Renewable, All-Natural Flute Membrane with Excellent Mechanical Properties for Osmotic Energy Harvesting

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