Large‐Area Fabrication of Robust, Foldable MOF/ANF Membrane

Abstract Metal‐organic frameworks (MOFs) hold huge potential in salinity gradient energy harvesting for the significant permeability. However, the MOF‐based membranes suffer severely in real application due to the poor flexibility and small preparation area. Here, a large‐area, roubst and foldable MOF/aramid nanofiber (ANF) heterogeneous membrane (≈137 cm ² , ≈4.8 µm thickness) is successfully prepared based on a construction strategy proposed by in situ growth of continuous rigid MOF particles on both sides of flexible polymer substrates. ANF with abundant reactive groups are compounded with metal ions and 2‐methylimidazole ligands to ensure the interfacial stability of MOFs on ANF membranes. The foldable membrane with high tensile strength (≈151.87 MPa) and fracture strain (≈9.9%) behaves excellent ion selectivity of 0.85 and power conversion density of 59.61 W m ⁻² under 500‐fold salinity gradient due to abundant angstrom/nano‐scale channels and surface electronegativity, which is at a high level compared to most of currently reported MOF‐based materials. Notably, the heterogeneous membrane holds excellent power generation stability after continuous testing for 14 days. With ANF as the substrate, the selection of different MOF particles can still achieve efficient salinity gradient energy conversion. This construction methodology provides a practical solution for flexible, large‐area and free‐standing MOF‐based nanofluidic membranes for osmotic energy conversion.