Ice-Confined Synthesis of Stacked Polymer Nanospheres as Osmotic Power Generation Membranes

Osmotic power extracts electricity from salinity gradients and provides a viable route toward clean energy. To improve the energy conversion efficiency, common strategies rely on fabricating precisely controlled nanopores to meet the requirements of high ionic conductivity and selectivity. We report ion transport through the free-volume networks in stacked polymer nanospheres for osmotic power harvesting. Such nanospheres, composed of coiled poly(acrylic acid) molecules, are synthesized at an ice-liquid interface where they self-assemble into continuous membranes with controlled thicknesses and morphologies. We achieve a rival power density of a few thousand watts per square meter, attributed to the fast and selective ion transport through the nanostructured membranes. The selectivity is further found to originate from the membranes' tunable charging states determined by the association/dissociation equilibrium of the residual groups and the presence of translocation ions. Our work suggests polymer membranes absent of straight-through pores as a new platform for efficient osmotic energy generation.