Environmental Engineering Reference
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Figure 15.5 Cyclic voltammograms obtained in 0.1 M H
2
SO
4
at a sweep rate of 0.1 V s
21
for
Pt/GC electrodes with mean particle sizes
¯
N
¼ 1.8 nm (1), 2.4 nm (2), and 2.8 nm (3), and Pt
electrodeposited on GC (4). See the text for details. (Curves have been replotted from Maillard
et al. [2004a, 2005]—Reproduced by permission of The Royal Society of Chemistry and the
PCCP Owner Societies.)
In Fig. 15.5, we plot cyclic voltammograms (CVs) for model Pt nanoparticles
supported on GC with different mean particle sizes
¯
N
¼ 1.8, 2.4, and 2.8 nm after
subtraction of the current originating from the GC support. As one may see, subtrac-
tion does not completely eliminate currents originating from electro-oxidation/
reduction of surface groups on GC. We explain this by alterations of GC interfacial
properties upon Pt deposition. An essential step in making a fair comparison for
particles of different average diameters is normalization of the currents to the real Pt
surface area. A common approach is to determine the latter from the charge of
H
UPD
. This approach is valid only if neither the stoichiometry of adsorption nor
the coverage of the surface with H
UPD
is altered by the PSEs. As we will show
below, however, this does not seem to be the case.
Table 15.1 compares surface areas of Pt calculated using coulometry of H
UPD
(A
H
),
CO
ad
stripping (A
CO
), and TEM (A
TEM
) for Pt nanoparticles supported on GC and for
comparison for Pt foil. A
TEM
was calculated assuming a (hemi)spherical particle
shape. One may see that for Pt foil, A
CO
, A
H
, in agreement with the fact that CO cov-
erage on low index Pt single crystals and on polycrystalline Pt is below 1. For electro-
deposited Pt(ed) and for particles about 3 nm in diameter, A
CO
and A
H
are in excellent
agreement with TEM data. This may be explained by the fact that CO preferably
adsorbs in an atop configuration on Pt atoms with low average coordination numbers.
For example, Climent and co-workers have documented an increase in CO coverage
along with an increase in step density [Climent et al., 1999].
The most remarkable fact to emerge from Table 15.1 is that for particles of average
size below about 3 nm, H
UPD
leads to considerable underestimation (up to a factor
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