Influence of hydrophilic properties on capacitive behavior of functionalized graphene

Super-hydrophobic graphene was treated with 4-benzenediazoniumsulfonate to obtain a series of functionalized graphene (FG) with enhanced hydrophilic properties. The results from Fourier transform infrared (FT-IR) spectra and thermogravimetric (TG) analyses demonstrate that -SO3H groups are covalently anchored to functionalized graphene and alter the thermal stability of graphene-based materials. In comparison to pristine graphene (PG), functionalized graphene as prepared exhibits enhanced hydrophilic properties which can be conducted by varying the diazotization-coupling reaction time. Cyclic voltammetry (CV) curves indicate that enhanced hydrophilic properties improve the capacitance of functionalized graphene up to twice than that of pristine graphene in Na2SO4 electrolytes. Moreover, electrochemical impedance spectroscopy (EIS) reveals that the high level of functionalization will cause the decrease of the electric conductivity and capacitive performance, suggesting that functionalization of graphene provides the competitive relationship between the positive hydrophilicity increase and the negative conductivity decrease to capacitive performance.