Synergistic 3D–2D Architectures in Cellulose-Based Asymmetric Nanofluidic Membranes for Osmotic Energy Conversion

The power density of nanofluidic membranes for osmotic energy conversion is fundamentally constrained by the long-standing trade-off between ion flux and selectivity. To address this limitation, we designed and fabricated an asymmetric nanofluidic membrane composed of a three-dimensional (3D) MOF@T-CNF layer (TEMPO-oxidized cellulose nanofibers) and a two-dimensional (2D) Lap layer (Li2Mg2O9Si3 nanosheets). Metal–organic framework (MOF) was grown in situ on the T-CNF network to enlarge and regulate ion-transport channels within the fibrous layer. Subsequently, 2D Lap nanosheets were assembled on top of the MOF@T-CNF layer, yielding a 3D/2D asymmetric architecture that enhances ion transport while maintaining selectivity. The resulting MOF@T-CNF/Lap composite membrane exhibited a maximum ionic conductivity of 3.04 × 10–4 S/cm at a MOF@T-CNF:Lap mass ratio of 2:3. Under a 50-fold KCl concentration gradient (0.01 M/0.5 M), the membrane delivered a power density of 2.32 W m–2, and it maintained a high output power of 2.09 W m–2 under realistic seawater/lake water conditions. Additionally, the mechanical strength increased to 113.2 MPa. Overall, combining the 3D T-CNF network with 2D nanosheet channels provides an effective route to improve power output in cellulose-based nanofluidic membranes, highlighting cellulose as a promising platform for osmotic energy conversion.