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

► Pt-Au bimetallic surfaces are prepared on Au(1 1 1) by MBE. ► Topmost surface structures are verified with RHEED, STM, and IRRAS in UHV. ► ORR activities are evaluated after sample transfer from UHV to EC system. ► The MBE-prepared Pt0.3 nm/Au(1 1 1) shows higher ORR activity than clean Pt(1 1 1). ► Surface defects contribute to the ORR enhancement of MBE-prepared Pt/Au(1 1 1).