Environmental Engineering Reference
In-Depth Information
Figure 14.10 CO bulk electro-oxidation at Ru(0001) and Ru(0001) modified by 0.05, 0.23,
and 0.9 ML Pt, measured at 10 mV s
21
in a flow cell with a CO-saturated electrolyte (0.1 M
HClO
4
): (a) expanded current scale to visualize the onset behavior; (b) entire current region.
described by the following scheme and also illustrated in Fig. 14.11:
A(Ru)
þ
A(Pt edge)
þ
H
2
O
!
OH
ad
(Ru)
þ
H
ad
(Pt edge)
[see (14
:
8)]
H
ad
(Pt, edge)
þ
H
2
O
!
A(Pt)
þ
H
3
O
þ
þ
e
[see (14
:
7)]
CO
ad
(Ru)
þ
OH
ad
(Ru)
rds
COOH
ad
(Ru)
þ
A(Ru)
[see (14
:
9)]
COOH
ad
(Ru)
þ
H
2
O
fast
CO
2
þ
A(Ru)
þ
H
3
O
þ
þ
e
[see (14
:
10)]
A(Ru)
þ
CO
!
CO
ad
(Ru)
[see (14
:
11)]
It is important to note that reaction of CO
ad
occurs only at sufficiently high coverages,
equivalent to a reduced reaction barrier (see the discussion of CO oxidation on
Ru(0001) above). The high coverage is maintained by continuous OH
ad
formation,
in competition with re-adsorption of CO. The Pt islands help in maintaining the
high coverage via (14.8). Finally, additional CO adsorption on the Pt monolayer
islands and reaction with OH
ad
on the Ru(0001) areas may be possible as well, and
this would further increase the overall reaction rate. At these potentials, however,
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