Ultrathin 2D Sheets of Graphene and WS2 for Energy Storage Applications

Abstract

Ultrathin 2D-nanomaterials are currently being exploited and employed for energy storage applications. Graphene nanosheets (GNS) are the most favorable candidate for energy storage and charge transfer due to its extraordinary novel properties. Other than graphene, various 2D materials like transition metal dichalcogenides (TMDs) are used in charge storage applications too. In this article, ultrathin 2D sheets of various 2D materials like graphene and TMDs like WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> were being prepared by liquid phase exfoliation method. The exfoliated 2D sheets were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectrometer, and atomic force microscopy (AFM). SEM and AFM being used to determine the morphology and dimensional aspects of prepared exfoliated sheets, respectively. The exfoliated sheets were coated over PET membranes in single layer and layer by layer assembly for evaluating their supercapacitance, respectively. The prepared films were tested with galvanostatic charge-discharge cycles and cyclic voltammetry (CV) in 1 M Na <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> as electrolyte. Results obtained from layer by layer assembly of WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -GNS showed a high efficiency of 96% charge retention after 1000 cycles. The WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /GNS multilayer films can exhibit a high value of specific capacitance about 800 F kg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and area calculated for this capacitance was 70 F m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> under 10 mVs <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> scan rate. And the film exhibits good cycle stability over 1000 cycles. The results suggest that the WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -GNS layer by layer assembly is quite suitable as well as favorable electrode materials for high performance energy storage devices like supercapacitors.