GENERALIZED HOPF, SADDLE-NODE INFINITE PERIOD BIFURCATIONS AND EXCITABILITY DURING THE ELECTRODISSOLUTION AND PASSIVATION OF IRON IN A SULFURIC ACID SOLUTION

Periodic current oscillations of relaxation type are observed in a certain potential range during iron electrodissolution in sulfuric acid solutions when the iron electrode turns from the active to the passive state and vice versa. The system displays in the current-potential (I-E) plane a hysteresis loop consisting of the stable active and passive steady states and an unstable steady state which corresponds to an intermediate situation between active and passive states. In the present study, the dynamical characteristics of the I-E polarization curve were studied. It was shown that transition from the oscillatory to the active steady state goes via a generalized Hopf bifurcation, whereas transition from the oscillatory to the passive steady state goes via a saddle-node infinite-period (SNIPER) bifurcation. Single pulse and pulse series stimulation of the active and passive steady states proved that both steady states are excitable. The refractory periods and the thresholds of excitability were measured. Further perturbation experiments were carried out at the two steady states away from the bifurcation points, and it was shown that the active steady state is a stable focus and the passive one is a stable node.