Metal–Organic Frameworks as Metal Ion Precursors for the Synthesis of Nanocomposites for Lithium-Ion Batteries

Metal–organic frameworks (MOFs) are promising materials with fascinating properties. Their widespread applications are sometimes hindered by the intrinsic instability of frameworks. However, this instability of MOFs can also be exploited for useful purposes. Herein, we report the use of MOFs as metal ion precursors for constructing functional nanocomposites by utilizing the instability of MOFs. The heterogeneous growth process of nanostructures on substrates involves the release of metal ions, nucleation on substrates, and formation of a covering structure. Specifically, the synthesized CoS with carbon nanotubes as substrates display enhanced performance in a lithium-ion battery. Such strategy not only presents a new way for exploiting the instability of MOFs but also supplies a prospect for designing versatile functional nanocomposites.     

Dual Dopamine Derived Polydopamine Coated N-Doped Porous Carbon Spheres as a Sulfur Host for High-Performance Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are considered to be one of the most promising energy storage systems owing to their high energy density and low cost. However, their wide application is still limited by the rapid capacity fading. Herein, polydopamine (PDA)-coated N-doped hierarchical porous carbon spheres (NPC@PDA) are reported as sulfur hosts for high-performance Li-S batteries. The NPC core with abundant and interconnected pores provides fast electron/ion transport pathways and strong trapping ability towards lithium polysulfide intermediates. The PDA shell could further suppress the loss of lithium polysulfide intermediates through polar–polar interactions. Benefiting from the dual function design, the NPC/S@PDA composite cathode exhibits an initial capacity of 1331 mAh g⁻¹ and remains at 720 mAh g⁻¹ after 200 cycles at 0.5 C. At the pouch cell level with a high sulfur mass loading, the NPC/S@PDA composite cathode still exhibits a high capacity of 1062 mAh g⁻¹ at a current density of 0.4 mA cm⁻².     

Recent Progress in Organic–Inorganic Composite Solid Electrolytes for All-Solid-State Lithium Batteries

Conventional lithium-ion batteries, with flammable organic liquid electrolytes, have serious safety problems, which greatly limit their application. All-solid-state batteries (ASSBs) have received extensive attention from large-scale energy-storage fields, such as electric vehicles (EVs) and intelligent power grids, due to their benefits in safety, energy density, and thermostability. As the key component of ASSBs, solid electrolytes determine the properties of ASSBs. In past decades, various kinds of solid electrolytes, such as polymers and inorganic electrolytes, have been explored. Among these candidates, organic–inorganic composite solid electrolytes (CSEs) that integrate the advantages of these two different electrolytes have been regarded as promising electrolytes for high-performance ASSBs, and extensive studies have been carried out. Herein, recent progress in organic–inorganic CSEs is summarized in terms of the inorganic component, electrochemical performance, effects of the inorganic ceramic nanostructure, and ionic conducting mechanism. Finally, the main challenges and perspectives of organic–inorganic CSEs are highlighted for future development.     

Multifunctional Electrocatalytic Cathodes Derived from Metal–Organic Frameworks for Advanced Lithium-Sulfur Batteries

The rechargeable lithium-sulfur (Li-S) battery is a promising candidate for the next generation of energy storage technology, owing to the high theoretical capacity, high specific energy density, and low cost of electrode materials. The main drawbacks in the development of long-life Li-S batteries are capacity fading and the sluggish kinetics at the cathode caused by the polysulfides shuttle. These limitations are addressed through the design of novel nanocages containing cobalt phosphide (CoP) nanoparticles embedded in highly porous nitrogen-doped carbon (CoP-N-GC) by thermal annealing of ZIF-67 in a reductive atmosphere followed by a phosphidation step using sodium hypophosphite. The CoP nanoparticles, with large surface area and uniform homogeneous distribution within the N-doped nanocage graphitic carbon, act as electrocatalysts to suppress the shuttle of soluble polysulfides through strong chemical interactions and catalyze the sulfur redox. As a result, the S@CoP-N-GC electrode delivers an extremely high specific capacity of 1410 mA h g⁻¹ at 0.1 C (1 C=1675 mA g⁻¹) with an excellent coulombic efficiency of 99.7 %. Moreover, capacity retention from 864 to 678 mA h g⁻¹ is obtained after 460 cycles with a very low decay rate of 0.046 % per cycle at 0.5 C. Therefore, the combination of the CoP catalyst and polar conductive porous carbon effectively stabilizes the sulfur cathode, enhancing the electrochemical performance and stability of the battery.     

Two-Dimensional Metal–Organic Framework Nanosheets with Cobalt-Porphyrins for High-Performance CO2 Electroreduction

The electrochemical reduction of CO₂ presents a promising strategy to mitigate the greenhouse effect and reduce excess carbon dioxide emission to realize a carbon-neutral energy cycle, but it suffers from the lack of high-performance electrocatalysts. In this work, catalytic active cobalt porphyrin [TCPP(Co)=(5,10,15,20)-tetrakis(4-carboxyphenyl)porphyrin-Co^II] was precisely anchored onto water-stable 2D metal–organic framework (MOF) nanosheets (Zr-BTB) to obtain ultrathin 2D MOF nanosheets [TCPP(Co)/Zr-BTB] with accessible catalytic sites for the CO₂ reduction reaction. Compared with molecular cobalt porphyrin, the TCPP(Co)/Zr-BTB exhibits an ultrahigh turnover frequency (TOF=4768 h⁻¹ at −0.919 V vs. reversible hydrogen electrode, RHE) owing to high active-site utilization. In addition, three post-modified 2D MOF nanosheets [TCPP(Co)/Zr-BTB-PABA, TCPP(Co)/Zr-BTB-PSBA, TCPP(Co)/Zr-BTB-PSABA] were obtained, with the modifiers of p-(aminomethyl)benzoic acid (PABA), p-sulfobenzoic acid potassium (PSBA), and p-sulfamidobenzoic acid (PSABA), to change the micro-environments around TCPP(Co) through the tuning of steric effects. Among them, the TCPP(Co)/Zr-BTB-PSABA exhibited the best performance with a faradaic efficiency (FE_CO) of 85.1 %, TOF of 5315 h⁻¹, and j_total of 6 mA cm⁻² at −0.769 V (vs. RHE). In addition, the long-term durability of the electrocatalysts is evaluated and the role of pH buffer is revealed.     

Designing Heteroatom-Codoped Iron Metal–Organic Framework for Promotional Photoreduction of Carbon Dioxide to Ethylene

Rational engineering active sites and vantage defects of catalysts are promising but grand challenging task to enhance photoreduction CO₂ to high value-added C2 products. In this study, we designed an N,S-codoped Fe-based MIL-88B catalyst with well-defined bipyramidal hexagonal prism morphology via a facile and effective process, which was synthesized by addition of appropriate 1,2-benzisothiazolin-3-one (BIT) and acetic acid to the reaction solution. Under simulated solar irradiation, the designed catalyst exhibits high C₂H₄ evolution yield of 17.7 μmol g⁻¹⋅h, which has been rarely achieved in photocatalytic CO₂ reduction process. The synergistic effect of Fe-N coordinated sites and reasonable defects in the N,S-codoped photocatalyst can accelerate the migration of photogenerated carriers, resulting in high electron density, and this in turn helps to facilitate the formation and dimerization of C−C coupling intermediates for C₂H₄ effectively.     

Metal–Organic Framework Crystal–Glass Composite Membranes with Preferential Permeation of Ethane

Metal–organic framework (MOF) glass is an easy to process and self-supported amorphous material that is suitable for fabricating gas separation membranes. However, MOF glasses, such as ZIF-62 and ZIF-4 have low porosity, which makes it difficult to obtain membranes with high permeance. Here, a self-supported MOF crystal–glass composite (CGC) membrane was prepared by melt quenching a mixture of ZIF-62 as the membrane matrix and ZIF-8 as the filler. The conversion of ZIF-62 from crystal to glass and the simultaneous partial melting of ZIF-8 facilitated by the melt state of ZIF-62 make the CGC membrane monolithic, eliminating non-selective grain boundaries and improving selectivity. The thickness of CGC membrane can be adjusted to fabricate a membrane without the need of a support substrate. CGC membranes exhibit a C₂H₆ permeance of 41 569 gas permeation units (GPU) and a C₂H₆/C₂H₄ selectivity of 7.16. The CGC membrane has abundant pores from the glassy state of ZIF-62 and the crystalline ZIF-8, which enables high gas permeance. ZIF-8 has preferential adsorption for C₂H₆ and promotes C₂H₆ transport in the membrane, and thus the GCG membrane exhibits ultrahigh C₂H₆ permeance and good C₂H₆/C₂H₄ selectivity.     

In Situ Construction of an Ultra-Stable Conductive Composite Interface for High-Voltage All-Solid-State Lithium Metal Batteries

The garnet electrolyte presents poor wettability with Li metal, resulting in an extremely large interfacial impedance and drastic growth of Li dendrites. Herein, a novel ultra-stable conductive composite interface (CCI) consisting of Li_ySn alloy and Li₃N is constructed in situ between Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) pellet and Li metal by a conversion reaction of SnN_x with Li metal at 300 °C. The Li_ySn alloy as a continuous and robust bridge between LLZTO and Li metal can effectively reduce the LLZTO/Li interfacial resistance from 4468.0 Ω to 164.8 Ω. Meanwhile, the Li₃N as a fast Li-ion channel can efficiently transfer Li ions and give their uniform distribution at the LLZTO/Li interface. Therefore, the Li/LLZTO@CCI/Li symmetric battery stably cycles for 1200 h without short circuit, and the all-solid-state high-voltage Li/LLZTO@CCI/LiNi_0.5Co_0.2Mn_0.3O₂ battery achieves a specific capacity of 161.4 mAh g⁻¹ at 0.25 C with a capacity retention rate of 92.6 % and coulombic efficiency of 100.0 % after 200 cycles at 25 °C.     

Metal–Organic Framework Membrane Nanopores as Biomimetic Photoresponsive Ion Channels and Photodriven Ion Pumps

Biological ion channels and ion pumps with sub-nanometer sizes modulate ion transport in response to external stimuli. Realizing such functions with sub-nanometer solid-state nanopores has been an important topic with wide practical applications. Herein, we demonstrate a biomimetic photoresponsive ion channel and photodriven ion pump using a porphyrin-based metal–organic framework membrane with pore sizes comparable to hydrated ions. We show that the molecular-size pores enable precise and robust optoelectronic ion transport modulation in a broad range of concentrations, unparalleled with conventional solid-state nanopores. Upon decoration with platinum nanoparticles to form a Schottky barrier photodiode, photovoltage across the membrane is generated with “uphill” ion transport from low concentration to high concentration. These results may spark applications in energy conversion, ion sieving, and artificial photosynthesis.     

Hierarchical Porous N-Doped Carbon Nanosheets Obtained by Organic–Inorganic Bipolymeric Engineering for Improved Lithium–Sulfur Batteries

A new route for obtaining N-doped carbon nanosheets through an in situ solid-state thermal organic–inorganic polymerization and carbonization method, with glucose and melamine as precursors, due to different temperature intervals for glucose or melamine polymerization, is reported. At a current rate of 0.2 C, as a cathode for a lithium–sulfur cell, the N-doped carbon nanosheet/sulfur hybrid delivers a high capacity of 1313 and 722 mA h g⁻¹ in the 1st and 200th cycles, respectively; these values are over 40 % higher than that of cells with glucose-derived carbon nanosheets.     

A Redox-Active 2D Metal–Organic Framework for Efficient Lithium Storage with Extraordinary High Capacity

Metal–organic framework cathodes usually exhibit low capacity and poor electrochemical performance for Li-ion storage owing to intrinsic low conductivity and inferior redox activity. Now a redox-active 2D copper–benzoquinoid (Cu-THQ) MOF has been synthesized by a simple solvothermal method. The abundant porosity and intrinsic redox character endow the 2D Cu-THQ MOF with promising electrochemical activity. Superior performance is achieved as a Li-ion battery cathode with a high reversible capacity (387 mA h g⁻¹), large specific energy density (775 Wh kg⁻¹), and good cycling stability. The reaction mechanism is unveiled by comprehensive spectroscopic techniques: a three-electron redox reaction per coordination unit and one-electron redox reaction per copper ion mechanism is demonstrated. This elucidatory understanding sheds new light on future rational design of high-performance MOF-based cathode materials for efficient energy storage and conversion.     

Partially Pyrolyzed Binary Metal–Organic Framework Nanosheets for Efficient Electrochemical Hydrogen Peroxide Synthesis

Herein, we developed a partially controlled pyrolysis strategy to create evenly distributed NiO nanoparticles within NiFe-MOF nanosheets (MOF NSs) for electrochemical synthesis of H₂O₂ by a two-electron oxygen reduction reaction (ORR). The elemental Ni can be partially transformed to NiO and uniformly distributed on the surface of the MOF NSs, which is crucial for the formation of the particular structure. The optimized MOF NSs-300 exhibits the highest activity for ORR with near-zero overpotential and excellent H₂O₂ selectivity (ca. 99 %) in 0.1 m KOH solution. A high-yield H₂O₂ production rate of 6.5 mol g_cat⁻¹ h⁻¹ has also been achieved by MOF NSs-300 in 0.1 m KOH and at 0.6 V (vs. RHE). In contrast to completely pyrolyzed products, the enhanced catalytic activities of partially pyrolyzed MOF NSs-300 originates mainly from the retained MOF structure and the newly generated NiO nanoparticles, forming the coordinatively unsaturated Ni atoms and tuning the performance towards electrochemical H₂O₂ synthesis.     

The Significance of Metal Coordination in Imidazole-Functionalized Metal–Organic Frameworks for Carbon Dioxide Utilization

The grafting of imidazole species onto coordinatively unsaturated sites within metal–organic framework MIL-101(Cr) enables enhanced CO₂ capture in close proximity to catalytic sites. The subsequent combination of CO₂ and epoxide binding sites, as shown through theoretical findings, significantly improves the rate of cyclic carbonate formation, producing a highly active CO₂ utilization catalyst. An array of spectroscopic investigations, in combination with theoretical calculations reveal the nature of the active sites and associated catalytic mechanism which validates the careful design of the hybrid MIL-101(Cr).     

Quencher-Delocalized Emission Strategy of AIEgen-Based Metal–Organic Framework for Profiling of Subcellular Glutathione

Distinguishing glutathione (GSH) level in different subcellular locations is critical for studying its antioxidant function in the signaling system. However, traditional methods for imaging subcellular GSH were achieved in isolated organelles or fixed cells. In this work, we report a quencher-delocalized emission strategy for in situ profiling of GSH at different subcellular locations in living cells. A nonemissive metal–organic framework (MOF) nanoprobe was designed with AIEgen as the linker and Cu^II as the node and quencher. The AIEgen in MOF structure was lightened up with green emission in a neutral environment due to partial Cu^II delocalization by competitive binding to GSH. Meanwhile, along with the protonation of AIEgen ligand under acidic environment, the AIEgen-based MOF could be completely dissociated in the presence of GSH to yield yellow emission. The two-channel ratiometric analysis of dual-colored emission of AIEgen-based MOF allows visualization of GSH in cytoplasm and lysosome in living cells, which is also able to report the drug effects on different subcellular GSH levels.     

2D Semiconducting Metal–Organic Framework Thin Films for Organic Spin Valves

2D conductive metal–organic frameworks (2D c-MOFs) feature promising applications as chemiresistive sensors, electrode materials, electrocatalysts, and electronic devices. However, exploration of the spin-polarized transport in this emerging materials and development of the relevant spintronics have not yet been implemented. In this work, layer-by-layer assembly was applied to fabricate highly crystalline and oriented thin films of a 2D c-MOF, Cu₃(HHTP)₂, (HHTP: 2,3,6,7,10,11-hexahydroxytriphenylene), with tunable thicknesses on the La_0.67Sr_0.33MnO₃ (LSMO) ferromagnetic electrode. The magnetoresistance (MR) of the LSMO/Cu₃(HHTP)₂/Co organic spin valves (OSVs) reaches up to 25 % at 10 K. The MR can be retained with good film thickness adaptability varied from 30 to 100 nm and also at high temperatures (up to 200 K). This work demonstrates the first potential applications of 2D c-MOFs in spintronics.     

Ferroelectric Metal–Organic Framework as a Host Material for Sulfur to Alleviate the Shuttle Effect of Lithium–Sulfur Battery

Ferroelectricity has an excellent reversible polarization conversion behavior under an external electric field. Herein, we propose an interesting strategy to alleviate the shuttle effect of lithium–sulfur battery by utilizing ferroelectric metal–organic framework (FMOF) as a host material for the first time. Compared to other MOF with same structure but without ferroelectricity and commercial carbon black, the cathode based on FMOF exhibits a low capacity decay and high cycling stability. These results demonstrate that the polarization switching behaviors of FMOF under the discharge voltage of lithium–sulfur battery can effectively trap polysulfides by polar–polar interactions, decrease polysulfides shuttle and improve the electrochemical performance of lithium–sulfur battery.     

2D Metal–Organic Framework Derived CuCo Alloy Nanoparticles Encapsulated by Nitrogen-Doped Carbonaceous Nanoleaves for Efficient Bifunctional Oxygen Electrocatalyst and Zinc–Air Batteries

The development of efficient bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) still remains a challenge in a wide range of renewable energy technologies. Herein, CuCo alloy nanoparticles encapsulated by nitrogen-doped carbonaceous nanoleaves (CuCo-NC) have been synthesized from a Cu(OH)₂/2D leaf-like zeolitic imidazolate framework (ZIF-L)-pyrolysis approach. Leaf-like Cu(OH)₂ is first prepared by the ultrasound-induced self-assembly of Cu(OH)₂ nanowires. The efficient encapsulation of Cu(OH)₂ in ZIF-L is obtained owing to the morphology fitting between the leaf-like Cu(OH)₂ and ZIF-L. CuCo-NC catalysts present superior electrocatalytic activity and stability toward ORR and OER over the commercial Pt/C and IrO₂, respectively, which are further used as bifunctional oxygen electrocatalysts in Zn–air batteries and exhibit impressive performance, with a high peak power density of 303.7 mW cm⁻², large specific capacity of up to 751.4 mAh g⁻¹ at 20 mA cm⁻², and a superior recharge stability.     

Cucurbit[7]uril-Based Metal–Organic Rotaxane Framework for Dual-Capture of Molecular Iodine and Cationic Potassium Ion

Metal–organic rotaxane frameworks (MORFs) attracted much attention in the past years for construction of intelligent functional materials. Herein, a one-pot synthesis is reported of a three-dimensional (3D) cucurbit[7]uril (Q[7])-based MORF under hydrothermal conditions, namely Q[7]-MORF-1 , formed by encapsulating the anionic benzoate moieties of the tricarboxylate ligand into the cavity of Q[7]. Furthermore, Q[7]-MORF-1 shows dual-capture capacity for iodine and K⁺ selectively among the alkali metal ions. The captured molecular iodine is included in the cavity of Q[7] through halogen-bonding interactions and the K⁺ cations are positioned at the carbonyl port of the Q[7] through K−O coordination interactions.     

In Situ Electrochemical Activation of Hydroxyl Polymer Cathode for High-Performance Aqueous Zinc–Organic Batteries

The slow reaction kinetics and structural instability of organic electrode materials limit the further performance improvement of aqueous zinc-organic batteries. Herein, we have synthesized a Z-folded hydroxyl polymer polytetrafluorohydroquinone (PTFHQ) with inert hydroxyl groups that could be partially oxidized to the active carbonyl groups through the in situ activation process and then undertake the storage/release of Zn²⁺. In the activated PTFHQ, the hydroxyl groups and S atoms enlarge the electronegativity region near the electrochemically active carbonyl groups, enhancing their electrochemical activity. Simultaneously, the residual hydroxyl groups could act as hydrophilic groups to enhance the electrolyte wettability while ensuring the stability of the polymer chain in the electrolyte. Also, the Z-folded structure of PTFHQ plays an important role in reversible binding with Zn²⁺ and fast ion diffusion. All these benefits make the activated PTFHQ exhibit a high specific capacity of 215 mAh g⁻¹ at 0.1 A g⁻¹, over 3400 stable cycles with a capacity retention of 92 %, and an outstanding rate capability of 196 mAh g⁻¹ at 20 A g⁻¹.     

Incarceration of Iodine in a Pyrene-Based Metal–Organic Framework

A pyrene-based metal-organic framework (MOF) SION-8 captured iodine (I₂) vapor with a capacity of 460 and 250 mg g⁻¹_MOF at room temperature and 75 °C, respectively. Single-crystal X-ray diffraction analysis and van-der-Waals-corrected density functional theory calculations confirmed the presence of I₂ molecules within the pores of SION-8 and their interaction with the pyrene-based ligands. The I₂–pyrene interactions in the I₂-loaded SION-8 led to a 10⁴-fold increase of its electrical conductivity compared to the bare SION-8 . Upon adsorption, ≥95 % of I₂ molecules were incarcerated and could not be washed out, signifying the potential of SION-8 towards the permanent capture of radioactive I₂ at room temperature.