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Scalable free-standing polypyrrole films for wrist-band type flexible thermoelectric power generator

Bharti, Meetu, Jha, P., Singh, Ajay, Chauhan, A.K., Misra, Shantanu, Yamazoe, Masato, Debnath, A.K., Marumoto, Kazuhiro, Muthe, K.P., Aswal, D.K.
Energy 2019 v.176 pp. 853-860
X-ray photoelectron spectroscopy, cyclohexanes, electric potential difference, electrical conductivity, electron paramagnetic resonance spectroscopy, ferric chloride, generators (equipment), oxidants, p-toluenesulfonic acid, polymerization, pyrroles, temperature
Highly flexible free-standing polypyrrole films were prepared by the interfacial chemical polymerization of pyrrole (in cyclohexane) using aqueous FeCl3 as an oxidant and p-toluene sulphonic acid (PTSA) as a dopant. Morphological characterization revealed the granular morphology of the synthesized films and also suggested a reduction in their thickness with the increase in PTSA concentration. The increase of the doping content in these polypyrrole films, also resulted in the enhancement of electrical conductivity from 4.8 S/cm to 162.7 S/cm without much affecting the Seebeck coefficient ∼4–8 μV/K. The combined results of X-ray photoelectron spectroscopy and Electron spin resonance spectroscopy (ESR) confirms the enhancement of doping content (N+/N content) i.e. formation of charge carriers such as polarons/bipolarons with the increase in PTSA concentration. The synergetic combination of high electrical conductivity along with moderate Seebeck coefficient in the doped free-standing PPy films resulted in the highest average power factor of ∼0.45 μW/mK2. A wrist-band type thermoelectric power generator was also designed by integrating seven number of free-standing PPy films to manifest their potential for practical thermoelectric applications. The fabricated device exhibited maximum open-circuit voltage and current respectively as 336 μV and ∼46 nA, for a temperature difference of 80 °C. The work reveals new avenues towards the development of wearable energy harvesting devices that can be possibly designed using free-standing PPy films.