We report a coaxial fiber supercapacitor, which consists of carbon microfiber bundles coated with multiwalled carbon nanotubes as a core electrode and carbon nanofiber paper as an outer electrode. The ratio of electrode volumes was determined by a half-cell test of each electrode. The capacitance reached 6.3 mF cm(-1) (86.8 mF cm(-2)) at a core electrode diameter of 230 μm and the measured energy density was 0.7 μWh cm(-1) (9.8 μWh cm(-2)) at a power density of 13.7 μW cm(-1) (189.4 μW cm(-2)), which were much higher than the previous reports. The change in the cyclic voltammetry characteristics was negligible at 180° bending, with excellent cycling performance. The high capacitance, high energy density, and power density of the coaxial fiber supercapacitor are attributed to not only high effective surface area due to its coaxial structure and bundle of the core electrode, but also all-carbon materials electrodes which have high conductivity. Our coaxial fiber supercapacitor can promote the development of textile electronics in near future.

The engineering of polymorphs in two-dimensional layered materials has recently attracted significant interest. Although the semiconducting (2H) and metallic (1T) phases are known to be stable in thin-film MoTe2, semiconducting 2H-MoS2 is locally converted into metallic 1T-MoS2 through chemical lithiation. In this paper, we describe the observation of the 2H, 1T, and 1T' phases coexisting in Li-treated MoS2, which result in unusual transport phenomena. Although multiphase MoS2 shows no transistor-gating response, the channel resistance decreases in proportion to the temperature, similar to the behavior of a typical semiconductor. Transmission electron microscopy images clearly show that the 1T and 1T' phases are randomly distributed and intervened with 2H-MoS2, which is referred to as the 1T and 1T' puddling phenomenon. The resistance curve fits well with 2D-variable range-hopping transport behavior, where electrons hop over 1T domains that are bounded by semiconducting 2H phases. However, near 30 K, electrons hop over charge puddles. The large temperature coefficient of resistance (TCR) of multiphase MoS2, -2.0 × 10(-2) K(-1) at 300 K, allows for efficient IR detection at room temperature by means of the photothermal effect.

The in-plane thermal conductivities of suspended monolayer, bilayer, and multilayer MoS films were measured in vacuum by using non-invasive Raman spectroscopy. The samples were prepared by chemical vapor deposition (CVD) and transferred onto preformed cavities on a Au-coated SiO/Si substrate. The measured thermal conductivity (13.3 ± 1.4 W m K) of the suspended monolayer MoS was below the previously reported value of 34.5 ± 4 W m K. We demonstrate that this discrepancy arises from the experimental conditions that differ from vacuum conditions and small absorbance. The measured in-plane thermal conductivity of the suspended MoS films increased in proportion to the number of layers, reaching 43.4 ± 9.1 W m K for the multilayer MoS, which explicitly follows the Fuchs-Sondheimer suppression function. The increase in the thermal conductivity with the number of MoS layers is explained by the reduced phonon boundary scattering. We also observe that the Fuchs-Sondheimer model works for the thickness-dependent thermal conductivity of MoS down to 10 nm in thickness at room temperature, yielding a phonon mean free path of 17 nm for bulk.