Chemically Engineered TEMPO-KCNF Membranes with High Solution Stability for Osmotic-Energy Harvesting

The utilization of biomass-derived native cellulose to fabricate freestanding membranes has garnered increasing attention in the field of osmotic-energy harvesting. However, the poor film-forming stability and low surface charge density of natural fiber membranes severely restrict their practical performance. Here, a kelp membrane with a nanocellulose structure was prepared by dissolution-regeneration, followed by 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO)-mediated oxidation. Chemically engineered and integrated TEMPO-Kelp cellulose nanofibril (KCNF) membranes deliver an output power density of 5.2 W m–2 while retaining 97.9% of their initial performance over 2000 s of continuous operation owing to the abundant negatively charged carboxylate groups. The membranes demonstrate robust adaptability across diverse saline environments in China, achieving an impressive 6.2 W m–2 in natural seawater. This work highlights TEMPO-mediated oxidation to prepare natural native celluloses for high-efficiency energy-conversion applications.