A composite hydrogel with porous and homogeneous structure for efficient osmotic energy conversion

With the impact of energy crisis and environmental problems, it is urgent to develop green sustainable energy. Osmotic energy stored in the salinity difference between seawater and river water is one of the sustainable, abundant, and renewable energy. However, the membranes used to capture osmotic energy by reverse electrodialysis (RED) always suffer from low ion selectivity, low stability and low power. Hydrogels with three-dimensional (3D) networks have shown great potential for ion transportation and energy conversion. In this work, based on the homogeneity and porosity characteristics of acrylamide (AM) hydrogel, as well as the remarkable stability and abundant negative charge of 3-sulfopropyl acrylate potassium salt (SPAK), a high-performance AM/SPAK cation-selective hydrogel membrane was successfully developed for harvesting osmotic energy. Compared to AM hydrogels, utilizing AM/SPAK as a monomer mixture greatly facilitated the preparation of homogeneous polymers, exhibiting a porous structure, exceptional ion selectivity, and remarkable stability. A maximum output power density of 13.73 W/m² was achieved at a 50-fold NaCl concentration gradient, exceeding the commercial requirement of 5 W/m². This work broadens the idea for the construction and application of composite hydrogel in high efficiency osmotic energy conversion.