Space‐Confined Synthesis of Sulfonated Covalent Organic Framework‒Polymer Membranes for Enhanced Osmotic Energy Conversion

Osmotic energy, an infinite, clean energy source, can be efficiently harnessed through reverse electrodialysis using ion-selective membranes. While polymeric membranes are excellent candidates due to their solution-processability and scalability, their non-uniform pore architecture and high resistance limit their power density output. Here, an in situ space-confined synthesis strategy is proposed to fabricate sulfonated covalent organic frameworks within a sulfonated polymeric network, resulting in interconnected, well-defined ion channels. This allows a maximum power density reaching up to 40.33 W m^-2 under a 500-fold salinity gradient and a real-world power density of 14.84 W m^-2 when extracting osmotic energy from natural seawater and river water. This study underscores the potential of space-confined synthesis strategies in creating flexible and scalable ion-selective membranes for efficient salinity gradient energy harvesting, marking a significant step toward their practical applications.