2D Graphene Oxide-Polyelectrolytes Composite Membranes with Enhanced Ion Sieving for Nanofluidic Energy Generation.

2D nanofluidic membranes, with their nano-structured lamella architecture, offer effective control over ion transport, making them promising candidates for osmotic energy harvesting based on electrolyte concentration gradients. However, low-concentration electrolytes increase internal resistance, which leads to reduced output power, thereby limiting the practical application of nanofluidic energy generators. In this study, a high-power nanofluidic energy generator is proposed by replacing the low-concentration electrolytes with the high-concentration divalent electrolytes. Here, oppositely charged graphene oxide (GO)-polyelectrolytes composite membranes produce a high membrane potential by selectively allowing the transport of a single ionic species among various ions, such as biological ion channels. By modifying GO with polyelectrolytes to increase surface charge density and applying additional mild heating to adjust the interlayer spacing, ion sieving properties of the GO membranes are enhanced. As a result, the cation-selective membrane achieved a K⁺/Mg⁺ selectivity ratio of 41.6, while the anion-selective membrane attained a Cl⁻/SO₄⁻ selectivity ratio of 30.8. The energy device using the GO-polyelectrolyte membrane pairs achieved a power density of 5.49 W m⁻ under a 50-fold concentration gradient of NaCl, which is further improved to 9.48 W m⁻ in a system utilizing high-concentration divalent ions.