NiOx xerogels were formed by the sol-gel method followed by heat-treatment under ambient pressure. The structure and properties of these materials were characterized by using X-ray diffraction, XPS, TEM, TGA-DTA and N-2 (77 K) adsorption. Electrodes with the xerogels were activated by cyclic voltammetry (CV) and their capacitive performance was evaluated by CV and galvanostatic technique in 7 M KOH solutions. A maximum specific capacitance of 696 Fg(-1) was obtained by constant current discharge with a current density of 2.0 mA cm(-2) for the NiOx xerogels heat-treated at 250 degrees C. The results of in situ XRD of the NiOx xerogels after the charge/discharge recycling test showed that the NiOx xerogels might exhibit faradaic pseudocapacitance by surface redox from Ni(OH)(2) to NiOOH. The high performance obtained indicates that these materials are promising electrode materials for supercapacitors. (c) 2005 Elsevier B.V. All rights reserved.