Chemical Ordering and Surface Segregation in Cu–Pt Nanoalloys: The Synergetic Roles in the Formation of Multishell Structures

Abstract

We performed Monte Carlo simulations coupled with MAEAM potentials to study the surface segregation and chemical ordering patterns in Cu−Pt nanoalloy particles for a broad range of sizes, shapes, composition, and temperature. It was found that both the Cu segregation on the surface and the chemical ordering in the core are the general rules and usually compete with each other. Surface segregation of Cu is enhanced with increasing particle size or surface openness or global Cu composition. Despite their different morphologies, most of the types of ordered phases in the core region are the same as bulk alloys. Due to the modification or suppression effects of surface segregation, the degrees of chemical ordering shift to the Ptricher side and are more apparent in a large-sized particle. Particularly, at a narrow composition range, the multishell structures (onion-ring or multishell/maze-like core) form in (truncated) octahedrons, illustrating a subtle synergy between the segregated Cu {111} facets and the L1 1 ordering. The possibility and advantage of transformation from these multishell structures to Pt multilayer shell/single Cu-rich core ORR catalysts by selective etching of Cu were also discussed.

Thermodynamics of CuPt nanoalloys

“…5 right panel, we identify an onion-shell elemental distribution, both according to itMD and NS calculations: the outermost shell contains two thirds of the total copper population; the subsurface is Pt-rich (hitting the ); the third and fourth layers have a 60% of Cu and 40% Pt, respectively. This onion-shell chemical ordering is preserved above the melting point and high temperature NS configurations show that it is the most favourable up to 2500 K, supporting the idea that it should be considered as the equilibrium chemical arrangement, in agreement with previous in-silico 32 , 63 and in-vitro 48 studies. It is interesting to note that in correspondence of the melting transition the radial distribution function identifies an atom at the center of the cluster, while earlier the center of mass of the system felt in between atoms.…”

Atomically Resolved Anisotropic Electrochemical Shaping of Nano-electrocatalyst

“…64 This effect may explain the striving of Pt atoms to segregate to {100} and {111} facets. On the other hand, in high Cu content, Cu atoms will most favorably occupy sites with lower coordination number: 60 the vertex, next the edge, and later the {100} and {111} facet sites, conversely to Pt.…”

Nanometal Thermocatalysts: Transformations, Deactivation, and Mitigation

“…c) Reproduced with permission. [ 8 ] Copyright 2015, American Chemical Society. d) Reproduced with permission.…”

“…Nanometals, namely metallic nanoparticles, [ 1–3 ] have become a rising star in the large family of thermal catalysts. [ 4–6 ] Compared with the traditional bulky metallic catalysts, the nanometal has a much smaller particle size and thus a much larger specific surface area, [ 7–9 ] which generates a great amount of active sites and better catalytic activities. [ 10–12 ] Also, the nanoscale particle size induces a transition of the composing atoms from metallic bonding toward individual atoms, [ 3,13,14 ] thereby increasing the concentration of dangling surface bonds and enhancing the intrinsic catalytic activities of nanometals.…”