Enhanced electrochemical response of activated carbon nanostructures from tree-bark biomass waste in polymer-gel active electrolytes

Abstract

Activated carbon (ACB) obtained from tree bark waste biomass was obtained by adopting an optimized activation and carbonization route using potassium hydroxide (KOH) pellets. The morphological and structural characteristics of the optimized carbon material revealed a porous network suitable for charge storage. The potential of the ACB material as a suitable supercapacitor electrode was investigated in a symmetric two electrode cell configuration using a polymer-gel/KOH active electrolyte. The KOH was included to improve ionic mobility within the polyvinyl alcohol (PVA) gel, while carbon acetylene black and a polymer-fullerene blend acted as the conductive additives. The cell exhibited an EDLC behaviour in all electrolytes with the PVA/KOH/carbon black (PKCB) electrolyte portraying the best electrochemical response with a 1.4 V voltage window. A specific capacitance (C_SP) of ∼227 F g⁻¹ was obtained with a corresponding energy density of 15.5 W h kg⁻¹ and power density of 700 W kg⁻¹ at a current density of 0.5 A g⁻¹. An excellent stability was exhibited with a coulombic efficiency of 98% after 5000 continuous cycles at 5.0 A g⁻¹ and a slight deterioration of the ideal electrochemical behavior was observed after further subjecting the electrode to a floating test for 120 h (5 days) at 1.4 V. Interestingly, the gel-based electrolyte showed a peculiar “recuperating behavior” after further floating process and negligible charge loss after a self-discharge process for 30 h at 1.0 A g⁻¹ which demonstrates the viability for adopting gel-electrolytes in SC devices from plant biomass waste.