Influence of polymerization method on the thermoelectric properties of multi-walled carbon nanotubes/polypyrrole composites

• MWCNTs/PPy composites were prepared by in-situ/interfacial polymerization method.
• The TE properties and formation mechanism of both composites were investigated.
• The in-situ polymerized composite showed higher electrical conductivity.
• The highest power factor is 26.5 times greater than that of pure PPy.

Multi-walled carbon nanotubes (MWCNTs)/polypyrrole (PPy) thermoelectric composites with MWCNT content ranging from 0 to 68 wt% have been prepared by in-situ polymerization or interfacial polymerization method. Both methods have enhanced the thermoelectric properties of PPy significantly. TEM observation shows that the in-situ polymerized composite consists of MWCNTs/PPy core/shell structures, while the interfacial polymerized composite is inhomogeneous: only a small amount of MWCNTs being coated with PPy and most of the MWCNTs aggregated into bundles and clusters. Due to the uniform dispersion of MWCNTs in the PPy matrix and therefore the stronger π–π interactions between MWCNTs and PPy, the in-situ polymerized composite shows higher electrical conductivity than the interfacial polymerized composite. Both of the composites have similar Seebeck coefficients. The power factor of an in-situ polymerized composite with 68 wt% MWCNTs reaches 2.20 μW/mK2, which is 26.5 times greater than that of pure PPy.