A multimetallic nanoscale catalyst having a core portion enveloped by a shell portion and exhibiting high catalytic activity and improved catalytic durability. In various embodiments, the core/shell nanoparticles comprise a gold particle coated with a catalytically active platinum bimetallic material. The shape of the nanoparticles is substantially defined by the particle shape of the core portion. The nanoparticles may be dispersed on a high surface area substrate for use as a catalyst and is characterized by no significant loss in surface area and specific activity following extended potential cycling.