Solid-type supercapacitor of reduced graphene oxide-metal organic framework composite coated on carbon fiber paper

The Utilization of Metal-Organic Frameworks and Their Derivatives Composite in Supercapacitor Electrodes

Up to now, the mainstream adoption of renewable energy has brought about substantial transformations in the electricity and energy sector. This shift has garnered considerable attention within the scientific community. Supercapacitors, known for their exceptional performance metrics like good charge/discharge capability, strong power density, as well as extended cycle longevity, have gained widespread traction across various sectors, including transportation and aviation. Metal-organic frameworks (MOFs) with unique traits including adaptable structure, highly customizable synthetic methods, and high specific surface area, have emerged as strong candidates for electrode materials. For enhancing the performance, MOFs are commonly compounded with other conducting materials to increase capacitance. This paper provides a detailed analysis of various common preparation strategies and characteristics of MOFs. It summarizes the recent application of MOFs and their derivatives as supercapacitor electrodes alongside other carbon materials, metal compounds, and conductive polymers. Additionally, the challenges encountered by MOFs in the realm of supercapacitor applications are thoroughly discussed. Compared to previous reviews, the content of this paper is more comprehensive, offering readers a deeper understanding of the diverse applications of MOFs. Furthermore, it provides valuable suggestions and guidance for future progress and development in the field of MOFs.

A molecularly imprinted electrochemical sensor MIP/Cu-MOF/rGO/AuNPs/GCE for highly sensitive detection of electroneutral organophosphorus pesticide residues

A novel electrochemical sensor, MIP/Cu-MOF/rGO/AuNPs/GCE, was developed by depositing gold nanoparticles, coating Cu-MOF/GO on the surface of glassy carbon electrode (GCE) before electroreducing graphene oxide (GO) to rGO and covering molecularly imprinted membrane by electropolymerization for highly sensitive detection of electroneutral organophosphorus pesticide residues in agricultural product. Cyclic voltammetry, differential pulse voltametry, scanning electron microscopy, energy-dispersive spectroscopy, and atomic force microscopy were used to characterize the imprinted sensor. Several key factors such as chitosan concentration, suspension volume, pH of polymerization solution, and polymerization scanning rate during preparation of the imprinted sensor were optimized in detail. When electroneutral phosmet was used as a template, the linear range of MIP/Cu-MOF/rGO/AuNPs/GCE for detecting phosmet was 1.00 × 10-14-5.00 × 10-7 mol/L with the limit of detection of 7.20 × 10-15 mol/L at working potentials of - 0.2 to 0.6 V. The selectivity, reproducibility, and repeatability of MIP/Cu-MOF/rGO/AuNPs/GCE were all acceptable. The recoveries of this method for determining phosmet in real samples ranged from 94.2 to 106.5%. The MIP/Cu-MOF/rGO/AuNPs/GCE sensor could be applied to detect electroneutral pesticide residues in organisms and agricultural products.

Facile synthesis of a three-dimensional Ln-MOF@FCNT composite for the fabrication of a symmetric supercapacitor device with ultra-high energy density: overcoming the energy storage barrier

In order to quench the thirst for efficient energy storage devices, a novel praseodymium-based state-of-the-art three-dimensional metal-organic framework (MOF), {[Pr(pdc)2]Me2NH2}n (YK-1), has been synthesized by using a simple solvothermal method employing a readily available ligand. YK-1 was characterised by single-crystal XRD and crystallographic analysis. The electrochemical measurements of YK-1 show that it exhibits a specific capacitance of 363.5 F g-1 at a current density of 1.5 A g-1 with 83.8% retention after 5000 cycles. In order to enhance its electrochemical performance for practical application, two composites of YK-1 with graphene oxide (GO) and functionalised multi-walled carbon nanotubes (FCNTs), namely YK-1@GO and YK-1@FCNT, were fabricated by employing a facile ultrasonication technique. The as-synthesized MOF and the composites were characterized by PXRD, FTIR, SEM, and TEM techniques. YK-1@GO and YK-1@FCNT offer enhanced specific capacitances of 488.2 F g-1 and 730.2 F g-1 at the same current density with 93.8% and 97.7% capacity retention after 5000 cycles, respectively (at 16 A g-1). Fascinated by the outstanding results shown by YK-1@FCNT, a symmetric supercapacitor device (SSC) based on it was fabricated. The assembled SSC achieved a remarkable energy density (87.6 W h kg-1) and power density (750.2 W kg-1) at a current density of 1 A g-1, along with very good cycling stability of 91.4% even after 5000 GCD cycles. The SSC device was able to power up several LED lights and even operated a DC brushless fan for a significant amount of time. To the best of our knowledge, the assembled SSC device exhibits the highest energy density among the MOF composite-based SSCs reported so far.

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.

Incorporation of α-MnO2 Nanoflowers into Zinc-Terephthalate Metal-Organic Frameworks for High-Performance Asymmetric Supercapacitors

Herein, we report the synthesis of α-MnO₂ nanoflower-incorporated zinc-terephthalate MOFs (MnO₂@Zn-MOFs) via the conventional solution phase synthesis technique as an electrode material for supercapacitor applications. The material was characterized by powder-X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy techniques. The prepared electrode material exhibited a specific capacitance of 880.58 F g^-1 at 5 A g^-1, which is higher than the pure Zn-BDC (610.83 F g^-1) and pure α-MnO₂ (541.69 F g^-1). Also, it showed a 94% capacitance retention of its initial value after 10,000 cycles at 10 A g^-1. The improved performance is attributed to the increased number of reactive sites and improved redox activity due to MnO₂ inclusion. Moreover, an asymmetric supercapacitor assembled using MnO₂@Zn-MOF as the anode and carbon black as the cathode delivered a specific capacitance of 160 F g^-1 at 3 A g^-1 with a high energy density of 40.68 W h kg^-1 at a power density of 20.24 kW kg^-1 with an operating potential of 0-1.35 V. The ASC also exhibited a good cycle stability of 90% of its initial capacitance.

A Portable Electrochemical Sensor Based on Manganese Porphyrin-Functionalized Carbon Cloth for Highly Sensitive Detection of Nitroaromatics and Gaseous Phenol

Organic pollutants (OPs) have garnered a considerable amount of attention in recent times due to their extreme toxicity toward humans and the ecosystem. The need for an inexpensive yet robust, sensitive, selective, and easy-to-operate method for detecting OPs remains a challenge. Herein, a portable electrochemical sensor is proposed based on manganese porphyrin-functionalized carbon cloth (CC). To explain the electrochemical performance of the sensor, cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were employed. The presence of manganese(III) ion in the center of the porphyrin ligand acted as an agent for the transfer of electrons and enhanced sensitivity toward analyte-specific redox catalysis. Moreover, it allowed for the concurrent detection of multiple analytes in a complex environment. The modified CC electrode can selectively detect nitroaromatic and phenolic compounds with accessible data collected through wireless means onto a smartphone device. The as-synthesized electrode demonstrated a higher sensitivity toward the detection of nitrobenzene (NB) and aqueous phenol with a limit of detection (LOD) found to be 5.9268 × 10^-10 M and 4.0178 × 10^-10 M, respectively. Additionally, our proposed portable electrochemical sensor demonstrates a high selectivity and reproducibility toward nitroaromatic and phenolic compounds, which can be employed in real complex water samples. With regard to the sensor's remarkable electrochemical performance, it is envisaged that such a sensor could pave the way for environmental point of care (POC) testing.

Metal-Organic Framework Materials for Electrochemical Supercapacitors

Exploring new materials with high stability and capacity is full of challenges in sustainable energy conversion and storage systems. Metal-organic frameworks (MOFs), as a new type of porous material, show the advantages of large specific surface area, high porosity, low density, and adjustable pore size, exhibiting a broad application prospect in the field of electrocatalytic reactions, batteries, particularly in the field of supercapacitors. This comprehensive review outlines the recent progress in synthetic methods and electrochemical performances of MOF materials, as well as their applications in supercapacitors. Additionally, the superiorities of MOFs-related materials are highlighted, while major challenges or opportunities for future research on them for electrochemical supercapacitors have been discussed and displayed, along with extensive experimental experiences.

Synthesis of various dimensional metal organic frameworks (MOFs) and their hybrid composites for emerging applications - A review

Metal organic frameworks (MOFs) represent the organic and inorganic hybrid porous materials. MOFs are low dense and highly porous materials which in turn provide large surface area that can accumulate and store numerous molecules within the pores. The pore size may also act as a mesh to separate molecules. The porous nature of MOFs is beneficial for altering the intrinsic properties of the materials. Over the past decade, different types of hybrid MOFs have been reported in combination with polymers, carbon materials, metal nanoparticles, metal oxides, and biomolecules for various applications. MOFs have also been used in the fabrication of electronic devices, sensors, energy storage, gas separation, supercapacitors, drug delivery and environmental clean-up. In this review, the unique structural orientation, exceptional properties and recent applications of MOFs have been discussed in the first section along with their porosity, stability and other influencing factors. In addition, various methods and techniques involved in the synthesis and designing of MOFs such as solvothermal, electrochemical, mechanochemical, ultrasonication and microwave methods are highlighted. In order to understand the scientific feasibility of MOFs in developing new products, various strategies have been applied to obtain different dimensional MOFs (0D, 1D, 2D and 3D) and their composite materials are also been conferred. Finally, the future prospects of MOFs, remaining challenges, research gaps and possible solutions that need to be addressed by advanced experimental design, computational models, simulation techniques and theoretical concepts have been deliberated.

Electrochemical Performance of MnO2/Graphene Flower-like Microspheres Prepared by Thermally-Exfoliated Graphite

To enhance the electrochemical performance of MnO₂/graphene composite, herein, thermally-exfoliated graphite (TE-G) is adopted as a raw material, and a hydrothermal reaction is conducted to achieve the exfoliation of TE-G and the loading of MnO₂ nanosheets. Through optimizing the TE-G/KMnO₄ ratio in the redox reaction between carbon and KMnO₄, flower-like MnO₂/G microspheres (MnO₂/G-10) are obtained with 83.2% MnO₂ and 16.8% residual graphene. Meanwhile, corresponding MnO₂/rGO composites are prepared by using rGO as raw materials. Serving as a working electrode in a three-electrode system, MnO₂/G-10 composite displays a specific capacitance of 500 F g⁻¹ at 1 A g⁻¹, outstanding rate performance, and capacitance retention of 85.3% for 5,000 cycles. The performance is much better than that of optimized MnO₂/rGO composite. We ascribe this to the high carbon fraction in TE-G resulting in a high fraction of MnO₂ in composite, and the oxygen-containing groups in rGO reduce the resulting MnO₂ fraction in the composite. The superior electrochemical performance of MnO₂/G-10 is dependent on the hierarchical porous structure constructed by MnO₂ nanosheet arrays and the residual graphene layer in the composite. In addition, a supercapacitor assembled by TE-G negative electrode and MnO₂/G positive electrode also exhibits superior performance. In consideration of the low cost of raw materials, the MnO₂/G composite exhibits great application potential in the field of supercapacitors.

MOFs-Graphene Composites Synthesis and Application for Electrochemical Supercapacitor: A Review

Today's world requires high-performance energy storage devices such as hybrid supercapacitors (HSc), which play an important role in the modern electronic market because supercapacitors (Sc) show better electrical properties for electronics devices. In the last few years, the scientific community has focused on the coupling of Sc and battery-type materials to improve energy and power density. Recently, various hybrid electrode materials have been reported in the literature; out of these, coordination polymers such as metal-organic frameworks (MOFs) are highly porous, stable, and widely explored for various applications. The poor conductivity of classical MOFs restricts their applications. The composite of MOFs with highly porous graphene (G), graphene oxide (GO), or reduced graphene oxide (rGO) nanomaterials is a promising strategy in the field of electrochemical applications. In this review, we have discussed the strategy, device structure, and function of the MOFs/G, MOFs/GO, and MOFs/rGO nanocomposites on Sc. The structural, morphological, and electrochemical performance of coordination polymers composites towards Sc application has been discussed. The reported results indicate the considerable improvement in the structural, surface morphological, and electrochemical performance of the Sc due to their positive synergistic effect. Finally, we focused on the recent development in preparation methods optimization, and the opportunities for MOFs/G based nanomaterials as electrode materials for energy storage applications have been discussed in detail.

Recent progress on pristine two-dimensional metal-organic frameworks as active components in supercapacitors

Two-dimensional (2D) metal-organic frameworks (MOFs) are a new generation of 2D materials that can provide uniform active sites and unique open channels as well as excellent catalytic abilities, interesting magnetic properties, and reasonable electrical conductivities. Thus, these MOFs are uniquely qualified for use in applications in energy-related fields or portable devices because they possess fast charge and discharge ability, high power density, and ultralong cycle life factors. There has been worldwide research interest in 2D conducting MOFs, and numerous techniques and strategies have been developed to synthesize these MOFs and their derivatives. Thus, this is the opportune time to review recent research progress on the development of 2D MOFs as electrodes in supercapacitors. This review covers synthetic design strategies, electrochemical performances, and working mechanisms. We will divide these 2D MOFs into two types on the basis of their conductive aspects: 2D conductive MOFs and 2D layered MOFs (including pillar-layered MOFs and 2D nanosheets). The challenges and perspectives of 2D MOFs are also provided.

Metal-Organic-Framework-Derived Nanostructures as Multifaceted Electrodes in Metal-Sulfur Batteries

Metal-sulfur batteries (MSBs) are considered up-and-coming future-generation energy storage systems because of their prominent theoretical energy density. However, the practical applications of MSBs are still hampered by several critical challenges, i.e., the shuttle effects, sluggish redox kinetics, and low conductivity of sulfur species. Recently, benefiting from the high surface area, regulated networks, molecular/atomic-level reactive sites, the metal-organic frameworks (MOFs)-derived nanostructures have emerged as efficient and durable multifaceted electrodes in MSBs. Herein, a timely review is presented on recent advancements in designing MOF-derived electrodes, including fabricating strategies, composition management, topography control, and electrochemical performance assessment. Particularly, the inherent charge transfer, intrinsic polysulfide immobilization, and catalytic conversion on designing and engineering of MOF nanostructures for efficient MSBs are systematically discussed. In the end, the essence of how MOFs' nanostructures influence their electrochemical properties in MSBs and conclude the future tendencies regarding the construction of MOF-derived electrodes in MSBs is exposed. It is believed that this progress review will provide significant experimental/theoretical guidance in designing and understanding the MOF-derived nanostructures as multifaceted electrodes, thus offering promising orientations for the future development of fast-kinetic and robust MSBs in broad energy fields.

Facile synthesis of PEDOT-rGO/HKUST-1 for high performance symmetrical supercapacitor device

A novel poly(3,4-ethylenedioxythiophene)-reduced graphene oxide/copper-based metal-organic framework (PrGO/HKUST-1) has been successfully fabricated by incorporating electrochemically synthesized poly(3,4-ethylenedioxythiophene)-reduced graphene oxide (PrGO) and hydrothermally synthesized copper-based metal-organic framework (HKUST-1). The field emission scanning microscopy (FESEM) and elemental mapping analysis revealed an even distribution of poly(3,4-ethylenedioxythiophene) (PEDOT), reduced graphene oxide (rGO) and HKUST-1. The crystalline structure and vibration modes of PrGO/HKUST-1 were validated utilizing X-ray diffraction (XRD) as well as Raman spectroscopy, respectively. A remarkable specific capacitance (360.5 F/g) was obtained for PrGO/HKUST-1 compared to HKUST-1 (103.1 F/g), PrGO (98.5 F/g) and PEDOT (50.8 F/g) using KCl/PVA as a gel electrolyte. Moreover, PrGO/HKUST-1 composite with the longest charge/discharge time displayed excellent specific energy (21.0 Wh/kg), specific power (479.7 W/kg) and an outstanding cycle life (95.5%) over 4000 cycles. Thus, the PrGO/HKUST-1 can be recognized as a promising energy storage material.

Recent progress in metal-organic framework/graphene-derived materials for energy storage and conversion: design, preparation, and application

Graphene or chemically modified graphene, because of its high specific surface area and abundant functional groups, provides an ideal template for the controllable growth of metal-organic framework (MOF) particles. The nanocomposite assembled from graphene and MOFs can effectively overcome the limitations of low stability and poor conductivity of MOFs, greatly widening their application in the field of electrochemistry. Furthermore, it can also be utilized as a versatile precursor due to the tunable structure and composition for various derivatives with sophisticated structures, showing their unique advantages and great potential in many applications, especially energy storage and conversion. Therefore, the related studies have been becoming a hot research topic and have achieved great progress. This review summarizes comprehensively the latest methods of synthesizing MOFs/graphene and their derivatives, and their application in energy storage and conversion with a detailed analysis of the structure-property relationship. Additionally, the current challenges and opportunities in this field will be discussed with an outlook also provided.

MWCNT-mesoporous silica nanocomposites inserted in a polyhedral metal–organic framework as an advanced hybrid material for energy storage device

Hybridizing of trimetallic HKUST-1 with mesoporous SBA/CNT is highly desirable fot the improvement of energy and power densities in supercapacitors.

Metalloporphyrin-Based Metal-Organic Frameworks on Flexible Carbon Paper for Electrocatalytic Nitrite Oxidation

Deposition of redox-active metal-organic frameworks (MOFs) as thin films on conductive substrates is of great importance to improve their electrochemical performance and durability. In this work, a series of metalloporphyrinic MOF crystals was successfully deposited as thin films on carbon fiber paper (CFP) substrates, which is an alternative to rigid glass substrates. The specific dimensions of the obtained films could be adjusted easily by simple cutting. Metalloporphyrinic MOFs on CFP with different active metal species have been employed for electrochemical conversion of the carcinogenic nitrite into the less toxic nitrate. The MOFs on CFP exhibit remarkable improvement in terms of the electrocatalytic performance and reusability compared with the electrodes prepared from MOF powder. The contribution from metal species of the porphyrin units and reaction mechanisms was elucidated based on the findings from X-ray photoelectron spectroscopy (XPS) and in situ X-ray absorption near edge structure (XANES) measured during the electrochemical reaction. By integrating the redox-active property of metalloporphyrinic MOFs and high conductivity of CFP, MOF thin films on CFP provided a significant improvement of electrocatalytic performance to detoxify the carcinogenic nitrite with good stability.

An electrochemical sensor based on copper-based metal-organic framework-reduced graphene oxide composites for determination of 2,4-dichlorophenol in water

In the present work, we reported the fabrication of a novel electrochemical sensing platform to detect 2,4-dichlorophenol (2,4-DCP) by using a copper benzene-1,3,5-tricarboxylate-graphene oxide (Cu-BTC/GO) composite. The sensor was prepared by drop-casting Cu-BTC/GO suspension onto the electrode surface followed by electrochemical reduction, leading to the generation of an electrochemically reduced graphene oxide network (ErGO). By combining the large specific area of the Cu-BTC matrix with the electrical percolation from the graphene network, the number of accessible reaction sites was strongly increased, which consequently improved the detection performance. The electrochemical characteristics of the composite were revealed by cyclic voltammetry and electrochemical impedance spectroscopy. For the detection of 2,4-DCP, differential pulse voltammetry was used to emphasize the faradaic reaction related to the oxidation of the analyte. The results displayed a low detection limit (83 × 10-9 M) and a linear range from 1.5 × 10-6 M to 24 × 10-6 M alongside high reproducibility (RSD = 2.5% for eight independent sensors) and good stability. Importantly, the prepared sensors were sufficiently selective against interference from other pollutants in the same electrochemical window. Notably, the presented sensors have already proven their ability in detecting 2,4-DCP in real field samples with high accuracy (recovery range = 97.17-104.15%).

The Application of Metal-Organic Frameworks and Their Derivatives for Supercapacitors

Supercapacitors (SCs), one of the most popular types of energy-storage devices, present lots of advantages, such as large power density and fast charge/discharge capability. Being the promising SCs electrode materials, metal-organic frameworks (MOFs) and their derivatives have gained ever-increasing attention due to their large specific surface area, controllable porous structure and rich diversity. Herein, the recent development of MOFs-based materials and their application in SCs as the electrode are reviewed and summarized. The preparation method, the morphology of the materials and the electrical performance of various MOFs and their derivatives (such as carbon, metal oxide/hydroxide and metal sulfide) are briefly discussed. Most of recent works concentrate on Ni-, Co- and Mn-MOFs and their composites/derivatives. Conclusions and our outlook for the researches are also given, which would be a valuable guideline for the rational design of MOFs materials for SCs in the near future.

Graphene Oxide Protected Copper Benzene-1,3,5-Tricarboxylate for Clean Energy Gas Adsorption

Among microporous storage materials copper benzene-1,3,5-tricarboxylate (CuBTC MOF, Cu3(BTC)2 or HKUST-1) holds the greatest potential for clean energy gases. However, its usefulness is challenged by water vapor, either in the gas to be stored or in the environment. To determine the protection potential of graphene oxide (GO) HKUST1@GO composites containing 0-25% GO were synthesized and studied. In the highest concentration, GO was found to strongly affect HKUST-1 crystal growth in solvothermal conditions by increasing the pH of the reaction mixture. Otherwise, the GO content had practically no influence on the H2, CH4 and CO2 storage capacities, which were very similar to those from the findings of other groups. The water vapor resistance of a selected composite was compared to that of HKUST-1. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric (TG/DTG) and N2 adsorption techniques were used to monitor the changes in the crystal and pore structure. It was found that GO saves the copper-carboxyl coordination bonds by sacrificing the ester groups, formed during the solvothermal synthesis, between ethanol and the carboxyl groups on the GO sheets.

Advances in metal-organic framework coatings: versatile synthesis and broad applications

Metal-organic frameworks (MOFs) as a new kind of porous crystalline materials have attracted much interest in many applications due to their high porosity, diverse structures, and controllable chemical structures. However, the specific geometrical morphologies, limited functions and unsatisfactory performances of pure MOFs hinder their further applications. In recent years, an efficient approach to synthesize new composites to overcome the above issues has been achieved, by integrating MOF coatings with other functional materials, which have synergistic advantages in many potential applications, including batteries, supercapacitors, catalysis, gas storage and separation, sensors, drug delivery/cytoprotection and so on. Nevertheless, the systemic synthesis strategies and the relationships between their structures and application performances have not been reviewed comprehensively yet. This review emphasizes the recent advances in versatile synthesis strategies and broad applications of MOF coatings. A comprehensive discussion of the fundamental chemistry, classifications and functions of MOF coatings is provided first. Next, by modulating the different states (e.g. solid, liquid, and gas) of metal ion sources and organic ligands, the synthesis methods for MOF coatings on functional materials are systematically summarized. Then, many potential applications of MOF coatings are highlighted and their structure-property correlations are discussed. Finally, the opportunities and challenges for the future research of MOF coatings are proposed. This review on the deep understanding of MOF coatings will bring better directions into the rational design of high-performance MOF-based materials and open up new opportunities for MOF applications.

Nickel and cobalt metal-organic-frameworks-derived hollow microspheres porous carbon assembled from nanorods and nanospheres for outstanding supercapacitors

The development of efficient electrode materials is essential to promote the performance of energy storage equipment. Nowadays, metal organic frameworks (MOFs) have been widely regarded as active materials for supercapacitors mainly thanks to their adjustable structure and outstanding porosity. Here, highly optimized Nickel and Cobalt MOF-derived N-doped porous carbon (Ni/Co-MOF-NPC) are considered the best choice for electrode materials due to their unique structural properties and excellent electrochemical performance. Pure cobalt oxide rarely reaches a specific capacitance of 104.3 F g^-1 when the current density is 1 A g^-1, but the optimized Ni/Co-MOF-NPC-2:1 offers an ultra-high specific capacitance of 1214 F g^-1, which is much higher than that of pure cobalt oxide in a three-electrode test system. When the current density is 10 A g^-1, after 6000 cycles, the capacitance can still maintain 98.8% of the initial capacitance. Asymmetric supercapacitors were assembled using the prepared Ni/Co-MOF-NPC-2:1 as the positive electrode material, corrugated paper activated carbon (CPAC) as the negative electrode material, the prepared Ni/Co-MOF-NPC-2:1//CPAC exhibits an outstanding energy density of 55.4 Wh kg^-1 at 758.5 W kg^-1, and has a significant cycle stability of 75.2% retention after 20,000 cycles. This excellent MOF synthesis strategy reduced the gap between the experimental synthesis and practical application of MOF in fast energy storage.

Bimetallic MOF Nanosheets Decorated on Electrospun Nanofibers for High-Performance Asymmetric Supercapacitors

The rational design of metal-organic framework (MOF)-based materials with a huge specific surface area, high redox activity, and favorable conductivity is currently a hot subject for their potential usage in supercapacitor electrodes. Herein, novel bimetallic MOFs with a flowerlike nanosheet structure grown on the electrospun nanofibers (PPNF@M-Ni MOF, M = Co, Zn, Cu, Fe) have been prepared by controlling the incorporation of various types of metal ions, which display superior electrochemical performance. For example, PPNF@Co-Ni MOF possesses a large specific capacitance of 1096.2 F g^-1 (specific capacity of 548.1 C g^-1) at 1 A g^-1 and excellent rate performance. In addition, an asymmetric solid-state device composed of PPNF@Co-Ni MOF (positive materials) and KOH-activated carbon nanofibers embedded with reduced graphene oxide (negative materials) reaches a maximum energy density of 93.6 Wh kg^-1 at the power density of 1600.0 W kg^-1 and long cycling life. This work may greatly advance the research toward the design of supported MOF-based electrode materials for a promising prospect in energy conversion and storage.

Metal–organic frameworks with different spatial dimensions for supercapacitors

Recent progress in MOF materials for SCs with different spatial dimensions, such as 2D MOFs, including conductive MOFs and nanosheets, and 3D MOFs, categorized as single metallic and multiple metallic MOFs, are reviewed.

Construction of Hierarchical NiCo2O4@Ni-MOF Hybrid Arrays on Carbon Cloth as Superior Battery-Type Electrodes for Flexible Solid-State Hybrid Supercapacitors

Metal-organic frameworks (MOFs) have been considered as a class of promising electrode materials for supercapacitors owing to their large surface area, rich porosity, and variable redox sites; however, direct application of pristine MOFs in energy storage has been largely hindered by their poor electrical conductivity and stability issues. In this work, we demonstrate a facile two-step approach to address the controlled growth of Ni-MOF arrays on the surface of NiCo₂O₄ nanowires by modulating the formation reaction of MOFs. By taking advantage of the intriguing merits from the NiCo₂O₄ core and Ni-MOF shell as well as their synergistic effects, the optimized NiCo₂O₄@Ni-MOF hybrid electrode exhibits boosted electrochemical performance, in terms of high specific capacity (208.8 mA h/g at 2 mA/cm²) and good rate capability. In addition, the assembled flexible solid-state HSC device based on the optimized NiCo₂O₄@Ni-MOF and activated carbon as the cathode and anode achieves a maximum energy density of 32.6 W h/kg at a power density of 348.9 W/kg without sacrificing its outstanding cycling performance (nearly 100% retention over 6000 cycles at 8 mA/cm²) and mechanical stability, outperforming most recently reported MOF-based HSC devices in an aqueous electrolyte. Our work demonstrates the possibility of exploiting novel MOF-based hybrid arrays as battery-type electrodes with enhanced electrochemical properties, which exhibits great potential in flexible energy storage devices.

Dual Functionalized CuMOF-Based Composite for High-Performance Supercapacitors

Herein, we utilized our previously reported highly porous CuMOF, {[Cu₂(L)(H₂O)₂]·(5DMF)·(4H₂O)}_n, decorated with amine and trifluoromethyl functional groups for energy storage application. This robust framework in CuMOF enhances the chemical and thermal stabilities as well as improves the interfacial binding interactions. The poor conductivity of CuMOF usually restricts its practical utility in energy storage systems, due to which rGO was introduced along with CuMOF to form a CuMOF/rGO composite (1) through a facile ultrasonication technique. The synergistic effects between CuMOF and rGO induce a dramatic enhancement in specific capacitance (462 F g^-1 at 0.8 A g^-1) of 1 with a cycle life of 93.75% up to 1000 cycles. The results highlight 1 as an emerging contestant for next generation supercapacitors.

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.

High-Performance Symmetrical Supercapacitor with a Combination of a ZIF-67/rGO Composite Electrode and a Redox Additive Electrolyte

The synthesis of a highly porous composite of ZIF-67 and reduced graphene oxide (rGO) using a simple stirring approach is reported. The composite has been investigated as an electrode to be assembled in a supercapacitor. In the presence of an optimized redox additive electrolyte (RAE), that is, 0.2 M K3[Fe(CN)6] in 1 M Na2SO4, the ZIF-67/rGO composite electrode has combined the properties of improved conductivity, high specific surface area, and low resistance. The proposed composite electrode in the three-electrode system shows an ultrahigh specific capacitance of 1453 F g-1 at a current density of 4.5 A g-1 within a potential window of -0.1 to 0.5 V. Further, the ZIF-67/rGO composite electrode was used to fabricate a symmetrical supercapacitor whose operation in the presence of the RAE has delivered high values of specific capacitance (326 F g-1 at a current density of 3 A g-1) and energy density (25.5 W h kg-1 at a power density of 2.7 kW kg-1). The device could retain about 88% of its initial specific capacitance after 1000 repeated charge-discharge cycles. The practical usefulness of the device was also verified by combining two symmetrical supercapacitors in series and then lighting a white light-emitting diode (illumination for 3 min). This study, for the first time, reports the application of a ZIF-based composite (ZIF-67/rGO) in the presence of an RAE to design an efficient supercapacitor electrode. This proposed design is also scalable to a flexible symmetric device delivering high values of specific capacitance and energy density.