Recent Developments in the Electrocatalysis of the O Reduction Reaction - Fuel Cell Catalysis: A Surface Science Approach - page 282

Figure 9.10 Like Pt, the ordered Pt 3 Co phase has the fcc structure and is represented by the
thermodynamically most stable (111) facet. These diagrams show high symmetry adsorption
sites identified for O and O 2 on (a) monolayer Pt skin on Pt 3 Co(111) and (b, c) Pt 3 Co(111).
Large circles represent Pt atoms, medium gray circles represent Co atoms, and small open circles
represent O atoms. The surface unit cells are delineated. (Reproduced with permission from Xu
et al. [2004].)
defects when deposited on Ru(0001) [Schlapka et al., 2003], which suggests that the
observed Pt skin could be compressed so as to conform to the slightly contracted lat-
tices of the underlying alloys (2% for Pt 3 Co and 1.5% for Pt 3 Fe vs. bulk Pt). In an
attempt to decouple the possible ligand effect (electronic interaction with the sub-
strate) from the strain effect (conforming to the substrate geometry) [Kitchin et al.,
2004], a 2% compressed Pt(111) surface was separately investigated.
The stoichiometric Pt 3 Co(111) surface has one-quarter of the Pt atoms replaced
with Co atoms. Bulk Co is very reactive toward oxygen, on which O 2 dissociation
is probably non-activated. The Co atoms on the alloy surface are diluted by Pt, but