Electrocatalytic properties of platinum layers overgrown on cubic, octahedral, and spherical gold nanocrystals were investigated. Electrochemically active surface area per unit mass of platinum was significantly different, depending on the shape of gold core nanocrystal. CO stripping results showed that binding of surface platinum atoms to CO was stronger than Pt black when platinum partially covered the gold surface. Au core@Pt shell composite nanoparticles generally demonstrated enhanced mass activity for methanol oxidation, formic acid oxidation, and oxygen reduction compared to Pt black; however, the extent of improvement differed considerably for the various shapes. Most notably, when specific activity was compared, platinum overgrown on octahedral gold crystals showed enhanced activity per unit area for formic acid oxidation and oxygen reduction. The shape of the underlying core nanocrystals significantly affects the electrocatalytic properties of surface platinum overgrown on the gold core. (C) 2010 Elsevier B.V. All rights reserved.