Adaptation of the scanning vibrating electrode technique to ac mode:: Local electrochemical impedance measurement

A novel method of measuring local electrochemical impedance using a single vibrating probe electrode has been developed by modification of a commercial device of scanning vibrating electrode technique (SVET). The small size of the vibrating probe used by the SVET, increases the space resolution of the current distribution. Furthermore, the local impedance as defined here takes into account not only the local current density but also the local electrode potential, as opposed to the measurements proposed up to now in the literature. Simulation calculations demonstrate that this definition is the only one which leads to understandable results. The signal processing used to obtain this impedance is explained in detail and tested on a dummy cell including a phototransistor to simulate a vibrating electrode. The local impedances of a corroding Ni disk and of an electrode simulating pitting corrosion are also measured with this system.