Present article introduces the electrochemical fabrication of cobalt oxide nanostructures on electroetched carbon fiber (ECF) by a cathodic potential step method. The morphology and composition of the nanostructures were studied by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction analysis (XRD) and thermal analysis (TA) methods. FE-SEM images confirm the formation of flower-like Co3O4 nanoflakes on ECF (Co3O4-ECF). Cobalt hydroxide nanostructures transform into spinel structure after annealing in air at 300 degrees C for 2 hours. The electrochemical and supercapacitive performance of Co3O4-ECF was investigated by cyclic voltammetry (CV), galvanostatic charge-discharge, and electrochemical impedance spectroscopy (EIS) in both three and two electrode systems in KOH solution. Results confirm the excellent supercapacitive behavior of nanostructured Co3O4-ECF with excellent cycling stability and capacitance retention. These characteristics can be attributed to three dimensional (3D) structures of nanoflakes which allow facile electrolyte movement during charge or discharge processes. A specific capacitance of 598.9 F g(-1) at a currents density of 6.25 A g(-1) was obtained for Co3O4-ECF electrode in addition to high energy (40.75 Wh kg(-1)) and power densities (27.69 kW kg(-1)). (C) 2014 Elsevier Ltd. All rights reserved.