Effects of sodium hydroxide on the yield and electrochemical performance of sulfonated poly(ether-ether-ketone) functionalized graphene

An environmentally friendly method for the one-step electrochemical synthesis of water dispersible graphene directly from graphite is reported. Sulfonated poly(ether-ether-ketone) (SPEEK) dissolved in deionised water was used as an electrolyte and a surface modifying agent for graphene. The effects of sodium hydroxide (NaOH) on the production yield and electrochemical performance of graphene were investigated in detail. The production yield of few-layer graphene increased to above 40%, as compared to the 6% in the absence of NaOH. Fourier transform infrared and X-ray photoelectron spectroscopy (XPS) analyses suggested that the oxygen functionalities (hydroxyl and carboxyl) generated during the electrochemical exfoliation of graphite in the absence of NaOH were decreased significantly during the electrolysis experiment in an alkaline solution of SPEEK. This is attributed to the NaOH induced reduction of oxygen functionalities present on the surface of graphene sheets. XPS elemental analysis also confirmed the removal of oxygen functionalities in an alkaline medium during the graphite exfoliation experiment. Transmission electron microscopy and atomic force microscopy analyses confirmed the formation of single layer functionalized graphene. A charge-discharge experiment showed that the specific capacitance of the as-prepared graphene in the absence of NaOH was 18 F g^-1 at a current density of 2.2 A g^-1. In contrast, the specific capacitance was increased to 244 F g^-1 for graphene prepared under alkaline condition indicating its suitability as an energy storage electrode material. The high electrochemical performance may be due to the large surface area of graphene (433 m² g^-1) prepared under alkaline condition as observed by the Brunauer-Emmett-Teller surface area analysis.