The Faradaic and non-Faradaic characteristics of a series of activated carbon particles (used to produce composite carbon-polymer electrodes for redox flow cells) have been determined using aqueous electrolytes (sulfuric acid and sodium polysulfide) at 295 K. The particles were mounted as a circular section (ca. 0.80cm(2)) shallow packed bed of 2.5 mm thickness in the direction of electrolyte flow (mean linear flow velocity approximate to 6 mm s(-1)). Cyclic voltammetry in deaerated, 1 mol dm(-3) H2SO4 at 295 K indicated a specific capacitance in the range of 50-140 Fg(-1). Linear sweep voltammetry and galvanostatic step studies in an alkaline sodium polysulfide electrolyte (1.8 mol dm(-3) Na2S2.11) have demonstrated marked differences amongst various types of activated carbon. Such differences are highlighted during galvanostatic charge-discharge cycling of half-cell electrodes in the polysulfide electrolyte. The electrochemical characteristics are compared to those based on (N-2 adsorption) gas porosimetry measurements. (C) 2008 Elsevier B.V. All rights reserved.