Environmental Engineering Reference
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detection limit of AES (0.01 monolayers (ML)). Pt was evaporated from an electron
beam evaporator (Omicron FOCUS EFM 3), with the substrate at 300 - 350K and
typical deposition rates of about 0.25 ML min
21
. The resulting Pt coverages were
analyzed by quantitative evaluation of STM images and by AES. In some cases,
the Ru(0001) surface was covered with oxygen prior to Pt deposition to attain a
higher Pt island density. Surface alloys were formed by flash annealing to 1350K.
14.2.3 Electrochemical Measurements
For the electrochemical measurements, sample and sample holder were transferred
into a small pre-chamber via a magnetically coupled transfer rod. The pre-chamber
was continuously pumped by a turbomolecular pump (Pfeiffer, TMU 71) to minimize
possible contaminations of the clean surface or of the main chamber (typical working
pressure 10
29
mbar). After the sample transfer, the pre-chamber was separated from
the main chamber and the turbo pump by two gate valves and filled with clean nitrogen
to ambient pressure. Subsequently, a miniaturized electrochemical flow cell, made of
KEL-F and mounted on top of a glass tube, was moved up into the pre-chamber
through an opened gate valve and brought into contact with the single crystal from
below (Fig. 14.1b). The model electrode was then pressed to an O-ring gasket
(made of Kalrez) on top of the flow cell by a small wobble stick, which also
provided a direct electrical contact to the sample. A continuous electrolyte flow
(about 0.5 mL s
21
) could be maintained for measurements requiring enhanced mass
transport. Cyclic base voltammograms (base CVs) were recorded either in resting or
in flowing electrolyte. The mass-transport-limited currents attained under electrolyte
flow conditions are in the range of those reached by a rotating disk electrode at 900
rev min
21
, for example around 1.5 mA cm
22
for the electro-oxidation of CO
[Markovic et al., 1999]. A reversible hydrogen electrode (RHE), which was coupled
to the cell via the electrolyte inlet, was used as reference electrode. All potentials in
this chapter are given with respect to that of the RHE electrode. Potential values
from the work of other groups were converted into RHE potentials for easier compari-
son. In all measurements at Ru(0001) model electrodes, a total charge of one electron
per surface atom equals 0.253 mC cm
22
. All integrated charges are corrected for a
double layer contribution of 20 mFcm
22
as previously used for bare Ru(0001)
[El-Aziz and Kibler, 2002].
14.3 RESULTS
14.3.1 Structure and Electrochemical Properties of Bare
and Pt Film-Modified Ru(0001) Electrodes
14.3.1.1 Unmodified Ru(0001) Electrodes
Related UHV Studies
The interaction of molecules relevant for the present
purpose, such as H
2
,O
2
, and H
2
O, with Ru(0001) surfaces under UHV conditions
has been studied in much detail over the last decades [Diemant et al., 2003; Liu
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