Atomic-scale insights into the structure evolution of nanocatalysts under reaction conditions are critical for correlating their structure-properties relationship. Detailed information at atomic scale, obtained by in situ TEM is therefore an essential complement to other in situ techniques (e.g., XPS, FTIR, etc.). In this talk, we present our in situ TEM studies of three nanocatalyst systems: (1) In situ kinetic growth of free standing Pt nanowire, which is one of the promising catalysts for oxygen reduction reaction (ORR); (2) Facet-dependent oxidation of Pt3Co ORR catalysts; (3) In situ investigation of the stability of Ir-dimer catalyst. Atomic-scale information into the kinetic growth of catalysts is critical for the optimization of the synthesis process. Here, dynamic growth of free standing Pt nanowire-network in solid state under an reducing atmosphere is observed by using our in situ gas cell technique. 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. In addition, an understanding of how the surface composition and structure of nanocatalysts may be controlled by external means is useful for their efficient production. We here show the result of surface composition and dynamics involved in facet-dependent oxidation of equilibrium-shaped Pt3Co nanoparticles in an initially disordered state. Evolution of the surface of the Pt3Co nanoparticles was monitored at atomic scale during their exposure to an oxygen atmosphere at elevated temperature to mimic an oxidizing environment of ORR, and it was found that Co segregation and oxidation take place on {111} surfaces but not on {100} surfaces, suggesting {100} facets may play an important role in maintaining the activity of disordered Pt3Co ORR catalysts Another example of our in situ TEM studies 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.

In situ transmission electron microscopy studies of nanocatalysts at atomic resolution

256th National Meeting (2018)

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