Controlled synthesis of NiCo2S4@NiCo2O4 core@Shell nanostructured arrays decorated over the rGO sheets for high-performance asymmetric supercapacitor

Fabrication of Hierarchical MOF-Derived NiCo2S4@Mo-Doped Co-LDH Arrays for High-Energy-Density Asymmetric Supercapacitors

The rational fabrication of composite structures made of mixed components has shown great potential for boosting the energy density of supercapacitors. Herein, an elaborate hierarchical MOF-derived NiCo2S4@Mo-doped Co-LDH arrays hybrid electrode was fabricated through a step-wise method. By leveraging the synergistic effects of a uniform array of NiCo2S4 nanowires as the core and an MOF-derived porous shell, the NiCo2S4@Mo-doped Co-LDH hybrid electrode demonstrates an exceptional specific capacitance of 3049.3 F g-1 at 1 A g-1. Even at a higher current density of 20 A g-1, the capacitance remains high at 2458.8 F g-1. Moreover, the electrode exhibits remarkable cycling stability, with 91% of the initial capacitance maintained after 10,000 cycles at 10 A g-1. Additionally, the as-fabricated asymmetric supercapacitor (ASC) based on the NiCo2S4@Mo-doped Co-LDH electrode achieves an impressive energy density of 97.5 Wh kg-1 at a power density of 835.6 W kg-1. These findings provide a promising approach for the development of hybrid-structured electrodes, enabling the realization of high-energy-density asymmetric supercapacitors.

Solvent-Controlled Morphology of Zinc-Cobalt Bimetallic Sulfides for Supercapacitors

Bimetallic sulfides offer high theoretical specific capacitance and good stability as electrode materials due to their diverse redox reactions, larger specific surface areas, and better conductivity. The morphology of the electrode material is an important influencing factor for the electrochemical properties. Herein, a series of ZnCoS electrode materials with different morphologies were prepared by varying the solvent in the solvothermal reaction, and the effects of different microstructures on the electrochemical properties of ZnCoS were investigated. The ratio of water and ethanol in the solvent was controlled to modulate the microstructure of the as-prepared ZnCoS materials. XRD and XPS revealed the physical and chemical structure of the ZnCoS materials. SEM and TEM observations showed that the microstructure of ZnCoS transformed from one-dimensional wires to two-dimensional sheets with increasing amounts of ethanol. The maximum specific capacitance of the as-prepared ZnCoS materials is 6.22 F cm-2 at a current density of 5 mA cm-2, which is superior to that of most previously reported bimetallic sulfides. The enhanced electrochemical performance could be ascribed to its sheet-assembled spherical structure, which not only shortens the path of ion diffusion but also increases the contact between surface active sites and the electrolyte. Moreover, the spherical structure provides numerous void spaces for buffering the volume expansion and penetration of the electrolyte, which would be favorable for electrochemical reactions. Furthermore, the ZnCoS electrodes were coupled with activated carbon (AC) electrodes to build asymmetric supercapacitors (ASCs). The ASC device exhibits a maximum energy density of 0.124 mWh cm-2 under a power density of 2.1 mW cm-2. Moreover, even under a high-power density of 21 mW cm-2, the energy density can still reach 0.055 mWh cm-2.

Graphitic Carbon Nitride-Induced Multifold Enhancement in Electrochemical Charge Storage of CoS-NiCo2S4 for All-Solid-State Hybrid Supercapacitors

In order to improve the electro-microstructural physiognomics of electrode materials for applications in better efficiency supercapacitors, herein graphitic carbon nitride (GCN)-heterostructurized CoS-NiCo₂S₄ is designed using a controlled material growth synthesis procedure. The developed CoS-NiCo₂S₄/GCN possesses ample hydrophilicity, possible charge transfer between GCN and CoS-NiCo₂S₄, uniform phase distribution, and distinctive microstructural characteristics. The preliminary electrochemical studies in the three-electrode setup show GCN-induced lower charge transfer resistance and very unique Warburg profile corresponding to extremely low diffusion resistance in CoS-NiCo₂S₄/GCN as compared to pristine CoS-NiCo₂S₄. Furthermore, GCN is found to significantly induce surface-controlled (capacitive-type) charge storage and frequency-independent specific capacitance up to 10 Hz in CoS-NiCo₂S₄. Furthermore, the CoS-NiCo₂S₄||N-rGO and CoS-NiCo₂S₄/GCN||N-rGO all-solid-state hybrid supercapacitor (ASSHSC) devices were fabricated using N-rGO as the negative electrode material, and the inducing effect of GCN on the supercapacitive charge storage performance of the devices is thoroughly studied. Results demonstrate that the mass specific capacitance and areal capacitance of CoS-NiCo₂S₄/GCN||N-rGO are ∼2 and ∼4 times more than those of the CoS-NiCo₂S₄||N-rGO ASSHSC device, respectively. Furthermore, the CoS-NiCo₂S₄/GCN||N-rGO offers more energy density, rate energy density, and additional charge-discharge durability (over ∼10,000 cycles) than the CoS-NiCo₂S₄||N-rGO ASSHSC device. The multifold performance improvement of CoS-NiCo₂S₄ with GCN heterostructurization is ascribed to GCN-induced supplemented porosity and pore widening, ionic nonstoichiometry (Ni^2±δ, Co^2±δ, and Co^3±δ), wettability, integrated enhancement in the conductivity, and electroactive-ion accessibility in the CoS-NiCo₂S₄/GCN heterocomposite. The present study offers vital physicoelectrochemical insights toward the future development of low cost and high-performance electrode materials, and their implementation in high-rate and operationally stable all-solid-state hybrid supercapacitor devices, for application in the next-generation front-line technologies.

Design of an Internal/External Bicontinuous Conductive Network for High-Performance Asymmetrical Supercapacitors

High-energy density supercapacitors have attracted extensive attention due to their electrode structure design. A synergistic effect related to core-shell structure can improve the energy storage capacity and power density of electrode materials. The Ni-foam (NF) substrate coupled with polypyrrole (PPy) conductive coating can serve as an internal/external bicontinuous conductive network. In this work, the distinctive PPy@FeNi₂S₄@NF and PPy@NiCo₂S₄@NF materials were prepared by a simple two-step hydrothermal synthesis with a subsequent in situ polymerization method. PPy@FeNi₂S₄@NF and PPy@NiCo₂S₄@NF could deliver ultrahigh specific capacitances of 3870.3 and 5771.4 F·g^-1 at 1 A·g^-1 and marvelous cycling capability performances of 81.39% and 93.02% after 5000 cycles. The asymmetric supercapacitors composed of the prepared materials provided a high-energy density of over 47.2 Wh·kg^-1 at 699.9 W·kg^-1 power density and 67.11 Wh·kg^-1 at 800 W·kg^-1 power density. Therefore, the self-assembled core-shell structure can effectively improve the electrochemical performance and will have an effective service in advanced energy-storage devices.

Hierarchically urchin-like hollow NiCo2S4 prepared by a facile template-free method for high-performance supercapacitors

Hollow structures draw much attention for high energy density supercapacitors due to their large hollow cavities, high specific surface area, and low interfacial contact resistance. However, constructing hierarchical hollow structures remains a challenge. Herein, we reported a facile template-free method for a novel urchin-like hollow nickel cobalt sulfide (NiCo₂S₄). The hollow interior and urchin exterior remarkably improved the specific capacitance and accommodated structural collapse caused by electrochemical reactions. Owing to these features, the urchin-like hollow NiCo₂S₄ spheres exhibited an impressive capacitance of 1398F g^-1 at 1 A g^-1 and maintained 1110F g^-1 with a large current density of 10 A g^-1. The hybrid supercapacitor fabricated by NiCo₂S₄ and active carbon possesses an energy density of 39.3 Wh kg^-1 at a power density of 749.6 W kg^-1 and an outstanding cycling stability of 74.4% retention after 5000 cycles. Our work presents a facile method of constructing a hollow structure of binary sulfide materials and also makes progress on highly efficient supercapacitors.

Controllable synthesis of ZIF-derived NixCo3-xO4 nanotube array hierarchical structures based on self-assembly for high-performance hybrid alkaline batteries

In this study, a novel NixCo3-xO4 nanotube array hierarchical structure derived from zeolitic imidazolate frameworks (ZIFs) is grown on Ni foam (NixCo3-xO4 NAHS/Ni foam) using the template-assisted and self-assembly approach for a high-performance hybrid energy storage device in alkaline solution. The material characteristics of the resultant samples were characterized by XPS, XRD, ICP, SEM, TEM and BET. Due to the unique hollow structure with a large specific surface area and the exposure of large active sites originating from ZIFs, the optimal NixCo3-xO4 NAHS/Ni foam exhibits substantially enhanced electrochemical properties. The NixCo3-xO4 NAHS/Ni foam directly acts as an electrode, which provides an excellent specific capacity of 290.48 mA h g-1 at 1 A g-1. Subsequently, the corresponding hybrid alkaline batteries that consist of NixCo3-xO4 NAHS/Ni foam and carbon materials display a highly satisfactory specific capacity of 54.94 mA h g-1 at 1 A g-1, a satisfactory long-term stability of 85.47% after 2000 cycles, a maximum energy density of 43.95 W h kg-1 and a power density of 8000 W kg-1. This work combines the design of the electronic structure with the optimization of composition, and provides a reference for the application of hybrid rechargeable alkaline batteries (RABs).

Modish Designation of Hollow-Tubular rGO-NiMoO4@Ni-Co-S Hybrid Core-shell Electrodes with Multichannel Superconductive Pathways for High-Performance Asymmetric Supercapacitors

The scrupulous designation of hollow and porous electroactive materials incorporating prolific redox-active polyphase transition-metal oxide decorated with polyphase transition-metal sulfide onto rGO (reduced graphene oxide)-supported conductive substrate has never been an easy task due to the very good coordination affair of sulfur toward transition metals. Herein, cost-effective hydrothermal growth followed by a metal-organic framework (MOF)-mediated sulfidation approach is employed to achieve burl-like Ni-Co-S nanomaterial-integrated hollow and porous NiMoO₄ nanotubes onto rGO-coated Ni foam (rGO-NiMoO₄@Ni-Co-S) as the electrode material for supercapacitors. The open framework of the rGO-Co-MOF template after the etching and sulfidation process not only enables the creation of a tubular structure of NiMoO₄ nanorods but also provides convenient ion-electron pathways to promote rapid faradic reactions for the hybrid composite electrode. Owing to the unique hollow and tubular structure, the as-fabricated rGO-NiMoO₄@Ni-Co-S electrode exhibits a high specific capacity of 318 mA h g^-1 at 1 A g^-1 and remarkable cyclic performance of 88.87% after 10,000 consecutive charge-discharge cycles in an aqueous 2 M KOH electrolyte on a three-electrode configuration. Moreover, the assembled rGO-NiMoO₄@Ni-Co-S//rGO-MDC (MOF-derived carbon) asymmetric supercapacitor device exhibits a satisfactory energy density of 57.24 W h kg^-1 at a power density of 801.8 W kg^-1 with an admirable life span of 90.89% after 10,000 repeated cycles.

Sponge-like NiCo2S4 nanosheets supported on nickel foam as high-performance electrode materials for asymmetric supercapacitors

Herein, binder-free sponge-like NiCo₂S₄ nanosheets supported on Ni foam with ultra-high mass loading were synthesized via a facile one-step hydrothermal route.

Fabrication of a High-Energy Flexible All-Solid-State Supercapacitor Using Pseudocapacitive 2D-Ti3C2Tx-MXene and Battery-Type Reduced Graphene Oxide/Nickel-Cobalt Bimetal Oxide Electrode Materials

Owing to excellent metallic conductivity, hydrophilic surfaces, and surface redox properties, a two-dimensional (2D) metal carbide of Ti₃C₂T_x-MXene could serve as a promising pseudocapacitive electrode material for energy storage devices. Meanwhile, the 2D reduced graphene oxide (rGO) combining with the hierarchical cubic spinel nickel-cobalt bimetal oxide (NiCo₂O₄) nanospikes could control ion diffusion for charge storage, thereby facilitating the improvement of the energy density of a supercapacitor. As per the strategy, the pseudocapacitive 2D Ti₃C₂T_x was loaded on a flexible acid-treated carbon fiber (ACF) backbone to prepare a Ti₃C₂T_x/ACF negative electrode by a convenient drop-casting method. Meanwhile, 2D rGO was deposited on ACF by a simple dip-dry process, which was further decorated by the spinel NiCo₂O₄ nanospikes using a hydrothermal method to obtain a NiCo₂O₄@rGO/ACF positive electrode. The fabricated Ti₃C₂T_x/ACF electrode exhibited an excellent specific capacitance of 246.9 F/g (197.5 mF/cm²) at 4 mA/cm² along with 96.7% capacity retention over 5000 charge/discharge cycles, whereas the NiCo₂O₄@rGO/ACF electrode showed a specific capacitance of 1487 F/g (458.3 mA h/g) at 3 mA/cm² with a cycling stability of 88.2% over 10 000 charge/discharge cycles. As a result, a flexible all-solid-state hybrid supercapacitor (FHSC) device using the pseudocapacitive Ti₃C₂T_x/ACF on the negative side with a widespread voltage window and the battery-type NiCo₂O₄@rGO/ACF on the positive side with high electrochemical activity delivered an excellent volumetric capacitance of 2.32 F/cm³ (141.9 F/g) at a current density of 5 mA/cm² with a high-energy density of 44.36 Wh/kg (0.72 mWh/cm³) at a power density of 985 W/kg (16.13 mW/cm³) along with a cycling stability of 90.48% over 4500 charge/discharge cycles. Therefore, the pseudocapacitive 2D Ti₃C₂T_x/ACF negative electrode could replace carbon-based electrodes and a combination of it with the battery-type NiCo₂O₄@rGO/ACF positive electrode should be a promising way to step up the energy density of a supercapacitor.

Designing vertically aligned porous NiCo2O4@MnMoO4 Core@Shell nanostructures for high-performance asymmetric supercapacitors

NiCo₂O₄@MnMoO₄ core@shell nanostructures are synthesized as electrode material using hydrothermal method for the fabrication of asymmetric supercapacitor (ASC) device. The NiCo₂O₄@MnMoO₄ electrode shows better electrochemical performance with specific capacitance (SC) of 1821 F/g at current density of 5 A/g and cycling stability of 94%. The NiCo₂O₄@MnMoO₄ core@shell electrode shows better SC compared to pure NiCo₂O₄ and MnMoO₄ electrodes. An ASC device is fabricated using NiCo₂O₄@MnMoO₄ as a positive and rGO/Fe₂O₃ as negative electrode materials. Remarkably, the fabricated device shows a SC of 294 F/g at current density 4 A/g, with an energy density of 91.87 Wh/kg at a power density of 374.15 W/kg. The device shows good reversibility with cycling stability of 68% after 2,000 cycles. The ASC device is used to illuminate nine green color LEDs for 35 min. Therefore, the present report provides a simple method to fabricate efficient and stable energy storage devices for industrial applications.

Synergistic effect of MoS2 and Fe3O4 decorated reduced graphene oxide as a ternary hybrid for high-performance and stable asymmetric supercapacitors

Today, two-dimensional materials for use in energy devices have attracted the attention of researchers. Molybdenum disulfide is promising as an electrode material with unique physical properties and a high exposed surface area. However, there are still problems that need to be addressed. In this study, we prepared a hybrid containing MoS₂, Fe₃O₄, and reduced graphene oxide (rGO) by a two-step hydrothermal method. This nanocomposite is well structurally and morphologically identified, and its electrochemical performance is then evaluated for use in supercapacitors. According to the galvanostatic charge-discharge results, this nanocomposite shows a good specific capacity, equivalent to 527 F g^-1 at 0.5 mA cm^-2. The results of the multi-cycle stability test (5000 cycles) indicate a significant stability rate capability, with 93% of the electrode capacity remaining after 5000 cycles. The reason for this could be the synergistic effect between rGO and MoS₂ as well as between molybdenum and iron in the faradic reaction in the charge storage process. Fe₃O₄ and MoS₂ provide electroactive sites for the faradic process and electrolyte accessibility and rGO supply conductivity.

Fabrication of NiCo2S4/carbon-filled nickel foam complex as an advanced binder-free electrode for supercapacitors

A novel strategy, composed of epoxy-resin filling, carbonization, and hydrothermal growing of NiCo2S4 nanorods, was developed to enlarge the surface area of nickel foam (NF) for loading electrochemically active materials and to successfully fabricate NiCo2S4/carbon-filled NF binder-free electrodes. Due to the certain electrical conductivity of the filled epoxy-resin-derived carbon and the enlarged loading surface area, the targeted electrode possesses outstanding electrochemical energy storage performance, with a maximum specific capacitance of 9.28 F cm-2 at a current density of 4 mA cm-2, more than 6 times the 1.46 F cm-2 of the NF-based electrode formed via directly growing NiCo2S4 on NF, and with a specific capacitance retention of about 60% after 2000 charge/discharge cycles. Our strategy provides a promising avenue for constructing a high-performance NF-based binder-free electrode and our resultant electrode presents great application potential in electrochemical energy storage.

Charcoal derived graphene quantum dots for flexible supercapacitor oriented applications

In this article, charcoal is used as a new raw material for the synthesis of high yield graphene quantum dots (GQDs) for supercapacitor application.