A novel redox-mediated aqueous electrolyte is prepared by adding sodium persulfate (Na2S2O8) into KOH alkaline electrolyte for the application in most metal oxide based supercapacitors. The electrochemical behaviors of nickel oxide (NiO) electrode in 2M KOH and 2M KOH containing different concentration of Na2S2O8 electrolytes, respectively, were characterized by cyclic voltammetry and electrochemical impedance spectroscopy methods. The results indicate that the reaction mechanism of NiO electrode in Na2S2O8 mixed electrolytes appears to be the reversible redox of Ni2+ to Ni3+ on two different channels, which is different with that in KOH electrolyte. Charge-discharge experiments show that the discharge ability of the NiO electrode in redox electrolyte is excellent. When added Na2S2O8 into KOH electrolyte, the charge time is shorted and the discharge time is increased sharply. The specific capacitance was up to 6317.5Fg−1 at 0.5Ag−1 in mixed 2M KOH and 0.03M Na2S2O8, more than 100% coulombic efficiency. Fortunately, this new redox-mediated aqueous electrolyte not only suitable for the metal oxide based electrode, but also have much effect to the metal sulfide, vanadate, and phosphate electrode et al.