Application of GUITAR on the Negative Electrode of the Vanadium Redox Flow Battery: Improved V3+/2+ Heterogeneous Electron Transfer with Reduced Hydrogen Gassing

Abstract

GUITAR (Graphene from the University of Idaho Thermolyzed Asphalt Reaction) has the classical basal and edge plane morphology of graphites and thin layer graphenes with similar X-ray photoelectron spectroscopy (XPS), Raman and IR characteristics. However previous investigations indicated GUITAR is different electrochemically from graphenes and classical graphites. GUITAR has faster heterogeneous electron transfer across its basal plane and an electrochemical window that exceeds graphitic materials by 1 V. These beneficial properties are examined for application in the negative electrode of the vanadium redox flow battery (VRFB). Graphitic materials in this application suffer from hydrogen gassing and slow electron transfer kinetics for the V2+/3+ redox couple. Cyclic voltammetry of the V2+/3+ redox couple (0.05 M V3+ in 1 M H2SO4) on bare KFD graphite felt gives an estimated standard rate constant (k0) of 8.2 × 10−7 cm/s. The GUITAR-coated KFD graphite felt improves that quantity to 8.6 × 10−6 cm/s. The total contribution of the cyclic voltammetric currents at −1.0 V vs. Ag/AgCl to hydrogen evolution is 3% on GUITAR-coated KFD graphite felt. On bare KFD graphite felt, this is 22%. These results establish GUITAR as an excellent alternative material for the negative electrode in the vanadium redox flow battery.