Phosphorylated Natural Bamboo Membrane for Osmotic Energy Harvesting

The development of low-cost and environment friendly ion-selective nanofluidic membranes with a high-performance is necessary for osmotic power generation. Natural bamboo membranes with a layered structure provides water and nutrients transport channels for bamboo growth. Here, we introduce ionized phosphate groups into natural bamboo membranes through a urea-assisted dehydration reaction between the hydroxyl groups in cellulose and phosphoric acid. The phosphorylated bamboo membrane exhibits surface-charge-governed ion transport with a cationic selectivity. When applied for osmotic energy harvesting, it achieves a power density of 6.42 W/m 2 under a 50-fold salinity gradient formed by 0.5/0.01 m KCl, and a rising value of 22.1 W/m 2 in hypersaline water, outperforming reported synthetic cellulose membranes and natural membranes. A tandem stack of 24 units produces 1.8 V voltage, serving as the power source for a calculator. Our work presents a promising strategy for developing sustainable nanofluidic membranes from nature for efficient osmotic energy conversion.