Scalable fabrication of regenerated cellulose nanohybrid membranes integrating opposite charges and aligned nanochannels for continuous osmotic energy harvesting

Nanomaterials are widely used in constructing reverse electrodialysis (RED) systems with charged nanochannels for osmotic energy harvesting. However, preparing low-cost, large-scale, and high-performance RED systems with significantly improved ion selectivity, ion flux, and output power density is still a challenge. Herein, we develop a facile solution-casting method to fabricate oriented regenerated cellulose (RC)/carbon nanotubes (CNTs) nanohybrid membranes. After integrating chemical modification (i.e., TEMPO oxidation and quaternization) and structural densification, both negatively charged N-RC/N-CNTs and positively charged P-RC/P-CNTs membranes demonstrated significantly enhanced ionic conductivity in a low-concentration solution (4.02 ×10−4 and 3.59 ×10−4 S cm−1, respectively). Particularly, the P–N unit not only yields an output power density of 5.28 W m−2 in a 50-fold concentration gradient, which exceeds the commercial standard (5 W m−2), but also achieves long-term stability over 50 days. As a proof of concept, we created a RED system with 20 P–N units connected in series which successfully powered an electronic calculator with an output voltage of 2.06 V under artificial seawater and river water conditions. This work improves the development of natural renewable materials for high-performance osmotic energy conversion.