Pt_xCu_y nanocrystals with hexa-pod morphology and their electrocatalytic performances towards oxygen reduction reaction

Bimetallic Pt_xCu_y nanocrystals (NCs) with well-defined hexa-pod morphology were synthesized via a wet chemistry approach. The as-synthesized convex NCs with dimensions of around 20 nm show exposed low-index (111) facets on the seeds and various high-index facets on the pods. The growth mechanism involved preferred growth along the < 100 > crystallographic direction on cuboctahedral seeds. The synthetic protocol could be applied to the synthesis of Pt_xCu_y NCs with various Cu/Pt ratios. The electro-catalytic activity of the hexa-pod PtxCuy NCs supported on carbon black towards the oxygen reduction reaction (ORR) was studied. The hexa-pod PtCu₂/C catalysts exhibit the highest specific activity (3.7 mA/cm_Pt²) and mass activity (2.4 A/mg_Pt) reported to date for Pt_xCu_y. Comparison with other morphological forms of Pt_xCu_y indicated that the enhanced activity originated from morphological factors. The existence of high-index facets as well as abundant edges and steps on the pods could reasonably explain the enhanced catalytic activity. The hexa-pod Pt_xCu_y/C catalysts also show high morphological stability and activity after accelerated durability tests. The as-synthesized hexa-pod Pt_xCu_y NCs have high potential as cathode electro-catalysts for proton exchange membrane fuel cells.