Rice husk-derived activated carbon electrode in redox-active electrolyte – New approach for enhancing supercapacitor performance

Processing of renewable, abundant, and low-cost biomass into porous carbon materials for application in supercapacitor electrodes has been attracting interest in last years. In this study, activated carbons (ACs) were produced via carbonization of rice husk followed by the chemical activation with KOH. SEM, Raman spectroscopy, XPS, and low temperature nitrogen physisorption were used to characterize the morphology, defectiveness, surface composition and textural parameters of the synthesized ACs. Activation significantly increased the specific surface area of AC up to 2700 m2·g−1 forming a well-developed porous structure favorable for charge accumulation. The electrochemical performance of ACs was tested in the 1 M Na2SO4 and 1 M Na2SO4 + 0.03 M K3Fe[CN]6 electrolytes by cyclic voltammetry, galvanostatic charge – discharge measurements and impedance spectroscopy. The addition of redox-active K3Fe[CN]6 to the conventional 1 M Na2SO4 electrolyte noticeably (in 3.6 times) increased the specific capacitance of the AC-based electrode up to 400 F·g−1 at a current density of 0.5 A·g−1. The high capacitance retentions of 99.6 % in 1 M Na2SO4 and 97.7 % in 1 M Na2SO4 + 0.03 M K3Fe[CN]6 after 5000 charge–discharge cycles, developed microporosity and high electrochemical performance make the rice husk-derived AC a promising electrode material for energy storage applications. At a current density of 0.5 A·g−1 the symmetric AC2-based supercapacitor with the redox-active electrolyte delivered an energy density of 16.7 Wh·kg−1 at power density of 0.4 kW·kg−1.