Waste frying oil derived carbon nano-onions as a cost-effective cathode material for high-voltage zinc-ion hybrid supercapacitors

Energy crisis and environmental pollution are two major worldwide issues that can be solved by developing sustainable, commercial, and long-durability energy storage systems from the reutilization of waste material. Waste frying oil, a known waste, is used as a carbon source for the synthesis of carbon nano-onions (CNOs) using economically viable and environmentally friendly wick pyrolysis techniques. The as-synthesized CNOs were used as a cost-effective cathode in zinc-ions hybrid supercapacitors (Zn–HSCs). CNOs with a fractal-like structure in an interconnected network and more accessible active available surface area provide great advantage as a cathode to fabricate Zn–HSCs. The CNOs-based active cathode material in aqueous Zn–HSCs present a high specific capacitance of 342 F g−1 at a current density of 0.5 A g−1 under a high working potential window (0–1.9 V). Zn–HSCs achieve a maximum 8.2 kW kg−1 of power density and 164.33 W h kg−1 of energy density. More significantly, excellent long-term durability with 83 % of capacity retention and 100 % retention of coulombic efficiency was also achieved after 10,000 cycles at a high 10 A g−1 of current density. The overall work represents a way of utilizing waste frying oil as a cost-effective and efficient cathode material for aqueous Zn–HSCs, which could aid-in the commercialization of Zn–HSCs.