Evaluation of power generation characteristics of reverse electrodialysis using ion exchange membranes with a novel concavo–convex structure

In recent years, salinity gradient energy (SGE), generated by mixing two salt solutions of different concentrations has gained increasing attention as a renewable energy source. Reverse electrodialysis (RED) uses ion exchange membranes to convert SGE into electrical energy. Enhancing RED power output requires reducing electrical resistance in the low-concentration side-flow channels of the RED stack. This can be achieved using profiled (PF) membranes with convex structures formed on the membrane surfaces. In this study, a novel PF membrane with a convex structure, termed ORIGAMI PF membrane, was fabricated from a single flat membrane forming convex structures keeping the membrane thickness unaffected unlike conventional PF membranes. In power generation tests using NaCl solutions with conductivities of 50 mS/cm and 0.3 mS/cm, the stack constructed with this PF membrane demonstrated a power density of 1.44 W/m², which was 48 % higher than that of the flat membrane stack. In addition, at a linear velocity of 1 cm/s, the PF membrane stack exhibited a 18 % lower pressure drop than the flat membrane stack; hence, net power density of the PF membrane was 1.24 W/m², and 70 % higher than that of the flat one. When high-concentration NaCl solutions with conductivities of 95 mS/cm and 185 mS/cm were used as the high-concentration feed solutions, the PF membrane stack achieved maximum gross power densities of 2.10 W/m² and 2.54 W/m², respectively, demonstrating a 48 % and 33 % increase, respectively, compared to the flat membrane stack under the same conditions. These results demonstrate that the developed PF membrane exhibits superior RED power generation performance compared to flat membranes, even under high-salinity conditions.