with a high fermi level, the carrier must absorb enough energy material to pass this barrier, macroscopically appearing as an endotherm. Conversely, when a carrier flows from a conductor with a high fermi level to a conductor with a low fermi level, energy is released and macroscopically appears as heat. The peltier effect can be used for cooling or heating. The power generation or refrigeration technology has the advantages of no moving parts, no pollution discharge, no noise generation and the like, and is a new energy material technology which is concerned at present.

Currently, the thermoelectric materials commonly used include bismuth telluride, cobalt antimonide, lead telluride, and silicon germanium, wherein bismuth telluride is suitable for the normal temperature region, cobalt antimonide is suitable for the medium temperature region, and lead telluride and silicon germanium are suitable for the high temperature region. In recent years, copper-based chalcogenides of the formula Cu have been used₂X, wherein X is sulfur, selenium and tellurium, exhibit excellent thermoelectric properties and have been widely studied. The chalcogenide sublattice is a good channel for electron transportation, and copper ions are easy to migrate, so that phonons can be scattered violently, and a part of lattice vibration transverse wave mode in the shearing direction can be reduced, thereby reducing lattice heat capacity and greatly reducing thermal conductivity. Compared with selenium and tellurium elements, the sulfur content is rich, the cost is low, the toxicity is low, and the copper-sulfur-based compound has more practical significance. Therefore, the research on the copper-sulfur-based thermoelectric material is particularly urgent.

The thermoelectric material prepared by the method has the advantages of simple preparation process, low cost and the like, and overcomes the defect of high toxicity of the traditional thermoelectric materials such as bismuth telluride, lead telluride and the like. The thermal conductivity of the material is lower than 0.8W/mK at 100-400 ℃, and the thermoelectric figure of merit is more than 0.1 at the temperature of more than 100 ℃. Therefore, the thermoelectric material based on potassium, copper and sulfur elements is a thermoelectric material with better application prospect.

Disclosure of Invention

The invention aims to provide a ternary thermoelectric compound material based on potassium, copper and sulfur elements and a preparation method thereof, and a certain thermoelectric output performance is obtained.

The chemical structural formula of the compound material provided by the invention is KCu_7-xS₄Wherein x is more than or equal to 0.01 and less than or equal to 0.5.

The preparation method of the copper-sulfur-based thermoelectric compound material comprises the following steps:

1) weighing potassium sulfide powder and cuprous chloride powder with corresponding weight according to weight ratio of potassium disulfide, dipotassium pentasulfide or dipotassium hexasulfide/cuprous chloride being 0.5-4 in a glove box filled with inert gases such as argon or nitrogen, and transferring the potassium sulfide powder and the cuprous chloride powder into a three-neck flask filled with hexamethylene diamine;

2) heating the three-necked flask to 80-150 ℃ in an oil bath or sand bath, preserving the heat for 3-8 hours, and introducing nitrogen for stirring;

3) immersing a copper sheet in the liquid composition in a three-neck flask, keeping the temperature at 80-150 ℃ for 4-10 hours, and introducing nitrogen for stirring;

4) transferring, washing with water and alcohol, vacuum drying at 40-80 deg.C for 4-24 hr, and grinding to obtain powder;

5) performing spark plasma sintering on the obtained powder, heating to 350-500 ℃ for 5-10 min, and keeping the temperature for 4-10 min under the pressure of 40-60MPa to obtain KCu_7-xS₃The thermoelectric bulk material is characterized in that x is more than or equal to 0.01 and less than or equal to 0.5.

Use of the above compounds in thermoelectric devices. The thermoelectric device comprises a thermoelectric power generation or thermoelectric refrigeration device in a medium-high temperature region, such as a thermoelectric refrigeration device in the fields of automobile waste heat power generation, industrial waste heat power generation, electronics and the like.

The thermoelectric compound prepared by the method has the advantages of simple process, low cost and the like, and overcomes the defect of high toxicity of the traditional thermoelectric materials such as bismuth telluride, lead telluride and the like. Therefore, the novel thermoelectric compound material based on potassium, copper and sulfur elements is a thermoelectric material with good application prospect.

Drawings

FIG. 1 is a KCu prepared by the process of the present invention_6.98S₄And KCu_6.94S₄Powder X-ray diffraction pattern of thermoelectric material.

FIG. 2 is a KCu prepared by the process of the present invention_6.98S₄Scanning electron microscope images of the block cross section.

FIG. 3 is Cu prepared by the method of the present invention_6.98S₄And KCu_6.94S₄The electrical conductivity of the thermoelectric block is plotted as a function of temperature.

FIG. 4 is Cu prepared by the method of the present invention_6.98S₄And KCu_6.94S₄And the absolute value of the seebeck coefficient of the thermoelectric block is plotted along with the change of the temperature.

FIG. 5 shows Cu prepared by the method of the present invention_6.98S₄And KCu_6.94S₄Thermal conductivity of a thermoelectric block is plotted as a function of temperature.

FIG. 6 is Cu prepared by the method of the present invention_6.98S₄And KCu_6.94S₄The thermoelectric figure of merit of the thermoelectric block body is plotted as a function of temperature.

Detailed Description

The preparation method of the thermoelectric compound material comprises the following steps:

2) heating the three-necked flask to 80-150 ℃ in an oil bath or sand bath, preserving the heat for 3-8 hours, and introducing nitrogen for stirring; 3) immersing a copper sheet in the liquid composition in a three-neck flask, keeping the temperature at 80-150 ℃ for 4-10 hours, and introducing nitrogen for stirring;

5) performing spark plasma sintering on the obtained powder, heating to 400 ℃ for 5-10 minutes, and keeping the temperature for 4-10 minutes under the pressure of 40-60MPa to obtain KCu_4-xS₃The thermoelectric bulk material is characterized in that x is more than or equal to 0.01 and less than or equal to 0.5.

The thermal conductivity of the crystal lattice of the thermoelectric material based on potassium, copper and sulfur prepared by the method is as follows0.4-0.80W/m.K at 100-400 ℃, and the maximum thermoelectric figure of merit is 0.4. FIG. 1 is KCu_6.98S₄And KCu_6.94S₄The powder has no obvious impurity phase, and the KCu is successfully synthesized by the invention_4-xS₃The thermoelectric powder material has x not less than 0.01 and not more than 0.5. As an example, FIG. 2 is a diagram of a synthesized KCu_6.98S₄The sectional scanning electron microscope image of the block shows that the sintered block has certain porosity. FIG. 3 is a diagram of the synthesis of KCu_6.98S₄And KCu_6.94S₄Conductivity of the bulk, it can be seen that the composition is KCu_6.94S₄The bulk material of (a) is relatively high in conductivity due to the increased carrier concentration resulting from the more copper defects providing more holes. FIG. 4 is a diagram of synthetic KCu_6.98S₄And KCu_6.94S₄The Seebeck coefficient of the block can be seen as KCu_6.94S₄The seebeck coefficient of a bulk material is relatively low due to its high carrier concentration. FIG. 5 is a diagram of the synthesized KCu_6.98S₄And KCu_6.94S₄Thermal conductivity of bulk material, it can be seen that the composition is KCu_6.94S₄Is low due to scattering of defects. And KCu_6.98S₄And KCu_6.94S₄The thermal conductivity of the bulk material is lower than 0.8W/mK at 100-400 ℃. FIG. 6 is a diagram of synthesized KCu_6.98S₄And KCu_6.94S₄Thermoelectric figure of merit of bulk Material, KCu can be seen_6.94S₄The thermoelectric figure of merit of the material is relatively high, reaching 0.44 at 400 ℃. In the ternary compound structure prepared by the invention, Cu atoms are not only present in CuS₄In tetrahedron, and is present in CuS₃In a triangle. Both distorted with respect to regular tetrahedrons and regular triangles. CuS₄Tetrahedron and CuS₃The triangles share vertices and edges. Is located in CuS₄The Cu in the central position of the tetrahedron accounts for 75%. In addition, a pseudo one-dimensional tunnel structure containing potassium ions is formed in the compound, so that phonons are scattered violently, and thermal conduction is greatly inhibited.

The present invention will be described in further detail with reference to the accompanying drawings and examples.

Example 1: the chemical composition of the preparation is KCu_6.98S₄Thermoelectric material of

a. Weighing potassium sulfide powder and cuprous chloride powder with corresponding weight according to the weight ratio of potassium disulfide/cuprous chloride to 2 in a glove box filled with inert gases such as argon or nitrogen, and transferring the potassium sulfide powder and the cuprous chloride powder into a three-neck flask filled with 60ml of hexamethylenediamine;

b. heating the three-neck flask to 114 ℃ in an oil bath or sand bath, preserving the heat for 4 hours, and introducing nitrogen for stirring; immersing a copper sheet in the liquid composition in a three-neck flask, keeping the temperature at 114 ℃ for 7 hours, and introducing nitrogen for stirring;

c. transferring, washing with water and alcohol, vacuum drying at 40-80 deg.C for 4-24 hr, and grinding to obtain powder;

d. performing discharge plasma sintering on the obtained thermoelectric powder, heating to 410 ℃ for 6 minutes, and keeping the temperature for 5 minutes under the pressure of 50MPa to obtain KCu_6.98S₄Thermoelectric bulk material.

Example 2: the chemical composition of the preparation is KCu_6.94S₄The thermoelectric material of (a):

a. weighing potassium sulfide powder and cuprous chloride powder with corresponding weight according to the weight ratio of potassium disulfide/cuprous chloride to 2 in a glove box filled with inert gases such as argon or nitrogen, and transferring the potassium sulfide powder and the cuprous chloride powder into a three-neck flask filled with 50ml of hexamethylenediamine;

b. heating the three-neck flask to 110 ℃ in an oil bath or sand bath, preserving the heat for 5 hours, and introducing nitrogen for stirring; immersing a copper sheet in the liquid composition in a three-neck flask, keeping the temperature at 110 ℃ for 6.4 hours, and introducing nitrogen for stirring;

c. transferring, washing with water and washing with alcohol, vacuum drying at 60 deg.C for 4 hr, and grinding to obtain thermoelectric powder;

d. performing discharge plasma sintering on the obtained thermoelectric powder, heating to 400 ℃ for 5 minutes, and keeping the temperature for 4 minutes under the pressure of 60MPa to obtain KCu_6.94S₄Thermoelectric bulk material.

Example 3: the chemical composition of the preparation is KCu_6.92S₄The thermoelectric material of (a):

a. weighing potassium sulfide powder and cuprous chloride powder with corresponding weight in a glove box filled with inert gases such as argon or nitrogen according to the weight ratio of potassium disulfide/cuprous chloride to 2, and transferring the potassium sulfide powder and the cuprous chloride powder into a three-neck flask filled with 55ml of hexamethylenediamine;

b. heating the three-necked flask to 105 ℃ in an oil bath or sand bath, preserving the heat for 4 hours, and introducing nitrogen for stirring; immersing a copper sheet in the liquid composition in a three-neck flask, keeping the temperature at 105 ℃ for 5.5 hours, and introducing nitrogen for stirring;

c. transferring, washing with water and washing with alcohol, vacuum drying at 40 deg.C for 6 hr, and grinding to obtain thermoelectric powder;

The above embodiments describe the technical solutions of the present invention in detail. It will be clear that the invention is not limited to the described embodiments. Based on the embodiments of the present invention, those skilled in the art can make various changes, but any changes equivalent or similar to the present invention are within the protection scope of the present invention.

Claims

1. The preparation method of the copper-sulfur-based thermoelectric compound is characterized in that the chemical structural formula of the compound is KCu_7- _xS₄Wherein x is more than or equal to 0.01 and less than or equal to 0.5; the preparation method comprises the following steps:

a. weighing potassium sulfide powder and cuprous chloride powder in a weight ratio of potassium sulfide/cuprous chloride to 0.5-4 in a glove box filled with inert gas, and transferring the potassium sulfide powder and the cuprous chloride powder into a three-neck flask filled with hexamethylenediamine;

b. heating the three-necked flask to 80-150 ℃ in an oil bath or sand bath, preserving the heat for 3-8 hours, and introducing nitrogen for stirring;

c. immersing a copper sheet into the liquid composition in the three-neck flask, keeping the temperature at 80-150 ℃ for 4-10 hours, and introducing nitrogen for stirring;

d. transferring, washing with water and washing with alcohol, vacuum drying at 40-80 deg.C for 4-24 hr, and grinding to obtain thermoelectric powder;

e. transferring the obtained thermoelectric powder into a mold for spark plasma sintering, heating to 350-500 ℃ for 5-10 min, and keeping the temperature for 4-10 min under the pressure of 40-60MPa to obtain KCu_7-xS₄The thermoelectric bulk material is characterized in that x is more than or equal to 0.01 and less than or equal to 0.5.

2. The method of claim 1, wherein the compound has a thermal conductivity of less than 0.8W/mK between 100 ℃ and 400 ℃ and a thermoelectric figure of merit of 0.1 or greater.

3. The method of claim 1, wherein the inert gas in step a is argon or nitrogen; the potassium sulfide is potassium disulfide or dipotassium pentasulfide or dipotassium hexasulfide.

4. The method of claim 1, wherein the sintering step e uses a graphite mold, and boron nitride insulation is sprayed inside the mold and at the upper and lower indenters.