Proton donor-induced phase deposition in aramid nanofiber membranes for efficient osmotic energy harvesting

High-performance fiber-based nanofluidic membranes exhibit significant potential in osmotic energy harvesting, yet conventional aramid nanofibers (ANFs) membrane is limited by insufficient ion selectivity for efficient power generation. This study proposes a simple yet ingenious proton donor-induced phase deposition strategy to construct ANFs membrane with ultrafast ion transport capabilities. By introducing negatively charged cellulose acetate (CA) as proton donor in aramid deprotonation system (KOH/DMSO), a CA-cellulose-water ternary proton-donor system spontaneously forms in this strong alkaline environment. This system markedly enhances ANFs dispersion through a mild and stepwise proton release mechanism. Even more fortunately, during the reaction, the deacetylation of CA generates insoluble cellulose, which is deposited in situ on the fibers, narrowing the fiber spacing. This endows the membrane with sub-nanometer ion transport channels, featuring an interlayer spacing of 4.59 Å and channel diameters of 2 nm. The fabricated membrane exhibits exceptional ion selectivity (cation transport number of 0.9), achieves a power density of 22.13 W/m 2 and 28.14 W/m 2 using simulated- and natural seawater-river water, outperforming most current membranes. Simultaneously, it demonstrates high mechanical strength (122 MPa tensile strength at 1 μm thickness). This research provides novel insights into the application of ANFs membranes for efficient osmotic energy conversion.