Ionic shortcut currents via manifolds in reverse electrodialysis stacks

Reverse electrodialysis (RED) is a blue energy technology for clean and sustainable electricity harvesting from the mixing entropy of salinity gradients. Recently, many efforts have been devoted to improving the performance of RED units by developing new ion-exchange membranes and by reducing the detrimental phenomena affecting the process. Among these sources of “irreversibility”, the shortcut currents (or parasitic currents) flowing through alternative pathways may affect the process efficiency. Although such phenomena occur in several electrochemical processes (e.g. fuel cells, bipolar plate cells and vanadium redox flow batteries), they have received a poor attention in RED units. In this work, a process simulator with distributed parameters was developed and experimentally validated to characterize the shortcut currents and to assess their impact in RED stack performance under different designs and operating conditions. Results showed that shortcut currents can play a crucial role in stacks with a large number of cell pairs when the electrical resistance of the parasitic pathways is relatively low, e.g. configurations with concentrated brines, high resistance membranes, short channels or large manifolds. Future designs of efficient industrial-scale units cannot ignore these aspects. Finally, the model can be easily adapted for the simulation of electrodialysis and other electromembrane processes.