Low-temperature thermoelectric performance of novel polyaniline/iron oxide composites with superior Seebeck coefficient

The large amount of heat loss at low temperatures (up to 250 °C), more than 70% of the total waste heat, motivates the market to develop new materials for low-temperature thermoelectric applications. To this end, organic materials can be excellent potential candidates with the additional advantages of light weight, ease of synthesis and processing, eco-friendly and being sustainable materials. Herein, we demonstrate the synthesis of polyaniline (PANI) in its conductive emeraldine form via a facile chemical oxidative polymerization process. The conductivity of the fabricated PANI, with exceptional low degree of protonation and additional structure deflection, originates from the excess Cl⁻ anions/imines (–N=) interactions. Micro/nano-spheres and different regular shapes are formed with inherent nano-flakes/fibers structures. These structures are intrinsically ferric oxide clouds that finally result in a novel composite of PANI/ferric oxide, as confirmed via the FESEM, EDX, XRD and FTIR analyses. Different dopant concentrations (0.1–2 M HCl) and initiator concentrations (0.5–3 M FeCl₃) were screened to identify the appropriate yield with the highest thermoelectric energy conversion efficiency. Our recipe with low degree of protonation resulted in semiconductor-to-metallic transformation point with a composite that has a superior Seebeck coefficient of 158 µV/k, which has not ever reported for pristine PANI and also with a moderate electrical conductivity of 0.0017 S/cm at 150 °C.