Corrosion behavior of a positive graphite electrode in vanadium redox flow battery

The graphite plate is easily suffered from corosion because of CO2 evolution when it acts as the positive electrode for vanadium redox flow battery. The aim is to obtain the initial potential for gas evolution on a positive graphite electrode in 2 mol dm−3 H2SO4 + 2 mol dm−3 VOSO4 solution. The effects of polarization potential, operating temperature and polarization time on extent of graphite corrosion are investigated by potentiodynamic and potentiostatic techniques. The surface characteristics of graphite electrode before and after corrosion are examined by scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The results show that the gas begins to evolve on the graphite electrode when the anodic polarization potential is higher than 1.60 V vs saturated calomel electrode at 20 °C. The CO2 evolution on the graphite electrode can lead to intergranular corrosion of the graphite when the polarization potential reaches 1.75 V. In addition, the functional groups of COOH and CO introduced on the surface of graphite electrode during corrosion can catalyze the formation of CO2, therefore, accelerates the corrosion rate of graphite electrode.

The overpotential for gas evolution on positive graphite electrode decreases due to the functional groups of COOH and CO introduced on the surface of graphite electrode during corrosion process, which can self-catalyze the oxidation of carbon atoms therefore, accelerates corrosion process.Figure optionsDownload as PowerPoint slideHighlights
► Initial potential for gas evolution is higher than 1.60 V vs SCE.
► Factors affecting the graphite corrosion are investigated.
► Functional groups of COOH and CO introduced during corrosion process.
► The groups can self-catalyze the oxidation of carbon atoms.