Yujin Chen

Graphene/polyaniline nanorod arrays: synthesis and excellent electromagnetic absorption properties

In the paper, we find that graphene has a strong dielectric loss, but exhibits very weak attenuation properties to electromagnetic waves due to its high conductivity. As polyaniline nanorods are perpendicularly grown on the surface of graphene by an in situ polymerization process, the electromagnetic absorption properties of the nanocomposite are significantly enhanced. The maximum reflection loss reaches −45.1 dB with a thickness of the absorber of only 2.5 mm. Theoretical simulation in terms of the Cole–Cole dispersion law shows that the Debye relaxation processes in graphene/polyaniline nanorod arrays are improved compared to polyaniline nanorods. The enhanced electromagnetic absorption properties are attributed to the unique structural characteristics and the charge transfer between graphene and polyaniline nanorods. Our results demonstrate that the deposition of other dielectric nanostructures on the surface of graphene sheets is an efficient way to fabricate lightweight materials for strong electromagnetic wave absorbents.

Porous Co3O4 nanoneedle arrays growing directly on copper foils and their ultrafast charging/discharging as lithium-ion battery anodes

Ultrafast charging/discharging of lithium-ion battery anodes is realized from porous Co(3)O(4) nanoneedle arrays growing on copper foils. Their charge time can be shortened to ∼6 s, their reversible capacity at 0.5C rate is 1167 mAh/g. This implies that nano-arrays growing directly on copper foils are good candidates for anodes.

Graphene–Fe3O4 nanohybrids: Synthesis and excellent electromagnetic absorption properties

Graphene (G)–Fe3O4 nanohybrids were fabricated by first depositing β-FeOOH crystals with diameter of 3–5 nm on the surface of the graphene sheets. After annealing under Ar flow, β-FeOOH nanocrystals were reduced to Fe3O4 nanoparticles by the graphene sheets, and thus G–Fe3O4 nanohybrids were obtained. The Fe3O4 nanoparticles with a diameter of about 25 nm were uniformly dispersed over the surface of the graphene sheets. Moreover, compared with other magnetic materials and the graphene, the nanohybrids exhibited significantly increased electromagnetic absorption properties owing to high surface areas, interfacial polarizations, and good separation of magnetic nanoparticles. The maximum reflection loss was up to −40.36 dB for G–Fe3O4 nanohybrids with a thickness of 5.0 mm. The nanohybrids are very promising for lightweight and strong electromagnetic attenuation materials.

A sandwich-type three-dimensional layered double hydroxide nanosheet array/graphene composite: fabrication and high supercapacitor performance

In this study, we have developed, for the first time, a facile in situ growth process to prepare a hierarchical three-dimensional (3D) composite composed of graphene layers with layered double hydroxide (LDH) nanosheet arrays grown on both sides. The fabrication process involves coating AlOOH colloids onto the graphene surfaces and the subsequent in situ growth of layered NiAl–LDH nanosheet arrays on the surfaces of graphene sheets via a hydrothermal process. It is found that the NiAl–LDH nanosheet arrays grow perpendicularly and uniformly on both sides of the graphene sheets, constructing a hierarchical 3D nanocomposite with an interesting sandwich structure. This uniquely structured composite has a large specific surface area (184.7 m2 g−1) and typical mesoporous characteristics, which are favorable for achieving high pseudocapacitance performance. Our results reveal that the composite has a specific capacitance of 1329 F g−1 at a current density of 3.57 A g−1, and the specific capacitance still remains as high as 851 F g−1 even when the current density is increased to 17.86 A g−1. The specific capacitance remains at 91% (823 F g−1) after 500 cycles at 15.30 A g−1 compared with 74% for pure Ni/Al–LDH. The in situ growth method may pave a way to design and fabricate diverse LDH/graphene composites with interesting structures for potential application in supercapacitors and other fields.

Three‐Dimensional Hierarchical Architectures Constructed by Graphene/MoS2 Nanoflake Arrays and Their Rapid Charging/Discharging Properties as Lithium‐Ion Battery Anodes

Charged up: Three-dimensional architectures constructed from graphene/MoS2 nanoflake arrays have been successfully fabricated by a one-step hydrothermal method. MoS2 nanoflakes with thicknesses less than 13 nm grow vertically on both sides of graphene sheets (see figure), which allows the architectures to be more stable during charging and discharging. Even at a high current density of 8000 mA g(-1), their discharge capacity is still up to 516 mA h g(-1).

Graphene–Co3O4 nanocomposite as an efficient bifunctional catalyst for lithium–air batteries

A facile hydrothermal route has been developed to prepare graphene–Co3O4 nanocomposites. The graphene–Co3O4 nanocomposite catalyst demonstrates an excellent catalytic activity toward oxygen-reduction reaction including a considerably more positive half-wave potential (−0.23 V) than that of pristine graphene (−0.39 V), as well as higher cathodic currents. More importantly, this catalyst shows better long-term durability than the commercial Pt/C catalyst in an alkaline solution. The preliminary results indicate that the graphene–Co3O4 nanocomposite is an efficient and stable bifunctional catalyst for Li–air batteries and may be an alternative to the high-cost commercial Pt/C catalyst for the ORR/OER in alkaline solutions.

Growth of Ultrathin MoS2 Nanosheets with Expanded Spacing of (002) Plane on Carbon Nanotubes for High-Performance Sodium-Ion Battery Anodes

A hydrothermal method was developed to grow ultrathin MoS2 nanosheets, with an expanded spacing of the (002) planes, on carbon nanotubes. When used as a sodium-ion battery anode, the composite exhibited a specific capacity of 495.9 mAh g(-1), and 84.8% of the initial capacity was retained after 80 cycles, even at a current density of 200 mA g(-1). X-ray diffraction analyses show that the sodiation/desodiation mechanismis based on a conversion reaction. The high capacity and long-term stability at a high current ate demonstrate that the composite is a very promising candidate for use as an anode material in sodium-ion batteries.

Three-dimensional hierarchical MoS2 nanoflake array/carbon cloth as high-performance flexible lithium-ion battery anodes

Flexible lithium-ion batteries are the key to powering a new generation of flexible electronics such as roll-up displays, smart electronics, and wearable devices. Here we report, for the first time, one-step hydrothermal synthesis of a three-dimensional (3D) hierarchical MoS2 nanoflake array/carbon cloth which shows potential for improving the performance of flexible lithium-ion batteries. Structural characterizations show that the 3D hierarchical MoS2 nanoflake array/carbon cloth has a similar ordered woven structure to the bare carbon cloth. Each carbon microfiber is covered with many highly ordered 3D MoS2 nanoflake arrays, and a typical MoS2 nanoflake, with expanded spacing of the (002) crystal plane, has a uniform width of about 400 nm and a thickness of less than 15 nm. The flexible 3D MoS2 nanoflake array/carbon cloth as a flexible lithium-ion battery anode has a high reversible capacity of 3.0–3.5 mA h cm−2 at a current density of 0.15 mA cm−2 and outstanding discharging/charging rate stability. Moreover, a fabricated full battery, with commercial LiCoO2 powder and the hierarchical architectures as electrodes, exhibits high flexibility and good electrochemical performance, and can light a commercial red LED even after 50 cycles of bending the full battery.

Synthesis, magnetic and electromagnetic wave absorption properties of porous Fe3O4/Fe/SiO2 core/shell nanorods

Porous Fe3O4/Fe/SiO2 core/shell nanorods were fabricated, in which the diameter of the pores was 5–30 nm. The magnetic and electromagnetic properties were investigated. The temperature dependent magnetic measurements showed that these nanorods were ferromagnetic with a Verwey temperature of 129 K. The electromagnetic data indicated that effective complementarities between the dielectric loss and the magnetic loss were realized, suggesting that they have excellent electromagnetic wave absorption properties. Thus the porous core/shell nanorods could be used as a kind of candidate absorber.

Molybdenum carbide nanocrystal embedded N-doped carbon nanotubes as electrocatalysts for hydrogen generation

N-doped carbon nanotubes embedded with molybdenum carbide nanocrystals with a size less than 3 nm were fabricated. Due to their small size, tubular characteristics and high conductivity, the hybrid nanotubes exhibit superior activity for the hydrogen evolution reaction, including small overpotential, large cathodic current density and high exchange current density.