Optimization of Electrochemical Flow Capacitor (EFC) design via finite element modeling

Abstract

Abstract The Electrochemical Flow Capacitor (EFC) is the recently introduced electrical energy storage device for large-scale energy applications. Utilization of high surface area of carbon-based electrode suspended in the electrolyte is the key to the electrical energy storage, by forming a double layer of charges at the interface. In this study, the finite element model was used to examine the behavior of the ionic charge distribution and the maximum current density in EFCs. The current density distribution in the flow channels demonstrated significant dependence on the design and the depth of the flow channel, which ranged from 0.5 mm to 5 mm. The underutilization of the active surface area of carbon continuously increases with increasing channel depth. The geometry of flow channels affected the overall current density by strengthening it at the sharp edges between the current collector and the separating membrane. The geometries based on flow channel shape (circular and box) were tested by varying the depth of the flow channels, current collector shape, and their area in contact with the slurry electrodes to study current density distribution in the flow channel. The experiments were performed with circular flow channels (each 5 mm wide) separated by a 150 µm thick ion-conducting membrane; then, the results were used to optimize the model. The slurry was composed of 0.1 M Na2SO4, 3 wt% Carboxymethyl Cellulose (CMC), and activated carbon powder suspended in water. The studies showed that the maximum activity is observed near the current collector boundary, and slurry underutilization is observed as the distance from the edge increases. Simulations results accorded well with experimental data, including the estimation of the stationary-state current that is achieved during the charging of the slurry.