Generating Power Through Salinity Gradients in Osmotic Engines via Microfluidic Synthesized Hydrogel Particles

Salinity-gradient energy at river deltas represents a promising yet underexploited renewable resource. Osmotic engines can harvest this energy by converting chemical potential differences between fresh and saline water into mechanical power. Hydrogels are potential osmotic matrix materials due to their high water-uptake capacity, salt-responsive swelling, and mechanical resilience. Cyclic swelling in fresh water and deswelling in saline water of hydrogels drives piston motion in the osmotic engine, enabling mechanical energy generation. In this work, monodisperse hydrogel particles are synthesized via a microfluidic device and the effects of key synthesis parameters on hydrogel properties are investigated. Two osmotic engines with different volumes and height-to-diameter ratios are designed and evaluated, with operating parameters including gel mass, cycle time, applied pressure, and flow rate optimized to maximize power output. The maximum power of 13.20 W per 1 kg dry hydrogel is achieved with deionized water and NaCl solution of 43 g·L$^{−1}$ using poly(acrylic acid) hydrogels with a diameter of 233 µm and a degree of crosslinking of 0.5 mol%. ... mehrThese results highlight the potential of microfluidic-synthesized hydrogel particles as osmotic matrix materials and demonstrate that rational engine design and operating parameter optimization significantly enhance the performance of energy conversion from salinity gradients.