Salinity gradients could be a great source of energy in the future. Capacitive energy extraction based on Donnan Potential (CDP) is a new technique to directly convert this energy into electricity. COP uses a supercapacitor-like device combining ion exchange membranes and capacitive materials to adsorb and desorb ions with the Donnan Potential of the membranes as only driving force. The resulting current can be extracted through an external load. In this study, traditional electrochemical techniques: galvanostatic charge-discharge and cyclic voltammetry were used to investigate intrinsic properties of this open system. This study demonstrates the feasibility to characterize the capacitive behavior of the cell in low concentration (0.5 M). Presence of membranes, as well as the possibility of having the electrolyte flowing through the cell was investigated. In the studied cell, the presence of membranes showed a limitation by the anion exchange membrane at low current densities but no effect at high current densities. The flow rate did not influence the capacitance of the system either. (C) 2012 Elsevier Ltd. All rights reserved.