Phytogenic generation of NiO nanoparticles as green-electrode material for high performance asymmetric supercapacitor applications

Herein, we report a simple, cost-effective, one-step green synthesis of nickel oxide nanoparticles (NiO–NPs) from Opuntia ficus-indica leaves extract for asymmetric
percapacitor application. The plant extract derived
NiO–NPs exhibits an exceptional half-cell specific capacitance of 644 Fg − 1 (~89.4 mAhg− 1 ) at 0.5 Ag − 1
.The assembled asymmetric NiO–NPs|| activated carbon (AC) supercapacitor cell delivers high specific capacitance of
~280 Fg − 1 (~38.8 mAhg− 1 ), excellent specific energy of 25 Wh kg− 1 . In addition, the NiO–NPs|AC device works
until 1.4 V with 0.1 M KOH as electrolyte delivering an excellent rate capability and high coulombic efficiency of
124% even after 10,000 cycles. Moreover, the biomass derived NiO NPs performs better than the other reported NiO based compounds, due to its presence of nickel-rich natural minerals. Through these findings, the use of plant leaves like Opuntia ficus-indica is hereby shown to be low-cost, environment-friendly alternative for pre- paring NiO- based composites for energy storage applications.