Recent Progress of Nanoscale Metal-Organic Frameworks in Synthesis and Battery Applications

As one type of promising inorganic-organic hybrid crystal material, metal-organic frameworks (MOFs) have attracted widespread attention in many potential fields, particularly in energy storage and conversion. Recently, effective strategies have been developed to construct uniform nanoscale MOFs (NMOFs), which not only retain inherent advantages of MOFs but also develop some improved superiorities, including shorter diffusion pathway for guest transportation and more accessible active sites for surface adsorption and reaction. Additonally, their nanometer size provides more opportunity for post-functionalization and hybridization. In this review, recent progress on the preparation of NMOFs is summarized, primarily through bottom-up strategies including reaction parameter- and coordination-assisted synthesis, and top-down strategies such as liquid exfoliation and salt-template confinement. Additionally, recent applications of NMOFs in batteries as electrodes, separators, and electrolytes is discussed. Finally, some important issues concerning the fabrication and application are emphasized, which should be paid attention in future.

Single-Atom and Dual-Atom Electrocatalysts Derived from Metal Organic Frameworks: Current Progress and Perspectives

Single-atom catalysts (SACs) have attracted increasing research interests owing to their unique electronic structures, quantum size effects and maximum utilization rate of atoms. Metal organic frameworks (MOFs) are good candidates to prepare SACs owing to the atomically dispersed metal nodes in MOFs and abundant N and C species to stabilize the single atoms. In addition, the distance of adjacent metal atoms can be turned by adjusting the size of ligands and adding volatile metal centers to promote the formation of isolated metal atoms. Moreover, the diverse metal centers in MOFs can promote the preparation of dual-atom catalysts (DACs) to improve the metal loading and optimize the electronic structures of the catalysts. The applications of MOFs derived SACs and DACs for electrocatalysis, including oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, carbon dioxide reduction reaction and nitrogen reduction reaction are systematically summarized in this Review. The corresponding synthesis strategies, atomic structures and electrocatalytic performances of the catalysts are discussed to provide a deep understanding of MOFs-based atomic electrocatalysts. The catalytic mechanisms of the catalysts are presented, and the crucial challenges and perspectives are proposed to promote further design and applications of atomic electrocatalysts.

Construction of Titanium-Based Metal-Organic Frameworks Based on the Ti/Cu Heteronuclear Cluster

Presented here are two titanium-based metal-organic frameworks (Ti-MOFs) based on well-defined [Ti₆Cu₆(μ₃-O)₂(μ₂-O)₉(HSO₄)₂(SO₄)₆], which can be easily obtained from a cheap Ti source and CuSO₄ and exhibited interesting magnetic properties. Furthermore, this clusters can be isolated in pure phase. Numerous uncoordinated sites of SO₄ and labile ligands on the Ti and Cu centers of this cluster make it a good candidate as a secondary building unit to construct various Ti-MOFs in the future.

Calcination activation of three-dimensional cobalt organic phosphate nanoflake assemblies for supercapacitors

Three-dimensional organic phosphate nanoflake assemblies were obtained by calcination activation. In the two-electrode system, 3D COP assemblies showed excellent cycle stability, and the capacity retention was 99.61% after 3000 long cycles.

Recent advances in process engineering and upcoming applications of metal-organic frameworks

Progress in metal-organic frameworks (MOFs) has advanced from fundamental chemistry to engineering processes and applications, resulting in new industrial opportunities. The unique features of MOFs, such as their permanent porosity, high surface area, and structural flexibility, continue to draw industrial interest outside the traditional MOF field, both to solve existing challenges and to create new businesses. In this context, diverse research has been directed toward commercializing MOFs, but such studies have been performed according to a variety of individual goals. Therefore, there have been limited opportunities to share the challenges, goals, and findings with most of the MOF field. In this review, we examine the issues and demands for MOF commercialization and investigate recent advances in MOF process engineering and applications. Specifically, we discuss the criteria for MOF commercialization from the views of stability, producibility, regulations, and production cost. This review covers progress in the mass production and formation of MOFs along with future applications that are not currently well known but have high potential for new areas of MOF commercialization.

Metal–organic framework-engaged synthesis of core–shell MoO2/ZnSe@N-C nanorods as anodes in high-performance lithium-ion batteries

A MoO₂/ZnSe@N-C nanorod was prepared through novel carbonization and selenization methods, shedding light on the design and application of metal selenides.

Particle size-controlled synthesis of high-performance MnCo-based materials for alkaline OER at fluctuating potentials

Mn and Co containing nanocubes were produced by hydrothermal synthesis. The materials consist of metal spinels and carbonates, where spinels ensure high activity and carbonates contribute to high stability in the oxygen evolution reaction.

A pillar-layered binuclear 3D cobalt(ii) coordination polymer as an electrocatalyst for overall water splitting and as a chemosensor for Cr(vi) anion detection

A 3D pillar-layered cobalt(ii) CP with a 3D (4,6)-connected {44·610·8}{44·62} fsc net was designed and it showed great potential as an electrocatalyst in the overall water splitting and as a chemosensor for Cr(vi) anion detection.

Porphyrin-based frameworks for oxygen electrocatalysis and catalytic reduction of carbon dioxide

The recent progress made on porphyrin-based frameworks and their applications in energy-related conversion technologies (e.g., ORR, OER and CO₂RR) and storage technologies (e.g., Zn–air batteries).

A bimetal hierarchical layer structure MOF grown on Ni foam as a bifunctional catalyst for the OER and HER

The as-synthesized NiFe-MOF-5 exhibited an overpotential of 168 mV at 10 mA cm⁻² for OER and a voltage of 1.57 V at 10 mA cm⁻² for overall water splitting, outperforming most non-noble metal catalysts reported in 1 M KOH.

Co2P nanoparticle/multi-doped porous carbon nanosheets for the oxygen evolution reaction

Co₂P hybridized with multi-doped carbon nanoleaves is obtained via direct carbonization of ZIF-L/PEI/PA and show good electro-catalytic performance in OER.

Surface Atom Regulation on Polyoxometalate Electrocatalyst for Simultaneous Low-Voltage H2 Production and Phenol Degradation

The electrocatalytic hydrogen evolution reaction is an ideal method for H₂ production. To improve the performance of polyoxometalate-based electrocatalyst in the hydrogen evolution reaction, one O^2- in polyoxometalate is replaced by S^2-. This weakens the binding of polyoxometalate to H*, facilitates its desorption, and improves the H₂ generation property. Vulcanized polyoxometalate only requires 55 mV to achieve 10 mA·cm^-2 current in the hydrogen evolution reaction. This electrocatalyst also exhibits promising performance in phenol degradation reaction, which is an ideal substitute for high-energy-consuming oxygen evolution reaction in H₂ production due to low voltage to drive. To acquire 100 and 200 mA·cm^-2 in the phenol degradation reaction, this vulcanized polyoxometalate only consumes 1.38 and 1.41 V. With this electrocatalyst working as a cathode and an anode simultaneously, an electrolyzer is constructed by employing phenol-containing KOH as an electrolyte. To obtain 100 and 200 mA·cm^-2 current, the electrolyzer only requires 1.54 and 1.57 V. Because energy-efficient phenol degradation reaction occurs, these values are obviously lower than the oxygen evolution reaction involved in the overall water-splitting H₂ production. This work provides a universal method to enhance the hydrogen evolution reaction (HER) activity of polyoxometalates. Furthermore, a new method is explored, which achieves energy conservation and phenol degradation simultaneously in H₂ production.

Catching and killing of airborne SARS-CoV-2 to control spread of COVID-19 by a heated air disinfection system

Airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) via air-conditioning systems poses a significant threat for the continued escalation of the current coronavirus disease (COVID-19) pandemic. Considering that SARS-CoV-2 cannot tolerate temperatures above 70 °C, here we designed and fabricated efficient filters based on heated nickel (Ni) foam to catch and kill SARS-CoV-2. Virus test results revealed that 99.8% of the aerosolized SARS-CoV-2 was caught and killed by a single pass through a novel Ni-foam-based filter when heated up to 200 °C. In addition, the same filter was also used to catch and kill 99.9% of Bacillus anthracis, an airborne spore. This study paves the way for preventing transmission of SARS-CoV-2 and other highly infectious airborne agents in closed environments.

Metal-Organic-Framework-Based Photocatalysts Optimized by Spatially Separated Cocatalysts for Overall Water Splitting

Efficient charge separation and utilization are critical factors in photocatalysis. Herein, it is demonstrated that the complete spatial separation of oxidation and reduction cocatalysts enhances the efficacy of charge separation and surface reaction. Specifically, a Pt@NH₂ -UiO-66@MnO_x (PUM) heterostructured photocatalyst with Pt and MnO_x as cocatalysts is designed for the optimization of the NH₂ -UiO-66 photocatalyst. Compared with the pristine NH₂ -UiO-66, Pt@NH₂ -UiO-66 (PU), and NH₂ -UiO-66@MnO_x (UM) samples, the PUM sample exhibits the highest hydrogen production activity. As cocatalysts, Pt favors trapping of electrons, while MnO_x tends to collect holes. Upon generation from NH₂ -UiO-66, electrons and holes flow inward and outward of the metal-organic framework photocatalyst, accumulating on the corresponding cocatalysts, and then take part in the redox reactions. The PUM photocatalyst greatly prolongs the lifetime of the photogenerated electrons and holes, which favors the electron-hole separation. Furthermore, the PUM sample facilitates overall water splitting in the absence of sacrificial agents, thereby demonstrating its potential as a modification method of MOF-type semiconductors for the overall water-splitting reaction.

Encapsulation of Co3 O4 Nanocone Arrays via Ultrathin NiO for Superior Performance Asymmetric Supercapacitors

Designing of multicomponent transition metal oxide system through the employment of advanced atomic layer deposition (ALD) technique over nanostructures obtained from wet chemical process is a novel approach to construct rational supercapacitor electrodes. Following the strategy, core-shell type NiO/Co₃ O₄ nanocone array structures are architectured over Ni-foam (NF) substrate. The high-aspect-ratio Co₃ O₄ nanocones are hydrothermally grown over NF following the precision controlled deposition of shell NiO considering Co₃ O₄ nanocone as host. NiO thickness of 5 nm exhibits the highest specific capacity of 1242 C g^-1 (2760 F g^-1 ) at current density 2 A g^-1 , which is greater than pristine Co₃ O₄ @NF (1045.8 C g^-1 or 2324 F g^-1 ). The rate capability with 5 nm NiO/Co₃ O₄ @NF nanocone structures is about 77% whereas Co₃ O₄ @NF retains 46 % of capability at 10 A g^-1 . The ultrathin ALD 5 nm NiO accelerates both rate capability and 95.5% cyclic stability after 12 000 charge-discharge cycles. An asymmetric device fabricated between 5 nm NiO/Co₃ O₄ @NF (positive) || activated carbon (negative) achieves an energy density of 81.45 Wh kg^-1 (4268 W kg^-1 ) with good cycling device stability. Additionally, LEDs can be energized by two ASC device in series. This work opens the path in both advanced electrode material and surface modification of earth-abundant systems for efficient and real-time supercapacitor applications.

A carbon-coated shuttle-like Fe2O3/Fe1-x S heterostructure derived from metal-organic frameworks with high pseudocapacitance for ultrafast lithium storage

Pursuing active, low-cost, and stable electrode materials with superior rate capability and long-life cycling performances for lithium-ion batteries remains a big challenge. In this study, a carbon-coated shuttle-like Fe2O3/Fe1-x S heterostructure is synthesized by simply annealing Fe-based metal-organic frameworks (MIL-88(Fe)) as precursors and sublimed sulfur. Carbon-coated Fe2O3/Fe1-x S displays a unique structure with ultrafine Fe2O3/Fe1-x S nanoparticles distributed in the hollow and porous carbon matrix, which offers a large specific surface area and fast charge transfer ability, and alleviates the volume change upon cycling. When evaluated as an anode material for lithium-ion batteries, it exhibits an ultra-high specific capacity of 1200 mA h g-1 at 0.1 A g-1, and superior high rate capability with a capacity of 345 mA h g-1 at a very high current density of 5.0 A g-1 owing to its high electrical conductivity and enhanced pseudocapacitive contribution from surface effects. The current strategy is promising to synthesize the carbon-coated porous structure from metal-organic frameworks for next-generation energy-storage applications.

Synthesis and Optimization of Zeolitic Imidazolate Frameworks for the Oxygen Evolution Reaction

Metal-organic frameworks/zeolitic imidazolate frameworks (MOFs/ZIFs) and their post-synthesis modified nanostructures, such as oxides, hydroxides, and carbons have generated significant interest for electrocatalytic reactions. In this work, a high and durable oxygen evolution reaction (OER) performance directly from bimetallic Zn_100-x Co_x -ZIF samples is reported, without carrying out high-temperature calcination and/or carbonization. ZIFs can be reproducibly and readily synthesized in large scale at ambient conditions. The bimetallic ZIFs show a systematic and gradually improved OER activity with increasing cobalt concentration. A further increase in OER activity is evidenced in ZIF-67 polyhedrons with controlled particle size of <200 nm among samples of different sizes between 50 nm and 2 μm. Building on this, a significantly enhanced, >50 %, OER activity is obtained with ZIF-67/carbon black, which shows a low overpotential of approximately 320 mV in 1.0 m KOH electrolyte. Such activity is comparable to or better than numerous MOF/ZIF-derived electrocatalysts. The optimized ZIF-67 sample also exhibits increased activity and durability over 24 h, which is attributed to an in situ developed active cobalt oxide/oxyhydroxide related nanophase.

Ultrafine NiFe clusters anchored on N-doped carbon as bifunctional electrocatalysts for efficient water and urea oxidation

Hydrogen production through electrocatalysis is crucial in renewable energy technologies but significantly impeded by sluggish anodic reactions. Developing bifunctional anode noble-metal-free electrocatalysts towards oxygen evolution reaction (OER) and urea oxidation reaction (UOR) to boost cathodic hydrogen evolution reaction (HER) is promising but challenging to meet different reaction media and multiple applications for simultaneous clean energy production and pollution treatment. Herein, a facile one-pot thermal treatment strategy is presented to anchor NiFe nanoclusters (with a size of about 2 nm) on N-doped carbon as bifunctional electrocatalysts for both OER and UOR. Such an electrocatalyst can deliver a current density of 20 mA cm-2 with a low overpotential of 260 mV and a small Tafel slope of 42 mV dec-1 for OER, superior to the state-of-the-art Ru-based materials. Besides, this electrocatalyst also shows excellent activity for UOR with the need for just 1.37 V (vs. RHE) to attain a current density of 100 mA cm-2. In a two-electrode electrolyzer for both cathodic HER and anodic UOR, only a cell voltage of 1.50 V is required to drive a current density of 10 mA cm-2, which is 140 mV lower than that of overall water splitting electrolysis (1.64 V). The excellent electrooxidative performance can be attributed to the improved conductivity, abundant active sites and fast charge transfer and transport benefiting from the ultrafine structure of NiFe clusters and their synergistic effect with N-doped carbon.

High-Performance Zinc-Air Batteries with Scalable Metal-Organic Frameworks and Platinum Carbon Black Bifunctional Catalysts

Metal-organic framework (MOF)-related derivatives have generated significant interest in numerous energy conversion and storage applications, such as adsorption, catalysis, and batteries. However, such materials' real-world applicability is hindered because of scalability and reproducibility issues as they are produced by multistep postsynthesis modification of MOFs, often with high-temperature carbonization and/or calcination. In this process, MOFs act as self-sacrificial templates to develop functional materials at the expense of severe mass loss, and the resultant materials exhibit complex process-performance relationships. In this work, we report the direct applicability of a readily synthesized and commercially available MOF, a zeolitic imidazolate framework (ZIF-8), in a rechargeable zinc-air battery. The composite of cobalt-based ZIF-8 and platinum carbon black (ZIF-67@Pt/CB) prepared via facile solution mixing shows a promising bifunctional electrocatalytic activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), the key charge and discharge mechanisms in a battery. ZIF-67@Pt/CB exhibits long OER/ORR activity durability, notably, a significantly enhanced ORR stability compared to Pt/CB, 85 versus 52%. Interestingly, a ZIF-67@Pt/CB-based battery delivers high performance with a power density of >150 mW cm^-2 and long stability for 100 h of charge-discharge cyclic test runs. Such remarkable activities from as-produced ZIF-67 are attributed to the electrochemically driven in situ development of an active cobalt-(oxy)hydroxide nanophase and interfacial interaction with platinum nanoparticles. This work shows commercial feasibility of zinc-air batteries as MOF-cathode materials can be reproducibly synthesized in mass scale and applied as produced.

Luminescent triphenylamine-based metal-organic frameworks: recent advances in nitroaromatics detection

Luminescent metal-organic frameworks (LMOFs), as one branch of MOFs, have attracted considerable attention in recent years due to their good crystallinity, structural diversity, tunable porosity and easily induced fluorescence emission. Importantly, their photoluminescence (PL) properties can be adjusted by altering metal ions or metal clusters and organic ligands in one hybrid system. Among the various sensing applications, using LMOFs as chemical sensors to detect the explosive and environment pollution causing nitroaromatic compounds (NACs) is an important topic. In this account, we describe the recent advancements in the field of NAC detection by LMOFs based on the triphenylamine (TPA) unit as the π-conjugated fluorophore.

Synthesis of a Magnetic 2D Co@NC-600 Material by Designing a MOF Precursor for Efficient Catalytic Reduction of Water Pollutants

2D metal-organic framework (MOFs) can be ideal sacrificial templates for fabricating nanomaterials because of active sites exposed on the surface rather than in pores and channels, often exhibiting improved performance in catalysis applications. In this study, the novel 2D layered cobalt-based MOF [Co(TPT)(fma)(H₂O)₂]·3H₂O (Co-MOF) has been constructed by the selection of high N atom content ligands. On this basis, a 2D nitrogen-doped carbon-coated cobalt nanoparticle composite (Co@NC) was prepared by using this MOF as a precursor. Magnetic Co@NC has excellent catalytic activity and recycling features regarding the reaction of 4-nitrophenol (4-NP) reducing to 4-aminophenol (4-AP) in the presence of NaBH₄ at ambient temperature. 2D Co@NC-600 can reach nearly 100% conversion within 120 s and its stability remains almost unchanged after five reaction cycles. Moreover, this Co@NC catalyst also is highly active for catalytic reduction of dyes such as Rhodamine B (RhB) and Methylene blue (MB).

A hierarchical porous P-doped carbon electrode through hydrothermal carbonization of pomelo valves for high-performance supercapacitors

Porous carbon materials are synthesized from pomelo valves by the hydrothermal activation of H3PO4 followed by simple carbonization. The as-synthesized hierarchically porous carbon electrode exhibits a high specific capacitance of 966.4 F g-1 at 1 A g-1 and an ultra-high stability of 95.6% even after 10 000 cycles. Moreover, the supercapacitor also demonstrates a maximum energy of 36.39 W h kg-1 and a maximum power of 33.33 kW kg-1 with an energy retention of 25.56 W h kg-1, which paves the way for the development of high-performance, green supercapacitors for advanced energy storage systems.

Applications of Dynamic Covalent Chemistry Concept towards Tailored Covalent Organic Framework Nanomaterials: A Review

Covalent organic frameworks (COFs) are a rapidly developing class of materials that has been of immense research interest during the last ten years. Numerous reviews have been devoted to summarizing the synthesis and applications of COFs. However, the underlying dynamic covalent chemistry (DCC), which is the foundation of COFs synthesis, has never been systematically reviewed in this context. Dynamic covalent chemistry is the practice of using thermodynamic equilibriums to molecular assemblies. This Critical Review will cover the state-of-the-art use of DCC to both synthesize COFs and expand the applications of COFs. Five synthetic strategies for COF synthesis are rationalized, namely: modulation, mixed linker/linkage, sub-stoichiometric reaction, framework isomerism, and linker exchange, which highlight the dynamic covalent chemistry to regulate the growth and to modify the properties of COFs. Furthermore, the challenges in these approaches and potential future perspectives in the field of COF chemistry are also provided.

2D Coordination Network of Trioxotriangulene with Multiple Redox Abilities and Its Rechargeable Battery Performance

A three-fold symmetric trioxotriangulene derivative with three pyridyl groups as coordinating sites was designed and synthesized. In a cyclic voltammetry measurement, the trioxotriangulene skeleton exhibited a multi-stage redox ability from neutral radical to radical tetra-anion species. In the zinc complex of monoanion species, three pyridyl groups coordinated to the zinc ion to build up a two-dimensional coordination network with a cavity larger than 12 Å in diameter. This complex was utilized as a cathode active material of a lithium ion battery, and it exhibited a capacity of ca. 60 mAh g^-1 per the weight of the active material with a stable cycling performance up to 1000 cycles. This work shows that the coordination network formed by the trioxotriangulene-based ligand was effective in the improvement of cycle performance of the organic rechargeable battery.

Integration of Cd:ZnS QDs into ZIF-8 for enhanced selectivity toward Cu2+ detection

Cd:ZnS QDs were integrated into ZIF-8 that could specifically interact with Cu²⁺ for enhanced selectivity toward Cu²⁺ detection.

Functional metal–organic frameworks as effective sensors of gases and volatile compounds

This review summarizes the recent advances of metal organic framework (MOF) based sensing of gases and volatile compounds.

Coordination polymers as heterogeneous catalysts in hydrogen evolution and oxygen evolution reactions

This article highlights various strategies of designing coordination polymers for catalysing water splitting reactions.

Evolution of metal organic frameworks as electrocatalysts for water oxidation

The development of metal organic framework based water oxidation catalysts is discussed here in connection with various design strategies.

Advances in nanomaterials for electrochromic devices

This review article systematically highlights the recent advances regarding the design, preparation, performance and application of new and unique nanomaterials for electrochromic devices.