Oxygen reduction reaction activities of Pt/Au(111) surfaces prepared by molecular beam epitaxy

Iijima, Yuki; Takahashi, Yu; Matsumoto, Ken-ichi; Hayashi, Takehiro; Todoroki, Naoto; Wadayama, Toshimasa

Oxygen reduction reaction activities of Pt/Au(111) surfaces prepared by molecular beam epitaxy

2012

Pt-deposited Au(111) surfaces were prepared by molecular beam epitaxy (MBE). Surface structures of the samples were verified with reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM) and infrared reflection absorption spectroscopy (IRRAS) for adsorbed carbon monoxide in an ultra-high vacuum (UHV) condition. The UHV-results show that epitaxial growth of Pt(111) on clean Au(111). A 0.3-nm-thick Pt deposition found to almost cover the Au surface. In addition, monoatomic-height Pt islands were observed on the topmost surface. Electrochemical properties were evaluated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) using a rotating disk electrode apparatus set in an N₂-purged glove box. A CV curve of the Pt₀.₃ₙₘ/Au(111) recorded in the potential region of 0.05–1.0V vs. reversible hydrogen electrode (RHE) was similar to that of clean Pt(111), except for the lack of ‘butterfly’ peaks at 0.8V. Oxygen reduction reaction (ORR) activities of the samples were evaluated by kinetic controlled current densities at 0.9V; the activity of the Pt₀.₃ₙₘ/Au(111) was ca. 1.8 times higher than that of the clean Pt(111). During CV curve measurements of the Pt₀.₃ₙₘ/Au(111) in the region of 0.05–1.7V, a redox feature at 0.13V became apparent; the ORR activity evaluated after the CV measurements was higher than the as-prepared sample. An UHV-STM image collected after re-transfer from the glove box showed two to three monoatomic-height Pt mounds whose slopes were 10–20°. The results clearly showed that surface defects at the topmost Pt(111) layer such as steps contribute to the ORR enhancement of MBE-prepared Pt/Au(111).

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