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Sheng Dai1 Wenpei Gao1 Xingxu Yan1 Xiaoqing Pan1 2

1, University of California Irvine, Irvine, California, United States
2, University of California Irvine, Irvine, California, United States

Significant developments in micro-electrical-mechanical systems (MEMS) - based devices for use in transmission electron microscopy (TEM) sample holders have recently led to the commercialization of windowed gas cells that now enable the atomic-resolution visualization of phenomena occurring during gas-solid interactions at atmospheric pressure. In situ TEM study under atmospheric pressures provides unique information that is beneficial to correlating the structure-properties relationship of catalytic nanomaterials, particularly under real gaseous environments. In this talk, we illustrate the capability of this device as applied to our study of three catalyst systems: (1) In situ kinetic growth of free standing Pt nanowires; (2) Facet-dependent oxidation of Pt3Co nanoparticles; (3) In situ investigation of the stability of Ir-dimer catalyst.
Atomic-scale insights into the kinetic growth of catalytic nanomaterials are critical for optimization of the synthesis process. We observe the growth of free standing Pt nanowire-network in solid state under a gaseous environment, by using in situ TEM approach. The captured dynamics controlled by the gas adsorbate shows a three-stage process including nucleation, coalescence and oriented attachment, which represent a potential route for nanostructure synthesis.
Moreover, an understanding of how the surface composition and structure of catalytic nanomaterials may be controlled by external means is useful for their efficient production. By taking advantage of the high spatial resolution of TEM, we study the surface composition and the dynamics involved in facet-dependent oxidation of equilibrium-shaped Pt3Co nanoparticles in an initially disordered state. In brief, using our advanced in situ gas cell technique, evolution of the surface of the Pt3Co nanoparticles was monitored at the atomic scale during their exposure to an oxygen atmosphere at elevated temperature, and it was found that Co segregation and oxidation take place on {111} surfaces but not on {100} surfaces. Another example we show here is the investigation of the stability of Ir-dimer catalyst. Beyond single atom catalysts, emerging Ir dimer atom catalyst has been successfully fabricated on iron oxide support, showing an ultra high durability for the water-splitting. The structure of Ir-dimer catalyst has experimentally demonstrated by atomic-resolution STEM imaging coupled with EDX/EELS elemental analysis. It is found that the Ir dimer active sites were strongly bonded on the iron oxide support through in situ TEM observation.

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