Structure and Oxidation Behavior of Nickel Nanoparticles Supported by YSZ(111)

Abstract

Nickel nanoparticles supported by the yttria-stabilized zirconia (111) surface show several preferential epitaxial relationships, as revealed by in situ X-ray diffraction. The two main nanoparticle orientations are found to have their [111] direction parallel to the substrate surface normal and ∼41.3 degrees tilted from this direction. The former orientation is described by a cube-on-cube stacking at the oxide–metal interface and the latter by a so-called coherent tilt strain-relieving mechanism, which is hitherto unreported for nanoparticles in literature. A modified Wulff construction used for the 111-oriented particles results in a value of the adhesion energy ranging from 1.4 to 2.2 Jm2, whereby the lower end corresponds to more rounded particles and the upper to relatively flat geometries. Upon oxidation at 10–3 Pa of molecular oxygen and 673 K, a NiO shell forms epitaxially on the [111]-oriented particles. Only a monolayer of metallic nickel of the top (111) facets oxidizes, whereas the side facets seem to react more severely. An apparent size increase of the remaining metallic Ni core is discussed in relation to a size-dependent oxidation mechanism, whereby smaller nanoparticles react at a faster rate. We argue that such a preferential oxidation mechanism, which inactivates the smallest and most reactive metal nanoparticles, might play a role for the long-term degradation of solid oxide fuel cells.

Origin of the synergistic effect between TiO2 crystalline phases in the Ni/TiO2-catalyzed CO2 methanation reaction

“…The lower amount of Ni 0 on 10Ni/TiO2-P25 is in accordance with the TPR results, and should be due to the smaller particle size measured for this catalyst. Indeed, small Ni 0 particles interact strongly with the support, and react with oxygen at a faster rate than with large particles [49]. Regarding the difference between 10Ni/TiO2-anatase (36 % Ni 0 ) and 10Ni/TiO2-rutile (25.5 % Ni 0 ), it might be related to the different Ni/Ti surface atomic ratios in these samples.…”

Approaches to modelling the shape of nanocrystals

“…Indeed, a significant number of recent papers incorrectly described kinetically controlled nanocrystal shapes as thermodynamic ones [ 65 – 67 ] with others explicitly stating that Wulff constructions can only be used to determine thermodynamic equilibrium [ 68 , 69 ]. The propagation of the incorrect idea of “one Wulff construction” has not exclusively led to confusion regarding kinetics vs thermodynamics: the Winterbottom construction has been referred to as “the Wulff construction” [ 70 ] or “modified Wulff construction” [ 71 ], and the kinetic Wulff construction has been called a “modified Wulff construction” [ 72 ]. These names are often not strictly incorrect, but the use of a more precise terminology would clarify which mathematical construct is used and help readers apply them in their own systems.…”

Contrasting H-Etching to OH-Etching in Plasma-Assisted Nucleation of Carbon Nanotubes

“…In the OH case, active water formation leads to a large fraction of dissolved oxygen atoms, which oxidize and structurally modify the Ni 55 nanocluster. This phenomenon can be connected to the experimental finding that Ni nanoparticles smaller than 5.5 nm burn up completely during the oxygen treatment, even at low temperatures (<600 K). The number of dissolved O atoms keeps rising until saturation.…”