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▼ [7a-C22-10] Semiconducting Single-walled Carbon Nanotubes Extracted by Flavin Compound for Thermoelectric Materials
キーワード：Thermoelectric conversion, Semiconducting carbon nanotubes, Seebeck coefficient
Single-walled carbon nanotubes (SWNTs) have attracted strong attention as thermoelectric (TE) material due to their extremely high electrical conductivity (σ), light weight, mechanical toughness and flexibility. However, SWNTs are produced as a mixture of metallic (m-) and semiconducting SWNTs (s-SWNTs). s-SWNTs were proved to have large Seebeck coefficient (S) theoretically and experimentally [1, 2], however, the contamination of m-SWNTs decreased the S. To date, many extraction methods of s-SWNT have been developed such as selective dispersion using polyfluorene (PFO), density gradient ultracentrifugation (DGU) and gel chromatography (GC) [4]. However, these method are either hard to remove the dispersant or time consuming. Previously, our group reported that flavin derivative (dmc12) can extract s-SWNTs from SWNT mixture [3] simply by one step solubilization, in which dmc12 can be easily removed from s-SWNTs by washing with chloroform or methylene chloride. In addition, this simple separation process introduces little damage to SWNTs, which enables the characterization of inherent TE properties for s-SWNTs.
In this study, we extracted s-SWNTs by flavin compound and fabricated free-standing s-SWNT sheet. The TE properties of the s-SWNT and SWNT sheet (before extraction) were evaluated by ZEM-3 (ADVANCE RIKO) and Thermowave Analyzer TA (Bethel Co., Ltd.)
We measured the UV-vis spectra of the supernatant of SWNT mixture and s-SWNT, and found that after extraction, a huge decrease of m-SWNT peak was observed, indicating that the extraction of s-SWNTs. We also measured the in plane σ, S, power factor (PF) and thermal diffusivity (TD) of the SWNT and s-SWNT sheets at 30 ºC. s-SWNT sheet has an S (59.2 uV/K) almost twice as high as SWNT sheet (34.4 uV/K). On the other hand, σ of s-SWNT sheet (35197 S/m) was 20% smaller than that of SWNT sheet (43762 S/m), which is a much smaller difference than other extraction methods probably due to the less damage or breaking of SWNTs during the extraction. All these factors lead to a higher PF of the s-SWNT sheets (123.4 µW m-1K-2). TD of s-SWNT sheet (2.24 E-5 m2 s-1) is smaller than SWNT sheet (3.50 E-5 m2 s-1) probably due to larger thermal resistance between s-SWNTs than between s-SWNT and m-SWNT.
[1] Ferguson, A. J. et al. Nature Energy, 1, 16033 (2016) [2] Maniwa, Y. et al, Appl. Phys. Express, 7, 025103 (2014) [3] Nakashima, N., et al, Chem. Lett., 44, 566 (2015) [4] Liu, Y. et al, Chem. Soc. Rev., 40, 1324 (2011)
In this study, we extracted s-SWNTs by flavin compound and fabricated free-standing s-SWNT sheet. The TE properties of the s-SWNT and SWNT sheet (before extraction) were evaluated by ZEM-3 (ADVANCE RIKO) and Thermowave Analyzer TA (Bethel Co., Ltd.)
We measured the UV-vis spectra of the supernatant of SWNT mixture and s-SWNT, and found that after extraction, a huge decrease of m-SWNT peak was observed, indicating that the extraction of s-SWNTs. We also measured the in plane σ, S, power factor (PF) and thermal diffusivity (TD) of the SWNT and s-SWNT sheets at 30 ºC. s-SWNT sheet has an S (59.2 uV/K) almost twice as high as SWNT sheet (34.4 uV/K). On the other hand, σ of s-SWNT sheet (35197 S/m) was 20% smaller than that of SWNT sheet (43762 S/m), which is a much smaller difference than other extraction methods probably due to the less damage or breaking of SWNTs during the extraction. All these factors lead to a higher PF of the s-SWNT sheets (123.4 µW m-1K-2). TD of s-SWNT sheet (2.24 E-5 m2 s-1) is smaller than SWNT sheet (3.50 E-5 m2 s-1) probably due to larger thermal resistance between s-SWNTs than between s-SWNT and m-SWNT.
[1] Ferguson, A. J. et al. Nature Energy, 1, 16033 (2016) [2] Maniwa, Y. et al, Appl. Phys. Express, 7, 025103 (2014) [3] Nakashima, N., et al, Chem. Lett., 44, 566 (2015) [4] Liu, Y. et al, Chem. Soc. Rev., 40, 1324 (2011)