Manganese oxide nanoparticles were grown on multiwalled carbon nanotubes (MWCNT) by a simple and cost effective reduction of KMnO4. Characterization of the material revealed the formation of alpha-MnO2 nanoparticles wound around MWCNT. This nanocomposite of alpha-MnO2/MWCNT was investigated for its hybrid supercapacitor performance in a three electrode system and exhibited a specific capacitance (C-s) of 255 F g(-1) at a scan rate of 2 mV s(-1). Further, an asymmetric supercapacitor (AS) device was designed using alpha-MnO2/MWCNT as positive electrode and activated carbon as negative electrode. The device showed C-s of 99.7 F g(-1) at a scan rate of 1 mV s(-1) in a wide potential window of 0-2 V in 1 M Na2SO4. The device also exhibited a high energy density of 263 Wh kg(-1) with a maximum power density of 29.4 kW kg(-1). Highlight of this work is that the device when subjected to 20,000 charge-discharge cycles at a high current density of 50 A g(-1) retained 77% of its initial C-s. The AS device was efficiently used as power source to light four red LEDs arranged in parallel for about 12 min after charging the device for 30 s at a current density of 1 A g(-1). (C) 2016 Elsevier B.V. All rights reserved.