MoS 2 /Reduced Graphene Oxide-Based 2D Nancomposites for Boosting the Energy Density of Electric Double-Layer Capacitor
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MoS2/Reduced Graphene Oxide-Based 2D Nancomposites for Boosting the Energy Density of Electric Double-Layer Capacitor Anishkumar Manoharan1, 3, Z. Ryan Tian2, 3, and Simon S. Ang1, 3 1 Electrical Engineering, University of Arkansas, AR 72701 2 Chemistry and Biochemistry, University of Arkansas, AR 72701 3 High Density Electronics Center, University of Arkansas, AR 72701 ABSTRACT A method for synthesizing and structuring 2D-MoS2/rGO (molybdenum disulfide/reduced graphene oxide) nanocomposite-based electric double layer capacitor (EDLC) that has a slower discharge rate and higher energy density than rGO-based EDLC (RG-EDLC) is reported. The rGO electrode and the nanocomposite were characterized using powder XRD and SEM for their physical and structural properties. Cyclic voltammetry (CV) was used to analyze the electrochemical behavior of the EDLCs. A maximum current density at which the MoS2/rGO nanocomposite-based EDLC (MRG-EDLC) can charge and discharge was 2.5 A/g, while it was 1A/g for the RG-EDLC. The specific capacitance of the MRG-EDLC was 14.52 F/g at 0.5 A/g with an energy density of 8.06 Wh/kg. INTRODUCTION An electric double-layer capacitor or supercapacitor can store energy with exponential charge and discharge behavior in comparison to standard capacitors. Although double-layer capacitors have high electrical conductance, they still possess a low potential of not more than 3V. Continuous research is underway to develop novel active materials and membranes to boost their energy and power densities. Storing charge in supercapacitors depends on the formation of an interfacial double layer on active electrode materials [1]. Recently, several research works have been reported on EDLCs with reduced graphene oxide as the electrode material [2−5] because of its excellent life cycle, high electric conductivity and chemical stability [6, 7]. Electrolytes such as potassium hydroxide, organic electrolyte, and ionic liquids were used in the EDLCs to improve their specific capacitance [8-11], energy and power densities. In particular, a graphene-based supercapacitor with a curved morphology was reported to possess high energy density with a capacitance of 154.1 F/g at 1 A/g current density [12]. On that basis, Yanwu et al. [13] modified this process and improved the capacitance properties using the same ionic liquid. However, the reduction of their graphene oxide in powder or sheet form made use of hydrazine. Without using a reducing chemical, graphene oxide powder has also been reduced under high temperatures at about 1000oC [14]. During our investigation, it was found that rGO nanosheets would lose its physical properties above 350oC. As such, rGO nanosheets were prepared by thermally reducing them at 350oC in nitrogen ambient without using a toxic chemical in this work. MoS2, an archetypal layered transition metal sulfide, has three atomic layers (S-Mo-S) stacked and fused together using van der Waals bonding. This two-dimensional transition-metal dichalcogenide (2D-TMD) has a 2H phase crystal structure with a mono
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