Production of Few-Layer Graphene via Enhanced High-Pressure Shear Exfoliation in Liquid for Supercapacitor Applications

A novel method for producing graphene via enhanced shear exfoliation in a high-pressure fluid has been developed. In the process of exfoliation, graphite flakes, dispersed in a solution of N-methyl-2-pyrrolidone (NMP), were pushed through the exfoliation tube by a high-pressure pump, which produces high shear stresses on the graphite flakes due to the turbulent flow, causing the peeling-off of graphene sheets from the graphite flake. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) images show that produced graphene sheets have thicknesses ranging from monolayer to about 12 layers. The results of X-ray photoelectron spectroscopy (XPS) and Raman and infrared (IR) spectroscopy analyses reveal that neither basal-plane defects nor oxides were noticeably introduced to graphene sheets in the process. The graphite solution can be continuously treated in a circular loop. At a pressure of 100 MPa and after 2 h of treatment, exfoliated graphene was obtained with a yield of about 15 +/- 0.3%. This method is highly efficient and could be facilely scaled up to process large quantities of materials either in batches or continuously. The exfoliated graphene thus produced has been used for preparing the electrodes of supercapacitors which showed a specific capacitance of 135 F/g, along with good cycling and rate capabilities in an aqueous solution of 6 M KOH acting as the electrolyte.