Predicted Trends of Core−Shell Preferences for 132 Late Transition-Metal Binary-Alloy Nanoparticles

Abstract

Transition-metal alloyed nanoparticles with core-shell features (shell enrichment by one of the metals) are becoming ubiquitous, from (electro-)catalysis to biomedical applications, due to their size control, performance, biocompatibility, and cost. We investigate 132 binary-alloyed nanoparticle systems (groups 8 to 11 in the Periodic Table) using density functional theory (DFT) and systematically explore their segregation energies to determine core-shell preferences. We find that core-shell preferences are generally described by two independent factors: (1) cohesive energy (related to vapor pressure) and (2) atomic size (quantified by the Wigner-Seitz radius), and the interplay between them. These independent factors are shown to provide general trends for the surface segregation preference for atoms in nanoparticles, as well as semi-infinite surfaces, and give a simple correlation (a "design map") for the alloying and catalytic behavior. Finally, we provide a universal description of core-shell preference via tight-binding theory (band-energy differences) that (i) quantitatively reproduces the DFT segregation energies and (ii) confirms the electronic origins and correlations for core-shell behavior.

Enhanced methanol oxidation and oxygen reduction reactions on palladium-decorated FeCo@Fe/C core–shell nanocatalysts in alkaline medium

“…For ''core'' and ''shell'' preferences, note that transition metal with larger cohesive energy and a smaller WS radius prefers the core region, while the metal with smaller cohesive energy and larger atomic size prefers the shell position. 27,28 Because of its larger cohesive energy (4.5 eV) and a smaller atomic size (1.40 Å) than Fe (4.3 eV and 1.47 Å), Co will prefer the core region while Fe migrates to the surface forming a Fe-rich shell. To make the FeCo@Fe@Pd/C nanoparticles, the as-prepared carbon supported FeCo@Fe (1 mmol) was thoroughly mixed with PdCl 2 (3 mmol) in ethylene glycol solution containing polyvinylpyrolidone and subjected to rapid microwave irradiation (using the Anton Parr Synthos 3000 microwave reactor) at 500 W, 80 bars, and B198 1C for 15 min.…”

Nanocrystalline intermetallics and alloys

“…This is an intriguing phenomenon. Recently, some groups have reported theoretical calculations on bi-metallic materials [23,24]. For example, it was shown that the surface atoms of the gold particles formed in an initial reduction step carry slightly negative charges, which facilitates the subsequent adsorption of Ag + cations on the gold particle surface [23,25].…”

Investigação <i>ab initio</i> dos mecanismos de formação de nanoligas <i>core-shell</i> com platina e metais de transição dos períodos 3<i>d</i>, 4<i>d</i> e 5<i>d</i>

“…A configuração ICO core-shell para Pt 13 Cu 42 com Pt na região de caroço, por sua vez, possui energia relativa de apenas 5,98 eV e não configura o arranjo menos estável entre os investigados, podendo, ainda, serem observadas nanoligas com Pt segregada na superfície como os arranjos menos estáveis. Essa diferença de energia das estruturas core-shell de nanoligas com MT do período 3d pode ser entendida sob o ponto de vista de Wang et al, 94 que estudaram a energia de segregação de átomos de Pt sobre nanoclusters de 55 átomos. Esses autores observaram que as estruturas ICO de Fe 55 , Co 55 e Ni 55 possuem valores negativos (i.e., de −2,71 eV, −0,95 eV, −0,61 eV, respectivamente) e a estrutura ICO de Cu 55 possui valor positivo (i.e., de 0,41 eV) de energia de segregação quando um átomo da superfície é substituído por Pt na superfície.…”