SnSe / SWCNTs composite thermoelectric material and preparation method and application thereof

Abstract

The invention discloses a SnSe / SWCNTs composite thermoelectric material and a preparation method and application thereof, and belongs to the technical field of thermoelectric materials. The SnSe / SWCNTs composite material is successfully prepared by using an inorganic thermoelectric matrix material tin selenide and an organic conductive material single-walled carbon nanotube to construct a composite material system in an in-situ compounding manner. By adopting the raw materials and the preparation process, C-Sn covalent bonds can be formed in the SnSe / SWCNTs composite material, the SWCNTs are uniformly dispersed in the composite material in the form of the C-Sn covalent bonds, a good conductive network and a stress transfer path are established in a SnSe matrix, phonon scattering is increased while the electric transport performance and the mechanical performance are improved, the heat conductivity is reduced, and the thermal conductivity is improved. Therefore, decoupling of the electric transport performance and the heat transport performance and remarkable improvement of the thermoelectric performance are achieved, and a new thought is provided for design and development of the high-performance composite thermoelectric material.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric materials technology, specifically relating to a SnSe / SWCNTs composite thermoelectric material, its preparation method, and its application. Background Technology

[0002] Driven by the continuous advancement of global industrialization and the rapid development of science and technology, the contradiction between energy demand and environmental carrying capacity has become increasingly prominent, posing a core challenge to the sustainable development of all countries. Currently, the energy structure of many countries still relies heavily on fossil fuels (coal, oil, natural gas, etc.). The energy utilization rate of fossil fuels is only 30%–40%, with over 60% of the energy lost as waste heat. Therefore, improving the utilization rate of fossil fuels and developing clean energy conversion technologies have become a focus of global research. Thermoelectric conversion technology can utilize the Seebeck and Peltier effects of semiconductors to achieve the direct conversion between temperature difference and electrical energy. It can convert surplus or wasted heat (industrial waste heat, vehicle exhaust, etc.) into useful clean electrical energy, making it an ideal solid-state refrigeration and thermoelectric power generation technology.

[0003] As the core carrier of thermoelectric energy conversion technology, the performance of thermoelectric materials directly determines the power generation efficiency and application value of thermoelectric devices. The key indicator for measuring the performance of thermoelectric materials is the "thermoelectric figure of merit" (ZT value), which is mathematically expressed as: ZT = (S... 2 The expression for ZT value clearly shows that the conversion efficiency of thermoelectric materials is positively correlated with the ZT value; the higher the ZT value, the higher the energy conversion efficiency of the thermoelectric device. Therefore, the core objective of improving the performance of thermoelectric materials is to optimize the electrical transport properties of the material (increasing the power factor S). 2 The key technical bottleneck to improving the performance of thermoelectric materials is to achieve "effective decoupling" between the thermal transport properties of the thermoelectric material (σ) and the thermal transport properties of the material (reducing the total thermal conductivity κ).

[0004] Composite engineering combines materials with different properties to achieve a synergistic effect where "1+1>2". By altering the matrix's energy band and crystal structure, increasing carrier concentration and mobility, and simultaneously constructing multi-scale microstructures to enhance phonon scattering and reduce lattice thermal conductivity, significant improvements in thermoelectric performance are achieved. However, in the preparation and application of inorganic / organic composite thermoelectric materials, the "interface problem" remains a key challenge restricting performance improvement. Improper design can lead to defects, chemical incompatibilities, or energy barriers, resulting in decreased carrier mobility, increased thermal conductivity, and ultimately, performance collapse. Summary of the Invention

[0005] In view of the above-mentioned prior art, the present invention provides a SnSe / SWCNTs composite thermoelectric material, its preparation method and application, so as to solve the technical problem of low performance of thermoelectric materials in the prior art due to interface problems.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is to provide a method for preparing SnSe / SWCNTs composite thermoelectric materials, comprising the following steps: S1: Dissolve sodium hydroxide in water to prepare a sodium hydroxide solution; dissolve stannous chloride and selenium dioxide together in a solvent to obtain a mixed solution; disperse single-walled carbon nanotubes in water to obtain a single-walled carbon nanotube dispersion. S2: Add sodium hydroxide solution dropwise to the mixed solution and stir until the color changes; then add single-walled carbon nanotube dispersion dropwise to the discolored system and stir evenly to obtain the reaction system; S3: Transfer the reaction system to a closed reaction vessel and react at 200~250 ℃ for 10~15 h. Then separate the precipitate, wash and dry it to obtain the final product.

[0007] Based on the above technical solution, the present invention can be further improved as follows.

[0008] Furthermore, the concentration of the sodium hydroxide solution is 0.4 g / mL.

[0009] Furthermore, the molar ratio of stannous chloride to selenium dioxide is 1:1; the feed-to-solvent ratio of stannous chloride to solvent is 1 mol: 1 L; and the solvent is ethylene glycol.

[0010] Furthermore, the concentration of the single-walled carbon nanotube dispersion is 0.15 wt%.

[0011] Furthermore, the volume ratio of the sodium hydroxide solution to the mixed solution is 1:6.

[0012] Furthermore, the amount of single-walled carbon nanotube dispersion added is based on the mass percentage of single-walled carbon nanotubes in the obtained SnSe / SWCNTs composite thermoelectric material being 0.1% to 1%.

[0013] Furthermore, the reaction temperature in S3 is 230 °C, and the reaction time is 12 h.

[0014] Furthermore, the drying temperature in S3 is 60 ℃, and the drying time is 6 h.

[0015] The present invention also discloses a SnSe / SWCNTs composite thermoelectric material prepared by the above preparation method.

[0016] The present invention also discloses the application of the above-mentioned SnSe / SWCNTs composite thermoelectric material in the preparation of thermoelectric energy conversion components.

[0017] The beneficial effects of this invention are: This invention constructs a composite material system using the inorganic thermoelectric matrix material tin selenide (SnSe) and the organic conductive material single-walled carbon nanotubes (SWCNTs). SnSe / SWCNTs composite materials were successfully prepared through in-situ composite synthesis. Using the raw materials and preparation process described in this invention, C-Sn covalent bonds are formed within the SnSe / SWCNTs composite material, and SWCNTs are uniformly dispersed within the composite material in the form of C-Sn covalent bonds. This establishes a good conductive network and stress transfer path within the SnSe matrix, improving electrical transport and mechanical properties while increasing phonon scattering and reducing thermal conductivity. This achieves decoupling of electrical and thermal transport properties and a significant improvement in thermoelectric performance, providing a new approach for the design and development of high-performance composite thermoelectric materials. Attached Figure Description

[0018] Figure 1 XRD patterns of the composite thermoelectric material SnSe / SWCNTs; Figure 2 XPS spectra of the composite thermoelectric material SnSe / 0.25wt%SWCNTs; Figure 3 SEM image of the composite thermoelectric material SnSe / 0.25wt%; Figure 4 Temperature dependence curve of conductivity of composite thermoelectric material SnSe / SWCNTs; Figure 5 Temperature dependence curve of Seebeck coefficient for composite thermoelectric material SnSe / SWCNTs; Figure 6 Temperature dependence curve of thermal conductivity of composite thermoelectric material SnSe / SWCNTs; Figure 7 Temperature dependence curve of ZT value for SnSe / SWCNTs composite thermoelectric material Figure 8 Vickers hardness (HV) of the composite thermoelectric material SnSe / SWCNTs. Detailed Implementation

[0019] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0020] Example 1 A SnSe / SWCNTs composite thermoelectric material is prepared by the following steps: S1: Dissolve 4 g of sodium hydroxide (NaOH) in 10 mL of deionized water to prepare a sodium hydroxide solution; dissolve 5 mmol of stannous chloride (SnCl2·2H2O) and 5 mmol of selenium dioxide (SeO2) in 60 mL of ethylene glycol to obtain a mixed solution; disperse single-walled carbon nanotubes (SWCNTs) in water to obtain a single-walled carbon nanotube dispersion with a concentration of 0.15 wt%. S2: Slowly add sodium hydroxide solution to the mixed solution and stir until the color changes; then add single-walled carbon nanotube dispersion to the discolored system. The amount of single-walled carbon nanotube dispersion added should be based on the mass ratio of single-walled carbon nanotubes in the obtained SnSe / SWCNTs composite thermoelectric material being 0.1%. Continue stirring for 10 min to obtain the reaction system. S3: Transfer the reaction system to a 100 mL Teflon-lined container, ensuring it is sealed in the reactor, and then heat it in an oven at 230 °C for 12 h. After air cooling to room temperature, remove it from the oven. S4: Pour off the supernatant of the cooled solution, filter the resulting precipitate multiple times, and wash it continuously with deionized water and anhydrous ethanol. After multiple washings, transfer it to a vacuum drying oven at 60 °C and dry it for 6 h to obtain the SnSe / SWCNTs composite thermoelectric material, denoted as SnSe / 0.1wt%SWCNTs.

[0021] Example 2 A SnSe / SWCNTs composite thermoelectric material is prepared by the following steps: S1: Dissolve 4 g of sodium hydroxide (NaOH) in 10 mL of deionized water to prepare a sodium hydroxide solution; dissolve 5 mmol of stannous chloride (SnCl2·2H2O) and 5 mmol of selenium dioxide (SeO2) in 60 mL of ethylene glycol to obtain a mixed solution; disperse single-walled carbon nanotubes (SWCNTs) in water to obtain a single-walled carbon nanotube dispersion with a concentration of 0.15 wt%. S2: Slowly add sodium hydroxide solution to the mixed solution and stir until the color changes; then add single-walled carbon nanotube dispersion to the discolored system. The amount of single-walled carbon nanotube dispersion added should be based on the mass ratio of single-walled carbon nanotubes in the obtained SnSe / SWCNTs composite thermoelectric material being 0.25%. Continue stirring for 10 min to obtain the reaction system. S3: Transfer the reaction system to a 100 mL Teflon-lined container, ensuring it is sealed in the reactor, and then heat it in an oven at 230 °C for 12 h. After air cooling to room temperature, remove it from the oven. S4: Pour off the supernatant of the cooled solution, filter the resulting precipitate multiple times, and wash it continuously with deionized water and anhydrous ethanol. After multiple washings, transfer it to a vacuum drying oven at 60 °C and dry it for 6 h to obtain the SnSe / SWCNTs composite thermoelectric material, denoted as SnSe / 0.25wt%SWCNTs.

[0022] Example 3 A SnSe / SWCNTs composite thermoelectric material is prepared by the following steps: S1: Dissolve 4 g of sodium hydroxide (NaOH) in 10 mL of deionized water to prepare a sodium hydroxide solution; dissolve 5 mmol of stannous chloride (SnCl2·2H2O) and 5 mmol of selenium dioxide (SeO2) in 60 mL of ethylene glycol to obtain a mixed solution; disperse single-walled carbon nanotubes (SWCNTs) in water to obtain a single-walled carbon nanotube dispersion with a concentration of 0.15 wt%. S2: Slowly add sodium hydroxide solution to the mixed solution and stir until the color changes; then add single-walled carbon nanotube dispersion to the discolored system. The amount of single-walled carbon nanotube dispersion added should be based on the mass ratio of single-walled carbon nanotubes in the obtained SnSe / SWCNTs composite thermoelectric material being 0.5%. Continue stirring for 10 min to obtain the reaction system. S3: Transfer the reaction system to a 100 mL Teflon-lined container, ensuring it is sealed in the reactor, and then heat it in an oven at 230 °C for 12 h. After air cooling to room temperature, remove it from the oven. S4: Pour off the supernatant of the cooled solution, filter the resulting precipitate multiple times, and wash it continuously with deionized water and anhydrous ethanol. After multiple washings, transfer it to a vacuum drying oven at 60 °C and dry it for 6 h to obtain the SnSe / SWCNTs composite thermoelectric material, denoted as SnSe / 0.5wt%SWCNTs.

[0023] Example 4 A SnSe / SWCNTs composite thermoelectric material is prepared by the following steps: S1: Dissolve 4 g of sodium hydroxide (NaOH) in 10 mL of deionized water to prepare a sodium hydroxide solution; dissolve 5 mmol of stannous chloride (SnCl2·2H2O) and 5 mmol of selenium dioxide (SeO2) in 60 mL of ethylene glycol to obtain a mixed solution; disperse single-walled carbon nanotubes (SWCNTs) in water to obtain a single-walled carbon nanotube dispersion with a concentration of 0.15 wt%. S2: Slowly add sodium hydroxide solution to the mixed solution and stir until the color changes; then add single-walled carbon nanotube dispersion to the discolored system. The amount of single-walled carbon nanotube dispersion added should be based on the mass ratio of single-walled carbon nanotubes in the obtained SnSe / SWCNTs composite thermoelectric material being 0.75%. Continue stirring for 10 min to obtain the reaction system. S3: Transfer the reaction system to a 100 mL Teflon-lined container, ensuring it is sealed in the reactor, and then heat it in an oven at 230 °C for 12 h. After air cooling to room temperature, remove it from the oven. S4: Pour off the supernatant of the cooled solution, filter the resulting precipitate multiple times, and wash it continuously with deionized water and anhydrous ethanol. After multiple washings, transfer it to a vacuum drying oven at 60 °C and dry it for 6 h to obtain the SnSe / SWCNTs composite thermoelectric material, denoted as SnSe / 0.75wt%SWCNTs.

[0024] Example 5 A SnSe thermoelectric material is prepared by the following steps: S1: Dissolve 4 g of sodium hydroxide (NaOH) in 10 mL of deionized water to prepare a sodium hydroxide solution; dissolve 5 mmol of stannous chloride (SnCl2·2H2O) and 5 mmol of selenium dioxide (SeO2) in 60 mL of ethylene glycol to obtain a mixed solution; S2: Slowly add sodium hydroxide solution dropwise to the mixed solution and stir until the color changes to obtain the reaction system; S3: Transfer the reaction system to a 100 mL Teflon-lined container, ensuring it is sealed in the reactor, and then heat it in an oven at 230 °C for 12 h. After air cooling to room temperature, remove it from the oven. S4: Pour off the supernatant of the cooled solution, filter the resulting precipitate multiple times, and wash it continuously with deionized water and anhydrous ethanol. After multiple washings, transfer it to a vacuum drying oven at 60 °C and dry it for 6 h to obtain SnSe thermoelectric material, denoted as SnSe / 0wt%SWCNTs.

[0025] Experimental Example The powdered thermoelectric materials prepared in the above embodiments were made into bulk samples using rapid hot pressing technology. The rapid hot pressing process is as follows: the powdered thermoelectric materials are kept at a vacuum of 823 K and 50 MPa for 30 min and then pressed to obtain bulk thermoelectric material samples.

[0026] XRD analysis was performed on the thermoelectric materials prepared in the above embodiments, and the results are as follows: Figure 1 As shown. From Figure 1As can be seen, the typical X-ray diffraction peaks of SnSe in the obtained thermoelectric material are located at 2θ=31.2, 31.3, and 31.4°, which is consistent with the standard data (PDF#48-1224). Meanwhile, the diffraction peaks of the SnSe / SWCNTs composite material show an overall leftward shift, but this leftward shift reaches its maximum at 0.25 wt%, and then undergoes a certain rightward shift. Therefore, excessive SWCNTs doping can lead to severe enrichment.

[0027] XPS analysis was performed on the thermoelectric materials SnSe / 0.25wt%SWCNTs and pure SWCNTs prepared in Example 2 above. The results are as follows: Figure 2 As shown. From Figure 2 As can be seen, the SnSe / 0.25wt%SWCNTs composite material shows three peaks, corresponding to C-Sn, C=C and C-OH bonds respectively, indicating that SWCNTs participated in the in-situ synthesis of SnSe and formed C-Sn covalent bonds between SnSe and SWCNTs.

[0028] SEM analysis was performed on the thermoelectric material SnSe / 0.25wt%SWCNTs prepared in Example 2 above, and the results are as follows: Figure 3 As shown in (a). From Figure 3 As shown in (a), SWCNTs are uniformly distributed around the SnSe particles (arrows in the figure) and are tightly integrated with the main SnSe particles; the morphology and structure of the SnSe / SWCNTs composite material are shown in the figure below. Figure 3 As shown in (b).

[0029] The electrical transport properties of the prepared bulk samples were tested and analyzed in detail using a Seebeck coefficient analyzer; the thermal transport properties of the prepared bulk samples were tested and analyzed in detail using a flash laser thermal conductivity meter.

[0030] Based on the obtained electrical performance data, the conductivity versus temperature (T) curve was plotted. The conductivity of SnSe with different SWCNT composite amounts x (x = 0, 0.10, 0.25, 0.50, 0.75 wt%) was compared. The results are as follows: Figure 4 As shown. From Figure 4As can be seen, the overall conductivity of the composite material after SWCNT doping is higher than that of undoped (x=0) pure SnSe. With increasing SWCNT doping amount (x), the conductivity first increases and then decreases, with the sample doped with 0.25wt% SWCNTs exhibiting the highest conductivity, followed by 0.50wt%. This indicates that the addition of SWCNTs establishes a good conductive network and stress transmission path within the SnSe matrix, optimizing the overall conductivity of the SnSe / xwt%SWCNTs composite material. Therefore, appropriate SWCNT doping can significantly improve conductivity and optimize its temperature response. However, excessive SWCNT doping can lead to SWCNT enrichment, resulting in deterioration of conductivity performance.

[0031] The Seebeck coefficient as a function of temperature (T) is shown in the curve. Figure 5 As shown. From Figure 5 As can be seen, after doping with SWCNTs, the Seebeck coefficient of the composite material is generally lower than that of undoped (x=0) pure SnSe. With the increase of SWCNT doping amount (x), the Seebeck coefficient first decreases and then increases, with the sample doped with 0.50wt% SWCNTs having the lowest Seebeck coefficient. This is because after the doping of the second phase SWCNTs, the internal interface of the material increases significantly, introducing additional charge carriers. The Fermi level shifts into the conduction band, reducing band asymmetry and lowering the Seebeck coefficient. At the same time, the carrier scattering is enhanced by the addition of SWCNTs, and the difference between high and low energy charge carriers decreases, further reducing the Seebeck coefficient.

[0032] The curve of the total thermal conductivity κ of the SnSe / SWCNTs composite material as a function of temperature is shown below. Figure 6 As shown. From Figure 6 As can be seen, κ generally shows a trend of first decreasing slowly and then leveling off with increasing temperature, with values ​​concentrated in the range of 0.3 to 0.7 W / m. -1 K -1 Between the two, undoped SnSe exhibits the highest thermal conductivity. The overall κ decreases after incorporating SWCNTs, and this decreases monotonically with increasing doping concentration (x), with the 0.75 wt% sample showing the lowest thermal conductivity. This indicates that while an appropriate amount of SWCNTs improves conductivity, it also creates strong phonon scattering centers, leading to a decrease in thermal conductivity.

[0033] The ZT value of the SnSe / SWCNTs composite material as a function of temperature is shown in the following curve. Figure 7 As shown. From Figure 7As can be seen, ZT first increases and then decreases with increasing temperature, reaching a peak around 750 K. The pure SnSe sample has the lowest ZT, with a peak ZT < 0.5. The sample doped with 0.25 wt% SWCNTs has the highest ZT, with a peak value of approximately 1.05; followed by 0.10 wt%, and then decreasing to 0.50 wt% and 0.75 wt%. Therefore, the appropriate amount of carbon nanotubes (≈0.25 wt%) in the composite material achieves decoupling of thermal and electrical transport properties, improving electrical transport properties while effectively suppressing thermal conductivity, thus significantly increasing ZT.

[0034] The Vickers hardness (HV) of SnSe / SWCNTs composites is as follows: Figure 8 As shown. From Figure 8 As can be seen, the hardness of pure SnSe (x=0) is approximately 19 HV. With increasing composite content x, the hardness increases significantly; it reaches approximately 27 HV ​​at 0.10 wt%, further increasing to approximately 47 HV at 0.25 wt%, after which the increase slows down, remaining in the 40-50 HV range at 0.50 wt% and 0.75 wt%, showing a saturation trend. This indicates that SWCNTs form a good stress transfer path within the composite material, improving the Vickers hardness. When the SWCNT content is too high, SWCNT enrichment leads to performance degradation.

[0035] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A method for preparing a SnSe / SWCNTs composite thermoelectric material, characterized in that, Includes the following steps: S1: Dissolve sodium hydroxide in water to prepare a sodium hydroxide solution; dissolve stannous chloride and selenium dioxide together in a solvent to obtain a mixed solution; disperse single-walled carbon nanotubes in water to obtain a single-walled carbon nanotube dispersion. S2: Add sodium hydroxide solution dropwise to the mixed solution and stir until the color changes; then add single-walled carbon nanotube dispersion dropwise to the discolored system and stir evenly to obtain the reaction system; S3: Transfer the reaction system to a closed reaction vessel and react at 200~250 ℃ for 10~15 h. Then separate the precipitate, wash and dry it to obtain the final product.

2. The preparation method according to claim 1, characterized in that: The concentration of the sodium hydroxide solution is 0.4 g / mL.

3. The preparation method according to claim 2, characterized in that: The molar ratio of stannous chloride to selenium dioxide is 1:1; the ratio of stannous chloride to solvent is 1 mol: 12 L; and the solvent is ethylene glycol.

4. The preparation method according to claim 3, characterized in that: The concentration of the single-walled carbon nanotube dispersion is 0.15 wt%.

5. The preparation method according to claim 4, characterized in that: The volume ratio of the sodium hydroxide solution to the mixed solution is 1:

6.

6. The preparation method according to claim 5, characterized in that: The amount of single-walled carbon nanotube dispersion added should be based on the mass ratio of single-walled carbon nanotubes in the obtained SnSe / SWCNTs composite thermoelectric material being 0.1% to 1%.

7. The preparation method according to claim 1, characterized in that: The reaction temperature in S3 is 230 °C, and the reaction time is 12 h.

8. The preparation method according to claim 1, characterized in that: The drying temperature in S3 is 60 ℃, and the drying time is 6 h.

9. The SnSe / SWCNTs composite thermoelectric material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the SnSe / SWCNTs composite thermoelectric material according to claim 9 in the preparation of thermoelectric energy conversion components.

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