Abstract
The cyclic voltammetric (CV) behaviour of gold adsorbed on Pt{
h
k
l} electrodes is reported. It is found that stepped surfaces vicinal to Pt{1
1
1} exhibit preferential adsorption of gold at step sites. However, for stepped surfaces containing Pt{1
0
0} terraces, adsorption of gold at step and terrace site occurs with equal probability, although for Pt{
n
1
1} electrodes with
n
<
7 (i.e. electrodes containing short Pt{1
0
0} terraces), slight preference for step site adsorption is still observed. This behaviour is similar to that reported previously for Bi adsorption on Pt{
h
k
l} and is interpreted in terms of slower rates of gold atom surface diffusion across Pt{1
0
0} vs. Pt{1
1
1} terraces. By comparing the electrochemical response of gold adlayers on Pt{
h
k
l} with previously published bulk Au{
h
k
l} voltammetry, it is deduced that the gold overlayers on Pt{
h
k
l} are pseudomorphic in nature. This finding is in agreement with previous UHV and electrochemical results for gold deposition on platinum. Using such gold modified Pt{
h
k
l} electrodes as model surfaces, we also report, for the first time, the electrooxidation of ethanol on Au/Pt{
h
k
l} in alkaline aqueous solution. The ethanol oxidation reaction (EOR) is shown to be structure sensitive
for submonolayer gold coverages. In fact, a maximum in the rate of EOR at platinum sites
adjacent to gold islands is observed between approximately 0.4–0.6 monolayers of gold on Pt{1
0
0}, Pt{1
1
1} and Pt{1
1
0} in 0.1
M NaOH(aq). A second electrooxidation state at more positive potentials for 0
<
θ
Au
<
1 ascribed to EOR at pure gold sites is also observed, at least for Pt{1
1
1} and Pt{1
0
0}. On Pt{1
1
1}, the potential range and activity of EOR in this second process is similar to bulk gold whereas for submonolayer gold films on Pt{1
0
0}, the peak is shifted to more negative potentials.