Bio-waste derived carbon nano-onions as an efficient electrode material for symmetric and lead-carbon hybrid ultracapacitors

Carbon and metal oxide nanocomposites have been extensively studied as electrode materials to develop energy and power-dense supercapacitors in recent years. Nevertheless, nano carbons with improved porosity and functional moieties are the most eco-friendly and cost-effective supercapacitor materials. In this work, carbon nano-onions (CNOs) synthesized by a single-step flame soot collection method, subsequently calcined at 600 degrees C in an inert environment (CNO-600), are used as electrode material for the supercapacitors. CNO-600 s have a layer-by-layer nano onion structure with a similar to 25 nm particle size and a Brunauer-Emmett-Teller surface area of 147 m(2) g(-1). CNO-600 delivers 266 and 186 F g(-1) of capacitance at 0.5 A g(-1) for half cells and symmetric ultracapacitors, respectively. Ultracapacitors show capacitance retention of 91% with 20 000 GO) cycles in 1 M H2SO4 electrolyte. The stable capacitance of CNO-600 is due to easy intercalation/de-intercalation of electrolyte ions and electrons in the layer-by-layer structure of CNOs, contributing to pseudocapacitive charge storage with electric double layer capacitor behavior. The lead-carbon hybrid ultracapacitor fabricated using CNO-600 as anode material and PbO2 as cathode delivers a specific capacitance of 515 F at 1 A g(-1) in 4.5 M H2SO4 electrolyte in the voltage range of 2.3 and 0.6 V. The substantial improvement of charge storage in CNO-based symmetric and lead-carbon hybrid system, demonstrate an excellent opportunity for the development of high-performance supercapacitors.