Stability of stationary states, multiplicity, and oscillations during anodic dissolution of metals in a potentiostatic regime: Effect of the passivating-film formation kinetics

A mathematical description is presented and an analysis is realized of the behavior exhibited by electrochemical systems in which the anodic dissolution (cathodic deposition) in a potentiostatic regime is accompanied by the formation of a passivating film at the electrode surface. It is demonstrated that certain regions of the system’s parameters are characterized by the instability of steady states and by spontaneous transition to the multiplicity of steady states or to an oscillatory regime. The reason for the emergence of oscillations is the presence of the stage of the formation and dissolution of the passivating film on the electrode surface. Mathematical description of the stages of the formation and dissolution of the passivating film substantially depends on the film’s thickness. Considered is a thin film, which comprises a few monolayers and which is represented as a two-dimensional phase, with the alteration of an activation energy as a function of the coverage θ taken into account. It is demonstrated, by considering a mechanism of the anodic metal oxidation in an acid environment, that accounting for the specific features of the passivation stage successfully explains the emergence of the oscillations and the multiplicity of steady states and the necessary and sufficient conditions for their realization are found. Bifurcation diagrams are constructed in the plane of kinetic parameters of the system. The conditions leading to the emergence of a hysteresis loop are shown. The vertical inflection in an i, V curve at the point of an active-passive transition is explained.