Time-dependency of impedance spectroscopic studies of oscillatory systems

Non-steady state nature of impedance spectroscopy for the investigation of electrochemical systems displaying oscillatory behavior was shown. To this aim, an electrochemical oscillator involving metal dissolution was chosen as a typical example. It was demonstrated that the impedance spectra recorded for the Fe/H3PO4 system are strongly time-dependent, which is attributed to the growth of passive layer on the electrode surface. Indeed, resistance of the passive film formed on the electrode surface increases gradually, which has a significant effect on the system dynamic. Interestingly, impedance measurements recorded suggest instability of the system (and consequently appearance of oscillatory behavior) for certain values of film resistance and indeed at a certain time range of the experiments. Generally, as a typical example, it was demonstrated that how time-dependency of complex systems with complicated dynamics such as oscillators could be a source of errors in their analyzing. (C) 2004 Published by Elsevier B.V.