Local enhancement of concentration gradient through the hydrogel-functionalized anodic aluminum oxide membranes for osmotic power generation

The salinity gradient between seawater and river water is a type of Gibbs energy that can be converted into electrical energy by an ion-exchange membrane. Although the salinity gradient between two aqueous solutions can be adjusted in a laboratory to improve the energy-harvesting performance, the salinity gradient in natural resources is rather constant, restricting the prospects of membrane-mediated power generation. To address this issue, we demonstrate the local enhancement of the salinity gradient through hydrogel-functionalized anodic aluminum oxide (AAO) membranes. In the composite structure, the surface-modified AAO membrane attracts the mobile counter ions from the hydrogels to increase the local concentration of mobile ions inside the nanopores of AAO membrane. Owing to the local concentration enhancement, the hydrogel-functionalized AAO membranes could extract electrical energy with improved efficiency, which could power small electronic devices. Graphical Abstract Hydrogel-functionalized anodic aluminum oxide (AAO) membranes have been prepared, which could locally enhance a concentration gradient in the salinity-gradient cells to extract electric energy with improved efficiency.