Large-area MoS(2) atomic layers are synthesized on SiO(2) substrates by chemical vapor deposition using MoO(3) and S powders as the reactants. Optical, microscopic and electrical measurements suggest that the synthetic process leads to the growth of MoS(2) monolayer. The TEM images verify that the synthesized MoS(2) sheets are highly crystalline.

The Ni3S2 nanoparticles with the diameters ranging from 10 to 80 nm are grown on the backbone of conductive multiwalled carbon nanotubes (MWCNTs) using a glucose-assisted hydrothermal method. It is found that the Ni3S2 nanoparticles deposited on MWCNTs disassemble into smaller components after the composite electrode is activated by the consecutive cyclic voltammetry scan in a 2 M KOH solution. Therefore, the active surface area of the Ni3S2 nanoparticles is increased, which further enhances the capacitive performance of the composite electrode. Because the synergistic effect of the Ni3S2 nanoparticles and MWCNTs on the capacitive performance of the composite electrode is pronounced, the composite electrode shows a high specific capacitance of 800 F/g and great cycling stability at a current density of 3.2 A/g. To examine the capacitive performance of the composite electrode in a full-cell configuration, an asymmetric supercapacitor device was fabricated by using the composite of Ni3S2 and MWCNTs as the cathode and activated carbon as the anode. The fabricated device can be operated reversibly between 0 and 1.6 V, and obtain a high specific capacitance of 55.8 F/g at 1 A/g, which delivers a maximum energy density of 19.8 Wh/kg at a power density of 798 W/kg. Furthermore, the asymmetric supercapacitor shows great stability based on the fact that the device retains 90% of its initial capacitance after a consecutive 5000 cycles of galvanostatic charge-discharge performed at a current density of 4 A/g.

In the current study, the nanocomposite of molybdenum disulfide and multi-walled carbon nanotubes (MWCNT@MoS 2 ) was proposed for the first time as a counter electrode (CE) catalyst in dye-sensitized solar cells (DSSCs) to speed up the reduction of triiodide (I 3 À ) to iodide (I À ). This novel catalyst was synthesized by simply mixing MWCNTs and MoS 2 in an acidic solution and then converting the solid intermediate into the MWCNT@MoS 2 nanocomposite in a H 2 flow at 650 C. X-ray powder diffraction, Raman and X-ray photoemission spectroscopy confirmed the composition and the structure of the MWCNT@MoS 2 nanocomposite. The microstructure details of the nanocomposite were studied by transmission electron microscopy, showing that only a few-layers of the MoS 2 nanosheets were formed on the MWCNT surface. This unique structure is beneficial to the improvement of the catalytic activity of MWCNT@MoS 2 towards the reduction of I 3 À. The extensive cyclic voltammograms (CV) showed that the cathodic current density of the MWCNT@MoS 2 CE was higher than those of MoS 2 , MWCNT and sputtered Pt CEs due to the increased active surface area of the former. Moreover, the peak current densities of the MWCNT@MoS 2 CE showed no sign of degradation after consecutive 100 CV tests, suggesting the great electrochemical stability of the MWCNT@MoS 2 CE. Furthermore, the MWCNT@MoS 2 CE demonstrated an impressive low chargetransfer resistance (1.69 U cm 2 ) for I 3 À reduction. Finally, the DSSC assembled with the MWCNT@MoS 2 CE showed a high power conversion efficiency of 6.45%, which is comparable to the DSSC with Pt CE (6.41%).

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