Three-Dimensional Ni-MOF as a High-Performance Supercapacitor Anode Material; Experimental and Theoretical Insight

A three-dimensional (3D) Ni-MOF of the formula [Ni(C4H4N2)(CHO2)2]n, has been reported, which shows a capacitance of 2150 F/g at a current density of 1A/g in a three-electrode setup (5.0 M KOH). Post-mortem analysis of the sample after three-electrode measurements revealed the bias-induced transformation of Ni-MOF to Ni(OH)2, which has organic constituents intercalated within the sample exhibiting better storage performance than bulk Ni(OH)2. Afterward, the synthesized MOF and reduced graphene (rGO) were used as the anode and cathode electrode material, respectively, and a two-electrode asymmetric supercapacitor device (ASC) setup was designed that exhibited a capacitance of 125 F/g (at 0.2 A/g) with a high energy density of 50.17 Wh/kg at a power density of 335.1 W/kg. The ASC further has a very high reversibility (97.9% Coulombic efficiency) and cyclic stability (94%) after 5000 constant charge-discharge cycles. Its applicability was also demonstrated by running a digital watch. Using sophisticated density functional theory simulations, the electronic properties, diffusion energy barrier for the electrolytic ions (K+), and quantum capacitance for the Ni(OH)2 electrode have been reported. The lower diffusion energy barrier (0.275 eV) and higher quantum capacitance (1150 μF/cm2) are attributed to the higher charge storage performance of the Ni-MOF-transformed Ni(OH)2 electrode as observed in the experiment.

Bifunctional Cu(II)-based 2D coordination polymer and its composite for high-performance photocatalysis and electrochemical energy storage

Coordination polymers (CPs) have been widely proven as sacrificial electrode materials for energy storage applications because of their high porosity, specific surface area and tunable structural topology. In this work, a new 2D Cu(II)-based CP, formulated as [Cu2(btc)(μ-Cl)2(H2O)4]n (CP-1) (H3btc = benzene-1,3,5-tricarboxylic acid), fabrication of copper oxide nanoparticles (CuO NPs) and its composite (CuO@CP-1) were successfully synthesized using solvothermal, precipitation and mechanochemical grinding approaches. Single-crystal X-ray analysis authenticated a two-dimensional (2D) layered network of CP-1. Further, CP-1, CuO NPs and composite were characterized by diffraction (Powder-XRD), spectroscopic (FTIR), microscopic (SEM), and thermal (TGA) techniques. The porosity and surface behavior of CP-1 and the composite were demonstrated using BET analyzer. Topological simplification of CP-1 shows a 3-c connected hcb periodic net. The photocatalytic behavior of CP-1 was examined over methyl red (MR) dye in the presence of sunlight and showed a promising degradation efficiency of 96.80%. The electrochemical energy storage properties of CP-1, CuO NPs and composite were investigated using cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) analysis under aqueous 1 M H2SO4 electrolyte. The electrochemical results show better charge storage performance of CP-1 with a specific capacitance of 602.25 F g-1 at 1 A g-1 current density by maintaining a retention of up to 84.51% after 5000 cycles at 10 A g-1 current density. Comparative electrochemical studies reveal that CP-1 is a promising electrode material for energy storage.

Unleashing the Full Potential of Electrochromic Heterostructured Nickel-Cobalt Phosphate for Optically Active High-Performance Asymmetric Quasi-Solid-State Supercapacitor Devices

The rational design of hybrid systems that combine capacitor and battery merits is crucial to enable the fabrication of high energy and power density devices. However, the development of such systems remains a significant barrier to overcome. Herein, we report the design of a Ni-Co phosphate (Ni3-xCox(PO4)2·8H2O) nanoplatelet-based system via a facile coprecipitation method at ambient conditions. The nanoplatelets exhibit multicomponent synergy, exceptional charge storage capabilities, rich redox active sites (ameliorating the redox reaction activity), and high ionic diffusion rate/electron transfer kinetics. The designed Ni3-xCox(PO4)2·8H2O offered a respectable gravimetric specific capacity and marvelous capability rate (966 and 595 C g-1 at 1 and 15 A g-1) over the Ni3(PO4)2·8H2O (327.3 C g-1) and Co3(PO4)2·8H2O (68 C g-1) counterparts. Additionally, the nanoplatelets showed enhanced photoactive storage performance with a 9.7% increase in the recorded photocurrent density. Upon integration of Ni3-xCox(PO4)2·8H2O as a positive pole and commercial activated carbon as a negative pole, the constructed hybrid supercapacitor device with PVA@KOH quasi-gel electrolyte exhibits great energy and power densities of 77.7 Wh kg-1 and 15998.54 W kg-1 with remarkable cycling stability of 6000 charging/discharging cycles and prominent Coulombic efficiency of 100%. Interestingly, two assembled devices are capable of glowing a red LED bulb for nearly 180 s. This research paves the way to design and fabricate electroactive species via a facile approach for boosting the design of a plethora of supercapattery devices.

UiO-66-NH2: a recyclable and efficient sorbent for dispersive solid-phase extraction of fluorinated aromatic carboxylic acids from aqueous matrices

The present study describes the trace analysis of 23 fluorinated aromatic carboxylic acids based on the dispersive solid-phase extraction (dSPE) technique using UiO-66-NH₂ MOF as efficient, recyclable sorbent, and GC-MS negative ionization mass spectrometry (NICI MS) as determination technique. All 23 fluorobenzoic acids (FBAs) were enriched, separated, and eluted in a shorter retention time; the derivatization was done by pentafluorobenzyl bromide (1% in acetone), in which the use of inorganic base K₂CO₃ was improved by triethylamine to increase the lifespan of the GC column. The performance of UiO-66-NH₂ was evaluated by dSPE in Milli-Q water, artificial seawater, and tap water samples, and the impact of various parameters on the extraction efficiency was investigated by GC-NICI MS. The method was found to be precise, reproducible, and applicable to the seawater samples. In the linearity range, the regression value was found to be >0.98; LOD and LOQ were found to be in the range of 0.33-1.17 ng/mL and 1.23-3.33 ng/mL, respectively; and the value of the extraction efficiency was found to range between 98.45 and 104.39% for Milli-Q water samples, 69.13-105.48% for salt-rich seawater samples, and 92.56-103.50% for tap water samples with a maximum RSD value of 6.87% that confirms the applicability of the method to different water matrices.

Ligand-Controlled Growth of Different Morphological Bimetallic Metal-Organic Frameworks for Enhanced Charge-Storage Performance and Quasi-Solid-State Hybrid Supercapacitors

The present research work facilitates a ligand-mediated effective strategy to achieve different morphological surface structures of bimetallic (Ni and Co) metal-organic frameworks (MOFs) by utilizing different types of organic ligands like terephthalic acid (BDC), 2-methylimidazole (2-Melm), and trimesic acid (BTC). Different morphological structures, rectangular-like nanosheets, petal-like nanosheets, and nanosheet-assembled flower-like spheres (NSFS) of NiCo MOFs, are confirmed from the structural characterization for ligands BDC, 2-Melm, and BTC, respectively. The basic characterization studies like scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and Brunauer-Emmett-Teller revealed that the NiCo MOF prepared by using trimesic acid as the ligand (NiCo MOF_BTC) with a long organic linker exhibits a three-dimensional architecture of NSFS that possesses higher surface area and pore dimensions, which enables better ion kinetics. Also, the NiCo MOF_BTC delivered the highest capacity of 1471.4 C g^-1 (and 408 mA h g^-1) at 1 A g^-1 current density, compared to the other prepared NiCo MOFs and already reported different NiCo MOF structures. High interaction of trimesic acid with the metal ions confirmed from ultraviolet-visible spectroscopy and X-ray photoelectron spectroscopy leads to a NSFS structure of NiCo MOF_BTC. For practical application, an asymmetric supercapacitor device (NiCo MOF_BTC//AC) is fabricated by taking NiCo MOF_BTC and activated carbon as the positive and negative electrode, respectively, where the PVA + KOH gel electrolyte serves as a separator as well as an electrolyte. The device delivered an outstanding energy density of 78.1 Wh kg^-1 at a power density of 750 W kg^-1 in an operating potential window of 1.5 V. In addition, it displays a long cycle life of 5000 cycles with only 12% decay of the initial specific capacitance. Therefore, these findings manifest the morphology control of MOFs by using different ligands and the mechanism behind the different morphologies that will provide an effective way to synthesize differently structured MOF materials for future energy-storage applications.

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.

Bimetallic Metal-Organic Frameworks (BMOF) and BMOF- Incorporated Membranes for Energy and Environmental Applications

Bimetallic metal organic frameworks (BMOFs) are a class of crystalline solids and their structure comprises two metal ions in the lattice. BMOFs show a synergistic effect of two metal centres and enhanced properties compared to MOFs. By controlling the composition and relative distribution of two metal ions in the lattice the structure, morphology, and topology of BMOFs could be regulated resulting in an improvement in the tunability of pore structure, activity, and selectivity. Thus, developing BMOFs and BMOF incorporated membranes for applications such as adsorption, separation, catalysis, and sensing is a promising strategy to mitigate environmental pollution and address the looming energy crisis. Herein we present an overview of recent advancements in the area of BMOFs and a comprehensive review of BMOF incorporated membranes reported to date. The scope, challenges as well as future perspectives for BMOFs and BMOF incorporated membranes are presented.

Heterogeneous Catalytic Ozonation: Solution pH and Initial Concentration of Pollutants as Two Important Factors for the Removal of Micropollutants from Water

There are several publications on heterogeneous catalytic ozonation; however, their conclusions and the comparisons between them are not always consistent due to the variety of applied experimental conditions and the different solid materials used as catalysts. This review attempts to limit the major influencing factors in order to reach more vigorous conclusions. Particularly, it highlights two specific factors/parameters as the most important for the evaluation and comparison of heterogeneous catalytic ozonation processes, i.e., (1) the pH value of the solution and (2) the initial concentration of the (micro-)pollutants. Based on these, the role of Point of Zero Charge (PZC), which concerns the respective solid materials/catalysts in the decomposition of ozone towards the production of oxidative radicals, is highlighted. The discussed observations indicate that for the pH range 6–8 and when the initial organic pollutants’ concentrations are around 1 mg/L (or even lower, i.e., micropollutant), then heterogeneous catalytic ozonation follows a radical mechanism, whereas the applied solid materials show their highest catalytic activity under their neutral charge. Furthermore, carbons are considered as a rather controversial group of catalysts for this process due to their possible instability under intense ozone oxidizing conditions.

Electrode Materials for Supercapacitors in Hybrid Electric Vehicles: Challenges and Current Progress

For hybrid electric vehicles, supercapacitors are an attractive technology which, when used in conjunction with the batteries as a hybrid system, could solve the shortcomings of the battery. Supercapacitors would allow hybrid electric vehicles to achieve high efficiency and better power control. Supercapacitors possess very good power density. Besides this, their charge-discharge cycling stability and comparatively reasonable cost make them an incredible energy-storing device. The manufacturing strategy and the major parts like electrodes, current collector, binder, separator, and electrolyte define the performance of a supercapacitor. Among these, electrode materials play an important role when it comes to the performance of supercapacitors. They resolve the charge storage in the device and thus decide the capacitance. Porous carbon, conductive polymers, metal hydroxide, and metal oxides, which are some of the usual materials used for the electrodes in the supercapacitors, have some limits when it comes to energy density and stability. Major research in supercapacitors has focused on the design of stable, highly efficient electrodes with low cost. In this review, the most recent electrode materials used in supercapacitors are discussed. The challenges, current progress, and future development of supercapacitors are discussed as well. This study clearly shows that the performance of supercapacitors has increased considerably over the years and this has made them a promising alternative in the energy sector.

Dual-ligand strategies to assemble S, N-containing metal organic framework nanoflowers for hybrid supercapacitors

Ni-MOF [Ni(Tdc)(Bpy)]n was successfully prepared, and the Ni-MOF//AC hybrid supercapacitor exhibited superior energy density and cycling stability.

Preparation of Flower-like Nickel-Based Bimetallic Organic Framework Electrodes for High-Efficiency Hybrid Supercapacitors

Metal organic frameworks (MOFs) have been rapidly developed in the application of electrode materials due to their controllable morphology and ultra-high porosity. In this research, flower-like layered nickel-based bimetallic MOFs microspheres with different metal central ions were synthesized by solvothermal method. Compared with Ni-MOFs, the optimization of the specific capacitance of NiCo-MOFs and NiMn-MOFs was been confirmed. For example, the specific capacitance of NiCo-MOFs can reach 882 F·g−1 at 0.5 A·g−1 while maintaining satisfactory cycle life (the specific capacity remains 90.1% of the initial value after 3000 charge-discharge cycles at 5 A·g−1). In addition, the NiCo-MOFs//AC HSCs, which are composed of NiCo-MOFs and activated carbon (AC), achieved a maximum energy density of 18.33 Wh·kg−1 at a power density of 400 W·kg−1, and showed satisfactory cycle life (82.4% after 3000 cycles). These outstanding electrochemical properties can be ascribed to the synergistic effect between metal ions, the optimized conductivity, and the unique layered stacked flower structure, which provides a smooth transmission channel for electrons/ions. In addition, this research gives a general method for the application of MOFs in the field of supercapacitors.

Review on recent progress in metal-organic framework-based materials for fabricating electrochemical glucose sensors

Diabetes is a type of disease that threatens human health, which can be diagnosed based on the level of glucose in the blood. Recently, various MOF-based materials have been developed as efficient electrochemical glucose sensors because of their tunable pore channels, large specific surface area well dispersed metallic active sites, etc. In this review, the significance of glucose detection and the advantages of MOF-based materials for this application are primarily discussed. Then, the application of MOF-based materials can be categorized into two types of glucose sensors: enzymatic biosensors and non-enzymatic sensors. Finally, insights into the current research challenges and future breakthrough possibilities regarding electrochemical glucose sensors are considered.

From Co-MOF to CoNi-MOF to Ni-MOF: A Facile Synthesis of 1D Micro-/Nanomaterials

Controlling the growth of metal-organic frameworks (MOFs) at the micro-/nanoscopic scale will result in new physical properties and novel functions into the materials without changing the chemical identities and the characteristic features of the MOFs themselves. Herein, we report a facile approach to synthesize a series of MOFs [Co-MOF, Co_xNi_y-MOFs (x and y represent the molar ratio of Co²⁺ and Ni²⁺ and x/y = 1:1, 1:5, 1:10, 1:15, and 1:20), and Ni-MOF] with a one-dimensional micro-/nanoscaled rod-like architecture. From Co-MOF to Co_xNi_y-MOFs to Ni-MOF, the diameters of the rods turn to be spindly with the increase of Ni²⁺ content which will facilitate the supercapacitor performances. Interestingly, Co₁Ni₂₀-MOF exhibits a highest specific capacity of 597 F g^-1 at 0.5 A g^-1 and excellent cycle performance (retained 93.59% after 4000 cycles) among these MOF materials owing to its micro-/nanorod structure with a smaller diameter and the synergy effect between the optimum molar ratio of Co²⁺ and Ni²⁺.

Electropolymerization of poly(methylene blue) on flower-like nickel-based MOFs used for ratiometric electrochemical sensing of total polyphenolic content in chrysanthemum tea

A ratiometric electrochemical sensor for caffeic acid (CAE) detection was constructed using a glassy carbon electrode modified with poly(methylene blue) and flower-like nickel-based metal organic frameworks (PMB@Ni-TPA/GCE). The electrochemical behavior of CAE was investigated at the PMB@Ni-TPA/GCE, and was found to follow a two-electron, two-proton electrooxidation process. PMB was used as the internal reference probe, and Ni-TPA can enhance the electrochemical signals of both CAE and PMB. As the CAE concentration increases, the oxidation peak current of CAE is enhanced but that of PMB keeps almost unchanged. The oxidation peak current ratio between CAE and PMB recorded by differential pulse voltammetry changes linearly with CAE concentration over the range of 0.25-15.0 μM, with a detection limit of 0.2 μM. The proposed sensor was successfully employed to evaluate the total polyphenolic content as CAE equivalent in chrysanthemum tea, and the results were comparable with those given by the reference Folin-Ciocalteu spectrophotometry.

Construction of high-performance electrode materials of NiCo2O4 nanoparticles encapsulated in ultrathin N-doped carbon nanosheets for supercapacitors

Highly dispersed nitrogen doped carbon (N-C) is decomposed by 2-methylimidazole (C₄H₆N₂) and is used as a composite material with nickel cobaltite (NiCo₂O₄). The N-C and NiCo₂O₄ composites are obtained by a one-step hydrothermal method and subsequent calcination. In addition, N-C is used to control the morphology and structure of NiCo₂O₄ to obtain excellent capacitor materials. The N-C/NiCo₂O₄ electrode shows an excellent specific capacitance of 157.97 mA h g^-1 (1263.75 F g^-1) at 1 A g^-1. Herein, we successfully develop a N-C/NiCo₂O₄//AC asymmetric supercapacitor (ASC), which is prepared using N-C/NiCo₂O₄ as a cathode coupled with activated carbon (AC) as an anode at a voltage of 1.6 V. The prepared N-C/NiCo₂O₄//AC device shows an excellent volumetric energy density of 66.44 mW h kg^-1. The promising performance of N-C/NiCo₂O₄//AC illustrated its potential for portable supercapacitor applications.

The Evolution in Electrochemical Performance of Honeycomb-Like Ni(OH)2 Derived from MOF Template with Morphology as a High-Performance Electrode Material for Supercapacitors

Ni(OH)2 derived from an MOF template was synthesized as an electrode material for supercapacitors. The electrochemical performance of the electrode was adjusted by effectively regulating the morphology of Ni(OH)2. The evolution of electrochemical performance of the electrode with morphology of Ni(OH)2 was highlighted in detail, based on which honeycomb-like Ni(OH)2 was successfully synthesized, and endowed the electrode with outstanding electrochemical performance. For the three-electrode testing system, honeycomb-like Ni(OH)2 exhibited a very high specific capacitance (1865 F·g-1 at 1 A·g-1, 1550 F·g-1 at 5 mV·s-1). Moreover, it also presented an excellent rate capability and cycling stability, due to 59.46 % of the initial value (1 A·g-1) being retained at 10 A·g-1, and 172% of initial value (first circle at 50 mV·s-1) being retained after 20,000 cycles. With respect to the assembled hybrid supercapacitor, honeycomb-like Ni(OH)2 also displayed superior electrochemical performance, with a high energy density (83.9 Wh·kg-1 at a power density of 374.8 W·kg-1). The outstanding electrochemical performance of Ni(OH)2 should be attributed to its unique honeycomb-like structure, with a very high specific surface area, which greatly accelerates the transformation and diffusion of active ions.

Three-dimensional Co/Ni bimetallic organic frameworks for high-efficient catalytic ozonation of atrazine: Mechanism, effect parameters, and degradation pathways analysis

Herein, the potential of bimetallic MOFs in catalytic ozonation was investigated for the first time. Three novel ozonation catalysts, i.e. cobalt-based, nickel-based and cobalt/nickel-based metal-organic frameworks (Co-MOF, Ni-MOF and Co/Ni-MOF), were synthesized, characterized by XRD, SEM, N₂ sorption-desorption isotherms, FTIR and XPS, and applied in catalytic ozonation for atrazine removal. It was found that the catalysts showed outstanding performance in the catalytic ozonation, especially Co/Ni-MOF which was attributed to multiple metal sites, higher coordination unsaturation, metal centers with larger electron density, and better efficiency in electron transfer than its single-metal counterparts. Under specific experimental conditions, 47.8%, 67.0%, 75.5%, and 93.9% of atrazine were removed after adsorption and degradation in the ozonation system without catalyst, and the catalytic ozonation systems with Co-MOF, Ni-MOF and Co/Ni-MOF, respectively. Higher removal rates could be achieved by growing initial pH, increasing oxidant dosage and reducing pollutant concentration, while an excess of Co/Ni-MOF was not favorable for the catalytic ozonation. Surface hydroxyl groups and acid sites were considered as the critical catalytic sites on Co/Ni-MOF. From the results of EPR tests, O₂·^-, ¹O₂ and ·OH were ascertained as the main reactive species in the degradation. It was suspected that O₂·^- and H₂O₂ played important roles in the formation of ·OH and the cycle of Co(II)/Co(III) and Ni(II)/Ni(III). Additionally, Co/Ni-MOF displayed good stability and reusability in cycling experiments, ascribed to the enhancement of the porosity and pore hydrophobicity. Finally, based on MS/MS analysis at different reaction times, major degradation pathways for atrazine were proposed.

Solvent-Controlled Morphology of Amino-Functionalized Bimetal Metal-Organic Frameworks for Asymmetric Supercapacitors

The composition-tuned, structure-modified, and morphology-controlled nanoscale metal-organic frameworks (MOFs) are quite important to improve the electrochemical performances for supercapacitors. In this work, a solvent-controlled method to prepare amino-functionalized bimetal MOFs with various morphologies is proposed. Three different morphologies of NiCo-MOFs, such as nanospheres, nanosheet-assembled hollow spheres (NSHSs), and rhombus sheets, have been successfully synthesized by using different solvents. The as-prepared three nanoscale NiCo-MOFs are comparatively characterized and are endowed a possible mechanism on nucleation and crystal growth controlling morphology. When used as electrode materials for supercapacitors, all NiCo-MOFs have excellent electrochemical properties. Specifically, the NiCo-MOF NSHS owns the best specific capacitance, which can achieve 1126.7 F g^-1 at the current density of 0.5 A g^-1 and maintain 93% of its original capacitance at the current density of 10 A g^-1 after 3000 charge-discharge cycles. Moreover, an asymmetric supercapacitor device (NiCo-MOF NSHS//AC) assembled with NiCo-MOF NSHS as the positive electrode and activated carbon (AC) as the negative electrode achieves an energy density of 20.94 Wh kg^-1 at a power density of 750.84 W kg^-1. This work is facile and highly reproducible and can be extended to prepare other nano-MOFs in energy storage and conversion fields. In addition, it opens up an effective approach to synthesizing amino-functionalized MOFs by a solvent-controlled method without any other changes in the experimental conditions.

Bimetallic metal-organic frameworks and their derivatives

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

Mechanistic insight into bimetallic CoNi-MOF arrays with enhanced performance for supercapacitors

Engineering multicomponent electroactive materials is an effective strategy to improve electrochemical performance by adjusting the atomic and electronic structure. In this work, we directly synthesize oriented bimetallic CoNi-MOF nanosheets on CFP (carbon fiber paper). The CoNi-MOF/CFP shows high specific capacitance, outstanding rate capability and long-term cycling stability compared to a monometallic Ni-MOF or Co-MOF. By adjusting the Co/Ni molar ratio, CoNi23/CFP (Co : Ni = 2 : 3) displays the highest specific capacitance (2033 F g^-1 at 1 A g^-1). The introduction of Co into the Ni-MOF matrix shortens Co/Ni-centered bond distances, resulting in improved bond strength, facilitating the charge transfer and increasing the electrical conductivity of the CoNi-MOF, which were proved by X-ray absorption fine structure (XAFS) spectroscopy, high angle annular dark field (HAADF) imaging, and electrochemical impedance spectroscopy (EIS). Our study demonstrates the origin of performance improvements and, therefore, may provide a feasible scheme to unlock high-performance MOF electrode materials.

Recent highlights and future prospects on mixed-metal MOFs as emerging supercapacitor candidates

Mixed-metal metal-organic frameworks (M-MOFs) consist of at least two different metal ions as nodes in the same framework. The incorporation of a second or more metal ions provides structural/compositional diversity, multi-functionality and stability to the framework. Moreover, the periodical array of different metal ions in the framework may alter the physical/chemical properties of M-MOFs and result in fascinating applications. M-MOFs with exciting structural features offer superior supercapacitor performances compared to single metal MOFs due to the synergic effect of different metal ions. In this review, we summarize several synthetic methods to construct M-MOFs by employing various organic ligands or metalloligands. Further, we discuss the electrochemical performance of several M-MOFs and their derived composite materials for supercapacitor applications.

The Synthesis of N-(Pyridin-2-yl)-Benzamides from Aminopyridine and Trans-Beta-Nitrostyrene by Fe2Ni-BDC Bimetallic Metal–Organic Frameworks

A bimetallic metal–organic framework material, which was generated by bridging iron (III) cations and nickel (II) cations with 1,4-Benzenedicarboxylic anions (Fe2Ni-BDC), was synthesized by a solvothermal approach using nickel (II) nitrate hexahydrate and iron (III) chloride hexahydrate as the mixed metal source and 1,4-Benzenedicarboxylic acid (H2BDC) as the organic ligand source. The structure of samples was determined by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, and nitrogen physisorption measurements. The catalytic activity and recyclability of the Fe2Ni-BDC catalyst for the Michael addition amidation reaction of 2-aminopyridine and nitroolefins were estimated. The results illustrated that the Fe2Ni-BDC catalyst demonstrated good efficiency in the reaction under optimal conditions. Based on these results, a reaction mechanism was proposed. When the molar ratio of 2-aminopyridine and trans-β-nitrostyrene was 1:1, and the solvent was dichloromethane, the isolated yield of pyridyl benzamide reached 82%; at 80 °C over 24 h. The catalyst can be reused without a substantial reduction in catalytic activity with 77% yield after six times of reuse.

A dual metal organic framework based on copper-iron clusters integrated sulphur doped graphene as a porous material for supercapacitor with remarkable performance characteristics

Herein, a novel bimetallic metal organic framework (MOF) using copper and iron as the metal centers with 1,3,5-tricarboxylic acid as a ligand (CuFeBTC) and its composite with sulphur doped graphene (S-GNS) have been investigated for supercapacitive performance. The synthesis of materials has been carried out using a facile wet chemical route. The physicochemical characterization of the materials employing various structural and surface techniques has been performed which confirms the successful formation of nanocomposite. The capacitive behavior of CuFeBTC, S-GNS and CuFeBTC/S-GNS has been systematically examined using 1 M Na₂SO₄ as an electrolyte in a three and two electrode assembly. The electrochemical studies reveal that CuFeBTC/S-GNS electrode demonstrates highest specific capacitance of 1164.3 F g^-1 at 0.5 A g^-1 with suffice rate capability as compared to CuFeBTC and S-GNS electrodes. Moreover, a symmetric supercapacitor is configured using the CuFeBTC/S-GNS nanocomposite electrodes which deliver remarkable energy and power output of 96.57 Wh kg^-1 and 1595.12 W kg^-1 at an operating voltage of 1.8 V. The as-fabricated symmetric supercapacitor displays competent energy storage retention of 50.2 Wh kg^-1 even at current density of 20.0 A g^-1 with high power density 26973.13 W kg^-1. These deliverables epitomize the latest performance record of bimetallic MOFs based supercapacitors, suggesting that CuFeBTC/S-GNS is a promising active material for high performance electrochemical energy storage applications.

Study of the supercapacitive activity of a Eu-MOF as an electrode material

High surface area and redox activity are indispensable characteristics for a material to be considered as an electrode material in pseudocapacitors.