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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.
Highlights
Supported nanoparticles are used on a tremendously large scale for catalytic reactions
Solid oxide fuel cells (SOFCs) are devices used for energy conversion and are considered as an important future green technology
We find that Ni nanoparticles grow with two very distinct orientations on yttria-stabilized zirconia (YSZ)(111), in contrast to MgO(100)
Summary
Supported nanoparticles are used on a tremendously large scale for catalytic reactions. Nickel films grown on MgO(100) have been found to show several preferential orientations, forming a complex epitaxial system and of which the core is stable toward high temperature oxidation.7 This raises the question how smaller particles in the size regime from 3−10 nm, as typically encountered on the anodes of SOFCs behave when in contact with a solid electrolyte. At the do not indicate any considerable changes after Ni evaporation and after the oxygen treatment Because these CTRs probe the 3D atomic structure of the YSZ(111) surface, which is partly covered by the NPs, we conclude that each of these processing steps does not result in any significant atomic relaxations of the substrate
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