HIGH-PRESSURE SONOELECTROCHEMISTRY IN AQUEOUS-SOLUTION - SOFT CAVITATION UNDER CO2

A novel high-pressure sonoelectrochemical cell has been developed in o rder to study the effect of pressure on cavitation and acoustic stream ing in electrochemical processes. The reversible one electron reductio n of a solution of Ru(NH3)(6)(3+) in aqueous 0.1 M KCl at a 25 mu m di ameter Pt microdisk electrode was studied under up to 60 bar pressure of argon and carbon dioxide and in the presence of ultrasound. The res ulting cathodic current response was interpreted to be composed of a s teady macroscopic streaming induced component and a transient spikelik e component detected after the onset of the cavitation. The threshold for the cavitation process was strongly dependent on pressure and incr eased monotonically in the presence of argon. However, the threshold a ppeared at lower ultrasound power when pressurizing with carbon dioxid e and even decreased at higher pressures (>40 bar) in the presence of CO2. The analysis of the observed phenomena is possible in terms of th e mechanical pressure, the surface tension, and the formation of a liq uid CO2 phase.