Cobalt Metal-Organic Framework Based on Layered Double Nanosheets for Enhanced Electrocatalytic Water Oxidation in Neutral Media

New Layered Chalcogenide-Type Metal Sulfide Materials with Improved Properties for Solar Fuel Production Applications

Novel lamellar chalcogenide materials, named as ITQ-75, are synthesized, focusing on the advancement and alteration of metal (tin and zinc) sulfide-based microstructured materials. These are achieved via hydro(solvo)thermal processes in the presence of N-heterocyclic aromatic structural directing agents. The comprehensive characterization of these materials included fine-tuning their electronic structure through a metal doping strategy and enhancing their accessibility by modifying the synthesis gel composition. This modification involved altering the gel's viscosity or incorporating mesoporogen agents such as saccharide moieties. The most promisingly modified ITQ-75-type materials demonstrated optical band gap values of ≈2.0 eV, falling within the optimal range for efficient solar fuel production processes. Furthermore, the photocatalytic performance of these optimized lamellar chalcogenides is assessed using the water-splitting reaction for hydrogen generation in the gas phase and without any sacrificial reagent. These new noble metal-free materials are revealed to be among the most efficient to date (up to 7 µmolH2 h cm- 2). The results confirm the potential of these materials as promising photocatalysts for solar fuel production applications.

Nanosheet arrays derived from ZIF-67 grown on three-dimensional frameworks for the electrocatalytic oxygen evolution reaction

Hydrogen energy has become one of the most promising substitutes for conventional fuels because of its high calorific value and green and renewable advantages. Among various hydrogen production strategies, the water splitting hydrogen production strategy stands out. Therefore, it is very important to develop efficient and cheap oxygen evolution reaction (OER) electrocatalysts for hydrogen production by electrolysis of water. In this work, nickel selenide grown on nickel foam (NF) with good electrical conductivity and excellent catalytic performance, i.e. NiSex/NF, was selected as the three-dimensional conducting substrate, and the active material ZIF-67 was successfully compounded on the conductive substrate by using the in situ growth strategy. A series of self-supporting materials ZIF-67/NiSex/NF were obtained, which can be directly used as working electrodes for the electrocatalytic OER. The self-supporting material ZIF-67/NiSex/NF-1 can achieve a low overpotential of 353 mV at a current density of 100 mA cm-2 with a small Tafel slope of 107 mV dec-1, and excellent stability for 55 hours of continuous OER at a current density of 50 mA cm-2 in an alkaline medium. Benefiting from the unique layered structure and the synergy between Co and Se optimizing the electronic structure, ZIF-67/NiSex/NF-1 when used directly as an electrode shows exceptional OER catalytic performance at high current density.

Rational Construction of Co4(μ-O)6(COO)6 SBU-Based MOFs through Mixed-Ligand Strategy to Enhance Electrocatalytic Oxygen Evolution Performance

Metal-organic frameworks (MOFs) are increasingly becoming an important choice for developing robust and efficient electrocatalysts; therefore, exploring the relationship between the structure, catalytic activity, and stability of MOFs is of great significance. MOFs 1-3 with different spatial configurations are designed and synthesized based on linear pyridine ligands, tetragonal carboxylic acid ligands, and triangular carboxylic acid ligands, while MOF 4 displays a three-dimensional (3D) supramolecule assembled through a mixed-ligand strategy. Compared with MOFs 1-3, MOF 4 has the lowest overpotential of 106 mV (at 10 mA·cm-2) and a Tafel slope of 80.9 mV·dec-1, as well as sturdy long-term stability in the process of oxygen evolution reaction (OER). The presence of dense metal clusters and μ3-O promotes the optimal catalytic performance of MOF 4. Density functional theory (DFT) calculations of MOF 4 demonstrate that the process from O* to OOH* is the rate-determining step. This investigation further reveals the relationship between MOF structural composition and electrocatalytic OER performance and provides an effective strategy for the assembly of MOF-based electrocatalysts.

Efficient Electrochemical Sensing of Chlorpromazine with a Composite of Multiwalled Carbon Nanotubes and a Thiacalix[4]arene-Based Metal-Organic Framework

Chlorpromazine (CPMZ) is a representative drug for the treatment of psychiatric disorders. Excessive use of CPMZ could result in some serious health problems, and therefore, construction of a sensitive electrochemical sensor for CPMZ detection is greatly significant for human health. Herein, a feasible electrochemical method for the detection of CPMZ was provided. To design a suitable electrode surface modifier, a new two-dimensional (2D) thiacalix[4]arene-based metal-organic framework was designed and synthesized under solvothermal conditions, namely, [Co(TMPA)Cl2]MeOH·2EtOH·2H2O (Co-TMPA). Afterward, a series of composite materials was prepared by combining Co-TMPA with highly conductive carbon materials. Markedly, Co-TMPA/MWCNT-2@GCE (GCE = glassy carbon electrode, MWCNT = multiwalled carbon nanotube) exhibited the best electrocatalytic performance for CPMZ detection due to the synergistic effect between MWCNT and Co-TMPA. Particularly, it featured a low limit of detection (8 nM) and a wide linear range (0.05 to 1350 μM) in quantitative determination of CPMZ. Meanwhile, the sensor possessed excellent stability, selectivity, and reproducibility. Importantly, Co-TMPA/MWCNT-2@GCE was employed to analyze CPMZ in urine and serum with satisfactory recoveries (98.87-102.17%) and relative standard deviations (1.44-3.80%). Furthermore, the electrochemical detection accuracy of the Co-TMPA/MWCNT-2@GCE sensor was verified with the ultraviolet-visible spectroscopy technique. This work offers a promising sensor for the efficient analysis of drug molecules.

Shape-Preserved CoFeNi-MOF/NF Exhibiting Superior Performance for Overall Water Splitting across Alkaline and Neutral Conditions

This study reported a multi-functional Co0.45Fe0.45Ni0.9-MOF/NF catalyst for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting, which was synthesized via a novel shape-preserving two-step hydrothermal method. The resulting bowknot flake structure on NF enhanced the exposure of active sites, fostering a superior electrocatalytic surface, and the synergistic effect between Co, Fe, and Ni enhanced the catalytic activity of the active site. In an alkaline environment, the catalyst exhibited impressive overpotentials of 244 mV and 287 mV at current densities of 50 mA cm-2 and 100 mA cm-2, respectively. Transitioning to a neutral environment, an overpotential of 505 mV at a current density of 10 mA cm-2 was achieved with the same catalyst, showing a superior property compared to similar catalysts. Furthermore, it was demonstrated that Co0.45Fe0.45Ni0.9-MOF/NF shows versatility as a bifunctional catalyst, excelling in both OER and HER, as well as overall water splitting. The innovative shape-preserving synthesis method presented in this study offers a facile method to develop an efficient electrocatalyst for OER under both alkaline and neutral conditions, which makes it a promising catalyst for hydrogen production by water splitting.

A series of isostructural metal-organic frameworks for an enhanced electro-catalytic oxygen evolution reaction

Three new isostructural MOFs (ZnTIA, CoTIA and CdTIA) were synthesized by the solvothermal synthesis of the organic linker 5-triazole isophthalic acid (5-TIA) with the transition metals Zn(II), Co(II) and Cd(II) in the presence of the structure directing agent tetramethyl ammonium chloride (TMA). These three MOFs were characterized thoroughly by ScXRD, PXRD, FT-IR, TGA, BET and SEM. They have excellent thermal and water stabilities. Among all these MOFs mentioned, pristine CoTIA exhibited excellent electrocatalytic activity toward the oxygen evolution reaction (OER). It exhibits a Tafel slope of 68.9 mV dec-1 with an overpotential of 337 mV at 10 mA cm-2 current density. The OER activity of the CoTIA MOF is relatively equivalent to that of the state-of-the-art catalyst (RuO2). Furthermore, the mechanical stability of crystalline ZnTIA, CoTIA and CdTIA MOFs was tested under ball mill pressure. The result showed that all the MOFs exhibit low tolerance to mechanical force because their structure was highly distorted or collapsed under such pressure, which is reflected by their poor electrocatalytic OER activity.

A mixed-ligand Co metal-organic framework and its carbon composites as excellent electrocatalysts for the oxygen evolution reaction in green-energy devices

Oxygen evolution reaction (OER) electrocatalysts are frequently made from noble metal-based oxides like ruthenium/iridium oxides. However, because of their scarcity and high price, researchers are now focusing on creating innovative OER catalysts based on affordable transition metals that have improved electrical conductivity and accessibility to active sites. Metal-organic frameworks (MOFs), a unique class of inorganic materials with excellent physical and chemical properties, have witnessed significant progress in promising green energy systems. In this work, a novel mixed-ligand metal-organic framework [Co(μ-1κN,2κN'-BDP)(μ3-1κoo',2κo''2κo'''-BTC)]n·nH2O (BDP = boron-dipyrromethene or BODIPY; BTC = benzene tricarboxylate) denoted as CoBDPMOF has been synthesized, and its composites with different carbon materials have been designed. Compared to the pristine MOF, the composites showed enhanced electrocatalytic activity toward the oxygen evolution reaction (OER) in alkaline media. In addition, the CoBDPMOF with activated carbon showed the highest OER performance with a low Tafel slope (82 mV dec-1) and the highest j600 (59.8 mA cm-2), outperforming noble metal IrO2, the OER benchmark electrocatalyst. This study presents new insights into the design and application of CoBDPMOF-based materials for energy conversion and suggests promising avenues for further research and development in electrocatalysis.

2D Materials Nanoarchitectonics for 3D Structures/Functions

It has become clear that superior material functions are derived from precisely controlled nanostructures. This has been greatly accelerated by the development of nanotechnology. The next step is to assemble materials with knowledge of their nano-level structures. This task is assigned to the post-nanotechnology concept of nanoarchitectonics. However, nanoarchitectonics, which creates intricate three-dimensional functional structures, is not always easy. Two-dimensional nanoarchitectonics based on reactions and arrangements at the surface may be an easier target to tackle. A better methodology would be to define a two-dimensional structure and then develop it into a three-dimensional structure and function. According to these backgrounds, this review paper is organized as follows. The introduction is followed by a summary of the three issues; (i) 2D to 3D dynamic structure control: liquid crystal commanded by the surface, (ii) 2D to 3D rational construction: a metal-organic framework (MOF) and a covalent organic framework (COF); (iii) 2D to 3D functional amplification: cells regulated by the surface. In addition, this review summarizes the important aspects of the ultimate three-dimensional nanoarchitectonics as a perspective. The goal of this paper is to establish an integrated concept of functional material creation by reconsidering various reported cases from the viewpoint of nanoarchitectonics, where nanoarchitectonics can be regarded as a method for everything in materials science.

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.

Enhancing the electrocatalytic activities of metal organic frameworks for the oxygen evolution reaction with bimetallic groups

Controlling the ratio of metals in bimetallic organic frameworks (MOFs) can not only alter the structures but also tailor the properties of MOFs. Herein, we report a series of electrocatalytically active CoxNiy-based bimetallic MOFs that are synthesized with the 3,5-pyridinedicarboxylic acid (3,5-H2pdc) ligand (where x : y = 20 : 1, 15 : 1, 10 : 1, 5 : 1, 1 : 1, and 1 : 20) and a facile, scalable, low temperature synthetic route. The materials have one-dimensional (1D), rod-like microstructures with different aspect ratios. While they all electrocatalyze the oxygen evolution reaction (OER) in alkaline solution (1 M KOH), their electrocatalytic performances vary substantially depending on their compositions. The CoxNiy-MOF with an optimal ratio of x : y = 15 : 1 (Co15Ni1-MOF) electrocatalyzes the OER with the highest maximum current density (92.2 mA cm-2 at 1.75 V vs. RHE) and the smallest overpotential (384 mV vs. RHE at 10 mA cm-2) in a 1 M KOH solution. It is also stable under constant current application during the electrocatalytic OER. This work demonstrates the application of bimetallic MOFs that are synthesized following a simple, low temperature synthetic route for the OER and their tailorable electrocatalytic properties for the OER by varying the ratio of two metals and the synthetic conditions used to produce them.

Pouch-Type Asymmetric Supercapacitor Based on Nickel-Cobalt Metal-Organic Framework

Bimetal-organic frameworks (BMOFs) have attracted considerable attention as electrode materials for energy storage devices because of the precise control of their porous structure, surface area, and pore volume. BMOFs can promote multiple redox reactions because of the enhanced charge transfer between different metal ions. Therefore, the electroactivity of the electrodes can be significantly improved. Herein, we report a NiCo-MOF (NCMF) with a three-dimensional hierarchical nanorod-like structure prepared using a facile solvo-hydrothermal method. The as-prepared NCMF was used as the positive electrode in a hybrid pouch-type asymmetric supercapacitor device (HPASD) with a gel electrolyte (KOH+PVA) and activated carbon as the negative electrode. Because of the matchable potential windows and specific capacitances of the two electrodes, the assembled HPASD exhibits a specific capacitance of 161 F·g^-1 at 0.5 A·g^-1, an energy density of 50.3 Wh·kg^-1 at a power density of 375 W·kg^-1, and a cycling stability of 87.6% after 6000 cycles. The reported unique synthesis strategy is promising for producing high-energy-density electrode materials for supercapacitors.

Phase Purity Regulated by Mechano-Chemical Synthesis of Metal-Organic Frameworks for the Electrocatalytic Oxygen Evolution Reaction

Three new metal organic frameworks (ZnTIA-1mc, CuTIA-1mc, and CoTIA-1mc) were synthesized by the mechanochemical grinding (mc) method in the unadulterated form. They compared with their solvothermally synthesized (st) counterparts, where the mixtures of isomeric forms have been isolated. Kinetics study with the function of grinding time during the mechanosynthesis process revealed the formation of new metastable phases. Less crystallinity and short of mechanical defects in the structure of synthesized mc metal organic frameworks showed enhanced electrocatalytic activity toward oxygen evolution reaction (OER). Among all, CoTIA-1mc showed high OER activity with 289 mV overpotential, 10 mA cm^-2 current density, and 55.4 mV dec^-1 Tafel slope in 1 M KOH which is close to the commercially used RuO₂.

Enhanced Activity of Enzyme Immobilized on Hydrophobic ZIF-8 Modified by Ni2+ Ions

The development of efficient enzyme immobilization to promote their recyclability and activity is highly desirable. Zeolitic imidazolate framework-8 (ZIF-8) has been proved to be an effective platform for enzyme immobilization due to its easy preparation and biocompatibility. However, the intrinsic hydrophobic characteristic hinders its further development in this filed. Herein, a facile synthesis approach was developed to immobilize pepsin (PEP) on the ZIF-8 carrier by using Ni²⁺ ions as anchor (ZIF-8@PEP-Ni). By contrast, the direct coating of PEP on the surface of ZIF-8 (ZIF-8@PEP) generated significant conformational changes. Electrochemical oxygen evolution reaction (OER) was employed to study the catalytic activity of immobilized PEP. The ZIF-8@PEP-Ni composite attains remarkable OER performance with an ultralow overpotential of only 127 mV at 10 mA cm^-2 , which is much lower than the 690 and 919 mV overpotential values of ZIF-8@PEP and PEP, respectively.

Metal-Organic Framework Integrating Ionic Framework and Bimetallic Coupling Effect for Highly Efficient Oxygen Evolution Reaction

Metal-organic frameworks (MOFs) are recognized as promising electrocatalysts for the oxygen evolution reaction (OER) because of their permanent porosity and rich architectural diversity; however, ionic MOFs enabling fast ions exchange during OER are rarely explored. Here, an ionic MOF (Ni-btz) constructed with an azolate ligand is selected, and continuous 3D bimetallic MOF (NiFe-btz) films deriving from high-degree intergrowth of microsized MOFs particles are fabricated. The as-prepared NiFe-btz/NF-OH electrode exhibits excellent OER performance with a low overpotential of 239 mV at 10 mA cm-2 under alkaline condition. The OER charge transfer process and bimetallic coupling effect in ionic NiFe-btz are probed by density functional theory calculations and confirmed via X-ray photoelectron spectroscopy and in situ Raman measurements. The partial density of states of NiFe-btz indicates that the main contribution for electron density around the Fermi level is from Cl ions clarifying the profitable impact of ionic MOF framework. This work systematically demonstrates the relationship of electronic structure and OER activity in ionic, bimetallic MOFs and expands the scope of 3D MOF films for efficient OER.

Conductive Co-triazole metal-organic framework exploited as an oxygen evolution electrocatalyst

A Co-triazole metal-organic framework (Co-trz) endowed with electrical conductivity was synthesized effortlessly via a microwave-based method. Providing a high density of catalytic centers with electrically conductive features, as suggested by DFT calculations, the framework exhibited a low overpotential for the oxygen evolution reaction (OER) with good kinetics. A mechanistic reaction pathway was proposed based on monitoring alterations in the oxidation state and local coordination environment of Co centers upon the occurrence of the OER. Due to its performance and its chemical and electrochemical robustness, the framework was highlighted as a promising MOF electrocatalyst for the OER.

Post-exfoliation functionalisation of metal-organic framework nanosheets via click chemistry

The liquid exfoliation of layered metal-organic frameworks (MOFs) to form nanosheets (MONs) exposes buried functional groups making them useful in a range of sensing and catalytic applications. Here we show how high yielding click reactions can be used post-exfoliation to systematically modify the surface chemistry of MONs allowing for tuning of their surface properties and their use in new applications. A layered amino-functionalised framework is converted through conventional post-synthetic functionalisation of the bulk MOF to form azide functionalised frameworks of up to >99% yield. Ultrasonic liquid exfoliation is then used to form few-layer nanosheets, which are further functionalised through post exfoliation functionalisation using Cu(I)-catalysed azide-alkyne cycloaddition reactions. Here we demonstrate the advantages of post-exfoliation functionalisation in enabling: (1) a range of functional groups to be incorporated in high yields; (2) tuning of nanosheet surface properties without the need for extensive recharacterisation; (3) the addition of fluorescent functional groups to enable their use in the sensing of hazardous nitrobenzene. We anticipate that the versatility of different functional groups that can be introduced through high yielding click reactions will lead to advances in the use of MONs and other 2D materials for a variety of applications.

Enhanced CO2 electroconversion of Rhodobacter sphaeroides by cobalt-phosphate complex assisted water oxidation

CO₂ can be a next generation feedstock for electricity-driven bioproduction due to its abundance and availability. Microbial electrosynthesis (MES), a promising technique for CO₂ electroconversion, provides an attractive route for the production of valuable products from CO₂, but issues surrounding efficiency and reasonable productivity should be resolved. Improving the anode performance for water oxidation under neutral pH is one of the most important aspects to advance current MES. Here, we introduce cobalt-phosphate (Co-Pi) assisted water oxidation at the counter electrode (i.e., anode) to upgrade the MES performance at pH 7.0. We show that CO₂ can be converted by photochemoautotrophic bacterium, Rhodobacter sphaeroides into organic acids and carotenoids in the MES reactor. Planktonic cells of R. sphareroides in the Co-Pi anode equipped MES reactor was ca. 1.5-fold higher than in the control condition (w/o Co-Pi). The faradaic efficiency of the Co-Pi anode equipped MES reactor was remarkably higher (58.3%) than that of the bare anode (27.8%). While the system can improve the CO₂ electroconversion nonetheless there are some further optimizations are necessary.

Construction of Ni(CN)2 /NiSe2 Heterostructures by Stepwise Topochemical Pathways for Efficient Electrocatalytic Oxygen Evolution

Exploiting effective electrocatalysts based on elaborate heterostructures for the oxygen evolution reaction (OER) has been considered as a promising strategy for boosting water splitting efficiency to produce the clean energy-hydrogen. However, constructing catalytically active heterostructures with novel composition and architecture remains poorly developed due to the synthetic challenge. In this work, it is demonstrated that unique Ni(CN)₂ /NiSe₂ heterostructures, composed of single-crystalline Ni(CN)₂ nanoplates surrounded by crystallographically aligned NiSe₂ nanosatellites, can be created from nickel-based Hofmann-type coordination polymers through stepwise topochemical pathways. When employed as the OER electrocatalyst, the Ni(CN)₂ /NiSe₂ heterostructures show enhanced performance, which could be attributed to optimized geometric and electronic structures of the catalytic sites endowed by the synergy between the two components. This work demonstrates a rational synthetic route for creating a novel Ni-based OER electrocatalyst that possesses nanoscale heterostructure, whose composition, spatial organization, and interface configuration can be finely manipulated.

Polyoxometalate-based Composite Cluster with Core-Shell Structure: Co4(PW9)2@Graphdiyne as Stable Electrocatalyst for Oxygen Evolution and its Mechanism Research

A composite cluster with core-shell structure which is composed of polyoxometalates (POMs) and graphdiyne (GDY) was synthesized and applied for the electrochemical oxygen evolution reaction (OER). Compared with the original...

Tailoring the electron density of cobalt oxide clusters to provide highly selective superoxide and peroxide species for aerobic cyclohexane oxidation

The catalytic aerobic cyclohexane oxidation to cyclohexanol and cyclohexanone (KA oil) is an industrially relevant reaction. This work is focused on the synthesis of tailor-made catalysts based on the well-known Co₄O₄ core in order to successfully deal with cyclohexane oxidation reaction. The catalytic activity and selectivity of the synthesized catalysts can be correlated with the electronic density of the cluster, modulated by changing the organic ligands. This is not trivial in cyclohexane oxidation. Furthermore, the reaction mechanism is discussed on the basis of kinetics and spin trapping experiments, confirming that the electronic density of the catalyst has a clear influence on the distribution of the reaction products. In addition, in situ Raman spectroscopy was used to characterize the oxygen species formed on the cobalt cluster during the oxidation reaction. Altogether, it can be concluded that the catalyst with the highest oxidation potential promotes the formation of peroxide and superoxide species, which is the best way to oxidize inactivated CH bonds in alkanes. Finally, based on the results of the mechanistic studies, the contribution of these cobalt oxide clusters in each single reaction step of the whole process has been proposed.

Common Strategy: Mounting the Rod-like Ni-Based MOF on Hydrangea-Shaped Nickel Hydroxide for Superior Electrocatalytic Methanol Oxidation Reaction

Developing efficient metal-organic framework (MOF)-based electrocatalysts with improvable activity and persistence toward the methanol oxidation reaction (MOR) is attracting great research attention but still remains an enormous challenge. Herein, a facile strategy, hydrangea-shaped nickel hydroxide template-directed synthesis of the hierarchically structured Ni-MOF on the Ni(OH)₂ heterocomposite (denoted as Ni-Ni) for efficient MOR, is developed. The unique hierarchical structure and synergistic effect of the heterocomposite afford more exposed active sites, a facile ion diffusion path, and improved conductivity, favorable for improving MOR catalytic performance. Remarkably, the optimized Ni-Ni-2 material delivers an excellent activity with a high peak current density (24.6 mA cm^-2). Furthermore, to prove the universality of this strategy, Ni_xCu_1-x(OH)₂ isometallic hydroxide was used as the precursor, and a series of MOF-74/Cu_xNi_1-x(OH)₂ (denoted as Ni-NiCu) heterogeneous materials have been prepared and could be used as an effective electrocatalyst to catalyze MOR. The results indicate that this strategy can be used in the synthesis of other new composite materials with specific hierarchical structures for a more efficient electrocatalytic system.

Synthesis and electrochemical properties of metal(ii)-carboxyethylphenylphosphinates

We report herein the synthesis, structural characterization and electrocatalytic properties of three new coordination polymers, resulting from the combination of divalent metal (Ca²⁺, Cd²⁺ or Co²⁺) salts with (2-carboxyethyl)(phenyl)phosphinic acid. In addition to the usual hydrothermal procedure, the Co²⁺ derivative could also be prepared by microwave-assisted synthesis, in much shorter times. The crystal structures were solved by ab initio calculations, from powder diffraction data. Compounds M^II[O₂P(CH₂CH₂COOH)(C₆H₅)]₂ {M = Cd (1) or Ca (2)} crystallize in the monoclinic system and display a layered topology, with the phenyl groups pointing toward the interlayer space in a interdigitated fashion. Compound Co₂[(O₂P(CH₂CH₂COO)(C₆H₅)(H₂O)]₂·2H₂O (3) presents a 1D structure composed of zig-zag chains, formed by edge-sharing cobalt octahedra, with the phenyl groups pointing outside. Packing of these chains is favored by hydrogen bond interactions via lattice water molecules. In addition, H-bonds along the chains are established with the participation of the water molecules and the hydrophilic groups from the ligand. However, the solid exhibits a low proton conductivity, attributed to the isolation of the hydrophilic regions caused by the arrangement of hydrophobic phenyl groups. Preliminary studies on the electrocatalytic performance for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) have been conducted for compound 3 and its pyrolytic derivatives, which were previously thoroughly characterized. By comparison, another Co²⁺ phosphinate, 4, obtained by microwave-assisted synthesis, but with distinct stoichiometry and a known structure was also tested. For the OER, the best performance was achieved with a derivative of 3, prepared by heating this compound in N₂ at 200 °C. This derivative showed overpotential (339 mV, at a current density of 10 mA cm^-2) and Tafel slope (51.7 mV dec^-1) values comparable to those of other Co²⁺ related materials.

Encapsulation of Ultrafine Metal-Organic Framework Nanoparticles within Multichamber Carbon Spheres by a Two-Step Double-Solvent Strategy for High-Performance Catalysts

Carbon-encapsulated metal-organic framework (MOF) composite is one kind of emerging new catalyst with high efficiency and has gained much attention. However, for this kind of composite catalyst, the key to improving its catalytic activity and durability is to realize the effective dispersion of MOF nanoparticles (NPs) and enhance the interaction between MOF NPs and the carbon matrix, which remain a significant challenge. Herein, ultrafine MOF NPs within multichamber carbon spheres (MOF@MCCS), for the first time, have been rationally synthesized by a two-step double-solvent strategy for high-performance catalysts. The precise loading of guest MOFs can be achieved by adjusting the multichamber structure and calcination extent of the multichamber polymer (MCP), and the particle size of MOFs can be as low as 13.2 nm. Due to the formation of abundant carbon defects in the pyrolysis process of MCPs, the special structure and synergistic effect make the material exhibit higher catalytic activity and durability. More importantly, this method is universal and can be extended to different MOF systems. The two-step double-solvent strategy not only prepares a unique structure of MOF@MCCS-type host-guest-encapsulated catalysts but also provides a new idea for the design of high-efficiency catalysts with better performance and higher durability.

Iron and nitrogen Co-doped CoSe2 nanosheet arrays for robust electrocatalytic water oxidation

Fe–N–CoSe₂ electrocatalysts with good OER performance and long-term durability were synthesized using an anion and cation co-doping strategy.