Membrane-free osmotic power generators with high-performance energy conversion

Abstract

Osmotic energy between two solutions with salinity gradients, is sustainable and converted generally into electricity through membrane-based processes. However, high membrane resistance limits extremely output power densities to 10 W m -2 at a large scale. Herein, we developed a membrane-free osmotic power generator (OPG), using immiscible polycation and polyanion aqueous sols. With two sols stacking, polyelectrolyte bilayers assemble spontaneously at the interphase, thereby enabling bidirectional cation/anion selective transport. Combining 50-fold NaCl salinity gradients, a single membrane-free OPG unit can exhibit the optimal output power densities of 39.4 (Na + gradients) or 74.9 (Cl -gradients) W m -2 due to quite low internal resistance, which are far higher than reported works (< 10 W m -2 ) under the simialr condition. Moreover, these polyelectrolyte bilayers were self-healing and kept stable output current after puncturing. Integrated OPGs can be connected in series by alternatively liquid-liquid stacking, performing designable voltage output (i.e., ~0.035 V pair -1 ). As a proof-of-concept, integrated OPGs can be packed as flexible power supply for other electronics. This work propose a new approach to design high-performance OPGs for the practical applicaitions.