1.2 Volt manganese oxide symmetric supercapacitor

Abstract

Capacitance fading of MnO 2 supercapacitor electrode under negative polarization below 0.0 V (versus Ag/AgCl/sat. KCl (aq)) arises from extensive reduction of Mn(IV) to form inactive Mn(II) species, and this has typically limited the operating voltage window of an aqueous symmetric MnO 2 supercapacitor to be no greater than 0.8 V. As this lower potential limit is close to the onset potential of MnO 2-catalyzed oxygen reduction reaction (ORR), the fading problem can be alleviated by effectively passing the accumulated electrons in the oxide electrode to the dissolved oxygen molecules in electrolyte in order to avoid the formation of the surface Mn(II) species. This has been demonstrated by either increasing the dissolved oxygen content or using the Ti(IV)/Ti(III) redox couple in the electrolyte as a charge-transfer mediator to enhance the electrocatalytic activity of MnO 2 for ORR. Therefore, a MnO 2 symmetric supercapacitor showing remarkable cycling stability over an operating voltage window of 1.2 V has been achieved by using Ti(IV)-containing neutral electrolyte (1 M KCl (aq)).