Novel green biosynthesis of vanadium pentoxide by the extraction of the white hibiscus sabdariffa leaves as electrode material for super capacitor Applications

Ngom B D

Abstract

A novel green biosynthesis of the vanadium pentoxide@white hibiscus sabdariffa (V2O5@WHS) nano-flowers- like structures was successfully synthesized by solvothermal method. The X-ray diffraction analysis of the materials revealed the orthorhombic structure V2O5. No other peaks from the white hibiscus sabdariffa were observed in the XRD pattern which revealing the high phase purity of the V2O5@WHS material. The X-ray photoelectron spectroscopy spectrum of the materials exhibited the presence of V3+, V4+ and V5+ in the binding energies of the V2O5@WHS. The electrochemical performance of the electrode material was evaluated using a 6 M KOH aqueous electrolyte. The specific capacity of the V2O5@WHS reached a value of 50.4 mA h g-1 at a current density of 0.5 A g-1. An asymmetric capacitor was also fabricated by adopting an activated carbon negative electrode obtained from the peanut shell waste as raw material and the V2O5@WHS as the positive electrode in 6 M KOH electrolyte. The hybrid capacitor of V2O5@WHS//AC displayed a high energy density of 33 W h kg−1 with a corresponding high power density of 470 W kg−1 at 1 A g−1 in a large voltage window of 0.0 - 1.7 V. The device also exhibited an excellent cycling stability with 87% capacity retention recorded for up to 20.000 constant charging–discharge cycles and an excellent ageing test at a specific current of 10 A g-1.