An effective route to produce few-layer graphene using combinatorial ball milling and strong aqueous exfoliants

In this paper, a simple, cost effective, and scalable process for production of few-layer graphene is reported by combining ball milling with exfoliants. The graphene was derived from low-cost graphite, which was subjected to high-energy ball milling in an aqueous medium containing a strong exfoliant (1-pyrenecarboxylic acid) and a common solvent methanol. Such a combinatorial approach has not been used before. At a fixed concentration of 1-pyrenecarboxylic acid, the extent of exfoliation was found to be strongly dependent upon the energy input from the ball milling process (expressed as number of hours of milling) and the solvent used. The graphene produced had the distinctive Raman signature, x-ray diffraction crystallinity, scanning electron microscopic image features, transmission electron microscopic images, and high conductivity values (6.7 x 10(3) S m(-1)) in 4-probe electrical measurements all of which compared reasonably with typical values achieved for few-layer graphene. Application of the few-layer graphene was investigated as an electrode for supercapacitors. The graphene-coated electrode showed good specific capacitance and area capacitance (similar to 176 F g(-1) and 1.6 F cm(-2)), superior to conventionally processed graphene. Also demonstrated is good stability in multiple cyclic voltammetric cycles as also a low fade in capacitance after 100 cycles. Based on the obtained characteristics, which show high degree of fidelity when compared to commercial graphene, the few-layer graphene was considered to be a good cost-effective and scalable alternative for applications in energy and other fields. (C) 2013 AIP Publishing LLC.