Construction of Hierarchical NiCo2S4@Ni(OH)2 Core-Shell Hybrid Nanosheet Arrays on Ni Foam for High-Performance Aqueous Hybrid Supercapacitors

Analyzing synthesis routes for BaCuPO4: implications for hydrogen evolution and supercapattery performance

In recent years, energy storage and conversion tools have evolved significantly in response to rising energy demands. Owing to their large surface area, superior electric and chemical stabilities, and thermal conductivities, barium copper phosphate (BaCuPO4) materials are promising electrode materials for electrochemical energy storage systems. In this study, the synthesis of nanostructures (NSs) using hydrothermal and chemical precipitation methods and exploring the electrochemical characteristics of BaCuPO4 in asymmetric supercapacitors provides a comparative investigation. Systematic characterization shows that nanomaterials prepared by applying the hydrothermal method have a more crystalline and large surface area than chemical precipitation. In the three cell arrangements, the hydrothermally prepared BaCuPO4 NSs delivered a high specific capacity (764.4 C g-1) compared to the chemical precipitation route (660 C g-1). Additionally, the supercapattery associated with the two electrode assemblages delivers an optimum specific capacity of 77 C g-1. The energy and power density of BaCuPO4//AC NSs were 52.13 W h kg-1 and 950 W kg-1, respectively. A durability test was also performed with BaCuPO4//AC NSs for 5000 consecutive cycles. Further, the coulombic efficiency and capacity retention of BaCuPO4//AC after 5000 cycles were 81% and 92%, respectively. Bimetallic phosphate is comparatively suggested for future perspectives towards HER to overcome the performance of single metal phosphate materials. This is the first approach, we are aware of, for investigating the electrochemical behavior of BaCuPO4, and our results suggest that it may be useful as an electrode material in electrochemical systems requiring high energy and rate capabilities.

Three-dimensional graphene encapsulated hollow CoSe2-SnSe2nanoboxes for high performance asymmetric supercapacitors

Construction of metal selenides with a large specific surface area and a hollow structure is one of the effective methods to improve the electrochemical performance of supercapacitors. However, the nano-material easily agglomerates due to the lack of support, resulting in the loss of electrochemical performance. Herein, we successfully design a three-dimensional graphene (3DG) encapsulation-protected hollow nanoboxes (CoSe₂-SnSe₂) composite aerogel (3DG/CoSe₂-SnSe₂) via a co-precipitation method coupled with self-assembly route, followed by a high temperature selenidation strategy. The obtained aerogel possesses porous 3DG conductive network, large specific surface area and plenty of reactive active sites. It could be used as a flexible and binder-free electrode after a facile mechanical compression process, which provided a high specific capacitance of 460 F g^-1at 0.5 A g^-1, good rate capability of 212.7 F g^-1at 10 A g^-1The capacitance retention rate is 80% at 2 A g^-1after 5000 cycles due to the fast electron/ion transfer and electrolyte diffusion. With the as-prepared 3DG/CoSe₂-SnSe₂as positive electrodes and the AC (activated carbon) as negative electrodes, an asymmetric supercapacitor (3DG/CoSe₂-SnSe₂//AC) was fabricated, which delivered a high specific capacity of 38 F g^-1at 1 A g^-1and an energy density of 11.89 Wh kg^-1at 749.9 W kg^-1, as well as excellent cycle stability. This work provides a new method for preparing electrode material.

Effect of oxygen vacancies on the electronic structure and electrochemical performance of MnMoO4: computational simulation and experimental verification

Porous nanopetals of MnMoO4 with oxygen vacancies (MnMoO4–OV) were synthesized and deliver preferable energy storage performance.

Constructing nickel cobaltate @nickel-manganese layered double hydroxide hybrid composite on carbon cloth for high-performance flexible supercapacitors

Flexible supercapacitors have received considerable interest owing to their potential application in wearable electronics. Designing subtle hybridization of active materials and constructing smart electrode architectures are effective strategies for developing high-performance flexible supercapacitors. Herein, a hierarchically hybrid electrode is engineered by integrating nanoneedle-like structural NiCo₂O₄ and NiMn layered double hydroxide (NiMn-LDH) composite on highly conductive carbon cloth (CC). This architecture can endow abundant active sites, rapid electron collection pathways and efficient ion transport channels. The resultant hybrid electrode delivers high areal capacitance of 4010.4 mF cm^-2, excellent cyclic stability and good rate performance. Furthermore, by pairing with an activated carbon (AC)/CC anode, a flexible solid-state asymmetric supercapacitor (ASC) is assembled, which exhibits the high areal energy/power density of 0.78 mWh cm^-2/40.4 mW cm^-2 and superior capacitive stability at bending deformation. Meanwhile, the assembled ASC possesses outstanding cycling stability with 97.7% capacitance retention after 10,000 cycles. This work presents the effects of rational design of hybrid electrode with high electrochemical properties and flexibility, holding great potential for flexible energy storages.

Facile Synthesis of Zn-Co-S Nanostrip Cluster Arrays on Ni Foam for High-Performance Hybrid Supercapacitors

Mixed metal sulfides exhibit outstanding electrochemical performance compared to single metal sulfides and mixed metal oxides because of their richer redox reactions and high electronic conductivity. In the present study, Zn-Co-S nanostrip cluster arrays were formed from ZnCo₂O₄ grown on Ni foam by an anion exchange reaction using a two-step hydrothermal process. Morphological characterization confirmed that the Zn-Co-S nanostrip cluster arrays had grown homogeneously on the skeleton of the 3D Ni foam. The length of the nanostrip was approximately 8 µm, and the width ranged from 600 to 800 nm. The Ni foam-supported Zn-Co-S nanostrip cluster arrays were assessed directly for electrochemical supercapacitor applications. Compared to ZnCo₂O₄, the Zn-Co-S electrode exhibited a three-fold higher specific capacity of 830 C g⁻¹ at a specific current of 2.0 A g⁻¹. The higher polarizability, lower electro-negativity, and larger size of the S²⁻ ion played an important role in substituting oxygen with sulfur, which enhanced the performance. The Zn-Co-S//AC hybrid device delivered a maximum specific energy of 19.0 Wh kg⁻¹ at a specific power of 514 W kg⁻¹. The remarkable performance of Zn-Co-S nanostrip cluster arrays highlights their potential as a positive electrode for hybrid supercapacitor applications.

Fabrication of Nanoflower-like MCoP (M = Fe and Ni) Composites for High-Performance Supercapacitors

Elaborating the development of functional materials with excellent performance for supercapacitors is important in energy storage devices. In the present study, nanoflower-like MCoP (M = Ni and Fe) composites were successfully fabricated on Ni foam (denoted as NF@MCoP) by a cost-effective hydrothermal and low-temperature phosphating method. Simultaneously, the unique three-dimensional structure, nanoflower morphology, and the conductive substrate provide a favorable large electroactive area, shorter electron transfer distance, and rapid electron conductivity. The as-synthesized nanoflower-like MCoP composites exhibit outstanding energy density, power density, and long-term cycling stability. These results show that the developed electrode materials with excellent performance have great application prospects in the field of supercapacitor applications.

A highly conductive Ni(OH)2 nano-sheet wrapped CuCo2S4 nano-tube electrode with a core-shell structure for high performance supercapacitors

The design of microstructures and the optimum selection of electrode materials have substantial effects on the electrochemical performances of supercapacitors. A core-shell structured CuCo2S4@Ni(OH)2 electrode material was designed, with CuCo2S4 nanotubes as the core wrapped by interlaced Ni(OH)2 nano-sheets as the shell. The hydrothermal and electro-deposition processes were adopted to synthesize CuCo2S4@Ni(OH)2 materials. The CuCo2S4 nanotubes can both provide specific capacitance and act as a "superhighway" for electrons due to their highly conductive skeleton structure. The Ni(OH)2 nano-sheets will boost the electrochemically active sites and enhance the specific surface area. Meanwhile, the mutually restricted core-shell CuCo2S4@Ni(OH)2 electrode could regulate the volume deformation to improve its stability. The CuCo2S4@Ni(OH)2 electrode had a maximum specific capacitance of 2668.4 F g-1 at a current density of 1 A g-1 and a superior cycling stability of 90.3% after 10 000 cycles. Moreover, a CuCo2S4@Ni(OH)2//active carbon asymmetric supercapacitor with a maximum energy density of 44 W h kg-1 was assembled, suggesting that CuCo2S4@Ni(OH)2 is a successful binder-free electrode material for high performance supercapacitors.

Hierarchical CoO@Ni(OH)2 core-shell heterostructure arrays for advanced asymmetric supercapacitors

Constructing multicomponent electrode materials with a rational structure is an effective route to develop high-performance supercapacitors. We herein report a novel nickel-foam-supported hierarchical CoO@Ni(OH)₂ nanowire-nanosheet core-shell heterostructure array synthesized by a facile hydrothermal-electrodeposition strategy. The core CoO nanowire arrays with good electrical conductivity and shell Ni(OH)₂ nanosheets with thickness of ∼ 2 nm synergistically contributes to increased active sites, fast mass transfer, and improved structural stability. Consequently, the optimal CoO@Ni(OH)₂-400 s architecture delivers a high specific capacitance of 1418.2 F g^-1 at 1 A g^-1 and 93.7% retention after 5000 cycles. Furthermore, the CoO@Ni(OH)₂//activated carbon asymmetric supercapacitor could achieve an outstanding energy density of up to 92.47 W h kg^-1 at 800 W kg^-1. This simple but effective strategy provides insight into the development of core-shell hierarchical architectures for constructing high-performance supercapacitors.

Development of vertically aligned trimetallic Mg-Ni-Co oxide grass-like nanostructure for high-performance energy storage applications

Direct growth of nanostructured trimetallic oxide on substrate is considered as one of the promising electrode fabrication for high-performance hybrid supercapacitors. Herein, binder-free one-dimensional grass-like nanostructure was constructed on nickel foam by using electrodeposition approach. The admirable enhancement in rate capability was observed by the substitution of Mg and Ni in cobalt oxide crystallite. The prepared nickel cobalt oxide (NCO) and cobalt oxide (CO) electrode exhibited a rate capability of 57% and 58% (2 to 10 A g^-1) respectively. Interestingly, the rate capability was increased to 87% by the substitution of Mg and Ni simultaneously. The novel vertically aligned trimetallic Mg-Ni-Co oxide (MNCO) grass-like nanostructure electrode exhibited a high specific capacity of 846 C g^-1 at 2 A g^-1_, retained 97.3% specific capacity and showed an outstanding coulombic efficiency of 99% after 10,000 charge-discharge cycles. Moreover, we assembled hybrid supercapacitor (HSC) device for practical applications by using MNCO and activated carbon (AC) as the positive and negative electrode materials, respectively. HSC device exhibited a high specific capacity of 144 C g^-1 at 0.5 A g^-1. The high energy density of 31.5 Wh kg^-1 and the power density of 7.99 kW kg^-1 were achieved. All these interesting and attractive results demonstrate the significance of the vertically aligned electrode material towards practical applications.

A free-standing manganese cobalt sulfide@cobalt nickel layered double hydroxide core-shell heterostructure for an asymmetric supercapacitor

Rational design of self-supported electrode materials is important to develop high-performance supercapacitors. Herein, a free-standing MnCo₂S₄@CoNi LDH (MCS@CN LDH) core-shell heterostructure is successfully prepared on Ni foam using the hydrothermal reaction and electrodeposition. In this architecture, the inner MnCo₂S₄ nanotube provides an ultra-high electrical conductivity and the CoNi LDH nanosheets can offer more electrochemical active sites for better faradaic reactions. Moreover, the core-shell heterostructure can also maintain the structural integrity during the processes of continuous charge/discharge. The MCS@CN LDH electrode displays a satisfactory specific capacitance of 1206 C g^-1 and excellent cycling performance with ∼92% retention after 10 000 cycles. In addition, an asymmetric supercapacitor (ASC), in which MCS@CN LDH and N-doped rGO are used as the positive electrode and the negative electrode, was assembled which exhibits an energy density of 48.8 W h kg^-1 with superior cycling stability, indicating the potential of this electrode in practical energy storage.

Construction of Co3O4 three-dimensional mesoporous framework structures from zeolitic imidazolate framework-67 with enhanced lithium storage properties

High-porosity mesoporous framework structures are attractive for electrochemical energy storage and other applications. Herein we demonstrate a novel synthesis strategy to make zeolitic imidazolate framework-67 oxidize to a Co₃O₄ three-dimensional mesoporous framework structure. This strategy relies on the oxygen-limitation effect of the closed nanocage and the affinity effect of polyvinylpyrrolidone towards zeolitic imidazolate framework-67. Several TiO₂ nanospheres, as the unique structure junctions, are uniformly embedded within the Co₃O₄ framework to enhance the framework strength. The TiO₂/hydrous titania polyhedron nanocage, as the protecting shell, further encapsulates the Co₃O₄ framework, forming a perfect capsule-type hybrid. As anode materials for lithium-ion batteries, TiO₂@Co₃O₄ framework capsules show superior lithium storage performance with high reversible capacity, stable cycling life and good rate capability. A reversible capacity of 1042 mAh g^-1 can be delivered after 200 cycles at a current density of 300 mA g^-1. The average discharge capacity over 200 cycles reaches 926 mAh g^-1. This demonstrates the superiority of this material structure and its great potential as an anode for high-performance lithium-ion batteries. This work indicates a new strategy to take advantage of metal-organic frameworks to synthesize their mesoporous framework derivatives.

Construction of Hierarchical NiCo2O4@Ni-MOF Hybrid Arrays on Carbon Cloth as Superior Battery-Type Electrodes for Flexible Solid-State Hybrid Supercapacitors

Metal-organic frameworks (MOFs) have been considered as a class of promising electrode materials for supercapacitors owing to their large surface area, rich porosity, and variable redox sites; however, direct application of pristine MOFs in energy storage has been largely hindered by their poor electrical conductivity and stability issues. In this work, we demonstrate a facile two-step approach to address the controlled growth of Ni-MOF arrays on the surface of NiCo₂O₄ nanowires by modulating the formation reaction of MOFs. By taking advantage of the intriguing merits from the NiCo₂O₄ core and Ni-MOF shell as well as their synergistic effects, the optimized NiCo₂O₄@Ni-MOF hybrid electrode exhibits boosted electrochemical performance, in terms of high specific capacity (208.8 mA h/g at 2 mA/cm²) and good rate capability. In addition, the assembled flexible solid-state HSC device based on the optimized NiCo₂O₄@Ni-MOF and activated carbon as the cathode and anode achieves a maximum energy density of 32.6 W h/kg at a power density of 348.9 W/kg without sacrificing its outstanding cycling performance (nearly 100% retention over 6000 cycles at 8 mA/cm²) and mechanical stability, outperforming most recently reported MOF-based HSC devices in an aqueous electrolyte. Our work demonstrates the possibility of exploiting novel MOF-based hybrid arrays as battery-type electrodes with enhanced electrochemical properties, which exhibits great potential in flexible energy storage devices.

The Synthesis of NiCo2O4-MnO2 Core-Shell Nanowires by Electrodeposition and Its Supercapacitive Properties

Hierarchical composite films grown on current collectors are popularly reported to be directly used as electrodes for supercapacitors. Highly dense and conductive NiCo2O4 nanowires are ideal backbones to support guest materials. In this work, low crystalline MnO2 nanoflakes are electrodeposited onto the surface of NiCo2O4 nanowire films pre-coated on nickel foam. Each building block in the composite films is a NiCo2O4-MnO2 core-shell nanowire on conductive nickel foam. Due to the co-presence of MnO2 and NiCo2O4, the MnO2@NiCo2O4@Ni electrode exhibits higher specific capacitance and larger working voltage than the NiCo2O4@Ni electrode. It can have a high specific capacitance of 1186 F·g-1 at 1 A·g-1. When the core-shell NiCo2O4-MnO2 composite and activated carbon are assembled as a hybrid capacitor, it has the highest energy density of 29.6 Wh·kg-1 at a power density of 425 W·kg-1 with an operating voltage of 1.7 V. This work shows readers an easy method to synthesize composite films for energy storage.

Ni(OH)2 Nanoflakes Supported on 3D Ni3 Se2 Nanowire Array as Highly Efficient Electrodes for Asymmetric Supercapacitor and Ni/MH Battery

Porous Ni(OH)₂ nanoflakes are directly grown on the surface of nickel foam supported Ni₃ Se₂ nanowire arrays using an in situ growth procedure to form 3D Ni₃ Se₂ @Ni(OH)₂ hybrid material. Owing to good conductivity of Ni₃ Se₂ , high specific capacitance of Ni(OH)₂ and its unique architecture, the obtained Ni₃ Se₂ @Ni(OH)₂ exhibits a high specific capacitance of 1689 µAh cm^-2 (281.5 mAh g^-1 ) at a discharge current of 3 mA cm^-2 and a superior rate capability. Both the high energy density of 59.47 Wh kg^-1 at a power density of 100.54 W kg^-1 and remarkable cycling stability with only a 16.4% capacity loss after 10 000 cycles are demonstrated in an asymmetric supercapacitor cell comprising Ni₃ Se₂ @Ni(OH)₂ as a positive electrode and activated carbon as a negative electrode. Furthermore, the cell achieved a high energy density of 50.9 Wh L^-1 at a power density of 83.62 W L^-1 in combination with an extraordinary coulombic efficiency of 97% and an energy efficiency of 88.36% at 5 mA cm^-2 when activated carbon is replaced by metal hydride from a commercial NiMH battery. Excellent electrochemical performance indicates that Ni₃ Se₂ @Ni(OH)₂ composite can become a promising electrode material for energy storage applications.

Polyoxometalate-Incorporated Metallacalixarene@Graphene Composite Electrodes for High-Performance Supercapacitors

Composites of polyoxometalate (POM)/metallacalixarene/graphene-based electrode materials not only integrate the superiority of the individual components perfectly but also ameliorate the demerits to some extent, providing a promising route to approach high-performance supercapacitors. Herein, first, we report the preparations, structures, and electrochemical performance of two fascinating POM-incorporated metallacalixarene compounds [Ag₅(C₂H₂N₃)₆][H₅ ⊂ SiMo₁₂O₄₀] (1) and [Ag₅(C₂H₂N₃)₆][H₅ ⊂ SiW₁₂O₄₀] (2); (C₂H₂N₃ = 1 H-1,2,4-triazole). Single-crystal X-ray diffraction analyses illustrated that both 1 and 2 possess intriguing POM-sandwiched metallacalix[6]arene frameworks. Nevertheless, our investigations, including the electrochemical cyclic voltammetry, galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy, reveal that the oxidation ability of the Keggin ions is a primary effect in electrochemical performance of these POM-incorporated metallacalixarene compounds. Namely, the electrodes containing Mo as metal atoms in the Keggin POM shows much higher capacitance than the corresponding W-containing ones. Moreover, compound 1@graphene oxide (GO) composite electrodes are fabricated and systematically explored for their supercapacitor performance. Thanks to the synergetic effects of GO and POM-incorporated metallacalixarenes, the compound 1@15%GO-based electrode exhibits the highest specific capacitance of up to 230.2 F g^-1 (current density equal to 0.5 A g^-1), which is superior to majority of the reported POM-based electrode materials.

Electrodeposited Ni(OH)2-modified CuS core–shell-like hybrids as binder-free electrodes for high-performance supercapacitors

In this work, binder-free electrodes of CuS@Ni(OH)₂ were fabricated by hydrothermal and electrodeposition methods.

One-step sulfuration synthesis of hierarchical NiCo2S4@NiCo2S4 nanotube/nanosheet arrays on carbon cloth as advanced electrodes for high-performance flexible solid-state hybrid supercapacitors

To obtain high-performance hybrid supercapacitors (HSCs), a new class of battery-type electrode materials with hierarchical core/shell structure, high conductivity and rich porosity are needed. Herein, we propose a facile one-step sulfuration approach to achieve the fabrication of hierarchical NiCo₂S₄@NiCo₂S₄ hybrid nanotube/nanosheet arrays (NTSAs) on carbon cloth, by taking hydrothermally grown Ni–Co precursor@Ni–Co precursor nanowire/nanosheet arrays (NWSAs) as the starting templates. The optimized electrode of NiCo₂S₄@NiCo₂S₄ hybrid NTSAs demonstrates an enhanced areal capacity of 245 μA h cm⁻² at 2 mA cm⁻² with outstanding rate capability (73% from 2 to 20 mA cm⁻²) and cycling stability (86% at 10 mA cm⁻² over 3000 cycles). In addition, flexible solid-state HSC devices are assembled by using NiCo₂S₄@NiCo₂S₄ hybrid NTSAs and activated carbon as the positive and negative electrodes, respectively, which manifest a maximum volumetric energy density of 1.03 mW h cm⁻³ at a power density of 11.4 mW cm⁻³, with excellent cycling stability. Our work indicates the feasibility of designing and fabricating core/shell structured metal sulfides through such a facile one-step sulfuration process and the great potential of these materials as advanced electrodes for high-performance HSC devices.

One-step sulfuration synthesis of NiCo₂S₄@NiCo₂S₄ core–shell arrays on carbon cloth.

Hierarchical urchin-like Co9S8@Ni(OH)2 heterostructures with superior electrochemical performance for hybrid supercapacitors

The hierarchical core–shell heterostructure of Co₉S₈@Ni(OH)₂ with high open channels enables rapid electrolyte diffusion, thus enhancing the electrochemical performance.

Construction of hierarchical NiCo2S4 nanotube@NiMoO4 nanosheet hybrid arrays as advanced battery-type electrodes for hybrid supercapacitors

Hierarchical NiCo₂S₄@NiMoO₄ nanotube/nanosheet arrays were successfully fabricated on Ni foam as battery-type electrodes for high-performance hybrid supercapacitors.

A Ni(OH)2 nanopetals network for high-performance supercapacitors synthesized by immersing Ni nanofoam in water

Developing a facile and environmentally friendly approach to the synthesis of nanostructured Ni(OH)₂ electrodes for high-performance supercapacitor applications is a great challenge. In this work, we report an extremely simple route to prepare a Ni(OH)₂ nanopetals network by immersing Ni nanofoam in water. A binder-free composite electrode, consisting of Ni(OH)₂ nanopetals network, Ni nanofoam interlayer and Ni-based metallic glass matrix (Ni(OH)₂/Ni-NF/MG) with sandwich structure and good flexibility, was designed and finally achieved. Microstructure and morphology of the Ni(OH)₂ nanopetals were characterized. It is found that the Ni(OH)₂ nanopetals interweave with each other and grow vertically on the surface of Ni nanofoam to form an "ion reservoir", which facilitates the ion diffusion in the electrode reaction. Electrochemical measurements show that the Ni(OH)₂/Ni-NF/MG electrode, after immersion in water for seven days, reveals a high volumetric capacitance of 966.4 F/cm³ at a current density of 0.5 A/cm³. The electrode immersed for five days exhibits an excellent cycling stability (83.7% of the initial capacity after 3000 cycles at a current density of 1 A/cm³). Furthermore, symmetric supercapacitor (SC) devices were assembled using ribbons immersed for seven days and showed a maximum volumetric energy density of ca. 32.7 mWh/cm³ at a power density of 0.8 W/cm³, and of 13.7 mWh/cm³ when the power density was increased to 2 W/cm³. The fully charged SC devices could light up a red LED. The work provides a new idea for the synthesis of nanostructured Ni(OH)₂ by a simple approach and ultra-low cost, which largely extends the prospect of commercial application in flexible or wearable devices.

Interlaced NiMn-LDH nanosheet decorated NiCo2O4 nanowire arrays on carbon cloth as advanced electrodes for high-performance flexible solid-state hybrid supercapacitors

3D hierarchical NiCo₂O₄@NiMn-LDH nanowire/nanosheet arrays have been successfully fabricated on carbon cloth as superior battery-type electrode for high-performance flexible solid-state HSC devices.

NiCo2S4@Ni3S2 hybrid nanoarray on Ni foam for high-performance supercapacitors

Integrated hybrid nanoarrays with hierarchical porous structures have attracted much attention as energy materials for their excellent synergistic effects.

NiCo-layered double-hydroxide and carbon nanosheets microarray derived from MOFs for high performance hybrid supercapacitors

Exploring porous nano-structured materials has great significance for energy storage equipment. The metal-organic frameworks (MOFs) can be used as the outstanding sacrificial templates for electrode material of high performance supercapacitors due to their superior features that high specific surface area and tunable pore size distribution. However, the poor conductivity of MOFs is one of the biggest barriers to achieve high rate capacity and stable cycling performance. Herein, MOFs derived NiCo-layered double-hydroxide (NiCo-LDH) and nitrogen-doped carbon nanosheets (NC) on the flexible carbon nanotubes (CNTs) film are rationally designed, both of which as the binder-free electrodes can greatly improve the specific surface area and reaction sites. An asymmetric supercapacitor based on porous NiCo-LDH nanosheets on CNTs (CNT@NiCo-LDH) as the positive electrode and the NC nanosheets on carbon nanotubes film (CNT@NC) as the negative electrode exhibits the maximum energy density of 37.4 W h/kg at the power density of 750 W/kg, as well as a long-term cycling stability (94.5% capacity retention after 5000 cycles). Rationally design such combination is a meaningful process for energy storage equipment with excellent electrochemical performance.

Anion Exchange of Ni-Co Layered Double Hydroxide (LDH) Nanoarrays for a High-Capacitance Supercapacitor Electrode: A Comparison of Alkali Anion Exchange and Sulfuration

A facile and new anion exchange process is presented, which involves the conversion of NiCo-CO₃ layered double hydroxide (LDH) nanosheet arrays in an alkaline solution. The anion exchange between CO₃ ^2- and OH^- results in the construction of a reservoir for OH^- anions, and the decoration of thin nanoflakes on the surface of nanosheets effectively enlarges the surface area of NiCo LDH nanoarrays. The capacitance of the as-soaked NiCo LDH nanoarrays electrode increases from 1.78 F cm^-2 (684 F g^-1 ) to 6.22 F cm^-2 (2391 F g^-1 ) at 2 mA cm^-2 after soaking for 12 h. Moreover, the soaked NiCo-OH LDH electrode exhibits an enhanced rate capacity, high coulombic efficiency, and good cycling stability compared with the Ni-Co-S nanosheet electrode synthesized through a hydrothermal sulfuration process. The as-assembled all-solid-state NiCo LDH//active carbon asymmetric supercapacitor shows a maximum energy density of 83.4 W h kg^-1 at a power density of 1066 W kg^-1 .

Mixed Nickel-Cobalt-Molybdenum Metal Oxide Nanosheet Arrays for Hybrid Supercapacitor Applications

Mixed metal oxide nanomaterials have been demonstrated to be promising positive electrodes for energy storage applications because of the synergistic enhancement effects. In this work, nickel-cobalt-molybdenum metal oxide (NCMO) nanosheets with hierarchical, porous structures were directly developed on nickel foam (NF) through a hydrothermal method and ensuing annealing treatment. Electrochemical tests in three-electrode configurations revealed that the as-prepared NCMO nanosheets possessed high specific capacitance (1366 F g−1 at the current density of 2 A g−1), good rate capability (71.3% at the current density of 40 A g−1), as well as excellent cycling stability (89.75% retention after 5000 cycles). Additionally, a hybrid supercapacitor was assembled and achieved an energy density of 46.2 Wh kg−1 at a power density of 713 W kg−1. Based on the systematic analysis of microstructure, morphology, and element compositions, the excellent electrochemical performance of the NCMO nanosheets could be attributed to the mesoporous feature, desirable compositions, excellent mechanical and electrical contacts, and fast ion/electron transportation rates. This study shows that the NCMO nanosheets offer great potentials for application in supercapacitors.

In Situ Growth of Zeolitic Imidazolate Framework-67-derived Nanoporous Carbon@K0.5 Mn2 O4 for High-Performance 2.4 V Aqueous Asymmetric Supercapacitors

Aqueous asymmetric supercapacitors (ASCs) with a wide voltage window can effectively improve energy storage capacity of energy storage devices. Zeolitic imidazolate framework-67 (ZIF-67) was used as a precursor to prepare nanoporous carbon (NC), and K_0.5 Mn₂ O₄ nanosheets were subsequently grown on the NC surface through a facile in situ redox process (denoted as NCMO). The electrode potential window of NCMO was extended to 1.2 V in a three-electrode system and the value of the potential window was higher than that of most reported manganese oxides. To assemble the asymmetric supercapacitor with a high voltage range, the as-prepared NCMO and NC (with a potential window of -1.2-0 V) were used as the positive and negative electrode, respectively. A 2.4 V NCMO//NC aqueous ASC was constructed and displayed a large energy density of 60 Wh kg^-1 at a power density of 1200 W kg^-1 and excellent rate performance (41 Wh kg^-1 even at a specific power density of 12.3 kW kg^-1 ) as well as good cycling stability (92.6 % capacitance retention over 10 000 cycles at 10 A g^-1 ). This work provides new opportunities for the development of high voltage ASCs with a high energy density for further practical application.

Facile synthesis of NiCo2S4/CNTs nanocomposites for high-performance supercapacitors

Herein, porous NiCo2S4/CNTs nanocomposites were synthesized via a simple hydrothermal method followed by the sulphurization process using different sulfide sources. By comparing two different sulfur sources, the samples using thioacetamide as sulfide source delivered more remarkable electrochemical performance with a high specific capacitance of 1765 F g-1 at 1 A g-1 and an admirable cycling stability with capacitance retention of 71.7% at a high current density of 10 A g-1 after 5000 cycles in 2 M KOH aqueous electrolyte. Furthermore, an asymmetric supercapacitor (ASC) device was successfully fabricated with the NiCo2S4/CNTs electrode as the positive electrode and graphene as the negative electrode. The device provided a maximum energy density of 29.44 W h kg-1 at a power density of 812 W kg-1. Even at a high power density of 8006 W kg-1, the energy density still reaches 16.68 W h kg-1. Moreover, the ASC presents 89.8% specific capacitance retention after 5000 cycles at 5 A g-1. These results reveal its great potential for supercapacitors in electrochemical energy storage field.