Differentiation between graphene oxide and reduced graphene by electrochemical impedance spectroscopy (EIS)

We report a novel method of differentiating 2 types of graphene nanomaterial: graphene oxide (GO) and reduced graphene (RG). GO, synthesized by modified Hummer's method, was subsequently reduced electrochemically (ERG) and photocatalytically (PRG). GO and RG have typically been discriminated by x-ray diffraction spectroscopy (XRD), Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS). Electrochemical impedance spectroscopy (EIS) has usually been used to obtain the electronic transfer properties, based on Nyquist diagrams. However, in this report, we demonstrate that EIS can distinguish GO and RG graphene forms using the impedance modulus and shift-phase angle-versus-frequency Bode diagrams. The impedance modulus Bode diagram exhibits 2 time constants for a glassy carbon electrode (GCE) that has been modified with GO versus only 1 time constant for GCE that is modified with ERG and PRG. Thus, this spectroscopic technique can unambiguously determine whether graphene is in its oxidized or reduced form. (c) 2012 Elsevier B.V. All rights reserved.