Atomically Flat Pt Skin and Striking Enrichment of
Co in Underlying Alloy at Pt<sub>3</sub>Co(111) Single Crystal with
Unprecedented Activity for the Oxygen Reduction Reaction
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Abstract
By the use of in situ scanning tunneling
microscopy and surface
X-ray scattering techniques, we have clarified the surface structure
and the layer-by-layer compositions of a Pt skin/Pt<sub>3</sub>Co(111)
single-crystal electrode, which exhibited extremely high activity
for the oxygen reduction reaction. The topmost layer was found to
be an atomically flat Pt skin with (1 × 1) structure. Cobalt
was enriched in the second layer up to 98 atom %, whereas the Co content
in the third and fourth layers was slightly smaller than that in the
bulk. By X-ray photoelectron spectroscopy, the Co in the subsurface
layers was found to be positively charged, which is consistent with
an electronic modification of the Pt skin. The extremely high activity
at the Pt skin/Pt<sub>3</sub>Co(111) single crystal is correlated
with this specific surface structure