Metal-organic framework derived ZnO/ZnFe2O4/C nanocages as stable cathode material for reversible lithium-oxygen batteries

Freestanding MOF-Derived Honeycomb-Shape Porous MnOC@CC as an Electrocatalyst for Reversible LiOH Chemistry in Li-O2 Batteries

In rechargeable Li-O₂ batteries, the electrolyte and the electrode are prone to be attacked by aggressive intermediates (O₂^- and LiO₂) and products (Li₂O₂), resulting in low energy efficiency. It has been reported that in the presence of water, the formation of low-activity LiOH is more stable for electrolyte and electrode, effectively reducing the production of parasitic products. However, the reversible formation and decomposition of LiOH catalyzed by solid catalysts is still a challenge. Here, a freestanding metal-organic framework (MOF)-derived honeycomb-shape porous MnOC@CC cathode was prepared for Li-O₂ batteries by in situ growth of urchin-like Mn-MOFs on carbon cloth (CC) and carbonization. The battery with the MnOC@CC cathode exhibits an ultrahigh practical discharge specific capacity of 22,838 mAh g^-1 at 200 mA g^-1, high-rate capability, and more stable cycling, which is superior to the MnOC powder cathode. X-ray diffraction and Fourier transform infrared results identify that the discharge product of the batteries is LiOH rather than highly active Li₂O₂, and no parasitic products were found during operation. The MnOC@CC cathode can induce the formation of flower-like LiOH in the presence of water due to its unique porous structure and directional alignment of Mn-O centers. This work achieves the reversible formation and decomposition of LiOH in the presence of water, offering some insights into the practical application of semiopen Li-O₂ batteries.

Anisotropy Engineering of ZnO Nanoporous Frameworks: A Lattice Dynamics Simulation

The anisotropy engineering of nanoporous zinc oxide (ZnO) frameworks has been performed by lattice dynamics simulation. A series of zinc oxide (ZnO) nanoporous framework structures was designed by creating nanopores with different sizes and shapes. We examined the size effects of varying several features of the nanoporous framework (namely, the removal of layers of atoms, surface-area-to-volume ratio, coordination number, porosity, and density) on its mechanical properties (including bulk modulus, Young's modulus, elastic constant, and Poisson ratio) with both lattice dynamics simulations. We also found that the anisotropy of nanoporous framework can be drastically tuned by changing the shape of nanopores. The maximum anisotropy (defined by Y_max/Y_min) of the Young's modulus value increases from 1.2 for bulk ZnO to 2.5 for hexagon-prism-shaped ZnO nanoporous framework structures, with a density of 2.72 g/cm³, and, even more remarkably, to 89.8 for a diamond-prism-shape at a density of 1.72 g/cm³. Our findings suggest a new route for desirable anisotropy and mechanical property engineering with nanoporous frameworks by editing the shapes of the nanopores for the desired anisotropy.

Au nanoparticles decorated ZnO/ZnFe2O4 composite SERS-active substrate for melamine detection

Surface-enhanced Raman scattering (SERS) based on plasmonic metal nanoparticles and semiconductors has been used as performance-enhancing structures for sensing trace chemicals. We have selected a case of oxide functional oxide organic nanostructure between ZnFe₂O₄ and ZnO, denoted as ZZF. By decorating such nanostructure with AuNPs, to identify R6G in varying concentrations (10^-6 M - 10^-12 M), an enhancement factor of 1.6 × 10⁸ was observed. The material was used for the identification of melamine in the concentration range of 0.39 μM-7.92 μM. This high-performance nanocomposite provides improved melamine sensitivity towards SERS and the limit of detection as low as 0.39 μM. The Au-ZZF SERS substrate can yield a SERS enhancement factor of 1.37 × 10⁷. The experimental performance demonstrates that excellent SERS enhancement is due to electrons movement within ZZF and Au nanoparticles. Owing to its easy and effective synthesis methodology, this sensitive and specific SERS substrate is a promising technique to detect trace chemicals. We further study the best energetically favorable orientation of melamine molecules over the substrate leading to the SERS activity using density functional theoretical study.

Rational Design of MOF-Based Materials for Next-Generation Rechargeable Batteries

This review summarizes recent progresses in pristine metal–organic frameworks (MOFs), MOF composites, and their derivatives for next-generation rechargeable batteries including lithium–sulfur batteries, lithium–oxygen batteries, sodium-ion batteries, potassium-ion batteries, Zn-ion batteries, and Zn–air batteries.

The design strategies for MOF-based materials as the electrode, separator, and electrolyte are outlined and discussed.

The challenges and development strategies and of MOF-related materials for battery applications are highlighted.

Metal–organic framework (MOF)-based materials with high porosity, tunable compositions, diverse structures, and versatile functionalities provide great scope for next-generation rechargeable battery applications. Herein, this review summarizes recent advances in pristine MOFs, MOF composites, MOF derivatives, and MOF composite derivatives for high-performance sodium-ion batteries, potassium-ion batteries, Zn-ion batteries, lithium–sulfur batteries, lithium–oxygen batteries, and Zn–air batteries in which the unique roles of MOFs as electrodes, separators, and even electrolyte are highlighted. Furthermore, through the discussion of MOF-based materials in each battery system, the key principles for controllable synthesis of diverse MOF-based materials and electrochemical performance improvement mechanisms are discussed in detail. Finally, the major challenges and perspectives of MOFs are also proposed for next-generation battery applications.

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.

Hollow-Structured Metal Oxides as Oxygen-Related Catalysts

Metal oxide hollow structures with large surface area, low density, and high loading capacity have received great attention for energy-related applications. Acting as oxygen-related catalysts, hollow-structured transition metal oxides offer low overpotential, fast reaction rate, and excellent stability. Herein, recent progress in the oxygen-related catalysis (e.g., oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and metal-air batteries) of hollow-structured transition metal oxides is discussed. Through a comprehensive outline of hollow-structured spinels, perovskites, rutiles, etc., a rational design strategy is provided for an enhanced oxygen-related catalysis performance from the viewpoint of crystal structures. Urgent challenges and further research directions are presented for hollow-structured transition metal oxides toward excellent oxygen-related catalysis.

Metal–organic framework derived Co–N-reduced graphene oxide as electrode materials for rechargeable Li–O2 batteries

With tailored deposition sites and morphology of discharge products, the Li–O₂ batteries based on Co–N-rGO electrodes exhibit significant enhancement.

Ru-Coated metal–organic framework-derived Co-based particles embedded in porous N-doped carbon nanocubes as a catalytic cathode for a Li–O2 battery

Ru-Co₄N/Co-NC is prepared and used as a cathode for a Li–O₂ battery, which shows high-capacity, low overpotential and long cycle-life.

All solid-state lithium–oxygen batteries with MOF-derived nickel cobaltate nanoflake arrays as high-performance oxygen cathodes

Solid-state lithium oxygen batteries with MOF-converted nickel cobaltate nanoflake arrays as high-performance oxygen cathodes were prepared, delivering high reversibility and long-term cycling stability over 90 cycles.

Metal–organic framework derived hollow porous CuO–CuCo2O4 dodecahedrons as a cathode catalyst for Li–O2 batteries

Metal–organic framework derived porous CuO–CuCo₂O₄ dodecahedrons as a cathode catalyst for Li–O₂ batteries with significantly enhanced rate and cyclic performance.

Urchin-like NiO-NiCo2O4 heterostructure microsphere catalysts for enhanced rechargeable non-aqueous Li-O2 batteries

Urchin-like NiO-NiCo2O4 microspheres with heterostructures were successfully synthesized through a facile hydrothermal method, followed by thermal treatment. The unique structure of NiO-NiCo2O4 with the synergetic effect between NiCo2O4 and NiO, and the heterostructure favour the catalytic activity towards Li-O2 batteries. NiCo2O4 is helpful for boosting both the oxygen reduction reaction and oxygen evolution reaction for the Li-O2 batteries and NiO is likely to promote the decomposition of certain by-products. The special urchin-like morphology facilitates the continuous oxygen flow and accommodates Li2O2. Moreover, benefitting from the heterostructure, NiO-NiCo2O4 microspheres are able to promote the transport of Li ions and electrons to further improve battery performance. Li-O2 batteries utilizing a NiO-NiCo2O4 microsphere electrode show a much higher specific capacity and a lower overpotential than those with a Super P electrode. Moreover, they exhibit an enhanced cycling stability. The electrode can be continuously discharged and charged without obvious terminal voltage variation for 80 cycles, as the discharge capacity is restricted at 600 mA h g-1, suggesting that NiO-NiCo2O4 is a promising catalyst for Li-O2 batteries.

MOF-Derived Metal Oxide Composites for Advanced Electrochemical Energy Storage

Over the past two decades, metal-organic frameworks (MOFs), a type of porous material, have aroused great interest as precursors or templates for the derivation of metal oxides and composites for the next generation of electrochemical energy storage applications owing to their high specific surface areas, controllable structures, and adjustable pore sizes. The electrode materials, which affect the performance in practical applications, are pivotal components of batteries and supercapacitors. Metal oxide composites derived from metal-organic frameworks possessing high reversible capacity and superior rate and cycle performance are excellent electrode materials. In this Review, potential applications for MOF-derived metal oxide composites for lithium-ion batteries, sodium-ion batteries, lithium-oxygen batteries, and supercapacitors are studied and summarized. Finally, the challenges and opportunities for future research on MOF-derived metal oxide composites are proposed on the basis of academic knowledge from the reported literature as well as from experimental experience.

Transition Metal Hollow Nanocages as Promising Cathodes for the Long-Term Cyclability of Li⁻O₂ Batteries

As a step towards efficient and cost-effective electrocatalytic cathodes for Li⁻O₂ batteries, highly porous hausmannite-type Mn₃O₄ hollow nanocages (MOHNs) of a large diameter of ~250 nm and a high surface area of 90.65 m²·g−1 were synthesized and their physicochemical and electrochemical properties were studied in addition to their formation mechanism. A facile approach using carbon spheres as the template and MnCl₂ as the precursor was adopted to suit the purpose. The MOHNs/Ketjenblack cathode-based Li⁻O₂ battery demonstrated an improved cyclability of 50 discharge⁻charge cycles at a specific current of 400 mA·g−1 and a specific capacity of 600 mAh·g−1. In contrast, the Ketjenblack cathode-based one can sustain only 15 cycles under the same electrolytic system comprised of 1 M LiTFSI/TEGDME. It is surmised that the unique hollow nanocage morphology of MOHNs is responsible for the high electrochemical performance. The hollow nanocages were a result of the aggregation of crystalline nanoparticles of 25⁻35 nm size, and the mesoscopic pores between the nanoparticles gave rise to a loosely mesoporous structure for accommodating the volume change in the MOHNs/Ketjenblack cathode during electrocatalytic reactions. The improved cyclic stability is mainly due to the faster mass transport of the O₂ through the mesoscopic pores. This work is comparable to the state-of-the-art experimentations on cathodes for Li⁻O₂ batteries that focus on the use of non-precious transition materials.

One-Pot Synthesis of Co-Based Coordination Polymer Nanowire for Li-Ion Batteries with Great Capacity and Stable Cycling Stability

Nanowire coordination polymer cobalt-terephthalonitrile (Co-BDCN) was successfully synthesized using a simple solvothermal method and applied as anode material for lithium-ion batteries (LIBs). A reversible capacity of 1132 mAh g^-1 was retained after 100 cycles at a rate of 100 mA g^-1, which should be one of the best LIBs performances among metal organic frameworks and coordination polymers-based anode materials at such a rate. On the basis of the comprehensive structural and morphology characterizations including fourier transform infrared spectroscopy, ¹H NMR, ¹³C NMR, and scanning electron microscopy, we demonstrated that the great electrochemical performance of the as-synthesized Co-BDCN coordination polymer can be attributed to the synergistic effect of metal centers and organic ligands, as well as the stability of the nanowire morphology during cycling.

Electrocatalysts Derived from Metal-Organic Frameworks for Oxygen Reduction and Evolution Reactions in Aqueous Media

Electrochemical energy conversion and storage devices such as fuel cells and metal-air batteries have been extensively studied in recent decades for their excellent conversion efficiency, high energy capacity, and low environmental impact. However, sluggish kinetics of the oxygen-related reactions at air cathodes, i.e., oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), are still worth improving. Noble metals such as platinum (Pt), iridium (Ir), ruthenium (Ru) and their oxides are considered as the benchmark ORR and OER electrocatalysts, but they are expensive and prone to be poisoned due to the fuel crossover effect, and may suffer from agglomeration and leaching after long-term usage. To mitigate these limits, it is highly desirable to design alternative ORR/OER electrocatalysts with prominent performance. Metal-organic frameworks (MOFs) are a class of porous crystalline materials consisting metal ions/clusters coordinated by organic ligands. Their crystalline structure, tunable pore size and high surface area afford them wide opportunities as catalytic materials. This Review covers MOF-derived ORR/OER catalysts in electrochemical energy conversion, with a focus on the different strategies of material design and preparation, such as composition control and nanostructure fabrication, to improve the activity and durability of MOF-derived electrocatalysts.

Metal-Organic Framework-Derived Reduced Graphene Oxide-Supported ZnO/ZnCo2O4/C Hollow Nanocages as Cathode Catalysts for Aluminum-O2 Batteries

Aluminum-air battery is a promising candidate for large-scale energy applications because of its low cost and high energy density. Remarkably, tremendous efforts have been concentrated on developing efficient and stable cathode electrocatalysts toward the oxygen reduction reaction. In this work, a hydrothermal-calcination approach was utilized to prepare novel reduced graphene oxide (rGO)-supported hollow ZnO/ZnCo₂O₄ nanoparticle-embedded carbon nanocages (ZnO/ZnCo₂O₄/C@rGO) using a zeolitic imidazolate framework (ZIF-67)/graphene oxide/zinc nitrate composite as the precursor. The ZnO/ZnCo₂O₄/C@rGO hybrid exhibits remarkable electrocatalytic performance for oxygen reduction reaction under alkaline conditions and superior stability and methanol tolerance to those of the commercial Pt/C catalyst. Furthermore, novel and simple Al-air coin cells were first fabricated using the hybrid materials as cathode catalysts under ambient air conditions to further investigate their catalytic performance. The coin cell with the ZnO/ZnCo₂O₄/C@rGO cathode catalyst displays a higher open circuit voltage and discharge voltage and more sluggish potential drop than those of the cell with the ZnO/ZnCo₂O₄/C cathode catalyst, which confirms that rGO can enhance the electrocatalytic activity and stability of the catalyst system. The excellent electrocatalytic performance of the ZnO/ZnCo₂O₄/C@rGO hybrid is attributed to the prominent conductivity and high specific surface area resulting from rGO, the more accessible catalytic active sites induced by the unique porous hollow nanocage structure, and synergic covalent coupling between rGO sheets and ZnO/ZnCo₂O₄/C nanocages.

Influence of Enhanced O2 Provision on the Discharge Performance of Li-air Batteries by Incorporating Fluoroether

As the first step during discharge, the mass transfer of oxygen should play a crucial role in Li-air batteries to tailor the growth of discharge products, however, not enough attention has been paid to this issue. Herein, we introduce an oxygen-enriching cosolvent, 1,2-(1,1,2,2-tetrafluoroethoxy) ethane (FE1), into the electrolyte, and investigate its influence on the discharge performance. The incorporation of this novel cosolvent consistently enhances the oxygen solubility of the electrolyte, and improves the oxygen diffusivity following a volcano-shape trend peaking at 50 % FE1. It is interesting that the discharge capacities obtained with the investigated electrolytes share the similar volcano trends as the oxygen transport under 50 mA g_carbon^-1 and higher current densities. The improved oxygen diffusion could benefit the volumetric utilization of the air cathode, especially at the separator side, probably owing to the fast oxygen transport to moderate its concentration gradient. Our results demonstrate the importance of oxygen provision, which easily becomes the capacity-determining factor.

Nanoarchitectured Design of Porous Materials and Nanocomposites from Metal-Organic Frameworks

The emergence of metal-organic frameworks (MOFs) as a new class of crystalline porous materials is attracting considerable attention in many fields such as catalysis, energy storage and conversion, sensors, and environmental remediation due to their controllable composition, structure and pore size. MOFs are versatile precursors for the preparation of various forms of nanomaterials as well as new multifunctional nanocomposites/hybrids, which exhibit superior functional properties compared to the individual components assembling the composites. This review provides an overview of recent developments achieved in the fabrication of porous MOF-derived nanostructures including carbons, metal oxides, metal chalcogenides (metal sulfides and selenides), metal carbides, metal phosphides and their composites. Finally, the challenges and future trends and prospects associated with the development of MOF-derived nanomaterials are also examined.

Nitrogen-Doped Yolk-Shell-Structured CoSe/C Dodecahedra for High-Performance Sodium Ion Batteries

In this work, nitrogen-doped, yolk-shell-structured CoSe/C mesoporous dodecahedra are successfully prepared by using cobalt-based metal-organic frameworks (ZIF-67) as sacrificial templates. The CoSe nanoparticles are in situ produced by reacting the cobalt species in the metal-organic frameworks with selenium (Se) powder, and the organic species are simultaneously converted into nitrogen-doped carbon material in an inert atmosphere at temperatures between 700 and 900 °C for 4 h. For the composite synthesized at 800 °C, the carbon framework has a relatively higher extent of graphitization, with high nitrogen content (17.65%). Furthermore, the CoSe nanoparticles, with a size of around 15 nm, are coherently confined in the mesoporous carbon framework. When evaluated as novel anode materials for sodium ion batteries, the CoSe/C composites exhibit high capacity and superior rate capability. The composite electrode delivers the specific capacities of 597.2 and 361.9 mA h g^-1 at 0.2 and 16 A g^-1, respectively.

Room-temperature synthesis of a cobalt 2,3,5,6-tetrafluoroterephthalic coordination polymer with enhanced capacity and cycling stability for lithium batteries

A cobalt 2,3,5,6-tetrafluoroterephthalic coordination-polymer named Co-TFBDC has been synthesized at room temperature and show a high capacity of 1074.6 mA h g⁻¹ after 50 cycles at a current of 100 mA g⁻¹ when applied as anode material for lithium-ion battery.

NiMn2O4 as an efficient cathode catalyst for rechargeable lithium–air batteries

Intermediate spinel structured NiMn₂O₄-FT performs better than normal spinel oxide NiMn₂O₄-PH as a cathode bi-functional catalyst for Li–air batteries.

Zeolitic imidazole framework derived composites of nitrogen-doped porous carbon and reduced graphene oxide as high-efficiency cathode catalysts for Li–O2 batteries

MOF derived nitrogen-doped porous carbon and reduced graphene oxide composites were prepared and they exhibit outstanding electrochemical performance for lithium–oxygen batteries.

Two new metal–organic frameworks based on tetrazole–heterocyclic ligands accompanied by in situ ligand formation

Two new MOFs have been constructed by the Dimroth rearrangement of the in situ generated organic ligand 5-((2H-tetrazol-5-yl)amino)isophthalic acid (H₃L).

A cuboidal [Ni4O4] cluster as a precursor for recyclable, carbon-supported nickel nanoparticle reduction catalysts

A pyridine alkoxide ligated cuboidal [Ni₄O₄] cluster has been selected as the precursor to synthesize carbon-hosted Ni nanoparticles for catalytic conversion of 4-nitrophenol to 4-aminophenol.

Facile Synthesis of Nix Zn1-x Fe2 O4 (x=0, 0.25, 0.5, 0.75, 1) as Anode Materials for Lithium Storage

Ni_x Zn_1-x Fe₂ O₄ (x=0, 0.25, 0.5, 0.75, 1) compounds were prepared by a hydrothermal method and subsequent heat treatment. The physical characteristics of the samples were investigated by field-emission SEM, XRD, X-ray photoelectron spectroscopy, and TEM. The electrochemical properties of Ni_x Zn_1-x Fe₂ O₄ (x=0, 0.25, 0.5, 0.75, 1) as anode materials were tested for lithium-ion batteries. The lithium-storage properties of the electrodes were assessed by cyclic voltammetry and galvanostatic cycling. Among the five samples, Ni_0.25 Zn_0.75 Fe₂ O₄ shows good electrochemical performance with a discharge capacity of 1488 mAh g^-1 in the initial cycle and 856 mAh g^-1 after 100 cycles.

Formation of Prussian-Blue-Analog Nanocages via a Direct Etching Method and their Conversion into Ni-Co-Mixed Oxide for Enhanced Oxygen Evolution

Novel Ni-Co-Prussian-blue-analog nano-cages consisting of pyramid-like walls were prepared via a facile chemical etching process with ammonia at room temperature. After annealing in air, the derived Ni-Co mixed oxide nanocages exhibit enhanced electrocatalytic activity and excellent stability toward the oxygen-evolution reaction.

Cage-Type Highly Graphitic Porous Carbon-Co3O4 Polyhedron as the Cathode of Lithium-Oxygen Batteries

A novel cage-type highly graphitic porous carbon-Co3O4 (GPC-Co3O4) polyhedron was designed and successfully prepared for the first time by executing a two-step annealing of core-shell structured metal-organic frameworks (MOFs). The low graphitic carbon cores were selectively removed during the secondary annealing in air atmospheres, leaving the interior voids due to their lower thermal stability compared with the graphitic carbon shells. Inspired by the unique properties of the cage-type GPC-Co3O4 polyhedron, GPC-Co3O4 was assembled as an oxygen electrode for a rechargeable Li-O2 battery without the additional conductive agent. The efficient generation of Li2O2 during discharging and the reversible decomposition of Li2O2 during charging were clearly observed by XRD patterns and SEM images. The GPC-Co3O4 polyhedron integrates the beneficial properties, including high electronic conductivity, the rigid cage-type structure consisting of the mesoporous walls and interior void space, as well as the uniformly embedded catalytically active Co3O4 nanoparticles. As a result, the GPC-Co3O4 cathode displays a low charge overpotential of 0.58 V, a good rate capability, and a long cycle life in a Li-O2 battery.

Capacity control of ferric coordination polymers by zinc nitrate for lithium-ion batteries

Improved morphology leads to improved Li⁺ storage performance.

A versatile strategy to fabricate MOFs/carbon material integrations and their derivatives for enhanced electrocatalysis

This work proposed a versatile strategy to fabricate MOFs/carbon materials integrations for enhanced electrocatalysis.

Metal-Organic Frameworks (MOFs) as Sandwich Coating Cushion for Silicon Anode in Lithium Ion Batteries

A novel metal-organic framework (MOF) sandwich coating method (denoted as MOF-SC) is developed for hybrid Li ion battery electrode preparation, in which the MOF films are casted on the surface of a silicon layer and sandwiched between the active silicon and the separator. The obtained electrodes show improved cycling performance. The areal capacity of the cheap and readily available microsized Si treated with MOF-SC can reach 1700 μAh cm(-2) at 265 μA cm(-2) and maintain at 850 μAh cm(-2) after 50 cycles. Beyond the above, the commercial nanosized Si treated by MOF-SC also shows greatly enhanced areal capacity and outstanding cycle stability, 600 μAh cm(-2) for 100 cycles without any apparent fading. By virtue of the novel structure prepared by the MOFs, this new MOF-SC structure serves as an efficient protection cushion for the drastic volume change of silicon during charge/discharge cycles. Furthermore, this MOF layer, with large pore volume and high surface area, can adsorb electrolyte and allow faster diffusion of Li(+) as evidenced by decreased impedance and improved rate performance.

In situ preparation of cobalt doped ZnO@C/CNT composites by the pyrolysis of a cobalt doped MOF for high performance lithium ion batteries

A cobalt doped MOF acted as a catalyst and carbon source for a CNTs containing anode material with better performance.