Electrochemical activation of graphite felt electrode for VO2+/VO2+ redox couple application

Abstract

In this work, the electrochemical activation of graphite felt electrode for vanadium redox flow battery (VRB) was studied. Graphite felt (GF) electrode was oxidized at a range of electrochemical oxidation degrees in H2SO4 solution. The electrochemical performance of the treaded GF was discussed, and the law of the surface properties of GF which changed along with the electrochemical oxidation degree was proposed. The structure, composition, surface tension and electrochemical properties of the oxidized GF (OGF) were characterized using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), contact angle measurements, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The GF oxidized at 560–840mAhg−1 exhibited the best activity toward VO2+/VO2+ redox reaction, according with the highest COH and COOH content (ca. 34%) on its surface. The mechanisms of VO2+/VO2+ redox reaction on OGF were also discussed. VRB single cell with pristine GF and OGF as the electrode were test at various charge–discharge current densities, respectively. The columbic efficiency (CE), voltage efficiency (VE) and energy efficiency (EE) of the cell using OGF electrode are much higher than the cell using pristine GF, suggested that the electro-oxidation method is a promising technology for the activation of GF electrode.