Effects of ultrasound on the yield of hydrogen and chlorine during electrolysis of aqueous solutions of NaCl or HCl

Recently there has been renewed interest in sonochemistry, a branch of chemistry which studies the effects of ultrasound on chemical systems [1,2]. Essentially, the chemical effects of ultrasound are ascribed to the generation and implosion of microbubbles when a liquid medium is irradiated with these mechanical waves. This phenomenon is known as cavitation [1,2]. Sonoelectrochemistry could be defined by analogy as the branch of electrochemistry which studies any electrochemical process assisted, promoted or affected by ultrasound. It should be immediately underlined that very little work has been published in this field even in recent years [1,21. Moreover, a large part of these recent works deals with the advantages offered by sonication during electroplating, during electro-initiated polymerization of vinyl and dienic monomers, and in organic electrosynthesis [3]. Pionering work in the field of sonoelectrochemistry was performed during 1930-1940 [4-61. In this work the depolarizing effects of ultrasound were emphasized for the first time. It was found that the hydrogen or chlorine deposition potential is affected by an intense ultrasonic field operating at 280 kHz [5] or at 1200 kHz [6]. It was reported that at constant current density, there exists an acoustical intensity above which depolarization suddenly increases and, for example, the deposition potential of hydrogen is decreased by 0.7-0.8 V [5,6] and reaches the equilibrium potential. On the other hand at constant acoustical intensity, there exists a current density above which depolarization due to ultrasound becomes comparable to that offered by a violent stirring of the solution, while at lower current density the depolarization effect due to ultrasound is very high in comparison with that caused by strong stirring at the same current density Ed.