Enhanced Osmotic Energy Conversion with Ultrahigh Ionic Conductivity in Sodium Polystyrenesulfonate/Cellulose Nanofiber Composite Membranes

Biomimetic nanofluidic membranes have made great progress but still suffer from various imperfections, including complex preparation and insufficient charge density, leading to low ionic conductivity, suboptimal ion selectivity, and insufficient energy conversion efficiency. In this study, we present an approach to fabricate a polymer-based nanofluidic membrane composed of sodium polystyrenesulfonate (PSS) rich in sulfonic acid groups and cellulose nanofibers (CNFs) abundant in carboxyl groups, using a simple solvent evaporation method. At low KCl concentrations, the composite membrane demonstrated an impressive ionic conductivity of up to 0.12 S cm–1. Moreover, the resulting nanofluidic osmotic energy generator, based on the PSS/CNF composite membrane, yields a remarkable output power density of 1.75 W m–2 when exposed to a 50-fold salinity gradient KCl solution at room temperature. Notably, the composite membranes exhibit significant pH responsiveness with the output power density reaching 1.97 W m–2 at pH 11. Furthermore, we conducted a numerical simulation to investigate and analyze the impact of charge density on ion transport properties for both the pristine CNF membrane and PSS/CNF composite membrane. This work provides inspiration for the development of polymer-based nanofluidic devices aimed at enhancing osmotic energy conversion and expanding applications in the field of seawater desalination.