One-pore synthesis of ionic nanogel osmotic power generators

Selective ion transport is fundamental to technologies ranging from water desalination to sustainable energy generation, yet achieving both high selectivity and permeability in nanoporous membranes remains a long-standing challenge. Here, we present a voltage-directed in-pore gelation strategy to create ultrathin ionic nanogels within solid-state SiNx nanopores. By spatially confining the Ca2+ crosslinking reaction in sodium alginate at the single-pore level, we fabricate hydrogel membranes with tunable ion selectivity, switchable between cations and anions via solute encapsulation. Incorporation of phosphate compounds into the polymer matrix serves to enhance cation selectivity, while outperforming conventional ion-exchange membranes by several orders of magnitude in permeability by virtue of the nanoscale thinness, thereby enabling osmotic power densities up to 213 kW/m² with single nanogels. This scalable, one-pore synthesis approach offers a versatile platform for next-generation ionic membranes, opening new avenues in blue energy harvesting and ion separation systems. Selective ion transport is fundamental to technologies including water desalination and sustainable energy generation, yet achieving high selectivity and permeability in nanoporous membranes is a challenge. Here, a voltage-directed in-pore gelation strategy is used to create ultrathin ionic nanogels within solid-state SiNx nanopores.