Shanthi Murali is a Ph.D. student completing her dissertation this semester under the supervision of Rodney S. Ruoff. Her research focuses on carbon based materials for Electrical Double Layer Capacitors (EDLC). She is now on a short internship at Intel Labs.
Electrochemical double layer capacitors (also called supercapacitors or ultracapacitors) are high power density energy storage devices that operate through the separation of charge at the electrochemical interface between an electrode and a supporting electrolyte. Numerous types of carbon materials with high surface area and internal porosity, such as activated carbon, carbon fabrics, nanotubes, and reduced graphene oxide have been studied as electrode materials. Electrolytes such as aqueous alkaline and acid solutions often give high capacitance, while organic and ionic liquids provide a wider operating voltage. Graphene, due to its high theoretical surface area of 2630 m2/g, good electrical conductivity, and relatively low density, shows great potential as an electrode material in EDLCs. The goal of Shanthi’s research is thus to study effective methods for synthesis of graphene-based materials, and to investigate their behavior in EDLCs.
Shanthi’s work explored microwave assisted synthesis of graphite oxide (‘MEGO’, prepared in less than one minute by irradiation of graphite oxide by microwave). This material was further chemically activated to obtain a unique carbon material, activated microwave exfoliated graphite oxide (‘a-MEGO’) with specific surface areas up to 3100 m2/g. Gas adsorption measurements were used to study the specific surface area and porosity of a set of a-MEGO samples, which were also studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for their structure, and by combustion analysis (i.e., elemental analysis) and X-ray photoelectron spectroscopy (XPS) to understand their elemental composition. Cyclic voltammetry (CV), galvanostatic charge/discharge, and frequency response, tests were done in order to study the performance of these new carbon materials as electrodes in both aqueous and organic electrolytes in a two electrode cell set up.
Ultracapacitor response of a-MEGO (SSA ~ 3100 m2/g) with 1.0 M TEA BF4/AN electrolyte. (A) CV curves for three different scan rates. Rectangular shapes indicate capacitive behavior. (B) Galvanostatic charge/discharge curves for three different constant currents.
Atomic resolution electron micrograph of activated graphene in single sheets of crystalline carbon which are highly curved to form a three-dimensional porous network.