Oxygen reduction reaction activities for Pt-enriched Co/Pt(111), Co/Pt(100), and Co/Pt(110) model catalyst surfaces prepared by molecular beam epitaxy

► Co-Pt bimetallic surfaces prepared on low-index Pt single crystals surfaces by MBE. ► ORR activities are evaluated after sample transfer from UHV to EC system. ► The Pt-enriched Co/Pt(111) is the most ORR active. ► The ORR activity for the Co/Pt(111) rapidly decreases by potential cycling. ► Atomic arrangements of the surface Pt and the underlaying Co determine ORR activity.