Metal sonoelectrochemistry

Sonoelectrochemistry has been employed in a number of fields such as in electroplating for the achievement of deposits and films of higher density and superior quality, in the deposition of conducting polymers, in the generation of highly active metal particles and in electroanalysis. Furtlienuore, the sonolysis of water to produce hydroxyl radicals can be exploited to initiate radical reactions in aqueous solutions coupled to electrode reactions. 

Apphcations of ultrasound to electrochemistry have also seen substantial recent progress. Beneficial effects of ultrasound on electroplating and on organic synthetic apphcations of organic electrochemistry (71) have been known for quite some time. More recent studies have focused on the underlying physical theory of enhanced mass transport near electrode surfaces (72,73). Another important appHcation for sonoelectrochemistry has been developed by J. Reisse and co-workers for the electroreductive synthesis of submicrometer powders of transition metals (74). 

Abstract In the last decade, the sonoelectrochemical synthesis of inorganic materials has experienced an important development motivated by the emerging interest in the nanostructures production. However, other traditional sonoelectrochemical synthesis such as gas production, metal deposits and metallic oxide films have also been improved with the simultaneous application of both electric and ultrasound fields. In this chapter, a summary of the fundamental basis, experimental set-up and different applications found in literature are reported, giving the reader a general approach to this branch of Applied Sonoelectrochemistry. 

Deposits of materials other than metals can be obtained by sonoelectrochemistry and, among them, metal oxides are of particular interest specially in electrochemistry. 

Synthesis of metallic magnesium by sonoelectrochemistry Hass I, Gedanken A (2008) Chem Commun 1795-1797... 

A novel method of generating finely divided zinc metal is by the use of pulsed sonoelectrochemistry using an ultrasonic horn as the cathode [85], Normal electrolysis of ZnCl2 in aqueous NH4CI affords a zinc deposit on the cathode. When the electrolysis is pulsed at 300 ms on/off and the cathode is pulsed ultrasonically at a 100 ms 200 ms on off ratio the zinc is produced as a fine powder. This powder is considerably more active than commercial zinc powder e. g. in the addition of allyl bromide to benzaldehyde (Eq. 3.9). 

Although the topic of sonoelectrochemistry will be treated in the subsequent section, it should also be mentioned that pulsed sonoelectroreduction of metallic salts gives rise to finely divided reactive metals which can be employed in organometallic synthesis see above [85]. The synthesis of nanocompounds of semiconductors such as cadmium and lead selenides can also be achieved using similar methodology [169]. 

Russian workers have looked at acoustic waves produced during the electrochemical oxidation of antimony [ 147], almost a reverse application of sonoelectrochemistry. Antimony was anodized in aqueous H3B03 solutions galvanostatically (2.2 x 1(T3 A/cm2) and isothermally (292 K). The formation voltage increased to >200 V with time, which is characteristic of the valve metals. Acoustic waves were observed in this electrochemical oxidation with amplitudes that did not differ essentially from the very beginning of the oxidation. The energy of the acoustic wave had only one sharply distinct peak which coincided in time with the appearance of the electrochemical breakdown products. 

Sonoelectrochemistry has been shown to provide an efficient and low cost way of synthesizing metallic nano-powders in aqueous media, thus presenting an easy alternative to more conventional and expensive methods. 

Tab. 4 Summary of the different metallic nano-powders synthesized using sonoelectrochemistry [59]...

Prominent applications of sonoelectrochemistry are electroplating [296], since very smooth layers have been generated this way, furthermore production of nanomaterials, nanoparticles and very line metallic powders [297-299]. Among the latest achievements was sonoelectrochemical generation of quantum dots [300]. 

---