3D nitrogen-doped carbon frameworks with hierarchical pores and graphitic carbon channels for high-performance hybrid energy storages.

In principle, hybrid energy storages can utilize the advantages of capacitor-type cathodes and battery-type anodes, but their cathode and anode materials still cannot realize a high energy density, fast rechargeable capability, and long-cycle stability. Herein, we report a strategy to synthesize cathode and anode materials as a solution to overcome this challenge. Firstly, 3D nitrogen-doped hierarchical porous graphitic carbon (NHPGC) frameworks were synthesized as cathode materials using Co-Zn mixed metal-organic frameworks (MOFs). A high capacity is achieved due to the abundant nitrogen and micropores produced by the MOF nanocages and evaporation of Zn. Also, fast ion/electron transport channels were derived through the Co-catalyzed hierarchical porosity control and graphitization. Moreover, tin oxide precursors were introduced in NHPGC to form the SnO2@NHPGC anode. Operando X-ray diffraction revealed that the rescaled subnanoparticles as anodic units facilitated the high capacity during ion insertion-induced rescaling. Besides, the Sn-N bonds endowed the anode with a cycling stability. Furthermore, the NHPGC cathode and SnO2@NHPGC achieved an ultrahigh energy density (up to 244.5 W h kg-1 for Li and 146.1 W h kg-1 for Na), fast rechargeable capability (up to 93C-rate for Li and 147C-rate for Na) as exhibited by photovoltaic recharge within a minute and a long-cycle stability with ∼100% coulombic efficiency over 10 000 cycles.

Direct photocatalytic patterning of colloidal emissive nanomaterials.

We present a universal direct photocatalytic patterning method that can completely preserve the optical properties of perovskite nanocrystals (PeNCs) and other emissive nanomaterials. Solubility change of PeNCs is achieved mainly by a photoinduced thiol-ene click reaction between specially tailored surface ligands and a dual-role photocatalytic reagent, pentaerythritol tetrakis(3-mercaptopropionate) (PTMP), where the thiol-ene reaction is enabled at a low light intensity dose (~ 30 millijoules per square centimeter) by the strong photocatalytic activity of PeNCs. The photochemical reaction mechanism was investigated using various analyses at each patterning step. The PTMP also acts as a defect passivation agent for the PeNCs and even enhances their photoluminescence quantum yield (by ~5%) and photostability. Multicolor patterns of cesium lead halide (CsPbX3)PeNCs were fabricated with high resolution (<1 micrometer). Our method is widely applicable to other classes of nanomaterials including colloidal cadmium selenide-based and indium phosphide-based quantum dots and light-emitting polymers; this generality provides a nondestructive and simple way to pattern various functional materials and devices.

3D Porous Oxygen-Doped and Nitrogen-Doped Graphitic Carbons Derived from Metal Azolate Frameworks as Cathode and Anode Materials for High-Performance Dual-Carbon Sodium-Ion Hybrid Capacitors.

Sodium-ion hybrid capacitors (SIHCs) in principle can utilize the advantages of batteries and supercapacitors and satisfy the cost demand of large-scale energy storage systems, but the sluggish kinetics and low capacities of its anode and cathode are yet to be overcome. Here, a strategy is reported to realize high-performance dual-carbon SIHCs using 3D porous graphitic carbon cathode and anode materials derived from metal-azolate framework-6s (MAF-6s). First, MAF-6s, with or without urea loading, are pyrolyzed to synthesize MAF-derived carbons (MDCs). Then, cathode materials are synthesized via the controlled KOH-assisted pyrolysis of MDCs (K-MDCs). K-MDCs, 3D graphitic carbons, resulting in a record-high surface area (5214 m2  g-1 ) being ≈four-fold higher than pristine MAF-6, oxygen-doped sites for high capacity, rich mesopores affording fast ion transport, and high capacity retention over 5000 charge/discharge cycles. Moreover, 3D porous MDC anode materials are synthesized from N-containing MAF-6 and exhibited to allow cycle stability over 5000 cycles. Furthermore, dual-carbon MDC//K-MDC SIHCs with different loadings (3 to 6 mg cm-2 ) are demonstrated to achieve high energy densities exceeding those of sodium-ion batteries and supercapacitors. Additionally, it allows an ultrafast-chargeable high power density of 20000 W kg-1 and robust cycle stability overcoming those of a typical battery.

Fast Charge Transfer and High Stability via Hybridization of Hygroscopic Cu-BTC Metal-Organic Framework Nanocrystals with a Light-Absorbing Layer for Perovskite Solar Cells.

Perovskite solar cells (PSCs) have great potential as an efficient solar energy harvesting system due to their outstanding optoelectronic properties, but the charge accumulation and recombination, as well as the moisture-induced degradation of the light-absorbing perovskite layers, remain great bottlenecks in practical applications for future technology. As a solution to this challenge, here we report a strategy to realize moisture-stable PSCs allowing fast charge transfer that, in turn, leads to high power conversion efficiency (PCE). Hybridization of hygroscopic copper(II) benzene-1,3,5-tricarboxylate metal-organic frameworks (Cu-BTC MOFs) with a light-absorbing perovskite layer for PSCs, where a moderate level of moisture attracted by Cu-BTC MOFs during the synthesis step, leads to enhanced perovskite crystallization. Besides, the perovskite-MOF hybrid facilitates the transfer of photoexcited electrons from the perovskite to TiO2 by providing additional channels for electron extraction. This enables a high PCE of 20.5% in a triple-cation perovskite-MOF device with negligible hysteresis compared to reference devices. Moreover, the perovskite-MOF hybrid exhibits high stability in ambient air under dark conditions over a long period (up to 22 months), while the unmodified counterpart quickly decomposes into PbI2. Consequently, this work provides a promising clue to realizeing fast charge transfer and high stability for high-performance PSCs.

Coiled Conformation Hollow Carbon Nanosphere Cathode and Anode for High Energy Density and Ultrafast Chargeable Hybrid Energy Storage.

Lithium-ion batteries and pseudocapacitors are nowadays popular electrochemical energy storage for many applications, but their cathodes and anodes are still limited to accommodate rich redox ions not only for high energy density but also sluggish ion diffusivity and poor electron conductivity, hindering fast recharge. Here, we report a strategy to realize high-capacity/high-rate cathode and anode as a solution to this challenge. Multiporous conductive hollow carbon (HC) nanospheres with microporous shells for high capacity and hollow cores/mesoporous shells for rapid ion transfer are synthesized as cathode materials using quinoid:benzenoid (Q:B) unit resins of coiled conformation, leading to ∼5-fold higher capacities than benzenoid:benzenoid resins of linear conformation. Also, Ge-embedded Q:B HC nanospheres are derived as anode materials. The atomic configuration and energy storage mechanism elucidate the existence of mononuclear GeOx units giving ∼7-fold higher ion diffusivity than bulk Ge while suppressing volume changes during long ion-insertion/desertion cycles. Moreover, hybrid energy storage with a Q:B HC cathode and Ge-Q:B HC anode exploit the advantages of capacitor-type cathode and battery-type anode electrodes, as exhibited by battery-compatible high energy density (up to 285 Wh kg-1) and capacitor-compatible ultrafast rechargeable power density (up to 22 600 W kg-1), affording recharge within a minute.

In Situ Mapping and Local Negative Uptake Behavior of Adsorbates in Individual Pores of Metal-Organic Frameworks.

Herein, we report the adsorbate behavior in individual local pores of MIL-101, which is a metal-organic framework (MOF) with two heterogeneous mesopores and different metal sites, by combining adsorbate isotherms and in situ crystallography profiles. The in situ mapping shows that the substrate-adsorbate interaction affects the initial adsorption and pore condensation steps. The monolayer adsorption gradient changes greatly depending on the framework metal-adsorbate attraction force. Also, broad inflection points are found in adsorption isotherms, and the initial shape depends on the different metals. Besides, the capillary condensation at a pore draws adsorbates from other local pores. This leads to the local negative uptake behavior in individual pore isotherms. At higher pressure, they move to a larger space, whereas in a relatively low-pressure range the attraction force between the MOF framework and guest molecule influences the amount of rearranged guest molecules. Furthermore, the origin of the characteristic adsorption behavior based on the metals constituting the MOFs and the relative strength of substrate-adsorbate and adsorbate-adsorbate interactions are elucidated through the combined study of electron densities in pores, electron paramagnetic resonance spectroscopy spectra, and density functional theory and Monte Carlo simulations to uncover the previously veiled information on adsorption behavior.

Physicochemical Understanding of the Impact of Pore Environment and Species of Adsorbates on Adsorption Behaviour.

For a better design of adsorbents, it is important to know the intermolecular interaction among adsorbates and host material, leading to improved guest selectivity and uptake capacity. In this study, we demonstrate the influence of the interaction among adsorbates and substrate, controlled by the pore environment and species of adsorbates, on the adsorption behaviour. We report the unique CO2 adsorption behaviour of MOF-205 due to distinct pore geometry. The precise analysis through gas-adsorption crystallography with molecular simulation shows that capillary condensation of CO2 in MOF-205 occurs preferentially in the large dodecahedral pore rather than the small tetrahedral pore, because the interaction of CO2 with MOF-205 framework is weaker than that among CO2 molecules, while Ar and N2 are sequentially filled into two different pores of MOF-205 according to their size. Comparison of the materials with different pore environments reveals that the relative strength of the adsorbate-adsorbate and adsorbate-substrate interaction gives rise to different shapes of isotherms.

Metal-Organic Fragments with Adhesive Excipient and Their Utilization to Stabilize Multimetallic Electrocatalysts for High Activity and Robust Durability in Oxygen Evolution Reaction.

Multimetallic electrocatalysts have shown great potential to improve electrocatalytic performance, but their deteriorations in activity and durability are yet to be overcome. Here, metal-organic fragments with adhesive excipient to realize high activity with good durability in oxygen evolution reaction (OER) are developed. First, a leaf-like zeolitic-imidazolate framework (ZIF-L) is synthesized. Then, ionized species in hydrogen plasma attack preferentially the organic linkers of ZIF-L to derive cobalt-imidazole fragments (CIFs) as adhesive excipient, while they are designed to retain the coordinated cobalt nodes. Moreover, the vacant coordination sites at cobalt nodes and the unbound nitrogen at organic linkers induce high porosity and conductivity. The CIFs serve to stably impregnate trimetallic FeNiMo electrocatalysts (CIF:FeNiMo), and CIF:FeNiMo containing Fe contents of 22% and hexavalent Mo contents show to enable high activity with low overpotentials (203 mV at 10 mA cm-2 and 238 mV at 100 mA cm-2 ) in OER. The near O K-edge extended X-ray absorption fine structure proves further that high activity for OER originates from the partially filled eg orbitals. Additionally, CIF:FeNiMo exhibit good durability, as demonstrated by high activity retention during at least 45 days in OER.

Strain-Induced Metallization and Defect Suppression at Zipper-like Interdigitated Atomically Thin Interfaces Enabling High-Efficiency Halide Perovskite Solar Cells.

Halide perovskite light absorbers have great advantages for photovoltaics such as efficient solar energy absorption, but charge accumulation and recombination at the interface with an electron transport layer (ETL) remain major challenges in realizing the absorbers' full potential. Here we report the experimental realization of a zipper-like interdigitated interface between a Pb-based halide perovskite light absorber and an oxide ETL by the PbO capping of the ETL surface, which produces an atomically thin two-dimensional metallic layer that can significantly enhance the perovskite/ETL charge extraction process. As the atomistic origin of the emergent two-dimensional interfacial metallicity, first-principles calculations performed on the representative MAPbI3/TiO2 interface identify the interfacial strain induced by the simultaneous formation of stretched I-substitutional Pb bonds (and thus Pb-I-Pb bonds bridging MAPbI3 and TiO2) and contracted substitutional Pb-O bonds. Direct and indirect experimental evidence for the presence of interfacial metallic states are provided, and a nonconventional defect-passivating nature of the strained interdigitated perovskite/ETL interface is emphasized. It is experimentally demonstrated that the PbO capping method is generally applicable to other ETL materials, including ZnO and SrTiO3, and that the zipper-like interdigitated metallic interface leads to about a 2-fold increase in the charge extraction rate. Finally, in terms of the photovoltaic efficiency, we observe a volcano-type behavior with the highest performance achieved at the monolayer-level PbO capping. This work establishes a general perovskite/ETL interface engineering approach to realize high-performance perovskite solar cells.

Generic Strategy to Synthesize High-Tap Density Anode and Cathode Structures with Stratified Graphene Pliable Pockets via Monomeric Polymerization and Evaporation, and Their Utilization to Enable Ultrahigh Performance in Hybrid Energy Storages.

Hybrid energy storage systems have shown great promise for many applications; however, achieving high energy and power densities with long cycle stability remains a major challenge. Here, a strategy to synthesize high-tap density anode and cathode structures that yield ultrahigh performance in hybrid energy storage is reported. First, vinyl acetate monomers are polymerized into molecular sizes via chain reactions controlled by the surface free radicals of graphene and metals. Subsequently, molecular-size polymers are thermally evaporated to construct battery-type anode structures with encapsulated tin metals for high-capacity and stratified graphene pliable pockets (GPPs) for fast charge transfer. Similarly, sulfur particles are attached to GPPs via monomeric polymerization, and capacitor-type hollow GPP (H@GPP) cathode structures are produced by evaporating sulfur, where sublimated S particles yield mesopores for rapid anion movement and micropores for high capacity. Moreover, hybrid full-cell devices with high-tap density anodes and cathodes show high gravimetric energy densities of up to 206.9 Wh kg-1 , exceeding those of capacitors by ≈16-fold, and excellent volumetric energy densities of up to 92.7 Wh L-1 . Additionally, they attain high power densities of up to 23 678 W kg-1 , outperforming conventional devices by a factor of ≈100, and long cycle stability over 10 000 cycles.

Autogenous Production and Stabilization of Highly Loaded Sub-Nanometric Particles within Multishell Hollow Metal-Organic Frameworks and Their Utilization for High Performance in Li-O2 Batteries.

Sub-nanometric particles (SNPs) of atomic cluster sizes have shown great promise in many fields such as full atom-to-atom utilization, but their precise production and stabilization at high mass loadings remain a great challenge. As a solution to overcome this challenge, a strategy allowing synthesis and preservation of SNPs at high mass loadings within multishell hollow metal-organic frameworks (MOFs) is demonstrated. First, alternating water-decomposable and water-stable MOFs are stacked in succession to build multilayer MOFs. Next, using controlled hydrogen bonding affinity, isolated water molecules are selectively sieved through the hydrophobic nanocages of water-stable MOFs and transferred one by one to water-decomposable MOFs. The transmission of water molecules via controlled hydrogen bonding affinity through the water-stable MOF layers is a key step to realize SNPs from various types of alternating water-decomposable and water-stable layers. This process transforms multilayer MOFs into SNP-embedded multishell hollow MOFs. Additionally, the multishell stabilizes SNPs by π-backbonding allowing high conductivity to be achieved via the hopping mechanism, and hollow interspaces minimize transport resistance. These features, as demonstrated using SNP-embedded multishell hollow MOFs with up to five shells, lead to high electrochemical performances including high volumetric capacities and low overpotentials in Li-O2 batteries.

Synthesis of Nitrogen-Doped Mesoporous Structures from Metal-Organic Frameworks and Their Utilization Enabling High Performances in Hybrid Sodium-Ion Energy Storages.

Sodium-ion energy storage is of the most attractive candidate for commercialization adoption due to the safety and cost demands of large-scale energy storage systems, but its low energy density, slow charging capability, and poor cycle stability are yet to be overcome. Here, a strategy is reported to realize high-performance sodium-ion energy storage using battery-type anode and capacitor-type cathode materials. First, nitrogen-doped mesoporous titanium dioxide (NMTiO2) structures are synthesized via the controlled pyrolysis of metal-organic frameworks. They exhibit interconnected open mesopores allowing fast ion transport and robust cycle stability with nearly 100% coulombic efficiency, along with rich redox-reactive sites allowing high capacity even at a high rate of ≈90 C. Moreover, assembling the NMTiO2 anode with the nitrogen-doped graphene (NG) cathode in an asymmetric full cell shows a high energy density exceeding its counterpart symmetric cell by more than threefold as well as robust cycle stability over 10 000 cycles. Additionally, it gives a high-power density close to 26 000 W kg-1 outperforming that of a conventional sodium-ion battery by several hundred fold, so that full cells can be charged within a few tens of seconds by the flexible photovoltaic charging and universal serial bus charging modules.

Gas-Permeable Inorganic Shell Improves the Coking Stability and Electrochemical Reactivity of Pt toward Methane Oxidation.

Solid oxide fuel cells produce electricity directly by oxidizing methane, which is the most attractive natural gas fuel, and metal nanocatalysts are a promising means of overcoming the poor catalytic activity of conventional ceramic electrodes. However, the lack of thermal and chemical stability of nanocatalysts is a major bottleneck in the effort to ensure the lifetime of metal-decorated electrodes for methane oxidation. Here, for the first time, this issue is addressed by encapsulating metal nanoparticles with gas-permeable inorganic shells. Pt particles approximately 10 nm in size are dispersed on the surface of a porous La0.75Sr0.25Cr0.5Mn0.5O3 (LSCM) electrode via wet infiltration and are then coated with an ultrathin Al2O3 layer via atomic layer deposition. The Al2O3 overcoat, despite being an insulator, significantly enhances the immunity to carbon coking and provides high activity for the electrochemical oxidation of methane, thereby reducing the reaction impedance of the Pt-decorated electrode by more than 2 orders of magnitude and making the electrode activity of the Pt-decorated sample at 650 °C comparable with those reported at 800 °C for pristine LSCM electrodes. These observations provide a new perspective on strategies to lower the operation temperature, which has long been a challenge related to hydrocarbon-fueled solid oxide fuel cells.

Cobalt-Phosphate Catalysts with Reduced Bivalent Co-Ion States and Doped Nitrogen Atoms Playing as Active Sites for Facile Adsorption, Fast Charge Transfer, and Robust Stability in Photoelectrochemical Water Oxidation.

A cobalt-phosphate (Co-Pi) catalyst having octahedral CoO6 molecular units as reaction sites is a key component in photoelectrochemical (PEC) water oxidation systems, but its limited adsorption sites for oxygen-evolving intermediates (*OH, *OOH), slow charge transfer rates, and fast degradation of reaction sites are yet to be overcome. Here, we report that Co-Pi nanoparticles with low-coordinate Co ions and doped nitrogen atoms could be decorated on hematite nanorod arrays to form N-CoPi/hematite composites. Moreover, the local atomic configuration and bond distance studies show that trivalent Co3+ states are partially reduced through nitrogen radicals in the plasma to low-coordinate bivalent Co2+ states playing as the facile adsorption sites of oxygen-evolving intermediates due to the decreased activation barrier for water oxidation. Electron transport is also reinforced by nitrogen species due to the formation of hybridizing N 2p orbitals that give the acceptor levels in the bandgap. As a result, both the incident photon-to-electron conversion efficiency and the charge transfer resistance on N-CoPi/hematite outperform those on a bare hematite by about 3 fold. Furthermore, N-CoPi/hematite gives high activity retention over 90% after the long operation of water oxidation, in support of the reaction sites on N-CoPi not degrading during the successive water oxidation.

Isotherms of individual pores by gas adsorption crystallography.

Accurate measurements and assessments of gas adsorption isotherms are important to characterize porous materials and develop their applications. Although these isotherms provide knowledge of the overall gas uptake within a material, they do not directly give critical information concerning the adsorption behaviour of adsorbates in each individual pore, especially in porous materials in which multiple types of pore are present. Here we show how gas adsorption isotherms can be accurately decomposed into multiple sub-isotherms that correspond to each type of pore within a material. Specifically, two metal-organic frameworks, PCN-224 and ZIF-412, which contain two and three different types of pore, respectively, were used to generate isotherms of individual pores by combining gas adsorption measurements with in situ X-ray diffraction. This isotherm decomposition approach gives access to information about the gas uptake capacity, surface area and accessible pore volume of each individual pore, as well as the impact of pore geometry on the uptake and distribution of different adsorbates within the pores.

Ultrafine Metallic Nickel Domains and Reduced Molybdenum States Improve Oxygen Evolution Reaction of NiFeMo Electrocatalysts.

An electrocatalyst for oxygen evolution reaction (OER) is essential in the realization of renewable energy conversion technologies, but its large overpotential, slow charge transfer, and degradation of surface reaction sites are yet to be overcome. Here, it is found that the metallic nickel domains and high-valence reduced molybdenum ions of NiFeMo electrocatalysts grown on a 3D conductive and porous electrode without using binders enable ultrahigh performance in OER. High resolution-transmission electron microscope and extended X-ray absorption fine structure analyses show that metallic nickel domains with Ni-Ni bonds are generated on the catalyst surface via a dry synthesis using nitrogen plasma. Also, Mo K-edge X-ray absorption near-edge spectroscopy reveals that Mo6+ ions are reduced into high-valence modulating Mo4+ ions. With the metallic nickel domains facilitating the adsorption of oxygen intermediates to low-coordinated Ni0 and the Mo4+ pulling their electrons, the catalyst exhibits about 60-fold higher activity than a Mo-free NiFe catalyst, while giving about threefold faster charge transfer along with longer stability over 100 h and repeated 100 cycles compared to a bare NiFeMo catalyst. Additionally, these metallic domains and high-valence modulating metal ions are exhibited to give high Faradaic efficiency over 95%.

Size-controlled CdSe quantum dots to boost light harvesting capability and stability of perovskite photovoltaic cells.

Here, we report that incorporation of size-controlled CdSe quantum dots (QDs) into perovskite photovoltaic cells (PSCs) boosts their light harvesting capability. X-ray photoemission and optical absorption spectroscopy analyses also show that the electronic structure of CdSe QDs makes them efficient charge transfer mediators between perovskite and Spiro-MeOTAD layers. In addition, electrochemical impedance spectroscopy experiments demonstrate that QDs help to decrease charge transfer resistance at the interfaces. Additionally, time-correlated single photon counting measurements show that small (2 nm) QDs enhance visible light collection of PSCs in the short wavelength region via Förster resonance energy transfer while large (4 nm) QDs improve light collection of PSCs in the long wavelength region via enhanced light backscattering at the perovskite/QD interface. Moreover, the photocurrent density in the PSCs with QDs retained over 95% of the initial value in a 100 h stability test, thus supporting that the perovskite layer that has been encapsulated with QDs acts to prevent penetration of water molecules through the perovskite layer. Consequently, these results support that utilization of size-controlled hybrid QDs could open up a new route to realize high-performance PSCs even under humid conditions.

Broadband Light Absorption and Efficient Charge Separation Using a Light Scattering Layer with Mixed Cavities for High-Performance Perovskite Photovoltaic Cells with Stability.

CH3 NH3 PbI3 is one of the promising light sensitizers for perovskite photovoltaic cells, but a thick layer is required to enhance light absorption in the long-wavelength regime ranging from PbI2 absorption edge (500 nm) to its optical band-gap edge (780 nm) in visible light. Meanwhile, the thick perovskite layer suppresses visible-light absorption in the short wavelengths below 500 nm and charge extraction capability of electron-hole pairs produced upon light absorption. Herein, we find that a new light scattering layer with the mixed cavities of sizes in 100 and 200 nm between transparent fluorine-doped tin oxide and mesoporous titanium dioxide electron transport layer enables full absorption of short-wavelength photons (λ < 500 nm) to the perovskite along with enhanced absorption of long-wavelength photons (500 nm < λ < 780 nm). Moreover, the light-driven electric field is proven to allow efficient charge extraction upon light absorption, thereby leading to the increased photocurrent density as well as the fill factor prompted by the slow recombination rate. Additionally, the photocurrent density of the cell with a light scattering layer of mixed cavities is stabilized due to suppressed charge accumulation. Consequently, this work provides a new route to realize broadband light harvesting of visible light for high-performance perovskite photovoltaic cells.

Synergistic interaction of Re complex and amine functionalized multiple ligands in metal-organic frameworks for conversion of carbon dioxide.

A metal-organic framework (MOF) is composed of secondary building units (SBUs) of metal ions and organic ligands to link each SBU. Moreover, the photosynthetic synthesis of a valuable CO chemical from carbon dioxide (CO2) represents an important class of appealing methods. Herein, we find that a molecular photocatalyst with high selectivity and activity can be designed via a fine balance in the proximity of Re complex (ReI(CO)3(BPYDC)(Cl), BPYDC = 2,2'-bipyridine-5,5'-dicarboxylate) and -NH2 functionalized multiple ligands composing a MOF photocatalyst, denoted as Re-MOF-NH2. These ligands in Re-MOF-NH2 has been confirmed by infrared, UV-visible, and 1H nuclear magnetic resonance spectra. Moreover, we show from extended X-ray absorption fine structure and in-situ infrared spectra that the bond corresponding to Re-CO upon introduction of -NH2 functional groups is divided into asymmetric bonds of 1.4 Å and 2.3 Å along with different CO2 vibrations, thus making the configuration of carbonyl groups in a Re metal complex become asymmetric in addition to aiding formation of CO2 intermediates within Re-MOF-NH2. Indeed, both of the uneven electron distribution in asymmetric carbonyl groups for Re-CO and the intermolecular stabilization of carbamate intermediates are proven to give the approximately 3-fold increase in photocatalytic activity for conversion of CO2 into CO.

Encapsulation of redox polysulphides via chemical interaction with nitrogen atoms in the organic linkers of metal-organic framework nanocrystals.

Lithium polysulphides generated during discharge in the cathode of a lithium-sulphur redox cell are important, but their dissolution into the electrolyte from the cathode during each redox cycle leads to a shortened cycle life. Herein, we use in situ spectroelectrochemical measurements to demonstrate that sp(2) nitrogen atoms in the organic linkers of nanocrystalline metal-organic framework-867 (nMOF-867) are able to encapsulate lithium polysulphides inside the microcages of nMOF-867, thus helping to prevent their dissolution into the electrolyte during discharge/charge cycles. This encapsulation mechanism of lithiated/delithiated polysulphides was further confirmed by observations of shifted FTIR spectra for the C = N and C-N bonds, the XPS spectra for the Li-N bonds from nMOF-867, and a visualization method, demonstrating that nMOF-867 prevents lithium polysulphides from being dissolved in the electrolyte. Indeed, a cathode fabricated using nMOF-867 exhibited excellent capacity retention over a long cycle life of 500 discharge/charge cycles, with a capacity loss of approximately 0.027% per cycle from a discharge capacity of 788 mAh/g at a high current rate of 835 mA/g.