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 (κ). To develop graphene-based thermoelectric devices, reduction of κ is highly desired while maintaining reasonably high electrical conductivity (σ). Herein, multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) fillers have been added into few layered graphene (FLG) to produce all-carbon composites yielding ultra-low thermal conductivity (κ) desired for thermoelectric applications. The novel preparation method of pristine FLG realized very low κ of 6.90 W m⁻¹ K⁻¹ at 1248 K, which further reduced to 0.32, 0.55 and 0.50 W m⁻¹ K⁻¹ at 824 K, 874 K and 974 K for FLG+MWCNTs, FLG+CB and FLG+MWCNTs+CB, respectively. As prepared FLG composites also maintained reasonably high σ, whilst the Seebeck coefficient showed over a factor of five improvement after the inclusion of carbon-based fillers. Consequently, power factor (PF) has been significantly improved. The ultralow κ is attributed to the increased thermal boundary resistance between graphene sheet boundaries. The realisation of ultralow κ with simultaneous improvement in Seebeck coefficients and relatively small drops in σ with a facile and unique synthesis technique, highlight the potential of these composites.