Preparation method of composite thermoelectric material with excellent mechanical properties

Abstract

The application discloses a preparation method of a composite thermoelectric material with excellent mechanical properties, and comprises the following steps: a, adding carbon nanotubes into a sodium polystyrene sulfonate solution and performing ultrasonic dispersion to obtain a carbon nanotube suspension; b, adding 3,4-ethylenedioxythiophene monomers into the carbon nanotube suspension and adding an oxidant so that the 3,4-ethylenedioxythiophene monomers are polymerized into PEDOT on the surface of the carbon nanotubes, and then a PEDOT@CNT film is obtained through vacuum filtration; c, cutting and grinding the PEDOT@CNT film, and then dispersing the film in dichloromethane through ultrasonic dispersion to form a PEDOT@CNT suspension, and then adding an ionic liquid and continuing ultrasonic dispersion; d, dissolving polycarbonate particles in boiling dichloromethane to form a PC solution, mixing the solution obtained in the step c with the PC solution in an ultrasonic tank, and then pouring the mixture into a polytetrafluoroethylene mold, and drying to obtain a PEDOT@CNT / PC film.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric materials technology, and more specifically to a method for preparing a composite thermoelectric material with excellent mechanical properties. Background Technology

[0002] Thermoelectric materials, as a type of clean energy material that can directly convert heat energy into electrical energy, can effectively utilize a large amount of waste heat generated in industry and daily life, thereby improving energy efficiency and reducing energy consumption and emissions. They have advantages such as being pollution-free, safe and reliable, noiseless, and easy to maintain, and have very broad application prospects in fields such as waste heat power generation, microelectronics, refrigeration, and sensing.

[0003] Traditional thermoelectric materials are inorganic semiconductor materials and their alloys. However, most inorganic semiconductor materials and their alloys are scarce in the Earth's crust, expensive, and some elements are highly toxic. This has greatly limited the further development and application of inorganic thermoelectric materials. Due to these insurmountable drawbacks of inorganic materials, organic thermoelectric materials have attracted increasing attention in recent years. Currently, the most studied organic thermoelectric materials are mainly based on conjugated conductive polymers, such as PEDOT, polyaniline (PANI), polythiophene (PTh), and polypyrrole (PPy). Since good mechanical properties are a necessary condition for materials to be used in complex environments, the question of how to improve the mechanical properties of thermoelectric materials has also attracted researchers' attention.

[0004] Currently, a common method to improve the mechanical properties of thermoelectric materials is to blend them with thermoplastic polymers that have excellent mechanical properties. However, the improvement in mechanical properties often comes at the cost of thermoelectric properties, and vice versa. For example, Taroni et al. improved the mechanical properties of PEDOT:PSS / PU by changing the polyurethane (PU) content [PJTaroni, et al.Adv.Funct.Mater.2018,28,1704285.], but at the same time sacrificed the thermoelectric properties of the material (power factor PF value decreased from 11 Wm). -1 K -2 It dropped to 2Wm -1 K -2 Therefore, preparing polymer composite thermoelectric materials with excellent mechanical properties without seriously sacrificing thermoelectric performance remains a challenging task. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing composite thermoelectric materials with excellent mechanical properties.

[0006] To solve the above-mentioned technical problems, the present invention provides a method for preparing a composite thermoelectric material with excellent mechanical properties, comprising:

[0007] a. Carbon nanotubes are added to a sodium polystyrene sulfonate solution and ultrasonically dispersed to obtain a carbon nanotube suspension; wherein the weight of the carbon nanotubes does not exceed 120 mg.

[0008] b. Add 3,4-ethylenedioxythiophene monomer to carbon nanotube suspension and add oxidant to polymerize 3,4-ethylenedioxythiophene monomer on carbon nanotube surface to form PEDOT, and then obtain PEDOT@CNT film by vacuum filtration.

[0009] c. The obtained PEDOT@CNT film is cut into pieces and ground into particles. The PEDOT@CNT particles are then dispersed in dichloromethane by ultrasonication to form a PEDOT@CNT suspension. The ultrasonication time is 30 min. Then, 18.8-75 mg of ionic liquid is added, and ultrasonication is continued for another 30 min.

[0010] d. Dissolve polycarbonate particles in boiling dichloromethane to form a PC solution. Then, mechanically mix the solution obtained in step c with the PC solution under ultrasonic conditions at 50°C for 20 minutes. Pour the mixed solution into a polytetrafluoroethylene mold and dry it to obtain a PEDOT@CNT / PC film.

[0011] The further technical solution is as follows: In step a, carbon nanotubes are dispersed in sodium polystyrene sulfonate solution using probe-type ultrasound, and the ultrasonic dispersion time is 30 min, 1 h or 2 h.

[0012] The further technical solution is as follows: In step b, 3,4-ethylenedioxythiophene monomer is polymerized in situ on the surface of carbon nanotubes to form PEDOT using oxidants ammonium persulfate and ferric chloride, and the polymerization time is 6h, 12h or 24h.

[0013] The further technical solution is as follows: In step c, the ionic liquid EMI-TFSI is slowly added dropwise to the PEDOT@CNT suspension.

[0014] The further technical solution is as follows: In step c, the PEDOT@CNT film is cut into pieces and then ground into 50μm particles in a mortar.

[0015] The further technical solution is as follows: In step d, the food is placed in an oven for drying for 12 hours, 24 hours or 48 hours, and the oven temperature is 50°C, 60°C or 70°C.

[0016] Compared with existing technologies, this invention utilizes ionic liquids to regulate the transformation of PEDOT molecular conformation from benzene to quinone, and can simultaneously promote the dispersion of PEDOT@CNT in suspension. By synergistically utilizing the improved dispersibility of CNTs and the high electrical conductivity of the quinone conformation of PEDOT, the overall electrical conductivity of the composite thermoelectric material is significantly improved. Furthermore, PC in the system also provides excellent mechanical properties. Therefore, the composite thermoelectric material prepared by the method of this invention possesses both high thermoelectric performance and excellent mechanical properties, namely, the high electrical conductivity of CNTs, the high electrical conductivity and high Seebeck coefficient of the quinone conformation of PEDOT, and the high mechanical properties of PC. It is evident that the preparation method of this invention maintains high mechanical properties of the material without severely sacrificing the thermoelectric performance of the composite material, which is of significant importance. Moreover, the preparation method is simple and conducive to widespread application. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of the preparation method of the composite thermoelectric material with excellent mechanical properties according to the present invention.

[0018] Figure 2 This is a transmission electron microscope (TEM) image of PEDOT-coated CNTs (i.e., PEDOT@CNTs) in Embodiment 4 of the present invention. Detailed Implementation

[0019] To enable those skilled in the art to more clearly understand the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0020] Reference Figure 1 , Figure 1 This is a schematic flowchart of a method for preparing a composite thermoelectric material with excellent mechanical properties according to the present invention. The preparation method includes:

[0021] S101. Carbon nanotubes are added to a sodium polystyrene sulfonate solution and ultrasonically dispersed to obtain a carbon nanotube suspension.

[0022] Specifically, in this step, carbon nanotubes (CNTs) of different weights can be weighed and added to sodium polystyrene sulfonate (NaPSS) solution. In this invention, the weight of carbon nanotubes does not exceed 120 mg. Preferably, carbon nanotubes (CNTs) are dispersed in sodium polystyrene sulfonate solution using probe-type ultrasound. The ultrasonic dispersion time can be 30 min, 1 h, or 2 h, with 30 min being the preferred time.

[0023] S102. Add 3,4-ethylenedioxythiophene monomer to carbon nanotube suspension and add oxidant to polymerize 3,4-ethylenedioxythiophene monomer on carbon nanotube surface to form PEDOT, and then obtain PEDOT@CNT film by vacuum filtration.

[0024] In this step, after 3,4-ethylenedioxythiophene monomer (EDOT) is added to the carbon nanotube suspension, EDOT is adsorbed on the CNT surface under π-π action. The oxidant ammonium persulfate (APS) and ferric chloride (FeCl3) are used to polymerize 3,4-ethylenedioxythiophene monomer (EDOT) in situ on the carbon nanotube surface to form PEDOT. The polymerization time can be 6h, 12h or 24h, with 12h being the preferred time.

[0025] S103. The obtained PEDOT@CNT film is cut into pieces and ground into particles. The PEDOT@CNT particles are then ultrasonically dispersed in dichloromethane to form a PEDOT@CNT suspension for 30 minutes. Then, 18.8-75 mg of ionic liquid is added, and ultrasonication continues for another 30 minutes.

[0026] In this step, the PEDOT@CNT film is cut into pieces and ground into 50μm particles in a mortar. Preferably, the ionic liquid EMI-TFSI is slowly added dropwise to the PEDOT@CNT suspension. The ionic liquid can also be other imidazole-type ionic liquids that can regulate the conformation of PEDOT molecules and promote the dispersion of CNTs. The slow dropwise addition method allows the ionic liquid to interact better with the PEDOT on the surface of PEDOT@CNTs, and also promotes the dispersion of PEDOT@CNTs.

[0027] S104. Dissolve polycarbonate particles in boiling dichloromethane to form a PC solution. Then, mechanically mix the solution obtained in step S103 with the PC solution under ultrasonic conditions at 50°C for 20 minutes. Pour the mixed solution into a polytetrafluoroethylene mold and dry it to obtain a PEDOT@CNT / PC film.

[0028] In this step, the solution obtained in step S103 is mixed with the PC solution under ultrasonic conditions in a three-necked flask. The drying is carried out in an oven for 12 hours, 24 hours or 48 hours, and the oven temperature is 50°C, 60°C or 70°C. The preferred time is 24 hours and the preferred temperature is 60°C.

[0029] Understandably, the carbon nanotubes (CNTs) used in the preparation method of the present invention are preferably NTP8012 type single-walled carbon nanotubes produced by Shenzhen Nanoport Co., Ltd., with a diameter of 1-2 nm and a purity of >90%, and the polymer PC is preferably polycarbonate (grade PC2407) produced by Covestro Polymers (China) Co., Ltd.

[0030] The preparation method of the composite thermoelectric material with excellent mechanical properties of the present invention will be described below with reference to specific embodiments.

[0031] Example 1

[0032] (1) 3.3 mg of CNTs were added to NaPSS solution and ultrasonically dispersed for 30 min to obtain a carbon nanotube suspension;

[0033] (2) Add 18 mg of 3,4-ethylenedioxythiophene (EDOT) monomer to the carbon nanotube suspension, then add 0.25 g of ammonium persulfate (APS) oxidant and 2 ml of 30 mg / mL ammonium persulfate solution. -1 EDOT was mixed with ferric chloride (FeCl3) for 30 min, and under the action of oxidant, EDOT was polymerized on the CNT surface to form PEDOT. The polymerization time was 12 h, thus obtaining PEDOT@CNT. PEDOT@CNT film was obtained by vacuum filtration.

[0034] (3) The PEDOT@CNT film obtained in step (2) is cut into pieces and ground into particles of about 50 μm in a mortar. The PEDOT@CNT particles are then dispersed in dichloromethane by ultrasonication to form a suspension. The ultrasonication time is 30 min. Then, 18.8 mg of ionic liquid is slowly added dropwise and ultrasonication is continued for another 30 min.

[0035] (4) Dissolve 12 mg of PC particles in boiling dichloromethane to form a solution. Then, mechanically mix the above PEDOT@CNT suspension and PC solution in a three-necked flask under ultrasonic conditions at 50°C for 20 min. Pour the mixed solution into a polytetrafluoroethylene mold and dry it in an oven at 60°C for 24 h to obtain a PEDOT@CNT / PC film.

[0036] As is well known, the evaluation index for the thermoelectric properties of materials is the dimensionless thermoelectric figure of merit ZT = S. 2 σT / κ, where S, σ, T, and κ are the Seebeck coefficient, electrical conductivity, absolute temperature, and thermal conductivity of the material, respectively. Therefore, to obtain excellent thermoelectric properties, a material requires a large Seebeck coefficient, high electrical conductivity, and low thermal conductivity. For organic polymers and their composites, due to their low thermal conductivity, the power factor PF = S is often used. 2 σ is used to measure the quality of a material's thermoelectric properties.

[0037] The thermoelectric and mechanical properties of the PEDOT@CNT / PC film obtained according to the formulation of this embodiment are as follows: the electrical conductivity σ is 467.9±128.6 S cm⁻¹. -1 The Seebeck coefficient is 20.3 ± 0.39 μV K. -1 The power factor (PF) is 18.8 ± 6.1 μWm. -1 K -2 The tensile modulus E is 1.8 ± 0.5 GPa, and the breaking strength σ bThe strength was 52.3 ± 8.9 MPa, and the elongation at break was 5.1 ± 2.3%.

[0038] Example 2

[0039] The method is the same as in Example 1, except that the 3.3 mg of CNT in step (1) of implementation 1 is changed to 7.5 mg. Based on this ratio, the conductivity σ of the final PEDOT@CNT / PC film is 792.8 ± 71.1 S cm⁻¹. -1 The Seebeck coefficient is 21.2 ± 0.63 μVK. -1 The power factor (PF) is 36.3 ± 2.8 μW / m. -1 K -2 The tensile modulus E is 3.3 ± 0.4 GPa, and the breaking strength σ b The strength was 146.4 ± 20.3 MPa, and the elongation at break was 4.1 ± 1.6%.

[0040] Example 3

[0041] The method is the same as in Example 1, except that the 3.3 mg of CNT in step (1) of Example 1 is replaced with 20 mg; and the 18.8 mg of ionic liquid in step (3) is replaced with 25 mg. Based on this ratio, the conductivity σ of the final PEDOT@CNT / PC film is 1761.7 ± 107.9 S cm⁻¹. -1 The Seebeck coefficient is 22.2 ± 0.57 μV K. -1 The power factor (PF) is 89.1 ± 6.5 μW / m. -1 K -2 The tensile modulus E is 4.6 ± 0.8 GPa, and the breaking strength σ b The strength was 193.6 ± 19.5 MPa, and the elongation at break was 6.3 ± 2.2%.

[0042] Example 4

[0043] The method is the same as in Example 1, except that the 3.3 mg of CNT in step (1) of Example 1 is changed to 45 mg; and the 18.8 mg of ionic liquid in step (3) is changed to 37.5 mg; refer to Figure 2 , Figure 2 The image shown is a transmission electron microscope (TEM) image of the PEDOT-coated CNT (i.e., PEDOT@CNT) in this embodiment, showing that PEDOT is coated on the surface of the CNT. Based on this formulation, the final PEDOT@CNT / PC film has a conductivity σ of 1831.3 ± 104.3 S cm⁻¹. -1 The Seebeck coefficient is 24.3 ± 0.42 μV K. -1 The power factor PF is 106.1 ± 8.2 μW / m. -1 K-2 The tensile modulus E is 4.1 ± 0.8 GPa, and the breaking strength σ b The strength was 143.5 ± 12.1 MPa, and the elongation at break was 6.3 ± 3.7%.

[0044] Understandably, in order to compare the changes in thermoelectric and mechanical properties of PEDOT / CNT composite thermoelectric materials after the addition of ionic liquid, a comparative example can be set up, using the same method as in Example 4, except that the ionic liquid in step (3) of Example 4 is not added. The resulting PEDOT@CNT / PC film has a conductivity σ of 1121.8 ± 96.1 S cm⁻¹. -1 The Seebeck coefficient is 24.1 ± 0.4 μV K. -1 The power factor (PF) is 65.2 ± 5.9 μW / m. -1 K -2 The tensile modulus E is 3.3 ± 0.3 GPa, and the breaking strength σ b The strength was 92.2 ± 13.8 MPa, and the elongation at break was 4.3 ± 1.8%. This indicates that the thermoelectric and mechanical properties were significantly improved after the addition of ionic liquid.

[0045] Example 5

[0046] The method is the same as in Example 1, except that the 3.3 mg of CNT in step (1) of Example 1 is replaced with 120 mg; and the 18.8 mg of ionic liquid in step (3) is replaced with 75 mg. Based on this ratio, the conductivity σ of the final PEDOT@CNT / PC film is 816.4 ± 32.6 S cm⁻¹. -1 The Seebeck coefficient is 25.2 ± 0.31 μV K. -1 The power factor (PF) is 55.8 ± 3.9 μW / m. -1 K -2 The tensile modulus E is 2.9 ± 0.3 GPa, and the breaking strength σ b The strength was 56.2 ± 11.9 MPa, and the elongation at break was 3.2 ± 1.2%.

[0047] In summary, this invention utilizes ionic liquids to regulate the molecular conformation of PEDOT from benzene to quinone, and simultaneously promotes the dispersion of PEDOT@CNT in suspension. By synergistically utilizing the improved dispersibility of CNTs and the high electrical conductivity of the quinone conformation of PEDOT, the overall electrical conductivity of the composite thermoelectric material is significantly improved. Furthermore, PC in the system provides excellent mechanical properties. Therefore, the composite thermoelectric material prepared by this invention possesses both high thermoelectric performance and excellent mechanical properties, namely, the high electrical conductivity of CNTs, the high electrical conductivity and high Seebeck coefficient of the quinone conformation of PEDOT, and the high mechanical properties of PC. It is evident that the preparation method of this invention maintains high mechanical properties of the material without severely sacrificing its thermoelectric performance, which is of significant importance. Moreover, the preparation method is simple, easy to control, and uses conventional equipment, resulting in low investment and easy application.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Those skilled in the art can make various equivalent changes and improvements based on the above embodiments, and all equivalent variations or modifications made within the scope of the claims should fall within the protection scope of the present invention.

Claims

1. A method for preparing a composite thermoelectric material with excellent mechanical properties, characterized in that, include: a. Carbon nanotubes are added to a sodium polystyrene sulfonate solution and ultrasonically dispersed to obtain a carbon nanotube suspension; wherein the weight of the carbon nanotubes does not exceed 120 mg. b. Add 3,4-ethylenedioxythiophene monomer to carbon nanotube suspension and add oxidant to polymerize 3,4-ethylenedioxythiophene monomer on carbon nanotube surface to form PEDOT, and then obtain PEDOT@CNT film by vacuum filtration. c. The obtained PEDOT@CNT film is cut into pieces and ground into particles. The PEDOT@CNT particles are then dispersed in dichloromethane by ultrasonication to form a PEDOT@CNT suspension. The ultrasonication time is 30 min. Then, 18.8-75 mg of ionic liquid is added, and ultrasonication is continued for another 30 min. d. Dissolve polycarbonate particles in boiling dichloromethane to form a PC solution. Then, mechanically mix the solution obtained in step c with the PC solution under ultrasonic conditions at 50°C for 20 minutes. Pour the mixed solution into a polytetrafluoroethylene mold and dry it to obtain a PEDOT@CNT / PC film. In step c, the ionic liquid EMI-TFSI is slowly added dropwise to the PEDOT@CNT suspension.

2. The method for preparing the composite thermoelectric material with excellent mechanical properties as described in claim 1, characterized in that, In step a, carbon nanotubes are dispersed in sodium polystyrene sulfonate solution using probe-type ultrasound for 30 min, 1 h, or 2 h.

3. The method for preparing a composite thermoelectric material with excellent mechanical properties as described in claim 1, characterized in that, In step b, 3,4-ethylenedioxythiophene monomer is polymerized in situ on the surface of carbon nanotubes to form PEDOT using oxidants ammonium persulfate and ferric chloride, with a polymerization time of 6h, 12h, or 24h.

4. The method for preparing a composite thermoelectric material with excellent mechanical properties as described in claim 1, characterized in that, In step c, the PEDOT@CNT film is cut into pieces and then ground into 50μm particles in a mortar.

5. The method for preparing a composite thermoelectric material with excellent mechanical properties as described in claim 1, characterized in that, In step d, the food is placed in an oven for drying for 12 hours, 24 hours, or 48 hours, at a temperature of 50°C, 60°C, or 70°C.

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