Enhanced thermoelectric performance by single-walled carbon nanotube composites for thermoelectric generators: A review

Globally, over 60% of useful energy is not harnessed for any productive use, but is instead dissipated to the environment as waste heat, which if harvested could contribute significantly towards meeting the increasing energy demand. Thus, thermoelectric generators (TEGs) have emerged recently as an essential part of the so-lution to alleviate the current energy crisis due to their potential to effectively utilize waste heat by converting it directly to electricity via the Seebeck effect. However, TEGs are not yet suitable for large-scale practical appli-cations due to the scarcity, high-cost, toxicity, complex fabrication procedures and low thermoelectric (TE) performance of commonly used inorganic TE materials. Consequently, organic TE materials, such as carbon -based materials, in particular, single-walled carbon nanotubes (SWCNTs), have been developed recently owing to their low-cost, facile fabrication procedures, easy scalability, lightweight, excellent flexibility, non -toxicity, high electrical conductivity, tunable band gap, and the natural abundance of carbon. Most importantly, it is possible to tune, and hence optimize the TE properties of SWCNTs to compete with those of traditional inorganic TE materials, especially by preparing nanocomposites to optimize charge carrier transport primarily via the material orientation effect and energy filtering effect, which increases electrical conductivity and the Seebeck coefficient, respectively. In addition, SWCNT-based nanocomposites help to improve TE performance by lowering the lattice thermal conductivity via the phonon scattering effect, and they also help to increase sus-tainability by enhancing the mechanical and chemical stability of TE materials and devices. Thus, this review highlights the recent breakthroughs in improving TE performance, covering the period from 2018 to 2022, by preparing SWCNT-based nanocomposites, as well as discussing the benefits, challenges and future directions for fabricating highly efficient, sustainable, low-cost and environmentally friendly TEGs for commercial applications.