Effect of Interfacial Structure on Gold-assisted Growth of Oxides

Abstract

, have profound significance for many energy-related reactions such as low-temperature CO oxidation and selective oxidation of alcohols. [1][2] In spite of their technological and scientific importance, the underlying catalytic mechanism remains largely unclear in literature. Many plausible hypotheses are related to the Au/oxide interface, which either plays a role in controlling the morphology of Au nanoparticles or has a direct contribution to their catalytic behaviors. [3][4][5] Nevertheless, it is crucial to fully clarify the interfacial structure, including the atomic arrangement and chemical bonding nature. In order to facilitate structural characterization, we synthesized model systems with Au nanoparticles on a single-crystal oxide support by the presence of an Au overlayer and the application of heat.A new phenomenon, we have discovered recently in those systems, involves the dewetted gold nanoparticle acting as a seed causing crystalline substrates to spontaneously grow underneath the gold nanoparticle.[5] Fig.1 shows intricate nano-structures including dewetted gold nanoparticles supporting by the regrowth oxide bases. As shown in the HAADF (Z-contrast) images, gold nanoparticles, with well-defined facets on crystalline bases, share the same contrast with the substrate. The composition and the crystallographic orientation of the bases are further confirmed by the electron energy-loss spectroscopy and diffraction techniques, respectively. The formation of such intricate nanostructures depends on a few parameters such as the thickness of the Au overlayer and the heating treatment.Limited to the Au-TiO 2 and Au-MgAl 2 O 4 systems we have studied so far, the intricate nano-structures include: a). gold nanoparticles, normally close to the Wulff equilibrium shape, have a few preferential crystallographic orientations with respect to the single-crystal substrates; b). regrowth oxide bases, with a well-defined shape, are epitaxially aligned with the single-crystal substrates; and c). interfacial monolayers, which have completely different atomic arrangement, extends both the gold and oxide lattices. The formation of such interfacial monolayers always accompanies with the regrowth of the substrates. Those unique interfacial structures may be responsible for the epitaxial growth of the substrate under self-organized gold nanoparticles.The interfacial monolayers referred as rearranged Au atoms between the gold and oxide lattices. We detected an interfacial bilayer between the gold nanoparticles and spinel bases, labeled by the red and blue arrows in Fig.2. On top of monolayer A with Au atoms extending the spinel lattice, the monolayer B exhibits an oscillating contrast in the HAADF image when viewed from [110] MgAl2O4 . In the case of Au-TiO 2 with much large lattice mismatch, different interfacial structures have been observed with different crystallographic orientations between the gold and rutile lattice. Fig.3 shows the interfacial monolayers varies from single monolayer to a few monolayers viewed from [001...

Applications of Cryogenic Electron Microscopy in Characterizing Electrochemical Materials and Interfaces

“…Significant advancements have been made in studying the interfacial composition together with lithium state of lithium batteries using cryo-EM. Li et al advanced cryo-EM further into the field of electrocatalysis, elucidating the specific function of metallic lithium and its SEI in ammonia electrosynthesis through experiments [4]. Contrary to traditional views, it was discovered that the SEI layer impedes nitrogen fixation, thus necessitating the destruction of the SEI layer to activate catalytic properties.…”