No abstract

We report a facile approach to synthesize nanocomposites with Fe 3 O 4 nanopaticles (NPs) attached to reduced graphene oxide (rGO) sheets by a solvothermal process, which combines the growth of Fe 3 O 4 NPs and the reduction of GOs in one single step. These Fe 3 O 4 /rGO nanocomposites were further used to fabricate thin film supercapacitor electrodes by using a spray deposition technique without the addition of insulating binders. It was found that the Fe 3 O 4 /rGO nanocomposites showed much higher specific capacitances than that of either pure rGO or pure Fe 3 O 4 NPs. We further carried out electrochemical characterization of the Fe 3 O 4 /rGO nanocomposites with different Fe 3 O 4 : rGO weight ratios (e.g. I Fe 3 O 4 : rGO ) and showed that Fe 3 O 4 /rGO nanocomposites with I Fe 3 O 4 : rGO ¼ 2.8 exhibited the highest specific capacitance of 480 F g À1 at a discharge current density of 5 A g À1 with the corresponding energy density of 67 W h kg À1 at a power density of 5506 W kg À1 . These Fe 3 O 4 /rGO nanocomposites also showed stable cycling performance without any decrease in the specific capacitance after 1000 charge/discharge cycles.

We show that embedding of a surface ligand can dramatically affect the metal-metal interfacial energy, making it possible to create nanostructures in defiance of traditional wisdom. Despite matching Au-Ag lattices, Au-Ag hybrid NPs can be continuously tuned from concentric core-shell, eccentric core-shell, acorn, to dimer structures. This method can be extended to tune even Au-Au and Ag-Ag interfaces.

In this work, we show that the maximum thermopower of few layers graphene (FLG) films could be greatly enhanced up to ∼700 μV/K after oxygen plasma treatment. The electrical conductivities of these plasma treated FLG films remain high, for example, ∼10(4) S/m, which results in power factors as high as ∼4.5 × 10(-3) W K(-2) m(-1). In comparison, the pristine FLG films show a maximum thermopower of ∼80 μV/K with an electrical conductivity of ∼5 × 10(4) S/m. The proposed mechanism is due to generation of local disordered carbon that opens the band gap. Measured thermopowers of single-layer graphene (SLG) films and reduced graphene oxide (rGO) films were in the range of -40 to 50 and -10 to 20 μV/K, respectively. However, such oxygen plasma treatment is not suitable for SLG and rGO films. The SLG films were easily destroyed during the treatment while the electrical conductivity of rGO films is too low.

Although theoretical calculations indicate that the thermoelectric figure of merit, ZT, of carbon nanotubes (CNTs) could reach >2, the experimentally reported ZT values of CNTs are typically in the range of 10 À3 -10 À2 , which is not attractive for thermal energy conversion applications. In this work, we report the preparation of flexible CNT bulky paper for thermoelectric applications. The ZT values of the CNT bulky papers could be significantly enhanced by Ar plasma treatment, i.e. increasing it from 0.01 for pristine CNTs to 0.4 for Ar-plasma treated CNTs. The improved thermoelectric properties were mainly due to the greatly increased Seebeck coefficients and a reduction in the thermal conductivities, although the electrical conductivities also decreased. Such an improvement makes the plasma treated CNT bulky papers promising as a new type of thermoelectric material for certain niche applications as they are easily processed, mechanically flexible and durable, and chemically stable.