Cation-π and Electrostatic Interplay in Ultraselective Polymeric Nanofluidics for Exceptional Osmotic Energy Conversion Efficiency

Fast ion transport across nanofluidics, driven by salinity gradients, has drawn ever-increasing attention, due to its huge potential in osmotic energy generators. Previous studies have reported a concentration polarization (CP) effect over highly conductive nanofluidics surfaces, where the rate of ion dissipation surpasses ion accumulation. The phenomenon results in low cation/anion transmembrane selectivity, especially for large-scale nanofluidics, thereby limiting the energy conversion efficiency. Here, we propose a strategy of cation-π and electrostatics interplay to design ultraselective polymeric nanofluidics with great immunity to CP, using two polyanions with carbazole and sulfonic moieties. Experimental results show an anomalous CP effect that is contrary to ion dissipation-dominated salinity gradient decline in typical nanofluidics. Through simulations, we reveal an "adsorption-to-transport" mechanism, relying on cation accumulation driven by strong cation-π forces. On the two sides of nanofluidics, the interphase salinity gradients are increased to weaken cation dissipation and promote cation/anion transmembrane selectivity. Applied to osmotic power generators, a record single-cell voltage output and ultrahigh energy conversion efficiency are provided for over 72 days. This work provides inspiring insights into the role of supramolecular effects on ultraselective nanofluidic systems.