Air-Stable n-Type Single-Walled Carbon Nanotubes Doped with Benzimidazole Derivatives for Thermoelectric Conversion and Their Air-Stable Mechanism

The development of n-type single-walled carbon nanotubes (SWCNTs) stable under an air atmosphere is a key issue to prepare an efficient and stable thermoelectric conversion device using SWCNTs. Doping of SWCNT sheets with 2-(2-methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzo[d]imidazole (o-MeO–DMBI) offers air-stable n-type SWCNT sheets. However, a clear mechanism of the stabilization in air has not been clarified yet. In this study, air stability is found to largely depend on the doping concentration. Adsorption isotherm experiments of the dopant onto SWCNT sheet reveal that the entire coverage of the SWCNT surface by o-MeO–DMBI cation is the key requirement to realize the air stability, which is well-supported by the theoretical calculation. This finding provides useful guidelines to develop air-stable n-type SWCNTs with various n-dopants.