Pillararene-based supramolecular polymeric sub-nanochannel membranes with enhanced cation selectivity for osmotic energy conversion

Abstract

The development of ion-selective sub-nanochannel membranes with high ionic flux and low electrical resistance remains a huge challenge. Herein, pillararene-based supramolecular polymeric membranes were assembled using the network-structured sulfo group poly(pillar[5]arene) and sulfonated poly(ether ether ketone). Highly selective cation transport and efficient salinity gradient energy conversion were achieved by reconstructing the ion transport channel and introducing free volume to make the channel size less than 1 nm. Pore size distribution was adjusted by increasing the pillararene content, improving the microstructure and macroscopic properties of nanochannel membranes, and promoting ion transport. The ion transport mechanism within the transport channel was generated via multiple synergistic effects of increasing charge density, free volume, and cation-π interactions. As osmotic energy generators, pillararene-based supramolecular polymeric membranes exhibited an impressive output power density of 19.3 W m⁻² and an ultra-high Na⁺ transference number (0.98), with an energy conversion efficiency of 46.1 % at a 50-fold NaCl concentration gradient. These results present a novel strategy to construct angstrom-scale channel for the application toward emerging energy technologies.