The dependence of the electronic conductivity of activated carbon electrodes on their potential in aqueous electrolyte solutions was explored as a function of level of activation, electrolyte concentration, and pH. In general, the conductivity of molecular sieve carbon electrodes in electrolyte solutions strongly depends on their potential. While porous carbon electrodes exhibit the expected behavior, namely, a parabolic dependence of the conductivity on the potential, with a minimum at the PZC, an unusual trend is observed in the case of porous carbon electrodes in concentrated aqueous KCl solutions. That is, a monotonic dependence of the conductivity on the potential is measured. Conductivity vs. potential measurements in solutions of different pH values were conducted in order to elucidate the role of H+ in electro-adsorption processes of porous carbon electrodes, even in neutral solutions. Under these conditions (i.e., high salt concentrations), the potential region of cation electro-adsorption becomes wider (> 1 V). This cation electro-adsorption within a wide potential range leads to the monotonous dependence of the conductivity on the electrodes' potential. (c) 2006 Elsevier B.V. All rights reserved.