The capacitive behaviour of four commonly studied electrochemical capacitor systems has been analyzed using the step potential electrochemical spectroscopy (SPECS) method. Electrode-electrolyte combinations with different charge storage mechanisms were characterized, including activated carbon in aqueous (H2SO4) and organic (TEABF(4) in acetonitrile) electrolytes, manganese dioxide (Na2SO4) and anhydrous ruthenium oxide (H2SO4). The SPECS method was used to separate the charge storage contributions from double layer capacitance (CDL) and diffusion-limited pseudo-capacitance (CD) at scan rates ranging from 0.08 to 125 mV/s. The relative contributions from each process are related to the physicochemical properties of the electrode. Additionally, the effects of these electrode properties on the overall performance of each system, in terms of specific power and energy, are identified. (C) 2016 Published by Elsevier B.V.