Enhanced oxidation of nanoscale In particles at the interface with a Si nanowire

Proc. Natl. Acad. Sci. U.S.A.

Tong

Jungjohann

et al. 2013

The oxidation of bimetallic alloy nanoparticles comprising a noble and a nonnoble metal is expected to cause the formation of a single-component surface oxide of the nonnoble metal, surrounding a core enriched with the noble metal. Studying the room temperature oxidation of Au-In nanoparticles, we show that this simple picture does not apply to an important class of bimetallic alloys, in which the oxidation proceeds via predominant oxygen diffusion. Instead of a crystalline In 2 O 3 shell, such oxidation leads to an amorphous shell of mixed Au-In oxide that remains stable to high temperatures and whose surface layer is enriched with Au. The Au-rich mixed oxide is capable of adsorbing both CO and O 2 and converting them to CO 2 , which desorbs near room temperature. The oxidation of Au-In alloys to a mixed Au-In oxide shows significant promise as a viable approach toward Au-based oxidation catalysts, which do not require any complex synthesis processes and resist deactivation up to at least 300°C.transmission electron microscopy | temperature programmed desorption | X-ray photoelectron spectroscopy T he importance of metal nanoparticles for a wide variety of applications, e.g., in catalysis, sensing, etc., has sparked interest in understanding and controlling their oxidation. The formation of an oxide layer negatively affects performance in applications that require pure metal surfaces. However, oxidation can be advantageous as it opens a way for engineering complex structures. Our understanding of room temperature oxidation has been established primarily in studies on the oxidation of bulk materials or planar films (1). Most of this insight should apply directly to the oxidation of nanoparticles, but important aspects arise in the geometry of small particles. For example, the high curvature in a nanoparticle can drive oxidation to larger thicknesses than in the planar case (2-4). Nanoscale junctions and interfaces to other materials can promote enhanced oxidation, as well as the formation of well-ordered epitaxial oxide segments (5). The oxidation of nanoparticles is also a powerful mechanism to produce nanoscale heterostructures. Metals that oxidize via predominant anion diffusion [In (2, 5), Pb (6), Sn, among others] form metal-oxide core-shell nanoparticles. For metals that oxidize via fast cation diffusion [Co (7), Al (6), Fe (8), Ni (9), among others], nanoscale porosity buildup creates hollow oxide nanocrystals that can be used as cages, e.g., to be filled with different materials (7) for storage or protection.Bimetallic (alloy, core-shell, etc.) nanoparticles promise widely tunable properties, and much progress has recently been made in their controlled synthesis (10). The oxidation of bimetallic nanoparticles has been studied much less than that of elemental metals, but it could provide even more interesting opportunities for the fabrication of functional nanomaterials, for example in catalysis.Alloys that comprise a noble and a less noble metal component are of interest because their oxidation can give ...

Section: Resultsmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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Oxidation of nanoscale Au–In alloy particles as a possible route toward stable Au-based catalysts

Proc. Natl. Acad. Sci. U.S.A.

Tong

Jungjohann

et al. 2013

“…In the other limiting case, predominant anion (e.g., O − ) migration and reaction at the oxide–metal interface, the oxidation process produces metal‐oxide core–shell nanostructures. [1b], For such systems, nanoscale size effects have recently been established in the oxidation process of pure metal (e.g., In) nanoparticles, and interesting functional properties have been identified for binary alloys containing such metals (e.g., Au‐In), demonstrating for example that they give rise to a new class of stable, Au‐based catalysts for low‐temperature oxidation reactions …”

Section: Introductionmentioning

confidence: 99%

Size‐Dependent Room Temperature Oxidation of Tin Particles

Ivars‐Barceló

Part & Part Syst Charact

2014

879wileyonlinelibrary.com www.particle-journal.com www.MaterialsViews.com Using transmission electron microscopy, the size-dependent room temperature oxidation of tin nanoparticles is studied. The oxide that forms during room temperature oxidation of Sn particles is amorphous SnO, and it retains this stoichiometry and structure over extended time periods. From the investigation of arrays of Sn nanoparticles with broad size distribution, under identical conditions, the Sn oxide thickness is evaluated as a function of size and oxidation time. The oxide thickness depends strongly on the size of the Sn nanoparticles, which is in excellent agreement with predictions for a Mott-Cabrera model corrected for a non-uniform electric fi eld. The results demonstrate the accelerated oxidation kinetics of nanoscale particles with high curvature, due to the amplifi ed electric fi eld at the interface to a continuously shrinking metal core.Here, we consider the room temperature oxidation of Sn nanoparticles, focusing in particular on possible nanoparticle size effects on the oxidation rate, as well as the structure and stoichiometry of the resulting oxide. Sn nanoparticles, invariably terminated by either SnO 2 or SnO following their exposure to air, are of interest for a wide range of applications, for example gas sensors, [ 4 ] optoelectronic devices and solar cells, [ 5 ] and Li-ion battery anodes. [ 6 ] Gas sensors often show an unwanted long-term drift in their sensing characteristics while operating in air near room temperature, generally attributed to oxygen diffusion into the oxide. [ 7 ] SnO 2 or Sn-SnO 2 core-shell nanostructures, produced by complete or partial oxidation of fi lms of Sn clusters, [ 8 ] Sn particles, [ 4a,b , 9 ] and nanowires, [ 7,10 ] provide high sensitivity [ 9,11 ] and fast response in gas sensing applications, [ 12 ] but are usually characterized by a large spread in sizes. [ 4a,b , 13 ] Hence, a size-dependent oxidation rate will give rise to non-uniform oxide thickness, which will impact the sensing characteristics. The thickness of a native Sn-oxide shell also critically affects the application of Sn nanoparticles as a Li-ion battery anode material, where the surface oxide causes a decrease in the reversible Li-ion capacity due to an irreversible fi rst-discharge reaction to Li 2 O. Naturally, possible size effects on the oxidation rate would be expected to be important in polydisperse Sn nanoparticle ensembles. [ 9,14 ] However, even precise colloidal synthesis protocols developed recently, capable of generating monodisperse Sn (or Sn-Sn oxide) nanocrystals with size spread below 10%, [ 6 ] may not be suffi cient to eliminate nonuniform oxides. Indeed, clear differences observed in the native oxide thickness for colloidal Sn particles at the low and high ends of a 10% size distribution [ 6 ] suggest the existence of very strongly size-dependent effects in the oxidation of Sn, which are important to applications in energy storage and others.Despite several decades of fundamental research ...

“…Sn, similar to In 40,41 and Pb, 42 oxidizes at room temperature by preferential oxygen anion migration through the oxide. 43 The diffusion of metal cations is kinetically limited.…”

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Alloy oxidation as a route to chemically active nanocomposites of gold atoms in a reducible oxide matrix

et al. 2016

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