Environmental Engineering Reference
In-Depth Information
Reactions (6.8) - (6.10) corresponding to the proposed EC mechanism, and not taking
into account the initiation step (which involves a small fraction of the charge), it is
possible to obtain an analytical expression for the voltammetric CO stripping peak
[Herrero et al., 2004]:
exp
k
app
RT
Fv
þ
b
FE
RT
FE
RT
k
app
exp
exp
j
¼
Q
(6
:
11)
þ
b
þ
1
2
exp
k
app
RT
Fv
FE
RT
exp
where Q is the charge associated to the oxidation of the adsorbed CO, k
app
is the
apparent rate constant for the process measured at 0 V (RHE), v is the scan rate, and
b is a parameter that groups all the initial values for the process (essentially, the initial
potential for the voltammetric scan, E
ini
, and the initial coverage value, u
in
). The
voltammetric peaks for CO oxidation on Pt(111) and Pt(100) were fitted using
(6.11). A very good fitting was obtained for both electrodes, validating the approach
used. It should be mentioned that the peak width depends strongly on the mechanism;
the good fit obtained indicates that the proposed reaction mechanism is a good
approximation to the process (Fig. 6.5). This approach was used to calculate the
value of k
app
for different electrodes under different conditions.
The variation of k
app
with the temperature was used to determine the apparent
activation energy of the process at 0 V for both electrodes. The values of the activation
Figure 6.5 CO
ads
voltammetric stripping peak (symbols) and the fits obtained from (6.11)
(lines) for the Pt(111) electrode in 0.5 M H
2
SO
4
at different temperatures. The scan rate was
50 mV/s.
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