Synthesis of Pd-Pt bimetallic nanocrystals with a concave structure through a bromide-induced galvanic replacement reaction

This article describes a systematic study of the galvanic replacement reaction between PtCl₆^2- ions and Pd nanocrystals with different shapes, including cubes, cuboctahedrons, and octahedrons. It was found that Br^- ions played an important role in initiating, facilitating, and directing the replacement reaction. The presence of Br^- ions led to the selective initiation of galvanic replacement from the {100} facets of Pd nanocrystals, likely due to the preferential adsorption of Br^- ions on this crystallographic plane. The site-selective galvanic replacement resulted in the formation of Pd-Pt bimetallic nanocrystals with a concave structure owing to simultaneous dissolution of Pd atoms from the {100} facets and deposition of the resultant Pt atoms on the {111} facets. The Pd-Pt concave nanocubes with different weight percentages of Pt at 3.4, 10.4, 19.9, and 34.4 were also evaluated as electrocatalysts for the oxygen reduction reaction (ORR). Significantly, the sample with a 3.4 wt.% of Pt exhibited the largest specific electrochemical surface area and was found to be four times as active as the commercial Pt/C catalyst for the ORR in terms of equivalent Pt mass.