Nucleation and growth mechanisms for Pd-Pt bimetallic nanodendrites and their electrocatalytic properties

Abstract

In a seed-mediated synthesis, nanocrystal growth is often described by assuming the absence of homogeneous nucleation in the solution. Here we provide new insights into the nucleation and growth mechanisms underlying the formation of bimetallic nanodendrites that are characterized by a dense array of Pt branches anchored to a Pd nanocrystal core. These nanostructures can be easily prepared by a one-step, seeded growth method that involves the reduction of K 2 PtCl 4 by L-ascorbic acid in the presence of 9-nm truncated octahedral Pd seeds in an aqueous solution. Transmission electron microscopy (TEM) and high-resolution TEM analyses revealed that both homogeneous and heterogeneous nucleation of Pt occurred at the very early stages of the synthesis and the Pt branches grew through oriented attachment of small Pt particles that had been formed via homogeneous nucleation. These new findings contradict the generally accepted mechanism for seeded growth that only involves heterogeneous nucleation and simple growth via atomic addition. We have also investigated the electrocatalytic properties of the Pd-Pt nanodendrites for the oxygen reduction and formic acid oxidation reactions by conducting a comparative study with foam-like Pt nanostructures prepared in the absence of Pd seeds under otherwise identical conditions.

Nanocrystalline intermetallics and alloys

“…However, design of facile and general strategies for the synthesis of other intermetallics and alloys with high surface areas still remains a great challenge. Undoubtedly, the emergence and development of nanoscience and nanotechnology offer new opportunities in this area [14][15][16][17][18].…”

“…However, design of facile and general strategies for the synthesis of other intermetallics and alloys with high surface areas still remains a great challenge. Undoubtedly, the emergence and development of nanoscience and nanotechnology offer new opportunities in this area [14][15][16][17][18].Recently, we developed a general strategy for the synthesis of various nanocrystals, whereby noble metal ions can be reduced to monodisperse noble metal nanocrystals by a mixture of ethanol and linoleic acid [19]. However, attempts to synthesize intermetallics and alloys of noble and non-noble metals (e.g., FePt, NiPt, and CoPd) with this strategy were unsuccessful, mainly due to the low reducing power of ethanol and linoleic acid.…”

Synthesis and characterization of silver/montmorillonite/chitosan bionanocomposites by chemical reduction method and their antibacterial activity

“…29 Nowadays, a succession of chemical reductants can been used for the synthesis of noble metal nanoparticles which contain NaBH 4 35 formaldehyde, 36 formamide, 37 Tollens' reagents, 38 ethylene glycol, 39 ethanol, 40 citrate, 32,40 aniline, 41 polyaniline, 42 or ascorbic acid. 43 Layered silicates, eg, montmorillonite (MMT), have been used in polymer nanocomposites with a significant improvement in mechanical properties. 44,45 MMT possesses a 2-to-1 layered structure with a single octahedral aluminum layer located between two layers of tetrahedral silicon.…”

Bimetallic Catalysts Containing Gold and Palladium for Environmentally Important Reactions

“…The factors that determine the nature of growth are as follows: lattice-matching structure, lattice-mismatching structure, surface and interface energy correlations, and the difference between the electronegativities of the two metals. For instance, improved catalytic activity in the proton exchange membrane can be achieved by using Pt-based hetero-nanocatalysts in the fuel cell [38]. Xia et al claimed that the hetero-structure of Pd-Pt is almost more active by factor of 2.5 compared to an equivalent mass of Pt created by using heterogeneous seeded growth [39].…”