Bioinspired Fractal Design of (Reverse) Electrodialysis Stacks

This paper offers a perspective on the future of energy harvesting through reverse electrodialysis (RED), particularly in systems using seawater and river water as feed solutions. Although significant progress has been made in membrane development and in optimizing flow configurations—through the introduction of alternative spacers and profiled membranes that enhance mixing and reduce polarization—the overall advancement of RED technology has stagnated for nearly a decade. A persistent negative scale factor continues to favor small-scale applications while limiting the feasibility of large-scale power generation. We propose that renewed progress may arise from fractal-inspired system architectures, in which the efficiency of small RED units is preserved and amplified through hierarchical organization and cooperative operation of many such elements. Two conceptual approaches are outlined. The first explores fractal geometries within the intermembrane compartments, focusing particularly on the river water compartment, which typically exhibits the highest ohmic resistance. The second envisions the modular aggregation of numerous cross-flow stacks into large-scale assemblies whose overall performance scales constructively with the number of units. Together, these ideas suggest a new design paradigm in which scalability and efficiency are reconciled through fractal system organization.