High- performance aqueous electrolyte based supercapacitor of carboxylic acid functionalized carbon-nanotubes and graphene nano composite

Abstract

High specific capacitance of supercapacitors is the most prominent factor for its implementation in industrial use. However various methods has been employed to intensify the specific capacitance of supercapacitors by fabricating electrodes using graphene composite as active electrode material. However those methods have been able to attain the desired specific capacitance of the supercapacitors but there still remains some disadvantageous factors that act as hurdles for their implementation in practical field. In this work the synthesis and supercapacitor electrode fabrication of carboxylic acid functionalized carbon nanotubes/graphene composite (rGO/FCNT) has been reported without destroying the 2D sheets structures of reduced graphene oxide sheets. The carboxylic functionalities were introduced into the surface of the carbon nanotubes by treatment with H2SO4/HNO3 mixture. The final composites were synthesized by in-situ reduction of graphene oxide (GO) in presence of functionalized carbon nanotubes by the addition of hydrazine hydrate. Supercapacitor electrodes were fabricated using these composites where stainless steel plates of 1 cm2 area were used as current collectors. The materials were characterized by FTIR, Raman Spectroscopy, Scanning Electron Microscopy (SEM), X-ray photo electron spectroscopy (XPS) and XRD analysis. The surface area of the composite was determined by BET isotherm analysis. The electrochemical properties of the electrodes were evaluated by cyclic voltammetry (CV), galvenostatic charge discharge study and impedance spectroscopy. The material shows a specific capacitance of 302 F/g at a current density of 1 A/g. The newly prepared composite hold an optimistic potential to be used as electrode material in energy storage devices. The inter planer distance between the graphene nanosheets and the nature of interaction between graphene and functionalized carbon nanotubes were theoretically studied by Density Functional Theory (DFT) study.