Unleashing the potential in energy storage : the impact of redox electrolytes on specific energy in an asymmetric supercapacitor

Abstract

Adding redox-active species to potassium hydroxide (KOH) enhances the electrolyte's charge storage capacity through redox reactions, thereby improving stability and broadening the potential window. This study introduces a novel mediated electrolyte with good solubility, stability, and improved reversibility. Different concentrations (0.05 M, 0.07 M, and 0.09 M) of potassium ferrocyanide (KF) were separately mixed with 3 M KOH (K3) in equal volume ratios to form the redox-active electrolytes. 0.07 M (KF70) showed superior electrochemical properties when mixed with K3. The electrolyte's ionic conductivity increased from 25.3 mS/cm for KF70 to 257.3 mS/cm after adding KF70 into K3 (K3_KF70), with a corresponding viscosity of 1.32 mPas. Hexagonal boron nitride/activated carbon composite (hBN/AC-1:0.05) electrode's specific capacity rose from 676.5C/g in K3 to 847.0C/g in K3_KF70, measured in a half-cell configuration within a potential range of 0.0–0.4 V vs. Ag/AgCl. The constructed device revealed a specific energy of 58 Wh/kg in K3_KF70, which is higher compared to 24.1 Wh/kg in K3. Additionally, the device presented a specific power of 993.7 W/kg. These results present a potential pathway for significantly enhancing specific energy in supercapacitors by facilitating additional charge storage through Faradaic redox reactions occurring within the electrolyte.

HIGHLIGHTS • Chronoamperometric electrodeposition was used for composite synthesis. • A redox additive improved the aqueous electrolyte performance. • Redox electrolyte influences charge storage in composite materials. • Improved specific energy is achieved in the redox electrolyte supercapacitors.