The effect of ultrasonic frequency and intensity upon electrode kinetic parameters for the Ag(S2O3)23-/Ag redox couple

This paper describes the effect of ultrasound on electrochemical parameters important in the removal of silver from photographic processing solutions. Decomposition voltages (obtained galvanostatically) and discharge potentials (obtained potentiostatically) for the reduction of the silver complex, Ag(S2O3)(2)(3-) was studied in dilute aqueous Na2S2O3/NaHSO3 solution on stainless steel and carbon disc electrodes in both the absence and presence of ultrasound. Under silent conditions, silver deposition is the main reaction occurring at the electrode. Under sonication at 20 kHz and 500 kHz, the reduction wave shifts anodically with increasing ultrasonic intensity. Similarly, the discharge of hydrogen and oxygen shifts anodically and cathodically respectively with increasing ultrasonic power. The decrease in decomposition voltage in the presence of ultrasound is due to the combined effect of a decrease in anodic overpotential and an increase in cathodic overpotential.