Ultrathin Iron‐Cobalt Oxide Nanosheets with Abundant Oxygen Vacancies for the Oxygen Evolution Reaction

Electrochemical water splitting is a promising method for storing light/electrical energy in the form of H₂ fuel; however, it is limited by the sluggish anodic oxygen evolution reaction (OER). To improve the accessibility of H₂ production, it is necessary to develop an efficient OER catalyst with large surface area, abundant active sites, and good stability, through a low‐cost fabrication route. Herein, a facile solution reduction method using NaBH₄ as a reductant is developed to prepare iron‐cobalt oxide nanosheets (Fe_x Co_y ‐ONSs) with a large specific surface area (up to 261.1 m² g^?1), ultrathin thickness (1.2 nm), and, importantly, abundant oxygen vacancies. The mass activity of Fe₁Co₁‐ONS measured at an overpotential of 350 mV reaches up to 54.9 A g^?1, while its Tafel slope is 36.8 mV dec^?1; both of which are superior to those of commercial RuO₂, crystalline Fe₁Co₁‐ONP, and most reported OER catalysts. The excellent OER catalytic activity of Fe₁Co₁‐ONS can be attributed to its specific structure, e.g., ultrathin nanosheets that could facilitate mass diffusion/transport of OH^? ions and provide more active sites for OER catalysis, and oxygen vacancies that could improve electronic conductivity and facilitate adsorption of H₂O onto nearby Co³⁺ sites.     

Bimetallic Metal‐Organic Frameworks: Probing the Lewis Acid Site for CO2 Conversion

A highly porous metal‐organic framework (MOF) incorporating two kinds of second building units (SBUs), i.e., dimeric paddlewheel (Zn₂(COO)₄) and tetrameric (Zn₄(O)(CO₂)₆), is successfully assembled by the reaction of a tricarboxylate ligand with Zn^II ion. Subsequently, single‐crystal‐to‐single‐crystal metal cation exchange using the constructed MOF is investigated, and the results show that Cu^II and Co^II ions can selectively be introduced into the MOF without compromising the crystallinity of the pristine framework. This metal cation‐exchangeable MOF provides a useful platform for studying the metal effect on both gas adsorption and catalytic activity of the resulted MOFs. While the gas adsorption experiments reveal that Cu^II and Co^II exchanged samples exhibit comparable CO₂ adsorption capability to the pristine Zn^II‐based MOF under the same conditions, catalytic investigations for the cycloaddition reaction of CO₂ with epoxides into related carbonates demonstrate that Zn^II‐based MOF affords the highest catalytic activity as compared with Cu^II and Co^II exchanged ones. Molecular dynamic simulations are carried out to further confirm the catalytic performance of these constructed MOFs on chemical fixation of CO₂ to carbonates. This research sheds light on how metal exchange can influence intrinsic properties of MOFs.     

Facile Synthesis of Vanadium Metal‐Organic Frameworks for High‐Performance Supercapacitors

Compared to traditional metal oxides, metal‐organic frameworks exhibit excellent properties, such as a high surface area, significant thermal stability, low density, and excellent electrochemical performance. Here, a simple process is proposed for the fabrication of rod‐like vanadium metal‐organic frameworks (V^IV(O)(bdc), bdc = 1,4‐benzenedicarboxylate, or MIL‐47), and the effect of the structure on the electrochemical performance is investigated via a series of electrochemical measurements. The V^IV(O)(bdc) electrode exhibits a maximum specific capacitance of 572.1 F g^?1 at current densities of 0.5 A g^?1. More significantly, aqueous and solid‐state asymmetric supercapacitors are successfully assembled. The solid‐state device shows an excellent energy density of 6.72 mWh cm^?3 at a power density of 70.35 mW cm^?3. This superior performance confirms that V^IV(O)(bdc) electrodes are promising materials for applications in supercapacitors.     

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.     

Metal‐Organic Frameworks for CO2 Chemical Transformations

Carbon dioxide (CO₂), as the primary greenhouse gas in the atmosphere, triggers a series of environmental and energy related problems in the world. Therefore, there is an urgent need to develop multiple methods to capture and convert CO₂ into useful chemical products, which can significantly improve the environment and promote sustainable development. Over the past several decades, metal‐organic frameworks (MOFs) have shown outstanding heterogeneous catalytic activity due in part to their high internal surface area and chemical functionalities. These properties and the ability to synthesize MOF platforms allow experiments to test structure‐function relationships for transforming CO₂ into useful chemicals. Herein, recent developments are highlighted for MOFs participating as catalysts for the chemical fixation and photochemical reduction of CO₂. Finally, opportunities and challenges facing MOF catalysts are discussed in this ongoing research area.     

Nanoparticle Cookies Derived from Metal‐Organic Frameworks: Controlled Synthesis and Application in Anode Materials for Lithium‐Ion Batteries

The capacity of anode materials plays a critical role in the performance of lithium‐ion batteries. Using the nanocrystals of oxygen‐free metal‐organic framework ZIF‐67 as precursor, a one‐step calcination approach toward the controlled synthesis of CoO nanoparticle cookies with excellent anodic performances is developed in this work. The CoO nanoparticle cookies feature highly porous structure composed of small CoO nanoparticles (≈12 nm in diameter) and nitrogen‐rich graphitic carbon matrix (≈18 at% in nitrogen content). Benefiting from such unique structure, the CoO nanoparticle cookies are capable of delivering superior specific capacity and cycling stability (1383 mA h g^?1 after 200 runs at 100 mA g^?1) over those of CoO and graphite.     

Nanoporous Carbons Derived from Metal‐Organic Frameworks as Novel Matrices for Surface‐Assisted Laser Desorption/Ionization Mass Spectrometry

Surface‐assisted laser desorption/ionization mass spectrometry (SALDI‐MS) represents a powerful tool for the analysis of biomolecules, synthetic polymers, and even small organic compounds; its performances largely depend on the type of matrix materials utilized. Here, for the first time the employment of nanoporous carbons derived from metal‐organic frameworks (MOFs) as novel matrices for SALDI‐MS is demonstrated. The nanoporous carbons derived from MOFs not only circumvent the shortcomings of existing matrix materials but also demonstrate much higher efficiency of laser desorption/ionization for various compounds than any other nanoporous carbons reported so far. A new perspective for the development of matrix materials for SALDI‐MS application is therefore provided.     

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.     

Highly Ordered N‐Doped Carbon Dots Photosensitizer on Metal–Organic Framework‐Decorated ZnO Nanotubes for Improved Photoelectrochemical Water Splitting

In spite of having several advantages such as low cost, high chemical stability, and environmentally safe and benign synthetic as well as operational procedures, the full potential of carbon dots (CDs) is yet to be explored as photosensitizers due to the challenges associated with the fabrication of well‐arrayed CDs with many other photocatalytic heterostructures. In the present study, a unique combination of metal–organic framework (MOF)‐decorated zinc oxide (ZnO) 1D nanostructures as host and CDs as guest species are explored on account of their potential application in photoelectrochemical (PEC) water splitting performance. The synthetic strategy to incorporate well‐defined nitrogen‐doped carbon dots (N‐CDs) arrays onto a zeolitic imidazolate framework‐8 (ZIF‐8) anchored on ZnO 1D nanostructures allows a facile unification of different components which subsequently plays a decisive role in improving the material's PEC water splitting performance. Simple extension of such strategies is expected to offer significant advantages for the preparation of CD‐based heterostructures for photo(electro)catalytics and other related applications.     

Enhancing Oxygen Evolution Reaction through Modulating Electronic Structure of Trimetallic Electrocatalysts Derived from Metal–Organic Frameworks

The construction of efficient, durable, and non‐noble metal electrocatalysts for oxygen evolution reaction (OER) is of great value but challenging. Herein, a facile method is developed to synthesize a series of trimetallic (W/Co/Fe) metal–organic frameworks (MOFs)‐derived carbon nanoflakes (CNF) with various Fe content, and an Fe‐dependent volcano‐type plot can be drawn out for WCoFe_x ‐CNF. The optimized WCoFe_0.3‐CNF (when the feed ratio of Fe/Co is 0.3) demonstrates superior electrocatalytic performance with a low overpotential of only 254 mV@10 mA cm^?2 and excellent durability of 100 h. Further researches show that appropriate amount of iron doping can regulate the electronic structure, resulting in a favorable synergistic environment. This method may stimulate the exploration of electrocatalysts by utilizing MOFs as precursors while realizing electronic modulation by multimetal doping.