Modeling the effect of temperature on performance of an iron-vanadium redox flow battery with deep eutectic solvent (DES) electrolyte

Extensive models have been developed to study the performance of aqueous redox flow batteries, especially for all-vanadium flow battery. Nevertheless, there are few established models to study the non-aqueous deep eutectic solvent (DES)-based flow batteries, which have wider electrochemical window and higher energy density than do the aqueous redox flow batteries. In this study, a stationary two-dimensional model is set up to study the performance of iron-vanadium redox flow battery using DES as electrolyte, in which the property parameters of the DES are experimentally determined. The effects of temperature on the over-potentials, pump power loss, distribution of ions concentration and local current density are studied. The simulation results show that with the increase of temperature, the over-potentials decrease mildly; the electrochemical reactions inside the DES-electrolyte redox flow battery mainly happen in the area close to the membrane, which is different from the aqueous one, and the rise of temperature also leads to an improvement of electrode utilization. For the DES electrolyte with higher viscosity, the pump power loss could not be neglected. It is found that the pumping loss of the entire porous electrode largely decreases from 0.138 W at 25 °C to 0.022 W at 55 °C (with 84.05% reduction). These results are in good agreement with the experimental outcomes. Therefore, this model can be applied to predict the performance of DES based battery and further to develop new kinds of non-aqueous flow batteries.