Vonk V, Khorshidi N, Stierle A
Deutsches Elektronen-Synchrotron (DESY) , 22607 Hamburg, Germany.
Max Planck Institute for Intelligent Systems, 70569 Stuttgart, Germany; Former Max Planck Institute for Metals Research, 70569 Stuttgart, Germany; Physics Department, University of Hamburg, 20355 Hamburg, Germany.
J Phys Chem C Nanomater Interfaces. 2017 Feb 9;121(5):2798-2806. doi: 10.1021/acs.jpcc.6b11342. Epub 2017 Jan 18.
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 Jm, whereby the lower end corresponds to more rounded particles and the upper to relatively flat geometries. Upon oxidation at 10 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.
原位X射线衍射显示，氧化钇稳定的氧化锆（111）表面负载的镍纳米颗粒呈现出几种优先外延关系。发现两种主要的纳米颗粒取向，其[111]方向与衬底表面法线平行，且与该方向倾斜约41.3度。前一种取向在氧化物-金属界面处由立方对立方堆叠描述，后一种由所谓的相干倾斜应变缓解机制描述，这在文献中尚未见报道。用于111取向颗粒的改进型伍尔夫构造得出的粘附能值在1.4至2.2 J/m之间，其中较低值对应于更圆的颗粒，较高值对应于相对扁平的几何形状。在10 Pa分子氧和673 K下氧化时，NiO壳层在[111]取向的颗粒上外延形成。仅顶部（111）面的单层金属镍发生氧化，而侧面似乎反应更剧烈。结合尺寸依赖性氧化机制讨论了剩余金属镍核明显的尺寸增加，其中较小的纳米颗粒反应速率更快。我们认为，这种优先氧化机制使最小且最具反应性的金属纳米颗粒失活，可能在固体氧化物燃料电池的长期降解中起作用。
