Improving the electrochemical performances of active carbon-based supercapacitors through the combination of introducing functional groups and using redox additive electrolyte

Abstract

High-performance and low-cost electrochemical capacitors (ECs) are essential for large-scale applications in energy storage. In this work, the specific capacitance of active carbon (AC) electrode was significantly improved through the combination of introducing functional groups on the surface of AC and adding redox-active molecules (K3Fe(CN)6) into 2 M KOH aqueous electrolytes. The surface-oxygen functionalized AC (FAC) was synthesized using HNO3 echoed as the electrode and 2 M KOH with 0.1 M K3Fe(CN)6 as the electrolyte. The surface functional groups of the AC not only contribute to the pseudocapacitance but also increase the active sites of the electrode/electrolyte interface, which enhances the electrochemical activity of the Fe(CN)63−/Fe(CN)64− redox pair, thus leading to high capacitance. In the redox electrolyte, the specific capacitance was much higher in 229.17 F g−1 (1 A g−1) achieved for those FAC than in raw AC (only 147.06 F g−1). Similarly, the FAC electrode suggested high energy density and extended cycling stability in the KOH + K3Fe(CN)6 electrolyte.