A comprehensive understanding of the characteristics of graphene, with regard to its unique electrical and structural attributes, would be incomplete unless the inevitable presence of defects have been considered. While such imperfections may limit the realization of theoretically predicted characteristics, they may also be vital for uncovering new fundamental phenomena and related applications. Here we show that the charged defect generation, through argon ion based plasma processing, in few layer graphene (FLG) could be integral to the substantial enhancement of the electrical capacitance, and be of potential use in electrochemical (EC) energy storage. By combining EC characterization techniques with detailed Raman spectroscopic analysis, we elucidate the contributions of plasma-induced defects to electrostatic and quantum capacitance.

We then show that charged defect generation, through argon ion based plasma processing, in FLG could substantially enhance the electrical capacitance, and could be used for electrochemical energy storage. Detailed consideration of the constituent space charge and quantum capacitances were used to delineate a new length scale, correlated to electrically active defects contributing to the capacitance, and which was found to be smaller than a structural correlation length determined through Raman spectroscopy. The study offers insights into an industrially viable method (i.e., plasma processing) for modifying and enhancing the energy density of graphene-based electrochemical capacitors.