Stabilization of cryptomelane α-MnO2 nanowires tunnels widths for enhanced electrochemical energy storage

Abstract

One dimensional manganese oxides with tunnel structures have attracted as an effective electrochemical energy storage material because of its efficient electrolyte/cation interfacial charge transports which enables improved pseudo capacitive performance. We have reported a simple one step hydrothermal technique to incorporate K+ ions to maintain the tunnel width of cryptomelane α-MnO2 nanowires during cycling performance. The effects of K+ ions on the electrochemical performance is studied by tuning the phases of α-KMnO2 nanowires to Mn3O4 through an intermediate phase of Mn2O3 by subsequent calcinations at various temperatures. K+ ions doped α-MnO2 nanowires exhibit a highest specific capacitance of 402 Fg-1 at a current density of 1 Ag-1 in 1 M Na2SO4 electrolyte solution compared to Mn2O3 and Mn3O4. The as synthesized α-KMnO2 nanowires have a wider tunnel widths and enriched OH radical species and hence the electrolyte cations (Na+) penetrate the tunnels very easily resulting the polarization enhanced intercalation pseudo capacitance. The symmetric α-KMnO2 nanowire supercapacitor device shows very high energy density (15.83 Wh kg−1), power density (128.35 W kg−1) and excellent cyclic stability with 88% retention of the initial capacitance after 3000 cycles.