A MODEL FOR THE EFFECT OF ROUGHNESS OF SINGLE-CRYSTAL ELECTRODES ON PARSONS-ZOBEL PLOTS

At single-crystal electrodes and in the absence of ionic specific adsorption, Parsons-Zobel (PZ) plots exhibit slopes which are often less than unity at zero charge density, and increase to become equal to, or slightly greater than, unity as the absolute value of the charge density is increased slightly. This behaviour is herein explained on the basis of a model which accounts for the curvature of the asperities on the electrode surface. These asperities are simulated either by hemispheres of a given average radius a or by hemicylinders of a given average cross-sectional radius a'. By a suitable choice of either a or a', the curvature and slope of experimental PZ plots at the various charge densities are satisfactorily accounted for. It is shown that surface roughnesses as low as 1.05 may give rise to PZ plots at zero charge with slopes as low as 0.6, provided that the radius a (or a') is sufficiently small.