Oxygen reduction reaction activities of Pt/Au(1 1 1) surfaces prepared by molecular beam epitaxy

Pt-deposited Au(1 1 1) 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(1 1 1) on clean Au(1 1 1). 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(1 1 1) recorded in the potential region of 0.05–1.0 V vs. reversible hydrogen electrode (RHE) was similar to that of clean Pt(1 1 1), except for the lack of ‘butterfly’ peaks at 0.8 V. Oxygen reduction reaction (ORR) activities of the samples were evaluated by kinetic controlled current densities at 0.9 V; the activity of the Pt0.3nm/Au(1 1 1) was ca. 1.8 times higher than that of the clean Pt(1 1 1). During CV curve measurements of the Pt0.3nm/Au(1 1 1) in the region of 0.05–1.7 V, a redox feature at 0.13 V 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(1 1 1) layer such as steps contribute to the ORR enhancement of MBE-prepared Pt/Au(1 1 1).