A series of carbon-supported core-shell nanoparticles with PdxCuy-rich cores and Pt-rich shells (Pt@PdxCuy/C) has been synthesized by a polyol reduction of the precursors followed by heat treatment to obtain the PdxCuy/C (1 <= x <= 3 and 0 <= y <= 5) cores and the galvanic displacement of PdxCuy with [PtCl4](2-) to form the Pt shell. The nanoparticles have also been investigated with respect to the oxygen reduction reaction (ORR) in proton-exchange-membrane fuel cells (PEMFCs). X-ray diffraction (XRD) analysis suggests that the cores are highly alloyed and that the galvanic displacement results in a certain amount of alloying between Pt and the underlying PdxCuy alloy core. Transmission electron microscopy (TEM) images show that the Pt@PdxCuy/C catalysts (where y > 0) have mean particle sizes of <8 nm. Compositional analysis by energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) clearly shows Pt enrichment in the near-surface region of the nanoparticles. Cyclic voltammograms show a positive shift of as much as 40 mV for the onset of Pt-OH formation in the Pt@PdxCuy/C electrocatalysts compared to that in Pt/C. Rotating disk electrode (RDE) measurements of Pt@PdCu5/C show an increase in the Pt mass activity by 3.5-fold and noble metal activity by 2.5-fold compared to that of Pt/C. The activity enhancements in RDE and PEMFC measurements are believed to be a result of the delay in the onset of Pt-OH formation.