Experimental and modeling study of the current-potential behavior of an acid-base flow battery. Electrical performance determination as function of the number of single cell unit in stack

This work presents an experimental and modeling study of the current-potential behavior of an acid-base flow battery (AB-FB) by means of charge and discharge polarization curves in steady-state as function of the number of single cell units (SCUs) stacked within the battery. A three-dimensional (3D) electric model and a simplified equivalent resistance circuit (S-ERC) model of the AB-FB were proposed, both models were solved in steady-state regime. To validate the predictions of both models, a series of experiments were done in a commercial AB-FB conformed by four single cell units. The prediction error of the experimental polarization curves with the 3D electrical model was 2 %, while an error of 12 % was obtained with the S-ERC model. The 3D electric model simulations evidence the root source of shunt currents in the parallel electrolyte's feed/exit lines inside the AB-FB, which cause a 41 % of open circuit voltage (OCV) loss for 50 SCUs stacked within the battery, by reducing the cationic and anionic membrane thicknesses to 30 μm, the OCV loss for 50 SCUs stacked was 27 %. Extensive research work must be focused to reduce shunt currents on AB-FB, and related technologies, because they impact the battery electrical performance by reducing its gross power, voltage efficiency, open circuit voltage (OCV), and gross power density (GPD).