Graphene Suspension from Modified Electrochemical Exfoliation of Graphite

Abstract

Graphene has emerged as one of the most exciting materials since its discovery in 2004. Graphene is a term used for one to ten layers of sp2 hybridized carbon atoms arranged in a hexagonal pattern. Monolayer graphene is the building block of all graphitic structures and has high electron mobility, high thermal conductivity, high specific surface area, extremely high resistance to gas permeation and high optical transmittance. These exceptional properties make monolayer graphene attractive for potential applications as a catalyst or catalyst support in direct methanol fuel cells (DMFC), proton exchange membrane fuel cells (PEMFC), electrode in lithium-ion batteries, supercapacitors, as well as in thermally and electrically conductive sensors. AB-stacked bilayer and trilayer graphene have applications in the electronic industry, such as fabrication of field-effect transistors (FEts) and light detectors, due to an induced bandgap in the presence of an applied electric field. In addition, graphene finds major applications in the optoelectronic industry, such as electrode materials in solar cells, supercapacitors and transparent LCDs.Graphene is traditionally synthesized using the simple mechanical exfoliation of graphite, which is not scalable, or from chemical vapour deposition of a carbon source on a suitable substrate, which is both a complex and an expensive method. Hence, a scalable and economic graphene synthesis method is needed to harness the remarkable properties of graphene. The electrochemical exfoliation of graphite provides a promising route for the bulk production of graphene because it provides graphene flakes with the largest size and a smaller defect density than the well-known chemical synthesis methods such as Hummer or modified Hummer processes. The large size flakes resulting from electrochemical exfoliation are suitable for scalable electronic device fabrication methods. Electrochemical exfoliation proceeds via intercalation of the ions present in the electrolyte and is followed by the subsequent expansion and later exfoliation of graphite. However, this strategy produces graphene with a scatter in the layer numbers. A polydisperse suspension of graphene is undesirable because the electronic properties of graphene change with the number of layers. The intermediate graphite intercalation compounds are formed by the insertion of intercalants between the layers of the graphite host material. The intercalants can be atoms, ions or molecules. Graphite intercalation occurs in stages where the stage number indicates the number of graphene layers between the two nearest intercalant layers. In the present study, a modified electrochemical exfoliation route of graphite is explored, which proceeds through the exfoliation of a stage pure graphite intercalation compound followed by low-intensity ultrasonication. The modified electrochemical exfoliation of graphite is capable of providing a monodisperse graphene suspension