Mass transfer in flow batteries characterized by comparison of electrical potentials according to regions of porous electrodes

Abstract

In this study, we introduce a segmented cell that can measure the electrochemical reaction kinetics occurring in a porous electrode for a vanadium redox flow battery in real time. The segmented cells visualize the non-uniform mass transfer characteristics of porous electrodes through locally characterized electrical potentials. The transfer of vanadium ions and electrons occurring at the interface between the electrode and the electrolyte is an important indicator that determines the electrochemical performance. Therefore, we discuss the mass transfer characteristics of porous electrodes through the change of electrical potential according to the essential operating factors of flow batteries such as charge/discharge process, current density and flow rate. The active area of the porous electrode was indirectly segmented through 25 current collector layers. The polarization effect of each position of the felt electrode during the charging and discharging process are explained by comparing the voltage deviation of the divided active regions. For the single-cell used in the experiment, the optimal flow rate for improving electrochemical reversibility in both charge/discharge processes is 400 mL min−1. Also, since the effect of the current load is less on charge process than on discharge process, a charging process with relatively high current densities is possible.