Effect of Surfactants on the Thermoelectric Performance of Double‐Walled Carbon Nanotubes

• Published in: Energy & environmental materials (Hoboken, N.J.) N.J.), 2023-01, Vol.6 (1), p.274-n/a
• Main Authors: Saadi, Zakaria, King, Simon G., Anguita, José V., Stolojan, Vlad, Silva, S. Ravi P.
• Format: Article
• Language: English
• Subjects: Carbon; Carbon nanotubes; Decoupling; Density of states; DWCNT; Electrical conductivity; Electrical resistivity; functionalization; Heat conductivity; Heat transfer; Hydrophobicity; Molecular chains; Nanotechnology; Nanotubes; Seebeck effect; surfactant; Surfactants; Temperature gradients; Thermal conductivity; thermoelectric; Thermoelectric generators; Thermoelectricity; Thin films
• ISSN: 2575-0356; 2575-0348; 2575-0356
• DOI: 10.1002/eem2.12281

Thermoelectrics are a promising solution to the recovery of some of the 60% of the worldwide energy wasted as heat. However, their conversion efficiency is low and the best performing materials are brittle, toxic, and made of expensive ceramics. The challenge in developing better performing materials is in disrupting the electrical vs thermal conductivity correlation, to achieve low thermal conductivity simultaneously with a high electrical conductivity. Carbon nanotubes allow for the decoupling of the electronic density of states from the phonon density of states and this paper shows that flexible, thin films of double‐walled carbon nanotube (DWCNT) can form effective n‐ and p‐doped semiconductors that can achieve a combined Seebeck coefficient of 157.6 µV K−1, the highest reported for a single DWCNT device to date. This is achieved through selected surfactant doping, whose role is correlated with the length of the hydrocarbon chain of the hydrophobic tail group of the surfactant’s molecules. CNTs functionalized with Triton X‐405 show the highest output power consisting of a single junction of p‐ and n‐type thermoelectric elements, reaching as high as 67 nW for a 45 K temperature gradient. Thus enabling flexible, cheaper, and more efficient thermoelectric generators through the use of functionalized CNTs. Thermoelectrics can help recover ~60% of worldwide energy wasted as heat. Much heat waste results from energy conversion during generation and in the use of mechanical machines. The present technology leaders in thermoelectrics are typically inorganic, toxic, inflexible, have low conversion efficiency, and expensive. Developing low‐cost hybrids that decouple the electronic and phonon density of states to give high Seebeck values has been a challenge. In this work, the 1D nature of the CNT is exploited to achieve a combined Seebeck coefficient of 157.6 µV K−1, the highest reported for double‐wall CNT devices via selected surfactant doping.