Enhanced electrochemical performance of HC/NiCo@ 800 C//HC using redox-active electrolytes showing increased energy density

Abstract

Supercapacitors are regarded as a promising energy storage devices, in which the energy storage mechanism is based on both electrical double layer capacitance (EDLC) and pseudo-capacitance. Herein, we fabricated an innovative hybrid system that combines two different energy storage processes, viz., electrophysically (EDLC) and electrochemically (pseudo-capacitance). The pseudo-capacitance is brought about in two ways, i.e., both in electrode [using hetero-atom doped carbon along with bimetallic oxide (NiCo oxide)] and electrolyte (using redox-active electrolytes). The redox-active electrolytes containing iodide ions i.e., KI and RbI promote the Faradaic reactions and improves the capacitance of the prepared material. The hetero-atom doped carbon (HC) containing ‘O′ and ‘N′ atoms in the carbon framework is prepared from polybenzoxazine source. The calcination temperature of 800 ℃ is efficient in forming the activated porous carbon i.e., HC/NiCo@ 800 C. From the preliminary examination of HC/NiCo@ 800 C, it is found that the spinel oxide was successfully prepared at 800 ℃, as evidenced by (311) (111) (220) and (440) planes of cubic NiCo from XRD and it is well incorporated into the porous carbon framework, indicated by increased intensity of ‘D′ band (degree of disorder) in the Raman spectrum. The electrochemical characterizations of the prepared electrode in redox-active electrolytes (i.e., KI and RbI) and aqueous electrolyte (i.e., KOH) are performed using CV, GCD and EIS studies. The promising effect of iodide ion is observed, showing an increased specific capacitance of 2334 and 2076 F g–1 @ 1 A g–1 for RbI and KI electrolytes, respectively. Further, an asymmetric two-electrode device is fabricated [HC/NiCo@ 800 C//HC], exhibiting a specific capacitance of 232 F g–1 with an increased energy density of 96.57 W-h kg–1, using RbI as an electrolyte.