Two-dimensional metal-organic framework nanocomposite membranes with shortened ion pathways for enhanced salinity gradient power harvesting

Harnessing energy through the reverse electrodialysis-based salinity gradient power conversion is an exciting and promising technological endeavor. The key to its success lies in developing the advanced ion-selective membrane capable of enhancing ion flux and accelerating ion transport at confined nanospaces. Traditional two-dimensional (2D) membranes typically employ a layer-by-layer arrangement of nanosheets with an extremely narrow layer separation, limiting ion flux and creating elongated 2D ion pathways. In response to this limitation, our study introduces an innovative design of the 2D metal-organic framework (MOF)-based nanocomposite membrane (named as Cu-TCPP@SNF), which is composed of the 2D Cu-TCPP and natural-based silk nanofibers (SNFs). We show that the introduction of the space-charged SNFs can significantly enhance the stability of the 2D MOF nanocomposite membrane in electrolyte solutions, and this unique framework facilitates a multitude of abundant one-dimensional ion pathways across the membrane while maintaining the advantage of minimal layer separation. Our results demonstrate that the Cu-TCPP@SNF exhibits low resistance, thus facilitating ion transport. Furthermore, numerical simulations elucidate the impacts of the SNF content and membrane thickness on power performance. Remarkably, our membrane achieves a notable power density of -6.48 W/m2 by mixing artificial seawater and river water. Impressively, an ultrahigh performance of -29.5 W/m2 can be achieved under a 5 M/0.01 M NaCl gradient, surpassing the existing advanced membranes. These findings hold significant promise for the future of composite 2D membrane development, paving the way for scalable applications in salinity-based energy harvesting.