Ultra-thin pore-filling membranes with mirror-image wave patterns for improved power density and reduced pressure drops in stacks of reverse electrodialysis

Abstract

Reverse electrodialysis (RED) emerged as a promising membrane-based technology due to an increased interest in salinity gradient energy. We report on the fabrication and characterization of ion-exchange membranes wave-patterned with non-conductive materials and supported by thin (16-μm-thick) pore-filling membranes. These membranes, which are double-sided or single-sided, are designed to secure stable electrolyte channels based on wave lines with mirror images. Cross-flow RED stacks were evaluated as functions of cell pairs and flow rates. The non-conductive material increases the membrane resistance for anion and cation exchange, maintaining permselectivity approximately constant. The gross power density of a flat stack is higher than that of a single-sided patterned membrane stack; however, the latter exhibits superior net power density, particularly at high flow rates. The pressure drop of the single-sided wave-patterned membrane is significantly lower (~3 × ) than that of the flat membrane. The maximum gross power density was 1.39 W/m2 for 10-cell pairs, and the optimum cell pairs were 30, with the highest net energy efficiency of 9.4%. The net energy efficiency can be maximized by optimizing the design and operating conditions of the RED stack and net power density, via the addition of an ionic conductivity function to the patterned structure.