In-situ Measurements of Vanadium Crossover Diffusivities in All-Vanadium Redox Flow Batteries During Charge-Discharge Cycles

The transport phenomena of species through the ion exchange membrane of the all-vanadium redox flow battery (VRFB) can be described using multicomponent diffusion equations, i.e. Stefan-Maxwell equations. In this work, a three-dimensional, transient, non-isothermal VRFB model is further developed based on the concentrated solution theory for ions with high concentration. The model accounts for electrochemical reactions, heat generation, species/heat transport, and furthermore, interactions between vanadium ions (V2+ V3+, VO2+ and VO2+) are included based on the Stefan-Maxwell equations. Using the model, we investigate the effect of interactions between vanadium ions on the crossover behavior through the membrane during charge and discharge cycle. The model is applied on the single straight channel, and simulation results provide the change of vanadium ion crossover in form of multi-dimensional contours in the components of VRFB and polarization curves along the time. This work can contribute on the basic understanding of the behavior of highly concentrated solutions and be helpful for optimization of design and operation of VRFBs.