(Invited) Relationship of Pseudo-Capacitive Current in Sulphuric Acid and Vanadium Flow Battery Reaction Kinetics at Carbon Electrodes

Abstract

Flow battery technologies are promising solutions to the need for electricity storage driven by the increasing demand for energy supply at the same time as the electricity grid becomes more and more dependent on renewable sources such as solar, wind and ocean energy. Vanadium flow batteries (VFBs) are perhaps the most promising of these technologies and a growing number of commercial systems are in operation worldwide.The energy efficiency of vanadium flow batteries (VFBs) largely depends upon the performance of the electrodes. Poor electrode kinetics cause large overpotentials, which reduce the voltage efficiency. They can also lead to side reactions, such as hydrogen evolution at the negative electrode and oxidation of the positive electrode, which reduce the coulombic efficiency and the overall performance and durability.There is considerable variation in the data regarding the kinetics of vanadium redox reactions at carbon electrodes. We have previously reported that cathodic treatment enhances the kinetics of the positive (VIV-VV) electrode in VFBs but inhibits the kinetics of the negative (VII-VIII) electrode, while anodic treatment inhibits the kinetics of the positive electrode but enhances the kinetics of the negative electrode1-3. We also showed that the activity of carbon-based material is strongly dependent on the surface history, in particular the most positive and the most negative potential used to treat an electrode4. In this presentation we will further investigate the effect of electrochemical treatment of the carbon surface and show the relationship between the observed pseudo-capacitive behavior and the kinetics of the different vanadium redox couples. References Bourke, M. A. Miller, R. P. Lynch, X. Gao, J. Landon, J. S. Wainright, R. F. Savinell and D. N. Buckley, J. Electrochem. Soc. 163, A5097 (2016). A. Bourke, M. A. Miller, R. P. Lynch, J. S. Wainright, R. F. Savinell and D. N. Buckley, J. Electrochem. Soc., 162, A1547 (2015). M. A. Miller, A. Bourke, N. Quill, J. S. Wainright, R. P. Lynch, D. N. Buckley and R. F. Savinell, J. Electrochem. Soc., 163, A2095 (2016). M. Al Hajji Safi, A. Bourke, D. N. Buckley, R. P. Lynch, ECS Trans., 109, 67-84 (2022).