Investigation of the Stabilization Mechanism of Air Stable n-Type Single-Walled Carbon Nanotubes Sheets Based on Adsorption Isotherm Measurements

Abstract

In spite of the remarkable growth of microelectronics such as wearable devices, remote sensors, etc. On the market in recent years, almost all of them are still powered by batteries that are required to be recharged or replaced at stated periods. If these electronic devices can run continuously for an extended time without any external interference, the benefits would be further enhanced. One such solution is to produce energy from the human body heat, where the thermoelectric (TE) generation mechanism is used to generate electricity from temperature difference. The principle behind TE generation is the Seebeck effect. It is a phenomenon to produce potential difference from the temperature difference between the ends of a TE generator. The efficiency of this TE conversion can be evaluated by the figure of merit, ZT = S2σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity. TE generators with a high Seebeck coefficient, high electrical conductivity, and low thermal conductivity are expected to have good TE properties. To fabricate the TE devices, p- and n-type materials are necessary and the research of TE materials using inorganic semiconductors such as Bi2Te3 have been done for a long time as they illustrate high performance more than ZT = 1. However, these materials contain rare and toxic elements and they are difficult to process. Therefore, among the several candidates including conducting polymers, single-walled carbon nanotubes (SWNTs) are emerged as the promising candidate due to their non-toxicity, processability, remarkable electrical and thermal conductivity, potentially large Seebeck coefficient and light weight. However, due to air oxidation, SWNTs show only p-type semiconducting property in air. In the development of the SWNTs-based TE devices, instability of the n-type SWNTs has been a crucial issue, since n-type SWNT are easily oxidized due to an electrophilic chemisorption of oxygen on the charge polarization.1 Under such background, we have reported that air-stable n-type SWNTs can be formed by adsorbing 2-(2-methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzo [d] imidazole (o-MeO-DMBI). However, the stabilization mechanism is not clear. herefore, in this research we studied the stabilization mechanism based on the adsorption isotherm measurements, where the SWNT sheets were dipped in the ethanol solution of o-MeO-DMBI in different concentrations at 25 ºC. From the adsorption isotherm, we revealed that SWNTs sheets adsorbed below monolayer of o-MeO-DMBI showed unstable in n-type, while SWNT sheets adsorption of o-MeO-DMBI showed stable n-type property over full coverage3. 1) Zhu, X.-Q.; Zhang, M.-T.; Yu, A.; Wang, C.-H.; Cheng, J.-P. J. Am. Chem. Soc. 2008, 130, 2501. 2) Nakashima, Y.; Nakashima, N.; Fujigaya, T. Synthetic. Metals. 2017, 76, 225. 3) Nakashima, Y.; Yamaguchi, R.; Fujigaya, T. submitted.