Environmental Engineering Reference
In-Depth Information
and also Pt(111) (energetic modification). In addition, the lower overall cover-
age on these surfaces affords a more facile H
2
O dissociation/OH
ad
formation
process (kinetic modification). In total, these two effects result in a further
downshift of the onset potential for CO bulk oxidation at higher Pt contents,
and
in
a
significantly steeper
slope
of
the
j2E
curves
compared
with
Ru(0001), Pt(111), and Pt monolayer-modified Ru(0001).
From a methodological point of view, the results presented and discussed in this
chapter demonstrate the potential of using structurally well-defined bimetallic elec-
trode surfaces, whose local surface structure and composition is quantitatively
known on a atomic scale, as model systems for systematic studies of the local adsorp-
tion properties, and thus of the modifications brought about by the bimetallic nature of
the surface. In contrast to surfaces of bulk alloys, the bulk composition and therefore
also the neighborhoods of the surface atoms, are known. Hence, maps of the atomic
distribution in the outermost layer contain all the information needed to quantitatively
link structure and composition on the one hand to adsorption and electrocatalytic prop-
erties on the other. Because of their well-defined structure and composition, these
planar model systems allow a distinction to be drawn between contributions from
different effects such as the electronic ligand, the geometric ensemble, or the lattice
strain effect, and even to quantify the order of magnitude of their different contri-
butions. Furthermore, these surfaces are particularly suited for quantitative compari-
son with theory, in particular with results of DFT calculations and Monte Carlo
simulations. The combination of experiment and theory leads to an unprecedented
understanding of the electrochemical and electrocatalytic properties of bimetallic elec-
trodes and catalysts on a microscopic scale, and in an atomistic picture. The good
agreement between experiment and theory achieved so far indicates that the descrip-
tion of the above properties in a local picture can, at least for the present scale of exper-
imental and theoretical accuracy, provide an appropriate model of electrochemical/
electrocatalytic reactions as sums of elementary processes.
ACKNOWLEDGMENTS
We are indebted to O. B. Alves for providing data prior to publication. Furthermore, we grate-
fully acknowledge fruitful discussions with O. B. Alves, A. Bergbreiter, J. Bansmann,
T. Diemant, A. Groß, L. A. Kibler (all Ulm University), M. Janik (Pennsylvania State
University, USA), M. T. M. Koper (Leiden University, Leiden, The Netherlands), and
J. K. Nørskov (Danish Technical University, Lyngby, Denmark).
REFERENCES
Andersson K, Nikitin A, Pettersson LGM, Nilsson A, Ogasawara H. 2004. Water dissociation
on Ru(001): An activated process. Phys Rev Lett 93: 196101.
Assmann J, Narkhede V, Breuer A, Muhler M, Seitsonen AP, Knapp M, Crihan D, Farkas A,
Mellau G, Over H. 2003. Heterogeneous oxidation catalysis on ruthenium: Bridging the
pressure and materials gaps and beyond. J Phys Cond Matt 20: 184017.
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