Cu-template-dependent synthesis of PtCu nanotubes for oxygen reduction reactions

The development of electrocatalysts with high activity and durability for oxygen reduction reaction (ORR) in acidic electrolyte environments remains a serious challenge for clean and efficient energy conversion. Synergistic effects between Pt and inexpensive metals, the d band center of Pt and catalyst morphology could adjust the adsorption and desorption of oxygen intermediates by the Pt. All the factors affect the catalytic performance of Pt-based nanocrystals. Here, we prepared Cu@PtCu₃ NWs with an average diameter of 74.9 nm for Cu and about 10 nm PtCu₃ layer. After etching, the Cu@PtCu₃ nanowires is transformed into PtCu nanotube structure, due to the removal of copper from the surface and interior. PtCu NTs for ORR shows excellent activities and durability due to the integration of structural advantages and synergistic effects. Notably, the mass activity and specific activity of PtCu NTs (0.105 A mg^?1_Pt and 0.230 mA cm^?2_Pt) are 2.0 and 3.8 times higher than that of commercial Pt/C (0.053 A mg^?1_Pt and 0.06 mA cm^?2_Pt). The etching process to change the morphology of the catalyst and alter the electronic structure of the catalyst is expected to be useful for the design of future structured Pt-based alloy nanocatalysts.     

In situ characterization of LiY(WO4)2 nanotubes for electrochemical energy storage

Here, LiY(WO₄)₂ nanotubes are prepared via a feasible electrospinning technique. This new anode material shows excellent electrochemical properties. The capacity loss of LiY(WO₄)₂ nanotubes is as low as 6.9% after 156 cycles, while bulk LiY(WO₄)₂ presents the capacity loss higher than 55.0%. Even after 600 long-life cycles, the capacity loss of the nanotubes is only 9%. It can be seen that the hollow structure with a rough surface and a porous morphology contributes to the improvement of electrochemical performance. Furthermore, online X-ray diffraction (XRD) method is firstly applied to understand the lithium ions insertion/extraction mechanism of LiY(WO₄)₂ nanotubes. It can be concluded that it is an asymmetrical two-phase reaction. A phase transformation from LiY(WO₄)₂ to Li₃Y(WO₄)₂ can be obviously seen from the in situ XRD during discharge process. While Li₂Y(WO₄)₂ appears as an intermediate phase with a reverse charge reaction. In addition, in situ XRD also demonstrates that LiY(WO₄)₂ nanotubes have surprised electrochemical reversibility. All the above results indicate that LiY(WO₄)₂ nanotubes can be expected to be anode candidate for rechargeable lithium ion batteries (LIBs).     

Discrimination of B–C–N nanotubes through energy-filtering electron microscopy

Various multi-walled nanotubes in the B–C–N system are thoroughly investigated using a JEOL-3100FEF high-resolution field emission transmission electron microscope operating at 300 kV and equipped with an in-column built Omega filter. Spatially-resolved B, C and N elemental maps of the nanotubes are constructed. It is realized that a wide variety of tubular arrays composed of B, C and N atoms may exist in the system. Sandwich-like BN-rich and C-rich alternating tubular shells, graphitic C layers inside and outside of pure BN shells induced either by surface contamination, or electron beam irradiation, separation of C-rich and BN-rich tubes and/or BN particles within tubular bunches may take place. One should carefully take these effects into account while analyzing nanotube physical properties, e.g., electrical or optical, rather than simply rely on electron energy loss spectra typically collected from B, C and N containing nanostructures as a whole. Striking dependence of an individual nanotube electrical conductivity on tubular shell chemistry is demonstrated using I–V curve recording in an atomic force microscope.     

Rational Synthesis of Metal Nanotubes and Nanowires from Lamellar Structures

A generic method has been developed for the synthesis of crystalline metal nanowires or nanotubes (such as bismuth nanotubes, tungsten nanowires) from lamellar structures. In a typical process, lamellar surfactant/inorganic composite precursors are first prepared by reacting cationic or anionic surfactants with inorganic species under appropriate conditions. After treating these precursors by hydrothermal pyrolysis, or other processes, crystalline metallic nanotubes or nanowires are obtained.     

Nanoweb Formation: 2D Self‐Assembly of Semiconductor Gallium Oxide Nanowires/Nanotubes

This paper reports a method to produce networks of crystalline gallium oxide comprised of one‐dimensional (1D) nanostructures. Because of the unique arrangement of wires, these crystalline networks are termed as ‘nanowebs’. Nanowebs are of great technological interest since they contain wire densities of the order of 10⁹ cm^–2. A possible mechanism for the fast self‐assembly of crystalline metal oxide nanowires involves multiple nucleation and coalescence via oxidation–reduction reactions at the molecular level. The preferential growth of nanowires parallel to the substrate enabled them to coalesce into regular polygonal networks. The individual segments of the polygonal network consist of both nanowires and nanotubules of β‐gallium oxide. Individual wire properties contribute to a nanoweb’s overall capacity and the implications for devices based on nanowebs are expected to be enormous.     

Hierarchical Self‐Assembly of Peptide‐Coated Carbon Nanotubes

Numerous applications, from molecular electronics to super‐strong composites, have been suggested for carbon nanotubes. Despite this promise, difficulty in assembling raw carbon nanotubes into functional structures is a deterrent for applications. In contrast, biological materials have evolved to self‐assemble, and the lessons of their self‐assembly can be applied to synthetic materials such as carbon nanotubes. Here we show that single‐walled carbon nanotubes, coated with a designed amphiphilic peptide, can be assembled into ordered hierarchical structures. This novel methodology offers a new route for controlling the physical properties of nanotube systems at all length scales from the nano‐ to the macroscale. Moreover, this technique is not limited to assembling carbon nanotubes, and could be modified to serve as a general procedure for controllably assembling other nanostructures into functional materials.