Facile and robust assessment of membrane transport properties in course of standard electrochemical tests of vanadium redox flow batteries

Crossover of vanadium ions and consequent capacity loss during the cycling of the vanadium redox flow batteries remain an issue for its long-term operation. This work describes novel methods to study the diffusion of vanadium ions through cation (FS-940) and anion (FAP-450) exchange membranes to understand the vanadium crossover processes during charging and resting of the battery. The proposed methods are implemented for ∼0 % SoC and ∼100 % SoC of the battery. The experimental setup do not require any additional technique besides a potentiostat/battery tester and therefore can be widely used in flow battery studies. The self-discharge method provided a facile determination of vanadium ions diffusion coefficients from the linear relation of capacity change, ΔQ, over the charging and resting period of the battery. The steady-state current method described the effect of applied constant voltage on the diffusion of vanadium ions during cycling. The electrochemical titration method described the diffusion of vanadium ions based on the linear relation between ΔQ during cycling of the battery with enriched and deficient half-cells. The results of these methods are in good agreement with each other with good accuracy as well as with the literature.