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 PtCl (6) (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.