Energy Harvesting: a universal model for reverse electro-dialysis

Reverse-Electro-Dialysis (RED) allows us to tap into the naturally occurring concentration asymmetry between seawater and freshwater to generate sustainable electricity. This salt concentration asymmetry is abundant and self-sustained by way of the water cycle and thus presents a novel sustainable energy source that could revolutionize the global energy market. However, much of RED’s microscopic details are not thoroughly understood due to the complex geometry and material properties of the ion-selective membranes. This has led to the conventional reliance on trial-and-error for optimizing RED systems. To overcome these challenges, we derived a universal model for all RED systems that accounts for the key parameters of these systems. We found analytical expressions for the open-circuit electric voltage and the Ohmic resistance. Our model is confirmed by numerical simulations and existing analytic models and thus delineates the transport characteristics of RED systems. Notably, the physics of energy harvesting via RED has been elucidated, and our findings can be used to improve and expedite the design of any RED system using permselective materials for ion transport.