Fanghong Xue

Catalytically active single-atom niobium in graphitic layers

Carbides of groups IV through VI (Ti, V and Cr groups) have long been proposed as substitutes for noble metal-based electrocatalysts in polymer electrolyte fuel cells. However, their catalytic activity has been extremely limited because of the low density and stability of catalytically active sites. Here we report the excellent performance of a niobium-carbon structure for catalysing the cathodic oxygen reduction reaction. A large number of single niobium atoms and ultra small clusters trapped in graphitic layers are directly identified using state-of-the-art aberration-corrected scanning transmission electron microscopy. This structure not only enhances the overall conductivity for accelerating the exchange of ions and electrons, but it suppresses the chemical/thermal coarsening of the active particles. Experimental results coupled with theory calculations reveal that the single niobium atoms incorporated within the graphitic layers produce a redistribution of d-band electrons and become surprisingly active for O2 adsorption and dissociation, and also exhibit high stability.

Manipulated electromagnetic losses by integrating chemically heterogeneous components in Fe-based core/shell architecture

Existing techniques for stabilizing and functionalizing metal nanostructures required precise control of complex procedures and probably introduce undesirable impurities. We herein report an arc-discharge chemical vapor deposition strategy for the synthesis of chemically heterogeneous core/shell metal/oxide nanocapsules Fe/TiFe2O4, Fe/MnFe2O4, and Fe/Al2O3. A universal formation mechanism based on the co-effect of oxygen potential and surface energy is further proposed, derived from fundamental thermodynamics. Such core/shell nanocapsules, integrated with tunable components, present an effective manipulability of microwave absorption at expected frequency, originating from the various dielectric behaviors of the heterogeneous oxide shells.

Formation mechanism and optical characterization of polymorphic silicon nanostructures by DC arc-discharge

Silicon nanoparticles (Si NPs), silicon nanosheets (Si NSs), and silicon nanoribbons (Si NRs) were fabricated by means of DC arc-discharge under diverse atmospheres (hydrogen, mixtures of hydrogen and inert gas). It is shown that these as-prepared Si NPs are approximately 5–50 nm in diameter, Si NSs are about 10–30 nm in width and about 2.8 nm in thickness, and Si NRs consist of fine sheets with a length as long as 200 nm, width of 13 nm, and thickness of 3.1 nm. BET measurements reveal that the specific surfaces are 110.9, 108.8, and 164.2 m2 g−1 for Si NPs, Si NSs, Si NRs, respectively. Formation mechanisms for polymorphic Si nanostructures are elucidated, revealing that the anisotropic or isotropic growth of Si nanostructures is greatly induced by high energetic inert gas and hydrogen atoms, and finally results in the formation of polymorphic Si nanostructures. A visible down-shift of Raman frequency for these Si nanostructures is mainly attributed to the size effect. The band gaps are experimentally measured as 2.89 eV (Si NPs), 2.92 eV (Si NSs), and 3.02 eV (Si NRs) for direct transition, and 1.99 eV (Si NPs), 1.26 eV (Si NSs), and 1.36 eV (Si NRs) for indirect transition. These are noticeably enlarged with respect to bulk Si (1.1 eV).

The preparation and electrochemical performances of Al-Si/C nanocomposite anode for lithium ion battery

The microstructure and electrochemical performance of Al-Si, Al-Si/C nanocomposite were investigated as the anode for lithium ion battery. The Al-Si nanoparticles were prepared by the arc-discharge method. The Al-Si/C nanoparticles were obtained by coated Al-Si nanoparticles with the precursor of glucose (C6H12O6) as the carbon source. It was indicated that the carbon coating on Al-Si nanoparticles can eliminate the negative effects on the electrochemical insertion/extractions of lithium ions, improve the initial capacity and cycle performances.