The effect of ultrasound on the electrochemical loading of hydrogen in palladium

Although the application of ultrasound for the control
and modulation of various chemical processes is a subject
of continued interest [l], there is surprisingly little discus-
sion in the recent literature of the effects of ultrasound on
fundamental electrochemical processes. In early systematic
studies of the hydrogen evolution reaction under acidic
conditions [2,3], it was observed that, on a platinum elec-
trode, the overvoltage for hydrogen evolution decreased by
up to 30mV on the application of ultrasound, and that this
decrease was largely independent of current density in the
approximate range l-100 mA cm-‘, i.e. the Tafel slope
was largely unaffected under these conditions. On removal
of the ultrasound, the original polarization was regained
only on continued electrolysis for up to 1 h. These results
refer to electrolytes which had been pre-electrolysed for 10
to 20h. With more extensive pre-electrolysis (36h), the
results were generally similar; however, the polarization
decrease on the application of ultrasound was smaller (by a
factor of two) under comparable conditions, and the origi-
nal polarization was recovered rapidly on cessation of
irradiation. On the application of ultrasound to a nickel
electrode evolving hydrogen, the same general phe-
nomenon was observed, i.e. a decrease in overvoltage
without a significant change in Tafel slope [3]. For these
experiments, the acoustic frequency was 3OOkHz and the
;icoustic intensity was estimated to be approximately
I Wcmw2 of electrode area.