We have reported the electrochemical performance of K+ ion doped Mn(OH)(4) and MnO2 nanorods as a positive electrode and a highly porous activated carbon nanosheet (AC) made from Prosopis juliflora as negative electrode asymmetric supercapacitor (ASC) with high rate capability and capacity retention. The cation K+ doped Mn(OH)(4) and MnO2 nanorods with large tunnel sizes allow the electrolyte to penetrate through a well-defined pathway and hence benefits from the intercalation pseudocapacitance and surface redox reactions. As a result, they exhibit good electrochemical performance in neutral aqueous electrolytes. More specifically, the K+-Mn(OH)(4) nanorods exhibit higher capacitance values than K+-MnO2 nanorods due to the homogenous distribution of 1D nanorods and optimum amount of O-H bonds. The fabricated K+-Mn (OH)(4) symmetric electrochemical Pseudocapacitor shows very high energy density of 10.11 Wh/kg and high-power density of 51.04 W/kg over the range of 1.0 V in aqueous electrolyte. The energy density of AC parallel to K+-Mn(OH)(4) ASC is improved significantly compared to those of symmetric supercapacitors. The fabricated ASC exhibits a wide working voltage window (1.6 V), high power (143.37 W/kg) and energy densities (41.38 Wh/kg) at 0.2 A g(-1), and excellent cycling behavior with 107.3% capacitance retention after 6000 cycles at 2 A g(-1) indicating the promising practical applications in electrochemical supercapacitors. (C) 2020 Elsevier Inc. All rights reserved.