[202, 203] has been recently reported. Gold nanoparticles electrodeposited on planar gold electrodes lead to a four-electron process for oxygen reduction in an acidic
medium. The hydrodynamic voltammetric experiments do not show well-defined
limiting waves; this may be due to a mixed control of diffusion and kinetic limitations [205].
Studies on the catalytic oxidation of CO and methanol are of great significance in
several areas of research and technology [206]. The most commonly used catalysts
for methanol oxidation belong to the Pt group. One disadvantage however, is that
these catalysts tend to get poisoned by the CO-like species formed during the process. Zhong and co-workers have prepared faceted thiolate-capped AuaPt alloy
nanoparticles that possess the dual advantage of methanol oxidation at the Pt sites
and CO oxidation at the Au sites [207]. The alloy particles are deposited on a GCE
surface by the exchange-crosslinking-precipitation route and used for methanol
oxidation [208]. The authors propose the involvement of gold oxide in the electrocatalytic process. In an earlier paper, the same group followed the electrocatalytic
oxidation of CO using thiolate-capped gold particles [209]. Copper–palladium and
silver–palladium alloy particles have also been explored as catalysts for methanol
oxidation [210] in alkaline media. The alloying process causes deterioration in the
performance of pure palladium clusters. Nanosized PtaPd particles have been
synthesized and the electrocatalytic behaviour has been studied in order to understand the dissociative adsorption of methanol and formic acid [211]. Boron-doped
diamond electrodes have recently come into prominence for a variety of applications including sensing, electrocatalysis and electrochemical decontamination
[212, 213]. Platinum nanoparticles have been used to modify the boron-doped diamond electrodes [214] towards achieving electrocatalysis of methanol oxidation.
The high dispersity inside the nano-honeycomb matrix and the high surface area
of the nanoparticles leads to very good electrocatalytic activity. The electrocatalytic
activities of nanosized platinum particles for methanol, formic acid and formaldehyde electrooxidation have been recently reported [215]. The sensitivity of the catalyst particles has been interpreted in terms of a ‘catalyst ensemble effect’ but the
detailed microscopic behaviour is incomplete. Martin and co-workers [216] have
demonstrated the incorporation of catalytic metal nanoparticles such as Pt, Ru and
Pt/Ru into carbon nanotubes and further used them in the electrocatalysis of
oxygen reduction, methanol electrooxidation and gas phase catalysis of hydrocarbons. A related work on the incorporation of platinum nanoparticles in carbon
nanotubes has recently been reported to show promising electrocatalytic activity for
oxygen reduction [217].
There have been many attempts to utilize nanosized materials for battery applications [218]. Nanosized alloys of SnaSb dispersed on carbon are found to be good
anodes for lithium batteries [218b]. Though high reversible capacities have been
reported for the alloy, there is considerable loss in subsequent cycles that is
ascribed to the decomposition of surface oxide, formation of solid electrolyte
interphase and aggregation of alloy particles during cycling. Dunn and co-workers
[219] used nanosized ruthenium particles with carbon aerogels to develop supercapacitors having specific capacitances of the order of 100 F g
À1 .
20.7 Electrocatalysis 679
medium. The hydrodynamic voltammetric experiments do not show well-defined
limiting waves; this may be due to a mixed control of diffusion and kinetic limitations [205].
Studies on the catalytic oxidation of CO and methanol are of great significance in
several areas of research and technology [206]. The most commonly used catalysts
for methanol oxidation belong to the Pt group. One disadvantage however, is that
these catalysts tend to get poisoned by the CO-like species formed during the process. Zhong and co-workers have prepared faceted thiolate-capped AuaPt alloy
nanoparticles that possess the dual advantage of methanol oxidation at the Pt sites
and CO oxidation at the Au sites [207]. The alloy particles are deposited on a GCE
surface by the exchange-crosslinking-precipitation route and used for methanol
oxidation [208]. The authors propose the involvement of gold oxide in the electrocatalytic process. In an earlier paper, the same group followed the electrocatalytic
oxidation of CO using thiolate-capped gold particles [209]. Copper–palladium and
silver–palladium alloy particles have also been explored as catalysts for methanol
oxidation [210] in alkaline media. The alloying process causes deterioration in the
performance of pure palladium clusters. Nanosized PtaPd particles have been
synthesized and the electrocatalytic behaviour has been studied in order to understand the dissociative adsorption of methanol and formic acid [211]. Boron-doped
diamond electrodes have recently come into prominence for a variety of applications including sensing, electrocatalysis and electrochemical decontamination
[212, 213]. Platinum nanoparticles have been used to modify the boron-doped diamond electrodes [214] towards achieving electrocatalysis of methanol oxidation.
The high dispersity inside the nano-honeycomb matrix and the high surface area
of the nanoparticles leads to very good electrocatalytic activity. The electrocatalytic
activities of nanosized platinum particles for methanol, formic acid and formaldehyde electrooxidation have been recently reported [215]. The sensitivity of the catalyst particles has been interpreted in terms of a ‘catalyst ensemble effect’ but the
detailed microscopic behaviour is incomplete. Martin and co-workers [216] have
demonstrated the incorporation of catalytic metal nanoparticles such as Pt, Ru and
Pt/Ru into carbon nanotubes and further used them in the electrocatalysis of
oxygen reduction, methanol electrooxidation and gas phase catalysis of hydrocarbons. A related work on the incorporation of platinum nanoparticles in carbon
nanotubes has recently been reported to show promising electrocatalytic activity for
oxygen reduction [217].
There have been many attempts to utilize nanosized materials for battery applications [218]. Nanosized alloys of SnaSb dispersed on carbon are found to be good
anodes for lithium batteries [218b]. Though high reversible capacities have been
reported for the alloy, there is considerable loss in subsequent cycles that is
ascribed to the decomposition of surface oxide, formation of solid electrolyte
interphase and aggregation of alloy particles during cycling. Dunn and co-workers
[219] used nanosized ruthenium particles with carbon aerogels to develop supercapacitors having specific capacitances of the order of 100 F g
À1 .
20.7 Electrocatalysis 679