Four-way diffusion in miniaturised devices of reverse electrodialysis

The growing demand for flexible, biocompatible, and environmentally friendly power sources for wearable devices has led to an increased interest in alternative technologies. Among them, reverse electrodialysis (RED) stands out as a promising renewable energy technology, harnessing salinity gradients between seawater and river water to generate electricity. Although RED has a high potential as a power source, conventional RED designs face challenges in increasing power density, stability, and versatility particularly when it is miniaturised for portable applications. Owing to its serially stacked structure, RED can only provide very small currents to the external load, as the internal resistance increases proportionally with the number of membranes. Additionally, RED may produce an unstable voltage output because the current cannot bypass blockages or broken circuits through alternative pathways. In this study, we address these challenges by introducing a novel parallel structure, four-way diffusion compact RED (cRED), which enhances the stability while increasing the power density by reducing the total volume. Theoretical properties of various forms of parallel-connected series RED (pRED) and cRED were investigated. cRED can achieve up to twice higher volumetric power density compared to pRED due to its compact structure. Furthermore, cRED exhibits superior voltage stability and current amplification to those of conventional series designs. The advancement enables the utilisation of the miniaturised RED as a power source, preventing waste from conventional batteries where only a small power is required, offering a compact, versatile, and sustainable alternative for renewable energy generation, promising environmentally friendly energy solutions. A novel four-way diffusion structure for Reverse Electrodialysis (RED), named compact RED (cRED), addresses the stability and power density challenges of the conventional series design, leading to substantial improvements in both metrics.