Roughness effects on the double-layer charge capacitance: the case of Helmholtz layer induced roughness attenuation

For electrical double layers, the presence of a Helmholtz layer could lead to electrode roughness attenuation. The latter is assumed of self-affine type which is characterized by the roughness amplitude w, the correlation length xi, and the roughness exponent H. For sufficiently rough metal electrode surfaces (H much less than 1 and/or ratios w/xi greater than or equal to 0. 1) the diffuse/Helmholtz layer interface would not have the same roughness parameters with the metal electrode surface. If the latter is smoothened at lateral length scales smaller than a healing length Lambda (much less than xi), the diffuse charge capacitance decreases and approaches values close to that of the Gouy-Chapman theory for flat electrodes. (C) 2003 Elsevier B.V. All rights reserved.