An unsupported Cu-Pt core-shell catalyst is prepared by a transmetalation reaction between copper and Pt2+ ions, and a Cu-Pt bimetallic alloy catalyst by a simultaneous reduction reaction. Both catalysts are subjected to electrochemical leaching without further treatment and their electrochemical characteristics and ORR activities are compared to that of a standard Pt black catalyst. Potential cycling in 0.1 M HClO4 and 0.5 M H2SO4 shows that the core-shell catalyst is highly stable and the electrochemical features show that it is purely Pt on the catalyst surface. The electrochemical surface area of the Cu-Pt core-shell catalyst is much higher than that of the Pt black. When the Pt loading on the electrode is increased with Pt black catalyst to match its geometric electrochemical surface area (cm(2)/electrode area (cm(2))) with that of Cu-Pt core-shell catalyst, the activity of the latter is still higher. The mass activities of Pt black, Cu-Pt binary alloy, and Cu-Pt core-shell catalysts measured using a rotating disk electrode are 0.053, 0.153 and 0.262 A mg(-1) Pt, and their respective specific activities are 197, 496, and 710 mu A cm(-2) Pt. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.039207jes] All rights reserved.