At-substituted a-cobalt hydroxide was prepared by a potentiostatic deposition process at - 1.0 V (vs. Ag/AgCl) onto stainless steel electrodes by using a mixed aqueous solution of cobalt nitrate and aluminum nitrate. Their structure and surface morphology were studied by using X-ray diffraction analysis, energy dispersive X-ray spectroscopy and scanning electron microscopy. The SEM images showed changes in the nanostructure of a-cobalt hydroxide by the addition of Al. Galvanostatic charge-discharge curves showed a drastic improvement in the capacitive characteristics of a-cobalt hydroxide, with a specific energy increase from 11.3 to 18.7 Wh kg(-1) by the substitution of just 8 at.% Al, and a specific capacitance of 843 F g(-1) between 0 and 0.4 V. The cycle stability data suggest no significant changes in the discharge characteristics of alpha-cobalt hydroxide by the addition of Al. (C) 2007 Elsevier B.V. All rights reserved.