A mathematical model of an electric double layer capacitor is developed treating the capacitance as a matrix instead of a scalar. Model explicitly demonstrates that when two electrodes are immersed an electrolyte and a potential difference applied, a stable double layer that store energy is created. It is suggested that supercapacitors could be modeled on the basis of capacitance matrices whose elements parameterize the geometry of the porous electrode. (C) 2010 Elsevier B.V. All rights reserved.