Generalized nano-thermodynamic model for capturing size-dependent surface segregation in multi-metal alloy nanoparticles

Divi, Srikanth; Chatterjee, Abhijit

doi:10.1039/c8ra00945g

Cited by 28 publications

(20 citation statements)

References 42 publications

(58 reference statements)

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“…[32][33][34][35][36][37] In these systems, Group 11 metals segregate to the surface after annealing, while Group 10 metals migrate to the subsurface, forming core@shell nanostructures. 22 The thermodynamics of such segregation phenomenon has been studied extensively in the computational literature as a function of size mismatch, miscibility, composition, cluster size, cluster shape, and temperature, especially for Pd-doped Group 11 systems: Pd@Cu; 19,31,[38][39][40][41][42][43][44] Pd@Ag; Pd@Au. 45,62,68,[70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85] Thermodynamically, surface segregation can be understood within the framework of the quasi-chemical approximation, 86 where surface and subsurface species are modeled to be in a state of chemical equilibrium.…”

Section: Introductionmentioning

confidence: 99%

Automated Detection and Characterization of Surface Restructuring Events in Bimetallic Catalysts

et al. 2019

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Surface restructuring in bimetallic systems has recently been shown to play a crucial role in heterogeneous catalysis. In particular, the segregation in binary alloys can be reversed in the presence of strongly bound adsorbates. Mechanistic characterization of such restructuring phenomena at the atomic level remains scarce and challenging due to the large configurational space that must be explored. To this end, we propose an 1 2 automated method to discover elementary surface restructuring processes in an unbiased fashion, using Pd/Ag as an example. We employ high-temperature classical molecular dynamics (MD) to rapidly detect restructuring events, isolate them, and optimize using density functional theory (DFT). In addition to confirming the known exchange descent mechanism, our systematic approach has revealed three new predominant classes of events at step edges of close-packed surfaces that have not been considered before: (1) vacancy insertion; (2) direct exchange; (3) interlayer exchange. The discovered events enable us to construct the complete set of mechanistic pathways by which Pd is incorporated into the Ag host in vacuum at the single-atom limit. These atomistic insights provide a step toward systematic understanding and engineering of surface segregation dynamics in bimetallic catalysts.

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Section: Introductionmentioning

confidence: 99%

Automated Detection and Characterization of Surface Restructuring Events in Bimetallic Catalysts

et al. 2019

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“…Although interfaces between metal nanoparticles and the metal oxide support have been extensively investigated, less is known about interfaces that form on alloys themselves, independent of the support. Phase segregation on metallic alloy nanoparticles can form metal/metal interfaces primarily arising from differences in surface free energy of the metal components and unfavorable mixing enthalpies [7][8][9] . Under oxidizing conditions, complex metal/oxide and oxide/oxide interfaces can form by phase separation and surface segregation arising from differences in metal-oxygen bonding 10,11 .…”

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confidence: 99%

Hydrogen migration at restructuring palladium–silver oxide boundaries dramatically enhances reduction rate of silver oxide

et al. 2020

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Heterogeneous catalysts are complex materials with multiple interfaces. A critical proposition in exploiting bifunctionality in alloy catalysts is to achieve surface migration across interfaces separating functionally dissimilar regions. Herein, we demonstrate the enhancement of more than 10 4 in the rate of molecular hydrogen reduction of a silver surface oxide in the presence of palladium oxide compared to pure silver oxide resulting from the transfer of atomic hydrogen from palladium oxide islands onto the surrounding surface formed from oxidation of a palladium-silver alloy. The palladium-silver interface also dynamically restructures during reduction, resulting in silver-palladium intermixing. This study clearly demonstrates the migration of reaction intermediates and catalyst material across surface interfacial boundaries in alloys with a significant effect on surface reactivity, having broad implications for the catalytic function of bimetallic materials.

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“…50,51 Systems such as Cu−Ag, Au−Ni, and Au−Pt have positive heats of mixing that favor phasesegregation whereas systems such as Pt−Pd, Ag−Au, and Ni− Pd have negative heats of mixing that enable alloying. 18 Galvanic replacement could also be used in tandem with other postsynthetic steps when synthesizing more complex geometries or multicomponent nanostructures. The insights presented in this work could be used to achieve a higher level of synthetic control in a wide selection of binary NCs for applications in energy storage, catalysis, nanomedicine, and photonics.…”

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confidence: 99%

Self-Limiting Shell Formation in Cu@Ag Core–Shell Nanocrystals during Galvanic Replacement

Kamat

Yan

Osowiecki

et al. 2020

J. Phys. Chem. Lett.

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The understanding of synthetic pathways of bimetallic nanocrystals remains limited due to the complex energy landscapes and dynamics involved. In this work, we investigate the formation of self-limiting Cu@Ag core–shell nanoparticles starting from Cu nanocrystals followed by galvanic replacement with Ag ions. Bulk quantification with atomic emission spectroscopy and spatially resolved elemental mapping with electron microscopy reveal distinct nucleation regimes that produce nanoparticles with a tunable Ag shell thickness, but only up to a certain limiting thickness. We develop a quantitative transport model that explains this observed self-limiting structure as arising from the balance between entropy-driven interdiffusion and a positive mixing enthalpy. The proposed model depends only on the intrinsic physical properties of the system such as diffusivity and mixing energy and directly yields a high level of agreement with the elemental mapping profiles without requiring additional fit parameters.

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Generalized nano-thermodynamic model for capturing size-dependent surface segregation in multi-metal alloy nanoparticles

Abstract: Nano-thermodynamic model captures thermodynamic preference of metal species for different regions of a nanoparticle while accounting for size effects.

Cited by 28 publications

References 42 publications

Automated Detection and Characterization of Surface Restructuring Events in Bimetallic Catalysts

Automated Detection and Characterization of Surface Restructuring Events in Bimetallic Catalysts

Hydrogen migration at restructuring palladium–silver oxide boundaries dramatically enhances reduction rate of silver oxide

Self-Limiting Shell Formation in Cu@Ag Core–Shell Nanocrystals during Galvanic Replacement

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