From Trash to Treasure: Direct Transformation of Onion Husks into Three-Dimensional Interconnected Porous Carbon Frameworks for High-Performance Supercapacitors in Organic Electrolyte

Onion husks (Allium cepa L.), an abundant biomass, has been tentatively explored as a renewable carbon source to prepare value-added three-dimensional interconnected porous carbon frameworks (OHCFs) by means of direct carbonization & activation process, and the synthetic procedure is quite simple as easy to be scaled up for industrial applications. The two-electrode symmetric supercapacitor based on the OHCF-2 sample (synthesized from 2 M K2CO3 solution) exhibits excellent electrochemical performance with large specific capacitance (up to 188 F/g at 1 A/g), good cycling stability (92.5% capacity retention after 2000 cycles), small IR drop (0.48 V at 30 A/g), outstanding rate capability (74.9% from 1 A/g to 30 A/g), and unusually high energy densities of 35.4-47.6 Wh/kg at power densities of 675-20250 W/kg in organic electrolyte. This facile, efficient and template-free synthesis strategy holds great promise for preparing novel porous carbons from renewable biomass resources for application in state-of-art energy storage devices. (C) 2016 Elsevier Ltd. All rights reserved.