Interconnected network of MnO₂ nanowires with a "cocoonlike" morphology: Redox couple-mediated performance enhancement in symmetric aqueous supercapacitor

Low electronic conductivity and slow faradic processes limit the performance of MnO₂ as an electrochemical pseudocapacitor with respect to cycling and power density. Herein, we report preparation of single-phase α-MnO₂, composed of an interconnected nanowire network with "cocoonlike" morphology, and its application as electrode in a symmetric aqueous supercapacitor. Increased "effective" surface area, coexistence of micropores and mesopores, and enhanced electron transport in these nanowire networks result in a specific pseudocapacitance (C _S) of 775 F·g^-1 in 3 M KOH, derived from cyclic voltammetry in the potential window of -1 to +1 V at a scan rate of 2 mV·s^-1, the highest reported for two-electrode symmetric configuration. Furthermore, introduction of K₄Fe(CN)₆ as a redox-Active additive to KOH results in ∼7 times increase in energy density at a power density of ∼6000 W·kg^-1. The presence of the Fe(CN)₆^4-/Fe(CN)₆^3- redox couple provides an electron buffer source compensating for the slow faradic reactions. The results demonstrate that this simple approach might be an effective way to enhance the redox kinetics and reversibility of transition metal oxide-based pseudocapacitors.