Dacheng Zhang

One-Step Electrophoretic Deposition of Reduced Graphene Oxide and Ni(OH)2 Composite Films for Controlled Syntheses Supercapacitor Electrodes

A facile, rapid, scalable, and environmentally friendly electrophoretic deposition (EPD) approach has been developed for the fabrication of reduced graphene oxide (RGO) and Ni(OH)(2) syntheses based on EPD of graphene oxide (GO) and Ni(NO(3))(2) colloidal suspension. Nickel ion decoration made GO positively charged and further made cathodic EPD feasible. Direct assembly by one-step EPD facilitated transformation from GO to RGO and resulted in multilayer or flower-like RGO/Ni(OH)(2) hybrid films on different substrates. X-ray diffraction analysis suggested that the crystal structures of Ni(OH)(2) depended on the colloidal suspension and the substrate. Further transmission electron microscopy characterization indicated that Ni(OH)(2) nanoclusters composed of 5-10 nm nanoparticles in grain size were homogeneously dispersed and anchored on the RGO. The resulting 100% binder-free RGO/Ni(OH)(2) electrodes exhibited excellent pseudocapacitive behavior with high specific capacitance of 1404 F g(-1) at 2 A g(-1), high rate capability, and good electrochemical cyclic stability. These results paved the way for EPD to produce RGO-based nanocomposite films for high-performance energy storage devices.

High-performance supercapacitors based on a graphene–activated carbon composite prepared by chemical activation

Graphene has been widely applied as a promising supercapacitor material based on the electric double-layer mechanism. In order to solve the dispersed problem of graphene, noncovalent functionalized graphene is prepared. However, not all of these functionalized graphene materials can be employed in supercapacitors due to non-electrochemically activated molecules absorbed on graphene. Here we find a route of chemical activation with KOH to transfer noncovalent functionalized graphene to a graphene–activated carbon composite with a high specific surface area. Stable graphene colloids absorbed by oligomers of p-phenylene diamine was produced during the reduction of graphite oxide. KOH can homogeneously contact the solid graphene nanosheets after drying the colloid. Chemical activation by annealing the graphene based hybrid with KOH leads to a greatly increased specific surface area of 798 m2 g−1. The resulting graphene–activated carbon composite has a good capacitance of 122 F g−1 and energy density of 6.1 Wh kg−1 in aqueous electrolyte. The supercapacitor exhibits maximum energy densities of 52.2 and 99.2 Wh kg−1 in an ionic liquid electrolyte at room temperature and 80 °C, respectively.

Large-Scale Production of Nanographene Sheets with a Controlled Mesoporous Architecture as High-Performance Electrochemical Electrode Materials

Graphene is considered as a rising-star material because of its unique properties and it is a promising material for applications in many fields. In recent years, experiments on graphene fabricated by using versatile methods have shed light on the crucial problem of aggregation and restacking, which is induced by strong π-π stacking and van der Waals forces, but preparation methods for real-world applications are still a great challenge. Here we report a facile, rapid, and environmentally friendly process, the burn-quench method, that allows large-scale and controlled synthesis of ordered mesoporous nanographene with 1-5 layers, which has a high surface area and electric conductivity. Electrodes composed of nanographene with a mesoporous architecture used both in electrochemical capacitors and lithium-ion batteries have a high specific capacitance, rate capability, energy density, and cyclic stability. Our results represent an important step toward large-scale graphene synthesis based on this new burn-quench method for applications in high-performance electrochemical energy storage devices.