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) 6 3− /Fe(CN) 6 4− can induce S 2 O 8 2− to produce the sulfate radical ( S O 4 · - ). Strong oxidizing species, including S 2 O 8 2− , Fe(CN) 6 3− and S O 4 · - , can accelerate oxidation of the CoO electrode surface from Co 2+ to Co 3+ 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 .