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 45th day. The cyclic stability was determined after 1000 cycles by CV measured on the 0th and 45th 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-NiO14 has 75.5 %.