Abstract
PtPd nanoparticles are among the most widely studied nanoscale systems, mainly because of their applications as catalysts in chemical reactions. In this work, a combined experimental-theoretical study is presented about the dependence of growth shape of PtPd alloy nanocrystals on their composition. The particles are grown in the gas phase and characterized by STEM-HRTEM. PtPd nanoalloys present a bimodal size distribution. The size of the larger population can be tuned between 3.8 ± 0.4 and 14.1 ± 2.0 nm by controlling the deposition parameters. A strong dependence of the particle shape on the composition is found: Pd-rich nanocrystals present more rounded shapes whereas Pt-rich ones exhibit sharp tips. Molecular dynamics simulations and excess energy calculations show that the growth structures are out of equilibrium. The growth simulations are able to follow the growth shape evolution and growth pathways at the atomic level, reproducing the structures in good agreement with the experimental results. Finally the optical absorption properties are calculated for PtPd nanoalloys of the same shapes and sizes grown in our experiments.
Highlights
Binary metallic clusters and nanoparticles (BNPs, known as nanoalloys) [1,2,3,4,5] have received increasing attention in recent years due to their applications in various fields, among which catalysis is traditionally the most important
In Ref. [8], we focused on the analysis of their chemical ordering, showing that the gas-phase growth leads to the formation of structures with a peculiar type of non-equilibrium patterns, in which the core of the nanoparticle contains both metals, while the shell is strongly enriched in the majority element (PtPd@Pt and PtPd@Pd chemical ordering, for Pt-rich and Pd-rich nanoalloys, respectively)
Similar features were observed in PtPd systems grown by a chemical synthesis approach [34]
Summary
Binary metallic clusters and nanoparticles (BNPs, known as nanoalloys) [1,2,3,4,5] have received increasing attention in recent years due to their applications in various fields, among which catalysis is traditionally the most important. This further degree of freedom increases the complexity of the energy landscapes compared to elemental nanoparticles so that the control of nanoalloy shapes in their formation process may be more challenging. For this reason, detailed studies of the formation processes of nanoalloys are extremely important. The study of growth processes in very clean environments, such as the gas phase [7], is essential to unravel the dominant pathways leading to the growth of nanoparticles of different shapes. These studies often take advantage of combined experiment-simulation efforts [8,9,10,11,12,13,14,15,16,17,18,19,20]
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