Revealing the anisotropy in thermoelectric transport performances in CNT/PANI composites

Although the carbon nanotube (CNT) based organic composites thermoelectric materials arouses considerable attentions, up to now the anisotropy in their thermoelectric performances has been overlooked. Herein, strong anisotropy in the temperature-dependent thermal and electrical transport properties have been demonstrated for organic composites thermoelectric materials, made by cold pressing the CNT powders coated by in situ polymerized polyaniline (PANI). The Seebeck coefficient, electrical and thermal conductivity are larger along the direction perpendicular to the cold pressing axis compared to the direction parallel to pressing axis. The anisotropy observed in the thermal conductivity and electrical conductivity maximizes at a CNT content of 30-40% (expressed in mass%), while the one observed for the Seebeck coefficient is small. The highest thermoelectric performances of the thermoelectric composites are achieved at a CNT mass ratio of ∼40% for both multi-walled CNT (MCNT)/PANI and single-walled CNT (SCNT)/PANI at a direction perpendicular to the cold pressing axis. These results highlight the importance of optimizing the CNT contents during the in situ polymerization with PANI to achieve a homogeneous nanostructure and reducing the agglomerate of the uncoated CNTs, in order to obtain high thermoelectric properties.