Abstract
Excellent performance characteristics have been obtained with the all‐vanadium redox flow cell employing V(II)/V(III) and V(IV)/V(V) redox couples for the negative and positive half‐cells, respectively. Using 1.5M vanadium solutions in 
, carbon felt electrodes and a polystyrene sulfonic acid cation selective membrane, the cell was charged at 40 mA/cm2 and discharged across various loads. The coulombic efficiency was 90%, while the voltage efficiency calculated over the range 10–90% state‐of‐charge was 81%. An overall energy efficiency for the cell of 73% which, together with the simplicity of the system, makes the vanadium redox cell one of the promising energy storage systems currently under development.