Vertex-Directed and Asymmetric Metal Overgrowth of Intermetallic Pd3Pb@PtNi Nanocubes for the Oxygen Reduction Reaction

Strain engineering of core@shell nano-architectures is one of the most effective methods to control properties of functional nanomaterials. Core@shell nanoparticles with a well-defined shape and architecture are desired for optical, magnetic, and electrochemical applications. However,such structural control remains a synthetic challenge, especially in systems where the depositing shell is put in tension and has large lattice mismatch with the underlying materials. Here, we report the deposition of PtNi shells on intermetallic Pd3Pb nanocubes as seeds. This system has a large lattice mismatch (similar to 7.7%) and was selected as, in the ideal case, shells would be placed in tension, in contrast to more-well studied systems where shells are often compressively strained. Vertex-directed and asymmetric overgrowths were observed from the intermetallic nanocubic seeds.The specific mode of overgrowth was impacted by the amount of capping agent and reaction temperature, with lower reaction temperatures and concentrations of the capping agent facilitating vertex-directed overgrowth as evidenced from transmission electron microscopy analysis of products. Comparison of the various core@shell nanoparticles to Pt/C and PtNi/C standards for the oxygen reduction reaction found that the intermetallic Pd3Pb@PtNi nanocatalysts with asymmetric-directed overgrowth achieved the highest specific activity for the oxygen reduction reaction, while intermetallic Pd3Pb@Pt nanocatalysts prepared for comparison achieved the highest mass activity. These results highlight the importance of fine architectural control for core@shell nanoparticles,which can be achieved through judicious selection of synthetic conditions during seed-mediated overgrowth.