Metal Organic Framework Derived Materials: Progress and Prospects for the Energy Conversion and Storage

Metal-Organic Framework-Based Hierarchically Porous Materials: Synthesis and Applications

Metal-organic frameworks (MOFs) have been widely recognized as one of the most fascinating classes of materials from science and engineering perspectives, benefiting from their high porosity and well-defined and tailored structures and components at the atomic level. Although their intrinsic micropores endow size-selective capability and high surface area, etc., the narrow pores limit their applications toward diffusion-control and large-size species involved processes. In recent years, the construction of hierarchically porous MOFs (HP-MOFs), MOF-based hierarchically porous composites, and MOF-based hierarchically porous derivatives has captured widespread interest to extend the applications of conventional MOF-based materials. In this Review, the recent advances in the design, synthesis, and functional applications of MOF-based hierarchically porous materials are summarized. Their structural characters toward various applications, including catalysis, gas storage and separation, air filtration, sewage treatment, sensing and energy storage, have been demonstrated with typical reports. The comparison of HP-MOFs with traditional porous materials (e.g., zeolite, porous silica, carbons, metal oxides, and polymers), subsisting challenges, as well as future directions in this research field, are also indicated.

Ruthenium-Benzothiadiazole Building Block Derived Dynamic Heterometallic Ru-Ag Coordination Polymer and Its Enhanced Water-Splitting Feature

This article deals with the development of the unprecedented redox-mediated heterometallic coordination polymer {[Ru^III(acac)₂(μ-bis-η¹-N,η¹-N-BTD)₂Ag^I(ClO₄)]ClO₄}_n (3) via the oxidation of the monomeric building block cis-[Ru^II(acac)₂(η¹-N-BTD)₂] (1) by AgClO₄ (BTD = exodentate 2,1,3-benzothiadiazole, acac = acetylacetonate). Monomeric cis-[Ru^II(acac)₂(η¹-N-BTD)₂] (1) and [Ru^II(acac)₂(η¹-N-BTD)(CH₃CN)] (2) were simultaneously obtained from the electron-deficient BTD heterocycle and the electron-rich metal precursor Ru^II(acac)₂(CH₃CN)₂ in refluxing CH₃CN. Molecular identities of 1-3 were authenticated by their single-crystal X-ray structures as well as by solution spectral features. These results also reflected the elusive trigonal-planar geometry of the Ag ion in Ru-Ag-derived polymeric 3. Ru(III) (S = 1/2)-derived 3 displayed metal-based anisotropic EPR with ⟨g⟩/Δg = 2.12/0.56 and paramagnetically shifted ¹H NMR. Spectroelectrochemistry in combination with DFT/TD-DFT calculations of 1ⁿ and 2ⁿ (n = 1+, 0, 1-) determined a metal-based (Ru^II/Ru^III) oxidation and BTD-based reduction (BTD/BTD^•-). The drastic decrease in the emission intensity and quantum yield but insignificant change in the lifetime of 3 with respect to 1 could be addressed in terms of static quenching and/or a paramagnetism-induced phenomenon. A homogeneously dispersed dumbbell-shaped morphology and the particle diameter of 3 were established by microscopic (TEM-EDX/SEM) and DLS analysis, respectively. Moreover, the dynamic nature of polymeric 3 was highlighted by its degradation to the η¹-N-BTD coordinated monomeric fragment 1, which could also be followed spectrophotometrically in polar protic EtOH. Interestingly, both monomeric 1 and polymeric 3 exhibited efficient electrocatalytic activity toward water oxidation processes (OER, HER) on immobilization on an FTO support, which also divulged the better intrinsic water oxidation activity of 3 in comparison to 1.

Metal-Organic-Framework-Derived Nanostructures as Multifaceted Electrodes in Metal-Sulfur Batteries

Metal-sulfur batteries (MSBs) are considered up-and-coming future-generation energy storage systems because of their prominent theoretical energy density. However, the practical applications of MSBs are still hampered by several critical challenges, i.e., the shuttle effects, sluggish redox kinetics, and low conductivity of sulfur species. Recently, benefiting from the high surface area, regulated networks, molecular/atomic-level reactive sites, the metal-organic frameworks (MOFs)-derived nanostructures have emerged as efficient and durable multifaceted electrodes in MSBs. Herein, a timely review is presented on recent advancements in designing MOF-derived electrodes, including fabricating strategies, composition management, topography control, and electrochemical performance assessment. Particularly, the inherent charge transfer, intrinsic polysulfide immobilization, and catalytic conversion on designing and engineering of MOF nanostructures for efficient MSBs are systematically discussed. In the end, the essence of how MOFs' nanostructures influence their electrochemical properties in MSBs and conclude the future tendencies regarding the construction of MOF-derived electrodes in MSBs is exposed. It is believed that this progress review will provide significant experimental/theoretical guidance in designing and understanding the MOF-derived nanostructures as multifaceted electrodes, thus offering promising orientations for the future development of fast-kinetic and robust MSBs in broad energy fields.

Self-assembly of carbon nanotubes on a hollow carbon polyhedron to enhance the potassium storage cycling stability of metal organic framework-derived metallic selenide anodes

Potassium-ion batteries (PIBs) is increasingly studied because of their suitable redox potential and high natural abundance. However, potential anode materials with long-term cycling stability are still in high demand because of the large radius of K⁺. Herein, an MOF-derived hierarchical carbon structure and the self-assembly of CNTs on hollow carbon polyhedrons are used as carbon matrices to disperse and stabilize metal selenides(Co-Se@CNNCP). When the hybrid is utilized in PIBs, it displays a specific capacity of 410 mA h g^-1 at 0.1 A g^-1 after 80 cycles and 253 mA h g^-1 at 0.5 A g^-1 after 200 cycles with a capacity retention of 100%, while the metal selenides dispersed on hollow carbon polyhedrons without CNTs (Zn-Co-Se@NCP) lose 86% of their capacity after 200 cycles. The superior cycling stability of the hybrid is mainly attributed to the large amounts of CNTs suppressing the agglomeration of the metal selenide nanoparticles on the surface, and the hollow carbon polyhedrons cause a high structural integrity during the repreated K⁺ insertion and extraction process. This work offers a feasible route to design a hierarchical carbon matrix for use as the anode materials of PIBs with long-term cycling stability.

Metal-Organic Frameworks and Their Derivatives: Designing Principles and Advances toward Advanced Cathode Materials for Alkali Metal Ion Batteries

Metal-organic frameworks (MOFs) and their derivatives have attracted enormous attention in the field of energy storage, due to their high specific surface area, tunable structure, highly ordered pores, and uniform metal sites. Compared with the wide research of MOFs and their related materials on anode materials for alkali metal ion batteries, few works are on cathode materials. In this review, design principles for promoting the electrochemical performance of MOF-related materials in terms of component/structure design, composite fabrication, and morphology engineering are presented. By summarizing the advancement of MOFs and their derivatives, Prussian blue and its analogs, and MOF surface coating, challenges and opportunities for future outlooks of MOF-related cathode materials are discussed.

Hollow Spherical Superstructure of Carbon Nanosheets for Bifunctional Oxygen Reduction and Evolution Electrocatalysis

The pyrolysis of metal-organic frameworks (MOFs) is an ingenious way to synthesize carbon-based materials with unique morphology for various applications including electrocatalysis. In this work, we reported a facile morphology regulation strategy for the synthesis of a spherical superstructure of MOF nanosheets. The use of metal hydroxide nanosheets on Zn particles as precursors/templates allowed MOFs with general polyhedron shape to form nanosheets and assemble into a spherical superstructure in the ligand solution. Further, a hollow spherical superstructure of carbon nanosheets decorated with metal-based nanoparticles was fabricated through the pyrolysis of MOF nanosheet superstructures at 950 °C, where the substrate/template Zn particle cores were evaporated away. The obtained composites possess carbon-based superstructures with abundant mesopores and metal-based nanoparticles with rich alloy/oxide interfaces. These features endow this MOF-derived carbon-based material with outstanding bifunctional activity for oxygen reduction/evolution reactions and great performances in Zn-air batteries.

Gentle fabrication of colorful superhydrophobic bamboo based on metal-organic framework

The efficient use of abundant renewable bamboo as high value-added decoration and building materials is of great significance for mitigating carbon dioxide emissions and maintaining sustainable development. The key challenge is to explore efficient and gentle methods to improve the undesirable surface properties of bamboo. Herein, a colorful and superhydrophobic bamboo is gently fabricated by a facile in-situ growth and conversion method based on metal-organic framework (for constructing micro-nano composite structures) and subsequent coating of sodium laurate (for reducing surface energy) at room temperature. The resulting sodium laurate-coated cobalt-nickel double hydroxide layer (CoNi-DH-La) is demonstrated as an efficient superhydrophobic layer to exhibit excellent chemical and mechanical stability. Impressively, the as-obtained CoNi-DH-La-coated bamboo sheet (BS-CoNi-DH-La) shows positive performances in terms of mildew resistance, flame retardancy, and self-cleaning. More importantly, this gentle method can endow bamboo with multiple unfading colors by changing the type of inorganic salts during the preparation process and display good potential for large-scale production.

Branched In2O3 Mesocrystal of Ordered Architecture Derived from the Oriented Alignment of a Metal-Organic Framework for Accelerated Hydrogen Evolution over In2O3-ZnIn2S4

It is fascinating yet challenging to assemble anisotropic nanowires into ordered architectures of high complexity and intriguing functions. We exploited a facile strategy involving oriented etching of a metal-organic fragment (MOF) to advance the rational design of highly ordered nanostructures. As a proof of concept, a microscale MIL-68(In) single crystal was etched with a K₃[Co(CN)₆] solution to give a microtube composed of aligned MIL-68(In) nanorods. Annealing such a MIL-68(In) microtube readily created an unprecedented branched In₂O₃ mesocrystal by assembly of In₂O₃ nanorods aligned in order. The derived ordered-In₂O₃-ZnIn₂S₄ is more efficient in catalyzing visible-light-driven H₂ evolution (8753 μmol h^-1 g^-1) outperforming the disordered-In₂O₃-ZnIn₂S₄ counterpart (2700 μmol h^-1 g^-1) as well as many other state-of-the-art ZnIn₂S₄-based photocatalysts. The ordered architecture significantly boosts the short-range electron transfer in an In₂O₃-ZnIn₂S₄ heterojunction but has a negligible impact on the long-range electron transfer among In₂O₃ mesocrystals. The density functional theory (DFT) calculation reveals that the oriented etching is achieved by the selective binding of the [Co(CN)₆]^3- etchant on the (110) plane of MIL-68(In), which can drag the In atoms out of the framework in order. Our findings could broaden the technical sense toward advanced photocatalyst design and impose scientific impacts on unveiling how ordered photosystems operate.

Metal-Organic Frameworks Derived Functional Materials for Electrochemical Energy Storage and Conversion: A Mini Review

With many apparent advantages including high surface area, tunable pore sizes and topologies, and diverse periodic organic-inorganic ingredients, metal-organic frameworks (MOFs) have been identified as versatile precursors or sacrificial templates for preparing functional materials as advanced electrodes or high-efficiency catalysts for electrochemical energy storage and conversion (EESC). In this Mini Review, we first briefly summarize the material design strategies to show the rich possibilities of the chemical compositions and physical structures of MOFs derivatives. We next highlight the latest advances focusing on the composition/structure/performance relationship and discuss their practical applications in various EESC systems, such as supercapacitors, rechargeable batteries, fuel cells, water electrolyzers, and carbon dioxide/nitrogen reduction reactions. Finally, we provide some of our own insights into the major challenges and prospective solutions of MOF-derived functional materials for EESC, hoping to shed some light on the future development of this highly exciting field.

Hierarchically activated porous carbon derived from zinc-based fluorine containing metal-organic framework as extremely high specific capacitance and rate performance electrode material for advanced supercapacitors

In this work, a hierarchically activated porous carbon (APC) was synthesized using fluorine-containing metal-organic framework via facile combined carbonization and KOH activation treatments. The influences of activation conditions on the surface structures and electrochemical performance of APC were systematically studied. Afterwards, the electrochemical responses of APC electrode were further assessed from the cyclic voltammetry and galvanostatic charge-discharge examinations by 6 M KOH electrolyte. The as-obtained APC electrode delivered the high specific capacitances of 540.8 and 280 F g^-1 at 1 and 500 A g^-1, correspondingly with superior capacitance retention of 94% after 250,000 cycles even at 100 A g^-1, which is showing that its outstanding capacitance, remarkable rate capacity, and very-long cyclic life. Furthermore, the as-assembled APC-based symmetrical supercapacitor offers a superb energy density of 19 Wh kg^-1 at 182 W kg^-1, indicating its large-scale application. Thus, this work proposes a potential route to synthesize highly efficient porous carbon material for the future development of energy storage systems.

Advanced Electrocatalysis for Energy and Environmental Sustainability via Water and Nitrogen Reactions

Clean and efficient energy storage and conversion via sustainable water and nitrogen reactions have attracted substantial attention to address the energy and environmental issues due to the overwhelming use of fossil fuels. These electrochemical reactions are crucial for desirable clean energy technologies, including advanced water electrolyzers, hydrogen fuel cells, and ammonia electrosynthesis and utilization. Their sluggish reaction kinetics lead to inefficient energy conversion. Innovative electrocatalysis, i.e., catalysis at the interface between the electrode and electrolyte to facilitate charge transfer and mass transport, plays a vital role in boosting energy conversion efficiency and providing sufficient performance and durability for these energy technologies. Herein, a comprehensive review on recent progress, achievements, and remaining challenges for these electrocatalysis processes related to water (i.e., oxygen evolution reaction, OER, and oxygen reduction reaction, ORR) and nitrogen (i.e., nitrogen reduction reaction, NRR, for ammonia synthesis and ammonia oxidation reaction, AOR, for energy utilization) is provided. Catalysts, electrolytes, and interfaces between the two within electrodes for these electrocatalysis processes are discussed. The primary emphasis is device performance of OER-related proton exchange membrane (PEM) electrolyzers, ORR-related PEM fuel cells, NRR-driven ammonia electrosynthesis from water and nitrogen, and AOR-related direct ammonia fuel cells.

Strain Engineering of a MXene/CNT Hierarchical Porous Hollow Microsphere Electrocatalyst for a High-Efficiency Lithium Polysulfide Conversion Process

Tensile-strained Mxene/carbon nanotube (CNT) porous microspheres were developed as an electrocatalyst for the lithium polysulfide (LiPS) redox reaction. The internal stress on the surface results in lattice distortion with expanding Ti-Ti bonds, endowing the Mxene nanosheet with abundant active sites and regulating the d-band center of Ti atoms upshifted closer to the Fermi level, leading to strengthened LiPS adsorbability and accelerated catalytic conversion. The macroporous framework offers uniformed sulfur distribution, potent sulfur immobilization, and large surface area. The composite interwoven by CNT tentacle enhances conductivity and prevents the restacking of Mxene sheets. This combination of tensile strain effect and hierarchical architecture design results in smooth and favorable trapping-diffusion-conversion of LiPS on the interface. The Li-S battery exhibits an initial capacity of 1451 mAh g^-1 at 0.2 C, rate capability up to 8 C, and prolonged cycle life.

Synthesis, structure, and fluorescence properties of coordination polymers of 3,5-bis(1′,2′,4′-triazol-1′-yl) pyridine

Four coordination polymers based on 3,5-bis(1′,2′,4′-triazol-1′-yl) pyridine were synthesized. Compounds [Cd₃(btc)₂(btap)(H₂O)₆] and [Cd(oa)(btap)] exhibited high sensitivity luminescence response towards Fe³⁺, Ce³⁺, Cr₂O₇²⁻ and MnO₄⁻ in aqueous solution.

Linker Defects Triggering Boosted Oxygen Reduction Activity of Co/Zn-ZIF Nanosheet Arrays for Rechargeable Zn-Air batteries

The poor electronic conductivity and low intrinsically electrocatalytic activity of most metal-organic frameworks (MOFs) greatly limit their direct applications as oxygen reduction reaction (ORR) electrocatalysts. In this work, it is reported that introduction of linker defects can effectively trigger the ORR activity of leaf-shaped zeolitic imidazolate framework (ZIF) by increasing the intrinsic activity of metal sites and electrical conductivity. Experimental results show that part of imidazole molecules is successfully removed from ZIF after a low-temperature thermal treatment without destroying its structure integrity, resulting in the formation of unsaturated metal sites and faster electron transport rate. Consequently, the ZIF with imidazole molecules defects (D-ZIF) exhibits a superior ORR activity than the pristine ZIF, possessing an onset potential of 0.86 V and higher half-wave potential of 0.60 V. Furthermore, the home-made Zn-air batteries with D-ZIF as air cathode exhibit high open-circuit voltage and well cycling stability. The developed linker-deficient modulation strategy can provide a new prospect to enable MOF-based electrocatalysts with efficient catalytic activity.

Metal–organic frameworks and their derivatives as electrocatalysts for the oxygen evolution reaction

This review summarizes the recent progress on MOFs and their derivatives used for OER electrocatalysis in terms of their morphology, composition and structure–performance relationship.

Electrochemical Aptasensors Based on Hybrid Metal-Organic Frameworks

Metal-organic frameworks (MOFs) offer a unique variety of properties and morphology of the structure that make it possible to extend the performance of existing and design new electrochemical biosensors. High porosity, variable size and morphology, compatibility with common components of electrochemical sensors, and easy combination with bioreceptors make MOFs very attractive for application in the assembly of electrochemical aptasensors. In this review, the progress in the synthesis and application of the MOFs in electrochemical aptasensors are considered with an emphasis on the role of the MOF materials in aptamer immobilization and signal generation. The literature information of the use of MOFs in electrochemical aptasensors is classified in accordance with the nature and role of MOFs and a signal mode. In conclusion, future trends in the application of MOFs in electrochemical aptasensors are briefly discussed.

MOF-Derived 2D/3D Hierarchical N-Doped Graphene as Support for Advanced Pt Utilization in Ethanol Fuel Cell

Development of bifunctional catalysts with low platinum (Pt) content for the ethanol oxidation reaction (EOR) and the oxygen reduction reaction (ORR) is highly desirable, yet challenging. Herein, we present structural engineering of a series of two-dimensional/three-dimensional (2D/3D) hierarchical N-doped graphene-supported nanosized Pt₃Co alloys and Co clusters (PtCo@N-GNSs) via a hydrolysis-pyrolysis route. For the ORR, the optimal PtCo@N-GNS exhibits a high mass activity of 3.01 A mg_Pt^-1, which is comparable to the best Pt-based catalyst obtained through sophisticated synthesis. It also possesses excellent stability with minor decay after 50 000 cyclic voltammograms (CV) cycles in acidic medium. For the EOR, PtCo@N-GNS achieves the highest mass-specific and area-specific activities of 1.96 A mg_Pt^-1 and 5.75 mA cm^-2, respectively, among all of the reported EOR catalysts to date. The unique 2D/3D hierarchy, high Pt utilization, and valid encapsulation of nanosized Pt₃Co/Co synergistically contribute to the robust ORR and EOR activities of the present PtCo@N-GNS. A direct ethanol fuel cell based on PtCo@N-GNS delivers a high open-circuit potential of 0.9 V, a stable power density of 10.5 mW cm^-2, and an excellent rate performance, implying the feasibility of the bifunctional PtCo@N-GNS. This work offers a new strategy for designing an ultralow Pt loading yet highly active and durable catalyst for ethanol fuel cell application.

Metal-organic framework based bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries: current progress and prospects

Zinc-air batteries (ZABs) are regarded as ideal candidates for next-generation energy storage equipment due to their high energy density, non-toxicity, high safety, and environmental friendliness. However, the slow oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics on the air cathode limit their efficiency and the development of highly efficient, low cost and stable bifunctional electrocatalysts is still challenging. Metal-Organic Framework (MOF) based bifunctional oxygen electrocatalysts have been demonstrated as promising alternative catalysts due to the regular structure, tunable chemistry, high specific surface area, and simple and easy preparation of MOFs, and great progress has been made in this area. Herein, we summarize the latest research progress of MOF-based bifunctional oxygen electrocatalysts for ZABs, including pristine MOFs, derivatives of MOFs and MOF composites. The effects of the catalysts' composites, morphologies, specific surface areas and active sites on catalytic performances are specifically addressed to reveal the underlying mechanisms for different catalytic activity of MOF based catalysts. Finally, the main challenges and prospects for developing advanced MOF-based bifunctional electrocatalysts are proposed.

2D MOFs with Ni(II), Cu(II), and Co(II) as Efficient Oxygen Evolution Electrocatalysts: Rationalization of Catalytic Performance vs Structure of the MOFs and Potential of the Redox Couples

Earth-abundant transition-metal-based metal-organic frameworks (MOFs) are of immense interest for the development of efficient and durable heterogeneous water splitting electrocatalysts. This repot explores the design of two-dimensional (2D) MOFs with redox-active metal centers (Ni(II), Co(II), and Cu(II)) containing two types of electron-rich linkers such as bis(5-azabenzimidazole), linear L₁ and angular L₂, and aromatic dicarboxylates. The electron-rich linkers are considered to stabilize the higher oxidation state of the redox-active metal centers in the course of the electrocatalytic oxygen evolution reaction (OER) process. The 2D MOFs of L₁ and L₂ with Co(II) (1 and 3) and Ni(II) (2 and 4) have been produced via the conventional hydrothermal synthesis, while the MOFs of Cu(II) (Cu@1 and Cu@3) are obtained by the postsynthetic transmetallation reaction of MOFs 1 and 3. The electrocatalytic OER activities of the six MOFs have been studied to explore the influence of the redox potential of the transition-metal quasi-reversible couples and the coordination environment around the redox-active metal centers in the electrocatalytic activity. The lowest overpotential of 370 mV exhibited by MOF 2 with the highest current density and TOF value indicates the importance of the presence of coordinated water molecules and the lowest redox potential value of the most favorable quasi-reversible couple Ni⁺²/Ni⁺³. These catalysts exhibit a remarkable stability up to 1000 OER cycles. These studies pave the way for the design of MOF materials toward the development of a promising heterogeneous OER electrocatalyst.

Cobalt(II) Tetraaminophthalocyanine-modified Multiwall Carbon Nanotubes as an Efficient Sulfur Redox Catalyst for Lithium-Sulfur Batteries

An efficient Li-S redox catalyst consisting of MWCNTs covalently modified by cobalt(II) tetraaminophthalocyanines (TaPcCo-MWCNTs) is developed. Effective lithium polysulfide (LiPS) capturing is enabled by the lithiophilic N-containing phthalocyanine rings and the sulfiphilic Co central atoms. This adsorption geometry utilizes the Co unoccupied d-orbitals as electron super-exchange highways. Elevated kinetics of LiPSs reactions in the liquid phase as well as liquid-solid transitions were revealed by electrochemical measurements and density functional theory calculations. Uniform deposition of Li₂ S films was also observed, which preserves cathode integrity and sulfur utilization during cell cycling. The catalyzed sulfur redox is also significantly facilitated by the fast electron and Li-ion transport to and from the reaction sites through the conductive MWCNT skeletons and the lithiophilic substituent amino groups on TaPcCo. With 6 wt % addition of TaPcCo-MWCNT in the cathode coatings, high sulfur utilization is achieved with areal sulfur loadings of up to 7 mg cm^-2 . Stable long-term cycling is achieved at 1 C at a sulfur loading of 5 mg cm^-2 , with an initial areal capacity of 4.4 mAh cm^-2 retention of 3.5 mAh cm^-2 after 500 cycles. Considering the high structural diversity of phthalocyanines macromolecules, this study provides opportunities for a new class of Li-S catalysts.

Facile synthesis of novel tungsten-based hierarchical core-shell composite for ultrahigh volumetric lithium storage

The development of novel high volumetric capacity electrode materials is crucial to the application of lithium-ion batteries (LIBs) in miniaturized consumer electronics. In this work, a novel tungsten-based octahedron (CoWO₄/Co₃O₄) with unique hierarchical core-shell structure is successfully fabricated by simply calcinating a cyanide-metal framework precursor. Benefitting from the heavy element W, the CoWO₄/Co₃O₄ octahedrons show a high mass density of 5.18 g cm^-3. When applied as anode materials for LIBs, the CoWO₄/Co₃O₄ octahedrons exhibit an ultrahigh volumetric capacity (6226 mAh cm^-3 after 350 cycles at 0.4 A g^-1), superior rate capability (3165 mAh cm^-3 at 3.0 A g^-1) and outstanding long-term cycling performance (4703 mAh cm^-3 at 1.0 A g^-1 after 800 cycles). The extraordinary lithium storage performance can be ascribed to the unique hierarchical core-shell structure and the possible synergistic effect between W and Co, which provide more Li⁺ insertion sites and effectively buffer the volume variation during cycling. This work not only provides an ultrahigh volumetric lithium storage anode, but also gives a simple and general strategy for the synthesis of novel anode materials for high volumetric energy density LIBs.

Bimetallic metal-organic frameworks and their derivatives

Bimetallic metal-organic frameworks (MOFs) have two different metal ions in the inorganic nodes. According to the metal distribution, the architecture of bimetallic MOFs can be classified into two main categories namely solid solution and core-shell structures. Various strategies have been developed to prepare bimetallic MOFs with controlled compositions and structures. Bimetallic MOFs show a synergistic effect and enhanced properties compared to their monometallic counterparts and have found many applications in the fields of gas adsorption, catalysis, energy storage and conversion, and luminescence sensing. Moreover, bimetallic MOFs can serve as excellent precursors/templates for the synthesis of functional nanomaterials with controlled sizes, compositions, and structures. Bimetallic MOF derivatives show exposed active sites, good stability and conductivity, enabling them to extend their applications to the catalysis of more challenging reactions and electrochemical energy storage and conversion. This review provides an overview of the significant advances in the development of bimetallic MOFs and their derivatives with special emphases on their preparation and applications.

Zeolitic imidazolate framework derived ZnCo2O4 hollow tubular nanofibers for long-life supercapacitors

Uniform one-dimensional metal oxide hollow tubular nanofibers (HTNs) have been controllably prepared using a calcination strategy using electrospun polymer nanofibers as soft templates and zeolitic imidazolate framework nanoparticles as precursors. Utilizing the general synthesis method, the ZnO HTNs, Co3O4 HTNs and ZnCo2O4 HTNs have been successfully prepared. The optimal ZnCo2O4 HTNs, as a representative substance applied in supercapacitors as the positive electrode, delivers a high specific capacity of 181 C g-1 at a current density of 0.5 A g-1, an excellent rate performance of 75.14% and a superior capacity retention of 97.42% after 10 000 cycles. Furthermore, an asymmetric supercapacitor assembled from ZnCo2O4 HTNs and active carbon also shows a stable and ultrahigh cycling stability with 95.38% of its original capacity after 20 000 cycle tests.

Conversion of a microwave synthesized alkali-metal MOF to a carbonaceous anode for Li-ion batteries

Hierarchical carbon-rich materials have shown immense potential for various electrochemical applications. Metal-organic frameworks (MOFs) are well suited precursors for obtaining such templated carbon matrices. Usually these conversions are carried out by energy intensive processes and lead to the presence of toxic transition metal residues. Herein, we demonstrate the green, scalable, microwave-assisted synthesis of a three-dimensional s-block metal based MOF and its efficient transformation into a carbonaceous material. The MOF-derived solid functions as a negative electrode for lithium-ion batteries having moderate low-rate capacities and cycling stability.

Metal-Organic Framework Derived CoS2 Wrapped with Nitrogen-Doped Carbon for Enhanced Lithium/Sodium Storage Performance

Transition metal sulfides are attractive electrode materials for both lithium-ion (LIBs) and sodium-ion batteries (SIBs). Starting from micron-sized Co(IPC)·H₂O (IPC: 4-(imidazole-1-yl) phthalic acid) and polydopamine as the metal-organic framework (MOF) precursor and carbon source, respectively, we produced a CoS₂/C/C composite constituting CoS₂ nanoparticles decorated with N-doped carbon layers and subjected to sulfurization. N-doped carbon layers provided a robust network for the CoS₂ nanoparticles, enhancing the structural integrity and electronic conductivity of the resulting CoS₂/C/C composite, which exhibited electrochemical performance superior to most existing CoS₂ composites, and was one of the best among all MOF derived CoS₂ anodes for LIBs and SIBs. The use of nanosized CoS₂ particles reduced the diffusion length for the transfer of Li⁺/Na⁺ ions, resulting in a high specific capacity at a higher current rate. N-doped carbon layers derived from the MOF precursor and polydopamine provided an electrically conductive network between the CoS₂ nanoparticles, thus preventing their aggregation and inhibiting adverse side reactions between the electrolyte and the surface of the electrode, and the high pseudocapacitive contribution resulted in the enhanced rate performance of the CoS₂/C/C electrodes.

Hierarchical Porous Carbon Arising from Metal-Organic Framework-Encapsulated Bacteria and Its Energy Storage Potential

Hierarchical porous carbons (HPCs) hold great promise in energy-related applications owing to their excellent chemical stability and well-developed porous structures. Attention has been drawn toward developing new synthetic strategies and precursor materials that permit greater control over composition, size, morphology, and pore structure. There is a growing trend of employing metal-organic frameworks (MOFs) as HPC precursors as their highly customizable characteristics favor new HPC syntheses. In this article, we report a biomimetically grown bacterial-templated MOF synthesis where the bacteria not only facilitate the formation of MOF nanocrystals but also provide morphology and porosity control. The resultant HPCs show improved electrochemical capacity behavior compared to pristine MOF-derived HPCs. Considering the broad availability of bacteria and ease of their production, in addition to significantly improved MOF growth efficiency on bacterial templates, we believe that the bacterial-templated MOF is a promising strategy to produce a new generation of HPCs.

Anhydride Post-Synthetic Modification in a Hierarchical Metal-Organic Framework

Metal-organic frameworks (MOFs) are important porous materials. Post-synthetic modification (PSM) of MOFs via the pendant groups or secondary functional groups of organic linkers has been widely used to introduce new or enhance existing properties of MOFs for various practical applications. In this work, we have constructed, for the first time, a novel platform for PSM of MOFs by introducing an anhydride functional group into a hierarchically porous MOF (MIL-121) as an effective anchor. We have demonstrated that the combination of the high reactivity of anhydride and hierarchical porosity makes this protocol particularly novel and important, as it led to excellent opportunities of incorporating not only a wide variety of organic molecules with different sizes and chemical nature but also the noble metal complexes in MOFs. Specifically, we show that the anhydride group decorated in the MOF exhibits a high reactivity toward covalently binding 10 different guest molecules including alcohols, amines, thiols, and noble metal (Pt(II)/Pt(IV)) complexes, whereas the hierarchical pores created in the MOF allow the incorporation of guest species varying in size from methanol to larger molecules such as polyaromatic amines. This novel approach provides the community with a new avenue to prepare MOF-based materials for targeted applications. To illustrate this point, we furnish an example of using this new platform to prepare a Pt-based electrocatalyst which shows excellent catalytic activity toward the oxygen reduction reaction (ORR), a pivotal half-reaction in hydrogen-oxygen fuel cells and other energy storage and conversion devices.

Bottom-Up Fabrication of a Sandwich-Like Carbon/Graphene Heterostructure with Built-In FeNC Dopants as Non-Noble Electrocatalyst for Oxygen Reduction Reaction

High-performance non-noble electrocatalysts for oxygen reduction reaction (ORR) are the prerequisite for large-scale utilization of fuel cells. Herein, a type of sandwiched-like non-noble electrocatalyst with highly dispersed FeN_x active sites embedded in a hierarchically porous carbon/graphene heterostructure was fabricated using a bottom-up strategy. The in situ ion substitution of Fe³⁺ in a nitrogen-containing MOF (ZIF-8) allows the Fe-heteroatoms to be uniformly distributed in the MOF precursor, and the assembly of Fe-doped ZIF-8 nano-crystals with graphene-oxide and in situ reduction of graphene-oxide afford a sandwiched-like Fe-doped ZIF-8/graphene heterostructure. This type of heterostructure enables simultaneous optimization of FeN_x active sites, architecture and interface properties for obtaining an electron-catalyst after a one-step carbonization. The synergistic effect of these factors render the resulting catalysts with excellent ORR activities. The half-wave potential of 0.88 V vs. RHE outperforms most of the none-noble metal catalyst and is comparable with the commercial Pt/C (20 wt %) catalyst. Apart from the high activity, this catalyst exhibits excellent durability and good methanol-tolerance. Detailed investigations demonstrate that a moderate content of Fe dopants can effectively increase the intrinsic activities, and the hybridization of graphene can enhance the reaction kinetics of ORR. The strategy proposed in this work gives an inspiration towards developing efficient noble-metal-free electrocatalysts for ORR.