Multi-ion transport in reverse electrodialysis: A validated model for design and optimization

Reverse electrodialysis (RED) generates electric energy converted from salinity gradient by using membranes. As the lower concentration results in current loss by ionic resistance, multi-ionic RED has been proposed to enhance RED performance. This study focused on a complete description of ionic transport behavior in the multi-ionic RED. Analytical models for the entire membrane active area were constructed in three-dimensional Multiphysics using fluid dynamics and the Nernst-Planck framework. To effectively estimate multi-ion transport and device performance, a calibration for the diffusion coefficient, which is an inaccessible parameter in the membrane region, was progressed and validated with experimental data. Open circuit voltage and short circuit current tracked the diffusion coefficient in relation to the volumetric flow rate of the electrolytes. By incorporating an additional regression analysis model for calibration, the performance of the geometrically modified devices for membrane active area, electrolyte thickness, and flow mode of the electrolyte was predicted and also verified for membrane active area. This method facilitates accurate multi-ionic transport analysis with simplified computation and a complete reflection of numerous factors in the diffusion coefficient. Our predictive tools were consequently applied to design a highly efficient RED device with complex ion composition and optimize the operating fluid conditions.