Current oscillations and mass-transport control during electrodissolution of iron in phosphoric acid solutions

Simultaneous observation of current oscillations and porous film growth during anodization of InP

The observation of spontaneous oscillations in current during the anodization of InP in relatively high concentrations of KOH electrolytes is reported. Oscillations were observed under potential sweep and constant potential conditions. Well-defined oscillations are observed during linear potential sweeps of InP in 5 mol dm(-)(3) KOH to potentials above approximately 1.7 V (SCE) at scan rates in the range of 50 to 500 mV s(-)(1). The oscillations observed exhibit an asymmetrical current versus potential profile, and the charge per cycle was found to increase linearly with potential. More complex oscillatory behavior was observed under constant potential conditions. Periodic damped oscillations are observed in high concentrations of electrolyte whereas undamped sinusoidal oscillations are observed in relatively lower concentrations. In both cases, the anodization of InP results in porous InP formation, and the current in the oscillatory region corresponds to the cyclical effective area changes due to pitting dissolution of the InP surface with the coincidental growth of a thick porous In(2)O(3) film.

Chaotic, mixed-mode and periodic oscillations during the electro-oxidation of copper in trichloroacetic acid

The current oscillations of a copper electrode in trichloroacetic acid solutions were studied in this paper. The Cu/CCl3COOH system is a new electrochemical oscillator, showing rich dynamic behaviour on two controllable parameters: the trichloroacetic acid concentration (CCCl3COOH) and the imposed potential (E). Phase trajectories were reconstructed from time series using time delaymethods in order that the complex oscillations could be analyzed. Five kinds of oscillations, periodic and quasiperiodic mixed-mode, aperiodic, small amplitude and chaotic current oscillations, were observed. The EDS (energy dispersive spectroscopy) technique was used to analyze the elemental composition of the film formed on the surface of the copper electrode after the current oscillations.