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

Abstract

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-NH 2 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-NH 2 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/m 2 and 665 A/m 2 permeability from a 500-fold concentration gradient interface at 3 KΩ and 9.20 W/m 2 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.

Charge-Gradient Sulfonated Poly(ether ether ketone) Membrane with Enhanced Ion Selectivity for Osmotic Energy Conversion

“…These curves showed distinguishable ion transmembrane conductance, attributed to the superhydrophilic nature and the high channel density of −SO 3 H groups in the membrane. 11 Notably, the ionic conductance of the CG-SPEEK-L 15 H 5 membrane (70. The transmembrane ionic conductance of these three membranes deviated from the bulk value when the electrolyte concentration was <0.1 M, indicating that ion transport through these membranes was primarily governed by the surface charge.…”

“…These approaches leverage the creation of an ionic diode effect, facilitating oneway ion diffusion while preventing the generation of reverse current and mitigating the ion polarization phenomenon. 7−11 For instance, researchers have developed an asymmetric heterostructured membrane composed of ordered mesoporous silica (∼8.3 nm) and macroporous alumina (∼80 nm), 11 achieving an output power density of up to 4.5 W m −2 under mixing seawater and river water, attributed to its ionic diode effect. While asymmetric heterostructures are promising, a critical limitation of heterogeneous membranes lies in the potential incompatibility at interfaces between dissimilar materials, leading to delamination and low interfacial ionic transport efficiency.…”

Ion transport and conduction in metal–organic framework glasses

“…76 This behaviour is more commonly observed in asymmetrical polymer nanopores, but has also been observed recently in crystalline MOF-on-MOFs. 71,92 Unidirectional ion transport arises due to an ion concentration gradient induced by the asymmetrical distribution of surface charged groups along the pore, which enhances ion conduction in one direction but restricts conduction in the opposite direction. 76 The conduction of ion is typically favoured going from the narrow/tip side with high surface charge density to the larger/base side.…”

Leveraging metal node-linker self-assembly to access functional anisotropy of zirconium-based MOF-on-MOF epitaxial heterostructure thin films

“…Comparative analysis with the original MOFs has demonstrated improved adsorption, diffusion and catalytic properties in these heterostructures. 32–34…”