Qing-Ping Feng

Enhanced Microwave Absorption Performance of Coated Carbon Nanotubes by Optimizing the Fe3O4 Nanocoating Structure

It is well accepted that the microwave absorption performance (MAP) of carbon nanotubes (CNTs) can be enhanced via coating magnetic nanoparticles on their surfaces. However, it is still unclear if the magnetic coating structure has a significant influence on the microwave absorption behavior. In this work, nano-Fe3O4 compact-coated CNTs (FCCs) and Fe3O4 loose-coated CNTs (FLCs) are prepared using a simple solvothermal method. The MAP of the Fe3O4-coated CNTs is shown to be adjustable via controlling the Fe3O4 nanocoating structure. The results reveal that the overall MAP of coated CNTs strongly depends on the magnetic coating structure. In addition, the FCCs show a much better MAP than the FLCs. It is shown that the microwave absorption difference between the FLCs and FCCs is due to the disparate complementarities between the dielectric loss and the magnetic loss, which are related to the coverage density of Fe3O4 nanoparticles on the surfaces of CNTs. For FCCs, the mass ratio of CNTs to Fe3+ is then optimized to maximize the effective complementarities between the dielectric loss and the magnetic loss. Finally, a comparison is made with the literature on Fe3O4-carbon-based composites. The FCCs at the optimized CNT to Fe3+ ratio in the present work show the most effective specific RLmin (28.7 dB·mm-1) and the widest effective bandwidth (RL < -10 dB) (8.3 GHz). The excellent MAP of the as-prepared FCC sample is demonstrated to result from the consequent dielectric relaxation process and the improved magnetic loss. Consequently, the structure-property relationship revealed is significant for the design and preparation of CNT-based materials with effective microwave absorption.

Rapid Laser Printing of Paper-Based Multilayer Circuits

Laser printing has been widely used in daily life, and the fabricating process is highly efficient and mask-free. Here we propose a laser printing process for the rapid fabrication of paper-based multilayer circuits. It does not require wetting of the paper, which is more competitive in manufacturing paper-based circuits compared to conventional liquid printing process. In the laser printed circuits, silver nanowires (Ag-NWs) are used as conducting material for their excellent electrical and mechanical properties. By repeating the printing process, multilayer three-dimensional (3D) structured circuits can be obtained, which is quite significant for complex circuit applications. In particular, the performance of the printed circuits can be exactly controlled by varying the process parameters including Ag-NW content and laminating temperature, which offers a great opportunity for rapid prototyping of customized products with designed properties. A paper-based high-frequency radio frequency identification (RFID) label with optimized performance is successfully demonstrated. By adjusting the laminating temperature to 180 °C and the top-layer Ag-NW areal density to 0.3 mg cm(-2), the printed RFID antenna can be conjugately matched with the chip, and a big reading range of ∼12.3 cm with about 2.0 cm over that of the commercial etched Al antenna is achieved. This work provides a promising approach for fast and quality-controlled fabrication of multilayer circuits on common paper and may be enlightening for development of paper-based devices.

Electrical anisotropy and multidimensional pressure sensor of aligned Fe3O4@silver nanowire/polyaniline composite films under an extremely low magnetic field

A low magnetic field is preferred in preparing aligned composites since a high magnetic field may be harmful to human health. In this study, fine-sized Fe3O4 nanoparticles with diameters of several nanometers are decorated on the surface of Ag-NWs (Fe3O4@Ag-NWs). Controllably aligned Fe3O4@Ag nanowire (Ag-NW)/polyaniline (PANI) composite films are then prepared under an extremely low magnetic field of 26–42 mT, which is much lower than those reported previously (0.1–10 T). As a result, the as-prepared Fe3O4@Ag-NW/PANI composite films show an excellent electrical conductivity from 5.5 × 102 to 4.1 × 103 S cm−1 and a controllable electrical conductivity anisotropy from 1.1 to 6.7. Furthermore, the anisotropic responsive behavior of the Fe3O4@Ag-NW/PANI composite film makes it an ideal candidate for the fabrication of multidimensional pressure sensors. In most studies, conventional strain sensors are fabricated because they are only capable of detecting strains in one single direction due to a strongly coupled electrical conductance change. Finally, the fabrication of a multidimensional pressure sensor based on the as-prepared Fe3O4@Ag-NW/PANI composite film is demonstrated for the first time and a unique anisotropic pressure sensitivity is reported.

Reduced Graphene Oxide Coating with Anti-corrosion and Electrochemical Property Enhancing Effects Applied in Hydrogen Storage System.

Low-capacity retention is the most prominent problem of the magnesium nickel alloy (Mg2Ni), which prevents it from being commercially applied. Here, we propose a practical method for enhancing the cycle stability of the Mg2Ni alloy. Reduced graphene oxide (rGO) possesses a graphene-based structure, which could provide high-quality barriers that block the hydroxyl in the aqueous electrolyte; it also possesses good hydrophilicity. rGO has been successfully coated on the amorphous-structured Mg2Ni alloy via electrostatic assembly to form the rGO-encapsulated Mg2Ni alloy composite (rGO/Mg2Ni). The experimental results show that ζ potentials of rGO and the modified Mg2Ni alloy are totally opposite in water, with values of -11.0 and +22.4 mV, respectively. The crumpled structure of rGO sheets and the contents of the carbon element on the surface of the alloy are measured using scanning electron microscopy, transmission electron microscopy, and energy dispersive spectrometry. The Tafel polarization test indicates that the rGO/Mg2Ni system exhibits a much higher anticorrosion ability against the alkaline solution during charging/discharging. As a result, high-capacity retentions of 94% (557 mAh g-1) at the 10th cycle and 60% (358 mAh g-1) at the 50th cycle have been achieved, which are much higher than the results on Mg2Ni capacity retention combined with the absolute value reported so far to our knowledge. In addition, both the charge-transfer reaction rate and the hydrogen diffusion rate are proven to be boosted with the rGO encapsulation. Overall, this work demonstrates the effective anticorrosion and electrochemical property-enhancing effects of rGO coating and shows its applicability in the Mg-based hydrogen storage system.

Enhancement in mode II interlaminar fracture toughness at cryogenic temperature of glass fiber/epoxy composites through matrix modification by carbon nanotubes and n-butyl glycidyl ether

A typical diglycidyl ether of bisphenol-F (DGEBF)/diethyl toluene diamine (DETD) epoxy system modified by multiwalled carbon nanotubes (MWCNTs) and a reactive aliphatic diluent named n-butyl glycidyl ether (BGE) was used as the matrix for glass fiber composites. The glass fiber (GF) reinforced composites based on the unmodified and modified epoxy matrices were prepared by the hand lay-up hot-press process. Mode II interlaminar fracture toughness at both room temperature (RT) and cryogenic temperature (77K) of the GF reinforced epoxy composites was investigated to examine the effect of the matrix modification. The result showed that the introduction of MWCNTs and BGE at their previously reported optimal contents led to the remarkable enhancement in mode II interlaminar fracture toughness of the composites. Namely, the 22.9% enhancement at RT and the 31.4% enhancement at 77K were observed for mode II interlaminar fracture toughness of the fiber composite based on the optimally modified epoxy matrix by MWCNTs and BGE compared to the unmodified case.

A Novel Type of Battery–Supercapacitor Hybrid Device with Highly Switchable Dual Performances Based on a Carbon Skeleton/Mg2Ni Free-Standing Hydrogen Storage Electrode

The sharp proliferation of high power electronics and electrical vehicles has promoted growing demands for power sources with both high energy and power densities. Under these circumstances, battery-supercapacitor hybrid devices are attracting considerable attention as they combine the advantages of both batteries and supercapacitors. Here, a novel type of hybrid device based on a carbon skeleton/Mg2Ni free-standing electrode without the traditional nickel foam current collector is reported, which has been designed and fabricated through a dispersing-freeze-drying method by employing reduced graphene oxide (rGO) and multiwalled carbon nanotubes (MWCNTs) as a hybrid skeleton. As a result, the Mg2Ni alloy is able to deliver a high discharge capacity of 644 mAh g-1 and, more importantly, a high cycling stability with a retention of over 78% after 50 charge/discharge cycles have been achieved, which exceeds almost all the results ever reported on the Mg2Ni alloy. Simultaneously, the electrode could also exhibit excellent supercapacitor performances including high specific capacities (296 F g-1) and outstanding cycling stability (100% retention after 100 cycles). Moreover, the hybrid device can switch between battery and supercapacitor modes immediately as needed during application. These features make the C skeleton/alloy electrode a highly promising candidate for battery-supercapacitor hybrid devices with high power/energy density and favorable cycling stability.