Current density, graphene

Fig. 6.7 (a) The variation of electrical conductivity of PVA-EG hybrid with increasing graphene content. Inset shows the dependence of dielectric constant for the hybrid, (b) The variation of conductivity of the polystyrene-graphene hybrid with filler content. Inset shows the four probe setup for in-plane and transverse measurements and the computed distributions of the current density for in-plane condition (reference [8]). 

As mentioned above, electronic properties of CNTs depend on the chirality and presence of defects in the scrolled graphene layer. Metallic nanotubes can have an electric current density more than 1,000 times greater than metals such as silver and copper. All nanotubes are expected to be very good thermal conductors along the tube, but good insulators laterally to the tube axis.8... 

Because of the symmetry and unique electronic structure of graphene, the structure of a nanotube strongly affects its electrical properties. For a given (n,m) nanotube, ifn-m = 3q (where is an integer), then the nanotube is metallic, otherwise the nanotube is a semiconductor. Thus, all armchair (n = m) nanotubes are metallic, and nanotubes (5,0), (6,4), (9,1), etc. are semiconducting. In theory, metallic nanotubes can have an electrical current density more than 1000 times greater than metals such as silver and copper [5]. 

The oxides of heavier, second-row transition metal elements are commonly discarded for their use in high gravimetric capacity applications. Nevertheless, an enhanced nanoscale conduction capability of a Mo02/Graphene composite for high performance anodes in lithium-ion batteries should be highlighted. The composite electrode showed a reversible capacity of 605 mA h g" in the initial cycle at current density of 540 mA g and upon increasing the current density to 2045 mA g" the electrode shows a reversible capacity of 300 mA h g" [135]. 

Keywords-. Li-ion battery, conducting polymers, polyaniline, polypyrrole, polythiophene, graphene, carbon nanotubes, LiFePO, MnO, V Oj, Si, SnO, Fe O, nanocomposites, intercalation, electrolyte, electrode, cathode, anode, energy density, power density, rate capability, voltage, current density, charge/discharge capacity, Nyquist plots, efficiency, cyclability... 

Among the composites of graphene/polymer, graphene/CPs can be produced not only by in situ chemical polymerization but also by in situ electrochemical polymerization [149,150]. Electrochemical polymerization yields mechanically stable composite films and they can be directly used as the electrodes of energy storage devices. Furthermore, electrochemical polymerization can be precisely controlled by the applied potential, current density, and polymerization time. 

Hierarchical porous graphene/polyaniline composite film with a superior rate performance for supercapacitors was fabricated by chemical polymerization method. This composite exhibited 385 F/g at a current density of 0.5 A/g, with a capacity retention of 94% as current density was varied from 0.5 to 10 A/g. This superior rate performance was demonstrated to be due to the interconnected porous structure of the film, which allowed electrolyte ions to pass through quickly during the rapid charge-discharge process [62]. 

Three-dimensional (3D) polyaniline (PANI)-graphene nanoribbon (GNR)-carbon nanotube (CNT) composite, PANI-GNR-CNT, was prepared via in-situ polymerization of aniline monomer on the surface of a GNR-CNT hybrid. This hierarchical PANI-GNR-CNT composite with the two-electrode cell assembly showed much higher specific capacitance (890 F/g) than the GNR-CNT hybrid (195 F/g) and neat PANI (283 F/g) at a discharge current density of 0.5 A/g. This composite exhibited good cycling stability with a retention ratio of 89% after 1000 cycles [63]. 

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