Developments in highly-active cathode-electrode

catalysts for oxygen reduction reaction (ORR) are one of the most important subjects to achieve high efficiency for polymer electrolyte fuel cells (PEFCs). Alloying Pt with non-precious metals such as Fe, Co and Ni enhances ORR activities. In particular, generation of Pt-enriched outermost layer (Pt-skin) is a key to achieve high ORR activity [1, 2]. Stamenkovic et al. studied the ORR activity for the Pt-skins generated on Pt3Ni single-crystal surfaces and showed marked dependence of the surface symmetries on the activity [3]. However, to date, there are few studies focusing on stabilities of well-defined bimetallic surface systems. In this study, we fabricate Ni/Pt(111) model catalyst surfaces by using molecular beam epitaxy (MBE) and evaluate their ORR activity and stability in electrolyte