One-step electrochemical synthesis of 6-amino-4-hydroxy-2-napthalene- sulfonic acid functionalized graphene for green energy storage electrode materials

A green approach for the one-step electrochemical synthesis of water dispersible graphene is reported. An alkaline solution of 6-amino-4-hydroxy-2- naphthalene-sulfonic acid (ANS) serves the role of electrolyte as well as surface modifier. High-purity graphite rods are used as electrodes which can be exfoliated under a constant electrical potential (∼20 V) to form ANS functionalized graphene (ANEG). The aqueous dispersion of ANEG obeyed Beer's law at moderate concentrations, as evidenced from ultraviolet-visible spectroscopy analysis. X-ray diffraction analysis suggests complete exfoliation of graphite into graphene. Fourier transform infrared and x-ray photoelectron spectroscopy not only confirm the functionalization of graphene with ANS, but also suggest the formation of oxygen containing functional groups on the surface of ANEG. Raman spectra analysis indicates the presence of defects in ANEG as compared to pure graphite. Cyclic voltammetry and charge-discharge measurements of ANEG using three electrode systems show a specific capacitance of 115 F g ^-1 at a current density of 4 A g^-1. The ANEG electrode exhibits 93% retention in specific capacitance after 1000 charge-discharge cycles, confirming its utility as a green energy storage electrode material.