Ternary preleached Pd-Pt-Ni and binary Pd-Pt catalysts have been synthesized, characterized, and evaluated as oxygen reduction reaction (ORR) electrocatalysts in single cell proton exchange membrane fuel cells (PEMFC), and the data have been compared with those of Pd-Pt-Ni catalyst. All the three catalysts show much improved Pt-mass activity compared to the state-of-the-art Pt catalyst. The preleached catalyst shows surface catalytic activity improvement by a factor of 2 in terms of Pt-mass activity and 3.5 in terms of specific activity compared to commercial Pt. Based on compositional analysis before and after the fuel cell test, the enhanced activity is attributed to an active phase with a Pd-rich core and Pt-rich shell structure. The strain introduced in the outer shell layer by the lattice parameter mismatch between the core and shell could downshift the metal d-band center, reduce the adsorption energy of hydroxyl species, and thus increase the intrinsic activity. The surface morphology and geometric effect induced by compositional and structural changes may also play a role. (c) 2010 Elsevier B.V. All rights reserved.