similar sensor based on the attachment of Au particles through a self-assembled
monolayer has been developed by Li and co-workers [196]. Au nanoparticles are
assembled on a Pt disk electrode using cysteine as a linker molecule. The presence
of the nanoparticles increases the active surface area available for sensing and catalysis purposes. SO 2 goes through a gas permeable membrane and comes into
contact with the electrolyte. When NaOH is used as the electrolyte, SO 2 dissolves
in it, and, at a potential of 0.6 V, gives rise to an anodic reaction: SO 3
2À þ 2OH
À À
2e
À , SO 4
2À þ H 2 O. This oxidation process is catalyzed by the Au nanoparticles.
NaOH is found to give the best current response compared to other electrolytes
with a minimum detectable concentration of 2.6 pM. Other gases such as CO, NO,
NH 3 and CO 2 do not cause any interference. The same group also designed sensors for analytes such as O 2 and CO based on a similar protocol [197, 198].
20.7
Electrocatalysis
The use of nanoparticles for electrocatalysis has been well documented [40a,
199a–d]. Improving the performance of electrochemical energy devices has driven
the research on the use of nanoparticles for catalyzing various redox reactions with
the aim of using them in fuel cells. Since the literature on this topic is vast, we
have attempted to summarize only the recent literature on the electrocatalysis of
certain reactions. Excellent reviews on various aspects of electrocatalysis are already
available [40a, 199a].
Nanometer-sized palladium islands on highly oriented pyrolytic graphite
(HOPG) have been found to be very useful in catalyzing hydrogen electroadsorption and desorption and hydrazine oxidation [200]. The enhancement is related to the fractal nature of the metal island formed on HOPG. Polymer hosts
such as Nafion have also been used for incorporating platinum nanoparticles to
effect oxygen reduction electrocatalysis [201a]. Supriya and Sampath have prepared
uniformly dispersed AuaAg nanoalloy colloids in sol–gel-derived aminosilicate
matrices and used them for oxygen reduction electrocatalysis [201b].
Platinised platinum electrodes have been used in electrocatalysis reactions for a
long time [199b, 199c]. The effects of surface restructuring phenomena on the
electrocatalysis are discussed in detail [202]. The catalytic surface is prepared by
the electrodeposition of platinum nanoparticles on a planar platinum surface from
0.1 M chloroplatinic acid. An increase in the mean particle size of platinum is observed with aging by potential cycling, resulting in a decrease in the surface area
and roughness. The consequences are observed in the oxygen coverage and activity
of different electrodes. The strength of the PtaO bond varies as the electrode is
aged and hence the reactivity of adsorbed oxygen varies. The same authors also
probed the desorption of hydrogen, oxygen and the oxidation of formic acid using
Pt nanoparticles incorporated on gold electrodes [203]. The use of silver nanoparticles to enhance the redox activity of organosulfur compounds [204] and that
of nanocrytalline platinum particles on the electrochemical oxidation of oxalic acid
20 Electrochemistry with Nanoparticles
678
monolayer has been developed by Li and co-workers [196]. Au nanoparticles are
assembled on a Pt disk electrode using cysteine as a linker molecule. The presence
of the nanoparticles increases the active surface area available for sensing and catalysis purposes. SO 2 goes through a gas permeable membrane and comes into
contact with the electrolyte. When NaOH is used as the electrolyte, SO 2 dissolves
in it, and, at a potential of 0.6 V, gives rise to an anodic reaction: SO 3
2À þ 2OH
À À
2e
À , SO 4
2À þ H 2 O. This oxidation process is catalyzed by the Au nanoparticles.
NaOH is found to give the best current response compared to other electrolytes
with a minimum detectable concentration of 2.6 pM. Other gases such as CO, NO,
NH 3 and CO 2 do not cause any interference. The same group also designed sensors for analytes such as O 2 and CO based on a similar protocol [197, 198].
20.7
Electrocatalysis
The use of nanoparticles for electrocatalysis has been well documented [40a,
199a–d]. Improving the performance of electrochemical energy devices has driven
the research on the use of nanoparticles for catalyzing various redox reactions with
the aim of using them in fuel cells. Since the literature on this topic is vast, we
have attempted to summarize only the recent literature on the electrocatalysis of
certain reactions. Excellent reviews on various aspects of electrocatalysis are already
available [40a, 199a].
Nanometer-sized palladium islands on highly oriented pyrolytic graphite
(HOPG) have been found to be very useful in catalyzing hydrogen electroadsorption and desorption and hydrazine oxidation [200]. The enhancement is related to the fractal nature of the metal island formed on HOPG. Polymer hosts
such as Nafion have also been used for incorporating platinum nanoparticles to
effect oxygen reduction electrocatalysis [201a]. Supriya and Sampath have prepared
uniformly dispersed AuaAg nanoalloy colloids in sol–gel-derived aminosilicate
matrices and used them for oxygen reduction electrocatalysis [201b].
Platinised platinum electrodes have been used in electrocatalysis reactions for a
long time [199b, 199c]. The effects of surface restructuring phenomena on the
electrocatalysis are discussed in detail [202]. The catalytic surface is prepared by
the electrodeposition of platinum nanoparticles on a planar platinum surface from
0.1 M chloroplatinic acid. An increase in the mean particle size of platinum is observed with aging by potential cycling, resulting in a decrease in the surface area
and roughness. The consequences are observed in the oxygen coverage and activity
of different electrodes. The strength of the PtaO bond varies as the electrode is
aged and hence the reactivity of adsorbed oxygen varies. The same authors also
probed the desorption of hydrogen, oxygen and the oxidation of formic acid using
Pt nanoparticles incorporated on gold electrodes [203]. The use of silver nanoparticles to enhance the redox activity of organosulfur compounds [204] and that
of nanocrytalline platinum particles on the electrochemical oxidation of oxalic acid
20 Electrochemistry with Nanoparticles
678