Molecular dynamics study on structural and atomic evolution between Au and Ni nanoparticles through coalescence.

Motivated by the structure evolution experiments of Janus NiAu nanoparticles (NPs), we present a detailed study on the thermodynamic evolution of Ni and Au NPs with different ratios of Au and Ni through the molecular dynamics (MD) simulations. It is found that, for fixed Ni particle size (5.8 nm in diameter), the energy variation with the increasing temperature is related to the Au sizes (1.5-9.6 nm in diameter), due to the diverse atomic segregation modes. For a small Au particle, due to lattice induction, the structure will change from order to disorder and then to order. The interface defects of the merging NPs could be automatically eliminated by coalescence processes. The change in energy as the temperature increases is similar to that of monometallic NPs. For larger Au particles, the irregular variation of energy occurs and the atomic energy experience one or two reductions at least with the increase of the temperature. The segregation of Au atoms to the surface of Ni particle is dominant during the continuous heating process. The coalescence processes of Au atoms strongly determine the final morphology of the particles. Dumbbell-like, Janus and eccentric core-shell spherical structures could be obtained during the heating process. Our results will provide an effective approach to the design of novel materials with specific properties through thermal control.

Morphology-Controlled Synthesis of Hematite Nanocrystals and Their Optical, Magnetic and Electrochemical Performance.

A series of α-Fe2O3 nanocrystals (NCs) with fascinating morphologies, such as hollow nanoolives, nanotubes, nanospindles, and nanoplates, were prepared through a simple template-free hydrothermal synthesis process. The results showed that the morphologies could be easily controlled by SO42- and H2PO4-. Physical property analysis showed that the α-Fe2O3 NCs exhibited shape- and size-dependent ferromagnetic and optical behaviors. The absorption band peak of the α-Fe2O3 NCs could be tuned from 320 to 610 nm. Furthermore, when applied as electrode material for supercapacitor, the hollow olive-structure exhibited the highest capacitance (285.9 F·g-1) and an excellent long-term cycling stability (93% after 3000 cycles), indicating that it could serve as a candidate electrode material for a supercapacitor.

Porous Pt-NiO x nanostructures with ultrasmall building blocks and enhanced electrocatalytic activity for the ethanol oxidation reaction.

Oxidized species on surfaces would significantly improve the electrocatalytic activity of Pt-based materials. Constructing three-dimensional porous structures would endow the catalysts with good stability. Here, we report a simple strategy to synthesize porous Pt-NiO x nanostructures composed of ultrasmall (about 3.0 nm) building blocks in an ethanol-water solvent. Structure and component analysis revealed that the as-prepared material consisted of interconnected Pt nanocrystals and amorphous NiO x species. The formation mechanism investigation revealed that the preformed amorphous compounds were vital for the construction of porous structure. In the ethanol oxidation reaction, Pt-NiO x /C exhibited current densities of 0.50 mA cmPt -2 at 0.45 V (vs. SCE), which were 16.7 times higher than that of a commercial Pt/C catalyst. Potentiostatic tests showed that Pt-NiO x /C had much higher current and better tolerance towards CO poisoning than the Pt/C catalyst under 0.45 V (vs. SCE). In addition, the NiO x species on the surface also outperformed an alloyed Ni component in the test. These results indicate that the Pt-NiO x porous nanomaterial is promising for use in direct ethanol fuel cells.