Conformal sulfidation of HKUST-1 for constructing porous Cu2S/CuO octahedrons realizing highly sensitive non-enzymatic glucose detection

Metal-organic frameworks (MOFs) are believed to be promising precursors for constructing novel and efficient catalysts for glucose sensing. Herein, HKUST-1 precursors are first fabricated using a one-pot hydrothermal approach, and then HKUST-1 is converted into porous Cu2S/CuO octahedrons through conformal sulfidation with the help of OH-ions. The as-obtained Cu2S/CuO composite can provide rich electrochemical active sites and promoted electric transfer kinetics. Benefiting from these combined merits, the as-fabricated Cu2S/CuO composite is confirmed to be a high-performance catalyst, with high sensitivities of 8269.45 and 4140.82μA mM-1cm-2in the corresponding ranges of 0.05 ∼ 0.6 mM and 0.6 ∼ 1.2 mM, respectively. Moreover, the as-prepared electrode materials possess good anti-interference ability, reproducibility and long-term stability. This work opens up new avenues for the design and preparation of transition metal sulfide composites.

Mesoporous Cubic Nanocages Assembled by Coupled Monolayers With 100% Theoretical Capacity and Robust Cycling

High capacity and long cycling often conflict with each other in electrode materials. Despite extensive efforts in structural design, it remains challenging to simultaneously achieve dual high electrochemical properties. In this study, we prepared brand-new completely uniform mesoporous cubic-cages assembled by large d-spacing Ni(OH)2 coupled monolayers intercalated with VO4 3- (NiCMCs) using a biomimetic approach. Such unique mesoporous structural configuration results in an almost full atomic exposure with an amazing specific surface area of 505 m2/g and atomic utilization efficiency close to the theoretical limit, which is the highest value and far surpasses all of the reported Ni(OH)2. Thus, a breakthrough in simultaneously attaining high capacity approaching the 100% theoretical value and robust cycling of 10,000 cycles is achieved, setting a new precedent in achieving double-high attributes. When combined with high-performance Bi2O3 hexagonal nanotubes, the resulting aqueous battery exhibits an ultrahigh energy density of 115 Wh/kg and an outstanding power density of 9.5 kW/kg among the same kind. Characterizations and simulations reveal the important role of large interlayer spacing intercalation units and mesoporous cages for excellent electrochemical thermodynamics and kinetics. This work represents a milestone in developing "double-high" electrode materials, pointing in the direction for related research and paving the way for their practical application.

Layered double hydroxide-based electrode materials derived from metal-organic frameworks: synthesis and applications in supercapacitors

Metal-organic frameworks (MOFs) have emerged as promising electrode materials for supercapacitors (SCs) due to their highly porous structures, tunable chemical compositions, and diverse morphologies. However, their applications are hindered by low conductivity and poor cycling performance. A novel approach for resolving this issue involves the growth of layered double hydroxides (LDHs) using MOFs as efficient templates or precursors for electrode material preparation. This method effectively enhances the stability, electrical conductivity, and mass transport ability of MOFs. The MOF-derived LDH exhibits a well-defined porous micro-/nano-structure, facilitating the dispersion of active sites and preventing the aggregation of LDHs. Firstly, this paper introduces synthesis strategies for converting MOFs into LDHs. Subsequently, recent research progress in MOF-derived LDHs encompassing pristine LDH powders, LDH composites, and LDH-based arrays, along with their applications in SCs, is overviewed. Finally, the challenges associated with MOF-derived LDH electrode materials and potential solutions are discussed.

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.

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.

Self-Assembly of Metal-Organic Frameworks on Graphene Oxide Nanosheets and In Situ Conversion into a Nickel Hydroxide/Graphene Oxide Battery-Type Electrode

Graphene oxide (GO) has been widely reported as a supercapacitor electrode. Especially, GO is usually utilized to composite with electrochemical active materials, such as transition-metal oxide/hydroxide/sulfide, due to its considerable conductivity and mechanical strength. However, the ideal design and treatment for compositing GO with active materials are still challenging. Herein, an Ni-metal-organic framework (MOF) was self-assembled on GO nanosheets via the solvothermal method and was subsequently etched into the Ni(OH)₂-GO composite electrode material through a gentle hydrolysis strategy. The GO support enables fast electron transport within the composite material, and the nickel hydroxide growth on GO nanosheets can prevent their aggregation, guaranteeing rapid ion migration. The improved Ni(OH)₂-GO battery-type electrode features outstanding stability (capacity retention of 108% at 8000 cycles) and a considerable specific capacity (SC) of 1007.5 C g^-1 at a current density of 0.5 A g^-1. Compared with MOF-derived Ni(OH)₂ obtained through hydrolysis, Ni(OH)₂-GO only contains 7.41% wt GO, while its SC is almost 50% higher. An asymmetric supercapacitor has an energy density of 65.22 W h kg^-1 and a power density of 395.27 W kg^-1 utilizing p-phenylenediamine-functional reduced GO as the negative electrode, and it can maintain 73.08% capacity during 8000 cycles at a current density of 5 A g^-1.

Flower-like Ni3Sn2@Ni3S2 with core-shell nanostructure as electrode material for supercapacitors with high rate and capacitance

To enhance the specific capacitance as well as maintain satisfactory rate performance of nickel hydroxide and nickel sulfide, in this work, the ultra-fine nickel-tin nanoparticles with high conductivity are selected to synthesize Ni₃Sn₂@Ni(OH)₂ and Ni₃Sn₂@Ni₃S₂ nanoflowers. Alloy as the core material improves the electrical conductivity of the composite, and the nanosheets prepared by electrochemical corrosion effectively avoid aggregation as well as increase the active sites of the electrode material. By adjusting the corrosion time, the Ni₃Sn₂@Ni(OH)₂ with better morphology displays a high specific capacitance (1277.37C g^-1 at 1 A g^-1) and good rate performance (1028C g^-1 at 20 A g^-1). After sulfurization, the optimal Ni₃Sn₂@Ni₃S₂ perfectly retains the morphological characterizations of the precursor and exhibits ultra-high specific capacitance (1619.02C g^-1 at 1 A g^-1) as well as outstanding rate performance (1312C g^-1 at 20 A g^-1). The samples before and after vulcanization both have the excellent electrochemical properties, which is attributed to the rational design and construction of the alloy-based core-shell nanostructures. Besides, the all-solid-state hybrid supercapacitor (HSC) is assembled by Ni₃Sn₂@Ni₃S₂ as the positive electrode and activated carbon as the negative electrode, displaying outstanding energy density of 70.54 Wh kg^-1 at 808.67 W kg^-1 and excellent cycling stability (93.21 % after 10,000 cycles). This work provides a novel ingenuity for synthesizing high-performance supercapacitor electrodes.

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.

Improved ionic diffusion and interfacial charge/mass transfer of ZIF-67-derived Ni–Co-LDH electrodes with bare ZIF-residual for enhanced supercapacitor performance

The crystallization of Ni–Co-LDH and the morphology of the hierarchical structure can be simply optimized to achieve improved ionic diffusion and reduce reaction resistance of charge/mass transfer between the electrode/electrolyte interfaces.

In situ semi-transformation from heterometallic MOFs to Fe-Ni LDH/MOF hierarchical architectures for boosted oxygen evolution reaction

Metal-organic frameworks (MOFs) with large surface area, abundant coordination metal centers and tunable structures are regarded as promising electrocatalysts for the water splitting reaction. However, the less accessible active sites and poor stability of MOFs hinder their potential practical applications. Hierarchical double-layer hydroxide (LDH)/MOF electrocatalysts that combine the advantages of two materials are expected to overcome these drawbacks. Herein, we develop a simple and universal strategy, in situ pseudomorphic transformation, to construct hierarchical LDH/MOF electrocatalysts. Accordingly, ultra-thin Fe-Ni LDH nanosheets are in situ produced in the heterometallic MOF during the transformation process. Profiting from the abundant metal sites and the extended electron transport channel from the inserted ultra-thin LDH arrays, the hierarchical Fe-Ni LDH/MOFs exhibit striking electrochemical activities for the oxygen evolution reaction (OER). In particular, the as-synthesized Fe-Ni LDH/MOF-b2 delivers the best OER performance, exhibiting an ultralow overpotential (255 mV at 10 mA cm^-2), minimum Tafel slope (24 mV dec^-1) and outstanding cycling durability. Meanwhile, the evolution process of the hierarchical Fe-Ni LDH/MOF has been monitored with the controllable in situ semi-transformation strategy. This also provides an opportunity to decipher the original active species for the OER process. Mechanism analysis indicates that the bimetallic MOF and bimetallic LDH are both active species, and the excellent OER performance of hierarchical Fe-Ni LDH/MOF could be attributed to the effect of "a whole greater than the sum of the parts".

Electronegativity principles in metal oxides based supercapacitors

To meet growing demands for energy consumptions in modern society, it is necessary to develop different energy sources. Renewable energy such as wind and solar sources are intermittent, therefore, energy storage devices become more and more important to store energy for use when no wind or no light. Supercapacitors play a key role in energy storage, mainly due to their high power density and long cycling life. However, supercapacitors are facing the obstacle of low energy density, one of the most intensive approaches is to rationally design new electrode materials. In this review, we focus on metal oxides-based materials and present an electronegativity criterion for the design and appropriate selection of new electrode chemical compositions. Metal elements with proper electronegativity scale have the potential to transfer electron for energy storage. Suitable positive and negative electrodes matching can enhance many properties of supercapacitors, which may overcome many related obstacles. Furthermore, electronegativity scale may also help people to find novel metal oxides based supercapacitors.

Hollow nanostructures of metal oxides as emerging electrode materials for high performance supercapacitors

Comparative study of TMO based hollow and solid nanostructures for supercapacitor applications.

La3+:Ni–Cl oxyhydroxide gels with enhanced electroactivity as positive materials for hybrid supercapacitors

Novel poorly crystalline La³⁺:Ni–Cl oxyhydroxide gels with sufficient electroactive sites and atomically homogeneous distribution of Ni²⁺, La³⁺, and Cl⁻ ions were synthesized.

"HOT" Alkaline Hydrolysis of Amorphous MOF Microspheres to Produce Ultrastable Bimetal Hydroxide Electrode with Boosted Cycling Stability

Nickel/cobalt hydroxide is a promising battery-type electrode material for supercapacitors. However, its low cycle stability hinders further applications. Herein, Ni_0.7 Co_0.3 (OH)₂ core-shell microspheres exhibiting extreme-prolonged cycling life are successfully synthesized, employing Ni-Co-metal-organic framework (MOF) as the precursor/template and a specific hydrolysis strategy. The Ni-Co-MOF and KOH aqueous solution are separated and heated to 120 °C before mixing, rather than mixing before heating. Through this hydrolysis strategy, no MOF residual exists in the product, contributing to close stacking of the hydroxide nanoflakes to generate Ni_0.7 Co_0.3 (OH)₂ microspheres with a robust core-shell structure. The electrode material exhibits high specific capacity (945 C g^-1 at 0.5 A g^-1 ) and unprecedented cycling performance (100% after 10 000 cycles). The fabricated asymmetric supercapacitor delivers an energy density of 40.14 Wh kg^-1 at a power density of 400.56 W kg^-1 and excellent cycling stability (100% after 20 000 cycles). As far as is known, it is the best cycling performance for pure Ni/Co(OH)₂ .

Temperature controlled diffusion of hydroxide ions in 1D channels of Ni-MOF-74 for its complete conformal hydrolysis to hierarchical Ni(OH)2 supercapacitor electrodes

Conformal hydrolysis of MOF precursors is a promising strategy to prepare hierarchical metal hydroxide electrode materials on a large scale with low cost and high efficiency. However, a complete transformation is challenging due to the normal "outside-in" conversion process. After studying the hydrolysis of Ni-MOF-74, which has regular 1D channels, we suggest that the transformation to Ni(OH)2 can occur simultaneously outside and within the precursor depending on the treatment temperature. Molecular dynamics simulations reveal that a higher temperature weakens the steric effects of OH- ions and facilitates the diffusion in the regular channels, and therefore, a complete transformation from Ni-MOF-74 to Ni(OH)2 is achieved. It is for the first time demonstrated that the 1D channels of MOFs are utilized for the complete conformal hydrolysis of Ni-MOF-74 to Ni(OH)2 electrode materials. Meanwhile, we also perform pioneering work illustrating that the complete conformal hydrolysis is the key to the improved supercapacitor performances of the MOF-derived Ni(OH)2 electrodes. The prepared Ni(OH)2 electrode under the optimized conditions has a specific capacity of 713.2 C g-1 at a current density of 1 A g-1, which is at least 28% larger than those of the Ni(OH)2 prepared at other temperatures. The detailed analyses based on CV and EIS of the obtained Ni(OH)2 electrodes indicate that the residual MOFs within electrodes due to incomplete hydrolysis significantly influence the diffusion length and diffusion efficiency of OH-, drastically lowering the supercapacitor performances.

Core–shell assembly of Co3O4@NiO-ZnO nanoarrays as battery-type electrodes for high-performance supercapatteries

Core–shell Co₃O₄@NiO-ZnO nanoarrays are fabricated by annealing metal–organic framework assisted precursors and investigated as battery-type electrode for supercapattery.