Investigation of Treated Graphene Oxides for Vanadium Redox Flow Battery

Thermically treated graphene oxides (TT-GOs) are obtained at different temperatures, 100°C, 150°C, 200°C and 300°C in reduced environment. Physico-chemical characterizations were carried out to evaluate the electrochemical results in terms of reversibility and electrochemical impedance spectroscopy (EIS) in a three electrode half-cell. The TT-GO sample treated at 100°C (TT-GO-100), characterized by the presence of hydroxyl (-OH) and carboxyl (-COOH) species, shows an higher reversibility towards the VO²⁺/VO₂⁺ redox reactions with respect to the all investigated samples. The electrochemical performance results confirm how the hydroxyl and carboxyl species prevalence play a fundamental role as active sites for the [VO]²⁺/[VO₂]⁺ redox reaction process. The TT-GO-150, TT-GO-200 and TT-GO-300 sample, characterized by the prevalence of carbonyl species, phenolic (C-OH) and epoxide groups (C-O-C) on the basal plane of the structure, show a lower reversibility attributable to the higher ohmic and charge transfer resistances.