Conventional alkaline solutions used for capacitive performance of electrodeposited cobalt hydroxides have a number of disadvantages as they are corrosive, environmentally unfriendly and provide a small working potential range. In this study, the capacitive properties of electrodeposited cobalt hydroxide/oxide were investigated in 1 M Na2SO4 solution with pH 5.5 by means of cyclic voltammetry, galvanostatic charging/discharging experiments and electrochemical impedance spectroscopy. The capacitance of the cobalt hydroxide/oxide was demonstrated to have high values of 141 Fg(-1) at scan rate 8 mV s(-1) in this 1 M Na2SO4 solution. The anodic potential range is extended by 0.8-1.3 V vs. Ag/AgCl. A good cyclic stability and reversibility were observed. (C) 2012 Elsevier Ltd. All rights reserved.