Synthesis and characterization of aryl substituted functionalized graphene sheets and their electrochemical behavior

We report the electrochemical behavior of free-standing functionalized graphene sheet electrode in a potential window corresponding to that of high-voltage cathode of lithium-ion batteries. Electrochemical exfoliation of graphite yielded graphene oxide sheets that were subsequently heat-treated at 300 degrees C in inert gas atmosphere. Chemical functionalization of resulting graphene sheets with C6H4CF3, C6H4COOH, and C6H4N(C2H5)(2) groups was performed using diazonium chemistry. As-prepared graphene oxide and heat-treated unmodified and modified graphene electrodes were characterized by elemental analysis, 4-point probe measurements, Raman spectroscopy, X-ray photoelectron spectroscopy, galvanostatic cycling, and cyclic voltammetry. A smaller voltammetric charge was obtained for electrodes made with graphene sheets functionalized with aryl groups compared to that of unmodified graphene. In addition, the irreversible charge (difference between oxidation and reduction charge) for C6H4CF3-functionalized graphene electrode is much smaller than that of unmodified electrode. These observations suggest that substituted aryl groups grafted on graphene sheets surface can mitigate side reactions at the electrode/electrolyte interface, and the resulting materials could be useful as conductive additive of a high voltage composite electrode.