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Understanding the mechanism of nucleation and growth of nanocrystals is crucial for designing and regulating the structure and properties of nanocrystals. However, the process from molecules to nanocrystals remains unclear because of the rapid and complicated dynamics of evolution under reaction conditions. Here, the complete evolution process of solid‐phase chloroplatinic acid during the electron beam irradiation triggered reduction and nucleation of platinum nanocrystals is recorded. Aberration‐corrected environmental transmission electron microscopy is used for direct visualization of the dynamic evolution from H2PtCl6 to Pt nanocrystals at the atomic scale, including the formation and growth of amorphous clusters, crystallization, and growth of clusters, and the ripening of Pt nanocrystals. At the first two stages, there exists a critical size of ≈2.0 nm, which represents the start of crystallization. Crystallization from the center and density fluctuation are observed in the second stage of the crystallization of a few clusters with a size obviously larger than the critical size. The work provides valuable information to understand the kinetics of the early stage of nanocrystal nucleation and crystallization at atomic scale. [ABSTRACT FROM AUTHOR]

Highly uniform dispersed bimetallic Pt3Zn alloy nanocrystals (NCs) with unique geometries are obtained via a facile one‐pot synthesis process by regulating different reductants. To investigate the morphology and composition of the prepared catalysts, the transmission electron microscopy, X‐ray diffraction and X‐ray photoelectron spectroscopy are utilized. Electrochemical measurements reveal that the Pt3Zn NCs significantly exhibited larger electrochemically active surface areas and excellent catalytic activity towards electro‐oxidation of methanol and ethanol in comparison to the commercial Pt/C. The optimized Pt3Zn (AA) NCs exhibit excellent mass activities in both methanol oxidation reaction (1251.4 mA mgPt−1) and ethanol oxidation reaction (975.7 mA mgPt−1) in acidic media, which are respectively 4.28 times and 3.02 times higher than those of commercial Pt/C. Moreover, the Pt3Zn NCs show a higher stability and better resistance to the COads poisoning. The activity enhancements are attributed to electronic effects and a bifunctional mechanism. [ABSTRACT FROM AUTHOR]

An in-situ composite methodology was first proposed to prepare carbon supported PtNix (X = 1, 3, 1/3) via online reaction, nucleation and growth of nanocrystals (NCs) on carbon support along the microfluidic channel. Uniform dispersed ultra-small PtNi X NCs (1 nm–3 nm) with high surface exposed Pt atoms and enhanced nanocrystal-carbon interface interaction can be constructed. The annealed nanocomposites with a Pt/Ni ratio of 1/3 exhibit a mass catalytic activity of 7.6 times higher than the commercial Pt/C nanocatalysts in the ethanol oxidation reaction. The chronoamperometry measurement indicates that their mass activity still retains 3.6 times of the commercial Pt/C nanocatalysts at 4000 s. Moreover, PtNi 3 /C nanocatalysts have the highest tolerance to CO poisoning according to CO stripping measurements. [ABSTRACT FROM AUTHOR]