Kinetics of the Deposition and Dissolution of Silver

Abstract

Galvanostatic measurements, made on spherical silver electrodes in highly purified aqueous acid solutions of silver perchlorate at current densities up to 10 amp cm—2, gave overpotential as a function of time and Faradaic current density at constant total current. Variables were total current density, concentration of silver ions and state of the electrode surface. The theory of the surface diffusion kinetics was developed to encompass high current density regions and the surface adion concentration (cad0) evaluated. A theoretical analysis of the steady state of surface diffusion control of the metal-ion exchange reaction shows that the current is distributed nonuniformly between growing sites, with constant potential over the electrode surface. An equation previously developed by Rojter, Juza, and Polujan has been modified and shown to be applicable to galvanostatic transients when the transfer reaction is rate controlling. The symmetry factor β, of electrode kinetics, is shown to be potential dependent, and, in systems of sufficiently high i0 values, to tend to zero at high overpotential. This results in a limiting current density for a transfer controlled process. The tendency towards such a current was observed and shown to be quantitatively consistent with the discussion of β.