Large-Area Ultrathin Metal-Organic Framework Membranes Fabricated on Flexible Polymer Supports for Gas Separations.

Ultrathin continuous metal-organic framework (MOF) membranes have the potential to achieve high gas permeance and selectivity simultaneously for otherwise difficult gas separations, but with few exceptions for zeolitic-imidazolate frameworks (ZIF) membranes, current methods cannot conveniently realize practical large-area fabrication. Here, we propose a ligand back diffusion-assisted bipolymer-directed metal ion distribution strategy for preparing large-area ultrathin MOF membranes on flexible polymeric support layers. The bipolymer directs metal ions to form a cross-linked two-dimensional (2D) network with a uniform distribution of metal ions on support layers. Ligand back diffusion controls the feed of ligand molecules available for nuclei formation, resulting in the continuous growth of large-area ultrathin MOF membranes. We report the practical fabrication of three representative defect-free MOF membranes with areas larger than 2,400 cm2 and ultrathin selective layers (50-130 nm), including ZIFs and carboxylate-linker MOFs. Among these, the ZIF-8 membrane displays high gas permeance of 3,979 GPU for C3H6, with good mixed gas selectivity (43.88 for C3H6/C3H8). To illustrate its scale-up practicality, MOF membranes were prepared and incorporated into spiral-wound membrane modules with an active area of 4,800 cm2. The ZIF-8 membrane module presents high gas permeance (3,930 GPU for C3H6) with acceptable ideal gas selectivity (37.45 for C3H6/C3H8).

Ultrathin Low-Crystallinity MOF Membranes Fabricated by Interface Layer Polarization Induction.

Practical, ultrathin metal-organic framework (MOF) membranes have the potential to achieve otherwise difficult separations, but current fabrication methods still face challenges in the simultaneous improvement of both selectivity and permeance. Here, ultrathin, low-crystallinity-state MOF (LC-MOF) membranes are realized by a facile general method of interface layer polarization induction. This is achieved using an interface layer having metal ions with dense and uniform distribution, resulting in the creation of abundant open metal sites. Three types of LC-MOF membranes (45-150 nm) are fabricated, among which ZIF-8 membranes modified in situ with diethanolamine (DZIF-8) display the best performance for propylene/propane separation, showing unprecedented propylene permeance (2000-3000 Gas Permeance Units) with very high propylene/propane selectivity (90-120).

Bifunctional semi-closed YF3-doped 1D carbon nanofibers with 3D porous network structure including fluorinating interphases and polysulfide confinement for lithium-sulfur batteries.

In this study, semi-closed YF3-doped 1D carbon nanofibers with 3D porous networks (SC-YF3-doped 3D in 1D CNFs) are fabricated for the first time via electro-blown spinning technology. The internal 3D porous networks not only offer a stable 3D electrode structure to accommodate the volume expansion, but also enable a high sulfur loading (80%). More importantly, the external semi-enclosed carbon layer maintains outstanding conductivity and further blocks polysulfide diffusion, which significantly breaks the limitation of a traditional carbon matrix. On the other hand, the YF3 nanoparticles are beneficial for forming more uniform fluorinating electrode interphases, achieving the excellent synergistic effect of chemical and physical adsorption to polysulfide. Therefore, the assembled Li-S batteries exhibit a high reversible discharge capacity of 954.2 mA h g-1 with a decay of merely 0.043% per cycle after 600 cycles at 1C rate. Moreover, the discharge capacity decay can be as low as 0.029% per cycle during 800 cycles at a high current density of 2C rate. Even at a high rate of 5C, the cells still possess a favorable capacity of 636.5 mA h g-1 while steadily operating for 700 cycles with a capacity decay rate of merely 0.056%, implying the great potential of this stable semi-closed cathode structure for industrialization.

CeF3-Doped Porous Carbon Nanofibers as Sulfur Immobilizers in Cathode Material for High-Performance Lithium-Sulfur Batteries.

In this study, the CeF3-doped porous carbon nanofibers (PCNFs), prepared via electroblown spinning technique and carbonization process, are used as sulfur immobilizers in cathodes for lithium-sulfur (Li-S) batteries for the first time. The cathode composed of CeF3-doped PCNFs, carbon nanotubes (CNTs), and S is successfully prepared through the ball-milling and heating method. The formed porous structure in the PCNFs and CNTs facilitates the construction of highly electrically conductive pathways and effectively alleviates volume changes, which can maintain the stability of the cathode structure and make them in close contact between the electrodes. Meanwhile, the intermediate polysulfide dissolved and lost in the electrolyte can also be suppressed because of the hierarchical porous carbon nanofibers and CeF3. The Li-S battery using the cathode can display excellent electrochemical properties and stable capacity retention, presenting an initial discharge capacity of 1395.0 mAh g-1 and retaining a capacity of 901.2 mAh g-1 after 500 cycles at 0.5C. During the rate capability tests of battery, the discharge capacity of Li-S battery with the electrode slowed down from the discharge capacity of 1284.6 mAh g-1 at 0.5C to 1038.6 mAh g-1 at 1C and 819.3 mAh g-1 at 2C, respectively. It is noteworthy that the battery can still endow an outstanding discharge capacity of 1269.73 mAh g-1 with a high retention of 99.2% when the current density returns to 0.5C.