Showing papers by "Yong Wang published in 2013"

Graphene-wrapped CoS nanoparticles for high-capacity lithium-ion storage.

Abstract: Graphene-wrapped CoS nanoparticles are synthesized by a solvothermal approach. The product is significantly different from porous CoS microspheres prepared in the absence of graphene under similar preparation conditions. The CoS microspheres and CoS/graphene composite are fabricated as anode materials for lithium-ion batteries. The CoS/graphene composite is found to be better suitable as an anode in terms of higher capacity and better cycling performances. The nanocomposite exhibits an unprecedented high reversible capacity of 1056 mA h/g among all cobalt sulfide-based anode materials. Good cycling performances are also observed at both small and high current rates.

Interconnected tin disulfide nanosheets grown on graphene for Li-ion storage and photocatalytic applications.

Abstract: Reduced graphene oxide (RGO) nanosheet-supported SnS2 nanosheets are prepared by a one-step microwave-assisted technique. These SnS2 nanosheets are linked with each other and dispersed uniformly on RGO surface. The SnS2-RGO sheet-on-sheet nanostructure exhibits good electrochemical performances as an anode material for lithium ion batteries. It shows larger-than-theoretical reversible capacities at 0.1 C and excellent high-rate capability at 1 C and 5 C. The composite is also for the first time identified as an excellent visible light-driven catalyst of rhodamine B and phenol with high degradation efficiencies. The removal rates of rhodamine B and phenol are 100 and 83.2%, respectively, for the SnS2-RGO composite, whereas these values are only 64.8 and 51.5% for pristine SnS2 after the same irradiation times. The outstanding electrochemical or photocatalytic performances of the composite have been attributed to the complementary effect of RGO and SnS2 in the perfect sheet-on-sheet composition nanostructure.

Large and fast reversible Li-ion storages in Fe2O3-graphene sheet-on-sheet sandwich-like nanocomposites

Abstract: Fe2O3 nanosheets and nanoparticles are grown on graphene by simply varying reaction solvents in a facile solvothermal/hydrothermal preparation. Fe2O3 nanosheets are uniformly dispersed among graphene nanosheets, forming a unique sheet-on-sheet nanostructure. Due to the structure affinity between two types of two dimensional nanostructures, graphene nanosheets are separated better by Fe2O3 nanosheets compared to nanoparticles and their agglomeration is largely prevented. A large surface area of 173.9 m2 g−1 is observed for Fe2O3-graphene sheet-on-sheet composite, which is more than two times as large as that of Fe2O3-graphene particle-on-sheet composite (81.5 m2 g−1). The sheet-on-sheet composite is found to be better suitable as an anode for Li-ion battery. A high reversible capacity of 662.4 mAh g−1 can be observed after 100 cycles at 1000 mA g−1. The substantially improved cycling performance is ascribed to the unique structure affinity between Fe2O3 nanosheets and graphene nanosheets, thus offering complementary property improvement.

Confined Volume Change in Sn-Co-C Ternary Tube-in-Tube Composites for High-Capacity and Long-Life Lithium Storage

Abstract: All high capacity Li-alloy anodes for Li-ion battery suffer from enormous volume expansion and extraction during the lithium-ion insertion and extraction process. A Sn-Co-CNT@CNT ternary tube-in-tube nanostructure is prepared by an in situ template technique and shows perfect structure suitability to solve the critical volume change problem. The morphology, size, and quantity of the filled CNT-supported Sn-Co nanoparticles can be also tuned by adjusting the experimental conditions to achieve optimal electrochemical performances. The tube-in-tube product exhibits larger-than-theoretical reversible capacities of 890–811 mA h g−1 at 0.1C in 200 cycles and excellent rate capability and high-rate cycling stability. The excellent electrochemical performance is mainly attributed to the confined volume change in the nanotube cavities and ensured permanent electrical connectivity of the immobilized Sn-Co anodes.

Microwave-assisted solvothermal synthesis of 3D carnation-like SnS2 nanostructures with high visible light photocatalytic activity

Abstract: Novel 3D carnation-flowerlike hexagonal SnS2 hierarchical structures have been successfully synthesized through a simple microwave-assisted solvothermal process. The as-prepared products were characterized by power X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high-resolution transmission electron micrographs (HRTEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activity of the sample under visible-light irradiation (λ > 420 nm) was evaluated by the degradation of two different organic pollutants, rhodamine B (RhB) and phenol. The results reveal that the carnation-flowerlike SnS2 architectures show much higher photocatalytic activity than the SnS2 nanoparticles. The high catalytic performance of the SnS2 architectures comes from their hierarchical mesoporous structures, high BET surface area, high surface-to-volume ratios, and increased light absorbance. In addition, the SnS2 hierarchical architectures are stable during the photocatalytic reaction and can be used repeatedly.

Sulfur film-coated reduced graphene oxide composite for lithium–sulfur batteries

Abstract: This paper reports a cathode material of a graphene–sulfur film nanostructure synthesized by a facile wet chemical oxidation technique. The hybrid material is synthesized by using ferric chloride as an oxidizing agent and polysulfide as the sulfur source. The oxidizing agent FeCl3 is introduced as a soft film template to form a sulfur film on graphene oxide (GO). This is ascribed to the formation of a ferric cations double layer (FCDL) on the graphene oxide surface with many negative functional groups. Material characterizations reveal that GO is reduced to reduced graphene oxide (RGO) and the sulfur materials are embedded in a three dimensional conducting composite network of RGO and polyethylene glycol (PEG), forming a continuous sulfur film coating on RGO. When fabricated as a cathode material for rechargeable lithium ion batteries, the sulfur film-coated graphene composite electrode exhibits high capacity, improved Coulombic efficiency and extraordinarily stable cycling performance. It is believed that the sulfur film is coated on RGO and protected by the PEG network, and therefore the high solubility of the polysulfide anions formed as the reaction intermediate in the discharge and charge processes is relieved to a large extent. The electronic conductivity of insulating sulfur is also improved substantially in the RGO–S–PEG network.