Electrolyte additive induced fast-charge/slow-discharge process: Potassium ferricyanide and potassium persulfate for CoO-based supercapacitors.

The electrolyte additives of potassium ferricyanide and potassium persulfate can ensure that CoO-supercapacitors achieve a fast charge/slow discharge and long cycling stability. The redox couple of Fe(CN)63-/Fe(CN)64- can induce S2O82- to produce the sulfate radical ( [Formula: see text] ). Strong oxidizing species, including S2O82-, Fe(CN)63- and [Formula: see text] , can accelerate oxidation of the CoO electrode surface from Co2+ to Co3+ in the charge process. The additives can achieve a good synergistic effect on accelerating CoO oxidation during the charge process. In a three-electrode cell, a CoO electrode with electrolyte additives achieves a fast-charge and slow-discharge time of 939 s and 1699 s at a current density of 1 A g-1, respectively. The capacitance retention can be maintained at 84.5% after 10,000 cycles at a current density of 5 A g-1. As a supercapacitor, the device can achieve a fast-charge and slow-discharge time of 156 s and 191 s at a current density of 1 A g-1, respectively. The capacitance retention can be maintained at 85.5% after 10,000 cycles at a current density of 5 A g-1.