The interfacial impedance of polycrystalline solid electrodes in the absence of Faradaic reactions is never purely capacitive; the deviation from ideal capacitive behaviour is usually larger on rough electrodes than on smooth ones. We present qualitative experiments to demonstrate that the frequency dependence of capacitance on solid electrodes is due to the atomic scale inhomogeneities rather than to the geometry aspect of roughness. (C) 2000 Elsevier Science Ltd. All rights reserved.