Thermoelectric properties of oil fly ash-derived carbon nanotubes coated with polypyrrole

Oil fly ash has been reported to be suitable for producing low-cost carbon nanotubes (CNTs). These CNTs exhibit zigzag curved walls with an almost bamboo-like structure. Owing to this structure, these CNTs exhibit very low thermal conductivity as compared to other graphitic carbon materials. They also exhibit relatively low electrical conductivity. However, they exhibit a Seebeck coefficient comparable to that of commercially available CNTs. Therefore, it is of great importance to evaluate the thermoelectric (TE) properties of oil fly ash-derived CNTs. In this study, the TE properties of oil fly ash-derived CNTs were investigated. The CNTs were further coated with polypyrrole (PPy) to enhance their TE performance. PPy was used for the modification because of its attractive TE properties and its suitability as a binder for CNTs. The PPy coating significantly enhanced the electrical conductivity of the CNTs from ∼500 to ∼1300 S/m at room temperature. A small increase in the Seebeck coefficient was also observed. The power factor value increased from 0.1 to 0.6 μW/m K2. At 440 K, the power factor value was 1.4 μW/m K2. The thermal conductivity of the CNTs (∼1 W/m K) decreased significantly by a factor of 10 after the modification with PPy. The power generation characteristics of a single leg module made up of the p-type coated CNTs were investigated under real-time conditions in air. The results demonstrated the potential of the oil fly ash-derived CNTs coated with PPy for applications as TE materials.