Leveraging Natural Wood Structures for Sustainable and High‐Performance Osmotic Energy Harvesting

ABSTRACT Among emerging energy‐harvesting technologies, salinity gradient energy via reverse electrodialysis is a promising route to mitigate energy and environmental pressures. Delignified natural wood framework provides natural ion‐transport channels for osmotic energy harvesting and holds significant promise, yet its low surface‐charge density constrains efficiency. Accordingly, a wood framework/sodium alginate (W/SA) heterogeneous membrane was produced by infiltrating SA, which is rich in negatively charged groups, into the delignified natural wood framework and crosslinking to form a stable, ion‐selective architecture. The W/SA membrane delivers a power density of 14.43 W m − 2 under a 50‐fold NaCl gradient, 2.88 times the 5.0 W m − 2 commercial standard. In KCl, it reaches 19.76 W m − 2 , outperforming most reported wood‐based or fiber‐based membranes. Ion transport is markedly enhanced, and conductivity at 10 − 6 m NaCl rises from 1.12 × 10 − 5 to 5.11 × 10 − 4 S cm − 1 , facilitating ion diffusion and migration. W/SA membrane (0.6 × 5 × 20 mm 3 ) can support 500 g, and a 15‐unit series device outputs 2.16 V, evidencing practical feasibility. The construction of this ion‐selective membrane not only offers a practical, green and sustainable strategy for low‐cost fabrication of high‐performance ion‐selective membranes but also opens new possibilities for its future application in commercial membrane manufacturing.