Investigation into the stability of chemical doping and the structure of carbon nanotube

Thermoelectric power generation using carbon nanotubes (CNTs) has attracted considerable attention as a clean energy technology. A variety of chemical dopants that are stable in air have been reported to improve the thermoelectric performance of CNT; however, the stability of the chemical dopants is sometimes not reproducible. Therefore, we focused on the effects of CNT and chemical n-dopant structures on the stability and thermoelectric properties. We n-doped CNTs with different properties and measured their transient responses for 180 days. The stability was found to strongly depend on not only the dopant structure but also the structure of the CNT, especially the diameter. This is because CNTs with small diameters have a wide bandgap and a high energy level of the conduction band, and chemical dopants with a stronger electron-donating ability are required to obtain stable n-type CNTs. Therefore, the stability of chemical dopants strongly depends not only on the dopant structure but also on the structure of the CNT itself. This study focuses on the diameter among all the different structural parameters of CNTs. However, our findings indicate that the structure of CNTs is an essential factor to be considered while discussing the stability of chemical dopants.