A Single-Crystal Open-Capsule Metal-Organic Framework

Vanadium-doped metal-organic framework@Znln2S4 core-shell heterojunction-attenuated photoelectrochemical immunoassay

Considering that cancer has become the second leading cause of death in humans, it is essential to develop an analytical approach that can sensitively detect tumor markers for early detection. We report an attenuated photoelectrochemical (PEC) immunoassay based on the organic-inorganic heterojunction 10MIL-88B(FeV)/ZnIn2S4 (10M88B(FeV)/ZIS) as a photoactive material for monitoring carcinoembryonic antigen (CEA). The 10M88B(FeV)/ZIS heterojunctions have excellent light-harvesting properties and high electrical conductivity, which are attributed to the advantages of both organic and inorganic semiconductors, namely, remarkable photogenerated carrier separation efficiency and long photogenerated carrier lifetime. Horseradish peroxidase (HRP) in the presence of H2O2 can catalyze 3,3'-diaminofenamide (DAB) producing brown precipitates (oxDAB), which is then loaded onto the 10M88B(FeV)/ZIS heterojunction to reduce the photocurrent and enable the quantitative detection of CEA. Under optimal conditions, the photocurrent values of the PEC biosensor are linearly related to the logarithm of the CEA concentrations, ranging from 0.01 ng mL-1 to 100 ng mL-1 with a detection limit (LOD) of 4.0 pg mL-1. Notably, the accuracy of the PEC biosensor is in agreement with that of the human CEA enzyme-linked immunosorbent assay (ELISA) kit.

Porous Flower-Like Nanoarchitectures Derived from Nickel Phosphide Nanocrystals Anchored on Amorphous Vanadium Phosphate Nanosheet Nanohybrids for Superior Overall Water Splitting

Transition metal phosphides (TMPs) and phosphates (TM-Pis) nanostructures are promising functional materials for energy storage and conversion. Nonetheless, controllable synthesis of crystalline/amorphous heterogeneous TMPs/TM-Pis nanohybrids or related nanoarchitectures remains challenging, and their electrocatalytic applications toward overall water splitting (OWS) are not fully explored. Herein, the Ni2P nanocrystals anchored on amorphous V-Pi nanosheet based porous flower-like nanohybrid architectures that are self-supported on carbon cloth (CC) substrate (Ni2P/V-Pi/CC) are fabricated by conformal oxidation and phosphorization of pre-synthesized NiV-LDH/CC. Due to the unique microstructures and strong synergistic effects of crystalline Ni2P and amorphous V-Pi components, the obtained Ni2P/V-Pi/CC owns abundant active sites, suitable surface/interface electronic structure and optimized adsorption-desorption of reaction intermediates, resulting in outstanding electrocatalytic performances toward hydrogen and oxygen evolution reactions in alkaline media. Correspondingly, the assembled Ni2P/V-Pi/CC||Ni2P/V-Pi/CC electrolyzer only needs an ultralow cell voltage (1.44 V) to deliver 10 mA cm-2 water-splitting currents, exceeding its counterparts, recently reported bifunctional catalysts-based devices, and Pt/C/CC||IrO2/CC pairs. Moreover, the Ni2P/V-Pi/CC||Ni2P/V-Pi/CC manifests remarkable stability. Also, such device shows a certain prospect for OWS in acidic media. This work may spur the development of TMPs/TMPis-based nanohybrid architectures by combining structure and phase engineering, and push their applications in OWS or other clean energy options.

Rational Construction of 3D Self-Supported MOF-Derived Cobalt Phosphide-Based Hollow Nanowall Arrays for Efficient Overall Water Splitting At large Current Density

Developing efficient nonprecious bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) in the same electrolyte with a low overpotential and large current density presents an appealing yet challenging goal for large-scale water electrolysis. Herein, a unique 3D self-branched hierarchical nanostructure composed of ultra-small cobalt phosphide (CoP) nanoparticles embedded into N, P-codoped carbon nanotubes knitted hollow nanowall arrays (CoPʘNPCNTs HNWAs) on carbon textiles (CTs) through a carbonization-phosphatization process is presented. Benefiting from the uniform protrusion distributions of CoP nanoparticles, the optimum CoPʘNPCNTs HNWAs composites with high abundant porosity exhibit superior electrocatalytic activity and excellent stability for OER in alkaline conditions, as well as for HER in both acidic and alkaline electrolytes, even under large current densities. Furthermore, the assembled CoPʘNPCNTs/CTs||CoPʘNPCNTs/CTs electrolyzer demonstrates exceptional performance, requiring an ultralow cell voltage of 1.50 V to deliver the current density of 10 mA cm-2 for overall water splitting (OWS) with favorable stability, even achieving a large current density of 200 mA cm-2 at a low cell voltage of 1.78 V. Density functional theory (DFT) calculation further reveals that all the C atoms between N and P atoms in CoPʘNPCNTs/CTs act as the most efficient active sites, significantly enhancing the electrocatalytic properties. This strategy, utilizing 2D MOF arrays as a structural and compositional material to create multifunctional composites/hybrids, opens new avenues for the exploration of highly efficient and robust non-noble-metal catalysts for energy-conversion reactions.

Recent Advances of Bimetallic-Metal Organic Frameworks: Preparation, Properties, and Fluorescence-Based Biochemical Sensing Applications

Bimetallic-metal organic frameworks (BiM-MOFs) or bimetallic organic frameworks represent an innovative and promising class of porous materials, distinguished from traditional monometallic MOFs by their incorporation of two metal ions alongside organic linkers. BiM-MOFs, with their unique crystal structure, physicochemical properties, and composition, demonstrate distinct advantages in the realm of biochemical sensing applications, displaying improvements in optical properties, stability, selectivity, and sensitivity. This comprehensive review explores into recent advancements in leveraging BiM-MOFs for fluorescence-based biochemical sensing, providing insights into their design, synthesis, and practical applications in both chemical and biological sensing. Emphasizing fluorescence emission as a transduction mechanism, the review aims to guide researchers in maximizing the potential of BiM-MOFs across a broader spectrum of investigations. Furthermore, it explores prospective research directions and addresses challenges, offering valuable perspectives on the evolving landscape of fluorescence-based probes rooted in BiM-MOFs.

Facile Fabrication of Hollow Nanoporous Carbon Architectures by Controlling MOF Crystalline Inhomogeneity for Ultra-Stable Na-Ion Storage

Hollow nanoporous carbon architectures (HNCs) present significant utilitarian value for a wide variety of applications. Facile and efficient preparation of HNCs has long been pursued but still remains challenging. Herein, we for the first time demonstrate that single-component metal-organic frameworks (MOFs) crystals, rather than the widely reported hybrid ones which necessitate tedious operations for preparation, could enable the facile and versatile syntheses of functional HNCs. By controlling the growth kinetics, the MOFs crystals (STU-1) are readily engineered into different shapes with designated styles of crystalline inhomogeneity. A subsequent one-step pyrolysis of these MOFs with intraparticle difference can induce a simultaneous self-hollowing and carbonization process, thereby producing various functional HNCs including yolk-shell polyhedrons, hollow microspheres, mesoporous architectures, and superstructures. Superior to the existing methods, this synthetic strategy relies only on the complex nature of single-component MOFs crystals without involving tedious operations like coating, etching, or ligand exchange, making it convenient, efficient, and easy to scale up. An ultra-stable Na-ion battery anode is demonstrated by the HNCs with extraordinary cyclability (93 % capacity retention over 8000 cycles), highlighting a high level of functionality of the HNCs.

Facet engineering of a two-dimensional metal-organic framework with uniquely oriented layered-structure for electrocatalytic oxygen reduction reaction

The properties of metal-organic framework (MOF) nanocrystals are highly dependent on their sizes, morphologies, and exposed facets. Facet engineering of MOFs offers an efficient strategy to tailor the active sites and optimize the catalytic activity of both MOFs and their derivatives. In this study, we prepared 1D zeolitic imidazolate framework-nanorod (ZIF-NR) through facet engineering of the parental 2D ZIF-L. The introduction of cetyltrimethylammonium bromide (CTABr) surfactant into the synthesis solution hindered the crystal growth along the c-axis of leaf-like ZIF-L, resulting in the formation of 1D ZIF-NR. The derived Co nanoparticle encapsulated N doped carbon nanorod (denoted as Co-NCR) exhibited high activity and stability for electrocatalytic oxygen reduction reactions and Zn-air batteries. Facet engineering of a 2D MOF with a uniquely oriented layered structure demonstrates the possibility of designing novel electrocatalysts.

3D Hierarchical MOF-Derived Defect-Rich NiFe Spinel Ferrite as a Highly Efficient Electrocatalyst for Oxygen Redox Reactions in Zinc-Air Batteries

The strategy of defect engineering is increasingly recognized for its pivotal role in modulating the electronic structure, thereby significantly improving the electrocatalytic performance of materials. In this study, we present defect-enriched nickel and iron oxides as highly active and cost-effective electrocatalysts, denoted as Ni0.6Fe2.4O4@NC, derived from NiFe-based metal-organic frameworks (MOFs) for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). XANES and EXAFS confirm that the crystals have a distorted structure and metal vacancies. The cation defect-rich Ni0.6Fe2.4O4@NC electrocatalyst exhibits exceptional ORR and OER activities (ΔE = 0.68 V). Mechanistic pathways of electrochemical reactions are studied by DFT calculations. Furthermore, a rechargeable zinc-air battery (RZAB) using the Ni0.6Fe2.4O4@NC catalyst demonstrates a peak power density of 187 mW cm-2 and remarkable long-term cycling stability. The flexible solid-state ZAB using the Ni0.6Fe2.4O4@NC catalyst exhibits a power density of 66 mW cm-2. The proposed structural design strategy allows for the rational design of electronic delocalization of cation defect-rich NiFe spinel ferrite attached to ultrathin N-doped graphitic carbon sheets in order to enhance active site availability and facilitate mass and electron transport.

Iodine Adsorption-Desorption-Induced Structural Transformation and Improved Ag+ Turn-On Luminescent Sensing Performance of a Nonporous Eu(III) Metal-Organic Framework

Posttreatment of pristine metal-organic frameworks (MOFs) with suitable vapor may be an effective way to regulate their structures and properties but has been less explored. Herein, we report an interesting example in which a crystalline nonporous Eu(III)-MOF was transferred to a porous amorphous MOF (aMOF) via iodine vapor adsorption-desorption posttreatment, and the resulting aMOF showed improved turn-on sensing properties with respect to Ag+ ions. The crystalline Eu-MOF, namely, Eu-IPDA, was assembled from Eu(III) and 4,4'-{4-[4-(1H-imidazol-1-yl)phenyl]pyridine-2,6-diyl}dibenzoic acid (H2IPDA) and exhibited a two-dimensional (2D) coordination network based on one-dimensional secondary building blocks. The close packing of the 2D networks gives rise to a three-dimensional supramolecular framework without any significant pores. Interestingly, the nonporous Eu-IPDA could absorb iodine molecules when Eu-IPDA crystals were placed in iodine vapor at 85 °C, and the adsorption capacity was 1.90 g/g, which is comparable to those of many MOFs with large BET surfaces. The adsorption of iodine is attributed to the strong interactions among the iodine molecule, the carboxy group, and the N-containing group and leads to the amorphization of the framework. After immersion of the iodine-loaded Eu-IPDA in EtOH, approximately 89.7% of the iodine was removed, resulting in a porous amorphous MOF, denoted as a-Eu-IPDA. In addition, the remaining iodine in the a-Eu-IPDA framework causes strong luminescent quenching in the fluorescence emission region of the Eu(III) center when compared with that in Eu-IPDA. The luminescence intensity of a-Eu-IPDA in water suspensions was significantly enhanced when Ag+ ions were added, with a detection limit of 4.76 × 10-6 M, which is 1000 times that of pristine Eu-IPDA. It also showed strong anti-interference ability over many common competitive metal ions and has the potential to sense Ag+ in natural water bodies and traditional Chinese medicine preparations. A mechanistic study showed that the interactions between Ag+ and the absorbed iodine, the carboxylate group, and the N atoms all contribute to the sensing performance of a-Eu-IPDA.

Architecting N-doped Carbon Nanotube-Rich Carbon Nanofibers with Biomimetic Vine-Leaf-Whisker Structure as Robust Bifunctional Electrocatalysts for Rechargeable Zn-Air Batteries

Efficient and durable bifunctional catalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are urgently desirable but challenging for rechargeable Zn-air batteries (ZABs), especially flexible wearable ZABs. Inspired by the vine-leaf-whisker structure in nature, we proposed a three-dimensional (3D) hierarchical bifunctional catalyst (denoted as Co-Fe-Zn@N-CNT/CNF) consisting of N-doped carbon nanotubes embedded with abundant CoFe alloy nanoparticles, leaf-shaped N-doped carbon nanoflakes, and porous carbon fibers for rechargeable ZABs. The special biomimetic structure provides a large specific surface area, allowing for high exposure of the active site and ensuring fast mass transport/charge transfer. The close combination of CoFe bimetallic alloys and N-doped carbon nanotubes delivers high electrocatalytic activity, while the coexistence of various active sites such as metal nanoparticles (NPs), metal-Nx, doped N species, and their synergistic interactions endows the catalysts with more active sites. As such, the Co-Fe-Zn@N-CNT/CNF catalyst achieves superior bifunctional catalytic activities for the ORR (a half-wave potential of 0.84 V) and the OER (an overpotential of 326 mV at 10 mA cm-2) in alkaline media, comparable to commercial Pt/C and RuO2. Remarkably, both aqueous and solid-state ZABs assembled with Co-Fe-Zn@N-CNT/CNF catalysts as air electrodes demonstrate excellent charging/discharging performance, high peak power density, and robust long-term cycling stability. More interestingly, the flexible ZAB performs well even under bending conditions, displaying satisfactory device stability and mechanical flexibility. This study presents a new collective morphological-composition-structural engineering strategy for exploiting the efficient bifunctional oxygen electrocatalysts, which is of great significance for high-performance rechargeable ZABs and wearable energy storage devices.

A Gas-Steamed Route to Mesoporous Open Metal-Organic Framework Cages Enhancing Flame Retardancy and Smoke Suppression of Polyurea

Up to now, metal-organic frameworks (MOFs) with open nanostructures have shown outstanding capabilities in trapping smoke particles compared to the original MOFs. However, only a few MOF-based strategies have been reported to synthesize hierarchical porous cages thus far, which are mainly restricted to environmentally unfriendly wet-chemical liquid methods. Herein, as a proof-of-concept, a gas-steamed metal-organic framework approach was designed to fabricate a series of cheeselike open cages with hierarchical porosity. Briefly, zeolitic imidazolate framework-67 (ZIF-67) and phytic acid were employed as precursor and etchant, respectively. Abandoning the conventional wet-chemical method, the coordination bond of ZIF-67 was cleaved by acidic steam, forming an open framework with a high specific surface area and a hierarchical porous structure. The universality of this method was also confirmed by the selection of different etchants. Impressively, they also show outstanding fume-toxic adsorption capability and labyrinth effects based on abundant and complex porous channels. At only 5 wt % loading, Co3O4@open ZIF-67 cage-2 (Co3O4@OZC-2) imparted polyurea (PUA) composites with a 21.2% limiting oxygen index, and the peak of heat release rate, total heat release, and total smoke production were reduced by around 37.5, 25.5, and 40.4%, respectively, compared to neat PUA. This work will shed light on the advanced structural design of polymer composites with high fire safety, especially smoke suppression performance, so as to obtain more feasible applications.

In Situ Regulating Cobalt/Iron Oxide-Oxyhydroxide Exchange by Dynamic Iron Incorporation for Robust Oxygen Evolution at Large Current Density

The key dilemma for green hydrogen production via electrocatalytic water splitting is the high overpotential required for anodic oxygen evolution reaction (OER). Co/Fe-based materials show superior catalytic OER activity to noble metal-based catalysts, but still lag far behind the state-of-the-art Ni/Fe-based catalysts probably due to undesirable side segregation of FeOOH with poor conductivity and unsatisfied structural durability under large current density. Here, a robust and durable OER catalyst affording current densities of 500 and 1000 mA cm-2 at extremely low overpotentials of 290 and 304 mV in base is reported. This catalyst evolves from amorphous bimetallic FeOOH/Co(OH)2 heterostructure microsheet arrays fabricated by a facile mechanical stirring strategy. Especially, in situ X-ray photoelectron spectroscopy (XPS) and Raman analysis decipher the rapid reconstruction of FeOOH/Co(OH)2 into dynamically stable Co1-x Fex OOH active phase through in situ iron incorporation into CoOOH, which perform as the real active sites accelerating the rate-determining step supported by density functional theory calculations. By coupling with MoNi4 /MoO2 cathode, the self-assembled alkaline electrolyzer can deliver 500 mA cm-2 at a low cell voltage of 1.613 V, better than commercial IrO2 (+) ||Pt/C(-) and most of reported transition metal-based electrolyzers. This work provides a feasible strategy for the exploration and design of industrial water-splitting catalysts for large-scale green hydrogen production.

Insights on MOF-derived metal-carbon nanostructures for oxygen evolution

Electrochemical water splitting has been regarded a promising method for the production of green hydrogen, addressing the need for efficient energy conversion and storage. However, it is severely hindered by the oxygen evolution reaction (OER) because of its multi-step four-electron transfer pathway with sluggish reaction kinetics. Microporous metal-organic-frameworks (MOFs), by virtue of large specific surface area, high porosity, tunable composition and morphology, find widespread use as precursors of metal-carbon nanostructures. The resulting carbon nanomaterials can well inherit the characteristics and advantages of the crystalline MOF precursors, and exhibit versatile application prospects in the fields of environment and energy, particularly in OER. Herein, a meticulous overview of the synthesis strategy for MOF-derived metal-carbon nanostructures and the origins of their enhanced OER properties has been demonstrated. We comprehensively illustrate these aspects across three dimensions: MOF selection, metal introduction, and carbon structures. Finally, the challenges and future prospects for this emerging field will be presented.

Versatile Structural Engineering of Metal-Organic Frameworks Enabling Switchable Catalytic Selectivity

The structure engineering of metal-organic frameworks (MOFs) forms the cornerstone of their applications. Nonetheless, realizing the simultaneous versatile structure engineering of MOFs remains a significant challenge. Herein, a dynamically mediated synthesis strategy to simultaneously engineer the crystal structure, defect structure, and nanostructure of MOFs is proposed. These include amorphous Zr-ODB nanoparticles, crystalline Zr-ODB-hz (ODB = 4,4'-oxalyldibenzoate, hz = hydrazine) nanosheets, and defective d-Zr-ODB-hz nanosheets. Aberration-corrected scanning transmission electron microscopy combined with low-dose high-angle annular dark-field imaging technique vividly portrays these engineered structures. Concurrently, the introduced hydrazine moieties confer self-reduction properties to the respective MOF structures, allowing the in situ installation of catalytic Pd nanoparticles. Remarkably, in the hydrogenation of vanillin-like biomass derivatives, Pd/Zr-ODB-hz yields partially hydrogenated alcohols as the primary products, whereas Pd/d-Zr-ODB-hz exclusively produces fully hydrogenated alkanes. Density functional theory calculations, coupled with experimental evidence, uncover the catalytic selectivity switch triggered by the change in structure type. The proposed strategy of versatile structure engineering of MOFs introduces an innovative pathway for the development of high-performance MOF-based catalysts for various reactions.

Amorphous copper(II)-cyanoimidazole frameworks as peroxidase mimics for hydrogen sulfide assay

Metal-organic frameworks with hierarchical porosities and exposed active sites are promising for ideal enzyme mimics. In this work, we developed a simple and feasible air oxidation strategy to prepare amorphous Cu(II)-cyanoimidazole frameworks (aCu(II)-CIFs) using CuI as the metal source in dimethylsulfoxide. Benefiting from coordination unsaturation and hierarchical porosities, aCu(II)-CIFs exhibit inherent peroxidase-mimic activity for rapid colorimetric reaction of 3,3',5,5'-tetramethylbenzidine (TMB). aCu(II)-CIFs were utilized to develop a colorimetric platform for specific H2S assay in the range of 0.6-30 μM, achieving a limit of detection (LOD) of 0.071 μM. Structural collapse of aCu(II)-CIFs and subsequent generation of stable CuS particles, along with reducibility of H2S, are likely responsible for suppressing TMBox conversion. The proposed method successfully detected H2S in real water samples, with a relative standard deviation (RSD) lower than 8.4%. This contribution is expected to offer unique insights into the amorphization mechanisms of MOFs and their potential applications.

Metal Alloys-Structured Electrocatalysts: Metal-Metal Interactions, Coordination Microenvironments, and Structural Property-Reactivity Relationships

Metal alloys-structured electrocatalysts (MAECs) have made essential contributions to accelerating the practical applications of electrocatalytic devices in renewable energy systems. However, due to the complex atomic structures, varied electronic states, and abundant supports, precisely decoding the metal-metal interactions and structure-activity relationships of MAECs still confronts great challenges, which is critical to direct the future engineering and optimization of MAECs. Here, this timely review comprehensively summarizes the latest advances in creating the MAECs, including the metal-metal interactions, coordination microenvironments, and structure-activity relationships. First, the fundamental classification, design, characterization, and structural reconstruction of MAECs are outlined. Then, the electrocatalytic merits and modulation strategies of recent breakthroughs for noble and non-noble metal-structured MAECs are thoroughly discussed, such as solid solution alloys, intermetallic alloys, and single-atom alloys. Particularly, unique insights into the bond interactions, theoretical understanding, and operando techniques for mechanism disclosure are given. Thereafter, the current states of diverse MAECs with a unique focus on structural property-reactivity relationships, reaction pathways, and performance comparisons are discussed. Finally, the future challenges and perspectives for MAECs are systematically discussed. It is believed that this comprehensive review can offer a substantial impact on stimulating the widespread utilization of metal alloys-structured materials in electrocatalysis.

Construction of High-Density Binuclear Site Catalysts from Double Framework Interfaces at the Cooling Stage

Low-nuclear site catalysts with dual atoms have the potential for applications in energy and catalysis chemistry. Understanding the formation mechanism of dual metal sites is crucial for optimizing local structures and designing desired binuclear sites catalysts. In this study, we demonstrate for the first time the formation process of dual atoms through the pyrolysis of the interface of a double framework using Zn atoms in metal-organic frameworks and Co atoms in covalent organic frameworks. We unambiguously revealed that the cooling stage is the key point to form the binuclear sites by employing the in situ synchrotron radiation X-ray absorption spectrum technique. The binuclear site catalysts show higher activity and selectivity than single dispersed atom catalysts for electrocatalytic oxygen reduction. This work guides us to synthesize and optimize the various binuclear sites for extensive catalytic applications.

(Fe-Co-Ni-Zn)-Based Metal-Organic Framework-Derived Electrocatalyst for Zinc-Air Batteries

Zinc-air batteries (ZABs) have garnered significant interest as a viable substitute for lithium-ion batteries (LIBs), primarily due to their impressive energy density and low cost. However, the efficacy of zinc-air batteries is heavily dependent on electrocatalysts, which play a vital role in enhancing reaction efficiency and stability. This scholarly review article highlights the crucial significance of electrocatalysts in zinc-air batteries and explores the rationale behind employing Fe-Co-Ni-Zn-based metal-organic framework (MOF)-derived hybrid materials as potential electrocatalysts. These MOF-derived electrocatalysts offer advantages such as abundancy, high catalytic activity, tunability, and structural stability. Various synthesis methods and characterization techniques are employed to optimize the properties of MOF-derived electrocatalysts. Such electrocatalysts exhibit excellent catalytic activity, stability, and selectivity, making them suitable for applications in ZABs. Furthermore, they demonstrate notable capabilities in the realm of ZABs, encompassing elevated energy density, efficacy, and prolonged longevity. It is imperative to continue extensively researching and developing this area to propel the advancement of ZAB technology forward and pave the way for its practical implementation across diverse fields.

Cyclobutanedicarboxylate Metal-Organic Frameworks as a Platform for Dramatic Amplification of Pore Partition Effect

Ultrafine tuning of MOF structures at subangstrom or picometer levels can help improve separation selectivity for gases with subtle differences. However, for MOFs with a large enough pore size, the effect from ultrafine tuning on sorption can be muted. Here we show an integrative strategy that couples extreme pore compression with ultrafine pore tuning. This strategy is made possible by unique combination of two features of the partitioned acs (pacs) platform: multimodular framework and exceptional tolerance toward isoreticular replacement. Specifically, we use one module (ligand 1, L1) to shrink the pore size to an extreme minimum on pacs. A compression ratio of about 30% was achieved (based on the unit cell c/a ratio) from prototypical 1,4-benzenedicarboxylate-pacs to trans-1,3-cyclobutanedicarboxylate-pacs. This is followed by using another module (ligand 2, L2) for ultrafine pore tuning (<3% compression). This L1-L2 strategy increases the C2H2/CO2 selectivity from 2.6 to 20.8 and gives rise to an excellent experimental breakthrough performance. As the shortest cyclic dicarboxylate that mimics p-benzene-based moieties using a bioisosteric (BIS) strategy on pacs, trans-1,3-cyclobutanedicarboxylate offers new opportunities in MOF chemistry.

N-Doped Carbon Shells Encapsulated Ru-Ni Nanoalloys for Efficient Hydrogen Evolution Reaction

The alkaline hydrogen evolution reaction (HER) is of great significance for the large-scale green H₂ production. Currently, pressing challenges in the fabrication of cost-effective HER electrocatalysts are related to their sluggish water dissociation kinetics. Herein, a facile strategy to accelerate the desorption of HER intermediates and water dissociation is proposed. RuNi nanoalloy confined within N-doped carbon shells (Ru₇ Ni₃ @NC/C) with optimized Ru/Ni ratio and the dicyandiamide dosage was prepared. It displays an overpotential (η₁₀ ) of 16 mV, Tafel slope of 29.9 mV dec^-1 , and long-term stability over 10 000 cycles. The decent HER performance on Ru₇ Ni₃ @NC/C stems from the core-shell structure that is favoring the exposure of dispersed active sites, and the synergistic effect to promote water capture and dissociation. This work provides insight into the relationship between the HER performance and the electrochemical behavior of the intermediate adsorbed state, and paves an avenue toward rational design efficient electrocatalysts for HER.

Advances of Electroactive Metal-Organic Frameworks

The preparation of electroactive metal-organic frameworks (MOFs) for applications of supercapacitors and batteries has received much attention and remarkable progress during the past few years. MOF-based materials including pristine MOFs, hybrid MOFs or MOF composites, and MOF derivatives are well designed by a combination of organic linkers (e.g., carboxylic acids, conjugated aromatic phenols/thiols, conjugated aromatic amines, and N-heterocyclic donors) and metal salts to construct predictable structures with appropriate properties. This review will focus on construction strategies of pristine MOFs and hybrid MOFs as anodes, cathodes, separators, and electrolytes in supercapacitors and batteries. Descriptions and discussions follow categories of electrochemical double-layer capacitors (EDLCs), pseudocapacitors (PSCs), and hybrid supercapacitors (HSCs) for supercapacitors. In contrast, Li-ion batteries (LIBs), Lithium-sulfur batteries (LSBs), Lithium-oxygen batteries (LOBs), Sodium-ion batteries (SIBs), Sodium-sulfur batteries (SSBs), Zinc-ion batteries (ZIBs), Zinc-air batteries (ZABs), Aluminum-sulfur batteries (ASBs), and others (e.g., LiSe, NiZn, H⁺ , alkaline, organic, and redox flow batteries) are categorized for batteries.

Highly Stable Fe/Co-TPY-MIL-88(NH2) Metal-Organic Framework (MOF) in Enzymatic Cascade Reactions for Chemiluminescence-Based Detection of Extracellular Vesicles

Metal-Organic Frameworks (MOFs) can deliver many advantages when acting as enzyme mimics to assist with signal amplification in molecular detection: they have abundant active catalytic sites per unit volume of the material; their structures and elemental compositions are highly tunable, and their high specific surface area and porous property can assist with target separation and enrichment. In the present work, we have demonstrated that, by adding the pore partition agent, 2,4,6-tris(4-pyridyl)pyridine (TPY) during synthesis of the bimetallic Fe/Co-MIL-88(NH₂) MOF to block the open metal sites, a highly porous MOF of Fe/Co-TPY-MIL-88(NH₂) can be produced. This material also exhibits high stability in basic solutions and biofluids and possesses high peroxidase-mimicking activity, which can be utilized to produce long-lasting chemiluminescence (CL) from luminol and H₂O₂. Moreover, acting as the peroxidase-mimic, the Fe/Co-TPY-MIL-88(NH₂) MOF can form the enzymatic cascade with glucose oxidase (GOx) for biomarker detection. When applied to detect extracellular vesicles (EVs), the MOF material and GOx are brought to the proximity on the EVs through two surface proteins, which triggers the enzyme cascade to produce high CL from glucose and luminol. EVs within the concentration range of 5 × 10⁵ to 4 × 10⁷ particles/mL can be detected with an LOD of 1 × 10⁵ particles/mL, and the method can be used to analyze EV contents in human serum without sample preparation and EV purification. Overall, our work demonstrates that the high versatility and tunability of the MOF structures could bring in significant benefits to biosensing and enable ultrasensitive detection of biomarkers with judicious material designs.

Construction of Bimetallic Metal-Organic Frameworks with the Nanosheet-Assembled Hierarchical Hollow Structure for CO2 Fixation

Incorporating secondary metal nodes with functionality into organic ligand nodes to form a bimetallic metal-organic frameworks (MOFs) would facilitate an enhancement in properties and broaden applied areas of MOFs. Hierarchical tubular Cu/Zn-MOF-74 assembled by nanosheet arrays is synthesized at ambient temperature and pressure by phase transformation of Cu-based precursor MOF in immersion solution with Zn²⁺. The content of Zn in Cu/Zn-MOF-74 can be controlled by adjusting the concentration of Zn²⁺ in immersion solution, and it can reach a maximum of 36.4%. Moreover, the catalytic activity toward cycloaddition of CO₂ with styrene oxide of Cu/Zn-MOF-74 is improved significantly compared with that of monometallic Cu-MOF-74. Meanwhile, the advanced hierarchical tubular structure contributing to enhancement in catalytic activity enables Cu/Zn-MOF-74 to present higher conversion toward this cycloaddition of CO₂ than traditional rod-like Cu/Zn-MOF-74. This templated synthesis would provide an opportunity for designing various bimetallic MOFs or MOF-based compounds with improved performances in multiple applications.

Bimetallic Metal-Organic Framework Fe/Co-MIL-88(NH2) Exhibiting High Peroxidase-like Activity and Its Application in Detection of Extracellular Vesicles

Metal-organic frameworks (MOFs) have many attractive features, including tunable composition, rigid structure, controllable pore size, and large specific surface area, and thus are highly applicable in molecular analysis. Depending on the MOF structure, a high number of unsaturated metal sites can be exposed to catalyze chemical reactions. In the present work, we report that using both Co(II) and Fe(III) to prepare the MIL-88(NH₂) MOF, we can produce the bimetallic MOF that can catalyze the conversion of 3,3',5,5″-tetramethylbenzidine (TMB) to a color product through a reaction with H₂O₂ at a higher reaction rate than the monometallic Fe-MIL-88(NH₂). The Michaelis constants (K_m) of the catalytic reaction for TMB and H₂O₂ are 3-5 times smaller, and the catalytic constants (k_cat) are 5-10 times higher than those of the horseradish peroxidase (HRP), supporting ultrahigh peroxidase-like activity. These values are also much more superior to those of the HRP-mimicking MOFs reported previously. Interestingly, the bimetallic MOF can be coupled with glucose oxidase (GOx) to trigger the cascade enzymatic reaction for highly sensitive detection of extracellular vesicles (EVs), a family of important biomarkers. Through conjugation to the aptamer that recognizes the marker protein on EV surface, the MOF can help isolate the EVs from biological matrices, which are subsequently labeled by GOx via antibody recognition. The cascade enzymatic reaction between MOF and GOx enables the detection of EVs at a concentration as low as 7.8 × 10⁴ particles/mL. The assay can be applied to monitor EV secretion by cultured cells and also can successfully detect the different EV quantities in the sera samples collected from cancer patients and healthy controls. Overall, we prove that the bimetallic Fe/Co-MIL-88(NH₂) MOF, with its high peroxidase activity and high biocompatibility, is a valuable tool deployable in clinical assays to facilitate disease diagnosis and prognosis.

Phase-Controlled Synthesis of Nickel-Iron Nitride Nanocrystals Armored with Amorphous N-Doped Carbon Nanoparticles Nanocubes for Enhanced Overall Water Splitting

Transition metal nitrides (TMNs) nanostructures possess distinctive electronic, optical, and catalytic properties, showing great promise to apply in clean energy, optoelectronics, and catalysis fields. Nonetheless, phase-regulation of NiFe-bimetallic nitrides nanocrystals or nanohybrid architectures confronts challenges and their electrocatalytic overall water splitting (OWS) performances are underexplored. Herein, novel pure-phase Ni_{2+ x} Fe_{2- x} N nanocrystals armored with amorphous N-doped carbon (NC) nanoparticles nanocubes (NPNCs) are obtained by controllable nitridation of NiFe-Prussian-blue analogues derived oxides/NC NPNCs under Ar/NH₃ atmosphere. Such Ni_{2+ x} Fe_{2- x} N/NC NPNCs possess mesoporous structures and show enhanced electrocatalytic activity in 1 m KOH electrolyte with the overpotential of 101 and 270 mV to attain 10 and 50 mA cm^-2 current toward hydrogen and oxygen evolution reactions, outperforming their counterparts (mixed-phase NiFe₂ O₄ /Ni₃ FeN/NC and NiFe oxides/NC NPNCs). Remarkably, utilizing them as bifunctional catalysts, the assembled Ni_{2+ x} Fe_{2- x} N/NC||Ni_{2+ x} Fe_{2- x} N/NC electrolyzer only needs 1.51 V cell voltage for driving OWS to approach 10 mA cm^-2 water-splitting current, exceeding their counterparts and the-state-of-art reported bifunctional catalysts-based devices, and Pt/C||IrO₂ couples. Additionally, the Ni_{2+ x} Fe_{2- x} N/NC||Ni_{2+ x} Fe_{2- x} N/NC manifests excellent durability for OWS. The findings presented here may spur the development of advanced TMNs nanostructures by combining phase, structure engineering, and hybridization strategies and stimulate their applications toward OWS or other clean energy fields.

Optimizing Photodetectors in Two-Dimensional Metal-Metalloporphyrinic Framework Thin Films

Two-dimensional (2D) metalloporphyrin-based MOF thin films possessing abundant π-π interactions are promising materials for photoelectronic devices, but no reports on fabrication of photodetectors are available so far. Herein, a series of 2D MOF Zn2[TCPP(M)] (named ZnTCPP(M); TCPP = 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin; M = Zn, Mn, Fe, and H2) films with [001] orientation are fabricated on SiO2/Si substrates by the liquid-phase epitaxial (LPE) layer-by-layer (lbl) approach and further assembled to photodetectors. The obtained ZnTCPP(M)-based photodetectors exhibit an excellent photoresponse due to abundant π-π stacking between the MOF layers. Moreover, the metalloporphyrinic groups in ZnTCPP(M) have a significant influence on modulating the photoresponse of the photodetectors, among which the prepared ZnTCPP(Zn) film-based device exhibits the best photodetection performance with a high on/off ratio of 2.3 × 104, responsivity (Rλ, up to 10.3 A W-1), short rise/fall times (0.09/0.07 s), and a large detectivity (D*) of 8.1 × 1013 Jones. Density functional theory (DFT) calculations reveal that the perturbation of the ring π-electron system and the introduction of low-lying states as well as the large delocalization of the metalloporphyrinic group will adjust the photodetection performance of ZnTCPP(M) films. These results will provide a new understanding of the modulation of 2D metalloporphyrinic MOFs toward photodetection performance and perspective for the fabrication of photoelectronic devices.

Zeolitic imidazolate framework (ZIF-8)/polyacrylonitrile derived millimeter-sized hierarchical porous carbon beads for peroxymonosulfate catalysis

Well dispersed nanocatalysts on porous substrate with macroscopic morphology are highly desired for the application of heterogeneous catalysis. Traditional fabrication process suffers from multiple steps for controlling the structure on nanocatalysts and matrix or both. Herein, we report a facile strategy for the synthesis of millimeter-sized hierarchical porous carbon beads (HPCBs) which containing well dispersed hollow-nano carbon boxes for peroxymonosulfate catalysis. Specially, the precursors of HPCBs were prepared by phase inversion method, which involving introduction of zeolitic imidazolate framework (ZIF-8) nanocubes into polyacrylonitrile (PAN) solutions followed by solidification of the mixture. After pyrolysis, nitrogen doped and hierarchical porous HPCBs with diameter of about 1.2 mm were obtained. The merits of our synthesis strategy lie in that synchronizes the hollow microstructure evolution with the shaping of ZIF-8 nanocubes into millimeter scale beads. Attribute to its special structure feature and the appropriate chemical composition, the resultant millimeter-sized HPCBs exhibit enhanced catalytic performance by activation of peroxymonosulfate (PMS) for tetracycline degradation. The degradation efficiency of TC is up to 85.1% within 120 min, which is 18% higher than that of ZIF8-Solid/PAN carbon bead (SPCBs). In addition, the possible decomposition pathways, main reactive oxygen species, and reasonable enhanced mechanism for the HPCBs/PMS system are systematically investigated by quenching experiments, electron paramagnetic resonance (EPR) and liquid chromatography-mass spectrometry (LC-MS). This work addresses the issue of easy aggregation and recycling of carbon materials in industrial productions and extends the prospects of carbon materials in engineering applications.

Simultaneous Control of Pore-Space Partition and Charge Distribution in Multi-Modular Metal-Organic Frameworks

We report here a strategy for making anionic pacs type porous materials by combining pore space partition with charge reallocation. The method uses the first negatively charged pore partition ligand (2,5,8-tri-(4-pyridyl)-1,3,4,6,7,9-hexaazaphenalene, H-tph) that simultaneously enables pore partition and charge reallocation. Over two dozen anionic pacs materials have been made to demonstrate their excellent chemical stability and a high degree of tunability. Notably, Ni₃ -bdt-tph (bdt=1,4-benzeneditetrazolate) exhibits month-long water stability, while CoV-bdt-tph sets a new benchmark for C₂ H₂ storage capacity under ambient conditions for ionic MOFs. In addition to tunable in-framework modules, we show feasibility to tune the type and concentration of extra-framework counter cations and their influence on both stability and capability to separate industrial C₃ H₈ /C₃ H₆ and C₆ H₆ /C₆ H₁₂ mixtures.

Process of metal-organic framework (MOF)/covalent-organic framework (COF) hybrids-based derivatives and their applications on energy transfer and storage

The fossil-fuel shortage and severe environmental issues have posed ever-increasing demands on clean and renewable energy sources, for which the exploration of electrocatalysts has been a big challenge toward energy transfer and storage. Some indispensable features of electrocatalysts, such as large surface area, controlled structure, high porosity, and effective functionalization, have been proved to be critical for the improvement of electrocatalytic activities. Recently, the rapid expansion of metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and porous-organic polymers has provided extensive opportunities for the development of various electrocatalysts. Moreover, combining diverse descriptions of porous-organic frameworks (such as MOFs and COFs) can generate amazing and fantastic properties, affording the formed MOF/COF (including core-shell MOF@MOF and MOF@COF and layer-on-layer MOF-on-MOF or COF-on-MOF) heterostructures wide applications in diverse fields, especially in clean energy and energy transfer. To further boosts electronic conductivity, catalytic performances, and energy storage abilities, these MOF/COF hybrid materials have been widely utilized as versatile precursors for the manufacture of transition metal catalysts embedded within mesoporous carbon nitrides (M@CN_x) and porous carbon nitride frameworks (CN_x) via a facile pyrolysis process. Given that these M@CN_x and CN_x hybrids are composed of abundant catalytic centers, rich functionalities, and large specific surface areas, vast applications in energy transfer and energy storage fields can be realized. In this mini-review, we summarize the preparation strategies of MOF/COF-based hybrids, as well as their derivatives, nanostructure formation mechanism of M@CN_x and CN_x hybrids from MOF/COF-based hybrid materials, and their applications as catalysts for driving diverse reactions and electrode materials for energy storage. Further, current challenges and future prospects of applying these derivatives into energy conversion and storage devices are also discussed.

ZIF-Derived Metal/N-Doped Porous Carbon Nanocomposites: Efficient Catalysts for Organic Transformations

Recently, zeolitic imidazolate framework (ZIF)-derived metal/N-doped porous carbon nanocomposites (M@NCs) have emerged as a class of appealing heterogeneous catalysts applied in organic synthesis, and the striking features mainly involve low-cost...

Recent advancement in bimetallic metal organic frameworks (M’MOFs): Synthetic challenges and applications

Metal-organic frameworks (MOFs) is a burgeoning research field and has received increasing interest in recent years due to their inherent advantages of inorganic metal ions, range of organic linkers, tunable...

A Ni(ii) metal–organic framework with helical channels for the capture of iodine via guest exchange induced amorphization

A Ni(ii) MOF based on a imidazole–tetrazole heterotopic tripodal ligand was constructed. It exhibits abilities for the stable capture of iodine molecules present in cyclohexane, water, and vapor, via amorphization induced by guest exchange.

Aluminum molecular rings bearing amino-polyalcohol for iodine capture

Amino-polyalcohol-solvothermal synthesis leads to the isolation of a broad range of aluminum molecular rings, which exhibit considerable affinity towards iodine molecules.

State of the art developments and prospects of metal-organic frameworks for energy applications

The progress on technologies for the cleaner and ecological transformation and storage of energy to combat effluence or pollution and the impending energy dilemma has recently attracted interest from energy research groups, particularly in the field of coordination chemistry, among inorganic chemists. Carriers for storing energy or facilitating mass and e^- transport are considered significant for energy conversion. Accordingly, considering their properties such as large surface area, low cost, customizable pore diameter, tunable topologies, low densities, and variable frameworks, MOFs (metal-organic frameworks) and their derivatives are well-suited for this purpose. MOFs are an innovative category of porous and crystalline materials, which have gained significant interest in recent years. Thus, herein, we highlight the state of the art progress on MOFs for energy-based applications, as perfect compounds and elements in compound assemblies for converting solar energy, lithium-ion arrays, fuel devices, hydrogen production, photocatalytic CO₂ reduction, proton conduction, etc. In addition, the substantial progress achieved in the production of various composites and derivatives containing MOFs with particular focus on supercapacitors and gas adsorption and storage is summarized, concentrating on the correlation between their coordination structural frameworks and applications in the field of energy. The current improved strategies, challenges, and future prospects are also presented in view of the coordination chemistry governing the structural modification of MOFs for energy applications.

Concluding remarks: current and next generation MOFs

This paper describes the content of my "Concluding remarks" talk at the Faraday Discussion meeting on "MOFs for energy and the environment" (online, 23-25 June 2021). The panel consisted of sessions on the design of MOFs and MOF hybrids (synthetic chemistry), their applications (e.g., capture, storage, separation, electrical devices, photocatalysis), advanced characterization (e.g., transmission electron microscopy, solid-state nuclear magnetic resonance), theory and modeling, and commercialization. MOF chemistry is undergoing a significant evolution from simply network chemistry to the chemistry of synergistic integration with heterogeneous materials involving other disciplines (we call this the fourth generation type). As reflected in the papers of the invited speakers and discussions with the participants, the present and future of this field will be described in detail.

Impact of Iron in Three-Dimensional Co-MOF for Electrocatalytic Water Oxidation

The integration of iron (Fe) into a cobalt metal-organic framework (Co-MOF) tunes the electronic structure of the parent MOF as well as enhances their electrocatalytic characteristics. By using pyrazine and hydrofluoric acid, we have synthesized three-dimensional Co-MOF [CoFC₄H₄N₂(SO₄)_0.5], (1), and Fe-MOF [FeFC₄H₄N₂(SO₄)_0.5], (2), through a single-step solvothermal method. Further, a series of bimetallic (having both Co and Fe metal centers) MOFs [Co_1-xFe_xFC₄H₄N₂(SO₄)_0.5] were synthesized with variable concentrations of Fe, and their electrocatalytic performances were analyzed. The optimized amount of Fe significantly impacted the electrocatalytic behavior of the bimetallic MOF toward water oxidation. Particularly, the Co_0.75Fe_0.25-MOF needs only 239 and 257 mV of overpotential to deliver 10 and 50 mA/cm² current density, respectively, in alkaline electrolytic conditions. The Co_0.75Fe_0.25-MOF shows a lower Tafel slope (42 mV/dec.) among other bimetallic MOFs and even the commercial RuO₂, and it has excellent durability (with ∼8 mV increases in overpotential after 18 h of electrolysis) and 97.05% Faradaic efficiency, which further evident its catalytic excellency. These findings explore the intrinsic properties of MOF-based electrocatalysts and prospect the suitability for future water electrolysis.

A Gas-Steamed MOF Route to P-Doped Open Carbon Cages with Enhanced Zn-Ion Energy Storage Capability and Ultrastability

Carbon micro/nanocages have received great attention, especially in electrochemical energy-storage systems. Herein, as a proof-of-concept, a solid-state gas-steamed metal-organic-framework approach is designed to fabricate carbon cages with controlled openings on walls, and N, P dopants. Taking advantage of the fabricated carbon cages with large openings on their walls for enhanced kinetics of mass transport and N, P dopants within the carbon matrix for favoring chemical adsorption of Zn ions, when used as carbon cathodes for advanced aqueous Zn-ion hybrid supercapacitors (ZHSCs), such open carbon cages (OCCs) display a wide operation voltage of 2.0 V and an enhanced capacity of 225 mAh g^-1 at 0.1 A g^-1 . Also, they exhibit an ultralong cycling lifespan of up to 300 000 cycles with 96.5% capacity retention. Particularly, such OCCs as electrode materials lead to a soft-pack ZHSC device, delivering a high energy density of 97 Wh kg^-1 and a superb power density of 6.5 kW kg^-1 . Further, the device can operate in a wide temperature range from -25 to + 40 °C, covering the temperatures for practical applications in daily life.

Recent Advances on MOF Derivatives for Non-Noble Metal Oxygen Electrocatalysts in Zinc-Air Batteries

Oxygen electrocatalysts are of great importance for the air electrode in zinc-air batteries (ZABs). Owing to the high specific surface area, controllable pore size and unsaturated metal active sites, metal-organic frameworks (MOFs) derivatives have been widely studied as oxygen electrocatalysts in ZABs. To date, many strategies have been developed to generate efficient oxygen electrocatalysts from MOFs for improving the performance of ZABs. In this review, the latest progress of the MOF-derived non-noble metal-oxygen electrocatalysts in ZABs is reviewed. The performance of these MOF-derived catalysts toward oxygen reduction, and oxygen evolution reactions is discussed based on the categories of metal-free carbon materials, single-atom catalysts, metal cluster/carbon composites and metal compound/carbon composites. Moreover, we provide a comprehensive overview on the design strategies of various MOF-derived non-noble metal-oxygen electrocatalysts and their structure-performance relationship. Finally, the challenges and perspectives are provided for further advancing the MOF-derived oxygen electrocatalysts in ZABs.

Divergent Paths, Same Goal: A Pair-Electrosynthesis Tactic for Cost-Efficient and Exclusive Formate Production by Metal-Organic-Framework-Derived 2D Electrocatalysts

Electrosynthesis of formic acid/formate is a promising alternative protocol to industrial processes. Herein, a pioneering pair-electrosynthesis tactic is reported for exclusively producing formate via coupling selectively electrocatalytic methanol oxidation reaction (MOR) and CO₂ reduction reaction (CO₂ RR), in which the electrode derived from Ni-based metal-organic framework (Ni-MOF) nanosheet arrays (Ni-NF-Af), as well as the Bi-MOF-derived ultrathin bismuthenes (Bi-enes), both obtained through an in situ electrochemical conversion process, are used as efficient anodic and cathodic electrocatalysts, respectively, achieving concurrent yielding of the same high-value product at both electrodes with greatly reduced energy input. The as-prepared Ni-NF-Af only needs quite low potentials to reach large current densities (e.g., 100 mA cm^-2 @1.345 V) with ≈100% selectivity for anodic methanol-to-formate conversion. Meanwhile, for CO₂ RR in the cathode, the as-prepared Bi-enes can simultaneously exhibit near-unity selectivity, large current densities, and good stability in a wide potential window toward formate production. Consequently, the coupled MOR//CO₂ RR system based on the distinctive MOF-derived catalysts displays excellent performance for pair-electrosynthesis of formate, delivering high current densities and nearly 100% selectivity for formate production in both the anode and the cathode. This work provides a novel way to design advanced MOF-derived electrocatalysts and innovative electrolytic systems for electrochemical production of value-added feedstocks.

In Situ Anchoring Polymetallic Phosphide Nanoparticles within Porous Prussian Blue Analogue Nanocages for Boosting Oxygen Evolution Catalysis

The controllable synthesis of metal-based nanoclusters for heterogeneous catalytic reactions has received considerable attention. Nevertheless, manufacturing these architectures, while avoiding aggregation and retaining surface activity, remains challenging. Herein, for the first time we designed NiCoFe-Prussian blue analogue (PBA) nanocages as a support for in situ dispersion and anchoring of polymetallic phosphide nanoparticles (pMP-NPs). Benefiting from the porous surfaces and the synergistic effects between pMP-NPs and the cyano groups in PBA, the NiCoFe-P-NP@NiCoFe-PBA nanocages exhibit a significantly enhanced catalytic activity for oxygen evolution reaction (OER) with an overpotential of 223 mV at 10 mA cm^-2 and a Tafel slope of 78 mV dec^-1, outperforming the NiCoFe-PBA nanocubes, NiCoFe-P nanocages, NiFe-P-NP@NiFe-PBA nanocubes, and CoFe-P-NP@CoFe-PBA nanoboxes. This work not only offers the synthesis strategy of in situ anchoring pMP-NPs on PBA nanocages but also provides a new insight into optimized Gibbs free energy of OER by regulating electron transfer from metallic phosphides to PBA substrate.

Single-Atom Catalysts Derived from Metal-Organic Frameworks for Electrochemical Applications

Single-atom catalysts (SACs) have received tremendous attention due to their extraordinary catalytic performances. The synthesis of this kind of catalysts is highly desired and challenging. In the last few years, metal-organic frameworks (MOFs) have been demonstrated as a promising precursor for fabricating SACs. In this review, the progress and recent advances in the synthesis of MOF-derived SACs and their electrochemical applications are summarized. First, the synthetic approaches based on MOFs and accessible characterization techniques for SACs as well as their advantages/disadvantages are discussed. Then, the electrochemical applications of these MOF-derived SACs including the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), CO₂ reduction reaction (CO₂ RR), nitrogen reduction reaction (NRR), and other energy-related reactions are reviewed. Finally, insights into the current challenges and future prospects of this field are briefly presented.

Designing MOF Nanoarchitectures for Electrochemical Water Splitting

Electrochemical water splitting has attracted significant attention as a key pathway for the development of renewable energy systems. Fabricating efficient electrocatalysts for these processes is intensely desired to reduce their overpotentials and facilitate practical applications. Recently, metal-organic framework (MOF) nanoarchitectures featuring ultrahigh surface areas, tunable nanostructures, and excellent porosities have emerged as promising materials for the development of highly active catalysts for electrochemical water splitting. Herein, the most pivotal advances in recent research on engineering MOF nanoarchitectures for efficient electrochemical water splitting are presented. First, the design of catalytic centers for MOF-based/derived electrocatalysts is summarized and compared from the aspects of chemical composition optimization and structural functionalization at the atomic and molecular levels. Subsequently, the fast-growing breakthroughs in catalytic activities, identification of highly active sites, and fundamental mechanisms are thoroughly discussed. Finally, a comprehensive commentary on the current primary challenges and future perspectives in water splitting and its commercialization for hydrogen production is provided. Hereby, new insights into the synthetic principles and electrocatalysis for designing MOF nanoarchitectures for the practical utilization of water splitting are offered, thus further promoting their future prosperity for a wide range of applications.