Zunxian Yang

Synthesis of uniform TiO2@carbon composite nanofibers as anode for lithium ion batteries with enhanced electrochemical performance

Very large area, uniform TiO2@carbon composite nanofibers were easily prepared by thermal pyrolysis and oxidization of electrospun titanium(IV) isopropoxide/polyacrylonitrile (PAN) nanofibers in argon. The composite nanostructures exhibit the unique feature of having TiO2 nanocrystals encapsulated inside a porous carbon matrix. The unique orderly-bonded nanostructure, porous characteristics, and highly conductive carbon matrix favour excellent electrochemical performance of the TiO2@carbon nanofiber electrode. The TiO2@carbon hybrid nanofibers exhibited highly reversible capacity of 206 mAh g−1 up to 100 cycles at current density of 30 mA g−1 and excellent cycling stability, indicating that the composite is a promising anode candidate for Li-ion batteries.

Dispersion of SnO2 nanocrystals on TiO2(B) nanowires as anode material for lithium ion battery applications

TiO2(B)@SnO2 core–shell hybrid nanowires have been synthesized by a facile hydrothermal process and subsequent liquid phase reaction. Hybrid nanowire electrodes exhibit excellent reversible lithium storage capacity rate capability and good cyclability, mainly due to the particular architecture of the composite, which features an open continuous channel along its axis, facilitating lithium ion diffusion, and provides effective mechanical support for the TiO2(B) core, alleviating the stress produced during discharge–charge cycling and also preventing the pulverization of the Sn nanoparticles. Owing to its superior electrochemical performance, this composite could be a promising potential anode material for lithium ion batteries.

TiO2(B)@carbon composite nanowires as anode for lithium ion batteries with enhanced reversible capacity and cyclic performance

Novel TiO2(B)@carbon composite nanowires were simply prepared by a two-step hydrothermal process with subsequent heat treatment in argon. The nanostructures exhibit the unique feature of having TiO2(B) encapsulated inside and an amorphous carbon layer coating the outside. The unique core/shell structure and chemical composition is likely to lead to perfect performance in many applications. In this paper, the results of Li-ion battery testing are presented to demonstrate the superior cyclic performance and rate capability of the TiO2(B)@carbon nanowires. The composite nanowires exhibit a high reversible capacity of 560 mAh g−1 after 100 cycles at the current density of 30 mA g−1, and excellent cycling stability and rate capability (200 mAh g−1 when cycled at the current density of 750 mA g−1), indicating that the composite is a promising anode candidate for Li-ion batteries.

Highly uniform TiO2/SnO2/carbon hybrid nanofibers with greatly enhanced lithium storage performance

Highly uniform, relatively large area TiO2/SnO2/carbon hybrid nanofibers were synthesized by a simple method based on thermal pyrolysis and oxidation of an as-spun titanium–tin/polyacrylonitrile nanoweb composite in an argon atmosphere. This novel composite features the uniform dispersion and encapsulation of highly uniform nanoscale TiO2/SnO2 crystals in a porous carbon matrix. The high porosity of the nanofiber composite material, together with the conductive carbon matrix, enhanced the electrochemical performance of the TiO2/SnO2/carbon nanofiber electrode. The TiO2/SnO2/carbon nanofiber electrode displays a reversible capacity of 442.8 mA h g−1 for up to 100 cycles, and exhibits excellent rate capability. The results indicate that the composite could be a promising anode candidate for lithium ion batteries.

Encapsulation of TiO2(B) nanowire cores into SnO2/carbon nanoparticle shells and their high performance in lithium storage

TiO(2)(B)@SnO(2)/carbon hybrid nanowires have been synthesized by two simple hydrothermal processes and subsequent heat treatment in argon. The composite has a unique architecture, as its morphology consists of particles having a TiO(2)(B) nanowire core and a porous SnO(2)/carbon nanoparticle shell layer. The unique core/shell structure and chemical composition will be useful for many potential applications, including the lithium ion battery. The electrochemical results on the composite are presented to demonstrate the superior cycling performance and rate capability of the TiO(2)(B)@SnO(2)/carbon nanowires. This composite exhibits a high reversible capacity of ∼669mAhg(-1), and excellent cycling stability, indicating that the composite is a promising anode material for Li-ion batteries.

Plum-branch-like carbon nanofibers decorated with SnO2 nanocrystals

Novel plum-branch-like carbon nanofibers (CNFs) decorated with SnO2 nanocrystals have been synthesized by electrospinning and subsequent thermal treatment in an Ar/H2O atmosphere. The morphologies of the as-synthesized SnO2/CNF composites and the contents of carbon and SnO2 can be controlled by adjusting the heat treatment temperature. It is proposed that the growth of SnO2/CNF composites follows the outward diffusion of tin composites from the as-spun tin composite/polyacrylonitrile (PAN) nanofibers, pyrolysis of PAN and oxidation of tin composites, and then formation of SnO2 nanocrystals around the CNFs. This novel 1D SnO2/CNF composite may have potential application in nanobatteries, nano fuel cells, and nanosensors. A preliminary result has revealed that the SnO2/CNF composite presents favourable electrochemical performance in lithium-ion batteries.

Ammonia borane nanofibers supported by poly(vinyl pyrrolidone) for dehydrogenation

An effective strategy of utilizing electrospinning techniques to fabricate MgCl2 catalyzed ammonia borane (AB) nanofibers with a tunable fiber diameter is reported. The synergistic effect obtained by combining nanofibers and metallic catalyst plays a crucial role in the decomposition of MgCl2-doped AB nanofibers, which leads to significant improvements in dehydrogenation kinetics and complete suppression of unwanted byproducts. The results of dehydrogenation show that MgCl2-doped AB nanofibers were able to release over 10.0 wt % pure H2 below 100 °C with favorable kinetics, a significant advance over releases from bulk AB. Furthermore, the dehydrogenation of MgCl2-doped AB nanofibers gives a weak exothermic reaction, −3.84 kJ mol−1 H2, which is dramatically lower than that of neat AB (−21 kJ mol−1 H2), which suggests that the electrospun sample is potentially more feasible to reverse. The findings in this paper provide general guidelines and inspiration for the design and synthesis of novel nano-fibrous materials with controllable dimensions for hydrogen storage applications.

Facile Synthesis of Coaxial CNTs/MnOx-Carbon Hybrid Nanofibers and Their Greatly Enhanced Lithium Storage Performance

Carbon nanotubes (CNTs)/MnOx-Carbon hybrid nanofibers have been successfully synthesized by the combination of a liquid chemical redox reaction (LCRR) and a subsequent carbonization heat treatment. The nanostructures exhibit a unique one-dimensional core/shell architecture, with one-dimensional CNTs encapsulated inside and a MnOx-carbon composite nanoparticle layer on the outside. The particular porous characteristics with many meso/micro holes/pores, the highly conductive one-dimensional CNT core, as well as the encapsulating carbon matrix on the outside of the MnOx nanoparticles, lead to excellent electrochemical performance of the electrode. The CNTs/MnOx-Carbon hybrid nanofibers exhibit a high initial reversible capacity of 762.9 mAhg−1, a high reversible specific capacity of 560.5 mAhg−1 after 100 cycles, and excellent cycling stability and rate capability, with specific capacity of 396.2 mAhg−1 when cycled at the current density of 1000 mAg−1, indicating that the CNTs/MnOx-Carbon hybrid nanofibers are a promising anode candidate for Li-ion batteries.

Encapsulation of Fe3O4 nanoparticles into N, S co-doped graphene sheets with greatly enhanced electrochemical performance

Particular N, S co-doped graphene/Fe3O4 hybrids have been successfully synthesized by the combination of a simple hydrothermal process and a subsequent carbonization heat treatment. The nanostructures exhibit a unique composite architecture, with uniformly dispersed Fe3O4 nanoparticles and N, S co-doped graphene encapsulant. The particular porous characteristics with many meso/micro holes/pores, the highly conductive N, S co-doped graphene, as well as the encapsulating N, S co-doped graphene with the high-level nitrogen and sulfur doping, lead to excellent electrochemical performance of the electrode. The N-S-G/Fe3O4 composite electrode exhibits a high initial reversible capacity of 1362.2 mAhg−1, a high reversible specific capacity of 1055.20 mAhg−1 after 100 cycles, and excellent cycling stability and rate capability, with specific capacity of 556.69 mAhg−1 when cycled at the current density of 1000 mAg−1, indicating that the N-S-G/Fe3O4 composite is a promising anode candidate for Li-ion batteries.

A simple spraying process greatly enhanced field emission of novel T-ZnO-supported CNT emitters

T-ZnO-supported CNT emitters were fabricated by using a simple process involving two spraying steps followed by heat treatment in air. The T-ZnO-supported CNT emitter was observed to form a particular architecture with the T-ZnO support containing a vertically aligned CNT emitter firmly attached to the electrode. These particular T-ZnO-supported carbon nanotube emitters displayed good contacts with the substrate, vertically aligned CNT emitters and density-controllable T-ZnO supports, which all appear to explain the excellent field emission performance of the electrode. Of the materials tested, the T-ZnO-supported CNT emitters exhibited the best field emission capability, i.e., the lowest turn-on electrical field, with a value of 0.96 V μm−1 at a current density of 0.01 mA cm−2, and the highest field enhancement factor, with a value of 13 883, as well as good emission stability, with only ∼18% of the current attenuated over an operating span of ∼200 min. These characteristics indicate that the T-ZnO-supported CNT emitters constitute a very promising cathode material candidate for field emission.