Impact of air oxygen presence on the stability of the V3+ ions in the vanadium redox flow batteries

This work is intended to define the role of oxygen on the stability of vanadium ions V(III) in the vanadium redox flow batteries. The UV-visible spectrophotometry revealed that, not only the oxygen presence in the anolyte solution strongly limits the V(IV) to V(II) reduction in the negative half-cell electrolyte, due to the rapid oxidation of the V(II) by dissolved oxygen. Most important, the oxygen presence in the same solution also makes very unstable the V(III) ions that tend to be oxidized in short time. This effect, never previously well quantified, shows that the presence of O2 must be absolutely excluded in the storage reservoir in order to keep stable the concentration of V(III).