Synthesis of Pd−Pt Bimetallic Nanocrystals with a Concave Structure through a Bromide-Induced Galvanic Replacement Reaction

Abstract

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.

Shape control of bimetallic nanocatalysts through well-designed colloidal chemistry approaches

“…The shape control of bimetallic NCs can be further modulated by several variables of the two constituting metals, including the reduction potential, relative decomposition/reduction rate of precursors and interfacial energy. Through different synthesis routes, researchers have prepared bimetallic core-shell, heterostructure and alloy NCs with various morphologies such as polyhedrons (single-crystalline [7][8][9][10][11] and multi-twinned 12 ), nanorods 13 and nanowires, 14,15 nanodendrites, 16,17 multi-pods, 18,19 hollow structure, 20,21 concave structure, 22,23 etc. These synthetic routes can be categorized into four types: (1) continuous growth, (2) crystallites coalescence, (3) seeded growth, and (4) galvanic replacement reaction, as illustrated in Fig.…”

“…In this route, facet-specific capping agents can be used to direct the formation of many complex bimetallic nanostructures such as concave cubes and multipod structures. 18 …”

“…In a recent work of Xia and co-workers, the galvanic replacement reaction between Pd nanocubes and PtCl 6 2À was used to prepare Pt-Pd heterostructure NCs in the presence of Br À ions. 18 Since Br À ions facilitated the dissolution of surface atoms on {100} facets, and the eight corners of nanocubes were more accessible for Pt II monomers, the oxidation half-reaction preferentially occurred on six {100} facets and the reduction half-reaction preferentially occurred at eight corners. As a result, the {100} facets of Pd nanocubes shrunk gradually and Pt atoms deposited on eight corners.…”

Facet‐Controlled Synthetic Strategy of Cu2O‐Based Crystals for Catalysis and Sensing

“…To date, CAs have played an important role on shape‐controlled synthesis of NCs,137, 138, 139, 140, 141, 142 and there are many successful examples in preparing Cu 2 O NCs 7, 8, 75, 107, 122, 125, 143. We will introduce some classic synthetic routes of Cu 2 O NCs enclosed by low‐index facets.…”

Engineering the architectural diversity of heterogeneous metallic nanocrystals

“…2iii). The electrons released from the galvanic replacement reaction then accumulate preferentially on certain NC sites [25][26][27][28][29] . In this way, a spatially heterogeneous electron distribution is created, which can be used to direct the deposition of satellite NCs on electron-rich sites.…”