Cobalt-Based Layered Metal-Organic Framework as an Ultrahigh Capacity Supercapacitor Electrode Material

Thiol-functionalized conductive Co-MOF and its derivatives S-doped Co(OH)2 nanoflowers for high-performance supercapacitors

The low conductivity of many traditional metal-organic-framework (MOF)-based electrode limits their developments in the field of electrochemical energy storage and still of great challenge. The controllable preparation of various kinds of nanomaterials using thiol-functionalized MOF shows great prospects. In this work, a thiol-functionalized metal-organic framework sheet structure (Co-MOF/NF) on nickel foam was successfully prepared by in situ interfacial growth synthesis, which was transformed into its derivatives S-doped β-Co(OH)2 nanoflowers Co-x/NF (x = 1, 2 and 6) in different concentrations of KOH solutions through ion etching/exchange reaction. The pristine thiol-functionalized Co-MOF/NF and its derivatives Co-x/NF (x = 1, 2 and 6) nanoflower-like arrays could be used as positive electrode materials for effective supercapacitors. Among them, the transformation of the nanoflower-like Co-1/NF electrode exhibits excellent electrochemical properties with high areal capacitance (1925 ± 23 mF/cm2 at 1 mA/cm2), good rate performance, excellent conductivity and decent cycling stability. The Co-1//AC ASC device provides a high energy density of 0.176 mWh/cm2 (92.6 Wh/kg) at a power density of 0.745 mW/cm2 (392.1 W/kg). And this Co-1//AC ASC device exhibits a good cycling stability and practical application in energy storage field. This study provides a new strategy for the pristine thiol-functionalized MOF and its conversion nanostructures for energy storage applications.

Concrete-based energy storage: exploring electrode and electrolyte enhancements

The exploration of concrete-based energy storage devices represents a demanding field of research that aligns with the emerging concept of creating multifunctional and intelligent building solutions. The increasing need to attain zero carbon emissions and harness renewable energy sources underscores the importance of advancing energy storage technologies. A recent focus has been on structural supercapacitors, which not only store electrochemical energy but also support mechanical loads, presenting a promising avenue for research. We comprehensively review concrete-based energy storage devices, focusing on their unique properties, such as durability, widespread availability, low environmental impact, and advantages. First, we elucidate how concrete and its composites revolutionize basic building blocks for the design and fabrication of intrinsically strong structural materials. Afterward, we categorized concrete into two major parts of a supercapacitor, i.e., electrode and electrolyte materials. We further describe the synthesis of concrete-based electrodes and electrolytes and highlight the main points to be addressed while synthesizing porous surface/electroactive matrices. The incorporation of carbon, polymers, metals, etc., enhances the energy density and durability of electrode materials. Furthermore, as an electrolyte, how concrete accommodates metal salts and the mode of diffusion/transport have been described. Although pure concrete electrolytes exhibit poor ionic conductivity, the addition of conducting polymers, metal/metal oxides, and carbon increases the overall performance of energy storage devices. At the end of the review, we discuss the challenges and perspectives on future research directions and provide overall conclusions.

Tailoring the Coordination Microenvironment of Polymolybdate within a Metal-Organic Coordination System for Enhanced Capacitive Activity

The design of a low-cost and efficient electrode material is crucial for electrochemical energy storage. Effectual utilization of polymolybdate as an electrode material for a supercapacitor is promising. Meanwhile, the coordination microenvironments of polymolybdate sho potential effects on its performance. Herein, we designed and synthesized four polymolybdate-based metal-organic complexes using a structure design strategy. Their structures were characterized and analyzed using single crystallographic data. The theoretical calculations revealed that the coordination microenvironments of polymolybdate play a vital role in the hydrogen ions migration. High H adsorption capacity can obviously boost the electrochemical activity. The 1-based glassy carbon electrode showed the highest specific capacitance value of 1739.4 F·g-1 at the current density of 1 A·g-1. Meanwhile, the carbon cloth-based electrode fabricated by complex 1 (1/CC) also displayed a high capacitance performance. A hybrid supercapacitor was assembled using the 1/CC electrodes and showed a high energy density of 29.0 Wh kg-1 at the power density of 0.80 kW kg-1.

Electrodeposition of porous metal-organic frameworks for efficient charge storage

Efficient charge storage is a key requirement for a range of applications, including energy storage devices and catalysis. Metal-organic frameworks are potential materials for efficient charge storage due to their self-supported three-dimensional design. MOFs are high surface area materials made up of coordination of appropriate amounts of metal ions and organic linkers, hence used in various applications. Yet, creating an effective MOF nanostructure with reduced random crystal formation continues to be a difficult task. The energy efficiency and electrochemical yield of bulk electrodes are improved in this study by demonstrating an effective technique for growing MOFs over a conducting substrate utilizing electrodeposition. An exceptionally stable asymmetric supercapacitor is created when activated carbon cloth is combined with the resulting MOF structure that was directly synthesized via an electrochemical method resulting in 97% stability over 5k cycles which is higher than conventional processes. High performance in supercapacitors is ensured by this practical approach for producing MOF electrodes, making it a suitable structure for effective charge storage.

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.

Al-MOF-derived porous carbon-modified Pt/C catalyst for constructing a high-performance super fuel cell via an ORR + EDLC parallel-discharge mechanism

In order to reduce the high polarization caused by the hysteresis effect of O2 diffusion and boost the power density of oxygen cathodes under a transient heavy load, an Al-MOF-derived porous carbon-modified Pt/C catalyst is proposed as a new capacitive ORR catalyst to construct super fuel cells (SFCs) via an ORR + EDLC dual-discharge parallel process. Herein, a capacitive porous carbon material (BTCC-2) with a large specific surface area (SSA) and high graphitization was synthesized via one-step carbonization of Al-MOFs (Al-BTC). After compounding BTCC-2 with commercial Pt/C catalysts, electrochemical tests were performed and revealed that the composite with 40% BTCC-2 provided the highest transient discharge performance. Moreover, the composite had a higher onset potential and limiting current density (5.236 mA cm-2) than Pt/C and a half-wave potential (0.833 V) comparable to that of Pt/C. The abundant pore structure and large surface of BTCC-2 greatly increased the interaction between oxygen and the catalyst surface. Besides, the contained BTCC-2 serve as a significant power bank to remarkably buffer and relieve the rapidly decreasing output voltage under an instant heavy load owing to the oxygen deficiencies in a Zn-air battery through the ORR + EDLC dual-parallel-discharge process. The proposed SFC design has potential as a universal method to solve the sluggish ORR process and provide high transient power density for fuel cell-driven vehicles.

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.

Ultrafast and Scalable Fabrication of Coordination Polymer Films on Network Substrates via Thermal Current-Induced Dewetting

Coordination polymers are among the most favored active materials by researchers due to their broad application prospects. However, most of them are usually difficult to directly process into applicable devices because of their unsatisfied processability. One process of great concern for researchers is the in situ preparation of the coordination polymer on the applicable substrate, especially for the favored network substrates with good mechanical properties and 3D porous structure, which could provide obvious convenience and facilitation in the application process. Herein, we present an ultrafast and scalable thermal current-induced dewetting strategy to obtain uniform coordination polymer film in situ on network substrates, which could enable unprecedented convenience to obtain directly usable coordination polymer composites such as practical catalytic electrodes with excellent electrocatalytic performance. The proposed thermal current-induced dewetting method provides a highly adaptable and efficient practical production approach to integrate coordination polymer materials with network substrates and also provides new inspiration for understanding and applying the dewetting process on complex 3D network substrates.

Co-containing metal-organic framework for high-performance asymmetric supercapacitors with functionalized reduced graphene oxide

Nowadays, supercapacitors are the most coveted eco-friendly and sustainable next-generation energy storage devices. In this regard, developing supercapacitors with high energy density and power density has always been a challenge for researchers. Herein, we have exploited an electroactive Co-containing metal-organic framework (Co-MOF) using cheap and commercially available starting materials under refluxing conditions and explored its energy storage properties in three- and two-electrode methods. The Co-MOF exhibited a specific capacitance of 425 F g-1 at 2 A g-1, maintaining a capacitance of ∼78% over 2200 successive charge-discharge cycles in a three-electrode system. The two-electrode asymmetric supercapacitor (ASC) using Co-MOF as the working electrode and as-synthesized p-phenylenediamine (PPD)-functionalized reduced graphene oxide (PPD-rGO) as the counter electrode divulged a specific capacitance of 72.5 F g-1 at 2 A g-1 current density with ∼70% capacitive retention after 2200 successive charge-discharge cycles over a broad potential window of 0-1.6 V. Moreover, the ASC demonstrated a maximum power density of 11.9 kW kg-1 at 10 A g-1 and a maximum energy density of 25.8 W h kg-1 at 2 A g-1 current density. Owing to the stable electrochemical redox (Co2+/Co3+)-mediated pseudocapacitive behavior of the Co-MOF and the high surface area and electrical conductivity of in situ generated PPD-intercalated rGO, the fabricated ASC unveiled high-performance supercapacitive behaviors. To investigate the practical applicability of this material, solid-state (ASC) devices were fabricated by employing the Co-MOF as the positive electrode and PPD-rGO as the negative electrode in a KOH-based gel electrolyte, which could power a commercially available light-emitting diode bulb (∼1.8 V) for several seconds. Therefore, the elucidated high electrochemical energy storage performance of the prepared Co-MOF makes it a very promising electrode material for supercapacitors.

A Cobalt-Based Metal-Organic Framework Nanosheet as the Electrode for High-Performance Asymmetric Supercapacitor

Inspired by the significant advantages of the bottom-up synthesis whose structures and functionalities can be customized by the selection of molecular components, a 2D metal-organic framework (MOF) nanosheet Co-BTB-LB has been synthesized by a liquid-liquid interface-assisted method. The as-prepared Co-BTB-LB is identified by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDX) and X-ray photoelectron spectroscopy (XPS), and the sheet-like structure is verified by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and atomic force microscopy (AFM). Co-BTB-LB electrode exhibits an excellent capacity of 4969.3 F g-1 at 1 A g-1 and good cycling stability with 75% capacity retention after 1000 cycles. The asymmetric supercapacitor device with Co-BTB-LB as the positive electrode shows a maximum energy density of 150.2 Wh kg-1 at a power density of 1619.2 W kg-1 and good cycling stability with a capacitance retention of 97.1% after 10000 cycles. This represents a state-of-the-art performance reported for asymmetric supercapacitor device using electroactive bottom-up metal-complex nanosheet, which will clearly lead to a significant expansion of the applicability of this type of 2D nanomaterials.

Direct decoration of commercial cotton fabrics by binary nickel-cobalt metal-organic frameworks for flexible glucose sensing in next-generation wearable sensors

Having a prime significance in diagonsing and predicting the dangerous symptoms of chronic diseases in the early stages, special attention has been drawn by wearable glucose-sensing platforms in recent years. Herein, modified commercial cotton fabrics, decorated with binary Ni-Co metal-organic frameworks (NC-MOFs) through a one-pot scalable hydrothermal route, were directly utilized as flexible electrodes for non-enzymatic glucose amperometric sensing. Glucose sensitivities of 105.2 μA mM^-1 cm^-2 and 23 μA mM^-1 cm^-2 were acheived within two distinct linear dynamic ranges of 0.04-3.13 mM and 3.63-8.28 mM, respectively. Receiving benefits from a remarkable glucose sensitivity behavior in co-existence of iso-structures and interferences, rapid response (4.2 s), and remarkable reproducibility and repeatability, NC-MOF-modified cotton fabric electrodes are imensilly promising for developing high-performance wearable glucose sensing platfroms. The sensing performance of fabricated electrodes was further investigated in human blood serum and saliva.

A one-dimensional cobalt-based coordination polymer as a cathode material of lithium-ion batteries

For obtaining high-performance lithium-ion batteries, it is important to develop new cathode materials with high capacity. Herein, a one-dimensional coordination polymer [Co(4-DTBPT) (DMF)₂(H₂O)₂] (4-DTBPT) (C₁₀H₄O₈) (Co-DTBPT) (4-DTBPT = 2,7-di(4H-1,2,4-triazol-4yl)benzo[lmn][3,8] phenanthroline-1,3,6,8-(2H,7H)-tetraone; DMF = dimethylformamide) was synthesized and its electrochemical performance as the cathode material of lithium-ion batteries was first investigated. The Co-DTBPT electrode showed better cycling stability and a specific capacity of 55 mA h g^-1 at 50 mA g^-1 after 50 cycles, and the coulombic efficiency was close to 100%. The capacity contribution of the Co-DTBPT electrode may be ascribed to the redox reaction of the Co(II) ion and the 4-DTBPT ligand in the process of charge and discharge. Our work proves once again that using one-dimensional coordination polymers as cathode materials for lithium-ion batteries is a feasible way.

Bridging the Gap between Charge Storage Site and Transportation Pathway in Molecular-Cage-Based Flexible Electrodes

Porous materials have been widely applied for supercapacitors; however, the relationship between the electrochemical behaviors and the spatial structures has rarely been discussed before. Herein, we report a series of porous coordination cage (PCC) flexible supercapacitors with tunable three-dimensional (3D) cavities and redox centers. PCCs exhibit excellent capacitor performances with a superior molecular capacitance of 2510 F mmol^-1, high areal capacitances of 250 mF cm^-2, and unique cycle stability. The electrochemical behavior of PCCs is dictated by the size, type, and open-close state of the cavities. Both the charge binding site and the charge transportation pathway are unambiguously elucidated for PCC supercapacitors. These findings provide central theoretical support for the "structure-property relationship" for designing powerful electrode materials for flexible energy storage devices.

Effect of Electrolytic Cations on a 3D Cd-MOF for Supercapacitive Electrodes

A cadmium-based metal-organic framework (Cd-MOF) is synthesized in a facile manner at ambient temperature by an easy slow diffusion process. The three-dimensional (3D) structure of Cd-MOF is authenticated by single-crystal X-ray diffraction studies and exhibits a cuboid-shaped morphology with an average edge length of ∼1.13 μm. The prepared Cd-MOF was found to be electroactive in nature, which resulted in a specific capacitance of 647 F g^-1 at 4 A g^-1 by maintaining a retention of ∼78% over 10,000 successive cycles in the absence of any binder. Further, to distinguish the efficiency of Cd-MOF electrodes, different electrolytes (NaOH, KOH, and LiOH) were explored, wherein NaOH revealed a higher capacitive response due to its combined effect of ionic and hydrated ionic radii. To investigate the practical applicability, an asymmetric supercapacitor (ASC) device is fabricated by employing Cd-MOF as the positive electrode and activated carbon (AC) as the negative electrode, enabling it to light a commercial light-emitting diode (LED) bulb (∼1.8 V). The as-fabricated ASC device delivers comparable energy density and power density.

A three-dimensional Mn-based MOF as a high-performance supercapacitor electrode

Developing new high-performance electrode materials for improving the energy density of supercapacitors is an important task. Herein, a new three-dimensional (3D) metal-orgainc framework (MOF) [Mn(BGPD)(H₂O)₂] (Mn-BGPD; BGPD = N,N'-bis(glycinyl)pyromellitic diimide) was synthesized. When Mn-BGPD is used as the electrode material of supercapacitors, in a three-electrode setup, it shows an outstanding specific capacitance of 832.6 F g^-1 at a current density of 1 A g^-1. The asymmetrical supercapacitor of Mn-BGPD shows an attractive specific capacitance of 100 F g^-1 at 1 A g^-1, which corresponds to an excellent energy density of 35.5 W h kg^-1. Moreover, better cycling stability with a capacitance retention of 46.7% is also shown. The high electrochemical performance makes Mn-BGPD a very promising electrode material for supercapacitors.

2D Metal-Organic Frameworks: Properties, Synthesis, and Applications in Electrochemical and Optical Biosensors

Two-dimensional (2D) nanomaterials like graphene, layered double hydroxides, etc., have received increasing attention owing to their unique properties imparted by their 2D structure. The newest member in this family is based on metal-organic frameworks (MOFs), which have been long known for their exceptional physicochemical properties-high surface area, tunable pore size, catalytic properties, etc., to list a few. 2D MOFs are promising materials for various applications as they combine the exciting properties of 2D materials and MOFs. Recently, they have been extensively used in biosensors by virtue of their enormous surface area and abundant, accessible active sites. In this review, we provide a synopsis of the recent progress in the field of 2D MOFs for sensor applications. Initially, the properties and synthesis techniques of 2D MOFs are briefly outlined with examples. Further, electrochemical and optical biosensors based on 2D MOFs are summarized, and the associated challenges are outlined.

Solid-State Synthesis of Cobalt/NCS Electrocatalyst for Oxygen Reduction Reaction in Dual Chamber Microbial Fuel Cells

Due to the high cost of presently utilized Pt/C catalysts, a quick and sustainable synthesis of electrocatalysts made of cost-effective and earth-abundant metals is urgently needed. In this work, we demonstrated a mechanochemically synthesized cobalt nanoparticles supported on N and S doped carbons derived from a solid-state-reaction between zinc acetate and 2-amino thiazole as metal, organic ligand in presence of cobalt (Co) metal ions ZnxCox(C3H4N2S). Pyrolysis of the ZnxCox(C3H4N2S) produced, Co/NSC catalyst in which Co nanoparticles are evenly distributed on the nitrogen and sulfur doped carbon support. The Co/NSC catalyst have been characterized with various physical and electrochemical characterization techniques. The Co content in the ZnxCox(C3H4N2S) is carefully adjusted by varying the Co content and the optimized Co/NSC-3 catalyst is subjected to the oxygen reduction reaction in 0.1 M HClO4 electrolyte. The optimized Co/NSC-3 catalyst reveals acceptable ORR activity with the half-wave potential of ~0.63 V vs. RHE in acidic electrolytes. In addition, the Co/NSC-3 catalyst showed excellent stability with no loss in the ORR activity after 10,000 potential cycles. When applied as cathode catalysts in dual chamber microbial fuel cells, the Co/NCS catalyst delivered satisfactory volumetric power density in comparison with Pt/C.

Surface morphology evolution of cobalt nanoparticles induced by hydrogen adsorption: a theoretical study

Determining the surface structure and morphology under working conditions is essential to obtain facet-dependent catalytic performance.

Hierarchical hollow-tubular porous carbon microtubes prepared via a mild method for supercapacitor electrode materials with high volumetric capacitance

In this paper, hollow-tubular porous carbons were synthesized from abundant biomass Cycas fluff (CF) through simple carbonization followed by an NaHCO₃ mild activation process. After activation, the tubular structure of the CF was retained, and a hierarchical structure of micropores, mesopores and macropores was formed. When the optimal mass ratio of NaHCO₃/CF is 2, the obtained porous carbon CF-HPC-2 sample has a large specific surface area (SSA) of 516.70 m² g⁻¹ in Brunauer–Emmett–Teller (BET) tests and a total pore volume of 0.33 cm³ g⁻¹. The C, O, N and S contents of CF-HPC-2 were tested as 91.77 at%, 4.09 at%, 3.54 at%, and 0.6 at%, respectively, by elemental analysis. Remarkably, CF-HPC-2 exhibits a high volume capacitance (349.1 F cm⁻³ at 1 A g⁻¹) as well as a higher rate capability than other biomass carbon materials (289.1 F cm⁻³ at 10 A g⁻¹). Additionally, the energy density of the CF-HPC-2 based symmetric supercapacitor in 2 M Na₂SO₄ electrolyte at 20 kW kg⁻¹ is 27.72 W h kg⁻¹. The particular hollow tubular morphology and activated porous structure determine the excellent electrochemical performance of the material. Hence, this synthetic method provides a new way of storing energy for porous carbon as high volumetric capacitance supercapacitor materials.

In this paper, hollow-tubular porous carbons were synthesized from abundant biomass Cycas fluff (CF) through simple carbonization followed by an NaHCO₃ mild activation process.

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

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

One-dimensional metal-organic frameworks for electrochemical applications

Metal-organic frameworks (MOFs) are as a category of crystalline porous materials. Extensive interest has been devoted to energy storage and energy conversion applications owing to their unique advantages of periodic architecture, high specific surface area, high adsorption, high conductivity, high specific capacitance, and high porosity. One-dimensional (1D) nanostructures have unique surface effects, easily regulated size, good agglutination of the substrate, and other distinct properties amenable to the field of energy storage and conversion. Therefore, 1D nanostructures could further improve the characteristic properties of MOFs, and it is of great importance for practical applications to control the size and morphological characteristics of MOFs. The electrochemical application of 1D MOFs is mainly discussed in this review, including energy storage applications in supercapacitors and batteries and energy conversion applications in catalysis. In addition, various synthesis strategies for 1D MOFs and their architectures are presented.

Construction of a Cu-Based Metal-Organic Framework by Employing a Mixed-Ligand Strategy and Its Facile Conversion into Nanofibrous CuO for Electrochemical Energy Storage Applications

Recently, metal-organic frameworks (MOFs) have been widely employed as a sacrificial template for the construction of nanostructured materials for a range of applications including energy storage. Herein, we report a facile mixed-ligand strategy for the synthesis of a Cu-MOF, [Cu₃(Azopy)₃(BTTC)₃(H₂O)₃·2H₂O]_n (where BTTC = 1,2,4,5-benzenetetracarboxylic acid and Azopy = 4,4'-azopyridine), via a slow-diffusion method at room temperature. X-ray analysis authenticates the two-dimensional (2D)-layered framework of Cu-MOF. Topologically, this 2D-layered structure is assigned as a 4-connected unimodal net with sql topology. Further, nanostructured CuO is obtained via a simple precipitation method by employing Cu-MOF as a precursor. After analysis of their physicochemical properties through various techniques, both materials are used as surface modifiers of glassy carbon electrodes for a comparative electrochemical study. The results reveal a superior charge storage performance of CuO (244.2 F g^-1 at a current density of 0.8 A g^-1) with a high rate capability compared to Cu-MOF. This observation paves the pathway for the strategic design of high-performing supercapacitor electrode materials.

Copper-bipyridine grid frameworks incorporating redox-active tetrathiafulvalene: structures and supercapacitance

Redox active tetrathiafulvalene (TTF) and its derivatives when used as electrode additives have exhibited improved energy efficiency and sustainability in batteries. However, the structure-property relationship has not been investigated in detail until very recently. In this work, three redox-active TTF compounds were synthesized, and formulated as [Cu(HL)₂(bpa)₂]_n (1), [Cu(bpe)₂(H₂O)₂]_n·2n(HL)·nMeOH·nH₂O (2), and [Cu(bpp)₂(H₂O)₂]_n·2n(HL) (3) (L = dimethylthio-tetrathiafulvalene-bicarboxylate) for this work. The effects of conjugated state and spacer length of the linkers on structural assembly and band gap as well as the interactions of TTF-TTF/TTF-bpy are discussed. Compound 1 is a bpa and HL co-coordinated 1D Cu(ii) polymer. Compounds 2 and 3 are 2D Cu(ii)-bipyridine (4,4) MOFs incorporating HL (1^-) as free anion columns. The photocurrent density of 2 is larger than those of 1 and 3 due to a strong charge transfer from TTF to bpe in compound 2. The supercapacitance performances of these compounds were evaluated by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) techniques. The results revealed that the 2D MOF structures of 2 and 3 are beneficial for good specific capacitance values (C_sp). This work revealed the structure-property relationships of TTF derivatives for use as electrode active materials in energy transfer and storage.

Effective enhancement of capacitive performance by the facile exfoliation of bulk metal-organic frameworks into 2D-functionalized nanosheets

Recently, much attention has been paid to two-dimensional MOF nanosheets (MONs) due to their widespread application in many specific areas. In this work, a simple and efficient congenerous-exfoliation strategy was developed to prepare vast and uniform few-layered Ni²⁺@Ce-MOF (Ce-MOF: {[Ce(HPIA)(PIA)(H₂O)₂]·H₂O}_n) nanosheets with a thickness of ca. 10 nm. In the exfoliation process, the synergistic action of Ni²⁺ and methanol solvents under ultrasonication plays a major role in restraining the interactions between the layers. Importantly, supercapacitor applications indicate that the exfoliated Ni²⁺@Ce-MOF nanosheet shows a remarkable improvement in the specific capacitance (921.05%) in comparison with that of the bulk Ce-MOF sample before modification.

Water-Driven Structural Transformation in Cobalt Trimesate Metal-Organic Frameworks

We report on the synthesis and the characterization of a novel cobalt trimesate metal-organic framework, designated as KCL-102. Powder X-ray diffraction pattern of KCL-102 is dominated by a reflection at 10.2° (d-spacing = 8.7 Å), while diffuse reflectance UV-Vis spectroscopy indicates that the divalent cobalt centers are in two different coordination geometries: tetrahedral and octahedral. Further, the material shows low stability in humid air, and it transforms into the well-known phase of hydrous cobalt trimesate, Co3(BTC)2·12H2O. We associated this transition with the conversion of the tetrahedral cobalt to octahedral cobalt.

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.

Zinc-based triazole metal complexes for efficient iodine adsorption in water

Radioactive iodine is extremely harmful to the environment, and it is of great significance to develop materials that efficiently remove iodine. We prepared two triazole metal complexes with simple method, denoted as Zn(tr)(OAc) and Zn(ttr)(OAc), which were used to adsorb iodine from aqueous solution. The properties and adsorption mechanism of the two materials were studied by different techniques including XRD, SEM, N2 porosimetry at 77 K, FTIR, TGA, elemental analysis (EDS), and X-ray photoelectron spectroscopy (XPS). The results showed that both materials had good water and thermal stability. Pseudo-second-order kinetic model was better at describing the iodine adsorption kinetics onto the adsorbents. It was proved that chemical adsorption dominated, iodine mainly enriched on the materials in the form of I3-1. Zn(ttr)(OAc) had a higher adsorption capacity than Zn(tr)(OAc) due to the electron-donating group -NH2. The maximum adsorption capacity of the two materials for iodine reached 714.501 mg·g-1 and 846.108 mg·g-1 at 25 °C.

Design and Fabrication of Hierarchical NiCoP-MOF Heterostructure with Enhanced Pseudocapacitive Properties

Metal-organic framework (MOF)-derived heterostructures possessing the merits of each component are thought to display the enhanced energy storage performance due to their synergistic effect. Herein, a functional heterostructure (NiCoP-MOF) composed of nickel/cobalt-MOF (NiCo-MOF) and phosphide (NiCoP) is designed and fabricated via the localized phosphorization of unusual lamellar brick-stacked NiCo-MOF assemblies obtained by a hydrothermal method. The experimental and computational analyses reveal that such-fabricated heterostructures possess the modulated electronic structure, abundant active sites, and hybrid crystalline feature, which is kinetically beneficial for fast electron/ion transport to enhance the charge storage capability. Examined as the supercapacitor electrode, the obtained NiCoP-MOF compared to the NiCo-MOF delivers a high capacity of 728 C g^-1 (1.82 C cm^-2 ) at 1 A g^-1 with a high capacity retention of 430 C g^-1 (1.08 C cm^-2 ) when increasing the current density to 20 A g^-1 . Importantly, the assembled solid-state NiCoP-MOF-based hybrid supercapacitor displays superior properties regarding the capacity (226.3 C g^-1 ), energy density (50.3 Wh kg^-1 ), and durability (≈100% capacity retention over 10 000 cycles). This in situ heterogenization approach sheds light on the electronic structure modulation while maintaining the well-defined porosity and morphology, holding promise for designing MOF-based derivatives for high performance energy storage devices.

Diblock copolymers directing construction of hierarchically porous metal-organic frameworks for enhanced-performance supercapacitors

A rationally designed strategy is developed to synthesize hierarchically porous Fe-based metal-organic frameworks (P-Fe-MOF) via solution-based self-assembly of diblock copolymers. The well-chosen amphiphilic diblock copolymers (BCP) of polystyrene-block-poly(acrylic acid) (PS-b-PAA) exhibits outstanding tolerance capability of rigorous conditions (e.g. strong acidity or basicity, high temperature and pressure), steering the peripheral crystallization of Fe-based MOF by anchoring ferric ions with outer PAA block. Importantly, the introduction of BCP endows MOF materials with additional mesopores (∼40 nm) penetrating whole crystals, along with their inherent micropores and introduced macropores. The unique hierarchically porous architecture contributes to fast charge transport and electrolyte ion diffusion, and thus promotes their redox reaction kinetics processes. Accordingly, the resultant P-Fe-MOF material as a new electrode material for supercapacitors delivers the unprecedented highest specific capacitance up to 78.3 mAh g^-1 at a current density of 1 A g^-1, which is 9.8 times than that of Fe-based MOF/carbon nanotubes composite electrode reported previously. This study may inspire new design of porous metal coordination polymers and advanced electrode materials for energy storage and conversion field.