Co3O4/Ni-based MOFs on carbon cloth for flexible alkaline battery-supercapacitor hybrid devices and near-infrared photocatalytic hydrogen evolution

Metal-Organic Frameworks and Their Derivatives-Based Nanostructure with Different Dimensionalities for Supercapacitors

With the urgent demand for the achievement of carbon neutrality, novel nanomaterials, and environmentally friendly nanotechnologies are constantly being explored and continue to drive the sustainable development of energy storage and conversion installations. Among various candidate materials, metal-organic frameworks (MOFs) and their derivatives with unique nanostructures have attracted increasing attention and intensive investigation for the construction of next generation electrode materials, benefitting from their unique intrinsic characteristics such as large specific surface area, high porosity, and chemical tunability as well as the interconnected channels. Nevertheless, the poor electrochemical conductivity severely limits their application prospects, hence a variety of nanocomposites with multifarious structures have been designed and proposed from different dimensionalities. In this review, recent advances based on MOFs and their derivatives in different dimensionalities ranging from 1D nanopowders to 2D nanofilms and 3D aerogels, as well as 4D self-supporting electrodes for supercapacitors are summarized and highlighted. Furthermore, the key challenges and perspectives of MOFs and their derivatives-based materials for the practical and sustainable electrochemical energy conversion and storage applications are also briefly discussed, which may be served as a guideline for the design of next-generation electrode materials from different dimensionalities.

Road Map for In Situ Grown Binder-Free MOFs and Their Derivatives as Freestanding Electrodes for Supercapacitors

Among several electrocatalysts for energy storage purposes including supercapacitors, metal-organic frameworks (MOFs), and their derivatives have spurred wide spread interest owing to their structural merits, multifariousness with tailor-made functionalities and tunable pore sizes. The electrochemical performance of supercapacitors can be further enhanced using in situ grown MOFs and their derivatives, eliminating the role of insulating binders whose "dead mass" contribution hampers the device capability otherwise. The expulsion of binders not only ensures better adhesion of catalyst material with the current collector but also facilitates the transport of electron and electrolyte ions and remedy cycle performance deterioration with better chemical stability. This review systematically summarizes different kinds of metal-ligand combinations for in situ grown MOFs and derivatives, preparation techniques, modification strategies, properties, and charge transport mechanisms as freestanding electrode materials in determining the performance of supercapacitors. In the end, the review also highlights potential promises, challenges, and state-of-the-art advancement in the rational design of electrodes to overcome the bottlenecks and to improve the capability of MOFs in energy storage applications.

Approaches to Enhancing Electrical Conductivity of Pristine Metal-Organic Frameworks for Supercapacitor Applications

Metal-organic frameworks (MOFs), known as porous coordination polymers, have attracted intense interest as electrode materials for supercapacitors (SCs) owing to their advantageous features including high surface area, tunable porous structure, structural diversity, etc. However, the insulating nature of most MOFs has impeded their further electrochemical applications. A common solution for this issue is to transform pristine MOFs into more stable and conductive metal compounds/porous carbon materials through pyrolysis, which however losses the inherent merits of MOFs. To find a consummate solution, recently a surge of research devoted to improving the electrical conductivity of pristine MOFs for SCs has been carried out. In this review, the most related research work on pristine MOF-based materials is reviewed and three effective strategies (chemical structure design of conductive MOFs (c-MOFs), composite design, and binder-free structure design) which can significantly increase their conductivity and consequently the electrochemical performance in SCs are proposed. The conductivity enhancement mechanism in each approach is well analyzed. The representative research works on using pristine MOFs for SCs are also critically discussed. It is hoped that the new insights can provide guidance for developing high-performance electrode materials based on pristine MOFs with high conductivity for SCs in the future.

Freestanding Metal-Organic Frameworks and Their Derivatives: An Emerging Platform for Electrochemical Energy Storage and Conversion

Metal–organic frameworks (MOFs) have recently emerged as ideal electrode materials and precursors for electrochemical energy storage and conversion (EESC) owing to their large specific surface areas, highly tunable porosities, abundant active sites, and diversified choices of metal nodes and organic linkers. Both MOF-based and MOF-derived materials in powder form have been widely investigated in relation to their synthesis methods, structure and morphology controls, and performance advantages in targeted applications. However, to engage them for energy applications, both binders and additives would be required to form postprocessed electrodes, fundamentally eliminating some of the active sites and thus degrading the superior effects of the MOF-based/derived materials. The advancement of freestanding electrodes provides a new promising platform for MOF-based/derived materials in EESC thanks to their apparent merits, including fast electron/charge transmission and seamless contact between active materials and current collectors. Benefiting from the synergistic effect of freestanding structures and MOF-based/derived materials, outstanding electrochemical performance in EESC can be achieved, stimulating the increasing enthusiasm in recent years. This review provides a timely and comprehensive overview on the structural features and fabrication techniques of freestanding MOF-based/derived electrodes. Then, the latest advances in freestanding MOF-based/derived electrodes are summarized from electrochemical energy storage devices to electrocatalysis. Finally, insights into the currently faced challenges and further perspectives on these feasible solutions of freestanding MOF-based/derived electrodes for EESC are discussed, aiming at providing a new set of guidance to promote their further development in scale-up production and commercial applications.

Transition Metal Oxide Electrode Materials for Supercapacitors: A Review of Recent Developments

In the past decades, the energy consumption of nonrenewable fossil fuels has been increasing, which severely threatens human life. Thus, it is very urgent to develop renewable and reliable energy storage devices with features of environmental harmlessness and low cost. High power density, excellent cycle stability, and a fast charge/discharge process make supercapacitors a promising energy device. However, the energy density of supercapacitors is still less than that of ordinary batteries. As is known to all, the electrochemical performance of supercapacitors is largely dependent on electrode materials. In this review, we firstly introduced six typical transition metal oxides (TMOs) for supercapacitor electrodes, including RuO₂, Co₃O₄, MnO₂, ZnO, XCo₂O₄ (X = Mn, Cu, Ni), and AMoO₄ (A = Co, Mn, Ni, Zn). Secondly, the problems of these TMOs in practical application are presented and the corresponding feasible solutions are clarified. Then, we summarize the latest developments of the six TMOs for supercapacitor electrodes. Finally, we discuss the developing trend of supercapacitors and give some recommendations for the future of supercapacitors.

Three-phase composites of NiFe2O4/Ni@C nanoparticles derived from metal-organic frameworks as electrocatalysts for the oxygen evolution reaction

Composite electrocatalysts of carbon and metals or metal compounds with homogeneous active sites can be obtained through the carbonization of metal organic framework (MOF) materials under inert atmosphere. In this work, a three-phase composite electrocatalysts NiFe₂O₄/Ni@C were prepared via pyrolysis from self-assembled MOF nanosheets aggregates. The excellent electrocatalytic activity of the obtained electrocatalysts with various Ni:Fe ratios is demonstrated. Especially, the NiFe₂O₄/Ni@C sample with the mole ratio of Ni:Fe = 1:1 can use the overpotential (η) of 330 and 423 mV to drive 10 and 50 mA cm^-2 respectively. After 80 000 s/22 h, the current density could retained 90% of the initial current density. The excellent activity and stability of the electrocatalysts are attributed to nickel and iron ions with uniform dispersion at atomic level in the NiFe₂O₄ phase and the synergistic effect of nickel and NiFe₂O₄ nanoparticles with amorphous carbon atoms or nanoparticles around.

Oxygen Vacancy Engineering of MOF-Derived Zn-Doped Co3O4 Nanopolyhedrons for Enhanced Electrochemical Nitrogen Fixation

Introducing oxygen vacancy (V_o) has been considered as an effective and significant method to accelerate the sluggish electrocatalytic nitrogen reduction reaction (NRR). In this work, a series of bimetallic zeolitic imidazolate frameworks based on ZIF-67 and ZIF-8 with varied ratios of Co/Zn have been applied as precursors to prepare V_o-rich Zn-doped Co₃O₄ nanopolyhedrons (Zn-Co₃O₄) by a low-temperature oxidation strategy. Zn-Co₃O₄ presents an ammonia yield of 22.71 μg h^-1 mg_cat.^-1 with a high faradaic efficiency of 11.9% for NRR under ambient conditions. The remarkable catalytic performances are believed to result from the plentiful V_o as the Lewis acid sites and electron-rich Co sites to promote the adsorption and dissociation of N₂ molecules. Remarkably, Zn-Co₃O₄ also demonstrates a high electrochemical stability. This work presents a guiding method for developing a stable and efficient electrocatalyst for the NRR.

Liquid-Phase Deposition Synthesis of ZIF-67-Derived Synthesis of Co3O4@TiO2 Composite for Efficient Electrochemical Water Splitting

In this article, a novel Co3O4@TiO2 composite is synthesized by applying two-step methods. ZIF-67 is synthesized and used as a template for the synthesis of the composite. The composite is designed by using the effective photocatalytic properties of Co3O4 and TiO2. The resulting synthesized composite is supposed to offer superior properties compared to their counterparts. The synthesized Co3O4@TiO2 composite is characterized by powder X-ray diffraction (PXRD), Brunauer–Emmet–Teller (BET), atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Electrochemical water splitting, including hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) studies on the Co3O4@TiO2 composite, is evaluated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) analysis in a 2M aqueous KOH electrolyte. The current generation stability of these samples is deliberated by chronoamperometric measurements. It is observed, from LSV results at a 1 mV/s scan rate, that metal oxides incorporated on other metal oxides have a higher current density and lower onset potential as compared to pure metal oxides. From the obtained results, it has become evident that synthesized studies on the Co3O4@TiO2 composite possess significant potential for electrochemical water splitting with the lowest onset potential, highest current density, better OER, and HER activity.

Fabrication of ZIF-71/Fe3O4/polythionine nanoarray-functionalized carbon cotton cloth for simultaneous extraction and quantitation of febuxostat and diclofenac

Synthesis of a material based on carbonized cotton cloth/zeolite imidazolate framework was applied to ultrasound-assisted dispersive magnetic solid-phase extraction and high-performance liquid chromatography-ultraviolet to detect diclofenac and febuxostat in human plasma.

In situ deposition of MOF-74(Cu) nanosheet arrays onto carbon cloth to fabricate a sensitive and selective electrocatalytic biosensor and its application for the determination of glucose in human serum

A new electrocatalytic biosensor (MOF-74(Cu) NS-CC) based on the in situ deposition of MOF-74(Cu) nanosheet on carbon cloth via a bottom-up synthetic approach in a glass tube was developed. The electrocatalytic activity of the deposited MOF-74(Cu) NS was demonstrated in the oxidation of glucose to gluconate under alkaline conditions. The results revealed that the proposed method of in situ formation of MOF-74(Cu) NS onto a carbon cloth surface in a multi-layer solution is capable to generate a stable MOF-74(Cu) NS-CC electrode with excellent sensing performance. When the as-synthesized MOF-74(Cu) NS-CC was applied directly as the working electrode for glucose sensing, it showed much higher conductivity and redox activity than MOF-74(Cu) NS-GCE. With the potential applied at 0.55 V (vs. Ag/AgCl), this new electrocatalytic biosensor exhibits an excellent linear relationship between current density and concentration of glucose. Moreover, a wide linear range of detection (1.0 to 1000 μM) was observed. The limit of detection was found to be 0.41 μM (S/N = 3). The response sensitivity is 3.35 mA mM^-1 cm^-2 when the concentration of glucose is in the range 1-100 μM and 3.81 mA mM^-1 cm^-2 for the 100-1000 μM concentration range. This study provides a low-cost, easy to prepare, and reproducible methodology for the synthesis of highly redox-active nanomaterials based on the in situ formation of two-dimensional MOF-74(Cu) NS for the development of new electrocatalytic biosensors. Graphical abstract.

A longitudinally expanded Ni-based metal-organic framework with enhanced double nickel cation catalysis reaction channels for a non-enzymatic sweat glucose biosensor

Nickel-based metal-organic frameworks (Ni-MOFs) have attracted increasing attention in non-enzymatic glucose sensing. However, the insufficient active Ni cation sites from a stacked MOF layer, the unclear Ni catalysis mechanism, and the severe liquid alkaline electrolyte remain challenging for practical applications. In this work, the sonication-induced longitudinal-expansion of Ni-MOFs increases the active nickel ion sites, which not only enhances the current response to glucose detection, but also shows the oxidation peak evolution of nickel ions with different sonication times, revealing the mechanism of different glucose detection channels. The Ni-MOF sonicated for 60 min (60 min Ni-MOF) displays enhanced Ni(iii)/Ni(ii) and more significant Ni(iv)/Ni(iii) double nickel cation channels for catalyzing glucose into glucolactone compared to the 0 min Ni-MOF (without sonication), showing optimized glucose detection ability with a high sensitivity of 3297.10 μA mM-1 cm-2, a low detection limit of ∼8.97 μM (signal-to-noise = 3) and a wide linear response range from 10 to 400 μM from the cyclic voltammetry test as well as a high sensitivity of 3.03 μA mM-1 cm-2, a low detection limit of ∼1.16 μM (signal-to-noise = 3) and a wide linear response range from 10 to 2000 μM from the chronoamperometry test. More importantly, an all-solid-state glucose biosensor using a PVA/NaOH solid-state electrolyte and a disposable 60 min Ni-MOF working electrode is assembled for non-enzymatic sweat glucose detection.

Flexible supercapacitor electrodes using metal-organic frameworks

Advancements in the field of flexible and wearable devices require flexible energy storage devices to cater their power demands. Metal-ion batteries (such as lithium-ion batteries, sodium-ion batteries, etc.) and electrochemical capacitors (also called supercapacitors or ultracapacitors) have achieved great interest in the recent past due to their superior energy storage characteristics like high power density and long cycle life. A major bottleneck of using metal-ion batteries in wearable devices is their lack of flexibility. Low power density, toxicity and flammability due to organic electrolytes inhibit them from safe on-body device applications. On the other hand, supercapacitors can be made with aqueous electrolytes, making them a safer alternative for wearable applications. Metal-organic frameworks (MOFs) are novel candidates as electrode materials due to their salient features such as large surface area, three-dimensional porous architecture, permeability to foreign entities, structural tailorability, etc. Though pristine MOFs suffer from poor intrinsic conductivity, this can be rectified by preparing composites with other electronically conducting materials. MOF-based electrodes are highly promising for flexible and wearable supercapacitors since they exhibit good energy and power densities. This review focuses on the new developments in the field of MOF-based composite electrodes for developing flexible supercapacitors.

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.

0D/2D spatial structure of CdxZn1−xS/Ni-MOF-74 for efficient photocatalytic hydrogen evolution

A novel zero-dimensional/two-dimensional Cd_xZn_1−xS/Ni-MOF-74 (CZS/NMF) heterojunction was rationally constructed via a simple hydrothermal and physical mixing method.

Ce-Doped Graphitic Carbon Nitride Derived from Metal Organic Frameworks as a Visible Light-Responsive Photocatalyst for H2 Production

Novel fibrous graphitic carbon nitride (g-C₃N₄) derivatives prepared from metal organic frameworks (MOFs) were doped with Ce³⁺ (Ce-C₃N₄) as photocatalytic materials. Ce-C₃N₄ was characterized using various techniques, revealing its high specific surface area, excellent photocatalytic activity, and stability for H₂ evolution under visible light irradiation. The fluorine modified samples show superior photocatalytic activity under visible light irradiation, which is due to the presence of more active sites and enhanced absorption of solar energy. This work provides a new synthetic route for MOF-derived g-C₃N₄ that can be doped with different metal ions. The fluorine modified Ce-C₃N₄ is an efficient photocatalyst with potential for many applications related to energy and the environment.

Integrated System of Solar Cells with Hierarchical NiCo2O4 Battery-Supercapacitor Hybrid Devices for Self-Driving Light-Emitting Diodes

An integrated system has been provided with a-Si/H solar cells as energy conversion device, NiCo₂O₄ battery-supercapacitor hybrid (BSH) as energy storage device, and light emitting diodes (LEDs) as energy utilization device. By designing three-dimensional hierarchical NiCo₂O₄ arrays as faradic electrode, with capacitive electrode of active carbon (AC), BSHs were assembled with energy density of 16.6 Wh kg^-1, power density of 7285 W kg^-1, long-term stability with 100% retention after 15,000 cycles, and rather low self-discharge. The NiCo₂O₄//AC BSH was charged to 1.6 V in 1 s by solar cells and acted as reliable sources for powering LEDs. The integrated system is rational for operation, having an overall efficiency of 8.1% with storage efficiency of 74.24%. The integrated system demonstrates a stable solar power conversion, outstanding energy storage behavior, and reliable light emitting. Our study offers a precious strategy to design a self-driven integrated system for highly efficient energy utilization.

Enhanced electrocatalytic hydrodechlorination of 2,4-dichlorophenoxyacetic acid by a Pd-Co3O4/Ni foam electrode

A new Pd-Co₃O₄/Ni foam electrode was synthesized by a facile two-step method comprising co-electrodeposition and calcination. Compared with Ni foam-supported Pd electrodes obtained by electrodeposition or chemical deposition, the new Pd-Co₃O₄/Ni foam electrode exhibited greatly enhanced catalytic hydrodechlorination activity. The introduction of Co₃O₄ reduced the amount of Pd required. For the same degree of dechlorination of 2,4-D, only 25% of the Pd was required in the Pd-Co₃O₄/Ni foam electrode compared with the Ni foam electrode prepared by chemical deposition. Various characterizations indicated that Co₃O₄ on the surface of the Ni foam enhanced catalytic performance through accelerated generation of atomic H*. In addition, the good distribution of macropores, providing a larger specific surface area and lower electron transfer impedance, enabled more adsorption of atomic .

The Pd-Co₃O₄/Ni foam electrode enhanced the electrocatalytic dechlorination performance.

CdS p–n heterojunction co-boosting with Co3O4 and Ni-MOF-74 for photocatalytic hydrogen evolution

A high-efficiency Ni-MOF-74/CdS/Co₃O₄ composite catalyst, the CdS co-boosting with Ni-MOF-74 and Co₃O₄, is successfully prepared.