Activity for the ORR on Pt-Pd-Co ternary alloy electrodes is markedly affected by surface structure and composition

[Display omitted] •Pt-Pd-Co ternary alloy single crystal electrodes are prepared for the ORR.•Pt45Pd45Co10(110) and Pt77Pd8Co15(111) show remarkably high ORR activity.•Rich Pd and Co on the subsurface enhance the ORR for Pt77Pd8Co15(111).•Pt, Pd, and Co are homogenously dissolved in underlayer of Pt77Pd8Co15(111). The oxygen reduction reaction (ORR) has been studied on single crystals of the ternary alloys Pt45Pd45Co10 and Pt77Pd8Co15 in O2-saturated 0.1 M HClO4 using a hanging meniscus rotating disk electrode. Specific activity for the ORR depends markedly on the composition and surface structure of the single crystal electrodes. The activity on Pt45Pd45Co10(hkl) increases in the order Pt45Pd45Co10(100) ≈ Pt45Pd45Co10(111)