Intercalant-induced V t2g orbital occupation in vanadium oxide cathode toward fast-charging aqueous zinc-ion batteries.

Intercalation-type layered oxides have been widely explored as cathode materials for aqueous zinc-ion batteries (ZIBs). Although high-rate capability has been achieved based on the pillar effect of various intercalants for widening interlayer space, an in-depth understanding of atomic orbital variations induced by intercalants is still unknown. Herein, we design an NH4+-intercalated vanadium oxide (NH4+-V2O5) for high-rate ZIBs, together with deeply investigating the role of the intercalant in terms of atomic orbital. Besides extended layer spacing, our X-ray spectroscopies reveal that the insertion of NH4+ could promote electron transition to 3dxy state of V t2g orbital in V2O5, which significantly accelerates the electron transfer and Zn-ion migration, further verified by DFT calculations. As results, the NH4+-V2O5 electrode delivers a high capacity of 430.0 mA h g-1 at 0.1 A g-1, especially excellent rate capability (101.0 mA h g-1 at 200 C), enabling fast charging within 18 s. Moreover, the reversible V t2g orbital and lattice space variation during cycling are found via ex-situ soft X-ray absorption spectrum and in-situ synchrotron radiation X-ray diffraction, respectively. This work provides an insight at orbital level in advanced cathode materials.

Nanostructurally Engineering Covalent Organic Frameworks for Boosting CO2 Photoreduction.

Herein, a series of imine-linked covalent organic frameworks (COFs) are developed with advanced ordered mesoporous hollow spherical nanomorphology and ultra-large mesopores (4.6 nm in size), named OMHS-COF-M (M = H, Co, and Ni). The ordered mesoporous hollow spherical nanomorphology is revealed to be formed via an Ostwald ripening mechanism based on a one-step self-templated strategy. Encouraged by its unique structural features and outstanding photoelectrical property, the OMHS-COF-Co material is applied as the photocatalyst for CO2-to-CO reduction. Remarkably, it delivers an impressive CO production rate as high as 15 874 µmol g-1 h-1, a large selectivity of 92.4%, and a preeminent cycling stability. From in/ex situ experiments and density functional theory (DFT) calculations, the excellent CO2 photoreduction performance is ascribed to the desirable cooperation of unique ordered mesoporous hollow spherical host and abundant isolated Co active sites, enhancing CO2 activation, and improving electron transfer kinetics as well as reducing the energy barriers for intermediates *COOH generation and CO desorption.

Universal Intercalation/Alloying Hybrid Mechanism with -ICOHP Criterion in MAX Toward Steadily Ascending Lithium-Ion Batteries.

Profiting from the unique atomic laminated structure, metallic conductivity, and superior mechanical properties, transition metal carbides and nitrides named MAX phases have shown great potential as anodes in lithium-ion batteries. However, the complexity of MAX configurations poses a challenge. To accelerate such application, a minus integrated crystal orbital Hamilton populations descriptor is innovatively proposed to rapidly evaluate the lithium storage potential of various MAX, along with density functional theory computations. It confirms that surface A-element atoms bound to lithium ions have odds of escaping from MAX. Interestingly, the activated A-element atoms enhance the reversible uptake of lithium ions by MAX anodes through an efficient alloying reaction. As an experimental verification, the charge compensation and SnxLiy phase evolution of designed Zr2SnC MAX with optimized structure is visualized via in situ synchrotron radiation XRD and XAFS technique, which further clarifies the theoretically expected intercalation/alloying hybrid storage mechanism. Notably, Zr2SnC electrodes achieve remarkably 219.8% negative capacity attenuation over 3200 cycles at 1 A g-1. In principle, this work provides a reference for the design and development of advanced MAX electrodes, which is essential to explore diversified applications of the MAX family in specific energy fields.

N-methyl Formamide Electrolyte Additive Enabling Highly Reversible Zn Anodes.

Parasitic side reactions and dendrites formation hinder the application of aqueous zinc ion batteries due to inferior cycling life and low reversibility. Against this background, N-methyl formamide (NMF), a multi-function electrolyte additive is applied to enhance the electrochemical performance. Studied via advanced synchrotron radiation spectroscopy and DFT calculations, the NMF additive simultaneously modifies the Zn2+ solvation structure and ensures uniform zinc deposition, thus suppressing both parasitic side reactions and dendrite formation. More importantly, an ultralong cycling life of 3115 h in the Zn||Zn symmetric cell at a current density of 0.5 mA cm-2 is achieved with the NMF additive. Practically, the Zn||PANI full cell utilizing NMF electrolyte shows better rate and cycling performance compared to the pristine ZnSO4 aqueous electrolyte. This work provides useful insights for the development of high-performance aqueous metal batteries.

12 Connecting Sites Linked Three-dimensional Covalent Organic Frameworks with Intrinsic Non-interpenetrated shp Topology for Photocatalytic H2O2 Synthesis.

Developing high connectivity (>8) three-dimensional (3D) covalent organic frameworks (COFs) towards new topologies and functions remains a great challenge owing to the difficulty in getting high connectivity organic building blocks. This however represents the most important step towards promoting the diversity of COFs due to the still limited dynamic covalent bonds available for constructing COFs at this stage. Herein, highly connected phthalocyanine-based (Pc-based) 3D COFs MPc-THHI-COFs (M=H2, Ni) were afforded from the reaction between 2,3,9,10,16,17,23,24-octacarboxyphthalocyanine M(TAPc) (M=H2, Ni) and 5,5',5'',5''',5'''',5'''''-(triphenylene-2,3,6,7,10,11-hexayl)hexa(isophthalohydrazide) (THHI) with 12 connecting sites. Powder X-ray diffraction analysis together with theoretical simulations and transmission electron microscopy reveals their crystalline nature with an unprecedented non-interpenetrated shp topology. Experimental and theoretical investigations disclose the broadened visible light absorption range and narrow optical band gap of MPc-THHI-COFs. This in combination with their 3D nanochannels endows them with efficient photocatalysis performance for H2O2 generation from O2 and H2O via 2e- oxygen reduction reaction and 2e- water oxidation reaction under visible-light irradiation (λ >400 nm). This work provides valuable result for the development of high connectivity functional COFs towards diverse application potentials.

Highly Connected Three-Dimensional Covalent Organic Framework with Flu Topology for High-Performance Li-S Batteries.

Lithium-sulfur batteries (LSBs) have been considered as a promising candidate for next-generation energy storage devices, which however still suffer from the shuttle effect of the intermediate lithium polysulfides (LiPSs). Covalent-organic frameworks (COFs) have exhibited great potential as sulfur hosts for LSBs to solve such a problem. Herein, a pentiptycene-based D2h symmetrical octatopic polyaldehyde, 6,13-dimethoxy-2,3,9,10,18,19,24,25-octa(4'-formylphenyl)pentiptycene (DMOPTP), was prepared and utilized as a building block toward preparing COFs. Condensation of DMOPTP with 4-connected tetrakis(4-aminophenyl)methane affords an expanded [8 + 4] connected network 3D-flu-COF, with a flu topology. The non-interpenetrated nature of the flu topology endows 3D-flu-COF with a high Brunauer-Emmett-Teller surface area of 2860 m2 g-1, large octahedral cavities, and cross-linked tunnels in the framework, enabling a high loading capacity of sulfur (∼70 wt %), strong LiPS adsorption capability, and facile ion diffusion. Remarkably, when used as a sulfur host for LSBs, 3D-flu-COF delivers a high capacity of 1249 mA h g-1 at 0.2 C (1.0 C = 1675 mA g-1), outstanding rate capability (764 mA h g-1 at 5.0 C), and excellent stability, representing one of the best results among the thus far reported COF-based sulfur host materials for LSBs and being competitive with the state-of-the-art inorganic host materials.

Observation of Interpenetrated Topology Isomerism for Covalent Organic Frameworks with Atom-Resolution Single Crystal Structures.

Rational control and understanding of isomerism are of significance but still remain a great challenge in reticular frameworks, in particular, for covalent organic frameworks (COFs) due to the complicated synthesis and energy factors. Herein, reaction of 3,3',5,5'-tetra(4-formylphenyl)-2,2',6,6'-tetramethoxy-1,1'-biphenyl (TFTB) with 3,3',5,5'-tetrakis(4-aminophenyl)bimesityl (TAPB) under different reaction conditions affords single crystals of two 3D COF isomers, namely, USTB-20-dia and USTB-20-qtz. Their structures with resolutions up to 0.9-1.1 Å have been directly solved by three-dimensional electron diffraction (3D ED) and synchrotron single crystal X-ray diffraction, respectively. USTB-20-dia and USTB-20-qtz show rare 2 × 2-fold interpenetrated dia-b nets and 3-fold interpenetrated qtz-b frameworks. Comparative studies of the crystal structures of these COFs and theoretical simulation results indicate the crucial role of the flexible molecular configurations of building blocks in the present interpenetrated topology isomerism. This work not only presents the rare COF isomers but also gains an understanding of the formation of framework isomerism from both single crystal structures and theoretical simulation perspectives.

A Hierarchical CuO Nanowire@CoFe-Layered Double Hydroxide Nanosheet Array as a High-Efficiency Seawater Oxidation Electrocatalyst.

Seawater electrolysis has great potential to generate clean hydrogen energy, but it is a formidable challenge. In this study, we report CoFe-LDH nanosheet uniformly decorated on a CuO nanowire array on Cu foam (CuO@CoFe-LDH/CF) for seawater oxidation. Such CuO@CoFe-LDH/CF exhibits high oxygen evolution reaction electrocatalytic activity, demanding only an overpotential of 336 mV to generate a current density of 100 mA cm-2 in alkaline seawater. Moreover, it can operate continuously for at least 50 h without obvious activity attenuation.

Piperazine-Linked Metalphthalocyanine Frameworks for Highly Efficient Visible-Light-Driven H2O2 Photosynthesis.

Artificial photosynthesis of H2O2 from O2 reduction provides an energy-saving, safe, and green approach. However, it is still critical to develop highly active and selective 2e- oxygen reduction reaction photocatalysts for efficient H2O2 production owing to the unsatisfactory photosynthesis productivity. Herein, two new two-dimensional piperazine-linked CoPc-based covalent organic frameworks (COFs), namely, CoPc-BTM-COF and CoPc-DAB-COF, were afforded from the nucleophilic substitution reaction of hexadecafluorophthalocyaninato cobalt(II) (CoPcF16) with 1,2,4,5-benzenetetramine (BTM) or 3,3'-diaminobenzidine (DAB). Powder X-ray diffraction analysis in combination with electron microscopy and a series of spectroscopic technologies reveals their crystalline porous framework with a fully conjugated structure and eclipsed π-stacking model. Ultraviolet-visible diffuse reflectance absorption spectra unveil their excellent light absorption capacity in a wide range of 400-1000 nm. This, together with their enhanced photo-induced charge separation and transport efficiency as disclosed by photocurrent response and photoluminescence measurements, endows the as-prepared piperazine-linked CoPc-based COFs with superior photocatalytic activity toward O2-to-H2O2 conversion under visible-light irradiation (λ > 400 nm). In particular, CoPc-BTM-COF exhibits a record-high H2O2 yield of 2096 µmol h-1 g-1 among the COF-based photocatalysts and an impressive apparent quantum yield of 7.2% at 630 nm. The present result should be helpful for fabricating high-performance and low-cost photocatalysts for visible-light-driven H2O2 photosynthesis.

Conjugated Three-Dimensional High-Connected Covalent Organic Frameworks for Lithium-Sulfur Batteries.

Developing conjugated three-dimensional (3D) covalent organic frameworks (COFs) still remains an extremely difficult task due to the lack of enough conjugated 3D building blocks. Herein, condensation between an 8-connected pentiptycene-based D2h building block (DMOPTP) and 4-connected square-planar linkers affords two 3D COFs (named 3D-scu-COF-1 and 3D-scu-COF-2). A combination of the 3D homoaromatic conjugated structure of the former building block with the 2D conjugated structure of the latter linking units enables the π-electron delocalization over the whole frameworks of both COFs, endowing them with excellent conductivities of 3.2-3.5 × 10-5 S cm-1. In particular, the 3D rigid quadrangular prism shape of DMOPTP guides the formation of a twofold interpenetrated scu 3D topology and high-connected permanent porosity with a large Brunauer-Emmett-Teller (BET) surface area of 2340 and 1602 m2 g-1 for 3D-scu-COF-1 and 3D-scu-COF-2, respectively, ensuring effective small molecule storage and mass transport characteristics. This, in combination with their good charge transport properties, renders them promising sulfur host materials for lithium-sulfur batteries (LSBs) with high capacities (1035-1155 mA h g-1 at 0.2 C, 1 C = 1675 mA g-1), excellent rate capabilities (713-757 mA h g-1 at 5.0 C), and superior cycling stability (71-83% capacity retention at 2.0 C after 500 cycles), surpassing the most of organic LSB cathodes reported thus far.

Mesoporous Polyimide-Linked Covalent Organic Framework with Multiple Redox-Active Sites for High-Performance Cathodic Li Storage.

Covalent organic frameworks (COFs) are gaining increasing attention as renewable cathode materials for Li-ion batteries. However, COF electrodes reported so far still exhibit unsatisfying capacity due to their limited active site density and insufficient utilization. Herein, a new two-dimensional polyimide-linked COF, HATN-AQ-COF with multiple redox-active sites for storing Li+ ions, was designed and fabricated from a new module of 2,3,8,9,14,15-hexacarboxyl hexaazatrinaphthalene trianhydrides with a 2,6-diaminoanthraquinone linker. HATN-AQ-COF possessing excellent stability, good conductivity, and a large pore size of 3.8 nm enables the stable and fast ion transport. This, in combination with the abundant redox active sites, results in a high reversible capacity of 319 mAh g-1 at 0.5 C (1 C=358 mA g-1 ) for the HATN-AQ-COF electrode with a high active site utilization of 89 % and good cycle performance, representing one of the best performances among the reported COF electrodes.

Thermal-Triggered Dynamic Disulfide Bond Self-Heals Inorganic Perovskite Solar Cells.

One great challenge for perovskite solar cells (PSCs) lies in their poor operational stability under harsh stimuli by humidity, heat, light, etc. Herein, a thermal-triggered self-healing polyurethane (PU) is tailored to simultaneously improve the efficiency and stability of inorganic CsPbIBr2 PSCs. The dynamic covalent disulfide bonds between adjacent molecule chains in PU at high temperatures self-heal the in-service formed defects within the CsPbIBr2 perovskite film. Finally, the best device free of encapsulation achieves a champion efficiency up to 10.61 % and an excellent long-term stability in an air atmosphere over 80 days and persistent heat attack (85 °C) over 35 days. Moreover, the photovoltaic performances are recovered by a simple heat treatment.

p-Type Charge Transfer Doping of Graphene Oxide with (NiCo)1-y Fey Ox for Air-Stable, All-Inorganic CsPbIBr2 Perovskite Solar Cells.

The precise regulation of interfacial charge distribution highly determines the power conversion efficiency of perovskite solar cells (PSCs). Herein, inorganic (NiCo)1-y Fey Ox nanoparticle decorated graphene oxide (GO) is successfully demonstrated as a hole booster for all-inorganic CsPbIBr2 PSC free of precious metal electrode. Arising from the spontaneous electron transfer induced p-type doping of GO from edged oxygen-containing functional groups to (NiCo)1-y Fey Ox , the best all-inorganic CsPbIBr2 PSC achieves an efficiency of 10.95 % under one standard sun owing to the eliminated paradox between charge extraction and charge localization in GO surface. Furthermore, the champion device exhibits an excellent long-term stability at 10 % relative humidity without encapsulation over 70 days because of the suppressed ions migration.

Interfacial Strain Release from the WS2 /CsPbBr3 van der Waals Heterostructure for 1.7†V Voltage All-Inorganic Perovskite Solar Cells.

Perovskite lattice distortion induced by residual tensile strain from the thermal expansion mismatch between the electron-transporting layer (ETL) and perovskite film causes a sluggish charge extraction and transfer dynamics in all-inorganic CsPbBr3 perovskite solar cells (PSCs) because of their higher crystallization temperatures and thermal expansion coefficients. Herein, the interfacial strain is released by fabricating a WS2 /CsPbBr3 van der Waals heterostructure owing to their matched crystal lattice structure and the atomically smooth dangling bond-free surface to act as a lubricant between ETL and CsPbBr3 perovskite. Arising from the strain-released interface and condensed perovskite lattice, the best device achieves an efficiency of 10.65 % with an ultrahigh open-circuit voltage of 1.70 V and significantly improved stability under persistent light irradiation and humidity (80 %) attack over 120 days.

Alkyl-Chain-Regulated Charge Transfer in Fluorescent Inorganic CsPbBr3 Perovskite Solar Cells.

Improved charge extraction and wide spectral absorption promote power conversion efficiency of perovskite solar cells (PSCs). The state-of-the-art carbon-based CsPbBr3 PSCs have an inferior power output capacity because of the large optical band gap of the perovskite film and the high energy barrier at perovskite/carbon interface. Herein, we use alkyl-chain regulated quantum dots as hole-conductors to reduce charge recombination. By precisely controlling alkyl-chain length of ligands, a balance between the surface dipole induced charge coulomb repulsive force and quantum tunneling distance is achieved to maximize charge extraction. A fluorescent carbon electrode is used as a cathode to harvest the unabsorbed incident light and to emit fluorescent light at 516 nm for re-absorption by the perovskite film. The optimized PSC free of encapsulation achieves a maximum power conversion efficiency up to 10.85 % with nearly unchanged photovoltaic performances under 80 %RH, 80 °C, or light irradiation in air.

Enhancing the colorimetric detection of H2O2 and ascorbic acid on polypyrrole coated fluconazole-functionalized POMOFs.

A new fluconazole-functionalized polyoxometalate-based metal-organic framework (POMOF) [Ag3(FKZ)2(H2O)2][H3SiW12O40] (AgFKZSiW12) was successfully constructed, and its polypyrrole (PPy) coated composite AgFKZSiW12@PPy was also obtained via a facile 'in situ' oxidation polymerization process. The peroxidase-like activity evaluation indicates that the maximized synergistic effect from the integration of PPy, SiW12 clusters, HFKZ drug molecules, and Ag ions deeply enhanced the overall performance. More importantly, AgFKZSiW12@PPy exhibits the fastest response time (30 s) among all the reported peroxidase mimics to date, including the pristine AgFKZSiW12 (2 min). Moreover, the AgFKZSiW12@PPy-based colorimetric biosensing platform towards H2O2 and ascorbic acid (AA) exhibits limits of detection (LOD) as low as 0.12 µM and 2.7 µM, respectively. This work reveals a promising prospect in medical diagnosis and biotechnology for colorimetric biosensor fabrication with high performance through the introduction of PPy.

Hole-Boosted Cu(Cr,M)O2 Nanocrystals for All-Inorganic CsPbBr3 Perovskite Solar Cells.

The all-inorganic CsPbBr3 perovskite solar cell (PSC) is a promising solution to balance the high efficiency and poor stability of state-of-the-art organic-inorganic PSCs. Setting inorganic hole-transporting layers at the perovskite/electrode interface decreases charge carrier recombination without sacrificing superiority in air. Now, M-substituted, p-type inorganic Cu(Cr,M)O2 (M=Ba2+ , Ca2+ , or Ni2+ ) nanocrystals with enhanced hole-transporting characteristics by increasing interstitial oxygen effectively extract holes from perovskite. The all-inorganic CsPbBr3 PSC with a device structure of FTO/c-TiO2 /m-TiO2 /CsPbBr3 /Cu(Cr,M)O2 /carbon achieves an efficiency up to 10.18 % and it increases to 10.79 % by doping Sm3+ ions into perovskite halide, which is much higher than 7.39 % for the hole-free device. The unencapsulated Cu(Cr,Ba)O2 -based PSC presents a remarkable stability in air in either 80 % humidity over 60 days or 80 °C conditions over 40 days or light illumination for 7 days.

Assembly of Multifold Helical Polyoxometalate-Based Metal-Organic Frameworks as Anode Materials in Lithium-Ion Batteries.

For exploring the multifold helical fabrication of polyoxometalate (POM)-based hybrid compounds, four POM-based crystalline compounds with different meso-helices, H3[Ag27(trz)16(H2O)6][SiW12O40]2·5H2O (1), H[Ag27(trz)16(H2O)4][PW12O40]2·2H2O (2), [Ag23(trz)14(H2O)2][HSiW12O40] (3), and [Ag23(trz)14(H2O)2][PW12O40] (4), were successfully isolated by using the delicate 1,2,3-triazole ligand and silver ions in this work. Crystal analysis reveals that compounds 1 and 2 and compounds 3 and 4 are isomorphous and display 2-/4-fold mixed meso-helices and simple 2-fold meso-helices, respectively. In addition, due to the reversible multielectron redox behavior and electron storage functions of POMs, compounds 1 and 3 were studied as anode materials in lithium-ion batteries (LIBs). Compounds 1 and 3 show very high lithiation capacities (1356 and 1140 mAh g-1, respectively) in the initial cycle, which are much higher than those of (NBu4)4[SiW12O40] and commercial graphite at the current density of 100 mA g-1. More importantly, both compounds also show good stable performance after 100 cycles.

Polyoxometalates Templated Metal Ag-Carbene Frameworks Anodic Material for Lithium-Ion Batteries.

A POMs templated 3D Ag-carbene framework with lvt-a topology was hydrothermally synthesized. The POMs templated MCF combining the advantages of POMs, MOFs, and carbene not only shows excellent thermal and chemical stabilities but also possesses a good discharge capacity of 481 mAh·g-1 after 100 cycles applied as anode material in LIBs.

Polyoxometalate-Incorporated Metallapillararene/Metallacalixarene Metal-Organic Frameworks as Anode Materials for Lithium Ion Batteries.

A series of remarkable crystalline compounds containing metallapillararene/metallacalixarene metal-organic frameworks (MOFs), [Ag5(pyttz)3·Cl·(H2O)][H3SiMo12O40]·3H2O (1), [Ag5(trz)6][H5SiMo12O40] (2), [Ag5(trz)6][H5GeMo12O40] (3), and [Ag5(trz)6][H4PW12O40] (4) (pyttz = 3-(pyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, trz = 1,2,4-triazole), have been obtained by using a simple one-step hydrothermal reaction of silver nitrate, pyttz for 1 and trz for 2-4, and Keggin type polyoxometalates (POMs). Crystal analysis reveals that Keggin POMs have been successfully incorporated in the windows of the metallapillararene/metallacalixarene MOFs in compounds 1-4. In addition, the Keggin silicomolybdenate-based hybrid compounds 1 and 2 were used as anode materials in lithium ion batteries (LIBs), which exhibited promising electrochemical performance with the first discharge capacities of 1344 mAh g-1 for 1 and 1452 mAh g-1 for 2, and this stabilized at 520 mAh g-1 for 1 and 570 mAh g-1 for 2 after 100 cycles at a current density of 100 mA g-1. The performances are better than that of (NBu4)4[SiMo12O40] matrix and commercial graphite anodes.