A light-fostered supercapacitor performance of multi-layered ReS2 grown on conducting substrates.

The light-fostered supercapacitor performance introduces a new realm in the field of smart energy storage applications. Transition metal dichalcogenides (TMDCs) with direct band gap are intriguing candidates for developing a light-induced supercapacitor that can enhance energy storage when shined with light. Many TMDCs show a transition from a direct to indirect band gap as the layer number increases, while ReS2 possesses a direct band gap in both bulk and monolayer forms. The growth of such multi-layered 2D materials with high surface area on conducting substrates makes them suitable for smart energy storage applications with the ability to tune their performance with light irradiation. In this report, we present the growth of vertically aligned multi-layered ReS2 with large areal coverage on various conducting and non-conducting substrates, including stainless steel via chemical vapor deposition (CVD). To investigate the effect of light illumination on the charge storage performance, electrochemical measurements have been performed in dark and light conditions. Cyclic voltammetry (CV) curves showed an increase in the area enclosed by the curve, manifesting the increased charge storage capacity under light illumination as compared to dark. The volumetric capacitance value calculated from charging-discharging curves has increased from 17.9 F cm-3 to 29.8 F cm-3 with the irradiation of light for the as-grown ReS2 on a stainless steel plate. More than 1.5 times the capacitance enhancement is attributed to excess electron-hole pairs generated upon light illumination, contributing to the charge storage in the presence of light. The electrochemical impedance spectroscopy further augments these results. The high cyclic stability is attained with a capacitance retention value of 81% even after 10 000 repeated charging-discharging cycles.

Fabrication of iron oxide-CNT based flexible asymmetric solid state supercapacitor device with high cyclic stability.

Integration of high surface area nanostructures with conducting and deformable electrodes at large scale are of significant importance for flexible supercapacitors with high cyclic stability and low cost. Here, we report water assisted meter scale growth of aligned iron oxide and CNT 1D nanostructures on flexible stainless steel mesh for asymmetric supercapacitor device applications. Electron microscopic investigations revealed the uniform coverage of both iron oxide and CNT forest nanostructures over one meter length of SS mesh. Both iron oxide and CNT nanostructures were tested for supercapacitor electrode material in neutral electrolytes. Further, asymmetric solid state devices were fabricated and connected in serial fashion to demonstrate glowing of LEDs as well as rotation of 5 V micro fan. In addition, at bending angle of 90°, device showed 68% increase whereas, at 180° it showed 13% decrease in capacitance. The calculated specific capacitance for single device is found to be 14.4 mF cm-2. Corresponding energy density and power density are found to be 3 µW-hr cm-2 and 0.74 mW cm-2 respectively. The device showed remarkable capacitance retention of 87% over 25 000 charge discharge cycles. The flexible nature with remarkable cyclic stability of solid state iron oxide/CNT device is suitable for low cost flexible and wearable supercapacitor applications.

Significant enhancement in thermoelectric performance of nanostructured higher manganese silicides synthesized employing a melt spinning technique.

The limited thermoelectric performance of p-type Higher Manganese Silicides (HMS) in terms of their low figure-of-merit (ZT), which is far below unity, is the main bottle-neck for realising an efficient HMS based thermoelectric generator, which has been recognized as the most promising material for harnessing waste-heat in the mid-temperature range, owing to its thermal stability, earth-abundant and environmentally friendly nature of its constituent elements. We report a significant enhancement in the thermoelectric performance of nanostructured HMS synthesized using rapid solidification by optimizing the cooling rates during melt-spinning followed by spark plasma sintering of the resulting melt-spun ribbons. By employing this experimental strategy, an unprecedented ZT ∼ 0.82 at 800 K was realized in spark plasma sintered 5 at% Al-doped MnSi1.73 HMS, melt spun at an optimized high cooling rate of ∼2 × 107 K s-1. This enhancement in ZT represents a ∼25% increase over the best reported values thus far for HMS and primarily originates from a nano-crystalline microstructure consisting of a HMS matrix (20-40 nm) with excess Si (3-9 nm) uniformly distributed in it. This nanostructure, resulting from the high cooling rates employed during the melt-spinning of HMS, introduces a high density of nano-crystallite boundaries in a wide spectrum of nano-scale dimensions, which scatter the low-to-mid-wavelength heat-carrying phonons. This abundant phonon scattering results in a significantly reduced thermal conductivity of ∼1.5 W m-1 K-1 at 800 K, which primarily contributes to the enhancement in ZT.