Effect of Functional Groups on the Thermoelectric Performance of Carbon Nanotubes

Single-wall carbon nanotubes (SWCNTs) have received much attention in the past decade due to their excellent electric and mechanical properties. The quantum confinement effect of charge carriers in an individual carbon nanotube (CNT), together with the flexible topology and high tensile strength, make it a potential candidate thermoelectric (TE) material. However, the low Seebeck coefficient and high thermal conductivity of SWCNTs limits further development for a good TE material with high performance. Although many efforts have been focused on the improvement of TE performance for SWCNTs by doping and composites, few works have been devoted to investigation of functional groups in SWCNTs. In this work, we investigated the TE performance of SWCNT films in detail with different functional groups (hydroxyl, carboxyl, and amino). It is found that the Seebeck coefficient of SWCNTs with different functional groups have an obvious improvement with the decrease in electrical conductivity. An optimal power factor of 47.8 μW m−1 K−2 was obtained for SWCNTs with a hydroxyl group comparable to pure SWCNTs. Significantly, the introduction of functional groups results in a marked reduction in thermal conductivity and an enhanced TE figure of merit (ZT). This work provides an alternative strategy to optimize the TE performance of SWCNTs.