137
DFT calculations increased the understanding of the methanol electrooxidation
on the surfaces of Pt ML supported on different substrates. The onset potential for
methanol electrooxidation on the Pt ML /metal surfaces was estimated by calculating
the binding energies and free energies of CO and OH (Fig. 8.27). The DFT-predicted
trend in reactivity agreed well with the experimental observations, showing in
decreasing sequence, Pt ML /Au(111) > Pt(111) > Pt ML /Pd(111) > Pt ML /Ir(111) > Pt ML /
Rh(111) > Pt ML /Ru(0001). Pt ML /Au(111) displays the highest activity, where Pt ML is
stretched by over 4%, and exhibits enhanced reactivity in the dehydrogenative
adsorption of alcohol molecules (yielding Pt-CO) and the dissociation of water (PtOH formation). That is, the strain effect due to the Au support results in a Pt with
moderate reactivity, being able to bind the adsorbates strongly enough to activate
methanol, yet weakly enough to prevent CO poisoning and allow the formation of
CO 2 . In situ IRRAS study showed the enhanced MOR activity in Pt ML /Au(111) was
due to the formation of COH ads , instead of poisoning CO ads , and the promoted oxidation of COH ads directly to CO 2 . The enhanced MOR activity was attributed to the
combined geometric and electronic effect.
-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0
1
2
3
4
5
m
c
*
A
m
/
y
t
i
s
n
e
D
t
n
e
r
r
u
C
-2
E / V vs. Ag/AgCl
Pt(111)
Pt ML /Au(111)
Pt ML /Pd(111)
Pt ML /Ir(111)
Pt ML /Rh(111)
Pt ML /Ru(0001)
MOR
Fig. 8.25 Comparison of
methanol oxidation on
single-crystal (top), and
nanoparticle Pt ML -covered
surfaces (bottom) in 0.1 M
HClO 4  + 0.5 M CH 3 OH
solution [43]. Reproduced
with permission of the
American Chemical
Society
8.3 Methanol Oxidation on Platinum Monolayer Electrocatalysts