Synthesis and electrochemical characterization of nanostructured Ni-Co-MOF/graphene oxide composites as capacitor electrodes

Fabrication and assembly of supercapacitors based on Ni-based MOFs and their derivative materials for enhancing their electrochemical performances

Metal-organic frameworks (MOFs) are a class of porous materials that have been gradually applied in the field of supercapacitors, but they still present major challenges due to their inherent instability and poor conductivity. Herein, in order to solve these problems, Ni-based MOFs and their derivative materials with a particular spherical structure were prepared using a special calcination method. This unique structure not only improves the conductivity of the electrode, but also promotes the transport of electrons and ions during the electrochemical energy storage process. The as-prepared Ni-MOF@M-a4 has an amazing specific capacitance (637.78 F g-1) and a relatively low impedance. The fabricated asymmetric supercapacitor (ASC) consisted of Ni-MOF@M-a4 and activated carbon (AC) as positive and negative electrodes, respectively. The specific capacitance of this ASC was 18.14 F g-1. The maximum energy and power densities of the device reached 1.23 W h kg-1 and 175.00 W kg-1, showing good electrochemical performance. In this work, both an innovative strategy for the rational preparation of MOF arrays with good orientation and a special material preparation method are proposed, which have promising application potential in the field of asymmetric supercapacitors.

Plasma Engineering of Co4N/CoN Heterostructure for Boosting Supercapacitor Performance

Supercapacitor electrode materials play a decisive role in charge storage and significantly affect the cost and capacitive performance of the final device. Engineering of the heterostructure of metal-organic framework (MOF)-derived transition metal nitrides (TMNs) can be conducive to excellent electrochemical performance owing to the synergistic effect, optimized charge transport/mass transfer properties, and high electrical conductivity. In this study, a Co4N/CoN heterostructure was incorporated into a nitrogen-doped support by radio-frequency (RF) plasma after simple pyrolysis of Co-based formate frameworks (Co-MFFs), with the framework structure well retained. Plasma engineering can effectively increase the ratio of Co4N in the Co4N/CoN heterostructure, accelerating the electron transfer rate and resulting in a rough surface due to the reduction effect of high-energy electrons and the etching effect of ions. Benefiting from the plasma modification, the obtained electrode material Co4N/CoN@C-P exhibits a high specific capacitance of 346.2 F·g-1 at a current density of 1 A·g-1, approximately 1.7 times that of CoN/Co4N@C prepared by pyrolysis. The specific capacitance of Co4N/CoN@C-P reaches 335.6 F·g-1 at 10 A·g-1, approximately 96.9% of that at 1 A·g-1, indicating remarkable rate capability. Additionally, the capacitance retention remains at 100% even after 1000 cycles, suggesting excellent cycling stability. The rational design and plasma engineering of the TMN heterostructures at the nanoscale are responsible for the excellent electrochemical performance of this novel composite material.

Development of an aptasensor for highly sensitive detection of cardiac troponin I using cobalt-nickel metal-organic framework (CoNi-MOF)

Objective and rationale

This study aimed to develop a highly sensitive and selective single-stranded DNA (ssDNA) aptamer targeting cardiac troponin I (cTnI), a crucial biomarker for acute myocardial infarction (AMI). The objective was to fabricate a novel aptamer electrochemical sensor using a composite material of cobalt-nickel metal-organic framework (CoNi-MOF) on screen-printed carbon electrodes (SPCE), leveraging the composite's large surface area and excellent electrical conductivity alongside the aptamer's high affinity for cTnI.

Methods

The aptamer electrochemical sensor was fabricated using the CoNi-MOF composite on SPCE and characterized its properties. They conducted electrochemical measurements to assess the sensor's performance in detecting cTnI. The sensor's stability, reproducibility, and electro-catalytic activity were evaluated.

Results

The sensor demonstrated linear detection of cTnI over a concentration range of 5-75 pg/mL, with a low limit of detection (LOD) of 13.2 pM. Remarkable stability and reproducibility were observed in cTnI detection. The sensor exhibited exceptional electro-catalytic activity, enabling accurate quantification of cTnI levels in various solutions.

Conclusions

This research presents a significant advancement towards the development of reliable, cost-effective, and easily deployable cTnI sensors for clinical applications. The sensor's versatility in detecting cTnI across different concentration ranges highlights its potential utility in diverse clinical settings, particularly for early detection and monitoring of cardiac conditions.

Integration of a Bismuth-Based Tris-Mononuclear Complex with 2D Functional Materials for Highly Efficient and Durable Aqueous Electrocatalytic Hydrogen Evolution

The eminence of transitioning from traditional fossil fuel-based energy resources to renewable and sustainable energy sources is most evidently crucial. The potential of hydrogen as an alternative energy source has specifically focuses the electrocatalytic water splitting (EWS) as a promising technique for generating hydrogen. Development of efficient electrocatalysts to facilitate the EWS process while rationalizing the limitations of noble metal catalysts like platinum has become one of the daunting tasks. Consequently, porous functional materials such as metal complexes (MCs) and graphene oxide (GO) can act as potential catalysts for EWS. Therefore, a composite of GO and a mononuclear bismuth metal complex is synthesized through in situ facile synthesis, which is further utilized as an efficient electrocatalyst for the hydrogen evolution reaction (HER). Several potential electrocatalytic MC@GO composite (BMGO-3,5,7) materials were prepared with compositional variation of GO (3, 5, and 7 wt %). The experimental results demonstrate that the BMGO5 composite exhibits excellent HER activity with a low overpotential value of 105 mV at 10 mA cm-2 and a low Tafel slope of 44 mV dec-1 in 1 M KOH solution. Furthermore, a comprehensive investigation on the potentiality of the BMC-GO composite for hydrogen evolution from river water splitting was performed in order to address the issue of freshwater depletion. Inclusion of a mononuclear MC for facile synthesis of functional GO-based efficient electrocatalyst material is very scanty in the literature. This unique approach could assist future research endeavors toward designing efficient electrocatalysts for sustainable renewable energy generation. This is one of the first of its kind, where mononuclear MCs were utilized to develop GO-based functional composite materials for efficient electrocatalysis toward sustainable renewable energy generation.

Morphology Control of Mixed Metallic Organic Framework for High-Performance Hybrid Supercapacitors

The study presents the binder-free synthesis of mixed metallic organic frameworks (MMOFs) supported on a ternary metal oxide (TMO) core as an innovative three-dimensional (3D) approach to enhance electron transport and mass transfer during the electrochemical charge-discharge process, resulting in high-performance hybrid supercapacitors. The research demonstrates that the choice of organic linkers can be used to tailor the morphology of these MMOFs, thus optimizing their electrochemical efficiency. Specifically, a NiCo-MOF@NiCoO2@Ni electrode, based on terephthalic linkers, exhibits highly ordered porosity and a vast internal surface area, achieving a maximum specific capacity of 2320 mC cm-2, while maintaining excellent rate capability and cycle stability. With these performances, the hybrid supercapacitor (HSC) achieves a maximum specific capacitance of 424.6 mF cm-2 (specific capacity 653.8 mC cm-2) and 30.7 F cm-3 with energy density values of 10.1 mWh cm-3 at 167.4 mW cm-3 (139.8 µWh cm-2 at 2310 µW cm-2), which are higher than those of previously reported MMOFs based electrodes. This research introduces a novel approach for metal organic framework based HSC electrodes, diverging from the traditional emphasis on metal ions, in order to achieve the desired electrochemical performance.

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.

Electrochemical Nanosensor for the Simultaneous Determination of Anticancer Drugs Epirubicin and Topotecan Using UiO-66-NH2/GO Nanocomposite Modified Electrode

In this work, UiO-66-NH2/GO nanocomposite was prepared using a simple solvothermal technique, and its structure and morphology were characterized using field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). An enhanced electrochemical sensor for the detection of epirubicin (EP) was proposed, which utilized a UiO-66-NH2/GO nanocomposite-modified screen-printed graphite electrode (UiO-66-NH2/GO/SPGE). The prepared UiO-66-NH2/GO nanocomposite improved the electrochemical performance of the SPGE towards the redox reaction of EP. Under optimized experimental conditions, this sensor demonstrates a remarkable limit of detection (LOD) of 0.003 µM and a linear dynamic range from 0.008 to 200.0 µM, providing a highly capable platform for sensing EP. Furthermore, the simultaneous electro-catalytic oxidation of EP and topotecan (TP) was investigated at the UiO-66-NH2/GO/SPGE surface utilizing differential pulse voltammetry (DPV). DPV measurements revealed the presence of two distinct oxidation peaks of EP and TP, with a peak potential separation of 200 mV. Finally, the UiO-66-NH2/GO/SPGE sensor was successfully utilized for the quantitative analysis of EP and TP in pharmaceutical injection, yielding highly satisfactory results.

Strategies for Advanced Supercapacitors Based on 2D Transition Metal Dichalcogenides: From Material Design to Device Setup

Recently, the development of new materials and devices has become the main research focus in the field of energy. Supercapacitors (SCs) have attracted significant attention due to their high power density, fast charge/discharge rate, and excellent cycling stability. With a lamellar structure, 2D transition metal dichalcogenides (2D TMDs) emerge as electrode materials for SCs. Although many 2D TMDs with excellent energy storage capability have been reported, further optimization of electrode materials and devices is still needed for competitive electrochemical performance. Previous reviews have focused on the performance of 2D TMDs as electrode materials in SCs, especially on their modification. Herein, the effects of element doping, morphology, structure and phase, composite, hybrid configuration, and electrolyte are emphatically discussed on the overall performance of 2D TMDs-based SCs from the perspective of device optimization. Finally, the opportunities and challenges of 2D TMDs-based SCs in the field are highlighted, and personal perspectives on methods and ideas for high-performance energy storage devices are provided.

Redox active pyridine-3,5-di-carboxylate- and 1,2,3,4-cyclopentane tetra-carboxylate-based cobalt metal-organic frameworks for hybrid supercapacitors

In the pursuit of developing superior energy storage devices, an integrated approach has been advocated to harness the desirable features of both batteries and supercapacitors, particularly their high energy density, and high-power density. Consequently, the emergence of hybrid supercapacitors has become a subject of increasing interest, as they offer the potential to merge the complementary attributes of these two technologies into a single device, thereby surpassing the limitations of conventional energy storage systems. In this context the Metal-Organic Frameworks (MOFs), consisting of metal centers and organic linkers, have emerged as highly trending materials for energy storage by virtue of their high porosity. Here, we investigate the electrochemical performance of cobalt-pyridine-3,5-di-carboxylate-MOF (Co-PDC-MOF) and cobalt-1,2,3,4-cyclopentane tetra-carboxylate-MOF (Co-CPTC-MOF). In the setup involving the analysis of Co-PDC-MOF and Co-CPTC-MOF materials, a configuration comprising three electrodes was utilized. Drawing upon the promising initial properties of CPTC, a battery device was fabricated, comprising Co-CPTC-MOF, and activated carbon (AC) electrodes. Retaining a reversible capacity of 97% the device showcased impressive energy and power density of 20.7 W h g^-1 and 2608.5 W kg^-1, respectively. Dunn's model was employed, to gain deeper insights into the capacitive and diffusive contributions of the device.

Three-dimensional graphene/metal-organic framework composites for electrochemical energy storage and conversion

Three-dimensional graphene (3DG)/metal-organic framework (MOF)-based composites have attracted more and more attention in the field of energy due to their unique hierarchical porous structure and properties. The combination of graphene with MOFs can not only effectively overcome the limitations of poor electrical conductivity and low stability of MOFs, but also prevent the aggregation and reaccumulation between graphene sheets. Moreover, 3DG/MOF composites can also be used as multifunctional precursors with adjustable structures and composition of derivatives, thus expanding their applications in the field of electrochemistry. This feature article elaborates the latest synthesis methods of 3DG/MOF composites and their derivatives, along with their applications in batteries, supercapacitors (SCs) and electrocatalysis. In addition, the current challenges and future prospects of 3DG/MOF-based composites are discussed.

MOF-Derived Ultrathin NiCo-S Nanosheet Hybrid Array Electrodes Prepared on Nickel Foam for High-Performance Supercapacitors

At present, binary bimetallic sulfides are widely studied in supercapacitors due to their high conductivity and excellent specific capacitance (SC). In this article, NiCo-S nanostructured hybrid electrode materials were prepared on nickel foam (NF) by using a binary metal-organic skeleton as the sacrificial template via a two-step hydrothermal method. Comparative analysis was carried out with Ni-S and Co-S in situ on NF to verify the excellent electrochemical performance of bimetallic sulfide as an electrode material for supercapacitors. NiCo-S/NF exhibited an SC of 2081 F∙g^-1 at 1 A∙g^-1, significantly superior to Ni-S/NF (1520.8 F∙g^-1 at 1 A∙g^-1) and Co-S/NF (1427 F∙g^-1 at 1 A∙g^-1). In addition, the material demonstrated better rate performance and cycle stability, with a specific capacity retention rate of 58% at 10 A∙g^-1 than at 1 A∙g^-1, and 75.7% of capacity was retained after 5000 cycles. The hybrid supercapacitor assembled by NiCo-S//AC exhibited a high energy density of 25.58 Wh∙kg^-1 at a power density of 400 W∙kg^-1.

In Situ Synthesis of Ni-BTC Metal-Organic Framework@Graphene Oxide Composites for High-Performance Supercapacitor Electrodes

In response to serious ecological and environmental problems worldwide, a novel graphene oxide (GO) induction method for the in situ synthesis of GO/metal organic framework (MOF) composites (Ni-BTC@GO) for supercapacitors with excellent performance is presented in this study. For the synthesis of the composites, 1,3,5-benzenetricarboxylic acid (BTC) is used as an organic ligand due to its economic advantages. The optimum amount of GO is determined by a comprehensive analysis of morphological characteristics and electrochemical tests. 3D Ni-BTC@GO composites show a similar spatial structure to that of Ni-BTC, revealing that Ni-BTC could provide an effective framework and avoid GO aggregation. The Ni-BTC@GO composites have a more stable electrolyte-electrode interface and an improved electron transfer route than pristine GO and Ni-BTC. The synergistic effects of GO dispersion and Ni-BTC framework on electrochemical behavior are determined, where Ni-BTC@GO 2 achieves the best performance in energy storage performance. Based on the results, the maximum specific capacitance is 1199 F/g at 1 A/g. Ni-BTC@GO 2 has an excellent cycling stability of 84.47% after 5000 cycles at 10 A/g. Moreover, the assembled asymmetric capacitor exhibits an energy density of 40.89 Wh/kg at 800 W/kg, and it still remains at 24.44 Wh/kg at 7998 W/kg. This material is expected to contribute to the design of excellent GO-based supercapacitor electrodes.

Metal-Organic Framework Composites and Their Derivatives as Efficient Electrodes for Energy Storage Applications: Recent Progress and Future Perspectives

Metal-organic frameworks (MOFs) have been important electrochemical energy storage (EES) materials because of their rich species, large specific surface area, high porosity and rich active sites. Nevertheless, the poor conductivity, low mechanical and electrochemical stability of pristine MOFs have hindered their further applications. Although single component MOF derivatives have higher conductivity, self-aggregation often occurs during preparation. Composite design can overcome the shortcomings of MOFs and derivatives and create synergistic effects, resulting in improved electrochemical properties for EES. In this review, recent applications of MOF composites and derivatives as electrodes in different types of batteries and supercapacitors are critically discussed. The advantages, challenges, and future perspectives of MOF composites and derivatives have been given. This review may guide the development of high-performance MOF composites and derivatives in the field of EES.

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.

Ni-MOF composite polypyrrole applied to supercapacitor energy storage

Electrodes for supercapacitors made from metal-organic frameworks (MOFs) are still hindered by electron transfer properties. Therefore, an electrode composite material Ni-MOF@PPy was synthesized from a Ni-based metal-organic framework (Ni-MOF) doped with poly-pyrrole (PPy) using a simple chemical oxidation method to improve its electron transfer property. After introducing the electrochemically active substance K₄Fe(CN)₆ into the electrolyte, the composite material had a specific capacitance of 1815.4 F g^-1 at a current density of 1 A g^-1. Ni-MOF@PPy and active carbon (AC) as the positive and negative electrodes have been used, respectively, to assemble asymmetric supercapacitors (ASCs) in the KOH and K₄Fe(CN)₆ mixed electrolyte. This novel Ni-MOF@PPy//AC ASC energy storage device can provide 38.5 W h kg^-1 energy density, 7001 W kg^-1 power density, and 90.2% capacitance retention after 3000 cycles. Therefore, Ni-MOF@PPy//AC ASC is an excellent energy storage device with practical and economic value. The synergistic effect strategy proposed in this work can be easily applied to develop other MOFs with unique crystal structures as well as other redox active additives, providing new avenues and research ideas for exploring novel energy storage devices.

Architecting Nanostructured Co-BTC@GO Composites for Supercapacitor Electrode Application

Herein, we present an innovative graphene oxide (GO)-induced strategy for synthesizing GO-based metal-organic-framework composites (Co-BTC@GO) for high-performance supercapacitors. 1,3,5-Benzene tricarboxylic acid (BTC) is used as an inexpensive organic ligand for the synthesis of composites. An optimal GO dosage was ascertained by the combined analysis of morphology characterization and electrochemical measurement. The 3D Co-BTC@GO composites display a microsphere morphology similar to that of Co-BTC, indicating the framework effect of Co-BTC on GO dispersion. The Co-BTC@GO composites own a stable interface between the electrolyte and electrodes, as well as a better charge transfer path than pristine GO and Co-BTC. A study was conducted to determine the synergistic effects and electrochemical behavior of GO content on Co-BTC. The highest energy storage performance was achieved for Co-BTC@GO 2 (GO dosage is 0.02 g). The maximum specific capacitance was 1144 F/g at 1 A/g, with an excellent rate capability. After 2000 cycles, Co-BTC@GO 2 maintains outstanding life stability of 88.1%. It is expected that this material will throw light on the development of supercapacitor electrodes that hold good electrochemical properties.

One-Step Solvothermal Synthesis of Raspberry-like NiCo-MOF for High-Performance Flexible Supercapacitors for a Wide Operation Temperature Range

As a novel electrode material for energy storage, metal-organic frameworks (MOFs) emerge with plenty of merits and certain drawbacks in the field of supercapacitors. Nevertheless, most MOFs synthesized for the moment are faced with dimension/distribution issues and dissatisfactory electrical conductivity. Hence, in this paper, NiCo-MOF was successfully fabricated by applying a one-step solvothermal method, from which NiCo-MOF-3 presents an optimal electrochemical performance compared to other NiCo-MOFs and Ni/Co-MOF. Owing to its unique three-dimensional spherical raspberry structure, NiCo-MOF-3 demonstrates an available internal resistance and electron transfer resistance to ameliorate electrical energy storage, exhibiting an excellent mass specific capacitance of 639.8 F/g at 1 A/g. Then, a flexible quasi-solid-state asymmetric supercapacitor was assembled with NiCo-MOF-3 as the positive electrode. The introduction of K₃[Fe(CN)₆] and glycerin in the gel electrolyte facilitates the maximum energy density of 66.3 Wh/kg of the device, with a corresponding power density reaching its maximum of 12,047 W/kg. The device's apparent energy density, excellent flexibility, and temperature resistance reveal that our method to prepare supercapacitor electrode material possesses more advantages than those in the former literature.

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.

Metal-organic framework (MOF) composites as promising materials for energy storage applications

Metal-organic framework (MOF) composites are considered to be one of the most vital energy storage materials due to their advantages of high porousness, multifunction, various structures and controllable chemical compositions, which provide a great possibility to find suitable electrode materials for batteries and supercapacitors. However, MOF composites are still in the face of various challenges and difficulties that hinder their practical application. In this review, we introduce and summarize the applications of MOF composites in batteries, covering metal-ion batteries, lithium-sulfur batteries, lithium-oxygen batteries and zinc-air batteries, as well as supercapacitors. In addition, the application challenges of MOF composites in batteries and supercapacitors are also summarized. Finally, the basic ideas and directions for further development of these two types of electrochemical energy storage devices are proposed.

Rising of MXenes: Novel 2D-functionalized nanomaterials as a new milestone in corrosion science - a critical review

Corrosion is a natural process between a metal and its environment that can gradually cause catastrophic damage to the metal equipment, which would have economic implications. Consequently, several protective methods have been utilized to prevent metals from severe degradation. Organic polymeric coatings have been widely used as the most convenient and cost-effective method to boost metals' anti-corrosion properties. Nonetheless, these coatings have a significant amount of solvent, resulting in shrinkage and micro defects in the films during the curing process. Many studies have verified that transition metal carbides/nitrides (MXenes) can form a "labyrinth effect" in the polymeric coatings due to their "nano-barrier effect". Furthermore, based on their sheet-like structures, they can considerably cover the surface defects of the polymeric films. Therefore, the penetration of corrosive elements can be substantially curbed. It is the first review that specifically focused on the new family of 2D nanomaterials, i.e., MXenes, and discussed their applications in corrosion protection systems. The MXenes' pros and cons in the polymeric matrixes as nanofillers will be clarified. Moreover, the synthesis and functionalization methods of the MXenes, their applications, and corrosion protection mechanism will be explored. Subsequently, the MXenes' superiority over other 2D nanomaterials will be highlighted while their future perspectives and industrial applications will be predicted.

The Growth of Metal–Organic Frameworks in the Presence of Graphene Oxide: A Mini Review

Integrated metal–organic frameworks (MOFs) with graphene oxide (GO) have aroused huge interest in recent years due to their unique properties and excellent performance compared to MOFs or GO alone. While a lot of attention has been focused on the synthesis methodologies and the performance analysis of the composite materials in recent years, the fundamental formation/crystallization mechanism(s) is (are) still not fully understood. Ascribed to the distinctive structural and functional properties of GO, the nucleation and crystallization process of MOFs could be altered/promoted, forming MOF/GO composite materials with different nanostructures. Furthermore, the MOF’s parental structure could also influence how the GO and MOF bond together. Thus, this short review attempted to provide critical and indepth discussions of recent research results with a particular focus on the factors that influence the directional growth of parent MOFs in the presence of graphene oxide. Due to the unique structure and enhanced properties, the derived MOF/GO composites have a wide range of applications including gas separation, electrochemistry, and photocatalysis. We hope this review will be of interest to researchers working on MOF design, crystal structure control (e.g., orientation), and composite materials development.

Design of ZIF-67 MOF-derived Co3O4/NiCo2O4 nanosheets for supercapacitor electrode materials

Binary transition metal oxides exhibit improved properties including good redox potentials and electrical conductivities compared with single metal oxides as electrode materials in energy storage. Herein, ZIF-67 is prepared by a one-step method using Co2+ as the central metal ion, 2-methylimidazole as the organic ligand, and methanol as an organic solvent at room temperature. Hollow NiCo2O4 and sheet-like Co3O4/NiCo2O4 derived from bimetallic imidazolate framework precursors were synthesized by adding cobalt and nickel ions in appropriate proportions. A hollow and porous structure is achieved for the reaction between a nickel salt and ZIF-67, and this unique nanostructure provides a high active surface area, which is beneficial to the electrochemical properties. Several samples are prepared and used as electrode materials for electrochemical tests in 6 M KOH. As a result, the Co3O4/NiCo2O4 electrode with a sheet nanostructure showed a high specific capacitance of 846 F g−1 at a current density of 0.5 A g−1. This Co3O4/NiCo2O4 electrode material is promising for future studies on high-performance supercapacitors to solve emerging energy-related problems.

[Formula: see text]

Electrically Conductive Networks from Hybrids of Carbon Nanotubes and Graphene Created by Laser Radiation

A technology for the formation of electrically conductive nanostructures from single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), and their hybrids with reduced graphene oxide (rGO) on Si substrate has been developed. Under the action of single pulses of laser irradiation, nanowelding of SWCNT and MWCNT nanotubes with graphene sheets was obtained. Dependences of electromagnetic wave absorption by films of short and long nanotubes with subnanometer and nanometer diameters on wavelength are calculated. It was determined from dependences that absorption maxima of various types of nanotubes are in the wavelength region of about 266 nm. It was found that contact between nanotube and graphene was formed in time up to 400 fs. Formation of networks of SWCNT/MWCNT and their hybrids with rGO at threshold energy densities of 0.3/0.5 J/cm² is shown. With an increase in energy density above the threshold value, formation of amorphous carbon nanoinclusions on the surface of nanotubes was demonstrated. For all films, except the MWCNT film, an increase in defectiveness after laser irradiation was obtained, which is associated with appearance of C–C bonds with neighboring nanotubes or graphene sheets. CNTs played the role of bridges connecting graphene sheets. Laser-synthesized hybrid nanostructures demonstrated the highest hardness compared to pure nanotubes. Maximum hardness (52.7 GPa) was obtained for MWCNT/rGO topology. Regularity of an increase in electrical conductivity of nanostructures after laser irradiation has been established for films made of all nanomaterials. Hybrid structures of nanotubes and graphene sheets have the highest electrical conductivity compared to networks of pure nanotubes. Maximum electrical conductivity was obtained for MWCNT/rGO hybrid structure (~22.6 kS/m). Networks of nanotubes and CNT/rGO hybrids can be used to form strong electrically conductive interconnections in nanoelectronics, as well as to create components for flexible electronics and bioelectronics, including intelligent wearable devices (IWDs).

Porous carbon derived from ZIF-8 modified molecularly imprinted electrochemical sensor for the detection of tert-butyl hydroquinone (TBHQ) in edible oil

In this manuscript, ZIF-8 derived nanoporous carbon material (ZC) was prepared and used as modification material to construct a molecularly imprinted electrochemical sensor for the direct detection of tert-butyl hydroquinone (TBHQ) in edible oil. Electrochemical characterizations, scanning electron microscopy and X-ray diffraction show that ZC has excellent conductivity, high electrochemical active area and stable porous framework structure. Using TBHQ as template and o-phenylenediamine as functional monomer, the sensor was constructed. Experimental parameters such as the number of polymerization cycle, polymerization speed, and pH of the measured solution, removal and rebinding time were studied. Under optimized conditions, the prepared sensor showed a wider linear range from 1.0 μmol L^-1 to 75.0 μmol L^-1 with the detection limit of 0.42 μmol L^-1 (S/N = 3). Meanwhile, the sensor also expressed good selectivity, repeatability, reproducibility, stability and successfully applied for the determination of TBHQ in real edible oil, giving satisfactory results.

Enhanced electrochemical and capacitive deionization performance of metal organic framework/holey graphene composite electrodes

In this paper, we designed and prepared a novel metal organic framework (MOF)/holey graphene (HG) composites as electrode materials for electrochemistry and capacitive deionization (CDI). The MOF nanoparticles were attached to the surface of the HG sheets to form layered porous structure, which promoted the transport of ions and electrons in the electrode/electrolyte interfaces. Additionally, the synergistic effect of these composite electrodes, which combined pseudocapacitance performance of MOF and the high conductivity of graphene, contributed to enhancing the performance of electrochemistry and CDI. The MOF/HG-2 exhibited high capacitances of 526 F g^-1 at current rates of 0.1 A g^-1, low charge transfer resistance of 0.53 Ω, and excellent cycling stability (retention of about 90.3% after 5000 cycles at 2 A g^-1). As electrode materials for CDI, the MOF/HG-2 displayed a remarkable electrosorption capacity of 39.6 mg g^-1 with initial salt concentration of 800 mg L^-1, and there was no obvious attenuation after 20 CDI regeneration cycles. These results confirmed that MOF/HG was a promising electrode material for the actual application of CDI.

Enhanced capacitive performance of a Ag-functionalized low crystalline Co3O4/graphene composite

The addition of Ag increased the capacitance of Co3O4 nanowires by about 5.8 times.

Metal-Organosulfide Coordination Polymer Nanosheet Array as a Battery-Type Electrode for an Asymmetric Supercapacitor

Metal-organosulfide coordination polymers (MOSCPs) are important functional materials with attractive application prospects. Herein a two-dimensional structural MOSCP was fabricated on nickel foam with nanosheet array morphology. When as the binder-free battery-type electrode for a supercapacitor, the as-prepared Co-based MOSCP showed high specific capacitance (759 F g^-1/379.5 C g^-1/105.4 mAh g^-1 at 0.5 A g^-1), excellent rate performance (58.8% after the current density increased 20 times), and good cycle stability (73.4% after 5000 cycles). In addition, a maximum energy density of 31.97 Wh kg^-1 was obtained at a power density of 375.01 W kg^-1 in the assembled asymmetric supercapacitor device. These results indicated that this work would open up a new path to design and prepare the battery-type electrode for a supercapacitor by exploring nanoscale MOSCP materials.

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.

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.

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.

Nitrogen-doped carbon integrated nickel–cobalt metal phosphide marigold flowers as a high capacity electrode for hybrid supercapacitors

The fabrication of advanced MOF-derived multicomponent NiCoP/NC marigold flowers electrode for high-performance hybrid supercapacitors.

N-Doped porous tremella-like Fe3C/C electrocatalysts derived from metal–organic frameworks for oxygen reduction reaction

A tremella-like porous Fe₃C/C nanocomposite derived from metal–organic frameworks shows improved oxygen reduction reaction performance.

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.