Trade-off between reduced electrode resistance contribution and shortcut-current-induced voltage losses in reverse electrodialysis stacks

The number of membrane pairs ( N )—a critical design parameter in reverse electrodialysis (RED)—simultaneously influences internal resistance and stack voltage. In this study, we investigated the effect of N on RED performance across varying low-salinity (LS) conductivities (0.50–2.0 mS cm −1 ) and solution linear velocities (0.50–2.0 cm s −1 ), focusing on the trade-off between reduced relative contribution of electrode resistance and voltage losses induced by ionic shortcut currents. Increasing N consistently reduced the contribution of the electrode resistance to the total stack resistance. However, an increase in the open-circuit voltage ( V OC ) progressively deviated from the theoretical linear relationship, particularly at large N and low LS conductivities. Segment-wise voltage measurements provided experimental evidence that this deviation is likely attributed to ionic shortcut currents flowing through the manifolds, which redistribute the potential along the stack and reduce the effective voltage contribution of membrane pairs in the central region of large stacks. Owing to these competing effects, the power density ( Pd ) increased when N increased from 20 to ~40, whereas further increases in N led to diminishing returns or even a decrease in Pd , depending on the operating conditions. The effects of the LS conductivity and solution linear velocity on Pd were governed primarily by their influence on the effective V OC . These findings indicate that, in RED systems with stack configurations prone to ionic shortcut currents, increasing N does not necessarily lead to an improvement in power density, underscoring the need for stack design and scale-up strategies that account for shortcut-current-induced voltage losses to achieve optimal RED performance.