Well-defined ultrathin films of palladium, with coverages ranging from
submonolayer, ΘPd = 0.5 monolayer (ML), to multilayer, ΘP d = 8 ML, were
electrochemically deposited on Pt(111) using potentiostatic and potentiodynamic
methods. In both methods, between the coverage regimes studied, the growth of the Pd
films follows the Stranski-Krastanov mechanism.
The interfacial electrochemical properties associated with the film-to-bulk
transition were characterized by conventional voltammetric techniques in combination
with low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES).
The voltammetric peaks associated with H-atom adsorption and desorption on terrace
sites indicate that the Pd electrodeposit starts to exhibit bulk-like properties at a coverage
of 3 ML.
Voltammetric cycling, in sulfuric acid solution, between the hydrogen evolution
and the double-layer regions, was found to exert minimal influence on the annealing
(smoothening) of the electrodeposited Pd films. However, cycling within the same
potential region in the presence of bromide anions (at which Br- adsorption/Br
desorption takes place) smoothens the initially rough Pd films essentially as well as
high-temperature annealing.
The influence of chemisorbed bromine on the anodic dissolution of Pd was also
studied; this was for comparison with previous work on the anodic dissolution of Pd, in
inert electrolyte, catalyzed by chemisorbed iodine. The present studies indicated that a
small but measurable amount of bromine was desorbed along with dissolution of the Pd
step atoms; bromine at the Pd terrace behaved identically to iodine in that the coverage
of iodine is maintained regardless of the amount or origin of the of anodically stripped
Pd.
Atomically smooth, well-defined ultrathin Pd films were prepared by a constant
potential deposition (CPD) method followed by multiple potential cycles, in dilute Brsolution,
within the double-layer region and reductive removal of Brads, by simple
emersion at a potential just before the hydrogen evolution reaction potential (EHER). A
previously adapted method for the same purpose involved the chemisorption of iodine
onto ultrathin PdCPD films, from dilute I- solution, followed by reductive desorption of
Iads in iodide-free solution at pH 10 and at a potential just before EHER.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/2309 |
| Date | 29 August 2005 |
| Creators | Park, Yeon Su |
| Contributors | Soriaga, Manuel P. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 5494504 bytes, electronic, application/pdf, born digital |
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