Systematic synthesis of ZIF-67 derived Co3O4 and N-doped carbon composite for supercapacitors via successive oxidation and carbonization

Zeolitic imidazolate framework-67-derived chalcogenides as electrode materials for supercapacitors

With the rapid development of new energy technologies, hybrid supercapacitors have received widespread attention owing to their advantages of high power density, fast charging/discharging rate and long cycle life. In this case, the selection and design of electrode materials are the key to improving the energy storage performance of supercapacitors. Herein, zeolitic imidazolate framework-67 (ZIF-67) is presented as a good candidate material for the fabrication of supercapacitor electrodes because of its controllable pore size, constant cavity size and large specific area. Moreover, pristine ZIF-67 and ZIF-67-derived porous carbon have shown exemplary performances in supercapacitors. However, they belong to the class of electric double layer capacitor materials and have a lower magnitude of energy storage compared with pseudocapacitor materials. Therefore, to improve the energy density of hybrid supercapacitors, other ZIF-67 derivatives need to be explored, especially chalcogenides. This review mainly reports the application of ZIF-67-derived transition metal chalcogenides (TMCs, C including Oxide, Sulfide, Selenide, Telluride) in supercapacitors. Moreover, the strategies for the preparation of ZIF-67-derived TMCs and their electrochemical performance in supercapacitors are further discussed. Finally, the remaining challenges and future perspectives are highlighted.

A tremella-like in situ synthesis of ZIF-67Co(OH)F@Co3O4 on carbon cloth as an electrode material for supercapacitors

In this study, a simple in situ technique followed by hydrothermal method is used to synthesize a novel tremella-like structure of ZIF-67Co(OH)F@Co3O4/CC metal-organic framework (MOF) derived from zeolite imidazole. The in situ synthesis of metal-organic frameworks (MOFs) increases their conductivity and produces more active sites for ion insertion. Their unique, scalable design not only provides more space to accommodate volume change but also facilitates electrolyte penetration into the electrode resulting in more active materials being utilized and ion-electron transfer occurring faster during the cycle. As a result, the binder-free ZIF-67Co(OH)F@Co3O4/CC supercapacitor electrode exhibits typical pseudo-capacitance behaviour, with a specific capacitance of 442 F g-1 and excellent long-term cycling stability of 90% after 5000 cycles at 10 A g-1.

N-doped lignin-based activated carbon aerogel derived from bamboo black pulp liquor for efficient removal of malachite green in wastewater

In this study, a lignin-based aerogel (LA) was prepared through acid precipitation of BPBL, followed by sol-gel method and freeze-drying. Additionally, a one-step activation-carbonization method was used to acquire nitrogen-doped lignin-based activated carbon aerogel (NLACA). The adsorption and catalytic degradation performance for malachite green (MG) were examined. The specific surface area of NLACA after N-doping was 2644.5 m2/g. The adsorption capacity for MG was increased to 3433 mg/g with the presence of nitrogenous functional groups on surface of NLACA compared without N-doping. Meanwhile, non-radical singlet oxygen is the primary active substance and degradation efficiency arrives at 91.8% after the catalytic degradation within 20 min and it has good stability and reuse. Three possible degradation pathways during degradation were analyzed by LC-MS technique. The adsorption isotherm and kinetic data demonstrated conformity with both the Langmuir model and the pseudo-second-order kinetic model. The primary mechanisms of the adsorption for MG dyes on NLACA include hydrogen bonding, π-π interactions, attraction of electrostatic and pore filling. Hence, NLACA derived from BPBL acts as a cost-effective and high-performance adsorbent and catalyst for removal of MG in dye wastewater. This concept introduces an innovative approach of "treatment of waste with waste" for developing a low-consumption, high-efficiency dye wastewater treatment and provides significant reference to treatment dye wastewater.

Molybdenum Sulfide Nanoflowers as Electrodes for Efficient and Scalable Lithium-Ion Capacitors

Hybrid supercapacitors (HSCs) bridge the unique advantages of batteries and capacitors and are considered promising energy storage devices for hybrid vehicles and other electronic gadgets. Lithium-ion capacitors (LICs) have attained particular interest due to their higher energy and power density than traditional supercapacitor devices. The limited voltage window and the deterioration of anode materials upsurged the demand for efficient and stable electrode materials. Two-dimensional (2D) molybdenum sulfide (MoS2) is a promising candidate for developing efficient and durable LICs due to its wide lithiation potential and unique layer structure, enhancing charge storage efficiency. Modifying the extrinsic features, such as the dimensions and shape at the nanoscale, serves as a potential path to overcome the sluggish kinetics observed in the LICs. Herein, the MoS2 nanoflowers have been synthesized through a hydrothermal route. The developed LIC exhibited a specific capacitance of 202.4 F g-1 at 0.25 A g-1 and capacitance retention of >90 % over 5,000 cycles. Using an ether electrolyte improved the voltage window (2.0 V) and enhanced the stability performance. The ex-situ material characterization after the stability test reveals that the storage mechanism in MoS2-LICs is not diffusion-controlled. Instead, the fast surface redox reactions, especially intercalation/deintercalation of ions, are more prominent for charge storage.

Research progress on metal-organic framework compounds (MOFs) in electrocatalysis

Metal-organic frameworks (MOFs) have favorable characteristics such as large specific surface area, high porosity, structural diversity, and pore surface modification, giving them great potential for development and attractive prospects in the research area of modern materials electrocatalysis. However, unsatisfactory catalytic activity and poor electronic conductivity are the main challenges facing MOFs. This review focuses on MOF-based materials used in electrocatalysis, based on the types of catalytic reactions that have used MOF-based materials in recent years along with their applications, and also looks at some new electrocatalytic materials and their future development prospects.

Co3O4/activated carbon nanocomposites as electrocatalysts for the oxygen evolution reaction

The Oxygen Evolution Reaction (OER) is crucial in various processes such as hydrogen production via water splitting. Several electrocatalysts, including metal oxides, have been evaluated to enhance the reaction efficiency. Zeolitic Imidazolate Framework-67 (ZIF-67) has been employed as a precursor to produce Co3O4, showing high OER activity. Additionally, the formation of composites with carbon-based materials improves the activity of these materials. Thus, this work focuses on synthesizing ZIF-67 and commercial activated carbon (AC) composites, which were used as precursors to obtain Co3O4/C electrocatalysts by calculating ZIF-67/CX (X = 10, 30, and 50, the mass percentage of AC). The obtained materials were thoroughly characterized by employing X-ray powder diffraction (XRD), confirming the cobalt oxide structure with a sphere-like morphology as observed in the TEM images. The presence of oxygen vacancies was confirmed by infrared spectroscopy and EPR measurements. The electrocatalytic performance in the OER was investigated by linear sweep voltammetry (LSV), which revealed an overpotential of 325 mV at 10 mA cm-2 and a Tafel slope value of 65.32 mV dec-1 for Co3O4/C10, superior in activity to several previously reported studies in the literature and electrochemical stability of up to 8 hours. The reduced value of charge transfer resistance, high double-layer capacitance, and the presence of Co3+ ions justify the superior performance of the Co3O4/C10 electrocatalyst.

Diffusion controlled electrochemical analysis of MoS2 and MOF derived metal oxide-carbon hybrids for high performance supercapacitors

In the context of emerging electric devices, the demand for advanced energy storage materials has intensified. These materials must encompass both surface and diffusion-driven charge storage mechanisms. While diffusion-driven reactions offer high capacitance by utilizing the bulk of the material, their effectiveness diminishes at higher discharge rates. Conversely, surface-controlled reactions provide rapid charge/discharge rates and high power density. To strike a balance between these attributes, we devised a tri-composite material, TiO2/Carbon/MoS2 (T10/MoS2). This innovative design features a highly porous carbon core for efficient diffusion and redox-active MoS2 nanosheets on the surface. Leveraging these characteristics, the T10/MoS2 composite exhibited impressive specific capacitance (436 F/g at 5 mV/s), with a significant contribution from the diffusion-controlled process (82%). Furthermore, our symmetrical device achieved a notable energy density of ~ 50 Wh/kg at a power density of 1.3 kW/kg. This concept holds promise for extending the approach to other Metal-Organic Framework (MOF) structures, enabling enhanced diffusion-controlled processes in energy storage applications.

Controlled Synthesis of Flower-like Hierarchical NiCo-Layered Double Hydroxide Integrated with Metal-Organic Framework-Derived Co@C for Supercapacitors

Layered double hydroxides (LDHs) have come to the foreground recently, considering their unique layered structure and short ion channels when they act as electrode materials for supercapacitors (SCs). However, due to their poor rate and cycle performance, they are not highly sought after in the market. Therefore, a flower-like hierarchical NiCo-LDH@C nanostructure with flake NiCo-LDH anchored on the carbon skeleton has emerged here, which is constructed by calcination and hydrothermal reaction and applying flake ZIF-67 as a precursor. In this structure, NiCo-LDH grows outward with abundant and homogeneously distributed Co nanoparticles on Co@C as nucleation sites, forming a hierarchical structure that is combined tightly with the carbon skeleton. The flower-like hierarchical nanostructures formed by the composite of metal-organic frameworks (MOFs) and LDHs have successfully enhanced the cycle and rate performance of LDH materials on the strength of strong structural stability, large specific surface area, and unique cooperative effect. The NiCo-LDH@C electrode displays superb electrochemical performance, with a specific capacitance of 2210.6 F g^-1 at 1 A g^-1 and 88.8% capacitance retention at 10 A g^-1. Furthermore, the asymmetric supercapacitor (ASC) constructed with NiCo-LDH@C//RGO reveals a remarkable energy density of 45.02 W h kg^-1 with a power density of 799.96 W kg^-1. This project aims to propose a novel avenue to exploit NiCo-LDH electrode materials and provide theory and methodological guidance for deriving complex structures from MOF derivatives.

Ligand Incorporating Sequence-dependent ZIF67 Derivatives as Active Material of Supercapacitor: Competition between Ammonia Fluoride and 2-Methylimidazole

The zeolitic imidazolate framework 67 (ZIF67) derivative is a potential active material of supercapacitors (SC), owing to high specific surface area and porosity and possible formation of cobalt compounds. A novel ZIF67 derivative is synthesized using a one-step solution process with cobalt precursor 2-methylimidazole (2-Melm) and ammonia fluoride in our previous work. Due to its facile synthesis and excellent electrocapacitive behavior, it is crucial to understand the competition between ammonia fluoride and 2-Melm on forming derivatives with cobalt ions and to create more efficient ZIF67 derivatives for charge storage. In this work, several ZIF67 derivatives are designed using a one-step solution process with 2-Melm and ammonia fluoride incorporated in different sequences. The reaction durations for a single ligand and two ligands are controlled. The largest capacity of 176.33 mAh/g corresponding to the specific capacitance of 1057.99 F/g is achieved for the ZIF67 derivative electrode prepared by reacting ammonia fluoride and a cobalt precursor for 0.5 h and then incorporating 2-Melm for another 23.5 h of reaction (NM0.5). This derivative composed of highly conductive CoF₂, NiF₂, Co(OH)F, and Ni(OH)F presents high specific surface area and porosity. The relevant SC presents a maximum energy density of 19.5 Wh/kg at 430 W/kg, a capacity retention of 92%, and Coulombic efficiency of 96% in 10000 cycles.

Novel direct growth of ZIF-67 derived Co3O4 and N-doped carbon composites on carbon cloth as supercapacitor electrodes

Zeolitic imidazolate framework-67 (ZIF67) derivatives are considered as promising active materials for energy storage owing to the possible formation of cobalt oxide and N-doped graphite. Cobalt oxide has multiple redox states for generating redox reactions for charge storage, while N-doped graphite can provide high electrical conductivity for charge transfer. In this study, it is the first time to synthesize binder-free electrodes composed of cobalt oxide and N-doped graphite derived from ZIF67 on carbon cloth (CC) for supercapacitor (SC). Successive oxidation and carbonization along with additional coverage of ZIF67 derivatives are applied to synthesize ZIF67 derivatives composed of cobalt oxide, N-doped graphite and cobalt oxide/N-doped graphite composites with different layer compositions. The highest specific capacitance (C_F) of 90.0F/g at 20 mV/s is obtained for the oxidized ZIF67/carbonized ZIF67/carbon cloth (O67/C67/CC) electrode, due to the large surface area and high electrical conductivity benefitted from preferable morphology and growing sequence of Co₃O₄ and N-doped graphite. The symmetric SC composed of O67/C67/CC electrodes shows the maximum energy density of 2.53 Wh/kg at the power density of 50 W/kg. Cycling stability with C_F retention of 70% and Coulombic efficiency of 65% after 6000 times repeatedly charge/discharge process is also obtained for this symmetric SC.

A colorimetric detection strategy and micromotor-assisted photo-Fenton like degradation for hydroquinone based on the peroxidase-like activity of Co3O4–CeO2 nanocages

Co3O4–CeO2 micromotors were fabricated and the colorimetric detection and micromotor-assisted photodegradation capability were studied.

Novel In Situ Synthesis of Freestanding Carbonized ZIF67/Polymer Nanofiber Electrodes for Supercapacitors via Electrospinning and Pyrolysis Techniques

Zeolitic imidazolate framework-67 (ZIF67) has been regarded as an effective energy storage material due to its high surface area and electroactive cobalt center. Carbonizing ZIF67 can enhance electrical conductivity by converting 2-methylimidazole (2-melm) to carbon with cobalt doping. In this work, a novel in situ electrospinning is proposed to fabricate carbonized ZIF67 on carbon fiber (C67@PAN-OC) as a freestanding supercapacitor electrode. Polyacrylonitrile solution containing a cobalt precursor is used for electrospinning, and produced fibers are immersed in 2-melm to form ZIF67. Individually grown carbonized ZIF67 on carbon fiber is obtained using the in situ electrospinning method, while the one-body mixed carbon electrode is formed using the ex situ electrospinning method. A highest specific capacitance (C_F) of 386.3 F/g at 20 mV/s is obtained for the in situ synthesized C67@PAN-OC electrode due to the largest electrochemical surface area and the smallest resistance, while the ex situ synthesized electrode only shows a C_F value of 27.7 F/g. A symmetric supercapacitor (SSC) assembled using the optimized C67@PAN-OC electrodes and gel electrolytes shows a maximum energy density of 9.64 kWh/kg at 0.55 kW/kg and a C_F retention of 59.5% after 1000 times charge/discharge process. A C_F retention of 75.6% after bending 100 times is also obtained for SSC.