Ternary composites of PPy/MWCNTs/metals hydroxide for thermoelectric applications

To improve the thermoelectric properties of conducting polymers, a series of polypyrrole/multi-walled carbon nanotube (MWCNTs)/metal hydroxide composites were synthesized. The polypyrrole (PPy) component was obtained through oxidative polymerization, while the metal hydroxides (MH) of Sr, Zn, Ni, and Co (e.g., Sr(OH)2, Zn(OH)2, Ni(OH)2, and Co(OH)2) were prepared using the sol–gel method in the presence of MWCNTs. An in-situ approach was employed to polymerize the pyrrole monomer on the surface of the resulting metal hydroxides and MWCNTs. The composites’ structural and surface properties were characterized using a range of techniques. Subsequently, the composites were compacted into pellets, and their thermoelectric properties were evaluated. The inclusion of metal hydroxides, particularly Ni(OH)2, and MWCNTs into the PPy matrix resulted in a significant enhancement of the power factor to approximately 0.2 µW/m K2 at room temperature. This value is approximately 2.5 times higher than that of pure PPy. Additionally, the figure of merit for the nanocomposite incorporating Ni(OH)2 was measured to be 0.6 × 10−3, which is approximately 10 times higher than that of pure PPy. The observed enhancement is attributed to the strong interaction between PPy and metal hydroxides, facilitated by π–π stacking between the polymer chains and the metal hydroxides, as well as the presence of MWCNTs. Notably, the nanocomposites, particularly those containing Ni(OH)2, exhibited a significant reduction in thermal conductivity and an increase in charge carrier density. These findings suggest that the synthesized composites possess great potential for utilization in scalable thermoelectric materials and devices. Their unique properties and high thermoelectric performance position them as a promising solution for addressing global energy challenges.