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 alpha-MnO2 nanowires during cycling performance. The effects of K+ ions on the electrochemical performance is studied by tuning the phases of alpha-KMnO2 nanowires to Mn3O4 through an intermediate phase of Mn2O3 by subsequent calcinations at various temperatures. K+ ions doped alpha-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 Mn(2)O3 and Mn3O4. The as synthesized alpha-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 a-KMnO2 nanowire supercapacitor device shows very high energy density (15.83 Wh kg(-1)), power density (128.35 Wkg(-1)) and excellent cyclic stability with 88% retention of the initial capacitance after 3000 cycles. (C) 2018 Elsevier Ltd. All rights reserved.