| Affiliation: | [1] Univ Estadual Campinas, Inst Chem, BR-13083970 Campinas, SP - Brazil
[2] Univ Estadual Campinas, Ctr Innovat New Energies, BR-13083841 Campinas, SP - Brazil
[3] St Louis Univ, Dept Chem, 3501 Laclede Ave, St Louis, MO 63103 - USA
Total Affiliations: 3
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Among many chemical systems displaying oscillatory behavior, the anodic dissolution of transition metals is considered one of the first, with the reports dating from as early as 1828. Since then, electrochemical oscillators have been studied as single or in a multielectrode configuration coupled under different network topologies. The coupling is basically made up of electrical connections between the electrodes, keeping them far apart from each other in such a way that only electric coupling is present. Here, we report experimental studies of the coupling between two electrochemical oscillators, namely, the oscillatory corrosion of Ni and Fe, not as two separated electrodes but as in the form of an alloy. The phenomenon is described in terms of stationary and dynamic electrochemical techniques as well as a bifurcation diagram, depicting the region of a R-ext versus E plane in which the oscillations are found. Also, a plot with the rate of the electrode potential change was calculated, which revealed the separation of the activation and passivation processes during an oscillatory cycle. These results suggest that there is a change in the mechanism by which the oscillations are observed when comparing Ni, Ni-Fe, and Fe. It is shown that, for the alloy, at potentials lower than the Flade potential, there is a mixed contribution from both Ni and Fe dissolution on the oscillations. This is a different potential region in comparison to Ni (similar to 1.2 to 1.5 V vs SCE), which is at the transpassive domain and compared to Fe (similar to 0.4 to 0.6 V vs SCE), with a mass transport-limited process at the current plateau just before the complete passivation. It is proposed that the oscillations found for the dissolution of the Ni-Fe alloy are produced by a mixed contribution from Fe and Ni in terms of their oxides and salts present in the passivation step, which impacts on the nonlinear dynamics of the system. In conclusion, a small amount of Fe (only 20%) is enough to induce a change in the mechanism by which the oscillations emerge, suggesting that a new process is taking place. (AU) |