Calendar ageing without applying potential for polypyrrole/Ni-oxide supercapacitors

Abstract

Polypyrrole (PPy) was electropolymerized on disposable pencil graphite (G), and then Ni-oxide (NiO) was electrodeposited on G/PPy varying the charge density from 14 to 562 mC/cm². The molecular structure was studied by Fourier transform infrared spectroscopy. The morphology was investigated by scanning electron microscopy and the composition was determined by energy-dispersive X-ray spectrometry. The capacitive behavior was examined by cyclic voltammetry (CV) and galvanostatic charge-discharge technique (GCD). The specific capacitance was calculated as 570.4 F/g for the G/PPy-NiO electrode having NiO with a charge density of 14 mC/cm². As the charge density increases the specific capacitance decreases. Supercapacitors were fabricated using these G/PPy-NiO electrodes, and PVA-H₂SO₄ and PVA-H₃PO₄ gel electrolytes. The capacitive behavior was analyzed using CV and GCD. The calculated specific capacitance is 403.4 F/g for the PPy-NiO-14//PVA-H₂SO₄//PPy-NiO-14 and 44.4 F/g for PPy-NiO-14//PVA-H₃PO₄//PPy-NiO-14 supercapacitors. The devices were aged by keeping them at room conditions, and the measurements were repeated every 15 days until the 45^th day. The cyclic stability was determined after 1000 cycles by CV measured on the 0^th and 45^th day. The capacitance retention and hence the shelf life were determined. PPy-NiO-14//PVA-H₂SO₄//PPy-NiO-14 supercapacitor has capacitance retention (c.t.) of 101% after 45 days while the PPy-NiO-14//PVA-H₃PO₄//PPy-NiO-14 has 75.5%.