Ultralow Thermal Conductivity Achieved by All Carbon Nanocomposites for Thermoelectric Applications

Carbon-based materials are becoming a promising candidate for thermoelectricity. Among them, graphene shows limited scope due to its ultra-high thermal conductivity (kappa). To develop graphene-based thermoelectric devices, reduction of kappa is highly desired while maintaining reasonably high electrical conductivity (sigma). Herein, multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) fillers are added into few layered graphene (FLG) to produce all-carbon composites yielding ultra-low thermal conductivity (kappa) desired for thermoelectric applications. The novel preparation method of pristine FLG realizes very low kappa of 6.90 W m(-1) K-1 at 1248 K, which further reduces to 0.57, 0.81, and 0.69 W m(-1) K-1 at the same temperature for FLG + MWCNTs, FLG + CB, and FLG + MWCNTs + CB, respectively. As-prepared FLG composites also maintain reasonably high sigma, whilst the Seebeck coefficient shows over a factor of five improvement after the inclusion of carbon-based fillers. Consequently, the power factor (PF) is significantly improved. The ultralow kappa is attributed to the increased thermal boundary resistance among graphene sheet boundaries. The realization of ultralow kappa with simultaneous improvement in Seebeck coefficients and relatively small drops in sigma with a facile and unique synthesis technique, highlight the potential of these composites.