Carbon Nano-Onions from Waste Oil for Application in Energy Storage Devices

The demand for long-term, sustainable, and durable energy storage devices has been increasing to overcome global challenges and concerns associated with energy and environment conservation. In this context, it is required to develop high performance carbon-based electrode materials for energy storage devices using simple, economical, and green techniques. The present study proposes an environment-friendly approach for facile, large-scale synthesis of onion-like carbon nano-particles (CNOs) for their application in high-performance and durable supercapacitors (SCs). CNOs were synthesized by a traditional pyrolysis technique using waste frying oil as the free carbon source. The as-synthesized CNO particles were connected to each other to form a chain-like interconnected network, effectively providing accelerated ion-transport, reduced resistance for electron transport and more active sites for charge storage. SCs based on activated CNOs (a-CNOs) demonstrated a gravimetric capacitance of 71 F g-1 in organic electrolytes at 2 A g-1. Moreover, a-CNOs delivered good volumetric capacitance of 63 F cm-3 with a high packing density of ~0.89 g cm-3, which is better than that of the activated carbon. Furthermore, the capacitance retention was ~80% even after 10,000 galvanostatic charge discharge cycles. Overall, this approach presents a new way to utilize waste material for creating advanced porous carbons for developing the next generation of sustainable energy storage devices.