High-strength sulfonated cellulose nanofiber membranes with high pore density for efficient osmotic power generation

Osmotic energy, as a clean and renewable energy source derived from the salinity gradient between seawater and river water, holds great potential for alleviating global energy shortages. However, the development of high-performance nanofluidic membranes with both high ion selectivity and ion flux remains a critical bottleneck for its practical application. Herein, we report a sulfonated cellulose nanofibers (SCNF) membranes constructed with three-dimensional (3D) nanochannels featuring high charge density and pore density (2 × 10 10  cm −2 ). Under a 50-fold salinity gradient, the SCNF membrane exhibits an exceptional cation selectivity of up to 0.977. These superior ion transport properties directly translate into outstanding osmotic energy conversion performance: the maximum power densities reach 14.85 W m −2 and 111.06 W m −2 under 50-fold and 500-fold concentration gradients, respectively. Notably, the SCNF membrane maintains its power density stably for 60 days, demonstrating remarkable long-term operational durability. When mixing seawater and real river, the membrane achieves a maximum output power density of up to 16.37 W m −2 ; even upon scaling up the active testing area to 7.07 mm 2 , a considerable output power density of 1.64 W m −2 is still attained. This work provides a promising green membrane material for advancing the commercialization of osmotic energy technology.