Phosphorylation-assisted cell wall engineering enables ultra-strong, highly ion-conductive bio-membranes for high-power salinity gradient energy harvesting

Nanofluidic membranes derived from cellulose-based biomaterials have garnered increasing attention for ion transport and regulation due to their modifiable nature, ordered structures, sustainability, and excellent compatibility. However, their practical applications in ionic circuits, energy conversion, and sensing have been limited by insufficient mechanical strength and suboptimal ion transport properties. In this study, we report ultra-strong, highly ion-conductive bio-membranes fabricated through phosphorylation-assisted cell wall engineering. This process introduces high-density anionic phosphate groups onto cellulose chains while preserving their natural hierarchical alignment across macroscopic to molecular scales. The resulting PhosWood-40 membrane (bio-membranes phosphorylated for 40 minutes) shows exceptional performance, with a record-high ion conductivity of 21.01 mS cm^-1 in 1.0 × 10^-5 mol L^-1 KCl aqueous solution, an ionic selectivity of 0.95, and a high tensile strength up to 241 MPa under dry conditions and 66 MPa under wet conditions. Phosphorylation enhances the membrane's ionic conductivity by 100-fold and improves cation/anion ratio by 38-fold compared to the unmodified membrane, primarily due to the increased surface charge density and optimized ion channel accessibility. Under simulated conditions of artificial seawater (0.5 mol L^-1) and river water (0.01 mol L^-1), the phosphorylated PhosWood-40 membranes achieve a remarkable output power density of 6.4 W m^-2, surpassing unmodified membranes by 30-fold and outperforming other bio-based nanofluidic systems. This work highlights the potential of renewable and easily modifiable cellulose-based biomaterials for developing high-performance nanofluidic systems.