One of the key technical challenges for polymer electrolyte fuel-cell researchers is improving both the activity and stability of the oxygen reduction reaction (ORR) catalysts at the cathode. Pt-based alloys have shown great promise for achieving these targets. Herein, we report a new strategy for producing a highly active and stable class of PtCu catalysts with tunable compositions. Several unique nanoparticle catalysts were prepared by galvanically displacing a monolithic nanoporous Cu support with Pt, leading to a Pt-enriched PtCu shell over a PtCu core. It was observed that temperature during galvanic displacement is a key experimental parameter and a novel means to control catalyst particle size. This paper presents several modifications to the galvanic displacement process and describes the resulting enhancements in ORR activity (up to 2.1 mA/cm(2)Pt) and stability relative to pure Pt. (C) 2014 Elsevier Inc. All rights reserved.