Heterogeneous membranes that exhibit an ionic diode effect are promising candidates for osmotic energy conversion. However, existing heterogeneous membranes lack molecular-level designed ion channels, thereby limiting their power densities. Here, we demonstrate ionic diode covalent organic framework (COF) membranes with well-defined ion channels, asymmetric geometry and surface charge polarity as high-performance osmotic power generators. The COF diode membranes are comprised of heterojunctions combining a positively charged ultrathin COF layer and a negatively charged COF layer supported by a porous COF nanofiber scaffold, exhibiting an ionic diode effect that effectuates fast unidirectional ion diffusion and anion selectivity. Density functional theory calculations reveal that the differentiated interactions between anions and COF channels contributed to superior I- transport over other anions. Consequently, the COF diode membranes achieved high output power densities of 19.2 and 210.1 W m-2 under a 50-fold NaCl and NaI gradient, respectively, outperforming state-of-the-art heterogeneous membranes. This work suggests the great potential of COF diode membranes for anion transport and energy-related applications.
Bibliographical noteFunding Information:
This work was supported by the KAUST Centre Competitive Fund FCC/1/1972-19 and KAUST baseline fund BAS/1/1375-01.
© 2022 American Chemical Society.
- covalent organic framework membranes
- high charge density
- ion transport
- ionic diodes
- osmotic energy conversion
ASJC Scopus subject areas
- General Materials Science
- General Engineering
- General Physics and Astronomy