7,7,8,8-Tetracyanoquinodimethane-assisted one-step electrochemical exfoliation of graphite and its performance as an electrode material

Abstract

A green approach for the preparation of water-dispersible functionalized graphene via one-step electrochemical exfoliation of graphite using 7,7,8,8-tetracyanoquinodimethane (TCNQ) anions as surface modifiers and electrolytes was described. TCNQ is an organic charge-transfer complex with electron accepting and noteworthy electrical properties. The exfoliation of graphite to a few-layer graphene sheets was confirmed by transmission electron microscopy (TEM) and atomic force microscopy (AFM) image analysis. The chemical state, surface functional groups and chemical compositions of bulk graphite as well as TCNQ-functionalized graphene sheets were investigated by Fourier-transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis. Adsorption of TCNQ onto the surface of graphene sheets was confirmed by the appearance of the N1s peak at ∼399.4 eV in the XPS of TCNQ-functionalized graphene. Exfoliation of bulk graphite to functionalized graphene sheets was further confirmed by the appearance of a sharp single peak at ∼2695 cm⁻¹ along with increased intensity ratios of the D-band to the G-band. Electrochemical performance of a TCNQ-functionalized graphene sheet was investigated using 1 M Na₂SO₄ and 1 M KOH aqueous solutions. Cyclic voltammetry (CV) and galvanometric charge–discharge experiments revealed that TCNQ-functionalized graphene could be used as a supercapacitor electrode material. The specific capacitance values of TCNQ-modified graphene measured with electrolytes (1 M KOH and 1 M Na₂SO₄) were 324 and 140 F g⁻¹, respectively, at a current density of 1 A g⁻¹. Impedance spectroscopic analysis revealed that the charge transfer process was dependent on surface functionalization and interaction between the electrode and the electrolyte.