Yifa Chen

Flexible Solid-State Supercapacitor Based on a Metal–Organic Framework Interwoven by Electrochemically-Deposited PANI

Metal-organic frameworks (MOFs) have received increasing attention as promising electrode materials in supercapacitors (SCs). Yet poor conductivity in most MOFs largely thwarts their capacitance and/or rate performance. In this work, an effective strategy was developed to reduce the bulk electric resistance of MOFs by interweaving MOF crystals with polyaniline (PANI) chains that are electrochemically deposited on MOFs. Specifically we synthesized cobalt-based MOF crystals (ZIF-67) onto carbon cloth (CC) and further electrically deposited PANI to give a flexible conductive porous electrode (noted as PANI-ZIF-67-CC) without altering the underlying structure of the MOF. Electrochemical studies showed that the PANI-ZIF-67-CC exhibits an extraordinary areal capacitance of 2146 mF cm(-2) at 10 mV s(-1). A symmetric flexible solid-state supercapacitor was also assembled and tested. This strategy may shed light on designing new MOF-based supercapacitors and other electrochemical devices.

Rational design of a metal–organic framework host for sulfur storage in fast, long-cycle Li–S batteries

Unlike an intercalation cathode, which has an intrinsic host structure made of redox metal sites allowing the transport of Li+/e−, sulfur as a conversion cathode requires an additional host to store and immobilize the mobile redox centers, polysulfides. Metal–organic frameworks (MOFs) as a class of highly porous and well-defined crystalline materials are a promising platform to search for an effective host through rational design. With the appropriate selection of an electrolyte and a cutoff voltage range, sulfur stored in an appropriate MOF host can take advantage of both intercalation (fast and stable) and conversion (high energy density) cathodes. Herein, we describe a fast cathode with long cycle life based on sulfur and ZIF-8 nanocrystals. With 30 wt% sulfur loading in the electrode, it achieves remarkable discharge capacities of 1055 mA h g−1 (based on sulfur) at 0.1 C and 710 mA h g−1 at 1 C. The decay over 300 cycles at 0.5 C is 0.08% per cycle, prominent in long-cycle Li–S batteries. By comparing with another three distinct MOFs, MIL-53 (Al), NH2-MIL-53 (Al) and HKUST-1, as well as two sets of ZIF-8 with particle sizes in the micrometer range, it reveals that (i) the small particle size of the MOF host is appreciable to achieve a high capacity and (ii) small apertures, associated with functionalities in the open framework that have affinity with the polysulfide anions, can help achieve a stable cycling. We believe that the findings are general and applicable for the rational design of new hosts for sulfur in other porous material families to produce more effective and stable Li–S batteries.

Photoinduced Postsynthetic Polymerization of a Metal–Organic Framework toward a Flexible Stand‐Alone Membrane

Metal-organic frameworks (MOFs) are a promising class of nanoporous polymeric materials. However, the processing of such fragile crystalline powders into desired shapes for further applications is often difficult. A photoinduced postsynthetic polymerization (PSP) strategy was now employed to covalently link MOF crystals by flexible polymer chains, thus endowing the MOF powders with processability and flexibility. Nanosized UiO-66-NH2 was first functionalized with polymerizable functional groups, and its subsequent copolymerization with monomers was easily induced by UV light under solvent-free and mild conditions. Because of the improved interaction between MOF particles and polymer chains, the resulting stand-alone and elastic MOF-based PSP-derived membranes possess crack-free and uniform structures and outstanding separation capabilities for Cr(VI) ions from water.

In Situ Growth of MOFs on the Surface of Si Nanoparticles for Highly Efficient Lithium Storage: Si@MOF Nanocomposites as Anode Materials for Lithium-Ion Batteries

A simple yet powerful one-pot strategy is developed to prepare metal-organic framework-coated silicon nanoparticles via in situ mechanochemical synthesis. After simple pyrolysis, the thus-obtained composite shows exceptional electrochemical properties with a lithium storage capacity up to 1050 mA h g(-1), excellent cycle stability (>99% capacity retention after 500 cycles) and outstanding rate performance. These characteristics, combined with their high stability and ease of fabrication, make such Si@MOF nanocomposites ideal alternative candidates as high-energy anode materials in lithium-ion batteries.

Shaping of Metal–Organic Frameworks: From Fluid to Shaped Bodies and Robust Foams

The applications of metal-organic frameworks (MOFs) toward industrial separation, catalysis, sensing, and some sophisticated devices are drastically affected by their intrinsic fragility and poor processability. Unlike organic polymers, MOF crystals are insoluble in any solvents and are usually not thermoplastic, which means traditional solvent- or melting-based processing techniques are not applicable for MOFs. Herein, a continuous phase transformation processing strategy is proposed for fabricating and shaping MOFs into processable fluids, shaped bodies, and even MOF foams that are capable of reversible transformation among these states. Based on this strategy, a cup-shaped Cu-MOF composite and hierarchically porous MOF foam were developed for highly efficient catalytic C-H oxidation (conv. 76% and sele. 93% for cup-shaped Cu-MOF composite and conv. 92% and sele. 97% for porous foam) with ease of recycling and dramatically improved kinetics. Furthermore, various MOF-based foams with low densities (<0.1 g cm(-3)) and high MOF loadings (up to 80 wt %) were obtained via this protocol. Imparted with hierarchically porous structures and fully accessible MOFs uniformly distributed, these foams presented low energy penalty (pressure drop <20 Pa, at 500 mL min(-1)) and showed potential applications as efficient membrane reactors.

Roll‐to‐Roll Production of Metal‐Organic Framework Coatings for Particulate Matter Removal

A powerful roll-to-roll hot-pressing strategy for mass production of metal-organic framework (MOF)-based filters (MOFilters) using various MOF systems with ranges of substrates is presented. Thus-obtained MOFilters show superior particulate matter removal efficiency under desired working temperatures. Such versatile MOFilters can be scaled up and purposely designed, which endows MOFilters with great potentials in both residential and industrial pollution control.

Metal‐Organic Framework Templated Synthesis of Copper Azide as the Primary Explosive with Low Electrostatic Sensitivity and Excellent Initiation Ability

A powerful yet safe primary explosive, embedded in a conductive carbon scaffold, is prepared by using a metal-organic framework as precursor. It simultaneously possesses low electrostatic sensitivity, good flame sensitivity, and excellent initiation ability. This method is simple, scalable, and provides a new platform for the development of energetic materials especially those employed in miniaturized explosive systems.

Facile fabrication of magnetically recyclable metal–organic framework nanocomposites for highly efficient and selective catalytic oxidation of benzylic C–H bonds

HKUST-1@Fe3O4 chemically bonded core-shell nanoparticles have been prepared by growing HKUST-1 thin layers joined by carboxyl groups onto Fe3O4 nanospheres. These magnetic core-shell MOF nanostructures show exceptional catalytic activity for the oxidation of benzylic C-H bonds and they can be recovered by magnetic separation and reused without losing any activity.

A Tale of Copper Coordination Frameworks: Controlled Single-Crystal-to-Single-Crystal Transformations and Their Catalytic C-H Bond Activation Properties.

Metal-organic frameworks (MOFs), as a class of microporous materials with well-defined channels and rich functionalities, hold great promise for various applications. Yet the formation and crystallization processes of various MOFs with distinct topology, connectivity, and properties remain largely unclear, and the control of such processes is rather challenging. Starting from a 0D Cu coordination polyhedron, MOP-1, we successfully unfolded it to give a new 1D-MOF by a single-crystal-to-single-crystal (SCSC) transformation process at room temperature as confirmed by SXRD. We also monitored the continuous transformation states by FTIR and PXRD. Cu MOFs with 2D and 3D networks were also obtained from this 1D-MOF by SCSC transformations. Furthermore, Cu MOFs with 0D, 1D, and 3D networks, MOP-1, 1D-MOF, and HKUST-1, show unique performances in the kinetics of the C-H bond catalytic oxidation reaction.

Defect engineering of highly stable lanthanide metal–organic frameworks by particle modulation for coating catalysis

By virtue of their structural periodicity, tunability, high porosity and rich functionality, metal–organic frameworks (MOFs) are of great interest in catalysis. However, MOF crystals are fragile and difficult to use as robust adsorbents or catalysts without processing into shapes. Precise control of particle size and catalytic sites for MOFs during the shaping procedures is also highly desired yet hard to realize. A versatile size control method for lanthanide MOFs, especially our newly designed Ce-MOF (BIT-58), is developed. The coordination and steric effects of various modulators are investigated. With size reduction from micrometers to nanometers (∼25 μm to ∼30 nm), more accessible metal sites of BIT-58 are exposed (10 times increased acid site amount; 7 times higher mesopore volume) and the catalytic performance is significantly improved. Furthermore, nano-sized BIT-58 can be processed into films or coatings with excellent catalytic activity, which holds great potential in batch or continuous-flow catalytic processes.