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Multi-angle modulation properties of electrolyte gated graphene visible-infrared modulators with supercapacitor structures have been examined in both experiment and theory. Both transmission and reflection geometries have been studied, and the results show that all the modulations of these devices are gate voltage and wavelength dependent. Maximum modulation depths for transmission device ∼3% and reflection modulator ∼5% are obtained, which can be attributed to the electrolyte assistant considerable change of the Fermi energy with tunable gate voltage. Moreover, little incident angle dependency can be observed with a certain gate voltage. Theoretical analysis based on the different tangential and normal optical responses of the quartz/graphene/eletrolyte interface has been used to explain the phenomena, which indicated a common effect of p -polarized and s -polarized light. This work offers useful insight into a multi-angle application of the graphene-based optical modulator in visible-infrared region. [ABSTRACT FROM AUTHOR]

A simple hard template method and hydrothermal process have been employed to fabricate a self-standing hierarchical porous MnO 2 /graphene film. Thus-constructed electrode materials for binder-free supercapacitors exhibit a high specific capacitance of 266.3 F g −1 at the density of 0.2 A g −1 . Moreover, the two-electrode device demonstrates an excellent rate capability and cycling stability with capacitance retention of 85.1% after 2000 charge–discharge cycles at a current density of 1 A g −1 . The porous nanostructured design can effectively improve the specific surface areas and account for the shorter relaxation time for the electrodes, resulting in a high electrochemical performance. [ABSTRACT FROM AUTHOR]

Abstract: Incorporation of reduced graphene oxide (rGO) in Co3O4 matrix is systematically investigated through a chemical route for supercapacitors. The α-Co(OH)2 supported by graphene oxide is first fabricated by a chemical precipitation approach. Thermal decompositions of these precursors at the given temperature (150°C) lead to rGO/Co3O4 composites. Measurement results show that the morphology and electrochemical activity of the rGO/Co3O4 composites are influenced significantly by the mass ratios of rGO to Co3O4. When used as electrode materials in supercapacitors, the composite with mass ratio of 0.22:1 (rGO:Co3O4) achieves the specific capacitance as high as 291Fg−1 at 1Ag−1 in the potential range of −0.4 to 0.55V, as compared with each individual counterpart (56 and 161Fg−1 for rGO and Co3O4, respectively). In addition, the excellent rate capability and well cycling ability are observed in the composite electrodes. The enhanced electrochemical performance is indicative of a positive synergistic effect between rGO and Co3O4. These results suggest the importance and great potential of graphene based composites in the development of high-performance energy-storage systems. [Copyright &y& Elsevier]

Abstract: This work demonstrates a novel and facile route for preparing graphene-based composites comprising of metal oxide nanoparticles and graphene. A graphene nanosheet–bismuth oxide composite as electrode materials of supercapacitors was firstly synthesized by thermally treating the graphene–bismuth composite, which was obtained through simultaneous solvothermal reduction of the colloidal dispersions of negatively charged graphene oxide sheets in N,N-dimethyl formamide (DMF) solution of bismuth cations at 180°C. The morphology, composition, and microstructure of the composites together with pure graphite oxide, and graphene were characterized using powder X-ray diffraction (XRD), FT-IR, field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), thermogravimetry and differential thermogravimetry (TG–DTG). The electrochemical behaviors were measured by cyclic voltammogram (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS). The specific capacitance of 255Fg−1 (based on composite) is obtained at a specific current of 1Ag−1 as compared with 71Fg−1 for pure graphene. The loaded-bismuth oxide achieves a specific capacitance as high as 757Fg−1 even at 10Ag−1. In addition, the graphene nanosheet–bismuth oxide composite electrode exhibits the excellent rate capability and well reversibility. [Copyright &y& Elsevier]