Enhanced thermoelectric properties of bismuth telluride (Bi2Te3) and multiwall carbon nanotube (MWCNT) composites

Abstract

Solid solutions based on bismuth telluride are the traditional thermoelectric materials that are commercially utilized in the industry close to room temperature applications, where energy scavenging is a big challenge due to low quality and energy density. However, their broader applications are still limited due to low efficiency. The focus of the present work is to enhance the energy conversion efficiency of Bi2Te3 by mixing one-dimensional (1D) multiwall carbon nanotubes (MWCNTs) via facile powder processing by synergistically utilizing the nanostructuring and quantum confinement effects. Thus, different vol% of MWCNTs ranging from 0.5, 1.0, 1.5, and 2 were uniformly dispersed in a fine powder of Bi2Te3 that was ball milled from course Bi2Te3 in an inert environment. The coarse Bi2Te3 and fine composite powders were consolidated in a spark plasma-sintering furnace at ∼400 °C under uniaxial pressure of ∼40 MPa. Thermoelectric properties of Bi2Te3-based MWCNTs composites were evaluated in the temperature range from ∼300 to ∼525 K. The electrical conductivity of 1.5 vol% MWCNT composite has significantly enhanced from pristine Bi2Te3. This increase indicates that electrical transport dominantly involves a percolating network of MWCNTs. The concomitant increase in the Seebeck coefficient of 1.5 vol% Bi2Te3 composite suggests the enhanced energy-dependent scattering of charge carriers. Consequently, a substantially improved power factor is observed for the composite. The thermal conductivity of all the composites decreases, and considerable reduction is achieved for 0.5 vol% due to enhanced phonon scattering through nanostructuring and uniform distribution of the nanotubes. Hence, the significant decrease in thermal conductivity with improved power factor leads to substantial improvement in the thermoelectric figure of merit of 1.5 vol% Bi2Te3 composite from pristine Bi2Te3.