Abstract
An aqueous potassium ion-based asymmetric supercapacitor has been successfully developed using nitrogen-doped porous carbon (NPC) derived from waste orange peel and sea urchin-like intercrossed and interconnected NiCo2O4 array on Ni foam for negative and positive electrodes, respectively. A negative electrode was designed using NPC developed via hydrothermal method. Subsequent KOH activation of waste orange peel resulted in NPC. Nitrogen doping increased the wettability, which enhanced its capacitance during electrochemical performance. NPC yielded a typical electrical double layer capacitor with a high capacitance of 268 F/g, and robust cyclic stability (92%) with up to 6000 cycles and good working potential (0 to -1 V) in an aqueous electrolyte. Hydrothermally synthesized sea urchin-like intercrossed and interlinked NiCo2O4@NF was used as a negative electrode with a high capacitance of 1300 F/g at a current density of 1 A/g and excellent rate as well as enhanced cyclic performance up to 3500 cycles. NiCo2O4//NPC-assembled asymmetric supercapacitor exhibited excellent life cycle with 100% capacitance retention up to 8000 cycles and delivered maximum energy density of 32.08 Wh/kg at a power density of 700.43 W/kg in a 2M KOH electrolyte. The enhanced performance of the negative electrode was attributed to higher porosity and doping in NPC, which facilitates the diffusion of electrolyte ions into the electroactive material during electrochemical performance. The unique porous morphology exposed a large number of surface electroactive sites to redox reactions and prevented phase damage caused by volume expansion and redox reactions during electrochemical activity resulting in enhanced performance of the positive electrode. (c) 2018 Elsevier Ltd. All rights reserved.