An ionic aqueous pseudocapacitor system: electroactive ions in both a salt electrode and redox electrolyte

Abstract

We designed a new type of ionic pseudocapacitor system with excellent contributions from ionic-state redox mediators, including a redox couple [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ in the electrolyte and redox cations in highly electroactive colloid electrodes. The highest pseudocapacitance value of 12 658 mF cm⁻² was obtained, which is a 7-fold increase in the specific capacitance of the CoCl₂ electrode for K₃Fe(CN)₆ in a KOH alkaline electrolyte at a current density of 20 mA cm⁻² and at a potential interval of 0.55 V. The currently designed supercapacitor systems show a versatile strategy to design high-performance supercapacitors with CoCl₂, CuCl₂, NiCl₂, and FeCl₃ electrodes.