Polyaniline-carbon based binder-free asymmetric supercapacitor in neutral aqueous electrolyte

By Simotwo, Silas K.; Kalra, Vibha
Published in Electrochimica Acta 2018

Abstract

We demonstrate the fabrication of self-standing, binder-free activated porous carbon nanofibers (A-PCNFs) and polyaniline-carbon nanofibers (PANI-PCNFs) as electrodes for asymmetric supercapacitor. The A-PCNFs are generated through the electrospinning process followed by pyrolysis and chemical activation of the spun fibers. The PANI-CNFs are obtained via galvanostatic deposition of aniline on porous carbon nanofibers. We also provide insight into the electroactivity of PANI in a neutral aqueous electrolyte (1 M Li2SO4) using in situ Fourier Transform Infrared Spectroelectrochemical study. Potential dependent oxidation of the polymer in the neutral electrolyte is observed through emergence of characteristics IR absorption bands associated with different structures of PANI in oxidized and doped state. The IR band at 1566 cm?1 typically associated with quinoid structure of the polymer chain is shown to increase in intensity as the potential is applied, indicating oxidation of the benzoquinoid structure. Doping of the polymer chain by Li+ was also observed by increase in the intensity of the IR band at 1038 cm?1 associated with electron delocalization. Asymmetric supercapacitor (ASC) based on binder-less PANI-PCNFs cathode and A-PCNFs anode achieved an energy density of 29 W h kg?1 at an operating voltage window of 1.8 V. The cell retained 75% of its capacitance over 4500 cycles at 2 A g?1 with the capacitance remaining largely constant after the first 500 cycles. Such high capacitance in a neutral electrolyte is attributed to the excellent pore distribution in the A-PCNF network (surface area of 2218 m2 g?1), which leads to high double layer capacitance and thin, conformal coating of PANI, which contributes to high pseudocapacitance.

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