Fe3O4 nanoparticle decorated three-dimensional porous carbon/MoS2 composites as anodes for high performance lithium-ion batteries.

Molybdenum disulfide (MoS2) is a promising anode material for lithium-ion batteries owing to its high theoretical capacity and low cost. However, it exhibits low electrical conductivity and volume expansion, resulting in poor electrochemical performance. In this work, three-dimensional porous carbon/MoS2 composites with Fe3O4 nanoparticles (C-MF) are synthesized via a mix-bake-wash method. The few-layered MoS2 in the porous carbon matrix provides improved electrical conductivity and facilitates lithium ion diffusion, so the composites exhibit a high specific capacity of 939.6 mA h g-1 on average at 0.1 A g-1 and a high rate capability (515.9 mA h g-1 at 5 A g-1). Moreover, the Fe3O4 nanoparticles in C-MF, which are anchored on the composites, improve the specific capacity and effectively mitigate diffusion of lithium polysulfides during cycling, resulting in remarkable cycling stability (590.1 mA h g-1 after 500 cycles at 2 A g-1). This work suggests that not only C-MF but also C@MoS2 with other metal oxides synthesized using this facile strategy have potential for energy-related applications.

Multi-Heteroatom-Doped Hollow Carbon Attached on Graphene Using LiFePO4 Nanoparticles as Hard Templates for High-Performance Lithium-Sulfur Batteries.

P, O, and N heteroatom-doped hollow carbon on graphene (PONHC/G) from nanosized LiFePO4 (LFP) as a hard template is shown to be a very efficient sulfur host for lithium-sulfur (Li-S) batteries. The PONHC/G made from LFP nanoparticles as hard materials provides sufficient voids with various pore sizes for sulfur storage, and doping of the carbon structures with various heteroatoms minimized dissolution/diffusion of the polysulfides. The obtained PONHC/G can store sulfur and mitigate diffusion of the dissolved polysulfide owing to the well-organized host structure and the strong chemical affinity for polysulfides because of the polarization effect of the heteroatom dopants. As a cathode, S@PONHC/G shows excellent cycle stability and rate capability, as confirmed by polysulfide adsorption analysis. Therefore, PONHC/G may show high potential as a sulfur scaffold in the commercialization of Li-S batteries through additional modification and optimization of these host materials.

Electrochemically exfoliated graphene as a novel microwave susceptor: the ultrafast microwave-assisted synthesis of carbon-coated silicon-graphene film as a lithium-ion battery anode.

Graphene nanocomposites have attracted much attention in many applications due to their superior properties. However, preparing graphene nanocomposites requires a time-consuming thermal treatment to reduce the graphene or synthesize nanomaterials, in most cases. We present an ultrafast synthesis of a carbon-coated silicon-graphene nanocomposite using a commercial microwave system. Electrochemically exfoliated graphene is used as a novel microwave susceptor to deliver efficient microwave energy conversion. Unlike graphene oxide, it does not require a time-consuming pre-thermal reduction or toxic chemical reduction to absorb microwave radiation efficiently. A carbon-coated silicon nanoparticle-electrochemically exfoliated graphene nanocomposite film was prepared by a few seconds' microwave irradiation. The sp2 domains of graphene absorb microwave radiation and generate heat to simultaneously reduce the graphene and carbonize the polydopamine carbon precursor. The as-prepared N-doped carbon-coated silicon-graphene film was used as a lithium-ion battery anode. The N-doped carbon coating decreases the contact resistance between silicon nanoparticles and graphene provides a wide range conductive network. Consequently, it exhibited a reversible capacity of 1744 mA h g-1 at a current density of 0.1 A g-1 and 662 mA h g-1 at 1.0 A g-1 after 200 cycles. This method can potentially be a general approach to prepare various graphene nanocomposites in an extremely short time.

A sensitive electrochemical sensor using an iron oxide/graphene composite for the simultaneous detection of heavy metal ions.

We report an analytical assessment of an iron oxide (Fe2O3)/graphene (G) nanocomposite electrode used in combination with in situ plated bismuth (Bi) working as an electrochemical sensor for the determination of trace Zn(2+), Cd(2+), and Pb(2+). The as-synthesized nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, thermo-gravimetric analyzer, and X-ray diffraction. The electrochemical properties of the Fe2O3/G/Bi composite modified electrode were investigated. Differential pulse anodic stripping voltammetry was applied for the detection of metal ions. Due to the synergetic effect between graphene and the Fe2O3 nanoparticles, the modified electrode showed improved electrochemical catalytic activity high sensitivity toward trace heavy metal ions. Several parameters such as the preconcentration potential, bismuth concentration, preconcentration time, and pH were carefully optimized to determine the target metal ions. Under optimized conditions, the linear range of the electrode was 1-100µgL(-1) for Zn(2+), Cd(2+), and Pb(2+), and the detection limits were 0.11µgL(-1), 0.08µgL(-1), and 0.07µgL(-1), respectively (S/N =3). Repeatability (% RSD) was found to be 1.68% for Zn(2+), 0.92% for Cd(2+), and 1.69% for Pb(2+) for single sensor with 10 measurements and 0.89% for Zn(2+), 1.15% for Cd(2+), and 0.91% for Pb(2+) for 5 different electrodes. The Fe2O3/G/Bi composite electrode was successfully applied to the analysis of trace metal ions in real samples. The solventless thermal decomposition method applied to the simple and easy synthesis of nanocomposite electrode materials can be extended to the synthesis of nanocomposites and promising electrode materials for the determination of heavy metal ions.