Renewable,\nAll-Natural Flute Membrane with Excellent\nMechanical Properties for Osmotic Energy Harvesting

Ion-selective\nmembranes serve as key materials for reverse electrodialysis\n(RED) technology in osmotic energy harvesting, and the search for\na class of membranes that are economical, highly robust, and sustainable\nhas been a relentless goal for researchers. In this work, all-natural\nbiomass membranes (reed membranes) are often used as a flute diaphragm,\nwhich makes the flute produce a brighter and crisper sound, presenting\nhigh strength and elasticity. Ultrathin natural reed membranes (thickness\nof ≈4.06 μm) were selected as representative materials\ndue to their impressive mechanical properties with a top-level combination\nof yield strength (≈63.5 MPa) and strain (∼2%) among\nall reported natural materials. More importantly, there are numerous\nnanoscale pores and negatively charged −OH groups on the reed\nsurface, providing tiny nanofluidic channels for efficient cation\ntransmembrane transport, which endow the flute membrane with excellent\nselectivity for caution and stable salinity-gradient energy conversion\nperformance. The reed membrane delivers excellent osmotic energy conversion\nperformance with a power output density of 22.2 W m<sup>–2</sup> in 500-fold NaCl concentration as well as high stability (power\ndensity maintained at 98.53% for more than 6000 s). This work provides\na strategy for all-natural ion-selective membranes in terms of economy,\nfabrication simplicity, and stability, which has potential utility\nin various applications such as osmotic energy harvesting.