Surface and subsurface structures of PtSn surface alloy on Pt(111) were determined using in situ scanning tunneling microscopy (STM) and X-ray diffraction. Different ordered structures of the PtSn alloy layer were observed by STM in HClO 4 at coverage of θ Sn ≤ 0.23. Superstructure of (√3 × √7)R19.1°with small domain size was formed at θ Sn = 0.23. This structure promoted the catalytic activity for the ethanol oxidation reaction with high durability. X-ray structural analysis showed that the ratio of Sn in the subsurface was below 3(2)%, The PtSn alloy layer was mainly formed at the surface of the Pt(111) electrode. The Sn atoms protruded by 0.02 nm from the Pt layer, which was similar to the surface structure of Pt 3 Sn(111). One Pt atom in the (√3 × √7)R19.1°structure contacts to one or two surrounding Sn atoms, which lead to the highest activity for the EOR.
The interfacial structure and activity
for the oxygen reduction
reaction (ORR) were investigated on a PtNi surface alloy on a Pt(111)
electrode (PtNi/Pt(111)). The PtNi surface alloy was prepared by thermal
annealing of Ni
2+
modified on Pt(111) at 573–803
K. After optimizing the alloying temperature and the amount of added
Ni, the ORR current density of PtNi/Pt(111) at 0.9 V (reversible hydrogen
electrode) is enhanced 9.5 times compared with that of Pt(111), and
the activity is decreased by 24% after 1000 potential cycles. The
atomic composition and subsurface structure of PtNi/Pt(111) were determined
by in situ infrared reflection–absorption spectroscopy and
X-ray diffraction. The surface contains a (111)-oriented Pt-skin and
the subsurface of the 2nd–5th layers of the PtNi alloy contains
less than 11% Ni atoms. The layer spacings of the surface alloy layers
are slightly expanded compared with those of bare Pt(111). Homogeneous
alloying with a small amount of Ni in the subsurface layers achieves
the high ORR activity and durability.
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