The utilization of electrode materials could be greatly promoted by the employment of a mesh-type stainless steel (SS) current collector in comparison with a plate-type one. The capacitive behavior of activated carbon (AC) and AC-ruthenium (AC-Ru) composites fabricated by the wet impregnation were systematically investigated in 0.1 M H2SO4 by cyclic voltammetry (CV) and chronopotentiometry (CP). The specific capacitance of AC reached a maximum (ca. 117 Fg(-1)) through a combination of the impregnation of ruthenium precursors and the chemical conversion of the chloride precursors into hydroxides in an ultrasonic bath of NaOH for 30 min (AC-Ru(OH)(x)). The stability of AC-Ru(OH)(x) composites was greatly promoted by annealing in air at 240 degreesC although a significant loss in total capacitance was found. The crystalline information and chemical environment of the impregnated oxy-hydroxyl-Ru species with annealing was, respectively, obtained from the X-ray diffraction (XRD) patterns and X-ray photoelectron spectra (XPS). The specific surface area and pore size distribution of these composites were analyzed by the Brunauer-Emmett-Teller (BET) method. (C) 2003 Elsevier B.V. All rights reserved.