Experimental analysis of an upscaled reverse electrodialysis unit featuring electrode segmentation

Abstract

Reverse electrodialysis (RED) is a technology that produces renewable energy from salinity gradients. In 2024, the EU has identified the RED process as a potential soon-to-be marketable technology for osmotic energy exploitation. For this purpose, high power densities and energy efficiencies are essential to achieve to increase the technology readiness level (TRL) of this technology. In this context, it is crucial to study the transition from lab-scale set-ups to pilot-scale units with larger membrane area. In this work, an upscaled RED unit (10 × 80 cm2), equipped with segmented electrodes, was employed in an extensive experimental study where (i) flow velocities, (ii) high saline solution concentrations (up to 5.0 mol/L NaCl), and (iii) electrode configurations were varied to assess the influence of channels length on power generation and energy efficiency. Larger energy efficiencies obtained with long channels improved the overall power output and resources exploitation, reaching yield values of ∼0.5 kWh/m3, the highest ever reported in the literature. The electrode segmentation feature, explored for the first time with hypersaline solutions, allowed current density to be optimized across different sections of the unit, yielding up to a 21% increase in power density (maximum net power density of 4.1 W/m2) compared to undivided electrodes. Results marked useful indications for future RED commercial implementation.