Bioinspired Angstrom-Scale Heterogeneous MOF-on-MOF Membrane for Osmotic Energy Harvesting

Membrane-based salinity gradient energy generation from the osmotic potential at the interface of a river and seawater through reverse electrodialysis is a promising route for realizing clean, abundant, and sustainable energy. Membrane permeability and selective ion transport are crucial for efficient osmotic energy harvesting. However, balancing these two parameters in the membrane design and synthesis remains challenging. Herein, a hybridized bilayer metal–organic frameworks (MOF-on-MOF) membrane is fabricated for efficient transmembrane conductance for enhanced osmotic power generation. The heterogeneous membrane is constructed from imidazolate framework-8 (ZIF-8) deposited on a UiO-66-NH2 membrane intercalated with poly(sodium-4-styrenesulfonate) (PSS). The angstrom-scale cavities in the ZIF-8 layer promote ion selectivity by size exclusion, and the PSS-intercalated UiO-66-NH2 film ensures cation permeability. The synergistic effect is a simultaneous improvement in ion transport and selectivity from an overlapped electric double layer generating 40.01 W/m2 and 665 A/m2 permeability from a 500-fold concentration gradient interface at 3 KΩ and 9.20 W/m2 from mixing of real sea–river water. This work demonstrates a rational design strategy for hybrid membranes with improved ion selectivity and permeability for the water–energy nexus.