Electrospun NiO nanofibers as cathode materials for high performance asymmetric supercapacitors

Asymmetric supercapacitors (ASCs) based on aqueous electrolytes have received widespread attention in energy research in recent years because they provide high energy and power densities in addition to being 'green electrolyte'. Herein, we report an ASC built with electrospun nanofibers of NiO as battery type cathode material and commercially available high surface area activated carbon as capacitor type anode material with appropriate mass loadings. We synthesized high aspect ratio nanofibers of NiO by simple and cost effective sol-gel based electrospinning followed by annealing. In the end, these nanofibers were composed of densely packed hexagonal nanoparticles of polycrystalline NiO having diameters of similar to 15 nm. The ASC was capable of operating in the potential window of 1.5 V in 6 M KOH solution with a gravimetric capacitance of 141 F g super(-1) and energy density of 43.75 W h kg super(-1). The ASC showed high retention of the specific capacitance for 5000 galvanostatic charge-discharge cycles with improved coulombic efficiency.