Effect of the carbon nanotube type on the thermoelectric properties of CNT/Nafion nanocomposites

The effect of different carbon nanotube (CNT) types on the thermoelectric performance of CNT/polymer nanocomposites was studied. Three different kinds of CNTs, single- (SWCNTs), few- (FWCNTs) and multi-walled CNTs (MWCNTs), were effectively dispersed in an aqueous solution of Nafion. The electrical properties of the CNT/Nafion nanocomposites were primarily affected by the CNTs since the Nafion acts as an electrically non-conducting matrix, while the thermal conductivity of the nanocomposites was dominated by the Nafion mainly due to weak van der Waals interaction. In this way, electrical and thermal transport can be separated. In all three types of CNTs, both the electrical conductivity and Seebeck coefficient increased as the concentration of CNTs was increased. While the electrical conductivity depends on the type of CNT, the behavior of the Seebeck coefficient was relatively insensitive of the CNT type at high CNT loading. This indicates that high-energy-charges can participate in transport processes irrespective of the type of CNT. It is suggested that FWCNTs and MWCNTs are preferred over SWCNTs in CNT/Nafion nanocomposites for thermoelectric applications.