Environmental Engineering Reference
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(STEM) to investigate the chemical nature of the ORR catalytic sites on the atomic
scale. Iron atoms are often found along the edges of the defective graphene sheets
attached to the intact inner walls of few-walled nanotubes, and they often appear
next to nitrogen atoms. This provides the first indication of the atomically resolved
structure of the ORR catalyst.
Functionalized graphene sheets have been used as the cathode support for Pt
electrocatalysts to show higher electrochemical surface area and oxygen reduction
activity with improved stability as compared with that of the commercial catalysts.
Similarly Pt-decorated graphene has been shown to have better methanol oxidation
activity than its commercial counterpart [
44
-
50
]. It is worth to mention that in a
recent review by Wu et al., the extensive use of graphene-transition metal oxide
composites occupies an important role area and it may not be too far that the future
devices could be made from any one of these composites [
108
].
10 Recent Developments in Pt-Based Electrocatalysts
for PEMFC Applications
Platinum (Pt), especially in the form of small particles (\5 nm) on a support, plays
an outstanding role as a multifunctional catalyst for many industrial reactions.
Similarly, it is the only efficient fuel cell electrocatalyst (which is very hard to
replace) for many reactions, irrespective of the nature of the reaction, i.e. oxidation
or reduction. However, the high cost of platinum (currently about $1,500 per
ounce) [
109
] remains a challenge that demands its full or partial replacement
without affecting the performance for commercial applications [
110
]. The design
of inexpensive and robust electrocatalysts for fuel cells for this replacement
requires a thorough understanding of the behaviour of Pt in anodic and cathodic
environments of PEMFCs. In this context, manipulation of the size and shape of
platinum at the nanoscale can thus contribute to the lowering of Pt usage enabling
the much-needed cost reduction. Interestingly, it has been established that the
catalytic reactivity of platinum nanostructures depends highly on their morphol-
ogy, and therefore, the design and synthesis of well-controlled shapes and sizes of
platinum nanostructures is crucial for their applications, especially in the field of
catalysis and electrocatalysis [
111
]. In our recent review [
112
], we have com-
prehended up to date endeavours in the area of shape selective synthesis of Pt
nanostructures through several routes, concomitantly discussing some of the core
issues related to stabilizing cubes, hexagons, multipods, discs, rods, etc. Impor-
tantly, recent accomplishments in the area of shape-dependent electrocatalysis of
these nanostructures have been summarized, by giving special emphasis to elec-
trocatalytic reactions relevant for microfuel cells.
Recently, our group has demonstrated an entirely different route for the syn-
thesis of Pt multipods at room temperature by adopting a template-assisted elec-
trodeposition using a porous alumina membrane (PAM) [
113
]. For example,
Fig.
7
b shows a distribution of multipods, where the number of arms of each
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