Thermoelectric characterization of multi-walled carbon nanotube/ Sodium cobalt oxide prepared by a low-cost flame sintering technique

Abstract

© 2017 Elsevier Ltd and Techna Group S.r.l. Multi-walled carbon nanotubes/sodium cobalt oxide (MWCNTs/NaxCoO2) composites were successfully obtained via a flame sintering method. Such sintering is accountable for a surface densification that can preserve the MWCNTs entity within the composites. Raman spectroscopy confirmed the presence of MWCNTs in the composites, with NaxCoO2being present as a single phase (γ) as revealed by X-ray diffraction. EDX results suggested non-uniform distribution of MWCNTs within the NaxCoO2material, although their presence resulted in increased electrical conductivity through enhancements in charge mobility. The effect of MWCNTs addition on the thermoelectric performance of NaxCoO2was examined. Addition of MWCNTs results in increased levels of phonon scattering in the composites, leading to decreased thermal conductivity. Although Seebeck coefficients decreased due to an increase in charge density, the thermoelectric efficiency of the composites reported as ZT values was enhanced in comparison to those in material without added MWCNTs, with optimum conditions found in composites derived from 0.25 wt%MWCNTs/NaxCoO2(with ZT enhancement by ca. 60% at 398 K).