Preparation and thermoelectric properties of multi-walled carbon nanotubes/polypyrrole composites

Multi-walled carbon nanotubes (MWCNT)/polypyrrole (PPy) composite powders with MWCNT content ranging from 0 to 20 wt% were prepared by an in-situ polymerization method using p-toluenesulfonic acid (TSA) as a dopant and iron chloride (FeCl3) as an oxidant. The powders were examined by X-ray diffraction, thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The composite powders consist of PPy nanoparticles and quasi-one-dimensional MWCNT/PPy core/shell nanostructures. The electrical conductivity and Seebeck coefficient of the cold pressed powders were measured from 295 to 375 K. The electrical conductivity of the samples increases with the MWCNT content when the MWCNT is lower than 15% and then decreases when higher than 15%, whereas the Seebeck coefficient of the samples first gradually increases with the MWCNT content and then increases quickly when the MWCNT content is higher than 15%. As a result, the power factor of the samples increases with the MWCNT content and the maximum value is 2.079 μW m−1 K−2 when the MWCNT content is 20%. It is about 26 times as high as that of pure PPy.