Engineered sulfonated porous carbon/cellulose nanofiber hybrid membrane for high-efficiency osmotic energy conversion...

Harnessing ionic gradients to generate electricity has inspired the development of nanofluidic membranes with charged nanochannels for osmotic energy conversion. However, achieving high-performance osmotic energy output remains elusive due to the trade-off between ion selectivity and nanochannel membrane permeability. In this study, we report a homogeneous nanofluidic membrane, composed of sulfonated nanoporous carbon (SPC) and TEMPO-oxidized cellulose nanofibers (T-CNF), engineered to overcome these limitations. Incorporation of carboxyl groups on the T-CNF surface and the sulfonic acid groups within SPC confers high cation selectivity, reaching up to 0.88, and enhances high energy conversion efficiency to 38.3 %. Furthermore, the SPC component forms three-dimensional interconnected nanopore channels that serve as extensive ion transport pathways, allowing the hybrid membranes to exhibit high transmembrane ion flux. This structural design enhances ion conductivity, reaching up to 0.8 S/cm at low KCl concentrations (≤0.01 M). With their high ion selectivity and rapid ion transport capabilities, SPC/T-CNF hybrid membranes achieve high-performance osmotic energy conversion, delivering an output power density of 1.08 W/m² under conditions simulating the interface of seawater and river water, while maintaining stability over 25 days. This economical and easily fabricated porous nanofluidic hybrid membrane featuring nano-porous carbon paves the way for advanced energy-harvesting devices.