Multifunctional Boron Nitride/Sodium Alginate Lamellar Membranes for Robust Osmotic Energy Harvesting and Thermal Management

Osmotic energy, derived from salinity-gradient-driven mixing, is a clean renewable resource that may help address energy and environmental challenges. Ion-exchange membranes incorporating two-dimensional (2D) materials are attractive for reverse electrodialysis, yet manufacturing large-area membranes with low transport resistance remains challenging. In this work, 2D boron nitride (BN)/sodium alginate (SA) composite membranes are fabricated through polymer-assisted ball-milling exfoliation and doctor-blade casting; subsequent Ca2+-induced ionic crosslinking of SA is used to strengthen their stability in water. The as-prepared membranes possess a mesoscopic lamellar architecture that supports ion migration. At a BN content of 50 wt %, the composite membrane achieves a thermal conductivity of 24.1 W m–1 K–1 and an elastic modulus of 4.1 GPa. Under a 50-fold salinity gradient, a single membrane device delivers a peak output power of 3753 nW with a device-level internal resistance of approximately 450 Ω. The membrane also retains osmotic power generation across the tested temperature (1.5–36 °C) and pH (2–12) windows. Overall, this study establishes a scalable route to multifunctional BN/SA composite membranes and broadens their potential use in osmotic energy harvesting and related ion-transport applications.