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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]

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]

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]

Abstract Ultrathin single crystalline nanoplates of Ni 12 P 5 are synthesized via a facile, template-free, wet chemical method. The thickness is about 6 nm with sizes tunable from 5 to 50 nm. The exposed plate surface is formed of { 2 ¯ 11 } lattice plane. Benefitting from the high electrical conductivity and the two dimensional (2D) nanostructures, the Ni 12 P 5 nanoplates exhibit excellent supercapacitor properties. The specific capacity is about 697 C/g at the current density of 1 A/g. Even at 20 A/g, it is measured as 446 C/g, with 64.0% retention indicating an outstanding rate capability. The charge storage mechanisms include a battery-type behavior related to the bulk redox processes and a double-layer capacitance arising from the 2D geometric morphology. In particular, the morphological effects accounts for about 63% of the total charge storage effects at the voltage sweep rate of 2 mV/s in the cyclic voltammetry measurement, and is even higher percentage-wise at a higher sweep rate. This is, by far, the best performance with facile synthesis techniques for single crystalline nickel phosphides. Graphical abstract Image 1 Highlights • Single-crystalline Ni 12 P 5 nanoplates by a facile, template-free wet chemical route. • Nanoplate surface is of { 2 ¯ 11 } crystal plane, and its thickness, about 7 nm. • The growth mechanism is by Kirkendall effect. • High specific capacity is 697 C/g at the current density of 1 A/g. • Surface term accounts for about 2/3 of the specific capacity, and the bulk, 1/3. [ABSTRACT FROM AUTHOR]

Interfacial atomic configuration plays a vital role in the structural stability and functionality of nanocomposites composed of metal nanoparticles (NPs) and two−dimensional semiconductors. In situ transmission electron microscope (TEM) provides a real−time technique to observe the interface structure at atomic resolution. Herein, we loaded bimetallic NiPt truncated octahedral NPs (TONPs) on MoS2 nanosheets and constructed a NiPt TONPs/MoS2 heterostructure. The interfacial structure evolution of NiPt TONPs on MoS2 was in situ investigated using aberration−corrected TEM. It was observed that some NiPt TONPs exhibited lattice matching with MoS2 and displayed remarkable stability under electron beam irradiation. Intriguingly, the rotation of an individual NiPt TONP can be triggered by the electron beam to match the MoS2 lattice underneath. Furthermore, the coalescence kinetics of NiPt TONPs can be quantitatively described by the relationship between neck radius (r) and time (t), expressed as rn = Kt. Our work offers a detailed analysis of the lattice alignment relationship of NiPt TONPs on MoS2, which may enlighten the design and preparation of stable bimetallic metal NPs/MoS2 heterostructures. [ABSTRACT FROM AUTHOR]

Herein, the microstructure stability of a newly developed hot‐working die (HWD700) steel at elevated temperatures up to 700 °C is investigated using transmission electron microscopy (TEM), selected‐area electron diffraction, energy‐dispersive spectrometer, and high‐resolution transmission electron microscope. The results show that the HWD700 steel exhibits a higher thermal stability than the commercial H13 steel when the temperature is up to 700 °C. After quenching and tempering, high densities of intra‐lath rodlike and inter‐lath spherical MC nano‐carbides and inter‐lath strip‐like M7C3 nano‐carbides are observed in the HWD700 steel. These carbides remain nanoscale at temperatures up to 700 °C. For comparison, rod‐shaped MC nano‐carbides in the tempered H13 steel tend to coarsen and transform into larger M23C6 carbides at temperatures up to 650 °C. The TEM observation further reveals that the interface misfit between the MC nano‐carbide and matrix in the HWD700 steel is as low as 0.88%, lower than that of 14.8% in the H13 steel. This can be the main reason for the improved stability of the HWD700 steel by pinning dislocations and grain boundaries and thereby hindering the recrystallization process at an elevated temperature. [ABSTRACT FROM AUTHOR]

The effects of vanadium content on the microstructural and mechanical properties of a newly developed hot-work die steel (MPS700V) at room and elevated temperatures have been investigated in this paper. It shows that the ultimate tensile strength (UTS) of MPS700V at room temperature and 700 °C are both strongly dependent on the V content. With the increase of V content from 0 to 1.2% V, The UTS at room temperature increases from 1127 MPa to 1442 MPa, and the UTS at 700 °C increases from 400 MPa to 550 MPa. The transmission electron microscope (TEM) shows that the addition of V is beneficial to increase the nucleation rate and volume fraction of MC nano-carbides during the tempering process, and the size of the MC nano-carbides decreases with the increase of V content. The addition of V also increases the thermal stability of MC nano-carbides at 700 °C, which can be related to the reducing the interface mismatch between MC and matrix. Furthermore, a transformation from Orowan bypass strengthening mechanism to shearing strengthening mechanism caused by the V addition is proposed based on the theoretical analysis and TEM observation. [ABSTRACT FROM AUTHOR]