Graphite/Metal Electrodes for Electrochemical Exfoliation: Few Layers Graphene with Low Defects

Abstract

Graphene was obtained by electrochemical exfoliation of graphite and metal/graphite electrodes of different compositions and electrical conductivities. Metal/graphite electrodes were prepared using high purity copper and nickel precursor and commercial graphite. Processes of rapid expansion and direct exfoliation of graphite in a H2SO4 solution were observed using voltages from 2V to 15V and currents of 0.03 mA to 0.08 mA. The total time for each process was one hour and the maximal concentration of few layers graphene flakes was 0.002 mg/mL. X rays powder diffraction of the expanded electrodes showed the effect of the electrochemical process in the crystallinity and the increasing of interlayer distance. A characterization of a large amount of graphene flakes was performed by Raman spectroscopy and optical microscopy. Typical size of the flakes are between 1 μm and 10 μm and the Raman spectra indicate number of layers from single or bilayers to approximately ten layers. The greatest variations in thickness of flakes are observed when the intercalation process concludes before the expansion of the layers. A low degree of oxidation and of structural defects was characteristic of the experiments with lower acid concentration.