In this study, we have investigated the oxygen reduction reaction (ORR) activity of Pt/Ni/Pt(111) model catalyst surfaces prepared by molecular beam epitaxy. Compared with Pt(111), 1-4-monolayer-thick Pt on Ni/Pt(111) surfaces showed 9-, 12-, 8-, and 7-fold higher activities, respectively. Cyclic voltammetry measurements and X-ray photoelectron spectroscopic analysis clearly revealed that electrochemical and electronic properties of the Pt(111) surface lattice approach those of clean Pt(111) surface with increasing Pt surface layer thickness. The results demonstrated that tuning Pt shell thickness is a key for generating highly active Pt-bimetallic catalysts for ORR.
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