Electrochemically Engineered Graphite for Supercapacitor Application

Abstract

Supercapacitors are also known as electrochemical capacitors (ECs) attracted considerable attention because of properties like high power density, rapid charge-discharge rate (few seconds), long cycle life (>100000 cycles) and low maintenance cost. These properties make EC an excellent candidate for applications like hybrid electric vehicles, frequency regulations in smart grids etc. However, designing freestanding binder-free electrodes with superior mechanical strength and suitable capacitance is still in the development stage. Graphene, a 2D form of carbon is one of the best candidates for supercapacitor electrode material, because of its properties, like, high surface area (~2630 m2 g-1), high intrinsic electrical conductivity, and chemical stability. Restacking and aggregation of graphene sheets during electrode fabrication process leads to ineffective use of its high surface area. Vertically oriented graphene (VOG) sheets on a conductive substrate can be a useful electrode for supercapacitor application. Exposed graphene sheets on the surface of graphite, increases the surface area of the electrode by order of magnitude and reduces the contact resistance since graphene sheets remain attached to the substrate. Here, we demonstrate an electrochemical approach for engineering graphite surface in such a way that we can directly grow vertically oriented graphene on the graphite substrate itself. Electrochemical exfoliation process increases interlayer spacing causing more and easy access to the surface area by electrolyte ions, thus reducing diffusion resistance. Anodization of graphite in 1 M H2SO4 leads to the growth of VOGs on a graphite substrate. Exfoliated graphite (EG) not only act as a current collector but also stores enough charges in the interlayer spaces. EG shows excellent capacitive performance in 1 M sodium sulphate electrolyte. The capacitance of graphite, 0.05 F cm-2 increases to 0.75 F cm-2 (scan rate of 5 mV s-1) in case of EG.