Aligned regenerated cellulose-based nanofluidic fibers with ultrahigh ionic conductivity and underwater stability for osmotic energy harvesting

The growing interest in biomass-based nanofluids has revealed flaws in large-scale manufacturing, customizable aligned nanostructures, and the weak interaction of structural components, resulting in low ionic conductivity, unsatisfactory long-term reliability underwater, and insufficient energy conversion efficiency. Herein, we present a bottom-up strategy integrating cellulose dissolution, orientation, regeneration, and densification to construct regenerated cellulose-based nanofluidic fibers (RCNFs) comprising a high weight content of acidified carbon nanotubes (40 %), aligned nanochannels (3–4 nm), and negatively charged surfaces (–3.05 mC m⁻²). Benefited from the synergistic alignment and spatial confinement of CNTs by the cross-linked cellulose network, the RCNFs realized a high underwater strength (29 MPa), unprecedentedly high ionic conductivity (0.07 S cm⁻¹) at low salt concentrations (<0.001 M), and high long-term output power density (2.57 W m⁻² over 43 days) in an artificial river water–seawater system. In a proof-of-concept experiment, customizable RCNF-based devices connected in series powered a calculator and LED lights at a 50-fold concentration gradient. This work can promote the application of regenerated cellulose in high-performance osmotic energy conversion systems.