Yi Guo

Foldable interpenetrated metal-organic frameworks/carbon nanotubes thin film for lithium–sulfur batteries

Lithium–sulfur batteries are promising technologies for powering flexible devices due to their high energy density, low cost and environmental friendliness, when the insulating nature, shuttle effect and volume expansion of sulfur electrodes are well addressed. Here, we report a strategy of using foldable interpenetrated metal-organic frameworks/carbon nanotubes thin film for binder-free advanced lithium–sulfur batteries through a facile confinement conversion. The carbon nanotubes interpenetrate through the metal-organic frameworks crystal and interweave the electrode into a stratified structure to provide both conductivity and structural integrity, while the highly porous metal-organic frameworks endow the electrode with strong sulfur confinement to achieve good cyclability. These hierarchical porous interpenetrated three-dimensional conductive networks with well confined S8 lead to high sulfur loading and utilization, as well as high volumetric energy density.

Polystyrene Sulfonate Threaded through a Metal–Organic Framework Membrane for Fast and Selective Lithium‐Ion Separation

Extraction of lithium ions from salt-lake brines is very important to produce lithium compounds. Herein, we report a new approach to construct polystyrene sulfonate (PSS) threaded HKUST-1 metal-organic framework (MOF) membranes through an in situ confinement conversion process. The resulting membrane PSS@HKUST-1-6.7, with unique anchored three-dimensional sulfonate networks, shows a very high Li+ conductivity of 5.53×10-4  S cm-1 at 25 °C, 1.89×10-3  S cm-1 at 70 °C, and Li+ flux of 6.75 mol m-2  h-1 , which are five orders higher than that of the pristine HKUST-1 membrane. Attributed to the different size sieving effects and the affinity differences of the Li+ , Na+ , K+ , and Mg2+ ions to the sulfonate groups, the PSS@HKUST-1-6.7 membrane exhibits ideal selectivities of 78, 99, and 10296 for Li+ /Na+ , Li+ /K+ , Li+ /Mg2+ and real binary ion selectivities of 35, 67, and 1815, respectively, the highest ever reported among ionic conductors and Li+ extraction membranes.

Flexible and Binder-Free Hierarchical Porous Carbon Film for Supercapacitor Electrodes Derived from MOFs/CNT

Rational design of free-standing porous carbon materials with large specific surface area and high conductivity is a great need for ligh-weight suprecapacitors. Here, we report a flexible porous carbon film composed of metal-organic framework (MOF)-derived porous carbon polyhedrons and carbon nanotubes (CNTs) as binder-free supercapacitor electrode for the first time. Due to the synergistic combination of carbon polyhedrons and CNT, the obtained carbon electrode shows a specific capacitance of 381.2 F g-1 at 5 mV s-1 and 194.8 F g-1 at 2 A g-1 and outstanding cycling stability with a Coulombic effciency above 95% after 10000 cycles at 10 A g-1. The assembled aqueous symmetrical supercapacitor exhibits an energy density of 9.1 Wh kg-1 with a power density of 3500 W kg-1. The work opens a new way to design flexible MOF-based hierarchical porous carbon film as binder-free electrodes for high-performance energy storage devices.

Hierarchical Mesoporous Metal–Organic Frameworks for Enhanced CO2 Capture

Hierarchical porous materials are promising for catalyst, separation and sorption applications. A ligand-assisted etching process is developed for template-free synthesis of hierarchical mesoporous MOFs as single crystals and well-intergrown membranes at 40 °C. At 223 K, the hierarchical porous structures significantly improve the CO2 capture capacity of HKUST-1 by more than 44 % at pressures up to 20 kPa and 13 % at 100 kPa. Even at 323 K, the enhancement of CO2 uptake is above 25 % at pressures up to 20 kPa and 7 % at 100 kPa. The mesoporous structures not only enhance the CO2 uptake capacity but also improve the diffusion and mass transportation of CO2 . Similarly, well-intergrown mesoporous HKUST-1 membranes are synthesized, which hold the potential for film-like porous devices. Mesoporous MOF-5 crystals are also obtained by a similar ligand-assisted etching process. This may provide a facile way to prepare hierarchical porous MOF single crystals and membranes for wide-ranging applications.

A DNA‐Threaded ZIF‐8 Membrane with High Proton Conductivity and Low Methanol Permeability

Natural biomolecules have potential as proton-conducting materials, in which the hydrogen-bond networks can facilitate proton transportation. Herein, a biomolecule/metal-organic framework (MOF) approach to develop hybrid proton-conductive membranes is reported. Single-strand DNA molecules are introduced into DNA@ZIF-8 membranes through a solid-confined conversion process. The DNA-threaded ZIF-8 membrane exhibits high proton conductivity of 3.40 × 10-4 S cm-1 at 25 °C and the highest one ever reported of 0.17 S cm-1 at 75 °C, under 97% relatively humidity, attributed to the formed hydrogen-bond networks between the DNA molecules and the water molecules inside the cavities of the ZIF-8, but very low methanol permeability of 1.25 × 10-8 cm2 s-1 due to the small pore entrance of the DNA@ZIF-8 membranes. The selectivity of the DNA@ZIF-8 membrane is thus significantly higher than that of developed proton-exchange membranes for fuel cells. After assembling the DNA@ZIF-8 hybrid membrane into direct methanol fuel cells, it exhibits a power density of 9.87 mW cm-2 . This is the first MOF-based proton-conductivity membrane used for direct methanol fuel cells, providing bright promise for such hybrid membranes in this application.

Solid Confinement of Quantum Dots in ZIF-8 for Efficient and Stable Color-Conversion White LEDs

The powder form and low photoluminescence quantum yield (PLQY) of fluorescent metal-organic frameworks (MOFs) present a serious obstacle to fabricating high-efficiency film-like lighting devices. Here, we present a facile way to produce thin films of CdSex S1-x /ZnS quantum dots (QDs)@ZIF-8 with high PLQY by encapsulating red, green, and blue CdSex S1-x /ZnS QDs in ZIF-8 through a one-pot solid-confinement conversion process. The QDs@ZIF-8 thin film emits warm white light with good color quality and presents good thermal stability and long-term durability.

Blocking Polysulfides and Facilitating Lithium-Ion Transport: Polystyrene Sulfonate@HKUST-1 Membrane for Lithium–Sulfur Batteries

Minimizing the shuttle effect of polysulfides (PS) is crucial for practical applications of lithium-sulfur (Li-S) batteries. However, the trade-off between effective suppression of the shuttle effect and fast redox reaction kinetics is inevitable for separator-based Li-S batteries. Herein, via a self-confined solid-conversion process, we develop a polystyrene sulfonate (PSS)-threaded well-intergrown HKUST-1 (Cu3(BTC)2) (BTC: 1,3,5-benzenetricarboxylic acid)-coated Celgard separator (PSS@HKUST-1/Celgard, PHC) for high-performance Li-S batteries. The PHC membrane favors the interception and accommodation of long-chain PS. Notably, enormous sulfonate groups of the three-dimensional PSS networks in PSS@HKUST-1 membrane significantly facilitate lithium-ion transport, which guarantee fast redox kinetics. The PHC separator demonstrates efficient inhibition of PS (i.e., 4 orders of magnitude lower in PS permeation rate) with fast Li+ transportation (i.e., 71% higher in ionic conductivity) than the Celgard separator. When applying the PHC membrane in Li-S batteries with conventional sulfur/super P carbon cathode, highly reversible capacity with an average fading rate of 0.05% per cycle is maintained for 500 cycles at 0.5 C, excellent rate performance up to 5 C, and high areal capacity over 7 mA h cm-2 are also achieved. This work paves a new way for addressing the trade-off between suppressing the PS shuttle effect and fast kinetic reaction for separator-based Li-S batteries.

Enhanced Gas Separation through Nanoconfined Ionic Liquid in Laminated MoS2 Membrane

Two-dimensional (2D) materials-based membranes show great potential for gas separation. Herein an ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), was confined in the 2D channels of MoS2-laminated membranes via an infiltration process. Compared with the corresponding bulk [BMIM][BF4], nanoconfined [BMIM][BF4] shows an obvious incremental increase in freezing point and a shift of vibration bands. The resulting MoS2-supported ionic liquid membrane (MoS2 SILM) exhibits excellent CO2 separation performance with high CO2 permeance (47.88 GPU) and superb selectivity for CO2/N2 (131.42), CO2/CH4 (43.52), and CO2/H2 (14.95), which is much better than that of neat [BMIM][BF4] and [BMIM][BF4]-based membranes. The outstanding performance of MoS2 SILMs is attributed to the nanoconfined [BMIM][BF4], which enables fast transport of CO2. Long-term operation also reveals the durability and stability of the prepared MoS2 SILMs. The method of confining ILs in the 2D nanochannels of 2D materials may pave a new way for CO2 capture and separation.

Mechanical enhancement of a nanoconfined-electrodeposited nacre-like Cu2O layered crystal/graphene oxide nanosheet composite thin film

Graphene oxide (GO) based two dimensional (2D) nanosheets show great advantages for constructing nacre-like composites. Among the existing nacre structures, GO sheets were mostly used as hard inorganic components as those in nacre to improve the mechanical properties. Here, a novel nanoconfined electrodeposition process was explored to fabricate nacre-like Cu2O/graphene oxide (GO) thin films, where GO nanosheets functioned as the soft organic components in nacre. The inter-layer spaces between the GO nanosheets were used as templates for the growth of single crystalline Cu2O nanolayers, with thicknesses of several to tens of nanometers, though Cu2O belongs to the cubic phase. Due to the small lattice mismatch between the (10) plane of Cu2O and the (001) plane of GO, the Cu2O nanolayers most likely grew on the (001) plane of GO. The resulting nacre-like thin film demonstrates a 6 times greater hardness and a 3 times greater Young’s modulus, than those of pure GO thin films. This technique provides a promising route for the synthesis of nacre-like metal (metal-oxide)/GO composites.

CO2-philic WS2 laminated membranes with a nanoconfined ionic liquid

The modern global climate change and global warming of Earth make it an urgent need to develop emerging CO2 capture and storage techniques. Herein, we first reported the use of WS2 nanosheets to construct laminated membranes for CO2 separation. However, the WS2 membrane showed poor CO2 separation performance with Knudsen selectivities for N2/CO2 (1.28), CH4/CO2 (1.72) and H2/CO2 (4.96). To improve the performance, an ionic liquid (IL) 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM][BF4]) with high CO2 solubility and practically no vapour pressure was used for filling the nanochannels of the WS2 membrane. Compared to the bulk IL, the nanoconfined IL exhibits higher freezing temperature, shift of vibration bands and higher interaction energy between CO2 and ILs. Besides, the prepared WS2 laminated membrane with the nanoconfined ionic liquid shows excellent selectivities for CO2/N2 (153.21), CO2/CH4 (68.81) and CO2/H2 (13.56) in single gas measurements as well as good CO2 permeance due to the nanoconfinement of the IL. The simulation results further confirmed and explained the CO2 separation mechanism. It indicates that the nanoconfinement of ILs into the nanochannels of two-dimensional materials is a novel way to achieve CO2-philic membranes to efficiently separate CO2 from other light gases.