Residual currents were measured at an open circuit by connecting a columnar structured gold or platinum electrode of high roughness factor with another flat electrode of the same material, both immersed in the same electrolytic solution. Such currents are interpreted as the consequence of capacitance changes associated to the potential difference between both electrodes provenient from surface-free energy differences. An equation has been derived which allows an estimation of the surface diffusion coefficients for metal atoms in contact with electrolytes from current vs. time plots.