This paper describes a new approach to the synthesis of PtAg alloy nanostructures rich in Pt at the surface through a selective electrochemical dissolution of Ag from PtAg alloy nanoparticles that are made from platinum acetylacetonate, Pt(acac)(2), and silver stearate, Ag(St). The surface and bulk compositions, size, and architecture of these heterogeneous nanostructures are controlled synergistically by changing the upper limits of cycling potentials in perchloric acid (HClO4) aqueous solution to dissolve Ag deterministically. The structures and elemental distributions of Ag and Pt in the resulting heterogeneous nanoparticles are characterized by high-resolution transmission electron microscopy (HR-TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray (EDX). These Pt-surface rich PtAg nanostructures exhibit much higher activity than Pt nanoparticles as electrocatalysts in formic acid oxidation reaction (FAOR).