Tracing the impact of stack configuration on interface resistances in reverse electrodialysis by in situ electrochemical impedance spectroscopy

• RED performance and stack resistance were studied by EIS and LSV. • Interface resistance were discriminated from Ohmic resistance by EIS. • Impacts of spacer shadow effect and concentration polarization were analyzed. • Ionic short current reduced the power density for more cell pairs. • The results enabled to predict RED performance with different configurations. Reverse electrodialysis (RED) is an emerging membrane-based technology for the production of renewable energy from mixing waters with different salinities. Herein, the impact of the stack configuration on the Ohmic and non-Ohmic resistances as well as the performance of RED were systematically studied by using in situ electrochemical impedance spectroscopy (EIS). Three different parameters (membrane type, number of cell pairs and spacer design) were controlled. The Ohmic and non-Ohmic resistances were evaluated for RED stacks equipped with two types of commercial membranes (Type I and Type II) supplied by Fujifilm Manufacturing Europe B.V: Type I Fuji membranes displayed higher Ohmic and non-Ohmic resistances than Type II membranes, which was mainly attributed to the difference in fixed charge density. The output power of the stack was observed to decrease with the increasing number of cell pairs mainly due to the increase in ionic shortcut currents. With the reduction in spacer thickness from 750 to 200 µm, the permselectivity of membranes in the stack decreased from 0.86 to 0.79 whereas the energy efficiency losses increased from 31% to 49%. Overall, the output of the present study provides a basis for understanding the impact of stack design on internal losses during the scaling-up of RED.