Salinity-Ultrasensitive Hydrogels for High-Performance Salinity Gradient Energy Conversion and Harvesting

Abstract

Salinity gradient energy is an abundant clean energy source, and its conversion into mechanical energy holds great significance. The development and performance of salinity-ultrasensitive polyzwitterionic hydrogels have been investigated here for efficient salinity gradient energy conversion. The ionic hydrogels were then synthesized using varying crosslinking densities and demonstrated significant volume changes in response to low-concentration salt solutions. The poly(acryloyloxyethyltrimethyl ammonium chloride-co-2-(methacryloyloxy) ethyl dimethyl sulfopropyl ammonium hydroxide) hydrogels (PNS) exhibited a highly sensitive polyelectrolyte effect, with volume changes reaching up to 60 times in a 0.1 M NaCl solution. The optimal crosslinking density was determined to be 0.4%, which provided a balance between the swelling capacity, mechanical stability, and cycle time for energy recovery. Smaller hydrogel particles (1 mm) showed a higher energy recovery efficiency, achieving up to 202.98 mW/kg under a 20 g external load. The hydrogels also exhibited excellent recyclability and stability over multiple cycles, even when exposed to complex mixed salt solutions. These findings highlighted the potential of the PNS hydrogels as a promising material for sustainable and efficient salinity gradient energy conversion, thereby offering a novel approach for the harnessing of osmotic energy from seawater and other saline sources.