Atomic resolution imaging of polyhedral PtPd core-shell nanoparticles by Cs-corrected STEM.

Bimetallic nanoparticles present different properties than their monometallic counterparts, opening a wide range of possibilities for different applications. PtPd nanoparticles have raised interest for their many applications in fuel cells, ethanol and methanol oxidation reactions, hydrogen storage, etc. However, the cost of Pt makes it unpractical to use in big quantities; therefore, one of the big challenges is to synthesize very small catalysts in order to maximize the efficiency in their use. In this work, we synthesized polyhedral PtPd core-shell nanoparticles under 20 nm and characterized them by Cs-corrected scanning transmission electron microscopy. This technique allowed us to probe the structure at the atomic level of these nanoparticles revealing new structural information. We determined the structure of the three main polyhedral morphologies obtained in the synthesis: octahedral, decahedral and triangular plates. Decahedral PtPd core-shell nanoparticles are novel morphologies for this system. Morphology and defects present in the nanoparticles are shown and discussed.