Related Phenomena Current Oscillations

Oscillatory behavior of electrochemical systems is not uncommon. The most familiar in this respect are the systems containing surface-active substances. Most surfactants are capable of forming inhibiting adsorption layers, which are responsible for a significant decrease in the cathodic current in a certain range of potentials. For instance, the electroreduction of copper [106] or tin [107] in the presence of inhibitors is accompanied by oscillation phenomena. 

The most vivid example of another group of electrochemical oscillators might be the Hg In(III), SCN system involving potential-dependent catalysis by thiocyanate of In(III) reduction. This system was investigated rather extensively [108-112]. According to the mechanism proposed in [109], the formation of adsorbed InfSCN) complexes is the rate-determining step followed by fast electroreduction of this species. As in the case of aforementioned systems, the 

As in the case of anodic processes, current oscillations occur in the potential region where there is a transition between the metal active and passive state and vice versa. The systems exhibiting oscillations are related to electrodissolution of iron and less to that of other metals such as cobalt, stainless steel, copper, and silver (see, e.g., [113-116] and references therein). In this case, the periodic process involves formation and dissolution of comparatively thick films of metal oxides, hydroxides, or other insoluble compounds. 

Periodic phenomena including electrochemical oscillators have been the subject of a vast number of recent investigations. A comprehensive list of references regarding various aspects of oscillatory behavior and related phenomena seems to be too long to present here. However, it is fair to refer to earlier work on the relationship between impedance spectroscopy and stability by de Levie [110]. The usefulness of impedance diagrams in discussing the stability properties of electrochemical cells has been studied in detail by Epelboin and coworkers the main results are reviewed in [117]. 

Several reasons maybe responsible for the first inequality potential-dependent adsorption of inhibitor or desorption of catalyst, electrostatic effect at low ionic strength, (e.g., a reduction of anions at negatively charged surface), or the case when the available electrode surface decreases with an increase in polarization (inhibition or passivation). 

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