The electrochemical deposition of rhodium on Au(111) was studied by means o
f in-situ STM and cyclic voltammetry. A phase transition within the [RhCl6]
(3-) adlayer was found for Au(111) in 0.1 M H2SO4 + 10(-4) M RhCl3 + 10(-3)
M HCl at 520 mV versus SCE, where a (root 13 x root 13)R13.9 degrees-super
structure of [RhCl6](3-) is formed on the gold substrate. Rhodium starts to
deposit irreversibly around 200 mV versus SCE. First a rhodium bilayer gro
ws, the electrochemical behaviour of which is similar to that of a well-ord
ered Rh(111) surface. On top of the second rhodium monolayer the formation
of small, three-dimensional clusters is observed. The electrocatalytic prop
erties of rhodium films with an average thickness up to ten monolayers were
studied by using CO oxidation as a test reaction. The influence of the sur
face structure on the CO oxidation kinetics is discussed briefly. (C) 1999
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