Carbon Nanotube Yarns Tailored Using Dispersants and Surfactants for Flexible and Wearable Thermoelectric Generators

Carbon nanotube (CNT) yarns have emerged as a promising candidate for flexible and fabric-type wearable thermoelectric devices. This study developed CNT yarns tailored by a low-cost, fast, and environmentally friendly CNT dispersion method using glycerol as a dispersant and polyoxyethylene(50) stearyl ether as a surfactant. A high power factor of 242 μW m–1 K–2 was obtained, which is ca. three times higher than that of the previous dispersion method. The significant contribution is the 2-fold increase of electrical conductivity (from 325 to 747 S cm–1), which originates from the higher degree of disentanglement in dispersion and better CNT alignment in the yarn. Another contribution is the suppression of the increase in thermal conductivity as a possible side effect of the CNT alignment, which is concluded to be due to the surfactant adsorbed on CNT bundles. As a result, the figure of merit ZT value was successfully improved by ca. a factor of 3.