Hydrophobic Porous Organic Cage Membranes for Enhanced Ion Transport and Osmotic Energy Harvesting

Porous organic cages (POCs) exhibit excellent solubility and processability, enabling their facile fabrication into membranes, which makes them promising for efficient, sustainable osmotic energy harvesting. However, POCs linked by reversible imine bonds are unstable in aqueous media, limiting their practical applications. Herein, we fabricate a cation-selective hydrophobic TpOMe-CDA/AAO nanofluidic membrane. The hydrophobic environment around the imine bond prevents cage molecule hydrolysis, enhancing stability. Hydrated ions sliding through subnanometer windows and hydrophobic internal and external cavities of TpOMe-CDA, ensuring high ion permeability and selectivity. Consequently, a maximum power density of 81.61 W m^-2 is achieved under 500-fold NaCl gradient in osmotic energy harvesting, superior to most recently reported nanofluidic membranes. In comparison, hydrophilic CC19 and moderately hydrophobic CC3 membranes attain decreased power densities of 9.57 and 22.98 W m^-2, respectively. This work highlights efficient ion transport in the hydrophobic nanochannels of POCs membranes and its potential role in osmotic energy harvesting.