Bimetal-organic frameworks derived redox-type composite materials for high-performance energy storage

Electrodes and electroactive materials are crucial components in the development of supercapacitors due to their geometric properties. In this study, bimetal-organic frameworks (Bi-MOFs, ZIF-8@ZIF-67) were utilized as electrode materials for a high-performance hybrid supercapacitor (HSC) by designing a novel synthesis of metallic carbonate hydroxide/oxides. In particular, the Bi-MOFs function as a sacrificial precursor in the synthesis of hollow NiMn(CO3)0.5·0·.11H2O/ZnO@Co3O4 CNCs (NM-CH/ZnO@Co3O4 CNCs) cubic composite materials by a straightforward low-temperature treatment. The NM-CH/ZnO@Co3O4 CNCs exhibited exceptional electrochemical performance with high specific capacity of 196.3 ± 0.08 mAh/g, specific capacitance of 1179 ± 0.10 F g-1 at 0.5 A g-1, and outstanding cycling stability of 98% after 25,000 cycles compared to the other electrode materials. The porous and hollow structure, along with a large surface area, contributed to the enhanced electrochemical properties of the composite material. An HSC was constructed using NM-CH/ZnO@Co3O4 CNCs as the cathode and activated porous carbon (APC) as the anode, resulting in a device with a specific energy of 33 ± 0.12 Wh kg-1 and a power density of 19354 ± 0.07 W kg-1. The use of Bi-MOF electrodes presents new avenues for the development of high-performance energy storage materials, with the potential for industrial energy storage application demonstrated though the successful powering of portable lightbulbs.

3D net-like Co3O4@NiO nanostructures for high performance supercapacitors

Co3O4@NiO composite electrode materials were successfully synthesized by a two-step hydrothermal method followed by annealing treatment. Due to their three-dimensional network structure, these composite materials exhibited a large specific surface area, enhancing their electrochemical performance. Consequently, the Co3O4@NiO electrode demonstrated a specific capacitance of 1306 F g-1 at a current density of 1 A g-1, an excellent specific capacitance retention rate of 95.5% after 3000 cycles even at 8 A g-1 and a coulombic efficiency approaching 100%. These outstanding properties make the Co3O4@NiO composite materials promising electrode materials for high performance supercapacitors.

Negative electrodes for supercapacitors with good performance using conductive bismuth-catecholate metal-organic frameworks

Metal-organic frameworks (MOFs) have attracted increasing research interest in various fields. Unfortunately, the poor conductivity of most traditional MOFs considerably hinders their application in energy storage. Benefiting from the full charge delocalization in the atomic plane, two-dimensional conductive coordination frameworks achieve good electrochemical performance. In this work, π-π coupling conductive bismuth-catecholate nanobelts with tunable lengths, Bi(HHTP) (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene), are synthesized by a simple hydrothermal reaction and their length-dependent electrochemical properties are also investigated. The Bi(HHTP) nanobelts (about 10 μm in length) possess appropriate porosity, numerous redox active sites and good electrical conductivity. Being a negative electrode for supercapacitors, Bi(HHTP) nanobelts display a high specific capacitance of 234.0 F g^-1 and good cycling stability of 72% after 1000 cycles. Furthermore, the mechanism of charge storage is interpreted for both battery-type and surface-capacitive behavior. It is believed that the results of this work will help to develop battery-type negative electrode materials with promising electrochemical performance using some newly designed π-π coupling conductive coordination frameworks.

Co3O4@NiMoO4 composite electrode materials for flexible hybrid capacitors

Co₃O₄ nanomaterials as electrodes have been studied widely in the past decade due to their unique structural characteristics. However, their performance does not yet reach the level required for practical applications. It is, nevertheless, an effective strategy to synthesize hybrid electrode materials with high energy density. Herein we prepare Co₃O₄@NiMoO₄ nanowires by a two-step hydrothermal method. The as-obtained sample can be directly used as cathode material of supercapacitors; with specific capacitance of 600 C/g at 1 A/g. An assembled capacitor delivers an energy density of 36.1 Wh/kg at 2700 W/kg, and retains 98.2% of the initial capacity after 8000 cycles.

Core-shell coaxially structured NiCo2S4@TiO2nanorod arrays as advanced electrode for solid-state asymmetric supercapacitors

An integrated electrode of core-shell coaxially structured NiCo₂S₄@TiO₂nanorod arrays/carbon cloth (NiCo₂S₄@TiO₂@CC) have been fabricated, via a two-step hydrothermal method. Comprehensive structural and compositional analyzes are performed to understand the effects of the NiCo₂S₄shell on the TiO₂core. Such core-shell arrays structure can significantly provide abundant electroactive sites for redox reactions, convenient ion transport paths, and favorable structure stability. The NiCo₂S₄@TiO₂@CC electrode represents a splendid specific capacitance (650 F g^-1at 1 A g^-1) and enhanced cycling stability (capacitance retention of 97% over 10 000 cycles at 5 A g^-1). Additionally, the assembled NiCo₂S₄@TiO₂@CC//CNT@CC solid-state asymmetric supercapacitors exhibit a maximal energy density of 0.6 mWh cm^-3at 32.4 W cm^-3, and topping cycling stability (85% capacitance retention after 5000 cycles at 5 mA cm^-2). The results demonstrate that the well-designed NiCo₂S₄@TiO₂@CC presented in this work are applicable for the development of electrode materials in energy storage devices.

Novel synthesis of hierarchical NiGa2O4@MnO2 core-shell hetero-nanostructured nanowall arrays on carbon cloth for high-performance all-solid-state asymmetrical supercapacitors

A hierarchical NiGa₂O₄@MnO₂ core-shell nanowall arrays have been grown on carbon cloth by stepwise design and fabrication. Ultrathin MnO₂ nanoflakes are revealed to grow uniformly on the porous NiGa₂O₄ nanowalls with many interparticle mesopores, resulting in the formation of 3D core-shell nanowall arrays with hierarchical architecture. The as-synthesized product as a binder-free electrode possesses a high specific capacitance of 1700 F g^-1 at 1 A g^-1 and 90% capacitance retention after 10,000 cycles at 10 A g^-1. Furthermore, an asymmetrical solid-state supercapacitor assembled by the NiGa₂O₄@MnO₂ and N-CMK-3 exhibits an energy density of 0.59 Wh cm^-3 at a power density of 48 W cm^-3, and excellent cycling stability (80% of initial capacitance retention after 5000 cycles at 6 mA cm^-2). The remarkable electrochemical performances can be attributed to its novel nanostructure with high surface area, convenient ion transport paths and favorable structure stability. These results display an effective method for fabrication of different core-shell nanostructure on conductive substrates, which brings new design opportunities of device configuration for next energy storage devices.

Freestanding Needle Flower Structure CuCo2S4 on Carbon Cloth for Flexible High Energy Supercapacitors With the Gel Electrolyte

A facile hydrothermal approach was adopted to the direct synthesis of bimetallic sulfide (CuCo₂S₄) on carbon cloth (CC) without binders for the supercapacitor's electrodes. A possible formation mechanism was proposed. The prepared bimetallic electrode exhibited a high specific capacitance (Csp) of 1,312 F·g⁻¹ at 1 A·g⁻¹, and an excellent capacitance retention of 94% at 5 A·g⁻¹ over 5,000 cycles. In addition, the asymmetric supercapacitor (CuCo₂S₄/CC//AC/CC) exhibited energy density (42.9 wh·kg⁻¹ at 0.8 kW·kg⁻¹) and outstanding cycle performance (80% initial capacity retention after 5,000 cycles at 10 A·g⁻¹). It should be noted that the electrochemical performance of a supercapacitor device is quite stable at different bending angles. Two charged devices in series can light 28 red-colored LEDs (2.0 V) for 5 min. All of this serves to indicate the potentially high application value of CuCo₂S₄.

Recent Advance in Co3O4 and Co3O4-Containing Electrode Materials for High-Performance Supercapacitors

Among the popular electrochemical energy storage devices, supercapacitors (SCs) have attracted much attention due to their long cycle life, fast charge and discharge, safety, and reliability. Transition metal oxides are one of the most widely used electrode materials in SCs because of the high specific capacitance. Among various transition metal oxides, Co3O4 and related composites are widely reported in SCs electrodes. In this review, we introduce the synthetic methods of Co3O4, including the hydrothermal/solvothermal method, sol-gel method, thermal decomposition, chemical precipitation, electrodeposition, chemical bath deposition, and the template method. The recent progress of Co3O4-containing electrode materials is summarized in detail, involving Co3O4/carbon, Co3O4/conducting polymer, and Co3O4/metal compound composites. Finally, the current challenges and outlook of Co3O4 and Co3O4-containing composites are put forward.

A unique core-shell structured ZnO/NiO heterojunction to improve the performance of supercapacitors produced using a chemical bath deposition approach

The integration of metal oxide composite nanostructures has attracted great attention in supercapacitor (SC) applications. Herein, we fabricated a series of metal oxide composite nanostructures, including ZnO nanowires, NiO nanosheets, ZnO/CuO nanowire arrays, ZnO/FeO nanocrystals, ZnO/NiO nanosheets and ZnO/PbO nanotubes, via a simple and cost-effective chemical bath deposition (CBD) method. The electrochemical properties of the produced SCs were examined by performing cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) analysis, and electrochemical impedance spectroscopy (EIS). Of the different metal oxides and metal oxide composites tested, the unique surface morphology of the ZnO/NiO nanosheets most effectively increased the electron transfer rate and electrical conductivity, which resulted in improved energy storage properties. The binder-free ZnO/NiO electrode delivered a high specific capacitance/capacity of 1248 F g-1 (599 mA h g-1) at 8 mA cm-2 and long-term cycling stability over the course of 3000 cycles with a capacity retention of 79%. These results suggested a superiority in performance of the ZnO/NiO nanosheets relative to the nanowires, nanowire arrays, nanocrystals, and nanotubes. Thus, the present work has provided an opportunity to fabricate new metal oxide composite nanostructures with high-performance energy storage devices.

Bi-functional Mo and P co-doped ZnCo-LDH nanosheets as high performance electrocatalysts for boosting overall water splitting

To rationally construct electrode structures with high activity is very significant for bi-functionalization conversion systems.

Enhanced electrochemical performances of ZnCo2O4@CoMoO4 core–shell structures with long cycling stabilities

Developing electrode materials with high specific capacitance and excellent stability for energy storage is necessary to solve energy shortage issues.

Hierarchical PANI/NiCo-LDH Core-Shell Composite Networks on Carbon Cloth for High Performance Asymmetric Supercapacitor

In this work, a facile two-step strategy is adopted to construct hierarchical polyaniline/NiCo-layered double hydroxide (PANI/NiCo-LDH) core-shell composite nanofiber networks on carbon cloth (CC). Three-dimensional (3D) porous PANI nanofiber networks are firstly uniformly anchored on CC by in-situ oxidative polymerization, followed by growth of NiCo-LDH nanoflakes on the crosslinked PANI framework via electrochemical deposition. The morphology and electrochemical properties of PANI/NiCo-LDH composites are controlled by the deposition time of LDH. Benefiting from rapid electron transport and ion diffusion, the well-defined PANI/NiCo-LDH hierarchical composite with 200 s deposition of LDH delivers a large capacitance of 1845 F g⁻¹ at 0.5 A g⁻¹ and excellent cycling stability of 82% capacitance retention after 5000 cycles at a very high current density of 10.0 A g⁻¹. Furthermore, an asymmetric supercapacitor (ASC) assembled with PANI/NiCo-LDH as a positive electrode and activated carbon (AC) as a negative electrode exhibits a high capacitance of 147.2 F g⁻¹ in a potential range from 0 to 1.5 V and superior energy density of 46.0 Wh kg⁻¹ at a power density of 351.6 W kg⁻¹.

Engineering PPy decorated MnCo2O4 urchins for quasi-solid-state hybrid capacitors

In this work, three dimensional PPy decorated MnCo₂O₄ urchins on Ni foam are fabricated via a hydrothermal strategy and an electro-polymerization process.

Asymmetric pseudo-capacitors based on dendrite-like MnO2 nanostructures

Dendrite-like MnO₂ nanostructures grown on carbon cloth are successfully prepared by a facile one-step route.

Toward a high performance asymmetric hybrid capacitor by electrode optimization

Molybdenum disulfide (MoS₂) is an extremely promising electrode material for supercapacitors due to its superior electrochemical performance and conductivity.

Mixed transition metal oxide nanowire arrays enabling hybrid capacitor performance enhancement

Herein, we report MnO₂@NiCo₂O₄ nanowire bundles grown on Ni foam by a facile hydrothermal route. The as-prepared products exhibit high areal capacitance of 452.1 C g⁻¹ at 10 A g⁻¹ and 88.6% of initial capacitance after 10 000 cycles.

Transition metal oxide@hydroxide assemblies as electrode materials for asymmetric hybrid capacitors with excellent cycling stabilities

In this work, three-dimensional cactus-like Co₃O₄@Ni(OH)₂ electrode materials are grown directly on Ni foam via a two-step hydrothermal method. The as-prepared products possess a specific capacitance of 464.5 C g⁻¹ at 0.5 A g⁻¹ and 91.67% capacitance retention after 20 000 cycles. The as-assembled device using the as-synthesized samples as positive electrodes delivers an energy density of 112.5 W h kg⁻¹ at a power density of 1350 W h kg⁻¹. The superior electrochemical performance of the electrode materials can be attributed to their unique structure, the synergistic effect between Co₃O₄ and Ni(OH)₂ materials and reversible reaction kinetics. It suggests that the products are potential alternatives in future energy storage devices.

In this work, three-dimensional cactus-like Co₃O₄@Ni(OH)₂ electrode materials are grown directly on Ni foam via a two-step hydrothermal method.

Porous α-Fe₂O₃@C Nanowire Arrays as Flexible Supercapacitors Electrode Materials with Excellent Electrochemical Performances

Porous α-Fe₂O₃ nanowire arrays coated with a layer of carbon shell have been prepared by a simple hydrothermal route. The as-synthesized products show an excellent electrochemical performance with high specific capacitance and good cycling life after 9000 cycles. A solid state asymmetric supercapacitor (ASC) with a 2 V operation voltage window has been assembled by porous α-Fe₂O₃/C nanowire arrays as the anode materials, and MnO₂ nanosheets as the cathode materials, which gives rise to a maximum energy density of 30.625 Wh kg⁻¹and a maximum power density of 5000 W kg⁻¹ with an excellent cycling performance of 82% retention after 10,000 cycles.

Formation of ZnCo2O4@MnO2 core–shell electrode materials for hybrid supercapacitor

In this work, ZnCo₂O₄@MnO₂ core–shell structures are successfully prepared on nickel foam by a simple hydrothermal approach.

Hierarchical Co3O4@Co9S8 nanowall structures assembled by many nanosheets for high performance asymmetric supercapacitors

Herein, we report hierarchical Co₃O₄@Co₉S₈ nanowalls assembled by many nanosheets. The as-synthesized products are characterized in detail using various characterization methods. They can be directly used as supercapacitor electrodes with excellent electrochemical performance due to the synergy effect between Co₃O₄ and Co₉S₈. Furthermore, a flexible asymmetric supercapacitor is fabricated by using the as-synthesized Co₃O₄@Co₉S₈ structures as the cathode and the active carbon as the anode, which reveals a specific capacitance of 266.6 mF cm⁻² at a current density of 4 mA cm⁻². In addition, the supercapacitor shows an excellent capacity retention rate of 86.5% after 10 000 cycles at a current density of 10 mA cm⁻². Finally, three supercapacitor devices connected in series can light a blue LED lamp for 5 min.

Herein, we report hierarchical Co₃O₄@Co₉S₈ nanowalls assembled by many nanosheets.