Yongsheng Zhou

A hierarchical scaffold: natural growth of three-dimensional nanowire bundles from microporous Ta

The relatively high melting temperature and the inability to process Ta structures via conventional processing routes have limited the acceptance of tantalum, in spite of its excellent biocompatibility. Here we report, for the first time, a method of processing Ta to create porous structures consisting of self-assembled nanowire bundles from three-dimensional (3D) microporous Ta scaffolds via facile high temperature heat treatment. Porous Ta samples have been characterized for their mechanical properties. The results show that the Youngs modulus of porous Ta can be tailored between 0.06 and 1.69 GPa by changing the heat treatment temperature between 2200 °C and 2400 °C. These porous Ta structures resemble cancellous bone structures on the micro/macroscale. This remarkably simple process can be employed as an enabling technique for applications in nanotechnology and biotechnology.

High-performance symmetric supercapacitors based on carbon nanotube/graphite nanofiber nanocomposites

This work reports the nanocomposites of graphitic nanofibers (GNFs) and carbon nanotubes (CNTs) as the electrode material for supercapacitors. The hybrid CNTs/GNFs was prepared via a synthesis route that involved catalytic chemical vapor deposition (CVD) method. The structure and morphology of CNTs/GNFs can be precisely controlled by adjusting the flow rates of reactant gases. The nest shape entanglement of CNTs and GNFs which could not only have high conductivity to facilitate ion transmission, but could also increase surface area for more electrolyte ions access. When assembled in a symmetric two-electrode system, the CNTs/GNFs-based supercapacitor showed a very good cycling stability of 96% after 10 000 charge/discharge cycles. Moreover, CNTs/GNFs-based symmetric device can deliver a maximum specific energy of 72.2 Wh kg−1 at a power density of 686.0 W kg−1. The high performance of the hybrid performance can be attributed to the wheat like GNFs which provide sufficient accessible sites for charge storage, and the CNTs skeleton which provide channels for charge transport.

A nitrogen-doped 3D open-structured graphite nanofiber matrix for high-performance supercapacitors

An N-doped 3D ordered mesoporous graphite nanofiber (3D OMGNF-N) with an N-doping level of up to 16.5 at% for high-performance supercapacitors is designed and synthesized. OMGNF-N shows a conductive 3D open-structured matrix, large surface area, hierarchical porous structure, and great number of electrochemically active sites by N-doping. The supercapacitors (SCs) based on OMGNF-N show a remarkably excellent electrochemical behavior with a high specific capacitance of 460, 420, and 345 F g−1, respectively, in KOH, H2SO4, and KCl electrolytes when measured in a three-electrode configuration. In practical devices, the material can achieve a remarkably high capacitance of 426 F g−1, good cycling stability with 92% capacitance retention after 50 000 cycles. Moreover, the OMGNF-N based SCs show a remarkably excellent electrochemical behavior with good rate capability and low internal resistance, thereby leading to both high power density and relatively high energy density.

IN SITU UNZIPPING OF CARBON NANOTUBES TO FORM GRAPHENE NANORIBBONS

We report the one step facile synthesis of graphene nanoribbons (GNRs) by unzipping carbon nanotubes (CNTs) from glucose (C6H12O6) precursor, using a simple chemical vapor deposition method. Some nanotubes are partially cut resulting in a GNR–CNT hybrid whereas others are fully cut to form GNRs. The average length of GNRs achieved by this method is typically in the range of 1–10 μm. The formation of GNRs is ascribed to the in situ oxygen-driven unzipping of CNTs. The process is free from aggressive oxidants and utilizes the in situ unzipping. This method offers an alternative approach for making GNRs, compared to previously used techniques to synthesize GNRs.