Interference of Adsorption, Condensation, and Double-Layer Charging in Kinetic Studies of Film Formation. 1. Constant Double-Layer Potential

Abstract

The current response after a single potential step experiment reflects the kinetics of nonfaradaic phase transitions. In the present paper, a classification of possible shapes of current transients under potentiostatic control is proposed. The possible shapes of current transients were simulated by a model, which describes the condensation process as a coupled process of adsorption, nucleation, and growth. Due to the coupling of these three processes, the surface concentration of the expanded phase and therefore the supersaturation as the driving force for the condensation become time dependent. The classification of the transients is carried out according to the location of the final potential in respect to the potential of maximum adsorption on one hand and according to an additional possible dipole contribution due to a reorientation of molecules during the phase transition on the other hand. Apart from the well-known nonmonotonic current transients, which stand for a phase transition process independent of whether the phase transition is of faradaic or nonfaradaic nature, new shapes of current transients were additionally simulated. From the appearance and the location of such new shapes in a system, one can draw conclusions about the direction of reorientation during the phase transitions as well as about the location of the potential of maximum adsorption.