Abstract
A 'sonoelectrochemical reactor' with an ultrasonic source and the electrochemical equipment has been devised to monitor various ultrasonic parameters (wave frequency, geometry and position of working electrode). Methylviologen and ferricyanide reduction and pyrrole oxidation were studied in order to obtain informations on the modifications occurring in the course of the reactions. Studies conducted on ferricyanide reduction show that the voltammograms obtained under ultrasonic conditions at 20 or 500 kHz exhibit an enhancement of the diffusion process at the electrode surface where cavitation occurs. The best and most reproductible limiting currents were obtained at 500 kHz when the electrode is near the gas-liquid interface; the current density increases with ultrasonic power. At 20 kHz, the limiting current is higher when the electrode is close to the ultrasonic source and almost independent of the ultrasonic power. Coupling ultrasound with electrochemistry suppresses the electrode passivation that occurs during the methylviologen electroreduction at a glassy carbon electrode. Ultrasound was also efficient at hindering the electrodeposition of polypyrrole film at a platinum electrode and cleaning the surface coated by electrodeposited polypyrrole film. In addition, it is clearly shown that ultrasonic irradiation can modify the electrochemical reactivity at electrode-electrolyte interface.