Reduced Hopping Barrier Potential in NiO Nanoparticle-Incorporated, Polypyrrole-Coated Graphene with Enhanced Thermoelectric Properties

In view of the limiting factor in the thermoelectric conversion efficiency, an attempt has been made in this work with molecular-levelenergy barrier engineering in NiO-incorporated, polypyrrole-coated graphene (NiO@PPy/Gr). A simple, inexpensive, and ultrasonic technique has been adopted for preparation of NiO@PPy/Gr composites through an in situ oxidative polymerization process. For exploring the physical properties of the prepared NiO@PPy/Gr composites, X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM) images, UV-visible absorption spectra, and Raman spectra were analyzed. On studying the electrical conductivity (sigma) and Seebeck coefficient (S), inspiring enhancement has been observed in thermoelectric properties of NiO@PPy/Gr as compared to those of pure polypyrrole (PPy). This enhancement is mainly attributed to the strong pi-pi interactions between the conjugated structure of PPy and the pi-bonded surface of graphene (Gr), which leads to the formation of more ordered regions with high crystallinity in the composite. Additionally, NiO acts as a bridge between PPy and Gr in the composites, remarkably improving the charge transport and charge carrier dynamics toward enhanced thermoelectric properties. A notable 855 times enhanced power factor (PF) of 28.22 mu W/mK(2) was recorded as compared with that of pure PPy, with a temperature difference of only 100 degrees C.