VOLTAMMETRY IN THE PRESENCE OF ULTRASOUND - THE LIMIT OF ACOUSTIC STREAMING INDUCED DIFFUSION LAYER THINNING AND THE EFFECT OF SOLVENT VISCOSITY

Fundamental aspects and applications of power ultrasound in electroche mistry are presently in rapid development. However, from the many lite rature reports using various types of, sometimes not very well charact erized, sonoelectrochemical reactor, only a fragmented, often contradi ctory picture of the associated physicochemical processes arises. In t his study, a classification of different sonoelectrochemical cell type s depending on the effect of insonation is given and experimental resu lts for 'face-on', 'side-on', and sonotrode geometries are compared. I n particular, a minimum decrease in the diffusion layer thinning or a maximum increase in the transport-limited current can respectively be observed as the ultrasound power is increased. The comparative mass tr ansport characteristics and the effect of solvent viscosity allow turb ulent acoustic streaming to be identified as a major physical process which governs the mass transport in undivided sonoelectrochemical cell s employing an immersion horn transducer. The effect of solvent viscos ity on the limit of diffusion layer thinning is investigated using the electrochemical reduction of tetracyanoquinodimethane dissolved in di chloromethane, acetonitrile, dimethylformamide, and dimethylsulfoxide. A reciprocal relationship between the kinematic viscosity nu and the limiting value for the diffusion layer thickness delta(lim) is observe d.