Mass-produced metallic multiwalled carbon nanotube hybrids exhibiting high N-type thermoelectric performances

Abstract

Finding a stable n-type flexible thermoelectric (TE) material with a high power factor and mass production is a challenge for wearable TE devices. In this paper, we report that metallic multiwalled carbon nanotubes (MWCNTs) and their hybrids are converted from p-type to n-type with an n-type dopant, 1,3-dimethyl-2-phenyl-2,3-dihydro-1h-benzoimidazole (NDMBI), with a high n-type Seebeck coefficient. The maximum power factor of the n-type hybrid is 195 μW m⁻¹ K² at 373 K which is 2–3 orders higher than those of most n-type MWCNT based organic materials in the literature. This high TE performance may be attributed to the high n-type Seebeck coefficient of MWCNTs derived from the effective n-type doping. The theoretical calculation results indicate that the effective n-type doping could increase the Seebeck coefficients of metallic MWCNTs without sacrificing their electrical conductivities when their Fermi level shifts to approach the one-dimensional van Hove singularity. The results suggest that the trade-off relationship between the electrical conductivity and the Seebeck coefficient of one-dimensional metallic materials could be solved, which are promising candidates for preparing large scalable, low-cost, and high-performance flexible TE devices for wearable electronics. This may promote the evolution of developing high performance organic and inorganic TE materials with metallic one-dimensional nanomaterials.