as 1934. As for the case of sonochemistry, the use of ultrasound in electrochemistry went through a period of neglect until the early 1980s when there was again an
upsurge of interest in the field. At present, ultrasound is used in a wide range of
electrochemical processes such as: metal plating, deposition of polymers, electrogeneration of gases and solids, and electrochemical waste processing.
Ultrasound and electrochemistry provide a powerful combination for several
reasons. Ultrasound is well known for its capacity to promote heterogeneous reactions, mainly through increased mass-transport, interfacial cleaning, and thermal effects. Effects of ultrasound in electrochemistry may be divided into several
important branches: (1) Ultrasound greatly enhances mass transport, thereby altering the rate, and sometimes the mechanism, of the electrochemical reactions.
(2) Ultrasound is known to affect surface morphology through cavitation jets at the
electrode–electrolyte interface; it usually acts to increase the surface area. (3) Ultrasound reduces diffusion layer thickness and therefore ion depletion. A comprehensive review of the field has recently been given by Compton et al. [145].
However, it is only recently that the potential benefits of combining sonochemistry with electrochemistry have increasingly been studied. It should be noted that
electrochemical methods, mainly electrodeposition, are well established for the
preparation of metals and semiconductor nanomaterials (for a review see Mastai
et al. [146]).
6.2.1
Sonoelectrochemical Synthesis of Nanocrystalline Materials
Reisse and co-workers [147–149] were the first to describe a novel device for the
production of metal powders using pulsed sonoelectrochemical reduction. This
device exposes only the flat circular area at the end of the sonic tip to the electrodeposition solution. The exposed area acts as both cathode and ultrasound emitter,
named by Reisse et al. as ‘‘sonoelectrode’’. A pulse of electric current produces a
high density of fine metal nuclei. This is immediately followed by a burst of ultrasonic energy that removes the metal particles from the cathode, cleans the surface
of the cathode, and replenishes the double layer with metal cations by stirring the
solution. In [145], a list is given of chemically pure fine crystalline powders, mostly
metals or metallic alloys, prepared by this method, with particle sizes varying between 10 and 1000 nm depending on deposition conditions.
Powder CdSe nanoparticles prepared by a pulsed sonoelectrochemical technique
with a sonoelectrochemical device similar to that described by Reisse, namely the
‘‘sonoelectrode’’, were reported first by Mastai et al. [150]. In Figure 6.8 we present
the experimental set-up for pulsed sonoelectrochemical deposition of CdSe nanoparticles, namely the ‘‘sonoelectrode’’, and schematics of the sonic and electrochemical waveforms.
In the ‘‘sonoelectrode’’ design, a titanium horn acts both as the cathode and the
ultrasound emitter. The electroactive part of the sonoelectrode is the planar circular
surface at the bottom of the horn. This sonoelectrode produces a sonic pulse that is
triggered immediately following a current pulse. One pulse driver is used to con6.2 Sonoelectrochemistry 149
upsurge of interest in the field. At present, ultrasound is used in a wide range of
electrochemical processes such as: metal plating, deposition of polymers, electrogeneration of gases and solids, and electrochemical waste processing.
Ultrasound and electrochemistry provide a powerful combination for several
reasons. Ultrasound is well known for its capacity to promote heterogeneous reactions, mainly through increased mass-transport, interfacial cleaning, and thermal effects. Effects of ultrasound in electrochemistry may be divided into several
important branches: (1) Ultrasound greatly enhances mass transport, thereby altering the rate, and sometimes the mechanism, of the electrochemical reactions.
(2) Ultrasound is known to affect surface morphology through cavitation jets at the
electrode–electrolyte interface; it usually acts to increase the surface area. (3) Ultrasound reduces diffusion layer thickness and therefore ion depletion. A comprehensive review of the field has recently been given by Compton et al. [145].
However, it is only recently that the potential benefits of combining sonochemistry with electrochemistry have increasingly been studied. It should be noted that
electrochemical methods, mainly electrodeposition, are well established for the
preparation of metals and semiconductor nanomaterials (for a review see Mastai
et al. [146]).
6.2.1
Sonoelectrochemical Synthesis of Nanocrystalline Materials
Reisse and co-workers [147–149] were the first to describe a novel device for the
production of metal powders using pulsed sonoelectrochemical reduction. This
device exposes only the flat circular area at the end of the sonic tip to the electrodeposition solution. The exposed area acts as both cathode and ultrasound emitter,
named by Reisse et al. as ‘‘sonoelectrode’’. A pulse of electric current produces a
high density of fine metal nuclei. This is immediately followed by a burst of ultrasonic energy that removes the metal particles from the cathode, cleans the surface
of the cathode, and replenishes the double layer with metal cations by stirring the
solution. In [145], a list is given of chemically pure fine crystalline powders, mostly
metals or metallic alloys, prepared by this method, with particle sizes varying between 10 and 1000 nm depending on deposition conditions.
Powder CdSe nanoparticles prepared by a pulsed sonoelectrochemical technique
with a sonoelectrochemical device similar to that described by Reisse, namely the
‘‘sonoelectrode’’, were reported first by Mastai et al. [150]. In Figure 6.8 we present
the experimental set-up for pulsed sonoelectrochemical deposition of CdSe nanoparticles, namely the ‘‘sonoelectrode’’, and schematics of the sonic and electrochemical waveforms.
In the ‘‘sonoelectrode’’ design, a titanium horn acts both as the cathode and the
ultrasound emitter. The electroactive part of the sonoelectrode is the planar circular
surface at the bottom of the horn. This sonoelectrode produces a sonic pulse that is
triggered immediately following a current pulse. One pulse driver is used to con6.2 Sonoelectrochemistry 149