Pore-scale investigation of reactive transfer process in a deep eutectic solvent (DES) electrolyte-based vanadium-iron redox flow battery

Abstract

In order to promote the applicability of redox flow batteries (RFBs), the deep eutectic solvents (DESs) have been proposed as a better choice for non-aqueous electrolyte of RFBs. The reactive transfer process within the RFB plays a key role in determining the cell performance. In this work, cyclic voltammetry experiment is conducted to obtain the reactive transfer property parameters of iron and vanadium ions in ethaline DES electrolyte. Then, a lattice Boltzmann method (LBM) model is utilized to reveal the reactive transfer mechanism of vanadium-iron RFB with DES electrolyte at the pore-scale. The numerical results present the influences of porous electrode morphology and DES electrolyte transfer properties on the performance of vanadium-iron RFB during galvanostatic discharging. This work suggests that the porous electrodes with the lower porosity and smaller fibre diameter lead to a more sufficient depletion time of reactant in DES electrolyte under the galvanostatic discharging and a given pumping power condition. Meanwhile, the larger fibre diameter yields the more widespread pore size distribution, resulting in the more apparent non-uniformity of local current density into the porous electrode. In addition, the results show the similar state of charge(SOC) in the cathode and anode under the same flow condition. By contrast, the absolute value of overpotential in the anode is significantly higher than that in the cathode. Furthermore, the reactive transfer process of this DES electrolyte-based vanadium-iron RFB is compared to all vanadium RFB with aqueous electrolyte under the galvanostatic discharging.