Huaihe Song

Hollow graphene oxide spheres self-assembled by W/O emulsion

Hollow graphene oxide spheres (HGOSs) were fabricated from graphene oxide nanosheets (GONs) utilizing a water-in-oil (W/O) emulsion technique without surfactant. Effects of oxidation treatment and water removal on the formation and morphology of HGOSs are investigated. The oxidation time for preparing GONs is a crucial factor for the formation and morphology of HGOSs. We found that with increasing oxidation time, the morphology and surface topography of HGOSs vary from irregular and rough to uniform and smooth shape with decreasing diameter. Moreover, the electrochemical performance of HGOSs as anode materials in lithium-ion batteries was evaluated. The heat-treated HGOSs exhibit a 485 mAh g−1 reversible capacity and high rate performance thanks to the hollow structure, thin and porous shells consisting of graphene.

Synthesis and high-rate capability of quadrangular carbon nanotubes with one open end as anode materials for lithium-ion batteries

Novel carbon nanotubes (CNTs) were prepared on a large-scale. Their morphology and structure were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman measurements. It was found that the prepared CNTs possess a quadrangular cross section, as well as one open end and “herringbone”-like walls, so these novel CNTs were named q-CNTs. The unique morphology of q-CNTs implies broad potential applications in many fields, including drug delivery, conductive and high-strength composites, field emission displays and radiation sources, hydrogen storage media, and supercapacitors. When used as the anode materials for lithium-ion batteries, q-CNTs exhibit excellent high-rate performance (a high-reversible capacity of 181 mAh g−1 at the current density of 1000 mA g−1 (ca. 3 C)), which is much higher than that of the common multi-wall carbon nanotubes. This high-rate performance should be attributed to the unique nanostructure of q-CNTs, which results in a high diffusion coefficient for lithium ions in the q-CNTs.

Influence of ferrocene addition on the morphology and structure of carbon from petroleum residue

Abstract Nano-sized iron particle/carbon composites have been synthesized from a petroleum residue by heating at 420xa0°C with ferrocene under pressure. The morphologies and structural features of the composites were investigated using TEM, HREM and XRD measurements. The effect of ferrocene addition on the development of turbostratic carbon from the petroleum residue was discussed. It was found that, by increasing the amount of ferrocene added from 3% to 20%, the size of the nano-iron particles tended to increase from 20–80 nm to 30–180 nm. The iron particles pyrolyzed from ferrocene mainly exist in the forms Fe–O and Fe1−xS when the ferrocene content was low (3% and 6%), and α-Fe when ferrocene contents were high (10% and 20%). Upon further heat treatment in the range 500 to 900xa0°C, the iron particles tended to aggregate and Fe–O and Fe1−xS were transformed into α-Fe and austenite. In comparison with the carbon formed without ferrocene addition, the resulting carbon exhibited a turbostratic structure as shown by HREM, in which the d002 spacing decreased with the increase of ferrocene loading and increasing temperature, suggesting the carbonization was promoted by the catalysis of the nano-iron particles.

Effect of graphene nanosheet addition on the electrochemical performance of anode materials for lithium-ion batteries.

The structure and electronic properties of graphene nanosheet (GNS) render it a promising conducting agent in a lithium-ion battery. A graphite electrode loaded with GNS exhibits superior electrochemical properties including higher rate performance, increased specific capacity and better cycle performance compared with that obtained by adding the traditional conducting agent-acetylene black. The high-quality sp(2) carbon lattice, quasi-two-dimensional crystal structure and high aspect ratio of GNS provide the basis for a continuous conducting network to counter the decrease in electrode conductivity with increasing number of cycles, and guarantee efficient and fast electronic transport throughout the anode. Effects of GNS loading content on the electrochemical properties of graphite electrode are investigated and results indicate that the amount of conductive additives needed is decreased by using GNS. The kinetics and mechanism of lithium-storage for a GNS-loaded electrode are explored using a series of electrochemical testing techniques.

Phase transition and huge ferroelectric polarization observed in BiFe1−xGaxO3 thin films

We prepared the chemical-solution deposited films of BiFe1−xGaxO3, which was previously only possibly synthesized under high-pressure and high-temperature. The thin films crystallized in rhombohedral perovskite structure (R3c) up to xu2009=u20090.05 and in tetragonal-like monoclinic structure (Cm) above xu2009=u20090.2. The coexistence of R3c and Cm phases was observed at xu2009=u20090.1. It is found that Bi-based film with coexistence phase exhibits a huge ferroelectric polarization of 230u2009μCu2009cm−2, which can be attributed to the presence of the morphotropic phase boundary.

Improving the capacitive deionisation performance by optimising pore structures of the electrodes.

In this paper, three types of ordered mesoporous carbons (OMCs) were synthesised by an original template method and a modified sol-gel process involving nickel salts. The effects of pore arrangement pattern (ordered and random), and pore size distribution (mesoporous and microporous) on the desalination performance were investigated by comparing mesoporous carbons with activated carbons (ACs). It is found that the mesoporous carbons prepared by addition of nickel salts demonstrated higher specific capacitances than mesoporous carbons without nickel salts and the activated carbon electrodes. Their electrosorptive deionisation properties were also compared in a dilute NaCl solution (conductivity 100 microS cm(-1)), the amount of adsorbed ions are measured by a flow though apparatus in the laboratory. It is found that the amounts of the adsorbed ions are 15.9 micromol g(-1) for OMCs involving nickel in the synthesis process, 10.3 micromol g(-1) for OMC not involving nickel salts and 4.7 micromol g(-1) for ACs.

Self-sintering mechanism of stabilising mesophase pitch fibres

Abstract The ribbon mesophase pitch fibres (MPFs) can be sintered into bulk graphite materials with high thermal conductivity by one-step hot pressing method without introducing any binder. The contents of elements and group compositions as well as oxygenic functional groups of MPFs with different oxidation degrees were investigated by means of group composition analysis, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Then, the self-sintering mechanisms of the MPFs with different oxidation degrees were discussed in terms of their sintering ability and the influences on the structural performances of target materials. The results show that the fibres oxidised moderately have appropriate amount of phenol hydroxyl and carboxyl on their surface, which are beneficial to self-sintering. Meanwhile, the axial preferred orientation of aromatic macromolecules obtained during melt spinning can be maintained in fibre under a high temperature. For example, the materials, self-sintered from the ribbon MPFs oxidised at 260°C, have a thermal conductivity of 609 W m−1 K and a bending strength of 126 MPa.