Influence of chemical functionalization on the thermoelectric properties of monodispersed single-walled carbon nanotubes

Abstract

Single-walled carbon nanotubes (SWCNTs) networks have attracted great attention for electronic and energy-harvesting applications, including thermoelectric (TE) devices. However, the simultaneous production of metallic SWCNTs (m-SWCTNs) and semiconducting SWCNTs (s-SWCNTs) randomly with distinct electronic structures always hinders the specific usage. The investigation of the influence of different electronic structures by nature or artificially on the TE performances of monodispersed SWCNTs is significative. In this report, high purity of separated m- and s-SWCNTs was chemically functionalized with 4-bromobenzene diazonium tetrafluoroborate, leading to the hybridization of C atoms changed from sp2 to sp3. The influence of the electronic type of SWCNTs on the TE properties as a function of the modifier agent was systematically investigated. As a consequence, the maximum power factor of s-SWCNTs networks was as high as 244.2 μW m−1 K−2 under the optimal condition, whereas it was only 5.3 μW m−1 K−2 for m-SWCNTs networks. In addition, grafting of functional groups onto the sidewall of nanotubes was predicted to further decrease the thermal conductivity, which is beneficial to increment of the ZT values. Based on these results, we believe that the pure s-SWCNTs and a variety of chemically functionalized composites have great potential as candidate for TE applications.